diff --git a/.config/CredScanSuppressions.json b/.config/CredScanSuppressions.json
index da14baee20e321..984a86f68e69e6 100644
--- a/.config/CredScanSuppressions.json
+++ b/.config/CredScanSuppressions.json
@@ -1,49 +1,70 @@
 {
- "tool": "Credential Scanner",
- "suppressions": [
-  {
-    "file": [
-      "/eng/common/internal-feed-operations.ps1",
-      "/eng/common/internal-feed-operations.sh",
-      "/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp_types.cs",
-      "/src/libraries/Common/src/System/Security/Cryptography/EccSecurityTransforms.cs",
-      "/src/libraries/Common/tests/System/Net/Configuration.Certificates.cs",
-      "/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Authentication.cs",
-      "/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.cs",
-      "/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.DefaultProxyCredentials.cs",
-      "/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Proxy.cs",
-      "/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.ServerCertificates.cs",
-      "/src/libraries/Common/tests/System/Net/Http/PostScenarioTest.cs",
-      "/src/libraries/Common/tests/System/Net/Prerequisites/Deployment/setup_certificates.ps1",
-      "/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/EC/ECKeyFileTests.cs",
-      "/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/EC/ECKeyFileTests.LimitedPrivate.cs",
-      "/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/RSA/RSAKeyFileTests.cs",
-      "/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/RSA/RSAKeyPemTests.cs",
-      "/src/libraries/System.Data.Common/tests/System/Data/Common/DbConnectionStringBuilderTest.cs",
-      "/src/libraries/System.Diagnostics.Process/tests/ProcessStartInfoTests.cs",
-      "/src/libraries/System.DirectoryServices.AccountManagement/src/System/DirectoryServices/AccountManagement/constants.cs",
-      "/src/libraries/System.DirectoryServices.AccountManagement/tests/PrincipalTest.cs",
-      "/src/libraries/System.DirectoryServices.AccountManagement/tests/UserPrincipalTest.cs",
-      "/src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.cs",
-      "/src/libraries/System.Net.Http/tests/UnitTests/DigestAuthenticationTests.cs",
-      "/src/libraries/System.Net.Http/tests/UnitTests/HttpEnvironmentProxyTest.cs",
-      "/src/libraries/System.Net.Mail/tests/Functional/SmtpClientTest.cs",
-      "/src/libraries/System.Net.Requests/src/System/Net/FtpControlStream.cs",
-      "/src/libraries/System.Net.Requests/src/System/Net/FtpWebRequest.cs",
-      "/src/libraries/System.Net.WebSockets.Client/tests/ConnectTest.cs",
-      "/src/libraries/System.Private.Uri/tests/ExtendedFunctionalTests/UriRelativeResolutionTest.cs",
-      "/src/libraries/System.Private.Uri/tests/FunctionalTests/UriBuilderRefreshTest.cs",
-      "/src/libraries/System.Private.Uri/tests/FunctionalTests/UriBuilderTests.cs",
-      "/src/libraries/System.Private.Uri/tests/FunctionalTests/UriRelativeResolutionTest.cs",
-      "/src/libraries/System.Runtime/tests/System/Uri.CreateStringTests.cs",
-      "/src/libraries/System.Security.Cryptography.Algorithms/tests/Rfc2898Tests.cs",
-      "/src/libraries/System.Security.Cryptography.Pkcs/tests/Pkcs12/Pkcs12Documents.cs",
-      "/src/libraries/System.Security.Cryptography.X509Certificates/tests/ExportTests.cs",
-      "/src/libraries/System.Security.Cryptography.Xml/tests/EncryptedXmlTest.cs",
-      "/src/libraries/System.Security.Cryptography.Xml/tests/SignedXmlTest.cs",
-      "/src/libraries/System.Security.Cryptography.Xml/tests/TestHelpers.cs"
-    ],
-    "_justification": "Mostly test files. Other files contain harmless examples or constants."
-  },
- ]
+    "tool": "Credential Scanner",
+    "suppressions": [
+        {
+            "_justification": "Unit test containing connection strings under the test.",
+            "file": [
+                "src/libraries/System.Data.Common/tests/System/Data/Common/DbConnectionStringBuilderTest.cs"
+            ]
+        },
+        {
+            "_justification": "Private key for testing purpose.",
+            "file": [
+                "src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/DSA/DSAKeyPemTests.cs",
+                "src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/EC/ECKeyPemTests.cs",
+                "src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/RSA/RSAKeyPemTests.cs",
+                "src/libraries/System.Security.Cryptography.X509Certificates/tests/TestData.cs"
+            ],
+            "placeholder": [
+                "-----BEGIN PRIVATE KEY-----",
+                "-----BEGIN * PRIVATE KEY-----"
+            ]
+        },
+        {
+            "_justification": "Test credential for Uri testing",
+            "file": [
+                "src/libraries/System.Net.Http/tests/UnitTests/HttpEnvironmentProxyTest.cs",
+                "src/libraries/System.Private.Uri/tests/ExtendedFunctionalTests/UriRelativeResolutionTest.cs",
+                "src/libraries/System.Private.Uri/tests/FunctionalTests/UriBuilderRefreshTest.cs",
+                "src/libraries/System.Private.Uri/tests/FunctionalTests/UriBuilderTests.cs",
+                "src/libraries/System.Private.Uri/tests/FunctionalTests/UriRelativeResolutionTest.cs",
+                "src/libraries/System.Runtime/tests/System/Uri.CreateStringTests.cs"
+            ],
+            "placeholder": [
+                "//*:;&$=123USERINFO@",
+                "//*:bar@",
+                "//*:bar1@",
+                "//*:password1@",
+                "//*:psw@",
+                "//*:userinfo2@"
+            ]
+        },
+        {
+            "_justification": "Generic test password.",
+            "file": [
+                "src/libraries/Common/tests/System/Net/Configuration.Certificates.cs",
+                "src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Authentication.cs",
+                "src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.cs",
+                "src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.DefaultProxyCredentials.cs",
+                "src/libraries/Common/tests/System/Net/Http/PostScenarioTest.cs",
+                "src/libraries/Common/tests/System/Net/Prerequisites/Deployment/setup_certificates.ps1",
+                "src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.cs",
+                "src/libraries/System.Net.Http/tests/UnitTests/DigestAuthenticationTests.cs",
+                "src/libraries/System.Net.Http/tests/UnitTests/HttpEnvironmentProxyTest.cs",
+                "src/libraries/System.Net.Mail/tests/Functional/SmtpClientTest.cs",
+                "src/libraries/System.Security.Cryptography.Xml/tests/SignedXmlTest.cs",
+                "src/libraries/System.Security.Cryptography.Xml/tests/TestHelpers.cs"
+            ],
+            "placeholder": [
+                "\"anotherpassword\"",
+                "\"bar\"",
+                "\"mono\"",
+                "\"password1\"",
+                "\"rightpassword\"",
+                "\"testcertificate\"",
+                "\"unused\"",
+                "\"wrongpassword\""
+            ]
+        }
+    ]
 }
diff --git a/.config/dotnet-tools.json b/.config/dotnet-tools.json
index 5199430949475a..d6009aca5b521f 100644
--- a/.config/dotnet-tools.json
+++ b/.config/dotnet-tools.json
@@ -15,7 +15,7 @@
       ]
     },
     "microsoft.dotnet.xharness.cli": {
-      "version": "1.0.0-prerelease.20352.2",
+      "version": "1.0.0-prerelease.20403.2",
       "commands": [
         "xharness"
       ]
diff --git a/.editorconfig b/.editorconfig
index e8c010f6a2e157..9d03bd30636c9f 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -184,6 +184,10 @@ indent_size = 2
 [*.{props,targets,config,nuspec}]
 indent_size = 2
 
+# YAML config files
+[*.{yml,yaml}]
+indent_size = 2
+
 # Shell scripts
 [*.sh]
 end_of_line = lf
diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index 3f2a376ee71129..e5a4552409f541 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -7,6 +7,12 @@
 /src/libraries/System.Buffers/                                      @ahsonkhan
 /src/libraries/System.Memory/                                       @ahsonkhan
 
+# CoreCLR Code Owners
+
+/src/coreclr/src/inc/corinfo.h @dotnet/jit-contrib
+/src/coreclr/src/inc/corjit.h @dotnet/jit-contrib
+/src/coreclr/src/jit/ @dotnet/jit-contrib
+
 # Mono Code Owners
 
 /src/mono @marek-safar
diff --git a/Build.proj b/Build.proj
index dc4a15ab5f413d..2041d3d4fcc1f3 100644
--- a/Build.proj
+++ b/Build.proj
@@ -1,5 +1,9 @@
 <Project Sdk="Microsoft.Build.Traversal">
 
+  <PropertyGroup>
+    <TraversalGlobalProperties>BuildTargetFramework=$([MSBuild]::ValueOrDefault('$(BuildTargetFramework)', '$(NetCoreAppCurrent)'))</TraversalGlobalProperties>
+  </PropertyGroup>
+
   <!--
     Subsets are already imported by Directory.Build.props.
     Reference the projects for traversal build. Ordering matters here.
@@ -35,7 +39,7 @@
 
   <Target Name="RestoreWithoutStaticGraph"
           BeforeTargets="Restore">
-    <MSBuild Projects="@(LibrariesRestoreProject);@(DepprojProjectToBuild);@(PkgprojProjectToBuild);@(BundleProjectToBuild)"
+    <MSBuild Projects="@(DepprojProjectToBuild);@(PkgprojProjectToBuild);@(BundleProjectToBuild)"
              Properties="MSBuildRestoreSessionId=$([System.Guid]::NewGuid());RestoreUseStaticGraphEvaluation=false"
              Targets="Restore" />
   </Target>
diff --git a/Directory.Build.props b/Directory.Build.props
index e8f9a65ba21783..c4bcb9a6255898 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -40,7 +40,7 @@
     <!-- Installer specific, required during restore. -->
     <InstallerTasksOutputPath>$([MSBuild]::NormalizeDirectory('$(ArtifactsBinDir)', 'installer.tasks'))</InstallerTasksOutputPath>
     <InstallerTasksAssemblyPath Condition="'$(MSBuildRuntimeType)' == 'Core'">$([MSBuild]::NormalizePath('$(InstallerTasksOutputPath)', 'Debug', 'netstandard2.0', 'installer.tasks.dll'))</InstallerTasksAssemblyPath>
-    <InstallerTasksAssemblyPath Condition="'$(MSBuildRuntimeType)' != 'Core'">$([MSBuild]::NormalizePath('$(InstallerTasksOutputPath)', 'Debug', 'net46', 'installer.tasks.dll'))</InstallerTasksAssemblyPath>
+    <InstallerTasksAssemblyPath Condition="'$(MSBuildRuntimeType)' != 'Core'">$([MSBuild]::NormalizePath('$(InstallerTasksOutputPath)', 'Debug', 'net461', 'installer.tasks.dll'))</InstallerTasksAssemblyPath>
 
     <DocsDir>$([MSBuild]::NormalizeDirectory('$(RepoRoot)', 'docs'))</DocsDir>
     <ManPagesDir>$([MSBuild]::NormalizeDirectory('$(DocsDir)', 'manpages'))</ManPagesDir>
diff --git a/docs/area-owners.md b/docs/area-owners.md
index e696729861dff8..210243387b0ce2 100644
--- a/docs/area-owners.md
+++ b/docs/area-owners.md
@@ -1,4 +1,10 @@
-If you need to tag folks on an issue or PR, you will generally want to tag the owners (not the lead)
+# Pull Requests Tagging
+
+If you need to tag folks on an issue or PR, you will generally want to tag the owners (not the lead) for [area](#areas) to which the change or issue is closest to. For areas which are large and can be operating system or architecture specific it's better to tag owners of [OS](#operating-systems) or [Architecture](#architectures).
+
+## Areas
+
+Note: Editing this file doesn't update the mapping used by the `@msftbot` issue notification bot to tag owners. Some area owners prefer not to get those notifications. To update those notifications, contact any one of `@danmosemsft`, `@jeffschw`, `@marek-safar`, `@ericstj`, or `@karelz`. If you're a community member interested in these notifications, you won't appear in this table but we can add you to notifications - just let us know.
 
 | Area                                           | Lead          | Owners (area experts to tag in PR's and issues)     | Description                                                                                                                                                                                                                                                                               |
 |------------------------------------------------|---------------|-----------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
@@ -118,4 +124,21 @@ If you need to tag folks on an issue or PR, you will generally want to tag the o
 | area-TypeSystem-coreclr                        | @mangod9      | @davidwrighton @MichalStrehovsky @janvorli @mangod9 |                                                                                                                                                                                                                                                                                           |
 | area-UWP                                       | @tommcdon     | @jashook                                            | UWP-specific issues including Microsoft.NETCore.UniversalWindowsPlatform and Microsoft.Net.UWPCoreRuntimeSdk                                                                                                                                                                              |
 | area-VM-coreclr                                | @mangod9      | @mangod9                                            |                                                                                                                                                                                                                                                                                           |
-| area-VM-meta-mono                              | @SamMonoRT    | @lambdageek                                         |                                                                                                                                                                                                                                                                                           |
+| area-VM-meta-mono                              | @SamMonoRT    | @lambdageek @CoffeeFlux                             |                                                                                                                                                                                                                                                                                           |
+## Operating Systems
+
+| Operating System | Lead          | Owners (area experts to tag in PR's and issues)     | Description  |
+|------------------|---------------|-----------------------------------------------------|--------------|
+| os-alpine        |               |                                                     |              |
+| os-android       | @steveisok    | @akoeplinger                                        |              |
+| os-freebsd       |               |                                                     |              |
+| os-mac-os-x      | @steveisok    |                                                     |              |
+| os-ios           | @steveisok    | @vargaz                                             |              |
+| os-tvos          | @steveisok    | @vargaz                                             |              |
+
+## Architectures
+
+| Architecture    | Lead          | Owners (area experts to tag in PR's and issues)     | Description  |
+|-----------------|---------------|-----------------------------------------------------|--------------|
+| arch-wasm       | @lewing       | @lewing @BrzVlad                                    |              |
+
diff --git a/docs/coding-guidelines/api-guidelines/nullability.md b/docs/coding-guidelines/api-guidelines/nullability.md
index 8c029d01fccef7..62e0fe3958884a 100644
--- a/docs/coding-guidelines/api-guidelines/nullability.md
+++ b/docs/coding-guidelines/api-guidelines/nullability.md
@@ -99,6 +99,7 @@ The C# compiler respects a set of attributes that impact its flow analysis.  We
 - **DO** add `[NotNullIfNotNull(string)]` if nullable ref argument will be non-`null` upon exit, when an other argument passed evaluated to non-`null`, pass that argument name as string. Example: `public void Exchange([NotNullIfNotNull("value")] ref object? location, object? value);`.
 - **DO** add `[return: NotNullIfNotNull(string)]` if a method would not return `null` in case an argument passed evaluated to non-`null`, pass that argument name as string. Example: `[return: NotNullIfNotNull("name")] public string? FormatName(string? name);`
 - **DO** add `[MemberNotNull(string fieldName)]` to a helper method which initializes member field(s), passing in the field name. Example: `[MemberNotNull("_buffer")] private void InitializeBuffer()`.  This will help to avoid spurious warnings at call sites that call the initialization method and then proceed to use the specified field.  Note that there are two constructors to `MemberNotNull`; one that takes a single `string`, and one that takes a `params string[]`.  When the number of fields initialized is small (e.g. <= 3), it's preferable to use multiple `[MemberNotNull(string)]` attributes on the method rather than one `[MemberNotNull(string, string, string, ...)]` attribute, as the latter is not CLS compliant and will likely require `#pragma warning disable` and `#pragma warning restore` around the line to suppress warnings.
+- **AVOID** using `[MaybeNull]`, not because it's problematic, but because there's almost always a better option, such as `T?` (as of this writing, in all of the dotnet/runtime there are only 7 occurrences of `[MaybeNull]`).  One example of where it's applicable is `AsyncLocal<T>.Value`; `[DisallowNull]` can't be used here, because `null` is valid if `T` is nullable, and `T?` shouldn't be used because `Value` shouldn't be set to `null` if `T` isn't nullable.  Another is in the relatively rare case where a public or protected field is exposed, may begin life as null, but shouldn't be explicitly set to null.
 
 ## Code Review Guidance
 
diff --git a/docs/coding-guidelines/project-guidelines.md b/docs/coding-guidelines/project-guidelines.md
index 36a43555afff8e..afc05f4037b220 100644
--- a/docs/coding-guidelines/project-guidelines.md
+++ b/docs/coding-guidelines/project-guidelines.md
@@ -1,41 +1,33 @@
 # Build Project Guidelines
-In order to work in dotnet/runtime repo you must first run build.cmd/sh from the root of the repo at least
-once before you can iterate and work on a given library project.
+In order to work in the dotnet/runtime repo you must first run build.cmd/sh from the root of the repo at least once before you can iterate and work on a given library project.
 
 ## Behind the scenes with build.cmd/sh
 
-- Setup tools (currently done in restore in build.cmd/sh)
+- Restore tools
 - Restore external dependencies
  - CoreCLR - Copy to `bin\runtime\$(BuildTargetFramework)-$(TargetOS)-$(Configuration)-$(TargetArchitecture)`
- - Netstandard Library - Copy to `bin\ref\netstandard2.0`
- - NetFx targeting pack - Copy to `bin\ref\net472`
 - Build targeting pack
  - Build src\libraries\ref.proj which builds all references assembly projects. For reference assembly project information see [ref](#ref)
 - Build product
  - Build src\libraries\src.proj which builds all the source library projects. For source library project information see [src](#src).
-- Sign product
- - Build src\sign.proj
 
 # Build Pivots
 Below is a list of all the various options we pivot the project builds on:
 
-- **Target Frameworks:** NetFx (aka Desktop), netstandard (aka dotnet/Portable), NETCoreApp (aka .NET Core)
-- **Platform Runtimes:** NetFx (aka CLR/Desktop), CoreCLR, Mono
+- **Target Frameworks:** .NETFramework, .NETStandard, .NETCoreApp
+- **Platform Runtimes:** .NETFramework (aka CLR/Desktop), CoreCLR, Mono
 - **OS:** Windows_NT, Linux, OSX, FreeBSD, AnyOS
 - **Flavor:** Debug, Release
-- **Architecture:** x86, x64, arm, arm64, AnyCPU
 
 ## Individual build properties
 The following are the properties associated with each build pivot
 
-- `$(BuildTargetFramework) -> netstandard2.1 | net5.0 | net472`
+- `$(BuildTargetFramework) -> Any .NETCoreApp or .NETFramework TFM, e.g. net5.0`
 - `$(TargetOS) -> Windows | Linux | OSX | FreeBSD | [defaults to running OS when empty]`
 - `$(Configuration) -> Release | [defaults to Debug when empty]`
 - `$(TargetArchitecture) - x86 | x64 | arm | arm64 | [defaults to x64 when empty]`
 - `$(RuntimeOS) - win7 | osx10.10 | ubuntu.14.04 | [any other RID OS+version] | [defaults to running OS when empty]` See [RIDs](https://github.com/dotnet/runtime/tree/master/src/libraries/pkg/Microsoft.NETCore.Platforms) for more info.
 
-For more information on various targets see also [.NET Standard](https://github.com/dotnet/standard/blob/master/docs/versions.md)
-
 ## Aggregate build properties
 Each project will define a set of supported TargetFrameworks
 
@@ -60,21 +52,8 @@ Pure netstandard configuration:
 All supported targets with unique windows/unix build for netcoreapp:
 ```
 <PropertyGroup>
-  <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
-<PropertyGroup>
-```
-
-### Placeholder Target Frameworks
-Placeholder Target Framework can be added to the `<TargetFrameworks>` property to indicate the build system that the specific project is inbox in that framework and that Build Setting needs to be ignored.
-
-Placeholder target frameworks start with _ prefix.
-
-Example:
-When we have a project that has a `netstandard2.0` target framework that means that this project is compatible with any build setting. So if we do a vertical build for `net472` this project will be built as part of the vertical because `net472` is compatible with `netstandard2.0`. This means that in the runtime and testhost binaries the netstandard2.0 implementation will be included, and we will test against those assets instead of testing against the framework inbox asset. In order to tell the build system to not include this project as part of the `net472` vertical we need to add a placeholder target framework:
-```
+  <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;net461-Windows_NT</TargetFrameworks>
 <PropertyGroup>
-  <TargetFrameworks>netstandard2.0;_net472</TargetFrameworks>
-</PropertyGroup>
 ```
 
 ## Options for building
@@ -94,7 +73,7 @@ When building an individual project the `BuildTargetFramework` and `TargetOS` wi
 
 ## Supported full build settings
 - .NET Core latest on current OS (default) -> `$(NetCoreAppCurrent)-[RunningOS]`
-- .NET Framework latest -> `$(NetFrameworkCurrent)-Windows_NT`
+- .NET Framework latest -> `net48-Windows_NT`
 
 # Library project guidelines
 
@@ -152,44 +131,34 @@ Reference assemblies are required for any library that has more than one impleme
 In the ref directory for the library there should be at most **one** `.csproj` that contains the latest API for the reference assembly for the library. That project can contain multiple entries in its `TargetFrameworks` property. Ref projects should use `<ProjectReference>` for its dependencies.
 
 ### ref output
-The output for the ref project build will be a flat targeting pack folder in the following directory:
+All ref outputs should be under
 
-`bin\ref\$(TargetFramework)`
-
-<BR/>//**CONSIDER**: Do we need a specific BuildTargetFramework version of TargetFramework for this output path to ensure all projects output to same targeting path?
+`bin\$(MSBuildProjectName)\ref\$(TargetFramework)`
 
 ## src
 In the src directory for a library there should be only **one** `.csproj` file that contains any information necessary to build the library in various target frameworks. All supported target frameworks should be listed in the `TargetFrameworks` property.
 
-All libraries should use `<Reference Include="..." />` for all their project references. That will cause them to be resolved against a targeting pack (i.e. `bin\ref\net5.0` or `\bin\ref\netstandard2.0`) based on the project target framework. There should not be any direct project references to other libraries. The only exception to that rule right now is for partial facades which directly reference System.Private.CoreLib and thus need to directly reference other partial facades to avoid type conflicts.
-<BR>//**CONSIDER**: just using Reference and use a reference to System.Private.CoreLib as a trigger to turn the other References into a ProjectReference automatically. That will allow us to have consistency where all projects just use Reference.
+All libraries should use `<Reference Include="..." />` for all their references to libraries that compose the shared framework of the current .NETCoreApp. That will cause them to be resolved against the locally built targeting pack which is located at `artifacts\bin\microsoft.netcore.app.ref`. The only exception to that rule right now is for partial facades which directly reference System.Private.CoreLib and thus need to directly reference other partial facades to avoid type conflicts.
 
-### src output
-The output for the src product build will be a flat runtime folder into the following directory:
+Other target frameworks than .NETCoreApp latest (i.e. `netstandard2.0`, `net461`, `netcoreapp3.0`) should use ProjectReference items to reference dependencies.
 
-`bin\runtime\$(BuildSettings)`
+### src output
+All src outputs are under
 
-Note: The `BuildSettings` is a global property and not the project setting because we need all projects to output to the same runtime directory no matter which compatible target framework we select and build the project with.
-```<BuildSettings>$(BuildTargetFramework)-$(TargetOS)-(Configuration)-(TargetArchitecture)</BuildSettings>```
+`bin\$(MSBuildProjectName)\$(TargetFramework)`
 
 ## pkg
 In the pkg directory for the library there should be only **one** `.pkgproj` for the primary package for the library. If the library has platform-specific implementations those should be split into platform specific projects in a subfolder for each platform. (see [Package projects](./package-projects.md))
 
-TODO: Outline changes needed for pkgprojs
-
 ## tests
 Similar to the src projects tests projects will define a `TargetFrameworks` property so they can list out the set of target frameworks they support.
 
-Tests should not have any `<Reference>` or `<ProjectReference>` items in their project because they will automatically reference everything in the targeting pack based on the TargetFramework they are building in. The only exception to this is a `<ProjectReference>` can be used to reference other test helper libraries or assets.
-
-In order to build and run a test project in a given build target framework a root level build.cmd/sh must have been completed for that build target framework first. Tests will run on the live built runtime at `bin\runtime\$(BuildSettings)`.
-TODO: We need update our test host so that it can run from the shared runtime directory as well as resolve assemblies from the test output directory.
+Tests don't need to reference default references which are part of the targeting packs (i.e. `mscorlib` on .NETFramework or `System.Runtime` on .NETCoreApp). Everything on top of targeting packs should be referenced via ProjectReference items for live built assets.
 
 ### tests output
 All test outputs should be under
 
-`bin\tests\$(MSBuildProjectName)\$(TargetFramework)` or
-`bin\tests\$(MSBuildProjectName)\netstandard2.0`
+`bin\$(MSBuildProjectName)\$(TargetFramework)`
 
 ## Facades
 Facade are unique in that they don't have any code and instead are generated by finding a contract reference assembly with the matching identity and generating type forwards for all the types to where they live in the implementation assemblies (aka facade seeds). There are also partial facades which contain some type forwards as well as some code definitions. All the various build configurations should be contained in the one csproj file per library.
diff --git a/docs/design/coreclr/botr/xplat-minidump-generation.md b/docs/design/coreclr/botr/xplat-minidump-generation.md
index f0836ae5c2143b..16b506dbb313f2 100644
--- a/docs/design/coreclr/botr/xplat-minidump-generation.md
+++ b/docs/design/coreclr/botr/xplat-minidump-generation.md
@@ -1,6 +1,6 @@
 # Introduction #
 
-Core dump generation on Linux and other non-Windows platforms has several challenges. Dumps can be very large and the default name/location of a dump is not consistent across all our supported platforms.  The size of a full core dumps can be controlled somewhat with the "coredump_filter" file/flags but even with the smallest settings may be still too large and may not contain all the managed state needed for debugging. By default, some platforms use _core_ as the name and place the core dump in the current directory from where the program is launched; others add the _pid_ to the name. Configuring the core name and location requires superuser permission. Requiring superuser to make this consistent is not a satisfactory option.
+Dump generation on Windows, Linux and other non-Windows platforms has several challenges. Dumps can be very large and the default name/location of a dump is not consistent across all our supported platforms.  The size of a full core dumps can be controlled somewhat with the "coredump_filter" file/flags but even with the smallest settings may be still too large and may not contain all the managed state needed for debugging. By default, some platforms use _core_ as the name and place the core dump in the current directory from where the program is launched; others add the _pid_ to the name. Configuring the core name and location requires superuser permission. Requiring superuser to make this consistent is not a satisfactory option.
 
 Our goal is to generate core dumps that are on par with WER (Windows Error Reporting) crash dumps on any supported Linux platform. To the very least we want to enable the following:
 - automatic generation of minimal size minidumps. The quality and quantity of the information contained in the dump should be on par with the information contained in a traditional Windows mini-dump.
@@ -12,7 +12,7 @@ Our solution at this time is to intercept any unhandled exception in the PAL lay
 
 We looked at the existing technologies like Breakpad and its derivatives (e.g.: an internal MS version called _msbreakpad_ from the SQL team....). Breakpad generates Windows minidumps but they are not compatible with existing tools like Windbg, etc. Msbreakpad even more so. There is a minidump to Linux core conversion utility but it seems like a wasted extra step. _Breakpad_ does allow the minidump to be generated in-process inside the signal handlers. It restricts the APIs to what was allowed in a "async" signal handler (like SIGSEGV) and has a small subset of the C++ runtime that was also similarly constrained. We also need to add the set of memory regions for the "managed" state which requires loading and using the _DAC_'s (*) enumerate memory interfaces. Loading modules is not allowed in an async signal handler but forking/execve is allowed so launching an utility that loads the _DAC_, enumerates the list of memory regions and writes the dump is the only reasonable option. It would also allow uploading the dump to a server too.
 
-\* The _DAC_ is a special build of parts of the coreclr runtime that allows inspection of the runtime's managed state (stacks, variables, GC state heaps) out of context. One of the many interfaces it provides is [ICLRDataEnumMemoryRegions](https://github.com/dotnet/runtime/blob/master/src/coreclr/src/debug/daccess/dacimpl.h) which enumerates all the managed state a minidump would require to enable a fuitful debugging experience.
+\* The _DAC_ is a special build of parts of the coreclr runtime that allows inspection of the runtime's managed state (stacks, variables, GC state heaps) out of context. One of the many interfaces it provides is [ICLRDataEnumMemoryRegions](https://github.com/dotnet/runtime/blob/master/src/coreclr/src/debug/daccess/dacimpl.h) which enumerates all the managed state a minidump would require to enable a fruitful debugging experience.
 
 _Breakpad_ could have still been used out of context in the generation utility but there seemed no value to their Windows-like minidump format when it would have to be converted to the native Linux core format away because in most scenarios using the platform tools like _lldb_ is necessary. It also adds a coreclr build dependency on Google's _Breakpad_ or SQL's _msbreakpad_ source repo. The only advantage is that the breakpad minidumps may be a little smaller because minidumps memory regions are byte granule and Linux core memory regions need to be page granule.
 
@@ -42,7 +42,11 @@ There will be some differences gathering the crash information but these platfor
 
 ### OS X ###
 
-Gathering the crash information on OS X will be quite a bit different than Linux and the core dump will be written in the Mach-O format instead of ELF. The OS X support currently has not been implemented.
+As of .NET Core 5.0, createdump is supported on MacOS but instead of the MachO dump format, it generates the ELF coredumps. This is because of time constraints developing a MachO dump writer on the generation side and a MachO reader for the diagnostics tooling side (dotnet-dump and CLRMD). This means the native debuggers like gdb and lldb will not work with these dumps but the dotnet-dump tool will allow the managed state to be analyzed. Because of this behavior an additional environment variable will need to be set (COMPlus_DbgEnableElfDumpOnMacOS=1) along with the ones below in the Configuration/Policy section.
+
+### Windows ###
+
+As of .NET Core 5.0, createdump and the below configuration environment variables are supported on Windows. It is implemented using the Windows MiniDumpWriteDump API. This allows consistent crash/unhandled exception dumps across all of our platforms. 
 
 # Configuration/Policy #
 
diff --git a/docs/project/library-servicing.md b/docs/project/library-servicing.md
index 29934d1606f1f5..3dc16895951d68 100644
--- a/docs/project/library-servicing.md
+++ b/docs/project/library-servicing.md
@@ -4,7 +4,7 @@ This document provides the steps necessary after modifying a CoreFx library in a
 
 ## Check for existence of a .pkgproj
 
-Most CoreFx libraries are not packaged by default. Some libraries have their output packaged in `Microsoft.Private.CoreFx.NetCoreApp`, which is always built, while other libraries have their own specific packages, which are only built on-demand. Your first step is to determine whether or not your library has its own package. To do this, go into the root folder for the library you've made changes to. If there is a `pkg` folder there (which should have a `.pkgproj` file inside of it), your library does have its own package. If there is no `pkg` folder there, the library should be built as part of `Microsoft.Private.CoreFx.NetCoreApp` and shipped as part of `Microsoft.NetCore.App`. To confirm this, check for the `IsNETCoreApp` property being set to `true` in the library's `Directory.Build.props` (or dir.props). If it is, then there is nothing that needs to be done. If it's not, contact a member of the servicing team for guidance, as this situation goes against our convention.
+Most libraries are not packaged by default. Some libraries have their output packaged in `Microsoft.Private.CoreFx.NetCoreApp`, which is always built, while other libraries have their own specific packages, which are only built on-demand. Your first step is to determine whether or not your library has its own package. To do this, go into the root folder for the library you've made changes to. If there is a `pkg` folder there (which should have a `.pkgproj` file inside of it), your library does have its own package. If there is no `pkg` folder there, the library should be built as part of `Microsoft.Private.CoreFx.NetCoreApp` and shipped as part of `Microsoft.NetCore.App`. To confirm this, check if the library is listed in NetCoreAppLibrary.props. If it is, then there is nothing that needs to be done. If it's not, contact a member of the servicing team for guidance, as this situation goes against our convention.
 
 For example, if you made changes to [System.Data.SqlClient](https://github.com/dotnet/runtime/tree/master/src/libraries/Microsoft.Win32.Registry), then you have a .pkgproj, and will have to follow the steps in this document. However, if you made changes to [System.Collections](https://github.com/dotnet/runtime/tree/master/src/libraries/System.Collections), then you don't have a .pkgproj, and you do not need to do any further work for servicing.
 
diff --git a/docs/project/list-of-obsoletions.md b/docs/project/list-of-obsoletions.md
index 3b7d6696c62da6..35bae5551e4d11 100644
--- a/docs/project/list-of-obsoletions.md
+++ b/docs/project/list-of-obsoletions.md
@@ -24,3 +24,4 @@ Currently the identifiers `SYSLIB0001` through `SYSLIB0999` are carved out for o
 |  __`SYSLIB0009`__ | The AuthenticationManager Authenticate and PreAuthenticate methods are not supported and throw PlatformNotSupportedException. |
 |  __`SYSLIB0010`__ | This Remoting API is not supported and throws PlatformNotSupportedException. |
 |  __`SYSLIB0011`__ | `BinaryFormatter` serialization is obsolete and should not be used. See https://aka.ms/binaryformatter for recommended alternatives. |
+|  __`SYSLIB0012`__ | Use Location instead. |
diff --git a/docs/workflow/building/libraries/README.md b/docs/workflow/building/libraries/README.md
index 44eb0eb209eee1..ec0f52388e693a 100644
--- a/docs/workflow/building/libraries/README.md
+++ b/docs/workflow/building/libraries/README.md
@@ -9,7 +9,7 @@ Here is one example of a daily workflow for a developer working mainly on the li
 git clean -xdf
 git pull upstream master & git push origin master
 :: Build Debug libraries on top of Release runtime:
-build -subset clr+libs -runtimeConfiguration Release
+build clr+libs -rc Release
 :: The above you may only perform once in a day, or when you pull down significant new changes.
 
 :: If you use Visual Studio, you might open System.Text.RegularExpressions.sln here.
@@ -33,7 +33,7 @@ The instructions for Linux and macOS are essentially the same:
 git clean -xdf
 git pull upstream master & git push origin master
 # Build Debug libraries on top of Release runtime:
-./build.sh -subset clr+libs -runtimeconfiguration Release
+./build.sh clr+libs -rc Release
 # The above you may only perform once in a day, or when you pull down significant new changes.
 
 # Switch to working on a given library (RegularExpressions in this case)
@@ -56,12 +56,12 @@ These example commands will build a release CoreCLR (and CoreLib), debug librari
 
 For Linux:
 ```bash
-./build.sh -runtimeConfiguration Release
+./build.sh -rc Release
 ```
 
 For Windows:
 ```bat
-./build.cmd -runtimeConfiguration Release
+./build.cmd -rc Release
 ```
 
 Detailed information about building and testing runtimes and the libraries is in the documents linked below.
@@ -74,7 +74,7 @@ The libraries build has two logical components, the native build which produces
 
 The build settings (BuildTargetFramework, TargetOS, Configuration, Architecture) are generally defaulted based on where you are building (i.e. which OS or which architecture) but we have a few shortcuts for the individual properties that can be passed to the build scripts:
 
-- `-framework|-f` identifies the target framework for the build. Possible values include `net5.0` (currently the latest .NET version) or `net472`. (msbuild property `BuildTargetFramework`)
+- `-framework|-f` identifies the target framework for the build. Possible values include `net5.0` (currently the latest .NET version) or `net48` (the latest .NETFramework version). (msbuild property `BuildTargetFramework`)
 - `-os` identifies the OS for the build. It defaults to the OS you are running on but possible values include `Windows_NT`, `Unix`, `Linux`, or `OSX`. (msbuild property `TargetOS`)
 - `-configuration|-c Debug|Release` controls the optimization level the compilers use for the build. It defaults to `Debug`. (msbuild property `Configuration`)
 - `-arch` identifies the architecture for the build. It defaults to `x64` but possible values include `x64`, `x86`, `arm`, or `arm64`. (msbuild property `TargetArchitecture`)
@@ -83,26 +83,20 @@ For more details on the build settings see [project-guidelines](../../../coding-
 
 If you invoke the `build` script without any actions, the default action chain `-restore -build` is executed.
 
-By default the `build` script only builds the product libraries and none of the tests. If you want to include tests, you want to add the subset `-subset libtests`. If you want to run the tests you want to use the `-test` action instead of the `-build`, e.g. `build.cmd/sh -subset libs.tests -test`. To specify just the libraries, use `-subset libs`.
+By default the `build` script only builds the product libraries and none of the tests. If you want to include tests, you want to add the subset `libs.tests`. If you want to run the tests you want to use the `-test` action instead of the `-build`, e.g. `build.cmd/sh libs.tests -test`. To specify just the libraries, use `libs`.
 
 **Examples**
 - Building in release mode for platform x64 (restore and build are implicit here as no actions are passed in)
 ```bash
-./build.sh -subset libs -c Release -arch x64
+./build.sh libs -c Release -arch x64
 ```
 
 - Building the src assemblies and build and run tests (running all tests takes a considerable amount of time!)
 ```bash
-./build.sh -subset libs -test
+./build.sh libs -test
 ```
 
-- Building for different target frameworks (restore and build are implicit again as no action is passed in)
-```bash
-./build.sh -subset libs -framework net5.0
-./build.sh -subset libs -framework net472
-```
-
-- Clean the entire solution
+- Clean the entire artifacts folder
 ```bash
 ./build.sh -clean
 ```
@@ -199,24 +193,24 @@ You can use the same workflow for mono runtime by using `mono.corelib+libs.prete
 By default the libraries will attempt to build using the CoreCLR version of `System.Private.CoreLib.dll`. In order to build against the Mono version you need to use the `/p:RuntimeFlavor=Mono` argument.
 
 ```
-.\build.cmd -subset libs /p:RuntimeFlavor=Mono
+.\build.cmd libs /p:RuntimeFlavor=Mono
 ```
 
 ### Building all for other OSes
 
 By default, building from the root will only build the libraries for the OS you are running on. One can
-build for another OS by specifying `./build.sh -subset libs -os [value]`.
+build for another OS by specifying `./build.sh libs -os [value]`.
 
 Note that you cannot generally build native components for another OS but you can for managed components so if you need to do that you can do it at the individual project level or build all via passing `/p:BuildNative=false`.
 
 ### Building in Release or Debug
 
 By default, building from the root or within a project will build the libraries in Debug mode.
-One can build in Debug or Release mode from the root by doing `./build.sh -subset libs -c Release` or `./build.sh -subset libs -c Debug`.
+One can build in Debug or Release mode from the root by doing `./build.sh libs -c Release` or `./build.sh libs`.
 
 ### Building other Architectures
 
-One can build 32- or 64-bit binaries or for any architecture by specifying in the root `./build.sh -subset libs -arch [value]` or in a project `/p:TargetArchitecture=[value]` after the `dotnet build` command.
+One can build 32- or 64-bit binaries or for any architecture by specifying in the root `./build.sh libs -arch [value]` or in a project `/p:TargetArchitecture=[value]` after the `dotnet build` command.
 
 ## Working in Visual Studio
 
@@ -227,3 +221,17 @@ If you are working on Windows, and use Visual Studio, you can open individual li
 For more details about running tests inside Visual Studio, [go here](../../testing/visualstudio.md).
 
 For more about running tests, read the [running tests](../../testing/libraries/testing.md) document.
+
+## Build packages
+To build a library's package, simply invoke `dotnet pack` on the src project after you successfully built the .NETCoreApp vertical from root:
+
+```
+build libs
+dotnet pack src\libraries\System.Text.Json\src\
+```
+
+Same as for `dotnet build` or `dotnet publish`, you can specify the desired configuration via the `-c` flag:
+
+```
+dotnet pack src\libraries\System.Text.Json\src\ -c Release
+```
diff --git a/docs/workflow/building/libraries/webassembly-instructions.md b/docs/workflow/building/libraries/webassembly-instructions.md
index c3195a30665e33..408aa4e908270d 100644
--- a/docs/workflow/building/libraries/webassembly-instructions.md
+++ b/docs/workflow/building/libraries/webassembly-instructions.md
@@ -34,12 +34,12 @@ The libraries build contains some native code. This includes shims over libc, op
 
 - Building in debug mode for platform wasm and Browser operating system
 ```bash
-./build.sh --arch wasm --os Browser --subset Libs.Native --configuration Debug
+./build.sh libs.native --arch wasm --os Browser
 ```
 
 - Building in release mode for platform wasm and Browser operating system
 ```bash
-./build.sh --arch wasm --os Browser --subset Libs.Native --configuration Release
+./build.sh libs.native --arch wasm --os Browser -c Release
 ```
 
 ## How to build mono System.Private.CoreLib
@@ -48,20 +48,19 @@ If you are working on core parts of mono libraries you will probably need to bui
 
 
 ```bash
-./build.sh --arch wasm --os Browser --configuration release --subset Mono
+./build.sh mono --arch wasm --os Browser -c Release
 ```
 
 To build just SPC without mono you can use the Mono.CoreLib subset.
 
 ```bash
-./build.sh --arch wasm --os Browser --configuration release --subset Mono.CoreLib
+./build.sh mono.corelib --arch wasm --os Browser -c Release
 ```
 
-
 Building the managed libraries as well:
 
 ```bash
-./build.sh --arch wasm --os Browser --configuration release --subset Mono+Libs
+./build.sh mono+libs --arch wasm --os Browser -c Release
 ```
 
 ## Building individual libraries
@@ -71,16 +70,16 @@ Individual projects and libraries can be build by specifying the build configura
 Building individual libraries
 **Examples**
 
-- Build all projects for a given library (e.g.: System.Net.Http) including running the tests
+- Build all projects for a given library (e.g.: System.Net.Http) including the tests
 
 ```bash
- ./build.sh --arch wasm --os Browser --configuration release --projects src/libraries/System.Net.Http/System.Net.Http.sln
+ ./build.sh --arch wasm --os Browser -c Release --projects src/libraries/System.Net.Http/System.Net.Http.sln
 ```
 
 - Build only the source project of a given library (e.g.: System.Net.Http)
 
 ```bash
- ./build.sh --arch wasm --os Browser --configuration release --projects src/libraries/System.Net.Http/src/System.Net.Http.csproj
+ ./build.sh --arch wasm --os Browser -c Release --projects src/libraries/System.Net.Http/src/System.Net.Http.csproj
 ```
 
 More information and examples can be found in the [libraries](./README.md#building-individual-libraries) document.
@@ -91,7 +90,7 @@ The WebAssembly implementation files are built and made available in the artifac
 
 For Linux and MacOSX:
 ```bash
-./dotnet.sh build /p:Configuration=Debug|Release /p:TargetArchitecture=wasm /p:TargetOS=Browser src/libraries/src.proj /t:NativeBinPlace 
+./dotnet.sh build /p:Configuration=Debug|Release /p:TargetArchitecture=wasm /p:TargetOS=Browser src/libraries/src.proj /t:BuildWasmRuntimes 
 ```
 
 __Note__: A `Debug` build sets the following environment variables by default.  When built from the command line this way the `Configuration` value is case sensitive.
@@ -155,4 +154,4 @@ container:
     registry: mcr
 ```
 
-Open a PR request with the new image. 
\ No newline at end of file
+Open a PR request with the new image. 
diff --git a/docs/workflow/requirements/freebsd-requirements.md b/docs/workflow/requirements/freebsd-requirements.md
index 59b3c64d928f15..66e50ec878b361 100644
--- a/docs/workflow/requirements/freebsd-requirements.md
+++ b/docs/workflow/requirements/freebsd-requirements.md
@@ -21,7 +21,7 @@ with all needed prerequisites to build. As the example bellow may become stale,
 
 ```sh
 TAG=mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-18.04-cross-freebsd-11-20200430154008-a84b0d2
-docker run --rm --volume $(pwd):$(pwd) --workdir $(pwd) --env ROOTFS_DIR=/crossrootfs/x64 -ti  $TAG ./build.sh -cross -FreeBSD
+docker run --rm --volume $(pwd):$(pwd) --workdir $(pwd) --env ROOTFS_DIR=/crossrootfs/x64 -ti  $TAG ./build.sh -cross -os FreeBSD
 ```
 
 Build using Toolchain Setup
diff --git a/docs/workflow/testing/using-your-build.md b/docs/workflow/testing/using-your-build.md
index 31a7f6bc8d3fe5..33e5ef19e17409 100644
--- a/docs/workflow/testing/using-your-build.md
+++ b/docs/workflow/testing/using-your-build.md
@@ -1,7 +1,7 @@
 
 # Using your .NET Runtime Build
 
-We assume that you have successfully built CoreCLR repository and thus have files of the form
+We assume that you have successfully built the repository and thus have files of the form
 ```
     ~/runtime/artifacts/bin/coreclr/<OS>.<arch>.<flavor>/
 ```
@@ -11,7 +11,7 @@ a 'host' program that will load the Runtime as well as all the other .NET librar
 code that your application needs. The easiest way to get all this other stuff is to simply use the
 standard 'dotnet' host that installs with .NET SDK.
 
-The released version of 'dotnet' tool may not be compatible with the live CoreCLR repository. The following steps
+The released version of 'dotnet' tool may not be compatible with the live repository. The following steps
 assume use of a dogfood build of the .NET SDK.
 
 ## Acquire the latest nightly .NET SDK
@@ -157,7 +157,7 @@ Assert failure(PID 13452 [0x0000348c], Thread: 10784 [0x2a20]): Consistency chec
 ## Using .NET SDK to run your .NET Application
 
 If you don't like the idea of copying files manually you can follow [these instructions](../using-dotnet-cli.md) to use dotnet cli to do this for you.
-However the steps described here are the simplest and most commonly used by CoreCLR developers for ad-hoc testing.
+However the steps described here are the simplest and most commonly used by runtime developers for ad-hoc testing.
 
 ## Using CoreRun to run your .NET Application
 
diff --git a/docs/workflow/testing/visualstudio.md b/docs/workflow/testing/visualstudio.md
index c8c20b9cfc7fa3..106f069f7df78a 100644
--- a/docs/workflow/testing/visualstudio.md
+++ b/docs/workflow/testing/visualstudio.md
@@ -1,9 +1,25 @@
-# Visual Studio Test Explorer support
-For Visual Studio Test Explorer to work in dotnet/runtime, the following test settings need to be enabled: 
-- Test parameters (like which `dotnet` host to use) are persisted in an auto-generated .runsettings file. For that to work, make sure that the "Auto detect runsettings Files" (`Options -> Test`) option is enabled.
-- Make sure that the "Processor Architecture for AnyCPU project" (`Test Explore pane -> Test Explorer toolbar options --> Settings`) value is set to `auto`.
+# Working in dotnet/runtime using Visual Studio
+
+Visual Studio is a great tool to use when working in the dotnet/runtime repo. 
+
+Almost all its features should work well, but there are a few special considerations to bear in mind:
+
+## Test Explorer 
+
+You can run tests from the Visual Studio Test Explorer, but there are a few settings you need:
+- Enable `Auto detect runsettings Files` (`Test Explorer window -> Settings button -> Options`). Test parameters (like which `dotnet` host to use) are persisted in an auto-generated .runsettings file, and it's important that Visual Studio knows to use it.
+- Set `Processor Architecture for AnyCPU project` to `auto` (`Test Explorer window -> Settings button`).
+- Consider whether to disable `Discover tests in real time from C# and Visual Basic .NET source files` (`Test explorer window -> Settings button -> Options`). 
+    - You may want it enabled if you're actively writing new tests and want them to show up in Test Explorer without building first.
+    - You may want it disabled if you're mostly running existing tests, and some of them have conditional attributes. Many of our unit tests have attributes, like `[SkipOnTargetFramework]`, to indicate that they're only valid in certain configurations. Because the real-time discovery feature does not currently recognize these attributes the tests will show up in Test Explorer as well, and fail or possibly hang when you try to run them.
+- Consider whether to enable `Run tests in Parallel` (`Test Explorer window -> Settings button`). 
+    - You may want it enabled if some of the unit tests you're working with run slowly or there's many of them.
+    - You may want it disabled if you want to simplify debugging or viewing debug output.
+
+If you encounter puzzling behavior while running tests within Visual Studio, first check the settings above, verify they run correctly from the command line, and also make sure you're using the latest Visual Studio. It can be helpful to enable detailed logging of the test runner (`Test explorer window -> Settings button -> Options > Logging Level: Trace`) - it may suggest the problem, or at least provide more information to share.
+
+## Start with Debugging (F5)
 
-# Visual Studio F5 Debugging support
 dotnet/runtime uses `dotnet test` ([VSTest](https://github.com/Microsoft/vstest)) which spawns child processes during test execution.
 Visual Studio by default doesn't automatically debug child processes, therefore preliminary steps need to be done to enable Debugging "F5" support.
 Note that these steps aren't necessary for Visual Studio Test Explorer support.
@@ -14,3 +30,4 @@ Note that these steps aren't necessary for Visual Studio Test Explorer support.
 ## References
 - https://github.com/dotnet/project-system/issues/6176 tracks enabling the native code debugging functionality for multiple projects without user interaction.
 - https://github.com/dotnet/sdk/issues/7419#issuecomment-298261617 explains the necessary steps to install and enable the mentioned extension in more detail.
+- https://github.com/microsoft/vstest/ is the repo for issues with the Visual Studio test execution features.
diff --git a/docs/workflow/trimming/feature-switches.md b/docs/workflow/trimming/feature-switches.md
index ad911e818d7a53..40d3a2299f474b 100644
--- a/docs/workflow/trimming/feature-switches.md
+++ b/docs/workflow/trimming/feature-switches.md
@@ -14,7 +14,7 @@ configurations but their defaults might vary as any SDK can set the defaults dif
 | EventSourceSupport | System.Diagnostics.Tracing.EventSource.IsSupported | Any EventSource related code or logic is trimmed when set to false |
 | InvariantGlobalization | System.Globalization.Invariant | All globalization specific code and data is trimmed when set to true |
 | UseSystemResourceKeys | System.Resources.UseSystemResourceKeys |  Any localizable resources for system assemblies is trimmed when set to true |
-| - | System.Net.Http.EnableActivityPropagation | Any dependency related to diagnostics support for System.Net.Http is trimmed when set to false |
+| HttpActivityPropagationSupport | System.Net.Http.EnableActivityPropagation | Any dependency related to diagnostics support for System.Net.Http is trimmed when set to false |
 
 Any feature-switch which defines property can be set in csproj file or
 on the command line as any other MSBuild property. Those without predefined property name
diff --git a/docs/workflow/using-dotnet-cli.md b/docs/workflow/using-dotnet-cli.md
index 7c9efa28c829d2..68cadd5bf4f831 100644
--- a/docs/workflow/using-dotnet-cli.md
+++ b/docs/workflow/using-dotnet-cli.md
@@ -1,23 +1,23 @@
 
 # Using your .NET Runtime build with .NET SDK
 
-This walkthrough explains how to run against your local CoreCLR build using .NET SDK only.
+This walkthrough explains how to run your own app against your local build using only the .NET SDK.
 
 For other walkthroughs see:
 
-- [Using Your Build - Update CoreCLR from raw binary output](./testing/using-your-build.md)
+- [Using Your Build - Update from raw build output](./testing/using-your-build.md)
 - [Using CoreRun To Run .NET Application](./testing/using-corerun.md)
 - [Dogfooding .NET SDK](https://github.com/dotnet/runtime/blob/master/docs/project/dogfooding.md).
 
 ## Prerequisites
 
-1. Successfully built CoreCLR repository and thus have files of the form shown below. From now on we call this folder NuGet package folder.
+1. Successfully built this repository and thus have files of the form shown below. From now on we call this folder NuGet package folder.
 
 ```
-    artifacts\bin\coreclr\<OS>.<arch>.<flavor>\.nuget\pkg\runtime.<OS>-<arch>.Microsoft.NETCore.Runtime.CoreCLR.<version>.nupkg
+    artifacts\packages\<configuration>\Shipping\
 ```
 
-2. Acquired the latest nightly .NET SDK from [here](https://github.com/dotnet/cli/blob/master/README.md#installers-and-binaries) and added it's root folder to your [path](requirements/windows-requirements.md#adding-to-the-default-path-variable)
+2. Acquired the latest nightly .NET SDK from [here](https://github.com/dotnet/installer) and added its root folder to your [path](requirements/windows-requirements.md#adding-to-the-default-path-variable)
 
 ## First Run
 
@@ -29,13 +29,11 @@ From now on all instructions relate to this folder as "app folder".
 
 ### 2. Create NuGet.Config file
 
-The build script creates NuGet packages and puts them to `artifacts\bin\coreclr\<OS>.<arch>.<flavor>\.nuget\pkg\`. .NET SDK has no idea about its existence and we need to tell it where to search for the packages.
+The build script creates NuGet packages and puts them to `artifacts\packages\<configuration>\Shipping\`. .NET SDK has no idea about its existence and we need to tell it where to search for the packages.
 
 Please run `dotnet new nugetconfig` in the app folder and update the created `NuGet.Config` file:
 
-* **set path to local CoreCLR NuGet folder!!**
-* add address to dotnet core tools NuGet feed
-
+* ** adjust path below to point to your in-repo NuGet folder**
 
 ```xml
 <?xml version="1.0" encoding="utf-8"?>
@@ -44,11 +42,9 @@ Please run `dotnet new nugetconfig` in the app folder and update the created `Nu
     <!--To inherit the global NuGet package sources remove the <clear/> line below -->
     <clear />
 
-    <add key="local CoreCLR" value="C:\runtime\artifacts\bin\coreclr\Windows_NT.x64.Debug\.nuget\pkg" /> <!-- CHANGE THIS PATH to your local output path -->
-    <add key="dotnet-core" value="https://dotnet.myget.org/F/dotnet-core/api/v3/index.json" /> <!-- link to corefx NuGet feed -->
+    <add key="local runtime" value="C:\runtime\artifacts\artifacts\packages\Release\Shipping\" /> <!-- CHANGE THIS PATH to your local output path -->
   </packageSources>
 </configuration>
-
 ```
 
 ### 3. Create and update the Project file
@@ -60,39 +56,34 @@ Please run `dotnet new console` in the app folder and update the created `.cspro
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFramework>net5.0</TargetFramework>
     <RuntimeIdentifier>win-x64</RuntimeIdentifier>
-    <RuntimeFrameworkVersion>3.0.0-preview1-26210-0</RuntimeFrameworkVersion>
+    <RuntimeFrameworkVersion>5.0.0-dev</RuntimeFrameworkVersion>
   </PropertyGroup>
 
-  <ItemGroup>
-    <PackageReference Include="runtime.win-x64.Microsoft.NETCore.Runtime.CoreCLR" Version="3.0.0-preview1-26210-0" />
-    <PackageReference Include="runtime.win-x64.Microsoft.NETCore.Jit" Version="3.0.0-preview1-26210-0" />
-  </ItemGroup>
-
 </Project>
 ```
 
 **You have to set the correct values for `RuntimeIdentifier` (RI), `RuntimeFrameworkVersion` and versions of both packages.**
 
 You can generally figure that out by looking at the packages you found in your output.
-In our example you will see there is a package with the name `runtime.win-x64.Microsoft.NETCore.Runtime.CoreCLR.3.0.0-preview1-26210-0.nupkg`
+In our example you will see there is a package with the name `Microsoft.NETCore.App.Runtime.win-x64.5.0.0-dev.nupkg`
 
 ```
-runtime.win-x64.Microsoft.NETCore.Runtime.CoreCLR.3.0.0-preview1-26210-0.nupkg
-       ^--RI---^                                 ^--------version-------^
+Microsoft.NETCore.App.Runtime.win-x64.5.0.0-dev.nupkg
+                              ^-RI--^ ^version^
 ```
 
 ### 4. Change Program.cs
 
-To make sure that you run against your local coreclr build please change your `Main` method in `Program.cs` file to:
+To make sure that you run against your local build of this repo please change your `Main` method in `Program.cs` file to:
 
 ```cs
 static void Main(string[] args)
 {
-	var coreAssemblyInfo = System.Diagnostics.FileVersionInfo.GetVersionInfo(typeof(object).Assembly.Location);
-	Console.WriteLine($"Hello World from Core {coreAssemblyInfo.ProductVersion}");
-	Console.WriteLine($"The location is {typeof(object).Assembly.Location}");
+    var coreAssemblyInfo = System.Diagnostics.FileVersionInfo.GetVersionInfo(typeof(object).Assembly.Location);
+    Console.WriteLine($"Hello World from .NET {coreAssemblyInfo.ProductVersion}");
+    Console.WriteLine($"The location is {typeof(object).Assembly.Location}");
 }
 ```
 
@@ -108,40 +99,56 @@ dotnet publish
 Make sure that restoring done by `dotnet publish` installed the explicit version of the Runtime that you have specified:
 
 ```
-PS C:\coreclr\helloWorld> dotnet publish
-  Restoring packages for C:\coreclr\helloWorld\helloWorld.csproj...
-  Installing runtime.win-x64.Microsoft.NETCore.Runtime.CoreCLR 3.0.0-preview1-26210-
+c:\runtime\helloworld>dotnet publish
+Microsoft (R) Build Engine version 16.7.0-preview-20360-03+188921e2f for .NET
+Copyright (C) Microsoft Corporation. All rights reserved.
+
+  Determining projects to restore...
+  Restored c:\runtime\helloworld\helloworld.csproj (in 114 ms).
+  You are using a preview version of .NET. See: https://aka.ms/dotnet-core-preview
+  helloworld -> c:\runtime\helloworld\bin\Debug\net5.0\win-x64\helloworld.dll
+  helloworld -> c:\runtime\helloworld\bin\Debug\net5.0\win-x64\publish\
 ```
 
 If you see something like the message below it means that it has failed to restore your local runtime packages. In such case double check your `NuGet.config` file and paths used in it.
 
 ```
-C:\coreclr\helloWorld\helloWorld.csproj : warning NU1603: helloWorld depends on runtime.win-x64.Microsoft.NETCore.Runtime.CoreCLR (>= 3.0.0-preview1-26210-0) but runtime.win-x64.Microsoft.NETCore.Runtime.CoreCLR 3.0.0-preview1-26210-0 was not found. An approximate best match of runtime.win-x64.Microsoft.NETCore.Runtime.CoreCLR 3.0.0-preview2-25501-02 was resolved.
+c:\runtime\helloworld>dotnet publish
+Microsoft (R) Build Engine version 16.7.0-preview-20360-03+188921e2f for .NET
+Copyright (C) Microsoft Corporation. All rights reserved.
+
+  Determining projects to restore...
+c:\runtime\helloworld\helloworld.csproj : error NU1102: Unable to find package Microsoft.NETCore.App.Runtime.win-x64 with version (= 5.0.0-does-not-exist)
+c:\runtime\helloworld\helloworld.csproj : error NU1102:   - Found 25 version(s) in nuget [ Nearest version: 5.0.0-preview.1.20120.5 ]
+c:\runtime\helloworld\helloworld.csproj : error NU1102:   - Found 1 version(s) in local runtime [ Nearest version: 5.0.0-dev ]
+c:\runtime\helloworld\helloworld.csproj : error NU1102: Unable to find package Microsoft.NETCore.App.Host.win-x64 with version (= 5.0.0-does-not-exist)
+c:\runtime\helloworld\helloworld.csproj : error NU1102:   - Found 27 version(s) in nuget [ Nearest version: 5.0.0-preview.1.20120.5 ]
+c:\runtime\helloworld\helloworld.csproj : error NU1102:   - Found 1 version(s) in local runtime [ Nearest version: 5.0.0-dev ]
+  Failed to restore c:\runtime\helloworld\helloworld.csproj (in 519 ms).
 ```
 
 ### 6. Run the app
 
-After you publish you will find all the binaries needed to run your application under `bin\Debug\netcoreapp3.0\win-x64\publish\`.
+After you publish you will find all the binaries needed to run your application under `bin\Debug\net5.0\win-x64\publish\`.
 To run the application simply run the EXE that is in this publish directory (it is the name of the app, or specified in the project file).
 
 ```
-.\bin\Debug\netcoreapp3.0\win-x64\publish\HelloWorld.exe
+.\bin\Debug\net5.0\win-x64\publish\HelloWorld.exe
 ```
 
-Running the app should tell you the version and which user and machine build the assembly as well as the commit hash of the code
-at the time of building:
+Running the app should tell you the version and where the location of System.Private.CoreLib in the publish directory:
 
 ```
-Hello World from Core 4.6.26210.0 @BuiltBy: adsitnik-MININT-O513E3V @SrcCode: https://github.com/dotnet/runtime/tree/3d6da797d1f7dc47d5934189787a4e8006ab3a04
-The location is C:\coreclr\helloWorld\bin\Debug\netcoreapp3.0\win-x64\publish\System.Private.CoreLib.dll
+Hello World from .NET 5.0.0-dev
+The location is c:\runtime\helloworld\bin\Debug\net5.0\win-x64\publish\System.Private.CoreLib.dll
 ```
 
-**Congratulations! You have just run your first app against local CoreCLR build!**
+**Congratulations! You have just run your first app against your local build of this repo**
 
-## Update CoreCLR using runtime nuget package
+## Update using runtime nuget package
 
-Updating CoreCLR from raw binary output is easier for quick one-off testing but using the nuget package is better
-for referencing your CoreCLR build in your actual application because of it does not require manual copying of files
+Updating the runtime from raw binary output is easier for quick one-off testing but using the nuget package is better
+for referencing your build in your actual application because of it does not require manual copying of files
 around each time the application is built and plugs into the rest of the tool chain. This set of instructions will cover
 the further steps needed to consume the runtime nuget package.
 
diff --git a/eng/AvoidRestoreCycleOnSelfReference.targets b/eng/AvoidRestoreCycleOnSelfReference.targets
new file mode 100644
index 00000000000000..cb665cb070d988
--- /dev/null
+++ b/eng/AvoidRestoreCycleOnSelfReference.targets
@@ -0,0 +1,14 @@
+<Project>
+  <!-- Set PackageId to a temporary value to avoid NuGet restore cycle error NU1108: https://github.com/NuGet/Home/issues/6754 -->
+  <PropertyGroup>
+    <_PackageIdTemp>$(PackageId)</_PackageIdTemp>
+    <PackageId>$(PackageId)_temp</PackageId>
+  </PropertyGroup>
+
+  <Target Name="_UpdatePackageId"
+          BeforeTargets="$(PackDependsOn)" >
+    <PropertyGroup>
+      <PackageId>$(_PackageIdTemp)</PackageId>
+    </PropertyGroup>
+  </Target>
+</Project>
\ No newline at end of file
diff --git a/eng/BeforeTargetFrameworkInference.targets b/eng/BeforeTargetFrameworkInference.targets
index 92adb5df635380..abef4c8981a28e 100644
--- a/eng/BeforeTargetFrameworkInference.targets
+++ b/eng/BeforeTargetFrameworkInference.targets
@@ -6,10 +6,6 @@
     <TargetFramework>$(TargetFramework.SubString(0, $(TargetFramework.IndexOf('-'))))</TargetFramework>
   </PropertyGroup>
 
-  <PropertyGroup>
-    <RefPath>$([MSBuild]::NormalizeDirectory('$(RefRootPath)', '$(TargetFramework)'))</RefPath>  
-  </PropertyGroup>
-
   <Import Project="$(MSBuildThisDirectory)targetframeworksuffix.props" Condition="'$(DesignTimeBuild)' == 'true'" />
 
   <PropertyGroup>
diff --git a/eng/Configurations.props b/eng/Configurations.props
index aa8e9add17dd81..3d123f81972aef 100644
--- a/eng/Configurations.props
+++ b/eng/Configurations.props
@@ -29,9 +29,6 @@
     <NETCoreAppFramework>$(NetCoreAppCurrent)</NETCoreAppFramework>
     <SharedFrameworkName>Microsoft.NETCore.App</SharedFrameworkName>
     <NetCoreAppCurrentBrandName>.NET $(NetCoreAppCurrentVersion)</NetCoreAppCurrentBrandName>
-
-    <NetFrameworkCurrent>net472</NetFrameworkCurrent>
-    <MinimiumSupportedWindowsPlatform>WINDOWS7.0</MinimiumSupportedWindowsPlatform>
   </PropertyGroup>
 
   <!-- Honor the generic RuntimeConfiguration property. -->
diff --git a/eng/DefaultGenApiDocIds.txt b/eng/DefaultGenApiDocIds.txt
index 5576d9fad6ae21..51ea5986f536fb 100644
--- a/eng/DefaultGenApiDocIds.txt
+++ b/eng/DefaultGenApiDocIds.txt
@@ -1,6 +1,5 @@
 // These attributes should be excluded from reference assemblies.
 
-T:System.ComponentModel.DesignerAttribute
 T:System.ComponentModel.Design.Serialization.DesignerSerializerAttribute
 T:System.ComponentModel.Design.Serialization.RootDesignerSerializerAttribute
 T:System.ComponentModel.EditorAttribute
diff --git a/eng/Subsets.props b/eng/Subsets.props
index b27d1e55a8bdd9..f7f61f98f6e9bf 100644
--- a/eng/Subsets.props
+++ b/eng/Subsets.props
@@ -57,9 +57,9 @@
     <DefaultCoreClrSubsets>clr.runtime+linuxdac+clr.corelib+clr.nativecorelib+clr.tools+clr.packages</DefaultCoreClrSubsets>
 
     <DefaultMonoSubsets Condition="'$(MonoEnableLLVM)' == 'true' and '$(MonoLLVMDir)' == ''">mono.llvm+</DefaultMonoSubsets>
-    <DefaultMonoSubsets>$(DefaultMonoSubsets)mono.runtime+mono.corelib</DefaultMonoSubsets>
+    <DefaultMonoSubsets>$(DefaultMonoSubsets)mono.runtime+mono.corelib+mono.packages</DefaultMonoSubsets>
 
-    <DefaultLibrariesSubsets>libs.depprojs+libs.native+libs.ref+libs.src+libs.pretest+libs.packages</DefaultLibrariesSubsets>
+    <DefaultLibrariesSubsets>libs.native+libs.ref+libs.src+libs.pretest+libs.packages</DefaultLibrariesSubsets>
 
     <DefaultInstallerSubsets>corehost+installer.managed+installer.depprojs+installer.pkgprojs+bundles+installers+installer.tests</DefaultInstallerSubsets>
     <DefaultInstallerSubsets Condition="'$(RuntimeFlavor)' == 'Mono'">installer.pkgprojs</DefaultInstallerSubsets>
@@ -70,6 +70,7 @@
     <_subset>$(_subset.Replace('+mono+', '+$(DefaultMonoSubsets)+'))</_subset>
     <_subset>$(_subset.Replace('+libs+', '+$(DefaultLibrariesSubsets)+'))</_subset>
     <_subset>$(_subset.Replace('+installer+', '+$(DefaultInstallerSubsets)+'))</_subset>
+    <_subset>$(_subset.Replace('+installer.nocorehost+', '+$(DefaultInstallerSubsets.Replace('corehost+', ''))+'))</_subset>
 
     <!-- Surround _subset in dashes to simplify checks below -->
     <_subset>+$(_subset.Trim('+'))+</_subset>
@@ -79,21 +80,23 @@
     <!-- CoreClr -->
     <SubsetName Include="Clr" Description="The CoreCLR runtime, LinuxDac, CoreLib (+ native), tools and packages." />
     <SubsetName Include="Clr.Runtime" Description="The CoreCLR .NET runtime." />
-    <SubsetName Include="LinuxDac" Condition="$([MSBuild]::IsOsPlatform(Windows))" Description="The cross-OS Windows->libc-based Linux DAC. Skipped on x86." />
-    <SubsetName Include="AlpineDac" Condition="$([MSBuild]::IsOsPlatform(Windows))" OnDemand="true" Description="The cross-OS Windows->musl-libc-based Linux DAC. Skipped on x86." />
     <SubsetName Include="Clr.CoreLib" Description="The managed System.Private.CoreLib library for CoreCLR." />
     <SubsetName Include="Clr.NativeCoreLib" Description="Run crossgen on System.Private.CoreLib library for CoreCLR." />
     <SubsetName Include="Clr.Tools" Description="Managed tools that support CoreCLR development and testing." />
     <SubsetName Include="Clr.Packages" Description="The projects that produce NuGet packages for the CoreCLR runtime, crossgen, and IL tools." />
+    <SubsetName Include="LinuxDac" Condition="$([MSBuild]::IsOsPlatform(Windows))" Description="The cross-OS Windows->libc-based Linux DAC. Skipped on x86." />
+    <SubsetName Include="AlpineDac" Condition="$([MSBuild]::IsOsPlatform(Windows))" OnDemand="true" Description="The cross-OS Windows->musl-libc-based Linux DAC. Skipped on x86 and arm." />
+    <SubsetName Include="CrossDacPack" OnDemand="true"
+            Description="Packaging of cross OS DAC. Requires all assets needed to be present at a folder specified by $(CrossDacArtifactsDir). See 'Microsoft.CrossOsDiag.Private.CoreCLR.proj' for details." />
 
     <!-- Mono -->
     <SubsetName Include="Mono" Description="The Mono runtime and CoreLib." />
     <SubsetName Include="Mono.Runtime" Description="The Mono .NET runtime." />
     <SubsetName Include="Mono.CoreLib" Description="The managed System.Private.CoreLib library for Mono." />
+    <SubsetName Include="Mono.Packages" Description="The projects that produce NuGet packages for the Mono runtime." />
 
     <!-- Libs -->
     <SubsetName Include="Libs" Description="The libraries native part, refs and source assemblies, test infra and packages, but NOT the tests (use Libs.Tests to request those explicitly)" />
-    <SubsetName Include="Libs.Depprojs" Description="The libraries upfront restore projects." />
     <SubsetName Include="Libs.Native" Description="The native libraries used in the shared framework." />
     <SubsetName Include="Libs.Ref" Description="The managed reference libraries." />
     <SubsetName Include="Libs.Src" Description="The managed implementation libraries." />
@@ -104,6 +107,7 @@
     <!-- Installer -->
     <SubsetName Include="Installer" Description="The .NET Core hosts, hosting libraries, bundles, and installers. Includes these projects' tests." />
     <SubsetName Include="CoreHost" Description="The .NET Core hosts." />
+    <SubsetName Include="Installer.NoCoreHost" Description="Hosting libraries, bundles, and installers. Includes these projects' tests." />
     <SubsetName Include="Installer.Managed" Description="The managed .NET hosting projects. This includes HostModel." />
     <SubsetName Include="Installer.DepProjs" Description="The dependency projects. These gather shared framework files and run crossgen on them to turn them into ready-to-run (R2R) assemblies for the current platform." />
     <SubsetName Include="Installer.PkgProjs" Description="The packaging projects. These produce NETCoreApp assets: NuGet packages, installers, zips, and Linux packages." />
@@ -136,10 +140,14 @@
     <ProjectToBuild Include="$(CoreClrProjectRoot)runtime.proj" AdditionalProperties="%(AdditionalProperties);CrossDac=linux" Category="clr" />
   </ItemGroup>
 
-  <ItemGroup Condition="$(_subset.Contains('+alpinedac+')) and $([MSBuild]::IsOsPlatform(Windows)) and '$(TargetArchitecture)' != 'x86'">
+  <ItemGroup Condition="$(_subset.Contains('+alpinedac+')) and $([MSBuild]::IsOsPlatform(Windows)) and '$(TargetArchitecture)' != 'x86' and '$(TargetArchitecture)' != 'arm'">
     <ProjectToBuild Include="$(CoreClrProjectRoot)runtime.proj" AdditionalProperties="%(AdditionalProperties);CrossDac=alpine" Category="clr" />
   </ItemGroup>
 
+  <ItemGroup Condition="$(_subset.Contains('+crossdacpack+'))">
+    <ProjectToBuild Include="$(CoreClrProjectRoot)src\.nuget\Microsoft.CrossOsDiag.Private.CoreCLR\Microsoft.CrossOsDiag.Private.CoreCLR.proj" Category="clr" />
+  </ItemGroup>
+
   <ItemGroup Condition="$(_subset.Contains('+clr.nativecorelib+'))">
     <ProjectToBuild Include="$(CoreClrProjectRoot)crossgen-corelib.proj" Category="clr" />
   </ItemGroup>
@@ -162,6 +170,10 @@
     <ProjectToBuild Include="$(MonoProjectRoot)llvm\llvm-init.proj" Category="mono" />
   </ItemGroup>
 
+  <ItemGroup Condition="$(_subset.Contains('+mono.packages+'))">
+    <ProjectToBuild Include="$(MonoProjectRoot)netcore\nuget\mono-packages.proj" Category="mono" Pack="true" />
+  </ItemGroup>
+
   <ItemGroup Condition="$(_subset.Contains('+mono.runtime+'))">
     <ProjectToBuild Include="$(MonoProjectRoot)mono.proj" Category="mono" />
   </ItemGroup>
@@ -171,12 +183,6 @@
   </ItemGroup>
 
   <!-- Libraries sets -->
-  <ItemGroup Condition="$(_subset.Contains('+libs.depprojs+'))">
-    <LibrariesRestoreProject Include="$(LibrariesProjectRoot)restore\depproj.proj">
-      <AdditionalProperties Condition="'$(LibrariesConfiguration)' != ''">Configuration=$(LibrariesConfiguration)</AdditionalProperties>
-    </LibrariesRestoreProject>
-  </ItemGroup>
-
   <ItemGroup Condition="$(_subset.Contains('+libs.native+'))">
     <ProjectToBuild Include="$(LibrariesProjectRoot)Native\build-native.proj" Category="libs" />
   </ItemGroup>
@@ -203,7 +209,7 @@
 
   <!-- Installer sets -->
   <ItemGroup Condition="$(_subset.Contains('+corehost+'))">
-    <CorehostProjectToBuild Include="$(InstallerProjectRoot)corehost\build.proj" SignPhase="Binaries" />
+    <CorehostProjectToBuild Include="$(InstallerProjectRoot)corehost\corehost.proj" SignPhase="Binaries" />
     <ProjectToBuild Include="@(CorehostProjectToBuild)" BuildInParallel="true" Pack="true" Category="installer" />
   </ItemGroup>
 
@@ -216,15 +222,11 @@
   <ItemGroup Condition="$(_subset.Contains('+installer.depprojs+'))">
     <DepprojProjectToBuild Condition="'$(RuntimeFlavor)' == 'CoreCLR'" Include="$(InstallerProjectRoot)pkg\projects\**\*.depproj" SignPhase="R2RBinaries" BuildInParallel="false" />
     <DepprojProjectToBuild Condition="'$(RuntimeFlavor)' == 'Mono'" Include="$(InstallerProjectRoot)pkg\projects\**\*.depproj" SignPhase="Binaries" BuildInParallel="false" />
-    <!-- Disable netstandard infra for now and discuss if we should delete it: https://github.com/dotnet/runtime/issues/2294-->
-    <DepprojProjectToBuild Remove="$(InstallerProjectRoot)pkg\projects\netstandard\src\netstandard.depproj" BuildInParallel="true" />
     <ProjectToBuild Include="@(DepprojProjectToBuild)" Pack="true" Category="installer" />
   </ItemGroup>
 
   <ItemGroup Condition="$(_subset.Contains('+installer.pkgprojs+'))">
     <PkgprojProjectToBuild Include="$(InstallerProjectRoot)pkg\projects\**\*.pkgproj" SignPhase="MsiFiles" BuildInParallel="false" />
-    <!-- Disable netstandard infra for now and discuss if we should delete it: https://github.com/dotnet/runtime/issues/2294-->
-    <PkgprojProjectToBuild Remove="$(InstallerProjectRoot)pkg\projects\netstandard\pkg\NETStandard.Library.Ref.pkgproj" BuildInParallel="true" />
     <ProjectToBuild Include="@(PkgprojProjectToBuild)" Pack="true" Category="installer" />
   </ItemGroup>
 
@@ -256,9 +258,9 @@
   <!-- Set default configurations. -->
   <ItemGroup>
     <ProjectToBuild Update="@(ProjectToBuild)">
-      <AdditionalProperties Condition="'%(ProjectToBuild.Category)' == 'clr' and '$(CoreCLRConfiguration)' != ''">Configuration=$(CoreCLRConfiguration)</AdditionalProperties>
-      <AdditionalProperties Condition="'%(ProjectToBuild.Category)' == 'mono' and '$(MonoConfiguration)' != ''">Configuration=$(MonoConfiguration)</AdditionalProperties>
-      <AdditionalProperties Condition="'%(ProjectToBuild.Category)' == 'libs' and '$(LibrariesConfiguration)' != ''">Configuration=$(LibrariesConfiguration)</AdditionalProperties>
+      <AdditionalProperties Condition="'%(ProjectToBuild.Category)' == 'clr' and '$(CoreCLRConfiguration)' != ''">%(AdditionalProperties);Configuration=$(CoreCLRConfiguration)</AdditionalProperties>
+      <AdditionalProperties Condition="'%(ProjectToBuild.Category)' == 'mono' and '$(MonoConfiguration)' != ''">%(AdditionalProperties);Configuration=$(MonoConfiguration)</AdditionalProperties>
+      <AdditionalProperties Condition="'%(ProjectToBuild.Category)' == 'libs' and '$(LibrariesConfiguration)' != ''">%(AdditionalProperties);Configuration=$(LibrariesConfiguration)</AdditionalProperties>
     </ProjectToBuild>
   </ItemGroup>
 
diff --git a/eng/Version.Details.xml b/eng/Version.Details.xml
index 098240ee26cbd9..ea4afb6ae2adce 100644
--- a/eng/Version.Details.xml
+++ b/eng/Version.Details.xml
@@ -4,67 +4,67 @@
       <Uri>https://github.com/dotnet/standard</Uri>
       <Sha>cfe95a23647c7de1fe1a349343115bd7720d6949</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.NETCore.Runtime.ICU.Transport" Version="5.0.0-preview.8.20365.1">
+    <Dependency Name="Microsoft.NETCore.Runtime.ICU.Transport" Version="5.0.0-preview.8.20403.1">
       <Uri>https://github.com/dotnet/icu</Uri>
-      <Sha>7247fa0d9e8faee2cceee6f04856b2c447f41bca</Sha>
+      <Sha>f58ab86d7e07a66ea189859f298843ccf41a0914</Sha>
     </Dependency>
   </ProductDependencies>
   <ToolsetDependencies>
-    <Dependency Name="Microsoft.DotNet.Arcade.Sdk" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.Arcade.Sdk" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.Helix.Sdk" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.Helix.Sdk" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.ApiCompat" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.ApiCompat" Version="5.0.0-beta.20381.6">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>39c3b73c4b2b79981405e865e5a4fa096662f13a</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.GenAPI" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.GenAPI" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.GenFacades" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.GenFacades" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.XUnitExtensions" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.XUnitExtensions" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.XUnitConsoleRunner" Version="2.5.1-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.XUnitConsoleRunner" Version="2.5.1-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.Build.Tasks.Packaging" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.Build.Tasks.Packaging" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.CodeAnalysis" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.CodeAnalysis" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.Build.Tasks.TargetFramework.Sdk" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.Build.Tasks.TargetFramework.Sdk" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.RemoteExecutor" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.RemoteExecutor" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.Build.Tasks.Feed" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.Build.Tasks.Feed" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.VersionTools.Tasks" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.VersionTools.Tasks" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk" Version="5.0.0-beta.20364.3">
+    <Dependency Name="Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk" Version="5.0.0-beta.20374.1">
       <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>ff5d4b6c8dbdaeacb6e6159d3f8185118dffd915</Sha>
+      <Sha>f6192d1e284a08ac05041d05fa6e60dec74b24f5</Sha>
     </Dependency>
     <Dependency Name="optimization.windows_nt-x64.IBC.CoreFx" Version="99.99.99-master-20190716.1">
       <Uri>https://dev.azure.com/dnceng/internal/_git/dotnet-optimization</Uri>
@@ -86,73 +86,73 @@
       <Uri>https://dev.azure.com/dnceng/internal/_git/dotnet-optimization</Uri>
       <Sha>d0bb63d2ec7060714e63ee4082fac48f2e57f3e2</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.NET.Test.Sdk" Version="16.8.0-preview-20200708-01">
+    <Dependency Name="Microsoft.NET.Test.Sdk" Version="16.8.0-preview-20200730-03">
       <Uri>https://github.com/microsoft/vstest</Uri>
-      <Sha>b9296fc900e2f2d717d507b4ee2a4306521796d4</Sha>
+      <Sha>ddb755f58160c0e7fab50964d665be1bf47ff579</Sha>
     </Dependency>
-    <Dependency Name="System.ComponentModel.TypeConverter.TestData" Version="5.0.0-beta.20360.1">
+    <Dependency Name="System.ComponentModel.TypeConverter.TestData" Version="5.0.0-beta.20377.1">
       <Uri>https://github.com/dotnet/runtime-assets</Uri>
-      <Sha>b34a70799faa67f13c2e72852e4f3af463ff4d6c</Sha>
+      <Sha>4d5781485294568e51a4673719c8ae5ae8955e70</Sha>
     </Dependency>
-    <Dependency Name="System.Drawing.Common.TestData" Version="5.0.0-beta.20360.1">
+    <Dependency Name="System.Drawing.Common.TestData" Version="5.0.0-beta.20377.1">
       <Uri>https://github.com/dotnet/runtime-assets</Uri>
-      <Sha>b34a70799faa67f13c2e72852e4f3af463ff4d6c</Sha>
+      <Sha>4d5781485294568e51a4673719c8ae5ae8955e70</Sha>
     </Dependency>
-    <Dependency Name="System.IO.Compression.TestData" Version="5.0.0-beta.20360.1">
+    <Dependency Name="System.IO.Compression.TestData" Version="5.0.0-beta.20377.1">
       <Uri>https://github.com/dotnet/runtime-assets</Uri>
-      <Sha>b34a70799faa67f13c2e72852e4f3af463ff4d6c</Sha>
+      <Sha>4d5781485294568e51a4673719c8ae5ae8955e70</Sha>
     </Dependency>
-    <Dependency Name="System.IO.Packaging.TestData" Version="5.0.0-beta.20360.1">
+    <Dependency Name="System.IO.Packaging.TestData" Version="5.0.0-beta.20377.1">
       <Uri>https://github.com/dotnet/runtime-assets</Uri>
-      <Sha>b34a70799faa67f13c2e72852e4f3af463ff4d6c</Sha>
+      <Sha>4d5781485294568e51a4673719c8ae5ae8955e70</Sha>
     </Dependency>
-    <Dependency Name="System.Net.TestData" Version="5.0.0-beta.20360.1">
+    <Dependency Name="System.Net.TestData" Version="5.0.0-beta.20377.1">
       <Uri>https://github.com/dotnet/runtime-assets</Uri>
-      <Sha>b34a70799faa67f13c2e72852e4f3af463ff4d6c</Sha>
+      <Sha>4d5781485294568e51a4673719c8ae5ae8955e70</Sha>
     </Dependency>
-    <Dependency Name="System.Private.Runtime.UnicodeData" Version="5.0.0-beta.20360.1">
+    <Dependency Name="System.Private.Runtime.UnicodeData" Version="5.0.0-beta.20377.1">
       <Uri>https://github.com/dotnet/runtime-assets</Uri>
-      <Sha>b34a70799faa67f13c2e72852e4f3af463ff4d6c</Sha>
+      <Sha>4d5781485294568e51a4673719c8ae5ae8955e70</Sha>
     </Dependency>
-    <Dependency Name="System.Security.Cryptography.X509Certificates.TestData" Version="5.0.0-beta.20360.1">
+    <Dependency Name="System.Security.Cryptography.X509Certificates.TestData" Version="5.0.0-beta.20377.1">
       <Uri>https://github.com/dotnet/runtime-assets</Uri>
-      <Sha>b34a70799faa67f13c2e72852e4f3af463ff4d6c</Sha>
+      <Sha>4d5781485294568e51a4673719c8ae5ae8955e70</Sha>
     </Dependency>
-    <Dependency Name="System.Windows.Extensions.TestData" Version="5.0.0-beta.20360.1">
+    <Dependency Name="System.Windows.Extensions.TestData" Version="5.0.0-beta.20377.1">
       <Uri>https://github.com/dotnet/runtime-assets</Uri>
-      <Sha>b34a70799faa67f13c2e72852e4f3af463ff4d6c</Sha>
+      <Sha>4d5781485294568e51a4673719c8ae5ae8955e70</Sha>
     </Dependency>
-    <Dependency Name="runtime.linux-arm64.Microsoft.NETCore.Runtime.Mono.LLVM.Sdk" Version="9.0.1-alpha.1.20356.1">
+    <Dependency Name="runtime.linux-arm64.Microsoft.NETCore.Runtime.Mono.LLVM.Sdk" Version="9.0.1-alpha.1.20403.1">
       <Uri>https://github.com/dotnet/llvm-project</Uri>
-      <Sha>266c9f5b5c1e94333e01ca77fa74d76563969842</Sha>
+      <Sha>62d9a4d09b44ebaa1c9f94bca1066aef426a5bbf</Sha>
     </Dependency>
-    <Dependency Name="runtime.linux-arm64.Microsoft.NETCore.Runtime.Mono.LLVM.Tools" Version="9.0.1-alpha.1.20356.1">
+    <Dependency Name="runtime.linux-arm64.Microsoft.NETCore.Runtime.Mono.LLVM.Tools" Version="9.0.1-alpha.1.20403.1">
       <Uri>https://github.com/dotnet/llvm-project</Uri>
-      <Sha>266c9f5b5c1e94333e01ca77fa74d76563969842</Sha>
+      <Sha>62d9a4d09b44ebaa1c9f94bca1066aef426a5bbf</Sha>
     </Dependency>
-    <Dependency Name="runtime.linux-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Sdk" Version="9.0.1-alpha.1.20356.1">
+    <Dependency Name="runtime.linux-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Sdk" Version="9.0.1-alpha.1.20403.1">
       <Uri>https://github.com/dotnet/llvm-project</Uri>
-      <Sha>266c9f5b5c1e94333e01ca77fa74d76563969842</Sha>
+      <Sha>62d9a4d09b44ebaa1c9f94bca1066aef426a5bbf</Sha>
     </Dependency>
-    <Dependency Name="runtime.linux-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Tools" Version="9.0.1-alpha.1.20356.1">
+    <Dependency Name="runtime.linux-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Tools" Version="9.0.1-alpha.1.20403.1">
       <Uri>https://github.com/dotnet/llvm-project</Uri>
-      <Sha>266c9f5b5c1e94333e01ca77fa74d76563969842</Sha>
+      <Sha>62d9a4d09b44ebaa1c9f94bca1066aef426a5bbf</Sha>
     </Dependency>
-    <Dependency Name="runtime.win-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Sdk" Version="9.0.1-alpha.1.20356.1">
+    <Dependency Name="runtime.win-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Sdk" Version="9.0.1-alpha.1.20403.1">
       <Uri>https://github.com/dotnet/llvm-project</Uri>
-      <Sha>266c9f5b5c1e94333e01ca77fa74d76563969842</Sha>
+      <Sha>62d9a4d09b44ebaa1c9f94bca1066aef426a5bbf</Sha>
     </Dependency>
-    <Dependency Name="runtime.win-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Tools" Version="9.0.1-alpha.1.20356.1">
+    <Dependency Name="runtime.win-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Tools" Version="9.0.1-alpha.1.20403.1">
       <Uri>https://github.com/dotnet/llvm-project</Uri>
-      <Sha>266c9f5b5c1e94333e01ca77fa74d76563969842</Sha>
+      <Sha>62d9a4d09b44ebaa1c9f94bca1066aef426a5bbf</Sha>
     </Dependency>
-    <Dependency Name="runtime.osx.10.12-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Sdk" Version="9.0.1-alpha.1.20356.1">
+    <Dependency Name="runtime.osx.10.12-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Sdk" Version="9.0.1-alpha.1.20403.1">
       <Uri>https://github.com/dotnet/llvm-project</Uri>
-      <Sha>266c9f5b5c1e94333e01ca77fa74d76563969842</Sha>
+      <Sha>62d9a4d09b44ebaa1c9f94bca1066aef426a5bbf</Sha>
     </Dependency>
-    <Dependency Name="runtime.osx.10.12-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Tools" Version="9.0.1-alpha.1.20356.1">
+    <Dependency Name="runtime.osx.10.12-x64.Microsoft.NETCore.Runtime.Mono.LLVM.Tools" Version="9.0.1-alpha.1.20403.1">
       <Uri>https://github.com/dotnet/llvm-project</Uri>
-      <Sha>266c9f5b5c1e94333e01ca77fa74d76563969842</Sha>
+      <Sha>62d9a4d09b44ebaa1c9f94bca1066aef426a5bbf</Sha>
     </Dependency>
     <Dependency Name="Microsoft.NETCore.App" Version="5.0.0-preview.4.20202.18">
       <Uri>https://github.com/dotnet/runtime</Uri>
@@ -182,17 +182,17 @@
       <Uri>https://github.com/dotnet/runtime</Uri>
       <Sha>0375524a91a47ca4db3ee1be548f74bab7e26e76</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.NET.ILLink.Tasks" Version="5.0.0-preview.3.20363.5">
+    <Dependency Name="Microsoft.NET.ILLink.Tasks" Version="5.0.0-preview.3.20403.5">
       <Uri>https://github.com/mono/linker</Uri>
-      <Sha>e76321851c05c5016df3d1243885c02e875b9912</Sha>
+      <Sha>8f32ed57a05eeb0bae3790c4db75b316c3da76c7</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.XHarness.TestRunners.Xunit" Version="1.0.0-prerelease.20352.3">
+    <Dependency Name="Microsoft.DotNet.XHarness.TestRunners.Xunit" Version="1.0.0-prerelease.20403.2">
       <Uri>https://github.com/dotnet/xharness</Uri>
-      <Sha>5c95b40b725e1aa9d596411c453900385cf6f84c</Sha>
+      <Sha>abc6d581ce00214ef763fb8510d1ba0aa54e7717</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.XHarness.CLI" Version="1.0.0-prerelease.20352.3">
+    <Dependency Name="Microsoft.DotNet.XHarness.CLI" Version="1.0.0-prerelease.20403.2">
       <Uri>https://github.com/dotnet/xharness</Uri>
-      <Sha>5c95b40b725e1aa9d596411c453900385cf6f84c</Sha>
+      <Sha>abc6d581ce00214ef763fb8510d1ba0aa54e7717</Sha>
     </Dependency>
   </ToolsetDependencies>
 </Dependencies>
diff --git a/eng/Versions.props b/eng/Versions.props
index 8366710273c7d5..02bd975b4fa169 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -16,8 +16,11 @@
     <DotNetFinalVersionKind Condition="'$(StabilizePackageVersion)' == 'true'">release</DotNetFinalVersionKind>
     <!-- Opt-in/out repo features -->
     <UsingToolMicrosoftNetCompilers>true</UsingToolMicrosoftNetCompilers>
+    <!-- TODO: Upgrade compiler version to enable T?; remove this once the employed SDK uses a new enough version. -->
+    <MicrosoftNetCompilersToolsetVersion>3.8.0-2.20379.3</MicrosoftNetCompilersToolsetVersion>
     <UsingToolIbcOptimization>true</UsingToolIbcOptimization>
     <UsingToolXliff>false</UsingToolXliff>
+    <UsingToolNetFrameworkReferenceAssemblies>true</UsingToolNetFrameworkReferenceAssemblies>
     <!-- Blob storage container that has the "Latest" channel to publish to. -->
     <ContainerName>dotnet</ContainerName>
     <ChecksumContainerName>$(ContainerName)</ChecksumContainerName>
@@ -45,22 +48,19 @@
   <ItemGroup>
     <!-- Targeting packs are only patched in extreme cases. -->
     <ProjectServicingConfiguration Include="Microsoft.NETCore.App.Ref" PatchVersion="0" />
-    <!-- Setting PatchVersion to "N/A" to not build it now or in the future, as "N/A" will never match the actual patch version. -->
-    <!-- For more info see this issue: https://github.com/dotnet/runtime/issues/2294 -->
-    <ProjectServicingConfiguration Include="NETStandard.Library.Ref" PatchVersion="N/A" />
   </ItemGroup>
   <PropertyGroup>
     <!-- Arcade dependencies -->
-    <MicrosoftDotNetApiCompatVersion>5.0.0-beta.20364.3</MicrosoftDotNetApiCompatVersion>
-    <MicrosoftDotNetBuildTasksFeedVersion>5.0.0-beta.20364.3</MicrosoftDotNetBuildTasksFeedVersion>
-    <MicrosoftDotNetCodeAnalysisVersion>5.0.0-beta.20364.3</MicrosoftDotNetCodeAnalysisVersion>
-    <MicrosoftDotNetGenAPIVersion>5.0.0-beta.20364.3</MicrosoftDotNetGenAPIVersion>
-    <MicrosoftDotNetGenFacadesVersion>5.0.0-beta.20364.3</MicrosoftDotNetGenFacadesVersion>
-    <MicrosoftDotNetXUnitExtensionsVersion>5.0.0-beta.20364.3</MicrosoftDotNetXUnitExtensionsVersion>
-    <MicrosoftDotNetXUnitConsoleRunnerVersion>2.5.1-beta.20364.3</MicrosoftDotNetXUnitConsoleRunnerVersion>
-    <MicrosoftDotNetBuildTasksPackagingVersion>5.0.0-beta.20364.3</MicrosoftDotNetBuildTasksPackagingVersion>
-    <MicrosoftDotNetRemoteExecutorVersion>5.0.0-beta.20364.3</MicrosoftDotNetRemoteExecutorVersion>
-    <MicrosoftDotNetVersionToolsTasksVersion>5.0.0-beta.20364.3</MicrosoftDotNetVersionToolsTasksVersion>
+    <MicrosoftDotNetApiCompatVersion>5.0.0-beta.20381.6</MicrosoftDotNetApiCompatVersion>
+    <MicrosoftDotNetBuildTasksFeedVersion>5.0.0-beta.20374.1</MicrosoftDotNetBuildTasksFeedVersion>
+    <MicrosoftDotNetCodeAnalysisVersion>5.0.0-beta.20374.1</MicrosoftDotNetCodeAnalysisVersion>
+    <MicrosoftDotNetGenAPIVersion>5.0.0-beta.20374.1</MicrosoftDotNetGenAPIVersion>
+    <MicrosoftDotNetGenFacadesVersion>5.0.0-beta.20374.1</MicrosoftDotNetGenFacadesVersion>
+    <MicrosoftDotNetXUnitExtensionsVersion>5.0.0-beta.20374.1</MicrosoftDotNetXUnitExtensionsVersion>
+    <MicrosoftDotNetXUnitConsoleRunnerVersion>2.5.1-beta.20374.1</MicrosoftDotNetXUnitConsoleRunnerVersion>
+    <MicrosoftDotNetBuildTasksPackagingVersion>5.0.0-beta.20374.1</MicrosoftDotNetBuildTasksPackagingVersion>
+    <MicrosoftDotNetRemoteExecutorVersion>5.0.0-beta.20374.1</MicrosoftDotNetRemoteExecutorVersion>
+    <MicrosoftDotNetVersionToolsTasksVersion>5.0.0-beta.20374.1</MicrosoftDotNetVersionToolsTasksVersion>
     <!-- Installer dependencies -->
     <MicrosoftNETCoreAppVersion>5.0.0-preview.4.20202.18</MicrosoftNETCoreAppVersion>
     <MicrosoftNETCoreDotNetHostVersion>5.0.0-preview.4.20202.18</MicrosoftNETCoreDotNetHostVersion>
@@ -69,19 +69,49 @@
     <!-- CoreClr dependencies -->
     <MicrosoftNETCoreILAsmVersion>5.0.0-preview.8.20359.4</MicrosoftNETCoreILAsmVersion>
     <!-- Libraries dependencies -->
+    <SystemBuffersVersion>4.5.1</SystemBuffersVersion>
+    <SystemCollectionsVersion>4.3.0</SystemCollectionsVersion>
+    <SystemCollectionsConcurrentVersion>4.3.0</SystemCollectionsConcurrentVersion>
+    <SystemComponentModelAnnotationsVersion>4.7.0</SystemComponentModelAnnotationsVersion>
+    <SystemDataSqlClientVersion>4.8.1</SystemDataSqlClientVersion>
+    <SystemDiagnosticsContractsVersion>4.3.0</SystemDiagnosticsContractsVersion>
+    <SystemDiagnosticsDebugVersion>4.3.0</SystemDiagnosticsDebugVersion>
+    <SystemDiagnosticsTracingVersion>4.3.0</SystemDiagnosticsTracingVersion>
+    <SystemDynamicRuntimeVersion>4.3.0</SystemDynamicRuntimeVersion>
+    <SystemLinqExpressionsVersion>4.3.0</SystemLinqExpressionsVersion>
+    <SystemMemoryVersion>4.5.4</SystemMemoryVersion>
+    <SystemNetHttpVersion>4.3.4</SystemNetHttpVersion>
+    <SystemNetPrimitivesVersion>4.3.1</SystemNetPrimitivesVersion>
+    <SystemNumericsVectorsVersion>4.5.0</SystemNumericsVectorsVersion>
+    <SystemResourcesResourceManagerVersion>4.3.0</SystemResourcesResourceManagerVersion>
+    <SystemRuntimeVersion>4.3.1</SystemRuntimeVersion>
+    <SystemRuntimeExtensionsVersion>4.3.1</SystemRuntimeExtensionsVersion>
+    <SystemRuntimeInteropServicesVersion>4.3.0</SystemRuntimeInteropServicesVersion>
+    <SystemRuntimeInteropServicesRuntimeInformationVersion>4.3.0</SystemRuntimeInteropServicesRuntimeInformationVersion>
+    <SystemRuntimeSerializationPrimitivesVersion>4.3.0</SystemRuntimeSerializationPrimitivesVersion>
+    <SystemSecurityCryptographyAlgorithmsVersion>4.3.1</SystemSecurityCryptographyAlgorithmsVersion>
+    <SystemSecurityCryptographyCngVersion>4.7.0</SystemSecurityCryptographyCngVersion>
+    <SystemSecurityCryptographyPkcsVersion>4.7.0</SystemSecurityCryptographyPkcsVersion>
+    <SystemSecurityCryptographyOpenSslVersion>4.7.0</SystemSecurityCryptographyOpenSslVersion>
     <SystemTextJsonVersion>5.0.0-preview.4.20202.18</SystemTextJsonVersion>
+    <SystemThreadingVersion>4.3.0</SystemThreadingVersion>
+    <SystemThreadingTasksExtensionsVersion>4.5.4</SystemThreadingTasksExtensionsVersion>
+    <SystemValueTupleVersion>4.5.0</SystemValueTupleVersion>
+    <MicrosoftBclAsyncInterfacesVersion>1.1.1</MicrosoftBclAsyncInterfacesVersion>
+    <MicrosoftWin32PrimitivesVersion>4.3.0</MicrosoftWin32PrimitivesVersion>
     <runtimenativeSystemIOPortsVersion>5.0.0-alpha.1.19563.3</runtimenativeSystemIOPortsVersion>
     <!-- Runtime-Assets dependencies -->
-    <SystemComponentModelTypeConverterTestDataVersion>5.0.0-beta.20360.1</SystemComponentModelTypeConverterTestDataVersion>
-    <SystemDrawingCommonTestDataVersion>5.0.0-beta.20360.1</SystemDrawingCommonTestDataVersion>
-    <SystemIOCompressionTestDataVersion>5.0.0-beta.20360.1</SystemIOCompressionTestDataVersion>
-    <SystemIOPackagingTestDataVersion>5.0.0-beta.20360.1</SystemIOPackagingTestDataVersion>
-    <SystemNetTestDataVersion>5.0.0-beta.20360.1</SystemNetTestDataVersion>
-    <SystemPrivateRuntimeUnicodeDataVersion>5.0.0-beta.20360.1</SystemPrivateRuntimeUnicodeDataVersion>
-    <SystemSecurityCryptographyX509CertificatesTestDataVersion>5.0.0-beta.20360.1</SystemSecurityCryptographyX509CertificatesTestDataVersion>
-    <SystemWindowsExtensionsTestDataVersion>5.0.0-beta.20360.1</SystemWindowsExtensionsTestDataVersion>
+    <SystemComponentModelTypeConverterTestDataVersion>5.0.0-beta.20377.1</SystemComponentModelTypeConverterTestDataVersion>
+    <SystemDrawingCommonTestDataVersion>5.0.0-beta.20377.1</SystemDrawingCommonTestDataVersion>
+    <SystemIOCompressionTestDataVersion>5.0.0-beta.20377.1</SystemIOCompressionTestDataVersion>
+    <SystemIOPackagingTestDataVersion>5.0.0-beta.20377.1</SystemIOPackagingTestDataVersion>
+    <SystemNetTestDataVersion>5.0.0-beta.20377.1</SystemNetTestDataVersion>
+    <SystemPrivateRuntimeUnicodeDataVersion>5.0.0-beta.20377.1</SystemPrivateRuntimeUnicodeDataVersion>
+    <SystemSecurityCryptographyX509CertificatesTestDataVersion>5.0.0-beta.20377.1</SystemSecurityCryptographyX509CertificatesTestDataVersion>
+    <SystemWindowsExtensionsTestDataVersion>5.0.0-beta.20377.1</SystemWindowsExtensionsTestDataVersion>
     <!-- Standard dependencies -->
     <NETStandardLibraryVersion>2.2.0-prerelease.19564.1</NETStandardLibraryVersion>
+    <NetStandardLibrary20Version>2.0.3</NetStandardLibrary20Version>
     <!-- dotnet-optimization dependencies -->
     <optimizationwindows_ntx64IBCCoreFxVersion>99.99.99-master-20200228.3</optimizationwindows_ntx64IBCCoreFxVersion>
     <optimizationlinuxx64IBCCoreFxVersion>99.99.99-master-20200228.3</optimizationlinuxx64IBCCoreFxVersion>
@@ -101,33 +131,32 @@
     <RefOnlyMicrosoftBuildUtilitiesCoreVersion>$(RefOnlyMicrosoftBuildVersion)</RefOnlyMicrosoftBuildUtilitiesCoreVersion>
     <RefOnlyNugetProjectModelVersion>4.9.4</RefOnlyNugetProjectModelVersion>
     <RefOnlyNugetPackagingVersion>4.9.4</RefOnlyNugetPackagingVersion>
-    <!-- System.Data.SqlClient -->
-    <SystemDataSqlClientVersion>4.8.0</SystemDataSqlClientVersion>
     <!-- Testing -->
-    <MicrosoftNETTestSdkVersion>16.8.0-preview-20200708-01</MicrosoftNETTestSdkVersion>
-    <MicrosoftDotNetXHarnessTestRunnersXunitVersion>1.0.0-prerelease.20352.3</MicrosoftDotNetXHarnessTestRunnersXunitVersion>
-    <MicrosoftDotNetXHarnessCLIVersion>1.0.0-prerelease.20352.3</MicrosoftDotNetXHarnessCLIVersion>
+    <MicrosoftNETTestSdkVersion>16.8.0-preview-20200730-03</MicrosoftNETTestSdkVersion>
+    <MicrosoftDotNetXHarnessTestRunnersXunitVersion>1.0.0-prerelease.20403.2</MicrosoftDotNetXHarnessTestRunnersXunitVersion>
+    <MicrosoftDotNetXHarnessCLIVersion>1.0.0-prerelease.20403.2</MicrosoftDotNetXHarnessCLIVersion>
     <XUnitVersion>2.4.1</XUnitVersion>
     <XUnitRunnerVisualStudioVersion>2.4.2</XUnitRunnerVisualStudioVersion>
     <CoverletCollectorVersion>1.3.0</CoverletCollectorVersion>
     <TraceEventVersion>2.0.5</TraceEventVersion>
     <NewtonsoftJsonVersion>12.0.3</NewtonsoftJsonVersion>
     <MoqVersion>4.12.0</MoqVersion>
+    <FsCheckVersion>2.14.3</FsCheckVersion>
     <!-- Docs -->
     <MicrosoftPrivateIntellisenseVersion>3.0.0-preview-20200715.1</MicrosoftPrivateIntellisenseVersion>
     <!-- ILLink -->
-    <MicrosoftNETILLinkTasksVersion>5.0.0-preview.3.20363.5</MicrosoftNETILLinkTasksVersion>
+    <MicrosoftNETILLinkTasksVersion>5.0.0-preview.3.20403.5</MicrosoftNETILLinkTasksVersion>
     <!-- ICU -->
-    <MicrosoftNETCoreRuntimeICUTransportVersion>5.0.0-preview.8.20365.1</MicrosoftNETCoreRuntimeICUTransportVersion>
+    <MicrosoftNETCoreRuntimeICUTransportVersion>5.0.0-preview.8.20403.1</MicrosoftNETCoreRuntimeICUTransportVersion>
     <!-- Mono LLVM -->
-    <runtimelinuxarm64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>9.0.1-alpha.1.20356.1</runtimelinuxarm64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>
-    <runtimelinuxarm64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>9.0.1-alpha.1.20356.1</runtimelinuxarm64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>
-    <runtimelinuxx64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>9.0.1-alpha.1.20356.1</runtimelinuxx64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>
-    <runtimelinuxx64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>9.0.1-alpha.1.20356.1</runtimelinuxx64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>
-    <runtimewinx64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>9.0.1-alpha.1.20356.1</runtimewinx64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>
-    <runtimewinx64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>9.0.1-alpha.1.20356.1</runtimewinx64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>
-    <runtimeosx1012x64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>9.0.1-alpha.1.20356.1</runtimeosx1012x64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>
-    <runtimeosx1012x64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>9.0.1-alpha.1.20356.1</runtimeosx1012x64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>
+    <runtimelinuxarm64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>9.0.1-alpha.1.20403.1</runtimelinuxarm64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>
+    <runtimelinuxarm64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>9.0.1-alpha.1.20403.1</runtimelinuxarm64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>
+    <runtimelinuxx64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>9.0.1-alpha.1.20403.1</runtimelinuxx64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>
+    <runtimelinuxx64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>9.0.1-alpha.1.20403.1</runtimelinuxx64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>
+    <runtimewinx64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>9.0.1-alpha.1.20403.1</runtimewinx64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>
+    <runtimewinx64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>9.0.1-alpha.1.20403.1</runtimewinx64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>
+    <runtimeosx1012x64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>9.0.1-alpha.1.20403.1</runtimeosx1012x64MicrosoftNETCoreRuntimeMonoLLVMSdkVersion>
+    <runtimeosx1012x64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>9.0.1-alpha.1.20403.1</runtimeosx1012x64MicrosoftNETCoreRuntimeMonoLLVMToolsVersion>
   </PropertyGroup>
   <!-- Package names -->
   <PropertyGroup>
@@ -146,7 +175,7 @@
     <MicrosoftNETCoreRuntimeICUTransportPackage>Microsoft.NETCore.Runtime.ICU.Transport</MicrosoftNETCoreRuntimeICUTransportPackage>
     <!-- XmlDocFileRoot needs to be defined here since we use it in packaging.props and docs.targets.
     It also uses Arcade defined property NuGetPackageRoot, this is the only codepath shared in between
-    packaging.props and docs.targets with arcade properties defined. 
+    packaging.props and docs.targets with arcade properties defined.
     -->
     <XmlDocFileRoot>$([MSBuild]::NormalizeDirectory('$(NuGetPackageRoot)', '$(MicrosoftPrivateIntellisensePackage)', '$(MicrosoftPrivateIntellisenseVersion)', 'IntellisenseFiles', 'net'))</XmlDocFileRoot>
   </PropertyGroup>
diff --git a/eng/build.ps1 b/eng/build.ps1
index f8b205bd3930a1..016ed15d2035a9 100644
--- a/eng/build.ps1
+++ b/eng/build.ps1
@@ -65,7 +65,7 @@ function Get-Help() {
   Write-Host "Libraries settings:"
   Write-Host "  -allconfigurations      Build packages for all build configurations."
   Write-Host "  -coverage               Collect code coverage when testing."
-  Write-Host "  -framework (-f)         Build framework: net5.0 or net472."
+  Write-Host "  -framework (-f)         Build framework: net5.0 or net48."
   Write-Host "                          [Default: net5.0]"
   Write-Host "  -testnobuild            Skip building tests when invoking -test."
   Write-Host "  -testscope              Scope tests, allowed values: innerloop, outerloop, all."
diff --git a/eng/build.sh b/eng/build.sh
index eb0cb586ebf325..da8e3770f595a5 100755
--- a/eng/build.sh
+++ b/eng/build.sh
@@ -60,7 +60,7 @@ usage()
   echo "Libraries settings:"
   echo "  --allconfigurations        Build packages for all build configurations."
   echo "  --coverage                 Collect code coverage when testing."
-  echo "  --framework (-f)           Build framework: net5.0 or net472."
+  echo "  --framework (-f)           Build framework: net5.0 or net48."
   echo "                             [Default: net5.0]"
   echo "  --testnobuild              Skip building tests when invoking -test."
   echo "  --testscope                Test scope, allowed values: innerloop, outerloop, all."
diff --git a/eng/codeOptimization.targets b/eng/codeOptimization.targets
index 6ed7e997487bd6..73e19c9560557f 100644
--- a/eng/codeOptimization.targets
+++ b/eng/codeOptimization.targets
@@ -4,12 +4,7 @@
      <IsEligibleForNgenOptimization>true</IsEligibleForNgenOptimization>
      <IsEligibleForNgenOptimization Condition="'$(IsReferenceAssembly)' == 'true'">false</IsEligibleForNgenOptimization>
      <IsEligibleForNgenOptimization Condition="'$(GeneratePlatformNotSupportedAssembly)' == 'true' or '$(GeneratePlatformNotSupportedAssemblyMessage)' != ''">false</IsEligibleForNgenOptimization>
-      <!-- There's an issue causing IBCMerge failures because of mismatched MVIDs
-           across many of our assemblies on Mac, so disable
-           IBCMerge optimizations on Mac for now to unblock the offical build.
-           See issue https://github.com/dotnet/runtime/issues/33303
-      -->
-      <IsEligibleForNgenOptimization Condition="'$(TargetOS)' == 'OSX' or '$(TargetsMobile)' == 'true'">false</IsEligibleForNgenOptimization>
+     <IsEligibleForNgenOptimization Condition="'$(TargetsMobile)' == 'true'">false</IsEligibleForNgenOptimization>
   </PropertyGroup>
 
   <Target Name="SetApplyNgenOptimization"
diff --git a/eng/common/cross/toolchain.cmake b/eng/common/cross/toolchain.cmake
index 88a758afb19c15..b9fe796f0da75f 100644
--- a/eng/common/cross/toolchain.cmake
+++ b/eng/common/cross/toolchain.cmake
@@ -127,29 +127,40 @@ endif()
 
 # Specify link flags
 
+function(add_toolchain_linker_flag Flag)
+  set(Config "${ARGV1}")
+  set(CONFIG_SUFFIX "")
+  if (NOT Config STREQUAL "")
+    set(CONFIG_SUFFIX "_${Config}")
+  endif()
+  set("CMAKE_EXE_LINKER_FLAGS${CONFIG_SUFFIX}" "${CMAKE_EXE_LINKER_FLAGS${CONFIG_SUFFIX}} ${Flag}" PARENT_SCOPE)
+  set("CMAKE_SHARED_LINKER_FLAGS${CONFIG_SUFFIX}" "${CMAKE_SHARED_LINKER_FLAGS${CONFIG_SUFFIX}} ${Flag}" PARENT_SCOPE)
+endfunction()
+
+
 if(TARGET_ARCH_NAME STREQUAL "armel")
   if(DEFINED TIZEN_TOOLCHAIN) # For Tizen only
-    add_link_options("-B${CROSS_ROOTFS}/usr/lib/gcc/${TIZEN_TOOLCHAIN}")
-    add_link_options("-L${CROSS_ROOTFS}/lib")
-    add_link_options("-L${CROSS_ROOTFS}/usr/lib")
-    add_link_options("-L${CROSS_ROOTFS}/usr/lib/gcc/${TIZEN_TOOLCHAIN}")
+    add_toolchain_linker_flag("-B${CROSS_ROOTFS}/usr/lib/gcc/${TIZEN_TOOLCHAIN}")
+    add_toolchain_linker_flag("-L${CROSS_ROOTFS}/lib")
+    add_toolchain_linker_flag("-L${CROSS_ROOTFS}/usr/lib")
+    add_toolchain_linker_flag("-L${CROSS_ROOTFS}/usr/lib/gcc/${TIZEN_TOOLCHAIN}")
   endif()
 elseif(TARGET_ARCH_NAME STREQUAL "arm64")
   if(DEFINED TIZEN_TOOLCHAIN) # For Tizen only
-    add_link_options("-B${CROSS_ROOTFS}/usr/lib64/gcc/${TIZEN_TOOLCHAIN}")
-    add_link_options("-L${CROSS_ROOTFS}/lib64")
-    add_link_options("-L${CROSS_ROOTFS}/usr/lib64")
-    add_link_options("-L${CROSS_ROOTFS}/usr/lib64/gcc/${TIZEN_TOOLCHAIN}")
-
-    add_link_options("-Wl,--rpath-link=${CROSS_ROOTFS}/lib64")
-    add_link_options("-Wl,--rpath-link=${CROSS_ROOTFS}/usr/lib64")
-    add_link_options("-Wl,--rpath-link=${CROSS_ROOTFS}/usr/lib64/gcc/${TIZEN_TOOLCHAIN}")
+    add_toolchain_linker_flag("-B${CROSS_ROOTFS}/usr/lib64/gcc/${TIZEN_TOOLCHAIN}")
+    add_toolchain_linker_flag("-L${CROSS_ROOTFS}/lib64")
+    add_toolchain_linker_flag("-L${CROSS_ROOTFS}/usr/lib64")
+    add_toolchain_linker_flag("-L${CROSS_ROOTFS}/usr/lib64/gcc/${TIZEN_TOOLCHAIN}")
+
+    add_toolchain_linker_flag("-Wl,--rpath-link=${CROSS_ROOTFS}/lib64")
+    add_toolchain_linker_flag("-Wl,--rpath-link=${CROSS_ROOTFS}/usr/lib64")
+    add_toolchain_linker_flag("-Wl,--rpath-link=${CROSS_ROOTFS}/usr/lib64/gcc/${TIZEN_TOOLCHAIN}")
   endif()
 elseif(TARGET_ARCH_NAME STREQUAL "x86")
-  add_link_options(-m32)
+  add_toolchain_linker_flag(-m32)
 elseif(ILLUMOS)
-   add_link_options("-L${CROSS_ROOTFS}/lib/amd64")
-   add_link_options("-L${CROSS_ROOTFS}/usr/amd64/lib")
+  add_toolchain_linker_flag("-L${CROSS_ROOTFS}/lib/amd64")
+  add_toolchain_linker_flag("-L${CROSS_ROOTFS}/usr/amd64/lib")
 endif()
 
 # Specify compile options
diff --git a/eng/common/performance/crossgen_perf.proj b/eng/common/performance/crossgen_perf.proj
new file mode 100644
index 00000000000000..3c8c33d7055c98
--- /dev/null
+++ b/eng/common/performance/crossgen_perf.proj
@@ -0,0 +1,81 @@
+<Project Sdk="Microsoft.DotNet.Helix.Sdk" DefaultTargets="Test">
+
+  <PropertyGroup Condition="'$(AGENT_OS)' == 'Windows_NT'">
+    <Python>py -3</Python>
+    <HelixPreCommands>$(HelixPreCommands);call %HELIX_CORRELATION_PAYLOAD%\performance\tools\machine-setup.cmd;set PYTHONPATH=%HELIX_WORKITEM_PAYLOAD%\scripts%3B%HELIX_WORKITEM_PAYLOAD%</HelixPreCommands>
+    <ArtifactsDirectory>%HELIX_CORRELATION_PAYLOAD%\artifacts\BenchmarkDotNet.Artifacts</ArtifactsDirectory>
+    <BaseDirectory>$HELIX_CORRELATION_PAYLOAD</BaseDirectory>
+    <PerformanceDirectory>$(BaseDirectory)/performance</PerformanceDirectory>
+  </PropertyGroup>
+
+ <PropertyGroup Condition="'$(AGENT_OS)' != 'Windows_NT'">
+    <WorkItemCommand>$(PerformanceDirectory)/scripts/benchmarks_ci.py --csproj $(PerformanceDirectory)/$(TargetCsproj)</WorkItemCommand>
+    <CliArguments>--dotnet-versions $DOTNET_VERSION --cli-source-info args --cli-branch $PERFLAB_BRANCH --cli-commit-sha $PERFLAB_HASH --cli-repository https://github.com/$PERFLAB_REPO --cli-source-timestamp $PERFLAB_BUILDTIMESTAMP</CliArguments>
+    <Python>python3</Python>
+    <CoreRun>$(BaseDirectory)/Core_Root/corerun</CoreRun>
+    <HelixPreCommands>$(HelixPreCommands);chmod +x $(PerformanceDirectory)/tools/machine-setup.sh;. $(PerformanceDirectory)/tools/machine-setup.sh</HelixPreCommands>
+    <ArtifactsDirectory>$(BaseDirectory)/artifacts/BenchmarkDotNet.Artifacts</ArtifactsDirectory>
+    <BaselineArtifactsDirectory>$(BaseDirectory)/artifacts/BenchmarkDotNet.Artifacts_Baseline</BaselineArtifactsDirectory>
+    <ResultsComparer>$(PerformanceDirectory)/src/tools/ResultsComparer/ResultsComparer.csproj</ResultsComparer>
+    <DotnetExe>$(PerformanceDirectory)/tools/dotnet/$(Architecture)/dotnet</DotnetExe>
+    <Percent>%25</Percent>
+    <XMLResults>$HELIX_WORKITEM_ROOT/testResults.xml</XMLResults>
+  </PropertyGroup> 
+
+  <ItemGroup>
+    <HelixCorrelationPayload Include="$(CorrelationPayloadDirectory)">
+      <PayloadDirectory>%(Identity)</PayloadDirectory>
+    </HelixCorrelationPayload>
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(AGENT_OS)' == 'Windows_NT'">
+    <HelixWorkItem Include="Crossgen System.Private.Xml.dll">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen\test.py crossgen --test-name System.Private.Xml.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
+    </HelixWorkItem>
+    <HelixWorkItem Include="Crossgen System.Linq.Expressions.dll">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen\test.py crossgen --test-name System.Linq.Expressions.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
+    </HelixWorkItem>
+    <HelixWorkItem Include="Crossgen Microsoft.CodeAnalysis.VisualBasic.dll">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen\test.py crossgen --test-name Microsoft.CodeAnalysis.VisualBasic.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
+    </HelixWorkItem>
+    <HelixWorkItem Include="Crossgen Microsoft.CodeAnalysis.CSharp.dll">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen\test.py crossgen --test-name Microsoft.CodeAnalysis.CSharp.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
+    </HelixWorkItem>
+    <HelixWorkItem Include="Crossgen System.Private.CoreLib.dll">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen\test.py crossgen --test-name System.Private.CoreLib.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
+    </HelixWorkItem>
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(AGENT_OS)' == 'Windows_NT' and '$(Architecture)' == 'x64'">
+    <HelixWorkItem Include="Crossgen2 System.Private.Xml.dll">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --single System.Private.Xml.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
+    </HelixWorkItem>
+    <HelixWorkItem Include="Crossgen2 System.Linq.Expressions.dll">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --single System.Linq.Expressions.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
+    </HelixWorkItem>
+    <HelixWorkItem Include="Crossgen2 Microsoft.CodeAnalysis.VisualBasic.dll">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --single Microsoft.CodeAnalysis.VisualBasic.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
+    </HelixWorkItem>     
+    <HelixWorkItem Include="Crossgen2 Microsoft.CodeAnalysis.CSharp.dll">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --single Microsoft.CodeAnalysis.CSharp.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
+    </HelixWorkItem>
+    <HelixWorkItem Include="Crossgen2 System.Private.CoreLib.dll">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --single System.Private.CoreLib.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
+    </HelixWorkItem>
+    <HelixWorkItem Include="Crossgen2 Composite Framework R2R">
+      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>	
+      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --composite %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\framework-r2r.dll.rsp --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>	
+      <Timeout>1:00</Timeout>  
+    </HelixWorkItem>
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/eng/common/performance/perfhelixpublish.proj b/eng/common/performance/microbenchmarks.proj
similarity index 66%
rename from eng/common/performance/perfhelixpublish.proj
rename to eng/common/performance/microbenchmarks.proj
index 272366da95fca8..71114b074e1b26 100644
--- a/eng/common/performance/perfhelixpublish.proj
+++ b/eng/common/performance/microbenchmarks.proj
@@ -41,6 +41,10 @@
     <XMLResults>$HELIX_WORKITEM_ROOT/testResults.xml</XMLResults>
   </PropertyGroup>
 
+  <PropertyGroup Condition="'$(WasmDotnet)' == 'true'">
+    <CliArguments>$(CliArguments) --wasm</CliArguments>
+  </PropertyGroup>
+
   <PropertyGroup Condition="'$(MonoDotnet)' == 'true' and '$(AGENT_OS)' == 'Windows_NT'">
     <CoreRunArgument>--corerun %HELIX_CORRELATION_PAYLOAD%\dotnet-mono\shared\Microsoft.NETCore.App\5.0.0\corerun.exe</CoreRunArgument>
   </PropertyGroup>
@@ -65,7 +69,7 @@
   </PropertyGroup>
   
   <PropertyGroup>
-    <WorkItemTimeout>2:30</WorkItemTimeout>
+    <WorkItemTimeout>12:30</WorkItemTimeout>
     <WorkItemTimeout Condition="'$(HelixSourcePrefix)' != 'official'">0:15</WorkItemTimeout>
   </PropertyGroup>
 
@@ -137,56 +141,4 @@
       <Timeout>4:00</Timeout>
     </HelixWorkItem>
   </ItemGroup>
-
-  <ItemGroup Condition="'$(AGENT_OS)' == 'Windows_NT'">
-    <HelixWorkItem Include="Crossgen System.Private.Xml.dll">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen\test.py crossgen --test-name System.Private.Xml.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
-    </HelixWorkItem>
-    <HelixWorkItem Include="Crossgen System.Linq.Expressions.dll">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen\test.py crossgen --test-name System.Linq.Expressions.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
-    </HelixWorkItem>
-    <HelixWorkItem Include="Crossgen Microsoft.CodeAnalysis.VisualBasic.dll">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen\test.py crossgen --test-name Microsoft.CodeAnalysis.VisualBasic.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
-    </HelixWorkItem>
-    <HelixWorkItem Include="Crossgen Microsoft.CodeAnalysis.CSharp.dll">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen\test.py crossgen --test-name Microsoft.CodeAnalysis.CSharp.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
-    </HelixWorkItem>
-    <HelixWorkItem Include="Crossgen System.Private.CoreLib.dll">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen\test.py crossgen --test-name System.Private.CoreLib.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
-    </HelixWorkItem>
-  </ItemGroup>
-
-  <ItemGroup Condition="'$(AGENT_OS)' == 'Windows_NT' and '$(Architecture)' == 'x64'">
-    <HelixWorkItem Include="Crossgen2 System.Private.Xml.dll">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --single System.Private.Xml.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
-    </HelixWorkItem>
-    <HelixWorkItem Include="Crossgen2 System.Linq.Expressions.dll">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --single System.Linq.Expressions.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
-    </HelixWorkItem>
-    <HelixWorkItem Include="Crossgen2 Microsoft.CodeAnalysis.VisualBasic.dll">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --single Microsoft.CodeAnalysis.VisualBasic.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
-    </HelixWorkItem>     
-    <HelixWorkItem Include="Crossgen2 Microsoft.CodeAnalysis.CSharp.dll">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --single Microsoft.CodeAnalysis.CSharp.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
-    </HelixWorkItem>
-    <HelixWorkItem Include="Crossgen2 System.Private.CoreLib.dll">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --single System.Private.CoreLib.dll --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>
-    </HelixWorkItem>
-    <HelixWorkItem Include="Crossgen2 Composite Framework R2R">
-      <PayloadDirectory>$(WorkItemDirectory)\ScenarioCorrelation</PayloadDirectory>	
-      <Command>$(Python) %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\test.py crossgen2 --composite %HELIX_CORRELATION_PAYLOAD%\performance\src\scenarios\crossgen2\framework-r2r.dll.rsp --core-root %HELIX_CORRELATION_PAYLOAD%\Core_Root</Command>	
-      <Timeout>1:00</Timeout>  
-    </HelixWorkItem>
-
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/eng/common/performance/performance-setup.sh b/eng/common/performance/performance-setup.sh
index c87cbf0fc23265..66f63a397a0fc0 100755
--- a/eng/common/performance/performance-setup.sh
+++ b/eng/common/performance/performance-setup.sh
@@ -24,6 +24,8 @@ run_from_perf_repo=false
 use_core_run=true
 use_baseline_core_run=true
 using_mono=false
+wasm_runtime_loc=
+using_wasm=false
 
 while (($# > 0)); do
   lowerI="$(echo $1 | awk '{print tolower($0)}')"
@@ -70,7 +72,7 @@ while (($# > 0)); do
       ;;
     --kind)
       kind=$2
-      configurations="CompliationMode=$compilation_mode RunKind=$kind"
+      configurations="CompilationMode=$compilation_mode RunKind=$kind"
       shift 2
       ;;
     --runcategories)
@@ -101,6 +103,10 @@ while (($# > 0)); do
       mono_dotnet=$2
       shift 2
       ;;
+    --wasm)
+      wasm_runtime_loc=$2
+      shift 2
+      ;;
     --compare)
       compare=true
       shift 1
@@ -130,6 +136,7 @@ while (($# > 0)); do
       echo "  --runcategories <value>        Related to csproj. Categories of benchmarks to run. Defaults to \"coreclr corefx\""
       echo "  --internal                     If the benchmarks are running as an official job."
       echo "  --monodotnet                   Pass the path to the mono dotnet for mono performance testing."
+      echo "  --wasm                         Path to the unpacled wasm runtime pack."
       echo ""
       exit 0
       ;;
@@ -141,7 +148,7 @@ if [ "$repository" == "dotnet/performance" ] || [ "$repository" == "dotnet-perfo
 fi
 
 if [ -z "$configurations" ]; then
-    configurations="CompliationMode=$compilation_mode"
+    configurations="CompilationMode=$compilation_mode"
 fi
 
 if [ -z "$core_root_directory" ]; then
@@ -191,11 +198,15 @@ if [[ "$mono_dotnet" != "" ]]; then
     configurations="$configurations LLVM=$llvm MonoInterpreter=$monointerpreter MonoAOT=$monoaot"
 fi
 
+if [[ "$wasm_runtime_loc" != "" ]]; then
+    configurations="CompilationMode=wasm;RunKind=micro"
+fi
+
 if [[ "$monointerpreter" == "true" ]]; then
-    extra_benchmark_dotnet_arguments="--category-exclusion-filter NoInterpreter"
+    extra_benchmark_dotnet_arguments="$extra_benchmark_dotnet_arguments --category-exclusion-filter NoInterpreter"
 fi
 
-common_setup_arguments="--channel master --queue $queue --build-number $build_number --build-configs $configurations --architecture $architecture"
+common_setup_arguments="--channel master --queue $queue --build-number $build_number --build-configs \"$configurations\" --architecture $architecture"
 setup_arguments="--repository https://github.com/$repository --branch $branch --get-perf-hash --commit-sha $commit_sha $common_setup_arguments"
 
 
@@ -217,6 +228,17 @@ else
     mv $docs_directory $workitem_directory
 fi
 
+if [[ "$wasm_runtime_loc" != "" ]]; then
+    using_wasm=true
+    
+    wasm_dotnet_path=$payload_directory/dotnet-wasm
+    
+    mv $wasm_runtime_loc $wasm_dotnet_path
+    
+    extra_benchmark_dotnet_arguments="$extra_benchmark_dotnet_arguments --wasmMainJS \$HELIX_CORRELATION_PAYLOAD/dotnet-wasm/runtime-test.js --wasmEngine /home/helixbot/.jsvu/v8 --customRuntimePack \$HELIX_CORRELATION_PAYLOAD/dotnet-wasm"
+    
+fi
+
 if [[ "$mono_dotnet" != "" ]]; then
     using_mono=true
     mono_dotnet_path=$payload_directory/dotnet-mono
@@ -259,3 +281,4 @@ Write-PipelineSetVariable -name "Kind" -value "$kind" -is_multi_job_variable fal
 Write-PipelineSetVariable -name "_BuildConfig" -value "$architecture.$kind.$framework" -is_multi_job_variable false
 Write-PipelineSetVariable -name "Compare" -value "$compare" -is_multi_job_variable false
 Write-PipelineSetVariable -name "MonoDotnet" -value "$using_mono" -is_multi_job_variable false
+Write-PipelineSetVariable -name "WasmDotnet" -value "$using_wasm" -is_multi_job_variable false
diff --git a/eng/common/templates/steps/perf-send-to-helix.yml b/eng/common/templates/steps/perf-send-to-helix.yml
index b3ea9acf1f1607..1e3bed764cfaca 100644
--- a/eng/common/templates/steps/perf-send-to-helix.yml
+++ b/eng/common/templates/steps/perf-send-to-helix.yml
@@ -1,10 +1,11 @@
 # Please remember to update the documentation if you make changes to these parameters!
 parameters:
+  ProjectFile: ''                        # required -- project file that specifies the helix workitems
   HelixSource: 'pr/default'              # required -- sources must start with pr/, official/, prodcon/, or agent/
   HelixType: 'tests/default/'            # required -- Helix telemetry which identifies what type of data this is; should include "test" for clarity and must end in '/'
   HelixBuild: $(Build.BuildNumber)       # required -- the build number Helix will use to identify this -- automatically set to the AzDO build number
-  HelixTargetQueues: ''                  # required -- semicolon delimited list of Helix queues to test on; see https://helix.dot.net/ for a list of queues
-  HelixAccessToken: ''                   # required -- access token to make Helix API requests; should be provided by the appropriate variable group
+  HelixTargetQueues: ''                  # required -- semicolon delimited list of Helix queues to test on; see https://helix.dot.net/ for a list 0of queues
+  HelixAccessToken: ''                   # required -- access token to make Helix API requests; should be provided by the appropriate variable group        
   HelixPreCommands: ''                   # optional -- commands to run before Helix work item execution
   HelixPostCommands: ''                  # optional -- commands to run after Helix work item execution
   WorkItemDirectory: ''                  # optional -- a payload directory to zip up and send to Helix; requires WorkItemCommand; incompatible with XUnitProjects
@@ -18,9 +19,10 @@ parameters:
   DisplayNamePrefix: 'Send job to Helix' # optional -- rename the beginning of the displayName of the steps in AzDO 
   condition: succeeded()                 # optional -- condition for step to execute; defaults to succeeded()
   continueOnError: false                 # optional -- determines whether to continue the build if the step errors; defaults to false
+            
 
 steps:
-  - powershell: $(Build.SourcesDirectory)\eng\common\msbuild.ps1 $(Build.SourcesDirectory)\eng\common\performance\perfhelixpublish.proj /restore /t:Test /bl:$(Build.SourcesDirectory)\artifacts\log\$env:BuildConfig\SendToHelix.binlog
+  - powershell: $(Build.SourcesDirectory)\eng\common\msbuild.ps1 $(Build.SourcesDirectory)\eng\common\performance\${{ parameters.ProjectFile }} /restore /t:Test /bl:$(Build.SourcesDirectory)\artifacts\log\$env:BuildConfig\SendToHelix.binlog
     displayName: ${{ parameters.DisplayNamePrefix }} (Windows)
     env:
       BuildConfig: $(_BuildConfig)
@@ -42,7 +44,7 @@ steps:
       SYSTEM_ACCESSTOKEN: $(System.AccessToken)
     condition: and(${{ parameters.condition }}, eq(variables['Agent.Os'], 'Windows_NT'))
     continueOnError: ${{ parameters.continueOnError }}
-  - script: $BUILD_SOURCESDIRECTORY/eng/common/msbuild.sh $BUILD_SOURCESDIRECTORY/eng/common/performance/perfhelixpublish.proj /restore /t:Test /bl:$BUILD_SOURCESDIRECTORY/artifacts/log/$BuildConfig/SendToHelix.binlog
+  - script: $BUILD_SOURCESDIRECTORY/eng/common/msbuild.sh $BUILD_SOURCESDIRECTORY/eng/common/performance/${{ parameters.ProjectFile }} /restore /t:Test /bl:$BUILD_SOURCESDIRECTORY/artifacts/log/$BuildConfig/SendToHelix.binlog
     displayName: ${{ parameters.DisplayNamePrefix }} (Unix)
     env:
       BuildConfig: $(_BuildConfig)
diff --git a/eng/illink.targets b/eng/illink.targets
index 601b0b798fbca7..d27feb5f466242 100644
--- a/eng/illink.targets
+++ b/eng/illink.targets
@@ -27,7 +27,7 @@
   <PropertyGroup>
     <ILLinkTasksDir>$([MSBuild]::NormalizeDirectory('$(PkgMicrosoft_NET_ILLink_Tasks)', 'tools'))</ILLinkTasksDir>
     <ILLinkTasksPath Condition="'$(ILLinkTasksPath)' == '' and '$(MSBuildRuntimeType)' == 'core'">$(ILLinkTasksDir)netcoreapp3.0/ILLink.Tasks.dll</ILLinkTasksPath>
-    <ILLinkTasksPath Condition="'$(ILLinkTasksPath)' == '' and '$(MSBuildRuntimeType)' != 'core'">$(ILLinkTasksDir)$(NetFrameworkCurrent)/ILLink.Tasks.dll</ILLinkTasksPath>
+    <ILLinkTasksPath Condition="'$(ILLinkTasksPath)' == '' and '$(MSBuildRuntimeType)' != 'core'">$(ILLinkTasksDir)net472/ILLink.Tasks.dll</ILLinkTasksPath>
     <ILLinkTrimAssemblyPath>$(IntermediateOutputPath)$(TargetName)$(TargetExt)</ILLinkTrimAssemblyPath>
     <ILLinkTrimAssemblySymbols>$(IntermediateOutputPath)$(TargetName).pdb</ILLinkTrimAssemblySymbols>
     <ILLinkTrimInputPath>$(IntermediateOutputPath)PreTrim/</ILLinkTrimInputPath>
@@ -184,22 +184,37 @@
     </PropertyGroup>
   </Target>
 
+  <!-- ILLink.Tasks arguments common to runs for both individual libraries and for the entire runtime pack -->
+  <Target Name="SetCommonILLinkArgs">
+    <PropertyGroup>
+      <!-- keep type-forward assemblies (facades) -->
+      <ILLinkArgs>$(ILLinkArgs) -t</ILLinkArgs>
+      <!-- don't remove the embedded link attributes xml resource since ILLink may run again on the assembly -->
+      <!-- and ignore the link attributes xml file during the library build, since we need the attributes preserved until the final app is linked -->
+      <ILLinkArgs>$(ILLinkArgs) --strip-link-attributes false --ignore-link-attributes true</ILLinkArgs>
+      <!-- ignore unresolved references -->
+      <ILLinkArgs>$(ILLinkArgs) --skip-unresolved true</ILLinkArgs>
+      <!-- keep interface implementations -->
+      <ILLinkArgs>$(ILLinkArgs) --disable-opt unusedinterfaces</ILLinkArgs>
+    </PropertyGroup>
+  </Target>
+
   <!-- ILLinkTrimAssembly
        Examines the "input assembly" for IL that is unreachable from public API and trims that,
        rewriting the assembly to an "output assembly"
   -->
   <UsingTask TaskName="ILLink" AssemblyFile="$(ILLinkTasksPath)" />
-  <Target Name="ILLinkTrimAssembly" Condition="'$(ILLinkTrimAssembly)' == 'true'">
+  <Target Name="ILLinkTrimAssembly"
+          Condition="'$(ILLinkTrimAssembly)' == 'true'"
+          DependsOnTargets="SetCommonILLinkArgs">
     <PropertyGroup>
-      <ILLinkArgs>$(ILLinkArgs)-r $(TargetName)</ILLinkArgs>
+      <ILLinkArgs>$(ILLinkArgs) -r $(TargetName)</ILLinkArgs>
       <!-- default action for core assemblies -->
       <ILLinkArgs>$(ILLinkArgs) -c skip</ILLinkArgs>
       <!-- default action for non-core assemblies -->
       <ILLinkArgs>$(ILLinkArgs) -u skip</ILLinkArgs>
       <!-- trim the target assembly -->
       <ILLinkArgs>$(ILLinkArgs) -p link $(TargetName)</ILLinkArgs>
-      <!-- keep type-forward assemblies (facades) -->
-      <ILLinkArgs>$(ILLinkArgs) -t</ILLinkArgs>
       <ILLinkArgs Condition="'$(ILLinkRewritePDBs)' == 'true' and Exists('$(ILLinkTrimAssemblySymbols)')">$(ILLinkArgs) -b true</ILLinkArgs>
       <!-- don't remove the embedded root xml resource since ILLink may run again on the assembly -->
       <ILLinkArgs Condition="'$(ILLinkTrimXml)' != ''">$(ILLinkArgs) --strip-descriptors false</ILLinkArgs>
@@ -207,15 +222,21 @@
       <ILLinkArgs Condition="'$(ILLinkTrimXmlLibraryBuild)' != ''">$(ILLinkArgs) -x "$(ILLinkTrimXmlLibraryBuild)"</ILLinkArgs>
       <!-- don't remove the embedded substitutions xml resource since ILLink may run again on the assembly -->
       <ILLinkArgs Condition="'$(ILLinkSubstitutionsXml)' != ''">$(ILLinkArgs) --strip-substitutions false</ILLinkArgs>
-      <!-- don't remove the embedded link attributes xml resource since ILLink may run again on the assembly -->
-      <!-- and ignore the link attributes xml file during the library build, since we need the attributes preserved until the final app is linked -->
-      <ILLinkArgs>$(ILLinkArgs) --strip-link-attributes false --ignore-link-attributes true</ILLinkArgs>
-      <!-- ignore unresolved references -->
-      <ILLinkArgs>$(ILLinkArgs) --skip-unresolved true</ILLinkArgs>
-      <!-- keep interface implementations -->
-      <ILLinkArgs>$(ILLinkArgs) --disable-opt unusedinterfaces</ILLinkArgs>
       <!-- keep DynamicDependencyAttribute unless a project explicitly disables it -->
       <ILLinkArgs Condition="'$(ILLinkKeepDepAttributes)' != 'false'">$(ILLinkArgs) --keep-dep-attributes true</ILLinkArgs>
+      <!-- suppress warnings with the following codes:
+           IL2006: The generic parameter 'T' from A with dynamically accessed member kinds B is passed into the generic parameter
+                   'T' from 'System.Lazy<T>' which requires dynamically accessed member kinds 'PublicParameterlessConstructor'
+           IL2008: Could not find type A specified in resource B
+           IL2009: Could not find method A in type B specified in resource C
+           IL2012: Could not find field A in type B specified in resource C
+           IL2025: Duplicate preserve of A in B
+           IL2026: Calling A which has B can break functionality when trimming application code. The target method might be removed.
+           IL2035: Unresolved assembly A in DynamicDependencyAttribute on B
+           IL2050: P/invoke method A declares a parameter with COM marshalling. Correctness of COM interop
+                   cannot be guaranteed after trimming. Interfaces and interface members might be removed.
+      -->
+      <ILLinkArgs>$(ILLinkArgs) --nowarn IL2006;IL2008;IL2009;IL2012;IL2025;IL2026;IL2035;IL2050</ILLinkArgs>
     </PropertyGroup>
 
     <MakeDir Directories="$(ILLinkTrimInputPath)" />
@@ -255,9 +276,8 @@
     <!-- When running from Desktop MSBuild, DOTNET_HOST_PATH is not set.
          In this case, explicitly specify the path to the dotnet host. -->
     <PropertyGroup Condition=" '$(DOTNET_HOST_PATH)' == '' ">
-      <_DotNetHostDirectory>$(NetCoreRoot)</_DotNetHostDirectory>
-      <_DotNetHostFileName>dotnet</_DotNetHostFileName>
-      <_DotNetHostFileName Condition=" '$(OS)' == 'Windows_NT' ">dotnet.exe</_DotNetHostFileName>
+      <_DotNetHostDirectory>$(DotNetRoot)</_DotNetHostDirectory>
+      <_DotNetHostFileName>$([System.IO.Path]::GetFileName('$(DotNetTool)'))</_DotNetHostFileName>
     </PropertyGroup>
 
     <ILLink AssemblyPaths="$(ILLinkTrimInputAssembly)"
diff --git a/eng/install-native-dependencies.sh b/eng/install-native-dependencies.sh
index 00be5a6287289f..e8ab193c2d51b0 100755
--- a/eng/install-native-dependencies.sh
+++ b/eng/install-native-dependencies.sh
@@ -11,6 +11,7 @@ if [ "$1" = "Linux" ]; then
     fi
 elif [ "$1" = "OSX" ] || [ "$1" = "tvOS" ] || [ "$1" = "iOS" ]; then
     engdir=$(dirname "${BASH_SOURCE[0]}")
+    brew update --preinstall
     brew bundle --no-lock --file "${engdir}/Brewfile"
     if [ "$?" != "0" ]; then
         exit 1;
diff --git a/eng/native/build-commons.sh b/eng/native/build-commons.sh
index b976f5fdc6cf11..29c29a194e6157 100755
--- a/eng/native/build-commons.sh
+++ b/eng/native/build-commons.sh
@@ -48,11 +48,6 @@ check_prereqs()
 {
     echo "Checking prerequisites..."
 
-    if ! cmake --help 2>&1 | grep -q \\-B; then
-        echo "Please install cmake v3.14.5 or newer from https://www.cmake.org/download/."
-        exit 1
-    fi
-
     if [[ "$__HostOS" == "OSX" ]]; then
         # Check presence of pkg-config on the path
         command -v pkg-config 2>/dev/null || { echo >&2 "Please install pkg-config before running this script, see https://github.com/dotnet/runtime/blob/master/docs/workflow/requirements/macos-requirements.md"; exit 1; }
@@ -177,8 +172,8 @@ EOF
             cmake_command="emcmake $cmake_command"
         fi
 
-        echo "Executing $cmake_command --build \"$intermediatesDir\" --target install -j $__NumProc"
-        $cmake_command --build "$intermediatesDir" --target install -j "$__NumProc"
+        echo "Executing $cmake_command --build \"$intermediatesDir\" --target install -- -j $__NumProc"
+        $cmake_command --build "$intermediatesDir" --target install -- -j "$__NumProc"
     fi
 
     local exit_code="$?"
@@ -234,6 +229,20 @@ __BuildOS=$os
 
 __msbuildonunsupportedplatform=0
 
+# Get the number of processors available to the scheduler
+# Other techniques such as `nproc` only get the number of
+# processors available to a single process.
+platform="$(uname)"
+if [[ "$platform" == "FreeBSD" ]]; then
+  __NumProc=$(sysctl hw.ncpu | awk '{ print $2+1 }')
+elif [[ "$platform" == "NetBSD" || "$platform" == "SunOS" ]]; then
+  __NumProc=$(($(getconf NPROCESSORS_ONLN)+1))
+elif [[ "$platform" == "Darwin" ]]; then
+  __NumProc=$(($(getconf _NPROCESSORS_ONLN)+1))
+else
+  __NumProc=$(nproc --all)
+fi
+
 while :; do
     if [[ "$#" -le 0 ]]; then
         break
@@ -400,20 +409,6 @@ while :; do
     shift
 done
 
-# Get the number of processors available to the scheduler
-# Other techniques such as `nproc` only get the number of
-# processors available to a single process.
-platform="$(uname)"
-if [[ "$platform" == "FreeBSD" ]]; then
-  __NumProc=$(sysctl hw.ncpu | awk '{ print $2+1 }')
-elif [[ "$platform" == "NetBSD" || "$platform" == "SunOS" ]]; then
-  __NumProc=$(($(getconf NPROCESSORS_ONLN)+1))
-elif [[ "$platform" == "Darwin" ]]; then
-  __NumProc=$(($(getconf _NPROCESSORS_ONLN)+1))
-else
-  __NumProc=$(nproc --all)
-fi
-
 __CommonMSBuildArgs="/p:TargetArchitecture=$__BuildArch /p:Configuration=$__BuildType /p:TargetOS=$__TargetOS /nodeReuse:false $__OfficialBuildIdArg $__SignTypeArg $__SkipRestoreArg"
 
 # Configure environment if we are doing a verbose build
diff --git a/eng/native/configurecompiler.cmake b/eng/native/configurecompiler.cmake
index 9d1b88f080113b..02611fa19272e5 100644
--- a/eng/native/configurecompiler.cmake
+++ b/eng/native/configurecompiler.cmake
@@ -8,8 +8,6 @@ set(CMAKE_C_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
-cmake_policy(SET CMP0083 NEW)
-
 include(CheckCXXCompilerFlag)
 
 # "configureoptimization.cmake" must be included after CLR_CMAKE_HOST_UNIX has been set.
@@ -19,9 +17,7 @@ include(${CMAKE_CURRENT_LIST_DIR}/configureoptimization.cmake)
 # Initialize Cmake compiler flags and other variables
 #-----------------------------------------------------
 
-if(MSVC)
-    add_compile_options(/Zi /FC /Zc:strictStrings)
-elseif (CLR_CMAKE_HOST_UNIX)
+if (CLR_CMAKE_HOST_UNIX)
     add_compile_options(-g)
     add_compile_options(-Wall)
     if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
@@ -40,11 +36,18 @@ set(CMAKE_CXX_FLAGS_CHECKED "")
 set(CMAKE_EXE_LINKER_FLAGS_CHECKED "")
 set(CMAKE_SHARED_LINKER_FLAGS_CHECKED "")
 
+set(CMAKE_SHARED_LINKER_FLAGS_DEBUG "")
+set(CMAKE_SHARED_LINKER_FLAGS_RELEASE "")
+set(CMAKE_SHARED_LINKER_FLAGS_RELWITHDEBINFO "")
+set(CMAKE_EXE_LINKER_FLAGS_DEBUG "")
+set(CMAKE_EXE_LINKER_FLAGS_DEBUG "")
+set(CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO "")
+
 add_compile_definitions("$<$<OR:$<CONFIG:DEBUG>,$<CONFIG:CHECKED>>:DEBUG;_DEBUG;_DBG;URTBLDENV_FRIENDLY=Checked;BUILDENV_CHECKED=1>")
 add_compile_definitions("$<$<OR:$<CONFIG:RELEASE>,$<CONFIG:RELWITHDEBINFO>>:NDEBUG;URTBLDENV_FRIENDLY=Retail>")
 
 if (MSVC)
-  add_link_options(/GUARD:CF)
+  add_linker_flag(/GUARD:CF)
 
   # Linker flags
   #
@@ -57,48 +60,51 @@ if (MSVC)
   endif ()
 
   #Do not create Side-by-Side Assembly Manifest
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:/MANIFEST:NO>)
+  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /MANIFEST:NO")
   # can handle addresses larger than 2 gigabytes
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:/LARGEADDRESSAWARE>)
+  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /LARGEADDRESSAWARE")
   #Compatible with Data Execution Prevention
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:/NXCOMPAT>)
+  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /NXCOMPAT")
   #Use address space layout randomization
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:/DYNAMICBASE>)
+  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /DYNAMICBASE")
   #shrink pdb size
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:/PDBCOMPRESS>)
+  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /PDBCOMPRESS")
 
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:/DEBUG>)
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:/IGNORE:4197,4013,4254,4070,4221>)
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:/SUBSYSTEM:WINDOWS,${WINDOWS_SUBSYSTEM_VERSION}>)
+  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /DEBUG")
+  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /IGNORE:4197,4013,4254,4070,4221")
+  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /SUBSYSTEM:WINDOWS,${WINDOWS_SUBSYSTEM_VERSION}")
 
   set(CMAKE_STATIC_LINKER_FLAGS "${CMAKE_STATIC_LINKER_FLAGS} /IGNORE:4221")
 
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,EXECUTABLE>:/DEBUG>)
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,EXECUTABLE>:/PDBCOMPRESS>)
-  add_link_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,EXECUTABLE>:/STACK:1572864>)
+  set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /DEBUG")
+  set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /PDBCOMPRESS")
+  set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /STACK:1572864")
 
   # Debug build specific flags
-  add_link_options($<$<AND:$<OR:$<CONFIG:DEBUG>,$<CONFIG:CHECKED>>,$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>>:/NOVCFEATURE>)
+  set(CMAKE_SHARED_LINKER_FLAGS_DEBUG "${CMAKE_SHARED_LINKER_FLAGS_DEBUG} /NOVCFEATURE")
+  set(CMAKE_SHARED_LINKER_FLAGS_CHECKED "${CMAKE_SHARED_LINKER_FLAGS_CHECKED} /NOVCFEATURE")
 
   # Checked build specific flags
-  add_link_options($<$<CONFIG:CHECKED>:/INCREMENTAL:NO>) # prevent "warning LNK4075: ignoring '/INCREMENTAL' due to '/OPT:REF' specification"
-  add_link_options($<$<CONFIG:CHECKED>:/OPT:REF>)
-  add_link_options($<$<CONFIG:CHECKED>:/OPT:NOICF>)
+  add_linker_flag(/INCREMENTAL:NO CHECKED) # prevent "warning LNK4075: ignoring '/INCREMENTAL' due to '/OPT:REF' specification"
+  add_linker_flag(/OPT:REF CHECKED)
+  add_linker_flag(/OPT:NOICF CHECKED)
 
   # Release build specific flags
-  add_link_options($<$<CONFIG:RELEASE>:/LTCG>)
-  add_link_options($<$<CONFIG:RELEASE>:/OPT:REF>)
-  add_link_options($<$<CONFIG:RELEASE>:/OPT:ICF>)
+  add_linker_flag(/LTCG RELEASE)
+  add_linker_flag(/OPT:REF RELEASE)
+  add_linker_flag(/OPT:ICF RELEASE)
+  add_linker_flag(/INCREMENTAL:NO RELEASE)
   set(CMAKE_STATIC_LINKER_FLAGS_RELEASE "${CMAKE_STATIC_LINKER_FLAGS_RELEASE} /LTCG")
 
   # ReleaseWithDebugInfo build specific flags
-  add_link_options($<$<CONFIG:RELWITHDEBINFO>:/LTCG>)
-  add_link_options($<$<CONFIG:RELWITHDEBINFO>:/OPT:REF>)
-  add_link_options($<$<CONFIG:RELWITHDEBINFO>:/OPT:ICF>)
+  add_linker_flag(/LTCG RELWITHDEBINFO)
+  add_linker_flag(/OPT:REF RELWITHDEBINFO)
+  add_linker_flag(/OPT:ICF RELWITHDEBINFO)
   set(CMAKE_STATIC_LINKER_FLAGS_RELWITHDEBINFO "${CMAKE_STATIC_LINKER_FLAGS_RELWITHDEBINFO} /LTCG")
 
   # Force uCRT to be dynamically linked for Release build
-  add_link_options("$<$<CONFIG:RELEASE>:/NODEFAULTLIB:libucrt.lib;/DEFAULTLIB:ucrt.lib>")
+  add_linker_flag(/NODEFAULTLIB:libucrt.lib RELEASE)
+  add_linker_flag(/DEFAULTLIB:ucrt.lib RELEASE)
 
 elseif (CLR_CMAKE_HOST_UNIX)
   # Set the values to display when interactively configuring CMAKE_BUILD_TYPE
@@ -157,11 +163,10 @@ elseif (CLR_CMAKE_HOST_UNIX)
 
       # -fdata-sections -ffunction-sections: each function has own section instead of one per .o file (needed for --gc-sections)
       # -O1: optimization level used instead of -O0 to avoid compile error "invalid operand for inline asm constraint"
-      add_compile_definitions("$<$<OR:$<CONFIG:DEBUG>,$<CONFIG:CHECKED>>:${CLR_SANITIZE_CXX_OPTIONS};-fdata-sections;--ffunction-sections;-O1>")
-      add_link_options($<$<AND:$<OR:$<CONFIG:DEBUG>,$<CONFIG:CHECKED>>,$<STREQUAL:$<TARGET_PROPERTY:TYPE>,EXECUTABLE>>:${CLR_SANITIZE_LINK_OPTIONS}>)
-
+      add_compile_options("$<$<OR:$<CONFIG:DEBUG>,$<CONFIG:CHECKED>>:${CLR_SANITIZE_CXX_OPTIONS};-fdata-sections;--ffunction-sections;-O1>")
+      add_linker_flag("${CLR_SANITIZE_LINK_OPTIONS}" DEBUG CHECKED)
       # -Wl and --gc-sections: drop unused sections\functions (similar to Windows /Gy function-level-linking)
-      add_link_options("$<$<AND:$<OR:$<CONFIG:DEBUG>,$<CONFIG:CHECKED>>,$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>>:${CLR_SANITIZE_LINK_OPTIONS};-Wl,--gc-sections>")
+      add_linker_flag("-Wl,--gc-sections" DEBUG CHECKED)
     endif ()
   endif(UPPERCASE_CMAKE_BUILD_TYPE STREQUAL DEBUG OR UPPERCASE_CMAKE_BUILD_TYPE STREQUAL CHECKED)
 endif(MSVC)
@@ -173,15 +178,18 @@ endif(MSVC)
 #       ./build-native.sh cmakeargs "-DCLR_ADDITIONAL_COMPILER_OPTIONS=<...>" cmakeargs "-DCLR_ADDITIONAL_LINKER_FLAGS=<...>"
 #
 if(CLR_CMAKE_HOST_UNIX)
-    add_link_options(${CLR_ADDITIONAL_LINKER_FLAGS})
+  foreach(ADDTL_LINKER_FLAG ${CLR_ADDITIONAL_LINKER_FLAGS})
+    add_linker_flag(${ADDTL_LINKER_FLAG})
+  endforeach()
 endif(CLR_CMAKE_HOST_UNIX)
 
 if(CLR_CMAKE_HOST_LINUX)
   add_compile_options($<$<COMPILE_LANGUAGE:ASM>:-Wa,--noexecstack>)
-  add_link_options(-Wl,--build-id=sha1 -Wl,-z,relro,-z,now)
+  add_linker_flag(-Wl,--build-id=sha1)
+  add_linker_flag(-Wl,-z,relro,-z,now)
 elseif(CLR_CMAKE_HOST_FREEBSD)
   add_compile_options($<$<COMPILE_LANGUAGE:ASM>:-Wa,--noexecstack>)
-  add_link_options(LINKER:--build-id=sha1)
+  add_linker_flag("-Wl,--build-id=sha1")
 elseif(CLR_CMAKE_HOST_SUNOS)
   add_compile_options($<$<COMPILE_LANGUAGE:ASM>:-Wa,--noexecstack>)
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fstack-protector")
@@ -361,7 +369,7 @@ if (CLR_CMAKE_HOST_UNIX)
   if(CLR_CMAKE_HOST_OSX)
     set(MACOS_VERSION_MIN_FLAGS -mmacosx-version-min=10.12)
     add_compile_options(${MACOS_VERSION_MIN_FLAGS})
-    add_link_options(${MACOS_VERSION_MIN_FLAGS})
+    add_linker_flag(${MACOS_VERSION_MIN_FLAGS})
   endif(CLR_CMAKE_HOST_OSX)
 endif(CLR_CMAKE_HOST_UNIX)
 
@@ -417,25 +425,20 @@ endif(CLR_CMAKE_HOST_UNIX)
 if (MSVC)
   # Compile options for targeting windows
 
-  # The following options are set by the razzle build
   add_compile_options(/TP) # compile all files as C++
   add_compile_options(/nologo) # Suppress Startup Banner
   add_compile_options(/W3) # set warning level to 3
   add_compile_options(/WX) # treat warnings as errors
   add_compile_options(/Oi) # enable intrinsics
   add_compile_options(/Oy-) # disable suppressing of the creation of frame pointers on the call stack for quicker function calls
-  add_compile_options(/U_MT) # undefine the predefined _MT macro
-  add_compile_options(/GF) # enable read-only string pooling
   add_compile_options(/Gm-) # disable minimal rebuild
   add_compile_options(/Zp8) # pack structs on 8-byte boundary
   add_compile_options(/Gy) # separate functions for linker
-  add_compile_options(/Zc:wchar_t-) # C++ language conformance: wchar_t is NOT the native type, but a typedef
-  add_compile_options(/Zc:forScope) # C++ language conformance: enforce Standard C++ for scoping rules
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /GR-") # disable C++ RTTI
   add_compile_options(/FC) # use full pathnames in diagnostics
   add_compile_options(/MP) # Build with Multiple Processes (number of processes equal to the number of processors)
-  add_compile_options(/GS) # Buffer Security Check
   add_compile_options(/Zm200) # Specify Precompiled Header Memory Allocation Limit of 150MB
+  add_compile_options(/Zc:strictStrings) # Disable string-literal to char* or wchar_t* conversion
 
   add_compile_options(/wd4960 /wd4961 /wd4603 /wd4627 /wd4838 /wd4456 /wd4457 /wd4458 /wd4459 /wd4091 /we4640)
 
@@ -517,7 +520,7 @@ if(CLR_CMAKE_ENABLE_CODE_COVERAGE)
 
     add_compile_options(-fprofile-arcs)
     add_compile_options(-ftest-coverage)
-    add_link_options(--coverage)
+    add_linker_flag(--coverage)
   else()
     message(FATAL_ERROR "Code coverage builds not supported on current platform")
   endif(CLR_CMAKE_HOST_UNIX)
diff --git a/eng/native/configureplatform.cmake b/eng/native/configureplatform.cmake
index c65274141dd49c..dbfadfda599146 100644
--- a/eng/native/configureplatform.cmake
+++ b/eng/native/configureplatform.cmake
@@ -1,4 +1,3 @@
-include(CheckPIESupported)
 include(${CMAKE_CURRENT_LIST_DIR}/functions.cmake)
 
 # If set, indicates that this is not an officially supported release
@@ -382,24 +381,11 @@ else()
 endif()
 
 if(NOT CLR_CMAKE_TARGET_BROWSER)
-    # Skip check_pie_supported call on Android as ld from llvm toolchain with NDK API level 21
-    # complains about missing linker flag `-no-pie` (while level 28's ld does support this flag,
-    # but since we know that PIE is supported, we can safely skip this redundant check).
-    #
     # The default linker on Solaris also does not support PIE.
-    if(NOT CLR_CMAKE_TARGET_ANDROID AND NOT CLR_CMAKE_TARGET_SUNOS)
-        # All code we build should be compiled as position independent
-        get_property(languages GLOBAL PROPERTY ENABLED_LANGUAGES)
-        if("CXX" IN_LIST languages)
-            set(CLR_PIE_LANGUAGE CXX)
-        else()
-            set(CLR_PIE_LANGUAGE C)
-        endif()
-        check_pie_supported(OUTPUT_VARIABLE PIE_SUPPORT_OUTPUT LANGUAGES ${CLR_PIE_LANGUAGE})
-        if(NOT MSVC AND NOT CMAKE_${CLR_PIE_LANGUAGE}_LINK_PIE_SUPPORTED)
-            message(WARNING "PIE is not supported at link time: ${PIE_SUPPORT_OUTPUT}.\n"
-                      "PIE link options will not be passed to linker.")
-        endif()
+    if(NOT CLR_CMAKE_TARGET_ANDROID AND NOT CLR_CMAKE_TARGET_SUNOS AND NOT CLR_CMAKE_TARGET_OSX AND NOT CLR_CMAKE_HOST_TVOS AND NOT CLR_CMAKE_HOST_IOS AND NOT MSVC)
+        set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -pie")
+        add_compile_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,EXECUTABLE>:-fPIE>)
+        add_compile_options($<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:-fPIC>)
     endif()
 
     set(CMAKE_POSITION_INDEPENDENT_CODE ON)
diff --git a/eng/native/functions.cmake b/eng/native/functions.cmake
index 8b73581ed1426a..1509a17fa59b0a 100644
--- a/eng/native/functions.cmake
+++ b/eng/native/functions.cmake
@@ -148,7 +148,7 @@ function(preprocess_compile_asm)
   set(options "")
   set(oneValueArgs TARGET OUTPUT_OBJECTS)
   set(multiValueArgs ASM_FILES)
-  cmake_parse_arguments(PARSE_ARGV 0 COMPILE_ASM "${options}" "${oneValueArgs}" "${multiValueArgs}")
+  cmake_parse_arguments(COMPILE_ASM "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGV})
 
   get_include_directories_asm(ASM_INCLUDE_DIRECTORIES)
 
@@ -241,7 +241,7 @@ function(target_precompile_header)
   set(options "")
   set(oneValueArgs TARGET HEADER)
   set(multiValueArgs ADDITIONAL_INCLUDE_DIRECTORIES)
-  cmake_parse_arguments(PARSE_ARGV 0 PRECOMPILE_HEADERS "${options}" "${oneValueArgs}" "${multiValueArgs}")
+  cmake_parse_arguments(PRECOMPILE_HEADERS "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGV})
 
   if ("${PRECOMPILE_HEADERS_TARGET}" STREQUAL "")
   message(SEND_ERROR "No target supplied to target_precompile_header.")
@@ -360,7 +360,7 @@ endfunction()
 function(install_clr)
   set(oneValueArgs ADDITIONAL_DESTINATION)
   set(multiValueArgs TARGETS)
-  cmake_parse_arguments(PARSE_ARGV 0 INSTALL_CLR "${options}" "${oneValueArgs}" "${multiValueArgs}")
+  cmake_parse_arguments(INSTALL_CLR "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGV})
 
   if ("${INSTALL_CLR_TARGETS}" STREQUAL "")
     message(FATAL_ERROR "At least one target must be passed to install_clr(TARGETS )")
@@ -416,6 +416,15 @@ function(disable_pax_mprotect targetName)
   endif()
 endfunction()
 
+if (CMAKE_VERSION VERSION_LESS "3.12")
+  # Polyfill add_compile_definitions when it is unavailable
+  function(add_compile_definitions)
+    get_directory_property(DIR_COMPILE_DEFINITIONS COMPILE_DEFINITIONS)
+    list(APPEND DIR_COMPILE_DEFINITIONS ${ARGV})
+    set_directory_properties(PROPERTIES COMPILE_DEFINITIONS "${DIR_COMPILE_DEFINITIONS}")
+  endfunction()
+endif()
+
 function(_add_executable)
     if(NOT WIN32)
       add_executable(${ARGV} ${VERSION_FILE_PATH})
@@ -479,3 +488,16 @@ function(generate_module_index Target ModuleIndexFile)
         DEPENDS ${ModuleIndexFile}
     )
 endfunction(generate_module_index)
+
+# add_linker_flag(Flag [Config1 Config2 ...])
+function(add_linker_flag Flag)
+  if (ARGN STREQUAL "")
+    set("CMAKE_EXE_LINKER_FLAGS" "${CMAKE_EXE_LINKER_FLAGS} ${Flag}" PARENT_SCOPE)
+    set("CMAKE_SHARED_LINKER_FLAGS" "${CMAKE_SHARED_LINKER_FLAGS} ${Flag}" PARENT_SCOPE)
+  else()
+    foreach(Config ${ARGN})
+      set("CMAKE_EXE_LINKER_FLAGS_${Config}" "${CMAKE_EXE_LINKER_FLAGS_${Config}} ${Flag}" PARENT_SCOPE)
+      set("CMAKE_SHARED_LINKER_FLAGS_${Config}" "${CMAKE_SHARED_LINKER_FLAGS_${Config}} ${Flag}" PARENT_SCOPE)
+    endforeach()
+  endif()
+endfunction()
diff --git a/eng/native/gen-buildsys.sh b/eng/native/gen-buildsys.sh
index f27bb33e357785..1b4c2e02c597fd 100755
--- a/eng/native/gen-buildsys.sh
+++ b/eng/native/gen-buildsys.sh
@@ -91,6 +91,9 @@ if [[ "$build_arch" == "wasm" ]]; then
     cmake_command="emcmake $cmake_command"
 fi
 
+# We have to be able to build with CMake 3.6.2, so we can't use the -S or -B options
+pushd "$3"
+
 # Include CMAKE_USER_MAKE_RULES_OVERRIDE as uninitialized since it will hold its value in the CMake cache otherwise can cause issues when branch switching
 $cmake_command \
   -G "$generator" \
@@ -98,5 +101,6 @@ $cmake_command \
   "-DCMAKE_INSTALL_PREFIX=$__CMakeBinDir" \
   $cmake_extra_defines \
   $__UnprocessedCMakeArgs \
-  -S "$1" \
-  -B "$3"
+  "$1"
+
+popd
diff --git a/eng/packaging.targets b/eng/packaging.targets
index e0f7edaeac7f1a..0891a5a2f9f468 100644
--- a/eng/packaging.targets
+++ b/eng/packaging.targets
@@ -26,4 +26,16 @@
                       '$(_excludeCompile)' == 'true' and
                       '%(Dependency.Identity)' != '_._'" />
   </Target>
-</Project>
\ No newline at end of file
+
+  <PropertyGroup>
+    <PkgProjPath>$(MSBuildProjectDirectory)\..\pkg\$(MSBuildProjectName).pkgproj</PkgProjPath>
+    <!-- Point to our custom pack target which builds the pkgproj instead. -->
+    <PackDependsOn Condition="'$(IsSourceProject)' == 'true' and
+                              Exists('$(PkgProjPath)')">_BuildPkgProj</PackDependsOn>
+  </PropertyGroup>
+
+  <Target Name="_BuildPkgProj">
+    <MSBuild Projects="$(PkgProjPath)"
+             Targets="Build" />
+  </Target>
+</Project>
diff --git a/eng/pipelines/common/createdump-entitlements.plist b/eng/pipelines/common/createdump-entitlements.plist
new file mode 100644
index 00000000000000..1f2d3798ee2f6e
--- /dev/null
+++ b/eng/pipelines/common/createdump-entitlements.plist
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+  <dict>
+    <key>com.apple.security.cs.allow-dyld-environment-variables</key>
+      <true/>
+    <key>com.apple.security.cs.disable-library-validation</key>
+      <true/>
+    <key>com.apple.security.cs.debugger</key>
+      <true/>
+  </dict>
+</plist>
diff --git a/eng/pipelines/common/entitlements.plist b/eng/pipelines/common/entitlements.plist
new file mode 100644
index 00000000000000..f4ea418fb45a8d
--- /dev/null
+++ b/eng/pipelines/common/entitlements.plist
@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+  <dict>
+    <key>com.apple.security.cs.allow-jit</key>
+      <true/>
+    <key>com.apple.security.cs.allow-unsigned-executable-memory</key>
+      <true/>
+    <key>com.apple.security.cs.allow-dyld-environment-variables</key>
+      <true/>
+    <key>com.apple.security.cs.disable-library-validation</key>
+      <true/>
+    <key>com.apple.security.cs.debugger</key>
+      <true/>
+    <key>com.apple.security.get-task-allow</key>
+      <true/>
+  </dict>
+</plist>
diff --git a/eng/pipelines/common/global-build-job.yml b/eng/pipelines/common/global-build-job.yml
index dcbba9fb3654f5..3f22f762be8c3d 100644
--- a/eng/pipelines/common/global-build-job.yml
+++ b/eng/pipelines/common/global-build-job.yml
@@ -25,11 +25,17 @@ jobs:
     dependsOn: checkout
     pool: ${{ parameters.pool }}
     container: ${{ parameters.container }}
-    timeoutInMinutes: ${{ parameters.timeoutInMinutes }}
     condition: and(succeeded(), ${{ parameters.condition }})
     workspace:
       clean: all
 
+    # macOS hosted pool machines are slower so we need to give a greater timeout for global-build
+    # which builds multiple subsets.
+    ${{ if and(contains(parameters.pool.vmImage, 'macOS'), eq(parameters.timeoutInMinutes, '')) }}:
+      timeoutInMinutes: 120
+    ${{ if or(not(contains(parameters.pool.vmImage, 'macOS')), ne(parameters.timeoutInMinutes, '')) }}:
+      timeoutInMinutes: ${{ parameters.timeoutInMinutes }}
+
     variables:
       - name: _osParameter
         value: -os ${{ parameters.osGroup }}
diff --git a/eng/pipelines/common/macos-sign-with-entitlements.yml b/eng/pipelines/common/macos-sign-with-entitlements.yml
new file mode 100644
index 00000000000000..6c65193845d70c
--- /dev/null
+++ b/eng/pipelines/common/macos-sign-with-entitlements.yml
@@ -0,0 +1,65 @@
+parameters:
+  filesToSign: []
+
+steps:
+  - task: UseDotNet@2
+    displayName: 'Use .NET Core SDK 2.1.808'
+    inputs:
+      packageType: sdk
+      version: 2.1.808
+
+  - ${{ each file in parameters.filesToSign }}:
+    - script: codesign -s - -f --entitlements ${{ file.entitlementsFile }} ${{ file.path }}/${{ file.name }}
+      displayName: 'Add entitlements to ${{ file.name }}'
+
+    - task: CopyFiles@2
+      displayName: 'Copy entitled file ${{ file.name }}'
+      inputs:
+        contents: '${{ file.path }}/${{ file.name }}'
+        targetFolder: '$(Build.ArtifactStagingDirectory)/mac_entitled'
+        overWrite: true
+
+  - task: ArchiveFiles@2
+    displayName: 'Zip MacOS files for signing'
+    inputs:
+      rootFolderOrFile:  '$(Build.ArtifactStagingDirectory)/mac_entitled'
+      archiveFile:       '$(Build.ArtifactStagingDirectory)/mac_entitled_to_sign.zip'
+      archiveType:       zip
+      includeRootFolder: true
+      replaceExistingArchive: true
+
+  - task: SFP.build-tasks.custom-build-task-1.EsrpCodeSigning@1
+    displayName: 'ESRP CodeSigning'
+    inputs:
+      ConnectedServiceName: 'ESRP CodeSigning'
+      FolderPath: '$(Build.ArtifactStagingDirectory)/'
+      Pattern: 'mac_entitled_to_sign.zip'
+      UseMinimatch: true
+      signConfigType: inlineSignParams
+      inlineOperation: |
+        [
+          {
+            "keyCode": "CP-401337-Apple",
+            "operationCode": "MacAppDeveloperSign",
+            "parameters" : {
+              "hardening": "Enable"
+            },
+            "toolName": "sign",
+            "toolVersion": "1.0"
+          }
+        ]  
+
+  - task: ExtractFiles@1
+    displayName: 'Extract MacOS after signing'
+    inputs:
+      archiveFilePatterns: '$(Build.ArtifactStagingDirectory)/mac_entitled_to_sign.zip'
+      destinationFolder: '$(Build.ArtifactStagingDirectory)/mac_entitled_signed'
+
+  - ${{ each file in parameters.filesToSign }}:
+    - task: CopyFiles@2
+      displayName: 'Copy ${{ file.name }} to destination'
+      inputs:
+        contents: ${{ file.name }}
+        sourceFolder: '$(Build.ArtifactStagingDirectory)/mac_entitled_signed'
+        targetFolder: '${{ file.path }}'
+        overWrite: true
diff --git a/eng/pipelines/common/platform-matrix.yml b/eng/pipelines/common/platform-matrix.yml
index b4f80202400629..a7a3a167004c22 100644
--- a/eng/pipelines/common/platform-matrix.yml
+++ b/eng/pipelines/common/platform-matrix.yml
@@ -86,11 +86,7 @@ jobs:
       archType: x64
       platform: Linux_musl_x64
       container:
-        # alpine coreclr cmake errors on newer builds
-        ${{ if eq(parameters.runtimeFlavor, 'mono') }}:
-          image: alpine-3.9-WithNode-0fc54a3-20200131134036
-        ${{ if eq(parameters.runtimeFlavor, 'coreclr') }}:
-          image: alpine-3.9-WithNode-0fc54a3-20190918214015
+        image: alpine-3.9-WithNode-20200602002639-0fc54a3
         registry: mcr
       jobParameters:
         runtimeFlavor: ${{ parameters.runtimeFlavor }}
diff --git a/eng/pipelines/common/templates/runtimes/build-test-job.yml b/eng/pipelines/common/templates/runtimes/build-test-job.yml
index 0f3c188d20e89a..56fa8dffddc1b7 100644
--- a/eng/pipelines/common/templates/runtimes/build-test-job.yml
+++ b/eng/pipelines/common/templates/runtimes/build-test-job.yml
@@ -22,6 +22,7 @@ parameters:
   runtimeFlavor: 'coreclr'
   runtimeFlavorDisplayName: 'CoreCLR'
   runtimeVariant: ''
+  dependsOn: []
 
 ### Build managed test components (native components are getting built as part
 ### of the the product build job).
@@ -63,10 +64,13 @@ jobs:
     # See https://docs.microsoft.com/azure/devops/pipelines/process/conditions
     condition: and(succeeded(), ${{ parameters.condition }})
 
+    ${{ if ne(parameters.dependsOn[0], '') }}:
+      dependsOn: ${{ parameters.dependsOn }}
+
     # TODO: Build of managed test components currently depends on the corresponding build job
     # because it needs System.Private.Corelib; we should be able to remove this dependency
     # by switching over to using reference assembly.
-    ${{ if ne(parameters.stagedBuild, true) }}:
+    ${{ if and(ne(parameters.stagedBuild, true), eq(parameters.dependsOn[0], '')) }}:
       dependsOn:
       - ${{ format('coreclr_{0}_product_build_{1}{2}_{3}_{4}', parameters.runtimeVariant, parameters.osGroup, parameters.osSubgroup, parameters.archType, coalesce(parameters.liveRuntimeBuildConfig, parameters.buildConfig)) }}
       - ${{ if ne(parameters.liveLibrariesBuildConfig, '') }}:
diff --git a/eng/pipelines/common/templates/runtimes/run-test-job.yml b/eng/pipelines/common/templates/runtimes/run-test-job.yml
index 39616a833b0e4c..4d93701584fe62 100644
--- a/eng/pipelines/common/templates/runtimes/run-test-job.yml
+++ b/eng/pipelines/common/templates/runtimes/run-test-job.yml
@@ -20,6 +20,7 @@ parameters:
   pool: ''
   runtimeFlavor: 'coreclr'
   runtimeFlavorDisplayName: 'CoreCLR'
+  dependsOn: []
 
 ### Test run job
 
@@ -47,15 +48,19 @@ jobs:
     ${{ if eq(variables['System.TeamProject'], 'internal') }}:
       continueOnError: true
 
-    dependsOn:
-    - ${{ if in(parameters.testGroup, 'innerloop', 'clrinterpreter') }}:
-      - '${{ parameters.runtimeFlavor }}_common_test_build_p0_AnyOS_AnyCPU_${{parameters.buildConfig }}'
-    - ${{ if notIn(parameters.testGroup, 'innerloop', 'clrinterpreter') }}:
-      - '${{ parameters.runtimeFlavor }}_common_test_build_p1_AnyOS_AnyCPU_${{parameters.buildConfig }}'
-    - ${{ if ne(parameters.stagedBuild, true) }}:
-      - ${{ format('{0}_{1}_product_build_{2}{3}_{4}_{5}', parameters.runtimeFlavor, parameters.runtimeVariant, parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig) }}
-      - ${{ if ne(parameters.liveLibrariesBuildConfig, '') }}:
-        - ${{ format('libraries_build_{0}{1}_{2}_{3}', parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.liveLibrariesBuildConfig) }}
+    ${{ if ne(parameters.dependsOn[0], '') }}:
+      dependsOn: ${{ parameters.dependsOn }}
+
+    ${{ if eq(parameters.dependsOn[0], '') }}:
+      dependsOn:
+      - ${{ if in(parameters.testGroup, 'innerloop', 'clrinterpreter') }}:
+        - '${{ parameters.runtimeFlavor }}_common_test_build_p0_AnyOS_AnyCPU_${{parameters.buildConfig }}'
+      - ${{ if notIn(parameters.testGroup, 'innerloop', 'clrinterpreter') }}:
+        - '${{ parameters.runtimeFlavor }}_common_test_build_p1_AnyOS_AnyCPU_${{parameters.buildConfig }}'
+      - ${{ if ne(parameters.stagedBuild, true) }}:
+        - ${{ format('{0}_{1}_product_build_{2}{3}_{4}_{5}', parameters.runtimeFlavor, parameters.runtimeVariant, parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig) }}
+        - ${{ if ne(parameters.liveLibrariesBuildConfig, '') }}:
+          - ${{ format('libraries_build_{0}{1}_{2}_{3}', parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.liveLibrariesBuildConfig) }}
 
     # Compute job name from template parameters
     ${{ if in(parameters.testGroup, 'innerloop', 'clrinterpreter') }}:
diff --git a/eng/pipelines/coreclr/ci.yml b/eng/pipelines/coreclr/ci.yml
index 7e72c87e16b866..c58c4804174b15 100644
--- a/eng/pipelines/coreclr/ci.yml
+++ b/eng/pipelines/coreclr/ci.yml
@@ -164,4 +164,5 @@ jobs:
     jobTemplate: /eng/pipelines/coreclr/templates/format-job.yml
     platforms:
     - Linux_x64
-    - Windows_NT_x64
+    # Isssue: https://github.com/dotnet/runtime/issues/40034
+    #- Windows_NT_x64
diff --git a/eng/pipelines/coreclr/crossgen2-gcstress.yml b/eng/pipelines/coreclr/crossgen2-gcstress.yml
new file mode 100644
index 00000000000000..7942e747e26f64
--- /dev/null
+++ b/eng/pipelines/coreclr/crossgen2-gcstress.yml
@@ -0,0 +1,60 @@
+trigger: none
+
+pr: none
+
+schedules:
+- cron: "0 6 * * 0,1"
+  displayName: Sat and Sun at 10:00 PM (UTC-8:00)
+  branches:
+    include:
+    - master
+  always: true
+
+jobs:
+#
+# Checkout repository
+#
+- template: /eng/pipelines/common/checkout-job.yml
+
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/common/build-coreclr-and-libraries-job.yml
+    buildConfig: checked
+    platforms:
+    - Linux_x64
+    - Linux_arm64
+    - OSX_x64
+    - Windows_NT_x64
+    - Windows_NT_arm64
+    - CoreClrTestBuildHost # Either OSX_x64 or Linux_x64
+    jobParameters:
+      testGroup: gcstress-extra
+
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/common/templates/runtimes/build-test-job.yml
+    buildConfig: checked
+    platforms:
+    - CoreClrTestBuildHost # Either OSX_x64 or Linux_x64
+    jobParameters:
+      testGroup: gcstress-extra
+      liveLibrariesBuildConfig: Release
+
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/common/templates/runtimes/run-test-job.yml
+    helixQueuesTemplate: /eng/pipelines/coreclr/templates/helix-queues-setup.yml
+    buildConfig: checked
+    platforms:
+    - Linux_x64
+    - Linux_arm64
+    - OSX_x64
+    - Windows_NT_x64
+    - Windows_NT_arm64
+    jobParameters:
+      testGroup: gcstress-extra
+      readyToRun: true
+      crossgen2: true
+      compositeBuildMode: true
+      displayNameArgs: Composite
+      liveLibrariesBuildConfig: Release
diff --git a/eng/pipelines/coreclr/jitstress.yml b/eng/pipelines/coreclr/jitstress.yml
index 5bd57f564e4c4b..adb906ea7bf26d 100644
--- a/eng/pipelines/coreclr/jitstress.yml
+++ b/eng/pipelines/coreclr/jitstress.yml
@@ -28,7 +28,6 @@ jobs:
     - Linux_x64
     - Windows_NT_x64
     - Windows_NT_x86
-    - Windows_NT_arm
     - Windows_NT_arm64
     - CoreClrTestBuildHost # Either OSX_x64 or Linux_x64
     jobParameters:
@@ -56,7 +55,6 @@ jobs:
     - Linux_x64
     - Windows_NT_x64
     - Windows_NT_x86
-    - Windows_NT_arm
     - Windows_NT_arm64
     helixQueueGroup: ci
     helixQueuesTemplate: /eng/pipelines/coreclr/templates/helix-queues-setup.yml
diff --git a/eng/pipelines/coreclr/jitstress2-jitstressregs.yml b/eng/pipelines/coreclr/jitstress2-jitstressregs.yml
index b163671960a1df..743e071e08e899 100644
--- a/eng/pipelines/coreclr/jitstress2-jitstressregs.yml
+++ b/eng/pipelines/coreclr/jitstress2-jitstressregs.yml
@@ -28,7 +28,6 @@ jobs:
     - Linux_x64
     - Windows_NT_x64
     - Windows_NT_x86
-    - Windows_NT_arm
     - Windows_NT_arm64
     - CoreClrTestBuildHost # Either OSX_x64 or Linux_x64
     jobParameters:
@@ -56,7 +55,6 @@ jobs:
     - Linux_x64
     - Windows_NT_x64
     - Windows_NT_x86
-    - Windows_NT_arm
     - Windows_NT_arm64
     helixQueueGroup: ci
     helixQueuesTemplate: /eng/pipelines/coreclr/templates/helix-queues-setup.yml
diff --git a/eng/pipelines/coreclr/jitstressregs.yml b/eng/pipelines/coreclr/jitstressregs.yml
index 6df9790231a92f..12c8fc5158873f 100644
--- a/eng/pipelines/coreclr/jitstressregs.yml
+++ b/eng/pipelines/coreclr/jitstressregs.yml
@@ -28,7 +28,6 @@ jobs:
     - Linux_x64
     - Windows_NT_x64
     - Windows_NT_x86
-    - Windows_NT_arm
     - Windows_NT_arm64
     - CoreClrTestBuildHost # Either OSX_x64 or Linux_x64
     jobParameters:
@@ -56,7 +55,6 @@ jobs:
     - Linux_x64
     - Windows_NT_x64
     - Windows_NT_x86
-    - Windows_NT_arm
     - Windows_NT_arm64
     helixQueueGroup: ci
     helixQueuesTemplate: /eng/pipelines/coreclr/templates/helix-queues-setup.yml
diff --git a/eng/pipelines/coreclr/perf.yml b/eng/pipelines/coreclr/perf.yml
index 149eb1aed6fb85..dd120af2255e4b 100644
--- a/eng/pipelines/coreclr/perf.yml
+++ b/eng/pipelines/coreclr/perf.yml
@@ -17,25 +17,8 @@ trigger:
     - README.md
     - SECURITY.md
     - THIRD-PARTY-NOTICES.TXT
-
-
-pr:
-  branches:
-    include:
-    - master
-  paths:
-    include:
-    - '*'
-    - src/libraries/System.Private.CoreLib/*
-    exclude:
-    - docs/*
-    - CODE-OF-CONDUCT.md
-    - CONTRIBUTING.md
-    - LICENSE.TXT
-    - PATENTS.TXT
-    - README.md
-    - SECURITY.md
-    - THIRD-PARTY-NOTICES.TXT
+  
+pr: none
 
 jobs:
 #
@@ -43,6 +26,7 @@ jobs:
 #
 - template: /eng/pipelines/common/checkout-job.yml
 
+# build coreclr and libraries
 - template: /eng/pipelines/common/platform-matrix.yml
   parameters:
     jobTemplate: /eng/pipelines/common/build-coreclr-and-libraries-job.yml
@@ -54,6 +38,22 @@ jobs:
     jobParameters:
       testGroup: perf
 
+# build mono
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/common/global-build-job.yml
+    buildConfig: release
+    runtimeFlavor: mono
+    platforms:
+    - Browser_wasm
+    jobParameters:
+      buildArgs: -s mono+libs+installer -c $(_BuildConfig)
+      nameSuffix: wasm
+      isOfficialBuild: ${{ variables.isOfficialBuild }}
+      extraStepsTemplate: /eng/pipelines/common/upload-unsigned-artifacts-step.yml
+      extraStepsParameters:
+        name: MonoRuntimePacks
+
 - template: /eng/pipelines/common/platform-matrix.yml
   parameters:
     jobTemplate: /eng/pipelines/mono/templates/build-job.yml
@@ -62,6 +62,7 @@ jobs:
     platforms:
     - Linux_x64
 
+# run mono perf job
 - template: /eng/pipelines/common/platform-matrix.yml
   parameters:
     jobTemplate: /eng/pipelines/coreclr/templates/perf-job.yml
@@ -73,21 +74,42 @@ jobs:
       testGroup: perf
       liveLibrariesBuildConfig: Release
       runtimeType: mono
+      projectFile: microbenchmarks.proj
+      runKind: micro_mono
 
-- ${{ if and(ne(variables['System.TeamProject'], 'public'), notin(variables['Build.Reason'], 'PullRequest')) }}:
-  - template: /eng/pipelines/common/platform-matrix.yml
-    parameters:
-      jobTemplate: /eng/pipelines/coreclr/templates/perf-job.yml
-      buildConfig: release
-      runtimeFlavor: mono
-      platforms:
-      - Linux_x64
-      jobParameters:
-        testGroup: perf
-        liveLibrariesBuildConfig: Release
-        runtimeType: mono
-        codeGenType: 'Interpreter'
+# run mono interpreter job
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/coreclr/templates/perf-job.yml
+    buildConfig: release
+    runtimeFlavor: mono
+    platforms:
+    - Linux_x64
+    jobParameters:
+      testGroup: perf
+      liveLibrariesBuildConfig: Release
+      runtimeType: mono
+      codeGenType: 'Interpreter'
+      projectFile: microbenchmarks.proj
+      runKind: micro_mono
 
+# run mono wasm microbenchmarks perf job
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/coreclr/templates/perf-job.yml
+    buildConfig: release
+    runtimeFlavor: wasm
+    platforms:
+    - Linux_x64
+    jobParameters:
+      testGroup: perf
+      liveLibrariesBuildConfig: Release
+      runtimeType: wasm
+      codeGenType: 'wasm'
+      projectFile: microbenchmarks.proj
+      runKind: micro
+      
+# run coreclr microbenchmarks perf job
 - template: /eng/pipelines/common/platform-matrix.yml
   parameters:
     jobTemplate: /eng/pipelines/coreclr/templates/perf-job.yml
@@ -100,3 +122,22 @@ jobs:
     jobParameters:
       testGroup: perf
       liveLibrariesBuildConfig: Release
+      projectFile: microbenchmarks.proj
+      runKind: micro
+
+# run coreclr crossgen perf job
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/coreclr/templates/perf-job.yml
+    buildConfig: release
+    runtimeFlavor: coreclr
+    platforms:
+    #- Linux_x64
+    - Windows_NT_x64
+    - Windows_NT_x86
+    jobParameters:
+      testGroup: perf
+      liveLibrariesBuildConfig: Release
+      projectFile: crossgen_perf.proj
+      runKind: crossgen_scenarios
+
diff --git a/eng/pipelines/coreclr/templates/build-job.yml b/eng/pipelines/coreclr/templates/build-job.yml
index 9b7975156ab6e6..f56c06f56ad6f5 100644
--- a/eng/pipelines/coreclr/templates/build-job.yml
+++ b/eng/pipelines/coreclr/templates/build-job.yml
@@ -133,7 +133,7 @@ jobs:
     - ${{ if and(eq(variables['System.TeamProject'], 'internal'), ne(variables['Build.Reason'], 'PullRequest')) }}:
       - template: /eng/pipelines/common/restore-internal-tools.yml
 
-    - ${{ if in(parameters.osGroup, 'OSX', 'iOS','tvOS') }}: 
+    - ${{ if in(parameters.osGroup, 'OSX', 'iOS','tvOS') }}:
       - script: |
           du -sh $(Build.SourcesDirectory)/*
           df -h
@@ -147,16 +147,12 @@ jobs:
       - script: set __TestIntermediateDir=int&&$(coreClrRepoRootDir)build-runtime$(scriptExt) $(buildConfig) $(archType) -ci $(enforcePgoArg) $(officialBuildIdArg) $(clrInterpreterBuildArg)
         displayName: Build CoreCLR Runtime
 
-    - ${{ if in(parameters.osGroup, 'OSX', 'iOS','tvOS') }}: 
+    - ${{ if in(parameters.osGroup, 'OSX', 'iOS','tvOS') }}:
       - script: |
           du -sh $(Build.SourcesDirectory)/*
           df -h
         displayName: Disk Usage after Build
 
-    - ${{ if and(eq(parameters.osGroup, 'Windows_NT'), ne(parameters.archType, 'x86')) }}:
-      - script: set __TestIntermediateDir=int&&$(coreClrRepoRootDir)build-runtime$(scriptExt) $(buildConfig) $(archType) -ci -linuxdac $(officialBuildIdArg)
-        displayName: Build Cross OS Linux DAC for Windows
-
     # Build CoreCLR Managed Components
     - script: $(Build.SourcesDirectory)$(dir)build$(scriptExt) -subset clr.corelib+clr.nativecorelib+clr.tools+clr.packages $(crossArg) -arch $(archType) $(osArg) -c $(buildConfig) $(officialBuildIdArg) -ci
       displayName: Build managed product components and packages
@@ -171,6 +167,28 @@ jobs:
       - script: $(coreClrRepoRootDir)build-test$(scriptExt) skipstressdependencies skipmanaged skipgeneratelayout $(buildConfig) $(archType) $(crossArg) $(osArg) $(priorityArg) $(compilerArg)
         displayName: Build native test components
 
+    # Sign and add entitlements to these MacOS binaries
+    - ${{ if and(ne(variables['System.TeamProject'], 'public'), notin(variables['Build.Reason'], 'PullRequest')) }}:
+      - ${{ if eq(parameters.osGroup, 'OSX') }}:
+
+        - template: /eng/pipelines/common/macos-sign-with-entitlements.yml
+          parameters:
+            filesToSign: 
+            - name: createdump
+              path: $(buildProductRootFolderPath)
+              entitlementsFile: $(Build.SourcesDirectory)/eng/pipelines/common/createdump-entitlements.plist
+            - name: corerun
+              path: $(buildProductRootFolderPath)
+              entitlementsFile: $(Build.SourcesDirectory)/eng/pipelines/common/entitlements.plist
+
+        - task: CopyFiles@2
+          displayName: 'Copy signed createdump to sharedFramework'
+          inputs:
+            contents: createdump
+            sourceFolder: $(buildProductRootFolderPath)
+            targetFolder: $(buildProductRootFolderPath)/sharedFramework
+            overWrite: true
+
     # Sign on Windows
     - ${{ if and(eq(parameters.osGroup, 'Windows_NT'), eq(parameters.signBinaries, 'true'), ne(parameters.testGroup, 'clrTools')) }}:
       - powershell: eng\common\build.ps1 -ci -sign -restore -configuration:$(buildConfig) -warnaserror:0 /p:ArcadeBuild=true /p:OfficialBuild=true /p:TargetOS=$(osGroup) /p:TargetArchitecture=$(archType) /p:Configuration=$(_BuildConfig) /p:DotNetSignType=$env:_SignType -projects $(Build.SourcesDirectory)\eng\empty.csproj
@@ -197,6 +215,13 @@ jobs:
           artifactName: $(buildProductArtifactName)
           displayName: 'product build'
 
+    - ${{ if and(ne(parameters.osGroup, 'OSX'), ne(parameters.archType, 'x86'), ne(parameters.compilerName, 'gcc'), ne(parameters.testGroup, 'clrTools')) }}:
+      - template: /eng/pipelines/coreclr/templates/crossdac-build.yml
+        parameters:
+          archType: ${{ parameters.archType }}
+          osGroup: ${{ parameters.osGroup }}
+          osSubgroup: ${{ parameters.osSubgroup }}
+
     - ${{ if and(ne(parameters.compilerName, 'gcc'), ne(parameters.testGroup, ''), ne(parameters.testGroup, 'clrTools')) }}:
       # Publish test native components for consumption by test execution.
       - ${{ if ne(parameters.isOfficialBuild, true) }}:
diff --git a/eng/pipelines/coreclr/templates/crossdac-build.yml b/eng/pipelines/coreclr/templates/crossdac-build.yml
new file mode 100644
index 00000000000000..b17b72af8325ca
--- /dev/null
+++ b/eng/pipelines/coreclr/templates/crossdac-build.yml
@@ -0,0 +1,53 @@
+parameters:
+  archType: ''
+  osGroup: ''
+  osSubgroup: ''
+
+steps:
+    # Always build the crossdac, that way we know in CI/PR if things break to build.
+    - ${{ if eq(parameters.osGroup, 'Windows_NT') }}:
+      - ${{ if notin(parameters.archType, 'x86') }}:
+        - script: set __TestIntermediateDir=int&&$(coreClrRepoRootDir)build-runtime$(scriptExt) $(buildConfig) $(archType) -ci -linuxdac $(officialBuildIdArg)
+          displayName: Build Cross OS Linux DAC for Windows
+
+
+    # Make the assets available in a single container for the packaging job.
+    - ${{ if and(ne(variables['System.TeamProject'], 'public'), ne(variables['Build.Reason'], 'PullRequest')) }}:
+      - ${{ if eq(parameters.osGroup, 'Windows_NT') }}:
+        - ${{ if notin(parameters.archType, 'x86', 'arm') }}:
+          - script: set __TestIntermediateDir=int&&$(coreClrRepoRootDir)build-runtime$(scriptExt) $(buildConfig) $(archType) -ci -alpinedac $(officialBuildIdArg)
+            displayName: Build Cross OS Linux-musl DAC for Windows
+
+        - task: CopyFiles@2
+          displayName: Gather CrossDac Artifacts (Linux)
+          inputs:
+            SourceFolder: $(buildLinuxDacRootFolderPath)
+            Contents: |
+              **/*
+              !**/sharedFramework/**/*
+            TargetFolder: $(buildLinuxDacStagingPath)
+
+        - ${{ if ne(parameters.archType, 'arm') }}:
+          - task: CopyFiles@2
+            displayName: Gather CrossDac Artifacts (Linux_musl)
+            inputs:
+              SourceFolder: $(buildMuslDacRootFolderPath)
+              Contents: |
+                **/*
+                !**/sharedFramework/**/*
+              TargetFolder: '$(buildMuslDacStagingPath)'
+
+      - ${{ if eq(parameters.osGroup, 'Linux') }}:
+        - task: CopyFiles@2
+          displayName: Gather runtime for CrossDac
+          inputs:
+            SourceFolder: $(coreClrProductRootFolderPath)
+            Contents: libcoreclr.so
+            TargetFolder: '$(crossDacArtifactPath)/${{ parameters.osGroup }}${{ parameters.osSubgroup }}.$(archType).$(buildConfigUpper)/$(crossDacHostArch)'
+
+      - task: PublishBuildArtifacts@1
+        displayName: Publish runtime for CrossDac
+        inputs:
+          pathtoPublish:  $(crossDacArtifactPath)
+          PublishLocation: Container
+          artifactName:  $(buildCrossDacArtifactName)
diff --git a/eng/pipelines/coreclr/templates/crossdac-pack.yml b/eng/pipelines/coreclr/templates/crossdac-pack.yml
new file mode 100644
index 00000000000000..f876a85d33febb
--- /dev/null
+++ b/eng/pipelines/coreclr/templates/crossdac-pack.yml
@@ -0,0 +1,74 @@
+parameters:
+  archType: ''
+  buildConfig: ''
+  container: ''
+  crossDacPlatforms: {}
+  isOfficialBuild: false
+  osGroup: ''
+  osSubgroup: ''
+  platform: ''
+  pool: ''
+  runtimeVariant: ''
+  stagedBuild: false
+  testGroup: ''
+  timeoutInMinutes: ''
+  variables: {}
+
+jobs:
+- template: xplat-pipeline-job.yml
+  parameters:
+    archType: ${{ parameters.archType }}
+    buildConfig: ${{ parameters.buildConfig }}
+    container: ${{ parameters.container }}
+    condition: ${{ parameters.isOfficialBuild }}
+    helixType: 'build/product/'
+    osGroup: ${{ parameters.osGroup }}
+    osSubgroup: ${{ parameters.osSubgroup }}
+    pool: ${{ parameters.pool }}
+    runtimeVariant: ${{ parameters.runtimeVariant }}
+    stagedBuild: ${{ parameters.stagedBuild }}
+    timeoutInMinutes: ${{ parameters.timeoutInMinutes }}
+
+    name: crossdacpack
+    displayName: CrossDac Packaging
+
+    variables:
+    - name: officialBuildIdArg
+      value: ''
+    - name: crossDacArgs
+      value: ''
+    - ${{ if and(eq(variables['System.TeamProject'], 'internal'), ne(variables['Build.Reason'], 'PullRequest')) }}:
+      - name: officialBuildIdArg
+        value: '/p:OfficialBuildId=$(Build.BuildNumber)'
+      - name: crossDacArgs
+        value: '/p:CrossDacArtifactsDir=$(crossDacArtifactPath)/$(buildCrossDacArtifactName)'
+    - ${{ parameters.variables }}
+
+    dependsOn:
+    - ${{ if ne(parameters.crossDacPlatforms, '') }}:
+      - ${{ each platform in parameters.crossDacPlatforms }}:
+        - ${{ parameters.runtimeFlavor }}_${{ parameters.runtimeVariant }}_product_build_${{ platform }}_${{ parameters.buildConfig }}
+
+    steps:
+    - task: DownloadBuildArtifacts@0
+      displayName: Download CrossDac artifacts
+      inputs:
+        artifactName: $(buildCrossDacArtifactName)
+        downloadPath: $(crossDacArtifactPath)
+
+    - script: $(Build.SourcesDirectory)$(dir)build$(scriptExt) -subset crossdacpack -arch $(archType) $(osArg) -c $(buildConfig) $(officialBuildIdArg) $(crossDacArgs) -ci
+      displayName: Build crossdac packaging
+
+    # Save packages using the prepare-signed-artifacts format.
+    - template: /eng/pipelines/common/upload-unsigned-artifacts-step.yml
+      parameters:
+        name: ${{ parameters.platform }}
+
+    # Upload to artifacts to be signed
+    - task: PublishPipelineArtifact@1
+      displayName: Publish Logs
+      inputs:
+        targetPath: $(Build.SourcesDirectory)/artifacts/log
+        artifactName: 'CrossDacPackagingLogs'
+      continueOnError: true
+      condition: always()
diff --git a/eng/pipelines/coreclr/templates/helix-queues-setup.yml b/eng/pipelines/coreclr/templates/helix-queues-setup.yml
index c7c62451b779dc..caebaea069a026 100644
--- a/eng/pipelines/coreclr/templates/helix-queues-setup.yml
+++ b/eng/pipelines/coreclr/templates/helix-queues-setup.yml
@@ -124,7 +124,7 @@ jobs:
     # Windows_NT arm64
     - ${{ if eq(parameters.platform, 'Windows_NT_arm64') }}:
       - ${{ if and(eq(variables['System.TeamProject'], 'public'), in(parameters.jobParameters.helixQueueGroup, 'pr', 'ci', 'libraries')) }}:
-        - Windows.10.Arm64.Open
+        - Windows.10.Arm64v8.Open
       - ${{ if eq(variables['System.TeamProject'], 'internal') }}:
         - Windows.10.Arm64
 
diff --git a/eng/pipelines/coreclr/templates/perf-job.yml b/eng/pipelines/coreclr/templates/perf-job.yml
index 4284a79368f907..21799d64354d5c 100644
--- a/eng/pipelines/coreclr/templates/perf-job.yml
+++ b/eng/pipelines/coreclr/templates/perf-job.yml
@@ -11,6 +11,8 @@ parameters:
   runtimeType: 'coreclr'
   pool: ''
   codeGenType: 'JIT'
+  projetFile: ''
+  runKind: ''
 
 ### Perf job
 
@@ -21,8 +23,8 @@ jobs:
 - template: run-performance-job.yml
   parameters:
     # Compute job name from template parameters
-    jobName: ${{ format('perfbuild_{0}{1}_{2}_{3}_{4}_{5}', parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig, parameters.runtimeType, parameters.codeGenType) }}
-    displayName: ${{ format('Performance {0}{1} {2} {3} {4} {5}', parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig, parameters.runtimeType, parameters.codeGenType) }}
+    jobName: ${{ format('perfbuild_{0}{1}_{2}_{3}_{4}_{5}_{6}', parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig, parameters.runtimeType, parameters.codeGenType, parameters.runKind) }}
+    displayName: ${{ format('Performance {0}{1} {2} {3} {4} {5} {6}', parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig, parameters.runtimeType, parameters.codeGenType, parameters.runKind) }}
     pool: ${{ parameters.pool }}
     buildConfig: ${{ parameters.buildConfig }}
     archType: ${{ parameters.archType }}
@@ -32,6 +34,8 @@ jobs:
     liveLibrariesBuildConfig: ${{ parameters.liveLibrariesBuildConfig }}
     runtimeType: ${{ parameters.runtimeType }}
     codeGenType: ${{ parameters.codeGenType }}
+    projectFile: ${{ parameters.projectFile }}
+    runKind: ${{ parameters.runKind }}
     # Test job depends on the corresponding build job
     dependsOn:
     - ${{ format('coreclr_{0}_product_build_{1}{2}_{3}_{4}', parameters.runtimeVariant, parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig) }}
@@ -39,6 +43,8 @@ jobs:
       - ${{ format('libraries_build_{0}{1}_{2}_{3}', parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.liveLibrariesBuildConfig) }}
     - ${{ if eq(parameters.runtimeType, 'mono') }}:
       - ${{ format('mono_{0}_product_build_{1}{2}_{3}_{4}', parameters.runtimeVariant, parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig) }}
+    - ${{ if eq(parameters.runtimeType, 'wasm') }}:
+      - ${{ format('build_{0}{1}_{2}_{3}_{4}', 'Browser', '', 'wasm', parameters.buildConfig, parameters.runtimeType) }}
 
     ${{ if eq(parameters.osGroup, 'Windows_NT') }}:
       ${{ if eq(parameters.runtimeType, 'mono') }}:
@@ -48,7 +54,9 @@ jobs:
     ${{ if ne(parameters.osGroup, 'Windows_NT') }}:
       ${{ if eq(parameters.runtimeType, 'mono') }}:
         extraSetupParameters: --architecture ${{ parameters.archType }} --monodotnet $(Build.SourcesDirectory)/.dotnet-mono --kind micro_mono
-      ${{ if ne(parameters.runtimeType, 'mono') }}:
+      ${{ if eq(parameters.runtimeType, 'wasm') }}:
+        extraSetupParameters: --architecture ${{ parameters.archType }} --wasm $(librariesDownloadDir)/bin/wasm --kind micro
+      ${{ if eq(parameters.runtimeType, 'coreclr') }}:
         extraSetupParameters: --corerootdirectory $(Build.SourcesDirectory)/artifacts/tests/coreclr/${{ parameters.osGroup }}.${{ parameters.archType }}.Release/Tests/Core_Root --architecture ${{ parameters.archType }}
 
     variables: ${{ parameters.variables }}
@@ -86,15 +94,30 @@ jobs:
           artifactName: 'MonoProduct_${{ parameters.runtimeVariant }}_$(osGroup)_$(archType)_$(buildConfig)'
           displayName: 'Mono runtime'
 
+    - ${{ if eq(parameters.runtimeType, 'wasm') }}:
+      # Download artifact
+      - task: DownloadBuildArtifacts@0
+        displayName: 'Download WASM Runtime Pack'
+        inputs:
+          buildType: current
+          downloadType: single
+          downloadPath: '$(Build.SourcesDirectory)/__download__'
+          artifactName: 'IntermediateUnsignedArtifacts'
+
+      - script: "mkdir $(librariesDownloadDir)/bin/wasm;unzip -o $(Build.SourcesDirectory)/__download__/IntermediateUnsignedArtifacts/MonoRuntimePacks/Shipping/Microsoft.NETCore.App.Runtime.browser-wasm.5.0.0-ci.nupkg data/* runtimes/* -d $(librariesDownloadDir)/bin/wasm;cp src/mono/wasm/runtime-test.js $(librariesDownloadDir)/bin/wasm/runtime-test.js;find $(librariesDownloadDir)/bin/wasm -type f -exec chmod 664 {} \\;"
+        displayName: "Create wasm directory (Linux)"
+
     # Create Core_Root
     - script: $(coreClrRepoRootDir)build-test$(scriptExt) $(buildConfig) $(archType) generatelayoutonly $(librariesOverrideArg)
       displayName: Create Core_Root
       condition: and(succeeded(), ne(variables.runtimeFlavorName, 'Mono'))
 
-    - script: "build.cmd -subset libs.pretest -configuration release -ci -arch $(archType) -testscope innerloop /p:RuntimeArtifactsPath=$(librariesDownloadDir)\\bin\\mono\\$(osGroup).$(archType).$(buildConfigUpper) /p:RuntimeFlavor=mono;xcopy $(Build.SourcesDirectory)\\artifacts\\bin\\testhost\\$(_Framework)-$(osGroup)-$(buildConfigUpper)-$(archType)\\* $(Build.SourcesDirectory)\\.dotnet-mono /E /I /Y;copy $(Build.SourcesDirectory)\\artifacts\\bin\\coreclr\\$(osGroup).$(archType).$(buildConfigUpper)\\corerun.exe $(Build.SourcesDirectory)\\.dotnet-mono\\shared\\Microsoft.NETCore.App\\5.0.0\\corerun.exe"
+      # Copy the runtime directory into the testhost folder to include OOBs.
+
+    - script: "build.cmd -subset libs.pretest -configuration release -ci -arch $(archType) -testscope innerloop /p:RuntimeArtifactsPath=$(librariesDownloadDir)\\bin\\mono\\$(osGroup).$(archType).$(buildConfigUpper) /p:RuntimeFlavor=mono;xcopy $(Build.SourcesDirectory)\\artifacts\\bin\\runtime\\$(_Framework)-$(osGroup)-$(buildConfigUpper)-$(archType)\\* $(Build.SourcesDirectory)\\artifacts\\bin\\testhost\\$(_Framework)-$(osGroup)-$(buildConfigUpper)-$(archType)\\shared\\Microsoft.NETCore.App\\5.0.0 /E /I /Y;xcopy $(Build.SourcesDirectory)\\artifacts\\bin\\testhost\\$(_Framework)-$(osGroup)-$(buildConfigUpper)-$(archType)\\* $(Build.SourcesDirectory)\\.dotnet-mono /E /I /Y;copy $(Build.SourcesDirectory)\\artifacts\\bin\\coreclr\\$(osGroup).$(archType).$(buildConfigUpper)\\corerun.exe $(Build.SourcesDirectory)\\.dotnet-mono\\shared\\Microsoft.NETCore.App\\5.0.0\\corerun.exe"
       displayName: "Create mono dotnet (Windows)"
       condition: and(and(succeeded(), eq(variables.runtimeFlavorName, 'Mono')), eq(variables.osGroup, 'Windows_NT'))
 
-    - script: "mkdir $(Build.SourcesDirectory)/.dotnet-mono;./build.sh -subset libs.pretest -configuration release -ci -arch $(archType) -testscope innerloop /p:RuntimeArtifactsPath=$(librariesDownloadDir)/bin/mono/$(osGroup).$(archType).$(buildConfigUpper) /p:RuntimeFlavor=mono;cp $(Build.SourcesDirectory)/artifacts/bin/testhost/$(_Framework)-$(osGroup)-$(buildConfigUpper)-$(archType)/* $(Build.SourcesDirectory)/.dotnet-mono -r;cp $(Build.SourcesDirectory)/artifacts/bin/coreclr/$(osGroup).$(archType).$(buildConfigUpper)/corerun $(Build.SourcesDirectory)/.dotnet-mono/shared/Microsoft.NETCore.App/5.0.0/corerun"
+    - script: "mkdir $(Build.SourcesDirectory)/.dotnet-mono;./build.sh -subset libs.pretest -configuration release -ci -arch $(archType) -testscope innerloop /p:RuntimeArtifactsPath=$(librariesDownloadDir)/bin/mono/$(osGroup).$(archType).$(buildConfigUpper) /p:RuntimeFlavor=mono;cp $(Build.SourcesDirectory)/artifacts/bin/runtime/$(_Framework)-$(osGroup)-$(buildConfigUpper)-$(archType)/* $(Build.SourcesDirectory)/artifacts/bin/testhost/$(_Framework)-$(osGroup)-$(buildConfigUpper)-$(archType)/shared/Microsoft.NETCore.App/5.0.0 -rf;cp $(Build.SourcesDirectory)/artifacts/bin/testhost/$(_Framework)-$(osGroup)-$(buildConfigUpper)-$(archType)/* $(Build.SourcesDirectory)/.dotnet-mono -r;cp $(Build.SourcesDirectory)/artifacts/bin/coreclr/$(osGroup).$(archType).$(buildConfigUpper)/corerun $(Build.SourcesDirectory)/.dotnet-mono/shared/Microsoft.NETCore.App/5.0.0/corerun"
       displayName: "Create mono dotnet (Linux)"
       condition: and(and(succeeded(), eq(variables.runtimeFlavorName, 'Mono')), ne(variables.osGroup, 'Windows_NT'))
diff --git a/eng/pipelines/coreclr/templates/run-performance-job.yml b/eng/pipelines/coreclr/templates/run-performance-job.yml
index 7dadb9bd5eee02..c38d33405cca44 100644
--- a/eng/pipelines/coreclr/templates/run-performance-job.yml
+++ b/eng/pipelines/coreclr/templates/run-performance-job.yml
@@ -18,6 +18,8 @@ parameters:
   liveLibrariesBuildConfig: ''    # optional -- live-live libraries configuration to use for the run
   runtimeType: 'coreclr'          # optional -- Sets the runtime as coreclr or mono
   codeGenType: 'JIT'              # optional -- Decides on the codegen technology if running on mono
+  projectFile: ''                 # required -- project file to build helix workitems
+  runKind: ''                     # required -- test category
 
 jobs:
 - template: xplat-pipeline-job.yml
@@ -51,7 +53,7 @@ jobs:
     - IsInternal: ''
     - HelixApiAccessToken: ''
     - HelixPreCommandStemWindows: 'py -3 -m venv %HELIX_WORKITEM_PAYLOAD%\.venv;call %HELIX_WORKITEM_PAYLOAD%\.venv\Scripts\activate.bat;set PYTHONPATH=;py -3 -m pip install --user azure.storage.blob==12.0.0 --force-reinstall;py -3 -m pip install --user azure.storage.queue==12.0.0 --force-reinstall;set "PERFLAB_UPLOAD_TOKEN=$(PerfCommandUploadToken)"'
-    - HelixPreCommandStemLinux: 'sudo apt-get -y install python3-venv;python3 -m venv $HELIX_WORKITEM_PAYLOAD/.venv;source $HELIX_WORKITEM_PAYLOAD/.venv/Scripts/activate;export PYTHONPATH=;pip3 install --user azure.storage.blob==12.0.0 --force-reinstall;pip3 install --user azure.storage.queue==12.0.0 --force-reinstall;export PERFLAB_UPLOAD_TOKEN="$(PerfCommandUploadTokenLinux)"'
+    - HelixPreCommandStemLinux: 'sudo apt-get -y install python3-venv;python3 -m venv $HELIX_WORKITEM_PAYLOAD/.venv;source $HELIX_WORKITEM_PAYLOAD/.venv/Scripts/activate;export PYTHONPATH=;pip3 install --user azure.storage.blob==12.0.0 --force-reinstall;pip3 install --user azure.storage.queue==12.0.0 --force-reinstall;sudo apt-get -y install nodejs;sudo apt-get -y install npm;npm install --prefix $HELIX_WORKITEM_PAYLOAD jsvu -g;$HELIX_WORKITEM_PAYLOAD/bin/jsvu --os=linux64 --engines=v8;export PERFLAB_UPLOAD_TOKEN="$(PerfCommandUploadTokenLinux)"'
     - ExtraMSBuildLogsWindows: 'set MSBUILDDEBUGCOMM=1;set "MSBUILDDEBUGPATH=%HELIX_WORKITEM_UPLOAD_ROOT%"'
     - ExtraMSBuildLogsLinux: 'export MSBUILDDEBUGCOMM=1;export "MSBUILDDEBUGPATH=$HELIX_WORKITEM_UPLOAD_ROOT"'
     - HelixPreCommand: ''
@@ -71,7 +73,7 @@ jobs:
       - ${{ if eq( parameters.osGroup, 'Windows_NT') }}:
         - HelixPreCommand: $(ExtraMSBuildLogsWindows)
       - ${{ if ne(parameters.osGroup, 'Windows_NT') }}:
-          - HelixPreCommand: $(ExtraMSBuildLogsLinux)
+          - HelixPreCommand: $(ExtraMSBuildLogsLinux);npm install --prefix $HELIX_WORKITEM_PAYLOAD jsvu -g;$HELIX_WORKITEM_PAYLOAD/bin/jsvu --os=linux64 --engines=v8
     
 
     - ${{ if and(eq(parameters.codeGenType, 'Interpreter'), eq(parameters.runtimeType, 'mono')) }}:
@@ -102,11 +104,11 @@ jobs:
             _Framework: ${{ framework }}
     steps:
     - ${{ parameters.steps }}
-    - powershell: $(Build.SourcesDirectory)\eng\common\performance\performance-setup.ps1 $(IsInternal)$(Interpreter) -Framework $(_Framework) ${{ parameters.extraSetupParameters }}
+    - powershell: $(Build.SourcesDirectory)\eng\common\performance\performance-setup.ps1 $(IsInternal)$(Interpreter) -Framework $(_Framework) -Kind ${{ parameters.runKind }} ${{ parameters.extraSetupParameters }}
       displayName: Performance Setup (Windows)
       condition: and(succeeded(), eq(variables['Agent.Os'], 'Windows_NT'))
       continueOnError: ${{ parameters.continueOnError }}
-    - script: $(Build.SourcesDirectory)/eng/common/performance/performance-setup.sh $(IsInternal)$(Interpreter) --framework $(_Framework) ${{ parameters.extraSetupParameters }}
+    - script: $(Build.SourcesDirectory)/eng/common/performance/performance-setup.sh $(IsInternal)$(Interpreter) --framework $(_Framework) --kind ${{ parameters.runKind }} ${{ parameters.extraSetupParameters }}
       displayName: Performance Setup (Unix)
       condition: and(succeeded(), ne(variables['Agent.Os'], 'Windows_NT'))
       continueOnError: ${{ parameters.continueOnError }}
@@ -132,10 +134,11 @@ jobs:
         WorkItemTimeout: 4:00 # 4 hours
         WorkItemDirectory: '$(WorkItemDirectory)' # WorkItemDirectory can not be empty, so we send it some docs to keep it happy
         CorrelationPayloadDirectory: '$(PayloadDirectory)' # it gets checked out to a folder with shorter path than WorkItemDirectory so we can avoid file name too long exceptions
+        ProjectFile: ${{ parameters.projectFile }}
     - task: PublishPipelineArtifact@1
       displayName: Publish Logs
       inputs:
         targetPath: $(Build.SourcesDirectory)/artifacts/log
-        artifactName: 'Performance_Run_$(osGroup)$(osSubgroup)_$(archType)_$(buildConfig)_${{ parameters.runtimeType }}_${{ parameters.codeGenType }}'
+        artifactName: 'Performance_Run_$(osGroup)$(osSubgroup)_$(archType)_$(buildConfig)_${{ parameters.runtimeType }}_${{ parameters.codeGenType }}_${{ parameters.runKind }}'
       continueOnError: true
       condition: always()
diff --git a/eng/pipelines/coreclr/templates/xplat-pipeline-job.yml b/eng/pipelines/coreclr/templates/xplat-pipeline-job.yml
index dfcf6652e25e4b..0e789b84e91991 100644
--- a/eng/pipelines/coreclr/templates/xplat-pipeline-job.yml
+++ b/eng/pipelines/coreclr/templates/xplat-pipeline-job.yml
@@ -65,7 +65,7 @@ jobs:
 
     - name: binTestsPath
       value: '$(Build.SourcesDirectory)/artifacts/tests/coreclr'
-     
+
     # Build product defines what we are trying to build, either coreclr or mono
     - name: buildProductArtifactName
       value: 'CoreCLRProduct_${{ parameters.runtimeVariant }}_$(osGroup)$(osSubgroup)_$(archType)_$(buildConfig)'
@@ -73,6 +73,31 @@ jobs:
     - name: buildProductRootFolderPath
       value: '$(Build.SourcesDirectory)/artifacts/bin/coreclr/$(osGroup).$(archType).$(buildConfigUpper)'
 
+    - name: buildCrossDacArtifactName
+      value: CoreCLRCrossDacArtifacts
+
+    - name: crossDacArtifactPath
+      value: $(Build.SourcesDirectory)/artifacts/$(buildCrossDacArtifactName)
+
+    - name: buildMuslDacRootFolderPath
+      value: '$(Build.SourcesDirectory)/artifacts/bin/coreclr/alpine.$(archType).$(buildConfigUpper)'
+
+    - name: buildMuslDacStagingPath
+      value: '$(crossDacArtifactPath)/Linux_musl.$(archType).$(buildConfigUpper)'
+
+    - name: buildLinuxDacRootFolderPath
+      value: '$(Build.SourcesDirectory)/artifacts/bin/coreclr/Linux.$(archType).$(buildConfigUpper)'
+
+    - name: buildLinuxDacStagingPath
+      value: '$(crossDacArtifactPath)/Linux.$(archType).$(buildConfigUpper)'
+
+    - name: crossDacHostArch
+      value: x64
+
+    - ${{ if eq(parameters.archType, 'arm') }}:
+      - name: crossDacHostArch
+        value: x86
+
     # We need this because both mono and coreclr build currently depends on CoreClr
     - name: coreClrProductArtifactName
       value: 'CoreCLRProduct_${{ parameters.runtimeVariant }}_$(osGroup)$(osSubgroup)_$(archType)_$(buildConfig)'
diff --git a/eng/pipelines/installer/jobs/base-job.yml b/eng/pipelines/installer/jobs/base-job.yml
index b74bf18fb60ce6..9ad565067c7481 100644
--- a/eng/pipelines/installer/jobs/base-job.yml
+++ b/eng/pipelines/installer/jobs/base-job.yml
@@ -132,7 +132,7 @@ jobs:
 
     - name: BaseJobBuildCommand
       value: >-
-        $(Build.SourcesDirectory)/build.sh -subset installer -ci
+        $(Build.SourcesDirectory)/build.sh -ci
         $(BuildAction)
         -configuration $(_BuildConfig)
         $(LiveOverridePathArgs)
@@ -456,8 +456,29 @@ jobs:
         df -h
       displayName: Disk Usage before Build
 
-  - script: $(BaseJobBuildCommand)
-    displayName: Build
+  # Build the default subset non-MacOS platforms
+  - ${{ if ne(parameters.osGroup, 'OSX') }}:
+    - script: $(BaseJobBuildCommand)
+      displayName: Build
+
+  # Build corehost, sign and add entitlements to MacOS binaries
+  - ${{ if eq(parameters.osGroup, 'OSX') }}:
+    - script: $(BaseJobBuildCommand) -subset corehost
+      displayName: Build CoreHost
+
+    - ${{ if and(ne(variables['System.TeamProject'], 'public'), notin(variables['Build.Reason'], 'PullRequest')) }}:
+      - template: /eng/pipelines/common/macos-sign-with-entitlements.yml
+        parameters:
+          filesToSign: 
+          - name: dotnet
+            path: $(Build.SourcesDirectory)/artifacts/bin/osx-${{ parameters.archType }}.$(_BuildConfig)/corehost
+            entitlementsFile: $(Build.SourcesDirectory)/eng/pipelines/common/entitlements.plist
+          - name: apphost
+            path: $(Build.SourcesDirectory)/artifacts/bin/osx-${{ parameters.archType }}.$(_BuildConfig)/corehost
+            entitlementsFile: $(Build.SourcesDirectory)/eng/pipelines/common/entitlements.plist
+
+    - script: $(BaseJobBuildCommand) -subset installer.nocorehost
+      displayName: Build and Package
 
   - ${{ if in(parameters.osGroup, 'OSX', 'iOS','tvOS') }}: 
     - script: |
diff --git a/eng/pipelines/libraries/base-job.yml b/eng/pipelines/libraries/base-job.yml
index 99e62714189943..2ae778e893939a 100644
--- a/eng/pipelines/libraries/base-job.yml
+++ b/eng/pipelines/libraries/base-job.yml
@@ -4,7 +4,7 @@ parameters:
   archType: ''
   osSubgroup: ''
   crossrootfsDir: ''
-  framework: ''
+  framework: 'net5.0'
   isOfficialAllConfigurations: false
   isSourceBuild: false
   liveRuntimeBuildConfig: ''
@@ -20,14 +20,15 @@ parameters:
   testDisplayName: ''
   testScope: ''
   pool: ''
+  runTests: false
 
 jobs:
   - template: /eng/common/templates/job/job.yml
     parameters:
-      ${{ if notIn(parameters.framework, 'allConfigurations', 'net472') }}:
+      ${{ if notIn(parameters.framework, 'allConfigurations', 'net48') }}:
         displayName: ${{ format('Libraries {0} {1}{2} {3} {4}', parameters.displayName, parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig) }}
         name: ${{ format('libraries_{0}_{1}{2}_{3}_{4}', parameters.name, parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig) }}
-      ${{ if in(parameters.framework, 'allConfigurations', 'net472') }}:
+      ${{ if in(parameters.framework, 'allConfigurations', 'net48') }}:
         displayName: ${{ format('Libraries {0} {1} {2} {3} {4}', parameters.displayName, parameters.osGroup, parameters.framework, parameters.archType, parameters.buildConfig) }}
         name: ${{ format('libraries_{0}_{1}_{2}{3}_{4}_{5}', parameters.name, parameters.framework, parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig) }}
 
@@ -91,6 +92,9 @@ jobs:
         - ${{ if ne(parameters.liveRuntimeBuildConfig, '') }}:
           - _runtimeDownloadPath: '$(Build.SourcesDirectory)/artifacts/transport/${{ parameters.runtimeFlavor }}'
           - _runtimeConfigurationArg: -rc ${{ parameters.liveRuntimeBuildConfig }}
+          - ${{ if eq(parameters.runTests, true) }}:
+            - _runtimeArtifactName: '$(runtimeFlavorName)Product_${{ parameters.runtimeVariant}}_${{ parameters.osGroup }}${{ parameters.osSubgroup }}_${{ parameters.archType }}_${{ parameters.liveRuntimeBuildConfig }}'
+            - _runtimeArtifactsPathArg: ' /p:RuntimeArtifactsPath=$(_runtimeDownloadPath)'
           - ${{ if eq(parameters.testDisplayName, '') }}:
             - _testRunNamePrefixSuffix: $(runtimeFlavorName)_${{ parameters.liveRuntimeBuildConfig }}
           - ${{ if ne(parameters.testDisplayName, '') }}:
@@ -121,4 +125,13 @@ jobs:
 
       steps:
       - template: /eng/pipelines/common/clone-checkout-bundle-step.yml
+
+      - ${{ if and(ne(parameters.liveRuntimeBuildConfig, ''), eq(parameters.runTests, true)) }}:
+        - template: /eng/pipelines/common/download-artifact-step.yml
+          parameters:
+            unpackFolder: $(_runtimeDownloadPath)
+            artifactFileName: '$(_runtimeArtifactName)$(archiveExtension)'
+            artifactName: '$(_runtimeArtifactName)'
+            displayName: '$(runtimeFlavorName) build drop'
+
       - ${{ parameters.steps }}
diff --git a/eng/pipelines/libraries/build-job.yml b/eng/pipelines/libraries/build-job.yml
index f2e8ff21683c4c..4854b682716afa 100644
--- a/eng/pipelines/libraries/build-job.yml
+++ b/eng/pipelines/libraries/build-job.yml
@@ -4,7 +4,7 @@ parameters:
   osSubgroup: ''
   archType: ''
   crossrootfsDir: ''
-  framework: ''
+  framework: 'net5.0'
   isOfficialBuild: false
   isOfficialAllConfigurations: false
   runtimeVariant: ''
@@ -41,6 +41,7 @@ jobs:
       isOfficialAllConfigurations: ${{ parameters.isOfficialAllConfigurations }}
       liveRuntimeBuildConfig: ${{ parameters.liveRuntimeBuildConfig }}
       runtimeFlavor: ${{ parameters.runtimeFlavor }}
+      runTests: ${{ parameters.runTests }}
       timeoutInMinutes: ${{ parameters.timeoutInMinutes }}
       preBuildSteps: ${{ parameters.preBuildSteps }}
       container: ${{ parameters.container }}
@@ -51,6 +52,11 @@ jobs:
       name: build
       displayName: 'Build'
 
+      ${{ if and(ne(parameters.liveRuntimeBuildConfig, ''), eq(parameters.runTests, true)) }}:
+        dependsOn:
+        # Use full product dependency for test runs
+        - ${{ format('{0}_{1}_product_build_{2}{3}_{4}_{5}', parameters.runtimeFlavor, parameters.runtimeVariant, parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.liveRuntimeBuildConfig) }}
+
       variables:
         - librariesTestsArtifactName: ${{ format('libraries_test_assets_{0}_{1}_{2}', parameters.osGroup, parameters.archType, parameters.buildConfig) }}
         - _subset: libs
@@ -59,7 +65,7 @@ jobs:
         - ${{ if eq(parameters.osGroup, 'Browser') }}:
           - EMSDK_PATH: /usr/local/emscripten
 
-        # Tests only run for 'allConfiguration' and 'net472' build-jobs
+        # Tests only run for 'allConfiguration' and 'net48' build-jobs
         # If platform is in testBuildPlatforms we build tests as well.
         - ${{ if or(eq(parameters.runTests, true), containsValue(parameters.testBuildPlatforms, parameters.platform)) }}:
           - _subset: libs+libs.tests
@@ -93,55 +99,9 @@ jobs:
             displayName: Disk Usage after Build
 
         - ${{ if eq(parameters.runTests, false) }}:
-          - ${{ if ne(parameters.isOfficialBuild, true) }}:          
-            - task: CopyFiles@2
-              displayName: Prepare testhost folder to publish
-              inputs:
-                sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/testhost
-                targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/testhost
-
-            - task: CopyFiles@2
-              displayName: Prepare runtime folder to publish
-              inputs:
-                sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/runtime
-                targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/runtime
-
-            - task: CopyFiles@2
-              displayName: Prepare ref folder to publish
-              inputs:
-                sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/ref
-                targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/ref
-
-          - task: CopyFiles@2
-            displayName: Prepare shared framework ref assemblies to publish
-            inputs:
-              sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/ref/microsoft.netcore.app
-              targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/ref/microsoft.netcore.app
-
-          - task: CopyFiles@2
-            displayName: Prepare shared framework runtime folder to publish
-            inputs:
-              sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/pkg
-              targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/pkg
-
-          - task: CopyFiles@2
-            displayName: Prepare docs folder to publish
-            inputs:
-              sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/docs
-              targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/docs
-
-          - task: CopyFiles@2
-            displayName: Prepare native folder to publish
-            inputs:
-              sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/native
-              targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/native
-
-          - task: CopyFiles@2
-            displayName: Prepare artifacts packages folder to publish
-            inputs:
-              sourceFolder: $(Build.SourcesDirectory)/artifacts/packages
-              targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/packages
-            condition: and(succeeded(), eq(variables['_librariesBuildProducedPackages'], true))
+          - template: /eng/pipelines/libraries/prepare-for-bin-publish.yml
+            parameters:
+              isOfficialBuild: ${{ parameters.isOfficialBuild }}
 
           - template: /eng/pipelines/common/upload-artifact-step.yml
             parameters:
diff --git a/eng/pipelines/libraries/helix-queues-setup.yml b/eng/pipelines/libraries/helix-queues-setup.yml
index 58d1f89fe3c08a..33d0ea5aa9dbdd 100644
--- a/eng/pipelines/libraries/helix-queues-setup.yml
+++ b/eng/pipelines/libraries/helix-queues-setup.yml
@@ -88,7 +88,7 @@ jobs:
     # Windows_NT x64
     - ${{ if eq(parameters.platform, 'Windows_NT_x64') }}:
       # netcoreapp
-      - ${{ if notIn(parameters.jobParameters.framework, 'allConfigurations', 'net472') }}:
+      - ${{ if notIn(parameters.jobParameters.framework, 'allConfigurations', 'net48') }}:
         - ${{ if eq(parameters.jobParameters.isFullMatrix, true) }}:
           - Windows.81.Amd64.Open
           - Windows.10.Amd64.ServerRS5.Open
@@ -101,8 +101,8 @@ jobs:
           - ${{ if ne(parameters.jobParameters.runtimeFlavor, 'mono') }}:
             - (Windows.Nano.1809.Amd64.Open)windows.10.amd64.serverrs5.open@mcr.microsoft.com/dotnet-buildtools/prereqs:nanoserver-1809-helix-amd64-08e8e40-20200107182504
 
-      # NET472
-      - ${{ if eq(parameters.jobParameters.framework, 'net472') }}:
+      # .NETFramework
+      - ${{ if eq(parameters.jobParameters.framework, 'net48') }}:
         - Windows.10.Amd64.Client19H1.Open
       
       # AllConfigurations
@@ -112,7 +112,7 @@ jobs:
     # Windows_NT x86
     - ${{ if eq(parameters.platform, 'Windows_NT_x86') }}:
       # netcoreapp
-      - ${{ if notIn(parameters.jobParameters.framework, 'allConfigurations', 'net472') }}:
+      - ${{ if notIn(parameters.jobParameters.framework, 'allConfigurations', 'net48') }}:
         - ${{ if eq(parameters.jobParameters.isFullMatrix, true) }}:
           - Windows.7.Amd64.Open
           - Windows.10.Amd64.ServerRS5.Open
@@ -124,8 +124,8 @@ jobs:
             - Windows.7.Amd64.Open
             - Windows.10.Amd64.Server19H1.Open
 
-      # NET472
-      - ${{ if eq(parameters.jobParameters.framework, 'net472') }}:
+      # .NETFramework
+      - ${{ if eq(parameters.jobParameters.framework, 'net48') }}:
         - Windows.10.Amd64.Client19H1.Open
 
     # Windows_NT arm
diff --git a/eng/pipelines/libraries/outerloop.yml b/eng/pipelines/libraries/outerloop.yml
index 9afbf206e5f369..d88481ea37dd4b 100644
--- a/eng/pipelines/libraries/outerloop.yml
+++ b/eng/pipelines/libraries/outerloop.yml
@@ -99,6 +99,6 @@ jobs:
         jobParameters:
           isOfficialBuild: ${{ variables['isOfficialBuild'] }}
           isFullMatrix: ${{ variables['isFullMatrix'] }}
-          framework: net472
+          framework: net48
           runTests: true
           testScope: outerloop
\ No newline at end of file
diff --git a/eng/pipelines/libraries/prepare-for-bin-publish.yml b/eng/pipelines/libraries/prepare-for-bin-publish.yml
new file mode 100644
index 00000000000000..fa71beaae65fd1
--- /dev/null
+++ b/eng/pipelines/libraries/prepare-for-bin-publish.yml
@@ -0,0 +1,55 @@
+# Steps used to prepare the Artifacts Staging Directory with required files for
+# executing libraries tests as well as shared framework assets
+parameters:
+  isOfficialBuild: ''
+
+steps:
+  - ${{ if ne(parameters.isOfficialBuild, true) }}:
+    - task: CopyFiles@2
+      displayName: Prepare testhost folder to publish
+      inputs:
+        sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/testhost
+        targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/testhost
+
+    - task: CopyFiles@2
+      displayName: Prepare runtime folder to publish
+      inputs:
+        sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/runtime
+        targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/runtime
+
+    - task: CopyFiles@2
+      displayName: Prepare ref folder to publish
+      inputs:
+        sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/ref
+        targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/ref
+
+  - task: CopyFiles@2
+    displayName: Prepare shared framework ref assemblies to publish
+    inputs:
+      sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/ref/microsoft.netcore.app
+      targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/ref/microsoft.netcore.app
+
+  - task: CopyFiles@2
+    displayName: Prepare docs folder to publish
+    inputs:
+      sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/docs
+      targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/docs
+
+  - task: CopyFiles@2
+    displayName: Prepare shared framework runtime folder to publish
+    inputs:
+      sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/pkg
+      targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/pkg
+  
+  - task: CopyFiles@2
+    displayName: Prepare native folder to publish
+    inputs:
+      sourceFolder: $(Build.SourcesDirectory)/artifacts/bin/native
+      targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/bin/native
+  
+  - task: CopyFiles@2
+    displayName: Prepare artifacts packages folder to publish
+    inputs:
+      sourceFolder: $(Build.SourcesDirectory)/artifacts/packages
+      targetFolder: $(Build.ArtifactStagingDirectory)/artifacts/packages
+    condition: and(succeeded(), eq(variables['_librariesBuildProducedPackages'], true))
diff --git a/eng/pipelines/libraries/run-test-job.yml b/eng/pipelines/libraries/run-test-job.yml
index cf6324e790685e..faa5ab29e30029 100644
--- a/eng/pipelines/libraries/run-test-job.yml
+++ b/eng/pipelines/libraries/run-test-job.yml
@@ -3,7 +3,7 @@ parameters:
   osGroup: ''
   osSubgroup: ''
   archType: ''
-  framework: ''
+  framework: 'net5.0'
   isOfficialBuild: false
   liveRuntimeBuildConfig: ''
   runtimeFlavor: 'coreclr'
@@ -22,6 +22,7 @@ parameters:
   # stress modes that each test will be run with. This is the same usage as 'testGroup' in
   # eng/pipelines/common/templates/runtimes/run-test-job.yml.
   coreclrTestGroup: ''
+  dependsOn: []
 
 jobs:
   - template: /eng/pipelines/libraries/base-job.yml
@@ -40,6 +41,7 @@ jobs:
       condition: ${{ parameters.condition }}
       pool: ${{ parameters.pool }}
       testScope: ${{ parameters.testScope }}
+      runTests: true
       ${{ if ne(parameters.liveRuntimeBuildConfig, '') }}:
         displayName: ${{ format('Test Run {0} {1}', parameters.liveRuntimeBuildConfig, parameters.runtimeDisplayName) }}
         name: ${{ format('test_run_{0}_{1}', parameters.liveRuntimeBuildConfig, parameters.runtimeDisplayName) }}
@@ -50,21 +52,20 @@ jobs:
         testDisplayName: ${{ parameters.runtimeFlavor }}_interpreter_${{ parameters.liveRuntimeBuildConfig }}
 
       dependsOn:
-      - ${{ if notIn(parameters.framework, 'allConfigurations', 'net472') }}:
-        - ${{ format('libraries_build_{0}{1}_{2}_{3}', parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig) }}
-        # tests are built as part of product build
-        - ${{ if or(ne(parameters.archType, parameters.dependsOnTestArchitecture), ne(parameters.buildConfig, parameters.dependsOnTestBuildConfiguration)) }}:
-          - ${{ format('libraries_build_{0}_{1}_{2}', parameters.osGroup, parameters.dependsOnTestArchitecture, parameters.dependsOnTestBuildConfiguration) }}
-      - ${{ if ne(parameters.liveRuntimeBuildConfig, '') }}:
-        - ${{ format('{0}_{1}_product_build_{2}{3}_{4}_{5}', parameters.runtimeFlavor, parameters.runtimeVariant, parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.liveRuntimeBuildConfig) }}
+      - ${{ if ne(parameters.dependsOn[0], '') }}:
+        - ${{ parameters.dependsOn }}
+      - ${{ if eq(parameters.dependsOn[0], '') }}:
+        - ${{ if notIn(parameters.framework, 'allConfigurations', 'net48') }}:
+          - ${{ format('libraries_build_{0}{1}_{2}_{3}', parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.buildConfig) }}
+          # tests are built as part of product build
+          - ${{ if or(ne(parameters.archType, parameters.dependsOnTestArchitecture), ne(parameters.buildConfig, parameters.dependsOnTestBuildConfiguration)) }}:
+            - ${{ format('libraries_build_{0}_{1}_{2}', parameters.osGroup, parameters.dependsOnTestArchitecture, parameters.dependsOnTestBuildConfiguration) }}
+        - ${{ if ne(parameters.liveRuntimeBuildConfig, '') }}:
+          - ${{ format('{0}_{1}_product_build_{2}{3}_{4}_{5}', parameters.runtimeFlavor, parameters.runtimeVariant, parameters.osGroup, parameters.osSubgroup, parameters.archType, parameters.liveRuntimeBuildConfig) }}
 
       variables:
         - librariesTestsArtifactName: ${{ format('libraries_test_assets_{0}_{1}_{2}', parameters.osGroup, parameters.dependsOnTestArchitecture, parameters.dependsOnTestBuildConfiguration) }}
         - _archiveTestsParameter: /p:ArchiveTests=true
-        
-        - ${{ if ne(parameters.liveRuntimeBuildConfig, '') }}:
-          - _runtimeArtifactName: '$(runtimeFlavorName)Product_${{ parameters.runtimeVariant}}_${{ parameters.osGroup }}${{ parameters.osSubgroup }}_${{ parameters.archType }}_${{ parameters.liveRuntimeBuildConfig }}'
-          - _runtimeArtifactsPathArg: ' /p:RuntimeArtifactsPath=$(_runtimeDownloadPath)'
 
         - ${{ parameters.variables }}
 
@@ -84,14 +85,6 @@ jobs:
             artifactName: $(librariesTestsArtifactName)
             artifactFileName: $(librariesTestsArtifactName)$(archiveExtension)
             unpackFolder: $(Build.SourcesDirectory)/artifacts
-        
-        - ${{ if ne(parameters.liveRuntimeBuildConfig, '') }}:
-          - template: /eng/pipelines/common/download-artifact-step.yml
-            parameters:
-              unpackFolder: $(_runtimeDownloadPath)
-              artifactFileName: '$(_runtimeArtifactName)$(archiveExtension)'
-              artifactName: '$(_runtimeArtifactName)'
-              displayName: '$(runtimeFlavorName) build drop'
 
         - ${{ if in(parameters.coreclrTestGroup, 'gcstress0x3-gcstress0xc', 'gcstress-extra') }}:
           # We need to find and download the GC stress dependencies (namely, coredistools). Put them
diff --git a/eng/pipelines/runtime-linker-tests.yml b/eng/pipelines/runtime-linker-tests.yml
index ceffb1e237e76c..bb51f3c0c73655 100644
--- a/eng/pipelines/runtime-linker-tests.yml
+++ b/eng/pipelines/runtime-linker-tests.yml
@@ -64,6 +64,7 @@ jobs:
     - Linux_x64
     jobParameters:
       testGroup: innerloop
+      timeoutInMinutes: 120
       nameSuffix: Runtime_Release
       buildArgs: -s clr+libs -c $(_BuildConfig)
       extraStepsTemplate: /eng/pipelines/libraries/execute-trimming-tests-steps.yml
diff --git a/eng/pipelines/runtime-official.yml b/eng/pipelines/runtime-official.yml
index 3d335e198d7d4f..e1a3f8e7eefb1d 100644
--- a/eng/pipelines/runtime-official.yml
+++ b/eng/pipelines/runtime-official.yml
@@ -4,6 +4,7 @@ trigger:
     include:
     - master
     - release/*
+    - internal/release/*
   paths:
     include:
     - '*'
@@ -61,6 +62,23 @@ stages:
       jobParameters:
         isOfficialBuild: ${{ variables.isOfficialBuild }}
 
+  - template: /eng/pipelines/common/platform-matrix.yml
+    parameters:
+      jobTemplate: /eng/pipelines/coreclr/templates/crossdac-pack.yml
+      buildConfig: release
+      platforms:
+      - Linux_musl_x64
+      jobParameters:
+        isOfficialBuild: ${{ variables.isOfficialBuild }}
+        crossDacPlatforms:
+        - Linux_x64
+        - Linux_arm
+        - Linux_arm64
+        - Linux_musl_x64
+        - Linux_musl_arm64
+        - Windows_NT_x64
+        - Windows_NT_arm
+        - Windows_NT_arm64
   #
   # Build Mono runtime packs
   #
diff --git a/eng/pipelines/runtime.yml b/eng/pipelines/runtime.yml
index 6d70e6cd190dbc..3dcbae5869842c 100644
--- a/eng/pipelines/runtime.yml
+++ b/eng/pipelines/runtime.yml
@@ -226,7 +226,8 @@ jobs:
     jobTemplate: /eng/pipelines/coreclr/templates/format-job.yml
     platforms:
     - Linux_x64
-    - Windows_NT_x64
+    # Isssue: https://github.com/dotnet/runtime/issues/40034
+    #- Windows_NT_x64
     jobParameters:
       condition: >-
         and(
@@ -576,7 +577,7 @@ jobs:
     helixQueuesTemplate: /eng/pipelines/libraries/helix-queues-setup.yml
     jobParameters:
       isFullMatrix: ${{ variables.isFullMatrix }}
-      framework: net472
+      framework: net48
       runTests: true
       testScope: innerloop
       condition: >-
@@ -595,7 +596,6 @@ jobs:
       isFullMatrix: ${{ variables.isFullMatrix }}
       framework: allConfigurations
       runTests: true
-      liveRuntimeBuildConfig: release
       condition: >-
         or(
           eq(dependencies.checkout.outputs['SetPathVars_libraries.containsChange'], true),
@@ -682,7 +682,6 @@ jobs:
     platforms:
     - Linux_arm
     - Windows_NT_x86
-    - Windows_NT_arm
     - Windows_NT_arm64
     helixQueueGroup: pr
     helixQueuesTemplate: /eng/pipelines/coreclr/templates/helix-queues-setup.yml
@@ -850,7 +849,6 @@ jobs:
     platforms:
     - Windows_NT_x86
     - ${{ if eq(variables['isFullMatrix'], true) }}:
-      - Windows_NT_arm
       - Windows_NT_arm64
     helixQueuesTemplate: /eng/pipelines/libraries/helix-queues-setup.yml
     jobParameters:
diff --git a/eng/pipelines/runtimelab.yml b/eng/pipelines/runtimelab.yml
new file mode 100644
index 00000000000000..6f00e775b943dd
--- /dev/null
+++ b/eng/pipelines/runtimelab.yml
@@ -0,0 +1,185 @@
+# Setting batch to true, triggers one build at a time.
+# if there is a push while a build in progress, it will wait,
+# until the running build finishes, and produce a build with all the changes
+# that happened during the last build.
+trigger:
+  batch: true
+  branches:
+    include:
+    # Add Experiment branch here
+  paths:
+    include:
+    - '*'
+    - docs/manpages/*
+    exclude:
+    - eng/Version.Details.xml
+    - .github/*
+    - docs/*
+    - CODE-OF-CONDUCT.md
+    - CONTRIBUTING.md
+    - LICENSE.TXT
+    - PATENTS.TXT
+    - README.md
+    - SECURITY.md
+    - THIRD-PARTY-NOTICES.TXT
+
+pr:
+  branches:
+    include:
+    # Add Experiment branch here
+  paths:
+    include:
+    - '*'
+    - docs/manpages/*
+    exclude:
+    - eng/Version.Details.xml
+    - .github/*
+    - docs/*
+    - CODE-OF-CONDUCT.md
+    - CONTRIBUTING.md
+    - LICENSE.TXT
+    - PATENTS.TXT
+    - README.md
+    - SECURITY.md
+    - THIRD-PARTY-NOTICES.TXT
+
+variables:
+  - template: /eng/pipelines/common/variables.yml
+
+jobs:
+#
+# Checkout repository
+#
+- template: /eng/pipelines/common/checkout-job.yml
+
+#
+# Build with Debug config and Checked runtimeConfiguration
+#
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/common/global-build-job.yml
+    buildConfig: Checked
+    platforms:
+    - Linux_x64
+    - Windows_NT_x64
+    jobParameters:
+      testGroup: innerloop
+      buildArgs: -s clr+libs+installer -c debug -runtimeConfiguration Checked
+      extraStepsTemplate: /eng/pipelines/runtimelab/runtimelab-post-build-steps.yml
+
+#
+# Build with Release config and Release runtimeConfiguration
+#
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/common/global-build-job.yml
+    buildConfig: Release
+    platforms:
+    - Linux_x64
+    - Windows_NT_x64
+    jobParameters:
+      testGroup: innerloop
+      buildArgs: -s clr+libs+libs.tests+installer -c $(_BuildConfig) /p:ArchiveTests=true
+      extraStepsTemplate: /eng/pipelines/runtimelab/runtimelab-post-build-steps.yml
+      extraStepsParameters:
+        uploadTests: true
+
+#
+# Build with Release allConfigurations to produce packages
+#
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/common/global-build-job.yml
+    buildConfig: release
+    platforms:
+    - Windows_NT_x64
+    jobParameters:
+      testGroup: innerloop
+      nameSuffix: All_Configurations
+      buildArgs: -s libs -c $(_BuildConfig) -allConfigurations
+
+#
+# CoreCLR Test builds using live libraries release build
+#
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/common/templates/runtimes/build-test-job.yml
+    buildConfig: Checked
+    platforms:
+    - Linux_x64
+    jobParameters:
+      testGroup: innerloop
+      liveLibrariesBuildConfig: Release
+      dependsOn:
+      - build_Linux_x64_Checked_
+      - build_Linux_x64_Release_
+
+#
+# CoreCLR Test executions using live libraries
+#
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/common/templates/runtimes/run-test-job.yml
+    buildConfig: Checked
+    platforms:
+    - Linux_x64
+    helixQueueGroup: pr
+    helixQueuesTemplate: /eng/pipelines/coreclr/templates/helix-queues-setup.yml
+    jobParameters:
+      testGroup: innerloop
+      liveLibrariesBuildConfig: Release
+      dependsOn:
+      - coreclr_common_test_build_p0_AnyOS_AnyCPU_Checked
+
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/common/templates/runtimes/run-test-job.yml
+    buildConfig: Checked
+    platforms:
+    - Windows_NT_x64
+    helixQueueGroup: pr
+    helixQueuesTemplate: /eng/pipelines/coreclr/templates/helix-queues-setup.yml
+    jobParameters:
+      testGroup: innerloop
+      liveLibrariesBuildConfig: Release
+      dependsOn:
+      - coreclr_common_test_build_p0_AnyOS_AnyCPU_Checked
+      - build_Windows_NT_x64_Checked_
+      - build_Windows_NT_x64_Release_
+
+#
+# Libraries Release Test Execution against a release coreclr runtime
+#
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/libraries/run-test-job.yml
+    buildConfig: Release
+    platforms:
+    - Linux_x64
+    helixQueuesTemplate: /eng/pipelines/libraries/helix-queues-setup.yml
+    jobParameters:
+      isFullMatrix: false
+      isOfficialBuild: false
+      testScope: innerloop
+      liveRuntimeBuildConfig: Release
+      dependsOnTestBuildConfiguration: Release
+      dependsOnTestArchitecture: x64
+      dependsOn:
+      - build_Linux_x64_Release_
+
+- template: /eng/pipelines/common/platform-matrix.yml
+  parameters:
+    jobTemplate: /eng/pipelines/libraries/run-test-job.yml
+    buildConfig: Release
+    platforms:
+    - Windows_NT_x64
+    helixQueuesTemplate: /eng/pipelines/libraries/helix-queues-setup.yml
+    jobParameters:
+      isFullMatrix: false
+      isOfficialBuild: false
+      testScope: innerloop
+      liveRuntimeBuildConfig: Release
+      dependsOnTestBuildConfiguration: Release
+      dependsOnTestArchitecture: x64
+      dependsOn:
+      - build_Windows_NT_x64_Release_
diff --git a/eng/pipelines/runtimelab/runtimelab-post-build-steps.yml b/eng/pipelines/runtimelab/runtimelab-post-build-steps.yml
new file mode 100644
index 00000000000000..e5fbcba7bc9515
--- /dev/null
+++ b/eng/pipelines/runtimelab/runtimelab-post-build-steps.yml
@@ -0,0 +1,59 @@
+parameters:
+  buildConfig: ''
+  archType: ''
+  osGroup: ''
+  osSubgroup: ''
+  uploadTests: false
+
+steps:
+  # Build coreclr native test output
+  - script: $(Build.SourcesDirectory)/src/coreclr/build-test$(scriptExt) skipstressdependencies skipmanaged skipgeneratelayout $(buildConfigUpper) ${{ parameters.archType }}
+    displayName: Build native test components
+
+  # Copy all build output into artifacts staging directory
+  - template: /eng/pipelines/libraries/prepare-for-bin-publish.yml
+
+  # Zip CoreCLR Build Output
+  - template: /eng/pipelines/common/upload-artifact-step.yml
+    parameters:
+      rootFolder: $(Build.SourcesDirectory)/artifacts/bin/coreclr/${{ parameters.osGroup }}.${{ parameters.archType }}.$(buildConfigUpper)
+      archiveType: $(archiveType)
+      tarCompression: $(tarCompression)
+      includeRootFolder: false
+      archiveExtension: $(archiveExtension)
+      artifactName: CoreCLRProduct__${{ parameters.osGroup }}${{ parameters.osSubgroup }}_${{ parameters.archType }}_${{ parameters.buildConfig }}
+      displayName: 'CoreCLR product build'
+
+  # Zip Test Build
+  - ${{ if eq(parameters.uploadTests, true) }}:
+    - template: /eng/pipelines/common/upload-artifact-step.yml
+      parameters:
+        rootFolder: $(Build.SourcesDirectory)/artifacts/helix
+        includeRootFolder: true
+        archiveType: $(archiveType)
+        archiveExtension: $(archiveExtension)
+        tarCompression: $(tarCompression)
+        artifactName: libraries_test_assets_${{ parameters.osGroup }}_${{ parameters.archType }}_${{ parameters.buildConfig }}
+        displayName: Test Assets
+
+  # Zip product native assets for use by Tests
+  - template: /eng/pipelines/common/upload-artifact-step.yml
+    parameters:
+      rootFolder: $(Build.SourcesDirectory)/artifacts/tests/coreclr/obj/${{ parameters.osGroup }}.${{ parameters.archType }}.$(buildConfigUpper)
+      includeRootFolder: false
+      archiveType: $(archiveType)
+      tarCompression: $(tarCompression)
+      archiveExtension: $(archiveExtension)
+      artifactName: CoreCLRNativeTestArtifacts_${{ parameters.osGroup }}${{ parameters.osSubgroup }}_${{ parameters.archType }}_${{ parameters.buildConfig }}
+      displayName: 'native test components'
+
+  # Zip Libraries Build Output
+  - template: /eng/pipelines/common/upload-artifact-step.yml
+    parameters:
+      rootFolder: $(Build.ArtifactStagingDirectory)/artifacts
+      archiveType: $(archiveType)
+      tarCompression: $(tarCompression)
+      includeRootFolder: false
+      archiveExtension: $(archiveExtension)
+      artifactName: libraries_bin_${{ parameters.osGroup }}${{ parameters.osSubgroup }}_${{ parameters.archType }}_${{ parameters.buildConfig }}
+      displayName: Build Assets
diff --git a/eng/referenceAssemblies.props b/eng/referenceAssemblies.props
index a5e0e553f12f7a..94508fa244ad3d 100644
--- a/eng/referenceAssemblies.props
+++ b/eng/referenceAssemblies.props
@@ -1,9 +1,9 @@
 <Project>
   <PropertyGroup Condition="'$(BuildAllProjects)' == 'true' and
-                            !$(BuildTargetFramework.StartsWith('netstandard'))">
-    <AdditionalBuildTargetFrameworks Condition="!$(BuildTargetFramework.StartsWith('net45'))">$(AdditionalBuildTargetFrameworks);netstandard2.0</AdditionalBuildTargetFrameworks>
-    <AdditionalBuildTargetFrameworks Condition="!$(BuildTargetFramework.StartsWith('netcoreapp2.0')) and
-                                                !$(BuildTargetFramework.StartsWith('net4'))">$(AdditionalBuildTargetFrameworks);netstandard2.1</AdditionalBuildTargetFrameworks>
+                            !$(BuildTargetFramework.StartsWith('netstandard')) and
+                            !$(BuildTargetFramework.StartsWith('net4'))">
+    <AdditionalBuildTargetFrameworks>$(AdditionalBuildTargetFrameworks);netstandard2.0</AdditionalBuildTargetFrameworks>
+    <AdditionalBuildTargetFrameworks Condition="!$(BuildTargetFramework.StartsWith('netcoreapp2.0'))">$(AdditionalBuildTargetFrameworks);netstandard2.1</AdditionalBuildTargetFrameworks>
   </PropertyGroup>
 
   <PropertyGroup>
diff --git a/eng/referenceFromRuntime.targets b/eng/referenceFromRuntime.targets
deleted file mode 100644
index 34d0eb49199c8c..00000000000000
--- a/eng/referenceFromRuntime.targets
+++ /dev/null
@@ -1,124 +0,0 @@
-<Project>
-  <PropertyGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' and '$(TargetFramework)' != '$(NetCoreAppCurrent)'">
-    <PrepareProjectReferencesDependsOn>
-      AddRuntimeProjectReference;
-      $(PrepareProjectReferencesDependsOn);
-    </PrepareProjectReferencesDependsOn>
-    <ResolveReferencesDependsOn>
-      AddRuntimeProjectReference;
-      $(ResolveReferencesDependsOn);
-    </ResolveReferencesDependsOn>
-    <CleanDependsOn>
-      AddRuntimeProjectReference;
-      $(CleanDependsOn)
-    </CleanDependsOn>
-  </PropertyGroup>
-  
-  <PropertyGroup>
-    <RuntimeProjectFile>$([MSBuild]::NormalizePath('$(LibrariesProjectRoot)', 'restore', 'runtime', 'runtime.depproj'))</RuntimeProjectFile>
-  </PropertyGroup>
-
-  <Target Name="AddRuntimeProjectReference"
-          Condition="'$(IsTestProject)' != 'true' and '$(IsTestSupportProject)' != 'true' and '@(ReferenceFromRuntime)' != ''">
-    <Error Text="ReferenceFromRuntime may not be used from reference assemblies."
-           Condition="'$(IsReferenceAssembly)' == 'true' and '$(AllowReferenceFromRuntime)' != 'true'" />
-
-    <ItemGroup>
-      <ProjectReference Include="$(RuntimeProjectFile)">
-        <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
-        <OutputItemType>_referencePathFromRestoredRuntime</OutputItemType>
-      </ProjectReference>
-    </ItemGroup>
-  </Target>
-
-  <Target Name="GetFilesFromRuntime" Returns="@(RuntimeFiles)" DependsOnTargets="GetFilesFromCoreClr;GetFilesFromMono">
-    <ItemGroup>
-      <RuntimeFiles Include="@(RuntimeFiles)" />
-    </ItemGroup>
-  </Target>
-
-  <!-- 
-    The check must use != Mono because we don't consistently set this value to CoreCLR
-    https://github.com/dotnet/runtime/issues/32884
-  -->
-  <Target Name="GetFilesFromCoreCLR" 
-          Condition="'$(RuntimeFlavor)' != 'Mono'"
-          Returns="@(RuntimeFiles)"
-          DependsOnTargets="ResolveRuntimeFilesFromLocalBuild" />
-
-  <Target Name="GetFilesFromMono" 
-          Condition="'$(RuntimeFlavor)' == 'Mono'"
-          Returns="@(RuntimeFiles)"
-          DependsOnTargets="ResolveRuntimeFilesFromLocalBuild" />
-
-  <Target Name="FilterReferenceFromRuntime"
-          AfterTargets="ResolveProjectReferences"
-          Condition="'@(ReferenceFromRuntime)' != ''">
-
-    <Error Condition="'$(IsReferenceAssembly)' == 'true' and '$(AllowReferenceFromRuntime)' != 'true'" Text="ReferenceFromRuntime may not be used from reference assemblies." />
-
-    <MSBuild Projects="$(MSBuildProjectFile)" Targets="GetFilesFromRuntime" Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-      <Output TaskParameter="TargetOutputs" ItemName="RuntimeFiles" />
-    </MSBuild>
-
-    <ItemGroup>
-      <_referencePathFromRuntime Include="@(RuntimeFiles)" Private="false" />
-      <_referencePathFromRuntime Include="@(_referencePathFromRestoredRuntime)" Private="false" />
-      <!-- If this is a test project, also use the $(RuntimePath) to find a @(ReferenceFromRuntime) assembly. -->
-      <_referencePathFromRuntime Include="@(ReferenceFromRuntime->'$(RuntimePath)%(Identity).dll')" Condition="'$(IsTestProject)' == 'true' or '$(IsTestSupportProject)' == 'true'" />
-      <!-- transform to filename in order to intersect -->
-      <_referencePathFromRuntimeByFileName Include="@(_referencePathFromRuntime->'%(FileName)')" Condition="'%(_referencePathFromRuntime.Extension)' == '.dll'" >
-        <ReferencePath>%(Identity)</ReferencePath>
-      </_referencePathFromRuntimeByFileName>
-    </ItemGroup>
-
-    <RemoveDuplicates Inputs="@(_referencePathFromRuntimeByFileName)">
-      <Output TaskParameter="Filtered" ItemName="_referencePathFromRuntimeByFileNameFiltered" />
-    </RemoveDuplicates>
-
-    <ItemGroup>
-
-      <!-- intersect with ReferenceFromRuntime -->
-      <_filteredReferencePathFromRuntimeByFileName Include="@(_referencePathFromRuntimeByFileNameFiltered)"
-          Condition="'@(_referencePathFromRuntimeByFileNameFiltered)' == '@(ReferenceFromRuntime)' and '%(Identity)' != ''">
-        <Aliases>@(ReferenceFromRuntime->'%(Aliases)')</Aliases>
-      </_filteredReferencePathFromRuntimeByFileName>
-
-      <_remainingReferenceFromRuntime Include="@(ReferenceFromRuntime)" Exclude="@(_filteredReferencePathFromRuntimeByFileName)" />
-
-      <!-- Fallback and check for native images for the references as well -->
-      <_remainingReferenceFromRuntimeWithNI Include="@(_remainingReferenceFromRuntime->'%(Identity).ni')">
-        <OriginalReferenceFromRuntime>%(Identity)</OriginalReferenceFromRuntime>
-      </_remainingReferenceFromRuntimeWithNI>
-
-      <_filteredReferencePathFromRuntimeByFileName Include="@(_referencePathFromRuntimeByFileNameFiltered)"
-          Condition="'@(_referencePathFromRuntimeByFileNameFiltered)' == '@(_remainingReferenceFromRuntimeWithNI)' and '%(Identity)' != ''">
-        <Aliases>@(_remainingReferenceFromRuntimeWithNI->'%(Aliases)')</Aliases>
-      </_filteredReferencePathFromRuntimeByFileName>
-
-      <_missingReferenceFromRuntime Include="@(_remainingReferenceFromRuntimeWithNI)" Exclude="@(_filteredReferencePathFromRuntimeByFileName)" />
-
-      <!-- transform back to path -->
-      <!-- We are adding two items(with and without aliases) for references having Aliases. The major reason behind this to not use the Aliases for all the types in that reference.  -->
-      <!-- We can't use a Reference item for both since only the first one will be kept. -->
-      <!-- Aliases provides no way to encode both an alias and a non-aliased reference : https://github.com/dotnet/roslyn/issues/42604 -->
-      <!-- Use ReferencePath for the second reference so it will still be passed to the compiler. -->
-      <Reference Include="@(_filteredReferencePathFromRuntimeByFileName->'%(ReferencePath)')" />
-      <_aliasedReferencePathFromRuntime Include="@(_filteredReferencePathFromRuntimeByFileName->'%(ReferencePath)')" Condition="'%(_filteredReferencePathFromRuntimeByFileName.Aliases)' != ''" />
-      <ReferencePath Include="@(_aliasedReferencePathFromRuntime)" Aliases=""/>
-    </ItemGroup>
-
-    <Error Condition="'@(_missingReferenceFromRuntime)' != ''"
-           Text="Could not resolve ReferenceFromRuntime item(s) '%(_missingReferenceFromRuntime.OriginalReferenceFromRuntime)' from '$(RuntimeProjectFile)'." />
-  </Target>
-
-  <Target Name="RemoveAliasedReferenceFromRuntime"
-          AfterTargets="CoreCompile"
-          Condition="'@(_aliasedReferencePathFromRuntime)' != ''">
-    <!-- SDK's GenerateBuildDependencyFile will break when they encounter two identical reference paths, fix by removing the aliased ones -->
-    <ItemGroup>
-      <ReferencePath Remove="@(_aliasedReferencePathFromRuntime)"/>
-    </ItemGroup>
-  </Target>
-
-</Project>
diff --git a/eng/references.targets b/eng/references.targets
index efcac7d0515214..38037cf78ab022 100644
--- a/eng/references.targets
+++ b/eng/references.targets
@@ -1,67 +1,56 @@
 <Project>
   <PropertyGroup>
-    <ContractDependencyPaths>$(RefPath)</ContractDependencyPaths>
-    <FrameworkPathOverride>$(RefPath)</FrameworkPathOverride>
-    <AssemblySearchPaths>$(AssemblySearchPaths);$(RefPath);{RawFileName}</AssemblySearchPaths>
     <!-- Disable RAR from transitively discovering dependencies for References -->
     <_FindDependencies>false</_FindDependencies>
-    <!--
-      We don't use any of MSBuild's resolution logic for resolving the framework, so just set these two properties to any folder
-      that exists to skip the GenerateReferenceAssemblyPaths task (not target) and to prevent it from outputting a warning (MSB3644).
-      Need to set these after the common targets import.
-      -->
-    <_TargetFrameworkDirectories>$(MSBuildThisFileDirectory)</_TargetFrameworkDirectories>
-    <_FullFrameworkReferenceAssemblyPaths>$(MSBuildThisFileDirectory)</_FullFrameworkReferenceAssemblyPaths>
-  </PropertyGroup>
-  <PropertyGroup Condition="'$(IncludeDefaultReferences)' == ''">
-    <IncludeDefaultReferences Condition="'$(MSBuildProjectExtension)' == '.csproj'">true</IncludeDefaultReferences>
-    <IncludeDefaultReferences Condition="'$(MSBuildProjectExtension)' == '.vbproj'">true</IncludeDefaultReferences>
   </PropertyGroup>
 
-  <Target Name="SetupDefaultReferences">
-    <ItemGroup Condition="'$(IncludeDefaultReferences)' == 'true'">
-      <!-- netstandard is a default reference whenever building for NETStandard or building an implementation assembly -->
-      <DefaultReference Condition="('$(TargetFrameworkIdentifier)' == '.NETStandard' or '$(IsReferenceAssembly)' != 'true') and Exists('$(RefPath)netstandard.dll')" Include="netstandard" />
-    </ItemGroup>
-  </Target>
-  <Target Name="UpdateReferenceItems" DependsOnTargets="SetupDefaultReferences" BeforeTargets="AddReferencesDynamically">
-    <ItemGroup>
-      <Reference Include="@(DefaultReference)" />
-    </ItemGroup>
-    <ItemGroup>
-      <!-- Simple name references will be resolved from the targeting pack folders and should never be copied to output -->
-      <Reference Condition="'%(Reference.Extension)' != '.dll'">
-        <Private>false</Private>
-      </Reference>
-    </ItemGroup>
-  </Target>
+  <!-- netstandard is a default reference whenever building an implementation assembly for .NETCoreApp. -->
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                        '$(IsSourceProject)' == 'true'">
+    <Reference Include="netstandard"
+               Private="false" />
+  </ItemGroup>
 
-  <Target Name="AddDefaultTestReferences" BeforeTargets="SetupDefaultReferences" Condition="'$(IsTestProject)' == 'true' or '$(IsTestSupportProject)' == 'true'">
-    <ItemGroup>
-      <DefaultReferenceExclusions Include="@(ReferenceFromRuntime)"/>
+   <!-- If a CoreLib ProjectReference is present, make all P2P assets non transitive. -->
+  <ItemGroup Condition="'@(ProjectReference)' != '' and
+                         @(ProjectReference->AnyHaveMetadataValue('Identity', '$(CoreLibProject)'))">
+    <ProjectReference Update="@(ProjectReference)"
+                      PrivateAssets="all" />
+  </ItemGroup>
 
-      <!-- Reference everything in the targeting pack directory -->
-      <DefaultReferenceDirs Include="$(RefPath)" />
-      <DefaultReferenceItems Include="%(DefaultReferenceDirs.Identity)/*.dll" />
+  <!-- Project references shouldn't be copied to the output for non test apps. -->
+  <ItemDefinitionGroup Condition="'$(IsTestProject)' != 'true' and '$(IsTestSupportProject)' != 'true'">
+    <ProjectReference>
+      <Private>false</Private>
+    </ProjectReference>
+  </ItemDefinitionGroup>
 
-      <DefaultReferenceExclusions>
-        <RefDir>%(DefaultReferenceDirs.Identity)</RefDir>
-      </DefaultReferenceExclusions>
-      <_defaultReferenceExclusionsFullPath Include="%(DefaultReferenceExclusions.RefDir)%(DefaultReferenceExclusions.Identity).dll" />
-
-      <!-- Ensure conflict resolution can see these references. -->
-      <Reference Include="%(DefaultReferenceItems.FullPath)" Private="false" />
+  <!-- Filter out transitive P2Ps which should be excluded. -->
+  <Target Name="FilterTransitiveProjectReferences"
+          AfterTargets="IncludeTransitiveProjectReferences"
+          Condition="'$(DisableTransitiveProjectReferences)' != 'true' and
+                     '@(DefaultReferenceExclusion)' != ''">
+    <ItemGroup>
+      <_transitiveProjectReferenceWithExclusion Include="@(ProjectReference)">
+        <Exclusion>%(DefaultReferenceExclusion.Identity)</Exclusion>
+      </_transitiveProjectReferenceWithExclusion>
+      <ProjectReference Remove="@(_transitiveProjectReferenceWithExclusion)"
+                        Condition="'%(_transitiveProjectReferenceWithExclusion.NuGetPackageId)' == '%(_transitiveProjectReferenceWithExclusion.Exclusion)'" />
     </ItemGroup>
   </Target>
 
-  <Target Name="RemoveConflictResolutionAssetsForTests"
-          AfterTargets="_HandlePackageFileConflicts"
-          DependsOnTargets="AddDefaultTestReferences"
-          Condition="'@(_defaultReferenceExclusionsFullPath)' != ''">
+  <!-- Make shared framework assemblies not app-local (non private). -->
+  <Target Name="UpdateProjectReferencesWithPrivateAttribute"
+          AfterTargets="AssignProjectConfiguration"
+          BeforeTargets="PrepareProjectReferences"
+          Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                     ('$(IsTestProject)' == 'true' or '$(IsTestSupportProject)' == 'true') and
+                     '@(ProjectReferenceWithConfiguration)' != ''">
     <ItemGroup>
-      <Reference Remove="@(_defaultReferenceExclusionsFullPath)" />
+      <ProjectReferenceWithConfiguration PrivateAssets="all"
+                                         Private="false"
+                                         Condition="$(NetCoreAppLibrary.Contains('%(Filename);'))" />
     </ItemGroup>
   </Target>
 
-  <Target Name="AddReferencesDynamically" BeforeTargets="PrepareForBuild" />
-</Project>
\ No newline at end of file
+</Project>
diff --git a/eng/resolveContract.targets b/eng/resolveContract.targets
index 2f59f5d9a51734..6f4bb0e253ee30 100644
--- a/eng/resolveContract.targets
+++ b/eng/resolveContract.targets
@@ -1,8 +1,18 @@
 <Project>
+  <PropertyGroup>
+    <ContractDependencyPaths Condition="'$(DisableImplicitFrameworkReferences)' == 'true' and
+                                        '$(TargetFrameworkIdentifier)' == '.NETCoreApp'">$(MicrosoftNetCoreAppRefPackRefDir)</ContractDependencyPaths>
+    <!-- Use implementation referencepath if no contract tfm is set. -->
+    <ContractDependencyPaths Condition="'$(ContractDependencyPaths)' == ''">$(ContractDependencyPaths);@(ReferencePath->'%(RelativeDir)'->Distinct())</ContractDependencyPaths>
+  </PropertyGroup>
+
   <PropertyGroup Condition="'$(IsSourceProject)' == 'true'">
-    <ContractProject Condition="'$(ContractProject)' == ''">$(LibrariesProjectRoot)$(MSBuildProjectName)/ref/$(MSBuildProjectName).csproj</ContractProject>
+    <ContractProject Condition="'$(ContractProject)' == ''">$(LibrariesProjectRoot)$(MSBuildProjectName)\ref\$(MSBuildProjectName).csproj</ContractProject>
     <HasMatchingContract Condition="'$(HasMatchingContract)' == '' and Exists('$(ContractProject)')">true</HasMatchingContract>
-    <ContractAssemblyPath Condition="'$(ContractAssemblyPath)' == ''">$(RefPath)/$(MSBuildProjectName).dll</ContractAssemblyPath>
+    <ContractAssemblyPath Condition="'$(ContractAssemblyPath)' == '' and
+                                     '$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                                     $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '$(NETCoreAppCurrentVersion)'))">$(NetCoreAppCurrentRefPath)$(TargetFileName)</ContractAssemblyPath>
+    <ContractAssemblyPath Condition="'$(ContractAssemblyPath)' == ''">$([MSBuild]::NormalizePath('$(BaseOutputPath)', 'ref', '$(TargetFramework)-$(Configuration)', '$(TargetFileName)'))</ContractAssemblyPath>
 
     <!-- Disable API compat if the project doesn't have reference assembly -->
     <RunApiCompat Condition="'$(HasMatchingContract)' != 'true'">false</RunApiCompat>
@@ -10,8 +20,43 @@
 
   <ItemGroup Condition="'$(HasMatchingContract)' == 'true'">
     <ResolvedMatchingContract Condition="Exists('$(ContractAssemblyPath)')" Include="$(ContractAssemblyPath)" />
+    <!-- If the contract doesn't exist in the default contract output path add a project reference to the contract project to resolve -->
+    <ProjectReference Condition="'@(ResolvedMatchingContract)' == ''" Include="$(ContractProject)">
+      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
+      <OutputItemType>ResolvedMatchingContract</OutputItemType>
+    </ProjectReference>
   </ItemGroup>
 
   <!-- intentionally empty since we no longer need a target -->
   <Target Name="ResolveMatchingContract" />
+
+  <!-- Allow P2Ps that target a source project to build against the corresponding ref project. -->
+  <Target Name="AnnotateTargetPathWithTargetPlatformMonikerWithReferenceAssembly"
+          Condition="'$(HasMatchingContract)' == 'true'"
+          AfterTargets="GetTargetPathWithTargetPlatformMoniker">
+    <ItemGroup>
+      <TargetPathWithTargetPlatformMoniker ReferenceAssembly="@(ResolvedMatchingContract)" />
+    </ItemGroup>
+  </Target>
+
+  <Target Name="HandleReferenceAssemblyAttributeForProjectReferences"
+          AfterTargets="ResolveProjectReferences"
+          BeforeTargets="FindReferenceAssembliesForReferences"
+          Condition="'@(ProjectReference)' != '' and '@(_ResolvedProjectReferencePaths)' != ''">
+    <!-- If we have a ProjectReference to CoreLib, we need to compile against implementation assemblies. -->
+    <PropertyGroup Condition="@(_ResolvedProjectReferencePaths->AnyHaveMetadataValue('MSBuildSourceProjectFile', '$(CoreLibProject)'))">
+      <CompileUsingReferenceAssemblies>false</CompileUsingReferenceAssemblies>
+    </PropertyGroup>
+    <!-- Clear the ReferenceAssembly attribute on resolved P2Ps that set SkipUseReferenceAssembly to true. -->
+    <ItemGroup>
+       <_resolvedP2PFiltered Include="@(ProjectReference)">
+        <ProjectReferenceItemSpec>$([System.IO.Path]::GetFullPath('%(ProjectReference.Identity)'))</ProjectReferenceItemSpec>
+        <SkipUseReferenceAssembly>%(ProjectReference.SkipUseReferenceAssembly)</SkipUseReferenceAssembly>
+      </_resolvedP2PFiltered>
+      <_ResolvedProjectReferencePaths Update="@(_resolvedProjectReferenceFiltred)"
+                                      Condition="'%(_resolvedP2PFiltered.ProjectReferenceItemSpec)' == '%(_resolvedP2PFiltered.MSBuildSourceProjectFile)' and
+                                                 '%(_resolvedP2PFiltered.SkipUseReferenceAssembly)' == 'true'"
+                                      ReferenceAssembly="" />
+    </ItemGroup>
+  </Target>
 </Project>
\ No newline at end of file
diff --git a/eng/restore/repoRestore.props b/eng/restore/repoRestore.props
index 300c542e8cbe1c..d2ca92d6db0131 100644
--- a/eng/restore/repoRestore.props
+++ b/eng/restore/repoRestore.props
@@ -1,5 +1,6 @@
 <Project TreatAsLocalProperty="ExcludeRestorePackageImports">
   <PropertyGroup>
+    <ToolSetCommonDirectory>$(RepoRoot)artifacts\toolset\Common\</ToolSetCommonDirectory>
     <RestoreUseStaticGraphEvaluation>false</RestoreUseStaticGraphEvaluation>
     <!-- Need to set ProjectAssetsFile to something so it doesn't get set to the Tools.proj assets file when we import the generated props -->
     <ProjectAssetsFile Condition="'$(ProjectAssetsFile)' == ''">unused</ProjectAssetsFile>
diff --git a/eng/targetingpacks.targets b/eng/targetingpacks.targets
new file mode 100644
index 00000000000000..e39ce8fdada6b0
--- /dev/null
+++ b/eng/targetingpacks.targets
@@ -0,0 +1,106 @@
+<Project>
+  <PropertyGroup Condition="'$(DisableImplicitFrameworkReferences)' != 'true' and
+                            '$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                            $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '$(NETCoreAppCurrentVersion)'))">
+    <_UseLocalTargetingRuntimePack>true</_UseLocalTargetingRuntimePack>
+    <EnableTargetingPackDownload>false</EnableTargetingPackDownload>
+  </PropertyGroup>
+
+  <!-- .NETCoreApp 2.x DisableImplicitAssemblyReferences support. -->
+  <Choose>
+    <When Condition="'$(DisableImplicitAssemblyReferences)' == 'true' and
+                     '$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                     $([MSBuild]::VersionLessThan($(TargetFrameworkVersion), '3.0'))">
+    <PropertyGroup>
+      <MicrosoftNetCoreAppRefPackRefDir>$(PkgMicrosoft_NETCore_App)\ref\$(_ShortFrameworkIdentifier)$(_ShortFrameworkVersion)\</MicrosoftNetCoreAppRefPackRefDir>
+    </PropertyGroup>
+    <ItemGroup>
+      <PackageReference Update="Microsoft.NETCore.App"
+                        ExcludeAssets="all"
+                        GeneratePathProperty="true" />
+    </ItemGroup>
+    </When>
+  </Choose>
+
+  <!-- Simple name references will be resolved from the targeting pack folders and should never be copied to the output. -->
+  <ItemGroup>
+    <Reference Update="@(Reference)">
+      <Private Condition="'%(Reference.Extension)' != '.dll'">false</Private>
+    </Reference>
+  </ItemGroup>
+
+  <!-- .NETCoreApp > 2.x DisableImplicitAssemblyReferences support. -->
+  <Target Name="RemoveFrameworkReferences"
+          BeforeTargets="_HandlePackageFileConflicts"
+          AfterTargets="ResolveTargetingPackAssets"
+          Condition="'$(DisableImplicitAssemblyReferences)' == 'true' and
+                     '$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                     $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '3.0'))">
+    <PropertyGroup>
+      <MicrosoftNetCoreAppRefPackRefDir>%(ResolvedFrameworkReference.TargetingPackPath)\ref\$(_ShortFrameworkIdentifier)$(_ShortFrameworkVersion)\</MicrosoftNetCoreAppRefPackRefDir>
+    </PropertyGroup>
+    <ItemGroup>
+      <Reference Remove="@(Reference)"
+                 Condition="'%(Reference.FrameworkReferenceName)' == '$(SharedFrameworkName)'" />
+    </ItemGroup>
+  </Target>
+
+  <!-- Add the resolved targeting pack to the assembly search path. -->
+  <Target Name="UseTargetingPackForAssemblySearchPaths"
+          BeforeTargets="ResolveAssemblyReferences;
+                         DesignTimeResolveAssemblyReferences"
+          Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
+    <PropertyGroup>
+      <AssemblySearchPaths>$(AssemblySearchPaths);$(MicrosoftNetCoreAppRefPackRefDir.TrimEnd('/\'))</AssemblySearchPaths>
+      <DesignTimeAssemblySearchPaths>$(DesignTimeAssemblySearchPaths);$(MicrosoftNetCoreAppRefPackRefDir.TrimEnd('/\'))</DesignTimeAssemblySearchPaths>
+    </PropertyGroup>
+  </Target>
+
+  <!-- Use local targeting pack for NetCoreAppCurrent. -->
+  <Target Name="UpdateTargetingAndRuntimePack"
+          Condition="'$(_UseLocalTargetingRuntimePack)' == 'true'"
+          AfterTargets="ResolveFrameworkReferences">
+    <ItemGroup>
+      <ResolvedTargetingPack Path="$(MicrosoftNetCoreAppRefPackDir.TrimEnd('/\'))"
+                             NuGetPackageVersion="$(ProductVersion)"
+                             PackageDirectory="$(MicrosoftNetCoreAppRefPackDir.TrimEnd('/\'))"
+                             Condition="'%(ResolvedTargetingPack.RuntimeFrameworkName)' == '$(SharedFrameworkName)' and
+                                        Exists('$(MicrosoftNetCoreAppRefPackDataDir)FrameworkList.xml')" />
+      <ResolvedRuntimePack PackageDirectory="$(MicrosoftNetCoreAppRuntimePackDir)"
+                           Condition="'%(ResolvedRuntimePack.FrameworkName)' == '$(SharedFrameworkName)'" />
+      <ResolvedFrameworkReference TargetingPackPath="$(MicrosoftNetCoreAppRefPackDir.TrimEnd('/\'))"
+                                  TargetingPackVersion="$(ProductVersion)"
+                                  Condition="'%(Identity)' == '$(SharedFrameworkName)'" />
+    </ItemGroup>
+  </Target>
+
+  <!-- Update the local targeting pack's version as it's written into the runtimeconfig.json file to select the shared framework. -->
+  <Target Name="UpdateRuntimeFrameworkVersion"
+          Condition="'$(_UseLocalTargetingRuntimePack)' == 'true'"
+          AfterTargets="ResolveTargetingPackAssets">
+    <ItemGroup>
+      <RuntimeFramework Version="$(ProductVersion)"
+                        Condition="'%(RuntimeFramework.FrameworkName)' == '$(SharedFrameworkName)'" />
+    </ItemGroup>
+  </Target>
+  
+  <!-- Filter out conflicting implicit assembly references. -->
+  <Target Name="FilterImplicitAssemblyReferences"
+          Condition="'$(DisableImplicitAssemblyReferences)' != 'true'"
+          DependsOnTargets="ResolveProjectReferences"
+          AfterTargets="ResolveTargetingPackAssets">
+    <ItemGroup>
+      <_targetingPackReferenceExclusion Include="$(TargetName)" />
+      <_targetingPackReferenceExclusion Include="@(_ResolvedProjectReferencePaths->'%(Filename)')" />
+      <_targetingPackReferenceExclusion Include="@(DefaultReferenceExclusion)" />
+    </ItemGroup>
+
+    <ItemGroup>
+      <_targetingPackReferenceWithExclusion Include="@(Reference)">
+        <Exclusion>%(_targetingPackReferenceExclusion.Identity)</Exclusion>
+      </_targetingPackReferenceWithExclusion>
+      <Reference Remove="@(_targetingPackReferenceWithExclusion)"
+                 Condition="'%(_targetingPackReferenceWithExclusion.ExternallyResolved)' == 'true' and '%(_targetingPackReferenceWithExclusion.Filename)' == '%(_targetingPackReferenceWithExclusion.Exclusion)'" />
+    </ItemGroup>
+  </Target>
+</Project>
\ No newline at end of file
diff --git a/eng/testing/.runsettings b/eng/testing/.runsettings
index fabc0310a7aa51..cf00c4a467379f 100644
--- a/eng/testing/.runsettings
+++ b/eng/testing/.runsettings
@@ -18,10 +18,6 @@
     <!-- Filter out failing (wrong framwork, platform, runtime or activeissue) tests -->
     <TestCaseFilter>$$TESTCASEFILTER$$</TestCaseFilter>
     <DotNetHostPath>$$DOTNETHOSTPATH$$</DotNetHostPath>
-    <EnvironmentVariables>
-      <!-- Use our self-built framework on .NET Framework -->
-      <DEVPATH>$$DEVPATH$$</DEVPATH>
-    </EnvironmentVariables>
   </RunConfiguration>
   <LoggerRunSettings>
     <Loggers>
diff --git a/eng/testing/RunnerTemplate.cmd b/eng/testing/RunnerTemplate.cmd
index fe28e9157a6e2b..10737eabe70950 100644
--- a/eng/testing/RunnerTemplate.cmd
+++ b/eng/testing/RunnerTemplate.cmd
@@ -41,12 +41,6 @@ set EXECUTION_DIR=%~dp0
 
 :argparser_end
 
-if not defined RUNTIME_PATH (
-  echo error: -r^|--runtime-path argument is required.
-  call :usage
-  exit /b -1
-)
-
 :: Don't use a globally installed SDK.
 set DOTNET_MULTILEVEL_LOOKUP=0
 
diff --git a/eng/testing/linker/SupportFiles/Directory.Build.targets b/eng/testing/linker/SupportFiles/Directory.Build.targets
index 49422a33b9be30..a9dfda8012d9fa 100644
--- a/eng/testing/linker/SupportFiles/Directory.Build.targets
+++ b/eng/testing/linker/SupportFiles/Directory.Build.targets
@@ -20,11 +20,14 @@
   </Target>
 
   <Target Name="EnsureAllAssembliesAreLinked"
-          AfterTargets="PrepareForILLink"> 
+          BeforeTargets="PrepareForILLink"> 
     <ItemGroup>
       <ManagedAssemblyToLink>
         <TrimMode>link</TrimMode>
       </ManagedAssemblyToLink>
+
+      <!-- Pass the app assembly as a root -->
+      <TrimmerRootAssembly Include="@(IntermediateAssembly)" />
     </ItemGroup>
   </Target>
 
diff --git a/eng/testing/linker/project.csproj.template b/eng/testing/linker/project.csproj.template
index ef63096e8019c0..2f1f26c2fd875e 100644
--- a/eng/testing/linker/project.csproj.template
+++ b/eng/testing/linker/project.csproj.template
@@ -6,9 +6,17 @@
     <RuntimeIdentifier>{RuntimeIdentifier}</RuntimeIdentifier>
     <RuntimePackDir>{RuntimePackDir}</RuntimePackDir>
     <TargetingPackDir>{TargetingPackDir}</TargetingPackDir>
-    <_ExtraTrimmerArgs>{ExtraTrimmerArgs} $(_ExtraTrimmerArgs)</_ExtraTrimmerArgs>
+
+    <LinkerNoWarn>IL2006;IL2026</LinkerNoWarn>
+    <!-- https://github.com/dotnet/runtime/issues/40336 - need to suppress IL2008;IL2009;IL2037 on non-Windows -->
+    <LinkerNoWarn Condition="!$(RuntimeIdentifier.StartsWith('win'))">$(LinkerNoWarn);IL2008;IL2009;IL2037</LinkerNoWarn>
+    <_ExtraTrimmerArgs>{ExtraTrimmerArgs} $(_ExtraTrimmerArgs) --nowarn $(LinkerNoWarn)</_ExtraTrimmerArgs>
   </PropertyGroup>
 
+  <ItemGroup>
+    {AdditionalProjectReferences}
+  </ItemGroup>
+
   <!-- Logic to override the default IlLink tasks that come from the SDK and use the one
   we use in dotnet/runtime repo -->
 
@@ -28,4 +36,4 @@
                       GeneratePathProperty="true" />
   </ItemGroup>
 
-</Project>
\ No newline at end of file
+</Project>
diff --git a/eng/testing/linker/trimmingTests.targets b/eng/testing/linker/trimmingTests.targets
index 3729bd306bca94..6d89002d9e0c6a 100644
--- a/eng/testing/linker/trimmingTests.targets
+++ b/eng/testing/linker/trimmingTests.targets
@@ -57,6 +57,15 @@
       <_projectSourceFile>%(TestConsoleApps.ProjectCompileItems)</_projectSourceFile>
     </PropertyGroup>
 
+    <ItemGroup Condition="'$(AdditionalProjectReferences)' != ''">
+      <_additionalProjectReferenceTemp Include="$(AdditionalProjectReferences)" />
+      <_additionalProjectReference Include="&lt;ProjectReference Include=&quot;$(LibrariesProjectRoot)%(_additionalProjectReferenceTemp.Identity)\src\%(_additionalProjectReferenceTemp.Identity).csproj&quot; SkipUseReferenceAssembly=&quot;true&quot; /&gt;" />
+    </ItemGroup>
+    
+    <PropertyGroup>
+      <_additionalProjectReferencesString>@(_additionalProjectReference, '%0a')</_additionalProjectReferencesString>
+    </PropertyGroup>
+
     <ItemGroup>
       <_additionalProjectSourceFiles Include="%(TestConsoleApps.AdditionalSourceFiles)" />
     </ItemGroup>
@@ -69,7 +78,8 @@
                                                  .Replace('{TargetingPackDir}','$(MicrosoftNetCoreAppRefPackDir)')
                                                  .Replace('{RuntimeIdentifier}','%(TestConsoleApps.TestRuntimeIdentifier)')
                                                  .Replace('{MicrosoftNETILLinkTasksVersion}', '$(MicrosoftNETILLinkTasksVersion)')
-                                                 .Replace('{ExtraTrimmerArgs}', '%(TestConsoleApps.ExtraTrimmerArgs)'))"
+                                                 .Replace('{ExtraTrimmerArgs}', '%(TestConsoleApps.ExtraTrimmerArgs)')
+                                                 .Replace('{AdditionalProjectReferences}', '$(_additionalProjectReferencesString)'))"
                       Overwrite="true" />
     <Copy SourceFiles="$(_projectSourceFile)"
           DestinationFolder="$(_projectDir)" />
diff --git a/eng/testing/netfx.exe.config b/eng/testing/netfx.exe.config
index ed7d7d082438c8..e131497fc76118 100644
--- a/eng/testing/netfx.exe.config
+++ b/eng/testing/netfx.exe.config
@@ -1,7 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
   <runtime>
-    <developmentMode developerInstallation="true" />
     <UseRandomizedStringHashAlgorithm enabled="1" />
   </runtime>
 </configuration>
\ No newline at end of file
diff --git a/eng/testing/outerBuild.targets b/eng/testing/outerBuild.targets
index 4623b0e54d2504..c071944c21d93d 100644
--- a/eng/testing/outerBuild.targets
+++ b/eng/testing/outerBuild.targets
@@ -1,8 +1,12 @@
 <Project>
   <Target Name="Test" DependsOnTargets="GetProjectWithBestTargetFrameworks">    
     <MSBuild Projects="@(InnerBuildProjectsWithBestTargetFramework)"
-             Targets="Test"
-             BuildInParallel="$(BuildInParallel)">
+             Targets="Test">
+    </MSBuild>
+  </Target>
+  <Target Name="VSTest" DependsOnTargets="GetProjectWithBestTargetFrameworks">    
+    <MSBuild Projects="@(InnerBuildProjectsWithBestTargetFramework)"
+             Targets="VSTest">
     </MSBuild>
   </Target>
 </Project>
\ No newline at end of file
diff --git a/eng/testing/runsettings.targets b/eng/testing/runsettings.targets
index 10496127b8a90a..5a2c9a84d6893d 100644
--- a/eng/testing/runsettings.targets
+++ b/eng/testing/runsettings.targets
@@ -36,7 +36,6 @@
                                                       .Replace('$$DISABLEPARALLELIZATION$$', '$([MSBuild]::ValueOrDefault('$(TestDisableParallelization)', 'false'))')
                                                       .Replace('$$DISABLEAPPDOMAIN$$', '$([MSBuild]::ValueOrDefault('$(TestDisableAppDomain)', 'false'))')
                                                       .Replace('$$TESTCASEFILTER$$', '$(_testFilter)')
-                                                      .Replace('$$DEVPATH$$', '$(TestHostRootPath)')
                                                       .Replace('$$DOTNETHOSTPATH$$', '$(TestHostRootPath)$([System.IO.Path]::GetFileName('$(DotNetTool)'))'))</RunSettingsFileContent>
     </PropertyGroup>
 
diff --git a/eng/testing/runtimeConfiguration.targets b/eng/testing/runtimeConfiguration.targets
index f687adfad40f97..d69182992c7b30 100644
--- a/eng/testing/runtimeConfiguration.targets
+++ b/eng/testing/runtimeConfiguration.targets
@@ -1,45 +1,31 @@
 <Project> 
   <PropertyGroup>
-    <!-- Copies the app.config file to the OutDir. -->
-    <TestRuntimeConfigurationFile Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'">$(MSBuildThisFileDirectory)netfx.exe.config</TestRuntimeConfigurationFile>
-
     <!-- By default copy the test runtime config file for executable test projects (+ test support projects). -->
-    <GenerateRuntimeConfigurationFiles Condition="'$(IsTestProject)' == 'true' or '$(OutputType.ToLower())' == 'exe'">true</GenerateRuntimeConfigurationFiles>
+    <IsTestProjectOrExecutable Condition="'$(IsTestProject)' == 'true' or
+                                          '$(OutputType.ToLower())' == 'exe'">true</IsTestProjectOrExecutable>
+    <GenerateRuntimeConfigurationFiles Condition="'$(GenerateRuntimeConfigurationFiles)' == '' and
+                                                  '$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                                                  '$(IsTestProjectOrExecutable)' == 'true'">true</GenerateRuntimeConfigurationFiles>
+    <GenerateAppConfigurationFile Condition="'$(IsTestProjectOrExecutable)' == 'true' and
+                                             '$(TargetFrameworkIdentifier)' == '.NETFramework'">true</GenerateAppConfigurationFile>
+    <AppConfig Condition="'$(GenerateAppConfigurationFile)' == 'true'">$(MSBuildThisFileDirectory)netfx.exe.config</AppConfig>
+    <!-- TODO: Change in RemoteExecutor -->
+    <RemoteClientAppConfigFile Condition="'$(GenerateAppConfigurationFile)' == 'true'">$(TargetPath).config</RemoteClientAppConfigFile>
   </PropertyGroup>
 
-  <ItemGroup Condition="'$(GenerateRuntimeConfigurationFiles)' == 'true'">
-    <None Include="$(TestRuntimeConfigurationFile)"
-          Condition="Exists('$(TestRuntimeConfigurationFile)')"
-          Link="$(TargetName).exe.config"
-          CopyToOutputDirectory="PreserveNewest"
-          Visible="false" />
+  <ItemGroup Condition="'$(IsTestProjectOrExecutable)' == 'true'">
     <!--
       Include deps.json and runtimeconfig.json in ContentWithTargetPath so they will
       be copied to the output folder of projects that reference this one.
       Tracking issue: https://github.com/dotnet/sdk/issues/1675
     -->
     <ContentWithTargetPath Include="$(ProjectDepsFilePath)"
-                           Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' and '$(GenerateDependencyFile)' == 'true'"
+                           Condition="'$(GenerateDependencyFile)' == 'true'"
                            CopyToOutputDirectory="PreserveNewest"
                            TargetPath="$(ProjectDepsFileName)" />
     <ContentWithTargetPath Include="$(ProjectRuntimeConfigFilePath)"
-                           Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'"
+                           Condition="'$(GenerateRuntimeConfigurationFiles)' == 'true'"
                            CopyToOutputDirectory="PreserveNewest"
                            TargetPath="$(ProjectRuntimeConfigFileName)" />
   </ItemGroup>
-
-    <!--
-    We disabled implicit framework references but still want to be treated as framework dependent:
-    1. To have runtimeTargets in the deps file.
-    2. To populate the framework node in the runtimeconfig's runtimeOptions 
-    To do this we manually set the RuntimeFramework.
-    At that point restore and conflict resolution already happened therefore setting the item here has no side effects.
-   -->
-  <Target Name="_SetRuntimeFrameworksForTestAssemblies"
-          Condition="'$(SelfContained)' != 'true' and '$(MSBuildProjectExtension)' != '.depproj'"
-          BeforeTargets="GenerateBuildDependencyFile">
-    <ItemGroup>
-      <RuntimeFramework Include="Microsoft.NETCore.App" Version="$(ProductVersion)" />
-    </ItemGroup>
-  </Target>
 </Project>
\ No newline at end of file
diff --git a/eng/testing/tests.mobile.targets b/eng/testing/tests.mobile.targets
index 266a6d37be6518..84b8337494a465 100644
--- a/eng/testing/tests.mobile.targets
+++ b/eng/testing/tests.mobile.targets
@@ -14,7 +14,7 @@
 
   <PropertyGroup Condition="'$(TargetOS)' == 'Browser'">
     <!-- We need to set this in order to get extensibility on xunit category traits and other arguments we pass down to xunit via MSBuild properties -->
-    <RunScriptCommand>$HARNESS_RUNNER wasm test --engine=$(JSEngine) $(JSEngineArgs) --js-file=runtime.js -v --output-directory=$XHARNESS_OUT -- --enable-zoneinfo --run WasmTestRunner.dll $(AssemblyName).dll</RunScriptCommand>
+    <RunScriptCommand>$HARNESS_RUNNER wasm test --engine=$(JSEngine) $(JSEngineArgs) --js-file=runtime.js -v --output-directory=$XHARNESS_OUT -- --run WasmTestRunner.dll $(AssemblyName).dll</RunScriptCommand>
   </PropertyGroup>
 
   <!-- Generate a self-contained app bundle for Android with tests. -->
@@ -132,30 +132,23 @@
       <WasmFilesToIncludeInFileSystem Include="@(ContentWithTargetPath)" />
       <WasmFilesToIncludeInFileSystem Include="@(ReferenceCopyLocalPaths)" Condition="'%(ReferenceCopyLocalPaths.BuildReference)' == 'true' and !$([System.String]::new('%(ReferenceCopyLocalPaths.Identity)').EndsWith('.resources.dll'))" />
       <WasmFilesToIncludeInFileSystem Include="@(WasmSatelliteAssemblies)" TargetPath="%(WasmSatelliteAssemblies.CultureName)\%(WasmSatelliteAssemblies.Filename)%(WasmSatelliteAssemblies.Extension)" />
+      <!-- Include files specified by test projects from publish dir -->
+      <WasmFilesToIncludeInFileSystem Include="@(WasmFilesToIncludeFromPublishDir -> '$(PublishDir)%(Identity)')" />
       <ExtraAssemblies Include="$(PublishDir)$(AssemblyName).dll" />
-      <!-- we need to preserve these facades for BinaryFormatter tests -->
+      <!-- We need these facades for some tests. -->
       <ExtraAssemblies Include="$(PublishDir)mscorlib.dll" />
-      <ExtraAssemblies Include="$(PublishDir)System.dll" />
-      <ExtraAssemblies Include="$(PublishDir)System.ComponentModel.DataAnnotations.dll" />
-      <ExtraAssemblies Include="$(PublishDir)System.Configuration.dll" />
-      <ExtraAssemblies Include="$(PublishDir)System.Core.dll" />
-      <ExtraAssemblies Include="$(PublishDir)System.Data.dll" />
       <ExtraAssemblies Include="$(PublishDir)System.Drawing.dll" />
-      <ExtraAssemblies Include="$(PublishDir)System.Numerics.dll" />
-      <ExtraAssemblies Include="$(PublishDir)System.Runtime.Serialization.dll" />
-      <ExtraAssemblies Include="$(PublishDir)System.Transactions.dll" />
-      <ExtraAssemblies Include="$(PublishDir)System.Xml.dll" />
-      <ExtraAssemblies Include="$(PublishDir)WindowsBase.dll" />
     </ItemGroup>
     <Error Condition="!Exists('$(MicrosoftNetCoreAppRuntimePackRidDir)')" Text="MicrosoftNetCoreAppRuntimePackRidDir=$(MicrosoftNetCoreAppRuntimePackRidDir) doesn't exist" />
     <WasmAppBuilder
       AppDir="$(BundleDir)"
+      InvariantGlobalization="$(InvariantGlobalization)"
       MicrosoftNetCoreAppRuntimePackDir="$(MicrosoftNetCoreAppRuntimePackRidDir)"
       MainAssembly="$(PublishDir)WasmTestRunner.dll"
       MainJS="$(MonoProjectRoot)\wasm\runtime-test.js"
       ExtraAssemblies="@(ExtraAssemblies)"
       FilesToIncludeInFileSystem="@(WasmFilesToIncludeInFileSystem)"
-      AssemblySearchPaths="@(AssemblySearchPaths)"/>
+      AssemblySearchPaths="@(AssemblySearchPaths)" />
   </Target>
 
   <Target Name="AddTestRunnersToPublishedFiles"
@@ -170,21 +163,8 @@
     </ItemGroup>
   </Target>
 
-  <Target Name="AddFrameworkReference">
-    <ItemGroup>
-      <FrameworkReference Include="$(SharedFrameworkName)" />
-    </ItemGroup>
-  </Target>
-
-  <Target Name="UpdateRuntimePack"
-          DependsOnTargets="AddFrameworkReference;ResolveFrameworkReferences">
-    <ItemGroup>
-      <ResolvedRuntimePack Update="@(ResolvedRuntimePack)" PackageDirectory="$(MicrosoftNetCoreAppRuntimePackDir)" />
-    </ItemGroup>
-  </Target>
-
   <Target Name="PublishTestAsSelfContained"
           Condition="'$(IsCrossTargetingBuild)' != 'true'"
           AfterTargets="Build"
-          DependsOnTargets="UpdateRuntimePack;Publish;BundleTestAppleApp;BundleTestAndroidApp;BundleTestWasmApp;ArchiveTests" />
+          DependsOnTargets="Publish;BundleTestAppleApp;BundleTestAndroidApp;BundleTestWasmApp;ArchiveTests" />
 </Project>
diff --git a/eng/testing/tests.props b/eng/testing/tests.props
index bf2f93fcceb39b..65664f7f74992b 100644
--- a/eng/testing/tests.props
+++ b/eng/testing/tests.props
@@ -29,8 +29,6 @@
 
     <RuntimeIdentifier>$(PackageRID)</RuntimeIdentifier>
     <SelfContained>true</SelfContained>
-    <EnableTargetingPackDownload>false</EnableTargetingPackDownload>
-    <PlatformManifestFile />
   </PropertyGroup>
 
   <!-- Provide runtime options to Mono (interpreter, aot, debugging, etc) -->
diff --git a/eng/testing/tests.targets b/eng/testing/tests.targets
index 1534c3aa0dadd9..2fe669a10ba05a 100644
--- a/eng/testing/tests.targets
+++ b/eng/testing/tests.targets
@@ -19,11 +19,6 @@
     <RunScriptHost Condition="'$(TargetOS)' != 'Windows_NT'">$(RunScriptHostDir)dotnet</RunScriptHost>
   </PropertyGroup>
 
-  <!-- Set env variable to use the local netfx assemblies instead of the ones in the GAC. -->
-  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'">
-    <RunScriptCommands Include="set DEVPATH=%RUNTIME_PATH%" />
-  </ItemGroup>
-
   <PropertyGroup>
     <ArchiveTestsAfterTargets>PrepareForRun</ArchiveTestsAfterTargets>
 
@@ -41,7 +36,6 @@
     <Error Condition="'$(TestArchiveTestsDir)' == ''" Text="TestArchiveTestsDir property to archive the test folder must be set." />
 
     <PropertyGroup>
-      <BundleDir>$([MSBuild]::NormalizeDirectory('$(OutDir)', 'AppBundle'))</BundleDir>
       <_ZipSourceDirectory>$(OutDir)</_ZipSourceDirectory>
       <_ZipSourceDirectory Condition="'$(TargetOS)' == 'Browser'">$(BundleDir)</_ZipSourceDirectory>
     </PropertyGroup>
@@ -50,6 +44,8 @@
     <ZipDirectory SourceDirectory="$(_ZipSourceDirectory)"
                   DestinationFile="$([MSBuild]::NormalizePath('$(TestArchiveTestsDir)', '$(TestProjectName).zip'))"
                   Overwrite="true" />
+    <!-- delete the BundleDir and PublishDir in CI builds to save disk space on build agents since they're no longer needed -->
+    <RemoveDir Condition="'$(ContinuousIntegrationBuild)' == 'true'" Directories="$(BundleDir);$(PublishDir)" />
   </Target>
 
   <UsingTask TaskName="GenerateRunScript" AssemblyFile="$(InstallerTasksAssemblyPath)"/>
@@ -95,7 +91,10 @@
 
   <Target Name="RunTests">
     <PropertyGroup>
-      <RunTestsCommand>"$(RunScriptOutputPath)" --runtime-path "$(TestHostRootPath.TrimEnd('\/'))"</RunTestsCommand>
+      <RunTestsCommand>"$(RunScriptOutputPath)"</RunTestsCommand>
+      <!-- Use runtime path only for the live built shared framework (NetCoreAppCurrent). -->
+      <RunTestsCommand Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                                  $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '$(NETCoreAppCurrentVersion)'))">$(RunTestsCommand) --runtime-path "$(TestHostRootPath.TrimEnd('\/'))"</RunTestsCommand>
       <RunTestsCommand Condition="'$(TestRspFile)' != '' and '$(RuntimeFlavor)' != 'Mono'">$(RunTestsCommand) --rsp-file "$(TestRspFile)"</RunTestsCommand>
       <RunTestsCommand Condition="'$(TargetsMobile)' == 'true'">"$(RunScriptOutputPath)" $(AssemblyName) $(TargetArchitecture)</RunTestsCommand>
       <RunTestsCommand Condition="'$(TargetOS)' == 'Browser'">"$(RunScriptOutputPath)" $(JSEngine) $(AssemblyName).dll $(_withoutCategories.Replace(';', ' -notrait category='))</RunTestsCommand>
diff --git a/eng/testing/xunit/xunit.console.targets b/eng/testing/xunit/xunit.console.targets
index 837b432a99eb7d..5b71327e96450b 100644
--- a/eng/testing/xunit/xunit.console.targets
+++ b/eng/testing/xunit/xunit.console.targets
@@ -37,24 +37,23 @@
                       Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'" />
     <PackageReference Include="xunit.runner.console"
                       Version="$(XUnitVersion)"
+                      GeneratePathProperty="true"
                       Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'" />
   </ItemGroup>
 
   <!-- Overwrite the runner config file with the app local one. -->
   <Target Name="OverwriteDesktopTestRunnerConfigs"
-          Condition="'$(GenerateRuntimeConfigurationFiles)' == 'true' and '$(TargetFrameworkIdentifier)' == '.NETFramework'"
+          Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework' and 
+                     '$(GenerateAppConfigurationFile)' == 'true' and
+                     '@(AppConfigWithTargetPath)' != ''"
           AfterTargets="CopyFilesToOutputDirectory">
-
     <ItemGroup>
-      <_testRunnerConfigSourceFile Include="$(TargetDir)$(TargetName).exe.config" />
       <_testRunnerConfigDestFile Include="$(TargetDir)xunit.console.exe.config" />
     </ItemGroup>
 
-    <Copy SourceFiles="@(_testRunnerConfigSourceFile)"
-          Condition="'@(_testRunnerConfigSourceFile)' != ''"
+    <Copy SourceFiles="@(AppConfigWithTargetPath)"
           DestinationFiles="@(_testRunnerConfigDestFile)"
           SkipUnchangedFiles="true" />
-
   </Target>
 
   <!-- ResolveAssemblyReferences is the target that populates ReferenceCopyLocalPaths which is what is copied to output directory. -->
@@ -62,7 +61,9 @@
     <ItemGroup>
       <!-- Copy test runner to output directory -->
       <None Include="$([System.IO.Path]::GetDirectoryName('$(XunitConsole472Path)'))\*"
-            Exclude="$([System.IO.Path]::GetDirectoryName('$(XunitConsole472Path)'))\xunit.console.*exe.config;$([System.IO.Path]::GetDirectoryName('$(XunitConsole472Path)'))\xunit.console.x86.exe"
+            Exclude="$([System.IO.Path]::GetDirectoryName('$(XunitConsole472Path)'))\xunit.console.*exe.config;
+                     $([System.IO.Path]::GetDirectoryName('$(XunitConsole472Path)'))\xunit.console.x86.exe;
+                     $([System.IO.Path]::GetDirectoryName('$(XunitConsole472Path)'))\xunit.abstractions.dll"
             Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework' and '$(XunitConsole472Path)' != ''"
             CopyToOutputDirectory="PreserveNewest"
             Visible="false" />
@@ -74,5 +75,13 @@
             CopyToOutputDirectory="PreserveNewest"
             Visible="false" />
     </ItemGroup>
+
+    <!-- Workaround for https://github.com/xunit/xunit/issues/1651 -->
+    <ItemGroup Condition="'$(ArchiveTests)' != 'true'">
+      <None Remove="$(Pkgxunit_runner_visualstudio)\build\net452\xunit.runner.utility.net452.dll" />
+      <None Remove="$(Pkgxunit_runner_visualstudio)\build\net452\xunit.runner.reporters.net452.dll" />
+      <None Remove="$(Pkgxunit_runner_visualstudio)\build\netcoreapp2.1\xunit.runner.utility.netcoreapp10.dll" />
+      <None Remove="$(Pkgxunit_runner_visualstudio)\build\netcoreapp2.1\xunit.runner.reporters.netcoreapp10.dll" />
+    </ItemGroup>
   </Target>
 </Project>
diff --git a/eng/testing/xunit/xunit.props b/eng/testing/xunit/xunit.props
index 8b21cecac618e3..69355a452a48ee 100644
--- a/eng/testing/xunit/xunit.props
+++ b/eng/testing/xunit/xunit.props
@@ -16,7 +16,7 @@
   <ItemGroup Condition="'$(ArchiveTests)' != 'true'">
     <!-- Microsoft.Net.Test.Sdk brings a lot of assemblies with it. To reduce helix payload submission size we disable it on CI. -->
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="$(MicrosoftNETTestSdkVersion)" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="$(XUnitRunnerVisualStudioVersion)" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="$(XUnitRunnerVisualStudioVersion)" GeneratePathProperty="true" />
     <!--
       Microsoft.Net.Test.Sdk has a dependency on Newtonsoft.Json v9.0.1. We upgrade the dependency version
       with the one used in libraries to have a consistent set of dependency versions. Additionally this works
diff --git a/eng/testing/xunit/xunit.targets b/eng/testing/xunit/xunit.targets
index b14d3b7cbf227c..feb429aab6bf4d 100644
--- a/eng/testing/xunit/xunit.targets
+++ b/eng/testing/xunit/xunit.targets
@@ -1,4 +1,11 @@
 <Project>
+  <ItemGroup>
+    <!-- Upgrade the NETStandard.Library transitive xunit dependency to avoid transitive 1.x NS dependencies. -->
+    <PackageReference Include="NETStandard.Library"
+                      Version="$(NetStandardLibrary20Version)"
+                      Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'" />
+  </ItemGroup>
+
   <!-- Run target (F5) support. -->
   <PropertyGroup>
     <RunWorkingDirectory>$(OutDir)</RunWorkingDirectory>
diff --git a/eng/versioning.targets b/eng/versioning.targets
index 1eba158bb6beae..2a2f10dbcafb90 100644
--- a/eng/versioning.targets
+++ b/eng/versioning.targets
@@ -22,10 +22,17 @@
     </AssemblyMetadata>
   </ItemGroup>
 
-  <!-- Adds MinimumOSPlatform attribute for Windows Specific libraries -->
+  <!-- Adds SupportedOSPlatform attribute for Windows Specific libraries -->
   <ItemGroup Condition="'$(IsWindowsSpecific)' == 'true' and '$(IsTestProject)' != 'true'">
-    <AssemblyAttribute Include="System.Runtime.Versioning.MinimumOSPlatform">
-        <_Parameter1>$(MinimiumSupportedWindowsPlatform)</_Parameter1>
+    <AssemblyAttribute Include="System.Runtime.Versioning.SupportedOSPlatform">
+        <_Parameter1>windows</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
+
+  <!-- Adds UnsupportedOSPlatform attribute for requested libraries -->
+  <ItemGroup Condition="'$(UnsupportedOSPlatform)' != '' and '$(IsTestProject)' != 'true'">
+    <AssemblyAttribute Include="System.Runtime.Versioning.UnsupportedOSPlatform">
+        <_Parameter1>$(UnsupportedOSPlatform)</_Parameter1>
     </AssemblyAttribute>
   </ItemGroup>
 
diff --git a/global.json b/global.json
index 64916dd7429cba..5d4b27ae61c0c7 100644
--- a/global.json
+++ b/global.json
@@ -12,10 +12,10 @@
     "python3": "3.7.1"
   },
   "msbuild-sdks": {
-    "Microsoft.DotNet.Build.Tasks.TargetFramework.Sdk": "5.0.0-beta.20364.3",
-    "Microsoft.DotNet.Arcade.Sdk": "5.0.0-beta.20364.3",
-    "Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk": "5.0.0-beta.20364.3",
-    "Microsoft.DotNet.Helix.Sdk": "5.0.0-beta.20364.3",
+    "Microsoft.DotNet.Build.Tasks.TargetFramework.Sdk": "5.0.0-beta.20374.1",
+    "Microsoft.DotNet.Arcade.Sdk": "5.0.0-beta.20374.1",
+    "Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk": "5.0.0-beta.20374.1",
+    "Microsoft.DotNet.Helix.Sdk": "5.0.0-beta.20374.1",
     "Microsoft.FIX-85B6-MERGE-9C38-CONFLICT": "1.0.0",
     "Microsoft.NET.Sdk.IL": "5.0.0-preview.8.20359.4",
     "Microsoft.Build.NoTargets": "1.0.53",
diff --git a/src/coreclr/CMakeLists.txt b/src/coreclr/CMakeLists.txt
index 0d60cf16fc1066..b94eb54a671540 100644
--- a/src/coreclr/CMakeLists.txt
+++ b/src/coreclr/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.14.5)
+cmake_minimum_required(VERSION 3.6.2)
 
 cmake_policy(SET CMP0042 NEW)
 
diff --git a/src/coreclr/build-test.cmd b/src/coreclr/build-test.cmd
index 62fe83149b50e5..d0d1a333196792 100644
--- a/src/coreclr/build-test.cmd
+++ b/src/coreclr/build-test.cmd
@@ -653,17 +653,14 @@ if defined __CompositeBuildMode (
 )
 
 for %%F in ("%CORE_ROOT%\System.*.dll";"%CORE_ROOT%\Microsoft.*.dll";%CORE_ROOT%\netstandard.dll;%CORE_ROOT%\mscorlib.dll) do (
-    if not "%%~nxF"=="Microsoft.CodeAnalysis.VisualBasic.dll" (
-    if not "%%~nxF"=="Microsoft.CodeAnalysis.CSharp.dll" (
-    if not "%%~nxF"=="Microsoft.CodeAnalysis.dll" (
     if not "%%~nxF"=="System.Runtime.WindowsRuntime.dll" (
         if defined __CompositeBuildMode (
             echo %%F>>!__CompositeResponseFile!
         ) else (
-            call :PrecompileAssembly "%%F" %%~nxF __TotalPrecompiled __FailedToPrecompile __FailedAssemblies
+            call :PrecompileAssembly %%F %%~nxF __TotalPrecompiled __FailedToPrecompile __FailedAssemblies
             echo Processed: !__TotalPrecompiled!, failed !__FailedToPrecompile!
         )
-    )))))
+    ))
 )
 
 if defined __CompositeBuildMode (
@@ -695,19 +692,33 @@ set AssemblyName=%2
 
 REM Intentionally avoid using the .dll extension to prevent
 REM subsequent compilations from picking it up as a reference
-set __CrossgenOutputFile="%CORE_ROOT%\temp.ni._dll"
+set __CrossgenOutputFile=%CORE_ROOT%\temp.ni._dll
+set __CrossgenResponseFile="%CORE_ROOT%\%AssemblyName%.rsp
 set __CrossgenCmd=
 
+del /Q %__CrossgenResponseFile%
+
 if defined __DoCrossgen (
-    set __CrossgenCmd=!__CrossgenExe! /Platform_Assemblies_Paths "!CORE_ROOT!" /in !AssemblyPath! /out !__CrossgenOutputFile!
-    echo !__CrossgenCmd!
-    !__CrossgenCmd!
+    set __CrossgenCmd=!__CrossgenExe! @!__CrossgenResponseFile!
+    echo /Platform_Assemblies_Paths "!CORE_ROOT!">>!__CrossgenResponseFile!
+    echo /in !AssemblyPath!>>!__CrossgenResponseFile!
+    echo /out !__CrossgenOutputFile!>>!__CrossgenResponseFile!
 ) else (
-    set __CrossgenCmd=!__Crossgen2Dll! -r:"!CORE_ROOT!\System.*.dll" -r:"!CORE_ROOT!\Microsoft.*.dll" -r:"!CORE_ROOT!\mscorlib.dll" -r:"!CORE_ROOT!\netstandard.dll" -O --inputbubble --out:!__CrossgenOutputFile! !AssemblyPath! --targetarch %__BuildArch%
-    echo !__CrossgenCmd!
-    call !__CrossgenCmd!
+    set __CrossgenCmd=!__Crossgen2Dll! @!__CrossgenResponseFile!
+    echo -r:!CORE_ROOT!\System.*.dll>>!__CrossgenResponseFile!
+    echo -r:!CORE_ROOT!\Microsoft.*.dll>>!__CrossgenResponseFile!
+    echo -r:!CORE_ROOT!\mscorlib.dll>>!__CrossgenResponseFile!
+    echo -r:!CORE_ROOT!\netstandard.dll>>!__CrossgenResponseFile!
+    echo -O>>!__CrossgenResponseFile!
+    echo --inputbubble>>!__CrossgenResponseFile!
+    echo --out:!__CrossgenOutputFile!>>!__CrossgenResponseFile!
+    echo !AssemblyPath!>>!__CrossgenResponseFile!
+    echo --targetarch:!__BuildArch!>>!__CrossgenResponseFile!
 )
 
+echo !__CrossgenCmd!
+call !__CrossgenCmd!
+
 set /a __exitCode = !errorlevel!
 
 set /a "%~3+=1"
diff --git a/src/coreclr/build-test.sh b/src/coreclr/build-test.sh
index f1a26c565e3b02..b67fbef45f92ad 100755
--- a/src/coreclr/build-test.sh
+++ b/src/coreclr/build-test.sh
@@ -131,7 +131,6 @@ generate_layout()
     mkdir -p "$CORE_ROOT"
 
     chmod +x "$__BinDir"/corerun
-    chmod +x "$__CrossgenExe"
 
     build_MSBuild_projects "Tests_Overlay_Managed" "${__ProjectDir}/tests/src/runtest.proj" "Creating test overlay" "/t:CreateTestOverlay"
 
@@ -149,6 +148,7 @@ generate_layout()
 
     # Precompile framework assemblies with crossgen if required
     if [[ "$__DoCrossgen" != 0 || "$__DoCrossgen2" != 0 ]]; then
+        chmod +x "$__CrossgenExe"
         if [[ "$__SkipCrossgenFramework" == 0 ]]; then
             precompile_coreroot_fx
         fi
@@ -168,35 +168,30 @@ precompile_coreroot_fx()
     local outputDir="$overlayDir"/out
 
     # Delete previously crossgened assemblies
-    rm "$overlayDir"/*.ni.dll
-
-    # Collect reference assemblies for Crossgen2
-    local crossgen2References=""
+    rm "$overlayDir"/*.ni.dll 2>/dev/null
 
     if [[ "$__DoCrossgen2" != 0 ]]; then
         compilerName=Crossgen2
 
         mkdir "$outputDir"
-
-        skipCrossGenFiles+=('Microsoft.CodeAnalysis.CSharp.dll')
-        skipCrossGenFiles+=('Microsoft.CodeAnalysis.dll')
-        skipCrossGenFiles+=('Microsoft.CodeAnalysis.VisualBasic.dll')
-
-        for reference in "$overlayDir"/*.dll; do
-            crossgen2References+=" -r:${reference}"
-        done
     fi
 
     echo "${__MsgPrefix}Running ${compilerName} on framework assemblies in CORE_ROOT: '${CORE_ROOT}'"
 
     local totalPrecompiled=0
     local failedToPrecompile=0
-    local compositeCommandLine="${__DotNetCli}"
-    compositeCommandLine+=" $__Crossgen2Dll"
-    compositeCommandLine+=" --composite"
-    compositeCommandLine+=" -O"
-    compositeCommandLine+=" --out:$outputDir/framework-r2r.dll"
-    compositeCommandLine+=" --targetarch ${__BuildArch}"
+    local compositeOutputFile=$outputDir/framework-r2r.dll
+    local compositeResponseFile=$compositeOutputFile.rsp
+    local compositeCommandLine="${__DotNetCli} $__Crossgen2Dll @$compositeResponseFile"
+
+    if [[ "$__CompositeBuildMode" != 0 ]]; then
+        rm $compositeResponseFile 2>/dev/null
+        echo --composite>>$compositeResponseFile
+        echo -O>>$compositeResponseFile
+        echo --out:$compositeOutputFile>>$compositeResponseFile
+        echo --targetarch:${__BuildArch}>>$compositeResponseFile
+    fi
+
     declare -a failedAssemblies
 
     filesToPrecompile=$(find -L "$overlayDir" -maxdepth 1 -iname Microsoft.\*.dll -o -iname System.\*.dll -o -iname netstandard.dll -o -iname mscorlib.dll -type f)
@@ -207,18 +202,32 @@ precompile_coreroot_fx()
         fi
 
         if [[ "$__CompositeBuildMode" != 0 ]]; then
-            compositeCommandLine+=" $filename"
+            echo $filename>>$compositeResponseFile
             continue
         fi
 
         local commandLine=""
+        local responseFile="$overlayDir/$(basename $filename).rsp"
+
+        rm $responseFile 2>/dev/null
 
         if [[ "$__DoCrossgen" != 0 ]]; then
-            commandLine="$__CrossgenExe /Platform_Assemblies_Paths $overlayDir $filename"
+            commandLine="$__CrossgenExe @$responseFile"
+            echo /Platform_Assemblies_Paths>>$responseFile
+            echo $overlayDir>>$responseFile
+            echo $filename>>$responseFile
         fi
 
         if [[ "$__DoCrossgen2" != 0 ]]; then
-            commandLine="${__DotNetCli} $__Crossgen2Dll $crossgen2References -O --inputbubble --out $outputDir/$(basename $filename) $filename --targetarch ${__BuildArch}"
+            commandLine="${__DotNetCli} $__Crossgen2Dll @$responseFile"
+            echo -O>>$responseFile
+            echo --inputbubble>>$responseFile
+            echo --out:$outputDir/$(basename $filename)>>$responseFile
+            echo --targetarch:${__BuildArch}>>$responseFile
+            echo $filename>>$responseFile
+            for reference in $overlayDir/*.dll; do
+                echo -r:$reference>>$responseFile
+            done
         fi
 
         echo Precompiling "$filename"
@@ -245,6 +254,8 @@ precompile_coreroot_fx()
 
     if [[ "$__CompositeBuildMode" != 0 ]]; then
         # Compile the entire framework in composite build mode
+        echo "Response file: $compositeResponseFile"
+        cat $compositeResponseFile
         echo "Compiling composite R2R framework: $compositeCommandLine"
         $compositeCommandLine
         local exitCode="$?"
diff --git a/src/coreclr/clr.featuredefines.props b/src/coreclr/clr.featuredefines.props
index b5979c8d239013..c5119c80424d23 100644
--- a/src/coreclr/clr.featuredefines.props
+++ b/src/coreclr/clr.featuredefines.props
@@ -66,9 +66,5 @@
 
         <DefineConstants Condition="'$(ProfilingSupportedBuild)' == 'true'">$(DefineConstants);PROFILING_SUPPORTED</DefineConstants>
         <DefineConstants Condition="'$(FeatureProfAttach)' == 'true'">$(DefineConstants);FEATURE_PROFAPI_ATTACH_DETACH</DefineConstants>
-
-        <DefineConstants Condition="'$(TargetsUnix)' == 'true'">$(DefineConstants);TARGET_UNIX</DefineConstants>
-        <DefineConstants Condition="'$(TargetsWindows)' == 'true'">$(DefineConstants);TARGET_WINDOWS</DefineConstants>
-        <DefineConstants Condition="'$(TargetsOSX)' == 'true'">$(DefineConstants);TARGET_OSX</DefineConstants>
     </PropertyGroup>
 </Project>
diff --git a/src/coreclr/clrdefinitions.cmake b/src/coreclr/clrdefinitions.cmake
index 7be0a6915051af..b717c10d840a40 100644
--- a/src/coreclr/clrdefinitions.cmake
+++ b/src/coreclr/clrdefinitions.cmake
@@ -30,7 +30,6 @@ if (CLR_CMAKE_TARGET_UNIX)
 
   if(CLR_CMAKE_TARGET_OSX)
     add_definitions(-D_XOPEN_SOURCE)
-    add_definitions(-DFEATURE_DATATARGET4)
   endif(CLR_CMAKE_TARGET_OSX)
 
   if (CLR_CMAKE_TARGET_ARCH_AMD64)
@@ -173,9 +172,9 @@ set(FEATURE_READYTORUN 1)
 
 add_compile_definitions($<$<NOT:$<BOOL:$<TARGET_PROPERTY:CROSSGEN_COMPONENT>>>:FEATURE_REJIT>)
 
-if (CLR_CMAKE_HOST_UNIX AND CLR_CMAKE_TARGET_UNIX AND NOT CLR_CMAKE_TARGET_OSX)
+if (CLR_CMAKE_HOST_UNIX AND CLR_CMAKE_TARGET_UNIX)
   add_definitions(-DFEATURE_REMOTE_PROC_MEM)
-endif (CLR_CMAKE_HOST_UNIX AND CLR_CMAKE_TARGET_UNIX AND NOT CLR_CMAKE_TARGET_OSX)
+endif (CLR_CMAKE_HOST_UNIX AND CLR_CMAKE_TARGET_UNIX)
 
 if (CLR_CMAKE_TARGET_UNIX OR CLR_CMAKE_TARGET_ARCH_ARM64)
     add_definitions(-DFEATURE_STUBS_AS_IL)
diff --git a/src/coreclr/pgosupport.cmake b/src/coreclr/pgosupport.cmake
index 4b11980901712d..04bde2bc20bca0 100644
--- a/src/coreclr/pgosupport.cmake
+++ b/src/coreclr/pgosupport.cmake
@@ -1,5 +1,18 @@
-include(CheckIPOSupported)
-check_ipo_supported(RESULT HAVE_LTO)
+include(CheckCXXSourceCompiles)
+include(CheckCXXCompilerFlag)
+
+# VC++ guarantees support for LTCG (LTO's equivalent)
+if(NOT WIN32)
+  # Function required to give CMAKE_REQUIRED_* local scope
+  function(check_have_lto)
+    set(CMAKE_REQUIRED_FLAGS -flto)
+    set(CMAKE_REQUIRED_LIBRARIES -flto -fuse-ld=gold)
+    check_cxx_source_compiles("int main() { return 0; }" HAVE_LTO)
+  endfunction(check_have_lto)
+  check_have_lto()
+
+  check_cxx_compiler_flag(-faligned-new COMPILER_SUPPORTS_F_ALIGNED_NEW)
+endif(NOT WIN32)
 
 # Adds Profile Guided Optimization (PGO) flags to the current target
 function(add_pgo TargetName)
diff --git a/src/coreclr/scripts/superpmi.py b/src/coreclr/scripts/superpmi.py
index fa0f3e2f165ded..12be260c67a91b 100755
--- a/src/coreclr/scripts/superpmi.py
+++ b/src/coreclr/scripts/superpmi.py
@@ -860,7 +860,8 @@ def replay(self):
             altjit_string = "*" if self.coreclr_args.altjit else ""
             altjit_flags = [
                 "-jitoption", "force", "AltJit=" + altjit_string,
-                "-jitoption", "force", "AltJitNgen=" + altjit_string
+                "-jitoption", "force", "AltJitNgen=" + altjit_string,
+                "-jitoption", "force", "EnableExtraSuperPmiQueries=0"
             ]
             flags += altjit_flags
 
@@ -1032,8 +1033,10 @@ def replay_with_asm_diffs(self):
                 altjit_flags = [
                     "-jitoption", "force", "AltJit=" + altjit_string,
                     "-jitoption", "force", "AltJitNgen=" + altjit_string,
+                    "-jitoption", "force", "EnableExtraSuperPmiQueries=0",
                     "-jit2option", "force", "AltJit=" + altjit_string,
-                    "-jit2option", "force", "AltJitNgen=" + altjit_string
+                    "-jit2option", "force", "AltJitNgen=" + altjit_string,
+                    "-jit2option", "force", "EnableExtraSuperPmiQueries=0"
                 ]
                 flags += altjit_flags
 
@@ -1208,7 +1211,8 @@ def replay_with_asm_diffs(self):
                 altjit_string = "*" if self.coreclr_args.altjit else ""
                 altjit_flags = [
                     "-jitoption", "force", "AltJit=" + altjit_string,
-                    "-jitoption", "force", "AltJitNgen=" + altjit_string
+                    "-jitoption", "force", "AltJitNgen=" + altjit_string,
+                    "-jitoption", "force", "EnableExtraSuperPmiQueries=0"
                 ]
 
                 async def create_asm(print_prefix, item, self, text_differences, base_asm_location, diff_asm_location):
@@ -2128,7 +2132,7 @@ def verify_superpmi_common_args():
             # yielding
             # [0]: ""
             # [1]: "\Windows_NT.x64.Checked"
-            standard_location_split = os.path.dirname(coreclr_args.jit_path).split(os.path.dirname(coreclr_args.product_location))
+            standard_location_split = os.path.dirname(coreclr_args.base_jit_path).split(os.path.dirname(coreclr_args.product_location))
             assert(coreclr_args.host_os in standard_location_split[1])
 
             # Get arch/flavor. Remove leading slash.
diff --git a/src/coreclr/src/.nuget/Directory.Build.props b/src/coreclr/src/.nuget/Directory.Build.props
index 1a8f5c0d7414b4..257da02a7ffc9a 100644
--- a/src/coreclr/src/.nuget/Directory.Build.props
+++ b/src/coreclr/src/.nuget/Directory.Build.props
@@ -3,14 +3,19 @@
 
   <!-- Packaging projects (.pkgproj) are non-SDK-style, so they need to directly import Directory.Build.props -->
   <Import Project="../Directory.Build.props" />
+
+  <Import Project="$(NuGetPackageRoot)\microsoft.dotnet.build.tasks.packaging\$(MicrosoftDotNetBuildTasksPackagingVersion)\build\Microsoft.DotNet.Build.Tasks.Packaging.props" />
+
   <Import Project="packaging.props" />
 
   <PropertyGroup>
     <!-- defined in Packaging.targets, but we need this before targets are imported -->
     <PackagePlatform>AnyCPU</PackagePlatform>
 
-    <!-- build the transport package which includes product and symbols in addition to standard packages -->
-    <CreatePackedPackage Condition="'$(CreatePackedPackage)' == ''">true</CreatePackedPackage>
+    <!-- build the transport package which includes product and symbols in addition to standard packages
+    This is a legacy setting as we tend to use symbol packages for symbol indexing and we don't use
+    transport packages to flow dependencies anymore -->
+    <CreatePackedPackage Condition="'$(CreatePackedPackage)' == ''">false</CreatePackedPackage>
 
     <!-- indicates that lib prefix is not added to library names for Unix-like operating systems -->
     <SkipLibraryPrefixFromUnix>true</SkipLibraryPrefixFromUnix>
diff --git a/src/coreclr/src/.nuget/Microsoft.CrossOsDiag.Private.CoreCLR/Microsoft.CrossOsDiag.Private.CoreCLR.pkgproj b/src/coreclr/src/.nuget/Microsoft.CrossOsDiag.Private.CoreCLR/Microsoft.CrossOsDiag.Private.CoreCLR.pkgproj
new file mode 100644
index 00000000000000..54a1cc17dfbc4a
--- /dev/null
+++ b/src/coreclr/src/.nuget/Microsoft.CrossOsDiag.Private.CoreCLR/Microsoft.CrossOsDiag.Private.CoreCLR.pkgproj
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props))" />
+  <PropertyGroup>
+    <CreatePackedPackage>false</CreatePackedPackage>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <!-- Intentional rather than globbing here, even if very manual, to make sure we publish the Cross OS Dac -->
+    <NativeBinary Include="$(CrossDacBinRoot)/mscordaccore.dll" />
+    <NativeBinary Include="$(CrossDacBinRoot)/mscordbi.dll" />
+    <!-- The infrastructure, and this package is only for indexing. Avoid creating a transport package and just let this one have the symbols itself -->
+    <File Include="@(NativeBinary -> '%(RootDir)%(Directory)/%(Filename).pdb')">
+      <TargetPath>runtimes/$(PackageTargetRuntime)/native</TargetPath>
+    </File>
+
+    <NativeBinary Include="$(CrossDacBinRoot)/libcoreclr.so" />
+  </ItemGroup>
+
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets))" />
+</Project>
diff --git a/src/coreclr/src/.nuget/Microsoft.CrossOsDiag.Private.CoreCLR/Microsoft.CrossOsDiag.Private.CoreCLR.proj b/src/coreclr/src/.nuget/Microsoft.CrossOsDiag.Private.CoreCLR/Microsoft.CrossOsDiag.Private.CoreCLR.proj
new file mode 100644
index 00000000000000..037a6b102605b5
--- /dev/null
+++ b/src/coreclr/src/.nuget/Microsoft.CrossOsDiag.Private.CoreCLR/Microsoft.CrossOsDiag.Private.CoreCLR.proj
@@ -0,0 +1,35 @@
+<Project>
+  <Import Sdk="Microsoft.Build.Traversal" Project="Sdk.props" />
+
+  <PropertyGroup>
+    <BuildIdentityPackage>false</BuildIdentityPackage>
+    <SupportedRids>linux-x64;linux-musl-x64;linux-arm64;linux-musl-arm64;linux-arm;</SupportedRids>
+  </PropertyGroup>
+
+  <Target Name="VerifyCrossDacProperties" BeforeTargets="Build">
+    <Error Condition="'$(CrossDacArtifactsDir)' == '' or !Exists('$(CrossDacArtifactsDir)')"
+          Text="Packaging the Cross OS DAC requires property CrossDacArtifactsDir to to a path containing all cross OS DAC assets needed." />
+  </Target>
+
+  <Target Name="FilterSupportedCrossOsDacPackages" BeforeTargets="Build">
+    <ItemGroup>
+      <_projectsToBuild Include="@(Project)" Condition="$(SupportedRids.Contains('%(Project.PackageTargetRuntime)'))">
+        <AdditionalProperties Condition="'%(Project.PackageTargetRuntime)' == 'linux-x64'">%(AdditionalProperties);CrossDacBinRoot=$(CrossDacArtifactsDir)/Linux.x64.$(Configuration)/x64</AdditionalProperties>
+        <AdditionalProperties Condition="'%(Project.PackageTargetRuntime)' == 'linux-musl-x64'">%(AdditionalProperties);CrossDacBinRoot=$(CrossDacArtifactsDir)/Linux_musl.x64.$(Configuration)/x64</AdditionalProperties>
+        <AdditionalProperties Condition="'%(Project.PackageTargetRuntime)' == 'linux-arm64'">%(AdditionalProperties);CrossDacBinRoot=$(CrossDacArtifactsDir)/Linux.arm64.$(Configuration)/x64</AdditionalProperties>
+        <AdditionalProperties Condition="'%(Project.PackageTargetRuntime)' == 'linux-musl-arm64'">%(AdditionalProperties);CrossDacBinRoot=$(CrossDacArtifactsDir)/Linux_musl.arm64.$(Configuration)/x64</AdditionalProperties>
+        <AdditionalProperties Condition="'%(Project.PackageTargetRuntime)' == 'linux-arm'">%(AdditionalProperties);CrossDacBinRoot=$(CrossDacArtifactsDir)/Linux.arm.$(Configuration)/x86</AdditionalProperties>
+      </_projectsToBuild>
+    </ItemGroup>
+
+    <ItemGroup>
+      <ProjectReference Include="@(_projectsToBuild)" />
+    </ItemGroup>
+  </Target>
+
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(versioning.targets))" />
+  <Import Sdk="Microsoft.Build.Traversal" Project="Sdk.targets" />
+
+  <!-- Ordering matters! Overwriting the Pack target which should just invoke Build. -->
+  <Target Name="Pack" DependsOnTargets="Build" />
+</Project>
diff --git a/src/coreclr/src/.nuget/coreclr-packages.proj b/src/coreclr/src/.nuget/coreclr-packages.proj
index f460db9bcd3d1b..83b95cd3748202 100644
--- a/src/coreclr/src/.nuget/coreclr-packages.proj
+++ b/src/coreclr/src/.nuget/coreclr-packages.proj
@@ -13,36 +13,8 @@
     <ProjectReference Include="Microsoft.NETCore.ILDAsm\Microsoft.NETCore.ILDAsm.proj" />
   </ItemGroup>
 
-  <!-- Generate a version.txt file we include in our packages
-       The InitializeSourceControlInformationFromSourceControlManager is part of Microsoft.Build.Tasks.Git
-       and is responsible for setting SourceRevisionId -->
-  <Target Name="GenerateVersionInfoFileForPackages"
-          BeforeTargets="Build"
-          DependsOnTargets="InitializeSourceControlInformationFromSourceControlManager">
-
-    <Error Condition="'$(SourceRevisionId)' == ''" Text="SourceRevisionId is not set, which means the SourceLink targets are not included in the build. Those are needed to produce a correct sha for our build outputs." />
-
-    <MakeDir Directories="$([System.IO.Path]::GetDirectoryName($(VersionTxtFile)))" />
-    <WriteLinesToFile
-      File="$(VersionTxtFile)"
-      Lines="$(SourceRevisionId)"
-      Overwrite="true" />
-  </Target>
-
-  <!-- Update the project references with additional properties calculated during the execution phase.
-       _InitializeAssemblyVersion is provided by Arcade. It sets the AssemblyVersion and FileVersion properties.
-       We depend on this private Arcade target instead of the SDK-defined GetAssemblyVersion since the packaging
-       build does not use the .NET SDK -->
-  <Target Name="UpdateAdditionalProperties"
-          BeforeTargets="Build"
-          DependsOnTargets="_InitializeAssemblyVersion">
-    <ItemGroup>
-      <!-- Pass the FileVersion calculated by _InitializeAssemblyVersion to referenced projects -->
-      <ProjectReference Update="@(ProjectReference)"
-                        AdditionalProperties="%(ProjectReference.AdditionalProperties);FileVersion=$(FileVersion)" />
-    </ItemGroup>
-  </Target>
 
+  <Import Project="versioning.targets" />
   <Import Sdk="Microsoft.Build.Traversal" Project="Sdk.targets" />
 
   <!-- Ordering matters! Overwriting the Pack target which should just invoke Build. -->
diff --git a/src/coreclr/src/.nuget/descriptions.json b/src/coreclr/src/.nuget/descriptions.json
index e9ac7c58fcc1fc..c172fed61b84c8 100644
--- a/src/coreclr/src/.nuget/descriptions.json
+++ b/src/coreclr/src/.nuget/descriptions.json
@@ -9,6 +9,11 @@
         "Description": "When using NuGet 3.x this package requires at least version {0}.",
         "CommonTypes": [ ]
     },
+    {
+        "Name": "Microsoft.CrossOsDiag.Private.CoreCLR",
+        "Description": "Private transport package for .NET Core cross OS diagnostic tooling.",
+        "CommonTypes": [ ]
+    },
     {
         "Name": "Microsoft.NETCore.ILAsm",
         "Description": "The .NET IL Assembler.",
diff --git a/src/coreclr/src/.nuget/versioning.targets b/src/coreclr/src/.nuget/versioning.targets
new file mode 100644
index 00000000000000..9b5ea266a93f12
--- /dev/null
+++ b/src/coreclr/src/.nuget/versioning.targets
@@ -0,0 +1,31 @@
+<Project>
+  <!-- Generate a version.txt file we include in our packages
+       The InitializeSourceControlInformationFromSourceControlManager is part of Microsoft.Build.Tasks.Git
+       and is responsible for setting SourceRevisionId -->
+  <Target Name="GenerateVersionInfoFileForPackages"
+          BeforeTargets="Build"
+          DependsOnTargets="InitializeSourceControlInformationFromSourceControlManager">
+
+    <Error Condition="'$(SourceRevisionId)' == ''" Text="SourceRevisionId is not set, which means the SourceLink targets are not included in the build. Those are needed to produce a correct sha for our build outputs." />
+
+    <MakeDir Directories="$([System.IO.Path]::GetDirectoryName($(VersionTxtFile)))" />
+    <WriteLinesToFile
+      File="$(VersionTxtFile)"
+      Lines="$(SourceRevisionId)"
+      Overwrite="true" />
+  </Target>
+
+  <!-- Update the project references with additional properties calculated during the execution phase.
+       _InitializeAssemblyVersion is provided by Arcade. It sets the AssemblyVersion and FileVersion properties.
+       We depend on this private Arcade target instead of the SDK-defined GetAssemblyVersion since the packaging
+       build does not use the .NET SDK -->
+  <Target Name="UpdateAdditionalProperties"
+          BeforeTargets="Build"
+          DependsOnTargets="_InitializeAssemblyVersion">
+    <ItemGroup>
+      <!-- Pass the FileVersion calculated by _InitializeAssemblyVersion to referenced projects -->
+      <ProjectReference Update="@(ProjectReference)"
+                        AdditionalProperties="%(ProjectReference.AdditionalProperties);FileVersion=$(FileVersion)" />
+    </ItemGroup>
+  </Target>
+</Project>
diff --git a/src/coreclr/src/System.Private.CoreLib/CreateRuntimeRootILLinkDescriptorFile.targets b/src/coreclr/src/System.Private.CoreLib/CreateRuntimeRootILLinkDescriptorFile.targets
index 18a6d21e57dcb7..4b232bbfdc21e0 100644
--- a/src/coreclr/src/System.Private.CoreLib/CreateRuntimeRootILLinkDescriptorFile.targets
+++ b/src/coreclr/src/System.Private.CoreLib/CreateRuntimeRootILLinkDescriptorFile.targets
@@ -7,12 +7,12 @@
   <PropertyGroup>
     <_ILLinkRuntimeRootDescriptorFilePath>$(ILLinkTrimXml)</_ILLinkRuntimeRootDescriptorFilePath>
     <_NamespaceFilePath Condition=" '$(_NamespaceFilePath)' == '' ">$(MSBuildThisFileDirectory)..\vm\namespace.h</_NamespaceFilePath>
-    <_MscorlibFilePath Condition=" '$(_MscorlibFilePath)' == '' ">$(MSBuildThisFileDirectory)..\vm\mscorlib.h</_MscorlibFilePath>
+    <_MscorlibFilePath Condition=" '$(_MscorlibFilePath)' == '' ">$(MSBuildThisFileDirectory)..\vm\corelib.h</_MscorlibFilePath>
     <_CortypeFilePath Condition=" '$(_CortypeFilePath)' == '' ">$(MSBuildThisFileDirectory)..\inc\cortypeinfo.h</_CortypeFilePath>
     <_RexcepFilePath Condition=" '$(_RexcepFilePath)' == '' ">$(MSBuildThisFileDirectory)..\vm\rexcep.h</_RexcepFilePath>
     <_ILLinkDescriptorsIntermediatePath>$(IntermediateOutputPath)ILLink.Descriptors.Combined.xml</_ILLinkDescriptorsIntermediatePath>
     <_ILLinkTasksToolsDir>$(PkgMicrosoft_NET_ILLink_Tasks)/tools</_ILLinkTasksToolsDir>
-    <_ILLinkTasksDir>$(_ILLinkTasksToolsDir)/$(NetFrameworkCurrent)/</_ILLinkTasksDir>
+    <_ILLinkTasksDir>$(_ILLinkTasksToolsDir)/net472/</_ILLinkTasksDir>
     <_ILLinkTasksDir Condition="'$(MSBuildRuntimeType)' == 'Core'">$(_ILLinkTasksToolsDir)/netcoreapp3.0/</_ILLinkTasksDir>
     <_ILLinkTasksPath>$(_ILLinkTasksDir)ILLink.Tasks.dll</_ILLinkTasksPath>
   </PropertyGroup>
diff --git a/src/coreclr/src/System.Private.CoreLib/ILLinkTrim.xml b/src/coreclr/src/System.Private.CoreLib/ILLinkTrim.xml
index 11a67fdac31329..8031688ca0b98b 100644
--- a/src/coreclr/src/System.Private.CoreLib/ILLinkTrim.xml
+++ b/src/coreclr/src/System.Private.CoreLib/ILLinkTrim.xml
@@ -17,5 +17,12 @@
     <type fullname="System.Runtime.InteropServices.IDispatch" />
     <type fullname="System.Runtime.InteropServices.IMarshal" />
     <type fullname="Internal.Runtime.InteropServices.IClassFactory2" />
+
+    <!-- GetActualImplementationForArrayGenericIListOrIReadOnlyListMethod depends on slots of these interfaces not changing -->
+    <type fullname="System.Collections.Generic.IEnumerable`1" />
+    <type fullname="System.Collections.Generic.ICollection`1" />
+    <type fullname="System.Collections.Generic.IReadOnlyCollection`1" />
+    <type fullname="System.Collections.Generic.IList`1" />
+    <type fullname="System.Collections.Generic.IReadOnlyList`1" />
   </assembly>
 </linker>
diff --git a/src/coreclr/src/System.Private.CoreLib/System.Private.CoreLib.csproj b/src/coreclr/src/System.Private.CoreLib/System.Private.CoreLib.csproj
index 501487c6a111bb..1665f9ac692502 100644
--- a/src/coreclr/src/System.Private.CoreLib/System.Private.CoreLib.csproj
+++ b/src/coreclr/src/System.Private.CoreLib/System.Private.CoreLib.csproj
@@ -224,6 +224,7 @@
     <Compile Include="$(BclSourcesRoot)\System\Runtime\InteropServices\Marshal.CoreCLR.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Runtime\InteropServices\MemoryMarshal.CoreCLR.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Runtime\InteropServices\NativeLibrary.CoreCLR.cs" />
+    <Compile Include="$(BclSourcesRoot)\System\Runtime\Intrinsics\X86\X86Base.CoreCLR.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Runtime\Loader\AssemblyLoadContext.CoreCLR.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Runtime\Versioning\CompatibilitySwitch.cs" />
     <Compile Include="$(BclSourcesRoot)\System\RuntimeArgumentHandle.cs" />
diff --git a/src/coreclr/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.cs b/src/coreclr/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.cs
index 45f4d4839fb864..c41d4dd966169d 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.cs
@@ -25,7 +25,7 @@ public interface IClassFactory
         void CreateInstance(
             [MarshalAs(UnmanagedType.Interface)] object? pUnkOuter,
             ref Guid riid,
-            [MarshalAs(UnmanagedType.Interface)] out object? ppvObject);
+            out IntPtr ppvObject);
 
         void LockServer([MarshalAs(UnmanagedType.Bool)] bool fLock);
     }
@@ -51,7 +51,7 @@ internal interface IClassFactory2 : IClassFactory
         new void CreateInstance(
             [MarshalAs(UnmanagedType.Interface)] object? pUnkOuter,
             ref Guid riid,
-            [MarshalAs(UnmanagedType.Interface)] out object? ppvObject);
+            out IntPtr ppvObject);
 
         new void LockServer([MarshalAs(UnmanagedType.Bool)] bool fLock);
 
@@ -66,7 +66,7 @@ void CreateInstanceLic(
             [MarshalAs(UnmanagedType.Interface)] object? pUnkReserved,
             ref Guid riid,
             [MarshalAs(UnmanagedType.BStr)] string bstrKey,
-            [MarshalAs(UnmanagedType.Interface)] out object ppvObject);
+            out IntPtr ppvObject);
     }
 
     [StructLayout(LayoutKind.Sequential)]
@@ -493,28 +493,32 @@ public static Type GetValidatedInterfaceType(Type classType, ref Guid riid, obje
 #endif
             }
 
-            public static void ValidateObjectIsMarshallableAsInterface(object obj, Type interfaceType)
+            public static IntPtr GetObjectAsInterface(object obj, Type interfaceType)
             {
 #if FEATURE_COMINTEROP_UNMANAGED_ACTIVATION
-                // If the requested "interface type" is type object then return
-                // because type object is always marshallable.
+                // If the requested "interface type" is type object then return as IUnknown
                 if (interfaceType == typeof(object))
                 {
-                    return;
+                    return Marshal.GetIUnknownForObject(obj);
                 }
 
                 Debug.Assert(interfaceType.IsInterface);
 
-                // The intent of this call is to validate the interface can be
+                // The intent of this call is to get AND validate the interface can be
                 // marshalled to native code. An exception will be thrown if the
                 // type is unable to be marshalled to native code.
                 // Scenarios where this is relevant:
                 //  - Interfaces that use Generics
                 //  - Interfaces that define implementation
-                IntPtr ptr = Marshal.GetComInterfaceForObject(obj, interfaceType, CustomQueryInterfaceMode.Ignore);
+                IntPtr interfaceMaybe = Marshal.GetComInterfaceForObject(obj, interfaceType, CustomQueryInterfaceMode.Ignore);
 
-                // Decrement the above 'Marshal.GetComInterfaceForObject()'
-                Marshal.Release(ptr);
+                if (interfaceMaybe == IntPtr.Zero)
+                {
+                    // E_NOINTERFACE
+                    throw new InvalidCastException();
+                }
+
+                return interfaceMaybe;
 #else
                 throw new PlatformNotSupportedException();
 #endif
@@ -544,18 +548,18 @@ public static object CreateAggregatedObject(object pUnkOuter, object comObject)
             public void CreateInstance(
                 [MarshalAs(UnmanagedType.Interface)] object? pUnkOuter,
                 ref Guid riid,
-                [MarshalAs(UnmanagedType.Interface)] out object? ppvObject)
+                out IntPtr ppvObject)
             {
 #if FEATURE_COMINTEROP_UNMANAGED_ACTIVATION
                 Type interfaceType = BasicClassFactory.GetValidatedInterfaceType(_classType, ref riid, pUnkOuter);
 
-                ppvObject = Activator.CreateInstance(_classType)!;
+                object obj = Activator.CreateInstance(_classType)!;
                 if (pUnkOuter != null)
                 {
-                    ppvObject = BasicClassFactory.CreateAggregatedObject(pUnkOuter, ppvObject);
+                    obj = BasicClassFactory.CreateAggregatedObject(pUnkOuter, obj);
                 }
 
-                BasicClassFactory.ValidateObjectIsMarshallableAsInterface(ppvObject, interfaceType);
+                ppvObject = BasicClassFactory.GetObjectAsInterface(obj, interfaceType);
 #else
                 throw new PlatformNotSupportedException();
 #endif
@@ -593,7 +597,7 @@ public LicenseClassFactory(Guid clsid, Type classType)
             public void CreateInstance(
                 [MarshalAs(UnmanagedType.Interface)] object? pUnkOuter,
                 ref Guid riid,
-                [MarshalAs(UnmanagedType.Interface)] out object? ppvObject)
+                out IntPtr ppvObject)
             {
 #if FEATURE_COMINTEROP_UNMANAGED_ACTIVATION
                 CreateInstanceInner(pUnkOuter, ref riid, key: null, isDesignTime: true, out ppvObject);
@@ -640,7 +644,7 @@ public void CreateInstanceLic(
                 [MarshalAs(UnmanagedType.Interface)] object? pUnkReserved,
                 ref Guid riid,
                 [MarshalAs(UnmanagedType.BStr)] string bstrKey,
-                [MarshalAs(UnmanagedType.Interface)] out object ppvObject)
+                out IntPtr ppvObject)
             {
 #if FEATURE_COMINTEROP_UNMANAGED_ACTIVATION
                 Debug.Assert(pUnkReserved == null);
@@ -655,18 +659,18 @@ private void CreateInstanceInner(
                 ref Guid riid,
                 string? key,
                 bool isDesignTime,
-                out object ppvObject)
+                out IntPtr ppvObject)
             {
 #if FEATURE_COMINTEROP_UNMANAGED_ACTIVATION
                 Type interfaceType = BasicClassFactory.GetValidatedInterfaceType(_classType, ref riid, pUnkOuter);
 
-                ppvObject = _licenseProxy.AllocateAndValidateLicense(_classType, key, isDesignTime);
+                object obj = _licenseProxy.AllocateAndValidateLicense(_classType, key, isDesignTime);
                 if (pUnkOuter != null)
                 {
-                    ppvObject = BasicClassFactory.CreateAggregatedObject(pUnkOuter, ppvObject);
+                    obj = BasicClassFactory.CreateAggregatedObject(pUnkOuter, obj);
                 }
 
-                BasicClassFactory.ValidateObjectIsMarshallableAsInterface(ppvObject, interfaceType);
+                ppvObject = BasicClassFactory.GetObjectAsInterface(obj, interfaceType);
 #else
                 throw new PlatformNotSupportedException();
 #endif
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Environment.CoreCLR.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Environment.CoreCLR.cs
index d2ea1e3fbdd0a0..82d9af92c643ff 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Environment.CoreCLR.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Environment.CoreCLR.cs
@@ -83,9 +83,7 @@ public static string[] GetCommandLineArgs()
         [DllImport(RuntimeHelpers.QCall, CharSet = CharSet.Unicode)]
         private static extern int GetProcessorCount();
 
-        // If you change this method's signature then you must change the code that calls it
-        // in excep.cpp and probably you will have to visit mscorlib.h to add the new signature
-        // as well as metasig.h to create the new signature type
+        // Used by VM
         internal static string? GetResourceStringLocal(string key) => SR.GetResourceString(key);
 
         public static string StackTrace
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Exception.CoreCLR.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Exception.CoreCLR.cs
index c3f1e5b4fd43fd..d6bb435387b07c 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Exception.CoreCLR.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Exception.CoreCLR.cs
@@ -266,8 +266,8 @@ private string? SerializationStackTraceString
         }
 
         // This piece of infrastructure exists to help avoid deadlocks
-        // between parts of mscorlib that might throw an exception while
-        // holding a lock that are also used by mscorlib's ResourceManager
+        // between parts of CoreLib that might throw an exception while
+        // holding a lock that are also used by CoreLib's ResourceManager
         // instance.  As a special case of code that may throw while holding
         // a lock, we also need to fix our asynchronous exceptions to use
         // Win32 resources as well (assuming we ever call a managed
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/GC.cs b/src/coreclr/src/System.Private.CoreLib/src/System/GC.cs
index 865600fe8d2db0..cb011de2ef2b19 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/GC.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/GC.cs
@@ -294,7 +294,7 @@ public static int GetGeneration(WeakReference wo)
 
         public static void WaitForPendingFinalizers()
         {
-            // QCalls can not be exposed from mscorlib directly, need to wrap it.
+            // QCalls can not be exposed directly, need to wrap it.
             _WaitForPendingFinalizers();
         }
 
@@ -659,7 +659,7 @@ internal static void UnregisterMemoryLoadChangeNotification(Action notification)
         /// If pinned is set to true, <typeparamref name="T"/> must not be a reference type or a type that contains object references.
         /// </remarks>
         [MethodImpl(MethodImplOptions.AggressiveInlining)] // forced to ensure no perf drop for small memory buffers (hot path)
-        public static T[] AllocateUninitializedArray<T>(int length, bool pinned = false)
+        public static T[] AllocateUninitializedArray<T>(int length, bool pinned = false) // T[] rather than T?[] to match `new T[length]` behavior
         {
             if (!pinned)
             {
@@ -705,7 +705,7 @@ static T[] AllocateNewUninitializedArray(int length, bool pinned)
         /// <remarks>
         /// If pinned is set to true, <typeparamref name="T"/> must not be a reference type or a type that contains object references.
         /// </remarks>
-        public static T[] AllocateArray<T>(int length, bool pinned = false)
+        public static T[] AllocateArray<T>(int length, bool pinned = false) // T[] rather than T?[] to match `new T[length]` behavior
         {
             GC_ALLOC_FLAGS flags = GC_ALLOC_FLAGS.GC_ALLOC_NO_FLAGS;
 
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Math.CoreCLR.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Math.CoreCLR.cs
index 74aca4342ee39f..beeb322b52c0cd 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Math.CoreCLR.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Math.CoreCLR.cs
@@ -56,6 +56,7 @@ public static partial class Math
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern double Cbrt(double d);
 
+        [Intrinsic]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern double Ceiling(double a);
 
@@ -71,6 +72,7 @@ public static partial class Math
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern double Exp(double d);
 
+        [Intrinsic]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern double Floor(double d);
 
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/MathF.CoreCLR.cs b/src/coreclr/src/System.Private.CoreLib/src/System/MathF.CoreCLR.cs
index 371780f6abe02e..f3dd3289c1c26d 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/MathF.CoreCLR.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/MathF.CoreCLR.cs
@@ -45,6 +45,7 @@ public static partial class MathF
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern float Cbrt(float x);
 
+        [Intrinsic]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern float Ceiling(float x);
 
@@ -60,6 +61,7 @@ public static partial class MathF
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern float Exp(float x);
 
+        [Intrinsic]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern float Floor(float x);
 
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/AssemblyBuilder.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/AssemblyBuilder.cs
index e1ce8a9f61f926..7313b405bf0ef7 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/AssemblyBuilder.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/AssemblyBuilder.cs
@@ -105,6 +105,7 @@ public override FileStream[] GetFiles(bool getResourceModules)
 
         public override string? CodeBase => throw new NotSupportedException(SR.NotSupported_DynamicAssembly);
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type[] GetExportedTypes()
         {
             throw new NotSupportedException(SR.NotSupported_DynamicAssembly);
@@ -477,12 +478,14 @@ public override FileStream[] GetFiles(bool getResourceModules)
         /// <sumary>
         /// Get an array of all the public types defined in this assembly.
         /// </sumary>
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type[] GetExportedTypes() => InternalAssembly.GetExportedTypes();
 
         public override AssemblyName GetName(bool copiedName) => InternalAssembly.GetName(copiedName);
 
         public override string? FullName => InternalAssembly.FullName;
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type? GetType(string name, bool throwOnError, bool ignoreCase)
         {
             return InternalAssembly.GetType(name, throwOnError, ignoreCase);
@@ -494,6 +497,7 @@ public override FileStream[] GetFiles(bool getResourceModules)
 
         public override Module? GetModule(string name) => InternalAssembly.GetModule(name);
 
+        [RequiresUnreferencedCode("Assembly references might be removed")]
         public override AssemblyName[] GetReferencedAssemblies()
         {
             return InternalAssembly.GetReferencedAssemblies();
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.cs
index 788969f7209774..4d52ddcb876f81 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.cs
@@ -63,6 +63,7 @@ public FieldBuilder DefineLiteral(string literalName, object? literalValue)
         /// </summary>
         public override Guid GUID => m_typeBuilder.GUID;
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(
             string name,
             BindingFlags invokeAttr,
@@ -92,6 +93,7 @@ public FieldBuilder DefineLiteral(string literalName, object? literalValue)
 
         public override bool IsByRefLike => false;
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo? GetConstructorImpl(BindingFlags bindingAttr, Binder? binder,
                 CallingConventions callConvention, Type[] types, ParameterModifier[]? modifiers)
         {
@@ -99,11 +101,13 @@ public FieldBuilder DefineLiteral(string literalName, object? literalValue)
                             types, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetConstructors(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo? GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder,
                 CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers)
         {
@@ -113,16 +117,19 @@ public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
                 return m_typeBuilder.GetMethod(name, bindingAttr, binder, callConvention, types, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetMethods(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo? GetField(string name, BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetField(name, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetFields(bindingAttr);
@@ -138,42 +145,50 @@ public override Type[] GetInterfaces()
             return m_typeBuilder.GetInterfaces();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo? GetEvent(string name, BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetEvent(name, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents)]
         public override EventInfo[] GetEvents()
         {
             return m_typeBuilder.GetEvents();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo GetPropertyImpl(string name, BindingFlags bindingAttr, Binder? binder,
                 Type? returnType, Type[]? types, ParameterModifier[]? modifiers)
         {
             throw new NotSupportedException(SR.NotSupported_DynamicModule);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetProperties(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetNestedTypes(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type? GetNestedType(string name, BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetNestedType(name, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetMember(name, type, bindingAttr);
         }
 
+       [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetMembers(bindingAttr);
@@ -184,6 +199,7 @@ public override InterfaceMapping GetInterfaceMap(Type interfaceType)
             return m_typeBuilder.GetInterfaceMap(interfaceType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr)
         {
             return m_typeBuilder.GetEvents(bindingAttr);
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/GenericTypeParameterBuilder.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/GenericTypeParameterBuilder.cs
index ffa61eaa0a706f..e21b2c1a6a84bd 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/GenericTypeParameterBuilder.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/GenericTypeParameterBuilder.cs
@@ -82,6 +82,7 @@ public override Type MakeArrayType(int rank)
 
         public override Guid GUID => throw new NotSupportedException();
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target, object?[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters) { throw new NotSupportedException(); }
 
         public override Assembly Assembly => m_type.Assembly;
@@ -96,40 +97,55 @@ public override Type MakeArrayType(int rank)
 
         public override Type? BaseType => m_type.BaseType;
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo GetConstructorImpl(BindingFlags bindingAttr, Binder? binder, CallingConventions callConvention, Type[] types, ParameterModifier[]? modifiers) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder, CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo GetField(string name, BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
         public override Type GetInterface(string name, bool ignoreCase) { throw new NotSupportedException(); }
 
         public override Type[] GetInterfaces() { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo GetEvent(string name, BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents)]
         public override EventInfo[] GetEvents() { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo GetPropertyImpl(string name, BindingFlags bindingAttr, Binder? binder, Type? returnType, Type[]? types, ParameterModifier[]? modifiers) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type GetNestedType(string name, BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
         public override InterfaceMapping GetInterfaceMap(Type interfaceType) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
         protected override TypeAttributes GetAttributeFlagsImpl() { return TypeAttributes.Public; }
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.cs
index 4a719065ba42c5..aec1ca393d4cd8 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.cs
@@ -524,6 +524,7 @@ public override IList<CustomAttributeData> GetCustomAttributesData()
 
         #region Module Overrides
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type[] GetTypes()
         {
             lock (SyncRoot)
@@ -558,16 +559,19 @@ internal Type[] GetTypesNoLock()
             return typeList;
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type? GetType(string className)
         {
             return GetType(className, false, false);
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type? GetType(string className, bool ignoreCase)
         {
             return GetType(className, false, ignoreCase);
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type? GetType(string className, bool throwOnError, bool ignoreCase)
         {
             lock (SyncRoot)
@@ -677,31 +681,37 @@ internal Type[] GetTypesNoLock()
 
         public override string FullyQualifiedName => _moduleData._moduleName;
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override byte[] ResolveSignature(int metadataToken)
         {
             return InternalModule.ResolveSignature(metadataToken);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override MethodBase? ResolveMethod(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             return InternalModule.ResolveMethod(metadataToken, genericTypeArguments, genericMethodArguments);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override FieldInfo? ResolveField(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             return InternalModule.ResolveField(metadataToken, genericTypeArguments, genericMethodArguments);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override Type ResolveType(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             return InternalModule.ResolveType(metadataToken, genericTypeArguments, genericMethodArguments);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override MemberInfo? ResolveMember(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             return InternalModule.ResolveMember(metadataToken, genericTypeArguments, genericMethodArguments);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override string ResolveString(int metadataToken)
         {
             return InternalModule.ResolveString(metadataToken);
@@ -720,21 +730,25 @@ public override void GetPEKind(out PortableExecutableKinds peKind, out ImageFile
 
         public override bool IsResource() => InternalModule.IsResource();
 
+        [RequiresUnreferencedCode("Fields might be removed")]
         public override FieldInfo[] GetFields(BindingFlags bindingFlags)
         {
             return InternalModule.GetFields(bindingFlags);
         }
 
+        [RequiresUnreferencedCode("Fields might be removed")]
         public override FieldInfo? GetField(string name, BindingFlags bindingAttr)
         {
             return InternalModule.GetField(name, bindingAttr);
         }
 
+        [RequiresUnreferencedCode("Methods might be removed")]
         public override MethodInfo[] GetMethods(BindingFlags bindingFlags)
         {
             return InternalModule.GetMethods(bindingFlags);
         }
 
+        [RequiresUnreferencedCode("Methods might be removed")]
         protected override MethodInfo? GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder,
             CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers)
         {
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/SymbolType.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/SymbolType.cs
index fa49a2256681e7..fbd9102b894beb 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/SymbolType.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/SymbolType.cs
@@ -300,6 +300,7 @@ public override int GetArrayRank()
 
         public override Guid GUID => throw new NotSupportedException(SR.NotSupported_NonReflectedType);
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target,
             object?[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters)
         {
@@ -358,33 +359,39 @@ public override string ToString()
 
         public override Type BaseType => typeof(System.Array);
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo GetConstructorImpl(BindingFlags bindingAttr, Binder? binder,
                 CallingConventions callConvention, Type[] types, ParameterModifier[]? modifiers)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder,
                 CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo GetField(string name, BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
@@ -400,42 +407,50 @@ public override Type[] GetInterfaces()
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo GetEvent(string name, BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents)]
         public override EventInfo[] GetEvents()
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo GetPropertyImpl(string name, BindingFlags bindingAttr, Binder? binder,
                 Type? returnType, Type[]? types, ParameterModifier[]? modifiers)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type GetNestedType(string name, BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
@@ -446,6 +461,7 @@ public override InterfaceMapping GetInterfaceMap(Type interfaceType)
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(SR.NotSupported_NonReflectedType);
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.cs
index 47c3dea104ee3c..5b2acd1605bb24 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.cs
@@ -744,6 +744,7 @@ public override Guid GUID
             }
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target,
             object?[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters)
         {
@@ -765,6 +766,7 @@ public override Guid GUID
 
         public override Type? BaseType => m_typeParent;
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo? GetConstructorImpl(BindingFlags bindingAttr, Binder? binder,
                 CallingConventions callConvention, Type[] types, ParameterModifier[]? modifiers)
         {
@@ -774,6 +776,7 @@ public override Guid GUID
             return m_bakedRuntimeType.GetConstructor(bindingAttr, binder, callConvention, types, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
         {
             if (!IsCreated())
@@ -782,6 +785,7 @@ public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
             return m_bakedRuntimeType.GetConstructors(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo? GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder,
                 CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers)
         {
@@ -798,6 +802,7 @@ public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
             }
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
         {
             if (!IsCreated())
@@ -806,6 +811,7 @@ public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
             return m_bakedRuntimeType.GetMethods(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo? GetField(string name, BindingFlags bindingAttr)
         {
             if (!IsCreated())
@@ -814,6 +820,7 @@ public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
             return m_bakedRuntimeType.GetField(name, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr)
         {
             if (!IsCreated())
@@ -845,6 +852,7 @@ public override Type[] GetInterfaces()
             return m_typeInterfaces.ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo? GetEvent(string name, BindingFlags bindingAttr)
         {
             if (!IsCreated())
@@ -853,6 +861,7 @@ public override Type[] GetInterfaces()
             return m_bakedRuntimeType.GetEvent(name, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents)]
         public override EventInfo[] GetEvents()
         {
             if (!IsCreated())
@@ -861,12 +870,14 @@ public override EventInfo[] GetEvents()
             return m_bakedRuntimeType.GetEvents();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo GetPropertyImpl(string name, BindingFlags bindingAttr, Binder? binder,
                 Type? returnType, Type[]? types, ParameterModifier[]? modifiers)
         {
             throw new NotSupportedException(SR.NotSupported_DynamicModule);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr)
         {
             if (!IsCreated())
@@ -875,6 +886,7 @@ public override PropertyInfo[] GetProperties(BindingFlags bindingAttr)
             return m_bakedRuntimeType.GetProperties(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr)
         {
             if (!IsCreated())
@@ -883,6 +895,7 @@ public override Type[] GetNestedTypes(BindingFlags bindingAttr)
             return m_bakedRuntimeType.GetNestedTypes(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type? GetNestedType(string name, BindingFlags bindingAttr)
         {
             if (!IsCreated())
@@ -891,6 +904,7 @@ public override Type[] GetNestedTypes(BindingFlags bindingAttr)
             return m_bakedRuntimeType.GetNestedType(name, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr)
         {
             if (!IsCreated())
@@ -907,6 +921,7 @@ public override InterfaceMapping GetInterfaceMap(Type interfaceType)
             return m_bakedRuntimeType.GetInterfaceMap(interfaceType);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr)
         {
             if (!IsCreated())
@@ -915,6 +930,7 @@ public override EventInfo[] GetEvents(BindingFlags bindingAttr)
             return m_bakedRuntimeType.GetEvents(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
         {
             if (!IsCreated())
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilderInstantiation.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilderInstantiation.cs
index 1a6e10196af898..4e3844dac940cd 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilderInstantiation.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilderInstantiation.cs
@@ -97,7 +97,10 @@ public override Type MakeArrayType(int rank)
             return SymbolType.FormCompoundType(s, this, 0)!;
         }
         public override Guid GUID => throw new NotSupportedException();
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target, object?[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters) { throw new NotSupportedException(); }
+
         public override Assembly Assembly => m_type.Assembly;
         public override RuntimeTypeHandle TypeHandle => throw new NotSupportedException();
         public override string? FullName => m_strFullQualName ??= TypeNameBuilder.ToString(this, TypeNameBuilder.Format.FullName);
@@ -152,26 +155,56 @@ public override Type? BaseType
                 return typeBldrBaseAs.Substitute(GetGenericArguments());
             }
         }
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo GetConstructorImpl(BindingFlags bindingAttr, Binder? binder, CallingConventions callConvention, Type[] types, ParameterModifier[]? modifiers) { throw new NotSupportedException(); }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder, CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo GetField(string name, BindingFlags bindingAttr) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr) { throw new NotSupportedException(); }
+
         public override Type GetInterface(string name, bool ignoreCase) { throw new NotSupportedException(); }
         public override Type[] GetInterfaces() { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo GetEvent(string name, BindingFlags bindingAttr) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents)]
         public override EventInfo[] GetEvents() { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo GetPropertyImpl(string name, BindingFlags bindingAttr, Binder? binder, Type? returnType, Type[]? types, ParameterModifier[]? modifiers) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type GetNestedType(string name, BindingFlags bindingAttr) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr) { throw new NotSupportedException(); }
 
         public override InterfaceMapping GetInterfaceMap(Type interfaceType) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr) { throw new NotSupportedException(); }
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr) { throw new NotSupportedException(); }
+
         protected override TypeAttributes GetAttributeFlagsImpl() { return m_type.Attributes; }
 
         public override bool IsTypeDefinition => false;
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/INVOCATION_FLAGS.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/INVOCATION_FLAGS.cs
index e7d9b97ac5c6c5..b6a55518914a22 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/INVOCATION_FLAGS.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/INVOCATION_FLAGS.cs
@@ -14,7 +14,8 @@ internal enum INVOCATION_FLAGS : uint
         INVOCATION_FLAGS_INITIALIZED = 0x00000001,
         // it's used for both method and field to signify that no access is allowed
         INVOCATION_FLAGS_NO_INVOKE = 0x00000002,
-        /* unused 0x00000004 */
+        // Set for static ctors, to ensure that the static ctor is run as a static ctor before it is explicitly executed via reflection
+        INVOCATION_FLAGS_RUN_CLASS_CONSTRUCTOR = 0x00000004,
         // Set for static ctors and ctors on abstract types, which
         // can be invoked only if the "this" object is provided (even if it's null).
         INVOCATION_FLAGS_NO_CTOR_INVOKE = 0x00000008,
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs
index 4aa7b486c723fa..d2476660973fd3 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs
@@ -3,6 +3,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using CultureInfo = System.Globalization.CultureInfo;
 using System.IO;
 using System.Configuration.Assemblies;
@@ -158,6 +159,7 @@ private static extern void GetType(QCallAssembly assembly,
                                             ObjectHandleOnStack keepAlive,
                                             ObjectHandleOnStack assemblyLoadContext);
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type? GetType(string name, bool throwOnError, bool ignoreCase)
         {
             // throw on null strings regardless of the value of "throwOnError"
@@ -184,6 +186,7 @@ private static extern void GetType(QCallAssembly assembly,
         [DllImport(RuntimeHelpers.QCall, CharSet = CharSet.Unicode)]
         private static extern void GetExportedTypes(QCallAssembly assembly, ObjectHandleOnStack retTypes);
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type[] GetExportedTypes()
         {
             Type[]? types = null;
@@ -194,6 +197,7 @@ public override Type[] GetExportedTypes()
 
         public override IEnumerable<TypeInfo> DefinedTypes
         {
+            [RequiresUnreferencedCode("Types might be removed")]
             get
             {
                 RuntimeModule[] modules = GetModulesInternal(true, false);
@@ -394,6 +398,7 @@ public override string[] GetManifestResourceNames()
         [MethodImpl(MethodImplOptions.InternalCall)]
         private static extern AssemblyName[] GetReferencedAssemblies(RuntimeAssembly assembly);
 
+        [RequiresUnreferencedCode("Assembly references might be removed")]
         public override AssemblyName[] GetReferencedAssemblies()
         {
             return GetReferencedAssemblies(GetNativeHandle());
@@ -607,6 +612,7 @@ public override Module[] GetLoadedModules(bool getResourceModules)
         [MethodImpl(MethodImplOptions.InternalCall)]
         internal static extern int GetToken(RuntimeAssembly assembly);
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public sealed override Type[] GetForwardedTypes()
         {
             List<Type> types = new List<Type>();
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeConstructorInfo.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeConstructorInfo.cs
index 9d0086ca442536..e06251e6ad851b 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeConstructorInfo.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeConstructorInfo.cs
@@ -5,6 +5,7 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
+using System.Runtime.CompilerServices;
 using System.Text;
 using RuntimeTypeCache = System.RuntimeType.RuntimeTypeCache;
 
@@ -47,7 +48,12 @@ internal INVOCATION_FLAGS InvocationFlags
                         // We don't need other flags if this method cannot be invoked
                         invocationFlags |= INVOCATION_FLAGS.INVOCATION_FLAGS_NO_INVOKE;
                     }
-                    else if (IsStatic || declaringType != null && declaringType.IsAbstract)
+                    else if (IsStatic)
+                    {
+                        invocationFlags |= INVOCATION_FLAGS.INVOCATION_FLAGS_RUN_CLASS_CONSTRUCTOR |
+                                           INVOCATION_FLAGS.INVOCATION_FLAGS_NO_CTOR_INVOKE;
+                    }
+                    else if (declaringType != null && declaringType.IsAbstract)
                     {
                         invocationFlags |= INVOCATION_FLAGS.INVOCATION_FLAGS_NO_CTOR_INVOKE;
                     }
@@ -280,6 +286,21 @@ internal void ThrowNoInvokeException()
             // check basic method consistency. This call will throw if there are problems in the target/method relationship
             CheckConsistency(obj);
 
+            if ((invocationFlags & INVOCATION_FLAGS.INVOCATION_FLAGS_RUN_CLASS_CONSTRUCTOR) != 0)
+            {
+                // Run the class constructor through the class constructor mechanism instead of the Invoke path.
+                // This avoids allowing mutation of readonly static fields, and initializes the type correctly.
+
+                var declaringType = DeclaringType;
+
+                if (declaringType != null)
+                    RuntimeHelpers.RunClassConstructor(declaringType.TypeHandle);
+                else
+                    RuntimeHelpers.RunModuleConstructor(Module.ModuleHandle);
+
+                return null;
+            }
+
             Signature sig = Signature;
 
             // get the signature
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeModule.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeModule.cs
index 3835866b99bfd5..990b52854a05fb 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeModule.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Reflection/RuntimeModule.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.InteropServices;
 using System.Runtime.Serialization;
 using System.Collections.Generic;
@@ -60,6 +61,7 @@ internal RuntimeType[] GetDefinedTypes()
             return typeHandleArgs;
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override byte[] ResolveSignature(int metadataToken)
         {
             MetadataToken tk = new MetadataToken(metadataToken);
@@ -86,6 +88,7 @@ public override byte[] ResolveSignature(int metadataToken)
             return sig;
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override MethodBase? ResolveMethod(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             MetadataToken tk = new MetadataToken(metadataToken);
@@ -165,6 +168,7 @@ public override byte[] ResolveSignature(int metadataToken)
             }
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override FieldInfo? ResolveField(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             MetadataToken tk = new MetadataToken(metadataToken);
@@ -219,6 +223,7 @@ public override byte[] ResolveSignature(int metadataToken)
             }
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override Type ResolveType(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             MetadataToken tk = new MetadataToken(metadataToken);
@@ -251,6 +256,7 @@ public override Type ResolveType(int metadataToken, Type[]? genericTypeArguments
             }
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override MemberInfo? ResolveMember(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             MetadataToken tk = new MetadataToken(metadataToken);
@@ -295,6 +301,7 @@ public override Type ResolveType(int metadataToken, Type[]? genericTypeArguments
                 nameof(metadataToken));
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override string ResolveString(int metadataToken)
         {
             MetadataToken tk = new MetadataToken(metadataToken);
@@ -336,6 +343,7 @@ public override void GetPEKind(out PortableExecutableKinds peKind, out ImageFile
         #endregion
 
         #region Protected Virtuals
+        [RequiresUnreferencedCode("Methods might be removed")]
         protected override MethodInfo? GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder,
             CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers)
         {
@@ -415,6 +423,7 @@ public override void GetObjectData(SerializationInfo info, StreamingContext cont
             throw new PlatformNotSupportedException();
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type? GetType(string className, bool throwOnError, bool ignoreCase)
         {
             // throw on null strings regardless of the value of "throwOnError"
@@ -439,6 +448,7 @@ internal string GetFullyQualifiedName()
 
         public override string FullyQualifiedName => GetFullyQualifiedName();
 
+      [RequiresUnreferencedCode("Types might be removed")]
         public override Type[] GetTypes()
         {
             return GetTypes(GetNativeHandle());
@@ -464,6 +474,7 @@ public override bool IsResource()
             return IsResource(GetNativeHandle());
         }
 
+        [RequiresUnreferencedCode("Fields might be removed")]
         public override FieldInfo[] GetFields(BindingFlags bindingFlags)
         {
             if (RuntimeType == null)
@@ -472,6 +483,7 @@ public override FieldInfo[] GetFields(BindingFlags bindingFlags)
             return RuntimeType.GetFields(bindingFlags);
         }
 
+        [RequiresUnreferencedCode("Fields might be removed")]
         public override FieldInfo? GetField(string name, BindingFlags bindingAttr)
         {
             if (name == null)
@@ -483,6 +495,7 @@ public override FieldInfo[] GetFields(BindingFlags bindingFlags)
             return RuntimeType.GetField(name, bindingAttr);
         }
 
+        [RequiresUnreferencedCode("Methods might be removed")]
         public override MethodInfo[] GetMethods(BindingFlags bindingFlags)
         {
             if (RuntimeType == null)
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs
index 513a96b668cfbf..016d9502d694ec 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs
@@ -5,6 +5,7 @@
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices.ComTypes;
+using System.Runtime.Versioning;
 using System.StubHelpers;
 
 namespace System.Runtime.InteropServices
@@ -306,6 +307,7 @@ public static IntPtr ReAllocHGlobal(IntPtr pv, IntPtr cb)
         /// <summary>
         /// Given a managed object that wraps an ITypeInfo, return its name.
         /// </summary>
+        [SupportedOSPlatform("windows")]
         public static string GetTypeInfoName(ITypeInfo typeInfo)
         {
             if (typeInfo is null)
@@ -319,12 +321,14 @@ public static string GetTypeInfoName(ITypeInfo typeInfo)
 
         // This method is identical to Type.GetTypeFromCLSID. Since it's interop specific, we expose it
         // on Marshal for more consistent API surface.
+        [SupportedOSPlatform("windows")]
         public static Type? GetTypeFromCLSID(Guid clsid) => RuntimeType.GetTypeFromCLSIDImpl(clsid, null, throwOnError: false);
 
         /// <summary>
         /// Return the IUnknown* for an Object if the current context is the one
         /// where the RCW was first seen. Will return null otherwise.
         /// </summary>
+        [SupportedOSPlatform("windows")]
         public static IntPtr /* IUnknown* */ GetIUnknownForObject(object o)
         {
             if (o is null)
@@ -348,6 +352,7 @@ public static string GetTypeInfoName(ITypeInfo typeInfo)
         /// <summary>
         /// Return the IDispatch* for an Object.
         /// </summary>
+        [SupportedOSPlatform("windows")]
         public static IntPtr /* IDispatch */ GetIDispatchForObject(object o)
         {
             if (o is null)
@@ -365,6 +370,7 @@ public static string GetTypeInfoName(ITypeInfo typeInfo)
         /// Return the IUnknown* representing the interface for the Object.
         /// Object o should support Type T
         /// </summary>
+        [SupportedOSPlatform("windows")]
         public static IntPtr /* IUnknown* */ GetComInterfaceForObject(object o, Type T)
         {
             if (o is null)
@@ -380,6 +386,7 @@ public static string GetTypeInfoName(ITypeInfo typeInfo)
             return GetComInterfaceForObjectNative(o, T, false, true);
         }
 
+        [SupportedOSPlatform("windows")]
         public static IntPtr GetComInterfaceForObject<T, TInterface>([DisallowNull] T o) => GetComInterfaceForObject(o!, typeof(TInterface));
 
         /// <summary>
@@ -387,6 +394,7 @@ public static string GetTypeInfoName(ITypeInfo typeInfo)
         /// Object o should support Type T, it refer the value of mode to
         /// invoke customized QueryInterface or not.
         /// </summary>
+        [SupportedOSPlatform("windows")]
         public static IntPtr /* IUnknown* */ GetComInterfaceForObject(object o, Type T, CustomQueryInterfaceMode mode)
         {
             if (o is null)
@@ -409,6 +417,7 @@ public static string GetTypeInfoName(ITypeInfo typeInfo)
         /// <summary>
         /// Return the managed object representing the IUnknown*
         /// </summary>
+        [SupportedOSPlatform("windows")]
         public static object GetObjectForIUnknown(IntPtr /* IUnknown* */ pUnk)
         {
             if (pUnk == IntPtr.Zero)
@@ -422,6 +431,7 @@ public static object GetObjectForIUnknown(IntPtr /* IUnknown* */ pUnk)
         [MethodImpl(MethodImplOptions.InternalCall)]
         private static extern object GetObjectForIUnknownNative(IntPtr /* IUnknown* */ pUnk);
 
+        [SupportedOSPlatform("windows")]
         public static object GetUniqueObjectForIUnknown(IntPtr unknown)
         {
             if (unknown == IntPtr.Zero)
@@ -445,12 +455,15 @@ public static object GetUniqueObjectForIUnknown(IntPtr unknown)
         /// Return an Object for IUnknown, using the Type T.
         /// Type T should be either a COM imported Type or a sub-type of COM imported Type
         /// </summary>
+        [SupportedOSPlatform("windows")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern object GetTypedObjectForIUnknown(IntPtr /* IUnknown* */ pUnk, Type t);
 
+        [SupportedOSPlatform("windows")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern IntPtr CreateAggregatedObject(IntPtr pOuter, object o);
 
+        [SupportedOSPlatform("windows")]
         public static IntPtr CreateAggregatedObject<T>(IntPtr pOuter, T o) where T : notnull
         {
             return CreateAggregatedObject(pOuter, (object)o);
@@ -549,6 +562,7 @@ public static string PtrToStringBSTR(IntPtr ptr)
         /// Release the COM component and if the reference hits 0 zombie this object.
         /// Further usage of this Object might throw an exception
         /// </summary>
+        [SupportedOSPlatform("windows")]
         public static int ReleaseComObject(object o)
         {
             if (o is null)
@@ -571,6 +585,7 @@ public static int ReleaseComObject(object o)
         /// Release the COM component and zombie this object.
         /// Further usage of this Object might throw an exception
         /// </summary>
+        [SupportedOSPlatform("windows")]
         public static int FinalReleaseComObject(object o)
         {
             if (o is null)
@@ -589,6 +604,7 @@ public static int FinalReleaseComObject(object o)
         [MethodImpl(MethodImplOptions.InternalCall)]
         internal static extern void InternalFinalReleaseComObject(object o);
 
+        [SupportedOSPlatform("windows")]
         public static object? GetComObjectData(object obj, object key)
         {
             if (obj is null)
@@ -614,6 +630,7 @@ public static int FinalReleaseComObject(object o)
         /// false if the data could not be added because there already was data for the
         /// specified key.
         /// </summary>
+        [SupportedOSPlatform("windows")]
         public static bool SetComObjectData(object obj, object key, object? data)
         {
             if (obj is null)
@@ -637,6 +654,7 @@ public static bool SetComObjectData(object obj, object key, object? data)
         /// This method takes the given COM object and wraps it in an object
         /// of the specified type. The type must be derived from __ComObject.
         /// </summary>
+        [SupportedOSPlatform("windows")]
         [return: NotNullIfNotNull("o")]
         public static object? CreateWrapperOfType(object? o, Type t)
         {
@@ -687,7 +705,8 @@ public static bool SetComObjectData(object obj, object key, object? data)
             return Wrapper;
         }
 
-        public static TWrapper CreateWrapperOfType<T, TWrapper>([AllowNull] T o)
+        [SupportedOSPlatform("windows")]
+        public static TWrapper CreateWrapperOfType<T, TWrapper>(T? o)
         {
             return (TWrapper)CreateWrapperOfType(o, typeof(TWrapper))!;
         }
@@ -701,35 +720,62 @@ public static TWrapper CreateWrapperOfType<T, TWrapper>([AllowNull] T o)
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern bool IsTypeVisibleFromCom(Type t);
 
-        [MethodImpl(MethodImplOptions.InternalCall)]
-        public static extern int /* HRESULT */ QueryInterface(IntPtr /* IUnknown */ pUnk, ref Guid iid, out IntPtr ppv);
+        [SupportedOSPlatform("windows")]
+        public static unsafe int QueryInterface(IntPtr pUnk, ref Guid iid, out IntPtr ppv)
+        {
+            if (pUnk == IntPtr.Zero)
+                throw new ArgumentNullException(nameof(pUnk));
 
-        [MethodImpl(MethodImplOptions.InternalCall)]
-        public static extern int /* ULONG */ AddRef(IntPtr /* IUnknown */ pUnk);
+            fixed (Guid* pIID = &iid)
+            fixed (IntPtr* p = &ppv)
+            {
+                return ((delegate * stdcall <IntPtr, Guid*, IntPtr*, int>)(*(*(void***)pUnk + 0 /* IUnknown.QueryInterface slot */)))(pUnk, pIID, p);
+            }
+        }
 
-        [MethodImpl(MethodImplOptions.InternalCall)]
-        public static extern int /* ULONG */ Release(IntPtr /* IUnknown */ pUnk);
+        [SupportedOSPlatform("windows")]
+        public static unsafe int AddRef(IntPtr pUnk)
+        {
+            if (pUnk == IntPtr.Zero)
+                throw new ArgumentNullException(nameof(pUnk));
+
+            return ((delegate * stdcall <IntPtr, int>)(*(*(void***)pUnk + 1 /* IUnknown.AddRef slot */)))(pUnk);
+        }
+
+        [SupportedOSPlatform("windows")]
+        public static unsafe int Release(IntPtr pUnk)
+        {
+            if (pUnk == IntPtr.Zero)
+                throw new ArgumentNullException(nameof(pUnk));
+
+            return ((delegate * stdcall <IntPtr, int>)(*(*(void***)pUnk + 2 /* IUnknown.Release slot */)))(pUnk);
+        }
 
+        [SupportedOSPlatform("windows")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern void GetNativeVariantForObject(object? obj, /* VARIANT * */ IntPtr pDstNativeVariant);
 
-        public static void GetNativeVariantForObject<T>([AllowNull] T obj, IntPtr pDstNativeVariant)
+        [SupportedOSPlatform("windows")]
+        public static void GetNativeVariantForObject<T>(T? obj, IntPtr pDstNativeVariant)
         {
             GetNativeVariantForObject((object?)obj, pDstNativeVariant);
         }
 
+        [SupportedOSPlatform("windows")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern object? GetObjectForNativeVariant(/* VARIANT * */ IntPtr pSrcNativeVariant);
 
-        [return: MaybeNull]
-        public static T GetObjectForNativeVariant<T>(IntPtr pSrcNativeVariant)
+        [SupportedOSPlatform("windows")]
+        public static T? GetObjectForNativeVariant<T>(IntPtr pSrcNativeVariant)
         {
-            return (T)GetObjectForNativeVariant(pSrcNativeVariant)!;
+            return (T?)GetObjectForNativeVariant(pSrcNativeVariant);
         }
 
+        [SupportedOSPlatform("windows")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern object?[] GetObjectsForNativeVariants(/* VARIANT * */ IntPtr aSrcNativeVariant, int cVars);
 
+        [SupportedOSPlatform("windows")]
         public static T[] GetObjectsForNativeVariants<T>(IntPtr aSrcNativeVariant, int cVars)
         {
             object?[] objects = GetObjectsForNativeVariants(aSrcNativeVariant, cVars);
@@ -744,15 +790,18 @@ public static T[] GetObjectsForNativeVariants<T>(IntPtr aSrcNativeVariant, int c
         /// <para>Returns the first valid COM slot that GetMethodInfoForSlot will work on
         /// This will be 3 for IUnknown based interfaces and 7 for IDispatch based interfaces. </para>
         /// </summary>
+        [SupportedOSPlatform("windows")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern int GetStartComSlot(Type t);
 
         /// <summary>
         /// <para>Returns the last valid COM slot that GetMethodInfoForSlot will work on. </para>
         /// </summary>
+        [SupportedOSPlatform("windows")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern int GetEndComSlot(Type t);
 
+        [SupportedOSPlatform("windows")]
         public static object BindToMoniker(string monikerName)
         {
             CreateBindCtx(0, out IBindCtx bindctx);
@@ -772,6 +821,7 @@ public static object BindToMoniker(string monikerName)
         [DllImport(Interop.Libraries.Ole32, PreserveSig = false)]
         private static extern void BindMoniker(IMoniker pmk, uint grfOpt, ref Guid iidResult, [MarshalAs(UnmanagedType.Interface)] out object ppvResult);
 
+        [SupportedOSPlatform("windows")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern void ChangeWrapperHandleStrength(object otp, bool fIsWeak);
 #endif // FEATURE_COMINTEROP
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.CoreCLR.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.CoreCLR.cs
new file mode 100644
index 00000000000000..e523487f0d6b65
--- /dev/null
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.CoreCLR.cs
@@ -0,0 +1,14 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace System.Runtime.Intrinsics.X86
+{
+    public abstract partial class X86Base
+    {
+        [DllImport(RuntimeHelpers.QCall)]
+        private static extern unsafe void __cpuidex(int* cpuInfo, int functionId, int subFunctionId);
+    }
+}
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/Versioning/CompatibilitySwitch.cs b/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/Versioning/CompatibilitySwitch.cs
index 3b69f789e61c68..d90f81d48e986d 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/Versioning/CompatibilitySwitch.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/Versioning/CompatibilitySwitch.cs
@@ -7,24 +7,7 @@ namespace System.Runtime.Versioning
 {
     internal static class CompatibilitySwitch
     {
-        /* This class contains 3 sets of api:
-                * 1. internal apis : These apis are supposed to be used by mscorlib.dll and other assemblies which use the <runtime> section in config
-                *                          These apis query for the value of quirk not only in windows quirk DB but also in runtime section of config files,
-                *                          registry and environment vars.
-                * 2. public apis : These apis are supposed to be used by FX assemblies which do not read the runtime section of config files and have
-                *                       have their own section in config files or do not use configs at all.
-                *
-                * 3. specialized apis: These apis are defined in order to retrieve a specific value defined in CLR Config. That value can have specific look-up rules
-                *                        for the order and location of the config sources used.
-                *
-                *     These apis are for internal use only for FX assemblies. It has not been decided if they can be used by OOB components due to EULA restrictions
-                */
-        internal static string? GetValueInternal(string compatibilitySwitchName)
-        {
-            return GetValueInternalCall(compatibilitySwitchName, false);
-        }
-
         [MethodImpl(MethodImplOptions.InternalCall)]
-        private static extern string? GetValueInternalCall(string compatibilitySwitchName, bool onlyDB);
+        internal static extern string? GetValueInternal(string compatibilitySwitchName);
     }
 }
diff --git a/src/coreclr/src/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs b/src/coreclr/src/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs
index f4e9ac9829664a..0dbfbf7f0c6193 100644
--- a/src/coreclr/src/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs
+++ b/src/coreclr/src/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs
@@ -234,6 +234,48 @@ internal MemberInfoCache(RuntimeTypeCache runtimeTypeCache)
 
                 internal MethodBase AddMethod(RuntimeType declaringType, RuntimeMethodHandleInternal method, CacheType cacheType)
                 {
+                    // First, see if we've already cached an RuntimeMethodInfo or
+                    // RuntimeConstructorInfo that corresponds to this member. Since another
+                    // thread could be updating the backing store at the same time it's
+                    // possible that the check below will result in a false negative. That's
+                    // ok; we'll handle any concurrency issues in the later call to Insert.
+
+                    T?[]? allMembersLocal = m_allMembers;
+                    if (allMembersLocal != null)
+                    {
+                        // if not a Method or a Constructor, fall through
+                        if (cacheType == CacheType.Method)
+                        {
+                            foreach (T? candidate in allMembersLocal)
+                            {
+                                if (candidate is null)
+                                {
+                                    break; // end of list; stop iteration and fall through to slower path
+                                }
+
+                                if (candidate is RuntimeMethodInfo candidateRMI && candidateRMI.MethodHandle.Value == method.Value)
+                                {
+                                    return candidateRMI; // match!
+                                }
+                            }
+                        }
+                        else if (cacheType == CacheType.Constructor)
+                        {
+                            foreach (T? candidate in allMembersLocal)
+                            {
+                                if (candidate is null)
+                                {
+                                    break; // end of list; stop iteration and fall through to slower path
+                                }
+
+                                if (candidate is RuntimeConstructorInfo candidateRCI && candidateRCI.MethodHandle.Value == method.Value)
+                                {
+                                    return candidateRCI; // match!
+                                }
+                            }
+                        }
+                    }
+
                     T[] list = null!;
                     MethodAttributes methodAttributes = RuntimeMethodHandle.GetAttributes(method);
                     bool isPublic = (methodAttributes & MethodAttributes.MemberAccessMask) == MethodAttributes.Public;
@@ -264,6 +306,29 @@ internal MethodBase AddMethod(RuntimeType declaringType, RuntimeMethodHandleInte
 
                 internal FieldInfo AddField(RuntimeFieldHandleInternal field)
                 {
+                    // First, see if we've already cached an RtFieldInfo that corresponds
+                    // to this field. Since another thread could be updating the backing
+                    // store at the same time it's possible that the check below will
+                    // result in a false negative. That's ok; we'll handle any concurrency
+                    // issues in the later call to Insert.
+
+                    T?[]? allMembersLocal = m_allMembers;
+                    if (allMembersLocal != null)
+                    {
+                        foreach (T? candidate in allMembersLocal)
+                        {
+                            if (candidate is null)
+                            {
+                                break; // end of list; stop iteration and fall through to slower path
+                            }
+
+                            if (candidate is RtFieldInfo candidateRtFI && candidateRtFI.GetFieldHandle() == field.Value)
+                            {
+                                return candidateRtFI; // match!
+                            }
+                        }
+                    }
+
                     // create the runtime field info
                     FieldAttributes fieldAttributes = RuntimeFieldHandle.GetAttributes(field);
                     bool isPublic = (fieldAttributes & FieldAttributes.FieldAccessMask) == FieldAttributes.Public;
@@ -507,7 +572,7 @@ private void MergeWithGlobalList(T[] list)
                             }
 
                             Debug.Assert(cachedMembers![freeSlotIndex] == null);
-                            cachedMembers[freeSlotIndex] = newMemberInfo;
+                            Volatile.Write(ref cachedMembers[freeSlotIndex], newMemberInfo); // value may be read outside of lock
                             freeSlotIndex++;
                         }
                     }
@@ -2532,26 +2597,31 @@ private ListBuilder<Type> GetNestedTypeCandidates(string? fullname, BindingFlags
         #endregion
 
         #region Get All XXXInfos
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
         {
             return GetMethodCandidates(null, GenericParameterCountAny, bindingAttr, CallingConventions.Any, null, false).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
         {
             return GetConstructorCandidates(null, bindingAttr, CallingConventions.Any, null, false).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr)
         {
             return GetPropertyCandidates(null, bindingAttr, null, false).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr)
         {
             return GetEventCandidates(null, bindingAttr, false).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr)
         {
             return GetFieldCandidates(null, bindingAttr, false).ToArray();
@@ -2563,11 +2633,13 @@ public override Type[] GetInterfaces()
             return new ReadOnlySpan<Type>(candidates).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr)
         {
             return GetNestedTypeCandidates(null, bindingAttr, false).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
         {
             ListBuilder<MethodInfo> methods = GetMethodCandidates(null, GenericParameterCountAny, bindingAttr, CallingConventions.Any, null, false);
@@ -2663,6 +2735,7 @@ public override InterfaceMapping GetInterfaceMap(Type ifaceType)
 
         #region Find XXXInfo
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo? GetMethodImpl(
             string name, BindingFlags bindingAttr, Binder? binder, CallingConventions callConv,
             Type[]? types, ParameterModifier[]? modifiers)
@@ -2670,6 +2743,7 @@ public override InterfaceMapping GetInterfaceMap(Type ifaceType)
             return GetMethodImplCommon(name, GenericParameterCountAny, bindingAttr, binder, callConv, types, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo? GetMethodImpl(
             string name, int genericParameterCount, BindingFlags bindingAttr, Binder? binder, CallingConventions callConv,
             Type[]? types, ParameterModifier[]? modifiers)
@@ -2714,6 +2788,7 @@ public override InterfaceMapping GetInterfaceMap(Type ifaceType)
             return binder.SelectMethod(bindingAttr, candidates.ToArray(), types, modifiers) as MethodInfo;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo? GetConstructorImpl(
             BindingFlags bindingAttr, Binder? binder, CallingConventions callConvention,
             Type[] types, ParameterModifier[]? modifiers)
@@ -2741,6 +2816,7 @@ public override InterfaceMapping GetInterfaceMap(Type ifaceType)
             return binder.SelectMethod(bindingAttr, candidates.ToArray(), types, modifiers) as ConstructorInfo;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo? GetPropertyImpl(
             string name, BindingFlags bindingAttr, Binder? binder, Type? returnType, Type[]? types, ParameterModifier[]? modifiers)
         {
@@ -2778,6 +2854,7 @@ public override InterfaceMapping GetInterfaceMap(Type ifaceType)
             return binder.SelectProperty(bindingAttr, candidates.ToArray(), returnType, types, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo? GetEvent(string name, BindingFlags bindingAttr)
         {
             if (name is null) throw new ArgumentNullException(nameof(name));
@@ -2804,6 +2881,7 @@ public override InterfaceMapping GetInterfaceMap(Type ifaceType)
             return match;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo? GetField(string name, BindingFlags bindingAttr)
         {
             if (name is null) throw new ArgumentNullException();
@@ -2875,6 +2953,7 @@ public override InterfaceMapping GetInterfaceMap(Type ifaceType)
             return match;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type? GetNestedType(string fullname, BindingFlags bindingAttr)
         {
             if (fullname is null) throw new ArgumentNullException(nameof(fullname));
@@ -2903,6 +2982,7 @@ public override InterfaceMapping GetInterfaceMap(Type ifaceType)
             return match;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr)
         {
             if (name is null) throw new ArgumentNullException(nameof(name));
diff --git a/src/coreclr/src/ToolBox/SOS/DacTableGen/CMakeLists.txt b/src/coreclr/src/ToolBox/SOS/DacTableGen/CMakeLists.txt
index e3fc3ed9e3a5e1..98cc178b8a3005 100644
--- a/src/coreclr/src/ToolBox/SOS/DacTableGen/CMakeLists.txt
+++ b/src/coreclr/src/ToolBox/SOS/DacTableGen/CMakeLists.txt
@@ -1,3 +1,4 @@
+cmake_minimum_required(VERSION 3.8)
 # Quick note: The CMake C# support is using the CSC bundled with the MSBuild that the native build runs on, not the one supplied by the local .NET SDK.
 
 project(DacTableGen LANGUAGES CSharp)
diff --git a/src/coreclr/src/binder/CMakeLists.txt b/src/coreclr/src/binder/CMakeLists.txt
index 9c242ed1518df0..208f1214dd0da5 100644
--- a/src/coreclr/src/binder/CMakeLists.txt
+++ b/src/coreclr/src/binder/CMakeLists.txt
@@ -82,11 +82,13 @@ endif(CLR_CMAKE_TARGET_WIN32)
 convert_to_absolute_path(BINDER_SOURCES ${BINDER_SOURCES})
 convert_to_absolute_path(BINDER_CROSSGEN_SOURCES ${BINDER_CROSSGEN_SOURCES})
 
-add_library_clr(v3binder
+add_library_clr(v3binder_obj
     OBJECT
     ${BINDER_SOURCES}
 )
-add_dependencies(v3binder eventing_headers)
+add_dependencies(v3binder_obj eventing_headers)
+add_library(v3binder INTERFACE)
+target_sources(v3binder INTERFACE $<TARGET_OBJECTS:v3binder_obj>)
 
 add_library_clr(v3binder_crossgen
     STATIC
diff --git a/src/coreclr/src/binder/assemblybinder.cpp b/src/coreclr/src/binder/assemblybinder.cpp
index 5f13adc7b2c826..02a3646dab4a16 100644
--- a/src/coreclr/src/binder/assemblybinder.cpp
+++ b/src/coreclr/src/binder/assemblybinder.cpp
@@ -447,25 +447,25 @@ namespace BINDER_SPACE
         // Satellite assembly's path:
         //   * Absolute path when looking for a file on disk
         //   * Bundle-relative path when looking within the single-file bundle.
-        StackSString sMscorlibSatellite;
+        StackSString sCoreLibSatellite;
 
         BinderTracing::PathSource pathSource = BinderTracing::PathSource::Bundle;
         BundleFileLocation bundleFileLocation = Bundle::ProbeAppBundle(relativePath, /*pathIsBundleRelative */ true);
         if (!bundleFileLocation.IsValid())
         {
-            sMscorlibSatellite.Set(systemDirectory);
+            sCoreLibSatellite.Set(systemDirectory);
             pathSource = BinderTracing::PathSource::ApplicationAssemblies;
         }
-        CombinePath(sMscorlibSatellite, relativePath, sMscorlibSatellite);
+        CombinePath(sCoreLibSatellite, relativePath, sCoreLibSatellite);
 
         ReleaseHolder<Assembly> pSystemAssembly;
-        IF_FAIL_GO(AssemblyBinder::GetAssembly(sMscorlibSatellite,
+        IF_FAIL_GO(AssemblyBinder::GetAssembly(sCoreLibSatellite,
                                                TRUE /* fIsInGAC */,
                                                FALSE /* fExplicitBindToNativeImage */,
                                                &pSystemAssembly,
                                                NULL /* szMDAssemblyPath */,
                                                bundleFileLocation));
-        BinderTracing::PathProbed(sMscorlibSatellite, pathSource, hr);
+        BinderTracing::PathProbed(sCoreLibSatellite, pathSource, hr);
 
         *ppSystemAssembly = pSystemAssembly.Extract();
 
diff --git a/src/coreclr/src/binder/assemblyname.cpp b/src/coreclr/src/binder/assemblyname.cpp
index b073dc66f88b1d..71e70283c0b313 100644
--- a/src/coreclr/src/binder/assemblyname.cpp
+++ b/src/coreclr/src/binder/assemblyname.cpp
@@ -315,10 +315,10 @@ namespace BINDER_SPACE
         return ulRef;
     }
 
-    BOOL AssemblyName::IsMscorlib()
+    BOOL AssemblyName::IsCoreLib()
     {
         // TODO: Is this simple comparison enough?
-        return EqualsCaseInsensitive(GetSimpleName(), g_BinderVariables->mscorlib);
+        return EqualsCaseInsensitive(GetSimpleName(), g_BinderVariables->corelib);
     }
 
     ULONG AssemblyName::Hash(DWORD dwIncludeFlags)
diff --git a/src/coreclr/src/binder/bindertracing.cpp b/src/coreclr/src/binder/bindertracing.cpp
index 2e5c83d7b09bd2..29ba819ee6c9e7 100644
--- a/src/coreclr/src/binder/bindertracing.cpp
+++ b/src/coreclr/src/binder/bindertracing.cpp
@@ -216,14 +216,14 @@ namespace BinderTracing
 
     AssemblyBindOperation::~AssemblyBindOperation()
     {
-        if (!BinderTracing::IsEnabled() || ShouldIgnoreBind())
-            return;
-
-        // Make sure the bind request is populated. Tracing may have been enabled mid-bind.
-        if (!m_populatedBindRequest)
-            PopulateBindRequest(m_bindRequest);
+        if (BinderTracing::IsEnabled() && !ShouldIgnoreBind())
+        {
+            // Make sure the bind request is populated. Tracing may have been enabled mid-bind.
+            if (!m_populatedBindRequest)
+                PopulateBindRequest(m_bindRequest);
 
-        FireAssemblyLoadStop(m_bindRequest, m_resultAssembly, m_cached);
+            FireAssemblyLoadStop(m_bindRequest, m_resultAssembly, m_cached);
+        }
 
         if (m_resultAssembly != nullptr)
             m_resultAssembly->Release();
@@ -246,7 +246,7 @@ namespace BinderTracing
 
         // ActivityTracker or EventSource may have triggered the system satellite load.
         // Don't track system satellite binding to avoid potential infinite recursion.
-        m_ignoreBind = m_bindRequest.AssemblySpec->IsMscorlibSatellite();
+        m_ignoreBind = m_bindRequest.AssemblySpec->IsCoreLibSatellite();
         m_checkedIgnoreBind = true;
         return m_ignoreBind;
     }
diff --git a/src/coreclr/src/binder/clrprivbinderassemblyloadcontext.cpp b/src/coreclr/src/binder/clrprivbinderassemblyloadcontext.cpp
index f492adfab28b45..69d8d83372893e 100644
--- a/src/coreclr/src/binder/clrprivbinderassemblyloadcontext.cpp
+++ b/src/coreclr/src/binder/clrprivbinderassemblyloadcontext.cpp
@@ -20,8 +20,8 @@ HRESULT CLRPrivBinderAssemblyLoadContext::BindAssemblyByNameWorker(BINDER_SPACE:
     HRESULT hr = S_OK;
 
 #ifdef _DEBUG
-    // MSCORLIB should be bound using BindToSystem
-    _ASSERTE(!pAssemblyName->IsMscorlib());
+    // CoreLib should be bound using BindToSystem
+    _ASSERTE(!pAssemblyName->IsCoreLib());
 #endif
 
     // Do we have the assembly already loaded in the context of the current binder?
@@ -145,7 +145,7 @@ HRESULT CLRPrivBinderAssemblyLoadContext::BindUsingPEImage( /* in */ PEImage *pP
 
         // Disallow attempt to bind to the core library. Aside from that,
         // the LoadContext can load any assembly (even if it was in a different LoadContext like TPA).
-        if (pAssemblyName->IsMscorlib())
+        if (pAssemblyName->IsCoreLib())
         {
             IF_FAIL_GO(HRESULT_FROM_WIN32(ERROR_FILE_NOT_FOUND));
         }
diff --git a/src/coreclr/src/binder/clrprivbindercoreclr.cpp b/src/coreclr/src/binder/clrprivbindercoreclr.cpp
index 1045cb93e76da5..292ad99fd85543 100644
--- a/src/coreclr/src/binder/clrprivbindercoreclr.cpp
+++ b/src/coreclr/src/binder/clrprivbindercoreclr.cpp
@@ -20,8 +20,8 @@ HRESULT CLRPrivBinderCoreCLR::BindAssemblyByNameWorker(BINDER_SPACE::AssemblyNam
     HRESULT hr = S_OK;
 
 #ifdef _DEBUG
-    // MSCORLIB should be bound using BindToSystem
-    _ASSERTE(!pAssemblyName->IsMscorlib());
+    // CoreLib should be bound using BindToSystem
+    _ASSERTE(!pAssemblyName->IsCoreLib());
 #endif
 
     hr = AssemblyBinder::BindAssembly(&m_appContext,
@@ -155,8 +155,8 @@ HRESULT CLRPrivBinderCoreCLR::BindUsingPEImage( /* in */ PEImage *pPEImage,
             IF_FAIL_GO(HRESULT_FROM_WIN32(ERROR_BAD_FORMAT));
         }
 
-        // Easy out for mscorlib
-        if (pAssemblyName->IsMscorlib())
+        // Easy out for CoreLib
+        if (pAssemblyName->IsCoreLib())
         {
             IF_FAIL_GO(HRESULT_FROM_WIN32(ERROR_FILE_NOT_FOUND));
         }
diff --git a/src/coreclr/src/binder/inc/assemblyname.hpp b/src/coreclr/src/binder/inc/assemblyname.hpp
index 38590e09f78a6b..fb66d9830e0a3a 100644
--- a/src/coreclr/src/binder/inc/assemblyname.hpp
+++ b/src/coreclr/src/binder/inc/assemblyname.hpp
@@ -65,7 +65,7 @@ namespace BINDER_SPACE
 
         inline void SetHave(DWORD dwIdentityFlags);
 
-        BOOL IsMscorlib();
+        BOOL IsCoreLib();
 
         ULONG Hash(/* in */ DWORD dwIncludeFlags);
         BOOL Equals(/* in */ AssemblyName *pAssemblyName,
diff --git a/src/coreclr/src/binder/inc/variables.hpp b/src/coreclr/src/binder/inc/variables.hpp
index 50f392d0366ed0..d060a691bbecca 100644
--- a/src/coreclr/src/binder/inc/variables.hpp
+++ b/src/coreclr/src/binder/inc/variables.hpp
@@ -31,7 +31,7 @@ namespace BINDER_SPACE
 
         // AssemblyName string constants
         SString cultureNeutral;
-        SString mscorlib;
+        SString corelib;
     };
 
     extern Variables *g_BinderVariables;
diff --git a/src/coreclr/src/binder/variables.cpp b/src/coreclr/src/binder/variables.cpp
index d9c3f672657de0..fbdd106b4dd2fe 100644
--- a/src/coreclr/src/binder/variables.cpp
+++ b/src/coreclr/src/binder/variables.cpp
@@ -40,7 +40,7 @@ namespace BINDER_SPACE
 
             // AssemblyName string constants
             cultureNeutral.SetLiteral(W("neutral"));
-            mscorlib.SetLiteral(CoreLibName_W);
+            corelib.SetLiteral(CoreLibName_W);
         }
         EX_CATCH_HRESULT(hr);
 
diff --git a/src/coreclr/src/classlibnative/bcltype/CMakeLists.txt b/src/coreclr/src/classlibnative/bcltype/CMakeLists.txt
index c3122ec12ec3d8..fdcf344c16ac56 100644
--- a/src/coreclr/src/classlibnative/bcltype/CMakeLists.txt
+++ b/src/coreclr/src/classlibnative/bcltype/CMakeLists.txt
@@ -10,9 +10,11 @@ set(BCLTYPE_SOURCES
     variant.cpp
 )
 
-add_library_clr(bcltype
+add_library_clr(bcltype_obj
     OBJECT
     ${BCLTYPE_SOURCES}
 )
 
-add_dependencies(bcltype eventing_headers)
+add_dependencies(bcltype_obj eventing_headers)
+add_library(bcltype INTERFACE)
+target_sources(bcltype INTERFACE $<TARGET_OBJECTS:bcltype_obj>)
diff --git a/src/coreclr/src/classlibnative/bcltype/system.cpp b/src/coreclr/src/classlibnative/bcltype/system.cpp
index c037236f695960..6bd072f13ea847 100644
--- a/src/coreclr/src/classlibnative/bcltype/system.cpp
+++ b/src/coreclr/src/classlibnative/bcltype/system.cpp
@@ -607,9 +607,17 @@ BOOL QCALLTYPE SystemNative::WinRTSupported()
 
 #endif // FEATURE_COMINTEROP
 
+#if defined(TARGET_X86) || defined(TARGET_AMD64)
 
+void QCALLTYPE SystemNative::X86BaseCpuId(int cpuInfo[4], int functionId, int subFunctionId)
+{
+    QCALL_CONTRACT;
 
+    BEGIN_QCALL;
 
+    __cpuidex(cpuInfo, functionId, subFunctionId);
 
+    END_QCALL;
+}
 
-
+#endif // defined(TARGET_X86) || defined(TARGET_AMD64)
diff --git a/src/coreclr/src/classlibnative/bcltype/system.h b/src/coreclr/src/classlibnative/bcltype/system.h
index 20d357c17302df..ff6720f0a8c09f 100644
--- a/src/coreclr/src/classlibnative/bcltype/system.h
+++ b/src/coreclr/src/classlibnative/bcltype/system.h
@@ -81,6 +81,10 @@ class SystemNative
     // Return a method info for the method were the exception was thrown
     static FCDECL1(ReflectMethodObject*, GetMethodFromStackTrace, ArrayBase* pStackTraceUNSAFE);
 
+#if defined(TARGET_X86) || defined(TARGET_AMD64)
+    static void QCALLTYPE X86BaseCpuId(int cpuInfo[4], int functionId, int subFunctionId);
+#endif // defined(TARGET_X86) || defined(TARGET_AMD64)
+
 private:
     // Common processing code for FailFast
     static void GenericFailFast(STRINGREF refMesgString, EXCEPTIONREF refExceptionForWatsonBucketing, UINT_PTR retAddress, UINT exitCode, STRINGREF errorSource);
diff --git a/src/coreclr/src/classlibnative/bcltype/varargsnative.cpp b/src/coreclr/src/classlibnative/bcltype/varargsnative.cpp
index fb2c1aefe3c760..3a9ed227cfdd25 100644
--- a/src/coreclr/src/classlibnative/bcltype/varargsnative.cpp
+++ b/src/coreclr/src/classlibnative/bcltype/varargsnative.cpp
@@ -502,7 +502,7 @@ VarArgsNative::GetNextArgHelper(
             value->data = (BYTE*)origArgPtr + (sizeof(void*)-1);
         }
 #endif
-        value->type = MscorlibBinder::GetElementType(elemType);
+        value->type = CoreLibBinder::GetElementType(elemType);
         break;
 
         case ELEMENT_TYPE_I2:
@@ -513,7 +513,7 @@ VarArgsNative::GetNextArgHelper(
             value->data = (BYTE*)origArgPtr + (sizeof(void*)-2);
         }
 #endif
-        value->type = MscorlibBinder::GetElementType(elemType);
+        value->type = CoreLibBinder::GetElementType(elemType);
         break;
 
         case ELEMENT_TYPE_I4:
@@ -522,13 +522,13 @@ VarArgsNative::GetNextArgHelper(
         case ELEMENT_TYPE_STRING:
         case ELEMENT_TYPE_I:
         case ELEMENT_TYPE_U:
-        value->type = MscorlibBinder::GetElementType(elemType);
+        value->type = CoreLibBinder::GetElementType(elemType);
         break;
 
         case ELEMENT_TYPE_I8:
         case ELEMENT_TYPE_U8:
         case ELEMENT_TYPE_R8:
-        value->type = MscorlibBinder::GetElementType(elemType);
+        value->type = CoreLibBinder::GetElementType(elemType);
 #if !defined(HOST_64BIT) && (DATA_ALIGNMENT > 4)
         if ( fData && origArgPtr == value->data ) {
             // allocate an aligned copy of the value
diff --git a/src/coreclr/src/classlibnative/float/CMakeLists.txt b/src/coreclr/src/classlibnative/float/CMakeLists.txt
index 2345ad0b91354b..b2c47ea39b65ea 100644
--- a/src/coreclr/src/classlibnative/float/CMakeLists.txt
+++ b/src/coreclr/src/classlibnative/float/CMakeLists.txt
@@ -7,9 +7,12 @@ set(FLOAT_SOURCES
     floatsingle.cpp
 )
 
-add_library_clr(comfloat_wks
+add_library_clr(comfloat_wks_obj
     OBJECT
     ${FLOAT_SOURCES}
 )
 
-add_dependencies(comfloat_wks eventing_headers)
+add_dependencies(comfloat_wks_obj eventing_headers)
+
+add_library(comfloat_wks INTERFACE)
+target_sources(comfloat_wks INTERFACE $<TARGET_OBJECTS:comfloat_wks_obj>)
\ No newline at end of file
diff --git a/src/coreclr/src/debug/createdump/main.cpp b/src/coreclr/src/debug/createdump/main.cpp
index 626175c2903c09..902ee1a693fa4b 100644
--- a/src/coreclr/src/debug/createdump/main.cpp
+++ b/src/coreclr/src/debug/createdump/main.cpp
@@ -35,10 +35,20 @@ int __cdecl main(const int argc, const char* argv[])
                                                  MiniDumpWithFullMemoryInfo |
                                                  MiniDumpWithThreadInfo |
                                                  MiniDumpWithTokenInformation);
+    const char* dumpType = "minidump with heap";
     const char* dumpPathTemplate = nullptr;
     int exitCode = 0;
     int pid = 0;
 
+#ifdef __APPLE__
+    char* enabled = getenv("COMPlus_DbgEnableElfDumpOnMacOS");
+    if (enabled == nullptr || strcmp(enabled, "1") != 0)
+    {
+        fprintf(stderr, "MachO coredumps are not supported. To enable ELF coredumps on MacOS, set the COMPlus_DbgEnableElfDumpOnMacOS environment variable to 1.\n");
+        return -1;
+    }
+#endif
+
 #ifdef HOST_UNIX
     exitCode = PAL_InitializeDLL();
     if (exitCode != 0)
@@ -60,11 +70,13 @@ int __cdecl main(const int argc, const char* argv[])
             }
             else if ((strcmp(*argv, "-n") == 0) || (strcmp(*argv, "--normal") == 0))
             {
+                dumpType = "minidump";
                 minidumpType = (MINIDUMP_TYPE)(MiniDumpNormal |
                                                MiniDumpWithThreadInfo);
             }
             else if ((strcmp(*argv, "-h") == 0) || (strcmp(*argv, "--withheap") == 0))
             {
+                dumpType = "minidump with heap";
                 minidumpType = (MINIDUMP_TYPE)(MiniDumpWithPrivateReadWriteMemory |
                                                MiniDumpWithDataSegs |
                                                MiniDumpWithHandleData |
@@ -75,11 +87,13 @@ int __cdecl main(const int argc, const char* argv[])
             }
             else if ((strcmp(*argv, "-t") == 0) || (strcmp(*argv, "--triage") == 0))
             {
+                dumpType = "triage minidump";
                 minidumpType = (MINIDUMP_TYPE)(MiniDumpFilterTriage |
                                                MiniDumpWithThreadInfo);
             }
             else if ((strcmp(*argv, "-u") == 0) || (strcmp(*argv, "--full") == 0))
             {
+                dumpType = "full dump";
                 minidumpType = (MINIDUMP_TYPE)(MiniDumpWithFullMemory |
                                                MiniDumpWithDataSegs |
                                                MiniDumpWithHandleData |
@@ -122,24 +136,6 @@ int __cdecl main(const int argc, const char* argv[])
 
         snprintf(dumpPath, MAX_LONGPATH, dumpPathTemplate, pid);
 
-        const char* dumpType = "minidump";
-        switch (minidumpType)
-        {
-            case MiniDumpWithPrivateReadWriteMemory:
-                dumpType = "minidump with heap";
-                break;
-
-            case MiniDumpFilterTriage:
-                dumpType = "triage minidump";
-                break;
-
-            case MiniDumpWithFullMemory:
-                dumpType = "full dump";
-                break;
-
-            default:
-                break;
-        }
         printf("Writing %s to file %s\n", dumpType, (char*)dumpPath);
 
         if (CreateDump(dumpPath, pid, minidumpType))
diff --git a/src/coreclr/src/debug/daccess/daccess.cpp b/src/coreclr/src/debug/daccess/daccess.cpp
index 1e40f07a5c5e2c..e999ec866f7d04 100644
--- a/src/coreclr/src/debug/daccess/daccess.cpp
+++ b/src/coreclr/src/debug/daccess/daccess.cpp
@@ -3293,6 +3293,10 @@ ClrDataAccess::QueryInterface(THIS_
     {
         ifaceRet = static_cast<ISOSDacInterface8*>(this);
     }
+    else if (IsEqualIID(interfaceId, __uuidof(ISOSDacInterface9)))
+    {
+        ifaceRet = static_cast<ISOSDacInterface9*>(this);
+    }
     else
     {
         *iface = NULL;
diff --git a/src/coreclr/src/debug/daccess/dacdbiimpl.cpp b/src/coreclr/src/debug/daccess/dacdbiimpl.cpp
index 4bcd6f2ff4cbe8..c0e0a23f53a330 100644
--- a/src/coreclr/src/debug/daccess/dacdbiimpl.cpp
+++ b/src/coreclr/src/debug/daccess/dacdbiimpl.cpp
@@ -2399,7 +2399,7 @@ TypeHandle DacDbiInterfaceImpl::FindLoadedElementType(CorElementType elementType
     // Lookup operations run the class loader in non-load mode.
     ENABLE_FORBID_GC_LOADER_USE_IN_THIS_SCOPE();
 
-    MethodTable * pMethodTable = (&g_Mscorlib)->GetElementType(elementType);
+    MethodTable * pMethodTable = (&g_CoreLib)->GetElementType(elementType);
 
     return TypeHandle(pMethodTable);
 } // DacDbiInterfaceImpl::FindLoadedElementType
@@ -4272,6 +4272,30 @@ void DacDbiInterfaceImpl::GetModuleSimpleName(VMPTR_Module vmModule, IStringHold
     IfFailThrow(pStrFilename->AssignCopy(convert.GetUnicode()));
 }
 
+HRESULT DacDbiInterfaceImpl::IsModuleMapped(VMPTR_Module pModule, OUT BOOL *isModuleMapped)
+{
+    LOG((LF_CORDB, LL_INFO10000, "DDBII::IMM - TADDR 0x%x\n", pModule));
+    DD_ENTER_MAY_THROW;
+
+    HRESULT hr = S_FALSE;
+    PTR_Module pTargetModule = pModule.GetDacPtr();
+
+    EX_TRY
+    {
+        PTR_PEFile pPEFile = pTargetModule->GetFile();
+        _ASSERTE(pPEFile != NULL);
+
+        if (pPEFile->HasLoadedIL())
+        {
+            *isModuleMapped = pPEFile->GetLoadedIL()->IsMapped();
+            hr = S_OK;
+        }
+    }
+    EX_CATCH_HRESULT(hr);
+
+    return hr;
+}
+
 // Helper to intialize a TargetBuffer from a MemoryRange
 //
 // Arguments:
@@ -7240,7 +7264,7 @@ HRESULT DacDbiInterfaceImpl::GetArrayLayout(COR_TYPEID id, COR_ARRAY_LAYOUT *pLa
     if (mt->IsString())
     {
         COR_TYPEID token;
-        token.token1 = MscorlibBinder::GetElementType(ELEMENT_TYPE_CHAR).GetAddr();
+        token.token1 = CoreLibBinder::GetElementType(ELEMENT_TYPE_CHAR).GetAddr();
         token.token2 = 0;
 
         pLayout->componentID = token;
diff --git a/src/coreclr/src/debug/daccess/dacdbiimpl.h b/src/coreclr/src/debug/daccess/dacdbiimpl.h
index 9178e71736260f..219b51dc77af16 100644
--- a/src/coreclr/src/debug/daccess/dacdbiimpl.h
+++ b/src/coreclr/src/debug/daccess/dacdbiimpl.h
@@ -363,6 +363,8 @@ class DacDbiInterfaceImpl :
 
     HRESULT GetLoaderHeapMemoryRanges(OUT DacDbiArrayList<COR_MEMORY_RANGE> * pRanges);
 
+    HRESULT IsModuleMapped(VMPTR_Module pModule, OUT BOOL *isModuleMapped);
+
     // retrieves the list of COM interfaces implemented by vmObject, as it is known at
     // the time of the call (the list may change as new interface types become available
     // in the runtime)
diff --git a/src/coreclr/src/debug/daccess/dacimpl.h b/src/coreclr/src/debug/daccess/dacimpl.h
index efbd19da6f1a58..c0809924bc3e1d 100644
--- a/src/coreclr/src/debug/daccess/dacimpl.h
+++ b/src/coreclr/src/debug/daccess/dacimpl.h
@@ -840,7 +840,8 @@ class ClrDataAccess
       public ISOSDacInterface5,
       public ISOSDacInterface6,
       public ISOSDacInterface7,
-      public ISOSDacInterface8
+      public ISOSDacInterface8,
+      public ISOSDacInterface9
 {
 public:
     ClrDataAccess(ICorDebugDataTarget * pTarget, ICLRDataTarget * pLegacyTarget=0);
@@ -1205,6 +1206,9 @@ class ClrDataAccess
 
     virtual HRESULT STDMETHODCALLTYPE GetAssemblyLoadContext(CLRDATA_ADDRESS methodTable, CLRDATA_ADDRESS* assemblyLoadContext);
 
+    // ISOSDacInterface9
+    virtual HRESULT STDMETHODCALLTYPE GetBreakingChangeVersion(int* pVersion);
+
     //
     // ClrDataAccess.
     //
diff --git a/src/coreclr/src/debug/daccess/enummem.cpp b/src/coreclr/src/debug/daccess/enummem.cpp
index 95909b89e3f8d4..a746aa46b3d13d 100644
--- a/src/coreclr/src/debug/daccess/enummem.cpp
+++ b/src/coreclr/src/debug/daccess/enummem.cpp
@@ -276,7 +276,7 @@ HRESULT ClrDataAccess::EnumMemCLRStatic(IN CLRDataEnumMemoryFlags flags)
     }
     CATCH_ALL_EXCEPT_RETHROW_COR_E_OPERATIONCANCELLED( g_pEEDbgInterfaceImpl.EnumMem(); )
     CATCH_ALL_EXCEPT_RETHROW_COR_E_OPERATIONCANCELLED( g_CORDebuggerControlFlags.EnumMem(); )
-    CATCH_ALL_EXCEPT_RETHROW_COR_E_OPERATIONCANCELLED( g_Mscorlib.EnumMem(); )
+    CATCH_ALL_EXCEPT_RETHROW_COR_E_OPERATIONCANCELLED( g_CoreLib.EnumMem(); )
     CATCH_ALL_EXCEPT_RETHROW_COR_E_OPERATIONCANCELLED( g_pPredefinedArrayTypes[ELEMENT_TYPE_OBJECT].EnumMemoryRegions(flags); )
     CATCH_ALL_EXCEPT_RETHROW_COR_E_OPERATIONCANCELLED( StubManager::EnumMemoryRegions(flags); )
     CATCH_ALL_EXCEPT_RETHROW_COR_E_OPERATIONCANCELLED( g_pFinalizerThread.EnumMem(); )
diff --git a/src/coreclr/src/debug/daccess/inspect.cpp b/src/coreclr/src/debug/daccess/inspect.cpp
index 75cfcc3cadcea2..28375862bd38a9 100644
--- a/src/coreclr/src/debug/daccess/inspect.cpp
+++ b/src/coreclr/src/debug/daccess/inspect.cpp
@@ -136,7 +136,7 @@ GetTypeFieldValueFlags(TypeHandle typeHandle,
         // Perform extra checks to identify well-known classes.
         //
 
-        if ((&g_Mscorlib)->IsClass(typeHandle.GetMethodTable(), CLASS__STRING))
+        if ((&g_CoreLib)->IsClass(typeHandle.GetMethodTable(), CLASS__STRING))
         {
             otherFlags |= CLRDATA_VALUE_IS_STRING;
         }
diff --git a/src/coreclr/src/debug/daccess/nidump.cpp b/src/coreclr/src/debug/daccess/nidump.cpp
index 5a0bbfd81006f4..b385e278d69842 100644
--- a/src/coreclr/src/debug/daccess/nidump.cpp
+++ b/src/coreclr/src/debug/daccess/nidump.cpp
@@ -477,7 +477,7 @@ NativeImageDumper::NativeImageDumper(PTR_VOID loadedBase,
     m_dis(dis),
     m_MetadataSize(0),
     m_ILHostCopy(NULL),
-    m_isMscorlibHardBound(false),
+    m_isCoreLibHardBound(false),
     m_sectionAlignment(0)
 {
     IfFailThrow(m_display->GetDumpOptions(&m_dumpOptions));
@@ -1132,54 +1132,54 @@ NativeImageDumper::DumpNativeImage()
 
         /* XXX Wed 12/14/2005
          * Now for the real insanity.  I need to initialize static classes in
-         * the DAC.  First I need to find mscorlib's dependency entry.  Search
+         * the DAC.  First I need to find CoreLib's dependency entry.  Search
          * through all of the dependencies to find the one marked as
-         * fIsMscorlib.  If I don't find anything marked that way, then "self"
-         * is mscorlib.
+         * fIsCoreLib.  If I don't find anything marked that way, then "self"
+         * is CoreLib.
          */
-        Dependency * mscorlib = NULL;
+        Dependency * corelib = NULL;
         for( COUNT_T i = 0; i < m_numDependencies; ++i )
         {
-            if( m_dependencies[i].fIsMscorlib )
+            if( m_dependencies[i].fIsCoreLib )
             {
-                mscorlib = &m_dependencies[i];
+                corelib = &m_dependencies[i];
                 break;
             }
         }
 
-        //If we're actually dumping mscorlib, remap the mscorlib dependency to our own native image.
-        if( (mscorlib == NULL) || !wcscmp(m_name, CoreLibName_W))
+        //If we're actually dumping CoreLib, remap the CoreLib dependency to our own native image.
+        if( (corelib == NULL) || !wcscmp(m_name, CoreLibName_W))
         {
-            mscorlib = GetDependency(0);
-            mscorlib->fIsMscorlib = TRUE;
-            _ASSERTE(mscorlib->fIsHardbound);
+            corelib = GetDependency(0);
+            corelib->fIsCoreLib = TRUE;
+            _ASSERTE(corelib->fIsHardbound);
         }
 
-        _ASSERTE(mscorlib != NULL);
-        if( mscorlib->fIsHardbound )
+        _ASSERTE(corelib != NULL);
+        if( corelib->fIsHardbound )
         {
-            m_isMscorlibHardBound = true;
+            m_isCoreLibHardBound = true;
         }
-        if( m_isMscorlibHardBound )
+        if( m_isCoreLibHardBound )
         {
             //go through the module to the binder.
-            PTR_Module mscorlibModule = mscorlib->pModule;
+            PTR_Module corelibModule = corelib->pModule;
 
-            PTR_MscorlibBinder binder = mscorlibModule->m_pBinder;
-            g_Mscorlib = *binder;
+            PTR_CoreLibBinder binder = corelibModule->m_pBinder;
+            g_CoreLib = *binder;
 
-            PTR_MethodTable mt = MscorlibBinder::GetExistingClass(CLASS__OBJECT);
+            PTR_MethodTable mt = CoreLibBinder::GetExistingClass(CLASS__OBJECT);
             g_pObjectClass = mt;
         }
 
 
         if (g_pObjectClass == NULL)
         {
-            //if mscorlib is not hard bound, then warn the user (many features of nidump are shut off)
-            m_display->ErrorPrintF( "Assembly %S is soft bound to mscorlib.  nidump cannot dump MethodTables completely.\n", m_name );
+            //if CoreLib is not hard bound, then warn the user (many features of nidump are shut off)
+            m_display->ErrorPrintF( "Assembly %S is soft bound to CoreLib.  nidump cannot dump MethodTables completely.\n", m_name );
             // TritonTODO: reason?
             // reset "hard bound state"
-            m_isMscorlibHardBound = false;
+            m_isCoreLibHardBound = false;
 
         }
     }
@@ -1267,8 +1267,8 @@ void NativeImageDumper::TraceDumpDependency(int idx, NativeImageDumper::Dependen
         m_display->ErrorPrintF("\tSize: %x (%d)\n", dependency->size, dependency->size);
         m_display->ErrorPrintF("\tModule: P=%p, L=%p\n", DataPtrToDisplay(dac_cast<TADDR>(dependency->pModule)),
                                PTR_TO_TADDR(dependency->pModule));
-        m_display->ErrorPrintF("Mscorlib=%s, Hardbound=%s\n",
-                               (dependency->fIsMscorlib ? "true" : "false"),
+        m_display->ErrorPrintF("CoreLib=%s, Hardbound=%s\n",
+                               (dependency->fIsCoreLib ? "true" : "false"),
                                (dependency->fIsHardbound ? "true" : "false"));
         m_display->ErrorPrintF("Name: %S\n", dependency->name);
     }
@@ -2391,7 +2391,7 @@ mdAssemblyRef NativeImageDumper::MapAssemblyRefToManifest(mdAssemblyRef token, I
             }
             else if (wcscmp(szAssemblyName, CoreLibName_W) == 0)
             {
-                // Mscorlib is special - version number and public key token are ignored.
+                // CoreLib is special - version number and public key token are ignored.
                 ret = currentRef;
                 break;
             }
@@ -2400,7 +2400,7 @@ mdAssemblyRef NativeImageDumper::MapAssemblyRefToManifest(mdAssemblyRef token, I
                      metadata.usBuildNumber == 255 &&
                      metadata.usRevisionNumber == 255)
             {
-                // WinMDs encode all assemblyrefs with version 255.255.255.255 including CLR assembly dependencies (mscorlib, System).
+                // WinMDs encode all assemblyrefs with version 255.255.255.255 including CLR assembly dependencies (corelib, System).
                 ret = currentRef;
             }
             else
@@ -2602,8 +2602,8 @@ NativeImageDumper::Dependency *NativeImageDumper::OpenDependency(int index)
             Dependency& dependency = m_dependencies[index];
             AppendTokenName(entry->dwAssemblyRef, buf, m_manifestImport, true);
             bool isHardBound = !!(entry->signNativeImage != INVALID_NGEN_SIGNATURE);
-            SString mscorlibStr(SString::Literal, CoreLibName_W);
-            bool isMscorlib = (0 == buf.Compare( mscorlibStr ));
+            SString corelibStr(SString::Literal, CoreLibName_W);
+            bool isCoreLib = (0 == buf.Compare( corelibStr ));
             dependency.fIsHardbound = isHardBound;
             wcscpy_s(dependency.name, _countof(dependency.name),
                      (const WCHAR*)buf);
@@ -2703,7 +2703,7 @@ NativeImageDumper::Dependency *NativeImageDumper::OpenDependency(int index)
                                                       ofRead,
                                                       IID_IMetaDataImport2,
                                                       (IUnknown **) &dependency.pImport));
-            dependency.fIsMscorlib = isMscorlib;
+            dependency.fIsCoreLib = isCoreLib;
         }
 
         m_dependencies[index].entry = entry;
@@ -3716,7 +3716,7 @@ void NativeImageDumper::DumpModule( PTR_Module module )
     /* REVISIT_TODO Fri 10/14/2005
      * Dump the binder
      */
-    PTR_MscorlibBinder binder = module->m_pBinder;
+    PTR_CoreLibBinder binder = module->m_pBinder;
     if( NULL != binder )
     {
         DisplayStartStructureWithOffset( m_pBinder, DPtrToPreferredAddr(binder),
@@ -3726,38 +3726,38 @@ void NativeImageDumper::DumpModule( PTR_Module module )
         //these four fields don't have anything useful in ngen images.
         DisplayWriteFieldPointer( m_classDescriptions,
                                   DPtrToPreferredAddr(binder->m_classDescriptions),
-                                  MscorlibBinder, MODULE );
+                                  CoreLibBinder, MODULE );
         DisplayWriteFieldPointer( m_methodDescriptions,
                                   DPtrToPreferredAddr(binder->m_methodDescriptions),
-                                  MscorlibBinder, MODULE );
+                                  CoreLibBinder, MODULE );
         DisplayWriteFieldPointer( m_fieldDescriptions,
                                   DPtrToPreferredAddr(binder->m_fieldDescriptions),
-                                  MscorlibBinder, MODULE );
+                                  CoreLibBinder, MODULE );
         DisplayWriteFieldPointer( m_pModule,
                                   DPtrToPreferredAddr(binder->m_pModule),
-                                  MscorlibBinder, MODULE );
+                                  CoreLibBinder, MODULE );
 
-        DisplayWriteFieldInt( m_cClasses, binder->m_cClasses, MscorlibBinder,
+        DisplayWriteFieldInt( m_cClasses, binder->m_cClasses, CoreLibBinder,
                               MODULE );
         DisplayWriteFieldAddress( m_pClasses,
                                   DPtrToPreferredAddr(binder->m_pClasses),
                                   sizeof(*binder->m_pClasses)
                                   * binder->m_cClasses,
-                                  MscorlibBinder, MODULE );
-        DisplayWriteFieldInt( m_cFields, binder->m_cFields, MscorlibBinder,
+                                  CoreLibBinder, MODULE );
+        DisplayWriteFieldInt( m_cFields, binder->m_cFields, CoreLibBinder,
                               MODULE );
         DisplayWriteFieldAddress( m_pFields,
                                   DPtrToPreferredAddr(binder->m_pFields),
                                   sizeof(*binder->m_pFields)
                                   * binder->m_cFields,
-                                  MscorlibBinder, MODULE );
-        DisplayWriteFieldInt( m_cMethods, binder->m_cMethods, MscorlibBinder,
+                                  CoreLibBinder, MODULE );
+        DisplayWriteFieldInt( m_cMethods, binder->m_cMethods, CoreLibBinder,
                               MODULE );
         DisplayWriteFieldAddress( m_pMethods,
                                   DPtrToPreferredAddr(binder->m_pMethods),
                                   sizeof(*binder->m_pMethods)
                                   * binder->m_cMethods,
-                                  MscorlibBinder, MODULE );
+                                  CoreLibBinder, MODULE );
 
         DisplayEndStructure( MODULE ); //m_pBinder
     }
@@ -6766,11 +6766,11 @@ NativeImageDumper::DumpMethodTable( PTR_MethodTable mt, const char * name,
         MethodTableToString( mt, buf );
         m_display->ErrorPrintF( "WARNING! MethodTable %S is generic but is not hard bound to its EEClass.  Cannot compute generic dictionary sizes.\n", (const WCHAR *)buf );
     }
-    else if( !m_isMscorlibHardBound )
+    else if( !m_isCoreLibHardBound )
     {
         /* REVISIT_TODO Mon 8/20/2007
-         * If we're not hard bound to mscorlib, most things don't work.  They depend on knowing what
-         * g_pObjectClass is.  Without the hard binding to mscorlib, I can't figure that out.
+         * If we're not hard bound to CoreLib, most things don't work.  They depend on knowing what
+         * g_pObjectClass is.  Without the hard binding to CoreLib, I can't figure that out.
          */
         haveCompleteExtents = false;
     }
@@ -7996,7 +7996,7 @@ void NativeImageDumper::DumpMethodDesc( PTR_MethodDesc md, PTR_Module module )
                               InstantiatedMethodDesc, METHODDESCS );
 
 #ifdef FEATURE_COMINTEROP
-        if (imd->IMD_HasComPlusCallInfo())
+        if (imd->IsGenericComPlusCall())
         {
             PTR_ComPlusCallInfo compluscall = imd->IMD_GetComPlusCallInfo();
             DumpComPlusCallInfo( compluscall, METHODDESCS );
diff --git a/src/coreclr/src/debug/daccess/nidump.h b/src/coreclr/src/debug/daccess/nidump.h
index b8c0a04ddb4170..a6e9461a475ae6 100644
--- a/src/coreclr/src/debug/daccess/nidump.h
+++ b/src/coreclr/src/debug/daccess/nidump.h
@@ -305,7 +305,7 @@ class NativeImageDumper
         TADDR pMetadataStartTarget;
         TADDR pMetadataStartHost;
         SIZE_T MetadataSize;
-        bool fIsMscorlib;
+        bool fIsCoreLib;
         bool fIsHardbound;
         WCHAR name[128];
     };
@@ -548,9 +548,9 @@ class NativeImageDumper
     COUNT_T m_ILSectionSize;
 #endif
 
-    //This is true if we are hard bound to mscorlib.  This enables various forms of generics dumping and MT
+    //This is true if we are hard bound to corelib.  This enables various forms of generics dumping and MT
     //dumping that require g_pObjectClass to be set.
-    bool m_isMscorlibHardBound;
+    bool m_isCoreLibHardBound;
 
 #if 0
     PTR_CCOR_SIGNATURE metadataToHostDAC( PCCOR_SIGNATURE pSig,
diff --git a/src/coreclr/src/debug/daccess/request.cpp b/src/coreclr/src/debug/daccess/request.cpp
index b9a589fd609fa3..5047421d595970 100644
--- a/src/coreclr/src/debug/daccess/request.cpp
+++ b/src/coreclr/src/debug/daccess/request.cpp
@@ -1058,7 +1058,7 @@ HRESULT ClrDataAccess::GetMethodDescData(
                     OBJECTREF value = pResolver->GetManagedResolver();
                     if (value)
                     {
-                        FieldDesc *pField = (&g_Mscorlib)->GetField(FIELD__DYNAMICRESOLVER__DYNAMIC_METHOD);
+                        FieldDesc *pField = (&g_CoreLib)->GetField(FIELD__DYNAMICRESOLVER__DYNAMIC_METHOD);
                         _ASSERTE(pField);
                         value = pField->GetRefValue(value);
                         if (value)
@@ -4732,3 +4732,12 @@ HRESULT ClrDataAccess::GetAssemblyLoadContext(CLRDATA_ADDRESS methodTable, CLRDA
     SOSDacLeave();
     return hr;
 }
+
+HRESULT ClrDataAccess::GetBreakingChangeVersion(int* pVersion)
+{
+    if (pVersion == nullptr)
+        return E_INVALIDARG;
+
+    *pVersion = SOS_BREAKING_CHANGE_VERSION;
+    return S_OK;
+}
diff --git a/src/coreclr/src/debug/daccess/stack.cpp b/src/coreclr/src/debug/daccess/stack.cpp
index 09e16b4979ab1c..94ef49b972ad23 100644
--- a/src/coreclr/src/debug/daccess/stack.cpp
+++ b/src/coreclr/src/debug/daccess/stack.cpp
@@ -1391,7 +1391,7 @@ ClrDataFrame::ValueFromDebugInfo(MetaSig* sig,
             // XXX Microsoft - Sometimes types can't be looked
             // up and this at least allows the value to be used,
             // but is it the right behavior?
-            argType = TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_U8));
+            argType = TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_U8));
             valueFlags = 0;
         }
         else
diff --git a/src/coreclr/src/debug/dbgutil/machoreader.cpp b/src/coreclr/src/debug/dbgutil/machoreader.cpp
index 155ec15a3af004..fa94b49b8d4a40 100644
--- a/src/coreclr/src/debug/dbgutil/machoreader.cpp
+++ b/src/coreclr/src/debug/dbgutil/machoreader.cpp
@@ -401,6 +401,7 @@ MachOReader::ReadString(const char* address, std::string& str)
         char c = 0;
         if (!ReadMemory((void*)(address + i), &c, sizeof(char)))
         {
+            Trace("ERROR: Failed to read string at %p\n", (void*)(address + i));
             return false;
         }
         if (c == '\0')
diff --git a/src/coreclr/src/debug/debug-pal/CMakeLists.txt b/src/coreclr/src/debug/debug-pal/CMakeLists.txt
index 12a0005c053220..213fa59e784c51 100644
--- a/src/coreclr/src/debug/debug-pal/CMakeLists.txt
+++ b/src/coreclr/src/debug/debug-pal/CMakeLists.txt
@@ -34,4 +34,6 @@ if(CLR_CMAKE_HOST_UNIX)
 
 endif(CLR_CMAKE_HOST_UNIX)
 
-_add_library(debug-pal OBJECT ${TWO_WAY_PIPE_SOURCES})
+_add_library(debug-pal_obj OBJECT ${TWO_WAY_PIPE_SOURCES})
+add_library(debug-pal INTERFACE)
+target_sources(debug-pal INTERFACE $<TARGET_OBJECTS:debug-pal_obj>)
diff --git a/src/coreclr/src/debug/debug-pal/unix/diagnosticsipc.cpp b/src/coreclr/src/debug/debug-pal/unix/diagnosticsipc.cpp
index e8830422930aac..a718c2bc34e2d0 100644
--- a/src/coreclr/src/debug/debug-pal/unix/diagnosticsipc.cpp
+++ b/src/coreclr/src/debug/debug-pal/unix/diagnosticsipc.cpp
@@ -187,6 +187,10 @@ IpcStream *IpcStream::DiagnosticsIpc::Connect(ErrorCallback callback)
     {
         if (callback != nullptr)
             callback(strerror(errno), errno);
+
+        const bool fCloseSuccess = ::close(clientSocket) == 0;
+        if (!fCloseSuccess && callback != nullptr)
+            callback(strerror(errno), errno);
         return nullptr;
     }
 
@@ -223,12 +227,11 @@ int32_t IpcStream::DiagnosticsIpc::Poll(IpcPollHandle *rgIpcPollHandles, uint32_
     // Check results
     if (retval < 0)
     {
-        for (uint32_t i = 0; i < nHandles; i++)
-        {
-            if ((pollfds[i].revents & POLLERR) && callback != nullptr)
-                callback(strerror(errno), errno);
-            rgIpcPollHandles[i].revents = (uint8_t)PollEvents::ERR;
-        }
+        //     If poll() returns with an error, including one due to an interrupted call, the fds
+        //  array will be unmodified and the global variable errno will be set to indicate the error.
+        // - POLL(2)
+        if (callback != nullptr)
+            callback(strerror(errno), errno);
         delete[] pollfds;
         return -1;
     }
@@ -243,6 +246,8 @@ int32_t IpcStream::DiagnosticsIpc::Poll(IpcPollHandle *rgIpcPollHandles, uint32_
     {
         if (pollfds[i].revents != 0)
         {
+            if (callback != nullptr)
+                callback("IpcStream::DiagnosticsIpc::Poll - poll revents", (uint32_t)pollfds[i].revents);
             // error check FIRST
             if (pollfds[i].revents & POLLHUP)
             {
@@ -250,21 +255,22 @@ int32_t IpcStream::DiagnosticsIpc::Poll(IpcPollHandle *rgIpcPollHandles, uint32_
                 // will technically meet the requirements for POLLIN
                 // i.e., a call to recv/read won't block
                 rgIpcPollHandles[i].revents = (uint8_t)PollEvents::HANGUP;
-                delete[] pollfds;
-                return -1;
             }
             else if ((pollfds[i].revents & (POLLERR|POLLNVAL)))
             {
                 if (callback != nullptr)
                     callback("Poll error", (uint32_t)pollfds[i].revents);
                 rgIpcPollHandles[i].revents = (uint8_t)PollEvents::ERR;
-                delete[] pollfds;
-                return -1;
             }
-            else if (pollfds[i].revents & POLLIN)
+            else if (pollfds[i].revents & (POLLIN|POLLPRI))
             {
                 rgIpcPollHandles[i].revents = (uint8_t)PollEvents::SIGNALED;
-                break;
+            }
+            else
+            {
+                rgIpcPollHandles[i].revents = (uint8_t)PollEvents::UNKNOWN;
+                if (callback != nullptr)
+                    callback("unkown poll response", (uint32_t)pollfds[i].revents);
             }
         }
     }
@@ -338,7 +344,7 @@ bool IpcStream::Read(void *lpBuffer, const uint32_t nBytesToRead, uint32_t &nByt
         pfd.fd = _clientSocket;
         pfd.events = POLLIN;
         int retval = poll(&pfd, 1, timeoutMs);
-        if (retval <= 0 || pfd.revents != POLLIN)
+        if (retval <= 0 || !(pfd.revents & POLLIN))
         {
             // timeout or error
             return false;
@@ -379,7 +385,7 @@ bool IpcStream::Write(const void *lpBuffer, const uint32_t nBytesToWrite, uint32
         pfd.fd = _clientSocket;
         pfd.events = POLLOUT;
         int retval = poll(&pfd, 1, timeoutMs);
-        if (retval <= 0 || pfd.revents != POLLOUT)
+        if (retval <= 0 || !(pfd.revents & POLLOUT))
         {
             // timeout or error
             return false;
diff --git a/src/coreclr/src/debug/debug-pal/win/diagnosticsipc.cpp b/src/coreclr/src/debug/debug-pal/win/diagnosticsipc.cpp
index 6c1b55e3111843..2b6c38463c1bf2 100644
--- a/src/coreclr/src/debug/debug-pal/win/diagnosticsipc.cpp
+++ b/src/coreclr/src/debug/debug-pal/win/diagnosticsipc.cpp
@@ -119,6 +119,7 @@ bool IpcStream::DiagnosticsIpc::Listen(ErrorCallback callback)
                 _hPipe = INVALID_HANDLE_VALUE;
                 ::CloseHandle(_oOverlap.hEvent);
                 _oOverlap.hEvent = INVALID_HANDLE_VALUE;
+                memset(&_oOverlap, 0, sizeof(OVERLAPPED)); // clear the overlapped objects state
                 return false;
         }
     }
@@ -193,11 +194,15 @@ IpcStream *IpcStream::DiagnosticsIpc::Connect(ErrorCallback callback)
     return new IpcStream(hPipe, mode);
 }
 
-void IpcStream::DiagnosticsIpc::Close(bool isShutdown, ErrorCallback)
+void IpcStream::DiagnosticsIpc::Close(bool isShutdown, ErrorCallback callback)
 {
     // don't attempt cleanup on shutdown and let the OS handle it
     if (isShutdown)
+    {
+        if (callback != nullptr)
+            callback("Closing without cleaning underlying handles", 100);
         return;
+    }
 
     if (_hPipe != INVALID_HANDLE_VALUE)
     {
@@ -205,15 +210,22 @@ void IpcStream::DiagnosticsIpc::Close(bool isShutdown, ErrorCallback)
         {
             const BOOL fSuccessDisconnectNamedPipe = ::DisconnectNamedPipe(_hPipe);
             _ASSERTE(fSuccessDisconnectNamedPipe != 0);
+            if (fSuccessDisconnectNamedPipe != 0 && callback != nullptr)
+                callback("Failed to disconnect NamedPipe", ::GetLastError());
         }
 
         const BOOL fSuccessCloseHandle = ::CloseHandle(_hPipe);
         _ASSERTE(fSuccessCloseHandle != 0);
+        if (fSuccessCloseHandle != 0 && callback != nullptr)
+            callback("Failed to close pipe handle", ::GetLastError());
     }
 
     if (_oOverlap.hEvent != INVALID_HANDLE_VALUE)
     {
-        ::CloseHandle(_oOverlap.hEvent);
+        const BOOL fSuccessCloseEvent = ::CloseHandle(_oOverlap.hEvent);
+        _ASSERTE(fSuccessCloseEvent != 0);
+        if (fSuccessCloseEvent != 0 && callback != nullptr)
+            callback("Failed to close overlap event handle", ::GetLastError());
     }
 }
 
@@ -230,7 +242,7 @@ IpcStream::~IpcStream()
     Close();
 }
 
-void IpcStream::Close(ErrorCallback)
+void IpcStream::Close(ErrorCallback callback)
 {
     if (_hPipe != INVALID_HANDLE_VALUE)
     {
@@ -240,15 +252,22 @@ void IpcStream::Close(ErrorCallback)
         {
             const BOOL fSuccessDisconnectNamedPipe = ::DisconnectNamedPipe(_hPipe);
             _ASSERTE(fSuccessDisconnectNamedPipe != 0);
+            if (fSuccessDisconnectNamedPipe != 0 && callback != nullptr)
+                callback("Failed to disconnect NamedPipe", ::GetLastError());
         }
 
         const BOOL fSuccessCloseHandle = ::CloseHandle(_hPipe);
         _ASSERTE(fSuccessCloseHandle != 0);
+        if (fSuccessCloseHandle != 0 && callback != nullptr)
+            callback("Failed to close pipe handle", ::GetLastError());
     }
 
     if (_oOverlap.hEvent != INVALID_HANDLE_VALUE)
     {
-        ::CloseHandle(_oOverlap.hEvent);
+        const BOOL fSuccessCloseEvent = ::CloseHandle(_oOverlap.hEvent);
+        _ASSERTE(fSuccessCloseEvent != 0);
+        if (fSuccessCloseEvent != 0 && callback != nullptr)
+            callback("Failed to close overlapped event handle", ::GetLastError());
     }
 }
 
@@ -302,6 +321,11 @@ int32_t IpcStream::DiagnosticsIpc::Poll(IpcPollHandle *rgIpcPollHandles, uint32_
                             return -1;
                     }
                 }
+                else
+                {
+                    // there's already data to be read
+                    pHandles[i] = rgIpcPollHandles[i].pStream->_oOverlap.hEvent;
+                }
             }
             else
             {
diff --git a/src/coreclr/src/debug/di/module.cpp b/src/coreclr/src/debug/di/module.cpp
index d02dfdd08146a9..9554f61dc86060 100644
--- a/src/coreclr/src/debug/di/module.cpp
+++ b/src/coreclr/src/debug/di/module.cpp
@@ -1200,6 +1200,10 @@ HRESULT CordbModule::QueryInterface(REFIID id, void **pInterface)
     {
         *pInterface = static_cast<ICorDebugModule3*>(this);
     }
+    else if (id == IID_ICorDebugModule4)
+    {
+        *pInterface = static_cast<ICorDebugModule4*>(this);
+    }
     else if (id == IID_IUnknown)
     {
         *pInterface = static_cast<IUnknown*>(static_cast<ICorDebugModule*>(this));
@@ -2752,6 +2756,24 @@ HRESULT CordbModule::GetJITCompilerFlags(DWORD *pdwFlags )
     return hr;
 }
 
+HRESULT CordbModule::IsMappedLayout(BOOL *isMapped)
+{
+    VALIDATE_POINTER_TO_OBJECT(isMapped, BOOL*);
+    FAIL_IF_NEUTERED(this);
+
+    HRESULT hr = S_OK;
+    CordbProcess *pProcess = GetProcess();
+
+    ATT_REQUIRE_STOPPED_MAY_FAIL(pProcess);
+    PUBLIC_API_BEGIN(pProcess);
+    {
+        hr = pProcess->GetDAC()->IsModuleMapped(m_vmModule, isMapped);
+    }
+    PUBLIC_API_END(hr);
+
+    return hr;
+}
+
 /* ------------------------------------------------------------------------- *
  * CordbCode class
  * ------------------------------------------------------------------------- */
diff --git a/src/coreclr/src/debug/di/rspriv.h b/src/coreclr/src/debug/di/rspriv.h
index 1bb48df2356c2c..4dc93ebf731729 100644
--- a/src/coreclr/src/debug/di/rspriv.h
+++ b/src/coreclr/src/debug/di/rspriv.h
@@ -4139,7 +4139,8 @@ class CordbProcess :
 class CordbModule : public CordbBase,
                     public ICorDebugModule,
                     public ICorDebugModule2,
-                    public ICorDebugModule3
+                    public ICorDebugModule3,
+                    public ICorDebugModule4
 {
 public:
     CordbModule(CordbProcess *      process,
@@ -4234,6 +4235,11 @@ class CordbModule : public CordbBase,
     COM_METHOD CreateReaderForInMemorySymbols(REFIID riid,
                                               void** ppObj);
 
+    //-----------------------------------------------------------
+    // ICorDebugModule4
+    //-----------------------------------------------------------
+    COM_METHOD IsMappedLayout(BOOL *isMapped);
+
     //-----------------------------------------------------------
     // Internal members
     //-----------------------------------------------------------
diff --git a/src/coreclr/src/debug/di/rstype.cpp b/src/coreclr/src/debug/di/rstype.cpp
index 36b137949664ce..a7412dea57134e 100644
--- a/src/coreclr/src/debug/di/rstype.cpp
+++ b/src/coreclr/src/debug/di/rstype.cpp
@@ -683,7 +683,7 @@ HRESULT CordbType::GetType(CorElementType *pType)
         // Determining if something is a VC or not can involve asking the EE.
         // We could do it ourselves based on the metadata but it's non-trivial
         // determining if a class has System.ValueType as a parent (we have
-        // to find and OpenScope the mscorlib.dll which we don't currently do
+        // to find and OpenScope the System.Private.CoreLib.dll which we don't currently do
         // on the right-side).  But the IsValueClass call can fail if the
         // class is not yet loaded on the right side.  In that case we
         // ignore the failure and return ELEMENT_TYPE_CLASS
diff --git a/src/coreclr/src/debug/di/shimremotedatatarget.cpp b/src/coreclr/src/debug/di/shimremotedatatarget.cpp
index 38bf162e430f05..9a01508e211585 100644
--- a/src/coreclr/src/debug/di/shimremotedatatarget.cpp
+++ b/src/coreclr/src/debug/di/shimremotedatatarget.cpp
@@ -68,7 +68,7 @@ class ShimRemoteDataTarget : public ShimDataTarget
     DbgTransportTarget  * m_pProxy;
     DbgTransportSession * m_pTransport;
 #ifdef FEATURE_REMOTE_PROC_MEM
-    int m_fd;                           // /proc/<pid>/mem handle
+    DWORD m_memoryHandle;                   // PAL_ReadProcessMemory handle or UINT32_MAX if fallback
 #endif
 };
 
@@ -106,9 +106,7 @@ ShimRemoteDataTarget::ShimRemoteDataTarget(DWORD processId,
     m_pContinueStatusChangedUserData = NULL;
 
 #ifdef FEATURE_REMOTE_PROC_MEM
-    char memPath[128];
-    _snprintf_s(memPath, sizeof(memPath), sizeof(memPath), "/proc/%lu/mem", m_processId);
-    m_fd = _open(memPath, 0); // O_RDONLY
+    PAL_OpenProcessMemory(m_processId, &m_memoryHandle);
 #endif
 }
 
@@ -135,11 +133,8 @@ ShimRemoteDataTarget::~ShimRemoteDataTarget()
 void ShimRemoteDataTarget::Dispose()
 {
 #ifdef FEATURE_REMOTE_PROC_MEM
-    if (m_fd != -1)
-    {
-        _close(m_fd);
-        m_fd = -1;
-    }
+    PAL_CloseProcessMemory(m_memoryHandle);
+    m_memoryHandle = UINT32_MAX;
 #endif
     if (m_pTransport != NULL)
     {
@@ -269,10 +264,9 @@ ShimRemoteDataTarget::ReadVirtual(
     HRESULT hr = S_OK;
 
 #ifdef FEATURE_REMOTE_PROC_MEM
-    if (m_fd != -1)
+    if (m_memoryHandle != UINT32_MAX)
     {
-        read = _pread(m_fd, pBuffer, cbRequestSize, (ULONG64)address);
-        if (read == (size_t)-1)
+        if (!PAL_ReadProcessMemory(m_memoryHandle, (ULONG64)address, pBuffer, cbRequestSize, &read))
         {
             hr = E_FAIL;
         }
diff --git a/src/coreclr/src/debug/ee/debugger.cpp b/src/coreclr/src/debug/ee/debugger.cpp
index 7b2cd48b22ed55..5ead858581acac 100644
--- a/src/coreclr/src/debug/ee/debugger.cpp
+++ b/src/coreclr/src/debug/ee/debugger.cpp
@@ -3458,14 +3458,14 @@ void Debugger::getBoundaries(MethodDesc * md,
 
     if (pModule == SystemDomain::SystemModule())
     {
-        // We don't look up PDBs for mscorlib.  This is not quite right, but avoids
+        // We don't look up PDBs for CoreLib.  This is not quite right, but avoids
         // a bootstrapping problem.  When an EXE loads, it has the option of setting
         // the COM apartment model to STA if we need to.  It is important that no
         // other Coinitialize happens before this.  Since loading the PDB reader uses
         // com we can not come first.  However managed code IS run before the COM
         // apartment model is set, and thus we have a problem since this code is
         // called for when JITTing managed code.    We avoid the problem by just
-        // bailing for mscorlib.
+        // bailing for CoreLib.
         return;
     }
 
@@ -15242,15 +15242,6 @@ HRESULT Debugger::FuncEvalSetup(DebuggerIPCE_FuncEvalInfo *pEvalInfo,
         return CORDBG_E_FUNC_EVAL_BAD_START_POINT;
     }
 
-    if (MethodDescBackpatchInfoTracker::IsLockOwnedByAnyThread())
-    {
-        // A thread may have suspended for the debugger while holding the slot backpatching lock while trying to enter
-        // cooperative GC mode. If the FuncEval calls a method that is eligible for slot backpatching (virtual or interface
-        // methods that are eligible for tiering), the FuncEval may deadlock on trying to acquire the same lock. Fail the
-        // FuncEval to avoid the issue.
-        return CORDBG_E_FUNC_EVAL_BAD_START_POINT;
-    }
-
     // Create a DebuggerEval to hold info about this eval while its in progress. Constructor copies the thread's
     // CONTEXT.
     DebuggerEval *pDE = new (interopsafe, nothrow) DebuggerEval(filterContext, pEvalInfo, fInException);
diff --git a/src/coreclr/src/debug/ee/debugger.h b/src/coreclr/src/debug/ee/debugger.h
index 2450ab65d4f9ef..6c113315852b13 100644
--- a/src/coreclr/src/debug/ee/debugger.h
+++ b/src/coreclr/src/debug/ee/debugger.h
@@ -725,37 +725,6 @@ class DebuggerRCThread
         return GetRCThreadSendBuffer();
     }
 
-    DebuggerIPCEvent *GetIPCEventSendBufferContinuation(
-        DebuggerIPCEvent *eventCur)
-    {
-        CONTRACTL
-        {
-            NOTHROW;
-            GC_NOTRIGGER;
-            PRECONDITION(eventCur != NULL);
-            PRECONDITION(eventCur->next == NULL);
-        }
-        CONTRACTL_END;
-
-        DebuggerIPCEvent *dipce = (DebuggerIPCEvent *) new (nothrow) BYTE [CorDBIPC_BUFFER_SIZE];
-        dipce->next = NULL;
-
-        LOG((LF_CORDB,LL_INFO1000000, "About to GIPCESBC 0x%x\n",dipce));
-
-        if (dipce != NULL)
-        {
-            eventCur->next = dipce;
-        }
-#ifdef _DEBUG
-        else
-        {
-            _ASSERTE( !"GetIPCEventSendBufferContinuation failed to allocate mem!" );
-        }
-#endif //_DEBUG
-
-        return dipce;
-    }
-
     // Send an IPCEvent once we're ready for sending. This should be done inbetween
     // SENDIPCEVENT_BEGIN & SENDIPCEVENT_END. See definition of SENDIPCEVENT_BEGIN
     // for usage pattern
diff --git a/src/coreclr/src/debug/ee/wks/CMakeLists.txt b/src/coreclr/src/debug/ee/wks/CMakeLists.txt
index a6891ebb052cb3..3dd5e3612dfc8a 100644
--- a/src/coreclr/src/debug/ee/wks/CMakeLists.txt
+++ b/src/coreclr/src/debug/ee/wks/CMakeLists.txt
@@ -9,9 +9,9 @@ if (CLR_CMAKE_TARGET_WIN32)
 
   if(CLR_CMAKE_HOST_ARCH_ARM OR CLR_CMAKE_HOST_ARCH_ARM64)
 
-    preprocess_compile_asm(TARGET cordbee_wks ASM_FILES ${ASM_FILE} OUTPUT_OBJECTS ASM_OBJECTS)
+    preprocess_compile_asm(TARGET cordbee_wks_obj ASM_FILES ${ASM_FILE} OUTPUT_OBJECTS ASM_OBJECTS)
 
-    add_library_clr(cordbee_wks OBJECT ${CORDBEE_SOURCES_WKS} ${ASM_FILE} ${ASM_OBJECTS})
+    add_library_clr(cordbee_wks_obj OBJECT ${CORDBEE_SOURCES_WKS} ${ASM_FILE} ${ASM_OBJECTS})
 
   else ()
 
@@ -23,19 +23,21 @@ if (CLR_CMAKE_TARGET_WIN32)
 
     set_source_files_properties(${ASM_FILE} PROPERTIES COMPILE_OPTIONS "${ASM_OPTIONS}")
 
-    add_library_clr(cordbee_wks OBJECT ${CORDBEE_SOURCES_WKS} ${ASM_FILE})
+    add_library_clr(cordbee_wks_obj OBJECT ${CORDBEE_SOURCES_WKS} ${ASM_FILE})
 
   endif()
 
 else ()
 
   if(CLR_CMAKE_HOST_ARCH_AMD64 OR CLR_CMAKE_HOST_ARCH_ARM OR CLR_CMAKE_HOST_ARCH_ARM64 OR CLR_CMAKE_HOST_ARCH_I386)
-    add_library_clr(cordbee_wks OBJECT ${CORDBEE_SOURCES_WKS} ../${ARCH_SOURCES_DIR}/dbghelpers.S)
+    add_library_clr(cordbee_wks_obj OBJECT ${CORDBEE_SOURCES_WKS} ../${ARCH_SOURCES_DIR}/dbghelpers.S)
   else()
     message(FATAL_ERROR "Unknown platform")
   endif()
 
 endif (CLR_CMAKE_TARGET_WIN32)
 
-target_precompile_header(TARGET cordbee_wks HEADER stdafx.h)
-add_dependencies(cordbee_wks eventing_headers)
+target_precompile_header(TARGET cordbee_wks_obj HEADER stdafx.h)
+add_dependencies(cordbee_wks_obj eventing_headers)
+add_library(cordbee_wks INTERFACE)
+target_sources(cordbee_wks INTERFACE $<TARGET_OBJECTS:cordbee_wks_obj>)
diff --git a/src/coreclr/src/debug/ildbsymlib/CMakeLists.txt b/src/coreclr/src/debug/ildbsymlib/CMakeLists.txt
index b5b249228d26f6..362da1f6483020 100644
--- a/src/coreclr/src/debug/ildbsymlib/CMakeLists.txt
+++ b/src/coreclr/src/debug/ildbsymlib/CMakeLists.txt
@@ -10,5 +10,6 @@ set( ILDBSYMLIB_SOURCES
   symwrite.cpp
 )
 
-add_library_clr(ildbsymlib OBJECT ${ILDBSYMLIB_SOURCES})
-
+add_library_clr(ildbsymlib_obj OBJECT ${ILDBSYMLIB_SOURCES})
+add_library(ildbsymlib INTERFACE)
+target_sources(ildbsymlib INTERFACE $<TARGET_OBJECTS:ildbsymlib_obj>)
diff --git a/src/coreclr/src/debug/inc/amd64/primitives.h b/src/coreclr/src/debug/inc/amd64/primitives.h
index d1e02238ece842..a119c2b3639fe3 100644
--- a/src/coreclr/src/debug/inc/amd64/primitives.h
+++ b/src/coreclr/src/debug/inc/amd64/primitives.h
@@ -53,7 +53,7 @@ inline CORDB_ADDRESS GetPatchEndAddr(CORDB_ADDRESS patchAddr)
     CORDbgInsertBreakpoint((CORDB_ADDRESS_TYPE *)((_buffer) + ((_patchAddr) - (_requestedAddr))));
 
 
-SELECTANY const CorDebugRegister g_JITToCorDbgReg[] =
+constexpr CorDebugRegister g_JITToCorDbgReg[] =
 {
     REGISTER_AMD64_RAX,
     REGISTER_AMD64_RCX,
diff --git a/src/coreclr/src/debug/inc/arm/primitives.h b/src/coreclr/src/debug/inc/arm/primitives.h
index a360737b89734e..269281eb006bed 100644
--- a/src/coreclr/src/debug/inc/arm/primitives.h
+++ b/src/coreclr/src/debug/inc/arm/primitives.h
@@ -63,7 +63,7 @@ inline T _ClearThumbBit(T addr)
     CORDbgInsertBreakpointExImpl((CORDB_ADDRESS_TYPE *)((_buffer) + (_ClearThumbBit(_patchAddr) - (_requestedAddr))));
 
 
-SELECTANY const CorDebugRegister g_JITToCorDbgReg[] =
+constexpr CorDebugRegister g_JITToCorDbgReg[] =
 {
     REGISTER_ARM_R0,
     REGISTER_ARM_R1,
diff --git a/src/coreclr/src/debug/inc/arm64/primitives.h b/src/coreclr/src/debug/inc/arm64/primitives.h
index b0ab65bac15e23..f359680370dfe5 100644
--- a/src/coreclr/src/debug/inc/arm64/primitives.h
+++ b/src/coreclr/src/debug/inc/arm64/primitives.h
@@ -56,7 +56,7 @@ inline CORDB_ADDRESS GetPatchEndAddr(CORDB_ADDRESS patchAddr)
     CORDbgInsertBreakpointExImpl((CORDB_ADDRESS_TYPE *)((_buffer) + (_patchAddr) - (_requestedAddr)));
 
 
-SELECTANY const CorDebugRegister g_JITToCorDbgReg[] =
+constexpr CorDebugRegister g_JITToCorDbgReg[] =
 {
     REGISTER_ARM64_X0,
     REGISTER_ARM64_X1,
diff --git a/src/coreclr/src/debug/inc/dacdbiinterface.h b/src/coreclr/src/debug/inc/dacdbiinterface.h
index 79405d60e3d841..1f99f5f2966587 100644
--- a/src/coreclr/src/debug/inc/dacdbiinterface.h
+++ b/src/coreclr/src/debug/inc/dacdbiinterface.h
@@ -2733,6 +2733,9 @@ class IDacDbiInterface
     virtual
     HRESULT GetLoaderHeapMemoryRanges(OUT DacDbiArrayList<COR_MEMORY_RANGE> *pRanges) = 0;
 
+    virtual
+    HRESULT IsModuleMapped(VMPTR_Module pModule, OUT BOOL *isModuleMapped) = 0;
+
     // The following tag tells the DD-marshalling tool to stop scanning.
     // END_MARSHAL
 
diff --git a/src/coreclr/src/debug/inc/dbgipcevents.h b/src/coreclr/src/debug/inc/dbgipcevents.h
index 5c433c2bf6131a..6fd2cf197c65af 100644
--- a/src/coreclr/src/debug/inc/dbgipcevents.h
+++ b/src/coreclr/src/debug/inc/dbgipcevents.h
@@ -848,7 +848,7 @@ typedef VMPTR_Base<DT_CONTEXT, void > VMPTR_CONTEXT;
 #endif
 
 // DomainFile is a base-class for a CLR module, with app-domain affinity.
-// For domain-neutral modules (like mscorlib), there is a DomainFile instance
+// For domain-neutral modules (like CoreLib), there is a DomainFile instance
 // for each appdomain the module lives in.
 // This is the canonical handle ICorDebug uses to a CLR module.
 DEFINE_VMPTR(class DomainFile,      PTR_DomainFile,     VMPTR_DomainFile);
@@ -984,20 +984,9 @@ struct MSLAYOUT IPCEventTypeNameMapping
             const char *            eventName;
 };
 
-extern const IPCEventTypeNameMapping DECLSPEC_SELECTANY DbgIPCEventTypeNames[] =
-{
-    #define IPC_EVENT_TYPE0(type, val)  { type, #type },
-    #define IPC_EVENT_TYPE1(type, val)  { type, #type },
-    #define IPC_EVENT_TYPE2(type, val)  { type, #type },
-    #include "dbgipceventtypes.h"
-    #undef IPC_EVENT_TYPE2
-    #undef IPC_EVENT_TYPE1
-    #undef IPC_EVENT_TYPE0
-    { DB_IPCE_INVALID_EVENT, "DB_IPCE_Error" }
-};
-
-const size_t nameCount = sizeof(DbgIPCEventTypeNames) / sizeof(DbgIPCEventTypeNames[0]);
+extern const IPCEventTypeNameMapping DbgIPCEventTypeNames[];
 
+extern const size_t nameCount;
 
 struct MSLAYOUT IPCENames // We use a class/struct so that the function can remain in a shared header file
 {
@@ -1028,7 +1017,7 @@ struct MSLAYOUT IPCENames // We use a class/struct so that the function can rema
         #undef IPC_EVENT_TYPE0
         };
 
-        unsigned int i, lim;
+        size_t i, lim;
 
         if (eventType < DB_IPCE_DEBUGGER_FIRST)
         {
diff --git a/src/coreclr/src/debug/inc/diagnosticsipc.h b/src/coreclr/src/debug/inc/diagnosticsipc.h
index 57c0576b9447ed..ecbf9db7dfef83 100644
--- a/src/coreclr/src/debug/inc/diagnosticsipc.h
+++ b/src/coreclr/src/debug/inc/diagnosticsipc.h
@@ -16,6 +16,7 @@ typedef void (*ErrorCallback)(const char *szMessage, uint32_t code);
 
 class IpcStream final
 {
+    friend class IpcStreamFactory;
 public:
     static constexpr int32_t InfiniteTimeout = -1;
     ~IpcStream();
@@ -26,6 +27,7 @@ class IpcStream final
 
     class DiagnosticsIpc final
     {
+        friend class IpcStreamFactory;
     public:
         enum ConnectionMode
         {
@@ -35,10 +37,11 @@ class IpcStream final
 
         enum class PollEvents : uint8_t
         {
-            TIMEOUT  = 0x00, // implies timeout
+            NONE     = 0x00, // no events
             SIGNALED = 0x01, // ready for use
             HANGUP   = 0x02, // connection remotely closed
-            ERR      = 0x04  // other error
+            ERR      = 0x04, // error
+            UNKNOWN   = 0x80  // unknown state
         };
 
         // The bookeeping struct used for polling on server and client structs
@@ -125,7 +128,7 @@ class IpcStream final
 private:
 #ifdef TARGET_UNIX
     int _clientSocket = -1;
-    IpcStream(int clientSocket, int serverSocket, DiagnosticsIpc::ConnectionMode mode = DiagnosticsIpc::ConnectionMode::SERVER)
+    IpcStream(int clientSocket, DiagnosticsIpc::ConnectionMode mode = DiagnosticsIpc::ConnectionMode::SERVER)
         : _clientSocket(clientSocket), _mode(mode) {}
 #else
     HANDLE _hPipe = INVALID_HANDLE_VALUE;
diff --git a/src/coreclr/src/debug/inc/i386/primitives.h b/src/coreclr/src/debug/inc/i386/primitives.h
index 05b696a4a0f692..980dc2707bb0f6 100644
--- a/src/coreclr/src/debug/inc/i386/primitives.h
+++ b/src/coreclr/src/debug/inc/i386/primitives.h
@@ -48,7 +48,7 @@ inline CORDB_ADDRESS GetPatchEndAddr(CORDB_ADDRESS patchAddr)
     CORDbgInsertBreakpoint((CORDB_ADDRESS_TYPE *)((_buffer) + ((_patchAddr) - (_requestedAddr))));
 
 
-SELECTANY const CorDebugRegister g_JITToCorDbgReg[] =
+constexpr CorDebugRegister g_JITToCorDbgReg[] =
 {
     REGISTER_X86_EAX,
     REGISTER_X86_ECX,
diff --git a/src/coreclr/src/debug/shared/utils.cpp b/src/coreclr/src/debug/shared/utils.cpp
index 5363e30ee8a88d..b9c7d72db3f703 100644
--- a/src/coreclr/src/debug/shared/utils.cpp
+++ b/src/coreclr/src/debug/shared/utils.cpp
@@ -200,3 +200,17 @@ void ExportILToNativeMap(ULONG32 cMap,             // [in] Min size of mapExt, m
 #endif // _DEBUG
     }
 }
+
+const IPCEventTypeNameMapping DbgIPCEventTypeNames[] =
+{
+    #define IPC_EVENT_TYPE0(type, val)  { type, #type },
+    #define IPC_EVENT_TYPE1(type, val)  { type, #type },
+    #define IPC_EVENT_TYPE2(type, val)  { type, #type },
+    #include "dbgipceventtypes.h"
+    #undef IPC_EVENT_TYPE2
+    #undef IPC_EVENT_TYPE1
+    #undef IPC_EVENT_TYPE0
+    { DB_IPCE_INVALID_EVENT, "DB_IPCE_Error" }
+};
+
+const size_t nameCount = sizeof(DbgIPCEventTypeNames) / sizeof(DbgIPCEventTypeNames[0]);
diff --git a/src/coreclr/src/dlls/mscordac/mscordac_unixexports.src b/src/coreclr/src/dlls/mscordac/mscordac_unixexports.src
index 29c010b9e84909..31dd9ea4875e99 100644
--- a/src/coreclr/src/dlls/mscordac/mscordac_unixexports.src
+++ b/src/coreclr/src/dlls/mscordac/mscordac_unixexports.src
@@ -43,6 +43,9 @@ nativeStringResourceTable_mscorrc
 #PAL_InitializeDLL
 #PAL_TerminateEx
 #PAL_IsDebuggerPresent
+#PAL_OpenProcessMemory
+#PAL_CloseProcessMemory
+#PAL_ReadProcessMemory
 #PAL_ProbeMemory
 #PAL_Random
 #PAL_memcpy
diff --git a/src/coreclr/src/dlls/mscoree/coreclr/CMakeLists.txt b/src/coreclr/src/dlls/mscoree/coreclr/CMakeLists.txt
index f01133ce40ffbc..2a25b2119b366b 100644
--- a/src/coreclr/src/dlls/mscoree/coreclr/CMakeLists.txt
+++ b/src/coreclr/src/dlls/mscoree/coreclr/CMakeLists.txt
@@ -10,17 +10,17 @@ if (CLR_CMAKE_HOST_WIN32)
 
     list(APPEND CLR_SOURCES ${CMAKE_CURRENT_BINARY_DIR}/coreclr.def)
 
-    add_link_options(/ENTRY:CoreDllMain)
+    add_linker_flag("/ENTRY:CoreDllMain")
 
     # Incremental linking results in the linker inserting extra padding and routing function calls via thunks that can break the
     # invariants (e.g. size of region between Jit_PatchedCodeLast-Jit_PatchCodeStart needs to fit in a page).
-    add_link_options(/INCREMENTAL:NO)
+    add_linker_flag("/INCREMENTAL:NO")
 
     # Delay load libraries required for WinRT as that is not supported on all platforms
-    add_link_options("/DELAYLOAD:api-ms-win-core-winrt-l1-1-0.dll")
+    add_linker_flag("/DELAYLOAD:api-ms-win-core-winrt-l1-1-0.dll")
 
     # Delay load version.dll so that we can specify how to search when loading it as it is not part of Windows' known DLLs
-    add_link_options("/DELAYLOAD:version.dll")
+    add_linker_flag("/DELAYLOAD:version.dll")
 
     # No library groups for Win32
     set(START_LIBRARY_GROUP)
@@ -33,7 +33,7 @@ else(CLR_CMAKE_HOST_WIN32)
     if(CLR_CMAKE_TARGET_LINUX OR CLR_CMAKE_TARGET_FREEBSD OR CLR_CMAKE_TARGET_NETBSD OR CLR_CMAKE_TARGET_SUNOS)
         # This option is necessary to ensure that the overloaded delete operator defined inside
         # of the utilcode will be used instead of the standard library delete operator.
-        add_link_options("LINKER:-Bsymbolic")
+        add_linker_flag("-Wl,-Bsymbolic")
 
         # The following linked options can be inserted into the linker libraries list to
         # ensure proper resolving of circular references between a subset of the libraries.
@@ -109,7 +109,7 @@ set(CORECLR_LIBRARIES
     ildbsymlib
     utilcode
     v3binder
-    System.Globalization.Native-Static
+    System.Globalization.Native-static
     interop
 )
 
@@ -168,8 +168,10 @@ if(FEATURE_MERGE_JIT_AND_ENGINE)
     set(CLRJIT_STATIC clrjit_static)
 endif(FEATURE_MERGE_JIT_AND_ENGINE)
 
-target_link_libraries(coreclr PUBLIC ${CORECLR_LIBRARIES} ${CLRJIT_STATIC} cee_wks cee_wks_core)
-target_link_libraries(coreclr_static PUBLIC ${CORECLR_LIBRARIES} clrjit_static cee_wks_mergeable cee_wks_core)
+target_sources(coreclr PUBLIC $<TARGET_OBJECTS:cee_wks_core>)
+target_link_libraries(coreclr PUBLIC ${CORECLR_LIBRARIES} ${CLRJIT_STATIC} cee_wks)
+target_sources(coreclr_static PUBLIC $<TARGET_OBJECTS:cee_wks_core>)
+target_link_libraries(coreclr_static PUBLIC ${CORECLR_LIBRARIES} clrjit_static cee_wks_mergeable)
 
 # Create the runtime module index header file containing the coreclr build id
 # for xplat and the timestamp/size on Windows.
diff --git a/src/coreclr/src/dlls/mscoree/mscoree.cpp b/src/coreclr/src/dlls/mscoree/mscoree.cpp
index 810a3e88f3fed0..f9e1e3d89ef68c 100644
--- a/src/coreclr/src/dlls/mscoree/mscoree.cpp
+++ b/src/coreclr/src/dlls/mscoree/mscoree.cpp
@@ -444,7 +444,7 @@ HRESULT SetInternalSystemDirectory()
 }
 
 #if defined(CROSSGEN_COMPILE)
-void SetMscorlibPath(LPCWSTR wzSystemDirectory)
+void SetCoreLibPath(LPCWSTR wzSystemDirectory)
 {
     DWORD len = (DWORD)wcslen(wzSystemDirectory);
     bool appendSeparator = wzSystemDirectory[len-1] != DIRECTORY_SEPARATOR_CHAR_W;
diff --git a/src/coreclr/src/dlls/mscoree/unixinterface.cpp b/src/coreclr/src/dlls/mscoree/unixinterface.cpp
index def87726531269..e23ece98722448 100644
--- a/src/coreclr/src/dlls/mscoree/unixinterface.cpp
+++ b/src/coreclr/src/dlls/mscoree/unixinterface.cpp
@@ -27,6 +27,9 @@ typedef NewArrayHolder<const WCHAR> ConstWStringHolder;
 // Specifies whether coreclr is embedded or standalone
 extern bool g_coreclr_embedded;
 
+// Specifies whether hostpolicy is embedded in executable or standalone
+extern bool g_hostpolicy_embedded;
+
 // Holder for array of wide strings
 class ConstWStringArrayHolder : public NewArrayHolder<LPCWSTR>
 {
@@ -116,7 +119,8 @@ static void ConvertConfigPropertiesToUnicode(
     int propertyCount,
     LPCWSTR** propertyKeysWRef,
     LPCWSTR** propertyValuesWRef,
-    BundleProbe** bundleProbe)
+    BundleProbe** bundleProbe,
+    bool* hostPolicyEmbedded)
 {
     LPCWSTR* propertyKeysW = new (nothrow) LPCWSTR[propertyCount];
     ASSERTE_ALL_BUILDS(propertyKeysW != nullptr);
@@ -135,6 +139,11 @@ static void ConvertConfigPropertiesToUnicode(
             // is passed in as the value of "BUNDLE_PROBE" property (encoded as a string).
             *bundleProbe = (BundleProbe*)_wcstoui64(propertyValuesW[propertyIndex], nullptr, 0);
         }
+        else if (strcmp(propertyKeys[propertyIndex], "HOSTPOLICY_EMBEDDED") == 0)
+        {
+            // The HOSTPOLICY_EMBEDDED property indicates if the executable has hostpolicy statically linked in
+            *hostPolicyEmbedded = (wcscmp(propertyValuesW[propertyIndex], W("true")) == 0);
+        }
     }
 
     *propertyKeysWRef = propertyKeysW;
@@ -177,6 +186,7 @@ int coreclr_initialize(
     LPCWSTR* propertyKeysW;
     LPCWSTR* propertyValuesW;
     BundleProbe* bundleProbe = nullptr;
+    bool hostPolicyEmbedded = false;
 
     ConvertConfigPropertiesToUnicode(
         propertyKeys,
@@ -184,7 +194,8 @@ int coreclr_initialize(
         propertyCount,
         &propertyKeysW,
         &propertyValuesW,
-        &bundleProbe);
+        &bundleProbe,
+        &hostPolicyEmbedded);
 
 #ifdef TARGET_UNIX
     DWORD error = PAL_InitializeCoreCLR(exePath, g_coreclr_embedded);
@@ -198,6 +209,8 @@ int coreclr_initialize(
     }
 #endif
 
+    g_hostpolicy_embedded = hostPolicyEmbedded;
+
     ReleaseHolder<ICLRRuntimeHost4> host;
 
     hr = CorHost2::CreateObject(IID_ICLRRuntimeHost4, (void**)&host);
diff --git a/src/coreclr/src/dlls/mscorpe/ceefilegenwriter.cpp b/src/coreclr/src/dlls/mscorpe/ceefilegenwriter.cpp
index 77afa5a83024cf..0fb18b0629b2a8 100644
--- a/src/coreclr/src/dlls/mscorpe/ceefilegenwriter.cpp
+++ b/src/coreclr/src/dlls/mscorpe/ceefilegenwriter.cpp
@@ -12,10 +12,168 @@
 #include <limits.h>
 
 #include "corerror.h"
-#include "stubs.h"
 #include <posterror.h>
 #include <shlwapi.h>
 
+// The following block contains a template for the default entry point stubs of a COM+
+// IL only program.  One can emit these stubs (with some fix-ups) and make
+// the code supplied the entry point value for the image.  The fix-ups will
+// in turn cause mscoree.dll to be loaded and the correct entry point to be
+// called.
+//
+// Note: Although these stubs contain x86 specific code, they are used
+// for all platforms
+
+
+//*****************************************************************************
+// This stub is designed for a x86 Windows application.  It will call the
+// _CorExeMain function in mscoree.dll.  This entry point will in turn load
+// and run the IL program.
+//
+//    jump _CorExeMain();
+//
+// The code jumps to the imported function _CorExeMain using the iat.
+// The address in the template is address of the iat entry which is
+// fixed up by the loader when the image is paged in.
+//*****************************************************************************
+
+const BYTE ExeMainX86Template[] =
+{
+	// Jump through IAT to _CorExeMain
+	0xFF, 0x25,				// jmp [iat:_CorDllMain entry]
+		0x00, 0x00, 0x00, 0x00,		//   address to replace
+
+};
+
+#define ExeMainX86TemplateSize		sizeof(ExeMainX86Template)
+#define CorExeMainX86IATOffset		2
+
+//*****************************************************************************
+// This stub is designed for a x86 Windows application.  It will call the
+// _CorDllMain function in mscoree.dll with with the base entry point for
+// the loaded DLL.  This entry point will in turn load and run the IL program.
+//
+//    jump _CorDllMain
+//
+// The code jumps to the imported function _CorExeMain using the iat.
+// The address in the template is address of the iat entry which is
+// fixed up by the loader when the image is paged in.
+//*****************************************************************************
+
+const BYTE DllMainX86Template[] =
+{
+	// Jump through IAT to CorDllMain
+	0xFF, 0x25,				// jmp [iat:_CorDllMain entry]
+		0x00, 0x00, 0x00, 0x00,		//   address to replace
+};
+
+#define DllMainX86TemplateSize		sizeof(DllMainX86Template)
+#define CorDllMainX86IATOffset		2
+
+//*****************************************************************************
+// This stub is designed for a AMD64 Windows application.  It will call the
+// _CorExeMain function in mscoree.dll.  This entry point will in turn load
+// and run the IL program.
+//
+//    mov rax, _CorExeMain();
+//    jmp [rax]
+//
+// The code jumps to the imported function _CorExeMain using the iat.
+// The address in the template is address of the iat entry which is
+// fixed up by the loader when the image is paged in.
+//*****************************************************************************
+
+const BYTE ExeMainAMD64Template[] =
+{
+	// Jump through IAT to _CorExeMain
+	0x48, 0xA1,				// rex.w rex.b mov rax,[following address]
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,//address of iat:_CorExeMain entry
+    0xFF, 0xE0              // jmp [rax]
+};
+
+#define ExeMainAMD64TemplateSize		sizeof(ExeMainAMD64Template)
+#define CorExeMainAMD64IATOffset		2
+
+//*****************************************************************************
+// This stub is designed for a AMD64 Windows application.  It will call the
+// _CorDllMain function in mscoree.dll with with the base entry point for
+// the loaded DLL.  This entry point will in turn load and run the IL program.
+//
+//    mov rax, _CorDllMain();
+//    jmp [rax]
+//
+// The code jumps to the imported function _CorDllMain using the iat.
+// The address in the template is address of the iat entry which is
+// fixed up by the loader when the image is paged in.
+//*****************************************************************************
+
+const BYTE DllMainAMD64Template[] =
+{
+	// Jump through IAT to CorDllMain
+	0x48, 0xA1,				// rex.w rex.b mov rax,[following address]
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,//address of iat:_CorDllMain entry
+    0xFF, 0xE0              // jmp [rax]
+};
+
+#define DllMainAMD64TemplateSize		sizeof(DllMainAMD64Template)
+#define CorDllMainAMD64IATOffset		2
+
+//*****************************************************************************
+// This stub is designed for an ia64 Windows application.  It will call the
+// _CorExeMain function in mscoree.dll.  This entry point will in turn load
+// and run the IL program.
+//
+//    jump _CorExeMain();
+//
+// The code jumps to the imported function _CorExeMain using the iat.
+// We set the value of gp to point at the iat table entry for _CorExeMain
+//*****************************************************************************
+
+const BYTE ExeMainIA64Template[] =
+{
+    // ld8    r9  = [gp]    ;;
+    // ld8    r10 = [r9],8
+    // nop.i                ;;
+    // ld8    gp  = [r9]
+    // mov    b6  = r10
+    // br.cond.sptk.few  b6
+    //
+    0x0B, 0x48, 0x00, 0x02, 0x18, 0x10, 0xA0, 0x40,
+    0x24, 0x30, 0x28, 0x00, 0x00, 0x00, 0x04, 0x00,
+    0x10, 0x08, 0x00, 0x12, 0x18, 0x10, 0x60, 0x50,
+    0x04, 0x80, 0x03, 0x00, 0x60, 0x00, 0x80, 0x00
+};
+
+#define ExeMainIA64TemplateSize		sizeof(ExeMainIA64Template)
+
+//*****************************************************************************
+// This stub is designed for an ia64 Windows application.  It will call the
+// _CorDllMain function in mscoree.dll with with the base entry point for
+// the loaded DLL.  This entry point will in turn load and run the IL program.
+//
+//    jump _CorDllMain
+//
+// The code jumps to the imported function _CorExeMain using the iat.
+// We set the value of gp to point at the iat table entry for _CorExeMain
+//*****************************************************************************
+
+const BYTE DllMainIA64Template[] =
+{
+    // ld8    r9  = [gp]    ;;
+    // ld8    r10 = [r9],8
+    // nop.i                ;;
+    // ld8    gp  = [r9]
+    // mov    b6  = r10
+    // br.cond.sptk.few  b6
+    //
+    0x0B, 0x48, 0x00, 0x02, 0x18, 0x10, 0xA0, 0x40,
+    0x24, 0x30, 0x28, 0x00, 0x00, 0x00, 0x04, 0x00,
+    0x10, 0x08, 0x00, 0x12, 0x18, 0x10, 0x60, 0x50,
+    0x04, 0x80, 0x03, 0x00, 0x60, 0x00, 0x80, 0x00
+};
+
+#define DllMainIA64TemplateSize		sizeof(DllMainIA64Template)
+
 #ifdef EMIT_FIXUPS
 
 // Emitted PEFIXUP structure looks like this
diff --git a/src/coreclr/src/dlls/mscorpe/stubs.h b/src/coreclr/src/dlls/mscorpe/stubs.h
deleted file mode 100644
index 893fc4783a2758..00000000000000
--- a/src/coreclr/src/dlls/mscorpe/stubs.h
+++ /dev/null
@@ -1,168 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-//*****************************************************************************
-// Stubs.h
-//
-// This file contains a template for the default entry point stubs of a COM+
-// IL only program.  One can emit these stubs (with some fix-ups) and make
-// the code supplied the entry point value for the image.  The fix-ups will
-// in turn cause mscoree.dll to be loaded and the correct entry point to be
-// called.
-//
-// Note: Although these stubs contain x86 specific code, they are used
-// for all platforms
-//
-//*****************************************************************************
-#ifndef __STUBS_H__
-#define __STUBS_H__
-
-//*****************************************************************************
-// This stub is designed for a x86 Windows application.  It will call the
-// _CorExeMain function in mscoree.dll.  This entry point will in turn load
-// and run the IL program.
-//
-//    jump _CorExeMain();
-//
-// The code jumps to the imported function _CorExeMain using the iat.
-// The address in the template is address of the iat entry which is
-// fixed up by the loader when the image is paged in.
-//*****************************************************************************
-
-SELECTANY const BYTE ExeMainX86Template[] =
-{
-	// Jump through IAT to _CorExeMain
-	0xFF, 0x25,				// jmp [iat:_CorDllMain entry]
-		0x00, 0x00, 0x00, 0x00,		//   address to replace
-
-};
-
-#define ExeMainX86TemplateSize		sizeof(ExeMainX86Template)
-#define CorExeMainX86IATOffset		2
-
-//*****************************************************************************
-// This stub is designed for a x86 Windows application.  It will call the
-// _CorDllMain function in mscoree.dll with with the base entry point for
-// the loaded DLL.  This entry point will in turn load and run the IL program.
-//
-//    jump _CorDllMain
-//
-// The code jumps to the imported function _CorExeMain using the iat.
-// The address in the template is address of the iat entry which is
-// fixed up by the loader when the image is paged in.
-//*****************************************************************************
-
-SELECTANY const BYTE DllMainX86Template[] =
-{
-	// Jump through IAT to CorDllMain
-	0xFF, 0x25,				// jmp [iat:_CorDllMain entry]
-		0x00, 0x00, 0x00, 0x00,		//   address to replace
-};
-
-#define DllMainX86TemplateSize		sizeof(DllMainX86Template)
-#define CorDllMainX86IATOffset		2
-
-//*****************************************************************************
-// This stub is designed for a AMD64 Windows application.  It will call the
-// _CorExeMain function in mscoree.dll.  This entry point will in turn load
-// and run the IL program.
-//
-//    mov rax, _CorExeMain();
-//    jmp [rax]
-//
-// The code jumps to the imported function _CorExeMain using the iat.
-// The address in the template is address of the iat entry which is
-// fixed up by the loader when the image is paged in.
-//*****************************************************************************
-
-SELECTANY const BYTE ExeMainAMD64Template[] =
-{
-	// Jump through IAT to _CorExeMain
-	0x48, 0xA1,				// rex.w rex.b mov rax,[following address]
-    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,//address of iat:_CorExeMain entry
-    0xFF, 0xE0              // jmp [rax]
-};
-
-#define ExeMainAMD64TemplateSize		sizeof(ExeMainAMD64Template)
-#define CorExeMainAMD64IATOffset		2
-
-//*****************************************************************************
-// This stub is designed for a AMD64 Windows application.  It will call the
-// _CorDllMain function in mscoree.dll with with the base entry point for
-// the loaded DLL.  This entry point will in turn load and run the IL program.
-//
-//    mov rax, _CorDllMain();
-//    jmp [rax]
-//
-// The code jumps to the imported function _CorDllMain using the iat.
-// The address in the template is address of the iat entry which is
-// fixed up by the loader when the image is paged in.
-//*****************************************************************************
-
-SELECTANY const BYTE DllMainAMD64Template[] =
-{
-	// Jump through IAT to CorDllMain
-	0x48, 0xA1,				// rex.w rex.b mov rax,[following address]
-    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,//address of iat:_CorDllMain entry
-    0xFF, 0xE0              // jmp [rax]
-};
-
-#define DllMainAMD64TemplateSize		sizeof(DllMainAMD64Template)
-#define CorDllMainAMD64IATOffset		2
-
-//*****************************************************************************
-// This stub is designed for an ia64 Windows application.  It will call the
-// _CorExeMain function in mscoree.dll.  This entry point will in turn load
-// and run the IL program.
-//
-//    jump _CorExeMain();
-//
-// The code jumps to the imported function _CorExeMain using the iat.
-// We set the value of gp to point at the iat table entry for _CorExeMain
-//*****************************************************************************
-
-SELECTANY const BYTE ExeMainIA64Template[] =
-{
-    // ld8    r9  = [gp]    ;;
-    // ld8    r10 = [r9],8
-    // nop.i                ;;
-    // ld8    gp  = [r9]
-    // mov    b6  = r10
-    // br.cond.sptk.few  b6
-    //
-    0x0B, 0x48, 0x00, 0x02, 0x18, 0x10, 0xA0, 0x40,
-    0x24, 0x30, 0x28, 0x00, 0x00, 0x00, 0x04, 0x00,
-    0x10, 0x08, 0x00, 0x12, 0x18, 0x10, 0x60, 0x50,
-    0x04, 0x80, 0x03, 0x00, 0x60, 0x00, 0x80, 0x00
-};
-
-#define ExeMainIA64TemplateSize		sizeof(ExeMainIA64Template)
-
-//*****************************************************************************
-// This stub is designed for an ia64 Windows application.  It will call the
-// _CorDllMain function in mscoree.dll with with the base entry point for
-// the loaded DLL.  This entry point will in turn load and run the IL program.
-//
-//    jump _CorDllMain
-//
-// The code jumps to the imported function _CorExeMain using the iat.
-// We set the value of gp to point at the iat table entry for _CorExeMain
-//*****************************************************************************
-
-SELECTANY const BYTE DllMainIA64Template[] =
-{
-    // ld8    r9  = [gp]    ;;
-    // ld8    r10 = [r9],8
-    // nop.i                ;;
-    // ld8    gp  = [r9]
-    // mov    b6  = r10
-    // br.cond.sptk.few  b6
-    //
-    0x0B, 0x48, 0x00, 0x02, 0x18, 0x10, 0xA0, 0x40,
-    0x24, 0x30, 0x28, 0x00, 0x00, 0x00, 0x04, 0x00,
-    0x10, 0x08, 0x00, 0x12, 0x18, 0x10, 0x60, 0x50,
-    0x04, 0x80, 0x03, 0x00, 0x60, 0x00, 0x80, 0x00
-};
-
-#define DllMainIA64TemplateSize		sizeof(DllMainIA64Template)
-
-#endif  // __STUBS_H__
diff --git a/src/coreclr/src/dlls/mscorrc/CMakeLists.txt b/src/coreclr/src/dlls/mscorrc/CMakeLists.txt
index ed5ee887650877..e114ec19cea63e 100644
--- a/src/coreclr/src/dlls/mscorrc/CMakeLists.txt
+++ b/src/coreclr/src/dlls/mscorrc/CMakeLists.txt
@@ -19,7 +19,9 @@ if(CLR_CMAKE_HOST_WIN32)
 else()
     build_resources(${CMAKE_CURRENT_SOURCE_DIR}/include.rc mscorrc TARGET_CPP_FILE)
 
-    add_library_clr(mscorrc OBJECT
+    add_library_clr(mscorrc_obj OBJECT
         ${TARGET_CPP_FILE}
     )
+    add_library(mscorrc INTERFACE)
+    target_sources(mscorrc INTERFACE $<TARGET_OBJECTS:mscorrc_obj>)
 endif(CLR_CMAKE_HOST_WIN32)
diff --git a/src/coreclr/src/dlls/mscorrc/mscorrc.rc b/src/coreclr/src/dlls/mscorrc/mscorrc.rc
index a50f742cef007c..360442044ca439 100644
--- a/src/coreclr/src/dlls/mscorrc/mscorrc.rc
+++ b/src/coreclr/src/dlls/mscorrc/mscorrc.rc
@@ -182,6 +182,7 @@ BEGIN
     IDS_EE_NDIRECT_UNSUPPORTED_SIG          "Method's type signature is not PInvoke compatible."
     IDS_EE_COM_UNSUPPORTED_SIG              "Method's type signature is not Interop compatible."
     IDS_EE_COM_UNSUPPORTED_TYPE             "The method returned a COM Variant type that is not Interop compatible."
+    IDS_EE_MULTIPLE_CALLCONV_UNSUPPORTED    "Multiple unmanaged calling conventions are specified. Only a single calling convention is supported."
     IDS_EE_NDIRECT_BADNATL                  "Invalid PInvoke or UnmanagedFunctionPointer metadata format."
     IDS_EE_NDIRECT_BADNATL_CALLCONV         "Invalid PInvoke or UnmanagedFunctionPointer calling convention."
     IDS_EE_NDIRECT_BADNATL_VARARGS_CALLCONV "Invalid PInvoke calling convention. Vararg functions must use the cdecl calling convention."
diff --git a/src/coreclr/src/dlls/mscorrc/resource.h b/src/coreclr/src/dlls/mscorrc/resource.h
index 738b751c7faec9..b78c5d84c304a0 100644
--- a/src/coreclr/src/dlls/mscorrc/resource.h
+++ b/src/coreclr/src/dlls/mscorrc/resource.h
@@ -43,6 +43,7 @@
 #define IDS_EE_COM_UNSUPPORTED_SIG              0x170d
 #define IDS_EE_NOSYNCHRONIZED                   0x170f
 #define IDS_EE_NDIRECT_BADNATL_THISCALL         0x1710
+#define IDS_EE_MULTIPLE_CALLCONV_UNSUPPORTED    0x1711
 
 #define IDS_EE_LOAD_BAD_MAIN_SIG                0x1712
 #define IDS_EE_COM_UNSUPPORTED_TYPE             0x1713
diff --git a/src/coreclr/src/gc/gc.cpp b/src/coreclr/src/gc/gc.cpp
index 6bf8e51a6bcefb..e20daab80ed273 100644
--- a/src/coreclr/src/gc/gc.cpp
+++ b/src/coreclr/src/gc/gc.cpp
@@ -8347,6 +8347,8 @@ void gc_heap::sort_mark_list()
 {
     if (settings.condemned_generation >= max_generation)
     {
+        // fake a mark list overflow so merge_mark_lists knows to quit early
+        mark_list_index = mark_list_end + 1;
         return;
     }
 
@@ -8397,7 +8399,7 @@ void gc_heap::sort_mark_list()
         high = max (high, heap_segment_allocated (hp->ephemeral_heap_segment));
     }
 
-    // give up if this is not an ephemeral GC or the mark list size is unreasonably large
+    // give up if the mark list size is unreasonably large
     if (total_mark_list_size > (total_ephemeral_size / 256))
     {
         mark_list_index = mark_list_end + 1;
@@ -18088,12 +18090,12 @@ uint8_t* gc_heap::find_object (uint8_t* interior)
     {
         // this is a pointer to a UOH object
         heap_segment* seg = find_segment (interior, FALSE);
-        if (seg
+        if (seg)
+        {
 #ifdef FEATURE_CONSERVATIVE_GC
-            && (GCConfig::GetConservativeGC() || interior <= heap_segment_allocated(seg))
+            if (interior >= heap_segment_allocated(seg))
+                return 0;
 #endif
-            )
-        {
             // If interior falls within the first free object at the beginning of a generation,
             // we don't have brick entry for it, and we may incorrectly treat it as on large object heap.
             int align_const = get_alignment_constant (heap_segment_read_only_p (seg)
@@ -38607,8 +38609,8 @@ void gc_heap::walk_heap_per_heap (walk_fn fn, void* context, int gen_number, BOO
                      generation_allocation_start (gen));
 
     uint8_t*       end = heap_segment_allocated (seg);
-    BOOL small_object_segments = TRUE;
-    int align_const = get_alignment_constant (small_object_segments);
+    int align_const = get_alignment_constant (TRUE);
+    BOOL walk_pinned_object_heap = walk_large_object_heap_p;
 
     while (1)
 
@@ -38623,20 +38625,25 @@ void gc_heap::walk_heap_per_heap (walk_fn fn, void* context, int gen_number, BOO
             }
             else
             {
-                if (small_object_segments && walk_large_object_heap_p)
-
+                if (walk_large_object_heap_p)
                 {
-                    small_object_segments = FALSE;
-                    align_const = get_alignment_constant (small_object_segments);
+                    walk_large_object_heap_p = FALSE;
                     seg = generation_start_segment (large_object_generation);
-                    x = heap_segment_mem (seg);
-                    end = heap_segment_allocated (seg);
-                    continue;
+                }
+                else if (walk_pinned_object_heap)
+                {
+                    walk_pinned_object_heap = FALSE;
+                    seg = generation_start_segment (pinned_object_generation);
                 }
                 else
                 {
                     break;
                 }
+
+                align_const = get_alignment_constant (FALSE);
+                x = heap_segment_mem (seg);
+                end = heap_segment_allocated (seg);
+                continue;
             }
         }
 
diff --git a/src/coreclr/src/gc/gcconfig.h b/src/coreclr/src/gc/gcconfig.h
index 085562f56dd486..7d667b6a15ea6d 100644
--- a/src/coreclr/src/gc/gcconfig.h
+++ b/src/coreclr/src/gc/gcconfig.h
@@ -75,7 +75,7 @@ class GCConfigStringHolder
     BOOL_CONFIG  (LogEnabled,             "GCLogEnabled",           NULL,                             false,             "Specifies if you want to turn on logging in GC")                                         \
     BOOL_CONFIG  (ConfigLogEnabled,       "GCConfigLogEnabled",     NULL,                             false,             "Specifies the name of the GC config log file")                                           \
     BOOL_CONFIG  (GCNumaAware,            "GCNumaAware",            NULL,                             true,              "Enables numa allocations in the GC")                                                     \
-    BOOL_CONFIG  (GCCpuGroup,             "GCCpuGroup",             NULL,                             false,             "Enables CPU groups in the GC")                                                           \
+    BOOL_CONFIG  (GCCpuGroup,             "GCCpuGroup",             "System.GC.CpuGroup",             false,             "Enables CPU groups in the GC")                                                           \
     BOOL_CONFIG  (GCLargePages,           "GCLargePages",           "System.GC.LargePages",           false,             "Enables using Large Pages in the GC")                                                    \
     INT_CONFIG   (HeapVerifyLevel,        "HeapVerify",             NULL,                             HEAPVERIFY_NONE,   "When set verifies the integrity of the managed heap on entry and exit of each GC")       \
     INT_CONFIG   (LOHCompactionMode,      "GCLOHCompact",           NULL,                             0,                 "Specifies the LOH compaction mode")                                                      \
@@ -92,13 +92,13 @@ class GCConfigStringHolder
     INT_CONFIG   (LogFileSize,            "GCLogFileSize",          NULL,                             0,                 "Specifies the GC log file size")                                                         \
     INT_CONFIG   (CompactRatio,           "GCCompactRatio",         NULL,                             0,                 "Specifies the ratio compacting GCs vs sweeping")                                         \
     INT_CONFIG   (GCHeapAffinitizeMask,   "GCHeapAffinitizeMask",   "System.GC.HeapAffinitizeMask",   0,                 "Specifies processor mask for Server GC threads")                                         \
-    STRING_CONFIG(GCHeapAffinitizeRanges, "GCHeapAffinitizeRanges", NULL,                                                "Specifies list of processors for Server GC threads. The format is a comma separated "    \
+    STRING_CONFIG(GCHeapAffinitizeRanges, "GCHeapAffinitizeRanges", "System.GC.HeapAffinitizeRanges",                    "Specifies list of processors for Server GC threads. The format is a comma separated "    \
                                                                                                                          "list of processor numbers or ranges of processor numbers. On Windows, each entry is "    \
                                                                                                                          "prefixed by the CPU group number. Example: Unix - 1,3,5,7-9,12, Windows - 0:1,1:7-9")    \
-    INT_CONFIG   (GCHighMemPercent,       "GCHighMemPercent",       NULL,                             0,                 "The percent for GC to consider as high memory")                                          \
+    INT_CONFIG   (GCHighMemPercent,       "GCHighMemPercent",       "System.GC.HighMemoryPercent",    0,                 "The percent for GC to consider as high memory")                                          \
     INT_CONFIG   (GCProvModeStress,       "GCProvModeStress",       NULL,                             0,                 "Stress the provisional modes")                                                           \
     INT_CONFIG   (GCGen0MaxBudget,        "GCGen0MaxBudget",        NULL,                             0,                 "Specifies the largest gen0 allocation budget")                                           \
-    INT_CONFIG   (GCHeapHardLimit,        "GCHeapHardLimit",        NULL,                             0,                 "Specifies a hard limit for the GC heap")                                                 \
+    INT_CONFIG   (GCHeapHardLimit,        "GCHeapHardLimit",        "System.GC.HeapHardLimit",        0,                 "Specifies a hard limit for the GC heap")                                                 \
     INT_CONFIG   (GCHeapHardLimitPercent, "GCHeapHardLimitPercent", "System.GC.HeapHardLimitPercent", 0,                 "Specifies the GC heap usage as a percentage of the total memory")                        \
     INT_CONFIG   (GCTotalPhysicalMemory,  "GCTotalPhysicalMemory",  NULL,                             0,                 "Specifies what the GC should consider to be total physical memory")                      \
     STRING_CONFIG(LogFile,                "GCLogFile",              NULL,                                                "Specifies the name of the GC log file")                                                  \
@@ -122,13 +122,13 @@ class GCConfigStringHolder
     INT_CONFIG   (BGCFLEnableTBH,         "BGCFLEnableTBH",         NULL,                             0,                 "Enables TBH")                                                                            \
     INT_CONFIG   (BGCFLEnableFF,          "BGCFLEnableFF",          NULL,                             0,                 "Enables FF")                                                                             \
     INT_CONFIG   (BGCG2RatioStep,         "BGCG2RatioStep",         NULL,                             5,                 "Ratio correction factor for ML loop")                                                    \
-    INT_CONFIG   (GCHeapHardLimitSOH,     "GCHeapHardLimitSOH",     NULL,                             0,                 "Specifies a hard limit for the GC heap SOH")                                             \
-    INT_CONFIG   (GCHeapHardLimitLOH,     "GCHeapHardLimitLOH",     NULL,                             0,                 "Specifies a hard limit for the GC heap LOH")                                             \
-    INT_CONFIG   (GCHeapHardLimitPOH,     "GCHeapHardLimitPOH",     NULL,                             0,                 "Specifies a hard limit for the GC heap POH")                                             \
-    INT_CONFIG   (GCHeapHardLimitSOHPercent, "GCHeapHardLimitSOHPercent", NULL,                             0,                 "Specifies the GC heap SOH usage as a percentage of the total memory")              \
-    INT_CONFIG   (GCHeapHardLimitLOHPercent, "GCHeapHardLimitLOHPercent", NULL,                             0,                 "Specifies the GC heap LOH usage as a percentage of the total memory")              \
-    INT_CONFIG   (GCHeapHardLimitPOHPercent, "GCHeapHardLimitPOHPercent", NULL,                             0,                 "Specifies the GC heap POH usage as a percentage of the total memory")              \
-    INT_CONFIG   (GCEnabledInstructionSets, "GCEnabledInstructionSets", NULL,                        -1,                 "Specifies whether GC can use AVX2 or AVX512F - 0 for neither, 1 for AVX2, 3 for AVX512F")\
+    INT_CONFIG   (GCHeapHardLimitSOH,     "GCHeapHardLimitSOH",     "System.GC.HeapHardLimitSOH",     0,                 "Specifies a hard limit for the GC heap SOH")                                             \
+    INT_CONFIG   (GCHeapHardLimitLOH,     "GCHeapHardLimitLOH",     "System.GC.HeapHardLimitLOH",     0,                 "Specifies a hard limit for the GC heap LOH")                                             \
+    INT_CONFIG   (GCHeapHardLimitPOH,     "GCHeapHardLimitPOH",     "System.GC.HeapHardLimitPOH",     0,                 "Specifies a hard limit for the GC heap POH")                                             \
+    INT_CONFIG   (GCHeapHardLimitSOHPercent, "GCHeapHardLimitSOHPercent", "System.GC.HeapHardLimitSOHPercent", 0,        "Specifies the GC heap SOH usage as a percentage of the total memory")                    \
+    INT_CONFIG   (GCHeapHardLimitLOHPercent, "GCHeapHardLimitLOHPercent", "System.GC.HeapHardLimitLOHPercent", 0,        "Specifies the GC heap LOH usage as a percentage of the total memory")                    \
+    INT_CONFIG   (GCHeapHardLimitPOHPercent, "GCHeapHardLimitPOHPercent", "System.GC.HeapHardLimitPOHPercent", 0,        "Specifies the GC heap POH usage as a percentage of the total memory")                    \
+    INT_CONFIG   (GCEnabledInstructionSets,  "GCEnabledInstructionSets",  NULL,                                -1,       "Specifies whether GC can use AVX2 or AVX512F - 0 for neither, 1 for AVX2, 3 for AVX512F")\
 
 // This class is responsible for retreiving configuration information
 // for how the GC should operate.
diff --git a/src/coreclr/src/gc/gcinterface.h b/src/coreclr/src/gc/gcinterface.h
index 331f8e12210842..bfe02b7db9da3b 100644
--- a/src/coreclr/src/gc/gcinterface.h
+++ b/src/coreclr/src/gc/gcinterface.h
@@ -396,7 +396,7 @@ typedef enum
      * They are currently used for EnC for adding new field members to existing instantiations under EnC modes where
      * the primary object is the original instantiation and the secondary represents the added field.
      *
-     * They are also used to implement the ConditionalWeakTable class in mscorlib.dll. If you want to use
+     * They are also used to implement the managed ConditionalWeakTable class. If you want to use
      * these from managed code, they are exposed to BCL through the managed DependentHandle class.
      *
      *
@@ -587,7 +587,7 @@ class IGCHeap {
 
     /*
     ===========================================================================
-    BCL routines. These are routines that are directly exposed by mscorlib
+    BCL routines. These are routines that are directly exposed by CoreLib
     as a part of the `System.GC` class. These routines behave in the same
     manner as the functions on `System.GC`.
     ===========================================================================
@@ -640,14 +640,14 @@ class IGCHeap {
     virtual int GetGcLatencyMode() = 0;
 
     // Sets the current GC latency mode. newLatencyMode has already been
-    // verified by mscorlib to be valid.
+    // verified by CoreLib to be valid.
     virtual int SetGcLatencyMode(int newLatencyMode) = 0;
 
     // Gets the current LOH compaction mode.
     virtual int GetLOHCompactionMode() = 0;
 
     // Sets the current LOH compaction mode. newLOHCompactionMode has
-    // already been verified by mscorlib to be valid.
+    // already been verified by CoreLib to be valid.
     virtual void SetLOHCompactionMode(int newLOHCompactionMode) = 0;
 
     // Registers for a full GC notification, raising a notification if the gen 2 or
diff --git a/src/coreclr/src/gc/unix/config.gc.h.in b/src/coreclr/src/gc/unix/config.gc.h.in
index 954176f74a346b..42b6429be80e58 100644
--- a/src/coreclr/src/gc/unix/config.gc.h.in
+++ b/src/coreclr/src/gc/unix/config.gc.h.in
@@ -18,7 +18,8 @@
 #cmakedefine01 HAVE_PTHREAD_CONDATTR_SETCLOCK
 #cmakedefine01 HAVE_MACH_ABSOLUTE_TIME
 #cmakedefine01 HAVE_SCHED_GETAFFINITY
-#cmakedefine01 HAVE_PTHREAD_GETAFFINITY_NP
+#cmakedefine01 HAVE_SCHED_SETAFFINITY
+#cmakedefine01 HAVE_PTHREAD_SETAFFINITY_NP
 #cmakedefine01 HAVE_PTHREAD_NP_H
 #cmakedefine01 HAVE_CPUSET_T
 #cmakedefine01 HAVE__SC_AVPHYS_PAGES
diff --git a/src/coreclr/src/gc/unix/configure.cmake b/src/coreclr/src/gc/unix/configure.cmake
index cc7fb90265d8be..6d190a8c467350 100644
--- a/src/coreclr/src/gc/unix/configure.cmake
+++ b/src/coreclr/src/gc/unix/configure.cmake
@@ -86,6 +86,7 @@ check_cxx_source_runs("
 
 
 check_library_exists(c sched_getaffinity "" HAVE_SCHED_GETAFFINITY)
+check_library_exists(c sched_setaffinity "" HAVE_SCHED_SETAFFINITY)
 check_library_exists(pthread pthread_create "" HAVE_LIBPTHREAD)
 
 if (HAVE_LIBPTHREAD)
@@ -94,7 +95,7 @@ elseif (HAVE_PTHREAD_IN_LIBC)
   set(PTHREAD_LIBRARY c)
 endif()
 
-check_library_exists(${PTHREAD_LIBRARY} pthread_getaffinity_np "" HAVE_PTHREAD_GETAFFINITY_NP)
+check_library_exists(${PTHREAD_LIBRARY} pthread_setaffinity_np "" HAVE_PTHREAD_SETAFFINITY_NP)
 
 check_cxx_symbol_exists(_SC_PHYS_PAGES unistd.h HAVE__SC_PHYS_PAGES)
 check_cxx_symbol_exists(_SC_AVPHYS_PAGES unistd.h HAVE__SC_AVPHYS_PAGES)
diff --git a/src/coreclr/src/gc/unix/gcenv.unix.cpp b/src/coreclr/src/gc/unix/gcenv.unix.cpp
index e7a12249869987..76a9efaf36e56e 100644
--- a/src/coreclr/src/gc/unix/gcenv.unix.cpp
+++ b/src/coreclr/src/gc/unix/gcenv.unix.cpp
@@ -985,19 +985,32 @@ size_t GCToOSInterface::GetCacheSizePerLogicalCpu(bool trueSize)
 //  true if setting the affinity was successful, false otherwise.
 bool GCToOSInterface::SetThreadAffinity(uint16_t procNo)
 {
-#if HAVE_PTHREAD_GETAFFINITY_NP
+#if HAVE_SCHED_SETAFFINITY || HAVE_PTHREAD_SETAFFINITY_NP
     cpu_set_t cpuSet;
     CPU_ZERO(&cpuSet);
     CPU_SET((int)procNo, &cpuSet);
 
+    // Snap's default strict confinement does not allow sched_setaffinity(<nonzeroPid>, ...) without manually connecting the
+    // process-control plug. sched_setaffinity(<currentThreadPid>, ...) is also currently not allowed, only
+    // sched_setaffinity(0, ...). pthread_setaffinity_np(pthread_self(), ...) seems to call
+    // sched_setaffinity(<currentThreadPid>, ...) in at least one implementation, and does not work. To work around those
+    // issues, use sched_setaffinity(0, ...) if available and only otherwise fall back to pthread_setaffinity_np(). See the
+    // following for more information:
+    // - https://github.com/dotnet/runtime/pull/38795
+    // - https://github.com/dotnet/runtime/issues/1634
+    // - https://forum.snapcraft.io/t/requesting-autoconnect-for-interfaces-in-pigmeat-process-control-home/17987/13
+#if HAVE_SCHED_SETAFFINITY
+    int st = sched_setaffinity(0, sizeof(cpu_set_t), &cpuSet);
+#else
     int st = pthread_setaffinity_np(pthread_self(), sizeof(cpu_set_t), &cpuSet);
+#endif
 
     return (st == 0);
 
-#else  // HAVE_PTHREAD_GETAFFINITY_NP
+#else  // !(HAVE_SCHED_SETAFFINITY || HAVE_PTHREAD_SETAFFINITY_NP)
     // There is no API to manage thread affinity, so let's ignore the request
     return false;
-#endif // HAVE_PTHREAD_GETAFFINITY_NP
+#endif // HAVE_SCHED_SETAFFINITY || HAVE_PTHREAD_SETAFFINITY_NP
 }
 
 // Boosts the calling thread's thread priority to a level higher than the default
diff --git a/src/coreclr/src/gcinfo/CMakeLists.txt b/src/coreclr/src/gcinfo/CMakeLists.txt
index 3862de8633d0cb..f40ff3deb83a0b 100644
--- a/src/coreclr/src/gcinfo/CMakeLists.txt
+++ b/src/coreclr/src/gcinfo/CMakeLists.txt
@@ -3,6 +3,7 @@ set(CMAKE_INCLUDE_CURRENT_DIR ON)
 set( GCINFO_SOURCES
   arraylist.cpp
   gcinfoencoder.cpp
+  simplerhash.cpp
 )
 
 
@@ -16,11 +17,14 @@ endif(CLR_CMAKE_TARGET_ARCH_I386)
 
 convert_to_absolute_path(GCINFO_SOURCES ${GCINFO_SOURCES})
 
-add_library_clr(gcinfo
+add_library_clr(gcinfo_obj
     OBJECT
     ${GCINFO_SOURCES}
 )
 
+add_library(gcinfo INTERFACE)
+target_sources(gcinfo INTERFACE $<TARGET_OBJECTS:gcinfo_obj>)
+
 add_library_clr(gcinfo_crossgen
     STATIC
     ${GCINFO_SOURCES}
diff --git a/src/coreclr/src/gcinfo/simplerhash.cpp b/src/coreclr/src/gcinfo/simplerhash.cpp
new file mode 100644
index 00000000000000..1233b91538c263
--- /dev/null
+++ b/src/coreclr/src/gcinfo/simplerhash.cpp
@@ -0,0 +1,41 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#include "simplerhash.h"
+
+// Table of primes and their magic-number-divide constant.
+// For more info see the book "Hacker's Delight" chapter 10.9 "Unsigned Division by Divisors >= 1"
+// These were selected by looking for primes, each roughly twice as big as the next, having
+// 32-bit magic numbers, (because the algorithm for using 33-bit magic numbers is slightly slower).
+//
+
+const PrimeInfo primeInfo[] =
+{
+    PrimeInfo(9,         0x38e38e39, 1),
+    PrimeInfo(23,        0xb21642c9, 4),
+    PrimeInfo(59,        0x22b63cbf, 3),
+    PrimeInfo(131,       0xfa232cf3, 7),
+    PrimeInfo(239,       0x891ac73b, 7),
+    PrimeInfo(433,       0x975a751,  4),
+    PrimeInfo(761,       0x561e46a5, 8),
+    PrimeInfo(1399,      0xbb612aa3, 10),
+    PrimeInfo(2473,      0x6a009f01, 10),
+    PrimeInfo(4327,      0xf2555049, 12),
+    PrimeInfo(7499,      0x45ea155f, 11),
+    PrimeInfo(12973,     0x1434f6d3, 10),
+    PrimeInfo(22433,     0x2ebe18db, 12),
+    PrimeInfo(46559,     0xb42bebd5, 15),
+    PrimeInfo(96581,     0xadb61b1b, 16),
+    PrimeInfo(200341,    0x29df2461, 15),
+    PrimeInfo(415517,    0xa181c46d, 18),
+    PrimeInfo(861719,    0x4de0bde5, 18),
+    PrimeInfo(1787021,   0x9636c46f, 20),
+    PrimeInfo(3705617,   0x4870adc1, 20),
+    PrimeInfo(7684087,   0x8bbc5b83, 22),
+    PrimeInfo(15933877,  0x86c65361, 23),
+    PrimeInfo(33040633,  0x40fec79b, 23),
+    PrimeInfo(68513161,  0x7d605cd1, 25),
+    PrimeInfo(142069021, 0xf1da390b, 27),
+    PrimeInfo(294594427, 0x74a2507d, 27),
+    PrimeInfo(733045421, 0x5dbec447, 28),
+};
diff --git a/src/coreclr/src/ildasm/dasm.cpp b/src/coreclr/src/ildasm/dasm.cpp
index da3d12f0f33684..eecd1edbf263fe 100644
--- a/src/coreclr/src/ildasm/dasm.cpp
+++ b/src/coreclr/src/ildasm/dasm.cpp
@@ -3300,7 +3300,9 @@ void DumpGenericParsCA(mdToken tok, void* GUICookie/*=NULL*/)
     } //end if(g_fShowCA)
 }
 
-// Sets *pbOverridingTypeSpec to TRUE if we are overriding a method declared by a type spec.
+// Sets *pbOverridingTypeSpec to TRUE if we are overriding a method declared by a type spec or
+// if the method has a signature which does not exactly match between the overrider and overridee.
+// That case is commonly caused by covariant overrides.
 // In that case the syntax is slightly different (there are additional 'method' keywords).
 // Refer to Expert .NET 2.0 IL Assembler page 242.
 void PrettyPrintOverrideDecl(ULONG i, __inout __nullterminated char* szString, void* GUICookie, mdToken tkOverrider,
@@ -3320,6 +3322,11 @@ void PrettyPrintOverrideDecl(ULONG i, __inout __nullterminated char* szString, v
 
     if(g_pImport->IsValidToken(tkDecl))
     {
+        bool needsFullTokenPrint = false;
+        bool hasTkDeclParent = false;
+
+        // Determine if the decl is a typespec method, in which case the "method" syntax + full token print
+        // must be used to generate the disassembly.
         if(SUCCEEDED(g_pImport->GetParentToken(tkDecl,&tkDeclParent)))
         {
             if(g_pImport->IsValidToken(tkDeclParent))
@@ -3334,20 +3341,99 @@ void PrettyPrintOverrideDecl(ULONG i, __inout __nullterminated char* szString, v
                 {
                     if(TypeFromToken(tkDeclParent)==mdtTypeSpec)
                     {
-                        szptr += sprintf_s(szptr,SZSTRING_REMAINING_SIZE(szptr), " %s ",KEYWORD("method"));
-                        PrettyPrintToken(szString,tkDecl,g_pImport,GUICookie,tkOverrider);
-
-                        *pbOverridingTypeSpec = TRUE;
-                        return;
+                        needsFullTokenPrint = true;
                     }
-                    PrettyPrintToken(szString, tkDeclParent, g_pImport,GUICookie,tkOverrider);
-                    strcat_s(szString, SZSTRING_SIZE,"::");
-                    szptr = &szString[strlen(szString)];
+                    hasTkDeclParent = true;
                 }
             }
             else
                 szptr+=sprintf_s(szptr,SZSTRING_REMAINING_SIZE(szptr),"%s",ERRORMSG("INVALID OVERRIDDEN METHOD'S PARENT TOKEN"));
         }
+
+        // Determine if the sig of the decl does not match the sig of the body
+        // In that case the full "method" syntax must be used
+        if ((TypeFromToken(tkOverrider) == mdtMethodDef) && !needsFullTokenPrint)
+        {
+            PCCOR_SIGNATURE pComSigDecl;
+            ULONG cComSigDecl;
+            mdToken tkDeclSigTok = tkDecl;
+            bool successfullyGotDeclSig = false;
+            bool successfullyGotBodySig = false;
+
+            if (TypeFromToken(tkDeclSigTok) == mdtMethodSpec)
+            {
+                mdToken         meth=0;
+                if (SUCCEEDED(g_pImport->GetMethodSpecProps(tkDeclSigTok, &meth, NULL, NULL)))
+                {
+                    tkDeclSigTok = meth;
+                }
+            }
+
+            if (TypeFromToken(tkDeclSigTok) == mdtMethodDef)
+            {
+                if (SUCCEEDED(g_pImport->GetSigOfMethodDef(tkDeclSigTok, &cComSigDecl, &pComSigDecl)))
+                {
+                    successfullyGotDeclSig = true;
+                }
+            }
+            else if (TypeFromToken(tkDeclSigTok) == mdtMemberRef)
+            {
+                const char *pszMemberNameUnused;
+                if (SUCCEEDED(g_pImport->GetNameAndSigOfMemberRef(
+                    tkDeclSigTok,
+                    &pComSigDecl,
+                    &cComSigDecl,
+                    &pszMemberNameUnused)))
+                {
+                    successfullyGotDeclSig = true;
+                }
+            }
+
+            PCCOR_SIGNATURE pComSigBody;
+            ULONG cComSigBody;
+            if (SUCCEEDED(g_pImport->GetSigOfMethodDef(tkOverrider, &cComSigBody, &pComSigBody)))
+            {
+                successfullyGotBodySig = true;
+            }
+
+            if (successfullyGotDeclSig && successfullyGotBodySig)
+            {
+                if (cComSigBody != cComSigDecl)
+                {
+                    needsFullTokenPrint = true;
+                }
+                else if (memcmp(pComSigBody, pComSigDecl, cComSigBody) != 0)
+                {
+                    needsFullTokenPrint = true;
+                }
+
+                // Signature are binary identical, full sig printing not needed
+            }
+            else
+            {
+                szptr+=sprintf_s(szptr,SZSTRING_REMAINING_SIZE(szptr),"%s",ERRORMSG("INVALID BODY OR DECL SIG"));
+            }
+        }
+
+        if (needsFullTokenPrint)
+        {
+            // In this case, the shortcut syntax cannot be used, and a full token must be printed.
+            // Print the full token and return.
+            szptr += sprintf_s(szptr,SZSTRING_REMAINING_SIZE(szptr), " %s ",KEYWORD("method"));
+            PrettyPrintToken(szString,tkDecl,g_pImport,GUICookie,tkOverrider);
+
+            *pbOverridingTypeSpec = TRUE;
+            return;
+        }
+
+        if (hasTkDeclParent)
+        {
+            // If the tkDeclParent was successfully retrieved during parent discovery print it here.
+            PrettyPrintToken(szString, tkDeclParent, g_pImport,GUICookie,tkOverrider);
+            strcat_s(szString, SZSTRING_SIZE,"::");
+            szptr = &szString[strlen(szString)];
+        }
+
         if(TypeFromToken(tkDecl) == mdtMethodSpec)
         {
             mdToken         meth=0;
diff --git a/src/coreclr/src/inc/CMakeLists.txt b/src/coreclr/src/inc/CMakeLists.txt
index 81762201251665..4f75d3a882d4c1 100644
--- a/src/coreclr/src/inc/CMakeLists.txt
+++ b/src/coreclr/src/inc/CMakeLists.txt
@@ -58,7 +58,9 @@ if(FEATURE_JIT_PITCHING)
 endif(FEATURE_JIT_PITCHING)
 
 # Compile *_i.cpp to lib
-_add_library(corguids OBJECT ${CORGUIDS_SOURCES})
+_add_library(corguids_obj OBJECT ${CORGUIDS_SOURCES})
+add_library(corguids INTERFACE)
+target_sources(corguids INTERFACE $<TARGET_OBJECTS:corguids_obj>)
 
 # Binplace the inc files for packaging later.
 
@@ -75,4 +77,3 @@ _install (FILES cfi.h
                gcinfoencoder.h
                gcinfotypes.h
                DESTINATION inc)
-_install (TARGETS corguids DESTINATION lib)
diff --git a/src/coreclr/src/inc/clr/fs/path.h b/src/coreclr/src/inc/clr/fs/path.h
index 7f1d0e00d73823..efc21a5cdd4392 100644
--- a/src/coreclr/src/inc/clr/fs/path.h
+++ b/src/coreclr/src/inc/clr/fs/path.h
@@ -9,7 +9,6 @@
 #define _clr_fs_Path_h_
 
 #include "clrtypes.h"
-#include "cor.h" // SELECTANY
 
 #include "strsafe.h"
 
diff --git a/src/coreclr/src/inc/clrconfigvalues.h b/src/coreclr/src/inc/clrconfigvalues.h
index ddb1db3ce647d8..3cd7db89bb7e9e 100644
--- a/src/coreclr/src/inc/clrconfigvalues.h
+++ b/src/coreclr/src/inc/clrconfigvalues.h
@@ -553,6 +553,8 @@ RETAIL_CONFIG_DWORD_INFO(INTERNAL_ThreadSuspendInjection, W("INTERNAL_ThreadSusp
 RETAIL_CONFIG_DWORD_INFO(INTERNAL_DefaultStackSize, W("DefaultStackSize"), 0, "Stack size to use for new VM threads when thread is created with default stack size (dwStackSize == 0).")
 RETAIL_CONFIG_DWORD_INFO(INTERNAL_Thread_DeadThreadCountThresholdForGCTrigger, W("Thread_DeadThreadCountThresholdForGCTrigger"), 75, "In the heuristics to clean up dead threads, this threshold must be reached before triggering a GC will be considered. Set to 0 to disable triggering a GC based on dead threads.")
 RETAIL_CONFIG_DWORD_INFO(INTERNAL_Thread_DeadThreadGCTriggerPeriodMilliseconds, W("Thread_DeadThreadGCTriggerPeriodMilliseconds"), 1000 * 60 * 30, "In the heuristics to clean up dead threads, this much time must have elapsed since the previous max-generation GC before triggering another GC will be considered")
+RETAIL_CONFIG_DWORD_INFO(EXTERNAL_Thread_UseAllCpuGroups, W("Thread_UseAllCpuGroups"), 0, "Specifies whether to query and use CPU group information for determining the processor count.")
+RETAIL_CONFIG_DWORD_INFO(EXTERNAL_Thread_AssignCpuGroups, W("Thread_AssignCpuGroups"), 1, "Specifies whether to automatically distribute threads created by the CLR across CPU Groups. Effective only when Thread_UseAllCpuGroups and GCCpuGroup are enabled.")
 
 ///
 /// Threadpool
@@ -568,7 +570,6 @@ RETAIL_CONFIG_DWORD_INFO(INTERNAL_ThreadPool_UnfairSemaphoreSpinLimit, W("Thread
 #else // !TARGET_ARM64
 RETAIL_CONFIG_DWORD_INFO(INTERNAL_ThreadPool_UnfairSemaphoreSpinLimit, W("ThreadPool_UnfairSemaphoreSpinLimit"), 0x46, "Maximum number of spins a thread pool worker thread performs before waiting for work")
 #endif // TARGET_ARM64
-RETAIL_CONFIG_DWORD_INFO(EXTERNAL_Thread_UseAllCpuGroups, W("Thread_UseAllCpuGroups"), 0, "Specifies if to automatically distribute thread across CPU Groups")
 
 CONFIG_DWORD_INFO(INTERNAL_ThreadpoolTickCountAdjustment, W("ThreadpoolTickCountAdjustment"), 0, "")
 
@@ -691,7 +692,6 @@ RETAIL_CONFIG_STRING_INFO(INTERNAL_EventNameFilter, W("EventNameFilter"), "")
 /// Interop
 ///
 CONFIG_DWORD_INFO_DIRECT_ACCESS(INTERNAL_ExposeExceptionsInCOM, W("ExposeExceptionsInCOM"), "")
-RETAIL_CONFIG_STRING_INFO_EX(EXTERNAL_PInvokeInline, W("PInvokeInline"), "", CLRConfig::EEConfig_default)
 RETAIL_CONFIG_DWORD_INFO(UNSUPPORTED_InteropValidatePinnedObjects, W("InteropValidatePinnedObjects"), 0, "After returning from a managed-to-unmanaged interop call, validate GC heap around objects pinned by IL stubs.")
 RETAIL_CONFIG_DWORD_INFO(EXTERNAL_InteropLogArguments, W("InteropLogArguments"), 0, "Log all pinned arguments passed to an interop call")
 RETAIL_CONFIG_STRING_INFO(UNSUPPORTED_LogCCWRefCountChange, W("LogCCWRefCountChange"), "Outputs debug information and calls LogCCWRefCountChange_BREAKPOINT when AddRef or Release is called on a CCW.")
diff --git a/src/coreclr/src/inc/cor.h b/src/coreclr/src/inc/cor.h
index 9625641288ca6b..035ba44e7f87f4 100644
--- a/src/coreclr/src/inc/cor.h
+++ b/src/coreclr/src/inc/cor.h
@@ -2093,15 +2093,7 @@ inline ULONG CorSigUncompressData(      // return number of bytes of that compre
 }
 
 
-#if !defined(SELECTANY)
-#if defined(__GNUC__)
-    #define SELECTANY extern __attribute__((weak))
-#else
-    #define SELECTANY extern __declspec(selectany)
-#endif
-#endif
-
-SELECTANY const mdToken g_tkCorEncodeToken[4] ={mdtTypeDef, mdtTypeRef, mdtTypeSpec, mdtBaseType};
+extern const mdToken g_tkCorEncodeToken[];
 
 // uncompress a token
 inline mdToken CorSigUncompressToken(   // return the token.
diff --git a/src/coreclr/src/inc/corcompile.h b/src/coreclr/src/inc/corcompile.h
index f02a7a1475d003..82308d7b899acc 100644
--- a/src/coreclr/src/inc/corcompile.h
+++ b/src/coreclr/src/inc/corcompile.h
@@ -1412,7 +1412,7 @@ class ICorCompileInfo
     // So, the host must call StartupAsCompilationProcess before compiling
     // any code, and Shutdown after finishing.
     //
-    // The arguments control which native image of mscorlib to use.
+    // The arguments control which native image of CoreLib to use.
     // This matters for hardbinding.
     //
 
@@ -1548,8 +1548,8 @@ class ICorCompileInfo
             mdFieldDef             *token
             ) = 0;
 
-    // Get the loader module for mscorlib
-    virtual CORINFO_MODULE_HANDLE GetLoaderModuleForMscorlib() = 0;
+    // Get the loader module for CoreLib
+    virtual CORINFO_MODULE_HANDLE GetLoaderModuleForCoreLib() = 0;
 
     // Get the loader module for a type (where the type is regarded as
     // living for the purposes of loading, unloading, and ngen).
diff --git a/src/coreclr/src/inc/cordebug.idl b/src/coreclr/src/inc/cordebug.idl
index 7ab2867d9f2827..efecf3b55063c3 100644
--- a/src/coreclr/src/inc/cordebug.idl
+++ b/src/coreclr/src/inc/cordebug.idl
@@ -2361,7 +2361,7 @@ interface ICorDebugAppDomain4 : IUnknown
  * Assembly interface
  * An ICorDebugAssembly instance corresponds to a a managed assembly loaded
  * into a specific AppDomain in the CLR.  For assemblies shared between multiple
- * AppDomains (eg. mscorlib), there will be a separate ICorDebugAssembly instance
+ * AppDomains (eg. CoreLib), there will be a separate ICorDebugAssembly instance
  * per AppDomain in which it is used.
  * ------------------------------------------------------------------------- */
 [
@@ -5173,6 +5173,30 @@ interface ICorDebugModule3 : IUnknown
                                            [out][iid_is(riid)] void **ppObj);
 }
 
+/*
+ * ICorDebugModule4 is a logical extension to ICorDebugModule.
+ */
+[
+    object,
+    local,
+    uuid(FF8B8EAF-25CD-4316-8859-84416DE4402E),
+    pointer_default(unique)
+]
+interface ICorDebugModule4 : IUnknown
+{
+    /*
+     * Query to see if the module is loaded into memory in mapped/hydrated format
+     *
+     * Arguments:
+     *     pIsMapped - BOOL to store mapping information. TRUE will represent mapped
+                      format while FALSE represents flat format.
+     * Return Value:
+     *     S_OK in successful case.
+     * Notes:
+     */
+    HRESULT IsMappedLayout([out] BOOL *pIsMapped);
+}
+
 /*
  * ICorDebugRuntimeUnwindableFrame is a specialized interface of ICorDebugFrame for unmanaged methods
  * which requires special knowledge to unwind.  They are not jitted code.  When the debugger sees this type
@@ -5196,7 +5220,7 @@ interface ICorDebugRuntimeUnwindableFrame : ICorDebugFrame
  * specific AppDomain.  Normally this is an executable or a DLL, but it may also be
  * some other file of a multi-module assembly.  There is an ICorDebugModule instance
  * for each AppDomain a module is loaded into, even in the case of shared modules like
- * mscorlib.
+ * CoreLib.
  */
 
 [
diff --git a/src/coreclr/src/inc/corerror.xml b/src/coreclr/src/inc/corerror.xml
index 94fe6a1ddceaef..b1a0b5b53ca090 100644
--- a/src/coreclr/src/inc/corerror.xml
+++ b/src/coreclr/src/inc/corerror.xml
@@ -2201,12 +2201,6 @@
 	<Comment> File is PE32 </Comment>
 </HRESULT>
 
-<HRESULT NumericValue="0x80131f06">
-	<SymbolicName>NGEN_E_SYS_ASM_NI_MISSING</SymbolicName>
-	<Message>"NGen cannot proceed because Mscorlib.dll does not have a native image"</Message>
-	<Comment>Compiling any assembly other than mscorlib in the absence of mscorlib.ni.dll is not allowed.</Comment>
-</HRESULT>
-
 <HRESULT NumericValue="0x80131fff">
 	<SymbolicName>CLDB_E_INTERNALERROR</SymbolicName>
 </HRESULT>
@@ -2249,8 +2243,8 @@
 
 <HRESULT NumericValue="0x80132006">
 	<SymbolicName>CLR_E_BIND_SYS_ASM_NI_MISSING</SymbolicName>
-	<Message>"Could not use native image because Mscorlib.dll is missing a native image"</Message>
-	<Comment>Returned when loading an assembly that only has a native image and no IL and cannot hardbind to mscorlib.ni.dll.</Comment>
+	<Message>"Could not use native image because System.Private.CoreLib.dll is missing a native image"</Message>
+	<Comment>Returned when loading an assembly that only has a native image and no IL and cannot hardbind to System.Private.CoreLib.ni.dll.</Comment>
 </HRESULT>
 
 <HRESULT NumericValue="0x80132007">
diff --git a/src/coreclr/src/inc/corexcep.h b/src/coreclr/src/inc/corexcep.h
index faca6b49c593be..e1c00b50b32175 100644
--- a/src/coreclr/src/inc/corexcep.h
+++ b/src/coreclr/src/inc/corexcep.h
@@ -13,7 +13,7 @@
 
 // All COM+ exceptions are expressed as a RaiseException with this exception
 // code.  If you change this value, you must also change
-// mscorlib\src\system\Exception.cs's _COMPlusExceptionCode value.
+// Exception.cs's _COMPlusExceptionCode value.
 
 #define EXCEPTION_MSVC    0xe06d7363    // 0xe0000000 | 'msc'
 
diff --git a/src/coreclr/src/inc/corinfo.h b/src/coreclr/src/inc/corinfo.h
index f7f6d8ecf2ea4e..7870683ecf4399 100644
--- a/src/coreclr/src/inc/corinfo.h
+++ b/src/coreclr/src/inc/corinfo.h
@@ -208,19 +208,11 @@ TODO: Talk about initializing strutures before use
 //
 //////////////////////////////////////////////////////////////////////////////////////////////////////////
 
-#if !defined(SELECTANY)
-#if defined(__GNUC__)
-    #define SELECTANY extern __attribute__((weak))
-#else
-    #define SELECTANY extern __declspec(selectany)
-#endif
-#endif
-
-SELECTANY const GUID JITEEVersionIdentifier = { /* 7af97117-55be-4c76-afb2-e26261cb140e */
-    0x7af97117,
-    0x55be,
-    0x4c76,
-    { 0xaf, 0xb2, 0xe2, 0x62, 0x61, 0xcb, 0x14, 0x0e }
+constexpr GUID JITEEVersionIdentifier = { /* a5eec3a4-4176-43a7-8c2b-a05b551d4f49 */
+    0xa5eec3a4,
+    0x4176,
+    0x43a7,
+    {0x8c, 0x2b, 0xa0, 0x5b, 0x55, 0x1d, 0x4f, 0x49}
 };
 
 //////////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -899,28 +891,6 @@ enum CorInfoException
 
 enum CorInfoIntrinsics
 {
-    CORINFO_INTRINSIC_Sin,
-    CORINFO_INTRINSIC_Cos,
-    CORINFO_INTRINSIC_Cbrt,
-    CORINFO_INTRINSIC_Sqrt,
-    CORINFO_INTRINSIC_Abs,
-    CORINFO_INTRINSIC_Round,
-    CORINFO_INTRINSIC_Cosh,
-    CORINFO_INTRINSIC_Sinh,
-    CORINFO_INTRINSIC_Tan,
-    CORINFO_INTRINSIC_Tanh,
-    CORINFO_INTRINSIC_Asin,
-    CORINFO_INTRINSIC_Asinh,
-    CORINFO_INTRINSIC_Acos,
-    CORINFO_INTRINSIC_Acosh,
-    CORINFO_INTRINSIC_Atan,
-    CORINFO_INTRINSIC_Atan2,
-    CORINFO_INTRINSIC_Atanh,
-    CORINFO_INTRINSIC_Log10,
-    CORINFO_INTRINSIC_Pow,
-    CORINFO_INTRINSIC_Exp,
-    CORINFO_INTRINSIC_Ceiling,
-    CORINFO_INTRINSIC_Floor,
     CORINFO_INTRINSIC_GetChar,              // fetch character out of string
     CORINFO_INTRINSIC_Array_GetDimLength,   // Get number of elements in a given dimension of an array
     CORINFO_INTRINSIC_Array_Get,            // Get the value of an element in an array
diff --git a/src/coreclr/src/inc/corpriv.h b/src/coreclr/src/inc/corpriv.h
index 52cf63a0ee07b5..fb0b39924cc877 100644
--- a/src/coreclr/src/inc/corpriv.h
+++ b/src/coreclr/src/inc/corpriv.h
@@ -235,7 +235,7 @@ typedef enum CorElementTypeZapSig
     // where the encoding/decoding takes place.
     ELEMENT_TYPE_NATIVE_VALUETYPE_ZAPSIG = 0x3d,
 
-    ELEMENT_TYPE_CANON_ZAPSIG            = 0x3e,     // zapsig encoding for [mscorlib]System.__Canon
+    ELEMENT_TYPE_CANON_ZAPSIG            = 0x3e,     // zapsig encoding for System.__Canon
     ELEMENT_TYPE_MODULE_ZAPSIG           = 0x3f,     // zapsig encoding for external module id#
 
 } CorElementTypeZapSig;
diff --git a/src/coreclr/src/inc/dacvars.h b/src/coreclr/src/inc/dacvars.h
index f480851e1b27fb..92f3edf77855bc 100644
--- a/src/coreclr/src/inc/dacvars.h
+++ b/src/coreclr/src/inc/dacvars.h
@@ -144,7 +144,7 @@ DEFINE_DACVAR(ULONG, PTR_GcNotification, dac__g_pGcNotificationTable, ::g_pGcNot
 
 DEFINE_DACVAR(ULONG, PTR_EEConfig, dac__g_pConfig, ::g_pConfig)
 
-DEFINE_DACVAR(ULONG, MscorlibBinder, dac__g_Mscorlib, ::g_Mscorlib)
+DEFINE_DACVAR(ULONG, CoreLibBinder, dac__g_CoreLib, ::g_CoreLib)
 
 #if defined(PROFILING_SUPPORTED) || defined(PROFILING_SUPPORTED_DATA)
 DEFINE_DACVAR(ULONG, ProfControlBlock, dac__g_profControlBlock, ::g_profControlBlock)
diff --git a/src/coreclr/src/inc/delayloadhelpers.h b/src/coreclr/src/inc/delayloadhelpers.h
deleted file mode 100644
index 740999926a28cd..00000000000000
--- a/src/coreclr/src/inc/delayloadhelpers.h
+++ /dev/null
@@ -1,112 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-//
-
-//
-// Contains convenience functionality for lazily loading modules
-// and getting entrypoints within them.
-//
-
-#ifndef DelayLoadHelpers_h
-#define DelayLoadHelpers_h
-
-#include "volatile.h"
-
-namespace DelayLoad
-{
-    //=================================================================================================================
-    // Contains information needed to load and cache a module. Use through
-    // the DELAY_LOADED_MODULE macro defined below.
-    struct Module
-    {
-        LPCWSTR const   m_wzDllName;
-        HMODULE         m_hMod;
-        HRESULT         m_hr;
-        Volatile<bool>  m_fInitialized;
-
-        // Returns a non-ref-counted HMODULE; will load the module if necessary.
-        // Do not FreeLibrary the returned value.
-        HRESULT GetValue(HMODULE *pHMODULE);
-    };
-}
-
-//=====================================================================================================================
-// Use at global scope to declare a delay loaded module represented as a
-// DelayLoad::Module instance. The module may then be accessed as
-// 'DelayLoad::Modules::DLL_NAME'.
-//
-// Parameters:
-//      DLL_NAME - the simple name (without extension) of the DLL.
-//
-// Example:
-//      DELAY_LOADED_MODULE(Kernel32);
-//      void Foo() {
-//          HMODULE hModKernel32 = nullptr;
-//          IfFailThrow(DelayLoad::Modules::Kernel32.GetValue(&hModKernel32));
-//          // Use hModKernel32 as needed. Do not FreeLibrary the value!
-//      }
-
-#define DELAY_LOADED_MODULE(DLL_NAME) \
-    namespace DelayLoad { \
-        namespace Modules { \
-            SELECTANY Module DLL_NAME = { L#DLL_NAME W(".dll"), nullptr, S_OK, false }; \
-        } \
-    }
-
-namespace DelayLoad
-{
-    //=================================================================================================================
-    // Contains information needed to load a function pointer from a DLL. Builds
-    // on the DelayLoad::Module functionality, and should be used through
-    // the DELAY_LOADED_FUNCTION macro defined below.
-    struct Function
-    {
-        Module * const  m_pModule;
-        LPCSTR const    m_szFunctionName;
-        PVOID           m_pvFunction;
-        HRESULT         m_hr;
-        Volatile<bool>  m_fInitialized;
-
-        // On success, ppvFunc is set to point to the entrypoint corresponding to
-        // m_szFunctionName as exported from m_pModule.
-        HRESULT GetValue(LPVOID * ppvFunc);
-
-        // Convenience function that does the necessary casting for you.
-        template <typename FnT> inline
-        HRESULT GetValue(FnT ** ppFunc)
-        {
-            return GetValue(reinterpret_cast<LPVOID*>(ppFunc));
-        }
-    };
-}
-
-//=====================================================================================================================
-// Use at global scope to declare a delay loaded function and its associated module,
-// represented as DelayLoad::Function and DelayLoad::Module instances, respectively.
-// The function may then be accessed as 'DelayLoad::DLL_NAME::FUNC_NAME', and the
-// module may be access as described in DELAY_LOADED_MODULE's comment.
-//
-// Parameters:
-//      DLL_NAME  - unquoted simple name (without extension) of the DLL containing
-//                  the function.
-//      FUNC_NAME - unquoted entrypoint name exported from the DLL.
-//
-// Example:
-//      DELAY_LOADED_FUNCTION(MyDll, MyFunction);
-//      HRESULT Foo(...) {
-//          typedef HRESULT MyFunction_t(<args>);
-//          MyFunction_t * pFunc = nullptr;
-//          IfFailRet(DelayLoad::WinTypes::RoResolveNamespace.GetValue(&pFunc));
-//          return (*pFunc)(...);
-//      }
-
-#define DELAY_LOADED_FUNCTION(DLL_NAME, FUNC_NAME) \
-    DELAY_LOADED_MODULE(DLL_NAME) \
-    namespace DelayLoad { \
-        namespace DLL_NAME { \
-            SELECTANY Function FUNC_NAME = { &Modules::##DLL_NAME, #FUNC_NAME, nullptr, S_OK, false }; \
-        } \
-    }
-
-#endif // DelayLoadHelpers_h
-
diff --git a/src/coreclr/src/inc/eventtrace.h b/src/coreclr/src/inc/eventtrace.h
index ef999a716c6943..1a930deebfa3e1 100644
--- a/src/coreclr/src/inc/eventtrace.h
+++ b/src/coreclr/src/inc/eventtrace.h
@@ -172,6 +172,8 @@ namespace ETW
         static void Cleanup();
         static VOID DeleteTypeHashNoLock(AllLoggedTypes **ppAllLoggedTypes);
         static VOID FlushObjectAllocationEvents();
+        static UINT32 TypeLoadBegin();
+        static VOID TypeLoadEnd(UINT32 typeLoad, TypeHandle th, UINT16 loadLevel);
 
     private:
         static BOOL ShouldLogType(TypeHandle th);
diff --git a/src/coreclr/src/inc/eventtracebase.h b/src/coreclr/src/inc/eventtracebase.h
index 771460b2db14de..863f704ab87b57 100644
--- a/src/coreclr/src/inc/eventtracebase.h
+++ b/src/coreclr/src/inc/eventtracebase.h
@@ -918,6 +918,7 @@ namespace ETW
         static const UINT8 MethodFlagsJitOptimizationTierShift = 7;
         static const unsigned int MethodFlagsJitOptimizationTierLowMask = 0x7;
 
+        static VOID GetR2RGetEntryPointStart(MethodDesc *pMethodDesc);
         static VOID GetR2RGetEntryPoint(MethodDesc *pMethodDesc, PCODE pEntryPoint);
         static VOID MethodJitting(MethodDesc *pMethodDesc, SString *namespaceOrClassName, SString *methodName, SString *methodSignature);
         static VOID MethodJitted(MethodDesc *pMethodDesc, SString *namespaceOrClassName, SString *methodName, SString *methodSignature, PCODE pNativeCodeStartAddress, PrepareCodeConfig *pConfig);
@@ -928,6 +929,7 @@ namespace ETW
         static VOID DynamicMethodDestroyed(MethodDesc *pMethodDesc);
 #else // FEATURE_EVENT_TRACE
     public:
+        static VOID GetR2RGetEntryPointStart(MethodDesc *pMethodDesc) {};
         static VOID GetR2RGetEntryPoint(MethodDesc *pMethodDesc, PCODE pEntryPoint) {};
         static VOID MethodJitting(MethodDesc *pMethodDesc, SString *namespaceOrClassName, SString *methodName, SString *methodSignature);
         static VOID MethodJitted(MethodDesc *pMethodDesc, SString *namespaceOrClassName, SString *methodName, SString *methodSignature, PCODE pNativeCodeStartAddress, PrepareCodeConfig *pConfig);
diff --git a/src/coreclr/src/inc/palclr.h b/src/coreclr/src/inc/palclr.h
index 40a68dd91384c1..2ab9c62c3e8446 100644
--- a/src/coreclr/src/inc/palclr.h
+++ b/src/coreclr/src/inc/palclr.h
@@ -485,26 +485,6 @@
 #define PAL_CPP_CATCH_EXCEPTION_NOARG catch (Exception *)
 
 
-//  SELECTANY macro is intended to prevent duplication of static const
-//  arrays declared in .h files in binary modules.
-//  The problem is that const variables have static internal linkage
-//  in C++.  That means that if a const variable is declared in a .h file
-//  the compiler will emit it into every translation unit that uses that .h file.
-//  That will cause duplication of the data when those translation units
-//  are linked into a binary module.
-//  SELECTANY declares a variable as extern to give it external linkage
-//  and it provides __declspec(selectany) to instruct the linker to merge
-//  duplicate external const static data copies into one.
-//
-#if defined(SOURCE_FORMATTING)
-#define SELECTANY extern
-#else
-#if defined(__GNUC__)
-#define SELECTANY extern __attribute__((weak))
-#else
-#define SELECTANY extern __declspec(selectany)
-#endif
-#endif
 #if defined(SOURCE_FORMATTING)
 #define __annotation(x)
 #endif
diff --git a/src/coreclr/src/inc/random.h b/src/coreclr/src/inc/random.h
index 53cc17d64908fa..f2501c356832c4 100644
--- a/src/coreclr/src/inc/random.h
+++ b/src/coreclr/src/inc/random.h
@@ -5,8 +5,7 @@
 //
 
 //
-// Defines a random number generator, initially from the System.Random code in the BCL.  If you notice any problems,
-// please compare to the implementation in src\mscorlib\src\system\random.cs.
+// Defines a random number generator, initially from the System.Random code in the BCL.
 //
 // Main advantages over rand() are:
 //
diff --git a/src/coreclr/src/inc/readytorun.h b/src/coreclr/src/inc/readytorun.h
index b883f4b558e9b5..e1719a2843eb74 100644
--- a/src/coreclr/src/inc/readytorun.h
+++ b/src/coreclr/src/inc/readytorun.h
@@ -395,4 +395,13 @@ enum ReadyToRunRuntimeConstants : DWORD
     READYTORUN_ReversePInvokeTransitionFrameSizeInPointerUnits = 2
 };
 
+enum ReadyToRunHFAElemType : DWORD
+{
+    READYTORUN_HFA_ELEMTYPE_None = 0,
+    READYTORUN_HFA_ELEMTYPE_Float32 = 1,
+    READYTORUN_HFA_ELEMTYPE_Float64 = 2,
+    READYTORUN_HFA_ELEMTYPE_Vector64 = 3,
+    READYTORUN_HFA_ELEMTYPE_Vector128 = 4,
+};
+
 #endif // __READYTORUN_H__
diff --git a/src/coreclr/src/inc/safemath.h b/src/coreclr/src/inc/safemath.h
index 84ea377c54b826..d93e4a57011e53 100644
--- a/src/coreclr/src/inc/safemath.h
+++ b/src/coreclr/src/inc/safemath.h
@@ -154,8 +154,7 @@ inline bool DoubleFitsInIntType(double val)
 
  //-----------------------------------------------------------------------------
 //
-// Liberally lifted from the Office example on MSDN and modified.
-// http://msdn.microsoft.com/library/en-us/dncode/html/secure01142004.asp
+// Liberally lifted from https://github.com/dcleblanc/SafeInt and modified.
 //
 // Modified to track an overflow bit instead of throwing exceptions.  In most
 // cases the Visual C++ optimizer (Whidbey beta1 - v14.00.40607) is able to
diff --git a/src/coreclr/src/inc/simplerhash.h b/src/coreclr/src/inc/simplerhash.h
index ebd8a3e6871ee7..83c552eda19f74 100644
--- a/src/coreclr/src/inc/simplerhash.h
+++ b/src/coreclr/src/inc/simplerhash.h
@@ -68,8 +68,8 @@ class DefaultSimplerHashBehavior
 class PrimeInfo
 {
 public:
-    PrimeInfo() : prime(0), magic(0), shift(0) {}
-    PrimeInfo(unsigned p, unsigned m, unsigned s) : prime(p), magic(m), shift(s) {}
+    constexpr PrimeInfo() : prime(0), magic(0), shift(0) {}
+    constexpr PrimeInfo(unsigned p, unsigned m, unsigned s) : prime(p), magic(m), shift(s) {}
     unsigned prime;
     unsigned magic;
     unsigned shift;
diff --git a/src/coreclr/src/inc/simplerhash.inl b/src/coreclr/src/inc/simplerhash.inl
index 10a6b157ce99cd..6694ab61212bcc 100644
--- a/src/coreclr/src/inc/simplerhash.inl
+++ b/src/coreclr/src/inc/simplerhash.inl
@@ -303,36 +303,7 @@ void SimplerHashTable<Key,KeyFuncs,Value,Behavior>::Reallocate(unsigned newTable
 // 32-bit magic numbers, (because the algorithm for using 33-bit magic numbers is slightly slower).
 //
 
-SELECTANY const PrimeInfo primeInfo[] =
-{
-    PrimeInfo(9,         0x38e38e39, 1),
-    PrimeInfo(23,        0xb21642c9, 4),
-    PrimeInfo(59,        0x22b63cbf, 3),
-    PrimeInfo(131,       0xfa232cf3, 7),
-    PrimeInfo(239,       0x891ac73b, 7),
-    PrimeInfo(433,       0x975a751,  4),
-    PrimeInfo(761,       0x561e46a5, 8),
-    PrimeInfo(1399,      0xbb612aa3, 10),
-    PrimeInfo(2473,      0x6a009f01, 10),
-    PrimeInfo(4327,      0xf2555049, 12),
-    PrimeInfo(7499,      0x45ea155f, 11),
-    PrimeInfo(12973,     0x1434f6d3, 10),
-    PrimeInfo(22433,     0x2ebe18db, 12),
-    PrimeInfo(46559,     0xb42bebd5, 15),
-    PrimeInfo(96581,     0xadb61b1b, 16),
-    PrimeInfo(200341,    0x29df2461, 15),
-    PrimeInfo(415517,    0xa181c46d, 18),
-    PrimeInfo(861719,    0x4de0bde5, 18),
-    PrimeInfo(1787021,   0x9636c46f, 20),
-    PrimeInfo(3705617,   0x4870adc1, 20),
-    PrimeInfo(7684087,   0x8bbc5b83, 22),
-    PrimeInfo(15933877,  0x86c65361, 23),
-    PrimeInfo(33040633,  0x40fec79b, 23),
-    PrimeInfo(68513161,  0x7d605cd1, 25),
-    PrimeInfo(142069021, 0xf1da390b, 27),
-    PrimeInfo(294594427, 0x74a2507d, 27),
-    PrimeInfo(733045421, 0x5dbec447, 28),
-};
+extern const PrimeInfo primeInfo[27];
 
 template <typename Key, typename KeyFuncs, typename Value, typename Behavior>
 PrimeInfo SimplerHashTable<Key,KeyFuncs,Value,Behavior>::NextPrime(unsigned number)
diff --git a/src/coreclr/src/inc/sospriv.idl b/src/coreclr/src/inc/sospriv.idl
index d5a5913f736fe5..770d5b56f749cc 100644
--- a/src/coreclr/src/inc/sospriv.idl
+++ b/src/coreclr/src/inc/sospriv.idl
@@ -409,3 +409,18 @@ interface ISOSDacInterface8 : IUnknown
 
     HRESULT GetAssemblyLoadContext(CLRDATA_ADDRESS methodTable, CLRDATA_ADDRESS* assemblyLoadContext);
 }
+
+// Increment anytime there is a change in the data structures that SOS depends on like
+// stress log structs (StressMsg, StressLogChunck, ThreadStressLog, etc), exception
+// stack traces (StackTraceElement), the PredefinedTlsSlots enums, etc.
+cpp_quote("#define SOS_BREAKING_CHANGE_VERSION 1")
+
+[
+    object,
+    local,
+    uuid(4eca42d8-7e7b-4c8a-a116-7bfbf6929267)
+]
+interface ISOSDacInterface9 : IUnknown
+{
+    HRESULT GetBreakingChangeVersion(int* pVersion);
+}
diff --git a/src/coreclr/src/inc/utilcode.h b/src/coreclr/src/inc/utilcode.h
index f02e58aeaf7db0..4ed456df94c7e1 100644
--- a/src/coreclr/src/inc/utilcode.h
+++ b/src/coreclr/src/inc/utilcode.h
@@ -1272,6 +1272,7 @@ class CPUGroupInfo
     static WORD m_nProcessors;
     static BOOL m_enableGCCPUGroups;
     static BOOL m_threadUseAllCpuGroups;
+    static BOOL m_threadAssignCpuGroups;
     static WORD m_initialGroup;
     static CPU_Group_Info *m_CPUGroupInfoArray;
     static bool s_hadSingleProcessorAtStartup;
@@ -1285,6 +1286,7 @@ class CPUGroupInfo
     static void EnsureInitialized();
     static BOOL CanEnableGCCPUGroups();
     static BOOL CanEnableThreadUseAllCpuGroups();
+    static BOOL CanAssignCpuGroupsToThreads();
     static WORD GetNumActiveProcessors();
     static void GetGroupForProcessor(WORD processor_number,
 		    WORD *group_number, WORD *group_processor_number);
@@ -4071,13 +4073,14 @@ HRESULT GetImageRuntimeVersionString(PVOID pMetaData, LPCSTR* pString);
 // The registry keys and values that contain the information regarding
 // the default registered unmanaged debugger.
 //*****************************************************************************
-SELECTANY const WCHAR kDebugApplicationsPoliciesKey[] = W("SOFTWARE\\Policies\\Microsoft\\Windows\\Windows Error Reporting\\DebugApplications");
-SELECTANY const WCHAR kDebugApplicationsKey[] = W("SOFTWARE\\Microsoft\\Windows\\Windows Error Reporting\\DebugApplications");
 
-SELECTANY const WCHAR kUnmanagedDebuggerKey[] = W("SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug");
-SELECTANY const WCHAR kUnmanagedDebuggerValue[] = W("Debugger");
-SELECTANY const WCHAR kUnmanagedDebuggerAutoValue[] = W("Auto");
-SELECTANY const WCHAR kUnmanagedDebuggerAutoExclusionListKey[] = W("SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug\\AutoExclusionList");
+#define kDebugApplicationsPoliciesKey W("SOFTWARE\\Policies\\Microsoft\\Windows\\Windows Error Reporting\\DebugApplications")
+#define kDebugApplicationsKey  W("SOFTWARE\\Microsoft\\Windows\\Windows Error Reporting\\DebugApplications")
+
+#define kUnmanagedDebuggerKey W("SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug")
+#define kUnmanagedDebuggerValue W("Debugger")
+#define kUnmanagedDebuggerAutoValue W("Auto")
+#define kUnmanagedDebuggerAutoExclusionListKey W("SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug\\AutoExclusionList")
 
 BOOL GetRegistryLongValue(HKEY    hKeyParent,              // Parent key.
                           LPCWSTR szKey,                   // Key name to look at.
diff --git a/src/coreclr/src/inc/zapper.h b/src/coreclr/src/inc/zapper.h
index ba4f65b15dd916..b88d4d51b676fb 100644
--- a/src/coreclr/src/inc/zapper.h
+++ b/src/coreclr/src/inc/zapper.h
@@ -285,7 +285,7 @@ class Zapper
 
     ~Zapper();
 
-    // The arguments control which native image of mscorlib to use.
+    // The arguments control which native image of CoreLib to use.
     // This matters for hardbinding.
     void InitEE(BOOL fForceDebug, BOOL fForceProfile, BOOL fForceInstrument);
     void LoadAndInitializeJITForNgen(LPCWSTR pwzJitName, OUT HINSTANCE* phJit, OUT ICorJitCompiler** ppICorJitCompiler);
diff --git a/src/coreclr/src/interop/CMakeLists.txt b/src/coreclr/src/interop/CMakeLists.txt
index b8a0e769318db3..1642f55a04da5f 100644
--- a/src/coreclr/src/interop/CMakeLists.txt
+++ b/src/coreclr/src/interop/CMakeLists.txt
@@ -30,7 +30,10 @@ endif(WIN32)
 
 convert_to_absolute_path(INTEROP_SOURCES ${INTEROP_SOURCES})
 
-add_library_clr(interop
+add_library_clr(interop_obj
     OBJECT
     ${INTEROP_SOURCES}
 )
+
+add_library(interop INTERFACE)
+target_sources(interop INTERFACE $<TARGET_OBJECTS:interop_obj>)
\ No newline at end of file
diff --git a/src/coreclr/src/jit/CMakeLists.txt b/src/coreclr/src/jit/CMakeLists.txt
index 15aa4d59b63ccd..3f695823be4f63 100644
--- a/src/coreclr/src/jit/CMakeLists.txt
+++ b/src/coreclr/src/jit/CMakeLists.txt
@@ -54,6 +54,7 @@ set( JIT_SOURCES
   instr.cpp
   jitconfig.cpp
   jiteh.cpp
+  jithashtable.cpp
   jittelemetry.cpp
   lclmorph.cpp
   lclvars.cpp
diff --git a/src/coreclr/src/jit/_typeinfo.h b/src/coreclr/src/jit/_typeinfo.h
index 4aa38c540b220b..26173db3fae494 100644
--- a/src/coreclr/src/jit/_typeinfo.h
+++ b/src/coreclr/src/jit/_typeinfo.h
@@ -42,7 +42,7 @@ enum ti_types
 namespace
 {
 #endif // _MSC_VER
-SELECTANY const char* g_ti_type_names_map[] = {
+const char* g_ti_type_names_map[] = {
 #define DEF_TI(ti, nm) nm,
 #include "titypes.h"
 #undef DEF_TI
@@ -57,7 +57,7 @@ SELECTANY const char* g_ti_type_names_map[] = {
 namespace
 {
 #endif //  _MSC_VER
-SELECTANY const ti_types g_jit_types_map[] = {
+const ti_types g_jit_types_map[] = {
 #define DEF_TP(tn, nm, jitType, verType, sz, sze, asze, st, al, tf, howUsed) verType,
 #include "typelist.h"
 #undef DEF_TP
@@ -92,7 +92,7 @@ inline ti_types varType2tiType(var_types type)
 namespace
 {
 #endif // _MSC_VER
-SELECTANY const ti_types g_ti_types_map[CORINFO_TYPE_COUNT] = {
+const ti_types g_ti_types_map[CORINFO_TYPE_COUNT] = {
     // see the definition of enum CorInfoType in file inc/corinfo.h
     TI_ERROR,  // CORINFO_TYPE_UNDEF           = 0x0,
     TI_ERROR,  // CORINFO_TYPE_VOID            = 0x1,
diff --git a/src/coreclr/src/jit/codegen.h b/src/coreclr/src/jit/codegen.h
index d6e14d7a308c18..e876b155ce3546 100644
--- a/src/coreclr/src/jit/codegen.h
+++ b/src/coreclr/src/jit/codegen.h
@@ -341,12 +341,12 @@ class CodeGen final : public CodeGenInterface
     void genSaveCalleeSavedRegistersHelp(regMaskTP regsToSaveMask, int lowestCalleeSavedOffset, int spDelta);
     void genRestoreCalleeSavedRegistersHelp(regMaskTP regsToRestoreMask, int lowestCalleeSavedOffset, int spDelta);
 
-    void genPushCalleeSavedRegisters(regNumber initReg, bool* pInitRegModified);
+    void genPushCalleeSavedRegisters(regNumber initReg, bool* pInitRegZeroed);
 #else
     void genPushCalleeSavedRegisters();
 #endif
 
-    void genAllocLclFrame(unsigned frameSize, regNumber initReg, bool* pInitRegModified, regMaskTP maskArgRegsLiveIn);
+    void genAllocLclFrame(unsigned frameSize, regNumber initReg, bool* pInitRegZeroed, regMaskTP maskArgRegsLiveIn);
 
 #if defined(TARGET_ARM)
 
@@ -434,18 +434,18 @@ class CodeGen final : public CodeGenInterface
 
     void genZeroInitFltRegs(const regMaskTP& initFltRegs, const regMaskTP& initDblRegs, const regNumber& initReg);
 
-    regNumber genGetZeroReg(regNumber initReg, bool* pInitRegModified);
+    regNumber genGetZeroReg(regNumber initReg, bool* pInitRegZeroed);
 
-    void genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg, bool* pInitRegModified);
+    void genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg, bool* pInitRegZeroed);
 
-    void genReportGenericContextArg(regNumber initReg, bool* pInitRegModified);
+    void genReportGenericContextArg(regNumber initReg, bool* pInitRegZeroed);
 
-    void genSetGSSecurityCookie(regNumber initReg, bool* pInitRegModified);
+    void genSetGSSecurityCookie(regNumber initReg, bool* pInitRegZeroed);
 
     void genFinalizeFrame();
 
 #ifdef PROFILING_SUPPORTED
-    void genProfilingEnterCallback(regNumber initReg, bool* pInitRegModified);
+    void genProfilingEnterCallback(regNumber initReg, bool* pInitRegZeroed);
     void genProfilingLeaveCallback(unsigned helper);
 #endif // PROFILING_SUPPORTED
 
@@ -511,7 +511,7 @@ class CodeGen final : public CodeGenInterface
     void genFuncletEpilog();
     void genCaptureFuncletPrologEpilogInfo();
 
-    void genSetPSPSym(regNumber initReg, bool* pInitRegModified);
+    void genSetPSPSym(regNumber initReg, bool* pInitRegZeroed);
 
     void genUpdateCurrentFunclet(BasicBlock* block);
 #if defined(TARGET_ARM)
diff --git a/src/coreclr/src/jit/codegenarm.cpp b/src/coreclr/src/jit/codegenarm.cpp
index 0407c710e4041d..2eaa80862396dd 100644
--- a/src/coreclr/src/jit/codegenarm.cpp
+++ b/src/coreclr/src/jit/codegenarm.cpp
@@ -45,7 +45,8 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 //                          if caller knows for certain the constant will fit.
 //
 // Return Value:
-//    returns true if the immediate was too large and tmpReg was used and modified.
+//    returns true if the immediate was small enough to be encoded inside instruction. If not,
+//    returns false meaning the immediate was too large and tmpReg was used and modified.
 //
 bool CodeGen::genInstrWithConstant(
     instruction ins, emitAttr attr, regNumber reg1, regNumber reg2, ssize_t imm, insFlags flags, regNumber tmpReg)
@@ -100,7 +101,8 @@ bool CodeGen::genInstrWithConstant(
 //    tmpReg                  - an available temporary register
 //
 // Return Value:
-//    true if `tmpReg` was used.
+//    returns true if the immediate was small enough to be encoded inside instruction. If not,
+//    returns false meaning the immediate was too large and tmpReg was used and modified.
 //
 bool CodeGen::genStackPointerAdjustment(ssize_t spDelta, regNumber tmpReg)
 {
@@ -1650,14 +1652,14 @@ void CodeGen::genCodeForMulLong(GenTreeMultiRegOp* node)
 // genProfilingEnterCallback: Generate the profiling function enter callback.
 //
 // Arguments:
-//     initReg          - register to use as scratch register
-//     pInitRegModified - OUT parameter. *pInitRegModified set to 'true' if and only if
-//                        this call sets 'initReg' to a non-zero value.
+//     initReg        - register to use as scratch register
+//     pInitRegZeroed - OUT parameter. *pInitRegZeroed set to 'false' if 'initReg' is
+//                      not zero after this call.
 //
 // Return Value:
 //     None
 //
-void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegModified)
+void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegZeroed)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -1690,7 +1692,7 @@ void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegModifie
 
     if (initReg == argReg)
     {
-        *pInitRegModified = true;
+        *pInitRegZeroed = false;
     }
 }
 
@@ -1820,17 +1822,14 @@ void CodeGen::genProfilingLeaveCallback(unsigned helper)
 // Arguments:
 //      frameSize         - the size of the stack frame being allocated.
 //      initReg           - register to use as a scratch register.
-//      pInitRegModified  - OUT parameter. *pInitRegModified is set to 'true' if and only if
+//      pInitRegZeroed    - OUT parameter. *pInitRegZeroed is set to 'false' if and only if
 //                          this call sets 'initReg' to a non-zero value.
 //      maskArgRegsLiveIn - incoming argument registers that are currently live.
 //
 // Return value:
 //      None
 //
-void CodeGen::genAllocLclFrame(unsigned  frameSize,
-                               regNumber initReg,
-                               bool*     pInitRegModified,
-                               regMaskTP maskArgRegsLiveIn)
+void CodeGen::genAllocLclFrame(unsigned frameSize, regNumber initReg, bool* pInitRegZeroed, regMaskTP maskArgRegsLiveIn)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -1860,7 +1859,7 @@ void CodeGen::genAllocLclFrame(unsigned  frameSize,
         }
 
         regSet.verifyRegUsed(initReg);
-        *pInitRegModified = true;
+        *pInitRegZeroed = false; // The initReg does not contain zero
 
         instGen_Set_Reg_To_Imm(EA_PTRSIZE, initReg, frameSize);
         compiler->unwindPadding();
@@ -1880,7 +1879,7 @@ void CodeGen::genAllocLclFrame(unsigned  frameSize,
         if ((genRegMask(initReg) & (RBM_STACK_PROBE_HELPER_ARG | RBM_STACK_PROBE_HELPER_CALL_TARGET |
                                     RBM_STACK_PROBE_HELPER_TRASH)) != RBM_NONE)
         {
-            *pInitRegModified = true;
+            *pInitRegZeroed = false;
         }
     }
 
diff --git a/src/coreclr/src/jit/codegenarm64.cpp b/src/coreclr/src/jit/codegenarm64.cpp
index 8ce7617de5d0ed..a85e2ce06bf957 100644
--- a/src/coreclr/src/jit/codegenarm64.cpp
+++ b/src/coreclr/src/jit/codegenarm64.cpp
@@ -156,7 +156,9 @@ void CodeGen::genStackPointerAdjustment(ssize_t spDelta, regNumber tmpReg, bool*
     // Even though INS_add is specified here, the encoder will choose either
     // an INS_add or an INS_sub and encode the immediate as a positive value
     //
-    if (genInstrWithConstant(INS_add, EA_PTRSIZE, REG_SPBASE, REG_SPBASE, spDelta, tmpReg, true))
+    bool wasTempRegisterUsedForImm =
+        !genInstrWithConstant(INS_add, EA_PTRSIZE, REG_SPBASE, REG_SPBASE, spDelta, tmpReg, true);
+    if (wasTempRegisterUsedForImm)
     {
         if (pTmpRegIsZero != nullptr)
         {
@@ -4699,7 +4701,7 @@ void CodeGen::genStoreIndTypeSIMD12(GenTree* treeNode)
 
     genConsumeOperands(treeNode->AsOp());
 
-    // Need an addtional integer register to extract upper 4 bytes from data.
+    // Need an additional integer register to extract upper 4 bytes from data.
     regNumber tmpReg = treeNode->GetSingleTempReg();
     assert(tmpReg != addr->GetRegNum());
 
@@ -4766,16 +4768,13 @@ void CodeGen::genStoreLclTypeSIMD12(GenTree* treeNode)
 {
     assert((treeNode->OperGet() == GT_STORE_LCL_FLD) || (treeNode->OperGet() == GT_STORE_LCL_VAR));
 
-    unsigned offs   = 0;
-    unsigned varNum = treeNode->AsLclVarCommon()->GetLclNum();
-    assert(varNum < compiler->lvaCount);
+    GenTreeLclVarCommon* lclVar = treeNode->AsLclVarCommon();
 
-    if (treeNode->OperGet() == GT_STORE_LCL_FLD)
-    {
-        offs = treeNode->AsLclFld()->GetLclOffs();
-    }
+    unsigned offs   = lclVar->GetLclOffs();
+    unsigned varNum = lclVar->GetLclNum();
+    assert(varNum < compiler->lvaCount);
 
-    GenTree* op1 = treeNode->AsOp()->gtOp1;
+    GenTree* op1 = lclVar->gtGetOp1();
 
     if (op1->isContained())
     {
@@ -4792,8 +4791,8 @@ void CodeGen::genStoreLclTypeSIMD12(GenTree* treeNode)
     }
     regNumber operandReg = genConsumeReg(op1);
 
-    // Need an addtional integer register to extract upper 4 bytes from data.
-    regNumber tmpReg = treeNode->GetSingleTempReg();
+    // Need an additional integer register to extract upper 4 bytes from data.
+    regNumber tmpReg = lclVar->GetSingleTempReg();
 
     // store lower 8 bytes
     GetEmitter()->emitIns_S_R(INS_str, EA_8BYTE, operandReg, varNum, offs);
@@ -4813,14 +4812,14 @@ void CodeGen::genStoreLclTypeSIMD12(GenTree* treeNode)
 // genProfilingEnterCallback: Generate the profiling function enter callback.
 //
 // Arguments:
-//     initReg          - register to use as scratch register
-//     pInitRegModified - OUT parameter. *pInitRegModified set to 'true' if 'initReg' is
-//                        not zero after this call.
+//     initReg        - register to use as scratch register
+//     pInitRegZeroed - OUT parameter. *pInitRegZeroed set to 'false' if 'initReg' is
+//                      set to non-zero value after this call.
 //
 // Return Value:
 //     None
 //
-void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegModified)
+void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegZeroed)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -4848,7 +4847,7 @@ void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegModifie
 
     if ((genRegMask(initReg) & RBM_PROFILER_ENTER_TRASH) != RBM_NONE)
     {
-        *pInitRegModified = true;
+        *pInitRegZeroed = false;
     }
 }
 
@@ -9595,19 +9594,16 @@ void CodeGen::genArm64EmitterUnitTests()
 //      on Windows as well just to be consistent, even though it should not be necessary.
 //
 // Arguments:
-//      frameSize          - the size of the stack frame being allocated.
-//      initReg            - register to use as a scratch register.
-//      pInitRegModified   - OUT parameter. *pInitRegModified is set to 'true' if and only if
-//                           this call sets 'initReg' to a non-zero value.
-//      maskArgRegsLiveIn  - incoming argument registers that are currently live.
+//      frameSize         - the size of the stack frame being allocated.
+//      initReg           - register to use as a scratch register.
+//      pInitRegZeroed    - OUT parameter. *pInitRegZeroed is set to 'false' if and only if
+//                          this call sets 'initReg' to a non-zero value. Otherwise, it is unchanged.
+//      maskArgRegsLiveIn - incoming argument registers that are currently live.
 //
 // Return value:
 //      None
 //
-void CodeGen::genAllocLclFrame(unsigned  frameSize,
-                               regNumber initReg,
-                               bool*     pInitRegModified,
-                               regMaskTP maskArgRegsLiveIn)
+void CodeGen::genAllocLclFrame(unsigned frameSize, regNumber initReg, bool* pInitRegZeroed, regMaskTP maskArgRegsLiveIn)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -9644,7 +9640,7 @@ void CodeGen::genAllocLclFrame(unsigned  frameSize,
             instGen_Set_Reg_To_Imm(EA_PTRSIZE, initReg, -(ssize_t)probeOffset);
             GetEmitter()->emitIns_R_R_R(INS_ldr, EA_4BYTE, REG_ZR, REG_SPBASE, initReg);
             regSet.verifyRegUsed(initReg);
-            *pInitRegModified = true;
+            *pInitRegZeroed = false; // The initReg does not contain zero
 
             lastTouchDelta -= pageSize;
         }
@@ -9704,7 +9700,7 @@ void CodeGen::genAllocLclFrame(unsigned  frameSize,
         GetEmitter()->emitIns_R_R(INS_cmp, EA_PTRSIZE, rLimit, rOffset); // If equal, we need to probe again
         GetEmitter()->emitIns_J(INS_bls, NULL, -4);
 
-        *pInitRegModified = true;
+        *pInitRegZeroed = false; // The initReg does not contain zero
 
         compiler->unwindPadding();
 
@@ -9719,7 +9715,7 @@ void CodeGen::genAllocLclFrame(unsigned  frameSize,
         compiler->unwindPadding();
 
         regSet.verifyRegUsed(initReg);
-        *pInitRegModified = true;
+        *pInitRegZeroed = false; // The initReg does not contain zero
     }
 }
 
diff --git a/src/coreclr/src/jit/codegenarmarch.cpp b/src/coreclr/src/jit/codegenarmarch.cpp
index 7dd95d2fdab6b8..c1dcc7319afca8 100644
--- a/src/coreclr/src/jit/codegenarmarch.cpp
+++ b/src/coreclr/src/jit/codegenarmarch.cpp
@@ -561,14 +561,14 @@ void CodeGen::genSetRegToIcon(regNumber reg, ssize_t val, var_types type, insFla
 // genSetGSSecurityCookie: Set the "GS" security cookie in the prolog.
 //
 // Arguments:
-//     initReg          - register to use as a scratch register
-//     pInitRegModified - OUT parameter. *pInitRegModified is set to 'true' if and only if
-//                        this call sets 'initReg' to a non-zero value.
+//     initReg        - register to use as a scratch register
+//     pInitRegZeroed - OUT parameter. *pInitRegZeroed is set to 'false' if and only if
+//                      this call sets 'initReg' to a non-zero value.
 //
 // Return Value:
 //     None
 //
-void CodeGen::genSetGSSecurityCookie(regNumber initReg, bool* pInitRegModified)
+void CodeGen::genSetGSSecurityCookie(regNumber initReg, bool* pInitRegZeroed)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -593,7 +593,7 @@ void CodeGen::genSetGSSecurityCookie(regNumber initReg, bool* pInitRegModified)
         GetEmitter()->emitIns_S_R(INS_str, EA_PTRSIZE, initReg, compiler->lvaGSSecurityCookie, 0);
     }
 
-    *pInitRegModified = true;
+    *pInitRegZeroed = false;
 }
 
 //---------------------------------------------------------------------
@@ -616,31 +616,31 @@ void CodeGen::genIntrinsic(GenTree* treeNode)
 
     // Right now only Abs/Ceiling/Floor/Round/Sqrt are treated as math intrinsics.
     //
-    switch (treeNode->AsIntrinsic()->gtIntrinsicId)
+    switch (treeNode->AsIntrinsic()->gtIntrinsicName)
     {
-        case CORINFO_INTRINSIC_Abs:
+        case NI_System_Math_Abs:
             genConsumeOperands(treeNode->AsOp());
             GetEmitter()->emitInsBinary(INS_ABS, emitActualTypeSize(treeNode), treeNode, srcNode);
             break;
 
 #ifdef TARGET_ARM64
-        case CORINFO_INTRINSIC_Ceiling:
+        case NI_System_Math_Ceiling:
             genConsumeOperands(treeNode->AsOp());
             GetEmitter()->emitInsBinary(INS_frintp, emitActualTypeSize(treeNode), treeNode, srcNode);
             break;
 
-        case CORINFO_INTRINSIC_Floor:
+        case NI_System_Math_Floor:
             genConsumeOperands(treeNode->AsOp());
             GetEmitter()->emitInsBinary(INS_frintm, emitActualTypeSize(treeNode), treeNode, srcNode);
             break;
 
-        case CORINFO_INTRINSIC_Round:
+        case NI_System_Math_Round:
             genConsumeOperands(treeNode->AsOp());
             GetEmitter()->emitInsBinary(INS_frintn, emitActualTypeSize(treeNode), treeNode, srcNode);
             break;
 #endif // TARGET_ARM64
 
-        case CORINFO_INTRINSIC_Sqrt:
+        case NI_System_Math_Sqrt:
             genConsumeOperands(treeNode->AsOp());
             GetEmitter()->emitInsBinary(INS_SQRT, emitActualTypeSize(treeNode), treeNode, srcNode);
             break;
@@ -815,11 +815,15 @@ void CodeGen::genPutArgStk(GenTreePutArgStk* treeNode)
                     // so update 'source' to point this GT_LCL_VAR_ADDR node
                     // and continue to the codegen for the LCL_VAR node below
                     //
+                    assert(addrNode->isContained());
                     varNode  = addrNode->AsLclVarCommon();
                     addrNode = nullptr;
                 }
                 else // addrNode is used
                 {
+                    // TODO-Cleanup: `Lowering::NewPutArg` marks only `LCL_VAR_ADDR` as contained nowadays,
+                    // but we use `genConsumeAddress` as a precaution, use `genConsumeReg()` instead.
+                    assert(!addrNode->isContained());
                     // Generate code to load the address that we need into a register
                     genConsumeAddress(addrNode);
                     addrReg = addrNode->GetRegNum();
@@ -1253,6 +1257,7 @@ void CodeGen::genPutArgSplit(GenTreePutArgSplit* treeNode)
 
         if (varNode != nullptr)
         {
+            assert(varNode->isContained());
             srcVarNum = varNode->GetLclNum();
             assert(srcVarNum < compiler->lvaCount);
 
@@ -1270,6 +1275,9 @@ void CodeGen::genPutArgSplit(GenTreePutArgSplit* treeNode)
         else // addrNode is used
         {
             assert(addrNode != nullptr);
+            // TODO-Cleanup: `Lowering::NewPutArg` marks only `LCL_VAR_ADDR` as contained nowadays,
+            // but we use `genConsumeAddress` as a precaution, use `genConsumeReg()` instead.
+            assert(!addrNode->isContained());
 
             // Generate code to load the address that we need into a register
             genConsumeAddress(addrNode);
@@ -1959,11 +1967,7 @@ void CodeGen::genCodeForInitBlkUnroll(GenTreeBlk* node)
     {
         assert(dstAddr->OperIsLocalAddr());
         dstLclNum = dstAddr->AsLclVarCommon()->GetLclNum();
-
-        if (dstAddr->OperIs(GT_LCL_FLD_ADDR))
-        {
-            dstOffset = dstAddr->AsLclFld()->GetLclOffs();
-        }
+        dstOffset = dstAddr->AsLclVarCommon()->GetLclOffs();
     }
 
     regNumber srcReg;
@@ -2095,11 +2099,7 @@ void CodeGen::genCodeForCpBlkUnroll(GenTreeBlk* node)
 
         assert(dstAddr->OperIsLocalAddr());
         dstLclNum = dstAddr->AsLclVarCommon()->GetLclNum();
-
-        if (dstAddr->OperIs(GT_LCL_FLD_ADDR))
-        {
-            dstOffset = dstAddr->AsLclFld()->GetLclOffs();
-        }
+        dstOffset = dstAddr->AsLclVarCommon()->GetLclOffs();
     }
 
     unsigned  srcLclNum      = BAD_VAR_NUM;
@@ -2112,11 +2112,7 @@ void CodeGen::genCodeForCpBlkUnroll(GenTreeBlk* node)
     if (src->OperIs(GT_LCL_VAR, GT_LCL_FLD))
     {
         srcLclNum = src->AsLclVarCommon()->GetLclNum();
-
-        if (src->OperIs(GT_LCL_FLD))
-        {
-            srcOffset = src->AsLclFld()->GetLclOffs();
-        }
+        srcOffset = src->AsLclVarCommon()->GetLclOffs();
     }
     else
     {
@@ -2136,11 +2132,7 @@ void CodeGen::genCodeForCpBlkUnroll(GenTreeBlk* node)
         {
             assert(srcAddr->OperIsLocalAddr());
             srcLclNum = srcAddr->AsLclVarCommon()->GetLclNum();
-
-            if (srcAddr->OperIs(GT_LCL_FLD_ADDR))
-            {
-                srcOffset = srcAddr->AsLclFld()->GetLclOffs();
-            }
+            srcOffset = srcAddr->AsLclVarCommon()->GetLclOffs();
         }
     }
 
diff --git a/src/coreclr/src/jit/codegencommon.cpp b/src/coreclr/src/jit/codegencommon.cpp
index ccfd7567f46ae6..5923e6512f406e 100644
--- a/src/coreclr/src/jit/codegencommon.cpp
+++ b/src/coreclr/src/jit/codegencommon.cpp
@@ -4821,7 +4821,7 @@ void CodeGen::genCheckUseBlockInit()
  */
 
 #if defined(TARGET_ARM64)
-void CodeGen::genPushCalleeSavedRegisters(regNumber initReg, bool* pInitRegModified)
+void CodeGen::genPushCalleeSavedRegisters(regNumber initReg, bool* pInitRegZeroed)
 #else
 void          CodeGen::genPushCalleeSavedRegisters()
 #endif
@@ -4873,7 +4873,7 @@ void          CodeGen::genPushCalleeSavedRegisters()
     // - Generate fully interruptible code for loops that contains calls
     // - Generate fully interruptible code for leaf methods
     //
-    // Given the limited benefit from this optimization (<10k for mscorlib NGen image), the extra complexity
+    // Given the limited benefit from this optimization (<10k for CoreLib NGen image), the extra complexity
     // is not worth it.
     //
     rsPushRegs |= RBM_LR; // We must save the return address (in the LR register)
@@ -5310,8 +5310,7 @@ void          CodeGen::genPushCalleeSavedRegisters()
 
             JITDUMP("    spAdjustment2=%d\n", spAdjustment2);
 
-            genPrologSaveRegPair(REG_FP, REG_LR, alignmentAdjustment2, -spAdjustment2, false, initReg,
-                                 pInitRegModified);
+            genPrologSaveRegPair(REG_FP, REG_LR, alignmentAdjustment2, -spAdjustment2, false, initReg, pInitRegZeroed);
             offset += spAdjustment2;
 
             // Now subtract off the #outsz (or the rest of the #outsz if it was unaligned, and the above "sub"
@@ -5331,13 +5330,13 @@ void          CodeGen::genPushCalleeSavedRegisters()
 
             // We've already established the frame pointer, so no need to report the stack pointer change to unwind
             // info.
-            genStackPointerAdjustment(-spAdjustment3, initReg, pInitRegModified, /* reportUnwindData */ false);
+            genStackPointerAdjustment(-spAdjustment3, initReg, pInitRegZeroed, /* reportUnwindData */ false);
             offset += spAdjustment3;
         }
         else
         {
             genPrologSaveRegPair(REG_FP, REG_LR, compiler->lvaOutgoingArgSpaceSize, -remainingFrameSz, false, initReg,
-                                 pInitRegModified);
+                                 pInitRegZeroed);
             offset += remainingFrameSz;
 
             offsetSpToSavedFp = compiler->lvaOutgoingArgSpaceSize;
@@ -5369,7 +5368,7 @@ void          CodeGen::genPushCalleeSavedRegisters()
         JITDUMP("    remainingFrameSz=%d\n", remainingFrameSz);
 
         // We've already established the frame pointer, so no need to report the stack pointer change to unwind info.
-        genStackPointerAdjustment(-remainingFrameSz, initReg, pInitRegModified, /* reportUnwindData */ false);
+        genStackPointerAdjustment(-remainingFrameSz, initReg, pInitRegZeroed, /* reportUnwindData */ false);
         offset += remainingFrameSz;
     }
     else
@@ -6098,17 +6097,17 @@ void CodeGen::genPopCalleeSavedRegisters(bool jmpEpilog)
 
 #endif // TARGET*
 
-// We need a register with value zero. Zero the initReg, if necessary, and set *pInitRegModified if so.
+// We need a register with value zero. Zero the initReg, if necessary, and set *pInitRegZeroed if so.
 // Return the register to use. On ARM64, we never touch the initReg, and always just return REG_ZR.
-regNumber CodeGen::genGetZeroReg(regNumber initReg, bool* pInitRegModified)
+regNumber CodeGen::genGetZeroReg(regNumber initReg, bool* pInitRegZeroed)
 {
 #ifdef TARGET_ARM64
     return REG_ZR;
 #else  // !TARGET_ARM64
-    if (*pInitRegModified)
+    if (*pInitRegZeroed == false)
     {
         instGen_Set_Reg_To_Zero(EA_PTRSIZE, initReg);
-        *pInitRegModified = false;
+        *pInitRegZeroed = true;
     }
     return initReg;
 #endif // !TARGET_ARM64
@@ -6118,14 +6117,14 @@ regNumber CodeGen::genGetZeroReg(regNumber initReg, bool* pInitRegModified)
 // genZeroInitFrame: Zero any untracked pointer locals and/or initialize memory for locspace
 //
 // Arguments:
-//    untrLclHi        - (Untracked locals High-Offset)  The upper bound offset at which the zero init
-//                                                       code will end initializing memory (not inclusive).
-//    untrLclLo        - (Untracked locals Low-Offset)   The lower bound at which the zero init code will
-//                                                       start zero initializing memory.
-//    initReg          - A scratch register (that gets set to zero on some platforms).
-//    pInitRegModified - Sets a flag that tells the callee whether or not the initReg register got zeroed.
-//
-void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg, bool* pInitRegModified)
+//    untrLclHi      - (Untracked locals High-Offset)  The upper bound offset at which the zero init
+//                                                     code will end initializing memory (not inclusive).
+//    untrLclLo      - (Untracked locals Low-Offset)   The lower bound at which the zero init code will
+//                                                     start zero initializing memory.
+//    initReg        - A scratch register (that gets set to zero on some platforms).
+//    pInitRegZeroed - OUT parameter. *pInitRegZeroed is set to 'true' if this method sets initReg register to zero,
+//                     'false' if initReg was set to a non-zero value, and left unchanged if initReg was not touched.
+void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg, bool* pInitRegZeroed)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -6200,8 +6199,8 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
 
 #else // !define(TARGET_ARM)
 
-        rAddr             = initReg;
-        *pInitRegModified = true;
+        rAddr           = initReg;
+        *pInitRegZeroed = false;
 
 #endif // !defined(TARGET_ARM)
 
@@ -6242,7 +6241,7 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
             // Load immediate into the InitReg register
             instGen_Set_Reg_To_Imm(EA_PTRSIZE, initReg, (ssize_t)untrLclLo);
             GetEmitter()->emitIns_R_R_R(INS_add, EA_PTRSIZE, rAddr, genFramePointerReg(), initReg);
-            *pInitRegModified = true;
+            *pInitRegZeroed = false;
         }
 
         if (useLoop)
@@ -6254,7 +6253,7 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
         }
 
 #if defined(TARGET_ARM)
-        rZero1 = genGetZeroReg(initReg, pInitRegModified);
+        rZero1 = genGetZeroReg(initReg, pInitRegZeroed);
         instGen_Set_Reg_To_Zero(EA_PTRSIZE, rZero2);
         target_ssize_t stmImm = (target_ssize_t)(genRegMask(rZero1) | genRegMask(rZero2));
 #endif // TARGET_ARM
@@ -6343,7 +6342,7 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
 #endif
         if (blkSize < minSimdSize)
         {
-            zeroReg = genGetZeroReg(initReg, pInitRegModified);
+            zeroReg = genGetZeroReg(initReg, pInitRegZeroed);
 
             int i = 0;
             for (; i + REGSIZE_BYTES <= blkSize; i += REGSIZE_BYTES)
@@ -6405,7 +6404,7 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
                 assert(alignmentLoBlkSize < XMM_REGSIZE_BYTES);
                 assert((alignedLclLo - alignmentLoBlkSize) == untrLclLo);
 
-                zeroReg = genGetZeroReg(initReg, pInitRegModified);
+                zeroReg = genGetZeroReg(initReg, pInitRegZeroed);
 
                 int i = 0;
                 for (; i + REGSIZE_BYTES <= alignmentLoBlkSize; i += REGSIZE_BYTES)
@@ -6513,7 +6512,7 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
                 emit->emitIns_J(INS_jne, nullptr, -5);
 
                 // initReg will be zero at end of the loop
-                *pInitRegModified = false;
+                *pInitRegZeroed = true;
             }
 
             if (untrLclHi != alignedLclHi)
@@ -6522,7 +6521,7 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
                 assert(alignmentHiBlkSize < XMM_REGSIZE_BYTES);
                 assert((alignedLclHi + alignmentHiBlkSize) == untrLclHi);
 
-                zeroReg = genGetZeroReg(initReg, pInitRegModified);
+                zeroReg = genGetZeroReg(initReg, pInitRegZeroed);
 
                 int i = 0;
                 for (; i + REGSIZE_BYTES <= alignmentHiBlkSize; i += REGSIZE_BYTES)
@@ -6589,13 +6588,13 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
                     if (layout->IsGCPtr(i))
                     {
                         GetEmitter()->emitIns_S_R(ins_Store(TYP_I_IMPL), EA_PTRSIZE,
-                                                  genGetZeroReg(initReg, pInitRegModified), varNum, i * REGSIZE_BYTES);
+                                                  genGetZeroReg(initReg, pInitRegZeroed), varNum, i * REGSIZE_BYTES);
                     }
                 }
             }
             else
             {
-                regNumber zeroReg = genGetZeroReg(initReg, pInitRegModified);
+                regNumber zeroReg = genGetZeroReg(initReg, pInitRegZeroed);
 
                 // zero out the whole thing rounded up to a single stack slot size
                 unsigned lclSize = roundUp(compiler->lvaLclSize(varNum), (unsigned)sizeof(int));
@@ -6627,7 +6626,7 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
 
             // printf("initialize untracked spillTmp [EBP-%04X]\n", stkOffs);
 
-            inst_ST_RV(ins_Store(TYP_I_IMPL), tempThis, 0, genGetZeroReg(initReg, pInitRegModified), TYP_I_IMPL);
+            inst_ST_RV(ins_Store(TYP_I_IMPL), tempThis, 0, genGetZeroReg(initReg, pInitRegZeroed), TYP_I_IMPL);
         }
     }
 
@@ -6762,7 +6761,7 @@ void CodeGen::genZeroInitFrame(int untrLclHi, int untrLclLo, regNumber initReg,
  *  ICodeManager::GetParamTypeArg().
  */
 
-void CodeGen::genReportGenericContextArg(regNumber initReg, bool* pInitRegModified)
+void CodeGen::genReportGenericContextArg(regNumber initReg, bool* pInitRegZeroed)
 {
     // For OSR the original method has set this up for us.
     if (compiler->opts.IsOSR())
@@ -6827,8 +6826,8 @@ void CodeGen::genReportGenericContextArg(regNumber initReg, bool* pInitRegModifi
 
         // We will just use the initReg since it is an available register
         // and we are probably done using it anyway...
-        reg               = initReg;
-        *pInitRegModified = true;
+        reg             = initReg;
+        *pInitRegZeroed = false;
 
         // mov reg, [compiler->info.compTypeCtxtArg]
         GetEmitter()->emitIns_R_AR(ins_Load(TYP_I_IMPL), EA_PTRSIZE, reg, genFramePointerReg(), varDsc->lvStkOffs);
@@ -7672,9 +7671,13 @@ void CodeGen::genFnProlog()
 
     /* Choose the register to use for zero initialization */
 
-    regNumber initReg         = REG_SCRATCH; // Unless we find a better register below
-    bool      initRegModified = true;
-    regMaskTP excludeMask     = intRegState.rsCalleeRegArgMaskLiveIn;
+    regNumber initReg = REG_SCRATCH; // Unless we find a better register below
+
+    // Track if initReg holds non-zero value. Start conservative and assume it has non-zero value.
+    // If initReg is ever set to zero, this variable is set to true and zero initializing initReg
+    // will be skipped.
+    bool      initRegZeroed = false;
+    regMaskTP excludeMask   = intRegState.rsCalleeRegArgMaskLiveIn;
     regMaskTP tempMask;
 
     // We should not use the special PINVOKE registers as the initReg
@@ -7807,11 +7810,11 @@ void CodeGen::genFnProlog()
     // been calculated to be one of the callee-saved registers (say, if all the integer argument registers are
     // in use, and perhaps with other conditions being satisfied). This is ok in other cases, after the callee-saved
     // registers have been saved. So instead of letting genAllocLclFrame use initReg as a temporary register,
-    // always use REG_SCRATCH. We don't care if it trashes it, so ignore the initRegModified output argument.
-    bool ignoreInitRegModified = true;
-    genAllocLclFrame(compiler->compLclFrameSize, REG_SCRATCH, &ignoreInitRegModified,
+    // always use REG_SCRATCH. We don't care if it trashes it, so ignore the initRegZeroed output argument.
+    bool ignoreInitRegZeroed = false;
+    genAllocLclFrame(compiler->compLclFrameSize, REG_SCRATCH, &ignoreInitRegZeroed,
                      intRegState.rsCalleeRegArgMaskLiveIn);
-    genPushCalleeSavedRegisters(initReg, &initRegModified);
+    genPushCalleeSavedRegisters(initReg, &initRegZeroed);
 #else  // !TARGET_ARM64
     genPushCalleeSavedRegisters();
 #endif // !TARGET_ARM64
@@ -7855,7 +7858,7 @@ void CodeGen::genFnProlog()
 
     if (maskStackAlloc == RBM_NONE)
     {
-        genAllocLclFrame(compiler->compLclFrameSize, initReg, &initRegModified, intRegState.rsCalleeRegArgMaskLiveIn);
+        genAllocLclFrame(compiler->compLclFrameSize, initReg, &initRegZeroed, intRegState.rsCalleeRegArgMaskLiveIn);
     }
 #endif // !TARGET_ARM64
 
@@ -7918,11 +7921,11 @@ void CodeGen::genFnProlog()
     // Zero out the frame as needed
     //
 
-    genZeroInitFrame(untrLclHi, untrLclLo, initReg, &initRegModified);
+    genZeroInitFrame(untrLclHi, untrLclLo, initReg, &initRegZeroed);
 
 #if defined(FEATURE_EH_FUNCLETS)
 
-    genSetPSPSym(initReg, &initRegModified);
+    genSetPSPSym(initReg, &initRegZeroed);
 
 #else // !FEATURE_EH_FUNCLETS
 
@@ -7935,10 +7938,10 @@ void CodeGen::genFnProlog()
         // Zero out the slot for nesting level 0
         unsigned firstSlotOffs = filterEndOffsetSlotOffs - TARGET_POINTER_SIZE;
 
-        if (initRegModified)
+        if (!initRegZeroed)
         {
             instGen_Set_Reg_To_Zero(EA_PTRSIZE, initReg);
-            initRegModified = false;
+            initRegZeroed = true;
         }
 
         GetEmitter()->emitIns_S_R(ins_Store(TYP_I_IMPL), EA_PTRSIZE, initReg, compiler->lvaShadowSPslotsVar,
@@ -7947,7 +7950,7 @@ void CodeGen::genFnProlog()
 
 #endif // !FEATURE_EH_FUNCLETS
 
-    genReportGenericContextArg(initReg, &initRegModified);
+    genReportGenericContextArg(initReg, &initRegZeroed);
 
 #ifdef JIT32_GCENCODER
     // Initialize the LocalAllocSP slot if there is localloc in the function.
@@ -7959,7 +7962,7 @@ void CodeGen::genFnProlog()
 
     // Set up the GS security cookie
 
-    genSetGSSecurityCookie(initReg, &initRegModified);
+    genSetGSSecurityCookie(initReg, &initRegZeroed);
 
 #ifdef PROFILING_SUPPORTED
 
@@ -7967,7 +7970,7 @@ void CodeGen::genFnProlog()
     // OSR methods aren't called, so don't have enter hooks.
     if (!compiler->opts.IsOSR())
     {
-        genProfilingEnterCallback(initReg, &initRegModified);
+        genProfilingEnterCallback(initReg, &initRegZeroed);
     }
 
 #endif // PROFILING_SUPPORTED
@@ -8029,15 +8032,15 @@ void CodeGen::genFnProlog()
                 }
                 else
                 {
-                    xtraReg         = REG_SCRATCH;
-                    initRegModified = true;
+                    xtraReg       = REG_SCRATCH;
+                    initRegZeroed = false;
                 }
 
                 genFnPrologCalleeRegArgs(xtraReg, &xtraRegClobbered, regState);
 
                 if (xtraRegClobbered)
                 {
-                    initRegModified = true;
+                    initRegZeroed = false;
                 }
             }
         }
@@ -8057,7 +8060,7 @@ void CodeGen::genFnProlog()
             if (regMask & initRegs)
             {
                 // Check if we have already zeroed this register
-                if ((reg == initReg) && !initRegModified)
+                if ((reg == initReg) && initRegZeroed)
                 {
                     continue;
                 }
@@ -8066,7 +8069,7 @@ void CodeGen::genFnProlog()
                     instGen_Set_Reg_To_Zero(EA_PTRSIZE, reg);
                     if (reg == initReg)
                     {
-                        initRegModified = false;
+                        initRegZeroed = true;
                     }
                 }
             }
@@ -8078,17 +8081,17 @@ void CodeGen::genFnProlog()
         // If initReg is not in initRegs then we will use REG_SCRATCH
         if ((genRegMask(initReg) & initRegs) == 0)
         {
-            initReg         = REG_SCRATCH;
-            initRegModified = true;
+            initReg       = REG_SCRATCH;
+            initRegZeroed = false;
         }
 
 #ifdef TARGET_ARM
         // This is needed only for Arm since it can use a zero initialized int register
         // to initialize vfp registers.
-        if (initRegModified)
+        if (!initRegZeroed)
         {
             instGen_Set_Reg_To_Zero(EA_PTRSIZE, initReg);
-            initRegModified = false;
+            initRegZeroed = true;
         }
 #endif // TARGET_ARM
 
@@ -9095,12 +9098,12 @@ void CodeGen::genFuncletProlog(BasicBlock* block)
         maskArgRegsLiveIn = RBM_R0;
     }
 
-    regNumber initReg         = REG_R3; // R3 is never live on entry to a funclet, so it can be trashed
-    bool      initRegModified = true;
+    regNumber initReg       = REG_R3; // R3 is never live on entry to a funclet, so it can be trashed
+    bool      initRegZeroed = false;
 
     if (maskStackAlloc == RBM_NONE)
     {
-        genAllocLclFrame(genFuncletInfo.fiSpDelta, initReg, &initRegModified, maskArgRegsLiveIn);
+        genAllocLclFrame(genFuncletInfo.fiSpDelta, initReg, &initRegZeroed, maskArgRegsLiveIn);
     }
 
     // This is the end of the OS-reported prolog for purposes of unwinding
@@ -9397,10 +9400,10 @@ void CodeGen::genFuncletProlog(BasicBlock* block)
         maskArgRegsLiveIn = RBM_ARG_0 | RBM_ARG_2;
     }
 
-    regNumber initReg         = REG_EBP; // We already saved EBP, so it can be trashed
-    bool      initRegModified = true;
+    regNumber initReg       = REG_EBP; // We already saved EBP, so it can be trashed
+    bool      initRegZeroed = false;
 
-    genAllocLclFrame(genFuncletInfo.fiSpDelta, initReg, &initRegModified, maskArgRegsLiveIn);
+    genAllocLclFrame(genFuncletInfo.fiSpDelta, initReg, &initRegZeroed, maskArgRegsLiveIn);
 
     // Callee saved float registers are copied to stack in their assigned stack slots
     // after allocating space for them as part of funclet frame.
@@ -9739,7 +9742,7 @@ void CodeGen::genCaptureFuncletPrologEpilogInfo()
  *  correctly reported, the PSPSym could be omitted in some cases.)
  ***********************************
  */
-void CodeGen::genSetPSPSym(regNumber initReg, bool* pInitRegModified)
+void CodeGen::genSetPSPSym(regNumber initReg, bool* pInitRegZeroed)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -9785,8 +9788,8 @@ void CodeGen::genSetPSPSym(regNumber initReg, bool* pInitRegModified)
 
     // We will just use the initReg since it is an available register
     // and we are probably done using it anyway...
-    regNumber regTmp  = initReg;
-    *pInitRegModified = true;
+    regNumber regTmp = initReg;
+    *pInitRegZeroed  = false;
 
     GetEmitter()->emitIns_R_R_I(INS_add, EA_PTRSIZE, regTmp, regBase, callerSPOffs);
     GetEmitter()->emitIns_S_R(INS_str, EA_PTRSIZE, regTmp, compiler->lvaPSPSym, 0);
@@ -9797,8 +9800,8 @@ void CodeGen::genSetPSPSym(regNumber initReg, bool* pInitRegModified)
 
     // We will just use the initReg since it is an available register
     // and we are probably done using it anyway...
-    regNumber regTmp  = initReg;
-    *pInitRegModified = true;
+    regNumber regTmp = initReg;
+    *pInitRegZeroed  = false;
 
     GetEmitter()->emitIns_R_R_Imm(INS_add, EA_PTRSIZE, regTmp, REG_SPBASE, SPtoCallerSPdelta);
     GetEmitter()->emitIns_S_R(INS_str, EA_PTRSIZE, regTmp, compiler->lvaPSPSym, 0);
diff --git a/src/coreclr/src/jit/codegenlinear.cpp b/src/coreclr/src/jit/codegenlinear.cpp
index 94306e936549fe..cf0d1cd149a00a 100644
--- a/src/coreclr/src/jit/codegenlinear.cpp
+++ b/src/coreclr/src/jit/codegenlinear.cpp
@@ -344,7 +344,6 @@ void CodeGen::genCodeForBBlist()
             needLabel = true;
         }
 
-#if defined(DEBUG) || defined(LATE_DISASM)
         // We also want to start a new Instruction group by calling emitAddLabel below,
         // when we need accurate bbWeights for this block in the emitter.  We force this
         // whenever our previous block was a BBJ_COND and it has a different weight than us.
@@ -356,7 +355,6 @@ void CodeGen::genCodeForBBlist()
         {
             needLabel = true;
         }
-#endif // DEBUG || LATE_DISASM
 
         if (needLabel)
         {
@@ -1741,15 +1739,11 @@ void CodeGen::genConsumePutStructArgStk(GenTreePutArgStk* putArgNode,
         {
             // The OperLocalAddr is always contained.
             assert(srcAddr->isContained());
-            GenTreeLclVarCommon* lclNode = srcAddr->AsLclVarCommon();
+            const GenTreeLclVarCommon* lclNode = srcAddr->AsLclVarCommon();
 
             // Generate LEA instruction to load the LclVar address in RSI.
             // Source is known to be on the stack. Use EA_PTRSIZE.
-            unsigned int offset = 0;
-            if (srcAddr->OperGet() == GT_LCL_FLD_ADDR)
-            {
-                offset = srcAddr->AsLclFld()->GetLclOffs();
-            }
+            unsigned int offset = lclNode->GetLclOffs();
             GetEmitter()->emitIns_R_S(INS_lea, EA_PTRSIZE, srcReg, lclNode->GetLclNum(), offset);
         }
         else
diff --git a/src/coreclr/src/jit/codegenxarch.cpp b/src/coreclr/src/jit/codegenxarch.cpp
index 207cef87d94e38..88c021ac73d016 100644
--- a/src/coreclr/src/jit/codegenxarch.cpp
+++ b/src/coreclr/src/jit/codegenxarch.cpp
@@ -53,14 +53,14 @@ void CodeGen::genSetRegToIcon(regNumber reg, ssize_t val, var_types type, insFla
 // genSetGSSecurityCookie: Set the "GS" security cookie in the prolog.
 //
 // Arguments:
-//     initReg           - register to use as a scratch register
-//     pInitRegModified  - OUT parameter. *pInitRegModified is set to 'true' if and only if
-//                         this call sets 'initReg' to a non-zero value.
+//     initReg        - register to use as a scratch register
+//     pInitRegZeroed - OUT parameter. *pInitRegZeroed is set to 'false' if and only if
+//                      this call sets 'initReg' to a non-zero value.
 //
 // Return Value:
 //     None
 //
-void CodeGen::genSetGSSecurityCookie(regNumber initReg, bool* pInitRegModified)
+void CodeGen::genSetGSSecurityCookie(regNumber initReg, bool* pInitRegZeroed)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -84,7 +84,7 @@ void CodeGen::genSetGSSecurityCookie(regNumber initReg, bool* pInitRegModified)
             // initReg = #GlobalSecurityCookieVal64; [frame.GSSecurityCookie] = initReg
             genSetRegToIcon(initReg, compiler->gsGlobalSecurityCookieVal, TYP_I_IMPL);
             GetEmitter()->emitIns_S_R(INS_mov, EA_PTRSIZE, initReg, compiler->lvaGSSecurityCookie, 0);
-            *pInitRegModified = true;
+            *pInitRegZeroed = false;
         }
         else
 #endif
@@ -105,7 +105,7 @@ void CodeGen::genSetGSSecurityCookie(regNumber initReg, bool* pInitRegModified)
         GetEmitter()->emitIns_S_R(INS_mov, EA_PTRSIZE, REG_EAX, compiler->lvaGSSecurityCookie, 0);
         if (initReg == REG_EAX)
         {
-            *pInitRegModified = true;
+            *pInitRegZeroed = false;
         }
     }
 }
@@ -1950,19 +1950,16 @@ void CodeGen::genMultiRegStoreToSIMDLocal(GenTreeLclVar* lclNode)
 // genAllocLclFrame: Probe the stack and allocate the local stack frame - subtract from SP.
 //
 // Arguments:
-//      frameSize          - the size of the stack frame being allocated.
-//      initReg            - register to use as a scratch register.
-//      pInitRegModified   - OUT parameter. *pInitRegModified is set to 'true' if and only if
-//                           this call sets 'initReg' to a non-zero value.
-//      maskArgRegsLiveIn  - incoming argument registers that are currently live.
+//      frameSize         - the size of the stack frame being allocated.
+//      initReg           - register to use as a scratch register.
+//      pInitRegZeroed    - OUT parameter. *pInitRegZeroed is set to 'false' if and only if
+//                          this call sets 'initReg' to a non-zero value.
+//      maskArgRegsLiveIn - incoming argument registers that are currently live.
 //
 // Return value:
 //      None
 //
-void CodeGen::genAllocLclFrame(unsigned  frameSize,
-                               regNumber initReg,
-                               bool*     pInitRegModified,
-                               regMaskTP maskArgRegsLiveIn)
+void CodeGen::genAllocLclFrame(unsigned frameSize, regNumber initReg, bool* pInitRegZeroed, regMaskTP maskArgRegsLiveIn)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -2046,7 +2043,7 @@ void CodeGen::genAllocLclFrame(unsigned  frameSize,
 
         if (initReg == REG_DEFAULT_HELPER_CALL_TARGET)
         {
-            *pInitRegModified = true;
+            *pInitRegZeroed = false;
         }
 
         static_assert_no_msg((RBM_STACK_PROBE_HELPER_TRASH & RBM_STACK_PROBE_HELPER_ARG) == RBM_NONE);
@@ -2056,7 +2053,7 @@ void CodeGen::genAllocLclFrame(unsigned  frameSize,
 
         if (initReg == REG_STACK_PROBE_HELPER_ARG)
         {
-            *pInitRegModified = true;
+            *pInitRegZeroed = false;
         }
     }
 
@@ -2694,11 +2691,7 @@ void CodeGen::genCodeForInitBlkUnroll(GenTreeBlk* node)
     {
         assert(dstAddr->OperIsLocalAddr());
         dstLclNum = dstAddr->AsLclVarCommon()->GetLclNum();
-
-        if (dstAddr->OperIs(GT_LCL_FLD_ADDR))
-        {
-            dstOffset = dstAddr->AsLclFld()->GetLclOffs();
-        }
+        dstOffset = dstAddr->AsLclVarCommon()->GetLclOffs();
     }
 
     regNumber srcIntReg = REG_NA;
@@ -2819,11 +2812,9 @@ void CodeGen::genCodeForLoadOffset(instruction ins, emitAttr size, regNumber dst
 
     if (baseNode->OperIsLocalAddr())
     {
-        if (baseNode->gtOper == GT_LCL_FLD_ADDR)
-        {
-            offset += baseNode->AsLclFld()->GetLclOffs();
-        }
-        emit->emitIns_R_S(ins, size, dst, baseNode->AsLclVarCommon()->GetLclNum(), offset);
+        const GenTreeLclVarCommon* lclVar = baseNode->AsLclVarCommon();
+        offset += lclVar->GetLclOffs();
+        emit->emitIns_R_S(ins, size, dst, lclVar->GetLclNum(), offset);
     }
     else
     {
@@ -2873,12 +2864,9 @@ void CodeGen::genCodeForCpBlkUnroll(GenTreeBlk* node)
     else
     {
         assert(dstAddr->OperIsLocalAddr());
-        dstLclNum = dstAddr->AsLclVarCommon()->GetLclNum();
-
-        if (dstAddr->OperIs(GT_LCL_FLD_ADDR))
-        {
-            dstOffset = dstAddr->AsLclFld()->GetLclOffs();
-        }
+        const GenTreeLclVarCommon* lclVar = dstAddr->AsLclVarCommon();
+        dstLclNum                         = lclVar->GetLclNum();
+        dstOffset                         = lclVar->GetLclOffs();
     }
 
     unsigned  srcLclNum         = BAD_VAR_NUM;
@@ -2893,11 +2881,7 @@ void CodeGen::genCodeForCpBlkUnroll(GenTreeBlk* node)
     if (src->OperIs(GT_LCL_VAR, GT_LCL_FLD))
     {
         srcLclNum = src->AsLclVarCommon()->GetLclNum();
-
-        if (src->OperIs(GT_LCL_FLD))
-        {
-            srcOffset = src->AsLclFld()->GetLclOffs();
-        }
+        srcOffset = src->AsLclVarCommon()->GetLclOffs();
     }
     else
     {
@@ -2929,11 +2913,7 @@ void CodeGen::genCodeForCpBlkUnroll(GenTreeBlk* node)
         {
             assert(srcAddr->OperIsLocalAddr());
             srcLclNum = srcAddr->AsLclVarCommon()->GetLclNum();
-
-            if (srcAddr->OperIs(GT_LCL_FLD_ADDR))
-            {
-                srcOffset = srcAddr->AsLclFld()->GetLclOffs();
-            }
+            srcOffset = srcAddr->AsLclVarCommon()->GetLclOffs();
         }
     }
 
@@ -6798,7 +6778,7 @@ void CodeGen::genSSE2BitwiseOp(GenTree* treeNode)
             break;
 
         case GT_INTRINSIC:
-            assert(treeNode->AsIntrinsic()->gtIntrinsicId == CORINFO_INTRINSIC_Abs);
+            assert(treeNode->AsIntrinsic()->gtIntrinsicName == NI_System_Math_Abs);
 
             // Abs(x) = set sign-bit to zero
             // Abs(f) = f & 0x7fffffff
@@ -6876,7 +6856,7 @@ void CodeGen::genSSE2BitwiseOp(GenTree* treeNode)
 //    ii) treeNode oper is a GT_INTRINSIC
 //   iii) treeNode type is a floating point type
 //    iv) treeNode is not used from memory
-//     v) tree oper is CORINFO_INTRINSIC_Round, _Ceiling, or _Floor
+//     v) tree oper is NI_System_Math{F}_Round, _Ceiling, or _Floor
 //    vi) caller of this routine needs to call genProduceReg()
 void CodeGen::genSSE41RoundOp(GenTreeOp* treeNode)
 {
@@ -6904,18 +6884,18 @@ void CodeGen::genSSE41RoundOp(GenTreeOp* treeNode)
 
     unsigned ival = 0;
 
-    // v) tree oper is CORINFO_INTRINSIC_Round, _Ceiling, or _Floor
-    switch (treeNode->AsIntrinsic()->gtIntrinsicId)
+    // v) tree oper is NI_System_Math{F}_Round, _Ceiling, or _Floor
+    switch (treeNode->AsIntrinsic()->gtIntrinsicName)
     {
-        case CORINFO_INTRINSIC_Round:
+        case NI_System_Math_Round:
             ival = 4;
             break;
 
-        case CORINFO_INTRINSIC_Ceiling:
+        case NI_System_Math_Ceiling:
             ival = 10;
             break;
 
-        case CORINFO_INTRINSIC_Floor:
+        case NI_System_Math_Floor:
             ival = 9;
             break;
 
@@ -6951,9 +6931,11 @@ void CodeGen::genSSE41RoundOp(GenTreeOp* treeNode)
             switch (memBase->OperGet())
             {
                 case GT_LCL_VAR_ADDR:
+                case GT_LCL_FLD_ADDR:
                 {
+                    assert(memBase->isContained());
                     varNum = memBase->AsLclVarCommon()->GetLclNum();
-                    offset = 0;
+                    offset = memBase->AsLclVarCommon()->GetLclOffs();
 
                     // Ensure that all the GenTreeIndir values are set to their defaults.
                     assert(memBase->GetRegNum() == REG_NA);
@@ -7037,9 +7019,9 @@ void CodeGen::genSSE41RoundOp(GenTreeOp* treeNode)
 void CodeGen::genIntrinsic(GenTree* treeNode)
 {
     // Right now only Sqrt/Abs are treated as math intrinsics.
-    switch (treeNode->AsIntrinsic()->gtIntrinsicId)
+    switch (treeNode->AsIntrinsic()->gtIntrinsicName)
     {
-        case CORINFO_INTRINSIC_Sqrt:
+        case NI_System_Math_Sqrt:
         {
             // Both operand and its result must be of the same floating point type.
             GenTree* srcNode = treeNode->AsOp()->gtOp1;
@@ -7051,13 +7033,13 @@ void CodeGen::genIntrinsic(GenTree* treeNode)
             break;
         }
 
-        case CORINFO_INTRINSIC_Abs:
+        case NI_System_Math_Abs:
             genSSE2BitwiseOp(treeNode);
             break;
 
-        case CORINFO_INTRINSIC_Round:
-        case CORINFO_INTRINSIC_Ceiling:
-        case CORINFO_INTRINSIC_Floor:
+        case NI_System_Math_Round:
+        case NI_System_Math_Ceiling:
+        case NI_System_Math_Floor:
             genSSE41RoundOp(treeNode->AsOp());
             break;
 
@@ -7941,11 +7923,8 @@ void CodeGen::genPutStructArgStk(GenTreePutArgStk* putArgStk)
         {
             assert(srcAddr->OperIsLocalAddr());
 
-            srcLclNum = srcAddr->AsLclVarCommon()->GetLclNum();
-            if (srcAddr->OperGet() == GT_LCL_FLD_ADDR)
-            {
-                srcLclOffset = srcAddr->AsLclFld()->GetLclOffs();
-            }
+            srcLclNum    = srcAddr->AsLclVarCommon()->GetLclNum();
+            srcLclOffset = srcAddr->AsLclVarCommon()->GetLclOffs();
         }
 
         for (int i = numSlots - 1; i >= 0; --i)
@@ -8470,9 +8449,8 @@ void CodeGen::genAmd64EmitterUnitTests()
 // genProfilingEnterCallback: Generate the profiling function enter callback.
 //
 // Arguments:
-//     initReg          - register to use as scratch register
-//     pInitRegModified - OUT parameter. *pInitRegModified set to 'true' if 'initReg' is
-//                        not zero after this call.
+//     initReg        - register to use as scratch register
+//     pInitRegZeroed - OUT parameter. This variable remains unchanged.
 //
 // Return Value:
 //     None
@@ -8491,7 +8469,7 @@ void CodeGen::genAmd64EmitterUnitTests()
 // 4. All registers are preserved.
 // 5. The helper pops the FunctionIDOrClientID argument from the stack.
 //
-void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegModified)
+void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegZeroed)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -8636,14 +8614,14 @@ void CodeGen::genProfilingLeaveCallback(unsigned helper)
 // genProfilingEnterCallback: Generate the profiling function enter callback.
 //
 // Arguments:
-//     initReg          - register to use as scratch register
-//     pInitRegModified - OUT parameter. *pInitRegModified set to 'true' if 'initReg' is
-//                        not zero after this call.
+//     initReg        - register to use as scratch register
+//     pInitRegZeroed - OUT parameter. *pInitRegZeroed is set to 'false' if and only if
+//                      this call sets 'initReg' to a non-zero value.
 //
 // Return Value:
 //     None
 //
-void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegModified)
+void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegZeroed)
 {
     assert(compiler->compGeneratingProlog);
 
@@ -8780,7 +8758,7 @@ void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegModifie
     // If initReg is one of RBM_CALLEE_TRASH, then it needs to be zero'ed before using.
     if ((RBM_CALLEE_TRASH & genRegMask(initReg)) != 0)
     {
-        *pInitRegModified = true;
+        *pInitRegZeroed = false;
     }
 
 #else // !defined(UNIX_AMD64_ABI)
@@ -8829,7 +8807,7 @@ void CodeGen::genProfilingEnterCallback(regNumber initReg, bool* pInitRegModifie
     // If initReg is one of RBM_CALLEE_TRASH, then it needs to be zero'ed before using.
     if ((RBM_CALLEE_TRASH & genRegMask(initReg)) != 0)
     {
-        *pInitRegModified = true;
+        *pInitRegZeroed = false;
     }
 
 #endif // !defined(UNIX_AMD64_ABI)
diff --git a/src/coreclr/src/jit/compiler.cpp b/src/coreclr/src/jit/compiler.cpp
index c78ee4477e0d80..b836a2efa2f2c7 100644
--- a/src/coreclr/src/jit/compiler.cpp
+++ b/src/coreclr/src/jit/compiler.cpp
@@ -1764,6 +1764,10 @@ void Compiler::compInit(ArenaAllocator*       pAlloc,
     info.compPerfScore = 0.0;
 #endif // defined(DEBUG) || defined(LATE_DISASM)
 
+#if defined(DEBUG) || defined(INLINE_DATA)
+    info.compMethodHashPrivate = 0;
+#endif // defined(DEBUG) || defined(INLINE_DATA)
+
 #ifdef DEBUG
     // Opt-in to jit stress based on method hash ranges.
     //
@@ -5287,10 +5291,6 @@ int Compiler::compCompile(CORINFO_MODULE_HANDLE classPtr,
     verbose = compIsForInlining() ? impInlineInfo->InlinerCompiler->verbose : false;
 #endif
 
-#if defined(DEBUG) || defined(INLINE_DATA)
-    info.compMethodHashPrivate = 0;
-#endif // defined(DEBUG) || defined(INLINE_DATA)
-
 #if FUNC_INFO_LOGGING
     LPCWSTR tmpJitFuncInfoFilename = JitConfig.JitFuncInfoFile();
 
@@ -9285,3 +9285,24 @@ bool Compiler::lvaIsOSRLocal(unsigned varNum)
 
     return false;
 }
+
+//------------------------------------------------------------------------------
+// gtChangeOperToNullCheck: helper to change tree oper to a NULLCHECK.
+//
+// Arguments:
+//    tree       - the node to change;
+//    basicBlock - basic block of the node.
+//
+// Notes:
+//    the function should not be called after lowering for platforms that do not support
+//    emitting NULLCHECK nodes, like arm32. Use `Lowering::TransformUnusedIndirection`
+//    that handles it and calls this function when appropriate.
+//
+void Compiler::gtChangeOperToNullCheck(GenTree* tree, BasicBlock* block)
+{
+    assert(tree->OperIs(GT_FIELD, GT_IND, GT_OBJ, GT_BLK, GT_DYN_BLK));
+    tree->ChangeOper(GT_NULLCHECK);
+    tree->ChangeType(TYP_INT);
+    block->bbFlags |= BBF_HAS_NULLCHECK;
+    optMethodFlags |= OMF_HAS_NULLCHECK;
+}
diff --git a/src/coreclr/src/jit/compiler.h b/src/coreclr/src/jit/compiler.h
index c5f571838d4b29..9924c5ffe1db71 100644
--- a/src/coreclr/src/jit/compiler.h
+++ b/src/coreclr/src/jit/compiler.h
@@ -2701,6 +2701,8 @@ class Compiler
 
     GenTree* gtNewNullCheck(GenTree* addr, BasicBlock* basicBlock);
 
+    void gtChangeOperToNullCheck(GenTree* tree, BasicBlock* block);
+
     GenTreeArgList* gtNewArgList(GenTree* op);
     GenTreeArgList* gtNewArgList(GenTree* op1, GenTree* op2);
     GenTreeArgList* gtNewArgList(GenTree* op1, GenTree* op2, GenTree* op3);
@@ -3741,7 +3743,7 @@ class Compiler
     GenTree* impMathIntrinsic(CORINFO_METHOD_HANDLE method,
                               CORINFO_SIG_INFO*     sig,
                               var_types             callType,
-                              CorInfoIntrinsics     intrinsicID,
+                              NamedIntrinsic        intrinsicName,
                               bool                  tailCall);
     NamedIntrinsic lookupNamedIntrinsic(CORINFO_METHOD_HANDLE method);
     GenTree* impUnsupportedNamedIntrinsic(unsigned              helper,
@@ -3937,9 +3939,9 @@ class Compiler
     bool VarTypeIsMultiByteAndCanEnreg(
         var_types type, CORINFO_CLASS_HANDLE typeClass, unsigned* typeSize, bool forReturn, bool isVarArg);
 
-    bool IsIntrinsicImplementedByUserCall(CorInfoIntrinsics intrinsicId);
-    bool IsTargetIntrinsic(CorInfoIntrinsics intrinsicId);
-    bool IsMathIntrinsic(CorInfoIntrinsics intrinsicId);
+    bool IsIntrinsicImplementedByUserCall(NamedIntrinsic intrinsicName);
+    bool IsTargetIntrinsic(NamedIntrinsic intrinsicName);
+    bool IsMathIntrinsic(NamedIntrinsic intrinsicName);
     bool IsMathIntrinsic(GenTree* tree);
 
 private:
@@ -4633,6 +4635,9 @@ class Compiler
 
     void fgComputeLifeLIR(VARSET_TP& life, BasicBlock* block, VARSET_VALARG_TP volatileVars);
 
+    bool fgTryRemoveNonLocal(GenTree* node, LIR::Range* blockRange);
+
+    void fgRemoveDeadStoreLIR(GenTree* store, BasicBlock* block);
     bool fgRemoveDeadStore(GenTree**        pTree,
                            LclVarDsc*       varDsc,
                            VARSET_VALARG_TP life,
@@ -4964,7 +4969,7 @@ class Compiler
 
     // When the flow graph changes, we need to update the block numbers, predecessor lists, reachability sets, and
     // dominators.
-    void fgUpdateChangedFlowGraph();
+    void fgUpdateChangedFlowGraph(bool computeDoms = true);
 
 public:
     // Compute the predecessors of the blocks in the control flow graph.
@@ -6326,11 +6331,12 @@ class Compiler
 
     struct CSEdsc
     {
-        CSEdsc* csdNextInBucket; // used by the hash table
-
-        unsigned csdHashKey; // the orginal hashkey
-
-        unsigned csdIndex; // 1..optCSECandidateCount
+        CSEdsc*  csdNextInBucket;  // used by the hash table
+        size_t   csdHashKey;       // the orginal hashkey
+        ssize_t  csdConstDefValue; // When we CSE similar constants, this is the value that we use as the def
+        ValueNum csdConstDefVN;    // When we CSE similar constants, this is the ValueNumber that we use for the LclVar
+                                   // assignment
+        unsigned csdIndex;         // 1..optCSECandidateCount
         bool     csdLiveAcrossCall;
 
         unsigned short csdDefCount; // definition   count
@@ -6359,9 +6365,15 @@ class Compiler
 
         ValueNum defConservNormVN; // if all def occurrences share the same conservative normal value
                                    // number, this will reflect it; otherwise, NoVN.
+                                   // not used for shared const CSE's
     };
 
-    static const size_t s_optCSEhashSize;
+    static const size_t s_optCSEhashSizeInitial;
+    static const size_t s_optCSEhashGrowthFactor;
+    static const size_t s_optCSEhashBucketSize;
+    size_t              optCSEhashSize;                 // The current size of hashtable
+    size_t              optCSEhashCount;                // Number of entries in hashtable
+    size_t              optCSEhashMaxCountBeforeResize; // Number of entries before resize
     CSEdsc**            optCSEhash;
     CSEdsc**            optCSEtab;
 
@@ -6406,6 +6418,16 @@ class Compiler
     void optEnsureClearCSEInfo();
 #endif // DEBUG
 
+    static bool Is_Shared_Const_CSE(size_t key)
+    {
+        return ((key & TARGET_SIGN_BIT) != 0);
+    }
+
+    static size_t Decode_Shared_Const_CSE_Value(size_t key)
+    {
+        return (key & ~TARGET_SIGN_BIT) << CSE_CONST_SHARED_LOW_BITS;
+    }
+
 #endif // FEATURE_ANYCSE
 
 #if FEATURE_VALNUM_CSE
@@ -8190,7 +8212,7 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 #if defined(TARGET_XARCH)
         if (getSIMDSupportLevel() == SIMD_AVX2_Supported)
         {
-            return TYP_SIMD32;
+            return JitConfig.EnableHWIntrinsic() ? TYP_SIMD32 : TYP_SIMD16;
         }
         else
         {
@@ -8231,7 +8253,7 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 #if defined(TARGET_XARCH)
         if (getSIMDSupportLevel() == SIMD_AVX2_Supported)
         {
-            return YMM_REGSIZE_BYTES;
+            return JitConfig.EnableHWIntrinsic() ? YMM_REGSIZE_BYTES : XMM_REGSIZE_BYTES;
         }
         else
         {
@@ -8261,7 +8283,7 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 #if defined(FEATURE_HW_INTRINSICS) && defined(TARGET_XARCH)
         if (compOpportunisticallyDependsOn(InstructionSet_AVX))
         {
-            return YMM_REGSIZE_BYTES;
+            return JitConfig.EnableHWIntrinsic() ? YMM_REGSIZE_BYTES : XMM_REGSIZE_BYTES;
         }
         else
         {
@@ -8802,8 +8824,7 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
         bool doLateDisasm; // Run the late disassembler
 #endif                     // LATE_DISASM
 
-#if DUMP_GC_TABLES && !defined(DEBUG) && defined(JIT32_GCENCODER)
-// Only the JIT32_GCENCODER implements GC dumping in non-DEBUG code.
+#if DUMP_GC_TABLES && !defined(DEBUG)
 #pragma message("NOTE: this non-debug build has GC ptr table dumping always enabled!")
         static const bool dspGCtbls = true;
 #endif
@@ -9001,7 +9022,7 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
     {
 #if 0
         // Switching between size & speed has measurable throughput impact
-        // (3.5% on NGen mscorlib when measured). It used to be enabled for
+        // (3.5% on NGen CoreLib when measured). It used to be enabled for
         // DEBUG, but should generate identical code between CHK & RET builds,
         // so that's not acceptable.
         // TODO-Throughput: Figure out what to do about size vs. speed & throughput.
@@ -9067,7 +9088,7 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
         bool compIsVarArgs : 1;          // Does the method have varargs parameters?
         bool compInitMem : 1;            // Is the CORINFO_OPT_INIT_LOCALS bit set in the method info options?
         bool compProfilerCallback : 1;   // JIT inserted a profiler Enter callback
-        bool compPublishStubParam : 1;   // EAX captured in prolog will be available through an instrinsic
+        bool compPublishStubParam : 1;   // EAX captured in prolog will be available through an intrinsic
         bool compRetBuffDefStack : 1;    // The ret buff argument definitely points into the stack.
         bool compHasNextCallRetAddr : 1; // The NextCallReturnAddress intrinsic is used.
 
diff --git a/src/coreclr/src/jit/compiler.hpp b/src/coreclr/src/jit/compiler.hpp
index c12bacd94d7a96..ca3ed3c6fc668b 100644
--- a/src/coreclr/src/jit/compiler.hpp
+++ b/src/coreclr/src/jit/compiler.hpp
@@ -3169,6 +3169,7 @@ inline regMaskTP genIntAllRegArgMask(unsigned numRegs)
 
 inline regMaskTP genFltAllRegArgMask(unsigned numRegs)
 {
+#ifndef TARGET_X86
     assert(numRegs <= MAX_FLOAT_REG_ARG);
 
     regMaskTP result = RBM_NONE;
@@ -3177,6 +3178,10 @@ inline regMaskTP genFltAllRegArgMask(unsigned numRegs)
         result |= fltArgMasks[i];
     }
     return result;
+#else
+    assert(!"no x86 float arg regs\n");
+    return RBM_NONE;
+#endif
 }
 
 /*
diff --git a/src/coreclr/src/jit/ee_il_dll.cpp b/src/coreclr/src/jit/ee_il_dll.cpp
index 150efed411f6af..bfd80ffb120005 100644
--- a/src/coreclr/src/jit/ee_il_dll.cpp
+++ b/src/coreclr/src/jit/ee_il_dll.cpp
@@ -316,7 +316,8 @@ unsigned CILJit::getMaxIntrinsicSIMDVectorLength(CORJIT_FLAGS cpuCompileFlags)
         // ensure that AVX2 is actually supported. Otherwise, we will end up getting asserts downstream.
         if ((JitConfig.EnableAVX2() != 0) && (JitConfig.EnableAVX() != 0) && (JitConfig.EnableSSE42() != 0) &&
             (JitConfig.EnableSSE41() != 0) && (JitConfig.EnableSSSE3() != 0) && (JitConfig.EnableSSE3_4() != 0) &&
-            (JitConfig.EnableSSE3() != 0) && (JitConfig.EnableSSE2() != 0) && (JitConfig.EnableSSE() != 0))
+            (JitConfig.EnableSSE3() != 0) && (JitConfig.EnableSSE2() != 0) && (JitConfig.EnableSSE() != 0) &&
+            (JitConfig.EnableHWIntrinsic() != 0))
         {
             if (GetJitTls() != nullptr && JitTls::GetCompiler() != nullptr)
             {
diff --git a/src/coreclr/src/jit/emit.cpp b/src/coreclr/src/jit/emit.cpp
index cc12dabc5492eb..ab1c281ea5eb99 100644
--- a/src/coreclr/src/jit/emit.cpp
+++ b/src/coreclr/src/jit/emit.cpp
@@ -7692,7 +7692,12 @@ regMaskTP emitter::emitGetGCRegsKilledByNoGCCall(CorInfoHelpFunc helper)
             break;
 
         case CORINFO_HELP_PROF_FCN_LEAVE:
+#if defined(TARGET_ARM)
+            // profiler scratch remains gc live
+            result = RBM_PROFILER_LEAVE_TRASH & ~RBM_PROFILER_RET_SCRATCH;
+#else
             result = RBM_PROFILER_LEAVE_TRASH;
+#endif
             break;
 
         case CORINFO_HELP_PROF_FCN_TAILCALL:
diff --git a/src/coreclr/src/jit/emitarm64.cpp b/src/coreclr/src/jit/emitarm64.cpp
index 9a82b01063b710..a23aef5812a618 100644
--- a/src/coreclr/src/jit/emitarm64.cpp
+++ b/src/coreclr/src/jit/emitarm64.cpp
@@ -13396,11 +13396,7 @@ void emitter::emitInsLoadStoreOp(instruction ins, emitAttr attr, regNumber dataR
             {
                 GenTreeLclVarCommon* varNode = addr->AsLclVarCommon();
                 unsigned             lclNum  = varNode->GetLclNum();
-                unsigned             offset  = 0;
-                if (addr->OperIs(GT_LCL_FLD_ADDR))
-                {
-                    offset = varNode->AsLclFld()->GetLclOffs();
-                }
+                unsigned             offset  = varNode->GetLclOffs();
                 if (emitInsIsStore(ins))
                 {
                     emitIns_S_R(ins, attr, dataReg, lclNum, offset);
diff --git a/src/coreclr/src/jit/emitxarch.cpp b/src/coreclr/src/jit/emitxarch.cpp
index 81f9ce8ef68108..f21b1170eb83cc 100644
--- a/src/coreclr/src/jit/emitxarch.cpp
+++ b/src/coreclr/src/jit/emitxarch.cpp
@@ -163,8 +163,10 @@ bool emitter::IsDstSrcSrcAVXInstruction(instruction ins)
 
 bool emitter::AreUpper32BitsZero(regNumber reg)
 {
-    // Don't look back across IG boundaries (possible control flow)
-    if (emitCurIGinsCnt == 0)
+    // If there are no instructions in this IG, we can look back at
+    // the previous IG's instructions if this IG is an extension.
+    //
+    if ((emitCurIGinsCnt == 0) && ((emitCurIG->igFlags & IGF_EXTEND) == 0))
     {
         return false;
     }
@@ -2956,24 +2958,27 @@ void emitter::emitHandleMemOp(GenTreeIndir* indir, instrDesc* id, insFormat fmt,
     }
     else
     {
+        regNumber amBaseReg = REG_NA;
         if (memBase != nullptr)
         {
-            id->idAddr()->iiaAddrMode.amBaseReg = memBase->GetRegNum();
-        }
-        else
-        {
-            id->idAddr()->iiaAddrMode.amBaseReg = REG_NA;
+            assert(!memBase->isContained());
+            amBaseReg = memBase->GetRegNum();
+            assert(amBaseReg != REG_NA);
         }
 
+        regNumber amIndxReg = REG_NA;
         if (indir->HasIndex())
         {
-            id->idAddr()->iiaAddrMode.amIndxReg = indir->Index()->GetRegNum();
-        }
-        else
-        {
-            id->idAddr()->iiaAddrMode.amIndxReg = REG_NA;
+            GenTree* index = indir->Index();
+            assert(!index->isContained());
+            amIndxReg = index->GetRegNum();
+            assert(amIndxReg != REG_NA);
         }
-        id->idAddr()->iiaAddrMode.amScale = emitEncodeScale(indir->Scale());
+
+        assert((amBaseReg != REG_NA) || (amIndxReg != REG_NA) || (indir->Offset() != 0)); // At least one should be set.
+        id->idAddr()->iiaAddrMode.amBaseReg = amBaseReg;
+        id->idAddr()->iiaAddrMode.amIndxReg = amIndxReg;
+        id->idAddr()->iiaAddrMode.amScale   = emitEncodeScale(indir->Scale());
 
         id->idInsFmt(emitMapFmtForIns(fmt, ins));
 
@@ -3043,11 +3048,7 @@ void emitter::emitInsLoadInd(instruction ins, emitAttr attr, regNumber dstReg, G
     if (addr->OperIs(GT_LCL_VAR_ADDR, GT_LCL_FLD_ADDR))
     {
         GenTreeLclVarCommon* varNode = addr->AsLclVarCommon();
-        unsigned             offset  = 0;
-        if (addr->OperIs(GT_LCL_FLD_ADDR))
-        {
-            offset = varNode->AsLclFld()->GetLclOffs();
-        }
+        unsigned             offset  = varNode->GetLclOffs();
         emitIns_R_S(ins, attr, dstReg, varNode->GetLclNum(), offset);
 
         // Updating variable liveness after instruction was emitted
@@ -3100,11 +3101,7 @@ void emitter::emitInsStoreInd(instruction ins, emitAttr attr, GenTreeStoreInd* m
     if (addr->OperIs(GT_LCL_VAR_ADDR, GT_LCL_FLD_ADDR))
     {
         GenTreeLclVarCommon* varNode = addr->AsLclVarCommon();
-        unsigned             offset  = 0;
-        if (addr->OperIs(GT_LCL_FLD_ADDR))
-        {
-            offset = varNode->AsLclFld()->GetLclOffs();
-        }
+        unsigned             offset  = varNode->GetLclOffs();
         if (data->isContainedIntOrIImmed())
         {
             emitIns_S_I(ins, attr, varNode->GetLclNum(), offset, (int)data->AsIntConCommon()->IconValue());
@@ -3292,9 +3289,11 @@ regNumber emitter::emitInsBinary(instruction ins, emitAttr attr, GenTree* dst, G
             switch (memBase->OperGet())
             {
                 case GT_LCL_VAR_ADDR:
+                case GT_LCL_FLD_ADDR:
                 {
+                    assert(memBase->isContained());
                     varNum = memBase->AsLclVarCommon()->GetLclNum();
-                    offset = 0;
+                    offset = memBase->AsLclVarCommon()->GetLclOffs();
 
                     // Ensure that all the GenTreeIndir values are set to their defaults.
                     assert(!memIndir->HasIndex());
@@ -3605,8 +3604,7 @@ void emitter::emitInsRMW(instruction ins, emitAttr attr, GenTreeStoreInd* storeI
 {
     GenTree* addr = storeInd->Addr();
     addr          = addr->gtSkipReloadOrCopy();
-    assert(addr->OperGet() == GT_LCL_VAR || addr->OperGet() == GT_LCL_VAR_ADDR || addr->OperGet() == GT_LEA ||
-           addr->OperGet() == GT_CLS_VAR_ADDR || addr->OperGet() == GT_CNS_INT);
+    assert(addr->OperIs(GT_LCL_VAR, GT_LCL_VAR_ADDR, GT_LEA, GT_CLS_VAR_ADDR, GT_CNS_INT));
 
     instrDesc*     id = nullptr;
     UNATIVE_OFFSET sz;
@@ -3685,8 +3683,7 @@ void emitter::emitInsRMW(instruction ins, emitAttr attr, GenTreeStoreInd* storeI
 {
     GenTree* addr = storeInd->Addr();
     addr          = addr->gtSkipReloadOrCopy();
-    assert(addr->OperGet() == GT_LCL_VAR || addr->OperGet() == GT_LCL_VAR_ADDR || addr->OperGet() == GT_CLS_VAR_ADDR ||
-           addr->OperGet() == GT_LEA || addr->OperGet() == GT_CNS_INT);
+    assert(addr->OperIs(GT_LCL_VAR, GT_LCL_VAR_ADDR, GT_CLS_VAR_ADDR, GT_LEA, GT_CNS_INT));
 
     ssize_t offset = 0;
     if (addr->OperGet() != GT_CLS_VAR_ADDR)
diff --git a/src/coreclr/src/jit/flowgraph.cpp b/src/coreclr/src/jit/flowgraph.cpp
index e870a8f4c0fe63..242a4c56791e2e 100644
--- a/src/coreclr/src/jit/flowgraph.cpp
+++ b/src/coreclr/src/jit/flowgraph.cpp
@@ -175,6 +175,8 @@ void Compiler::fgInit()
 #ifdef FEATURE_SIMD
     fgPreviousCandidateSIMDFieldAsgStmt = nullptr;
 #endif
+
+    fgHasSwitch = false;
 }
 
 bool Compiler::fgHaveProfileData()
@@ -476,7 +478,8 @@ void Compiler::fgEnsureFirstBBisScratch()
 
     noway_assert(fgLastBB != nullptr);
 
-    block->bbFlags |= (BBF_INTERNAL | BBF_IMPORTED);
+    // Set the expected flags
+    block->bbFlags |= (BBF_INTERNAL | BBF_IMPORTED | BBF_JMP_TARGET | BBF_HAS_LABEL);
 
     // This new first BB has an implicit ref, and no others.
     block->bbRefs = 1;
@@ -1865,7 +1868,7 @@ bool Compiler::fgReachable(BasicBlock* b1, BasicBlock* b2)
  *  it again.
  */
 
-void Compiler::fgUpdateChangedFlowGraph()
+void Compiler::fgUpdateChangedFlowGraph(bool computeDoms)
 {
     // We need to clear this so we don't hit an assert calling fgRenumberBlocks().
     fgDomsComputed = false;
@@ -1876,7 +1879,10 @@ void Compiler::fgUpdateChangedFlowGraph()
     fgComputePreds();
     fgComputeEnterBlocksSet();
     fgComputeReachabilitySets();
-    fgComputeDoms();
+    if (computeDoms)
+    {
+        fgComputeDoms();
+    }
 }
 
 /*****************************************************************************
@@ -3650,6 +3656,7 @@ PhaseStatus Compiler::fgInsertGCPolls()
             case BBJ_SWITCH:
             case BBJ_NONE:
             case BBJ_THROW:
+            case BBJ_CALLFINALLY:
                 break;
             default:
                 assert(!"Unexpected block kind");
@@ -3698,6 +3705,18 @@ PhaseStatus Compiler::fgInsertGCPolls()
             // We don't want to deal with all the outgoing edges of a switch block.
             pollType = GCPOLL_CALL;
         }
+        else if ((block->bbFlags & BBF_COLD) != 0)
+        {
+#ifdef DEBUG
+            if (verbose)
+            {
+                printf("Selecting CALL poll in block " FMT_BB " because it is a cold block\n", block->bbNum);
+            }
+#endif // DEBUG
+
+            // We don't want to split a cold block.
+            pollType = GCPOLL_CALL;
+        }
 
         BasicBlock* curBasicBlock = fgCreateGCPoll(pollType, block);
         createdPollBlocks |= (block != curBasicBlock);
@@ -3710,7 +3729,8 @@ PhaseStatus Compiler::fgInsertGCPolls()
     {
         noway_assert(opts.OptimizationEnabled());
         fgReorderBlocks();
-        fgUpdateChangedFlowGraph();
+        constexpr bool computeDoms = false;
+        fgUpdateChangedFlowGraph(computeDoms);
     }
 #ifdef DEBUG
     if (verbose)
@@ -4058,9 +4078,11 @@ BasicBlock* Compiler::fgCreateGCPoll(GCPollType pollType, BasicBlock* block)
         createdPollBlocks = false;
 
         Statement* newStmt = nullptr;
-        if (block->bbJumpKind == BBJ_ALWAYS)
+        if ((block->bbJumpKind == BBJ_ALWAYS) || (block->bbJumpKind == BBJ_CALLFINALLY) ||
+            (block->bbJumpKind == BBJ_NONE))
         {
-            // for BBJ_ALWAYS I don't need to insert it before the condition.  Just append it.
+            // For BBJ_ALWAYS, BBJ_CALLFINALLY, and BBJ_NONE and  we don't need to insert it before the condition.
+            // Just append it.
             newStmt = fgNewStmtAtEnd(block, call);
         }
         else
@@ -4138,9 +4160,12 @@ BasicBlock* Compiler::fgCreateGCPoll(GCPollType pollType, BasicBlock* block)
 
         // We are allowed to split loops and we need to keep a few other flags...
         //
-        noway_assert((originalFlags & (BBF_SPLIT_NONEXIST & ~(BBF_LOOP_HEAD | BBF_LOOP_CALL0 | BBF_LOOP_CALL1))) == 0);
-        top->bbFlags = originalFlags & (~BBF_SPLIT_LOST | BBF_GC_SAFE_POINT);
-        bottom->bbFlags |= originalFlags & (BBF_SPLIT_GAINED | BBF_IMPORTED | BBF_GC_SAFE_POINT);
+        noway_assert((originalFlags & (BBF_SPLIT_NONEXIST &
+                                       ~(BBF_LOOP_HEAD | BBF_LOOP_CALL0 | BBF_LOOP_CALL1 | BBF_LOOP_PREHEADER |
+                                         BBF_RETLESS_CALL))) == 0);
+        top->bbFlags = originalFlags & (~(BBF_SPLIT_LOST | BBF_LOOP_PREHEADER | BBF_RETLESS_CALL) | BBF_GC_SAFE_POINT);
+        bottom->bbFlags |= originalFlags & (BBF_SPLIT_GAINED | BBF_IMPORTED | BBF_GC_SAFE_POINT | BBF_LOOP_PREHEADER |
+                                            BBF_RETLESS_CALL);
         bottom->inheritWeight(top);
         poll->bbFlags |= originalFlags & (BBF_SPLIT_GAINED | BBF_IMPORTED | BBF_GC_SAFE_POINT);
 
@@ -4265,6 +4290,7 @@ BasicBlock* Compiler::fgCreateGCPoll(GCPollType pollType, BasicBlock* block)
                 __fallthrough;
 
             case BBJ_ALWAYS:
+            case BBJ_CALLFINALLY:
                 fgReplacePred(bottom->bbJumpDest, top, bottom);
                 break;
             case BBJ_SWITCH:
@@ -7232,7 +7258,7 @@ bool Compiler::fgIsThrow(GenTree* tree)
         return true;
     }
 
-    // TODO-CQ: there are a bunch of managed methods in [mscorlib]System.ThrowHelper
+    // TODO-CQ: there are a bunch of managed methods in System.ThrowHelper
     // that would be nice to recognize.
 
     return false;
@@ -14678,9 +14704,9 @@ bool Compiler::fgOptimizeSwitchBranches(BasicBlock* block)
             LIR::ReadOnlyRange range(zeroConstNode, switchTree);
             m_pLowering->LowerRange(block, range);
         }
-        else
+        else if (fgStmtListThreaded)
         {
-            // Re-link the nodes for this statement.
+            gtSetStmtInfo(switchStmt);
             fgSetStmtSeq(switchStmt);
         }
 
diff --git a/src/coreclr/src/jit/gcencode.cpp b/src/coreclr/src/jit/gcencode.cpp
index 3c45137b059367..81edb0b0d29e13 100644
--- a/src/coreclr/src/jit/gcencode.cpp
+++ b/src/coreclr/src/jit/gcencode.cpp
@@ -3633,7 +3633,10 @@ void GCInfo::gcFindPtrsInFrame(const void* infoBlock, const void* codeBlock, uns
 template class JitHashTable<RegSlotIdKey, RegSlotIdKey, GcSlotId>;
 template class JitHashTable<StackSlotIdKey, StackSlotIdKey, GcSlotId>;
 
-#ifdef DEBUG
+#if defined(DEBUG) || DUMP_GC_TABLES
+
+// This is a copy of GcStackSlotBaseNames from gcinfotypes.h so we can compile in to non-DEBUG builds.
+const char* const JitGcStackSlotBaseNames[] = {"caller.sp", "sp", "frame"};
 
 static const char* const GcSlotFlagsNames[] = {"",
                                                "(byref) ",
@@ -3652,7 +3655,7 @@ class GcInfoEncoderWithLogging
 
 public:
     GcInfoEncoderWithLogging(GcInfoEncoder* gcInfoEncoder, bool verbose)
-        : m_gcInfoEncoder(gcInfoEncoder), m_doLogging(verbose || JitConfig.JitGCInfoLogging() != 0)
+        : m_gcInfoEncoder(gcInfoEncoder), m_doLogging(verbose INDEBUG(|| JitConfig.JitGCInfoLogging() != 0))
     {
     }
 
@@ -3662,7 +3665,7 @@ class GcInfoEncoderWithLogging
         if (m_doLogging)
         {
             printf("Stack slot id for offset %d (0x%x) (%s) %s= %d.\n", spOffset, spOffset,
-                   GcStackSlotBaseNames[spBase], GcSlotFlagsNames[flags & 7], newSlotId);
+                   JitGcStackSlotBaseNames[spBase], GcSlotFlagsNames[flags & 7], newSlotId);
         }
         return newSlotId;
     }
@@ -3827,14 +3830,14 @@ class GcInfoEncoderWithLogging
 };
 
 #define GCENCODER_WITH_LOGGING(withLog, realEncoder)                                                                   \
-    GcInfoEncoderWithLogging  withLog##Var(realEncoder, compiler->verbose || compiler->opts.dspGCtbls);                \
+    GcInfoEncoderWithLogging  withLog##Var(realEncoder, INDEBUG(compiler->verbose ||) compiler->opts.dspGCtbls);       \
     GcInfoEncoderWithLogging* withLog = &withLog##Var;
 
-#else // DEBUG
+#else // !(defined(DEBUG) || DUMP_GC_TABLES)
 
 #define GCENCODER_WITH_LOGGING(withLog, realEncoder) GcInfoEncoder* withLog = realEncoder;
 
-#endif // DEBUG
+#endif // !(defined(DEBUG) || DUMP_GC_TABLES)
 
 void GCInfo::gcInfoBlockHdrSave(GcInfoEncoder* gcInfoEncoder, unsigned methodSize, unsigned prologSize)
 {
@@ -4006,7 +4009,7 @@ void GCInfo::gcInfoBlockHdrSave(GcInfoEncoder* gcInfoEncoder, unsigned methodSiz
 #endif // DISPLAY_SIZES
 }
 
-#ifdef DEBUG
+#if defined(DEBUG) || DUMP_GC_TABLES
 #define Encoder GcInfoEncoderWithLogging
 #else
 #define Encoder GcInfoEncoder
diff --git a/src/coreclr/src/jit/gentree.cpp b/src/coreclr/src/jit/gentree.cpp
index 8ca9a49a2ce7db..2e0e96a0e9a61b 100644
--- a/src/coreclr/src/jit/gentree.cpp
+++ b/src/coreclr/src/jit/gentree.cpp
@@ -3250,78 +3250,138 @@ unsigned Compiler::gtSetEvalOrder(GenTree* tree)
         switch (oper)
         {
 #ifdef TARGET_ARM
-            case GT_CNS_LNG:
-                costSz = 9;
-                costEx = 4;
-                goto COMMON_CNS;
-
             case GT_CNS_STR:
                 // Uses movw/movt
-                costSz = 7;
-                costEx = 3;
+                costSz = 8;
+                costEx = 2;
                 goto COMMON_CNS;
 
+            case GT_CNS_LNG:
+            {
+                GenTreeIntConCommon* con = tree->AsIntConCommon();
+
+                INT64 lngVal = con->LngValue();
+                INT32 loVal  = (INT32)(lngVal & 0xffffffff);
+                INT32 hiVal  = (INT32)(lngVal >> 32);
+
+                if (lngVal == 0)
+                {
+                    costSz = 1;
+                    costEx = 1;
+                }
+                else
+                {
+                    // Minimum of one instruction to setup hiVal,
+                    // and one instruction to setup loVal
+                    costSz = 4 + 4;
+                    costEx = 1 + 1;
+
+                    if (!codeGen->validImmForInstr(INS_mov, (target_ssize_t)hiVal) &&
+                        !codeGen->validImmForInstr(INS_mvn, (target_ssize_t)hiVal))
+                    {
+                        // Needs extra instruction: movw/movt
+                        costSz += 4;
+                        costEx += 1;
+                    }
+
+                    if (!codeGen->validImmForInstr(INS_mov, (target_ssize_t)loVal) &&
+                        !codeGen->validImmForInstr(INS_mvn, (target_ssize_t)loVal))
+                    {
+                        // Needs extra instruction: movw/movt
+                        costSz += 4;
+                        costEx += 1;
+                    }
+                }
+                goto COMMON_CNS;
+            }
+
             case GT_CNS_INT:
             {
                 // If the constant is a handle then it will need to have a relocation
                 //  applied to it.
                 // Any constant that requires a reloc must use the movw/movt sequence
                 //
-                GenTreeIntConCommon* con = tree->AsIntConCommon();
+                GenTreeIntConCommon* con    = tree->AsIntConCommon();
+                INT32                conVal = con->IconValue();
 
-                if (con->ImmedValNeedsReloc(this) ||
-                    !codeGen->validImmForInstr(INS_mov, (target_ssize_t)tree->AsIntCon()->gtIconVal))
+                if (con->ImmedValNeedsReloc(this))
                 {
-                    // Uses movw/movt
-                    costSz = 7;
-                    costEx = 3;
+                    // Requires movw/movt
+                    costSz = 8;
+                    costEx = 2;
                 }
-                else if (((unsigned)tree->AsIntCon()->gtIconVal) <= 0x00ff)
+                else if (codeGen->validImmForInstr(INS_add, (target_ssize_t)conVal))
                 {
-                    // mov  Rd, <const8>
-                    costSz = 1;
+                    // Typically included with parent oper
+                    costSz = 2;
                     costEx = 1;
                 }
-                else
+                else if (codeGen->validImmForInstr(INS_mov, (target_ssize_t)conVal) &&
+                         codeGen->validImmForInstr(INS_mvn, (target_ssize_t)conVal))
                 {
-                    // Uses movw/mvn
-                    costSz = 3;
+                    // Uses mov or mvn
+                    costSz = 4;
                     costEx = 1;
                 }
+                else
+                {
+                    // Needs movw/movt
+                    costSz = 8;
+                    costEx = 2;
+                }
                 goto COMMON_CNS;
             }
 
 #elif defined TARGET_XARCH
 
-            case GT_CNS_LNG:
-                costSz = 10;
-                costEx = 3;
-                goto COMMON_CNS;
-
             case GT_CNS_STR:
+#ifdef TARGET_AMD64
+                costSz = 10;
+                costEx = 2;
+#else // TARGET_X86
                 costSz = 4;
                 costEx = 1;
+#endif
                 goto COMMON_CNS;
 
+            case GT_CNS_LNG:
             case GT_CNS_INT:
             {
+                GenTreeIntConCommon* con       = tree->AsIntConCommon();
+                ssize_t              conVal    = (oper == GT_CNS_LNG) ? (ssize_t)con->LngValue() : con->IconValue();
+                bool                 fitsInVal = true;
+
+#ifdef TARGET_X86
+                if (oper == GT_CNS_LNG)
+                {
+                    INT64 lngVal = con->LngValue();
+
+                    conVal = (ssize_t)lngVal; // truncate to 32-bits
+
+                    fitsInVal = ((INT64)conVal == lngVal);
+                }
+#endif // TARGET_X86
+
                 // If the constant is a handle then it will need to have a relocation
                 //  applied to it.
                 //
-                GenTreeIntConCommon* con = tree->AsIntConCommon();
-
                 bool iconNeedsReloc = con->ImmedValNeedsReloc(this);
 
-                if (!iconNeedsReloc && con->FitsInI8())
+                if (iconNeedsReloc)
+                {
+                    costSz = 4;
+                    costEx = 1;
+                }
+                else if (fitsInVal && GenTreeIntConCommon::FitsInI8(conVal))
                 {
                     costSz = 1;
                     costEx = 1;
                 }
-#if defined(TARGET_AMD64)
-                else if (iconNeedsReloc || !con->FitsInI32())
+#ifdef TARGET_AMD64
+                else if (!GenTreeIntConCommon::FitsInI32(conVal))
                 {
                     costSz = 10;
-                    costEx = 3;
+                    costEx = 2;
                 }
 #endif // TARGET_AMD64
                 else
@@ -3329,21 +3389,83 @@ unsigned Compiler::gtSetEvalOrder(GenTree* tree)
                     costSz = 4;
                     costEx = 1;
                 }
+#ifdef TARGET_X86
+                if (oper == GT_CNS_LNG)
+                {
+                    costSz += fitsInVal ? 1 : 4;
+                    costEx += 1;
+                }
+#endif // TARGET_X86
+
                 goto COMMON_CNS;
             }
 
 #elif defined(TARGET_ARM64)
-            case GT_CNS_LNG:
+
             case GT_CNS_STR:
+            case GT_CNS_LNG:
             case GT_CNS_INT:
-                // TODO-ARM64-NYI: Need cost estimates.
-                costSz = 1;
-                costEx = 1;
+            {
+                GenTreeIntConCommon* con            = tree->AsIntConCommon();
+                bool                 iconNeedsReloc = con->ImmedValNeedsReloc(this);
+                INT64                imm            = con->LngValue();
+                emitAttr             size           = EA_SIZE(emitActualTypeSize(tree));
+
+                if (iconNeedsReloc)
+                {
+                    costSz = 8;
+                    costEx = 2;
+                }
+                else if (emitter::emitIns_valid_imm_for_add(imm, size))
+                {
+                    costSz = 2;
+                    costEx = 1;
+                }
+                else if (emitter::emitIns_valid_imm_for_mov(imm, size))
+                {
+                    costSz = 4;
+                    costEx = 1;
+                }
+                else
+                {
+                    // Arm64 allows any arbitrary 16-bit constant to be loaded into a register halfword
+                    // There are three forms
+                    //    movk which loads into any halfword preserving the remaining halfwords
+                    //    movz which loads into any halfword zeroing the remaining halfwords
+                    //    movn which loads into any halfword zeroing the remaining halfwords then bitwise inverting
+                    //    the register
+                    // In some cases it is preferable to use movn, because it has the side effect of filling the
+                    // other halfwords
+                    // with ones
+
+                    // Determine whether movn or movz will require the fewest instructions to populate the immediate
+                    bool preferMovz       = false;
+                    bool preferMovn       = false;
+                    int  instructionCount = 4;
+
+                    for (int i = (size == EA_8BYTE) ? 48 : 16; i >= 0; i -= 16)
+                    {
+                        if (!preferMovn && (uint16_t(imm >> i) == 0x0000))
+                        {
+                            preferMovz = true; // by using a movk to start we can save one instruction
+                            instructionCount--;
+                        }
+                        else if (!preferMovz && (uint16_t(imm >> i) == 0xffff))
+                        {
+                            preferMovn = true; // by using a movn to start we can save one instruction
+                            instructionCount--;
+                        }
+                    }
+
+                    costEx = instructionCount;
+                    costSz = 4 * instructionCount;
+                }
+            }
                 goto COMMON_CNS;
 
 #else
-            case GT_CNS_LNG:
             case GT_CNS_STR:
+            case GT_CNS_LNG:
             case GT_CNS_INT:
 #error "Unknown TARGET"
 #endif
@@ -3502,6 +3624,8 @@ unsigned Compiler::gtSetEvalOrder(GenTree* tree)
 
             level = gtSetEvalOrder(op1);
 
+            GenTreeIntrinsic* intrinsic;
+
             /* Special handling for some operators */
 
             switch (oper)
@@ -3563,54 +3687,82 @@ unsigned Compiler::gtSetEvalOrder(GenTree* tree)
                     break;
 
                 case GT_INTRINSIC:
-                    // GT_INTRINSIC intrinsics Sin, Cos, Sqrt, Abs ... have higher costs.
-                    // TODO: tune these costs target specific as some of these are
-                    // target intrinsics and would cost less to generate code.
-                    switch (tree->AsIntrinsic()->gtIntrinsicId)
+                    intrinsic = tree->AsIntrinsic();
+                    if (intrinsic->gtIntrinsicId == CORINFO_INTRINSIC_Illegal)
                     {
-                        default:
-                            assert(!"missing case for gtIntrinsicId");
-                            costEx = 12;
-                            costSz = 12;
-                            break;
+                        // named intrinsic
+                        assert(intrinsic->gtIntrinsicName != NI_Illegal);
 
-                        case CORINFO_INTRINSIC_Sin:
-                        case CORINFO_INTRINSIC_Cos:
-                        case CORINFO_INTRINSIC_Sqrt:
-                        case CORINFO_INTRINSIC_Cbrt:
-                        case CORINFO_INTRINSIC_Cosh:
-                        case CORINFO_INTRINSIC_Sinh:
-                        case CORINFO_INTRINSIC_Tan:
-                        case CORINFO_INTRINSIC_Tanh:
-                        case CORINFO_INTRINSIC_Asin:
-                        case CORINFO_INTRINSIC_Asinh:
-                        case CORINFO_INTRINSIC_Acos:
-                        case CORINFO_INTRINSIC_Acosh:
-                        case CORINFO_INTRINSIC_Atan:
-                        case CORINFO_INTRINSIC_Atanh:
-                        case CORINFO_INTRINSIC_Atan2:
-                        case CORINFO_INTRINSIC_Log10:
-                        case CORINFO_INTRINSIC_Pow:
-                        case CORINFO_INTRINSIC_Exp:
-                        case CORINFO_INTRINSIC_Ceiling:
-                        case CORINFO_INTRINSIC_Floor:
-                        case CORINFO_INTRINSIC_Object_GetType:
-                            // Giving intrinsics a large fixed execution cost is because we'd like to CSE
-                            // them, even if they are implemented by calls. This is different from modeling
-                            // user calls since we never CSE user calls.
-                            costEx = 36;
-                            costSz = 4;
-                            break;
+                        // GT_INTRINSIC intrinsics Sin, Cos, Sqrt, Abs ... have higher costs.
+                        // TODO: tune these costs target specific as some of these are
+                        // target intrinsics and would cost less to generate code.
+                        switch (intrinsic->gtIntrinsicName)
+                        {
+                            default:
+                                assert(!"missing case for gtIntrinsicName");
+                                costEx = 12;
+                                costSz = 12;
+                                break;
 
-                        case CORINFO_INTRINSIC_Abs:
-                            costEx = 5;
-                            costSz = 15;
-                            break;
+                            case NI_System_Math_Sin:
+                            case NI_System_Math_Cos:
+                            case NI_System_Math_Sqrt:
+                            case NI_System_Math_Cbrt:
+                            case NI_System_Math_Cosh:
+                            case NI_System_Math_Sinh:
+                            case NI_System_Math_Tan:
+                            case NI_System_Math_Tanh:
+                            case NI_System_Math_Asin:
+                            case NI_System_Math_Asinh:
+                            case NI_System_Math_Acos:
+                            case NI_System_Math_Acosh:
+                            case NI_System_Math_Atan:
+                            case NI_System_Math_Atanh:
+                            case NI_System_Math_Atan2:
+                            case NI_System_Math_Log10:
+                            case NI_System_Math_Pow:
+                            case NI_System_Math_Exp:
+                            case NI_System_Math_Ceiling:
+                            case NI_System_Math_Floor:
+                                // Giving intrinsics a large fixed execution cost is because we'd like to CSE
+                                // them, even if they are implemented by calls. This is different from modeling
+                                // user calls since we never CSE user calls.
+                                costEx = 36;
+                                costSz = 4;
+                                break;
 
-                        case CORINFO_INTRINSIC_Round:
-                            costEx = 3;
-                            costSz = 4;
-                            break;
+                            case NI_System_Math_Abs:
+                                costEx = 5;
+                                costSz = 15;
+                                break;
+
+                            case NI_System_Math_Round:
+                                costEx = 3;
+                                costSz = 4;
+                                break;
+                        }
+                    }
+                    else
+                    {
+                        // old style intrinsic
+                        assert(intrinsic->gtIntrinsicName == NI_Illegal);
+
+                        switch (intrinsic->gtIntrinsicId)
+                        {
+                            default:
+                                assert(!"missing case for gtIntrinsicId");
+                                costEx = 12;
+                                costSz = 12;
+                                break;
+
+                            case CORINFO_INTRINSIC_Object_GetType:
+                                // Giving intrinsics a large fixed execution cost is because we'd like to CSE
+                                // them, even if they are implemented by calls. This is different from modeling
+                                // user calls since we never CSE user calls.
+                                costEx = 36;
+                                costSz = 4;
+                                break;
+                        }
                     }
                     level++;
                     break;
@@ -4093,10 +4245,10 @@ unsigned Compiler::gtSetEvalOrder(GenTree* tree)
 
             case GT_INTRINSIC:
 
-                switch (tree->AsIntrinsic()->gtIntrinsicId)
+                switch (tree->AsIntrinsic()->gtIntrinsicName)
                 {
-                    case CORINFO_INTRINSIC_Atan2:
-                    case CORINFO_INTRINSIC_Pow:
+                    case NI_System_Math_Atan2:
+                    case NI_System_Math_Pow:
                         // These math intrinsics are actually implemented by user calls.
                         // Increase the Sethi 'complexity' by two to reflect the argument
                         // register requirement.
@@ -4153,7 +4305,7 @@ unsigned Compiler::gtSetEvalOrder(GenTree* tree)
             // so if possible it was set above.
             tryToSwap = false;
         }
-        else if ((oper == GT_INTRINSIC) && IsIntrinsicImplementedByUserCall(tree->AsIntrinsic()->gtIntrinsicId))
+        else if ((oper == GT_INTRINSIC) && IsIntrinsicImplementedByUserCall(tree->AsIntrinsic()->gtIntrinsicName))
         {
             // We do not swap operand execution order for intrinsics that are implemented by user calls
             // because of trickiness around ensuring the execution order does not change during rationalization.
@@ -5355,7 +5507,7 @@ bool GenTree::OperRequiresCallFlag(Compiler* comp)
             return true;
 
         case GT_INTRINSIC:
-            return comp->IsIntrinsicImplementedByUserCall(this->AsIntrinsic()->gtIntrinsicId);
+            return comp->IsIntrinsicImplementedByUserCall(this->AsIntrinsic()->gtIntrinsicName);
 
 #if FEATURE_FIXED_OUT_ARGS && !defined(TARGET_64BIT)
         case GT_LSH:
@@ -7577,7 +7729,8 @@ GenTree* Compiler::gtCloneExpr(
             case GT_INTRINSIC:
                 copy = new (this, GT_INTRINSIC)
                     GenTreeIntrinsic(tree->TypeGet(), tree->AsOp()->gtOp1, tree->AsOp()->gtOp2,
-                                     tree->AsIntrinsic()->gtIntrinsicId, tree->AsIntrinsic()->gtMethodHandle);
+                                     tree->AsIntrinsic()->gtIntrinsicId, tree->AsIntrinsic()->gtIntrinsicName,
+                                     tree->AsIntrinsic()->gtMethodHandle);
 #ifdef FEATURE_READYTORUN_COMPILER
                 copy->AsIntrinsic()->gtEntryPoint = tree->AsIntrinsic()->gtEntryPoint;
 #endif
@@ -11338,80 +11491,98 @@ void Compiler::gtDispTree(GenTree*     tree,
 
         if (tree->gtOper == GT_INTRINSIC)
         {
-            switch (tree->AsIntrinsic()->gtIntrinsicId)
+            GenTreeIntrinsic* intrinsic = tree->AsIntrinsic();
+
+            if (intrinsic->gtIntrinsicId == CORINFO_INTRINSIC_Illegal)
             {
-                case CORINFO_INTRINSIC_Sin:
-                    printf(" sin");
-                    break;
-                case CORINFO_INTRINSIC_Cos:
-                    printf(" cos");
-                    break;
-                case CORINFO_INTRINSIC_Cbrt:
-                    printf(" cbrt");
-                    break;
-                case CORINFO_INTRINSIC_Sqrt:
-                    printf(" sqrt");
-                    break;
-                case CORINFO_INTRINSIC_Abs:
-                    printf(" abs");
-                    break;
-                case CORINFO_INTRINSIC_Round:
-                    printf(" round");
-                    break;
-                case CORINFO_INTRINSIC_Cosh:
-                    printf(" cosh");
-                    break;
-                case CORINFO_INTRINSIC_Sinh:
-                    printf(" sinh");
-                    break;
-                case CORINFO_INTRINSIC_Tan:
-                    printf(" tan");
-                    break;
-                case CORINFO_INTRINSIC_Tanh:
-                    printf(" tanh");
-                    break;
-                case CORINFO_INTRINSIC_Asin:
-                    printf(" asin");
-                    break;
-                case CORINFO_INTRINSIC_Asinh:
-                    printf(" asinh");
-                    break;
-                case CORINFO_INTRINSIC_Acos:
-                    printf(" acos");
-                    break;
-                case CORINFO_INTRINSIC_Acosh:
-                    printf(" acosh");
-                    break;
-                case CORINFO_INTRINSIC_Atan:
-                    printf(" atan");
-                    break;
-                case CORINFO_INTRINSIC_Atan2:
-                    printf(" atan2");
-                    break;
-                case CORINFO_INTRINSIC_Atanh:
-                    printf(" atanh");
-                    break;
-                case CORINFO_INTRINSIC_Log10:
-                    printf(" log10");
-                    break;
-                case CORINFO_INTRINSIC_Pow:
-                    printf(" pow");
-                    break;
-                case CORINFO_INTRINSIC_Exp:
-                    printf(" exp");
-                    break;
-                case CORINFO_INTRINSIC_Ceiling:
-                    printf(" ceiling");
-                    break;
-                case CORINFO_INTRINSIC_Floor:
-                    printf(" floor");
-                    break;
-                case CORINFO_INTRINSIC_Object_GetType:
-                    printf(" objGetType");
-                    break;
+                // named intrinsic
+                assert(intrinsic->gtIntrinsicName != NI_Illegal);
+                switch (intrinsic->gtIntrinsicName)
+                {
+                    case NI_System_Math_Sin:
+                        printf(" sin");
+                        break;
+                    case NI_System_Math_Cos:
+                        printf(" cos");
+                        break;
+                    case NI_System_Math_Cbrt:
+                        printf(" cbrt");
+                        break;
+                    case NI_System_Math_Sqrt:
+                        printf(" sqrt");
+                        break;
+                    case NI_System_Math_Abs:
+                        printf(" abs");
+                        break;
+                    case NI_System_Math_Round:
+                        printf(" round");
+                        break;
+                    case NI_System_Math_Cosh:
+                        printf(" cosh");
+                        break;
+                    case NI_System_Math_Sinh:
+                        printf(" sinh");
+                        break;
+                    case NI_System_Math_Tan:
+                        printf(" tan");
+                        break;
+                    case NI_System_Math_Tanh:
+                        printf(" tanh");
+                        break;
+                    case NI_System_Math_Asin:
+                        printf(" asin");
+                        break;
+                    case NI_System_Math_Asinh:
+                        printf(" asinh");
+                        break;
+                    case NI_System_Math_Acos:
+                        printf(" acos");
+                        break;
+                    case NI_System_Math_Acosh:
+                        printf(" acosh");
+                        break;
+                    case NI_System_Math_Atan:
+                        printf(" atan");
+                        break;
+                    case NI_System_Math_Atan2:
+                        printf(" atan2");
+                        break;
+                    case NI_System_Math_Atanh:
+                        printf(" atanh");
+                        break;
+                    case NI_System_Math_Log10:
+                        printf(" log10");
+                        break;
+                    case NI_System_Math_Pow:
+                        printf(" pow");
+                        break;
+                    case NI_System_Math_Exp:
+                        printf(" exp");
+                        break;
+                    case NI_System_Math_Ceiling:
+                        printf(" ceiling");
+                        break;
+                    case NI_System_Math_Floor:
+                        printf(" floor");
+                        break;
 
-                default:
-                    unreached();
+                    default:
+                        unreached();
+                }
+            }
+            else
+            {
+                // old style intrinsic
+                assert(intrinsic->gtIntrinsicName == NI_Illegal);
+                switch (intrinsic->gtIntrinsicId)
+                {
+                    case CORINFO_INTRINSIC_Object_GetType:
+                        printf(" objGetType");
+                        break;
+
+                    default:
+                        unreached();
+                }
             }
         }
 
@@ -13611,16 +13782,13 @@ GenTree* Compiler::gtTryRemoveBoxUpstreamEffects(GenTree* op, BoxRemovalOptions
         // For struct types read the first byte of the
         // source struct; there's no need to read the
         // entire thing, and no place to put it.
-        assert(copySrc->gtOper == GT_OBJ || copySrc->gtOper == GT_IND || copySrc->gtOper == GT_FIELD);
+        assert(copySrc->OperIs(GT_OBJ, GT_IND, GT_FIELD));
         copyStmt->SetRootNode(copySrc);
 
         if (options == BR_REMOVE_AND_NARROW || options == BR_REMOVE_AND_NARROW_WANT_TYPE_HANDLE)
         {
             JITDUMP(" to read first byte of struct via modified [%06u]\n", dspTreeID(copySrc));
-            copySrc->ChangeOper(GT_NULLCHECK);
-            copySrc->gtType = TYP_BYTE;
-            compCurBB->bbFlags |= BBF_HAS_NULLCHECK;
-            optMethodFlags |= OMF_HAS_NULLCHECK;
+            gtChangeOperToNullCheck(copySrc, compCurBB);
         }
         else
         {
@@ -15799,6 +15967,11 @@ void Compiler::gtExtractSideEffList(GenTree*  expr,
                 if (m_compiler->gtNodeHasSideEffects(node, m_flags))
                 {
                     m_sideEffects.Push(node);
+                    if (node->OperIsBlk() && !node->OperIsStoreBlk())
+                    {
+                        JITDUMP("Replace an unused OBJ/BLK node [%06d] with a NULLCHECK\n", dspTreeID(node));
+                        m_compiler->gtChangeOperToNullCheck(node, m_compiler->compCurBB);
+                    }
                     return Compiler::WALK_SKIP_SUBTREES;
                 }
 
@@ -16365,11 +16538,7 @@ bool GenTree::DefinesLocalAddr(Compiler* comp, unsigned width, GenTreeLclVarComm
             *pLclVarTree                    = addrArgLcl;
             if (pIsEntire != nullptr)
             {
-                unsigned lclOffset = 0;
-                if (addrArg->OperIsLocalField())
-                {
-                    lclOffset = addrArg->AsLclFld()->GetLclOffs();
-                }
+                unsigned lclOffset = addrArgLcl->GetLclOffs();
 
                 if (lclOffset != 0)
                 {
@@ -17475,7 +17644,9 @@ CORINFO_CLASS_HANDLE Compiler::gtGetStructHandleIfPresent(GenTree* tree)
                             {
                                 CORINFO_FIELD_HANDLE fieldHnd = fieldSeq->m_fieldHnd;
                                 CorInfoType fieldCorType      = info.compCompHnd->getFieldType(fieldHnd, &structHnd);
-                                assert(fieldCorType == CORINFO_TYPE_VALUECLASS);
+                                // With unsafe code and type casts
+                                // this can return a primitive type and have nullptr for structHnd
+                                // see runtime/issues/38541
                             }
                         }
                     }
@@ -18638,7 +18809,7 @@ bool GenTree::isCommutativeSIMDIntrinsic()
     }
 }
 
-// Returns true for the SIMD Instrinsic instructions that have MemoryLoad semantics, false otherwise
+// Returns true for the SIMD Intrinsic instructions that have MemoryLoad semantics, false otherwise
 bool GenTreeSIMD::OperIsMemoryLoad() const
 {
     if (gtSIMDIntrinsicID == SIMDIntrinsicInitArray)
@@ -18860,7 +19031,7 @@ GenTreeHWIntrinsic* Compiler::gtNewScalarHWIntrinsicNode(
         GenTreeHWIntrinsic(type, gtNewArgList(op1, op2, op3), hwIntrinsicID, TYP_UNKNOWN, 0);
 }
 
-// Returns true for the HW Instrinsic instructions that have MemoryLoad semantics, false otherwise
+// Returns true for the HW Intrinsic instructions that have MemoryLoad semantics, false otherwise
 bool GenTreeHWIntrinsic::OperIsMemoryLoad() const
 {
 #if defined(TARGET_XARCH) || defined(TARGET_ARM64)
@@ -18903,7 +19074,7 @@ bool GenTreeHWIntrinsic::OperIsMemoryLoad() const
     return false;
 }
 
-// Returns true for the HW Instrinsic instructions that have MemoryStore semantics, false otherwise
+// Returns true for the HW Intrinsic instructions that have MemoryStore semantics, false otherwise
 bool GenTreeHWIntrinsic::OperIsMemoryStore() const
 {
 #if defined(TARGET_XARCH) || defined(TARGET_ARM64)
@@ -18939,7 +19110,7 @@ bool GenTreeHWIntrinsic::OperIsMemoryStore() const
     return false;
 }
 
-// Returns true for the HW Instrinsic instructions that have MemoryLoad semantics, false otherwise
+// Returns true for the HW Intrinsic instructions that have MemoryLoad semantics, false otherwise
 bool GenTreeHWIntrinsic::OperIsMemoryLoadOrStore() const
 {
 #if defined(TARGET_XARCH) || defined(TARGET_ARM64)
@@ -19350,6 +19521,25 @@ regNumber GenTree::ExtractTempReg(regMaskTP mask /* = (regMaskTP)-1 */)
     return genRegNumFromMask(tempRegMask);
 }
 
+//------------------------------------------------------------------------
+// GetLclOffs: if `this` is a field or a field address it returns offset
+// of the field inside the struct, for not a field it returns 0.
+//
+// Return Value:
+//    The offset value.
+//
+uint16_t GenTreeLclVarCommon::GetLclOffs() const
+{
+    if (OperIsLocalField())
+    {
+        return AsLclFld()->GetLclOffs();
+    }
+    else
+    {
+        return 0;
+    }
+}
+
 #ifdef TARGET_ARM
 //------------------------------------------------------------------------
 // IsOffsetMisaligned: check if the field needs a special handling on arm.
diff --git a/src/coreclr/src/jit/gentree.h b/src/coreclr/src/jit/gentree.h
index 5e51988d76686c..7e25365730720c 100644
--- a/src/coreclr/src/jit/gentree.h
+++ b/src/coreclr/src/jit/gentree.h
@@ -3180,6 +3180,8 @@ struct GenTreeLclVarCommon : public GenTreeUnOp
         _gtSsaNum = SsaConfig::RESERVED_SSA_NUM;
     }
 
+    uint16_t GetLclOffs() const;
+
     unsigned GetSsaNum() const
     {
         return _gtSsaNum;
@@ -4727,6 +4729,7 @@ struct GenTreeQmark : public GenTreeOp
 struct GenTreeIntrinsic : public GenTreeOp
 {
     CorInfoIntrinsics     gtIntrinsicId;
+    NamedIntrinsic        gtIntrinsicName;
     CORINFO_METHOD_HANDLE gtMethodHandle; // Method handle of the method which is treated as an intrinsic.
 
 #ifdef FEATURE_READYTORUN_COMPILER
@@ -4734,15 +4737,31 @@ struct GenTreeIntrinsic : public GenTreeOp
     CORINFO_CONST_LOOKUP gtEntryPoint;
 #endif
 
-    GenTreeIntrinsic(var_types type, GenTree* op1, CorInfoIntrinsics intrinsicId, CORINFO_METHOD_HANDLE methodHandle)
-        : GenTreeOp(GT_INTRINSIC, type, op1, nullptr), gtIntrinsicId(intrinsicId), gtMethodHandle(methodHandle)
+    GenTreeIntrinsic(var_types             type,
+                     GenTree*              op1,
+                     CorInfoIntrinsics     intrinsicId,
+                     NamedIntrinsic        intrinsicName,
+                     CORINFO_METHOD_HANDLE methodHandle)
+        : GenTreeOp(GT_INTRINSIC, type, op1, nullptr)
+        , gtIntrinsicId(intrinsicId)
+        , gtIntrinsicName(intrinsicName)
+        , gtMethodHandle(methodHandle)
     {
+        assert(intrinsicId != CORINFO_INTRINSIC_Illegal || intrinsicName != NI_Illegal);
     }
 
-    GenTreeIntrinsic(
-        var_types type, GenTree* op1, GenTree* op2, CorInfoIntrinsics intrinsicId, CORINFO_METHOD_HANDLE methodHandle)
-        : GenTreeOp(GT_INTRINSIC, type, op1, op2), gtIntrinsicId(intrinsicId), gtMethodHandle(methodHandle)
+    GenTreeIntrinsic(var_types             type,
+                     GenTree*              op1,
+                     GenTree*              op2,
+                     CorInfoIntrinsics     intrinsicId,
+                     NamedIntrinsic        intrinsicName,
+                     CORINFO_METHOD_HANDLE methodHandle)
+        : GenTreeOp(GT_INTRINSIC, type, op1, op2)
+        , gtIntrinsicId(intrinsicId)
+        , gtIntrinsicName(intrinsicName)
+        , gtMethodHandle(methodHandle)
     {
+        assert(intrinsicId != CORINFO_INTRINSIC_Illegal || intrinsicName != NI_Illegal);
     }
 
 #if DEBUGGABLE_GENTREE
@@ -4846,7 +4865,7 @@ struct GenTreeSIMD : public GenTreeJitIntrinsic
         gtSIMDIntrinsicID = simdIntrinsicID;
     }
 
-    bool OperIsMemoryLoad() const; // Returns true for the SIMD Instrinsic instructions that have MemoryLoad semantics,
+    bool OperIsMemoryLoad() const; // Returns true for the SIMD Intrinsic instructions that have MemoryLoad semantics,
                                    // false otherwise
 
 #if DEBUGGABLE_GENTREE
@@ -4887,15 +4906,15 @@ struct GenTreeHWIntrinsic : public GenTreeJitIntrinsic
         }
     }
 
-    // Note that HW Instrinsic instructions are a sub class of GenTreeOp which only supports two operands
-    // However there are HW Instrinsic instructions that have 3 or even 4 operands and this is
+    // Note that HW Intrinsic instructions are a sub class of GenTreeOp which only supports two operands
+    // However there are HW Intrinsic instructions that have 3 or even 4 operands and this is
     // supported using a single op1 and using an ArgList for it:  gtNewArgList(op1, op2, op3)
 
-    bool OperIsMemoryLoad() const;  // Returns true for the HW Instrinsic instructions that have MemoryLoad semantics,
+    bool OperIsMemoryLoad() const;  // Returns true for the HW Intrinsic instructions that have MemoryLoad semantics,
                                     // false otherwise
-    bool OperIsMemoryStore() const; // Returns true for the HW Instrinsic instructions that have MemoryStore semantics,
+    bool OperIsMemoryStore() const; // Returns true for the HW Intrinsic instructions that have MemoryStore semantics,
                                     // false otherwise
-    bool OperIsMemoryLoadOrStore() const; // Returns true for the HW Instrinsic instructions that have MemoryLoad or
+    bool OperIsMemoryLoadOrStore() const; // Returns true for the HW Intrinsic instructions that have MemoryLoad or
                                           // MemoryStore semantics, false otherwise
 
 #if DEBUGGABLE_GENTREE
diff --git a/src/coreclr/src/jit/hwintrinsic.cpp b/src/coreclr/src/jit/hwintrinsic.cpp
index 5e7eda61c30d26..5723ac8f322b41 100644
--- a/src/coreclr/src/jit/hwintrinsic.cpp
+++ b/src/coreclr/src/jit/hwintrinsic.cpp
@@ -202,7 +202,7 @@ CORINFO_CLASS_HANDLE Compiler::gtGetStructHandleForHWSIMD(var_types simdType, va
 {
     int numArgs = HWIntrinsicInfo::lookupNumArgs(hwIntrinsicID);
 
-    // HW Instrinsic's with -1 for numArgs have a varying number of args, so we currently
+    // HW Intrinsic's with -1 for numArgs have a varying number of args, so we currently
     // give themm a unique value number them, and don't add an extra argument.
     //
     if (numArgs == -1)
@@ -210,7 +210,7 @@ CORINFO_CLASS_HANDLE Compiler::gtGetStructHandleForHWSIMD(var_types simdType, va
         return false;
     }
 
-    // We iterate over all of the different baseType's for this instrinsic in the HWIntrinsicInfo table
+    // We iterate over all of the different baseType's for this intrinsic in the HWIntrinsicInfo table
     // We set  diffInsCount to the number of instructions that can execute differently.
     //
     unsigned diffInsCount = 0;
diff --git a/src/coreclr/src/jit/hwintrinsiccodegenxarch.cpp b/src/coreclr/src/jit/hwintrinsiccodegenxarch.cpp
index 574e8c48d15f89..ddca579f34ab11 100644
--- a/src/coreclr/src/jit/hwintrinsiccodegenxarch.cpp
+++ b/src/coreclr/src/jit/hwintrinsiccodegenxarch.cpp
@@ -469,9 +469,11 @@ void CodeGen::genHWIntrinsic_R_RM(
             switch (addr->OperGet())
             {
                 case GT_LCL_VAR_ADDR:
+                case GT_LCL_FLD_ADDR:
                 {
+                    assert(addr->isContained());
                     varNum = addr->AsLclVarCommon()->GetLclNum();
-                    offset = 0;
+                    offset = addr->AsLclVarCommon()->GetLclOffs();
                     break;
                 }
 
@@ -698,9 +700,11 @@ void CodeGen::genHWIntrinsic_R_R_RM_I(GenTreeHWIntrinsic* node, instruction ins,
             switch (addr->OperGet())
             {
                 case GT_LCL_VAR_ADDR:
+                case GT_LCL_FLD_ADDR:
                 {
+                    assert(addr->isContained());
                     varNum = addr->AsLclVarCommon()->GetLclNum();
-                    offset = 0;
+                    offset = addr->AsLclVarCommon()->GetLclOffs();
                     break;
                 }
 
@@ -861,9 +865,11 @@ void CodeGen::genHWIntrinsic_R_R_RM_R(GenTreeHWIntrinsic* node, instruction ins)
             switch (addr->OperGet())
             {
                 case GT_LCL_VAR_ADDR:
+                case GT_LCL_FLD_ADDR:
                 {
+                    assert(addr->isContained());
                     varNum = addr->AsLclVarCommon()->GetLclNum();
-                    offset = 0;
+                    offset = addr->AsLclVarCommon()->GetLclOffs();
                     break;
                 }
 
@@ -986,9 +992,11 @@ void CodeGen::genHWIntrinsic_R_R_R_RM(
             switch (addr->OperGet())
             {
                 case GT_LCL_VAR_ADDR:
+                case GT_LCL_FLD_ADDR:
                 {
+                    assert(addr->isContained());
                     varNum = addr->AsLclVarCommon()->GetLclNum();
-                    offset = 0;
+                    offset = addr->AsLclVarCommon()->GetLclOffs();
                     break;
                 }
 
diff --git a/src/coreclr/src/jit/hwintrinsicxarch.cpp b/src/coreclr/src/jit/hwintrinsicxarch.cpp
index 8d7824ea189b64..e624f18e713f94 100644
--- a/src/coreclr/src/jit/hwintrinsicxarch.cpp
+++ b/src/coreclr/src/jit/hwintrinsicxarch.cpp
@@ -405,11 +405,12 @@ bool HWIntrinsicInfo::isScalarIsa(CORINFO_InstructionSet isa)
         case InstructionSet_BMI2_X64:
         case InstructionSet_LZCNT:
         case InstructionSet_LZCNT_X64:
-        case InstructionSet_POPCNT:
-        case InstructionSet_POPCNT_X64:
         case InstructionSet_X86Base:
         case InstructionSet_X86Base_X64:
         {
+            // InstructionSet_POPCNT and InstructionSet_POPCNT_X64 are excluded
+            // even though they are "scalar" ISA because they depend on SSE4.2
+            // and Popcnt.IsSupported implies Sse42.IsSupported
             return true;
         }
 
diff --git a/src/coreclr/src/jit/importer.cpp b/src/coreclr/src/jit/importer.cpp
index e3efd08dbe309e..463054b9b989ad 100644
--- a/src/coreclr/src/jit/importer.cpp
+++ b/src/coreclr/src/jit/importer.cpp
@@ -1392,8 +1392,8 @@ GenTree* Compiler::impAssignStructPtr(GenTree*             destAddr,
     }
     else if (asgType == TYP_STRUCT)
     {
-        asgType     = impNormStructType(structHnd);
-        src->gtType = asgType;
+        // It should already have the appropriate type.
+        assert(asgType == impNormStructType(structHnd));
     }
     if ((dest == nullptr) && (destAddr->OperGet() == GT_ADDR))
     {
@@ -2117,11 +2117,18 @@ GenTree* Compiler::impRuntimeLookupToTree(CORINFO_RESOLVED_TOKEN* pResolvedToken
                                       nullptr DEBUGARG("impRuntimeLookup indirectOffset"));
         }
 
+        // The last indirection could be subject to a size check (dynamic dictionary expansion)
+        bool isLastIndirectionWithSizeCheck =
+            ((i == pRuntimeLookup->indirections - 1) && (pRuntimeLookup->sizeOffset != CORINFO_NO_SIZE_CHECK));
+
         if (i != 0)
         {
             slotPtrTree = gtNewOperNode(GT_IND, TYP_I_IMPL, slotPtrTree);
             slotPtrTree->gtFlags |= GTF_IND_NONFAULTING;
-            slotPtrTree->gtFlags |= GTF_IND_INVARIANT;
+            if (!isLastIndirectionWithSizeCheck)
+            {
+                slotPtrTree->gtFlags |= GTF_IND_INVARIANT;
+            }
         }
 
         if ((i == 1 && pRuntimeLookup->indirectFirstOffset) || (i == 2 && pRuntimeLookup->indirectSecondOffset))
@@ -2131,8 +2138,7 @@ GenTree* Compiler::impRuntimeLookupToTree(CORINFO_RESOLVED_TOKEN* pResolvedToken
 
         if (pRuntimeLookup->offsets[i] != 0)
         {
-            // The last indirection could be subject to a size check (dynamic dictionary expansion)
-            if (i == pRuntimeLookup->indirections - 1 && pRuntimeLookup->sizeOffset != CORINFO_NO_SIZE_CHECK)
+            if (isLastIndirectionWithSizeCheck)
             {
                 lastIndOfTree = impCloneExpr(slotPtrTree, &slotPtrTree, NO_CLASS_HANDLE, (unsigned)CHECK_SPILL_ALL,
                                              nullptr DEBUGARG("impRuntimeLookup indirectOffset"));
@@ -3623,31 +3629,6 @@ GenTree* Compiler::impIntrinsic(GenTree*                newobjThis,
         GenTree* op1;
         GenTree* op2;
 
-        case CORINFO_INTRINSIC_Sin:
-        case CORINFO_INTRINSIC_Cbrt:
-        case CORINFO_INTRINSIC_Sqrt:
-        case CORINFO_INTRINSIC_Abs:
-        case CORINFO_INTRINSIC_Cos:
-        case CORINFO_INTRINSIC_Round:
-        case CORINFO_INTRINSIC_Cosh:
-        case CORINFO_INTRINSIC_Sinh:
-        case CORINFO_INTRINSIC_Tan:
-        case CORINFO_INTRINSIC_Tanh:
-        case CORINFO_INTRINSIC_Asin:
-        case CORINFO_INTRINSIC_Asinh:
-        case CORINFO_INTRINSIC_Acos:
-        case CORINFO_INTRINSIC_Acosh:
-        case CORINFO_INTRINSIC_Atan:
-        case CORINFO_INTRINSIC_Atan2:
-        case CORINFO_INTRINSIC_Atanh:
-        case CORINFO_INTRINSIC_Log10:
-        case CORINFO_INTRINSIC_Pow:
-        case CORINFO_INTRINSIC_Exp:
-        case CORINFO_INTRINSIC_Ceiling:
-        case CORINFO_INTRINSIC_Floor:
-            retNode = impMathIntrinsic(method, sig, callType, intrinsicID, tailCall);
-            break;
-
 #if defined(TARGET_XARCH) || defined(TARGET_ARM64)
         // TODO-ARM-CQ: reenable treating Interlocked operation as intrinsic
 
@@ -3921,7 +3902,7 @@ GenTree* Compiler::impIntrinsic(GenTree*                newobjThis,
             {
                 JITDUMP("Expanding as special intrinsic\n");
                 impPopStack();
-                op1 = new (this, GT_INTRINSIC) GenTreeIntrinsic(genActualType(callType), op1, intrinsicID, method);
+                op1 = new (this, GT_INTRINSIC) GenTreeIntrinsic(genActualType(callType), op1, intrinsicID, ni, method);
 
                 // Set the CALL flag to indicate that the operator is implemented by a call.
                 // Set also the EXCEPTION flag because the native implementation of
@@ -4218,7 +4199,6 @@ GenTree* Compiler::impIntrinsic(GenTree*                newobjThis,
 
 #ifdef FEATURE_HW_INTRINSICS
             case NI_System_Math_FusedMultiplyAdd:
-            case NI_System_MathF_FusedMultiplyAdd:
             {
 #ifdef TARGET_XARCH
                 if (compExactlyDependsOn(InstructionSet_FMA) && supportSIMDTypes())
@@ -4227,9 +4207,9 @@ GenTree* Compiler::impIntrinsic(GenTree*                newobjThis,
 
                     // We are constructing a chain of intrinsics similar to:
                     //    return FMA.MultiplyAddScalar(
-                    //        Vector128.CreateScalar(x),
-                    //        Vector128.CreateScalar(y),
-                    //        Vector128.CreateScalar(z)
+                    //        Vector128.CreateScalarUnsafe(x),
+                    //        Vector128.CreateScalarUnsafe(y),
+                    //        Vector128.CreateScalarUnsafe(z)
                     //    ).ToScalar();
 
                     GenTree* op3 = gtNewSimdHWIntrinsicNode(TYP_SIMD16, impPopStack().val,
@@ -4243,20 +4223,66 @@ GenTree* Compiler::impIntrinsic(GenTree*                newobjThis,
 
                     retNode = gtNewSimdHWIntrinsicNode(callType, res, NI_Vector128_ToScalar, callType, 16);
                 }
-#endif // TARGET_XARCH
+#elif defined(TARGET_ARM64)
+                if (compExactlyDependsOn(InstructionSet_AdvSimd))
+                {
+                    assert(varTypeIsFloating(callType));
+
+                    // We are constructing a chain of intrinsics similar to:
+                    //    return AdvSimd.FusedMultiplyAddScalar(
+                    //        Vector64.Create{ScalarUnsafe}(z),
+                    //        Vector64.Create{ScalarUnsafe}(y),
+                    //        Vector64.Create{ScalarUnsafe}(x)
+                    //    ).ToScalar();
+
+                    NamedIntrinsic createVector64 =
+                        (callType == TYP_DOUBLE) ? NI_Vector64_Create : NI_Vector64_CreateScalarUnsafe;
+
+                    constexpr unsigned int simdSize = 8;
+
+                    GenTree* op3 =
+                        gtNewSimdHWIntrinsicNode(TYP_SIMD8, impPopStack().val, createVector64, callType, simdSize);
+                    GenTree* op2 =
+                        gtNewSimdHWIntrinsicNode(TYP_SIMD8, impPopStack().val, createVector64, callType, simdSize);
+                    GenTree* op1 =
+                        gtNewSimdHWIntrinsicNode(TYP_SIMD8, impPopStack().val, createVector64, callType, simdSize);
+
+                    // Note that AdvSimd.FusedMultiplyAddScalar(op1,op2,op3) corresponds to op1 + op2 * op3
+                    // while Math{F}.FusedMultiplyAddScalar(op1,op2,op3) corresponds to op1 * op2 + op3
+                    retNode = gtNewSimdHWIntrinsicNode(TYP_SIMD8, op3, op2, op1, NI_AdvSimd_FusedMultiplyAddScalar,
+                                                       callType, simdSize);
+
+                    retNode = gtNewSimdHWIntrinsicNode(callType, retNode, NI_Vector64_ToScalar, callType, simdSize);
+                }
+#endif
                 break;
             }
 #endif // FEATURE_HW_INTRINSICS
 
+            case NI_System_Math_Sin:
+            case NI_System_Math_Cbrt:
+            case NI_System_Math_Sqrt:
+            case NI_System_Math_Abs:
+            case NI_System_Math_Cos:
             case NI_System_Math_Round:
-            case NI_System_MathF_Round:
-            {
-                // Math.Round and MathF.Round used to be a traditional JIT intrinsic. In order
-                // to simplify the transition, we will just treat it as if it was still the
-                // old intrinsic, CORINFO_INTRINSIC_Round. This should end up flowing properly
-                // everywhere else.
-
-                retNode = impMathIntrinsic(method, sig, callType, CORINFO_INTRINSIC_Round, tailCall);
+            case NI_System_Math_Cosh:
+            case NI_System_Math_Sinh:
+            case NI_System_Math_Tan:
+            case NI_System_Math_Tanh:
+            case NI_System_Math_Asin:
+            case NI_System_Math_Asinh:
+            case NI_System_Math_Acos:
+            case NI_System_Math_Acosh:
+            case NI_System_Math_Atan:
+            case NI_System_Math_Atan2:
+            case NI_System_Math_Atanh:
+            case NI_System_Math_Log10:
+            case NI_System_Math_Pow:
+            case NI_System_Math_Exp:
+            case NI_System_Math_Ceiling:
+            case NI_System_Math_Floor:
+            {
+                retNode = impMathIntrinsic(method, sig, callType, ni, tailCall);
                 break;
             }
 
@@ -4345,14 +4371,14 @@ GenTree* Compiler::impIntrinsic(GenTree*                newobjThis,
 GenTree* Compiler::impMathIntrinsic(CORINFO_METHOD_HANDLE method,
                                     CORINFO_SIG_INFO*     sig,
                                     var_types             callType,
-                                    CorInfoIntrinsics     intrinsicID,
+                                    NamedIntrinsic        intrinsicName,
                                     bool                  tailCall)
 {
     GenTree* op1;
     GenTree* op2;
 
     assert(callType != TYP_STRUCT);
-    assert(IsMathIntrinsic(intrinsicID));
+    assert(IsMathIntrinsic(intrinsicName));
 
     op1 = nullptr;
 
@@ -4363,12 +4389,12 @@ GenTree* Compiler::impMathIntrinsic(CORINFO_METHOD_HANDLE method,
     //  a) For back compatibility reasons on desktop .NET Framework 4.6 / 4.6.1
     //  b) It will be non-trivial task or too late to re-materialize a surviving
     //     tail prefixed GT_INTRINSIC as tail call in rationalizer.
-    if (!IsIntrinsicImplementedByUserCall(intrinsicID) || !tailCall)
+    if (!IsIntrinsicImplementedByUserCall(intrinsicName) || !tailCall)
 #else
     // On x86 RyuJIT, importing intrinsics that are implemented as user calls can cause incorrect calculation
     // of the depth of the stack if these intrinsics are used as arguments to another call. This causes bad
     // code generation for certain EH constructs.
-    if (!IsIntrinsicImplementedByUserCall(intrinsicID))
+    if (!IsIntrinsicImplementedByUserCall(intrinsicName))
 #endif
     {
         switch (sig->numArgs)
@@ -4383,7 +4409,8 @@ GenTree* Compiler::impMathIntrinsic(CORINFO_METHOD_HANDLE method,
                     op1 = gtNewCastNode(callType, op1, false, callType);
                 }
 
-                op1 = new (this, GT_INTRINSIC) GenTreeIntrinsic(genActualType(callType), op1, intrinsicID, method);
+                op1 = new (this, GT_INTRINSIC)
+                    GenTreeIntrinsic(genActualType(callType), op1, CORINFO_INTRINSIC_Illegal, intrinsicName, method);
                 break;
 
             case 2:
@@ -4402,14 +4429,15 @@ GenTree* Compiler::impMathIntrinsic(CORINFO_METHOD_HANDLE method,
                     op1 = gtNewCastNode(callType, op1, false, callType);
                 }
 
-                op1 = new (this, GT_INTRINSIC) GenTreeIntrinsic(genActualType(callType), op1, op2, intrinsicID, method);
+                op1 = new (this, GT_INTRINSIC) GenTreeIntrinsic(genActualType(callType), op1, op2,
+                                                                CORINFO_INTRINSIC_Illegal, intrinsicName, method);
                 break;
 
             default:
-                NO_WAY("Unsupported number of args for Math Instrinsic");
+                NO_WAY("Unsupported number of args for Math Intrinsic");
         }
 
-        if (IsIntrinsicImplementedByUserCall(intrinsicID))
+        if (IsIntrinsicImplementedByUserCall(intrinsicName))
         {
             op1->gtFlags |= GTF_CALL;
         }
@@ -4474,31 +4502,99 @@ NamedIntrinsic Compiler::lookupNamedIntrinsic(CORINFO_METHOD_HANDLE method)
         {
             result = NI_System_Enum_HasFlag;
         }
-        else if (strncmp(className, "Math", 4) == 0)
+        else if (strcmp(className, "Math") == 0 || strcmp(className, "MathF") == 0)
         {
-            className += 4;
-
-            if (className[0] == '\0')
+            if (strcmp(methodName, "FusedMultiplyAdd") == 0)
             {
-                if (strcmp(methodName, "FusedMultiplyAdd") == 0)
-                {
-                    result = NI_System_Math_FusedMultiplyAdd;
-                }
-                else if (strcmp(methodName, "Round") == 0)
-                {
-                    result = NI_System_Math_Round;
-                }
+                result = NI_System_Math_FusedMultiplyAdd;
             }
-            else if (strcmp(className, "F") == 0)
+            else if (strcmp(methodName, "Round") == 0)
             {
-                if (strcmp(methodName, "FusedMultiplyAdd") == 0)
-                {
-                    result = NI_System_MathF_FusedMultiplyAdd;
-                }
-                else if (strcmp(methodName, "Round") == 0)
-                {
-                    result = NI_System_MathF_Round;
-                }
+                result = NI_System_Math_Round;
+            }
+            else if (strcmp(methodName, "Sin") == 0)
+            {
+                result = NI_System_Math_Sin;
+            }
+            else if (strcmp(methodName, "Cos") == 0)
+            {
+                result = NI_System_Math_Cos;
+            }
+            else if (strcmp(methodName, "Cbrt") == 0)
+            {
+                result = NI_System_Math_Cbrt;
+            }
+            else if (strcmp(methodName, "Sqrt") == 0)
+            {
+                result = NI_System_Math_Sqrt;
+            }
+            else if (strcmp(methodName, "Abs") == 0)
+            {
+                result = NI_System_Math_Abs;
+            }
+            else if (strcmp(methodName, "Cosh") == 0)
+            {
+                result = NI_System_Math_Cosh;
+            }
+            else if (strcmp(methodName, "Sinh") == 0)
+            {
+                result = NI_System_Math_Sinh;
+            }
+            else if (strcmp(methodName, "Tan") == 0)
+            {
+                result = NI_System_Math_Tan;
+            }
+            else if (strcmp(methodName, "Tanh") == 0)
+            {
+                result = NI_System_Math_Tanh;
+            }
+            else if (strcmp(methodName, "Asin") == 0)
+            {
+                result = NI_System_Math_Asin;
+            }
+            else if (strcmp(methodName, "Asinh") == 0)
+            {
+                result = NI_System_Math_Asinh;
+            }
+            else if (strcmp(methodName, "Acos") == 0)
+            {
+                result = NI_System_Math_Acos;
+            }
+            else if (strcmp(methodName, "Acosh") == 0)
+            {
+                result = NI_System_Math_Acosh;
+            }
+            else if (strcmp(methodName, "Atan") == 0)
+            {
+                result = NI_System_Math_Atan;
+            }
+            else if (strcmp(methodName, "Atan2") == 0)
+            {
+                result = NI_System_Math_Atan2;
+            }
+            else if (strcmp(methodName, "Atanh") == 0)
+            {
+                result = NI_System_Math_Atanh;
+            }
+            else if (strcmp(methodName, "Log10") == 0)
+            {
+                result = NI_System_Math_Log10;
+            }
+            else if (strcmp(methodName, "Pow") == 0)
+            {
+                result = NI_System_Math_Pow;
+            }
+            else if (strcmp(methodName, "Exp") == 0)
+            {
+                result = NI_System_Math_Exp;
+            }
+            else if (strcmp(methodName, "Ceiling") == 0)
+            {
+                result = NI_System_Math_Ceiling;
+            }
+            else if (strcmp(methodName, "Floor") == 0)
+            {
+                result = NI_System_Math_Floor;
             }
         }
         else if (strcmp(className, "GC") == 0)
@@ -4796,7 +4892,14 @@ GenTree* Compiler::impArrayAccessIntrinsic(
 
     if (intrinsicID != CORINFO_INTRINSIC_Array_Address)
     {
-        arrElem = gtNewOperNode(GT_IND, elemType, arrElem);
+        if (varTypeIsStruct(elemType))
+        {
+            arrElem = gtNewObjNode(sig->retTypeClass, arrElem);
+        }
+        else
+        {
+            arrElem = gtNewOperNode(GT_IND, elemType, arrElem);
+        }
     }
 
     if (intrinsicID == CORINFO_INTRINSIC_Array_Set)
@@ -7709,7 +7812,7 @@ var_types Compiler::impImportCall(OPCODE                  opcode,
         // If this is a call to JitTestLabel.Mark, do "early inlining", and record the test attribute.
 
         // This recognition should really be done by knowing the methHnd of the relevant Mark method(s).
-        // These should be in mscorlib.h, and available through a JIT/EE interface call.
+        // These should be in corelib.h, and available through a JIT/EE interface call.
         const char* modName;
         const char* className;
         const char* methodName;
@@ -7944,9 +8047,9 @@ var_types Compiler::impImportCall(OPCODE                  opcode,
                 // This is for a non-virtual, non-interface etc. call
                 call = gtNewCallNode(CT_USER_FUNC, callInfo->hMethod, callRetTyp, nullptr, ilOffset);
 
-                // We remove the nullcheck for the GetType call instrinsic.
+                // We remove the nullcheck for the GetType call intrinsic.
                 // TODO-CQ: JIT64 does not introduce the null check for many more helper calls
-                // and instrinsics.
+                // and intrinsics.
                 if (callInfo->nullInstanceCheck &&
                     !((mflags & CORINFO_FLG_INTRINSIC) != 0 && (intrinsicID == CORINFO_INTRINSIC_Object_GetType)))
                 {
@@ -8577,7 +8680,7 @@ var_types Compiler::impImportCall(OPCODE                  opcode,
 
         if (canTailCall &&
             !impTailCallRetTypeCompatible(info.compRetType, info.compMethodInfo->args.retTypeClass, callRetTyp,
-                                          callInfo->sig.retTypeClass))
+                                          sig->retTypeClass))
         {
             canTailCall             = false;
             szCanTailCallFailReason = "Return types are not tail call compatible";
@@ -13188,10 +13291,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
                             // via an underlying address, just null check the address.
                             if (op1->OperIs(GT_FIELD, GT_IND, GT_OBJ))
                             {
-                                op1->ChangeOper(GT_NULLCHECK);
-                                block->bbFlags |= BBF_HAS_NULLCHECK;
-                                optMethodFlags |= OMF_HAS_NULLCHECK;
-                                op1->gtType = TYP_BYTE;
+                                gtChangeOperToNullCheck(op1, block);
                             }
                             else
                             {
@@ -20072,10 +20172,10 @@ void Compiler::impMarkInlineCandidateHelper(GenTreeCall*           call,
 // Returns true if the given intrinsic will be implemented by target-specific
 // instructions
 
-bool Compiler::IsTargetIntrinsic(CorInfoIntrinsics intrinsicId)
+bool Compiler::IsTargetIntrinsic(NamedIntrinsic intrinsicName)
 {
 #if defined(TARGET_XARCH)
-    switch (intrinsicId)
+    switch (intrinsicName)
     {
         // AMD64/x86 has SSE2 instructions to directly compute sqrt/abs and SSE4.1
         // instructions to directly compute round/ceiling/floor.
@@ -20086,37 +20186,37 @@ bool Compiler::IsTargetIntrinsic(CorInfoIntrinsics intrinsicId)
         //       a CQ problem, it may be necessary to change the implementation of
         //       the helper calls to decrease call overhead or switch back to the
         //       x87 instructions. This is tracked by #7097.
-        case CORINFO_INTRINSIC_Sqrt:
-        case CORINFO_INTRINSIC_Abs:
+        case NI_System_Math_Sqrt:
+        case NI_System_Math_Abs:
             return true;
 
-        case CORINFO_INTRINSIC_Round:
-        case CORINFO_INTRINSIC_Ceiling:
-        case CORINFO_INTRINSIC_Floor:
+        case NI_System_Math_Round:
+        case NI_System_Math_Ceiling:
+        case NI_System_Math_Floor:
             return compOpportunisticallyDependsOn(InstructionSet_SSE41);
 
         default:
             return false;
     }
 #elif defined(TARGET_ARM64)
-    switch (intrinsicId)
+    switch (intrinsicName)
     {
-        case CORINFO_INTRINSIC_Sqrt:
-        case CORINFO_INTRINSIC_Abs:
-        case CORINFO_INTRINSIC_Round:
-        case CORINFO_INTRINSIC_Floor:
-        case CORINFO_INTRINSIC_Ceiling:
+        case NI_System_Math_Sqrt:
+        case NI_System_Math_Abs:
+        case NI_System_Math_Round:
+        case NI_System_Math_Floor:
+        case NI_System_Math_Ceiling:
             return true;
 
         default:
             return false;
     }
 #elif defined(TARGET_ARM)
-    switch (intrinsicId)
+    switch (intrinsicName)
     {
-        case CORINFO_INTRINSIC_Sqrt:
-        case CORINFO_INTRINSIC_Abs:
-        case CORINFO_INTRINSIC_Round:
+        case NI_System_Math_Sqrt:
+        case NI_System_Math_Abs:
+        case NI_System_Math_Round:
             return true;
 
         default:
@@ -20134,41 +20234,41 @@ bool Compiler::IsTargetIntrinsic(CorInfoIntrinsics intrinsicId)
 // Returns true if the given intrinsic will be implemented by calling System.Math
 // methods.
 
-bool Compiler::IsIntrinsicImplementedByUserCall(CorInfoIntrinsics intrinsicId)
+bool Compiler::IsIntrinsicImplementedByUserCall(NamedIntrinsic intrinsicName)
 {
     // Currently, if a math intrinsic is not implemented by target-specific
     // instructions, it will be implemented by a System.Math call. In the
     // future, if we turn to implementing some of them with helper calls,
     // this predicate needs to be revisited.
-    return !IsTargetIntrinsic(intrinsicId);
+    return !IsTargetIntrinsic(intrinsicName);
 }
 
-bool Compiler::IsMathIntrinsic(CorInfoIntrinsics intrinsicId)
+bool Compiler::IsMathIntrinsic(NamedIntrinsic intrinsicName)
 {
-    switch (intrinsicId)
-    {
-        case CORINFO_INTRINSIC_Sin:
-        case CORINFO_INTRINSIC_Cbrt:
-        case CORINFO_INTRINSIC_Sqrt:
-        case CORINFO_INTRINSIC_Abs:
-        case CORINFO_INTRINSIC_Cos:
-        case CORINFO_INTRINSIC_Round:
-        case CORINFO_INTRINSIC_Cosh:
-        case CORINFO_INTRINSIC_Sinh:
-        case CORINFO_INTRINSIC_Tan:
-        case CORINFO_INTRINSIC_Tanh:
-        case CORINFO_INTRINSIC_Asin:
-        case CORINFO_INTRINSIC_Asinh:
-        case CORINFO_INTRINSIC_Acos:
-        case CORINFO_INTRINSIC_Acosh:
-        case CORINFO_INTRINSIC_Atan:
-        case CORINFO_INTRINSIC_Atan2:
-        case CORINFO_INTRINSIC_Atanh:
-        case CORINFO_INTRINSIC_Log10:
-        case CORINFO_INTRINSIC_Pow:
-        case CORINFO_INTRINSIC_Exp:
-        case CORINFO_INTRINSIC_Ceiling:
-        case CORINFO_INTRINSIC_Floor:
+    switch (intrinsicName)
+    {
+        case NI_System_Math_Sin:
+        case NI_System_Math_Cbrt:
+        case NI_System_Math_Sqrt:
+        case NI_System_Math_Abs:
+        case NI_System_Math_Cos:
+        case NI_System_Math_Round:
+        case NI_System_Math_Cosh:
+        case NI_System_Math_Sinh:
+        case NI_System_Math_Tan:
+        case NI_System_Math_Tanh:
+        case NI_System_Math_Asin:
+        case NI_System_Math_Asinh:
+        case NI_System_Math_Acos:
+        case NI_System_Math_Acosh:
+        case NI_System_Math_Atan:
+        case NI_System_Math_Atan2:
+        case NI_System_Math_Atanh:
+        case NI_System_Math_Log10:
+        case NI_System_Math_Pow:
+        case NI_System_Math_Exp:
+        case NI_System_Math_Ceiling:
+        case NI_System_Math_Floor:
             return true;
         default:
             return false;
@@ -20177,7 +20277,7 @@ bool Compiler::IsMathIntrinsic(CorInfoIntrinsics intrinsicId)
 
 bool Compiler::IsMathIntrinsic(GenTree* tree)
 {
-    return (tree->OperGet() == GT_INTRINSIC) && IsMathIntrinsic(tree->AsIntrinsic()->gtIntrinsicId);
+    return (tree->OperGet() == GT_INTRINSIC) && IsMathIntrinsic(tree->AsIntrinsic()->gtIntrinsicName);
 }
 
 //------------------------------------------------------------------------
diff --git a/src/coreclr/src/jit/inline.cpp b/src/coreclr/src/jit/inline.cpp
index 9b4d6f1686145f..759a6e36618129 100644
--- a/src/coreclr/src/jit/inline.cpp
+++ b/src/coreclr/src/jit/inline.cpp
@@ -1624,7 +1624,7 @@ void InlineStrategy::DumpXml(FILE* file, unsigned indent)
 
     // Root context will be null if we're not optimizing the method.
     //
-    // Note there are cases of this in mscorlib even in release builds,
+    // Note there are cases of this in System.Private.CoreLib even in release builds,
     // eg Task.NotifyDebuggerOfWaitCompletion.
     //
     // For such methods there aren't any inlines.
diff --git a/src/coreclr/src/jit/inlinepolicy.cpp b/src/coreclr/src/jit/inlinepolicy.cpp
index 8852991cf20010..09a029f9966382 100644
--- a/src/coreclr/src/jit/inlinepolicy.cpp
+++ b/src/coreclr/src/jit/inlinepolicy.cpp
@@ -1700,7 +1700,7 @@ void DiscretionaryPolicy::MethodInfoObservations(CORINFO_METHOD_INFO* methodInfo
 //   0.100 * m_CalleeNativeSizeEstimate +
 //  -0.100 * m_CallsiteNativeSizeEstimate
 //
-// On the inlines in CoreCLR's mscorlib, release windows x64, this
+// On the inlines in CoreCLR's CoreLib, release windows x64, this
 // yields scores of R=0.42, MSE=228, and MAE=7.25.
 //
 // This estimate can be improved slighly by refitting, resulting in
diff --git a/src/coreclr/src/jit/instr.cpp b/src/coreclr/src/jit/instr.cpp
index a13887baa0f6dc..d6f4c98f6b9470 100644
--- a/src/coreclr/src/jit/instr.cpp
+++ b/src/coreclr/src/jit/instr.cpp
@@ -478,7 +478,7 @@ void CodeGen::inst_IV_handle(instruction ins, int val)
 void CodeGen::inst_set_SV_var(GenTree* tree)
 {
 #ifdef DEBUG
-    assert(tree && (tree->gtOper == GT_LCL_VAR || tree->gtOper == GT_LCL_VAR_ADDR || tree->gtOper == GT_STORE_LCL_VAR));
+    assert((tree != nullptr) && tree->OperIs(GT_LCL_VAR, GT_LCL_VAR_ADDR, GT_STORE_LCL_VAR));
     assert(tree->AsLclVarCommon()->GetLclNum() < compiler->lvaCount);
 
     GetEmitter()->emitVarRefOffs = tree->AsLclVar()->gtLclILoffs;
@@ -1019,9 +1019,11 @@ void CodeGen::inst_RV_TT_IV(instruction ins, emitAttr attr, regNumber reg1, GenT
             switch (addr->OperGet())
             {
                 case GT_LCL_VAR_ADDR:
+                case GT_LCL_FLD_ADDR:
                 {
+                    assert(addr->isContained());
                     varNum = addr->AsLclVarCommon()->GetLclNum();
-                    offset = 0;
+                    offset = addr->AsLclVarCommon()->GetLclOffs();
                     break;
                 }
 
@@ -1146,9 +1148,11 @@ void CodeGen::inst_RV_RV_TT(
             switch (addr->OperGet())
             {
                 case GT_LCL_VAR_ADDR:
+                case GT_LCL_FLD_ADDR:
                 {
+                    assert(addr->isContained());
                     varNum = addr->AsLclVarCommon()->GetLclNum();
-                    offset = 0;
+                    offset = addr->AsLclVarCommon()->GetLclOffs();
                     break;
                 }
 
diff --git a/src/coreclr/src/jit/jitconfigvalues.h b/src/coreclr/src/jit/jitconfigvalues.h
index e6c1ab307e460a..329f526e90046d 100644
--- a/src/coreclr/src/jit/jitconfigvalues.h
+++ b/src/coreclr/src/jit/jitconfigvalues.h
@@ -285,6 +285,20 @@ CONFIG_INTEGER(JitDisableSimdVN, W("JitDisableSimdVN"), 0) // Default 0, ValueNu
                                                            // If 3, disable both SIMD and HW Intrinsic nodes
 #endif                                                     // FEATURE_SIMD
 
+// Default 0, enable the CSE of Constants, including nearby offsets. (only for ARM64)
+// If 1, disable all the CSE of Constants
+// If 2, enable the CSE of Constants but don't combine with nearby offsets. (only for ARM64)
+// If 3, enable the CSE of Constants including nearby offsets. (all platforms)
+// If 4, enable the CSE of Constants but don't combine with nearby offsets. (all platforms)
+//
+CONFIG_INTEGER(JitConstCSE, W("JitConstCSE"), 0)
+
+#define CONST_CSE_ENABLE_ARM64 0
+#define CONST_CSE_DISABLE_ALL 1
+#define CONST_CSE_ENABLE_ARM64_NO_SHARING 2
+#define CONST_CSE_ENABLE_ALL 3
+#define CONST_CSE_ENABLE_ALL_NO_SHARING 4
+
 ///
 /// JIT
 ///
diff --git a/src/coreclr/src/jit/jithashtable.cpp b/src/coreclr/src/jit/jithashtable.cpp
new file mode 100644
index 00000000000000..cf9f22639efe16
--- /dev/null
+++ b/src/coreclr/src/jit/jithashtable.cpp
@@ -0,0 +1,53 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#include "jitpch.h"
+
+#if defined(_MSC_VER)
+#pragma hdrstop
+#endif // defined(_MSC_VER)
+
+// Table of primes and their magic-number-divide constant.
+// For more info see the book "Hacker's Delight" chapter 10.9 "Unsigned Division by Divisors >= 1"
+// These were selected by looking for primes, each roughly twice as big as the next, having
+// 32-bit magic numbers, (because the algorithm for using 33-bit magic numbers is slightly slower).
+
+#include "jithashtable.h"
+
+// Table of primes and their magic-number-divide constant.
+// For more info see the book "Hacker's Delight" chapter 10.9 "Unsigned Division by Divisors >= 1"
+// These were selected by looking for primes, each roughly twice as big as the next, having
+// 32-bit magic numbers, (because the algorithm for using 33-bit magic numbers is slightly slower).
+
+// clang-format off
+const JitPrimeInfo jitPrimeInfo[]
+{
+    JitPrimeInfo(9,         0x38e38e39, 1),
+    JitPrimeInfo(23,        0xb21642c9, 4),
+    JitPrimeInfo(59,        0x22b63cbf, 3),
+    JitPrimeInfo(131,       0xfa232cf3, 7),
+    JitPrimeInfo(239,       0x891ac73b, 7),
+    JitPrimeInfo(433,       0x975a751,  4),
+    JitPrimeInfo(761,       0x561e46a5, 8),
+    JitPrimeInfo(1399,      0xbb612aa3, 10),
+    JitPrimeInfo(2473,      0x6a009f01, 10),
+    JitPrimeInfo(4327,      0xf2555049, 12),
+    JitPrimeInfo(7499,      0x45ea155f, 11),
+    JitPrimeInfo(12973,     0x1434f6d3, 10),
+    JitPrimeInfo(22433,     0x2ebe18db, 12),
+    JitPrimeInfo(46559,     0xb42bebd5, 15),
+    JitPrimeInfo(96581,     0xadb61b1b, 16),
+    JitPrimeInfo(200341,    0x29df2461, 15),
+    JitPrimeInfo(415517,    0xa181c46d, 18),
+    JitPrimeInfo(861719,    0x4de0bde5, 18),
+    JitPrimeInfo(1787021,   0x9636c46f, 20),
+    JitPrimeInfo(3705617,   0x4870adc1, 20),
+    JitPrimeInfo(7684087,   0x8bbc5b83, 22),
+    JitPrimeInfo(15933877,  0x86c65361, 23),
+    JitPrimeInfo(33040633,  0x40fec79b, 23),
+    JitPrimeInfo(68513161,  0x7d605cd1, 25),
+    JitPrimeInfo(142069021, 0xf1da390b, 27),
+    JitPrimeInfo(294594427, 0x74a2507d, 27),
+    JitPrimeInfo(733045421, 0x5dbec447, 28),
+};
+// clang-format on
diff --git a/src/coreclr/src/jit/jithashtable.h b/src/coreclr/src/jit/jithashtable.h
index 4d2d19d1389ff4..131f804a1127fd 100644
--- a/src/coreclr/src/jit/jithashtable.h
+++ b/src/coreclr/src/jit/jithashtable.h
@@ -57,10 +57,10 @@ class JitHashTableBehavior
 class JitPrimeInfo
 {
 public:
-    JitPrimeInfo() : prime(0), magic(0), shift(0)
+    constexpr JitPrimeInfo() : prime(0), magic(0), shift(0)
     {
     }
-    JitPrimeInfo(unsigned p, unsigned m, unsigned s) : prime(p), magic(m), shift(s)
+    constexpr JitPrimeInfo(unsigned p, unsigned m, unsigned s) : prime(p), magic(m), shift(s)
     {
     }
     unsigned prime;
@@ -91,38 +91,7 @@ class JitPrimeInfo
 // These were selected by looking for primes, each roughly twice as big as the next, having
 // 32-bit magic numbers, (because the algorithm for using 33-bit magic numbers is slightly slower).
 
-// clang-format off
-SELECTANY const JitPrimeInfo jitPrimeInfo[]
-{
-    JitPrimeInfo(9,         0x38e38e39, 1),
-    JitPrimeInfo(23,        0xb21642c9, 4),
-    JitPrimeInfo(59,        0x22b63cbf, 3),
-    JitPrimeInfo(131,       0xfa232cf3, 7),
-    JitPrimeInfo(239,       0x891ac73b, 7),
-    JitPrimeInfo(433,       0x975a751,  4),
-    JitPrimeInfo(761,       0x561e46a5, 8),
-    JitPrimeInfo(1399,      0xbb612aa3, 10),
-    JitPrimeInfo(2473,      0x6a009f01, 10),
-    JitPrimeInfo(4327,      0xf2555049, 12),
-    JitPrimeInfo(7499,      0x45ea155f, 11),
-    JitPrimeInfo(12973,     0x1434f6d3, 10),
-    JitPrimeInfo(22433,     0x2ebe18db, 12),
-    JitPrimeInfo(46559,     0xb42bebd5, 15),
-    JitPrimeInfo(96581,     0xadb61b1b, 16),
-    JitPrimeInfo(200341,    0x29df2461, 15),
-    JitPrimeInfo(415517,    0xa181c46d, 18),
-    JitPrimeInfo(861719,    0x4de0bde5, 18),
-    JitPrimeInfo(1787021,   0x9636c46f, 20),
-    JitPrimeInfo(3705617,   0x4870adc1, 20),
-    JitPrimeInfo(7684087,   0x8bbc5b83, 22),
-    JitPrimeInfo(15933877,  0x86c65361, 23),
-    JitPrimeInfo(33040633,  0x40fec79b, 23),
-    JitPrimeInfo(68513161,  0x7d605cd1, 25),
-    JitPrimeInfo(142069021, 0xf1da390b, 27),
-    JitPrimeInfo(294594427, 0x74a2507d, 27),
-    JitPrimeInfo(733045421, 0x5dbec447, 28),
-};
-// clang-format on
+extern const JitPrimeInfo jitPrimeInfo[27];
 
 // Hash table class definition
 
diff --git a/src/coreclr/src/jit/liveness.cpp b/src/coreclr/src/jit/liveness.cpp
index feb8f23a222eda..cbc4ebbd05af51 100644
--- a/src/coreclr/src/jit/liveness.cpp
+++ b/src/coreclr/src/jit/liveness.cpp
@@ -1980,17 +1980,13 @@ void Compiler::fgComputeLifeLIR(VARSET_TP& life, BasicBlock* block, VARSET_VALAR
                             GenTree* data =
                                 store->OperIs(GT_STOREIND) ? store->AsStoreInd()->Data() : store->AsBlk()->Data();
                             data->SetUnusedValue();
+
                             if (data->isIndir())
                             {
-                                // This is a block assignment. An indirection of the rhs is not considered
-                                // to happen until the assignment so mark it as non-faulting.
-                                data->gtFlags |= GTF_IND_NONFAULTING;
+                                Lowering::TransformUnusedIndirection(data->AsIndir(), this, block);
                             }
 
-                            blockRange.Remove(store);
-
-                            assert(!opts.MinOpts());
-                            fgStmtRemoved = true;
+                            fgRemoveDeadStoreLIR(store, block);
                         }
                     }
                 }
@@ -2019,25 +2015,7 @@ void Compiler::fgComputeLifeLIR(VARSET_TP& life, BasicBlock* block, VARSET_VALAR
                     // Remove the store. DCE will iteratively clean up any ununsed operands.
                     lclVarNode->gtOp1->SetUnusedValue();
 
-                    // If the store is marked as a late argument, it is referenced by a call. Instead of removing
-                    // it, bash it to a NOP.
-                    if ((node->gtFlags & GTF_LATE_ARG) != 0)
-                    {
-                        JITDUMP("node is a late arg; replacing with NOP\n");
-                        node->gtBashToNOP();
-
-                        // NOTE: this is a bit of a hack. We need to keep these nodes around as they are
-                        // referenced by the call, but they're considered side-effect-free non-value-producing
-                        // nodes, so they will be removed if we don't do this.
-                        node->gtFlags |= GTF_ORDER_SIDEEFF;
-                    }
-                    else
-                    {
-                        blockRange.Remove(node);
-                    }
-
-                    assert(!opts.MinOpts());
-                    fgStmtRemoved = true;
+                    fgRemoveDeadStoreLIR(node, block);
                 }
 
                 break;
@@ -2109,40 +2087,112 @@ void Compiler::fgComputeLifeLIR(VARSET_TP& life, BasicBlock* block, VARSET_VALAR
                 break;
 
             case GT_NOP:
+            {
                 // NOTE: we need to keep some NOPs around because they are referenced by calls. See the dead store
                 // removal code above (case GT_STORE_LCL_VAR) for more explanation.
                 if ((node->gtFlags & GTF_ORDER_SIDEEFF) != 0)
                 {
                     break;
                 }
-                __fallthrough;
+                fgTryRemoveNonLocal(node, &blockRange);
+            }
+            break;
 
-            default:
-                assert(!node->OperIsLocal());
-                if (!node->IsValue() || node->IsUnusedValue())
+            case GT_BLK:
+            case GT_OBJ:
+            case GT_DYN_BLK:
+            {
+                bool removed = fgTryRemoveNonLocal(node, &blockRange);
+                if (!removed && node->IsUnusedValue())
                 {
-                    // We are only interested in avoiding the removal of nodes with direct side-effects
-                    // (as opposed to side effects of their children).
-                    // This default case should never include calls or assignments.
-                    assert(!node->OperRequiresAsgFlag() && !node->OperIs(GT_CALL));
-                    if (!node->gtSetFlags() && !node->OperMayThrow(this))
-                    {
-                        JITDUMP("Removing dead node:\n");
-                        DISPNODE(node);
-
-                        node->VisitOperands([](GenTree* operand) -> GenTree::VisitResult {
-                            operand->SetUnusedValue();
-                            return GenTree::VisitResult::Continue;
-                        });
-
-                        blockRange.Remove(node);
-                    }
+                    // IR doesn't expect dummy uses of `GT_OBJ/BLK/DYN_BLK`.
+                    JITDUMP("Transform an unused OBJ/BLK node [%06d]\n", dspTreeID(node));
+                    Lowering::TransformUnusedIndirection(node->AsIndir(), this, block);
                 }
+            }
+            break;
+
+            default:
+                fgTryRemoveNonLocal(node, &blockRange);
                 break;
         }
     }
 }
 
+//---------------------------------------------------------------------
+// fgTryRemoveNonLocal - try to remove a node if it is unused and has no direct
+//   side effects.
+//
+// Arguments
+//    node       - the non-local node to try;
+//    blockRange - the block range that contains the node.
+//
+// Return value:
+//    None
+//
+// Notes: local nodes are processed independently and are not expected in this function.
+//
+bool Compiler::fgTryRemoveNonLocal(GenTree* node, LIR::Range* blockRange)
+{
+    assert(!node->OperIsLocal());
+    if (!node->IsValue() || node->IsUnusedValue())
+    {
+        // We are only interested in avoiding the removal of nodes with direct side effects
+        // (as opposed to side effects of their children).
+        // This default case should never include calls or assignments.
+        assert(!node->OperRequiresAsgFlag() && !node->OperIs(GT_CALL));
+        if (!node->gtSetFlags() && !node->OperMayThrow(this))
+        {
+            JITDUMP("Removing dead node:\n");
+            DISPNODE(node);
+
+            node->VisitOperands([](GenTree* operand) -> GenTree::VisitResult {
+                operand->SetUnusedValue();
+                return GenTree::VisitResult::Continue;
+            });
+
+            blockRange->Remove(node);
+            return true;
+        }
+    }
+    return false;
+}
+
+//---------------------------------------------------------------------
+// fgRemoveDeadStoreSimple - remove a dead store
+//
+//   pTree          - GenTree** to local, including store-form local or local addr (post-rationalize)
+//   varDsc         - var that is being stored to
+//   life           - current live tracked vars (maintained as we walk backwards)
+//   doAgain        - out parameter, true if we should restart the statement
+//   pStmtInfoDirty - should defer the cost computation to the point after the reverse walk is completed?
+//
+void Compiler::fgRemoveDeadStoreLIR(GenTree* store, BasicBlock* block)
+{
+    LIR::Range& blockRange = LIR::AsRange(block);
+
+    // If the store is marked as a late argument, it is referenced by a call.
+    // Instead of removing it, bash it to a NOP.
+    if ((store->gtFlags & GTF_LATE_ARG) != 0)
+    {
+        JITDUMP("node is a late arg; replacing with NOP\n");
+        store->gtBashToNOP();
+
+        // NOTE: this is a bit of a hack. We need to keep these nodes around as they are
+        // referenced by the call, but they're considered side-effect-free non-value-producing
+        // nodes, so they will be removed if we don't do this.
+        store->gtFlags |= GTF_ORDER_SIDEEFF;
+    }
+    else
+    {
+        blockRange.Remove(store);
+    }
+
+    assert(!opts.MinOpts());
+    fgStmtRemoved = true;
+}
+
+//---------------------------------------------------------------------
 // fgRemoveDeadStore - remove a store to a local which has no exposed uses.
 //
 //   pTree          - GenTree** to local, including store-form local or local addr (post-rationalize)
@@ -2285,17 +2335,6 @@ bool Compiler::fgRemoveDeadStore(GenTree**        pTree,
             }
 #endif // DEBUG
             // Extract the side effects
-            if (rhsNode->TypeGet() == TYP_STRUCT)
-            {
-                // This is a block assignment. An indirection of the rhs is not considered to
-                // happen until the assignment, so we will extract the side effects from only
-                // the address.
-                if (rhsNode->OperIsIndir())
-                {
-                    assert(rhsNode->OperGet() != GT_NULLCHECK);
-                    rhsNode = rhsNode->AsIndir()->Addr();
-                }
-            }
             gtExtractSideEffList(rhsNode, &sideEffList);
         }
 
diff --git a/src/coreclr/src/jit/lower.cpp b/src/coreclr/src/jit/lower.cpp
index cc9e2891e9a47c..a401a843dd0a54 100644
--- a/src/coreclr/src/jit/lower.cpp
+++ b/src/coreclr/src/jit/lower.cpp
@@ -3181,7 +3181,9 @@ void Lowering::LowerStoreLocCommon(GenTreeLclVarCommon* lclStore)
             // Create the assignment node.
             lclStore->ChangeOper(GT_STORE_OBJ);
             GenTreeBlk* objStore = lclStore->AsObj();
-            objStore->gtFlags    = GTF_ASG | GTF_IND_NONFAULTING | GTF_IND_TGT_NOT_HEAP;
+            // Only the GTF_LATE_ARG flag (if present) is preserved.
+            objStore->gtFlags &= GTF_LATE_ARG;
+            objStore->gtFlags |= GTF_ASG | GTF_IND_NONFAULTING | GTF_IND_TGT_NOT_HEAP;
 #ifndef JIT32_GCENCODER
             objStore->gtBlkOpGcUnsafe = false;
 #endif
@@ -6450,41 +6452,7 @@ void Lowering::LowerIndir(GenTreeIndir* ind)
 
         if (ind->OperIs(GT_NULLCHECK) || ind->IsUnusedValue())
         {
-            // A nullcheck is essentially the same as an indirection with no use.
-            // The difference lies in whether a target register must be allocated.
-            // On XARCH we can generate a compare with no target register as long as the addresss
-            // is not contained.
-            // On ARM64 we can generate a load to REG_ZR in all cases.
-            // However, on ARM we must always generate a load to a register.
-            // In the case where we require a target register, it is better to use GT_IND, since
-            // GT_NULLCHECK is a non-value node and would therefore require an internal register
-            // to use as the target. That is non-optimal because it will be modeled as conflicting
-            // with the source register(s).
-            // So, to summarize:
-            // - On ARM64, always use GT_NULLCHECK for a dead indirection.
-            // - On ARM, always use GT_IND.
-            // - On XARCH, use GT_IND if we have a contained address, and GT_NULLCHECK otherwise.
-            // In all cases, change the type to TYP_INT.
-            //
-            ind->gtType = TYP_INT;
-#ifdef TARGET_ARM64
-            bool useNullCheck = true;
-#elif TARGET_ARM
-            bool useNullCheck = false;
-#else  // TARGET_XARCH
-            bool useNullCheck = !ind->Addr()->isContained();
-#endif // !TARGET_XARCH
-
-            if (useNullCheck && ind->OperIs(GT_IND))
-            {
-                ind->ChangeOper(GT_NULLCHECK);
-                ind->ClearUnusedValue();
-            }
-            else if (!useNullCheck && ind->OperIs(GT_NULLCHECK))
-            {
-                ind->ChangeOper(GT_IND);
-                ind->SetUnusedValue();
-            }
+            TransformUnusedIndirection(ind, comp, m_block);
         }
     }
     else
@@ -6496,6 +6464,55 @@ void Lowering::LowerIndir(GenTreeIndir* ind)
     }
 }
 
+//------------------------------------------------------------------------
+// TransformUnusedIndirection: change the opcode and the type of the unused indirection.
+//
+// Arguments:
+//    ind   - Indirection to transform.
+//    comp  - Compiler instance.
+//    block - Basic block of the indirection.
+//
+void Lowering::TransformUnusedIndirection(GenTreeIndir* ind, Compiler* comp, BasicBlock* block)
+{
+    // A nullcheck is essentially the same as an indirection with no use.
+    // The difference lies in whether a target register must be allocated.
+    // On XARCH we can generate a compare with no target register as long as the addresss
+    // is not contained.
+    // On ARM64 we can generate a load to REG_ZR in all cases.
+    // However, on ARM we must always generate a load to a register.
+    // In the case where we require a target register, it is better to use GT_IND, since
+    // GT_NULLCHECK is a non-value node and would therefore require an internal register
+    // to use as the target. That is non-optimal because it will be modeled as conflicting
+    // with the source register(s).
+    // So, to summarize:
+    // - On ARM64, always use GT_NULLCHECK for a dead indirection.
+    // - On ARM, always use GT_IND.
+    // - On XARCH, use GT_IND if we have a contained address, and GT_NULLCHECK otherwise.
+    // In all cases, change the type to TYP_INT.
+    //
+    assert(ind->OperIs(GT_NULLCHECK, GT_IND, GT_BLK, GT_OBJ));
+
+    ind->gtType = TYP_INT;
+#ifdef TARGET_ARM64
+    bool useNullCheck = true;
+#elif TARGET_ARM
+    bool useNullCheck = false;
+#else  // TARGET_XARCH
+    bool useNullCheck = !ind->Addr()->isContained();
+#endif // !TARGET_XARCH
+
+    if (useNullCheck && !ind->OperIs(GT_NULLCHECK))
+    {
+        comp->gtChangeOperToNullCheck(ind, block);
+        ind->ClearUnusedValue();
+    }
+    else if (!useNullCheck && !ind->OperIs(GT_IND))
+    {
+        ind->ChangeOper(GT_IND);
+        ind->SetUnusedValue();
+    }
+}
+
 //------------------------------------------------------------------------
 // LowerBlockStoreCommon: a common logic to lower STORE_OBJ/BLK/DYN_BLK.
 //
diff --git a/src/coreclr/src/jit/lower.h b/src/coreclr/src/jit/lower.h
index 0c620aebeb0f6b..ff13302c1ba992 100644
--- a/src/coreclr/src/jit/lower.h
+++ b/src/coreclr/src/jit/lower.h
@@ -8,6 +8,7 @@ XX                               Lower                                       XX
 XX                                                                           XX
 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 */
 
 #ifndef _LOWER_H_
@@ -326,12 +327,12 @@ class Lowering final : public Phase
     void LowerHWIntrinsicCmpOp(GenTreeHWIntrinsic* node, genTreeOps cmpOp);
     void LowerHWIntrinsicCreate(GenTreeHWIntrinsic* node);
     void LowerHWIntrinsicDot(GenTreeHWIntrinsic* node);
-    void LowerFusedMultiplyAdd(GenTreeHWIntrinsic* node);
-
 #if defined(TARGET_XARCH)
+    void LowerFusedMultiplyAdd(GenTreeHWIntrinsic* node);
     void LowerHWIntrinsicToScalar(GenTreeHWIntrinsic* node);
 #elif defined(TARGET_ARM64)
     bool IsValidConstForMovImm(GenTreeHWIntrinsic* node);
+    void LowerHWIntrinsicFusedMultiplyAddScalar(GenTreeHWIntrinsic* node);
 #endif // !TARGET_XARCH && !TARGET_ARM64
 
     union VectorConstant {
@@ -532,6 +533,8 @@ class Lowering final : public Phase
     bool IsContainableHWIntrinsicOp(GenTreeHWIntrinsic* containingNode, GenTree* node, bool* supportsRegOptional);
 #endif // FEATURE_HW_INTRINSICS
 
+    static void TransformUnusedIndirection(GenTreeIndir* ind, Compiler* comp, BasicBlock* block);
+
 private:
     static bool NodesAreEquivalentLeaves(GenTree* candidate, GenTree* storeInd);
 
diff --git a/src/coreclr/src/jit/lowerarmarch.cpp b/src/coreclr/src/jit/lowerarmarch.cpp
index 2ab6fa947822e0..6d46545f718d3d 100644
--- a/src/coreclr/src/jit/lowerarmarch.cpp
+++ b/src/coreclr/src/jit/lowerarmarch.cpp
@@ -517,6 +517,76 @@ void Lowering::LowerSIMD(GenTreeSIMD* simdNode)
 #endif // FEATURE_SIMD
 
 #ifdef FEATURE_HW_INTRINSICS
+
+//----------------------------------------------------------------------------------------------
+// LowerHWIntrinsicFusedMultiplyAddScalar: Lowers AdvSimd_FusedMultiplyAddScalar intrinsics
+//   when some of the operands are negated by "containing" such negation.
+//
+//  Arguments:
+//     node - The original hardware intrinsic node
+//
+// |  op1 | op2 | op3 |
+// |  +   |  +  |  +  | AdvSimd_FusedMultiplyAddScalar
+// |  +   |  +  |  -  | AdvSimd_FusedMultiplySubtractScalar
+// |  +   |  -  |  +  | AdvSimd_FusedMultiplySubtractScalar
+// |  +   |  -  |  -  | AdvSimd_FusedMultiplyAddScalar
+// |  -   |  +  |  +  | AdvSimd_FusedMultiplySubtractNegatedScalar
+// |  -   |  +  |  -  | AdvSimd_FusedMultiplyAddNegatedScalar
+// |  -   |  -  |  +  | AdvSimd_FusedMultiplyAddNegatedScalar
+// |  -   |  -  |  -  | AdvSimd_FusedMultiplySubtractNegatedScalar
+//
+void Lowering::LowerHWIntrinsicFusedMultiplyAddScalar(GenTreeHWIntrinsic* node)
+{
+    assert(node->gtHWIntrinsicId == NI_AdvSimd_FusedMultiplyAddScalar);
+
+    const HWIntrinsic intrin(node);
+
+    GenTree* op1 = intrin.op1;
+    GenTree* op2 = intrin.op2;
+    GenTree* op3 = intrin.op3;
+
+    auto lowerOperand = [this](GenTree* op) {
+        bool wasNegated = false;
+
+        if (op->OperIsHWIntrinsic() &&
+            ((op->AsHWIntrinsic()->gtHWIntrinsicId == NI_AdvSimd_Arm64_DuplicateToVector64) ||
+             (op->AsHWIntrinsic()->gtHWIntrinsicId == NI_Vector64_CreateScalarUnsafe)))
+        {
+            GenTreeHWIntrinsic* createVector64 = op->AsHWIntrinsic();
+            GenTree*            valueOp        = createVector64->gtGetOp1();
+
+            if (valueOp->OperIs(GT_NEG))
+            {
+                createVector64->gtOp1 = valueOp->gtGetOp1();
+                BlockRange().Remove(valueOp);
+                wasNegated = true;
+            }
+        }
+
+        return wasNegated;
+    };
+
+    const bool op1WasNegated = lowerOperand(op1);
+    const bool op2WasNegated = lowerOperand(op2);
+    const bool op3WasNegated = lowerOperand(op3);
+
+    if (op1WasNegated)
+    {
+        if (op2WasNegated != op3WasNegated)
+        {
+            node->gtHWIntrinsicId = NI_AdvSimd_FusedMultiplyAddNegatedScalar;
+        }
+        else
+        {
+            node->gtHWIntrinsicId = NI_AdvSimd_FusedMultiplySubtractNegatedScalar;
+        }
+    }
+    else if (op2WasNegated != op3WasNegated)
+    {
+        node->gtHWIntrinsicId = NI_AdvSimd_FusedMultiplySubtractScalar;
+    }
+}
+
 //----------------------------------------------------------------------------------------------
 // Lowering::LowerHWIntrinsic: Perform containment analysis for a hardware intrinsic node.
 //
@@ -573,6 +643,10 @@ void Lowering::LowerHWIntrinsic(GenTreeHWIntrinsic* node)
             return;
         }
 
+        case NI_AdvSimd_FusedMultiplyAddScalar:
+            LowerHWIntrinsicFusedMultiplyAddScalar(node);
+            break;
+
         default:
             break;
     }
diff --git a/src/coreclr/src/jit/lowerxarch.cpp b/src/coreclr/src/jit/lowerxarch.cpp
index 331c674eab9e7f..5266da117cf844 100644
--- a/src/coreclr/src/jit/lowerxarch.cpp
+++ b/src/coreclr/src/jit/lowerxarch.cpp
@@ -592,7 +592,7 @@ void Lowering::LowerPutArgStk(GenTreePutArgStk* putArgStk)
  *
  * TODO-XArch-CQ: (Low-pri): Jit64 generates in-line code of 8 instructions for (i) above.
  * There are hardly any occurrences of this conversion operation in platform
- * assemblies or in CQ perf benchmarks (1 occurrence in mscorlib, microsoft.jscript,
+ * assemblies or in CQ perf benchmarks (1 occurrence in corelib, microsoft.jscript,
  * 1 occurence in Roslyn and no occurrences in system, system.core, system.numerics
  * system.windows.forms, scimark, fractals, bio mums). If we ever find evidence that
  * doing this optimization is a win, should consider generating in-lined code.
@@ -3439,8 +3439,7 @@ bool Lowering::IsRMWMemOpRootedAtStoreInd(GenTree* tree, GenTree** outIndirCandi
     assert(storeInd->IsRMWStatusUnknown());
 
     // Early out if indirDst is not one of the supported memory operands.
-    if (indirDst->OperGet() != GT_LEA && indirDst->OperGet() != GT_LCL_VAR && indirDst->OperGet() != GT_LCL_VAR_ADDR &&
-        indirDst->OperGet() != GT_CLS_VAR_ADDR && indirDst->OperGet() != GT_CNS_INT)
+    if (!indirDst->OperIs(GT_LEA, GT_LCL_VAR, GT_LCL_VAR_ADDR, GT_CLS_VAR_ADDR, GT_CNS_INT))
     {
         storeInd->SetRMWStatus(STOREIND_RMW_UNSUPPORTED_ADDR);
         return false;
@@ -4452,14 +4451,13 @@ bool Lowering::LowerRMWMemOp(GenTreeIndir* storeInd)
     }
     else
     {
-        assert(indirCandidateChild->OperGet() == GT_LCL_VAR || indirCandidateChild->OperGet() == GT_LCL_VAR_ADDR ||
-               indirCandidateChild->OperGet() == GT_CLS_VAR_ADDR || indirCandidateChild->OperGet() == GT_CNS_INT);
+        assert(indirCandidateChild->OperIs(GT_LCL_VAR, GT_LCL_VAR_ADDR, GT_CLS_VAR_ADDR, GT_CNS_INT));
 
         // If it is a GT_LCL_VAR, it still needs the reg to hold the address.
         // We would still need a reg for GT_CNS_INT if it doesn't fit within addressing mode base.
         // For GT_CLS_VAR_ADDR, we don't need a reg to hold the address, because field address value is known at jit
         // time. Also, we don't need a reg for GT_CLS_VAR_ADDR.
-        if (indirCandidateChild->OperGet() == GT_LCL_VAR_ADDR || indirCandidateChild->OperGet() == GT_CLS_VAR_ADDR)
+        if (indirCandidateChild->OperIs(GT_LCL_VAR_ADDR, GT_CLS_VAR_ADDR))
         {
             indirDst->SetContained();
         }
@@ -4616,10 +4614,10 @@ void Lowering::ContainCheckIntrinsic(GenTreeOp* node)
 {
     assert(node->OperIs(GT_INTRINSIC));
 
-    CorInfoIntrinsics intrinsicId = node->AsIntrinsic()->gtIntrinsicId;
+    NamedIntrinsic intrinsicName = node->AsIntrinsic()->gtIntrinsicName;
 
-    if (intrinsicId == CORINFO_INTRINSIC_Sqrt || intrinsicId == CORINFO_INTRINSIC_Round ||
-        intrinsicId == CORINFO_INTRINSIC_Ceiling || intrinsicId == CORINFO_INTRINSIC_Floor)
+    if (intrinsicName == NI_System_Math_Sqrt || intrinsicName == NI_System_Math_Round ||
+        intrinsicName == NI_System_Math_Ceiling || intrinsicName == NI_System_Math_Floor)
     {
         GenTree* op1 = node->gtGetOp1();
         if (IsContainableMemoryOp(op1) || op1->IsCnsNonZeroFltOrDbl())
@@ -5138,7 +5136,7 @@ void Lowering::ContainCheckHWIntrinsicAddr(GenTreeHWIntrinsic* node, GenTree* ad
 {
     assert((addr->TypeGet() == TYP_I_IMPL) || (addr->TypeGet() == TYP_BYREF));
     TryCreateAddrMode(addr, true);
-    if ((addr->OperIs(GT_CLS_VAR_ADDR, GT_LCL_VAR_ADDR, GT_LEA) ||
+    if ((addr->OperIs(GT_CLS_VAR_ADDR, GT_LCL_VAR_ADDR, GT_LCL_FLD_ADDR, GT_LEA) ||
          (addr->IsCnsIntOrI() && addr->AsIntConCommon()->FitsInAddrBase(comp))) &&
         IsSafeToContainMem(node, addr))
     {
diff --git a/src/coreclr/src/jit/lsraarm.cpp b/src/coreclr/src/jit/lsraarm.cpp
index f3b480fddd6d01..8402bcdefc0fe4 100644
--- a/src/coreclr/src/jit/lsraarm.cpp
+++ b/src/coreclr/src/jit/lsraarm.cpp
@@ -290,10 +290,10 @@ int LinearScan::BuildNode(GenTree* tree)
             BuildUse(op1);
             srcCount = 1;
 
-            switch (tree->AsIntrinsic()->gtIntrinsicId)
+            switch (tree->AsIntrinsic()->gtIntrinsicName)
             {
-                case CORINFO_INTRINSIC_Abs:
-                case CORINFO_INTRINSIC_Sqrt:
+                case NI_System_Math_Abs:
+                case NI_System_Math_Sqrt:
                     assert(dstCount == 1);
                     BuildDef(tree);
                     break;
@@ -491,6 +491,8 @@ int LinearScan::BuildNode(GenTree* tree)
 
         case GT_RETURN:
             srcCount = BuildReturn(tree);
+            killMask = getKillSetForReturn();
+            BuildDefsWithKills(tree, 0, RBM_NONE, killMask);
             break;
 
         case GT_RETFILT:
diff --git a/src/coreclr/src/jit/lsraarm64.cpp b/src/coreclr/src/jit/lsraarm64.cpp
index 514ed90feef468..2138b782c53e49 100644
--- a/src/coreclr/src/jit/lsraarm64.cpp
+++ b/src/coreclr/src/jit/lsraarm64.cpp
@@ -319,11 +319,11 @@ int LinearScan::BuildNode(GenTree* tree)
 
         case GT_INTRINSIC:
         {
-            noway_assert((tree->AsIntrinsic()->gtIntrinsicId == CORINFO_INTRINSIC_Abs) ||
-                         (tree->AsIntrinsic()->gtIntrinsicId == CORINFO_INTRINSIC_Ceiling) ||
-                         (tree->AsIntrinsic()->gtIntrinsicId == CORINFO_INTRINSIC_Floor) ||
-                         (tree->AsIntrinsic()->gtIntrinsicId == CORINFO_INTRINSIC_Round) ||
-                         (tree->AsIntrinsic()->gtIntrinsicId == CORINFO_INTRINSIC_Sqrt));
+            noway_assert((tree->AsIntrinsic()->gtIntrinsicName == NI_System_Math_Abs) ||
+                         (tree->AsIntrinsic()->gtIntrinsicName == NI_System_Math_Ceiling) ||
+                         (tree->AsIntrinsic()->gtIntrinsicName == NI_System_Math_Floor) ||
+                         (tree->AsIntrinsic()->gtIntrinsicName == NI_System_Math_Round) ||
+                         (tree->AsIntrinsic()->gtIntrinsicName == NI_System_Math_Sqrt));
 
             // Both operand and its result must be of the same floating point type.
             GenTree* op1 = tree->gtGetOp1();
@@ -1050,9 +1050,24 @@ int LinearScan::BuildHWIntrinsic(GenTreeHWIntrinsic* intrinsicTree)
 
     if (intrin.op1 != nullptr)
     {
-        // If we have an RMW intrinsic, we want to preference op1Reg to the target if
-        // op1 is not contained.
-        if (isRMW)
+        bool simdRegToSimdRegMove = false;
+
+        if ((intrin.id == NI_Vector64_CreateScalarUnsafe) || (intrin.id == NI_Vector128_CreateScalarUnsafe))
+        {
+            simdRegToSimdRegMove = varTypeIsFloating(intrin.op1);
+        }
+        else if (intrin.id == NI_AdvSimd_Arm64_DuplicateToVector64)
+        {
+            simdRegToSimdRegMove = (intrin.op1->TypeGet() == TYP_DOUBLE);
+        }
+        else if ((intrin.id == NI_Vector64_ToScalar) || (intrin.id == NI_Vector128_ToScalar))
+        {
+            simdRegToSimdRegMove = varTypeIsFloating(intrinsicTree);
+        }
+
+        // If we have an RMW intrinsic or an intrinsic with simple move semantic between two SIMD registers,
+        // we want to preference op1Reg to the target if op1 is not contained.
+        if (isRMW || simdRegToSimdRegMove)
         {
             tgtPrefOp1 = !intrin.op1->isContained();
         }
diff --git a/src/coreclr/src/jit/lsraxarch.cpp b/src/coreclr/src/jit/lsraxarch.cpp
index 8895dc95ecec9f..e0be880d16d757 100644
--- a/src/coreclr/src/jit/lsraxarch.cpp
+++ b/src/coreclr/src/jit/lsraxarch.cpp
@@ -1779,9 +1779,9 @@ int LinearScan::BuildIntrinsic(GenTree* tree)
     assert(op1->TypeGet() == tree->TypeGet());
     RefPosition* internalFloatDef = nullptr;
 
-    switch (tree->AsIntrinsic()->gtIntrinsicId)
+    switch (tree->AsIntrinsic()->gtIntrinsicName)
     {
-        case CORINFO_INTRINSIC_Abs:
+        case NI_System_Math_Abs:
             // Abs(float x) = x & 0x7fffffff
             // Abs(double x) = x & 0x7ffffff ffffffff
 
@@ -1798,16 +1798,16 @@ int LinearScan::BuildIntrinsic(GenTree* tree)
             break;
 
 #ifdef TARGET_X86
-        case CORINFO_INTRINSIC_Cos:
-        case CORINFO_INTRINSIC_Sin:
+        case NI_System_Math_Cos:
+        case NI_System_Math_Sin:
             NYI_X86("Math intrinsics Cos and Sin");
             break;
 #endif // TARGET_X86
 
-        case CORINFO_INTRINSIC_Sqrt:
-        case CORINFO_INTRINSIC_Round:
-        case CORINFO_INTRINSIC_Ceiling:
-        case CORINFO_INTRINSIC_Floor:
+        case NI_System_Math_Sqrt:
+        case NI_System_Math_Round:
+        case NI_System_Math_Ceiling:
+        case NI_System_Math_Floor:
             break;
 
         default:
diff --git a/src/coreclr/src/jit/morph.cpp b/src/coreclr/src/jit/morph.cpp
index 4d420dabaa8091..81342722a3807e 100644
--- a/src/coreclr/src/jit/morph.cpp
+++ b/src/coreclr/src/jit/morph.cpp
@@ -2707,6 +2707,13 @@ void Compiler::fgInitArgInfo(GenTreeCall* call)
         indirectCellAddress->AsIntCon()->gtTargetHandle = (size_t)call->gtCallMethHnd;
 #endif
         indirectCellAddress->SetRegNum(REG_R2R_INDIRECT_PARAM);
+#ifdef TARGET_ARM
+        // Issue #xxxx : Don't attempt to CSE this constant on ARM32
+        //
+        // This constant has specific register requirements, and LSRA doesn't currently correctly
+        // handle them when the value is in a CSE'd local.
+        indirectCellAddress->SetDoNotCSE();
+#endif // TARGET_ARM
 
         // Push the stub address onto the list of arguments.
         call->gtCallArgs = gtPrependNewCallArg(indirectCellAddress, call->gtCallArgs);
@@ -4602,7 +4609,7 @@ GenTree* Compiler::fgMorphMultiregStructArg(GenTree* arg, fgArgTabEntry* fgEntry
             assert(varNum < lvaCount);
             LclVarDsc* varDsc = &lvaTable[varNum];
 
-            unsigned baseOffset = argValue->OperIs(GT_LCL_FLD) ? argValue->AsLclFld()->GetLclOffs() : 0;
+            unsigned baseOffset = varNode->GetLclOffs();
             unsigned lastOffset = baseOffset + structSize;
 
             // The allocated size of our LocalVar must be at least as big as lastOffset
@@ -5735,7 +5742,9 @@ GenTree* Compiler::fgMorphStackArgForVarArgs(unsigned lclNum, var_types varType,
         GenTree* tree;
         if (varTypeIsStruct(varType))
         {
-            tree = new (this, GT_BLK) GenTreeBlk(GT_BLK, TYP_STRUCT, ptrArg, typGetBlkLayout(varDsc->lvExactSize));
+            CORINFO_CLASS_HANDLE typeHnd = varDsc->lvVerTypeInfo.GetClassHandle();
+            assert(typeHnd != nullptr);
+            tree = gtNewObjNode(typeHnd, ptrArg);
         }
         else
         {
@@ -5883,7 +5892,7 @@ GenTree* Compiler::fgMorphField(GenTree* tree, MorphAddrContext* mac)
     }
 
 #ifdef FEATURE_SIMD
-    // if this field belongs to simd struct, translate it to simd instrinsic.
+    // if this field belongs to simd struct, translate it to simd intrinsic.
     if (mac == nullptr)
     {
         GenTree* newTree = fgMorphFieldToSIMDIntrinsicGet(tree);
@@ -7894,21 +7903,54 @@ GenTree* Compiler::fgCreateCallDispatcherAndGetResult(GenTreeCall*          orig
 
     // Add return value arg.
     GenTree*     retValArg;
-    GenTree*     retVal    = nullptr;
-    unsigned int newRetLcl = BAD_VAR_NUM;
+    GenTree*     retVal           = nullptr;
+    unsigned int newRetLcl        = BAD_VAR_NUM;
+    GenTree*     copyToRetBufNode = nullptr;
 
-    // Use existing retbuf if there is one.
     if (origCall->HasRetBufArg())
     {
         JITDUMP("Transferring retbuf\n");
         GenTree* retBufArg = origCall->gtCallArgs->GetNode();
-        assert((info.compRetBuffArg != BAD_VAR_NUM) && retBufArg->OperIsLocal() &&
-               (retBufArg->AsLclVarCommon()->GetLclNum() == info.compRetBuffArg));
 
-        retValArg = retBufArg;
+        assert(info.compRetBuffArg != BAD_VAR_NUM);
+        assert(retBufArg->OperIsLocal());
+        assert(retBufArg->AsLclVarCommon()->GetLclNum() == info.compRetBuffArg);
+
+        if (info.compRetBuffDefStack)
+        {
+            // Use existing retbuf.
+            retValArg = retBufArg;
+        }
+        else
+        {
+            // Caller return buffer argument retBufArg can point to GC heap while the dispatcher expects
+            // the return value argument retValArg to point to the stack.
+            // We use a temporary stack allocated return buffer to hold the value during the dispatcher call
+            // and copy the value back to the caller return buffer after that.
+            unsigned int tmpRetBufNum = lvaGrabTemp(true DEBUGARG("substitute local for return buffer"));
+
+            constexpr bool unsafeValueClsCheck = false;
+            lvaSetStruct(tmpRetBufNum, origCall->gtRetClsHnd, unsafeValueClsCheck);
+            lvaSetVarAddrExposed(tmpRetBufNum);
+
+            var_types tmpRetBufType = lvaGetDesc(tmpRetBufNum)->TypeGet();
+
+            retValArg = gtNewOperNode(GT_ADDR, TYP_I_IMPL, gtNewLclvNode(tmpRetBufNum, tmpRetBufType));
+
+            var_types callerRetBufType = lvaGetDesc(info.compRetBuffArg)->TypeGet();
+
+            GenTree* dstAddr = gtNewLclvNode(info.compRetBuffArg, callerRetBufType);
+            GenTree* dst     = gtNewObjNode(info.compMethodInfo->args.retTypeClass, dstAddr);
+            GenTree* src     = gtNewLclvNode(tmpRetBufNum, tmpRetBufType);
+
+            constexpr bool isVolatile  = false;
+            constexpr bool isCopyBlock = true;
+            copyToRetBufNode           = gtNewBlkOpNode(dst, src, isVolatile, isCopyBlock);
+        }
+
         if (origCall->gtType != TYP_VOID)
         {
-            retVal = gtClone(retValArg);
+            retVal = gtClone(retBufArg);
         }
     }
     else if (origCall->gtType != TYP_VOID)
@@ -7962,22 +8004,30 @@ GenTree* Compiler::fgCreateCallDispatcherAndGetResult(GenTreeCall*          orig
     GenTree* retAddrSlot           = gtNewOperNode(GT_ADDR, TYP_I_IMPL, gtNewLclvNode(lvaRetAddrVar, TYP_I_IMPL));
     callDispatcherNode->gtCallArgs = gtPrependNewCallArg(retAddrSlot, callDispatcherNode->gtCallArgs);
 
+    GenTree* finalTree = callDispatcherNode;
+
+    if (copyToRetBufNode != nullptr)
+    {
+        finalTree = gtNewOperNode(GT_COMMA, TYP_VOID, callDispatcherNode, copyToRetBufNode);
+    }
+
     if (origCall->gtType == TYP_VOID)
     {
-        return callDispatcherNode;
+        return finalTree;
     }
 
     assert(retVal != nullptr);
-    GenTree* comma = gtNewOperNode(GT_COMMA, origCall->TypeGet(), callDispatcherNode, retVal);
+    finalTree = gtNewOperNode(GT_COMMA, origCall->TypeGet(), finalTree, retVal);
+
     // The JIT seems to want to CSE this comma and messes up multi-reg ret
     // values in the process. Just avoid CSE'ing this tree entirely in that
     // case.
     if (origCall->HasMultiRegRetVal())
     {
-        comma->gtFlags |= GTF_DONT_CSE;
+        finalTree->gtFlags |= GTF_DONT_CSE;
     }
 
-    return comma;
+    return finalTree;
 }
 
 //------------------------------------------------------------------------
@@ -8898,7 +8948,7 @@ GenTree* Compiler::fgMorphCall(GenTreeCall* call)
 
         GenTree* dest = call->gtCallArgs->GetNode();
         assert(dest->OperGet() != GT_ARGPLACE); // If it was, we'd be in a remorph, which we've already excluded above.
-        if (dest->gtType == TYP_BYREF && !(dest->OperGet() == GT_ADDR && dest->AsOp()->gtOp1->OperGet() == GT_LCL_VAR))
+        if (dest->TypeIs(TYP_BYREF) && !dest->IsLocalAddrExpr())
         {
             // We'll exempt helper calls from this, assuming that the helper implementation
             // follows the old convention, and does whatever barrier is required.
@@ -12159,7 +12209,7 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac)
 
 #ifdef TARGET_ARM
         case GT_INTRINSIC:
-            if (tree->AsIntrinsic()->gtIntrinsicId == CORINFO_INTRINSIC_Round)
+            if (tree->AsIntrinsic()->gtIntrinsicName == NI_System_Math_Round)
             {
                 switch (tree->TypeGet())
                 {
diff --git a/src/coreclr/src/jit/namedintrinsiclist.h b/src/coreclr/src/jit/namedintrinsiclist.h
index 63d79fbeff19d0..bc84f851deac8a 100644
--- a/src/coreclr/src/jit/namedintrinsiclist.h
+++ b/src/coreclr/src/jit/namedintrinsiclist.h
@@ -12,9 +12,28 @@ enum NamedIntrinsic : unsigned short
 
     NI_System_Enum_HasFlag,
     NI_System_Math_FusedMultiplyAdd,
+    NI_System_Math_Sin,
+    NI_System_Math_Cos,
+    NI_System_Math_Cbrt,
+    NI_System_Math_Sqrt,
+    NI_System_Math_Abs,
     NI_System_Math_Round,
-    NI_System_MathF_FusedMultiplyAdd,
-    NI_System_MathF_Round,
+    NI_System_Math_Cosh,
+    NI_System_Math_Sinh,
+    NI_System_Math_Tan,
+    NI_System_Math_Tanh,
+    NI_System_Math_Asin,
+    NI_System_Math_Asinh,
+    NI_System_Math_Acos,
+    NI_System_Math_Acosh,
+    NI_System_Math_Atan,
+    NI_System_Math_Atan2,
+    NI_System_Math_Atanh,
+    NI_System_Math_Log10,
+    NI_System_Math_Pow,
+    NI_System_Math_Exp,
+    NI_System_Math_Ceiling,
+    NI_System_Math_Floor,
     NI_System_Collections_Generic_EqualityComparer_get_Default,
     NI_System_Buffers_Binary_BinaryPrimitives_ReverseEndianness,
     NI_System_GC_KeepAlive,
diff --git a/src/coreclr/src/jit/optcse.cpp b/src/coreclr/src/jit/optcse.cpp
index 46e834df0dc4f0..06339353826b3b 100644
--- a/src/coreclr/src/jit/optcse.cpp
+++ b/src/coreclr/src/jit/optcse.cpp
@@ -20,7 +20,9 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 /*****************************************************************************/
 
 /* static */
-const size_t Compiler::s_optCSEhashSize = EXPSET_SZ * 2;
+const size_t Compiler::s_optCSEhashSizeInitial  = EXPSET_SZ * 2;
+const size_t Compiler::s_optCSEhashGrowthFactor = 2;
+const size_t Compiler::s_optCSEhashBucketSize   = 4;
 
 /*****************************************************************************
  *
@@ -36,11 +38,11 @@ void Compiler::optCSEstop()
 
     CSEdsc*  dsc;
     CSEdsc** ptr;
-    unsigned cnt;
+    size_t   cnt;
 
     optCSEtab = new (this, CMK_CSE) CSEdsc*[optCSECandidateCount]();
 
-    for (cnt = s_optCSEhashSize, ptr = optCSEhash; cnt; cnt--, ptr++)
+    for (cnt = optCSEhashSize, ptr = optCSEhash; cnt; cnt--, ptr++)
     {
         for (dsc = *ptr; dsc; dsc = dsc->csdNextInBucket)
         {
@@ -373,7 +375,11 @@ void Compiler::optValnumCSE_Init()
     cseMaskTraits = nullptr;
 
     // Allocate and clear the hash bucket table
-    optCSEhash = new (this, CMK_CSE) CSEdsc*[s_optCSEhashSize]();
+    optCSEhash = new (this, CMK_CSE) CSEdsc*[s_optCSEhashSizeInitial]();
+
+    optCSEhashSize                 = s_optCSEhashSizeInitial;
+    optCSEhashMaxCountBeforeResize = optCSEhashSize * s_optCSEhashBucketSize;
+    optCSEhashCount                = 0;
 
     optCSECandidateCount = 0;
     optDoCSE             = false; // Stays false until we find duplicate CSE tree
@@ -382,6 +388,20 @@ void Compiler::optValnumCSE_Init()
     optCseCheckedBoundMap = nullptr;
 }
 
+unsigned optCSEKeyToHashIndex(size_t key, size_t optCSEhashSize)
+{
+    unsigned hash;
+
+    hash = (unsigned)key;
+#ifdef TARGET_64BIT
+    hash ^= (unsigned)(key >> 32);
+#endif
+    hash *= (unsigned)(optCSEhashSize + 1);
+    hash >>= 7;
+
+    return hash % optCSEhashSize;
+}
+
 //---------------------------------------------------------------------------
 // optValnumCSE_Index:
 //               - Returns the CSE index to use for this tree,
@@ -401,10 +421,26 @@ void Compiler::optValnumCSE_Init()
 //
 unsigned Compiler::optValnumCSE_Index(GenTree* tree, Statement* stmt)
 {
-    unsigned key;
-    unsigned hash;
+    size_t   key;
     unsigned hval;
     CSEdsc*  hashDsc;
+    bool     isIntConstHash       = false;
+    bool     enableSharedConstCSE = false;
+    int      configValue          = JitConfig.JitConstCSE();
+
+#if defined(TARGET_ARM64)
+    // ARM64 - allow to combine with nearby offsets, when config is not 2 or 4
+    if ((configValue != CONST_CSE_ENABLE_ARM64_NO_SHARING) && (configValue != CONST_CSE_ENABLE_ALL_NO_SHARING))
+    {
+        enableSharedConstCSE = true;
+    }
+#endif // TARGET_ARM64
+
+    // All Platforms - also allow to combine with nearby offsets, when config is 3
+    if (configValue == CONST_CSE_ENABLE_ALL)
+    {
+        enableSharedConstCSE = true;
+    }
 
     // We use the liberal Value numbers when building the set of CSE
     ValueNum vnLib     = tree->GetVN(VNK_Liberal);
@@ -446,11 +482,11 @@ unsigned Compiler::optValnumCSE_Index(GenTree* tree, Statement* stmt)
         //
         if (vnOp2Lib != vnLib)
         {
-            key = (unsigned)vnLib; // include the exc set in the hash key
+            key = vnLib; // include the exc set in the hash key
         }
         else
         {
-            key = (unsigned)vnLibNorm;
+            key = vnLibNorm;
         }
 
         // If we didn't do the above we would have op1 as the CSE def
@@ -459,18 +495,33 @@ unsigned Compiler::optValnumCSE_Index(GenTree* tree, Statement* stmt)
         //
         assert(vnLibNorm == vnStore->VNNormalValue(vnOp2Lib));
     }
-    else // Not a GT_COMMA
+    else if (enableSharedConstCSE && tree->IsIntegralConst())
+    {
+        assert(vnStore->IsVNConstant(vnLibNorm));
+        key = vnStore->CoercedConstantValue<size_t>(vnLibNorm);
+
+        // We don't shared small offset constants when we require a reloc
+        if (!tree->AsIntConCommon()->ImmedValNeedsReloc(this))
+        {
+            // Make constants that have the same upper bits use the same key
+
+            // Shift the key right by CSE_CONST_SHARED_LOW_BITS bits, this sets the upper bits to zero
+            key >>= CSE_CONST_SHARED_LOW_BITS;
+        }
+        assert((key & TARGET_SIGN_BIT) == 0);
+
+        // We use the sign bit of 'key' as the flag
+        // that we are hashing constants (with a shared offset)
+        key |= TARGET_SIGN_BIT;
+    }
+    else // Not a GT_COMMA or a GT_CNS_INT
     {
-        key = (unsigned)vnLibNorm;
+        key = vnLibNorm;
     }
 
     // Compute the hash value for the expression
 
-    hash = key;
-    hash *= (unsigned)(s_optCSEhashSize + 1);
-    hash >>= 7;
-
-    hval = hash % s_optCSEhashSize;
+    hval = optCSEKeyToHashIndex(key, optCSEhashSize);
 
     /* Look for a matching index in the hash table */
 
@@ -480,6 +531,12 @@ unsigned Compiler::optValnumCSE_Index(GenTree* tree, Statement* stmt)
     {
         if (hashDsc->csdHashKey == key)
         {
+            // Check for mismatched types on GT_CNS_INT nodes
+            if ((tree->OperGet() == GT_CNS_INT) && (tree->TypeGet() != hashDsc->csdTree->TypeGet()))
+            {
+                continue;
+            }
+
             treeStmtLst* newElem;
 
             /* Have we started the list of matching nodes? */
@@ -582,9 +639,42 @@ unsigned Compiler::optValnumCSE_Index(GenTree* tree, Statement* stmt)
 
         if (optCSECandidateCount < MAX_CSE_CNT)
         {
+            if (optCSEhashCount == optCSEhashMaxCountBeforeResize)
+            {
+                size_t   newOptCSEhashSize = optCSEhashSize * s_optCSEhashGrowthFactor;
+                CSEdsc** newOptCSEhash     = new (this, CMK_CSE) CSEdsc*[newOptCSEhashSize]();
+
+                // Iterate through each existing entry, moving to the new table
+                CSEdsc** ptr;
+                CSEdsc*  dsc;
+                size_t   cnt;
+                for (cnt = optCSEhashSize, ptr = optCSEhash; cnt; cnt--, ptr++)
+                {
+                    for (dsc = *ptr; dsc;)
+                    {
+                        CSEdsc* nextDsc = dsc->csdNextInBucket;
+
+                        size_t newHval = optCSEKeyToHashIndex(dsc->csdHashKey, newOptCSEhashSize);
+
+                        // Move CSEdsc to bucket in enlarged table
+                        dsc->csdNextInBucket   = newOptCSEhash[newHval];
+                        newOptCSEhash[newHval] = dsc;
+
+                        dsc = nextDsc;
+                    }
+                }
+
+                optCSEhash                     = newOptCSEhash;
+                optCSEhashSize                 = newOptCSEhashSize;
+                optCSEhashMaxCountBeforeResize = optCSEhashMaxCountBeforeResize * s_optCSEhashGrowthFactor;
+            }
+
+            ++optCSEhashCount;
             hashDsc = new (this, CMK_CSE) CSEdsc;
 
             hashDsc->csdHashKey        = key;
+            hashDsc->csdConstDefValue  = 0;
+            hashDsc->csdConstDefVN     = vnStore->VNForNull(); // uninit value
             hashDsc->csdIndex          = 0;
             hashDsc->csdLiveAcrossCall = false;
             hashDsc->csdDefCount       = 0;
@@ -645,8 +735,17 @@ unsigned Compiler::optValnumCSE_Index(GenTree* tree, Statement* stmt)
 #ifdef DEBUG
         if (verbose)
         {
-            printf("\nCSE candidate #%02u, vn=", CSEindex);
-            vnPrint(key, 0);
+            printf("\nCSE candidate #%02u, key=", CSEindex);
+            if (!Compiler::Is_Shared_Const_CSE(key))
+            {
+                vnPrint((unsigned)key, 0);
+            }
+            else
+            {
+                size_t kVal = Compiler::Decode_Shared_Const_CSE_Value(key);
+                printf("K_%p", dspPtr(kVal));
+            }
+
             printf(" in " FMT_BB ", [cost=%2u, size=%2u]: \n", compCurBB->bbNum, tree->GetCostEx(), tree->GetCostSz());
             gtDispTree(tree);
         }
@@ -666,6 +765,29 @@ unsigned Compiler::optValnumCSE_Locate()
 {
     // Locate CSE candidates and assign them indices
 
+    bool enableConstCSE = true;
+
+    int configValue = JitConfig.JitConstCSE();
+
+    // all platforms - disable CSE of constant values when config is 1
+    if (configValue == CONST_CSE_DISABLE_ALL)
+    {
+        enableConstCSE = false;
+    }
+
+#if !defined(TARGET_ARM64)
+    // non-ARM64 platforms - disable by default
+    //
+    enableConstCSE = false;
+
+    // Check for the two enable cases for all platforms
+    //
+    if ((configValue == CONST_CSE_ENABLE_ALL) || (configValue == CONST_CSE_ENABLE_ALL_NO_SHARING))
+    {
+        enableConstCSE = true;
+    }
+#endif
+
     for (BasicBlock* block = fgFirstBB; block != nullptr; block = block->bbNext)
     {
         /* Make the block publicly available */
@@ -691,6 +813,16 @@ unsigned Compiler::optValnumCSE_Locate()
                     optCseUpdateCheckedBoundMap(tree);
                 }
 
+                // Don't allow CSE of constants if it is disabled
+                //
+                if (tree->IsIntegralConst())
+                {
+                    if (!enableConstCSE)
+                    {
+                        continue;
+                    }
+                }
+
                 if (!optIsCSEcandidate(tree))
                 {
                     continue;
@@ -701,15 +833,17 @@ unsigned Compiler::optValnumCSE_Locate()
                     continue;
                 }
 
-                // Don't CSE constant values, instead let the Value Number
-                // based Assertion Prop phase handle them.  Here, unlike
-                // the rest of optCSE, we use the conservative value number
+                // We want to CSE simple constant leaf nodes, but we don't want to
+                // CSE non-leaf trees that compute CSE constant values.
+                // Instead we let the Value Number based Assertion Prop phase handle them.
+                //
+                // Here, unlike the rest of optCSE, we use the conservative value number
                 // rather than the liberal one, since the conservative one
                 // is what the Value Number based Assertion Prop will use
                 // and the point is to avoid optimizing cases that it will
                 // handle.
                 //
-                if (vnStore->IsVNConstant(vnStore->VNConservativeNormalValue(tree->gtVNPair)))
+                if (!tree->OperIsLeaf() && vnStore->IsVNConstant(vnStore->VNConservativeNormalValue(tree->gtVNPair)))
                 {
                     continue;
                 }
@@ -1428,23 +1562,28 @@ void Compiler::optValnumCSE_Availablity()
                             }
                         }
 
-                        // Record or update the value of desc->defConservNormVN
+                        // For shared const CSE we don't set/use the defConservNormVN
                         //
-                        ValueNum theConservNormVN = vnStore->VNConservativeNormalValue(tree->gtVNPair);
-
-                        // Is defConservNormVN still set to the uninit marker value of VNForNull() ?
-                        if (desc->defConservNormVN == vnStore->VNForNull())
-                        {
-                            // This is the first def that we have visited, set defConservNormVN
-                            desc->defConservNormVN = theConservNormVN;
-                        }
-                        else
+                        if (!Is_Shared_Const_CSE(desc->csdHashKey))
                         {
-                            // Check to see if all defs have the same conservative normal VN
-                            if (theConservNormVN != desc->defConservNormVN)
+                            // Record or update the value of desc->defConservNormVN
+                            //
+                            ValueNum theConservNormVN = vnStore->VNConservativeNormalValue(tree->gtVNPair);
+
+                            // Is defConservNormVN still set to the uninit marker value of VNForNull() ?
+                            if (desc->defConservNormVN == vnStore->VNForNull())
+                            {
+                                // This is the first def that we have visited, set defConservNormVN
+                                desc->defConservNormVN = theConservNormVN;
+                            }
+                            else
                             {
-                                // This candidate has defs with differing conservative normal VNs, mark it with NoVN
-                                desc->defConservNormVN = ValueNumStore::NoVN; // record the marker for differing VNs
+                                // Check to see if all defs have the same conservative normal VN
+                                if (theConservNormVN != desc->defConservNormVN)
+                                {
+                                    // This candidate has defs with differing conservative normal VNs, mark it with NoVN
+                                    desc->defConservNormVN = ValueNumStore::NoVN; // record the marker for differing VNs
+                                }
                             }
                         }
 
@@ -1894,9 +2033,19 @@ class CSE_Heuristic
                     cost = dsc->csdTree->GetCostEx();
                 }
 
-                printf("CSE #%02u, {$%-3x, $%-3x} useCnt=%d: [def=%3u, use=%3u, cost=%3u%s]\n        :: ",
-                       dsc->csdIndex, dsc->csdHashKey, dsc->defExcSetPromise, dsc->csdUseCount, def, use, cost,
-                       dsc->csdLiveAcrossCall ? ", call" : "      ");
+                if (!Compiler::Is_Shared_Const_CSE(dsc->csdHashKey))
+                {
+                    printf("CSE #%02u, {$%-3x, $%-3x} useCnt=%d: [def=%3u, use=%3u, cost=%3u%s]\n        :: ",
+                           dsc->csdIndex, dsc->csdHashKey, dsc->defExcSetPromise, dsc->csdUseCount, def, use, cost,
+                           dsc->csdLiveAcrossCall ? ", call" : "      ");
+                }
+                else
+                {
+                    size_t kVal = Compiler::Decode_Shared_Const_CSE_Value(dsc->csdHashKey);
+                    printf("CSE #%02u, {K_%p} useCnt=%d: [def=%3u, use=%3u, cost=%3u%s]\n        :: ", dsc->csdIndex,
+                           dspPtr(kVal), dsc->csdUseCount, def, use, cost,
+                           dsc->csdLiveAcrossCall ? ", call" : "      ");
+                }
 
                 m_pCompiler->gtDispTree(expr, nullptr, nullptr, true);
             }
@@ -2377,8 +2526,9 @@ class CSE_Heuristic
 #ifdef DEBUG
                     if (m_pCompiler->verbose)
                     {
-                        printf("Moderate CSE Promotion (CSE is live across a call) (%u >= %u)\n", cseRefCnt,
-                               moderateRefCnt);
+                        printf("Moderate CSE Promotion (%s) (%u >= %u)\n",
+                               candidate->LiveAcrossCall() ? "CSE is live across a call" : "not enregisterable",
+                               cseRefCnt, moderateRefCnt);
                     }
 #endif
                     cse_def_cost = 2;
@@ -2409,8 +2559,9 @@ class CSE_Heuristic
 #ifdef DEBUG
                     if (m_pCompiler->verbose)
                     {
-                        printf("Conservative CSE Promotion (CSE never live at call) (%u < %u)\n", cseRefCnt,
-                               moderateRefCnt);
+                        printf("Conservative CSE Promotion (%s) (%u < %u)\n",
+                               candidate->LiveAcrossCall() ? "CSE is live across a call" : "not enregisterable",
+                               cseRefCnt, moderateRefCnt);
                     }
 #endif
                     cse_def_cost = 2;
@@ -2660,8 +2811,7 @@ class CSE_Heuristic
         //
         //  Later we will unmark any nested CSE's for the CSE uses.
         //
-        Compiler::CSEdsc*      dsc = successfulCandidate->CseDsc();
-        Compiler::treeStmtLst* lst;
+        Compiler::CSEdsc* dsc = successfulCandidate->CseDsc();
 
         // If there's just a single def for the CSE, we'll put this
         // CSE into SSA form on the fly. We won't need any PHIs.
@@ -2678,53 +2828,122 @@ class CSE_Heuristic
             cseSsaNum               = m_pCompiler->lvaTable[cseLclVarNum].lvPerSsaData.AllocSsaNum(allocator);
         }
 
-#ifdef DEBUG
         // Verify that all of the ValueNumbers in this list are correct as
         // Morph will change them when it performs a mutating operation.
         //
-        ValueNum firstVN = ValueNumStore::NoVN;
-        ValueNum currVN;
-        bool     allSame = true;
+        bool                   setRefCnt      = true;
+        bool                   allSame        = true;
+        bool                   isSharedConst  = Compiler::Is_Shared_Const_CSE(dsc->csdHashKey);
+        ValueNum               bestVN         = ValueNumStore::NoVN;
+        bool                   bestIsDef      = false;
+        ssize_t                bestConstValue = 0;
+        Compiler::treeStmtLst* lst            = dsc->csdTreeList;
 
-        lst = dsc->csdTreeList;
         while (lst != nullptr)
         {
             // Ignore this node if the gtCSEnum value has been cleared
             if (IS_CSE_INDEX(lst->tslTree->gtCSEnum))
             {
                 // We used the liberal Value numbers when building the set of CSE
-                currVN = m_pCompiler->vnStore->VNLiberalNormalValue(lst->tslTree->gtVNPair);
+                ValueNum currVN = m_pCompiler->vnStore->VNLiberalNormalValue(lst->tslTree->gtVNPair);
                 assert(currVN != ValueNumStore::NoVN);
+                ssize_t curConstValue = isSharedConst ? m_pCompiler->vnStore->CoercedConstantValue<ssize_t>(currVN) : 0;
+
+                GenTree* exp   = lst->tslTree;
+                bool     isDef = IS_CSE_DEF(exp->gtCSEnum);
 
-                if (firstVN == ValueNumStore::NoVN)
+                if (bestVN == ValueNumStore::NoVN)
                 {
-                    firstVN = currVN;
+                    // first entry
+                    // set bestVN
+                    bestVN = currVN;
+
+                    if (isSharedConst)
+                    {
+                        // set bestConstValue and bestIsDef
+                        bestConstValue = curConstValue;
+                        bestIsDef      = isDef;
+                    }
                 }
-                else if (currVN != firstVN)
+                else if (currVN != bestVN)
                 {
+                    assert(isSharedConst); // Must be true when we have differing VNs
+
+                    // subsequent entry
+                    // clear allSame and check for a lower constant
                     allSame = false;
-                    break;
+
+                    ssize_t diff = curConstValue - bestConstValue;
+
+                    // The ARM64 ldr addressing modes allow for a subtraction of up to 255
+                    // so we will allow the diff to be up to -255 before replacing a CSE def
+                    // This will minimize the number of extra subtract instructions.
+                    //
+                    if ((bestIsDef && (diff < -255)) || (!bestIsDef && (diff < 0)))
+                    {
+                        // set new bestVN, bestConstValue and bestIsDef
+                        bestVN         = currVN;
+                        bestConstValue = curConstValue;
+                        bestIsDef      = isDef;
+                    }
+                }
+
+                BasicBlock*          blk       = lst->tslBlock;
+                BasicBlock::weight_t curWeight = blk->getBBWeight(m_pCompiler);
+
+                if (setRefCnt)
+                {
+                    m_pCompiler->lvaTable[cseLclVarNum].setLvRefCnt(1);
+                    m_pCompiler->lvaTable[cseLclVarNum].setLvRefCntWtd(curWeight);
+                    setRefCnt = false;
+                }
+                else
+                {
+                    m_pCompiler->lvaTable[cseLclVarNum].incRefCnts(curWeight, m_pCompiler);
+                }
+
+                // A CSE Def references the LclVar twice
+                //
+                if (isDef)
+                {
+                    m_pCompiler->lvaTable[cseLclVarNum].incRefCnts(curWeight, m_pCompiler);
                 }
             }
             lst = lst->tslNext;
         }
-        if (!allSame)
+
+        dsc->csdConstDefValue = bestConstValue;
+        dsc->csdConstDefVN    = bestVN;
+
+#ifdef DEBUG
+        if (m_pCompiler->verbose)
         {
-            lst                = dsc->csdTreeList;
-            GenTree* firstTree = lst->tslTree;
-            printf("In %s, CSE (oper = %s, type = %s) has differing VNs: ", m_pCompiler->info.compFullName,
-                   GenTree::OpName(firstTree->OperGet()), varTypeName(firstTree->TypeGet()));
-            while (lst != nullptr)
+            if (!allSame)
             {
-                if (IS_CSE_INDEX(lst->tslTree->gtCSEnum))
+                if (isSharedConst)
                 {
-                    currVN = m_pCompiler->vnStore->VNLiberalNormalValue(lst->tslTree->gtVNPair);
-                    printf("0x%x(%s " FMT_VN ") ", lst->tslTree, IS_CSE_USE(lst->tslTree->gtCSEnum) ? "use" : "def",
-                           currVN);
+                    printf("\nWe have shared Const CSE's and selected " FMT_VN " with a value of 0x%p as the base.\n",
+                           dsc->csdConstDefVN, dspPtr(dsc->csdConstDefValue));
+                }
+                else // !isSharedConst
+                {
+                    lst                = dsc->csdTreeList;
+                    GenTree* firstTree = lst->tslTree;
+                    printf("In %s, CSE (oper = %s, type = %s) has differing VNs: ", m_pCompiler->info.compFullName,
+                           GenTree::OpName(firstTree->OperGet()), varTypeName(firstTree->TypeGet()));
+                    while (lst != nullptr)
+                    {
+                        if (IS_CSE_INDEX(lst->tslTree->gtCSEnum))
+                        {
+                            ValueNum currVN = m_pCompiler->vnStore->VNLiberalNormalValue(lst->tslTree->gtVNPair);
+                            printf("0x%x(%s " FMT_VN ") ", lst->tslTree,
+                                   IS_CSE_USE(lst->tslTree->gtCSEnum) ? "use" : "def", currVN);
+                        }
+                        lst = lst->tslNext;
+                    }
+                    printf("\n");
                 }
-                lst = lst->tslNext;
             }
-            printf("\n");
         }
 #endif // DEBUG
 
@@ -2762,7 +2981,8 @@ class CSE_Heuristic
 
             // The cseLclVarType must be a compatible with expTyp
             //
-            noway_assert(IsCompatibleType(cseLclVarTyp, expTyp));
+            ValueNumStore* vnStore = m_pCompiler->vnStore;
+            noway_assert(IsCompatibleType(cseLclVarTyp, expTyp) || (dsc->csdConstDefVN != vnStore->VNForNull()));
 
             // This will contain the replacement tree for exp
             // It will either be the CSE def or CSE ref
@@ -2790,63 +3010,86 @@ class CSE_Heuristic
                 // We will replace the CSE ref with a new tree
                 // this is typically just a simple use of the new CSE LclVar
                 //
-                ValueNumStore* vnStore = m_pCompiler->vnStore;
-                cse                    = m_pCompiler->gtNewLclvNode(cseLclVarNum, cseLclVarTyp);
 
-                // Assign the ssa num for the use. Note it may be the reserved num.
-                cse->AsLclVarCommon()->SetSsaNum(cseSsaNum);
+                // Create a reference to the CSE temp
+                GenTree* cseLclVar = m_pCompiler->gtNewLclvNode(cseLclVarNum, cseLclVarTyp);
+                cseLclVar->gtVNPair.SetBoth(dsc->csdConstDefVN);
 
-                // assign the proper ValueNumber, A CSE use discards any exceptions
-                cse->gtVNPair = vnStore->VNPNormalPair(exp->gtVNPair);
-
-                ValueNum theConservativeVN = successfulCandidate->CseDsc()->defConservNormVN;
+                // Assign the ssa num for the lclvar use. Note it may be the reserved num.
+                cseLclVar->AsLclVarCommon()->SetSsaNum(cseSsaNum);
 
-                if (theConservativeVN != ValueNumStore::NoVN)
+                cse = cseLclVar;
+                if (isSharedConst)
                 {
-                    // All defs of this CSE share the same normal conservative VN, and we are rewriting this
-                    // use to fetch the same value with no reload, so we can safely propagate that
-                    // conservative VN to this use.  This can help range check elimination later on.
-                    cse->gtVNPair.SetConservative(theConservativeVN);
-
-                    // If the old VN was flagged as a checked bound, propagate that to the new VN
-                    // to make sure assertion prop will pay attention to this VN.
-                    ValueNum oldVN = exp->gtVNPair.GetConservative();
-                    if (!vnStore->IsVNConstant(theConservativeVN) && vnStore->IsVNCheckedBound(oldVN))
+                    ValueNum currVN   = m_pCompiler->vnStore->VNLiberalNormalValue(exp->gtVNPair);
+                    ssize_t  curValue = m_pCompiler->vnStore->CoercedConstantValue<ssize_t>(currVN);
+                    ssize_t  delta    = curValue - dsc->csdConstDefValue;
+                    if (delta != 0)
                     {
-                        vnStore->SetVNIsCheckedBound(theConservativeVN);
+                        GenTree* deltaNode = m_pCompiler->gtNewIconNode(delta, cseLclVarTyp);
+                        cse                = m_pCompiler->gtNewOperNode(GT_ADD, cseLclVarTyp, cseLclVar, deltaNode);
+                        cse->SetDoNotCSE();
                     }
+                }
 
-                    GenTree* cmp;
-                    if ((m_pCompiler->optCseCheckedBoundMap != nullptr) &&
-                        (m_pCompiler->optCseCheckedBoundMap->Lookup(exp, &cmp)))
-                    {
-                        // Propagate the new value number to this compare node as well, since
-                        // subsequent range check elimination will try to correlate it with
-                        // the other appearances that are getting CSEd.
+                // assign the proper ValueNumber, A CSE use discards any exceptions
+                cse->gtVNPair = vnStore->VNPNormalPair(exp->gtVNPair);
 
-                        ValueNum oldCmpVN = cmp->gtVNPair.GetConservative();
-                        ValueNum newCmpArgVN;
+                // shared const CSE has the correct value number assigned
+                // and both liberal and conservative are identical
+                // and they do not use theConservativeVN
+                //
+                if (!isSharedConst)
+                {
+                    ValueNum theConservativeVN = successfulCandidate->CseDsc()->defConservNormVN;
 
-                        ValueNumStore::CompareCheckedBoundArithInfo info;
-                        if (vnStore->IsVNCompareCheckedBound(oldCmpVN))
+                    if (theConservativeVN != ValueNumStore::NoVN)
+                    {
+                        // All defs of this CSE share the same normal conservative VN, and we are rewriting this
+                        // use to fetch the same value with no reload, so we can safely propagate that
+                        // conservative VN to this use.  This can help range check elimination later on.
+                        cse->gtVNPair.SetConservative(theConservativeVN);
+
+                        // If the old VN was flagged as a checked bound, propagate that to the new VN
+                        // to make sure assertion prop will pay attention to this VN.
+                        ValueNum oldVN = exp->gtVNPair.GetConservative();
+                        if (!vnStore->IsVNConstant(theConservativeVN) && vnStore->IsVNCheckedBound(oldVN))
                         {
-                            // Comparison is against the bound directly.
-
-                            newCmpArgVN = theConservativeVN;
-                            vnStore->GetCompareCheckedBound(oldCmpVN, &info);
+                            vnStore->SetVNIsCheckedBound(theConservativeVN);
                         }
-                        else
+
+                        GenTree* cmp;
+                        if ((m_pCompiler->optCseCheckedBoundMap != nullptr) &&
+                            (m_pCompiler->optCseCheckedBoundMap->Lookup(exp, &cmp)))
                         {
-                            // Comparison is against the bound +/- some offset.
+                            // Propagate the new value number to this compare node as well, since
+                            // subsequent range check elimination will try to correlate it with
+                            // the other appearances that are getting CSEd.
+
+                            ValueNum oldCmpVN = cmp->gtVNPair.GetConservative();
+                            ValueNum newCmpArgVN;
+
+                            ValueNumStore::CompareCheckedBoundArithInfo info;
+                            if (vnStore->IsVNCompareCheckedBound(oldCmpVN))
+                            {
+                                // Comparison is against the bound directly.
 
-                            assert(vnStore->IsVNCompareCheckedBoundArith(oldCmpVN));
-                            vnStore->GetCompareCheckedBoundArithInfo(oldCmpVN, &info);
-                            newCmpArgVN = vnStore->VNForFunc(vnStore->TypeOfVN(info.arrOp), (VNFunc)info.arrOper,
-                                                             info.arrOp, theConservativeVN);
+                                newCmpArgVN = theConservativeVN;
+                                vnStore->GetCompareCheckedBound(oldCmpVN, &info);
+                            }
+                            else
+                            {
+                                // Comparison is against the bound +/- some offset.
+
+                                assert(vnStore->IsVNCompareCheckedBoundArith(oldCmpVN));
+                                vnStore->GetCompareCheckedBoundArithInfo(oldCmpVN, &info);
+                                newCmpArgVN = vnStore->VNForFunc(vnStore->TypeOfVN(info.arrOp), (VNFunc)info.arrOper,
+                                                                 info.arrOp, theConservativeVN);
+                            }
+                            ValueNum newCmpVN = vnStore->VNForFunc(vnStore->TypeOfVN(oldCmpVN), (VNFunc)info.cmpOper,
+                                                                   info.cmpOp, newCmpArgVN);
+                            cmp->gtVNPair.SetConservative(newCmpVN);
                         }
-                        ValueNum newCmpVN = vnStore->VNForFunc(vnStore->TypeOfVN(oldCmpVN), (VNFunc)info.cmpOper,
-                                                               info.cmpOp, newCmpArgVN);
-                        cmp->gtVNPair.SetConservative(newCmpVN);
                     }
                 }
 #ifdef DEBUG
@@ -2878,10 +3121,9 @@ class CSE_Heuristic
                     }
 #endif
 
-                    GenTree*       cseVal         = cse;
-                    GenTree*       curSideEff     = sideEffList;
-                    ValueNumStore* vnStore        = m_pCompiler->vnStore;
-                    ValueNumPair   exceptions_vnp = ValueNumStore::VNPForEmptyExcSet();
+                    GenTree*     cseVal         = cse;
+                    GenTree*     curSideEff     = sideEffList;
+                    ValueNumPair exceptions_vnp = ValueNumStore::VNPForEmptyExcSet();
 
                     while ((curSideEff->OperGet() == GT_COMMA) || (curSideEff->OperGet() == GT_ASG))
                     {
@@ -2936,6 +3178,17 @@ class CSE_Heuristic
                 exp->gtCSEnum = NO_CSE; // clear the gtCSEnum field
 
                 GenTree* val = exp;
+                if (isSharedConst)
+                {
+                    ValueNum currVN   = m_pCompiler->vnStore->VNLiberalNormalValue(exp->gtVNPair);
+                    ssize_t  curValue = m_pCompiler->vnStore->CoercedConstantValue<ssize_t>(currVN);
+                    ssize_t  delta    = curValue - dsc->csdConstDefValue;
+                    if (delta != 0)
+                    {
+                        val = m_pCompiler->gtNewIconNode(dsc->csdConstDefValue, cseLclVarTyp);
+                        val->gtVNPair.SetBoth(dsc->csdConstDefVN);
+                    }
+                }
 
                 /* Create an assignment of the value to the temp */
                 GenTree* asg     = m_pCompiler->gtNewTempAssign(cseLclVarNum, val);
@@ -2977,19 +3230,37 @@ class CSE_Heuristic
                 }
 
                 /* Create a reference to the CSE temp */
-                GenTree* ref  = m_pCompiler->gtNewLclvNode(cseLclVarNum, cseLclVarTyp);
-                ref->gtVNPair = val->gtVNPair; // The new 'ref' is the same as 'val'
+                GenTree* cseLclVar = m_pCompiler->gtNewLclvNode(cseLclVarNum, cseLclVarTyp);
+                cseLclVar->gtVNPair.SetBoth(dsc->csdConstDefVN);
+
+                // Assign the ssa num for the lclvar use. Note it may be the reserved num.
+                cseLclVar->AsLclVarCommon()->SetSsaNum(cseSsaNum);
 
-                // Assign the ssa num for the ref use. Note it may be the reserved num.
-                ref->AsLclVarCommon()->SetSsaNum(cseSsaNum);
+                GenTree* cseUse = cseLclVar;
+                if (isSharedConst)
+                {
+                    ValueNum currVN   = m_pCompiler->vnStore->VNLiberalNormalValue(exp->gtVNPair);
+                    ssize_t  curValue = m_pCompiler->vnStore->CoercedConstantValue<ssize_t>(currVN);
+                    ssize_t  delta    = curValue - dsc->csdConstDefValue;
+                    if (delta != 0)
+                    {
+                        GenTree* deltaNode = m_pCompiler->gtNewIconNode(delta, cseLclVarTyp);
+                        cseUse             = m_pCompiler->gtNewOperNode(GT_ADD, cseLclVarTyp, cseLclVar, deltaNode);
+                        cseUse->SetDoNotCSE();
+                    }
+                }
+                cseUse->gtVNPair = val->gtVNPair; // The 'cseUse' is equal to 'val'
 
                 /* Create a comma node for the CSE assignment */
-                cse           = m_pCompiler->gtNewOperNode(GT_COMMA, expTyp, origAsg, ref);
-                cse->gtVNPair = ref->gtVNPair; // The comma's value is the same as 'val'
-                                               // as the assignment to the CSE LclVar
-                                               // cannot add any new exceptions
+                cse           = m_pCompiler->gtNewOperNode(GT_COMMA, expTyp, origAsg, cseUse);
+                cse->gtVNPair = cseUse->gtVNPair; // The comma's value is the same as 'val'
+                                                  // as the assignment to the CSE LclVar
+                                                  // cannot add any new exceptions
             }
 
+            cse->CopyReg(exp);  // The cse inheirits any reg num property from the orginal exp node
+            exp->ClearRegNum(); // The exp node (for a CSE def) no longer has a register requirement
+
             // Walk the statement 'stmt' and find the pointer
             // in the tree is pointing to 'exp'
             //
@@ -3069,9 +3340,19 @@ class CSE_Heuristic
 #ifdef DEBUG
             if (m_pCompiler->verbose)
             {
-                printf("\nConsidering CSE #%02u {$%-3x, $%-3x} [def=%3u, use=%3u, cost=%3u%s]\n", candidate.CseIndex(),
-                       dsc->csdHashKey, dsc->defExcSetPromise, candidate.DefCount(), candidate.UseCount(),
-                       candidate.Cost(), dsc->csdLiveAcrossCall ? ", call" : "      ");
+                if (!Compiler::Is_Shared_Const_CSE(dsc->csdHashKey))
+                {
+                    printf("\nConsidering CSE #%02u {$%-3x, $%-3x} [def=%3u, use=%3u, cost=%3u%s]\n",
+                           candidate.CseIndex(), dsc->csdHashKey, dsc->defExcSetPromise, candidate.DefCount(),
+                           candidate.UseCount(), candidate.Cost(), dsc->csdLiveAcrossCall ? ", call" : "      ");
+                }
+                else
+                {
+                    size_t kVal = Compiler::Decode_Shared_Const_CSE_Value(dsc->csdHashKey);
+                    printf("\nConsidering CSE #%02u {K_%p} [def=%3u, use=%3u, cost=%3u%s]\n", candidate.CseIndex(),
+                           dspPtr(kVal), candidate.DefCount(), candidate.UseCount(), candidate.Cost(),
+                           dsc->csdLiveAcrossCall ? ", call" : "      ");
+                }
                 printf("CSE Expression : \n");
                 m_pCompiler->gtDispTree(candidate.Expr());
                 printf("\n");
@@ -3306,8 +3587,11 @@ bool Compiler::optIsCSEcandidate(GenTree* tree)
 
             return (tree->AsOp()->gtOp1->gtOper != GT_ARR_ELEM);
 
-        case GT_CNS_INT:
         case GT_CNS_LNG:
+#ifndef TARGET_64BIT
+            return false; // Don't CSE 64-bit constants on 32-bit platforms
+#endif
+        case GT_CNS_INT:
         case GT_CNS_DBL:
         case GT_CNS_STR:
             return true; // We reach here only when CSE_CONSTS is enabled
diff --git a/src/coreclr/src/jit/rationalize.cpp b/src/coreclr/src/jit/rationalize.cpp
index b878a30beeae03..8054fda6e8ef46 100644
--- a/src/coreclr/src/jit/rationalize.cpp
+++ b/src/coreclr/src/jit/rationalize.cpp
@@ -726,7 +726,7 @@ Compiler::fgWalkResult Rationalizer::RewriteNode(GenTree** useEdge, Compiler::Ge
 
         case GT_INTRINSIC:
             // Non-target intrinsics should have already been rewritten back into user calls.
-            assert(comp->IsTargetIntrinsic(node->AsIntrinsic()->gtIntrinsicId));
+            assert(comp->IsTargetIntrinsic(node->AsIntrinsic()->gtIntrinsicName));
             break;
 
 #ifdef FEATURE_SIMD
@@ -903,7 +903,7 @@ PhaseStatus Rationalizer::DoPhase()
         {
             GenTree* const node = *use;
             if (node->OperGet() == GT_INTRINSIC &&
-                m_rationalizer.comp->IsIntrinsicImplementedByUserCall(node->AsIntrinsic()->gtIntrinsicId))
+                m_rationalizer.comp->IsIntrinsicImplementedByUserCall(node->AsIntrinsic()->gtIntrinsicName))
             {
                 m_rationalizer.RewriteIntrinsicAsUserCall(use, this->m_ancestors);
             }
diff --git a/src/coreclr/src/jit/scopeinfo.cpp b/src/coreclr/src/jit/scopeinfo.cpp
index 5fc7bca119f4c2..77d8233cac6328 100644
--- a/src/coreclr/src/jit/scopeinfo.cpp
+++ b/src/coreclr/src/jit/scopeinfo.cpp
@@ -1673,7 +1673,7 @@ void CodeGen::psiEndProlog()
  We still report all the arguments at the very start of the method so that
  the user can see the arguments at the very start of the method (offset=0).
 
- Disabling this decreased the debug maps in mscorlib by 10% (01/2003)
+ Disabling this decreased the debug maps in CoreLib by 10% (01/2003)
  */
 
 #if 0
diff --git a/src/coreclr/src/jit/simdcodegenxarch.cpp b/src/coreclr/src/jit/simdcodegenxarch.cpp
index a1acdfd2f1a729..4045c9b97f6280 100644
--- a/src/coreclr/src/jit/simdcodegenxarch.cpp
+++ b/src/coreclr/src/jit/simdcodegenxarch.cpp
@@ -585,9 +585,9 @@ void CodeGen::genSIMDIntrinsicInit(GenTreeSIMD* simdNode)
             }
             else if (op1->OperIsLocalAddr())
             {
-                unsigned offset = op1->OperIs(GT_LCL_FLD_ADDR) ? op1->AsLclFld()->GetLclOffs() : 0;
-                GetEmitter()->emitIns_R_S(ins, emitTypeSize(targetType), targetReg, op1->AsLclVarCommon()->GetLclNum(),
-                                          offset);
+                const GenTreeLclVarCommon* lclVar = op1->AsLclVarCommon();
+                unsigned                   offset = lclVar->GetLclOffs();
+                GetEmitter()->emitIns_R_S(ins, emitTypeSize(targetType), targetReg, lclVar->GetLclNum(), offset);
             }
             else
             {
@@ -2143,17 +2143,14 @@ void CodeGen::genStoreLclTypeSIMD12(GenTree* treeNode)
 {
     assert((treeNode->OperGet() == GT_STORE_LCL_FLD) || (treeNode->OperGet() == GT_STORE_LCL_VAR));
 
-    unsigned offs   = 0;
-    unsigned varNum = treeNode->AsLclVarCommon()->GetLclNum();
-    assert(varNum < compiler->lvaCount);
+    const GenTreeLclVarCommon* lclVar = treeNode->AsLclVarCommon();
 
-    if (treeNode->OperGet() == GT_STORE_LCL_FLD)
-    {
-        offs = treeNode->AsLclFld()->GetLclOffs();
-    }
+    unsigned offs   = lclVar->GetLclOffs();
+    unsigned varNum = lclVar->GetLclNum();
+    assert(varNum < compiler->lvaCount);
 
     regNumber tmpReg = treeNode->GetSingleTempReg();
-    GenTree*  op1    = treeNode->AsOp()->gtOp1;
+    GenTree*  op1    = lclVar->gtOp1;
     if (op1->isContained())
     {
         // This is only possible for a zero-init.
@@ -2197,16 +2194,12 @@ void CodeGen::genLoadLclTypeSIMD12(GenTree* treeNode)
 {
     assert((treeNode->OperGet() == GT_LCL_FLD) || (treeNode->OperGet() == GT_LCL_VAR));
 
-    regNumber targetReg = treeNode->GetRegNum();
-    unsigned  offs      = 0;
-    unsigned  varNum    = treeNode->AsLclVarCommon()->GetLclNum();
+    const GenTreeLclVarCommon* lclVar    = treeNode->AsLclVarCommon();
+    regNumber                  targetReg = lclVar->GetRegNum();
+    unsigned                   offs      = lclVar->GetLclOffs();
+    unsigned                   varNum    = lclVar->GetLclNum();
     assert(varNum < compiler->lvaCount);
 
-    if (treeNode->OperGet() == GT_LCL_FLD)
-    {
-        offs = treeNode->AsLclFld()->GetLclOffs();
-    }
-
     // Need an additional Xmm register that is different from targetReg to read upper 4 bytes.
     regNumber tmpReg = treeNode->GetSingleTempReg();
     assert(tmpReg != targetReg);
diff --git a/src/coreclr/src/jit/ssabuilder.cpp b/src/coreclr/src/jit/ssabuilder.cpp
index d562065bf21655..62efd8696dac86 100644
--- a/src/coreclr/src/jit/ssabuilder.cpp
+++ b/src/coreclr/src/jit/ssabuilder.cpp
@@ -1656,8 +1656,6 @@ bool SsaBuilder::IncludeInSsa(unsigned lclNum)
         // - SSA doesn't allow a single node to contain multiple SSA definitions.
         // - and PROMOTION_TYPE_DEPENDEDNT fields  are never candidates for a register.
         //
-        // Example mscorlib method: CompatibilitySwitches:IsCompatibilitySwitchSet
-        //
         return false;
     }
     else if (varDsc->lvIsStructField && m_pCompiler->lvaGetDesc(varDsc->lvParentLcl)->lvIsMultiRegRet)
diff --git a/src/coreclr/src/jit/static/CMakeLists.txt b/src/coreclr/src/jit/static/CMakeLists.txt
index b4e62c041cd449..01bdbf5a731f5c 100644
--- a/src/coreclr/src/jit/static/CMakeLists.txt
+++ b/src/coreclr/src/jit/static/CMakeLists.txt
@@ -2,14 +2,17 @@ project(ClrJit)
 
 set_source_files_properties(${JIT_EXPORTS_FILE} PROPERTIES GENERATED TRUE)
 
-add_library_clr(clrjit_static
+add_library_clr(clrjit_obj
     OBJECT
     ${JIT_CORE_SOURCES}
     ${JIT_ARCH_SOURCES}
 )
 
 if(CLR_CMAKE_HOST_UNIX)
-    add_dependencies(clrjit_static coreclrpal gcinfo)
+    add_dependencies(clrjit_obj coreclrpal gcinfo)
 endif(CLR_CMAKE_HOST_UNIX)
 
-target_precompile_header(TARGET clrjit_static HEADER jitpch.h ADDITIONAL_INCLUDE_DIRECTORIES ${JIT_SOURCE_DIR})
+target_precompile_header(TARGET clrjit_obj HEADER jitpch.h ADDITIONAL_INCLUDE_DIRECTORIES ${JIT_SOURCE_DIR})
+
+add_library(clrjit_static INTERFACE)
+target_sources(clrjit_static INTERFACE $<TARGET_OBJECTS:clrjit_obj>)
diff --git a/src/coreclr/src/jit/target.h b/src/coreclr/src/jit/target.h
index c9fc28df7bb1c8..5b1f6cff48bca2 100644
--- a/src/coreclr/src/jit/target.h
+++ b/src/coreclr/src/jit/target.h
@@ -31,12 +31,15 @@
 // with static const members of Target
 #if defined(TARGET_XARCH)
 #define REGMASK_BITS 32
+#define CSE_CONST_SHARED_LOW_BITS 16
 
 #elif defined(TARGET_ARM)
 #define REGMASK_BITS 64
+#define CSE_CONST_SHARED_LOW_BITS 12
 
 #elif defined(TARGET_ARM64)
 #define REGMASK_BITS 64
+#define CSE_CONST_SHARED_LOW_BITS 12
 
 #else
 #error Unsupported or unset target architecture
@@ -433,6 +436,7 @@ typedef unsigned char   regNumberSmall;
   #define FIRST_ARG_STACK_OFFS    (2*REGSIZE_BYTES)   // Caller's saved EBP and return address
 
   #define MAX_REG_ARG              2
+  
   #define MAX_FLOAT_REG_ARG        0
   #define REG_ARG_FIRST            REG_ECX
   #define REG_ARG_LAST             REG_EDX
@@ -441,10 +445,8 @@ typedef unsigned char   regNumberSmall;
   #define REG_ARG_0                REG_ECX
   #define REG_ARG_1                REG_EDX
 
-  SELECTANY const regNumber intArgRegs [] = {REG_ECX, REG_EDX};
-  SELECTANY const regMaskTP intArgMasks[] = {RBM_ECX, RBM_EDX};
-  SELECTANY const regNumber fltArgRegs [] = {REG_XMM0, REG_XMM1, REG_XMM2, REG_XMM3};
-  SELECTANY const regMaskTP fltArgMasks[] = {RBM_XMM0, RBM_XMM1, RBM_XMM2, RBM_XMM3};
+  extern const regNumber intArgRegs [MAX_REG_ARG];
+  extern const regMaskTP intArgMasks[MAX_REG_ARG];
 
   #define RBM_ARG_0                RBM_ECX
   #define RBM_ARG_1                RBM_EDX
@@ -779,10 +781,10 @@ typedef unsigned char   regNumberSmall;
   #define REG_ARG_4                REG_R8
   #define REG_ARG_5                REG_R9
 
-  SELECTANY const regNumber intArgRegs [] = { REG_EDI, REG_ESI, REG_EDX, REG_ECX, REG_R8, REG_R9 };
-  SELECTANY const regMaskTP intArgMasks[] = { RBM_EDI, RBM_ESI, RBM_EDX, RBM_ECX, RBM_R8, RBM_R9 };
-  SELECTANY const regNumber fltArgRegs [] = { REG_XMM0, REG_XMM1, REG_XMM2, REG_XMM3, REG_XMM4, REG_XMM5, REG_XMM6, REG_XMM7 };
-  SELECTANY const regMaskTP fltArgMasks[] = { RBM_XMM0, RBM_XMM1, RBM_XMM2, RBM_XMM3, RBM_XMM4, RBM_XMM5, RBM_XMM6, RBM_XMM7 };
+  extern const regNumber intArgRegs [MAX_REG_ARG];
+  extern const regMaskTP intArgMasks[MAX_REG_ARG];
+  extern const regNumber fltArgRegs [MAX_FLOAT_REG_ARG];
+  extern const regMaskTP fltArgMasks[MAX_FLOAT_REG_ARG];
 
   #define RBM_ARG_0                RBM_RDI
   #define RBM_ARG_1                RBM_RSI
@@ -802,10 +804,10 @@ typedef unsigned char   regNumberSmall;
   #define REG_ARG_2                REG_R8
   #define REG_ARG_3                REG_R9
 
-  SELECTANY const regNumber intArgRegs [] = { REG_ECX, REG_EDX, REG_R8, REG_R9 };
-  SELECTANY const regMaskTP intArgMasks[] = { RBM_ECX, RBM_EDX, RBM_R8, RBM_R9 };
-  SELECTANY const regNumber fltArgRegs [] = { REG_XMM0, REG_XMM1, REG_XMM2, REG_XMM3 };
-  SELECTANY const regMaskTP fltArgMasks[] = { RBM_XMM0, RBM_XMM1, RBM_XMM2, RBM_XMM3 };
+  extern const regNumber intArgRegs [MAX_REG_ARG];
+  extern const regMaskTP intArgMasks[MAX_REG_ARG];
+  extern const regNumber fltArgRegs [MAX_FLOAT_REG_ARG];
+  extern const regMaskTP fltArgMasks[MAX_FLOAT_REG_ARG];
 
   #define RBM_ARG_0                RBM_ECX
   #define RBM_ARG_1                RBM_EDX
@@ -1103,7 +1105,9 @@ typedef unsigned char   regNumberSmall;
   // The registers trashed by profiler enter/leave/tailcall hook
   // See vm\arm\asmhelpers.asm for more details.
   #define RBM_PROFILER_ENTER_TRASH     RBM_NONE
-  #define RBM_PROFILER_LEAVE_TRASH     RBM_NONE
+  // While REG_PROFILER_RET_SCRATCH is not trashed by the method, the register allocator must
+  // consider it killed by the return.
+  #define RBM_PROFILER_LEAVE_TRASH     RBM_PROFILER_RET_SCRATCH
   #define RBM_PROFILER_TAILCALL_TRASH  RBM_NONE
 
   // Which register are int and long values returned in ?
@@ -1150,8 +1154,8 @@ typedef unsigned char   regNumberSmall;
   #define REG_ARG_2                REG_R2
   #define REG_ARG_3                REG_R3
 
-  SELECTANY const regNumber intArgRegs [] = {REG_R0, REG_R1, REG_R2, REG_R3};
-  SELECTANY const regMaskTP intArgMasks[] = {RBM_R0, RBM_R1, RBM_R2, RBM_R3};
+  extern const regNumber intArgRegs [MAX_REG_ARG];
+  extern const regMaskTP intArgMasks[MAX_REG_ARG];
 
   #define RBM_ARG_0                RBM_R0
   #define RBM_ARG_1                RBM_R1
@@ -1162,8 +1166,8 @@ typedef unsigned char   regNumberSmall;
   #define RBM_FLTARG_REGS         (RBM_F0|RBM_F1|RBM_F2|RBM_F3|RBM_F4|RBM_F5|RBM_F6|RBM_F7|RBM_F8|RBM_F9|RBM_F10|RBM_F11|RBM_F12|RBM_F13|RBM_F14|RBM_F15)
   #define RBM_DBL_REGS            RBM_ALLDOUBLE
 
-  SELECTANY const regNumber fltArgRegs [] = {REG_F0, REG_F1, REG_F2, REG_F3, REG_F4, REG_F5, REG_F6, REG_F7, REG_F8, REG_F9, REG_F10, REG_F11, REG_F12, REG_F13, REG_F14, REG_F15 };
-  SELECTANY const regMaskTP fltArgMasks[] = {RBM_F0, RBM_F1, RBM_F2, RBM_F3, RBM_F4, RBM_F5, RBM_F6, RBM_F7, RBM_F8, RBM_F9, RBM_F10, RBM_F11, RBM_F12, RBM_F13, RBM_F14, RBM_F15 };
+  extern const regNumber fltArgRegs [MAX_FLOAT_REG_ARG];
+  extern const regMaskTP fltArgMasks[MAX_FLOAT_REG_ARG];
 
   #define LBL_DIST_SMALL_MAX_NEG  (0)
   #define LBL_DIST_SMALL_MAX_POS  (+1020)
@@ -1484,8 +1488,8 @@ typedef unsigned char   regNumberSmall;
   #define REG_ARG_6                REG_R6
   #define REG_ARG_7                REG_R7
 
-  SELECTANY const regNumber intArgRegs [] = {REG_R0, REG_R1, REG_R2, REG_R3, REG_R4, REG_R5, REG_R6, REG_R7};
-  SELECTANY const regMaskTP intArgMasks[] = {RBM_R0, RBM_R1, RBM_R2, RBM_R3, RBM_R4, RBM_R5, RBM_R6, RBM_R7};
+  extern const regNumber intArgRegs [MAX_REG_ARG];
+  extern const regMaskTP intArgMasks[MAX_REG_ARG];
 
   #define RBM_ARG_0                RBM_R0
   #define RBM_ARG_1                RBM_R1
@@ -1517,8 +1521,8 @@ typedef unsigned char   regNumberSmall;
   #define RBM_ARG_REGS            (RBM_ARG_0|RBM_ARG_1|RBM_ARG_2|RBM_ARG_3|RBM_ARG_4|RBM_ARG_5|RBM_ARG_6|RBM_ARG_7)
   #define RBM_FLTARG_REGS         (RBM_FLTARG_0|RBM_FLTARG_1|RBM_FLTARG_2|RBM_FLTARG_3|RBM_FLTARG_4|RBM_FLTARG_5|RBM_FLTARG_6|RBM_FLTARG_7)
 
-  SELECTANY const regNumber fltArgRegs [] = {REG_V0, REG_V1, REG_V2, REG_V3, REG_V4, REG_V5, REG_V6, REG_V7 };
-  SELECTANY const regMaskTP fltArgMasks[] = {RBM_V0, RBM_V1, RBM_V2, RBM_V3, RBM_V4, RBM_V5, RBM_V6, RBM_V7 };
+  extern const regNumber fltArgRegs [MAX_FLOAT_REG_ARG];
+  extern const regMaskTP fltArgMasks[MAX_FLOAT_REG_ARG];
 
   #define LBL_DIST_SMALL_MAX_NEG  (-1048576)
   #define LBL_DIST_SMALL_MAX_POS  (+1048575)
@@ -1616,11 +1620,11 @@ class Target
     static const enum ArgOrder g_tgtArgOrder;
 };
 
-#if defined(DEBUG) || defined(LATE_DISASM)
+#if defined(DEBUG) || defined(LATE_DISASM) || DUMP_GC_TABLES
 const char* getRegName(unsigned reg, bool isFloat = false); // this is for gcencode.cpp and disasm.cpp that don't use
                                                             // the regNumber type
 const char* getRegName(regNumber reg, bool isFloat = false);
-#endif // defined(DEBUG) || defined(LATE_DISASM)
+#endif // defined(DEBUG) || defined(LATE_DISASM) || DUMP_GC_TABLES
 
 #ifdef DEBUG
 const char* getRegNameFloat(regNumber reg, var_types type);
@@ -1997,9 +2001,13 @@ C_ASSERT((RBM_INT_CALLEE_SAVED & RBM_FPBASE) == RBM_NONE);
 #ifdef TARGET_64BIT
 typedef unsigned __int64 target_size_t;
 typedef __int64          target_ssize_t;
-#else  // !TARGET_64BIT
+#define TARGET_SIGN_BIT (1ULL << 63)
+
+#else // !TARGET_64BIT
 typedef unsigned int target_size_t;
 typedef int          target_ssize_t;
+#define TARGET_SIGN_BIT (1ULL << 31)
+
 #endif // !TARGET_64BIT
 
 C_ASSERT(sizeof(target_size_t) == TARGET_POINTER_SIZE);
diff --git a/src/coreclr/src/jit/targetamd64.cpp b/src/coreclr/src/jit/targetamd64.cpp
index 143e6e4641803a..372c4dffc27b2b 100644
--- a/src/coreclr/src/jit/targetamd64.cpp
+++ b/src/coreclr/src/jit/targetamd64.cpp
@@ -15,4 +15,18 @@
 const char*            Target::g_tgtCPUName  = "x64";
 const Target::ArgOrder Target::g_tgtArgOrder = ARG_ORDER_R2L;
 
+// clang-format off
+#ifdef UNIX_AMD64_ABI
+const regNumber intArgRegs [] = { REG_EDI, REG_ESI, REG_EDX, REG_ECX, REG_R8, REG_R9 };
+const regMaskTP intArgMasks[] = { RBM_EDI, RBM_ESI, RBM_EDX, RBM_ECX, RBM_R8, RBM_R9 };
+const regNumber fltArgRegs [] = { REG_XMM0, REG_XMM1, REG_XMM2, REG_XMM3, REG_XMM4, REG_XMM5, REG_XMM6, REG_XMM7 };
+const regMaskTP fltArgMasks[] = { RBM_XMM0, RBM_XMM1, RBM_XMM2, RBM_XMM3, RBM_XMM4, RBM_XMM5, RBM_XMM6, RBM_XMM7 };
+#else // !UNIX_AMD64_ABI
+const regNumber intArgRegs [] = { REG_ECX, REG_EDX, REG_R8, REG_R9 };
+const regMaskTP intArgMasks[] = { RBM_ECX, RBM_EDX, RBM_R8, RBM_R9 };
+const regNumber fltArgRegs [] = { REG_XMM0, REG_XMM1, REG_XMM2, REG_XMM3 };
+const regMaskTP fltArgMasks[] = { RBM_XMM0, RBM_XMM1, RBM_XMM2, RBM_XMM3 };
+#endif // !UNIX_AMD64_ABI
+// clang-format on
+
 #endif // TARGET_AMD64
diff --git a/src/coreclr/src/jit/targetarm.cpp b/src/coreclr/src/jit/targetarm.cpp
index ca974a76af390f..da125cbb436a0e 100644
--- a/src/coreclr/src/jit/targetarm.cpp
+++ b/src/coreclr/src/jit/targetarm.cpp
@@ -15,4 +15,12 @@
 const char*            Target::g_tgtCPUName  = "arm";
 const Target::ArgOrder Target::g_tgtArgOrder = ARG_ORDER_R2L;
 
+// clang-format off
+const regNumber intArgRegs [] = {REG_R0, REG_R1, REG_R2, REG_R3};
+const regMaskTP intArgMasks[] = {RBM_R0, RBM_R1, RBM_R2, RBM_R3};
+
+const regNumber fltArgRegs [] = {REG_F0, REG_F1, REG_F2, REG_F3, REG_F4, REG_F5, REG_F6, REG_F7, REG_F8, REG_F9, REG_F10, REG_F11, REG_F12, REG_F13, REG_F14, REG_F15 };
+const regMaskTP fltArgMasks[] = {RBM_F0, RBM_F1, RBM_F2, RBM_F3, RBM_F4, RBM_F5, RBM_F6, RBM_F7, RBM_F8, RBM_F9, RBM_F10, RBM_F11, RBM_F12, RBM_F13, RBM_F14, RBM_F15 };
+// clang-format on
+
 #endif // TARGET_ARM
diff --git a/src/coreclr/src/jit/targetarm64.cpp b/src/coreclr/src/jit/targetarm64.cpp
index 7b035f145b01e3..8f5481a83e02d0 100644
--- a/src/coreclr/src/jit/targetarm64.cpp
+++ b/src/coreclr/src/jit/targetarm64.cpp
@@ -15,4 +15,12 @@
 const char*            Target::g_tgtCPUName  = "arm64";
 const Target::ArgOrder Target::g_tgtArgOrder = ARG_ORDER_R2L;
 
+// clang-format off
+const regNumber intArgRegs [] = {REG_R0, REG_R1, REG_R2, REG_R3, REG_R4, REG_R5, REG_R6, REG_R7};
+const regMaskTP intArgMasks[] = {RBM_R0, RBM_R1, RBM_R2, RBM_R3, RBM_R4, RBM_R5, RBM_R6, RBM_R7};
+
+const regNumber fltArgRegs [] = {REG_V0, REG_V1, REG_V2, REG_V3, REG_V4, REG_V5, REG_V6, REG_V7 };
+const regMaskTP fltArgMasks[] = {RBM_V0, RBM_V1, RBM_V2, RBM_V3, RBM_V4, RBM_V5, RBM_V6, RBM_V7 };
+// clang-format on
+
 #endif // TARGET_ARM64
diff --git a/src/coreclr/src/jit/targetx86.cpp b/src/coreclr/src/jit/targetx86.cpp
index 391a934e5b9e78..fab7286782a2d9 100644
--- a/src/coreclr/src/jit/targetx86.cpp
+++ b/src/coreclr/src/jit/targetx86.cpp
@@ -15,4 +15,9 @@
 const char*            Target::g_tgtCPUName  = "x86";
 const Target::ArgOrder Target::g_tgtArgOrder = ARG_ORDER_L2R;
 
+// clang-format off
+const regNumber intArgRegs [] = {REG_ECX, REG_EDX};
+const regMaskTP intArgMasks[] = {RBM_ECX, RBM_EDX};
+// clang-format on
+
 #endif // TARGET_X86
diff --git a/src/coreclr/src/jit/unwind.h b/src/coreclr/src/jit/unwind.h
index 5541450e0ef715..f510eb6f1d822a 100644
--- a/src/coreclr/src/jit/unwind.h
+++ b/src/coreclr/src/jit/unwind.h
@@ -150,7 +150,7 @@ class UnwindCodesBase
 
 class UnwindPrologCodes : public UnwindBase, public UnwindCodesBase
 {
-    // UPC_LOCAL_COUNT is the amount of memory local to this class. For ARM mscorlib.dll, the maximum size is 34.
+    // UPC_LOCAL_COUNT is the amount of memory local to this class. For ARM CoreLib, the maximum size is 34.
     // Here is a histogram of other interesting sizes:
     //     <=16  79%
     //     <=24  96%
@@ -314,7 +314,7 @@ class UnwindPrologCodes : public UnwindBase, public UnwindCodesBase
 
 class UnwindEpilogCodes : public UnwindBase, public UnwindCodesBase
 {
-    // UEC_LOCAL_COUNT is the amount of memory local to this class. For ARM mscorlib.dll, the maximum size is 6,
+    // UEC_LOCAL_COUNT is the amount of memory local to this class. For ARM CoreLib, the maximum size is 6,
     // while 89% of epilogs fit in 4. So, set it to 4 to maintain array alignment and hit most cases.
     static const int UEC_LOCAL_COUNT = 4;
 
diff --git a/src/coreclr/src/jit/utils.cpp b/src/coreclr/src/jit/utils.cpp
index 4477ceb16295b2..de1fd4a880b2c6 100644
--- a/src/coreclr/src/jit/utils.cpp
+++ b/src/coreclr/src/jit/utils.cpp
@@ -128,7 +128,7 @@ const char* varTypeName(var_types vt)
     return varTypeNames[vt];
 }
 
-#if defined(DEBUG) || defined(LATE_DISASM)
+#if defined(DEBUG) || defined(LATE_DISASM) || DUMP_GC_TABLES
 /*****************************************************************************
  *
  *  Return the name of the given register.
@@ -164,7 +164,7 @@ const char* getRegName(unsigned reg,
 {
     return getRegName((regNumber)reg, isFloat);
 }
-#endif // defined(DEBUG) || defined(LATE_DISASM)
+#endif // defined(DEBUG) || defined(LATE_DISASM) || DUMP_GC_TABLES
 
 #if defined(DEBUG)
 
@@ -767,11 +767,11 @@ void ConfigMethodRange::InitRanges(const WCHAR* rangeStr, unsigned capacity)
             }
             else if ((L'A' <= *p) && (*p <= L'F'))
             {
-                n = (*p++) - L'A';
+                n = (*p++) - L'A' + 10;
             }
             else if ((L'a' <= *p) && (*p <= L'f'))
             {
-                n = (*p++) - L'a';
+                n = (*p++) - L'a' + 10;
             }
 
             int j = 16 * i + n;
diff --git a/src/coreclr/src/jit/valuenum.cpp b/src/coreclr/src/jit/valuenum.cpp
index 1cc0cab621ca60..51e23701a77df7 100644
--- a/src/coreclr/src/jit/valuenum.cpp
+++ b/src/coreclr/src/jit/valuenum.cpp
@@ -4137,14 +4137,23 @@ ValueNum Compiler::fgValueNumberArrIndexVal(GenTree*             tree,
 
 ValueNum Compiler::fgValueNumberByrefExposedLoad(var_types type, ValueNum pointerVN)
 {
-    ValueNum memoryVN = fgCurMemoryVN[ByrefExposed];
-    // The memoization for VNFunc applications does not factor in the result type, so
-    // VNF_ByrefExposedLoad takes the loaded type as an explicit parameter.
-    ValueNum typeVN = vnStore->VNForIntCon(type);
-    ValueNum loadVN =
-        vnStore->VNForFunc(type, VNF_ByrefExposedLoad, typeVN, vnStore->VNNormalValue(pointerVN), memoryVN);
-
-    return loadVN;
+    if (type == TYP_STRUCT)
+    {
+        // We can't assign a value number for a read of a struct as we can't determine
+        // how many bytes will be read by this load, so return a new unique value number
+        //
+        return vnStore->VNForExpr(compCurBB, TYP_STRUCT);
+    }
+    else
+    {
+        ValueNum memoryVN = fgCurMemoryVN[ByrefExposed];
+        // The memoization for VNFunc applications does not factor in the result type, so
+        // VNF_ByrefExposedLoad takes the loaded type as an explicit parameter.
+        ValueNum typeVN = vnStore->VNForIntCon(type);
+        ValueNum loadVN =
+            vnStore->VNForFunc(type, VNF_ByrefExposedLoad, typeVN, vnStore->VNNormalValue(pointerVN), memoryVN);
+        return loadVN;
+    }
 }
 
 var_types ValueNumStore::TypeOfVN(ValueNum vn)
@@ -4548,7 +4557,7 @@ void ValueNumStore::SetVNIsCheckedBound(ValueNum vn)
     m_checkedBoundVNs.AddOrUpdate(vn, true);
 }
 
-ValueNum ValueNumStore::EvalMathFuncUnary(var_types typ, CorInfoIntrinsics gtMathFN, ValueNum arg0VN)
+ValueNum ValueNumStore::EvalMathFuncUnary(var_types typ, NamedIntrinsic gtMathFN, ValueNum arg0VN)
 {
     assert(arg0VN == VNNormalValue(arg0VN));
 
@@ -4568,25 +4577,25 @@ ValueNum ValueNumStore::EvalMathFuncUnary(var_types typ, CorInfoIntrinsics gtMat
             double res = 0.0;
             switch (gtMathFN)
             {
-                case CORINFO_INTRINSIC_Sin:
+                case NI_System_Math_Sin:
                     res = sin(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Cos:
+                case NI_System_Math_Cos:
                     res = cos(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Sqrt:
+                case NI_System_Math_Sqrt:
                     res = sqrt(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Abs:
+                case NI_System_Math_Abs:
                     res = fabs(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Ceiling:
+                case NI_System_Math_Ceiling:
                     res = ceil(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Floor:
+                case NI_System_Math_Floor:
                     res = floor(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Round:
+                case NI_System_Math_Round:
                     res = FloatingPointUtils::round(arg0Val);
                     break;
                 default:
@@ -4604,25 +4613,25 @@ ValueNum ValueNumStore::EvalMathFuncUnary(var_types typ, CorInfoIntrinsics gtMat
             float res = 0.0f;
             switch (gtMathFN)
             {
-                case CORINFO_INTRINSIC_Sin:
+                case NI_System_Math_Sin:
                     res = sinf(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Cos:
+                case NI_System_Math_Cos:
                     res = cosf(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Sqrt:
+                case NI_System_Math_Sqrt:
                     res = sqrtf(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Abs:
+                case NI_System_Math_Abs:
                     res = fabsf(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Ceiling:
+                case NI_System_Math_Ceiling:
                     res = ceilf(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Floor:
+                case NI_System_Math_Floor:
                     res = floorf(arg0Val);
                     break;
-                case CORINFO_INTRINSIC_Round:
+                case NI_System_Math_Round:
                     res = FloatingPointUtils::round(arg0Val);
                     break;
                 default:
@@ -4633,11 +4642,11 @@ ValueNum ValueNumStore::EvalMathFuncUnary(var_types typ, CorInfoIntrinsics gtMat
         }
         else
         {
-            // CORINFO_INTRINSIC_Round is currently the only intrinsic that takes floating-point arguments
-            // and that returns a non floating-point result.
+            // NI_System_Math{F}_Round are currently the only intrinsic that take floating-point arguments
+            // and return a non floating-point result.
 
             assert(typ == TYP_INT);
-            assert(gtMathFN == CORINFO_INTRINSIC_Round);
+            assert(gtMathFN == NI_System_Math_Round);
 
             int res = 0;
 
@@ -4664,27 +4673,27 @@ ValueNum ValueNumStore::EvalMathFuncUnary(var_types typ, CorInfoIntrinsics gtMat
     }
     else
     {
-        assert(typ == TYP_DOUBLE || typ == TYP_FLOAT || (typ == TYP_INT && gtMathFN == CORINFO_INTRINSIC_Round));
+        assert(typ == TYP_DOUBLE || typ == TYP_FLOAT || typ == TYP_INT && gtMathFN == NI_System_Math_Round);
 
         VNFunc vnf = VNF_Boundary;
         switch (gtMathFN)
         {
-            case CORINFO_INTRINSIC_Sin:
+            case NI_System_Math_Sin:
                 vnf = VNF_Sin;
                 break;
-            case CORINFO_INTRINSIC_Cos:
+            case NI_System_Math_Cos:
                 vnf = VNF_Cos;
                 break;
-            case CORINFO_INTRINSIC_Cbrt:
+            case NI_System_Math_Cbrt:
                 vnf = VNF_Cbrt;
                 break;
-            case CORINFO_INTRINSIC_Sqrt:
+            case NI_System_Math_Sqrt:
                 vnf = VNF_Sqrt;
                 break;
-            case CORINFO_INTRINSIC_Abs:
+            case NI_System_Math_Abs:
                 vnf = VNF_Abs;
                 break;
-            case CORINFO_INTRINSIC_Round:
+            case NI_System_Math_Round:
                 if (typ == TYP_DOUBLE)
                 {
                     vnf = VNF_RoundDouble;
@@ -4702,46 +4711,46 @@ ValueNum ValueNumStore::EvalMathFuncUnary(var_types typ, CorInfoIntrinsics gtMat
                     noway_assert(!"Invalid INTRINSIC_Round");
                 }
                 break;
-            case CORINFO_INTRINSIC_Cosh:
+            case NI_System_Math_Cosh:
                 vnf = VNF_Cosh;
                 break;
-            case CORINFO_INTRINSIC_Sinh:
+            case NI_System_Math_Sinh:
                 vnf = VNF_Sinh;
                 break;
-            case CORINFO_INTRINSIC_Tan:
+            case NI_System_Math_Tan:
                 vnf = VNF_Tan;
                 break;
-            case CORINFO_INTRINSIC_Tanh:
+            case NI_System_Math_Tanh:
                 vnf = VNF_Tanh;
                 break;
-            case CORINFO_INTRINSIC_Asin:
+            case NI_System_Math_Asin:
                 vnf = VNF_Asin;
                 break;
-            case CORINFO_INTRINSIC_Asinh:
+            case NI_System_Math_Asinh:
                 vnf = VNF_Asinh;
                 break;
-            case CORINFO_INTRINSIC_Acos:
+            case NI_System_Math_Acos:
                 vnf = VNF_Acos;
                 break;
-            case CORINFO_INTRINSIC_Acosh:
+            case NI_System_Math_Acosh:
                 vnf = VNF_Acosh;
                 break;
-            case CORINFO_INTRINSIC_Atan:
+            case NI_System_Math_Atan:
                 vnf = VNF_Atan;
                 break;
-            case CORINFO_INTRINSIC_Atanh:
+            case NI_System_Math_Atanh:
                 vnf = VNF_Atanh;
                 break;
-            case CORINFO_INTRINSIC_Log10:
+            case NI_System_Math_Log10:
                 vnf = VNF_Log10;
                 break;
-            case CORINFO_INTRINSIC_Exp:
+            case NI_System_Math_Exp:
                 vnf = VNF_Exp;
                 break;
-            case CORINFO_INTRINSIC_Ceiling:
+            case NI_System_Math_Ceiling:
                 vnf = VNF_Ceiling;
                 break;
-            case CORINFO_INTRINSIC_Floor:
+            case NI_System_Math_Floor:
                 vnf = VNF_Floor;
                 break;
             default:
@@ -4752,7 +4761,7 @@ ValueNum ValueNumStore::EvalMathFuncUnary(var_types typ, CorInfoIntrinsics gtMat
     }
 }
 
-ValueNum ValueNumStore::EvalMathFuncBinary(var_types typ, CorInfoIntrinsics gtMathFN, ValueNum arg0VN, ValueNum arg1VN)
+ValueNum ValueNumStore::EvalMathFuncBinary(var_types typ, NamedIntrinsic gtMathFN, ValueNum arg0VN, ValueNum arg1VN)
 {
     assert(varTypeIsFloating(typ));
     assert(arg0VN == VNNormalValue(arg0VN));
@@ -4765,11 +4774,11 @@ ValueNum ValueNumStore::EvalMathFuncBinary(var_types typ, CorInfoIntrinsics gtMa
 
     switch (gtMathFN)
     {
-        case CORINFO_INTRINSIC_Atan2:
+        case NI_System_Math_Atan2:
             vnf = VNF_Atan2;
             break;
 
-        case CORINFO_INTRINSIC_Pow:
+        case NI_System_Math_Pow:
             vnf = VNF_Pow;
             break;
 
@@ -8389,7 +8398,7 @@ void Compiler::fgValueNumberIntrinsic(GenTree* tree)
         vnStore->VNPUnpackExc(intrinsic->AsOp()->gtOp2->gtVNPair, &arg1VNP, &arg1VNPx);
     }
 
-    if (IsMathIntrinsic(intrinsic->gtIntrinsicId))
+    if (IsMathIntrinsic(intrinsic->gtIntrinsicName))
     {
         // GT_INTRINSIC is a currently a subtype of binary operators. But most of
         // the math intrinsics are actually unary operations.
@@ -8397,13 +8406,13 @@ void Compiler::fgValueNumberIntrinsic(GenTree* tree)
         if (intrinsic->AsOp()->gtOp2 == nullptr)
         {
             intrinsic->gtVNPair =
-                vnStore->VNPWithExc(vnStore->EvalMathFuncUnary(tree->TypeGet(), intrinsic->gtIntrinsicId, arg0VNP),
+                vnStore->VNPWithExc(vnStore->EvalMathFuncUnary(tree->TypeGet(), intrinsic->gtIntrinsicName, arg0VNP),
                                     arg0VNPx);
         }
         else
         {
             ValueNumPair newVNP =
-                vnStore->EvalMathFuncBinary(tree->TypeGet(), intrinsic->gtIntrinsicId, arg0VNP, arg1VNP);
+                vnStore->EvalMathFuncBinary(tree->TypeGet(), intrinsic->gtIntrinsicName, arg0VNP, arg1VNP);
             ValueNumPair excSet = vnStore->VNPExcSetUnion(arg0VNPx, arg1VNPx);
             intrinsic->gtVNPair = vnStore->VNPWithExc(newVNP, excSet);
         }
@@ -8615,7 +8624,7 @@ void Compiler::fgValueNumberHWIntrinsic(GenTree* tree)
     else if (tree->AsOp()->gtOp1->OperIs(GT_LIST) || (lookupNumArgs == -1))
     {
         // We have a HWINTRINSIC node in the GT_LIST form with 3 or more args
-        // Or the numArgs was specified as -1 in the numArgs column in "hwinstrinsiclistxarch.h"
+        // Or the numArgs was specified as -1 in the numArgs column in "hwintrinsiclistxarch.h"
         // For now we will generate a unique value number for this case.
 
         // Generate unique VN
diff --git a/src/coreclr/src/jit/valuenum.h b/src/coreclr/src/jit/valuenum.h
index 9f3cc2025be203..2f57b6323e6748 100644
--- a/src/coreclr/src/jit/valuenum.h
+++ b/src/coreclr/src/jit/valuenum.h
@@ -818,20 +818,17 @@ class ValueNumStore
     // "arg0VN". For binary ops, return the value number for the application of this function to "arg0VN" and
     // "arg1VN".
 
-    ValueNum EvalMathFuncUnary(var_types typ, CorInfoIntrinsics mthFunc, ValueNum arg0VN);
+    ValueNum EvalMathFuncUnary(var_types typ, NamedIntrinsic mthFunc, ValueNum arg0VN);
 
-    ValueNum EvalMathFuncBinary(var_types typ, CorInfoIntrinsics mthFunc, ValueNum arg0VN, ValueNum arg1VN);
+    ValueNum EvalMathFuncBinary(var_types typ, NamedIntrinsic mthFunc, ValueNum arg0VN, ValueNum arg1VN);
 
-    ValueNumPair EvalMathFuncUnary(var_types typ, CorInfoIntrinsics mthFunc, ValueNumPair arg0VNP)
+    ValueNumPair EvalMathFuncUnary(var_types typ, NamedIntrinsic mthFunc, ValueNumPair arg0VNP)
     {
         return ValueNumPair(EvalMathFuncUnary(typ, mthFunc, arg0VNP.GetLiberal()),
                             EvalMathFuncUnary(typ, mthFunc, arg0VNP.GetConservative()));
     }
 
-    ValueNumPair EvalMathFuncBinary(var_types         typ,
-                                    CorInfoIntrinsics mthFunc,
-                                    ValueNumPair      arg0VNP,
-                                    ValueNumPair      arg1VNP)
+    ValueNumPair EvalMathFuncBinary(var_types typ, NamedIntrinsic mthFunc, ValueNumPair arg0VNP, ValueNumPair arg1VNP)
     {
         return ValueNumPair(EvalMathFuncBinary(typ, mthFunc, arg0VNP.GetLiberal(), arg1VNP.GetLiberal()),
                             EvalMathFuncBinary(typ, mthFunc, arg0VNP.GetConservative(), arg1VNP.GetConservative()));
diff --git a/src/coreclr/src/md/ceefilegen/CMakeLists.txt b/src/coreclr/src/md/ceefilegen/CMakeLists.txt
index 39864c71817f55..fd0f8424d97f12 100644
--- a/src/coreclr/src/md/ceefilegen/CMakeLists.txt
+++ b/src/coreclr/src/md/ceefilegen/CMakeLists.txt
@@ -25,8 +25,11 @@ if (CLR_CMAKE_TARGET_WIN32)
     list(APPEND CEEFILEGEN_SOURCES ${CEEFILEGEN_HEADERS})
 endif (CLR_CMAKE_TARGET_WIN32)
 
-add_library_clr(ceefgen
+add_library_clr(ceefgen_obj
     OBJECT
     ${CEEFILEGEN_SOURCES}
 )
-target_precompile_header(TARGET ceefgen HEADER stdafx.h)
+target_precompile_header(TARGET ceefgen_obj HEADER stdafx.h)
+
+add_library(ceefgen INTERFACE)
+target_sources(ceefgen INTERFACE $<TARGET_OBJECTS:ceefgen_obj>)
diff --git a/src/coreclr/src/md/compiler/CMakeLists.txt b/src/coreclr/src/md/compiler/CMakeLists.txt
index 495fa4d70ca262..f32c80407c6a59 100644
--- a/src/coreclr/src/md/compiler/CMakeLists.txt
+++ b/src/coreclr/src/md/compiler/CMakeLists.txt
@@ -68,9 +68,11 @@ add_library_clr(mdcompiler_dac ${MDCOMPILER_SOURCES})
 set_target_properties(mdcompiler_dac PROPERTIES DAC_COMPONENT TRUE)
 target_precompile_header(TARGET mdcompiler_dac HEADER stdafx.h)
 
-add_library_clr(mdcompiler_wks OBJECT ${MDCOMPILER_WKS_SOURCES})
-target_compile_definitions(mdcompiler_wks PRIVATE FEATURE_METADATA_EMIT_ALL)
-target_precompile_header(TARGET mdcompiler_wks HEADER stdafx.h)
+add_library_clr(mdcompiler_wks_obj OBJECT ${MDCOMPILER_WKS_SOURCES})
+target_compile_definitions(mdcompiler_wks_obj PRIVATE FEATURE_METADATA_EMIT_ALL)
+target_precompile_header(TARGET mdcompiler_wks_obj HEADER stdafx.h)
+add_library(mdcompiler_wks INTERFACE)
+target_sources(mdcompiler_wks INTERFACE $<TARGET_OBJECTS:mdcompiler_wks_obj>)
 
 add_library_clr(mdcompiler-dbi ${MDCOMPILER_SOURCES})
 set_target_properties(mdcompiler-dbi PROPERTIES DBI_COMPONENT TRUE)
diff --git a/src/coreclr/src/md/enc/CMakeLists.txt b/src/coreclr/src/md/enc/CMakeLists.txt
index 14ed0a267fae67..e30c51b1e37c4e 100644
--- a/src/coreclr/src/md/enc/CMakeLists.txt
+++ b/src/coreclr/src/md/enc/CMakeLists.txt
@@ -52,9 +52,11 @@ add_library_clr(mdruntimerw_dac ${MDRUNTIMERW_SOURCES})
 set_target_properties(mdruntimerw_dac PROPERTIES DAC_COMPONENT TRUE)
 target_precompile_header(TARGET mdruntimerw_dac HEADER stdafx.h)
 
-add_library_clr(mdruntimerw_wks OBJECT ${MDRUNTIMERW_SOURCES})
-target_compile_definitions(mdruntimerw_wks PRIVATE FEATURE_METADATA_EMIT_ALL)
-target_precompile_header(TARGET mdruntimerw_wks HEADER stdafx.h)
+add_library_clr(mdruntimerw_wks_obj OBJECT ${MDRUNTIMERW_SOURCES})
+target_compile_definitions(mdruntimerw_wks_obj PRIVATE FEATURE_METADATA_EMIT_ALL)
+target_precompile_header(TARGET mdruntimerw_wks_obj HEADER stdafx.h)
+add_library(mdruntimerw_wks INTERFACE)
+target_sources(mdruntimerw_wks INTERFACE $<TARGET_OBJECTS:mdruntimerw_wks_obj>)
 
 add_library_clr(mdruntimerw-dbi ${MDRUNTIMERW_SOURCES})
 set_target_properties(mdruntimerw-dbi PROPERTIES DBI_COMPONENT TRUE)
diff --git a/src/coreclr/src/md/hotdata/CMakeLists.txt b/src/coreclr/src/md/hotdata/CMakeLists.txt
index 03430e292c75df..46381cf7dddd11 100644
--- a/src/coreclr/src/md/hotdata/CMakeLists.txt
+++ b/src/coreclr/src/md/hotdata/CMakeLists.txt
@@ -33,8 +33,10 @@ add_library_clr(mdhotdata_dac ${MDHOTDATA_SOURCES})
 set_target_properties(mdhotdata_dac PROPERTIES DAC_COMPONENT TRUE)
 target_precompile_header(TARGET mdhotdata_dac HEADER external.h)
 
-add_library_clr(mdhotdata_full OBJECT ${MDHOTDATA_SOURCES})
-target_precompile_header(TARGET mdhotdata_full HEADER external.h)
+add_library_clr(mdhotdata_full_obj OBJECT ${MDHOTDATA_SOURCES})
+target_precompile_header(TARGET mdhotdata_full_obj HEADER external.h)
+add_library(mdhotdata_full INTERFACE)
+target_sources(mdhotdata_full INTERFACE $<TARGET_OBJECTS:mdhotdata_full_obj>)
 
 add_library_clr(mdhotdata_crossgen ${MDHOTDATA_SOURCES})
 set_target_properties(mdhotdata_crossgen PROPERTIES CROSSGEN_COMPONENT TRUE)
diff --git a/src/coreclr/src/md/runtime/CMakeLists.txt b/src/coreclr/src/md/runtime/CMakeLists.txt
index 5753e655abf990..06e9e830001957 100644
--- a/src/coreclr/src/md/runtime/CMakeLists.txt
+++ b/src/coreclr/src/md/runtime/CMakeLists.txt
@@ -49,9 +49,11 @@ add_library_clr(mdruntime_dac ${MDRUNTIME_SOURCES})
 set_target_properties(mdruntime_dac PROPERTIES DAC_COMPONENT TRUE)
 target_precompile_header(TARGET mdruntime_dac HEADER stdafx.h)
 
-add_library_clr(mdruntime_wks OBJECT ${MDRUNTIME_SOURCES})
-target_compile_definitions(mdruntime_wks PRIVATE FEATURE_METADATA_EMIT_ALL)
-target_precompile_header(TARGET mdruntime_wks HEADER stdafx.h)
+add_library_clr(mdruntime_wks_obj OBJECT ${MDRUNTIME_SOURCES})
+target_compile_definitions(mdruntime_wks_obj PRIVATE FEATURE_METADATA_EMIT_ALL)
+target_precompile_header(TARGET mdruntime_wks_obj HEADER stdafx.h)
+add_library(mdruntime_wks INTERFACE)
+target_sources(mdruntime_wks INTERFACE $<TARGET_OBJECTS:mdruntime_wks_obj>)
 
 add_library_clr(mdruntime-dbi ${MDRUNTIME_SOURCES})
 set_target_properties(mdruntime-dbi PROPERTIES DBI_COMPONENT TRUE)
diff --git a/src/coreclr/src/pal/inc/pal.h b/src/coreclr/src/pal/inc/pal.h
index df658c54690561..fd56fc90c35357 100644
--- a/src/coreclr/src/pal/inc/pal.h
+++ b/src/coreclr/src/pal/inc/pal.h
@@ -511,6 +511,32 @@ PAL_Random(
     IN OUT LPVOID lpBuffer,
     IN DWORD dwLength);
 
+PALIMPORT
+BOOL
+PALAPI
+PAL_OpenProcessMemory(
+    IN DWORD processId,
+    OUT DWORD* pHandle
+);
+
+PALIMPORT
+VOID
+PALAPI
+PAL_CloseProcessMemory(
+    IN DWORD handle
+);
+
+PALIMPORT
+BOOL
+PALAPI
+PAL_ReadProcessMemory(
+    IN DWORD handle,
+    IN ULONG64 address,
+    IN LPVOID buffer,
+    IN SIZE_T size,
+    OUT SIZE_T* numberOfBytesRead
+);
+
 PALIMPORT
 BOOL
 PALAPI
diff --git a/src/coreclr/src/pal/inc/rt/guiddef.h b/src/coreclr/src/pal/inc/rt/guiddef.h
index 1a2ed05e16fefa..6650f11092fa24 100644
--- a/src/coreclr/src/pal/inc/rt/guiddef.h
+++ b/src/coreclr/src/pal/inc/rt/guiddef.h
@@ -17,7 +17,7 @@
 
 #ifdef INITGUID
 #define DEFINE_GUID(name, l, w1, w2, b1, b2, b3, b4, b5, b6, b7, b8) \
-        EXTERN_C DLLEXPORT const GUID DECLSPEC_SELECTANY name \
+        EXTERN_C DLLEXPORT constexpr GUID name \
                 = { l, w1, w2, { b1, b2,  b3,  b4,  b5,  b6,  b7,  b8 } }
 #else
 #define DEFINE_GUID(name, l, w1, w2, b1, b2, b3, b4, b5, b6, b7, b8) \
diff --git a/src/coreclr/src/pal/inc/rt/palrt.h b/src/coreclr/src/pal/inc/rt/palrt.h
index 23f627e1b8e5c6..b021277e437581 100644
--- a/src/coreclr/src/pal/inc/rt/palrt.h
+++ b/src/coreclr/src/pal/inc/rt/palrt.h
@@ -223,7 +223,6 @@ inline void *__cdecl operator new(size_t, void *_P)
 #define THIS                void
 
 #define DECLSPEC_NOVTABLE
-#define DECLSPEC_SELECTANY  __attribute__((weak))
 
 #define DECLARE_INTERFACE(iface)    interface DECLSPEC_NOVTABLE iface
 #define DECLARE_INTERFACE_(iface, baseiface)    interface DECLSPEC_NOVTABLE iface : public baseiface
diff --git a/src/coreclr/src/pal/inc/rt/rpc.h b/src/coreclr/src/pal/inc/rt/rpc.h
index 9b9f425f69fe52..9fd3c096882d61 100644
--- a/src/coreclr/src/pal/inc/rt/rpc.h
+++ b/src/coreclr/src/pal/inc/rt/rpc.h
@@ -25,7 +25,7 @@
 #define MIDL_INTERFACE(x)   struct DECLSPEC_UUID(x) DECLSPEC_NOVTABLE
 
 #define EXTERN_GUID(itf,l1,s1,s2,c1,c2,c3,c4,c5,c6,c7,c8) \
-    EXTERN_C const IID DECLSPEC_SELECTANY itf = {l1,s1,s2,{c1,c2,c3,c4,c5,c6,c7,c8}}
+    constexpr IID itf = {l1,s1,s2,{c1,c2,c3,c4,c5,c6,c7,c8}}
 
 interface IRpcStubBuffer;
 interface IRpcChannelBuffer;
diff --git a/src/coreclr/src/pal/prebuilt/corerror/mscorurt.rc b/src/coreclr/src/pal/prebuilt/corerror/mscorurt.rc
index f51e77ae1245c0..783d1adafb10a7 100644
--- a/src/coreclr/src/pal/prebuilt/corerror/mscorurt.rc
+++ b/src/coreclr/src/pal/prebuilt/corerror/mscorurt.rc
@@ -314,14 +314,13 @@ BEGIN
 	MSG_FOR_URT_HR(CORDBG_E_UNSUPPORTED_DELEGATE) "The delegate contains a delegate currently not supported by the API."
 	MSG_FOR_URT_HR(PEFMT_E_64BIT) "File is PE32+."
 	MSG_FOR_URT_HR(PEFMT_E_32BIT) "File is PE32"
-	MSG_FOR_URT_HR(NGEN_E_SYS_ASM_NI_MISSING) "NGen cannot proceed because Mscorlib.dll does not have a native image"
 	MSG_FOR_URT_HR(CLR_E_BIND_ASSEMBLY_VERSION_TOO_LOW) "The bound assembly has a version that is lower than that of the request."
 	MSG_FOR_URT_HR(CLR_E_BIND_ASSEMBLY_PUBLIC_KEY_MISMATCH) "The assembly version has a public key token that does not match that of the request."
 	MSG_FOR_URT_HR(CLR_E_BIND_IMAGE_UNAVAILABLE) "The requested image was not found or is unavailable."
 	MSG_FOR_URT_HR(CLR_E_BIND_UNRECOGNIZED_IDENTITY_FORMAT) "The provided identity format is not recognized."
 	MSG_FOR_URT_HR(CLR_E_BIND_ASSEMBLY_NOT_FOUND) "A binding for the specified assembly name was not found."
 	MSG_FOR_URT_HR(CLR_E_BIND_TYPE_NOT_FOUND) "A binding for the specified type name was not found."
-	MSG_FOR_URT_HR(CLR_E_BIND_SYS_ASM_NI_MISSING) "Could not use native image because Mscorlib.dll is missing a native image"
+	MSG_FOR_URT_HR(CLR_E_BIND_SYS_ASM_NI_MISSING) "Could not use native image because System.Private.CoreLib.dll is missing a native image"
 	MSG_FOR_URT_HR(CLR_E_BIND_NI_SECURITY_FAILURE) "Native image was generated in a different trust level than present at runtime"
 	MSG_FOR_URT_HR(CLR_E_BIND_NI_DEP_IDENTITY_MISMATCH) "Native image identity mismatch with respect to its dependencies"
 	MSG_FOR_URT_HR(CLR_E_GC_OOM) "Failfast due to an OOM during a GC"
diff --git a/src/coreclr/src/pal/prebuilt/idl/cordebug_i.cpp b/src/coreclr/src/pal/prebuilt/idl/cordebug_i.cpp
index 85d7ab575a51ff..5208843c10eb42 100644
--- a/src/coreclr/src/pal/prebuilt/idl/cordebug_i.cpp
+++ b/src/coreclr/src/pal/prebuilt/idl/cordebug_i.cpp
@@ -8,7 +8,7 @@
  /* File created by MIDL compiler version 8.01.0622 */
 /* at Mon Jan 18 19:14:07 2038
  */
-/* Compiler settings for E:/repos/runtime2/src/coreclr/src/inc/cordebug.idl:
+/* Compiler settings for runtime/src/coreclr/src/inc/cordebug.idl:
     Oicf, W1, Zp8, env=Win32 (32b run), target_arch=X86 8.01.0622
     protocol : dce , ms_ext, c_ext, robust
     error checks: allocation ref bounds_check enum stub_data
@@ -289,6 +289,9 @@ MIDL_DEFINE_GUID(IID, IID_ICorDebugNativeFrame2,0x35389FF1,0x3684,0x4c55,0xA2,0x
 MIDL_DEFINE_GUID(IID, IID_ICorDebugModule3,0x86F012BF,0xFF15,0x4372,0xBD,0x30,0xB6,0xF1,0x1C,0xAA,0xE1,0xDD);
 
 
+MIDL_DEFINE_GUID(IID, IID_ICorDebugModule4,0xFF8B8EAF,0x25CD,0x4316,0x88,0x59,0x84,0x41,0x6D,0xE4,0x40,0x2E);
+
+
 MIDL_DEFINE_GUID(IID, IID_ICorDebugRuntimeUnwindableFrame,0x879CAC0A,0x4A53,0x4668,0xB8,0xE3,0xCB,0x84,0x73,0xCB,0x18,0x7F);
 
 
diff --git a/src/coreclr/src/pal/prebuilt/idl/sospriv_i.cpp b/src/coreclr/src/pal/prebuilt/idl/sospriv_i.cpp
index 993737f7a0b358..ee2cd1d82010b3 100644
--- a/src/coreclr/src/pal/prebuilt/idl/sospriv_i.cpp
+++ b/src/coreclr/src/pal/prebuilt/idl/sospriv_i.cpp
@@ -1,6 +1,3 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
 
 
 /* this ALWAYS GENERATED file contains the IIDs and CLSIDs */
@@ -8,7 +5,17 @@
 /* link this file in with the server and any clients */
 
 
- /* File created by MIDL compiler version 8.00.0613 */
+ /* File created by MIDL compiler version 8.01.0622 */
+/* at Mon Jan 18 19:14:07 2038
+ */
+/* Compiler settings for C:/ssd/runtime/src/coreclr/src/inc/sospriv.idl:
+    Oicf, W1, Zp8, env=Win32 (32b run), target_arch=X86 8.01.0622 
+    protocol : dce , ms_ext, c_ext, robust
+    error checks: allocation ref bounds_check enum stub_data 
+    VC __declspec() decoration level: 
+         __declspec(uuid()), __declspec(selectany), __declspec(novtable)
+         DECLSPEC_UUID(), MIDL_INTERFACE()
+*/
 /* @@MIDL_FILE_HEADING(  ) */
 
 #pragma warning( disable: 4049 )  /* more than 64k source lines */
@@ -95,6 +102,9 @@ MIDL_DEFINE_GUID(IID, IID_ISOSDacInterface7,0xc1020dde,0xfe98,0x4536,0xa5,0x3b,0
 
 MIDL_DEFINE_GUID(IID, IID_ISOSDacInterface8,0xc12f35a9,0xe55c,0x4520,0xa8,0x94,0xb3,0xdc,0x51,0x65,0xdf,0xce);
 
+
+MIDL_DEFINE_GUID(IID, IID_ISOSDacInterface9,0x4eca42d8,0x7e7b,0x4c8a,0xa1,0x16,0x7b,0xfb,0xf6,0x92,0x92,0x67);
+
 #undef MIDL_DEFINE_GUID
 
 #ifdef __cplusplus
diff --git a/src/coreclr/src/pal/prebuilt/inc/cordebug.h b/src/coreclr/src/pal/prebuilt/inc/cordebug.h
index 3418b8cf9b30c9..b497d141c48086 100644
--- a/src/coreclr/src/pal/prebuilt/inc/cordebug.h
+++ b/src/coreclr/src/pal/prebuilt/inc/cordebug.h
@@ -6,7 +6,7 @@
  /* File created by MIDL compiler version 8.01.0622 */
 /* at Mon Jan 18 19:14:07 2038
  */
-/* Compiler settings for E:/repos/runtime2/src/coreclr/src/inc/cordebug.idl:
+/* Compiler settings for runtime/src/coreclr/src/inc/cordebug.idl:
     Oicf, W1, Zp8, env=Win32 (32b run), target_arch=X86 8.01.0622
     protocol : dce , ms_ext, c_ext, robust
     error checks: allocation ref bounds_check enum stub_data
@@ -563,6 +563,13 @@ typedef interface ICorDebugModule3 ICorDebugModule3;
 #endif 	/* __ICorDebugModule3_FWD_DEFINED__ */
 
 
+#ifndef __ICorDebugModule4_FWD_DEFINED__
+#define __ICorDebugModule4_FWD_DEFINED__
+typedef interface ICorDebugModule4 ICorDebugModule4;
+
+#endif 	/* __ICorDebugModule4_FWD_DEFINED__ */
+
+
 #ifndef __ICorDebugRuntimeUnwindableFrame_FWD_DEFINED__
 #define __ICorDebugRuntimeUnwindableFrame_FWD_DEFINED__
 typedef interface ICorDebugRuntimeUnwindableFrame ICorDebugRuntimeUnwindableFrame;
@@ -11691,6 +11698,86 @@ EXTERN_C const IID IID_ICorDebugModule3;
 #endif 	/* __ICorDebugModule3_INTERFACE_DEFINED__ */
 
 
+#ifndef __ICorDebugModule4_INTERFACE_DEFINED__
+#define __ICorDebugModule4_INTERFACE_DEFINED__
+
+/* interface ICorDebugModule4 */
+/* [unique][uuid][local][object] */
+
+
+EXTERN_C const IID IID_ICorDebugModule4;
+
+#if defined(__cplusplus) && !defined(CINTERFACE)
+
+    MIDL_INTERFACE("FF8B8EAF-25CD-4316-8859-84416DE4402E")
+    ICorDebugModule4 : public IUnknown
+    {
+    public:
+        virtual HRESULT STDMETHODCALLTYPE IsMappedLayout(
+            /* [out] */ BOOL *pIsMapped) = 0;
+
+    };
+
+
+#else 	/* C style interface */
+
+    typedef struct ICorDebugModule4Vtbl
+    {
+        BEGIN_INTERFACE
+
+        HRESULT ( STDMETHODCALLTYPE *QueryInterface )(
+            ICorDebugModule4 * This,
+            /* [in] */ REFIID riid,
+            /* [annotation][iid_is][out] */
+            _COM_Outptr_  void **ppvObject);
+
+        ULONG ( STDMETHODCALLTYPE *AddRef )(
+            ICorDebugModule4 * This);
+
+        ULONG ( STDMETHODCALLTYPE *Release )(
+            ICorDebugModule4 * This);
+
+        HRESULT ( STDMETHODCALLTYPE *IsMappedLayout )(
+            ICorDebugModule4 * This,
+            /* [out] */ BOOL *pIsMapped);
+
+        END_INTERFACE
+    } ICorDebugModule4Vtbl;
+
+    interface ICorDebugModule4
+    {
+        CONST_VTBL struct ICorDebugModule4Vtbl *lpVtbl;
+    };
+
+
+
+#ifdef COBJMACROS
+
+
+#define ICorDebugModule4_QueryInterface(This,riid,ppvObject)	\
+    ( (This)->lpVtbl -> QueryInterface(This,riid,ppvObject) )
+
+#define ICorDebugModule4_AddRef(This)	\
+    ( (This)->lpVtbl -> AddRef(This) )
+
+#define ICorDebugModule4_Release(This)	\
+    ( (This)->lpVtbl -> Release(This) )
+
+
+#define ICorDebugModule4_IsMappedLayout(This,pIsMapped)	\
+    ( (This)->lpVtbl -> IsMappedLayout(This,pIsMapped) )
+
+#endif /* COBJMACROS */
+
+
+#endif 	/* C style interface */
+
+
+
+
+#endif 	/* __ICorDebugModule4_INTERFACE_DEFINED__ */
+
+
 #ifndef __ICorDebugRuntimeUnwindableFrame_INTERFACE_DEFINED__
 #define __ICorDebugRuntimeUnwindableFrame_INTERFACE_DEFINED__
 
@@ -12075,14 +12162,14 @@ EXTERN_C const IID IID_ICorDebugModule;
 #endif 	/* __ICorDebugModule_INTERFACE_DEFINED__ */
 
 
-/* interface __MIDL_itf_cordebug_0000_0075 */
+/* interface __MIDL_itf_cordebug_0000_0076 */
 /* [local] */
 
 #pragma warning(pop)
 
 
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0075_v0_0_c_ifspec;
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0075_v0_0_s_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0076_v0_0_c_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0076_v0_0_s_ifspec;
 
 #ifndef __ICorDebugModule2_INTERFACE_DEFINED__
 #define __ICorDebugModule2_INTERFACE_DEFINED__
@@ -15129,15 +15216,15 @@ EXTERN_C const IID IID_ICorDebugBoxValue;
 #endif 	/* __ICorDebugBoxValue_INTERFACE_DEFINED__ */
 
 
-/* interface __MIDL_itf_cordebug_0000_0102 */
+/* interface __MIDL_itf_cordebug_0000_0103 */
 /* [local] */
 
 #pragma warning(push)
 #pragma warning(disable:28718)
 
 
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0102_v0_0_c_ifspec;
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0102_v0_0_s_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0103_v0_0_c_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0103_v0_0_s_ifspec;
 
 #ifndef __ICorDebugStringValue_INTERFACE_DEFINED__
 #define __ICorDebugStringValue_INTERFACE_DEFINED__
@@ -15277,14 +15364,14 @@ EXTERN_C const IID IID_ICorDebugStringValue;
 #endif 	/* __ICorDebugStringValue_INTERFACE_DEFINED__ */
 
 
-/* interface __MIDL_itf_cordebug_0000_0103 */
+/* interface __MIDL_itf_cordebug_0000_0104 */
 /* [local] */
 
 #pragma warning(pop)
 
 
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0103_v0_0_c_ifspec;
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0103_v0_0_s_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0104_v0_0_c_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0104_v0_0_s_ifspec;
 
 #ifndef __ICorDebugArrayValue_INTERFACE_DEFINED__
 #define __ICorDebugArrayValue_INTERFACE_DEFINED__
@@ -18059,15 +18146,15 @@ EXTERN_C const IID IID_ICorDebugBlockingObjectEnum;
 #endif 	/* __ICorDebugBlockingObjectEnum_INTERFACE_DEFINED__ */
 
 
-/* interface __MIDL_itf_cordebug_0000_0127 */
+/* interface __MIDL_itf_cordebug_0000_0128 */
 /* [local] */
 
 #pragma warning(push)
 #pragma warning(disable:28718)
 
 
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0127_v0_0_c_ifspec;
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0127_v0_0_s_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0128_v0_0_c_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0128_v0_0_s_ifspec;
 
 #ifndef __ICorDebugMDA_INTERFACE_DEFINED__
 #define __ICorDebugMDA_INTERFACE_DEFINED__
@@ -18207,7 +18294,7 @@ EXTERN_C const IID IID_ICorDebugMDA;
 #endif 	/* __ICorDebugMDA_INTERFACE_DEFINED__ */
 
 
-/* interface __MIDL_itf_cordebug_0000_0128 */
+/* interface __MIDL_itf_cordebug_0000_0129 */
 /* [local] */
 
 #pragma warning(pop)
@@ -18215,8 +18302,8 @@ EXTERN_C const IID IID_ICorDebugMDA;
 #pragma warning(disable:28718)
 
 
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0128_v0_0_c_ifspec;
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0128_v0_0_s_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0129_v0_0_c_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0129_v0_0_s_ifspec;
 
 #ifndef __ICorDebugEditAndContinueErrorInfo_INTERFACE_DEFINED__
 #define __ICorDebugEditAndContinueErrorInfo_INTERFACE_DEFINED__
@@ -18332,14 +18419,14 @@ EXTERN_C const IID IID_ICorDebugEditAndContinueErrorInfo;
 #endif 	/* __ICorDebugEditAndContinueErrorInfo_INTERFACE_DEFINED__ */
 
 
-/* interface __MIDL_itf_cordebug_0000_0129 */
+/* interface __MIDL_itf_cordebug_0000_0130 */
 /* [local] */
 
 #pragma warning(pop)
 
 
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0129_v0_0_c_ifspec;
-extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0129_v0_0_s_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0130_v0_0_c_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_cordebug_0000_0130_v0_0_s_ifspec;
 
 #ifndef __ICorDebugEditAndContinueSnapshot_INTERFACE_DEFINED__
 #define __ICorDebugEditAndContinueSnapshot_INTERFACE_DEFINED__
diff --git a/src/coreclr/src/pal/prebuilt/inc/corerror.h b/src/coreclr/src/pal/prebuilt/inc/corerror.h
index 31ba2d9c455458..0fe7c75d2d249d 100644
--- a/src/coreclr/src/pal/prebuilt/inc/corerror.h
+++ b/src/coreclr/src/pal/prebuilt/inc/corerror.h
@@ -385,7 +385,6 @@
 #define CORDBG_E_UNSUPPORTED_DELEGATE EMAKEHR(0x1c68)
 #define PEFMT_E_64BIT EMAKEHR(0x1d02)
 #define PEFMT_E_32BIT EMAKEHR(0x1d0b)
-#define NGEN_E_SYS_ASM_NI_MISSING EMAKEHR(0x1f06)
 #define CLDB_E_INTERNALERROR EMAKEHR(0x1fff)
 #define CLR_E_BIND_ASSEMBLY_VERSION_TOO_LOW EMAKEHR(0x2000)
 #define CLR_E_BIND_ASSEMBLY_PUBLIC_KEY_MISMATCH EMAKEHR(0x2001)
diff --git a/src/coreclr/src/pal/prebuilt/inc/sospriv.h b/src/coreclr/src/pal/prebuilt/inc/sospriv.h
index d76eac0ead666f..6fe59addcfe218 100644
--- a/src/coreclr/src/pal/prebuilt/inc/sospriv.h
+++ b/src/coreclr/src/pal/prebuilt/inc/sospriv.h
@@ -2644,7 +2644,7 @@ EXTERN_C const IID IID_ISOSDacInterface8;
 #define ISOSDacInterface8_GetFinalizationFillPointersSvr(This,heapAddr,cFillPointers,pFinalizationFillPointers,pNeeded) \
     ( (This)->lpVtbl -> GetFinalizationFillPointersSvr(This,heapAddr,cFillPointers,pFinalizationFillPointers,pNeeded) )
 
-#define ISOSDacInterface8_GetAssemblyLoadContext(This,methodTable,assemblyLoadContext)	\
+#define ISOSDacInterface8_GetAssemblyLoadContext(This,methodTable,assemblyLoadContext) \
     ( (This)->lpVtbl -> GetAssemblyLoadContext(This,methodTable,assemblyLoadContext) )
 
 #endif /* COBJMACROS */
@@ -2658,6 +2658,93 @@ EXTERN_C const IID IID_ISOSDacInterface8;
 #endif  /* __ISOSDacInterface8_INTERFACE_DEFINED__ */
 
 
+/* interface __MIDL_itf_sospriv_0000_0012 */
+/* [local] */ 
+
+#define SOS_BREAKING_CHANGE_VERSION 1
+
+
+extern RPC_IF_HANDLE __MIDL_itf_sospriv_0000_0012_v0_0_c_ifspec;
+extern RPC_IF_HANDLE __MIDL_itf_sospriv_0000_0012_v0_0_s_ifspec;
+
+#ifndef __ISOSDacInterface9_INTERFACE_DEFINED__
+#define __ISOSDacInterface9_INTERFACE_DEFINED__
+
+/* interface ISOSDacInterface9 */
+/* [uuid][local][object] */ 
+
+
+EXTERN_C const IID IID_ISOSDacInterface9;
+
+#if defined(__cplusplus) && !defined(CINTERFACE)
+    
+    MIDL_INTERFACE("4eca42d8-7e7b-4c8a-a116-7bfbf6929267")
+    ISOSDacInterface9 : public IUnknown
+    {
+    public:
+        virtual HRESULT STDMETHODCALLTYPE GetBreakingChangeVersion( 
+            int *pVersion) = 0;
+        
+    };
+    
+    
+#else  /* C style interface */
+
+    typedef struct ISOSDacInterface9Vtbl
+    {
+        BEGIN_INTERFACE
+        
+        HRESULT ( STDMETHODCALLTYPE *QueryInterface )( 
+            ISOSDacInterface9 * This,
+            /* [in] */ REFIID riid,
+            /* [annotation][iid_is][out] */ 
+            _COM_Outptr_  void **ppvObject);
+        
+        ULONG ( STDMETHODCALLTYPE *AddRef )( 
+            ISOSDacInterface9 * This);
+        
+        ULONG ( STDMETHODCALLTYPE *Release )( 
+            ISOSDacInterface9 * This);
+        
+        HRESULT ( STDMETHODCALLTYPE *GetBreakingChangeVersion )( 
+            ISOSDacInterface9 * This,
+            int *pVersion);
+        
+        END_INTERFACE
+    } ISOSDacInterface9Vtbl;
+
+    interface ISOSDacInterface9
+    {
+        CONST_VTBL struct ISOSDacInterface9Vtbl *lpVtbl;
+    };
+
+    
+
+#ifdef COBJMACROS
+
+
+#define ISOSDacInterface9_QueryInterface(This,riid,ppvObject) \
+    ( (This)->lpVtbl -> QueryInterface(This,riid,ppvObject) ) 
+
+#define ISOSDacInterface9_AddRef(This) \
+    ( (This)->lpVtbl -> AddRef(This) ) 
+
+#define ISOSDacInterface9_Release(This) \
+    ( (This)->lpVtbl -> Release(This) ) 
+
+
+#define ISOSDacInterface9_GetBreakingChangeVersion(This,pVersion) \
+    ( (This)->lpVtbl -> GetBreakingChangeVersion(This,pVersion) ) 
+
+#endif /* COBJMACROS */
+
+
+#endif  /* C style interface */
+
+
+#endif  /* __ISOSDacInterface9_INTERFACE_DEFINED__ */
+
+
 /* Additional Prototypes for ALL interfaces */
 
 /* end of Additional Prototypes */
@@ -2668,4 +2755,3 @@ EXTERN_C const IID IID_ISOSDacInterface8;
 
 #endif
 
-
diff --git a/src/coreclr/src/pal/src/CMakeLists.txt b/src/coreclr/src/pal/src/CMakeLists.txt
index 094f14cabf821a..712dabf46a3e68 100644
--- a/src/coreclr/src/pal/src/CMakeLists.txt
+++ b/src/coreclr/src/pal/src/CMakeLists.txt
@@ -267,10 +267,12 @@ endif(CLR_CMAKE_TARGET_OSX)
 # > warning for library: libtracepointprovider.a the table of contents is empty (no object file members in the library define global symbols)
 #
 if(CLR_CMAKE_TARGET_LINUX)
-  add_library(tracepointprovider
+  add_library(tracepointprovider_obj
     OBJECT
     misc/tracepointprovider.cpp
   )
+  add_library(tracepointprovider INTERFACE)
+  target_sources(tracepointprovider INTERFACE $<TARGET_OBJECTS:tracepointprovider_obj>)
 endif(CLR_CMAKE_TARGET_LINUX)
 
 if(CLR_CMAKE_TARGET_OSX)
diff --git a/src/coreclr/src/pal/src/config.h.in b/src/coreclr/src/pal/src/config.h.in
index 8e7e69288bc9e3..39a05ee0ff2232 100644
--- a/src/coreclr/src/pal/src/config.h.in
+++ b/src/coreclr/src/pal/src/config.h.in
@@ -36,7 +36,6 @@
 #cmakedefine01 HAVE_PTHREAD_GETCPUCLOCKID
 #cmakedefine01 HAVE_PTHREAD_SIGQUEUE
 #cmakedefine01 HAVE_PTHREAD_GETAFFINITY_NP
-#cmakedefine01 HAVE_PTHREAD_ATTR_SETAFFINITY_NP
 #cmakedefine01 HAVE_CPUSET_T
 #cmakedefine01 HAVE_SIGRETURN
 #cmakedefine01 HAVE__THREAD_SYS_SIGRETURN
@@ -66,6 +65,7 @@
 #cmakedefine01 HAVE_TTRACE
 #cmakedefine01 HAVE_PIPE2
 #cmakedefine01 HAVE_SCHED_GETAFFINITY
+#cmakedefine01 HAVE_SCHED_SETAFFINITY
 #cmakedefine HAVE_UNW_GET_SAVE_LOC
 #cmakedefine HAVE_UNW_GET_ACCESSORS
 #cmakedefine01 HAVE_XSWDEV
diff --git a/src/coreclr/src/pal/src/configure.cmake b/src/coreclr/src/pal/src/configure.cmake
index b67637b584ba69..5fb606a2983dca 100644
--- a/src/coreclr/src/pal/src/configure.cmake
+++ b/src/coreclr/src/pal/src/configure.cmake
@@ -81,6 +81,7 @@ check_include_files(gnu/lib-names.h HAVE_GNU_LIBNAMES_H)
 check_function_exists(kqueue HAVE_KQUEUE)
 
 check_library_exists(c sched_getaffinity "" HAVE_SCHED_GETAFFINITY)
+check_library_exists(c sched_setaffinity "" HAVE_SCHED_SETAFFINITY)
 check_library_exists(pthread pthread_create "" HAVE_LIBPTHREAD)
 check_library_exists(c pthread_create "" HAVE_PTHREAD_IN_LIBC)
 
@@ -100,7 +101,6 @@ check_library_exists(${PTHREAD_LIBRARY} pthread_getattr_np "" HAVE_PTHREAD_GETAT
 check_library_exists(${PTHREAD_LIBRARY} pthread_getcpuclockid "" HAVE_PTHREAD_GETCPUCLOCKID)
 check_library_exists(${PTHREAD_LIBRARY} pthread_sigqueue "" HAVE_PTHREAD_SIGQUEUE)
 check_library_exists(${PTHREAD_LIBRARY} pthread_getaffinity_np "" HAVE_PTHREAD_GETAFFINITY_NP)
-check_library_exists(${PTHREAD_LIBRARY} pthread_attr_setaffinity_np "" HAVE_PTHREAD_ATTR_SETAFFINITY_NP)
 
 check_function_exists(sigreturn HAVE_SIGRETURN)
 check_function_exists(_thread_sys_sigreturn HAVE__THREAD_SYS_SIGRETURN)
diff --git a/src/coreclr/src/pal/src/debug/debug.cpp b/src/coreclr/src/pal/src/debug/debug.cpp
index b58b2fe587e19d..7e7e368200587b 100644
--- a/src/coreclr/src/pal/src/debug/debug.cpp
+++ b/src/coreclr/src/pal/src/debug/debug.cpp
@@ -62,6 +62,11 @@ SET_DEFAULT_DEBUG_CHANNEL(DEBUG); // some headers have code with asserts, so do
 #include <procfs.h>
 #endif // HAVE_PROCFS_H
 
+#ifdef __APPLE__
+#include <mach/mach.h>
+#include <mach/mach_vm.h>
+#endif // __APPLE__
+
 #if HAVE_MACH_EXCEPTIONS
 #include "../exception/machexception.h"
 #endif // HAVE_MACH_EXCEPTIONS
@@ -69,6 +74,7 @@ SET_DEFAULT_DEBUG_CHANNEL(DEBUG); // some headers have code with asserts, so do
 using namespace CorUnix;
 
 extern "C" void DBG_DebugBreak_End();
+extern size_t OffsetWithinPage(off_t addr);
 
 #if HAVE_PROCFS_CTL
 #define CTL_ATTACH      "attach"
@@ -541,6 +547,184 @@ SetThreadContext(
     return ret;
 }
 
+/*++
+Function:
+  PAL_OpenProcessMemory
+
+Abstract
+  Creates the handle for PAL_ReadProcessMemory.
+
+Parameter
+  processId : process id to read memory
+  pHandle : returns a platform specific handle or UINT32_MAX if failed
+
+Return
+  true successful, false invalid process id or not supported.
+--*/
+BOOL
+PALAPI
+PAL_OpenProcessMemory(
+    IN DWORD processId,
+    OUT DWORD* pHandle
+)
+{
+    ENTRY("PAL_OpenProcessMemory(pid=%d)\n", processId);
+    _ASSERTE(pHandle != nullptr);
+    *pHandle = UINT32_MAX;
+#ifdef __APPLE__
+    mach_port_name_t port;
+    kern_return_t result = ::task_for_pid(mach_task_self(), (int)processId, &port);
+    if (result != KERN_SUCCESS)
+    {
+        ERROR("task_for_pid(%d) FAILED %x %s\n", processId, result, mach_error_string(result));
+        LOGEXIT("PAL_OpenProcessMemory FALSE\n");
+        return FALSE;
+    }
+    *pHandle = port;
+#else
+    char memPath[128];
+    _snprintf_s(memPath, sizeof(memPath), sizeof(memPath), "/proc/%lu/mem", processId);
+
+    int fd = open(memPath, O_RDONLY);
+    if (fd == -1)
+    {
+        ERROR("open(%s) FAILED %d (%s)\n", memPath, errno, strerror(errno));
+        LOGEXIT("PAL_OpenProcessMemory FALSE\n");
+        return FALSE;
+    }
+    *pHandle = fd;
+#endif
+    LOGEXIT("PAL_OpenProcessMemory TRUE\n");
+    return TRUE;
+}
+
+/*++
+Function:
+  PAL_CloseProcessMemory
+
+Abstract
+  Closes the PAL_OpenProcessMemory handle.
+
+Parameter
+  handle : from PAL_OpenProcessMemory
+
+Return
+  none
+--*/
+VOID
+PALAPI
+PAL_CloseProcessMemory(
+    IN DWORD handle
+)
+{
+    ENTRY("PAL_CloseProcessMemory(handle=%x)\n", handle);
+    if (handle != UINT32_MAX)
+    {
+#ifdef __APPLE__
+        kern_return_t result = ::mach_port_deallocate(mach_task_self(), (mach_port_name_t)handle);
+        if (result != KERN_SUCCESS)
+        {
+            ERROR("mach_port_deallocate FAILED %x %s\n", result, mach_error_string(result));
+        }
+#else
+        close(handle);
+#endif
+    }
+    LOGEXIT("PAL_CloseProcessMemory\n");
+}
+
+/*++
+Function:
+  PAL_ReadProcessMemory
+
+Abstract
+  Reads process memory. 
+
+Parameter
+  handle : from PAL_OpenProcessMemory
+  address : address of memory to read
+  buffer : buffer to read memory to
+  size : number of bytes to read
+  numberOfBytesRead: number of bytes read (optional)
+
+Return
+  true read memory is successful, false if not.
+--*/
+BOOL
+PALAPI
+PAL_ReadProcessMemory(
+    IN DWORD handle,
+    IN ULONG64 address,
+    IN LPVOID buffer,
+    IN SIZE_T size,
+    OUT SIZE_T* numberOfBytesRead)
+{
+    ENTRY("PAL_ReadProcessMemory(handle=%x, address=%p buffer=%p size=%d)\n", handle, (void*)address, buffer, size);
+    _ASSERTE(handle != 0);
+    _ASSERTE(numberOfBytesRead != nullptr);
+    BOOL result = TRUE;
+    size_t read = 0;
+#ifdef __APPLE__
+    vm_map_t task = (vm_map_t)handle;
+
+    // vm_read_overwrite usually requires that the address be page-aligned
+    // and the size be a multiple of the page size.  We can't differentiate
+    // between the cases in which that's required and those in which it
+    // isn't, so we do it all the time.
+    const size_t pageSize = GetVirtualPageSize();
+    vm_address_t addressAligned = ALIGN_DOWN(address, pageSize);
+    size_t offset = OffsetWithinPage(address);
+    size_t bytesToRead;
+
+    char *data = (char*)malloc(pageSize);
+    if (data == nullptr)
+    {
+        ERROR("malloc(%d) FAILED\n", pageSize);
+        result = FALSE;
+        goto exit;
+    }
+
+    while (size > 0)
+    {
+        vm_size_t bytesRead;
+        
+        bytesToRead = pageSize - offset;
+        if (bytesToRead > size)
+        {
+            bytesToRead = size;
+        }
+        bytesRead = pageSize;
+        kern_return_t result = ::vm_read_overwrite(task, addressAligned, pageSize, (vm_address_t)data, &bytesRead);
+        if (result != KERN_SUCCESS || bytesRead != pageSize)
+        {
+            ERROR("vm_read_overwrite failed for %d bytes from %p: %x %s\n", pageSize, (void*)addressAligned, result, mach_error_string(result));
+            result = FALSE;
+            goto exit;
+        }
+        memcpy((LPSTR)buffer + read , data + offset, bytesToRead);
+        addressAligned = addressAligned + pageSize;
+        read += bytesToRead;
+        size -= bytesToRead;
+        offset = 0;
+    }
+
+exit:
+    if (data != nullptr)
+    {
+        free(data);
+    }
+#else
+    read = pread(handle, buffer, size, address);
+    if (read == (size_t)-1)
+    {
+        result = FALSE;
+    }
+#endif
+    *numberOfBytesRead = read;
+    LOGEXIT("PAL_ReadProcessMemory result=%d bytes read=%d\n", result, read);
+    return result;
+}
+
 /*++
 Function:
   PAL_ProbeMemory
diff --git a/src/coreclr/src/pal/src/eventprovider/dummyprovider/CMakeLists.txt b/src/coreclr/src/pal/src/eventprovider/dummyprovider/CMakeLists.txt
index 39b9826d1ab5a0..8e6968cf783d4d 100644
--- a/src/coreclr/src/pal/src/eventprovider/dummyprovider/CMakeLists.txt
+++ b/src/coreclr/src/pal/src/eventprovider/dummyprovider/CMakeLists.txt
@@ -1,8 +1,8 @@
-include(FindPython)
+include(FindPythonInterp)
 
 set (GENERATE_SCRIPT ${CLR_DIR}/src/scripts/genDummyProvider.py)
 
-set(GENERATE_COMMAND ${Python_EXECUTABLE} ${GENERATE_SCRIPT} --man ${EVENT_MANIFEST} --intermediate ${CMAKE_CURRENT_BINARY_DIR})
+set(GENERATE_COMMAND ${PYTHON_EXECUTABLE} ${GENERATE_SCRIPT} --man ${EVENT_MANIFEST} --intermediate ${CMAKE_CURRENT_BINARY_DIR})
 
 execute_process(
   COMMAND ${GENERATE_COMMAND} --dry-run
diff --git a/src/coreclr/src/pal/src/eventprovider/lttngprovider/CMakeLists.txt b/src/coreclr/src/pal/src/eventprovider/lttngprovider/CMakeLists.txt
index 234dea19b753db..d55dab3557f35b 100644
--- a/src/coreclr/src/pal/src/eventprovider/lttngprovider/CMakeLists.txt
+++ b/src/coreclr/src/pal/src/eventprovider/lttngprovider/CMakeLists.txt
@@ -1,7 +1,7 @@
-include(FindPython)
+include(FindPythonInterp)
 set (GENERATE_SCRIPT ${CLR_DIR}/src/scripts/genLttngProvider.py)
 
-set(GENERATE_COMMAND ${Python_EXECUTABLE} ${GENERATE_SCRIPT} --man ${EVENT_MANIFEST} --intermediate ${CMAKE_CURRENT_BINARY_DIR})
+set(GENERATE_COMMAND ${PYTHON_EXECUTABLE} ${GENERATE_SCRIPT} --man ${EVENT_MANIFEST} --intermediate ${CMAKE_CURRENT_BINARY_DIR})
 
 execute_process(
   COMMAND ${GENERATE_COMMAND} --dry-run
diff --git a/src/coreclr/src/pal/src/locale/utf8.cpp b/src/coreclr/src/pal/src/locale/utf8.cpp
index b8a6f7ad5d6fdb..63bfc8661715d5 100644
--- a/src/coreclr/src/pal/src/locale/utf8.cpp
+++ b/src/coreclr/src/pal/src/locale/utf8.cpp
@@ -10,7 +10,7 @@ Module Name:
     unicode/utf8.c
 
 Abstract:
-    Functions to encode and decode UTF-8 strings. This is a port of the C# version from mscorlib.
+    Functions to encode and decode UTF-8 strings. This is a port of the C# version from Utf8Encoding.cs.
 
 Revision History:
 
diff --git a/src/coreclr/src/pal/src/map/map.cpp b/src/coreclr/src/pal/src/map/map.cpp
index 75405c7407c8bf..0cbaef5521d0fe 100644
--- a/src/coreclr/src/pal/src/map/map.cpp
+++ b/src/coreclr/src/pal/src/map/map.cpp
@@ -2137,7 +2137,7 @@ MAPRecordMapping(
     return palError;
 }
 
-static size_t OffsetWithinPage(off_t addr)
+size_t OffsetWithinPage(off_t addr)
 {
     return addr & (GetVirtualPageSize() - 1);
 }
diff --git a/src/coreclr/src/pal/src/thread/thread.cpp b/src/coreclr/src/pal/src/thread/thread.cpp
index 6efe93492bc3aa..89d805c3540410 100644
--- a/src/coreclr/src/pal/src/thread/thread.cpp
+++ b/src/coreclr/src/pal/src/thread/thread.cpp
@@ -740,41 +740,6 @@ CorUnix::InternalCreateThread(
     storedErrno = errno;
 #endif  // PTHREAD_CREATE_MODIFIES_ERRNO
 
-#if HAVE_PTHREAD_ATTR_SETAFFINITY_NP && HAVE_SCHED_GETAFFINITY
-    {
-        // Threads inherit their parent's affinity mask on Linux. This is not desired, so we reset
-        // the current thread's affinity mask to the mask of the current process.
-        cpu_set_t cpuSet;
-        CPU_ZERO(&cpuSet);
-
-        int st = sched_getaffinity(gPID, sizeof(cpu_set_t), &cpuSet);
-        if (st != 0)
-        {
-            ASSERT("sched_getaffinity failed!\n");
-            // the sched_getaffinity should never fail for getting affinity of the current process
-            palError = ERROR_INTERNAL_ERROR;
-            goto EXIT;
-        }
-
-        st = pthread_attr_setaffinity_np(&pthreadAttr, sizeof(cpu_set_t), &cpuSet);
-        if (st != 0)
-        {
-            if (st == ENOMEM)
-            {
-                palError = ERROR_NOT_ENOUGH_MEMORY;
-            }
-            else
-            {
-                ASSERT("pthread_attr_setaffinity_np failed!\n");
-                // The pthread_attr_setaffinity_np should never fail except of OOM when
-                // passed the mask extracted using sched_getaffinity.
-                palError = ERROR_INTERNAL_ERROR;
-            }
-            goto EXIT;
-        }
-    }
-#endif // HAVE_PTHREAD_GETAFFINITY_NP && HAVE_SCHED_GETAFFINITY
-
     iError = pthread_create(&pthread, &pthreadAttr, CPalThread::ThreadEntry, pNewThread);
 
 #if PTHREAD_CREATE_MODIFIES_ERRNO
@@ -1754,6 +1719,10 @@ CPalThread::ThreadEntry(
     PTHREAD_START_ROUTINE pfnStartRoutine;
     LPVOID pvPar;
     DWORD retValue;
+#if HAVE_SCHED_GETAFFINITY && HAVE_SCHED_SETAFFINITY
+    cpu_set_t cpuSet;
+    int st;
+#endif
 
     pThread = reinterpret_cast<CPalThread*>(pvParam);
 
@@ -1763,6 +1732,42 @@ CPalThread::ThreadEntry(
         goto fail;
     }
 
+#if HAVE_SCHED_GETAFFINITY && HAVE_SCHED_SETAFFINITY
+    // Threads inherit their parent's affinity mask on Linux. This is not desired, so we reset
+    // the current thread's affinity mask to the mask of the current process.
+    //
+    // Typically, we would use pthread_attr_setaffinity_np() and have pthread_create() create the thread with the specified
+    // affinity. At least one implementation of pthread_create() following a pthread_attr_setaffinity_np() calls
+    // sched_setaffinity(<newThreadPid>, ...), which is not allowed under Snap's default strict confinement without manually
+    // connecting the process-control plug. To work around that, have the thread set the affinity after it starts.
+    // sched_setaffinity(<currentThreadPid>, ...) is also currently not allowed, only sched_setaffinity(0, ...).
+    // pthread_setaffinity_np(pthread_self(), ...) seems to call sched_setaffinity(<currentThreadPid>, ...) in at least one
+    // implementation, and does not work. Use sched_setaffinity(0, ...) instead. See the following for more information:
+    // - https://github.com/dotnet/runtime/pull/38795
+    // - https://github.com/dotnet/runtime/issues/1634
+    // - https://forum.snapcraft.io/t/requesting-autoconnect-for-interfaces-in-pigmeat-process-control-home/17987/13
+
+    CPU_ZERO(&cpuSet);
+
+    st = sched_getaffinity(gPID, sizeof(cpu_set_t), &cpuSet);
+    if (st != 0)
+    {
+        ASSERT("sched_getaffinity failed!\n");
+        // The sched_getaffinity should never fail for getting affinity of the current process
+        palError = ERROR_INTERNAL_ERROR;
+        goto fail;
+    }
+
+    st = sched_setaffinity(0, sizeof(cpu_set_t), &cpuSet);
+    if (st != 0)
+    {
+        ASSERT("sched_setaffinity failed!\n");
+        // The sched_setaffinity should never fail when passed the mask extracted using sched_getaffinity
+        palError = ERROR_INTERNAL_ERROR;
+        goto fail;
+    }
+#endif // HAVE_SCHED_GETAFFINITY && HAVE_SCHED_SETAFFINITY
+
 #if !HAVE_MACH_EXCEPTIONS
     if (!pThread->EnsureSignalAlternateStack())
     {
@@ -2946,18 +2951,31 @@ BOOL
 PALAPI
 PAL_SetCurrentThreadAffinity(WORD procNo)
 {
-#if HAVE_PTHREAD_GETAFFINITY_NP
+#if HAVE_SCHED_SETAFFINITY || HAVE_PTHREAD_SETAFFINITY_NP
     cpu_set_t cpuSet;
     CPU_ZERO(&cpuSet);
-
     CPU_SET(procNo, &cpuSet);
+
+    // Snap's default strict confinement does not allow sched_setaffinity(<nonzeroPid>, ...) without manually connecting the
+    // process-control plug. sched_setaffinity(<currentThreadPid>, ...) is also currently not allowed, only
+    // sched_setaffinity(0, ...). pthread_setaffinity_np(pthread_self(), ...) seems to call
+    // sched_setaffinity(<currentThreadPid>, ...) in at least one implementation, and does not work. To work around those
+    // issues, use sched_setaffinity(0, ...) if available and only otherwise fall back to pthread_setaffinity_np(). See the
+    // following for more information:
+    // - https://github.com/dotnet/runtime/pull/38795
+    // - https://github.com/dotnet/runtime/issues/1634
+    // - https://forum.snapcraft.io/t/requesting-autoconnect-for-interfaces-in-pigmeat-process-control-home/17987/13
+#if HAVE_SCHED_SETAFFINITY
+    int st = sched_setaffinity(0, sizeof(cpu_set_t), &cpuSet);
+#else
     int st = pthread_setaffinity_np(pthread_self(), sizeof(cpu_set_t), &cpuSet);
+#endif
 
     return st == 0;
-#else  // HAVE_PTHREAD_GETAFFINITY_NP
+#else  // !(HAVE_SCHED_SETAFFINITY || HAVE_PTHREAD_SETAFFINITY_NP)
     // There is no API to manage thread affinity, so let's ignore the request
     return FALSE;
-#endif // HAVE_PTHREAD_GETAFFINITY_NP
+#endif // HAVE_SCHED_SETAFFINITY || HAVE_PTHREAD_SETAFFINITY_NP
 }
 
 /*++
diff --git a/src/coreclr/src/pal/tests/palsuite/common/ResultBuffer.cpp b/src/coreclr/src/pal/tests/palsuite/common/ResultBuffer.cpp
index 4119399b36181e..36924c3c30a2a0 100644
--- a/src/coreclr/src/pal/tests/palsuite/common/ResultBuffer.cpp
+++ b/src/coreclr/src/pal/tests/palsuite/common/ResultBuffer.cpp
@@ -3,11 +3,6 @@
 
 //#include "stdafx.h"
 #include "resultbuffer.h"
-//
-//#using <mscorlib.dll>
-//
-//using namespace System;
-
 
 ResultBuffer:: ResultBuffer(int ThreadCount, int ThreadLogSize)
 	{
diff --git a/src/coreclr/src/pal/tests/palsuite/composite/synchronization/nativecriticalsection/resultbuffer.cpp b/src/coreclr/src/pal/tests/palsuite/composite/synchronization/nativecriticalsection/resultbuffer.cpp
index e99e31ff31d36a..32e8f92b3e083d 100644
--- a/src/coreclr/src/pal/tests/palsuite/composite/synchronization/nativecriticalsection/resultbuffer.cpp
+++ b/src/coreclr/src/pal/tests/palsuite/composite/synchronization/nativecriticalsection/resultbuffer.cpp
@@ -3,11 +3,6 @@
 
 //#include "stdafx.h"
 #include "resultbuffer.h"
-//
-//#using <mscorlib.dll>
-//
-//using namespace System;
-
 
 ResultBuffer:: ResultBuffer(int ThreadCount, int ThreadLogSize)
 	{
diff --git a/src/coreclr/src/pal/tests/palsuite/composite/synchronization/nativecs_interlocked/resultbuffer.cpp b/src/coreclr/src/pal/tests/palsuite/composite/synchronization/nativecs_interlocked/resultbuffer.cpp
index e99e31ff31d36a..32e8f92b3e083d 100644
--- a/src/coreclr/src/pal/tests/palsuite/composite/synchronization/nativecs_interlocked/resultbuffer.cpp
+++ b/src/coreclr/src/pal/tests/palsuite/composite/synchronization/nativecs_interlocked/resultbuffer.cpp
@@ -3,11 +3,6 @@
 
 //#include "stdafx.h"
 #include "resultbuffer.h"
-//
-//#using <mscorlib.dll>
-//
-//using namespace System;
-
 
 ResultBuffer:: ResultBuffer(int ThreadCount, int ThreadLogSize)
 	{
diff --git a/src/coreclr/src/pal/tests/palsuite/eventprovider/CMakeLists.txt b/src/coreclr/src/pal/tests/palsuite/eventprovider/CMakeLists.txt
index 000ee2d2fb0d12..845fae656be41a 100644
--- a/src/coreclr/src/pal/tests/palsuite/eventprovider/CMakeLists.txt
+++ b/src/coreclr/src/pal/tests/palsuite/eventprovider/CMakeLists.txt
@@ -5,10 +5,10 @@ set(SOURCES
 set(EVENT_MANIFEST ${VM_DIR}/ClrEtwAll.man)
 set(TEST_GENERATOR ${CLR_DIR}/src/scripts/genEventingTests.py)
 
-include(FindPython)
+include(FindPythonInterp)
 
 add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/clralltestevents.cpp
-  COMMAND ${Python_EXECUTABLE} ${TEST_GENERATOR} --testdir "${CMAKE_CURRENT_BINARY_DIR}" --man "${EVENT_MANIFEST}"
+  COMMAND ${PYTHON_EXECUTABLE} ${TEST_GENERATOR} --testdir "${CMAKE_CURRENT_BINARY_DIR}" --man "${EVENT_MANIFEST}"
   DEPENDS ${EVENT_MANIFEST} ${TEST_GENERATOR}
   COMMENT "Updating clralltestevents.cpp"
 )
diff --git a/src/coreclr/src/scripts/genEtwProvider.py b/src/coreclr/src/scripts/genEtwProvider.py
index 1a146b5fda36ff..e7df63bb5b38ff 100644
--- a/src/coreclr/src/scripts/genEtwProvider.py
+++ b/src/coreclr/src/scripts/genEtwProvider.py
@@ -164,7 +164,7 @@ def genEtwMacroHeader(manifest, exclusion_filename, intermediate):
 
         header_file.write("#define NO_OF_ETW_PROVIDERS " + str(numOfProviders) + "\n")
         header_file.write("#define MAX_BYTES_PER_ETW_PROVIDER " + str(nMaxEventBytesPerProvider) + "\n")
-        header_file.write("EXTERN_C SELECTANY const BYTE etwStackSupportedEvents[NO_OF_ETW_PROVIDERS][MAX_BYTES_PER_ETW_PROVIDER] = \n{\n")
+        header_file.write("EXTERN_C constexpr BYTE etwStackSupportedEvents[NO_OF_ETW_PROVIDERS][MAX_BYTES_PER_ETW_PROVIDER] = \n{\n")
 
         for providerNode in tree.getElementsByTagName('provider'):
             stackSupportedEvents = [0]*nMaxEventBytesPerProvider
diff --git a/src/coreclr/src/scripts/genEventing.py b/src/coreclr/src/scripts/genEventing.py
index c591be8dc0640a..a7919768c3abc1 100644
--- a/src/coreclr/src/scripts/genEventing.py
+++ b/src/coreclr/src/scripts/genEventing.py
@@ -627,7 +627,7 @@ def generatePlatformIndependentFiles(sClrEtwAllMan, incDir, etmDummyFile, extern
 
             if is_windows:
                 eventpipeProviderCtxName = providerSymbol + "_EVENTPIPE_Context"
-                Clrallevents.write('SELECTANY EVENTPIPE_TRACE_CONTEXT const ' + eventpipeProviderCtxName + ' = { W("' + providerName + '"), 0, false, 0 };\n')
+                Clrallevents.write('constexpr EVENTPIPE_TRACE_CONTEXT ' + eventpipeProviderCtxName + ' = { W("' + providerName + '"), 0, false, 0 };\n')
 
     if write_xplatheader:
         clrproviders = os.path.join(incDir, "clrproviders.h")
@@ -676,14 +676,14 @@ def generatePlatformIndependentFiles(sClrEtwAllMan, incDir, etmDummyFile, extern
                     symbolName = eventNode.getAttribute('symbol')
                     keywords = eventNode.getAttribute('keywords')
                     level = convertToLevelId(levelName)
-                    Clrproviders.write("SELECTANY EVENT_DESCRIPTOR const " + symbolName + " = { " + str(level) + ", " + hex(getKeywordsMaskCombined(keywords, keywordsToMask)) + " };\n")
+                    Clrproviders.write("constexpr EVENT_DESCRIPTOR " + symbolName + " = { " + str(level) + ", " + hex(getKeywordsMaskCombined(keywords, keywordsToMask)) + " };\n")
 
                 allProviders.append("&" + providerSymbol + "_LTTNG_Context")
 
             # define and initialize runtime providers' DOTNET_TRACE_CONTEXT depending on the platform
             if not is_windows:
                 Clrproviders.write('#define NB_PROVIDERS ' + str(nbProviders) + '\n')
-                Clrproviders.write('SELECTANY LTTNG_TRACE_CONTEXT * const ALL_LTTNG_PROVIDERS_CONTEXT[NB_PROVIDERS] = { ')
+                Clrproviders.write('constexpr LTTNG_TRACE_CONTEXT * ALL_LTTNG_PROVIDERS_CONTEXT[NB_PROVIDERS] = { ')
                 Clrproviders.write(', '.join(allProviders))
                 Clrproviders.write(' };\n')
 
diff --git a/src/coreclr/src/tools/Common/Compiler/TypeExtensions.cs b/src/coreclr/src/tools/Common/Compiler/TypeExtensions.cs
index 89fd08f3dbab42..dd54a1387bdf9e 100644
--- a/src/coreclr/src/tools/Common/Compiler/TypeExtensions.cs
+++ b/src/coreclr/src/tools/Common/Compiler/TypeExtensions.cs
@@ -97,6 +97,19 @@ public static bool IsArrayAddressMethod(this MethodDesc method)
             return arrayMethod != null && arrayMethod.Kind == ArrayMethodKind.Address;
         }
 
+
+        /// <summary>
+        /// Returns true if '<paramref name="method"/>' is one of the special methods on multidimensional array types (set, get, address).
+        /// </summary>
+        public static bool IsArrayMethod(this MethodDesc method)
+        {
+            var arrayMethod = method as ArrayMethod;
+            return arrayMethod != null && (arrayMethod.Kind == ArrayMethodKind.Address || 
+                                           arrayMethod.Kind == ArrayMethodKind.Get || 
+                                           arrayMethod.Kind == ArrayMethodKind.Set || 
+                                           arrayMethod.Kind == ArrayMethodKind.Ctor);
+        }
+
         /// <summary>
         /// Gets a value indicating whether this type has any generic virtual methods.
         /// </summary>
diff --git a/src/coreclr/src/tools/Common/Internal/NativeFormat/NativeFormat.cs b/src/coreclr/src/tools/Common/Internal/NativeFormat/NativeFormat.cs
index e92c689d658b22..1ebbdac34811e8 100644
--- a/src/coreclr/src/tools/Common/Internal/NativeFormat/NativeFormat.cs
+++ b/src/coreclr/src/tools/Common/Internal/NativeFormat/NativeFormat.cs
@@ -84,8 +84,8 @@ enum FixupSignatureKind : uint
         MethodLdToken               = 0x08,
         AllocateObject              = 0x09,
         DefaultConstructor          = 0x0a,
-        TlsIndex                    = 0x0b,
-        TlsOffset                   = 0x0c,
+        ThreadStaticIndex           = 0x0b,
+        // unused                   = 0x0c,
         Method                      = 0x0d,
         IsInst                      = 0x0e,
         CastClass                   = 0x0f,
diff --git a/src/coreclr/src/tools/Common/Internal/Runtime/CorConstants.cs b/src/coreclr/src/tools/Common/Internal/Runtime/CorConstants.cs
index 0b9f35726a1364..57a3353a805d41 100644
--- a/src/coreclr/src/tools/Common/Internal/Runtime/CorConstants.cs
+++ b/src/coreclr/src/tools/Common/Internal/Runtime/CorConstants.cs
@@ -81,7 +81,7 @@ public enum CorElementType : byte
         // where the encoding/decoding takes place.
         ELEMENT_TYPE_NATIVE_VALUETYPE_ZAPSIG = 0x3d,
 
-        ELEMENT_TYPE_CANON_ZAPSIG = 0x3e,       // zapsig encoding for [mscorlib]System.__Canon
+        ELEMENT_TYPE_CANON_ZAPSIG = 0x3e,       // zapsig encoding for System.__Canon
         ELEMENT_TYPE_MODULE_ZAPSIG = 0x3f,      // zapsig encoding for external module id#
 
         ELEMENT_TYPE_HANDLE = 64,
diff --git a/src/coreclr/src/tools/Common/Internal/Runtime/ReadyToRunConstants.cs b/src/coreclr/src/tools/Common/Internal/Runtime/ReadyToRunConstants.cs
index ce6de5de37cac4..6d92e7b5d1227c 100644
--- a/src/coreclr/src/tools/Common/Internal/Runtime/ReadyToRunConstants.cs
+++ b/src/coreclr/src/tools/Common/Internal/Runtime/ReadyToRunConstants.cs
@@ -314,6 +314,17 @@ public enum ReadyToRunHelper
         TypeHandleToRuntimeTypeHandle,
     }
 
+    // Enum used for HFA type recognition.
+    // Supported across architectures, so that it can be used in altjits and cross-compilation.
+    public enum ReadyToRunHFAElemType
+    {
+        None = 0,
+        Float32 = 1,
+        Float64 = 2,
+        Vector64 = 3,
+        Vector128 = 4,
+    }
+
     public static class ReadyToRunRuntimeConstants
     {
         public const int READYTORUN_PInvokeTransitionFrameSizeInPointerUnits = 11;
diff --git a/src/coreclr/src/tools/Common/JitInterface/CorInfoImpl.Intrinsics.cs b/src/coreclr/src/tools/Common/JitInterface/CorInfoImpl.Intrinsics.cs
index 3f6c089744b217..46cac9f2e8d4e3 100644
--- a/src/coreclr/src/tools/Common/JitInterface/CorInfoImpl.Intrinsics.cs
+++ b/src/coreclr/src/tools/Common/JitInterface/CorInfoImpl.Intrinsics.cs
@@ -76,55 +76,6 @@ static IntrinsicHashtable InitializeIntrinsicHashtable()
         {
             IntrinsicHashtable table = new IntrinsicHashtable();
 
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Sin, "Sin", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Sin, "Sin", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Cos, "Cos", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Cos, "Cos", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Cbrt, "Cbrt", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Cbrt, "Cbrt", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Sqrt, "Sqrt", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Sqrt, "Sqrt", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Abs, "Abs", "System", "Math");
-            // No System.MathF entry for CORINFO_INTRTINSIC_Abs as System.Math exposes and handles both float and double
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Round, "Round", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Round, "Round", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Cosh, "Cosh", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Cosh, "Cosh", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Sinh, "Sinh", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Sinh, "Sinh", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Tan, "Tan", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Tan, "Tan", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Tanh, "Tanh", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Tanh, "Tanh", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Asin, "Asin", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Asin, "Asin", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Asinh, "Asinh", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Asinh, "Asinh", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Acos, "Acos", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Acos, "Acos", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Acosh, "Acosh", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Acosh, "Acosh", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Atan, "Atan", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Atan, "Atan", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Atan2, "Atan2", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Atan2, "Atan2", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Atanh, "Atanh", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Atanh, "Atanh", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Log10, "Log10", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Log10, "Log10", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Pow, "Pow", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Pow, "Pow", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Exp, "Exp", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Exp, "Exp", "System", "MathF");
-#if !READYTORUN
-            // These are normally handled via the SSE4.1 instructions ROUNDSS/ROUNDSD.
-            // However, we don't know the ISAs the target machine supports so we should
-            // fallback to the method call implementation instead.
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Ceiling, "Ceiling", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Ceiling, "Ceiling", "System", "MathF");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Floor, "Floor", "System", "Math");
-            table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Floor, "Floor", "System", "MathF");
-#endif
             // table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_GetChar, null, null, null); // unused
             // table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Array_GetDimLength, "GetLength", "System", "Array"); // not handled
             table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_Array_Get, "Get", null, null);
@@ -163,7 +114,7 @@ static IntrinsicHashtable InitializeIntrinsicHashtable()
             table.Add(CorInfoIntrinsics.CORINFO_INTRINSIC_GetRawHandle, "AllocatorOf", "System", "Activator");
 
             // If this assert fails, make sure to add the new intrinsics to the table above and update the expected count below.
-            Debug.Assert((int)CorInfoIntrinsics.CORINFO_INTRINSIC_Count == 56, "Please update intrinsic hash table");
+            Debug.Assert((int)CorInfoIntrinsics.CORINFO_INTRINSIC_Count == 34, "Please update intrinsic hash table");
 
             return table;
         }
@@ -201,14 +152,6 @@ private CorInfoIntrinsics getIntrinsicID(MethodDesc method, byte* pMustExpand)
             CorInfoIntrinsics id = entry.Id;
             switch (id)
             {
-                case CorInfoIntrinsics.CORINFO_INTRINSIC_Abs:
-                    {
-                        // RyuJIT handles floating point overloads only
-                        var returnTypeCategory = method.Signature.ReturnType.Category;
-                        if (returnTypeCategory != TypeFlags.Double && returnTypeCategory != TypeFlags.Single)
-                            return CorInfoIntrinsics.CORINFO_INTRINSIC_Illegal;
-                    }
-                    break;
                 case CorInfoIntrinsics.CORINFO_INTRINSIC_Array_Get:
                 case CorInfoIntrinsics.CORINFO_INTRINSIC_Array_Address:
                 case CorInfoIntrinsics.CORINFO_INTRINSIC_Array_Set:
diff --git a/src/coreclr/src/tools/Common/JitInterface/CorInfoImpl.cs b/src/coreclr/src/tools/Common/JitInterface/CorInfoImpl.cs
index da5d691a39cf6d..3d7dd28329b9bb 100644
--- a/src/coreclr/src/tools/Common/JitInterface/CorInfoImpl.cs
+++ b/src/coreclr/src/tools/Common/JitInterface/CorInfoImpl.cs
@@ -508,6 +508,7 @@ private bool TryGetUnmanagedCallingConventionFromModOpt(MethodSignature signatur
             if (!signature.HasEmbeddedSignatureData || signature.GetEmbeddedSignatureData() == null)
                 return false;
 
+            bool found = false;
             foreach (EmbeddedSignatureData data in signature.GetEmbeddedSignatureData())
             {
                 if (data.kind != EmbeddedSignatureDataKind.OptionalCustomModifier)
@@ -524,25 +525,28 @@ private bool TryGetUnmanagedCallingConventionFromModOpt(MethodSignature signatur
                 if (defType.Namespace != "System.Runtime.CompilerServices")
                     continue;
 
-                // Take the first recognized calling convention in metadata.
-                switch (defType.Name)
+                // Look for a recognized calling convention in metadata.
+                CorInfoCallConv? callConvLocal = defType.Name switch
                 {
-                    case "CallConvCdecl":
-                        callConv = CorInfoCallConv.CORINFO_CALLCONV_C;
-                        return true;
-                    case "CallConvStdcall":
-                        callConv = CorInfoCallConv.CORINFO_CALLCONV_STDCALL;
-                        return true;
-                    case "CallConvFastcall":
-                        callConv = CorInfoCallConv.CORINFO_CALLCONV_FASTCALL;
-                        return true;
-                    case "CallConvThiscall":
-                        callConv = CorInfoCallConv.CORINFO_CALLCONV_THISCALL;
-                        return true;
+                    "CallConvCdecl"     => CorInfoCallConv.CORINFO_CALLCONV_C,
+                    "CallConvStdcall"   => CorInfoCallConv.CORINFO_CALLCONV_STDCALL,
+                    "CallConvFastcall"  => CorInfoCallConv.CORINFO_CALLCONV_FASTCALL,
+                    "CallConvThiscall"  => CorInfoCallConv.CORINFO_CALLCONV_THISCALL,
+                    _ => null
+                };
+
+                if (callConvLocal.HasValue)
+                {
+                    // Error if there are multiple recognized calling conventions
+                    if (found)
+                        ThrowHelper.ThrowInvalidProgramException(ExceptionStringID.InvalidProgramMultipleCallConv, MethodBeingCompiled);
+ 
+                    callConv = callConvLocal.Value;
+                    found = true;
                 }
             }
 
-            return false;
+            return found;
         }
 
         private void Get_CORINFO_SIG_INFO(MethodSignature signature, CORINFO_SIG_INFO* sig)
@@ -811,7 +815,7 @@ private uint getMethodAttribsInternal(MethodDesc method)
                 // do a dynamic check instead.
                 if (
                     !HardwareIntrinsicHelpers.IsIsSupportedMethod(method)
-                    || !_compilation.IsHardwareInstrinsicWithRuntimeDeterminedSupport(method))
+                    || !_compilation.IsHardwareIntrinsicWithRuntimeDeterminedSupport(method))
 #endif
                 {
                     result |= CorInfoFlag.CORINFO_FLG_JIT_INTRINSIC;
diff --git a/src/coreclr/src/tools/Common/JitInterface/CorInfoTypes.cs b/src/coreclr/src/tools/Common/JitInterface/CorInfoTypes.cs
index c1a9f87533ad05..8f4b1f60b92a11 100644
--- a/src/coreclr/src/tools/Common/JitInterface/CorInfoTypes.cs
+++ b/src/coreclr/src/tools/Common/JitInterface/CorInfoTypes.cs
@@ -416,28 +416,6 @@ public enum CorInfoOptions
 
     public enum CorInfoIntrinsics
     {
-        CORINFO_INTRINSIC_Sin,
-        CORINFO_INTRINSIC_Cos,
-        CORINFO_INTRINSIC_Cbrt,
-        CORINFO_INTRINSIC_Sqrt,
-        CORINFO_INTRINSIC_Abs,
-        CORINFO_INTRINSIC_Round,
-        CORINFO_INTRINSIC_Cosh,
-        CORINFO_INTRINSIC_Sinh,
-        CORINFO_INTRINSIC_Tan,
-        CORINFO_INTRINSIC_Tanh,
-        CORINFO_INTRINSIC_Asin,
-        CORINFO_INTRINSIC_Asinh,
-        CORINFO_INTRINSIC_Acos,
-        CORINFO_INTRINSIC_Acosh,
-        CORINFO_INTRINSIC_Atan,
-        CORINFO_INTRINSIC_Atan2,
-        CORINFO_INTRINSIC_Atanh,
-        CORINFO_INTRINSIC_Log10,
-        CORINFO_INTRINSIC_Pow,
-        CORINFO_INTRINSIC_Exp,
-        CORINFO_INTRINSIC_Ceiling,
-        CORINFO_INTRINSIC_Floor,
         CORINFO_INTRINSIC_GetChar,              // fetch character out of string
         CORINFO_INTRINSIC_Array_GetDimLength,   // Get number of elements in a given dimension of an array
         CORINFO_INTRINSIC_Array_Get,            // Get the value of an element in an array
diff --git a/src/coreclr/src/tools/Common/JitInterface/ThunkGenerator/InstructionSetDesc.txt b/src/coreclr/src/tools/Common/JitInterface/ThunkGenerator/InstructionSetDesc.txt
index 615fc9648ed58a..d8fe3984a92515 100644
--- a/src/coreclr/src/tools/Common/JitInterface/ThunkGenerator/InstructionSetDesc.txt
+++ b/src/coreclr/src/tools/Common/JitInterface/ThunkGenerator/InstructionSetDesc.txt
@@ -15,6 +15,10 @@
 ; Copy instruction sets defined for other architecture at this point in the file.
 ; copyinstructionsets,<architecture>,<copytoarchitecture>
 
+; UPDATE JIT/EE INTERFACE GUID WHEN CHANGING THESE DEFINITIONS. The instruction set definitions are part of JIT/EE interface contract.
+
+; DO NOT CHANGE R2R NUMERIC VALUES OF THE EXISTING SETS. Changing R2R numberic values definitions would be R2R format breaking change.
+
 ; Definition of X86 instruction sets
 definearch         ,X86   ,32Bit     ,X64
 
diff --git a/src/coreclr/src/tools/Common/TypeSystem/Common/CastingHelper.cs b/src/coreclr/src/tools/Common/TypeSystem/Common/CastingHelper.cs
index d10a2dc0fec277..e10782ef0ad978 100644
--- a/src/coreclr/src/tools/Common/TypeSystem/Common/CastingHelper.cs
+++ b/src/coreclr/src/tools/Common/TypeSystem/Common/CastingHelper.cs
@@ -166,6 +166,17 @@ private static bool CanCastToInternal(this TypeDesc thisType, TypeDesc otherType
                 case TypeFlags.SzArray:
                     return ((ArrayType)thisType).CanCastArrayTo(otherType, protect);
 
+                case TypeFlags.ByRef:
+                case TypeFlags.Pointer:
+                    if (otherType.Category == thisType.Category)
+                    {
+                        return ((ParameterizedType)thisType).CanCastParamTo(((ParameterizedType)otherType).ParameterType, protect);
+                    }
+                    return false;
+
+                case TypeFlags.FunctionPointer:
+                    return false;
+
                 default:
                     Debug.Assert(thisType.IsDefType);
                     return thisType.CanCastToClassOrInterface(otherType, protect);
diff --git a/src/coreclr/src/tools/Common/TypeSystem/Common/ExceptionStringID.cs b/src/coreclr/src/tools/Common/TypeSystem/Common/ExceptionStringID.cs
index 00286eabe3a97b..d9d3de41634de8 100644
--- a/src/coreclr/src/tools/Common/TypeSystem/Common/ExceptionStringID.cs
+++ b/src/coreclr/src/tools/Common/TypeSystem/Common/ExceptionStringID.cs
@@ -36,6 +36,7 @@ public enum ExceptionStringID
         InvalidProgramNonStaticMethod,
         InvalidProgramGenericMethod,
         InvalidProgramNonBlittableTypes,
+        InvalidProgramMultipleCallConv,
 
         // BadImageFormatException
         BadImageFormatGeneric,
diff --git a/src/coreclr/src/tools/Common/TypeSystem/Common/MethodDesc.cs b/src/coreclr/src/tools/Common/TypeSystem/Common/MethodDesc.cs
index 0545857397ba1e..1da52dccd3bd0a 100644
--- a/src/coreclr/src/tools/Common/TypeSystem/Common/MethodDesc.cs
+++ b/src/coreclr/src/tools/Common/TypeSystem/Common/MethodDesc.cs
@@ -51,6 +51,14 @@ public sealed partial class MethodSignature : TypeSystemEntity
         // Value of <see cref="EmbeddedSignatureData.index" /> for any custom modifiers on the return type
         public const string IndexOfCustomModifiersOnReturnType = "0.1.1.1";
 
+        // Value of <see cref="EmbeddedSignatureData.index" /> for any custom modifiers on
+        // SomeStruct when SomeStruct *, or SomeStruct & is the type of a parameter or return type
+        // Parameter index 0 represents the return type, and indices 1-n represent the parameters to the signature
+        public static string GetIndexOfCustomModifierOnPointedAtTypeByParameterIndex(int parameterIndex)
+        {
+            return $"0.1.1.2.{(parameterIndex + 1).ToStringInvariant()}.1";
+        }
+
         public MethodSignature(MethodSignatureFlags flags, int genericParameterCount, TypeDesc returnType, TypeDesc[] parameters, EmbeddedSignatureData[] embeddedSignatureData = null)
         {
             _flags = flags;
diff --git a/src/coreclr/src/tools/Common/TypeSystem/Common/Properties/Resources.resx b/src/coreclr/src/tools/Common/TypeSystem/Common/Properties/Resources.resx
index 368145929e05a2..b0efd67b4adc55 100644
--- a/src/coreclr/src/tools/Common/TypeSystem/Common/Properties/Resources.resx
+++ b/src/coreclr/src/tools/Common/TypeSystem/Common/Properties/Resources.resx
@@ -174,7 +174,10 @@
   <data name="InvalidProgramNonBlittableTypes" xml:space="preserve">
     <value>UnmanagedCallersOnly attribute specified on method with non-blittable parameters '{0}'</value>
   </data>
+  <data name="InvalidProgramMultipleCallConv" xml:space="preserve">
+    <value>Multiple unmanaged calling conventions are specified. Only a single calling convention is supported.</value>
+  </data>
   <data name="BadImageFormatGeneric" xml:space="preserve">
     <value>The format of a DLL or executable being loaded is invalid</value>
   </data>
-</root>
\ No newline at end of file
+</root>
diff --git a/src/coreclr/src/tools/Common/TypeSystem/Common/ThrowHelper.cs b/src/coreclr/src/tools/Common/TypeSystem/Common/ThrowHelper.cs
index 9ab806e77ffe0e..094ade10facaa8 100644
--- a/src/coreclr/src/tools/Common/TypeSystem/Common/ThrowHelper.cs
+++ b/src/coreclr/src/tools/Common/TypeSystem/Common/ThrowHelper.cs
@@ -41,6 +41,12 @@ public static void ThrowInvalidProgramException()
             throw new TypeSystemException.InvalidProgramException();
         }
 
+        [System.Diagnostics.DebuggerHidden]
+        public static void ThrowInvalidProgramException(ExceptionStringID id)
+        {
+            throw new TypeSystemException.InvalidProgramException(id);
+        }
+
         [System.Diagnostics.DebuggerHidden]
         public static void ThrowInvalidProgramException(ExceptionStringID id, MethodDesc method)
         {
diff --git a/src/coreclr/src/tools/Common/TypeSystem/Common/TypeSystemException.Resources.cs b/src/coreclr/src/tools/Common/TypeSystem/Common/TypeSystemException.Resources.cs
new file mode 100644
index 00000000000000..bf5a3b97b292f4
--- /dev/null
+++ b/src/coreclr/src/tools/Common/TypeSystem/Common/TypeSystemException.Resources.cs
@@ -0,0 +1,24 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Resources;
+using System.Reflection;
+
+// This partial file is designed to allow the runtime variant of the type system to not
+// need to support accessing these strings via the ResourceManager
+namespace Internal.TypeSystem
+{
+    partial class TypeSystemException : Exception
+    {
+        private static Lazy<ResourceManager> s_stringResourceManager =
+            new Lazy<ResourceManager>(() => new ResourceManager("Internal.TypeSystem.Strings", typeof(TypeSystemException).GetTypeInfo().Assembly));
+
+        public static string GetFormatString(ExceptionStringID id)
+        {
+            return s_stringResourceManager.Value.GetString(id.ToString(), CultureInfo.InvariantCulture);
+        }
+    }
+}
diff --git a/src/coreclr/src/tools/Common/TypeSystem/Common/TypeSystemException.cs b/src/coreclr/src/tools/Common/TypeSystem/Common/TypeSystemException.cs
index c9a71236c4daf0..17836ca309bd0a 100644
--- a/src/coreclr/src/tools/Common/TypeSystem/Common/TypeSystemException.cs
+++ b/src/coreclr/src/tools/Common/TypeSystem/Common/TypeSystemException.cs
@@ -9,7 +9,7 @@ namespace Internal.TypeSystem
     /// <summary>
     /// Base type for all type system exceptions.
     /// </summary>
-    public abstract class TypeSystemException : Exception
+    public abstract partial class TypeSystemException : Exception
     {
         private string[] _arguments;
 
@@ -43,53 +43,19 @@ internal TypeSystemException(ExceptionStringID id, params string[] args)
             _arguments = args;
         }
 
-        private static string GetFormatString(ExceptionStringID id)
-        {
-            switch (id)
-            {
-                case ExceptionStringID.ClassLoadGeneral: return SR.ClassLoadGeneral;
-                case ExceptionStringID.ClassLoadBadFormat: return SR.ClassLoadBadFormat;
-                case ExceptionStringID.ClassLoadExplicitGeneric: return SR.ClassLoadExplicitGeneric;
-                case ExceptionStringID.ClassLoadExplicitLayout: return SR.ClassLoadExplicitLayout;
-                case ExceptionStringID.ClassLoadValueClassTooLarge: return SR.ClassLoadValueClassTooLarge;
-                case ExceptionStringID.ClassLoadRankTooLarge: return SR.ClassLoadRankTooLarge;
-                case ExceptionStringID.MissingMethod: return SR.MissingMethod;
-                case ExceptionStringID.MissingField: return SR.MissingField;
-                case ExceptionStringID.InvalidProgramDefault: return SR.InvalidProgramDefault;
-                case ExceptionStringID.InvalidProgramSpecific: return SR.InvalidProgramSpecific;
-                case ExceptionStringID.InvalidProgramVararg: return SR.InvalidProgramVararg;
-                case ExceptionStringID.InvalidProgramCallVirtFinalize: return SR.InvalidProgramCallVirtFinalize;
-                case ExceptionStringID.InvalidProgramUnmanagedCallersOnly: return SR.InvalidProgramUnmanagedCallersOnly;
-                case ExceptionStringID.InvalidProgramCallAbstractMethod: return SR.InvalidProgramCallAbstractMethod;
-                case ExceptionStringID.InvalidProgramCallVirtStatic: return SR.InvalidProgramCallVirtStatic;
-                case ExceptionStringID.InvalidProgramNonStaticMethod: return SR.InvalidProgramNonStaticMethod;
-                case ExceptionStringID.InvalidProgramGenericMethod: return SR.InvalidProgramGenericMethod;
-                case ExceptionStringID.InvalidProgramNonBlittableTypes: return SR.InvalidProgramNonBlittableTypes;
-                case ExceptionStringID.BadImageFormatGeneric: return SR.BadImageFormatGeneric;
-                case ExceptionStringID.FileLoadErrorGeneric: return SR.FileLoadErrorGeneric;
-            }
-#if !DEBUG
-            throw new Exception($"Unknown Exception string id {id}");
-#else
-            return null;
-#endif
-        }
-
         private static string GetExceptionString(ExceptionStringID id, string[] args)
         {
             string formatString = GetFormatString(id);
-#if !DEBUG
             try
             {
-#endif
-                return String.Format(formatString, (object[])args);
-#if !DEBUG
+                if (formatString != null)
+                {
+                    return String.Format(formatString, (object[])args);
+                }
             }
-            catch
-            {
-                return "[TEMPORARY EXCEPTION MESSAGE] " + id.ToString() + ": " + String.Join(", ", args);
-            }
-#endif
+            catch {}
+            
+            return "[TEMPORARY EXCEPTION MESSAGE] " + id.ToString() + ": " + String.Join(", ", args);
         }
 
         /// <summary>
@@ -172,6 +138,11 @@ internal InvalidProgramException(ExceptionStringID id, string method)
             {
             }
 
+            internal InvalidProgramException(ExceptionStringID id)
+                : base(id)
+            {
+            }
+
             internal InvalidProgramException()
                 : base(ExceptionStringID.InvalidProgramDefault)
             {
diff --git a/src/coreclr/src/tools/Common/TypeSystem/IL/Stubs/VolatileIntrinsics.cs b/src/coreclr/src/tools/Common/TypeSystem/IL/Stubs/VolatileIntrinsics.cs
index f9ab4c10605591..35dca8644ac9e7 100644
--- a/src/coreclr/src/tools/Common/TypeSystem/IL/Stubs/VolatileIntrinsics.cs
+++ b/src/coreclr/src/tools/Common/TypeSystem/IL/Stubs/VolatileIntrinsics.cs
@@ -63,7 +63,7 @@ public static MethodIL EmitIL(MethodDesc method)
                 //
                 // Ordinary volatile loads and stores only guarantee atomicity for pointer-sized (or smaller) data.
                 // So, on 32-bit platforms we must use Interlocked operations instead for the 64-bit types.
-                // The implementation in mscorlib already does this, so we will only substitute a new
+                // The implementation in CoreLib already does this, so we will only substitute a new
                 // IL body if we're running on a 64-bit platform.
                 //
                 case TypeFlags.Int64 when method.Context.Target.PointerSize == 8:
diff --git a/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/MarshalHelpers.cs b/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/MarshalHelpers.cs
index 956e4fc8e274df..7b05a9b4ed90bb 100644
--- a/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/MarshalHelpers.cs
+++ b/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/MarshalHelpers.cs
@@ -166,13 +166,44 @@ internal static TypeDesc GetNativeTypeFromMarshallerKind(TypeDesc type,
             }
         }
 
+        private static bool HasCopyConstructorCustomModifier(int? parameterIndex,
+            EmbeddedSignatureData[] customModifierData)
+        {
+            if (!parameterIndex.HasValue || customModifierData == null)
+                return false;
+
+            string customModifierIndex = MethodSignature.GetIndexOfCustomModifierOnPointedAtTypeByParameterIndex(parameterIndex.Value);
+            foreach (var customModifier in customModifierData)
+            {
+                if (customModifier.kind != EmbeddedSignatureDataKind.RequiredCustomModifier)
+                    continue;
+
+                if (customModifier.index != customModifierIndex)
+                    continue;
+
+                var customModifierType = customModifier.type as DefType;
+                if (customModifierType == null)
+                    continue;
+
+                if ((customModifierType.Namespace == "System.Runtime.CompilerServices" && customModifierType.Name == "IsCopyConstructed") ||
+                    (customModifierType.Namespace == "Microsoft.VisualC" && customModifierType.Name == "NeedsCopyConstructorModifier"))
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
         internal static MarshallerKind GetMarshallerKind(
-             TypeDesc type,
-             MarshalAsDescriptor marshalAs,
-             bool isReturn,
-             bool isAnsi,
-             MarshallerType marshallerType,
-             out MarshallerKind elementMarshallerKind)
+            TypeDesc type,
+            int? parameterIndex,
+            EmbeddedSignatureData[] customModifierData,
+            MarshalAsDescriptor marshalAs,
+            bool isReturn,
+            bool isAnsi,
+            MarshallerType marshallerType,
+            out MarshallerKind elementMarshallerKind)
         {
             elementMarshallerKind = MarshallerKind.Invalid;
 
@@ -183,6 +214,12 @@ internal static MarshallerKind GetMarshallerKind(
 
                 type = type.GetParameterType();
 
+                if (!type.IsPrimitive && type.IsValueType && marshallerType != MarshallerType.Field
+                    && HasCopyConstructorCustomModifier(parameterIndex, customModifierData))
+                {
+                    return MarshallerKind.BlittableValueClassWithCopyCtor;
+                }
+
                 // Compat note: CLR allows ref returning blittable structs for IJW
                 if (isReturn)
                     return MarshallerKind.Invalid;
@@ -444,7 +481,15 @@ internal static MarshallerKind GetMarshallerKind(
             else if (type.IsPointer)
             {
                 if (nativeType == NativeTypeKind.Default)
+                {
+                    var pointedAtType = type.GetParameterType();
+                    if (!pointedAtType.IsPrimitive && !type.IsEnum && marshallerType != MarshallerType.Field
+                        && HasCopyConstructorCustomModifier(parameterIndex, customModifierData))
+                    {
+                        return MarshallerKind.BlittableValueClassWithCopyCtor;
+                    }
                     return MarshallerKind.BlittableValue;
+                }
                 else
                     return MarshallerKind.Invalid;
             }
diff --git a/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/MarshalUtils.cs b/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/MarshalUtils.cs
index 65f0956943fbbf..f713f9cb0c29f6 100644
--- a/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/MarshalUtils.cs
+++ b/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/MarshalUtils.cs
@@ -44,6 +44,8 @@ public static bool IsBlittableType(TypeDesc type)
 
                 MarshallerKind marshallerKind = MarshalHelpers.GetMarshallerKind(
                     field.FieldType,
+                    parameterIndex : null,
+                    customModifierData: null,
                     field.GetMarshalAsDescriptor(),
                     isReturn: false,
                     isAnsi: mdType.PInvokeStringFormat == PInvokeStringFormat.AnsiClass,
diff --git a/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/Marshaller.cs b/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/Marshaller.cs
index 31c86946302508..ecd7b0df468085 100644
--- a/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/Marshaller.cs
+++ b/src/coreclr/src/tools/Common/TypeSystem/Interop/IL/Marshaller.cs
@@ -50,6 +50,7 @@ enum MarshallerKind
         AsAnyA,
         AsAnyW,
         ComInterface,
+        BlittableValueClassWithCopyCtor,
         Invalid
     }
     public enum MarshalDirection
@@ -271,6 +272,8 @@ protected Marshaller()
         /// <param name="parameterType">type of the parameter to marshal</param>
         /// <returns>The created Marshaller</returns>
         public static Marshaller CreateMarshaller(TypeDesc parameterType,
+            int? parameterIndex,
+            EmbeddedSignatureData[] customModifierData,
             MarshallerType marshallerType,
             MarshalAsDescriptor marshalAs,
             MarshalDirection direction,
@@ -286,6 +289,8 @@ public static Marshaller CreateMarshaller(TypeDesc parameterType,
         {
             MarshallerKind elementMarshallerKind;
             MarshallerKind marshallerKind = MarshalHelpers.GetMarshallerKind(parameterType,
+                                                parameterIndex,
+                                                customModifierData,
                                                 marshalAs,
                                                 isReturn,
                                                 flags.CharSet == CharSet.Ansi,
diff --git a/src/coreclr/src/tools/ILVerification/ILVerification.projitems b/src/coreclr/src/tools/ILVerification/ILVerification.projitems
index bc5bda42bc03cf..42f60611ee1813 100644
--- a/src/coreclr/src/tools/ILVerification/ILVerification.projitems
+++ b/src/coreclr/src/tools/ILVerification/ILVerification.projitems
@@ -13,18 +13,17 @@
     <Compile Include="$(MSBuildThisFileDirectory)Verifier.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)VerifierError.cs" />
   </ItemGroup>
+  <PropertyGroup>
+    <ToolsCommonPath>$(MSBuildThisFileDirectory)..\Common\</ToolsCommonPath>
+  </PropertyGroup>
   <ItemGroup>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Strings.resx">
       <LogicalName>ILVerification.Strings.resources</LogicalName>
     </EmbeddedResource>
-    <EmbeddedResource Include="..\Common\TypeSystem\Common\Properties\Resources.resx">
-      <GenerateSource>true</GenerateSource>
-      <ClassName>Internal.TypeSystem.SR</ClassName>
+    <EmbeddedResource Include="$(ToolsCommonPath)TypeSystem\Common\Properties\Resources.resx">
+      <LogicalName>Internal.TypeSystem.Strings.resources</LogicalName>
     </EmbeddedResource>
   </ItemGroup>
-  <PropertyGroup>
-    <ToolsCommonPath>$(MSBuildThisFileDirectory)..\Common\</ToolsCommonPath>
-  </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(ToolsCommonPath)TypeSystem\CodeGen\MethodDesc.CodeGen.cs">
       <Link>TypeSystem\CodeGen\MethodDesc.CodeGen.cs</Link>
@@ -53,6 +52,9 @@
     <Compile Include="$(ToolsCommonPath)TypeSystem\Common\TypeSystemException.cs">
       <Link>TypeSystem\Common\TypeSystemException.cs</Link>
     </Compile>
+    <Compile Include="$(ToolsCommonPath)TypeSystem\Common\TypeSystemException.Resources.cs">
+      <Link>TypeSystem\Common\TypeSystemException.Resources.cs</Link>
+    </Compile>
     <Compile Include="$(ToolsCommonPath)TypeSystem\Common\Utilities\CustomAttributeTypeNameParser.cs">
       <Link>Utilities\CustomAttributeTypeNameParser.cs</Link>
     </Compile>
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/CodeGen/ReadyToRunObjectWriter.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/CodeGen/ReadyToRunObjectWriter.cs
index 20d6dac16b8a93..68239af41359d7 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/CodeGen/ReadyToRunObjectWriter.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/CodeGen/ReadyToRunObjectWriter.cs
@@ -6,6 +6,7 @@
 using System.Diagnostics;
 using System.IO;
 using System.Linq;
+using System.Reflection.Metadata;
 using System.Reflection.PortableExecutable;
 
 using ILCompiler.DependencyAnalysis.ReadyToRun;
@@ -102,8 +103,9 @@ public void EmitPortableExecutable()
                 stopwatch.Start();
 
                 PEHeaderBuilder headerBuilder;
-                int timeDateStamp;
+                int? timeDateStamp;
                 ISymbolNode r2rHeaderExportSymbol;
+                Func<IEnumerable<Blob>, BlobContentId> peIdProvider = null;
 
                 if (_nodeFactory.CompilationModuleGroup.IsCompositeBuildMode && _componentModule == null)
                 {
@@ -112,8 +114,8 @@ public void EmitPortableExecutable()
                         dllCharacteristics: default(DllCharacteristics),
                         Subsystem.Unknown,
                         _nodeFactory.Target);
-                    // TODO: generate a non-zero timestamp: https://github.com/dotnet/runtime/issues/32507
-                    timeDateStamp = 0;
+                    peIdProvider = new Func<IEnumerable<Blob>, BlobContentId>(content => BlobContentId.FromHash(CryptographicHashProvider.ComputeSourceHash(content)));
+                    timeDateStamp = null;
                     r2rHeaderExportSymbol = _nodeFactory.Header;
                 }
                 else
@@ -135,7 +137,8 @@ public void EmitPortableExecutable()
                     r2rHeaderExportSymbol,
                     Path.GetFileName(_objectFilePath),
                     getRuntimeFunctionsTable,
-                    _customPESectionAlignment);
+                    _customPESectionAlignment,
+                    peIdProvider);
 
                 NativeDebugDirectoryEntryNode nativeDebugDirectoryEntryNode = null;
                 ISymbolDefinitionNode firstImportThunk = null;
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/CryptographicHashProvider.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/CryptographicHashProvider.cs
new file mode 100644
index 00000000000000..dafd0c1ae7bbdf
--- /dev/null
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/CryptographicHashProvider.cs
@@ -0,0 +1,252 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#nullable enable
+
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using System.Reflection.Metadata;
+using System.Security.Cryptography;
+
+namespace ILCompiler
+{
+    /// <summary>
+    /// Specifies a hash algorithms used for hashing source files.
+    /// </summary>
+    public enum SourceHashAlgorithm
+    {
+        /// <summary>
+        /// No algorithm specified.
+        /// </summary>
+        None = 0,
+
+        /// <summary>
+        /// Secure Hash Algorithm 1.
+        /// </summary>
+        Sha1 = 1,
+
+        /// <summary>
+        /// Secure Hash Algorithm 2 with a hash size of 256 bits.
+        /// </summary>
+        Sha256 = 2,
+    }
+
+    internal static class SourceHashAlgorithmUtils
+    {
+        public const SourceHashAlgorithm DefaultContentHashAlgorithm = SourceHashAlgorithm.Sha256;
+    }
+
+    internal abstract class CryptographicHashProvider
+    {
+        private ImmutableArray<byte> _lazySHA1Hash;
+        private ImmutableArray<byte> _lazySHA256Hash;
+        private ImmutableArray<byte> _lazySHA384Hash;
+        private ImmutableArray<byte> _lazySHA512Hash;
+        private ImmutableArray<byte> _lazyMD5Hash;
+
+        internal abstract ImmutableArray<byte> ComputeHash(HashAlgorithm algorithm);
+
+        internal ImmutableArray<byte> GetHash(AssemblyHashAlgorithm algorithmId)
+        {
+            using (HashAlgorithm? algorithm = TryGetAlgorithm(algorithmId))
+            {
+                // ERR_CryptoHashFailed has already been reported:
+                if (algorithm == null)
+                {
+                    return ImmutableArray.Create<byte>();
+                }
+
+                switch (algorithmId)
+                {
+                    case AssemblyHashAlgorithm.None:
+                    case AssemblyHashAlgorithm.Sha1:
+                        return GetHash(ref _lazySHA1Hash, algorithm);
+
+                    case AssemblyHashAlgorithm.Sha256:
+                        return GetHash(ref _lazySHA256Hash, algorithm);
+
+                    case AssemblyHashAlgorithm.Sha384:
+                        return GetHash(ref _lazySHA384Hash, algorithm);
+
+                    case AssemblyHashAlgorithm.Sha512:
+                        return GetHash(ref _lazySHA512Hash, algorithm);
+
+                    case AssemblyHashAlgorithm.MD5:
+                        return GetHash(ref _lazyMD5Hash, algorithm);
+
+                    default:
+                        throw new ArgumentException("algorithmId");
+                }
+            }
+        }
+
+        internal static int GetHashSize(SourceHashAlgorithm algorithmId)
+        {
+            switch (algorithmId)
+            {
+                case SourceHashAlgorithm.Sha1:
+                    return 160 / 8;
+
+                case SourceHashAlgorithm.Sha256:
+                    return 256 / 8;
+
+                default:
+                    throw new ArgumentException("algorithmId");
+            }
+        }
+
+        internal static HashAlgorithm? TryGetAlgorithm(SourceHashAlgorithm algorithmId)
+        {
+            switch (algorithmId)
+            {
+                case SourceHashAlgorithm.Sha1:
+                    return SHA1.Create();
+
+                case SourceHashAlgorithm.Sha256:
+                    return SHA256.Create();
+
+                default:
+                    return null;
+            }
+        }
+
+        internal static HashAlgorithmName GetAlgorithmName(SourceHashAlgorithm algorithmId)
+        {
+            switch (algorithmId)
+            {
+                case SourceHashAlgorithm.Sha1:
+                    return HashAlgorithmName.SHA1;
+
+                case SourceHashAlgorithm.Sha256:
+                    return HashAlgorithmName.SHA256;
+
+                default:
+                    throw new ArgumentException("algorithmId");
+            }
+        }
+
+        internal static HashAlgorithm? TryGetAlgorithm(AssemblyHashAlgorithm algorithmId)
+        {
+            switch (algorithmId)
+            {
+                case AssemblyHashAlgorithm.None:
+                case AssemblyHashAlgorithm.Sha1:
+                    return SHA1.Create();
+
+                case AssemblyHashAlgorithm.Sha256:
+                    return SHA256.Create();
+
+                case AssemblyHashAlgorithm.Sha384:
+                    return SHA384.Create();
+
+                case AssemblyHashAlgorithm.Sha512:
+                    return SHA512.Create();
+
+                case AssemblyHashAlgorithm.MD5:
+                    return MD5.Create();
+
+                default:
+                    return null;
+            }
+        }
+
+        internal static bool IsSupportedAlgorithm(AssemblyHashAlgorithm algorithmId)
+        {
+            switch (algorithmId)
+            {
+                case AssemblyHashAlgorithm.None:
+                case AssemblyHashAlgorithm.Sha1:
+                case AssemblyHashAlgorithm.Sha256:
+                case AssemblyHashAlgorithm.Sha384:
+                case AssemblyHashAlgorithm.Sha512:
+                case AssemblyHashAlgorithm.MD5:
+                    return true;
+
+                default:
+                    return false;
+            }
+        }
+
+        private ImmutableArray<byte> GetHash(ref ImmutableArray<byte> lazyHash, HashAlgorithm algorithm)
+        {
+            if (lazyHash.IsDefault)
+            {
+                ImmutableInterlocked.InterlockedCompareExchange(ref lazyHash, ComputeHash(algorithm), default(ImmutableArray<byte>));
+            }
+
+            return lazyHash;
+        }
+
+        internal const int Sha1HashSize = 20;
+
+        internal static ImmutableArray<byte> ComputeSha1(Stream stream)
+        {
+            if (stream != null)
+            {
+                stream.Seek(0, SeekOrigin.Begin);
+                using (var hashProvider = SHA1.Create())
+                {
+                    return ImmutableArray.Create(hashProvider.ComputeHash(stream));
+                }
+            }
+
+            return ImmutableArray<byte>.Empty;
+        }
+
+        internal static ImmutableArray<byte> ComputeSha1(ImmutableArray<byte> bytes)
+        {
+            return ComputeSha1(bytes.ToArray());
+        }
+
+        internal static ImmutableArray<byte> ComputeSha1(byte[] bytes)
+        {
+            using (var hashProvider = SHA1.Create())
+            {
+                return ImmutableArray.Create(hashProvider.ComputeHash(bytes));
+            }
+        }
+
+        internal static ImmutableArray<byte> ComputeHash(HashAlgorithmName algorithmName, IEnumerable<Blob> bytes)
+        {
+            using (var incrementalHash = IncrementalHash.CreateHash(algorithmName))
+            {
+                foreach (var blob in bytes)
+                {
+                    incrementalHash.AppendData(blob.GetBytes());
+                }
+                return ImmutableArray.Create(incrementalHash.GetHashAndReset());
+            }
+        }
+
+        internal static ImmutableArray<byte> ComputeHash(HashAlgorithmName algorithmName, IEnumerable<ArraySegment<byte>> bytes)
+        {
+            using (var incrementalHash = IncrementalHash.CreateHash(algorithmName))
+            {
+                foreach (var segment in bytes)
+                {
+                    incrementalHash.AppendData(segment);
+                }
+                return ImmutableArray.Create(incrementalHash.GetHashAndReset());
+            }
+        }
+
+        internal static ImmutableArray<byte> ComputeSourceHash(ImmutableArray<byte> bytes, SourceHashAlgorithm hashAlgorithm = SourceHashAlgorithmUtils.DefaultContentHashAlgorithm)
+        {
+            var algorithmName = GetAlgorithmName(hashAlgorithm);
+            using (var incrementalHash = IncrementalHash.CreateHash(algorithmName))
+            {
+                incrementalHash.AppendData(bytes.ToArray());
+                return ImmutableArray.Create(incrementalHash.GetHashAndReset());
+            }
+        }
+
+        internal static ImmutableArray<byte> ComputeSourceHash(IEnumerable<Blob> bytes, SourceHashAlgorithm hashAlgorithm = SourceHashAlgorithmUtils.DefaultContentHashAlgorithm)
+        {
+            return ComputeHash(GetAlgorithmName(hashAlgorithm), bytes);
+        }
+    }
+}
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/CopiedFieldRvaNode.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/CopiedFieldRvaNode.cs
index 8adc7341210bd5..e8596cf24c894a 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/CopiedFieldRvaNode.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/CopiedFieldRvaNode.cs
@@ -67,7 +67,7 @@ private unsafe byte[] GetRvaData(int targetPointerSize)
                 int currentFieldRid;
                 if (compressedFieldRef)
                 {
-                    currentFieldRid = metadataBlob.ReadInt16();
+                    currentFieldRid = metadataBlob.ReadUInt16();
                 }
                 else
                 {
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/CopiedMetadataBlobNode.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/CopiedMetadataBlobNode.cs
index 8f0ae4281c31d7..b38dbfba67b59e 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/CopiedMetadataBlobNode.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/CopiedMetadataBlobNode.cs
@@ -84,7 +84,7 @@ private void WriteFieldRvas(NodeFactory factory, ref ObjectDataBuilder builder,
                 int fieldToken;
                 if (compressedFieldRef)
                 {
-                    fieldToken = reader.ReadInt16();
+                    fieldToken = reader.ReadUInt16();
                 }
                 else
                 {
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/DebugDirectoryNode.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/DebugDirectoryNode.cs
index 08093ecd367114..175025449039bd 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/DebugDirectoryNode.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/DebugDirectoryNode.cs
@@ -26,10 +26,12 @@ public class DebugDirectoryNode : ObjectNode, ISymbolDefinitionNode
 
         private EcmaModule _module;
         private NativeDebugDirectoryEntryNode _nativeEntry;
+        private bool _insertDeterministicEntry;
 
         public DebugDirectoryNode(EcmaModule sourceModule, string outputFileName)
         {
             _module = sourceModule;
+            _insertDeterministicEntry = sourceModule == null; // Mark module as deterministic if generating composite image
             string pdbNameRoot = Path.GetFileNameWithoutExtension(outputFileName);
             if (sourceModule != null)
             {
@@ -50,7 +52,7 @@ public DebugDirectoryNode(EcmaModule sourceModule, string outputFileName)
 
         public int Offset => 0;
 
-        public int Size => (GetNumDebugDirectoryEntriesInModule() + 1) * ImageDebugDirectorySize;
+        public int Size => (GetNumDebugDirectoryEntriesInModule() + 1 + (_insertDeterministicEntry ? 1 : 0)) * ImageDebugDirectorySize;
 
         public void AppendMangledName(NameMangler nameMangler, Utf8StringBuilder sb)
         {
@@ -112,8 +114,21 @@ public override ObjectData GetData(NodeFactory factory, bool relocsOnly = false)
                 builder.EmitReloc(entry, RelocType.IMAGE_REL_FILE_ABSOLUTE);
             }
 
+            // If generating a composite image, emit the deterministic marker
+            if (_insertDeterministicEntry)
+            {
+                builder.EmitUInt(0 /* Characteristics */);
+                builder.EmitUInt(0);
+                builder.EmitUShort(0);
+                builder.EmitUShort(0);
+                builder.EmitInt((int)DebugDirectoryEntryType.Reproducible);
+                builder.EmitInt(0);
+                builder.EmitUInt(0);
+                builder.EmitUInt(0);
+            }
+
             // Second, copy existing entries from input module
-            for(int i = 0; i < numEntries; i++)
+            for (int i = 0; i < numEntries; i++)
             {
                 builder.EmitUInt(0 /* Characteristics */);
                 builder.EmitUInt(entries[i].Stamp);
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/FieldFixupSignature.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/FieldFixupSignature.cs
index ebeb537f5f152f..eb5431f29e529a 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/FieldFixupSignature.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/FieldFixupSignature.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics;
 
 using Internal.JitInterface;
 using Internal.Text;
@@ -13,17 +14,19 @@ namespace ILCompiler.DependencyAnalysis.ReadyToRun
 {
     public class FieldFixupSignature : Signature
     {
+        public const int MaxCheckableOffset = 0x1FFFFFFF;
         private readonly ReadyToRunFixupKind _fixupKind;
 
         private readonly FieldDesc _fieldDesc;
 
-        public FieldFixupSignature(ReadyToRunFixupKind fixupKind, FieldDesc fieldDesc)
+        public FieldFixupSignature(ReadyToRunFixupKind fixupKind, FieldDesc fieldDesc, NodeFactory factory)
         {
             _fixupKind = fixupKind;
             _fieldDesc = fieldDesc;
 
             // Ensure types in signature are loadable and resolvable, otherwise we'll fail later while emitting the signature
             ((CompilerTypeSystemContext)fieldDesc.Context).EnsureLoadableType(fieldDesc.OwningType);
+            Debug.Assert(factory.SignatureContext.GetTargetModule(_fieldDesc) != null);
         }
 
         public override int ClassCode => 271828182;
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/SignatureBuilder.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/SignatureBuilder.cs
index 54b9849aed8cef..fd80e7e74a582a 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/SignatureBuilder.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/SignatureBuilder.cs
@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Reflection.Metadata;
+using System.Reflection.Metadata.Ecma335;
 
 using Internal.TypeSystem;
 using Internal.TypeSystem.Ecma;
@@ -441,11 +442,18 @@ public void EmitMethodSignature(
 
                             // Owner type is needed for type specs to instantiating stubs or generics with signature variables still present
                             if (!method.Method.OwningType.IsDefType &&
-                                ((flags & (uint)ReadyToRunMethodSigFlags.READYTORUN_METHOD_SIG_InstantiatingStub) != 0 || method.Method.OwningType.ContainsSignatureVariables())
-                                || method.Method.IsArrayAddressMethod())
+                                ((flags & (uint)ReadyToRunMethodSigFlags.READYTORUN_METHOD_SIG_InstantiatingStub) != 0 || method.Method.OwningType.ContainsSignatureVariables()))
                             {
                                 flags |= (uint)ReadyToRunMethodSigFlags.READYTORUN_METHOD_SIG_OwnerType;
                             }
+                            else if (method.Method.IsArrayMethod())
+                            {
+                                var memberRefMethod = method.Token.Module.GetMethod(MetadataTokens.EntityHandle((int)method.Token.Token));
+                                if (memberRefMethod.OwningType != method.Method.OwningType)
+                                {
+                                    flags |= (uint)ReadyToRunMethodSigFlags.READYTORUN_METHOD_SIG_OwnerType;
+                                }
+                            }
 
                             EmitUInt(flags);
                             if ((flags & (uint)ReadyToRunMethodSigFlags.READYTORUN_METHOD_SIG_OwnerType) != 0)
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeFixupSignature.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeFixupSignature.cs
index 0bc86c7794cbf9..ea21b730330b9e 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeFixupSignature.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeFixupSignature.cs
@@ -81,16 +81,16 @@ private static void EncodeTypeLayout(ObjectDataSignatureBuilder dataBuilder, Typ
 
             if (defType.IsHomogeneousAggregate)
             {
-                CorElementType elementType = (defType.ValueTypeShapeCharacteristics & ValueTypeShapeCharacteristics.AggregateMask) switch
+                ReadyToRunHFAElemType hfaElementType = (defType.ValueTypeShapeCharacteristics & ValueTypeShapeCharacteristics.AggregateMask) switch
                 {
-                    ValueTypeShapeCharacteristics.Float32Aggregate => CorElementType.ELEMENT_TYPE_R4,
-                    ValueTypeShapeCharacteristics.Float64Aggregate => CorElementType.ELEMENT_TYPE_R8,
-                    ValueTypeShapeCharacteristics.Vector64Aggregate => CorElementType.ELEMENT_TYPE_R8,
+                    ValueTypeShapeCharacteristics.Float32Aggregate => ReadyToRunHFAElemType.Float32,
+                    ValueTypeShapeCharacteristics.Float64Aggregate => ReadyToRunHFAElemType.Float64,
+                    ValueTypeShapeCharacteristics.Vector64Aggregate => ReadyToRunHFAElemType.Vector64,
                     // See MethodTable::GetHFAType
-                    ValueTypeShapeCharacteristics.Vector128Aggregate => CorElementType.ELEMENT_TYPE_VALUETYPE,
-                    _ => CorElementType.Invalid
+                    ValueTypeShapeCharacteristics.Vector128Aggregate => ReadyToRunHFAElemType.Vector128,
+                    _ => throw new NotSupportedException()
                 };
-                dataBuilder.EmitUInt((uint)elementType);
+                dataBuilder.EmitUInt((uint)hfaElementType);
             }
             
             if (alignment != pointerSize)
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRunSymbolNodeFactory.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRunSymbolNodeFactory.cs
index 7ae68230d8a692..1178d4372c33a0 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRunSymbolNodeFactory.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRunSymbolNodeFactory.cs
@@ -70,7 +70,7 @@ private void CreateNodeCaches()
                     _codegenNodeFactory,
                     _codegenNodeFactory.HelperImports,
                     ReadyToRunHelper.DelayLoad_Helper,
-                    new FieldFixupSignature(ReadyToRunFixupKind.FieldAddress, key)
+                    new FieldFixupSignature(ReadyToRunFixupKind.FieldAddress, key, _codegenNodeFactory)
                 );
             });
 
@@ -78,7 +78,7 @@ private void CreateNodeCaches()
             {
                 return new PrecodeHelperImport(
                     _codegenNodeFactory,
-                    new FieldFixupSignature(ReadyToRunFixupKind.FieldOffset, key)
+                    new FieldFixupSignature(ReadyToRunFixupKind.FieldOffset, key, _codegenNodeFactory)
                 );
             });
 
@@ -94,7 +94,7 @@ private void CreateNodeCaches()
             {
                 return new PrecodeHelperImport(
                     _codegenNodeFactory,
-                    new FieldFixupSignature(_verifyTypeAndFieldLayout ? ReadyToRunFixupKind.Verify_FieldOffset : ReadyToRunFixupKind.Check_FieldOffset, key)
+                    new FieldFixupSignature(_verifyTypeAndFieldLayout ? ReadyToRunFixupKind.Verify_FieldOffset : ReadyToRunFixupKind.Check_FieldOffset, key, _codegenNodeFactory)
                 );
             });
 
@@ -356,7 +356,7 @@ private ISymbolNode CreateFieldHandleHelper(FieldDesc field)
         {
             return new PrecodeHelperImport(
                 _codegenNodeFactory,
-                new FieldFixupSignature(ReadyToRunFixupKind.FieldHandle, field));
+                new FieldFixupSignature(ReadyToRunFixupKind.FieldHandle, field, _codegenNodeFactory));
         }
 
         private ISymbolNode CreateCctorTrigger(TypeDesc type)
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/IBC/IBCProfileParser.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/IBC/IBCProfileParser.cs
index c42ecaa13c1ceb..718d4e650fa687 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/IBC/IBCProfileParser.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/IBC/IBCProfileParser.cs
@@ -113,7 +113,8 @@ public ProfileData ParseIBCDataFromModule(EcmaModule ecmaModule)
                             }
                             else
                             {
-                                _logger.Writer.WriteLine($"Token {0:x} does not refer to a method");
+                                if (_logger.IsVerbose)
+                                    _logger.Writer.WriteLine($"Token {(int)entry.Token:x} does not refer to a method");
                             }
                             break;
 
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/ILCompiler.ReadyToRun.csproj b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/ILCompiler.ReadyToRun.csproj
index 483973871a90b5..b8d01189009d15 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/ILCompiler.ReadyToRun.csproj
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/ILCompiler.ReadyToRun.csproj
@@ -98,6 +98,7 @@
     <Compile Include="ObjectWriter\MapFileBuilder.cs" />
     <Compile Include="CodeGen\ReadyToRunObjectWriter.cs" />
     <Compile Include="Compiler\CompilationModuleGroup.ReadyToRun.cs" />
+    <Compile Include="Compiler\CryptographicHashProvider.cs" />
     <Compile Include="Compiler\DependencyAnalysis\AllMethodsOnTypeNode.cs" />
     <Compile Include="Compiler\DependencyAnalysis\ArrayOfEmbeddedDataNode.cs" />
     <Compile Include="Compiler\DependencyAnalysis\ArrayOfEmbeddedPointersNode.cs" />
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Interop/IL/Marshaller.ReadyToRun.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Interop/IL/Marshaller.ReadyToRun.cs
index 4ca7a6f9596505..04b939334a21e1 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Interop/IL/Marshaller.ReadyToRun.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/Interop/IL/Marshaller.ReadyToRun.cs
@@ -70,6 +70,8 @@ public static Marshaller[] GetMarshallersForMethod(MethodDesc targetMethod)
 
                 TypeDesc parameterType = (i == 0) ? methodSig.ReturnType : methodSig[i - 1];  //first item is the return type
                 marshallers[i] = CreateMarshaller(parameterType,
+                                                    parameterIndex,
+                                                    methodSig.GetEmbeddedSignatureData(),
                                                     MarshallerType.Argument,
                                                     parameterMetadata.MarshalAsDescriptor,
                                                     direction,
@@ -121,6 +123,8 @@ public static bool IsMarshallingRequired(MethodSignature methodSig, ParameterMet
 
                 MarshallerKind marshallerKind = MarshalHelpers.GetMarshallerKind(
                     parameterType,
+                    parameterIndex: i,
+                    customModifierData: methodSig.GetEmbeddedSignatureData(),
                     parameterMetadata.MarshalAsDescriptor,
                     parameterMetadata.Return,
                     isAnsi: true,
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs
index 2c2085635f3482..57c4b738d690c1 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs
@@ -1012,7 +1012,7 @@ private void getFieldInfo(ref CORINFO_RESOLVED_TOKEN pResolvedToken, CORINFO_MET
                             CorInfoHelpFunc.CORINFO_HELP_GETGENERICS_NONGCSTATIC_BASE);
                     }
 
-                    if (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout)
+                    if (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout && (fieldOffset <= FieldFixupSignature.MaxCheckableOffset))
                     {
                         // ENCODE_CHECK_FIELD_OFFSET
                         _methodCodeNode.Fixups.Add(_compilation.SymbolNodeFactory.CheckFieldOffset(field));
@@ -1066,7 +1066,7 @@ private void getFieldInfo(ref CORINFO_RESOLVED_TOKEN pResolvedToken, CORINFO_MET
                     else
                     if (helperId != ReadyToRunHelperId.Invalid)
                     {
-                        if (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout)
+                        if (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout && (fieldOffset <= FieldFixupSignature.MaxCheckableOffset))
                         {
                             // ENCODE_CHECK_FIELD_OFFSET
                             _methodCodeNode.Fixups.Add(_compilation.SymbolNodeFactory.CheckFieldOffset(field));
@@ -1922,7 +1922,7 @@ private bool NeedsTypeLayoutCheck(TypeDesc type)
             if (!type.IsValueType)
                 return false;
 
-            return !_compilation.IsLayoutFixedInCurrentVersionBubble(type) || _compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout;
+            return !_compilation.IsLayoutFixedInCurrentVersionBubble(type) || (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout && !((MetadataType)type).IsNonVersionable());
         }
 
         private bool HasLayoutMetadata(TypeDesc type)
@@ -1963,6 +1963,9 @@ private void EncodeFieldBaseOffset(FieldDesc field, CORINFO_FIELD_INFO* pResult,
                 if (pMT.IsValueType)
                 {
                     // ENCODE_CHECK_FIELD_OFFSET
+                    if (pResult->offset > FieldFixupSignature.MaxCheckableOffset)
+                        throw new RequiresRuntimeJitException(callerMethod.ToString() + " -> " + field.ToString());
+
                     _methodCodeNode.Fixups.Add(_compilation.SymbolNodeFactory.CheckFieldOffset(field));
                     // No-op other than generating the check field offset fixup
                 }
@@ -1978,7 +1981,7 @@ private void EncodeFieldBaseOffset(FieldDesc field, CORINFO_FIELD_INFO* pResult,
             }
             else if (pMT.IsValueType)
             {
-                if (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout)
+                if (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout && !callerMethod.IsNonVersionable() && (pResult->offset <= FieldFixupSignature.MaxCheckableOffset))
                 {
                     // ENCODE_CHECK_FIELD_OFFSET
                     _methodCodeNode.Fixups.Add(_compilation.SymbolNodeFactory.CheckFieldOffset(field));
@@ -1987,7 +1990,7 @@ private void EncodeFieldBaseOffset(FieldDesc field, CORINFO_FIELD_INFO* pResult,
             }
             else if (_compilation.IsInheritanceChainLayoutFixedInCurrentVersionBubble(pMT.BaseType))
             {
-                if (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout)
+                if (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout && !callerMethod.IsNonVersionable() && (pResult->offset <= FieldFixupSignature.MaxCheckableOffset))
                 {
                     // ENCODE_CHECK_FIELD_OFFSET
                     _methodCodeNode.Fixups.Add(_compilation.SymbolNodeFactory.CheckFieldOffset(field));
@@ -2009,7 +2012,7 @@ private void EncodeFieldBaseOffset(FieldDesc field, CORINFO_FIELD_INFO* pResult,
             {
                 PreventRecursiveFieldInlinesOutsideVersionBubble(field, callerMethod);
 
-                if (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout)
+                if (_compilation.SymbolNodeFactory.VerifyTypeAndFieldLayout && !callerMethod.IsNonVersionable() && (pResult->offset <= FieldFixupSignature.MaxCheckableOffset))
                 {
                     // ENCODE_CHECK_FIELD_OFFSET
                     _methodCodeNode.Fixups.Add(_compilation.SymbolNodeFactory.CheckFieldOffset(field));
diff --git a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/ObjectWriter/R2RPEBuilder.cs b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/ObjectWriter/R2RPEBuilder.cs
index 839b1f21d11067..e1731e4c95f870 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/ObjectWriter/R2RPEBuilder.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.ReadyToRun/ObjectWriter/R2RPEBuilder.cs
@@ -173,8 +173,9 @@ public R2RPEBuilder(
             ISymbolNode r2rHeaderExportSymbol,
             string outputFileSimpleName,
             Func<RuntimeFunctionsTableNode> getRuntimeFunctionsTable,
-            int? customPESectionAlignment)
-            : base(peHeaderBuilder, deterministicIdProvider: null)
+            int? customPESectionAlignment,
+            Func<IEnumerable<Blob>, BlobContentId> deterministicIdProvider)
+            : base(peHeaderBuilder, deterministicIdProvider: deterministicIdProvider)
         {
             _target = target;
             _getRuntimeFunctionsTable = getRuntimeFunctionsTable;
@@ -288,7 +289,7 @@ public int GetSymbolFilePosition(ISymbolNode symbol)
         /// </summary>
         /// <param name="outputStream">Output stream for the final R2R PE file</param>
         /// <param name="timeDateStamp">Timestamp to set in the PE header of the output R2R executable</param>
-        public void Write(Stream outputStream, int timeDateStamp)
+        public void Write(Stream outputStream, int? timeDateStamp)
         {
             BlobBuilder outputPeFile = new BlobBuilder();
             Serialize(outputPeFile);
@@ -302,7 +303,8 @@ public void Write(Stream outputStream, int timeDateStamp)
 
             ApplyMachineOSOverride(outputStream);
 
-            SetPEHeaderTimeStamp(outputStream, timeDateStamp);
+            if (timeDateStamp.HasValue)
+                SetPEHeaderTimeStamp(outputStream, timeDateStamp.Value);
 
             _written = true;
         }
diff --git a/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/Amd64/UnwindInfo.cs b/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/Amd64/UnwindInfo.cs
index 1c5150bcedaf6d..08241e0a433d11 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/Amd64/UnwindInfo.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/Amd64/UnwindInfo.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Text;
 
 namespace ILCompiler.Reflection.ReadyToRun.Amd64
@@ -76,6 +77,19 @@ public UnwindCode(byte[] image, int index, ref int offset)
             FrameOffset = NativeReader.ReadUInt16(image, ref offset);
             NextFrameOffset = -1;
 
+            if (UnwindOp == UnwindOpCodes.UWOP_ALLOC_LARGE)
+            {
+                uint codedSize;
+                if (OpInfo == 0)
+                {
+                    codedSize = NativeReader.ReadUInt16(image, ref offset);
+                }
+                else if (OpInfo == 1)
+                {
+                    codedSize = NativeReader.ReadUInt32(image, ref offset);
+                }
+            }
+
             IsOpInfo = false;
         }
     }
@@ -95,7 +109,7 @@ public class UnwindInfo : BaseUnwindInfo
         public Registers FrameRegister { get; set; } //4 bits
         public byte FrameOffset { get; set; } //4 bits
         public UnwindCode[] UnwindCodeArray { get; set; }
-        public Dictionary<int, List<UnwindCode>> UnwindCodes { get; set; }
+        public Dictionary<int, UnwindCode> UnwindCodes { get; set; }
         public uint PersonalityRoutineRVA { get; set; }
 
         public UnwindInfo() { }
@@ -115,7 +129,7 @@ public UnwindInfo(byte[] image, int offset)
             FrameOffset = (byte)(frameRegisterAndOffset >> 4);
 
             UnwindCodeArray = new UnwindCode[CountOfUnwindCodes];
-            UnwindCodes = new Dictionary<int, List<UnwindCode>>();
+            UnwindCodes = new Dictionary<int, UnwindCode>();
             for (int i = 0; i < CountOfUnwindCodes; i++)
             {
                 UnwindCodeArray[i] = new UnwindCode(image, i, ref offset);
@@ -123,11 +137,8 @@ public UnwindInfo(byte[] image, int offset)
             for (int i = 0; i < CountOfUnwindCodes; i++)
             {
                 ParseUnwindCode(ref i);
-                if (!UnwindCodes.ContainsKey(UnwindCodeArray[i].CodeOffset))
-                {
-                    UnwindCodes[UnwindCodeArray[i].CodeOffset] = new List<UnwindCode>();
-                }
-                UnwindCodes[UnwindCodeArray[i].CodeOffset].Add(UnwindCodeArray[i]);
+                Debug.Assert(!UnwindCodes.ContainsKey(UnwindCodeArray[i].CodeOffset));
+                UnwindCodes.Add(UnwindCodeArray[i].CodeOffset, UnwindCodeArray[i]);
             }
 
             Size = _offsetofUnwindCode + CountOfUnwindCodes * _sizeofUnwindCode;
diff --git a/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/DebugInfo.cs b/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/DebugInfo.cs
index 706e98780acbf7..8a6766d42945aa 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/DebugInfo.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/DebugInfo.cs
@@ -17,15 +17,15 @@ namespace ILCompiler.Reflection.ReadyToRun
     /// </summary>
     public class DebugInfo
     {
-        private readonly ReadyToRunReader _readyToRunReader;
+        private readonly RuntimeFunction _runtimeFunction;
         private readonly int _offset;
         private List<DebugInfoBoundsEntry> _boundsList;
         private List<NativeVarInfo> _variablesList;
         private Machine _machine;
 
-        public DebugInfo(ReadyToRunReader readyToRunReader, int offset)
+        public DebugInfo(RuntimeFunction runtimeFunction, int offset)
         {
-            this._readyToRunReader = readyToRunReader;
+            this._runtimeFunction = runtimeFunction;
             this._offset = offset;
         }
 
@@ -83,6 +83,7 @@ private void EnsureInitialized()
             {
                 return;
             }
+            ReadyToRunReader _readyToRunReader = _runtimeFunction.ReadyToRunReader;
             int offset = _offset;
             _boundsList = new List<DebugInfoBoundsEntry>();
             _variablesList = new List<NativeVarInfo>();
@@ -156,6 +157,19 @@ private void ParseNativeVarInfo(byte[] image, int offset)
                 entry.StartOffset = reader.ReadUInt();
                 entry.EndOffset = entry.StartOffset + reader.ReadUInt();
                 entry.VariableNumber = (uint)(reader.ReadUInt() + (int)ImplicitILArguments.Max);
+                entry.Variable = new Variable();
+                // TODO: This is probably incomplete
+                // This does not handle any implicit arguments or var args
+                if (entry.VariableNumber < this._runtimeFunction.Method.Signature.ParameterTypes.Length)
+                {
+                    entry.Variable.Type = VariableType.Parameter;
+                    entry.Variable.Index = (int)entry.VariableNumber;
+                }
+                else
+                {
+                    entry.Variable.Type = VariableType.Local;
+                    entry.Variable.Index = (int)entry.VariableNumber - this._runtimeFunction.Method.Signature.ParameterTypes.Length;
+                }
 
                 var varLoc = new VarLoc();
                 varLoc.VarLocType = (VarLocType)reader.ReadUInt();
diff --git a/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/DebugInfoTypes.cs b/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/DebugInfoTypes.cs
index 73782f2344c38f..eef0ab4673cbe1 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/DebugInfoTypes.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/DebugInfoTypes.cs
@@ -17,10 +17,25 @@ public struct NativeVarInfo
     {
         public uint StartOffset;
         public uint EndOffset;
+        // TODO: Eliminate this
         public uint VariableNumber;
+        public Variable Variable { get; internal set; }
         public VarLoc VariableLocation;
     }
 
+    public enum VariableType
+    {
+        Parameter,
+        Local,
+        // TODO: Special
+    }
+
+    public class Variable
+    {
+        public VariableType Type { get; internal set; }
+        public int Index { get; internal set; }
+    }
+
     [Flags]
     public enum SourceTypes
     {
diff --git a/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunMethod.cs b/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunMethod.cs
index a00419f212c4ce..266a75bbddc134 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunMethod.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunMethod.cs
@@ -144,12 +144,24 @@ public DebugInfo DebugInfo
             {
                 if (_debugInfo == null)
                 {
-                    _readyToRunReader.RuntimeFunctionToDebugInfo.TryGetValue(Id, out _debugInfo);
+                    int offset;
+                    if (_readyToRunReader.RuntimeFunctionToDebugInfo.TryGetValue(Id, out offset))
+                    {
+                        this._debugInfo = new DebugInfo(this, offset);
+                    }
                 }
                 return _debugInfo;
             }
         }
 
+        internal ReadyToRunReader ReadyToRunReader
+        {
+            get
+            {
+                return _readyToRunReader;
+            }
+        }
+
         public RuntimeFunction(
             ReadyToRunReader readyToRunReader,
             int id,
@@ -218,6 +230,8 @@ public class ReadyToRunMethod
 
         public MethodSignature<string> Signature { get; }
 
+        public ImmutableArray<string> LocalSignature { get; }
+
         /// <summary>
         /// The type that the method belongs to
         /// </summary>
@@ -282,6 +296,7 @@ public IReadOnlyList<FixupCell> Fixups
         /// </summary>
         public ReadyToRunMethod(
             ReadyToRunReader readyToRunReader,
+            PEReader peReader,
             MetadataReader metadataReader,
             EntityHandle methodHandle,
             int entryPointId,
@@ -309,6 +324,15 @@ public ReadyToRunMethod(
                 case HandleKind.MethodDefinition:
                     {
                         MethodDefinition methodDef = MetadataReader.GetMethodDefinition((MethodDefinitionHandle)MethodHandle);
+                        if (methodDef.RelativeVirtualAddress != 0)
+                        {
+                            MethodBodyBlock mbb = peReader.GetMethodBody(methodDef.RelativeVirtualAddress);
+                            if (!mbb.LocalSignature.IsNil)
+                            {
+                                StandaloneSignature ss = MetadataReader.GetStandaloneSignature(mbb.LocalSignature);
+                                LocalSignature = ss.DecodeLocalSignature(typeProvider, genericContext);
+                            }
+                        }
                         Name = MetadataReader.GetString(methodDef.Name);
                         Signature = methodDef.DecodeSignature<string, DisassemblingGenericContext>(typeProvider, genericContext);
                         owningTypeHandle = methodDef.GetDeclaringType();
diff --git a/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunReader.cs b/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunReader.cs
index a829b58599e531..3fdb03f6724bc2 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunReader.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunReader.cs
@@ -80,7 +80,7 @@ public sealed class ReadyToRunReader
         private List<ReadyToRunCoreHeader> _readyToRunAssemblyHeaders;
 
         // DebugInfo
-        private Dictionary<int, DebugInfo> _runtimeFunctionToDebugInfo;
+        private Dictionary<int, int> _runtimeFunctionIdToDebugOffset;
 
         // ManifestReferences
         private MetadataReader _manifestReader;
@@ -322,12 +322,12 @@ public IReadOnlyDictionary<int, ReadyToRunSignature> ImportSignatures
 
         }
 
-        internal Dictionary<int, DebugInfo> RuntimeFunctionToDebugInfo
+        internal Dictionary<int, int> RuntimeFunctionToDebugInfo
         {
             get
             {
                 EnsureDebugInfo();
-                return _runtimeFunctionToDebugInfo;
+                return _runtimeFunctionIdToDebugOffset;
             }
         }
 
@@ -583,11 +583,11 @@ private unsafe void EnsureHeader()
 
         private void EnsureDebugInfo()
         {
-            if (_runtimeFunctionToDebugInfo != null)
+            if (_runtimeFunctionIdToDebugOffset != null)
             {
                 return;
             }
-            _runtimeFunctionToDebugInfo = new Dictionary<int, DebugInfo>();
+            _runtimeFunctionIdToDebugOffset = new Dictionary<int, int>();
             if (!ReadyToRunHeader.Sections.TryGetValue(ReadyToRunSectionType.DebugInfo, out ReadyToRunSection debugInfoSection))
             {
                 return;
@@ -604,8 +604,7 @@ private void EnsureDebugInfo()
                     continue;
                 }
 
-                var debugInfo = new DebugInfo(this, offset);
-                _runtimeFunctionToDebugInfo.Add((int)i, debugInfo);
+                _runtimeFunctionIdToDebugOffset.Add((int)i, offset);
             }
         }
 
@@ -741,7 +740,7 @@ private void ParseMethodDefEntrypointsSection(ReadyToRunSection section, Metadat
                     int runtimeFunctionId;
                     int? fixupOffset;
                     GetRuntimeFunctionIndexFromOffset(offset, out runtimeFunctionId, out fixupOffset);
-                    ReadyToRunMethod method = new ReadyToRunMethod(this, metadataReader, methodHandle, runtimeFunctionId, owningType: null, constrainedType: null, instanceArgs: null, fixupOffset: fixupOffset);
+                    ReadyToRunMethod method = new ReadyToRunMethod(this, this.PEReader, metadataReader, methodHandle, runtimeFunctionId, owningType: null, constrainedType: null, instanceArgs: null, fixupOffset: fixupOffset);
 
                     if (method.EntryPointRuntimeFunctionId < 0 || method.EntryPointRuntimeFunctionId >= isEntryPoint.Length)
                     {
@@ -889,6 +888,7 @@ private void ParseInstanceMethodEntrypoints(bool[] isEntryPoint)
                 GetRuntimeFunctionIndexFromOffset((int)decoder.Offset, out runtimeFunctionId, out fixupOffset);
                 ReadyToRunMethod method = new ReadyToRunMethod(
                     this,
+                    this.PEReader,
                     mdReader,
                     methodHandle,
                     runtimeFunctionId,
diff --git a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ExceptionStringTests.cs b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ExceptionStringTests.cs
new file mode 100644
index 00000000000000..d40bdf774126d8
--- /dev/null
+++ b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ExceptionStringTests.cs
@@ -0,0 +1,26 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using Internal.TypeSystem;
+
+using Xunit;
+
+namespace TypeSystemTests
+{
+    public class ExceptionStringTests
+    {
+        public ExceptionStringTests()
+        {
+        }
+
+        [Fact]
+        public void TestAllExceptionIdsHaveMessages()
+        {
+            foreach(var exceptionId in (ExceptionStringID[])Enum.GetValues(typeof(ExceptionStringID)))
+            {
+                Assert.NotNull(TypeSystemException.GetFormatString(exceptionId));
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ILCompiler.TypeSystem.ReadyToRun.Tests.csproj b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ILCompiler.TypeSystem.ReadyToRun.Tests.csproj
index 38e1dda8abaaf4..7567ab173f5db3 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ILCompiler.TypeSystem.ReadyToRun.Tests.csproj
+++ b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ILCompiler.TypeSystem.ReadyToRun.Tests.csproj
@@ -47,6 +47,7 @@
     <Compile Include="RuntimeDeterminedTypesTests.cs" />
     <Compile Include="SignatureTests.cs" />
     <Compile Include="SyntheticVirtualOverrideTests.cs" />
+    <Compile Include="SyntheticVirtualOverrideTests.DiagnosticName.cs" />
     <Compile Include="TestMetadataFieldLayoutAlgorithm.cs" />
     <Compile Include="TypeNameParsingTests.cs" />
     <Compile Include="UniversalGenericFieldLayoutTests.cs" />
@@ -56,5 +57,6 @@
     <Compile Include="StaticFieldLayoutTests.cs" />
     <Compile Include="TestTypeSystemContext.cs" />
     <Compile Include="WellKnownTypeTests.cs" />
+    <Compile Include="ExceptionStringTests.cs" />
   </ItemGroup>
 </Project>
diff --git a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ILTestAssembly/Signature.il b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ILTestAssembly/Signature.il
index b28c850616f7cd..02f33b81f04731 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ILTestAssembly/Signature.il
+++ b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/ILTestAssembly/Signature.il
@@ -1,6 +1,36 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+.class public auto ansi beforefieldinit ModOptTester
+       extends [CoreTestAssembly]System.Object
+{
+  .method public hidebysig specialname rtspecialname 
+          instance void  .ctor() cil managed
+  {
+    // Code size       8 (0x8)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  call       instance void [CoreTestAssembly]System.Object::.ctor()
+    IL_0006:  nop
+    IL_0007:  ret
+  } // end of method I::.ctor
+
+  .method public hidebysig instance int32 modopt([CoreTestAssembly]System.Void) modopt([CoreTestAssembly]System.Char) Method(int32 modopt(FooModifier)) cil managed
+  {
+     ret
+  }
+
+  .method public hidebysig instance int32 modopt([CoreTestAssembly]System.Void) & modopt([CoreTestAssembly]System.Char) Method2(int32 modopt(FooModifier)) cil managed
+  {
+     ret
+  }
+
+  .method public hidebysig instance int32 modopt([CoreTestAssembly]System.Void) & Method3(int32 modopt(FooModifier)*, int32 modopt(FooModifier)*) cil managed
+  {
+     ret
+  }
+}
+
 .class private auto ansi beforefieldinit Atom
        extends [CoreTestAssembly]System.Object
 {
diff --git a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SignatureTests.cs b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SignatureTests.cs
index cfaeef6ea437e3..60d717291196a0 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SignatureTests.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SignatureTests.cs
@@ -27,6 +27,58 @@ public SignatureTests()
             _testModule = _context.GetModuleForSimpleName("ILTestAssembly");
         }
 
+        private static string GetModOptMethodSignatureInfo(MethodSignature signature)
+        {
+            if (!signature.HasEmbeddedSignatureData || signature.GetEmbeddedSignatureData() == null)
+                return "";
+
+            StringBuilder sb = new StringBuilder();
+            foreach (EmbeddedSignatureData data in signature.GetEmbeddedSignatureData())
+            {
+                sb.Append(data.kind.ToString());
+                sb.Append(data.index);
+                sb.Append(((MetadataType)data.type).Name);
+            }
+            return sb.ToString();
+        }
+
+        [Fact]
+        public void TestSignatureMatches2ModOptsAtStartOfSig()
+        {
+            MetadataType modOptTester = _testModule.GetType("", "ModOptTester");
+            MethodSignature methodWith2ModOptsAtStartOfSig = modOptTester.GetMethods().Single(m => string.Equals(m.Name, "Method")).Signature;
+
+            // All modopts that are at the very beginning of the signature are given index 0.1.1.1
+            // Both the index and the order in the modopt array are significant for signature comparison
+            Assert.Equal(MethodSignature.IndexOfCustomModifiersOnReturnType, methodWith2ModOptsAtStartOfSig.GetEmbeddedSignatureData()[0].index);
+            Assert.Equal(MethodSignature.IndexOfCustomModifiersOnReturnType, methodWith2ModOptsAtStartOfSig.GetEmbeddedSignatureData()[1].index);
+            Assert.NotEqual(MethodSignature.IndexOfCustomModifiersOnReturnType, methodWith2ModOptsAtStartOfSig.GetEmbeddedSignatureData()[2].index);
+            Assert.Equal("OptionalCustomModifier0.1.1.1CharOptionalCustomModifier0.1.1.1VoidOptionalCustomModifier0.1.2.1FooModifier", GetModOptMethodSignatureInfo(methodWith2ModOptsAtStartOfSig));
+        }
+
+        [Fact]
+        public void TestSignatureMatchesModOptAtStartOfSigAndAfterByRef()
+        {
+            MetadataType modOptTester = _testModule.GetType("", "ModOptTester");
+            MethodSignature methodWithModOptAtStartOfSigAndAfterByRef = modOptTester.GetMethods().Single(m => string.Equals(m.Name, "Method2")).Signature;
+
+            // A modopts after an E_T_BYREF will look like 0.1.1.2.1.1
+            Assert.Equal(MethodSignature.IndexOfCustomModifiersOnReturnType, methodWithModOptAtStartOfSigAndAfterByRef.GetEmbeddedSignatureData()[0].index);
+            Assert.NotEqual(MethodSignature.IndexOfCustomModifiersOnReturnType, methodWithModOptAtStartOfSigAndAfterByRef.GetEmbeddedSignatureData()[1].index);
+            Assert.NotEqual(MethodSignature.IndexOfCustomModifiersOnReturnType, methodWithModOptAtStartOfSigAndAfterByRef.GetEmbeddedSignatureData()[2].index);
+            Assert.Equal("OptionalCustomModifier0.1.1.1CharOptionalCustomModifier0.1.1.2.1.1VoidOptionalCustomModifier0.1.2.1FooModifier", GetModOptMethodSignatureInfo(methodWithModOptAtStartOfSigAndAfterByRef));
+        }
+
+        [Fact]
+        public void TestSignatureMatchesModoptOnPointerOrRefModifiedType()
+        {
+            MetadataType modOptTester = _testModule.GetType("", "ModOptTester");
+            MethodSignature methodWithModOpt = modOptTester.GetMethods().Single(m => string.Equals(m.Name, "Method3")).Signature;
+            Assert.Equal(MethodSignature.GetIndexOfCustomModifierOnPointedAtTypeByParameterIndex(0), methodWithModOpt.GetEmbeddedSignatureData()[0].index);
+            Assert.Equal(MethodSignature.GetIndexOfCustomModifierOnPointedAtTypeByParameterIndex(1), methodWithModOpt.GetEmbeddedSignatureData()[1].index);
+            Assert.Equal(MethodSignature.GetIndexOfCustomModifierOnPointedAtTypeByParameterIndex(2), methodWithModOpt.GetEmbeddedSignatureData()[2].index);
+        }
+
         [Fact]
         public void TestSignatureMatches()
         {
diff --git a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SyntheticVirtualOverrideTests.DiagnosticName.cs b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SyntheticVirtualOverrideTests.DiagnosticName.cs
new file mode 100644
index 00000000000000..0ffbdd8a4c0a09
--- /dev/null
+++ b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SyntheticVirtualOverrideTests.DiagnosticName.cs
@@ -0,0 +1,28 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+using Internal.TypeSystem;
+
+using Xunit;
+
+
+namespace TypeSystemTests
+{
+    public partial class SyntheticVirtualOverrideTests
+    {
+        private partial class SyntheticMethod : MethodDesc
+        {
+            public override string DiagnosticName
+            {
+                get
+                {
+                    return _name;
+                }
+            }
+        }
+    }
+}
diff --git a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SyntheticVirtualOverrideTests.cs b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SyntheticVirtualOverrideTests.cs
index 11e0741684899d..9fc3b9bf7d0d0b 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SyntheticVirtualOverrideTests.cs
+++ b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun.Tests/SyntheticVirtualOverrideTests.cs
@@ -12,7 +12,7 @@
 
 namespace TypeSystemTests
 {
-    public class SyntheticVirtualOverrideTests
+    public partial class SyntheticVirtualOverrideTests
     {
         TestTypeSystemContext _context;
         ModuleDesc _testModule;
@@ -155,7 +155,7 @@ protected override IEnumerable<MethodDesc> GetAllMethods(TypeDesc type)
             }
         }
 
-        private class SyntheticMethod : MethodDesc
+        private partial class SyntheticMethod : MethodDesc
         {
             private TypeDesc _owningType;
             private MethodSignature _signature;
@@ -205,14 +205,6 @@ public override string Name
                 }
             }
 
-            public override string DiagnosticName
-            {
-                get
-                {
-                    return _name;
-                }
-            }
-
             public override TypeDesc OwningType
             {
                 get
diff --git a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun/ILCompiler.TypeSystem.ReadyToRun.csproj b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun/ILCompiler.TypeSystem.ReadyToRun.csproj
index 733bd833c140a7..cea2c969468d42 100644
--- a/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun/ILCompiler.TypeSystem.ReadyToRun.csproj
+++ b/src/coreclr/src/tools/aot/ILCompiler.TypeSystem.ReadyToRun/ILCompiler.TypeSystem.ReadyToRun.csproj
@@ -19,8 +19,7 @@
 
   <ItemGroup Label="Embedded Resources">
     <EmbeddedResource Include="..\..\Common\TypeSystem\Common\Properties\Resources.resx">
-      <GenerateSource>true</GenerateSource>
-      <ClassName>Internal.TypeSystem.SR</ClassName>
+      <LogicalName>Internal.TypeSystem.Strings.resources</LogicalName>
     </EmbeddedResource>
   </ItemGroup>
 
@@ -153,6 +152,9 @@
     <Compile Include="..\..\Common\TypeSystem\Common\TypeSystemException.cs">
       <Link>TypeSystem\Common\TypeSystemException.cs</Link>
     </Compile>
+    <Compile Include="..\..\Common\TypeSystem\Common\TypeSystemException.Resources.cs">
+      <Link>TypeSystem\Common\TypeSystemException.Resources.cs</Link>
+    </Compile>
     <Compile Include="..\..\Common\TypeSystem\Common\ThrowHelper.cs">
       <Link>TypeSystem\Common\ThrowHelper.cs</Link>
     </Compile>
diff --git a/src/coreclr/src/tools/aot/crossgen2/crossgen2.csproj b/src/coreclr/src/tools/aot/crossgen2/crossgen2.csproj
index b1e2d5a25130e8..2de5f56821453f 100644
--- a/src/coreclr/src/tools/aot/crossgen2/crossgen2.csproj
+++ b/src/coreclr/src/tools/aot/crossgen2/crossgen2.csproj
@@ -42,7 +42,7 @@
 
   <PropertyGroup>
     <CrossHostArch></CrossHostArch>
-    <CrossHostArch Condition="'$(TargetArchitecture)' == 'arm64'">x64</CrossHostArch>
+    <CrossHostArch Condition="'$(TargetArchitecture)' == 'arm64' and '$(BuildArchitecture)' == 'x64'">x64</CrossHostArch>
 
     <TargetOSComponent>unix</TargetOSComponent>
     <TargetOSComponent Condition="'$(TargetOS)' == 'Windows_NT'">win</TargetOSComponent>
diff --git a/src/coreclr/src/tools/aot/jitinterface/jitwrapper.cpp b/src/coreclr/src/tools/aot/jitinterface/jitwrapper.cpp
index b4b51185a1f400..1a1ef6ff17bbf8 100644
--- a/src/coreclr/src/tools/aot/jitinterface/jitwrapper.cpp
+++ b/src/coreclr/src/tools/aot/jitinterface/jitwrapper.cpp
@@ -26,11 +26,11 @@ class CORJIT_FLAGS
     uint64_t corJitFlags;
 };
 
-static const GUID JITEEVersionIdentifier = { /* 7af97117-55be-4c76-afb2-e26261cb140e */
-    0x7af97117,
-    0x55be,
-    0x4c76,
-    { 0xaf, 0xb2, 0xe2, 0x62, 0x61, 0xcb, 0x14, 0x0e }
+static const GUID JITEEVersionIdentifier = { /* a5eec3a4-4176-43a7-8c2b-a05b551d4f49 */
+    0xa5eec3a4,
+    0x4176,
+    0x43a7,
+    {0x8c, 0x2b, 0xa0, 0x5b, 0x55, 0x1d, 0x4f, 0x49}
 };
 
 class Jit
diff --git a/src/coreclr/src/tools/crossgen/CMakeLists.txt b/src/coreclr/src/tools/crossgen/CMakeLists.txt
index bf37a9cc75e573..8d861b68df52c7 100644
--- a/src/coreclr/src/tools/crossgen/CMakeLists.txt
+++ b/src/coreclr/src/tools/crossgen/CMakeLists.txt
@@ -50,7 +50,7 @@ target_link_libraries(crossgen
     ${CLRJIT_CROSSGEN}
     gcinfo_crossgen
     corzap_crossgen
-    mscorlib_crossgen
+    corelib_crossgen
     utilcode_crossgen
 )
 
diff --git a/src/coreclr/src/tools/crossgen/crossgen.cpp b/src/coreclr/src/tools/crossgen/crossgen.cpp
index 41da650119d8d9..803ea5aff6e7f5 100644
--- a/src/coreclr/src/tools/crossgen/crossgen.cpp
+++ b/src/coreclr/src/tools/crossgen/crossgen.cpp
@@ -35,7 +35,7 @@ enum ReturnValues
 STDAPI CreatePDBWorker(LPCWSTR pwzAssemblyPath, LPCWSTR pwzPlatformAssembliesPaths, LPCWSTR pwzTrustedPlatformAssemblies, LPCWSTR pwzPlatformResourceRoots, LPCWSTR pwzAppPaths, LPCWSTR pwzAppNiPaths, LPCWSTR pwzPdbPath, BOOL fGeneratePDBLinesInfo, LPCWSTR pwzManagedPdbSearchPath, LPCWSTR pwzDiasymreaderPath);
 STDAPI NGenWorker(LPCWSTR pwzFilename, DWORD dwFlags, LPCWSTR pwzPlatformAssembliesPaths, LPCWSTR pwzTrustedPlatformAssemblies, LPCWSTR pwzPlatformResourceRoots, LPCWSTR pwzAppPaths, LPCWSTR pwzOutputFilename=NULL, SIZE_T customBaseAddress=0, ICorSvcLogger *pLogger = NULL, LPCWSTR pwszCLRJITPath = nullptr);
 void SetSvcLogger(ICorSvcLogger *pCorSvcLogger);
-void SetMscorlibPath(LPCWSTR wzSystemDirectory);
+void SetCoreLibPath(LPCWSTR wzSystemDirectory);
 
 /* --------------------------------------------------------------------------- *
  * Console stuff
@@ -257,7 +257,7 @@ bool StringEndsWith(LPCWSTR pwzString, LPCWSTR pwzCandidate)
 // When using the Phone binding model (TrustedPlatformAssemblies), automatically
 // detect which path CoreLib.[ni.]dll lies in.
 //
-bool ComputeMscorlibPathFromTrustedPlatformAssemblies(SString& pwzMscorlibPath, LPCWSTR pwzTrustedPlatformAssemblies)
+bool ComputeCoreLibPathFromTrustedPlatformAssemblies(SString& pwzCoreLibPath, LPCWSTR pwzTrustedPlatformAssemblies)
 {
     LPWSTR wszTrustedPathCopy = new WCHAR[wcslen(pwzTrustedPlatformAssemblies) + 1];
     wcscpy_s(wszTrustedPathCopy, wcslen(pwzTrustedPlatformAssemblies) + 1, pwzTrustedPlatformAssemblies);
@@ -277,11 +277,11 @@ bool ComputeMscorlibPathFromTrustedPlatformAssemblies(SString& pwzMscorlibPath,
         if (StringEndsWith(wszSingleTrustedPath, DIRECTORY_SEPARATOR_STR_W CoreLibName_IL_W) ||
             StringEndsWith(wszSingleTrustedPath, DIRECTORY_SEPARATOR_STR_W CoreLibName_NI_W))
         {
-            pwzMscorlibPath.Set(wszSingleTrustedPath);
-            SString::Iterator pwzSeparator = pwzMscorlibPath.End();
+            pwzCoreLibPath.Set(wszSingleTrustedPath);
+            SString::Iterator pwzSeparator = pwzCoreLibPath.End();
             bool retval = true;
 
-            if (!SUCCEEDED(CopySystemDirectory(pwzMscorlibPath, pwzMscorlibPath)))
+            if (!SUCCEEDED(CopySystemDirectory(pwzCoreLibPath, pwzCoreLibPath)))
             {
                 retval = false;
             }
@@ -318,7 +318,7 @@ void PopulateTPAList(SString path, LPCWSTR pwszMask, SString &refTPAList, bool f
             // No NIs are supported when creating NI images (other than NI of System.Private.CoreLib.dll).
             if (!fCreatePDB)
             {
-                // Only CoreLib's ni.dll should be in the TPAList for the compilation of non-mscorlib assemblies.
+                // Only CoreLib's ni.dll should be in the TPAList for the compilation of non-CoreLib assemblies.
                 if (StringEndsWith((LPWSTR)pwszFilename, W(".ni.dll")))
                 {
                     fAddFileToTPAList = false;
@@ -837,10 +837,10 @@ int _cdecl wmain(int argc, __in_ecount(argc) WCHAR **argv)
 
     if (pwzTrustedPlatformAssemblies != nullptr)
     {
-        if (ComputeMscorlibPathFromTrustedPlatformAssemblies(wzTrustedPathRoot, pwzTrustedPlatformAssemblies))
+        if (ComputeCoreLibPathFromTrustedPlatformAssemblies(wzTrustedPathRoot, pwzTrustedPlatformAssemblies))
         {
             pwzPlatformAssembliesPaths = wzTrustedPathRoot.GetUnicode();
-            SetMscorlibPath(pwzPlatformAssembliesPaths);
+            SetCoreLibPath(pwzPlatformAssembliesPaths);
         }
     }
 
diff --git a/src/coreclr/src/tools/r2rdump/TextDumper.cs b/src/coreclr/src/tools/r2rdump/TextDumper.cs
index b3bf91845f380d..19aa23f791eae5 100644
--- a/src/coreclr/src/tools/r2rdump/TextDumper.cs
+++ b/src/coreclr/src/tools/r2rdump/TextDumper.cs
@@ -217,16 +217,13 @@ internal override void DumpDisasm(RuntimeFunction rtf, int imageOffset)
 
                 if (_r2r.Machine == Machine.Amd64 && ((ILCompiler.Reflection.ReadyToRun.Amd64.UnwindInfo)rtf.UnwindInfo).UnwindCodes.ContainsKey(codeOffset))
                 {
-                    List<ILCompiler.Reflection.ReadyToRun.Amd64.UnwindCode> codes = ((ILCompiler.Reflection.ReadyToRun.Amd64.UnwindInfo)rtf.UnwindInfo).UnwindCodes[codeOffset];
-                    foreach (ILCompiler.Reflection.ReadyToRun.Amd64.UnwindCode code in codes)
+                    ILCompiler.Reflection.ReadyToRun.Amd64.UnwindCode code = ((ILCompiler.Reflection.ReadyToRun.Amd64.UnwindInfo)rtf.UnwindInfo).UnwindCodes[codeOffset];                    
+                    _writer.Write($"{indentString}{code.UnwindOp} {code.OpInfoStr}");
+                    if (code.NextFrameOffset != -1)
                     {
-                        _writer.Write($"{indentString}{code.UnwindOp} {code.OpInfoStr}");
-                        if (code.NextFrameOffset != -1)
-                        {
-                            _writer.WriteLine($"{indentString}{code.NextFrameOffset}");
-                        }
-                        _writer.WriteLine();
+                        _writer.WriteLine($"{indentString}{code.NextFrameOffset}");
                     }
+                    _writer.WriteLine();
                 }
 
                 if (!_options.HideTransitions && rtf.Method.GcInfo?.Transitions != null && rtf.Method.GcInfo.Transitions.TryGetValue(codeOffset, out List<BaseGcTransition> transitionsForOffset))
diff --git a/src/coreclr/src/unwinder/CMakeLists.txt b/src/coreclr/src/unwinder/CMakeLists.txt
index 98cdb0c0b7a891..e9af2458140d17 100644
--- a/src/coreclr/src/unwinder/CMakeLists.txt
+++ b/src/coreclr/src/unwinder/CMakeLists.txt
@@ -20,8 +20,10 @@ list(APPEND UNWINDER_SOURCES
 convert_to_absolute_path(UNWINDER_SOURCES ${UNWINDER_SOURCES})
 
 if(CLR_CMAKE_HOST_UNIX)
-    add_library_clr(unwinder_wks OBJECT ${UNWINDER_SOURCES})
-    add_dependencies(unwinder_wks eventing_headers)
+    add_library_clr(unwinder_wks_obj OBJECT ${UNWINDER_SOURCES})
+    add_dependencies(unwinder_wks_obj eventing_headers)
+    add_library(unwinder_wks INTERFACE)
+    target_sources(unwinder_wks INTERFACE $<TARGET_OBJECTS:unwinder_wks_obj>)
 endif(CLR_CMAKE_HOST_UNIX)
 
 add_library_clr(unwinder_dac ${UNWINDER_SOURCES})
diff --git a/src/coreclr/src/utilcode/CMakeLists.txt b/src/coreclr/src/utilcode/CMakeLists.txt
index 4c1ce806b65101..9eeac28ae4fb71 100644
--- a/src/coreclr/src/utilcode/CMakeLists.txt
+++ b/src/coreclr/src/utilcode/CMakeLists.txt
@@ -26,7 +26,6 @@ set(UTILCODE_COMMON_SOURCES
   arraylist.cpp
   bitvector.cpp
   comex.cpp
-  delayloadhelpers.cpp
   guidfromname.cpp
   memorypool.cpp
   iallocator.cpp
@@ -97,7 +96,9 @@ convert_to_absolute_path(UTILCODE_CROSSGEN_SOURCES ${UTILCODE_CROSSGEN_SOURCES})
 convert_to_absolute_path(UTILCODE_STATICNOHOST_SOURCES ${UTILCODE_STATICNOHOST_SOURCES})
 
 add_library_clr(utilcode_dac STATIC ${UTILCODE_DAC_SOURCES})
-add_library_clr(utilcode OBJECT ${UTILCODE_SOURCES})
+add_library_clr(utilcode_obj OBJECT ${UTILCODE_SOURCES})
+add_library(utilcode INTERFACE)
+target_sources(utilcode INTERFACE $<TARGET_OBJECTS:utilcode_obj>)
 add_library_clr(utilcodestaticnohost STATIC ${UTILCODE_STATICNOHOST_SOURCES})
 add_library_clr(utilcode_crossgen STATIC ${UTILCODE_CROSSGEN_SOURCES})
 
@@ -105,9 +106,9 @@ if(CLR_CMAKE_HOST_UNIX)
   target_link_libraries(utilcodestaticnohost  nativeresourcestring)
   target_link_libraries(utilcode_crossgen  nativeresourcestring)
   target_link_libraries(utilcode_dac nativeresourcestring)
-  target_link_libraries(utilcode nativeresourcestring)
+  target_link_libraries(utilcode INTERFACE nativeresourcestring)
   add_dependencies(utilcode_dac coreclrpal)
-  add_dependencies(utilcode coreclrpal)
+  add_dependencies(utilcode_obj coreclrpal)
 endif(CLR_CMAKE_HOST_UNIX)
 
 
@@ -120,10 +121,10 @@ set_target_properties(utilcode_crossgen PROPERTIES CROSSGEN_COMPONENT TRUE)
 target_compile_definitions(utilcode_dac PRIVATE SELF_NO_HOST)
 target_compile_definitions(utilcodestaticnohost PRIVATE SELF_NO_HOST)
 add_dependencies(utilcode_dac ${UTILCODE_DEPENDENCIES})
-add_dependencies(utilcode ${UTILCODE_DEPENDENCIES})
+add_dependencies(utilcode_obj ${UTILCODE_DEPENDENCIES})
 add_dependencies(utilcode_crossgen ${UTILCODE_DEPENDENCIES})
 add_dependencies(utilcodestaticnohost ${UTILCODE_DEPENDENCIES})
 target_precompile_header(TARGET utilcode_dac HEADER stdafx.h)
-target_precompile_header(TARGET utilcode HEADER stdafx.h)
+target_precompile_header(TARGET utilcode_obj HEADER stdafx.h)
 target_precompile_header(TARGET utilcode_crossgen HEADER stdafx.h)
 target_precompile_header(TARGET utilcodestaticnohost HEADER stdafx.h)
diff --git a/src/coreclr/src/utilcode/delayloadhelpers.cpp b/src/coreclr/src/utilcode/delayloadhelpers.cpp
deleted file mode 100644
index 90936ccbcfc00c..00000000000000
--- a/src/coreclr/src/utilcode/delayloadhelpers.cpp
+++ /dev/null
@@ -1,113 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-//
-
-//
-// Contains convenience functionality for lazily loading modules
-// and getting entrypoints within them.
-//
-
-#include "stdafx.h"
-
-#include "crtwrap.h"
-#include "winwrap.h"
-#include "utilcode.h"
-#include "clrhost.h"
-#include "holder.h"
-#include "delayloadhelpers.h"
-
-namespace DelayLoad
-{
-    //=================================================================================================================
-    // Used to synchronize initialization. Is not used when initialization has already taken place.
-
-    static CRITSEC_COOKIE g_pLock = nullptr;
-
-    //=================================================================================================================
-    // Creates and initializes g_pLock when first used.
-
-    static HRESULT InitializeLock()
-    {
-        STATIC_CONTRACT_LIMITED_METHOD;
-        HRESULT hr = S_OK;
-
-        CRITSEC_COOKIE pLock = ClrCreateCriticalSection(CrstLeafLock, CRST_REENTRANCY);
-        IfNullRet(pLock);
-        if (InterlockedCompareExchangeT<CRITSEC_COOKIE>(&g_pLock, pLock, nullptr) != nullptr)
-        {
-            ClrDeleteCriticalSection(pLock);
-        }
-
-        return S_OK;
-    }
-
-    //=================================================================================================================
-    HRESULT Module::GetValue(HMODULE *pHMODULE)
-    {
-        STATIC_CONTRACT_LIMITED_METHOD;
-        HRESULT hr = S_OK;
-
-        if (pHMODULE == nullptr)
-        {
-            return E_INVALIDARG;
-        }
-
-        if (!m_fInitialized)
-        {
-            IfFailRet(InitializeLock());
-
-            HModuleHolder hMod = ::LoadLibraryW(m_wzDllName);
-            hr = (hMod == nullptr) ? HRESULT_FROM_GetLastError() : S_OK;
-            _ASSERTE(FAILED(hr) == (hMod == nullptr));
-
-            {   // Lock scope
-                CRITSEC_Holder lock(g_pLock);
-                if (!m_fInitialized)
-                {
-                    m_hr = hr;
-                    m_hMod = hMod.Extract();
-                    m_fInitialized = true;
-                }
-            }
-        }
-
-        _ASSERTE(m_fInitialized);
-        *pHMODULE = m_hMod;
-        return m_hr;
-    }
-
-    //=================================================================================================================
-    HRESULT Function::GetValue(LPVOID * ppvFunc)
-    {
-        STATIC_CONTRACT_LIMITED_METHOD;
-        HRESULT hr = S_OK;
-
-        if (ppvFunc == nullptr)
-        {
-            return E_INVALIDARG;
-        }
-
-        if (!m_fInitialized)
-        {
-            HMODULE hMod = nullptr;
-            IfFailRet(m_pModule->GetValue(&hMod));
-
-            LPVOID pvFunc = reinterpret_cast<LPVOID>(::GetProcAddress(hMod, m_szFunctionName));
-            hr = (pvFunc == nullptr) ? HRESULT_FROM_GetLastError() : S_OK;
-
-            {   // Lock scope
-                CRITSEC_Holder lock(g_pLock);
-                if (!m_fInitialized)
-                {
-                    m_hr = hr;
-                    m_pvFunction = pvFunc;
-                    m_fInitialized = true;
-                }
-            }
-        }
-
-        _ASSERTE(m_fInitialized);
-        *ppvFunc = m_pvFunction;
-        return m_hr;
-    }
-}
diff --git a/src/coreclr/src/utilcode/pedecoder.cpp b/src/coreclr/src/utilcode/pedecoder.cpp
index d0854bbc043fdf..91fde64d297c7b 100644
--- a/src/coreclr/src/utilcode/pedecoder.cpp
+++ b/src/coreclr/src/utilcode/pedecoder.cpp
@@ -1770,20 +1770,29 @@ void PEDecoder::LayoutILOnly(void *base, BOOL allowFullPE) const
                            PAGE_READONLY, &oldProtection))
         ThrowLastError();
 
-    // Finally, apply proper protection to copied sections
-    section = sectionStart;
-    while (section < sectionEnd)
+    // Finally, apply proper protection to copied sections    
+    for (section = sectionStart; section < sectionEnd; section++)
     {
         // Add appropriate page protection.
-        if ((section->Characteristics & VAL32(IMAGE_SCN_MEM_WRITE)) == 0)
+#if defined(CROSSGEN_COMPILE) || defined(TARGET_UNIX)
+        if (section->Characteristics & IMAGE_SCN_MEM_WRITE)
+            continue;
+
+        DWORD newProtection = PAGE_READONLY;
+#else
+        DWORD newProtection = section->Characteristics & IMAGE_SCN_MEM_EXECUTE ?
+            PAGE_EXECUTE_READ :
+            section->Characteristics & IMAGE_SCN_MEM_WRITE ?
+                PAGE_READWRITE :
+                PAGE_READONLY;
+#endif
+
+        if (!ClrVirtualProtect((void*)((BYTE*)base + VAL32(section->VirtualAddress)),
+            VAL32(section->Misc.VirtualSize),
+            newProtection, &oldProtection))
         {
-            if (!ClrVirtualProtect((void *) ((BYTE *)base + VAL32(section->VirtualAddress)),
-                                   VAL32(section->Misc.VirtualSize),
-                                   PAGE_READONLY, &oldProtection))
-                ThrowLastError();
+            ThrowLastError();
         }
-
-        section++;
     }
 
     RETURN;
diff --git a/src/coreclr/src/utilcode/sigbuilder.cpp b/src/coreclr/src/utilcode/sigbuilder.cpp
index 111164149e7ec4..4a8f8fe6c18357 100644
--- a/src/coreclr/src/utilcode/sigbuilder.cpp
+++ b/src/coreclr/src/utilcode/sigbuilder.cpp
@@ -6,6 +6,8 @@
 #include "sigbuilder.h"
 #include "ex.h"
 
+const mdToken g_tkCorEncodeToken[4] ={mdtTypeDef, mdtTypeRef, mdtTypeSpec, mdtBaseType};
+
 void SigBuilder::AppendByte(BYTE b)
 {
     STANDARD_VM_CONTRACT;
diff --git a/src/coreclr/src/utilcode/util.cpp b/src/coreclr/src/utilcode/util.cpp
index d697946beb8fef..ef35f09b17722e 100644
--- a/src/coreclr/src/utilcode/util.cpp
+++ b/src/coreclr/src/utilcode/util.cpp
@@ -850,6 +850,7 @@ BYTE * ClrVirtualAllocWithinRange(const BYTE *pMinAddr,
 
 /*static*/ BOOL CPUGroupInfo::m_enableGCCPUGroups = FALSE;
 /*static*/ BOOL CPUGroupInfo::m_threadUseAllCpuGroups = FALSE;
+/*static*/ BOOL CPUGroupInfo::m_threadAssignCpuGroups = FALSE;
 /*static*/ WORD CPUGroupInfo::m_nGroups = 0;
 /*static*/ WORD CPUGroupInfo::m_nProcessors = 0;
 /*static*/ WORD CPUGroupInfo::m_initialGroup = 0;
@@ -991,6 +992,7 @@ DWORD LCM(DWORD u, DWORD v)
 #if !defined(FEATURE_REDHAWK) && (defined(TARGET_AMD64) || defined(TARGET_ARM64))
     BOOL enableGCCPUGroups     = CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_GCCpuGroup) != 0;
     BOOL threadUseAllCpuGroups = CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_Thread_UseAllCpuGroups) != 0;
+    BOOL threadAssignCpuGroups = CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_Thread_AssignCpuGroups) != 0;
 
     if (!enableGCCPUGroups)
         return;
@@ -1006,10 +1008,11 @@ DWORD LCM(DWORD u, DWORD v)
     CPUGroupInfo::GetThreadGroupAffinity(GetCurrentThread(), &groupAffinity);
     m_initialGroup = groupAffinity.Group;
 
-	// only enable CPU groups if more than one group exists
-	BOOL hasMultipleGroups = m_nGroups > 1;
-	m_enableGCCPUGroups = enableGCCPUGroups && hasMultipleGroups;
-	m_threadUseAllCpuGroups = threadUseAllCpuGroups && hasMultipleGroups;
+    // only enable CPU groups if more than one group exists
+    BOOL hasMultipleGroups = m_nGroups > 1;
+    m_enableGCCPUGroups = enableGCCPUGroups && hasMultipleGroups;
+    m_threadUseAllCpuGroups = threadUseAllCpuGroups && hasMultipleGroups;
+    m_threadAssignCpuGroups = threadAssignCpuGroups && hasMultipleGroups;
 #endif // TARGET_AMD64 || TARGET_ARM64
 
     // Determine if the process is affinitized to a single processor (or if the system has a single processor)
@@ -1164,8 +1167,8 @@ DWORD LCM(DWORD u, DWORD v)
     WORD i, minGroup = 0;
     DWORD minWeight = 0;
 
-    // m_enableGCCPUGroups and m_threadUseAllCpuGroups must be TRUE
-    _ASSERTE(m_enableGCCPUGroups && m_threadUseAllCpuGroups);
+    // m_enableGCCPUGroups, m_threadUseAllCpuGroups, and m_threadAssignCpuGroups must be TRUE
+    _ASSERTE(m_enableGCCPUGroups && m_threadUseAllCpuGroups && m_threadAssignCpuGroups);
 
     for (i = 0; i < m_nGroups; i++)
     {
@@ -1204,8 +1207,8 @@ DWORD LCM(DWORD u, DWORD v)
 {
     LIMITED_METHOD_CONTRACT;
 #if (defined(TARGET_AMD64) || defined(TARGET_ARM64))
-    // m_enableGCCPUGroups and m_threadUseAllCpuGroups must be TRUE
-    _ASSERTE(m_enableGCCPUGroups && m_threadUseAllCpuGroups);
+    // m_enableGCCPUGroups, m_threadUseAllCpuGroups, and m_threadAssignCpuGroups must be TRUE
+    _ASSERTE(m_enableGCCPUGroups && m_threadUseAllCpuGroups && m_threadAssignCpuGroups);
 
     WORD group = gf->Group;
     m_CPUGroupInfoArray[group].activeThreadWeight -= m_CPUGroupInfoArray[group].groupWeight;
@@ -1238,6 +1241,12 @@ BOOL CPUGroupInfo::GetCPUGroupRange(WORD group_number, WORD* group_begin, WORD*
     LIMITED_METHOD_CONTRACT;
     return m_threadUseAllCpuGroups;
 }
+
+/*static*/ BOOL CPUGroupInfo::CanAssignCpuGroupsToThreads()
+{
+    LIMITED_METHOD_CONTRACT;
+    return m_threadAssignCpuGroups;
+}
 #endif // HOST_WINDOWS
 
 //******************************************************************************
diff --git a/src/coreclr/src/vm/CMakeLists.txt b/src/coreclr/src/vm/CMakeLists.txt
index 81d0e8c21b108d..83ebd3c3576e21 100644
--- a/src/coreclr/src/vm/CMakeLists.txt
+++ b/src/coreclr/src/vm/CMakeLists.txt
@@ -316,6 +316,7 @@ set(VM_SOURCES_WKS
     comthreadpool.cpp
     comutilnative.cpp
     comwaithandle.cpp
+    corelib.cpp # <DisablePrecompiledHeaders>true</DisablePrecompiledHeaders>
     customattribute.cpp
     custommarshalerinfo.cpp
     autotrace.cpp
@@ -370,7 +371,6 @@ set(VM_SOURCES_WKS
     marshalnative.cpp
     methodtablebuilder.cpp
     mlinfo.cpp
-    mscorlib.cpp # <DisablePrecompiledHeaders>true</DisablePrecompiledHeaders>
     multicorejit.cpp # Condition="'$(FeatureMulticoreJIT)' == 'true'
     multicorejitplayer.cpp # Condition="'$(FeatureMulticoreJIT)' == 'true'
     nativeeventsource.cpp
@@ -379,6 +379,7 @@ set(VM_SOURCES_WKS
     objectlist.cpp
     olevariant.cpp
     pendingload.cpp
+    processdiagnosticsprotocolhelper.cpp
     profdetach.cpp
     profilermetadataemitvalidator.cpp
     profilingenumerators.cpp
@@ -490,7 +491,7 @@ set(VM_HEADERS_WKS
     marshalnative.h
     methodtablebuilder.h
     mlinfo.h
-    mscorlib.h
+    corelib.h
     multicorejit.h
     multicorejitimpl.h
     nativeeventsource.h
@@ -499,6 +500,7 @@ set(VM_HEADERS_WKS
     objectlist.h
     olevariant.h
     pendingload.h
+    processdiagnosticsprotocolhelper.h
     profdetach.h
     profilermetadataemitvalidator.h
     profilingenumerators.h
@@ -921,7 +923,7 @@ list(APPEND VM_HEADERS_DAC
 
 if (CLR_CMAKE_TARGET_WIN32)
     list(APPEND VM_SOURCES_WKS ${VM_HEADERS_WKS})
-    list(APPEND VM_SOURCES_WKS_ARCH_ASM ${VM_HEADERS_WKS_ARCH_ASM})
+    list(APPEND VM_SOURCES_WKS ${VM_HEADERS_WKS_ARCH_ASM})
     list(APPEND VM_SOURCES_DAC ${VM_HEADERS_DAC})
 endif(CLR_CMAKE_TARGET_WIN32)
 
diff --git a/src/coreclr/src/vm/ClrEtwAll.man b/src/coreclr/src/vm/ClrEtwAll.man
index c68eac52ac28ea..cf2108b4e56ac3 100644
--- a/src/coreclr/src/vm/ClrEtwAll.man
+++ b/src/coreclr/src/vm/ClrEtwAll.man
@@ -83,6 +83,8 @@
                              message="$(string.RuntimePublisher.CompilationDiagnosticKeywordMessage)" symbol="CLR_COMPILATIONDIAGNOSTIC_KEYWORD" />
                     <keyword name="MethodDiagnosticKeyword" mask="0x4000000000"
                              message="$(string.RuntimePublisher.MethodDiagnosticKeywordMessage)" symbol="CLR_METHODDIAGNOSTIC_KEYWORD" />
+                    <keyword name="TypeDiagnosticKeyword" mask="0x8000000000"
+                             message="$(string.RuntimePublisher.TypeDiagnosticKeywordMessage)" symbol="CLR_TYPEDIAGNOSTIC_KEYWORD" />
                 </keywords>
                 <!--Tasks-->
                 <tasks>
@@ -401,7 +403,14 @@
                             <opcode name="KnownPathProbed" message="$(string.RuntimePublisher.KnownPathProbedOpcodeMessage)" symbol="CLR_BINDING_PATH_PROBED_OPCODE" value="15"/>
                         </opcodes>
                     </task>
-                <!--Next available ID is 33-->
+                    <task name="TypeLoad" symbol="CLR_TYPELOAD_TASK"
+                          value="33" eventGUID="{9DB1562B-512F-475D-8D4C-0C6D97C1E73C}"
+                          message="$(string.RuntimePublisher.TypeLoadTaskMessage)">
+                        <opcodes>
+                        </opcodes>
+                    </task>
+
+                <!--Next available ID is 34-->
                 </tasks>
                 <!--Maps-->
                 <maps>
@@ -1895,6 +1904,34 @@
                         </UserData>
                     </template>
 
+                    <template tid="TypeLoadStart">
+                        <data name="TypeLoadStartID" inType="win:UInt32" />
+                        <data name="ClrInstanceID" inType="win:UInt16" />
+                        <UserData>
+                            <TypeLoadStart xmlns="myNs">
+                                <TypeLoadStartID> %1 </TypeLoadStartID>
+                                <ClrInstanceID> %2 </ClrInstanceID>
+                            </TypeLoadStart>
+                        </UserData>
+                    </template>
+
+                    <template tid="TypeLoadStop">
+                        <data name="TypeLoadStartID" inType="win:UInt32" />
+                        <data name="ClrInstanceID" inType="win:UInt16" />
+                        <data name="LoadLevel" inType="win:UInt16" />
+                        <data name="TypeID" inType="win:UInt64" outType="win:HexInt64" />
+                        <data name="TypeName" inType="win:UnicodeString" />
+                        <UserData>
+                            <TypeLoadStop xmlns="myNs">
+                                <TypeLoadStartID> %1 </TypeLoadStartID>
+                                <ClrInstanceID> %2 </ClrInstanceID>
+                                <LoadLevel> %3 </LoadLevel>
+                                <TypeID> %4 </TypeID>
+                                <TypeName> %5 </TypeName>
+                            </TypeLoadStop>
+                        </UserData>
+                    </template>
+
                     <template tid="MethodLoadUnload">
                         <data name="MethodID" inType="win:UInt64" outType="win:HexInt64" />
                         <data name="ModuleID" inType="win:UInt64" outType="win:HexInt64" />
@@ -1980,6 +2017,17 @@
                         </UserData>
                     </template>
 
+                    <template tid="R2RGetEntryPointStart">
+                        <data name="MethodID" inType="win:UInt64" outType="win:HexInt64" />
+                        <data name="ClrInstanceID" inType="win:UInt16" />
+                        <UserData>
+                            <R2RGetEntryPointStart xmlns="myNs">
+                                <MethodID> %1 </MethodID>
+                                <ClrInstanceID> %2 </ClrInstanceID>
+                            </R2RGetEntryPointStart>
+                        </UserData>
+                    </template>
+
                     <template tid="MethodLoadUnloadVerbose">
                         <data name="MethodID" inType="win:UInt64" outType="win:HexInt64" />
                         <data name="ModuleID" inType="win:UInt64" outType="win:HexInt64" />
@@ -3200,6 +3248,7 @@
                            opcode="Running"
                            symbol="ThreadRunning"
                            message="$(string.RuntimePublisher.ThreadRunningEventMessage)"/>
+
                     <event value="72" version="0" level="win:Informational"  template="MethodDetails"
                            keywords="MethodDiagnosticKeyword"
                            task="CLRMethod"
@@ -3207,6 +3256,20 @@
                            symbol="MethodDetails"
                            message="$(string.RuntimePublisher.MethodDetailsEventMessage)"/>
 
+                    <event value="73" version="0" level="win:Informational"  template="TypeLoadStart"
+                           keywords="TypeDiagnosticKeyword"
+                           task="TypeLoad"
+                           opcode="win:Start"
+                           symbol="TypeLoadStart"
+                           message="$(string.RuntimePublisher.TypeLoadStartEventMessage)"/>
+
+                    <event value="74" version="0" level="win:Informational"  template="TypeLoadStop"
+                           keywords="TypeDiagnosticKeyword"
+                           task="TypeLoad"
+                           opcode="win:Stop"
+                           symbol="TypeLoadStop"
+                           message="$(string.RuntimePublisher.TypeLoadStopEventMessage)"/>
+
                     <!-- CLR Exception events -->
                     <event value="80" version="0" level="win:Informational"
                            opcode="win:Start"
@@ -3364,11 +3427,16 @@
                            task="CLRMethod"
                            symbol="MethodLoad_V2" message="$(string.RuntimePublisher.MethodLoad_V2EventMessage)"/>
 
-                    <event value="159" version="0" level="win:Verbose" template="R2RGetEntryPoint"
+                    <event value="159" version="0" level="win:Informational" template="R2RGetEntryPoint"
                            keywords ="CompilationDiagnosticKeyword" opcode="MethodLoad"
                            task="CLRMethod"
                            symbol="R2RGetEntryPoint" message="$(string.RuntimePublisher.R2RGetEntryPointEventMessage)"/>
 
+                    <event value="160" version="0" level="win:Informational" template="R2RGetEntryPointStart"
+                           keywords ="CompilationDiagnosticKeyword" opcode="MethodLoad"
+                           task="CLRMethod"
+                           symbol="R2RGetEntryPointStart" message="$(string.RuntimePublisher.R2RGetEntryPointStartEventMessage)"/>
+
                     <event value="142" version="0" level="win:Informational"  template="MethodLoadUnload"
                            keywords ="JitKeyword NGenKeyword" opcode="MethodUnload"
                            task="CLRMethod"
@@ -6899,6 +6967,8 @@
                 <string id="RuntimePublisher.ThreadCreatingEventMessage" value="ID=%1;%nClrInstanceID=%s" />
                 <string id="RuntimePublisher.ThreadRunningEventMessage" value="ID=%1;%nClrInstanceID=%s" />
                 <string id="RuntimePublisher.MethodDetailsEventMessage" value="MethodID=%1;%TypeID=%2;MethodToken=%3;TypeParameterCount=%4;LoaderModuleID=%5" />
+                <string id="RuntimePublisher.TypeLoadStartEventMessage" value="TypeLoadStartID=%1;ClrInstanceID=%2" />
+                <string id="RuntimePublisher.TypeLoadStopEventMessage" value="TypeLoadStartID=%1;ClrInstanceID=%2;LoadLevel=%3;TypeID=%4;TypeName=%5" />
                 <string id="RuntimePublisher.ExceptionExceptionThrownEventMessage" value="NONE" />
                 <string id="RuntimePublisher.ExceptionExceptionThrown_V1EventMessage" value="ExceptionType=%1;%nExceptionMessage=%2;%nExceptionEIP=%3;%nExceptionHRESULT=%4;%nExceptionFlags=%5;%nClrInstanceID=%6" />
                 <string id="RuntimePublisher.ExceptionExceptionHandlingEventMessage" value="EntryEIP=%1;%nMethodID=%2;%nMethodName=%3;%nClrInstanceID=%4" />
@@ -6917,6 +6987,7 @@
                 <string id="RuntimePublisher.MethodLoad_V1EventMessage" value="MethodID=%1;%nModuleID=%2;%nMethodStartAddress=%3;%nMethodSize=%4;%nMethodToken=%5;%nMethodFlags=%6;%nClrInstanceID=%7" />
                 <string id="RuntimePublisher.MethodLoad_V2EventMessage" value="MethodID=%1;%nModuleID=%2;%nMethodStartAddress=%3;%nMethodSize=%4;%nMethodToken=%5;%nMethodFlags=%6;%nClrInstanceID=%7;%nReJITID=%8" />
                 <string id="RuntimePublisher.R2RGetEntryPointEventMessage" value="MethodID=%1;%nMethodName=%2;%nEntryPoint=%3;%nClrInstanceID=%4" />
+                <string id="RuntimePublisher.R2RGetEntryPointStartEventMessage" value="MethodID=%1;%nClrInstanceID=%2" />
                 <string id="RuntimePublisher.MethodLoadVerboseEventMessage" value="MethodID=%1;%nModuleID=%2;%nMethodStartAddress=%3;%nMethodSize=%4;%nMethodToken=%5;%nMethodFlags=%6;%nMethodNamespace=%7;%nMethodName=%8;%nMethodSignature=%9" />
                 <string id="RuntimePublisher.MethodLoadVerbose_V1EventMessage" value="MethodID=%1;%nModuleID=%2;%nMethodStartAddress=%3;%nMethodSize=%4;%nMethodToken=%5;%nMethodFlags=%6;%nMethodNamespace=%7;%nMethodName=%8;%nMethodSignature=%9;%nClrInstanceID=%10" />
                 <string id="RuntimePublisher.MethodLoadVerbose_V2EventMessage" value="MethodID=%1;%nModuleID=%2;%nMethodStartAddress=%3;%nMethodSize=%4;%nMethodToken=%5;%nMethodFlags=%6;%nMethodNamespace=%7;%nMethodName=%8;%nMethodSignature=%9;%nClrInstanceID=%10;%nReJITID=%11" />
@@ -7149,6 +7220,7 @@
                 <string id="RuntimePublisher.CodeSymbolsTaskMessage" value="CodeSymbols" />
                 <string id="RuntimePublisher.TieredCompilationTaskMessage" value="TieredCompilation" />
                 <string id="RuntimePublisher.AssemblyLoaderTaskMessage" value="AssemblyLoader" />
+                <string id="RuntimePublisher.TypeLoadTaskMessage" value="TypeLoad" />
 
                 <string id="RundownPublisher.EEStartupTaskMessage" value="Runtime" />
                 <string id="RundownPublisher.MethodTaskMessage" value="Method" />
@@ -7475,6 +7547,7 @@
                 <string id="RuntimePublisher.CompilationKeywordMessage" value="Compilation" />
                 <string id="RuntimePublisher.CompilationDiagnosticKeywordMessage" value="CompilationDiagnostic" />
                 <string id="RuntimePublisher.MethodDiagnosticKeywordMessage" value="MethodDiagnostic" />
+                <string id="RuntimePublisher.TypeDiagnosticKeywordMessage" value="TypeDiagnostic" />
                 <string id="RundownPublisher.LoaderKeywordMessage" value="Loader" />
                 <string id="RundownPublisher.JitKeywordMessage" value="Jit" />
                 <string id="RundownPublisher.JittedMethodILToNativeMapRundownKeywordMessage" value="JittedMethodILToNativeMapRundown" />
diff --git a/src/coreclr/src/vm/amd64/AsmHelpers.asm b/src/coreclr/src/vm/amd64/AsmHelpers.asm
index cb5d1fad499d07..172b800f3feac2 100644
--- a/src/coreclr/src/vm/amd64/AsmHelpers.asm
+++ b/src/coreclr/src/vm/amd64/AsmHelpers.asm
@@ -667,27 +667,6 @@ NESTED_ENTRY ProfileTailcallNaked, _TEXT
 NESTED_END ProfileTailcallNaked, _TEXT
 
 
-;; extern "C" DWORD __stdcall getcpuid(DWORD arg, unsigned char result[16]);
-NESTED_ENTRY getcpuid, _TEXT
-
-        push_nonvol_reg    rbx
-        push_nonvol_reg    rsi
-    END_PROLOGUE
-
-        mov     eax, ecx                ; first arg
-        mov     rsi, rdx                ; second arg (result)
-        xor     ecx, ecx                ; clear ecx - needed for "Structured Extended Feature Flags"
-        cpuid
-        mov     [rsi+ 0], eax
-        mov     [rsi+ 4], ebx
-        mov     [rsi+ 8], ecx
-        mov     [rsi+12], edx
-        pop     rsi
-        pop     rbx
-        ret
-NESTED_END getcpuid, _TEXT
-
-
 ;; extern "C" DWORD __stdcall xmmYmmStateSupport();
 LEAF_ENTRY xmmYmmStateSupport, _TEXT
         mov     ecx, 0                  ; Specify xcr0
@@ -703,30 +682,6 @@ LEAF_ENTRY xmmYmmStateSupport, _TEXT
         ret
 LEAF_END xmmYmmStateSupport, _TEXT
 
-;The following function uses Deterministic Cache Parameter leafs to determine the cache hierarchy information on Prescott & Above platforms.
-;  This function takes 3 arguments:
-;     Arg1 is an input to ECX. Used as index to specify which cache level to return information on by CPUID.
-;         Arg1 is already passed in ECX on call to getextcpuid, so no explicit assignment is required;
-;     Arg2 is an input to EAX. For deterministic code enumeration, we pass in 4H in arg2.
-;     Arg3 is a pointer to the return dwbuffer
-NESTED_ENTRY getextcpuid, _TEXT
-        push_nonvol_reg    rbx
-        push_nonvol_reg    rsi
-    END_PROLOGUE
-
-        mov     eax, edx                ; second arg (input to  EAX)
-        mov     rsi, r8                 ; third arg  (pointer to return dwbuffer)
-        cpuid
-        mov     [rsi+ 0], eax
-        mov     [rsi+ 4], ebx
-        mov     [rsi+ 8], ecx
-        mov     [rsi+12], edx
-        pop     rsi
-        pop     rbx
-
-        ret
-NESTED_END getextcpuid, _TEXT
-
 
 ; EXTERN_C void moveOWord(LPVOID* src, LPVOID* target);
 ; <NOTE>
diff --git a/src/coreclr/src/vm/amd64/asmconstants.h b/src/coreclr/src/vm/amd64/asmconstants.h
index a073179f812172..8ef508e429885c 100644
--- a/src/coreclr/src/vm/amd64/asmconstants.h
+++ b/src/coreclr/src/vm/amd64/asmconstants.h
@@ -486,7 +486,7 @@ ASMCONSTANTS_C_ASSERT(OFFSET__TEB__ThreadLocalStoragePointer == offsetof(TEB, Th
 
 #define                     DELEGATE_FIELD_OFFSET__METHOD_AUX           0x20
 ASMCONSTANTS_RUNTIME_ASSERT(DELEGATE_FIELD_OFFSET__METHOD_AUX == Object::GetOffsetOfFirstField() +
-        MscorlibBinder::GetFieldOffset(FIELD__DELEGATE__METHOD_PTR_AUX));
+        CoreLibBinder::GetFieldOffset(FIELD__DELEGATE__METHOD_PTR_AUX));
 
 
 #define ASM_LARGE_OBJECT_SIZE 85000
diff --git a/src/coreclr/src/vm/amd64/asmhelpers.S b/src/coreclr/src/vm/amd64/asmhelpers.S
index 82d6984ab545df..7a70334d6383b3 100644
--- a/src/coreclr/src/vm/amd64/asmhelpers.S
+++ b/src/coreclr/src/vm/amd64/asmhelpers.S
@@ -52,17 +52,12 @@
 # we can align to 16 and be guaranteed to not exceed the frame size
 .equ STACK_FUDGE_FACTOR, 0x8
 
-# Space to keep xmm0 and xmm1
-.equ SIZEOF_FP_ARG_SPILL, 0x10*2
-
-.equ OFFSETOF_FP_ARG_SPILL, SIZEOF_PROFILE_PLATFORM_SPECIFIC_DATA + STACK_FUDGE_FACTOR
-
 # SIZEOF_STACK_FRAME is how many bytes we reserve in our ELT helpers below
 # There are three components, the first is space for profiler platform specific
 # data struct that we spill the general purpose registers to, then space to
 # spill xmm0 and xmm1, then finally 8 bytes of padding to ensure that the xmm
 # register reads/writes are aligned on 16 bytes.
-.equ SIZEOF_STACK_FRAME, SIZEOF_PROFILE_PLATFORM_SPECIFIC_DATA + SIZEOF_FP_ARG_SPILL + STACK_FUDGE_FACTOR
+.equ SIZEOF_STACK_FRAME, SIZEOF_PROFILE_PLATFORM_SPECIFIC_DATA + STACK_FUDGE_FACTOR
 
 .equ PROFILE_ENTER, 0x1
 .equ PROFILE_LEAVE, 0x2
@@ -131,15 +126,6 @@ NESTED_ENTRY ProfileEnterNaked, _TEXT, NoHandler
   mov                     r10, 0x1 # PROFILE_ENTER
   mov                     [rsp + 0xa8], r10d              #      -- struct flags field
 
-  # get aligned stack ptr (rsp + OFFSETOF_FP_ARG_SPILL) & (-16)
-  lea                     rax, [rsp + OFFSETOF_FP_ARG_SPILL]
-  and                     rax, -16
-
-  # we need to be able to restore the fp return register
-  # save fp return registers
-  movdqa                  [rax + 0x00], xmm0
-  movdqa                  [rax + 0x10], xmm1
-
   END_PROLOGUE
 
   # rdi already contains the clientInfo
@@ -148,10 +134,14 @@ NESTED_ENTRY ProfileEnterNaked, _TEXT, NoHandler
   call                    C_FUNC(ProfileEnter)
 
   # restore fp return registers
-  lea                     rax, [rsp + OFFSETOF_FP_ARG_SPILL]
-  and                     rax, -16
-  movdqa                  xmm0, [rax + 0x00]
-  movdqa                  xmm1, [rax + 0x10]
+  movsd                   xmm0, real8 ptr [rsp + 0x38]    #      -- struct flt0 field
+  movsd                   xmm1, real8 ptr [rsp + 0x40]    #      -- struct flt1 field
+  movsd                   xmm2, real8 ptr [rsp + 0x48]    #      -- struct flt2 field
+  movsd                   xmm3, real8 ptr [rsp + 0x50]    #      -- struct flt3 field
+  movsd                   xmm4, real8 ptr [rsp + 0x58]    #      -- struct flt4 field
+  movsd                   xmm5, real8 ptr [rsp + 0x60]    #      -- struct flt5 field
+  movsd                   xmm6, real8 ptr [rsp + 0x68]    #      -- struct flt6 field
+  movsd                   xmm7, real8 ptr [rsp + 0x70]    #      -- struct flt7 field
 
   # restore arg registers
   mov                     rdi, [rsp + 0x78]
@@ -216,15 +206,6 @@ NESTED_ENTRY ProfileLeaveNaked, _TEXT, NoHandler
   mov                     r10, 0x2  # PROFILE_LEAVE
   mov                     [rsp + 0xa8], r10d   # flags           -- struct flags field
 
-  # get aligned stack ptr (rsp + OFFSETOF_FP_ARG_SPILL) & (-16)
-  lea                     rax, [rsp + OFFSETOF_FP_ARG_SPILL]
-  and                     rax, -16
-
-  # we need to be able to restore the fp return register
-  # save fp return registers
-  movdqa                  [rax + 0x00], xmm0
-  movdqa                  [rax + 0x10], xmm1
-
   END_PROLOGUE
 
   # rdi already contains the clientInfo
@@ -232,10 +213,14 @@ NESTED_ENTRY ProfileLeaveNaked, _TEXT, NoHandler
   call                    C_FUNC(ProfileLeave)
 
   # restore fp return registers
-  lea                     rax, [rsp + OFFSETOF_FP_ARG_SPILL]
-  and                     rax, -16
-  movdqa                  xmm0, [rax + 0x00]
-  movdqa                  xmm1, [rax + 0x10]
+  movsd                   xmm0, real8 ptr [rsp + 0x38]    #      -- struct flt0 field
+  movsd                   xmm1, real8 ptr [rsp + 0x40]    #      -- struct flt1 field
+  movsd                   xmm2, real8 ptr [rsp + 0x48]    #      -- struct flt2 field
+  movsd                   xmm3, real8 ptr [rsp + 0x50]    #      -- struct flt3 field
+  movsd                   xmm4, real8 ptr [rsp + 0x58]    #      -- struct flt4 field
+  movsd                   xmm5, real8 ptr [rsp + 0x60]    #      -- struct flt5 field
+  movsd                   xmm6, real8 ptr [rsp + 0x68]    #      -- struct flt6 field
+  movsd                   xmm7, real8 ptr [rsp + 0x70]    #      -- struct flt7 field
 
   # restore int return register
   mov                     rax, [rsp + 0x28]
@@ -295,15 +280,6 @@ NESTED_ENTRY ProfileTailcallNaked, _TEXT, NoHandler
   mov                     r10, 0x2  # PROFILE_LEAVE
   mov                     [rsp + 0xa8], r10d   # flags           -- struct flags field
 
-  # get aligned stack ptr (rsp + OFFSETOF_FP_ARG_SPILL) & (-16)
-  lea                     rax, [rsp + OFFSETOF_FP_ARG_SPILL]
-  and                     rax, -16
-
-  # we need to be able to restore the fp return register
-  # save fp return registers
-  movdqa                  [rax + 0x00], xmm0
-  movdqa                  [rax + 0x10], xmm1
-
   END_PROLOGUE
 
   # rdi already contains the clientInfo
@@ -311,10 +287,14 @@ NESTED_ENTRY ProfileTailcallNaked, _TEXT, NoHandler
   call                    C_FUNC(ProfileTailcall)
 
   # restore fp return registers
-  lea                     rax, [rsp + OFFSETOF_FP_ARG_SPILL]
-  and                     rax, -16
-  movdqa                  xmm0, [rax + 0x00]
-  movdqa                  xmm1, [rax + 0x10]
+  movsd                   xmm0, real8 ptr [rsp + 0x38]    #      -- struct flt0 field
+  movsd                   xmm1, real8 ptr [rsp + 0x40]    #      -- struct flt1 field
+  movsd                   xmm2, real8 ptr [rsp + 0x48]    #      -- struct flt2 field
+  movsd                   xmm3, real8 ptr [rsp + 0x50]    #      -- struct flt3 field
+  movsd                   xmm4, real8 ptr [rsp + 0x58]    #      -- struct flt4 field
+  movsd                   xmm5, real8 ptr [rsp + 0x60]    #      -- struct flt5 field
+  movsd                   xmm6, real8 ptr [rsp + 0x68]    #      -- struct flt6 field
+  movsd                   xmm7, real8 ptr [rsp + 0x70]    #      -- struct flt7 field
 
   # restore int return register
   mov                     rax, [rsp + 0x28]
diff --git a/src/coreclr/src/vm/amd64/profiler.cpp b/src/coreclr/src/vm/amd64/profiler.cpp
index afe9685cda845b..025bfab6f56408 100644
--- a/src/coreclr/src/vm/amd64/profiler.cpp
+++ b/src/coreclr/src/vm/amd64/profiler.cpp
@@ -126,6 +126,7 @@ ProfileArgIterator::ProfileArgIterator(MetaSig * pSig, void * platformSpecificHa
     PROFILE_PLATFORM_SPECIFIC_DATA* pData = (PROFILE_PLATFORM_SPECIFIC_DATA*)m_handle;
 #ifdef UNIX_AMD64_ABI
     m_bufferPos = 0;
+    ZeroMemory(pData->buffer, PROFILE_PLATFORM_SPECIFIC_DATA_BUFFER_SIZE * sizeof(UINT64)); 
 #endif // UNIX_AMD64_ABI
 
     // unwind a frame and get the Rsp for the profiled method to make sure it matches
@@ -483,17 +484,46 @@ LPVOID ProfileArgIterator::GetReturnBufferAddr(void)
         // by our calling convention, but is required by our profiler spec.
         return (LPVOID)pData->rax;
     }
-
+    
     CorElementType t = m_argIterator.GetSig()->GetReturnType();
-    if (ELEMENT_TYPE_VOID != t)
+    if (ELEMENT_TYPE_VOID == t)
+    {
+        return NULL;
+    }
+
+#ifdef UNIX_AMD64_ABI
+    if (m_argIterator.GetSig()->GetReturnTypeSize() == 16)
     {
-        if (ELEMENT_TYPE_R4 == t || ELEMENT_TYPE_R8 == t)
-            pData->rax = pData->flt0;
+        _ASSERTE(m_bufferPos == 0 && "Nothing else should be using the scratch space during a return");
+
+        // The unix x64 ABI has a special case where a 16 byte struct will be passed in registers
+        // and if there are integer and float args it will be passed in rax/etc and xmm/etc, respectively
+        // which means the values are noncontiguous. Just like the argument passing above
+        // we copy it in to the buffer to fake it being contiguous.
+        UINT flags = m_argIterator.GetFPReturnSize();
 
-        return &(pData->rax);
+        // The lower two bits are used to indicate whether struct args are floating point or integer
+        if (flags & 1)
+        {
+            pData->buffer[0] = pData->flt0;
+            pData->buffer[1] = (flags & 2) ? pData->flt1 : pData->rax;
+        }
+        else
+        {
+            pData->buffer[0] = pData->rax;
+            pData->buffer[1] = (flags & 2) ? pData->flt0 : pData->rdx;
+        }
+
+        return pData->buffer;
     }
-    else
-        return NULL;
+#endif // UNIX_AMD64_ABI
+
+    if (ELEMENT_TYPE_R4 == t || ELEMENT_TYPE_R8 == t)
+    {
+        pData->rax = pData->flt0;
+    }
+    
+    return &(pData->rax);
 }
 
 #undef PROFILE_ENTER
diff --git a/src/coreclr/src/vm/amd64/unixstubs.cpp b/src/coreclr/src/vm/amd64/unixstubs.cpp
index 1de9b9a5b9d112..517eea98f6b6a2 100644
--- a/src/coreclr/src/vm/amd64/unixstubs.cpp
+++ b/src/coreclr/src/vm/amd64/unixstubs.cpp
@@ -10,35 +10,26 @@ extern "C"
         PORTABILITY_ASSERT("Implement for PAL");
     }
 
-    DWORD getcpuid(DWORD arg, unsigned char result[16])
+    void __cpuid(int cpuInfo[4], int function_id)
     {
-        DWORD eax;
-        __asm("  xor %%ecx, %%ecx\n" \
-              "  cpuid\n" \
-              "  mov %%eax, 0(%[result])\n" \
-              "  mov %%ebx, 4(%[result])\n" \
-              "  mov %%ecx, 8(%[result])\n" \
-              "  mov %%edx, 12(%[result])\n" \
-            : "=a"(eax) /*output in eax*/\
-            : "a"(arg), [result]"r"(result) /*inputs - arg in eax, result in any register*/\
-            : "rbx", "ecx", "edx", "memory" /* registers that are clobbered, *result is clobbered */
-          );
-        return eax;
+        // Based on the Clang implementation provided in cpuid.h:
+        // https://github.com/llvm/llvm-project/blob/master/clang/lib/Headers/cpuid.h
+
+        __asm("  cpuid\n" \
+            : "=a"(cpuInfo[0]), "=b"(cpuInfo[1]), "=c"(cpuInfo[2]), "=d"(cpuInfo[3]) \
+            : "0"(function_id)
+        );
     }
 
-    DWORD getextcpuid(DWORD arg1, DWORD arg2, unsigned char result[16])
+    void __cpuidex(int cpuInfo[4], int function_id, int subFunction_id)
     {
-        DWORD eax;
+        // Based on the Clang implementation provided in cpuid.h:
+        // https://github.com/llvm/llvm-project/blob/master/clang/lib/Headers/cpuid.h
+
         __asm("  cpuid\n" \
-              "  mov %%eax, 0(%[result])\n" \
-              "  mov %%ebx, 4(%[result])\n" \
-              "  mov %%ecx, 8(%[result])\n" \
-              "  mov %%edx, 12(%[result])\n" \
-            : "=a"(eax) /*output in eax*/\
-            : "c"(arg1), "a"(arg2), [result]"r"(result) /*inputs - arg1 in ecx, arg2 in eax, result in any register*/\
-            : "rbx", "edx", "memory" /* registers that are clobbered, *result is clobbered */
-          );
-        return eax;
+            : "=a"(cpuInfo[0]), "=b"(cpuInfo[1]), "=c"(cpuInfo[2]), "=d"(cpuInfo[3]) \
+            : "0"(function_id), "2"(subFunction_id)
+        );
     }
 
     DWORD xmmYmmStateSupport()
diff --git a/src/coreclr/src/vm/appdomain.cpp b/src/coreclr/src/vm/appdomain.cpp
index 8f5b4153d8e5a0..1ba7c47cd50a15 100644
--- a/src/coreclr/src/vm/appdomain.cpp
+++ b/src/coreclr/src/vm/appdomain.cpp
@@ -928,7 +928,7 @@ OBJECTREF AppDomain::GetMissingObject()
     if (!m_hndMissing)
     {
         // Get the field
-        FieldDesc *pValueFD = MscorlibBinder::GetField(FIELD__MISSING__VALUE);
+        FieldDesc *pValueFD = CoreLibBinder::GetField(FIELD__MISSING__VALUE);
 
         pValueFD->CheckRunClassInitThrowing();
 
@@ -1268,7 +1268,7 @@ void SystemDomain::Init()
 
     DWORD size = 0;
 
-    // Get the install directory so we can find mscorlib
+    // Get the install directory so we can find CoreLib
     hr = GetInternalSystemDirectory(NULL, &size);
     if (hr != HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER))
         ThrowHR(hr);
@@ -1307,7 +1307,7 @@ void SystemDomain::Init()
         }
 #endif
 
-        // Finish loading mscorlib now.
+        // Finish loading CoreLib now.
         m_pSystemAssembly->GetDomainAssembly()->EnsureActive();
     }
 
@@ -1424,36 +1424,36 @@ void SystemDomain::LoadBaseSystemClasses()
     // the globals in this function before finishing the load.
     m_pSystemAssembly = DefaultDomain()->LoadDomainAssembly(NULL, m_pSystemFile, FILE_LOAD_POST_LOADLIBRARY)->GetCurrentAssembly();
 
-    // Set up binder for mscorlib
-    MscorlibBinder::AttachModule(m_pSystemAssembly->GetManifestModule());
+    // Set up binder for CoreLib
+    CoreLibBinder::AttachModule(m_pSystemAssembly->GetManifestModule());
 
     // Load Object
-    g_pObjectClass = MscorlibBinder::GetClass(CLASS__OBJECT);
+    g_pObjectClass = CoreLibBinder::GetClass(CLASS__OBJECT);
 
     // Now that ObjectClass is loaded, we can set up
     // the system for finalizers.  There is no point in deferring this, since we need
     // to know this before we allocate our first object.
-    g_pObjectFinalizerMD = MscorlibBinder::GetMethod(METHOD__OBJECT__FINALIZE);
+    g_pObjectFinalizerMD = CoreLibBinder::GetMethod(METHOD__OBJECT__FINALIZE);
 
 
-    g_pCanonMethodTableClass = MscorlibBinder::GetClass(CLASS____CANON);
+    g_pCanonMethodTableClass = CoreLibBinder::GetClass(CLASS____CANON);
 
     // NOTE: !!!IMPORTANT!!! ValueType and Enum MUST be loaded one immediately after
     //                       the other, because we have coded MethodTable::IsChildValueType
     //                       in such a way that it depends on this behaviour.
     // Load the ValueType class
-    g_pValueTypeClass = MscorlibBinder::GetClass(CLASS__VALUE_TYPE);
+    g_pValueTypeClass = CoreLibBinder::GetClass(CLASS__VALUE_TYPE);
 
     // Load the enum class
-    g_pEnumClass = MscorlibBinder::GetClass(CLASS__ENUM);
+    g_pEnumClass = CoreLibBinder::GetClass(CLASS__ENUM);
     _ASSERTE(!g_pEnumClass->IsValueType());
 
     // Load System.RuntimeType
-    g_pRuntimeTypeClass = MscorlibBinder::GetClass(CLASS__CLASS);
+    g_pRuntimeTypeClass = CoreLibBinder::GetClass(CLASS__CLASS);
     _ASSERTE(g_pRuntimeTypeClass->IsFullyLoaded());
 
     // Load Array class
-    g_pArrayClass = MscorlibBinder::GetClass(CLASS__ARRAY);
+    g_pArrayClass = CoreLibBinder::GetClass(CLASS__ARRAY);
 
     // Calling a method on IList<T> for an array requires redirection to a method on
     // the SZArrayHelper class. Retrieving such methods means calling
@@ -1461,31 +1461,31 @@ void SystemDomain::LoadBaseSystemClasses()
     // the corresponding method on SZArrayHelper. This basically results in a class
     // load due to a method call, which the debugger cannot handle, so we pre-load
     // the SZArrayHelper class here.
-    g_pSZArrayHelperClass = MscorlibBinder::GetClass(CLASS__SZARRAYHELPER);
+    g_pSZArrayHelperClass = CoreLibBinder::GetClass(CLASS__SZARRAYHELPER);
 
     // Load ByReference class
     //
     // NOTE: ByReference<T> must be the first by-ref-like system type to be loaded,
     //       because MethodTable::ClassifyEightBytesWithManagedLayout depends on it.
-    g_pByReferenceClass = MscorlibBinder::GetClass(CLASS__BYREFERENCE);
+    g_pByReferenceClass = CoreLibBinder::GetClass(CLASS__BYREFERENCE);
 
     // Load Nullable class
-    g_pNullableClass = MscorlibBinder::GetClass(CLASS__NULLABLE);
+    g_pNullableClass = CoreLibBinder::GetClass(CLASS__NULLABLE);
 
     // Load the Object array class.
     g_pPredefinedArrayTypes[ELEMENT_TYPE_OBJECT] = ClassLoader::LoadArrayTypeThrowing(TypeHandle(g_pObjectClass));
 
-    // We have delayed allocation of mscorlib's static handles until we load the object class
-    MscorlibBinder::GetModule()->AllocateRegularStaticHandles(DefaultDomain());
+    // We have delayed allocation of CoreLib's static handles until we load the object class
+    CoreLibBinder::GetModule()->AllocateRegularStaticHandles(DefaultDomain());
 
     // Make sure all primitive types are loaded
     for (int et = ELEMENT_TYPE_VOID; et <= ELEMENT_TYPE_R8; et++)
-        MscorlibBinder::LoadPrimitiveType((CorElementType)et);
+        CoreLibBinder::LoadPrimitiveType((CorElementType)et);
 
-    MscorlibBinder::LoadPrimitiveType(ELEMENT_TYPE_I);
-    MscorlibBinder::LoadPrimitiveType(ELEMENT_TYPE_U);
+    CoreLibBinder::LoadPrimitiveType(ELEMENT_TYPE_I);
+    CoreLibBinder::LoadPrimitiveType(ELEMENT_TYPE_U);
 
-    g_TypedReferenceMT = MscorlibBinder::GetClass(CLASS__TYPED_REFERENCE);
+    g_TypedReferenceMT = CoreLibBinder::GetClass(CLASS__TYPED_REFERENCE);
 
     // unfortunately, the following cannot be delay loaded since the jit
     // uses it to compute method attributes within a function that cannot
@@ -1493,8 +1493,8 @@ void SystemDomain::LoadBaseSystemClasses()
     // where a complus exception can be thrown. It is unfortunate, because
     // we know that the delegate class and multidelegate class are always
     // guaranteed to be found.
-    g_pDelegateClass = MscorlibBinder::GetClass(CLASS__DELEGATE);
-    g_pMulticastDelegateClass = MscorlibBinder::GetClass(CLASS__MULTICAST_DELEGATE);
+    g_pDelegateClass = CoreLibBinder::GetClass(CLASS__DELEGATE);
+    g_pMulticastDelegateClass = CoreLibBinder::GetClass(CLASS__MULTICAST_DELEGATE);
 
 #ifndef CROSSGEN_COMPILE
     CrossLoaderAllocatorHashSetup::EnsureTypesLoaded();
@@ -1508,45 +1508,45 @@ void SystemDomain::LoadBaseSystemClasses()
 #endif // CROSSGEN_COMPILE
 
     // used by IsImplicitInterfaceOfSZArray
-    MscorlibBinder::GetClass(CLASS__IENUMERABLEGENERIC);
-    MscorlibBinder::GetClass(CLASS__ICOLLECTIONGENERIC);
-    MscorlibBinder::GetClass(CLASS__ILISTGENERIC);
-    MscorlibBinder::GetClass(CLASS__IREADONLYCOLLECTIONGENERIC);
-    MscorlibBinder::GetClass(CLASS__IREADONLYLISTGENERIC);
+    CoreLibBinder::GetClass(CLASS__IENUMERABLEGENERIC);
+    CoreLibBinder::GetClass(CLASS__ICOLLECTIONGENERIC);
+    CoreLibBinder::GetClass(CLASS__ILISTGENERIC);
+    CoreLibBinder::GetClass(CLASS__IREADONLYCOLLECTIONGENERIC);
+    CoreLibBinder::GetClass(CLASS__IREADONLYLISTGENERIC);
 
     // Load String
-    g_pStringClass = MscorlibBinder::LoadPrimitiveType(ELEMENT_TYPE_STRING);
+    g_pStringClass = CoreLibBinder::LoadPrimitiveType(ELEMENT_TYPE_STRING);
 
 #ifdef FEATURE_UTF8STRING
     // Load Utf8String
-    g_pUtf8StringClass = MscorlibBinder::GetClass(CLASS__UTF8_STRING);
+    g_pUtf8StringClass = CoreLibBinder::GetClass(CLASS__UTF8_STRING);
 #endif // FEATURE_UTF8STRING
 
 #ifndef CROSSGEN_COMPILE
     ECall::PopulateManagedStringConstructors();
 #endif // CROSSGEN_COMPILE
 
-    g_pExceptionClass = MscorlibBinder::GetClass(CLASS__EXCEPTION);
-    g_pOutOfMemoryExceptionClass = MscorlibBinder::GetException(kOutOfMemoryException);
-    g_pStackOverflowExceptionClass = MscorlibBinder::GetException(kStackOverflowException);
-    g_pExecutionEngineExceptionClass = MscorlibBinder::GetException(kExecutionEngineException);
-    g_pThreadAbortExceptionClass = MscorlibBinder::GetException(kThreadAbortException);
+    g_pExceptionClass = CoreLibBinder::GetClass(CLASS__EXCEPTION);
+    g_pOutOfMemoryExceptionClass = CoreLibBinder::GetException(kOutOfMemoryException);
+    g_pStackOverflowExceptionClass = CoreLibBinder::GetException(kStackOverflowException);
+    g_pExecutionEngineExceptionClass = CoreLibBinder::GetException(kExecutionEngineException);
+    g_pThreadAbortExceptionClass = CoreLibBinder::GetException(kThreadAbortException);
 
-    g_pThreadClass = MscorlibBinder::GetClass(CLASS__THREAD);
+    g_pThreadClass = CoreLibBinder::GetClass(CLASS__THREAD);
 
 #ifdef FEATURE_COMINTEROP
-    g_pBaseCOMObject = MscorlibBinder::GetClass(CLASS__COM_OBJECT);
+    g_pBaseCOMObject = CoreLibBinder::GetClass(CLASS__COM_OBJECT);
 #endif
 
-    g_pIDynamicInterfaceCastableInterface = MscorlibBinder::GetClass(CLASS__IDYNAMICINTERFACECASTABLE);
+    g_pIDynamicInterfaceCastableInterface = CoreLibBinder::GetClass(CLASS__IDYNAMICINTERFACECASTABLE);
 
 #ifdef FEATURE_ICASTABLE
-    g_pICastableInterface = MscorlibBinder::GetClass(CLASS__ICASTABLE);
+    g_pICastableInterface = CoreLibBinder::GetClass(CLASS__ICASTABLE);
 #endif // FEATURE_ICASTABLE
 
     // Make sure that FCall mapping for Monitor.Enter is initialized. We need it in case Monitor.Enter is used only as JIT helper.
     // For more details, see comment in code:JITutil_MonEnterWorker around "__me = GetEEFuncEntryPointMacro(JIT_MonEnter)".
-    ECall::GetFCallImpl(MscorlibBinder::GetMethod(METHOD__MONITOR__ENTER));
+    ECall::GetFCallImpl(CoreLibBinder::GetMethod(METHOD__MONITOR__ENTER));
 
 #ifdef PROFILING_SUPPORTED
     // Note that g_profControlBlock.fBaseSystemClassesLoaded must be set to TRUE only after
@@ -1559,7 +1559,7 @@ void SystemDomain::LoadBaseSystemClasses()
 #if defined(_DEBUG) && !defined(CROSSGEN_COMPILE)
     if (!NingenEnabled())
     {
-        g_Mscorlib.Check();
+        g_CoreLib.Check();
     }
 #endif
 
@@ -1567,8 +1567,8 @@ void SystemDomain::LoadBaseSystemClasses()
     if (GCStress<cfg_instr_ngen>::IsEnabled())
     {
         // Setting up gc coverage requires the base system classes
-        //  to be initialized. So we have deferred it until now for mscorlib.
-        Module *pModule = MscorlibBinder::GetModule();
+        //  to be initialized. So we have deferred it until now for CoreLib.
+        Module *pModule = CoreLibBinder::GetModule();
         _ASSERTE(pModule->IsSystem());
         if(pModule->HasNativeImage())
         {
@@ -1666,7 +1666,7 @@ bool SystemDomain::IsReflectionInvocationMethod(MethodDesc* pMeth)
 
     MethodTable* pCaller = pMeth->GetMethodTable();
 
-    // All Reflection Invocation methods are defined in mscorlib.dll
+    // All Reflection Invocation methods are defined in CoreLib
     if (!pCaller->GetModule()->IsSystem())
         return false;
 
@@ -1707,7 +1707,7 @@ bool SystemDomain::IsReflectionInvocationMethod(MethodDesc* pMeth)
         // Make sure all types are loaded so that we can use faster GetExistingClass()
         for (unsigned i = 0; i < NumItems(reflectionInvocationTypes); i++)
         {
-            MscorlibBinder::GetClass(reflectionInvocationTypes[i]);
+            CoreLibBinder::GetClass(reflectionInvocationTypes[i]);
         }
 
         VolatileStore(&fInited, true);
@@ -1717,7 +1717,7 @@ bool SystemDomain::IsReflectionInvocationMethod(MethodDesc* pMeth)
     {
         for (unsigned i = 0; i < NumItems(reflectionInvocationTypes); i++)
         {
-            if (MscorlibBinder::GetExistingClass(reflectionInvocationTypes[i]) == pCaller)
+            if (CoreLibBinder::GetExistingClass(reflectionInvocationTypes[i]) == pCaller)
                 return true;
         }
     }
@@ -1889,7 +1889,7 @@ StackWalkAction SystemDomain::CallersMethodCallbackWithStackMark(CrawlFrame* pCf
 
     // Skipping reflection frames. We don't need to be quite as exhaustive here
     // as the security or reflection stack walking code since we know this logic
-    // is only invoked for selected methods in mscorlib itself. So we're
+    // is only invoked for selected methods in CoreLib itself. So we're
     // reasonably sure we won't have any sensitive methods late bound invoked on
     // constructors, properties or events. This leaves being invoked via
     // MethodInfo, Type or Delegate (and depending on which invoke overload is
@@ -3162,8 +3162,8 @@ DomainFile *AppDomain::LoadDomainFile(FileLoadLock *pLock, FileLoadLevel targetL
     // Make sure we release the lock on exit
     FileLoadLockRefHolder lockRef(pLock);
 
-    // We need to perform the early steps of loading mscorlib without a domain transition.  This is
-    // important for bootstrapping purposes - we need to get mscorlib at least partially loaded
+    // We need to perform the early steps of loading CoreLib without a domain transition.  This is
+    // important for bootstrapping purposes - we need to get CoreLib at least partially loaded
     // into a domain before we can run serialization code to do the transition.
     //
     // Note that we cannot do this in general for all assemblies, because some of the security computations
@@ -3499,7 +3499,7 @@ void AppDomain::SetupSharedStatics()
     // Because we are allocating/referencing objects, need to be in cooperative mode
     GCX_COOP();
 
-    DomainLocalModule *pLocalModule = MscorlibBinder::GetModule()->GetDomainLocalModule();
+    DomainLocalModule *pLocalModule = CoreLibBinder::GetModule()->GetDomainLocalModule();
 
     // This is a convenient place to initialize String.Empty.
     // It is treated as intrinsic by the JIT as so the static constructor would never run.
@@ -3508,7 +3508,7 @@ void AppDomain::SetupSharedStatics()
     // String should not have any static constructors.
     _ASSERTE(g_pStringClass->IsClassPreInited());
 
-    FieldDesc * pEmptyStringFD = MscorlibBinder::GetField(FIELD__STRING__EMPTY);
+    FieldDesc * pEmptyStringFD = CoreLibBinder::GetField(FIELD__STRING__EMPTY);
     OBJECTREF* pEmptyStringHandle = (OBJECTREF*)
         ((TADDR)pLocalModule->GetPrecomputedGCStaticsBasePointer()+pEmptyStringFD->GetOffset());
     SetObjectReference( pEmptyStringHandle, StringObject::GetEmptyString());
@@ -3876,9 +3876,9 @@ BOOL AppDomain::IsCached(AssemblySpec *pSpec)
 {
     WRAPPER_NO_CONTRACT;
 
-    // Check to see if this fits our rather loose idea of a reference to mscorlib.
+    // Check to see if this fits our rather loose idea of a reference to CoreLib.
     // If so, don't use fusion to bind it - do it ourselves.
-    if (pSpec->IsMscorlib())
+    if (pSpec->IsCoreLib())
         return TRUE;
 
     return m_AssemblyCache.Contains(pSpec);
@@ -3906,9 +3906,9 @@ PEAssembly* AppDomain::FindCachedFile(AssemblySpec* pSpec, BOOL fThrow /*=TRUE*/
     }
     CONTRACTL_END;
 
-    // Check to see if this fits our rather loose idea of a reference to mscorlib.
+    // Check to see if this fits our rather loose idea of a reference to CoreLib.
     // If so, don't use fusion to bind it - do it ourselves.
-    if (fThrow && pSpec->IsMscorlib())
+    if (fThrow && pSpec->IsCoreLib())
     {
         CONSISTENCY_CHECK(SystemDomain::System()->SystemAssembly() != NULL);
         PEAssembly *pFile = SystemDomain::System()->SystemFile();
@@ -4002,15 +4002,15 @@ PEAssembly * AppDomain::BindAssemblySpec(
 
                     if (bindResult.Found())
                     {
-                        if (SystemDomain::SystemFile() && bindResult.IsMscorlib())
+                        if (SystemDomain::SystemFile() && bindResult.IsCoreLib())
                         {
-                            // Avoid rebinding to another copy of mscorlib
+                            // Avoid rebinding to another copy of CoreLib
                             result = SystemDomain::SystemFile();
                             result.SuppressRelease(); // Didn't get a refcount
                         }
                         else
                         {
-                            // IsSystem on the PEFile should be false, even for mscorlib satellites
+                            // IsSystem on the PEFile should be false, even for CoreLib satellites
                             result = PEAssembly::Open(&bindResult,
                                                       FALSE);
                         }
@@ -4034,7 +4034,7 @@ PEAssembly * AppDomain::BindAssemblySpec(
                         // return an assembly that does not match, and this can cause recursive resource lookups during error
                         // reporting. The CoreLib satellite assembly is loaded from relative locations based on the culture, see
                         // AssemblySpec::Bind().
-                        if (!pSpec->IsMscorlibSatellite())
+                        if (!pSpec->IsCoreLibSatellite())
                         {
                             // Trigger the resolve event also for non-throw situation.
                             AssemblySpec NewSpec(this);
@@ -4258,7 +4258,7 @@ void AppDomain::RaiseLoadingAssemblyEvent(DomainAssembly *pAssembly)
 
     EX_TRY
     {
-        if (MscorlibBinder::GetField(FIELD__ASSEMBLYLOADCONTEXT__ASSEMBLY_LOAD)->GetStaticOBJECTREF() != NULL)
+        if (CoreLibBinder::GetField(FIELD__ASSEMBLYLOADCONTEXT__ASSEMBLY_LOAD)->GetStaticOBJECTREF() != NULL)
         {
             struct _gc {
                 OBJECTREF    orThis;
@@ -4342,7 +4342,7 @@ AppDomain::RaiseUnhandledExceptionEvent(OBJECTREF *pThrowable, BOOL isTerminatin
 
     _ASSERTE(this == GetThread()->GetDomain());
 
-    OBJECTREF orDelegate = MscorlibBinder::GetField(FIELD__APPCONTEXT__UNHANDLED_EXCEPTION)->GetStaticOBJECTREF();
+    OBJECTREF orDelegate = CoreLibBinder::GetField(FIELD__APPCONTEXT__UNHANDLED_EXCEPTION)->GetStaticOBJECTREF();
     if (orDelegate == NULL)
         return FALSE;
 
@@ -5346,7 +5346,7 @@ HRESULT RuntimeInvokeHostAssemblyResolver(INT_PTR pManagedAssemblyLoadContextToB
         BinderTracing::ResolutionAttemptedOperation tracer{pAssemblyName, 0 /*binderID*/, pManagedAssemblyLoadContextToBindWithin, hr};
 
         // Allocate an AssemblyName managed object
-        _gcRefs.oRefAssemblyName = (ASSEMBLYNAMEREF) AllocateObject(MscorlibBinder::GetClass(CLASS__ASSEMBLY_NAME));
+        _gcRefs.oRefAssemblyName = (ASSEMBLYNAMEREF) AllocateObject(CoreLibBinder::GetClass(CLASS__ASSEMBLY_NAME));
 
         // Initialize the AssemblyName object from the AssemblySpec
         spec.AssemblyNameInit(&_gcRefs.oRefAssemblyName, NULL);
diff --git a/src/coreclr/src/vm/appdomain.hpp b/src/coreclr/src/vm/appdomain.hpp
index 8a73d95c8fcfc7..a84bd6a6d31b5f 100644
--- a/src/coreclr/src/vm/appdomain.hpp
+++ b/src/coreclr/src/vm/appdomain.hpp
@@ -2737,7 +2737,6 @@ class SystemDomain : public BaseDomain
 #endif // DACCESS_COMPILE
 
     //****************************************************************************************
-    // Routines to deal with the base library (currently mscorlib.dll)
     LPCWSTR BaseLibrary()
     {
         WRAPPER_NO_CONTRACT;
@@ -2750,11 +2749,11 @@ class SystemDomain : public BaseDomain
     {
         WRAPPER_NO_CONTRACT;
 
-        // See if it is the installation path to mscorlib
+        // See if it is the installation path to CoreLib
         if (path.EqualsCaseInsensitive(m_BaseLibrary))
             return TRUE;
 
-        // Or, it might be the GAC location of mscorlib
+        // Or, it might be the GAC location of CoreLib
         if (System()->SystemAssembly() != NULL
             && path.EqualsCaseInsensitive(System()->SystemAssembly()->GetManifestFile()->GetPath()))
             return TRUE;
@@ -2766,7 +2765,7 @@ class SystemDomain : public BaseDomain
     {
         WRAPPER_NO_CONTRACT;
 
-        // See if it is the installation path to mscorlib.resources
+        // See if it is the installation path to corelib.resources
         SString s(SString::Ascii,g_psBaseLibrarySatelliteAssemblyName);
         if (path.EqualsCaseInsensitive(s))
             return TRUE;
@@ -2842,7 +2841,7 @@ class SystemDomain : public BaseDomain
 #ifdef FEATURE_PREJIT
 protected:
 
-    // These flags let the correct native image of mscorlib to be loaded.
+    // These flags let the correct native image of CoreLib to be loaded.
     // This is important for hardbinding to it
 
     SVAL_DECL(BOOL, s_fForceDebug);
diff --git a/src/coreclr/src/vm/appdomainnative.cpp b/src/coreclr/src/vm/appdomainnative.cpp
index 9df486ba46ff87..2a2a8c561aca3d 100644
--- a/src/coreclr/src/vm/appdomainnative.cpp
+++ b/src/coreclr/src/vm/appdomainnative.cpp
@@ -60,7 +60,7 @@ FCIMPL0(Object*, AppDomainNative::GetLoadedAssemblies)
 
     HELPER_METHOD_FRAME_BEGIN_RET_PROTECT(gc);
 
-    MethodTable * pAssemblyClass = MscorlibBinder::GetClass(CLASS__ASSEMBLY);
+    MethodTable * pAssemblyClass = CoreLibBinder::GetClass(CLASS__ASSEMBLY);
 
     AppDomain * pApp = GetAppDomain();
 
diff --git a/src/coreclr/src/vm/arm/asmhelpers.S b/src/coreclr/src/vm/arm/asmhelpers.S
index dbc7baa9a175c7..dcdfda4df350d6 100644
--- a/src/coreclr/src/vm/arm/asmhelpers.S
+++ b/src/coreclr/src/vm/arm/asmhelpers.S
@@ -366,134 +366,87 @@ LEAF_ENTRY JIT_ProfilerEnterLeaveTailcallStub, _TEXT
     bx lr
 LEAF_END JIT_ProfilerEnterLeaveTailcallStub, _TEXT
 
-//
-// EXTERN_C void ProfileEnterNaked(FunctionIDOrClientID functionIDOrClientID);
-//
-NESTED_ENTRY ProfileEnterNaked, _TEXT, NoHandler
-    PROLOG_PUSH "{r4, r5, r7, r11, lr}"
-    PROLOG_STACK_SAVE_OFFSET r7, #8
-
-    // fields of PROFILE_PLATFORM_SPECIFIC_DATA, in reverse order
-
-    // UINT32      r0;         // Keep r0 & r1 contiguous to make returning 64-bit results easier
-    // UINT32      r1;
-    // void       *r11;
-    // void       *Pc;
-    // union                   // Float arg registers as 32-bit (s0-s15) and 64-bit (d0-d7)
-    // {
-    //     UINT32  s[16];
-    //     UINT64  d[8];
-    // };
-    // FunctionID  functionId;
-    // void       *probeSp;    // stack pointer of managed function
-    // void       *profiledSp; // location of arguments on stack
-    // LPVOID      hiddenArg;
-    // UINT32      flags;
-    movw        r4, #1
-    push        { /* flags      */ r4 }
-    movw        r4, #0
-    push        { /* hiddenArg  */ r4 }
-    add         r5, r11, #8
-    push        { /* profiledSp */ r5 }
-    add         r5, sp, #32
-    push        { /* probeSp    */ r5 }
-    push        { /* functionId */ r0 }
+#define PROFILE_ENTER    1
+#define PROFILE_LEAVE    2
+#define PROFILE_TAILCALL 4
+// size of profiler data structure plus alignment padding
+#define SIZEOF__PROFILE_PLATFORM_SPECIFIC_DATA 104+4
+
+// typedef struct _PROFILE_PLATFORM_SPECIFIC_DATA
+// {
+//     UINT32      r0;         // Keep r0 & r1 contiguous to make returning 64-bit results easier
+//     UINT32      r1;
+//     void       *R11;
+//     void       *Pc;
+//     union                   // Float arg registers as 32-bit (s0-s15) and 64-bit (d0-d7)
+//     {
+//         UINT32  s[16];
+//         UINT64  d[8];
+//     };
+//     FunctionID  functionId;
+//     void       *probeSp;    // stack pointer of managed function
+//     void       *profiledSp; // location of arguments on stack
+//     LPVOID      hiddenArg;
+//     UINT32      flags;
+// } PROFILE_PLATFORM_SPECIFIC_DATA, *PPROFILE_PLATFORM_SPECIFIC_DATA;
+
+.macro GenerateProfileHelper helper, flags
+NESTED_ENTRY \helper\()Naked, _TEXT, NoHandler
+    PROLOG_PUSH "{r0,r3,r9,r12}"
+
+    // for the 5 arguments that do not need popped plus 4 bytes of alignment 
+    alloc_stack 6*4
+
+    // push fp regs
     vpush.64    { d0 - d7 }
-    push        { lr }
-    push        { r11 }
-    push        { /* return value, r4 is NULL */ r4 }
-    push        { /* return value, r4 is NULL */ r4 }
-    mov         r1, sp
-    bl          C_FUNC(ProfileEnter)
-    EPILOG_STACK_RESTORE_OFFSET r7, #8
-    EPILOG_POP "{r4, r5, r7, r11, pc}"
-NESTED_END ProfileEnterNaked, _TEXT
 
-//
-// EXTERN_C void ProfileLeaveNaked(FunctionIDOrClientID functionIDOrClientID);
-//
-NESTED_ENTRY ProfileLeaveNaked, _TEXT, NoHandler
-    PROLOG_PUSH "{r1, r2, r4, r5, r7, r11, lr}"
-    PROLOG_STACK_SAVE_OFFSET r7, #16
-
-    // fields of PROFILE_PLATFORM_SPECIFIC_DATA, in reverse order
-
-    // UINT32      r0;         // Keep r0 & r1 contiguous to make returning 64-bit results easier
-    // UINT32      r1;
-    // void       *r11;
-    // void       *Pc;
-    // union                   // Float arg registers as 32-bit (s0-s15) and 64-bit (d0-d7)
-    // {
-    //     UINT32  s[16];
-    //     UINT64  d[8];
-    // };
-    // FunctionID  functionId;
-    // void       *probeSp;    // stack pointer of managed function
-    // void       *profiledSp; // location of arguments on stack
-    // LPVOID      hiddenArg;
-    // UINT32      flags;
-    movw        r4, #2
-    push        { /* flags      */ r4 }
-    movw        r4, #0
-    push        { /* hiddenArg  */ r4 }
-    add         r5, r11, #8
-    push        { /* profiledSp */ r5 }
-    add         r5, sp, #40
-    push        { /* probeSp    */ r5 }
-    push        { /* functionId */ r0 }
-    vpush.64    { d0 - d7 }
-    push        { lr }
-    push        { r11 }
-    push        { r1 }
-    push        { r0 }
-    mov         r1, sp
-    bl          C_FUNC(ProfileLeave)
-    EPILOG_STACK_RESTORE_OFFSET r7, #16
-    EPILOG_POP "{r1, r2, r4, r5, r7, r11, pc}"
-NESTED_END ProfileLeaveNaked, _TEXT
+    // next three fields pc, r11, r1
+    push        { r1, r11, lr}
 
-//
-// EXTERN_C void ProfileTailcallNaked(FunctionIDOrClientID functionIDOrClientID);
-//
-NESTED_ENTRY ProfileTailcallNaked, _TEXT, NoHandler
-    PROLOG_PUSH "{r1, r2, r4, r5, r7, r11, lr}"
-    PROLOG_STACK_SAVE_OFFSET r7, #16
-
-    // fields of PROFILE_PLATFORM_SPECIFIC_DATA, in reverse order
-
-    // UINT32      r0;         // Keep r0 & r1 contiguous to make returning 64-bit results easier
-    // UINT32      r1;
-    // void       *r11;
-    // void       *Pc;
-    // union                   // Float arg registers as 32-bit (s0-s15) and 64-bit (d0-d7)
-    // {
-    //     UINT32  s[16];
-    //     UINT64  d[8];
-    // };
-    // FunctionID  functionId;
-    // void       *probeSp;    // stack pointer of managed function
-    // void       *profiledSp; // location of arguments on stack
-    // LPVOID      hiddenArg;
-    // UINT32      flags;
-    movw        r4, #2
-    push        { /* flags      */ r4 }
-    movw        r4, #0
-    push        { /* hiddenArg  */ r4 }
-    add         r5, r11, #8
-    push        { /* profiledSp */ r5 }
-    add         r5, sp, #40
-    push        { /* probeSp    */ r5 }
-    push        { /* functionId */ r0 }
-    vpush.64    { d0 - d7 }
-    push        { lr }
-    push        { r11 }
-    push        { r1 }
-    push        { r0 }
+    // return value is in r2 instead of r0 because functionID is passed in r0
+    push        { r2 }
+
+    CHECK_STACK_ALIGNMENT
+
+    // set the other args, starting with functionID
+    str         r0, [sp, #80]
+
+    // probeSp is the original sp when this stub was called
+    add         r2, sp, SIZEOF__PROFILE_PLATFORM_SPECIFIC_DATA+20
+    str         r2, [sp, #84] 
+
+    // get the address of the arguments from the frame pointer, store in profiledSp
+    add         r2, r11, #8
+    str         r2, [sp, #88]
+
+    // clear hiddenArg
+    movw        r2, #0
+    str         r2, [sp, #92]
+    
+    // set the flag to indicate what hook this is
+    movw        r2, \flags
+    str         r2, [sp, #96]
+
+    // sp is the address of PROFILE_PLATFORM_SPECIFIC_DATA, then call to C++
     mov         r1, sp
-    bl          C_FUNC(ProfileTailcall)
-    EPILOG_STACK_RESTORE_OFFSET r7, #16
-    EPILOG_POP "{r1, r2, r4, r5, r7, r11, pc}"
-NESTED_END ProfileTailcallNaked, _TEXT
+    bl          C_FUNC(\helper)
+
+    // restore all our regs
+    pop         { r2 }
+    pop         { r1, r11, lr}
+    vpop.64     { d0 - d7 }
+
+    free_stack 6*4
+
+    EPILOG_POP "{r0,r3,r9,r12}"
+
+    bx          lr
+NESTED_END \helper\()Naked, _TEXT
+.endm
+
+GenerateProfileHelper ProfileEnter, PROFILE_ENTER
+GenerateProfileHelper ProfileLeave, PROFILE_LEAVE
+GenerateProfileHelper ProfileTailcall, PROFILE_TAILCALL
 
 #endif
 
diff --git a/src/coreclr/src/vm/arm/profiler.cpp b/src/coreclr/src/vm/arm/profiler.cpp
index 8bcd075fe986c4..670dedb8ca8ca1 100644
--- a/src/coreclr/src/vm/arm/profiler.cpp
+++ b/src/coreclr/src/vm/arm/profiler.cpp
@@ -144,7 +144,7 @@ Stack for the above call will look as follows (stack growing downwards):
         Thread::VirtualUnwindCallFrame(&ctx);
 
         // add the prespill register(r0-r3) size to get the stack pointer of previous function
-        _ASSERTE(pData->profiledSp == (void*)(ctx.Sp - 4*4));
+        _ASSERTE(pData->profiledSp == (void*)(ctx.Sp - 4*4) || pData->profiledSp == (void*)(ctx.Sp - 6*4));
     }
 #endif // _DEBUG
 
diff --git a/src/coreclr/src/vm/arm64/asmhelpers.S b/src/coreclr/src/vm/arm64/asmhelpers.S
index 9ff8203f22f4bf..a8b0a7c07873a4 100644
--- a/src/coreclr/src/vm/arm64/asmhelpers.S
+++ b/src/coreclr/src/vm/arm64/asmhelpers.S
@@ -1200,7 +1200,7 @@ LEAF_END JIT_ProfilerEnterLeaveTailcallStub, _TEXT
 #define PROFILE_ENTER    1
 #define PROFILE_LEAVE    2
 #define PROFILE_TAILCALL 4
-#define SIZEOF__PROFILE_PLATFORM_SPECIFIC_DATA 256
+#define SIZEOF__PROFILE_PLATFORM_SPECIFIC_DATA 272
 
 // ------------------------------------------------------------------
 .macro GenerateProfileHelper helper, flags
diff --git a/src/coreclr/src/vm/arm64/asmhelpers.asm b/src/coreclr/src/vm/arm64/asmhelpers.asm
index 1250bd32652004..2f9227b1d80df6 100644
--- a/src/coreclr/src/vm/arm64/asmhelpers.asm
+++ b/src/coreclr/src/vm/arm64/asmhelpers.asm
@@ -1427,7 +1427,7 @@ CallHelper2
  #define PROFILE_ENTER    1
  #define PROFILE_LEAVE    2
  #define PROFILE_TAILCALL 4
- #define SIZEOF__PROFILE_PLATFORM_SPECIFIC_DATA 256
+ #define SIZEOF__PROFILE_PLATFORM_SPECIFIC_DATA 272
 
 ; ------------------------------------------------------------------
     MACRO
diff --git a/src/coreclr/src/vm/arm64/profiler.cpp b/src/coreclr/src/vm/arm64/profiler.cpp
index 64bd9603c877b3..2b6a2e69ea51db 100644
--- a/src/coreclr/src/vm/arm64/profiler.cpp
+++ b/src/coreclr/src/vm/arm64/profiler.cpp
@@ -10,6 +10,9 @@
 #define PROFILE_LEAVE    2
 #define PROFILE_TAILCALL 4
 
+// Scratch space to store HFA return values (max 16 bytes)
+#define PROFILE_PLATFORM_SPECIFIC_DATA_BUFFER_SIZE 16
+
 typedef struct _PROFILE_PLATFORM_SPECIFIC_DATA
 {
     void*                  Fp;
@@ -23,6 +26,7 @@ typedef struct _PROFILE_PLATFORM_SPECIFIC_DATA
     void*                  hiddenArg;
     UINT32                 flags;
     UINT32                 unused;
+    BYTE                   buffer[PROFILE_PLATFORM_SPECIFIC_DATA_BUFFER_SIZE];
 } PROFILE_PLATFORM_SPECIFIC_DATA, *PPROFILE_PLATFORM_SPECIFIC_DATA;
 
 UINT_PTR ProfileGetIPFromPlatformSpecificHandle(void* pPlatformSpecificHandle)
@@ -45,7 +49,8 @@ void ProfileSetFunctionIDInPlatformSpecificHandle(void* pPlatformSpecificHandle,
 }
 
 ProfileArgIterator::ProfileArgIterator(MetaSig* pSig, void* pPlatformSpecificHandle)
-    : m_argIterator(pSig)
+    : m_argIterator(pSig),
+    m_bufferPos(0)
 {
     WRAPPER_NO_CONTRACT;
 
@@ -235,8 +240,49 @@ LPVOID ProfileArgIterator::GetReturnBufferAddr(void)
         }
     }
 
-    if (m_argIterator.GetFPReturnSize() != 0)
-    {
+    UINT fpReturnSize = m_argIterator.GetFPReturnSize();
+    if (fpReturnSize != 0)
+    {    
+        TypeHandle thReturnValueType;
+        m_argIterator.GetSig()->GetReturnTypeNormalized(&thReturnValueType);
+        if (!thReturnValueType.IsNull() && thReturnValueType.IsHFA())
+        {
+            UINT hfaFieldSize = fpReturnSize / 4;
+            UINT totalSize = m_argIterator.GetSig()->GetReturnTypeSize();
+            _ASSERTE(totalSize % hfaFieldSize == 0);
+            _ASSERTE(totalSize <= 16);
+
+            BYTE *dest = pData->buffer;
+            for (UINT floatRegIdx = 0; floatRegIdx < totalSize / hfaFieldSize; ++floatRegIdx)
+            {
+                if (hfaFieldSize == 4)
+                {
+                    *(UINT32*)dest = *(UINT32*)&pData->floatArgumentRegisters.q[floatRegIdx];
+                    dest += 4;
+                }
+                else if (hfaFieldSize == 8)
+                {
+                    *(UINT64*)dest = *(UINT64*)&pData->floatArgumentRegisters.q[floatRegIdx];
+                    dest += 8;
+                }
+                else
+                {
+                    _ASSERTE(hfaFieldSize == 16);
+                    *(NEON128*)dest = pData->floatArgumentRegisters.q[floatRegIdx];
+                    dest += 16;
+                }
+
+                if (floatRegIdx > 8)
+                {
+                    // There's only space for 8 arguments in buffer
+                    _ASSERTE(FALSE);
+                    break;
+                }
+            }
+
+            return pData->buffer;
+        }
+
         return &pData->floatArgumentRegisters.q[0];
     }
 
diff --git a/src/coreclr/src/vm/array.cpp b/src/coreclr/src/vm/array.cpp
index dd35b491e9d70f..767c2ccb0b02a4 100644
--- a/src/coreclr/src/vm/array.cpp
+++ b/src/coreclr/src/vm/array.cpp
@@ -765,7 +765,7 @@ class ArrayOpLinker : public ILStubLinker
         DWORD dwTotalLocalNum = NewLocal(ELEMENT_TYPE_I4);
         DWORD dwLengthLocalNum = NewLocal(ELEMENT_TYPE_I4);
 
-        mdToken tokRawData = GetToken(MscorlibBinder::GetField(FIELD__RAW_DATA__DATA));
+        mdToken tokRawData = GetToken(CoreLibBinder::GetField(FIELD__RAW_DATA__DATA));
 
         ILCodeLabel * pRangeExceptionLabel = NewCodeLabel();
         ILCodeLabel * pRangeExceptionLabel1 = NewCodeLabel();
@@ -979,14 +979,14 @@ class ArrayOpLinker : public ILStubLinker
         m_pCode->EmitLabel(pRangeExceptionLabel1); // Assumes that there is one "int" pushed on the stack
         m_pCode->EmitPOP();
 
-        mdToken tokIndexOutOfRangeCtorExcep = GetToken((MscorlibBinder::GetException(kIndexOutOfRangeException))->GetDefaultConstructor());
+        mdToken tokIndexOutOfRangeCtorExcep = GetToken((CoreLibBinder::GetException(kIndexOutOfRangeException))->GetDefaultConstructor());
         m_pCode->EmitLabel(pRangeExceptionLabel);
         m_pCode->EmitNEWOBJ(tokIndexOutOfRangeCtorExcep, 0);
         m_pCode->EmitTHROW();
 
         if(pTypeMismatchExceptionLabel != NULL)
         {
-            mdToken tokTypeMismatchExcepCtor = GetToken((MscorlibBinder::GetException(kArrayTypeMismatchException))->GetDefaultConstructor());
+            mdToken tokTypeMismatchExcepCtor = GetToken((CoreLibBinder::GetException(kArrayTypeMismatchException))->GetDefaultConstructor());
 
             m_pCode->EmitLabel(pTypeMismatchExceptionLabel);
             m_pCode->EmitNEWOBJ(tokTypeMismatchExcepCtor, 0);
@@ -1273,18 +1273,18 @@ BOOL IsImplicitInterfaceOfSZArray(MethodTable *pInterfaceMT)
     PRECONDITION(pInterfaceMT->IsInterface());
     PRECONDITION(pInterfaceMT->HasInstantiation());
 
-    // Is target interface Anything<T> in mscorlib?
+    // Is target interface Anything<T> in CoreLib?
     if (!pInterfaceMT->HasInstantiation() || !pInterfaceMT->GetModule()->IsSystem())
         return FALSE;
 
     unsigned rid = pInterfaceMT->GetTypeDefRid();
 
     // Is target interface IList<T> or one of its ancestors, or IReadOnlyList<T>?
-    return (rid == MscorlibBinder::GetExistingClass(CLASS__ILISTGENERIC)->GetTypeDefRid() ||
-            rid == MscorlibBinder::GetExistingClass(CLASS__ICOLLECTIONGENERIC)->GetTypeDefRid() ||
-            rid == MscorlibBinder::GetExistingClass(CLASS__IENUMERABLEGENERIC)->GetTypeDefRid() ||
-            rid == MscorlibBinder::GetExistingClass(CLASS__IREADONLYCOLLECTIONGENERIC)->GetTypeDefRid() ||
-            rid == MscorlibBinder::GetExistingClass(CLASS__IREADONLYLISTGENERIC)->GetTypeDefRid());
+    return (rid == CoreLibBinder::GetExistingClass(CLASS__ILISTGENERIC)->GetTypeDefRid() ||
+            rid == CoreLibBinder::GetExistingClass(CLASS__ICOLLECTIONGENERIC)->GetTypeDefRid() ||
+            rid == CoreLibBinder::GetExistingClass(CLASS__IENUMERABLEGENERIC)->GetTypeDefRid() ||
+            rid == CoreLibBinder::GetExistingClass(CLASS__IREADONLYCOLLECTIONGENERIC)->GetTypeDefRid() ||
+            rid == CoreLibBinder::GetExistingClass(CLASS__IREADONLYLISTGENERIC)->GetTypeDefRid());
 }
 
 //----------------------------------------------------------------------------------
@@ -1324,10 +1324,10 @@ MethodDesc* GetActualImplementationForArrayGenericIListOrIReadOnlyListMethod(Met
     unsigned int inheritanceDepth = pItfcMeth->GetMethodTable()->GetNumInterfaces() - 1;
     PREFIX_ASSUME(0 <= inheritanceDepth && inheritanceDepth < NumItems(startingMethod));
 
-    MethodDesc *pGenericImplementor = MscorlibBinder::GetMethod((BinderMethodID)(startingMethod[inheritanceDepth] + slot));
+    MethodDesc *pGenericImplementor = CoreLibBinder::GetMethod((BinderMethodID)(startingMethod[inheritanceDepth] + slot));
 
     // The most common reason for this assert is that the order of the SZArrayHelper methods in
-    // mscorlib.h does not match the order they are implemented on the generic interfaces.
+    // corelib.h does not match the order they are implemented on the generic interfaces.
     _ASSERTE(pGenericImplementor == MemberLoader::FindMethodByName(g_pSZArrayHelperClass, pItfcMeth->GetName()));
 
     // OPTIMIZATION: For any method other than GetEnumerator(), we can safely substitute
diff --git a/src/coreclr/src/vm/assembly.cpp b/src/coreclr/src/vm/assembly.cpp
index 8bfb3d283a7cbc..4934ae689708cf 100644
--- a/src/coreclr/src/vm/assembly.cpp
+++ b/src/coreclr/src/vm/assembly.cpp
@@ -190,6 +190,19 @@ void Assembly::Init(AllocMemTracker *pamTracker, LoaderAllocator *pLoaderAllocat
     //  loading it entirely.
     //CacheFriendAssemblyInfo();
 
+#ifndef CROSSGEN_COMPILE
+    if (IsCollectible())
+    {
+        COUNT_T size;
+        BYTE *start = (BYTE*)m_pManifest->GetFile()->GetLoadedImageContents(&size);
+        if (start != NULL)
+        {
+            GCX_COOP();
+            LoaderAllocator::AssociateMemoryWithLoaderAllocator(start, start + size, m_pLoaderAllocator);
+        }
+    }
+#endif
+
     {
         CANNOTTHROWCOMPLUSEXCEPTION();
         FAULT_FORBID();
diff --git a/src/coreclr/src/vm/assemblyname.cpp b/src/coreclr/src/vm/assemblyname.cpp
index 60b46cfc6449a2..3ccb15140f2bf4 100644
--- a/src/coreclr/src/vm/assemblyname.cpp
+++ b/src/coreclr/src/vm/assemblyname.cpp
@@ -45,7 +45,7 @@ FCIMPL1(Object*, AssemblyNameNative::GetFileInformation, StringObject* filenameU
     if (gc.filename->GetStringLength() == 0)
         COMPlusThrow(kArgumentException, W("Argument_EmptyFileName"));
 
-    gc.result = (ASSEMBLYNAMEREF) AllocateObject(MscorlibBinder::GetClass(CLASS__ASSEMBLY_NAME));
+    gc.result = (ASSEMBLYNAMEREF) AllocateObject(CoreLibBinder::GetClass(CLASS__ASSEMBLY_NAME));
 
 
     ///////////////////////////////////////////////
diff --git a/src/coreclr/src/vm/assemblynative.cpp b/src/coreclr/src/vm/assemblynative.cpp
index b5701e8bcbbec8..f73697d5a3ac0c 100644
--- a/src/coreclr/src/vm/assemblynative.cpp
+++ b/src/coreclr/src/vm/assemblynative.cpp
@@ -170,7 +170,7 @@ Assembly* AssemblyNative::LoadFromPEImage(ICLRPrivBinder* pBinderContext, PEImag
 
     DWORD dwMessageID = IDS_EE_FILELOAD_ERROR_GENERIC;
 
-    // Set the caller's assembly to be mscorlib
+    // Set the caller's assembly to be CoreLib
     DomainAssembly *pCallersAssembly = SystemDomain::System()->SystemAssembly()->GetDomainAssembly();
     PEAssembly *pParentAssembly = pCallersAssembly->GetFile();
 
@@ -705,7 +705,7 @@ void QCALLTYPE AssemblyNative::GetModules(QCall::AssemblyHandle pAssembly, BOOL
         GCPROTECT_BEGIN(orModules);
 
         // Return the modules
-        orModules = (PTRARRAYREF)AllocateObjectArray(modules.GetCount(), MscorlibBinder::GetClass(CLASS__MODULE));
+        orModules = (PTRARRAYREF)AllocateObjectArray(modules.GetCount(), CoreLibBinder::GetClass(CLASS__MODULE));
 
         for(COUNT_T i = 0; i < modules.GetCount(); i++)
         {
@@ -889,7 +889,7 @@ void QCALLTYPE AssemblyNative::GetExportedTypes(QCall::AssemblyHandle pAssembly,
         GCPROTECT_BEGIN(orTypes);
 
         // Return the types
-        orTypes = (PTRARRAYREF)AllocateObjectArray(types.GetCount(), MscorlibBinder::GetClass(CLASS__TYPE));
+        orTypes = (PTRARRAYREF)AllocateObjectArray(types.GetCount(), CoreLibBinder::GetClass(CLASS__TYPE));
 
         for(COUNT_T i = 0; i < types.GetCount(); i++)
         {
@@ -960,7 +960,7 @@ void QCALLTYPE AssemblyNative::GetForwardedTypes(QCall::AssemblyHandle pAssembly
         GCPROTECT_BEGIN(orTypes);
 
         // Return the types
-        orTypes = (PTRARRAYREF)AllocateObjectArray(types.GetCount(), MscorlibBinder::GetClass(CLASS__TYPE));
+        orTypes = (PTRARRAYREF)AllocateObjectArray(types.GetCount(), CoreLibBinder::GetClass(CLASS__TYPE));
 
         for(COUNT_T i = 0; i < types.GetCount(); i++)
         {
@@ -1051,7 +1051,7 @@ FCIMPL1(Object*, AssemblyNative::GetReferencedAssemblies, AssemblyBaseObject * p
 
     IMDInternalImport *pImport = pAssembly->GetAssembly()->GetManifestImport();
 
-    MethodTable* pAsmNameClass = MscorlibBinder::GetClass(CLASS__ASSEMBLY_NAME);
+    MethodTable* pAsmNameClass = CoreLibBinder::GetClass(CLASS__ASSEMBLY_NAME);
 
     HENUMInternalHolder phEnum(pImport);
     DWORD dwCount = 0;
diff --git a/src/coreclr/src/vm/assemblyspec.cpp b/src/coreclr/src/vm/assemblyspec.cpp
index ad035b2daf6256..946f5856f7ca21 100644
--- a/src/coreclr/src/vm/assemblyspec.cpp
+++ b/src/coreclr/src/vm/assemblyspec.cpp
@@ -244,7 +244,7 @@ void AssemblySpec::InitializeSpec(PEAssembly * pFile)
     {
         // We should aways having the binding context in the PEAssembly. The only exception to this are the following:
         //
-        // 1) when we are here during EEStartup and loading mscorlib.dll.
+        // 1) when we are here during EEStartup and loading CoreLib.
         // 2) We are dealing with dynamic assemblies
         _ASSERTE((pExpectedBinder != NULL) || pFile->IsSystem() || pFile->IsDynamic());
         SetBindingContext(pExpectedBinder);
@@ -423,7 +423,7 @@ void AssemblySpec::AssemblyNameInit(ASSEMBLYNAMEREF* pAsmName, PEImage* pImageIn
     if ((m_context.usMajorVersion != (USHORT) -1) &&
         (m_context.usMinorVersion != (USHORT) -1)) {
 
-        MethodTable* pVersion = MscorlibBinder::GetClass(CLASS__VERSION);
+        MethodTable* pVersion = CoreLibBinder::GetClass(CLASS__VERSION);
 
         // version
         gc.Version = AllocateObject(pVersion);
@@ -495,7 +495,7 @@ void AssemblySpec::AssemblyNameInit(ASSEMBLYNAMEREF* pAsmName, PEImage* pImageIn
     // cultureinfo
     if (m_context.szLocale) {
 
-        MethodTable* pCI = MscorlibBinder::GetClass(CLASS__CULTURE_INFO);
+        MethodTable* pCI = CoreLibBinder::GetClass(CLASS__CULTURE_INFO);
         gc.CultureInfo = AllocateObject(pCI);
 
         gc.Locale = StringObject::NewString(m_context.szLocale);
@@ -1029,7 +1029,7 @@ AssemblySpecBindingCache::AssemblyBinding* AssemblySpecBindingCache::LookupInter
 
     // Check if the AssemblySpec already has specified its binding context. This will be set for assemblies that are
     // attempted to be explicitly bound using AssemblyLoadContext LoadFrom* methods.
-    if(!pSpec->IsAssemblySpecForMscorlib())
+    if(!pSpec->IsAssemblySpecForCoreLib())
         pBinderContextForLookup = pSpec->GetBindingContext();
     else
     {
@@ -1046,9 +1046,9 @@ AssemblySpecBindingCache::AssemblyBinding* AssemblySpecBindingCache::LookupInter
 
     if (fGetBindingContextFromParent)
     {
-        // MScorlib does not have a binding context associated with it and its lookup will only be done
+        // CoreLib does not have a binding context associated with it and its lookup will only be done
         // using its AssemblySpec hash.
-        if (!pSpec->IsAssemblySpecForMscorlib())
+        if (!pSpec->IsAssemblySpecForCoreLib())
         {
             pBinderContextForLookup = pSpec->GetBindingContextFromParentAssembly(pSpecDomain);
             pSpec->SetBindingContext(pBinderContextForLookup);
@@ -1453,7 +1453,7 @@ BOOL AssemblySpecBindingCache::StoreException(AssemblySpec *pSpec, Exception* pE
         pBinderToSaveException = pSpec->GetBindingContext();
         if (pBinderToSaveException == NULL)
         {
-            if (!pSpec->IsAssemblySpecForMscorlib())
+            if (!pSpec->IsAssemblySpecForCoreLib())
             {
                 pBinderToSaveException = pSpec->GetBindingContextFromParentAssembly(pSpec->GetAppDomain());
                 UINT_PTR binderID = 0;
diff --git a/src/coreclr/src/vm/baseassemblyspec.cpp b/src/coreclr/src/vm/baseassemblyspec.cpp
index 864dd2ec44b098..5a57c0ba5d3e7a 100644
--- a/src/coreclr/src/vm/baseassemblyspec.cpp
+++ b/src/coreclr/src/vm/baseassemblyspec.cpp
@@ -73,7 +73,7 @@ VOID BaseAssemblySpec::CloneFieldsToStackingAllocator( StackingAllocator* alloc)
 }
 
 #ifndef DACCESS_COMPILE
-BOOL BaseAssemblySpec::IsMscorlib()
+BOOL BaseAssemblySpec::IsCoreLib()
 {
     CONTRACTL
     {
@@ -106,7 +106,7 @@ BOOL BaseAssemblySpec::IsMscorlib()
                ( (iNameLen == CoreLibNameLen) || (m_pAssemblyName[CoreLibNameLen] == ',') ) ) ) );
 }
 
-BOOL BaseAssemblySpec::IsAssemblySpecForMscorlib()
+BOOL BaseAssemblySpec::IsAssemblySpecForCoreLib()
 {
     CONTRACTL
     {
@@ -118,28 +118,28 @@ BOOL BaseAssemblySpec::IsAssemblySpecForMscorlib()
     }
     CONTRACTL_END;
 
-    BOOL fIsAssemblySpecForMscorlib = FALSE;
+    BOOL fIsAssemblySpecForCoreLib = FALSE;
 
     if (m_pAssemblyName)
     {
         size_t iNameLen = strlen(m_pAssemblyName);
-        fIsAssemblySpecForMscorlib = ( (iNameLen >= CoreLibNameLen) &&
+        fIsAssemblySpecForCoreLib = ( (iNameLen >= CoreLibNameLen) &&
                  ( (!_stricmp(m_pAssemblyName, g_psBaseLibrary)) ||
                  ( (!_strnicmp(m_pAssemblyName, g_psBaseLibraryName, CoreLibNameLen)) &&
                    ( (iNameLen == CoreLibNameLen) || (m_pAssemblyName[CoreLibNameLen] == ',') ) ) ) );
     }
 
-    return fIsAssemblySpecForMscorlib;
+    return fIsAssemblySpecForCoreLib;
 }
 
-#define MSCORLIB_PUBLICKEY g_rbTheSilverlightPlatformKey
+#define CORELIB_PUBLICKEY g_rbTheSilverlightPlatformKey
 
 
-// A satellite assembly for mscorlib is named "mscorlib.resources" or
-// mscorlib.debug.resources.dll and uses the same public key as mscorlib.
+// A satellite assembly for CoreLib is named "System.Private.CoreLib.resources" or
+// System.Private.CoreLib.debug.resources.dll and uses the same public key as CoreLib.
 // It does not necessarily have the same version, and the Culture will
 // always be set to something like "jp-JP".
-BOOL BaseAssemblySpec::IsMscorlibSatellite() const
+BOOL BaseAssemblySpec::IsCoreLibSatellite() const
 {
     CONTRACTL
     {
@@ -168,13 +168,13 @@ BOOL BaseAssemblySpec::IsMscorlibSatellite() const
     // <TODO>More of bug 213471</TODO>
     size_t iNameLen = strlen(m_pAssemblyName);
 
-    // we allow name to be of the form mscorlib.resources.dll only
-    BOOL r = ( (m_cbPublicKeyOrToken == sizeof(MSCORLIB_PUBLICKEY)) &&
+    // we allow name to be of the form System.Private.CoreLib.resources.dll only
+    BOOL r = ( (m_cbPublicKeyOrToken == sizeof(CORELIB_PUBLICKEY)) &&
              (iNameLen >= CoreLibSatelliteNameLen) &&
              (!SString::_strnicmp(m_pAssemblyName, g_psBaseLibrarySatelliteAssemblyName, CoreLibSatelliteNameLen)) &&
              ( (iNameLen == CoreLibSatelliteNameLen) || (m_pAssemblyName[CoreLibSatelliteNameLen] == ',') ) );
 
-    r = r && ( memcmp(m_pbPublicKeyOrToken,MSCORLIB_PUBLICKEY,sizeof(MSCORLIB_PUBLICKEY)) == 0);
+    r = r && ( memcmp(m_pbPublicKeyOrToken,CORELIB_PUBLICKEY,sizeof(CORELIB_PUBLICKEY)) == 0);
 
     return r;
 }
diff --git a/src/coreclr/src/vm/baseassemblyspec.h b/src/coreclr/src/vm/baseassemblyspec.h
index 180ce86e119fd8..150368c1c447c3 100644
--- a/src/coreclr/src/vm/baseassemblyspec.h
+++ b/src/coreclr/src/vm/baseassemblyspec.h
@@ -79,7 +79,7 @@ class BaseAssemblySpec
         return m_pBindingContext;
     }
 
-    BOOL IsAssemblySpecForMscorlib();
+    BOOL IsAssemblySpecForCoreLib();
 
     HRESULT ParseName();
     DWORD Hash();
@@ -106,8 +106,8 @@ class BaseAssemblySpec
     BOOL IsStrongNamed() const;
     BOOL HasPublicKey() const;
     BOOL HasPublicKeyToken() const;
-    BOOL IsMscorlibSatellite() const;
-    BOOL IsMscorlib();
+    BOOL IsCoreLibSatellite() const;
+    BOOL IsCoreLib();
 
     // Returns true
     inline BOOL HasUniqueIdentity() const
diff --git a/src/coreclr/src/vm/baseassemblyspec.inl b/src/coreclr/src/vm/baseassemblyspec.inl
index 5a6759506f5ab5..5e1496b5986e1f 100644
--- a/src/coreclr/src/vm/baseassemblyspec.inl
+++ b/src/coreclr/src/vm/baseassemblyspec.inl
@@ -320,7 +320,7 @@ inline BOOL BaseAssemblySpec::CompareEx(BaseAssemblySpec *pSpec, DWORD dwCompare
 
 
     // If the assemblySpec contains the binding context, then check if they match.
-    if (!(pSpec->IsAssemblySpecForMscorlib() && IsAssemblySpecForMscorlib()))
+    if (!(pSpec->IsAssemblySpecForCoreLib() && IsAssemblySpecForCoreLib()))
     {
         if (!AreSameBinderInstance(pSpec->m_pBindingContext, m_pBindingContext))
         {
diff --git a/src/coreclr/src/vm/binder.cpp b/src/coreclr/src/vm/binder.cpp
index bef7b479bc6031..3dbd8660596726 100644
--- a/src/coreclr/src/vm/binder.cpp
+++ b/src/coreclr/src/vm/binder.cpp
@@ -28,13 +28,13 @@
 //
 // Retrieve structures from ID.
 //
-NOINLINE PTR_MethodTable MscorlibBinder::LookupClass(BinderClassID id)
+NOINLINE PTR_MethodTable CoreLibBinder::LookupClass(BinderClassID id)
 {
     WRAPPER_NO_CONTRACT;
-    return (&g_Mscorlib)->LookupClassLocal(id);
+    return (&g_CoreLib)->LookupClassLocal(id);
 }
 
-PTR_MethodTable MscorlibBinder::GetClassLocal(BinderClassID id)
+PTR_MethodTable CoreLibBinder::GetClassLocal(BinderClassID id)
 {
     WRAPPER_NO_CONTRACT;
 
@@ -44,7 +44,7 @@ PTR_MethodTable MscorlibBinder::GetClassLocal(BinderClassID id)
     return pMT;
 }
 
-PTR_MethodTable MscorlibBinder::LookupClassLocal(BinderClassID id)
+PTR_MethodTable CoreLibBinder::LookupClassLocal(BinderClassID id)
 {
     CONTRACTL
     {
@@ -59,11 +59,11 @@ PTR_MethodTable MscorlibBinder::LookupClassLocal(BinderClassID id)
 
     PTR_MethodTable pMT = NULL;
 
-    // Binder methods are used for loading "known" types from mscorlib.dll. Thus they are unlikely to be part
+    // Binder methods are used for loading "known" types. Thus they are unlikely to be part
     // of a recursive cycle. This is used too broadly to force manual overrides at every callsite.
     OVERRIDE_TYPE_LOAD_LEVEL_LIMIT(CLASS_LOADED);
 
-    const MscorlibClassDescription *d = m_classDescriptions + (int)id;
+    const CoreLibClassDescription *d = m_classDescriptions + (int)id;
 
     pMT = ClassLoader::LoadTypeByNameThrowing(GetModule()->GetAssembly(), d->nameSpace, d->name).AsMethodTable();
 
@@ -76,13 +76,13 @@ PTR_MethodTable MscorlibBinder::LookupClassLocal(BinderClassID id)
     return pMT;
 }
 
-NOINLINE MethodDesc * MscorlibBinder::LookupMethod(BinderMethodID id)
+NOINLINE MethodDesc * CoreLibBinder::LookupMethod(BinderMethodID id)
 {
     WRAPPER_NO_CONTRACT;
-    return (&g_Mscorlib)->LookupMethodLocal(id);
+    return (&g_CoreLib)->LookupMethodLocal(id);
 }
 
-MethodDesc * MscorlibBinder::GetMethodLocal(BinderMethodID id)
+MethodDesc * CoreLibBinder::GetMethodLocal(BinderMethodID id)
 {
     WRAPPER_NO_CONTRACT;
 
@@ -92,7 +92,7 @@ MethodDesc * MscorlibBinder::GetMethodLocal(BinderMethodID id)
     return pMD;
 }
 
-MethodDesc * MscorlibBinder::LookupMethodLocal(BinderMethodID id)
+MethodDesc * CoreLibBinder::LookupMethodLocal(BinderMethodID id)
 {
     CONTRACTL
     {
@@ -108,10 +108,10 @@ MethodDesc * MscorlibBinder::LookupMethodLocal(BinderMethodID id)
 #ifndef DACCESS_COMPILE
     MethodDesc * pMD = NULL;
 
-    const MscorlibMethodDescription *d = m_methodDescriptions + (id - 1);
+    const CoreLibMethodDescription *d = m_methodDescriptions + (id - 1);
 
     MethodTable * pMT = GetClassLocal(d->classID);
-    _ASSERTE(pMT != NULL && "Couldn't find a type in mscorlib!");
+    _ASSERTE(pMT != NULL && "Couldn't find a type in System.Private.CoreLib!");
 
     if (d->sig != NULL)
     {
@@ -136,13 +136,13 @@ MethodDesc * MscorlibBinder::LookupMethodLocal(BinderMethodID id)
 #endif
 }
 
-NOINLINE FieldDesc * MscorlibBinder::LookupField(BinderFieldID id)
+NOINLINE FieldDesc * CoreLibBinder::LookupField(BinderFieldID id)
 {
     WRAPPER_NO_CONTRACT;
-    return (&g_Mscorlib)->LookupFieldLocal(id);
+    return (&g_CoreLib)->LookupFieldLocal(id);
 }
 
-FieldDesc * MscorlibBinder::GetFieldLocal(BinderFieldID id)
+FieldDesc * CoreLibBinder::GetFieldLocal(BinderFieldID id)
 {
     WRAPPER_NO_CONTRACT;
 
@@ -152,7 +152,7 @@ FieldDesc * MscorlibBinder::GetFieldLocal(BinderFieldID id)
     return pFD;
 }
 
-FieldDesc * MscorlibBinder::LookupFieldLocal(BinderFieldID id)
+FieldDesc * CoreLibBinder::LookupFieldLocal(BinderFieldID id)
 {
     CONTRACTL
     {
@@ -167,7 +167,7 @@ FieldDesc * MscorlibBinder::LookupFieldLocal(BinderFieldID id)
 
     FieldDesc * pFD = NULL;
 
-    const MscorlibFieldDescription *d = m_fieldDescriptions + (id - 1);
+    const CoreLibFieldDescription *d = m_fieldDescriptions + (id - 1);
 
     MethodTable * pMT = GetClassLocal(d->classID);
 
@@ -182,7 +182,7 @@ FieldDesc * MscorlibBinder::LookupFieldLocal(BinderFieldID id)
     return pFD;
 }
 
-NOINLINE PTR_MethodTable MscorlibBinder::LookupClassIfExist(BinderClassID id)
+NOINLINE PTR_MethodTable CoreLibBinder::LookupClassIfExist(BinderClassID id)
 {
     CONTRACTL
     {
@@ -192,18 +192,18 @@ NOINLINE PTR_MethodTable MscorlibBinder::LookupClassIfExist(BinderClassID id)
         MODE_ANY;
 
         PRECONDITION(id != CLASS__NIL);
-        PRECONDITION(id <= (&g_Mscorlib)->m_cClasses);
+        PRECONDITION(id <= (&g_CoreLib)->m_cClasses);
     }
     CONTRACTL_END;
 
     // Run the class loader in non-load mode.
     ENABLE_FORBID_GC_LOADER_USE_IN_THIS_SCOPE();
 
-    // Binder methods are used for loading "known" types from mscorlib.dll. Thus they are unlikely to be part
+    // Binder methods are used for loading "known" types. Thus they are unlikely to be part
     // of a recursive cycle. This is used too broadly to force manual overrides at every callsite.
     OVERRIDE_TYPE_LOAD_LEVEL_LIMIT(CLASS_LOADED);
 
-    const MscorlibClassDescription *d = (&g_Mscorlib)->m_classDescriptions + (int)id;
+    const CoreLibClassDescription *d = (&g_CoreLib)->m_classDescriptions + (int)id;
 
     PTR_MethodTable pMT = ClassLoader::LoadTypeByNameThrowing(GetModule()->GetAssembly(), d->nameSpace, d->name,
         ClassLoader::ReturnNullIfNotFound, ClassLoader::DontLoadTypes, CLASS_LOAD_UNRESTOREDTYPEKEY).AsMethodTable();
@@ -212,13 +212,13 @@ NOINLINE PTR_MethodTable MscorlibBinder::LookupClassIfExist(BinderClassID id)
 
 #ifndef DACCESS_COMPILE
     if ((pMT != NULL) && pMT->IsFullyLoaded())
-        VolatileStore(&(g_Mscorlib.m_pClasses[id]), pMT);
+        VolatileStore(&(g_CoreLib.m_pClasses[id]), pMT);
 #endif
 
     return pMT;
 }
 
-Signature MscorlibBinder::GetSignature(LPHARDCODEDMETASIG pHardcodedSig)
+Signature CoreLibBinder::GetSignature(LPHARDCODEDMETASIG pHardcodedSig)
 {
     CONTRACTL
     {
@@ -245,10 +245,10 @@ Signature MscorlibBinder::GetSignature(LPHARDCODEDMETASIG pHardcodedSig)
     }
 #endif
 
-    return (&g_Mscorlib)->GetSignatureLocal(pHardcodedSig);
+    return (&g_CoreLib)->GetSignatureLocal(pHardcodedSig);
 }
 
-Signature MscorlibBinder::GetTargetSignature(LPHARDCODEDMETASIG pHardcodedSig)
+Signature CoreLibBinder::GetTargetSignature(LPHARDCODEDMETASIG pHardcodedSig)
 {
     CONTRACTL
     {
@@ -262,12 +262,12 @@ Signature MscorlibBinder::GetTargetSignature(LPHARDCODEDMETASIG pHardcodedSig)
 #ifdef CROSSGEN_COMPILE
     return GetModule()->m_pBinder->GetSignatureLocal(pHardcodedSig);
 #else
-    return (&g_Mscorlib)->GetSignatureLocal(pHardcodedSig);
+    return (&g_CoreLib)->GetSignatureLocal(pHardcodedSig);
 #endif
 }
 
 // Get the metasig, do a one-time conversion if necessary
-Signature MscorlibBinder::GetSignatureLocal(LPHARDCODEDMETASIG pHardcodedSig)
+Signature CoreLibBinder::GetSignatureLocal(LPHARDCODEDMETASIG pHardcodedSig)
 {
     CONTRACTL
     {
@@ -311,7 +311,7 @@ Signature MscorlibBinder::GetSignatureLocal(LPHARDCODEDMETASIG pHardcodedSig)
 
 #ifndef DACCESS_COMPILE
 
-bool MscorlibBinder::ConvertType(const BYTE*& pSig, SigBuilder * pSigBuilder)
+bool CoreLibBinder::ConvertType(const BYTE*& pSig, SigBuilder * pSigBuilder)
 {
     bool bSomethingResolved = false;
 
@@ -389,7 +389,7 @@ bool MscorlibBinder::ConvertType(const BYTE*& pSig, SigBuilder * pSigBuilder)
 // Resolve type references in the hardcoded metasig.
 // Returns a new signature with type refences resolved.
 //------------------------------------------------------------------
-void MscorlibBinder::BuildConvertedSignature(const BYTE* pSig, SigBuilder * pSigBuilder)
+void CoreLibBinder::BuildConvertedSignature(const BYTE* pSig, SigBuilder * pSigBuilder)
 {
     CONTRACTL
     {
@@ -427,7 +427,7 @@ void MscorlibBinder::BuildConvertedSignature(const BYTE* pSig, SigBuilder * pSig
     _ASSERTE(bSomethingResolved);
 }
 
-const BYTE* MscorlibBinder::ConvertSignature(LPHARDCODEDMETASIG pHardcodedSig, const BYTE* pSig)
+const BYTE* CoreLibBinder::ConvertSignature(LPHARDCODEDMETASIG pHardcodedSig, const BYTE* pSig)
 {
     CONTRACTL
     {
@@ -469,7 +469,7 @@ const BYTE* MscorlibBinder::ConvertSignature(LPHARDCODEDMETASIG pHardcodedSig, c
 #endif // #ifndef DACCESS_COMPILE
 
 #ifdef _DEBUG
-void MscorlibBinder::TriggerGCUnderStress()
+void CoreLibBinder::TriggerGCUnderStress()
 {
     CONTRACTL
     {
@@ -498,7 +498,7 @@ void MscorlibBinder::TriggerGCUnderStress()
 }
 #endif // _DEBUG
 
-DWORD MscorlibBinder::GetFieldOffset(BinderFieldID id)
+DWORD CoreLibBinder::GetFieldOffset(BinderFieldID id)
 {
     WRAPPER_NO_CONTRACT;
 
@@ -507,10 +507,10 @@ DWORD MscorlibBinder::GetFieldOffset(BinderFieldID id)
 
 #ifndef DACCESS_COMPILE
 
-CrstStatic MscorlibBinder::s_SigConvertCrst;
+CrstStatic CoreLibBinder::s_SigConvertCrst;
 
 /*static*/
-void MscorlibBinder::Startup()
+void CoreLibBinder::Startup()
 {
     WRAPPER_NO_CONTRACT
     s_SigConvertCrst.Init(CrstSigConvert);
@@ -521,20 +521,20 @@ void MscorlibBinder::Startup()
 // NoClass is used to suppress check for unmanaged and managed size match
 #define NoClass char[USHRT_MAX]
 
-const MscorlibBinder::OffsetAndSizeCheck MscorlibBinder::OffsetsAndSizes[] =
+const CoreLibBinder::OffsetAndSizeCheck CoreLibBinder::OffsetsAndSizes[] =
 {
     #define DEFINE_CLASS_U(nameSpace, stringName, unmanagedType) \
         { PTR_CSTR((TADDR) g_ ## nameSpace ## NS ), PTR_CUTF8((TADDR) # stringName), sizeof(unmanagedType), 0, 0, 0 },
 
     #define DEFINE_FIELD_U(stringName, unmanagedContainingType, unmanagedOffset) \
         { 0, 0, 0, PTR_CUTF8((TADDR) # stringName), offsetof(unmanagedContainingType, unmanagedOffset), sizeof(((unmanagedContainingType*)1)->unmanagedOffset) },
-    #include "mscorlib.h"
+    #include "corelib.h"
 };
 
 //
-// check the basic consistency between mscorlib and mscorwks
+// check the basic consistency between CoreLib and VM
 //
-void MscorlibBinder::Check()
+void CoreLibBinder::Check()
 {
     STANDARD_VM_CONTRACT;
 
@@ -566,7 +566,7 @@ void MscorlibBinder::Check()
         else
         if (p->fieldName != NULL)
         {
-            // This assert will fire if there is DEFINE_FIELD_U macro without preceeding DEFINE_CLASS_U macro in mscorlib.h
+            // This assert will fire if there is DEFINE_FIELD_U macro without preceeding DEFINE_CLASS_U macro in corelib.h
             _ASSERTE(pMT != NULL);
 
             FieldDesc * pFD = MemberLoader::FindField(pMT, p->fieldName, NULL, 0, NULL);
@@ -876,32 +876,32 @@ static void FCallCheckSignature(MethodDesc* pMD, PCODE pImpl)
 #endif // CHECK_FCALL_SIGNATURE
 
 //
-// extended check of consistency between mscorlib and mscorwks:
-//  - verifies that all references from mscorlib to mscorwks are present
-//  - verifies that all references from mscorwks to mscorlib are present
+// extended check of consistency between CoreLib and VM:
+//  - verifies that all references from CoreLib to VM are present
+//  - verifies that all references from VM to CoreLib are present
 //  - limited detection of mismatches between managed and unmanaged fcall signatures
 //
-void MscorlibBinder::CheckExtended()
+void CoreLibBinder::CheckExtended()
 {
     STANDARD_VM_CONTRACT;
 
-    // check the consistency of BCL and VM
+    // check the consistency of CoreLib and VM
     // note: it is not enabled by default because of it is time consuming and
     // changes the bootstrap sequence of the EE
     if (!CLRConfig::GetConfigValue(CLRConfig::INTERNAL_ConsistencyCheck))
         return;
 
     //
-    // VM referencing BCL (mscorlib.h)
+    // VM referencing CoreLib (corelib.h)
     //
     for (BinderClassID cID = (BinderClassID) 1; (int)cID < m_cClasses; cID = (BinderClassID) (cID + 1))
     {
         bool fError = false;
         EX_TRY
         {
-            if (MscorlibBinder::GetClassName(cID) != NULL) // Allow for CorSigElement entries with no classes
+            if (CoreLibBinder::GetClassName(cID) != NULL) // Allow for CorSigElement entries with no classes
             {
-                if (NULL == MscorlibBinder::GetClass(cID))
+                if (NULL == CoreLibBinder::GetClass(cID))
                 {
                     fError = true;
                 }
@@ -915,17 +915,17 @@ void MscorlibBinder::CheckExtended()
 
         if (fError)
         {
-            printf("CheckExtended: VM expects type to exist:  %s.%s\n", MscorlibBinder::GetClassNameSpace(cID), MscorlibBinder::GetClassName(cID));
+            printf("CheckExtended: VM expects type to exist:  %s.%s\n", CoreLibBinder::GetClassNameSpace(cID), CoreLibBinder::GetClassName(cID));
         }
     }
 
-    for (BinderMethodID mID = (BinderMethodID) 1; mID < (BinderMethodID) MscorlibBinder::m_cMethods; mID = (BinderMethodID) (mID + 1))
+    for (BinderMethodID mID = (BinderMethodID) 1; mID < (BinderMethodID) CoreLibBinder::m_cMethods; mID = (BinderMethodID) (mID + 1))
     {
         bool fError = false;
         BinderClassID cID = m_methodDescriptions[mID-1].classID;
         EX_TRY
         {
-            if (NULL == MscorlibBinder::GetMethod(mID))
+            if (NULL == CoreLibBinder::GetMethod(mID))
             {
                 fError = true;
             }
@@ -938,17 +938,17 @@ void MscorlibBinder::CheckExtended()
 
         if (fError)
         {
-            printf("CheckExtended: VM expects method to exist:  %s.%s::%s\n", MscorlibBinder::GetClassNameSpace(cID), MscorlibBinder::GetClassName(cID), MscorlibBinder::GetMethodName(mID));
+            printf("CheckExtended: VM expects method to exist:  %s.%s::%s\n", CoreLibBinder::GetClassNameSpace(cID), CoreLibBinder::GetClassName(cID), CoreLibBinder::GetMethodName(mID));
         }
     }
 
-    for (BinderFieldID fID = (BinderFieldID) 1; fID < (BinderFieldID) MscorlibBinder::m_cFields; fID = (BinderFieldID) (fID + 1))
+    for (BinderFieldID fID = (BinderFieldID) 1; fID < (BinderFieldID) CoreLibBinder::m_cFields; fID = (BinderFieldID) (fID + 1))
     {
         bool fError = false;
         BinderClassID cID = m_fieldDescriptions[fID-1].classID;
         EX_TRY
         {
-            if (NULL == MscorlibBinder::GetField(fID))
+            if (NULL == CoreLibBinder::GetField(fID))
             {
                 fError = true;
             }
@@ -961,17 +961,17 @@ void MscorlibBinder::CheckExtended()
 
         if (fError)
         {
-            printf("CheckExtended: VM expects field to exist:  %s.%s::%s\n", MscorlibBinder::GetClassNameSpace(cID), MscorlibBinder::GetClassName(cID), MscorlibBinder::GetFieldName(fID));
+            printf("CheckExtended: VM expects field to exist:  %s.%s::%s\n", CoreLibBinder::GetClassNameSpace(cID), CoreLibBinder::GetClassName(cID), CoreLibBinder::GetFieldName(fID));
         }
     }
 
     //
-    // BCL referencing VM (ecall.cpp)
+    // CoreLib referencing VM (ecalllist.h)
     //
     SetSHash<DWORD> usedECallIds;
 
     HRESULT hr = S_OK;
-    Module *pModule = MscorlibBinder::m_pModule;
+    Module *pModule = CoreLibBinder::m_pModule;
     IMDInternalImport *pInternalImport = pModule->GetMDImport();
 
     HENUMInternal hEnum;
@@ -1014,7 +1014,7 @@ void MscorlibBinder::CheckExtended()
             {
                 pszClassName = pszNameSpace = "Invalid TypeDef record";
             }
-            printf("CheckExtended: Unable to load class from mscorlib: %s.%s\n", pszNameSpace, pszClassName);
+            printf("CheckExtended: Unable to load class from System.Private.CoreLib: %s.%s\n", pszNameSpace, pszClassName);
         }
         EX_END_CATCH(SwallowAllExceptions)
 
@@ -1099,7 +1099,7 @@ void MscorlibBinder::CheckExtended()
 #define ASMCONSTANTS_RUNTIME_ASSERT(cond) _ASSERTE(cond)
 #include "asmconstants.h"
 
-    _ASSERTE(sizeof(VARIANT) == MscorlibBinder::GetClass(CLASS__NATIVEVARIANT)->GetNativeSize());
+    _ASSERTE(sizeof(VARIANT) == CoreLibBinder::GetClass(CLASS__NATIVEVARIANT)->GetNativeSize());
 
     printf("CheckExtended: completed without exception.\n");
 
@@ -1109,45 +1109,45 @@ void MscorlibBinder::CheckExtended()
 
 #endif // _DEBUG && !CROSSGEN_COMPILE
 
-extern const MscorlibClassDescription c_rgMscorlibClassDescriptions[];
-extern const USHORT c_nMscorlibClassDescriptions;
+extern const CoreLibClassDescription c_rgCoreLibClassDescriptions[];
+extern const USHORT c_nCoreLibClassDescriptions;
 
-extern const MscorlibMethodDescription c_rgMscorlibMethodDescriptions[];
-extern const USHORT c_nMscorlibMethodDescriptions;
+extern const CoreLibMethodDescription c_rgCoreLibMethodDescriptions[];
+extern const USHORT c_nCoreLibMethodDescriptions;
 
-extern const MscorlibFieldDescription c_rgMscorlibFieldDescriptions[];
-extern const USHORT c_nMscorlibFieldDescriptions;
+extern const CoreLibFieldDescription c_rgCoreLibFieldDescriptions[];
+extern const USHORT c_nCoreLibFieldDescriptions;
 
 #ifdef CROSSGEN_COMPILE
-namespace CrossGenMscorlib
+namespace CrossGenCoreLib
 {
-    extern const MscorlibClassDescription c_rgMscorlibClassDescriptions[];
-    extern const USHORT c_nMscorlibClassDescriptions;
+    extern const CoreLibClassDescription c_rgCoreLibClassDescriptions[];
+    extern const USHORT c_nCoreLibClassDescriptions;
 
-    extern const MscorlibMethodDescription c_rgMscorlibMethodDescriptions[];
-    extern const USHORT c_nMscorlibMethodDescriptions;
+    extern const CoreLibMethodDescription c_rgCoreLibMethodDescriptions[];
+    extern const USHORT c_nCoreLibMethodDescriptions;
 
-    extern const MscorlibFieldDescription c_rgMscorlibFieldDescriptions[];
-    extern const USHORT c_nMscorlibFieldDescriptions;
+    extern const CoreLibFieldDescription c_rgCoreLibFieldDescriptions[];
+    extern const USHORT c_nCoreLibFieldDescriptions;
 };
 #endif
 
-void MscorlibBinder::AttachModule(Module * pModule)
+void CoreLibBinder::AttachModule(Module * pModule)
 {
     STANDARD_VM_CONTRACT;
 
-    MscorlibBinder * pGlobalBinder = &g_Mscorlib;
+    CoreLibBinder * pGlobalBinder = &g_CoreLib;
 
     pGlobalBinder->SetDescriptions(pModule,
-        c_rgMscorlibClassDescriptions,  c_nMscorlibClassDescriptions,
-        c_rgMscorlibMethodDescriptions, c_nMscorlibMethodDescriptions,
-        c_rgMscorlibFieldDescriptions,  c_nMscorlibFieldDescriptions);
+        c_rgCoreLibClassDescriptions,  c_nCoreLibClassDescriptions,
+        c_rgCoreLibMethodDescriptions, c_nCoreLibMethodDescriptions,
+        c_rgCoreLibFieldDescriptions,  c_nCoreLibFieldDescriptions);
 
 #if defined(FEATURE_PREJIT) && !defined(CROSSGEN_COMPILE)
-    MscorlibBinder * pPersistedBinder = pModule->m_pBinder;
+    CoreLibBinder * pPersistedBinder = pModule->m_pBinder;
 
     if (pPersistedBinder != NULL
-        // Do not use persisted binder for profiling native images. See comment in code:MscorlibBinder::Fixup.
+        // Do not use persisted binder for profiling native images. See comment in code:CoreLibBinder::Fixup.
         && !(pModule->GetNativeImage()->GetNativeVersionInfo()->wConfigFlags  & CORCOMPILE_CONFIG_PROFILING))
     {
         pGlobalBinder->m_pClasses = pPersistedBinder->m_pClasses;
@@ -1162,14 +1162,14 @@ void MscorlibBinder::AttachModule(Module * pModule)
     pGlobalBinder->AllocateTables();
 
 #ifdef CROSSGEN_COMPILE
-    MscorlibBinder * pTargetBinder = (MscorlibBinder *)(void *)
+    CoreLibBinder * pTargetBinder = (CoreLibBinder *)(void *)
         pModule->GetAssembly()->GetLowFrequencyHeap()
-            ->AllocMem(S_SIZE_T(sizeof(MscorlibBinder)));
+            ->AllocMem(S_SIZE_T(sizeof(CoreLibBinder)));
 
     pTargetBinder->SetDescriptions(pModule,
-        CrossGenMscorlib::c_rgMscorlibClassDescriptions,  CrossGenMscorlib::c_nMscorlibClassDescriptions,
-        CrossGenMscorlib::c_rgMscorlibMethodDescriptions, CrossGenMscorlib::c_nMscorlibMethodDescriptions,
-        CrossGenMscorlib::c_rgMscorlibFieldDescriptions,  CrossGenMscorlib::c_nMscorlibFieldDescriptions);
+        CrossGenCoreLib::c_rgCoreLibClassDescriptions,  CrossGenCoreLib::c_nCoreLibClassDescriptions,
+        CrossGenCoreLib::c_rgCoreLibMethodDescriptions, CrossGenCoreLib::c_nCoreLibMethodDescriptions,
+        CrossGenCoreLib::c_rgCoreLibFieldDescriptions,  CrossGenCoreLib::c_nCoreLibFieldDescriptions);
 
     pTargetBinder->AllocateTables();
 
@@ -1179,10 +1179,10 @@ void MscorlibBinder::AttachModule(Module * pModule)
 #endif
 }
 
-void MscorlibBinder::SetDescriptions(Module * pModule,
-    const MscorlibClassDescription * pClassDescriptions, USHORT nClasses,
-    const MscorlibMethodDescription * pMethodDescriptions, USHORT nMethods,
-    const MscorlibFieldDescription * pFieldDescriptions, USHORT nFields)
+void CoreLibBinder::SetDescriptions(Module * pModule,
+    const CoreLibClassDescription * pClassDescriptions, USHORT nClasses,
+    const CoreLibMethodDescription * pMethodDescriptions, USHORT nMethods,
+    const CoreLibFieldDescription * pFieldDescriptions, USHORT nFields)
 {
     LIMITED_METHOD_CONTRACT;
 
@@ -1198,7 +1198,7 @@ void MscorlibBinder::SetDescriptions(Module * pModule,
     m_cFields = nFields;
 }
 
-void MscorlibBinder::AllocateTables()
+void CoreLibBinder::AllocateTables()
 {
     STANDARD_VM_CONTRACT;
 
@@ -1220,20 +1220,20 @@ void MscorlibBinder::AllocateTables()
     // ZeroMemory(m_pFields, m_cFieldRIDs * sizeof(*m_pFields));
 }
 
-PTR_MethodTable MscorlibBinder::LoadPrimitiveType(CorElementType et)
+PTR_MethodTable CoreLibBinder::LoadPrimitiveType(CorElementType et)
 {
     STANDARD_VM_CONTRACT;
 
-    PTR_MethodTable pMT = g_Mscorlib.m_pClasses[et];
+    PTR_MethodTable pMT = g_CoreLib.m_pClasses[et];
 
     // Primitive types hit cyclic reference on binder during type loading so we have to load them in two steps
     if (pMT == NULL)
     {
-        const MscorlibClassDescription *d = (&g_Mscorlib)->m_classDescriptions + (int)et;
+        const CoreLibClassDescription *d = (&g_CoreLib)->m_classDescriptions + (int)et;
 
         pMT = ClassLoader::LoadTypeByNameThrowing(GetModule()->GetAssembly(), d->nameSpace, d->name,
             ClassLoader::ThrowIfNotFound, ClassLoader::LoadTypes, CLASS_LOAD_APPROXPARENTS).AsMethodTable();
-        g_Mscorlib.m_pClasses[et] = pMT;
+        g_CoreLib.m_pClasses[et] = pMT;
 
         ClassLoader::EnsureLoaded(pMT);
     }
@@ -1242,7 +1242,7 @@ PTR_MethodTable MscorlibBinder::LoadPrimitiveType(CorElementType et)
 }
 
 #ifdef FEATURE_NATIVE_IMAGE_GENERATION
-void MscorlibBinder::BindAll()
+void CoreLibBinder::BindAll()
 {
     STANDARD_VM_CONTRACT;
 
@@ -1259,11 +1259,11 @@ void MscorlibBinder::BindAll()
         GetFieldLocal(fID);
 }
 
-void MscorlibBinder::Save(DataImage *image)
+void CoreLibBinder::Save(DataImage *image)
 {
     STANDARD_VM_CONTRACT;
 
-    image->StoreStructure(this, sizeof(MscorlibBinder),
+    image->StoreStructure(this, sizeof(CoreLibBinder),
                           DataImage::ITEM_BINDER);
 
     image->StoreStructure(m_pClasses, m_cClasses * sizeof(*m_pClasses),
@@ -1276,15 +1276,15 @@ void MscorlibBinder::Save(DataImage *image)
                           DataImage::ITEM_BINDER_ITEMS);
 }
 
-void MscorlibBinder::Fixup(DataImage *image)
+void CoreLibBinder::Fixup(DataImage *image)
 {
     STANDARD_VM_CONTRACT;
 
-    image->FixupPointerField(this, offsetof(MscorlibBinder, m_pModule));
+    image->FixupPointerField(this, offsetof(CoreLibBinder, m_pModule));
 
     int i;
 
-    image->FixupPointerField(this, offsetof(MscorlibBinder, m_pClasses));
+    image->FixupPointerField(this, offsetof(CoreLibBinder, m_pClasses));
     for (i = 1; i < m_cClasses; i++)
     {
 #if _DEBUG
@@ -1304,7 +1304,7 @@ void MscorlibBinder::Fixup(DataImage *image)
         image->FixupPointerField(m_pClasses, i * sizeof(m_pClasses[0]));
     }
 
-    image->FixupPointerField(this, offsetof(MscorlibBinder, m_pMethods));
+    image->FixupPointerField(this, offsetof(CoreLibBinder, m_pMethods));
     for (i = 1; i < m_cMethods; i++)
     {
 #if _DEBUG
@@ -1318,15 +1318,15 @@ void MscorlibBinder::Fixup(DataImage *image)
         image->FixupPointerField(m_pMethods, i * sizeof(m_pMethods[0]));
     }
 
-    image->FixupPointerField(this, offsetof(MscorlibBinder, m_pFields));
+    image->FixupPointerField(this, offsetof(CoreLibBinder, m_pFields));
     for (i = 1; i < m_cFields; i++)
     {
         image->FixupPointerField(m_pFields, i * sizeof(m_pFields[0]));
     }
 
-    image->ZeroPointerField(this, offsetof(MscorlibBinder, m_classDescriptions));
-    image->ZeroPointerField(this, offsetof(MscorlibBinder, m_methodDescriptions));
-    image->ZeroPointerField(this, offsetof(MscorlibBinder, m_fieldDescriptions));
+    image->ZeroPointerField(this, offsetof(CoreLibBinder, m_classDescriptions));
+    image->ZeroPointerField(this, offsetof(CoreLibBinder, m_methodDescriptions));
+    image->ZeroPointerField(this, offsetof(CoreLibBinder, m_fieldDescriptions));
 }
 #endif // FEATURE_NATIVE_IMAGE_GENERATION
 
@@ -1335,17 +1335,17 @@ void MscorlibBinder::Fixup(DataImage *image)
 #ifdef DACCESS_COMPILE
 
 void
-MscorlibBinder::EnumMemoryRegions(CLRDataEnumMemoryFlags flags)
+CoreLibBinder::EnumMemoryRegions(CLRDataEnumMemoryFlags flags)
 {
     SUPPORTS_DAC;
     DAC_ENUM_DTHIS();
 
     DacEnumMemoryRegion(dac_cast<TADDR>(m_classDescriptions),
-                        m_cClasses * sizeof(MscorlibClassDescription));
+                        m_cClasses * sizeof(CoreLibClassDescription));
     DacEnumMemoryRegion(dac_cast<TADDR>(m_methodDescriptions),
-                        (m_cMethods - 1) * sizeof(MscorlibMethodDescription));
+                        (m_cMethods - 1) * sizeof(CoreLibMethodDescription));
     DacEnumMemoryRegion(dac_cast<TADDR>(m_fieldDescriptions),
-                        (m_cFields - 1) * sizeof(MscorlibFieldDescription));
+                        (m_cFields - 1) * sizeof(CoreLibFieldDescription));
 
     if (m_pModule.IsValid())
     {
@@ -1362,4 +1362,4 @@ MscorlibBinder::EnumMemoryRegions(CLRDataEnumMemoryFlags flags)
 
 #endif // #ifdef DACCESS_COMPILE
 
-GVAL_IMPL(MscorlibBinder, g_Mscorlib);
+GVAL_IMPL(CoreLibBinder, g_CoreLib);
diff --git a/src/coreclr/src/vm/binder.h b/src/coreclr/src/vm/binder.h
index 24db64e33fd167..4ff115d2b557ea 100644
--- a/src/coreclr/src/vm/binder.h
+++ b/src/coreclr/src/vm/binder.h
@@ -33,7 +33,7 @@ struct HardCodedMetaSig
 // Use the Binder objects to avoid doing unnecessary name lookup
 // (esp. in the prejit case)
 //
-// E.g. MscorlibBinder::GetClass(CLASS__APP_DOMAIN);
+// E.g. CoreLibBinder::GetClass(CLASS__APP_DOMAIN);
 //
 
 // BinderClassIDs are of the form CLASS__XXX
@@ -45,9 +45,9 @@ enum BinderClassID
 #undef TYPEINFO
 
 #define DEFINE_CLASS(i,n,s)         CLASS__ ## i,
-#include "mscorlib.h"
+#include "corelib.h"
 
-    CLASS__MSCORLIB_COUNT,
+    CLASS__CORELIB_COUNT,
 
     // Aliases for element type classids
     CLASS__NIL      = CLASS__ELEMENT_TYPE_END,
@@ -80,9 +80,9 @@ enum BinderMethodID : int
     METHOD__NIL = 0,
 
 #define DEFINE_METHOD(c,i,s,g)      METHOD__ ## c ## __ ## i,
-#include "mscorlib.h"
+#include "corelib.h"
 
-    METHOD__MSCORLIB_COUNT,
+    METHOD__CORELIB_COUNT,
 };
 
 // BinderFieldIDs are of the form FIELD__XXX__YYY,
@@ -93,31 +93,31 @@ enum BinderFieldID
     FIELD__NIL = 0,
 
 #define DEFINE_FIELD(c,i,s)                 FIELD__ ## c ## __ ## i,
-#include "mscorlib.h"
+#include "corelib.h"
 
-    FIELD__MSCORLIB_COUNT,
+    FIELD__CORELIB_COUNT,
 };
 
-struct MscorlibClassDescription
+struct CoreLibClassDescription
 {
     PTR_CSTR nameSpace;
     PTR_CSTR name;
 };
 
-struct MscorlibMethodDescription
+struct CoreLibMethodDescription
 {
     BinderClassID classID;
     PTR_CSTR name;
     PTR_HARDCODEDMETASIG sig;
 };
 
-struct MscorlibFieldDescription
+struct CoreLibFieldDescription
 {
     BinderClassID classID;
     PTR_CSTR name;
 };
 
-class MscorlibBinder
+class CoreLibBinder
 {
   public:
 #ifdef DACCESS_COMPILE
@@ -134,7 +134,7 @@ class MscorlibBinder
     //
     // Retrieve structures from ID.
     //
-    // Note that none of the MscorlibBinder methods trigger static
+    // Note that none of the CoreLibBinder methods trigger static
     // constructors. The JITed code takes care of triggering them.
     //
     static PTR_MethodTable GetClass(BinderClassID id);
@@ -189,24 +189,24 @@ class MscorlibBinder
     static MethodTable *GetException(RuntimeExceptionKind kind)
     {
         WRAPPER_NO_CONTRACT;
-        _ASSERTE(kind <= kLastExceptionInMscorlib);  // Not supported for exceptions defined outside mscorlib.
-        BinderClassID id = (BinderClassID) (kind + CLASS__MSCORLIB_COUNT);
+        _ASSERTE(kind < kLastException);
+        BinderClassID id = (BinderClassID) (kind + CLASS__CORELIB_COUNT);
         return GetClass(id);
     }
 
     static BOOL IsException(MethodTable *pMT, RuntimeExceptionKind kind)
     {
         WRAPPER_NO_CONTRACT;
-        _ASSERTE(kind <= kLastExceptionInMscorlib);  // Not supported for exceptions defined outside mscorlib.
-        BinderClassID id = (BinderClassID) (kind + CLASS__MSCORLIB_COUNT);
+        _ASSERTE(kind < kLastException);
+        BinderClassID id = (BinderClassID) (kind + CLASS__CORELIB_COUNT);
         return dac_cast<TADDR>(GetClassIfExist(id)) == dac_cast<TADDR>(pMT);
     }
 
     static LPCUTF8 GetExceptionName(RuntimeExceptionKind kind)
     {
         WRAPPER_NO_CONTRACT;
-        _ASSERTE(kind <= kLastExceptionInMscorlib);  // Not supported for exceptions defined outside mscorlib.
-        BinderClassID id = (BinderClassID) (kind + CLASS__MSCORLIB_COUNT);
+        _ASSERTE(kind < kLastException);
+        BinderClassID id = (BinderClassID) (kind + CLASS__CORELIB_COUNT);
         return GetClassName(id);
     }
 
@@ -281,9 +281,9 @@ class MscorlibBinder
     const BYTE* ConvertSignature(LPHARDCODEDMETASIG pHardcodedSig, const BYTE* pSig);
 
     void SetDescriptions(Module * pModule,
-        const MscorlibClassDescription * pClassDescriptions, USHORT nClasses,
-        const MscorlibMethodDescription * pMethodDescriptions, USHORT nMethods,
-        const MscorlibFieldDescription * pFieldDescriptions, USHORT nFields);
+        const CoreLibClassDescription * pClassDescriptions, USHORT nClasses,
+        const CoreLibMethodDescription * pMethodDescriptions, USHORT nMethods,
+        const CoreLibFieldDescription * pFieldDescriptions, USHORT nFields);
 
     void AllocateTables();
 
@@ -298,9 +298,9 @@ class MscorlibBinder
     DPTR(PTR_FieldDesc) m_pFields;
 
     // This is necessary to avoid embeding copy of the descriptions into mscordacwks
-    DPTR(const MscorlibClassDescription) m_classDescriptions;
-    DPTR(const MscorlibMethodDescription) m_methodDescriptions;
-    DPTR(const MscorlibFieldDescription) m_fieldDescriptions;
+    DPTR(const CoreLibClassDescription) m_classDescriptions;
+    DPTR(const CoreLibMethodDescription) m_methodDescriptions;
+    DPTR(const CoreLibFieldDescription) m_fieldDescriptions;
 
     USHORT m_cClasses;
     USHORT m_cMethods;
@@ -330,9 +330,9 @@ class MscorlibBinder
 // Global bound modules:
 //
 
-GVAL_DECL(MscorlibBinder, g_Mscorlib);
+GVAL_DECL(CoreLibBinder, g_CoreLib);
 
-FORCEINLINE PTR_MethodTable MscorlibBinder::GetClass(BinderClassID id)
+FORCEINLINE PTR_MethodTable CoreLibBinder::GetClass(BinderClassID id)
 {
     CONTRACTL
     {
@@ -341,21 +341,21 @@ FORCEINLINE PTR_MethodTable MscorlibBinder::GetClass(BinderClassID id)
         INJECT_FAULT(ThrowOutOfMemory());
 
         PRECONDITION(id != CLASS__NIL);
-        PRECONDITION((&g_Mscorlib)->m_cClasses > 0);  // Make sure mscorlib has been loaded.
-        PRECONDITION(id <= (&g_Mscorlib)->m_cClasses);
+        PRECONDITION((&g_CoreLib)->m_cClasses > 0);  // Make sure CoreLib has been loaded.
+        PRECONDITION(id <= (&g_CoreLib)->m_cClasses);
     }
     CONTRACTL_END;
 
     // Force a GC here under stress because type loading could trigger GC nondeterminsticly
     INDEBUG(TriggerGCUnderStress());
 
-    PTR_MethodTable pMT = VolatileLoad(&((&g_Mscorlib)->m_pClasses[id]));
+    PTR_MethodTable pMT = VolatileLoad(&((&g_CoreLib)->m_pClasses[id]));
     if (pMT == NULL)
         return LookupClass(id);
     return pMT;
 }
 
-FORCEINLINE MethodDesc * MscorlibBinder::GetMethod(BinderMethodID id)
+FORCEINLINE MethodDesc * CoreLibBinder::GetMethod(BinderMethodID id)
 {
     CONTRACTL
     {
@@ -364,20 +364,20 @@ FORCEINLINE MethodDesc * MscorlibBinder::GetMethod(BinderMethodID id)
         INJECT_FAULT(ThrowOutOfMemory());
 
         PRECONDITION(id != METHOD__NIL);
-        PRECONDITION(id <= (&g_Mscorlib)->m_cMethods);
+        PRECONDITION(id <= (&g_CoreLib)->m_cMethods);
     }
     CONTRACTL_END;
 
     // Force a GC here under stress because type loading could trigger GC nondeterminsticly
     INDEBUG(TriggerGCUnderStress());
 
-    MethodDesc * pMD = VolatileLoad(&((&g_Mscorlib)->m_pMethods[id]));
+    MethodDesc * pMD = VolatileLoad(&((&g_CoreLib)->m_pMethods[id]));
     if (pMD == NULL)
         return LookupMethod(id);
     return pMD;
 }
 
-FORCEINLINE FieldDesc * MscorlibBinder::GetField(BinderFieldID id)
+FORCEINLINE FieldDesc * CoreLibBinder::GetField(BinderFieldID id)
 {
     CONTRACTL
     {
@@ -386,44 +386,44 @@ FORCEINLINE FieldDesc * MscorlibBinder::GetField(BinderFieldID id)
         INJECT_FAULT(ThrowOutOfMemory());
 
         PRECONDITION(id != FIELD__NIL);
-        PRECONDITION(id <= (&g_Mscorlib)->m_cFields);
+        PRECONDITION(id <= (&g_CoreLib)->m_cFields);
     }
     CONTRACTL_END;
 
     // Force a GC here under stress because type loading could trigger GC nondeterminsticly
     INDEBUG(TriggerGCUnderStress());
 
-    FieldDesc * pFD = VolatileLoad(&((&g_Mscorlib)->m_pFields[id]));
+    FieldDesc * pFD = VolatileLoad(&((&g_CoreLib)->m_pFields[id]));
     if (pFD == NULL)
         return LookupField(id);
     return pFD;
 }
 
-FORCEINLINE PTR_MethodTable MscorlibBinder::GetExistingClass(BinderClassID id)
+FORCEINLINE PTR_MethodTable CoreLibBinder::GetExistingClass(BinderClassID id)
 {
     LIMITED_METHOD_DAC_CONTRACT;
-    PTR_MethodTable pMT = (&g_Mscorlib)->m_pClasses[id];
+    PTR_MethodTable pMT = (&g_CoreLib)->m_pClasses[id];
     _ASSERTE(pMT != NULL);
     return pMT;
 }
 
-FORCEINLINE MethodDesc * MscorlibBinder::GetExistingMethod(BinderMethodID id)
+FORCEINLINE MethodDesc * CoreLibBinder::GetExistingMethod(BinderMethodID id)
 {
     LIMITED_METHOD_DAC_CONTRACT;
-    MethodDesc * pMD = (&g_Mscorlib)->m_pMethods[id];
+    MethodDesc * pMD = (&g_CoreLib)->m_pMethods[id];
     _ASSERTE(pMD != NULL);
     return pMD;
 }
 
-FORCEINLINE FieldDesc * MscorlibBinder::GetExistingField(BinderFieldID id)
+FORCEINLINE FieldDesc * CoreLibBinder::GetExistingField(BinderFieldID id)
 {
     LIMITED_METHOD_DAC_CONTRACT;
-    FieldDesc * pFD = (&g_Mscorlib)->m_pFields[id];
+    FieldDesc * pFD = (&g_CoreLib)->m_pFields[id];
     _ASSERTE(pFD != NULL);
     return pFD;
 }
 
-FORCEINLINE PTR_MethodTable MscorlibBinder::GetClassIfExist(BinderClassID id)
+FORCEINLINE PTR_MethodTable CoreLibBinder::GetClassIfExist(BinderClassID id)
 {
     CONTRACTL
     {
@@ -433,68 +433,68 @@ FORCEINLINE PTR_MethodTable MscorlibBinder::GetClassIfExist(BinderClassID id)
         MODE_ANY;
 
         PRECONDITION(id != CLASS__NIL);
-        PRECONDITION(id <= (&g_Mscorlib)->m_cClasses);
+        PRECONDITION(id <= (&g_CoreLib)->m_cClasses);
     }
     CONTRACTL_END;
 
-    PTR_MethodTable pMT = VolatileLoad(&((&g_Mscorlib)->m_pClasses[id]));
+    PTR_MethodTable pMT = VolatileLoad(&((&g_CoreLib)->m_pClasses[id]));
     if (pMT == NULL)
         return LookupClassIfExist(id);
     return pMT;
 }
 
 
-FORCEINLINE PTR_Module MscorlibBinder::GetModule()
+FORCEINLINE PTR_Module CoreLibBinder::GetModule()
 {
     LIMITED_METHOD_DAC_CONTRACT;
-    PTR_Module pModule = (&g_Mscorlib)->m_pModule;
+    PTR_Module pModule = (&g_CoreLib)->m_pModule;
     _ASSERTE(pModule != NULL);
     return pModule;
 }
 
-FORCEINLINE LPCUTF8 MscorlibBinder::GetClassNameSpace(BinderClassID id)
+FORCEINLINE LPCUTF8 CoreLibBinder::GetClassNameSpace(BinderClassID id)
 {
     LIMITED_METHOD_CONTRACT;
 
     _ASSERTE(id != CLASS__NIL);
-    _ASSERTE(id <= (&g_Mscorlib)->m_cClasses);
-    return (&g_Mscorlib)->m_classDescriptions[id].nameSpace;
+    _ASSERTE(id <= (&g_CoreLib)->m_cClasses);
+    return (&g_CoreLib)->m_classDescriptions[id].nameSpace;
 }
 
-FORCEINLINE LPCUTF8 MscorlibBinder::GetClassName(BinderClassID id)
+FORCEINLINE LPCUTF8 CoreLibBinder::GetClassName(BinderClassID id)
 {
     LIMITED_METHOD_CONTRACT;
 
     _ASSERTE(id != CLASS__NIL);
-    _ASSERTE(id <= (&g_Mscorlib)->m_cClasses);
-    return (&g_Mscorlib)->m_classDescriptions[id].name;
+    _ASSERTE(id <= (&g_CoreLib)->m_cClasses);
+    return (&g_CoreLib)->m_classDescriptions[id].name;
 }
 
-FORCEINLINE LPCUTF8 MscorlibBinder::GetMethodName(BinderMethodID id)
+FORCEINLINE LPCUTF8 CoreLibBinder::GetMethodName(BinderMethodID id)
 {
     LIMITED_METHOD_CONTRACT;
 
     _ASSERTE(id != METHOD__NIL);
-    _ASSERTE(id <= (&g_Mscorlib)->m_cMethods);
-    return (&g_Mscorlib)->m_methodDescriptions[id-1].name;
+    _ASSERTE(id <= (&g_CoreLib)->m_cMethods);
+    return (&g_CoreLib)->m_methodDescriptions[id-1].name;
 }
 
-FORCEINLINE LPHARDCODEDMETASIG MscorlibBinder::GetMethodSig(BinderMethodID id)
+FORCEINLINE LPHARDCODEDMETASIG CoreLibBinder::GetMethodSig(BinderMethodID id)
 {
     LIMITED_METHOD_CONTRACT;
 
     _ASSERTE(id != METHOD__NIL);
-    _ASSERTE(id <= (&g_Mscorlib)->m_cMethods);
-    return (&g_Mscorlib)->m_methodDescriptions[id-1].sig;
+    _ASSERTE(id <= (&g_CoreLib)->m_cMethods);
+    return (&g_CoreLib)->m_methodDescriptions[id-1].sig;
 }
 
-FORCEINLINE LPCUTF8 MscorlibBinder::GetFieldName(BinderFieldID id)
+FORCEINLINE LPCUTF8 CoreLibBinder::GetFieldName(BinderFieldID id)
 {
     LIMITED_METHOD_CONTRACT;
 
     _ASSERTE(id != FIELD__NIL);
-    _ASSERTE(id <= (&g_Mscorlib)->m_cFields);
-    return (&g_Mscorlib)->m_fieldDescriptions[id-1].name;
+    _ASSERTE(id <= (&g_CoreLib)->m_cFields);
+    return (&g_CoreLib)->m_fieldDescriptions[id-1].name;
 }
 
 #endif // _BINDERMODULE_H_
diff --git a/src/coreclr/src/vm/callcounting.cpp b/src/coreclr/src/vm/callcounting.cpp
index aadb400295cda8..8c3678bfd8536d 100644
--- a/src/coreclr/src/vm/callcounting.cpp
+++ b/src/coreclr/src/vm/callcounting.cpp
@@ -474,7 +474,16 @@ void CallCountingManager::DisableCallCounting(NativeCodeVersion codeVersion)
 
     CodeVersionManager::LockHolder codeVersioningLockHolder;
 
-    _ASSERTE(m_callCountingInfoByCodeVersionHash.Lookup(codeVersion) == nullptr);
+    CallCountingInfo *callCountingInfo = m_callCountingInfoByCodeVersionHash.Lookup(codeVersion);
+    if (callCountingInfo != nullptr)
+    {
+        // Call counting may already have been disabled due to the possibility of concurrent or reentering JIT of the same
+        // native code version of a method. The call counting info is created with call counting enabled or disabled and it
+        // cannot be changed thereafter for consistency in dependents of the info.
+        _ASSERTE(callCountingInfo->GetStage() == CallCountingInfo::Stage::Disabled);
+        return;
+    }
+
     NewHolder<CallCountingInfo> callCountingInfoHolder = CallCountingInfo::CreateWithCallCountingDisabled(codeVersion);
     m_callCountingInfoByCodeVersionHash.Add(callCountingInfoHolder);
     callCountingInfoHolder.SuppressRelease();
@@ -815,8 +824,7 @@ void CallCountingManager::CompleteCallCounting()
     {
         CodeVersionManager *codeVersionManager = appDomain->GetCodeVersionManager();
 
-        MethodDescBackpatchInfoTracker::PollForDebuggerSuspension();
-        MethodDescBackpatchInfoTracker::ConditionalLockHolder slotBackpatchLockHolder;
+        MethodDescBackpatchInfoTracker::ConditionalLockHolderForGCCoop slotBackpatchLockHolder;
 
         // Backpatching entry point slots requires cooperative GC mode, see
         // MethodDescBackpatchInfoTracker::Backpatch_Locked(). The code version manager's table lock is an unsafe lock that
@@ -947,8 +955,7 @@ void CallCountingManager::StopAndDeleteAllCallCountingStubs()
     TieredCompilationManager *tieredCompilationManager = GetAppDomain()->GetTieredCompilationManager();
     bool scheduleTieringBackgroundWork = false;
     {
-        MethodDescBackpatchInfoTracker::PollForDebuggerSuspension();
-        MethodDescBackpatchInfoTracker::ConditionalLockHolder slotBackpatchLockHolder;
+        MethodDescBackpatchInfoTracker::ConditionalLockHolderForGCCoop slotBackpatchLockHolder;
 
         ThreadSuspend::SuspendEE(ThreadSuspend::SUSPEND_OTHER);
         struct AutoRestartEE
diff --git a/src/coreclr/src/vm/callhelpers.cpp b/src/coreclr/src/vm/callhelpers.cpp
index 25e2cc44385e01..910cc060f74ae2 100644
--- a/src/coreclr/src/vm/callhelpers.cpp
+++ b/src/coreclr/src/vm/callhelpers.cpp
@@ -285,11 +285,11 @@ void MethodDescCallSite::CallTargetWorker(const ARG_SLOT *pArguments, ARG_SLOT *
 
     _ASSERTE(!NingenEnabled() && "You cannot invoke managed code inside the ngen compilation process.");
 
-    // If we're invoking an mscorlib method, lift the restriction on type load limits. Calls into mscorlib are
+    // If we're invoking an CoreLib method, lift the restriction on type load limits. Calls into CoreLib are
     // typically calls into specific and controlled helper methods for security checks and other linktime tasks.
     //
     // @todo: In an ideal world, we would require each of those sites to do the override rather than disabling
-    // the assert broadly here. However, by limiting the override to mscorlib methods, we should still be able
+    // the assert broadly here. However, by limiting the override to CoreLib methods, we should still be able
     // to effectively enforce the more general rule about loader recursion.
     MAYBE_OVERRIDE_TYPE_LOAD_LEVEL_LIMIT(CLASS_LOADED, m_pMD->GetModule()->IsSystem());
 
diff --git a/src/coreclr/src/vm/callhelpers.h b/src/coreclr/src/vm/callhelpers.h
index a2503f15bb10a2..4640413d2889ce 100644
--- a/src/coreclr/src/vm/callhelpers.h
+++ b/src/coreclr/src/vm/callhelpers.h
@@ -154,12 +154,12 @@ class MethodDescCallSite
 #endif
 
 public:
-    // Used to avoid touching metadata for mscorlib methods.
+    // Used to avoid touching metadata for CoreLib methods.
     // instance methods must pass in the 'this' object
     // static methods must pass null
     MethodDescCallSite(BinderMethodID id, OBJECTREF* porProtectedThis = NULL) :
         m_pMD(
-            MscorlibBinder::GetMethod(id)
+            CoreLibBinder::GetMethod(id)
             ),
         m_methodSig(id),
         m_argIt(&m_methodSig)
@@ -174,12 +174,12 @@ class MethodDescCallSite
         DefaultInit(porProtectedThis);
     }
 
-    // Used to avoid touching metadata for mscorlib methods.
+    // Used to avoid touching metadata for CoreLib methods.
     // instance methods must pass in the 'this' object
     // static methods must pass null
     MethodDescCallSite(BinderMethodID id, OBJECTHANDLE hThis) :
         m_pMD(
-            MscorlibBinder::GetMethod(id)
+            CoreLibBinder::GetMethod(id)
             ),
         m_methodSig(id),
         m_argIt(&m_methodSig)
@@ -558,14 +558,14 @@ enum DispatchCallSimpleFlags
         PCODE __pSlot = VolatileLoad(&s_pAddr##id);         \
         if ( __pSlot == NULL )                              \
         {                                                   \
-            MethodDesc *pMeth = MscorlibBinder::GetMethod(id);   \
+            MethodDesc *pMeth = CoreLibBinder::GetMethod(id);   \
             _ASSERTE(pMeth);                                \
             __pSlot = pMeth->GetMultiCallableAddrOfCode();  \
             VolatileStore(&s_pAddr##id, __pSlot);           \
         }
 
 #define PREPARE_VIRTUAL_CALLSITE(id, objref)                \
-        MethodDesc *__pMeth = MscorlibBinder::GetMethod(id);     \
+        MethodDesc *__pMeth = CoreLibBinder::GetMethod(id);     \
         PCODE __pSlot = __pMeth->GetCallTarget(&objref);
 
 #define PREPARE_VIRTUAL_CALLSITE_USING_METHODDESC(pMD, objref)                \
@@ -590,7 +590,7 @@ enum DispatchCallSimpleFlags
         WORD __slot = VolatileLoad(&s_slot##id);                                 \
         if (__slot == MethodTable::NO_SLOT)                                      \
         {                                                                        \
-            MethodDesc *pMeth = MscorlibBinder::GetMethod(id);                        \
+            MethodDesc *pMeth = CoreLibBinder::GetMethod(id);                        \
             _ASSERTE(pMeth);                                                     \
             __slot = pMeth->GetSlot();                                           \
             VolatileStore(&s_slot##id, __slot);                                  \
diff --git a/src/coreclr/src/vm/callsiteinspect.cpp b/src/coreclr/src/vm/callsiteinspect.cpp
index eeb9678e9655a4..3773580bd0a5c6 100644
--- a/src/coreclr/src/vm/callsiteinspect.cpp
+++ b/src/coreclr/src/vm/callsiteinspect.cpp
@@ -53,7 +53,7 @@ namespace
                 if (ELEMENT_TYPE_PTR == eType)
                     COMPlusThrow(kNotSupportedException);
 
-                MethodTable *pMT = MscorlibBinder::GetElementType(eType);
+                MethodTable *pMT = CoreLibBinder::GetElementType(eType);
 
                 OBJECTREF pObj = pMT->Allocate();
                 if (fIsByRef)
@@ -337,7 +337,7 @@ void CallsiteInspect::GetCallsiteArgs(
 
         // Allocate all needed arrays for callsite arg details
         gc.Args = (PTRARRAYREF)AllocateObjectArray(numArgs, g_pObjectClass);
-        MethodTable *typeMT = MscorlibBinder::GetClass(CLASS__TYPE);
+        MethodTable *typeMT = CoreLibBinder::GetClass(CLASS__TYPE);
         gc.ArgsTypes = (PTRARRAYREF)AllocateObjectArray(numArgs, typeMT);
         gc.ArgsIsByRef = (BOOLARRAYREF)AllocatePrimitiveArray(ELEMENT_TYPE_BOOLEAN, numArgs);
 
diff --git a/src/coreclr/src/vm/castcache.cpp b/src/coreclr/src/vm/castcache.cpp
index b4a20162675255..6613c6fe5c9b31 100644
--- a/src/coreclr/src/vm/castcache.cpp
+++ b/src/coreclr/src/vm/castcache.cpp
@@ -124,7 +124,7 @@ void CastCache::Initialize()
     }
     CONTRACTL_END;
 
-    FieldDesc* pTableField = MscorlibBinder::GetField(FIELD__CASTHELPERS__TABLE);
+    FieldDesc* pTableField = CoreLibBinder::GetField(FIELD__CASTHELPERS__TABLE);
 
     GCX_COOP();
     s_pTableRef = (BASEARRAYREF*)pTableField->GetCurrentStaticAddress();
diff --git a/src/coreclr/src/vm/ceeload.cpp b/src/coreclr/src/vm/ceeload.cpp
index 75d1f0bd0c2dff..663c5a46ad2ff7 100644
--- a/src/coreclr/src/vm/ceeload.cpp
+++ b/src/coreclr/src/vm/ceeload.cpp
@@ -481,7 +481,7 @@ void Module::InitializeNativeImage(AllocMemTracker* pamTracker)
     if (GCStress<cfg_instr_ngen>::IsEnabled())
     {
         // Setting up gc coverage requires the base system classes
-        //  to be initialized. So we must defer this for mscorlib.
+        //  to be initialized. So we must defer this for CoreLib.
         if(!IsSystem())
         {
             SetupGcCoverageForNativeImage(this);
@@ -1512,11 +1512,11 @@ static bool IsLikelyDependencyOf(Module * pModule, Module * pOtherModule)
         if (!pOtherModule->IsLowLevelSystemAssemblyByName())
             return true;
 
-        // Every module depends upon mscorlib
+        // Every module depends upon CoreLib
         if (pModule->IsSystem())
             return true;
 
-        // mscorlib does not depend upon any other module
+        // CoreLib does not depend upon any other module
         if (pOtherModule->IsSystem())
             return false;
     }
@@ -1526,7 +1526,7 @@ static bool IsLikelyDependencyOf(Module * pModule, Module * pOtherModule)
             return false;
     }
 
-    // At this point neither pModule or pOtherModule is mscorlib
+    // At this point neither pModule or pOtherModule is CoreLib
 
 #ifndef DACCESS_COMPILE
     //
@@ -1591,8 +1591,8 @@ PTR_Module Module::ComputePreferredZapModuleHelper(
             RETURN dac_cast<PTR_Module>(pOpenModule);
     }
 
-    // The initial value of pCurrentPZM is the pDefinitionModule or mscorlib
-    Module* pCurrentPZM = (pDefinitionModule != NULL) ? pDefinitionModule : MscorlibBinder::GetModule();
+    // The initial value of pCurrentPZM is the pDefinitionModule or CoreLib
+    Module* pCurrentPZM = (pDefinitionModule != NULL) ? pDefinitionModule : CoreLibBinder::GetModule();
     bool preferredZapModuleBasedOnValueType = false;
 
     for (DWORD i = 0; i < totalArgs; i++)
@@ -1626,7 +1626,7 @@ PTR_Module Module::ComputePreferredZapModuleHelper(
                 //     pCurrentPZM is a dependency of pParamPZM
                 // and pParamPZM is not a dependency of pCurrentPZM
                 //
-                // note that the second condition is alway true when pCurrentPZM is mscorlib
+                // note that the second condition is alway true when pCurrentPZM is CoreLib
                 //
                 if (!IsLikelyDependencyOf(pParamPZM, pCurrentPZM))
                 {
@@ -2691,7 +2691,7 @@ ModuleIndex Module::AllocateModuleIndex()
 
     // For various reasons, the IDs issued by the IdDispenser start at 1.
     // Domain neutral module IDs have historically started at 0, and we
-    // have always assigned ID 0 to mscorlib. Thus, to make it so that
+    // have always assigned ID 0 to CoreLib. Thus, to make it so that
     // domain neutral module IDs start at 0, we will subtract 1 from the
     // ID that we got back from the ID dispenser.
     ModuleIndex index((SIZE_T)(val-1));
@@ -2861,7 +2861,7 @@ void Module::SetDomainFile(DomainFile *pDomainFile)
     m_ModuleID->SetDomainFile(pDomainFile);
 
     // Allocate static handles now.
-    // NOTE: Bootstrapping issue with mscorlib - we will manually allocate later
+    // NOTE: Bootstrapping issue with CoreLib - we will manually allocate later
     // If the assembly is collectible, we don't initialize static handles for them
     // as it is currently initialized through the DomainLocalModule::PopulateClass in MethodTable::CheckRunClassInitThrowing
     // (If we don't do this, it would allocate here unused regular static handles that will be overridden later)
@@ -4207,10 +4207,10 @@ OBJECTHANDLE Module::ResolveStringRef(DWORD token, BaseDomain *pDomain, bool bNe
         }
         /* Unfortunately, this assert won't work in some cases of generics, consider the following scenario:
 
-            1) Generic type in mscorlib.
+            1) Generic type in CoreLib.
             2) Instantiation of generic (1) (via valuetype) in another module
             3) other module now holds a copy of the code of the generic for that particular instantiation
-               however, it is resolving the string literals against mscorlib, which breaks the invariant
+               however, it is resolving the string literals against CoreLib, which breaks the invariant
                this assert was based on (no string fixups against other modules). In fact, with NoStringInterning,
                our behavior is not very intuitive.
         */
@@ -4758,7 +4758,7 @@ DomainAssembly * Module::LoadAssembly(mdAssemblyRef kAssemblyRef)
     if (pDomainAssembly != NULL)
     {
         _ASSERTE(
-            pDomainAssembly->IsSystem() ||                  // GetAssemblyIfLoaded will not find mscorlib (see AppDomain::FindCachedFile)
+            pDomainAssembly->IsSystem() ||                  // GetAssemblyIfLoaded will not find CoreLib (see AppDomain::FindCachedFile)
             !pDomainAssembly->IsLoaded() ||                 // GetAssemblyIfLoaded will not find not-yet-loaded assemblies
             GetAssemblyIfLoaded(kAssemblyRef, NULL, FALSE, pDomainAssembly->GetFile()->GetHostAssembly()) != NULL);     // GetAssemblyIfLoaded should find all remaining cases
 
diff --git a/src/coreclr/src/vm/ceeload.h b/src/coreclr/src/vm/ceeload.h
index 27c4c8f485ff78..b963624fb56619 100644
--- a/src/coreclr/src/vm/ceeload.h
+++ b/src/coreclr/src/vm/ceeload.h
@@ -157,7 +157,7 @@ typedef DPTR(struct LookupMapBase) PTR_LookupMapBase;
 //
 // This still leaves the problem of runtime lookup performance. Touches to the cold section of a LookupMap
 // aren't all that critical (after all the data is meant to be cold), but looking up the last entry of a map
-// with 22 thousand entries (roughly what the MethodDefToDesc map in mscorlib is sized at at the time of
+// with 22 thousand entries (roughly what the MethodDefToDesc map in CoreLib is sized at at the time of
 // writing) is still likely to so inefficient as to be noticeable. Remember that the issue is that we have to
 // decode all predecessor entries in order to compute the value of a given entry in the table.
 //
@@ -170,7 +170,7 @@ typedef DPTR(struct LookupMapBase) PTR_LookupMapBase;
 //
 // The main areas in which this algorithm can be tuned are the number of bits used as an index into the
 // encoding lengths table (kLookupMapLengthBits) and the frequency with which entries are bookmarked in the
-// index (kLookupMapIndexStride). The current values have been set based on looking at models of mscorlib,
+// index (kLookupMapIndexStride). The current values have been set based on looking at models of CoreLib,
 // PresentationCore and PresentationFramework built from the actual ridmap data in their ngen images and
 // methodically trying different values in order to maximize compression or balance size versus likely runtime
 // performance. An alternative strategy was considered using direct (non-length prefix) encoding of the
@@ -1597,8 +1597,8 @@ class Module
     PTR_EEClassHashTable    m_pAvailableClassesCaseIns;
 
     // Pointer to binder, if we have one
-    friend class MscorlibBinder;
-    PTR_MscorlibBinder      m_pBinder;
+    friend class CoreLibBinder;
+    PTR_CoreLibBinder      m_pBinder;
 
 public:
     BOOL IsCollectible()
diff --git a/src/coreclr/src/vm/ceemain.cpp b/src/coreclr/src/vm/ceemain.cpp
index 5c763f86039db1..962ba0d2298ac4 100644
--- a/src/coreclr/src/vm/ceemain.cpp
+++ b/src/coreclr/src/vm/ceemain.cpp
@@ -240,10 +240,14 @@ extern "C" HRESULT __cdecl CorDBGetInterface(DebugInterface** rcInterface);
 #endif // !CROSSGEN_COMPILE
 
 // g_coreclr_embedded indicates that coreclr is linked directly into the program
+// g_hostpolicy_embedded indicates that the hostpolicy library is linked directly into the executable
+// Note: that it can happen that the hostpolicy is embedded but coreclr isn't (on Windows singlefilehost is built that way)
 #ifdef CORECLR_EMBEDDED
 bool g_coreclr_embedded = true;
+bool g_hostpolicy_embedded = true; // We always embed hostpolicy if coreclr is also embedded
 #else
 bool g_coreclr_embedded = false;
+bool g_hostpolicy_embedded = false; // In this case the value may come from a runtime property and may change
 #endif
 
 // Remember how the last startup of EE went.
@@ -283,8 +287,8 @@ HRESULT EnsureEEStarted()
 
     HRESULT hr = E_FAIL;
 
-    // On non x86 platforms, when we load mscorlib.dll during EEStartup, we will
-    // re-enter _CorDllMain with a DLL_PROCESS_ATTACH for mscorlib.dll. We are
+    // On non x86 platforms, when we load CoreLib during EEStartup, we will
+    // re-enter _CorDllMain with a DLL_PROCESS_ATTACH for CoreLib. We are
     // far enough in startup that this is allowed, however we don't want to
     // re-start the startup code so we need to check to see if startup has
     // been initiated or completed before we call EEStartup.
@@ -677,6 +681,17 @@ void EEStartupHelper()
         PAL_SetShutdownCallback(EESocketCleanupHelper);
 #endif // TARGET_UNIX
 
+#ifdef STRESS_LOG
+        if (REGUTIL::GetConfigDWORD_DontUse_(CLRConfig::UNSUPPORTED_StressLog, g_pConfig->StressLog ()) != 0) {
+            unsigned facilities = REGUTIL::GetConfigDWORD_DontUse_(CLRConfig::INTERNAL_LogFacility, LF_ALL);
+            unsigned level = REGUTIL::GetConfigDWORD_DontUse_(CLRConfig::EXTERNAL_LogLevel, LL_INFO1000);
+            unsigned bytesPerThread = REGUTIL::GetConfigDWORD_DontUse_(CLRConfig::UNSUPPORTED_StressLogSize, STRESSLOG_CHUNK_SIZE * 4);
+            unsigned totalBytes = REGUTIL::GetConfigDWORD_DontUse_(CLRConfig::UNSUPPORTED_TotalStressLogSize, STRESSLOG_CHUNK_SIZE * 1024);
+            StressLog::Initialize(facilities, level, bytesPerThread, totalBytes, GetModuleInst());
+            g_pStressLog = &StressLog::theLog;
+        }
+#endif
+
 #ifdef FEATURE_PERFTRACING
         DiagnosticServer::Initialize();
         DiagnosticServer::PauseForDiagnosticsMonitor();
@@ -702,16 +717,6 @@ void EEStartupHelper()
 #endif // CROSSGEN_COMPILE
 
 
-#ifdef STRESS_LOG
-        if (REGUTIL::GetConfigDWORD_DontUse_(CLRConfig::UNSUPPORTED_StressLog, g_pConfig->StressLog ()) != 0) {
-            unsigned facilities = REGUTIL::GetConfigDWORD_DontUse_(CLRConfig::INTERNAL_LogFacility, LF_ALL);
-            unsigned level = REGUTIL::GetConfigDWORD_DontUse_(CLRConfig::EXTERNAL_LogLevel, LL_INFO1000);
-            unsigned bytesPerThread = REGUTIL::GetConfigDWORD_DontUse_(CLRConfig::UNSUPPORTED_StressLogSize, STRESSLOG_CHUNK_SIZE * 4);
-            unsigned totalBytes = REGUTIL::GetConfigDWORD_DontUse_(CLRConfig::UNSUPPORTED_TotalStressLogSize, STRESSLOG_CHUNK_SIZE * 1024);
-            StressLog::Initialize(facilities, level, bytesPerThread, totalBytes, GetModuleInst());
-            g_pStressLog = &StressLog::theLog;
-        }
-#endif
 
 #ifdef LOGGING
         InitializeLogging();
@@ -823,7 +828,7 @@ void EEStartupHelper()
 
         AccessCheckOptions::Startup();
 
-        MscorlibBinder::Startup();
+        CoreLibBinder::Startup();
 
         Stub::Init();
         StubLinkerCPU::Init();
@@ -1029,8 +1034,8 @@ void EEStartupHelper()
             SystemDomain::SystemModule()->ExpandAll();
         }
 
-        // Perform mscorlib consistency check if requested
-        g_Mscorlib.CheckExtended();
+        // Perform CoreLib consistency check if requested
+        g_CoreLib.CheckExtended();
 
 #endif // _DEBUG
 
@@ -1106,7 +1111,7 @@ LONG FilterStartupException(PEXCEPTION_POINTERS p, PVOID pv)
 // EEStartup is responsible for all the one time intialization of the runtime.  Some of the highlights of
 // what it does include
 //     * Creates the default and shared, appdomains.
-//     * Loads mscorlib.dll and loads up the fundamental types (System.Object ...)
+//     * Loads System.Private.CoreLib and loads up the fundamental types (System.Object ...)
 //
 // see code:EEStartup#TableOfContents for more on the runtime in general.
 // see code:#EEShutdown for a analagous routine run during shutdown.
diff --git a/src/coreclr/src/vm/cgensys.h b/src/coreclr/src/vm/cgensys.h
index 53e21461304d4b..216729938ae143 100644
--- a/src/coreclr/src/vm/cgensys.h
+++ b/src/coreclr/src/vm/cgensys.h
@@ -95,21 +95,22 @@ inline void GetSpecificCpuInfo(CORINFO_CPU * cpuInfo)
 #endif // !TARGET_X86
 
 #if (defined(TARGET_X86) || defined(TARGET_AMD64)) && !defined(CROSSGEN_COMPILE)
-extern "C" DWORD __stdcall getcpuid(DWORD arg, unsigned char result[16]);
-extern "C" DWORD __stdcall getextcpuid(DWORD arg1, DWORD arg2, unsigned char result[16]);
+#ifdef TARGET_UNIX
+// MSVC directly defines intrinsics for __cpuid and __cpuidex matching the below signatures
+// We define matching signatures for use on Unix platforms.
+
+extern "C" void __stdcall __cpuid(int cpuInfo[4], int function_id);
+extern "C" void __stdcall __cpuidex(int cpuInfo[4], int function_id, int subFunction_id);
+#endif // TARGET_UNIX
 extern "C" DWORD __stdcall xmmYmmStateSupport();
 #endif
 
 inline bool TargetHasAVXSupport()
 {
 #if (defined(TARGET_X86) || defined(TARGET_AMD64)) && !defined(CROSSGEN_COMPILE)
-    unsigned char buffer[16];
-    // All x86/AMD64 targets support cpuid.
-    (void) getcpuid(1, buffer);
-    // getcpuid executes cpuid with eax set to its first argument, and ecx cleared.
-    // It returns the resulting eax, ebx, ecx and edx (in that order) in buffer[].
-    // The AVX feature is ECX bit 28.
-    return ((buffer[11] & 0x10) != 0);
+    int cpuInfo[4];
+    __cpuid(cpuInfo, 0x00000001);           // All x86/AMD64 targets support cpuid.
+    return ((cpuInfo[3] & (1 << 28)) != 0); // The AVX feature is ECX bit 28.
 #endif // (defined(TARGET_X86) || defined(TARGET_AMD64)) && !defined(CROSSGEN_COMPILE)
     return false;
 }
@@ -143,7 +144,7 @@ BOOL GetAnyThunkTarget (T_CONTEXT *pctx, TADDR *pTarget, TADDR *pTargetMethodDes
 
 //
 // ResetProcessorStateHolder saves/restores processor state around calls to
-// mscorlib during exception handling.
+// CoreLib during exception handling.
 //
 class ResetProcessorStateHolder
 {
diff --git a/src/coreclr/src/vm/class.cpp b/src/coreclr/src/vm/class.cpp
index 8e18a47059f9fa..d56cb02b68d265 100644
--- a/src/coreclr/src/vm/class.cpp
+++ b/src/coreclr/src/vm/class.cpp
@@ -1184,107 +1184,129 @@ void ClassLoader::ValidateMethodsWithCovariantReturnTypes(MethodTable* pMT)
         return;
 
     // Step 1: Validate compatibility of return types on overriding methods
-
-    for (WORD i = 0; i < pParentMT->GetNumVirtuals(); i++)
+    if (pMT->GetClass()->HasCovariantOverride() && (!pMT->GetModule()->IsReadyToRun() || !pMT->GetModule()->GetReadyToRunInfo()->SkipTypeValidation()))
     {
-        MethodDesc* pMD = pMT->GetMethodDescForSlot(i);
-        MethodDesc* pParentMD = pParentMT->GetMethodDescForSlot(i);
-
-        if (pMD == pParentMD)
-            continue;
+        for (WORD i = 0; i < pParentMT->GetNumVirtuals(); i++)
+        {
+            if (pMT->GetRestoredSlot(i) == pParentMT->GetRestoredSlot(i))
+            {
+                // The real check is that the MethodDesc's must not match, but a simple VTable check will
+                // work most of the time, and is far faster than the GetMethodDescForSlot method.
+                _ASSERTE(pMT->GetMethodDescForSlot(i) == pParentMT->GetMethodDescForSlot(i));
+                continue;
+            }
+            MethodDesc* pMD = pMT->GetMethodDescForSlot(i);
+            MethodDesc* pParentMD = pParentMT->GetMethodDescForSlot(i);
 
-        if (!pMD->RequiresCovariantReturnTypeChecking() && !pParentMD->RequiresCovariantReturnTypeChecking())
-            continue;
+            if (pMD == pParentMD)
+                continue;
 
-        // If the bit is not set on this method, but we reach here because it's been set on the method at the same slot on
-        // the base type, set the bit for the current method to ensure any future overriding method down the chain gets checked.
-        if (!pMD->RequiresCovariantReturnTypeChecking())
-            pMD->SetRequiresCovariantReturnTypeChecking();
+            if (!pMD->RequiresCovariantReturnTypeChecking() && !pParentMD->RequiresCovariantReturnTypeChecking())
+                continue;
 
-        // The context used to load the return type of the parent method has to use the generic method arguments
-        // of the overriding method, otherwise the type comparison below will not work correctly
-        SigTypeContext context1(pParentMD->GetClassInstantiation(), pMD->GetMethodInstantiation());
-        MetaSig methodSig1(pParentMD);
-        TypeHandle hType1 = methodSig1.GetReturnProps().GetTypeHandleThrowing(pParentMD->GetModule(), &context1, ClassLoader::LoadTypesFlag::LoadTypes, CLASS_LOAD_EXACTPARENTS);
+            // If the bit is not set on this method, but we reach here because it's been set on the method at the same slot on
+            // the base type, set the bit for the current method to ensure any future overriding method down the chain gets checked.
+            if (!pMD->RequiresCovariantReturnTypeChecking())
+                pMD->SetRequiresCovariantReturnTypeChecking();
 
-        SigTypeContext context2(pMD);
-        MetaSig methodSig2(pMD);
-        TypeHandle hType2 = methodSig2.GetReturnProps().GetTypeHandleThrowing(pMD->GetModule(), &context2, ClassLoader::LoadTypesFlag::LoadTypes, CLASS_LOAD_EXACTPARENTS);
+            // The context used to load the return type of the parent method has to use the generic method arguments
+            // of the overriding method, otherwise the type comparison below will not work correctly
+            SigTypeContext context1(pParentMD->GetClassInstantiation(), pMD->GetMethodInstantiation());
+            MetaSig methodSig1(pParentMD);
+            TypeHandle hType1 = methodSig1.GetReturnProps().GetTypeHandleThrowing(pParentMD->GetModule(), &context1, ClassLoader::LoadTypesFlag::LoadTypes, CLASS_LOAD_EXACTPARENTS);
 
-        if (!IsCompatibleWith(hType1, hType2))
-        {
-            SString strAssemblyName;
-            pMD->GetAssembly()->GetDisplayName(strAssemblyName);
+            SigTypeContext context2(pMD);
+            MetaSig methodSig2(pMD);
+            TypeHandle hType2 = methodSig2.GetReturnProps().GetTypeHandleThrowing(pMD->GetModule(), &context2, ClassLoader::LoadTypesFlag::LoadTypes, CLASS_LOAD_EXACTPARENTS);
 
-            SString strInvalidTypeName;
-            TypeString::AppendType(strInvalidTypeName, TypeHandle(pMD->GetMethodTable()));
+            if (!IsCompatibleWith(hType1, hType2))
+            {
+                SString strAssemblyName;
+                pMD->GetAssembly()->GetDisplayName(strAssemblyName);
 
-            SString strInvalidMethodName;
-            TypeString::AppendMethod(strInvalidMethodName, pMD, pMD->GetMethodInstantiation());
+                SString strInvalidTypeName;
+                TypeString::AppendType(strInvalidTypeName, TypeHandle(pMD->GetMethodTable()));
 
-            SString strParentMethodName;
-            TypeString::AppendMethod(strParentMethodName, pParentMD, pParentMD->GetMethodInstantiation());
+                SString strInvalidMethodName;
+                SString strParentMethodName;
+                {
+                    CONTRACT_VIOLATION(LoadsTypeViolation);
+                    TypeString::AppendMethod(strInvalidMethodName, pMD, pMD->GetMethodInstantiation());
+                    TypeString::AppendMethod(strParentMethodName, pParentMD, pParentMD->GetMethodInstantiation());
+                }
 
-            COMPlusThrow(
-                kTypeLoadException,
-                IDS_CLASSLOAD_MI_BADRETURNTYPE,
-                strInvalidMethodName,
-                strInvalidTypeName,
-                strAssemblyName,
-                strParentMethodName);
+                COMPlusThrow(
+                    kTypeLoadException,
+                    IDS_CLASSLOAD_MI_BADRETURNTYPE,
+                    strInvalidMethodName,
+                    strInvalidTypeName,
+                    strAssemblyName,
+                    strParentMethodName);
+            }
         }
     }
 
     // Step 2: propate overriding MethodImpls to applicable vtable slots if the declaring method has the attribute
 
-    MethodTable::MethodDataWrapper hMTData(MethodTable::GetMethodData(pMT, FALSE));
-
-    for (WORD i = 0; i < pParentMT->GetNumVirtuals(); i++)
+    if (pMT->GetClass()->HasVTableMethodImpl())
     {
-        MethodDesc* pMD = pMT->GetMethodDescForSlot(i);
-        MethodDesc* pParentMD = pParentMT->GetMethodDescForSlot(i);
-        if (pMD == pParentMD)
-            continue;
+        MethodTable::MethodDataWrapper hMTData(MethodTable::GetMethodData(pMT, FALSE));
 
-        // The attribute is only applicable to MethodImpls. For anything else, it will be treated as a no-op
-        if (!pMD->IsMethodImpl())
-            continue;
-
-        // Search if the attribute has been applied on this vtable slot, either by the current MethodImpl, or by a previous
-        // MethodImpl somewhere in the base type hierarchy.
-        bool foundAttribute = false;
-        MethodTable* pCurrentMT = pMT;
-        while (!foundAttribute && pCurrentMT != NULL && i < pCurrentMT->GetNumVirtuals())
+        for (WORD i = 0; i < pParentMT->GetNumVirtuals(); i++)
         {
-            MethodDesc* pCurrentMD = pCurrentMT->GetMethodDescForSlot(i);
+            if (pMT->GetRestoredSlot(i) == pParentMT->GetRestoredSlot(i))
+            {
+                // The real check is that the MethodDesc's must not match, but a simple VTable check will
+                // work most of the time, and is far faster than the GetMethodDescForSlot method.
+                _ASSERTE(pMT->GetMethodDescForSlot(i) == pParentMT->GetMethodDescForSlot(i));
+                continue;
+            }
+
+            MethodDesc* pMD = pMT->GetMethodDescForSlot(i);
+            MethodDesc* pParentMD = pParentMT->GetMethodDescForSlot(i);
+            if (pMD == pParentMD)
+                continue;
 
             // The attribute is only applicable to MethodImpls. For anything else, it will be treated as a no-op
-            if (pCurrentMD->IsMethodImpl())
+            if (!pMD->IsMethodImpl())
+                continue;
+
+            // Search if the attribute has been applied on this vtable slot, either by the current MethodImpl, or by a previous
+            // MethodImpl somewhere in the base type hierarchy.
+            bool foundAttribute = false;
+            MethodTable* pCurrentMT = pMT;
+            while (!foundAttribute && pCurrentMT != NULL && i < pCurrentMT->GetNumVirtuals())
             {
-                BYTE* pVal = NULL;
-                ULONG cbVal = 0;
-                if (pCurrentMD->GetCustomAttribute(WellKnownAttribute::PreserveBaseOverridesAttribute, (const void**)&pVal, &cbVal) == S_OK)
-                    foundAttribute = true;
-            }
+                MethodDesc* pCurrentMD = pCurrentMT->GetMethodDescForSlot(i);
 
-            pCurrentMT = pCurrentMT->GetParentMethodTable();
-        }
+                // The attribute is only applicable to MethodImpls. For anything else, it will be treated as a no-op
+                if (pCurrentMD->IsMethodImpl())
+                {
+                    BYTE* pVal = NULL;
+                    ULONG cbVal = 0;
+                    if (pCurrentMD->GetCustomAttribute(WellKnownAttribute::PreserveBaseOverridesAttribute, (const void**)&pVal, &cbVal) == S_OK)
+                        foundAttribute = true;
+                }
 
-        if (!foundAttribute)
-            continue;
+                pCurrentMT = pCurrentMT->GetParentMethodTable();
+            }
 
-        // Search for any vtable slot still pointing at the parent method, and update it with the current overriding method
-        for (WORD j = i; j < pParentMT->GetNumVirtuals(); j++)
-        {
-            MethodDesc* pCurrentMD = pMT->GetMethodDescForSlot(j);
-            if (pCurrentMD == pParentMD)
+            if (!foundAttribute)
+                continue;
+
+            // Search for any vtable slot still pointing at the parent method, and update it with the current overriding method
+            for (WORD j = i; j < pParentMT->GetNumVirtuals(); j++)
             {
-                // This is a vtable slot that needs to be updated to the new overriding method because of the
-                // presence of the attribute.
-                pMT->SetSlot(j, pMT->GetSlot(i));
-                _ASSERT(pMT->GetMethodDescForSlot(j) == pMD);
+                MethodDesc* pCurrentMD = pMT->GetMethodDescForSlot(j);
+                if (pCurrentMD == pParentMD)
+                {
+                    // This is a vtable slot that needs to be updated to the new overriding method because of the
+                    // presence of the attribute.
+                    pMT->SetSlot(j, pMT->GetSlot(i));
+                    _ASSERT(pMT->GetMethodDescForSlot(j) == pMD);
 
-                hMTData->UpdateImplMethodDesc(pMD, j);
+                    hMTData->UpdateImplMethodDesc(pMD, j);
+                }
             }
         }
     }
diff --git a/src/coreclr/src/vm/class.h b/src/coreclr/src/vm/class.h
index 98a59dbba18218..179a082199a31d 100644
--- a/src/coreclr/src/vm/class.h
+++ b/src/coreclr/src/vm/class.h
@@ -1158,6 +1158,30 @@ class EEClass // DO NOT CREATE A NEW EEClass USING NEW!
     }
 #endif // FEATURE_COMINTEROP
 
+    inline void SetHasVTableMethodImpl()
+    {
+        LIMITED_METHOD_CONTRACT;
+        m_VMFlags |= VMFLAG_VTABLEMETHODIMPL;
+    }
+
+    inline BOOL HasVTableMethodImpl()
+    {
+        LIMITED_METHOD_CONTRACT;
+        return (m_VMFlags & VMFLAG_VTABLEMETHODIMPL);
+    }
+
+    inline void SetHasCovariantOverride()
+    {
+        LIMITED_METHOD_CONTRACT;
+        m_VMFlags |= VMFLAG_COVARIANTOVERRIDE;
+    }
+
+    inline BOOL HasCovariantOverride()
+    {
+        LIMITED_METHOD_CONTRACT;
+        return (m_VMFlags & VMFLAG_COVARIANTOVERRIDE);
+    }
+
 #ifdef _DEBUG
     inline DWORD IsDestroyed()
     {
@@ -1691,8 +1715,8 @@ class EEClass // DO NOT CREATE A NEW EEClass USING NEW!
         VMFLAG_HASCOCLASSATTRIB                = 0x01000000,
         VMFLAG_COMEVENTITFMASK                 = 0x02000000, // class is a special COM event interface
 #endif // FEATURE_COMINTEROP
-        // unused                              = 0x04000000,
-        // unused                              = 0x08000000,
+        VMFLAG_VTABLEMETHODIMPL                = 0x04000000, // class uses MethodImpl to override virtual function defined on class
+        VMFLAG_COVARIANTOVERRIDE               = 0x08000000, // class has a covariant override
 
         // This one indicates that the fields of the valuetype are
         // not tightly packed and is used to check whether we can
diff --git a/src/coreclr/src/vm/classcompat.cpp b/src/coreclr/src/vm/classcompat.cpp
index aab4e63d5ccc13..4f00fbf9448142 100644
--- a/src/coreclr/src/vm/classcompat.cpp
+++ b/src/coreclr/src/vm/classcompat.cpp
@@ -3010,49 +3010,6 @@ VOID    MethodTableBuilder::AllocateMethodWorkingMemory()
             }
             bmtVT->pParentMethodTable = bmtParent->pParentMethodTable;
         }
-
-#if 0
-        // @<TODO>todo: Figure out the right way to override Equals for value
-        // types only.
-        //
-        // This is broken because
-        // (a) g_pObjectClass->FindMethod("Equals", &gsig_IM_Obj_RetBool); will return
-        //      the EqualsValue method
-        // (b) When mscorlib has been preloaded (and thus the munge already done
-        //      ahead of time), we cannot easily find both methods
-        //      to compute EqualsAddr & EqualsSlot
-        //
-        // For now, the Equals method has a runtime check to see if it's
-        // comparing value types.
-        //</TODO>
-
-        // If it is a value type, over ride a few of the base class methods.
-        if (IsValueClass())
-        {
-            static WORD EqualsSlot;
-
-            // If we haven't been through here yet, get some stuff from the Object class definition.
-            if (EqualsSlot == NULL)
-            {
-                // Get the slot of the Equals method.
-                MethodDesc *pEqualsMD = g_pObjectClass->FindMethod("Equals", &gsig_IM_Obj_RetBool);
-                THROW_BAD_FORMAT_MAYBE(pEqualsMD != NULL, 0, this);
-                EqualsSlot = pEqualsMD->GetSlot();
-
-                // Get the address of the EqualsValue method.
-                MethodDesc *pEqualsValueMD = g_pObjectClass->FindMethod("EqualsValue", &gsig_IM_Obj_RetBool);
-                THROW_BAD_FORMAT_MAYBE(pEqualsValueMD != NULL, 0, this);
-
-                // Patch the EqualsValue method desc in a dangerous way to
-                // look like the Equals method desc.
-                pEqualsValueMD->SetSlot(EqualsSlot);
-                pEqualsValueMD->SetMemberDef(pEqualsMD->GetMemberDef());
-            }
-
-            // Override the valuetype "Equals" with "EqualsValue".
-            bmtVT->SetMethodDescForSlot(EqualsSlot, EqualsSlot);
-        }
-#endif // 0
     }
 
     if (NumDeclaredMethods() > 0)
diff --git a/src/coreclr/src/vm/classlayoutinfo.cpp b/src/coreclr/src/vm/classlayoutinfo.cpp
index a9c932886a8b73..e5f9345c88327a 100644
--- a/src/coreclr/src/vm/classlayoutinfo.cpp
+++ b/src/coreclr/src/vm/classlayoutinfo.cpp
@@ -903,16 +903,16 @@ EEClassNativeLayoutInfo* EEClassNativeLayoutInfo::CollectNativeLayoutFieldMetada
         // from the managed size and alignment.
         // Crossgen scenarios block Vector<T> from even being loaded, so only do this check when not in crossgen.
 #ifndef CROSSGEN_COMPILE
-        if (pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__VECTORT)))
+        if (pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__VECTORT)))
         {
             pNativeLayoutInfo->m_size = pEEClassLayoutInfo->GetManagedSize();
             pNativeLayoutInfo->m_alignmentRequirement = pEEClassLayoutInfo->m_ManagedLargestAlignmentRequirementOfAllMembers;
         }
         else
 #endif
-        if (pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__VECTOR64T)) ||
-            pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__VECTOR128T)) ||
-            pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__VECTOR256T)))
+        if (pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__VECTOR64T)) ||
+            pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__VECTOR128T)) ||
+            pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__VECTOR256T)))
         {
             pNativeLayoutInfo->m_alignmentRequirement = pEEClassLayoutInfo->m_ManagedLargestAlignmentRequirementOfAllMembers;
         }
diff --git a/src/coreclr/src/vm/clrex.cpp b/src/coreclr/src/vm/clrex.cpp
index 0965a32c3dae24..04a8d5b9be7d93 100644
--- a/src/coreclr/src/vm/clrex.cpp
+++ b/src/coreclr/src/vm/clrex.cpp
@@ -189,7 +189,7 @@ OBJECTREF CLRException::GetThrowable()
             //  CreateThrowable() and is being caught in this EX_TRY/EX_CATCH.)
             //  If that exception is the same as the one for which this GetThrowable()
             //  was called, we're in a recursive situation.
-            // Since the CreateThrowable() call should return a type from mscorlib,
+            // Since the CreateThrowable() call should return a type from CoreLib,
             //  there really shouldn't be much opportunity for error.  We could be
             //  out of memory, we could overflow the stack, or the runtime could
             //  be in a weird state(the thread could be aborted as well).
@@ -1071,7 +1071,7 @@ void EEException::GetMessage(SString &result)
         return;
 
     // Otherwise, report the class's generic message
-    LPCUTF8 pszExceptionName = MscorlibBinder::GetExceptionName(m_kind);
+    LPCUTF8 pszExceptionName = CoreLibBinder::GetExceptionName(m_kind);
     result.SetUTF8(pszExceptionName);
 }
 
@@ -1092,7 +1092,7 @@ OBJECTREF EEException::CreateThrowable()
     _ASSERTE(g_pPreallocatedOutOfMemoryException != NULL);
     static int allocCount = 0;
 
-    MethodTable *pMT = MscorlibBinder::GetException(m_kind);
+    MethodTable *pMT = CoreLibBinder::GetException(m_kind);
 
     ThreadPreventAsyncHolder preventAsyncHolder(m_kind == kThreadAbortException);
 
@@ -1218,7 +1218,7 @@ void EEResourceException::GetMessage(SString &result)
     //
 
     result.Printf("%s (message resource %s)",
-                  MscorlibBinder::GetExceptionName(m_kind), m_resourceName.GetUnicode());
+                  CoreLibBinder::GetExceptionName(m_kind), m_resourceName.GetUnicode());
 }
 
 BOOL EEResourceException::GetThrowableMessage(SString &result)
@@ -1420,7 +1420,7 @@ OBJECTREF EEArgumentException::CreateThrowable()
     ResMgrGetString(m_resourceName, &prot.s1);
     GCPROTECT_BEGIN(prot);
 
-    MethodTable *pMT = MscorlibBinder::GetException(m_kind);
+    MethodTable *pMT = CoreLibBinder::GetException(m_kind);
     prot.pThrowable = AllocateObject(pMT);
 
     MethodDesc* pMD = MemberLoader::FindMethod(prot.pThrowable->GetMethodTable(),
@@ -1547,7 +1547,7 @@ OBJECTREF EETypeLoadException::CreateThrowable()
     }
     CONTRACTL_END;
 
-    MethodTable *pMT = MscorlibBinder::GetException(kTypeLoadException);
+    MethodTable *pMT = CoreLibBinder::GetException(kTypeLoadException);
 
     struct _gc {
         OBJECTREF pNewException;
@@ -1752,7 +1752,7 @@ OBJECTREF EEFileLoadException::CreateThrowable()
     GCPROTECT_BEGIN(gc);
 
     gc.pNewFileString = StringObject::NewString(m_name);
-    gc.pNewException = AllocateObject(MscorlibBinder::GetException(m_kind));
+    gc.pNewException = AllocateObject(CoreLibBinder::GetException(m_kind));
 
     MethodDesc* pMD = MemberLoader::FindMethod(gc.pNewException->GetMethodTable(),
                             COR_CTOR_METHOD_NAME, &gsig_IM_Str_Int_RetVoid);
diff --git a/src/coreclr/src/vm/clsload.cpp b/src/coreclr/src/vm/clsload.cpp
index 851266f475765b..01278d32f8f217 100644
--- a/src/coreclr/src/vm/clsload.cpp
+++ b/src/coreclr/src/vm/clsload.cpp
@@ -63,7 +63,7 @@
 // Some useful effects of this rule (for ngen purposes) are:
 //
 // * G<object,...,object> lives in the module defining G
-// * non-mscorlib instantiations of mscorlib-defined generic types live in the module
+// * non-CoreLib instantiations of CoreLib-defined generic types live in the module
 //   of the instantiation (when only one module is invloved in the instantiation)
 //
 
@@ -138,9 +138,9 @@ PTR_Module ClassLoader::ComputeLoaderModuleWorker(
 
     if (pLoaderModule == NULL)
     {
-        CONSISTENCY_CHECK(MscorlibBinder::GetModule() && MscorlibBinder::GetModule()->IsSystem());
+        CONSISTENCY_CHECK(CoreLibBinder::GetModule() && CoreLibBinder::GetModule()->IsSystem());
 
-        pLoaderModule = MscorlibBinder::GetModule();
+        pLoaderModule = CoreLibBinder::GetModule();
     }
 
     if (FALSE)
@@ -250,7 +250,7 @@ PTR_Module ClassLoader::ComputeLoaderModuleForCompilation(
 
     // We're a little stuck - we can't force the item into an NGEN image at this point.  So just bail out
     // and use the loader module we've computed without recording the choice. The loader module should always
-    // be mscorlib in this case.
+    // be CoreLib in this case.
     AppDomain * pAppDomain = GetAppDomain();
     if (!pAppDomain->IsCompilationDomain() ||
         !pAppDomain->ToCompilationDomain()->GetTargetModule())
@@ -3282,7 +3282,7 @@ TypeHandle ClassLoader::CreateTypeHandleForTypeKey(TypeKey* pKey, AllocMemTracke
             // let <Type>* type have a method table
             // System.UIntPtr's method table is used for types like int*, void *, string * etc.
             if (kind == ELEMENT_TYPE_PTR)
-                templateMT = MscorlibBinder::GetElementType(ELEMENT_TYPE_U);
+                templateMT = CoreLibBinder::GetElementType(ELEMENT_TYPE_U);
             else
                 templateMT = NULL;
 
@@ -3589,6 +3589,10 @@ TypeHandle ClassLoader::LoadTypeHandleForTypeKey(TypeKey *pTypeKey,
     }
 #endif
 
+#if defined(FEATURE_EVENT_TRACE)
+    UINT32 typeLoad = ETW::TypeSystemLog::TypeLoadBegin();
+#endif
+
     // When using domain neutral assemblies (and not eagerly propagating dependency loads),
     // it's possible to get here without having injected the module into the current app domain.
     // GetDomainFile will accomplish that.
@@ -3611,6 +3615,13 @@ TypeHandle ClassLoader::LoadTypeHandleForTypeKey(TypeKey *pTypeKey,
 
     PushFinalLevels(typeHnd, targetLevel, pInstContext);
 
+#if defined(FEATURE_EVENT_TRACE)
+    if (ETW_EVENT_ENABLED(MICROSOFT_WINDOWS_DOTNETRUNTIME_PROVIDER_DOTNET_Context, TypeLoadStop))
+    {
+        ETW::TypeSystemLog::TypeLoadEnd(typeLoad, typeHnd, (UINT16)targetLevel);
+    }
+#endif
+
     return typeHnd;
 }
 
diff --git a/src/coreclr/src/vm/codeman.cpp b/src/coreclr/src/vm/codeman.cpp
index a04894fa77edfa..8b8070bdf2d598 100644
--- a/src/coreclr/src/vm/codeman.cpp
+++ b/src/coreclr/src/vm/codeman.cpp
@@ -1203,7 +1203,7 @@ EEJitManager::EEJitManager()
     m_CodeHeapCritSec( CrstSingleUseLock,
                         CrstFlags(CRST_UNSAFE_ANYMODE|CRST_DEBUGGER_THREAD|CRST_TAKEN_DURING_SHUTDOWN)),
     m_CPUCompileFlags(),
-    m_EHClauseCritSec( CrstSingleUseLock )
+    m_JitLoadCritSec( CrstSingleUseLock )
 {
     CONTRACTL {
         THROWS;
@@ -1308,115 +1308,110 @@ void EEJitManager::SetCpuInfo()
 
     // We will set the following flags:
     //   CORJIT_FLAG_USE_SSE2 is required
-    //      SSE       - EDX bit 25    (buffer[15] & 0x02)
-    //      SSE2      - EDX bit 26    (buffer[15] & 0x04)
+    //      SSE       - EDX bit 25
+    //      SSE2      - EDX bit 26
+    //   CORJIT_FLAG_USE_AES
+    //      CORJIT_FLAG_USE_SSE2
+    //      AES       - ECX bit 25
+    //   CORJIT_FLAG_USE_PCLMULQDQ
+    //      CORJIT_FLAG_USE_SSE2
+    //      PCLMULQDQ - ECX bit 1
     //   CORJIT_FLAG_USE_SSE3 if the following feature bits are set (input EAX of 1)
     //      CORJIT_FLAG_USE_SSE2
-    //      SSE3      - ECX bit 0     (buffer[8]  & 0x01)
+    //      SSE3      - ECX bit 0
     //   CORJIT_FLAG_USE_SSSE3 if the following feature bits are set (input EAX of 1)
     //      CORJIT_FLAG_USE_SSE3
-    //      SSSE3     - ECX bit 9     (buffer[9]  & 0x02)
+    //      SSSE3     - ECX bit 9
     //   CORJIT_FLAG_USE_SSE41 if the following feature bits are set (input EAX of 1)
     //      CORJIT_FLAG_USE_SSSE3
-    //      SSE4.1    - ECX bit 19    (buffer[10] & 0x08)
+    //      SSE4.1    - ECX bit 19
     //   CORJIT_FLAG_USE_SSE42 if the following feature bits are set (input EAX of 1)
     //      CORJIT_FLAG_USE_SSE41
-    //      SSE4.2    - ECX bit 20    (buffer[10] & 0x10)
+    //      SSE4.2    - ECX bit 20
     //   CORJIT_FLAG_USE_POPCNT if the following feature bits are set (input EAX of 1)
     //      CORJIT_FLAG_USE_SSE42
-    //      POPCNT    - ECX bit 23    (buffer[10] & 0x80)
+    //      POPCNT    - ECX bit 23
     //   CORJIT_FLAG_USE_AVX if the following feature bits are set (input EAX of 1), and xmmYmmStateSupport returns 1:
     //      CORJIT_FLAG_USE_SSE42
-    //      OSXSAVE   - ECX bit 27   (buffer[11] & 0x08)
+    //      OSXSAVE   - ECX bit 27
+    //      AVX       - ECX bit 28
     //      XGETBV    - XCR0[2:1]    11b
-    //      AVX       - ECX bit 28   (buffer[11] & 0x10)
     //   CORJIT_FLAG_USE_FMA if the following feature bits are set (input EAX of 1), and xmmYmmStateSupport returns 1:
     //      CORJIT_FLAG_USE_AVX
-    //      FMA       - ECX bit 12   (buffer[9]  & 0x10)
+    //      FMA       - ECX bit 12
     //   CORJIT_FLAG_USE_AVX2 if the following feature bit is set (input EAX of 0x07 and input ECX of 0):
     //      CORJIT_FLAG_USE_AVX
-    //      AVX2      - EBX bit 5    (buffer[4]  & 0x20)
+    //      AVX2      - EBX bit 5
     //   CORJIT_FLAG_USE_AVX_512 is not currently set, but defined so that it can be used in future without
-    //   CORJIT_FLAG_USE_AES
-    //      CORJIT_FLAG_USE_SSE2
-    //      AES       - ECX bit 25   (buffer[11] & 0x01)
-    //   CORJIT_FLAG_USE_PCLMULQDQ
-    //      CORJIT_FLAG_USE_SSE2
-    //      PCLMULQDQ - ECX bit 1    (buffer[8] & 0x01)
     //   CORJIT_FLAG_USE_BMI1 if the following feature bit is set (input EAX of 0x07 and input ECX of 0):
-    //      BMI1 - EBX bit 3         (buffer[4]  & 0x08)
+    //      BMI1 - EBX bit 3
     //   CORJIT_FLAG_USE_BMI2 if the following feature bit is set (input EAX of 0x07 and input ECX of 0):
-    //      BMI2 - EBX bit 8         (buffer[5]  & 0x01)
+    //      BMI2 - EBX bit 8
     //   CORJIT_FLAG_USE_LZCNT if the following feature bits are set (input EAX of 80000001H)
-    //      LZCNT - ECX bit 5        (buffer[8]  & 0x20)
+    //      LZCNT - ECX bit 5
     // synchronously updating VM and JIT.
 
-    unsigned char buffer[16];
-    DWORD maxCpuId = getcpuid(0, buffer);
+    int cpuidInfo[4];
+
+    __cpuid(cpuidInfo, 0x00000000);
+    uint32_t maxCpuId = static_cast<uint32_t>(cpuidInfo[0]);
 
     if (maxCpuId >= 1)
     {
-        // getcpuid executes cpuid with eax set to its first argument, and ecx cleared.
-        // It returns the resulting eax in buffer[0-3], ebx in buffer[4-7], ecx in buffer[8-11],
-        // and edx in buffer[12-15].
-
-        (void) getcpuid(1, buffer);
+        __cpuid(cpuidInfo, 0x00000001);
 
-        // If SSE/SSE2 is not enabled, there is no point in checking the rest.
-        //   SSE  is bit 25 of EDX   (buffer[15] & 0x02)
-        //   SSE2 is bit 26 of EDX   (buffer[15] & 0x04)
-
-        if ((buffer[15] & 0x06) == 0x06)                                    // SSE & SSE2
+        if (((cpuidInfo[3] & (1 << 25)) != 0) && ((cpuidInfo[3] & (1 << 26)) != 0))                     // SSE & SSE2
         {
             CPUCompileFlags.Set(InstructionSet_SSE);
             CPUCompileFlags.Set(InstructionSet_SSE2);
-            if ((buffer[11] & 0x02) != 0)                                   // AESNI
+
+            if ((cpuidInfo[2] & (1 << 25)) != 0)                                                      // AESNI
             {
                 CPUCompileFlags.Set(InstructionSet_AES);
             }
 
-            if ((buffer[8] & 0x02) != 0)                                    // PCLMULQDQ
+            if ((cpuidInfo[2] & (1 << 1)) != 0)                                                       // PCLMULQDQ
             {
                 CPUCompileFlags.Set(InstructionSet_PCLMULQDQ);
             }
 
-            if ((buffer[8] & 0x01) != 0)                                    // SSE3
+            if ((cpuidInfo[2] & (1 << 0)) != 0)                                                       // SSE3
             {
                 CPUCompileFlags.Set(InstructionSet_SSE3);
 
-                if ((buffer[9] & 0x02) != 0)                                // SSSE3
+                if ((cpuidInfo[2] & (1 << 9)) != 0)                                                   // SSSE3
                 {
                     CPUCompileFlags.Set(InstructionSet_SSSE3);
 
-                    if ((buffer[10] & 0x08) != 0)                           // SSE4.1
+                    if ((cpuidInfo[2] & (1 << 19)) != 0)                                              // SSE4.1
                     {
                         CPUCompileFlags.Set(InstructionSet_SSE41);
 
-                        if ((buffer[10] & 0x10) != 0)                       // SSE4.2
+                        if ((cpuidInfo[2] & (1 << 20)) != 0)                                          // SSE4.2
                         {
                             CPUCompileFlags.Set(InstructionSet_SSE42);
 
-                            if ((buffer[10] & 0x80) != 0)                   // POPCNT
+                            if ((cpuidInfo[2] & (1 << 23)) != 0)                                      // POPCNT
                             {
                                 CPUCompileFlags.Set(InstructionSet_POPCNT);
                             }
 
-                            if ((buffer[11] & 0x18) == 0x18)                // AVX & OSXSAVE
+                            if (((cpuidInfo[2] & (1 << 27)) != 0) && ((cpuidInfo[2] & (1 << 28)) != 0)) // OSXSAVE & AVX
                             {
-                                if(DoesOSSupportAVX() && (xmmYmmStateSupport() == 1))
+                                if(DoesOSSupportAVX() && (xmmYmmStateSupport() == 1))               // XGETBV == 11
                                 {
                                     CPUCompileFlags.Set(InstructionSet_AVX);
 
-                                    if ((buffer[9] & 0x10) != 0)            // FMA
+                                    if ((cpuidInfo[2] & (1 << 12)) != 0)                              // FMA
                                     {
                                         CPUCompileFlags.Set(InstructionSet_FMA);
                                     }
 
                                     if (maxCpuId >= 0x07)
                                     {
-                                        (void) getextcpuid(0, 0x07, buffer);
+                                        __cpuidex(cpuidInfo, 0x00000007, 0x00000000);
 
-                                        if ((buffer[4] & 0x20) != 0)        // AVX2
+                                        if ((cpuidInfo[1] & (1 << 5)) != 0)                           // AVX2
                                         {
                                             CPUCompileFlags.Set(InstructionSet_AVX2);
                                         }
@@ -1443,31 +1438,28 @@ void EEJitManager::SetCpuInfo()
 
         if (maxCpuId >= 0x07)
         {
-            (void)getextcpuid(0, 0x07, buffer);
+            __cpuidex(cpuidInfo, 0x00000007, 0x00000000);
 
-            if ((buffer[4] & 0x08) != 0)            // BMI1
+            if ((cpuidInfo[2] & (1 << 3)) != 0)                                                       // BMI1
             {
                 CPUCompileFlags.Set(InstructionSet_BMI1);
             }
 
-            if ((buffer[5] & 0x01) != 0)            // BMI2
+            if ((cpuidInfo[2] & (1 << 8)) != 0)                                                       // BMI2
             {
                 CPUCompileFlags.Set(InstructionSet_BMI2);
             }
         }
     }
 
-    DWORD maxCpuIdEx = getcpuid(0x80000000, buffer);
+    __cpuid(cpuidInfo, 0x80000000);
+    uint32_t maxCpuIdEx = static_cast<uint32_t>(cpuidInfo[0]);
 
     if (maxCpuIdEx >= 0x80000001)
     {
-        // getcpuid executes cpuid with eax set to its first argument, and ecx cleared.
-        // It returns the resulting eax in buffer[0-3], ebx in buffer[4-7], ecx in buffer[8-11],
-        // and edx in buffer[12-15].
+        __cpuid(cpuidInfo, 0x80000001);
 
-        (void) getcpuid(0x80000001, buffer);
-
-        if ((buffer[8] & 0x20) != 0)            // LZCNT
+        if ((cpuidInfo[3] & (1 << 5)) != 0)                                                           // LZCNT
         {
             CPUCompileFlags.Set(InstructionSet_LZCNT);
         }
@@ -1710,8 +1702,8 @@ BOOL EEJitManager::LoadJIT()
     if (IsJitLoaded())
         return TRUE;
 
-    // Abuse m_EHClauseCritSec to ensure that the JIT is loaded on one thread only
-    CrstHolder chRead(&m_EHClauseCritSec);
+    // Use m_JitLoadCritSec to ensure that the JIT is loaded on one thread only
+    CrstHolder chRead(&m_JitLoadCritSec);
 
     // Did someone load the JIT before we got the lock?
     if (IsJitLoaded())
@@ -3056,21 +3048,14 @@ TypeHandle EEJitManager::ResolveEHClause(EE_ILEXCEPTION_CLAUSE* pEHClause,
     TypeHandle typeHnd = TypeHandle();
     mdToken typeTok = mdTokenNil;
 
+    // CachedTypeHandle's are filled in at JIT time, and not cached when accessed multiple times
+    if (HasCachedTypeHandle(pEHClause))
     {
-        CrstHolder chRead(&m_EHClauseCritSec);
-        if (HasCachedTypeHandle(pEHClause))
-        {
-            typeHnd = TypeHandle::FromPtr(pEHClause->TypeHandle);
-        }
-        else
-        {
-            typeTok = pEHClause->ClassToken;
-        }
+        return TypeHandle::FromPtr(pEHClause->TypeHandle);
     }
-
-    if (!typeHnd.IsNull())
+    else
     {
-        return typeHnd;
+        typeTok = pEHClause->ClassToken;
     }
 
     MethodDesc* pMD = pCf->GetFunction();
@@ -3108,43 +3093,8 @@ TypeHandle EEJitManager::ResolveEHClause(EE_ILEXCEPTION_CLAUSE* pEHClause,
         }
     }
 
-    typeHnd = ClassLoader::LoadTypeDefOrRefOrSpecThrowing(pModule, typeTok, &typeContext,
-                                                          ClassLoader::ReturnNullIfNotFound);
-
-    // If the type (pModule,typeTok) was not loaded or not
-    // restored then the exception object won't have this type, because an
-    // object of this type has not been allocated.
-    if (typeHnd.IsNull())
-        return typeHnd;
-
-    // We can cache any exception specification except:
-    //   - If the type contains type variables in generic code,
-    //     e.g. catch E<T> where T is a type variable.
-    // We CANNOT cache E<T> in non-shared instantiations of generic code because
-    // there is only one EHClause cache for the IL, shared across all instantiations.
-    //
-    if((k & hasAnyVarsMask) == 0)
-    {
-        CrstHolder chWrite(&m_EHClauseCritSec);
-
-        // Note another thread might have beaten us to it ...
-        if (!HasCachedTypeHandle(pEHClause))
-        {
-            // We should never cache a NULL typeHnd.
-            _ASSERTE(!typeHnd.IsNull());
-            pEHClause->TypeHandle = typeHnd.AsPtr();
-            SetHasCachedTypeHandle(pEHClause);
-        }
-        else
-        {
-            // If we raced in here with another thread and got held up on the lock, then we just need to return the
-            // type handle that the other thread put into the clause.
-            // The typeHnd we found and the typeHnd the racing thread found should always be the same
-            _ASSERTE(typeHnd.AsPtr() == pEHClause->TypeHandle);
-            typeHnd = TypeHandle::FromPtr(pEHClause->TypeHandle);
-        }
-    }
-    return typeHnd;
+    return ClassLoader::LoadTypeDefOrRefOrSpecThrowing(pModule, typeTok, &typeContext,
+                                                       ClassLoader::ReturnNullIfNotFound);
 }
 
 void EEJitManager::RemoveJitData (CodeHeader * pCHdr, size_t GCinfo_len, size_t EHinfo_len)
diff --git a/src/coreclr/src/vm/codeman.h b/src/coreclr/src/vm/codeman.h
index cba802dc03b6bc..97d8b5f2b7f307 100644
--- a/src/coreclr/src/vm/codeman.h
+++ b/src/coreclr/src/vm/codeman.h
@@ -1116,7 +1116,7 @@ protected :
 private :
     PTR_HostCodeHeap    m_cleanupList;
     //When EH Clauses are resolved we need to atomically update the TypeHandle
-    Crst                m_EHClauseCritSec;
+    Crst                m_JitLoadCritSec;
 
 #if !defined CROSSGEN_COMPILE
     // must hold critical section to access this structure.
diff --git a/src/coreclr/src/vm/codeversion.cpp b/src/coreclr/src/vm/codeversion.cpp
index 5ae3940a1681c9..78f2ede9d5f991 100644
--- a/src/coreclr/src/vm/codeversion.cpp
+++ b/src/coreclr/src/vm/codeversion.cpp
@@ -1759,7 +1759,8 @@ PCODE CodeVersionManager::PublishVersionableCodeIfNecessary(
         do
         {
             bool mayHaveEntryPointSlotsToBackpatch = doPublish && pMethodDesc->MayHaveEntryPointSlotsToBackpatch();
-            MethodDescBackpatchInfoTracker::ConditionalLockHolder slotBackpatchLockHolder(mayHaveEntryPointSlotsToBackpatch);
+            MethodDescBackpatchInfoTracker::ConditionalLockHolderForGCCoop slotBackpatchLockHolder(
+                mayHaveEntryPointSlotsToBackpatch);
 
             // Try a faster check to see if we can avoid checking the currently active code version
             // - For the default code version, if a profiler is attached it may be notified of JIT events and may request rejit
diff --git a/src/coreclr/src/vm/comcallablewrapper.cpp b/src/coreclr/src/vm/comcallablewrapper.cpp
index 6fca4a141d6054..aa3068af22b759 100644
--- a/src/coreclr/src/vm/comcallablewrapper.cpp
+++ b/src/coreclr/src/vm/comcallablewrapper.cpp
@@ -1253,17 +1253,17 @@ BOOL SimpleComCallWrapper::SupportsIReflect(MethodTable *pClass)
     if (pClass == g_pRuntimeTypeClass)
         return FALSE;
 
-    if (MscorlibBinder::IsClass(pClass, CLASS__TYPE_BUILDER))
+    if (CoreLibBinder::IsClass(pClass, CLASS__TYPE_BUILDER))
         return FALSE;
 
-    if (MscorlibBinder::IsClass(pClass, CLASS__TYPE))
+    if (CoreLibBinder::IsClass(pClass, CLASS__TYPE))
         return FALSE;
 
-    if (MscorlibBinder::IsClass(pClass, CLASS__ENUM_BUILDER))
+    if (CoreLibBinder::IsClass(pClass, CLASS__ENUM_BUILDER))
         return FALSE;
 
     // Check to see if the MethodTable associated with the wrapper implements IExpando.
-    return pClass->ImplementsInterface(MscorlibBinder::GetClass(CLASS__IREFLECT));
+    return pClass->ImplementsInterface(CoreLibBinder::GetClass(CLASS__IREFLECT));
 }
 
 //--------------------------------------------------------------------------
@@ -1282,7 +1282,7 @@ BOOL SimpleComCallWrapper::SupportsIExpando(MethodTable *pClass)
     CONTRACTL_END;
 
     // Check to see if the MethodTable associated with the wrapper implements IExpando.
-    return pClass->ImplementsInterface(MscorlibBinder::GetClass(CLASS__IEXPANDO));
+    return pClass->ImplementsInterface(CoreLibBinder::GetClass(CLASS__IEXPANDO));
 }
 
 // NOINLINE to prevent RCWHolder from forcing caller to push/pop an FS:0 handler
@@ -4480,11 +4480,11 @@ BOOL ComCallWrapperTemplate::IsSafeTypeForMarshalling()
         // System.Reflection.MethodBody, and System.Reflection.ParameterInfo.
         // Some interesting derived types that get blocked as a result are:
         // System.Type, System.Reflection.TypeInfo, System.Reflection.MethodInfo, and System.Reflection.FieldInfo
-        if (pMt->CanCastToClass(MscorlibBinder::GetClass(CLASS__ASSEMBLYBASE)) ||
-        pMt->CanCastToClass(MscorlibBinder::GetClass(CLASS__MEMBER)) ||
-        pMt->CanCastToClass(MscorlibBinder::GetClass(CLASS__MODULEBASE)) ||
-        pMt->CanCastToClass(MscorlibBinder::GetClass(CLASS__RUNTIME_METHOD_BODY)) ||
-        pMt->CanCastToClass(MscorlibBinder::GetClass(CLASS__PARAMETER)))
+        if (pMt->CanCastToClass(CoreLibBinder::GetClass(CLASS__ASSEMBLYBASE)) ||
+        pMt->CanCastToClass(CoreLibBinder::GetClass(CLASS__MEMBER)) ||
+        pMt->CanCastToClass(CoreLibBinder::GetClass(CLASS__MODULEBASE)) ||
+        pMt->CanCastToClass(CoreLibBinder::GetClass(CLASS__RUNTIME_METHOD_BODY)) ||
+        pMt->CanCastToClass(CoreLibBinder::GetClass(CLASS__PARAMETER)))
         {
             isSafe = FALSE;
         }
@@ -5040,7 +5040,7 @@ ComMethodTable *ComCallWrapperTemplate::InitializeForInterface(MethodTable *pPar
 
     // update pItfMT in case code:CreateComMethodTableForInterface decided to redirect the interface
     pItfMT = pItfComMT->GetMethodTable();
-    if (pItfMT == MscorlibBinder::GetExistingClass(CLASS__ICUSTOM_QUERYINTERFACE))
+    if (pItfMT == CoreLibBinder::GetExistingClass(CLASS__ICUSTOM_QUERYINTERFACE))
     {
         m_flags |= enum_ImplementsICustomQueryInterface;
     }
@@ -5152,7 +5152,7 @@ ComCallWrapperTemplate* ComCallWrapperTemplate::CreateTemplate(TypeHandle thClas
         // Eagerly create the interface CMTs.
         // when iterate the interfaces implemented by the methodtable, we can check whether
         // the interface supports ICustomQueryInterface.
-        MscorlibBinder::GetClass(CLASS__ICUSTOM_QUERYINTERFACE);
+        CoreLibBinder::GetClass(CLASS__ICUSTOM_QUERYINTERFACE);
 
         it.Reset();
         while (it.Next())
@@ -5401,7 +5401,7 @@ MethodDesc * ComCallWrapperTemplate::GetICustomQueryInterfaceGetInterfaceMD()
 
     if (m_pICustomQueryInterfaceGetInterfaceMD == NULL)
         m_pICustomQueryInterfaceGetInterfaceMD = m_thClass.GetMethodTable()->GetMethodDescForInterfaceMethod(
-           MscorlibBinder::GetMethod(METHOD__ICUSTOM_QUERYINTERFACE__GET_INTERFACE),
+           CoreLibBinder::GetMethod(METHOD__ICUSTOM_QUERYINTERFACE__GET_INTERFACE),
            TRUE /* throwOnConflict */);
     RETURN m_pICustomQueryInterfaceGetInterfaceMD;
 }
diff --git a/src/coreclr/src/vm/comdelegate.cpp b/src/coreclr/src/vm/comdelegate.cpp
index 625513bf9cd3aa..9c5b48cc8ce730 100644
--- a/src/coreclr/src/vm/comdelegate.cpp
+++ b/src/coreclr/src/vm/comdelegate.cpp
@@ -2197,7 +2197,7 @@ FCIMPL1(PCODE, COMDelegate::GetMulticastInvoke, Object* refThisIn)
 
         // Get count of delegates
         pCode->EmitLoadThis();
-        pCode->EmitLDFLD(pCode->GetToken(MscorlibBinder::GetField(FIELD__MULTICAST_DELEGATE__INVOCATION_COUNT)));
+        pCode->EmitLDFLD(pCode->GetToken(CoreLibBinder::GetField(FIELD__MULTICAST_DELEGATE__INVOCATION_COUNT)));
         pCode->EmitSTLOC(dwInvocationCountNum);
 
         // initialize counter
@@ -2220,7 +2220,7 @@ FCIMPL1(PCODE, COMDelegate::GetMulticastInvoke, Object* refThisIn)
 
         // Load next delegate from array using LoopCounter as index
         pCode->EmitLoadThis();
-        pCode->EmitLDFLD(pCode->GetToken(MscorlibBinder::GetField(FIELD__MULTICAST_DELEGATE__INVOCATION_LIST)));
+        pCode->EmitLDFLD(pCode->GetToken(CoreLibBinder::GetField(FIELD__MULTICAST_DELEGATE__INVOCATION_LIST)));
         pCode->EmitLDLOC(dwLoopCounterNum);
         pCode->EmitLDELEM_REF();
 
@@ -2371,7 +2371,7 @@ PCODE COMDelegate::GetWrapperInvoke(MethodDesc* pMD)
 
         // Load the "real" delegate
         pCode->EmitLoadThis();
-        pCode->EmitLDFLD(pCode->GetToken(MscorlibBinder::GetField(FIELD__MULTICAST_DELEGATE__INVOCATION_LIST)));
+        pCode->EmitLDFLD(pCode->GetToken(CoreLibBinder::GetField(FIELD__MULTICAST_DELEGATE__INVOCATION_LIST)));
 
         // Load the arguments
         UINT paramCount = 0;
@@ -2955,17 +2955,17 @@ MethodDesc* COMDelegate::GetDelegateCtor(TypeHandle delegateType, MethodDesc *pT
         {
             // case 3
             if (isCollectible)
-                pRealCtor = MscorlibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_COLLECTIBLE_VIRTUAL_DISPATCH);
+                pRealCtor = CoreLibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_COLLECTIBLE_VIRTUAL_DISPATCH);
             else
-                pRealCtor = MscorlibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_VIRTUAL_DISPATCH);
+                pRealCtor = CoreLibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_VIRTUAL_DISPATCH);
         }
         else
         {
             // case 2, 6
             if (isCollectible)
-                pRealCtor = MscorlibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_COLLECTIBLE_OPENED);
+                pRealCtor = CoreLibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_COLLECTIBLE_OPENED);
             else
-                pRealCtor = MscorlibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_OPENED);
+                pRealCtor = CoreLibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_OPENED);
         }
         Stub *pShuffleThunk = NULL;
         if (!pTargetMethod->IsStatic() && pTargetMethod->HasRetBuffArg() && IsRetBuffPassedAsFirstArg())
@@ -3000,21 +3000,21 @@ MethodDesc* COMDelegate::GetDelegateCtor(TypeHandle delegateType, MethodDesc *pT
                     pTargetMethod->GetMethodTable()->IsValueType() && !pTargetMethod->IsUnboxingStub();
 
         if (needsRuntimeInfo)
-            pRealCtor = MscorlibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_RT_CLOSED);
+            pRealCtor = CoreLibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_RT_CLOSED);
         else
         {
             if (!isStatic)
-                pRealCtor = MscorlibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_CLOSED);
+                pRealCtor = CoreLibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_CLOSED);
             else
             {
                 if (isCollectible)
                 {
-                    pRealCtor = MscorlibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_COLLECTIBLE_CLOSED_STATIC);
+                    pRealCtor = CoreLibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_COLLECTIBLE_CLOSED_STATIC);
                     pCtorData->pArg3 = pTargetMethodLoaderAllocator->GetLoaderAllocatorObjectHandle();
                 }
                 else
                 {
-                    pRealCtor = MscorlibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_CLOSED_STATIC);
+                    pRealCtor = CoreLibBinder::GetMethod(METHOD__MULTICAST_DELEGATE__CTOR_CLOSED_STATIC);
                 }
             }
         }
@@ -3149,7 +3149,7 @@ static void TryConstructUnhandledExceptionArgs(OBJECTREF *pThrowable,
 
     EX_TRY
     {
-        MethodTable *pMT = MscorlibBinder::GetClass(CLASS__UNHANDLED_EVENTARGS);
+        MethodTable *pMT = CoreLibBinder::GetClass(CLASS__UNHANDLED_EVENTARGS);
         *pOutEventArgs = AllocateObject(pMT);
 
         MethodDescCallSite ctor(METHOD__UNHANDLED_EVENTARGS__CTOR, pOutEventArgs);
diff --git a/src/coreclr/src/vm/comdependenthandle.cpp b/src/coreclr/src/vm/comdependenthandle.cpp
index 6144483ddc6b80..e261f16064a6c5 100644
--- a/src/coreclr/src/vm/comdependenthandle.cpp
+++ b/src/coreclr/src/vm/comdependenthandle.cpp
@@ -86,6 +86,9 @@ FCIMPL2(VOID, DependentHandle::nSetPrimary, OBJECTHANDLE handle, Object *_primar
 
     _ASSERTE(handle != NULL);
 
+    // Avoid collision with MarshalNative::GCHandleInternalSet
+    FCUnique(0x12);
+
     IGCHandleManager *mgr = GCHandleUtilities::GetGCHandleManager();
     mgr->StoreObjectInHandle(handle, _primary);
 }
diff --git a/src/coreclr/src/vm/commodule.cpp b/src/coreclr/src/vm/commodule.cpp
index 0575cb9b261893..7ca511e7db6f9f 100644
--- a/src/coreclr/src/vm/commodule.cpp
+++ b/src/coreclr/src/vm/commodule.cpp
@@ -643,6 +643,12 @@ void QCALLTYPE COMModule::SetFieldRVAContent(QCall::ModuleHandle pModule, INT32
     if (pContent != NULL)
         memcpy(pvBlob, pContent, length);
 
+    if (pReflectionModule->IsCollectible())
+    {
+        GCX_COOP();
+        LoaderAllocator::AssociateMemoryWithLoaderAllocator((BYTE*)pvBlob, ((BYTE*)pvBlob) + length, pReflectionModule->GetLoaderAllocator());
+    }
+
     // set FieldRVA into metadata. Note that this is not final RVA in the image if save to disk. We will do another round of fix up upon save.
     IfFailThrow( pRCW->GetEmitter()->SetFieldRVA(tkField, dwRVA) );
 
@@ -958,7 +964,7 @@ Object* GetTypesInner(Module* pModule)
 
     if (pModule->IsResource())
     {
-        refArrClasses = (PTRARRAYREF) AllocateObjectArray(0, MscorlibBinder::GetClass(CLASS__CLASS));
+        refArrClasses = (PTRARRAYREF) AllocateObjectArray(0, CoreLibBinder::GetClass(CLASS__CLASS));
         RETURN(OBJECTREFToObject(refArrClasses));
     }
 
@@ -976,7 +982,7 @@ Object* GetTypesInner(Module* pModule)
     // Allocate the COM+ array
     bSystemAssembly = (pModule->GetAssembly() == SystemDomain::SystemAssembly());
     AllocSize = dwNumTypeDefs;
-    refArrClasses = (PTRARRAYREF) AllocateObjectArray(AllocSize, MscorlibBinder::GetClass(CLASS__CLASS));
+    refArrClasses = (PTRARRAYREF) AllocateObjectArray(AllocSize, CoreLibBinder::GetClass(CLASS__CLASS));
 
     int curPos = 0;
     OBJECTREF throwable = 0;
diff --git a/src/coreclr/src/vm/common.h b/src/coreclr/src/vm/common.h
index ab73f6746f4505..992c6a70b2ccff 100644
--- a/src/coreclr/src/vm/common.h
+++ b/src/coreclr/src/vm/common.h
@@ -144,7 +144,7 @@ typedef DPTR(class MethodDesc)          PTR_MethodDesc;
 typedef DPTR(class MethodDescChunk)     PTR_MethodDescChunk;
 typedef DPTR(class MethodImpl)          PTR_MethodImpl;
 typedef DPTR(class MethodTable)         PTR_MethodTable;
-typedef DPTR(class MscorlibBinder)      PTR_MscorlibBinder;
+typedef DPTR(class CoreLibBinder)      PTR_CoreLibBinder;
 typedef VPTR(class Module)              PTR_Module;
 typedef DPTR(class NDirectMethodDesc)   PTR_NDirectMethodDesc;
 typedef DPTR(class Thread)              PTR_Thread;
diff --git a/src/coreclr/src/vm/compatibilityswitch.cpp b/src/coreclr/src/vm/compatibilityswitch.cpp
index 3b36f58a9d247b..49ce4a400c6e8c 100644
--- a/src/coreclr/src/vm/compatibilityswitch.cpp
+++ b/src/coreclr/src/vm/compatibilityswitch.cpp
@@ -6,7 +6,7 @@
 #include "clrconfig.h"
 #include "compatibilityswitch.h"
 
-FCIMPL2(StringObject*, CompatibilitySwitch::GetValue, StringObject* switchNameUNSAFE, CLR_BOOL onlyDB) {
+FCIMPL1(StringObject*, CompatibilitySwitch::GetValue, StringObject* switchNameUNSAFE) {
     CONTRACTL {
         FCALL_CHECK;
     }
@@ -23,20 +23,7 @@ FCIMPL2(StringObject*, CompatibilitySwitch::GetValue, StringObject* switchNameUN
     HELPER_METHOD_FRAME_BEGIN_RET_1(name);
     CLRConfig::ConfigStringInfo info;
     info.name = name->GetBuffer();
-    if(onlyDB)
-    {
-        // for public managed apis we ignore checking in registry/config/env
-        // only check in windows appcompat DB
-        info.options = CLRConfig::IgnoreEnv |
-                       CLRConfig::IgnoreHKLM |
-                       CLRConfig::IgnoreHKCU;
-    }
-    else
-    {
-        // for mscorlib (i.e. which use internal apis) also check in
-        // registry/config/env in addition to windows appcompat DB
-        info.options = CLRConfig::EEConfig_default;
-    }
+    info.options = CLRConfig::EEConfig_default;
     LPWSTR strVal = CLRConfig::GetConfigValue(info);
     refName = StringObject::NewString(strVal);
     HELPER_METHOD_FRAME_END();
diff --git a/src/coreclr/src/vm/compatibilityswitch.h b/src/coreclr/src/vm/compatibilityswitch.h
index 810455ebaa5e35..bd291ee3e4428b 100644
--- a/src/coreclr/src/vm/compatibilityswitch.h
+++ b/src/coreclr/src/vm/compatibilityswitch.h
@@ -15,7 +15,7 @@
 class CompatibilitySwitch
 {
 public:
-    static FCDECL2(StringObject*, GetValue, StringObject *switchNameUNSAFE, CLR_BOOL onlyDB);
+    static FCDECL1(StringObject*, GetValue, StringObject *switchNameUNSAFE);
 };
 
 
diff --git a/src/coreclr/src/vm/compile.cpp b/src/coreclr/src/vm/compile.cpp
index 28716467474e5c..492079e9d22d01 100644
--- a/src/coreclr/src/vm/compile.cpp
+++ b/src/coreclr/src/vm/compile.cpp
@@ -276,7 +276,7 @@ HRESULT CEECompileInfo::LoadAssemblyByPath(
         AssemblySpec spec;
         spec.InitializeSpec(TokenFromRid(1, mdtAssembly), pImage->GetMDImport(), NULL);
 
-        if (spec.IsMscorlib())
+        if (spec.IsCoreLib())
         {
             pAssembly = SystemDomain::System()->SystemAssembly();
         }
@@ -424,18 +424,13 @@ HRESULT CEECompileInfo::SetCompilationTarget(CORINFO_ASSEMBLY_HANDLE     assembl
 
     if (!pAssembly->IsSystem())
     {
-        // It is possible to get through a compile without calling BindAssemblySpec on mscorlib.  This
-        // is because refs to mscorlib are short circuited in a number of places.  So, we will explicitly
+        // It is possible to get through a compile without calling BindAssemblySpec on CoreLib.  This
+        // is because refs to CoreLib are short circuited in a number of places.  So, we will explicitly
         // add it to our dependencies.
 
-        AssemblySpec mscorlib;
-        mscorlib.InitializeSpec(SystemDomain::SystemFile());
-        GetAppDomain()->BindAssemblySpec(&mscorlib,TRUE);
-
-        if (!IsReadyToRunCompilation() && !SystemDomain::SystemFile()->HasNativeImage())
-        {
-            return NGEN_E_SYS_ASM_NI_MISSING;
-        }
+        AssemblySpec corelib;
+        corelib.InitializeSpec(SystemDomain::SystemFile());
+        GetAppDomain()->BindAssemblySpec(&corelib,TRUE);
     }
 
     if (IsReadyToRunCompilation() && !pModule->GetFile()->IsILOnly())
@@ -1326,7 +1321,7 @@ void CEECompileInfo::EncodeClass(
     COOPERATIVE_TRANSITION_END();
 }
 
-CORINFO_MODULE_HANDLE CEECompileInfo::GetLoaderModuleForMscorlib()
+CORINFO_MODULE_HANDLE CEECompileInfo::GetLoaderModuleForCoreLib()
 {
     STANDARD_VM_CONTRACT;
 
@@ -1634,7 +1629,7 @@ void CEECompileInfo::EncodeGenericSignature(
 {
     STANDARD_VM_CONTRACT;
 
-    Module * pInfoModule = MscorlibBinder::GetModule();
+    Module * pInfoModule = CoreLibBinder::GetModule();
 
     SigPointer ptr((PCCOR_SIGNATURE)signature);
 
@@ -4819,7 +4814,7 @@ static void SpecializeComparer(SString& ss, Instantiation& inst)
     // Override the default ObjectComparer for special cases
     //
     if (elemTypeHnd.CanCastTo(
-        TypeHandle(MscorlibBinder::GetClass(CLASS__ICOMPARABLEGENERIC)).Instantiate(Instantiation(&elemTypeHnd, 1))))
+        TypeHandle(CoreLibBinder::GetClass(CLASS__ICOMPARABLEGENERIC)).Instantiate(Instantiation(&elemTypeHnd, 1))))
     {
         ss.Set(W("System.Collections.Generic.GenericComparer`1"));
         return;
@@ -4829,7 +4824,7 @@ static void SpecializeComparer(SString& ss, Instantiation& inst)
     {
         Instantiation nullableInst = elemTypeHnd.AsMethodTable()->GetInstantiation();
         if (nullableInst[0].CanCastTo(
-            TypeHandle(MscorlibBinder::GetClass(CLASS__ICOMPARABLEGENERIC)).Instantiate(nullableInst)))
+            TypeHandle(CoreLibBinder::GetClass(CLASS__ICOMPARABLEGENERIC)).Instantiate(nullableInst)))
         {
             ss.Set(W("System.Collections.Generic.NullableComparer`1"));
             inst = nullableInst;
@@ -4874,7 +4869,7 @@ static void SpecializeEqualityComparer(SString& ss, Instantiation& inst)
     // Override the default ObjectEqualityComparer for special cases
     //
     if (elemTypeHnd.CanCastTo(
-        TypeHandle(MscorlibBinder::GetClass(CLASS__IEQUATABLEGENERIC)).Instantiate(Instantiation(&elemTypeHnd, 1))))
+        TypeHandle(CoreLibBinder::GetClass(CLASS__IEQUATABLEGENERIC)).Instantiate(Instantiation(&elemTypeHnd, 1))))
     {
         ss.Set(W("System.Collections.Generic.GenericEqualityComparer`1"));
         return;
@@ -4884,7 +4879,7 @@ static void SpecializeEqualityComparer(SString& ss, Instantiation& inst)
     {
         Instantiation nullableInst = elemTypeHnd.AsMethodTable()->GetInstantiation();
         if (nullableInst[0].CanCastTo(
-            TypeHandle(MscorlibBinder::GetClass(CLASS__IEQUATABLEGENERIC)).Instantiate(nullableInst)))
+            TypeHandle(CoreLibBinder::GetClass(CLASS__IEQUATABLEGENERIC)).Instantiate(nullableInst)))
         {
             ss.Set(W("System.Collections.Generic.NullableEqualityComparer`1"));
             inst = nullableInst;
@@ -4925,7 +4920,7 @@ void CEEPreloader::ApplyTypeDependencyProductionsForType(TypeHandle t)
 
     pMT = pMT->GetCanonicalMethodTable();
 
-    // The TypeDependencyAttribute attribute is currently only allowed on mscorlib types
+    // The TypeDependencyAttribute attribute is currently only allowed on CoreLib types
     // Don't even look for the attribute on types in other assemblies.
     if(!pMT->GetModule()->IsSystem()) {
         return;
@@ -5004,7 +4999,7 @@ void CEEPreloader::ApplyTypeDependencyProductionsForType(TypeHandle t)
             TypeHandle typicalDepTH = TypeName::GetTypeUsingCASearchRules(ss.GetUnicode(), pMT->GetAssembly());
 
             _ASSERTE(!typicalDepTH.IsNull());
-            // This attribute is currently only allowed to refer to mscorlib types
+            // This attribute is currently only allowed to refer to CoreLib types
             _ASSERTE(typicalDepTH.GetModule()->IsSystem());
             if (!typicalDepTH.GetModule()->IsSystem())
                 continue;
@@ -5012,7 +5007,7 @@ void CEEPreloader::ApplyTypeDependencyProductionsForType(TypeHandle t)
             // For IList<T>, ICollection<T>, IEnumerable<T>, IReadOnlyCollection<T> & IReadOnlyList<T>, include SZArrayHelper's
             // generic methods (or at least the relevant ones) in the ngen image in
             // case someone casts a T[] to an IList<T> (or ICollection<T> or IEnumerable<T>, etc).
-            if (MscorlibBinder::IsClass(typicalDepTH.AsMethodTable(), CLASS__SZARRAYHELPER))
+            if (CoreLibBinder::IsClass(typicalDepTH.AsMethodTable(), CLASS__SZARRAYHELPER))
             {
 #ifdef FEATURE_FULL_NGEN
                 if (pMT->GetNumGenericArgs() != 1 || !pMT->IsInterface()) {
@@ -5091,14 +5086,14 @@ void CEEPreloader::ApplyTypeDependencyForSZArrayHelper(MethodTable * pInterfaceM
         METHOD__SZARRAYHELPER__REMOVEAT, // Last method of IList<T>
     };
 
-    // Assuming the binder ID's are properly laid out in mscorlib.h
+    // Assuming the binder ID's are properly laid out in corelib.h
 #if _DEBUG
     for(unsigned int i=0; i < NumItems(LastMethodOnGenericArrayInterfaces) - 1; i++) {
         _ASSERTE(LastMethodOnGenericArrayInterfaces[i] < LastMethodOnGenericArrayInterfaces[i+1]);
     }
 #endif
 
-    MethodTable* pExactMT = MscorlibBinder::GetClass(CLASS__SZARRAYHELPER);
+    MethodTable* pExactMT = CoreLibBinder::GetClass(CLASS__SZARRAYHELPER);
 
     // Subtract one from the non-generic IEnumerable that the generic IEnumerable<T>
     // inherits from.
@@ -5114,7 +5109,7 @@ void CEEPreloader::ApplyTypeDependencyForSZArrayHelper(MethodTable * pInterfaceM
         if (SZArrayHelperMethodIDs[i] > LastMethodOnGenericArrayInterfaces[inheritanceDepth])
             continue;
 
-        MethodDesc * pPrimaryMD = MscorlibBinder::GetMethod(SZArrayHelperMethodIDs[i]);
+        MethodDesc * pPrimaryMD = CoreLibBinder::GetMethod(SZArrayHelperMethodIDs[i]);
 
         MethodDesc * pInstantiatedMD = MethodDesc::FindOrCreateAssociatedMethodDesc(pPrimaryMD,
                                            pExactMT, false, Instantiation(&elemTypeHnd, 1), false);
@@ -6272,7 +6267,7 @@ CorCompileILRegion CEEPreloader::GetILRegion(mdMethodDef token)
             else
             if (MethodIsVisibleOutsideItsAssembly(pMD))
             {
-                // We are inlining only leaf methods, except for mscorlib. Thus we can assume that only methods
+                // We are inlining only leaf methods, except for CoreLib. Thus we can assume that only methods
                 // visible outside its assembly are likely to be inlined.
                 region = CORCOMPILE_ILREGION_INLINEABLE;
             }
@@ -6611,7 +6606,7 @@ HRESULT CompilationDomain::AddDependencyEntry(PEAssembly *pFile,
     if (pFile)
     {
         DomainAssembly *pAssembly = GetAppDomain()->LoadDomainAssembly(NULL, pFile, FILE_LOAD_CREATE);
-        // Note that this can trigger an assembly load (of mscorlib)
+        // Note that this can trigger an assembly load (of CoreLib)
         pAssembly->GetOptimizedIdentitySignature(&pDependency->signAssemblyDef);
 
 
@@ -6642,17 +6637,17 @@ HRESULT CompilationDomain::AddDependency(AssemblySpec *pRefSpec,
     // This assert prevents dependencies from silently being loaded without being recorded.
     _ASSERTE(m_pEmit);
 
-    // Normalize any reference to mscorlib; we don't want to record other non-canonical
-    // mscorlib references in the ngen image since fusion doesn't understand how to bind them.
+    // Normalize any reference to CoreLib; we don't want to record other non-canonical
+    // CoreLib references in the ngen image since fusion doesn't understand how to bind them.
     // (Not to mention the fact that they are redundant.)
     AssemblySpec spec;
-    if (pRefSpec->IsMscorlib())
+    if (pRefSpec->IsCoreLib())
     {
-        _ASSERTE(pFile); // mscorlib had better not be missing
+        _ASSERTE(pFile); // CoreLib had better not be missing
         if (!pFile)
             return E_UNEXPECTED;
 
-        // Don't store a binding from mscorlib to itself.
+        // Don't store a binding from CoreLib to itself.
         if (m_pTargetAssembly == SystemDomain::SystemAssembly())
             return S_OK;
 
@@ -6661,8 +6656,8 @@ HRESULT CompilationDomain::AddDependency(AssemblySpec *pRefSpec,
     }
     else if (m_pTargetAssembly == NULL && pFile)
     {
-        // If target assembly is still NULL, we must be loading either the target assembly or mscorlib.
-        // Mscorlib is already handled above, so we must be loading the target assembly if we get here.
+        // If target assembly is still NULL, we must be loading either the target assembly or CoreLib.
+        // CoreLib is already handled above, so we must be loading the target assembly if we get here.
         // Use the assembly name given in the target assembly so that the native image is deterministic
         // regardless of how the target assembly is specified on the command line.
         spec.InitializeSpec(pFile);
@@ -6761,7 +6756,7 @@ BOOL CompilationDomain::CanEagerBindToZapFile(Module *targetModule, BOOL limitTo
 
     //
     // CoreCLR does not have attributes for fine grained eager binding control.
-    // We hard bind to mscorlib.dll only.
+    // We hard bind to CoreLib only.
     //
     return targetModule->IsSystem();
 }
diff --git a/src/coreclr/src/vm/compile.h b/src/coreclr/src/vm/compile.h
index 7e858b1a25a4d4..a04e19307f3e9b 100644
--- a/src/coreclr/src/vm/compile.h
+++ b/src/coreclr/src/vm/compile.h
@@ -303,7 +303,7 @@ class CEECompileInfo : public ICorCompileInfo
                                  LPWSTR *pHardBindList,
                                  DWORD cHardBindList);
 
-    CORINFO_MODULE_HANDLE GetLoaderModuleForMscorlib();
+    CORINFO_MODULE_HANDLE GetLoaderModuleForCoreLib();
     CORINFO_MODULE_HANDLE GetLoaderModuleForEmbeddableType(CORINFO_CLASS_HANDLE classHandle);
     CORINFO_MODULE_HANDLE GetLoaderModuleForEmbeddableMethod(CORINFO_METHOD_HANDLE methodHandle);
     CORINFO_MODULE_HANDLE GetLoaderModuleForEmbeddableField(CORINFO_FIELD_HANDLE fieldHandle);
diff --git a/src/coreclr/src/vm/comsynchronizable.cpp b/src/coreclr/src/vm/comsynchronizable.cpp
index d8cdfe8d662681..687dbabcbc9084 100644
--- a/src/coreclr/src/vm/comsynchronizable.cpp
+++ b/src/coreclr/src/vm/comsynchronizable.cpp
@@ -227,7 +227,7 @@ void ThreadNative::KickOffThread_Worker(LPVOID ptr)
     _ASSERTE(pMeth);
     MethodDescCallSite invokeMethod(pMeth, &gc.orDelegate);
 
-    if (MscorlibBinder::IsClass(gc.orDelegate->GetMethodTable(), CLASS__PARAMETERIZEDTHREADSTART))
+    if (CoreLibBinder::IsClass(gc.orDelegate->GetMethodTable(), CLASS__PARAMETERIZEDTHREADSTART))
     {
         //Parameterized ThreadStart
         ARG_SLOT arg[2];
@@ -1392,7 +1392,7 @@ FCIMPL1(Object*, ThreadNative::GetThreadDeserializationTracker, StackCrawlMark*
     // To avoid reflection trying to bypass deserialization tracking, check the caller
     // and only allow SerializationInfo to call into this method.
     MethodTable* pCallerMT = SystemDomain::GetCallersType(stackMark);
-    if (pCallerMT != MscorlibBinder::GetClass(CLASS__SERIALIZATION_INFO))
+    if (pCallerMT != CoreLibBinder::GetClass(CLASS__SERIALIZATION_INFO))
     {
         COMPlusThrowArgumentException(W("stackMark"), NULL);
     }
diff --git a/src/coreclr/src/vm/comthreadpool.cpp b/src/coreclr/src/vm/comthreadpool.cpp
index be3a5a3c0d317a..edb8e33a2c6285 100644
--- a/src/coreclr/src/vm/comthreadpool.cpp
+++ b/src/coreclr/src/vm/comthreadpool.cpp
@@ -342,7 +342,7 @@ RegisterWaitForSingleObjectCallback_Worker(LPVOID ptr)
     orState = ObjectFromHandle(((DelegateInfo*) args->delegateInfo)->m_stateHandle);
 
 #ifdef _DEBUG
-    MethodDesc *pMeth = MscorlibBinder::GetMethod(METHOD__TPWAITORTIMER_HELPER__PERFORM_WAITORTIMER_CALLBACK);
+    MethodDesc *pMeth = CoreLibBinder::GetMethod(METHOD__TPWAITORTIMER_HELPER__PERFORM_WAITORTIMER_CALLBACK);
     LogCall(pMeth,"RWSOCallback");
 #endif
 
@@ -601,7 +601,7 @@ VOID BindIoCompletionCallBack_Worker(LPVOID args)
     // we set processed to TRUE, now it's our responsibility to guarantee proper cleanup
 
 #ifdef _DEBUG
-    MethodDesc *pMeth = MscorlibBinder::GetMethod(METHOD__IOCB_HELPER__PERFORM_IOCOMPLETION_CALLBACK);
+    MethodDesc *pMeth = CoreLibBinder::GetMethod(METHOD__IOCB_HELPER__PERFORM_IOCOMPLETION_CALLBACK);
     LogCall(pMeth,"IOCallback");
 #endif
 
@@ -769,7 +769,7 @@ void AppDomainTimerCallback_Worker(LPVOID ptr)
     CONTRACTL_END;
 
 #ifdef _DEBUG
-    MethodDesc *pMeth = MscorlibBinder::GetMethod(METHOD__TIMER_QUEUE__APPDOMAIN_TIMER_CALLBACK);
+    MethodDesc *pMeth = CoreLibBinder::GetMethod(METHOD__TIMER_QUEUE__APPDOMAIN_TIMER_CALLBACK);
     LogCall(pMeth,"AppDomainTimerCallback");
 #endif
 
diff --git a/src/coreclr/src/vm/comutilnative.cpp b/src/coreclr/src/vm/comutilnative.cpp
index 98344d4afb7f87..5f14adaeda712e 100644
--- a/src/coreclr/src/vm/comutilnative.cpp
+++ b/src/coreclr/src/vm/comutilnative.cpp
@@ -1750,7 +1750,7 @@ static BOOL HasOverriddenMethod(MethodTable* mt, MethodTable* classMT, WORD meth
 
     if (!classMT->IsZapped())
     {
-        // If mscorlib is JITed, the slots can be patched and thus we need to compare the actual MethodDescs
+        // If CoreLib is JITed, the slots can be patched and thus we need to compare the actual MethodDescs
         // to detect match reliably
         if (MethodTable::GetMethodDescForSlotAddress(actual) == MethodTable::GetMethodDescForSlotAddress(base))
         {
@@ -1784,9 +1784,9 @@ static BOOL CanCompareBitsOrUseFastGetHashCode(MethodTable* mt)
         return FALSE;
     }
 
-    MethodTable* valueTypeMT = MscorlibBinder::GetClass(CLASS__VALUE_TYPE);
-    WORD slotEquals = MscorlibBinder::GetMethod(METHOD__VALUE_TYPE__EQUALS)->GetSlot();
-    WORD slotGetHashCode = MscorlibBinder::GetMethod(METHOD__VALUE_TYPE__GET_HASH_CODE)->GetSlot();
+    MethodTable* valueTypeMT = CoreLibBinder::GetClass(CLASS__VALUE_TYPE);
+    WORD slotEquals = CoreLibBinder::GetMethod(METHOD__VALUE_TYPE__EQUALS)->GetSlot();
+    WORD slotGetHashCode = CoreLibBinder::GetMethod(METHOD__VALUE_TYPE__GET_HASH_CODE)->GetSlot();
 
     // Check the input type.
     if (HasOverriddenMethod(mt, valueTypeMT, slotEquals)
@@ -2116,7 +2116,7 @@ static bool HasOverriddenStreamMethod(MethodTable * pMT, WORD slot)
 
     if (!g_pStreamMT->IsZapped())
     {
-        // If mscorlib is JITed, the slots can be patched and thus we need to compare the actual MethodDescs
+        // If CoreLib is JITed, the slots can be patched and thus we need to compare the actual MethodDescs
         // to detect match reliably
         if (MethodTable::GetMethodDescForSlotAddress(actual) == MethodTable::GetMethodDescForSlotAddress(base))
             return false;
@@ -2135,9 +2135,9 @@ FCIMPL1(FC_BOOL_RET, StreamNative::HasOverriddenBeginEndRead, Object *stream)
     if (g_pStreamMT == NULL || g_slotBeginRead == 0 || g_slotEndRead == 0)
     {
         HELPER_METHOD_FRAME_BEGIN_RET_1(stream);
-        g_pStreamMT = MscorlibBinder::GetClass(CLASS__STREAM);
-        g_slotBeginRead = MscorlibBinder::GetMethod(METHOD__STREAM__BEGIN_READ)->GetSlot();
-        g_slotEndRead = MscorlibBinder::GetMethod(METHOD__STREAM__END_READ)->GetSlot();
+        g_pStreamMT = CoreLibBinder::GetClass(CLASS__STREAM);
+        g_slotBeginRead = CoreLibBinder::GetMethod(METHOD__STREAM__BEGIN_READ)->GetSlot();
+        g_slotEndRead = CoreLibBinder::GetMethod(METHOD__STREAM__END_READ)->GetSlot();
         HELPER_METHOD_FRAME_END();
     }
 
@@ -2157,9 +2157,9 @@ FCIMPL1(FC_BOOL_RET, StreamNative::HasOverriddenBeginEndWrite, Object *stream)
     if (g_pStreamMT == NULL || g_slotBeginWrite == 0 || g_slotEndWrite == 0)
     {
         HELPER_METHOD_FRAME_BEGIN_RET_1(stream);
-        g_pStreamMT = MscorlibBinder::GetClass(CLASS__STREAM);
-        g_slotBeginWrite = MscorlibBinder::GetMethod(METHOD__STREAM__BEGIN_WRITE)->GetSlot();
-        g_slotEndWrite = MscorlibBinder::GetMethod(METHOD__STREAM__END_WRITE)->GetSlot();
+        g_pStreamMT = CoreLibBinder::GetClass(CLASS__STREAM);
+        g_slotBeginWrite = CoreLibBinder::GetMethod(METHOD__STREAM__BEGIN_WRITE)->GetSlot();
+        g_slotEndWrite = CoreLibBinder::GetMethod(METHOD__STREAM__END_WRITE)->GetSlot();
         HELPER_METHOD_FRAME_END();
     }
 
diff --git a/src/coreclr/src/vm/coreassemblyspec.cpp b/src/coreclr/src/vm/coreassemblyspec.cpp
index 0a9471ec74c886..e9857a9b388c2f 100644
--- a/src/coreclr/src/vm/coreassemblyspec.cpp
+++ b/src/coreclr/src/vm/coreassemblyspec.cpp
@@ -91,7 +91,7 @@ VOID  AssemblySpec::Bind(AppDomain      *pAppDomain,
         STANDARD_VM_CHECK;
         PRECONDITION(CheckPointer(pResult));
         PRECONDITION(CheckPointer(pAppDomain));
-        PRECONDITION(IsMscorlib() == FALSE); // This should never be called for MSCORLIB (explicit loading)
+        PRECONDITION(IsCoreLib() == FALSE); // This should never be called for CoreLib (explicit loading)
     }
     CONTRACTL_END;
 
@@ -116,7 +116,7 @@ VOID  AssemblySpec::Bind(AppDomain      *pAppDomain,
     ReleaseHolder<ICLRPrivAssembly> pPrivAsm;
     _ASSERTE(pBinder != NULL);
 
-    if (m_wszCodeBase == NULL && IsMscorlibSatellite())
+    if (m_wszCodeBase == NULL && IsCoreLibSatellite())
     {
         StackSString sSystemDirectory(SystemDomain::System()->SystemDirectory());
         StackSString tmpString;
diff --git a/src/coreclr/src/vm/coreclr/corebindresult.h b/src/coreclr/src/vm/coreclr/corebindresult.h
index db6559d038ad4f..3c8b1cb282c18b 100644
--- a/src/coreclr/src/vm/coreclr/corebindresult.h
+++ b/src/coreclr/src/vm/coreclr/corebindresult.h
@@ -40,7 +40,7 @@ struct CoreBindResult : public IUnknown
 
     BOOL Found();
     PEImage* GetPEImage();
-    BOOL IsMscorlib();
+    BOOL IsCoreLib();
     void GetBindAssembly(ICLRPrivAssembly** ppAssembly);
 #ifdef FEATURE_PREJIT
     BOOL HasNativeImage();
diff --git a/src/coreclr/src/vm/coreclr/corebindresult.inl b/src/coreclr/src/vm/coreclr/corebindresult.inl
index 1568ccbe9e15a1..10f367b3f48392 100644
--- a/src/coreclr/src/vm/coreclr/corebindresult.inl
+++ b/src/coreclr/src/vm/coreclr/corebindresult.inl
@@ -18,7 +18,7 @@ inline BOOL CoreBindResult::Found()
     return (m_pAssembly!=NULL);
 };
 
-inline BOOL CoreBindResult::IsMscorlib()
+inline BOOL CoreBindResult::IsCoreLib()
 {
     CONTRACTL
     {
@@ -30,7 +30,7 @@ inline BOOL CoreBindResult::IsMscorlib()
 
     BINDER_SPACE::Assembly* pAssembly = BINDER_SPACE::GetAssemblyFromPrivAssemblyFast(m_pAssembly);
 #ifndef CROSSGEN_COMPILE
-    return pAssembly->GetAssemblyName()->IsMscorlib();
+    return pAssembly->GetAssemblyName()->IsCoreLib();
 #else
     return (pAssembly->GetPath()).EndsWithCaseInsensitive(SString(CoreLibName_IL_W));
 #endif
diff --git a/src/coreclr/src/vm/mscorlib.cpp b/src/coreclr/src/vm/corelib.cpp
similarity index 88%
rename from src/coreclr/src/vm/mscorlib.cpp
rename to src/coreclr/src/vm/corelib.cpp
index 70eeb9ba7563d6..4562e2e12ed28d 100644
--- a/src/coreclr/src/vm/mscorlib.cpp
+++ b/src/coreclr/src/vm/corelib.cpp
@@ -4,20 +4,20 @@
 
 
 //
-// This file defines tables for references between VM and mscorlib.
+// This file defines tables for references between VM and corelib.
 //
 // When compiling crossgen, this file is compiled with the FEATURE_XXX define settings matching the target.
 // It allows us to strip features (e.g. refection only load) from crossgen without stripping them from the target.
 //
 
-#ifdef CROSSGEN_MSCORLIB
+#ifdef CROSSGEN_CORELIB
 // Use minimal set of headers for crossgen
 #include "windows.h"
 #include "corinfo.h"
 #else
 #include "common.h"
 #include "ecall.h"
-#endif // CROSSGEN_MSCORLIB
+#endif // CROSSGEN_CORELIB
 
 #ifndef CROSSGEN_COMPILE
 //
@@ -88,10 +88,10 @@
 
 #include "tailcallhelp.h"
 
-#endif // CROSSGEN_MSCORLIB
+#endif // CROSSGEN_CORELIB
 
 
-#ifdef CROSSGEN_MSCORLIB
+#ifdef CROSSGEN_CORELIB
 
 ///////////////////////////////////////////////////////////////////////////////
 //
@@ -106,7 +106,7 @@ enum {
     FCFuncFlag_EndOfArray   = 0x01,
     FCFuncFlag_HasSignature = 0x02,
     FCFuncFlag_Unreferenced = 0x04, // Suppress unused fcall check
-    FCFuncFlag_QCall        = 0x08, // QCall - mscorlib.dll to mscorwks.dll transition implemented as PInvoke
+    FCFuncFlag_QCall        = 0x08, // QCall - CoreLib to VM transition implemented as PInvoke
 };
 
 struct ECClass
@@ -129,9 +129,9 @@ enum BinderClassID
 #undef TYPEINFO
 
 #define DEFINE_CLASS(i,n,s)         CLASS__ ## i,
-#include "mscorlib.h"
+#include "corelib.h"
 
-    CLASS__MSCORLIB_COUNT,
+    CLASS__CORELIB_COUNT,
 
     CLASS__VOID     = CLASS__ELEMENT_TYPE_VOID,
     CLASS__BOOLEAN  = CLASS__ELEMENT_TYPE_BOOLEAN,
@@ -153,31 +153,31 @@ enum BinderClassID
     CLASS__OBJECT   = CLASS__ELEMENT_TYPE_OBJECT
 };
 
-struct MscorlibClassDescription
+struct CoreLibClassDescription
 {
     LPCSTR  nameSpace;
     LPCSTR  name;
 };
 
-struct MscorlibMethodDescription
+struct CoreLibMethodDescription
 {
     BinderClassID classID;
     LPCSTR  name;
     const HardCodedMetaSig * sig;
 };
 
-struct MscorlibFieldDescription
+struct CoreLibFieldDescription
 {
     BinderClassID classID;
     LPCSTR  name;
 };
 
-#endif // CROSSGEN_MSCORLIB
+#endif // CROSSGEN_CORELIB
 
 
-#ifdef CROSSGEN_MSCORLIB
+#ifdef CROSSGEN_CORELIB
 // When compiling crossgen this namespace creates the second version of the tables than matches the target
-namespace CrossGenMscorlib {
+namespace CrossGenCoreLib {
 #endif
 
 
@@ -321,20 +321,20 @@ enum _gsigc {
 
 ///////////////////////////////////////////////////////////////////////////////
 //
-// Mscorlib binder
+// CoreLib binder
 //
 
 // Extern definitions so that binder.cpp can see these tables
-extern const MscorlibClassDescription c_rgMscorlibClassDescriptions[];
-extern const USHORT c_nMscorlibClassDescriptions;
+extern const CoreLibClassDescription c_rgCoreLibClassDescriptions[];
+extern const USHORT c_nCoreLibClassDescriptions;
 
-extern const MscorlibMethodDescription c_rgMscorlibMethodDescriptions[];
-extern const USHORT c_nMscorlibMethodDescriptions;
+extern const CoreLibMethodDescription c_rgCoreLibMethodDescriptions[];
+extern const USHORT c_nCoreLibMethodDescriptions;
 
-extern const MscorlibFieldDescription c_rgMscorlibFieldDescriptions[];
-extern const USHORT c_nMscorlibFieldDescriptions;
+extern const CoreLibFieldDescription c_rgCoreLibFieldDescriptions[];
+extern const USHORT c_nCoreLibFieldDescriptions;
 
-const MscorlibClassDescription c_rgMscorlibClassDescriptions[] =
+const CoreLibClassDescription c_rgCoreLibClassDescriptions[] =
 {
     #define TYPEINFO(e,ns,c,s,g,ia,ip,if,im,gv)   { ns, c },
     #include "cortypeinfo.h"
@@ -342,29 +342,29 @@ const MscorlibClassDescription c_rgMscorlibClassDescriptions[] =
 
     #define DEFINE_CLASS(i,n,s)        { g_ ## n ## NS, # s },
     #include "namespace.h"
-    #include "mscorlib.h"
+    #include "corelib.h"
 
-    // Include all exception types here that are defined in mscorlib.  Omit exceptions defined elsewhere.
+    // Include all exception types here that are defined in corelib.  Omit exceptions defined elsewhere.
     #define DEFINE_EXCEPTION(ns, reKind, bHRformessage, ...) { ns , # reKind },
     #include "rexcep.h"
 };
-const USHORT c_nMscorlibClassDescriptions = NumItems(c_rgMscorlibClassDescriptions);
+const USHORT c_nCoreLibClassDescriptions = NumItems(c_rgCoreLibClassDescriptions);
 
 #define gsig_NoSig (*(HardCodedMetaSig *)NULL)
 
-const MscorlibMethodDescription c_rgMscorlibMethodDescriptions[] =
+const CoreLibMethodDescription c_rgCoreLibMethodDescriptions[] =
 {
     #define DEFINE_METHOD(c,i,s,g)          { CLASS__ ## c , # s, & gsig_ ## g },
-    #include "mscorlib.h"
+    #include "corelib.h"
 };
-const USHORT c_nMscorlibMethodDescriptions = NumItems(c_rgMscorlibMethodDescriptions) + 1;
+const USHORT c_nCoreLibMethodDescriptions = NumItems(c_rgCoreLibMethodDescriptions) + 1;
 
-const MscorlibFieldDescription c_rgMscorlibFieldDescriptions[] =
+const CoreLibFieldDescription c_rgCoreLibFieldDescriptions[] =
 {
     #define DEFINE_FIELD(c,i,s)           { CLASS__ ## c , # s },
-    #include "mscorlib.h"
+    #include "corelib.h"
 };
-const USHORT c_nMscorlibFieldDescriptions = NumItems(c_rgMscorlibFieldDescriptions) + 1;
+const USHORT c_nCoreLibFieldDescriptions = NumItems(c_rgCoreLibFieldDescriptions) + 1;
 
 ///////////////////////////////////////////////////////////////////////////////
 //
@@ -375,7 +375,7 @@ const USHORT c_nMscorlibFieldDescriptions = NumItems(c_rgMscorlibFieldDescriptio
 EXTERN_C const LPVOID gPalGlobalizationNative[];
 
 // When compiling crossgen, we only need the target version of the ecall tables
-#if !defined(CROSSGEN_COMPILE) || defined(CROSSGEN_MSCORLIB)
+#if !defined(CROSSGEN_COMPILE) || defined(CROSSGEN_CORELIB)
 
 #ifdef CROSSGEN_COMPILE
 
@@ -433,9 +433,9 @@ const ECClass c_rgECClasses[] =
 
 const int c_nECClasses = NumItems(c_rgECClasses);
 
-#endif // !CROSSGEN_COMPILE && CROSSGEN_MSCORLIB
+#endif // !CROSSGEN_COMPILE && CROSSGEN_CORELIB
 
 
-#ifdef CROSSGEN_MSCORLIB
-}; // namespace CrossGenMscorlib
+#ifdef CROSSGEN_CORELIB
+}; // namespace CrossGenCoreLib
 #endif
diff --git a/src/coreclr/src/vm/mscorlib.h b/src/coreclr/src/vm/corelib.h
similarity index 99%
rename from src/coreclr/src/vm/mscorlib.h
rename to src/coreclr/src/vm/corelib.h
index fd2578fcaea82f..e7b66f25d5f905 100644
--- a/src/coreclr/src/vm/mscorlib.h
+++ b/src/coreclr/src/vm/corelib.h
@@ -1,6 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
-// This file contains the classes, methods, and field used by the EE from mscorlib
+// This file contains the classes, methods, and field used by the EE from corelib
 
 //
 // To use this, define one of the following macros & include the file like so:
@@ -8,7 +8,7 @@
 // #define DEFINE_CLASS(id, nameSpace, stringName)         CLASS__ ## id,
 // #define DEFINE_METHOD(classId, id, stringName, gSign)
 // #define DEFINE_FIELD(classId, id, stringName)
-// #include "mscorlib.h"
+// #include "corelib.h"
 //
 // Note: To determine if the namespace you want to use in DEFINE_CLASS is supported or not,
 //       examine vm\namespace.h. If it is not present, define it there and then proceed to use it below.
@@ -390,8 +390,6 @@ DEFINE_METHOD(STUBFIELDINFO,        CTOR,                   .ctor,
 #endif
 
 DEFINE_CLASS(FIELD,                 Reflection,             RuntimeFieldInfo)
-DEFINE_METHOD(FIELD,                SET_VALUE,              SetValue,                   IM_Obj_Obj_BindingFlags_Binder_CultureInfo_RetVoid)
-DEFINE_METHOD(FIELD,                GET_VALUE,              GetValue,                   IM_Obj_RetObj)
 
 DEFINE_CLASS(FIELD_HANDLE,          System,                 RuntimeFieldHandle)
 DEFINE_FIELD(FIELD_HANDLE,          M_FIELD,                m_ptr)
@@ -399,6 +397,8 @@ DEFINE_FIELD(FIELD_HANDLE,          M_FIELD,                m_ptr)
 DEFINE_CLASS(I_RT_FIELD_INFO,       System,                 IRuntimeFieldInfo)
 
 DEFINE_CLASS(FIELD_INFO,            Reflection,             FieldInfo)
+DEFINE_METHOD(FIELD_INFO,           SET_VALUE,              SetValue,                   IM_Obj_Obj_BindingFlags_Binder_CultureInfo_RetVoid)
+DEFINE_METHOD(FIELD_INFO,           GET_VALUE,              GetValue,                   IM_Obj_RetObj)
 
 
 DEFINE_CLASS(GUID,                  System,                 Guid)
diff --git a/src/coreclr/src/vm/crossgen/CMakeLists.txt b/src/coreclr/src/vm/crossgen/CMakeLists.txt
index a0b321a00e33ad..e8083ca860f87a 100644
--- a/src/coreclr/src/vm/crossgen/CMakeLists.txt
+++ b/src/coreclr/src/vm/crossgen/CMakeLists.txt
@@ -22,6 +22,7 @@ set(VM_CROSSGEN_SOURCES
   ../contractimpl.cpp
   ../coreassemblyspec.cpp
   ../corebindresult.cpp
+  ../corelib.cpp
   ../crossgencompile.cpp
   ../custommarshalerinfo.cpp
   ../dataimage.cpp
@@ -60,7 +61,6 @@ set(VM_CROSSGEN_SOURCES
   ../methodtable.cpp
   ../methodtablebuilder.cpp
   ../mlinfo.cpp
-  ../mscorlib.cpp
   ../nativeimage.cpp
   ../olevariant.cpp
   ../pefile.cpp
@@ -115,6 +115,7 @@ set(VM_CROSSGEN_HEADERS
   ../comdelegate.h
   ../compile.h
   ../contractimpl.h
+  ../corelib.h
   ../custommarshalerinfo.h
   ../dataimage.h
   ../debuginfostore.h
@@ -154,7 +155,6 @@ set(VM_CROSSGEN_HEADERS
   ../methodtablebuilder.h
   ../methodtablebuilder.inl
   ../mlinfo.h
-  ../mscorlib.h
   ../olevariant.h
   ../pefile.h
   ../pefile.inl
@@ -259,18 +259,18 @@ add_dependencies(cee_crossgen eventing_headers)
 set_target_properties(cee_crossgen PROPERTIES CROSSGEN_COMPONENT TRUE)
 target_precompile_header(TARGET cee_crossgen HEADER common.h)
 if (MSVC)
-  # mscorlib.cpp does not compile with precompiled header file
-  set_source_files_properties(../mscorlib.cpp PROPERTIES COMPILE_FLAGS "/Y-")
+  # corelib.cpp does not compile with precompiled header file
+  set_source_files_properties(../corelib.cpp PROPERTIES COMPILE_FLAGS "/Y-")
 endif()
 
-add_library_clr(mscorlib_crossgen ../mscorlib.cpp)
-add_dependencies(mscorlib_crossgen eventing_headers)
-target_compile_definitions(mscorlib_crossgen
+add_library_clr(corelib_crossgen ../corelib.cpp)
+add_dependencies(corelib_crossgen eventing_headers)
+target_compile_definitions(corelib_crossgen
     PRIVATE
         EnC_SUPPORTED
         FEATURE_EVENT_TRACE
         FEATURE_MULTICOREJIT
-        CROSSGEN_MSCORLIB)
+        CROSSGEN_CORELIB)
 
-set_target_properties(mscorlib_crossgen PROPERTIES CROSSGEN_COMPONENT TRUE)
+set_target_properties(corelib_crossgen PROPERTIES CROSSGEN_COMPONENT TRUE)
 
diff --git a/src/coreclr/src/vm/crossloaderallocatorhash.inl b/src/coreclr/src/vm/crossloaderallocatorhash.inl
index 1eb55509a87bb0..dab0f50f806ece 100644
--- a/src/coreclr/src/vm/crossloaderallocatorhash.inl
+++ b/src/coreclr/src/vm/crossloaderallocatorhash.inl
@@ -291,7 +291,7 @@ template<class TRAITS>
     LAHASHKEYTOTRACKERSREF hashKeyToTrackers;
     OBJECTREF keyValueStore;
 
-    if (hashKeyEntry->GetMethodTable() == MscorlibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
+    if (hashKeyEntry->GetMethodTable() == CoreLibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
     {
         hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)hashKeyEntry;
         keyValueStore = hashKeyToTrackers->_laLocalKeyValueStore;
@@ -321,7 +321,7 @@ template<class TKey>
     LAHASHKEYTOTRACKERSREF hashKeyToTrackers;
     OBJECTREF keyValueStore;
 
-    if (hashKeyEntry->GetMethodTable() == MscorlibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
+    if (hashKeyEntry->GetMethodTable() == CoreLibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
     {
         hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)hashKeyEntry;
         keyValueStore = hashKeyToTrackers->_laLocalKeyValueStore;
@@ -376,7 +376,7 @@ void CrossLoaderAllocatorHash<TRAITS>::Add(TKey key, TValue value, LoaderAllocat
 
             if (pLoaderAllocatorOfValue != m_pLoaderAllocator)
             {
-                gc.hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)AllocateObject(MscorlibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS));
+                gc.hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)AllocateObject(CoreLibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS));
                 SetObjectReference(&gc.hashKeyToTrackers->_laLocalKeyValueStore, gc.keyValueStore);
                 gc.hashKeyEntry = gc.hashKeyToTrackers;
             }
@@ -394,7 +394,7 @@ void CrossLoaderAllocatorHash<TRAITS>::Add(TKey key, TValue value, LoaderAllocat
         {
             gc.keyToTrackersHash.GetElement(index, gc.hashKeyEntry);
 
-            if (gc.hashKeyEntry->GetMethodTable() == MscorlibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
+            if (gc.hashKeyEntry->GetMethodTable() == CoreLibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
             {
                 gc.hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)gc.hashKeyEntry;
                 gc.keyValueStore = gc.hashKeyToTrackers->_laLocalKeyValueStore;
@@ -431,7 +431,7 @@ void CrossLoaderAllocatorHash<TRAITS>::Add(TKey key, TValue value, LoaderAllocat
             if (gc.hashKeyToTrackers == NULL)
             {
                 // Nothing has yet caused the trackers proxy object to be setup. Create it now, and update the keyToTrackersHash
-                gc.hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)AllocateObject(MscorlibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS));
+                gc.hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)AllocateObject(CoreLibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS));
                 SetObjectReference(&gc.hashKeyToTrackers->_laLocalKeyValueStore, gc.keyValueStore);
                 gc.hashKeyEntry = gc.hashKeyToTrackers;
                 gc.keyToTrackersHash.SetElement(index, gc.hashKeyEntry);
@@ -508,7 +508,7 @@ void CrossLoaderAllocatorHash<TRAITS>::Remove(TKey key, TValue value, LoaderAllo
         {
             gc.keyToTrackersHash.GetElement(index, gc.hashKeyEntry);
 
-            if (gc.hashKeyEntry->GetMethodTable() == MscorlibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
+            if (gc.hashKeyEntry->GetMethodTable() == CoreLibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
             {
                 gc.hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)gc.hashKeyEntry;
                 gc.keyValueStore = gc.hashKeyToTrackers->_laLocalKeyValueStore;
@@ -602,7 +602,7 @@ bool CrossLoaderAllocatorHash<TRAITS>::VisitValuesOfKey(TKey key, Visitor &visit
             // We have an entry in the hashtable for the key/dependenthandle.
             gc.keyToTrackersHash.GetElement(index, gc.hashKeyEntry);
 
-            if (gc.hashKeyEntry->GetMethodTable() == MscorlibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
+            if (gc.hashKeyEntry->GetMethodTable() == CoreLibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
             {
                 gc.hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)gc.hashKeyEntry;
                 gc.keyValueStore = gc.hashKeyToTrackers->_laLocalKeyValueStore;
@@ -621,7 +621,7 @@ bool CrossLoaderAllocatorHash<TRAITS>::VisitValuesOfKey(TKey key, Visitor &visit
             {
                 // Is there a single dependenttracker here, or a set.
 
-                if (gc.hashKeyToTrackers->_trackerOrTrackerSet->GetMethodTable() == MscorlibBinder::GetExistingClass(CLASS__LAHASHDEPENDENTHASHTRACKER))
+                if (gc.hashKeyToTrackers->_trackerOrTrackerSet->GetMethodTable() == CoreLibBinder::GetExistingClass(CLASS__LAHASHDEPENDENTHASHTRACKER))
                 {
                     gc.dependentTracker = (LAHASHDEPENDENTHASHTRACKERREF)gc.hashKeyToTrackers->_trackerOrTrackerSet;
                     result = VisitTracker(key, gc.dependentTracker, visitor);
@@ -785,7 +785,7 @@ void CrossLoaderAllocatorHash<TRAITS>::RemoveAll(TKey key)
             // We have an entry in the hashtable for the key/dependenthandle.
             gc.keyToTrackersHash.GetElement(index, gc.hashKeyEntry);
 
-            if (gc.hashKeyEntry->GetMethodTable() == MscorlibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
+            if (gc.hashKeyEntry->GetMethodTable() == CoreLibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
             {
                 gc.hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)gc.hashKeyEntry;
                 gc.keyValueStore = gc.hashKeyToTrackers->_laLocalKeyValueStore;
@@ -801,7 +801,7 @@ void CrossLoaderAllocatorHash<TRAITS>::RemoveAll(TKey key)
             {
                 // Is there a single dependenttracker here, or a set.
 
-                if (gc.hashKeyToTrackers->_trackerOrTrackerSet->GetMethodTable() == MscorlibBinder::GetExistingClass(CLASS__LAHASHDEPENDENTHASHTRACKER))
+                if (gc.hashKeyToTrackers->_trackerOrTrackerSet->GetMethodTable() == CoreLibBinder::GetExistingClass(CLASS__LAHASHDEPENDENTHASHTRACKER))
                 {
                     gc.dependentTracker = (LAHASHDEPENDENTHASHTRACKERREF)gc.hashKeyToTrackers->_trackerOrTrackerSet;
                     DeleteEntryTracker(key, gc.dependentTracker);
@@ -972,7 +972,7 @@ template <class Visitor>
 
     GCPROTECT_BEGIN(gc);
     {
-        if (gc.hashKeyEntry->GetMethodTable() == MscorlibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
+        if (gc.hashKeyEntry->GetMethodTable() == CoreLibBinder::GetExistingClass(CLASS__LAHASHKEYTOTRACKERS))
         {
             gc.hashKeyToTrackers = (LAHASHKEYTOTRACKERSREF)gc.hashKeyEntry;
             gc.keyValueStore = gc.hashKeyToTrackers->_laLocalKeyValueStore;
@@ -1028,14 +1028,14 @@ template <class TRAITS>
 {
     STANDARD_VM_CONTRACT;
 
-    // Force these types to be loaded, so that the hashtable logic can use MscorlibBinder::GetExistingClass
+    // Force these types to be loaded, so that the hashtable logic can use CoreLibBinder::GetExistingClass
     // throughout and avoid lock ordering issues
-    MscorlibBinder::GetClass(CLASS__LAHASHKEYTOTRACKERS);
-    MscorlibBinder::GetClass(CLASS__LAHASHDEPENDENTHASHTRACKER);
-    MscorlibBinder::GetClass(CLASS__GCHEAPHASH);
-    TypeHandle elemType = TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_I1));
+    CoreLibBinder::GetClass(CLASS__LAHASHKEYTOTRACKERS);
+    CoreLibBinder::GetClass(CLASS__LAHASHDEPENDENTHASHTRACKER);
+    CoreLibBinder::GetClass(CLASS__GCHEAPHASH);
+    TypeHandle elemType = TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_I1));
     TypeHandle typHnd = ClassLoader::LoadArrayTypeThrowing(elemType, ELEMENT_TYPE_SZARRAY, 0);
-    elemType = TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_OBJECT));
+    elemType = TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_OBJECT));
     typHnd = ClassLoader::LoadArrayTypeThrowing(elemType, ELEMENT_TYPE_SZARRAY, 0);
 }
 
@@ -1052,14 +1052,14 @@ void CrossLoaderAllocatorHash<TRAITS>::EnsureManagedObjectsInitted()
 
     if (m_loaderAllocatorToDependentTrackerHash == NULL)
     {
-        OBJECTREF laToDependentHandleHashObject = AllocateObject(MscorlibBinder::GetExistingClass(CLASS__GCHEAPHASH));
+        OBJECTREF laToDependentHandleHashObject = AllocateObject(CoreLibBinder::GetExistingClass(CLASS__GCHEAPHASH));
         m_loaderAllocatorToDependentTrackerHash = m_pLoaderAllocator->GetDomain()->CreateHandle(laToDependentHandleHashObject);
         m_pLoaderAllocator->RegisterHandleForCleanup(m_loaderAllocatorToDependentTrackerHash);
     }
 
     if (m_keyToDependentTrackersHash == NULL)
     {
-        OBJECTREF m_keyToDependentTrackersHashObject = AllocateObject(MscorlibBinder::GetExistingClass(CLASS__GCHEAPHASH));
+        OBJECTREF m_keyToDependentTrackersHashObject = AllocateObject(CoreLibBinder::GetExistingClass(CLASS__GCHEAPHASH));
         m_keyToDependentTrackersHash = m_pLoaderAllocator->GetDomain()->CreateHandle(m_keyToDependentTrackersHashObject);
         m_pLoaderAllocator->RegisterHandleForCleanup(m_keyToDependentTrackersHash);
     }
@@ -1096,8 +1096,8 @@ LAHASHDEPENDENTHASHTRACKERREF CrossLoaderAllocatorHash<TRAITS>::GetDependentTrac
         }
         else
         {
-            gc.dependentTracker = (LAHASHDEPENDENTHASHTRACKERREF)AllocateObject(MscorlibBinder::GetExistingClass(CLASS__LAHASHDEPENDENTHASHTRACKER));
-            gc.GCHeapHashForKeyToValueStore = (GCHEAPHASHOBJECTREF)AllocateObject(MscorlibBinder::GetExistingClass(CLASS__GCHEAPHASH));
+            gc.dependentTracker = (LAHASHDEPENDENTHASHTRACKERREF)AllocateObject(CoreLibBinder::GetExistingClass(CLASS__LAHASHDEPENDENTHASHTRACKER));
+            gc.GCHeapHashForKeyToValueStore = (GCHEAPHASHOBJECTREF)AllocateObject(CoreLibBinder::GetExistingClass(CLASS__GCHEAPHASH));
 
             OBJECTREF exposedObject = pLoaderAllocator->GetExposedObject();
             if (exposedObject == NULL)
@@ -1105,7 +1105,7 @@ LAHASHDEPENDENTHASHTRACKERREF CrossLoaderAllocatorHash<TRAITS>::GetDependentTrac
                 if (m_globalDependentTrackerRootHandle == NULL)
                 {
                     // Global LoaderAllocator does not have an exposed object, so create a fake one
-                    exposedObject = AllocateObject(MscorlibBinder::GetExistingClass(CLASS__OBJECT));
+                    exposedObject = AllocateObject(CoreLibBinder::GetExistingClass(CLASS__OBJECT));
                     m_globalDependentTrackerRootHandle = GetAppDomain()->CreateHandle(exposedObject);
                     m_pLoaderAllocator->RegisterHandleForCleanup(m_globalDependentTrackerRootHandle);
                 }
@@ -1162,7 +1162,7 @@ GCHEAPHASHOBJECTREF CrossLoaderAllocatorHash<TRAITS>::GetKeyToValueCrossLAHashFo
             gc.dependentTracker = GetDependentTrackerForLoaderAllocator(pValueLoaderAllocator);
             SetObjectReference(&gc.hashKeyToTrackers->_trackerOrTrackerSet, gc.dependentTracker);
         }
-        else if (gc.hashKeyToTrackers->_trackerOrTrackerSet->GetMethodTable() == MscorlibBinder::GetExistingClass(CLASS__LAHASHDEPENDENTHASHTRACKER))
+        else if (gc.hashKeyToTrackers->_trackerOrTrackerSet->GetMethodTable() == CoreLibBinder::GetExistingClass(CLASS__LAHASHDEPENDENTHASHTRACKER))
         {
             gc.dependentTrackerMaybe = (LAHASHDEPENDENTHASHTRACKERREF)gc.hashKeyToTrackers->_trackerOrTrackerSet;
             if (gc.dependentTrackerMaybe->IsTrackerFor(pValueLoaderAllocator))
@@ -1181,7 +1181,7 @@ GCHEAPHASHOBJECTREF CrossLoaderAllocatorHash<TRAITS>::GetKeyToValueCrossLAHashFo
                 {
                     // Allocate the dependent tracker hash
                     // Fill with the existing dependentTrackerMaybe, and gc.DependentTracker
-                    gc.dependentTrackerHash = GCHeapHashDependentHashTrackerHash(AllocateObject(MscorlibBinder::GetExistingClass(CLASS__GCHEAPHASH)));
+                    gc.dependentTrackerHash = GCHeapHashDependentHashTrackerHash(AllocateObject(CoreLibBinder::GetExistingClass(CLASS__GCHEAPHASH)));
                     LoaderAllocator *pLoaderAllocatorKey = gc.dependentTracker->GetLoaderAllocatorUnsafe();
                     gc.dependentTrackerHash.Add(&pLoaderAllocatorKey, [&gc](PTRARRAYREF arr, INT32 index)
                         {
diff --git a/src/coreclr/src/vm/crst.cpp b/src/coreclr/src/vm/crst.cpp
index 22f7a1ff975946..cbfb665285b44e 100644
--- a/src/coreclr/src/vm/crst.cpp
+++ b/src/coreclr/src/vm/crst.cpp
@@ -772,6 +772,91 @@ BOOL CrstBase::IsSafeToTake()
 
 #endif // _DEBUG
 
+CrstBase::CrstAndForbidSuspendForDebuggerHolder::CrstAndForbidSuspendForDebuggerHolder(CrstBase *pCrst)
+    : m_pCrst(pCrst), m_pThreadForExitingForbidRegion(nullptr)
+{
+    CONTRACTL
+    {
+        NOTHROW;
+        GC_TRIGGERS;
+        MODE_PREEMPTIVE;
+    }
+    CONTRACTL_END;
+
+    if (pCrst == nullptr)
+    {
+        return;
+    }
+
+    // Reentrant locks are currently not supported
+    _ASSERTE((pCrst->m_dwFlags & CRST_REENTRANCY) == 0);
+
+    Thread *pThread = GetThread();
+    _ASSERTE(pThread != nullptr);
+    if (pThread->IsInForbidSuspendForDebuggerRegion())
+    {
+        AcquireLock(pCrst);
+        return;
+    }
+
+    while (true)
+    {
+        // Enter the forbid region and make that state change visible to other threads (memory barrier) before checking for the
+        // TS_DebugSuspendPending state. The other interacting thread in SysStartSuspendForDebug(), sets TS_DebugSuspendPending
+        // and makes that state change visible to other threads (memory barrier) before checking for whether this thread is in
+        // the forbid region. This ensures that in race conditions where both threads update the respective state and make the
+        // state change visible to other threads, at least one of those threads will see the state change made by the other
+        // thread. If this thread sees the state change (TS_DebugSuspendPending), it will avoid entering the forbid region by
+        // exiting the lock and pulsing the GC mode to try suspending for the debugger. If SysStartSuspendForDebug() sees the
+        // state change (that this thread is in the forbid region), then it will flag this thread appropriately to sync for
+        // suspend, and the debugger will later identify this thread as synced after this thread leaves the forbid region.
+        //
+        // The forbid region could be entered after acquiring the lock, but an additional memory barrier would be necessary. It
+        // is entered before the lock just to make use of the implicit memory barrier from acquiring the lock. It is anyway a
+        // prerequisite for entering a lock along with entering a forbid-suspend-for-debugger region, that the lock is not held
+        // for too long such that the thread can suspend for the debugger in reasonable time.
+        pThread->EnterForbidSuspendForDebuggerRegion();
+        AcquireLock(pCrst); // implicit full memory barrier on all supported platforms
+
+        // This can be an opportunistic check (instead of a volatile load), because if the GC mode change below does not suspend
+        // for the debugger (which is also possible with a volatile load), it will just loop around and try again if necessary
+        if (!pThread->HasThreadStateOpportunistic(Thread::TS_DebugSuspendPending))
+        {
+            m_pThreadForExitingForbidRegion = pThread;
+            return;
+        }
+
+        // Cannot enter the forbid region when a suspend for the debugger is pending because there are likely to be subsequent
+        // changes to the GC mode inside the lock, and this thread needs to suspend for the debugger in reasonable time. Exit
+        // the lock and pulse the GC mode to suspend for the debugger.
+        ReleaseLock(pCrst);
+        pThread->ExitForbidSuspendForDebuggerRegion();
+        GCX_COOP();
+    }
+}
+
+CrstBase::CrstAndForbidSuspendForDebuggerHolder::~CrstAndForbidSuspendForDebuggerHolder()
+{
+    CONTRACTL
+    {
+        NOTHROW;
+        GC_NOTRIGGER;
+        MODE_PREEMPTIVE;
+    }
+    CONTRACTL_END;
+
+    if (m_pCrst == nullptr)
+    {
+        return;
+    }
+
+    ReleaseLock(m_pCrst);
+    if (m_pThreadForExitingForbidRegion != nullptr)
+    {
+        m_pThreadForExitingForbidRegion->ExitForbidSuspendForDebuggerRegion();
+    }
+}
+
 #endif // !DACCESS_COMPILE
 
 #ifdef TEST_DATA_CONSISTENCY
diff --git a/src/coreclr/src/vm/crst.h b/src/coreclr/src/vm/crst.h
index 8bdcaae4f919a3..ed1e393002a9cf 100644
--- a/src/coreclr/src/vm/crst.h
+++ b/src/coreclr/src/vm/crst.h
@@ -362,13 +362,14 @@ friend class Crst;
     {
         m_dwFlags = 0;
     }
+
     // ------------------------------- Holders ------------------------------
- public:
-     //
-     // CrstHolder is optimized for the common use that takes the lock in constructor
-     // and releases it in destructor. Users that require all Holder features
-     // can use CrstHolderWithState.
-     //
+public:
+    //
+    // CrstHolder is optimized for the common use that takes the lock in constructor
+    // and releases it in destructor. Users that require all Holder features
+    // can use CrstHolderWithState.
+    //
     class CrstHolder
     {
         CrstBase * m_pCrst;
@@ -397,11 +398,22 @@ friend class Crst;
     // Generally, it's better to use a regular CrstHolder, and then use the Release() / Acquire() methods on it.
     // This just exists to convert legacy OS Critical Section patterns over to holders.
     typedef DacHolder<CrstBase *, CrstBase::ReleaseLock, CrstBase::AcquireLock, 0, CompareDefault> UnsafeCrstInverseHolder;
+
+    class CrstAndForbidSuspendForDebuggerHolder
+    {
+    private:
+        CrstBase *m_pCrst;
+        Thread *m_pThreadForExitingForbidRegion;
+
+    public:
+        CrstAndForbidSuspendForDebuggerHolder(CrstBase *pCrst);
+        ~CrstAndForbidSuspendForDebuggerHolder();
+    };
 };
 
 typedef CrstBase::CrstHolder CrstHolder;
 typedef CrstBase::CrstHolderWithState CrstHolderWithState;
-
+typedef CrstBase::CrstAndForbidSuspendForDebuggerHolder CrstAndForbidSuspendForDebuggerHolder;
 
 // The CRST.
 class Crst : public CrstBase
diff --git a/src/coreclr/src/vm/customattribute.cpp b/src/coreclr/src/vm/customattribute.cpp
index a06cbf0cb9e8fa..b8fe16ebf4a1c8 100644
--- a/src/coreclr/src/vm/customattribute.cpp
+++ b/src/coreclr/src/vm/customattribute.cpp
@@ -169,7 +169,7 @@ CustomAttributeManagedValues Attribute::GetManagedCaValue(CaValue* pCaVal)
 
             if (length != (ULONG)-1)
             {
-                gc.array = (CaValueArrayREF)AllocateSzArray(TypeHandle(MscorlibBinder::GetClass(CLASS__CUSTOM_ATTRIBUTE_ENCODED_ARGUMENT)).MakeSZArray(), length);
+                gc.array = (CaValueArrayREF)AllocateSzArray(TypeHandle(CoreLibBinder::GetClass(CLASS__CUSTOM_ATTRIBUTE_ENCODED_ARGUMENT)).MakeSZArray(), length);
                 CustomAttributeValue* pValues = gc.array->GetDirectPointerToNonObjectElements();
 
                 for (COUNT_T i = 0; i < length; i ++)
@@ -929,9 +929,9 @@ FCIMPL7(void, COMCustomAttribute::GetPropertyOrFieldData, ReflectModuleBaseObjec
                 {
                     // load the proper type so that code in managed knows which property to load
                     if (fieldType == SERIALIZATION_TYPE_STRING)
-                        *pType = MscorlibBinder::GetElementType(ELEMENT_TYPE_STRING)->GetManagedClassObject();
+                        *pType = CoreLibBinder::GetElementType(ELEMENT_TYPE_STRING)->GetManagedClassObject();
                     else if (fieldType == SERIALIZATION_TYPE_TYPE)
-                        *pType = MscorlibBinder::GetClass(CLASS__TYPE)->GetManagedClassObject();
+                        *pType = CoreLibBinder::GetClass(CLASS__TYPE)->GetManagedClassObject();
                 }
                 break;
             case SERIALIZATION_TYPE_SZARRAY:
@@ -942,9 +942,9 @@ FCIMPL7(void, COMCustomAttribute::GetPropertyOrFieldData, ReflectModuleBaseObjec
                 {
                     _ASSERTE(!bObjectCreated);
                     if (arrayType == SERIALIZATION_TYPE_STRING)
-                        nullTH = TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_STRING));
+                        nullTH = TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_STRING));
                     else if (arrayType == SERIALIZATION_TYPE_TYPE)
-                        nullTH = TypeHandle(MscorlibBinder::GetClass(CLASS__TYPE));
+                        nullTH = TypeHandle(CoreLibBinder::GetClass(CLASS__TYPE));
                     else if (arrayType == SERIALIZATION_TYPE_TAGGED_OBJECT)
                         nullTH = TypeHandle(g_pObjectClass);
                     ReadArray(pCtorAssembly, arrayType, arraySize, nullTH, &pBlob, pBlobEnd, pModule, (BASEARRAYREF*)value);
@@ -955,17 +955,17 @@ FCIMPL7(void, COMCustomAttribute::GetPropertyOrFieldData, ReflectModuleBaseObjec
                     switch (arrayType)
                     {
                         case SERIALIZATION_TYPE_STRING:
-                            arrayTH = TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_STRING));
+                            arrayTH = TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_STRING));
                             break;
                         case SERIALIZATION_TYPE_TYPE:
-                            arrayTH = TypeHandle(MscorlibBinder::GetClass(CLASS__TYPE));
+                            arrayTH = TypeHandle(CoreLibBinder::GetClass(CLASS__TYPE));
                             break;
                         case SERIALIZATION_TYPE_TAGGED_OBJECT:
                             arrayTH = TypeHandle(g_pObjectClass);
                             break;
                         default:
                             if (SERIALIZATION_TYPE_BOOLEAN <= arrayType && arrayType <= SERIALIZATION_TYPE_R8)
-                                arrayTH = TypeHandle(MscorlibBinder::GetElementType((CorElementType)arrayType));
+                                arrayTH = TypeHandle(CoreLibBinder::GetElementType((CorElementType)arrayType));
                     }
                     if (!arrayTH.IsNull())
                     {
@@ -977,7 +977,7 @@ FCIMPL7(void, COMCustomAttribute::GetPropertyOrFieldData, ReflectModuleBaseObjec
             }
             default:
                 if (SERIALIZATION_TYPE_BOOLEAN <= fieldType && fieldType <= SERIALIZATION_TYPE_R8)
-                    pMTValue = MscorlibBinder::GetElementType((CorElementType)fieldType);
+                    pMTValue = CoreLibBinder::GetElementType((CorElementType)fieldType);
                 else if(fieldType == SERIALIZATION_TYPE_ENUM)
                     fieldType = (CorSerializationType)pMTValue->GetInternalCorElementType();
                 else
@@ -1027,12 +1027,12 @@ TypeHandle COMCustomAttribute::GetTypeHandleFromBlob(Assembly *pCtorAssembly,
     case SERIALIZATION_TYPE_U8:
     case SERIALIZATION_TYPE_R8:
     case SERIALIZATION_TYPE_STRING:
-        pMTType = MscorlibBinder::GetElementType((CorElementType)objType);
+        pMTType = CoreLibBinder::GetElementType((CorElementType)objType);
         RtnTypeHnd = TypeHandle(pMTType);
         break;
 
     case ELEMENT_TYPE_CLASS:
-        pMTType = MscorlibBinder::GetClass(CLASS__TYPE);
+        pMTType = CoreLibBinder::GetClass(CLASS__TYPE);
         RtnTypeHnd = TypeHandle(pMTType);
         break;
 
@@ -1386,7 +1386,7 @@ ARG_SLOT COMCustomAttribute::GetDataFromBlob(Assembly *pCtorAssembly,
                 goto stringType;
             else if (pMT == g_pObjectClass)
                 goto typeObject;
-            else if (MscorlibBinder::IsClass(pMT, CLASS__TYPE))
+            else if (CoreLibBinder::IsClass(pMT, CLASS__TYPE))
                 goto typeType;
         }
 
diff --git a/src/coreclr/src/vm/custommarshalerinfo.cpp b/src/coreclr/src/vm/custommarshalerinfo.cpp
index 8396b4520defbd..67acbff136ec36 100644
--- a/src/coreclr/src/vm/custommarshalerinfo.cpp
+++ b/src/coreclr/src/vm/custommarshalerinfo.cpp
@@ -43,7 +43,7 @@ CustomMarshalerInfo::CustomMarshalerInfo(LoaderAllocator *pLoaderAllocator, Type
 
 
     // Make sure the custom marshaller implements ICustomMarshaler.
-    if (!hndCustomMarshalerType.GetMethodTable()->CanCastToInterface(MscorlibBinder::GetClass(CLASS__ICUSTOM_MARSHALER)))
+    if (!hndCustomMarshalerType.GetMethodTable()->CanCastToInterface(CoreLibBinder::GetClass(CLASS__ICUSTOM_MARSHALER)))
     {
         DefineFullyQualifiedNameForClassW()
         COMPlusThrow(kApplicationException,
@@ -304,7 +304,7 @@ MethodDesc *CustomMarshalerInfo::GetCustomMarshalerMD(EnumCustomMarshalerMethods
 
     MethodTable *pMT = hndCustomMarshalertype.AsMethodTable();
 
-    _ASSERTE(pMT->CanCastToInterface(MscorlibBinder::GetClass(CLASS__ICUSTOM_MARSHALER)));
+    _ASSERTE(pMT->CanCastToInterface(CoreLibBinder::GetClass(CLASS__ICUSTOM_MARSHALER)));
 
     MethodDesc *pMD = NULL;
 
@@ -312,28 +312,28 @@ MethodDesc *CustomMarshalerInfo::GetCustomMarshalerMD(EnumCustomMarshalerMethods
     {
         case CustomMarshalerMethods_MarshalNativeToManaged:
             pMD = pMT->GetMethodDescForInterfaceMethod(
-                       MscorlibBinder::GetMethod(METHOD__ICUSTOM_MARSHALER__MARSHAL_NATIVE_TO_MANAGED),
+                       CoreLibBinder::GetMethod(METHOD__ICUSTOM_MARSHALER__MARSHAL_NATIVE_TO_MANAGED),
                        TRUE /* throwOnConflict */);
             break;
         case CustomMarshalerMethods_MarshalManagedToNative:
             pMD = pMT->GetMethodDescForInterfaceMethod(
-                       MscorlibBinder::GetMethod(METHOD__ICUSTOM_MARSHALER__MARSHAL_MANAGED_TO_NATIVE),
+                       CoreLibBinder::GetMethod(METHOD__ICUSTOM_MARSHALER__MARSHAL_MANAGED_TO_NATIVE),
                        TRUE /* throwOnConflict */);
             break;
         case CustomMarshalerMethods_CleanUpNativeData:
             pMD = pMT->GetMethodDescForInterfaceMethod(
-                        MscorlibBinder::GetMethod(METHOD__ICUSTOM_MARSHALER__CLEANUP_NATIVE_DATA),
+                        CoreLibBinder::GetMethod(METHOD__ICUSTOM_MARSHALER__CLEANUP_NATIVE_DATA),
                         TRUE /* throwOnConflict */);
             break;
 
         case CustomMarshalerMethods_CleanUpManagedData:
             pMD = pMT->GetMethodDescForInterfaceMethod(
-                        MscorlibBinder::GetMethod(METHOD__ICUSTOM_MARSHALER__CLEANUP_MANAGED_DATA),
+                        CoreLibBinder::GetMethod(METHOD__ICUSTOM_MARSHALER__CLEANUP_MANAGED_DATA),
                         TRUE /* throwOnConflict */);
             break;
         case CustomMarshalerMethods_GetNativeDataSize:
             pMD = pMT->GetMethodDescForInterfaceMethod(
-                        MscorlibBinder::GetMethod(METHOD__ICUSTOM_MARSHALER__GET_NATIVE_DATA_SIZE),
+                        CoreLibBinder::GetMethod(METHOD__ICUSTOM_MARSHALER__GET_NATIVE_DATA_SIZE),
                         TRUE /* throwOnConflict */);
             break;
         case CustomMarshalerMethods_GetInstance:
diff --git a/src/coreclr/src/vm/debugdebugger.cpp b/src/coreclr/src/vm/debugdebugger.cpp
index ad76de48d20fa7..29e6e3b8d6f7f8 100644
--- a/src/coreclr/src/vm/debugdebugger.cpp
+++ b/src/coreclr/src/vm/debugdebugger.cpp
@@ -51,7 +51,7 @@
 //    internal BCL helpful function doing permission check.  From bucketing perspetive it is
 //    more preferable to report the user managed code that invokes Debugger.Break instead.
 //
-//    User managed code is managed code in non-system assembly.   Currently, only mscorlib.dll
+//    User managed code is managed code in non-system assembly.   Currently, only CoreLib
 //    is marked as system assembly.
 //
 //----------------------------------------------------------------------------
@@ -578,7 +578,7 @@ FCIMPL4(void, DebugStackTrace::GetStackFramesInternal,
                     if (pISymUnmanagedReader != NULL)
                     {
                         // Found a ISymUnmanagedReader for the regular PDB so don't attempt to
-                        // read it as a portable PDB in mscorlib's StackFrameHelper.
+                        // read it as a portable PDB in CoreLib's StackFrameHelper.
                         fPortablePDB = FALSE;
 
                         ReleaseHolder<ISymUnmanagedMethod> pISymUnmanagedMethod;
diff --git a/src/coreclr/src/vm/diagnosticserver.cpp b/src/coreclr/src/vm/diagnosticserver.cpp
index a843cf311a25cf..7688cabe151158 100644
--- a/src/coreclr/src/vm/diagnosticserver.cpp
+++ b/src/coreclr/src/vm/diagnosticserver.cpp
@@ -7,6 +7,7 @@
 #include "eventpipeprotocolhelper.h"
 #include "dumpdiagnosticprotocolhelper.h"
 #include "profilerdiagnosticprotocolhelper.h"
+#include "processdiagnosticsprotocolhelper.h"
 #include "diagnosticsprotocol.h"
 
 #ifdef TARGET_UNIX
@@ -73,12 +74,10 @@ DWORD WINAPI DiagnosticServer::DiagnosticsServerThread(LPVOID)
                 continue;
             }
 
+            STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "DiagnosticServer - received IPC message with command set (%d) and command id (%d)\n", message.GetHeader().CommandSet, message.GetHeader().CommandId);
+
             switch ((DiagnosticsIpc::DiagnosticServerCommandSet)message.GetHeader().CommandSet)
             {
-            case DiagnosticsIpc::DiagnosticServerCommandSet::Server:
-                DiagnosticServerProtocolHelper::HandleIpcMessage(message, pStream);
-                break;
-
             case DiagnosticsIpc::DiagnosticServerCommandSet::EventPipe:
                 EventPipeProtocolHelper::HandleIpcMessage(message, pStream);
                 break;
@@ -87,6 +86,10 @@ DWORD WINAPI DiagnosticServer::DiagnosticsServerThread(LPVOID)
                 DumpDiagnosticProtocolHelper::HandleIpcMessage(message, pStream);
                 break;
 
+            case DiagnosticsIpc::DiagnosticServerCommandSet::Process:
+                ProcessDiagnosticsProtocolHelper::HandleIpcMessage(message,pStream);
+                break;
+
 #ifdef FEATURE_PROFAPI_ATTACH_DETACH
             case DiagnosticsIpc::DiagnosticServerCommandSet::Profiler:
                 ProfilerDiagnosticProtocolHelper::HandleIpcMessage(message, pStream);
@@ -291,49 +294,4 @@ void DiagnosticServer::ResumeRuntimeStartup()
         s_ResumeRuntimeStartupEvent->Set();
 }
 
-void DiagnosticServerProtocolHelper::HandleIpcMessage(DiagnosticsIpc::IpcMessage& message, IpcStream* pStream)
-{
-    CONTRACTL
-    {
-        THROWS;
-        GC_TRIGGERS;
-        MODE_ANY;
-        PRECONDITION(pStream != nullptr);
-    }
-    CONTRACTL_END;
-
-    switch ((DiagnosticsIpc::DiagnosticServerCommandId)message.GetHeader().CommandId)
-    {
-    case DiagnosticsIpc::DiagnosticServerCommandId::ResumeRuntime:
-        DiagnosticServerProtocolHelper::ResumeRuntimeStartup(message, pStream);
-        break;
-
-    default:
-        STRESS_LOG1(LF_DIAGNOSTICS_PORT, LL_WARNING, "Received unknown request type (%d)\n", message.GetHeader().CommandSet);
-        DiagnosticsIpc::IpcMessage::SendErrorMessage(pStream, CORDIAGIPC_E_UNKNOWN_COMMAND);
-        delete pStream;
-        break;
-    }
-}
-
-void DiagnosticServerProtocolHelper::ResumeRuntimeStartup(DiagnosticsIpc::IpcMessage& message, IpcStream *pStream)
-{
-    CONTRACTL
-    {
-        THROWS;
-        GC_TRIGGERS;
-        MODE_PREEMPTIVE;
-        PRECONDITION(pStream != nullptr);
-    }
-    CONTRACTL_END;
-
-    // no payload
-    DiagnosticServer::ResumeRuntimeStartup();
-    HRESULT res = S_OK;
-
-    DiagnosticsIpc::IpcMessage successResponse;
-    if (successResponse.Initialize(DiagnosticsIpc::GenericSuccessHeader, res))
-        successResponse.Send(pStream);
-}
-
 #endif // FEATURE_PERFTRACING
diff --git a/src/coreclr/src/vm/diagnosticserver.h b/src/coreclr/src/vm/diagnosticserver.h
index b7ea71d84192f4..3e001d600ea567 100644
--- a/src/coreclr/src/vm/diagnosticserver.h
+++ b/src/coreclr/src/vm/diagnosticserver.h
@@ -36,14 +36,6 @@ class DiagnosticServer final
     static CLREventStatic *s_ResumeRuntimeStartupEvent;
 };
 
-class DiagnosticServerProtocolHelper
-{
-public:
-    // IPC event handlers.
-    static void HandleIpcMessage(DiagnosticsIpc::IpcMessage& message, IpcStream *pStream);
-    static void ResumeRuntimeStartup(DiagnosticsIpc::IpcMessage& message, IpcStream *pStream);
-};
-
 #endif // FEATURE_PERFTRACING
 
 #endif // __DIAGNOSTIC_SERVER_H__
diff --git a/src/coreclr/src/vm/diagnosticsprotocol.h b/src/coreclr/src/vm/diagnosticsprotocol.h
index e3c471e80a212c..a31c698723a0f8 100644
--- a/src/coreclr/src/vm/diagnosticsprotocol.h
+++ b/src/coreclr/src/vm/diagnosticsprotocol.h
@@ -70,24 +70,15 @@ namespace DiagnosticsIpc
         Dump          = 0x01,
         EventPipe     = 0x02,
         Profiler      = 0x03,
+        Process       = 0x04,
 
         Server        = 0xFF,
     };
 
-    // Overlaps with DiagnosticServerResponseId
-    // DON'T create overlapping values
-    enum class DiagnosticServerCommandId : uint8_t
-    {
-        // 0x00 used in DiagnosticServerResponseId
-        ResumeRuntime = 0x01,
-        // 0xFF used DiagnosticServerResponseId
-    };
-
-    // Overlaps with DiagnosticServerCommandId
-    // DON'T create overlapping values
     enum class DiagnosticServerResponseId : uint8_t
     {
         OK            = 0x00,
+        // future
         Error         = 0xFF,
     };
 
@@ -206,12 +197,12 @@ namespace DiagnosticsIpc
     //
     // For more details on this pattern, look up "Substitution Failure Is Not An Error" or SFINAE
 
-    // template meta-programming to check for bool(Flatten)(void*) member function
+    // template meta-programming to check for bool(Flatten)(BYTE*&, uint16_t&) member function
     template <typename T>
     struct HasFlatten
     {
         template <typename U, U u> struct Has;
-        template <typename U> static std::true_type test(Has<bool (U::*)(void*), &U::Flatten>*);
+        template <typename U> static std::true_type test(Has<bool (U::*)(BYTE*&, uint16_t&), &U::Flatten>*);
         template <typename U> static std::false_type test(...);
         static constexpr bool value = decltype(test<T>(nullptr))::value;
     };
@@ -464,7 +455,7 @@ namespace DiagnosticsIpc
         // Handles the case where the payload structure exposes Flatten
         // and GetSize methods
         template <typename U,
-                  typename std::enable_if<HasFlatten<U>::value&& HasGetSize<U>::value, int>::type = 0>
+                  typename std::enable_if<HasFlatten<U>::value && HasGetSize<U>::value, int>::type = 0>
         bool FlattenImpl(U& payload)
         {
             CONTRACTL
@@ -483,6 +474,7 @@ namespace DiagnosticsIpc
             ASSERT(!temp_size.IsOverflow());
 
             m_Size = temp_size.Value();
+            uint16_t remainingBytes = temp_size.Value();
 
             BYTE* temp_buffer = new (nothrow) BYTE[m_Size];
             if (temp_buffer == nullptr)
@@ -497,13 +489,14 @@ namespace DiagnosticsIpc
 
             memcpy(temp_buffer_cursor, &m_Header, sizeof(struct IpcHeader));
             temp_buffer_cursor += sizeof(struct IpcHeader);
+            remainingBytes -= sizeof(struct IpcHeader);
 
-            payload.Flatten(temp_buffer_cursor);
+            const bool fSuccess = payload.Flatten(temp_buffer_cursor, remainingBytes);
 
             ASSERT(m_pData == nullptr);
             m_pData = temp_buffer;
 
-            return true;
+            return fSuccess;
         };
 
         // handles the case where we were handed a struct with no Flatten or GetSize method
diff --git a/src/coreclr/src/vm/dispatchinfo.cpp b/src/coreclr/src/vm/dispatchinfo.cpp
index 76ee48ff6a9238..817f74eac761d3 100644
--- a/src/coreclr/src/vm/dispatchinfo.cpp
+++ b/src/coreclr/src/vm/dispatchinfo.cpp
@@ -432,7 +432,7 @@ ComMTMethodProps * DispatchMemberInfo::GetMemberProps(OBJECTREF MemberInfoObj, C
     GCPROTECT_BEGIN(MemberInfoObj);
     {
         MethodTable *pMemberInfoClass = MemberInfoObj->GetMethodTable();
-        if (MscorlibBinder::IsClass(pMemberInfoClass, CLASS__METHOD))
+        if (CoreLibBinder::IsClass(pMemberInfoClass, CLASS__METHOD))
         {
             // Retrieve the MethodDesc from the MethodInfo.
             MethodDescCallSite getMethodHandle(METHOD__METHOD_BASE__GET_METHODDESC, &MemberInfoObj);
@@ -441,7 +441,7 @@ ComMTMethodProps * DispatchMemberInfo::GetMemberProps(OBJECTREF MemberInfoObj, C
             if (pMeth)
                 pMemberProps = pMemberMap->GetMethodProps(pMeth->GetMemberDef(), pMeth->GetModule());
         }
-        else if (MscorlibBinder::IsClass(pMemberInfoClass, CLASS__RT_FIELD_INFO))
+        else if (CoreLibBinder::IsClass(pMemberInfoClass, CLASS__RT_FIELD_INFO))
         {
             MethodDescCallSite getFieldHandle(METHOD__RTFIELD__GET_FIELDHANDLE, &MemberInfoObj);
             ARG_SLOT arg = ObjToArgSlot(MemberInfoObj);
@@ -449,7 +449,7 @@ ComMTMethodProps * DispatchMemberInfo::GetMemberProps(OBJECTREF MemberInfoObj, C
             if (pFld)
                 pMemberProps = pMemberMap->GetMethodProps(pFld->GetMemberDef(), pFld->GetModule());
         }
-        else if (MscorlibBinder::IsClass(pMemberInfoClass, CLASS__PROPERTY))
+        else if (CoreLibBinder::IsClass(pMemberInfoClass, CLASS__PROPERTY))
         {
             MethodDescCallSite getToken(METHOD__PROPERTY__GET_TOKEN, &MemberInfoObj);
             ARG_SLOT arg = ObjToArgSlot(MemberInfoObj);
@@ -672,7 +672,7 @@ void DispatchMemberInfo::DetermineCultureAwareness()
     CONTRACTL_END;
 
     // Load the LCIDConversionAttribute type.
-    MethodTable * pLcIdConvAttrClass = MscorlibBinder::GetClass(CLASS__LCID_CONVERSION_TYPE);
+    MethodTable * pLcIdConvAttrClass = CoreLibBinder::GetClass(CLASS__LCID_CONVERSION_TYPE);
 
     // Check to see if the attribute is set.
     OBJECTREF MemberInfoObj = GetMemberInfoObject();
@@ -739,7 +739,7 @@ void DispatchMemberInfo::SetUpParamMarshalerInfo()
     {
         MethodTable *pMemberInfoMT = MemberInfoObj->GetMethodTable();
 
-        if (MscorlibBinder::IsClass(pMemberInfoMT, CLASS__METHOD))
+        if (CoreLibBinder::IsClass(pMemberInfoMT, CLASS__METHOD))
         {
             MethodDescCallSite getMethodHandle(METHOD__METHOD_BASE__GET_METHODDESC, &MemberInfoObj);
             ARG_SLOT arg = ObjToArgSlot(MemberInfoObj);
@@ -747,11 +747,11 @@ void DispatchMemberInfo::SetUpParamMarshalerInfo()
             if (pMeth)
                 SetUpMethodMarshalerInfo(pMeth, FALSE);
         }
-        else if (MscorlibBinder::IsClass(pMemberInfoMT, CLASS__FIELD))
+        else if (CoreLibBinder::IsClass(pMemberInfoMT, CLASS__FIELD))
         {
             // We don't support non-default marshalling behavior for field getter/setter stubs invoked via IDispatch.
         }
-        else if (MscorlibBinder::IsClass(pMemberInfoMT, CLASS__PROPERTY))
+        else if (CoreLibBinder::IsClass(pMemberInfoMT, CLASS__PROPERTY))
         {
             BOOL isGetter = FALSE;
             MethodDescCallSite getSetter(METHOD__PROPERTY__GET_SETTER, &MemberInfoObj);
@@ -1602,7 +1602,7 @@ void DispatchInfo::InvokeMemberWorker(DispatchMemberInfo*   pDispMemberInfo,
                         COMPlusThrowHR(DISP_E_BADPARAMCOUNT);
 
                     // Retrieve the method descriptor that will be called on.
-                    MethodDesc *pMD = GetFieldInfoMD(METHOD__FIELD__GET_VALUE, pObjs->MemberInfo->GetTypeHandle());
+                    MethodDesc *pMD = GetFieldInfoMD(METHOD__FIELD_INFO__GET_VALUE, pObjs->MemberInfo->GetTypeHandle());
                     MethodDescCallSite getValue(pMD, &pObjs->MemberInfo);
 
                     // Prepare the arguments that will be passed to Invoke.
@@ -1624,7 +1624,7 @@ void DispatchInfo::InvokeMemberWorker(DispatchMemberInfo*   pDispMemberInfo,
                         COMPlusThrowHR(DISP_E_NONAMEDARGS);
 
                     // Retrieve the method descriptor that will be called on.
-                    MethodDesc *pMD = GetFieldInfoMD(METHOD__FIELD__SET_VALUE, pObjs->MemberInfo->GetTypeHandle());
+                    MethodDesc *pMD = GetFieldInfoMD(METHOD__FIELD_INFO__SET_VALUE, pObjs->MemberInfo->GetTypeHandle());
                     MethodDescCallSite setValue(pMD, &pObjs->MemberInfo);
 
                     // Prepare the arguments that will be passed to Invoke.
@@ -2540,7 +2540,7 @@ bool DispatchInfo::IsPropertyAccessorVisible(bool fIsSetter, OBJECTREF* pMemberI
 
     MethodTable *pMemberInfoClass = (*pMemberInfo)->GetMethodTable();
 
-    if (MscorlibBinder::IsClass(pMemberInfoClass, CLASS__PROPERTY))
+    if (CoreLibBinder::IsClass(pMemberInfoClass, CLASS__PROPERTY))
     {
         // Get the property's MethodDesc
         MethodDesc* pMDForProperty = NULL;
@@ -2606,14 +2606,14 @@ MethodDesc* DispatchInfo::GetFieldInfoMD(BinderMethodID Method, TypeHandle hndFi
     MethodDesc *pMD;
 
     // If the current class is the standard implementation then return the cached method desc
-    if (MscorlibBinder::IsClass(hndFieldInfoType.GetMethodTable(), CLASS__FIELD))
+    if (CoreLibBinder::IsClass(hndFieldInfoType.GetMethodTable(), CLASS__FIELD))
     {
-        pMD = MscorlibBinder::GetMethod(Method);
+        pMD = CoreLibBinder::GetMethod(Method);
     }
     else
     {
         pMD = MemberLoader::FindMethod(hndFieldInfoType.GetMethodTable(),
-                MscorlibBinder::GetMethodName(Method), MscorlibBinder::GetMethodSig(Method));
+                CoreLibBinder::GetMethodName(Method), CoreLibBinder::GetMethodSig(Method));
     }
     _ASSERTE(pMD && "Unable to find specified FieldInfo method");
 
@@ -2635,14 +2635,14 @@ MethodDesc* DispatchInfo::GetPropertyInfoMD(BinderMethodID Method, TypeHandle hn
     MethodDesc *pMD;
 
     // If the current class is the standard implementation then return the cached method desc if present.
-    if (MscorlibBinder::IsClass(hndPropInfoType.GetMethodTable(), CLASS__PROPERTY))
+    if (CoreLibBinder::IsClass(hndPropInfoType.GetMethodTable(), CLASS__PROPERTY))
     {
-        pMD = MscorlibBinder::GetMethod(Method);
+        pMD = CoreLibBinder::GetMethod(Method);
     }
     else
     {
         pMD = MemberLoader::FindMethod(hndPropInfoType.GetMethodTable(),
-                MscorlibBinder::GetMethodName(Method), MscorlibBinder::GetMethodSig(Method));
+                CoreLibBinder::GetMethodName(Method), CoreLibBinder::GetMethodSig(Method));
     }
     _ASSERTE(pMD && "Unable to find specified PropertyInfo method");
 
@@ -2664,14 +2664,14 @@ MethodDesc* DispatchInfo::GetMethodInfoMD(BinderMethodID Method, TypeHandle hndM
     MethodDesc *pMD;
 
     // If the current class is the standard implementation then return the cached method desc.
-    if (MscorlibBinder::IsClass(hndMethodInfoType.GetMethodTable(), CLASS__METHOD))
+    if (CoreLibBinder::IsClass(hndMethodInfoType.GetMethodTable(), CLASS__METHOD))
     {
-        pMD = MscorlibBinder::GetMethod(Method);
+        pMD = CoreLibBinder::GetMethod(Method);
     }
     else
     {
         pMD = MemberLoader::FindMethod(hndMethodInfoType.GetMethodTable(),
-                MscorlibBinder::GetMethodName(Method), MscorlibBinder::GetMethodSig(Method));
+                CoreLibBinder::GetMethodName(Method), CoreLibBinder::GetMethodSig(Method));
     }
     _ASSERTE(pMD && "Unable to find specified MethodInfo method");
 
@@ -2691,7 +2691,7 @@ MethodDesc* DispatchInfo::GetCustomAttrProviderMD(TypeHandle hndCustomAttrProvid
     CONTRACT_END;
 
     MethodTable *pMT = hndCustomAttrProvider.AsMethodTable();
-    MethodDesc *pMD = pMT->GetMethodDescForInterfaceMethod(MscorlibBinder::GetMethod(METHOD__ICUSTOM_ATTR_PROVIDER__GET_CUSTOM_ATTRIBUTES), TRUE /* throwOnConflict */);
+    MethodDesc *pMD = pMT->GetMethodDescForInterfaceMethod(CoreLibBinder::GetMethod(METHOD__ICUSTOM_ATTR_PROVIDER__GET_CUSTOM_ATTRIBUTES), TRUE /* throwOnConflict */);
 
     // Return the specified method desc.
     RETURN pMD;
@@ -2889,7 +2889,7 @@ OBJECTREF DispatchInfo::GetOleAutBinder()
     if (m_hndOleAutBinder)
         return ObjectFromHandle(m_hndOleAutBinder);
 
-    MethodTable *pOleAutBinderClass = MscorlibBinder::GetClass(CLASS__OLE_AUT_BINDER);
+    MethodTable *pOleAutBinderClass = CoreLibBinder::GetClass(CLASS__OLE_AUT_BINDER);
 
     // Allocate an instance of the OleAutBinder class.
     OBJECTREF OleAutBinder = AllocateObject(pOleAutBinderClass);
@@ -3021,7 +3021,7 @@ MethodDesc* DispatchInfo::GetInvokeMemberMD()
     }
     CONTRACT_END;
 
-    RETURN MscorlibBinder::GetMethod(METHOD__CLASS__INVOKE_MEMBER);
+    RETURN CoreLibBinder::GetMethod(METHOD__CLASS__INVOKE_MEMBER);
 }
 
 // Virtual method to retrieve the object associated with this DispatchInfo that
@@ -3526,7 +3526,7 @@ MethodDesc* DispatchExInfo::GetIReflectMD(BinderMethodID Method)
     CONTRACT_END;
 
     MethodTable *pMT = m_pSimpleWrapperOwner->GetMethodTable();
-    MethodDesc *pMD = pMT->GetMethodDescForInterfaceMethod(MscorlibBinder::GetMethod(Method), TRUE /* throwOnConflict */);
+    MethodDesc *pMD = pMT->GetMethodDescForInterfaceMethod(CoreLibBinder::GetMethod(Method), TRUE /* throwOnConflict */);
 
     // Return the specified method desc.
     RETURN pMD;
@@ -3546,7 +3546,7 @@ MethodDesc* DispatchExInfo::GetIExpandoMD(BinderMethodID Method)
     CONTRACT_END;
 
     MethodTable *pMT = m_pSimpleWrapperOwner->GetMethodTable();
-    MethodDesc *pMD = pMT->GetMethodDescForInterfaceMethod(MscorlibBinder::GetMethod(Method), TRUE /* throwOnConflict */);
+    MethodDesc *pMD = pMT->GetMethodDescForInterfaceMethod(CoreLibBinder::GetMethod(Method), TRUE /* throwOnConflict */);
 
     // Return the specified method desc.
     RETURN pMD;
diff --git a/src/coreclr/src/vm/dllimport.cpp b/src/coreclr/src/vm/dllimport.cpp
index 2fd2fefd1bc8aa..9a99718582fde3 100644
--- a/src/coreclr/src/vm/dllimport.cpp
+++ b/src/coreclr/src/vm/dllimport.cpp
@@ -54,6 +54,9 @@ using namespace clr::fs;
 // Specifies whether coreclr is embedded or standalone
 extern bool g_coreclr_embedded;
 
+// Specifies whether hostpolicy is embedded in executable or standalone
+extern bool g_hostpolicy_embedded;
+
 // remove when we get an updated SDK
 #define LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR 0x00000100
 #define LOAD_LIBRARY_SEARCH_DEFAULT_DIRS 0x00001000
@@ -365,7 +368,7 @@ class ILStubState : public StubState
             pcs->EmitCALL(METHOD__CULTURE_INFO__GET_CURRENT_CULTURE, 0, 1);
 
             // save the current culture
-            LocalDesc locDescCulture(MscorlibBinder::GetClass(CLASS__CULTURE_INFO));
+            LocalDesc locDescCulture(CoreLibBinder::GetClass(CLASS__CULTURE_INFO));
             DWORD dwCultureLocalNum = pcs->NewLocal(locDescCulture);
 
             pcs->EmitSTLOC(dwCultureLocalNum);
@@ -653,7 +656,7 @@ class ILStubState : public StubState
             MetaSig nsig(
                 GetStubTargetMethodSig(),
                 GetStubTargetMethodSigLength(),
-                MscorlibBinder::GetModule(),
+                CoreLibBinder::GetModule(),
                 &typeContext);
 
             CorElementType type;
@@ -881,7 +884,7 @@ class ILStubState : public StubState
             PCCOR_SIGNATURE pManagedSig;
             ULONG           cManagedSig;
 
-            IMDInternalImport* pIMDI = MscorlibBinder::GetModule()->GetMDImport();
+            IMDInternalImport* pIMDI = CoreLibBinder::GetModule()->GetMDImport();
 
             pStubMD->GetSig(&pManagedSig, &cManagedSig);
 
@@ -1246,7 +1249,7 @@ class StructMarshal_ILStubState : public ILStubState
         pCleanupStartLabel = pcsSetup->NewCodeLabel();
         pReturnLabel = pcsSetup->NewCodeLabel();
 
-        dwExceptionDispatchInfoLocal = pcsSetup->NewLocal(MscorlibBinder::GetClass(CLASS__EXCEPTION_DISPATCH_INFO));
+        dwExceptionDispatchInfoLocal = pcsSetup->NewLocal(CoreLibBinder::GetClass(CLASS__EXCEPTION_DISPATCH_INFO));
         pcsSetup->EmitLDNULL();
         pcsSetup->EmitSTLOC(dwExceptionDispatchInfoLocal);
 
@@ -1880,7 +1883,7 @@ void NDirectStubLinker::NeedsCleanupList()
         SetCleanupNeeded();
 
         // we setup a new local that will hold the cleanup work list
-        LocalDesc desc(MscorlibBinder::GetClass(CLASS__CLEANUP_WORK_LIST_ELEMENT));
+        LocalDesc desc(CoreLibBinder::GetClass(CLASS__CLEANUP_WORK_LIST_ELEMENT));
         m_dwCleanupWorkListLocalNum = NewLocal(desc);
     }
 }
@@ -1936,7 +1939,7 @@ void NDirectStubLinker::Begin(DWORD dwStubFlags)
             m_pcsDispatch->EmitADD();
             m_pcsDispatch->EmitLDIND_I();      // get OBJECTHANDLE
             m_pcsDispatch->EmitLDIND_REF();    // get Delegate object
-            m_pcsDispatch->EmitLDFLD(GetToken(MscorlibBinder::GetField(FIELD__DELEGATE__TARGET)));
+            m_pcsDispatch->EmitLDFLD(GetToken(CoreLibBinder::GetField(FIELD__DELEGATE__TARGET)));
         }
     }
 
@@ -2133,7 +2136,7 @@ void NDirectStubLinker::DoNDirect(ILCodeStream *pcsEmit, DWORD dwStubFlags, Meth
     {
         if (SF_IsDelegateStub(dwStubFlags)) // reverse P/Invoke via delegate
         {
-            int tokDelegate_methodPtr = pcsEmit->GetToken(MscorlibBinder::GetField(FIELD__DELEGATE__METHOD_PTR));
+            int tokDelegate_methodPtr = pcsEmit->GetToken(CoreLibBinder::GetField(FIELD__DELEGATE__METHOD_PTR));
 
             EmitLoadStubContext(pcsEmit, dwStubFlags);
             pcsEmit->EmitLDC(offsetof(UMEntryThunk, m_pObjectHandle));
@@ -2955,7 +2958,8 @@ namespace
         _In_ Module *pModule,
         _In_ PCCOR_SIGNATURE pSig,
         _In_ ULONG cSig,
-        _Out_ CorPinvokeMap *pPinvokeMapOut)
+        _Out_ CorPinvokeMap *pPinvokeMapOut,
+        _Out_ UINT *errorResID)
     {
         CONTRACTL
         {
@@ -2966,7 +2970,7 @@ namespace
         CONTRACTL_END
 
         CorUnmanagedCallingConvention callConvMaybe;
-        HRESULT hr = MetaSig::TryGetUnmanagedCallingConventionFromModOpt(pModule, pSig, cSig, &callConvMaybe);
+        HRESULT hr = MetaSig::TryGetUnmanagedCallingConventionFromModOpt(pModule, pSig, cSig, &callConvMaybe, errorResID);
         if (hr != S_OK)
             return hr;
         
@@ -2992,10 +2996,12 @@ void PInvokeStaticSigInfo::InitCallConv(CorPinvokeMap callConv, BOOL bIsVarArg)
         callConv = GetDefaultCallConv(bIsVarArg);
 
     CorPinvokeMap sigCallConv = (CorPinvokeMap)0;
-    HRESULT hr = GetUnmanagedPInvokeCallingConvention(m_pModule, m_sig.GetRawSig(), m_sig.GetRawSigLen(), &sigCallConv);
+    UINT errorResID;
+    HRESULT hr = GetUnmanagedPInvokeCallingConvention(m_pModule, m_sig.GetRawSig(), m_sig.GetRawSigLen(), &sigCallConv, &errorResID);
     if (FAILED(hr))
     {
-        SetError(IDS_EE_NDIRECT_BADNATL); //Bad metadata format
+        // Set an error message specific to P/Invokes or UnmanagedFunction for bad format.
+        SetError(hr == COR_E_BADIMAGEFORMAT ? IDS_EE_NDIRECT_BADNATL : errorResID);
     }
 
     // Do the same WinAPI to StdCall or CDecl for the signature calling convention as well. We need
@@ -4338,7 +4344,7 @@ void NDirect::PopulateNDirectMethodDesc(NDirectMethodDesc* pNMD, PInvokeStaticSi
             // so we have to special-case it here.
             // If a type doesn't have a native representation, we won't set this flag.
             // We'll throw an exception later when setting up the marshalling.
-            if (pRetMT != MscorlibBinder::GetClass(CLASS__DATE_TIME) && pRetMT->HasLayout() && IsUnmanagedValueTypeReturnedByRef(pRetMT->GetNativeSize()))
+            if (pRetMT != CoreLibBinder::GetClass(CLASS__DATE_TIME) && pRetMT->HasLayout() && IsUnmanagedValueTypeReturnedByRef(pRetMT->GetNativeSize()))
             {
                 ndirectflags |= NDirectMethodDesc::kStdCallWithRetBuf;
             }
@@ -5167,7 +5173,7 @@ MethodDesc* NDirect::CreateStructMarshalILStub(MethodTable* pMT)
     LocalDesc i4(ELEMENT_TYPE_I4);
     sigBuilder.NewArg(&i4);
 
-    LocalDesc cleanupWorkList(MscorlibBinder::GetClass(CLASS__CLEANUP_WORK_LIST_ELEMENT));
+    LocalDesc cleanupWorkList(CoreLibBinder::GetClass(CLASS__CLEANUP_WORK_LIST_ELEMENT));
     cleanupWorkList.MakeByRef();
     sigBuilder.NewArg(&cleanupWorkList);
 
@@ -6328,6 +6334,21 @@ namespace
         }
 #endif
 
+        if (g_hostpolicy_embedded)
+        {
+#ifdef TARGET_WINDOWS
+            if (wcscmp(wszLibName, W("hostpolicy.dll")) == 0)
+            {
+                return WszGetModuleHandle(NULL);
+            }
+#else
+            if (wcscmp(wszLibName, W("libhostpolicy")) == 0)
+            {
+                return PAL_LoadLibraryDirect(NULL);
+            }
+#endif
+        }
+
         AppDomain* pDomain = GetAppDomain();
         DWORD loadWithAlteredPathFlags = GetLoadWithAlteredSearchPathFlag();
         bool libNameIsRelativePath = Path::IsRelative(wszLibName);
@@ -6859,7 +6880,12 @@ PCODE GetILStubForCalli(VASigCookie *pVASigCookie, MethodDesc *pMD)
         if (callConv == IMAGE_CEE_CS_CALLCONV_UNMANAGED)
         {
             CorUnmanagedCallingConvention callConvMaybe;
-            if (S_OK == MetaSig::TryGetUnmanagedCallingConventionFromModOpt(pVASigCookie->pModule, signature.GetRawSig(), signature.GetRawSigLen(), &callConvMaybe))
+            UINT errorResID;
+            HRESULT hr = MetaSig::TryGetUnmanagedCallingConventionFromModOpt(pVASigCookie->pModule, signature.GetRawSig(), signature.GetRawSigLen(), &callConvMaybe, &errorResID);
+            if (FAILED(hr))
+                COMPlusThrowHR(hr, errorResID);
+
+            if (hr == S_OK)
             {
                 callConv = callConvMaybe;
             }
diff --git a/src/coreclr/src/vm/domainfile.cpp b/src/coreclr/src/vm/domainfile.cpp
index 2740c1881fab7c..a398b1a92cdab1 100644
--- a/src/coreclr/src/vm/domainfile.cpp
+++ b/src/coreclr/src/vm/domainfile.cpp
@@ -286,7 +286,7 @@ CHECK DomainFile::CheckLoaded()
     if (IsLoaded())
         CHECK_OK;
 
-    // Mscorlib is allowed to run managed code much earlier than other
+    // CoreLib is allowed to run managed code much earlier than other
     // assemblies for bootstrapping purposes.  This is because it has no
     // dependencies, security checks, and doesn't rely on loader notifications.
 
@@ -314,7 +314,7 @@ CHECK DomainFile::CheckActivated()
     if (IsActive())
         CHECK_OK;
 
-    // Mscorlib is allowed to run managed code much earlier than other
+    // CoreLib is allowed to run managed code much earlier than other
     // assemblies for bootstrapping purposes.  This is because it has no
     // dependencies, security checks, and doesn't rely on loader notifications.
 
@@ -423,11 +423,11 @@ OBJECTREF DomainFile::GetExposedModuleObject()
 
         if (GetFile()->IsDynamic())
         {
-            refClass = (REFLECTMODULEBASEREF) AllocateObject(MscorlibBinder::GetClass(CLASS__MODULE_BUILDER));
+            refClass = (REFLECTMODULEBASEREF) AllocateObject(CoreLibBinder::GetClass(CLASS__MODULE_BUILDER));
         }
         else
         {
-            refClass = (REFLECTMODULEBASEREF) AllocateObject(MscorlibBinder::GetClass(CLASS__MODULE));
+            refClass = (REFLECTMODULEBASEREF) AllocateObject(CoreLibBinder::GetClass(CLASS__MODULE));
         }
         refClass->SetModule(m_pModule);
 
@@ -645,7 +645,7 @@ void DomainFile::VerifyNativeImageDependencies(bool verifyOnly)
 
 
         //
-        // CoreCLR hard binds to mscorlib.dll only. Avoid going through the full load.
+        // CoreCLR hard binds to CoreLib only. Avoid going through the full load.
         //
 
 #ifdef _DEBUG
@@ -653,7 +653,7 @@ void DomainFile::VerifyNativeImageDependencies(bool verifyOnly)
         name.InitializeSpec(pDependency->dwAssemblyRef,
                             ((pManifestNativeImage != NULL) ? pManifestNativeImage : pNativeImage)->GetNativeMDImport(),
                             GetDomainAssembly());
-        _ASSERTE(name.IsMscorlib());
+        _ASSERTE(name.IsCoreLib());
 #endif
 
         PEAssembly * pDependencyFile = SystemDomain::SystemFile();
@@ -753,8 +753,8 @@ BOOL DomainFile::IsZapRequired()
         }
         else if (IsSystem())
         {
-            // mscorlib gets loaded before the CompilationDomain gets created.
-            // However, we may be ngening mscorlib itself
+            // CoreLib gets loaded before the CompilationDomain gets created.
+            // However, we may be ngening CoreLib itself
             fileIsBeingNGened = true;
         }
 
@@ -1226,12 +1226,12 @@ OBJECTREF DomainAssembly::GetExposedAssemblyObject()
             // This is unnecessary because the managed InternalAssemblyBuilder object
             // should have already been created at the time of DefineDynamicAssembly
             OVERRIDE_TYPE_LOAD_LEVEL_LIMIT(CLASS_LOADED);
-            pMT = MscorlibBinder::GetClass(CLASS__INTERNAL_ASSEMBLY_BUILDER);
+            pMT = CoreLibBinder::GetClass(CLASS__INTERNAL_ASSEMBLY_BUILDER);
         }
         else
         {
             OVERRIDE_TYPE_LOAD_LEVEL_LIMIT(CLASS_LOADED);
-            pMT = MscorlibBinder::GetClass(CLASS__ASSEMBLY);
+            pMT = CoreLibBinder::GetClass(CLASS__ASSEMBLY);
         }
 
         // Will be TRUE only if LoaderAllocator managed object was already collected and therefore we should
@@ -1793,7 +1793,7 @@ BOOL DomainAssembly::CheckZapDependencyIdentities(PEImage *pNativeImage)
     spec.InitializeSpec(this->GetFile());
 
     // The assembly spec should have the binding context associated with it
-    _ASSERTE(spec.GetBindingContext()  || spec.IsAssemblySpecForMscorlib());
+    _ASSERTE(spec.GetBindingContext()  || spec.IsAssemblySpecForCoreLib());
 
     CORCOMPILE_VERSION_INFO *pVersionInfo = pNativeImage->GetLoadedLayout()->GetNativeVersionInfo();
 
@@ -1818,7 +1818,7 @@ BOOL DomainAssembly::CheckZapDependencyIdentities(PEImage *pNativeImage)
             AssemblySpec name;
             name.InitializeSpec(pDependencies->dwAssemblyDef, pNativeImage->GetNativeMDImport(), this);
 
-            if (!name.IsAssemblySpecForMscorlib())
+            if (!name.IsAssemblySpecForCoreLib())
             {
                 // We just initialized the assembly spec for the NI dependency. This will not have binding context
                 // associated with it, so set it from that of the parent.
diff --git a/src/coreclr/src/vm/domainfile.h b/src/coreclr/src/vm/domainfile.h
index 2f1439b403fdf2..b3a0da389abd8a 100644
--- a/src/coreclr/src/vm/domainfile.h
+++ b/src/coreclr/src/vm/domainfile.h
@@ -445,7 +445,7 @@ enum ReasonForRejectingNativeImage
 {
     ReasonForRejectingNativeImage_NoNiForManifestModule = 0x101,
     ReasonForRejectingNativeImage_DependencyNotNative = 0x102,
-    ReasonForRejectingNativeImage_MscorlibNotNative = 0x103,
+    ReasonForRejectingNativeImage_CoreLibNotNative = 0x103,
     ReasonForRejectingNativeImage_FailedSecurityCheck = 0x104,
     ReasonForRejectingNativeImage_DependencyIdentityMismatch = 0x105,
     ReasonForRejectingNativeImage_CannotShareNiAssemblyNotDomainNeutral = 0x106,
diff --git a/src/coreclr/src/vm/dwreport.cpp b/src/coreclr/src/vm/dwreport.cpp
index 895ecbbadb53da..58aadd134e81b4 100644
--- a/src/coreclr/src/vm/dwreport.cpp
+++ b/src/coreclr/src/vm/dwreport.cpp
@@ -1096,7 +1096,7 @@ ContractFailureKind GetContractFailureKind(OBJECTREF obj)
 
     PTR_MethodTable pMT = obj->GetMethodTable();
 
-    if (MscorlibBinder::IsException(pMT, kContractException))
+    if (CoreLibBinder::IsException(pMT, kContractException))
         return CONTRACTEXCEPTIONREF(obj)->GetContractFailureKind();
 
     // there are cases where the code contracts rewriter will use a ContractException
@@ -1111,7 +1111,7 @@ ContractFailureKind GetContractFailureKind(OBJECTREF obj)
     ContractFailureKind result = CONTRACT_FAILURE_INVARIANT;
 
     // first compare the exception name.
-    PTR_MethodTable pContractExceptionMT = MscorlibBinder::GetClassIfExist(CLASS__CONTRACTEXCEPTION);
+    PTR_MethodTable pContractExceptionMT = CoreLibBinder::GetClassIfExist(CLASS__CONTRACTEXCEPTION);
     _ASSERTE(pContractExceptionMT);
 
     if (pContractExceptionMT)
diff --git a/src/coreclr/src/vm/ecall.cpp b/src/coreclr/src/vm/ecall.cpp
index 94a80c3c4a9408..a86d12c4b434a1 100644
--- a/src/coreclr/src/vm/ecall.cpp
+++ b/src/coreclr/src/vm/ecall.cpp
@@ -16,12 +16,12 @@
 #ifndef DACCESS_COMPILE
 
 #ifdef CROSSGEN_COMPILE
-namespace CrossGenMscorlib
+namespace CrossGenCoreLib
 {
     extern const ECClass c_rgECClasses[];
     extern const int c_nECClasses;
 };
-using namespace CrossGenMscorlib;
+using namespace CrossGenCoreLib;
 #else // CROSSGEN_COMPILE
 extern const ECClass c_rgECClasses[];
 extern const int c_nECClasses;
@@ -53,7 +53,7 @@ Utf8String, but String is similar.)
   add any void-returning metasig declarations if they haven't already been defined elsewhere.
   search "String_RetUtf8Str" for an example of how to do this.
 
-- src/vm/mscorlib.h, search "DEFINE_CLASS(UTF8_STRING" and add the new DEFINE_METHOD
+- src/vm/corelib.h, search "DEFINE_CLASS(UTF8_STRING" and add the new DEFINE_METHOD
   declarations for the Utf8String-returning Ctor methods, referencing the new metasig declarations.
 
 **********/
@@ -118,7 +118,7 @@ void ECall::PopulateManagedStringConstructors()
     _ASSERTE(g_pStringClass != NULL);
     for (int i = 0; i < NumberOfStringConstructors; i++)
     {
-        MethodDesc* pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__STRING__CTORF_FIRST + i));
+        MethodDesc* pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__STRING__CTORF_FIRST + i));
         _ASSERTE(pMD != NULL);
 
         PCODE pDest = pMD->GetMultiCallableAddrOfCode();
@@ -130,7 +130,7 @@ void ECall::PopulateManagedStringConstructors()
     _ASSERTE(g_pUtf8StringClass != NULL);
     for (int i = 0; i < NumberOfUtf8StringConstructors; i++)
     {
-        MethodDesc* pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__UTF8STRING__CTORF_FIRST + i));
+        MethodDesc* pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__UTF8STRING__CTORF_FIRST + i));
         _ASSERTE(pMD != NULL);
 
         PCODE pDest = pMD->GetMultiCallableAddrOfCode();
@@ -148,7 +148,7 @@ void ECall::PopulateManagedCastHelpers()
 
     STANDARD_VM_CONTRACT;
 
-    MethodDesc* pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__ISINSTANCEOFANY));
+    MethodDesc* pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__ISINSTANCEOFANY));
     PCODE pDest = pMD->GetMultiCallableAddrOfCode();
     SetJitHelperFunction(CORINFO_HELP_ISINSTANCEOFANY, pDest);
     // array cast uses the "ANY" helper
@@ -158,16 +158,16 @@ void ECall::PopulateManagedCastHelpers()
     // When interface table uses indirect references, just set interface casts to "ANY" helper
     SetJitHelperFunction(CORINFO_HELP_ISINSTANCEOFINTERFACE, pDest);
 #else
-    pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__ISINSTANCEOFINTERFACE));
+    pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__ISINSTANCEOFINTERFACE));
     pDest = pMD->GetMultiCallableAddrOfCode();
     SetJitHelperFunction(CORINFO_HELP_ISINSTANCEOFINTERFACE, pDest);
 #endif
 
-    pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__ISINSTANCEOFCLASS));
+    pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__ISINSTANCEOFCLASS));
     pDest = pMD->GetMultiCallableAddrOfCode();
     SetJitHelperFunction(CORINFO_HELP_ISINSTANCEOFCLASS, pDest);
 
-    pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__CHKCASTANY));
+    pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__CHKCASTANY));
     pDest = pMD->GetMultiCallableAddrOfCode();
     SetJitHelperFunction(CORINFO_HELP_CHKCASTANY, pDest);
     // array cast uses the "ANY" helper
@@ -177,20 +177,20 @@ void ECall::PopulateManagedCastHelpers()
     // When interface table uses indirect references, just set interface casts to "ANY" handler
     SetJitHelperFunction(CORINFO_HELP_CHKCASTINTERFACE, pDest);
 #else
-    pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__CHKCASTINTERFACE));
+    pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__CHKCASTINTERFACE));
     pDest = pMD->GetMultiCallableAddrOfCode();
     SetJitHelperFunction(CORINFO_HELP_CHKCASTINTERFACE, pDest);
 #endif
 
-    pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__CHKCASTCLASS));
+    pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__CHKCASTCLASS));
     pDest = pMD->GetMultiCallableAddrOfCode();
     SetJitHelperFunction(CORINFO_HELP_CHKCASTCLASS, pDest);
 
-    pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__CHKCASTCLASSSPECIAL));
+    pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__CHKCASTCLASSSPECIAL));
     pDest = pMD->GetMultiCallableAddrOfCode();
     SetJitHelperFunction(CORINFO_HELP_CHKCASTCLASS_SPECIAL, pDest);
 
-    pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__UNBOX));
+    pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__UNBOX));
     pDest = pMD->GetMultiCallableAddrOfCode();
     SetJitHelperFunction(CORINFO_HELP_UNBOX, pDest);
 
@@ -203,14 +203,14 @@ void ECall::PopulateManagedCastHelpers()
     //TODO: revise if this specialcasing is still needed when crossgen supports tailcall optimizations
     //      see: https://github.com/dotnet/runtime/issues/5857
 
-    pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__STELEMREF));
+    pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__STELEMREF));
     pMD->DoPrestub(NULL);
     // This helper is marked AggressiveOptimization and its native code is in its final form.
     // Get the code directly to avoid PreStub indirection.
     pDest = pMD->GetNativeCode();
     SetJitHelperFunction(CORINFO_HELP_ARRADDR_ST, pDest);
 
-    pMD = MscorlibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__LDELEMAREF));
+    pMD = CoreLibBinder::GetMethod((BinderMethodID)(METHOD__CASTHELPERS__LDELEMAREF));
     pMD->DoPrestub(NULL);
     // This helper is marked AggressiveOptimization and its native code is in its final form.
     // Get the code directly to avoid PreStub indirection.
@@ -344,11 +344,11 @@ static INT FindECIndexForMethod(MethodDesc *pMD, const LPVOID* impls)
 
         if (cur->HasSignature())
         {
-            Signature sig = MscorlibBinder::GetTargetSignature(cur->m_pMethodSig);
+            Signature sig = CoreLibBinder::GetTargetSignature(cur->m_pMethodSig);
 
             //@GENERICS: none of these methods belong to generic classes so there is no instantiation info to pass in
             if (!MetaSig::CompareMethodSigs(pMethodSig, cbMethodSigLen, pModule, NULL,
-                                            sig.GetRawSig(), sig.GetRawSigLen(), MscorlibBinder::GetModule(), NULL, FALSE))
+                                            sig.GetRawSig(), sig.GetRawSigLen(), CoreLibBinder::GetModule(), NULL, FALSE))
             {
                 continue;
             }
@@ -461,7 +461,7 @@ PCODE ECall::GetFCallImpl(MethodDesc * pMD, BOOL * pfSharedOrDynamicFCallImpl /*
         // We need to set up the ECFunc properly.  We don't want to use the pMD passed in,
         // since it may disappear.  Instead, use the stable one on Delegate.  Remember
         // that this is 1:M between the FCall and the pMDs.
-        return GetFCallImpl(MscorlibBinder::GetMethod(METHOD__DELEGATE__CONSTRUCT_DELEGATE));
+        return GetFCallImpl(CoreLibBinder::GetMethod(METHOD__DELEGATE__CONSTRUCT_DELEGATE));
     }
 
     // COM imported classes have special constructors
@@ -498,16 +498,16 @@ PCODE ECall::GetFCallImpl(MethodDesc * pMD, BOOL * pfSharedOrDynamicFCallImpl /*
     //
     // You'll see this assert in several situations, almost all being the fault of whomever
     // last touched a particular ecall or fcall method, either here or in the classlibs.
-    // However, you must also ensure you don't have stray copies of mscorlib.dll on your machine.
+    // However, you must also ensure you don't have stray copies of System.Private.CoreLib.dll on your machine.
     // 1) You forgot to add your class to c_rgECClasses, the list of classes w/ ecall & fcall methods.
     // 2) You forgot to add your particular method to the ECFunc array for your class.
     // 3) You misspelled the name of your function and/or classname.
     // 4) The signature of the managed function doesn't match the hardcoded metadata signature
     //    listed in your ECFunc array.  The hardcoded metadata sig is only necessary to disambiguate
     //    overloaded ecall functions - usually you can leave it set to NULL.
-    // 5) Your copy of mscorlib.dll & mscoree.dll are out of sync - rebuild both.
-    // 6) You've loaded the wrong copy of mscorlib.dll.  In msdev's debug menu,
-    //    select the "Modules..." dialog.  Verify the path for mscorlib is right.
+    // 5) Your copy of System.Private.CoreLib.dll & coreclr.dll are out of sync - rebuild both.
+    // 6) You've loaded the wrong copy of System.Private.CoreLib.dll.  In Visual Studio's debug menu,
+    //    select the "Modules..." dialog.  Verify the path for System.Private.CoreLib is right.
     // 7) Someone mucked around with how the signatures in metasig.h are parsed, changing the
     //    interpretation of a part of the signature (this is very rare & extremely unlikely,
     //    but has happened at least once).
@@ -631,7 +631,7 @@ BOOL ECall::CheckUnusedECalls(SetSHash<DWORD>& usedIDs)
 
                 if (!usedIDs.Contains(id))
                 {
-                    printf("CheckMscorlibExtended: Unused ecall found: %s.%s::%s\n", pECClass->m_szNameSpace, c_rgECClasses[ImplsIndex].m_szClassName, ptr->m_szMethodName);
+                    printf("CheckCoreLibExtended: Unused ecall found: %s.%s::%s\n", pECClass->m_szNameSpace, c_rgECClasses[ImplsIndex].m_szClassName, ptr->m_szMethodName);
                     fUnusedFCallsFound = TRUE;
                     continue;
                 }
@@ -641,7 +641,7 @@ BOOL ECall::CheckUnusedECalls(SetSHash<DWORD>& usedIDs)
 
         if (fUnreferencedType)
         {
-            printf("CheckMscorlibExtended: Unused type found: %s.%s\n", c_rgECClasses[ImplsIndex].m_szNameSpace, c_rgECClasses[ImplsIndex].m_szClassName);
+            printf("CheckCoreLibExtended: Unused type found: %s.%s\n", c_rgECClasses[ImplsIndex].m_szNameSpace, c_rgECClasses[ImplsIndex].m_szClassName);
             fUnusedFCallsFound = TRUE;
             continue;
         }
@@ -803,7 +803,7 @@ CorInfoIntrinsics ECall::GetIntrinsicID(MethodDesc* pMD)
         return(CORINFO_INTRINSIC_Illegal);
     }
 
-    // All intrinsic live in mscorlib.dll (FindECFuncForMethod does not work for non-mscorlib intrinsics)
+    // All intrinsic live in CoreLib (FindECFuncForMethod does not work for non-CoreLib intrinsics)
     if (!pMD->GetModule()->IsSystem())
     {
         return(CORINFO_INTRINSIC_Illegal);
diff --git a/src/coreclr/src/vm/ecall.h b/src/coreclr/src/vm/ecall.h
index b677cfe1d18316..19b87538287094 100644
--- a/src/coreclr/src/vm/ecall.h
+++ b/src/coreclr/src/vm/ecall.h
@@ -37,7 +37,7 @@ enum {
     FCFuncFlag_EndOfArray   = 0x01,
     FCFuncFlag_HasSignature = 0x02,
     FCFuncFlag_Unreferenced = 0x04, // Suppress unused fcall check
-    FCFuncFlag_QCall        = 0x08, // QCall - mscorlib.dll to mscorwks.dll transition implemented as PInvoke
+    FCFuncFlag_QCall        = 0x08, // QCall - CoreLib to VM transition implemented as PInvoke
 };
 
 struct ECFunc {
diff --git a/src/coreclr/src/vm/ecalllist.h b/src/coreclr/src/vm/ecalllist.h
index d6b592a8bb88ab..f1827fa3bd97af 100644
--- a/src/coreclr/src/vm/ecalllist.h
+++ b/src/coreclr/src/vm/ecalllist.h
@@ -415,7 +415,7 @@ FCFuncStart(gCOMClassWriter)
 FCFuncEnd()
 
 FCFuncStart(gCompatibilitySwitchFuncs)
-    FCFuncElement("GetValueInternalCall", CompatibilitySwitch::GetValue)
+    FCFuncElement("GetValueInternal", CompatibilitySwitch::GetValue)
 FCFuncEnd()
 
 FCFuncStart(gMdUtf8String)
@@ -530,65 +530,65 @@ FCFuncStart(gDelegateFuncs)
 FCFuncEnd()
 
 FCFuncStart(gMathFuncs)
-    FCIntrinsicSig("Abs", &gsig_SM_Dbl_RetDbl, COMDouble::Abs, CORINFO_INTRINSIC_Abs)
-    FCIntrinsicSig("Abs", &gsig_SM_Flt_RetFlt, COMSingle::Abs, CORINFO_INTRINSIC_Abs)
-    FCIntrinsic("Acos", COMDouble::Acos, CORINFO_INTRINSIC_Acos)
-    FCIntrinsic("Acosh", COMDouble::Acosh, CORINFO_INTRINSIC_Acosh)
-    FCIntrinsic("Asin", COMDouble::Asin, CORINFO_INTRINSIC_Asin)
-    FCIntrinsic("Asinh", COMDouble::Asinh, CORINFO_INTRINSIC_Asinh)
-    FCIntrinsic("Atan", COMDouble::Atan, CORINFO_INTRINSIC_Atan)
-    FCIntrinsic("Atanh", COMDouble::Atanh, CORINFO_INTRINSIC_Atanh)
-    FCIntrinsic("Atan2", COMDouble::Atan2, CORINFO_INTRINSIC_Atan2)
-    FCIntrinsic("Cbrt", COMDouble::Cbrt, CORINFO_INTRINSIC_Cbrt)
-    FCIntrinsic("Ceiling", COMDouble::Ceil, CORINFO_INTRINSIC_Ceiling)
-    FCIntrinsic("Cos", COMDouble::Cos, CORINFO_INTRINSIC_Cos)
-    FCIntrinsic("Cosh", COMDouble::Cosh, CORINFO_INTRINSIC_Cosh)
-    FCIntrinsic("Exp", COMDouble::Exp, CORINFO_INTRINSIC_Exp)
-    FCIntrinsic("Floor", COMDouble::Floor, CORINFO_INTRINSIC_Floor)
+    FCFuncElementSig("Abs", &gsig_SM_Dbl_RetDbl, COMDouble::Abs)
+    FCFuncElementSig("Abs", &gsig_SM_Flt_RetFlt, COMSingle::Abs)
+    FCFuncElement("Acos", COMDouble::Acos)
+    FCFuncElement("Acosh", COMDouble::Acosh)
+    FCFuncElement("Asin", COMDouble::Asin)
+    FCFuncElement("Asinh", COMDouble::Asinh)
+    FCFuncElement("Atan", COMDouble::Atan)
+    FCFuncElement("Atanh", COMDouble::Atanh)
+    FCFuncElement("Atan2", COMDouble::Atan2)
+    FCFuncElement("Cbrt", COMDouble::Cbrt)
+    FCFuncElement("Ceiling", COMDouble::Ceil)
+    FCFuncElement("Cos", COMDouble::Cos)
+    FCFuncElement("Cosh", COMDouble::Cosh)
+    FCFuncElement("Exp", COMDouble::Exp)
+    FCFuncElement("Floor", COMDouble::Floor)
     FCFuncElement("FMod", COMDouble::FMod)
     FCFuncElement("FusedMultiplyAdd", COMDouble::FusedMultiplyAdd)
     FCFuncElement("ILogB", COMDouble::ILogB)
     FCFuncElement("Log", COMDouble::Log)
     FCFuncElement("Log2", COMDouble::Log2)
-    FCIntrinsic("Log10", COMDouble::Log10, CORINFO_INTRINSIC_Log10)
+    FCFuncElement("Log10", COMDouble::Log10)
     FCFuncElement("ModF", COMDouble::ModF)
-    FCIntrinsic("Pow", COMDouble::Pow, CORINFO_INTRINSIC_Pow)
+    FCFuncElement("Pow", COMDouble::Pow)
     FCFuncElement("ScaleB", COMDouble::ScaleB)
-    FCIntrinsic("Sin", COMDouble::Sin, CORINFO_INTRINSIC_Sin)
-    FCIntrinsic("Sinh", COMDouble::Sinh, CORINFO_INTRINSIC_Sinh)
-    FCIntrinsic("Sqrt", COMDouble::Sqrt, CORINFO_INTRINSIC_Sqrt)
-    FCIntrinsic("Tan", COMDouble::Tan, CORINFO_INTRINSIC_Tan)
-    FCIntrinsic("Tanh", COMDouble::Tanh, CORINFO_INTRINSIC_Tanh)
+    FCFuncElement("Sin", COMDouble::Sin)
+    FCFuncElement("Sinh", COMDouble::Sinh)
+    FCFuncElement("Sqrt", COMDouble::Sqrt)
+    FCFuncElement("Tan", COMDouble::Tan)
+    FCFuncElement("Tanh", COMDouble::Tanh)
 FCFuncEnd()
 
 FCFuncStart(gMathFFuncs)
-    FCIntrinsic("Acos", COMSingle::Acos, CORINFO_INTRINSIC_Acos)
-    FCIntrinsic("Acosh", COMSingle::Acosh, CORINFO_INTRINSIC_Acosh)
-    FCIntrinsic("Asin", COMSingle::Asin, CORINFO_INTRINSIC_Asin)
-    FCIntrinsic("Asinh", COMSingle::Asinh, CORINFO_INTRINSIC_Asinh)
-    FCIntrinsic("Atan", COMSingle::Atan, CORINFO_INTRINSIC_Atan)
-    FCIntrinsic("Atanh", COMSingle::Atanh, CORINFO_INTRINSIC_Atanh)
-    FCIntrinsic("Atan2", COMSingle::Atan2, CORINFO_INTRINSIC_Atan2)
-    FCIntrinsic("Cbrt", COMSingle::Cbrt, CORINFO_INTRINSIC_Cbrt)
-    FCIntrinsic("Ceiling", COMSingle::Ceil, CORINFO_INTRINSIC_Ceiling)
-    FCIntrinsic("Cos", COMSingle::Cos, CORINFO_INTRINSIC_Cos)
-    FCIntrinsic("Cosh", COMSingle::Cosh, CORINFO_INTRINSIC_Cosh)
-    FCIntrinsic("Exp", COMSingle::Exp, CORINFO_INTRINSIC_Exp)
-    FCIntrinsic("Floor", COMSingle::Floor, CORINFO_INTRINSIC_Floor)
+    FCFuncElement("Acos", COMSingle::Acos)
+    FCFuncElement("Acosh", COMSingle::Acosh)
+    FCFuncElement("Asin", COMSingle::Asin)
+    FCFuncElement("Asinh", COMSingle::Asinh)
+    FCFuncElement("Atan", COMSingle::Atan)
+    FCFuncElement("Atanh", COMSingle::Atanh)
+    FCFuncElement("Atan2", COMSingle::Atan2)
+    FCFuncElement("Cbrt", COMSingle::Cbrt)
+    FCFuncElement("Ceiling", COMSingle::Ceil)
+    FCFuncElement("Cos", COMSingle::Cos)
+    FCFuncElement("Cosh", COMSingle::Cosh)
+    FCFuncElement("Exp", COMSingle::Exp)
+    FCFuncElement("Floor", COMSingle::Floor)
     FCFuncElement("FMod", COMSingle::FMod)
     FCFuncElement("FusedMultiplyAdd", COMSingle::FusedMultiplyAdd)
     FCFuncElement("ILogB", COMSingle::ILogB)
     FCFuncElement("Log", COMSingle::Log)
     FCFuncElement("Log2", COMSingle::Log2)
-    FCIntrinsic("Log10", COMSingle::Log10, CORINFO_INTRINSIC_Log10)
+    FCFuncElement("Log10", COMSingle::Log10)
     FCFuncElement("ModF", COMSingle::ModF)
-    FCIntrinsic("Pow", COMSingle::Pow, CORINFO_INTRINSIC_Pow)
+    FCFuncElement("Pow", COMSingle::Pow)
     FCFuncElement("ScaleB", COMSingle::ScaleB)
-    FCIntrinsic("Sin", COMSingle::Sin, CORINFO_INTRINSIC_Sin)
-    FCIntrinsic("Sinh", COMSingle::Sinh, CORINFO_INTRINSIC_Sinh)
-    FCIntrinsic("Sqrt", COMSingle::Sqrt, CORINFO_INTRINSIC_Sqrt)
-    FCIntrinsic("Tan", COMSingle::Tan, CORINFO_INTRINSIC_Tan)
-    FCIntrinsic("Tanh", COMSingle::Tanh, CORINFO_INTRINSIC_Tanh)
+    FCFuncElement("Sin", COMSingle::Sin)
+    FCFuncElement("Sinh", COMSingle::Sinh)
+    FCFuncElement("Sqrt", COMSingle::Sqrt)
+    FCFuncElement("Tan", COMSingle::Tan)
+    FCFuncElement("Tanh", COMSingle::Tanh)
 FCFuncEnd()
 
 FCFuncStart(gThreadFuncs)
@@ -776,12 +776,10 @@ FCFuncStart(gInteropMarshalFuncs)
     FCFuncElement("IsComObject", MarshalNative::IsComObject)
     FCFuncElement("GetObjectForIUnknownNative", MarshalNative::GetObjectForIUnknownNative)
     FCFuncElement("GetUniqueObjectForIUnknownNative", MarshalNative::GetUniqueObjectForIUnknownNative)
-    FCFuncElement("AddRef", MarshalNative::AddRef)
     FCFuncElement("GetNativeVariantForObject", MarshalNative::GetNativeVariantForObject)
     FCFuncElement("GetObjectForNativeVariant", MarshalNative::GetObjectForNativeVariant)
     FCFuncElement("InternalFinalReleaseComObject", MarshalNative::FinalReleaseComObject)
     FCFuncElement("IsTypeVisibleFromCom", MarshalNative::IsTypeVisibleFromCom)
-    FCFuncElement("QueryInterface", MarshalNative::QueryInterface)
     FCFuncElement("CreateAggregatedObject", MarshalNative::CreateAggregatedObject)
     FCFuncElement("AreComObjectsAvailableForCleanup", MarshalNative::AreComObjectsAvailableForCleanup)
     FCFuncElement("InternalCreateWrapperOfType", MarshalNative::InternalCreateWrapperOfType)
@@ -792,7 +790,6 @@ FCFuncStart(gInteropMarshalFuncs)
     FCFuncElement("GetIDispatchForObjectNative", MarshalNative::GetIDispatchForObjectNative)
     FCFuncElement("GetComInterfaceForObjectNative", MarshalNative::GetComInterfaceForObjectNative)
     FCFuncElement("InternalReleaseComObject", MarshalNative::ReleaseComObject)
-    FCFuncElement("Release", MarshalNative::Release)
     FCFuncElement("GetTypedObjectForIUnknown", MarshalNative::GetTypedObjectForIUnknown)
     FCFuncElement("ChangeWrapperHandleStrength", MarshalNative::ChangeWrapperHandleStrength)
     FCFuncElement("CleanupUnusedObjectsInCurrentContext", MarshalNative::CleanupUnusedObjectsInCurrentContext)
@@ -1091,6 +1088,12 @@ FCFuncStart(gPalOleAut32Funcs)
 FCFuncEnd()
 #endif
 
+#if defined(TARGET_X86) || defined(TARGET_AMD64)
+FCFuncStart(gX86BaseFuncs)
+    QCFuncElement("__cpuidex", SystemNative::X86BaseCpuId)
+FCFuncEnd()
+#endif // defined(TARGET_X86) || defined(TARGET_AMD64)
+
 #ifdef FEATURE_COMINTEROP
 
 //
@@ -1238,6 +1241,10 @@ FCClassElement("WaitHandle", "System.Threading", gWaitHandleFuncs)
 FCClassElement("WeakReference", "System", gWeakReferenceFuncs)
 FCClassElement("WeakReference`1", "System", gWeakReferenceOfTFuncs)
 
+#if defined(TARGET_X86) || defined(TARGET_AMD64)
+FCClassElement("X86Base", "System.Runtime.Intrinsics.X86", gX86BaseFuncs)
+#endif // defined(TARGET_X86) || defined(TARGET_AMD64)
+
 #if defined(FEATURE_EVENTSOURCE_XPLAT)
 FCClassElement("XplatEventLogger", "System.Diagnostics.Tracing", gEventLogger)
 #endif //defined(FEATURE_EVENTSOURCE_XPLAT)
diff --git a/src/coreclr/src/vm/eedbginterfaceimpl.cpp b/src/coreclr/src/vm/eedbginterfaceimpl.cpp
index 469c2221f47bb8..002250d72825e8 100644
--- a/src/coreclr/src/vm/eedbginterfaceimpl.cpp
+++ b/src/coreclr/src/vm/eedbginterfaceimpl.cpp
@@ -930,7 +930,7 @@ TypeHandle EEDbgInterfaceImpl::FindLoadedElementType(CorElementType et)
     // Lookup operations run the class loader in non-load mode.
     ENABLE_FORBID_GC_LOADER_USE_IN_THIS_SCOPE();
 
-    MethodTable *m = MscorlibBinder::GetElementType(et);
+    MethodTable *m = CoreLibBinder::GetElementType(et);
 
     return TypeHandle(m);
 }
@@ -1021,7 +1021,7 @@ TypeHandle EEDbgInterfaceImpl::LoadElementType(CorElementType et)
     }
     CONTRACTL_END;
 
-    MethodTable *m = MscorlibBinder::GetElementType(et);
+    MethodTable *m = CoreLibBinder::GetElementType(et);
 
     if (m == NULL)
     {
diff --git a/src/coreclr/src/vm/encee.cpp b/src/coreclr/src/vm/encee.cpp
index 7852863a4bfb65..a230ae29bb4844 100644
--- a/src/coreclr/src/vm/encee.cpp
+++ b/src/coreclr/src/vm/encee.cpp
@@ -1107,7 +1107,7 @@ EnCAddedField *EnCAddedField::Allocate(OBJECTREF thisPointer, EnCFieldDesc *pFD)
     // the OBJECTREF address so we need to hand out something else that is hooked up to the handle.
 
     GCPROTECT_BEGIN(thisPointer);
-    MethodTable *pHelperMT = MscorlibBinder::GetClass(CLASS__ENC_HELPER);
+    MethodTable *pHelperMT = CoreLibBinder::GetClass(CLASS__ENC_HELPER);
     pEntry->m_FieldData = pDomain->CreateDependentHandle(thisPointer, AllocateObject(pHelperMT));
     GCPROTECT_END();
 
@@ -1139,7 +1139,7 @@ EnCAddedField *EnCAddedField::Allocate(OBJECTREF thisPointer, EnCFieldDesc *pFD)
         GCPROTECT_BEGIN (obj);
 
         // Get a FieldDesc for the object reference field in the EnC helper object (warning: triggers)
-        FieldDesc *pHelperField = MscorlibBinder::GetField(FIELD__ENC_HELPER__OBJECT_REFERENCE);
+        FieldDesc *pHelperField = CoreLibBinder::GetField(FIELD__ENC_HELPER__OBJECT_REFERENCE);
 
         // store the empty boxed object into the helper object
         IGCHandleManager *mgr = GCHandleUtilities::GetGCHandleManager();
@@ -1260,7 +1260,7 @@ PTR_CBYTE EnCSyncBlockInfo::ResolveField(OBJECTREF thisPointer, EnCFieldDesc *pF
 
     // We _HAVE_ to call GetExistingField b/c (a) we can't throw exceptions, and
     // (b) we _DON'T_ want to run class init code, either.
-    pHelperFieldDesc = MscorlibBinder::GetExistingField(FIELD__ENC_HELPER__OBJECT_REFERENCE);
+    pHelperFieldDesc = CoreLibBinder::GetExistingField(FIELD__ENC_HELPER__OBJECT_REFERENCE);
     if (pHelperFieldDesc == NULL)
     {
         return NULL;
@@ -1348,7 +1348,7 @@ PTR_CBYTE EnCSyncBlockInfo::ResolveOrAllocateField(OBJECTREF thisPointer, EnCFie
 
     FieldDesc * pHelperField = NULL;
     GCPROTECT_BEGIN (pHelper);
-    pHelperField = MscorlibBinder::GetField(FIELD__ENC_HELPER__OBJECT_REFERENCE);
+    pHelperField = CoreLibBinder::GetField(FIELD__ENC_HELPER__OBJECT_REFERENCE);
     GCPROTECT_END ();
 
     return GetEnCFieldAddrFromHelperFieldDesc(pHelperField, pHelper, pFD);
diff --git a/src/coreclr/src/vm/eventing/CMakeLists.txt b/src/coreclr/src/vm/eventing/CMakeLists.txt
index 98dd158df54577..e2bf024fc59fd0 100644
--- a/src/coreclr/src/vm/eventing/CMakeLists.txt
+++ b/src/coreclr/src/vm/eventing/CMakeLists.txt
@@ -8,12 +8,13 @@ else()
   set(NEED_XPLAT_HEADER ON)
 endif()
 
-include(FindPython)
+include(FindPythonInterp)
 
 set (EventingHeaders
   ${GENERATED_INCLUDE_DIR}/etmdummy.h
   ${GENERATED_INCLUDE_DIR}/clretwallmain.h
   ${GENERATED_INCLUDE_DIR}/clreventpipewriteevents.h
+  ${GENERATED_INCLUDE_DIR}/clrproviders.h
 )
 
 if (NEED_XPLAT_HEADER)
@@ -24,7 +25,7 @@ endif()
 set(GENEVENTING_SCRIPT ${CLR_DIR}/src/scripts/genEventing.py)
 
 add_custom_target(eventing_headers
-  ${Python_EXECUTABLE} ${GENEVENTING_SCRIPT} --man ${EVENT_MANIFEST} --inc ${GENERATED_INCLUDE_DIR} --dummy ${GENERATED_INCLUDE_DIR}/etmdummy.h ${NONEXTERN_ARG} ${NOXPLATHEADER_ARG}
+  ${PYTHON_EXECUTABLE} ${GENEVENTING_SCRIPT} --man ${EVENT_MANIFEST} --inc ${GENERATED_INCLUDE_DIR} --dummy ${GENERATED_INCLUDE_DIR}/etmdummy.h ${NONEXTERN_ARG} ${NOXPLATHEADER_ARG}
   DEPENDS ${EVENT_MANIFEST} ${GENEVENTING_SCRIPT}
   VERBATIM
 )
diff --git a/src/coreclr/src/vm/eventing/EtwProvider/CMakeLists.txt b/src/coreclr/src/vm/eventing/EtwProvider/CMakeLists.txt
index 34a067e1ec5427..4c7df2fbb3cf1a 100644
--- a/src/coreclr/src/vm/eventing/EtwProvider/CMakeLists.txt
+++ b/src/coreclr/src/vm/eventing/EtwProvider/CMakeLists.txt
@@ -1,4 +1,4 @@
-include(FindPython)
+include(FindPythonInterp)
 
 set(ETW_PROVIDER_SCRIPT ${CLR_DIR}/src/scripts/genEtwProvider.py)
 
@@ -14,5 +14,5 @@ set (ETW_PROVIDER_OUTPUTS
 set_source_files_properties(${ETW_PROVIDER_OUTPUTS} PROPERTIES GENERATED TRUE)
 
 add_custom_target(eventprovider
-  ${Python_EXECUTABLE} ${ETW_PROVIDER_SCRIPT} --man ${EVENT_MANIFEST} --exc ${EVENT_EXCLUSIONS} --intermediate ${GENERATED_INCLUDE_DIR}
+  ${PYTHON_EXECUTABLE} ${ETW_PROVIDER_SCRIPT} --man ${EVENT_MANIFEST} --exc ${EVENT_EXCLUSIONS} --intermediate ${GENERATED_INCLUDE_DIR}
   DEPENDS ${EVENT_MANIFEST} ${EVENT_EXCLUSIONS} ${ETW_PROVIDER_SCRIPT})
diff --git a/src/coreclr/src/vm/eventing/eventpipe/CMakeLists.txt b/src/coreclr/src/vm/eventing/eventpipe/CMakeLists.txt
index 4e816676b8a755..00d79737e54cfc 100644
--- a/src/coreclr/src/vm/eventing/eventpipe/CMakeLists.txt
+++ b/src/coreclr/src/vm/eventing/eventpipe/CMakeLists.txt
@@ -1,9 +1,9 @@
-include(FindPython)
+include(FindPythonInterp)
 
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
 
 set(GENERATE_SCRIPT ${CLR_DIR}/src/scripts/genEventPipe.py)
-set(GENERATE_COMMAND ${Python_EXECUTABLE} ${GENERATE_SCRIPT} --man ${EVENT_MANIFEST} --exc ${EVENT_EXCLUSIONS} --intermediate ${CMAKE_CURRENT_BINARY_DIR} ${NONEXTERN_ARG})
+set(GENERATE_COMMAND ${PYTHON_EXECUTABLE} ${GENERATE_SCRIPT} --man ${EVENT_MANIFEST} --exc ${EVENT_EXCLUSIONS} --intermediate ${CMAKE_CURRENT_BINARY_DIR} ${NONEXTERN_ARG})
 
 execute_process(
   COMMAND ${GENERATE_COMMAND} --dry-run
@@ -28,10 +28,8 @@ add_custom_command(OUTPUT ${EVENTPIPE_SOURCES}
   COMMAND ${GENERATE_COMMAND}
   DEPENDS ${GENERATE_SCRIPT} ${EVENT_MANIFEST} ${EVENT_EXCLUSIONS})
 
-add_library_clr(eventpipe OBJECT ${EVENTPIPE_SOURCES})
-set_target_properties(eventpipe PROPERTIES LINKER_LANGUAGE CXX)
-add_dependencies(eventpipe eventing_headers)
-
-if (NOT CLR_CMAKE_TARGET_WIN32)
-  _install(TARGETS eventpipe DESTINATION lib)
-endif()
+add_library_clr(eventpipe_obj OBJECT ${EVENTPIPE_SOURCES})
+set_target_properties(eventpipe_obj PROPERTIES LINKER_LANGUAGE CXX)
+add_dependencies(eventpipe_obj eventing_headers)
+add_library(eventpipe INTERFACE)
+target_sources(eventpipe INTERFACE $<TARGET_OBJECTS:eventpipe_obj>)
diff --git a/src/coreclr/src/vm/eventpipeevent.cpp b/src/coreclr/src/vm/eventpipeevent.cpp
index 62d97c07820fc6..79c56d8bef7997 100644
--- a/src/coreclr/src/vm/eventpipeevent.cpp
+++ b/src/coreclr/src/vm/eventpipeevent.cpp
@@ -74,7 +74,7 @@ BYTE *EventPipeEvent::BuildMinimumMetadata()
     BYTE *minmumMetadata = new BYTE[MinimumMetadataLength];
     BYTE *currentPtr = minmumMetadata;
 
-    // the order of fields is defined in coreclr\src\mscorlib\shared\System\Diagnostics\Tracing\EventSource.cs DefineEventPipeEvents method
+    // the order of fields is defined in EventSource.cs DefineEventPipeEvents method
     memcpy(currentPtr, &m_eventID, sizeof(m_eventID));
     currentPtr += sizeof(m_eventID);
 
diff --git a/src/coreclr/src/vm/eventpipeeventsource.h b/src/coreclr/src/vm/eventpipeeventsource.h
index d271ce0f67f459..9100cbdef841f1 100644
--- a/src/coreclr/src/vm/eventpipeeventsource.h
+++ b/src/coreclr/src/vm/eventpipeeventsource.h
@@ -19,15 +19,15 @@ class EventPipeEventSource
     const static WCHAR* s_pProcessInfoEventName;
     EventPipeEvent *m_pProcessInfoEvent;
 
-    const static WCHAR* s_pOSInformation;
-    const static WCHAR* s_pArchInformation;
-
 public:
     EventPipeEventSource();
     ~EventPipeEventSource();
 
     void Enable(EventPipeSession *pSession);
     void SendProcessInfo(LPCWSTR pCommandLine);
+
+    const static WCHAR* s_pOSInformation;
+    const static WCHAR* s_pArchInformation;
 };
 
 #endif // FEATURE_PERFTRACING
diff --git a/src/coreclr/src/vm/eventpipeprovider.cpp b/src/coreclr/src/vm/eventpipeprovider.cpp
index 9bc84079a65e5d..7aaa31f887b14d 100644
--- a/src/coreclr/src/vm/eventpipeprovider.cpp
+++ b/src/coreclr/src/vm/eventpipeprovider.cpp
@@ -306,6 +306,9 @@ void EventPipeProvider::SetDeleteDeferred()
 {
     LIMITED_METHOD_CONTRACT;
     m_deleteDeferred = true;
+    // EventSources will be collected once they ungregister themselves,
+    // so we can't call back in to them.
+    m_pCallbackFunction = NULL;
 }
 
 void EventPipeProvider::RefreshAllEvents()
diff --git a/src/coreclr/src/vm/eventtrace.cpp b/src/coreclr/src/vm/eventtrace.cpp
index 8ec702036b0021..67a1340723976e 100644
--- a/src/coreclr/src/vm/eventtrace.cpp
+++ b/src/coreclr/src/vm/eventtrace.cpp
@@ -31,6 +31,7 @@
 #include "dbginterface.h"
 #include "finalizerthread.h"
 #include "clrversion.h"
+#include "typestring.h"
 
 #define Win32EventWrite EventWrite
 
@@ -3152,6 +3153,65 @@ CrstBase * ETW::TypeSystemLog::GetHashCrst()
     return &AllLoggedTypes::s_cs;
 }
 
+// The number of type load operations
+// NOTE: This isn't the count of types loaded, as some types may have multiple type loads
+//       occur to them as they transition up type loader levels
+LONG s_TypeLoadOps = 0;
+
+UINT32 ETW::TypeSystemLog::TypeLoadBegin()
+{
+    CONTRACTL{
+        NOTHROW;
+        GC_TRIGGERS;
+    } CONTRACTL_END;
+
+    UINT32 typeLoad = (UINT32)InterlockedIncrement(&s_TypeLoadOps);
+
+    if (ETW_EVENT_ENABLED(MICROSOFT_WINDOWS_DOTNETRUNTIME_PROVIDER_DOTNET_Context, TypeLoadStart))
+    {
+        FireEtwTypeLoadStart(
+            typeLoad,
+            GetClrInstanceId());
+    }
+
+    return typeLoad;
+}
+
+void ETW::TypeSystemLog::TypeLoadEnd(UINT32 typeLoad, TypeHandle th, UINT16 loadLevel)
+{
+    CONTRACTL{
+        NOTHROW;
+        THROWS;
+    } CONTRACTL_END;
+
+    if (ETW_EVENT_ENABLED(MICROSOFT_WINDOWS_DOTNETRUNTIME_PROVIDER_DOTNET_Context, TypeLoadStop))
+    {
+        EX_TRY
+        {
+            StackSString typeName;
+            const TypeString::FormatFlags formatFlags = static_cast<TypeString::FormatFlags>(
+                TypeString::FormatNamespace |
+                TypeString::FormatAngleBrackets);
+
+            TypeString::AppendType(typeName, th, formatFlags);
+
+            SCOUNT_T maxTypeNameLen = (cbMaxEtwEvent / 2) - 0x100;
+            if (typeName.GetCount() > (unsigned)maxTypeNameLen)
+            {
+                typeName.Truncate(typeName.Begin() + maxTypeNameLen);
+            }
+
+            FireEtwTypeLoadStop(
+                typeLoad,
+                GetClrInstanceId(),
+                loadLevel,
+                (UINT64)th.AsPtr(),
+                typeName
+                );
+        } EX_CATCH{ } EX_END_CATCH(SwallowAllExceptions);
+    }
+}
+
 //---------------------------------------------------------------------------------------
 //
 // Outermost level of ETW-type-logging.  Clients outside eventtrace.cpp call this to log
@@ -4669,7 +4729,7 @@ VOID ETW::ExceptionLog::ExceptionThrown(CrawlFrame  *pCf, BOOL bIsReThrownExcept
         _ASSERTE(pExInfo != NULL);
         bIsNestedException = (pExInfo->GetPreviousExceptionTracker() != NULL);
         bIsCLSCompliant = IsException((gc.exceptionObj)->GetMethodTable()) &&
-                          ((gc.exceptionObj)->GetMethodTable() != MscorlibBinder::GetException(kRuntimeWrappedException));
+                          ((gc.exceptionObj)->GetMethodTable() != CoreLibBinder::GetException(kRuntimeWrappedException));
 
         // A rethrown exception is also a nested exception
         // but since we have a separate flag for it, lets unset the nested flag
@@ -5305,6 +5365,22 @@ VOID ETW::MethodLog::GetR2RGetEntryPoint(MethodDesc *pMethodDesc, PCODE pEntryPo
     }
 }
 
+VOID ETW::MethodLog::GetR2RGetEntryPointStart(MethodDesc *pMethodDesc)
+{
+    CONTRACTL{
+        NOTHROW;
+        GC_TRIGGERS;
+    } CONTRACTL_END;
+
+    if (ETW_EVENT_ENABLED(MICROSOFT_WINDOWS_DOTNETRUNTIME_PROVIDER_DOTNET_Context, R2RGetEntryPointStart))
+    {
+        FireEtwR2RGetEntryPointStart(
+            (UINT64)pMethodDesc,
+            GetClrInstanceId());
+    }
+}
+
+
 /*******************************************************/
 /* This is called by the runtime when a method is jitted completely */
 /*******************************************************/
diff --git a/src/coreclr/src/vm/excep.cpp b/src/coreclr/src/vm/excep.cpp
index 2366aea21e7d81..258f3aedf00434 100644
--- a/src/coreclr/src/vm/excep.cpp
+++ b/src/coreclr/src/vm/excep.cpp
@@ -357,11 +357,11 @@ void SetExceptionAVParameters(              // No return.
     GCPROTECT_BEGIN(throwable)
     {
         // This should only be called for AccessViolationException
-        _ASSERTE(MscorlibBinder::GetException(kAccessViolationException) == throwable->GetMethodTable());
+        _ASSERTE(CoreLibBinder::GetException(kAccessViolationException) == throwable->GetMethodTable());
 
-        FieldDesc *pFD_ip = MscorlibBinder::GetField(FIELD__ACCESS_VIOLATION_EXCEPTION__IP);
-        FieldDesc *pFD_target = MscorlibBinder::GetField(FIELD__ACCESS_VIOLATION_EXCEPTION__TARGET);
-        FieldDesc *pFD_access = MscorlibBinder::GetField(FIELD__ACCESS_VIOLATION_EXCEPTION__ACCESSTYPE);
+        FieldDesc *pFD_ip = CoreLibBinder::GetField(FIELD__ACCESS_VIOLATION_EXCEPTION__IP);
+        FieldDesc *pFD_target = CoreLibBinder::GetField(FIELD__ACCESS_VIOLATION_EXCEPTION__TARGET);
+        FieldDesc *pFD_access = CoreLibBinder::GetField(FIELD__ACCESS_VIOLATION_EXCEPTION__ACCESSTYPE);
 
         _ASSERTE(pFD_ip->GetFieldType() == ELEMENT_TYPE_I);
         _ASSERTE(pFD_target->GetFieldType() == ELEMENT_TYPE_I);
@@ -456,12 +456,12 @@ void WrapNonCompliantException(OBJECTREF *ppThrowable)
     {
         // idempotent operations, so the race condition is okay.
         if (pMT_RuntimeWrappedException == NULL)
-            pMT_RuntimeWrappedException = MscorlibBinder::GetException(kRuntimeWrappedException);
+            pMT_RuntimeWrappedException = CoreLibBinder::GetException(kRuntimeWrappedException);
 
         if (pFD_WrappedException == NULL)
-            pFD_WrappedException = MscorlibBinder::GetField(FIELD__RUNTIME_WRAPPED_EXCEPTION__WRAPPED_EXCEPTION);
+            pFD_WrappedException = CoreLibBinder::GetField(FIELD__RUNTIME_WRAPPED_EXCEPTION__WRAPPED_EXCEPTION);
 
-        OBJECTREF orWrapper = AllocateObject(MscorlibBinder::GetException(kRuntimeWrappedException));
+        OBJECTREF orWrapper = AllocateObject(CoreLibBinder::GetException(kRuntimeWrappedException));
 
         GCPROTECT_BEGIN(orWrapper);
 
@@ -577,7 +577,7 @@ void CreateTypeInitializationExceptionObject(LPCWSTR pTypeThatFailed,
         // in the code that follows.
         if (!isAlreadyCreating.GetValue()) {
             pThread->SetIsCreatingTypeInitException();
-            pMT = MscorlibBinder::GetException(kTypeInitializationException);
+            pMT = CoreLibBinder::GetException(kTypeInitializationException);
             methodID = METHOD__TYPE_INIT_EXCEPTION__STR_EX_CTOR;
         }
         else {
@@ -3490,9 +3490,7 @@ BOOL IsExceptionOfType(RuntimeExceptionKind reKind, OBJECTREF *pThrowable)
 
     MethodTable *pThrowableMT = (*pThrowable)->GetMethodTable();
 
-    // IsExceptionOfType is supported for mscorlib exception types only
-    _ASSERTE(reKind <= kLastExceptionInMscorlib);
-    return MscorlibBinder::IsException(pThrowableMT, reKind);
+    return CoreLibBinder::IsException(pThrowableMT, reKind);
 }
 
 BOOL IsAsyncThreadException(OBJECTREF *pThrowable) {
@@ -10895,7 +10893,7 @@ BOOL IsProcessCorruptedStateException(DWORD dwExceptionCode, OBJECTREF throwable
     switch (dwExceptionCode)
     {
     case STATUS_ACCESS_VIOLATION:
-        if (throwable != NULL && MscorlibBinder::IsException(throwable->GetMethodTable(), kNullReferenceException))
+        if (throwable != NULL && CoreLibBinder::IsException(throwable->GetMethodTable(), kNullReferenceException))
             return FALSE;
         break;
     case STATUS_STACK_OVERFLOW:
@@ -10972,7 +10970,7 @@ void ExceptionNotifications::GetEventArgsForNotification(ExceptionNotificationHa
         switch(notificationType)
         {
             case FirstChanceExceptionHandler:
-                pMTEventArgs = MscorlibBinder::GetClass(CLASS__FIRSTCHANCE_EVENTARGS);
+                pMTEventArgs = CoreLibBinder::GetClass(CLASS__FIRSTCHANCE_EVENTARGS);
                 idEventArgsCtor = METHOD__FIRSTCHANCE_EVENTARGS__CTOR;
                 break;
             default:
@@ -11037,7 +11035,7 @@ BOOL ExceptionNotifications::CanDeliverNotificationToCurrentAppDomain(ExceptionN
     // Do we have handler(s) of the specific type wired up?
     if (notificationType == FirstChanceExceptionHandler)
     {
-        return MscorlibBinder::GetField(FIELD__APPCONTEXT__FIRST_CHANCE_EXCEPTION)->GetStaticOBJECTREF() != NULL;
+        return CoreLibBinder::GetField(FIELD__APPCONTEXT__FIRST_CHANCE_EXCEPTION)->GetStaticOBJECTREF() != NULL;
     }
     else
     {
@@ -11135,7 +11133,7 @@ void ExceptionNotifications::DeliverNotificationInternal(ExceptionNotificationHa
     // Get the reference to the delegate based upon the type of notification
     if (notificationType == FirstChanceExceptionHandler)
     {
-        gc.oNotificationDelegate = MscorlibBinder::GetField(FIELD__APPCONTEXT__FIRST_CHANCE_EXCEPTION)->GetStaticOBJECTREF();
+        gc.oNotificationDelegate = CoreLibBinder::GetField(FIELD__APPCONTEXT__FIRST_CHANCE_EXCEPTION)->GetStaticOBJECTREF();
     }
     else
     {
diff --git a/src/coreclr/src/vm/field.cpp b/src/coreclr/src/vm/field.cpp
index b3d4bde947a082..8256640de0639d 100644
--- a/src/coreclr/src/vm/field.cpp
+++ b/src/coreclr/src/vm/field.cpp
@@ -878,7 +878,7 @@ REFLECTFIELDREF FieldDesc::GetStubFieldInfo()
     CONTRACTL_END;
 
     REFLECTFIELDREF retVal;
-    REFLECTFIELDREF fieldRef = (REFLECTFIELDREF)AllocateObject(MscorlibBinder::GetClass(CLASS__STUBFIELDINFO));
+    REFLECTFIELDREF fieldRef = (REFLECTFIELDREF)AllocateObject(CoreLibBinder::GetClass(CLASS__STUBFIELDINFO));
     GCPROTECT_BEGIN(fieldRef);
 
     fieldRef->SetField(this);
diff --git a/src/coreclr/src/vm/fieldmarshaler.cpp b/src/coreclr/src/vm/fieldmarshaler.cpp
index c7b5910e54a509..47a0f2693f14b0 100644
--- a/src/coreclr/src/vm/fieldmarshaler.cpp
+++ b/src/coreclr/src/vm/fieldmarshaler.cpp
@@ -129,15 +129,15 @@ VOID ParseNativeType(Module*                     pModule,
 #endif
             break;
         case MarshalInfo::MARSHAL_TYPE_CURRENCY:
-            *pNFD = NativeFieldDescriptor(pFD, MscorlibBinder::GetClass(CLASS__CURRENCY));
+            *pNFD = NativeFieldDescriptor(pFD, CoreLibBinder::GetClass(CLASS__CURRENCY));
             break;
         case MarshalInfo::MARSHAL_TYPE_DECIMAL:
             // The decimal type can't be blittable since the managed and native alignment requirements differ.
             // Native needs 8-byte alignment since one field is a 64-bit integer, but managed only needs 4-byte alignment since all fields are ints.
-            *pNFD = NativeFieldDescriptor(pFD, MscorlibBinder::GetClass(CLASS__NATIVEDECIMAL));
+            *pNFD = NativeFieldDescriptor(pFD, CoreLibBinder::GetClass(CLASS__NATIVEDECIMAL));
             break;
         case MarshalInfo::MARSHAL_TYPE_GUID:
-            *pNFD = NativeFieldDescriptor(pFD, MscorlibBinder::GetClass(CLASS__GUID));
+            *pNFD = NativeFieldDescriptor(pFD, CoreLibBinder::GetClass(CLASS__GUID));
             break;
         case MarshalInfo::MARSHAL_TYPE_DATE:
             *pNFD = NativeFieldDescriptor(pFD, NativeFieldCategory::FLOAT, sizeof(double), sizeof(double));
@@ -168,7 +168,7 @@ VOID ParseNativeType(Module*                     pModule,
             break;
 #ifdef FEATURE_COMINTEROP
         case MarshalInfo::MARSHAL_TYPE_OBJECT:
-            *pNFD = NativeFieldDescriptor(pFD, MscorlibBinder::GetClass(CLASS__NATIVEVARIANT));
+            *pNFD = NativeFieldDescriptor(pFD, CoreLibBinder::GetClass(CLASS__NATIVEVARIANT));
             break;
 #endif
         case MarshalInfo::MARSHAL_TYPE_SAFEHANDLE:
@@ -184,17 +184,17 @@ VOID ParseNativeType(Module*                     pModule,
 
             if (pMT->IsEnum())
             {
-                pMT = MscorlibBinder::GetElementType(pMT->GetInternalCorElementType());
+                pMT = CoreLibBinder::GetElementType(pMT->GetInternalCorElementType());
             }
 
             *pNFD = NativeFieldDescriptor(pFD, OleVariant::GetNativeMethodTableForVarType(mops.elementType, pMT), mops.additive);
             break;
         }
         case MarshalInfo::MARSHAL_TYPE_FIXED_CSTR:
-            *pNFD = NativeFieldDescriptor(pFD, MscorlibBinder::GetClass(CLASS__BYTE), pargs->fs.fixedStringLength);
+            *pNFD = NativeFieldDescriptor(pFD, CoreLibBinder::GetClass(CLASS__BYTE), pargs->fs.fixedStringLength);
             break;
         case MarshalInfo::MARSHAL_TYPE_FIXED_WSTR:
-            *pNFD = NativeFieldDescriptor(pFD, MscorlibBinder::GetClass(CLASS__UINT16), pargs->fs.fixedStringLength);
+            *pNFD = NativeFieldDescriptor(pFD, CoreLibBinder::GetClass(CLASS__UINT16), pargs->fs.fixedStringLength);
             break;
         case MarshalInfo::MARSHAL_TYPE_UNKNOWN:
         default:
@@ -269,7 +269,7 @@ bool IsFieldBlittable(
             {
                 isBlittable = false;
             }
-            else if (valueTypeHandle.GetMethodTable() == MscorlibBinder::GetClass(CLASS__DECIMAL))
+            else if (valueTypeHandle.GetMethodTable() == CoreLibBinder::GetClass(CLASS__DECIMAL))
             {
                 // The alignment requirements of the managed System.Decimal type do not match the native DECIMAL type.
                 // As a result, a field of type System.Decimal can't be blittable.
@@ -277,7 +277,7 @@ bool IsFieldBlittable(
             }
             else
             {
-                isBlittable = !valueTypeHandle.GetMethodTable()->HasInstantiation() && valueTypeHandle.GetMethodTable()->IsBlittable();
+                isBlittable = valueTypeHandle.GetMethodTable()->IsBlittable();
             }
             break;
         default:
diff --git a/src/coreclr/src/vm/fptrstubs.cpp b/src/coreclr/src/vm/fptrstubs.cpp
index f76b7951027a72..cd3dd33d4d8630 100644
--- a/src/coreclr/src/vm/fptrstubs.cpp
+++ b/src/coreclr/src/vm/fptrstubs.cpp
@@ -151,10 +151,12 @@ PCODE FuncPtrStubs::GetFuncPtrStub(MethodDesc * pMD, PrecodeType type)
 
     if (setTargetAfterAddingToHashTable)
     {
+        GCX_PREEMP();
+
         _ASSERTE(pMD->IsVersionableWithVtableSlotBackpatch());
 
         PCODE temporaryEntryPoint = pMD->GetTemporaryEntryPoint();
-        MethodDescBackpatchInfoTracker::ConditionalLockHolder slotBackpatchLockHolder;
+        MethodDescBackpatchInfoTracker::ConditionalLockHolderForGCPreemp slotBackpatchLockHolder;
 
         // Set the funcptr stub's entry point to the current entry point inside the lock and after the funcptr stub is exposed,
         // to synchronize with backpatching in MethodDesc::BackpatchEntryPointSlots()
diff --git a/src/coreclr/src/vm/gccover.cpp b/src/coreclr/src/vm/gccover.cpp
index 2f6001a0858f23..cbe3873f364f40 100644
--- a/src/coreclr/src/vm/gccover.cpp
+++ b/src/coreclr/src/vm/gccover.cpp
@@ -1222,7 +1222,7 @@ bool IsGcCoverageInterrupt(LPVOID ip)
 // original instruction. Only one instruction must be used,
 // because multiple threads can be executing the same code stream.
 
-void RemoveGcCoverageInterrupt(TADDR instrPtr, BYTE * savedInstrPtr)
+void RemoveGcCoverageInterrupt(TADDR instrPtr, BYTE * savedInstrPtr, GCCoverageInfo* gcCover, DWORD offset)
 {
 #ifdef TARGET_ARM
         if (GetARMInstructionLength(savedInstrPtr) == 2)
@@ -1235,6 +1235,17 @@ void RemoveGcCoverageInterrupt(TADDR instrPtr, BYTE * savedInstrPtr)
         *(BYTE *)instrPtr = *savedInstrPtr;
 #endif
 
+#ifdef TARGET_X86
+    // Epilog checking relies on precise control of when instrumentation for the  first prolog 
+    // instruction is enabled or disabled. In particular, if a function has multiple epilogs, or
+    // the first execution of the function terminates via an exception, and subsequent completions
+    // do not, then the function may trigger a false stress fault if epilog checks are not disabled.
+    if (offset == 0)
+    {
+        gcCover->doingEpilogChecks = false;
+    }
+#endif // TARGET_X86
+
         FlushInstructionCache(GetCurrentProcess(), (LPCVOID)instrPtr, 4);
 }
 
@@ -1290,7 +1301,7 @@ BOOL OnGcCoverageInterrupt(PCONTEXT regs)
         // where the call could be coming from a thread unknown to the CLR and
         // we haven't created a thread yet - see PreStubWorker_Preemptive().
         _ASSERTE(pMD->HasUnmanagedCallersOnlyAttribute());
-        RemoveGcCoverageInterrupt(instrPtr, savedInstrPtr);
+        RemoveGcCoverageInterrupt(instrPtr, savedInstrPtr, gcCover, offset);
         return TRUE;
     }
 
@@ -1304,7 +1315,7 @@ BOOL OnGcCoverageInterrupt(PCONTEXT regs)
     // anything for this method at this point.
     if (!pThread->PreemptiveGCDisabled() && pMD->HasUnmanagedCallersOnlyAttribute())
     {
-        RemoveGcCoverageInterrupt(instrPtr, savedInstrPtr);
+        RemoveGcCoverageInterrupt(instrPtr, savedInstrPtr, gcCover, offset);
         return TRUE;
     }
 
@@ -1315,7 +1326,7 @@ BOOL OnGcCoverageInterrupt(PCONTEXT regs)
         Frame* pFrame = pThread->GetFrame();
         if (InlinedCallFrame::FrameHasActiveCall(pFrame))
         {
-            RemoveGcCoverageInterrupt(instrPtr, savedInstrPtr);
+            RemoveGcCoverageInterrupt(instrPtr, savedInstrPtr, gcCover, offset);
             return TRUE;
         }
     }
@@ -1325,7 +1336,7 @@ BOOL OnGcCoverageInterrupt(PCONTEXT regs)
     // location.
     if (!pThread->CheckForAndDoRedirectForGCStress(regs))
     {
-        RemoveGcCoverageInterrupt(instrPtr, savedInstrPtr);
+        RemoveGcCoverageInterrupt(instrPtr, savedInstrPtr, gcCover, offset);
     }
 
 #else // !USE_REDIRECT_FOR_GCSTRESS
@@ -1440,12 +1451,10 @@ void DoGcStress (PCONTEXT regs, NativeCodeVersion nativeCodeVersion)
     bool bShouldUpdateProlog = true;
     if (gcCover->doingEpilogChecks) {
         if (offset == 0) {
-            if (gcCover->callerThread == 0) {
-                if (FastInterlockCompareExchangePointer(&gcCover->callerThread, pThread, 0) == 0) {
-                    gcCover->callerRegs = *regs;
-                    gcCover->gcCount = GCHeapUtilities::GetGCHeap()->GetGcCount();
-                    bShouldUpdateProlog = false;
-                }
+            if ((gcCover->callerThread == 0) && (FastInterlockCompareExchangePointer(&gcCover->callerThread, pThread, 0) == 0)) {
+                gcCover->callerRegs = *regs;
+                gcCover->gcCount = GCHeapUtilities::GetGCHeap()->GetGcCount();
+                bShouldUpdateProlog = false;
             }
             else {
                 // We have been in this routine before.  Give up on epilog checking because
diff --git a/src/coreclr/src/vm/gchelpers.cpp b/src/coreclr/src/vm/gchelpers.cpp
index 5a8877423a0dea..d08a747839204e 100644
--- a/src/coreclr/src/vm/gchelpers.cpp
+++ b/src/coreclr/src/vm/gchelpers.cpp
@@ -757,7 +757,7 @@ OBJECTREF AllocatePrimitiveArray(CorElementType type, DWORD cElements)
     // Fetch the proper array type
     if (g_pPredefinedArrayTypes[type] == NULL)
     {
-        TypeHandle elemType = TypeHandle(MscorlibBinder::GetElementType(type));
+        TypeHandle elemType = TypeHandle(CoreLibBinder::GetElementType(type));
         TypeHandle typHnd = ClassLoader::LoadArrayTypeThrowing(elemType, ELEMENT_TYPE_SZARRAY, 0);
         g_pPredefinedArrayTypes[type] = typHnd;
     }
diff --git a/src/coreclr/src/vm/gdbjit.cpp b/src/coreclr/src/vm/gdbjit.cpp
index 9e12ec4b3cbf6c..1f358eb2d68b41 100644
--- a/src/coreclr/src/vm/gdbjit.cpp
+++ b/src/coreclr/src/vm/gdbjit.cpp
@@ -171,7 +171,7 @@ GetTypeInfoFromTypeHandle(TypeHandle typeHandle,
             refTypeInfo.SuppressRelease();
 
             TypeInfoBase* lengthTypeInfo = GetTypeInfoFromTypeHandle(
-                TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_I4)), pTypeMap, method);
+                TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_I4)), pTypeMap, method);
 
             TypeInfoBase* valTypeInfo = GetTypeInfoFromTypeHandle(typeHandle.GetArrayElementTypeHandle(), pTypeMap, method);
             info->m_array_type = new ArrayTypeInfo(typeHandle, 1, valTypeInfo);
@@ -188,7 +188,7 @@ GetTypeInfoFromTypeHandle(TypeHandle typeHandle,
 
             if (pMT->GetRank() != 1)
             {
-                TypeHandle dwordArray(MscorlibBinder::GetElementType(ELEMENT_TYPE_I4));
+                TypeHandle dwordArray(CoreLibBinder::GetElementType(ELEMENT_TYPE_I4));
                 info->m_array_bounds_type = new ArrayTypeInfo(dwordArray.MakeSZArray(), pMT->GetRank(), lengthTypeInfo);
                 info->members[2].m_member_name = new char[9];
                 strcpy(info->members[2].m_member_name, "m_Bounds");
diff --git a/src/coreclr/src/vm/genericdict.cpp b/src/coreclr/src/vm/genericdict.cpp
index b378f922579295..37044ef1d8c4b9 100644
--- a/src/coreclr/src/vm/genericdict.cpp
+++ b/src/coreclr/src/vm/genericdict.cpp
@@ -71,26 +71,39 @@ DictionaryLayout* DictionaryLayout::Allocate(WORD              numSlots,
 
 //---------------------------------------------------------------------------------------
 //
-// Count the number of bytes that are required in a dictionary with the specified layout
+// Total number of bytes for a dictionary with the specified layout (including optional back pointer
+// used by expanded dictionaries). The pSlotSize argument is used to return the size
+// to be stored in the size slot of the dictionary (not including the optional back pointer).
 // 
 //static
 DWORD 
 DictionaryLayout::GetDictionarySizeFromLayout(
     DWORD                numGenericArgs, 
-    PTR_DictionaryLayout pDictLayout)
+    PTR_DictionaryLayout pDictLayout,
+    DWORD*               pSlotSize)
 {
     LIMITED_METHOD_DAC_CONTRACT;
     PRECONDITION(numGenericArgs > 0);
     PRECONDITION(CheckPointer(pDictLayout, NULL_OK));
+    PRECONDITION(CheckPointer(pSlotSize));
 
-    DWORD bytes = numGenericArgs * sizeof(TypeHandle);          // Slots for instantiation arguments
+    DWORD slotBytes = numGenericArgs * sizeof(TypeHandle); // Slots for instantiation arguments
+    DWORD extraAllocBytes = 0;
     if (pDictLayout != NULL)
     {
-        bytes += sizeof(TADDR);                                 // Slot for dictionary size
-        bytes += pDictLayout->m_numSlots * sizeof(TADDR);       // Slots for dictionary slots based on a dictionary layout
+        DWORD numSlots = VolatileLoadWithoutBarrier(&pDictLayout->m_numSlots);
+
+        slotBytes += sizeof(TADDR);                        // Slot for dictionary size
+        slotBytes += numSlots * sizeof(TADDR);             // Slots for dictionary slots based on a dictionary layout
+
+        if (numSlots > pDictLayout->m_numInitialSlots)
+        {
+            extraAllocBytes = sizeof(PTR_Dictionary);      // Slot for the back-pointer in expanded dictionaries
+        }
     }
 
-    return bytes;
+    *pSlotSize = slotBytes;
+    return slotBytes + extraAllocBytes;
 }
 
 #ifndef DACCESS_COMPILE
@@ -800,10 +813,11 @@ Dictionary* Dictionary::GetMethodDictionaryWithSizeCheck(MethodDesc* pMD, ULONG
             InstantiatedMethodDesc* pIMD = pMD->AsInstantiatedMethodDesc();
             _ASSERTE(pDictLayout != NULL && pDictLayout->GetMaxSlots() > 0);
 
-            DWORD expectedDictionarySize = DictionaryLayout::GetDictionarySizeFromLayout(numGenericArgs, pDictLayout);
-            _ASSERT(currentDictionarySize < expectedDictionarySize);
+            DWORD expectedDictionarySlotSize;
+            DWORD expectedDictionaryAllocSize = DictionaryLayout::GetDictionarySizeFromLayout(numGenericArgs, pDictLayout, &expectedDictionarySlotSize);
+            _ASSERT(currentDictionarySize < expectedDictionarySlotSize);
 
-            Dictionary* pNewDictionary = (Dictionary*)(void*)pIMD->GetLoaderAllocator()->GetHighFrequencyHeap()->AllocMem(S_SIZE_T(expectedDictionarySize));
+            Dictionary* pNewDictionary = (Dictionary*)(void*)pIMD->GetLoaderAllocator()->GetHighFrequencyHeap()->AllocMem(S_SIZE_T(expectedDictionaryAllocSize));
 
             // Copy old dictionary entry contents
             for (DWORD i = 0; i < currentDictionarySize / sizeof(DictionaryEntry); i++)
@@ -813,7 +827,8 @@ Dictionary* Dictionary::GetMethodDictionaryWithSizeCheck(MethodDesc* pMD, ULONG
             }
 
             DWORD* pSizeSlot = (DWORD*)(pNewDictionary + numGenericArgs);
-            *pSizeSlot = expectedDictionarySize;
+            *pSizeSlot = expectedDictionarySlotSize;
+            *pNewDictionary->GetBackPointerSlot(numGenericArgs) = pDictionary;
 
             // Publish the new dictionary slots to the type.
             FastInterlockExchangePointer(pIMD->m_pPerInstInfo.GetValuePtr(), pNewDictionary);
@@ -855,11 +870,12 @@ Dictionary* Dictionary::GetTypeDictionaryWithSizeCheck(MethodTable* pMT, ULONG s
             DictionaryLayout* pDictLayout = pMT->GetClass()->GetDictionaryLayout();
             _ASSERTE(pDictLayout != NULL && pDictLayout->GetMaxSlots() > 0);
 
-            DWORD expectedDictionarySize = DictionaryLayout::GetDictionarySizeFromLayout(numGenericArgs, pDictLayout);
-            _ASSERT(currentDictionarySize < expectedDictionarySize);
+            DWORD expectedDictionarySlotSize;
+            DWORD expectedDictionaryAllocSize = DictionaryLayout::GetDictionarySizeFromLayout(numGenericArgs, pDictLayout, &expectedDictionarySlotSize);
+            _ASSERT(currentDictionarySize < expectedDictionarySlotSize);
 
             // Expand type dictionary
-            Dictionary* pNewDictionary = (Dictionary*)(void*)pMT->GetLoaderAllocator()->GetHighFrequencyHeap()->AllocMem(S_SIZE_T(expectedDictionarySize));
+            Dictionary* pNewDictionary = (Dictionary*)(void*)pMT->GetLoaderAllocator()->GetHighFrequencyHeap()->AllocMem(S_SIZE_T(expectedDictionaryAllocSize));
 
             // Copy old dictionary entry contents
             for (DWORD i = 0; i < currentDictionarySize / sizeof(DictionaryEntry); i++)
@@ -869,7 +885,8 @@ Dictionary* Dictionary::GetTypeDictionaryWithSizeCheck(MethodTable* pMT, ULONG s
             }
 
             DWORD* pSizeSlot = (DWORD*)(pNewDictionary + numGenericArgs);
-            *pSizeSlot = expectedDictionarySize;
+            *pSizeSlot = expectedDictionarySlotSize;
+            *pNewDictionary->GetBackPointerSlot(numGenericArgs) = pDictionary;
 
             // Publish the new dictionary slots to the type.
             ULONG dictionaryIndex = pMT->GetNumDicts() - 1;
@@ -977,11 +994,11 @@ Dictionary::PopulateEntry(
 
         Module * pContainingZapModule = ExecutionManager::FindZapModule(dac_cast<TADDR>(signature));
 
-        zapSigContext = ZapSig::Context(MscorlibBinder::GetModule(), (void *)pContainingZapModule, ZapSig::NormalTokens);
+        zapSigContext = ZapSig::Context(CoreLibBinder::GetModule(), (void *)pContainingZapModule, ZapSig::NormalTokens);
         pZapSigContext = (pContainingZapModule != NULL) ? &zapSigContext : NULL;
     }
 
-    Module * pLookupModule = (isReadyToRunModule) ? pZapSigContext->pInfoModule : MscorlibBinder::GetModule();
+    Module * pLookupModule = (isReadyToRunModule) ? pZapSigContext->pInfoModule : CoreLibBinder::GetModule();
 
     if (pMT != NULL)
     {
@@ -1490,12 +1507,46 @@ Dictionary::PopulateEntry(
 #if !defined(CROSSGEN_COMPILE)
         if (slotIndex != 0)
         {
-            Dictionary* pDictionary = (pMT != NULL) ?
-                GetTypeDictionaryWithSizeCheck(pMT, slotIndex) :
-                GetMethodDictionaryWithSizeCheck(pMD, slotIndex);
+            Dictionary* pDictionary;
+            DWORD numGenericArgs;
+            DictionaryLayout * pDictLayout;
+            if (pMT != NULL)
+            {
+                pDictionary = GetTypeDictionaryWithSizeCheck(pMT, slotIndex);
+                numGenericArgs = pMT->GetNumGenericArgs();
+                pDictLayout = pMT->GetClass()->GetDictionaryLayout();
+            }
+            else
+            {
+                pDictionary = GetMethodDictionaryWithSizeCheck(pMD, slotIndex);
+                numGenericArgs = pMD->GetNumGenericMethodArgs();
+                pDictLayout = pMD->GetDictionaryLayout();
+            }
+            DWORD minimumSizeOfDictionaryToPatch = (slotIndex + 1) * sizeof(DictionaryEntry *);
+            DWORD sizeOfInitialDictionary = (numGenericArgs + 1 + pDictLayout->GetNumInitialSlots()) * sizeof(DictionaryEntry *);
+
+            DictionaryEntry *slot = pDictionary->GetSlotAddr(0, slotIndex);
+            VolatileStoreWithoutBarrier(slot, (DictionaryEntry)result);
+            *ppSlot = slot;
 
-            VolatileStoreWithoutBarrier(pDictionary->GetSlotAddr(0, slotIndex), (DictionaryEntry)result);
-            *ppSlot = pDictionary->GetSlotAddr(0, slotIndex);
+            // Backpatch previous versions of the generic dictionary
+            DWORD dictionarySize = pDictionary->GetDictionarySlotsSize(numGenericArgs);
+            while (dictionarySize > sizeOfInitialDictionary)
+            {
+                pDictionary = *pDictionary->GetBackPointerSlot(numGenericArgs);
+                if (pDictionary == nullptr)
+                {
+                    // Initial dictionary allocated with higher number of slots than the initial layout slot count
+                    break;
+                }
+                dictionarySize = pDictionary->GetDictionarySlotsSize(numGenericArgs);
+                if (dictionarySize < minimumSizeOfDictionaryToPatch)
+                {
+                    // Previous dictionary is too short to patch, end iteration
+                    break;
+                }
+                VolatileStoreWithoutBarrier(pDictionary->GetSlotAddr(0, slotIndex), (DictionaryEntry)result);
+            }
         }
 #endif // !CROSSGEN_COMPILE
     }
diff --git a/src/coreclr/src/vm/genericdict.h b/src/coreclr/src/vm/genericdict.h
index 8637144466d626..43df31078a2b6e 100644
--- a/src/coreclr/src/vm/genericdict.h
+++ b/src/coreclr/src/vm/genericdict.h
@@ -146,9 +146,11 @@ class DictionaryLayout
     // Create an initial dictionary layout containing numSlots slots
     static DictionaryLayout* Allocate(WORD numSlots, LoaderAllocator *pAllocator, AllocMemTracker *pamTracker);
 
-    // Bytes used for this dictionary, which might be stored inline in
-    // another structure (e.g. MethodTable)
-    static DWORD GetDictionarySizeFromLayout(DWORD numGenericArgs, PTR_DictionaryLayout pDictLayout);
+    // Total number of bytes used for this dictionary, which might be stored inline in
+    // another structure (e.g. MethodTable). This may include the final back-pointer
+    // to previous dictionaries after dictionary expansion; pSlotSize is used to return
+    // the size to be stored in the "size slot" of the dictionary.
+    static DWORD GetDictionarySizeFromLayout(DWORD numGenericArgs, PTR_DictionaryLayout pDictLayout, DWORD *pSlotSize);
 
     static BOOL FindToken(MethodTable*                      pMT,
                           LoaderAllocator*                  pAllocator,
@@ -171,7 +173,7 @@ class DictionaryLayout
     DWORD GetMaxSlots();
     DWORD GetNumInitialSlots();
     DWORD GetNumUsedSlots();
-
+    
     PTR_DictionaryEntryLayout GetEntryLayout(DWORD i)
     {
         LIMITED_METHOD_CONTRACT;
@@ -300,6 +302,12 @@ class Dictionary
         LIMITED_METHOD_CONTRACT;
         return VolatileLoadWithoutBarrier((DWORD*)GetSlotAddr(numGenericArgs, 0));
     }
+    
+    inline Dictionary **GetBackPointerSlot(DWORD numGenericArgs)
+    {
+        LIMITED_METHOD_CONTRACT;
+        return (Dictionary **)((uint8_t *)m_pEntries + GetDictionarySlotsSize(numGenericArgs));
+    }
 #endif // #ifndef DACCESS_COMPILE
 
 public:
diff --git a/src/coreclr/src/vm/generics.cpp b/src/coreclr/src/vm/generics.cpp
index 4e95b52f009e7e..b616b84099c30a 100644
--- a/src/coreclr/src/vm/generics.cpp
+++ b/src/coreclr/src/vm/generics.cpp
@@ -266,14 +266,15 @@ ClassLoader::CreateTypeHandleForNonCanonicalGenericInstantiation(
     // creating this type. In other words: this type will have a smaller dictionary that its layout. This is not a
     // problem however because whenever we need to load a value from the dictionary of this type beyond its size, we
     // will expand the dictionary at that point.
-    DWORD cbInstAndDict = pOldMT->GetInstAndDictSize();
+    DWORD cbInstAndDictSlotSize;
+    DWORD cbInstAndDictAllocSize = pOldMT->GetInstAndDictSize(&cbInstAndDictSlotSize);
 
     // Allocate from the high frequence heap of the correct domain
     S_SIZE_T allocSize = safe_cbMT;
     allocSize += cbOptional;
     allocSize += cbIMap;
     allocSize += cbPerInst;
-    allocSize += cbInstAndDict;
+    allocSize += cbInstAndDictAllocSize;
 
     if (allocSize.IsOverflow())
     {
@@ -474,7 +475,7 @@ ClassLoader::CreateTypeHandleForNonCanonicalGenericInstantiation(
         _ASSERTE(pLayout->GetMaxSlots() > 0);
         PTR_Dictionary pDictionarySlots = pMT->GetPerInstInfo()[pOldMT->GetNumDicts() - 1].GetValue();
         DWORD* pSizeSlot = (DWORD*)(pDictionarySlots + ntypars);
-        *pSizeSlot = cbInstAndDict;
+        *pSizeSlot = cbInstAndDictSlotSize;
     }
 
     // Copy interface map across
diff --git a/src/coreclr/src/vm/genmeth.cpp b/src/coreclr/src/vm/genmeth.cpp
index 80ffce4f34e9e7..3b67c67e494694 100644
--- a/src/coreclr/src/vm/genmeth.cpp
+++ b/src/coreclr/src/vm/genmeth.cpp
@@ -386,15 +386,17 @@ InstantiatedMethodDesc::NewInstantiatedMethodDesc(MethodTable *pExactMT,
                 {
                     SString name;
                     TypeString::AppendMethodDebug(name, pGenericMDescInRepMT);
-                    LOG((LF_JIT, LL_INFO1000, "GENERICS: Created new dictionary layout for dictionary of size %d for %S\n",
-                        DictionaryLayout::GetDictionarySizeFromLayout(pGenericMDescInRepMT->GetNumGenericMethodArgs(), pDL), name.GetUnicode()));
+                    DWORD dictionarySlotSize;
+                    DWORD dictionaryAllocSize = DictionaryLayout::GetDictionarySizeFromLayout(pGenericMDescInRepMT->GetNumGenericMethodArgs(), pDL, &dictionarySlotSize);
+                    LOG((LF_JIT, LL_INFO1000, "GENERICS: Created new dictionary layout for dictionary of slot size %d / alloc size %d for %S\n",
+                        dictionarySlotSize, dictionaryAllocSize, name.GetUnicode()));
                 }
 #endif // _DEBUG
             }
 
             // Allocate space for the instantiation and dictionary
-            infoSize = DictionaryLayout::GetDictionarySizeFromLayout(methodInst.GetNumArgs(), pDL);
-            pInstOrPerInstInfo = (TypeHandle*)(void*)amt.Track(pAllocator->GetHighFrequencyHeap()->AllocMem(S_SIZE_T(infoSize)));
+            DWORD allocSize = DictionaryLayout::GetDictionarySizeFromLayout(methodInst.GetNumArgs(), pDL, &infoSize);
+            pInstOrPerInstInfo = (TypeHandle*)(void*)amt.Track(pAllocator->GetHighFrequencyHeap()->AllocMem(S_SIZE_T(allocSize)));
             for (DWORD i = 0; i < methodInst.GetNumArgs(); i++)
                 pInstOrPerInstInfo[i] = methodInst[i];
 
diff --git a/src/coreclr/src/vm/i386/cgenx86.cpp b/src/coreclr/src/vm/i386/cgenx86.cpp
index 58cbf0ffa00158..75ff1b7dff17b3 100644
--- a/src/coreclr/src/vm/i386/cgenx86.cpp
+++ b/src/coreclr/src/vm/i386/cgenx86.cpp
@@ -1139,54 +1139,6 @@ void ResumeAtJit(PCONTEXT pContext, LPVOID oldESP)
 #ifndef TARGET_UNIX
 #pragma warning(push)
 #pragma warning(disable: 4035)
-extern "C" DWORD __stdcall getcpuid(DWORD arg, unsigned char result[16])
-{
-    LIMITED_METHOD_CONTRACT
-
-    __asm
-    {
-        push    ebx
-        push    esi
-        mov     eax, arg
-        cpuid
-        mov     esi, result
-        mov     [esi+ 0], eax
-        mov     [esi+ 4], ebx
-        mov     [esi+ 8], ecx
-        mov     [esi+12], edx
-        pop     esi
-        pop     ebx
-    }
-}
-
-// The following function uses Deterministic Cache Parameter leafs to determine the cache hierarchy information on Prescott & Above platforms.
-//  This function takes 3 arguments:
-//     Arg1 is an input to ECX. Used as index to specify which cache level to return infoformation on by CPUID.
-//     Arg2 is an input to EAX. For deterministic code enumeration, we pass in 4H in arg2.
-//     Arg3 is a pointer to the return buffer
-//   No need to check whether or not CPUID is supported because we have already called CPUID with success to come here.
-
-extern "C" DWORD __stdcall getextcpuid(DWORD arg1, DWORD arg2, unsigned char result[16])
-{
-    LIMITED_METHOD_CONTRACT
-
-    __asm
-    {
-        push    ebx
-        push    esi
-        mov     ecx, arg1
-        mov     eax, arg2
-        cpuid
-        mov     esi, result
-        mov     [esi+ 0], eax
-        mov     [esi+ 4], ebx
-        mov     [esi+ 8], ecx
-        mov     [esi+12], edx
-        pop     esi
-        pop     ebx
-    }
-}
-
 extern "C" DWORD __stdcall xmmYmmStateSupport()
 {
     // No CONTRACT
@@ -1207,41 +1159,30 @@ extern "C" DWORD __stdcall xmmYmmStateSupport()
     done:
     }
 }
-
 #pragma warning(pop)
 
 #else // !TARGET_UNIX
 
-extern "C" DWORD __stdcall getcpuid(DWORD arg, unsigned char result[16])
+void __cpuid(int cpuInfo[4], int function_id)
 {
-    DWORD eax;
-    __asm("  xor %%ecx, %%ecx\n" \
-            "  cpuid\n" \
-            "  mov %%eax, 0(%[result])\n" \
-            "  mov %%ebx, 4(%[result])\n" \
-            "  mov %%ecx, 8(%[result])\n" \
-            "  mov %%edx, 12(%[result])\n" \
-        : "=a"(eax) /*output in eax*/\
-        : "a"(arg), [result]"r"(result) /*inputs - arg in eax, result in any register*/\
-        : "ebx", "ecx", "edx", "memory" /* registers that are clobbered, *result is clobbered */
-        );
-    return eax;
+    // Based on the Clang implementation provided in cpuid.h:
+    // https://github.com/llvm/llvm-project/blob/master/clang/lib/Headers/cpuid.h
+
+    __asm("  cpuid"
+        : "=a"(cpuInfo[0]), "=b"(cpuInfo[1]), "=c"(cpuInfo[2]), "=d"(cpuInfo[3]) \
+        : "0"(function_id)
+    );
 }
 
-extern "C" DWORD __stdcall getextcpuid(DWORD arg1, DWORD arg2, unsigned char result[16])
+void __cpuidex(int cpuInfo[4], int function_id, int subFunction_id)
 {
-    DWORD eax;
-    DWORD ecx;
-    __asm("  cpuid\n" \
-            "  mov %%eax, 0(%[result])\n" \
-            "  mov %%ebx, 4(%[result])\n" \
-            "  mov %%ecx, 8(%[result])\n" \
-            "  mov %%edx, 12(%[result])\n" \
-        : "=a"(eax), "=c"(ecx) /*output in eax, ecx is rewritten*/\
-        : "c"(arg1), "a"(arg2), [result]"r"(result) /*inputs - arg1 in ecx, arg2 in eax, result in any register*/\
-        : "ebx", "edx", "memory" /* registers that are clobbered, *result is clobbered */
-        );
-    return eax;
+    // Based on the Clang implementation provided in cpuid.h:
+    // https://github.com/llvm/llvm-project/blob/master/clang/lib/Headers/cpuid.h
+
+    __asm("  cpuid"
+        : "=a"(cpuInfo[0]), "=b"(cpuInfo[1]), "=c"(cpuInfo[2]), "=d"(cpuInfo[3]) \
+        : "0"(function_id), "2"(subFunction_id)
+    );
 }
 
 extern "C" DWORD __stdcall xmmYmmStateSupport()
diff --git a/src/coreclr/src/vm/ilmarshalers.cpp b/src/coreclr/src/vm/ilmarshalers.cpp
index 8f57b1cf156934..0e74014a45f158 100644
--- a/src/coreclr/src/vm/ilmarshalers.cpp
+++ b/src/coreclr/src/vm/ilmarshalers.cpp
@@ -19,7 +19,7 @@ LocalDesc ILReflectionObjectMarshaler::GetManagedType()
 {
     STANDARD_VM_CONTRACT;
 
-    return LocalDesc(MscorlibBinder::GetClass(GetManagedTypeBinderID()));
+    return LocalDesc(CoreLibBinder::GetClass(GetManagedTypeBinderID()));
 }
 
 LocalDesc ILReflectionObjectMarshaler::GetNativeType()
@@ -33,7 +33,7 @@ void ILReflectionObjectMarshaler::EmitConvertContentsCLRToNative(ILCodeStream* p
 {
     STANDARD_VM_CONTRACT;
 
-    int tokObject__m_handle = pslILEmit->GetToken(MscorlibBinder::GetField(GetObjectFieldID()));
+    int tokObject__m_handle = pslILEmit->GetToken(CoreLibBinder::GetField(GetObjectFieldID()));
     int tokStruct__m_object = 0;
     BinderFieldID structField = GetStructureFieldID();
 
@@ -41,7 +41,7 @@ void ILReflectionObjectMarshaler::EmitConvertContentsCLRToNative(ILCodeStream* p
     // marshaling a struct referring to an object containing a handle.
     if (structField != 0)
     {
-        tokStruct__m_object = pslILEmit->GetToken(MscorlibBinder::GetField(structField));
+        tokStruct__m_object = pslILEmit->GetToken(CoreLibBinder::GetField(structField));
     }
 
     ILCodeLabel* pNullLabel = pslILEmit->NewCodeLabel();
@@ -379,7 +379,7 @@ void ILWSTRMarshaler::EmitMarshalViaPinning(ILCodeStream* pslILEmit)
     LocalDesc locDesc = GetManagedType();
     locDesc.MakePinned();
     DWORD dwPinnedLocal = pslILEmit->NewLocal(locDesc);
-    int fieldDef = pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__STRING__M_FIRST_CHAR));
+    int fieldDef = pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__STRING__M_FIRST_CHAR));
     ILCodeLabel* pNullRefLabel = pslILEmit->NewCodeLabel();
 
     pslILEmit->EmitLoadNullPtr();
@@ -509,7 +509,7 @@ void ILOptimizedAllocMarshaler::EmitClearNative(ILCodeStream* pslILEmit)
 LocalDesc ILUTF8BufferMarshaler::GetManagedType()
 {
     STANDARD_VM_CONTRACT;
-    return LocalDesc(MscorlibBinder::GetClass(CLASS__STRING_BUILDER));
+    return LocalDesc(CoreLibBinder::GetClass(CLASS__STRING_BUILDER));
 }
 
 void ILUTF8BufferMarshaler::EmitConvertSpaceCLRToNative(ILCodeStream* pslILEmit)
@@ -659,7 +659,7 @@ LocalDesc ILWSTRBufferMarshaler::GetManagedType()
 {
     STANDARD_VM_CONTRACT;
 
-    return LocalDesc(MscorlibBinder::GetClass(CLASS__STRING_BUILDER));
+    return LocalDesc(CoreLibBinder::GetClass(CLASS__STRING_BUILDER));
 }
 
 void ILWSTRBufferMarshaler::EmitConvertSpaceCLRToNative(ILCodeStream* pslILEmit)
@@ -860,7 +860,7 @@ LocalDesc ILCSTRBufferMarshaler::GetManagedType()
 {
     STANDARD_VM_CONTRACT;
 
-    return LocalDesc(MscorlibBinder::GetClass(CLASS__STRING_BUILDER));
+    return LocalDesc(CoreLibBinder::GetClass(CLASS__STRING_BUILDER));
 }
 
 void ILCSTRBufferMarshaler::EmitConvertSpaceCLRToNative(ILCodeStream* pslILEmit)
@@ -885,7 +885,7 @@ void ILCSTRBufferMarshaler::EmitConvertSpaceCLRToNative(ILCodeStream* pslILEmit)
 
     // stack: capacity
 
-    pslILEmit->EmitLDSFLD(pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__MARSHAL__SYSTEM_MAX_DBCS_CHAR_SIZE)));
+    pslILEmit->EmitLDSFLD(pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__MARSHAL__SYSTEM_MAX_DBCS_CHAR_SIZE)));
     pslILEmit->EmitMUL_OVF();
 
     // stack: capacity_in_bytes
@@ -1141,7 +1141,7 @@ LocalDesc ILObjectMarshaler::GetNativeType()
 {
     STANDARD_VM_CONTRACT;
 
-    return LocalDesc(TypeHandle(MscorlibBinder::GetClass(CLASS__NATIVEVARIANT)));
+    return LocalDesc(TypeHandle(CoreLibBinder::GetClass(CLASS__NATIVEVARIANT)));
 }
 
 LocalDesc ILObjectMarshaler::GetManagedType()
@@ -1238,7 +1238,7 @@ LocalDesc ILDateMarshaler::GetManagedType()
 {
     STANDARD_VM_CONTRACT;
 
-    return LocalDesc(MscorlibBinder::GetClass(CLASS__DATE_TIME));
+    return LocalDesc(CoreLibBinder::GetClass(CLASS__DATE_TIME));
 }
 
 void ILDateMarshaler::EmitConvertContentsCLRToNative(ILCodeStream* pslILEmit)
@@ -1279,14 +1279,14 @@ LocalDesc ILCurrencyMarshaler::GetNativeType()
 {
     STANDARD_VM_CONTRACT;
 
-    return LocalDesc(TypeHandle(MscorlibBinder::GetClass(CLASS__CURRENCY)));
+    return LocalDesc(TypeHandle(CoreLibBinder::GetClass(CLASS__CURRENCY)));
 }
 
 LocalDesc ILCurrencyMarshaler::GetManagedType()
 {
     STANDARD_VM_CONTRACT;
 
-    return LocalDesc(TypeHandle(MscorlibBinder::GetClass(CLASS__DECIMAL)));
+    return LocalDesc(TypeHandle(CoreLibBinder::GetClass(CLASS__DECIMAL)));
 }
 
 
@@ -1295,7 +1295,7 @@ void ILCurrencyMarshaler::EmitReInitNative(ILCodeStream* pslILEmit)
     STANDARD_VM_CONTRACT;
 
     EmitLoadNativeHomeAddr(pslILEmit);
-    pslILEmit->EmitINITOBJ(pslILEmit->GetToken(TypeHandle(MscorlibBinder::GetClass(CLASS__CURRENCY))));
+    pslILEmit->EmitINITOBJ(pslILEmit->GetToken(TypeHandle(CoreLibBinder::GetClass(CLASS__CURRENCY))));
 }
 
 void ILCurrencyMarshaler::EmitConvertContentsCLRToNative(ILCodeStream* pslILEmit)
@@ -2075,7 +2075,7 @@ void ILCSTRMarshaler::EmitConvertContentsCLRToNative(ILCodeStream* pslILEmit)
         pslILEmit->EmitADD();
 
         // (String.Length + 2) * GetMaxDBCSCharByteSize()
-        pslILEmit->EmitLDSFLD(pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__MARSHAL__SYSTEM_MAX_DBCS_CHAR_SIZE)));
+        pslILEmit->EmitLDSFLD(pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__MARSHAL__SYSTEM_MAX_DBCS_CHAR_SIZE)));
         pslILEmit->EmitMUL_OVF();
 
         // BufSize = (String.Length + 2) * GetMaxDBCSCharByteSize()
@@ -2336,7 +2336,7 @@ void ILBlittablePtrMarshaler::EmitConvertContentsCLRToNative(ILCodeStream* pslIL
 
     ILCodeLabel* pNullRefLabel = pslILEmit->NewCodeLabel();
     UINT uNativeSize = m_pargs->m_pMT->GetNativeSize();
-    int fieldDef = pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__RAW_DATA__DATA));
+    int fieldDef = pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__RAW_DATA__DATA));
 
     EmitLoadNativeValue(pslILEmit);
     pslILEmit->EmitBRFALSE(pNullRefLabel);
@@ -2358,7 +2358,7 @@ void ILBlittablePtrMarshaler::EmitConvertContentsNativeToCLR(ILCodeStream* pslIL
 
     ILCodeLabel* pNullRefLabel = pslILEmit->NewCodeLabel();
     UINT uNativeSize = m_pargs->m_pMT->GetNativeSize();
-    int fieldDef = pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__RAW_DATA__DATA));
+    int fieldDef = pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__RAW_DATA__DATA));
 
     EmitLoadManagedValue(pslILEmit);
     pslILEmit->EmitBRFALSE(pNullRefLabel);
@@ -2478,7 +2478,7 @@ void ILBlittableLayoutClassMarshaler::EmitConvertContentsCLRToNative(ILCodeStrea
 
     ILCodeLabel* pNullRefLabel = pslILEmit->NewCodeLabel();
     UINT uNativeSize = m_pargs->m_pMT->GetNativeSize();
-    int fieldDef = pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__RAW_DATA__DATA));
+    int fieldDef = pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__RAW_DATA__DATA));
 
     EmitLoadNativeHomeAddr(pslILEmit);
     pslILEmit->EmitLDC(0);
@@ -2504,7 +2504,7 @@ void ILBlittableLayoutClassMarshaler::EmitConvertContentsNativeToCLR(ILCodeStrea
     STANDARD_VM_CONTRACT;
 
     UINT uNativeSize = m_pargs->m_pMT->GetNativeSize();
-    int fieldDef = pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__RAW_DATA__DATA));
+    int fieldDef = pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__RAW_DATA__DATA));
 
     pslILEmit->EmitLDTOKEN(pslILEmit->GetToken(m_pargs->m_pMT));
     pslILEmit->EmitCALL(METHOD__TYPE__GET_TYPE_FROM_HANDLE, 1, 1);
@@ -2550,11 +2550,11 @@ MarshalerOverrideStatus ILHandleRefMarshaler::ArgumentOverride(NDirectStubLinker
 
         // HandleRefs are valuetypes, so pinning is not needed.
         // The argument address is on the stack and will not move.
-        mdFieldDef handleField = pcsDispatch->GetToken(MscorlibBinder::GetField(FIELD__HANDLE_REF__HANDLE));
+        mdFieldDef handleField = pcsDispatch->GetToken(CoreLibBinder::GetField(FIELD__HANDLE_REF__HANDLE));
         pcsDispatch->EmitLDARG(argidx);
         pcsDispatch->EmitLDFLD(handleField);
 
-        mdFieldDef wrapperField = pcsUnmarshal->GetToken(MscorlibBinder::GetField(FIELD__HANDLE_REF__WRAPPER));
+        mdFieldDef wrapperField = pcsUnmarshal->GetToken(CoreLibBinder::GetField(FIELD__HANDLE_REF__WRAPPER));
         pcsUnmarshal->EmitLDARG(argidx);
         pcsUnmarshal->EmitLDFLD(wrapperField);
         pcsUnmarshal->EmitCALL(METHOD__GC__KEEP_ALIVE, 1, 0);
@@ -2606,7 +2606,7 @@ void ILSafeHandleMarshaler::EmitConvertContentsNativeToCLR(ILCodeStream* pslILEm
     EmitLoadManagedValue(pslILEmit);
     pslILEmit->EmitBRFALSE(failureLabel);
     EmitLoadManagedValue(pslILEmit);
-    pslILEmit->EmitLDFLD(pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__SAFE_HANDLE__HANDLE)));
+    pslILEmit->EmitLDFLD(pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__SAFE_HANDLE__HANDLE)));
     EmitLoadNativeValue(pslILEmit);
     pslILEmit->EmitBEQ(successLabel);
     pslILEmit->EmitLabel(failureLabel);
@@ -2659,7 +2659,7 @@ MarshalerOverrideStatus ILSafeHandleMarshaler::ArgumentOverride(NDirectStubLinke
 
             // Grab the token for the native handle field embedded inside the SafeHandle. We'll be using it to direct access the
             // native handle later.
-            mdToken tkNativeHandleField = pslIL->GetToken(MscorlibBinder::GetField(FIELD__SAFE_HANDLE__HANDLE));
+            mdToken tkNativeHandleField = pslIL->GetToken(CoreLibBinder::GetField(FIELD__SAFE_HANDLE__HANDLE));
 
             // The high level logic (note that the parameter may be in, out or both):
             // 1) If this is an input parameter we need to AddRef the SafeHandle and schedule a Release cleanup item.
@@ -2883,7 +2883,7 @@ ILSafeHandleMarshaler::ReturnOverride(
     pslIL->EmitNEWOBJ(pslIL->GetToken(pMDCtor), 0);
     pslIL->EmitSTLOC(dwReturnHandleLocal);
 
-    mdToken tkNativeHandleField = pslPostIL->GetToken(MscorlibBinder::GetField(FIELD__SAFE_HANDLE__HANDLE));
+    mdToken tkNativeHandleField = pslPostIL->GetToken(CoreLibBinder::GetField(FIELD__SAFE_HANDLE__HANDLE));
 
     // 3) create local to hold returned handle
     DWORD dwReturnNativeHandleLocal = pslIL->NewLocal(ELEMENT_TYPE_I);
@@ -2948,7 +2948,7 @@ void ILCriticalHandleMarshaler::EmitConvertContentsCLRToNative(ILCodeStream* psl
     _ASSERTE(IsFieldMarshal(m_dwMarshalFlags));
 
     EmitLoadManagedValue(pslILEmit);
-    pslILEmit->EmitLDFLD(pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__CRITICAL_HANDLE__HANDLE)));
+    pslILEmit->EmitLDFLD(pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__CRITICAL_HANDLE__HANDLE)));
     EmitStoreNativeValue(pslILEmit);
 }
 
@@ -2962,7 +2962,7 @@ void ILCriticalHandleMarshaler::EmitConvertContentsNativeToCLR(ILCodeStream* psl
     EmitLoadManagedValue(pslILEmit);
     pslILEmit->EmitBRFALSE(failureLabel);
     EmitLoadManagedValue(pslILEmit);
-    pslILEmit->EmitLDFLD(pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__CRITICAL_HANDLE__HANDLE)));
+    pslILEmit->EmitLDFLD(pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__CRITICAL_HANDLE__HANDLE)));
     EmitLoadNativeValue(pslILEmit);
     pslILEmit->EmitBEQ(successLabel);
     pslILEmit->EmitLabel(failureLabel);
@@ -3000,7 +3000,7 @@ MarshalerOverrideStatus ILCriticalHandleMarshaler::ArgumentOverride(NDirectStubL
 
         // Grab the token for the native handle field embedded inside the CriticalHandle. We'll be using it to direct access
         // the native handle later.
-        mdToken tkNativeHandleField = pslIL->GetToken(MscorlibBinder::GetField(FIELD__CRITICAL_HANDLE__HANDLE));
+        mdToken tkNativeHandleField = pslIL->GetToken(CoreLibBinder::GetField(FIELD__CRITICAL_HANDLE__HANDLE));
 
         if (byref)
         {
@@ -3218,7 +3218,7 @@ ILCriticalHandleMarshaler::ReturnOverride(
     pslIL->EmitNEWOBJ(pslIL->GetToken(pMDCtor), 0);
     pslIL->EmitSTLOC(dwReturnHandleLocal);
 
-    mdToken tkNativeHandleField = pslPostIL->GetToken(MscorlibBinder::GetField(FIELD__CRITICAL_HANDLE__HANDLE));
+    mdToken tkNativeHandleField = pslPostIL->GetToken(CoreLibBinder::GetField(FIELD__CRITICAL_HANDLE__HANDLE));
 
     // 3) create local to hold returned handle
     DWORD dwReturnNativeHandleLocal = pslIL->NewLocal(ELEMENT_TYPE_I);
@@ -3376,7 +3376,7 @@ LocalDesc ILArgIteratorMarshaler::GetManagedType()
 {
     STANDARD_VM_CONTRACT;
 
-    return LocalDesc(MscorlibBinder::GetClass(CLASS__ARG_ITERATOR));
+    return LocalDesc(CoreLibBinder::GetClass(CLASS__ARG_ITERATOR));
 }
 
 bool ILArgIteratorMarshaler::SupportsArgumentMarshal(DWORD dwMarshalFlags, UINT* pErrorResID)
@@ -3432,7 +3432,7 @@ LocalDesc ILArrayWithOffsetMarshaler::GetManagedType()
 {
     STANDARD_VM_CONTRACT;
 
-    return LocalDesc(MscorlibBinder::GetClass(CLASS__ARRAY_WITH_OFFSET));
+    return LocalDesc(CoreLibBinder::GetClass(CLASS__ARRAY_WITH_OFFSET));
 }
 
 bool ILArrayWithOffsetMarshaler::SupportsArgumentMarshal(DWORD dwMarshalFlags, UINT* pErrorResID)
@@ -3461,8 +3461,8 @@ void ILArrayWithOffsetMarshaler::EmitConvertSpaceAndContentsCLRToNativeTemp(ILCo
     }
     CONTRACTL_END;
 
-    int tokArrayWithOffset_m_array = pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__ARRAY_WITH_OFFSET__M_ARRAY));
-    int tokArrayWithOffset_m_count = pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__ARRAY_WITH_OFFSET__M_COUNT));
+    int tokArrayWithOffset_m_array = pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__ARRAY_WITH_OFFSET__M_ARRAY));
+    int tokArrayWithOffset_m_count = pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__ARRAY_WITH_OFFSET__M_COUNT));
 
     ILCodeLabel* pNonNullLabel = pslILEmit->NewCodeLabel();
     ILCodeLabel* pSlowAllocPathLabel = pslILEmit->NewCodeLabel();
@@ -3507,7 +3507,7 @@ void ILArrayWithOffsetMarshaler::EmitConvertSpaceAndContentsCLRToNativeTemp(ILCo
     // Convert the contents
     //
 
-    int tokArrayWithOffset_m_offset = pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__ARRAY_WITH_OFFSET__M_OFFSET));
+    int tokArrayWithOffset_m_offset = pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__ARRAY_WITH_OFFSET__M_OFFSET));
 
     ILCodeLabel* pNullRefLabel = pslILEmit->NewCodeLabel();
 
@@ -3560,7 +3560,7 @@ void ILArrayWithOffsetMarshaler::EmitConvertContentsNativeToCLR(ILCodeStream* ps
     }
     CONTRACTL_END;
 
-    int tokArrayWithOffset_m_array = pslILEmit->GetToken(MscorlibBinder::GetField(FIELD__ARRAY_WITH_OFFSET__M_ARRAY));
+    int tokArrayWithOffset_m_array = pslILEmit->GetToken(CoreLibBinder::GetField(FIELD__ARRAY_WITH_OFFSET__M_ARRAY));
 
     ILCodeLabel* pNullRefLabel = pslILEmit->NewCodeLabel();
 
@@ -3655,7 +3655,7 @@ void ILAsAnyMarshalerBase::EmitCreateMngdMarshaler(ILCodeStream* pslILEmit)
     }
     CONTRACTL_END;
 
-    LocalDesc marshalerType(MscorlibBinder::GetClass(CLASS__ASANY_MARSHALER));
+    LocalDesc marshalerType(CoreLibBinder::GetClass(CLASS__ASANY_MARSHALER));
     m_dwMngdMarshalerLocalNum = pslILEmit->NewLocal(marshalerType);
     DWORD dwTmpLocalNum = pslILEmit->NewLocal(ELEMENT_TYPE_I);
 
diff --git a/src/coreclr/src/vm/ilmarshalers.h b/src/coreclr/src/vm/ilmarshalers.h
index 2b4e6078518e6d..c08f4f3efc49be 100644
--- a/src/coreclr/src/vm/ilmarshalers.h
+++ b/src/coreclr/src/vm/ilmarshalers.h
@@ -1891,14 +1891,14 @@ class ILCopyMarshalerKnownStruct : public ILCopyMarshalerBase
         STANDARD_VM_CONTRACT;
 
         EmitLoadNativeHomeAddr(pslILEmit);
-        pslILEmit->EmitINITOBJ(pslILEmit->GetToken(MscorlibBinder::GetClass(CLASS__ID)));
+        pslILEmit->EmitINITOBJ(pslILEmit->GetToken(CoreLibBinder::GetClass(CLASS__ID)));
     }
 
     virtual LocalDesc GetNativeType()
     {
         STANDARD_VM_CONTRACT;
 
-        return LocalDesc(MscorlibBinder::GetClass(CLASS__ID));
+        return LocalDesc(CoreLibBinder::GetClass(CLASS__ID));
     }
 };
 
@@ -1972,7 +1972,7 @@ class ILReflectionObjectMarshaler : public ILMarshaler
         // marshaling a struct referring to an object containing a handle.
         if (structField != 0)
         {
-            int tokStruct__m_object = pslILEmit->GetToken(MscorlibBinder::GetField(structField));
+            int tokStruct__m_object = pslILEmit->GetToken(CoreLibBinder::GetField(structField));
             EmitLoadManagedHomeAddr(pslILEmit);
             pslILEmit->EmitLDFLD(tokStruct__m_object);
         }
@@ -2280,7 +2280,7 @@ class ILSafeHandleMarshaler : public ILMarshaler
     LocalDesc GetManagedType() override
     {
         LIMITED_METHOD_CONTRACT;
-        return LocalDesc(MscorlibBinder::GetClass(CLASS__SAFE_HANDLE));
+        return LocalDesc(CoreLibBinder::GetClass(CLASS__SAFE_HANDLE));
     }
 
     LocalDesc GetNativeType() override
@@ -2324,7 +2324,7 @@ class ILCriticalHandleMarshaler : public ILMarshaler
     LocalDesc GetManagedType() override
     {
         LIMITED_METHOD_CONTRACT;
-        return LocalDesc(MscorlibBinder::GetClass(CLASS__CRITICAL_HANDLE));
+        return LocalDesc(CoreLibBinder::GetClass(CLASS__CRITICAL_HANDLE));
     }
 
     LocalDesc GetNativeType() override
@@ -2501,7 +2501,7 @@ class ILValueClassPtrMarshaler : public ILMarshaler
         //
         // value class
         //
-        return LocalDesc(MscorlibBinder::GetClass(CLASS__ID));
+        return LocalDesc(CoreLibBinder::GetClass(CLASS__ID));
     }
 
     bool NeedsClearNative() override
@@ -2541,7 +2541,7 @@ class ILValueClassPtrMarshaler : public ILMarshaler
         {
             EmitLoadNativeValue(pslILEmit);     // dest
             EmitLoadManagedHomeAddr(pslILEmit); // src
-            pslILEmit->EmitCPOBJ(pslILEmit->GetToken(MscorlibBinder::GetClass(CLASS__ID)));
+            pslILEmit->EmitCPOBJ(pslILEmit->GetToken(CoreLibBinder::GetClass(CLASS__ID)));
         }
         else
         {
@@ -2554,7 +2554,7 @@ class ILValueClassPtrMarshaler : public ILMarshaler
     {
         STANDARD_VM_CONTRACT;
 
-        int tokType = pslILEmit->GetToken(MscorlibBinder::GetClass(CLASS__ID));
+        int tokType = pslILEmit->GetToken(CoreLibBinder::GetClass(CLASS__ID));
         ILCodeLabel *pNullLabel = pslILEmit->NewCodeLabel();
         ILCodeLabel *pJoinLabel = pslILEmit->NewCodeLabel();
 
@@ -3302,13 +3302,13 @@ class ILMngdMarshaler : public ILMarshaler
         EmitCallMngdMarshalerMethod(pslILEmit, GetClearManagedMethod());
     }
 
-    virtual MethodDesc *GetConvertSpaceToManagedMethod()    { WRAPPER_NO_CONTRACT; return (m_idConvertSpaceToManaged    == METHOD__NIL ? NULL : MscorlibBinder::GetMethod(m_idConvertSpaceToManaged));    }
-    virtual MethodDesc *GetConvertContentsToManagedMethod() { WRAPPER_NO_CONTRACT; return (m_idConvertContentsToManaged == METHOD__NIL ? NULL : MscorlibBinder::GetMethod(m_idConvertContentsToManaged)); }
-    virtual MethodDesc *GetConvertSpaceToNativeMethod()     { WRAPPER_NO_CONTRACT; return (m_idConvertSpaceToNative     == METHOD__NIL ? NULL : MscorlibBinder::GetMethod(m_idConvertSpaceToNative));     }
-    virtual MethodDesc *GetConvertContentsToNativeMethod()  { WRAPPER_NO_CONTRACT; return (m_idConvertContentsToNative  == METHOD__NIL ? NULL : MscorlibBinder::GetMethod(m_idConvertContentsToNative));  }
-    virtual MethodDesc *GetClearNativeMethod()              { WRAPPER_NO_CONTRACT; return (m_idClearNative              == METHOD__NIL ? NULL : MscorlibBinder::GetMethod(m_idClearNative));              }
-    virtual MethodDesc *GetClearNativeContentsMethod()      { WRAPPER_NO_CONTRACT; return (m_idClearNativeContents      == METHOD__NIL ? NULL : MscorlibBinder::GetMethod(m_idClearNativeContents));      }
-    virtual MethodDesc *GetClearManagedMethod()             { WRAPPER_NO_CONTRACT; return (m_idClearManaged             == METHOD__NIL ? NULL : MscorlibBinder::GetMethod(m_idClearManaged));             }
+    virtual MethodDesc *GetConvertSpaceToManagedMethod()    { WRAPPER_NO_CONTRACT; return (m_idConvertSpaceToManaged    == METHOD__NIL ? NULL : CoreLibBinder::GetMethod(m_idConvertSpaceToManaged));    }
+    virtual MethodDesc *GetConvertContentsToManagedMethod() { WRAPPER_NO_CONTRACT; return (m_idConvertContentsToManaged == METHOD__NIL ? NULL : CoreLibBinder::GetMethod(m_idConvertContentsToManaged)); }
+    virtual MethodDesc *GetConvertSpaceToNativeMethod()     { WRAPPER_NO_CONTRACT; return (m_idConvertSpaceToNative     == METHOD__NIL ? NULL : CoreLibBinder::GetMethod(m_idConvertSpaceToNative));     }
+    virtual MethodDesc *GetConvertContentsToNativeMethod()  { WRAPPER_NO_CONTRACT; return (m_idConvertContentsToNative  == METHOD__NIL ? NULL : CoreLibBinder::GetMethod(m_idConvertContentsToNative));  }
+    virtual MethodDesc *GetClearNativeMethod()              { WRAPPER_NO_CONTRACT; return (m_idClearNative              == METHOD__NIL ? NULL : CoreLibBinder::GetMethod(m_idClearNative));              }
+    virtual MethodDesc *GetClearNativeContentsMethod()      { WRAPPER_NO_CONTRACT; return (m_idClearNativeContents      == METHOD__NIL ? NULL : CoreLibBinder::GetMethod(m_idClearNativeContents));      }
+    virtual MethodDesc *GetClearManagedMethod()             { WRAPPER_NO_CONTRACT; return (m_idClearManaged             == METHOD__NIL ? NULL : CoreLibBinder::GetMethod(m_idClearManaged));             }
 
     const BinderMethodID m_idConvertSpaceToManaged;
     const BinderMethodID m_idConvertContentsToManaged;
diff --git a/src/coreclr/src/vm/ilstubcache.cpp b/src/coreclr/src/vm/ilstubcache.cpp
index fb9e0ea1eaf36b..64bd551b2c12ab 100644
--- a/src/coreclr/src/vm/ilstubcache.cpp
+++ b/src/coreclr/src/vm/ilstubcache.cpp
@@ -421,7 +421,7 @@ MethodTable* ILStubCache::GetOrCreateStubMethodTable(Module* pModule)
 //
 // We're relying on the fact that a VASigCookie may only mention types within the
 // corresponding module used to qualify the signature and the fact that interop
-// stubs may only reference mscorlib code or code related to a type mentioned in
+// stubs may only reference CoreLib code or code related to a type mentioned in
 // the signature.  Both of these are true unless the sig is allowed to contain
 // ELEMENT_TYPE_INTERNAL, which may refer to any type.
 //
diff --git a/src/coreclr/src/vm/interoputil.cpp b/src/coreclr/src/vm/interoputil.cpp
index 0a58c8144e7ad7..fc2fb3c7e1e914 100644
--- a/src/coreclr/src/vm/interoputil.cpp
+++ b/src/coreclr/src/vm/interoputil.cpp
@@ -317,7 +317,7 @@ void GetCultureInfoForLCID(LCID lcid, OBJECTREF *pCultureObj)
     GCPROTECT_BEGIN(CultureObj)
     {
         // Allocate a CultureInfo with the specified LCID.
-        CultureObj = AllocateObject(MscorlibBinder::GetClass(CLASS__CULTURE_INFO));
+        CultureObj = AllocateObject(CoreLibBinder::GetClass(CLASS__CULTURE_INFO));
 
         MethodDescCallSite cultureInfoCtor(METHOD__CULTURE_INFO__INT_CTOR, &CultureObj);
 
@@ -3145,7 +3145,7 @@ void DispInvokeConvertObjectToVariant(OBJECTREF *pSrcObj, VARIANT *pDestVar, Byr
             V_VT(pDestVar) = VT_VARIANT | VT_BYREF;
             pDestVar->pvarVal = &pByrefArgInfo->m_Val;
         }
-        else if (MscorlibBinder::IsClass((*pSrcObj)->GetMethodTable(), CLASS__VARIANT_WRAPPER))
+        else if (CoreLibBinder::IsClass((*pSrcObj)->GetMethodTable(), CLASS__VARIANT_WRAPPER))
         {
             OBJECTREF WrappedObj = (*((VARIANTWRAPPEROBJECTREF*)pSrcObj))->GetWrappedObject();
             GCPROTECT_BEGIN(WrappedObj)
diff --git a/src/coreclr/src/vm/interpreter.cpp b/src/coreclr/src/vm/interpreter.cpp
index b4f5a0dbf45bb5..ef14373dfcfefc 100644
--- a/src/coreclr/src/vm/interpreter.cpp
+++ b/src/coreclr/src/vm/interpreter.cpp
@@ -9077,7 +9077,7 @@ void Interpreter::DoCallWork(bool virtualCall, void* thisArg, CORINFO_RESOLVED_T
         }
 
         // Plus some other calls that we're going to treat "like" intrinsics...
-        if (methToCall == MscorlibBinder::GetMethod(METHOD__STUBHELPERS__SET_LAST_ERROR))
+        if (methToCall == CoreLibBinder::GetMethod(METHOD__STUBHELPERS__SET_LAST_ERROR))
         {
             // If we're interpreting a method that calls "SetLastError", it's very likely that the call(i) whose
             // error we're trying to capture was performed with MethodDescCallSite machinery that itself trashes
@@ -10281,7 +10281,7 @@ void Interpreter::CallI()
             }
             else
             {
-                pMD = MscorlibBinder::GetMethod(METHOD__INTERLOCKED__COMPARE_EXCHANGE_OBJECT);  // A random static method.
+                pMD = CoreLibBinder::GetMethod(METHOD__INTERLOCKED__COMPARE_EXCHANGE_OBJECT);  // A random static method.
             }
             MethodDescCallSite mdcs(pMD, &mSig, ftnPtr);
 #if 0
diff --git a/src/coreclr/src/vm/invokeutil.cpp b/src/coreclr/src/vm/invokeutil.cpp
index 7c1790821db7cb..44ef6b97aac4f8 100644
--- a/src/coreclr/src/vm/invokeutil.cpp
+++ b/src/coreclr/src/vm/invokeutil.cpp
@@ -53,7 +53,7 @@ BOOL InvokeUtil::IsVoidPtr(TypeHandle th)
     if (!th.IsPointer())
         return FALSE;
 
-    return th.AsTypeDesc()->GetTypeParam() == MscorlibBinder::GetElementType(ELEMENT_TYPE_VOID);
+    return th.AsTypeDesc()->GetTypeParam() == CoreLibBinder::GetElementType(ELEMENT_TYPE_VOID);
 }
 
 OBJECTREF InvokeUtil::CreatePointer(TypeHandle th, void * p)
@@ -70,7 +70,7 @@ OBJECTREF InvokeUtil::CreatePointer(TypeHandle th, void * p)
     OBJECTREF refObj = NULL;
     GCPROTECT_BEGIN(refObj);
 
-    refObj = AllocateObject(MscorlibBinder::GetClass(CLASS__POINTER));
+    refObj = AllocateObject(CoreLibBinder::GetClass(CLASS__POINTER));
 
     ((ReflectionPointer *)OBJECTREFToObject(refObj))->_ptr = p;
 
@@ -299,9 +299,9 @@ void InvokeUtil::CopyArg(TypeHandle th, OBJECTREF *pObjUNSAFE, ArgDestination *a
             *(PVOID *)pArgDst = 0;
         }
         else {
-            if (rObj->GetMethodTable() == MscorlibBinder::GetClassIfExist(CLASS__POINTER) && type == ELEMENT_TYPE_PTR)
+            if (rObj->GetMethodTable() == CoreLibBinder::GetClassIfExist(CLASS__POINTER) && type == ELEMENT_TYPE_PTR)
                 *(PVOID *)pArgDst = GetPointerValue(rObj);
-            else if (rObj->GetTypeHandle().AsMethodTable() == MscorlibBinder::GetElementType(ELEMENT_TYPE_I))
+            else if (rObj->GetTypeHandle().AsMethodTable() == CoreLibBinder::GetElementType(ELEMENT_TYPE_I))
             {
                 ARG_SLOT slot;
                 CreatePrimitiveValue(oType, oType, rObj, &slot);
@@ -592,7 +592,7 @@ void InvokeUtil::ValidField(TypeHandle th, OBJECTREF* value)
 
     // handle pointers
     if (type == ELEMENT_TYPE_PTR || type == ELEMENT_TYPE_FNPTR) {
-        if (MscorlibBinder::IsClass((*value)->GetMethodTable(), CLASS__POINTER) && type == ELEMENT_TYPE_PTR) {
+        if (CoreLibBinder::IsClass((*value)->GetMethodTable(), CLASS__POINTER) && type == ELEMENT_TYPE_PTR) {
             TypeHandle srcTH = GetPointerType(*value);
 
             if (!IsVoidPtr(th)) {
@@ -601,7 +601,7 @@ void InvokeUtil::ValidField(TypeHandle th, OBJECTREF* value)
             }
             return;
         }
-        else if (MscorlibBinder::IsClass((*value)->GetMethodTable(), CLASS__INTPTR)) {
+        else if (CoreLibBinder::IsClass((*value)->GetMethodTable(), CLASS__INTPTR)) {
             return;
         }
 
@@ -696,7 +696,7 @@ OBJECTREF InvokeUtil::CreateObjectAfterInvoke(TypeHandle th, void * pValue) {
         {
             LPVOID capturedValue = *(LPVOID*)pValue;
             INDEBUG(pValue = (LPVOID)(size_t)0xcccccccc); // We're about to allocate a GC object - can no longer trust pValue
-            obj = AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_I));
+            obj = AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_I));
             *(LPVOID*)(obj->UnBox()) = capturedValue;
         }
         break;
@@ -736,7 +736,7 @@ OBJECTREF InvokeUtil::CreateClassLoadExcept(OBJECTREF* classes, OBJECTREF* excep
     } gc;
     ZeroMemory(&gc, sizeof(gc));
 
-    MethodTable *pVMClassLoadExcept = MscorlibBinder::GetException(kReflectionTypeLoadException);
+    MethodTable *pVMClassLoadExcept = CoreLibBinder::GetException(kReflectionTypeLoadException);
     gc.o = AllocateObject(pVMClassLoadExcept);
     GCPROTECT_BEGIN(gc);
     ARG_SLOT args[4];
@@ -786,7 +786,7 @@ OBJECTREF InvokeUtil::CreateTargetExcept(OBJECTREF* except) {
     OBJECTREF o;
     OBJECTREF oRet = 0;
 
-    MethodTable *pVMTargetExcept = MscorlibBinder::GetException(kTargetInvocationException);
+    MethodTable *pVMTargetExcept = CoreLibBinder::GetException(kTargetInvocationException);
     o = AllocateObject(pVMTargetExcept);
     GCPROTECT_BEGIN(o);
     ARG_SLOT args[2];
@@ -1055,7 +1055,7 @@ void InvokeUtil::SetValidField(CorElementType fldType,
         break;
 
     case ELEMENT_TYPE_PTR:      // pointers
-        if (*valueObj != 0 && MscorlibBinder::IsClass((*valueObj)->GetMethodTable(), CLASS__POINTER)) {
+        if (*valueObj != 0 && CoreLibBinder::IsClass((*valueObj)->GetMethodTable(), CLASS__POINTER)) {
             valueptr = GetPointerValue(*valueObj);
             if (pField->IsStatic())
                 pField->SetStaticValuePtr(valueptr);
@@ -1291,7 +1291,7 @@ OBJECTREF InvokeUtil::GetFieldValue(FieldDesc* pField, TypeHandle fieldType, OBJ
         else
             value = pField->GetValuePtr(*target);
 
-        MethodTable *pIntPtrMT = MscorlibBinder::GetClass(CLASS__INTPTR);
+        MethodTable *pIntPtrMT = CoreLibBinder::GetClass(CLASS__INTPTR);
         obj = AllocateObject(pIntPtrMT);
         CopyValueClass(obj->UnBox(), &value, pIntPtrMT);
         break;
diff --git a/src/coreclr/src/vm/ipcstreamfactory.cpp b/src/coreclr/src/vm/ipcstreamfactory.cpp
index 3d9987b09a8c0a..6a82f166c1daab 100644
--- a/src/coreclr/src/vm/ipcstreamfactory.cpp
+++ b/src/coreclr/src/vm/ipcstreamfactory.cpp
@@ -12,8 +12,10 @@ Volatile<bool> IpcStreamFactory::s_isShutdown = false;
 
 bool IpcStreamFactory::ClientConnectionState::GetIpcPollHandle(IpcStream::DiagnosticsIpc::IpcPollHandle *pIpcPollHandle, ErrorCallback callback)
 {
+    STRESS_LOG0(LF_DIAGNOSTICS_PORT, LL_INFO1000, "IpcStreamFactory::ClientConnectionState::GetIpcPollHandle - ENTER.\n");
     if (_pStream == nullptr)
     {
+        STRESS_LOG0(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::ClientConnectionState::GetIpcPollHandle - cache was empty!\n");
         // cache is empty, reconnect, e.g., there was a disconnect
         IpcStream *pConnection = _pIpc->Connect(callback);
         if (pConnection == nullptr)
@@ -22,6 +24,11 @@ bool IpcStreamFactory::ClientConnectionState::GetIpcPollHandle(IpcStream::Diagno
                 callback("Failed to connect to client connection", -1);
             return false;
         }
+#ifdef TARGET_UNIX
+        STRESS_LOG1(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::ClientConnectionState::GetIpcPollHandle - returned connection { _clientSocket = %d }\n", pConnection->_clientSocket);
+#else
+        STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::ClientConnectionState::GetIpcPollHandle - returned connection { _hPipe = %d, _oOverlap.hEvent = %d }\n", pConnection->_hPipe, pConnection->_oOverlap.hEvent);
+#endif
         if (!DiagnosticsIpc::SendIpcAdvertise_V1(pConnection))
         {
             if (callback != nullptr)
@@ -33,6 +40,7 @@ bool IpcStreamFactory::ClientConnectionState::GetIpcPollHandle(IpcStream::Diagno
         _pStream = pConnection;
     }
     *pIpcPollHandle = { nullptr, _pStream, 0, this };
+    STRESS_LOG0(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::ClientConnectionState::GetIpcPollHandle - EXIT.\n");
     return true;
 }
 
@@ -139,6 +147,7 @@ int32_t IpcStreamFactory::GetNextTimeout(int32_t currentTimeoutMs)
 
 IpcStream *IpcStreamFactory::GetNextAvailableStream(ErrorCallback callback)
 {
+    STRESS_LOG0(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::GetNextAvailableStream - ENTER");
     IpcStream *pStream = nullptr;
     CQuickArrayList<IpcStream::DiagnosticsIpc::IpcPollHandle> rgIpcPollHandles;
 
@@ -166,9 +175,29 @@ IpcStream *IpcStreamFactory::GetNextAvailableStream(ErrorCallback callback)
             s_pollTimeoutInfinite :
             GetNextTimeout(pollTimeoutMs);
 
-        int32_t retval = IpcStream::DiagnosticsIpc::Poll(rgIpcPollHandles.Ptr(), (uint32_t)rgIpcPollHandles.Size(), pollTimeoutMs, callback);
         nPollAttempts++;
         STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::GetNextAvailableStream - Poll attempt: %d, timeout: %dms.\n", nPollAttempts, pollTimeoutMs);
+        for (uint32_t i = 0; i < rgIpcPollHandles.Size(); i++)
+        {
+            if (rgIpcPollHandles[i].pIpc != nullptr)
+            {
+#ifdef TARGET_UNIX
+                STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "\tSERVER IpcPollHandle[%d] = { _serverSocket = %d }\n", i, rgIpcPollHandles[i].pIpc->_serverSocket);
+#else
+                STRESS_LOG3(LF_DIAGNOSTICS_PORT, LL_INFO10, "\tSERVER IpcPollHandle[%d] = { _hPipe = %d, _oOverlap.hEvent = %d }\n", i, rgIpcPollHandles[i].pIpc->_hPipe, rgIpcPollHandles[i].pIpc->_oOverlap.hEvent);
+#endif
+            }
+            else
+            {
+#ifdef TARGET_UNIX
+                STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "\tCLIENT IpcPollHandle[%d] = { _clientSocket = %d }\n", i, rgIpcPollHandles[i].pStream->_clientSocket);
+#else
+                STRESS_LOG3(LF_DIAGNOSTICS_PORT, LL_INFO10, "\tCLIENT IpcPollHandle[%d] = { _hPipe = %d, _oOverlap.hEvent = %d }\n", i, rgIpcPollHandles[i].pStream->_hPipe, rgIpcPollHandles[i].pStream->_oOverlap.hEvent);
+#endif
+            }
+        }
+        int32_t retval = IpcStream::DiagnosticsIpc::Poll(rgIpcPollHandles.Ptr(), (uint32_t)rgIpcPollHandles.Size(), pollTimeoutMs, callback);
+        bool fSawError = false;
 
         if (retval != 0)
         {
@@ -178,27 +207,43 @@ IpcStream *IpcStreamFactory::GetNextAvailableStream(ErrorCallback callback)
                 {
                     case IpcStream::DiagnosticsIpc::PollEvents::HANGUP:
                         ((ConnectionState*)(rgIpcPollHandles[i].pUserData))->Reset(callback);
-                        STRESS_LOG1(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::GetNextAvailableStream - Poll attempt: %d, connection hung up.\n", nPollAttempts);
+                        STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::GetNextAvailableStream - HUP :: Poll attempt: %d, connection %d hung up.\n", nPollAttempts, i);
                         pollTimeoutMs = s_pollTimeoutMinMs;
                         break;
                     case IpcStream::DiagnosticsIpc::PollEvents::SIGNALED:
                         if (pStream == nullptr) // only use first signaled stream; will get others on subsequent calls
                             pStream = ((ConnectionState*)(rgIpcPollHandles[i].pUserData))->GetConnectedStream(callback);
+                        STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::GetNextAvailableStream - SIG :: Poll attempt: %d, connection %d signalled.\n", nPollAttempts, i);
                         break;
                     case IpcStream::DiagnosticsIpc::PollEvents::ERR:
-                        return nullptr;
+                        STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::GetNextAvailableStream - ERR :: Poll attempt: %d, connection %d errored.\n", nPollAttempts, i);
+                        fSawError = true;
+                        break;
+                    case IpcStream::DiagnosticsIpc::PollEvents::NONE:
+                        STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::GetNextAvailableStream - NON :: Poll attempt: %d, connection %d had no events.\n", nPollAttempts, i);
+                        break;
                     default:
-                        // TODO: Error handling
+                        STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::GetNextAvailableStream - UNK :: Poll attempt: %d, connection %d had invalid PollEvent.\n", nPollAttempts, i);
+                        fSawError = true;
                         break;
                 }
             }
         }
 
+
+        if (pStream == nullptr && fSawError)
+            return nullptr;
+
         // clear the view
         while (rgIpcPollHandles.Size() > 0)
             rgIpcPollHandles.Pop();
     }
 
+#ifdef TARGET_UNIX
+    STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::GetNextAvailableStream - EXIT :: Poll attempt: %d, stream using handle %d.\n", nPollAttempts, pStream->_clientSocket);
+#else
+    STRESS_LOG2(LF_DIAGNOSTICS_PORT, LL_INFO10, "IpcStreamFactory::GetNextAvailableStream - EXIT :: Poll attempt: %d, stream using handle %d.\n", nPollAttempts, pStream->_hPipe);
+#endif
     return pStream;
 }
 
diff --git a/src/coreclr/src/vm/jitinterface.cpp b/src/coreclr/src/vm/jitinterface.cpp
index 09c077665fe69c..9dc409db9ad5d6 100644
--- a/src/coreclr/src/vm/jitinterface.cpp
+++ b/src/coreclr/src/vm/jitinterface.cpp
@@ -515,7 +515,12 @@ CEEInfo::ConvToJitSig(
             static_assert_no_msg(CORINFO_CALLCONV_FASTCALL == (CorInfoCallConv)IMAGE_CEE_UNMANAGED_CALLCONV_FASTCALL);
 
             CorUnmanagedCallingConvention callConvMaybe;
-            if (S_OK == MetaSig::TryGetUnmanagedCallingConventionFromModOpt(module, pSig, cbSig, &callConvMaybe))
+            UINT errorResID;
+            HRESULT hr = MetaSig::TryGetUnmanagedCallingConventionFromModOpt(module, pSig, cbSig, &callConvMaybe, &errorResID);
+            if (FAILED(hr))
+                COMPlusThrowHR(hr, errorResID);
+
+            if (hr == S_OK)
             {
                 sigRet->callConv = (CorInfoCallConv)callConvMaybe;
             }
@@ -621,7 +626,7 @@ CORINFO_CLASS_HANDLE CEEInfo::getTokenTypeAsHandle (CORINFO_RESOLVED_TOKEN * pRe
         classID = CLASS__FIELD_HANDLE;
     }
 
-    tokenType = CORINFO_CLASS_HANDLE(MscorlibBinder::GetClass(classID));
+    tokenType = CORINFO_CLASS_HANDLE(CoreLibBinder::GetClass(classID));
 
     EE_TO_JIT_TRANSITION();
 
@@ -1360,25 +1365,25 @@ bool CEEInfo::tryResolveToken(CORINFO_RESOLVED_TOKEN* resolvedToken)
 }
 
 /*********************************************************************/
-// We have a few frequently used constants in mscorlib that are defined as
+// We have a few frequently used constants in CoreLib that are defined as
 // readonly static fields for historic reasons. Check for them here and
 // allow them to be treated as actual constants by the JIT.
 static CORINFO_FIELD_ACCESSOR getFieldIntrinsic(FieldDesc * field)
 {
     STANDARD_VM_CONTRACT;
 
-    if (MscorlibBinder::GetField(FIELD__STRING__EMPTY) == field)
+    if (CoreLibBinder::GetField(FIELD__STRING__EMPTY) == field)
     {
         return CORINFO_FIELD_INTRINSIC_EMPTY_STRING;
     }
     else
-    if ((MscorlibBinder::GetField(FIELD__INTPTR__ZERO) == field) ||
-        (MscorlibBinder::GetField(FIELD__UINTPTR__ZERO) == field))
+    if ((CoreLibBinder::GetField(FIELD__INTPTR__ZERO) == field) ||
+        (CoreLibBinder::GetField(FIELD__UINTPTR__ZERO) == field))
     {
         return CORINFO_FIELD_INTRINSIC_ZERO;
     }
     else
-    if (MscorlibBinder::GetField(FIELD__BITCONVERTER__ISLITTLEENDIAN) == field)
+    if (CoreLibBinder::GetField(FIELD__BITCONVERTER__ISLITTLEENDIAN) == field)
     {
         return CORINFO_FIELD_INTRINSIC_ISLITTLEENDIAN;
     }
@@ -4242,16 +4247,16 @@ CORINFO_CLASS_HANDLE CEEInfo::getBuiltinClass(CorInfoClassId classId)
         result = CORINFO_CLASS_HANDLE(g_TypedReferenceMT);
         break;
     case CLASSID_TYPE_HANDLE:
-        result = CORINFO_CLASS_HANDLE(MscorlibBinder::GetClass(CLASS__TYPE_HANDLE));
+        result = CORINFO_CLASS_HANDLE(CoreLibBinder::GetClass(CLASS__TYPE_HANDLE));
         break;
     case CLASSID_FIELD_HANDLE:
-        result = CORINFO_CLASS_HANDLE(MscorlibBinder::GetClass(CLASS__FIELD_HANDLE));
+        result = CORINFO_CLASS_HANDLE(CoreLibBinder::GetClass(CLASS__FIELD_HANDLE));
         break;
     case CLASSID_METHOD_HANDLE:
-        result = CORINFO_CLASS_HANDLE(MscorlibBinder::GetClass(CLASS__METHOD_HANDLE));
+        result = CORINFO_CLASS_HANDLE(CoreLibBinder::GetClass(CLASS__METHOD_HANDLE));
         break;
     case CLASSID_ARGUMENT_HANDLE:
-        result = CORINFO_CLASS_HANDLE(MscorlibBinder::GetClass(CLASS__ARGUMENT_HANDLE));
+        result = CORINFO_CLASS_HANDLE(CoreLibBinder::GetClass(CLASS__ARGUMENT_HANDLE));
         break;
     case CLASSID_STRING:
         result = CORINFO_CLASS_HANDLE(g_pStringClass);
@@ -5188,10 +5193,10 @@ void CEEInfo::getCallInfo(
             // null since the virtual method resolves to System.Enum's implementation and that's a reference type.
             // We can't do this for any other method since ToString and Equals have different semantics for enums
             // and their underlying type.
-            if (pMD->GetSlot() == MscorlibBinder::GetMethod(METHOD__OBJECT__GET_HASH_CODE)->GetSlot())
+            if (pMD->GetSlot() == CoreLibBinder::GetMethod(METHOD__OBJECT__GET_HASH_CODE)->GetSlot())
             {
                 // Pretend this was a "constrained. UnderlyingType" instruction prefix
-                constrainedType = TypeHandle(MscorlibBinder::GetElementType(constrainedType.GetVerifierCorElementType()));
+                constrainedType = TypeHandle(CoreLibBinder::GetElementType(constrainedType.GetVerifierCorElementType()));
 
                 // Native image signature encoder will use this field. It needs to match that pretended type, a bogus signature
                 // would be produced otherwise.
@@ -6812,8 +6817,8 @@ void CEEInfo::setMethodAttribs (
             }
             else
             {
-                // Don't cache inlining hints inside mscorlib during NGen of other assemblies,
-                // since mscorlib is loaded domain neutral and will survive worker process recycling,
+                // Don't cache inlining hints inside CoreLib during NGen of other assemblies,
+                // since CoreLib is loaded domain neutral and will survive worker process recycling,
                 // causing determinism problems.
                 Module * pModule = ftn->GetModule();
                 if (pModule->IsSystem() && pModule->HasNativeImage())
@@ -6898,8 +6903,8 @@ mdToken FindGenericMethodArgTypeSpec(IMDInternalImport* pInternalImport)
 /*********************************************************************
 
 IL is the most efficient and portable way to implement certain low level methods
-in mscorlib.dll. Unfortunately, there is no good way to link IL into mscorlib.dll today.
-Until we find a good way to link IL into mscorlib.dll, we will provide the IL implementation here.
+in CoreLib. Unfortunately, there is no good way to link IL into CoreLib today.
+Until we find a good way to link IL into CoreLib, we will provide the IL implementation here.
 
 - All IL intrinsincs are members of System.Runtime.CompilerServices.JitHelpers class
 - All IL intrinsincs should be kept very simple. Implement the minimal reusable version of
@@ -6914,11 +6919,11 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
 {
     STANDARD_VM_CONTRACT;
 
-    _ASSERTE(MscorlibBinder::IsClass(ftn->GetMethodTable(), CLASS__UNSAFE));
+    _ASSERTE(CoreLibBinder::IsClass(ftn->GetMethodTable(), CLASS__UNSAFE));
 
     mdMethodDef tk = ftn->GetMemberDef();
 
-    if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__AS_POINTER)->GetMemberDef())
+    if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__AS_POINTER)->GetMemberDef())
     {
         // Return the argument that was passed in.
         static const BYTE ilcode[] = { CEE_LDARG_0, CEE_CONV_U, CEE_RET };
@@ -6929,13 +6934,13 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__SIZEOF)->GetMemberDef())
+    if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__SIZEOF)->GetMemberDef())
     {
         _ASSERTE(ftn->HasMethodInstantiation());
         Instantiation inst = ftn->GetMethodInstantiation();
 
         _ASSERTE(ftn->GetNumGenericMethodArgs() == 1);
-        mdToken tokGenericArg = FindGenericMethodArgTypeSpec(MscorlibBinder::GetModule()->GetMDImport());
+        mdToken tokGenericArg = FindGenericMethodArgTypeSpec(CoreLibBinder::GetModule()->GetMDImport());
 
         static BYTE ilcode[] = { CEE_PREFIX1, (CEE_SIZEOF & 0xFF), 0,0,0,0, CEE_RET };
 
@@ -6951,10 +6956,10 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_AS)->GetMemberDef() ||
-             tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__OBJECT_AS)->GetMemberDef() ||
-             tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__AS_REF_POINTER)->GetMemberDef() ||
-             tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__AS_REF_IN)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_AS)->GetMemberDef() ||
+             tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__OBJECT_AS)->GetMemberDef() ||
+             tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__AS_REF_POINTER)->GetMemberDef() ||
+             tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__AS_REF_IN)->GetMemberDef())
     {
         // Return the argument that was passed in.
         static const BYTE ilcode[] = { CEE_LDARG_0, CEE_RET };
@@ -6965,10 +6970,10 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_ADD)->GetMemberDef() ||
-             tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__PTR_ADD)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_ADD)->GetMemberDef() ||
+             tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__PTR_ADD)->GetMemberDef())
     {
-        mdToken tokGenericArg = FindGenericMethodArgTypeSpec(MscorlibBinder::GetModule()->GetMDImport());
+        mdToken tokGenericArg = FindGenericMethodArgTypeSpec(CoreLibBinder::GetModule()->GetMDImport());
 
         static BYTE ilcode[] = { CEE_LDARG_1,
             CEE_PREFIX1, (CEE_SIZEOF & 0xFF), 0,0,0,0,
@@ -6990,9 +6995,9 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_INTPTR_ADD)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_INTPTR_ADD)->GetMemberDef())
     {
-        mdToken tokGenericArg = FindGenericMethodArgTypeSpec(MscorlibBinder::GetModule()->GetMDImport());
+        mdToken tokGenericArg = FindGenericMethodArgTypeSpec(CoreLibBinder::GetModule()->GetMDImport());
 
         static BYTE ilcode[] = { CEE_LDARG_1,
             CEE_PREFIX1, (CEE_SIZEOF & 0xFF), 0,0,0,0,
@@ -7013,7 +7018,7 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_ADD_BYTE_OFFSET)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_ADD_BYTE_OFFSET)->GetMemberDef())
     {
         static BYTE ilcode[] = { CEE_LDARG_0, CEE_LDARG_1, CEE_ADD, CEE_RET };
 
@@ -7024,7 +7029,7 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_ARE_SAME)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_ARE_SAME)->GetMemberDef())
     {
         // Compare the two arguments
         static const BYTE ilcode[] = { CEE_LDARG_0, CEE_LDARG_1, CEE_PREFIX1, (CEE_CEQ & 0xFF), CEE_RET };
@@ -7035,7 +7040,7 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_IS_ADDRESS_GREATER_THAN)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_IS_ADDRESS_GREATER_THAN)->GetMemberDef())
     {
         // Compare the two arguments
         static const BYTE ilcode[] = { CEE_LDARG_0, CEE_LDARG_1, CEE_PREFIX1, (CEE_CGT_UN & 0xFF), CEE_RET };
@@ -7046,7 +7051,7 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_IS_ADDRESS_LESS_THAN)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_IS_ADDRESS_LESS_THAN)->GetMemberDef())
     {
         // Compare the two arguments
         static const BYTE ilcode[] = { CEE_LDARG_0, CEE_LDARG_1, CEE_PREFIX1, (CEE_CLT_UN & 0xFF), CEE_RET };
@@ -7057,7 +7062,7 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_NULLREF)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_NULLREF)->GetMemberDef())
     {
         static const BYTE ilcode[] = { CEE_LDC_I4_0, CEE_CONV_U, CEE_RET };
         methInfo->ILCode = const_cast<BYTE*>(ilcode);
@@ -7067,7 +7072,7 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_IS_NULL)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_IS_NULL)->GetMemberDef())
     {
         // 'ldnull' opcode would produce type o, and we can't compare & against o (ECMA-335, Table III.4).
         // However, we can compare & against native int, so we'll use that instead.
@@ -7080,7 +7085,7 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_INIT_BLOCK_UNALIGNED)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_INIT_BLOCK_UNALIGNED)->GetMemberDef())
     {
         static const BYTE ilcode[] = { CEE_LDARG_0, CEE_LDARG_1, CEE_LDARG_2, CEE_PREFIX1, (CEE_UNALIGNED & 0xFF), 0x01, CEE_PREFIX1, (CEE_INITBLK & 0xFF), CEE_RET };
         methInfo->ILCode = const_cast<BYTE*>(ilcode);
@@ -7090,7 +7095,7 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_BYTE_OFFSET)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_BYTE_OFFSET)->GetMemberDef())
     {
         static const BYTE ilcode[] =
         {
@@ -7107,13 +7112,13 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_READ_UNALIGNED)->GetMemberDef() ||
-             tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__PTR_READ_UNALIGNED)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_READ_UNALIGNED)->GetMemberDef() ||
+             tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__PTR_READ_UNALIGNED)->GetMemberDef())
     {
         _ASSERTE(ftn->HasMethodInstantiation());
         Instantiation inst = ftn->GetMethodInstantiation();
         _ASSERTE(ftn->GetNumGenericMethodArgs() == 1);
-        mdToken tokGenericArg = FindGenericMethodArgTypeSpec(MscorlibBinder::GetModule()->GetMDImport());
+        mdToken tokGenericArg = FindGenericMethodArgTypeSpec(CoreLibBinder::GetModule()->GetMDImport());
 
         static const BYTE ilcode[]
         {
@@ -7130,13 +7135,13 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__BYREF_WRITE_UNALIGNED)->GetMemberDef() ||
-             tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__PTR_WRITE_UNALIGNED)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__BYREF_WRITE_UNALIGNED)->GetMemberDef() ||
+             tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__PTR_WRITE_UNALIGNED)->GetMemberDef())
     {
         _ASSERTE(ftn->HasMethodInstantiation());
         Instantiation inst = ftn->GetMethodInstantiation();
         _ASSERTE(ftn->GetNumGenericMethodArgs() == 1);
-        mdToken tokGenericArg = FindGenericMethodArgTypeSpec(MscorlibBinder::GetModule()->GetMDImport());
+        mdToken tokGenericArg = FindGenericMethodArgTypeSpec(CoreLibBinder::GetModule()->GetMDImport());
 
         static const BYTE ilcode[]
         {
@@ -7154,7 +7159,7 @@ bool getILIntrinsicImplementationForUnsafe(MethodDesc * ftn,
         methInfo->options = (CorInfoOptions)0;
         return true;
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__UNSAFE__SKIPINIT)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__UNSAFE__SKIPINIT)->GetMemberDef())
     {
         static BYTE ilcode[] = { CEE_RET };
 
@@ -7174,13 +7179,13 @@ bool getILIntrinsicImplementationForMemoryMarshal(MethodDesc * ftn,
 {
     STANDARD_VM_CONTRACT;
 
-    _ASSERTE(MscorlibBinder::IsClass(ftn->GetMethodTable(), CLASS__MEMORY_MARSHAL));
+    _ASSERTE(CoreLibBinder::IsClass(ftn->GetMethodTable(), CLASS__MEMORY_MARSHAL));
 
     mdMethodDef tk = ftn->GetMemberDef();
 
-    if (tk == MscorlibBinder::GetMethod(METHOD__MEMORY_MARSHAL__GET_ARRAY_DATA_REFERENCE)->GetMemberDef())
+    if (tk == CoreLibBinder::GetMethod(METHOD__MEMORY_MARSHAL__GET_ARRAY_DATA_REFERENCE)->GetMemberDef())
     {
-        mdToken tokRawSzArrayData = MscorlibBinder::GetField(FIELD__RAW_ARRAY_DATA__DATA)->GetMemberDef();
+        mdToken tokRawSzArrayData = CoreLibBinder::GetField(FIELD__RAW_ARRAY_DATA__DATA)->GetMemberDef();
 
         static BYTE ilcode[] = { CEE_LDARG_0,
                                  CEE_LDFLDA,0,0,0,0,
@@ -7208,7 +7213,7 @@ bool getILIntrinsicImplementationForVolatile(MethodDesc * ftn,
     STANDARD_VM_CONTRACT;
 
     //
-    // This replaces the implementations of Volatile.* in mscorlib with more efficient ones.
+    // This replaces the implementations of Volatile.* in CoreLib with more efficient ones.
     // We do this because we cannot otherwise express these in C#.  What we *want* to do is
     // to treat the byref args to these methods as "volatile."  In pseudo-C#, this would look
     // like:
@@ -7222,7 +7227,7 @@ bool getILIntrinsicImplementationForVolatile(MethodDesc * ftn,
     // we substitute raw IL bodies for these methods that use the correct volatile instructions.
     //
 
-    _ASSERTE(MscorlibBinder::IsClass(ftn->GetMethodTable(), CLASS__VOLATILE));
+    _ASSERTE(CoreLibBinder::IsClass(ftn->GetMethodTable(), CLASS__VOLATILE));
 
     const size_t VolatileMethodBodySize = 6;
 
@@ -7271,7 +7276,7 @@ bool getILIntrinsicImplementationForVolatile(MethodDesc * ftn,
         //
         // Ordinary volatile loads and stores only guarantee atomicity for pointer-sized (or smaller) data.
         // So, on 32-bit platforms we must use Interlocked operations instead for the 64-bit types.
-        // The implementation in mscorlib already does this, so we will only substitute a new
+        // The implementation in CoreLib already does this, so we will only substitute a new
         // IL body if we're running on a 64-bit platform.
         //
         IN_TARGET_64BIT(VOLATILE_IMPL(Long,  CEE_LDIND_I8, CEE_STIND_I8))
@@ -7282,7 +7287,7 @@ bool getILIntrinsicImplementationForVolatile(MethodDesc * ftn,
     mdMethodDef md = ftn->GetMemberDef();
     for (unsigned i = 0; i < NumItems(volatileImpls); i++)
     {
-        if (md == MscorlibBinder::GetMethod(volatileImpls[i].methodId)->GetMemberDef())
+        if (md == CoreLibBinder::GetMethod(volatileImpls[i].methodId)->GetMemberDef())
         {
             methInfo->ILCode = const_cast<BYTE*>(volatileImpls[i].body);
             methInfo->ILCodeSize = VolatileMethodBodySize;
@@ -7301,14 +7306,14 @@ bool getILIntrinsicImplementationForInterlocked(MethodDesc * ftn,
 {
     STANDARD_VM_CONTRACT;
 
-    _ASSERTE(MscorlibBinder::IsClass(ftn->GetMethodTable(), CLASS__INTERLOCKED));
+    _ASSERTE(CoreLibBinder::IsClass(ftn->GetMethodTable(), CLASS__INTERLOCKED));
 
     // We are only interested if ftn's token and CompareExchange<T> token match
-    if (ftn->GetMemberDef() != MscorlibBinder::GetMethod(METHOD__INTERLOCKED__COMPARE_EXCHANGE_T)->GetMemberDef())
+    if (ftn->GetMemberDef() != CoreLibBinder::GetMethod(METHOD__INTERLOCKED__COMPARE_EXCHANGE_T)->GetMemberDef())
         return false;
 
     // Get MethodDesc for non-generic System.Threading.Interlocked.CompareExchange()
-    MethodDesc* cmpxchgObject = MscorlibBinder::GetMethod(METHOD__INTERLOCKED__COMPARE_EXCHANGE_OBJECT);
+    MethodDesc* cmpxchgObject = CoreLibBinder::GetMethod(METHOD__INTERLOCKED__COMPARE_EXCHANGE_OBJECT);
 
     // Setup up the body of the method
     static BYTE il[] = {
@@ -7341,11 +7346,11 @@ bool getILIntrinsicImplementationForRuntimeHelpers(MethodDesc * ftn,
 {
     STANDARD_VM_CONTRACT;
 
-    _ASSERTE(MscorlibBinder::IsClass(ftn->GetMethodTable(), CLASS__RUNTIME_HELPERS));
+    _ASSERTE(CoreLibBinder::IsClass(ftn->GetMethodTable(), CLASS__RUNTIME_HELPERS));
 
     mdMethodDef tk = ftn->GetMemberDef();
 
-    if (tk == MscorlibBinder::GetMethod(METHOD__RUNTIME_HELPERS__IS_REFERENCE_OR_CONTAINS_REFERENCES)->GetMemberDef())
+    if (tk == CoreLibBinder::GetMethod(METHOD__RUNTIME_HELPERS__IS_REFERENCE_OR_CONTAINS_REFERENCES)->GetMemberDef())
     {
         _ASSERTE(ftn->HasMethodInstantiation());
         Instantiation inst = ftn->GetMethodInstantiation();
@@ -7373,7 +7378,7 @@ bool getILIntrinsicImplementationForRuntimeHelpers(MethodDesc * ftn,
         return true;
     }
 
-    if (tk == MscorlibBinder::GetMethod(METHOD__RUNTIME_HELPERS__IS_BITWISE_EQUATABLE)->GetMemberDef())
+    if (tk == CoreLibBinder::GetMethod(METHOD__RUNTIME_HELPERS__IS_BITWISE_EQUATABLE)->GetMemberDef())
     {
         _ASSERTE(ftn->HasMethodInstantiation());
         Instantiation inst = ftn->GetMethodInstantiation();
@@ -7391,22 +7396,22 @@ bool getILIntrinsicImplementationForRuntimeHelpers(MethodDesc * ftn,
         // n.b. This doesn't imply that the type's CompareTo method can be memcmp-implemented,
         // as a method like CompareTo may need to take a type's signedness into account.
 
-        if (methodTable == MscorlibBinder::GetClass(CLASS__BOOLEAN)
-            || methodTable == MscorlibBinder::GetClass(CLASS__BYTE)
-            || methodTable == MscorlibBinder::GetClass(CLASS__SBYTE)
+        if (methodTable == CoreLibBinder::GetClass(CLASS__BOOLEAN)
+            || methodTable == CoreLibBinder::GetClass(CLASS__BYTE)
+            || methodTable == CoreLibBinder::GetClass(CLASS__SBYTE)
 #ifdef FEATURE_UTF8STRING
-            || methodTable == MscorlibBinder::GetClass(CLASS__CHAR8)
+            || methodTable == CoreLibBinder::GetClass(CLASS__CHAR8)
 #endif // FEATURE_UTF8STRING
-            || methodTable == MscorlibBinder::GetClass(CLASS__CHAR)
-            || methodTable == MscorlibBinder::GetClass(CLASS__INT16)
-            || methodTable == MscorlibBinder::GetClass(CLASS__UINT16)
-            || methodTable == MscorlibBinder::GetClass(CLASS__INT32)
-            || methodTable == MscorlibBinder::GetClass(CLASS__UINT32)
-            || methodTable == MscorlibBinder::GetClass(CLASS__INT64)
-            || methodTable == MscorlibBinder::GetClass(CLASS__UINT64)
-            || methodTable == MscorlibBinder::GetClass(CLASS__INTPTR)
-            || methodTable == MscorlibBinder::GetClass(CLASS__UINTPTR)
-            || methodTable == MscorlibBinder::GetClass(CLASS__RUNE)
+            || methodTable == CoreLibBinder::GetClass(CLASS__CHAR)
+            || methodTable == CoreLibBinder::GetClass(CLASS__INT16)
+            || methodTable == CoreLibBinder::GetClass(CLASS__UINT16)
+            || methodTable == CoreLibBinder::GetClass(CLASS__INT32)
+            || methodTable == CoreLibBinder::GetClass(CLASS__UINT32)
+            || methodTable == CoreLibBinder::GetClass(CLASS__INT64)
+            || methodTable == CoreLibBinder::GetClass(CLASS__UINT64)
+            || methodTable == CoreLibBinder::GetClass(CLASS__INTPTR)
+            || methodTable == CoreLibBinder::GetClass(CLASS__UINTPTR)
+            || methodTable == CoreLibBinder::GetClass(CLASS__RUNE)
             || methodTable->IsEnum())
         {
             methInfo->ILCode = const_cast<BYTE*>(returnTrue);
@@ -7423,9 +7428,9 @@ bool getILIntrinsicImplementationForRuntimeHelpers(MethodDesc * ftn,
         return true;
     }
 
-    if (tk == MscorlibBinder::GetMethod(METHOD__RUNTIME_HELPERS__GET_METHOD_TABLE)->GetMemberDef())
+    if (tk == CoreLibBinder::GetMethod(METHOD__RUNTIME_HELPERS__GET_METHOD_TABLE)->GetMemberDef())
     {
-        mdToken tokRawData = MscorlibBinder::GetField(FIELD__RAW_DATA__DATA)->GetMemberDef();
+        mdToken tokRawData = CoreLibBinder::GetField(FIELD__RAW_DATA__DATA)->GetMemberDef();
 
         // In the CLR, an object is laid out as follows.
         // [ object_header || MethodTable* (64-bit pointer) || instance_data ]
@@ -7460,7 +7465,7 @@ bool getILIntrinsicImplementationForRuntimeHelpers(MethodDesc * ftn,
         return true;
     }
 
-    if (tk == MscorlibBinder::GetMethod(METHOD__RUNTIME_HELPERS__ENUM_EQUALS)->GetMemberDef())
+    if (tk == CoreLibBinder::GetMethod(METHOD__RUNTIME_HELPERS__ENUM_EQUALS)->GetMemberDef())
     {
         // Normally we would follow the above pattern and unconditionally replace the IL,
         // relying on generic type constraints to guarantee that it will only ever be instantiated
@@ -7500,7 +7505,7 @@ bool getILIntrinsicImplementationForRuntimeHelpers(MethodDesc * ftn,
             return true;
         }
     }
-    else if (tk == MscorlibBinder::GetMethod(METHOD__RUNTIME_HELPERS__ENUM_COMPARE_TO)->GetMemberDef())
+    else if (tk == CoreLibBinder::GetMethod(METHOD__RUNTIME_HELPERS__ENUM_COMPARE_TO)->GetMemberDef())
     {
         // The the comment above on why this is is not an unconditional replacement.  This case handles
         // Enums backed by 8 byte values.
@@ -7521,12 +7526,12 @@ bool getILIntrinsicImplementationForRuntimeHelpers(MethodDesc * ftn,
         {
             static BYTE ilcode[8][9];
 
-            TypeHandle thUnderlyingType = MscorlibBinder::GetElementType(et);
+            TypeHandle thUnderlyingType = CoreLibBinder::GetElementType(et);
 
-            TypeHandle thIComparable = TypeHandle(MscorlibBinder::GetClass(CLASS__ICOMPARABLEGENERIC)).Instantiate(Instantiation(&thUnderlyingType, 1));
+            TypeHandle thIComparable = TypeHandle(CoreLibBinder::GetClass(CLASS__ICOMPARABLEGENERIC)).Instantiate(Instantiation(&thUnderlyingType, 1));
 
             MethodDesc* pCompareToMD = thUnderlyingType.AsMethodTable()->GetMethodDescForInterfaceMethod(
-                thIComparable, MscorlibBinder::GetMethod(METHOD__ICOMPARABLEGENERIC__COMPARE_TO), TRUE /* throwOnConflict */);
+                thIComparable, CoreLibBinder::GetMethod(METHOD__ICOMPARABLEGENERIC__COMPARE_TO), TRUE /* throwOnConflict */);
 
             // Call CompareTo method on the primitive type
             int tokCompareTo = pCompareToMD->GetMemberDef();
@@ -7562,10 +7567,10 @@ bool getILIntrinsicImplementationForActivator(MethodDesc* ftn,
 {
     STANDARD_VM_CONTRACT;
 
-    _ASSERTE(MscorlibBinder::IsClass(ftn->GetMethodTable(), CLASS__ACTIVATOR));
+    _ASSERTE(CoreLibBinder::IsClass(ftn->GetMethodTable(), CLASS__ACTIVATOR));
 
     // We are only interested if ftn's token and CreateInstance<T> token match
-    if (ftn->GetMemberDef() != MscorlibBinder::GetMethod(METHOD__ACTIVATOR__CREATE_INSTANCE_OF_T)->GetMemberDef())
+    if (ftn->GetMemberDef() != CoreLibBinder::GetMethod(METHOD__ACTIVATOR__CREATE_INSTANCE_OF_T)->GetMemberDef())
         return false;
 
     _ASSERTE(ftn->HasMethodInstantiation());
@@ -7579,7 +7584,7 @@ bool getILIntrinsicImplementationForActivator(MethodDesc* ftn,
         return false;
 
     // Replace the body with implementation that just returns "default"
-    MethodDesc* createDefaultInstance = MscorlibBinder::GetMethod(METHOD__ACTIVATOR__CREATE_DEFAULT_INSTANCE_OF_T);
+    MethodDesc* createDefaultInstance = CoreLibBinder::GetMethod(METHOD__ACTIVATOR__CREATE_DEFAULT_INSTANCE_OF_T);
     COR_ILMETHOD_DECODER header(createDefaultInstance->GetILHeader(FALSE), createDefaultInstance->GetMDImport(), NULL);
     getMethodInfoILMethodHeaderHelper(&header, methInfo);
     *pSig = SigPointer(header.LocalVarSig, header.cbLocalVarSig);
@@ -7622,27 +7627,27 @@ getMethodInfoHelper(
 
         if (ftn->IsJitIntrinsic())
         {
-            if (MscorlibBinder::IsClass(pMT, CLASS__UNSAFE))
+            if (CoreLibBinder::IsClass(pMT, CLASS__UNSAFE))
             {
                 fILIntrinsic = getILIntrinsicImplementationForUnsafe(ftn, methInfo);
             }
-            else if (MscorlibBinder::IsClass(pMT, CLASS__MEMORY_MARSHAL))
+            else if (CoreLibBinder::IsClass(pMT, CLASS__MEMORY_MARSHAL))
             {
                 fILIntrinsic = getILIntrinsicImplementationForMemoryMarshal(ftn, methInfo);
             }
-            else if (MscorlibBinder::IsClass(pMT, CLASS__INTERLOCKED))
+            else if (CoreLibBinder::IsClass(pMT, CLASS__INTERLOCKED))
             {
                 fILIntrinsic = getILIntrinsicImplementationForInterlocked(ftn, methInfo);
             }
-            else if (MscorlibBinder::IsClass(pMT, CLASS__VOLATILE))
+            else if (CoreLibBinder::IsClass(pMT, CLASS__VOLATILE))
             {
                 fILIntrinsic = getILIntrinsicImplementationForVolatile(ftn, methInfo);
             }
-            else if (MscorlibBinder::IsClass(pMT, CLASS__RUNTIME_HELPERS))
+            else if (CoreLibBinder::IsClass(pMT, CLASS__RUNTIME_HELPERS))
             {
                 fILIntrinsic = getILIntrinsicImplementationForRuntimeHelpers(ftn, methInfo);
             }
-            else if (MscorlibBinder::IsClass(pMT, CLASS__ACTIVATOR))
+            else if (CoreLibBinder::IsClass(pMT, CLASS__ACTIVATOR))
             {
                 SigPointer localSig;
                 fILIntrinsic = getILIntrinsicImplementationForActivator(ftn, methInfo, &localSig);
@@ -7874,8 +7879,8 @@ bool containsStackCrawlMarkLocal(MethodDesc* ftn)
         mdToken token;
         IfFailThrow(ptr.GetToken(&token));
 
-        // We are inside mscorlib - simple token match is sufficient
-        if (token == MscorlibBinder::GetClass(CLASS__STACKCRAWMARK)->GetCl())
+        // We are inside CoreLib - simple token match is sufficient
+        if (token == CoreLibBinder::GetClass(CLASS__STACKCRAWMARK)->GetCl())
             return TRUE;
     }
 
@@ -8780,16 +8785,16 @@ CorInfoIntrinsics CEEInfo::getIntrinsicID(CORINFO_METHOD_HANDLE methodHnd,
                     *pMustExpand = true;
                 }
             }
-            else if (pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__SPAN)))
+            else if (pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__SPAN)))
             {
-                if (method->HasSameMethodDefAs(MscorlibBinder::GetMethod(METHOD__SPAN__GET_ITEM)))
+                if (method->HasSameMethodDefAs(CoreLibBinder::GetMethod(METHOD__SPAN__GET_ITEM)))
                 {
                     result = CORINFO_INTRINSIC_Span_GetItem;
                 }
             }
-            else if (pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__READONLY_SPAN)))
+            else if (pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__READONLY_SPAN)))
             {
-                if (method->HasSameMethodDefAs(MscorlibBinder::GetMethod(METHOD__READONLY_SPAN__GET_ITEM)))
+                if (method->HasSameMethodDefAs(CoreLibBinder::GetMethod(METHOD__READONLY_SPAN__GET_ITEM)))
                 {
                     result = CORINFO_INTRINSIC_ReadOnlySpan_GetItem;
                 }
@@ -9112,18 +9117,18 @@ CORINFO_CLASS_HANDLE CEEInfo::getDefaultEqualityComparerClassHelper(CORINFO_CLAS
     TypeHandle elemTypeHnd(elemType);
 
     // Special case for byte
-    if (elemTypeHnd.AsMethodTable()->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__ELEMENT_TYPE_U1)))
+    if (elemTypeHnd.AsMethodTable()->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__ELEMENT_TYPE_U1)))
     {
-        return CORINFO_CLASS_HANDLE(MscorlibBinder::GetClass(CLASS__BYTE_EQUALITYCOMPARER));
+        return CORINFO_CLASS_HANDLE(CoreLibBinder::GetClass(CLASS__BYTE_EQUALITYCOMPARER));
     }
 
     // Else we'll need to find the appropriate instantation
     Instantiation inst(&elemTypeHnd, 1);
 
     // If T implements IEquatable<T>
-    if (elemTypeHnd.CanCastTo(TypeHandle(MscorlibBinder::GetClass(CLASS__IEQUATABLEGENERIC)).Instantiate(inst)))
+    if (elemTypeHnd.CanCastTo(TypeHandle(CoreLibBinder::GetClass(CLASS__IEQUATABLEGENERIC)).Instantiate(inst)))
     {
-        TypeHandle resultTh = ((TypeHandle)MscorlibBinder::GetClass(CLASS__GENERIC_EQUALITYCOMPARER)).Instantiate(inst);
+        TypeHandle resultTh = ((TypeHandle)CoreLibBinder::GetClass(CLASS__GENERIC_EQUALITYCOMPARER)).Instantiate(inst);
         return CORINFO_CLASS_HANDLE(resultTh.GetMethodTable());
     }
 
@@ -9131,7 +9136,7 @@ CORINFO_CLASS_HANDLE CEEInfo::getDefaultEqualityComparerClassHelper(CORINFO_CLAS
     if (Nullable::IsNullableType(elemTypeHnd))
     {
         Instantiation nullableInst = elemTypeHnd.AsMethodTable()->GetInstantiation();
-        TypeHandle nullableComparer = TypeHandle(MscorlibBinder::GetClass(CLASS__IEQUATABLEGENERIC)).Instantiate(nullableInst);
+        TypeHandle nullableComparer = TypeHandle(CoreLibBinder::GetClass(CLASS__IEQUATABLEGENERIC)).Instantiate(nullableInst);
         if (nullableInst[0].CanCastTo(nullableComparer))
         {
             return CORINFO_CLASS_HANDLE(nullableComparer.GetMethodTable());
@@ -9158,7 +9163,7 @@ CORINFO_CLASS_HANDLE CEEInfo::getDefaultEqualityComparerClassHelper(CORINFO_CLAS
             case ELEMENT_TYPE_I8:
             case ELEMENT_TYPE_U8:
             {
-                targetClass = MscorlibBinder::GetClass(CLASS__ENUM_EQUALITYCOMPARER);
+                targetClass = CoreLibBinder::GetClass(CLASS__ENUM_EQUALITYCOMPARER);
                 break;
             }
 
@@ -9174,7 +9179,7 @@ CORINFO_CLASS_HANDLE CEEInfo::getDefaultEqualityComparerClassHelper(CORINFO_CLAS
     }
 
     // Default case
-    TypeHandle resultTh = ((TypeHandle)MscorlibBinder::GetClass(CLASS__OBJECT_EQUALITYCOMPARER)).Instantiate(inst);
+    TypeHandle resultTh = ((TypeHandle)CoreLibBinder::GetClass(CLASS__OBJECT_EQUALITYCOMPARER)).Instantiate(inst);
 
     return CORINFO_CLASS_HANDLE(resultTh.GetMethodTable());
 }
@@ -13546,7 +13551,7 @@ BOOL LoadDynamicInfoEntry(Module *currentModule,
             if (CORCOMPILE_IS_PCODE_TAGGED(result))
             {
                 // There is a rare case where the function entrypoint may not be aligned. This could happen only for FCalls,
-                // only on x86 and only if we failed to hardbind the fcall (e.g. ngen image for mscorlib.dll does not exist
+                // only on x86 and only if we failed to hardbind the fcall (e.g. ngen image for CoreLib does not exist
                 // and /nodependencies flag for ngen was used). The function entrypoints should be aligned in all other cases.
                 //
                 // We will wrap the unaligned method entrypoint by funcptr stub with aligned entrypoint.
@@ -13835,7 +13840,8 @@ BOOL LoadDynamicInfoEntry(Module *currentModule,
             DWORD baseOffset = CorSigUncompressData(pBlob);
             DWORD fieldOffset = CorSigUncompressData(pBlob);
             FieldDesc* pField = ZapSig::DecodeField(currentModule, pInfoModule, pBlob);
-            pField->GetEnclosingMethodTable()->CheckRestore();
+            MethodTable *pEnclosingMT = pField->GetApproxEnclosingMethodTable();
+            pEnclosingMT->CheckRestore();
             DWORD actualFieldOffset = pField->GetOffset();
             if (!pField->IsStatic() && !pField->IsFieldOfValueType())
             {
@@ -13844,10 +13850,10 @@ BOOL LoadDynamicInfoEntry(Module *currentModule,
 
             DWORD actualBaseOffset = 0;
             if (!pField->IsStatic() && 
-                pField->GetEnclosingMethodTable()->GetParentMethodTable() != NULL &&
-                !pField->GetEnclosingMethodTable()->IsValueType())
+                pEnclosingMT->GetParentMethodTable() != NULL &&
+                !pEnclosingMT->IsValueType())
             {
-                actualBaseOffset = ReadyToRunInfo::GetFieldBaseOffset(pField->GetEnclosingMethodTable());
+                actualBaseOffset = ReadyToRunInfo::GetFieldBaseOffset(pEnclosingMT);
             }
 
             if ((fieldOffset != actualFieldOffset) || (baseOffset != actualBaseOffset))
@@ -13858,7 +13864,7 @@ BOOL LoadDynamicInfoEntry(Module *currentModule,
 
                 SString fatalErrorString;
                 fatalErrorString.Printf(W("Verify_FieldOffset '%s.%s' %d!=%d || %d!=%d"), 
-                    GetFullyQualifiedNameForClassW(pField->GetEnclosingMethodTable()),
+                    GetFullyQualifiedNameForClassW(pEnclosingMT),
                     ssFieldName.GetUnicode(),
                     fieldOffset,
                     actualFieldOffset,
diff --git a/src/coreclr/src/vm/loaderallocator.cpp b/src/coreclr/src/vm/loaderallocator.cpp
index 0119f6510f46cb..4215b8c2e7c96b 100644
--- a/src/coreclr/src/vm/loaderallocator.cpp
+++ b/src/coreclr/src/vm/loaderallocator.cpp
@@ -662,6 +662,11 @@ BOOL QCALLTYPE LoaderAllocator::Destroy(QCall::LoaderAllocatorHandle pLoaderAllo
         STRESS_LOG1(LF_CLASSLOADER, LL_INFO100, "Begin LoaderAllocator::Destroy for loader allocator %p\n", reinterpret_cast<void *>(static_cast<PTR_LoaderAllocator>(pLoaderAllocator)));
         LoaderAllocatorID *pID = pLoaderAllocator->Id();
 
+        {
+            GCX_COOP();
+            LoaderAllocator::RemoveMemoryToLoaderAllocatorAssociation(pLoaderAllocator);
+        }
+
         // This will probably change for shared code unloading
         _ASSERTE(pID->GetType() == LAT_Assembly);
 
@@ -1008,7 +1013,7 @@ void LoaderAllocator::SetupManagedTracking(LOADERALLOCATORREF * pKeepLoaderAlloc
     // Initialize managed loader allocator reference holder
     //
 
-    MethodTable *pMT = MscorlibBinder::GetClass(CLASS__LOADERALLOCATOR);
+    MethodTable *pMT = CoreLibBinder::GetClass(CLASS__LOADERALLOCATOR);
 
     *pKeepLoaderAllocatorAlive = (LOADERALLOCATORREF)AllocateObject(pMT);
 
@@ -1984,6 +1989,44 @@ UMEntryThunkCache *LoaderAllocator::GetUMEntryThunkCache()
     return m_pUMEntryThunkCache;
 }
 
+/* static */
+void LoaderAllocator::RemoveMemoryToLoaderAllocatorAssociation(LoaderAllocator* pLoaderAllocator)
+{
+    CONTRACTL {
+        THROWS;
+        MODE_COOPERATIVE;
+    } CONTRACTL_END;
+
+    GlobalLoaderAllocator* pGlobalAllocator = (GlobalLoaderAllocator*)SystemDomain::GetGlobalLoaderAllocator();
+    pGlobalAllocator->m_memoryAssociations.RemoveRanges(pLoaderAllocator);
+}
+
+/* static */
+void LoaderAllocator::AssociateMemoryWithLoaderAllocator(BYTE *start, const BYTE *end, LoaderAllocator* pLoaderAllocator)
+{
+    CONTRACTL {
+        THROWS;
+        MODE_COOPERATIVE;
+    } CONTRACTL_END;
+
+    GlobalLoaderAllocator* pGlobalAllocator = (GlobalLoaderAllocator*)SystemDomain::GetGlobalLoaderAllocator();
+    pGlobalAllocator->m_memoryAssociations.AddRange(start, end, pLoaderAllocator);
+}
+
+/* static */
+PTR_LoaderAllocator LoaderAllocator::GetAssociatedLoaderAllocator_Unsafe(TADDR ptr)
+{
+    LIMITED_METHOD_CONTRACT;
+
+    GlobalLoaderAllocator* pGlobalAllocator = (GlobalLoaderAllocator*)SystemDomain::GetGlobalLoaderAllocator();
+    LoaderAllocator* pLoaderAllocator;
+    if (pGlobalAllocator->m_memoryAssociations.IsInRangeWorker_Unlocked(ptr, reinterpret_cast<TADDR *>(&pLoaderAllocator)))
+    {
+        return pLoaderAllocator;
+    }
+    return NULL;
+}
+
 #endif // !CROSSGEN_COMPILE
 
 #ifdef FEATURE_COMINTEROP
diff --git a/src/coreclr/src/vm/loaderallocator.hpp b/src/coreclr/src/vm/loaderallocator.hpp
index 70b7cd839ceab4..6028496573988c 100644
--- a/src/coreclr/src/vm/loaderallocator.hpp
+++ b/src/coreclr/src/vm/loaderallocator.hpp
@@ -23,6 +23,7 @@ class FuncPtrStubs;
 #include "methoddescbackpatchinfo.h"
 #include "crossloaderallocatorhash.h"
 #include "onstackreplacement.h"
+#include "lockedrangelist.h"
 
 #define VPTRU_LoaderAllocator 0x3200
 
@@ -405,6 +406,13 @@ class LoaderAllocator
     virtual LoaderAllocatorID* Id() =0;
     BOOL IsCollectible() { WRAPPER_NO_CONTRACT; return m_IsCollectible; }
 
+    // This function may only be called while the runtime is suspended
+    // As it does not lock around access to a RangeList
+    static PTR_LoaderAllocator GetAssociatedLoaderAllocator_Unsafe(TADDR ptr);
+
+    static void AssociateMemoryWithLoaderAllocator(BYTE *start, const BYTE *end, LoaderAllocator* pLoaderAllocator);
+    static void RemoveMemoryToLoaderAllocatorAssociation(LoaderAllocator* pLoaderAllocator);
+
 #ifdef DACCESS_COMPILE
     void EnumMemoryRegions(CLRDataEnumMemoryFlags flags);
 #endif
@@ -627,12 +635,16 @@ typedef VPTR(LoaderAllocator) PTR_LoaderAllocator;
 
 class GlobalLoaderAllocator : public LoaderAllocator
 {
+    friend class LoaderAllocator;
     VPTR_VTABLE_CLASS(GlobalLoaderAllocator, LoaderAllocator)
     VPTR_UNIQUE(VPTRU_LoaderAllocator+1)
 
     DAC_ALIGNAS(LoaderAllocator) // Align the first member to the alignment of the base class
     BYTE                m_ExecutableHeapInstance[sizeof(LoaderHeap)];
 
+    // Associate memory regions with loader allocator objects
+    LockedRangeList     m_memoryAssociations;
+
 protected:
     LoaderAllocatorID m_Id;
 
@@ -712,7 +724,6 @@ class AssemblyLoaderAllocator : public LoaderAllocator
 
 typedef VPTR(AssemblyLoaderAllocator) PTR_AssemblyLoaderAllocator;
 
-
 #include "loaderallocator.inl"
 
 #endif //  __LoaderAllocator_h__
diff --git a/src/coreclr/src/vm/lockedrangelist.h b/src/coreclr/src/vm/lockedrangelist.h
new file mode 100644
index 00000000000000..9289b58cdd2176
--- /dev/null
+++ b/src/coreclr/src/vm/lockedrangelist.h
@@ -0,0 +1,61 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#ifndef __LockedRangeList_h__
+#define __LockedRangeList_h__
+
+// -------------------------------------------------------
+// This just wraps the RangeList methods in a read or
+// write lock depending on the operation.
+// -------------------------------------------------------
+
+class LockedRangeList : public RangeList
+{
+  public:
+    VPTR_VTABLE_CLASS(LockedRangeList, RangeList)
+
+    LockedRangeList() : RangeList(), m_RangeListRWLock(COOPERATIVE_OR_PREEMPTIVE, LOCK_TYPE_DEFAULT)
+    {
+        LIMITED_METHOD_CONTRACT;
+    }
+
+    ~LockedRangeList()
+    {
+        LIMITED_METHOD_CONTRACT;
+    }
+
+    BOOL IsInRangeWorker_Unlocked(TADDR address, TADDR *pID = NULL)
+    {
+        WRAPPER_NO_CONTRACT;
+        SUPPORTS_DAC;
+        return RangeList::IsInRangeWorker(address, pID);
+    }
+
+  protected:
+
+    virtual BOOL AddRangeWorker(const BYTE *start, const BYTE *end, void *id)
+    {
+        WRAPPER_NO_CONTRACT;
+        SimpleWriteLockHolder lh(&m_RangeListRWLock);
+        return RangeList::AddRangeWorker(start,end,id);
+    }
+
+    virtual void RemoveRangesWorker(void *id, const BYTE *start = NULL, const BYTE *end = NULL)
+    {
+        WRAPPER_NO_CONTRACT;
+        SimpleWriteLockHolder lh(&m_RangeListRWLock);
+        RangeList::RemoveRangesWorker(id,start,end);
+    }
+
+    virtual BOOL IsInRangeWorker(TADDR address, TADDR *pID = NULL)
+    {
+        WRAPPER_NO_CONTRACT;
+        SUPPORTS_DAC;
+        SimpleReadLockHolder lh(&m_RangeListRWLock);
+        return RangeList::IsInRangeWorker(address, pID);
+    }
+
+    SimpleRWLock m_RangeListRWLock;
+};
+
+#endif // __LockedRangeList_h__
\ No newline at end of file
diff --git a/src/coreclr/src/vm/managedmdimport.cpp b/src/coreclr/src/vm/managedmdimport.cpp
index 973fa8ad44f6cc..6bea537f1c8e1e 100644
--- a/src/coreclr/src/vm/managedmdimport.cpp
+++ b/src/coreclr/src/vm/managedmdimport.cpp
@@ -1,9 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-// TODO: Re-implement with MC++ if we ever compile any mscorlib code with that
-
-
 
 #include "common.h"
 #include "mlinfo.h"
diff --git a/src/coreclr/src/vm/marshalnative.cpp b/src/coreclr/src/vm/marshalnative.cpp
index e4f95bb77394d4..46a7742ff7ce74 100644
--- a/src/coreclr/src/vm/marshalnative.cpp
+++ b/src/coreclr/src/vm/marshalnative.cpp
@@ -1226,83 +1226,6 @@ FCIMPL1(FC_BOOL_RET, MarshalNative::IsTypeVisibleFromCom, ReflectClassBaseObject
 }
 FCIMPLEND
 
-
-//====================================================================
-// IUnknown Helpers
-//====================================================================
-// IUnknown::QueryInterface
-FCIMPL3(HRESULT, MarshalNative::QueryInterface, IUnknown* pUnk, REFGUID iid, void** ppv)
-{
-    CONTRACTL
-    {
-        FCALL_CHECK;
-        PRECONDITION(CheckPointer(pUnk, NULL_OK));
-        PRECONDITION(CheckPointer(ppv));
-    }
-    CONTRACTL_END;
-
-    HRESULT hr = S_OK;
-    HELPER_METHOD_FRAME_BEGIN_RET_0();
-
-    if (!pUnk)
-        COMPlusThrowArgumentNull(W("pUnk"));
-
-    hr = SafeQueryInterface(pUnk,iid,(IUnknown**)ppv);
-    LogInteropQI(pUnk, iid, hr, "PInvoke::QI");
-
-    HELPER_METHOD_FRAME_END();
-    return hr;
-}
-FCIMPLEND
-
-// IUnknown::AddRef
-FCIMPL1(ULONG, MarshalNative::AddRef, IUnknown* pUnk)
-{
-    CONTRACTL
-    {
-        FCALL_CHECK;
-        PRECONDITION(CheckPointer(pUnk, NULL_OK));
-    }
-    CONTRACTL_END;
-
-    ULONG cbRef = 0;
-    HELPER_METHOD_FRAME_BEGIN_RET_0();
-
-    if (!pUnk)
-        COMPlusThrowArgumentNull(W("pUnk"));
-
-    cbRef = SafeAddRef(pUnk);
-    LogInteropAddRef(pUnk, cbRef, "PInvoke.AddRef");
-
-    HELPER_METHOD_FRAME_END();
-    return cbRef;
-}
-FCIMPLEND
-
-//IUnknown::Release
-FCIMPL1(ULONG, MarshalNative::Release, IUnknown* pUnk)
-{
-    CONTRACTL
-    {
-        FCALL_CHECK;
-        PRECONDITION(CheckPointer(pUnk, NULL_OK));
-    }
-    CONTRACTL_END;
-
-    ULONG cbRef = 0;
-    HELPER_METHOD_FRAME_BEGIN_RET_0();
-
-    if (!pUnk)
-        COMPlusThrowArgumentNull(W("pUnk"));
-
-    cbRef = SafeRelease(pUnk);
-    LogInteropRelease(pUnk, cbRef, "PInvoke.Release");
-
-    HELPER_METHOD_FRAME_END();
-    return cbRef;
-}
-FCIMPLEND
-
 FCIMPL2(void, MarshalNative::GetNativeVariantForObject, Object* ObjUNSAFE, LPVOID pDestNativeVariant)
 {
     CONTRACTL
diff --git a/src/coreclr/src/vm/marshalnative.h b/src/coreclr/src/vm/marshalnative.h
index 574d40c9d2c50e..5218e12c6fabb0 100644
--- a/src/coreclr/src/vm/marshalnative.h
+++ b/src/coreclr/src/vm/marshalnative.h
@@ -151,13 +151,6 @@ class MarshalNative
     //====================================================================
     static FCDECL1(FC_BOOL_RET, IsTypeVisibleFromCom, ReflectClassBaseObject* refClassUNSAFE);
 
-    //====================================================================
-    // IUnknown Helpers
-    //====================================================================
-    static FCDECL3(HRESULT, QueryInterface, IUnknown* pUnk, REFGUID iid, void** ppv);
-    static FCDECL1(ULONG, AddRef, IUnknown* pUnk);
-    static FCDECL1(ULONG, Release, IUnknown* pUnk);
-
     //====================================================================
     // These methods convert OLE variants to and from objects.
     //====================================================================
diff --git a/src/coreclr/src/vm/memberload.cpp b/src/coreclr/src/vm/memberload.cpp
index 8df00c959c3472..eec23198c21c14 100644
--- a/src/coreclr/src/vm/memberload.cpp
+++ b/src/coreclr/src/vm/memberload.cpp
@@ -1198,9 +1198,9 @@ MemberLoader::FindMethod(MethodTable * pMT, LPCUTF8 pwzName, LPHARDCODEDMETASIG
         MODE_ANY;
     } CONTRACTL_END;
 
-    Signature sig = MscorlibBinder::GetSignature(pwzSignature);
+    Signature sig = CoreLibBinder::GetSignature(pwzSignature);
 
-    return FindMethod(pMT, pwzName, sig.GetRawSig(), sig.GetRawSigLen(), MscorlibBinder::GetModule(), flags);
+    return FindMethod(pMT, pwzName, sig.GetRawSig(), sig.GetRawSigLen(), CoreLibBinder::GetModule(), flags);
 }
 
 //*******************************************************************************
@@ -1389,9 +1389,9 @@ MemberLoader::FindConstructor(MethodTable * pMT, LPHARDCODEDMETASIG pwzSignature
     }
     CONTRACTL_END
 
-    Signature sig = MscorlibBinder::GetSignature(pwzSignature);
+    Signature sig = CoreLibBinder::GetSignature(pwzSignature);
 
-    return FindConstructor(pMT, sig.GetRawSig(), sig.GetRawSigLen(), MscorlibBinder::GetModule());
+    return FindConstructor(pMT, sig.GetRawSig(), sig.GetRawSigLen(), CoreLibBinder::GetModule());
 }
 
 //*******************************************************************************
diff --git a/src/coreclr/src/vm/method.cpp b/src/coreclr/src/vm/method.cpp
index 9c247d6284a09c..ed6f44e7426ce5 100644
--- a/src/coreclr/src/vm/method.cpp
+++ b/src/coreclr/src/vm/method.cpp
@@ -83,7 +83,7 @@ static_assert_no_msg((sizeof(DynamicMethodDesc)     & MethodDesc::ALIGNMENT_MASK
     adjustment + sizeof(ComPlusCallMethodDesc),      /* mcComInterOp    */  \
     adjustment + sizeof(DynamicMethodDesc)           /* mcDynamic       */
 
-const SIZE_T MethodDesc::s_ClassificationSizeTable[] = {
+const BYTE MethodDesc::s_ClassificationSizeTable[] = {
     // This is the raw
     METHOD_DESC_SIZES(0),
 
@@ -91,7 +91,24 @@ const SIZE_T MethodDesc::s_ClassificationSizeTable[] = {
     // We index using optional slot flags into it
     METHOD_DESC_SIZES(sizeof(NonVtableSlot)),
     METHOD_DESC_SIZES(sizeof(MethodImpl)),
-    METHOD_DESC_SIZES(sizeof(NonVtableSlot) + sizeof(MethodImpl))
+    METHOD_DESC_SIZES(sizeof(NonVtableSlot) + sizeof(MethodImpl)),
+
+    METHOD_DESC_SIZES(sizeof(NativeCodeSlot)),
+    METHOD_DESC_SIZES(sizeof(NonVtableSlot) + sizeof(NativeCodeSlot)),
+    METHOD_DESC_SIZES(sizeof(MethodImpl) + sizeof(NativeCodeSlot)),
+    METHOD_DESC_SIZES(sizeof(NonVtableSlot) + sizeof(MethodImpl) + sizeof(NativeCodeSlot)),
+
+#ifdef FEATURE_COMINTEROP
+    METHOD_DESC_SIZES(sizeof(ComPlusCallInfo)),
+    METHOD_DESC_SIZES(sizeof(NonVtableSlot) + sizeof(ComPlusCallInfo)),
+    METHOD_DESC_SIZES(sizeof(MethodImpl) + sizeof(ComPlusCallInfo)),
+    METHOD_DESC_SIZES(sizeof(NonVtableSlot) + sizeof(MethodImpl) + sizeof(ComPlusCallInfo)),
+
+    METHOD_DESC_SIZES(sizeof(NativeCodeSlot) + sizeof(ComPlusCallInfo)),
+    METHOD_DESC_SIZES(sizeof(NonVtableSlot) + sizeof(NativeCodeSlot) + sizeof(ComPlusCallInfo)),
+    METHOD_DESC_SIZES(sizeof(MethodImpl) + sizeof(NativeCodeSlot) + sizeof(ComPlusCallInfo)),
+    METHOD_DESC_SIZES(sizeof(NonVtableSlot) + sizeof(MethodImpl) + sizeof(NativeCodeSlot) + sizeof(ComPlusCallInfo))
+#endif
 };
 
 #ifndef FEATURE_COMINTEROP
@@ -122,18 +139,22 @@ SIZE_T MethodDesc::SizeOf()
 {
     LIMITED_METHOD_DAC_CONTRACT;
 
-    SIZE_T size = s_ClassificationSizeTable[m_wFlags & (mdcClassification | mdcHasNonVtableSlot | mdcMethodImpl)];
+    SIZE_T size = s_ClassificationSizeTable[m_wFlags & 
+        (mdcClassification 
+        | mdcHasNonVtableSlot 
+        | mdcMethodImpl 
+#ifdef FEATURE_COMINTEROP
+        | mdcHasComPlusCallInfo
+#endif
+        | mdcHasNativeCodeSlot)];
 
+#ifdef FEATURE_PREJIT
     if (HasNativeCodeSlot())
     {
-        size += (*dac_cast<PTR_TADDR>(dac_cast<TADDR>(this) + size) & FIXUP_LIST_MASK) ?
-            (sizeof(NativeCodeSlot) + sizeof(FixupListSlot)) : sizeof(NativeCodeSlot);
+        size += (*dac_cast<PTR_TADDR>(GetAddrOfNativeCodeSlot()) & FIXUP_LIST_MASK) ? 
+            sizeof(FixupListSlot) : 0;
     }
-
-#ifdef FEATURE_COMINTEROP
-    if (IsGenericComPlusCall())
-        size += sizeof(ComPlusCallInfo);
-#endif // FEATURE_COMINTEROP
+#endif
 
     return size;
 }
@@ -2643,11 +2664,12 @@ void MethodDesc::Save(DataImage *image)
 
     if (GetMethodDictionary())
     {
-        DWORD cBytes = DictionaryLayout::GetDictionarySizeFromLayout(GetNumGenericMethodArgs(), GetDictionaryLayout());
+        DWORD cSlotBytes;
+        DWORD cAllocBytes = DictionaryLayout::GetDictionarySizeFromLayout(GetNumGenericMethodArgs(), GetDictionaryLayout(), &cSlotBytes);
         void* pBytes = GetMethodDictionary()->AsPtr();
 
-        LOG((LF_ZAP, LL_INFO10000, "    MethodDesc::Save dictionary size %d\n", cBytes));
-        image->StoreStructure(pBytes, cBytes,
+        LOG((LF_ZAP, LL_INFO10000, "    MethodDesc::Save dictionary size %d\n", cSlotBytes));
+        image->StoreStructure(pBytes, cSlotBytes,
                             DataImage::ITEM_DICTIONARY_WRITEABLE);
     }
 
@@ -3696,11 +3718,11 @@ void MethodDesc::SaveChunk::SaveOneChunk(COUNT_T start, COUNT_T count, ULONG siz
 
         if (pMethodInfo->m_fHasNativeCodeSlot)
         {
-            pNewMD->m_bFlags2 |= enum_flag2_HasNativeCodeSlot;
+            pNewMD->m_wFlags |= mdcHasNativeCodeSlot;
         }
         else
         {
-            pNewMD->m_bFlags2 &= ~enum_flag2_HasNativeCodeSlot;
+            pNewMD->m_wFlags &= ~mdcHasNativeCodeSlot;
         }
 
 #ifdef FEATURE_COMINTEROP
@@ -4882,8 +4904,10 @@ void MethodDesc::RecordAndBackpatchEntryPointSlot(
 {
     WRAPPER_NO_CONTRACT;
 
+    GCX_PREEMP();
+
     LoaderAllocator *mdLoaderAllocator = GetLoaderAllocator();
-    MethodDescBackpatchInfoTracker::ConditionalLockHolder slotBackpatchLockHolder;
+    MethodDescBackpatchInfoTracker::ConditionalLockHolderForGCCoop slotBackpatchLockHolder;
 
     RecordAndBackpatchEntryPointSlot_Locked(
         mdLoaderAllocator,
@@ -5729,7 +5753,7 @@ REFLECTMETHODREF MethodDesc::GetStubMethodInfo()
     CONTRACTL_END;
 
     REFLECTMETHODREF retVal;
-    REFLECTMETHODREF methodRef = (REFLECTMETHODREF)AllocateObject(MscorlibBinder::GetClass(CLASS__STUBMETHODINFO));
+    REFLECTMETHODREF methodRef = (REFLECTMETHODREF)AllocateObject(CoreLibBinder::GetClass(CLASS__STUBMETHODINFO));
     GCPROTECT_BEGIN(methodRef);
 
     methodRef->SetMethod(this);
diff --git a/src/coreclr/src/vm/method.hpp b/src/coreclr/src/vm/method.hpp
index 4103ec6e07e120..2d7fdc6e20bcd0 100644
--- a/src/coreclr/src/vm/method.hpp
+++ b/src/coreclr/src/vm/method.hpp
@@ -139,11 +139,18 @@ enum MethodDescClassification
     // where the function explicitly implements IInterface.foo() instead of foo().
     mdcMethodImpl                       = 0x0010,
 
-    // Method is static
-    mdcStatic                           = 0x0020,
+    // Has slot for native code
+    mdcHasNativeCodeSlot                = 0x0020,
 
+#ifdef FEATURE_COMINTEROP
+    mdcHasComPlusCallInfo               = 0x0040,
+#else
     // unused                           = 0x0040,
-    // unused                           = 0x0080,
+#endif
+
+    // Method is static
+    mdcStatic                           = 0x0080,
+
     // unused                           = 0x0100,
     // unused                           = 0x0200,
 
@@ -1832,7 +1839,7 @@ class MethodDesc
         enum_flag2_HasPrecode                           = 0x02,   // Precode has been allocated for this method
 
         enum_flag2_IsUnboxingStub                       = 0x04,
-        enum_flag2_HasNativeCodeSlot                    = 0x08,   // Has slot for native code
+        // unused                                       = 0x08,
 
         enum_flag2_IsJitIntrinsic                       = 0x10,   // Jit may expand method as an intrinsic
 
@@ -1881,13 +1888,13 @@ class MethodDesc
     inline BOOL HasNativeCodeSlot()
     {
         LIMITED_METHOD_DAC_CONTRACT;
-        return (m_bFlags2 & enum_flag2_HasNativeCodeSlot) != 0;
+        return (m_wFlags & mdcHasNativeCodeSlot) != 0;
     }
 
     inline void SetHasNativeCodeSlot()
     {
         LIMITED_METHOD_CONTRACT;
-        m_bFlags2 |= enum_flag2_HasNativeCodeSlot;
+        m_wFlags |= mdcHasNativeCodeSlot;
     }
 
     inline BOOL IsJitIntrinsic()
@@ -1915,7 +1922,7 @@ class MethodDesc
         m_bFlags2 |= enum_flag2_RequiresCovariantReturnTypeChecking;
     }
 
-    static const SIZE_T s_ClassificationSizeTable[];
+    static const BYTE s_ClassificationSizeTable[];
 
     static SIZE_T GetBaseSize(DWORD classification)
     {
@@ -2504,7 +2511,7 @@ class StoredSigMethodDesc : public MethodDesc
 {
   public:
     // Put the sig RVA in here - this allows us to avoid
-    // touching the method desc table when mscorlib is prejitted.
+    // touching the method desc table when CoreLib is prejitted.
 
     RelativePointer<TADDR>           m_pSig;
     DWORD           m_cSig;
@@ -3064,7 +3071,7 @@ class NDirectMethodDesc : public MethodDesc
         return (ndirect.m_wFlags & kThisCall) != 0;
     }
 
-    // Returns TRUE if this MethodDesc is internal call from mscorlib to mscorwks
+    // Returns TRUE if this MethodDesc is internal call from CoreLib to VM
     BOOL IsQCall() const
     {
         LIMITED_METHOD_DAC_CONTRACT;
@@ -3537,18 +3544,10 @@ class InstantiatedMethodDesc : public MethodDesc
     }
 
 #ifdef FEATURE_COMINTEROP
-    BOOL IMD_HasComPlusCallInfo()
-    {
-        LIMITED_METHOD_CONTRACT;
-        return ((m_wFlags2 & HasComPlusCallInfo) != 0);
-    }
-
     void IMD_SetupGenericComPlusCall()
     {
         LIMITED_METHOD_CONTRACT;
 
-        m_wFlags2 |= InstantiatedMethodDesc::HasComPlusCallInfo;
-
         IMD_GetComPlusCallInfo()->InitStackArgumentSize();
     }
 
@@ -3556,14 +3555,16 @@ class InstantiatedMethodDesc : public MethodDesc
     {
         LIMITED_METHOD_CONTRACT;
 
-        _ASSERTE(IMD_HasComPlusCallInfo());
-        SIZE_T size = s_ClassificationSizeTable[m_wFlags & (mdcClassification | mdcHasNonVtableSlot | mdcMethodImpl)];
+        _ASSERTE(IsGenericComPlusCall());
+        SIZE_T size = s_ClassificationSizeTable[m_wFlags & (mdcClassification | mdcHasNonVtableSlot | mdcMethodImpl | mdcHasNativeCodeSlot)];
 
+#ifdef FEATURE_PREJIT
         if (HasNativeCodeSlot())
         {
-            size += (*dac_cast<PTR_TADDR>(dac_cast<TADDR>(this) + size) & FIXUP_LIST_MASK) ?
-                (sizeof(NativeCodeSlot) + sizeof(FixupListSlot)) : sizeof(NativeCodeSlot);
+            size += (*dac_cast<PTR_TADDR>(GetAddrOfNativeCodeSlot()) & FIXUP_LIST_MASK) ? 
+                sizeof(FixupListSlot) : 0;
         }
+#endif
 
         return dac_cast<PTR_ComPlusCallInfo>(dac_cast<TADDR>(this) + size);
     }
diff --git a/src/coreclr/src/vm/method.inl b/src/coreclr/src/vm/method.inl
index d0d944d10e37c6..1175d2bd3aeb73 100644
--- a/src/coreclr/src/vm/method.inl
+++ b/src/coreclr/src/vm/method.inl
@@ -133,11 +133,14 @@ inline BOOL MethodDesc::IsQCall()
 FORCEINLINE DWORD MethodDesc::IsGenericComPlusCall()
 {
     LIMITED_METHOD_CONTRACT;
-    return (mcInstantiated == GetClassification() && AsInstantiatedMethodDesc()->IMD_HasComPlusCallInfo());
+    return m_wFlags & mdcHasComPlusCallInfo;
 }
+
 inline void MethodDesc::SetupGenericComPlusCall()
 {
     LIMITED_METHOD_CONTRACT;
+    m_wFlags |= mdcHasComPlusCallInfo;
+
     AsInstantiatedMethodDesc()->IMD_SetupGenericComPlusCall();
 }
 #endif // FEATURE_COMINTEROP
diff --git a/src/coreclr/src/vm/methoddescbackpatchinfo.cpp b/src/coreclr/src/vm/methoddescbackpatchinfo.cpp
index f6ea27e1fd9f88..efe1d04cf6f82c 100644
--- a/src/coreclr/src/vm/methoddescbackpatchinfo.cpp
+++ b/src/coreclr/src/vm/methoddescbackpatchinfo.cpp
@@ -65,7 +65,6 @@ void EntryPointSlots::Backpatch_Locked(TADDR slot, SlotType slotType, PCODE entr
 // MethodDescBackpatchInfoTracker
 
 CrstStatic MethodDescBackpatchInfoTracker::s_lock;
-bool MethodDescBackpatchInfoTracker::s_isLocked = false;
 
 #ifndef DACCESS_COMPILE
 
@@ -123,30 +122,4 @@ bool MethodDescBackpatchInfoTracker::IsLockOwnedByCurrentThread()
 }
 #endif // _DEBUG
 
-#ifndef DACCESS_COMPILE
-void MethodDescBackpatchInfoTracker::PollForDebuggerSuspension()
-{
-    CONTRACTL
-    {
-        NOTHROW;
-        GC_TRIGGERS;
-        MODE_PREEMPTIVE;
-    }
-    CONTRACTL_END;
-
-    _ASSERTE(!IsLockOwnedByCurrentThread());
-
-    // If suspension is pending for the debugger, pulse the GC mode to suspend the thread here. Following this call, typically
-    // the lock is acquired and the GC mode is changed, and suspending there would cause FuncEvals to fail (see
-    // Debugger::FuncEvalSetup() at the reference to IsLockOwnedByAnyThread()). Since this thread is in preemptive mode, the
-    // debugger may think it's already suspended and it would be unfortunate to suspend the thread with the lock held.
-    Thread *thread = GetThread();
-    _ASSERTE(thread != nullptr);
-    if (thread->HasThreadState(Thread::TS_DebugSuspendPending))
-    {
-        GCX_COOP();
-    }
-}
-#endif
-
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/src/coreclr/src/vm/methoddescbackpatchinfo.h b/src/coreclr/src/vm/methoddescbackpatchinfo.h
index a4d7a8c64fd6d4..2fc5e6c8e8f1c3 100644
--- a/src/coreclr/src/vm/methoddescbackpatchinfo.h
+++ b/src/coreclr/src/vm/methoddescbackpatchinfo.h
@@ -65,7 +65,6 @@ class MethodDescBackpatchInfoTracker
 {
 private:
     static CrstStatic s_lock;
-    static bool s_isLocked;
 
     class BackpatchInfoTrackerHashTraits : public NoRemoveDefaultCrossLoaderAllocatorHashTraits<MethodDesc *, UINT_PTR>
     {
@@ -97,63 +96,55 @@ class MethodDescBackpatchInfoTracker
     static bool IsLockOwnedByCurrentThread();
 #endif
 
-#ifndef DACCESS_COMPILE
 public:
-    static bool IsLockOwnedByAnyThread()
+    // To be used when the thread will remain in preemptive GC mode while holding the lock
+    class ConditionalLockHolderForGCPreemp : private CrstHolderWithState
     {
-        LIMITED_METHOD_CONTRACT;
-        return VolatileLoadWithoutBarrier(&s_isLocked);
-    }
-
-    static void PollForDebuggerSuspension();
-#endif
-
-public:
-    class ConditionalLockHolder : private CrstHolderWithState
-    {
-    private:
-        bool m_isLocked;
-
     public:
-        ConditionalLockHolder(bool acquireLock = true)
+        ConditionalLockHolderForGCPreemp(bool acquireLock = true)
             : CrstHolderWithState(
 #ifndef DACCESS_COMPILE
                 acquireLock ? &s_lock : nullptr
 #else
                 nullptr
 #endif
-                ),
-            m_isLocked(false)
+                )
         {
-            WRAPPER_NO_CONTRACT;
-
-        #ifndef DACCESS_COMPILE
-            if (acquireLock)
+            CONTRACTL
             {
-                _ASSERTE(IsLockOwnedByCurrentThread());
-                _ASSERTE(!s_isLocked);
-                m_isLocked = true;
-                s_isLocked = true;
+                NOTHROW;
+                GC_NOTRIGGER;
+                MODE_PREEMPTIVE;
             }
-        #endif
+            CONTRACTL_END;
         }
 
-        ~ConditionalLockHolder()
-        {
-            WRAPPER_NO_CONTRACT;
+        DISABLE_COPY(ConditionalLockHolderForGCPreemp);
+    };
 
-        #ifndef DACCESS_COMPILE
-            if (m_isLocked)
+#ifndef DACCESS_COMPILE
+public:
+    // To be used when the thread may enter cooperative GC mode while holding the lock. The thread enters a
+    // forbid-suspend-for-debugger region along with acquiring the lock, such that it would not suspend for the debugger while
+    // holding the lock, as that may otherwise cause a FuncEval to deadlock when trying to acquire the lock.
+    class ConditionalLockHolderForGCCoop : private CrstAndForbidSuspendForDebuggerHolder
+    {
+    public:
+        ConditionalLockHolderForGCCoop(bool acquireLock = true)
+            : CrstAndForbidSuspendForDebuggerHolder(acquireLock ? &s_lock : nullptr)
+        {
+            CONTRACTL
             {
-                _ASSERTE(IsLockOwnedByCurrentThread());
-                _ASSERTE(s_isLocked);
-                s_isLocked = false;
+                NOTHROW;
+                GC_NOTRIGGER;
+                MODE_PREEMPTIVE;
             }
-        #endif
+            CONTRACTL_END;
         }
 
-        DISABLE_COPY(ConditionalLockHolder);
+        DISABLE_COPY(ConditionalLockHolderForGCCoop);
     };
+#endif
 
 public:
     MethodDescBackpatchInfoTracker()
diff --git a/src/coreclr/src/vm/methodtable.cpp b/src/coreclr/src/vm/methodtable.cpp
index dee047519ee997..437162fa98f720 100644
--- a/src/coreclr/src/vm/methodtable.cpp
+++ b/src/coreclr/src/vm/methodtable.cpp
@@ -1375,6 +1375,14 @@ BOOL MethodTable::IsEquivalentTo_Worker(MethodTable *pOtherMT COMMA_INDEBUG(Type
         if (!pOtherMT->IsArray() || GetRank() != pOtherMT->GetRank())
             return FALSE;
 
+        if (IsMultiDimArray() != pOtherMT->IsMultiDimArray())
+        {
+            // A non-multidimensional array is not equivalent to an SzArray.
+            // This case is handling the case of a Rank 1 multidimensional array
+            // when compared to a normal array.
+            return FALSE;
+        }
+
         // arrays of structures have their own unshared MTs and will take this path
         return (GetArrayElementTypeHandle().IsEquivalentTo(pOtherMT->GetArrayElementTypeHandle() COMMA_INDEBUG(&newVisited)));
     }
@@ -3238,7 +3246,7 @@ void MethodTable::DoRunClassInitThrowing()
         // managed code to re-enter into this codepath, causing a locking order violation.
         pInitLock.Release();
 
-        if (MscorlibBinder::GetException(kTypeInitializationException) != gc.pInitException->GetMethodTable())
+        if (CoreLibBinder::GetException(kTypeInitializationException) != gc.pInitException->GetMethodTable())
         {
             DefineFullyQualifiedNameForClassWOnStack();
             LPCWSTR wszName = GetFullyQualifiedNameForClassW(this);
@@ -3342,7 +3350,7 @@ void MethodTable::DoRunClassInitThrowing()
                                 GetLoaderAllocator()->RegisterFailedTypeInitForCleanup(pEntry);
                             }
 
-                            _ASSERTE(g_pThreadAbortExceptionClass == MscorlibBinder::GetException(kThreadAbortException));
+                            _ASSERTE(g_pThreadAbortExceptionClass == CoreLibBinder::GetException(kThreadAbortException));
 
                             if(gc.pInnerException->GetMethodTable() == g_pThreadAbortExceptionClass)
                             {
@@ -4101,14 +4109,15 @@ void MethodTable::Save(DataImage *image, DWORD profilingFlags)
             fIsWriteable = FALSE;
         }
 
-
+        DWORD slotSize;
+        DWORD allocSize = GetInstAndDictSize(&slotSize);
         if (!fIsWriteable)
         {
-            image->StoreInternedStructure(pDictionary, GetInstAndDictSize(), DataImage::ITEM_DICTIONARY);
+            image->StoreInternedStructure(pDictionary, slotSize, DataImage::ITEM_DICTIONARY);
         }
         else
         {
-            image->StoreStructure(pDictionary, GetInstAndDictSize(), DataImage::ITEM_DICTIONARY_WRITEABLE);
+            image->StoreStructure(pDictionary, slotSize, DataImage::ITEM_DICTIONARY_WRITEABLE);
         }
     }
 
@@ -5956,7 +5965,7 @@ CorElementType MethodTable::GetInternalCorElementType()
         break;
 
     case enum_flag_Category_PrimitiveValueType:
-        // This path should only be taken for the builtin mscorlib types
+        // This path should only be taken for the builtin CoreLib types
         // and primitive valuetypes
         ret = GetClass()->GetInternalCorElementType();
         _ASSERTE((ret != ELEMENT_TYPE_CLASS) &&
@@ -8880,7 +8889,9 @@ MethodTable::EnumMemoryRegions(CLRDataEnumMemoryFlags flags)
 
     if (GetDictionary() != NULL)
     {
-        DacEnumMemoryRegion(dac_cast<TADDR>(GetDictionary()), GetInstAndDictSize());
+        DWORD slotSize;
+        DWORD allocSize = GetInstAndDictSize(&slotSize);
+        DacEnumMemoryRegion(dac_cast<TADDR>(GetDictionary()), slotSize);
     }
 
     VtableIndirectionSlotIterator it = IterateVtableIndirectionSlots();
diff --git a/src/coreclr/src/vm/methodtable.h b/src/coreclr/src/vm/methodtable.h
index 16f8d7dbc59329..6018c24f0d0108 100644
--- a/src/coreclr/src/vm/methodtable.h
+++ b/src/coreclr/src/vm/methodtable.h
@@ -3929,8 +3929,10 @@ public :
     inline DWORD GetInterfaceMapSize();
 
     // The instantiation/dictionary comes at the end of the MethodTable after
-    //  the interface map.
-    inline DWORD GetInstAndDictSize();
+    // the interface map. This is the total number of bytes used by the dictionary.
+    // The pSlotSize argument is used to return the size occupied by slots (not including
+    // the optional back pointer used when expanding dictionaries).
+    inline DWORD GetInstAndDictSize(DWORD *pSlotSize);
 
 private:
     // Helper template to compute the offsets at compile time
diff --git a/src/coreclr/src/vm/methodtable.inl b/src/coreclr/src/vm/methodtable.inl
index a20e1b4ca495ed..07b2c3c361ed14 100644
--- a/src/coreclr/src/vm/methodtable.inl
+++ b/src/coreclr/src/vm/methodtable.inl
@@ -1092,14 +1092,14 @@ inline DWORD MethodTable::GetInterfaceMapSize()
 //==========================================================================================
 // These are the generic dictionaries themselves and are come after
 //  the interface map.  In principle they need not be inline in the method table.
-inline DWORD MethodTable::GetInstAndDictSize()
+inline DWORD MethodTable::GetInstAndDictSize(DWORD *pSlotSize)
 {
     LIMITED_METHOD_DAC_CONTRACT;
 
     if (!HasInstantiation())
-        return 0;
+        return *pSlotSize = 0;
     else
-        return DictionaryLayout::GetDictionarySizeFromLayout(GetNumGenericArgs(), GetClass()->GetDictionaryLayout());
+        return DictionaryLayout::GetDictionarySizeFromLayout(GetNumGenericArgs(), GetClass()->GetDictionaryLayout(), pSlotSize);
 }
 
 //==========================================================================================
diff --git a/src/coreclr/src/vm/methodtablebuilder.cpp b/src/coreclr/src/vm/methodtablebuilder.cpp
index 21976325935c3f..666bb3bf252626 100644
--- a/src/coreclr/src/vm/methodtablebuilder.cpp
+++ b/src/coreclr/src/vm/methodtablebuilder.cpp
@@ -565,9 +565,9 @@ MethodTableBuilder::LoadApproxInterfaceMap()
             bmtGenerics->Debug_GetTypicalMethodTable()->Debug_HasInjectedInterfaceDuplicates();
 
         if (GetModule() == g_pObjectClass->GetModule())
-        {   // mscorlib has some weird hardcoded information about interfaces (e.g.
+        {   // CoreLib has some weird hardcoded information about interfaces (e.g.
             // code:CEEPreloader::ApplyTypeDependencyForSZArrayHelper), so we don't inject duplicates into
-            // mscorlib types
+            // CoreLib types
             bmtInterface->dbg_fShouldInjectInterfaceDuplicates = FALSE;
         }
     }
@@ -1350,7 +1350,7 @@ MethodTableBuilder::BuildMethodTableThrowing(
     ));
 #endif // _DEBUG
 
-    // If this is mscorlib, then don't perform some sanity checks on the layout
+    // If this is CoreLib, then don't perform some sanity checks on the layout
     bmtProp->fNoSanityChecks = pModule->IsSystem() ||
 #ifdef FEATURE_READYTORUN
         // No sanity checks for ready-to-run compiled images if possible
@@ -2410,6 +2410,7 @@ MethodTableBuilder::EnumerateMethodImpls()
 
                         compatibleSignatures = TRUE;
                         bmtMetaData->rgMethodImplTokens[i].fRequiresCovariantReturnTypeChecking = true;
+                        bmtMetaData->fHasCovariantOverride = true;
                     }
                 }
 
@@ -3003,7 +3004,7 @@ MethodTableBuilder::EnumerateClassMethods()
             }
             //@GENERICS:
             // Generic methods or methods in generic classes
-            // may not be part of a COM Import class, PInvoke, internal call outside mscorlib.
+            // may not be part of a COM Import class, PInvoke, internal call outside CoreLib.
             if ((bmtGenerics->GetNumGenericArgs() != 0 || numGenericMethodArgs != 0) &&
                 (
 #ifdef FEATURE_COMINTEROP
@@ -3025,8 +3026,9 @@ MethodTableBuilder::EnumerateClassMethods()
             }
 
             // Check the appearance of covariant and contravariant in the method signature
-            // Note that variance is only supported for interfaces
-            if (bmtGenerics->pVarianceInfo != NULL)
+            // Note that variance is only supported for interfaces, and these rules are not
+            // checked for static methods as they cannot be called variantly.
+            if ((bmtGenerics->pVarianceInfo != NULL) && !IsMdStatic(dwMemberAttrs))
             {
                 SigPointer sp(pMemberSignature, cMemberSignature);
                 ULONG callConv;
@@ -3513,7 +3515,7 @@ VOID    MethodTableBuilder::AllocateWorkingSlotTables()
         // This is broken because
         // (a) g_pObjectClass->FindMethod("Equals", &gsig_IM_Obj_RetBool); will return
         //      the EqualsValue method
-        // (b) When mscorlib has been preloaded (and thus the munge already done
+        // (b) When CoreLib has been preloaded (and thus the munge already done
         //      ahead of time), we cannot easily find both methods
         //      to compute EqualsAddr & EqualsSlot
         //
@@ -4870,15 +4872,15 @@ MethodTableBuilder::ValidateMethods()
 
     Signature sig;
 
-    sig = MscorlibBinder::GetSignature(&gsig_SM_RetVoid);
+    sig = CoreLibBinder::GetSignature(&gsig_SM_RetVoid);
 
-    MethodSignature cctorSig(MscorlibBinder::GetModule(),
+    MethodSignature cctorSig(CoreLibBinder::GetModule(),
                              COR_CCTOR_METHOD_NAME,
                              sig.GetRawSig(), sig.GetRawSigLen());
 
-    sig = MscorlibBinder::GetSignature(&gsig_IM_RetVoid);
+    sig = CoreLibBinder::GetSignature(&gsig_IM_RetVoid);
 
-    MethodSignature defaultCtorSig(MscorlibBinder::GetModule(),
+    MethodSignature defaultCtorSig(CoreLibBinder::GetModule(),
                                    COR_CTOR_METHOD_NAME,
                                    sig.GetRawSig(), sig.GetRawSigLen());
 
@@ -5589,6 +5591,19 @@ MethodTableBuilder::ProcessMethodImpls()
 {
     STANDARD_VM_CONTRACT;
 
+    if (bmtMetaData->fHasCovariantOverride)
+    {
+        GetHalfBakedClass()->SetHasCovariantOverride();
+    }
+    if (GetParentMethodTable() != NULL)
+    {
+        EEClass* parentClass = GetParentMethodTable()->GetClass();
+        if (parentClass->HasCovariantOverride())
+            GetHalfBakedClass()->SetHasCovariantOverride();
+        if (parentClass->HasVTableMethodImpl())
+            GetHalfBakedClass()->SetHasVTableMethodImpl();
+    }
+
     if (bmtMethod->dwNumberMethodImpls == 0)
         return;
 
@@ -5680,6 +5695,7 @@ MethodTableBuilder::ProcessMethodImpls()
                         }
 
                         Substitution *pDeclSubst = &bmtMetaData->pMethodDeclSubsts[m];
+                        
                         MethodTable * pDeclMT = NULL;
                         MethodSignature declSig(GetModule(), szName, pSig, cbSig, NULL);
 
@@ -5784,6 +5800,7 @@ MethodTableBuilder::ProcessMethodImpls()
                             }
                             else
                             {
+                                GetHalfBakedClass()->SetHasVTableMethodImpl();
                                 declMethod = FindDeclMethodOnClassInHierarchy(it, pDeclMT, declSig);
                             }
 
@@ -8747,8 +8764,10 @@ MethodTableBuilder::HandleGCForExplicitLayout()
         if (bmtParent->NumParentPointerSeries != 0)
         {
             size_t ParentGCSize = CGCDesc::ComputeSize(bmtParent->NumParentPointerSeries);
-            memcpy( (PVOID) (((BYTE*) pMT) - ParentGCSize),  (PVOID) (((BYTE*) GetParentMethodTable()) - ParentGCSize), ParentGCSize - sizeof(UINT) );
-
+            memcpy( (PVOID) (((BYTE*) pMT) - ParentGCSize),
+                    (PVOID) (((BYTE*) GetParentMethodTable()) - ParentGCSize),
+                    ParentGCSize - sizeof(size_t)   // sizeof(size_t) is the NumSeries count
+                  );
         }
 
         UINT32 dwInstanceSliceOffset = AlignUp(HasParent() ? GetParentMethodTable()->GetNumInstanceFieldBytes() : 0, TARGET_POINTER_SIZE);
@@ -8763,6 +8782,16 @@ MethodTableBuilder::HandleGCForExplicitLayout()
             pSeries->SetSeriesOffset(bmtGCSeries->pSeries[i].offset + OBJECT_SIZE + dwInstanceSliceOffset);
             pSeries++;
         }
+
+        // Adjust the inherited series - since the base size has increased by "# new field instance bytes", we need to
+        // subtract that from all the series (since the series always has BaseSize subtracted for it - see gcdesc.h)
+        CGCDescSeries *pHighest = CGCDesc::GetCGCDescFromMT(pMT)->GetHighestSeries();
+        while (pSeries <= pHighest)
+        {
+            CONSISTENCY_CHECK(CheckPointer(GetParentMethodTable()));
+            pSeries->SetSeriesSize( pSeries->GetSeriesSize() - ((size_t) pMT->GetBaseSize() - (size_t) GetParentMethodTable()->GetBaseSize()) );
+            pSeries++;
+        }
     }
 
     delete [] bmtGCSeries->pSeries;
@@ -10085,10 +10114,12 @@ MethodTableBuilder::SetupMethodTable2(
 
     EEClass *pClass = GetHalfBakedClass();
 
-    DWORD cbDict = bmtGenerics->HasInstantiation()
-                   ?  DictionaryLayout::GetDictionarySizeFromLayout(
-                          bmtGenerics->GetNumGenericArgs(), pClass->GetDictionaryLayout())
-                   : 0;
+    DWORD cbDictSlotSize = 0;
+    DWORD cbDictAllocSize = 0;
+    if (bmtGenerics->HasInstantiation())
+    {
+        cbDictAllocSize = DictionaryLayout::GetDictionarySizeFromLayout(bmtGenerics->GetNumGenericArgs(), pClass->GetDictionaryLayout(), &cbDictSlotSize);
+    }
 
 #ifdef FEATURE_COLLECTIBLE_TYPES
     BOOL fCollectible = pLoaderModule->IsCollectible();
@@ -10121,7 +10152,7 @@ MethodTableBuilder::SetupMethodTable2(
                                    dwGCSize,
                                    bmtInterface->dwInterfaceMapSize,
                                    bmtGenerics->numDicts,
-                                   cbDict,
+                                   cbDictAllocSize,
                                    GetParentMethodTable(),
                                    GetClassLoader(),
                                    bmtAllocator,
@@ -10341,7 +10372,7 @@ MethodTableBuilder::SetupMethodTable2(
 
             PTR_Dictionary pDictionarySlots = pMT->GetPerInstInfo()[bmtGenerics->numDicts - 1].GetValue();
             DWORD* pSizeSlot = (DWORD*)(pDictionarySlots + bmtGenerics->GetNumGenericArgs());
-            *pSizeSlot = cbDict;
+            *pSizeSlot = cbDictSlotSize;
         }
     }
 
@@ -10380,7 +10411,6 @@ MethodTableBuilder::SetupMethodTable2(
 
     if (GetModule()->IsSystem())
     {
-        // we are in mscorlib
         CheckForSystemTypes();
     }
 
@@ -11025,7 +11055,7 @@ VOID MethodTableBuilder::CheckForSpecialTypes()
     IMDInternalImport *pMDImport = pModule->GetMDImport();
 
     // Check to see if this type is a managed standard interface. All the managed
-    // standard interfaces live in mscorlib.dll so checking for that first
+    // standard interfaces live in CoreLib so checking for that first
     // makes the strcmp that comes afterwards acceptable.
     if (pModule->IsSystem())
     {
diff --git a/src/coreclr/src/vm/methodtablebuilder.h b/src/coreclr/src/vm/methodtablebuilder.h
index 34a040c4530c97..def6ab9d389e1a 100644
--- a/src/coreclr/src/vm/methodtablebuilder.h
+++ b/src/coreclr/src/vm/methodtablebuilder.h
@@ -2006,6 +2006,8 @@ class MethodTableBuilder
         MethodImplTokenPair *rgMethodImplTokens;
         Substitution *pMethodDeclSubsts;    // Used to interpret generic variables in the interface of the declaring type
 
+        bool fHasCovariantOverride;
+
         //-----------------------------------------------------------------------------------------
         inline bmtMetaDataInfo() { LIMITED_METHOD_CONTRACT; memset((void *)this, NULL, sizeof(*this)); }
     };  // struct bmtMetaDataInfo
@@ -2282,10 +2284,11 @@ class MethodTableBuilder
     class DeclaredMethodIterator
     {
       private:
-        MethodTableBuilder &m_mtb;
-        int                 m_idx; // not SLOT_INDEX?
+        const int            m_numDeclaredMethods;
+        bmtMDMethod ** const m_declaredMethods;
+        int                  m_idx; // not SLOT_INDEX?
 #ifdef _DEBUG
-        bmtMDMethod *       m_debug_pMethod;
+        bmtMDMethod *        m_debug_pMethod;
 #endif
 
       public:
diff --git a/src/coreclr/src/vm/methodtablebuilder.inl b/src/coreclr/src/vm/methodtablebuilder.inl
index 2d13e783fd5189..78424be5d14f6f 100644
--- a/src/coreclr/src/vm/methodtablebuilder.inl
+++ b/src/coreclr/src/vm/methodtablebuilder.inl
@@ -15,7 +15,10 @@
 
 //***************************************************************************************
 inline MethodTableBuilder::DeclaredMethodIterator::DeclaredMethodIterator(
-            MethodTableBuilder &mtb) : m_mtb(mtb), m_idx(-1)
+            MethodTableBuilder &mtb) : 
+                m_numDeclaredMethods((int)mtb.NumDeclaredMethods()),
+                m_declaredMethods(mtb.bmtMethod->m_rgDeclaredMethods),
+                m_idx(-1)
 {
     LIMITED_METHOD_CONTRACT;
 }
@@ -24,7 +27,7 @@ inline MethodTableBuilder::DeclaredMethodIterator::DeclaredMethodIterator(
 inline int MethodTableBuilder::DeclaredMethodIterator::CurrentIndex()
 {
     LIMITED_METHOD_CONTRACT;
-    CONSISTENCY_CHECK_MSG(0 <= m_idx && m_idx < (int)m_mtb.NumDeclaredMethods(),
+    CONSISTENCY_CHECK_MSG(0 <= m_idx && m_idx < m_numDeclaredMethods,
                           "Invalid iterator state.");
     return m_idx;
 }
@@ -33,7 +36,7 @@ inline int MethodTableBuilder::DeclaredMethodIterator::CurrentIndex()
 inline BOOL MethodTableBuilder::DeclaredMethodIterator::Next()
 {
     LIMITED_METHOD_CONTRACT;
-    if (m_idx + 1 >= (int)m_mtb.NumDeclaredMethods())
+    if (m_idx + 1 >= m_numDeclaredMethods)
         return FALSE;
     m_idx++;
     INDEBUG(m_debug_pMethod = GetMDMethod();)
@@ -55,7 +58,7 @@ inline BOOL MethodTableBuilder::DeclaredMethodIterator::Prev()
 inline void MethodTableBuilder::DeclaredMethodIterator::ResetToEnd()
 {
     LIMITED_METHOD_CONTRACT;
-    m_idx = (int)m_mtb.NumDeclaredMethods();
+    m_idx = m_numDeclaredMethods;
 }
 
 //***************************************************************************************
@@ -130,7 +133,7 @@ MethodTableBuilder::DeclaredMethodIterator::GetMDMethod() const
 {
     LIMITED_METHOD_CONTRACT;
     _ASSERTE(FitsIn<SLOT_INDEX>(m_idx)); // Review: m_idx should probably _be_ a SLOT_INDEX, but that asserts.
-    return (*m_mtb.bmtMethod)[static_cast<SLOT_INDEX>(m_idx)];
+    return m_declaredMethods[m_idx];
 }
 
 //*******************************************************************************
diff --git a/src/coreclr/src/vm/mlinfo.cpp b/src/coreclr/src/vm/mlinfo.cpp
index c4c479cb6d4206..36b07edcfce33c 100644
--- a/src/coreclr/src/vm/mlinfo.cpp
+++ b/src/coreclr/src/vm/mlinfo.cpp
@@ -1929,7 +1929,7 @@ MarshalInfo::MarshalInfo(Module* pModule,
                     }
                 }
 #endif // FEATURE_COMINTEROP
-                else if (sigTH.CanCastTo(TypeHandle(MscorlibBinder::GetClass(CLASS__SAFE_HANDLE))))
+                else if (sigTH.CanCastTo(TypeHandle(CoreLibBinder::GetClass(CLASS__SAFE_HANDLE))))
                 {
                     if (nativeType != NATIVE_TYPE_DEFAULT)
                     {
@@ -1939,7 +1939,7 @@ MarshalInfo::MarshalInfo(Module* pModule,
                     m_args.m_pMT = m_pMT;
                     m_type = MARSHAL_TYPE_SAFEHANDLE;
                 }
-                else if (sigTH.CanCastTo(TypeHandle(MscorlibBinder::GetClass(CLASS__CRITICAL_HANDLE))))
+                else if (sigTH.CanCastTo(TypeHandle(CoreLibBinder::GetClass(CLASS__CRITICAL_HANDLE))))
                 {
                     if (nativeType != NATIVE_TYPE_DEFAULT)
                     {
@@ -2304,14 +2304,14 @@ MarshalInfo::MarshalInfo(Module* pModule,
                     && (!m_pMT->IsBlittable()
                         || (m_pMT->HasSameTypeDefAs(g_pNullableClass)
                         || m_pMT->HasSameTypeDefAs(g_pByReferenceClass)
-                        || m_pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__SPAN))
-                        || m_pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__READONLY_SPAN))
-                        || m_pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__VECTOR64T))
-                        || m_pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__VECTOR128T))
-                        || m_pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__VECTOR256T))
+                        || m_pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__SPAN))
+                        || m_pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__READONLY_SPAN))
+                        || m_pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__VECTOR64T))
+                        || m_pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__VECTOR128T))
+                        || m_pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__VECTOR256T))
 #ifndef CROSSGEN_COMPILE
                             // Crossgen scenarios block Vector<T> from even being loaded
-                            || m_pMT->HasSameTypeDefAs(MscorlibBinder::GetClass(CLASS__VECTORT))
+                            || m_pMT->HasSameTypeDefAs(CoreLibBinder::GetClass(CLASS__VECTORT))
 #endif // !CROSSGEN_COMPILE
                     )))
                 {
@@ -4359,26 +4359,26 @@ void ArrayMarshalInfo::InitElementInfo(CorNativeType arrayNativeType, MarshalInf
             }
 #endif // FEATURE_COMINTEROP
         }
-        else if (m_thElement.CanCastTo(TypeHandle(MscorlibBinder::GetClass(CLASS__SAFE_HANDLE))))
+        else if (m_thElement.CanCastTo(TypeHandle(CoreLibBinder::GetClass(CLASS__SAFE_HANDLE))))
         {
             // Array's of SAFEHANDLEs are not supported.
             ReportInvalidArrayMarshalInfo(IDS_EE_BADMARSHAL_SAFEHANDLEARRAY);
         }
-        else if (m_thElement.CanCastTo(TypeHandle(MscorlibBinder::GetClass(CLASS__CRITICAL_HANDLE))))
+        else if (m_thElement.CanCastTo(TypeHandle(CoreLibBinder::GetClass(CLASS__CRITICAL_HANDLE))))
         {
             // Array's of CRITICALHANDLEs are not supported.
             ReportInvalidArrayMarshalInfo(IDS_EE_BADMARSHAL_CRITICALHANDLEARRAY);
         }
         else if (etElement == ELEMENT_TYPE_VALUETYPE)
         {
-            if (m_thElement == TypeHandle(MscorlibBinder::GetClass(CLASS__DATE_TIME)))
+            if (m_thElement == TypeHandle(CoreLibBinder::GetClass(CLASS__DATE_TIME)))
             {
                 if (ntElement == NATIVE_TYPE_STRUCT || ntElement == NATIVE_TYPE_DEFAULT)
                     m_vtElement = VT_DATE;
                 else
                     ReportInvalidArrayMarshalInfo(IDS_EE_BADMARSHAL_DATETIMEARRAY);
             }
-            else if (m_thElement == TypeHandle(MscorlibBinder::GetClass(CLASS__DECIMAL)))
+            else if (m_thElement == TypeHandle(CoreLibBinder::GetClass(CLASS__DECIMAL)))
             {
                 if (ntElement == NATIVE_TYPE_STRUCT || ntElement == NATIVE_TYPE_DEFAULT)
                     m_vtElement = VT_DECIMAL;
@@ -4395,7 +4395,7 @@ void ArrayMarshalInfo::InitElementInfo(CorNativeType arrayNativeType, MarshalInf
             }
         }
 #ifdef FEATURE_COMINTEROP
-        else if (m_thElement == TypeHandle(MscorlibBinder::GetClass(CLASS__ERROR_WRAPPER)))
+        else if (m_thElement == TypeHandle(CoreLibBinder::GetClass(CLASS__ERROR_WRAPPER)))
         {
             m_vtElement = VT_ERROR;
         }
diff --git a/src/coreclr/src/vm/nativeoverlapped.cpp b/src/coreclr/src/vm/nativeoverlapped.cpp
index 0657febc366dc7..46a8600d3ddfda 100644
--- a/src/coreclr/src/vm/nativeoverlapped.cpp
+++ b/src/coreclr/src/vm/nativeoverlapped.cpp
@@ -102,7 +102,7 @@ FCIMPL1(LPOVERLAPPED, AllocateNativeOverlapped, OverlappedDataObject* overlapped
 
     if (g_pOverlappedDataClass == NULL)
     {
-        g_pOverlappedDataClass = MscorlibBinder::GetClass(CLASS__OVERLAPPEDDATA);
+        g_pOverlappedDataClass = CoreLibBinder::GetClass(CLASS__OVERLAPPEDDATA);
         // We have optimization to avoid creating event if IO is in default domain.  This depends on default domain
         // can not be unloaded.
     }
diff --git a/src/coreclr/src/vm/object.cpp b/src/coreclr/src/vm/object.cpp
index 8966075d500553..55375739ae9b38 100644
--- a/src/coreclr/src/vm/object.cpp
+++ b/src/coreclr/src/vm/object.cpp
@@ -187,9 +187,7 @@ TypeHandle Object::GetGCSafeTypeHandleIfPossible() const
     //         MT of the innermost element is not getting unloaded. This then ensures the
     //         MT of the original object (i.e., array) itself must not be getting
     //         unloaded either, since the MTs of arrays and of their elements are
-    //         allocated on the same loader heap, except the case where the array is
-    //         Object[], in which case its MT is in mscorlib and thus doesn't unload.
-
+    //         allocated on the same loader allocator.
     Module * pLoaderModule = pMT->GetLoaderModule();
 
     // Don't look up types that are unloading due to Collectible Assemblies. Haven't been
@@ -1536,7 +1534,7 @@ void Nullable::CheckFieldOffsets(TypeHandle nullableType)
     MethodTable* nullableMT = nullableType.GetMethodTable();
 
         // insure that the managed version of the table is the same as the
-        // unmanaged.  Note that we can't do this in mscorlib.h because this
+        // unmanaged.  Note that we can't do this in corelib.h because this
         // class is generic and field layout depends on the instantiation.
 
     _ASSERTE(nullableMT->GetNumInstanceFields() == 2);
diff --git a/src/coreclr/src/vm/object.h b/src/coreclr/src/vm/object.h
index 5d6c3c3981eb3a..2acb6e334f5ae1 100644
--- a/src/coreclr/src/vm/object.h
+++ b/src/coreclr/src/vm/object.h
@@ -993,7 +993,7 @@ class BaseObjectWithCachedData : public Object
 //      this hasn't yet been defined.
 class ReflectClassBaseObject : public BaseObjectWithCachedData
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 protected:
     OBJECTREF           m_keepalive;
@@ -1123,7 +1123,7 @@ class Utf8StringObject : public Object
 // type that does not sufficiently match this data structure.
 class ReflectMethodObject : public BaseObjectWithCachedData
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 protected:
     OBJECTREF           m_object;
@@ -1166,7 +1166,7 @@ class ReflectMethodObject : public BaseObjectWithCachedData
 // type that does not sufficiently match this data structure.
 class ReflectFieldObject : public BaseObjectWithCachedData
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 protected:
     OBJECTREF           m_object;
@@ -1204,7 +1204,7 @@ class ReflectFieldObject : public BaseObjectWithCachedData
 //
 class ReflectModuleBaseObject : public Object
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
   protected:
     // READ ME:
@@ -1255,7 +1255,7 @@ typedef SafeHandle * SAFEHANDLEREF;
 class ThreadBaseObject;
 class SynchronizationContextObject: public Object
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 private:
     // These field are also defined in the managed representation.  (SecurityContext.cs)If you
     // add or change these field you must also change the managed code so that
@@ -1304,7 +1304,7 @@ __inline bool IsCultureEnglishOrInvariant(LPCWSTR localeName)
 
 class CultureInfoBaseObject : public Object
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 private:
     OBJECTREF _compareInfo;
@@ -1342,7 +1342,7 @@ class ThreadBaseObject : public Object
 {
     friend class ClrDataAccess;
     friend class ThreadNative;
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
     friend class Object;
 
 private:
@@ -1459,7 +1459,7 @@ class MarshalByRefObjectBaseObject : public Object
 class AssemblyBaseObject : public Object
 {
     friend class Assembly;
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
   protected:
     // READ ME:
@@ -1507,7 +1507,7 @@ NOINLINE AssemblyBaseObject* GetRuntimeAssemblyHelper(LPVOID __me, DomainAssembl
 #endif // defined(TARGET_X86) && !defined(TARGET_UNIX)
 class AssemblyLoadContextBaseObject : public Object
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
   protected:
     // READ ME:
@@ -1553,7 +1553,7 @@ class AssemblyNameBaseObject : public Object
 {
     friend class AssemblyNative;
     friend class AppDomainNative;
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
   protected:
     // READ ME:
@@ -1592,7 +1592,7 @@ class AssemblyNameBaseObject : public Object
 //
 class VersionBaseObject : public Object
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
   protected:
     // READ ME:
@@ -1720,7 +1720,7 @@ CHARARRAYREF AllocateCharArray(DWORD dwArrayLength);
 //-------------------------------------------------------------
 class ComObject : public MarshalByRefObjectBaseObject
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 protected:
 
@@ -1992,7 +1992,7 @@ typedef BStrWrapper*     BSTRWRAPPEROBJECTREF;
 
 class SafeHandle : public Object
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
   private:
     // READ ME:
@@ -2042,7 +2042,7 @@ typedef Holder<SAFEHANDLEREF*, AcquireSafeHandle, ReleaseSafeHandle> SafeHandleH
 
 class CriticalHandle : public Object
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
   private:
     // READ ME:
@@ -2072,7 +2072,7 @@ typedef CriticalHandle * CRITICALHANDLEREF;
 // Base class for WaitHandle
 class WaitHandleBase :public MarshalByRefObjectBaseObject
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 public:
     __inline LPVOID GetWaitHandle() {
@@ -2096,7 +2096,7 @@ typedef WaitHandleBase* WAITHANDLEREF;
 class DelegateObject : public Object
 {
     friend class CheckAsmOffsets;
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 public:
     BOOL IsWrapperDelegate() { LIMITED_METHOD_CONTRACT; return _methodPtrAux == NULL; }
@@ -2316,7 +2316,7 @@ class StackTraceArray
 
 class LoaderAllocatorScoutObject : public Object
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
     friend class LoaderAllocatorObject;
 
 protected:
@@ -2331,7 +2331,7 @@ typedef LoaderAllocatorScoutObject* LOADERALLOCATORSCOUTREF;
 
 class LoaderAllocatorObject : public Object
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 public:
     PTRARRAYREF GetHandleTable()
@@ -2393,7 +2393,7 @@ typedef DPTR(class ExceptionObject) PTR_ExceptionObject;
 #include "pshpack4.h"
 class ExceptionObject : public Object
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 public:
     void SetHResult(HRESULT hr)
@@ -2617,7 +2617,7 @@ enum ContractFailureKind
 typedef DPTR(class ContractExceptionObject) PTR_ContractExceptionObject;
 class ContractExceptionObject : public ExceptionObject
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 public:
     ContractFailureKind GetContractFailureKind()
@@ -2742,7 +2742,7 @@ class GCHeapHashObject : public Object
     friend class JIT_TrialAlloc;
     friend class CheckAsmOffsets;
     friend class COMString;
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
     private:
     BASEARRAYREF _data;
@@ -2799,7 +2799,7 @@ class LAHashDependentHashTrackerObject : public Object
     friend class ClrDataAccess;
 #endif
     friend class CheckAsmOffsets;
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
     private:
     OBJECTHANDLE _dependentHandle;
@@ -2837,7 +2837,7 @@ class LAHashKeyToTrackersObject : public Object
     friend class ClrDataAccess;
 #endif
     friend class CheckAsmOffsets;
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
     public:
     // _trackerOrTrackerSet is either a reference to a LAHashDependentHashTracker, or to a GCHeapHash of LAHashDependentHashTracker objects.
diff --git a/src/coreclr/src/vm/olevariant.cpp b/src/coreclr/src/vm/olevariant.cpp
index 1755add7d5e728..d4d256e01329ff 100644
--- a/src/coreclr/src/vm/olevariant.cpp
+++ b/src/coreclr/src/vm/olevariant.cpp
@@ -260,13 +260,13 @@ VARTYPE OleVariant::GetVarTypeForComVariant(VariantData *pComVariant)
 
 #ifdef FEATURE_COMINTEROP
         // SafeHandle's or CriticalHandle's cannot be stored in VARIANT's.
-        if (pMT->CanCastToClass(MscorlibBinder::GetClass(CLASS__SAFE_HANDLE)))
+        if (pMT->CanCastToClass(CoreLibBinder::GetClass(CLASS__SAFE_HANDLE)))
             COMPlusThrow(kArgumentException, IDS_EE_SH_IN_VARIANT_NOT_SUPPORTED);
-        if (pMT->CanCastToClass(MscorlibBinder::GetClass(CLASS__CRITICAL_HANDLE)))
+        if (pMT->CanCastToClass(CoreLibBinder::GetClass(CLASS__CRITICAL_HANDLE)))
             COMPlusThrow(kArgumentException, IDS_EE_CH_IN_VARIANT_NOT_SUPPORTED);
 
         // VariantWrappers cannot be stored in VARIANT's.
-        if (MscorlibBinder::IsClass(pMT, CLASS__VARIANT_WRAPPER))
+        if (CoreLibBinder::IsClass(pMT, CLASS__VARIANT_WRAPPER))
             COMPlusThrow(kArgumentException, IDS_EE_VAR_WRAP_IN_VAR_NOT_SUPPORTED);
 
         // We are dealing with a normal object (not a wrapper) so we will
@@ -311,37 +311,37 @@ VARTYPE OleVariant::GetVarTypeForTypeHandle(TypeHandle type)
         return VT_VARIANT;
 
     // We need to make sure the CVClasses table is populated.
-    if(MscorlibBinder::IsClass(pMT, CLASS__DATE_TIME))
+    if(CoreLibBinder::IsClass(pMT, CLASS__DATE_TIME))
         return VT_DATE;
-    if(MscorlibBinder::IsClass(pMT, CLASS__DECIMAL))
+    if(CoreLibBinder::IsClass(pMT, CLASS__DECIMAL))
         return VT_DECIMAL;
 
 #ifdef HOST_64BIT
-    if (MscorlibBinder::IsClass(pMT, CLASS__INTPTR))
+    if (CoreLibBinder::IsClass(pMT, CLASS__INTPTR))
         return VT_I8;
-    if (MscorlibBinder::IsClass(pMT, CLASS__UINTPTR))
+    if (CoreLibBinder::IsClass(pMT, CLASS__UINTPTR))
         return VT_UI8;
 #else
-    if (MscorlibBinder::IsClass(pMT, CLASS__INTPTR))
+    if (CoreLibBinder::IsClass(pMT, CLASS__INTPTR))
         return VT_INT;
-    if (MscorlibBinder::IsClass(pMT, CLASS__UINTPTR))
+    if (CoreLibBinder::IsClass(pMT, CLASS__UINTPTR))
         return VT_UINT;
 #endif
 
 #ifdef FEATURE_COMINTEROP
-    if (MscorlibBinder::IsClass(pMT, CLASS__DISPATCH_WRAPPER))
+    if (CoreLibBinder::IsClass(pMT, CLASS__DISPATCH_WRAPPER))
         return VT_DISPATCH;
-    if (MscorlibBinder::IsClass(pMT, CLASS__UNKNOWN_WRAPPER))
+    if (CoreLibBinder::IsClass(pMT, CLASS__UNKNOWN_WRAPPER))
         return VT_UNKNOWN;
-    if (MscorlibBinder::IsClass(pMT, CLASS__ERROR_WRAPPER))
+    if (CoreLibBinder::IsClass(pMT, CLASS__ERROR_WRAPPER))
         return VT_ERROR;
-    if (MscorlibBinder::IsClass(pMT, CLASS__CURRENCY_WRAPPER))
+    if (CoreLibBinder::IsClass(pMT, CLASS__CURRENCY_WRAPPER))
         return VT_CY;
-    if (MscorlibBinder::IsClass(pMT, CLASS__BSTR_WRAPPER))
+    if (CoreLibBinder::IsClass(pMT, CLASS__BSTR_WRAPPER))
         return VT_BSTR;
 
     // VariantWrappers cannot be stored in VARIANT's.
-    if (MscorlibBinder::IsClass(pMT, CLASS__VARIANT_WRAPPER))
+    if (CoreLibBinder::IsClass(pMT, CLASS__VARIANT_WRAPPER))
         COMPlusThrow(kArgumentException, IDS_EE_COM_UNSUPPORTED_SIG);
 #endif // FEATURE_COMINTEROP
 
@@ -357,9 +357,9 @@ VARTYPE OleVariant::GetVarTypeForTypeHandle(TypeHandle type)
 #ifdef FEATURE_COMINTEROP
     // There is no VT corresponding to SafeHandles as they cannot be stored in
     // VARIANTs or Arrays. The same applies to CriticalHandle.
-    if (type.CanCastTo(TypeHandle(MscorlibBinder::GetClass(CLASS__SAFE_HANDLE))))
+    if (type.CanCastTo(TypeHandle(CoreLibBinder::GetClass(CLASS__SAFE_HANDLE))))
         COMPlusThrow(kArgumentException, IDS_EE_COM_UNSUPPORTED_SIG);
-    if (type.CanCastTo(TypeHandle(MscorlibBinder::GetClass(CLASS__CRITICAL_HANDLE))))
+    if (type.CanCastTo(TypeHandle(CoreLibBinder::GetClass(CLASS__CRITICAL_HANDLE))))
         COMPlusThrow(kArgumentException, IDS_EE_COM_UNSUPPORTED_SIG);
 
     if (pMT->IsInterface())
@@ -639,15 +639,15 @@ TypeHandle OleVariant::GetArrayForVarType(VARTYPE vt, TypeHandle elemType, unsig
             break;
 
         case VT_CY:
-            baseType = TypeHandle(MscorlibBinder::GetClass(CLASS__DECIMAL));
+            baseType = TypeHandle(CoreLibBinder::GetClass(CLASS__DECIMAL));
             break;
 
         case VT_DATE:
-            baseType = TypeHandle(MscorlibBinder::GetClass(CLASS__DATE_TIME));
+            baseType = TypeHandle(CoreLibBinder::GetClass(CLASS__DATE_TIME));
             break;
 
         case VT_DECIMAL:
-            baseType = TypeHandle(MscorlibBinder::GetClass(CLASS__DECIMAL));
+            baseType = TypeHandle(CoreLibBinder::GetClass(CLASS__DECIMAL));
             break;
 
         case VT_VARIANT:
@@ -702,7 +702,7 @@ TypeHandle OleVariant::GetArrayForVarType(VARTYPE vt, TypeHandle elemType, unsig
     }
 
     if (baseType.IsNull())
-        baseType = TypeHandle(MscorlibBinder::GetElementType(baseElement));
+        baseType = TypeHandle(CoreLibBinder::GetElementType(baseElement));
 
     _ASSERTE(!baseType.IsNull());
 
@@ -806,21 +806,21 @@ MethodTable* OleVariant::GetNativeMethodTableForVarType(VARTYPE vt, MethodTable*
 
     if (vt & VT_ARRAY)
     {
-        return MscorlibBinder::GetClass(CLASS__INTPTR);
+        return CoreLibBinder::GetClass(CLASS__INTPTR);
     }
 
     switch (vt)
     {
         case VT_DATE:
-            return MscorlibBinder::GetClass(CLASS__DOUBLE);
+            return CoreLibBinder::GetClass(CLASS__DOUBLE);
         case VT_CY:
-            return MscorlibBinder::GetClass(CLASS__CURRENCY);
+            return CoreLibBinder::GetClass(CLASS__CURRENCY);
         case VTHACK_WINBOOL:
-            return MscorlibBinder::GetClass(CLASS__INT32);
+            return CoreLibBinder::GetClass(CLASS__INT32);
         case VT_BOOL:
-            return MscorlibBinder::GetClass(CLASS__INT16);
+            return CoreLibBinder::GetClass(CLASS__INT16);
         case VTHACK_CBOOL:
-            return MscorlibBinder::GetClass(CLASS__BYTE);
+            return CoreLibBinder::GetClass(CLASS__BYTE);
         case VT_DISPATCH:
         case VT_UNKNOWN:
         case VT_LPSTR:
@@ -829,19 +829,19 @@ MethodTable* OleVariant::GetNativeMethodTableForVarType(VARTYPE vt, MethodTable*
         case VT_USERDEFINED:
         case VT_SAFEARRAY:
         case VT_CARRAY:
-            return MscorlibBinder::GetClass(CLASS__INTPTR);
+            return CoreLibBinder::GetClass(CLASS__INTPTR);
         case VT_VARIANT:
-            return MscorlibBinder::GetClass(CLASS__NATIVEVARIANT);
+            return CoreLibBinder::GetClass(CLASS__NATIVEVARIANT);
         case VTHACK_ANSICHAR:
-            return MscorlibBinder::GetClass(CLASS__BYTE);
+            return CoreLibBinder::GetClass(CLASS__BYTE);
         case VT_UI2:
             // When CharSet = CharSet.Unicode, System.Char arrays are marshaled as VT_UI2.
             // However, since System.Char itself is CharSet.Ansi, the native size of
             // System.Char is 1 byte instead of 2. So here we explicitly return System.UInt16's
             // MethodTable to ensure the correct size.
-            return MscorlibBinder::GetClass(CLASS__UINT16);
+            return CoreLibBinder::GetClass(CLASS__UINT16);
         case VT_DECIMAL:
-            return MscorlibBinder::GetClass(CLASS__NATIVEDECIMAL);
+            return CoreLibBinder::GetClass(CLASS__NATIVEDECIMAL);
         default:
             PREFIX_ASSUME(pManagedMT != NULL);
             return pManagedMT;
@@ -1136,7 +1136,7 @@ void VariantData::NewVariant(VariantData * const& dest, const CVTypes type, INT6
 
         case CV_NULL:
         {
-            FieldDesc * pFD = MscorlibBinder::GetField(FIELD__NULL__VALUE);
+            FieldDesc * pFD = CoreLibBinder::GetField(FIELD__NULL__VALUE);
             _ASSERTE(pFD);
 
             pFD->CheckRunClassInitThrowing();
@@ -2520,7 +2520,7 @@ void OleVariant::MarshalDecimalVariantOleToCom(VARIANT *pOleVariant,
     }
     CONTRACTL_END;
 
-    OBJECTREF pDecimalRef = AllocateObject(MscorlibBinder::GetClass(CLASS__DECIMAL));
+    OBJECTREF pDecimalRef = AllocateObject(CoreLibBinder::GetClass(CLASS__DECIMAL));
 
     DECIMAL* pDecimal = (DECIMAL *) pDecimalRef->UnBox();
     *pDecimal = V_DECIMAL(pOleVariant);
@@ -2563,7 +2563,7 @@ void OleVariant::MarshalDecimalVariantOleRefToCom(VARIANT *pOleVariant,
     }
     CONTRACTL_END;
 
-    OBJECTREF pDecimalRef = AllocateObject(MscorlibBinder::GetClass(CLASS__DECIMAL));
+    OBJECTREF pDecimalRef = AllocateObject(CoreLibBinder::GetClass(CLASS__DECIMAL));
 
     DECIMAL* pDecimal = (DECIMAL *) pDecimalRef->UnBox();
     *pDecimal = *V_DECIMALREF(pOleVariant);
@@ -2781,7 +2781,7 @@ void OleVariant::MarshalOleVariantForObject(OBJECTREF * const & pObj, VARIANT *p
     else
     {
         MethodTable *pMT = (*pObj)->GetMethodTable();
-        if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_I4))
+        if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_I4))
         {
             V_I4(pOle) = *(LONG*)( (*pObj)->GetData() );
             V_VT(pOle) = VT_I4;
@@ -2802,52 +2802,52 @@ void OleVariant::MarshalOleVariantForObject(OBJECTREF * const & pObj, VARIANT *p
 
             V_VT(pOle) = VT_BSTR;
         }
-        else if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_I2))
+        else if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_I2))
         {
             V_I2(pOle) = *(SHORT*)( (*pObj)->GetData() );
             V_VT(pOle) = VT_I2;
         }
-        else if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_I1))
+        else if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_I1))
         {
             V_I1(pOle) = *(CHAR*)( (*pObj)->GetData() );
             V_VT(pOle) = VT_I1;
         }
-        else if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_U4))
+        else if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_U4))
         {
             V_UI4(pOle) = *(ULONG*)( (*pObj)->GetData() );
             V_VT(pOle) = VT_UI4;
         }
-        else if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_U2))
+        else if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_U2))
         {
             V_UI2(pOle) = *(USHORT*)( (*pObj)->GetData() );
             V_VT(pOle) = VT_UI2;
         }
-        else if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_U1))
+        else if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_U1))
         {
             V_UI1(pOle) = *(BYTE*)( (*pObj)->GetData() );
             V_VT(pOle) = VT_UI1;
         }
-        else if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_R4))
+        else if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_R4))
         {
             V_R4(pOle) = *(FLOAT*)( (*pObj)->GetData() );
             V_VT(pOle) = VT_R4;
         }
-        else if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_R8))
+        else if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_R8))
         {
             V_R8(pOle) = *(DOUBLE*)( (*pObj)->GetData() );
             V_VT(pOle) = VT_R8;
         }
-        else if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_BOOLEAN))
+        else if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_BOOLEAN))
         {
             V_BOOL(pOle) = *(U1*)( (*pObj)->GetData() ) ? VARIANT_TRUE : VARIANT_FALSE;
             V_VT(pOle) = VT_BOOL;
         }
-        else if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_I))
+        else if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_I))
         {
             *(LPVOID*)&(V_INT(pOle)) = *(LPVOID*)( (*pObj)->GetData() );
             V_VT(pOle) = VT_INT;
         }
-        else if (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_U))
+        else if (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_U))
         {
             *(LPVOID*)&(V_UINT(pOle)) = *(LPVOID*)( (*pObj)->GetData() );
             V_VT(pOle) = VT_UINT;
@@ -2972,49 +2972,49 @@ HRESULT OleVariant::MarshalCommonOleRefVariantForObject(OBJECTREF *pObj, VARIANT
     // Let's try to handle the common trivial cases quickly first before
     // running the generalized stuff.
     MethodTable *pMT = (*pObj) == NULL ? NULL : (*pObj)->GetMethodTable();
-    if ( (V_VT(pOle) == (VT_BYREF | VT_I4) || V_VT(pOle) == (VT_BYREF | VT_UI4)) && (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_I4) || pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_U4)) )
+    if ( (V_VT(pOle) == (VT_BYREF | VT_I4) || V_VT(pOle) == (VT_BYREF | VT_UI4)) && (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_I4) || pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_U4)) )
     {
         // deallocation of old value optimized away since there's nothing to
         // deallocate for this vartype.
 
         *(V_I4REF(pOle)) = *(LONG*)( (*pObj)->GetData() );
     }
-    else if ( (V_VT(pOle) == (VT_BYREF | VT_I2) || V_VT(pOle) == (VT_BYREF | VT_UI2)) && (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_I2) || pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_U2)) )
+    else if ( (V_VT(pOle) == (VT_BYREF | VT_I2) || V_VT(pOle) == (VT_BYREF | VT_UI2)) && (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_I2) || pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_U2)) )
     {
         // deallocation of old value optimized away since there's nothing to
         // deallocate for this vartype.
 
         *(V_I2REF(pOle)) = *(SHORT*)( (*pObj)->GetData() );
     }
-    else if ( (V_VT(pOle) == (VT_BYREF | VT_I1) || V_VT(pOle) == (VT_BYREF | VT_UI1)) && (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_I1) || pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_U1)) )
+    else if ( (V_VT(pOle) == (VT_BYREF | VT_I1) || V_VT(pOle) == (VT_BYREF | VT_UI1)) && (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_I1) || pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_U1)) )
     {
         // deallocation of old value optimized away since there's nothing to
         // deallocate for this vartype.
 
         *(V_I1REF(pOle)) = *(CHAR*)( (*pObj)->GetData() );
     }
-    else if ( V_VT(pOle) == (VT_BYREF | VT_R4) && pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_R4) )
+    else if ( V_VT(pOle) == (VT_BYREF | VT_R4) && pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_R4) )
     {
         // deallocation of old value optimized away since there's nothing to
         // deallocate for this vartype.
 
         *(V_R4REF(pOle)) = *(FLOAT*)( (*pObj)->GetData() );
     }
-    else if ( V_VT(pOle) == (VT_BYREF | VT_R8) && pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_R8) )
+    else if ( V_VT(pOle) == (VT_BYREF | VT_R8) && pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_R8) )
     {
         // deallocation of old value optimized away since there's nothing to
         // deallocate for this vartype.
 
         *(V_R8REF(pOle)) = *(DOUBLE*)( (*pObj)->GetData() );
     }
-    else if ( V_VT(pOle) == (VT_BYREF | VT_BOOL) && pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_BOOLEAN) )
+    else if ( V_VT(pOle) == (VT_BYREF | VT_BOOL) && pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_BOOLEAN) )
     {
         // deallocation of old value optimized away since there's nothing to
         // deallocate for this vartype.
 
         *(V_BOOLREF(pOle)) =  ( *(U1*)( (*pObj)->GetData() ) ) ? VARIANT_TRUE : VARIANT_FALSE;
     }
-    else if ( (V_VT(pOle) == (VT_BYREF | VT_INT) || V_VT(pOle) == (VT_BYREF | VT_UINT)) && (pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_I4) || pMT == MscorlibBinder::GetElementType(ELEMENT_TYPE_U4)) )
+    else if ( (V_VT(pOle) == (VT_BYREF | VT_INT) || V_VT(pOle) == (VT_BYREF | VT_UINT)) && (pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_I4) || pMT == CoreLibBinder::GetElementType(ELEMENT_TYPE_U4)) )
     {
         // deallocation of old value optimized away since there's nothing to
         // deallocate for this vartype.
@@ -3122,112 +3122,112 @@ void OleVariant::MarshalObjectForOleVariant(const VARIANT * pOle, OBJECTREF * co
         case VT_I4:
         case VT_INT:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_I4)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_I4)) );
             *(LONG*)((*pObj)->GetData()) = V_I4(pOle);
             break;
 
         case VT_BYREF|VT_I4:
         case VT_BYREF|VT_INT:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_I4)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_I4)) );
             *(LONG*)((*pObj)->GetData()) = *(V_I4REF(pOle));
             break;
 
         case VT_UI4:
         case VT_UINT:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_U4)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_U4)) );
             *(ULONG*)((*pObj)->GetData()) = V_UI4(pOle);
             break;
 
         case VT_BYREF|VT_UI4:
         case VT_BYREF|VT_UINT:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_U4)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_U4)) );
             *(ULONG*)((*pObj)->GetData()) = *(V_UI4REF(pOle));
             break;
 
         case VT_I2:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_I2)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_I2)) );
             (*(SHORT*)((*pObj)->GetData())) = V_I2(pOle);
             break;
 
         case VT_BYREF|VT_I2:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_I2)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_I2)) );
             *(SHORT*)((*pObj)->GetData()) = *(V_I2REF(pOle));
             break;
 
         case VT_UI2:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_U2)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_U2)) );
             *(USHORT*)((*pObj)->GetData()) = V_UI2(pOle);
             break;
 
         case VT_BYREF|VT_UI2:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_U2)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_U2)) );
             *(USHORT*)((*pObj)->GetData()) = *(V_UI2REF(pOle));
             break;
 
         case VT_I1:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_I1)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_I1)) );
             *(CHAR*)((*pObj)->GetData()) = V_I1(pOle);
             break;
 
         case VT_BYREF|VT_I1:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_I1)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_I1)) );
             *(CHAR*)((*pObj)->GetData()) = *(V_I1REF(pOle));
             break;
 
         case VT_UI1:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_U1)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_U1)) );
             *(BYTE*)((*pObj)->GetData()) = V_UI1(pOle);
             break;
 
         case VT_BYREF|VT_UI1:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_U1)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_U1)) );
             *(BYTE*)((*pObj)->GetData()) = *(V_UI1REF(pOle));
             break;
 
         case VT_R4:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_R4)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_R4)) );
             *(FLOAT*)((*pObj)->GetData()) = V_R4(pOle);
             break;
 
         case VT_BYREF|VT_R4:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_R4)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_R4)) );
             *(FLOAT*)((*pObj)->GetData()) = *(V_R4REF(pOle));
             break;
 
         case VT_R8:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_R8)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_R8)) );
             *(DOUBLE*)((*pObj)->GetData()) = V_R8(pOle);
             break;
 
         case VT_BYREF|VT_R8:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_R8)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_R8)) );
             *(DOUBLE*)((*pObj)->GetData()) = *(V_R8REF(pOle));
             break;
 
         case VT_BOOL:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_BOOLEAN)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_BOOLEAN)) );
             *(VARIANT_BOOL*)((*pObj)->GetData()) = V_BOOL(pOle) ? 1 : 0;
             break;
 
         case VT_BYREF|VT_BOOL:
             SetObjectReference( pObj,
-                                AllocateObject(MscorlibBinder::GetElementType(ELEMENT_TYPE_BOOLEAN)) );
+                                AllocateObject(CoreLibBinder::GetElementType(ELEMENT_TYPE_BOOLEAN)) );
             *(VARIANT_BOOL*)((*pObj)->GetData()) = *(V_BOOLREF(pOle)) ? 1 : 0;
             break;
 
@@ -3800,7 +3800,7 @@ void OleVariant::MarshalCurrencyVariantOleToCom(VARIANT *pOleVariant,
     }
     CONTRACTL_END;
 
-    OBJECTREF pDecimalRef = AllocateObject(MscorlibBinder::GetClass(CLASS__DECIMAL));
+    OBJECTREF pDecimalRef = AllocateObject(CoreLibBinder::GetClass(CLASS__DECIMAL));
     DECIMAL DecVal;
 
     // Convert the currency to a decimal.
@@ -3848,7 +3848,7 @@ void OleVariant::MarshalCurrencyVariantOleRefToCom(VARIANT *pOleVariant,
     }
     CONTRACTL_END;
 
-    OBJECTREF pDecimalRef = AllocateObject(MscorlibBinder::GetClass(CLASS__DECIMAL));
+    OBJECTREF pDecimalRef = AllocateObject(CoreLibBinder::GetClass(CLASS__DECIMAL));
     DECIMAL DecVal;
 
     // Convert the currency to a decimal.
@@ -4867,16 +4867,16 @@ BOOL OleVariant::IsArrayOfWrappers(BASEARRAYREF *pArray, BOOL *pbOfInterfaceWrap
 
     if (!hndElemType.IsTypeDesc())
     {
-        if (hndElemType == TypeHandle(MscorlibBinder::GetClass(CLASS__DISPATCH_WRAPPER)) ||
-            hndElemType == TypeHandle(MscorlibBinder::GetClass(CLASS__UNKNOWN_WRAPPER)))
+        if (hndElemType == TypeHandle(CoreLibBinder::GetClass(CLASS__DISPATCH_WRAPPER)) ||
+            hndElemType == TypeHandle(CoreLibBinder::GetClass(CLASS__UNKNOWN_WRAPPER)))
         {
             *pbOfInterfaceWrappers = TRUE;
             return TRUE;
         }
 
-        if (hndElemType == TypeHandle(MscorlibBinder::GetClass(CLASS__ERROR_WRAPPER)) ||
-            hndElemType == TypeHandle(MscorlibBinder::GetClass(CLASS__CURRENCY_WRAPPER)) ||
-            hndElemType == TypeHandle(MscorlibBinder::GetClass(CLASS__BSTR_WRAPPER)))
+        if (hndElemType == TypeHandle(CoreLibBinder::GetClass(CLASS__ERROR_WRAPPER)) ||
+            hndElemType == TypeHandle(CoreLibBinder::GetClass(CLASS__CURRENCY_WRAPPER)) ||
+            hndElemType == TypeHandle(CoreLibBinder::GetClass(CLASS__BSTR_WRAPPER)))
         {
             *pbOfInterfaceWrappers = FALSE;
             return TRUE;
@@ -4906,20 +4906,20 @@ BASEARRAYREF OleVariant::ExtractWrappedObjectsFromArray(BASEARRAYREF *pArray)
     BASEARRAYREF RetArray = NULL;
 
     // Retrieve the element type handle for the array to create.
-    if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__DISPATCH_WRAPPER)))
+    if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__DISPATCH_WRAPPER)))
         hndElemType = TypeHandle(g_pObjectClass);
 
-    else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__UNKNOWN_WRAPPER)))
+    else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__UNKNOWN_WRAPPER)))
         hndElemType = TypeHandle(g_pObjectClass);
 
-    else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__BSTR_WRAPPER)))
+    else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__BSTR_WRAPPER)))
         hndElemType = TypeHandle(g_pStringClass);
 
-    else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__ERROR_WRAPPER)))
-        hndElemType = TypeHandle(MscorlibBinder::GetClass(CLASS__INT32));
+    else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__ERROR_WRAPPER)))
+        hndElemType = TypeHandle(CoreLibBinder::GetClass(CLASS__INT32));
 
-    else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__CURRENCY_WRAPPER)))
-        hndElemType = TypeHandle(MscorlibBinder::GetClass(CLASS__DECIMAL));
+    else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__CURRENCY_WRAPPER)))
+        hndElemType = TypeHandle(CoreLibBinder::GetClass(CLASS__DECIMAL));
 
     else
         _ASSERTE(!"Invalid wrapper type");
@@ -4961,7 +4961,7 @@ BASEARRAYREF OleVariant::ExtractWrappedObjectsFromArray(BASEARRAYREF *pArray)
     {
         SIZE_T NumComponents = (*pArray)->GetNumComponents();
 
-        if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__DISPATCH_WRAPPER)))
+        if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__DISPATCH_WRAPPER)))
         {
             DISPATCHWRAPPEROBJECTREF *pSrc = (DISPATCHWRAPPEROBJECTREF *)(*pArray)->GetDataPtr();
             DISPATCHWRAPPEROBJECTREF *pSrcEnd = pSrc + NumComponents;
@@ -4969,7 +4969,7 @@ BASEARRAYREF OleVariant::ExtractWrappedObjectsFromArray(BASEARRAYREF *pArray)
             for (; pSrc < pSrcEnd; pSrc++, pDest++)
                 SetObjectReference(pDest, (*pSrc) != NULL ? (*pSrc)->GetWrappedObject() : NULL);
         }
-        else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__UNKNOWN_WRAPPER)))
+        else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__UNKNOWN_WRAPPER)))
         {
             UNKNOWNWRAPPEROBJECTREF *pSrc = (UNKNOWNWRAPPEROBJECTREF *)(*pArray)->GetDataPtr();
             UNKNOWNWRAPPEROBJECTREF *pSrcEnd = pSrc + NumComponents;
@@ -4977,7 +4977,7 @@ BASEARRAYREF OleVariant::ExtractWrappedObjectsFromArray(BASEARRAYREF *pArray)
             for (; pSrc < pSrcEnd; pSrc++, pDest++)
                 SetObjectReference(pDest, (*pSrc) != NULL ? (*pSrc)->GetWrappedObject() : NULL);
         }
-        else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__ERROR_WRAPPER)))
+        else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__ERROR_WRAPPER)))
         {
             ERRORWRAPPEROBJECTREF *pSrc = (ERRORWRAPPEROBJECTREF *)(*pArray)->GetDataPtr();
             ERRORWRAPPEROBJECTREF *pSrcEnd = pSrc + NumComponents;
@@ -4985,7 +4985,7 @@ BASEARRAYREF OleVariant::ExtractWrappedObjectsFromArray(BASEARRAYREF *pArray)
             for (; pSrc < pSrcEnd; pSrc++, pDest++)
                 *pDest = (*pSrc) != NULL ? (*pSrc)->GetErrorCode() : NULL;
         }
-        else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__CURRENCY_WRAPPER)))
+        else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__CURRENCY_WRAPPER)))
         {
             CURRENCYWRAPPEROBJECTREF *pSrc = (CURRENCYWRAPPEROBJECTREF *)(*pArray)->GetDataPtr();
             CURRENCYWRAPPEROBJECTREF *pSrcEnd = pSrc + NumComponents;
@@ -4998,7 +4998,7 @@ BASEARRAYREF OleVariant::ExtractWrappedObjectsFromArray(BASEARRAYREF *pArray)
                     memset(pDest, 0, sizeof(DECIMAL));
             }
         }
-        else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__BSTR_WRAPPER)))
+        else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__BSTR_WRAPPER)))
         {
             BSTRWRAPPEROBJECTREF *pSrc = (BSTRWRAPPEROBJECTREF *)(*pArray)->GetDataPtr();
             BSTRWRAPPEROBJECTREF *pSrcEnd = pSrc + NumComponents;
@@ -5034,22 +5034,22 @@ TypeHandle OleVariant::GetWrappedArrayElementType(BASEARRAYREF *pArray)
     TypeHandle hndWrapperType = (*pArray)->GetArrayElementTypeHandle();
     TypeHandle pWrappedObjType;
 
-    if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__DISPATCH_WRAPPER)) ||
-        hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__UNKNOWN_WRAPPER)))
+    if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__DISPATCH_WRAPPER)) ||
+        hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__UNKNOWN_WRAPPER)))
     {
         // There's no need to traverse the array up front. We'll use the default interface
         // for each element in code:OleVariant::MarshalInterfaceArrayComToOleHelper.
         pWrappedObjType = TypeHandle(g_pObjectClass);
     }
-    else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__ERROR_WRAPPER)))
+    else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__ERROR_WRAPPER)))
     {
-        pWrappedObjType = TypeHandle(MscorlibBinder::GetClass(CLASS__INT32));
+        pWrappedObjType = TypeHandle(CoreLibBinder::GetClass(CLASS__INT32));
     }
-    else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__CURRENCY_WRAPPER)))
+    else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__CURRENCY_WRAPPER)))
     {
-        pWrappedObjType = TypeHandle(MscorlibBinder::GetClass(CLASS__DECIMAL));
+        pWrappedObjType = TypeHandle(CoreLibBinder::GetClass(CLASS__DECIMAL));
     }
-    else if (hndWrapperType == TypeHandle(MscorlibBinder::GetClass(CLASS__BSTR_WRAPPER)))
+    else if (hndWrapperType == TypeHandle(CoreLibBinder::GetClass(CLASS__BSTR_WRAPPER)))
     {
         pWrappedObjType = TypeHandle(g_pStringClass);
     }
diff --git a/src/coreclr/src/vm/olevariant.h b/src/coreclr/src/vm/olevariant.h
index dfc846e2731b09..d8f49f7e23df45 100644
--- a/src/coreclr/src/vm/olevariant.h
+++ b/src/coreclr/src/vm/olevariant.h
@@ -75,7 +75,7 @@ inline TypeHandle GetTypeHandleForCVType(CVTypes elemType)
     }
     CONTRACT_END;
 
-    RETURN TypeHandle(MscorlibBinder::GetClass(CVTypeToBinderClassID[elemType]));
+    RETURN TypeHandle(CoreLibBinder::GetClass(CVTypeToBinderClassID[elemType]));
 }
 
 // Use this very carefully.  There is not a direct mapping between
@@ -116,7 +116,7 @@ extern CVTypes CorElementTypeToCVTypes(CorElementType type);
 
 struct VariantData
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
 public:
     static void NewVariant(VariantData * const& dest, const CVTypes type, INT64 data
diff --git a/src/coreclr/src/vm/packedfields.inl b/src/coreclr/src/vm/packedfields.inl
index 16544acd220835..aa070fdbcbbf9e 100644
--- a/src/coreclr/src/vm/packedfields.inl
+++ b/src/coreclr/src/vm/packedfields.inl
@@ -144,7 +144,7 @@ public:
             // to encode zero-valued fields with zero bits. Is this is deemed an important optimization in the
             // future we could always given up on a simple linear mapping of the size field and use a lookup
             // table to map values encoded into the real sizes. Experiments with EEClass packed fields over
-            // mscorlib show that this currently doesn't yield us much benefit, primarily due to the DWORD
+            // CoreLib show that this currently doesn't yield us much benefit, primarily due to the DWORD
             // round-up size semantic, which implies we'd need a lot more optimization than this to reduce the
             // average structure size below the next DWORD threshhold.
             BitVectorSet(dwOffset, kMaxLengthBits, dwFieldLength - 1);
diff --git a/src/coreclr/src/vm/pefile.h b/src/coreclr/src/vm/pefile.h
index 2ee625206163cc..383fb53de0534c 100644
--- a/src/coreclr/src/vm/pefile.h
+++ b/src/coreclr/src/vm/pefile.h
@@ -626,7 +626,7 @@ class PEAssembly : public PEFile
         PEImage *          pPEImageNI,
         ICLRPrivAssembly * pHostAssembly);
 
-    // This opens the canonical mscorlib.dll
+    // This opens the canonical System.Private.CoreLib.dll
     static PEAssembly *OpenSystem(IUnknown *pAppCtx);
 #ifdef DACCESS_COMPILE
     virtual void EnumMemoryRegions(CLRDataEnumMemoryFlags flags);
diff --git a/src/coreclr/src/vm/peimagelayout.cpp b/src/coreclr/src/vm/peimagelayout.cpp
index 88b27ba5d1b04f..00098c2748a05d 100644
--- a/src/coreclr/src/vm/peimagelayout.cpp
+++ b/src/coreclr/src/vm/peimagelayout.cpp
@@ -39,7 +39,7 @@ PEImageLayout* PEImageLayout::LoadFromFlat(PEImageLayout* pflatimage)
     return new ConvertedImageLayout(pflatimage);
 }
 
-PEImageLayout* PEImageLayout::LoadConverted(PEImage* pOwner)
+PEImageLayout* PEImageLayout::LoadConverted(PEImage* pOwner, BOOL isInBundle)
 {
     STANDARD_VM_CONTRACT;
 
@@ -47,7 +47,7 @@ PEImageLayout* PEImageLayout::LoadConverted(PEImage* pOwner)
     if (!pFlat->CheckFormat())
         ThrowHR(COR_E_BADIMAGEFORMAT);
 
-    return new ConvertedImageLayout(pFlat);
+    return new ConvertedImageLayout(pFlat, isInBundle);
 }
 
 PEImageLayout* PEImageLayout::Load(PEImage* pOwner, BOOL bNTSafeLoad, BOOL bThrowOnError)
@@ -59,7 +59,7 @@ PEImageLayout* PEImageLayout::Load(PEImage* pOwner, BOOL bNTSafeLoad, BOOL bThro
 #else
     if (pOwner->IsInBundle())
     {
-        return PEImageLayout::LoadConverted(pOwner);
+        return PEImageLayout::LoadConverted(pOwner, true);
     }
 
     PEImageLayoutHolder pAlloc(new LoadedImageLayout(pOwner,bNTSafeLoad,bThrowOnError));
@@ -386,7 +386,7 @@ RawImageLayout::RawImageLayout(const void *mapped, PEImage* pOwner, BOOL bTakeOw
     IfFailThrow(Init((void*)mapped,(bool)(bFixedUp!=FALSE)));
 }
 
-ConvertedImageLayout::ConvertedImageLayout(PEImageLayout* source)
+ConvertedImageLayout::ConvertedImageLayout(PEImageLayout* source, BOOL isInBundle)
 {
     CONTRACTL
     {
@@ -397,23 +397,37 @@ ConvertedImageLayout::ConvertedImageLayout(PEImageLayout* source)
     m_Layout=LAYOUT_LOADED;
     m_pOwner=source->m_pOwner;
     _ASSERTE(!source->IsMapped());
+    m_isInBundle = isInBundle;
+
+    m_pExceptionDir = NULL;
 
     if (!source->HasNTHeaders())
         EEFileLoadException::Throw(GetPath(), COR_E_BADIMAGEFORMAT);
     LOG((LF_LOADER, LL_INFO100, "PEImage: Opening manually mapped stream\n"));
 
+#if !defined(CROSSGEN_COMPILE) && !defined(TARGET_UNIX)
+    // on Windows we may want to enable execution if the image contains R2R sections
+    // so must ensure the mapping is compatible with that
+    m_FileMap.Assign(WszCreateFileMapping(INVALID_HANDLE_VALUE, NULL,
+        PAGE_EXECUTE_READWRITE, 0,
+        source->GetVirtualSize(), NULL));
 
+    DWORD allAccess = FILE_MAP_EXECUTE | FILE_MAP_WRITE;
+#else
     m_FileMap.Assign(WszCreateFileMapping(INVALID_HANDLE_VALUE, NULL,
-                                          PAGE_READWRITE, 0,
-                                          source->GetVirtualSize(), NULL));
+        PAGE_READWRITE, 0,
+        source->GetVirtualSize(), NULL));
+
+    DWORD allAccess = FILE_MAP_ALL_ACCESS;
+#endif
+
     if (m_FileMap == NULL)
         ThrowLastError();
 
-
-    m_FileView.Assign(CLRMapViewOfFile(m_FileMap, FILE_MAP_ALL_ACCESS, 0, 0, 0,
+    m_FileView.Assign(CLRMapViewOfFile(m_FileMap, allAccess, 0, 0, 0,
                                 (void *) source->GetPreferredBase()));
     if (m_FileView == NULL)
-        m_FileView.Assign(CLRMapViewOfFile(m_FileMap, FILE_MAP_ALL_ACCESS, 0, 0, 0));
+        m_FileView.Assign(CLRMapViewOfFile(m_FileMap, allAccess, 0, 0, 0));
 
     if (m_FileView == NULL)
         ThrowLastError();
@@ -421,9 +435,57 @@ ConvertedImageLayout::ConvertedImageLayout(PEImageLayout* source)
     source->LayoutILOnly(m_FileView, TRUE); //@TODO should be false for streams
     IfFailThrow(Init(m_FileView));
 
-#ifdef CROSSGEN_COMPILE
+#if defined(CROSSGEN_COMPILE)
     if (HasNativeHeader())
+    {
         ApplyBaseRelocations();
+    }
+#elif !defined(TARGET_UNIX)
+    if (m_isInBundle &&
+        HasCorHeader() &&
+        (HasNativeHeader() || HasReadyToRunHeader()) &&
+        g_fAllowNativeImages)
+    {
+        if (!IsNativeMachineFormat())
+            ThrowHR(COR_E_BADIMAGEFORMAT);
+
+        // Do base relocation for PE, if necessary.
+        // otherwise R2R will be disabled for this image.
+        ApplyBaseRelocations();
+
+        // Check if there is a static function table and install it. (except x86)
+#if !defined(TARGET_X86)
+        COUNT_T cbSize = 0;
+        PT_RUNTIME_FUNCTION   pExceptionDir = (PT_RUNTIME_FUNCTION)GetDirectoryEntryData(IMAGE_DIRECTORY_ENTRY_EXCEPTION, &cbSize);
+        DWORD tableSize = cbSize / sizeof(T_RUNTIME_FUNCTION);
+
+        if (pExceptionDir != NULL)
+        {
+            if (!RtlAddFunctionTable(pExceptionDir, tableSize, (DWORD64)this->GetBase()))
+                ThrowLastError();
+
+            m_pExceptionDir = pExceptionDir;
+        }
+#endif //TARGET_X86
+    }
+#endif
+}
+
+ConvertedImageLayout::~ConvertedImageLayout()
+{
+    CONTRACTL
+    {
+        NOTHROW;
+        GC_TRIGGERS;
+        MODE_ANY;
+    }
+    CONTRACTL_END;
+
+#if !defined(CROSSGEN_COMPILE) && !defined(TARGET_UNIX) && !defined(TARGET_X86)
+    if (m_pExceptionDir)
+    {
+        RtlDeleteFunctionTable(m_pExceptionDir);
+    }
 #endif
 }
 
diff --git a/src/coreclr/src/vm/peimagelayout.h b/src/coreclr/src/vm/peimagelayout.h
index 7a0242de4f2209..b5b0573a376f9a 100644
--- a/src/coreclr/src/vm/peimagelayout.h
+++ b/src/coreclr/src/vm/peimagelayout.h
@@ -53,7 +53,7 @@ class PEImageLayout : public PEDecoder
     static PEImageLayout* LoadFromFlat(PEImageLayout* pflatimage);
     static PEImageLayout* Load(PEImage* pOwner, BOOL bNTSafeLoad, BOOL bThrowOnError = TRUE);
     static PEImageLayout* LoadFlat(PEImage* pOwner);
-    static PEImageLayout* LoadConverted(PEImage* pOwner);
+    static PEImageLayout* LoadConverted(PEImage* pOwner, BOOL isInBundle = FALSE);
     static PEImageLayout* LoadNative(LPCWSTR fullPath);
     static PEImageLayout* Map(PEImage* pOwner);
 #endif
@@ -109,8 +109,12 @@ class ConvertedImageLayout: public PEImageLayout
     CLRMapViewHolder m_FileView;
 public:
 #ifndef DACCESS_COMPILE
-    ConvertedImageLayout(PEImageLayout* source);
+    ConvertedImageLayout(PEImageLayout* source, BOOL isInBundle = FALSE);
+    virtual ~ConvertedImageLayout();
 #endif
+private:
+    bool m_isInBundle;
+    PT_RUNTIME_FUNCTION m_pExceptionDir;
 };
 
 class MappedImageLayout: public PEImageLayout
diff --git a/src/coreclr/src/vm/perfmap.cpp b/src/coreclr/src/vm/perfmap.cpp
index 9fa9af72c67c6e..8eb8925f7e0b7d 100644
--- a/src/coreclr/src/vm/perfmap.cpp
+++ b/src/coreclr/src/vm/perfmap.cpp
@@ -401,7 +401,7 @@ NativeImagePerfMap::NativeImagePerfMap(Assembly * pAssembly, BSTR pDestPath)
     GetNativeImageSignature(pAssembly->GetManifestFile(), wszSignature, lengthof(wszSignature));
 
     // Build the path to the perfmap file, which consists of <inputpath><imagesimplename>.ni.<signature>.map.
-    // Example: /tmp/mscorlib.ni.{GUID}.map
+    // Example: /tmp/System.Private.CoreLib.ni.{GUID}.map
     SString sDestPerfMapPath;
     sDestPerfMapPath.Printf("%S%s.ni.%S.map", pDestPath, lpcSimpleName, wszSignature);
 
diff --git a/src/coreclr/src/vm/prestub.cpp b/src/coreclr/src/vm/prestub.cpp
index c6a3a58f98d3e3..d44c3cc062f850 100644
--- a/src/coreclr/src/vm/prestub.cpp
+++ b/src/coreclr/src/vm/prestub.cpp
@@ -95,7 +95,8 @@ PCODE MethodDesc::DoBackpatch(MethodTable * pMT, MethodTable *pDispatchingMT, BO
 
     // Only take the lock if the method is versionable with vtable slot backpatch, for recording slots and synchronizing with
     // backpatching slots
-    MethodDescBackpatchInfoTracker::ConditionalLockHolder slotBackpatchLockHolder(isVersionableWithVtableSlotBackpatch);
+    MethodDescBackpatchInfoTracker::ConditionalLockHolderForGCCoop slotBackpatchLockHolder(
+        isVersionableWithVtableSlotBackpatch);
 
     // Get the method entry point inside the lock above to synchronize with backpatching in
     // MethodDesc::BackpatchEntryPointSlots()
@@ -1063,11 +1064,21 @@ PCODE MethodDesc::JitCompileCodeLocked(PrepareCodeConfig* pConfig, JitListLockEn
     bool shouldCountCalls = false;
     if (pFlags->IsSet(CORJIT_FLAGS::CORJIT_FLAG_TIER0))
     {
-        _ASSERTE(pConfig->GetCodeVersion().GetOptimizationTier() == NativeCodeVersion::OptimizationTier0);
         _ASSERTE(pConfig->GetMethodDesc()->IsEligibleForTieredCompilation());
 
         if (pConfig->JitSwitchedToOptimized())
         {
+#ifdef _DEBUG
+            // Call counting may already have been disabled due to the possibility of concurrent or reentering JIT of the same
+            // native code version of a method. The current optimization tier should be consistent with the change being made
+            // (Tier 0 to Optimized), such that the tier is not changed in an unexpected way or at an unexpected time. Since
+            // changes to the optimization tier are unlocked, this assertion is just a speculative check on possible values.
+            NativeCodeVersion::OptimizationTier previousOptimizationTier = pConfig->GetCodeVersion().GetOptimizationTier();
+            _ASSERTE(
+                previousOptimizationTier == NativeCodeVersion::OptimizationTier0 ||
+                previousOptimizationTier == NativeCodeVersion::OptimizationTierOptimized);
+#endif // _DEBUG
+
             // Update the tier in the code version. The JIT may have decided to switch from tier 0 to optimized, in which case
             // call counting would have to be disabled for the method.
             NativeCodeVersion codeVersion = pConfig->GetCodeVersion();
@@ -1082,7 +1093,7 @@ PCODE MethodDesc::JitCompileCodeLocked(PrepareCodeConfig* pConfig, JitListLockEn
             shouldCountCalls = true;
         }
     }
-#endif
+#endif // FEATURE_TIERED_COMPILATION
 
     // Aside from rejit, performing a SetNativeCodeInterlocked at this point
     // generally ensures that there is only one winning version of the native
@@ -1475,7 +1486,7 @@ Stub * CreateUnboxingILStubForSharedGenericValueTypeMethods(MethodDesc* pTargetM
     CreateInstantiatingILStubTargetSig(pTargetMD, typeContext, &stubSigBuilder);
 
     // 2. Emit the method body
-    mdToken tokRawData = pCode->GetToken(MscorlibBinder::GetField(FIELD__RAW_DATA__DATA));
+    mdToken tokRawData = pCode->GetToken(CoreLibBinder::GetField(FIELD__RAW_DATA__DATA));
 
     // 2.1 Push the thisptr
     // We need to skip over the MethodTable*
@@ -2402,7 +2413,7 @@ EXTERN_C PCODE STDCALL ExternalMethodFixupWorker(TransitionBlock * pTransitionBl
     //
     // In this IL stub implementation we call the native method kernel32!GetFileAttributes,
     // and then we immediately try to save the Last Error code by calling the
-    // mscorlib method System.StubHelpers.StubHelpers.SetLastError().
+    // CoreLib method System.StubHelpers.StubHelpers.SetLastError().
     //
     // However when we are coming from a precompiled IL Stub in an ngen image
     // we must use an ExternalMethodFixup to find the target address of
@@ -3374,7 +3385,7 @@ PCODE DynamicHelperFixup(TransitionBlock * pTransitionBlock, TADDR * pCell, DWOR
                 }
                 else
                 {
-                    target = ECall::GetFCallImpl(MscorlibBinder::GetMethod(METHOD__DELEGATE__CONSTRUCT_DELEGATE));
+                    target = ECall::GetFCallImpl(CoreLibBinder::GetMethod(METHOD__DELEGATE__CONSTRUCT_DELEGATE));
                     ctorData.pArg3 = NULL;
                 }
 
diff --git a/src/coreclr/src/vm/processdiagnosticsprotocolhelper.cpp b/src/coreclr/src/vm/processdiagnosticsprotocolhelper.cpp
new file mode 100644
index 00000000000000..6aad9af96de0fe
--- /dev/null
+++ b/src/coreclr/src/vm/processdiagnosticsprotocolhelper.cpp
@@ -0,0 +1,214 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#include "common.h"
+#include "fastserializer.h"
+#include "processdiagnosticsprotocolhelper.h"
+#include "eventpipeeventsource.h"
+#include "diagnosticsprotocol.h"
+#include "diagnosticserver.h"
+
+#ifdef FEATURE_PERFTRACING
+
+static inline uint32_t GetStringLength(const WCHAR *&value)
+{
+    return static_cast<uint32_t>(wcslen(value) + 1);
+}
+
+static bool TryWriteString(uint8_t * &bufferCursor, uint16_t &bufferLen, const WCHAR *value)
+{
+    uint32_t stringLen = GetStringLength(value);
+    S_UINT16 totalStringSizeInBytes(stringLen * sizeof(WCHAR) + sizeof(uint32_t));
+    ASSERT(!totalStringSizeInBytes.IsOverflow());
+    ASSERT(bufferLen >= totalStringSizeInBytes.Value());
+    if (bufferLen < totalStringSizeInBytes.Value() || totalStringSizeInBytes.IsOverflow())
+        return false;
+
+    memcpy(bufferCursor, &stringLen, sizeof(stringLen));
+    bufferCursor += sizeof(stringLen);
+
+    memcpy(bufferCursor, value, stringLen * sizeof(WCHAR));
+    bufferCursor += stringLen * sizeof(WCHAR);
+
+    bufferLen -= totalStringSizeInBytes.Value();
+    return true;
+}
+
+uint16_t ProcessInfoPayload::GetSize()
+{
+    LIMITED_METHOD_CONTRACT;
+
+    // see IPC spec @ https://github.com/dotnet/diagnostics/blob/master/documentation/design-docs/ipc-protocol.md
+    // for definition of serialization format
+
+    // uint64_t ProcessId;  -> 8 bytes
+    // GUID RuntimeCookie;  -> 16 bytes
+    // LPCWSTR CommandLine; -> 4 bytes + strlen * sizeof(WCHAR)
+    // LPCWSTR OS;          -> 4 bytes + strlen * sizeof(WCHAR)
+    // LPCWSTR Arch;        -> 4 bytes + strlen * sizeof(WCHAR)
+
+    S_UINT16 size = S_UINT16(0);
+    size += sizeof(ProcessId);
+    size += sizeof(RuntimeCookie);
+
+    size += sizeof(uint32_t);
+    size += CommandLine != nullptr ?
+        S_UINT16(GetStringLength(CommandLine) * sizeof(WCHAR)) :
+        S_UINT16(0);
+
+    size += sizeof(uint32_t);
+    size += OS != nullptr ?
+        S_UINT16(GetStringLength(OS) * sizeof(WCHAR)) :
+        S_UINT16(0);
+
+    size += sizeof(uint32_t);
+    size += Arch != nullptr ?
+        S_UINT16(GetStringLength(Arch) * sizeof(WCHAR)) :
+        S_UINT16(0);
+
+    ASSERT(!size.IsOverflow());
+    return size.Value();
+}
+
+bool ProcessInfoPayload::Flatten(BYTE * &lpBuffer, uint16_t &cbSize)
+{
+    CONTRACTL
+    {
+        NOTHROW;
+        GC_TRIGGERS;
+        MODE_PREEMPTIVE;
+        PRECONDITION(cbSize == GetSize());
+        PRECONDITION(lpBuffer != nullptr);
+    }
+    CONTRACTL_END;
+
+    // see IPC spec @ https://github.com/dotnet/diagnostics/blob/master/documentation/design-docs/ipc-protocol.md
+    // for definition of serialization format
+
+    bool fSuccess = true;
+    // uint64_t ProcessId;
+    memcpy(lpBuffer, &ProcessId, sizeof(ProcessId));
+    lpBuffer += sizeof(ProcessId);
+    cbSize -= sizeof(ProcessId);
+
+    // GUID RuntimeCookie;
+    memcpy(lpBuffer, &RuntimeCookie, sizeof(RuntimeCookie));
+    lpBuffer += sizeof(RuntimeCookie);
+    cbSize -= sizeof(RuntimeCookie);
+
+    // LPCWSTR CommandLine;
+    fSuccess &= TryWriteString(lpBuffer, cbSize, CommandLine);
+
+    // LPCWSTR OS;
+    if (fSuccess)
+        fSuccess &= TryWriteString(lpBuffer, cbSize, OS);
+
+    // LPCWSTR Arch;
+    if (fSuccess)
+        fSuccess &= TryWriteString(lpBuffer, cbSize, Arch);
+
+    // Assert we've used the whole buffer we were given
+    ASSERT(cbSize == 0);
+
+    return fSuccess;
+}
+
+void ProcessDiagnosticsProtocolHelper::GetProcessInfo(DiagnosticsIpc::IpcMessage& message, IpcStream *pStream)
+{
+    CONTRACTL
+    {
+        THROWS;
+        GC_TRIGGERS;
+        MODE_PREEMPTIVE;
+        PRECONDITION(pStream != nullptr);
+    }
+    CONTRACTL_END;
+
+    struct ProcessInfoPayload payload = {};
+
+    // Get cmdline
+    payload.CommandLine = GetManagedCommandLine();
+
+    // Checkout https://github.com/dotnet/coreclr/pull/24433 for more information about this fall back.
+    if (payload.CommandLine == nullptr)
+    {
+        // Use the result from GetCommandLineW() instead
+        payload.CommandLine = GetCommandLineW();
+    }
+
+    // get OS + Arch info
+    payload.OS = EventPipeEventSource::s_pOSInformation;
+    payload.Arch = EventPipeEventSource::s_pArchInformation;
+
+    // Get the PID
+    payload.ProcessId = GetCurrentProcessId();
+
+    // Get the cookie
+    payload.RuntimeCookie = DiagnosticsIpc::GetAdvertiseCookie_V1();
+
+    DiagnosticsIpc::IpcMessage ProcessInfoResponse;
+    const bool fSuccess = ProcessInfoResponse.Initialize(DiagnosticsIpc::GenericSuccessHeader, payload) ?
+        ProcessInfoResponse.Send(pStream) :
+        DiagnosticsIpc::IpcMessage::SendErrorMessage(pStream, E_FAIL);
+
+    if (!fSuccess)
+        STRESS_LOG0(LF_DIAGNOSTICS_PORT, LL_WARNING, "Failed to send DiagnosticsIPC response");
+
+    delete pStream;
+}
+
+void ProcessDiagnosticsProtocolHelper::ResumeRuntimeStartup(DiagnosticsIpc::IpcMessage& message, IpcStream *pStream)
+{
+    CONTRACTL
+    {
+        THROWS;
+        GC_TRIGGERS;
+        MODE_PREEMPTIVE;
+        PRECONDITION(pStream != nullptr);
+    }
+    CONTRACTL_END;
+
+    // no payload
+    DiagnosticServer::ResumeRuntimeStartup();
+    HRESULT res = S_OK;
+
+    DiagnosticsIpc::IpcMessage successResponse;
+    const bool fSuccess = successResponse.Initialize(DiagnosticsIpc::GenericSuccessHeader, res) ?
+        successResponse.Send(pStream) :
+        DiagnosticsIpc::IpcMessage::SendErrorMessage(pStream, E_FAIL);
+    if (!fSuccess)
+        STRESS_LOG0(LF_DIAGNOSTICS_PORT, LL_WARNING, "Failed to send DiagnosticsIPC response");
+
+    delete pStream;
+}
+
+void ProcessDiagnosticsProtocolHelper::HandleIpcMessage(DiagnosticsIpc::IpcMessage& message, IpcStream* pStream)
+{
+    CONTRACTL
+    {
+        THROWS;
+        GC_TRIGGERS;
+        MODE_ANY;
+        PRECONDITION(pStream != nullptr);
+    }
+    CONTRACTL_END;
+
+    switch ((ProcessCommandId)message.GetHeader().CommandId)
+    {
+    case ProcessCommandId::GetProcessInfo:
+        ProcessDiagnosticsProtocolHelper::GetProcessInfo(message, pStream);
+        break;
+    case ProcessCommandId::ResumeRuntime:
+        ProcessDiagnosticsProtocolHelper::ResumeRuntimeStartup(message, pStream);
+        break;
+
+    default:
+        STRESS_LOG1(LF_DIAGNOSTICS_PORT, LL_WARNING, "Received unknown request type (%d)\n", message.GetHeader().CommandSet);
+        DiagnosticsIpc::IpcMessage::SendErrorMessage(pStream, CORDIAGIPC_E_UNKNOWN_COMMAND);
+        delete pStream;
+        break;
+    }
+}
+
+#endif // FEATURE_PERFTRACING
diff --git a/src/coreclr/src/vm/processdiagnosticsprotocolhelper.h b/src/coreclr/src/vm/processdiagnosticsprotocolhelper.h
new file mode 100644
index 00000000000000..ac4e1e5d1d50e1
--- /dev/null
+++ b/src/coreclr/src/vm/processdiagnosticsprotocolhelper.h
@@ -0,0 +1,59 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#ifndef __PROCESS_PROTOCOL_HELPER_H__
+#define __PROCESS_PROTOCOL_HELPER_H__
+
+#ifdef FEATURE_PERFTRACING
+
+#include "common.h"
+#include "eventpipe.h"
+#include "diagnosticsipc.h"
+#include "diagnosticsprotocol.h"
+
+class IpcStream;
+
+// The event pipe command set is 0x02
+// see diagnosticsipc.h and diagnosticserver.h for more details
+enum class ProcessCommandId : uint8_t
+{
+    GetProcessInfo = 0x00,
+    ResumeRuntime  = 0x01,
+    // future
+};
+
+// command = 0x0400
+struct ProcessInfoPayload
+{
+    // The protocol buffer is defined as:
+    // X, Y, Z means encode bytes for X followed by bytes for Y followed by bytes for Z
+    // uint = 4 little endian bytes
+    // long = 8 little endian bytes
+    // GUID = 16 little endian bytes
+    // wchar = 2 little endian bytes, UTF16 encoding
+    // array<T> = uint length, length # of Ts
+    // string = (array<char> where the last char must = 0) or (length = 0)
+
+    // ProcessInfo = long pid, string cmdline, string OS, string arch, GUID runtimeCookie
+    uint64_t ProcessId;
+    LPCWSTR CommandLine;
+    LPCWSTR OS;
+    LPCWSTR Arch;
+    GUID RuntimeCookie;
+    uint16_t GetSize();
+    bool Flatten(BYTE * &lpBuffer, uint16_t& cbSize);
+};
+
+class ProcessDiagnosticsProtocolHelper
+{
+public:
+    // IPC event handlers.
+    static void HandleIpcMessage(DiagnosticsIpc::IpcMessage& message, IpcStream *pStream);
+    static void GetProcessInfo(DiagnosticsIpc::IpcMessage& message, IpcStream *pStream);
+    static void ResumeRuntimeStartup(DiagnosticsIpc::IpcMessage& message, IpcStream *pStream);
+};
+
+#endif // FEATURE_PERFTRACING
+
+#endif // __PROCESS_PROTOCOL_HELPER_H__
diff --git a/src/coreclr/src/vm/proftoeeinterfaceimpl.h b/src/coreclr/src/vm/proftoeeinterfaceimpl.h
index 2fbfb8e80376c7..de5b75a3434d66 100644
--- a/src/coreclr/src/vm/proftoeeinterfaceimpl.h
+++ b/src/coreclr/src/vm/proftoeeinterfaceimpl.h
@@ -56,9 +56,9 @@ class ProfileArgIterator
 private:
     void        *m_handle;
     ArgIterator  m_argIterator;
-#ifdef UNIX_AMD64_ABI
+#if defined(UNIX_AMD64_ABI) || defined(TARGET_ARM64)
     UINT64       m_bufferPos;
-#endif // UNIX_AMD64_ABI
+#endif // defined(UNIX_AMD64_ABI) || defined(TARGET_ARM64)
 
 public:
     ProfileArgIterator(MetaSig * pMetaSig, void* platformSpecificHandle);
@@ -74,9 +74,12 @@ class ProfileArgIterator
         return m_argIterator.NumFixedArgs();
     }
 
-#ifdef UNIX_AMD64_ABI
+#if defined(UNIX_AMD64_ABI)
+    // On certain architectures we can pass args in non-sequential registers,
+    // this function will copy the struct so it is laid out as it would be in memory
+    // so it can be passed to the profiler
     LPVOID CopyStructFromRegisters();
-#endif // UNIX_AMD64_ABI
+#endif // defined(UNIX_AMD64_ABI)
 
     //
     // After initialization, this method is called repeatedly until it
diff --git a/src/coreclr/src/vm/qcall.cpp b/src/coreclr/src/vm/qcall.cpp
index e46ab2268c6b12..497cdff7adf000 100644
--- a/src/coreclr/src/vm/qcall.cpp
+++ b/src/coreclr/src/vm/qcall.cpp
@@ -70,7 +70,7 @@ void QCall::ObjectHandleOnStack::SetGuidArray(const GUID * p, COUNT_T length)
 
     GCX_COOP();
 
-    ::TypeHandle typeHandle = MscorlibBinder::GetClass(CLASS__GUID);
+    ::TypeHandle typeHandle = CoreLibBinder::GetClass(CLASS__GUID);
     BASEARRAYREF arr = (BASEARRAYREF) AllocateSzArray(typeHandle.MakeSZArray(), length);
     memcpyNoGCRefs(arr->GetDataPtr(), p, length * sizeof(GUID));
     Set(arr);
diff --git a/src/coreclr/src/vm/qcall.h b/src/coreclr/src/vm/qcall.h
index 581aefe4cf8319..2517f59953bb3d 100644
--- a/src/coreclr/src/vm/qcall.h
+++ b/src/coreclr/src/vm/qcall.h
@@ -13,8 +13,8 @@
 // QCALLS
 //
 
-// QCalls are internal calls from managed code in mscorlib.dll to unmanaged code in mscorwks.dll. QCalls are very much like
-// a normal P/Invoke from mscorlib.dll to mscorwks.dll.
+// QCalls are internal calls from managed code in CoreLib to unmanaged code in VM. QCalls are very much like
+// a normal P/Invoke from CoreLib to VM.
 //
 // Unlike FCalls, QCalls will marshal all arguments as unmanaged types like a normal P/Invoke. QCall also switch to preemptive
 // GC mode like a normal P/Invoke. These two features should make QCalls easier to write reliably compared to FCalls.
diff --git a/src/coreclr/src/vm/readytoruninfo.cpp b/src/coreclr/src/vm/readytoruninfo.cpp
index 06d238b44b6c58..72a559ab509174 100644
--- a/src/coreclr/src/vm/readytoruninfo.cpp
+++ b/src/coreclr/src/vm/readytoruninfo.cpp
@@ -830,6 +830,8 @@ PCODE ReadyToRunInfo::GetEntryPoint(MethodDesc * pMD, PrepareCodeConfig* pConfig
     if (m_readyToRunCodeDisabled)
         goto done;
 
+    ETW::MethodLog::GetR2RGetEntryPointStart(pMD);
+
     uint offset;
     if (pMD->HasClassOrMethodInstantiation())
     {
diff --git a/src/coreclr/src/vm/reflectioninvocation.cpp b/src/coreclr/src/vm/reflectioninvocation.cpp
index 41ce136349bed3..4ea56e358a7403 100644
--- a/src/coreclr/src/vm/reflectioninvocation.cpp
+++ b/src/coreclr/src/vm/reflectioninvocation.cpp
@@ -200,7 +200,7 @@ FCIMPL2(FC_BOOL_RET, ReflectionInvocation::CanValueSpecialCast, ReflectClassBase
     // the field type is a pointer
     if (targetCorElement == ELEMENT_TYPE_PTR || targetCorElement == ELEMENT_TYPE_FNPTR) {
         // the object must be an IntPtr or a System.Reflection.Pointer
-        if (valueType == TypeHandle(MscorlibBinder::GetClass(CLASS__INTPTR))) {
+        if (valueType == TypeHandle(CoreLibBinder::GetClass(CLASS__INTPTR))) {
             //
             // it's an IntPtr, it's good.
         }
@@ -1679,7 +1679,7 @@ FCIMPL5(void, RuntimeFieldHandle::SetValueDirect, ReflectFieldObject *pFieldUNSA
     case ELEMENT_TYPE_PTR:      // pointers
         if (gc.oValue != 0) {
             value = 0;
-            if (MscorlibBinder::IsClass(gc.oValue->GetMethodTable(), CLASS__POINTER)) {
+            if (CoreLibBinder::IsClass(gc.oValue->GetMethodTable(), CLASS__POINTER)) {
                 value = (size_t) InvokeUtil::GetPointerValue(gc.oValue);
 #ifdef _MSC_VER
 #pragma warning(disable: 4267) //work-around for compiler
@@ -2368,7 +2368,7 @@ FCIMPL1(Object *, ReflectionEnum::InternalGetEnumUnderlyingType, ReflectClassBas
     OBJECTREF result = NULL;
 
     HELPER_METHOD_FRAME_BEGIN_RET_0();
-    MethodTable *pMT = MscorlibBinder::GetElementType(th.AsMethodTable()->GetInternalCorElementType());
+    MethodTable *pMT = CoreLibBinder::GetElementType(th.AsMethodTable()->GetInternalCorElementType());
     result = pMT->GetManagedClassObject();
     HELPER_METHOD_FRAME_END();
 
@@ -2391,7 +2391,6 @@ FCIMPL1(INT32, ReflectionEnum::InternalGetCorElementType, Object *pRefThis) {
     return pMT->GetClass_NoLogging()->GetInternalCorElementType();
 }
 FCIMPLEND
-#include <optdefault.h>
 
 //*******************************************************************************
 struct TempEnumValue
@@ -2647,7 +2646,7 @@ FCIMPL2(FC_BOOL_RET, ReflectionEnum::InternalEquals, Object *pRefThis, Object* p
 }
 FCIMPLEND
 
-// preform (this & flags) != flags
+// perform (this & flags) == flags
 FCIMPL2(FC_BOOL_RET, ReflectionEnum::InternalHasFlag, Object *pRefThis, Object* pRefFlags)
 {
     FCALL_CONTRACT;
diff --git a/src/coreclr/src/vm/rejit.cpp b/src/coreclr/src/vm/rejit.cpp
index d9077a370ff605..ff180ceba33ae2 100644
--- a/src/coreclr/src/vm/rejit.cpp
+++ b/src/coreclr/src/vm/rejit.cpp
@@ -643,7 +643,7 @@ HRESULT ReJitManager::UpdateActiveILVersions(
     SHash<CodeActivationBatchTraits>::Iterator endIter = mgrToCodeActivationBatch.End();
 
     {
-        MethodDescBackpatchInfoTracker::ConditionalLockHolder slotBackpatchLockHolder;
+        MethodDescBackpatchInfoTracker::ConditionalLockHolderForGCCoop slotBackpatchLockHolder;
 
         for (SHash<CodeActivationBatchTraits>::Iterator iter = beginIter; iter != endIter; iter++)
         {
diff --git a/src/coreclr/src/vm/rexcep.h b/src/coreclr/src/vm/rexcep.h
index 03cfa3617f9ada..da7686af64e110 100644
--- a/src/coreclr/src/vm/rexcep.h
+++ b/src/coreclr/src/vm/rexcep.h
@@ -279,14 +279,4 @@ DEFINE_EXCEPTION(g_SystemNS,           OutOfMemoryException,           false,  E
 
 DEFINE_EXCEPTION(g_SystemNS,           ArgumentNullException,          false,  E_POINTER)
 
-#define kLastExceptionInMscorlib kArgumentNullException
-
-//
-// All exceptions defined in other .NET Framework assemblies have to be at the end
-//
-
-
-
-// Please see comments on at the top of this list
-
 #undef DEFINE_EXCEPTION
diff --git a/src/coreclr/src/vm/runtimecallablewrapper.cpp b/src/coreclr/src/vm/runtimecallablewrapper.cpp
index 05bbc24938bf1c..16d7e5e86302b4 100644
--- a/src/coreclr/src/vm/runtimecallablewrapper.cpp
+++ b/src/coreclr/src/vm/runtimecallablewrapper.cpp
@@ -2248,9 +2248,9 @@ HRESULT RCW::SafeQueryInterfaceRemoteAware(REFIID iid, IUnknown** ppResUnk)
 #endif //#ifndef CROSSGEN_COMPILE
 
 // Helper method to allow us to compare a MethodTable against a known method table
-// from mscorlib.  If the mscorlib type isn't loaded, we don't load it because we
+// from CoreLib.  If the CoreLib type isn't loaded, we don't load it because we
 // know that it can't be the MethodTable we're curious about.
-static bool MethodTableHasSameTypeDefAsMscorlibClass(MethodTable* pMT, BinderClassID classId)
+static bool MethodTableHasSameTypeDefAsCoreLibClass(MethodTable* pMT, BinderClassID classId)
 {
     CONTRACTL
     {
@@ -2260,11 +2260,11 @@ static bool MethodTableHasSameTypeDefAsMscorlibClass(MethodTable* pMT, BinderCla
     }
     CONTRACTL_END;
 
-    MethodTable* pMT_MscorlibClass = MscorlibBinder::GetClassIfExist(classId);
-    if (pMT_MscorlibClass == NULL)
+    MethodTable* pMT_CoreLibClass = CoreLibBinder::GetClassIfExist(classId);
+    if (pMT_CoreLibClass == NULL)
         return false;
 
-    return (pMT->HasSameTypeDefAs(pMT_MscorlibClass) != FALSE);
+    return (pMT->HasSameTypeDefAs(pMT_CoreLibClass) != FALSE);
 }
 
 #ifndef CROSSGEN_COMPILE
@@ -2542,7 +2542,7 @@ bool RCW::SupportsMngStdInterface(MethodTable *pItfMT)
 
         // If the requested interface is IEnumerable then we need to check to see if the
         // COM object implements IDispatch and has a member with DISPID_NEWENUM.
-        if (pItfMT == MscorlibBinder::GetClass(CLASS__IENUMERABLE))
+        if (pItfMT == CoreLibBinder::GetClass(CLASS__IENUMERABLE))
         {
             SafeComHolder<IDispatch> pDisp = GetIDispatch();
             if (pDisp)
@@ -2824,7 +2824,7 @@ void ComObject::ThrowInvalidCastException(OBJECTREF *pObj, MethodTable *pCastToM
             COMPlusThrow(kInvalidCastException, IDS_EE_RCW_INVALIDCAST_EVENTITF, strHRDescription.GetUnicode(), strComObjClassName.GetUnicode(),
                 strCastToName.GetUnicode(), strIID, strSrcItfIID);
         }
-        else if (thCastTo == TypeHandle(MscorlibBinder::GetClass(CLASS__IENUMERABLE)))
+        else if (thCastTo == TypeHandle(CoreLibBinder::GetClass(CLASS__IENUMERABLE)))
         {
             COMPlusThrow(kInvalidCastException, IDS_EE_RCW_INVALIDCAST_IENUMERABLE,
                 strHRDescription.GetUnicode(), strComObjClassName.GetUnicode(), strCastToName.GetUnicode(), strIID);
diff --git a/src/coreclr/src/vm/runtimehandles.cpp b/src/coreclr/src/vm/runtimehandles.cpp
index b34ee5c6023a34..14787a7faefc07 100644
--- a/src/coreclr/src/vm/runtimehandles.cpp
+++ b/src/coreclr/src/vm/runtimehandles.cpp
@@ -736,7 +736,7 @@ PTRARRAYREF CopyRuntimeTypeHandles(TypeHandle * prgTH, FixupPointer<TypeHandle>
     }
 
     GCPROTECT_BEGIN(refArray);
-    TypeHandle thRuntimeType = TypeHandle(MscorlibBinder::GetClass(arrayElemType));
+    TypeHandle thRuntimeType = TypeHandle(CoreLibBinder::GetClass(arrayElemType));
     TypeHandle arrayHandle = ClassLoader::LoadArrayTypeThrowing(thRuntimeType, ELEMENT_TYPE_SZARRAY);
     refArray = (PTRARRAYREF)AllocateSzArray(arrayHandle, numTypeHandles);
 
@@ -1954,7 +1954,7 @@ FCIMPL3(Object *, SignatureNative::GetCustomModifiers, SignatureNative* pSignatu
         // modifiers now that we know how long they should be.
         sp = argument;
 
-        MethodTable *pMT = MscorlibBinder::GetClass(CLASS__TYPE);
+        MethodTable *pMT = CoreLibBinder::GetClass(CLASS__TYPE);
         TypeHandle arrayHandle = ClassLoader::LoadArrayTypeThrowing(TypeHandle(pMT), ELEMENT_TYPE_SZARRAY);
 
         gc.retVal = (PTRARRAYREF) AllocateSzArray(arrayHandle, cMods);
@@ -2466,10 +2466,10 @@ FCIMPL2(RuntimeMethodBody *, RuntimeMethodHandle::GetMethodBody, ReflectMethodOb
 
         if (pILHeader)
         {
-            MethodTable * pExceptionHandlingClauseMT = MscorlibBinder::GetClass(CLASS__RUNTIME_EH_CLAUSE);
+            MethodTable * pExceptionHandlingClauseMT = CoreLibBinder::GetClass(CLASS__RUNTIME_EH_CLAUSE);
             TypeHandle thEHClauseArray = ClassLoader::LoadArrayTypeThrowing(TypeHandle(pExceptionHandlingClauseMT), ELEMENT_TYPE_SZARRAY);
 
-            MethodTable * pLocalVariableMT = MscorlibBinder::GetClass(CLASS__RUNTIME_LOCAL_VARIABLE_INFO);
+            MethodTable * pLocalVariableMT = CoreLibBinder::GetClass(CLASS__RUNTIME_LOCAL_VARIABLE_INFO);
             TypeHandle thLocalVariableArray = ClassLoader::LoadArrayTypeThrowing(TypeHandle(pLocalVariableMT), ELEMENT_TYPE_SZARRAY);
 
             Module* pModule = pMethod->GetModule();
@@ -2489,7 +2489,7 @@ FCIMPL2(RuntimeMethodBody *, RuntimeMethodHandle::GetMethodBody, ReflectMethodOb
                 }
             }
 
-            gc.MethodBodyObj = (RUNTIMEMETHODBODYREF)AllocateObject(MscorlibBinder::GetClass(CLASS__RUNTIME_METHOD_BODY));
+            gc.MethodBodyObj = (RUNTIMEMETHODBODYREF)AllocateObject(CoreLibBinder::GetClass(CLASS__RUNTIME_METHOD_BODY));
 
             gc.MethodBodyObj->_maxStackSize = header.GetMaxStack();
             gc.MethodBodyObj->_initLocals = !!(header.GetFlags() & CorILMethod_InitLocals);
diff --git a/src/coreclr/src/vm/safehandle.cpp b/src/coreclr/src/vm/safehandle.cpp
index 44c1f40766e527..38ee027a41f24d 100644
--- a/src/coreclr/src/vm/safehandle.cpp
+++ b/src/coreclr/src/vm/safehandle.cpp
@@ -41,10 +41,10 @@ void SafeHandle::Init()
     // methods involves calling .GetMethod which can fail, we are doing this
     // eagerly here, Otherwise we will have to do it at the time of the call,
     // and this could be at risk if .GetMethod failed.
-    MethodDesc* pMD = MscorlibBinder::GetMethod(METHOD__SAFE_HANDLE__GET_IS_INVALID);
+    MethodDesc* pMD = CoreLibBinder::GetMethod(METHOD__SAFE_HANDLE__GET_IS_INVALID);
     s_IsInvalidHandleMethodSlot = pMD->GetSlot();
 
-    pMD = MscorlibBinder::GetMethod(METHOD__SAFE_HANDLE__RELEASE_HANDLE);
+    pMD = CoreLibBinder::GetMethod(METHOD__SAFE_HANDLE__RELEASE_HANDLE);
     s_ReleaseHandleMethodSlot = pMD->GetSlot();
 }
 
diff --git a/src/coreclr/src/vm/siginfo.cpp b/src/coreclr/src/vm/siginfo.cpp
index ba2906f385ea42..5cdeb7af5decf1 100644
--- a/src/coreclr/src/vm/siginfo.cpp
+++ b/src/coreclr/src/vm/siginfo.cpp
@@ -728,12 +728,12 @@ MetaSig::MetaSig(BinderMethodID id)
     }
     CONTRACTL_END
 
-    Signature sig = MscorlibBinder::GetMethodSignature(id);
+    Signature sig = CoreLibBinder::GetMethodSignature(id);
 
-    _ASSERTE(MethodDescMatchesSig(MscorlibBinder::GetMethod(id),
-        sig.GetRawSig(), sig.GetRawSigLen(), MscorlibBinder::GetModule()));
+    _ASSERTE(MethodDescMatchesSig(CoreLibBinder::GetMethod(id),
+        sig.GetRawSig(), sig.GetRawSigLen(), CoreLibBinder::GetModule()));
 
-    Init(sig.GetRawSig(), sig.GetRawSigLen(), MscorlibBinder::GetModule(), NULL);
+    Init(sig.GetRawSig(), sig.GetRawSigLen(), CoreLibBinder::GetModule(), NULL);
 }
 
 MetaSig::MetaSig(LPHARDCODEDMETASIG pwzMetaSig)
@@ -748,9 +748,9 @@ MetaSig::MetaSig(LPHARDCODEDMETASIG pwzMetaSig)
     }
     CONTRACTL_END
 
-    Signature sig = MscorlibBinder::GetSignature(pwzMetaSig);
+    Signature sig = CoreLibBinder::GetSignature(pwzMetaSig);
 
-    Init(sig.GetRawSig(), sig.GetRawSigLen(), MscorlibBinder::GetModule(), NULL);
+    Init(sig.GetRawSig(), sig.GetRawSigLen(), CoreLibBinder::GetModule(), NULL);
 }
 
 // Helper constructor that constructs a field signature MetaSig from a FieldDesc
@@ -1086,7 +1086,7 @@ TypeHandle SigPointer::GetTypeHandleThrowing(
         // case ELEMENT_TYPE_STRING   = 0x0e,
         // case ELEMENT_TYPE_OBJECT   = 0x1c,
         //
-        thRet = TypeHandle(MscorlibBinder::GetElementType(typ));
+        thRet = TypeHandle(CoreLibBinder::GetElementType(typ));
     }
     else
     {
@@ -1288,7 +1288,7 @@ TypeHandle SigPointer::GetTypeHandleThrowing(
                 pGenericTypeModule = pModule;
             }
 
-            TypeHandle genericType = psig.GetGenericInstType(pModule, fLoadTypes, level, pZapSigContext);
+            TypeHandle genericType = psig.GetGenericInstType(pModule, fLoadTypes, level < CLASS_LOAD_APPROXPARENTS ? level : CLASS_LOAD_APPROXPARENTS, pZapSigContext);
 
             if (genericType.IsNull())
             {
@@ -1479,7 +1479,7 @@ TypeHandle SigPointer::GetTypeHandleThrowing(
             {
                 if (TypeFromToken(typeToken) == mdtTypeRef)
                 {
-                        loadedType = TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_VOID));
+                        loadedType = TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_VOID));
                         thRet = loadedType;
                         break;
                 }
@@ -2372,7 +2372,7 @@ CorElementType SigPointer::PeekElemTypeNormalized(Module* pModule, const SigType
             TypeHandle th = GetTypeHandleThrowing(pModule, pTypeContext, ClassLoader::LoadTypes, CLASS_LOAD_APPROXPARENTS, TRUE);
             if(th.IsNull())
             {
-                th = TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_VOID));
+                th = TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_VOID));
             }
 
             type = th.GetInternalCorElementType();
@@ -4613,9 +4613,9 @@ MetaSig::CompareElementTypeToToken(
     }
 
     return CompareTypeTokens(
-        MscorlibBinder::GetElementType(Type1)->GetCl(),
+        CoreLibBinder::GetElementType(Type1)->GetCl(),
         tk2,
-        MscorlibBinder::GetModule(),
+        CoreLibBinder::GetModule(),
         pModule2,
         pVisited);
 } // MetaSig::CompareElementTypeToToken
@@ -4765,10 +4765,10 @@ BOOL MetaSig::CompareVariableConstraints(const Substitution *pSubst1,
         // a) are vacuous, and
         // b) may be implicit (ie. absent) in the overriden variable's declaration
         if (!(CompareTypeDefOrRefOrSpec(pModule1, tkConstraintType1, NULL,
-                                       MscorlibBinder::GetModule(), g_pObjectClass->GetCl(), NULL, NULL) ||
+                                       CoreLibBinder::GetModule(), g_pObjectClass->GetCl(), NULL, NULL) ||
           (((specialConstraints1 & gpNotNullableValueTypeConstraint) != 0) &&
            (CompareTypeDefOrRefOrSpec(pModule1, tkConstraintType1, NULL,
-                      MscorlibBinder::GetModule(), g_pValueTypeClass->GetCl(), NULL, NULL)))))
+                      CoreLibBinder::GetModule(), g_pValueTypeClass->GetCl(), NULL, NULL)))))
         {
             HENUMInternalHolder hEnum2(pInternalImport2);
             mdGenericParamConstraint tkConstraint2;
@@ -4900,6 +4900,16 @@ void PromoteCarefully(promote_func   fn,
         return;
     }
 
+#ifndef CROSSGEN_COMPILE
+    if (sc->promotion)
+    {
+        LoaderAllocator*pLoaderAllocator = LoaderAllocator::GetAssociatedLoaderAllocator_Unsafe(PTR_TO_TADDR(*ppObj));
+        if (pLoaderAllocator != NULL)
+        {
+            GcReportLoaderAllocator(fn, sc, pLoaderAllocator);
+        }
+    }
+#endif // CROSSGEN_COMPILE
 #endif // !defined(DACCESS_COMPILE)
 
     (*fn) (ppObj, sc, flags);
@@ -5267,7 +5277,8 @@ MetaSig::TryGetUnmanagedCallingConventionFromModOpt(
     _In_ Module *pModule,
     _In_ PCCOR_SIGNATURE pSig,
     _In_ ULONG cSig,
-    _Out_ CorUnmanagedCallingConvention *callConvOut)
+    _Out_ CorUnmanagedCallingConvention *callConvOut,
+    _Out_ UINT *errorResID)
 {
     CONTRACTL
     {
@@ -5276,6 +5287,7 @@ MetaSig::TryGetUnmanagedCallingConventionFromModOpt(
         FORBID_FAULT;
         MODE_ANY;
         PRECONDITION(callConvOut != NULL);
+        PRECONDITION(errorResID != NULL);
     }
     CONTRACTL_END
 
@@ -5285,13 +5297,17 @@ MetaSig::TryGetUnmanagedCallingConventionFromModOpt(
     _ASSERTE(pWalk <= pSig + cSig);
 
     *callConvOut = (CorUnmanagedCallingConvention)0;
+    bool found = false;
     while ((pWalk < (pSig + cSig)) && ((*pWalk == ELEMENT_TYPE_CMOD_OPT) || (*pWalk == ELEMENT_TYPE_CMOD_REQD)))
     {
         BOOL fIsOptional = (*pWalk == ELEMENT_TYPE_CMOD_OPT);
 
         pWalk++;
         if (pWalk + CorSigUncompressedDataSize(pWalk) > pSig + cSig)
-            return E_FAIL; // Bad formatting
+        {
+            *errorResID = BFA_BAD_SIGNATURE;
+            return COR_E_BADIMAGEFORMAT; // Bad formatting
+        }
 
         mdToken tk;
         pWalk += CorSigUncompressToken(pWalk, &tk);
@@ -5320,16 +5336,23 @@ MetaSig::TryGetUnmanagedCallingConventionFromModOpt(
 
         for (const auto &callConv : knownCallConvs)
         {
-            // Take the first recognized calling convention in metadata.
+            // Look for a recognized calling convention in metadata.
             if (::strcmp(typeName, callConv.name) == 0)
             {
+                // Error if there are multiple recognized calling conventions
+                if (found)
+                {
+                    *errorResID = IDS_EE_MULTIPLE_CALLCONV_UNSUPPORTED;
+                    return COR_E_INVALIDPROGRAM;
+                }
+
                 *callConvOut = callConv.value;
-                return S_OK;
+                found = true;
             }
         }
     }
 
-    return S_FALSE;
+    return found ? S_OK : S_FALSE;
 }
 
 //---------------------------------------------------------------------------------------
diff --git a/src/coreclr/src/vm/siginfo.hpp b/src/coreclr/src/vm/siginfo.hpp
index 64c9341e693e91..c2f68e1dd755b4 100644
--- a/src/coreclr/src/vm/siginfo.hpp
+++ b/src/coreclr/src/vm/siginfo.hpp
@@ -566,7 +566,7 @@ class MetaSig
 
         MetaSig(FieldDesc *pFD, TypeHandle declaringType = TypeHandle());
 
-        // Used to avoid touching metadata for mscorlib methods.  Nb. only use for non-generic methods.
+        // Used to avoid touching metadata for CoreLib methods.  Nb. only use for non-generic methods.
         MetaSig(BinderMethodID id);
 
         MetaSig(LPHARDCODEDMETASIG pwzMetaSig);
@@ -781,20 +781,20 @@ class MetaSig
 
         //----------------------------------------------------------
         // Gets the unmanaged calling convention by reading any modopts.
-        // If there are multiple modopts specifying recognized calling
-        // conventions, the first one that is found in the metadata wins.
-        // Note: the order in the metadata is the reverse of that in IL.
         //
         // Returns:
-        //   E_FAIL - Signature had an invalid format
         //   S_OK - Calling convention was read from modopt
         //   S_FALSE - Calling convention was not read from modopt
+        //   COR_E_BADIMAGEFORMAT - Signature had an invalid format
+        //   COR_E_INVALIDPROGRAM - Program is considered invalid (more
+        //                          than one calling convention specified)
         //----------------------------------------------------------
         static HRESULT TryGetUnmanagedCallingConventionFromModOpt(
             _In_ Module *pModule,
             _In_ PCCOR_SIGNATURE pSig,
             _In_ ULONG cSig,
-            _Out_ CorUnmanagedCallingConvention *callConvOut);
+            _Out_ CorUnmanagedCallingConvention *callConvOut,
+            _Out_ UINT *errorResID);
 
         static CorUnmanagedCallingConvention GetDefaultUnmanagedCallingConvention()
         {
diff --git a/src/coreclr/src/vm/staticallocationhelpers.inl b/src/coreclr/src/vm/staticallocationhelpers.inl
index eba82d7ad24af4..a9047ba8f87188 100644
--- a/src/coreclr/src/vm/staticallocationhelpers.inl
+++ b/src/coreclr/src/vm/staticallocationhelpers.inl
@@ -20,7 +20,7 @@ static CorElementType ParseMetadataForStaticsIsValueTypeEnum(Module * pModule, I
     if (TypeFromToken(tk) != mdtTypeDef)
     {
         // At this point, we would have to load other assemblies. The only one we have guaranteed
-        // to be there is mscorlib.
+        // to be there is CoreLib.
         return ELEMENT_TYPE_END;
     }
 
diff --git a/src/coreclr/src/vm/stdinterfaces.cpp b/src/coreclr/src/vm/stdinterfaces.cpp
index d01a98efd80c16..1913546164cee8 100644
--- a/src/coreclr/src/vm/stdinterfaces.cpp
+++ b/src/coreclr/src/vm/stdinterfaces.cpp
@@ -56,7 +56,7 @@ static const GUID LIBID_STDOLE2 = { 0x00020430, 0x0000, 0x0000, { 0xc0, 0x00, 0x
 
 // Until the Windows SDK is updated, just hard-code the IAgileObject IID
 #ifndef __IAgileObject_INTERFACE_DEFINED__
-EXTERN_C SELECTANY const GUID IID_IAgileObject = { 0x94ea2b94, 0xe9cc, 0x49e0, { 0xc0, 0xff, 0xee, 0x64, 0xca, 0x8f, 0x5b, 0x90 } };
+EXTERN_C const GUID IID_IAgileObject = { 0x94ea2b94, 0xe9cc, 0x49e0, { 0xc0, 0xff, 0xee, 0x64, 0xca, 0x8f, 0x5b, 0x90 } };
 #endif // !__IAgileObject_INTERFACE_DEFINED__
 
 // Until the Windows SDK is updated, just hard-code the INoMarshal IID
diff --git a/src/coreclr/src/vm/stubgen.cpp b/src/coreclr/src/vm/stubgen.cpp
index 1be173a1888cad..d11d969fb36da1 100644
--- a/src/coreclr/src/vm/stubgen.cpp
+++ b/src/coreclr/src/vm/stubgen.cpp
@@ -133,7 +133,7 @@ void ILStubLinker::DumpIL_FormatToken(mdToken token, SString &strTokenFormatting
                 sig.GetSignature(&pSig, &cbSig);
             }
 
-            IMDInternalImport * pIMDI = MscorlibBinder::GetModule()->GetMDImport();
+            IMDInternalImport * pIMDI = CoreLibBinder::GetModule()->GetMDImport();
             CQuickBytes sigStr;
             PrettyPrintSig(pSig, cbSig, "", &sigStr, pIMDI, NULL);
 
@@ -1822,28 +1822,28 @@ void ILCodeStream::EmitUNALIGNED(BYTE alignment)
 void ILCodeStream::EmitNEWOBJ(BinderMethodID id, int numInArgs)
 {
     STANDARD_VM_CONTRACT;
-    EmitNEWOBJ(GetToken(MscorlibBinder::GetMethod(id)), numInArgs);
+    EmitNEWOBJ(GetToken(CoreLibBinder::GetMethod(id)), numInArgs);
 }
 
 void ILCodeStream::EmitCALL(BinderMethodID id, int numInArgs, int numRetArgs)
 {
     STANDARD_VM_CONTRACT;
-    EmitCALL(GetToken(MscorlibBinder::GetMethod(id)), numInArgs, numRetArgs);
+    EmitCALL(GetToken(CoreLibBinder::GetMethod(id)), numInArgs, numRetArgs);
 }
 void ILCodeStream::EmitLDFLD(BinderFieldID id)
 {
     STANDARD_VM_CONTRACT;
-    EmitLDFLD(GetToken(MscorlibBinder::GetField(id)));
+    EmitLDFLD(GetToken(CoreLibBinder::GetField(id)));
 }
 void ILCodeStream::EmitSTFLD(BinderFieldID id)
 {
     STANDARD_VM_CONTRACT;
-    EmitSTFLD(GetToken(MscorlibBinder::GetField(id)));
+    EmitSTFLD(GetToken(CoreLibBinder::GetField(id)));
 }
 void ILCodeStream::EmitLDFLDA(BinderFieldID id)
 {
     STANDARD_VM_CONTRACT;
-    EmitLDFLDA(GetToken(MscorlibBinder::GetField(id)));
+    EmitLDFLDA(GetToken(CoreLibBinder::GetField(id)));
 }
 
 void ILStubLinker::SetHasThis (bool fHasThis)
@@ -1881,7 +1881,7 @@ void ILCodeStream::EmitArgIteratorCreateAndLoad()
     //
     // we insert the ArgIterator in the same spot that the VASigCookie will go for sanity
     //
-    LocalDesc   aiLoc(MscorlibBinder::GetClass(CLASS__ARG_ITERATOR));
+    LocalDesc   aiLoc(CoreLibBinder::GetClass(CLASS__ARG_ITERATOR));
     int         aiLocNum;
 
     aiLocNum = NewLocal(aiLoc);
@@ -1895,7 +1895,7 @@ void ILCodeStream::EmitArgIteratorCreateAndLoad()
     aiLoc.ElementType[0]    = ELEMENT_TYPE_BYREF;
     aiLoc.ElementType[1]    = ELEMENT_TYPE_INTERNAL;
     aiLoc.cbType            = 2;
-    aiLoc.InternalToken     = MscorlibBinder::GetClass(CLASS__ARG_ITERATOR);
+    aiLoc.InternalToken     = CoreLibBinder::GetClass(CLASS__ARG_ITERATOR);
 
     SetStubTargetArgType(&aiLoc, false);
 }
diff --git a/src/coreclr/src/vm/stubmgr.h b/src/coreclr/src/vm/stubmgr.h
index d36db9f9009f23..471f456cf3260b 100644
--- a/src/coreclr/src/vm/stubmgr.h
+++ b/src/coreclr/src/vm/stubmgr.h
@@ -47,6 +47,7 @@
 #define __stubmgr_h__
 
 #include "simplerwlock.hpp"
+#include "lockedrangelist.h"
 
 // When 'TraceStub' returns, it gives the address of where the 'target' is for a stub'
 // TraceType indicates what this 'target' is
@@ -339,53 +340,6 @@ class StubManager
 #endif // !CROSSGEN_COMPILE
 };
 
-// -------------------------------------------------------
-// This just wraps the RangeList methods in a read or
-// write lock depending on the operation.
-// -------------------------------------------------------
-
-class LockedRangeList : public RangeList
-{
-  public:
-    VPTR_VTABLE_CLASS(LockedRangeList, RangeList)
-
-    LockedRangeList() : RangeList(), m_RangeListRWLock(COOPERATIVE_OR_PREEMPTIVE, LOCK_TYPE_DEFAULT)
-    {
-        LIMITED_METHOD_CONTRACT;
-    }
-
-    ~LockedRangeList()
-    {
-        LIMITED_METHOD_CONTRACT;
-    }
-
-  protected:
-
-    virtual BOOL AddRangeWorker(const BYTE *start, const BYTE *end, void *id)
-    {
-        WRAPPER_NO_CONTRACT;
-        SimpleWriteLockHolder lh(&m_RangeListRWLock);
-        return RangeList::AddRangeWorker(start,end,id);
-    }
-
-    virtual void RemoveRangesWorker(void *id, const BYTE *start = NULL, const BYTE *end = NULL)
-    {
-        WRAPPER_NO_CONTRACT;
-        SimpleWriteLockHolder lh(&m_RangeListRWLock);
-        RangeList::RemoveRangesWorker(id,start,end);
-    }
-
-    virtual BOOL IsInRangeWorker(TADDR address, TADDR *pID = NULL)
-    {
-        WRAPPER_NO_CONTRACT;
-        SUPPORTS_DAC;
-        SimpleReadLockHolder lh(&m_RangeListRWLock);
-        return RangeList::IsInRangeWorker(address, pID);
-    }
-
-    SimpleRWLock m_RangeListRWLock;
-};
-
 #ifndef CROSSGEN_COMPILE
 
 //-----------------------------------------------------------
diff --git a/src/coreclr/src/vm/tailcallhelp.cpp b/src/coreclr/src/vm/tailcallhelp.cpp
index 70dee8e5d867c0..0db1330b7b3c0e 100644
--- a/src/coreclr/src/vm/tailcallhelp.cpp
+++ b/src/coreclr/src/vm/tailcallhelp.cpp
@@ -119,7 +119,7 @@ MethodDesc* TailCallHelp::GetOrLoadTailCallDispatcherMD()
     CONTRACTL_END;
 
     if (s_tailCallDispatcherMD == NULL)
-        s_tailCallDispatcherMD = MscorlibBinder::GetMethod(METHOD__RUNTIME_HELPERS__DISPATCH_TAILCALLS);
+        s_tailCallDispatcherMD = CoreLibBinder::GetMethod(METHOD__RUNTIME_HELPERS__DISPATCH_TAILCALLS);
 
     return s_tailCallDispatcherMD;
 }
@@ -183,7 +183,7 @@ void TailCallHelp::LayOutArgBuffer(
         bool thisParamByRef = (calleeMD != NULL) ? calleeMD->GetMethodTable()->IsValueType() : thisArgByRef;
         if (thisParamByRef)
         {
-            thisHnd = TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_U1))
+            thisHnd = TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_U1))
                       .MakeByRef();
         }
         else
@@ -226,16 +226,16 @@ TypeHandle TailCallHelp::NormalizeSigType(TypeHandle tyHnd)
     }
     if (CorTypeInfo::IsObjRef(ety))
     {
-        return TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_OBJECT));
+        return TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_OBJECT));
     }
     if (tyHnd.IsPointer() || tyHnd.IsFnPtrType())
     {
-        return TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_I));
+        return TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_I));
     }
 
     if (tyHnd.IsByRef())
     {
-        return TypeHandle(MscorlibBinder::GetElementType(ELEMENT_TYPE_U1))
+        return TypeHandle(CoreLibBinder::GetElementType(ELEMENT_TYPE_U1))
                .MakeByRef();
     }
 
diff --git a/src/coreclr/src/vm/threads.cpp b/src/coreclr/src/vm/threads.cpp
index 32cc52c6f220ae..9dae20e9d487a0 100644
--- a/src/coreclr/src/vm/threads.cpp
+++ b/src/coreclr/src/vm/threads.cpp
@@ -510,10 +510,14 @@ void Thread::ChooseThreadCPUGroupAffinity()
         GC_TRIGGERS;
     }
     CONTRACTL_END;
-#ifndef TARGET_UNIX
-    if (!CPUGroupInfo::CanEnableGCCPUGroups() || !CPUGroupInfo::CanEnableThreadUseAllCpuGroups())
-         return;
 
+#ifndef TARGET_UNIX
+    if (!CPUGroupInfo::CanEnableGCCPUGroups() ||
+        !CPUGroupInfo::CanEnableThreadUseAllCpuGroups() ||
+        !CPUGroupInfo::CanAssignCpuGroupsToThreads())
+    {
+        return;
+    }
 
     //Borrow the ThreadStore Lock here: Lock ThreadStore before distributing threads
     ThreadStoreLockHolder TSLockHolder(TRUE);
@@ -541,10 +545,14 @@ void Thread::ClearThreadCPUGroupAffinity()
         GC_NOTRIGGER;
     }
     CONTRACTL_END;
-#ifndef TARGET_UNIX
-    if (!CPUGroupInfo::CanEnableGCCPUGroups() || !CPUGroupInfo::CanEnableThreadUseAllCpuGroups())
-         return;
 
+#ifndef TARGET_UNIX
+    if (!CPUGroupInfo::CanEnableGCCPUGroups() ||
+        !CPUGroupInfo::CanEnableThreadUseAllCpuGroups() ||
+        !CPUGroupInfo::CanAssignCpuGroupsToThreads())
+    {
+        return;
+    }
 
     ThreadStoreLockHolder TSLockHolder(TRUE);
 
@@ -1598,6 +1606,7 @@ Thread::Thread()
     m_DeserializationTracker = NULL;
 
     m_currentPrepareCodeConfig = nullptr;
+    m_isInForbidSuspendForDebuggerRegion = false;
 
 #ifdef _DEBUG
     memset(dangerousObjRefs, 0, sizeof(dangerousObjRefs));
@@ -1992,7 +2001,7 @@ void Thread::HandleThreadStartupFailure()
 
     GCPROTECT_BEGIN(args);
 
-    MethodTable *pMT = MscorlibBinder::GetException(kThreadStartException);
+    MethodTable *pMT = CoreLibBinder::GetException(kThreadStartException);
     args.pThrowable = AllocateObject(pMT);
 
     MethodDescCallSite exceptionCtor(METHOD__THREAD_START_EXCEPTION__EX_CTOR);
@@ -7844,7 +7853,7 @@ OBJECTREF Thread::GetCulture(BOOL bUICulture)
     }
     CONTRACTL_END;
 
-    // This is the case when we're building mscorlib and haven't yet created
+    // This is the case when we're building CoreLib and haven't yet created
     // the system assembly.
     if (SystemDomain::System()->SystemAssembly()==NULL || g_fForbidEnterEE) {
         return NULL;
@@ -8591,7 +8600,7 @@ OBJECTHANDLE Thread::GetOrCreateDeserializationTracker()
 
     _ASSERTE(this == GetThread());
 
-    MethodTable* pMT = MscorlibBinder::GetClass(CLASS__DESERIALIZATION_TRACKER);
+    MethodTable* pMT = CoreLibBinder::GetClass(CLASS__DESERIALIZATION_TRACKER);
     m_DeserializationTracker = CreateGlobalStrongHandle(AllocateObject(pMT));
 
     _ASSERTE(m_DeserializationTracker != NULL);
diff --git a/src/coreclr/src/vm/threads.h b/src/coreclr/src/vm/threads.h
index b835b4a6321c92..03aea2ea03cee8 100644
--- a/src/coreclr/src/vm/threads.h
+++ b/src/coreclr/src/vm/threads.h
@@ -977,7 +977,7 @@ struct PortableTailCallFrame
 
 class TailCallTls
 {
-    friend class MscorlibBinder;
+    friend class CoreLibBinder;
 
     PortableTailCallFrame* m_frame;
     char* m_argBuffer;
@@ -4750,6 +4750,21 @@ class Thread
 
 private:
     PrepareCodeConfig *m_currentPrepareCodeConfig;
+
+#ifndef DACCESS_COMPILE
+public:
+    bool IsInForbidSuspendForDebuggerRegion() const
+    {
+        LIMITED_METHOD_CONTRACT;
+        return m_isInForbidSuspendForDebuggerRegion;
+    }
+
+    void EnterForbidSuspendForDebuggerRegion();
+    void ExitForbidSuspendForDebuggerRegion();
+#endif
+
+private:
+    bool m_isInForbidSuspendForDebuggerRegion;
 };
 
 // End of class Thread
diff --git a/src/coreclr/src/vm/threads.inl b/src/coreclr/src/vm/threads.inl
index 68fa53b0ab6201..5dc6ef8d00e1c5 100644
--- a/src/coreclr/src/vm/threads.inl
+++ b/src/coreclr/src/vm/threads.inl
@@ -195,6 +195,24 @@ inline Thread::CurrentPrepareCodeConfigHolder::~CurrentPrepareCodeConfigHolder()
     config->SetNextInSameThread(nullptr);
 }
 
+inline void Thread::EnterForbidSuspendForDebuggerRegion()
+{
+    WRAPPER_NO_CONTRACT;
+    _ASSERTE(this == GetThread());
+
+    _ASSERTE(!m_isInForbidSuspendForDebuggerRegion);
+    m_isInForbidSuspendForDebuggerRegion = true;
+}
+
+inline void Thread::ExitForbidSuspendForDebuggerRegion()
+{
+    WRAPPER_NO_CONTRACT;
+    _ASSERTE(this == GetThread());
+
+    _ASSERTE(m_isInForbidSuspendForDebuggerRegion);
+    m_isInForbidSuspendForDebuggerRegion = false;
+}
+
 #ifdef HOST_WINDOWS
 inline size_t Thread::GetOffsetOfThreadStatic(void* pThreadStatic)
 {
diff --git a/src/coreclr/src/vm/threadsuspend.cpp b/src/coreclr/src/vm/threadsuspend.cpp
index 7d632cb27b1a0d..a9db60e8755ede 100644
--- a/src/coreclr/src/vm/threadsuspend.cpp
+++ b/src/coreclr/src/vm/threadsuspend.cpp
@@ -2262,6 +2262,8 @@ void Thread::RareDisablePreemptiveGC()
     // waiting for GC
     _ASSERTE ((m_StateNC & Thread::TSNC_OwnsSpinLock) == 0);
 
+    _ASSERTE(!MethodDescBackpatchInfoTracker::IsLockOwnedByCurrentThread() || IsInForbidSuspendForDebuggerRegion());
+
     if (!GCHeapUtilities::IsGCHeapInitialized())
     {
         goto Exit;
@@ -2561,6 +2563,8 @@ void Thread::RareEnablePreemptiveGC()
     // holding a spin lock in coop mode and transit to preemp mode will cause deadlock on GC
     _ASSERTE ((m_StateNC & Thread::TSNC_OwnsSpinLock) == 0);
 
+    _ASSERTE(!MethodDescBackpatchInfoTracker::IsLockOwnedByCurrentThread() || IsInForbidSuspendForDebuggerRegion());
+
     FastInterlockOr (&m_fPreemptiveGCDisabled, 0);
 
 #if defined(STRESS_HEAP) && defined(_DEBUG)
@@ -2582,7 +2586,7 @@ void Thread::RareEnablePreemptiveGC()
         // for GC, the fact that we are leaving the EE means that it no longer needs to
         // suspend us.  But if we are doing a non-GC suspend, we need to block now.
         // Give the debugger precedence over user suspensions:
-        while (m_State & TS_DebugSuspendPending)
+        while ((m_State & TS_DebugSuspendPending) && !IsInForbidSuspendForDebuggerRegion())
         {
 
 #ifdef DEBUGGING_SUPPORTED
@@ -4609,7 +4613,11 @@ bool Thread::SysStartSuspendForDebug(AppDomain *pAppDomain)
             // and the moment we enable TrapReturningThreads in MarkForSuspension.  However,
             // nothing bad happens if the thread has transitioned to preemptive before marking
             // the thread for suspension; the thread will later be identified as Synced in
-            // SysSweepThreadsForDebug
+            // SysSweepThreadsForDebug.
+            //
+            // If the thread transitions to preemptive mode and into a forbid-suspend-for-debugger
+            // region, SysSweepThreadsForDebug would similarly identify the thread as synced
+            // after it leaves the forbid region.
 #else  // DISABLE_THREADSUSPEND
             // Resume the thread and let it run to a safe point
             thread->ResumeThread();
@@ -4625,23 +4633,32 @@ bool Thread::SysStartSuspendForDebug(AppDomain *pAppDomain)
             // they attempt to re-enter they will trip.
             thread->MarkForSuspension(TS_DebugSuspendPending);
 
+            if (
 #ifdef DISABLE_THREADSUSPEND
-            // There'a a race above between the moment we first check m_fPreemptiveGCDisabled
-            // and the moment we enable TrapReturningThreads in MarkForSuspension.  To account
-            // for that we check whether the thread moved into cooperative mode, and if it had
-            // we mark it as a DebugWillSync thread, that will be handled later in
-            // SysSweepThreadsForDebug
-            if (thread->m_fPreemptiveGCDisabled)
+                // There'a a race above between the moment we first check m_fPreemptiveGCDisabled
+                // and the moment we enable TrapReturningThreads in MarkForSuspension.  To account
+                // for that we check whether the thread moved into cooperative mode, and if it had
+                // we mark it as a DebugWillSync thread, that will be handled later in
+                // SysSweepThreadsForDebug.
+                thread->m_fPreemptiveGCDisabled ||
+#endif // DISABLE_THREADSUSPEND
+                // The thread may have been suspended in a forbid-suspend-for-debugger region, or
+                // before the state change to set TS_DebugSuspendPending is made visible to other
+                // threads, the thread may have transitioned into a forbid region. In either case,
+                // flag the thread as TS_DebugWillSync and let SysSweepThreadsForDebug later
+                // identify the thread as synced after the thread leaves the forbid region.
+                thread->IsInForbidSuspendForDebuggerRegion())
             {
                 // Remember that this thread will be running to a safe point
                 FastInterlockIncrement(&m_DebugWillSyncCount);
                 thread->SetThreadState(TS_DebugWillSync);
             }
-#else  // DISABLE_THREADSUSPEND
+
+#ifndef DISABLE_THREADSUSPEND
             if (str == STR_Success) {
                 thread->ResumeThread();
             }
-#endif // DISABLE_THREADSUSPEND
+#endif // !DISABLE_THREADSUSPEND
 
             LOG((LF_CORDB, LL_INFO1000,
                  "[0x%x] SUSPEND: gc enabled.\n", thread->GetThreadId()));
@@ -4720,9 +4737,10 @@ bool Thread::SysSweepThreadsForDebug(bool forceSync)
         // this thread will happen after any earlier writes on a different
         // thread.
         FastInterlockOr(&thread->m_fPreemptiveGCDisabled, 0);
-        if (!thread->m_fPreemptiveGCDisabled)
+        if (!thread->m_fPreemptiveGCDisabled && !thread->IsInForbidSuspendForDebuggerRegion())
         {
-            // If the thread toggled to preemptive mode, then it's synced.
+            // If the thread toggled to preemptive mode and is not in a
+            // forbid-suspend-for-debugger region, then it's synced.
             goto Label_MarkThreadAsSynced;
         }
         else
@@ -4756,7 +4774,7 @@ bool Thread::SysSweepThreadsForDebug(bool forceSync)
         else if (str == STR_SwitchedOut)
         {
             // The thread was switched b/c of fiber-mode stuff.
-            if (!thread->m_fPreemptiveGCDisabled)
+            if (!thread->m_fPreemptiveGCDisabled && !thread->IsInForbidSuspendForDebuggerRegion())
             {
                 goto Label_MarkThreadAsSynced;
             }
@@ -4771,15 +4789,27 @@ bool Thread::SysSweepThreadsForDebug(bool forceSync)
         }
         else if (!thread->m_fPreemptiveGCDisabled)
         {
-            // If the thread toggled to preemptive mode, then it's synced.
+            // If the thread toggled to preemptive mode and is not in a
+            // forbid-suspend-for-debugger region, then it's synced.
 
             // We can safely resume the thread here b/c it's in PreemptiveMode and the
             // EE will trap anybody trying to re-enter cooperative. So letting it run free
             // won't hurt the runtime.
+            //
+            // If the thread is in a forbid-suspend-for-debugger region, the thread needs to
+            // be resumed to give it a chance to leave the forbid region. The EE will also
+            // trap the thread if it tries to re-enter a forbid region.
             _ASSERTE(str == STR_Success);
             thread->ResumeThread();
 
-            goto Label_MarkThreadAsSynced;
+            if (!thread->IsInForbidSuspendForDebuggerRegion())
+            {
+                goto Label_MarkThreadAsSynced;
+            }
+            else
+            {
+                continue;
+            }
         }
 #if defined(FEATURE_HIJACK) && !defined(TARGET_UNIX)
         // If the thread is in jitted code, HandledJitCase will try to hijack it; and the hijack
diff --git a/src/coreclr/src/vm/tieredcompilation.cpp b/src/coreclr/src/vm/tieredcompilation.cpp
index 311154f1ad7212..05fc6735ff7417 100644
--- a/src/coreclr/src/vm/tieredcompilation.cpp
+++ b/src/coreclr/src/vm/tieredcompilation.cpp
@@ -448,8 +448,7 @@ void TieredCompilationManager::DeactivateTieringDelay()
         COUNT_T methodCount = methodsPendingCounting->GetCount();
         CodeVersionManager *codeVersionManager = GetAppDomain()->GetCodeVersionManager();
 
-        MethodDescBackpatchInfoTracker::PollForDebuggerSuspension();
-        MethodDescBackpatchInfoTracker::ConditionalLockHolder slotBackpatchLockHolder;
+        MethodDescBackpatchInfoTracker::ConditionalLockHolderForGCCoop slotBackpatchLockHolder;
 
         // Backpatching entry point slots requires cooperative GC mode, see
         // MethodDescBackpatchInfoTracker::Backpatch_Locked(). The code version manager's table lock is an unsafe lock that
@@ -772,9 +771,15 @@ BOOL TieredCompilationManager::CompileCodeVersion(NativeCodeVersion nativeCodeVe
         PrepareCodeConfigBuffer configBuffer(nativeCodeVersion);
         PrepareCodeConfig *config = configBuffer.GetConfig();
 
+#if defined(TARGET_X86)
+        // Deferring X86 support until a need is observed or
+        // time permits investigation into all the potential issues.
+        // https://github.com/dotnet/runtime/issues/33582
+#else
         // This is a recompiling request which means the caller was
         // in COOP mode since the code already ran.
         _ASSERTE(!pMethod->HasUnmanagedCallersOnlyAttribute());
+#endif
         config->SetCallerGCMode(CallerGCMode::Coop);
         pCode = pMethod->PrepareCode(config);
         LOG((LF_TIEREDCOMPILATION, LL_INFO10000, "TieredCompilationManager::CompileCodeVersion Method=0x%pM (%s::%s), code version id=0x%x, code ptr=0x%p\n",
@@ -819,11 +824,8 @@ void TieredCompilationManager::ActivateCodeVersion(NativeCodeVersion nativeCodeV
     HRESULT hr = S_OK;
     {
         bool mayHaveEntryPointSlotsToBackpatch = pMethod->MayHaveEntryPointSlotsToBackpatch();
-        if (mayHaveEntryPointSlotsToBackpatch)
-        {
-            MethodDescBackpatchInfoTracker::PollForDebuggerSuspension();
-        }
-        MethodDescBackpatchInfoTracker::ConditionalLockHolder slotBackpatchLockHolder(mayHaveEntryPointSlotsToBackpatch);
+        MethodDescBackpatchInfoTracker::ConditionalLockHolderForGCCoop slotBackpatchLockHolder(
+            mayHaveEntryPointSlotsToBackpatch);
 
         // Backpatching entry point slots requires cooperative GC mode, see
         // MethodDescBackpatchInfoTracker::Backpatch_Locked(). The code version manager's table lock is an unsafe lock that
diff --git a/src/coreclr/src/vm/typedesc.inl b/src/coreclr/src/vm/typedesc.inl
index c6fbf654f0949d..d2b9f2b0f41e62 100644
--- a/src/coreclr/src/vm/typedesc.inl
+++ b/src/coreclr/src/vm/typedesc.inl
@@ -22,7 +22,7 @@ inline PTR_MethodTable  TypeDesc::GetMethodTable() {
         return NULL;
 
     if (GetInternalCorElementType() == ELEMENT_TYPE_FNPTR)
-        return MscorlibBinder::GetElementType(ELEMENT_TYPE_U);
+        return CoreLibBinder::GetElementType(ELEMENT_TYPE_U);
 
     _ASSERTE(HasTypeParam());
     ParamTypeDesc* asParam = dac_cast<PTR_ParamTypeDesc>(this);
diff --git a/src/coreclr/src/vm/typehandle.cpp b/src/coreclr/src/vm/typehandle.cpp
index 754f842ea70066..7883071fee28ea 100644
--- a/src/coreclr/src/vm/typehandle.cpp
+++ b/src/coreclr/src/vm/typehandle.cpp
@@ -1174,7 +1174,7 @@ OBJECTREF TypeHandle::GetManagedClassObject() const
 
             case ELEMENT_TYPE_FNPTR:
                 // A function pointer is mapped into typeof(IntPtr). It results in a loss of information.
-                return MscorlibBinder::GetElementType(ELEMENT_TYPE_I)->GetManagedClassObject();
+                return CoreLibBinder::GetElementType(ELEMENT_TYPE_I)->GetManagedClassObject();
 
             default:
                 _ASSERTE(!"Bad Element Type");
diff --git a/src/coreclr/src/vm/typehandle.inl b/src/coreclr/src/vm/typehandle.inl
index ba66ee3b02f4ff..e566d7c831e085 100644
--- a/src/coreclr/src/vm/typehandle.inl
+++ b/src/coreclr/src/vm/typehandle.inl
@@ -277,7 +277,7 @@ FORCEINLINE OBJECTREF TypeHandle::GetManagedClassObjectFast() const
 
         case ELEMENT_TYPE_FNPTR:
             // A function pointer is mapped into typeof(IntPtr). It results in a loss of information.
-            o = MscorlibBinder::GetElementType(ELEMENT_TYPE_I)->GetManagedClassObjectIfExists();
+            o = CoreLibBinder::GetElementType(ELEMENT_TYPE_I)->GetManagedClassObjectIfExists();
             break;
 
         default:
diff --git a/src/coreclr/src/vm/typeparse.cpp b/src/coreclr/src/vm/typeparse.cpp
index 1b69d0d815d095..007ef0813bc440 100644
--- a/src/coreclr/src/vm/typeparse.cpp
+++ b/src/coreclr/src/vm/typeparse.cpp
@@ -91,7 +91,7 @@ SAFEHANDLE TypeName::GetSafeHandle()
 
     GCPROTECT_BEGIN(objSafeHandle);
 
-    objSafeHandle = (SAFEHANDLE)AllocateObject(MscorlibBinder::GetClass(CLASS__SAFE_TYPENAMEPARSER_HANDLE));
+    objSafeHandle = (SAFEHANDLE)AllocateObject(CoreLibBinder::GetClass(CLASS__SAFE_TYPENAMEPARSER_HANDLE));
 
     MethodDescCallSite strCtor(METHOD__SAFE_TYPENAMEPARSER_HANDLE__CTOR);
 
@@ -226,7 +226,7 @@ void QCALLTYPE TypeName::QGetTypeArguments(TypeName * pTypeName, QCall::ObjectHa
 
         GCPROTECT_BEGIN(pReturnArguments);
 
-        pReturnArguments = (PTRARRAYREF)AllocateObjectArray(count, MscorlibBinder::GetClass(CLASS__SAFE_TYPENAMEPARSER_HANDLE));
+        pReturnArguments = (PTRARRAYREF)AllocateObjectArray(count, CoreLibBinder::GetClass(CLASS__SAFE_TYPENAMEPARSER_HANDLE));
 
         for (COUNT_T i = 0; i < count; i++)
         {
@@ -795,7 +795,7 @@ BOOL TypeName::TypeNameParser::NESTNAME()
 //    if szTypeName is not ASM-qualified, we will search for the types in the following order:
 //       - in pRequestingAssembly (if not NULL). pRequestingAssembly is the assembly that contained
 //         the custom attribute from which the typename was derived.
-//       - in mscorlib.dll
+//       - in CoreLib
 //       - raise an AssemblyResolveEvent() in the current appdomain
 //
 // pRequestingAssembly may be NULL. In that case, the "visibility" check will simply check that
diff --git a/src/coreclr/src/vm/typeparse.h b/src/coreclr/src/vm/typeparse.h
index 39e4211635d07d..3cf1df6ceb1e42 100644
--- a/src/coreclr/src/vm/typeparse.h
+++ b/src/coreclr/src/vm/typeparse.h
@@ -304,7 +304,7 @@ class TypeName
     //    if szTypeName is not ASM-qualified, we will search for the types in the following order:
     //       - in pRequestingAssembly (if not NULL). pRequestingAssembly is the assembly that contained
     //         the custom attribute from which the typename was derived.
-    //       - in mscorlib.dll
+    //       - in CoreLib
     //       - raise an AssemblyResolveEvent() in the current appdomain
     //
     // pRequestingAssembly may be NULL. In that case, the "visibility" check will simply check that
diff --git a/src/coreclr/src/vm/virtualcallstub.cpp b/src/coreclr/src/vm/virtualcallstub.cpp
index 828b56093b8cee..1f05aef2588806 100644
--- a/src/coreclr/src/vm/virtualcallstub.cpp
+++ b/src/coreclr/src/vm/virtualcallstub.cpp
@@ -2765,7 +2765,7 @@ DispatchHolder *VirtualCallStubManager::GenerateDispatchStub(PCODE            ad
         TADDR slot = holder->stub()->implTargetSlot(&slotType);
         pMD->RecordAndBackpatchEntryPointSlot(m_loaderAllocator, slot, slotType);
 
-        // RecordAndBackpatchEntryPointSlot() takes a lock that would exit and reenter cooperative GC mode
+        // RecordAndBackpatchEntryPointSlot() may exit and reenter cooperative GC mode
         *pMayHaveReenteredCooperativeGCMode = true;
     }
 #endif
@@ -2827,7 +2827,7 @@ DispatchHolder *VirtualCallStubManager::GenerateDispatchStubLong(PCODE
         TADDR slot = holder->stub()->implTargetSlot(&slotType);
         pMD->RecordAndBackpatchEntryPointSlot(m_loaderAllocator, slot, slotType);
 
-        // RecordAndBackpatchEntryPointSlot() takes a lock that would exit and reenter cooperative GC mode
+        // RecordAndBackpatchEntryPointSlot() may exit and reenter cooperative GC mode
         *pMayHaveReenteredCooperativeGCMode = true;
     }
 #endif
@@ -3020,7 +3020,7 @@ ResolveCacheElem *VirtualCallStubManager::GenerateResolveCacheElem(void *addrOfC
             (TADDR)&e->target,
             EntryPointSlots::SlotType_Normal);
 
-        // RecordAndBackpatchEntryPointSlot() takes a lock that would exit and reenter cooperative GC mode
+        // RecordAndBackpatchEntryPointSlot() may exit and reenter cooperative GC mode
         *pMayHaveReenteredCooperativeGCMode = true;
     }
 #endif
diff --git a/src/coreclr/src/vm/weakreferencenative.cpp b/src/coreclr/src/vm/weakreferencenative.cpp
index da6036abb15b7b..4d56975daa065d 100644
--- a/src/coreclr/src/vm/weakreferencenative.cpp
+++ b/src/coreclr/src/vm/weakreferencenative.cpp
@@ -439,7 +439,7 @@ FCIMPL3(void, WeakReferenceNative::Create, WeakReferenceObject * pThisUNSAFE, Ob
         COMPlusThrow(kNullReferenceException);
 
     if (pWeakReferenceMT == NULL)
-        pWeakReferenceMT = MscorlibBinder::GetClass(CLASS__WEAKREFERENCE);
+        pWeakReferenceMT = CoreLibBinder::GetClass(CLASS__WEAKREFERENCE);
 
     _ASSERTE(gc.pThis->GetMethodTable()->CanCastToClass(pWeakReferenceMT));
 
diff --git a/src/coreclr/src/vm/wks/CMakeLists.txt b/src/coreclr/src/vm/wks/CMakeLists.txt
index bd675204bd78ab..7c3dd84bd3d035 100644
--- a/src/coreclr/src/vm/wks/CMakeLists.txt
+++ b/src/coreclr/src/vm/wks/CMakeLists.txt
@@ -8,15 +8,21 @@ if (CLR_CMAKE_TARGET_WIN32)
 endif (CLR_CMAKE_TARGET_WIN32)
 
 add_library_clr(cee_wks_core OBJECT ${VM_SOURCES_WKS} ${VM_SOURCES_WKS_ARCH_ASM})
+add_library_clr(cee_wks_obj OBJECT ${VM_SOURCES_WKS_SPECIAL})
+add_library_clr(cee_wks_mergeable_obj OBJECT ${VM_SOURCES_WKS_SPECIAL})
 
 target_precompile_header(TARGET cee_wks_core HEADER common.h)
+target_precompile_header(TARGET cee_wks_obj HEADER common.h)
+target_precompile_header(TARGET cee_wks_mergeable_obj HEADER common.h)
 
 if (MSVC)
-    # mscorlib.cpp does not compile with precompiled header file
-    set_source_files_properties(../mscorlib.cpp PROPERTIES COMPILE_FLAGS "/Y-")
+    # corelib.cpp does not compile with precompiled header file
+    set_source_files_properties(../corelib.cpp PROPERTIES COMPILE_FLAGS "/Y-")
 endif()
 
 add_dependencies(cee_wks_core eventing_headers)
+add_dependencies(cee_wks_obj eventing_headers)
+add_dependencies(cee_wks_mergeable_obj eventing_headers)
 
 if (CLR_CMAKE_TARGET_WIN32)
 
@@ -49,20 +55,23 @@ if (CLR_CMAKE_TARGET_WIN32)
     )
 
     add_dependencies(cee_wks_core asmconstants_inc)
+    add_dependencies(cee_wks_obj asmconstants_inc)
+    add_dependencies(cee_wks_mergeable_obj asmconstants_inc)
 
   endif(NOT CLR_CMAKE_HOST_ARCH_ARM AND NOT CLR_CMAKE_HOST_ARCH_ARM64)
 
 endif (CLR_CMAKE_TARGET_WIN32)
 
-add_library_clr(cee_wks OBJECT ${VM_SOURCES_WKS_SPECIAL} $<TARGET_OBJECTS:cee_wks_core> ${VM_WKS_ARCH_ASM_OBJECTS})
-add_library_clr(cee_wks_mergeable OBJECT ${VM_SOURCES_WKS_SPECIAL} $<TARGET_OBJECTS:cee_wks_core> ${VM_WKS_ARCH_ASM_OBJECTS})
-
 add_custom_target(preprocessd_asm DEPENDS ${VM_WKS_ARCH_ASM_OBJECTS})
-add_dependencies(cee_wks preprocessd_asm)
-add_dependencies(cee_wks_mergeable preprocessd_asm)
+add_dependencies(cee_wks_core preprocessd_asm)
+add_dependencies(cee_wks_obj preprocessd_asm)
+add_dependencies(cee_wks_mergeable_obj preprocessd_asm)
+
 
-target_precompile_header(TARGET cee_wks HEADER common.h)
-target_precompile_header(TARGET cee_wks_mergeable HEADER common.h)
+target_compile_definitions(cee_wks_mergeable_obj PUBLIC FEATURE_MERGE_JIT_AND_ENGINE)
+target_compile_definitions(cee_wks_mergeable_obj PUBLIC CORECLR_EMBEDDED)
 
-target_compile_definitions(cee_wks_mergeable PUBLIC FEATURE_MERGE_JIT_AND_ENGINE)
-target_compile_definitions(cee_wks_mergeable PUBLIC CORECLR_EMBEDDED)
+add_library(cee_wks INTERFACE)
+target_sources(cee_wks INTERFACE $<TARGET_OBJECTS:cee_wks_obj> ${VM_WKS_ARCH_ASM_OBJECTS})
+add_library(cee_wks_mergeable INTERFACE)
+target_sources(cee_wks_mergeable INTERFACE $<TARGET_OBJECTS:cee_wks_mergeable_obj> $<TARGET_OBJECTS:cee_wks_core> ${VM_WKS_ARCH_ASM_OBJECTS})
diff --git a/src/coreclr/src/zap/zapimage.cpp b/src/coreclr/src/zap/zapimage.cpp
index bcd02a3b2c4294..693921963d84a4 100644
--- a/src/coreclr/src/zap/zapimage.cpp
+++ b/src/coreclr/src/zap/zapimage.cpp
@@ -1894,7 +1894,6 @@ void ZapImage::TryCompileMethodStub(LPVOID pContext, CORINFO_METHOD_HANDLE hStub
 //-----------------------------------------------------------------------------
 BOOL ZapImage::IsVTableGapMethod(mdMethodDef md)
 {
-#ifdef FEATURE_COMINTEROP
     HRESULT hr;
     DWORD dwAttributes;
 
@@ -1916,9 +1915,6 @@ BOOL ZapImage::IsVTableGapMethod(mdMethodDef md)
 
     // If we make it to here we have a vtable gap method.
     return TRUE;
-#else
-    return FALSE;
-#endif // FEATURE_COMINTEROP
 }
 
 //-----------------------------------------------------------------------------
@@ -2210,10 +2206,7 @@ ZapImage::CompileStatus ZapImage::TryCompileMethodWorker(CORINFO_METHOD_HANDLE h
 BOOL ZapImage::ShouldCompileMethodDef(mdMethodDef md)
 {
     DWORD partialNGenStressVal = PartialNGenStressPercentage();
-    if (partialNGenStressVal &&
-        // Module::AddCerListToRootTable has problems if mscorlib.dll is
-        // a partial ngen image
-        m_hModule != m_zapper->m_pEECompileInfo->GetLoaderModuleForMscorlib())
+    if (partialNGenStressVal)
     {
         _ASSERTE(partialNGenStressVal <= 100);
         DWORD methodPercentageVal = (md % 100) + 1;
@@ -2315,10 +2308,7 @@ BOOL ZapImage::ShouldCompileMethodDef(mdMethodDef md)
 BOOL ZapImage::ShouldCompileInstantiatedMethod(CORINFO_METHOD_HANDLE handle)
 {
     DWORD partialNGenStressVal = PartialNGenStressPercentage();
-    if (partialNGenStressVal &&
-        // Module::AddCerListToRootTable has problems if mscorlib.dll is
-        // a partial ngen image
-        m_hModule != m_zapper->m_pEECompileInfo->GetLoaderModuleForMscorlib())
+    if (partialNGenStressVal)
     {
         _ASSERTE(partialNGenStressVal <= 100);
         DWORD methodPercentageVal = (m_zapper->m_pEEJitInfo->getMethodHash(handle) % 100) + 1;
diff --git a/src/coreclr/src/zap/zapinfo.cpp b/src/coreclr/src/zap/zapinfo.cpp
index 203196851cc14a..e997efa396b1eb 100644
--- a/src/coreclr/src/zap/zapinfo.cpp
+++ b/src/coreclr/src/zap/zapinfo.cpp
@@ -450,7 +450,7 @@ void ZapInfo::CompileMethod()
     }
 #endif
 
-#if defined(TARGET_X86) || defined(TARGET_AMD64)
+#if defined(TARGET_X86) || defined(TARGET_AMD64) || defined(TARGET_ARM64)
     if (methodAttribs & CORINFO_FLG_JIT_INTRINSIC)
     {
         // Skip generating hardware intrinsic method bodies.
@@ -496,12 +496,22 @@ void ZapInfo::CompileMethod()
         m_pImage->m_stats->m_ilCodeSize += m_currentMethodInfo.ILCodeSize;
     }
 
-    CorJitResult res = CORJIT_SKIPPED;
+    CorJitResult res = CORJIT_SKIPPED;   // FAILED() returns true for this value
 
     BYTE *pCode;
     ULONG cCode;
+    bool  doNormalCompile = true;
 
 #ifdef ALLOW_SXS_JIT_NGEN
+
+    // Only retry the JIT compilation when we have a different JIT to run
+    // Often we see both COMPlus_AltJIT and COMPlus_AltJitNgen set
+    // which results in both JIT compilers set to the same altjit
+    //
+    doNormalCompile = (m_zapper->m_alternateJit != m_zapper->m_pJitCompiler);
+
+    // Compile this method using the AltJitNgen compiler
+    //
     if (m_zapper->m_alternateJit)
     {
         res = m_zapper->m_alternateJit->compileMethod( this,
@@ -509,23 +519,27 @@ void ZapInfo::CompileMethod()
                                                      CORJIT_FLAGS::CORJIT_FLAG_CALL_GETJITFLAGS,
                                                      &pCode,
                                                      &cCode);
-        if (FAILED(res))
+
+        // The above compileMethod call will typically return CORJIT_SKIPPED
+        if (doNormalCompile && FAILED(res))
         {
             // We will fall back to the "main" JIT on failure.
             ResetForJitRetry();
         }
     }
+
 #endif // ALLOW_SXS_JIT_NGEN
 
-    if (FAILED(res))
+    // Compile this method using the normal JIT compiler
+    //
+    if (doNormalCompile && FAILED(res))
     {
         ICorJitCompiler * pCompiler = m_zapper->m_pJitCompiler;
         res = pCompiler->compileMethod(this,
-                                    &m_currentMethodInfo,
-                                    CORJIT_FLAGS::CORJIT_FLAG_CALL_GETJITFLAGS,
-                                    &pCode,
-                                    &cCode);
-
+                                       &m_currentMethodInfo,
+                                       CORJIT_FLAGS::CORJIT_FLAG_CALL_GETJITFLAGS,
+                                       &pCode,
+                                       &cCode);
         if (FAILED(res))
         {
             ThrowExceptionForJitResult(res);
@@ -2150,15 +2164,17 @@ DWORD FilterNamedIntrinsicMethodAttribs(ZapInfo* pZapInfo, DWORD attribs, CORINF
         // is because they often change the code they emit based on what ISAs are supported by the compiler,
         // but we don't know what the target machine will support.
         //
-        // Additionally, we make sure none of the hardware intrinsic method bodies (except ARM64) get pregenerated in crossgen
+        // Additionally, we make sure none of the hardware intrinsic method bodies get pregenerated in crossgen
         // (see ZapInfo::CompileMethod) but get JITted instead. The JITted method will have the correct
         // answer for the CPU the code is running on.
 
-        // For Arm64, AdvSimd/ArmBase is the baseline that is suported and hence we do pregenerate the method bodies
-        // of ARM64 harware intrinsic.
-        fTreatAsRegularMethodCall = (fIsGetIsSupportedMethod && fIsPlatformHWIntrinsic);
-#if !defined(TARGET_ARM64)
-        fTreatAsRegularMethodCall |= (!fIsPlatformHWIntrinsic && fIsHWIntrinsic);
+        fTreatAsRegularMethodCall = fIsGetIsSupportedMethod && fIsPlatformHWIntrinsic;
+
+#if defined(TARGET_ARM64)
+        // On Arm64 AdvSimd ISA is required by CoreCLR, so we can expand Vector64<T> and Vector128<T> methods.
+        fTreatAsRegularMethodCall |= !fIsPlatformHWIntrinsic && fIsHWIntrinsic && (strcmp(className, "Vector64`1") != 0) && (strcmp(className, "Vector128`1") != 0);
+#else
+        fTreatAsRegularMethodCall |= !fIsPlatformHWIntrinsic && fIsHWIntrinsic;
 #endif 
 
         if (fIsPlatformHWIntrinsic)
@@ -2219,12 +2235,13 @@ DWORD FilterNamedIntrinsicMethodAttribs(ZapInfo* pZapInfo, DWORD attribs, CORINF
 #if defined(TARGET_X86) || defined(TARGET_AMD64)
         else if (strcmp(namespaceName, "System") == 0)
         {
-            if ((strcmp(className, "Math") == 0) || (strcmp(className, "MathF") == 0))
+            if (strcmp(className, "Math") == 0 || strcmp(className, "MathF") == 0)
             {
                 // These are normally handled via the SSE4.1 instructions ROUNDSS/ROUNDSD.
                 // However, we don't know the ISAs the target machine supports so we should
                 // fallback to the method call implementation instead.
-                fTreatAsRegularMethodCall = strcmp(methodName, "Round") == 0;
+                fTreatAsRegularMethodCall = strcmp(methodName, "Round") == 0 || strcmp(methodName, "Ceiling") == 0 ||
+                    strcmp(methodName, "Floor") == 0;
             }
         }
         else if (strcmp(namespaceName, "System.Numerics") == 0)
@@ -3991,19 +4008,7 @@ void ZapInfo::expandRawHandleIntrinsic(
 CorInfoIntrinsics ZapInfo::getIntrinsicID(CORINFO_METHOD_HANDLE method,
                                           bool * pMustExpand)
 {
-    CorInfoIntrinsics intrinsicID = m_pEEJitInfo->getIntrinsicID(method, pMustExpand);
-
-#if defined(TARGET_X86) || defined(TARGET_AMD64)
-    if ((intrinsicID == CORINFO_INTRINSIC_Ceiling) || (intrinsicID == CORINFO_INTRINSIC_Floor))
-    {
-        // These are normally handled via the SSE4.1 instructions ROUNDSS/ROUNDSD.
-        // However, we don't know the ISAs the target machine supports so we should
-        // fallback to the method call implementation instead.
-        intrinsicID = CORINFO_INTRINSIC_Illegal;
-    }
-#endif // defined(TARGET_X86) || defined(TARGET_AMD64)
-
-    return intrinsicID;
+    return m_pEEJitInfo->getIntrinsicID(method, pMustExpand);
 }
 
 bool ZapInfo::isIntrinsicType(CORINFO_CLASS_HANDLE classHnd)
diff --git a/src/coreclr/src/zap/zapper.cpp b/src/coreclr/src/zap/zapper.cpp
index 5b999a82f0e6e5..f232719b8d4e2f 100644
--- a/src/coreclr/src/zap/zapper.cpp
+++ b/src/coreclr/src/zap/zapper.cpp
@@ -805,10 +805,10 @@ BOOL Zapper::IsAssembly(LPCWSTR path)
 
 void Zapper::SetContextInfo(LPCWSTR assemblyName)
 {
-    // A special case:  If we're compiling mscorlib, ignore m_exeName and don't set any context.
-    // There can only be one mscorlib in the runtime, independent of any context.  If we don't
-    // check for mscorlib, and isExe == true, then CompilationDomain::SetContextInfo will call
-    // into mscorlib and cause the resulting mscorlib.ni.dll to be slightly different (checked
+    // A special case:  If we're compiling CoreLib, ignore m_exeName and don't set any context.
+    // There can only be one CoreLib in the runtime, independent of any context.  If we don't
+    // check for CoreLib, and isExe == true, then CompilationDomain::SetContextInfo will call
+    // into CoreLib and cause the resulting System.Private.CoreLib.ni.dll to be slightly different (checked
     // build only).
     if (assemblyName != NULL && _wcsnicmp(assemblyName, CoreLibName_W, CoreLibNameLen) == 0 && (wcslen(assemblyName) == CoreLibNameLen || assemblyName[CoreLibNameLen] == W(',')))
     {
@@ -975,18 +975,18 @@ HRESULT Zapper::Compile(LPCWSTR string, CORCOMPILE_NGEN_SIGNATURE * pNativeImage
 {
     HRESULT hr = S_OK;
 
-    bool fMscorlib = false;
+    bool fCoreLib = false;
     LPCWSTR fileName = PathFindFileName(string);
     if (fileName != NULL && SString::_wcsicmp(fileName, g_pwBaseLibrary) == 0)
     {
-        fMscorlib = true;
+        fCoreLib = true;
     }
 
 
-    if (fMscorlib)
+    if (fCoreLib)
     {
         //
-        // Disallow use of native image to force a new native image generation for mscorlib
+        // Disallow use of native image to force a new native image generation for CoreLib
         //
         g_fAllowNativeImages = false;
     }
@@ -1180,7 +1180,7 @@ void Zapper::InitializeCompilerFlags(CORCOMPILE_VERSION_INFO * pVersionInfo)
     // That way the actual support checks will always be jitted.
     // We only do this for CoreLib because forgetting to wrap intrinsics under IsSupported
     // checks can lead to illegal instruction traps (instead of a nice managed exception).
-    if (m_pEECompileInfo->GetAssemblyModule(m_hAssembly) == m_pEECompileInfo->GetLoaderModuleForMscorlib())
+    if (m_pEECompileInfo->GetAssemblyModule(m_hAssembly) == m_pEECompileInfo->GetLoaderModuleForCoreLib())
     {
         m_pOpt->m_compilerFlags.Set(CORJIT_FLAGS::CORJIT_FLAG_FEATURE_SIMD);
 
diff --git a/src/coreclr/src/zap/zapreadytorun.cpp b/src/coreclr/src/zap/zapreadytorun.cpp
index 27d79b3121d33c..d5bb25ab1b6ab2 100644
--- a/src/coreclr/src/zap/zapreadytorun.cpp
+++ b/src/coreclr/src/zap/zapreadytorun.cpp
@@ -741,7 +741,7 @@ void ZapImage::OutputAttributePresenceFilter(IMDInternalImport * pMDImport)
     // present. Other assemblies *MAY* benefit from this feature, but it doesn't show
     // as useful at this time.
 
-    if (m_hModule != m_zapper->m_pEECompileInfo->GetLoaderModuleForMscorlib())
+    if (m_hModule != m_zapper->m_pEECompileInfo->GetLoaderModuleForCoreLib())
         return;
 
     SArray<UINT16> table;
@@ -851,3 +851,13 @@ static_assert_no_msg((int)READYTORUN_FIXUP_Verify_TypeLayout          == (int)EN
 //
 static_assert_no_msg(sizeof(READYTORUN_EXCEPTION_LOOKUP_TABLE_ENTRY) == sizeof(CORCOMPILE_EXCEPTION_LOOKUP_TABLE_ENTRY));
 static_assert_no_msg(sizeof(READYTORUN_EXCEPTION_CLAUSE) == sizeof(CORCOMPILE_EXCEPTION_CLAUSE));
+
+//
+// ReadyToRunHFAElemType
+//
+static_assert_no_msg((int)READYTORUN_HFA_ELEMTYPE_None      == (int)CORINFO_HFA_ELEM_NONE);
+static_assert_no_msg((int)READYTORUN_HFA_ELEMTYPE_Float32   == (int)CORINFO_HFA_ELEM_FLOAT);
+static_assert_no_msg((int)READYTORUN_HFA_ELEMTYPE_Float64   == (int)CORINFO_HFA_ELEM_DOUBLE);
+static_assert_no_msg((int)READYTORUN_HFA_ELEMTYPE_Vector64  == (int)CORINFO_HFA_ELEM_VECTOR64);
+static_assert_no_msg((int)READYTORUN_HFA_ELEMTYPE_Vector128 == (int)CORINFO_HFA_ELEM_VECTOR128);
+
diff --git a/src/coreclr/tests/build.proj b/src/coreclr/tests/build.proj
index 424cd2567539cb..083ab2612b75b9 100644
--- a/src/coreclr/tests/build.proj
+++ b/src/coreclr/tests/build.proj
@@ -19,6 +19,7 @@
 
   <ItemGroup>
     <RestoreProjects Include="$(MSBuildThisFileDirectory)scripts\scripts.csproj" />
+    <RestoreProjects Include="$(MSBuildThisFileDirectory)src\Common\test_dependencies_fs\test_dependencies.fsproj" />
     <RestoreProjects Include="$(MSBuildThisFileDirectory)src\Common\test_dependencies\test_dependencies.csproj" />
     <RestoreProjects Include="$(RepoRoot)src\tests\Common\CoreCLRTestLibrary\CoreCLRTestLibrary.csproj" />
     <RestoreProjects Include="$(MSBuildThisFileDirectory)external\external.csproj" />
diff --git a/src/coreclr/tests/issues.targets b/src/coreclr/tests/issues.targets
index e19d521e42a47f..edfe25e4202157 100644
--- a/src/coreclr/tests/issues.targets
+++ b/src/coreclr/tests/issues.targets
@@ -5,9 +5,6 @@
         <ExcludeList Include="$(XunitTestBinBase)/tracing/tracecontrol/tracecontrol/*">
             <Issue>https://github.com/dotnet/runtime/issues/11204</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/tracing/eventpipe/gcdump/gcdump/*">
-            <Issue>https://github.com/dotnet/runtime/issues/39361</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/readytorun/DynamicMethodGCStress/DynamicMethodGCStress/*">
             <Issue>timeout</Issue>
         </ExcludeList>
@@ -24,9 +21,6 @@
         <ExcludeList Include="$(XunitTestBinBase)/JIT/SIMD/Vector3Interop_ro/*">
             <Issue>https://github.com/dotnet/runtime/issues/35798</Issue>
         </ExcludeList>
-        <ExcludeList Include = "$(XunitTestBinBase)/tracing/eventpipe/pauseonstart/pauseonstart/**">
-            <Issue>https://github.com/dotnet/runtime/issues/38847</Issue>
-        </ExcludeList>
     </ItemGroup>
 
     <!-- All OS/Arch CoreCLR excludes -->
@@ -310,6 +304,10 @@
         </ExcludeList>
     </ItemGroup>
 
+    <!-- Windows all architecture excludes -->
+    <ItemGroup Condition="'$(XunitTestBinBase)' != '' and '$(TargetsWindows)' == 'true' and '$(RuntimeFlavor)' == 'coreclr'">
+    </ItemGroup>
+
     <!-- Windows x64 specific excludes -->
     <ItemGroup Condition="'$(XunitTestBinBase)' != '' and '$(TargetArchitecture)' == 'x64' and '$(TargetsWindows)' == 'true' and '$(RuntimeFlavor)' == 'coreclr'">
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/GitHub_18056/Bool_And_Op_cs_do/*">
@@ -883,9 +881,6 @@
 
     <!-- Crossgen2 specific -->
     <ItemGroup Condition="'$(XunitTestBinBase)' != '' and '$(TestBuildMode)' == 'crossgen2' and '$(RuntimeFlavor)' == 'coreclr'">
-        <ExcludeList Include="$(XunitTestBinBase)/baseservices/threading/paramthreadstart/ThreadStartBool_1/*">
-            <Issue>https://github.com/dotnet/runtime/issues/33887</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/baseservices/TieredCompilation/BasicTest_DefaultMode_R2r/*">
             <Issue>https://github.com/dotnet/runtime/issues/38291</Issue>
         </ExcludeList>
@@ -919,21 +914,9 @@
         <ExcludeList Include="$(XunitTestBinBase)/Interop/IJW/FixupCallsHostWhenLoaded/FixupCallsHostWhenLoaded/*">
             <Issue>https://github.com/dotnet/runtime/issues/38096</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/Generics/Arrays/TypeParameters/MultiDim/**/*">
-            <Issue>https://github.com/dotnet/runtime/issues/38260</Issue>
-        </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/Intrinsics/TypeIntrinsics_r/*">
-            <Issue>https://github.com/dotnet/runtime/issues/32725</Issue>
-        </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/Intrinsics/TypeIntrinsics_ro/*">
-            <Issue>https://github.com/dotnet/runtime/issues/32725</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Methodical/tailcall_v4/hijacking/*">
             <Issue>https://github.com/dotnet/runtime/issues/7597</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/opt/ObjectStackAllocation/ObjectStackAllocationTests/*">
-            <Issue>Not compatible with crossgen2</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/clr-x64-JIT/v4.0/devdiv374539/DevDiv_374539/*">
             <Issue>https://github.com/dotnet/runtime/issues/32732</Issue>
         </ExcludeList>
@@ -943,18 +926,12 @@
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/CLR-x86-JIT/v2.1/DDB/B168384/LdfldaHack/*">
             <Issue>https://github.com/dotnet/runtime/issues/615</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/CLR-x86-JIT/V1.2-Beta1/b219940/b219940/*">
-            <Issue>https://github.com/dotnet/runtime/issues/37579</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/GitHub_27924/GitHub_27924/*">
             <Issue>https://github.com/dotnet/runtime/issues/34316</Issue>
         </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/JIT/SIMD/SimpleSIMDProgram/*">
             <Issue>https://github.com/dotnet/runtime/issues/35724</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/Stress/ABI/**/*">
-            <Issue>https://github.com/dotnet/runtime/issues/32725</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/JIT/superpmi/superpmicollect/*">
             <Issue>Not compatible with crossgen2</Issue>
         </ExcludeList>
@@ -967,9 +944,6 @@
         <ExcludeList Include="$(XunitTestBinBase)/Loader/binding/tracing/BinderTracingTest.Basic/*">
             <Issue>https://github.com/dotnet/runtime/issues/38290</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/regressions/Dev12_518401/dev12_518401/dev12_518401/*">
-            <Issue>https://github.com/dotnet/runtime/issues/38260</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/tracing/tracevalidation/tracelogging/tracelogging/*">
             <Issue>https://github.com/dotnet/runtime/issues/32728</Issue>
         </ExcludeList>
@@ -987,6 +961,12 @@
 
     <!-- Known failures for mono runtime on *all* architectures/operating systems -->
     <ItemGroup Condition="'$(RuntimeFlavor)' == 'mono'" >
+        <ExcludeList Include="$(XunitTestBinBase)/Loader/CollectibleAssemblies/ByRefLocals/**">
+            <Issue>https://github.com/dotnet/runtime/issues/40394</Issue>
+        </ExcludeList>
+        <ExcludeList Include="$(XunitTestBinBase)/Interop/PInvoke/Miscellaneous/CopyCtor/**">
+            <Issue>Handling for Copy constructors isn't present in mono interop</Issue>
+        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/Interop/StringMarshalling/AnsiBSTR/AnsiBStrTest/**">
             <Issue>Crashes during LLVM AOT compilation.</Issue>
         </ExcludeList>
@@ -1648,16 +1628,13 @@
         <ExcludeList Include="$(XunitTestBinBase)/Loader/ContextualReflection/ContextualReflection/**">
             <Issue>https://github.com/dotnet/runtime/issues/34072</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/profiler/unittest/getappdomainstaticaddress/**">
-            <Issue>needs triage</Issue>
-        </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/profiler/eventpipe/eventpipe/*">
+        <ExcludeList Include="$(XunitTestBinBase)/profiler/**">
             <Issue>needs triage</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/profiler/eventpipe/eventpipe_readevents/*">
+        <ExcludeList Include="$(XunitTestBinBase)/profiler/elt/slowpatheltenter/*">
             <Issue>needs triage</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/profiler/gc/gc/**">
+        <ExcludeList Include="$(XunitTestBinBase)/profiler/elt/slowpatheltleave/*">
             <Issue>needs triage</Issue>
         </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/profiler/unittest/metadatagetdispenser/**">
diff --git a/src/coreclr/tests/publishdependency.targets b/src/coreclr/tests/publishdependency.targets
index 1442ad037d947d..2fb248218c1ba6 100644
--- a/src/coreclr/tests/publishdependency.targets
+++ b/src/coreclr/tests/publishdependency.targets
@@ -16,6 +16,7 @@
     <!-- These projects are individually restored in order. Each
          subsequent restore only copies files that don't already exist
          in CORE_ROOT, so assets from the first project file win. -->
+    <CoreRootProjectFiles Include="$(RepoRoot)src\coreclr\tests\src\Common\test_dependencies_fs\test_dependencies.fsproj" />
     <CoreRootProjectFiles Include="$(RepoRoot)src\coreclr\tests\src\Common\test_dependencies\test_dependencies.csproj" />
   </ItemGroup>
 
diff --git a/src/coreclr/tests/src/CLRTest.CrossGen.targets b/src/coreclr/tests/src/CLRTest.CrossGen.targets
index a1104376140342..96a8233cb34133 100644
--- a/src/coreclr/tests/src/CLRTest.CrossGen.targets
+++ b/src/coreclr/tests/src/CLRTest.CrossGen.targets
@@ -72,6 +72,8 @@ if [ ! -z ${RunCrossGen2+x} ]%3B then
       fi
     fi
 
+    ExtraCrossGen2Args+=" $(CrossGen2TestExtraArguments)"
+
     if [ ! -z ${LargeVersionBubble+x} ]%3B then
         ExtraCrossGen2Args+=" --inputbubble"
     fi
@@ -84,6 +86,14 @@ if [ ! -z ${RunCrossGen2+x} ]%3B then
       __ResponseFile="$__OutputFile.rsp"
       rm $__ResponseFile
 
+      # Suppress the GC stress COMPlus for the duration of Crossgen2 execution
+      local gcStressModeToRestore=$COMPlus_GCStress;
+      local heapVerifyModeToRestore=$COMPlus_HeapVerify;
+      local readyToRunModeToRestore=$COMPlus_ReadyToRun;
+      export COMPlus_GCStress=
+      export COMPlus_HeapVerify=
+      export COMPlus_ReadyToRun=
+
       __Command=$_DebuggerFullPath
       # Tests run locally need __TestDotNetCmd (set by runtest.py) or a compatible 5.0 dotnet runtime in the path
       if [ ! -z ${__TestDotNetCmd+x} ] %3B then
@@ -101,6 +111,7 @@ if [ ! -z ${RunCrossGen2+x} ]%3B then
       echo -r:$CORE_ROOT/System.*.dll>>$__ResponseFile
       echo -r:$CORE_ROOT/Microsoft.*.dll>>$__ResponseFile
       echo -r:$CORE_ROOT/mscorlib.dll>>$__ResponseFile
+      echo --verify-type-and-field-layout>>$__ResponseFile
       echo --targetarch:$(TargetArchitecture)>>$__ResponseFile
       echo -O>>$__ResponseFile
 
@@ -109,10 +120,14 @@ if [ ! -z ${RunCrossGen2+x} ]%3B then
       echo "Running CrossGen2: $__Command"
       $__Command
       __cg2ExitCode=$?
+
+      export COMPlus_GCStress=$gcStressModeToRestore
+      export COMPlus_HeapVerify=$heapVerifyModeToRestore
+      export COMPlus_ReadyToRun=$readyToRunModeToRestore
   }
 
     if [ ! -z ${CompositeBuildMode+x} ]%3B then
-        ExtraCrossGen2Args+= --composite
+        ExtraCrossGen2Args+=" --composite"
         OneFileCrossgen2 "$PWD/composite-r2r.dll" "$PWD/IL/*.dll"
     else
         ExtraCrossGen2Args+= -r:$PWD/IL/*.dll
@@ -174,6 +189,8 @@ if defined RunCrossGen (
 )
 REM CrossGen2 Script
 if defined RunCrossGen2 (
+    set ExtraCrossGen2Args=!ExtraCrossGen2Args! $(CrossGen2TestExtraArguments)
+
     if defined LargeVersionBubble ( set ExtraCrossGen2Args=!ExtraCrossGen2Args! --inputbubble)
     call :TakeLock
     set CrossGen2Status=0
@@ -212,6 +229,14 @@ if defined RunCrossGen2 (
     set __ResponseFile=!__OutputFile!.rsp
     del /Q !__ResponseFile!
 
+    REM Suppress GC stress mode for the duration of Crossgen2 execution
+    set __gcStressModeToRestore=!COMPlus_GCStress!
+    set COMPlus_GCStress=
+    set __heapVerifyModeToRestore=!COMPlus_HeapVerify!
+    set COMPlus_HeapVerify=
+    set __readyToRunModeToRestore=!COMPlus_ReadyToRun!
+    set COMPlus_ReadyToRun=
+
     set __Command=!_DebuggerFullPath!
     REM Tests run locally need __TestDotNetCmd (set by runtest.py) or a compatible 5.0 dotnet runtime in the path
     if defined __TestDotNetCmd (
@@ -225,6 +250,7 @@ if defined RunCrossGen2 (
     echo !__InputFile!>>!__ResponseFile!
     echo -o:!__OutputFile!>>!__ResponseFile!
     echo --targetarch:$(TargetArchitecture)>>!__ResponseFile!
+    echo --verify-type-and-field-layout>>!__ResponseFile!
     echo -O>>!__ResponseFile!
     echo -r:!CORE_ROOT!\System.*.dll>>!__ResponseFile!
     echo -r:!CORE_ROOT!\Microsoft.*.dll>>!__ResponseFile!
@@ -237,6 +263,10 @@ if defined RunCrossGen2 (
     echo "!__Command!"
     call !__Command!
     set CrossGen2Status=!ERRORLEVEL!
+    set COMPlus_GCStress=!__gcStressModeToRestore!
+    set COMPlus_HeapVerify=!__heapVerifyModeToRestore!
+    set COMPlus_ReadyToRun=!__readyToRunModeToRestore!
+
     Exit /b 0
 
 :DoneCrossgen2Operations
diff --git a/src/coreclr/tests/src/Common/test_dependencies_fs/test_dependencies.fsproj b/src/coreclr/tests/src/Common/test_dependencies_fs/test_dependencies.fsproj
new file mode 100644
index 00000000000000..ce4a2c2b040620
--- /dev/null
+++ b/src/coreclr/tests/src/Common/test_dependencies_fs/test_dependencies.fsproj
@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <CLRTestKind>BuildOnly</CLRTestKind>
+    <IsTestProject>false</IsTestProject>
+    <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+    <DisableRarCache>true</DisableRarCache>
+    <DisablePackageAssetsCache>true</DisablePackageAssetsCache>
+    <RuntimeIdentifiers>win-arm;win-arm64;win-x64;win-x86;$(TargetRid)</RuntimeIdentifiers>
+    <IncludeOOBLibraries>true</IncludeOOBLibraries>
+    <LibrariesConfiguration>Release</LibrariesConfiguration>
+  </PropertyGroup>
+
+  <Target Name="Build" DependsOnTargets="$(TraversalBuildDependsOn)" />
+
+  <PropertyGroup>
+    <ProjectAssetsFile>$(RepoRoot)src\coreclr\tests\src\Common\test_dependencies_fs\obj\project.assets.json</ProjectAssetsFile>
+  </PropertyGroup>
+
+  <Import Project="$(RepositoryEngineeringDir)liveBuilds.targets" />
+
+  <Target Name="AddLibrariesToCoreRootFS" BeforeTargets="AddLibrariesToCoreRoot" DependsOnTargets="ResolveLibrariesFromLocalBuild">
+    <ItemGroup>
+      <RuntimeCopyLocalItems Include="@(LibrariesRuntimeFiles)" />
+    </ItemGroup>
+  </Target>
+</Project>
diff --git a/src/coreclr/tests/src/Directory.Build.props b/src/coreclr/tests/src/Directory.Build.props
index 73cb6257a0bb1f..4722ae5b3bb49f 100644
--- a/src/coreclr/tests/src/Directory.Build.props
+++ b/src/coreclr/tests/src/Directory.Build.props
@@ -139,6 +139,7 @@
   <PropertyGroup>
     <TargetsUnknownUnix Condition="'$(TargetsUnix)' == 'true' AND '$(TargetOS)' != 'FreeBSD' AND '$(TargetOS)' != 'Linux' AND '$(TargetOS)' != 'NetBSD' AND '$(TargetOS)' != 'OSX' AND '$(TargetOS)' != 'illumos' AND '$(TargetOS)' != 'Solaris'">true</TargetsUnknownUnix>
     <Language Condition="'$(Language)' == '' and  '$(MSBuildProjectExtension)' == '.csproj'">C#</Language>
+    <Language Condition="'$(Language)' == '' and  '$(MSBuildProjectExtension)' == '.fsproj'">F#</Language>
     <Language Condition="'$(Language)' == '' and  '$(MSBuildProjectExtension)' == '.ilproj'">IL</Language>
   </PropertyGroup>
 
diff --git a/src/coreclr/tests/src/dirs.proj b/src/coreclr/tests/src/dirs.proj
index 253aea50cb9121..9656ac5da61c94 100644
--- a/src/coreclr/tests/src/dirs.proj
+++ b/src/coreclr/tests/src/dirs.proj
@@ -24,6 +24,7 @@
 
     <ItemGroup>
       <AllProjects Include="$(TestRoot)**\*.csproj" Exclude="@(DisabledProjects)" />
+      <AllProjects Include="$(TestRoot)**\*.fsproj" Exclude="@(DisabledProjects)" />
       <AllProjects Include="$(TestRoot)**\*.ilproj" Exclude="@(DisabledProjects)" />
     </ItemGroup>
 
diff --git a/src/coreclr/tests/src/runtest.proj b/src/coreclr/tests/src/runtest.proj
index f4d3e4b8857154..1cb606ef520a87 100644
--- a/src/coreclr/tests/src/runtest.proj
+++ b/src/coreclr/tests/src/runtest.proj
@@ -405,6 +405,9 @@ namespace $([System.String]::Copy($(Category)).Replace(".","_").Replace("\","").
     <MSBuild Projects="$(MSBuildThisFileDirectory)Common\test_dependencies\test_dependencies.csproj"
              Condition=" '$(BuildWrappers)'=='true' " />
 
+    <MSBuild Projects="$(MSBuildThisFileDirectory)Common\test_dependencies_fs\test_dependencies.fsproj"
+             Condition=" '$(BuildWrappers)'=='true' " />
+
     <MSBuild Projects="$(MSBuildProjectFile)"
              Targets="MonoAotCompileTests"
              Properties=""
diff --git a/src/coreclr/tests/testenvironment.proj b/src/coreclr/tests/testenvironment.proj
index fcb722769e9e4a..65dbb3ffb10b74 100644
--- a/src/coreclr/tests/testenvironment.proj
+++ b/src/coreclr/tests/testenvironment.proj
@@ -15,6 +15,7 @@
     <COMPlusVariables>
       COMPlus_TieredCompilation;
       COMPlus_DbgEnableMiniDump;
+      COMPlus_DbgEnableElfDumpOnMacOS;
       COMPlus_DbgMiniDumpName;
       COMPlus_EnableAES;
       COMPlus_EnableAVX;
@@ -65,6 +66,7 @@
     <TestEnvironment>
       <TieredCompilation>0</TieredCompilation>
       <DbgEnableMiniDump Condition="'$(TargetsWindows)' != 'true'">1</DbgEnableMiniDump> <!-- Enable minidumps for all scenarios -->
+      <DbgEnableElfDumpOnMacOS Condition="'$(TargetsOSX)' == 'true'">1</DbgEnableElfDumpOnMacOS> <!-- Enable minidumps for OSX -->
       <DbgMiniDumpName Condition="'$(TargetsWindows)' != 'true'">$HELIX_DUMP_FOLDER/coredump.%d.dmp</DbgMiniDumpName>
     </TestEnvironment>
   </ItemDefinitionGroup>
diff --git a/src/installer/corehost/CMakeLists.txt b/src/installer/corehost/CMakeLists.txt
index 651a63be0cac9d..46d1c5e898142e 100644
--- a/src/installer/corehost/CMakeLists.txt
+++ b/src/installer/corehost/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.14.5)
+cmake_minimum_required(VERSION 3.6.2)
 
 project(corehost)
 
diff --git a/src/installer/corehost/cli/apphost/static/CMakeLists.txt b/src/installer/corehost/cli/apphost/static/CMakeLists.txt
index 6d8d3f431aef20..85ea6ffe642dfc 100644
--- a/src/installer/corehost/cli/apphost/static/CMakeLists.txt
+++ b/src/installer/corehost/cli/apphost/static/CMakeLists.txt
@@ -30,6 +30,8 @@ set(HEADERS
     ../../../hostfxr_resolver.h
 )
 
+list(APPEND SOURCES $<TARGET_OBJECTS:libhostfxr_static> $<TARGET_OBJECTS:libhostpolicy_static>)
+
 if(CLR_CMAKE_TARGET_WIN32)
     list(APPEND SOURCES
         ../apphost.windows.cpp)
@@ -199,8 +201,6 @@ endif(NOT CLR_CMAKE_TARGET_LINUX)
 set_property(TARGET singlefilehost PROPERTY ENABLE_EXPORTS 1)
 
 target_link_libraries(singlefilehost
-    libhostfxr_static
-    libhostpolicy_static
     libhostcommon
     ${CORECLR_LIBRARIES}
 
diff --git a/src/installer/corehost/cli/comhost/clsidmap.cpp b/src/installer/corehost/cli/comhost/clsidmap.cpp
index b119c50ee9c548..7d740b95ab456b 100644
--- a/src/installer/corehost/cli/comhost/clsidmap.cpp
+++ b/src/installer/corehost/cli/comhost/clsidmap.cpp
@@ -43,16 +43,8 @@ namespace
         return S_OK;
     }
 
-    clsid_map parse_stream(_Inout_ pal::istream_t &json_map_raw)
+    clsid_map get_map_from_json(_In_ const json_parser_t &json)
     {
-        json_parser_t json;
-
-        if (!json.parse_stream(json_map_raw, _X("<embedded .clsidmap>")))
-        {
-            trace::error(_X("Embedded .clsidmap format is invalid"));
-            throw HResultException{ StatusCode::InvalidConfigFile };
-        }
-
         // Process JSON and construct a map
         HRESULT hr;
         clsid_map mapping;
@@ -86,16 +78,6 @@ namespace
         return mapping;
     }
 
-    class memory_buffer : public std::basic_streambuf<pal::istream_t::char_type>
-    {
-    public:
-        memory_buffer(_In_ DWORD dataInBytes, _In_reads_bytes_(dataInBytes) void *data)
-        {
-            auto raw_begin = reinterpret_cast<pal::istream_t::char_type*>(data);
-            setg(raw_begin, raw_begin, raw_begin + (dataInBytes / sizeof(pal::istream_t::char_type)));
-        }
-    };
-
     clsid_map get_json_map_from_resource(bool &found_resource)
     {
         found_resource = false;
@@ -117,9 +99,14 @@ namespace
         if (data == nullptr)
             throw HResultException{ E_UNEXPECTED }; // This should never happen in Windows 7+
 
-        memory_buffer resourceBuffer{ size, data };
-        pal::istream_t stream{ &resourceBuffer };
-        return parse_stream(stream);
+        json_parser_t json;
+        if (!json.parse_raw_data(reinterpret_cast<char*>(data), size, _X("<embedded .clsidmap>")))
+        {
+            trace::error(_X("Embedded .clsidmap format is invalid"));
+            throw HResultException{ StatusCode::InvalidConfigFile };
+        }
+
+        return get_map_from_json(json);
     }
 
     bool is_binary_unsigned(const pal::string_t &path)
@@ -190,8 +177,14 @@ namespace
         if (!pal::file_exists(map_file_name))
             return {};
 
-        pal::ifstream_t file{ map_file_name };
-        return parse_stream(file);
+        json_parser_t json;
+        if (!json.parse_file(map_file_name))
+        {
+            trace::error(_X("File .clsidmap format is invalid"));
+            throw HResultException{ StatusCode::InvalidConfigFile };
+        }
+
+        return get_map_from_json(json);
     }
 }
 
diff --git a/src/installer/corehost/cli/exe.cmake b/src/installer/corehost/cli/exe.cmake
index fed0bdd455b274..6431edfbc4f9bd 100644
--- a/src/installer/corehost/cli/exe.cmake
+++ b/src/installer/corehost/cli/exe.cmake
@@ -4,7 +4,6 @@
 project (${DOTNET_PROJECT_NAME})
 
 cmake_policy(SET CMP0011 NEW)
-cmake_policy(SET CMP0083 NEW)
 
 include(${CMAKE_CURRENT_LIST_DIR}/common.cmake)
 include(${CMAKE_CURRENT_LIST_DIR}/hostmisc/hostmisc.cmake)
diff --git a/src/installer/corehost/cli/fxr/standalone/CMakeLists.txt b/src/installer/corehost/cli/fxr/standalone/CMakeLists.txt
index d6c147f8f58803..c6b07eba340c9b 100644
--- a/src/installer/corehost/cli/fxr/standalone/CMakeLists.txt
+++ b/src/installer/corehost/cli/fxr/standalone/CMakeLists.txt
@@ -12,6 +12,7 @@ include_directories(../../fxr)
 # CMake does not recommend using globbing since it messes with the freshness checks
 set(SOURCES
     ./hostpolicy_resolver.cpp
+    $<TARGET_OBJECTS:libhostfxr_static>
 )
 
 set(HEADERS
@@ -48,4 +49,4 @@ if(CLR_CMAKE_HOST_UNIX)
 endif(CLR_CMAKE_HOST_UNIX)
 
 install_with_stripped_symbols(hostfxr TARGETS corehost)
-target_link_libraries(hostfxr libhostcommon libhostfxr_static)
+target_link_libraries(hostfxr libhostcommon)
diff --git a/src/installer/corehost/cli/hostpolicy/coreclr.cpp b/src/installer/corehost/cli/hostpolicy/coreclr.cpp
index a54d04e8714fc8..d9564ac8fa6768 100644
--- a/src/installer/corehost/cli/hostpolicy/coreclr.cpp
+++ b/src/installer/corehost/cli/hostpolicy/coreclr.cpp
@@ -147,7 +147,8 @@ namespace
         _X("APP_PATHS"),
         _X("APP_NI_PATHS"),
         _X("RUNTIME_IDENTIFIER"),
-        _X("BUNDLE_PROBE")
+        _X("BUNDLE_PROBE"),
+        _X("HOSTPOLICY_EMBEDDED")
     };
 
     static_assert((sizeof(PropertyNameMapping) / sizeof(*PropertyNameMapping)) == static_cast<size_t>(common_property::Last), "Invalid property count");
diff --git a/src/installer/corehost/cli/hostpolicy/coreclr.h b/src/installer/corehost/cli/hostpolicy/coreclr.h
index 9567fb9cab724d..c086ba56e10b2d 100644
--- a/src/installer/corehost/cli/hostpolicy/coreclr.h
+++ b/src/installer/corehost/cli/hostpolicy/coreclr.h
@@ -66,6 +66,7 @@ enum class common_property
     AppNIPaths,
     RuntimeIdentifier,
     BundleProbe,
+    HostPolicyEmbedded,
     // Sentinel value - new values should be defined above
     Last
 };
diff --git a/src/installer/corehost/cli/hostpolicy/hostpolicy_context.cpp b/src/installer/corehost/cli/hostpolicy/hostpolicy_context.cpp
index 05c61bb7806463..f7daa5d8458704 100644
--- a/src/installer/corehost/cli/hostpolicy/hostpolicy_context.cpp
+++ b/src/installer/corehost/cli/hostpolicy/hostpolicy_context.cpp
@@ -231,8 +231,20 @@ int hostpolicy_context_t::initialize(hostpolicy_init_t &hostpolicy_init, const a
         pal::stringstream_t ptr_stream;
         ptr_stream << "0x" << std::hex << (size_t)(&bundle_probe);
 
-        coreclr_properties.add(common_property::BundleProbe, ptr_stream.str().c_str());
+        if (!coreclr_properties.add(common_property::BundleProbe, ptr_stream.str().c_str()))
+        {
+            log_duplicate_property_error(coreclr_property_bag_t::common_property_to_string(common_property::StartUpHooks));
+            return StatusCode::LibHostDuplicateProperty;
+        }
+    }
+
+#if defined(HOSTPOLICY_EMBEDDED)
+    if (!coreclr_properties.add(common_property::HostPolicyEmbedded, _X("true")))
+    {
+        log_duplicate_property_error(coreclr_property_bag_t::common_property_to_string(common_property::StartUpHooks));
+        return StatusCode::LibHostDuplicateProperty;
     }
+#endif
 
     return StatusCode::Success;
 }
diff --git a/src/installer/corehost/cli/hostpolicy/static/CMakeLists.txt b/src/installer/corehost/cli/hostpolicy/static/CMakeLists.txt
index 3ee012f475dd51..fcf95656f5fb15 100644
--- a/src/installer/corehost/cli/hostpolicy/static/CMakeLists.txt
+++ b/src/installer/corehost/cli/hostpolicy/static/CMakeLists.txt
@@ -46,3 +46,5 @@ set(HEADERS
 set(SKIP_VERSIONING 1)
 set(BUILD_OBJECT_LIBRARY 1)
 include(../../lib_static.cmake)
+
+add_definitions(-DHOSTPOLICY_EMBEDDED)
diff --git a/src/installer/corehost/cli/json_parser.cpp b/src/installer/corehost/cli/json_parser.cpp
index 3953de11310781..740b71494aa8d0 100644
--- a/src/installer/corehost/cli/json_parser.cpp
+++ b/src/installer/corehost/cli/json_parser.cpp
@@ -74,8 +74,10 @@ void json_parser_t::realloc_buffer(size_t size)
     m_json[size] = '\0';
 }
 
-bool json_parser_t::parse_json(char* data, int64_t size, const pal::string_t& context)
+bool json_parser_t::parse_raw_data(char* data, int64_t size, const pal::string_t& context)
 {
+    assert(data != nullptr);
+
     constexpr auto flags = rapidjson::ParseFlag::kParseStopWhenDoneFlag | rapidjson::ParseFlag::kParseCommentsFlag;
 #ifdef _WIN32
     // Can't use in-situ parsing on Windows, as JSON data is encoded in
@@ -109,26 +111,6 @@ bool json_parser_t::parse_json(char* data, int64_t size, const pal::string_t& co
     return true;
 }
 
-bool json_parser_t::parse_stream(pal::istream_t& stream,
-                                 const pal::string_t& context)
-{
-    if (!stream.good())
-    {
-        trace::error(_X("Cannot use stream for resource [%s]: %s"), context.c_str(), pal::strerror(errno));
-        return false;
-    }
-
-    auto current_pos = ::get_utf8_bom_length(stream);
-    stream.seekg(0, stream.end);
-    auto stream_size = stream.tellg();
-    stream.seekg(current_pos, stream.beg);
-
-    realloc_buffer(stream_size - current_pos);
-    stream.read(m_json.data(), stream_size - current_pos);
-
-    return parse_json(m_json.data(), m_json.size(), context);
-}
-
 bool json_parser_t::parse_file(const pal::string_t& path)
 {
     // This code assumes that the caller has checked that the file `path` exists
@@ -145,13 +127,33 @@ bool json_parser_t::parse_file(const pal::string_t& path)
 
         if (m_bundle_data != nullptr)
         {
-            bool result = parse_json(m_bundle_data, m_bundle_location->size, path);
+            bool result = parse_raw_data(m_bundle_data, m_bundle_location->size, path);
             return result;
         }
     }
 
     pal::ifstream_t file{ path };
-    return parse_stream(file, path);
+    if (!file.good())
+    {
+        trace::error(_X("Cannot use file stream for [%s]: %s"), path.c_str(), pal::strerror(errno));
+        return false;
+    }
+
+    auto current_pos = ::get_utf8_bom_length(file);
+    file.seekg(0, file.end);
+    auto stream_size = file.tellg();
+    if (stream_size == -1)
+    {
+        trace::error(_X("Failed to get size of file [%s]"), path.c_str());
+        return false;
+    }
+
+    file.seekg(current_pos, file.beg);
+
+    realloc_buffer(stream_size - current_pos);
+    file.read(m_json.data(), stream_size - current_pos);
+
+    return parse_raw_data(m_json.data(), m_json.size(), path);
 }
 
 json_parser_t::~json_parser_t()
diff --git a/src/installer/corehost/cli/json_parser.h b/src/installer/corehost/cli/json_parser.h
index 350ea14e6037b2..f4be31d09b79d0 100644
--- a/src/installer/corehost/cli/json_parser.h
+++ b/src/installer/corehost/cli/json_parser.h
@@ -30,7 +30,7 @@ class json_parser_t {
 
         const document_t& document() const { return m_document; }
 
-        bool parse_stream(pal::istream_t& stream, const pal::string_t& context);
+        bool parse_raw_data(char* data, int64_t size, const pal::string_t& context);
         bool parse_file(const pal::string_t& path);
 
         json_parser_t()
@@ -52,7 +52,6 @@ class json_parser_t {
         const bundle::location_t* m_bundle_location; // Location of this json file within the bundle.
 
         void realloc_buffer(size_t size);
-        bool parse_json(char* data, int64_t size, const pal::string_t& context);
 };
 
 #endif // __JSON_PARSER_H__
diff --git a/src/installer/corehost/cli/test/mockhostfxr/CMakeLists.txt b/src/installer/corehost/cli/test/mockhostfxr/CMakeLists.txt
index 94099c49c1d6e1..8b5a55fe9b1772 100644
--- a/src/installer/corehost/cli/test/mockhostfxr/CMakeLists.txt
+++ b/src/installer/corehost/cli/test/mockhostfxr/CMakeLists.txt
@@ -1,7 +1,6 @@
 # Licensed to the .NET Foundation under one or more agreements.
 # The .NET Foundation licenses this file to you under the MIT license.
 
-cmake_minimum_required (VERSION 3.14.5)
 project(mockhostfxr_2_2)
 
 set(DOTNET_PROJECT_NAME "mockhostfxr_2_2")
diff --git a/src/installer/corehost/build.proj b/src/installer/corehost/corehost.proj
similarity index 100%
rename from src/installer/corehost/build.proj
rename to src/installer/corehost/corehost.proj
diff --git a/src/installer/managed/Microsoft.NET.HostModel/Bundle/FileEntry.cs b/src/installer/managed/Microsoft.NET.HostModel/Bundle/FileEntry.cs
index 2a37afcecf8e65..237a2a550fb153 100644
--- a/src/installer/managed/Microsoft.NET.HostModel/Bundle/FileEntry.cs
+++ b/src/installer/managed/Microsoft.NET.HostModel/Bundle/FileEntry.cs
@@ -41,10 +41,7 @@ public void Write(BinaryWriter writer)
             writer.Write(RelativePath);
         }
 
-        public override string ToString()
-        {
-            return string.Format($"{RelativePath} [{Type}] @{Offset} Sz={Size}");
-        }
+        public override string ToString() => $"{RelativePath} [{Type}] @{Offset} Sz={Size}";
     }
 }
 
diff --git a/src/installer/managed/Microsoft.NET.HostModel/Bundle/FileSpec.cs b/src/installer/managed/Microsoft.NET.HostModel/Bundle/FileSpec.cs
index ca6d0d872f17db..e245b33a0c610a 100644
--- a/src/installer/managed/Microsoft.NET.HostModel/Bundle/FileSpec.cs
+++ b/src/installer/managed/Microsoft.NET.HostModel/Bundle/FileSpec.cs
@@ -31,10 +31,7 @@ public bool IsValid()
                    !string.IsNullOrWhiteSpace(BundleRelativePath);
         }
 
-        public override string ToString()
-        {
-            return string.Format($"SourcePath: {SourcePath}, RelativePath: {BundleRelativePath} {(Excluded ? "[Excluded]" : "")}");
-        }
+        public override string ToString() => $"SourcePath: {SourcePath}, RelativePath: {BundleRelativePath} {(Excluded ? "[Excluded]" : "")}";
     }
 }
 
diff --git a/src/installer/managed/Microsoft.NET.HostModel/Bundle/TargetInfo.cs b/src/installer/managed/Microsoft.NET.HostModel/Bundle/TargetInfo.cs
index d1797b75f5d84d..5db826b027c78a 100644
--- a/src/installer/managed/Microsoft.NET.HostModel/Bundle/TargetInfo.cs
+++ b/src/installer/managed/Microsoft.NET.HostModel/Bundle/TargetInfo.cs
@@ -63,7 +63,7 @@ public string GetAssemblyName(string hostName)
         public override string ToString()
         {
             string os = IsWindows ? "win" : IsLinux ? "linux" : "osx";
-            return string.Format($"OS: {os} FrameworkVersion: {FrameworkVersion}");
+            return $"OS: {os} FrameworkVersion: {FrameworkVersion}";
         }
 
         static OSPlatform HostOS => RuntimeInformation.IsOSPlatform(OSPlatform.Linux) ? OSPlatform.Linux :
diff --git a/src/installer/pkg/projects/descriptions.json b/src/installer/pkg/projects/descriptions.json
index b3e4471c47c737..4b4ae7f6d83b55 100644
--- a/src/installer/pkg/projects/descriptions.json
+++ b/src/installer/pkg/projects/descriptions.json
@@ -48,10 +48,5 @@
         "Name": "Microsoft.NETCore.App.Ref",
         "Description": "A set of .NET APIs that are included in the default .NET application model. Contains reference assemblies, documentation, and other design-time assets.",
         "CommonTypes": [ ]
-    },
-    {
-        "Name": "NETStandard.Library.Ref",
-        "Description": "A set of standard .NET APIs that are prescribed to be used and supported together. Contains reference assemblies, documentation, and other design-time assets.",
-        "CommonTypes": [ ]
     }
 ]
diff --git a/src/installer/pkg/projects/netcoreapp/pkg/Microsoft.NETCore.App.Crossgen2.pkgproj b/src/installer/pkg/projects/netcoreapp/pkg/Microsoft.NETCore.App.Crossgen2.pkgproj
index 08933b1336529e..e9fc92b2acbba5 100644
--- a/src/installer/pkg/projects/netcoreapp/pkg/Microsoft.NETCore.App.Crossgen2.pkgproj
+++ b/src/installer/pkg/projects/netcoreapp/pkg/Microsoft.NETCore.App.Crossgen2.pkgproj
@@ -38,7 +38,7 @@
           DependsOnTargets="ConvertItems"
           BeforeTargets="GetPackageFiles">
     <ItemGroup>
-      <RuntimeFile Include="@(File->HasMetadata('TargetPath'))" />
+      <RuntimeFile Include="@(File->HasMetadata('TargetPath'))" Exclude="$(PackageIconFullPath)" />
       <File Remove="@(RuntimeFile)" />
     </ItemGroup>
 
diff --git a/src/installer/pkg/projects/netstandard/Directory.Build.props b/src/installer/pkg/projects/netstandard/Directory.Build.props
deleted file mode 100644
index 1597af77869da2..00000000000000
--- a/src/installer/pkg/projects/netstandard/Directory.Build.props
+++ /dev/null
@@ -1,8 +0,0 @@
-<Project>
-  <PropertyGroup>
-    <RIDPropsFile>$(MSBuildThisFileDirectory)netstandardRIDs.props</RIDPropsFile>
-  </PropertyGroup>
-
-  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props, $(MSBuildThisFileDirectory)..))" />
-
-</Project>
diff --git a/src/installer/pkg/projects/netstandard/netstandardRIDs.props b/src/installer/pkg/projects/netstandard/netstandardRIDs.props
deleted file mode 100644
index 0b0cbcde167d27..00000000000000
--- a/src/installer/pkg/projects/netstandard/netstandardRIDs.props
+++ /dev/null
@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<Project ToolsVersion="14.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-
-  <!-- .NET Standard has no shared framework, so there are no RIDs. -->
-
-</Project>
diff --git a/src/installer/pkg/projects/netstandard/pkg/Directory.Build.props b/src/installer/pkg/projects/netstandard/pkg/Directory.Build.props
deleted file mode 100644
index 2826aeac134c75..00000000000000
--- a/src/installer/pkg/projects/netstandard/pkg/Directory.Build.props
+++ /dev/null
@@ -1,28 +0,0 @@
-<Project>
-  <PropertyGroup>
-    <IsFrameworkPackage>true</IsFrameworkPackage>
-    <ShortFrameworkName>netstandard</ShortFrameworkName>
-    <ProductBrandPrefix>Microsoft .NET Standard</ProductBrandPrefix>
-  </PropertyGroup>
-
-  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props, $(MSBuildThisFileDirectory)..))" />
-
-  <PropertyGroup>
-    <ProductBandVersion>2.1</ProductBandVersion>
-    <PatchVersion>$(NETStandardPatchVersion)</PatchVersion>
-
-    <FrameworkListName>.NET Standard 2.1</FrameworkListName>
-    <FrameworkListTargetFrameworkIdentifier>.NETStandard</FrameworkListTargetFrameworkIdentifier>
-    <FrameworkListTargetFrameworkVersion>2.1</FrameworkListTargetFrameworkVersion>
-    <FrameworkListFrameworkName>NETStandard.Library</FrameworkListFrameworkName>
-
-    <VSInsertionProductName>NetStandard</VSInsertionProductName>
-  </PropertyGroup>
-
-  <!-- Redistribute package content from other nuget packages. -->
-  <ItemGroup>
-    <ProjectReference Include="$(MSBuildThisFileDirectory)..\src\netstandard.depproj">
-      <AdditionalProperties Condition="'$(PackageTargetRuntime)' != ''">RuntimeIdentifier=$(PackageTargetRuntime)</AdditionalProperties>
-    </ProjectReference>
-  </ItemGroup>
-</Project>
diff --git a/src/installer/pkg/projects/netstandard/pkg/NETStandard.Library.Ref.pkgproj b/src/installer/pkg/projects/netstandard/pkg/NETStandard.Library.Ref.pkgproj
deleted file mode 100644
index b9391580563b03..00000000000000
--- a/src/installer/pkg/projects/netstandard/pkg/NETStandard.Library.Ref.pkgproj
+++ /dev/null
@@ -1,13 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-
-  <PropertyGroup>
-    <!-- .NET Standard has no shared framework, so there is no data for a platform manifest. -->
-    <PlatformManifestTargetPath />
-  </PropertyGroup>
-
-  <ItemGroup>
-    <!-- File contents are copied from https://github.com/dotnet/sdk/blob/ec2f3741092f164daeb023e7caa4364c810461e2/src/Tasks/Common/targets/Microsoft.NET.DefaultPackageConflictOverrides.targets#L133 -->
-    <File Include="PackageOverrides.txt" TargetPath="data/" />
-  </ItemGroup>
-
-</Project>
diff --git a/src/installer/pkg/projects/netstandard/pkg/PackageOverrides.txt b/src/installer/pkg/projects/netstandard/pkg/PackageOverrides.txt
deleted file mode 100644
index 8aa32ade39a8c9..00000000000000
--- a/src/installer/pkg/projects/netstandard/pkg/PackageOverrides.txt
+++ /dev/null
@@ -1,95 +0,0 @@
-Microsoft.Win32.Primitives|4.3.0
-System.AppContext|4.3.0
-System.Collections|4.3.0
-System.Collections.Concurrent|4.3.0
-System.Collections.Immutable|1.4.0
-System.Collections.NonGeneric|4.3.0
-System.Collections.Specialized|4.3.0
-System.ComponentModel|4.3.0
-System.ComponentModel.EventBasedAsync|4.3.0
-System.ComponentModel.Primitives|4.3.0
-System.ComponentModel.TypeConverter|4.3.0
-System.Console|4.3.0
-System.Data.Common|4.3.0
-System.Diagnostics.Contracts|4.3.0
-System.Diagnostics.Debug|4.3.0
-System.Diagnostics.FileVersionInfo|4.3.0
-System.Diagnostics.Process|4.3.0
-System.Diagnostics.StackTrace|4.3.0
-System.Diagnostics.TextWriterTraceListener|4.3.0
-System.Diagnostics.Tools|4.3.0
-System.Diagnostics.TraceSource|4.3.0
-System.Diagnostics.Tracing|4.3.0
-System.Dynamic.Runtime|4.3.0
-System.Globalization|4.3.0
-System.Globalization.Calendars|4.3.0
-System.Globalization.Extensions|4.3.0
-System.IO|4.3.0
-System.IO.Compression|4.3.0
-System.IO.Compression.ZipFile|4.3.0
-System.IO.FileSystem|4.3.0
-System.IO.FileSystem.DriveInfo|4.3.0
-System.IO.FileSystem.Primitives|4.3.0
-System.IO.FileSystem.Watcher|4.3.0
-System.IO.IsolatedStorage|4.3.0
-System.IO.MemoryMappedFiles|4.3.0
-System.IO.Pipes|4.3.0
-System.IO.UnmanagedMemoryStream|4.3.0
-System.Linq|4.3.0
-System.Linq.Expressions|4.3.0
-System.Linq.Queryable|4.3.0
-System.Net.Http|4.3.0
-System.Net.NameResolution|4.3.0
-System.Net.Primitives|4.3.0
-System.Net.Requests|4.3.0
-System.Net.Security|4.3.0
-System.Net.Sockets|4.3.0
-System.Net.WebHeaderCollection|4.3.0
-System.ObjectModel|4.3.0
-System.Private.DataContractSerialization|4.3.0
-System.Reflection|4.3.0
-System.Reflection.Emit|4.3.0
-System.Reflection.Emit.ILGeneration|4.3.0
-System.Reflection.Emit.Lightweight|4.3.0
-System.Reflection.Extensions|4.3.0
-System.Reflection.Primitives|4.3.0
-System.Reflection.TypeExtensions|4.3.0
-System.Resources.ResourceManager|4.3.0
-System.Runtime|4.3.0
-System.Runtime.Extensions|4.3.0
-System.Runtime.Handles|4.3.0
-System.Runtime.InteropServices|4.3.0
-System.Runtime.InteropServices.RuntimeInformation|4.3.0
-System.Runtime.Loader|4.3.0
-System.Runtime.Numerics|4.3.0
-System.Runtime.Serialization.Formatters|4.3.0
-System.Runtime.Serialization.Json|4.3.0
-System.Runtime.Serialization.Primitives|4.3.0
-System.Security.AccessControl|4.4.0
-System.Security.Claims|4.3.0
-System.Security.Cryptography.Algorithms|4.3.0
-System.Security.Cryptography.Csp|4.3.0
-System.Security.Cryptography.Encoding|4.3.0
-System.Security.Cryptography.Primitives|4.3.0
-System.Security.Cryptography.X509Certificates|4.3.0
-System.Security.Cryptography.Xml|4.4.0
-System.Security.Principal|4.3.0
-System.Security.Principal.Windows|4.4.0
-System.Text.Encoding|4.3.0
-System.Text.Encoding.Extensions|4.3.0
-System.Text.RegularExpressions|4.3.0
-System.Threading|4.3.0
-System.Threading.Overlapped|4.3.0
-System.Threading.Tasks|4.3.0
-System.Threading.Tasks.Extensions|4.3.0
-System.Threading.Tasks.Parallel|4.3.0
-System.Threading.Thread|4.3.0
-System.Threading.ThreadPool|4.3.0
-System.Threading.Timer|4.3.0
-System.ValueTuple|4.3.0
-System.Xml.ReaderWriter|4.3.0
-System.Xml.XDocument|4.3.0
-System.Xml.XmlDocument|4.3.0
-System.Xml.XmlSerializer|4.3.0
-System.Xml.XPath|4.3.0
-System.Xml.XPath.XDocument|4.3.0
diff --git a/src/installer/pkg/projects/netstandard/src/netstandard.depproj b/src/installer/pkg/projects/netstandard/src/netstandard.depproj
deleted file mode 100644
index ec841c9a3df97e..00000000000000
--- a/src/installer/pkg/projects/netstandard/src/netstandard.depproj
+++ /dev/null
@@ -1,25 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-
-  <PropertyGroup>
-    <NETStandardTargetFramework>netstandard2.1</NETStandardTargetFramework>
-  </PropertyGroup>
-
-  <ItemGroup>
-    <PackageReference Include="$(NETStandardLibraryPackage)" Version="$(NETStandardLibraryVersion)" />
-  </ItemGroup>
-
-  <!--
-    Redistribute files from the netstandard package's build/ dir. When this project consumes a 
-    transport package from dotnet/standard with ref assemblies in ref/netstandard2.1, this target
-    can be removed.
-  -->
-  <Target Name="GetNETStandardRefFilesToPackage"
-          BeforeTargets="GetFilesToPackage">
-    <ItemGroup>
-      <FilesToPackage
-        Include="$(NuGetPackageRoot)$(NETStandardLibraryPackage)\$(NETStandardLibraryVersion)\build\$(NETStandardTargetFramework)\ref\*"
-        TargetPath="ref/$(NETStandardTargetFramework)" />
-    </ItemGroup>
-  </Target>
-
-</Project>
diff --git a/src/installer/tests/Assets/TestProjects/ComLibrary/ComLibrary.csproj b/src/installer/tests/Assets/TestProjects/ComLibrary/ComLibrary.csproj
index 637cbf46c656dd..27861faa61056d 100644
--- a/src/installer/tests/Assets/TestProjects/ComLibrary/ComLibrary.csproj
+++ b/src/installer/tests/Assets/TestProjects/ComLibrary/ComLibrary.csproj
@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
     <RuntimeFrameworkVersion>$(MNAVersion)</RuntimeFrameworkVersion>
+    <GenerateRuntimeConfigurationFiles>true</GenerateRuntimeConfigurationFiles>
   </PropertyGroup>
 
 </Project>
diff --git a/src/installer/tests/HostActivation.Tests/NativeHosting/Comhost.cs b/src/installer/tests/HostActivation.Tests/NativeHosting/Comhost.cs
index ddf80fe20a2948..7c6f5976c630d1 100644
--- a/src/installer/tests/HostActivation.Tests/NativeHosting/Comhost.cs
+++ b/src/installer/tests/HostActivation.Tests/NativeHosting/Comhost.cs
@@ -1,10 +1,12 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using Microsoft.DotNet.Cli.Build.Framework;
-using Newtonsoft.Json.Linq;
 using System.IO;
+using System.Reflection.Metadata;
 using System.Runtime.InteropServices;
+
+using Microsoft.DotNet.Cli.Build.Framework;
+using Microsoft.NET.HostModel.ComHost;
 using Xunit;
 
 namespace Microsoft.DotNet.CoreSetup.Test.HostActivation.NativeHosting
@@ -136,26 +138,26 @@ public SharedTestState()
                     .EnsureRestored(RepoDirectories.CorehostPackages)
                     .BuildProject();
 
-                // [TODO] BEGIN - Remove once using .NET Core 3.0 to build tests
-                ComHostPath = Path.Combine(
-                    ComLibraryFixture.TestProject.BuiltApp.Location,
-                    $"{ ComLibraryFixture.TestProject.AssemblyName }.comhost.dll");
-
-                File.Copy(Path.Combine(RepoDirectories.CorehostPackages, "comhost.dll"), ComHostPath);
-
-                RuntimeConfig.FromFile(ComLibraryFixture.TestProject.RuntimeConfigJson)
-                    .WithFramework(new RuntimeConfig.Framework("Microsoft.NETCore.App", RepoDirectories.MicrosoftNETCoreAppVersion))
-                    .Save();
-
-                JObject clsidMap = new JObject()
+                // Create a .clsidmap from the assembly
+                string clsidMapPath = Path.Combine(BaseDirectory, $"{ ComLibraryFixture.TestProject.AssemblyName }.clsidmap");
+                using (var assemblyStream = new FileStream(ComLibraryFixture.TestProject.AppDll, FileMode.Open, FileAccess.Read, FileShare.Delete | FileShare.Read))
+                using (var peReader = new System.Reflection.PortableExecutable.PEReader(assemblyStream))
                 {
+                    if (peReader.HasMetadata)
                     {
-                        ClsidString,
-                        new JObject() { {"assembly", "ComLibrary" }, {"type", "ComLibrary.Server" } }
+                        MetadataReader reader = peReader.GetMetadataReader();
+                        ClsidMap.Create(reader, clsidMapPath);
                     }
-                };
-                File.WriteAllText($"{ ComHostPath }.clsidmap", clsidMap.ToString());
-                // [TODO] END - Remove once using .NET Core 3.0 to build tests
+                }
+
+                // Use the locally built comhost to create a comhost with the embedded .clsidmap 
+                ComHostPath = Path.Combine(
+                    ComLibraryFixture.TestProject.BuiltApp.Location,
+                    $"{ ComLibraryFixture.TestProject.AssemblyName }.comhost.dll");
+                ComHost.Create(
+                    Path.Combine(RepoDirectories.CorehostPackages, "comhost.dll"),
+                    ComHostPath,
+                    clsidMapPath);
             }
 
             protected override void Dispose(bool disposing)
diff --git a/src/installer/tests/Microsoft.DotNet.CoreSetup.Packaging.Tests/NETStandardTests.cs b/src/installer/tests/Microsoft.DotNet.CoreSetup.Packaging.Tests/NETStandardTests.cs
deleted file mode 100644
index 0c5c4a29b97ee8..00000000000000
--- a/src/installer/tests/Microsoft.DotNet.CoreSetup.Packaging.Tests/NETStandardTests.cs
+++ /dev/null
@@ -1,43 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Microsoft.DotNet.CoreSetup.Test;
-using Xunit;
-
-namespace Microsoft.DotNet.CoreSetup.Packaging.Tests
-{
-    public class NETStandardTests
-    {
-        private readonly RepoDirectoriesProvider dirs = new RepoDirectoriesProvider();
-
-        [Fact]
-        public void NETStandardTargetingPackIsValid()
-        {
-            using (var tester = NuGetArtifactTester.OpenOrNull(
-                dirs,
-                "NETStandard.Library.Ref"))
-            {
-                // Allow no targeting pack in case this is a servicing build.
-                // This condition should be tightened: https://github.com/dotnet/core-setup/issues/8830
-                if (tester == null)
-                {
-                    return;
-                }
-
-                tester.HasOnlyTheseDataFiles(
-                    "data/FrameworkList.xml",
-                    "data/PackageOverrides.txt");
-
-                tester.IsTargetingPack();
-
-                // Most artifacts in the repo use the global Major.Minor, this package doesn't. Test
-                // this to make sure infra doesn't regress and cause netstandard to lose its special
-                // 2.1 version. The versioning difference is because netstandard targeting pack
-                // creation doesn't actually belong in Core-Setup: https://github.com/dotnet/standard/issues/1209
-                Assert.Equal(
-                    (2, 1),
-                    (tester.PackageVersion.Major, tester.PackageVersion.Minor));
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/src/Extensions/ActivatorUtilities/ActivatorUtilities.cs b/src/libraries/Common/src/Extensions/ActivatorUtilities/ActivatorUtilities.cs
index 7f5b6c3aa0a529..574fd893febaae 100644
--- a/src/libraries/Common/src/Extensions/ActivatorUtilities/ActivatorUtilities.cs
+++ b/src/libraries/Common/src/Extensions/ActivatorUtilities/ActivatorUtilities.cs
@@ -40,7 +40,10 @@ static class ActivatorUtilities
         /// <param name="instanceType">The type to activate</param>
         /// <param name="parameters">Constructor arguments not provided by the <paramref name="provider"/>.</param>
         /// <returns>An activated object of type instanceType</returns>
-        public static object CreateInstance(IServiceProvider provider, Type instanceType, params object[] parameters)
+        public static object CreateInstance(
+            IServiceProvider provider,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type instanceType,
+            params object[] parameters)
         {
             int bestLength = -1;
             bool seenPreferred = false;
@@ -49,11 +52,9 @@ public static object CreateInstance(IServiceProvider provider, Type instanceType
 
             if (!instanceType.GetTypeInfo().IsAbstract)
             {
-                foreach (ConstructorInfo? constructor in instanceType
-                    .GetTypeInfo()
-                    .DeclaredConstructors)
+                foreach (ConstructorInfo? constructor in instanceType.GetConstructors())
                 {
-                    if (!constructor.IsStatic && constructor.IsPublic)
+                    if (!constructor.IsStatic)
                     {
                         var matcher = new ConstructorMatcher(constructor);
                         bool isPreferred = constructor.IsDefined(typeof(ActivatorUtilitiesConstructorAttribute), false);
@@ -104,7 +105,9 @@ public static object CreateInstance(IServiceProvider provider, Type instanceType
         /// A factory that will instantiate instanceType using an <see cref="IServiceProvider"/>
         /// and an argument array containing objects matching the types defined in argumentTypes
         /// </returns>
-        public static ObjectFactory CreateFactory(Type instanceType, Type[] argumentTypes)
+        public static ObjectFactory CreateFactory(
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type instanceType,
+            Type[] argumentTypes)
         {
             FindApplicableConstructor(instanceType, argumentTypes, out ConstructorInfo? constructor, out int?[]? parameterMap);
 
@@ -126,19 +129,18 @@ public static ObjectFactory CreateFactory(Type instanceType, Type[] argumentType
         /// <param name="provider">The service provider used to resolve dependencies</param>
         /// <param name="parameters">Constructor arguments not provided by the <paramref name="provider"/>.</param>
         /// <returns>An activated object of type T</returns>
-        public static T CreateInstance<T>(IServiceProvider provider, params object[] parameters)
+        public static T CreateInstance<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] T>(IServiceProvider provider, params object[] parameters)
         {
             return (T)CreateInstance(provider, typeof(T), parameters);
         }
 
-
         /// <summary>
         /// Retrieve an instance of the given type from the service provider. If one is not found then instantiate it directly.
         /// </summary>
         /// <typeparam name="T">The type of the service</typeparam>
         /// <param name="provider">The service provider used to resolve dependencies</param>
         /// <returns>The resolved service or created instance</returns>
-        public static T GetServiceOrCreateInstance<T>(IServiceProvider provider)
+        public static T GetServiceOrCreateInstance<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] T>(IServiceProvider provider)
         {
             return (T)GetServiceOrCreateInstance(provider, typeof(T));
         }
@@ -149,7 +151,9 @@ public static T GetServiceOrCreateInstance<T>(IServiceProvider provider)
         /// <param name="provider">The service provider</param>
         /// <param name="type">The type of the service</param>
         /// <returns>The resolved service or created instance</returns>
-        public static object GetServiceOrCreateInstance(IServiceProvider provider, Type type)
+        public static object GetServiceOrCreateInstance(
+            IServiceProvider provider,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type type)
         {
             return provider.GetService(type) ?? CreateInstance(provider, type);
         }
@@ -214,7 +218,7 @@ private static Expression BuildFactoryExpression(
         }
 
         private static void FindApplicableConstructor(
-            Type instanceType,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type instanceType,
             Type[] argumentTypes,
             out ConstructorInfo matchingConstructor,
             out int?[] matchingParameterMap)
@@ -235,14 +239,14 @@ private static void FindApplicableConstructor(
 
         // Tries to find constructor based on provided argument types
         private static bool TryFindMatchingConstructor(
-            Type instanceType,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type instanceType,
             Type[] argumentTypes,
             [NotNullWhen(true)] ref ConstructorInfo? matchingConstructor,
             [NotNullWhen(true)] ref int?[]? parameterMap)
         {
-            foreach (ConstructorInfo? constructor in instanceType.GetTypeInfo().DeclaredConstructors)
+            foreach (ConstructorInfo? constructor in instanceType.GetConstructors())
             {
-                if (constructor.IsStatic || !constructor.IsPublic)
+                if (constructor.IsStatic)
                 {
                     continue;
                 }
@@ -270,15 +274,15 @@ private static bool TryFindMatchingConstructor(
 
         // Tries to find constructor marked with ActivatorUtilitiesConstructorAttribute
         private static bool TryFindPreferredConstructor(
-            Type instanceType,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type instanceType,
             Type[] argumentTypes,
             [NotNullWhen(true)] ref ConstructorInfo? matchingConstructor,
             [NotNullWhen(true)] ref int?[]? parameterMap)
         {
             bool seenPreferred = false;
-            foreach (ConstructorInfo? constructor in instanceType.GetTypeInfo().DeclaredConstructors)
+            foreach (ConstructorInfo? constructor in instanceType.GetConstructors())
             {
-                if (constructor.IsStatic || !constructor.IsPublic)
+                if (constructor.IsStatic)
                 {
                     continue;
                 }
diff --git a/src/libraries/Common/src/Extensions/ParameterDefaultValue/ParameterDefaultValue.cs b/src/libraries/Common/src/Extensions/ParameterDefaultValue/ParameterDefaultValue.cs
index 03f1b26ec0e233..45e8a6aea1d0b7 100644
--- a/src/libraries/Common/src/Extensions/ParameterDefaultValue/ParameterDefaultValue.cs
+++ b/src/libraries/Common/src/Extensions/ParameterDefaultValue/ParameterDefaultValue.cs
@@ -4,6 +4,7 @@
 #nullable enable
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 
 namespace Microsoft.Extensions.Internal
@@ -41,9 +42,13 @@ public static bool TryGetDefaultValue(ParameterInfo parameter, out object? defau
                 // Workaround for https://github.com/dotnet/corefx/issues/11797
                 if (defaultValue == null && parameter.ParameterType.IsValueType)
                 {
-                    defaultValue = Activator.CreateInstance(parameter.ParameterType);
+                    defaultValue = CreateValueType(parameter.ParameterType);
                 }
 
+                [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2006:UnrecognizedReflectionPattern",
+                    Justification = "CreateInstance is only called on a ValueType, which will always have a default constructor.")]
+                object? CreateValueType(Type t) => Activator.CreateInstance(t);
+
                 // Handle nullable enums
                 if (defaultValue != null &&
                     parameter.ParameterType.IsGenericType &&
diff --git a/src/libraries/Common/src/Extensions/ProviderAliasUtilities/ProviderAliasUtilities.cs b/src/libraries/Common/src/Extensions/ProviderAliasUtilities/ProviderAliasUtilities.cs
index 4fb6f86ba23e6b..40e80be6447651 100644
--- a/src/libraries/Common/src/Extensions/ProviderAliasUtilities/ProviderAliasUtilities.cs
+++ b/src/libraries/Common/src/Extensions/ProviderAliasUtilities/ProviderAliasUtilities.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics;
 using System.Reflection;
 
 namespace Microsoft.Extensions.Logging
@@ -9,21 +10,18 @@ namespace Microsoft.Extensions.Logging
     internal static class ProviderAliasUtilities
     {
         private const string AliasAttibuteTypeFullName = "Microsoft.Extensions.Logging.ProviderAliasAttribute";
-        private const string AliasAttibuteAliasProperty = "Alias";
 
         internal static string GetAlias(Type providerType)
         {
-            foreach (object attribute in providerType.GetTypeInfo().GetCustomAttributes(inherit: false))
+            foreach (CustomAttributeData attributeData in CustomAttributeData.GetCustomAttributes(providerType))
             {
-                if (attribute.GetType().FullName == AliasAttibuteTypeFullName)
+                if (attributeData.AttributeType.FullName == AliasAttibuteTypeFullName)
                 {
-                    PropertyInfo valueProperty = attribute
-                        .GetType()
-                        .GetProperty(AliasAttibuteAliasProperty, BindingFlags.Public | BindingFlags.Instance);
-
-                    if (valueProperty != null)
+                    foreach (CustomAttributeTypedArgument arg in attributeData.ConstructorArguments)
                     {
-                        return valueProperty.GetValue(attribute) as string;
+                        Debug.Assert(arg.ArgumentType == typeof(string));
+
+                        return arg.Value?.ToString();
                     }
                 }
             }
diff --git a/src/libraries/Common/src/Interop/FreeBSD/Interop.Libraries.cs b/src/libraries/Common/src/Interop/FreeBSD/Interop.Libraries.cs
index 5f7687f057d82d..dc12091e1c02c2 100644
--- a/src/libraries/Common/src/Interop/FreeBSD/Interop.Libraries.cs
+++ b/src/libraries/Common/src/Interop/FreeBSD/Interop.Libraries.cs
@@ -6,6 +6,6 @@ internal static partial class Interop
     internal static partial class Libraries
     {
         internal const string Odbc32 = "libodbc.so.2";
-        internal const string MsQuic = "msquic";
+        internal const string MsQuic = "libmsquic.so";
     }
 }
diff --git a/src/libraries/Common/src/Interop/Interop.Calendar.cs b/src/libraries/Common/src/Interop/Interop.Calendar.cs
index 9be426d367a6e4..bf71a56cf3f08f 100644
--- a/src/libraries/Common/src/Interop/Interop.Calendar.cs
+++ b/src/libraries/Common/src/Interop/Interop.Calendar.cs
@@ -9,25 +9,14 @@ internal static partial class Interop
 {
     internal static partial class Globalization
     {
-        internal unsafe delegate void EnumCalendarInfoCallback(
-           char* calendarString,
-           IntPtr context);
-
         [DllImport(Libraries.GlobalizationNative, CharSet = CharSet.Unicode, EntryPoint = "GlobalizationNative_GetCalendars")]
         internal static extern int GetCalendars(string localeName, CalendarId[] calendars, int calendarsCapacity);
 
         [DllImport(Libraries.GlobalizationNative, CharSet = CharSet.Unicode, EntryPoint = "GlobalizationNative_GetCalendarInfo")]
         internal static extern unsafe ResultCode GetCalendarInfo(string localeName, CalendarId calendarId, CalendarDataType calendarDataType, char* result, int resultCapacity);
 
-#if TARGET_BROWSER
-        // Temp workaround for pinvoke callbacks for Mono-Wasm-Interpreter
-        // https://github.com/dotnet/runtime/issues/39100
-        [DllImport(Libraries.GlobalizationNative, CharSet = CharSet.Unicode, EntryPoint = "GlobalizationNative_EnumCalendarInfo")]
-        internal static extern bool EnumCalendarInfo(IntPtr callback, string localeName, CalendarId calendarId, CalendarDataType calendarDataType, IntPtr context);
-#else
         [DllImport(Libraries.GlobalizationNative, CharSet = CharSet.Unicode, EntryPoint = "GlobalizationNative_EnumCalendarInfo")]
-        internal static extern bool EnumCalendarInfo(EnumCalendarInfoCallback callback, string localeName, CalendarId calendarId, CalendarDataType calendarDataType, IntPtr context);
-#endif
+        internal static extern unsafe bool EnumCalendarInfo(delegate* <char*, IntPtr, void> callback, string localeName, CalendarId calendarId, CalendarDataType calendarDataType, IntPtr context);
 
         [DllImport(Libraries.GlobalizationNative, EntryPoint = "GlobalizationNative_GetLatestJapaneseEra")]
         internal static extern int GetLatestJapaneseEra();
diff --git a/src/libraries/Common/src/Interop/Interop.Odbc.cs b/src/libraries/Common/src/Interop/Interop.Odbc.cs
index 591ce1cadeb3a9..4113c59e4fefb1 100644
--- a/src/libraries/Common/src/Interop/Interop.Odbc.cs
+++ b/src/libraries/Common/src/Interop/Interop.Odbc.cs
@@ -250,9 +250,9 @@ internal static partial class Odbc
         [DllImport(Interop.Libraries.Odbc32, CharSet = CharSet.Unicode)]
         internal static extern /*SQLRETURN*/ODBC32.RetCode SQLPrimaryKeysW(
             /*SQLHSTMT*/OdbcStatementHandle StatementHandle,
-            /*SQLCHAR* */string CatalogName,
+            /*SQLCHAR* */string? CatalogName,
             /*SQLSMALLINT*/short NameLen1,
-            /*SQLCHAR* */ string SchemaName,
+            /*SQLCHAR* */ string? SchemaName,
             /*SQLSMALLINT*/short NameLen2,
             /*SQLCHAR* */string TableName,
             /*SQLSMALLINT*/short NameLen3);
@@ -260,13 +260,13 @@ internal static partial class Odbc
         [DllImport(Interop.Libraries.Odbc32, CharSet = CharSet.Unicode)]
         internal static extern /*SQLRETURN*/ODBC32.RetCode SQLProcedureColumnsW(
             /*SQLHSTMT*/OdbcStatementHandle StatementHandle,
-            /*SQLCHAR* */ string CatalogName,
+            /*SQLCHAR* */ string? CatalogName,
             /*SQLSMALLINT*/short NameLen1,
-            /*SQLCHAR* */ string SchemaName,
+            /*SQLCHAR* */ string? SchemaName,
             /*SQLSMALLINT*/short NameLen2,
-            /*SQLCHAR* */ string ProcName,
+            /*SQLCHAR* */ string? ProcName,
             /*SQLSMALLINT*/short NameLen3,
-            /*SQLCHAR* */ string ColumnName,
+            /*SQLCHAR* */ string? ColumnName,
             /*SQLSMALLINT*/short NameLen4);
 
         [DllImport(Interop.Libraries.Odbc32, CharSet = CharSet.Unicode)]
@@ -347,9 +347,9 @@ internal static partial class Odbc
         internal static extern /*SQLRETURN*/ODBC32.RetCode SQLSpecialColumnsW(
             /*SQLHSTMT*/OdbcStatementHandle StatementHandle,
             /*SQLUSMALLINT*/ODBC32.SQL_SPECIALCOLS IdentifierType,
-            /*SQLCHAR* */string CatalogName,
+            /*SQLCHAR* */string? CatalogName,
             /*SQLSMALLINT*/short NameLen1,
-            /*SQLCHAR* */string SchemaName,
+            /*SQLCHAR* */string? SchemaName,
             /*SQLSMALLINT*/short NameLen2,
             /*SQLCHAR* */string TableName,
             /*SQLSMALLINT*/short NameLen3,
@@ -359,9 +359,9 @@ internal static partial class Odbc
         [DllImport(Interop.Libraries.Odbc32, CharSet = CharSet.Unicode)]
         internal static extern /*SQLRETURN*/ODBC32.RetCode SQLStatisticsW(
             /*SQLHSTMT*/OdbcStatementHandle StatementHandle,
-            /*SQLCHAR* */string CatalogName,
+            /*SQLCHAR* */string? CatalogName,
             /*SQLSMALLINT*/short NameLen1,
-            /*SQLCHAR* */string SchemaName,
+            /*SQLCHAR* */string? SchemaName,
             /*SQLSMALLINT*/short NameLen2,
             /*SQLCHAR* */IntPtr TableName, // IntPtr instead of string because callee may mutate contents
             /*SQLSMALLINT*/short NameLen3,
diff --git a/src/libraries/Common/src/Interop/Linux/Interop.Libraries.cs b/src/libraries/Common/src/Interop/Linux/Interop.Libraries.cs
index 57946baca56402..f97cd058bbcc31 100644
--- a/src/libraries/Common/src/Interop/Linux/Interop.Libraries.cs
+++ b/src/libraries/Common/src/Interop/Linux/Interop.Libraries.cs
@@ -7,6 +7,6 @@ internal static partial class Libraries
     {
         internal const string Odbc32 = "libodbc.so.2";
         internal const string OpenLdap = "libldap-2.4.so.2";
-        internal const string MsQuic = "msquic";
+        internal const string MsQuic = "libmsquic.so";
     }
 }
diff --git a/src/libraries/Common/src/Interop/OSX/Interop.Libraries.cs b/src/libraries/Common/src/Interop/OSX/Interop.Libraries.cs
index 63e497aaa39b59..0681799147525d 100644
--- a/src/libraries/Common/src/Interop/OSX/Interop.Libraries.cs
+++ b/src/libraries/Common/src/Interop/OSX/Interop.Libraries.cs
@@ -10,12 +10,12 @@ internal static partial class Libraries
         internal const string CFNetworkLibrary = "/System/Library/Frameworks/CFNetwork.framework/CFNetwork";
         internal const string libobjc = "/usr/lib/libobjc.dylib";
         internal const string libproc = "/usr/lib/libproc.dylib";
-        internal const string LibSystemCommonCrypto = "/usr/lib/system/libcommonCrypto";
-        internal const string LibSystemKernel = "/usr/lib/system/libsystem_kernel";
+        internal const string LibSystemCommonCrypto = "/usr/lib/system/libcommonCrypto.dylib";
+        internal const string LibSystemKernel = "/usr/lib/system/libsystem_kernel.dylib";
         internal const string Odbc32 = "libodbc.2.dylib";
-        internal const string OpenLdap = "libldap";
+        internal const string OpenLdap = "libldap.dylib";
         internal const string SystemConfigurationLibrary = "/System/Library/Frameworks/SystemConfiguration.framework/SystemConfiguration";
-        internal const string AppleCryptoNative = "System.Security.Cryptography.Native.Apple";
-        internal const string MsQuic = "msquic";
+        internal const string AppleCryptoNative = "libSystem.Security.Cryptography.Native.Apple.dylib";
+        internal const string MsQuic = "libmsquic.dylib";
     }
 }
diff --git a/src/libraries/Common/src/Interop/OSX/System.Security.Cryptography.Native.Apple/Interop.Ssl.cs b/src/libraries/Common/src/Interop/OSX/System.Security.Cryptography.Native.Apple/Interop.Ssl.cs
index 4401dec463c544..577ee8126829ae 100644
--- a/src/libraries/Common/src/Interop/OSX/System.Security.Cryptography.Native.Apple/Interop.Ssl.cs
+++ b/src/libraries/Common/src/Interop/OSX/System.Security.Cryptography.Native.Apple/Interop.Ssl.cs
@@ -384,7 +384,7 @@ public static bool SslCheckHostnameMatch(SafeSslHandle handle, string hostName,
             // this code could be removed.
             //
             // It was verified as supporting case invariant match as of 10.12.1 (Sierra).
-            string matchName = s_idnMapping.GetAscii(hostName);
+            string matchName = string.IsNullOrEmpty(hostName) ? string.Empty : s_idnMapping.GetAscii(hostName);
 
             using (SafeCFDateHandle cfNotBefore = CoreFoundation.CFDateCreate(notBefore))
             using (SafeCreateHandle cfHostname = CoreFoundation.CFStringCreateWithCString(matchName))
diff --git a/src/libraries/Common/src/Interop/Unix/System.Native/Interop.GetPid.cs b/src/libraries/Common/src/Interop/Unix/System.Native/Interop.GetPid.cs
index bbd99dfb5ecb32..400dc554a366d4 100644
--- a/src/libraries/Common/src/Interop/Unix/System.Native/Interop.GetPid.cs
+++ b/src/libraries/Common/src/Interop/Unix/System.Native/Interop.GetPid.cs
@@ -10,6 +10,4 @@ internal static partial class Sys
         [DllImport(Libraries.SystemNative, EntryPoint = "SystemNative_GetPid")]
         internal static extern int GetPid();
     }
-
-    internal static uint GetCurrentProcessId() => (uint)Sys.GetPid();
 }
diff --git a/src/libraries/Common/src/Interop/Unix/System.Native/Interop.ProcessorArchitecture.cs b/src/libraries/Common/src/Interop/Unix/System.Native/Interop.ProcessorArchitecture.cs
index d18a153ae0f1a4..81dc2f936895eb 100644
--- a/src/libraries/Common/src/Interop/Unix/System.Native/Interop.ProcessorArchitecture.cs
+++ b/src/libraries/Common/src/Interop/Unix/System.Native/Interop.ProcessorArchitecture.cs
@@ -13,7 +13,8 @@ internal enum ProcessorArchitecture
             x86,
             x64,
             ARM,
-            ARM64
+            ARM64,
+            WASM
         }
     }
 }
diff --git a/src/libraries/Common/src/Interop/Unix/System.Security.Cryptography.Native/Interop.OpenSsl.cs b/src/libraries/Common/src/Interop/Unix/System.Security.Cryptography.Native/Interop.OpenSsl.cs
index 35f2309c34963c..4a8695f5d3d6fe 100644
--- a/src/libraries/Common/src/Interop/Unix/System.Security.Cryptography.Native/Interop.OpenSsl.cs
+++ b/src/libraries/Common/src/Interop/Unix/System.Security.Cryptography.Native/Interop.OpenSsl.cs
@@ -189,7 +189,7 @@ internal static SafeSslHandle AllocateSslContext(SslProtocols protocols, SafeX50
                     if (!sslAuthenticationOptions.IsServer)
                     {
                         // The IdnMapping converts unicode input into the IDNA punycode sequence.
-                        string punyCode = s_idnMapping.GetAscii(sslAuthenticationOptions.TargetHost!);
+                        string punyCode = string.IsNullOrEmpty(sslAuthenticationOptions.TargetHost) ? string.Empty : s_idnMapping.GetAscii(sslAuthenticationOptions.TargetHost!);
 
                         // Similar to windows behavior, set SNI on openssl by default for client context, ignore errors.
                         if (!Ssl.SslSetTlsExtHostName(context, punyCode))
diff --git a/src/libraries/Common/src/Interop/Windows/Crypt32/Interop.CERT_INFO.cs b/src/libraries/Common/src/Interop/Windows/Crypt32/Interop.CERT_INFO.cs
index 26efa43871aa4a..21f010177ac183 100644
--- a/src/libraries/Common/src/Interop/Windows/Crypt32/Interop.CERT_INFO.cs
+++ b/src/libraries/Common/src/Interop/Windows/Crypt32/Interop.CERT_INFO.cs
@@ -3,7 +3,6 @@
 
 using System;
 using System.Runtime.InteropServices;
-using System.Runtime.InteropServices.ComTypes;
 
 internal static partial class Interop
 {
@@ -16,8 +15,8 @@ internal struct CERT_INFO
             internal DATA_BLOB SerialNumber;
             internal CRYPT_ALGORITHM_IDENTIFIER SignatureAlgorithm;
             internal DATA_BLOB Issuer;
-            internal FILETIME NotBefore;
-            internal FILETIME NotAfter;
+            internal System.Runtime.InteropServices.ComTypes.FILETIME NotBefore;
+            internal System.Runtime.InteropServices.ComTypes.FILETIME NotAfter;
             internal DATA_BLOB Subject;
             internal CERT_PUBLIC_KEY_INFO SubjectPublicKeyInfo;
             internal CRYPT_BIT_BLOB IssuerUniqueId;
diff --git a/src/libraries/Common/src/Interop/Windows/Crypt32/Interop.certificates_types.cs b/src/libraries/Common/src/Interop/Windows/Crypt32/Interop.certificates_types.cs
index 3a5d9d31baf8f8..2fa029d9d8f301 100644
--- a/src/libraries/Common/src/Interop/Windows/Crypt32/Interop.certificates_types.cs
+++ b/src/libraries/Common/src/Interop/Windows/Crypt32/Interop.certificates_types.cs
@@ -86,16 +86,6 @@ internal static partial class CertChainPolicyErrors
             internal const uint CERT_E_ROLE = 0x800B0103;
         }
 
-        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
-        internal struct CERT_CONTEXT
-        {
-            internal uint dwCertEncodingType;
-            internal IntPtr pbCertEncoded;
-            internal uint cbCertEncoded;
-            internal IntPtr pCertInfo;
-            internal IntPtr hCertStore;
-        }
-
         [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
         internal unsafe struct SSL_EXTRA_CERT_CHAIN_POLICY_PARA
         {
diff --git a/src/libraries/Common/src/Interop/Windows/Interop.Libraries.cs b/src/libraries/Common/src/Interop/Windows/Interop.Libraries.cs
index 692cdd783f2f5f..74c014c7179935 100644
--- a/src/libraries/Common/src/Interop/Windows/Interop.Libraries.cs
+++ b/src/libraries/Common/src/Interop/Windows/Interop.Libraries.cs
@@ -7,16 +7,12 @@ internal static partial class Libraries
     {
         internal const string Advapi32 = "advapi32.dll";
         internal const string BCrypt = "BCrypt.dll";
-        internal const string CoreComm_L1_1_1 = "api-ms-win-core-comm-l1-1-1.dll";
-        internal const string CoreComm_L1_1_2 = "api-ms-win-core-comm-l1-1-2.dll";
         internal const string Crypt32 = "crypt32.dll";
         internal const string CryptUI = "cryptui.dll";
-        internal const string Error_L1 = "api-ms-win-core-winrt-error-l1-1-0.dll";
         internal const string Gdi32 = "gdi32.dll";
         internal const string HttpApi = "httpapi.dll";
         internal const string IpHlpApi = "iphlpapi.dll";
         internal const string Kernel32 = "kernel32.dll";
-        internal const string Memory_L1_3 = "api-ms-win-core-memory-l1-1-3.dll";
         internal const string Mswsock = "mswsock.dll";
         internal const string NCrypt = "ncrypt.dll";
         internal const string NtDll = "ntdll.dll";
@@ -24,7 +20,6 @@ internal static partial class Libraries
         internal const string Ole32 = "ole32.dll";
         internal const string OleAut32 = "oleaut32.dll";
         internal const string PerfCounter = "perfcounter.dll";
-        internal const string RoBuffer = "api-ms-win-core-winrt-robuffer-l1-1-0.dll";
         internal const string Secur32 = "secur32.dll";
         internal const string Shell32 = "shell32.dll";
         internal const string SspiCli = "sspicli.dll";
@@ -37,7 +32,6 @@ internal static partial class Libraries
         internal const string Ws2_32 = "ws2_32.dll";
         internal const string Wtsapi32 = "wtsapi32.dll";
         internal const string CompressionNative = "clrcompression.dll";
-        internal const string CoreWinRT = "api-ms-win-core-winrt-l1-1-0.dll";
         internal const string MsQuic = "msquic.dll";
         internal const string HostPolicy = "hostpolicy.dll";
     }
diff --git a/src/libraries/Common/src/Interop/Windows/Kernel32/Interop.GetCurrentProcessId.cs b/src/libraries/Common/src/Interop/Windows/Kernel32/Interop.GetCurrentProcessId.cs
index ff50d0d470bc11..70009c6f932359 100644
--- a/src/libraries/Common/src/Interop/Windows/Kernel32/Interop.GetCurrentProcessId.cs
+++ b/src/libraries/Common/src/Interop/Windows/Kernel32/Interop.GetCurrentProcessId.cs
@@ -10,6 +10,4 @@ internal static partial class Kernel32
         [DllImport(Libraries.Kernel32)]
         internal static extern uint GetCurrentProcessId();
     }
-
-    internal static uint GetCurrentProcessId() => Kernel32.GetCurrentProcessId();
 }
diff --git a/src/libraries/Common/src/Interop/Windows/Kernel32/Interop.Globalization.cs b/src/libraries/Common/src/Interop/Windows/Kernel32/Interop.Globalization.cs
index 78ba717b2306e8..d207e321ea4001 100644
--- a/src/libraries/Common/src/Interop/Windows/Kernel32/Interop.Globalization.cs
+++ b/src/libraries/Common/src/Interop/Windows/Kernel32/Interop.Globalization.cs
@@ -121,14 +121,10 @@ internal static extern bool IsNLSDefinedString(
         internal static extern int GetLocaleInfoEx(string lpLocaleName, uint LCType, void* lpLCData, int cchData);
 
         [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
-        internal static extern bool EnumSystemLocalesEx(EnumLocalesProcEx lpLocaleEnumProcEx, uint dwFlags, void* lParam, IntPtr reserved);
-
-        internal delegate BOOL EnumLocalesProcEx(char* lpLocaleString, uint dwFlags, void* lParam);
+        internal static extern bool EnumSystemLocalesEx(delegate* <char*, uint, void*, BOOL> lpLocaleEnumProcEx, uint dwFlags, void* lParam, IntPtr reserved);
 
         [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
-        internal static extern bool EnumTimeFormatsEx(EnumTimeFormatsProcEx lpTimeFmtEnumProcEx, string lpLocaleName, uint dwFlags, void* lParam);
-
-        internal delegate BOOL EnumTimeFormatsProcEx(char* lpTimeFormatString, void* lParam);
+        internal static extern bool EnumTimeFormatsEx(delegate* <char*, void*, BOOL> lpTimeFmtEnumProcEx, string lpLocaleName, uint dwFlags, void* lParam);
 
         [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
         internal static extern int GetCalendarInfoEx(string? lpLocaleName, uint Calendar, IntPtr lpReserved, uint CalType, IntPtr lpCalData, int cchData, out int lpValue);
@@ -143,9 +139,7 @@ internal static extern bool IsNLSDefinedString(
         internal static extern int GetGeoInfo(int location, int geoType, char* lpGeoData, int cchData, int LangId);
 
         [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
-        internal static extern bool EnumCalendarInfoExEx(EnumCalendarInfoProcExEx pCalInfoEnumProcExEx, string lpLocaleName, uint Calendar, string? lpReserved, uint CalType, void* lParam);
-
-        internal delegate BOOL EnumCalendarInfoProcExEx(char* lpCalendarInfoString, uint Calendar, IntPtr lpReserved, void* lParam);
+        internal static extern bool EnumCalendarInfoExEx(delegate* <char*, uint, IntPtr, void*, BOOL> pCalInfoEnumProcExEx, string lpLocaleName, uint Calendar, string? lpReserved, uint CalType, void* lParam);
 
         [StructLayout(LayoutKind.Sequential)]
         internal struct NlsVersionInfoEx
diff --git a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.GetCommPorts.cs b/src/libraries/Common/src/Interop/Windows/Mincore/Interop.GetCommPorts.cs
deleted file mode 100644
index 1ed2e964b7d4cb..00000000000000
--- a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.GetCommPorts.cs
+++ /dev/null
@@ -1,27 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Runtime.InteropServices;
-
-internal partial class Interop
-{
-    internal partial class mincore
-    {
-        [DllImport(Libraries.CoreComm_L1_1_2, SetLastError = true)]
-        private static extern unsafe int GetCommPorts(
-             uint* lpPortNumbers,
-             uint uPortNumbersCount,
-             out uint puPortNumbersFound);
-
-        internal static unsafe int GetCommPorts(
-            Span<uint> portNumbers,
-            out uint portNumbersFound)
-        {
-            fixed (uint* portNumbersBuffer = &MemoryMarshal.GetReference(portNumbers))
-            {
-                return GetCommPorts(portNumbersBuffer, (uint)portNumbers.Length, out portNumbersFound);
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.GetRestrictedErrorInfo.cs b/src/libraries/Common/src/Interop/Windows/Mincore/Interop.GetRestrictedErrorInfo.cs
deleted file mode 100644
index 8bfeebb4f3a30e..00000000000000
--- a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.GetRestrictedErrorInfo.cs
+++ /dev/null
@@ -1,15 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Runtime.InteropServices;
-using System.Runtime.InteropServices.WindowsRuntime;
-
-internal partial class Interop
-{
-    internal partial class mincore
-    {
-        [DllImport(Libraries.Error_L1, PreserveSig = false)]
-        internal static extern IRestrictedErrorInfo GetRestrictedErrorInfo();
-    }
-}
diff --git a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.OpenCommPort.cs b/src/libraries/Common/src/Interop/Windows/Mincore/Interop.OpenCommPort.cs
deleted file mode 100644
index 60a3408b3631a4..00000000000000
--- a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.OpenCommPort.cs
+++ /dev/null
@@ -1,19 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Microsoft.Win32.SafeHandles;
-using System;
-using System.IO;
-using System.Runtime.InteropServices;
-
-internal partial class Interop
-{
-    internal partial class mincore
-    {
-        [DllImport(Libraries.CoreComm_L1_1_1, SetLastError = true)]
-        internal static extern SafeFileHandle OpenCommPort(
-             uint uPortNumber,
-             int dwDesiredAccess,
-             int dwFlagsAndAttributes);
-    }
-}
diff --git a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.OpenFileMappingFromApp.cs b/src/libraries/Common/src/Interop/Windows/Mincore/Interop.OpenFileMappingFromApp.cs
deleted file mode 100644
index 01448ecf285319..00000000000000
--- a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.OpenFileMappingFromApp.cs
+++ /dev/null
@@ -1,18 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Microsoft.Win32.SafeHandles;
-using System;
-using System.Runtime.InteropServices;
-
-internal partial class Interop
-{
-    internal partial class mincore
-    {
-        [DllImport(Libraries.Memory_L1_3, CharSet = CharSet.Unicode, SetLastError = true)]
-        internal static extern SafeMemoryMappedFileHandle OpenFileMappingFromApp(
-            int DesiredAccess,
-            [MarshalAs(UnmanagedType.Bool)] bool InheritHandle,
-            string Name);
-    }
-}
diff --git a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.RoGetActivationFactory.cs b/src/libraries/Common/src/Interop/Windows/Mincore/Interop.RoGetActivationFactory.cs
deleted file mode 100644
index a8c9a93d592059..00000000000000
--- a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.RoGetActivationFactory.cs
+++ /dev/null
@@ -1,18 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Microsoft.Win32.SafeHandles;
-using System;
-using System.Runtime.InteropServices;
-
-internal partial class Interop
-{
-    internal partial class mincore
-    {
-        [DllImport(Libraries.CoreWinRT, PreserveSig = true)]
-        internal static extern int RoGetActivationFactory(
-            [MarshalAs(UnmanagedType.HString)] string activatableClassId,
-            [In] ref Guid iid,
-            [Out, MarshalAs(UnmanagedType.IInspectable)] out object factory);
-    }
-}
diff --git a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.RoGetBufferMarshaler.cs b/src/libraries/Common/src/Interop/Windows/Mincore/Interop.RoGetBufferMarshaler.cs
deleted file mode 100644
index 08ba5406387323..00000000000000
--- a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.RoGetBufferMarshaler.cs
+++ /dev/null
@@ -1,18 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Collections;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-using System.Text;
-
-internal partial class Interop
-{
-    internal partial class mincore
-    {
-        [DllImport(Libraries.RoBuffer, CallingConvention = CallingConvention.StdCall, PreserveSig = true)]
-        internal static extern int RoGetBufferMarshaler(out IMarshal bufferMarshalerPtr);
-    }
-}
diff --git a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.VirtualAllocFromApp.cs b/src/libraries/Common/src/Interop/Windows/Mincore/Interop.VirtualAllocFromApp.cs
deleted file mode 100644
index 179e6263ab254d..00000000000000
--- a/src/libraries/Common/src/Interop/Windows/Mincore/Interop.VirtualAllocFromApp.cs
+++ /dev/null
@@ -1,19 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Microsoft.Win32.SafeHandles;
-using System;
-using System.Runtime.InteropServices;
-
-internal partial class Interop
-{
-    internal partial class mincore
-    {
-        [DllImport(Libraries.Memory_L1_3, CharSet = CharSet.Unicode, SetLastError = true)]
-        internal static extern IntPtr VirtualAllocFromApp(
-            SafeHandle BaseAddress,
-            UIntPtr Size,
-            int AllocationType,
-            int Protection);
-    }
-}
diff --git a/src/libraries/Common/src/Interop/Windows/SspiCli/ISSPIInterface.cs b/src/libraries/Common/src/Interop/Windows/SspiCli/ISSPIInterface.cs
index 62daefd267e77f..7260037a70fd0d 100644
--- a/src/libraries/Common/src/Interop/Windows/SspiCli/ISSPIInterface.cs
+++ b/src/libraries/Common/src/Interop/Windows/SspiCli/ISSPIInterface.cs
@@ -13,7 +13,7 @@ internal interface ISSPIInterface
         SecurityPackageInfoClass[]? SecurityPackages { get; set; }
         int EnumerateSecurityPackages(out int pkgnum, out SafeFreeContextBuffer pkgArray);
         int AcquireCredentialsHandle(string moduleName, Interop.SspiCli.CredentialUse usage, ref SafeSspiAuthDataHandle authdata, out SafeFreeCredentials outCredential);
-        int AcquireCredentialsHandle(string moduleName, Interop.SspiCli.CredentialUse usage, ref Interop.SspiCli.SCHANNEL_CRED authdata, out SafeFreeCredentials outCredential);
+        unsafe int AcquireCredentialsHandle(string moduleName, Interop.SspiCli.CredentialUse usage, Interop.SspiCli.SCHANNEL_CRED* authdata, out SafeFreeCredentials outCredential);
         unsafe int AcquireCredentialsHandle(string moduleName, Interop.SspiCli.CredentialUse usage, Interop.SspiCli.SCH_CREDENTIALS* authdata, out SafeFreeCredentials outCredential);
         int AcquireDefaultCredential(string moduleName, Interop.SspiCli.CredentialUse usage, out SafeFreeCredentials outCredential);
         int AcceptSecurityContext(SafeFreeCredentials? credential, ref SafeDeleteSslContext? context, InputSecurityBuffers inputBuffers, Interop.SspiCli.ContextFlags inFlags, Interop.SspiCli.Endianness endianness, ref SecurityBuffer outputBuffer, ref Interop.SspiCli.ContextFlags outFlags);
diff --git a/src/libraries/Common/src/Interop/Windows/SspiCli/Interop.SSPI.cs b/src/libraries/Common/src/Interop/Windows/SspiCli/Interop.SSPI.cs
index 9556c5054533aa..93998b37ee7064 100644
--- a/src/libraries/Common/src/Interop/Windows/SspiCli/Interop.SSPI.cs
+++ b/src/libraries/Common/src/Interop/Windows/SspiCli/Interop.SSPI.cs
@@ -172,21 +172,14 @@ internal unsafe struct SecPkgContext_IssuerListInfoEx
         }
 
         [StructLayout(LayoutKind.Sequential)]
-        internal struct SCHANNEL_CRED
+        internal unsafe struct SCHANNEL_CRED
         {
             public const int CurrentVersion = 0x4;
 
             public int dwVersion;
             public int cCreds;
 
-            // ptr to an array of pointers
-            // There is a hack done with this field.  AcquireCredentialsHandle requires an array of
-            // certificate handles; we only ever use one.  In order to avoid pinning a one element array,
-            // we copy this value onto the stack, create a pointer on the stack to the copied value,
-            // and replace this field with the pointer, during the call to AcquireCredentialsHandle.
-            // Then we fix it up afterwards.  Fine as long as all the SSPI credentials are not
-            // supposed to be threadsafe.
-            public IntPtr paCred;
+            public Crypt32.CERT_CONTEXT** paCred;
 
             public IntPtr hRootStore;               // == always null, OTHERWISE NOT RELIABLE
             public int cMappers;
@@ -223,9 +216,7 @@ internal unsafe struct SCH_CREDENTIALS
             public int dwCredformat;
             public int cCreds;
 
-            // This is pointer to arry of CERT_CONTEXT*
-            // We do not use it directly in .NET. Instead, we wrap returned OS pointer in safe handle.
-            public void* paCred;
+            public Crypt32.CERT_CONTEXT** paCred;
 
             public IntPtr hRootStore;               // == always null, OTHERWISE NOT RELIABLE
             public int cMappers;
@@ -423,7 +414,7 @@ internal static extern unsafe int AcquireCredentialsHandleW(
                   [In] string moduleName,
                   [In] int usage,
                   [In] void* logonID,
-                  [In] ref SCHANNEL_CRED authData,
+                  [In] SCHANNEL_CRED* authData,
                   [In] void* keyCallback,
                   [In] void* keyArgument,
                   ref CredHandle handlePtr,
diff --git a/src/libraries/Common/src/Interop/Windows/SspiCli/SSPIAuthType.cs b/src/libraries/Common/src/Interop/Windows/SspiCli/SSPIAuthType.cs
index 7d359791a0fe11..415ef9d9f7a24e 100644
--- a/src/libraries/Common/src/Interop/Windows/SspiCli/SSPIAuthType.cs
+++ b/src/libraries/Common/src/Interop/Windows/SspiCli/SSPIAuthType.cs
@@ -40,9 +40,9 @@ public int AcquireDefaultCredential(string moduleName, Interop.SspiCli.Credentia
             return SafeFreeCredentials.AcquireDefaultCredential(moduleName, usage, out outCredential);
         }
 
-        public int AcquireCredentialsHandle(string moduleName, Interop.SspiCli.CredentialUse usage, ref Interop.SspiCli.SCHANNEL_CRED authdata, out SafeFreeCredentials outCredential)
+        public unsafe int AcquireCredentialsHandle(string moduleName, Interop.SspiCli.CredentialUse usage, Interop.SspiCli.SCHANNEL_CRED* authdata, out SafeFreeCredentials outCredential)
         {
-            return SafeFreeCredentials.AcquireCredentialsHandle(moduleName, usage, ref authdata, out outCredential);
+            return SafeFreeCredentials.AcquireCredentialsHandle(moduleName, usage, authdata, out outCredential);
         }
 
         public unsafe int AcquireCredentialsHandle(string moduleName, Interop.SspiCli.CredentialUse usage, Interop.SspiCli.SCH_CREDENTIALS* authdata, out SafeFreeCredentials outCredential)
diff --git a/src/libraries/Common/src/Interop/Windows/SspiCli/SSPISecureChannelType.cs b/src/libraries/Common/src/Interop/Windows/SspiCli/SSPISecureChannelType.cs
index e30e53d27262a8..fb1d93d356d6af 100644
--- a/src/libraries/Common/src/Interop/Windows/SspiCli/SSPISecureChannelType.cs
+++ b/src/libraries/Common/src/Interop/Windows/SspiCli/SSPISecureChannelType.cs
@@ -40,9 +40,9 @@ public int AcquireDefaultCredential(string moduleName, Interop.SspiCli.Credentia
             return SafeFreeCredentials.AcquireDefaultCredential(moduleName, usage, out outCredential);
         }
 
-        public int AcquireCredentialsHandle(string moduleName, Interop.SspiCli.CredentialUse usage, ref Interop.SspiCli.SCHANNEL_CRED authdata, out SafeFreeCredentials outCredential)
+        public unsafe int AcquireCredentialsHandle(string moduleName, Interop.SspiCli.CredentialUse usage, Interop.SspiCli.SCHANNEL_CRED* authdata, out SafeFreeCredentials outCredential)
         {
-            return SafeFreeCredentials.AcquireCredentialsHandle(moduleName, usage, ref authdata, out outCredential);
+            return SafeFreeCredentials.AcquireCredentialsHandle(moduleName, usage, authdata, out outCredential);
         }
 
         public unsafe int AcquireCredentialsHandle(string moduleName, Interop.SspiCli.CredentialUse usage, Interop.SspiCli.SCH_CREDENTIALS* authdata, out SafeFreeCredentials outCredential)
diff --git a/src/libraries/Common/src/Interop/Windows/SspiCli/SSPIWrapper.cs b/src/libraries/Common/src/Interop/Windows/SspiCli/SSPIWrapper.cs
index eaf912697a91ca..57ce6232943275 100644
--- a/src/libraries/Common/src/Interop/Windows/SspiCli/SSPIWrapper.cs
+++ b/src/libraries/Common/src/Interop/Windows/SspiCli/SSPIWrapper.cs
@@ -108,12 +108,12 @@ public static SafeFreeCredentials AcquireCredentialsHandle(ISSPIInterface secMod
             return credentialsHandle;
         }
 
-        public static SafeFreeCredentials AcquireCredentialsHandle(ISSPIInterface secModule, string package, Interop.SspiCli.CredentialUse intent, Interop.SspiCli.SCHANNEL_CRED scc)
+        public static unsafe SafeFreeCredentials AcquireCredentialsHandle(ISSPIInterface secModule, string package, Interop.SspiCli.CredentialUse intent, Interop.SspiCli.SCHANNEL_CRED* scc)
         {
             int errorCode = secModule.AcquireCredentialsHandle(
                                             package,
                                             intent,
-                                            ref scc,
+                                            scc,
                                             out SafeFreeCredentials outCredential);
 
             if (errorCode != 0)
diff --git a/src/libraries/Common/src/Interop/Windows/SspiCli/SecuritySafeHandles.cs b/src/libraries/Common/src/Interop/Windows/SspiCli/SecuritySafeHandles.cs
index bef2693adb8823..19d5a6a4836c03 100644
--- a/src/libraries/Common/src/Interop/Windows/SspiCli/SecuritySafeHandles.cs
+++ b/src/libraries/Common/src/Interop/Windows/SspiCli/SecuritySafeHandles.cs
@@ -257,40 +257,24 @@ public static unsafe int AcquireCredentialsHandle(
         public static unsafe int AcquireCredentialsHandle(
             string package,
             Interop.SspiCli.CredentialUse intent,
-            ref Interop.SspiCli.SCHANNEL_CRED authdata,
+            Interop.SspiCli.SCHANNEL_CRED* authdata,
             out SafeFreeCredentials outCredential)
         {
             int errorCode = -1;
             long timeStamp;
 
-            // If there is a certificate, wrap it into an array.
-            // Not threadsafe.
-            IntPtr copiedPtr = authdata.paCred;
-            try
-            {
-                IntPtr certArrayPtr = new IntPtr(&copiedPtr);
-                if (copiedPtr != IntPtr.Zero)
-                {
-                    authdata.paCred = certArrayPtr;
-                }
-
-                outCredential = new SafeFreeCredential_SECURITY();
+            outCredential = new SafeFreeCredential_SECURITY();
 
-                errorCode = Interop.SspiCli.AcquireCredentialsHandleW(
+            errorCode = Interop.SspiCli.AcquireCredentialsHandleW(
                                 null,
                                 package,
                                 (int)intent,
                                 null,
-                                ref authdata,
+                                authdata,
                                 null,
                                 null,
                                 ref outCredential._handle,
                                 out timeStamp);
-            }
-            finally
-            {
-                authdata.paCred = copiedPtr;
-            }
 
             if (NetEventSource.Log.IsEnabled()) NetEventSource.Verbose(null, $"{nameof(Interop.SspiCli.AcquireCredentialsHandleW)} returns 0x{errorCode:x}, handle = {outCredential}");
 
@@ -453,28 +437,50 @@ internal static unsafe int InitializeSecurityContext(
                     if (inSecBuffers.Count > 2)
                     {
                         inUnmanagedBuffer[2].BufferType = inSecBuffers._item2.Type;
-                        inUnmanagedBuffer[2].cbBuffer = inSecBuffers._item2.Token.Length;
-                        inUnmanagedBuffer[2].pvBuffer = inSecBuffers._item2.UnmanagedToken != null ?
-                            (IntPtr)inSecBuffers._item2.UnmanagedToken.DangerousGetHandle() :
-                            (IntPtr)pinnedToken2;
+                        if (inSecBuffers._item2.UnmanagedToken != null)
+                        {
+                            Debug.Assert(inSecBuffers._item2.Type == SecurityBufferType.SECBUFFER_CHANNEL_BINDINGS);
+                            inUnmanagedBuffer[2].pvBuffer = (IntPtr)inSecBuffers._item2.UnmanagedToken.DangerousGetHandle();
+                            inUnmanagedBuffer[2].cbBuffer = ((ChannelBinding)inSecBuffers._item2.UnmanagedToken).Size;
+                        }
+                        else
+                        {
+                            inUnmanagedBuffer[2].cbBuffer = inSecBuffers._item2.Token.Length;
+                            inUnmanagedBuffer[2].pvBuffer = (IntPtr)pinnedToken2;
+                        }
+
                     }
 
                     if (inSecBuffers.Count > 1)
                     {
                         inUnmanagedBuffer[1].BufferType = inSecBuffers._item1.Type;
-                        inUnmanagedBuffer[1].cbBuffer = inSecBuffers._item1.Token.Length;
-                        inUnmanagedBuffer[1].pvBuffer = inSecBuffers._item1.UnmanagedToken != null ?
-                            (IntPtr)inSecBuffers._item1.UnmanagedToken.DangerousGetHandle() :
-                            (IntPtr)pinnedToken1;
+                        if (inSecBuffers._item1.UnmanagedToken != null)
+                        {
+                            Debug.Assert(inSecBuffers._item1.Type == SecurityBufferType.SECBUFFER_CHANNEL_BINDINGS);
+                            inUnmanagedBuffer[1].pvBuffer = (IntPtr)inSecBuffers._item1.UnmanagedToken.DangerousGetHandle();
+                            inUnmanagedBuffer[1].cbBuffer = ((ChannelBinding)inSecBuffers._item1.UnmanagedToken).Size;
+                        }
+                        else
+                        {
+                            inUnmanagedBuffer[1].cbBuffer = inSecBuffers._item1.Token.Length;
+                            inUnmanagedBuffer[1].pvBuffer = (IntPtr)pinnedToken1;
+                        }
                     }
 
                     if (inSecBuffers.Count > 0)
                     {
                         inUnmanagedBuffer[0].BufferType = inSecBuffers._item0.Type;
-                        inUnmanagedBuffer[0].cbBuffer = inSecBuffers._item0.Token.Length;
-                        inUnmanagedBuffer[0].pvBuffer = inSecBuffers._item0.UnmanagedToken != null ?
-                            (IntPtr)inSecBuffers._item0.UnmanagedToken.DangerousGetHandle() :
-                            (IntPtr)pinnedToken0;
+                        if (inSecBuffers._item0.UnmanagedToken != null)
+                        {
+                            Debug.Assert(inSecBuffers._item0.Type == SecurityBufferType.SECBUFFER_CHANNEL_BINDINGS);
+                            inUnmanagedBuffer[0].pvBuffer = (IntPtr)inSecBuffers._item0.UnmanagedToken.DangerousGetHandle();
+                            inUnmanagedBuffer[0].cbBuffer = ((ChannelBinding)inSecBuffers._item0.UnmanagedToken).Size;
+                        }
+                        else
+                        {
+                            inUnmanagedBuffer[0].cbBuffer = inSecBuffers._item0.Token.Length;
+                            inUnmanagedBuffer[0].pvBuffer = (IntPtr)pinnedToken0;
+                        }
                     }
 
                     fixed (byte* pinnedOutBytes = outSecBuffer.token)
@@ -685,28 +691,50 @@ internal static unsafe int AcceptSecurityContext(
                     if (inSecBuffers.Count > 2)
                     {
                         inUnmanagedBuffer[2].BufferType = inSecBuffers._item2.Type;
-                        inUnmanagedBuffer[2].cbBuffer = inSecBuffers._item2.Token.Length;
-                        inUnmanagedBuffer[2].pvBuffer = inSecBuffers._item2.UnmanagedToken != null ?
-                            (IntPtr)inSecBuffers._item2.UnmanagedToken.DangerousGetHandle() :
-                            (IntPtr)pinnedToken2;
+                        if (inSecBuffers._item2.UnmanagedToken != null)
+                        {
+                            Debug.Assert(inSecBuffers._item2.Type == SecurityBufferType.SECBUFFER_CHANNEL_BINDINGS);
+                            inUnmanagedBuffer[2].pvBuffer = (IntPtr)inSecBuffers._item2.UnmanagedToken.DangerousGetHandle();
+                            inUnmanagedBuffer[2].cbBuffer = ((ChannelBinding)inSecBuffers._item2.UnmanagedToken).Size;
+                        }
+                        else
+                        {
+                            inUnmanagedBuffer[2].cbBuffer = inSecBuffers._item2.Token.Length;
+                            inUnmanagedBuffer[2].pvBuffer = (IntPtr)pinnedToken2;
+                        }
+
                     }
 
                     if (inSecBuffers.Count > 1)
                     {
                         inUnmanagedBuffer[1].BufferType = inSecBuffers._item1.Type;
-                        inUnmanagedBuffer[1].cbBuffer = inSecBuffers._item1.Token.Length;
-                        inUnmanagedBuffer[1].pvBuffer = inSecBuffers._item1.UnmanagedToken != null ?
-                            (IntPtr)inSecBuffers._item1.UnmanagedToken.DangerousGetHandle() :
-                            (IntPtr)pinnedToken1;
+                        if (inSecBuffers._item1.UnmanagedToken != null)
+                        {
+                            Debug.Assert(inSecBuffers._item1.Type == SecurityBufferType.SECBUFFER_CHANNEL_BINDINGS);
+                            inUnmanagedBuffer[1].pvBuffer = (IntPtr)inSecBuffers._item1.UnmanagedToken.DangerousGetHandle();
+                            inUnmanagedBuffer[1].cbBuffer = ((ChannelBinding)inSecBuffers._item1.UnmanagedToken).Size;
+                        }
+                        else
+                        {
+                            inUnmanagedBuffer[1].cbBuffer = inSecBuffers._item1.Token.Length;
+                            inUnmanagedBuffer[1].pvBuffer = (IntPtr)pinnedToken1;
+                        }
                     }
 
                     if (inSecBuffers.Count > 0)
                     {
                         inUnmanagedBuffer[0].BufferType = inSecBuffers._item0.Type;
-                        inUnmanagedBuffer[0].cbBuffer = inSecBuffers._item0.Token.Length;
-                        inUnmanagedBuffer[0].pvBuffer = inSecBuffers._item0.UnmanagedToken != null ?
-                            (IntPtr)inSecBuffers._item0.UnmanagedToken.DangerousGetHandle() :
-                            (IntPtr)pinnedToken0;
+                        if (inSecBuffers._item0.UnmanagedToken != null)
+                        {
+                            Debug.Assert(inSecBuffers._item0.Type == SecurityBufferType.SECBUFFER_CHANNEL_BINDINGS);
+                            inUnmanagedBuffer[0].pvBuffer = (IntPtr)inSecBuffers._item0.UnmanagedToken.DangerousGetHandle();
+                            inUnmanagedBuffer[0].cbBuffer = ((ChannelBinding)inSecBuffers._item0.UnmanagedToken).Size;
+                        }
+                        else
+                        {
+                            inUnmanagedBuffer[0].cbBuffer = inSecBuffers._item0.Token.Length;
+                            inUnmanagedBuffer[0].pvBuffer = (IntPtr)pinnedToken0;
+                        }
                     }
 
                     fixed (byte* pinnedOutBytes = outSecBuffer.token)
diff --git a/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp_types.cs b/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp_types.cs
index 9dd0d81b56cf12..0ab94178f5d5c3 100644
--- a/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp_types.cs
+++ b/src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp_types.cs
@@ -129,8 +129,10 @@ internal partial class WinHttp
         public const uint WINHTTP_AUTH_TARGET_PROXY = 0x00000001;
 
         public const uint WINHTTP_OPTION_USERNAME = 0x1000;
+        // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="It is property descriptor, not secret value.")]
         public const uint WINHTTP_OPTION_PASSWORD = 0x1001;
         public const uint WINHTTP_OPTION_PROXY_USERNAME = 0x1002;
+        // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="It is property descriptor, not secret value.")]
         public const uint WINHTTP_OPTION_PROXY_PASSWORD = 0x1003;
 
         public const uint WINHTTP_OPTION_SERVER_SPN_USED = 106;
diff --git a/src/libraries/Common/src/System/Data/Common/AdapterUtil.Drivers.cs b/src/libraries/Common/src/System/Data/Common/AdapterUtil.Drivers.cs
index 509aa984661e41..4ee63ade204ca3 100644
--- a/src/libraries/Common/src/System/Data/Common/AdapterUtil.Drivers.cs
+++ b/src/libraries/Common/src/System/Data/Common/AdapterUtil.Drivers.cs
@@ -8,7 +8,7 @@ namespace System.Data.Common
     internal static partial class ADP
     {
 
-        internal static Timer UnsafeCreateTimer(TimerCallback callback, object state, int dueTime, int period)
+        internal static Timer UnsafeCreateTimer(TimerCallback callback, object? state, int dueTime, int period)
         {
             // Don't capture the current ExecutionContext and its AsyncLocals onto
             // a global timer causing them to live forever
diff --git a/src/libraries/Common/src/System/Data/Common/AdapterUtil.cs b/src/libraries/Common/src/System/Data/Common/AdapterUtil.cs
index c61589b75e5b6a..3675641903c36c 100644
--- a/src/libraries/Common/src/System/Data/Common/AdapterUtil.cs
+++ b/src/libraries/Common/src/System/Data/Common/AdapterUtil.cs
@@ -1,13 +1,10 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-// TODO: Enable nullability as part of annotation System.Data.{Odbc,OleDb}
-#nullable disable
-#pragma warning disable CS8632
-
 using System.Collections;
 using System.Data.SqlTypes;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Runtime.CompilerServices;
 using System.Security;
@@ -22,11 +19,11 @@ internal static partial class ADP
     {
         // NOTE: Initializing a Task in SQL CLR requires the "UNSAFE" permission set (https://docs.microsoft.com/en-us/dotnet/framework/performance/sql-server-programming-and-host-protection-attributes)
         // Therefore we are lazily initializing these Tasks to avoid forcing customers to use the "UNSAFE" set when they are actually using no Async features
-        private static Task<bool> _trueTask;
-        internal static Task<bool> TrueTask => _trueTask ?? (_trueTask = Task.FromResult(true));
+        private static Task<bool>? _trueTask;
+        internal static Task<bool> TrueTask => _trueTask ??= Task.FromResult(true);
 
-        private static Task<bool> _falseTask;
-        internal static Task<bool> FalseTask => _falseTask ?? (_falseTask = Task.FromResult(false));
+        private static Task<bool>? _falseTask;
+        internal static Task<bool> FalseTask => _falseTask ??= Task.FromResult(false);
 
         internal const CompareOptions DefaultCompareOptions = CompareOptions.IgnoreKanaType | CompareOptions.IgnoreWidth | CompareOptions.IgnoreCase;
         internal const int DefaultConnectionTimeout = DbConnectionStringDefaults.ConnectTimeout;
@@ -51,14 +48,14 @@ internal static ArgumentException Argument(string error)
             return e;
         }
 
-        internal static ArgumentException Argument(string error, Exception inner)
+        internal static ArgumentException Argument(string error, Exception? inner)
         {
             ArgumentException e = new ArgumentException(error, inner);
             TraceExceptionAsReturnValue(e);
             return e;
         }
 
-        internal static ArgumentException Argument(string error, string parameter)
+        internal static ArgumentException Argument(string error, string? parameter)
         {
             ArgumentException e = new ArgumentException(error, parameter);
             TraceExceptionAsReturnValue(e);
@@ -105,7 +102,7 @@ internal static InvalidCastException InvalidCast(string error)
             return InvalidCast(error, null);
         }
 
-        internal static InvalidCastException InvalidCast(string error, Exception inner)
+        internal static InvalidCastException InvalidCast(string error, Exception? inner)
         {
             InvalidCastException e = new InvalidCastException(error, inner);
             TraceExceptionAsReturnValue(e);
@@ -135,7 +132,7 @@ internal static NotSupportedException NotSupported(string error)
 
         // the return value is true if the string was quoted and false if it was not
         // this allows the caller to determine if it is an error or not for the quotedString to not be quoted
-        internal static bool RemoveStringQuotes(string quotePrefix, string quoteSuffix, string quotedString, out string unquotedString)
+        internal static bool RemoveStringQuotes(string? quotePrefix, string? quoteSuffix, string? quotedString, out string? unquotedString)
         {
             int prefixLength = quotePrefix != null ? quotePrefix.Length : 0;
             int suffixLength = quoteSuffix != null ? quoteSuffix.Length : 0;
@@ -164,7 +161,7 @@ internal static bool RemoveStringQuotes(string quotePrefix, string quoteSuffix,
             // is the prefix present?
             if (prefixLength > 0)
             {
-                if (!quotedString.StartsWith(quotePrefix, StringComparison.Ordinal))
+                if (!quotedString.StartsWith(quotePrefix!, StringComparison.Ordinal))
                 {
                     unquotedString = quotedString;
                     return false;
@@ -174,7 +171,7 @@ internal static bool RemoveStringQuotes(string quotePrefix, string quoteSuffix,
             // is the suffix present?
             if (suffixLength > 0)
             {
-                if (!quotedString.EndsWith(quoteSuffix, StringComparison.Ordinal))
+                if (!quotedString.EndsWith(quoteSuffix!, StringComparison.Ordinal))
                 {
                     unquotedString = quotedString;
                     return false;
@@ -224,7 +221,7 @@ internal static ArgumentException InvalidMultipartNameToManyParts(string propert
             return e;
         }
 
-        internal static void CheckArgumentNull(object value, string parameterName)
+        internal static void CheckArgumentNull([NotNull] object? value, string parameterName)
         {
             if (null == value)
             {
@@ -290,7 +287,7 @@ internal static ArgumentException KeywordNotSupported(string keyword)
         {
             return Argument(SR.Format(SR.ADP_KeywordNotSupported, keyword));
         }
-        internal static ArgumentException ConvertFailed(Type fromType, Type toType, Exception innerException)
+        internal static ArgumentException ConvertFailed(Type fromType, Type toType, Exception? innerException)
         {
             return ADP.Argument(SR.Format(SR.SqlConvert_ConvertFailed, fromType.FullName, toType.FullName), innerException);
         }
@@ -302,7 +299,7 @@ internal static Exception InvalidConnectionOptionValue(string key)
         {
             return InvalidConnectionOptionValue(key, null);
         }
-        internal static Exception InvalidConnectionOptionValue(string key, Exception inner)
+        internal static Exception InvalidConnectionOptionValue(string key, Exception? inner)
         {
             return Argument(SR.Format(SR.ADP_InvalidConnectionOptionValue, key), inner);
         }
@@ -480,15 +477,15 @@ internal static bool CompareInsensitiveInvariant(string? strvalue, string? strco
 
         internal static int DstCompare(string strA, string strB) => CultureInfo.CurrentCulture.CompareInfo.Compare(strA, strB, ADP.DefaultCompareOptions);
 
-        internal static bool IsEmptyArray(string[] array) => (null == array) || (0 == array.Length);
+        internal static bool IsEmptyArray([NotNullWhen(false)] string?[]? array) => (null == array) || (0 == array.Length);
 
-        internal static bool IsNull(object value)
+        internal static bool IsNull(object? value)
         {
             if ((null == value) || (DBNull.Value == value))
             {
                 return true;
             }
-            INullable nullable = (value as INullable);
+            INullable? nullable = (value as INullable);
             return ((null != nullable) && nullable.IsNull);
         }
 
diff --git a/src/libraries/Common/src/System/Data/Common/BasicFieldNameLookup.cs b/src/libraries/Common/src/System/Data/Common/BasicFieldNameLookup.cs
index 4415ef3b82123c..fbe4a2c7355e83 100644
--- a/src/libraries/Common/src/System/Data/Common/BasicFieldNameLookup.cs
+++ b/src/libraries/Common/src/System/Data/Common/BasicFieldNameLookup.cs
@@ -11,13 +11,13 @@ namespace System.Data.ProviderBase
     internal class BasicFieldNameLookup
     {
         // Dictionary stores the index into the _fieldNames, match via case-sensitive
-        private Dictionary<string, int> _fieldNameLookup;
+        private Dictionary<string, int>? _fieldNameLookup;
 
         // original names for linear searches when exact matches fail
         private readonly string[] _fieldNames;
 
         // By default _compareInfo is set to InvariantCulture CompareInfo
-        private CompareInfo _compareInfo;
+        private CompareInfo? _compareInfo;
 
         public BasicFieldNameLookup(string[] fieldNames)
         {
@@ -74,7 +74,7 @@ public int IndexOfName(string fieldName)
 
             int value;
             // via case sensitive search, first match with lowest ordinal matches
-            return _fieldNameLookup.TryGetValue(fieldName, out value) ? value : -1;
+            return _fieldNameLookup!.TryGetValue(fieldName, out value) ? value : -1;
         }
 
         public int IndexOf(string fieldName)
@@ -85,7 +85,7 @@ public int IndexOf(string fieldName)
             }
             int index;
             // via case sensitive search, first match with lowest ordinal matches
-            if (!_fieldNameLookup.TryGetValue(fieldName, out index))
+            if (!_fieldNameLookup!.TryGetValue(fieldName, out index))
             {
                 // via case insensitive search, first match with lowest ordinal matches
                 index = LinearIndexOf(fieldName, CompareOptions.IgnoreCase);
@@ -116,7 +116,7 @@ private int LinearIndexOf(string fieldName, CompareOptions compareOptions)
             {
                 if (0 == _compareInfo.Compare(fieldName, _fieldNames[i], compareOptions))
                 {
-                    _fieldNameLookup[fieldName] = i; // add an exact match for the future
+                    _fieldNameLookup![fieldName] = i; // add an exact match for the future
                     return i;
                 }
             }
diff --git a/src/libraries/Common/src/System/Data/Common/DbConnectionOptions.Common.cs b/src/libraries/Common/src/System/Data/Common/DbConnectionOptions.Common.cs
index 83f6b892b6894e..fda8cc871d916d 100644
--- a/src/libraries/Common/src/System/Data/Common/DbConnectionOptions.Common.cs
+++ b/src/libraries/Common/src/System/Data/Common/DbConnectionOptions.Common.cs
@@ -1,10 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-// TODO: Remove this after System.Data.{Odbc,OleDb} are null-annotated
-#nullable disable
-#pragma warning disable CS8632
-
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
@@ -416,8 +412,7 @@ private static bool IsValueValidInternal(string? keyvalue)
             return true;
         }
 
-        // TODO: Annotate with [NotNullWhen(true)] when annotating System.Data.{Odbc,OleDb}
-        private static bool IsKeyNameValid(string? keyname)
+        private static bool IsKeyNameValid([NotNullWhen(true)] string? keyname)
         {
             if (null != keyname)
             {
diff --git a/src/libraries/Common/src/System/Data/Common/DbConnectionPoolKey.cs b/src/libraries/Common/src/System/Data/Common/DbConnectionPoolKey.cs
index a2cd4661611b76..6c5a567cf7ad7b 100644
--- a/src/libraries/Common/src/System/Data/Common/DbConnectionPoolKey.cs
+++ b/src/libraries/Common/src/System/Data/Common/DbConnectionPoolKey.cs
@@ -1,18 +1,15 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-// TODO: Remove this after System.Data.{Odbc,OleDb} are null-annotated
-#pragma warning disable CS8632
-
 namespace System.Data.Common
 {
     // DbConnectionPoolKey: Base class implementation of a key to connection pool groups
     //  Only connection string is used as a key
     internal class DbConnectionPoolKey : ICloneable
     {
-        private string _connectionString;
+        private string? _connectionString;
 
-        internal DbConnectionPoolKey(string connectionString)
+        internal DbConnectionPoolKey(string? connectionString)
         {
             _connectionString = connectionString;
         }
@@ -27,7 +24,7 @@ public virtual object Clone()
             return new DbConnectionPoolKey(this);
         }
 
-        internal virtual string ConnectionString
+        internal virtual string? ConnectionString
         {
             get
             {
diff --git a/src/libraries/Common/src/System/Data/Common/FieldNameLookup.cs b/src/libraries/Common/src/System/Data/Common/FieldNameLookup.cs
index 8e66d67458d6b9..7f5ab2cd9afb8e 100644
--- a/src/libraries/Common/src/System/Data/Common/FieldNameLookup.cs
+++ b/src/libraries/Common/src/System/Data/Common/FieldNameLookup.cs
@@ -33,7 +33,7 @@ public FieldNameLookup(IDataReader reader, int defaultLocaleID) : base(reader)
         //The compare info is specified by the server by specifying the default LocaleId.
         protected override CompareInfo GetCompareInfo()
         {
-            CompareInfo compareInfo = null;
+            CompareInfo? compareInfo = null;
             if (-1 != _defaultLocaleID)
             {
                 compareInfo = CompareInfo.GetCompareInfo(_defaultLocaleID);
diff --git a/src/libraries/Common/src/System/Data/Common/MultipartIdentifier.cs b/src/libraries/Common/src/System/Data/Common/MultipartIdentifier.cs
index 3338928bda1f5f..0aaca592d0711d 100644
--- a/src/libraries/Common/src/System/Data/Common/MultipartIdentifier.cs
+++ b/src/libraries/Common/src/System/Data/Common/MultipartIdentifier.cs
@@ -1,8 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-// TODO: Remove this after System.Data.{Odbc,OleDb} are null-annotated
-#pragma warning disable CS8632
 //------------------------------------------------------------------------------
 
 using System.Text;
diff --git a/src/libraries/Common/src/System/Data/Common/NameValuePair.cs b/src/libraries/Common/src/System/Data/Common/NameValuePair.cs
index 435b998ef33bd3..09ec22615fca61 100644
--- a/src/libraries/Common/src/System/Data/Common/NameValuePair.cs
+++ b/src/libraries/Common/src/System/Data/Common/NameValuePair.cs
@@ -1,9 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-// TODO: Remove this after System.Data.{Odbc,OleDb} are null-annotated
-#pragma warning disable CS8632
-
 using System.Diagnostics;
 
 namespace System.Data.Common
diff --git a/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionClosed.cs b/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionClosed.cs
index 11cc51501e28e8..3a7844763225d4 100644
--- a/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionClosed.cs
+++ b/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionClosed.cs
@@ -27,12 +27,12 @@ internal override void CloseConnection(DbConnection owningObject, DbConnectionFa
 
         protected override void Deactivate() => ADP.ClosedConnectionError();
 
-        protected internal override DataTable GetSchema(DbConnectionFactory factory, DbConnectionPoolGroup poolGroup, DbConnection outerConnection, string collectionName, string[] restrictions)
+        protected internal override DataTable GetSchema(DbConnectionFactory factory, DbConnectionPoolGroup poolGroup, DbConnection outerConnection, string collectionName, string?[]? restrictions)
             => throw ADP.ClosedConnectionError();
 
         protected override DbReferenceCollection CreateReferenceCollection() => throw ADP.ClosedConnectionError();
 
-        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
             => base.TryOpenConnectionInternal(outerConnection, connectionFactory, retry, userOptions);
     }
 
@@ -42,7 +42,7 @@ protected DbConnectionBusy(ConnectionState state) : base(state, true, false)
         {
         }
 
-        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
             => throw ADP.ConnectionAlreadyOpen(State);
     }
 
@@ -81,10 +81,10 @@ internal override void CloseConnection(DbConnection owningObject, DbConnectionFa
             connectionFactory.SetInnerConnectionTo(owningObject, DbConnectionClosedPreviouslyOpened.SingletonInstance);
         }
 
-        internal override bool TryReplaceConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal override bool TryReplaceConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
             => TryOpenConnection(outerConnection, connectionFactory, retry, userOptions);
 
-        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
         {
             if (retry == null || !retry.Task.IsCompleted)
             {
@@ -131,7 +131,7 @@ private DbConnectionClosedPreviouslyOpened() : base(ConnectionState.Closed, true
         {
         }
 
-        internal override bool TryReplaceConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal override bool TryReplaceConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
             => TryOpenConnection(outerConnection, connectionFactory, retry, userOptions);
     }
 }
diff --git a/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionFactory.cs b/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionFactory.cs
index 832006da95ca16..5418b4ff8bba76 100644
--- a/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionFactory.cs
+++ b/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionFactory.cs
@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Data.Common;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -22,8 +23,8 @@ internal abstract partial class DbConnectionFactory
         // s_pendingOpenNonPooled is an array of tasks used to throttle creation of non-pooled connections to
         // a maximum of Environment.ProcessorCount at a time.
         private static uint s_pendingOpenNonPooledNext;
-        private static readonly Task<DbConnectionInternal>[] s_pendingOpenNonPooled = new Task<DbConnectionInternal>[Environment.ProcessorCount];
-        private static Task<DbConnectionInternal> s_completedTask;
+        private static readonly Task<DbConnectionInternal?>[] s_pendingOpenNonPooled = new Task<DbConnectionInternal?>[Environment.ProcessorCount];
+        private static Task<DbConnectionInternal?>? s_completedTask;
 
         protected DbConnectionFactory()
         {
@@ -57,7 +58,7 @@ public void ClearPool(DbConnection connection)
         {
             ADP.CheckArgumentNull(connection, nameof(connection));
 
-            DbConnectionPoolGroup poolGroup = GetConnectionPoolGroup(connection);
+            DbConnectionPoolGroup? poolGroup = GetConnectionPoolGroup(connection);
             if (null != poolGroup)
             {
                 poolGroup.Clear();
@@ -69,7 +70,7 @@ public void ClearPool(DbConnectionPoolKey key)
             Debug.Assert(key != null, "key cannot be null");
             ADP.CheckArgumentNull(key.ConnectionString, nameof(key) + "." + nameof(key.ConnectionString));
 
-            DbConnectionPoolGroup poolGroup;
+            DbConnectionPoolGroup? poolGroup;
             Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> connectionPoolGroups = _connectionPoolGroups;
             if (connectionPoolGroups.TryGetValue(key, out poolGroup))
             {
@@ -77,22 +78,22 @@ public void ClearPool(DbConnectionPoolKey key)
             }
         }
 
-        internal virtual DbConnectionPoolProviderInfo CreateConnectionPoolProviderInfo(DbConnectionOptions connectionOptions)
+        internal virtual DbConnectionPoolProviderInfo? CreateConnectionPoolProviderInfo(DbConnectionOptions connectionOptions)
         {
             return null;
         }
 
 
-        internal DbConnectionInternal CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup, DbConnectionOptions userOptions)
+        internal DbConnectionInternal? CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup, DbConnectionOptions? userOptions)
         {
             Debug.Assert(null != owningConnection, "null owningConnection?");
             Debug.Assert(null != poolGroup, "null poolGroup?");
 
             DbConnectionOptions connectionOptions = poolGroup.ConnectionOptions;
-            DbConnectionPoolGroupProviderInfo poolGroupProviderInfo = poolGroup.ProviderInfo;
+            DbConnectionPoolGroupProviderInfo poolGroupProviderInfo = poolGroup.ProviderInfo!;
             DbConnectionPoolKey poolKey = poolGroup.PoolKey;
 
-            DbConnectionInternal newConnection = CreateConnection(connectionOptions, poolKey, poolGroupProviderInfo, null, owningConnection, userOptions);
+            DbConnectionInternal? newConnection = CreateConnection(connectionOptions, poolKey, poolGroupProviderInfo, null, owningConnection, userOptions);
             if (null != newConnection)
             {
                 newConnection.MakeNonPooledObject(owningConnection);
@@ -100,12 +101,12 @@ internal DbConnectionInternal CreateNonPooledConnection(DbConnection owningConne
             return newConnection;
         }
 
-        internal DbConnectionInternal CreatePooledConnection(DbConnectionPool pool, DbConnection owningObject, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions userOptions)
+        internal DbConnectionInternal? CreatePooledConnection(DbConnectionPool pool, DbConnection? owningObject, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions? userOptions)
         {
             Debug.Assert(null != pool, "null pool?");
-            DbConnectionPoolGroupProviderInfo poolGroupProviderInfo = pool.PoolGroup.ProviderInfo;
+            DbConnectionPoolGroupProviderInfo poolGroupProviderInfo = pool.PoolGroup.ProviderInfo!;
 
-            DbConnectionInternal newConnection = CreateConnection(options, poolKey, poolGroupProviderInfo, pool, owningObject, userOptions);
+            DbConnectionInternal? newConnection = CreateConnection(options, poolKey, poolGroupProviderInfo, pool, owningObject, userOptions);
             if (null != newConnection)
             {
                 newConnection.MakePooledConnection(pool);
@@ -113,7 +114,7 @@ internal DbConnectionInternal CreatePooledConnection(DbConnectionPool pool, DbCo
             return newConnection;
         }
 
-        internal virtual DbConnectionPoolGroupProviderInfo CreateConnectionPoolGroupProviderInfo(DbConnectionOptions connectionOptions)
+        internal virtual DbConnectionPoolGroupProviderInfo? CreateConnectionPoolGroupProviderInfo(DbConnectionOptions connectionOptions)
         {
             return null;
         }
@@ -125,12 +126,12 @@ private Timer CreatePruningTimer() =>
                 PruningDueTime,
                 PruningPeriod);
 
-        protected DbConnectionOptions FindConnectionOptions(DbConnectionPoolKey key)
+        protected DbConnectionOptions? FindConnectionOptions(DbConnectionPoolKey key)
         {
             Debug.Assert(key != null, "key cannot be null");
             if (!string.IsNullOrEmpty(key.ConnectionString))
             {
-                DbConnectionPoolGroup connectionPoolGroup;
+                DbConnectionPoolGroup? connectionPoolGroup;
                 Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> connectionPoolGroups = _connectionPoolGroups;
                 if (connectionPoolGroups.TryGetValue(key, out connectionPoolGroup))
                 {
@@ -140,13 +141,13 @@ protected DbConnectionOptions FindConnectionOptions(DbConnectionPoolKey key)
             return null;
         }
 
-        private static Task<DbConnectionInternal> GetCompletedTask()
+        private static Task<DbConnectionInternal?> GetCompletedTask()
         {
             Debug.Assert(Monitor.IsEntered(s_pendingOpenNonPooled), $"Expected {nameof(s_pendingOpenNonPooled)} lock to be held.");
-            return s_completedTask ?? (s_completedTask = Task.FromResult<DbConnectionInternal>(null));
+            return s_completedTask ?? (s_completedTask = Task.FromResult<DbConnectionInternal?>(null));
         }
 
-        private DbConnectionPool GetConnectionPool(DbConnection owningObject, DbConnectionPoolGroup connectionPoolGroup)
+        private DbConnectionPool? GetConnectionPool(DbConnection owningObject, DbConnectionPoolGroup connectionPoolGroup)
         {
             // if poolgroup is disabled, it will be replaced with a new entry
 
@@ -165,28 +166,28 @@ private DbConnectionPool GetConnectionPool(DbConnection owningObject, DbConnecti
             if (connectionPoolGroup.IsDisabled && (null != connectionPoolGroup.PoolGroupOptions))
             {
                 // reusing existing pool option in case user originally used SetConnectionPoolOptions
-                DbConnectionPoolGroupOptions poolOptions = connectionPoolGroup.PoolGroupOptions;
+                DbConnectionPoolGroupOptions? poolOptions = connectionPoolGroup.PoolGroupOptions;
 
                 // get the string to hash on again
-                DbConnectionOptions connectionOptions = connectionPoolGroup.ConnectionOptions;
+                DbConnectionOptions? connectionOptions = connectionPoolGroup.ConnectionOptions;
                 Debug.Assert(null != connectionOptions, "prevent expansion of connectionString");
 
-                connectionPoolGroup = GetConnectionPoolGroup(connectionPoolGroup.PoolKey, poolOptions, ref connectionOptions);
+                connectionPoolGroup = GetConnectionPoolGroup(connectionPoolGroup.PoolKey, poolOptions, ref connectionOptions)!;
                 Debug.Assert(null != connectionPoolGroup, "null connectionPoolGroup?");
                 SetConnectionPoolGroup(owningObject, connectionPoolGroup);
             }
-            DbConnectionPool connectionPool = connectionPoolGroup.GetConnectionPool(this);
+            DbConnectionPool? connectionPool = connectionPoolGroup.GetConnectionPool(this);
             return connectionPool;
         }
 
-        internal DbConnectionPoolGroup GetConnectionPoolGroup(DbConnectionPoolKey key, DbConnectionPoolGroupOptions poolOptions, ref DbConnectionOptions userConnectionOptions)
+        internal DbConnectionPoolGroup? GetConnectionPoolGroup(DbConnectionPoolKey key, DbConnectionPoolGroupOptions? poolOptions, ref DbConnectionOptions? userConnectionOptions)
         {
             if (string.IsNullOrEmpty(key.ConnectionString))
             {
-                return (DbConnectionPoolGroup)null;
+                return null;
             }
 
-            DbConnectionPoolGroup connectionPoolGroup;
+            DbConnectionPoolGroup? connectionPoolGroup;
             Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> connectionPoolGroups = _connectionPoolGroups;
             if (!connectionPoolGroups.TryGetValue(key, out connectionPoolGroup) || (connectionPoolGroup.IsDisabled && (null != connectionPoolGroup.PoolGroupOptions)))
             {
@@ -194,7 +195,7 @@ internal DbConnectionPoolGroup GetConnectionPoolGroup(DbConnectionPoolKey key, D
                 // our collection of pool entries, then we need to create a
                 // new pool entry and add it to our collection.
 
-                DbConnectionOptions connectionOptions = CreateConnectionOptions(key.ConnectionString, userConnectionOptions);
+                DbConnectionOptions? connectionOptions = CreateConnectionOptions(key.ConnectionString, userConnectionOptions);
                 if (null == connectionOptions)
                 {
                     throw ADP.InternalConnectionError(ADP.ConnectionError.ConnectionOptionsMissing);
@@ -225,7 +226,7 @@ internal DbConnectionPoolGroup GetConnectionPoolGroup(DbConnectionPoolKey key, D
                     connectionPoolGroups = _connectionPoolGroups;
                     if (!connectionPoolGroups.TryGetValue(key, out connectionPoolGroup))
                     {
-                        DbConnectionPoolGroup newConnectionPoolGroup = new DbConnectionPoolGroup(connectionOptions, key, poolOptions);
+                        DbConnectionPoolGroup newConnectionPoolGroup = new DbConnectionPoolGroup(connectionOptions, key, poolOptions!);
                         newConnectionPoolGroup.ProviderInfo = CreateConnectionPoolGroupProviderInfo(connectionOptions);
 
                         // build new dictionary with space for new connection string
@@ -256,7 +257,7 @@ internal DbConnectionPoolGroup GetConnectionPoolGroup(DbConnectionPoolKey key, D
         }
 
 
-        private void PruneConnectionPoolGroups(object state)
+        private void PruneConnectionPoolGroups(object? state)
         {
             // First, walk the pool release list and attempt to clear each
             // pool, when the pool is finally empty, we dispose of it.  If the
@@ -368,7 +369,7 @@ internal void QueuePoolGroupForRelease(DbConnectionPoolGroup poolGroup)
             }
         }
 
-        protected virtual DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions)
+        protected virtual DbConnectionInternal? CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool? pool, DbConnection? owningConnection, DbConnectionOptions? userOptions)
         {
             return CreateConnection(options, poolKey, poolGroupProviderInfo, pool, owningConnection);
         }
@@ -379,7 +380,7 @@ internal DbMetaDataFactory GetMetaDataFactory(DbConnectionPoolGroup connectionPo
 
             // get the matadatafactory from the pool entry. If it does not already have one
             // create one and save it on the pool entry
-            DbMetaDataFactory metaDataFactory = connectionPoolGroup.MetaDataFactory;
+            DbMetaDataFactory? metaDataFactory = connectionPoolGroup.MetaDataFactory;
 
             // consider serializing this so we don't construct multiple metadata factories
             // if two threads happen to hit this at the same time.  One will be GC'd
@@ -403,15 +404,15 @@ protected virtual DbMetaDataFactory CreateMetaDataFactory(DbConnectionInternal i
             throw ADP.NotSupported();
         }
 
-        protected abstract DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection);
+        protected abstract DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool? pool, DbConnection? owningConnection);
 
-        protected abstract DbConnectionOptions CreateConnectionOptions(string connectionString, DbConnectionOptions previous);
+        protected abstract DbConnectionOptions CreateConnectionOptions(string connectionString, DbConnectionOptions? previous);
 
-        protected abstract DbConnectionPoolGroupOptions CreateConnectionPoolGroupOptions(DbConnectionOptions options);
+        protected abstract DbConnectionPoolGroupOptions? CreateConnectionPoolGroupOptions(DbConnectionOptions options);
 
-        internal abstract DbConnectionPoolGroup GetConnectionPoolGroup(DbConnection connection);
+        internal abstract DbConnectionPoolGroup? GetConnectionPoolGroup(DbConnection connection);
 
-        internal abstract DbConnectionInternal GetInnerConnection(DbConnection connection);
+        internal abstract DbConnectionInternal? GetInnerConnection(DbConnection connection);
 
         internal abstract void PermissionDemand(DbConnection outerConnection);
 
diff --git a/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionInternal.cs b/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionInternal.cs
index 4afa5d32351dab..5c1c4c0034cd95 100644
--- a/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionInternal.cs
+++ b/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionInternal.cs
@@ -21,8 +21,8 @@ internal abstract partial class DbConnectionInternal
 
         private readonly WeakReference _owningObject = new WeakReference(null, false);  // [usage must be thread safe] the owning object, when not in the pool. (both Pooled and Non-Pooled connections)
 
-        private DbConnectionPool _connectionPool;           // the pooler that the connection came from (Pooled connections only)
-        private DbReferenceCollection _referenceCollection;      // collection of objects that we need to notify in some way when we're being deactivated
+        private DbConnectionPool? _connectionPool;           // the pooler that the connection came from (Pooled connections only)
+        private DbReferenceCollection? _referenceCollection;      // collection of objects that we need to notify in some way when we're being deactivated
         private int _pooledCount;              // [usage must be thread safe] the number of times this object has been pushed into the pool less the number of times it's been popped (0 != inPool)
 
         private bool _connectionIsDoomed;       // true when the connection should no longer be used.
@@ -113,17 +113,17 @@ internal bool IsInPool
         }
 
 
-        protected internal object Owner
+        protected internal object? Owner
         {
             // We use a weak reference to the owning object so we can identify when
-            // it has been garbage collected without thowing exceptions.
+            // it has been garbage collected without throwing exceptions.
             get
             {
                 return _owningObject.Target;
             }
         }
 
-        internal DbConnectionPool Pool
+        internal DbConnectionPool? Pool
         {
             get
             {
@@ -131,7 +131,7 @@ internal DbConnectionPool Pool
             }
         }
 
-        protected internal DbReferenceCollection ReferenceCollection
+        protected internal DbReferenceCollection? ReferenceCollection
         {
             get
             {
@@ -199,12 +199,12 @@ protected virtual void PrepareForCloseConnection()
             // By default, there is no preparation required
         }
 
-        protected virtual object ObtainAdditionalLocksForClose()
+        protected virtual object? ObtainAdditionalLocksForClose()
         {
             return null; // no additional locks in default implementation
         }
 
-        protected virtual void ReleaseAdditionalLocksForClose(object lockToken)
+        protected virtual void ReleaseAdditionalLocksForClose(object? lockToken)
         {
             // no additional locks in default implementation
         }
@@ -218,6 +218,8 @@ protected virtual DbReferenceCollection CreateReferenceCollection()
 
         internal void DeactivateConnection()
         {
+            Debug.Assert(Pool != null);
+
             // Internal method called from the connection pooler so we don't expose
             // the Deactivate method publicly.
 
@@ -251,7 +253,7 @@ protected internal void DoomThisConnection()
             _connectionIsDoomed = true;
         }
 
-        protected internal virtual DataTable GetSchema(DbConnectionFactory factory, DbConnectionPoolGroup poolGroup, DbConnection outerConnection, string collectionName, string[] restrictions)
+        protected internal virtual DataTable GetSchema(DbConnectionFactory factory, DbConnectionPoolGroup poolGroup, DbConnection outerConnection, string collectionName, string?[]? restrictions)
         {
             Debug.Assert(outerConnection != null, "outerConnection may not be null.");
 
@@ -282,7 +284,7 @@ internal void MakePooledConnection(DbConnectionPool connectionPool)
 
         internal void NotifyWeakReference(int message)
         {
-            DbReferenceCollection referenceCollection = ReferenceCollection;
+            DbReferenceCollection? referenceCollection = ReferenceCollection;
             if (null != referenceCollection)
             {
                 referenceCollection.Notify(message);
@@ -302,22 +304,22 @@ internal virtual void OpenConnection(DbConnection outerConnection, DbConnectionF
         /// override this and do the correct thing.</devdoc>
         // User code should either override DbConnectionInternal.Activate when it comes out of the pool
         // or override DbConnectionFactory.CreateConnection when the connection is created for non-pooled connections
-        internal virtual bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal virtual bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
         {
             throw ADP.ConnectionAlreadyOpen(State);
         }
 
-        internal virtual bool TryReplaceConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal virtual bool TryReplaceConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
         {
             throw ADP.MethodNotImplemented();
         }
 
-        protected bool TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        protected bool TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
         {
             // ?->Connecting: prevent set_ConnectionString during Open
             if (connectionFactory.SetInnerConnectionFrom(outerConnection, DbConnectionClosedConnecting.SingletonInstance, this))
             {
-                DbConnectionInternal openConnection = null;
+                DbConnectionInternal? openConnection = null;
                 try
                 {
                     connectionFactory.PermissionDemand(outerConnection);
@@ -343,7 +345,7 @@ protected bool TryOpenConnectionInternal(DbConnection outerConnection, DbConnect
             return true;
         }
 
-        internal void PrePush(object expectedOwner)
+        internal void PrePush(object? expectedOwner)
         {
             // Called by DbConnectionPool when we're about to be put into it's pool, we
             // take this opportunity to ensure ownership and pool counts are legit.
@@ -412,7 +414,7 @@ internal void PostPop(object newOwner)
 
         internal void RemoveWeakReference(object value)
         {
-            DbReferenceCollection referenceCollection = ReferenceCollection;
+            DbReferenceCollection? referenceCollection = ReferenceCollection;
             if (null != referenceCollection)
             {
                 referenceCollection.Remove(value);
diff --git a/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionPoolGroup.cs b/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionPoolGroup.cs
index eb0f8ed4f154c9..26ee3b6515ddb1 100644
--- a/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionPoolGroup.cs
+++ b/src/libraries/Common/src/System/Data/ProviderBase/DbConnectionPoolGroup.cs
@@ -34,8 +34,8 @@ internal sealed class DbConnectionPoolGroup
 
         private int _state;          // see PoolGroupState* below
 
-        private DbConnectionPoolGroupProviderInfo _providerInfo;
-        private DbMetaDataFactory _metaDataFactory;
+        private DbConnectionPoolGroupProviderInfo? _providerInfo;
+        private DbMetaDataFactory? _metaDataFactory;
 
         // always lock this before changing _state, we don't want to move out of the 'Disabled' state
         // PoolGroupStateUninitialized = 0;
@@ -63,7 +63,7 @@ internal DbConnectionPoolGroup(DbConnectionOptions connectionOptions, DbConnecti
 
         internal DbConnectionPoolKey PoolKey => _poolKey;
 
-        internal DbConnectionPoolGroupProviderInfo ProviderInfo
+        internal DbConnectionPoolGroupProviderInfo? ProviderInfo
         {
             get
             {
@@ -74,7 +74,7 @@ internal DbConnectionPoolGroupProviderInfo ProviderInfo
                 _providerInfo = value;
                 if (null != value)
                 {
-                    _providerInfo.PoolGroup = this;
+                    _providerInfo!.PoolGroup = this;
                 }
             }
         }
@@ -83,7 +83,7 @@ internal DbConnectionPoolGroupProviderInfo ProviderInfo
 
         internal DbConnectionPoolGroupOptions PoolGroupOptions => _poolGroupOptions;
 
-        internal DbMetaDataFactory MetaDataFactory
+        internal DbMetaDataFactory? MetaDataFactory
         {
             get
             {
@@ -102,7 +102,7 @@ internal int Clear()
             // will return the number of connections in the group after clearing has finished
 
             // First, note the old collection and create a new collection to be used
-            ConcurrentDictionary<DbConnectionPoolIdentity, DbConnectionPool> oldPoolCollection = null;
+            ConcurrentDictionary<DbConnectionPoolIdentity, DbConnectionPool>? oldPoolCollection = null;
             lock (this)
             {
                 if (_poolCollection.Count > 0)
@@ -130,7 +130,7 @@ internal int Clear()
             return _poolCollection.Count;
         }
 
-        internal DbConnectionPool GetConnectionPool(DbConnectionFactory connectionFactory)
+        internal DbConnectionPool? GetConnectionPool(DbConnectionFactory connectionFactory)
         {
             // When this method returns null it indicates that the connection
             // factory should not use pooling.
@@ -138,10 +138,10 @@ internal DbConnectionPool GetConnectionPool(DbConnectionFactory connectionFactor
             // We don't support connection pooling on Win9x;
             // PoolGroupOptions will only be null when we're not supposed to pool
             // connections.
-            DbConnectionPool pool = null;
+            DbConnectionPool? pool = null;
             if (null != _poolGroupOptions)
             {
-                DbConnectionPoolIdentity currentIdentity = DbConnectionPoolIdentity.NoIdentity;
+                DbConnectionPoolIdentity? currentIdentity = DbConnectionPoolIdentity.NoIdentity;
 
                 if (_poolGroupOptions.PoolByIdentity)
                 {
@@ -168,7 +168,7 @@ internal DbConnectionPool GetConnectionPool(DbConnectionFactory connectionFactor
                             // Did someone already add it to the list?
                             if (!_poolCollection.TryGetValue(currentIdentity, out pool))
                             {
-                                DbConnectionPoolProviderInfo connectionPoolProviderInfo = connectionFactory.CreateConnectionPoolProviderInfo(this.ConnectionOptions);
+                                DbConnectionPoolProviderInfo? connectionPoolProviderInfo = connectionFactory.CreateConnectionPoolProviderInfo(this.ConnectionOptions);
                                 DbConnectionPool newPool = new DbConnectionPool(connectionFactory, this, currentIdentity, connectionPoolProviderInfo);
 
                                 if (MarkPoolGroupAsActive())
diff --git a/src/libraries/Common/src/System/Data/ProviderBase/DbMetaDataFactory.cs b/src/libraries/Common/src/System/Data/ProviderBase/DbMetaDataFactory.cs
index 614b11c7710d9e..3a12fa546dfa5c 100644
--- a/src/libraries/Common/src/System/Data/ProviderBase/DbMetaDataFactory.cs
+++ b/src/libraries/Common/src/System/Data/ProviderBase/DbMetaDataFactory.cs
@@ -37,7 +37,8 @@ public DbMetaDataFactory(Stream xmlStream, string serverVersion, string normaliz
             ADP.CheckArgumentNull(serverVersion, nameof(serverVersion));
             ADP.CheckArgumentNull(normalizedServerVersion, nameof(normalizedServerVersion));
 
-            LoadDataSetFromXml(xmlStream);
+            _metaDataCollectionsDataSet = new DataSet { Locale = CultureInfo.InvariantCulture };
+            _metaDataCollectionsDataSet.ReadXml(xmlStream);
 
             _serverVersionString = serverVersion;
             _normalizedServerVersion = normalizedServerVersion;
@@ -49,14 +50,14 @@ public DbMetaDataFactory(Stream xmlStream, string serverVersion, string normaliz
 
         protected string ServerVersionNormalized => _normalizedServerVersion;
 
-        protected DataTable CloneAndFilterCollection(string collectionName, string[] hiddenColumnNames)
+        protected DataTable CloneAndFilterCollection(string collectionName, string[]? hiddenColumnNames)
         {
             DataTable destinationTable;
             DataColumn[] filteredSourceColumns;
             DataColumnCollection destinationColumns;
             DataRow newRow;
 
-            DataTable sourceTable = _metaDataCollectionsDataSet.Tables[collectionName];
+            DataTable? sourceTable = _metaDataCollectionsDataSet.Tables[collectionName];
 
             if ((sourceTable == null) || (collectionName != sourceTable.TableName))
             {
@@ -94,27 +95,27 @@ protected virtual void Dispose(bool disposing)
         {
             if (disposing)
             {
-                _normalizedServerVersion = null;
-                _serverVersionString = null;
+                _normalizedServerVersion = null!;
+                _serverVersionString = null!;
                 _metaDataCollectionsDataSet.Dispose();
             }
         }
 
-        private DataTable ExecuteCommand(DataRow requestedCollectionRow, string[] restrictions, DbConnection connection)
+        private DataTable ExecuteCommand(DataRow requestedCollectionRow, string?[]? restrictions, DbConnection connection)
         {
-            DataTable metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
-            DataColumn populationStringColumn = metaDataCollectionsTable.Columns[_populationString];
-            DataColumn numberOfRestrictionsColumn = metaDataCollectionsTable.Columns[_numberOfRestrictions];
-            DataColumn collectionNameColumn = metaDataCollectionsTable.Columns[_collectionName];
+            DataTable metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections]!;
+            DataColumn populationStringColumn = metaDataCollectionsTable.Columns[_populationString]!;
+            DataColumn numberOfRestrictionsColumn = metaDataCollectionsTable.Columns[_numberOfRestrictions]!;
+            DataColumn collectionNameColumn = metaDataCollectionsTable.Columns[_collectionName]!;
 
-            DataTable resultTable = null;
-            DbCommand command = null;
-            DataTable schemaTable = null;
+            DataTable? resultTable = null;
+            DbCommand? command = null;
+            DataTable? schemaTable = null;
 
             Debug.Assert(requestedCollectionRow != null);
-            string sqlCommand = requestedCollectionRow[populationStringColumn, DataRowVersion.Current] as string;
+            string sqlCommand = (requestedCollectionRow[populationStringColumn, DataRowVersion.Current] as string)!;
             int numberOfRestrictions = (int)requestedCollectionRow[numberOfRestrictionsColumn, DataRowVersion.Current];
-            string collectionName = requestedCollectionRow[collectionNameColumn, DataRowVersion.Current] as string;
+            string collectionName = (requestedCollectionRow[collectionNameColumn, DataRowVersion.Current] as string)!;
 
             if ((restrictions != null) && (restrictions.Length > numberOfRestrictions))
             {
@@ -145,7 +146,7 @@ private DataTable ExecuteCommand(DataRow requestedCollectionRow, string[] restri
                 command.Parameters.Add(restrictionParameter);
             }
 
-            DbDataReader reader = null;
+            DbDataReader? reader = null;
             try
             {
                 try
@@ -190,7 +191,7 @@ private DataTable ExecuteCommand(DataRow requestedCollectionRow, string[] restri
             return resultTable;
         }
 
-        private DataColumn[] FilterColumns(DataTable sourceTable, string[] hiddenColumnNames, DataColumnCollection destinationColumns)
+        private DataColumn[] FilterColumns(DataTable sourceTable, string[]? hiddenColumnNames, DataColumnCollection destinationColumns)
         {
             int columnCount = 0;
             foreach (DataColumn sourceColumn in sourceTable.Columns)
@@ -227,23 +228,23 @@ internal DataRow FindMetaDataCollectionRow(string collectionName)
             bool versionFailure;
             bool haveExactMatch;
             bool haveMultipleInexactMatches;
-            string candidateCollectionName;
+            string? candidateCollectionName;
 
-            DataTable metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
+            DataTable? metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
             if (metaDataCollectionsTable == null)
             {
                 throw ADP.InvalidXml();
             }
 
-            DataColumn collectionNameColumn = metaDataCollectionsTable.Columns[DbMetaDataColumnNames.CollectionName];
+            DataColumn? collectionNameColumn = metaDataCollectionsTable.Columns[DbMetaDataColumnNames.CollectionName];
 
             if ((null == collectionNameColumn) || (typeof(string) != collectionNameColumn.DataType))
             {
                 throw ADP.InvalidXmlMissingColumn(DbMetaDataCollectionNames.MetaDataCollections, DbMetaDataColumnNames.CollectionName);
             }
 
-            DataRow requestedCollectionRow = null;
-            string exactCollectionName = null;
+            DataRow? requestedCollectionRow = null;
+            string? exactCollectionName = null;
 
             // find the requested collection
             versionFailure = false;
@@ -316,8 +317,8 @@ internal DataRow FindMetaDataCollectionRow(string collectionName)
         private void FixUpVersion(DataTable dataSourceInfoTable)
         {
             Debug.Assert(dataSourceInfoTable.TableName == DbMetaDataCollectionNames.DataSourceInformation);
-            DataColumn versionColumn = dataSourceInfoTable.Columns[_dataSourceProductVersion];
-            DataColumn normalizedVersionColumn = dataSourceInfoTable.Columns[_dataSourceProductVersionNormalized];
+            DataColumn? versionColumn = dataSourceInfoTable.Columns[_dataSourceProductVersion];
+            DataColumn? normalizedVersionColumn = dataSourceInfoTable.Columns[_dataSourceProductVersionNormalized];
 
             if ((versionColumn == null) || (normalizedVersionColumn == null))
             {
@@ -340,14 +341,14 @@ private void FixUpVersion(DataTable dataSourceInfoTable)
         private string GetParameterName(string neededCollectionName, int neededRestrictionNumber)
         {
 
-            DataTable restrictionsTable = null;
-            DataColumnCollection restrictionColumns = null;
-            DataColumn collectionName = null;
-            DataColumn parameterName = null;
-            DataColumn restrictionName = null;
-            DataColumn restrictionNumber = null;
+            DataTable? restrictionsTable = null;
+            DataColumnCollection? restrictionColumns = null;
+            DataColumn? collectionName = null;
+            DataColumn? parameterName = null;
+            DataColumn? restrictionName = null;
+            DataColumn? restrictionNumber = null;
 
-            string result = null;
+            string? result = null;
 
             restrictionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.Restrictions];
             if (restrictionsTable != null)
@@ -367,7 +368,7 @@ private string GetParameterName(string neededCollectionName, int neededRestricti
                 throw ADP.MissingRestrictionColumn();
             }
 
-            foreach (DataRow restriction in restrictionsTable.Rows)
+            foreach (DataRow restriction in restrictionsTable!.Rows)
             {
 
                 if (((string)restriction[collectionName] == neededCollectionName) &&
@@ -388,27 +389,27 @@ private string GetParameterName(string neededCollectionName, int neededRestricti
             return result;
         }
 
-        public virtual DataTable GetSchema(DbConnection connection, string collectionName, string[] restrictions)
+        public virtual DataTable GetSchema(DbConnection connection, string collectionName, string?[]? restrictions)
         {
             Debug.Assert(_metaDataCollectionsDataSet != null);
 
-            DataTable metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
-            DataColumn populationMechanismColumn = metaDataCollectionsTable.Columns[_populationMechanism];
-            DataColumn collectionNameColumn = metaDataCollectionsTable.Columns[DbMetaDataColumnNames.CollectionName];
-            DataRow requestedCollectionRow = null;
-            DataTable requestedSchema = null;
-            string[] hiddenColumns;
-            string exactCollectionName = null;
+            DataTable metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections]!;
+            DataColumn populationMechanismColumn = metaDataCollectionsTable.Columns[_populationMechanism]!;
+            DataColumn collectionNameColumn = metaDataCollectionsTable.Columns[DbMetaDataColumnNames.CollectionName]!;
+            DataRow? requestedCollectionRow = null;
+            DataTable? requestedSchema = null;
+            string[]? hiddenColumns;
+            string? exactCollectionName = null;
 
             requestedCollectionRow = FindMetaDataCollectionRow(collectionName);
-            exactCollectionName = requestedCollectionRow[collectionNameColumn, DataRowVersion.Current] as string;
+            exactCollectionName = (requestedCollectionRow[collectionNameColumn, DataRowVersion.Current] as string)!;
 
             if (ADP.IsEmptyArray(restrictions) == false)
             {
 
                 for (int i = 0; i < restrictions.Length; i++)
                 {
-                    if ((restrictions[i] != null) && (restrictions[i].Length > 4096))
+                    if ((restrictions[i]?.Length > 4096))
                     {
                         // use a non-specific error because no new beta 2 error messages are allowed
                         // TODO: will add a more descriptive error in RTM
@@ -417,10 +418,9 @@ public virtual DataTable GetSchema(DbConnection connection, string collectionNam
                 }
             }
 
-            string populationMechanism = requestedCollectionRow[populationMechanismColumn, DataRowVersion.Current] as string;
+            string populationMechanism = (requestedCollectionRow[populationMechanismColumn, DataRowVersion.Current] as string)!;
             switch (populationMechanism)
             {
-
                 case _dataTable:
                     if (exactCollectionName == DbMetaDataCollectionNames.MetaDataCollections)
                     {
@@ -466,7 +466,7 @@ public virtual DataTable GetSchema(DbConnection connection, string collectionNam
             return requestedSchema;
         }
 
-        private bool IncludeThisColumn(DataColumn sourceColumn, string[] hiddenColumnNames)
+        private bool IncludeThisColumn(DataColumn sourceColumn, string[]? hiddenColumnNames)
         {
 
             bool result = true;
@@ -499,14 +499,7 @@ private bool IncludeThisColumn(DataColumn sourceColumn, string[] hiddenColumnNam
             return result;
         }
 
-        private void LoadDataSetFromXml(Stream XmlStream)
-        {
-            _metaDataCollectionsDataSet = new DataSet();
-            _metaDataCollectionsDataSet.Locale = System.Globalization.CultureInfo.InvariantCulture;
-            _metaDataCollectionsDataSet.ReadXml(XmlStream);
-        }
-
-        protected virtual DataTable PrepareCollection(string collectionName, string[] restrictions, DbConnection connection)
+        protected virtual DataTable PrepareCollection(string collectionName, string?[]? restrictions, DbConnection connection)
         {
             throw ADP.NotSupported();
         }
@@ -515,7 +508,7 @@ private bool SupportedByCurrentVersion(DataRow requestedCollectionRow)
         {
             bool result = true;
             DataColumnCollection tableColumns = requestedCollectionRow.Table.Columns;
-            DataColumn versionColumn;
+            DataColumn? versionColumn;
             object version;
 
             // check the minimum version first
diff --git a/src/libraries/Common/src/System/Data/ProviderBase/DbReferenceCollection.cs b/src/libraries/Common/src/System/Data/ProviderBase/DbReferenceCollection.cs
index b13b20ca26e76d..8d7aa930bcc6c3 100644
--- a/src/libraries/Common/src/System/Data/ProviderBase/DbReferenceCollection.cs
+++ b/src/libraries/Common/src/System/Data/ProviderBase/DbReferenceCollection.cs
@@ -6,6 +6,7 @@
 //------------------------------------------------------------------------------
 
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 
 namespace System.Data.ProviderBase
@@ -55,7 +56,7 @@ public int Tag
                 }
             }
 
-            public object Target
+            public object? Target
             {
                 get
                 {
@@ -136,7 +137,7 @@ protected void AddItem(object value, int tag)
             }
         }
 
-        internal T FindItem<T>(int tag, Func<T, bool> filterMethod) where T : class
+        internal T? FindItem<T>(int tag, Func<T, bool> filterMethod) where T : class
         {
             bool lockObtained = false;
             try
@@ -154,12 +155,11 @@ internal T FindItem<T>(int tag, Func<T, bool> filterMethod) where T : class
                             {
                                 // NOTE: Check if the returned value is null twice may seem wasteful, but this if for performance
                                 // Since checking for null twice is cheaper than calling both HasTarget and Target OR always attempting to typecast
-                                object value = _items[counter].Target;
+                                object? value = _items[counter].Target;
                                 if (value != null)
                                 {
                                     // Make sure the item has the correct type and passes the filtering
-                                    T tempItem = value as T;
-                                    if ((tempItem != null) && (filterMethod(tempItem)))
+                                    if (value is T tempItem && filterMethod(tempItem))
                                     {
                                         return tempItem;
                                     }
@@ -195,7 +195,7 @@ public void Notify(int message)
                         {
                             for (int index = 0; index <= _lastItemIndex; ++index)
                             {
-                                object value = _items[index].Target; // checks tag & gets target
+                                object? value = _items[index].Target; // checks tag & gets target
                                 if (null != value)
                                 {
                                     NotifyItem(message, _items[index].Tag, value);
diff --git a/src/libraries/Common/src/System/HexConverter.cs b/src/libraries/Common/src/System/HexConverter.cs
index d6160a18aa031e..d0cd3f074dc008 100644
--- a/src/libraries/Common/src/System/HexConverter.cs
+++ b/src/libraries/Common/src/System/HexConverter.cs
@@ -98,7 +98,7 @@ public static void EncodeToUtf16(ReadOnlySpan<byte> bytes, Span<char> chars, Cas
 #endif
         public static unsafe string ToString(ReadOnlySpan<byte> bytes, Casing casing = Casing.Upper)
         {
-#if NET45 || NET46 || NET461 || NET462 || NET47 || NET471 || NET472 || NETSTANDARD1_0 || NETSTANDARD1_3 || NETSTANDARD2_0
+#if NETFRAMEWORK || NETSTANDARD1_0 || NETSTANDARD1_3 || NETSTANDARD2_0
             Span<char> result = stackalloc char[0];
             if (bytes.Length > 16)
             {
@@ -120,7 +120,7 @@ public static unsafe string ToString(ReadOnlySpan<byte> bytes, Casing casing = C
 #else
             fixed (byte* bytesPtr = bytes)
             {
-                return string.Create(bytes.Length * 2, (Ptr: (IntPtr)bytesPtr, bytes.Length, casing), (chars, args) =>
+                return string.Create(bytes.Length * 2, (Ptr: (IntPtr)bytesPtr, bytes.Length, casing), static (chars, args) =>
                 {
                     var ros = new ReadOnlySpan<byte>((byte*)args.Ptr, args.Length);
                     EncodeToUtf16(ros, chars, args.casing);
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/HPackEncoder.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/HPackEncoder.cs
index d2fbc52232a994..4c3ac29527049f 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/HPackEncoder.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/HPackEncoder.cs
@@ -4,6 +4,7 @@
 #nullable enable
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Text;
 
 namespace System.Net.Http.HPack
 {
@@ -96,7 +97,7 @@ public static bool EncodeLiteralHeaderFieldWithoutIndexing(int index, string val
                 if (IntegerEncoder.Encode(index, 4, destination, out int indexLength))
                 {
                     Debug.Assert(indexLength >= 1);
-                    if (EncodeStringLiteral(value, destination.Slice(indexLength), out int nameLength))
+                    if (EncodeStringLiteral(value, valueEncoding: null, destination.Slice(indexLength), out int nameLength))
                     {
                         bytesWritten = indexLength + nameLength;
                         return true;
@@ -128,7 +129,7 @@ public static bool EncodeLiteralHeaderFieldNeverIndexing(int index, string value
                 if (IntegerEncoder.Encode(index, 4, destination, out int indexLength))
                 {
                     Debug.Assert(indexLength >= 1);
-                    if (EncodeStringLiteral(value, destination.Slice(indexLength), out int nameLength))
+                    if (EncodeStringLiteral(value, valueEncoding: null, destination.Slice(indexLength), out int nameLength))
                     {
                         bytesWritten = indexLength + nameLength;
                         return true;
@@ -160,7 +161,7 @@ public static bool EncodeLiteralHeaderFieldIndexing(int index, string value, Spa
                 if (IntegerEncoder.Encode(index, 6, destination, out int indexLength))
                 {
                     Debug.Assert(indexLength >= 1);
-                    if (EncodeStringLiteral(value, destination.Slice(indexLength), out int nameLength))
+                    if (EncodeStringLiteral(value, valueEncoding: null, destination.Slice(indexLength), out int nameLength))
                     {
                         bytesWritten = indexLength + nameLength;
                         return true;
@@ -276,7 +277,7 @@ private static bool EncodeLiteralHeaderNewNameCore(byte mask, string name, strin
             {
                 destination[0] = mask;
                 if (EncodeLiteralHeaderName(name, destination.Slice(1), out int nameLength) &&
-                    EncodeStringLiteral(value, destination.Slice(1 + nameLength), out int valueLength))
+                    EncodeStringLiteral(value, valueEncoding: null, destination.Slice(1 + nameLength), out int valueLength))
                 {
                     bytesWritten = 1 + nameLength + valueLength;
                     return true;
@@ -289,6 +290,11 @@ private static bool EncodeLiteralHeaderNewNameCore(byte mask, string name, strin
 
         /// <summary>Encodes a "Literal Header Field without Indexing - New Name".</summary>
         public static bool EncodeLiteralHeaderFieldWithoutIndexingNewName(string name, ReadOnlySpan<string> values, string separator, Span<byte> destination, out int bytesWritten)
+        {
+            return EncodeLiteralHeaderFieldWithoutIndexingNewName(name, values, separator, valueEncoding: null, destination, out bytesWritten);
+        }
+
+        public static bool EncodeLiteralHeaderFieldWithoutIndexingNewName(string name, ReadOnlySpan<string> values, string separator, Encoding? valueEncoding, Span<byte> destination, out int bytesWritten)
         {
             // From https://tools.ietf.org/html/rfc7541#section-6.2.2
             // ------------------------------------------------------
@@ -309,7 +315,7 @@ public static bool EncodeLiteralHeaderFieldWithoutIndexingNewName(string name, R
             {
                 destination[0] = 0;
                 if (EncodeLiteralHeaderName(name, destination.Slice(1), out int nameLength) &&
-                    EncodeStringLiterals(values, separator, destination.Slice(1 + nameLength), out int valueLength))
+                    EncodeStringLiterals(values, separator, valueEncoding, destination.Slice(1 + nameLength), out int valueLength))
                 {
                     bytesWritten = 1 + nameLength + valueLength;
                     return true;
@@ -395,27 +401,20 @@ private static bool EncodeLiteralHeaderName(string value, Span<byte> destination
             return false;
         }
 
-        private static bool EncodeStringLiteralValue(string value, Span<byte> destination, out int bytesWritten)
+        private static void EncodeValueStringPart(string value, Span<byte> destination)
         {
-            if (value.Length <= destination.Length)
+            Debug.Assert(destination.Length >= value.Length);
+
+            for (int i = 0; i < value.Length; i++)
             {
-                for (int i = 0; i < value.Length; i++)
+                char c = value[i];
+                if ((c & 0xFF80) != 0)
                 {
-                    char c = value[i];
-                    if ((c & 0xFF80) != 0)
-                    {
-                        throw new HttpRequestException(SR.net_http_request_invalid_char_encoding);
-                    }
-
-                    destination[i] = (byte)c;
+                    throw new HttpRequestException(SR.net_http_request_invalid_char_encoding);
                 }
 
-                bytesWritten = value.Length;
-                return true;
+                destination[i] = (byte)c;
             }
-
-            bytesWritten = 0;
-            return false;
         }
 
         public static bool EncodeStringLiteral(ReadOnlySpan<byte> value, Span<byte> destination, out int bytesWritten)
@@ -453,6 +452,11 @@ public static bool EncodeStringLiteral(ReadOnlySpan<byte> value, Span<byte> dest
         }
 
         public static bool EncodeStringLiteral(string value, Span<byte> destination, out int bytesWritten)
+        {
+            return EncodeStringLiteral(value, valueEncoding: null, destination, out bytesWritten);
+        }
+
+        public static bool EncodeStringLiteral(string value, Encoding? valueEncoding, Span<byte> destination, out int bytesWritten)
         {
             // From https://tools.ietf.org/html/rfc7541#section-5.2
             // ------------------------------------------------------
@@ -466,13 +470,28 @@ public static bool EncodeStringLiteral(string value, Span<byte> destination, out
             if (destination.Length != 0)
             {
                 destination[0] = 0; // TODO: Use Huffman encoding
-                if (IntegerEncoder.Encode(value.Length, 7, destination, out int integerLength))
+
+                int encodedStringLength = valueEncoding is null || ReferenceEquals(valueEncoding, Encoding.Latin1)
+                    ? value.Length
+                    : valueEncoding.GetByteCount(value);
+
+                if (IntegerEncoder.Encode(encodedStringLength, 7, destination, out int integerLength))
                 {
                     Debug.Assert(integerLength >= 1);
-
-                    if (EncodeStringLiteralValue(value, destination.Slice(integerLength), out int valueLength))
+                    destination = destination.Slice(integerLength);
+                    if (encodedStringLength <= destination.Length)
                     {
-                        bytesWritten = integerLength + valueLength;
+                        if (valueEncoding is null)
+                        {
+                            EncodeValueStringPart(value, destination);
+                        }
+                        else
+                        {
+                            int written = valueEncoding.GetBytes(value, destination);
+                            Debug.Assert(written == encodedStringLength);
+                        }
+
+                        bytesWritten = integerLength + encodedStringLength;
                         return true;
                     }
                 }
@@ -502,56 +521,87 @@ public static bool EncodeDynamicTableSizeUpdate(int value, Span<byte> destinatio
         }
 
         public static bool EncodeStringLiterals(ReadOnlySpan<string> values, string? separator, Span<byte> destination, out int bytesWritten)
+        {
+            return EncodeStringLiterals(values, separator, valueEncoding: null, destination, out bytesWritten);
+        }
+
+        public static bool EncodeStringLiterals(ReadOnlySpan<string> values, string? separator, Encoding? valueEncoding, Span<byte> destination, out int bytesWritten)
         {
             bytesWritten = 0;
 
             if (values.Length == 0)
             {
-                return EncodeStringLiteral("", destination, out bytesWritten);
+                return EncodeStringLiteral("", valueEncoding: null, destination, out bytesWritten);
             }
             else if (values.Length == 1)
             {
-                return EncodeStringLiteral(values[0], destination, out bytesWritten);
+                return EncodeStringLiteral(values[0], valueEncoding, destination, out bytesWritten);
             }
 
             if (destination.Length != 0)
             {
-                int valueLength = 0;
+                Debug.Assert(separator != null);
+                int valueLength;
 
                 // Calculate length of all parts and separators.
-                foreach (string part in values)
+                if (valueEncoding is null || ReferenceEquals(valueEncoding, Encoding.Latin1))
                 {
-                    valueLength = checked((int)(valueLength + part.Length));
+                    valueLength = checked((int)(values.Length - 1) * separator.Length);
+                    foreach (string part in values)
+                    {
+                        valueLength = checked((int)(valueLength + part.Length));
+                    }
+                }
+                else
+                {
+                    valueLength = checked((int)(values.Length - 1) * valueEncoding.GetByteCount(separator));
+                    foreach (string part in values)
+                    {
+                        valueLength = checked((int)(valueLength + valueEncoding.GetByteCount(part)));
+                    }
                 }
-
-                Debug.Assert(separator != null);
-                valueLength = checked((int)(valueLength + (values.Length - 1) * separator.Length));
 
                 destination[0] = 0;
                 if (IntegerEncoder.Encode(valueLength, 7, destination, out int integerLength))
                 {
                     Debug.Assert(integerLength >= 1);
-
-                    int encodedLength = 0;
-                    for (int j = 0; j < values.Length; j++)
+                    destination = destination.Slice(integerLength);
+                    if (destination.Length >= valueLength)
                     {
-                        if (j != 0 && !EncodeStringLiteralValue(separator, destination.Slice(integerLength), out encodedLength))
+                        if (valueEncoding is null)
                         {
-                            return false;
+                            string value = values[0];
+                            EncodeValueStringPart(value, destination);
+                            destination = destination.Slice(value.Length);
+
+                            for (int i = 1; i < values.Length; i++)
+                            {
+                                EncodeValueStringPart(separator, destination);
+                                destination = destination.Slice(separator.Length);
+
+                                value = values[i];
+                                EncodeValueStringPart(value, destination);
+                                destination = destination.Slice(value.Length);
+                            }
                         }
+                        else
+                        {
+                            int written = valueEncoding.GetBytes(values[0], destination);
+                            destination = destination.Slice(written);
 
-                        integerLength += encodedLength;
+                            for (int i = 1; i < values.Length; i++)
+                            {
+                                written = valueEncoding.GetBytes(separator, destination);
+                                destination = destination.Slice(written);
 
-                        if (!EncodeStringLiteralValue(values[j], destination.Slice(integerLength), out encodedLength))
-                        {
-                            return false;
+                                written = valueEncoding.GetBytes(values[i], destination);
+                                destination = destination.Slice(written);
+                            }
                         }
 
-                        integerLength += encodedLength;
+                        bytesWritten = integerLength + valueLength;
+                        return true;
                     }
-
-                    bytesWritten = integerLength;
-                    return true;
                 }
             }
 
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Http3/QPack/QPackEncoder.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Http3/QPack/QPackEncoder.cs
index be43dc3bc716ff..68e04ed2d4ce9c 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Http3/QPack/QPackEncoder.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Http3/QPack/QPackEncoder.cs
@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Net.Http.HPack;
+using System.Text;
 
 namespace System.Net.Http.QPack
 {
@@ -59,6 +60,11 @@ public static byte[] EncodeStaticIndexedHeaderFieldToArray(int index)
         // - T is constant 1 here, indicating a static table reference.
         // - H is constant 0 here, as we do not yet perform Huffman coding.
         public static bool EncodeLiteralHeaderFieldWithStaticNameReference(int index, string value, Span<byte> destination, out int bytesWritten)
+        {
+            return EncodeLiteralHeaderFieldWithStaticNameReference(index, value, valueEncoding: null, destination, out bytesWritten);
+        }
+
+        public static bool EncodeLiteralHeaderFieldWithStaticNameReference(int index, string value, Encoding? valueEncoding, Span<byte> destination, out int bytesWritten)
         {
             // Requires at least two bytes (one for name reference header, one for value length)
             if (destination.Length >= 2)
@@ -68,7 +74,7 @@ public static bool EncodeLiteralHeaderFieldWithStaticNameReference(int index, st
                 {
                     destination = destination.Slice(headerBytesWritten);
 
-                    if (EncodeValueString(value, destination, out int valueBytesWritten))
+                    if (EncodeValueString(value, valueEncoding, destination, out int valueBytesWritten))
                     {
                         bytesWritten = headerBytesWritten + valueBytesWritten;
                         return true;
@@ -81,7 +87,7 @@ public static bool EncodeLiteralHeaderFieldWithStaticNameReference(int index, st
         }
 
         /// <summary>
-        /// Encodes just the name part of a Literal Header Field With Static Name Reference. Must call <see cref="EncodeValueString(string, Span{byte}, out int)"/> after to encode the header's value.
+        /// Encodes just the name part of a Literal Header Field With Static Name Reference. Must call <see cref="EncodeValueString(string, Encoding?, Span{byte}, out int)"/> after to encode the header's value.
         /// </summary>
         public static byte[] EncodeLiteralHeaderFieldWithStaticNameReferenceToArray(int index)
         {
@@ -119,7 +125,12 @@ public static byte[] EncodeLiteralHeaderFieldWithStaticNameReferenceToArray(int
         // - H is constant 0 here, as we do not yet perform Huffman coding.
         public static bool EncodeLiteralHeaderFieldWithoutNameReference(string name, string value, Span<byte> destination, out int bytesWritten)
         {
-            if (EncodeNameString(name, destination, out int nameLength) && EncodeValueString(value, destination.Slice(nameLength), out int valueLength))
+            return EncodeLiteralHeaderFieldWithoutNameReference(name, value, valueEncoding: null, destination, out bytesWritten);
+        }
+
+        public static bool EncodeLiteralHeaderFieldWithoutNameReference(string name, string value, Encoding? valueEncoding, Span<byte> destination, out int bytesWritten)
+        {
+            if (EncodeNameString(name, destination, out int nameLength) && EncodeValueString(value, valueEncoding, destination.Slice(nameLength), out int valueLength))
             {
                 bytesWritten = nameLength + valueLength;
                 return true;
@@ -136,7 +147,12 @@ public static bool EncodeLiteralHeaderFieldWithoutNameReference(string name, str
         /// </summary>
         public static bool EncodeLiteralHeaderFieldWithoutNameReference(string name, ReadOnlySpan<string> values, string valueSeparator, Span<byte> destination, out int bytesWritten)
         {
-            if (EncodeNameString(name, destination, out int nameLength) && EncodeValueString(values, valueSeparator, destination.Slice(nameLength), out int valueLength))
+            return EncodeLiteralHeaderFieldWithoutNameReference(name, values, valueSeparator, valueEncoding: null, destination, out bytesWritten);
+        }
+
+        public static bool EncodeLiteralHeaderFieldWithoutNameReference(string name, ReadOnlySpan<string> values, string valueSeparator, Encoding? valueEncoding, Span<byte> destination, out int bytesWritten)
+        {
+            if (EncodeNameString(name, destination, out int nameLength) && EncodeValueString(values, valueSeparator, valueEncoding, destination.Slice(nameLength), out int valueLength))
             {
                 bytesWritten = nameLength + valueLength;
                 return true;
@@ -147,7 +163,7 @@ public static bool EncodeLiteralHeaderFieldWithoutNameReference(string name, Rea
         }
 
         /// <summary>
-        /// Encodes just the value part of a Literawl Header Field Without Static Name Reference. Must call <see cref="EncodeValueString(string, Span{byte}, out int)"/> after to encode the header's value.
+        /// Encodes just the value part of a Literawl Header Field Without Static Name Reference. Must call <see cref="EncodeValueString(string, Encoding?, Span{byte}, out int)"/> after to encode the header's value.
         /// </summary>
         public static byte[] EncodeLiteralHeaderFieldWithoutNameReferenceToArray(string name)
         {
@@ -169,19 +185,32 @@ public static byte[] EncodeLiteralHeaderFieldWithoutNameReferenceToArray(string
             return temp.Slice(0, bytesWritten).ToArray();
         }
 
-        private static bool EncodeValueString(string s, Span<byte> buffer, out int length)
+        private static bool EncodeValueString(string s, Encoding? valueEncoding, Span<byte> buffer, out int length)
         {
             if (buffer.Length != 0)
             {
                 buffer[0] = 0;
-                if (IntegerEncoder.Encode(s.Length, 7, buffer, out int nameLength))
+
+                int encodedStringLength = valueEncoding is null || ReferenceEquals(valueEncoding, Encoding.Latin1)
+                    ? s.Length
+                    : valueEncoding.GetByteCount(s);
+
+                if (IntegerEncoder.Encode(encodedStringLength, 7, buffer, out int nameLength))
                 {
                     buffer = buffer.Slice(nameLength);
-                    if (buffer.Length >= s.Length)
+                    if (buffer.Length >= encodedStringLength)
                     {
-                        EncodeValueStringPart(s, buffer);
+                        if (valueEncoding is null)
+                        {
+                            EncodeValueStringPart(s, buffer);
+                        }
+                        else
+                        {
+                            int written = valueEncoding.GetBytes(s, buffer);
+                            Debug.Assert(written == encodedStringLength);
+                        }
 
-                        length = nameLength + s.Length;
+                        length = nameLength + encodedStringLength;
                         return true;
                     }
                 }
@@ -195,25 +224,42 @@ private static bool EncodeValueString(string s, Span<byte> buffer, out int lengt
         /// Encodes a value by concatenating a collection of strings, separated by a separator string.
         /// </summary>
         public static bool EncodeValueString(ReadOnlySpan<string> values, string? separator, Span<byte> buffer, out int length)
+        {
+            return EncodeValueString(values, separator, valueEncoding: null, buffer, out length);
+        }
+
+        public static bool EncodeValueString(ReadOnlySpan<string> values, string? separator, Encoding? valueEncoding, Span<byte> buffer, out int length)
         {
             if (values.Length == 1)
             {
-                return EncodeValueString(values[0], buffer, out length);
+                return EncodeValueString(values[0], valueEncoding, buffer, out length);
             }
 
             if (values.Length == 0)
             {
                 // TODO: this will be called with a string array from HttpHeaderCollection. Can we ever get a 0-length array from that? Assert if not.
-                return EncodeValueString(string.Empty, buffer, out length);
+                return EncodeValueString(string.Empty, valueEncoding: null, buffer, out length);
             }
 
             if (buffer.Length > 0)
             {
                 Debug.Assert(separator != null);
-                int valueLength = separator.Length * (values.Length - 1);
-                for (int i = 0; i < values.Length; ++i)
+                int valueLength;
+                if (valueEncoding is null || ReferenceEquals(valueEncoding, Encoding.Latin1))
+                {
+                    valueLength = separator.Length * (values.Length - 1);
+                    foreach (string part in values)
+                    {
+                        valueLength += part.Length;
+                    }
+                }
+                else
                 {
-                    valueLength += values[i].Length;
+                    valueLength = valueEncoding.GetByteCount(separator) * (values.Length - 1);
+                    foreach (string part in values)
+                    {
+                        valueLength += valueEncoding.GetByteCount(part);
+                    }
                 }
 
                 buffer[0] = 0;
@@ -222,18 +268,35 @@ public static bool EncodeValueString(ReadOnlySpan<string> values, string? separa
                     buffer = buffer.Slice(nameLength);
                     if (buffer.Length >= valueLength)
                     {
-                        string value = values[0];
-                        EncodeValueStringPart(value, buffer);
-                        buffer = buffer.Slice(value.Length);
-
-                        for (int i = 1; i < values.Length; ++i)
+                        if (valueEncoding is null)
                         {
-                            EncodeValueStringPart(separator, buffer);
-                            buffer = buffer.Slice(separator.Length);
-
-                            value = values[i];
+                            string value = values[0];
                             EncodeValueStringPart(value, buffer);
                             buffer = buffer.Slice(value.Length);
+
+                            for (int i = 1; i < values.Length; i++)
+                            {
+                                EncodeValueStringPart(separator, buffer);
+                                buffer = buffer.Slice(separator.Length);
+
+                                value = values[i];
+                                EncodeValueStringPart(value, buffer);
+                                buffer = buffer.Slice(value.Length);
+                            }
+                        }
+                        else
+                        {
+                            int written = valueEncoding.GetBytes(values[0], buffer);
+                            buffer = buffer.Slice(written);
+
+                            for (int i = 1; i < values.Length; i++)
+                            {
+                                written = valueEncoding.GetBytes(separator, buffer);
+                                buffer = buffer.Slice(written);
+
+                                written = valueEncoding.GetBytes(values[i], buffer);
+                                buffer = buffer.Slice(written);
+                            }
                         }
 
                         length = nameLength + valueLength;
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicAddressHelpers.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicAddressHelpers.cs
index 38eb74b06accb6..a06a08f3b424a3 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicAddressHelpers.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicAddressHelpers.cs
@@ -11,7 +11,7 @@ internal static class MsQuicAddressHelpers
         internal const ushort IPv4 = 2;
         internal const ushort IPv6 = 23;
 
-        internal static unsafe IPEndPoint INetToIPEndPoint(SOCKADDR_INET inetAddress)
+        internal static unsafe IPEndPoint INetToIPEndPoint(ref SOCKADDR_INET inetAddress)
         {
             if (inetAddress.si_family == IPv4)
             {
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicApi.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicApi.cs
index 73c3e551ab4c6e..5c62f1dbc65971 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicApi.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicApi.cs
@@ -23,7 +23,7 @@ private unsafe MsQuicApi()
 
             try
             {
-                uint status = Interop.MsQuic.MsQuicOpen(version: 1, out registration);
+                uint status = Interop.MsQuic.MsQuicOpen(out registration);
                 if (!MsQuicStatusHelper.SuccessfulStatusCode(status))
                 {
                     throw new NotSupportedException(SR.net_quic_notsupported);
@@ -123,7 +123,13 @@ private unsafe MsQuicApi()
                 Marshal.GetDelegateForFunctionPointer<MsQuicNativeMethods.GetParamDelegate>(
                     nativeRegistration.GetParam);
 
-            RegistrationOpenDelegate(Encoding.UTF8.GetBytes("SystemNetQuic"), out IntPtr ctx);
+            var registrationConfig = new MsQuicNativeMethods.RegistrationConfig
+            {
+                AppName = "SystemNetQuic",
+                ExecutionProfile = QUIC_EXECUTION_PROFILE.QUIC_EXECUTION_PROFILE_LOW_LATENCY
+            };
+
+            RegistrationOpenDelegate(ref registrationConfig, out IntPtr ctx);
             _registrationContext = ctx;
         }
 
@@ -312,15 +318,26 @@ void SecCfgCreateCallbackHandler(
             return secConfig;
         }
 
-        public IntPtr SessionOpen(byte[] alpn)
+        public unsafe IntPtr SessionOpen(byte[] alpn)
         {
             IntPtr sessionPtr = IntPtr.Zero;
+            uint status;
 
-            uint status = SessionOpenDelegate(
-                _registrationContext,
-                alpn,
-                IntPtr.Zero,
-                ref sessionPtr);
+            fixed (byte* pAlpn = alpn)
+            {
+                var alpnBuffer = new MsQuicNativeMethods.QuicBuffer
+                {
+                    Length = (uint)alpn.Length,
+                    Buffer = pAlpn
+                };
+
+                status = SessionOpenDelegate(
+                    _registrationContext,
+                    &alpnBuffer,
+                    1,
+                    IntPtr.Zero,
+                    ref sessionPtr);
+            }
 
             QuicExceptionHelpers.ThrowIfFailed(status, "Could not open session.");
 
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicSession.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicSession.cs
index e35493a7745c6e..d5f1c11c4bf2bb 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicSession.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/Internal/MsQuicSession.cs
@@ -28,7 +28,7 @@ public IntPtr ConnectionOpen(QuicClientConnectionOptions options)
 
             QuicExceptionHelpers.ThrowIfFailed(MsQuicApi.Api.ConnectionOpenDelegate(
                 _nativeObjPtr,
-                MsQuicConnection.NativeCallbackHandler,
+                MsQuicConnection.s_connectionDelegate,
                 IntPtr.Zero,
                 out IntPtr connectionPtr),
                 "Could not open the connection.");
@@ -83,15 +83,15 @@ public void Dispose()
 
         public void SetPeerBiDirectionalStreamCount(ushort count)
         {
-            SetUshortParamter(QUIC_PARAM_SESSION.PEER_BIDI_STREAM_COUNT, count);
+            SetUshortParameter(QUIC_PARAM_SESSION.PEER_BIDI_STREAM_COUNT, count);
         }
 
         public void SetPeerUnidirectionalStreamCount(ushort count)
         {
-            SetUshortParamter(QUIC_PARAM_SESSION.PEER_UNIDI_STREAM_COUNT, count);
+            SetUshortParameter(QUIC_PARAM_SESSION.PEER_UNIDI_STREAM_COUNT, count);
         }
 
-        private unsafe void SetUshortParamter(QUIC_PARAM_SESSION param, ushort count)
+        private unsafe void SetUshortParameter(QUIC_PARAM_SESSION param, ushort count)
         {
             var buffer = new MsQuicNativeMethods.QuicBuffer()
             {
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicConnection.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicConnection.cs
index 0046c56abb0dea..708e15ee2ce46e 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicConnection.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicConnection.cs
@@ -2,9 +2,11 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 #nullable enable
+using System.Diagnostics;
 using System.IO;
 using System.Net.Quic.Implementations.MsQuic.Internal;
 using System.Net.Security;
+using System.Runtime.ExceptionServices;
 using System.Runtime.InteropServices;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
@@ -16,7 +18,7 @@ namespace System.Net.Quic.Implementations.MsQuic
 {
     internal sealed class MsQuicConnection : QuicConnectionProvider
     {
-        private MsQuicSession? _session;
+        private readonly MsQuicSession? _session;
 
         // Pointer to the underlying connection
         // TODO replace all IntPtr with SafeHandles
@@ -26,15 +28,17 @@ internal sealed class MsQuicConnection : QuicConnectionProvider
         private GCHandle _handle;
 
         // Delegate that wraps the static function that will be called when receiving an event.
-        // TODO investigate if the delegate can be static instead.
-        private ConnectionCallbackDelegate? _connectionDelegate;
+        internal static readonly ConnectionCallbackDelegate s_connectionDelegate = new ConnectionCallbackDelegate(NativeCallbackHandler);
 
         // Endpoint to either connect to or the endpoint already accepted.
         private IPEndPoint? _localEndPoint;
         private readonly IPEndPoint _remoteEndPoint;
 
-        private readonly ResettableCompletionSource<uint> _connectTcs = new ResettableCompletionSource<uint>();
-        private readonly ResettableCompletionSource<uint> _shutdownTcs = new ResettableCompletionSource<uint>();
+        private SslApplicationProtocol _negotiatedAlpnProtocol;
+
+        // TODO: only allocate these when there is an outstanding connect/shutdown.
+        private readonly TaskCompletionSource<uint> _connectTcs = new TaskCompletionSource<uint>();
+        private readonly TaskCompletionSource<uint> _shutdownTcs = new TaskCompletionSource<uint>();
 
         private bool _disposed;
         private bool _connected;
@@ -54,6 +58,7 @@ public MsQuicConnection(IPEndPoint localEndPoint, IPEndPoint remoteEndPoint, Int
             _localEndPoint = localEndPoint;
             _remoteEndPoint = remoteEndPoint;
             _ptr = nativeObjPtr;
+            _connected = true;
 
             SetCallbackHandler();
             SetIdleTimeout(TimeSpan.FromSeconds(120));
@@ -89,125 +94,96 @@ internal async ValueTask SetSecurityConfigForConnection(X509Certificate cert, st
 
         internal override IPEndPoint RemoteEndPoint => new IPEndPoint(_remoteEndPoint.Address, _remoteEndPoint.Port);
 
-        internal override SslApplicationProtocol NegotiatedApplicationProtocol => throw new NotImplementedException();
+        internal override SslApplicationProtocol NegotiatedApplicationProtocol => _negotiatedAlpnProtocol;
 
         internal override bool Connected => _connected;
 
         internal uint HandleEvent(ref ConnectionEvent connectionEvent)
         {
-            uint status = MsQuicStatusCodes.Success;
             try
             {
                 switch (connectionEvent.Type)
                 {
-                    // Connection is connected, can start to create streams.
                     case QUIC_CONNECTION_EVENT.CONNECTED:
-                        {
-                            status = HandleEventConnected(
-                                connectionEvent);
-                        }
-                        break;
-
-                    // Connection is being closed by the transport
+                        return HandleEventConnected(ref connectionEvent);
                     case QUIC_CONNECTION_EVENT.SHUTDOWN_INITIATED_BY_TRANSPORT:
-                        {
-                            status = HandleEventShutdownInitiatedByTransport(
-                                connectionEvent);
-                        }
-                        break;
-
-                    // Connection is being closed by the peer
+                        return HandleEventShutdownInitiatedByTransport(ref connectionEvent);
                     case QUIC_CONNECTION_EVENT.SHUTDOWN_INITIATED_BY_PEER:
-                        {
-                            status = HandleEventShutdownInitiatedByPeer(
-                                connectionEvent);
-                        }
-                        break;
-
-                    // Connection has been shutdown
+                        return HandleEventShutdownInitiatedByPeer(ref connectionEvent);
                     case QUIC_CONNECTION_EVENT.SHUTDOWN_COMPLETE:
-                        {
-                            status = HandleEventShutdownComplete(
-                                connectionEvent);
-                        }
-                        break;
-
+                        return HandleEventShutdownComplete(ref connectionEvent);
                     case QUIC_CONNECTION_EVENT.PEER_STREAM_STARTED:
-                        {
-                            status = HandleEventNewStream(
-                                connectionEvent);
-                        }
-                        break;
-
+                        return HandleEventNewStream(ref connectionEvent);
                     case QUIC_CONNECTION_EVENT.STREAMS_AVAILABLE:
-                        {
-                            status = HandleEventStreamsAvailable(
-                                connectionEvent);
-                        }
-                        break;
-
+                        return HandleEventStreamsAvailable(ref connectionEvent);
                     default:
-                        break;
+                        return MsQuicStatusCodes.Success;
                 }
             }
-            catch (Exception)
+            catch (Exception ex)
             {
-                // TODO we may want to either add a debug assert here or return specific error codes
-                // based on the exception caught.
+                if (NetEventSource.Log.IsEnabled())
+                {
+                    NetEventSource.Error(this, $"Exception occurred during connection callback: {ex.Message}");
+                }
+
+                // TODO: trigger an exception on any outstanding async calls.
+
                 return MsQuicStatusCodes.InternalError;
             }
-
-            return status;
         }
 
-        private uint HandleEventConnected(ConnectionEvent connectionEvent)
+        private uint HandleEventConnected(ref ConnectionEvent connectionEvent)
         {
-            SOCKADDR_INET inetAddress = MsQuicParameterHelpers.GetINetParam(MsQuicApi.Api, _ptr, (uint)QUIC_PARAM_LEVEL.CONNECTION, (uint)QUIC_PARAM_CONN.LOCAL_ADDRESS);
-            _localEndPoint = MsQuicAddressHelpers.INetToIPEndPoint(inetAddress);
+            if (!_connected)
+            {
+                // _connected will already be true for connections accepted from a listener.
 
-            _connected = true;
-            // I don't believe we need to lock here because
-            // handle event connected will not be called at the same time as
-            // handle event shutdown initiated by transport
-            _connectTcs.Complete(MsQuicStatusCodes.Success);
+                SOCKADDR_INET inetAddress = MsQuicParameterHelpers.GetINetParam(MsQuicApi.Api, _ptr, (uint)QUIC_PARAM_LEVEL.CONNECTION, (uint)QUIC_PARAM_CONN.LOCAL_ADDRESS);
+                _localEndPoint = MsQuicAddressHelpers.INetToIPEndPoint(ref inetAddress);
+
+                SetNegotiatedAlpn(connectionEvent.Data.Connected.NegotiatedAlpn, connectionEvent.Data.Connected.NegotiatedAlpnLength);
+
+                _connected = true;
+                _connectTcs.SetResult(MsQuicStatusCodes.Success);
+            }
 
             return MsQuicStatusCodes.Success;
         }
 
-        private uint HandleEventShutdownInitiatedByTransport(ConnectionEvent connectionEvent)
+        private uint HandleEventShutdownInitiatedByTransport(ref ConnectionEvent connectionEvent)
         {
             if (!_connected)
             {
-                _connectTcs.CompleteException(new IOException("Connection has been shutdown."));
+                _connectTcs.SetException(ExceptionDispatchInfo.SetCurrentStackTrace(new IOException("Connection has been shutdown.")));
             }
 
             _acceptQueue.Writer.Complete();
 
-
             return MsQuicStatusCodes.Success;
         }
 
-        private uint HandleEventShutdownInitiatedByPeer(ConnectionEvent connectionEvent)
+        private uint HandleEventShutdownInitiatedByPeer(ref ConnectionEvent connectionEvent)
         {
-            _abortErrorCode = connectionEvent.Data.ShutdownBeginPeer.ErrorCode;
+            _abortErrorCode = connectionEvent.Data.ShutdownInitiatedByPeer.ErrorCode;
             _acceptQueue.Writer.Complete();
             return MsQuicStatusCodes.Success;
         }
 
-        private uint HandleEventShutdownComplete(ConnectionEvent connectionEvent)
+        private uint HandleEventShutdownComplete(ref ConnectionEvent connectionEvent)
         {
-            _shutdownTcs.Complete(MsQuicStatusCodes.Success);
+            _shutdownTcs.SetResult(MsQuicStatusCodes.Success);
             return MsQuicStatusCodes.Success;
         }
 
-        private uint HandleEventNewStream(ConnectionEvent connectionEvent)
+        private uint HandleEventNewStream(ref ConnectionEvent connectionEvent)
         {
-            MsQuicStream msQuicStream = new MsQuicStream(this, connectionEvent.StreamFlags, connectionEvent.Data.NewStream.Stream, inbound: true);
+            MsQuicStream msQuicStream = new MsQuicStream(this, connectionEvent.StreamFlags, connectionEvent.Data.StreamStarted.Stream, inbound: true);
             _acceptQueue.Writer.TryWrite(msQuicStream);
             return MsQuicStatusCodes.Success;
         }
 
-        private uint HandleEventStreamsAvailable(ConnectionEvent connectionEvent)
+        private uint HandleEventStreamsAvailable(ref ConnectionEvent connectionEvent)
         {
             return MsQuicStatusCodes.Success;
         }
@@ -275,7 +251,7 @@ internal override ValueTask ConnectAsync(CancellationToken cancellationToken = d
                 (ushort)_remoteEndPoint.Port),
                 "Failed to connect to peer.");
 
-            return _connectTcs.GetTypelessValueTask();
+            return new ValueTask(_connectTcs.Task);
         }
 
         private MsQuicStream StreamOpen(
@@ -286,7 +262,7 @@ private MsQuicStream StreamOpen(
                 MsQuicApi.Api.StreamOpenDelegate(
                 _ptr,
                 (uint)flags,
-                MsQuicStream.NativeCallbackHandler,
+                MsQuicStream.s_streamDelegate,
                 IntPtr.Zero,
                 out streamPtr),
                 "Failed to open stream to peer.");
@@ -296,11 +272,12 @@ private MsQuicStream StreamOpen(
 
         private void SetCallbackHandler()
         {
+            Debug.Assert(!_handle.IsAllocated);
             _handle = GCHandle.Alloc(this);
-            _connectionDelegate = new ConnectionCallbackDelegate(NativeCallbackHandler);
+
             MsQuicApi.Api.SetCallbackHandlerDelegate(
                 _ptr,
-                _connectionDelegate,
+                s_connectionDelegate,
                 GCHandle.ToIntPtr(_handle));
         }
 
@@ -314,10 +291,20 @@ private ValueTask ShutdownAsync(
                 ErrorCode);
             QuicExceptionHelpers.ThrowIfFailed(status, "Failed to shutdown connection.");
 
-            return _shutdownTcs.GetTypelessValueTask();
+            return new ValueTask(_shutdownTcs.Task);
+        }
+
+        internal void SetNegotiatedAlpn(IntPtr alpn, int alpnLength)
+        {
+            if (alpn != IntPtr.Zero && alpnLength != 0)
+            {
+                var buffer = new byte[alpnLength];
+                Marshal.Copy(alpn, buffer, 0, alpnLength);
+                _negotiatedAlpnProtocol = new SslApplicationProtocol(buffer);
+            }
         }
 
-        internal static uint NativeCallbackHandler(
+        private static uint NativeCallbackHandler(
             IntPtr connection,
             IntPtr context,
             ref ConnectionEvent connectionEventStruct)
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicListener.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicListener.cs
index c8d338832398cd..721a8e554e4a6a 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicListener.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicListener.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 #nullable enable
+using System.Diagnostics;
 using System.Net.Quic.Implementations.MsQuic.Internal;
 using System.Net.Security;
 using System.Runtime.InteropServices;
@@ -15,7 +16,7 @@ namespace System.Net.Quic.Implementations.MsQuic
     internal sealed class MsQuicListener : QuicListenerProvider, IDisposable
     {
         // Security configuration for MsQuic
-        private MsQuicSession _session;
+        private readonly MsQuicSession _session;
 
         // Pointer to the underlying listener
         // TODO replace all IntPtr with SafeHandles
@@ -25,10 +26,10 @@ internal sealed class MsQuicListener : QuicListenerProvider, IDisposable
         private GCHandle _handle;
 
         // Delegate that wraps the static function that will be called when receiving an event.
-        private ListenerCallbackDelegate? _listenerDelegate;
+        private static readonly ListenerCallbackDelegate s_listenerDelegate = new ListenerCallbackDelegate(NativeCallbackHandler);
 
         // Ssl listening options (ALPN, cert, etc)
-        private SslServerAuthenticationOptions _sslOptions;
+        private readonly SslServerAuthenticationOptions _sslOptions;
 
         private QuicListenerOptions _options;
         private volatile bool _disposed;
@@ -142,11 +143,10 @@ private unsafe void SetListenPort()
         {
             SOCKADDR_INET inetAddress = MsQuicParameterHelpers.GetINetParam(MsQuicApi.Api, _ptr, (uint)QUIC_PARAM_LEVEL.LISTENER, (uint)QUIC_PARAM_LISTENER.LOCAL_ADDRESS);
 
-            _listenEndPoint = MsQuicAddressHelpers.INetToIPEndPoint(inetAddress);
+            _listenEndPoint = MsQuicAddressHelpers.INetToIPEndPoint(ref inetAddress);
         }
 
-        internal unsafe uint ListenerCallbackHandler(
-            ref ListenerEvent evt)
+        internal unsafe uint ListenerCallbackHandler(ref ListenerEvent evt)
         {
             try
             {
@@ -154,10 +154,14 @@ internal unsafe uint ListenerCallbackHandler(
                 {
                     case QUIC_LISTENER_EVENT.NEW_CONNECTION:
                         {
-                            NewConnectionInfo connectionInfo = *(NewConnectionInfo*)evt.Data.NewConnection.Info;
-                            IPEndPoint localEndPoint = MsQuicAddressHelpers.INetToIPEndPoint(*(SOCKADDR_INET*)connectionInfo.LocalAddress);
-                            IPEndPoint remoteEndPoint = MsQuicAddressHelpers.INetToIPEndPoint(*(SOCKADDR_INET*)connectionInfo.RemoteAddress);
+                            ref NewConnectionInfo connectionInfo = ref *(NewConnectionInfo*)evt.Data.NewConnection.Info;
+
+                            IPEndPoint localEndPoint = MsQuicAddressHelpers.INetToIPEndPoint(ref *(SOCKADDR_INET*)connectionInfo.LocalAddress);
+                            IPEndPoint remoteEndPoint = MsQuicAddressHelpers.INetToIPEndPoint(ref *(SOCKADDR_INET*)connectionInfo.RemoteAddress);
+
                             MsQuicConnection msQuicConnection = new MsQuicConnection(localEndPoint, remoteEndPoint, evt.Data.NewConnection.Connection);
+                            msQuicConnection.SetNegotiatedAlpn(connectionInfo.NegotiatedAlpn, connectionInfo.NegotiatedAlpnLength);
+
                             _acceptConnectionQueue.Writer.TryWrite(msQuicConnection);
                         }
                         // Always pend the new connection to wait for the security config to be resolved
@@ -167,8 +171,15 @@ internal unsafe uint ListenerCallbackHandler(
                         return MsQuicStatusCodes.InternalError;
                 }
             }
-            catch (Exception)
+            catch (Exception ex)
             {
+                if (NetEventSource.Log.IsEnabled())
+                {
+                    NetEventSource.Error(this, $"Exception occurred during connection callback: {ex.Message}");
+                }
+
+                // TODO: trigger an exception on any outstanding async calls.
+
                 return MsQuicStatusCodes.InternalError;
             }
         }
@@ -191,11 +202,12 @@ internal static uint NativeCallbackHandler(
 
         internal void SetCallbackHandler()
         {
+            Debug.Assert(!_handle.IsAllocated);
             _handle = GCHandle.Alloc(this);
-            _listenerDelegate = new ListenerCallbackDelegate(NativeCallbackHandler);
+
             MsQuicApi.Api.SetCallbackHandlerDelegate(
                 _ptr,
-                _listenerDelegate,
+                s_listenerDelegate,
                 GCHandle.ToIntPtr(_handle));
         }
 
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicStream.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicStream.cs
index 6b8e9ce362d9cb..be0e4a8d034acd 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicStream.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Implementations/MsQuic/MsQuicStream.cs
@@ -23,7 +23,7 @@ internal sealed class MsQuicStream : QuicStreamProvider
         private GCHandle _handle;
 
         // Delegate that wraps the static function that will be called when receiving an event.
-        private StreamCallbackDelegate? _callback;
+        internal static readonly StreamCallbackDelegate s_streamDelegate = new StreamCallbackDelegate(NativeCallbackHandler);
 
         // Backing for StreamId
         private long _streamId = -1;
@@ -62,10 +62,10 @@ internal sealed class MsQuicStream : QuicStreamProvider
 
         private volatile bool _disposed;
 
-        private List<QuicBuffer> _receiveQuicBuffers = new List<QuicBuffer>();
+        private readonly List<QuicBuffer> _receiveQuicBuffers = new List<QuicBuffer>();
 
         // TODO consider using Interlocked.Exchange instead of a sync if we can avoid it.
-        private object _sync = new object();
+        private readonly object _sync = new object();
 
         // Creates a new MsQuicStream
         internal MsQuicStream(MsQuicConnection connection, QUIC_STREAM_OPEN_FLAG flags, IntPtr nativeObjPtr, bool inbound)
@@ -79,17 +79,19 @@ internal MsQuicStream(MsQuicConnection connection, QUIC_STREAM_OPEN_FLAG flags,
             _shutdownWriteResettableCompletionSource = new ResettableCompletionSource<uint>();
             SetCallbackHandler();
 
+            bool isBidirectional = !flags.HasFlag(QUIC_STREAM_OPEN_FLAG.UNIDIRECTIONAL);
+
             if (inbound)
             {
-                _started = true;
-                _canWrite = !flags.HasFlag(QUIC_STREAM_OPEN_FLAG.UNIDIRECTIONAL);
                 _canRead = true;
+                _canWrite = isBidirectional;
+                _started = true;
             }
             else
             {
+                _canRead = isBidirectional;
                 _canWrite = true;
-                _canRead = !flags.HasFlag(QUIC_STREAM_OPEN_FLAG.UNIDIRECTIONAL);
-                StartWrites();
+                StartLocalStream();
             }
         }
 
@@ -396,7 +398,7 @@ internal override Task FlushAsync(CancellationToken cancellationToken = default)
         {
             ThrowIfDisposed();
 
-            return default!;
+            return Task.CompletedTask;
         }
 
         public override ValueTask DisposeAsync()
@@ -715,7 +717,6 @@ private uint HandleEventSendComplete(ref StreamEvent evt)
             CleanupSendState();
 
             // TODO throw if a write was canceled.
-            uint errorCode = evt.Data.SendComplete.Canceled;
 
             bool shouldComplete = false;
             lock (_sync)
@@ -753,10 +754,9 @@ private void SetCallbackHandler()
         {
             _handle = GCHandle.Alloc(this);
 
-            _callback = new StreamCallbackDelegate(NativeCallbackHandler);
             MsQuicApi.Api.SetCallbackHandlerDelegate(
                 _ptr,
-                _callback,
+                s_streamDelegate,
                 GCHandle.ToIntPtr(_handle));
         }
 
@@ -921,7 +921,10 @@ private unsafe ValueTask SendReadOnlyMemoryListAsync(
             return _sendResettableCompletionSource.GetTypelessValueTask();
         }
 
-        private void StartWrites()
+        /// <summary>
+        /// Assigns a stream ID and begins process the stream.
+        /// </summary>
+        private void StartLocalStream()
         {
             Debug.Assert(!_started);
             uint status = MsQuicApi.Api.StreamStartDelegate(
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/Interop.MsQuic.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/Interop.MsQuic.cs
index ab68320c1f7715..b873b789f1d221 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/Interop.MsQuic.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/Interop.MsQuic.cs
@@ -9,7 +9,7 @@ internal static partial class Interop
 {
     internal static class MsQuic
     {
-        [DllImport(Libraries.MsQuic)]
-        internal static unsafe extern uint MsQuicOpen(int version, out MsQuicNativeMethods.NativeApi* registration);
+        [DllImport(Libraries.MsQuic, CallingConvention = CallingConvention.Cdecl)]
+        internal static unsafe extern uint MsQuicOpen(out MsQuicNativeMethods.NativeApi* registration);
     }
 }
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/MsQuicEnums.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/MsQuicEnums.cs
index 62f8fab346c62e..5fc281c8670d47 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/MsQuicEnums.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/MsQuicEnums.cs
@@ -3,19 +3,26 @@
 
 namespace System.Net.Quic.Implementations.MsQuic.Internal
 {
+    internal enum QUIC_EXECUTION_PROFILE : uint
+    {
+        QUIC_EXECUTION_PROFILE_LOW_LATENCY,         // Default
+        QUIC_EXECUTION_PROFILE_TYPE_MAX_THROUGHPUT,
+        QUIC_EXECUTION_PROFILE_TYPE_SCAVENGER,
+        QUIC_EXECUTION_PROFILE_TYPE_REAL_TIME
+    }
+
     /// <summary>
     /// Flags to pass when creating a security config.
     /// </summary>
     [Flags]
     internal enum QUIC_SEC_CONFIG_FLAG : uint
     {
-        NONE = 0,
         CERT_HASH = 0x00000001,
         CERT_HASH_STORE = 0x00000002,
         CERT_CONTEXT = 0x00000004,
         CERT_FILE = 0x00000008,
         ENABL_OCSP = 0x00000010,
-        CERT_NULL = 0xF0000000,
+        CERT_NULL = 0xF0000000 // TODO: only valid for stub TLS.
     }
 
     [Flags]
@@ -67,22 +74,30 @@ internal enum QUIC_SEND_FLAG : uint
         NONE = 0,
         ALLOW_0_RTT = 0x00000001,
         FIN = 0x00000002,
+        DGRAM_PRIORITY = 0x00000004
     }
 
     internal enum QUIC_PARAM_LEVEL : uint
     {
-        REGISTRATION = 0,
-        SESSION = 1,
-        LISTENER = 2,
-        CONNECTION = 3,
-        TLS = 4,
-        STREAM = 5,
+        GLOBAL,
+        REGISTRATION,
+        SESSION,
+        LISTENER,
+        CONNECTION,
+        TLS,
+        STREAM
     }
 
-    internal enum QUIC_PARAM_REGISTRATION : uint
+    internal enum QUIC_PARAM_GLOBAL : uint
     {
         RETRY_MEMORY_PERCENT = 0,
-        CID_PREFIX = 1
+        SUPPORTED_VERSIONS = 1,
+        LOAD_BALANCING_MODE = 2,
+    }
+
+    internal enum QUIC_PARAM_REGISTRATION : uint
+    {
+        CID_PREFIX = 0
     }
 
     internal enum QUIC_PARAM_SESSION : uint
@@ -92,7 +107,10 @@ internal enum QUIC_PARAM_SESSION : uint
         PEER_UNIDI_STREAM_COUNT = 2,
         IDLE_TIMEOUT = 3,
         DISCONNECT_TIMEOUT = 4,
-        MAX_BYTES_PER_KEY = 5
+        MAX_BYTES_PER_KEY = 5,
+        MIGRATION_ENABLED = 6,
+        DATAGRAM_RECEIVE_ENABLED = 7,
+        SERVER_RESUMPTION_LEVEL = 8
     }
 
     internal enum QUIC_PARAM_LISTENER : uint
@@ -122,7 +140,11 @@ internal enum QUIC_PARAM_CONN : uint
         SEND_PACING = 16,
         SHARE_UDP_BINDING = 17,
         IDEAL_PROCESSOR = 18,
-        MAX_STREAM_IDS = 19
+        MAX_STREAM_IDS = 19,
+        STREAM_SCHEDULING_SCHEME = 20,
+        DATAGRAM_RECEIVE_ENABLED = 21,
+        DATAGRAM_SEND_ENABLED = 22,
+        DISABLE_1RTT_ENCRYPTION = 23
     }
 
     internal enum QUIC_PARAM_STREAM : uint
@@ -149,6 +171,11 @@ internal enum QUIC_CONNECTION_EVENT : uint
         STREAMS_AVAILABLE = 7,
         PEER_NEEDS_STREAMS = 8,
         IDEAL_PROCESSOR_CHANGED = 9,
+        DATAGRAM_STATE_CHANGED = 10,
+        DATAGRAM_RECEIVED = 11,
+        DATAGRAM_SEND_STATE_CHANGED = 12,
+        RESUMED = 13,
+        RESUMPTION_TICKET_RECEIVED = 14
     }
 
     internal enum QUIC_STREAM_EVENT : uint
diff --git a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/MsQuicNativeMethods.cs b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/MsQuicNativeMethods.cs
index 644787ea232b35..49903de27eceff 100644
--- a/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/MsQuicNativeMethods.cs
+++ b/src/libraries/Common/src/System/Net/Http/aspnetcore/Quic/Interop/MsQuicNativeMethods.cs
@@ -16,8 +16,6 @@ internal static unsafe class MsQuicNativeMethods
         [StructLayout(LayoutKind.Sequential)]
         internal struct NativeApi
         {
-            internal uint Version;
-
             internal IntPtr SetContext;
             internal IntPtr GetContext;
             internal IntPtr SetCallbackHandler;
@@ -44,6 +42,7 @@ internal struct NativeApi
             internal IntPtr ConnectionClose;
             internal IntPtr ConnectionShutdown;
             internal IntPtr ConnectionStart;
+            internal IntPtr ConnectionSendResumptionTicket;
 
             internal IntPtr StreamOpen;
             internal IntPtr StreamClose;
@@ -52,20 +51,26 @@ internal struct NativeApi
             internal IntPtr StreamSend;
             internal IntPtr StreamReceiveComplete;
             internal IntPtr StreamReceiveSetEnabled;
+
+            internal IntPtr DatagramSend;
         }
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint SetContextDelegate(
             IntPtr handle,
             IntPtr context);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate IntPtr GetContextDelegate(
             IntPtr handle);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate void SetCallbackHandlerDelegate(
             IntPtr handle,
             Delegate del,
             IntPtr context);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint SetParamDelegate(
             IntPtr handle,
             uint level,
@@ -73,6 +78,7 @@ internal delegate uint SetParamDelegate(
             uint bufferLength,
             byte* buffer);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint GetParamDelegate(
             IntPtr handle,
             uint level,
@@ -80,36 +86,53 @@ internal delegate uint GetParamDelegate(
             uint* bufferLength,
             byte* buffer);
 
-        internal delegate uint RegistrationOpenDelegate(byte[] appName, out IntPtr registrationContext);
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+        internal delegate uint RegistrationOpenDelegate(ref RegistrationConfig config, out IntPtr registrationContext);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate void RegistrationCloseDelegate(IntPtr registrationContext);
 
+        [StructLayout(LayoutKind.Sequential)]
+        internal struct RegistrationConfig
+        {
+            [MarshalAs(UnmanagedType.LPUTF8Str)]
+            internal string AppName;
+            internal QUIC_EXECUTION_PROFILE ExecutionProfile;
+        }
+
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate void SecConfigCreateCompleteDelegate(IntPtr context, uint status, IntPtr securityConfig);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint SecConfigCreateDelegate(
             IntPtr registrationContext,
             uint flags,
             IntPtr certificate,
-            [MarshalAs(UnmanagedType.LPStr)]string? principal,
+            [MarshalAs(UnmanagedType.LPUTF8Str)]string? principal,
             IntPtr context,
             SecConfigCreateCompleteDelegate completionHandler);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate void SecConfigDeleteDelegate(
             IntPtr securityConfig);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint SessionOpenDelegate(
             IntPtr registrationContext,
-            byte[] utf8String,
+            QuicBuffer *alpnBuffers,
+            uint alpnBufferCount,
             IntPtr context,
             ref IntPtr session);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate void SessionCloseDelegate(
             IntPtr session);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate void SessionShutdownDelegate(
             IntPtr session,
             uint flags,
-            ushort errorCode);
+            ulong errorCode);
 
         [StructLayout(LayoutKind.Sequential)]
         internal struct ListenerEvent
@@ -139,49 +162,58 @@ internal struct NewConnectionInfo
             internal uint QuicVersion;
             internal IntPtr LocalAddress;
             internal IntPtr RemoteAddress;
-            internal ushort CryptoBufferLength;
+            internal uint CryptoBufferLength;
             internal ushort AlpnListLength;
             internal ushort ServerNameLength;
+            internal byte NegotiatedAlpnLength;
             internal IntPtr CryptoBuffer;
-            internal IntPtr AlpnList;
+            internal IntPtr ClientAlpnList;
+            internal IntPtr NegotiatedAlpn;
             internal IntPtr ServerName;
         }
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint ListenerCallbackDelegate(
             IntPtr listener,
             IntPtr context,
             ref ListenerEvent evt);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint ListenerOpenDelegate(
            IntPtr session,
            ListenerCallbackDelegate handler,
            IntPtr context,
            out IntPtr listener);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint ListenerCloseDelegate(
             IntPtr listener);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint ListenerStartDelegate(
             IntPtr listener,
             ref SOCKADDR_INET localAddress);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint ListenerStopDelegate(
             IntPtr listener);
 
         [StructLayout(LayoutKind.Sequential)]
         internal struct ConnectionEventDataConnected
         {
-            internal bool EarlyDataAccepted;
+            internal bool SessionResumed;
+            internal byte NegotiatedAlpnLength;
+            internal IntPtr NegotiatedAlpn;
         }
 
         [StructLayout(LayoutKind.Sequential)]
-        internal struct ConnectionEventDataShutdownBegin
+        internal struct ConnectionEventDataShutdownInitiatedByTransport
         {
             internal uint Status;
         }
 
         [StructLayout(LayoutKind.Sequential)]
-        internal struct ConnectionEventDataShutdownBeginPeer
+        internal struct ConnectionEventDataShutdownInitiatedByPeer
         {
             internal long ErrorCode;
         }
@@ -205,7 +237,7 @@ internal struct ConnectionEventDataPeerAddrChanged
         }
 
         [StructLayout(LayoutKind.Sequential)]
-        internal struct ConnectionEventDataNewStream
+        internal struct ConnectionEventDataStreamStarted
         {
             internal IntPtr Stream;
             internal QUIC_STREAM_OPEN_FLAG Flags;
@@ -218,12 +250,6 @@ internal struct ConnectionEventDataStreamsAvailable
             internal ushort UniDirectionalCount;
         }
 
-        [StructLayout(LayoutKind.Sequential)]
-        internal struct ConnectionEventDataIdealSendBuffer
-        {
-            internal ulong NumBytes;
-        }
-
         [StructLayout(LayoutKind.Explicit)]
         internal struct ConnectionEventDataUnion
         {
@@ -231,10 +257,10 @@ internal struct ConnectionEventDataUnion
             internal ConnectionEventDataConnected Connected;
 
             [FieldOffset(0)]
-            internal ConnectionEventDataShutdownBegin ShutdownBegin;
+            internal ConnectionEventDataShutdownInitiatedByTransport ShutdownInitiatedByTransport;
 
             [FieldOffset(0)]
-            internal ConnectionEventDataShutdownBeginPeer ShutdownBeginPeer;
+            internal ConnectionEventDataShutdownInitiatedByPeer ShutdownInitiatedByPeer;
 
             [FieldOffset(0)]
             internal ConnectionEventDataShutdownComplete ShutdownComplete;
@@ -246,13 +272,10 @@ internal struct ConnectionEventDataUnion
             internal ConnectionEventDataPeerAddrChanged PeerAddrChanged;
 
             [FieldOffset(0)]
-            internal ConnectionEventDataNewStream NewStream;
+            internal ConnectionEventDataStreamStarted StreamStarted;
 
             [FieldOffset(0)]
             internal ConnectionEventDataStreamsAvailable StreamsAvailable;
-
-            [FieldOffset(0)]
-            internal ConnectionEventDataIdealSendBuffer IdealSendBuffer;
         }
 
         [StructLayout(LayoutKind.Sequential)]
@@ -261,37 +284,42 @@ internal struct ConnectionEvent
             internal QUIC_CONNECTION_EVENT Type;
             internal ConnectionEventDataUnion Data;
 
-            internal bool EarlyDataAccepted => Data.Connected.EarlyDataAccepted;
-            internal ulong NumBytes => Data.IdealSendBuffer.NumBytes;
-            internal uint ShutdownBeginStatus => Data.ShutdownBegin.Status;
-            internal long ShutdownBeginPeerStatus => Data.ShutdownBeginPeer.ErrorCode;
+            internal bool EarlyDataAccepted => Data.Connected.SessionResumed;
+            //internal ulong NumBytes => Data.IdealSendBuffer.NumBytes;
+            internal uint ShutdownBeginStatus => Data.ShutdownInitiatedByTransport.Status;
+            internal long ShutdownBeginPeerStatus => Data.ShutdownInitiatedByPeer.ErrorCode;
             internal bool ShutdownTimedOut => Data.ShutdownComplete.TimedOut;
             internal ushort BiDirectionalCount => Data.StreamsAvailable.BiDirectionalCount;
             internal ushort UniDirectionalCount => Data.StreamsAvailable.UniDirectionalCount;
-            internal QUIC_STREAM_OPEN_FLAG StreamFlags => Data.NewStream.Flags;
+            internal QUIC_STREAM_OPEN_FLAG StreamFlags => Data.StreamStarted.Flags;
         }
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint ConnectionCallbackDelegate(
             IntPtr connection,
             IntPtr context,
             ref ConnectionEvent connectionEvent);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint ConnectionOpenDelegate(
             IntPtr session,
             ConnectionCallbackDelegate handler,
             IntPtr context,
             out IntPtr connection);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint ConnectionCloseDelegate(
             IntPtr connection);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint ConnectionStartDelegate(
             IntPtr connection,
             ushort family,
-            [MarshalAs(UnmanagedType.LPStr)]
+            [MarshalAs(UnmanagedType.LPUTF8Str)]
             string serverName,
             ushort serverPort);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint ConnectionShutdownDelegate(
             IntPtr connection,
             uint flags,
@@ -304,21 +332,14 @@ internal struct StreamEventDataRecv
             internal ulong TotalBufferLength;
             internal QuicBuffer* Buffers;
             internal uint BufferCount;
-            internal uint Flags;
+            internal QUIC_RECEIVE_FLAG Flags;
         }
 
-        [StructLayout(LayoutKind.Explicit)]
+        [StructLayout(LayoutKind.Sequential)]
         internal struct StreamEventDataSendComplete
         {
-            [FieldOffset(0)]
-            internal byte Canceled;
-            [FieldOffset(1)]
+            internal bool Canceled;
             internal IntPtr ClientContext;
-
-            internal bool IsCanceled()
-            {
-                return Canceled != 0;
-            }
         }
 
         [StructLayout(LayoutKind.Sequential)]
@@ -432,11 +453,13 @@ internal struct SOCKADDR_INET
             internal ushort si_family;
         }
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint StreamCallbackDelegate(
             IntPtr stream,
             IntPtr context,
             ref StreamEvent streamEvent);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint StreamOpenDelegate(
             IntPtr connection,
             uint flags,
@@ -444,18 +467,22 @@ internal delegate uint StreamOpenDelegate(
             IntPtr context,
             out IntPtr stream);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint StreamStartDelegate(
             IntPtr stream,
             uint flags);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint StreamCloseDelegate(
             IntPtr stream);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint StreamShutdownDelegate(
             IntPtr stream,
             uint flags,
             long errorCode);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint StreamSendDelegate(
             IntPtr stream,
             QuicBuffer* buffers,
@@ -463,12 +490,15 @@ internal delegate uint StreamSendDelegate(
             uint flags,
             IntPtr clientSendContext);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint StreamReceiveCompleteDelegate(
             IntPtr stream,
             ulong bufferLength);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         internal delegate uint StreamReceiveSetEnabledDelegate(
             IntPtr stream,
+            [MarshalAs(UnmanagedType.U1)]
             bool enabled);
 
         [StructLayout(LayoutKind.Sequential)]
diff --git a/src/libraries/Common/src/System/Net/HttpKnownHeaderNames.TryGetHeaderName.cs b/src/libraries/Common/src/System/Net/HttpKnownHeaderNames.TryGetHeaderName.cs
index 05871eae320fdc..bd8a01a8e1e1a1 100644
--- a/src/libraries/Common/src/System/Net/HttpKnownHeaderNames.TryGetHeaderName.cs
+++ b/src/libraries/Common/src/System/Net/HttpKnownHeaderNames.TryGetHeaderName.cs
@@ -22,8 +22,8 @@ public static bool TryGetHeaderName(char[] array, int startIndex, int length, [N
 
             return TryGetHeaderName(
                 array, startIndex, length,
-                (arr, index) => arr[index],
-                (known, arr, start, len) => known.AsSpan().SequenceEqual(arr.AsSpan(start, len)),
+                static (arr, index) => arr[index],
+                static (known, arr, start, len) => known.AsSpan().SequenceEqual(arr.AsSpan(start, len)),
                 out name);
         }
 
@@ -46,8 +46,8 @@ public static unsafe bool TryGetHeaderName(IntPtr buffer, int length, out string
 
             return TryGetHeaderName(
                 buffer, startIndex, length,
-                (buf, index) => (char)((byte*)buf)[index],
-                (known, buf, start, len) => EqualsOrdinal(known, buf, len),
+                static (buf, index) => (char)((byte*)buf)[index],
+                static (known, buf, start, len) => EqualsOrdinal(known, buf, len),
                 out name);
         }
 
diff --git a/src/libraries/Common/src/System/Net/NetworkErrorHelper.cs b/src/libraries/Common/src/System/Net/NetworkErrorHelper.cs
new file mode 100644
index 00000000000000..e305163ed8fe1d
--- /dev/null
+++ b/src/libraries/Common/src/System/Net/NetworkErrorHelper.cs
@@ -0,0 +1,26 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Net.Sockets;
+
+namespace System.Net
+{
+    internal static class NetworkErrorHelper
+    {
+        internal static NetworkException MapSocketException(SocketException socketException)
+        {
+            NetworkError error = socketException.SocketErrorCode switch
+            {
+                SocketError.AddressAlreadyInUse => NetworkError.EndPointInUse,
+                SocketError.HostNotFound => NetworkError.HostNotFound,
+                SocketError.ConnectionRefused => NetworkError.ConnectionRefused,
+                SocketError.OperationAborted => NetworkError.OperationAborted,
+                SocketError.ConnectionAborted => NetworkError.ConnectionAborted,
+                SocketError.ConnectionReset => NetworkError.ConnectionReset,
+                _ => NetworkError.Unknown
+            };
+
+            return new NetworkException(error, socketException);
+        }
+    }
+}
diff --git a/src/libraries/Common/src/System/Net/NetworkInformation/HostInformationPal.Browser.cs b/src/libraries/Common/src/System/Net/NetworkInformation/HostInformationPal.Browser.cs
new file mode 100644
index 00000000000000..01c30fda1644ad
--- /dev/null
+++ b/src/libraries/Common/src/System/Net/NetworkInformation/HostInformationPal.Browser.cs
@@ -0,0 +1,18 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Net.NetworkInformation
+{
+    internal static class HostInformationPal
+    {
+        public static string GetHostName()
+        {
+            return Environment.MachineName;
+        }
+
+        public static string GetDomainName()
+        {
+            return Environment.UserDomainName;
+        }
+    }
+}
diff --git a/src/libraries/Common/src/System/Net/NetworkInformation/InterfaceInfoPal.Browser.cs b/src/libraries/Common/src/System/Net/NetworkInformation/InterfaceInfoPal.Browser.cs
new file mode 100644
index 00000000000000..d5d50a2aa33670
--- /dev/null
+++ b/src/libraries/Common/src/System/Net/NetworkInformation/InterfaceInfoPal.Browser.cs
@@ -0,0 +1,14 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Net.NetworkInformation
+{
+    internal static class InterfaceInfoPal
+    {
+        public static uint InterfaceNameToIndex(string interfaceName)
+        {
+            // zero means "unknown"
+            return 0;
+        }
+    }
+}
diff --git a/src/libraries/Common/src/System/Net/WebSockets/ManagedWebSocket.cs b/src/libraries/Common/src/System/Net/WebSockets/ManagedWebSocket.cs
index 77e89ea60a9749..38a83c25d151ca 100644
--- a/src/libraries/Common/src/System/Net/WebSockets/ManagedWebSocket.cs
+++ b/src/libraries/Common/src/System/Net/WebSockets/ManagedWebSocket.cs
@@ -182,7 +182,7 @@ private ManagedWebSocket(Stream stream, bool isServer, string? subprotocol, Time
             // Set up the abort source so that if it's triggered, we transition the instance appropriately.
             // There's no need to store the resulting CancellationTokenRegistration, as this instance owns
             // the CancellationTokenSource, and the lifetime of that CTS matches the lifetime of the registration.
-            _abortSource.Token.UnsafeRegister(s =>
+            _abortSource.Token.UnsafeRegister(static s =>
             {
                 var thisRef = (ManagedWebSocket)s!;
 
@@ -203,7 +203,7 @@ private ManagedWebSocket(Stream stream, bool isServer, string? subprotocol, Time
             // that could keep the web socket rooted in erroneous cases.
             if (keepAliveInterval > TimeSpan.Zero)
             {
-                _keepAliveTimer = new Timer(s =>
+                _keepAliveTimer = new Timer(static s =>
                 {
                     var wr = (WeakReference<ManagedWebSocket>)s!;
                     if (wr.TryGetTarget(out ManagedWebSocket? thisRef))
@@ -448,7 +448,7 @@ private async ValueTask SendFrameFallbackAsync(MessageOpcode opcode, bool endOfM
             try
             {
                 int sendBytes = WriteFrameToSendBuffer(opcode, endOfMessage, payloadBuffer.Span);
-                using (cancellationToken.Register(s => ((ManagedWebSocket)s!).Abort(), this))
+                using (cancellationToken.Register(static s => ((ManagedWebSocket)s!).Abort(), this))
                 {
                     await _stream.WriteAsync(new ReadOnlyMemory<byte>(_sendBuffer, 0, sendBytes), cancellationToken).ConfigureAwait(false);
                 }
@@ -523,7 +523,7 @@ private void SendKeepAliveFrameAsync()
                 else
                 {
                     // "Observe" any exception, ignoring it to prevent the unobserved exception event from being raised.
-                    t.AsTask().ContinueWith(p => { _ = p.Exception; },
+                    t.AsTask().ContinueWith(static p => { _ = p.Exception; },
                         CancellationToken.None,
                         TaskContinuationOptions.OnlyOnFaulted | TaskContinuationOptions.ExecuteSynchronously,
                         TaskScheduler.Default);
@@ -633,7 +633,7 @@ private async ValueTask<TWebSocketReceiveResult> ReceiveAsyncPrivate<TWebSocketR
             // those to be much less frequent (e.g. we should only get one close per websocket), and thus we can afford to pay
             // a bit more for readability and maintainability.
 
-            CancellationTokenRegistration registration = cancellationToken.Register(s => ((ManagedWebSocket)s!).Abort(), this);
+            CancellationTokenRegistration registration = cancellationToken.Register(static s => ((ManagedWebSocket)s!).Abort(), this);
             try
             {
                 while (true) // in case we get control frames that should be ignored from the user's perspective
@@ -868,7 +868,7 @@ private async ValueTask WaitForServerToCloseConnectionAsync(CancellationToken ca
             {
                 const int WaitForCloseTimeoutMs = 1_000; // arbitrary amount of time to give the server (same as netfx)
                 using (var finalCts = new CancellationTokenSource(WaitForCloseTimeoutMs))
-                using (finalCts.Token.Register(s => ((ManagedWebSocket)s!).Abort(), this))
+                using (finalCts.Token.Register(static s => ((ManagedWebSocket)s!).Abort(), this))
                 {
                     try
                     {
@@ -1138,7 +1138,7 @@ private async Task CloseAsyncPrivate(WebSocketCloseStatus closeStatus, string? s
                         // If this is an existing receive, and if we have a cancelable token, we need to register with that
                         // token while we wait, since it may not be the same one that was given to the receive initially.
                         Debug.Assert(receiveTask != null);
-                        using (usingExistingReceive ? cancellationToken.Register(s => ((ManagedWebSocket)s!).Abort(), this) : default)
+                        using (usingExistingReceive ? cancellationToken.Register(static s => ((ManagedWebSocket)s!).Abort(), this) : default)
                         {
                             await receiveTask.ConfigureAwait(false);
                         }
diff --git a/src/libraries/Common/src/System/Obsoletions.cs b/src/libraries/Common/src/System/Obsoletions.cs
index a7c5582f7bd8d5..6b08f78ce49180 100644
--- a/src/libraries/Common/src/System/Obsoletions.cs
+++ b/src/libraries/Common/src/System/Obsoletions.cs
@@ -39,5 +39,8 @@ internal static class Obsoletions
 
         internal const string BinaryFormatterMessage = "BinaryFormatter serialization is obsolete and should not be used. See https://aka.ms/binaryformatter for more information.";
         internal const string BinaryFormatterDiagId = "SYSLIB0011";
+
+        internal const string CodeBaseMessage = "Use Location instead.";
+        internal const string CodeBaseDiagId = "SYSLIB0012";
     }
 }
diff --git a/src/libraries/Common/src/System/Runtime/InteropServices/WindowsRuntime/IRestrictedErrorInfo.cs b/src/libraries/Common/src/System/Runtime/InteropServices/WindowsRuntime/IRestrictedErrorInfo.cs
deleted file mode 100644
index 1cf4566c761647..00000000000000
--- a/src/libraries/Common/src/System/Runtime/InteropServices/WindowsRuntime/IRestrictedErrorInfo.cs
+++ /dev/null
@@ -1,20 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-
-namespace System.Runtime.InteropServices.WindowsRuntime
-{
-    [ComImport]
-    [Guid("82BA7092-4C88-427D-A7BC-16DD93FEB67E")]
-    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
-    internal interface IRestrictedErrorInfo
-    {
-        void GetErrorDetails([MarshalAs(UnmanagedType.BStr)] out string description,
-                             out int error,
-                             [MarshalAs(UnmanagedType.BStr)] out string restrictedDescription,
-                             [MarshalAs(UnmanagedType.BStr)] out string capabilitySid);
-
-        void GetReference([MarshalAs(UnmanagedType.BStr)] out string reference);
-    }
-}
diff --git a/src/libraries/Common/src/System/Security/Cryptography/Asn1Reader/AsnValueReader.cs b/src/libraries/Common/src/System/Security/Cryptography/Asn1Reader/AsnValueReader.cs
index 06ac95d7f733e6..6e22b91fb36870 100644
--- a/src/libraries/Common/src/System/Security/Cryptography/Asn1Reader/AsnValueReader.cs
+++ b/src/libraries/Common/src/System/Security/Cryptography/Asn1Reader/AsnValueReader.cs
@@ -34,7 +34,7 @@ internal Asn1Tag PeekTag()
             return Asn1Tag.Decode(_span, out _);
         }
 
-        public ReadOnlySpan<byte> PeekEncodedValue()
+        internal ReadOnlySpan<byte> PeekEncodedValue()
         {
             AsnDecoder.ReadEncodedValue(_span, _ruleSet, out _, out _, out int consumed);
             return _span.Slice(0, consumed);
@@ -183,14 +183,14 @@ internal DateTimeOffset ReadUtcTime(Asn1Tag? expectedTag = default)
             return ret;
         }
 
-        public DateTimeOffset ReadGeneralizedTime(Asn1Tag? expectedTag = default)
+        internal DateTimeOffset ReadGeneralizedTime(Asn1Tag? expectedTag = default)
         {
             DateTimeOffset ret = AsnDecoder.ReadGeneralizedTime(_span, _ruleSet, out int consumed, expectedTag);
             _span = _span.Slice(consumed);
             return ret;
         }
 
-        public string ReadCharacterString(UniversalTagNumber encodingType, Asn1Tag? expectedTag = default)
+        internal string ReadCharacterString(UniversalTagNumber encodingType, Asn1Tag? expectedTag = default)
         {
             string ret = AsnDecoder.ReadCharacterString(_span, _ruleSet, encodingType, out int consumed, expectedTag);
             _span = _span.Slice(consumed);
diff --git a/src/libraries/Common/src/System/Security/Cryptography/DSACng.ImportExport.cs b/src/libraries/Common/src/System/Security/Cryptography/DSACng.ImportExport.cs
index 57e6261266137c..61ec4f336c6063 100644
--- a/src/libraries/Common/src/System/Security/Cryptography/DSACng.ImportExport.cs
+++ b/src/libraries/Common/src/System/Security/Cryptography/DSACng.ImportExport.cs
@@ -3,6 +3,7 @@
 
 #nullable enable
 using Internal.Cryptography;
+using System.Buffers.Binary;
 using System.Diagnostics;
 
 using static Interop.BCrypt;
@@ -359,7 +360,7 @@ public override DSAParameters ExportParameters(bool includePrivateParameters)
                             offset = sizeof(KeyBlobMagicNumber) + sizeof(int); // skip Magic and cbKey
 
                             // Read out a (V1) BCRYPT_DSA_KEY_BLOB structure.
-                            dsaParams.Counter = FromBigEndian(Interop.BCrypt.Consume(dsaBlob, ref offset, 4));
+                            dsaParams.Counter = BinaryPrimitives.ReadInt32BigEndian(Interop.BCrypt.Consume(dsaBlob, ref offset, 4));
                             dsaParams.Seed = Interop.BCrypt.Consume(dsaBlob, ref offset, Sha1HashOutputSize);
                             dsaParams.Q = Interop.BCrypt.Consume(dsaBlob, ref offset, Sha1HashOutputSize);
 
@@ -393,7 +394,7 @@ public override DSAParameters ExportParameters(bool includePrivateParameters)
                             offset = sizeof(BCRYPT_DSA_KEY_BLOB_V2) - 4; //skip to Count[4]
 
                             // Read out a BCRYPT_DSA_KEY_BLOB_V2 structure.
-                            dsaParams.Counter = FromBigEndian(Interop.BCrypt.Consume(dsaBlob, ref offset, 4));
+                            dsaParams.Counter = BinaryPrimitives.ReadInt32BigEndian(Interop.BCrypt.Consume(dsaBlob, ref offset, 4));
 
                             Debug.Assert(offset == sizeof(BCRYPT_DSA_KEY_BLOB_V2), $"Expected offset = sizeof(BCRYPT_DSA_KEY_BLOB_V2), got {offset} != {sizeof(BCRYPT_DSA_KEY_BLOB_V2)}");
 
@@ -422,11 +423,6 @@ public override DSAParameters ExportParameters(bool includePrivateParameters)
                 }
             }
 
-            private static int FromBigEndian(byte[] b)
-            {
-                return (b[0] << 24) | (b[1] << 16) | (b[2] << 8) | b[3];
-            }
-
             /// <summary>
             ///     This function checks the magic value in the key blob header
             /// </summary>
diff --git a/src/libraries/Common/src/System/Security/Cryptography/PasswordBasedEncryption.cs b/src/libraries/Common/src/System/Security/Cryptography/PasswordBasedEncryption.cs
index aad2de80b86fc3..07459e85f6f4bb 100644
--- a/src/libraries/Common/src/System/Security/Cryptography/PasswordBasedEncryption.cs
+++ b/src/libraries/Common/src/System/Security/Cryptography/PasswordBasedEncryption.cs
@@ -863,7 +863,7 @@ private static unsafe int Pkcs12PbeDecrypt(
                 algorithmIdentifier.Parameters.Value,
                 AsnEncodingRules.BER);
 
-            int iterationCount = NormalizeIterationCount(pbeParameters.IterationCount);
+            int iterationCount = NormalizeIterationCount(pbeParameters.IterationCount, IterationLimit);
             Span<byte> iv = stackalloc byte[cipher.BlockSize / 8];
             Span<byte> key = stackalloc byte[cipher.KeySize / 8];
             ReadOnlySpan<byte> saltSpan = pbeParameters.Salt.Span;
@@ -1070,19 +1070,9 @@ internal static void WritePbeAlgorithmIdentifier(
             writer.PopSequence();
         }
 
-        internal static int NormalizeIterationCount(uint iterationCount)
-        {
-            if (iterationCount == 0 || iterationCount > IterationLimit)
-            {
-                throw new CryptographicException(SR.Argument_InvalidValue);
-            }
-
-            return (int)iterationCount;
-        }
-
-        internal static int NormalizeIterationCount(int iterationCount)
+        internal static int NormalizeIterationCount(int iterationCount, int? iterationLimit = null)
         {
-            if (iterationCount <= 0 || iterationCount > IterationLimit)
+            if (iterationCount <= 0 || (iterationLimit.HasValue && iterationCount > iterationLimit.Value))
             {
                 throw new CryptographicException(SR.Argument_InvalidValue);
             }
diff --git a/src/libraries/Common/src/System/Text/StringBuilderCache.cs b/src/libraries/Common/src/System/Text/StringBuilderCache.cs
index 5e0ca8c6bfb742..b6041ac11e56dc 100644
--- a/src/libraries/Common/src/System/Text/StringBuilderCache.cs
+++ b/src/libraries/Common/src/System/Text/StringBuilderCache.cs
@@ -8,7 +8,7 @@ namespace System.Text
     internal static class StringBuilderCache
     {
         // The value 360 was chosen in discussion with performance experts as a compromise between using
-        // as litle memory per thread as possible and still covering a large part of short-lived
+        // as little memory per thread as possible and still covering a large part of short-lived
         // StringBuilder creations on the startup path of VS designers.
         internal const int MaxBuilderSize = 360;
         private const int DefaultCapacity = 16; // == StringBuilder.DefaultCapacity
diff --git a/src/libraries/Common/src/System/Threading/Tasks/RendezvousAwaitable.cs b/src/libraries/Common/src/System/Threading/Tasks/RendezvousAwaitable.cs
index 5c8cbc55cbeacc..b6d1b461380fd0 100644
--- a/src/libraries/Common/src/System/Threading/Tasks/RendezvousAwaitable.cs
+++ b/src/libraries/Common/src/System/Threading/Tasks/RendezvousAwaitable.cs
@@ -14,7 +14,7 @@ namespace System.Threading.Tasks
     internal class RendezvousAwaitable<TResult> : ICriticalNotifyCompletion
     {
         /// <summary>Sentinel object indicating that the operation has completed prior to OnCompleted being called.</summary>
-        private static readonly Action s_completionSentinel = () => Debug.Fail("Completion sentinel should never be invoked");
+        private static readonly Action s_completionSentinel = static () => Debug.Fail("Completion sentinel should never be invoked");
 
         /// <summary>
         /// The continuation to invoke when the operation completes, or <see cref="s_completionSentinel"/> if the operation
@@ -24,7 +24,7 @@ internal class RendezvousAwaitable<TResult> : ICriticalNotifyCompletion
         /// <summary>The exception representing the failed async operation, if it failed.</summary>
         private ExceptionDispatchInfo? _error;
         /// <summary>The result of the async operation, if it succeeded.</summary>
-        [AllowNull] private TResult _result = default;
+        private TResult? _result;
 #if DEBUG
         private bool _resultSet;
 #endif
@@ -64,7 +64,7 @@ public TResult GetResult()
             }
 
             // The operation completed successfully.  Clear and return the result.
-            TResult result = _result;
+            TResult result = _result!;
             _result = default(TResult);
 #if DEBUG
             _resultSet = false;
diff --git a/src/libraries/Common/src/System/Threading/Tasks/TaskCompletionSourceWithCancellation.cs b/src/libraries/Common/src/System/Threading/Tasks/TaskCompletionSourceWithCancellation.cs
index 56cea38604288d..4c1e370f6270f5 100644
--- a/src/libraries/Common/src/System/Threading/Tasks/TaskCompletionSourceWithCancellation.cs
+++ b/src/libraries/Common/src/System/Threading/Tasks/TaskCompletionSourceWithCancellation.cs
@@ -25,7 +25,7 @@ private void OnCancellation()
         public async ValueTask<T> WaitWithCancellationAsync(CancellationToken cancellationToken)
         {
             _cancellationToken = cancellationToken;
-            using (cancellationToken.UnsafeRegister(s => ((TaskCompletionSourceWithCancellation<T>)s!).OnCancellation(), this))
+            using (cancellationToken.UnsafeRegister(static s => ((TaskCompletionSourceWithCancellation<T>)s!).OnCancellation(), this))
             {
                 return await Task.ConfigureAwait(false);
             }
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/CultureReplacer.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/CultureReplacer.cs
deleted file mode 100644
index 85122f66f43ebc..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/CultureReplacer.cs
+++ /dev/null
@@ -1,79 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Globalization;
-using System.Threading;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class CultureReplacer : IDisposable
-    {
-        private const string _defaultCultureName = "en-GB";
-        private const string _defaultUICultureName = "en-US";
-        private static readonly CultureInfo _defaultCulture = new CultureInfo(_defaultCultureName);
-        private readonly CultureInfo _originalCulture;
-        private readonly CultureInfo _originalUICulture;
-        private readonly long _threadId;
-
-        // Culture => Formatting of dates/times/money/etc, defaults to en-GB because en-US is the same as InvariantCulture
-        // We want to be able to find issues where the InvariantCulture is used, but a specific culture should be.
-        //
-        // UICulture => Language
-        public CultureReplacer(string culture = _defaultCultureName, string uiCulture = _defaultUICultureName)
-            : this(new CultureInfo(culture), new CultureInfo(uiCulture))
-        {
-        }
-
-        public CultureReplacer(CultureInfo culture, CultureInfo uiCulture)
-        {
-            _originalCulture = CultureInfo.CurrentCulture;
-            _originalUICulture = CultureInfo.CurrentUICulture;
-            _threadId = Thread.CurrentThread.ManagedThreadId;
-            CultureInfo.CurrentCulture = culture;
-            CultureInfo.CurrentUICulture = uiCulture;
-        }
-
-        /// <summary>
-        /// The name of the culture that is used as the default value for CultureInfo.DefaultThreadCurrentCulture when CultureReplacer is used.
-        /// </summary>
-        public static string DefaultCultureName
-        {
-            get { return _defaultCultureName; }
-        }
-
-        /// <summary>
-        /// The name of the culture that is used as the default value for [Thread.CurrentThread(NET45)/CultureInfo(K10)].CurrentUICulture when CultureReplacer is used.
-        /// </summary>
-        public static string DefaultUICultureName
-        {
-            get { return _defaultUICultureName; }
-        }
-
-        /// <summary>
-        /// The culture that is used as the default value for [Thread.CurrentThread(NET45)/CultureInfo(K10)].CurrentCulture when CultureReplacer is used.
-        /// </summary>
-        public static CultureInfo DefaultCulture
-        {
-            get { return _defaultCulture; }
-        }
-
-        public void Dispose()
-        {
-            Dispose(true);
-            GC.SuppressFinalize(this);
-        }
-
-        private void Dispose(bool disposing)
-        {
-            if (disposing)
-            {
-                Assert.True(Thread.CurrentThread.ManagedThreadId == _threadId,
-                    "The current thread is not the same as the thread invoking the constructor. This should never happen.");
-                CultureInfo.CurrentCulture = _originalCulture;
-                CultureInfo.CurrentUICulture = _originalUICulture;
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ExceptionAssertions.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ExceptionAssertions.cs
deleted file mode 100644
index 10bc34142f866d..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ExceptionAssertions.cs
+++ /dev/null
@@ -1,271 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Reflection;
-using System.Threading.Tasks;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    // TODO: eventually want: public partial class Assert : Xunit.Assert
-    public static class ExceptionAssert
-    {
-        /// <summary>
-        /// Verifies that an exception of the given type (or optionally a derived type) is thrown.
-        /// </summary>
-        /// <typeparam name="TException">The type of the exception expected to be thrown</typeparam>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static TException Throws<TException>(Action testCode)
-            where TException : Exception
-        {
-            return VerifyException<TException>(RecordException(testCode));
-        }
-
-        /// <summary>
-        /// Verifies that an exception of the given type is thrown.
-        /// Also verifies that the exception message matches.
-        /// </summary>
-        /// <typeparam name="TException">The type of the exception expected to be thrown</typeparam>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="exceptionMessage">The exception message to verify</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static TException Throws<TException>(Action testCode, string exceptionMessage)
-            where TException : Exception
-        {
-            var ex = Throws<TException>(testCode);
-            VerifyExceptionMessage(ex, exceptionMessage);
-            return ex;
-        }
-
-        /// <summary>
-        /// Verifies that an exception of the given type is thrown.
-        /// Also verifies that the exception message matches.
-        /// </summary>
-        /// <typeparam name="TException">The type of the exception expected to be thrown</typeparam>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="exceptionMessage">The exception message to verify</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static async Task<TException> ThrowsAsync<TException>(Func<Task> testCode, string exceptionMessage)
-            where TException : Exception
-        {
-            // The 'testCode' Task might execute asynchronously in a different thread making it hard to enforce the thread culture.
-            // The correct way to verify exception messages in such a scenario would be to run the task synchronously inside of a
-            // culture enforced block.
-            var ex = await Assert.ThrowsAsync<TException>(testCode);
-            VerifyExceptionMessage(ex, exceptionMessage);
-            return ex;
-        }
-
-        /// <summary>
-        /// Verifies that an exception of the given type is thrown.
-        /// Also verified that the exception message matches.
-        /// </summary>
-        /// <typeparam name="TException">The type of the exception expected to be thrown</typeparam>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="exceptionMessage">The exception message to verify</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static TException Throws<TException>(Func<object> testCode, string exceptionMessage)
-            where TException : Exception
-        {
-            return Throws<TException>(() => { testCode(); }, exceptionMessage);
-        }
-
-        /// <summary>
-        /// Verifies that the code throws an <see cref="ArgumentException"/>.
-        /// </summary>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="paramName">The name of the parameter that should throw the exception</param>
-        /// <param name="exceptionMessage">The exception message to verify</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static ArgumentException ThrowsArgument(Action testCode, string paramName, string exceptionMessage)
-        {
-            return ThrowsArgumentInternal<ArgumentException>(testCode, paramName, exceptionMessage);
-        }
-
-        private static TException ThrowsArgumentInternal<TException>(
-            Action testCode,
-            string paramName,
-            string exceptionMessage)
-            where TException : ArgumentException
-        {
-            var ex = Throws<TException>(testCode);
-            if (paramName != null)
-            {
-                Assert.Equal(paramName, ex.ParamName);
-            }
-            VerifyExceptionMessage(ex, exceptionMessage, partialMatch: true);
-            return ex;
-        }
-
-        /// <summary>
-        /// Verifies that the code throws an <see cref="ArgumentException"/>.
-        /// </summary>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="paramName">The name of the parameter that should throw the exception</param>
-        /// <param name="exceptionMessage">The exception message to verify</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static Task<ArgumentException> ThrowsArgumentAsync(Func<Task> testCode, string paramName, string exceptionMessage)
-        {
-            return ThrowsArgumentAsyncInternal<ArgumentException>(testCode, paramName, exceptionMessage);
-        }
-
-        private static async Task<TException> ThrowsArgumentAsyncInternal<TException>(
-            Func<Task> testCode,
-            string paramName,
-            string exceptionMessage)
-            where TException : ArgumentException
-        {
-            var ex = await Assert.ThrowsAsync<TException>(testCode);
-            if (paramName != null)
-            {
-                Assert.Equal(paramName, ex.ParamName);
-            }
-            VerifyExceptionMessage(ex, exceptionMessage, partialMatch: true);
-            return ex;
-        }
-
-        /// <summary>
-        /// Verifies that the code throws an <see cref="ArgumentNullException"/>.
-        /// </summary>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="paramName">The name of the parameter that should throw the exception</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static ArgumentNullException ThrowsArgumentNull(Action testCode, string paramName)
-        {
-            var ex = Throws<ArgumentNullException>(testCode);
-            if (paramName != null)
-            {
-                Assert.Equal(paramName, ex.ParamName);
-            }
-            return ex;
-        }
-
-        /// <summary>
-        /// Verifies that the code throws an ArgumentException with the expected message that indicates that the value cannot
-        /// be null or empty.
-        /// </summary>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="paramName">The name of the parameter that should throw the exception</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static ArgumentException ThrowsArgumentNullOrEmpty(Action testCode, string paramName)
-        {
-            return ThrowsArgumentInternal<ArgumentException>(testCode, paramName, "Value cannot be null or empty.");
-        }
-
-        /// <summary>
-        /// Verifies that the code throws an ArgumentException with the expected message that indicates that the value cannot
-        /// be null or empty.
-        /// </summary>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="paramName">The name of the parameter that should throw the exception</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static Task<ArgumentException> ThrowsArgumentNullOrEmptyAsync(Func<Task> testCode, string paramName)
-        {
-            return ThrowsArgumentAsyncInternal<ArgumentException>(testCode, paramName, "Value cannot be null or empty.");
-        }
-
-        /// <summary>
-        /// Verifies that the code throws an ArgumentNullException with the expected message that indicates that the value cannot
-        /// be null or empty string.
-        /// </summary>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="paramName">The name of the parameter that should throw the exception</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static ArgumentException ThrowsArgumentNullOrEmptyString(Action testCode, string paramName)
-        {
-            return ThrowsArgumentInternal<ArgumentException>(testCode, paramName, "Value cannot be null or an empty string.");
-        }
-
-        /// <summary>
-        /// Verifies that the code throws an ArgumentNullException with the expected message that indicates that the value cannot
-        /// be null or empty string.
-        /// </summary>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="paramName">The name of the parameter that should throw the exception</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static Task<ArgumentException> ThrowsArgumentNullOrEmptyStringAsync(Func<Task> testCode, string paramName)
-        {
-            return ThrowsArgumentAsyncInternal<ArgumentException>(testCode, paramName, "Value cannot be null or an empty string.");
-        }
-
-        /// <summary>
-        /// Verifies that the code throws an ArgumentOutOfRangeException (or optionally any exception which derives from it).
-        /// </summary>
-        /// <param name="testCode">A delegate to the code to be tested</param>
-        /// <param name="paramName">The name of the parameter that should throw the exception</param>
-        /// <param name="exceptionMessage">The exception message to verify</param>
-        /// <param name="actualValue">The actual value provided</param>
-        /// <returns>The exception that was thrown, when successful</returns>
-        public static ArgumentOutOfRangeException ThrowsArgumentOutOfRange(Action testCode, string paramName, string exceptionMessage, object actualValue = null)
-        {
-            var ex = ThrowsArgumentInternal<ArgumentOutOfRangeException>(testCode, paramName, exceptionMessage);
-
-            if (paramName != null)
-            {
-                Assert.Equal(paramName, ex.ParamName);
-            }
-
-            if (actualValue != null)
-            {
-                Assert.Equal(actualValue, ex.ActualValue);
-            }
-
-            return ex;
-        }
-
-        // We've re-implemented all the xUnit.net Throws code so that we can get this
-        // updated implementation of RecordException which silently unwraps any instances
-        // of AggregateException. In addition to unwrapping exceptions, this method ensures
-        // that tests are executed in with a known set of Culture and UICulture. This prevents
-        // tests from failing when executed on a non-English machine.
-        private static Exception RecordException(Action testCode)
-        {
-            try
-            {
-                using (new CultureReplacer())
-                {
-                    testCode();
-                }
-                return null;
-            }
-            catch (Exception exception)
-            {
-                return UnwrapException(exception);
-            }
-        }
-
-        private static Exception UnwrapException(Exception exception)
-        {
-            var aggEx = exception as AggregateException;
-            return aggEx != null ? aggEx.GetBaseException() : exception;
-        }
-
-        private static TException VerifyException<TException>(Exception exception)
-        {
-            var tie = exception as TargetInvocationException;
-            if (tie != null)
-            {
-                exception = tie.InnerException;
-            }
-            Assert.NotNull(exception);
-            return Assert.IsAssignableFrom<TException>(exception);
-        }
-
-        private static void VerifyExceptionMessage(Exception exception, string expectedMessage, bool partialMatch = false)
-        {
-            if (expectedMessage != null)
-            {
-                if (!partialMatch)
-                {
-                    Assert.Equal(expectedMessage, exception.Message);
-                }
-                else
-                {
-                    Assert.Contains(expectedMessage, exception.Message);
-                }
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/FlakyOn.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/FlakyOn.cs
deleted file mode 100644
index 45b72e32926f14..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/FlakyOn.cs
+++ /dev/null
@@ -1,44 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Text;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public static class FlakyOn
-    {
-        public const string All = "All";
-
-        public static class Helix
-        {
-            public const string All = QueuePrefix + "All";
-
-            public const string Fedora28Amd64 = QueuePrefix + HelixQueues.Fedora28Amd64;
-            public const string Fedora27Amd64 = QueuePrefix + HelixQueues.Fedora27Amd64;
-            public const string Redhat7Amd64 = QueuePrefix + HelixQueues.Redhat7Amd64;
-            public const string Debian9Amd64 = QueuePrefix + HelixQueues.Debian9Amd64;
-            public const string Debian8Amd64 = QueuePrefix + HelixQueues.Debian8Amd64;
-            public const string Centos7Amd64 = QueuePrefix + HelixQueues.Centos7Amd64;
-            public const string Ubuntu1604Amd64 = QueuePrefix + HelixQueues.Ubuntu1604Amd64;
-            public const string Ubuntu1810Amd64 = QueuePrefix + HelixQueues.Ubuntu1810Amd64;
-            public const string macOS1012Amd64 = QueuePrefix + HelixQueues.macOS1012Amd64;
-            public const string Windows10Amd64 = QueuePrefix + HelixQueues.Windows10Amd64;
-
-            private const string Prefix = "Helix:";
-            private const string QueuePrefix = Prefix + "Queue:";
-        }
-
-        public static class AzP
-        {
-            public const string All = Prefix + "All";
-            public const string Windows = OsPrefix + "Windows_NT";
-            public const string macOS = OsPrefix + "Darwin";
-            public const string Linux = OsPrefix + "Linux";
-
-            private const string Prefix = "AzP:";
-            private const string OsPrefix = Prefix + "OS:";
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/HelixQueues.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/HelixQueues.cs
deleted file mode 100644
index 19b9fde028ae7f..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/HelixQueues.cs
+++ /dev/null
@@ -1,21 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public static class HelixQueues
-    {
-        public const string Fedora28Amd64 = "Fedora.28." + Amd64Suffix;
-        public const string Fedora27Amd64 = "Fedora.27." + Amd64Suffix;
-        public const string Redhat7Amd64 = "Redhat.7." + Amd64Suffix;
-        public const string Debian9Amd64 = "Debian.9." + Amd64Suffix;
-        public const string Debian8Amd64 = "Debian.8." + Amd64Suffix;
-        public const string Centos7Amd64 = "Centos.7." + Amd64Suffix;
-        public const string Ubuntu1604Amd64 = "Ubuntu.1604." + Amd64Suffix;
-        public const string Ubuntu1810Amd64 = "Ubuntu.1810." + Amd64Suffix;
-        public const string macOS1012Amd64 = "OSX.1012." + Amd64Suffix;
-        public const string Windows10Amd64 = "Windows.10.Amd64.ClientRS4.VS2017.Open"; // Doesn't have the default suffix!
-
-        private const string Amd64Suffix = "Amd64.Open";
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/HttpClientSlim.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/HttpClientSlim.cs
deleted file mode 100644
index 3ef092e3a392cf..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/HttpClientSlim.cs
+++ /dev/null
@@ -1,192 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Globalization;
-using System.IO;
-using System.Net;
-using System.Net.Http;
-using System.Net.Security;
-using System.Net.Sockets;
-using System.Runtime.InteropServices;
-using System.Security.Authentication;
-using System.Text;
-using System.Threading.Tasks;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Lightweight version of HttpClient implemented using Socket and SslStream.
-    /// </summary>
-    public static class HttpClientSlim
-    {
-        public static async Task<string> GetStringAsync(string requestUri, bool validateCertificate = true)
-            => await GetStringAsync(new Uri(requestUri), validateCertificate).ConfigureAwait(false);
-
-        public static async Task<string> GetStringAsync(Uri requestUri, bool validateCertificate = true)
-        {
-            return await RetryRequest(async () =>
-            {
-                using (var stream = await GetStream(requestUri, validateCertificate).ConfigureAwait(false))
-                {
-                    using (var writer = new StreamWriter(stream, Encoding.ASCII, bufferSize: 1024, leaveOpen: true))
-                    {
-                        await writer.WriteAsync($"GET {requestUri.PathAndQuery} HTTP/1.0\r\n").ConfigureAwait(false);
-                        await writer.WriteAsync($"Host: {GetHost(requestUri)}\r\n").ConfigureAwait(false);
-                        await writer.WriteAsync("\r\n").ConfigureAwait(false);
-                    }
-
-                    return await ReadResponse(stream).ConfigureAwait(false);
-                }
-            });
-        }
-
-        internal static string GetHost(Uri requestUri)
-        {
-            var authority = requestUri.Authority;
-            if (requestUri.HostNameType == UriHostNameType.IPv6)
-            {
-                // Make sure there's no % scope id. https://github.com/aspnet/KestrelHttpServer/issues/2637
-                var address = IPAddress.Parse(requestUri.Host);
-                address = new IPAddress(address.GetAddressBytes()); // Drop scope Id.
-                if (requestUri.IsDefaultPort)
-                {
-                    authority = $"[{address}]";
-                }
-                else
-                {
-                    authority = $"[{address}]:{requestUri.Port.ToString(CultureInfo.InvariantCulture)}";
-                }
-            }
-            return authority;
-        }
-
-        public static async Task<string> PostAsync(string requestUri, HttpContent content, bool validateCertificate = true)
-            => await PostAsync(new Uri(requestUri), content, validateCertificate).ConfigureAwait(false);
-
-        public static async Task<string> PostAsync(Uri requestUri, HttpContent content, bool validateCertificate = true)
-        {
-            return await RetryRequest(async () =>
-            {
-                using (var stream = await GetStream(requestUri, validateCertificate))
-                {
-                    using (var writer = new StreamWriter(stream, Encoding.ASCII, bufferSize: 1024, leaveOpen: true))
-                    {
-                        await writer.WriteAsync($"POST {requestUri.PathAndQuery} HTTP/1.0\r\n").ConfigureAwait(false);
-                        await writer.WriteAsync($"Host: {requestUri.Authority}\r\n").ConfigureAwait(false);
-                        await writer.WriteAsync($"Content-Type: {content.Headers.ContentType}\r\n").ConfigureAwait(false);
-                        await writer.WriteAsync($"Content-Length: {content.Headers.ContentLength}\r\n").ConfigureAwait(false);
-                        await writer.WriteAsync("\r\n").ConfigureAwait(false);
-                    }
-
-                    await content.CopyToAsync(stream).ConfigureAwait(false);
-
-                    return await ReadResponse(stream).ConfigureAwait(false);
-                }
-            });
-        }
-
-        private static async Task<string> ReadResponse(Stream stream)
-        {
-            using (var reader = new StreamReader(stream, Encoding.ASCII, detectEncodingFromByteOrderMarks: true,
-                bufferSize: 1024, leaveOpen: true))
-            {
-                var response = await reader.ReadToEndAsync().ConfigureAwait(false);
-
-                var status = GetStatus(response);
-                new HttpResponseMessage(status).EnsureSuccessStatusCode();
-
-                var body = response.Substring(response.IndexOf("\r\n\r\n") + 4);
-                return body;
-            }
-        }
-
-        private static async Task<string> RetryRequest(Func<Task<string>> retryBlock)
-        {
-            var retryCount = 1;
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
-            {
-                retryCount = 3;
-            }
-
-            for (var retry = 0; retry < retryCount; retry++)
-            {
-                try
-                {
-                    return await retryBlock().ConfigureAwait(false);
-                }
-                catch (InvalidDataException)
-                {
-                    if (retry == retryCount - 1)
-                    {
-                        throw;
-                    }
-                }
-            }
-
-            // This will never be hit.
-            throw new NotSupportedException();
-        }
-
-        private static HttpStatusCode GetStatus(string response)
-        {
-            var statusStart = response.IndexOf(' ') + 1;
-            var statusEnd = response.IndexOf(' ', statusStart) - 1;
-            var statusLength = statusEnd - statusStart + 1;
-
-            if (statusLength < 1)
-            {
-                throw new InvalidDataException($"No StatusCode found in '{response}'");
-            }
-
-            return (HttpStatusCode)int.Parse(response.Substring(statusStart, statusLength));
-        }
-
-        private static async Task<Stream> GetStream(Uri requestUri, bool validateCertificate)
-        {
-            var socket = await GetSocket(requestUri);
-            var stream = new NetworkStream(socket, ownsSocket: true);
-
-            if (requestUri.Scheme.Equals("https", StringComparison.OrdinalIgnoreCase))
-            {
-                var sslStream = new SslStream(stream, leaveInnerStreamOpen: false, userCertificateValidationCallback:
-                    validateCertificate ? null : (RemoteCertificateValidationCallback)((a, b, c, d) => true));
-
-                await sslStream.AuthenticateAsClientAsync(requestUri.Host, clientCertificates: null,
-                    enabledSslProtocols: SslProtocols.Tls11 | SslProtocols.Tls12,
-                    checkCertificateRevocation: validateCertificate).ConfigureAwait(false);
-                return sslStream;
-            }
-            else
-            {
-                return stream;
-            }
-        }
-
-        public static async Task<Socket> GetSocket(Uri requestUri)
-        {
-            var tcs = new TaskCompletionSource<Socket>();
-
-            var socketArgs = new SocketAsyncEventArgs();
-            socketArgs.RemoteEndPoint = new DnsEndPoint(requestUri.DnsSafeHost, requestUri.Port);
-            socketArgs.Completed += (s, e) => tcs.TrySetResult(e.ConnectSocket);
-
-            // Must use static ConnectAsync(), since instance Connect() does not support DNS names on OSX/Linux.
-            if (Socket.ConnectAsync(SocketType.Stream, ProtocolType.Tcp, socketArgs))
-            {
-                await tcs.Task.ConfigureAwait(false);
-            }
-
-            var socket = socketArgs.ConnectSocket;
-
-            if (socket == null)
-            {
-                throw new SocketException((int)socketArgs.SocketError);
-            }
-            else
-            {
-                return socket;
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ITestMethodLifecycle.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ITestMethodLifecycle.cs
deleted file mode 100644
index 7ea0bbf88cda6d..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ITestMethodLifecycle.cs
+++ /dev/null
@@ -1,23 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Defines a lifecycle for attributes or classes that want to know about tests starting
-    /// or ending. Implement this on a test class, or attribute at the method/class/assembly level.
-    /// </summary>
-    /// <remarks>
-    /// Requires defining <see cref="AspNetTestFramework"/> as the test framework.
-    /// </remarks>
-    public interface ITestMethodLifecycle
-    {
-        Task OnTestStartAsync(TestContext context, CancellationToken cancellationToken);
-
-        Task OnTestEndAsync(TestContext context, Exception exception, CancellationToken cancellationToken);
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/RepeatAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/RepeatAttribute.cs
deleted file mode 100644
index ca8c85c6a8dfee..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/RepeatAttribute.cs
+++ /dev/null
@@ -1,27 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.ComponentModel;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Runs a test multiple times to stress flaky tests that are believed to be fixed.
-    /// This can be used on an assembly, class, or method name. Requires using the AspNetCore test framework.
-    /// </summary>
-    [EditorBrowsable(EditorBrowsableState.Never)]
-    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class | AttributeTargets.Assembly, AllowMultiple = false)]
-    public class RepeatAttribute : Attribute
-    {
-        public RepeatAttribute(int runCount = 10)
-        {
-            RunCount = runCount;
-        }
-
-        /// <summary>
-        /// The number of times to run a test.
-        /// </summary>
-        public int RunCount { get; }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/RepeatContext.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/RepeatContext.cs
deleted file mode 100644
index 91aa921e07e3a1..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/RepeatContext.cs
+++ /dev/null
@@ -1,27 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Threading;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class RepeatContext
-    {
-        private static AsyncLocal<RepeatContext> _current = new AsyncLocal<RepeatContext>();
-
-        public static RepeatContext Current
-        {
-            get => _current.Value;
-            internal set => _current.Value = value;
-        }
-
-        public RepeatContext(int limit)
-        {
-            Limit = limit;
-        }
-
-        public int Limit { get; }
-
-        public int CurrentIteration { get; set; }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ReplaceCulture.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ReplaceCulture.cs
deleted file mode 100644
index 2c2fb51d5141d5..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ReplaceCulture.cs
+++ /dev/null
@@ -1,70 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Globalization;
-using System.Reflection;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Replaces the current culture and UI culture for the test.
-    /// </summary>
-    [AttributeUsage(AttributeTargets.Method)]
-    public class ReplaceCultureAttribute : BeforeAfterTestAttribute
-    {
-        private const string _defaultCultureName = "en-GB";
-        private const string _defaultUICultureName = "en-US";
-        private CultureInfo _originalCulture;
-        private CultureInfo _originalUICulture;
-
-        /// <summary>
-        /// Replaces the current culture and UI culture to en-GB and en-US respectively.
-        /// </summary>
-        public ReplaceCultureAttribute() :
-            this(_defaultCultureName, _defaultUICultureName)
-        {
-        }
-
-        /// <summary>
-        /// Replaces the current culture and UI culture based on specified values.
-        /// </summary>
-        public ReplaceCultureAttribute(string currentCulture, string currentUICulture)
-        {
-            Culture = new CultureInfo(currentCulture);
-            UICulture = new CultureInfo(currentUICulture);
-        }
-
-        /// <summary>
-        /// The <see cref="CultureInfo.CurrentCulture"/> for the test. Defaults to en-GB.
-        /// </summary>
-        /// <remarks>
-        /// en-GB is used here as the default because en-US is equivalent to the InvariantCulture. We
-        /// want to be able to find bugs where we're accidentally relying on the Invariant instead of the
-        /// user's culture.
-        /// </remarks>
-        public CultureInfo Culture { get; }
-
-        /// <summary>
-        /// The <see cref="CultureInfo.CurrentUICulture"/> for the test. Defaults to en-US.
-        /// </summary>
-        public CultureInfo UICulture { get; }
-
-        public override void Before(MethodInfo methodUnderTest)
-        {
-            _originalCulture = CultureInfo.CurrentCulture;
-            _originalUICulture = CultureInfo.CurrentUICulture;
-
-            CultureInfo.CurrentCulture = Culture;
-            CultureInfo.CurrentUICulture = UICulture;
-        }
-
-        public override void After(MethodInfo methodUnderTest)
-        {
-            CultureInfo.CurrentCulture = _originalCulture;
-            CultureInfo.CurrentUICulture = _originalUICulture;
-        }
-    }
-}
-
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ShortClassNameAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ShortClassNameAttribute.cs
deleted file mode 100644
index ab4f0e17f9ac35..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/ShortClassNameAttribute.cs
+++ /dev/null
@@ -1,17 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Used to specify that <see cref="TestFileOutputContext.TestClassName"/> should used the
-    /// unqualified class name. This is needed when a fully-qualified class name exceeds
-    /// max path for logging.
-    /// </summary>
-    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Assembly, AllowMultiple = false)]
-    public class ShortClassNameAttribute : Attribute
-    {
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TaskExtensions.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TaskExtensions.cs
deleted file mode 100644
index 9cde37ec28472e..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TaskExtensions.cs
+++ /dev/null
@@ -1,66 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Diagnostics;
-using System.Runtime.CompilerServices;
-using System.Threading;
-using System.Threading.Tasks;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public static class TaskExtensions
-    {
-        public static async Task<T> TimeoutAfter<T>(this Task<T> task, TimeSpan timeout,
-            [CallerFilePath] string filePath = null,
-            [CallerLineNumber] int lineNumber = default)
-        {
-            // Don't create a timer if the task is already completed
-            // or the debugger is attached
-            if (task.IsCompleted || Debugger.IsAttached)
-            {
-                return await task;
-            }
-
-            var cts = new CancellationTokenSource();
-            if (task == await Task.WhenAny(task, Task.Delay(timeout, cts.Token)))
-            {
-                cts.Cancel();
-                return await task;
-            }
-            else
-            {
-                throw new TimeoutException(CreateMessage(timeout, filePath, lineNumber));
-            }
-        }
-
-        public static async Task TimeoutAfter(this Task task, TimeSpan timeout,
-            [CallerFilePath] string filePath = null,
-            [CallerLineNumber] int lineNumber = default)
-        {
-            // Don't create a timer if the task is already completed
-            // or the debugger is attached
-            if (task.IsCompleted || Debugger.IsAttached)
-            {
-                await task;
-                return;
-            }
-
-            var cts = new CancellationTokenSource();
-            if (task == await Task.WhenAny(task, Task.Delay(timeout, cts.Token)))
-            {
-                cts.Cancel();
-                await task;
-            }
-            else
-            {
-                throw new TimeoutException(CreateMessage(timeout, filePath, lineNumber));
-            }
-        }
-
-        private static string CreateMessage(TimeSpan timeout, string filePath, int lineNumber)
-            => string.IsNullOrEmpty(filePath)
-            ? $"The operation timed out after reaching the limit of {timeout.TotalMilliseconds}ms."
-            : $"The operation at {filePath}:{lineNumber} timed out after reaching the limit of {timeout.TotalMilliseconds}ms.";
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestContext.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestContext.cs
deleted file mode 100644
index ead7052b70da01..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestContext.cs
+++ /dev/null
@@ -1,44 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Reflection;
-using Xunit.Abstractions;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Provides access to contextual information about the running tests. Get access by
-    /// implementing <see cref="ITestMethodLifecycle"/>.
-    /// </summary>
-    /// <remarks>
-    /// Requires defining <see cref="AspNetTestFramework"/> as the test framework.
-    /// </remarks>
-    public sealed class TestContext
-    {
-        private Lazy<TestFileOutputContext> _files;
-
-        public TestContext(
-            Type testClass,
-            object[] constructorArguments,
-            MethodInfo testMethod,
-            object[] methodArguments,
-            ITestOutputHelper output)
-        {
-            TestClass = testClass;
-            ConstructorArguments = constructorArguments;
-            TestMethod = testMethod;
-            MethodArguments = methodArguments;
-            Output = output;
-
-            _files = new Lazy<TestFileOutputContext>(() => new TestFileOutputContext(this));
-        }
-
-        public Type TestClass { get; }
-        public MethodInfo TestMethod { get; }
-        public object[] ConstructorArguments { get; }
-        public object[] MethodArguments { get; }
-        public ITestOutputHelper Output { get; }
-        public TestFileOutputContext FileOutput => _files.Value;
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestFileOutputContext.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestFileOutputContext.cs
deleted file mode 100644
index 91e9a1b378c76e..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestFileOutputContext.cs
+++ /dev/null
@@ -1,146 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.IO;
-using System.Linq;
-using System.Reflection;
-using System.Text;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Provides access to file storage for the running test. Get access by
-    /// implementing <see cref="ITestMethodLifecycle"/>, and accessing <see cref="TestContext.FileOutput"/>.
-    /// </summary>
-    /// <remarks>
-    /// Requires defining <see cref="AspNetTestFramework"/> as the test framework.
-    /// </remarks>
-    public sealed class TestFileOutputContext
-    {
-        private static char[] InvalidFileChars = new char[]
-        {
-            '\"', '<', '>', '|', '\0',
-            (char)1, (char)2, (char)3, (char)4, (char)5, (char)6, (char)7, (char)8, (char)9, (char)10,
-            (char)11, (char)12, (char)13, (char)14, (char)15, (char)16, (char)17, (char)18, (char)19, (char)20,
-            (char)21, (char)22, (char)23, (char)24, (char)25, (char)26, (char)27, (char)28, (char)29, (char)30,
-            (char)31, ':', '*', '?', '\\', '/', ' ', (char)127
-        };
-
-        private readonly TestContext _parent;
-
-        public TestFileOutputContext(TestContext parent)
-        {
-            _parent = parent;
-
-            TestName = GetTestMethodName(parent.TestMethod, parent.MethodArguments);
-            TestClassName = GetTestClassName(parent.TestClass);
-
-            AssemblyOutputDirectory = GetAssemblyBaseDirectory(_parent.TestClass.Assembly);
-            if (!string.IsNullOrEmpty(AssemblyOutputDirectory))
-            {
-                TestClassOutputDirectory = Path.Combine(AssemblyOutputDirectory, TestClassName);
-            }
-        }
-
-        public string TestName { get; }
-
-        public string TestClassName { get; }
-
-        public string AssemblyOutputDirectory { get; }
-
-        public string TestClassOutputDirectory { get; }
-
-        public string GetUniqueFileName(string prefix, string extension)
-        {
-            if (prefix == null)
-            {
-                throw new ArgumentNullException(nameof(prefix));
-            }
-
-            if (extension != null && !extension.StartsWith(".", StringComparison.Ordinal))
-            {
-                throw new ArgumentException("The extension must start with '.' if one is provided.", nameof(extension));
-            }
-
-            var path = Path.Combine(TestClassOutputDirectory, $"{prefix}{extension}");
-
-            var i = 1;
-            while (File.Exists(path))
-            {
-                path = Path.Combine(TestClassOutputDirectory, $"{prefix}{i++}{extension}");
-            }
-
-            return path;
-        }
-
-        // Gets the output directory without appending the TFM or assembly name.
-        public static string GetOutputDirectory(Assembly assembly)
-        {
-            var attribute = assembly.GetCustomAttributes().OfType<TestOutputDirectoryAttribute>().FirstOrDefault();
-            return attribute?.BaseDirectory;
-        }
-
-        public static string GetAssemblyBaseDirectory(Assembly assembly, string baseDirectory = null)
-        {
-            var attribute = assembly.GetCustomAttributes().OfType<TestOutputDirectoryAttribute>().FirstOrDefault();
-            baseDirectory = baseDirectory ?? attribute?.BaseDirectory;
-            if (string.IsNullOrEmpty(baseDirectory))
-            {
-                return string.Empty;
-            }
-
-            return Path.Combine(baseDirectory, assembly.GetName().Name, attribute.TargetFramework);
-        }
-
-        public static bool GetPreserveExistingLogsInOutput(Assembly assembly)
-        {
-            var attribute = assembly.GetCustomAttributes().OfType<TestOutputDirectoryAttribute>().FirstOrDefault();
-            return attribute.PreserveExistingLogsInOutput;
-        }
-
-        public static string GetTestClassName(Type type)
-        {
-            var shortNameAttribute =
-                type.GetCustomAttribute<ShortClassNameAttribute>() ??
-                type.Assembly.GetCustomAttribute<ShortClassNameAttribute>();
-            var name = shortNameAttribute == null ? type.FullName : type.Name;
-
-            // Try to shorten the class name using the assembly name
-            var assemblyName = type.Assembly.GetName().Name;
-            if (name.StartsWith(assemblyName + "."))
-            {
-                name = name.Substring(assemblyName.Length + 1);
-            }
-
-            return name;
-        }
-
-        public static string GetTestMethodName(MethodInfo method, object[] arguments)
-        {
-            var name = arguments.Aggregate(method.Name, (a, b) => $"{a}-{(b ?? "null")}");
-            return RemoveIllegalFileChars(name);
-        }
-
-        public static string RemoveIllegalFileChars(string s)
-        {
-            var sb = new StringBuilder();
-
-            foreach (var c in s)
-            {
-                if (InvalidFileChars.Contains(c))
-                {
-                    if (sb.Length > 0 && sb[sb.Length - 1] != '_')
-                    {
-                        sb.Append('_');
-                    }
-                }
-                else
-                {
-                    sb.Append(c);
-                }
-            }
-            return sb.ToString();
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestOutputDirectoryAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestOutputDirectoryAttribute.cs
deleted file mode 100644
index 1a80126300ec8d..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestOutputDirectoryAttribute.cs
+++ /dev/null
@@ -1,22 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = false, Inherited = true)]
-    public class TestOutputDirectoryAttribute : Attribute
-    {
-        public TestOutputDirectoryAttribute(string preserveExistingLogsInOutput, string targetFramework, string baseDirectory = null)
-        {
-            TargetFramework = targetFramework;
-            BaseDirectory = baseDirectory;
-            PreserveExistingLogsInOutput = bool.Parse(preserveExistingLogsInOutput);
-        }
-
-        public string BaseDirectory { get; }
-        public string TargetFramework { get; }
-        public bool PreserveExistingLogsInOutput { get; }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestPathUtilities.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestPathUtilities.cs
deleted file mode 100644
index b1711ce7a956b2..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestPathUtilities.cs
+++ /dev/null
@@ -1,37 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.IO;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [Obsolete("This API is obsolete and the pattern its usage encouraged should not be used anymore. See https://github.com/dotnet/extensions/issues/1697 for details.")]
-    public class TestPathUtilities
-    {
-        public static string GetRepoRootDirectory()
-        {
-            return GetSolutionRootDirectory("Extensions");
-        }
-
-        public static string GetSolutionRootDirectory(string solution)
-        {
-            var applicationBasePath = AppContext.BaseDirectory;
-            var directoryInfo = new DirectoryInfo(applicationBasePath);
-
-            do
-            {
-                var projectFileInfo = new FileInfo(Path.Combine(directoryInfo.FullName, $"{solution}.sln"));
-                if (projectFileInfo.Exists)
-                {
-                    return projectFileInfo.DirectoryName;
-                }
-
-                directoryInfo = directoryInfo.Parent;
-            }
-            while (directoryInfo.Parent != null);
-
-            throw new Exception($"Solution file {solution}.sln could not be found in {applicationBasePath} or its parent directories.");
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestPlatformHelper.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestPlatformHelper.cs
deleted file mode 100644
index 4d85c00d652d4e..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/TestPlatformHelper.cs
+++ /dev/null
@@ -1,23 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Runtime.InteropServices;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public static class TestPlatformHelper
-    {
-        public static bool IsMono =>
-            Type.GetType("Mono.Runtime") != null;
-
-        public static bool IsWindows =>
-            RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
-
-        public static bool IsLinux =>
-            RuntimeInformation.IsOSPlatform(OSPlatform.Linux);
-
-        public static bool IsMac =>
-            RuntimeInformation.IsOSPlatform(OSPlatform.OSX);
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/Tracing/CollectingEventListener.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/Tracing/CollectingEventListener.cs
deleted file mode 100644
index b9d392fde8d7c0..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/Tracing/CollectingEventListener.cs
+++ /dev/null
@@ -1,63 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Concurrent;
-using System.Collections.Generic;
-using System.Diagnostics.Tracing;
-using System.Linq;
-
-namespace Microsoft.AspNetCore.Testing.Tracing
-{
-    public class CollectingEventListener : EventListener
-    {
-        private ConcurrentQueue<EventWrittenEventArgs> _events = new ConcurrentQueue<EventWrittenEventArgs>();
-
-        private object _lock = new object();
-
-        private Dictionary<string, EventSource> _existingSources = new Dictionary<string, EventSource>(StringComparer.OrdinalIgnoreCase);
-        private HashSet<string> _requestedEventSources = new HashSet<string>();
-
-        public void CollectFrom(string eventSourceName)
-        {
-            lock(_lock)
-            {
-                // Check if it's already been created
-                if(_existingSources.TryGetValue(eventSourceName, out var existingSource))
-                {
-                    // It has, so just enable it now
-                    CollectFrom(existingSource);
-                }
-                else
-                {
-                    // It hasn't, so queue this request for when it is created
-                    _requestedEventSources.Add(eventSourceName);
-                }
-            }
-        }
-
-        public void CollectFrom(EventSource eventSource) => EnableEvents(eventSource, EventLevel.Verbose, EventKeywords.All);
-
-        public IReadOnlyList<EventWrittenEventArgs> GetEventsWritten() => _events.ToArray();
-
-        protected override void OnEventSourceCreated(EventSource eventSource)
-        {
-            lock (_lock)
-            {
-                // Add this to the list of existing sources for future CollectEventsFrom requests.
-                _existingSources[eventSource.Name] = eventSource;
-
-                // Check if we have a pending request to enable it
-                if (_requestedEventSources.Contains(eventSource.Name))
-                {
-                    CollectFrom(eventSource);
-                }
-            }
-        }
-
-        protected override void OnEventWritten(EventWrittenEventArgs eventData)
-        {
-            _events.Enqueue(eventData);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/Tracing/EventAssert.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/Tracing/EventAssert.cs
deleted file mode 100644
index d8601cf121be72..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/Tracing/EventAssert.cs
+++ /dev/null
@@ -1,63 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Diagnostics.Tracing;
-using System.Linq;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing.Tracing
-{
-    public class EventAssert
-    {
-        private readonly int _expectedId;
-        private readonly string _expectedName;
-        private readonly EventLevel _expectedLevel;
-        private readonly IList<(string name, Action<object> asserter)> _payloadAsserters = new List<(string, Action<object>)>();
-
-        public EventAssert(int expectedId, string expectedName, EventLevel expectedLevel)
-        {
-            _expectedId = expectedId;
-            _expectedName = expectedName;
-            _expectedLevel = expectedLevel;
-        }
-
-        public static void Collection(IEnumerable<EventWrittenEventArgs> events, params EventAssert[] asserts)
-        {
-            Assert.Collection(
-                events,
-                asserts.Select(a => a.CreateAsserter()).ToArray());
-        }
-
-        public static EventAssert Event(int id, string name, EventLevel level)
-        {
-            return new EventAssert(id, name, level);
-        }
-
-        public EventAssert Payload(string name, object expectedValue) => Payload(name, actualValue => Assert.Equal(expectedValue, actualValue));
-
-        public EventAssert Payload(string name, Action<object> asserter)
-        {
-            _payloadAsserters.Add((name, asserter));
-            return this;
-        }
-
-        private Action<EventWrittenEventArgs> CreateAsserter() => Execute;
-
-        private void Execute(EventWrittenEventArgs evt)
-        {
-            Assert.Equal(_expectedId, evt.EventId);
-            Assert.Equal(_expectedName, evt.EventName);
-            Assert.Equal(_expectedLevel, evt.Level);
-
-            Action<string> CreateNameAsserter((string name, Action<object> asserter) val)
-            {
-                return actualValue => Assert.Equal(val.name, actualValue);
-            }
-
-            Assert.Collection(evt.PayloadNames, _payloadAsserters.Select(CreateNameAsserter).ToArray());
-            Assert.Collection(evt.Payload, _payloadAsserters.Select(t => t.asserter).ToArray());
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/Tracing/EventSourceTestBase.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/Tracing/EventSourceTestBase.cs
deleted file mode 100644
index 012f4d5cbd03bb..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/Tracing/EventSourceTestBase.cs
+++ /dev/null
@@ -1,42 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Diagnostics.Tracing;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing.Tracing
-{
-    // This collection attribute is what makes the "magic" happen. It forces xunit to run all tests that inherit from this
-    // base class sequentially, preventing conflicts (since EventSource/EventListener is a process-global concept).
-    [Collection(CollectionName)]
-    public abstract class EventSourceTestBase : IDisposable
-    {
-        public const string CollectionName = "Microsoft.AspNetCore.Testing.Tracing.EventSourceTestCollection";
-
-        private readonly CollectingEventListener _listener;
-
-        public EventSourceTestBase()
-        {
-            _listener = new CollectingEventListener();
-        }
-
-        protected void CollectFrom(string eventSourceName)
-        {
-            _listener.CollectFrom(eventSourceName);
-        }
-
-        protected void CollectFrom(EventSource eventSource)
-        {
-            _listener.CollectFrom(eventSource);
-        }
-
-        protected IReadOnlyList<EventWrittenEventArgs> GetEvents() => _listener.GetEventsWritten();
-
-        public void Dispose()
-        {
-            _listener.Dispose();
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/contentFiles/cs/netstandard2.0/EventSourceTestCollection.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/contentFiles/cs/netstandard2.0/EventSourceTestCollection.cs
deleted file mode 100644
index 407efc8388a401..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/contentFiles/cs/netstandard2.0/EventSourceTestCollection.cs
+++ /dev/null
@@ -1,13 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-namespace Microsoft.AspNetCore.Testing.Tracing
-{
-    // This file comes from Microsoft.AspNetCore.Testing and has to be defined in the test assembly.
-    // It enables EventSourceTestBase's parallel isolation functionality.
-
-    [Xunit.CollectionDefinition(EventSourceTestBase.CollectionName, DisableParallelization = true)]
-    public class EventSourceTestCollection
-    {
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestAssemblyRunner.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestAssemblyRunner.cs
deleted file mode 100644
index fa954c2b97e4c1..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestAssemblyRunner.cs
+++ /dev/null
@@ -1,83 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading;
-using System.Threading.Tasks;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class AspNetTestAssemblyRunner : XunitTestAssemblyRunner
-    {
-        private readonly Dictionary<Type, object> _assemblyFixtureMappings = new Dictionary<Type, object>();
-
-        public AspNetTestAssemblyRunner(
-            ITestAssembly testAssembly,
-            IEnumerable<IXunitTestCase> testCases,
-            IMessageSink diagnosticMessageSink,
-            IMessageSink executionMessageSink,
-            ITestFrameworkExecutionOptions executionOptions)
-            : base(testAssembly, testCases, diagnosticMessageSink, executionMessageSink, executionOptions)
-        {
-        }
-
-        protected override async Task AfterTestAssemblyStartingAsync()
-        {
-            await base.AfterTestAssemblyStartingAsync();
-
-            // Find all the AssemblyFixtureAttributes on the test assembly
-            Aggregator.Run(() =>
-            {
-                var fixturesAttributes = ((IReflectionAssemblyInfo)TestAssembly.Assembly)
-                    .Assembly
-                    .GetCustomAttributes(typeof(AssemblyFixtureAttribute), false)
-                    .Cast<AssemblyFixtureAttribute>()
-                    .ToList();
-
-                // Instantiate all the fixtures
-                foreach (var fixtureAttribute in fixturesAttributes)
-                {
-                    var ctorWithDiagnostics = fixtureAttribute.FixtureType.GetConstructor(new[] { typeof(IMessageSink) });
-                    if (ctorWithDiagnostics != null)
-                    {
-                        _assemblyFixtureMappings[fixtureAttribute.FixtureType] = Activator.CreateInstance(fixtureAttribute.FixtureType, DiagnosticMessageSink);
-                    }
-                    else
-                    {
-                        _assemblyFixtureMappings[fixtureAttribute.FixtureType] = Activator.CreateInstance(fixtureAttribute.FixtureType);
-                    }
-                }
-            });
-        }
-
-        protected override Task BeforeTestAssemblyFinishedAsync()
-        {
-            // Dispose fixtures
-            foreach (var disposable in _assemblyFixtureMappings.Values.OfType<IDisposable>())
-            {
-                Aggregator.Run(disposable.Dispose);
-            }
-
-            return base.BeforeTestAssemblyFinishedAsync();
-        }
-
-        protected override Task<RunSummary> RunTestCollectionAsync(
-            IMessageBus messageBus,
-            ITestCollection testCollection,
-            IEnumerable<IXunitTestCase> testCases,
-            CancellationTokenSource cancellationTokenSource)
-            => new AspNetTestCollectionRunner(
-                _assemblyFixtureMappings,
-                testCollection,
-                testCases,
-                DiagnosticMessageSink,
-                messageBus,
-                TestCaseOrderer,
-                new ExceptionAggregator(Aggregator),
-                cancellationTokenSource).RunAsync();
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestCaseRunner.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestCaseRunner.cs
deleted file mode 100644
index 9fa8595d217ee3..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestCaseRunner.cs
+++ /dev/null
@@ -1,33 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Reflection;
-using System.Threading;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    internal class AspNetTestCaseRunner : XunitTestCaseRunner
-    {
-        public AspNetTestCaseRunner(
-            IXunitTestCase testCase,
-            string displayName,
-            string skipReason,
-            object[] constructorArguments,
-            object[] testMethodArguments,
-            IMessageBus messageBus,
-            ExceptionAggregator aggregator,
-            CancellationTokenSource cancellationTokenSource)
-            : base(testCase, displayName, skipReason, constructorArguments, testMethodArguments, messageBus, aggregator, cancellationTokenSource)
-        {
-        }
-
-        protected override XunitTestRunner CreateTestRunner(ITest test, IMessageBus messageBus, Type testClass, object[] constructorArguments, MethodInfo testMethod, object[] testMethodArguments, string skipReason, IReadOnlyList<BeforeAfterTestAttribute> beforeAfterAttributes, ExceptionAggregator aggregator, CancellationTokenSource cancellationTokenSource)
-        {
-            return new AspNetTestRunner(test, messageBus, testClass, constructorArguments, testMethod, testMethodArguments, skipReason, beforeAfterAttributes, aggregator, cancellationTokenSource);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestClassRunner.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestClassRunner.cs
deleted file mode 100644
index faddd9fe1bf737..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestClassRunner.cs
+++ /dev/null
@@ -1,44 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Threading;
-using System.Threading.Tasks;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    internal class AspNetTestClassRunner : XunitTestClassRunner
-    {
-        public AspNetTestClassRunner(
-            ITestClass testClass,
-            IReflectionTypeInfo @class,
-            IEnumerable<IXunitTestCase> testCases,
-            IMessageSink diagnosticMessageSink,
-            IMessageBus messageBus,
-            ITestCaseOrderer testCaseOrderer,
-            ExceptionAggregator aggregator,
-            CancellationTokenSource cancellationTokenSource,
-            IDictionary<Type, object> collectionFixtureMappings)
-            : base(testClass, @class, testCases, diagnosticMessageSink, messageBus, testCaseOrderer, aggregator, cancellationTokenSource, collectionFixtureMappings)
-        {
-        }
-
-        protected override Task<RunSummary> RunTestMethodAsync(ITestMethod testMethod, IReflectionMethodInfo method, IEnumerable<IXunitTestCase> testCases, object[] constructorArguments)
-        {
-            var runner = new AspNetTestMethodRunner(
-                testMethod,
-                Class,
-                method,
-                testCases,
-                DiagnosticMessageSink,
-                MessageBus,
-                new ExceptionAggregator(Aggregator),
-                CancellationTokenSource,
-                constructorArguments);
-            return runner.RunAsync();
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestCollectionRunner.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestCollectionRunner.cs
deleted file mode 100644
index 24c2cd16ddcb9a..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestCollectionRunner.cs
+++ /dev/null
@@ -1,75 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading;
-using System.Threading.Tasks;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class AspNetTestCollectionRunner : XunitTestCollectionRunner
-    {
-        private readonly IDictionary<Type, object> _assemblyFixtureMappings;
-        private readonly IMessageSink _diagnosticMessageSink;
-
-        public AspNetTestCollectionRunner(
-            Dictionary<Type, object> assemblyFixtureMappings,
-            ITestCollection testCollection,
-            IEnumerable<IXunitTestCase> testCases,
-            IMessageSink diagnosticMessageSink,
-            IMessageBus messageBus,
-            ITestCaseOrderer testCaseOrderer,
-            ExceptionAggregator aggregator,
-            CancellationTokenSource cancellationTokenSource)
-            : base(testCollection, testCases, diagnosticMessageSink, messageBus, testCaseOrderer, aggregator, cancellationTokenSource)
-        {
-            _assemblyFixtureMappings = assemblyFixtureMappings;
-            _diagnosticMessageSink = diagnosticMessageSink;
-        }
-
-        protected override async Task AfterTestCollectionStartingAsync()
-        {
-            await base.AfterTestCollectionStartingAsync();
-
-            // note: We pass the assembly fixtures into the runner as ICollectionFixture<> - this seems to work OK without any
-            // drawbacks. It's reasonable that we could add IAssemblyFixture<> and related plumbing if it ever became required.
-            //
-            // The reason for assembly fixture is when we want to start/stop something as the project scope - tests can only be
-            // in one test collection at a time.
-            foreach (var mapping in _assemblyFixtureMappings)
-            {
-                CollectionFixtureMappings.Add(mapping.Key, mapping.Value);
-            }
-        }
-
-        protected override Task BeforeTestCollectionFinishedAsync()
-        {
-            // We need to remove the assembly fixtures so they won't get disposed.
-            foreach (var mapping in _assemblyFixtureMappings)
-            {
-                CollectionFixtureMappings.Remove(mapping.Key);
-            }
-
-            return base.BeforeTestCollectionFinishedAsync();
-        }
-
-        protected override Task<RunSummary> RunTestClassAsync(ITestClass testClass, IReflectionTypeInfo @class, IEnumerable<IXunitTestCase> testCases)
-        {
-            var runner = new AspNetTestClassRunner(
-                testClass,
-                @class,
-                testCases,
-                DiagnosticMessageSink,
-                MessageBus,
-                TestCaseOrderer,
-                new ExceptionAggregator(Aggregator),
-                CancellationTokenSource,
-                CollectionFixtureMappings);
-            return runner.RunAsync();
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestFramework.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestFramework.cs
deleted file mode 100644
index 369dece7b12501..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestFramework.cs
+++ /dev/null
@@ -1,20 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Reflection;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class AspNetTestFramework : XunitTestFramework
-    {
-        public AspNetTestFramework(IMessageSink messageSink)
-            : base(messageSink)
-        {
-        }
-
-        protected override ITestFrameworkExecutor CreateExecutor(AssemblyName assemblyName)
-            => new AspNetTestFrameworkExecutor(assemblyName, SourceInformationProvider, DiagnosticMessageSink);
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestFrameworkExecutor.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestFrameworkExecutor.cs
deleted file mode 100644
index ffbab11f559e79..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestFrameworkExecutor.cs
+++ /dev/null
@@ -1,26 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Collections.Generic;
-using System.Reflection;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class AspNetTestFrameworkExecutor : XunitTestFrameworkExecutor
-    {
-        public AspNetTestFrameworkExecutor(AssemblyName assemblyName, ISourceInformationProvider sourceInformationProvider, IMessageSink diagnosticMessageSink)
-            : base(assemblyName, sourceInformationProvider, diagnosticMessageSink)
-        {
-        }
-
-        protected override async void RunTestCases(IEnumerable<IXunitTestCase> testCases, IMessageSink executionMessageSink, ITestFrameworkExecutionOptions executionOptions)
-        {
-            using (var assemblyRunner = new AspNetTestAssemblyRunner(TestAssembly, testCases, DiagnosticMessageSink, executionMessageSink, executionOptions))
-            {
-                await assemblyRunner.RunAsync();
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestInvoker.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestInvoker.cs
deleted file mode 100644
index 118c0bdecb2d9f..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestInvoker.cs
+++ /dev/null
@@ -1,84 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Reflection;
-using System.Threading;
-using System.Threading.Tasks;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    internal class AspNetTestInvoker : XunitTestInvoker
-    {
-        public AspNetTestInvoker(
-            ITest test,
-            IMessageBus messageBus,
-            Type testClass,
-            object[] constructorArguments,
-            MethodInfo testMethod,
-            object[] testMethodArguments,
-            IReadOnlyList<BeforeAfterTestAttribute> beforeAfterAttributes,
-            ExceptionAggregator aggregator,
-            CancellationTokenSource cancellationTokenSource)
-            : base(test, messageBus, testClass, constructorArguments, testMethod, testMethodArguments, beforeAfterAttributes, aggregator, cancellationTokenSource)
-        {
-        }
-
-        protected override async Task<decimal> InvokeTestMethodAsync(object testClassInstance)
-        {
-            var output = new TestOutputHelper();
-            output.Initialize(MessageBus, Test);
-
-            var context = new TestContext(TestClass, ConstructorArguments, TestMethod, TestMethodArguments, output);
-            var lifecycleHooks = GetLifecycleHooks(testClassInstance, TestClass, TestMethod);
-
-            await Aggregator.RunAsync(async () =>
-            {
-                foreach (var lifecycleHook in lifecycleHooks)
-                {
-                    await lifecycleHook.OnTestStartAsync(context, CancellationTokenSource.Token);
-                }
-            });
-
-            var time = await base.InvokeTestMethodAsync(testClassInstance);
-
-            await Aggregator.RunAsync(async () =>
-            {
-                var exception = Aggregator.HasExceptions ? Aggregator.ToException() : null;
-                foreach (var lifecycleHook in lifecycleHooks)
-                {
-                    await lifecycleHook.OnTestEndAsync(context, exception, CancellationTokenSource.Token);
-                }
-            });
-
-            return time;
-        }
-
-        private static IEnumerable<ITestMethodLifecycle> GetLifecycleHooks(object testClassInstance, Type testClass, MethodInfo testMethod)
-        {
-            foreach (var attribute in testMethod.GetCustomAttributes(inherit: true).OfType<ITestMethodLifecycle>())
-            {
-                yield return attribute;
-            }
-
-            if (testClassInstance is ITestMethodLifecycle instance)
-            {
-                yield return instance;
-            }
-
-            foreach (var attribute in testClass.GetCustomAttributes(inherit: true).OfType<ITestMethodLifecycle>())
-            {
-                yield return attribute;
-            }
-
-            foreach (var attribute in testClass.Assembly.GetCustomAttributes(inherit: true).OfType<ITestMethodLifecycle>())
-            {
-                yield return attribute;
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestMethodRunner.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestMethodRunner.cs
deleted file mode 100644
index 35f5e09de3e94c..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestMethodRunner.cs
+++ /dev/null
@@ -1,73 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Collections.Generic;
-using System.Threading;
-using System.Threading.Tasks;
-using Microsoft.AspNetCore.Testing.xunit;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    internal class AspNetTestMethodRunner : XunitTestMethodRunner
-    {
-        private readonly object[] _constructorArguments;
-        private readonly IMessageSink _diagnosticMessageSink;
-
-        public AspNetTestMethodRunner(
-            ITestMethod testMethod,
-            IReflectionTypeInfo @class,
-            IReflectionMethodInfo method,
-            IEnumerable<IXunitTestCase> testCases,
-            IMessageSink diagnosticMessageSink,
-            IMessageBus messageBus,
-            ExceptionAggregator aggregator,
-            CancellationTokenSource cancellationTokenSource,
-            object[] constructorArguments)
-            : base(testMethod, @class, method, testCases, diagnosticMessageSink, messageBus, aggregator, cancellationTokenSource, constructorArguments)
-        {
-            _diagnosticMessageSink = diagnosticMessageSink;
-            _constructorArguments = constructorArguments;
-        }
-
-        protected override Task<RunSummary> RunTestCaseAsync(IXunitTestCase testCase)
-        {
-            if (testCase.GetType() == typeof(XunitTestCase))
-            {
-                // If we get here this is a 'regular' test case, not something that represents a skipped test.
-                //
-                // We can take control of it's invocation thusly.
-                var runner = new AspNetTestCaseRunner(
-                    testCase,
-                    testCase.DisplayName,
-                    testCase.SkipReason,
-                    _constructorArguments,
-                    testCase.TestMethodArguments,
-                    MessageBus,
-                    new ExceptionAggregator(Aggregator),
-                    CancellationTokenSource);
-                return runner.RunAsync();
-            }
-
-            if (testCase.GetType() == typeof(XunitTheoryTestCase))
-            {
-                // If we get here this is a 'regular' theory test case, not something that represents a skipped test.
-                //
-                // We can take control of it's invocation thusly.
-                var runner = new AspNetTheoryTestCaseRunner(
-                    testCase,
-                    testCase.DisplayName,
-                    testCase.SkipReason,
-                    _constructorArguments,
-                    _diagnosticMessageSink,
-                    MessageBus,
-                    new ExceptionAggregator(Aggregator),
-                    CancellationTokenSource);
-                return runner.RunAsync();
-            }
-
-            return base.RunTestCaseAsync(testCase);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestRunner.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestRunner.cs
deleted file mode 100644
index f1f07947fac9f5..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTestRunner.cs
+++ /dev/null
@@ -1,78 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Reflection;
-using System.Threading;
-using System.Threading.Tasks;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    internal class AspNetTestRunner : XunitTestRunner
-    {
-        public AspNetTestRunner(
-            ITest test,
-            IMessageBus messageBus,
-            Type testClass,
-            object[] constructorArguments,
-            MethodInfo testMethod,
-            object[] testMethodArguments,
-            string skipReason,
-            IReadOnlyList<BeforeAfterTestAttribute> beforeAfterAttributes,
-            ExceptionAggregator aggregator,
-            CancellationTokenSource cancellationTokenSource)
-            : base(test, messageBus, testClass, constructorArguments, testMethod, testMethodArguments, skipReason, beforeAfterAttributes, aggregator, cancellationTokenSource)
-        {
-        }
-
-        protected override async Task<decimal> InvokeTestMethodAsync(ExceptionAggregator aggregator)
-        {
-            var repeatAttribute = GetRepeatAttribute(TestMethod);
-            if (repeatAttribute == null)
-            {
-                return await InvokeTestMethodCoreAsync(aggregator);
-            }
-
-            var repeatContext = new RepeatContext(repeatAttribute.RunCount);
-            RepeatContext.Current = repeatContext;
-
-            var timeTaken = 0.0M;
-            for (repeatContext.CurrentIteration = 0; repeatContext.CurrentIteration < repeatContext.Limit; repeatContext.CurrentIteration++)
-            {
-                timeTaken = await InvokeTestMethodCoreAsync(aggregator);
-                if (aggregator.HasExceptions)
-                {
-                    return timeTaken;
-                }
-            }
-
-            return timeTaken;
-        }
-
-        private Task<decimal> InvokeTestMethodCoreAsync(ExceptionAggregator aggregator)
-        {
-            var invoker = new AspNetTestInvoker(Test, MessageBus, TestClass, ConstructorArguments, TestMethod, TestMethodArguments, BeforeAfterAttributes, aggregator, CancellationTokenSource);
-            return invoker.RunAsync();
-        }
-
-        private RepeatAttribute GetRepeatAttribute(MethodInfo methodInfo)
-        {
-            var attributeCandidate = methodInfo.GetCustomAttribute<RepeatAttribute>();
-            if (attributeCandidate != null)
-            {
-                return attributeCandidate;
-            }
-
-            attributeCandidate = methodInfo.DeclaringType.GetCustomAttribute<RepeatAttribute>();
-            if (attributeCandidate != null)
-            {
-                return attributeCandidate;
-            }
-
-            return methodInfo.DeclaringType.Assembly.GetCustomAttribute<RepeatAttribute>();
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTheoryTestCaseRunner.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTheoryTestCaseRunner.cs
deleted file mode 100644
index f9d5810f99c63c..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AspNetTheoryTestCaseRunner.cs
+++ /dev/null
@@ -1,33 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Reflection;
-using System.Threading;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing.xunit
-{
-    internal class AspNetTheoryTestCaseRunner : XunitTheoryTestCaseRunner
-    {
-        public AspNetTheoryTestCaseRunner(
-            IXunitTestCase testCase,
-            string displayName,
-            string skipReason,
-            object[] constructorArguments,
-            IMessageSink diagnosticMessageSink,
-            IMessageBus messageBus,
-            ExceptionAggregator aggregator,
-            CancellationTokenSource cancellationTokenSource)
-            : base(testCase, displayName, skipReason, constructorArguments, diagnosticMessageSink, messageBus, aggregator, cancellationTokenSource)
-        {
-        }
-
-        protected override XunitTestRunner CreateTestRunner(ITest test, IMessageBus messageBus, Type testClass, object[] constructorArguments, MethodInfo testMethod, object[] testMethodArguments, string skipReason, IReadOnlyList<BeforeAfterTestAttribute> beforeAfterAttributes, ExceptionAggregator aggregator, CancellationTokenSource cancellationTokenSource)
-        {
-            return new AspNetTestRunner(test, messageBus, testClass, constructorArguments, testMethod, testMethodArguments, skipReason, beforeAfterAttributes, aggregator, cancellationTokenSource);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AssemblyFixtureAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AssemblyFixtureAttribute.cs
deleted file mode 100644
index 428eb021573013..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/AssemblyFixtureAttribute.cs
+++ /dev/null
@@ -1,18 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
-    public class AssemblyFixtureAttribute : Attribute
-    {
-        public AssemblyFixtureAttribute(Type fixtureType)
-        {
-            FixtureType = fixtureType;
-        }
-
-        public Type FixtureType { get; private set; }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalFactAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalFactAttribute.cs
deleted file mode 100644
index 8f128fdb1e2d11..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalFactAttribute.cs
+++ /dev/null
@@ -1,15 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using Xunit;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
-    [XunitTestCaseDiscoverer("Microsoft.AspNetCore.Testing." + nameof(ConditionalFactDiscoverer), "Microsoft.AspNetCore.Testing")]
-    public class ConditionalFactAttribute : FactAttribute
-    {
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalFactDiscoverer.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalFactDiscoverer.cs
deleted file mode 100644
index 339ee1d9202552..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalFactDiscoverer.cs
+++ /dev/null
@@ -1,28 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-// Do not change this namespace without changing the usage in ConditionalFactAttribute
-namespace Microsoft.AspNetCore.Testing
-{
-    internal class ConditionalFactDiscoverer : FactDiscoverer
-    {
-        private readonly IMessageSink _diagnosticMessageSink;
-
-        public ConditionalFactDiscoverer(IMessageSink diagnosticMessageSink)
-            : base(diagnosticMessageSink)
-        {
-            _diagnosticMessageSink = diagnosticMessageSink;
-        }
-
-        protected override IXunitTestCase CreateTestCase(ITestFrameworkDiscoveryOptions discoveryOptions, ITestMethod testMethod, IAttributeInfo factAttribute)
-        {
-            var skipReason = testMethod.EvaluateSkipConditions();
-            return skipReason != null
-                ? new SkippedTestCase(skipReason, _diagnosticMessageSink, discoveryOptions.MethodDisplayOrDefault(), TestMethodDisplayOptions.None, testMethod)
-                : base.CreateTestCase(discoveryOptions, testMethod, factAttribute);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalTheoryAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalTheoryAttribute.cs
deleted file mode 100644
index 6030392df69474..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalTheoryAttribute.cs
+++ /dev/null
@@ -1,15 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using Xunit;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
-    [XunitTestCaseDiscoverer("Microsoft.AspNetCore.Testing." + nameof(ConditionalTheoryDiscoverer), "Microsoft.AspNetCore.Testing")]
-    public class ConditionalTheoryAttribute : TheoryAttribute
-    {
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalTheoryDiscoverer.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalTheoryDiscoverer.cs
deleted file mode 100644
index 2fbff9bf2e7fd7..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ConditionalTheoryDiscoverer.cs
+++ /dev/null
@@ -1,87 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-// Do not change this namespace without changing the usage in ConditionalTheoryAttribute
-namespace Microsoft.AspNetCore.Testing
-{
-    internal class ConditionalTheoryDiscoverer : TheoryDiscoverer
-    {
-        public ConditionalTheoryDiscoverer(IMessageSink diagnosticMessageSink)
-            : base(diagnosticMessageSink)
-        {
-        }
-
-        private sealed class OptionsWithPreEnumerationEnabled : ITestFrameworkDiscoveryOptions
-        {
-            private const string PreEnumerateTheories = "xunit.discovery.PreEnumerateTheories";
-
-            private readonly ITestFrameworkDiscoveryOptions _original;
-
-            public OptionsWithPreEnumerationEnabled(ITestFrameworkDiscoveryOptions original)
-                => _original = original;
-
-            public TValue GetValue<TValue>(string name)
-                => (name == PreEnumerateTheories) ? (TValue)(object)true : _original.GetValue<TValue>(name);
-
-            public void SetValue<TValue>(string name, TValue value)
-                => _original.SetValue(name, value);
-        }
-
-        public override IEnumerable<IXunitTestCase> Discover(ITestFrameworkDiscoveryOptions discoveryOptions, ITestMethod testMethod, IAttributeInfo theoryAttribute)
-            => base.Discover(new OptionsWithPreEnumerationEnabled(discoveryOptions), testMethod, theoryAttribute);
-
-        protected override IEnumerable<IXunitTestCase> CreateTestCasesForTheory(ITestFrameworkDiscoveryOptions discoveryOptions, ITestMethod testMethod, IAttributeInfo theoryAttribute)
-        {
-            var skipReason = testMethod.EvaluateSkipConditions();
-            return skipReason != null
-               ? new[] { new SkippedTestCase(skipReason, DiagnosticMessageSink, discoveryOptions.MethodDisplayOrDefault(), TestMethodDisplayOptions.None, testMethod) }
-               : base.CreateTestCasesForTheory(discoveryOptions, testMethod, theoryAttribute);
-        }
-
-        protected override IEnumerable<IXunitTestCase> CreateTestCasesForDataRow(ITestFrameworkDiscoveryOptions discoveryOptions, ITestMethod testMethod, IAttributeInfo theoryAttribute, object[] dataRow)
-        {
-            var skipReason = testMethod.EvaluateSkipConditions();
-            if (skipReason == null && dataRow?.Length > 0)
-            {
-                var obj = dataRow[0];
-                if (obj != null)
-                {
-                    var type = obj.GetType();
-                    var property = type.GetProperty("Skip");
-                    if (property != null && property.PropertyType.Equals(typeof(string)))
-                    {
-                        skipReason = property.GetValue(obj) as string;
-                    }
-                }
-            }
-
-            return skipReason != null ?
-                base.CreateTestCasesForSkippedDataRow(discoveryOptions, testMethod, theoryAttribute, dataRow, skipReason)
-                : base.CreateTestCasesForDataRow(discoveryOptions, testMethod, theoryAttribute, dataRow);
-        }
-
-        protected override IEnumerable<IXunitTestCase> CreateTestCasesForSkippedDataRow(
-            ITestFrameworkDiscoveryOptions discoveryOptions,
-            ITestMethod testMethod,
-            IAttributeInfo theoryAttribute,
-            object[] dataRow,
-            string skipReason)
-        {
-            return new[]
-            {
-                new WORKAROUND_SkippedDataRowTestCase(DiagnosticMessageSink, discoveryOptions.MethodDisplayOrDefault(), discoveryOptions.MethodDisplayOptionsOrDefault(), testMethod, skipReason, dataRow),
-            };
-        }
-
-        [Obsolete]
-        protected override IXunitTestCase CreateTestCaseForSkippedDataRow(ITestFrameworkDiscoveryOptions discoveryOptions, ITestMethod testMethod, IAttributeInfo theoryAttribute, object[] dataRow, string skipReason)
-        {
-            return new WORKAROUND_SkippedDataRowTestCase(DiagnosticMessageSink, discoveryOptions.MethodDisplayOrDefault(), discoveryOptions.MethodDisplayOptionsOrDefault(), testMethod, skipReason, dataRow);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/DockerOnlyAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/DockerOnlyAttribute.cs
deleted file mode 100644
index 0536a9dc592898..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/DockerOnlyAttribute.cs
+++ /dev/null
@@ -1,38 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.IO;
-using System.Linq;
-using System.Runtime.InteropServices;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [AttributeUsage(AttributeTargets.Method, Inherited = true, AllowMultiple = false)]
-    public sealed class DockerOnlyAttribute : Attribute, ITestCondition
-    {
-        public string SkipReason { get; } = "This test can only run in a Docker container.";
-
-        public bool IsMet
-        {
-            get
-            {
-                if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-                {
-                    // we currently don't have a good way to detect if running in a Windows container
-                    return false;
-                }
-
-                const string procFile = "/proc/1/cgroup";
-                if (!File.Exists(procFile))
-                {
-                    return false;
-                }
-
-                var lines = File.ReadAllLines(procFile);
-                // typically the last line in the file is "1:name=openrc:/docker"
-                return lines.Reverse().Any(l => l.EndsWith("name=openrc:/docker", StringComparison.Ordinal));
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/EnvironmentVariableSkipConditionAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/EnvironmentVariableSkipConditionAttribute.cs
deleted file mode 100644
index b7dbed476b2efb..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/EnvironmentVariableSkipConditionAttribute.cs
+++ /dev/null
@@ -1,95 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Linq;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Skips a test when the value of an environment variable matches any of the supplied values.
-    /// </summary>
-    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class | AttributeTargets.Assembly, AllowMultiple = true)]
-    public class EnvironmentVariableSkipConditionAttribute : Attribute, ITestCondition
-    {
-        private readonly string _variableName;
-        private readonly string[] _values;
-        private string _currentValue;
-        private readonly IEnvironmentVariable _environmentVariable;
-
-        /// <summary>
-        /// Creates a new instance of <see cref="EnvironmentVariableSkipConditionAttribute"/>.
-        /// </summary>
-        /// <param name="variableName">Name of the environment variable.</param>
-        /// <param name="values">Value(s) of the environment variable to match for the test to be skipped</param>
-        public EnvironmentVariableSkipConditionAttribute(string variableName, params string[] values)
-            : this(new EnvironmentVariable(), variableName, values)
-        {
-        }
-
-        // To enable unit testing
-        internal EnvironmentVariableSkipConditionAttribute(
-            IEnvironmentVariable environmentVariable,
-            string variableName,
-            params string[] values)
-        {
-            if (environmentVariable == null)
-            {
-                throw new ArgumentNullException(nameof(environmentVariable));
-            }
-            if (variableName == null)
-            {
-                throw new ArgumentNullException(nameof(variableName));
-            }
-            if (values == null)
-            {
-                throw new ArgumentNullException(nameof(values));
-            }
-
-            _variableName = variableName;
-            _values = values;
-            _environmentVariable = environmentVariable;
-        }
-
-        /// <summary>
-        /// Runs the test only if the value of the variable matches any of the supplied values. Default is <c>True</c>.
-        /// </summary>
-        public bool RunOnMatch { get; set; } = true;
-
-        public bool IsMet
-        {
-            get
-            {
-                _currentValue = _environmentVariable.Get(_variableName);
-                var hasMatched = _values.Any(value => string.Compare(value, _currentValue, ignoreCase: true) == 0);
-
-                if (RunOnMatch)
-                {
-                    return hasMatched;
-                }
-                else
-                {
-                    return !hasMatched;
-                }
-            }
-        }
-
-        public string SkipReason
-        {
-            get
-            {
-                var value = _currentValue == null ? "(null)" : _currentValue;
-                return $"Test skipped on environment variable with name '{_variableName}' and value '{value}' " +
-                    $"for the '{nameof(RunOnMatch)}' value of '{RunOnMatch}'.";
-            }
-        }
-
-        private struct EnvironmentVariable : IEnvironmentVariable
-        {
-            public string Get(string name)
-            {
-                return Environment.GetEnvironmentVariable(name);
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/FlakyAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/FlakyAttribute.cs
deleted file mode 100644
index a08dac81b1257c..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/FlakyAttribute.cs
+++ /dev/null
@@ -1,95 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Marks a test as "Flaky" so that the build will sequester it and ignore failures.
-    /// </summary>
-    /// <remarks>
-    /// <para>
-    /// This attribute works by applying xUnit.net "Traits" based on the criteria specified in the attribute
-    /// properties. Once these traits are applied, build scripts can include/exclude tests based on them.
-    /// </para>
-    /// <para>
-    /// All flakiness-related traits start with <c>Flaky:</c> and are grouped first by the process running the tests: Azure Pipelines (AzP) or Helix.
-    /// Then there is a segment specifying the "selector" which indicates where the test is flaky. Finally a segment specifying the value of that selector.
-    /// The value of these traits is always either "true" or the trait is not present. We encode the entire selector in the name of the trait because xUnit.net only
-    /// provides "==" and "!=" operators for traits, there is no way to check if a trait "contains" or "does not contain" a value. VSTest does support "contains" checks
-    /// but does not appear to support "does not contain" checks. Using this pattern means we can use simple "==" and "!=" checks to either only run flaky tests, or exclude
-    /// flaky tests.
-    /// </para>
-    /// </remarks>
-    /// <example>
-    /// <code>
-    /// [Fact]
-    /// [Flaky("...", HelixQueues.Fedora28Amd64, AzurePipelines.macOS)]
-    /// public void FlakyTest()
-    /// {
-    ///     // Flakiness
-    /// }
-    /// </code>
-    ///
-    /// <para>
-    /// The above example generates the following facets:
-    /// </para>
-    ///
-    /// <list type="bullet">
-    /// <item>
-    ///     <description><c>Flaky:Helix:Queue:Fedora.28.Amd64.Open</c> = <c>true</c></description>
-    /// </item>
-    /// <item>
-    ///     <description><c>Flaky:AzP:OS:Darwin</c> = <c>true</c></description>
-    /// </item>
-    /// </list>
-    ///
-    /// <para>
-    /// Given the above attribute, the Azure Pipelines macOS run can easily filter this test out by passing <c>-notrait "Flaky:AzP:OS:all=true" -notrait "Flaky:AzP:OS:Darwin=true"</c>
-    /// to <c>xunit.console.exe</c>. Similarly, it can run only flaky tests using <c>-trait "Flaky:AzP:OS:all=true" -trait "Flaky:AzP:OS:Darwin=true"</c>
-    /// </para>
-    /// </example>
-    [TraitDiscoverer("Microsoft.AspNetCore.Testing." + nameof(FlakyTraitDiscoverer), "Microsoft.AspNetCore.Testing")]
-    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class | AttributeTargets.Assembly)]
-    public sealed class FlakyAttribute : Attribute, ITraitAttribute
-    {
-        /// <summary>
-        /// Gets a URL to a GitHub issue tracking this flaky test.
-        /// </summary>
-        public string GitHubIssueUrl { get; }
-
-        public IReadOnlyList<string> Filters { get; }
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="FlakyAttribute"/> class with the specified <see cref="GitHubIssueUrl"/> and a list of <see cref="Filters"/>. If no
-        /// filters are provided, the test is considered flaky in all environments.
-        /// </summary>
-        /// <remarks>
-        /// At least one filter is required.
-        /// </remarks>
-        /// <param name="gitHubIssueUrl">The URL to a GitHub issue tracking this flaky test.</param>
-        /// <param name="firstFilter">The first filter that indicates where the test is flaky. Use a value from <see cref="FlakyOn"/>.</param>
-        /// <param name="additionalFilters">A list of additional filters that define where this test is flaky. Use values in <see cref="FlakyOn"/>.</param>
-        public FlakyAttribute(string gitHubIssueUrl, string firstFilter, params string[] additionalFilters)
-        {
-            if (string.IsNullOrEmpty(gitHubIssueUrl))
-            {
-                throw new ArgumentNullException(nameof(gitHubIssueUrl));
-            }
-
-            if (string.IsNullOrEmpty(firstFilter))
-            {
-                throw new ArgumentNullException(nameof(firstFilter));
-            }
-
-            GitHubIssueUrl = gitHubIssueUrl;
-            var filters = new List<string>();
-            filters.Add(firstFilter);
-            filters.AddRange(additionalFilters);
-            Filters = filters;
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/FlakyTraitDiscoverer.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/FlakyTraitDiscoverer.cs
deleted file mode 100644
index 1964f20ddae2b6..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/FlakyTraitDiscoverer.cs
+++ /dev/null
@@ -1,41 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-// Do not change this namespace without changing the usage in FlakyAttribute
-namespace Microsoft.AspNetCore.Testing
-{
-    public class FlakyTraitDiscoverer : ITraitDiscoverer
-    {
-        public IEnumerable<KeyValuePair<string, string>> GetTraits(IAttributeInfo traitAttribute)
-        {
-            if (traitAttribute is ReflectionAttributeInfo attribute && attribute.Attribute is FlakyAttribute flakyAttribute)
-            {
-                return GetTraitsCore(flakyAttribute);
-            }
-            else
-            {
-                throw new InvalidOperationException("The 'Flaky' attribute is only supported via reflection.");
-            }
-        }
-
-        private IEnumerable<KeyValuePair<string, string>> GetTraitsCore(FlakyAttribute attribute)
-        {
-            if (attribute.Filters.Count > 0)
-            {
-                foreach (var filter in attribute.Filters)
-                {
-                    yield return new KeyValuePair<string, string>($"Flaky:{filter}", "true");
-                }
-            }
-            else
-            {
-                yield return new KeyValuePair<string, string>($"Flaky:All", "true");
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/FrameworkSkipConditionAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/FrameworkSkipConditionAttribute.cs
deleted file mode 100644
index 906f0c4d4604cc..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/FrameworkSkipConditionAttribute.cs
+++ /dev/null
@@ -1,57 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
-    public class FrameworkSkipConditionAttribute : Attribute, ITestCondition
-    {
-        private readonly RuntimeFrameworks _excludedFrameworks;
-
-        public FrameworkSkipConditionAttribute(RuntimeFrameworks excludedFrameworks)
-        {
-            _excludedFrameworks = excludedFrameworks;
-        }
-
-        public bool IsMet
-        {
-            get
-            {
-                return CanRunOnThisFramework(_excludedFrameworks);
-            }
-        }
-
-        public string SkipReason { get; set; } = "Test cannot run on this runtime framework.";
-
-        private static bool CanRunOnThisFramework(RuntimeFrameworks excludedFrameworks)
-        {
-            if (excludedFrameworks == RuntimeFrameworks.None)
-            {
-                return true;
-            }
-
-#if NETFRAMEWORK
-            if (excludedFrameworks.HasFlag(RuntimeFrameworks.Mono) &&
-                TestPlatformHelper.IsMono)
-            {
-                return false;
-            }
-
-            if (excludedFrameworks.HasFlag(RuntimeFrameworks.CLR))
-            {
-                return false;
-            }
-#elif NETSTANDARD2_0 || NETCOREAPP
-            if (excludedFrameworks.HasFlag(RuntimeFrameworks.CoreCLR))
-            {
-                return false;
-            }
-#else
-#error Target frameworks need to be updated.
-#endif
-            return true;
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ITestCondition.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ITestCondition.cs
deleted file mode 100644
index d15a78a4888288..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/ITestCondition.cs
+++ /dev/null
@@ -1,12 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public interface ITestCondition
-    {
-        bool IsMet { get; }
-
-        string SkipReason { get; }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/MaximumOSVersionAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/MaximumOSVersionAttribute.cs
deleted file mode 100644
index 29b89212d3a6ee..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/MaximumOSVersionAttribute.cs
+++ /dev/null
@@ -1,83 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Runtime.InteropServices;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Skips a test if the OS is the given type (Windows) and the OS version is greater than specified.
-    /// E.g. Specifying Window 8 skips on Win 10, but not on Linux. Combine with OSSkipConditionAttribute as needed.
-    /// </summary>
-    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class | AttributeTargets.Assembly, AllowMultiple = true)]
-    public class MaximumOSVersionAttribute : Attribute, ITestCondition
-    {
-        private readonly OperatingSystems _targetOS;
-        private readonly Version _maxVersion;
-        private readonly OperatingSystems _currentOS;
-        private readonly Version _currentVersion;
-        private readonly bool _skip;
-
-        public MaximumOSVersionAttribute(OperatingSystems operatingSystem, string maxVersion) :
-            this(operatingSystem, Version.Parse(maxVersion), GetCurrentOS(), GetCurrentOSVersion())
-        {
-        }
-
-        // to enable unit testing
-        internal MaximumOSVersionAttribute(OperatingSystems targetOS, Version maxVersion, OperatingSystems currentOS, Version currentVersion)
-        {
-            if (targetOS != OperatingSystems.Windows)
-            {
-                throw new NotImplementedException("Max version support is only implemented for Windows.");
-            }
-            _targetOS = targetOS;
-            _maxVersion = maxVersion;
-            _currentOS = currentOS;
-            // We drop the 4th field because it is not significant and it messes up the comparisons.
-            _currentVersion = new Version(currentVersion.Major, currentVersion.Minor,
-                // Major and Minor are required by the parser, but if Build isn't specified then it returns -1
-                // which the constructor rejects.
-                currentVersion.Build == -1 ? 0 : currentVersion.Build);
-
-            // Do not skip other OS's, Use OSSkipConditionAttribute or a separate MaximumOsVersionAttribute for that.
-            _skip = _targetOS == _currentOS && _maxVersion < _currentVersion;
-            SkipReason = $"This test requires {_targetOS} {_maxVersion} or earlier.";
-        }
-
-        // Since a test would be executed only if 'IsMet' is true, return false if we want to skip
-        public bool IsMet => !_skip;
-
-        public string SkipReason { get; set; }
-
-        private static OperatingSystems GetCurrentOS()
-        {
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-            {
-                return OperatingSystems.Windows;
-            }
-            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
-            {
-                return OperatingSystems.Linux;
-            }
-            else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
-            {
-                return OperatingSystems.MacOSX;
-            }
-            throw new PlatformNotSupportedException();
-        }
-
-        static private Version GetCurrentOSVersion()
-        {
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-            {
-                return Environment.OSVersion.Version;
-            }
-            else
-            {
-                // Not implemented, but this will still be called before the OS check happens so don't throw.
-                return new Version(0, 0);
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/MinimumOsVersionAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/MinimumOsVersionAttribute.cs
deleted file mode 100644
index bf37323fe45376..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/MinimumOsVersionAttribute.cs
+++ /dev/null
@@ -1,79 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Runtime.InteropServices;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Skips a test if the OS is the given type (Windows) and the OS version is less than specified.
-    /// E.g. Specifying Window 10.0 skips on Win 8, but not on Linux. Combine with OSSkipConditionAttribute as needed.
-    /// </summary>
-    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class | AttributeTargets.Assembly, AllowMultiple = true)]
-    public class MinimumOSVersionAttribute : Attribute, ITestCondition
-    {
-        private readonly OperatingSystems _targetOS;
-        private readonly Version _minVersion;
-        private readonly OperatingSystems _currentOS;
-        private readonly Version _currentVersion;
-        private readonly bool _skip;
-
-        public MinimumOSVersionAttribute(OperatingSystems operatingSystem, string minVersion) :
-            this(operatingSystem, Version.Parse(minVersion), GetCurrentOS(), GetCurrentOSVersion())
-        {
-        }
-
-        // to enable unit testing
-        internal MinimumOSVersionAttribute(OperatingSystems targetOS, Version minVersion, OperatingSystems currentOS, Version currentVersion)
-        {
-            if (targetOS != OperatingSystems.Windows)
-            {
-                throw new NotImplementedException("Min version support is only implemented for Windows.");
-            }
-            _targetOS = targetOS;
-            _minVersion = minVersion;
-            _currentOS = currentOS;
-            _currentVersion = currentVersion;
-
-            // Do not skip other OS's, Use OSSkipConditionAttribute or a separate MinimumOSVersionAttribute for that.
-            _skip = _targetOS == _currentOS && _minVersion > _currentVersion;
-            SkipReason = $"This test requires {_targetOS} {_minVersion} or later.";
-        }
-
-        // Since a test would be executed only if 'IsMet' is true, return false if we want to skip
-        public bool IsMet => !_skip;
-
-        public string SkipReason { get; set; }
-
-        private static OperatingSystems GetCurrentOS()
-        {
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-            {
-                return OperatingSystems.Windows;
-            }
-            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
-            {
-                return OperatingSystems.Linux;
-            }
-            else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
-            {
-                return OperatingSystems.MacOSX;
-            }
-            throw new PlatformNotSupportedException();
-        }
-
-        static private Version GetCurrentOSVersion()
-        {
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-            {
-                return Environment.OSVersion.Version;
-            }
-            else
-            {
-                // Not implemented, but this will still be called before the OS check happens so don't throw.
-                return new Version(0, 0);
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/OSSkipConditionAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/OSSkipConditionAttribute.cs
deleted file mode 100644
index 2a804e309865ce..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/OSSkipConditionAttribute.cs
+++ /dev/null
@@ -1,62 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Runtime.InteropServices;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class | AttributeTargets.Assembly, AllowMultiple = true)]
-    public class OSSkipConditionAttribute : Attribute, ITestCondition
-    {
-        private readonly OperatingSystems _excludedOperatingSystem;
-        private readonly OperatingSystems _osPlatform;
-
-        public OSSkipConditionAttribute(OperatingSystems operatingSystem) :
-            this(operatingSystem, GetCurrentOS())
-        {
-        }
-
-        [Obsolete("Use the Minimum/MaximumOSVersionAttribute for version checks.", error: true)]
-        public OSSkipConditionAttribute(OperatingSystems operatingSystem,  params string[] versions) :
-            this(operatingSystem, GetCurrentOS())
-        {
-        }
-
-        // to enable unit testing
-        internal OSSkipConditionAttribute(OperatingSystems operatingSystem, OperatingSystems osPlatform)
-        {
-            _excludedOperatingSystem = operatingSystem;
-            _osPlatform = osPlatform;
-        }
-
-        public bool IsMet
-        {
-            get
-            {
-                var skip = (_excludedOperatingSystem & _osPlatform) == _osPlatform;
-                // Since a test would be excuted only if 'IsMet' is true, return false if we want to skip
-                return !skip;
-            }
-        }
-
-        public string SkipReason { get; set; } = "Test cannot run on this operating system.";
-
-        static private OperatingSystems GetCurrentOS()
-        {
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-            {
-                return OperatingSystems.Windows;
-            }
-            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
-            {
-                return OperatingSystems.Linux;
-            }
-            else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
-            {
-                return OperatingSystems.MacOSX;
-            }
-            throw new PlatformNotSupportedException();
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/OperatingSystems.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/OperatingSystems.cs
deleted file mode 100644
index 7f04934ba65f8f..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/OperatingSystems.cs
+++ /dev/null
@@ -1,15 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [Flags]
-    public enum OperatingSystems
-    {
-        Linux = 1,
-        MacOSX = 2,
-        Windows = 4,
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/RuntimeFrameworks.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/RuntimeFrameworks.cs
deleted file mode 100644
index 274ea135735044..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/RuntimeFrameworks.cs
+++ /dev/null
@@ -1,16 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [Flags]
-    public enum RuntimeFrameworks
-    {
-        None = 0,
-        Mono = 1 << 0,
-        CLR = 1 << 1,
-        CoreCLR = 1 << 2
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/SkipOnCIAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/SkipOnCIAttribute.cs
deleted file mode 100644
index c89001ee9f9931..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/SkipOnCIAttribute.cs
+++ /dev/null
@@ -1,43 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Skip test if running on CI
-    /// </summary>
-    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, AllowMultiple = false)]
-    public class SkipOnCIAttribute : Attribute, ITestCondition
-    {
-        public SkipOnCIAttribute(string issueUrl = "")
-        {
-            IssueUrl = issueUrl;
-        }
-
-        public string IssueUrl { get; }
-
-        public bool IsMet
-        {
-            get
-            {
-                return !OnCI();
-            }
-        }
-
-        public string SkipReason
-        {
-            get
-            {
-                return $"This test is skipped on CI";
-            }
-        }
-
-        public static bool OnCI() => OnHelix() || OnAzdo();
-        public static bool OnHelix() => !string.IsNullOrEmpty(GetTargetHelixQueue());
-        public static string GetTargetHelixQueue() => Environment.GetEnvironmentVariable("helix");
-        public static bool OnAzdo() => !string.IsNullOrEmpty(GetIfOnAzdo());
-        public static string GetIfOnAzdo() => Environment.GetEnvironmentVariable("AGENT_OS");
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/SkipOnHelixAttribute.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/SkipOnHelixAttribute.cs
deleted file mode 100644
index f0aa92be054c56..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/SkipOnHelixAttribute.cs
+++ /dev/null
@@ -1,50 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Linq;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// Skip test if running on helix (or a particular helix queue).
-    /// </summary>
-    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, AllowMultiple = false)]
-    public class SkipOnHelixAttribute : Attribute, ITestCondition
-    {
-        public SkipOnHelixAttribute(string issueUrl)
-        {
-            if (string.IsNullOrEmpty(issueUrl))
-            {
-                throw new ArgumentException();
-            }
-            IssueUrl = issueUrl;
-        }
-
-        public string IssueUrl { get; }
-
-        public bool IsMet
-        {
-            get
-            {
-                var skip = OnHelix() && (Queues == null || Queues.ToLowerInvariant().Split(';').Contains(GetTargetHelixQueue().ToLowerInvariant()));
-                return !skip;
-            }
-        }
-
-        // Queues that should be skipped on, i.e. "Windows.10.Amd64.ClientRS4.VS2017.Open;OSX.1012.Amd64.Open"
-        public string Queues { get; set; }
-
-        public string SkipReason
-        {
-            get
-            {
-                return $"This test is skipped on helix";
-            }
-        }
-
-        public static bool OnHelix() => !string.IsNullOrEmpty(GetTargetHelixQueue());
-
-        public static string GetTargetHelixQueue() => Environment.GetEnvironmentVariable("helix");
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/SkippedTestCase.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/SkippedTestCase.cs
deleted file mode 100644
index 890bb35b967a58..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/SkippedTestCase.cs
+++ /dev/null
@@ -1,51 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class SkippedTestCase : XunitTestCase
-    {
-        private string _skipReason;
-
-        [Obsolete("Called by the de-serializer; should only be called by deriving classes for de-serialization purposes")]
-        public SkippedTestCase() : base()
-        {
-        }
-
-        public SkippedTestCase(
-            string skipReason,
-            IMessageSink diagnosticMessageSink,
-            TestMethodDisplay defaultMethodDisplay,
-            TestMethodDisplayOptions defaultMethodDisplayOptions,
-            ITestMethod testMethod,
-            object[] testMethodArguments = null)
-            : base(diagnosticMessageSink, defaultMethodDisplay, defaultMethodDisplayOptions, testMethod, testMethodArguments)
-        {
-            _skipReason = skipReason;
-        }
-
-        protected override string GetSkipReason(IAttributeInfo factAttribute)
-            => _skipReason ?? base.GetSkipReason(factAttribute);
-
-        public override void Deserialize(IXunitSerializationInfo data)
-        {
-            _skipReason = data.GetValue<string>(nameof(_skipReason));
-
-            // We need to call base after reading our value, because Deserialize will call
-            // into GetSkipReason.
-            base.Deserialize(data);
-        }
-
-        public override void Serialize(IXunitSerializationInfo data)
-        {
-            base.Serialize(data);
-            data.AddValue(nameof(_skipReason), _skipReason);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/TestMethodExtensions.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/TestMethodExtensions.cs
deleted file mode 100644
index 36b29195cb8bc7..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/TestMethodExtensions.cs
+++ /dev/null
@@ -1,34 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Linq;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public static class TestMethodExtensions
-    {
-        public static string EvaluateSkipConditions(this ITestMethod testMethod)
-        {
-            var testClass = testMethod.TestClass.Class;
-            var assembly = testMethod.TestClass.TestCollection.TestAssembly.Assembly;
-            var conditionAttributes = testMethod.Method
-                .GetCustomAttributes(typeof(ITestCondition))
-                .Concat(testClass.GetCustomAttributes(typeof(ITestCondition)))
-                .Concat(assembly.GetCustomAttributes(typeof(ITestCondition)))
-                .OfType<ReflectionAttributeInfo>()
-                .Select(attributeInfo => attributeInfo.Attribute);
-
-            foreach (ITestCondition condition in conditionAttributes)
-            {
-                if (!condition.IsMet)
-                {
-                    return condition.SkipReason;
-                }
-            }
-
-            return null;
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/WORKAROUND_SkippedDataRowTestCase.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/WORKAROUND_SkippedDataRowTestCase.cs
deleted file mode 100644
index 22dea010c21546..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/WORKAROUND_SkippedDataRowTestCase.cs
+++ /dev/null
@@ -1,83 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.ComponentModel;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    // This is a workaround for https://github.com/xunit/xunit/issues/1782 - as such, this code is a copy-paste
-    // from xUnit with the exception of fixing the bug.
-    //
-    // This will only work with [ConditionalTheory].
-    internal class WORKAROUND_SkippedDataRowTestCase : XunitTestCase
-    {
-        string skipReason;
-
-        /// <summary/>
-        [EditorBrowsable(EditorBrowsableState.Never)]
-        [Obsolete("Called by the de-serializer; should only be called by deriving classes for de-serialization purposes")]
-        public WORKAROUND_SkippedDataRowTestCase() { }
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="XunitSkippedDataRowTestCase"/> class.
-        /// </summary>
-        /// <param name="diagnosticMessageSink">The message sink used to send diagnostic messages</param>
-        /// <param name="defaultMethodDisplay">Default method display to use (when not customized).</param>
-        /// <param name="testMethod">The test method this test case belongs to.</param>
-        /// <param name="skipReason">The reason that this test case will be skipped</param>
-        /// <param name="testMethodArguments">The arguments for the test method.</param>
-        [Obsolete("Please call the constructor which takes TestMethodDisplayOptions")]
-        public WORKAROUND_SkippedDataRowTestCase(IMessageSink diagnosticMessageSink,
-                                           TestMethodDisplay defaultMethodDisplay,
-                                           ITestMethod testMethod,
-                                           string skipReason,
-                                           object[] testMethodArguments = null)
-            : this(diagnosticMessageSink, defaultMethodDisplay, TestMethodDisplayOptions.None, testMethod, skipReason, testMethodArguments) { }
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="XunitSkippedDataRowTestCase"/> class.
-        /// </summary>
-        /// <param name="diagnosticMessageSink">The message sink used to send diagnostic messages</param>
-        /// <param name="defaultMethodDisplay">Default method display to use (when not customized).</param>
-        /// <param name="defaultMethodDisplayOptions">Default method display options to use (when not customized).</param>
-        /// <param name="testMethod">The test method this test case belongs to.</param>
-        /// <param name="skipReason">The reason that this test case will be skipped</param>
-        /// <param name="testMethodArguments">The arguments for the test method.</param>
-        public WORKAROUND_SkippedDataRowTestCase(IMessageSink diagnosticMessageSink,
-                                           TestMethodDisplay defaultMethodDisplay,
-                                           TestMethodDisplayOptions defaultMethodDisplayOptions,
-                                           ITestMethod testMethod,
-                                           string skipReason,
-                                           object[] testMethodArguments = null)
-            : base(diagnosticMessageSink, defaultMethodDisplay, defaultMethodDisplayOptions, testMethod, testMethodArguments)
-        {
-            this.skipReason = skipReason;
-        }
-
-        /// <inheritdoc/>
-        public override void Deserialize(IXunitSerializationInfo data)
-        {
-            // SkipReason has to be read before we call base.Deserialize, this is the workaround.
-            this.skipReason = data.GetValue<string>("SkipReason");
-
-            base.Deserialize(data);
-        }
-
-        /// <inheritdoc/>
-        protected override string GetSkipReason(IAttributeInfo factAttribute)
-        {
-            return skipReason;
-        }
-
-        /// <inheritdoc/>
-        public override void Serialize(IXunitSerializationInfo data)
-        {
-            base.Serialize(data);
-
-            data.AddValue("SkipReason", skipReason);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/WindowsVersions.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/WindowsVersions.cs
deleted file mode 100644
index 09390468985051..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/WindowsVersions.cs
+++ /dev/null
@@ -1,49 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    /// <summary>
-    /// https://en.wikipedia.org/wiki/Windows_10_version_history
-    /// </summary>
-    public static class WindowsVersions
-    {
-        public const string Win7 = "6.1";
-
-        [Obsolete("Use Win7 instead.", error: true)]
-        public const string Win2008R2 = Win7;
-
-        public const string Win8 = "6.2";
-
-        public const string Win81 = "6.3";
-
-        public const string Win10 = "10.0";
-
-        /// <summary>
-        /// 1803, RS4, 17134
-        /// </summary>
-        public const string Win10_RS4 = "10.0.17134";
-
-        /// <summary>
-        /// 1809, RS5, 17763
-        /// </summary>
-        public const string Win10_RS5 = "10.0.17763";
-
-        /// <summary>
-        /// 1903, 19H1, 18362
-        /// </summary>
-        public const string Win10_19H1 = "10.0.18362";
-
-        /// <summary>
-        /// 1909, 19H2, 18363
-        /// </summary>
-        public const string Win10_19H2 = "10.0.18363";
-
-        /// <summary>
-        /// 2004, 20H1, 19033
-        /// </summary>
-        public const string Win10_20H1 = "10.0.19033";
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/AlphabeticalOrderer.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/AlphabeticalOrderer.cs
deleted file mode 100644
index 34eef71dffab0e..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/AlphabeticalOrderer.cs
+++ /dev/null
@@ -1,22 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using Xunit.Abstractions;
-using Xunit.Sdk;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class AlphabeticalOrderer : ITestCaseOrderer
-    {
-        public IEnumerable<TTestCase> OrderTestCases<TTestCase>(IEnumerable<TTestCase> testCases)
-                where TTestCase : ITestCase
-        {
-            var result = testCases.ToList();
-            result.Sort((x, y) => StringComparer.OrdinalIgnoreCase.Compare(x.TestMethod.Method.Name, y.TestMethod.Method.Name));
-            return result;
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/AssemblyFixtureTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/AssemblyFixtureTest.cs
deleted file mode 100644
index 15673ce896344c..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/AssemblyFixtureTest.cs
+++ /dev/null
@@ -1,47 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    // We include a collection and assembly fixture to verify that they both still work.
-    [Collection("MyCollection")]
-    [TestCaseOrderer("Microsoft.AspNetCore.Testing.AlphabeticalOrderer", "Microsoft.AspNetCore.Testing.Tests")]
-    public class AssemblyFixtureTest
-    {
-        public AssemblyFixtureTest(TestAssemblyFixture assemblyFixture, TestCollectionFixture collectionFixture)
-        {
-            AssemblyFixture = assemblyFixture;
-            CollectionFixture = collectionFixture;
-        }
-
-        public TestAssemblyFixture AssemblyFixture { get; }
-        public TestCollectionFixture CollectionFixture { get; }
-
-        [Fact]
-        public void A()
-        {
-            Assert.NotNull(AssemblyFixture);
-            Assert.Equal(0, AssemblyFixture.Count);
-
-            Assert.NotNull(CollectionFixture);
-            Assert.Equal(0, CollectionFixture.Count);
-
-            AssemblyFixture.Count++;
-            CollectionFixture.Count++;
-        }
-
-        [Fact]
-        public void B()
-        {
-            Assert.Equal(1, AssemblyFixture.Count);
-            Assert.Equal(1, CollectionFixture.Count);
-        }
-    }
-
-    [CollectionDefinition("MyCollection", DisableParallelization = true)]
-    public class MyCollection : ICollectionFixture<TestCollectionFixture>
-    {
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/CollectingEventListenerTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/CollectingEventListenerTest.cs
deleted file mode 100644
index 466a14ecdd1497..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/CollectingEventListenerTest.cs
+++ /dev/null
@@ -1,90 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Diagnostics.Tracing;
-using System.Threading.Tasks;
-using Microsoft.AspNetCore.Testing.Tracing;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing.Tests
-{
-    // We are verifying here that when event listener tests are spread among multiple classes, they still
-    // work, even when run in parallel. To do that we have a bunch of tests in different classes (since
-    // that affects parallelism) and do some Task.Yielding in them.
-    public class CollectingEventListenerTests
-    {
-        public abstract class CollectingTestBase : EventSourceTestBase
-        {
-            [Fact]
-            public async Task CollectingEventListenerTest()
-            {
-                CollectFrom("Microsoft-AspNetCore-Testing-Test");
-
-                await Task.Yield();
-                TestEventSource.Log.Test();
-                await Task.Yield();
-                TestEventSource.Log.TestWithPayload(42, 4.2);
-                await Task.Yield();
-
-                var events = GetEvents();
-                EventAssert.Collection(events,
-                    EventAssert.Event(1, "Test", EventLevel.Informational),
-                    EventAssert.Event(2, "TestWithPayload", EventLevel.Verbose)
-                        .Payload("payload1", 42)
-                        .Payload("payload2", 4.2));
-            }
-        }
-
-        // These tests are designed to interfere with the collecting ones by running in parallel and writing events
-        public abstract class NonCollectingTestBase
-        {
-            [Fact]
-            public async Task CollectingEventListenerTest()
-            {
-                await Task.Yield();
-                TestEventSource.Log.Test();
-                await Task.Yield();
-                TestEventSource.Log.TestWithPayload(42, 4.2);
-                await Task.Yield();
-            }
-        }
-
-        public class CollectingTests
-        {
-            public class A : CollectingTestBase { }
-            public class B : CollectingTestBase { }
-            public class C : CollectingTestBase { }
-            public class D : CollectingTestBase { }
-            public class E : CollectingTestBase { }
-            public class F : CollectingTestBase { }
-            public class G : CollectingTestBase { }
-        }
-
-        public class NonCollectingTests
-        {
-            public class A : NonCollectingTestBase { }
-            public class B : NonCollectingTestBase { }
-            public class C : NonCollectingTestBase { }
-            public class D : NonCollectingTestBase { }
-            public class E : NonCollectingTestBase { }
-            public class F : NonCollectingTestBase { }
-            public class G : NonCollectingTestBase { }
-        }
-    }
-
-    [EventSource(Name = "Microsoft-AspNetCore-Testing-Test")]
-    public class TestEventSource : EventSource
-    {
-        public static readonly TestEventSource Log = new TestEventSource();
-
-        private TestEventSource()
-        {
-        }
-
-        [Event(eventId: 1, Level = EventLevel.Informational, Message = "Test")]
-        public void Test() => WriteEvent(1);
-
-        [Event(eventId: 2, Level = EventLevel.Verbose, Message = "Test")]
-        public void TestWithPayload(int payload1, double payload2) => WriteEvent(2, payload1, payload2);
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ConditionalFactTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ConditionalFactTest.cs
deleted file mode 100644
index da0f988066e429..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ConditionalFactTest.cs
+++ /dev/null
@@ -1,66 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [TestCaseOrderer("Microsoft.AspNetCore.Testing.AlphabeticalOrderer", "Microsoft.AspNetCore.Testing.Tests")]
-    public class ConditionalFactTest : IClassFixture<ConditionalFactTest.ConditionalFactAsserter>
-    {
-        public ConditionalFactTest(ConditionalFactAsserter collector)
-        {
-            Asserter = collector;
-        }
-
-        private ConditionalFactAsserter Asserter { get; }
-
-        [Fact]
-        public void TestAlwaysRun()
-        {
-            // This is required to ensure that the type at least gets initialized.
-            Assert.True(true);
-        }
-
-        [ConditionalFact(Skip = "Test is always skipped.")]
-        public void ConditionalFactSkip()
-        {
-            Assert.True(false, "This test should always be skipped.");
-        }
-
-#if NETCOREAPP
-        [ConditionalFact]
-        [FrameworkSkipCondition(RuntimeFrameworks.CLR)]
-        public void ThisTestMustRunOnCoreCLR()
-        {
-            Asserter.TestRan = true;
-        }
-#elif NET472
-        [ConditionalFact]
-        [FrameworkSkipCondition(RuntimeFrameworks.CoreCLR)]
-        public void ThisTestMustRunOnCLR()
-        {
-            Asserter.TestRan = true;
-        }
-#else
-#error Target frameworks need to be updated.
-#endif
-
-        // Test is named this way to be the lowest test in the alphabet, it relies on test ordering
-        [Fact]
-        public void ZzzzzzzEnsureThisIsTheLastTest()
-        {
-            Assert.True(Asserter.TestRan);
-        }
-
-        public class ConditionalFactAsserter : IDisposable
-        {
-            public bool TestRan { get; set; }
-
-            public void Dispose()
-            {
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ConditionalTheoryTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ConditionalTheoryTest.cs
deleted file mode 100644
index a5fbb8ecc31778..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ConditionalTheoryTest.cs
+++ /dev/null
@@ -1,162 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using Xunit;
-using Xunit.Abstractions;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [TestCaseOrderer("Microsoft.AspNetCore.Testing.AlphabeticalOrderer", "Microsoft.AspNetCore.Testing.Tests")]
-    public class ConditionalTheoryTest : IClassFixture<ConditionalTheoryTest.ConditionalTheoryAsserter>
-    {
-        public ConditionalTheoryTest(ConditionalTheoryAsserter asserter)
-        {
-            Asserter = asserter;
-        }
-
-        public ConditionalTheoryAsserter Asserter { get; }
-
-        [ConditionalTheory(Skip = "Test is always skipped.")]
-        [InlineData(0)]
-        public void ConditionalTheorySkip(int arg)
-        {
-            Assert.True(false, "This test should always be skipped.");
-        }
-
-        private static int _conditionalTheoryRuns = 0;
-
-        [ConditionalTheory]
-        [InlineData(0)]
-        [InlineData(1)]
-        [InlineData(2, Skip = "Skip these data")]
-        public void ConditionalTheoryRunOncePerDataLine(int arg)
-        {
-            _conditionalTheoryRuns++;
-            Assert.True(_conditionalTheoryRuns <= 2, $"Theory should run 2 times, but ran {_conditionalTheoryRuns} times.");
-        }
-
-        [ConditionalTheory, Trait("Color", "Blue")]
-        [InlineData(1)]
-        public void ConditionalTheoriesShouldPreserveTraits(int arg)
-        {
-            Assert.True(true);
-        }
-
-        [ConditionalTheory(Skip = "Skip this")]
-        [MemberData(nameof(GetInts))]
-        public void ConditionalTheoriesWithSkippedMemberData(int arg)
-        {
-            Assert.True(false, "This should never run");
-        }
-
-        private static int _conditionalMemberDataRuns = 0;
-
-        [ConditionalTheory]
-        [InlineData(4)]
-        [MemberData(nameof(GetInts))]
-        public void ConditionalTheoriesWithMemberData(int arg)
-        {
-            _conditionalMemberDataRuns++;
-            Assert.True(_conditionalTheoryRuns <= 3, $"Theory should run 2 times, but ran {_conditionalMemberDataRuns} times.");
-        }
-
-        public static TheoryData<int> GetInts
-            => new TheoryData<int> { 0, 1 };
-
-        [ConditionalTheory]
-        [OSSkipCondition(OperatingSystems.Windows)]
-        [OSSkipCondition(OperatingSystems.MacOSX)]
-        [OSSkipCondition(OperatingSystems.Linux)]
-        [MemberData(nameof(GetActionTestData))]
-        public void ConditionalTheoryWithFuncs(Func<int, int> func)
-        {
-            Assert.True(false, "This should never run");
-        }
-
-        [Fact]
-        public void TestAlwaysRun()
-        {
-            // This is required to ensure that this type at least gets initialized.
-            Assert.True(true);
-        }
-
-#if NETCOREAPP
-        [ConditionalTheory]
-        [FrameworkSkipCondition(RuntimeFrameworks.CLR)]
-        [MemberData(nameof(GetInts))]
-        public void ThisTestMustRunOnCoreCLR(int value)
-        {
-            Asserter.TestRan = true;
-        }
-#elif NET472
-        [ConditionalTheory]
-        [FrameworkSkipCondition(RuntimeFrameworks.CoreCLR)]
-        [MemberData(nameof(GetInts))]
-        public void ThisTestMustRunOnCLR(int value)
-        {
-            Asserter.TestRan = true;
-        }
-#else
-#error Target frameworks need to be updated.
-#endif
-
-        // Test is named this way to be the lowest test in the alphabet, it relies on test ordering
-        [Fact]
-        public void ZzzzzzzEnsureThisIsTheLastTest()
-        {
-            Assert.True(Asserter.TestRan);
-        }
-
-        public static TheoryData<Func<int, int>> GetActionTestData
-            => new TheoryData<Func<int, int>>
-            {
-                (i) => i * 1
-            };
-
-        public class ConditionalTheoryAsserter : IDisposable
-        {
-            public bool TestRan { get; set; }
-
-            public void Dispose()
-            {
-            }
-        }
-
-        [ConditionalTheory]
-        [MemberData(nameof(SkippableData))]
-        public void WithSkipableData(Skippable skippable)
-        {
-            Assert.Null(skippable.Skip);
-            Assert.Equal(1, skippable.Data);
-        }
-
-        public static TheoryData<Skippable> SkippableData => new TheoryData<Skippable>
-        {
-            new Skippable() { Data = 1 },
-            new Skippable() { Data = 2, Skip = "This row should be skipped." }
-        };
-
-        public class Skippable : IXunitSerializable
-        {
-            public Skippable() { }
-            public int Data { get; set; }
-            public string Skip { get; set; }
-
-            public void Serialize(IXunitSerializationInfo info)
-            {
-                info.AddValue(nameof(Data), Data, typeof(int));
-            }
-
-            public void Deserialize(IXunitSerializationInfo info)
-            {
-                Data = info.GetValue<int>(nameof(Data));
-            }
-
-            public override string ToString()
-            {
-                return Data.ToString();
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/DockerTests.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/DockerTests.cs
deleted file mode 100644
index eb61e7cfe058bf..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/DockerTests.cs
+++ /dev/null
@@ -1,21 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Runtime.InteropServices;
-using Microsoft.AspNetCore.Testing;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class DockerTests
-    {
-        [ConditionalFact]
-        [DockerOnly]
-        [Trait("Docker", "true")]
-        public void DoesNotRunOnWindows()
-        {
-            Assert.False(RuntimeInformation.IsOSPlatform(OSPlatform.Windows));
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/EnvironmentVariableSkipConditionTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/EnvironmentVariableSkipConditionTest.cs
deleted file mode 100644
index e85552780c19ce..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/EnvironmentVariableSkipConditionTest.cs
+++ /dev/null
@@ -1,173 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class EnvironmentVariableSkipConditionTest
-    {
-        private readonly string _skipReason = "Test skipped on environment variable with name '{0}' and value '{1}'" +
-            $" for the '{nameof(EnvironmentVariableSkipConditionAttribute.RunOnMatch)}' value of '{{2}}'.";
-
-        [Theory]
-        [InlineData("false")]
-        [InlineData("")]
-        [InlineData(null)]
-        public void IsMet_DoesNotMatch(string environmentVariableValue)
-        {
-            // Arrange
-            var attribute = new EnvironmentVariableSkipConditionAttribute(
-                new TestEnvironmentVariable("Run", environmentVariableValue),
-                "Run",
-                "true");
-
-            // Act
-            var isMet = attribute.IsMet;
-
-            // Assert
-            Assert.False(isMet);
-        }
-
-        [Theory]
-        [InlineData("True")]
-        [InlineData("TRUE")]
-        [InlineData("true")]
-        public void IsMet_DoesCaseInsensitiveMatch_OnValue(string environmentVariableValue)
-        {
-            // Arrange
-            var attribute = new EnvironmentVariableSkipConditionAttribute(
-                new TestEnvironmentVariable("Run", environmentVariableValue),
-                "Run",
-                "true");
-
-            // Act
-            var isMet = attribute.IsMet;
-
-            // Assert
-            Assert.True(isMet);
-            Assert.Equal(
-                string.Format(_skipReason, "Run", environmentVariableValue, attribute.RunOnMatch),
-                attribute.SkipReason);
-        }
-
-        [Fact]
-        public void IsMet_DoesSuccessfulMatch_OnNull()
-        {
-            // Arrange
-            var attribute = new EnvironmentVariableSkipConditionAttribute(
-                new TestEnvironmentVariable("Run", null),
-                "Run",
-                "true", null); // skip the test when the variable 'Run' is explicitly set to 'true' or is null (default)
-
-            // Act
-            var isMet = attribute.IsMet;
-
-            // Assert
-            Assert.True(isMet);
-            Assert.Equal(
-                string.Format(_skipReason, "Run", "(null)", attribute.RunOnMatch),
-                attribute.SkipReason);
-        }
-
-        [Theory]
-        [InlineData("false")]
-        [InlineData("")]
-        [InlineData(null)]
-        public void IsMet_MatchesOnMultipleSkipValues(string environmentVariableValue)
-        {
-            // Arrange
-            var attribute = new EnvironmentVariableSkipConditionAttribute(
-                new TestEnvironmentVariable("Run", environmentVariableValue),
-                "Run",
-                "false", "", null);
-
-            // Act
-            var isMet = attribute.IsMet;
-
-            // Assert
-            Assert.True(isMet);
-        }
-
-        [Fact]
-        public void IsMet_DoesNotMatch_OnMultipleSkipValues()
-        {
-            // Arrange
-            var attribute = new EnvironmentVariableSkipConditionAttribute(
-                new TestEnvironmentVariable("Build", "100"),
-                "Build",
-                "125", "126");
-
-            // Act
-            var isMet = attribute.IsMet;
-
-            // Assert
-            Assert.False(isMet);
-        }
-
-        [Theory]
-        [InlineData("CentOS")]
-        [InlineData(null)]
-        [InlineData("")]
-        public void IsMet_Matches_WhenRunOnMatchIsFalse(string environmentVariableValue)
-        {
-            // Arrange
-            var attribute = new EnvironmentVariableSkipConditionAttribute(
-                new TestEnvironmentVariable("LinuxFlavor", environmentVariableValue),
-                "LinuxFlavor",
-                "Ubuntu14.04")
-            {
-                // Example: Run this test on all OSes except on "Ubuntu14.04"
-                RunOnMatch = false
-            };
-
-            // Act
-            var isMet = attribute.IsMet;
-
-            // Assert
-            Assert.True(isMet);
-        }
-
-        [Fact]
-        public void IsMet_DoesNotMatch_WhenRunOnMatchIsFalse()
-        {
-            // Arrange
-            var attribute = new EnvironmentVariableSkipConditionAttribute(
-                new TestEnvironmentVariable("LinuxFlavor", "Ubuntu14.04"),
-                "LinuxFlavor",
-                "Ubuntu14.04")
-            {
-                // Example: Run this test on all OSes except on "Ubuntu14.04"
-                RunOnMatch = false
-            };
-
-            // Act
-            var isMet = attribute.IsMet;
-
-            // Assert
-            Assert.False(isMet);
-        }
-
-        private struct TestEnvironmentVariable : IEnvironmentVariable
-        {
-            private readonly string _varName;
-
-            public TestEnvironmentVariable(string varName, string value)
-            {
-                _varName = varName;
-                Value = value;
-            }
-
-            public string Value { get; private set; }
-
-            public string Get(string name)
-            {
-                if(string.Equals(name, _varName, System.StringComparison.OrdinalIgnoreCase))
-                {
-                    return Value;
-                }
-                return string.Empty;
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ExceptionAssertTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ExceptionAssertTest.cs
deleted file mode 100644
index 52455b0694eeaf..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ExceptionAssertTest.cs
+++ /dev/null
@@ -1,39 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class ExceptionAssertTest
-    {
-        [Fact]
-        [ReplaceCulture("fr-FR", "fr-FR")]
-        public void AssertArgumentNullOrEmptyString_WorksInNonEnglishCultures()
-        {
-            // Arrange
-            Action action = () =>
-            {
-                throw new ArgumentException("Value cannot be null or an empty string.", "foo");
-            };
-
-            // Act and Assert
-            ExceptionAssert.ThrowsArgumentNullOrEmptyString(action, "foo");
-        }
-
-        [Fact]
-        [ReplaceCulture("fr-FR", "fr-FR")]
-        public void AssertArgumentOutOfRangeException_WorksInNonEnglishCultures()
-        {
-            // Arrange
-            Action action = () =>
-            {
-                throw new ArgumentOutOfRangeException("foo", 10, "exception message.");
-            };
-
-            // Act and Assert
-            ExceptionAssert.ThrowsArgumentOutOfRange(action, "foo", "exception message.", 10);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/FlakyAttributeTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/FlakyAttributeTest.cs
deleted file mode 100644
index db342c12b8629c..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/FlakyAttributeTest.cs
+++ /dev/null
@@ -1,99 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Collections.Generic;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing.Tests
-{
-    public class FlakyAttributeTest
-    {
-        [Fact(Skip = "These tests are nice when you need them but annoying when on all the time.")]
-        [Flaky("http://example.com", FlakyOn.All)]
-        public void AlwaysFlakyInCI()
-        {
-            if (!string.IsNullOrEmpty(Environment.GetEnvironmentVariable("HELIX")) || !string.IsNullOrEmpty(Environment.GetEnvironmentVariable("AGENT_OS")))
-            {
-                throw new Exception("Flaky!");
-            }
-        }
-
-        [Fact(Skip = "These tests are nice when you need them but annoying when on all the time.")]
-        [Flaky("http://example.com", FlakyOn.Helix.All)]
-        public void FlakyInHelixOnly()
-        {
-            if (!string.IsNullOrEmpty(Environment.GetEnvironmentVariable("HELIX")))
-            {
-                throw new Exception("Flaky on Helix!");
-            }
-        }
-
-        [Fact(Skip = "These tests are nice when you need them but annoying when on all the time.")]
-        [Flaky("http://example.com", FlakyOn.Helix.macOS1012Amd64, FlakyOn.Helix.Fedora28Amd64)]
-        public void FlakyInSpecificHelixQueue()
-        {
-            // Today we don't run Extensions tests on Helix, but this test should light up when we do.
-            var queueName = Environment.GetEnvironmentVariable("HELIX");
-            if (!string.IsNullOrEmpty(queueName))
-            {
-                var failingQueues = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { HelixQueues.macOS1012Amd64, HelixQueues.Fedora28Amd64 };
-                if (failingQueues.Contains(queueName))
-                {
-                    throw new Exception($"Flaky on Helix Queue '{queueName}' !");
-                }
-            }
-        }
-
-        [Fact(Skip = "These tests are nice when you need them but annoying when on all the time.")]
-        [Flaky("http://example.com", FlakyOn.AzP.All)]
-        public void FlakyInAzPOnly()
-        {
-            if (!string.IsNullOrEmpty(Environment.GetEnvironmentVariable("AGENT_OS")))
-            {
-                throw new Exception("Flaky on AzP!");
-            }
-        }
-
-        [Fact(Skip = "These tests are nice when you need them but annoying when on all the time.")]
-        [Flaky("http://example.com", FlakyOn.AzP.Windows)]
-        public void FlakyInAzPWindowsOnly()
-        {
-            if (string.Equals(Environment.GetEnvironmentVariable("AGENT_OS"), "Windows_NT"))
-            {
-                throw new Exception("Flaky on AzP Windows!");
-            }
-        }
-
-        [Fact(Skip = "These tests are nice when you need them but annoying when on all the time.")]
-        [Flaky("http://example.com", FlakyOn.AzP.macOS)]
-        public void FlakyInAzPmacOSOnly()
-        {
-            if (string.Equals(Environment.GetEnvironmentVariable("AGENT_OS"), "Darwin"))
-            {
-                throw new Exception("Flaky on AzP macOS!");
-            }
-        }
-
-        [Fact(Skip = "These tests are nice when you need them but annoying when on all the time.")]
-        [Flaky("http://example.com", FlakyOn.AzP.Linux)]
-        public void FlakyInAzPLinuxOnly()
-        {
-            if (string.Equals(Environment.GetEnvironmentVariable("AGENT_OS"), "Linux"))
-            {
-                throw new Exception("Flaky on AzP Linux!");
-            }
-        }
-
-        [Fact(Skip = "These tests are nice when you need them but annoying when on all the time.")]
-        [Flaky("http://example.com", FlakyOn.AzP.Linux, FlakyOn.AzP.macOS)]
-        public void FlakyInAzPNonWindowsOnly()
-        {
-            var agentOs = Environment.GetEnvironmentVariable("AGENT_OS");
-            if (string.Equals(agentOs, "Linux") || string.Equals(agentOs, "Darwin"))
-            {
-                throw new Exception("Flaky on AzP non-Windows!");
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/HttpClientSlimTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/HttpClientSlimTest.cs
deleted file mode 100644
index 10ae3f7a5ab8bb..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/HttpClientSlimTest.cs
+++ /dev/null
@@ -1,116 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Net;
-using System.Net.Http;
-using System.Text;
-using System.Threading.Tasks;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class HttpClientSlimTest
-    {
-        private static readonly byte[] _defaultResponse = Encoding.ASCII.GetBytes("test");
-
-        [Fact]
-        public async Task GetStringAsyncHttp()
-        {
-            using (var host = StartHost(out var address))
-            {
-                Assert.Equal("test", await HttpClientSlim.GetStringAsync(address));
-            }
-        }
-
-        [Fact]
-        public async Task GetStringAsyncThrowsForErrorResponse()
-        {
-            using (var host = StartHost(out var address, statusCode: 500))
-            {
-                await Assert.ThrowsAnyAsync<HttpRequestException>(() => HttpClientSlim.GetStringAsync(address));
-            }
-        }
-
-        [Fact]
-        public async Task PostAsyncHttp()
-        {
-            using (var host = StartHost(out var address, handler: context => context.Request.InputStream.CopyToAsync(context.Response.OutputStream)))
-            {
-                Assert.Equal("test post", await HttpClientSlim.PostAsync(address, new StringContent("test post")));
-            }
-        }
-
-        [Fact]
-        public async Task PostAsyncThrowsForErrorResponse()
-        {
-            using (var host = StartHost(out var address, statusCode: 500))
-            {
-                await Assert.ThrowsAnyAsync<HttpRequestException>(
-                    () => HttpClientSlim.PostAsync(address, new StringContent("")));
-            }
-        }
-
-        [Fact]
-        public void Ipv6ScopeIdsFilteredOut()
-        {
-            var requestUri = new Uri("http://[fe80::5d2a:d070:6fd6:1bac%7]:5003/");
-            Assert.Equal("[fe80::5d2a:d070:6fd6:1bac]:5003", HttpClientSlim.GetHost(requestUri));
-        }
-
-        [Fact]
-        public void GetHostExcludesDefaultPort()
-        {
-            var requestUri = new Uri("http://[fe80::5d2a:d070:6fd6:1bac%7]:80/");
-            Assert.Equal("[fe80::5d2a:d070:6fd6:1bac]", HttpClientSlim.GetHost(requestUri));
-        }
-
-        private HttpListener StartHost(out string address, int statusCode = 200, Func<HttpListenerContext, Task> handler = null)
-        {
-            var listener = new HttpListener();
-            var random = new Random();
-            address = null;
-
-            for (var i = 0; i < 10; i++)
-            {
-                try
-                {
-                    // HttpListener doesn't support requesting port 0 (dynamic).
-                    // Requesting port 0 from Sockets and then passing that to HttpListener is racy.
-                    // Just keep trying until we find a free one.
-                    address = $"http://localhost:{random.Next(1024, ushort.MaxValue)}/";
-                    listener.Prefixes.Add(address);
-                    listener.Start();
-                    break;
-                }
-                catch (HttpListenerException)
-                {
-                    // Address in use
-                    listener.Close();
-                    listener = new HttpListener();
-                }
-            }
-
-            Assert.True(listener.IsListening, "IsListening");
-
-            _ = listener.GetContextAsync().ContinueWith(async task =>
-            {
-                var context = task.Result;
-                context.Response.StatusCode = statusCode;
-
-                if (handler == null)
-                {
-                    await context.Response.OutputStream.WriteAsync(_defaultResponse, 0, _defaultResponse.Length);
-                }
-                else
-                {
-                    await handler(context);
-                }
-
-                context.Response.Close();
-            });
-
-            return listener;
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MaximumOSVersionAttributeTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MaximumOSVersionAttributeTest.cs
deleted file mode 100644
index 1cc772ce4e36fa..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MaximumOSVersionAttributeTest.cs
+++ /dev/null
@@ -1,89 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class MaximumOSVersionAttributeTest
-    {
-        [Fact]
-        public void Linux_ThrowsNotImplemeneted()
-        {
-            Assert.Throws<NotImplementedException>(() => new MaximumOSVersionAttribute(OperatingSystems.Linux, "2.5"));
-        }
-
-        [Fact]
-        public void Mac_ThrowsNotImplemeneted()
-        {
-            Assert.Throws<NotImplementedException>(() => new MaximumOSVersionAttribute(OperatingSystems.MacOSX, "2.5"));
-        }
-
-        [Fact]
-        public void WindowsOrLinux_ThrowsNotImplemeneted()
-        {
-            Assert.Throws<NotImplementedException>(() => new MaximumOSVersionAttribute(OperatingSystems.Linux | OperatingSystems.Windows, "2.5"));
-        }
-
-        [Fact]
-        public void DoesNotSkip_ShortVersions()
-        {
-            var osSkipAttribute = new MaximumOSVersionAttribute(
-                OperatingSystems.Windows,
-                new Version("2.5"),
-                OperatingSystems.Windows,
-                new Version("2.0"));
-
-            Assert.True(osSkipAttribute.IsMet);
-        }
-
-        [Fact]
-        public void DoesNotSkip_EarlierVersions()
-        {
-            var osSkipAttribute = new MaximumOSVersionAttribute(
-                OperatingSystems.Windows,
-                new Version("2.5.9"),
-                OperatingSystems.Windows,
-                new Version("2.0.10.12"));
-
-            Assert.True(osSkipAttribute.IsMet);
-        }
-
-        [Fact]
-        public void DoesNotSkip_SameVersion()
-        {
-            var osSkipAttribute = new MaximumOSVersionAttribute(
-                OperatingSystems.Windows,
-                new Version("2.5.10"),
-                OperatingSystems.Windows,
-                new Version("2.5.10.12"));
-
-            Assert.True(osSkipAttribute.IsMet);
-        }
-
-        [Fact]
-        public void Skip_LaterVersion()
-        {
-            var osSkipAttribute = new MaximumOSVersionAttribute(
-                OperatingSystems.Windows,
-                new Version("2.5.11"),
-                OperatingSystems.Windows,
-                new Version("3.0.10.12"));
-
-            Assert.False(osSkipAttribute.IsMet);
-        }
-
-        [Fact]
-        public void DoesNotSkip_WhenOnlyVersionsMatch()
-        {
-            var osSkipAttribute = new MaximumOSVersionAttribute(
-                OperatingSystems.Windows,
-                new Version("2.5.10.12"),
-                OperatingSystems.Linux,
-                new Version("2.5.10.12"));
-
-            Assert.True(osSkipAttribute.IsMet);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MaximumOSVersionTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MaximumOSVersionTest.cs
deleted file mode 100644
index 1b0586aeb99fa4..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MaximumOSVersionTest.cs
+++ /dev/null
@@ -1,92 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Runtime.InteropServices;
-using Microsoft.Win32;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
-    public class MaximumOSVersionTest
-    {
-        [ConditionalFact]
-        [MaximumOSVersion(OperatingSystems.Windows, WindowsVersions.Win7)]
-        public void RunTest_Win7DoesRunOnWin7()
-        {
-            Assert.True(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Windows) &&
-                Environment.OSVersion.Version.ToString().StartsWith("6.1"),
-                "Test should only be running on Win7 or Win2008R2.");
-        }
-
-        [ConditionalTheory]
-        [MaximumOSVersion(OperatingSystems.Windows, WindowsVersions.Win7)]
-        [InlineData(1)]
-        public void RunTheory_Win7DoesRunOnWin7(int arg)
-        {
-            Assert.True(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Windows) &&
-                Environment.OSVersion.Version.ToString().StartsWith("6.1"),
-                "Test should only be running on Win7 or Win2008R2.");
-        }
-
-        [ConditionalFact]
-        [FrameworkSkipCondition(RuntimeFrameworks.CLR, SkipReason = "https://github.com/xunit/xunit/issues/2076")]
-        [MaximumOSVersion(OperatingSystems.Windows, WindowsVersions.Win10_RS4)]
-        [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
-        public void RunTest_Win10_RS4()
-        {
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Windows));
-            var versionKey = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\Windows NT\CurrentVersion");
-            Assert.NotNull(versionKey);
-            var currentVersion = (string)versionKey.GetValue("CurrentBuildNumber");
-            Assert.NotNull(currentVersion);
-            Assert.True(17134 >= int.Parse(currentVersion), $"Unexpected build number {currentVersion} on {Environment.OSVersion.Version}.");
-        }
-
-        [ConditionalFact]
-        [FrameworkSkipCondition(RuntimeFrameworks.CLR, SkipReason = "https://github.com/xunit/xunit/issues/2076")]
-        [MaximumOSVersion(OperatingSystems.Windows, WindowsVersions.Win10_19H2)]
-        [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
-        public void RunTest_Win10_19H2()
-        {
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Windows));
-            var versionKey = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\Windows NT\CurrentVersion");
-            Assert.NotNull(versionKey);
-            var currentVersion = (string)versionKey.GetValue("CurrentBuildNumber");
-            Assert.NotNull(currentVersion);
-            Assert.True(18363 >= int.Parse(currentVersion), $"Unexpected build number {currentVersion} on {Environment.OSVersion.Version}.");
-        }
-    }
-
-    [MaximumOSVersion(OperatingSystems.Windows, WindowsVersions.Win7)]
-    [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
-    public class OSMaxVersionClassTest
-    {
-        [ConditionalFact]
-        public void TestSkipClass_Win7DoesRunOnWin7()
-        {
-            Assert.True(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Windows) &&
-                Environment.OSVersion.Version.ToString().StartsWith("6.1"),
-                "Test should only be running on Win7 or Win2008R2.");
-        }
-    }
-
-    // Let this one run cross plat just to check the constructor logic.
-    [MaximumOSVersion(OperatingSystems.Windows, WindowsVersions.Win7)]
-    public class OSMaxVersionCrossPlatTest
-    {
-        [ConditionalFact]
-        public void TestSkipClass_Win7DoesRunOnWin7()
-        {
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-            {
-                Assert.True(Environment.OSVersion.Version.ToString().StartsWith("6.1"),
-                    "Test should only be running on Win7 or Win2008R2.");
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MinimumOSVersionAttributeTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MinimumOSVersionAttributeTest.cs
deleted file mode 100644
index c4e1120bc8548c..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MinimumOSVersionAttributeTest.cs
+++ /dev/null
@@ -1,77 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class MinimumOSVersionAttributeTest
-    {
-        [Fact]
-        public void Linux_ThrowsNotImplemeneted()
-        {
-            Assert.Throws<NotImplementedException>(() => new MinimumOSVersionAttribute(OperatingSystems.Linux, "2.5"));
-        }
-
-        [Fact]
-        public void Mac_ThrowsNotImplemeneted()
-        {
-            Assert.Throws<NotImplementedException>(() => new MinimumOSVersionAttribute(OperatingSystems.MacOSX, "2.5"));
-        }
-
-        [Fact]
-        public void WindowsOrLinux_ThrowsNotImplemeneted()
-        {
-            Assert.Throws<NotImplementedException>(() => new MinimumOSVersionAttribute(OperatingSystems.Linux | OperatingSystems.Windows, "2.5"));
-        }
-
-        [Fact]
-        public void DoesNotSkip_LaterVersions()
-        {
-            var osSkipAttribute = new MinimumOSVersionAttribute(
-                OperatingSystems.Windows,
-                new Version("2.0"),
-                OperatingSystems.Windows,
-                new Version("2.5"));
-
-            Assert.True(osSkipAttribute.IsMet);
-        }
-
-        [Fact]
-        public void DoesNotSkip_SameVersion()
-        {
-            var osSkipAttribute = new MinimumOSVersionAttribute(
-                OperatingSystems.Windows,
-                new Version("2.5"),
-                OperatingSystems.Windows,
-                new Version("2.5"));
-
-            Assert.True(osSkipAttribute.IsMet);
-        }
-
-        [Fact]
-        public void Skip_EarlierVersion()
-        {
-            var osSkipAttribute = new MinimumOSVersionAttribute(
-                OperatingSystems.Windows,
-                new Version("3.0"),
-                OperatingSystems.Windows,
-                new Version("2.5"));
-
-            Assert.False(osSkipAttribute.IsMet);
-        }
-
-        [Fact]
-        public void DoesNotSkip_WhenOnlyVersionsMatch()
-        {
-            var osSkipAttribute = new MinimumOSVersionAttribute(
-                OperatingSystems.Windows,
-                new Version("2.5"),
-                OperatingSystems.Linux,
-                new Version("2.5"));
-
-            Assert.True(osSkipAttribute.IsMet);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MinimumOSVersionTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MinimumOSVersionTest.cs
deleted file mode 100644
index ba45f1c4306d2d..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/MinimumOSVersionTest.cs
+++ /dev/null
@@ -1,73 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Runtime.InteropServices;
-using Microsoft.Win32;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class MinimumOSVersionTest
-    {
-        [ConditionalFact]
-        [MinimumOSVersion(OperatingSystems.Windows, WindowsVersions.Win8)]
-        public void RunTest_Win8DoesNotRunOnWin7()
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Windows) &&
-                Environment.OSVersion.Version.ToString().StartsWith("6.1"),
-                "Test should not be running on Win7 or Win2008R2.");
-        }
-
-        [ConditionalTheory]
-        [MinimumOSVersion(OperatingSystems.Windows, WindowsVersions.Win8)]
-        [InlineData(1)]
-        public void RunTheory_Win8DoesNotRunOnWin7(int arg)
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Windows) &&
-                Environment.OSVersion.Version.ToString().StartsWith("6.1"),
-                "Test should not be running on Win7 or Win2008R2.");
-        }
-
-        [ConditionalFact]
-        [MinimumOSVersion(OperatingSystems.Windows, WindowsVersions.Win10_RS4)]
-        [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
-        public void RunTest_Win10_RS4()
-        {
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Windows));
-            var versionKey = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\Windows NT\CurrentVersion");
-            Assert.NotNull(versionKey);
-            var currentVersion = (string)versionKey.GetValue("CurrentBuildNumber");
-            Assert.NotNull(currentVersion);
-            Assert.True(17134 <= int.Parse(currentVersion));
-        }
-
-        [ConditionalFact]
-        [MinimumOSVersion(OperatingSystems.Windows, WindowsVersions.Win10_19H2)]
-        [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
-        public void RunTest_Win10_19H2()
-        {
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Windows));
-            var versionKey = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\Windows NT\CurrentVersion");
-            Assert.NotNull(versionKey);
-            var currentVersion = (string)versionKey.GetValue("CurrentBuildNumber");
-            Assert.NotNull(currentVersion);
-            Assert.True(18363 <= int.Parse(currentVersion));
-        }
-    }
-
-    [MinimumOSVersion(OperatingSystems.Windows, WindowsVersions.Win8)]
-    public class OSMinVersionClassTest
-    {
-        [ConditionalFact]
-        public void TestSkipClass_Win8DoesNotRunOnWin7()
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Windows) &&
-                Environment.OSVersion.Version.ToString().StartsWith("6.1"),
-                "Test should not be running on Win7 or Win2008R2.");
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/OSSkipConditionAttributeTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/OSSkipConditionAttributeTest.cs
deleted file mode 100644
index 53e2ed774ff364..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/OSSkipConditionAttributeTest.cs
+++ /dev/null
@@ -1,72 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Runtime.InteropServices;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class OSSkipConditionAttributeTest
-    {
-        [Fact]
-        public void Skips_WhenOperatingSystemMatches()
-        {
-            // Act
-            var osSkipAttribute = new OSSkipConditionAttribute(
-                OperatingSystems.Windows,
-                OperatingSystems.Windows);
-
-            // Assert
-            Assert.False(osSkipAttribute.IsMet);
-        }
-
-        [Fact]
-        public void DoesNotSkip_WhenOperatingSystemDoesNotMatch()
-        {
-            // Act
-            var osSkipAttribute = new OSSkipConditionAttribute(
-                OperatingSystems.Linux,
-                OperatingSystems.Windows);
-
-            // Assert
-            Assert.True(osSkipAttribute.IsMet);
-        }
-
-        [Fact]
-        public void Skips_BothMacOSXAndLinux()
-        {
-            // Act
-            var osSkipAttributeLinux = new OSSkipConditionAttribute(OperatingSystems.Linux | OperatingSystems.MacOSX, OperatingSystems.Linux);
-            var osSkipAttributeMacOSX = new OSSkipConditionAttribute(OperatingSystems.Linux | OperatingSystems.MacOSX, OperatingSystems.MacOSX);
-
-            // Assert
-            Assert.False(osSkipAttributeLinux.IsMet);
-            Assert.False(osSkipAttributeMacOSX.IsMet);
-        }
-
-        [Fact]
-        public void Skips_BothMacOSXAndWindows()
-        {
-            // Act
-            var osSkipAttribute = new OSSkipConditionAttribute(OperatingSystems.Windows | OperatingSystems.MacOSX, OperatingSystems.Windows);
-            var osSkipAttributeMacOSX = new OSSkipConditionAttribute(OperatingSystems.Windows | OperatingSystems.MacOSX, OperatingSystems.MacOSX);
-
-            // Assert
-            Assert.False(osSkipAttribute.IsMet);
-            Assert.False(osSkipAttributeMacOSX.IsMet);
-        }
-
-        [Fact]
-        public void Skips_BothWindowsAndLinux()
-        {
-            // Act
-            var osSkipAttribute = new OSSkipConditionAttribute(OperatingSystems.Linux | OperatingSystems.Windows, OperatingSystems.Windows);
-            var osSkipAttributeLinux = new OSSkipConditionAttribute(OperatingSystems.Linux | OperatingSystems.Windows, OperatingSystems.Linux);
-
-            // Assert
-            Assert.False(osSkipAttribute.IsMet);
-            Assert.False(osSkipAttributeLinux.IsMet);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/OSSkipConditionTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/OSSkipConditionTest.cs
deleted file mode 100644
index a058ade7c7284f..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/OSSkipConditionTest.cs
+++ /dev/null
@@ -1,105 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Runtime.InteropServices;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class OSSkipConditionTest
-    {
-        [ConditionalFact]
-        [OSSkipCondition(OperatingSystems.Linux)]
-        public void TestSkipLinux()
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Linux),
-                "Test should not be running on Linux");
-        }
-
-        [ConditionalFact]
-        [OSSkipCondition(OperatingSystems.MacOSX)]
-        public void TestSkipMacOSX()
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.OSX),
-                "Test should not be running on MacOSX.");
-        }
-
-        [ConditionalFact]
-        [OSSkipCondition(OperatingSystems.Windows)]
-        public void TestSkipWindows()
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Windows),
-                "Test should not be running on Windows.");
-        }
-
-        [ConditionalFact]
-        [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
-        public void TestSkipLinuxAndMacOSX()
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Linux),
-                "Test should not be running on Linux.");
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.OSX),
-                "Test should not be running on MacOSX.");
-        }
-
-        [ConditionalTheory]
-        [OSSkipCondition(OperatingSystems.Linux)]
-        [InlineData(1)]
-        public void TestTheorySkipLinux(int arg)
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Linux),
-                "Test should not be running on Linux");
-        }
-
-        [ConditionalTheory]
-        [OSSkipCondition(OperatingSystems.MacOSX)]
-        [InlineData(1)]
-        public void TestTheorySkipMacOS(int arg)
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.OSX),
-                "Test should not be running on MacOSX.");
-        }
-
-        [ConditionalTheory]
-        [OSSkipCondition(OperatingSystems.Windows)]
-        [InlineData(1)]
-        public void TestTheorySkipWindows(int arg)
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Windows),
-                "Test should not be running on Windows.");
-        }
-
-        [ConditionalTheory]
-        [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
-        [InlineData(1)]
-        public void TestTheorySkipLinuxAndMacOSX(int arg)
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Linux),
-                "Test should not be running on Linux.");
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.OSX),
-                "Test should not be running on MacOSX.");
-        }
-    }
-
-    [OSSkipCondition(OperatingSystems.Windows)]
-    public class OSSkipConditionClassTest
-    {
-        [ConditionalFact]
-        public void TestSkipClassWindows()
-        {
-            Assert.False(
-                RuntimeInformation.IsOSPlatform(OSPlatform.Windows),
-                "Test should not be running on Windows.");
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/Properties/AssemblyInfo.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/Properties/AssemblyInfo.cs
deleted file mode 100644
index 0f8d3c8a9cfbef..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/Properties/AssemblyInfo.cs
+++ /dev/null
@@ -1,9 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Microsoft.AspNetCore.Testing;
-using Xunit;
-
-[assembly: Repeat(1)]
-[assembly: AssemblyFixture(typeof(TestAssemblyFixture))]
-[assembly: TestFramework("Microsoft.AspNetCore.Testing.AspNetTestFramework", "Microsoft.AspNetCore.Testing")]
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/RepeatTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/RepeatTest.cs
deleted file mode 100644
index e5e1d5d6d05c17..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/RepeatTest.cs
+++ /dev/null
@@ -1,43 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [Repeat]
-    public class RepeatTest
-    {
-        public static int _runCount = 0;
-
-        [Fact]
-        [Repeat(5)]
-        public void RepeatLimitIsSetCorrectly()
-        {
-            Assert.Equal(5, RepeatContext.Current.Limit);
-        }
-
-        [Fact]
-        [Repeat(5)]
-        public void RepeatRunsTestSpecifiedNumberOfTimes()
-        {
-            Assert.Equal(RepeatContext.Current.CurrentIteration, _runCount);
-            _runCount++;
-        }
-
-        [Fact]
-        public void RepeatCanBeSetOnClass()
-        {
-            Assert.Equal(10, RepeatContext.Current.Limit);
-        }
-    }
-
-    public class LoggedTestXunitRepeatAssemblyTests
-    {
-        [Fact]
-        public void RepeatCanBeSetOnAssembly()
-        {
-            Assert.Equal(1, RepeatContext.Current.Limit);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ReplaceCultureAttributeTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ReplaceCultureAttributeTest.cs
deleted file mode 100644
index ff6740b80d9ac7..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/ReplaceCultureAttributeTest.cs
+++ /dev/null
@@ -1,66 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Globalization;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class RepalceCultureAttributeTest
-    {
-        [Fact]
-        public void DefaultsTo_EnGB_EnUS()
-        {
-            // Arrange
-            var culture = new CultureInfo("en-GB");
-            var uiCulture = new CultureInfo("en-US");
-
-            // Act
-            var replaceCulture = new ReplaceCultureAttribute();
-
-            // Assert
-            Assert.Equal(culture, replaceCulture.Culture);
-            Assert.Equal(uiCulture, replaceCulture.UICulture);
-        }
-
-        [Fact]
-        public void UsesSuppliedCultureAndUICulture()
-        {
-            // Arrange
-            var culture = "de-DE";
-            var uiCulture = "fr-CA";
-
-            // Act
-            var replaceCulture = new ReplaceCultureAttribute(culture, uiCulture);
-
-            // Assert
-            Assert.Equal(new CultureInfo(culture), replaceCulture.Culture);
-            Assert.Equal(new CultureInfo(uiCulture), replaceCulture.UICulture);
-        }
-
-        [Fact]
-        public void BeforeAndAfterTest_ReplacesCulture()
-        {
-            // Arrange
-            var originalCulture = CultureInfo.CurrentCulture;
-            var originalUICulture = CultureInfo.CurrentUICulture;
-            var culture = "de-DE";
-            var uiCulture = "fr-CA";
-            var replaceCulture = new ReplaceCultureAttribute(culture, uiCulture);
-
-            // Act
-            replaceCulture.Before(methodUnderTest: null);
-
-            // Assert
-            Assert.Equal(new CultureInfo(culture), CultureInfo.CurrentCulture);
-            Assert.Equal(new CultureInfo(uiCulture), CultureInfo.CurrentUICulture);
-
-            // Act
-            replaceCulture.After(methodUnderTest: null);
-
-            // Assert
-            Assert.Equal(originalCulture, CultureInfo.CurrentCulture);
-            Assert.Equal(originalUICulture, CultureInfo.CurrentUICulture);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/SkipOnCITests.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/SkipOnCITests.cs
deleted file mode 100644
index ee511c2bd59678..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/SkipOnCITests.cs
+++ /dev/null
@@ -1,22 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using Microsoft.AspNetCore.Testing;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing.Tests
-{
-    public class SkipOnCITests
-    {
-        [ConditionalFact]
-        [SkipOnCI]
-        public void AlwaysSkipOnCI()
-        {
-            if (!string.IsNullOrEmpty(Environment.GetEnvironmentVariable("HELIX")) || !string.IsNullOrEmpty(Environment.GetEnvironmentVariable("AGENT_OS")))
-            {
-                throw new Exception("Flaky!");
-            }
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TaskExtensionsTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TaskExtensionsTest.cs
deleted file mode 100644
index d9f4bbe2b62a46..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TaskExtensionsTest.cs
+++ /dev/null
@@ -1,18 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Threading.Tasks;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class TaskExtensionsTest
-    {
-        [Fact]
-        public async Task TimeoutAfterTest()
-        {
-            await Assert.ThrowsAsync<TimeoutException>(async () => await Task.Delay(1000).TimeoutAfter(TimeSpan.FromMilliseconds(50)));
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestContextTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestContextTest.cs
deleted file mode 100644
index 7a81f37dcac5b1..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestContextTest.cs
+++ /dev/null
@@ -1,83 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class TestContextTest : ITestMethodLifecycle
-    {
-        public TestContext Context { get; private set; }
-
-        [Fact]
-        public void FullName_IsUsed_ByDefault()
-        {
-            Assert.Equal(GetType().FullName, Context.FileOutput.TestClassName);
-        }
-
-        Task ITestMethodLifecycle.OnTestStartAsync(TestContext context, CancellationToken cancellationToken)
-        {
-            Context = context;
-            return Task.CompletedTask;
-        }
-
-        Task ITestMethodLifecycle.OnTestEndAsync(TestContext context, Exception exception, CancellationToken cancellationToken)
-        {
-            return Task.CompletedTask;
-        }
-    }
-}
-
-namespace Microsoft.AspNetCore.Testing.Tests
-{
-    public class TestContextNameShorteningTest : ITestMethodLifecycle
-    {
-        public TestContext Context { get; private set; }
-
-        [Fact]
-        public void NameIsShortenedWhenAssemblyNameIsAPrefix()
-        {
-            Assert.Equal(GetType().Name, Context.FileOutput.TestClassName);
-        }
-
-        Task ITestMethodLifecycle.OnTestStartAsync(TestContext context, CancellationToken cancellationToken)
-        {
-            Context = context;
-            return Task.CompletedTask;
-        }
-
-        Task ITestMethodLifecycle.OnTestEndAsync(TestContext context, Exception exception, CancellationToken cancellationToken)
-        {
-            return Task.CompletedTask;
-        }
-    }
-}
-
-namespace Microsoft.AspNetCore.Testing
-{
-    [ShortClassName]
-    public class TestContextTestClassShortNameAttributeTest : ITestMethodLifecycle
-    {
-        public TestContext Context { get; private set; }
-
-        [Fact]
-        public void ShortClassNameUsedWhenShortClassNameAttributeSpecified()
-        {
-            Assert.Equal(GetType().Name, Context.FileOutput.TestClassName);
-        }
-
-        Task ITestMethodLifecycle.OnTestStartAsync(TestContext context, CancellationToken cancellationToken)
-        {
-            Context = context;
-            return Task.CompletedTask;
-        }
-
-        Task ITestMethodLifecycle.OnTestEndAsync(TestContext context, Exception exception, CancellationToken cancellationToken)
-        {
-            return Task.CompletedTask;
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestPathUtilitiesTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestPathUtilitiesTest.cs
deleted file mode 100644
index 9810db94a410c5..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestPathUtilitiesTest.cs
+++ /dev/null
@@ -1,35 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.IO;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class TestPathUtilitiesTest
-    {
-        // Entire test pending removal - see https://github.com/dotnet/extensions/issues/1697
-#pragma warning disable 0618
-
-        [Fact]
-        public void GetSolutionRootDirectory_ResolvesSolutionRoot()
-        {
-            // Directory.GetCurrentDirectory() gives:
-            // Testing\test\Microsoft.AspNetCore.Testing.Tests\bin\Debug\netcoreapp2.0
-            // Testing\test\Microsoft.AspNetCore.Testing.Tests\bin\Debug\net461
-            // Testing\test\Microsoft.AspNetCore.Testing.Tests\bin\Debug\net46
-            var expectedPath = Path.GetFullPath(Path.Combine(Directory.GetCurrentDirectory(), "..", "..", "..", "..", ".."));
-
-            Assert.Equal(expectedPath, TestPathUtilities.GetSolutionRootDirectory("Extensions"));
-        }
-
-        [Fact]
-        public void GetSolutionRootDirectory_Throws_IfNotFound()
-        {
-            var exception = Assert.Throws<Exception>(() => TestPathUtilities.GetSolutionRootDirectory("NotTesting"));
-            Assert.Equal($"Solution file NotTesting.sln could not be found in {AppContext.BaseDirectory} or its parent directories.", exception.Message);
-        }
-#pragma warning restore 0618
-    }
-}
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestPlatformHelperTest.cs b/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestPlatformHelperTest.cs
deleted file mode 100644
index dcecc6b325294b..00000000000000
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestPlatformHelperTest.cs
+++ /dev/null
@@ -1,55 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using Microsoft.AspNetCore.Testing;
-using Xunit;
-
-namespace Microsoft.AspNetCore.Testing
-{
-    public class TestPlatformHelperTest
-    {
-        [ConditionalFact]
-        [OSSkipCondition(OperatingSystems.MacOSX)]
-        [OSSkipCondition(OperatingSystems.Windows)]
-        public void IsLinux_TrueOnLinux()
-        {
-            Assert.True(TestPlatformHelper.IsLinux);
-            Assert.False(TestPlatformHelper.IsMac);
-            Assert.False(TestPlatformHelper.IsWindows);
-        }
-
-        [ConditionalFact]
-        [OSSkipCondition(OperatingSystems.Linux)]
-        [OSSkipCondition(OperatingSystems.Windows)]
-        public void IsMac_TrueOnMac()
-        {
-            Assert.False(TestPlatformHelper.IsLinux);
-            Assert.True(TestPlatformHelper.IsMac);
-            Assert.False(TestPlatformHelper.IsWindows);
-        }
-
-        [ConditionalFact]
-        [OSSkipCondition(OperatingSystems.Linux)]
-        [OSSkipCondition(OperatingSystems.MacOSX)]
-        public void IsWindows_TrueOnWindows()
-        {
-            Assert.False(TestPlatformHelper.IsLinux);
-            Assert.False(TestPlatformHelper.IsMac);
-            Assert.True(TestPlatformHelper.IsWindows);
-        }
-
-        [ConditionalFact]
-        [FrameworkSkipCondition(RuntimeFrameworks.CLR | RuntimeFrameworks.CoreCLR | RuntimeFrameworks.None)]
-        public void IsMono_TrueOnMono()
-        {
-            Assert.True(TestPlatformHelper.IsMono);
-        }
-
-        [ConditionalFact]
-        [FrameworkSkipCondition(RuntimeFrameworks.Mono)]
-        public void IsMono_FalseElsewhere()
-        {
-            Assert.False(TestPlatformHelper.IsMono);
-        }
-    }
-}
diff --git a/src/libraries/Common/tests/System/Diagnostics/Tracing/TestEventListener.cs b/src/libraries/Common/tests/System/Diagnostics/Tracing/TestEventListener.cs
index bc210b2b83b537..b12f5022c62f18 100644
--- a/src/libraries/Common/tests/System/Diagnostics/Tracing/TestEventListener.cs
+++ b/src/libraries/Common/tests/System/Diagnostics/Tracing/TestEventListener.cs
@@ -12,24 +12,27 @@ internal sealed class TestEventListener : EventListener
         private readonly string _targetSourceName;
         private readonly Guid _targetSourceGuid;
         private readonly EventLevel _level;
+        private readonly double? _eventCounterInterval;
 
         private Action<EventWrittenEventArgs> _eventWritten;
         private List<EventSource> _tmpEventSourceList = new List<EventSource>();
 
-        public TestEventListener(string targetSourceName, EventLevel level)
+        public TestEventListener(string targetSourceName, EventLevel level, double? eventCounterInterval = null)
         {
             // Store the arguments
             _targetSourceName = targetSourceName;
             _level = level;
+            _eventCounterInterval = eventCounterInterval;
 
             LoadSourceList();
         }
 
-        public TestEventListener(Guid targetSourceGuid, EventLevel level)
+        public TestEventListener(Guid targetSourceGuid, EventLevel level, double? eventCounterInterval = null)
         {
             // Store the arguments
             _targetSourceGuid = targetSourceGuid;
             _level = level;
+            _eventCounterInterval = eventCounterInterval;
 
             LoadSourceList();
         }
@@ -80,7 +83,15 @@ private void EnableSourceIfMatch(EventSource source)
             if (source.Name.Equals(_targetSourceName) ||
                 source.Guid.Equals(_targetSourceGuid))
             {
-                EnableEvents(source, _level);
+                if (_eventCounterInterval != null)
+                {
+                    var args = new Dictionary<string, string> { { "EventCounterIntervalSec", _eventCounterInterval?.ToString() } };
+                    EnableEvents(source, _level, EventKeywords.All, args);
+                }
+                else
+                {
+                    EnableEvents(source, _level);
+                }
             }
         }
 
diff --git a/src/libraries/Common/tests/System/Net/Http/GenericLoopbackServer.cs b/src/libraries/Common/tests/System/Net/Http/GenericLoopbackServer.cs
index fd12e239e5d3cc..da6e915a237fcc 100644
--- a/src/libraries/Common/tests/System/Net/Http/GenericLoopbackServer.cs
+++ b/src/libraries/Common/tests/System/Net/Http/GenericLoopbackServer.cs
@@ -6,6 +6,8 @@
 using System.Text;
 using System.Threading.Tasks;
 using System.Security.Authentication;
+using System.IO;
+using System.Net.Sockets;
 
 namespace System.Net.Test.Common
 {
@@ -17,6 +19,8 @@ public abstract class LoopbackServerFactory
         public abstract GenericLoopbackServer CreateServer(GenericLoopbackOptions options = null);
         public abstract Task CreateServerAsync(Func<GenericLoopbackServer, Uri, Task> funcAsync, int millisecondsTimeout = 60_000, GenericLoopbackOptions options = null);
 
+        public abstract Task<GenericLoopbackConnection> CreateConnectionAsync(Socket socket, Stream stream, GenericLoopbackOptions options = null);
+
         public abstract Version Version { get; }
 
         // Common helper methods
@@ -58,6 +62,8 @@ public abstract class GenericLoopbackConnection : IDisposable
     {
         public abstract void Dispose();
 
+        public abstract Task InitializeConnectionAsync();
+
         /// <summary>Read request Headers and optionally request body as well.</summary>
         public abstract Task<HttpRequestData> ReadRequestDataAsync(bool readBody = true);
         /// <summary>Read complete request body if not done by ReadRequestData.</summary>
@@ -70,6 +76,9 @@ public abstract class GenericLoopbackConnection : IDisposable
         /// <summary>Sends Response body after SendResponse was called with isFinal: false.</summary>
         public abstract Task SendResponseBodyAsync(byte[] content, bool isFinal = true, int requestId = 0);
 
+        /// <summary>Reads Request, sends Response and closes connection.</summary>
+        public abstract Task<HttpRequestData> HandleRequestAsync(HttpStatusCode statusCode = HttpStatusCode.OK, IList<HttpHeaderData> headers = null, string content = "");
+
         /// <summary>Waits for the client to signal cancellation.</summary>
         public abstract Task WaitForCancellationAsync(bool ignoreIncomingData = true, int requestId = 0);
 
@@ -89,6 +98,8 @@ public class GenericLoopbackOptions
                 SslProtocols.Tls13 |
 #endif
                 SslProtocols.Tls12;
+
+        public int ListenBacklog { get; set; } = 1;
     }
 
     public struct HttpHeaderData
@@ -100,13 +111,15 @@ public struct HttpHeaderData
         public string Value { get; }
         public bool HuffmanEncoded { get; }
         public byte[] Raw { get; }
+        public Encoding ValueEncoding { get; }
 
-        public HttpHeaderData(string name, string value, bool huffmanEncoded = false, byte[] raw = null)
+        public HttpHeaderData(string name, string value, bool huffmanEncoded = false, byte[] raw = null, Encoding valueEncoding = null)
         {
             Name = name;
             Value = value;
             HuffmanEncoded = huffmanEncoded;
             Raw = raw;
+            ValueEncoding = valueEncoding;
         }
 
         public override string ToString() => Name == null ? "<empty>" : (Name + ": " + (Value ?? string.Empty));
diff --git a/src/libraries/Common/tests/System/Net/Http/HPackEncoder.cs b/src/libraries/Common/tests/System/Net/Http/HPackEncoder.cs
index bbdf89f223c21f..9ecaf44f723709 100644
--- a/src/libraries/Common/tests/System/Net/Http/HPackEncoder.cs
+++ b/src/libraries/Common/tests/System/Net/Http/HPackEncoder.cs
@@ -51,7 +51,7 @@ public static int EncodeHeader(int headerIndex, Span<byte> headerBlock)
         public static int EncodeHeader(int nameIdx, string value, HPackFlags flags, Span<byte> headerBlock)
         {
             Debug.Assert(nameIdx > 0);
-            return EncodeHeaderImpl(nameIdx, null, value, flags, headerBlock);
+            return EncodeHeaderImpl(nameIdx, null, value, valueEncoding: null, flags, headerBlock);
         }
 
         /// <summary>
@@ -63,10 +63,15 @@ public static int EncodeHeader(int nameIdx, string value, HPackFlags flags, Span
         /// <returns>The number of bytes written to <paramref name="headerBlock"/>.</returns>
         public static int EncodeHeader(string name, string value, HPackFlags flags, Span<byte> headerBlock)
         {
-            return EncodeHeaderImpl(0, name, value, flags, headerBlock);
+            return EncodeHeader(name, value, valueEncoding: null, flags, headerBlock);
         }
 
-        private static int EncodeHeaderImpl(int nameIdx, string name, string value, HPackFlags flags, Span<byte> headerBlock)
+        public static int EncodeHeader(string name, string value, Encoding valueEncoding, HPackFlags flags, Span<byte> headerBlock)
+        {
+            return EncodeHeaderImpl(0, name, value, valueEncoding, flags, headerBlock);
+        }
+
+        private static int EncodeHeaderImpl(int nameIdx, string name, string value, Encoding valueEncoding, HPackFlags flags, Span<byte> headerBlock)
         {
             const HPackFlags IndexingMask = HPackFlags.NeverIndexed | HPackFlags.NewIndexed | HPackFlags.WithoutIndexing;
 
@@ -97,16 +102,16 @@ private static int EncodeHeaderImpl(int nameIdx, string name, string value, HPac
 
             if (name != null)
             {
-                bytesGenerated += EncodeString(name, headerBlock.Slice(bytesGenerated), (flags & HPackFlags.HuffmanEncodeName) != 0);
+                bytesGenerated += EncodeString(name, Encoding.ASCII, headerBlock.Slice(bytesGenerated), (flags & HPackFlags.HuffmanEncodeName) != 0);
             }
 
-            bytesGenerated += EncodeString(value, headerBlock.Slice(bytesGenerated), (flags & HPackFlags.HuffmanEncodeValue) != 0);
+            bytesGenerated += EncodeString(value, valueEncoding, headerBlock.Slice(bytesGenerated), (flags & HPackFlags.HuffmanEncodeValue) != 0);
             return bytesGenerated;
         }
 
-        public static int EncodeString(string value, Span<byte> headerBlock, bool huffmanEncode)
+        public static int EncodeString(string value, Encoding valueEncoding, Span<byte> headerBlock, bool huffmanEncode)
         {
-            byte[] data = Encoding.ASCII.GetBytes(value);
+            byte[] data = (valueEncoding ?? Encoding.ASCII).GetBytes(value);
             byte prefix;
 
             if (!huffmanEncode)
diff --git a/src/libraries/Common/tests/System/Net/Http/Http2LoopbackConnection.cs b/src/libraries/Common/tests/System/Net/Http/Http2LoopbackConnection.cs
index 3750a36d15bef1..4701cecd248fba 100644
--- a/src/libraries/Common/tests/System/Net/Http/Http2LoopbackConnection.cs
+++ b/src/libraries/Common/tests/System/Net/Http/Http2LoopbackConnection.cs
@@ -7,6 +7,7 @@
 using System.Net.Http.Functional.Tests;
 using System.Net.Security;
 using System.Net.Sockets;
+using System.Security.Cryptography.X509Certificates;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -17,28 +18,40 @@ namespace System.Net.Test.Common
 {
     public class Http2LoopbackConnection : GenericLoopbackConnection
     {
+        public const string Http2Prefix = "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n";
+
         private Socket _connectionSocket;
         private Stream _connectionStream;
         private TaskCompletionSource<bool> _ignoredSettingsAckPromise;
         private bool _ignoreWindowUpdates;
-        public static TimeSpan Timeout => Http2LoopbackServer.Timeout;
+        private readonly TimeSpan _timeout;
         private int _lastStreamId;
 
-        private readonly byte[] _prefix;
+        private readonly byte[] _prefix = new byte[24];
         public string PrefixString => Encoding.UTF8.GetString(_prefix, 0, _prefix.Length);
         public bool IsInvalid => _connectionSocket == null;
         public Stream Stream => _connectionStream;
+        public Task<bool> SettingAckWaiter => _ignoredSettingsAckPromise?.Task;
 
-        public Http2LoopbackConnection(Socket socket, Http2Options httpOptions)
+        private Http2LoopbackConnection(Socket socket, Stream stream, TimeSpan timeout)
         {
             _connectionSocket = socket;
-            _connectionStream = new NetworkStream(_connectionSocket, true);
+            _connectionStream = stream;
+            _timeout = timeout;
+        }
+
+        public static Task<Http2LoopbackConnection> CreateAsync(Socket socket, Stream stream, Http2Options httpOptions)
+        {
+            return CreateAsync(socket, stream, httpOptions, Http2LoopbackServer.Timeout);
+        }
 
+        public static async Task<Http2LoopbackConnection> CreateAsync(Socket socket, Stream stream, Http2Options httpOptions, TimeSpan timeout)
+        {
             if (httpOptions.UseSsl)
             {
-                var sslStream = new SslStream(_connectionStream, false, delegate { return true; });
+                var sslStream = new SslStream(stream, false, delegate { return true; });
 
-                using (var cert = Configuration.Certificates.GetServerCertificate())
+                using (X509Certificate2 cert = Configuration.Certificates.GetServerCertificate())
                 {
 #if !NETFRAMEWORK
                     SslServerAuthenticationOptions options = new SslServerAuthenticationOptions();
@@ -47,28 +60,35 @@ public Http2LoopbackConnection(Socket socket, Http2Options httpOptions)
 
                     var protocols = new List<SslApplicationProtocol>();
                     protocols.Add(SslApplicationProtocol.Http2);
-                    protocols.Add(SslApplicationProtocol.Http11);
                     options.ApplicationProtocols = protocols;
 
                     options.ServerCertificate = cert;
 
                     options.ClientCertificateRequired = httpOptions.ClientCertificateRequired;
 
-                    sslStream.AuthenticateAsServerAsync(options, CancellationToken.None).Wait();
+                    await sslStream.AuthenticateAsServerAsync(options, CancellationToken.None).ConfigureAwait(false);
 #else
-                    sslStream.AuthenticateAsServerAsync(cert, httpOptions.ClientCertificateRequired, httpOptions.SslProtocols, checkCertificateRevocation: false).Wait();
+                    await sslStream.AuthenticateAsServerAsync(cert, httpOptions.ClientCertificateRequired, httpOptions.SslProtocols, checkCertificateRevocation: false).ConfigureAwait(false);
 #endif
                 }
 
-                _connectionStream = sslStream;
+                stream = sslStream;
             }
 
-            _prefix = new byte[24];
-            if (!FillBufferAsync(_prefix).Result)
+            var con = new Http2LoopbackConnection(socket, stream, timeout);
+            await con.ReadPrefixAsync().ConfigureAwait(false);
+
+            return con;
+        }
+
+        private async Task ReadPrefixAsync()
+        {
+            if (!await FillBufferAsync(_prefix))
             {
                 throw new Exception("Connection stream closed while attempting to read connection preface.");
             }
-            else if (Text.Encoding.ASCII.GetString(_prefix).Contains("HTTP/1.1"))
+
+            if (Text.Encoding.ASCII.GetString(_prefix).Contains("HTTP/1.1"))
             {
                 throw new Exception("HTTP 1.1 request received.");
             }
@@ -81,12 +101,12 @@ public async Task SendConnectionPrefaceAsync()
             await WriteFrameAsync(emptySettings).ConfigureAwait(false);
 
             // Receive and ACK the client settings frame.
-            Frame clientSettings = await ReadFrameAsync(Timeout).ConfigureAwait(false);
+            Frame clientSettings = await ReadFrameAsync(_timeout).ConfigureAwait(false);
             clientSettings.Flags = clientSettings.Flags | FrameFlags.Ack;
             await WriteFrameAsync(clientSettings).ConfigureAwait(false);
 
             // Receive the client ACK of the server settings frame.
-            clientSettings = await ReadFrameAsync(Timeout).ConfigureAwait(false);
+            clientSettings = await ReadFrameAsync(_timeout).ConfigureAwait(false);
         }
 
         public async Task WriteFrameAsync(Frame frame)
@@ -225,7 +245,7 @@ public void IgnoreWindowUpdates()
 
         public async Task ReadRstStreamAsync(int streamId)
         {
-            Frame frame = await ReadFrameAsync(Timeout);
+            Frame frame = await ReadFrameAsync(_timeout);
 
             if (frame == null)
             {
@@ -248,7 +268,7 @@ public async Task WaitForClientDisconnectAsync(bool ignoreUnexpectedFrames = fal
         {
             IgnoreWindowUpdates();
 
-            Frame frame = await ReadFrameAsync(Timeout).ConfigureAwait(false);
+            Frame frame = await ReadFrameAsync(_timeout).ConfigureAwait(false);
             if (frame != null)
             {
                 if (!ignoreUnexpectedFrames)
@@ -268,7 +288,7 @@ public async Task WaitForClientDisconnectAsync(bool ignoreUnexpectedFrames = fal
 
         public void ShutdownSend()
         {
-            _connectionSocket.Shutdown(SocketShutdown.Send);
+            _connectionSocket?.Shutdown(SocketShutdown.Send);
         }
 
         // This will cause a server-initiated shutdown of the connection.
@@ -310,7 +330,7 @@ public async Task<int> ReadRequestHeaderAsync()
         public async Task<HeadersFrame> ReadRequestHeaderFrameAsync()
         {
             // Receive HEADERS frame for request.
-            Frame frame = await ReadFrameAsync(Timeout).ConfigureAwait(false);
+            Frame frame = await ReadFrameAsync(_timeout).ConfigureAwait(false);
             if (frame == null)
             {
                 throw new IOException("Failed to read Headers frame.");
@@ -476,7 +496,7 @@ public async Task<byte[]> ReadBodyAsync(bool expectEndOfStream = false)
 
             do
             {
-                frame = await ReadFrameAsync(Timeout).ConfigureAwait(false);
+                frame = await ReadFrameAsync(_timeout).ConfigureAwait(false);
                 if (frame == null && expectEndOfStream)
                 {
                     break;
@@ -516,7 +536,7 @@ public async Task<byte[]> ReadBodyAsync(bool expectEndOfStream = false)
             HttpRequestData requestData = new HttpRequestData();
 
             // Receive HEADERS frame for request.
-            Frame frame = await ReadFrameAsync(Timeout).ConfigureAwait(false);
+            Frame frame = await ReadFrameAsync(_timeout).ConfigureAwait(false);
             if (frame == null)
             {
                 throw new IOException("Failed to read Headers frame.");
@@ -556,6 +576,41 @@ public async Task<byte[]> ReadBodyAsync(bool expectEndOfStream = false)
             return (streamId, requestData);
         }
 
+        public override Task InitializeConnectionAsync()
+        {
+            return ReadAndSendSettingsAsync(ackTimeout: null);
+        }
+
+        public async Task<SettingsFrame> ReadAndSendSettingsAsync(TimeSpan? ackTimeout, params SettingsEntry[] settingsEntries)
+        {
+            // Receive the initial client settings frame.
+            Frame receivedFrame = await ReadFrameAsync(_timeout).ConfigureAwait(false);
+            Assert.Equal(FrameType.Settings, receivedFrame.Type);
+            Assert.Equal(FrameFlags.None, receivedFrame.Flags);
+            Assert.Equal(0, receivedFrame.StreamId);
+
+            var clientSettingsFrame = (SettingsFrame)receivedFrame;
+
+            // Receive the initial client window update frame.
+            receivedFrame = await ReadFrameAsync(_timeout).ConfigureAwait(false);
+            Assert.Equal(FrameType.WindowUpdate, receivedFrame.Type);
+            Assert.Equal(FrameFlags.None, receivedFrame.Flags);
+            Assert.Equal(0, receivedFrame.StreamId);
+
+            // Send the initial server settings frame.
+            SettingsFrame settingsFrame = new SettingsFrame(settingsEntries);
+            await WriteFrameAsync(settingsFrame).ConfigureAwait(false);
+
+            // Send the client settings frame ACK.
+            Frame settingsAck = new Frame(0, FrameType.Settings, FrameFlags.Ack, 0);
+            await WriteFrameAsync(settingsAck).ConfigureAwait(false);
+
+            // The client will send us a SETTINGS ACK eventually, but not necessarily right away.
+            await ExpectSettingsAckAsync((int?)ackTimeout?.TotalMilliseconds ?? 5000);
+
+            return clientSettingsFrame;
+        }
+
         public async Task SendGoAway(int lastStreamId, ProtocolErrors errorCode = ProtocolErrors.NO_ERROR)
         {
             GoAwayFrame frame = new GoAwayFrame(lastStreamId, (int)errorCode, new byte[] { }, 0);
@@ -567,7 +622,7 @@ public async Task PingPong()
             byte[] pingData = new byte[8] { 1, 2, 3, 4, 50, 60, 70, 80 };
             PingFrame ping = new PingFrame(pingData, FrameFlags.None, 0);
             await WriteFrameAsync(ping).ConfigureAwait(false);
-            PingFrame pingAck = (PingFrame)await ReadFrameAsync(Timeout).ConfigureAwait(false);
+            PingFrame pingAck = (PingFrame)await ReadFrameAsync(_timeout).ConfigureAwait(false);
             if (pingAck == null || pingAck.Type != FrameType.Ping || !pingAck.AckFlag)
             {
                 throw new Exception("Expected PING ACK");
@@ -608,7 +663,7 @@ public async Task SendResponseHeadersAsync(int streamId, bool endStream = true,
             {
                 foreach (HttpHeaderData headerData in headers)
                 {
-                    bytesGenerated += HPackEncoder.EncodeHeader(headerData.Name, headerData.Value, headerData.HuffmanEncoded ? HPackFlags.HuffmanEncode : HPackFlags.None, headerBlock.AsSpan(bytesGenerated));
+                    bytesGenerated += HPackEncoder.EncodeHeader(headerData.Name, headerData.Value, headerData.ValueEncoding, headerData.HuffmanEncoded ? HPackFlags.HuffmanEncode : HPackFlags.None, headerBlock.AsSpan(bytesGenerated));
                 }
             }
 
@@ -643,7 +698,11 @@ public async Task SendResponseBodyAsync(int streamId, ReadOnlyMemory<byte> respo
 
         public override void Dispose()
         {
-            ShutdownIgnoringErrorsAsync(_lastStreamId).GetAwaiter().GetResult();
+            // Might have been already shutdown manually via WaitForConnectionShutdownAsync which nulls the _connectionStream.
+            if (_connectionStream != null)
+            {
+                ShutdownIgnoringErrorsAsync(_lastStreamId).GetAwaiter().GetResult();
+            }
         }
 
         //
@@ -729,6 +788,29 @@ public override Task SendResponseBodyAsync(byte[] body, bool isFinal = true, int
             return SendResponseBodyAsync(streamId, body, isFinal);
         }
 
+        public override async Task<HttpRequestData> HandleRequestAsync(HttpStatusCode statusCode = HttpStatusCode.OK, IList<HttpHeaderData> headers = null, string content = "")
+        {
+            (int streamId, HttpRequestData requestData) = await ReadAndParseRequestHeaderAsync().ConfigureAwait(false);
+
+            // We are about to close the connection, after we send the response.
+            // So, send a GOAWAY frame now so the client won't inadvertantly try to reuse the connection.
+            await SendGoAway(streamId).ConfigureAwait(false);
+
+            if (string.IsNullOrEmpty(content))
+            {
+                await SendResponseHeadersAsync(streamId, endStream: true, statusCode, isTrailingHeader: false, headers : headers).ConfigureAwait(false);
+            }
+            else
+            {
+                await SendResponseHeadersAsync(streamId, endStream: false, statusCode, isTrailingHeader: false, headers : headers).ConfigureAwait(false);
+                await SendResponseBodyAsync(streamId, Encoding.ASCII.GetBytes(content)).ConfigureAwait(false);
+            }
+
+            await WaitForConnectionShutdownAsync().ConfigureAwait(false);
+
+            return requestData;
+        }
+
         public override async Task WaitForCancellationAsync(bool ignoreIncomingData = true, int requestId = 0)
         {
             int streamId = requestId == 0 ? _lastStreamId : requestId;
diff --git a/src/libraries/Common/tests/System/Net/Http/Http2LoopbackServer.cs b/src/libraries/Common/tests/System/Net/Http/Http2LoopbackServer.cs
index a3ff123657a680..53757b9ad56711 100644
--- a/src/libraries/Common/tests/System/Net/Http/Http2LoopbackServer.cs
+++ b/src/libraries/Common/tests/System/Net/Http/Http2LoopbackServer.cs
@@ -74,7 +74,12 @@ private void RemoveInvalidConnections()
             _connections.RemoveAll((c) => c.IsInvalid);
         }
 
-        public async Task<Http2LoopbackConnection> AcceptConnectionAsync()
+        public Task<Http2LoopbackConnection> AcceptConnectionAsync()
+        {
+            return AcceptConnectionAsync(null);
+        }
+
+        public async Task<Http2LoopbackConnection> AcceptConnectionAsync(TimeSpan? timeout)
         {
             RemoveInvalidConnections();
 
@@ -85,7 +90,10 @@ public async Task<Http2LoopbackConnection> AcceptConnectionAsync()
 
             Socket connectionSocket = await _listenSocket.AcceptAsync().ConfigureAwait(false);
 
-            Http2LoopbackConnection connection = new Http2LoopbackConnection(connectionSocket, _options);
+            var stream = new NetworkStream(connectionSocket, ownsSocket: true);
+            Http2LoopbackConnection connection =
+                timeout != null ? await Http2LoopbackConnection.CreateAsync(connectionSocket, stream, _options, timeout.Value).ConfigureAwait(false) :
+                await Http2LoopbackConnection.CreateAsync(connectionSocket, stream, _options).ConfigureAwait(false);
             _connections.Add(connection);
 
             return connection;
@@ -96,40 +104,26 @@ public override async Task<GenericLoopbackConnection> EstablishGenericConnection
             return await EstablishConnectionAsync();
         }
 
-        public async Task<Http2LoopbackConnection> EstablishConnectionAsync(params SettingsEntry[] settingsEntries)
+        public Task<Http2LoopbackConnection> EstablishConnectionAsync(params SettingsEntry[] settingsEntries)
         {
-            (Http2LoopbackConnection connection, _) = await EstablishConnectionGetSettingsAsync(settingsEntries).ConfigureAwait(false);
-            return connection;
+            return EstablishConnectionAsync(timeout: null, ackTimeout: null, settingsEntries);
         }
 
-        public async Task<(Http2LoopbackConnection, SettingsFrame)> EstablishConnectionGetSettingsAsync(params SettingsEntry[] settingsEntries)
+        public async Task<Http2LoopbackConnection> EstablishConnectionAsync(TimeSpan? timeout, TimeSpan? ackTimeout, params SettingsEntry[] settingsEntries)
         {
-            Http2LoopbackConnection connection = await AcceptConnectionAsync().ConfigureAwait(false);
-
-            // Receive the initial client settings frame.
-            Frame receivedFrame = await connection.ReadFrameAsync(Timeout).ConfigureAwait(false);
-            Assert.Equal(FrameType.Settings, receivedFrame.Type);
-            Assert.Equal(FrameFlags.None, receivedFrame.Flags);
-            Assert.Equal(0, receivedFrame.StreamId);
-
-            var clientSettingsFrame = (SettingsFrame)receivedFrame;
-
-            // Receive the initial client window update frame.
-            receivedFrame = await connection.ReadFrameAsync(Timeout).ConfigureAwait(false);
-            Assert.Equal(FrameType.WindowUpdate, receivedFrame.Type);
-            Assert.Equal(FrameFlags.None, receivedFrame.Flags);
-            Assert.Equal(0, receivedFrame.StreamId);
-
-            // Send the initial server settings frame.
-            SettingsFrame settingsFrame = new SettingsFrame(settingsEntries);
-            await connection.WriteFrameAsync(settingsFrame).ConfigureAwait(false);
+            (Http2LoopbackConnection connection, _) = await EstablishConnectionGetSettingsAsync(timeout, ackTimeout, settingsEntries).ConfigureAwait(false);
+            return connection;
+        }
 
-            // Send the client settings frame ACK.
-            Frame settingsAck = new Frame(0, FrameType.Settings, FrameFlags.Ack, 0);
-            await connection.WriteFrameAsync(settingsAck).ConfigureAwait(false);
+        public Task<(Http2LoopbackConnection, SettingsFrame)> EstablishConnectionGetSettingsAsync(params SettingsEntry[] settingsEntries)
+        {
+            return EstablishConnectionGetSettingsAsync(timeout: null, ackTimeout: null, settingsEntries);
+        }
 
-            // The client will send us a SETTINGS ACK eventually, but not necessarily right away.
-            await connection.ExpectSettingsAckAsync();
+        public async Task<(Http2LoopbackConnection, SettingsFrame)> EstablishConnectionGetSettingsAsync(TimeSpan? timeout, TimeSpan? ackTimeout, params SettingsEntry[] settingsEntries)
+        {
+            Http2LoopbackConnection connection = await AcceptConnectionAsync(timeout).ConfigureAwait(false);
+            SettingsFrame clientSettingsFrame = await connection.ReadAndSendSettingsAsync(ackTimeout, settingsEntries).ConfigureAwait(false);
 
             return (connection, clientSettingsFrame);
         }
@@ -149,27 +143,10 @@ public override void Dispose()
 
         public override async Task<HttpRequestData> HandleRequestAsync(HttpStatusCode statusCode = HttpStatusCode.OK, IList<HttpHeaderData> headers = null, string content = "")
         {
-            Http2LoopbackConnection connection = await EstablishConnectionAsync().ConfigureAwait(false);
-
-            (int streamId, HttpRequestData requestData) = await connection.ReadAndParseRequestHeaderAsync().ConfigureAwait(false);
-
-            // We are about to close the connection, after we send the response.
-            // So, send a GOAWAY frame now so the client won't inadvertantly try to reuse the connection.
-            await connection.SendGoAway(streamId).ConfigureAwait(false);
-
-            if (string.IsNullOrEmpty(content))
-            {
-                await connection.SendResponseHeadersAsync(streamId, endStream: true, statusCode, isTrailingHeader: false, headers : headers).ConfigureAwait(false);
-            }
-            else
+            using (Http2LoopbackConnection connection = await EstablishConnectionAsync().ConfigureAwait(false))
             {
-                await connection.SendResponseHeadersAsync(streamId, endStream: false, statusCode, isTrailingHeader: false, headers : headers).ConfigureAwait(false);
-                await connection.SendResponseBodyAsync(streamId, Encoding.ASCII.GetBytes(content)).ConfigureAwait(false);
-            }
-
-            await connection.WaitForConnectionShutdownAsync().ConfigureAwait(false);
-
-            return requestData;
+                return await connection.HandleRequestAsync(statusCode, headers, content).ConfigureAwait(false);
+			}
         }
 
         public override async Task AcceptConnectionAsync(Func<GenericLoopbackConnection, Task> funcAsync)
@@ -199,13 +176,10 @@ public static async Task CreateClientAndServerAsync(Func<Uri, Task> clientFunc,
 
     public class Http2Options : GenericLoopbackOptions
     {
-        public int ListenBacklog { get; set; } = 1;
-
         public bool ClientCertificateRequired { get; set; }
 
         public Http2Options()
         {
-            UseSsl = PlatformDetection.SupportsAlpn && !Capability.Http2ForceUnencryptedLoopback();
             SslProtocols = SslProtocols.Tls12;
         }
     }
@@ -223,6 +197,16 @@ public static async Task CreateServerAsync(Func<Http2LoopbackServer, Uri, Task>
         }
 
         public override GenericLoopbackServer CreateServer(GenericLoopbackOptions options = null)
+        {
+            return Http2LoopbackServer.CreateServer(CreateOptions(options));
+        }
+
+        public override async Task<GenericLoopbackConnection> CreateConnectionAsync(Socket socket, Stream stream, GenericLoopbackOptions options = null)
+        {
+            return await Http2LoopbackConnection.CreateAsync(socket, stream, CreateOptions(options)).ConfigureAwait(false);
+        }
+
+        private static Http2Options CreateOptions(GenericLoopbackOptions options)
         {
             Http2Options http2Options = new Http2Options();
             if (options != null)
@@ -230,9 +214,9 @@ public override GenericLoopbackServer CreateServer(GenericLoopbackOptions option
                 http2Options.Address = options.Address;
                 http2Options.UseSsl = options.UseSsl;
                 http2Options.SslProtocols = options.SslProtocols;
+                http2Options.ListenBacklog = options.ListenBacklog;
             }
-
-            return Http2LoopbackServer.CreateServer(http2Options);
+            return http2Options;
         }
 
         public override async Task CreateServerAsync(Func<GenericLoopbackServer, Uri, Task> funcAsync, int millisecondsTimeout = 60_000, GenericLoopbackOptions options = null)
@@ -243,7 +227,7 @@ public override async Task CreateServerAsync(Func<GenericLoopbackServer, Uri, Ta
             }
         }
 
-    public override Version Version => HttpVersion20.Value;
+        public override Version Version => HttpVersion20.Value;
     }
 
     public enum ProtocolErrors
diff --git a/src/libraries/Common/tests/System/Net/Http/Http3LoopbackConnection.cs b/src/libraries/Common/tests/System/Net/Http/Http3LoopbackConnection.cs
index 5d6f3e70fe2d53..6a63bb3f39fb85 100644
--- a/src/libraries/Common/tests/System/Net/Http/Http3LoopbackConnection.cs
+++ b/src/libraries/Common/tests/System/Net/Http/Http3LoopbackConnection.cs
@@ -8,6 +8,7 @@
 using System.Text;
 using System.Threading.Tasks;
 using System.Linq;
+using System.Net.Http.Functional.Tests;
 
 namespace System.Net.Test.Common
 {
@@ -84,6 +85,11 @@ public Http3LoopbackStream GetOpenRequest(int requestId = 0)
             return requestId == 0 ? _currentStream : _openStreams[requestId - 1];
         }
 
+        public override Task InitializeConnectionAsync()
+        {
+            throw new NotImplementedException();
+        }
+
         public async Task<Http3LoopbackStream> AcceptStreamAsync()
         {
             QuicStream quicStream = await _connection.AcceptStreamAsync().ConfigureAwait(false);
@@ -162,6 +168,14 @@ private async Task SendResponseHeadersAsync(HttpStatusCode? statusCode = HttpSta
             await GetOpenRequest(requestId).SendHeadersFrameAsync(headers).ConfigureAwait(false);
         }
 
+        public override async Task<HttpRequestData> HandleRequestAsync(HttpStatusCode statusCode = HttpStatusCode.OK, IList<HttpHeaderData> headers = null, string content = "")
+        {
+            HttpRequestData request = await ReadRequestDataAsync().ConfigureAwait(false);
+            await SendResponseAsync(statusCode, headers, content).ConfigureAwait(false);
+            await CloseAsync(Http3LoopbackConnection.H3_NO_ERROR);
+            return request;
+        }
+
         public override async Task WaitForCancellationAsync(bool ignoreIncomingData = true, int requestId = 0)
         {
             await GetOpenRequest(requestId).WaitForCancellationAsync(ignoreIncomingData).ConfigureAwait(false);
diff --git a/src/libraries/Common/tests/System/Net/Http/Http3LoopbackServer.cs b/src/libraries/Common/tests/System/Net/Http/Http3LoopbackServer.cs
index 411557089b3d9f..b290c5a074ab88 100644
--- a/src/libraries/Common/tests/System/Net/Http/Http3LoopbackServer.cs
+++ b/src/libraries/Common/tests/System/Net/Http/Http3LoopbackServer.cs
@@ -3,8 +3,10 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.IO;
 using System.Net.Quic;
 using System.Net.Security;
+using System.Net.Sockets;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading.Tasks;
 
@@ -26,7 +28,7 @@ public Http3LoopbackServer(GenericLoopbackOptions options = null)
             var sslOpts = new SslServerAuthenticationOptions
             {
                 EnabledSslProtocols = options.SslProtocols,
-                ApplicationProtocols = new List<SslApplicationProtocol> { SslApplicationProtocol.Http3 },
+                ApplicationProtocols = new List<SslApplicationProtocol> { new SslApplicationProtocol("h3") },
                 //ServerCertificate = _cert,
                 ClientCertificateRequired = false
             };
@@ -56,11 +58,7 @@ public override async Task AcceptConnectionAsync(Func<GenericLoopbackConnection,
         public override async Task<HttpRequestData> HandleRequestAsync(HttpStatusCode statusCode = HttpStatusCode.OK, IList<HttpHeaderData> headers = null, string content = "")
         {
             using var con = (Http3LoopbackConnection)await EstablishGenericConnectionAsync().ConfigureAwait(false);
-
-            HttpRequestData request = await con.ReadRequestDataAsync().ConfigureAwait(false);
-            await con.SendResponseAsync(statusCode, headers, content).ConfigureAwait(false);
-            await con.CloseAsync(Http3LoopbackConnection.H3_NO_ERROR);
-            return request;
+            return await con.HandleRequestAsync(statusCode, headers, content).ConfigureAwait(false);
         }
     }
 
@@ -68,7 +66,7 @@ public sealed class Http3LoopbackServerFactory : LoopbackServerFactory
     {
         public static Http3LoopbackServerFactory Singleton { get; } = new Http3LoopbackServerFactory();
 
-        public override Version Version => HttpVersion.Version30;
+        public override Version Version { get; } = new Version(3, 0);
 
         public override GenericLoopbackServer CreateServer(GenericLoopbackOptions options = null)
         {
@@ -80,5 +78,12 @@ public override async Task CreateServerAsync(Func<GenericLoopbackServer, Uri, Ta
             using GenericLoopbackServer server = CreateServer(options);
             await funcAsync(server, server.Address).TimeoutAfter(millisecondsTimeout).ConfigureAwait(false);
         }
+
+        public override Task<GenericLoopbackConnection> CreateConnectionAsync(Socket socket, Stream stream, GenericLoopbackOptions options = null)
+        {
+            // TODO: make a new overload that takes a MultiplexedConnection.
+            // This method is always unacceptable to call for HTTP/3.
+            throw new NotImplementedException("HTTP/3 does not operate over a Socket.");
+        }
     }
 }
diff --git a/src/libraries/Common/tests/System/Net/Http/Http3LoopbackStream.cs b/src/libraries/Common/tests/System/Net/Http/Http3LoopbackStream.cs
index f13cbd6d958ab3..d0e8d433ec7098 100644
--- a/src/libraries/Common/tests/System/Net/Http/Http3LoopbackStream.cs
+++ b/src/libraries/Common/tests/System/Net/Http/Http3LoopbackStream.cs
@@ -78,7 +78,7 @@ public async Task SendHeadersFrameAsync(IEnumerable<HttpHeaderData> headers)
 
             foreach (HttpHeaderData header in headers)
             {
-                bytesWritten += QPackTestEncoder.EncodeHeader(buffer.AsSpan(bytesWritten), header.Name, header.Value, header.HuffmanEncoded ? QPackFlags.HuffmanEncode : QPackFlags.None);
+                bytesWritten += QPackTestEncoder.EncodeHeader(buffer.AsSpan(bytesWritten), header.Name, header.Value, header.ValueEncoding, header.HuffmanEncoded ? QPackFlags.HuffmanEncode : QPackFlags.None);
             }
 
             await SendFrameAsync(HeadersFrame, buffer.AsMemory(0, bytesWritten)).ConfigureAwait(false);
diff --git a/src/libraries/Common/tests/System/Net/Http/HttpAgnosticLoopbackServer.cs b/src/libraries/Common/tests/System/Net/Http/HttpAgnosticLoopbackServer.cs
new file mode 100644
index 00000000000000..6a6657b3adb025
--- /dev/null
+++ b/src/libraries/Common/tests/System/Net/Http/HttpAgnosticLoopbackServer.cs
@@ -0,0 +1,263 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Generic;
+using System.IO;
+using System.Net.Security;
+using System.Net.Sockets;
+using System.Security.Authentication;
+using System.Security.Cryptography.X509Certificates;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+
+using Xunit;
+
+namespace System.Net.Test.Common
+{
+    public class HttpAgnosticLoopbackServer : GenericLoopbackServer, IDisposable
+    {
+        private Socket _listenSocket;
+        private HttpAgnosticOptions _options;
+        private Uri _uri;
+
+        public override Uri Address => _uri;
+
+        public static HttpAgnosticLoopbackServer CreateServer()
+        {
+            return new HttpAgnosticLoopbackServer(new HttpAgnosticOptions());
+        }
+
+        public static HttpAgnosticLoopbackServer CreateServer(HttpAgnosticOptions options)
+        {
+            return new HttpAgnosticLoopbackServer(options);
+        }
+
+        private HttpAgnosticLoopbackServer(HttpAgnosticOptions options)
+        {
+            _options = options;
+            _listenSocket = new Socket(_options.Address.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
+            _listenSocket.Bind(new IPEndPoint(_options.Address, 0));
+            _listenSocket.Listen(_options.ListenBacklog);
+
+            var localEndPoint = (IPEndPoint)_listenSocket.LocalEndPoint;
+            var host = _options.Address.AddressFamily == AddressFamily.InterNetworkV6 ? $"[{localEndPoint.Address}]" : localEndPoint.Address.ToString();
+            var scheme = _options.UseSsl ? "https" : "http";
+            _uri = new Uri($"{scheme}://{host}:{localEndPoint.Port}/");
+        }
+
+        public override void Dispose()
+        {
+            if (_listenSocket != null)
+            {
+                _listenSocket.Dispose();
+                _listenSocket = null;
+            }
+        }
+        public override async Task<GenericLoopbackConnection> EstablishGenericConnectionAsync()
+        {
+            Socket socket = await _listenSocket.AcceptAsync().ConfigureAwait(false);
+            Stream stream = new NetworkStream(socket, ownsSocket: true);
+
+            if (_options.UseSsl)
+            {
+                var sslStream = new SslStream(stream, false, delegate { return true; });
+
+                using (X509Certificate2 cert = Configuration.Certificates.GetServerCertificate())
+                {
+                    SslServerAuthenticationOptions options = new SslServerAuthenticationOptions();
+
+                    options.EnabledSslProtocols = _options.SslProtocols;
+
+                    var protocols = new List<SslApplicationProtocol>();
+                    protocols.Add(SslApplicationProtocol.Http11);
+                    protocols.Add(SslApplicationProtocol.Http2);
+                    options.ApplicationProtocols = protocols;
+
+                    options.ServerCertificate = cert;
+
+                    await sslStream.AuthenticateAsServerAsync(options, CancellationToken.None).ConfigureAwait(false);
+                }
+
+                stream = sslStream;
+                if (sslStream.NegotiatedApplicationProtocol == SslApplicationProtocol.Http2)
+                {
+                    // Do not pass original options so the CreateConnectionAsync won't try to do ALPN again.
+                    return await Http2LoopbackServerFactory.Singleton.CreateConnectionAsync(socket, stream);
+                }
+                if (sslStream.NegotiatedApplicationProtocol == SslApplicationProtocol.Http11)
+                {
+                    // Do not pass original options so the CreateConnectionAsync won't try to do ALPN again.
+                    return await Http11LoopbackServerFactory.Singleton.CreateConnectionAsync(socket, stream);
+                }
+                throw new Exception($"Unsupported negotiated protocol {sslStream.NegotiatedApplicationProtocol}");
+            }
+
+            var buffer = new byte[24];
+            var position = 0;
+            while (position < buffer.Length)
+            {
+                var readBytes = await stream.ReadAsync(buffer, position, buffer.Length - position).ConfigureAwait(false);
+                if (readBytes == 0)
+                {
+                    break;
+                }
+                position += readBytes;
+            }
+            
+            var memory = new Memory<byte>(buffer, 0, position);
+            stream = new ReturnBufferStream(stream, memory);
+
+            var prefix = Text.Encoding.ASCII.GetString(memory.Span);
+            if (prefix == Http2LoopbackConnection.Http2Prefix)
+            {
+                if (_options.ClearTextVersion == HttpVersion.Version20 || _options.ClearTextVersion == HttpVersion.Unknown)
+                {
+                    return await Http2LoopbackServerFactory.Singleton.CreateConnectionAsync(socket, stream);
+                }
+            }
+            else
+            {
+                if (_options.ClearTextVersion == HttpVersion.Version11 || _options.ClearTextVersion == HttpVersion.Unknown)
+                {
+                    return await Http11LoopbackServerFactory.Singleton.CreateConnectionAsync(socket, stream);
+                }
+            }
+            
+            throw new Exception($"HTTP/{_options.ClearTextVersion} server cannot establish connection due to unexpected data: '{prefix}'");
+        }
+
+        public override async Task<HttpRequestData> HandleRequestAsync(HttpStatusCode statusCode = HttpStatusCode.OK, IList<HttpHeaderData> headers = null, string content = "")
+        {
+            using (GenericLoopbackConnection connection = await EstablishGenericConnectionAsync().ConfigureAwait(false))
+            {
+                return await connection.HandleRequestAsync(statusCode, headers, content).ConfigureAwait(false);
+            }
+        }
+
+        public override async Task AcceptConnectionAsync(Func<GenericLoopbackConnection, Task> funcAsync)
+        {
+            using (GenericLoopbackConnection connection = await EstablishGenericConnectionAsync().ConfigureAwait(false))
+            {
+                await funcAsync(connection).ConfigureAwait(false);
+            }
+        }
+
+        public static Task CreateClientAndServerAsync(Func<Uri, Task> clientFunc, Func<GenericLoopbackServer, Task> serverFunc, int timeout = 60_000)
+        {
+            return CreateClientAndServerAsync(clientFunc, serverFunc, null, timeout);
+        }
+
+        public static async Task CreateClientAndServerAsync(Func<Uri, Task> clientFunc, Func<GenericLoopbackServer, Task> serverFunc, HttpAgnosticOptions httpOptions, int timeout = 60_000)
+        {
+            using (var server = HttpAgnosticLoopbackServer.CreateServer(httpOptions ?? new HttpAgnosticOptions()))
+            {
+                Task clientTask = clientFunc(server.Address);
+                Task serverTask = serverFunc(server);
+
+                await new Task[] { clientTask, serverTask }.WhenAllOrAnyFailed(timeout).ConfigureAwait(false);
+            }
+        }
+    }
+
+    public class HttpAgnosticOptions : GenericLoopbackOptions
+    {
+        public Version ClearTextVersion { get; set; }
+
+        public HttpAgnosticOptions()
+        {
+            ClearTextVersion = HttpVersion.Version11;
+        }
+    }
+
+    public sealed class HttpAgnosticLoopbackServerFactory : LoopbackServerFactory
+    {
+        public static readonly HttpAgnosticLoopbackServerFactory Singleton = new HttpAgnosticLoopbackServerFactory();
+
+        public static async Task CreateServerAsync(Func<HttpAgnosticLoopbackServer, Uri, Task> funcAsync, int millisecondsTimeout = 60_000)
+        {
+            using (var server = HttpAgnosticLoopbackServer.CreateServer())
+            {
+                await funcAsync(server, server.Address).TimeoutAfter(millisecondsTimeout).ConfigureAwait(false);
+            }
+        }
+
+        public override GenericLoopbackServer CreateServer(GenericLoopbackOptions options = null)
+        {
+            return HttpAgnosticLoopbackServer.CreateServer(CreateOptions(options));
+        }
+
+        public override Task<GenericLoopbackConnection> CreateConnectionAsync(Socket socket, Stream stream, GenericLoopbackOptions options = null)
+        {
+            // This method is always unacceptable to call for an agnostic server.
+            throw new NotImplementedException("HttpAgnosticLoopbackServerFactory cannot create connection.");
+        }
+
+        private static HttpAgnosticOptions CreateOptions(GenericLoopbackOptions options)
+        {
+            HttpAgnosticOptions httpOptions = new HttpAgnosticOptions();
+            if (options != null)
+            {
+                httpOptions.Address = options.Address;
+                httpOptions.UseSsl = options.UseSsl;
+                httpOptions.SslProtocols = options.SslProtocols;
+                httpOptions.ListenBacklog = options.ListenBacklog;
+            }
+            return httpOptions;
+        }
+
+        public override async Task CreateServerAsync(Func<GenericLoopbackServer, Uri, Task> funcAsync, int millisecondsTimeout = 60_000, GenericLoopbackOptions options = null)
+        {
+            using (var server = CreateServer(options))
+            {
+                await funcAsync(server, server.Address).TimeoutAfter(millisecondsTimeout).ConfigureAwait(false);
+            }
+        }
+
+        public override Version Version => HttpVersion.Unknown;
+    }
+
+    internal class ReturnBufferStream : Stream
+    {
+        private Stream _stream;
+        private Memory<byte> _buffer;
+
+        public ReturnBufferStream(Stream stream, Memory<byte> buffer)
+        {
+            _stream = stream;
+            _buffer = buffer;
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            if (_buffer.IsEmpty)
+            {
+                return _stream.Read(buffer, offset, count);
+            }
+
+            var fromBuffer = Math.Min(_buffer.Length, count);
+            _buffer.Slice(0, fromBuffer).CopyTo(new Memory<byte>(buffer, offset, count));
+            _buffer = _buffer.Slice(fromBuffer);
+            offset += fromBuffer;
+            count -= fromBuffer;
+
+            if (count > 0)
+            {
+                return _stream.Read(buffer, offset, count) + fromBuffer;
+            }
+
+            return fromBuffer;
+        }
+
+        public override bool CanRead => _stream.CanRead;
+        public override bool CanSeek => _stream.CanSeek;
+        public override bool CanWrite => _stream.CanWrite;
+        public override long Length => _stream.Length;
+        public override long Position { get => _stream.Position; set => _stream.Position = value; }
+        public override void Flush() => _stream.Flush();
+        public override long Seek(long offset, SeekOrigin origin) => _stream.Seek(offset, origin);
+        public override void SetLength(long value) => _stream.SetLength(value);
+        public override void Write(byte[] buffer, int offset, int count) => _stream.Write(buffer, offset, count);
+
+    }
+}
diff --git a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Cookies.cs b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Cookies.cs
index 0efb7715376545..e722e8bb37c517 100644
--- a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Cookies.cs
+++ b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Cookies.cs
@@ -293,18 +293,19 @@ public async Task GetAsyncWithRedirect_SetCookieContainer_CorrectCookiesSent()
         {
             const string path1 = "/foo";
             const string path2 = "/bar";
+            const string unusedPath = "/unused";
 
             await LoopbackServerFactory.CreateClientAndServerAsync(async url =>
             {
                 Uri url1 = new Uri(url, path1);
                 Uri url2 = new Uri(url, path2);
-                Uri unusedUrl = new Uri(url, "/unused");
+                Uri unusedUrl = new Uri(url, unusedPath);
 
                 HttpClientHandler handler = CreateHttpClientHandler();
                 handler.CookieContainer = new CookieContainer();
-                handler.CookieContainer.Add(url1, new Cookie("cookie1", "value1"));
-                handler.CookieContainer.Add(url2, new Cookie("cookie2", "value2"));
-                handler.CookieContainer.Add(unusedUrl, new Cookie("cookie3", "value3"));
+                handler.CookieContainer.Add(url1, new Cookie("cookie1", "value1", path1));
+                handler.CookieContainer.Add(url2, new Cookie("cookie2", "value2", path2));
+                handler.CookieContainer.Add(unusedUrl, new Cookie("cookie3", "value3", unusedPath));
 
                 using (HttpClient client = CreateHttpClient(handler))
                 {
@@ -393,6 +394,112 @@ await LoopbackServerFactory.CreateServerAsync(async (server, url) =>
             });
         }
 
+        // Default path should be calculated according to https://tools.ietf.org/html/rfc6265#section-5.1.4
+        // When a cookie is being sent without an explicitly defined Path for a URL with URL-Path /path/sub,
+        // the cookie should be added with Path=/path.
+        // ConditionalFact: CookieContainer does not follow RFC6265 on .NET Framework, therefore the (WinHttpHandler) test is expected to fail
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotNetFramework))]
+        public async Task GetAsync_NoPathDefined_CookieAddedWithDefaultPath()
+        {
+            await LoopbackServerFactory.CreateServerAsync(async (server, serverUrl) =>
+            {
+                Uri requestUrl = new Uri(serverUrl, "path/sub");
+                HttpClientHandler handler = CreateHttpClientHandler();
+
+                using (HttpClient client = CreateHttpClient(handler))
+                {
+                    Task<HttpResponseMessage> getResponseTask = client.GetAsync(requestUrl);
+                    Task<HttpRequestData> serverTask = server.HandleRequestAsync(
+                        HttpStatusCode.OK,
+                        new HttpHeaderData[]
+                        {
+                            new HttpHeaderData("Set-Cookie", "A=1"),
+                        },
+                        s_simpleContent);
+                    await TestHelper.WhenAllCompletedOrAnyFailed(getResponseTask, serverTask);
+
+                    Cookie cookie = handler.CookieContainer.GetCookies(requestUrl)[0];
+                    Assert.Equal("/path", cookie.Path);
+                }
+            });
+        }
+
+        // According to RFC6265, cookie path is not expected to match the request's path,
+        // these cookies should be accepted by the client.
+        // ConditionalFact: CookieContainer does not follow RFC6265 on .NET Framework, therefore the (WinHttpHandler) test is expected to fail
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotNetFramework))]
+        public async Task GetAsync_CookiePathDoesNotMatchRequestPath_CookieAccepted()
+        {
+            await LoopbackServerFactory.CreateServerAsync(async (server, serverUrl) =>
+            {
+                Uri requestUrl = new Uri(serverUrl, "original");
+                Uri otherUrl = new Uri(serverUrl, "other");
+                HttpClientHandler handler = CreateHttpClientHandler();
+
+                using (HttpClient client = CreateHttpClient(handler))
+                {
+                    Task<HttpResponseMessage> getResponseTask = client.GetAsync(requestUrl);
+                    Task<HttpRequestData> serverTask = server.HandleRequestAsync(
+                        HttpStatusCode.OK,
+                        new[]
+                        {
+                            new HttpHeaderData("Set-Cookie", "A=1; Path=/other"),
+                        },
+                        s_simpleContent);
+                    await TestHelper.WhenAllCompletedOrAnyFailed(getResponseTask, serverTask);
+
+                    Cookie cookie = handler.CookieContainer.GetCookies(otherUrl)[0];
+                    Assert.Equal("/other", cookie.Path);
+                }
+            });
+        }
+
+        // Based on the OIDC login scenario described in comments:
+        // https://github.com/dotnet/runtime/pull/39250#issuecomment-659783480
+        // https://github.com/dotnet/runtime/issues/26141#issuecomment-612097147
+        // ConditionalFact: CookieContainer does not follow RFC6265 on .NET Framework, therefore the (WinHttpHandler) test is expected to fail
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotNetFramework))]
+        public async Task GetAsync_Redirect_CookiesArePreserved()
+        {
+            HttpClientHandler handler = CreateHttpClientHandler();
+
+            string loginPath = "/login/user";
+            string returnPath = "/return";
+
+            await LoopbackServerFactory.CreateClientAndServerAsync(async serverUrl =>
+                {
+                    Uri loginUrl = new Uri(serverUrl, loginPath);
+                    Uri returnUrl = new Uri(serverUrl, returnPath);
+                    CookieContainer cookies = handler.CookieContainer;
+
+                    using (HttpClient client = CreateHttpClient(handler))
+                    {
+                        client.DefaultRequestHeaders.ConnectionClose = true; // to avoid issues with connection pooling
+                        HttpResponseMessage response = await client.GetAsync(loginUrl);
+                        string content = await response.Content.ReadAsStringAsync();
+                        Assert.Equal(s_simpleContent, content);
+
+                        Cookie cookie = handler.CookieContainer.GetCookies(returnUrl)[0];
+                        Assert.Equal("LoggedIn", cookie.Name);
+                    }
+                },
+                async server =>
+                {
+                    HttpRequestData requestData1 = await server.HandleRequestAsync(HttpStatusCode.Found, new[]
+                    {
+                        new HttpHeaderData("Location", returnPath),
+                        new HttpHeaderData("Set-Cookie", "LoggedIn=true; Path=/return"),
+                    });
+
+                    Assert.Equal(0, requestData1.GetHeaderValueCount("Cookie"));
+
+                    HttpRequestData requestData2 = await server.HandleRequestAsync(content: s_simpleContent, headers: new[]{
+                        new HttpHeaderData("Set-Cookie", "LoggedIn=true; Path=/return"),
+                    });
+                    Assert.Equal("LoggedIn=true", requestData2.GetSingleHeaderValue("Cookie"));
+                });
+        }
+
         [Fact]
         public async Task GetAsync_ReceiveSetCookieHeader_CookieUpdated()
         {
diff --git a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Decompression.cs b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Decompression.cs
index 7ffddeadb45f00..4877f755162504 100644
--- a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Decompression.cs
+++ b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Decompression.cs
@@ -64,9 +64,6 @@ public static IEnumerable<object[]> DecompressedResponse_MethodSpecified_Decompr
             }
         }
 
-        private HttpRequestMessage CreateRequest(HttpMethod method, Uri uri, Version version) =>
-            new HttpRequestMessage(method, uri) { Version = version };
-
         [Theory]
         [MemberData(nameof(DecompressedResponse_MethodSpecified_DecompressedContentReturned_MemberData))]
         public async Task DecompressedResponse_MethodSpecified_DecompressedContentReturned(
diff --git a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Proxy.cs b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Proxy.cs
index ca4c5ce5562aae..2580ea977b29a5 100644
--- a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Proxy.cs
+++ b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Proxy.cs
@@ -261,8 +261,8 @@ public async Task Proxy_SendSecureRequestThruProxy_ConnectTunnelUsed()
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotWindowsNanoServer))]
         public async Task ProxyAuth_Digest_Succeeds()
         {
-            const string expectedUsername = "testusername";
-            const string expectedPassword = "testpassword";
+            const string expectedUsername = "user";
+            const string expectedPassword = "password";
             const string authHeader = "Proxy-Authenticate: Digest realm=\"NetCore\", nonce=\"PwOnWgAAAAAAjnbW438AAJSQi1kAAAAA\", qop=\"auth\", stale=false\r\n";
             LoopbackServer.Options options = new LoopbackServer.Options { IsProxy = true, Username = expectedUsername, Password = expectedPassword };
             var proxyCreds = new NetworkCredential(expectedUsername, expectedPassword);
diff --git a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.ServerCertificates.cs b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.ServerCertificates.cs
index dba69f304dd662..d04b1d7aee6860 100644
--- a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.ServerCertificates.cs
+++ b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.ServerCertificates.cs
@@ -108,7 +108,7 @@ public async Task UseCallback_HaveCredsAndUseAuthenticatedCustomProxyAndPostToSe
                 handler.ServerCertificateCustomValidationCallback = TestHelper.AllowAllCertificates;
                 handler.Proxy = new WebProxy(proxyServer.Uri)
                 {
-                    Credentials = new NetworkCredential("rightusername", "rightpassword")
+                    Credentials = new NetworkCredential("user", "password")
                 };
 
                 const string content = "This is a test";
diff --git a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.cs b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.cs
index e243987445c9f0..371c47f35527d2 100644
--- a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.cs
+++ b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.cs
@@ -230,22 +230,25 @@ public async Task GetAsync_IPv6LinkLocalAddressUri_Success()
                 return;
             }
 
-            using (HttpClient client = CreateHttpClient())
-            {
-                var options = new GenericLoopbackOptions { Address = TestHelper.GetIPv6LinkLocalAddress() };
-                if (options.Address == null)
-                {
-                    throw new SkipTestException("Unable to find valid IPv6 LL address.");
-                }
 
-                await LoopbackServerFactory.CreateServerAsync(async (server, url) =>
-                {
-                    _output.WriteLine(url.ToString());
-                    await TestHelper.WhenAllCompletedOrAnyFailed(
-                        server.AcceptConnectionSendResponseAndCloseAsync(),
-                        client.GetAsync(url));
-                }, options: options);
+            using HttpClientHandler handler = CreateHttpClientHandler();
+            handler.ServerCertificateCustomValidationCallback = TestHelper.AllowAllCertificates;
+
+            using HttpClient client = CreateHttpClient(handler);
+
+            var options = new GenericLoopbackOptions { Address = TestHelper.GetIPv6LinkLocalAddress() };
+            if (options.Address == null)
+            {
+                throw new SkipTestException("Unable to find valid IPv6 LL address.");
             }
+
+            await LoopbackServerFactory.CreateServerAsync(async (server, url) =>
+            {
+                _output.WriteLine(url.ToString());
+                await TestHelper.WhenAllCompletedOrAnyFailed(
+                    server.AcceptConnectionSendResponseAndCloseAsync(),
+                    client.SendAsync(CreateRequest(HttpMethod.Get, url, UseVersion, true)));
+            }, options: options);
         }
 
         [Theory]
@@ -257,17 +260,19 @@ public async Task GetAsync_IPBasedUri_Success(IPAddress address)
                 return;
             }
 
-            using (HttpClient client = CreateHttpClient())
+            using HttpClientHandler handler = CreateHttpClientHandler();
+            handler.ServerCertificateCustomValidationCallback = TestHelper.AllowAllCertificates;
+
+            using HttpClient client = CreateHttpClient(handler);
+
+            var options = new GenericLoopbackOptions { Address = address };
+            await LoopbackServerFactory.CreateServerAsync(async (server, url) =>
             {
-                var options = new GenericLoopbackOptions { Address = address };
-                await LoopbackServerFactory.CreateServerAsync(async (server, url) =>
-                {
-                    _output.WriteLine(url.ToString());
-                    await TestHelper.WhenAllCompletedOrAnyFailed(
-                        server.AcceptConnectionSendResponseAndCloseAsync(),
-                        client.GetAsync(url));
-                }, options: options);
-            }
+                _output.WriteLine(url.ToString());
+                await TestHelper.WhenAllCompletedOrAnyFailed(
+                    server.AcceptConnectionSendResponseAndCloseAsync(),
+                    client.SendAsync(CreateRequest(HttpMethod.Get, url, UseVersion, true)));
+            }, options: options);
         }
 
         public static IEnumerable<object[]> GetAsync_IPBasedUri_Success_MemberData()
@@ -1004,6 +1009,7 @@ await LoopbackServer.CreateClientAndServerAsync(async uri =>
                 $"Accept-Patch:{fold} text/example;charset=utf-8{newline}" +
                 $"Accept-Ranges:{fold} bytes{newline}" +
                 $"Age: {fold}12{newline}" +
+                // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy authorization.")]
                 $"Authorization: Bearer 63123a47139a49829bcd8d03005ca9d7{newline}" +
                 $"Allow: {fold}GET, HEAD{newline}" +
                 $"Alt-Svc:{fold} http/1.1=\"http2.example.com:8001\"; ma=7200{newline}" +
@@ -2115,6 +2121,45 @@ await server.AcceptConnectionAsync(async connection =>
             });
         }
 
+        [Fact]
+        public async Task SendAsync_Expect100Continue_RequestBodyFails_ThrowsContentException()
+        {
+            if (IsWinHttpHandler)
+            {
+                return;
+            }
+            if (!TestAsync && UseVersion >= HttpVersion20.Value)
+            {
+                return;
+            }
+
+            var clientFinished = new TaskCompletionSource<bool>();
+
+            await LoopbackServerFactory.CreateClientAndServerAsync(async uri =>
+            {
+                using (HttpClient client = CreateHttpClient())
+                {
+                    HttpRequestMessage initialMessage = new HttpRequestMessage(HttpMethod.Post, uri) { Version = UseVersion };
+                    initialMessage.Content = new ThrowingContent(() => new ThrowingContentException());
+                    initialMessage.Headers.ExpectContinue = true;
+                    await Assert.ThrowsAsync<ThrowingContentException>(() => client.SendAsync(TestAsync, initialMessage));
+
+                    clientFinished.SetResult(true);
+                }
+            }, async server =>
+            {
+                await server.AcceptConnectionAsync(async connection =>
+                {
+                    try
+                    {
+                        await connection.ReadRequestDataAsync(readBody: true);
+                    }
+                    catch { } // Eat errors from client disconnect.
+                    await clientFinished.Task.TimeoutAfter(TimeSpan.FromMinutes(2));
+                });
+            });
+        }
+
         [Fact]
         public async Task SendAsync_No100ContinueReceived_RequestBodySentEventually()
         {
diff --git a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTestBase.cs b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTestBase.cs
index 9d0e62ea4f443d..7aaeb06224c185 100644
--- a/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTestBase.cs
+++ b/src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTestBase.cs
@@ -20,6 +20,8 @@ namespace System.Net.Http.Functional.Tests
 
     public abstract partial class HttpClientHandlerTestBase : FileCleanupTestBase
     {
+        public static readonly Version HttpVersion30 = new Version(3, 0);
+
         public readonly ITestOutputHelper _output;
 
         protected virtual Version UseVersion => HttpVersion.Version11;
diff --git a/src/libraries/Common/tests/System/Net/Http/LoopbackServer.cs b/src/libraries/Common/tests/System/Net/Http/LoopbackServer.cs
index 208f9d7f29fa49..2c027ca702cd41 100644
--- a/src/libraries/Common/tests/System/Net/Http/LoopbackServer.cs
+++ b/src/libraries/Common/tests/System/Net/Http/LoopbackServer.cs
@@ -7,7 +7,9 @@
 using System.Net.Security;
 using System.Net.Sockets;
 using System.Security.Authentication;
+using System.Security.Cryptography.X509Certificates;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using Xunit;
 
@@ -15,6 +17,9 @@ namespace System.Net.Test.Common
 {
     public sealed partial class LoopbackServer : GenericLoopbackServer, IDisposable
     {
+        private static readonly byte[] s_newLineBytes = new byte[] { (byte)'\r', (byte)'\n' };
+        private static readonly byte[] s_colonSpaceBytes = new byte[] { (byte)':', (byte)' ' };
+
         private Socket _listenSocket;
         private Options _options;
         private Uri _uri;
@@ -101,26 +106,8 @@ public async Task<Connection> EstablishConnectionAsync()
                 catch (SocketException ex) when (ex.SocketErrorCode == SocketError.InvalidArgument && PlatformDetection.IsOSXLike) { }
 
                 Stream stream = new NetworkStream(s, ownsSocket: false);
-                if (_options.UseSsl)
-                {
-                    var sslStream = new SslStream(stream, false, delegate { return true; });
-                    using (var cert = Configuration.Certificates.GetServerCertificate())
-                    {
-                        await sslStream.AuthenticateAsServerAsync(
-                            cert,
-                            clientCertificateRequired: true, // allowed but not required
-                            enabledSslProtocols: _options.SslProtocols,
-                            checkCertificateRevocation: false).ConfigureAwait(false);
-                    }
-                    stream = sslStream;
-                }
-
-                if (_options.StreamWrapper != null)
-                {
-                    stream = _options.StreamWrapper(stream);
-                }
 
-                return new Connection(s, stream);
+                return await Connection.CreateAsync(s, stream, _options);
             }
             catch (Exception)
             {
@@ -386,7 +373,6 @@ public static string GetConnectionCloseResponse(HttpStatusCode statusCode = Http
 
         public class Options : GenericLoopbackOptions
         {
-            public int ListenBacklog { get; set; } = 1;
             public bool WebSocketEndpoint { get; set; } = false;
             public Func<Stream, Stream> StreamWrapper { get; set; }
             public string Username { get; set; }
@@ -433,6 +419,30 @@ public Connection(Socket socket, Stream stream)
             public Stream Stream => _stream;
             public StreamWriter Writer => _writer;
 
+            public static async Task<Connection> CreateAsync(Socket socket, Stream stream, Options httpOptions)
+            {
+                if (httpOptions.UseSsl)
+                {
+                    var sslStream = new SslStream(stream, false, delegate { return true; });
+                    using (X509Certificate2 cert = Configuration.Certificates.GetServerCertificate())
+                    {
+                        await sslStream.AuthenticateAsServerAsync(
+                            cert,
+                            clientCertificateRequired: true, // allowed but not required
+                            enabledSslProtocols: httpOptions.SslProtocols,
+                            checkCertificateRevocation: false).ConfigureAwait(false);
+                    }
+                    stream = sslStream;
+                }
+
+                if (httpOptions.StreamWrapper != null)
+                {
+                    stream = httpOptions.StreamWrapper(stream);
+                }
+
+                return new Connection(socket, stream);
+            }
+
             public async Task<int> ReadAsync(Memory<byte> buffer, int offset, int size)
             {
                 if (_readEnd - _readStart > 0)
@@ -532,6 +542,16 @@ public string ReadLine()
             }
 
             public async Task<string> ReadLineAsync()
+            {
+                byte[] lineBytes = await ReadLineBytesAsync().ConfigureAwait(false);
+
+                if (lineBytes is null)
+                    return null;
+
+                return Encoding.ASCII.GetString(lineBytes);
+            }
+
+            private async Task<byte[]> ReadLineBytesAsync()
             {
                 int index = 0;
                 int startSearch = _readStart;
@@ -578,7 +598,7 @@ public async Task<string> ReadLineAsync()
                     if (_readBuffer[_readStart + stringLength] == '\n') { stringLength--; }
                     if (_readBuffer[_readStart + stringLength] == '\r') { stringLength--; }
 
-                    string line = System.Text.Encoding.ASCII.GetString(_readBuffer, _readStart, stringLength + 1);
+                    byte[] line = _readBuffer.AsSpan(_readStart, stringLength + 1).ToArray();
                     _readStart = index + 1;
                     return line;
                 }
@@ -594,13 +614,18 @@ public override void Dispose()
                     // This seems to help avoid connection reset issues caused by buffered data
                     // that has not been sent/acked when the graceful shutdown timeout expires.
                     // This may throw if the socket was already closed, so eat any exception.
-                    _socket.Shutdown(SocketShutdown.Send);
+                    _socket?.Shutdown(SocketShutdown.Send);
                 }
                 catch (Exception) { }
 
                 _writer.Dispose();
                 _stream.Dispose();
-                _socket.Dispose();
+                _socket?.Dispose();
+            }
+
+            public override Task InitializeConnectionAsync()
+            {
+                return Task.CompletedTask;
             }
 
             public async Task<List<string>> ReadRequestHeaderAsync()
@@ -620,6 +645,32 @@ public async Task<List<string>> ReadRequestHeaderAsync()
                 return lines;
             }
 
+            private async Task<List<byte[]>> ReadRequestHeaderBytesAsync()
+            {
+                var lines = new List<byte[]>();
+
+                byte[] line;
+
+                while (true)
+                {
+                    line = await ReadLineBytesAsync().ConfigureAwait(false);
+
+                    if (line is null || line.Length == 0)
+                    {
+                        break;
+                    }
+
+                    lines.Add(line);
+                }
+
+                if (line == null)
+                {
+                    throw new IOException("Unexpected EOF trying to read request header");
+                }
+
+                return lines;
+            }
+
             public async Task SendResponseAsync(string response)
             {
                 await _writer.WriteAsync(response).ConfigureAwait(false);
@@ -658,24 +709,24 @@ public async Task<List<string>> ReadRequestHeaderAndSendResponseAsync(HttpStatus
 
             public override async Task<HttpRequestData> ReadRequestDataAsync(bool readBody = true)
             {
-                List<string> headerLines = null;
                 HttpRequestData requestData = new HttpRequestData();
 
-                headerLines = await ReadRequestHeaderAsync().ConfigureAwait(false);
+                List<byte[]> headerLines = await ReadRequestHeaderBytesAsync().ConfigureAwait(false);
 
                 // Parse method and path
-                string[] splits = headerLines[0].Split(' ');
+                string[] splits = Encoding.ASCII.GetString(headerLines[0]).Split(' ');
                 requestData.Method = splits[0];
                 requestData.Path = splits[1];
 
                 // Convert header lines to key/value pairs
                 // Skip first line since it's the status line
-                foreach (var line in headerLines.Skip(1))
+                foreach (byte[] lineBytes in headerLines.Skip(1))
                 {
+                    string line = Encoding.ASCII.GetString(lineBytes);
                     int offset = line.IndexOf(':');
                     string name = line.Substring(0, offset);
                     string value = line.Substring(offset + 1).TrimStart();
-                    requestData.Headers.Add(new HttpHeaderData(name, value));
+                    requestData.Headers.Add(new HttpHeaderData(name, value, raw: lineBytes));
                 }
 
                 if (requestData.Method != "GET")
@@ -755,7 +806,7 @@ public override async Task<Byte[]> ReadRequestBodyAsync()
 
             public override async Task SendResponseAsync(HttpStatusCode? statusCode = HttpStatusCode.OK, IList<HttpHeaderData> headers = null, string content = null, bool isFinal = true, int requestId = 0)
             {
-                string headerString = null;
+                MemoryStream headerBytes = new MemoryStream();
                 int contentLength = -1;
                 bool isChunked = false;
                 bool hasContentLength  = false;
@@ -780,22 +831,39 @@ public override async Task SendResponseAsync(HttpStatusCode? statusCode = HttpSt
                             isChunked = true;
                         }
 
-                        headerString = headerString + $"{headerData.Name}: {headerData.Value}\r\n";
+                        byte[] nameBytes = Encoding.ASCII.GetBytes(headerData.Name);
+                        headerBytes.Write(nameBytes, 0, nameBytes.Length);
+                        headerBytes.Write(s_colonSpaceBytes, 0, s_colonSpaceBytes.Length);
+
+                        byte[] valueBytes = (headerData.ValueEncoding ?? Encoding.ASCII).GetBytes(headerData.Value);
+                        headerBytes.Write(valueBytes, 0, valueBytes.Length);
+                        headerBytes.Write(s_newLineBytes, 0, s_newLineBytes.Length);
                     }
                 }
 
                 bool endHeaders = content != null || isFinal;
                 if (statusCode != null)
                 {
-                    // If we need to send status line, prepped it to headers and possibly add missing headers to the end.
-                    headerString =
+                    byte[] temp = headerBytes.ToArray();
+
+                    headerBytes.SetLength(0);
+
+                    byte[] headerStartBytes = Encoding.ASCII.GetBytes(
                         $"HTTP/1.1 {(int)statusCode} {GetStatusDescription((HttpStatusCode)statusCode)}\r\n" +
-                        (!hasContentLength && !isChunked && content != null ? $"Content-length: {content.Length}\r\n" : "") +
-                        headerString +
-                        (endHeaders ? "\r\n" : "");
+                        (!hasContentLength && !isChunked && content != null ? $"Content-length: {content.Length}\r\n" : ""));
+
+                    headerBytes.Write(headerStartBytes, 0, headerStartBytes.Length);
+                    headerBytes.Write(temp, 0, temp.Length);
+
+                    if (endHeaders)
+                    {
+                        headerBytes.Write(s_newLineBytes, 0, s_newLineBytes.Length);
+                    }
                 }
 
-                await SendResponseAsync(headerString).ConfigureAwait(false);
+                headerBytes.Position = 0;
+                await headerBytes.CopyToAsync(_stream).ConfigureAwait(false);
+
                 if (content != null)
                 {
                     await SendResponseBodyAsync(content, isFinal: isFinal, requestId: requestId).ConfigureAwait(false);
@@ -824,31 +892,9 @@ public override async Task SendResponseBodyAsync(byte[] body, bool isFinal = tru
                 await SendResponseAsync(Encoding.UTF8.GetString(body)).ConfigureAwait(false);
             }
 
-            public override async Task WaitForCancellationAsync(bool ignoreIncomingData = true, int requestId = 0)
-            {
-                var buffer = new byte[1024];
-                while (true)
-                {
-                    int bytesRead = await ReadAsync(buffer, 0, buffer.Length).ConfigureAwait(false);
-
-                    if (!ignoreIncomingData)
-                    {
-                        Assert.Equal(0, bytesRead);
-                    }
-
-                    if (bytesRead == 0)
-                    {
-                        break;
-                    }
-                }
-            }
-        }
-
-        public override async Task<HttpRequestData> HandleRequestAsync(HttpStatusCode statusCode = HttpStatusCode.OK, IList<HttpHeaderData> headers = null, string content = "")
-        {
-            using (Connection connection = await EstablishConnectionAsync().ConfigureAwait(false))
+            public override async Task<HttpRequestData> HandleRequestAsync(HttpStatusCode statusCode = HttpStatusCode.OK, IList<HttpHeaderData> headers = null, string content = "")
             {
-                HttpRequestData requestData = await connection.ReadRequestDataAsync().ConfigureAwait(false);
+                HttpRequestData requestData = await ReadRequestDataAsync().ConfigureAwait(false);
 
                 // For historical reasons, we added Date and "Connection: close" (to improve test reliability)
                 bool hasDate = false;
@@ -871,9 +917,36 @@ public override async Task<HttpRequestData> HandleRequestAsync(HttpStatusCode st
                     newHeaders.Add(new HttpHeaderData("Date", "{DateTimeOffset.UtcNow:R}"));
                 }
 
-                await connection.SendResponseAsync(statusCode, newHeaders, content: content).ConfigureAwait(false);
+                await SendResponseAsync(statusCode, newHeaders, content: content).ConfigureAwait(false);
                 return requestData;
             }
+
+            public override async Task WaitForCancellationAsync(bool ignoreIncomingData = true, int requestId = 0)
+            {
+                var buffer = new byte[1024];
+                while (true)
+                {
+                    int bytesRead = await ReadAsync(buffer, 0, buffer.Length).ConfigureAwait(false);
+
+                    if (!ignoreIncomingData)
+                    {
+                        Assert.Equal(0, bytesRead);
+                    }
+
+                    if (bytesRead == 0)
+                    {
+                        break;
+                    }
+                }
+            }
+        }
+
+        public override async Task<HttpRequestData> HandleRequestAsync(HttpStatusCode statusCode = HttpStatusCode.OK, IList<HttpHeaderData> headers = null, string content = "")
+        {
+            using (Connection connection = await EstablishConnectionAsync().ConfigureAwait(false))
+            {
+                return await connection.HandleRequestAsync(statusCode, headers, content).ConfigureAwait(false);
+            }
         }
 
         public override Task AcceptConnectionAsync(Func<GenericLoopbackConnection, Task> funcAsync)
@@ -896,12 +969,20 @@ public override Task CreateServerAsync(Func<GenericLoopbackServer, Uri, Task> fu
             return LoopbackServer.CreateServerAsync((server, uri) => funcAsync(server, uri), options: CreateOptions(options));
         }
 
+        public override async Task<GenericLoopbackConnection> CreateConnectionAsync(Socket socket, Stream stream, GenericLoopbackOptions options = null)
+        {
+            return await LoopbackServer.Connection.CreateAsync(socket, stream, CreateOptions(options));
+        }
+
         private static LoopbackServer.Options CreateOptions(GenericLoopbackOptions options)
         {
             LoopbackServer.Options newOptions = new LoopbackServer.Options();
             if (options != null)
             {
                 newOptions.Address = options.Address;
+                newOptions.UseSsl = options.UseSsl;
+                newOptions.SslProtocols = options.SslProtocols;
+                newOptions.ListenBacklog = options.ListenBacklog;
             }
             return newOptions;
         }
diff --git a/src/libraries/Common/tests/System/Net/Http/QPackTestEncoder.cs b/src/libraries/Common/tests/System/Net/Http/QPackTestEncoder.cs
index 3df439e4dfa578..a73f42067bcb7b 100644
--- a/src/libraries/Common/tests/System/Net/Http/QPackTestEncoder.cs
+++ b/src/libraries/Common/tests/System/Net/Http/QPackTestEncoder.cs
@@ -49,7 +49,7 @@ public static int EncodeHeader(Span<byte> buffer, int nameValueIdx, QPackFlags f
             return EncodeInteger(buffer, nameValueIdx, prefix, prefixMask);
         }
 
-        public static int EncodeHeader(Span<byte> buffer, int nameIdx, string value, QPackFlags flags = QPackFlags.StaticIndex)
+        public static int EncodeHeader(Span<byte> buffer, int nameIdx, string value, Encoding valueEncoding, QPackFlags flags = QPackFlags.StaticIndex)
         {
             byte prefix, prefixMask;
 
@@ -76,12 +76,12 @@ public static int EncodeHeader(Span<byte> buffer, int nameIdx, string value, QPa
             }
 
             int nameLen = EncodeInteger(buffer, nameIdx, prefix, prefixMask);
-            int valueLen = EncodeString(buffer.Slice(nameLen), value, flags.HasFlag(QPackFlags.HuffmanEncodeValue));
+            int valueLen = EncodeString(buffer.Slice(nameLen), value, valueEncoding, flags.HasFlag(QPackFlags.HuffmanEncodeValue));
 
             return nameLen + valueLen;
         }
 
-        public static int EncodeHeader(Span<byte> buffer, string name, string value, QPackFlags flags = QPackFlags.None)
+        public static int EncodeHeader(Span<byte> buffer, string name, string value, Encoding valueEncoding, QPackFlags flags = QPackFlags.None)
         {
             byte[] data = Encoding.ASCII.GetBytes(name);
             byte prefix;
@@ -116,14 +116,14 @@ public static int EncodeHeader(Span<byte> buffer, string name, string value, QPa
             bytesGenerated += data.Length;
 
             // write value string.
-            bytesGenerated += EncodeString(buffer.Slice(bytesGenerated), value, flags.HasFlag(QPackFlags.HuffmanEncodeValue));
+            bytesGenerated += EncodeString(buffer.Slice(bytesGenerated), value, valueEncoding, flags.HasFlag(QPackFlags.HuffmanEncodeValue));
 
             return bytesGenerated;
         }
 
-        public static int EncodeString(Span<byte> buffer, string value, bool huffmanCoded = false)
+        public static int EncodeString(Span<byte> buffer, string value, Encoding valueEncoding, bool huffmanCoded = false)
         {
-            return HPackEncoder.EncodeString(value, buffer, huffmanCoded);
+            return HPackEncoder.EncodeString(value, valueEncoding, buffer, huffmanCoded);
         }
 
         public static int EncodeInteger(Span<byte> buffer, int value, byte prefix, byte prefixMask)
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/ThrowingContent.cs b/src/libraries/Common/tests/System/Net/Http/ThrowingContent.cs
similarity index 88%
rename from src/libraries/System.Net.Http/tests/FunctionalTests/ThrowingContent.cs
rename to src/libraries/Common/tests/System/Net/Http/ThrowingContent.cs
index 276570552bd19f..8b757e8830ea94 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/ThrowingContent.cs
+++ b/src/libraries/Common/tests/System/Net/Http/ThrowingContent.cs
@@ -10,7 +10,7 @@
 namespace System.Net.Http.Functional.Tests
 {
     /// <summary>HttpContent that mocks exceptions on serialization.</summary>
-    public class ThrowingContent : HttpContent
+    public partial class ThrowingContent : HttpContent
     {
         private readonly Func<Exception> _exnFactory;
         private readonly int _length;
@@ -32,4 +32,7 @@ protected override bool TryComputeLength(out long length)
             return true;
         }
     }
+
+    public class ThrowingContentException : Exception
+    { }
 }
diff --git a/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetwork.cs b/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetwork.cs
index 77a4695d0364ba..141fe66284b3b0 100644
--- a/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetwork.cs
+++ b/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetwork.cs
@@ -14,7 +14,7 @@ public class VirtualNetworkConnectionBroken : Exception
             public VirtualNetworkConnectionBroken() : base("Connection broken") { }
         }
 
-        private readonly int WaitForReadDataTimeoutMilliseconds = 30 * 1000;
+        private readonly int WaitForReadDataTimeoutMilliseconds = 60 * 1000;
 
         private readonly ConcurrentQueue<byte[]> _clientWriteQueue = new ConcurrentQueue<byte[]>();
         private readonly ConcurrentQueue<byte[]> _serverWriteQueue = new ConcurrentQueue<byte[]>();
@@ -22,8 +22,11 @@ public VirtualNetworkConnectionBroken() : base("Connection broken") { }
         private readonly SemaphoreSlim _clientDataAvailable = new SemaphoreSlim(0);
         private readonly SemaphoreSlim _serverDataAvailable = new SemaphoreSlim(0);
 
+        private volatile bool _clientWriteShutdown = false;
+        private volatile bool _serverWriteShutdown = false;
+
         public bool DisableConnectionBreaking { get; set; } = false;
-        private bool _connectionBroken = false;
+        private volatile bool _connectionBroken = false;
 
         public byte[] ReadFrame(bool server) =>
             ReadFrameCoreAsync(server, sync: true, cancellationToken: default).GetAwaiter().GetResult();
@@ -75,6 +78,11 @@ private async Task<byte[]> ReadFrameCoreAsync(bool server, bool sync, Cancellati
                     return buffer;
                 }
 
+                if ((server && _clientWriteShutdown) || (!server && _serverWriteShutdown))
+                {
+                    return Array.Empty<byte>();
+                }
+
                 remainingTries--;
                 backOffDelayMilliseconds *= backOffDelayMilliseconds;
                 if (sync)
@@ -98,6 +106,16 @@ public void WriteFrame(bool server, byte[] buffer)
                 throw new VirtualNetworkConnectionBroken();
             }
 
+            if ((server && _serverWriteShutdown) || (!server && _clientWriteShutdown))
+            {
+                throw new InvalidOperationException("Writing to a shutdown side.");
+            }
+
+            if (buffer.Length == 0)
+            {
+                return;
+            }
+
             SemaphoreSlim semaphore;
             ConcurrentQueue<byte[]> packetQueue;
 
@@ -116,11 +134,25 @@ public void WriteFrame(bool server, byte[] buffer)
             semaphore.Release();
         }
 
+        public void GracefulShutdown(bool server)
+        {
+            if (server)
+            {
+                _serverWriteShutdown = true;
+                _serverDataAvailable.Release(1_000_000);
+            }
+            else
+            {
+                _clientWriteShutdown = true;
+                _clientDataAvailable.Release(1_000_000);
+            }
+        }
+
         public void BreakConnection()
         {
             if (!DisableConnectionBreaking)
             {
-                _connectionBroken = true;
+                _connectionBroken = !_serverWriteShutdown || !_clientWriteShutdown;
                 _serverDataAvailable.Release(1_000_000);
                 _clientDataAvailable.Release(1_000_000);
             }
diff --git a/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetworkConnectionListenerFactory.cs b/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetworkConnectionListenerFactory.cs
new file mode 100644
index 00000000000000..b25a612479e5d0
--- /dev/null
+++ b/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetworkConnectionListenerFactory.cs
@@ -0,0 +1,187 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics;
+using System.IO;
+using System.Net.Connections;
+using System.Threading;
+using System.Threading.Channels;
+using System.Threading.Tasks;
+
+namespace System.Net.Test.Common
+{
+
+    internal sealed class VirtualNetworkConnectionListenerFactory : ConnectionListenerFactory
+    {
+        public static ConnectionFactory GetConnectionFactory(ConnectionListener listener)
+        {
+            bool hasFactory = listener.ListenerProperties.TryGet(out VirtualConnectionFactory factory);
+            Debug.Assert(hasFactory);
+            return factory;
+        }
+
+        public override ValueTask<ConnectionListener> ListenAsync(EndPoint endPoint, IConnectionProperties options = null, CancellationToken cancellationToken = default)
+        {
+            if (cancellationToken.IsCancellationRequested) return ValueTask.FromCanceled<ConnectionListener>(cancellationToken);
+            return new ValueTask<ConnectionListener>(new VirtualConnectionListener(endPoint));
+        }
+
+        protected override void Dispose(bool disposing)
+        {
+        }
+
+        protected override ValueTask DisposeAsyncCore()
+        {
+            return default;
+        }
+
+        private sealed class VirtualConnectionListener : ConnectionListener, IConnectionProperties
+        {
+            private readonly Channel<TaskCompletionSource<Connection>> _pendingConnects;
+            private readonly VirtualConnectionFactory _connectionFactory;
+            private readonly CancellationTokenSource _cts = new CancellationTokenSource();
+
+            public override IConnectionProperties ListenerProperties => this;
+
+            public override EndPoint LocalEndPoint { get; }
+
+            public VirtualConnectionListener(EndPoint localEndPoint)
+            {
+                LocalEndPoint = localEndPoint;
+
+                _pendingConnects = Channel.CreateUnbounded<TaskCompletionSource<Connection>>();
+                _connectionFactory = new VirtualConnectionFactory(this);
+            }
+
+            public override async ValueTask<Connection> AcceptAsync(IConnectionProperties options = null, CancellationToken cancellationToken = default)
+            {
+                using CancellationTokenSource cts = CancellationTokenSource.CreateLinkedTokenSource(_cts.Token, cancellationToken);
+
+                var network = new VirtualNetwork();
+                var serverConnection = new VirtualConnection(network, isServer: true);
+                var clientConnection = new VirtualConnection(network, isServer: false);
+
+                while (true)
+                {
+                    TaskCompletionSource<Connection> tcs = await _pendingConnects.Reader.ReadAsync(cancellationToken);
+                    if (tcs.TrySetResult(clientConnection))
+                    {
+                        return serverConnection;
+                    }
+                }
+            }
+
+            internal async ValueTask<Connection> ConnectAsync(EndPoint endPoint, IConnectionProperties options = null, CancellationToken cancellationToken = default)
+            {
+                var tcs = new TaskCompletionSource<Connection>();
+                await _pendingConnects.Writer.WriteAsync(tcs, cancellationToken).ConfigureAwait(false);
+
+                using (CancellationTokenSource cts = CancellationTokenSource.CreateLinkedTokenSource(_cts.Token, cancellationToken))
+                using (cts.Token.UnsafeRegister(o => ((TaskCompletionSource<Connection>)o).TrySetCanceled(), tcs))
+                {
+                    return await tcs.Task.ConfigureAwait(false);
+                }
+            }
+
+            protected override void Dispose(bool disposing)
+            {
+                if (disposing)
+                {
+                    _cts.Cancel();
+                }
+            }
+
+            protected override ValueTask DisposeAsyncCore()
+            {
+                Dispose(true);
+                return default;
+            }
+
+            bool IConnectionProperties.TryGet(Type propertyKey, out object property)
+            {
+                if (propertyKey == typeof(VirtualConnectionFactory))
+                {
+                    property = _connectionFactory;
+                    return true;
+                }
+
+                property = null;
+                return false;
+            }
+        }
+
+        private sealed class VirtualConnectionFactory : ConnectionFactory
+        {
+            private readonly VirtualConnectionListener _listener;
+
+            public VirtualConnectionFactory(VirtualConnectionListener listener)
+            {
+                _listener = listener;
+            }
+
+            public override ValueTask<Connection> ConnectAsync(EndPoint endPoint, IConnectionProperties options = null, CancellationToken cancellationToken = default)
+            {
+                return _listener.ConnectAsync(endPoint, options, cancellationToken);
+            }
+
+            protected override void Dispose(bool disposing)
+            {
+                if (disposing)
+                {
+                    _listener.Dispose();
+                }
+            }
+
+            protected override ValueTask DisposeAsyncCore()
+            {
+                return _listener.DisposeAsync();
+            }
+        }
+
+        private sealed class VirtualConnection : Connection, IConnectionProperties
+        {
+            private readonly VirtualNetwork _network;
+            private bool _isServer;
+
+            public override IConnectionProperties ConnectionProperties => this;
+
+            public override EndPoint LocalEndPoint => null;
+
+            public override EndPoint RemoteEndPoint => null;
+
+            public VirtualConnection(VirtualNetwork network, bool isServer)
+            {
+                _network = network;
+                _isServer = isServer;
+            }
+
+            protected override Stream CreateStream()
+            {
+                return new VirtualNetworkStream(_network, _isServer, gracefulShutdown: true);
+            }
+
+            protected override ValueTask CloseAsyncCore(ConnectionCloseMethod method, CancellationToken cancellationToken)
+            {
+                if (cancellationToken.IsCancellationRequested) return ValueTask.FromCanceled(cancellationToken);
+
+                if (method == ConnectionCloseMethod.GracefulShutdown)
+                {
+                    _network.GracefulShutdown(_isServer);
+                }
+                else
+                {
+                    _network.BreakConnection();
+                }
+
+                return default;
+            }
+
+            bool IConnectionProperties.TryGet(Type propertyKey, out object property)
+            {
+                property = null;
+                return false;
+            }
+        }
+    }
+
+}
diff --git a/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetworkStream.cs b/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetworkStream.cs
index 57705531ec2b3a..aa0fb2e4f3b10f 100644
--- a/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetworkStream.cs
+++ b/src/libraries/Common/tests/System/Net/VirtualNetwork/VirtualNetworkStream.cs
@@ -12,13 +12,15 @@ internal class VirtualNetworkStream : Stream
         private readonly VirtualNetwork _network;
         private MemoryStream _readStream;
         private readonly bool _isServer;
+        private readonly bool _gracefulShutdown;
         private SemaphoreSlim _readStreamLock = new SemaphoreSlim(1, 1);
         private TaskCompletionSource _flushTcs;
 
-        public VirtualNetworkStream(VirtualNetwork network, bool isServer)
+        public VirtualNetworkStream(VirtualNetwork network, bool isServer, bool gracefulShutdown = false)
         {
             _network = network;
             _isServer = isServer;
+            _gracefulShutdown = gracefulShutdown;
         }
 
         public int DelayMilliseconds { get; set; }
@@ -79,7 +81,10 @@ public override int Read(byte[] buffer, int offset, int count)
             {
                 if (_readStream == null || (_readStream.Position >= _readStream.Length))
                 {
-                    _readStream = new MemoryStream(_network.ReadFrame(_isServer));
+                    byte[] frame = _network.ReadFrame(_isServer);
+                    if (frame.Length == 0) return 0;
+
+                    _readStream = new MemoryStream(frame);
                 }
 
                 return _readStream.Read(buffer, offset, count);
@@ -102,7 +107,10 @@ public override async Task<int> ReadAsync(byte[] buffer, int offset, int count,
 
                 if (_readStream == null || (_readStream.Position >= _readStream.Length))
                 {
-                    _readStream = new MemoryStream(await _network.ReadFrameAsync(_isServer, cancellationToken).ConfigureAwait(false));
+                    byte[] frame = await _network.ReadFrameAsync(_isServer, cancellationToken).ConfigureAwait(false);
+                    if (frame.Length == 0) return 0;
+
+                    _readStream = new MemoryStream(frame);
                 }
 
                 return await _readStream.ReadAsync(buffer, offset, count, cancellationToken).ConfigureAwait(false);
@@ -147,10 +155,22 @@ protected override void Dispose(bool disposing)
             if (disposing)
             {
                 Disposed = true;
-                _network.BreakConnection();
+                if (_gracefulShutdown)
+                {
+                    GracefulShutdown();
+                }
+                else
+                {
+                    _network.BreakConnection();
+                }
             }
 
             base.Dispose(disposing);
         }
+
+        public void GracefulShutdown()
+        {
+            _network.GracefulShutdown(_isServer);
+        }
     }
 }
diff --git a/src/libraries/Common/tests/System/Net/WebSockets/WebSocketCreateTest.cs b/src/libraries/Common/tests/System/Net/WebSockets/WebSocketCreateTest.cs
index b48bfb0c183cef..f22a8add7d96ae 100644
--- a/src/libraries/Common/tests/System/Net/WebSockets/WebSocketCreateTest.cs
+++ b/src/libraries/Common/tests/System/Net/WebSockets/WebSocketCreateTest.cs
@@ -101,6 +101,7 @@ public async Task ReceiveAsync_UTF8SplitAcrossMultipleBuffers_ValidDataReceived(
         }
 
         [Theory]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Net.Sockets is not supported on this platform.
         [ActiveIssue("https://github.com/dotnet/runtime/issues/34690", TestPlatforms.Windows, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
         [InlineData(0b_1000_0001, 0b_0_000_0001, false)] // fin + text, no mask + length == 1
         [InlineData(0b_1100_0001, 0b_0_000_0001, true)] // fin + rsv1 + text, no mask + length == 1
@@ -147,6 +148,7 @@ public async Task ReceiveAsync_InvalidFrameHeader_AbortsAndThrowsException(byte
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Net.Sockets is not supported on this platform.
         [ActiveIssue("https://github.com/dotnet/runtime/issues/34690", TestPlatforms.Windows, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
         public async Task ReceiveAsync_ServerSplitHeader_ValidDataReceived()
         {
diff --git a/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/DSA/DSAKeyFileTests.cs b/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/DSA/DSAKeyFileTests.cs
index 18f8aed713c8b0..97ff89830817cb 100644
--- a/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/DSA/DSAKeyFileTests.cs
+++ b/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/DSA/DSAKeyFileTests.cs
@@ -562,6 +562,47 @@ public static void DecryptPkcs12WithBytes()
             }
         }
 
+        [Fact]
+        public static void DecryptPkcs12PbeTooManyIterations()
+        {
+            // pbeWithSHAAnd3-KeyTripleDES-CBC with 600,001 iterations
+            byte[] high3DesIterationKey = Convert.FromBase64String(@"
+MIIBezAlBgoqhkiG9w0BDAEDMBcEEDH/8QAPoG1utiuJkzA4u4kCAwknwQSCAVD9BOoJTlihH9zP
+0AmAXtBa7fjJGnq4tZBJSYmJbNxszTSvM3tEkzyiqFWd6Ptm9bf0cOybad2LXIWnrtlIclGD0ibH
+earAf1YvAIBFlbDXfVF8v5//XL2R1d8kcp4fqTVKdRunTSvPS0rIFP5Mrfj89WacHO3HQOB6UMMT
+ZYSdI3qZj+6Rlo0a7/MEO23Y0zR9XLdUhyra+UixzVi05VslPoWn1dsFksbklwtV+IRJ9biMjCta
+8fr3uqHmtb57121dA3p4A2dya8bgcHOJlMPsYxJ012GV4twULSyaZz6hXOzVh3AL5uLlrzSkV7ZQ
+dkOGlpaaJkhGKtkfxRe82w3ZXhuLsVt3vPciDbbF5hIDf8JX7X1aANq5Ka9Tcs3Lyd/FVdkceqn7
+KaC843/LqYiSNoD7rBPpSpkyLtldwhqc7o2Wz7tyb1Oj8WF47AJD5OI=");
+
+            using (DSA key = DSAFactory.Create())
+            {
+                Assert.ThrowsAny<CryptographicException>(
+                    () => key.ImportEncryptedPkcs8PrivateKey("test", high3DesIterationKey, out _));
+            }
+        }
+
+        [Fact]
+        public static void ReadWriteDsa1024EncryptedPkcs8_Pbes2HighIterations()
+        {
+            // pkcs5PBES2 hmacWithSHA256 aes128-CBC with 600,001 iterations
+            ReadBase64EncryptedPkcs8(@"
+MIIBtjBgBgkqhkiG9w0BBQ0wUzAyBgkqhkiG9w0BBQwwJQQQ+ZTlQ9PG0lKomeY4b7lpZgIDCSfB
+MAwGCCqGSIb3DQIJBQAwHQYJYIZIAWUDBAECBBDoHELpGkGH/pPcq1/id3l4BIIBUHF74QMFkUdy
+XZiUndRy+u2d5KNct89WYj8b3Fb7/VTZQwWRfoIZbC2Of769SMvd2R1ViWNG/ZPX7gxZ2keHFiNL
+v/Dj6sNdfFGDF8RyPGOzFQSYu/PYteCHMCh4cYtLQqaGARbKQ1R46dfSyBgQ8IFh9Mnz7T57wSSt
+Af3nJkTjfvS28hjtErrufv0XrLCy95+K/fX80GicWuAsC/sLDbbMiiKWzOlLhug4uX5/gSRM3Oqy
+LGssZuyeza1fTIgU8NjijYQ/kJJUwEWjjn1PA7BWtDWYaqG5wLyz6z50S6pbpLRelvxV5s9dX1Yq
+aylTdOmNGHG+7yEVFQ+sgvJJVIG9mz+YP9tBbzm65UvbzPrXSvNldgm2XUF0Z8LZMRqrurKLYjLE
++TA4wBPaTRUeF0/9Sgk7MXcKHEjhG+OlTP9MExv6Wq3mIREamzu+EtVcPg==",
+                "test",
+                new PbeParameters(
+                    PbeEncryptionAlgorithm.Aes128Cbc,
+                    HashAlgorithmName.SHA256,
+                    600_001),
+                DSATestData.GetDSA1024Params());
+        }
+
         private static void ReadBase64EncryptedPkcs8(
             string base64EncPkcs8,
             string password,
diff --git a/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/EC/ECKeyFileTests.cs b/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/EC/ECKeyFileTests.cs
index 4fd534e937a1d2..62fc99addf55da 100644
--- a/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/EC/ECKeyFileTests.cs
+++ b/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/EC/ECKeyFileTests.cs
@@ -176,6 +176,7 @@ public void ReadNistP521EncryptedPkcs8_Pbes2_Aes128_Sha384()
         public void ReadNistP521EncryptedPkcs8_Pbes2_Aes128_Sha384_PasswordBytes()
         {
             // PBES2, PBKDF2 (SHA384), AES128
+            // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test key.")]
             const string base64 = @"
 MIIBXTBXBgkqhkiG9w0BBQ0wSjApBgkqhkiG9w0BBQwwHAQI/JyXWyp/t3kCAggA
 MAwGCCqGSIb3DQIKBQAwHQYJYIZIAWUDBAECBBA3H8mbFK5afB5GzIemCCQkBIIB
@@ -951,6 +952,41 @@ public void DecryptPkcs12WithBytes()
             }
         }
 
+        [Fact]
+        public void DecryptPkcs12PbeTooManyIterations()
+        {
+            // pbeWithSHAAnd3-KeyTripleDES-CBC with 600,001 iterations
+            byte[] high3DesIterationKey = Convert.FromBase64String(@"
+MIG6MCUGCiqGSIb3DQEMAQMwFwQQWOZyFrGwhyGTEd2nbKuLSQIDCSfBBIGQCgPLkx0OwmK3lJ9o
+VAdJAg/2nvOhboOHciu5I6oh5dRkxeDjUJixsadd3uhiZb5v7UgiohBQsFv+PWU12rmz6sgWR9rK
+V2UqV6Y5vrHJDlNJGI+CQKzOTF7LXyOT+EqaXHD+25TM2/kcZjZrOdigkgQBAFhbfn2/hV/t0TPe
+Tj/54rcY3i0gXT6da/r/o+qV");
+
+            using (T key = CreateKey())
+            {
+                Assert.ThrowsAny<CryptographicException>(
+                    () => key.ImportEncryptedPkcs8PrivateKey("test", high3DesIterationKey, out _));
+            }
+        }
+
+        [Fact]
+        public void ReadWriteEc256EncryptedPkcs8_Pbes2HighIterations()
+        {
+            // pkcs5PBES2 hmacWithSHA256 aes128-CBC with 600,001 iterations
+            ReadWriteBase64EncryptedPkcs8(@"
+MIH1MGAGCSqGSIb3DQEFDTBTMDIGCSqGSIb3DQEFDDAlBBA+rne0bUkwr614vLfQkwO4AgMJJ8Ew
+DAYIKoZIhvcNAgkFADAdBglghkgBZQMEAQIEEIm3c9r5igQ9Vlv1mKTZYp0EgZC8KZfmJtfYmsl4
+Z0Dc85ugFvtFHVeRbcvfYmFns23WL3gpGQ0mj4BKxttX+WuDk9duAsCslNLvXFY7m3MQRkWA6QHT
+A8DiR3j0l5TGBkErbTUrjmB3ftvEmmF9mleRLj6qEYmmKdCV2Tfk1YBOZ2mpB9bpCPipUansyqWs
+xoMaz20Yx+2TSN5dSm2FcD+0YFI=",
+                "test",
+                new PbeParameters(
+                    PbeEncryptionAlgorithm.Aes128Cbc,
+                    HashAlgorithmName.SHA256,
+                    600_001),
+                EccTestData.GetNistP256ReferenceKey());
+        }
+
         private void ReadWriteBase64EncryptedPkcs8(
             string base64EncryptedPkcs8,
             string password,
diff --git a/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/RSA/RSAKeyFileTests.cs b/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/RSA/RSAKeyFileTests.cs
index 35b50774b15670..d47ad3b3dca171 100644
--- a/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/RSA/RSAKeyFileTests.cs
+++ b/src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/RSA/RSAKeyFileTests.cs
@@ -763,6 +763,7 @@ public static void ReadPbes2Rc2EncryptedDiminishedDP()
         public static void ReadPbes2Rc2EncryptedDiminishedDP_PasswordBytes()
         {
             // PBES2: PBKDF2 + RC2-128
+            // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test key.")]
             const string base64 = @"
 MIIBrjBIBgkqhkiG9w0BBQ0wOzAeBgkqhkiG9w0BBQwwEQQIKZEFT76zCFECAggA
 AgEQMBkGCCqGSIb3DQMCMA0CAToECE1Yyzk6++IPBIIBYDDvaYLkET8eudcYLQMf
@@ -788,6 +789,7 @@ public static void ReadPbes2Rc2EncryptedDiminishedDP_PasswordBytes()
         [Fact]
         public static void ReadEncryptedDiminishedDP_EmptyPassword()
         {
+            // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test key.")]
             const string base64 = @"
 MIIBgTAbBgkqhkiG9w0BBQMwDgQIJtjMez/9Gg4CAggABIIBYElq9UOOphEPU3b7
 G/mV8M1uEdjigidMPih3b9IIJhrjMAEix2IjS+brFL7KRQgucpZZoaFU1utvkUHg
@@ -812,6 +814,7 @@ public static void ReadEncryptedDiminishedDP_EmptyPassword()
         [Fact]
         public static void ReadEncryptedDiminishedDP_EmptyPasswordBytes()
         {
+            // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test key.")]
             const string base64 = @"
 MIIBgTAbBgkqhkiG9w0BBQMwDgQIJtjMez/9Gg4CAggABIIBYElq9UOOphEPU3b7
 G/mV8M1uEdjigidMPih3b9IIJhrjMAEix2IjS+brFL7KRQgucpZZoaFU1utvkUHg
@@ -1248,6 +1251,79 @@ public static void DecryptPkcs12WithBytes()
             }
         }
 
+        [Fact]
+        public static void DecryptPkcs12PbeTooManyIterations()
+        {
+            // pbeWithSHAAnd3-KeyTripleDES-CBC with 600,001 iterations
+            byte[] high3DesIterationKey = Convert.FromBase64String(@"
+MIIE8zAlBgoqhkiG9w0BDAEDMBcEELqdfpwjkWlJZnr3xs2n+qACAwknwQSCBMgnZse/OHib1lMC
+jBuUdjQCib5+HEBd2PwrjRw8k/i3kOsPeuDRsTMVvqumYpN6frYWLxRSbd3oe7n5D6bxpBrGuhfO
+d/98Ustg1BDXPSdJzOyCXjS4nm+pr5ZETXxM8HUISvmpC62mrBJue3JwHVXbpXFepMcy9ywfSfjg
+GhNzSYPQwHLFLVHVd3Dcb8mApgVf9aMJIjw9SeE9KQ6PeOk1LXQsoMFf3h/Sap/nuR4M9F/qa9u/
+SEtjptJRlRDecXhQLS7su6cjQ/3Z5PQObORlqF2RASOaEYRyrjjvQjH0+ZAIkQ6zyv1PrPpbeT9I
+U5Hzlu00hfNyAy3TfR50EqT2jP7D6ugFbvnHoDRx0e3STTgBrfFc1tbdLijnq/rxb4QNBIV70+Kw
+QL2mc8CdM/lP4hT4f1vdtgLdRF2gmxndZolveNc5nAheUwqNa8I16OzZnny9090KztJxhGWd57H8
+QCvz2mS6z7FANeyo9cTZilHwwErkLUgmoaQXnnrs46VwF8oeH9ZhLiO4W+OfNLm6QvB/e3/inUj/
+FZFxnTYCvSeRBTD5YhME+SnyGPbJiHOPJuSIwWXyRpZeg6wmMWfduEeGuThNNSf4Fxm0baFrC6CZ
+4+jT0CurP6L4NxLPBafWP7BcA2XCeVQGQd1GT9cX2I1NkRcU7Q2u7oxWKMJaj0OELC+lZTTv6y3Q
+x3I96z0Eddm1qfKQr9HQq+i8LXMwSxqNH+LOtdOEA3kqYq4GU6MdPr8Nx1TaGsiwLcz14GqPl3UQ
+5so2ZKHZZsa9NSer/fWVaOwmYc50JW3N4jJpDFRjKVFP5GSzLfdTwl9nduM4atu4D9KZthQCwNGC
+nEZ1nwGJywmO/XvLWopOMj0cUx2GQYOUV2Hfu93+MriiKjTFEnMcT7B/BOFRpgz4jg4S+6DcHwJh
+cpdIvViajQXM3WwpxnVzskAxYNTYGV0aI9ZjrGBD4vZXM1s9hTlAZc41EmTqZlJPNZ75OzKD9LJS
+Iot/jiWjJ03+WT8VVqw/mfTSy2apCE3pGGKdde6wlcR/N6JI1+lQahC+0j9yvUCZyqhiiVpcwaOa
+dsxxZMJ+DiilMuRXMJCxKvx5kBZTpjuKR/WnKzSE70wgB1ulJE0RkZTYjWSUSf54bHC2XRGZLtfU
+sXDcycjA33H+b0cxe25OZNJUTOoFJqji9RqBvzHuAVMXJvZESORMKbl6q47DbWwFvivfweUJNVO+
+3fzCcrCfAFLwI0j+KaoVr0Qrfedr7OhVEZ/v57aYidUSl2VIpLmpJTUKRnvZ0rlg/WBauwWH1X4M
+u7AExd+aHO8iv0gj+rTg5co0EcOu9i8cbAowg1ZZ1m6zXvHD7fZgE9iamBmklVOQwQXOJO7BCecn
+C0ezYU4Ii8uo0fXJOMWkIA7KLGaQxBrxygnFK3A0RKNos7OXiLdB8RGDqjUZyqLUb3z/YisQEX8f
+R40NElq8tzOa/TudOpNAqC8mgS25uTm7ws472gUE0z9uvcq1/MgkqE++xgmLAxGUN/l7EHSAmYKG
+i33DDR38LaRqG9ho3brf466OkNooBv4MpD5SA63yfooytxOgeuaqbuTzKP/OSRqJNab9wctA9nfJ
+gms2YM+honjUS1sXk1zdm/8=");
+
+            using (RSA key = RSAFactory.Create())
+            {
+                Assert.ThrowsAny<CryptographicException>(
+                    () => key.ImportEncryptedPkcs8PrivateKey("test", high3DesIterationKey, out _));
+            }
+        }
+
+        [Fact]
+        public static void ReadWriteRsa2048EncryptedPkcs8_Pbes2HighIterations()
+        {
+            // pkcs5PBES2 hmacWithSHA256 aes128-CBC with 600,001 iterations
+            ReadBase64EncryptedPkcs8(@"
+MIIFNjBgBgkqhkiG9w0BBQ0wUzAyBgkqhkiG9w0BBQwwJQQQAx6OUUzmK+vwC7a+OwhXygIDCSfB
+MAwGCCqGSIb3DQIJBQAwHQYJYIZIAWUDBAECBBCoLaQQpG01FJnpQdIRq2ioBIIE0MPy/p2uwTnP
+mScPxFbrpBiPQHz5PKRjKLCN5JLArsppSz+XSHxfItFUSfBKEE7dYJrEXARmhA8e2roCrZkQnb9o
+TX551EivHZhqmd91p6WHYb3ZCDQ6la1JfiuV4aJiJOlG0bDAkzEaiM9m9LE3G0J3Z3ELX+mGEGKD
+W+Bz1a9jr204IJQc2VihTFe5t3mujV3X9UFZH3kqOCEreVVmmD64Ea2uDJ6dk3VgGhQ9QLjTDjc5
+OSjdfuyuA4gliK/7ibFubtmnVTDSbAm5Excy9tvJqVhejv/wRhfeYZ2rpv3tTLP58WKt25GEmyyV
+j86v3LB7DFnnBy4NkLCE55oVe64v/8StyEjEkMxz7Owz/ZW65EccPdk7JHZeBXPXNUdLxk1x40vW
+nSRzqhLckfggDwtTCk0kwGUNGBMqr2ezXKrSeO3Qj05dAUvFt9PvbnrVtSnOjFPwx0exiDMUxOFE
+Sz63M2tNNAJr43w60DXaIvMMoZ1kF1mwwL5GT+cs3Dn5KFHNLkZ5irIoHAkmKRHplI15Oqr+Ws2n
+MUtV9BjDjtYHlwp1s1oFpHr9hu8HHv7QIEvyZbyMdKfPv9PEaNJR0SRhkyave+vl9zHCBhP1H2wU
+4fESU1y+cJXZ5WUiJZ5C1wDYWyN5Q2z67Fd4OQXhRwHCeTCZPz3bykpadwlsihCNHrYybfLn61oz
+2CswZjBeQuhDmUKWaj87fsNvSEHaEGTDnyLGEzgNb1OuIrqGiT0DvjfRsVED4ZL6jlDKgAaJe+Uq
+EMt1UzKmAPeBA/IFOrNPw5B+rgKjVpsCdToX9I9b3cCvKhjxguuggpzkEOF4cdgR2MJk1mqdo7ck
+2fI2A5kJx9SuEVL6eKqxyFkPdBMmljKyhomAjdBAIKQ4xt2ojEip7Q9qhmWK3U3meOiIc3qrsM/K
+pGDiwH1CHc/0FbHAghiARawXAtzGGyfMXsZkUTAVnEqDfu5uw4pOlv+rm5GLWfLU8p73yc+kVfPR
+MdWZI6Ftct0FP/KEibc6VSaENoVRAk+XApadkeFaEUQzFzoU7RhN9FONmnCL8Ui76Kfi1kLAxYJo
+rXFQjatiLOAxV50uJSkE1ppmrU1YWHVyC3RkLLnQfq0Ypz9/x7W4PVDfCJQdnCCtOfHL5Qm8fL0l
+uE22Y+gPDzoM1BEKvSgmZWTlZrovXwL4u70/nPeaB1HAVUEzsoEMOSSWDkHuhmgiZHUgQwkvzNjA
+I3AJk0rl2tGBWdgsDtiiQamkXm0VwubTedIt2vj9h9kJYtUlvkCg7KfKxmTSJUynOyKfI1Mhx3vW
+fvni4lYc7KLUEkcNMqNu5AliaPEJQksNNkRiyX7wK5TvA+v9mlqm6Gg7GuJ2oa1DiFf8MUB9CgiJ
+pniangzMBkuSd+zvCAo9YAJoyrJoR2ibcWwo4wRSVwYsVF3bB4nB2w1GHQ6HAnPKHSjVDJZyoEh6
+TvoFEWjb86tn2BR+qMKqXNBVSrgF2pa06BIs0daHKimYKaU0bnuzE/T+pckJfI0VvWB/Z8jvE1Xy
+gpX/dwXfODsj4zcOw4gyP70lDxUWLEPtxhS5Ti0FEuge1XKn3+GOp3clVjGpXKpJTNLsPA/wlqlo
+8/ojymwPxe641Pcfa4DsMgfleHnUOEbNZ4je",
+                "test",
+                new PbeParameters(
+                    PbeEncryptionAlgorithm.Aes128Cbc,
+                    HashAlgorithmName.SHA256,
+                    600_001),
+                TestData.RSA2048Params);
+        }
+
         private static void ReadBase64EncryptedPkcs8(
             string base64EncPkcs8,
             string password,
diff --git a/src/libraries/Common/tests/System/Security/Cryptography/X509Certificates/CertificateAuthority.cs b/src/libraries/Common/tests/System/Security/Cryptography/X509Certificates/CertificateAuthority.cs
index f619379b0f812c..84a2607e002e5f 100644
--- a/src/libraries/Common/tests/System/Security/Cryptography/X509Certificates/CertificateAuthority.cs
+++ b/src/libraries/Common/tests/System/Security/Cryptography/X509Certificates/CertificateAuthority.cs
@@ -488,7 +488,7 @@ byKey                [2] KeyHash }
                     }
                 }
 
-                writer.WriteGeneralizedTime(now);
+                writer.WriteGeneralizedTime(now, omitFractionalSeconds: true);
 
                 using (writer.PushSequence())
                 {
diff --git a/src/libraries/Common/tests/System/Threading/Tasks/TaskTimeoutExtensions.cs b/src/libraries/Common/tests/System/Threading/Tasks/TaskTimeoutExtensions.cs
index 033cdd77029e27..a2a6c5e087b27f 100644
--- a/src/libraries/Common/tests/System/Threading/Tasks/TaskTimeoutExtensions.cs
+++ b/src/libraries/Common/tests/System/Threading/Tasks/TaskTimeoutExtensions.cs
@@ -60,6 +60,20 @@ public static async Task<TResult> TimeoutAfter<TResult>(this Task<TResult> task,
             }
         }
 
+#if !NETFRAMEWORK
+        public static Task TimeoutAfter(this ValueTask task, int millisecondsTimeout)
+            => task.AsTask().TimeoutAfter(TimeSpan.FromMilliseconds(millisecondsTimeout));
+
+        public static Task TimeoutAfter(this ValueTask task, TimeSpan timeout)
+            => task.AsTask().TimeoutAfter(timeout);
+
+        public static Task<TResult> TimeoutAfter<TResult>(this ValueTask<TResult> task, int millisecondsTimeout)
+            => task.AsTask().TimeoutAfter(TimeSpan.FromMilliseconds(millisecondsTimeout));
+
+        public static Task<TResult> TimeoutAfter<TResult>(this ValueTask<TResult> task, TimeSpan timeout)
+            => task.AsTask().TimeoutAfter(timeout);
+#endif
+
         public static async Task WhenAllOrAnyFailed(this Task[] tasks, int millisecondsTimeout)
         {
             var cts = new CancellationTokenSource();
diff --git a/src/libraries/Common/tests/TestUtilities/Interop/Interop.Libraries.cs b/src/libraries/Common/tests/TestUtilities/Interop/Interop.Libraries.cs
index c8839380369d9b..c182dbeb51bef4 100644
--- a/src/libraries/Common/tests/TestUtilities/Interop/Interop.Libraries.cs
+++ b/src/libraries/Common/tests/TestUtilities/Interop/Interop.Libraries.cs
@@ -6,7 +6,7 @@ internal static partial class Interop
     internal static partial class Libraries
     {
         // Shims
-        public const string CryptoNative = "System.Security.Cryptography.Native.OpenSsl";
-        public const string SystemNative = "System.Native";
+        public const string CryptoNative = "libSystem.Security.Cryptography.Native.OpenSsl";
+        public const string SystemNative = "libSystem.Native";
     }
 }
diff --git a/src/libraries/Common/tests/TestUtilities/System/AssemblyPathHelper.cs b/src/libraries/Common/tests/TestUtilities/System/AssemblyPathHelper.cs
new file mode 100644
index 00000000000000..10b3ee0cf2e971
--- /dev/null
+++ b/src/libraries/Common/tests/TestUtilities/System/AssemblyPathHelper.cs
@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Reflection;
+
+namespace System
+{
+    public static class AssemblyPathHelper
+    {
+        public static string GetAssemblyLocation(Assembly a)
+        {
+            // Note, in Browser, assemblies are loaded from memory and in that case, Assembly.Location will return an empty
+            // string.  For these tests, the assemblies will also be available in the VFS, so just specify the assembly name
+            // plus extension.
+            return (PlatformDetection.IsNotBrowser) ?
+                a.Location
+                : "/" + a.GetName().Name + ".dll";
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/libraries/Common/tests/TestUtilities/System/PlatformDetection.cs b/src/libraries/Common/tests/TestUtilities/System/PlatformDetection.cs
index 68d07741e57a7a..6d5811e101405e 100644
--- a/src/libraries/Common/tests/TestUtilities/System/PlatformDetection.cs
+++ b/src/libraries/Common/tests/TestUtilities/System/PlatformDetection.cs
@@ -29,6 +29,7 @@ public static partial class PlatformDetection
         public static bool IsSolaris => RuntimeInformation.IsOSPlatform(OSPlatform.Create("SOLARIS"));
         public static bool IsBrowser => RuntimeInformation.IsOSPlatform(OSPlatform.Create("BROWSER"));
         public static bool IsNotBrowser => !IsBrowser;
+        public static bool IsNotNetFramework => !IsNetFramework;
 
         public static bool IsArmProcess => RuntimeInformation.ProcessArchitecture == Architecture.Arm;
         public static bool IsNotArmProcess => !IsArmProcess;
@@ -125,6 +126,9 @@ public static bool IsNonZeroLowerBoundArraySupported
 
         public static bool SupportsClientAlpn => SupportsAlpn || IsOSX || IsiOS || IstvOS;
 
+        // TLS 1.1 and 1.2 can work on Windows7 but it is not enabled by default.
+        public static bool SupportsTls11 => !IsWindows7 && !IsDebian10;
+        public static bool SupportsTls12 => !IsWindows7;
         // OpenSSL 1.1.1 and above.
         public static bool SupportsTls13 => GetTls13Support();
 
diff --git a/src/libraries/Common/tests/TestUtilities/TestUtilities.csproj b/src/libraries/Common/tests/TestUtilities/TestUtilities.csproj
index cc22d6724e6a98..978aff534fa0d7 100644
--- a/src/libraries/Common/tests/TestUtilities/TestUtilities.csproj
+++ b/src/libraries/Common/tests/TestUtilities/TestUtilities.csproj
@@ -1,11 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <!-- For some reason, xunit.core.props isn't excluded in VS and sets this to true. -->
+    <IsTestProject>false</IsTestProject>
     <!--
       This assembly is referenced from rid agnostic configurations therefore we can't make it RID specific
       and instead use runtime checks.
     -->
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\AdminHelpers.cs" />
@@ -20,6 +22,7 @@
     <Compile Include="System\IO\FileCleanupTestBase.cs" />
     <Compile Include="System\TestEnvironment.cs" />
     <Compile Include="System\ThreadCultureChange.cs" />
+    <Compile Include="System\AssemblyPathHelper.cs" />
     <!-- We don't compile per but and instead use runtime platform checks. -->
     <Compile Include="System\PlatformDetection.cs" />
     <Compile Include="System\PlatformDetection.Unix.cs" />
@@ -63,4 +66,13 @@
     <PackageReference Include="xunit.core" Version="$(XUnitVersion)" ExcludeAssets="build" />
     <PackageReference Include="xunit.assert" Version="$(XUnitVersion)" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <!-- Upgrade the NetStandard.Library transitive xunit dependency to avoid 1.x NS dependencies. -->
+    <PackageReference Include="NETStandard.Library" Version="$(NetStandardLibrary20Version)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\ref\Microsoft.Win32.Registry.csproj" PrivateAssets="all" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\ref\System.Security.Principal.Windows.csproj" PrivateAssets="all" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/Directory.Build.props b/src/libraries/Directory.Build.props
index 834d3a24ce7cb1..98097c8ab3188f 100644
--- a/src/libraries/Directory.Build.props
+++ b/src/libraries/Directory.Build.props
@@ -3,6 +3,7 @@
     <SkipImportArcadeSdkFromRoot>true</SkipImportArcadeSdkFromRoot>
   </PropertyGroup>
   <Import Project="..\..\Directory.Build.props" />
+  <Import Project="NetCoreAppLibrary.props" />
 
   <PropertyGroup Condition="$(MSBuildProjectName.StartsWith('Microsoft.Extensions.'))">
     <IsAspNetCoreApp>true</IsAspNetCoreApp>
@@ -10,14 +11,11 @@
 
   <PropertyGroup>
     <BeforeTargetFrameworkInferenceTargets>$(RepositoryEngineeringDir)BeforeTargetFrameworkInference.targets</BeforeTargetFrameworkInferenceTargets>
-    <ToolSetCommonDirectory>$(RepoRoot)artifacts\toolset\Common\</ToolSetCommonDirectory>
     <IsSourceProject>$([System.Text.RegularExpressions.Regex]::IsMatch($(MSBuildProjectDirectory), 'src%24'))</IsSourceProject>
     <IsReferenceAssembly Condition="'$(IsReferenceAssembly)' == '' and ($(MSBuildProjectFullPath.Contains('\ref\')) or $(MSBuildProjectFullPath.Contains('/ref/')))">true</IsReferenceAssembly>
     <LanguageTargets Condition="'$(MSBuildProjectExtension)' == '.depproj'">$(RepositoryEngineeringDir)depProj.common.targets</LanguageTargets>
     <RuntimeGraph>$(LibrariesProjectRoot)OSGroups.json</RuntimeGraph>
-    <BuildTargetFramework>$(NetCoreAppCurrent)</BuildTargetFramework>
     <ShouldUnsetParentConfigurationAndPlatform>false</ShouldUnsetParentConfigurationAndPlatform>
-    <AdditionalBuildTargetFrameworks Condition="'$(BuildingInsideVisualStudio)' == 'true'">$(AdditionalBuildTargetFrameworks);$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser;$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS;$(NetCoreAppCurrent)-Android;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent)-NetBSD;$(NetCoreAppCurrent)-FreeBSD;$(NetCoreAppCurrent)-illumos;$(NetCoreAppCurrent)-Solaris</AdditionalBuildTargetFrameworks>
     <!-- Remove once is fixed: https://github.com/dotnet/roslyn/issues/42344 -->
     <GeneratePlatformNotSupportedAssemblyHeaderFile>$(RepositoryEngineeringDir)LicenseHeader.txt</GeneratePlatformNotSupportedAssemblyHeaderFile>
   </PropertyGroup>
@@ -40,10 +38,13 @@
          the build system to use browser/ios/android as the RuntimeOS for produced package RIDs. -->
     <RuntimeOS Condition="'$(TargetsMobile)' == 'true'">$(TargetOS.ToLowerInvariant())</RuntimeOS>
 
-    <!-- Initialize BuildSettings from the individual properties if it wasn't already explicitly set -->
-    <Configuration Condition="'$(Configuration)'==''">Debug</Configuration>
-    <BuildTargetFramework Condition="'$(BuildAllProjects)' != 'true' and '$(TargetFramework)' != ''">$(TargetFramework)</BuildTargetFramework>
-    <BuildSettings Condition="'$(BuildSettings)' == ''">$(BuildTargetFramework)-$(TargetOS)-$(Configuration)-$(TargetArchitecture)</BuildSettings>
+    <!-- Initialize BuildSettings from the individual properties. -->
+    <Configuration Condition="'$(Configuration)' == ''">Debug</Configuration>
+    <BuildTargetFramework Condition="'$(BuildTargetFramework)' == '' and '$(TargetFramework)' != ''">$(TargetFramework)</BuildTargetFramework>
+    <!-- Build all .NET Framework configurations when net48 is passed in. This is for convenience. -->
+    <AdditionalBuildTargetFrameworks Condition="'$(BuildTargetFramework)' == 'net48'">net45;net451;net452;net46;net461;net462;net47;net471;net472</AdditionalBuildTargetFrameworks>
+    <AdditionalBuildTargetFrameworks Condition="'$(DotNetBuildFromSource)' == 'true' and '$(BuildAllProjects)' == 'true'">$(AdditionalBuildTargetFrameworks);netstandard2.0</AdditionalBuildTargetFrameworks>
+    <BuildSettings>$(BuildTargetFramework)-$(TargetOS)-$(Configuration)-$(TargetArchitecture)</BuildSettings>
   </PropertyGroup>
 
   <!-- Define test projects and companions -->
@@ -142,11 +143,10 @@
     <PackageRID Condition="'$(PackageRID)' == ''">$(RuntimeOS)-$(TargetArchitecture)</PackageRID>
   </PropertyGroup>
 
-  <!-- set properties for each vertical -->
   <PropertyGroup>
-    <BuildingNETCoreAppVertical Condition="'$(BuildingNETCoreAppVertical)' == '' and ('$(BuildTargetFramework)' == '$(NetCoreAppCurrent)' or '$(BuildAllConfigurations)' == 'true')">true</BuildingNETCoreAppVertical>
-    <BuildingNETFxVertical Condition="'$(BuildingNETFxVertical)' == '' and ('$(BuildTargetFramework)' == '$(NetFrameworkCurrent)' or '$(BuildAllConfigurations)' == 'true')">true</BuildingNETFxVertical>
-    <BinPlaceNETCoreAppPackage Condition="'$(BuildingNETCoreAppVertical)' == 'true'">true</BinPlaceNETCoreAppPackage>
+    <BuildingNETCoreAppVertical Condition="'$(BuildTargetFramework)' == '$(NetCoreAppCurrent)' or
+                                           '$(BuildAllConfigurations)' == 'true'">true</BuildingNETCoreAppVertical>
+    <BinPlaceTestSharedFramework Condition="'$(BuildingNETCoreAppVertical)' == 'true'">true</BinPlaceTestSharedFramework>
   </PropertyGroup>
 
   <!--
@@ -216,13 +216,7 @@
 
   <!-- Disable some standard properties for building our projects -->
   <PropertyGroup>
-    <NoStdLib>true</NoStdLib>
-    <NoExplicitReferenceToStdLib>true</NoExplicitReferenceToStdLib>
-    <AddAdditionalExplicitAssemblyReferences>false</AddAdditionalExplicitAssemblyReferences>
-    <CopyNuGetImplementations>false</CopyNuGetImplementations>
     <DisableImplicitConfigurationDefines>true</DisableImplicitConfigurationDefines>
-    <!-- Don't reference implicit framework packages, all projects in this repo must be explicit -->
-    <DisableImplicitFrameworkReferences>true</DisableImplicitFrameworkReferences>
     <!-- We can't generate an apphost without restoring the targeting pack. -->
     <UseAppHost>false</UseAppHost>
   </PropertyGroup>
@@ -238,14 +232,7 @@
     <EnableAnalyzers Condition="'$(EnableAnalyzers)' == '' and '$(IsSourceProject)' == 'true' and '$(MSBuildProjectExtension)' != '.ilproj'">true</EnableAnalyzers>
   </PropertyGroup>
 
-  <!-- Set up some common paths -->
-  <PropertyGroup>
-    <CommonPathRoot>$([MSBuild]::NormalizeDirectory('$(LibrariesProjectRoot)', 'Common'))</CommonPathRoot>
-    <CommonPath>$([MSBuild]::NormalizeDirectory('$(CommonPathRoot)', 'src'))</CommonPath>
-    <CommonTestPath>$([MSBuild]::NormalizeDirectory('$(CommonPathRoot)', 'tests'))</CommonTestPath>
-  </PropertyGroup>
-
-  <!-- Set up the default output and intermediate paths -->
+  <!-- Set up common paths -->
   <PropertyGroup>
     <!--
       Microsoft.NET.TargetFrameworkInference.targets appends the TargetFramework.
@@ -253,11 +240,8 @@
     -->
     <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
 
-    <RuntimePath Condition="'$(RuntimePath)' == ''">$([MSBuild]::NormalizeDirectory('$(ArtifactsBinDir)', 'runtime', '$(BuildSettings)'))</RuntimePath>
-    <BuildTargetFrameworkRefPath>$([MSBuild]::NormalizeDirectory('$(RefRootPath)', '$(BuildTargetFramework)'))</BuildTargetFrameworkRefPath>
-    <NetStandard20RefPath>$([MSBuild]::NormalizeDirectory('$(RefRootPath)', 'netstandard2.0'))</NetStandard20RefPath>
-    <NetStandard21RefPath>$([MSBuild]::NormalizeDirectory('$(RefRootPath)', 'netstandard2.1'))</NetStandard21RefPath>
-    <NetFxRefPath>$([MSBuild]::NormalizeDirectory('$(RefRootPath)', '$(NetFrameworkCurrent)'))</NetFxRefPath>
+    <NetCoreAppCurrentRefPath>$([MSBuild]::NormalizeDirectory('$(RefRootPath)', '$(NetCoreAppCurrent)'))</NetCoreAppCurrentRefPath>
+    <NetCoreAppCurrentRuntimePath>$([MSBuild]::NormalizeDirectory('$(ArtifactsBinDir)', 'runtime', '$(NetCoreAppCurrent)-$(TargetOS)-$(Configuration)-$(TargetArchitecture)'))</NetCoreAppCurrentRuntimePath>
 
     <!-- System.Private.CoreLib -->
     <CoreLibProject Condition="'$(RuntimeFlavor)' == 'CoreCLR'">$([MSBuild]::NormalizePath('$(CoreClrProjectRoot)', 'src', 'System.Private.CoreLib', 'System.Private.CoreLib.csproj'))</CoreLibProject>
@@ -280,6 +264,7 @@
     <ASPNETCoreAppPackageRuntimePath>$(ArtifactsBinDir)pkg\aspnetcoreapp\lib</ASPNETCoreAppPackageRuntimePath>
 
     <TestHostRootPath>$([MSBuild]::NormalizeDirectory('$(ArtifactsBinDir)', 'testhost', '$(BuildSettings)'))</TestHostRootPath>
+    <NETCoreAppTestSharedFrameworkPath>$([MSBuild]::NormalizeDirectory('$(TestHostRootPath)', 'shared', '$(SharedFrameworkName)', '$(ProductVersion)'))</NETCoreAppTestSharedFrameworkPath>
 
     <MicrosoftNetCoreAppRefPackDir>$([MSBuild]::NormalizeDirectory('$(ArtifactsBinDir)', 'microsoft.netcore.app.ref'))</MicrosoftNetCoreAppRefPackDir>
     <MicrosoftNetCoreAppRefPackRefDir>$([MSBuild]::NormalizeDirectory('$(MicrosoftNetCoreAppRefPackDir)', 'ref', '$(NetCoreAppCurrent)'))</MicrosoftNetCoreAppRefPackRefDir>
@@ -292,7 +277,9 @@
 
     <VersionFileForPackages Condition="'$(VersionFileForPackages)' == ''">$(ArtifactsObjDir)version.txt</VersionFileForPackages>
 
-    <AdditionalBuildTargetFrameworks Condition="'$(DotNetBuildFromSource)' == 'true' and '$(BuildAllProjects)' == 'true'">$(AdditionalBuildTargetFrameworks);netstandard2.0</AdditionalBuildTargetFrameworks>
+    <CommonPathRoot>$([MSBuild]::NormalizeDirectory('$(LibrariesProjectRoot)', 'Common'))</CommonPathRoot>
+    <CommonPath>$([MSBuild]::NormalizeDirectory('$(CommonPathRoot)', 'src'))</CommonPath>
+    <CommonTestPath>$([MSBuild]::NormalizeDirectory('$(CommonPathRoot)', 'tests'))</CommonTestPath>
   </PropertyGroup>
 
   <!-- Import it at the end of the props file to override the OutputPath for reference assemblies and use common directory props -->
@@ -308,23 +295,6 @@
     <EnableDefaultItems>false</EnableDefaultItems>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(BuildAllConfigurations)' != 'true'">
-    <!-- We add extra binplacing for the test shared framework until we can get hardlinking with the runtime directory working on all platforms -->
-    <BinPlaceTestSharedFramework Condition="'$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'">true</BinPlaceTestSharedFramework>
-    <BinPlaceNETFXRuntime Condition="'$(BuildTargetFramework)' == '$(NetFrameworkCurrent)'">true</BinPlaceNETFXRuntime>
-
-    <NETCoreAppTestSharedFrameworkPath>$([MSBuild]::NormalizeDirectory('$(TestHostRootPath)', 'shared', 'Microsoft.NETCore.App', '$(ProductVersion)'))</NETCoreAppTestSharedFrameworkPath>
-
-    <TestHostRuntimePath Condition="'$(BinPlaceTestSharedFramework)' == 'true'">$(NETCoreAppTestSharedFrameworkPath)</TestHostRuntimePath>
-    <TestHostRuntimePath Condition="'$(BinPlaceNETFXRuntime)' == 'true'">$(TestHostRootPath)</TestHostRuntimePath>
-
-    <PlatformManifestFile Condition="'$(BinPlaceTestSharedFramework)' == 'true'">$(TestHostRuntimePath)PlatformManifest.txt</PlatformManifestFile>
-  </PropertyGroup>
-
-  <ItemGroup Condition="'$(PlatformManifestFile)' != '' and ('$(IsTestProject)' == 'true' or '$(IsTestSupportProject)' == 'true')">
-    <PackageConflictPlatformManifests Include="$(PlatformManifestFile)" />
-  </ItemGroup>
-
   <ItemGroup Condition="'$(IsTestProject)' == 'true'">
     <ProjectReference Include="$(CommonTestPath)TestUtilities\TestUtilities.csproj" />
   </ItemGroup>
@@ -354,24 +324,9 @@
     <CoverageIncludeDirectory Include="shared\Microsoft.NETCore.App\$(ProductVersion)" />
   </ItemGroup>
 
-  <ItemDefinitionGroup Condition="'$(IsTestProject)' != 'true' and '$(IsTestSupportProject)' != 'true'">
-    <!-- Project references for non-test assemblies should never be copied to the output. -->
-    <ProjectReference>
-      <Private>false</Private>
-    </ProjectReference>
-  </ItemDefinitionGroup>
-
-  <!--
-    The Utf8String package is experimental. We don't want tests to inadvertently take a dependency on this
-    feature unless they explicitly opt in to it. (Source projects explicitly reference their dependencies,
-    so they can't inadvertently take a dependency on it.)
-  -->
-  <ItemGroup Condition="('$(IsTestProject)' == 'true' or '$(IsTestSupportProject)' == 'true') and '$(IncludeUtf8StringAsmRef)' != 'true'">
-    <DefaultReferenceExclusions Include="System.Utf8String.Experimental" />
-  </ItemGroup>
-
   <PropertyGroup>
     <CLSCompliant Condition="'$(CLSCompliant)' == '' and ('$(IsTestProject)' == 'true' or '$(IsTestSupportProject)' == 'true')">false</CLSCompliant>
     <CLSCompliant Condition="'$(CLSCompliant)' == ''">true</CLSCompliant>
   </PropertyGroup>
+
 </Project>
diff --git a/src/libraries/Directory.Build.targets b/src/libraries/Directory.Build.targets
index 15be91dbe1c68a..83a2e140326c1d 100644
--- a/src/libraries/Directory.Build.targets
+++ b/src/libraries/Directory.Build.targets
@@ -1,12 +1,9 @@
 <Project InitialTargets="UpdateProjectReferencesWithAttributes">
-  <PropertyGroup>
-    <RefPath>$([MSBuild]::NormalizeDirectory('$(RefRootPath)', '$(TargetFramework)'))</RefPath>  
-  </PropertyGroup>
 
   <Import Project="..\..\Directory.Build.targets" />
 
   <PropertyGroup>
-    <NoWarn Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework' or '$(TargetFrameworkIdentifier)' == '.NETStandard' or '$(TargetFramework)' == 'netcoreapp2.1'">$(NoWarn);nullable</NoWarn>
+    <NoWarn Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework' or '$(TargetFrameworkIdentifier)' == '.NETStandard' or ('$(TargetFrameworkIdentifier)' == '.NETCoreApp' and $([MSBuild]::VersionLessThan($(TargetFrameworkVersion), '3.0')))">$(NoWarn);nullable</NoWarn>
     <NoWarn Condition="'$(GeneratePlatformNotSupportedAssembly)' == 'true' or '$(GeneratePlatformNotSupportedAssemblyMessage)' != ''">$(NoWarn);nullable</NoWarn>
     <!-- Ignore Obsolete errors within the generated shims that type-forward types.
          SYSLIB0003 is for CAS. SYSLIB0004 is the obsoletion of CER. -->
@@ -17,6 +14,22 @@
     <WarningsAsErrors Condition="'$(WarningsAsErrors)' == 'NU1605'" />
     <!-- Set the documentation output file globally. -->
     <DocumentationFile Condition="'$(IsSourceProject)' == 'true' and '$(DocumentationFile)' == '' and '$(MSBuildProjectExtension)' != '.vbproj'">$(OutputPath)$(MSBuildProjectName).xml</DocumentationFile>
+    <IsNETCoreAppSrc Condition="'$(IsNETCoreAppSrc)' == '' and
+                                '$(IsSourceProject)' == 'true' and
+                                $(NetCoreAppLibrary.Contains('$(AssemblyName);'))">true</IsNETCoreAppSrc>
+    <IsNETCoreAppRef Condition="'$(IsNETCoreAppRef)' == '' and
+                                '$(IsReferenceAssembly)' == 'true' and
+                                $(NetCoreAppLibrary.Contains('$(AssemblyName);')) and
+                                !$(NetCoreAppLibraryNoReference.Contains('$(AssemblyName);'))">true</IsNETCoreAppRef>
+    <!-- By default, disable implicit framework references for NetCoreAppCurrent libraries. -->
+    <DisableImplicitFrameworkReferences Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                                                   $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '$(NETCoreAppCurrentVersion)')) and
+                                                   ('$(IsNETCoreAppRef)' == 'true' or '$(IsNETCoreAppSrc)' == 'true')">true</DisableImplicitFrameworkReferences>
+    <!-- Disable implicit assembly references for .NETCoreApp refs and sources. -->
+    <DisableImplicitAssemblyReferences Condition="'$(DisableImplicitAssemblyReferences)' == '' and
+                                                  '$(DisableImplicitFrameworkReferences)' != 'true' and
+                                                  '$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                                                  ('$(IsReferenceAssembly)' == 'true' or '$(IsSourceProject)' == 'true')">true</DisableImplicitAssemblyReferences>
   </PropertyGroup>
 
   <PropertyGroup>
@@ -41,21 +54,18 @@
 
   <Import Project="$(RepositoryEngineeringDir)versioning.targets" />
 
-  <!-- Corefx-specific binplacing properties -->
+  <!-- Libraries-specific binplacing properties -->
   <PropertyGroup>
     <IsRuntimeAssembly Condition="'$(IsRuntimeAssembly)'=='' and '$(IsReferenceAssembly)' != 'true' and '$(BinPlaceRef)' != 'true' and '$(IsTestProject)' != 'true' and '$(IsTestSupportProject)' != 'true'">true</IsRuntimeAssembly>
     <!-- Try to determine if this is a simple library without a ref project.
          https://github.com/dotnet/corefx/issues/14291 is tracking cleaning this up -->
     <IsRuntimeAndReferenceAssembly Condition="'$(IsRuntimeAndReferenceAssembly)' == '' and '$(IsRuntimeAssembly)' == 'true' and Exists('$(LibrariesProjectRoot)$(MSBuildProjectName)') and !Exists('$(LibrariesProjectRoot)$(MSBuildProjectName)/ref') and !$(MSBuildProjectName.StartsWith('System.Private'))">true</IsRuntimeAndReferenceAssembly>
-    <IsNETCoreAppRef Condition="'$(IsNETCoreAppRef)' == ''">$(IsNETCoreApp)</IsNETCoreAppRef>
-    <IsNetFxNETStandardRef Condition="'$(IsNetFxNETStandardRef)' == ''">$(IsNetFxNETStandard)</IsNetFxNETStandardRef>
 
     <BinPlaceRef Condition="'$(BinPlaceRef)' == '' and ('$(IsReferenceAssembly)' == 'true' or '$(IsRuntimeAndReferenceAssembly)' == 'true')">true</BinPlaceRef>
     <BinPlaceRuntime Condition="'$(BinPlaceRuntime)' == '' and ('$(IsRuntimeAssembly)' == 'true' or '$(IsRuntimeAndReferenceAssembly)' == 'true')">true</BinPlaceRuntime>
     <BinPlaceForTargetVertical Condition="'$(BinPlaceForTargetVertical)' == ''">true</BinPlaceForTargetVertical>
-    <AllTargetFrameworks>net45;net451;net46;net461;net462;net47;net471;net472;netstandard1.0;netstandard1.1;netstandard1.2;netstandard1.3;netstandard1.4;netstandard1.5;netstandard1.6;netstandard2.0;netstandard2.0;netcoreapp2.0;netcoreapp2.1;netcoreapp3.0;$(netcoreappCurrent);</AllTargetFrameworks>
   </PropertyGroup>
-    
+
   <ItemGroup Condition="$(MSBuildProjectName.StartsWith('Microsoft.Extensions.'))">
     <!-- Microsoft.Extensions are not yet using the doc-file package -->
     <BinPlaceItem Include="$(DocumentationFile)" />
@@ -63,74 +73,52 @@
 
   <ItemGroup Condition="'@(BinPlaceTargetFrameworks)' == ''">
     <!-- binplace to directories for the target vertical -->
-    <BinPlaceTargetFrameworks Include="$(BuildTargetFramework)-$(TargetOS)" Condition="'$(BinPlaceForTargetVertical)' == 'true'">
-      <NativePath>$(RuntimePath)</NativePath>
-      <RefPath>$(BuildTargetFrameworkRefPath)</RefPath>
-      <RuntimePath>$(RuntimePath)</RuntimePath>
+    <BinPlaceTargetFrameworks Include="$(NetCoreAppCurrent)-$(TargetOS)"
+                              Condition="'$(BinPlaceForTargetVertical)' == 'true'">
+      <NativePath>$(NetCoreAppCurrentRuntimePath)</NativePath>
+      <RefPath>$(NetCoreAppCurrentRefPath)</RefPath>
+      <RuntimePath>$(NetCoreAppCurrentRuntimePath)</RuntimePath>
     </BinPlaceTargetFrameworks>
+
     <!-- binplace to directories for packages -->
-    <BinPlaceTargetFrameworks Condition="'$(IsNETCoreApp)' == 'true' and '$(BuildingNETCoreAppVertical)' == 'true'" Include="$(NetCoreAppCurrent)-$(TargetOS)">
-      <PackageFileNativePath>$(NETCoreAppPackageRuntimePath)</PackageFileNativePath>
+    <BinPlaceTargetFrameworks Include="$(NetCoreAppCurrent)-$(TargetOS)"
+                              Condition="'$(BuildingNETCoreAppVertical)' == 'true'">
+      <PackageFileNativePath Condition="'$(IsNETCoreAppSrc)' == 'true'">$(NETCoreAppPackageRuntimePath)</PackageFileNativePath>
       <PackageFileRefPath Condition="'$(IsNETCoreAppRef)' == 'true'">$(NETCoreAppPackageRefPath)</PackageFileRefPath>
-      <PackageFileRuntimePath>$(NETCoreAppPackageRuntimePath)</PackageFileRuntimePath>
-      <NativePath Condition="'$(BinPlaceNETCoreAppPackage)' == 'true'">$(NETCoreAppPackageRuntimePath)\..\runtime\$(TargetOS)-$(Configuration)-$(TargetArchitecture)</NativePath>
-      <RefPath Condition="'$(BinPlaceNETCoreAppPackage)' == 'true' and '$(IsNETCoreAppRef)' == 'true'">$(RefRootPath)microsoft.netcore.app\$(Configuration)</RefPath>
-      <RuntimePath Condition="'$(BinPlaceNETCoreAppPackage)' == 'true'">$(NETCoreAppPackageRuntimePath)\..\runtime\$(TargetOS)-$(Configuration)-$(TargetArchitecture)</RuntimePath>
+      <PackageFileRuntimePath Condition="'$(IsNETCoreAppSrc)' == 'true'">$(NETCoreAppPackageRuntimePath)</PackageFileRuntimePath>
+      <NativePath Condition="'$(IsNETCoreAppSrc)' == 'true'">$(NETCoreAppPackageRuntimePath)\..\runtime\$(TargetOS)-$(Configuration)-$(TargetArchitecture)</NativePath>
+      <RefPath Condition="'$(IsNETCoreAppRef)' == 'true'">$(RefRootPath)microsoft.netcore.app\$(Configuration)</RefPath>
+      <RuntimePath Condition="'$(IsNETCoreAppSrc)' == 'true'">$(NETCoreAppPackageRuntimePath)\..\runtime\$(TargetOS)-$(Configuration)-$(TargetArchitecture)</RuntimePath>
       <!-- enable trimming for any runtime project that's part of the shared framework and hasn't already set ILLinkTrimAssembly -->
-      <SetProperties Condition="'$(BinPlaceRuntime)' == 'true' and '$(ILLinkTrimAssembly)' == ''">ILLinkTrimAssembly=true</SetProperties>
+      <SetProperties Condition="'$(IsNETCoreAppSrc)' == 'true' and
+                                '$(BinPlaceRuntime)' == 'true' and
+                                '$(ILLinkTrimAssembly)' == ''">ILLinkTrimAssembly=true</SetProperties>
     </BinPlaceTargetFrameworks>
-    <BinPlaceTargetFrameworks Condition="'$(IsAspNetCoreApp)' == 'true'" Include="$(NetCoreAppCurrent)">
+    <BinPlaceTargetFrameworks Include="$(NetCoreAppCurrent)"
+                              Condition="'$(IsAspNetCoreApp)' == 'true'">
       <RuntimePath>$(ASPNETCoreAppPackageRuntimePath)</RuntimePath>
       <RefPath>$(ASPNETCoreAppPackageRefPath)</RefPath>
     </BinPlaceTargetFrameworks>
 
     <!-- Setup the shared framework directory for testing -->
-    <BinPlaceTargetFrameworks Condition="'$(BinPlaceTestSharedFramework)' == 'true'" Include="$(NetCoreAppCurrent)-$(TargetOS)">
-      <NativePath>$(NETCoreAppTestSharedFrameworkPath)</NativePath>
-      <RuntimePath>$(NETCoreAppTestSharedFrameworkPath)</RuntimePath>
-    </BinPlaceTargetFrameworks>
-    <BinPlaceTargetFrameworks Condition="'$(BinPlaceNETFXRuntime)' == 'true'" Include="$(NetFrameworkCurrent)-Windows_NT">
-      <NativePath>$(TestHostRootPath)</NativePath>
-      <RuntimePath>$(TestHostRootPath)</RuntimePath>
-    </BinPlaceTargetFrameworks>
-
-    <!-- Microsoft.NetCore.App.Ref targeting pack -->
-    <BinPlaceTargetFrameworks Include="$(NetCoreAppCurrent)">
-      <RefPath Condition="'$(IsNETCoreAppRef)' == 'true'">$(MicrosoftNetCoreAppRefPackRefDir)</RefPath>
+    <BinPlaceTargetFrameworks Include="$(NetCoreAppCurrent)-$(TargetOS)"
+                              Condition="'$(BinPlaceTestSharedFramework)' == 'true'">
+      <NativePath >$(NETCoreAppTestSharedFrameworkPath)</NativePath>
+      <RuntimePath Condition="'$(IsNETCoreAppSrc)' == 'true'">$(NETCoreAppTestSharedFrameworkPath)</RuntimePath>
     </BinPlaceTargetFrameworks>
 
-    <!-- Microsoft.NetCore.App.Runtime targeting pack -->
+    <!-- Microsoft.NetCore.App.Ref and Microsoft.NetCore.App.Runtime targeting packs -->
     <BinPlaceTargetFrameworks Include="$(NetCoreAppCurrent)-$(TargetOS)">
       <NativePath>$(MicrosoftNetCoreAppRuntimePackNativeDir)</NativePath>
-      <RuntimePath>$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)</RuntimePath>
-    </BinPlaceTargetFrameworks>
-
-    <!-- binplace targeting packs which may be different from Build TargetFramework -->
-    <BinPlaceTargetFrameworks Include="netstandard2.0">
-      <RefPath>$(NetStandard20RefPath)</RefPath>
-    </BinPlaceTargetFrameworks>
-    <BinPlaceTargetFrameworks Include="netstandard2.1">
-      <RefPath>$(NetStandard21RefPath)</RefPath>
-    </BinPlaceTargetFrameworks>
-    <!-- some libraries that produce packages will remain targeting netcoreapp2.0 -->
-    <BinPlaceTargetFrameworks Condition="'$(BuildingNETCoreAppVertical)' == 'true'" Include="netcoreapp2.0">
-      <RefPath>$(RefRootPath)netcoreapp2.0/</RefPath>
-    </BinPlaceTargetFrameworks>
-    <AllTargetFrameworkList Include="$(AllTargetFrameworks)"/>
-    <!-- for BuildAllConfigurations make sure all refpaths are created.  -->
-    <BinPlaceTargetFrameworks Condition="'$(BuildAllConfigurations)' == 'true'" Include="@(AllTargetFrameworkList)">
-      <RefPath>$(RefRootPath)%(Identity)/</RefPath>
-    </BinPlaceTargetFrameworks>
-    <!-- for BuildAllConfigurations make sure runtimepaths are created for all vertical target frameworks. -->
-    <BinPlaceTargetFrameworks Condition="'$(BuildAllConfigurations)' == 'true' and ('$(BinPlaceForTargetVertical)' == 'true' or ('$(TargetFramework)' != '$(NetCoreAppCurrent)' and '$(TargetFrameworkSuffix)' == ''))" Include="$(NetCoreAppCurrent)-$(TargetOS)">
-      <NativePath>$(ArtifactsBinDir)runtime/%(Identity)-$(Configuration)-$(TargetArchitecture)</NativePath>
-      <RuntimePath>$(ArtifactsBinDir)runtime/%(Identity)-$(Configuration)-$(TargetArchitecture)</RuntimePath>
+      <RefPath Condition="'$(IsNETCoreAppRef)' == 'true'">$(MicrosoftNetCoreAppRefPackRefDir)</RefPath>
+      <RuntimePath Condition="'$(IsNETCoreAppSrc)' == 'true'">$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)</RuntimePath>
     </BinPlaceTargetFrameworks>
 
     <BinPlaceTargetFrameworks Include="@(AdditionalBinPlaceTargetFrameworks)" />
   </ItemGroup>
 
   <Import Project="$(RepositoryEngineeringDir)codeOptimization.targets" />
+  <Import Project="$(RepositoryEngineeringDir)targetingpacks.targets" />
   <Import Project="$(RepositoryEngineeringDir)references.targets" />
   <Import Project="$(RepositoryEngineeringDir)resolveContract.targets" />
   <Import Project="$(RepositoryEngineeringDir)testing\tests.targets" Condition="'$(EnableTestSupport)' == 'true'" />
@@ -141,9 +129,9 @@
 
   <Import Sdk="Microsoft.DotNet.Build.Tasks.TargetFramework.Sdk" Project="Sdk.targets" />
   <Import Project="$(RepositoryEngineeringDir)restore\repoRestore.targets" Condition="'$(DisableProjectRestore)' == 'true'" />
-  <Import Project="$(RepositoryEngineeringDir)referenceFromRuntime.targets" />
   <Import Project="$(RepositoryEngineeringDir)illink.targets" Condition="'$(IsSourceProject)' == 'true'" />
   <Import Project="$(RepositoryEngineeringDir)notSupported.SourceBuild.targets" Condition="'$(DotNetBuildFromSource)' == 'true'" />
+  <Import Project="$(RepositoryEngineeringDir)AvoidRestoreCycleOnSelfReference.targets" Condition="'$(AvoidRestoreCycleOnSelfReference)' == 'true'" />
 
   <ItemGroup Condition="'$(IsSourceProject)' == 'true' or '$(IsReferenceAssembly)' == 'true' or '$(IsPartialFacadeAssembly)' == 'true'">
     <PackageReference Include="Microsoft.DotNet.Build.Tasks.Packaging" Version="$(MicrosoftDotNetBuildTasksPackagingVersion)" PrivateAssets="all" IsImplicitlyDefined="true" />
@@ -188,19 +176,27 @@
         <SkipGetTargetFrameworkProperties>true</SkipGetTargetFrameworkProperties>
       </ProjectReference>
       <ProjectReference Condition="'%(Filename)' == 'System.Private.CoreLib'">
-        <UndefineProperties>$(UndefineProperties);TargetFramework</UndefineProperties>
+        <!-- Don't flow TargetFramework and Platform to use same inputs and outputs as the CoreLib's build as part of the runtime. -->
+        <UndefineProperties>$(UndefineProperties);TargetFramework;Platform</UndefineProperties>
         <SetConfiguration Condition="'$(RuntimeFlavor)' == 'CoreCLR' and
                                      '$(Configuration)' != '$(CoreCLRConfiguration)'">Configuration=$(CoreCLRConfiguration)</SetConfiguration>
         <SetConfiguration Condition="'$(RuntimeFlavor)' == 'Mono' and
                                      '$(Configuration)' != '$(MonoConfiguration)'">Configuration=$(MonoConfiguration)</SetConfiguration>
+        <Private>false</Private>
       </ProjectReference>
     </ItemGroup>
+    <!-- Disable TargetArchitectureMismatch warning when we reference CoreLib which is platform specific. -->
+    <PropertyGroup Condition="@(ProjectReference->AnyHaveMetadataValue('Identity', '$(CoreLibProject)'))">
+      <ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>None</ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>
+    </PropertyGroup>
   </Target>
 
   <!-- Used for packaging -->
   <Target Name="IsNotNetCoreAppProject" Returns="@(IsNotNetCoreAppProjectResult)">
     <ItemGroup>
-      <IsNotNetCoreAppProjectResult Condition="'$(IsNetCoreApp)' != 'true'" Include="$(MSBuildProjectName)" Version="$(PackageVersion)" />
+      <IsNotNetCoreAppProjectResult Include="$(MSBuildProjectName)"
+                                    Version="$(PackageVersion)"
+                                    Condition="!$(NetCoreAppLibrary.Contains('$(MSBuildProjectName);'))" />
     </ItemGroup>
   </Target>
 
@@ -222,10 +218,19 @@
   <Target Name="GetDocumentationFile"
           Returns="$(DocumentationFile)"/>
 
-  <PropertyGroup>
-    <DefineConstants Condition="'$(IsPrerelease)' != 'false' and '$(TargetFramework)' != '$(NetCoreAppCurrent)'">$(DefineConstants),USE_INTERNAL_ACCESSIBILITY</DefineConstants>
-  </PropertyGroup>
-  
+  <!--
+    Do not clean binplace assets in the ref targeting pack to avoid incremental build failures
+    when the SDK tries to resolve the assets from the FrameworkList.
+  -->
+  <Target Name="RemoveTargetingPackIncrementalClean"
+          Condition="'@(AdditionalCleanDirectories)' != ''"
+          BeforeTargets="IncrementalCleanAdditionalDirectories;
+                         CleanAdditionalDirectories">
+    <ItemGroup>
+      <AdditionalCleanDirectories Remove="@(AdditionalCleanDirectories)" Condition="'%(Identity)' == '$(MicrosoftNetCoreAppRefPackRefDir)'" />
+    </ItemGroup>
+  </Target>
+
   <!-- Adds Nullable annotation attributes to netstandard <= 2.0 builds -->
   <Choose>
     <When Condition="'$(Nullable)' != '' and ($(TargetFramework.StartsWith('netstandard1')) or '$(TargetFramework)' == 'netstandard2.0' or $(TargetFramework.StartsWith('netcoreapp2')) or '$(TargetFrameworkIdentifier)' == '.NETFramework')">
@@ -234,10 +239,9 @@
       </ItemGroup>
     </When>
   </Choose>
-  
+
   <PropertyGroup>
     <ExcludeFromPackage Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' and '$(ExcludeCurrentNetCoreAppFromPackage)' == 'true'">true</ExcludeFromPackage>
-    <ExcludeFromPackage Condition="'$(TargetFramework)' == '$(NetFrameworkCurrent)' and '$(ExcludeCurrentFullFrameworkFromPackage)' == 'true'">true</ExcludeFromPackage>
   </PropertyGroup>
 
   <!-- Adds System.Runtime.Versioning*Platform* annotation attributes to < .NET 5 builds -->
@@ -257,7 +261,7 @@
   </ItemGroup>
 
   <PropertyGroup>
-    <SkipLocalsInit Condition="'$(SkipLocalsInit)' == '' and '$(IsSourceProject)' == 'true' and '$(MSBuildProjectExtension)' == '.csproj' and '$(IsNETCoreApp)' == 'true' and '$(TargetFramework)' == '$(NetCoreAppCurrent)'">true</SkipLocalsInit>
+    <SkipLocalsInit Condition="'$(SkipLocalsInit)' == '' and '$(MSBuildProjectExtension)' == '.csproj' and '$(IsNETCoreAppSrc)' == 'true' and '$(TargetFramework)' == '$(NetCoreAppCurrent)'">true</SkipLocalsInit>
   </PropertyGroup>
 
   <!--Instructs compiler not to emit .locals init, using SkipLocalsInitAttribute.-->
diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/Directory.Build.props b/src/libraries/Microsoft.Bcl.AsyncInterfaces/Directory.Build.props
new file mode 100644
index 00000000000000..363643c7a5e029
--- /dev/null
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/Directory.Build.props
@@ -0,0 +1,7 @@
+<Project>
+  <Import Project="..\Directory.Build.props" />
+  <PropertyGroup>
+    <StrongNameKeyId>Open</StrongNameKeyId>
+    <!-- This assembly should never be placed inbox as it is only for downlevel compatibility. -->
+  </PropertyGroup>
+</Project>
diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/Microsoft.Bcl.AsyncInterfaces.sln b/src/libraries/Microsoft.Bcl.AsyncInterfaces/Microsoft.Bcl.AsyncInterfaces.sln
new file mode 100644
index 00000000000000..1f6586d8aa7929
--- /dev/null
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/Microsoft.Bcl.AsyncInterfaces.sln
@@ -0,0 +1,51 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.30120.7
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Bcl.AsyncInterfaces", "src\Microsoft.Bcl.AsyncInterfaces.csproj", "{E6C08D1F-5DAC-470E-809D-42DBFAA56DD4}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{8FA3CF3F-DF33-4DC4-A261-4642AB786838}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "ref", "ref", "{0C330C14-95F7-4AD3-9BD0-8AAB6E3013D8}"
+	ProjectSection(SolutionItems) = preProject
+		ref\Microsoft.Bcl.AsyncInterfaces.csproj = ref\Microsoft.Bcl.AsyncInterfaces.csproj
+	EndProjectSection
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Bcl.AsyncInterfaces.Tests", "tests\Microsoft.Bcl.AsyncInterfaces.Tests.csproj", "{857B2747-4D8E-4A0C-9C38-521F690ED28E}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{78938ED3-0E8A-451A-A508-0E724E471B91}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TestUtilities", "..\Common\tests\TestUtilities\TestUtilities.csproj", "{95680D66-EE1B-4389-A84D-0C49AF570732}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{E6C08D1F-5DAC-470E-809D-42DBFAA56DD4}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{E6C08D1F-5DAC-470E-809D-42DBFAA56DD4}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{E6C08D1F-5DAC-470E-809D-42DBFAA56DD4}.Release|Any CPU.ActiveCfg = Debug|Any CPU
+		{E6C08D1F-5DAC-470E-809D-42DBFAA56DD4}.Release|Any CPU.Build.0 = Debug|Any CPU
+		{857B2747-4D8E-4A0C-9C38-521F690ED28E}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{857B2747-4D8E-4A0C-9C38-521F690ED28E}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{857B2747-4D8E-4A0C-9C38-521F690ED28E}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{857B2747-4D8E-4A0C-9C38-521F690ED28E}.Release|Any CPU.Build.0 = Release|Any CPU
+		{95680D66-EE1B-4389-A84D-0C49AF570732}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{95680D66-EE1B-4389-A84D-0C49AF570732}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{95680D66-EE1B-4389-A84D-0C49AF570732}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{95680D66-EE1B-4389-A84D-0C49AF570732}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(NestedProjects) = preSolution
+		{E6C08D1F-5DAC-470E-809D-42DBFAA56DD4} = {8FA3CF3F-DF33-4DC4-A261-4642AB786838}
+		{857B2747-4D8E-4A0C-9C38-521F690ED28E} = {78938ED3-0E8A-451A-A508-0E724E471B91}
+		{95680D66-EE1B-4389-A84D-0C49AF570732} = {78938ED3-0E8A-451A-A508-0E724E471B91}
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {48FA418B-CCC2-4EBD-9CDA-F31C72AC9B05}
+	EndGlobalSection
+EndGlobal
diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/pkg/Microsoft.Bcl.AsyncInterfaces.pkgproj b/src/libraries/Microsoft.Bcl.AsyncInterfaces/pkg/Microsoft.Bcl.AsyncInterfaces.pkgproj
new file mode 100644
index 00000000000000..f0630aaef6ecc1
--- /dev/null
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/pkg/Microsoft.Bcl.AsyncInterfaces.pkgproj
@@ -0,0 +1,9 @@
+<Project DefaultTargets="Build">
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), Directory.Build.props))\Directory.Build.props" />
+  <ItemGroup>
+    <ProjectReference Include="..\src\Microsoft.Bcl.AsyncInterfaces.csproj">
+      <SupportedFramework>net461;netcoreapp2.0;uap10.0.16299;$(AllXamarinFrameworks)</SupportedFramework>
+    </ProjectReference>
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), Directory.Build.targets))\Directory.Build.targets" />
+</Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/ref/Microsoft.Bcl.AsyncInterfaces.Forwards.cs b/src/libraries/Microsoft.Bcl.AsyncInterfaces/ref/Microsoft.Bcl.AsyncInterfaces.Forwards.cs
new file mode 100644
index 00000000000000..1d2d2cc64621b1
--- /dev/null
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/ref/Microsoft.Bcl.AsyncInterfaces.Forwards.cs
@@ -0,0 +1,14 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.IAsyncDisposable))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Collections.Generic.IAsyncEnumerable<>))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Collections.Generic.IAsyncEnumerator<>))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Runtime.CompilerServices.AsyncIteratorMethodBuilder))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Runtime.CompilerServices.AsyncIteratorStateMachineAttribute))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Runtime.CompilerServices.ConfiguredAsyncDisposable))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable<>))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Runtime.CompilerServices.EnumeratorCancellationAttribute))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Threading.Tasks.TaskAsyncEnumerableExtensions))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Threading.Tasks.Sources.ManualResetValueTaskSourceCore<>))]
diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/ref/Microsoft.Bcl.AsyncInterfaces.cs b/src/libraries/Microsoft.Bcl.AsyncInterfaces/ref/Microsoft.Bcl.AsyncInterfaces.cs
new file mode 100644
index 00000000000000..13bb163974c963
--- /dev/null
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/ref/Microsoft.Bcl.AsyncInterfaces.cs
@@ -0,0 +1,96 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// ------------------------------------------------------------------------------
+// Changes to this file must follow the https://aka.ms/api-review process.
+// ------------------------------------------------------------------------------
+
+namespace System
+{
+    public partial interface IAsyncDisposable
+    {
+        System.Threading.Tasks.ValueTask DisposeAsync();
+    }
+}
+namespace System.Collections.Generic
+{
+    public partial interface IAsyncEnumerable<out T>
+    {
+        System.Collections.Generic.IAsyncEnumerator<T> GetAsyncEnumerator(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken));
+    }
+    public partial interface IAsyncEnumerator<out T> : System.IAsyncDisposable
+    {
+        T Current { get; }
+        System.Threading.Tasks.ValueTask<bool> MoveNextAsync();
+    }
+}
+namespace System.Runtime.CompilerServices
+{
+    public partial struct AsyncIteratorMethodBuilder
+    {
+        private object _dummy;
+        private int _dummyPrimitive;
+        public void AwaitOnCompleted<TAwaiter, TStateMachine>(ref TAwaiter awaiter, ref TStateMachine stateMachine) where TAwaiter : System.Runtime.CompilerServices.INotifyCompletion where TStateMachine : System.Runtime.CompilerServices.IAsyncStateMachine { }
+        public void AwaitUnsafeOnCompleted<TAwaiter, TStateMachine>(ref TAwaiter awaiter, ref TStateMachine stateMachine) where TAwaiter : System.Runtime.CompilerServices.ICriticalNotifyCompletion where TStateMachine : System.Runtime.CompilerServices.IAsyncStateMachine { }
+        public void Complete() { }
+        public static System.Runtime.CompilerServices.AsyncIteratorMethodBuilder Create() { throw null; }
+        public void MoveNext<TStateMachine>(ref TStateMachine stateMachine) where TStateMachine : System.Runtime.CompilerServices.IAsyncStateMachine { }
+    }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Method, Inherited=false, AllowMultiple=false)]
+    public sealed partial class AsyncIteratorStateMachineAttribute : System.Runtime.CompilerServices.StateMachineAttribute
+    {
+        public AsyncIteratorStateMachineAttribute(System.Type stateMachineType) : base (default(System.Type)) { }
+    }
+    public readonly partial struct ConfiguredAsyncDisposable
+    {
+        private readonly object _dummy;
+        private readonly int _dummyPrimitive;
+        public System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable DisposeAsync() { throw null; }
+    }
+    public readonly partial struct ConfiguredCancelableAsyncEnumerable<T>
+    {
+        private readonly object _dummy;
+        private readonly int _dummyPrimitive;
+        public System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable<T> ConfigureAwait(bool continueOnCapturedContext) { throw null; }
+        public System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable<T>.Enumerator GetAsyncEnumerator() { throw null; }
+        public System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable<T> WithCancellation(System.Threading.CancellationToken cancellationToken) { throw null; }
+        public readonly partial struct Enumerator
+        {
+            private readonly object _dummy;
+            private readonly int _dummyPrimitive;
+            public T Current { get { throw null; } }
+            public System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable DisposeAsync() { throw null; }
+            public System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable<bool> MoveNextAsync() { throw null; }
+        }
+    }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Parameter, Inherited=false)]
+    public sealed partial class EnumeratorCancellationAttribute : System.Attribute
+    {
+        public EnumeratorCancellationAttribute() { }
+    }
+}
+namespace System.Threading.Tasks
+{
+    public static partial class TaskAsyncEnumerableExtensions
+    {
+        public static System.Runtime.CompilerServices.ConfiguredAsyncDisposable ConfigureAwait(this System.IAsyncDisposable source, bool continueOnCapturedContext) { throw null; }
+        public static System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable<T> ConfigureAwait<T>(this System.Collections.Generic.IAsyncEnumerable<T> source, bool continueOnCapturedContext) { throw null; }
+        public static System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable<T> WithCancellation<T>(this System.Collections.Generic.IAsyncEnumerable<T> source, System.Threading.CancellationToken cancellationToken) { throw null; }
+    }
+}
+namespace System.Threading.Tasks.Sources
+{
+    public partial struct ManualResetValueTaskSourceCore<TResult>
+    {
+        private TResult _result;
+        private object _dummy;
+        private int _dummyPrimitive;
+        public bool RunContinuationsAsynchronously { readonly get { throw null; } set { } }
+        public short Version { get { throw null; } }
+        public TResult GetResult(short token) { throw null; }
+        public System.Threading.Tasks.Sources.ValueTaskSourceStatus GetStatus(short token) { throw null; }
+        public void OnCompleted(System.Action<object> continuation, object state, short token, System.Threading.Tasks.Sources.ValueTaskSourceOnCompletedFlags flags) { }
+        public void Reset() { }
+        public void SetException(System.Exception error) { }
+        public void SetResult(TResult result) { }
+    }
+}
diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/ref/Microsoft.Bcl.AsyncInterfaces.csproj b/src/libraries/Microsoft.Bcl.AsyncInterfaces/ref/Microsoft.Bcl.AsyncInterfaces.csproj
new file mode 100644
index 00000000000000..603d16c0f724d4
--- /dev/null
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/ref/Microsoft.Bcl.AsyncInterfaces.csproj
@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworks>net461;netstandard2.0;netstandard2.1</TargetFrameworks>
+  </PropertyGroup>
+  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.1'">
+    <Compile Include="Microsoft.Bcl.AsyncInterfaces.cs" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.1'">
+    <Compile Include="Microsoft.Bcl.AsyncInterfaces.Forwards.cs" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.1'">
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
+  </ItemGroup>
+</Project>
diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/Microsoft.Bcl.AsyncInterfaces.csproj b/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/Microsoft.Bcl.AsyncInterfaces.csproj
new file mode 100644
index 00000000000000..a87ada3281e73f
--- /dev/null
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/Microsoft.Bcl.AsyncInterfaces.csproj
@@ -0,0 +1,39 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworks>net461;netstandard2.0;netstandard2.1</TargetFrameworks>
+  </PropertyGroup>
+  <PropertyGroup>
+    <IsPartialFacadeAssembly Condition="'$(TargetFramework)' == 'netstandard2.1'">true</IsPartialFacadeAssembly>
+  </PropertyGroup>
+  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
+    <Compile Include="System\Threading\Tasks\Sources\ManualResetValueTaskSourceCore.cs" />
+    <Compile Include="System\Runtime\CompilerServices\AsyncIteratorMethodBuilder.cs" />
+    <Compile Include="$(CoreLibSharedDir)\System\Collections\Generic\IAsyncEnumerable.cs">
+      <Link>System.Private.CoreLib\System\Collections\Generic\IAsyncEnumerable.cs</Link>
+    </Compile>
+    <Compile Include="$(CoreLibSharedDir)\System\Collections\Generic\IAsyncEnumerator.cs">
+      <Link>System.Private.CoreLib\System\Collections\Generic\IAsyncEnumerator.cs</Link>
+    </Compile>
+    <Compile Include="$(CoreLibSharedDir)\System\IAsyncDisposable.cs">
+      <Link>System.Private.CoreLib\System\IAsyncDisposable.cs</Link>
+    </Compile>
+    <Compile Include="$(CoreLibSharedDir)\System\Runtime\CompilerServices\AsyncIteratorStateMachineAttribute.cs">
+      <Link>System.Private.CoreLib\System\Runtime\CompilerServices\AsyncIteratorStateMachineAttribute.cs</Link>
+    </Compile>
+    <Compile Include="$(CoreLibSharedDir)\System\Runtime\CompilerServices\ConfiguredAsyncDisposable.cs">
+      <Link>System.Private.CoreLib\System\Runtime\CompilerServices\ConfiguredAsyncDisposable.cs</Link>
+    </Compile>
+    <Compile Include="$(CoreLibSharedDir)\System\Runtime\CompilerServices\ConfiguredCancelableAsyncEnumerable.cs">
+      <Link>System.Private.CoreLib\System\Runtime\CompilerServices\ConfiguredCancelableAsyncEnumerable.cs</Link>
+    </Compile>
+    <Compile Include="$(CoreLibSharedDir)\System\Threading\Tasks\TaskAsyncEnumerableExtensions.cs">
+      <Link>System.Private.CoreLib\System\Threading\Tasks\TaskAsyncEnumerableExtensions.cs</Link>
+    </Compile>
+    <Compile Include="$(CoreLibSharedDir)\System\Runtime\CompilerServices\EnumeratorCancellationAttribute.cs">
+      <Link>System.Private.CoreLib\System\Runtime\CompilerServices\EnumeratorCancellationAttribute.cs</Link>
+    </Compile>
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.1'">
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
+  </ItemGroup>
+</Project>
diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/System/Runtime/CompilerServices/AsyncIteratorMethodBuilder.cs b/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/System/Runtime/CompilerServices/AsyncIteratorMethodBuilder.cs
new file mode 100644
index 00000000000000..8943929e80c458
--- /dev/null
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/System/Runtime/CompilerServices/AsyncIteratorMethodBuilder.cs
@@ -0,0 +1,61 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// NOTE: This is a copy of
+// https://github.com/dotnet/coreclr/blame/07b3afc27304800f00975c8fd4836b319aaa8820/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/AsyncIteratorMethodBuilder.cs
+// modified to be compilable against .NET Standard 2.0.  Key differences:
+// - Uses the wrapped AsyncTaskMethodBuilder for Create and MoveNext.
+// - Uses a custom object for the debugger identity.
+// - Nullable annotations removed.
+
+using System.Runtime.InteropServices;
+using System.Threading;
+
+namespace System.Runtime.CompilerServices
+{
+    /// <summary>Represents a builder for asynchronous iterators.</summary>
+    [StructLayout(LayoutKind.Auto)]
+    public struct AsyncIteratorMethodBuilder
+    {
+        private AsyncTaskMethodBuilder _methodBuilder; // mutable struct; do not make it readonly
+        private object _id;
+
+        /// <summary>Creates an instance of the <see cref="AsyncIteratorMethodBuilder"/> struct.</summary>
+        /// <returns>The initialized instance.</returns>
+        public static AsyncIteratorMethodBuilder Create() =>
+            new AsyncIteratorMethodBuilder() { _methodBuilder = AsyncTaskMethodBuilder.Create() };
+
+        /// <summary>Invokes <see cref="IAsyncStateMachine.MoveNext"/> on the state machine while guarding the <see cref="ExecutionContext"/>.</summary>
+        /// <typeparam name="TStateMachine">The type of the state machine.</typeparam>
+        /// <param name="stateMachine">The state machine instance, passed by reference.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void MoveNext<TStateMachine>(ref TStateMachine stateMachine) where TStateMachine : IAsyncStateMachine =>
+            _methodBuilder.Start(ref stateMachine);
+
+        /// <summary>Schedules the state machine to proceed to the next action when the specified awaiter completes.</summary>
+        /// <typeparam name="TAwaiter">The type of the awaiter.</typeparam>
+        /// <typeparam name="TStateMachine">The type of the state machine.</typeparam>
+        /// <param name="awaiter">The awaiter.</param>
+        /// <param name="stateMachine">The state machine.</param>
+        public void AwaitOnCompleted<TAwaiter, TStateMachine>(ref TAwaiter awaiter, ref TStateMachine stateMachine)
+            where TAwaiter : INotifyCompletion
+            where TStateMachine : IAsyncStateMachine =>
+            _methodBuilder.AwaitOnCompleted(ref awaiter, ref stateMachine);
+
+        /// <summary>Schedules the state machine to proceed to the next action when the specified awaiter completes.</summary>
+        /// <typeparam name="TAwaiter">The type of the awaiter.</typeparam>
+        /// <typeparam name="TStateMachine">The type of the state machine.</typeparam>
+        /// <param name="awaiter">The awaiter.</param>
+        /// <param name="stateMachine">The state machine.</param>
+        public void AwaitUnsafeOnCompleted<TAwaiter, TStateMachine>(ref TAwaiter awaiter, ref TStateMachine stateMachine)
+            where TAwaiter : ICriticalNotifyCompletion
+            where TStateMachine : IAsyncStateMachine =>
+            _methodBuilder.AwaitUnsafeOnCompleted(ref awaiter, ref stateMachine);
+
+        /// <summary>Marks iteration as being completed, whether successfully or otherwise.</summary>
+        public void Complete() => _methodBuilder.SetResult();
+
+        /// <summary>Gets an object that may be used to uniquely identify this builder to the debugger.</summary>
+        internal object ObjectIdForDebugger => _id ?? Interlocked.CompareExchange(ref _id, new object(), null) ?? _id;
+    }
+}
diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/System/Threading/Tasks/Sources/ManualResetValueTaskSourceCore.cs b/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/System/Threading/Tasks/Sources/ManualResetValueTaskSourceCore.cs
new file mode 100644
index 00000000000000..3cb6e817aa614f
--- /dev/null
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/src/System/Threading/Tasks/Sources/ManualResetValueTaskSourceCore.cs
@@ -0,0 +1,271 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// NOTE: This is a copy of
+// https://github.com/dotnet/coreclr/blame/07b3afc27304800f00975c8fd4836b319aaa8820/src/System.Private.CoreLib/shared/System/Threading/Tasks/Sources/ManualResetValueTaskSourceCore.cs,
+// modified to be compilable against .NET Standard 2.0.  It is missing optimizations present in the .NET Core implementation and should
+// only be used when a .NET Standard 2.0 implementation is required.  Key differences:
+// - ThrowHelper call sites are replaced by normal exception throws.
+// - ThreadPool.{Unsafe}QueueUserWorkItem calls that accepted Action<object>/object/bool arguments are replaced by Task.Factory.StartNew usage.
+// - ExecutionContext.RunInternal are replaced by ExecutionContext.Run.
+// - Nullability annotations are removed.
+
+using System.Diagnostics;
+using System.Runtime.ExceptionServices;
+using System.Runtime.InteropServices;
+
+namespace System.Threading.Tasks.Sources
+{
+    /// <summary>Provides the core logic for implementing a manual-reset <see cref="IValueTaskSource"/> or <see cref="IValueTaskSource{TResult}"/>.</summary>
+    /// <typeparam name="TResult"></typeparam>
+    [StructLayout(LayoutKind.Auto)]
+    public struct ManualResetValueTaskSourceCore<TResult>
+    {
+        /// <summary>
+        /// The callback to invoke when the operation completes if <see cref="OnCompleted"/> was called before the operation completed,
+        /// or <see cref="ManualResetValueTaskSourceCoreShared.s_sentinel"/> if the operation completed before a callback was supplied,
+        /// or null if a callback hasn't yet been provided and the operation hasn't yet completed.
+        /// </summary>
+        private Action<object> _continuation;
+        /// <summary>State to pass to <see cref="_continuation"/>.</summary>
+        private object _continuationState;
+        /// <summary><see cref="ExecutionContext"/> to flow to the callback, or null if no flowing is required.</summary>
+        private ExecutionContext _executionContext;
+        /// <summary>
+        /// A "captured" <see cref="SynchronizationContext"/> or <see cref="TaskScheduler"/> with which to invoke the callback,
+        /// or null if no special context is required.
+        /// </summary>
+        private object _capturedContext;
+        /// <summary>Whether the current operation has completed.</summary>
+        private bool _completed;
+        /// <summary>The result with which the operation succeeded, or the default value if it hasn't yet completed or failed.</summary>
+        private TResult _result;
+        /// <summary>The exception with which the operation failed, or null if it hasn't yet completed or completed successfully.</summary>
+        private ExceptionDispatchInfo _error;
+        /// <summary>The current version of this value, used to help prevent misuse.</summary>
+        private short _version;
+
+        /// <summary>Gets or sets whether to force continuations to run asynchronously.</summary>
+        /// <remarks>Continuations may run asynchronously if this is false, but they'll never run synchronously if this is true.</remarks>
+        public bool RunContinuationsAsynchronously { get; set; }
+
+        /// <summary>Resets to prepare for the next operation.</summary>
+        public void Reset()
+        {
+            // Reset/update state for the next use/await of this instance.
+            _version++;
+            _completed = false;
+            _result = default!;
+            _error = null;
+            _executionContext = null;
+            _capturedContext = null;
+            _continuation = null;
+            _continuationState = null;
+        }
+
+        /// <summary>Completes with a successful result.</summary>
+        /// <param name="result">The result.</param>
+        public void SetResult(TResult result)
+        {
+            _result = result;
+            SignalCompletion();
+        }
+
+        /// <summary>Complets with an error.</summary>
+        /// <param name="error"></param>
+        public void SetException(Exception error)
+        {
+            _error = ExceptionDispatchInfo.Capture(error);
+            SignalCompletion();
+        }
+
+        /// <summary>Gets the operation version.</summary>
+        public short Version => _version;
+
+        /// <summary>Gets the status of the operation.</summary>
+        /// <param name="token">Opaque value that was provided to the <see cref="ValueTask"/>'s constructor.</param>
+        public ValueTaskSourceStatus GetStatus(short token)
+        {
+            ValidateToken(token);
+            return
+                _continuation == null || !_completed ? ValueTaskSourceStatus.Pending :
+                _error == null ? ValueTaskSourceStatus.Succeeded :
+                _error.SourceException is OperationCanceledException ? ValueTaskSourceStatus.Canceled :
+                ValueTaskSourceStatus.Faulted;
+        }
+
+        /// <summary>Gets the result of the operation.</summary>
+        /// <param name="token">Opaque value that was provided to the <see cref="ValueTask"/>'s constructor.</param>
+        public TResult GetResult(short token)
+        {
+            ValidateToken(token);
+            if (!_completed)
+            {
+                throw new InvalidOperationException();
+            }
+
+            _error?.Throw();
+            return _result;
+        }
+
+        /// <summary>Schedules the continuation action for this operation.</summary>
+        /// <param name="continuation">The continuation to invoke when the operation has completed.</param>
+        /// <param name="state">The state object to pass to <paramref name="continuation"/> when it's invoked.</param>
+        /// <param name="token">Opaque value that was provided to the <see cref="ValueTask"/>'s constructor.</param>
+        /// <param name="flags">The flags describing the behavior of the continuation.</param>
+        public void OnCompleted(Action<object> continuation, object state, short token, ValueTaskSourceOnCompletedFlags flags)
+        {
+            if (continuation == null)
+            {
+                throw new ArgumentNullException(nameof(continuation));
+            }
+            ValidateToken(token);
+
+            if ((flags & ValueTaskSourceOnCompletedFlags.FlowExecutionContext) != 0)
+            {
+                _executionContext = ExecutionContext.Capture();
+            }
+
+            if ((flags & ValueTaskSourceOnCompletedFlags.UseSchedulingContext) != 0)
+            {
+                SynchronizationContext sc = SynchronizationContext.Current;
+                if (sc != null && sc.GetType() != typeof(SynchronizationContext))
+                {
+                    _capturedContext = sc;
+                }
+                else
+                {
+                    TaskScheduler ts = TaskScheduler.Current;
+                    if (ts != TaskScheduler.Default)
+                    {
+                        _capturedContext = ts;
+                    }
+                }
+            }
+
+            // We need to set the continuation state before we swap in the delegate, so that
+            // if there's a race between this and SetResult/Exception and SetResult/Exception
+            // sees the _continuation as non-null, it'll be able to invoke it with the state
+            // stored here.  However, this also means that if this is used incorrectly (e.g.
+            // awaited twice concurrently), _continuationState might get erroneously overwritten.
+            // To minimize the chances of that, we check preemptively whether _continuation
+            // is already set to something other than the completion sentinel.
+
+            object oldContinuation = _continuation;
+            if (oldContinuation == null)
+            {
+                _continuationState = state;
+                oldContinuation = Interlocked.CompareExchange(ref _continuation, continuation, null);
+            }
+
+            if (oldContinuation != null)
+            {
+                // Operation already completed, so we need to queue the supplied callback.
+                if (!ReferenceEquals(oldContinuation, ManualResetValueTaskSourceCoreShared.s_sentinel))
+                {
+                    throw new InvalidOperationException();
+                }
+
+                switch (_capturedContext)
+                {
+                    case null:
+                        Task.Factory.StartNew(continuation, state, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
+                        break;
+
+                    case SynchronizationContext sc:
+                        sc.Post(s =>
+                        {
+                            var tuple = (Tuple<Action<object>, object>)s;
+                            tuple.Item1(tuple.Item2);
+                        }, Tuple.Create(continuation, state));
+                        break;
+
+                    case TaskScheduler ts:
+                        Task.Factory.StartNew(continuation, state, CancellationToken.None, TaskCreationOptions.DenyChildAttach, ts);
+                        break;
+                }
+            }
+        }
+
+        /// <summary>Ensures that the specified token matches the current version.</summary>
+        /// <param name="token">The token supplied by <see cref="ValueTask"/>.</param>
+        private void ValidateToken(short token)
+        {
+            if (token != _version)
+            {
+                throw new InvalidOperationException();
+            }
+        }
+
+        /// <summary>Signals that the operation has completed.  Invoked after the result or error has been set.</summary>
+        private void SignalCompletion()
+        {
+            if (_completed)
+            {
+                throw new InvalidOperationException();
+            }
+            _completed = true;
+
+            if (_continuation != null || Interlocked.CompareExchange(ref _continuation, ManualResetValueTaskSourceCoreShared.s_sentinel, null) != null)
+            {
+                if (_executionContext != null)
+                {
+                    ExecutionContext.Run(
+                        _executionContext,
+                        s => ((ManualResetValueTaskSourceCore<TResult>)s).InvokeContinuation(),
+                        this);
+                }
+                else
+                {
+                    InvokeContinuation();
+                }
+            }
+        }
+
+        /// <summary>
+        /// Invokes the continuation with the appropriate captured context / scheduler.
+        /// This assumes that if <see cref="_executionContext"/> is not null we're already
+        /// running within that <see cref="ExecutionContext"/>.
+        /// </summary>
+        private void InvokeContinuation()
+        {
+            Debug.Assert(_continuation != null);
+
+            switch (_capturedContext)
+            {
+                case null:
+                    if (RunContinuationsAsynchronously)
+                    {
+                        Task.Factory.StartNew(_continuation, _continuationState, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
+                    }
+                    else
+                    {
+                        _continuation(_continuationState);
+                    }
+                    break;
+
+                case SynchronizationContext sc:
+                    sc.Post(s =>
+                    {
+                        var state = (Tuple<Action<object>, object>)s;
+                        state.Item1(state.Item2);
+                    }, Tuple.Create(_continuation, _continuationState));
+                    break;
+
+                case TaskScheduler ts:
+                    Task.Factory.StartNew(_continuation, _continuationState, CancellationToken.None, TaskCreationOptions.DenyChildAttach, ts);
+                    break;
+            }
+        }
+    }
+
+    internal static class ManualResetValueTaskSourceCoreShared // separated out of generic to avoid unnecessary duplication
+    {
+        internal static readonly Action<object> s_sentinel = CompletionSentinel;
+        private static void CompletionSentinel(object _) // named method to aid debugging
+        {
+            Debug.Fail("The sentinel delegate should never be invoked.");
+            throw new InvalidOperationException();
+        }
+    }
+}
diff --git a/src/libraries/Microsoft.Bcl.AsyncInterfaces/tests/Microsoft.Bcl.AsyncInterfaces.Tests.csproj b/src/libraries/Microsoft.Bcl.AsyncInterfaces/tests/Microsoft.Bcl.AsyncInterfaces.Tests.csproj
new file mode 100644
index 00000000000000..79f4f9b7fc5259
--- /dev/null
+++ b/src/libraries/Microsoft.Bcl.AsyncInterfaces/tests/Microsoft.Bcl.AsyncInterfaces.Tests.csproj
@@ -0,0 +1,22 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="..\..\Common\tests\System\Threading\Tasks\Sources\ManualResetValueTaskSource.cs">
+      <Link>Common\tests\System\Threading\Tasks\Sources\ManualResetValueTaskSource.cs</Link>
+    </Compile>
+    <Compile Include="..\..\System.Threading.Tasks\tests\System.Runtime.CompilerServices\ConfiguredCancelableAsyncEnumerableTests.cs">
+      <Link>System.Threading.Tasks\tests\System.Runtime.CompilerServices\ConfiguredCancelableAsyncEnumerableTests.cs</Link>
+    </Compile>
+    <Compile Include="..\..\System.Threading.Tasks\tests\System.Runtime.CompilerServices\ConfiguredAsyncDisposable.cs">
+      <Link>System.Threading.Tasks\tests\System.Runtime.CompilerServices\ConfiguredAsyncDisposable.cs</Link>
+    </Compile>
+    <Compile Condition="'$(TargetFramework)' != 'net461'" Include="..\..\System.Threading.Tasks.Extensions\tests\ManualResetValueTaskSourceTests.cs">
+      <Link>System.Threading.Tasks.Extensions\tests\ManualResetValueTaskSourceTests.cs</Link>
+    </Compile>
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\Microsoft.Bcl.AsyncInterfaces.csproj" />
+  </ItemGroup>
+</Project>
diff --git a/src/libraries/Microsoft.CSharp/Directory.Build.props b/src/libraries/Microsoft.CSharp/Directory.Build.props
index 9155a7a0764984..5073e779defc13 100644
--- a/src/libraries/Microsoft.CSharp/Directory.Build.props
+++ b/src/libraries/Microsoft.CSharp/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/Microsoft.CSharp/src/Microsoft.CSharp.csproj b/src/libraries/Microsoft.CSharp/src/Microsoft.CSharp.csproj
index 0a85130f66d8b0..5aadca703ef16a 100644
--- a/src/libraries/Microsoft.CSharp/src/Microsoft.CSharp.csproj
+++ b/src/libraries/Microsoft.CSharp/src/Microsoft.CSharp.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>Microsoft.CSharp</AssemblyName>
-    <RootNamespace>Microsoft.CSharp</RootNamespace>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
     <NoWarn>$(NoWarn);nullable</NoWarn>
diff --git a/src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ComInterop.cs b/src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ComInterop.cs
index 275a6d50538656..b146f6fd807755 100644
--- a/src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ComInterop.cs
+++ b/src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ComInterop.cs
@@ -41,21 +41,6 @@ int TryInvoke(
             IntPtr puArgErr);
     }
 
-    /// <summary>
-    /// Layout of the IDispatch vtable
-    /// </summary>
-    internal enum IDispatchMethodIndices
-    {
-        IUnknown_QueryInterface,
-        IUnknown_AddRef,
-        IUnknown_Release,
-
-        IDispatch_GetTypeInfoCount,
-        IDispatch_GetTypeInfo,
-        IDispatch_GetIDsOfNames,
-        IDispatch_Invoke
-    }
-
     [ComImport]
     [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
     [Guid("B196B283-BAB4-101A-B69C-00AA00341D07")]
diff --git a/src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ComRuntimeHelpers.cs b/src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ComRuntimeHelpers.cs
index 01bc32bf59ae22..0814a30a0e88b7 100644
--- a/src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ComRuntimeHelpers.cs
+++ b/src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/ComRuntimeHelpers.cs
@@ -260,9 +260,9 @@ public static object GetObjectForVariant(Variant variant)
         }
 
         // This method is intended for use through reflection and should only be used directly by IUnknownReleaseNotZero
-        public static int IUnknownRelease(IntPtr interfacePointer)
+        public static unsafe int IUnknownRelease(IntPtr interfacePointer)
         {
-            return s_iUnknownRelease(interfacePointer);
+            return ((delegate* stdcall<IntPtr, int>)(*(*(void***)interfacePointer + 2 /* IUnknown.Release slot */)))(interfacePointer);
         }
 
         // This method is intended for use through reflection and should not be used directly
@@ -275,7 +275,7 @@ public static void IUnknownReleaseNotZero(IntPtr interfacePointer)
         }
 
         // This method is intended for use through reflection and should not be used directly
-        public static int IDispatchInvoke(
+        public static unsafe int IDispatchInvoke(
             IntPtr dispatchPointer,
             int memberDispId,
             ComTypes.INVOKEKIND flags,
@@ -284,31 +284,30 @@ public static int IDispatchInvoke(
             out ExcepInfo excepInfo,
             out uint argErr)
         {
-            int hresult = s_iDispatchInvoke(
-                dispatchPointer,
-                memberDispId,
-                flags,
-                ref dispParams,
-                out result,
-                out excepInfo,
-                out argErr
-            );
-
-            if (hresult == ComHresults.DISP_E_MEMBERNOTFOUND
-                && (flags & ComTypes.INVOKEKIND.INVOKE_FUNC) != 0
-                && (flags & (ComTypes.INVOKEKIND.INVOKE_PROPERTYPUT | ComTypes.INVOKEKIND.INVOKE_PROPERTYPUTREF)) == 0)
+            Guid IID_NULL = default;
+
+            fixed (ComTypes.DISPPARAMS* pDispParams = &dispParams)
+            fixed (Variant* pResult = &result)
+            fixed (ExcepInfo* pExcepInfo = &excepInfo)
+            fixed (uint* pArgErr = &argErr)
             {
-                // Re-invoke with no result argument to accomodate Word
-                hresult = _IDispatchInvokeNoResult(
-                    dispatchPointer,
-                    memberDispId,
-                    ComTypes.INVOKEKIND.INVOKE_FUNC,
-                    ref dispParams,
-                    out result,
-                    out excepInfo,
-                    out argErr);
+                var pfnIDispatchInvoke = (delegate* stdcall <IntPtr, int, Guid*, int, ushort, ComTypes.DISPPARAMS*, Variant*, ExcepInfo*, uint*, int>)
+                    (*(*(void***)dispatchPointer + 6 /* IDispatch.Invoke slot */));
+
+                int hresult = pfnIDispatchInvoke(dispatchPointer,
+                    memberDispId, &IID_NULL, 0, (ushort)flags, pDispParams, pResult, pExcepInfo, pArgErr);
+
+                if (hresult == ComHresults.DISP_E_MEMBERNOTFOUND
+                    && (flags & ComTypes.INVOKEKIND.INVOKE_FUNC) != 0
+                    && (flags & (ComTypes.INVOKEKIND.INVOKE_PROPERTYPUT | ComTypes.INVOKEKIND.INVOKE_PROPERTYPUTREF)) == 0)
+                {
+                    // Re-invoke with no result argument to accomodate Word
+                    hresult = pfnIDispatchInvoke(dispatchPointer,
+                        memberDispId, &IID_NULL, 0, (ushort)ComTypes.INVOKEKIND.INVOKE_FUNC, pDispParams, null, pExcepInfo, pArgErr);
+                }
+
+                return hresult;
             }
-            return hresult;
         }
 
         // This method is intended for use through reflection and should not be used directly
@@ -338,12 +337,6 @@ public static IntPtr GetIdsOfNamedParameters(IDispatch dispatch, string[] names,
 
         #region non-public members
 
-        private static void EmitLoadArg(ILGenerator il, int index)
-        {
-            Requires.Condition(index >= 0, nameof(index));
-            il.Emit(OpCodes.Ldarg, index);
-        }
-
         private static readonly object s_lock = new object();
         private static ModuleBuilder s_dynamicModule;
 
@@ -368,179 +361,6 @@ internal static ModuleBuilder DynamicModule
             }
         }
 
-        /// <summary>
-        /// We will emit an indirect call to an unmanaged function pointer from the vtable of the given interface pointer.
-        /// This approach can take only ~300 instructions on x86 compared with ~900 for Marshal.Release. We are relying on
-        /// the JIT-compiler to do pinvoke-stub-inlining and calling the pinvoke target directly.
-        /// </summary>
-        private delegate int IUnknownReleaseDelegate(IntPtr interfacePointer);
-        private static readonly IUnknownReleaseDelegate s_iUnknownRelease = Create_IUnknownRelease();
-
-        private static IUnknownReleaseDelegate Create_IUnknownRelease()
-        {
-            DynamicMethod dm = new DynamicMethod("IUnknownRelease", typeof(int), new Type[] { typeof(IntPtr) }, DynamicModule);
-
-            ILGenerator method = dm.GetILGenerator();
-
-            // return functionPtr(...)
-
-            method.Emit(OpCodes.Ldarg_0);
-
-            // functionPtr = *(IntPtr*)(*(interfacePointer) + VTABLE_OFFSET)
-            int iunknownReleaseOffset = ((int)IDispatchMethodIndices.IUnknown_Release) * Marshal.SizeOf(typeof(IntPtr));
-            method.Emit(OpCodes.Ldarg_0);
-            method.Emit(OpCodes.Ldind_I);
-            method.Emit(OpCodes.Ldc_I4, iunknownReleaseOffset);
-            method.Emit(OpCodes.Add);
-            method.Emit(OpCodes.Ldind_I);
-
-            method.EmitCalli(OpCodes.Calli, CallingConvention.Winapi, typeof(int), new[] { typeof(IntPtr) });
-
-            method.Emit(OpCodes.Ret);
-
-            return dm.CreateDelegate<IUnknownReleaseDelegate>();
-        }
-
-        internal static readonly IntPtr s_nullInterfaceId = GetNullInterfaceId();
-
-        private static IntPtr GetNullInterfaceId()
-        {
-            int size = Marshal.SizeOf(Guid.Empty);
-            IntPtr ptr = Marshal.AllocHGlobal(size);
-            for (int i = 0; i < size; i++)
-            {
-                Marshal.WriteByte(ptr, i, 0);
-            }
-            return ptr;
-        }
-
-        /// <summary>
-        /// We will emit an indirect call to an unmanaged function pointer from the vtable of the given IDispatch interface pointer.
-        /// It is not possible to express this in C#. Using an indirect pinvoke call allows us to do our own marshalling.
-        /// We can allocate the Variant arguments cheaply on the stack. We are relying on the JIT-compiler to do
-        /// pinvoke-stub-inlining and calling the pinvoke target directly.
-        /// The alternative of calling via a managed interface declaration of IDispatch would have a performance
-        /// penalty of going through a CLR stub that would have to re-push the arguments on the stack, etc.
-        /// Marshal.GetDelegateForFunctionPointer could be used here, but its too expensive (~2000 instructions on x86).
-        /// </summary>
-        private delegate int IDispatchInvokeDelegate(
-            IntPtr dispatchPointer,
-            int memberDispId,
-            ComTypes.INVOKEKIND flags,
-            ref ComTypes.DISPPARAMS dispParams,
-            out Variant result,
-            out ExcepInfo excepInfo,
-            out uint argErr
-        );
-
-        private static readonly IDispatchInvokeDelegate s_iDispatchInvoke = Create_IDispatchInvoke(true);
-        private static IDispatchInvokeDelegate s_iDispatchInvokeNoResultImpl;
-
-        private static IDispatchInvokeDelegate _IDispatchInvokeNoResult
-        {
-            get
-            {
-                if (s_iDispatchInvokeNoResultImpl == null)
-                {
-                    lock (s_iDispatchInvoke)
-                    {
-                        if (s_iDispatchInvokeNoResultImpl == null)
-                        {
-                            s_iDispatchInvokeNoResultImpl = Create_IDispatchInvoke(false);
-                        }
-                    }
-                }
-                return s_iDispatchInvokeNoResultImpl;
-            }
-        }
-
-        private static IDispatchInvokeDelegate Create_IDispatchInvoke(bool returnResult)
-        {
-            const int dispatchPointerIndex = 0;
-            const int memberDispIdIndex = 1;
-            const int flagsIndex = 2;
-            const int dispParamsIndex = 3;
-            const int resultIndex = 4;
-            const int exceptInfoIndex = 5;
-            const int argErrIndex = 6;
-            Debug.Assert(argErrIndex + 1 == typeof(IDispatchInvokeDelegate).GetMethod(nameof(IDispatchInvokeDelegate.Invoke)).GetParameters().Length);
-
-            Type[] paramTypes = new Type[argErrIndex + 1];
-            paramTypes[dispatchPointerIndex] = typeof(IntPtr);
-            paramTypes[memberDispIdIndex] = typeof(int);
-            paramTypes[flagsIndex] = typeof(ComTypes.INVOKEKIND);
-            paramTypes[dispParamsIndex] = typeof(ComTypes.DISPPARAMS).MakeByRefType();
-            paramTypes[resultIndex] = typeof(Variant).MakeByRefType();
-            paramTypes[exceptInfoIndex] = typeof(ExcepInfo).MakeByRefType();
-            paramTypes[argErrIndex] = typeof(uint).MakeByRefType();
-
-            // Define the dynamic method in our assembly so we skip verification
-            DynamicMethod dm = new DynamicMethod("IDispatchInvoke", typeof(int), paramTypes, DynamicModule);
-            ILGenerator method = dm.GetILGenerator();
-
-            // return functionPtr(...)
-
-            EmitLoadArg(method, dispatchPointerIndex);
-            EmitLoadArg(method, memberDispIdIndex);
-
-            // burn the address of our empty IID in directly.  This is never freed, relocated, etc...
-            // Note passing this as a Guid directly results in a ~30% perf hit for IDispatch invokes so
-            // we also pass it directly as an IntPtr instead.
-            if (IntPtr.Size == 4)
-            {
-                method.Emit(OpCodes.Ldc_I4, UnsafeMethods.s_nullInterfaceId.ToInt32()); // riid
-            }
-            else
-            {
-                method.Emit(OpCodes.Ldc_I8, UnsafeMethods.s_nullInterfaceId.ToInt64()); // riid
-            }
-            method.Emit(OpCodes.Conv_I);
-
-            method.Emit(OpCodes.Ldc_I4_0); // lcid
-            EmitLoadArg(method, flagsIndex);
-
-            EmitLoadArg(method, dispParamsIndex);
-            method.Emit(OpCodes.Conv_I);
-
-            if (returnResult)
-            {
-                EmitLoadArg(method, resultIndex);
-                method.Emit(OpCodes.Conv_I);
-            }
-            else
-            {
-                method.Emit(OpCodes.Ldsfld, typeof(IntPtr).GetField(nameof(IntPtr.Zero)));
-            }
-            EmitLoadArg(method, exceptInfoIndex);
-            method.Emit(OpCodes.Conv_I);
-            EmitLoadArg(method, argErrIndex);
-            method.Emit(OpCodes.Conv_I);
-
-            // functionPtr = *(IntPtr*)(*(dispatchPointer) + VTABLE_OFFSET)
-            int idispatchInvokeOffset = ((int)IDispatchMethodIndices.IDispatch_Invoke) * Marshal.SizeOf(typeof(IntPtr));
-            EmitLoadArg(method, dispatchPointerIndex);
-            method.Emit(OpCodes.Ldind_I);
-            method.Emit(OpCodes.Ldc_I4, idispatchInvokeOffset);
-            method.Emit(OpCodes.Add);
-            method.Emit(OpCodes.Ldind_I);
-
-            Type[] invokeParamTypes = new Type[] {
-                    typeof(IntPtr), // dispatchPointer
-                    typeof(int),    // memberDispId
-                    typeof(IntPtr), // riid
-                    typeof(int),    // lcid
-                    typeof(ushort), // flags
-                    typeof(IntPtr), // dispParams
-                    typeof(IntPtr), // result
-                    typeof(IntPtr), // excepInfo
-                    typeof(IntPtr), // argErr
-                };
-            method.EmitCalli(OpCodes.Calli, CallingConvention.Winapi, typeof(int), invokeParamTypes);
-
-            method.Emit(OpCodes.Ret);
-            return dm.CreateDelegate<IDispatchInvokeDelegate>();
-        }
-
         #endregion
     }
 }
diff --git a/src/libraries/Microsoft.CSharp/tests/Microsoft.CSharp.Tests.csproj b/src/libraries/Microsoft.CSharp/tests/Microsoft.CSharp.Tests.csproj
index 11dfc740701cd9..b36a8845bbd327 100644
--- a/src/libraries/Microsoft.CSharp/tests/Microsoft.CSharp.Tests.csproj
+++ b/src/libraries/Microsoft.CSharp/tests/Microsoft.CSharp.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net48</TargetFrameworks>
     <!-- 
     We wish to test operations that would result in
     "Operator '-' cannot be applied to operands of type 'ushort' and 'EnumArithmeticTests.UInt16Enum'"
@@ -37,4 +37,7 @@
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <Compile Include="AccessTests.netcoreapp.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
+    <Reference Include="Microsoft.CSharp" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/src/Microsoft.Diagnostics.Tracing.EventSource.Redist.csproj b/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/src/Microsoft.Diagnostics.Tracing.EventSource.Redist.csproj
index 9acca8dfc99205..8c2783236fc68f 100644
--- a/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/src/Microsoft.Diagnostics.Tracing.EventSource.Redist.csproj
+++ b/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/src/Microsoft.Diagnostics.Tracing.EventSource.Redist.csproj
@@ -2,8 +2,7 @@
   <PropertyGroup>
     <AssemblyName>Microsoft.Diagnostics.Tracing.EventSource</AssemblyName>
     <DefineConstants>$(DefineConstants);NO_EVENTCOMMANDEXECUTED_SUPPORT;ES_BUILD_STANDALONE;FEATURE_MANAGED_ETW;TARGET_WINDOWS</DefineConstants>
-    <TargetFrameworks>$(NetFrameworkCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>net461-Windows_NT</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup>
@@ -11,6 +10,7 @@
     <CheckForOverflowUnderflow>true</CheckForOverflowUnderflow>
   </PropertyGroup>
   <ItemGroup>
+    <Compile Include="Microsoft\Diagnostics\Tracing\StubEnvironment.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Errors.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Libraries.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Advapi32\Interop.ActivityControl.cs" />
@@ -37,7 +37,6 @@
     <Compile Include="..\..\System.Private.CoreLib\src\System\Diagnostics\Tracing\IncrementingEventCounter.cs" />
     <Compile Include="..\..\System.Private.CoreLib\src\System\Diagnostics\Tracing\IncrementingPollingCounter.cs" />
     <Compile Include="..\..\System.Private.CoreLib\src\System\Diagnostics\Tracing\PollingCounter.cs" />
-    <Compile Include="..\..\System.Private.CoreLib\src\System\Diagnostics\Tracing\StubEnvironment.cs" />
     <Compile Include="..\..\System.Private.CoreLib\src\System\Diagnostics\Tracing\Winmeta.cs" />
     <Compile Include="..\..\System.Private.CoreLib\src\System\Diagnostics\Tracing\TraceLogging\ArrayTypeInfo.cs" />
     <Compile Include="..\..\System.Private.CoreLib\src\System\Diagnostics\Tracing\TraceLogging\ConcurrentSet.cs" />
@@ -70,8 +69,4 @@
     <Compile Include="..\..\System.Private.CoreLib\src\System\Diagnostics\Tracing\TraceLogging\TraceLoggingTypeInfo.cs" />
     <Compile Include="..\..\System.Private.CoreLib\src\System\Diagnostics\Tracing\TraceLogging\TypeAnalysis.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/src/Microsoft/Diagnostics/Tracing/StubEnvironment.cs b/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/src/Microsoft/Diagnostics/Tracing/StubEnvironment.cs
new file mode 100644
index 00000000000000..7d437be5f43df1
--- /dev/null
+++ b/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/src/Microsoft/Diagnostics/Tracing/StubEnvironment.cs
@@ -0,0 +1,71 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Security;
+using System.Security.Permissions;
+
+namespace Microsoft.Diagnostics.Tracing
+{
+    internal static class Environment
+    {
+        public static readonly int ProcessId = GetCurrentProcessId();
+
+        private static int GetCurrentProcessId()
+        {
+            new SecurityPermission(PermissionState.Unrestricted).Assert();
+            return (int)Interop.Kernel32.GetCurrentProcessId();
+        }
+    }
+
+    internal static class BitOperations
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint RotateLeft(uint value, int offset)
+            => (value << offset) | (value >> (32 - offset));
+
+        public static int PopCount(uint value)
+        {
+            const uint c1 = 0x_55555555u;
+            const uint c2 = 0x_33333333u;
+            const uint c3 = 0x_0F0F0F0Fu;
+            const uint c4 = 0x_01010101u;
+
+            value = value - ((value >> 1) & c1);
+            value = (value & c2) + ((value >> 2) & c2);
+            value = (((value + (value >> 4)) & c3) * c4) >> 24;
+
+            return (int)value;
+        }
+
+        public static int TrailingZeroCount(uint value)
+        {
+            if (value == 0)
+                return 32;
+
+            int count = 0;
+            while ((value & 1) == 0)
+            {
+                value >>= 1;
+                count++;
+            }
+            return count;
+        }
+    }
+}
+
+internal static partial class Interop
+{
+    [SuppressUnmanagedCodeSecurityAttribute]
+    internal static partial class Kernel32
+    {
+        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
+        internal static extern int GetCurrentThreadId();
+
+        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
+        internal static extern uint GetCurrentProcessId();
+    }
+}
diff --git a/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/tests/Microsoft.Diagnostics.Tracing.EventSource.Redist.Tests.csproj b/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/tests/Microsoft.Diagnostics.Tracing.EventSource.Redist.Tests.csproj
index 050d2b686d0e75..b2043931b9a6b6 100644
--- a/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/tests/Microsoft.Diagnostics.Tracing.EventSource.Redist.Tests.csproj
+++ b/src/libraries/Microsoft.Diagnostics.Tracing.EventSource.Redist/tests/Microsoft.Diagnostics.Tracing.EventSource.Redist.Tests.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <DefineConstants>$(DefineConstants);USE_MDT_EVENTSOURCE</DefineConstants>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <PropertyGroup>
     <SDTTestDir>..\..\System.Diagnostics.Tracing\tests</SDTTestDir>
@@ -36,5 +36,6 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.Diagnostics.Tracing.TraceEvent" Version="$(TraceEventVersion)" />
+    <ProjectReference Include="..\src\Microsoft.Diagnostics.Tracing.EventSource.Redist.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.csproj
index ffcb96718ce0d3..1ef4e9bf60eaef 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Caching.Abstractions.cs" />
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/Microsoft.Extensions.Caching.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/Microsoft.Extensions.Caching.Abstractions.csproj
index 3ba2a9af6d414e..6e49dfd659d8b0 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/Microsoft.Extensions.Caching.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/Microsoft.Extensions.Caching.Abstractions.csproj
@@ -1,16 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Primitives" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Caching.Memory/ref/Microsoft.Extensions.Caching.Memory.csproj b/src/libraries/Microsoft.Extensions.Caching.Memory/ref/Microsoft.Extensions.Caching.Memory.csproj
index e971c59c800809..d62099807bb670 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Memory/ref/Microsoft.Extensions.Caching.Memory.csproj
+++ b/src/libraries/Microsoft.Extensions.Caching.Memory/ref/Microsoft.Extensions.Caching.Memory.csproj
@@ -1,13 +1,14 @@
-<!-- This file is automatically generated. -->
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
-<ItemGroup>
+  <ItemGroup>
     <Compile Include="Microsoft.Extensions.Caching.Memory.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Caching.Abstractions\ref\Microsoft.Extensions.Caching.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Caching.Abstractions\ref\Microsoft.Extensions.Caching.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Caching.Memory/src/Microsoft.Extensions.Caching.Memory.csproj b/src/libraries/Microsoft.Extensions.Caching.Memory/src/Microsoft.Extensions.Caching.Memory.csproj
index bb10223118146c..3992cb1adb5699 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Memory/src/Microsoft.Extensions.Caching.Memory.csproj
+++ b/src/libraries/Microsoft.Extensions.Caching.Memory/src/Microsoft.Extensions.Caching.Memory.csproj
@@ -1,22 +1,16 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Caching.Abstractions" />
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Options" />
-    <Reference Include="Microsoft.Extensions.Primitives" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Caching.Abstractions\src\Microsoft.Extensions.Caching.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Caching.Memory/tests/CapacityTests.cs b/src/libraries/Microsoft.Extensions.Caching.Memory/tests/CapacityTests.cs
index 4ea5c20c7113f5..e4d5ef4893568f 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Memory/tests/CapacityTests.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Memory/tests/CapacityTests.cs
@@ -110,6 +110,7 @@ public void DoNotAddEntryIfItExceedsCapacity()
         }
 
         [Fact]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/33993")]
         public async Task DoNotAddIfSizeOverflows()
         {
             var cache = new MemoryCache(new MemoryCacheOptions { SizeLimit = long.MaxValue });
diff --git a/src/libraries/Microsoft.Extensions.Caching.Memory/tests/Microsoft.Extensions.Caching.Memory.Tests.csproj b/src/libraries/Microsoft.Extensions.Caching.Memory/tests/Microsoft.Extensions.Caching.Memory.Tests.csproj
index 5cff85d11fe393..7046da24da6d6d 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Memory/tests/Microsoft.Extensions.Caching.Memory.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Caching.Memory/tests/Microsoft.Extensions.Caching.Memory.Tests.csproj
@@ -1,16 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Compile Include="..\..\Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\ExceptionAssertions.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\ExceptionAssertions.cs" />
-    <Compile Include="..\..\Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\CultureReplacer.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\CultureReplacer.cs" />
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Caching.Memory" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Caching.Memory.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Caching.Memory/tests/TimeExpirationTests.cs b/src/libraries/Microsoft.Extensions.Caching.Memory/tests/TimeExpirationTests.cs
index b35d42c92618e7..4a26ad05a9fd30 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Memory/tests/TimeExpirationTests.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Memory/tests/TimeExpirationTests.cs
@@ -3,7 +3,6 @@
 
 using System;
 using System.Threading;
-using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Internal;
 using Xunit;
 
@@ -97,14 +96,8 @@ public void NegativeRelativeExpirationThrows()
             var key = "myKey";
             var value = new object();
 
-            ExceptionAssert.ThrowsArgumentOutOfRange(() =>
-            {
-                var result = cache.Set(key, value, new MemoryCacheEntryOptions()
-                    .SetAbsoluteExpiration(TimeSpan.FromMinutes(-1)));
-            },
-            nameof(MemoryCacheEntryOptions.AbsoluteExpirationRelativeToNow),
-            "The relative expiration value must be positive.",
-            TimeSpan.FromMinutes(-1));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(nameof(MemoryCacheEntryOptions.AbsoluteExpirationRelativeToNow), () =>
+                cache.Set(key, value, new MemoryCacheEntryOptions().SetAbsoluteExpiration(TimeSpan.FromMinutes(-1))));
         }
 
         [Fact]
@@ -115,13 +108,8 @@ public void ZeroRelativeExpirationThrows()
             var key = "myKey";
             var value = new object();
 
-            ExceptionAssert.ThrowsArgumentOutOfRange(() =>
-            {
-                var result = cache.Set(key, value, new MemoryCacheEntryOptions().SetAbsoluteExpiration(TimeSpan.Zero));
-            },
-            nameof(MemoryCacheEntryOptions.AbsoluteExpirationRelativeToNow),
-            "The relative expiration value must be positive.",
-            TimeSpan.Zero);
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(nameof(MemoryCacheEntryOptions.AbsoluteExpirationRelativeToNow), () =>
+                cache.Set(key, value, new MemoryCacheEntryOptions().SetAbsoluteExpiration(TimeSpan.Zero)));
         }
 
         [Fact]
@@ -154,14 +142,8 @@ public void NegativeSlidingExpirationThrows()
             var key = "myKey";
             var value = new object();
 
-            ExceptionAssert.ThrowsArgumentOutOfRange(() =>
-            {
-                var result = cache.Set(key, value, new MemoryCacheEntryOptions()
-                    .SetSlidingExpiration(TimeSpan.FromMinutes(-1)));
-            },
-            nameof(MemoryCacheEntryOptions.SlidingExpiration),
-            "The sliding expiration value must be positive.",
-            TimeSpan.FromMinutes(-1));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(nameof(MemoryCacheEntryOptions.SlidingExpiration), () =>
+                cache.Set(key, value, new MemoryCacheEntryOptions().SetSlidingExpiration(TimeSpan.FromMinutes(-1))));
         }
 
         [Fact]
@@ -172,14 +154,8 @@ public void ZeroSlidingExpirationThrows()
             var key = "myKey";
             var value = new object();
 
-            ExceptionAssert.ThrowsArgumentOutOfRange(() =>
-            {
-                var result = cache.Set(key, value, new MemoryCacheEntryOptions()
-                    .SetSlidingExpiration(TimeSpan.Zero));
-            },
-            nameof(MemoryCacheEntryOptions.SlidingExpiration),
-            "The sliding expiration value must be positive.",
-            TimeSpan.Zero);
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(nameof(MemoryCacheEntryOptions.SlidingExpiration), () =>
+                cache.Set(key, value, new MemoryCacheEntryOptions().SetSlidingExpiration(TimeSpan.Zero)));
         }
 
         [Fact]
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj
index b7895cdb04d2b3..d6b7d921c7a1ec 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj
@@ -1,9 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.Abstractions.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
index 1bc83e66b5ce5c..c8f4913790420c 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
@@ -1,23 +1,16 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
+    <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Compile Include="*.cs" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Primitives" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.ValueTuple" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Binder/ref/Microsoft.Extensions.Configuration.Binder.csproj b/src/libraries/Microsoft.Extensions.Configuration.Binder/ref/Microsoft.Extensions.Configuration.Binder.csproj
index 4df616e013206b..3e14fd0db31e7a 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Binder/ref/Microsoft.Extensions.Configuration.Binder.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Binder/ref/Microsoft.Extensions.Configuration.Binder.csproj
@@ -1,10 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.Binder.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Binder/src/Microsoft.Extensions.Configuration.Binder.csproj b/src/libraries/Microsoft.Extensions.Configuration.Binder/src/Microsoft.Extensions.Configuration.Binder.csproj
index 2a1759b0d0c659..0295775fad12f9 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Binder/src/Microsoft.Extensions.Configuration.Binder.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Binder/src/Microsoft.Extensions.Configuration.Binder.csproj
@@ -1,20 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration" />
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Microsoft.Extensions.Configuration.Binder.Tests.csproj b/src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Microsoft.Extensions.Configuration.Binder.Tests.csproj
index 2f02865ce4f556..d2323d0b590cfc 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Microsoft.Extensions.Configuration.Binder.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Microsoft.Extensions.Configuration.Binder.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -13,7 +13,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Configuration.Binder" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Configuration.Binder.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.CommandLine/ref/Microsoft.Extensions.Configuration.CommandLine.csproj b/src/libraries/Microsoft.Extensions.Configuration.CommandLine/ref/Microsoft.Extensions.Configuration.CommandLine.csproj
index 152fd02a26577d..041fb7e77f76f4 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.CommandLine/ref/Microsoft.Extensions.Configuration.CommandLine.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.CommandLine/ref/Microsoft.Extensions.Configuration.CommandLine.csproj
@@ -1,10 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.CommandLine.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.CommandLine/src/Microsoft.Extensions.Configuration.CommandLine.csproj b/src/libraries/Microsoft.Extensions.Configuration.CommandLine/src/Microsoft.Extensions.Configuration.CommandLine.csproj
index 980c31e3b203b6..0c2ba3fbdfe606 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.CommandLine/src/Microsoft.Extensions.Configuration.CommandLine.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.CommandLine/src/Microsoft.Extensions.Configuration.CommandLine.csproj
@@ -1,18 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(DefaultNetCoreTargetFramework);net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration" />
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.CommandLine/tests/Microsoft.Extensions.Configuration.CommandLine.Tests.csproj b/src/libraries/Microsoft.Extensions.Configuration.CommandLine/tests/Microsoft.Extensions.Configuration.CommandLine.Tests.csproj
index 6fd320df92dbb2..14a7ec39efdc7d 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.CommandLine/tests/Microsoft.Extensions.Configuration.CommandLine.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.CommandLine/tests/Microsoft.Extensions.Configuration.CommandLine.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -15,7 +15,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Configuration.CommandLine" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Configuration.CommandLine.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
index 2cdfea08ba7b95..45d78b92ea24bc 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
@@ -1,10 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.EnvironmentVariables.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
index 7debc9c3c30e37..0c2ba3fbdfe606 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
@@ -1,19 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration" />
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/tests/Microsoft.Extensions.Configuration.EnvironmentVariables.Tests.csproj b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/tests/Microsoft.Extensions.Configuration.EnvironmentVariables.Tests.csproj
index ad7e1cb18d5322..62b5a8e31deb74 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/tests/Microsoft.Extensions.Configuration.EnvironmentVariables.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/tests/Microsoft.Extensions.Configuration.EnvironmentVariables.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -15,7 +15,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Configuration.EnvironmentVariables" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Configuration.EnvironmentVariables.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
   </ItemGroup>
   
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.csproj b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.csproj
index a40874d8ed4072..510044d8e6b327 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.csproj
@@ -1,12 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.FileExtensions.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileProviders.Physical\ref\Microsoft.Extensions.FileProviders.Physical.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Physical\ref\Microsoft.Extensions.FileProviders.Physical.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/Microsoft.Extensions.Configuration.FileExtensions.csproj b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/Microsoft.Extensions.Configuration.FileExtensions.csproj
index 9c7df603e5197d..4eb56f8e802f4b 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/Microsoft.Extensions.Configuration.FileExtensions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/Microsoft.Extensions.Configuration.FileExtensions.csproj
@@ -1,21 +1,16 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration" />
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.FileProviders.Abstractions" />
-    <Reference Include="Microsoft.Extensions.FileProviders.Physical" />
-    <Reference Include="Microsoft.Extensions.Primitives" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Physical\src\Microsoft.Extensions.FileProviders.Physical.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/tests/Microsoft.Extensions.Configuration.FileExtensions.Tests.csproj b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/tests/Microsoft.Extensions.Configuration.FileExtensions.Tests.csproj
index d3c63062e03880..89a8fb5ee48b43 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/tests/Microsoft.Extensions.Configuration.FileExtensions.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/tests/Microsoft.Extensions.Configuration.FileExtensions.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -12,6 +12,7 @@
 
   <ItemGroup>
     <PackageReference Include="Moq" Version="$(MoqVersion)" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.csproj b/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.csproj
index ea7d7410353542..84d96fe5db4a16 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.csproj
@@ -1,12 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.Ini.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.FileExtensions\ref\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.FileExtensions\ref\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Ini/src/Microsoft.Extensions.Configuration.Ini.csproj b/src/libraries/Microsoft.Extensions.Configuration.Ini/src/Microsoft.Extensions.Configuration.Ini.csproj
index 88f10cc47d332d..f30343e2fcb30d 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Ini/src/Microsoft.Extensions.Configuration.Ini.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Ini/src/Microsoft.Extensions.Configuration.Ini.csproj
@@ -1,20 +1,15 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration" />
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Configuration.FileExtensions" />
-    <Reference Include="Microsoft.Extensions.FileProviders.Abstractions" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.FileExtensions\src\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Ini/tests/Microsoft.Extensions.Configuration.Ini.Tests.csproj b/src/libraries/Microsoft.Extensions.Configuration.Ini/tests/Microsoft.Extensions.Configuration.Ini.Tests.csproj
index ea3ba9cfb77546..d395499e635505 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Ini/tests/Microsoft.Extensions.Configuration.Ini.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Ini/tests/Microsoft.Extensions.Configuration.Ini.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -15,7 +15,8 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Configuration.Ini" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Configuration.Ini.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Json/ref/Microsoft.Extensions.Configuration.Json.csproj b/src/libraries/Microsoft.Extensions.Configuration.Json/ref/Microsoft.Extensions.Configuration.Json.csproj
index ee7309646a160c..2ab4a8b6be9be1 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Json/ref/Microsoft.Extensions.Configuration.Json.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Json/ref/Microsoft.Extensions.Configuration.Json.csproj
@@ -1,14 +1,16 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.Json.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.FileExtensions\ref\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
-    <ProjectReference Include="..\..\System.Text.Json\ref\System.Text.Json.csproj" />
-    <Reference Include="System.Threading.Tasks.Extensions" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.FileExtensions\ref\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Json\ref\System.Text.Json.csproj" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Json/src/Microsoft.Extensions.Configuration.Json.csproj b/src/libraries/Microsoft.Extensions.Configuration.Json/src/Microsoft.Extensions.Configuration.Json.csproj
index d313804efd7d80..aa7b6ae1a86542 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Json/src/Microsoft.Extensions.Configuration.Json.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Json/src/Microsoft.Extensions.Configuration.Json.csproj
@@ -1,31 +1,22 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.1;netstandard2.0;net461</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration" />
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Configuration.FileExtensions" />
-    <Reference Include="Microsoft.Extensions.FileProviders.Abstractions" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Text.Json" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.FileExtensions\src\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Json\src\System.Text.Json.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Runtime" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Json/tests/Microsoft.Extensions.Configuration.Json.Tests.csproj b/src/libraries/Microsoft.Extensions.Configuration.Json/tests/Microsoft.Extensions.Configuration.Json.Tests.csproj
index 06c4ed8eefcdd3..a106c36d44094f 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Json/tests/Microsoft.Extensions.Configuration.Json.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Json/tests/Microsoft.Extensions.Configuration.Json.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -15,8 +15,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Configuration.Json" />
     <PackageReference Include="Newtonsoft.Json" Version="$(NewtonsoftJsonVersion)" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Configuration.Json.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj" />  
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/ref/Microsoft.Extensions.Configuration.UserSecrets.csproj b/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/ref/Microsoft.Extensions.Configuration.UserSecrets.csproj
index 97089510aa49ac..9d75126ff173f8 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/ref/Microsoft.Extensions.Configuration.UserSecrets.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/ref/Microsoft.Extensions.Configuration.UserSecrets.csproj
@@ -1,10 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.UserSecrets.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Json\ref\Microsoft.Extensions.Configuration.Json.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Json\ref\Microsoft.Extensions.Configuration.Json.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/src/Microsoft.Extensions.Configuration.UserSecrets.csproj b/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/src/Microsoft.Extensions.Configuration.UserSecrets.csproj
index 5df32c91033784..d4378be0324a29 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/src/Microsoft.Extensions.Configuration.UserSecrets.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/src/Microsoft.Extensions.Configuration.UserSecrets.csproj
@@ -1,21 +1,15 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Configuration.Json" />
-    <Reference Include="Microsoft.Extensions.FileProviders.Abstractions" />
-    <Reference Include="Microsoft.Extensions.FileProviders.Physical" />
-  </ItemGroup>
-  
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.IO.FileSystem" />
-    <Reference Include="System.Runtime" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Json\src\Microsoft.Extensions.Configuration.Json.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Physical\src\Microsoft.Extensions.FileProviders.Physical.csproj" />
   </ItemGroup>
 
   <ItemGroup>
@@ -23,11 +17,4 @@
     <Content Include="build\netstandard2.0\$(MSBuildProjectName).targets" PackagePath="%(Identity)" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration.Json" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-  </ItemGroup>
-
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/tests/Microsoft.Extensions.Configuration.UserSecrets.Tests.csproj b/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/tests/Microsoft.Extensions.Configuration.UserSecrets.Tests.csproj
index 6f5aa314eabcf6..5563693f653c0b 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/tests/Microsoft.Extensions.Configuration.UserSecrets.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.UserSecrets/tests/Microsoft.Extensions.Configuration.UserSecrets.Tests.csproj
@@ -1,13 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Configuration.UserSecrets" />
     <PackageReference Include="Newtonsoft.Json" Version="$(NewtonsoftJsonVersion)" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Configuration.UserSecrets.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Xml/ref/Microsoft.Extensions.Configuration.Xml.csproj b/src/libraries/Microsoft.Extensions.Configuration.Xml/ref/Microsoft.Extensions.Configuration.Xml.csproj
index 68a8306997a1c6..07a5625a3cedab 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Xml/ref/Microsoft.Extensions.Configuration.Xml.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Xml/ref/Microsoft.Extensions.Configuration.Xml.csproj
@@ -1,12 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.Xml.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.FileExtensions\ref\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.FileExtensions\ref\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Xml/src/Microsoft.Extensions.Configuration.Xml.csproj b/src/libraries/Microsoft.Extensions.Configuration.Xml/src/Microsoft.Extensions.Configuration.Xml.csproj
index 9260eb9ec9d09d..e1dad4a470de41 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Xml/src/Microsoft.Extensions.Configuration.Xml.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Xml/src/Microsoft.Extensions.Configuration.Xml.csproj
@@ -1,31 +1,19 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Xml.ReaderWriter" />
-  </ItemGroup>
-
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration" />
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Configuration.FileExtensions" />
-    <Reference Include="Microsoft.Extensions.FileProviders.Abstractions" />
-    <Reference Include="System.Security.Cryptography.Xml" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.FileExtensions\src\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Xml\src\System.Security.Cryptography.Xml.csproj" />
   </ItemGroup>
 
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.Xml" />
     <Reference Include="System.Security" />
   </ItemGroup>
 
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Xml/tests/Microsoft.Extensions.Configuration.Xml.Tests.csproj b/src/libraries/Microsoft.Extensions.Configuration.Xml/tests/Microsoft.Extensions.Configuration.Xml.Tests.csproj
index dfb45ab9f8cecc..40c5a18fe90db5 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Xml/tests/Microsoft.Extensions.Configuration.Xml.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Xml/tests/Microsoft.Extensions.Configuration.Xml.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -12,23 +12,15 @@
              Link="Microsoft.Extensions.Configuration\tests\Common\ConfigurationProviderExtensions.cs" />
     <Compile Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\tests\Common\TestStreamHelpers.cs"
              Link="Microsoft.Extensions.Configuration\tests\Common\TestStreamHelpers.cs" />
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\ReplaceCulture.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\ReplaceCulture.cs" />
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\xunit\FrameworkSkipConditionAttribute.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\xunit\FrameworkSkipConditionAttribute.cs" />
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\xunit\ITestCondition.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\xunit\ITestCondition.cs" />
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\xunit\RuntimeFrameworks.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\xunit\RuntimeFrameworks.cs" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetFrameworkCurrent)'">
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\TestPlatformHelper.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\TestPlatformHelper.cs" />
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj" />  
+    <ProjectReference Include="..\src\Microsoft.Extensions.Configuration.Xml.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
 
-  <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Configuration.Xml" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.Security" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Xml/tests/XmlConfigurationTest.cs b/src/libraries/Microsoft.Extensions.Configuration.Xml/tests/XmlConfigurationTest.cs
index cfff1fe2dec840..b9c59d93b4dc40 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Xml/tests/XmlConfigurationTest.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Xml/tests/XmlConfigurationTest.cs
@@ -5,8 +5,8 @@
 using System.IO;
 using System.Security.Cryptography;
 using System.Security.Cryptography.Xml;
+using System.Tests;
 using System.Xml;
-using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Configuration.Test;
 using Xunit;
 
@@ -318,7 +318,6 @@ public void SupportAndIgnoreProcessingInstructions()
         }
 
         [Fact]
-        [ReplaceCulture]
         public void ThrowExceptionWhenFindDTD()
         {
             var xml =
@@ -339,15 +338,19 @@ public void ThrowExceptionWhenFindDTD()
                         </Inventory>
                     </Data>
                 </settings>";
-            var xmlConfigSrc = new XmlConfigurationProvider(new XmlConfigurationSource());
-            var isMono = Type.GetType("Mono.Runtime") != null;
-            var expectedMsg = isMono ? "Document Type Declaration (DTD) is prohibited in this XML.  Line 1, position 10." : "For security reasons DTD is prohibited in this XML document. "
-                + "To enable DTD processing set the DtdProcessing property on XmlReaderSettings "
-                + "to Parse and pass the settings into XmlReader.Create method.";
 
-            var exception = Assert.Throws<System.Xml.XmlException>(() => xmlConfigSrc.Load(TestStreamHelpers.StringToStream(xml)));
+            using (new ThreadCultureChange("en-GB"))
+            {
+                var xmlConfigSrc = new XmlConfigurationProvider(new XmlConfigurationSource());
+                var isMono = Type.GetType("Mono.Runtime") != null;
+                var expectedMsg = isMono ? "Document Type Declaration (DTD) is prohibited in this XML.  Line 1, position 10." : "For security reasons DTD is prohibited in this XML document. "
+                    + "To enable DTD processing set the DtdProcessing property on XmlReaderSettings "
+                    + "to Parse and pass the settings into XmlReader.Create method.";
+
+                var exception = Assert.Throws<System.Xml.XmlException>(() => xmlConfigSrc.Load(TestStreamHelpers.StringToStream(xml)));
 
-            Assert.Equal(expectedMsg, exception.Message);
+                Assert.Equal(expectedMsg, exception.Message);
+            }
         }
 
         [Fact]
@@ -433,7 +436,6 @@ public void XmlConfiguration_Does_Not_Throw_On_Optional_Configuration()
 
         [Fact]
         [ActiveIssue("https://github.com/dotnet/runtime/issues/37669", TestPlatforms.Browser)]
-        [FrameworkSkipCondition(RuntimeFrameworks.Mono)]
         public void LoadKeyValuePairsFromValidEncryptedXml()
         {
             var xml = @"
diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
index 724bfef2ca5b4e..e1533c3eadf9ef 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
@@ -1,10 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj b/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
index 0c4d78a16ea3a7..a017ce7e5230b7 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
@@ -1,19 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Primitives" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration/tests/FunctionalTests/Microsoft.Extensions.Configuration.Functional.Tests.csproj b/src/libraries/Microsoft.Extensions.Configuration/tests/FunctionalTests/Microsoft.Extensions.Configuration.Functional.Tests.csproj
index c162152be6bdbd..c2e3a8eeef9e2b 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/tests/FunctionalTests/Microsoft.Extensions.Configuration.Functional.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration/tests/FunctionalTests/Microsoft.Extensions.Configuration.Functional.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -11,6 +11,15 @@
   </ItemGroup>
 
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.CommandLine\src\Microsoft.Extensions.Configuration.CommandLine.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.EnvironmentVariables\src\Microsoft.Extensions.Configuration.EnvironmentVariables.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Ini\src\Microsoft.Extensions.Configuration.Ini.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Json\src\Microsoft.Extensions.Configuration.Json.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.UserSecrets\src\Microsoft.Extensions.Configuration.UserSecrets.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Xml\src\Microsoft.Extensions.Configuration.Xml.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration/tests/Microsoft.Extensions.Configuration.Tests.csproj b/src/libraries/Microsoft.Extensions.Configuration/tests/Microsoft.Extensions.Configuration.Tests.csproj
index ddfc57ce028db5..a1bf18a9e98ba6 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/tests/Microsoft.Extensions.Configuration.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration/tests/Microsoft.Extensions.Configuration.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>
@@ -11,7 +11,9 @@
 
   <ItemGroup>
     <PackageReference Include="Moq" Version="$(MoqVersion)" />
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Configuration" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Configuration.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.cs b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.cs
index fa3699e2218fb1..dffd433b92de1e 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.cs
@@ -14,6 +14,7 @@ public static partial class ActivatorUtilities
         public static object GetServiceOrCreateInstance(System.IServiceProvider provider, System.Type type) { throw null; }
         public static T GetServiceOrCreateInstance<T>(System.IServiceProvider provider) { throw null; }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.All)]
     public partial class ActivatorUtilitiesConstructorAttribute : System.Attribute
     {
         public ActivatorUtilitiesConstructorAttribute() { }
@@ -69,9 +70,10 @@ public partial class ServiceDescriptor
     {
         public ServiceDescriptor(System.Type serviceType, System.Func<System.IServiceProvider, object> factory, Microsoft.Extensions.DependencyInjection.ServiceLifetime lifetime) { }
         public ServiceDescriptor(System.Type serviceType, object instance) { }
-        public ServiceDescriptor(System.Type serviceType, System.Type implementationType, Microsoft.Extensions.DependencyInjection.ServiceLifetime lifetime) { }
+        public ServiceDescriptor(System.Type serviceType, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] System.Type implementationType, Microsoft.Extensions.DependencyInjection.ServiceLifetime lifetime) { }
         public System.Func<System.IServiceProvider, object>? ImplementationFactory { get { throw null; } }
         public object? ImplementationInstance { get { throw null; } }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
         public System.Type? ImplementationType { get { throw null; } }
         public Microsoft.Extensions.DependencyInjection.ServiceLifetime Lifetime { get { throw null; } }
         public System.Type ServiceType { get { throw null; } }
@@ -109,8 +111,7 @@ public static partial class ServiceProviderServiceExtensions
         public static T GetRequiredService<T>(this System.IServiceProvider provider) where T : notnull { throw null; }
         public static System.Collections.Generic.IEnumerable<object?> GetServices(this System.IServiceProvider provider, System.Type serviceType) { throw null; }
         public static System.Collections.Generic.IEnumerable<T> GetServices<T>(this System.IServiceProvider provider) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T GetService<T>(this System.IServiceProvider provider) { throw null; }
+        public static T? GetService<T>(this System.IServiceProvider provider) { throw null; }
     }
 }
 namespace Microsoft.Extensions.DependencyInjection.Extensions
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.csproj b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.csproj
index 942dbe0ee15295..6b74303de9eec6 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.csproj
@@ -1,9 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.DependencyInjection.Abstractions.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/Extensions/ServiceCollectionDescriptorExtensions.cs b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/Extensions/ServiceCollectionDescriptorExtensions.cs
index ad5be9396bf955..b1d8704fe0cbad 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/Extensions/ServiceCollectionDescriptorExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/Extensions/ServiceCollectionDescriptorExtensions.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 namespace Microsoft.Extensions.DependencyInjection.Extensions
@@ -124,7 +125,7 @@ public static void TryAdd(
         /// <param name="service">The type of the service to register.</param>
         public static void TryAddTransient(
             this IServiceCollection collection,
-            Type service)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type service)
         {
             if (collection == null)
             {
@@ -151,7 +152,7 @@ public static void TryAddTransient(
         public static void TryAddTransient(
             this IServiceCollection collection,
             Type service,
-            Type implementationType)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType)
         {
             if (collection == null)
             {
@@ -210,7 +211,7 @@ public static void TryAddTransient(
         /// </summary>
         /// <typeparam name="TService">The type of the service to add.</typeparam>
         /// <param name="collection">The <see cref="IServiceCollection"/>.</param>
-        public static void TryAddTransient<TService>(this IServiceCollection collection)
+        public static void TryAddTransient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TService>(this IServiceCollection collection)
             where TService : class
         {
             if (collection == null)
@@ -229,7 +230,7 @@ public static void TryAddTransient<TService>(this IServiceCollection collection)
         /// <typeparam name="TService">The type of the service to add.</typeparam>
         /// <typeparam name="TImplementation">The type of the implementation to use.</typeparam>
         /// <param name="collection">The <see cref="IServiceCollection"/>.</param>
-        public static void TryAddTransient<TService, TImplementation>(this IServiceCollection collection)
+        public static void TryAddTransient<TService, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(this IServiceCollection collection)
             where TService : class
             where TImplementation : class, TService
         {
@@ -265,7 +266,7 @@ public static void TryAddTransient<TService>(
         /// <param name="service">The type of the service to register.</param>
         public static void TryAddScoped(
             this IServiceCollection collection,
-            Type service)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type service)
         {
             if (collection == null)
             {
@@ -292,7 +293,7 @@ public static void TryAddScoped(
         public static void TryAddScoped(
             this IServiceCollection collection,
             Type service,
-            Type implementationType)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType)
         {
             if (collection == null)
             {
@@ -351,7 +352,7 @@ public static void TryAddScoped(
         /// </summary>
         /// <typeparam name="TService">The type of the service to add.</typeparam>
         /// <param name="collection">The <see cref="IServiceCollection"/>.</param>
-        public static void TryAddScoped<TService>(this IServiceCollection collection)
+        public static void TryAddScoped<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TService>(this IServiceCollection collection)
             where TService : class
         {
             if (collection == null)
@@ -370,7 +371,7 @@ public static void TryAddScoped<TService>(this IServiceCollection collection)
         /// <typeparam name="TService">The type of the service to add.</typeparam>
         /// <typeparam name="TImplementation">The type of the implementation to use.</typeparam>
         /// <param name="collection">The <see cref="IServiceCollection"/>.</param>
-        public static void TryAddScoped<TService, TImplementation>(this IServiceCollection collection)
+        public static void TryAddScoped<TService, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(this IServiceCollection collection)
             where TService : class
             where TImplementation : class, TService
         {
@@ -406,7 +407,7 @@ public static void TryAddScoped<TService>(
         /// <param name="service">The type of the service to register.</param>
         public static void TryAddSingleton(
             this IServiceCollection collection,
-            Type service)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type service)
         {
             if (collection == null)
             {
@@ -433,7 +434,7 @@ public static void TryAddSingleton(
         public static void TryAddSingleton(
             this IServiceCollection collection,
             Type service,
-            Type implementationType)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType)
         {
             if (collection == null)
             {
@@ -492,7 +493,7 @@ public static void TryAddSingleton(
         /// </summary>
         /// <typeparam name="TService">The type of the service to add.</typeparam>
         /// <param name="collection">The <see cref="IServiceCollection"/>.</param>
-        public static void TryAddSingleton<TService>(this IServiceCollection collection)
+        public static void TryAddSingleton<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TService>(this IServiceCollection collection)
             where TService : class
         {
             if (collection == null)
@@ -511,7 +512,7 @@ public static void TryAddSingleton<TService>(this IServiceCollection collection)
         /// <typeparam name="TService">The type of the service to add.</typeparam>
         /// <typeparam name="TImplementation">The type of the implementation to use.</typeparam>
         /// <param name="collection">The <see cref="IServiceCollection"/>.</param>
-        public static void TryAddSingleton<TService, TImplementation>(this IServiceCollection collection)
+        public static void TryAddSingleton<TService, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(this IServiceCollection collection)
             where TService : class
             where TImplementation : class, TService
         {
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/Microsoft.Extensions.DependencyInjection.Abstractions.csproj b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/Microsoft.Extensions.DependencyInjection.Abstractions.csproj
index 0d3119d83d6b5e..d1955eaf4e8998 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/Microsoft.Extensions.DependencyInjection.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/Microsoft.Extensions.DependencyInjection.Abstractions.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <DefineConstants>$(DefineConstants);ActivatorUtilities_In_DependencyInjection</DefineConstants>
     <EnableDefaultItems>true</EnableDefaultItems>
     <Nullable>enable</Nullable>
@@ -17,12 +16,9 @@
              Link="Common\src\Extensions\ActivatorUtilities\ActivatorUtilitiesConstructorAttribute.cs" />
     <Compile Include="$(CommonPath)Extensions\ActivatorUtilities\ObjectFactory.cs"
              Link="Common\src\Extensions\ActivatorUtilities\ObjectFactory.cs" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
-    <Reference Include="System" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\UnconditionalSuppressMessageAttribute.cs" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceCollectionServiceExtensions.cs b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceCollectionServiceExtensions.cs
index 23cf01a1272d39..1de2b83d156f0c 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceCollectionServiceExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceCollectionServiceExtensions.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.Extensions.DependencyInjection
 {
@@ -23,7 +24,7 @@ public static class ServiceCollectionServiceExtensions
         public static IServiceCollection AddTransient(
             this IServiceCollection services,
             Type serviceType,
-            Type implementationType)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType)
         {
             if (services == null)
             {
@@ -86,7 +87,7 @@ public static IServiceCollection AddTransient(
         /// <param name="services">The <see cref="IServiceCollection"/> to add the service to.</param>
         /// <returns>A reference to this instance after the operation has completed.</returns>
         /// <seealso cref="ServiceLifetime.Transient"/>
-        public static IServiceCollection AddTransient<TService, TImplementation>(this IServiceCollection services)
+        public static IServiceCollection AddTransient<TService, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(this IServiceCollection services)
             where TService : class
             where TImplementation : class, TService
         {
@@ -108,7 +109,7 @@ public static IServiceCollection AddTransient<TService, TImplementation>(this IS
         /// <seealso cref="ServiceLifetime.Transient"/>
         public static IServiceCollection AddTransient(
             this IServiceCollection services,
-            Type serviceType)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type serviceType)
         {
             if (services == null)
             {
@@ -131,7 +132,7 @@ public static IServiceCollection AddTransient(
         /// <param name="services">The <see cref="IServiceCollection"/> to add the service to.</param>
         /// <returns>A reference to this instance after the operation has completed.</returns>
         /// <seealso cref="ServiceLifetime.Transient"/>
-        public static IServiceCollection AddTransient<TService>(this IServiceCollection services)
+        public static IServiceCollection AddTransient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TService>(this IServiceCollection services)
             where TService : class
         {
             if (services == null)
@@ -201,8 +202,6 @@ public static IServiceCollection AddTransient<TService, TImplementation>(
             return services.AddTransient(typeof(TService), implementationFactory);
         }
 
-
-
         /// <summary>
         /// Adds a scoped service of the type specified in <paramref name="serviceType"/> with an
         /// implementation of the type specified in <paramref name="implementationType"/> to the
@@ -216,7 +215,7 @@ public static IServiceCollection AddTransient<TService, TImplementation>(
         public static IServiceCollection AddScoped(
             this IServiceCollection services,
             Type serviceType,
-            Type implementationType)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType)
         {
             if (services == null)
             {
@@ -279,7 +278,7 @@ public static IServiceCollection AddScoped(
         /// <param name="services">The <see cref="IServiceCollection"/> to add the service to.</param>
         /// <returns>A reference to this instance after the operation has completed.</returns>
         /// <seealso cref="ServiceLifetime.Scoped"/>
-        public static IServiceCollection AddScoped<TService, TImplementation>(this IServiceCollection services)
+        public static IServiceCollection AddScoped<TService, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(this IServiceCollection services)
             where TService : class
             where TImplementation : class, TService
         {
@@ -301,7 +300,7 @@ public static IServiceCollection AddScoped<TService, TImplementation>(this IServ
         /// <seealso cref="ServiceLifetime.Scoped"/>
         public static IServiceCollection AddScoped(
             this IServiceCollection services,
-            Type serviceType)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type serviceType)
         {
             if (services == null)
             {
@@ -324,7 +323,7 @@ public static IServiceCollection AddScoped(
         /// <param name="services">The <see cref="IServiceCollection"/> to add the service to.</param>
         /// <returns>A reference to this instance after the operation has completed.</returns>
         /// <seealso cref="ServiceLifetime.Scoped"/>
-        public static IServiceCollection AddScoped<TService>(this IServiceCollection services)
+        public static IServiceCollection AddScoped<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TService>(this IServiceCollection services)
             where TService : class
         {
             if (services == null)
@@ -408,7 +407,7 @@ public static IServiceCollection AddScoped<TService, TImplementation>(
         public static IServiceCollection AddSingleton(
             this IServiceCollection services,
             Type serviceType,
-            Type implementationType)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType)
         {
             if (services == null)
             {
@@ -471,7 +470,7 @@ public static IServiceCollection AddSingleton(
         /// <param name="services">The <see cref="IServiceCollection"/> to add the service to.</param>
         /// <returns>A reference to this instance after the operation has completed.</returns>
         /// <seealso cref="ServiceLifetime.Singleton"/>
-        public static IServiceCollection AddSingleton<TService, TImplementation>(this IServiceCollection services)
+        public static IServiceCollection AddSingleton<TService, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(this IServiceCollection services)
             where TService : class
             where TImplementation : class, TService
         {
@@ -493,7 +492,7 @@ public static IServiceCollection AddSingleton<TService, TImplementation>(this IS
         /// <seealso cref="ServiceLifetime.Singleton"/>
         public static IServiceCollection AddSingleton(
             this IServiceCollection services,
-            Type serviceType)
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type serviceType)
         {
             if (services == null)
             {
@@ -516,7 +515,7 @@ public static IServiceCollection AddSingleton(
         /// <param name="services">The <see cref="IServiceCollection"/> to add the service to.</param>
         /// <returns>A reference to this instance after the operation has completed.</returns>
         /// <seealso cref="ServiceLifetime.Singleton"/>
-        public static IServiceCollection AddSingleton<TService>(this IServiceCollection services)
+        public static IServiceCollection AddSingleton<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TService>(this IServiceCollection services)
             where TService : class
         {
             if (services == null)
@@ -651,7 +650,7 @@ public static IServiceCollection AddSingleton<TService>(
         private static IServiceCollection Add(
             IServiceCollection collection,
             Type serviceType,
-            Type implementationType,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType,
             ServiceLifetime lifetime)
         {
             var descriptor = new ServiceDescriptor(serviceType, implementationType, lifetime);
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceDescriptor.cs b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceDescriptor.cs
index d5fed233c6b59c..57a6d8d33f7d7d 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceDescriptor.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceDescriptor.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.Extensions.DependencyInjection
 {
@@ -20,7 +21,7 @@ public class ServiceDescriptor
         /// <param name="lifetime">The <see cref="ServiceLifetime"/> of the service.</param>
         public ServiceDescriptor(
             Type serviceType,
-            Type implementationType,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType,
             ServiceLifetime lifetime)
             : this(serviceType, lifetime)
         {
@@ -96,6 +97,7 @@ private ServiceDescriptor(Type serviceType, ServiceLifetime lifetime)
 
         public Type ServiceType { get; }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)]
         public Type? ImplementationType { get; }
 
         public object? ImplementationInstance { get; }
@@ -151,7 +153,7 @@ internal Type GetImplementationType()
         /// <typeparam name="TService">The type of the service.</typeparam>
         /// <typeparam name="TImplementation">The type of the implementation.</typeparam>
         /// <returns>A new instance of <see cref="ServiceDescriptor"/>.</returns>
-        public static ServiceDescriptor Transient<TService, TImplementation>()
+        public static ServiceDescriptor Transient<TService, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>()
             where TService : class
             where TImplementation : class, TService
         {
@@ -166,7 +168,9 @@ public static ServiceDescriptor Transient<TService, TImplementation>()
         /// <param name="service">The type of the service.</param>
         /// <param name="implementationType">The type of the implementation.</param>
         /// <returns>A new instance of <see cref="ServiceDescriptor"/>.</returns>
-        public static ServiceDescriptor Transient(Type service, Type implementationType)
+        public static ServiceDescriptor Transient(
+            Type service,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType)
         {
             if (service == null)
             {
@@ -254,7 +258,7 @@ public static ServiceDescriptor Transient(Type service, Func<IServiceProvider, o
         /// <typeparam name="TService">The type of the service.</typeparam>
         /// <typeparam name="TImplementation">The type of the implementation.</typeparam>
         /// <returns>A new instance of <see cref="ServiceDescriptor"/>.</returns>
-        public static ServiceDescriptor Scoped<TService, TImplementation>()
+        public static ServiceDescriptor Scoped<TService, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>()
             where TService : class
             where TImplementation : class, TService
         {
@@ -269,7 +273,9 @@ public static ServiceDescriptor Scoped<TService, TImplementation>()
         /// <param name="service">The type of the service.</param>
         /// <param name="implementationType">The type of the implementation.</param>
         /// <returns>A new instance of <see cref="ServiceDescriptor"/>.</returns>
-        public static ServiceDescriptor Scoped(Type service, Type implementationType)
+        public static ServiceDescriptor Scoped(
+            Type service,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType)
         {
             return Describe(service, implementationType, ServiceLifetime.Scoped);
         }
@@ -347,7 +353,7 @@ public static ServiceDescriptor Scoped(Type service, Func<IServiceProvider, obje
         /// <typeparam name="TService">The type of the service.</typeparam>
         /// <typeparam name="TImplementation">The type of the implementation.</typeparam>
         /// <returns>A new instance of <see cref="ServiceDescriptor"/>.</returns>
-        public static ServiceDescriptor Singleton<TService, TImplementation>()
+        public static ServiceDescriptor Singleton<TService, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>()
             where TService : class
             where TImplementation : class, TService
         {
@@ -362,7 +368,9 @@ public static ServiceDescriptor Singleton<TService, TImplementation>()
         /// <param name="service">The type of the service.</param>
         /// <param name="implementationType">The type of the implementation.</param>
         /// <returns>A new instance of <see cref="ServiceDescriptor"/>.</returns>
-        public static ServiceDescriptor Singleton(Type service, Type implementationType)
+        public static ServiceDescriptor Singleton(
+            Type service,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType)
         {
             if (service == null)
             {
@@ -488,7 +496,7 @@ public static ServiceDescriptor Singleton(
             return new ServiceDescriptor(serviceType, implementationInstance);
         }
 
-        private static ServiceDescriptor Describe<TService, TImplementation>(ServiceLifetime lifetime)
+        private static ServiceDescriptor Describe<TService, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(ServiceLifetime lifetime)
             where TService : class
             where TImplementation : class, TService
         {
@@ -507,7 +515,10 @@ private static ServiceDescriptor Describe<TService, TImplementation>(ServiceLife
         /// <param name="implementationType">The type of the implementation.</param>
         /// <param name="lifetime">The lifetime of the service.</param>
         /// <returns>A new instance of <see cref="ServiceDescriptor"/>.</returns>
-        public static ServiceDescriptor Describe(Type serviceType, Type implementationType, ServiceLifetime lifetime)
+        public static ServiceDescriptor Describe(
+            Type serviceType,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType,
+            ServiceLifetime lifetime)
         {
             return new ServiceDescriptor(serviceType, implementationType, lifetime);
         }
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceProviderServiceExtensions.cs b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceProviderServiceExtensions.cs
index e35fc654614294..29fcd6cef52d41 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceProviderServiceExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceProviderServiceExtensions.cs
@@ -18,15 +18,14 @@ public static class ServiceProviderServiceExtensions
         /// <typeparam name="T">The type of service object to get.</typeparam>
         /// <param name="provider">The <see cref="IServiceProvider"/> to retrieve the service object from.</param>
         /// <returns>A service object of type <typeparamref name="T"/> or null if there is no such service.</returns>
-        [return: MaybeNull]
-        public static T GetService<T>(this IServiceProvider provider)
+        public static T? GetService<T>(this IServiceProvider provider)
         {
             if (provider == null)
             {
                 throw new ArgumentNullException(nameof(provider));
             }
 
-            return (T)provider.GetService(typeof(T));
+            return (T?)provider.GetService(typeof(T));
         }
 
         /// <summary>
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/ref/Microsoft.Extensions.DependencyInjection.csproj b/src/libraries/Microsoft.Extensions.DependencyInjection/ref/Microsoft.Extensions.DependencyInjection.csproj
index d4098d54f3b8d6..b1b514112a7c05 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/ref/Microsoft.Extensions.DependencyInjection.csproj
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/ref/Microsoft.Extensions.DependencyInjection.csproj
@@ -1,13 +1,15 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.DependencyInjection.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-    <Reference Include="System.Threading.Tasks.Extensions"  />
-    <Reference Include="Microsoft.Bcl.AsyncInterfaces"  />
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.1'">
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Bcl.AsyncInterfaces\ref\Microsoft.Bcl.AsyncInterfaces.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/src/Microsoft.Extensions.DependencyInjection.csproj b/src/libraries/Microsoft.Extensions.DependencyInjection/src/Microsoft.Extensions.DependencyInjection.csproj
index 50cdcabc140e56..d7df2f2725f918 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/src/Microsoft.Extensions.DependencyInjection.csproj
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/src/Microsoft.Extensions.DependencyInjection.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent);net461;netstandard2.0;netstandard2.1</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461;netstandard2.0;netstandard2.1</TargetFrameworks>
     <!-- Debug IL generation -->
     <ILEmitBackendSaveAssemblies>False</ILEmitBackendSaveAssemblies>
   </PropertyGroup>
@@ -14,36 +13,6 @@
     <DefineConstants Condition="$(TargetFramework.StartsWith('net4')) and '$(ILEmitBackendSaveAssemblies)' == 'True'">$(DefineConstants);SAVE_ASSEMBLIES</DefineConstants>  
   </PropertyGroup>
 
-  <ItemGroup>
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4')) Or '$(TargetFramework)' == 'netstandard2.0'">
-    <Reference Include="Microsoft.Bcl.AsyncInterfaces" />
-    <Reference Include="System.Threading.Tasks.Extensions" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Linq.Expressions" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-  </ItemGroup>
-
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Collections.Concurrent" />
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.Diagnostics.Tracing" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Linq.Expressions" />
-    <Reference Include="System.Reflection.Emit.ILGeneration" />
-    <Reference Include="System.Reflection.Emit.Lightweight" />
-    <Reference Include="System.Reflection.Primitives" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Threading" />
-  </ItemGroup>
-
   <ItemGroup>
     <Compile Include="**\*.cs" />
     <Compile Remove="ServiceLookup\ILEmit\**\*.cs" />
@@ -56,4 +25,34 @@
              Link="Common\src\Extensions\TypeNameHelper\TypeNameHelper.cs" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)'">
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\UnconditionalSuppressMessageAttribute.cs" />
+  </ItemGroup>
+  
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">	
+    <Reference Include="System.Collections" />	
+    <Reference Include="System.Collections.Concurrent" />	
+    <Reference Include="System.ComponentModel" />	
+    <Reference Include="System.Diagnostics.Tracing" />	
+    <Reference Include="System.Linq" />	
+    <Reference Include="System.Linq.Expressions" />	
+    <Reference Include="System.Reflection.Emit.ILGeneration" />	
+    <Reference Include="System.Reflection.Emit.Lightweight" />	
+    <Reference Include="System.Reflection.Primitives" />	
+    <Reference Include="System.Runtime" />	
+    <Reference Include="System.Threading" />	
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Bcl.AsyncInterfaces\src\Microsoft.Bcl.AsyncInterfaces.csproj" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/CallSiteFactory.cs b/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/CallSiteFactory.cs
index 2bf5ee16fc8e15..4aec44848ae0e1 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/CallSiteFactory.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/CallSiteFactory.cs
@@ -5,6 +5,7 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;
 using Microsoft.Extensions.Internal;
@@ -244,16 +245,16 @@ private ServiceCallSite TryCreateOpenGeneric(ServiceDescriptor descriptor, Type
             return null;
         }
 
-        private ServiceCallSite CreateConstructorCallSite(ResultCache lifetime, Type serviceType, Type implementationType,
+        private ServiceCallSite CreateConstructorCallSite(
+            ResultCache lifetime,
+            Type serviceType,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType,
             CallSiteChain callSiteChain)
         {
             try
             {
                 callSiteChain.Add(serviceType, implementationType);
-                ConstructorInfo[] constructors = implementationType.GetTypeInfo()
-                    .DeclaredConstructors
-                    .Where(constructor => constructor.IsPublic)
-                    .ToArray();
+                ConstructorInfo[] constructors = implementationType.GetConstructors();
 
                 ServiceCallSite[] parameterCallSites = null;
 
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.External.Tests/Microsoft.Extensions.DependencyInjection.ExternalContainers.Tests.csproj b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.External.Tests/Microsoft.Extensions.DependencyInjection.ExternalContainers.Tests.csproj
index bf641d02f32f89..9357badc0f94f6 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.External.Tests/Microsoft.Extensions.DependencyInjection.ExternalContainers.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.External.Tests/Microsoft.Extensions.DependencyInjection.ExternalContainers.Tests.csproj
@@ -1,23 +1,23 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
     <NoWarn>$(NoWarn);CS8002</NoWarn>
-    <SignAssembly Condition="$(TargetFramework.StartsWith('net4'))">false</SignAssembly>
+  </PropertyGroup>
+
+  <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
+  <PropertyGroup>
+    <SignAssembly Condition="'$(TargetFramework)' == 'net461'">false</SignAssembly>
   </PropertyGroup>
 
   <ItemGroup>
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\ExceptionAssertions.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\ExceptionAssertions.cs" />
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\CultureReplacer.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\CultureReplacer.cs" />
     <Compile Include="..\DI.Specification.Tests\**\*.cs" />
   </ItemGroup>
 
   <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.DependencyInjection" />
-    <ReferenceFromRuntime Include="Microsoft.Extensions.DependencyInjection.Abstractions" Aliases="DIAbstractions" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" SkipUseReferenceAssembly="true" />
     <PackageReference Include="Newtonsoft.Json" Version="$(NewtonsoftJsonVersion)" />
     <PackageReference Include="Autofac.Extensions.DependencyInjection" Version="4.3.1"/>
     <PackageReference Include="DryIoc.Microsoft.DependencyInjection"  Version="2.1.0"/>
@@ -29,4 +29,15 @@
     <PackageReference Include="Unity.Microsoft.DependencyInjection" Version="2.1.3" />
   </ItemGroup>
 
+  <!-- Include these transitive dependencies to overrule NuGet's ProjectReference over PackageReferene behavior: https://github.com/NuGet/Home/issues/9354. -->
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <PackageReference Include="Microsoft.Win32.Primitives" Version="$(MicrosoftWin32PrimitivesVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Runtime" Version="$(SystemRuntimeVersion)" />
+    <PackageReference Include="System.Runtime.Extensions" Version="$(SystemRuntimeExtensionsVersion)" />
+    <PackageReference Include="System.Net.Primitives" Version="$(SystemNetPrimitivesVersion)" />
+    <PackageReference Include="System.Collections" Version="$(SystemCollectionsVersion)" />
+    <PackageReference Include="System.Runtime.InteropServices" Version="$(SystemRuntimeInteropServicesVersion)" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/Microsoft.Extensions.DependencyInjection.Tests.csproj b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/Microsoft.Extensions.DependencyInjection.Tests.csproj
index 6a2b15545e1608..762664f48f7331 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/Microsoft.Extensions.DependencyInjection.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/Microsoft.Extensions.DependencyInjection.Tests.csproj
@@ -1,25 +1,18 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\ExceptionAssertions.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\ExceptionAssertions.cs" />
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\CultureReplacer.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\CultureReplacer.cs" />
     <Compile Include="..\DI.Specification.Tests\**\*.cs" />
   </ItemGroup>
 
-  <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.DependencyInjection" />
-    <ReferenceFromRuntime Include="Microsoft.Extensions.DependencyInjection.Abstractions" Aliases="DIAbstractions" />
-  </ItemGroup>
-
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="$(NewtonsoftJsonVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="..\..\src\Microsoft.Extensions.DependencyInjection.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceCollectionServiceExtensionsTest.cs b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceCollectionServiceExtensionsTest.cs
index 2ceeab1ac0b5db..3acb7de6679db0 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceCollectionServiceExtensionsTest.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceCollectionServiceExtensionsTest.cs
@@ -1,15 +1,11 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
-extern alias DIAbstractions;
 
 using System;
-using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.DependencyInjection.Specification.Fakes;
 using Xunit;
 
-using AbstractionsSR = DIAbstractions::System.SR;
-
 namespace Microsoft.Extensions.DependencyInjection
 {
     public class ServiceCollectionServiceExtensionsTest
@@ -346,11 +342,8 @@ public void TryAddEnumerable_ThrowsWhenAddingIndistinguishableImplementationType
             // Arrange
             var collection = new ServiceCollection();
 
-            // Act & Assert
-            ExceptionAssert.ThrowsArgument(
-                () => collection.TryAddEnumerable(descriptor),
-                "descriptor",
-                AbstractionsSR.Format(AbstractionsSR.TryAddIndistinguishableTypeToEnumerable, implementationType, serviceType));
+            AssertExtensions.ThrowsContains<ArgumentException>(() => collection.TryAddEnumerable(descriptor), 
+                string.Format(@"Implementation type cannot be '{0}' because it is indistinguishable from other services registered for '{1}'.", implementationType, serviceType));
         }
 
         [Fact]
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceProviderServiceExtensionsTest.cs b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceProviderServiceExtensionsTest.cs
index 015350ecad2f7c..9bed4bfe5ab80b 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceProviderServiceExtensionsTest.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceProviderServiceExtensionsTest.cs
@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using Microsoft.AspNetCore.Testing;
 using Xunit;
 
 namespace Microsoft.Extensions.DependencyInjection
@@ -44,7 +43,7 @@ public void GetRequiredService_Throws_WhenNoServiceRegistered()
             var serviceProvider = CreateTestServiceProvider(0);
 
             // Act + Assert
-            ExceptionAssert.Throws<InvalidOperationException>(() => serviceProvider.GetRequiredService<IFoo>(),
+            AssertExtensions.Throws<InvalidOperationException>(() => serviceProvider.GetRequiredService<IFoo>(),
                 $"No service for type '{typeof(IFoo)}' has been registered.");
         }
 
@@ -55,7 +54,7 @@ public void ISupportRequiredService_GetRequiredService_Throws_WhenNoServiceRegis
             var serviceProvider = new RequiredServiceSupportingProvider();
 
             // Act + Assert
-            ExceptionAssert.Throws<RankException>(() => serviceProvider.GetRequiredService<IFoo>());
+            AssertExtensions.Throws<RankException>(() => serviceProvider.GetRequiredService<IFoo>());
         }
 
         [Fact]
@@ -65,7 +64,7 @@ public void NonGeneric_GetRequiredService_Throws_WhenNoServiceRegistered()
             var serviceProvider = CreateTestServiceProvider(0);
 
             // Act + Assert
-            ExceptionAssert.Throws<InvalidOperationException>(() => serviceProvider.GetRequiredService(typeof(IFoo)),
+            AssertExtensions.Throws<InvalidOperationException>(() => serviceProvider.GetRequiredService(typeof(IFoo)),
                 $"No service for type '{typeof(IFoo)}' has been registered.");
         }
 
@@ -76,7 +75,7 @@ public void ISupportRequiredService_NonGeneric_GetRequiredService_Throws_WhenNoS
             var serviceProvider = new RequiredServiceSupportingProvider();
 
             // Act + Assert
-            ExceptionAssert.Throws<RankException>(() => serviceProvider.GetRequiredService(typeof(IFoo)));
+            AssertExtensions.Throws<RankException>(() => serviceProvider.GetRequiredService(typeof(IFoo)));
         }
 
         [Fact]
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceTableTest.cs b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceTableTest.cs
index 198308d4254df3..b2843e39983639 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceTableTest.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceTableTest.cs
@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using Microsoft.AspNetCore.Testing;
 using Xunit;
 
 namespace Microsoft.Extensions.DependencyInjection.ServiceLookup
@@ -23,10 +22,7 @@ public void Constructor_WithImplementationType_ThrowsIfServiceTypeIsOpenGenericA
             };
 
             // Act and Assert
-            ExceptionAssert.ThrowsArgument(
-                () => new CallSiteFactory(serviceDescriptors),
-                "descriptors",
-                $"Open generic service type '{typeof(IList<>)}' requires registering an open generic implementation type.");
+            AssertExtensions.Throws<ArgumentException>("descriptors", () => new CallSiteFactory(serviceDescriptors));
         }
 
         public static TheoryData Constructor_WithInstance_ThrowsIfServiceTypeIsOpenGenericData =>
@@ -48,10 +44,7 @@ public void Constructor_WithInstance_ThrowsIfServiceTypeIsOpenGeneric(object ins
             };
 
             // Act and Assert
-            var ex = ExceptionAssert.ThrowsArgument(
-                () => new CallSiteFactory(serviceDescriptors),
-                "descriptors",
-                $"Open generic service type '{typeof(IEnumerable<>)}' requires registering an open generic implementation type.");
+            AssertExtensions.Throws<ArgumentException>("descriptors", () => new CallSiteFactory(serviceDescriptors));
         }
 
         [Fact]
@@ -64,10 +57,7 @@ public void Constructor_WithFactory_ThrowsIfServiceTypeIsOpenGeneric()
             };
 
             // Act and Assert
-            var ex = ExceptionAssert.ThrowsArgument(
-                () => new CallSiteFactory(serviceDescriptors),
-                "descriptors",
-                $"Open generic service type '{typeof(Tuple<>)}' requires registering an open generic implementation type.");
+            AssertExtensions.Throws<ArgumentException>("descriptors", () => new CallSiteFactory(serviceDescriptors));
         }
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/TrimmingTests/ActivatorUtilitiesTests.cs b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/TrimmingTests/ActivatorUtilitiesTests.cs
new file mode 100644
index 00000000000000..2a3e22724e26f4
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/TrimmingTests/ActivatorUtilitiesTests.cs
@@ -0,0 +1,37 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using Microsoft.Extensions.DependencyInjection;
+
+class Program
+{
+    static int Main(string[] args)
+    {
+        ServiceProvider provider = new ServiceCollection().BuildServiceProvider();
+
+        ObjectFactory factory = ActivatorUtilities.CreateFactory(typeof(ServiceA), Array.Empty<Type>());
+        ServiceA serviceA = factory(provider, null) as ServiceA;
+        ServiceB serviceB = ActivatorUtilities.CreateInstance(provider, typeof(ServiceB)) as ServiceB;
+        ServiceC serviceC = ActivatorUtilities.CreateInstance<ServiceC>(provider);
+        ServiceD serviceD = ActivatorUtilities.GetServiceOrCreateInstance(provider, typeof(ServiceD)) as ServiceD;
+        ServiceE serviceE = ActivatorUtilities.GetServiceOrCreateInstance<ServiceE>(provider);
+
+        if (serviceA is null ||
+            serviceB is null ||
+            serviceC is null ||
+            serviceD is null ||
+            serviceE is null)
+        {
+            return -1;
+        }
+
+        return 100;
+    }
+
+    private class ServiceA { }
+    private class ServiceB { }
+    private class ServiceC { }
+    private class ServiceD { }
+    private class ServiceE { }
+}
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/TrimmingTests/Microsoft.Extensions.DependencyInjection.TrimmingTests.proj b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/TrimmingTests/Microsoft.Extensions.DependencyInjection.TrimmingTests.proj
new file mode 100644
index 00000000000000..e1f5ef6af8cd5b
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/TrimmingTests/Microsoft.Extensions.DependencyInjection.TrimmingTests.proj
@@ -0,0 +1,14 @@
+<Project DefaultTargets="Build">
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props))" />
+
+  <PropertyGroup>
+    <AdditionalProjectReferences>Microsoft.Extensions.DependencyInjection</AdditionalProjectReferences>
+  </PropertyGroup>
+  
+  <ItemGroup>
+    <TestConsoleAppSourceFiles Include="ActivatorUtilitiesTests.cs" />
+    <TestConsoleAppSourceFiles Include="ServiceCollectionExtensionsTests.cs" />
+  </ItemGroup>
+
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets))" />
+</Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/TrimmingTests/ServiceCollectionExtensionsTests.cs b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/TrimmingTests/ServiceCollectionExtensionsTests.cs
new file mode 100644
index 00000000000000..58a1c8b10ab40c
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/TrimmingTests/ServiceCollectionExtensionsTests.cs
@@ -0,0 +1,83 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Extensions.DependencyInjection;
+
+class Program
+{
+    static int Main(string[] args)
+    {
+        IServiceCollection descriptors = new ServiceCollection();
+        descriptors.AddTransient<ServiceA>();
+        descriptors.AddScoped(typeof(ServiceB));
+        descriptors.AddSingleton(typeof(IServiceC), typeof(ServiceC));
+
+        descriptors.AddTransient<IServiceD, ServiceD>();
+        descriptors.AddTransient<IServiceE, ServiceE>();
+        descriptors.AddTransient(typeof(IServiceF), typeof(ServiceF));
+
+        descriptors.AddTransient<IServiceG, ServiceG>();
+        descriptors.AddTransient(typeof(Logger<>));
+
+        descriptors.AddTransient<IServiceH, ServiceH1>();
+        descriptors.AddTransient<IServiceH, ServiceH2>();
+
+        ServiceProvider provider = descriptors.BuildServiceProvider();
+
+        if (provider.GetService<ServiceA>() is null ||
+            provider.GetService<ServiceB>() is null ||
+            provider.GetService<IServiceC>() is null ||
+            provider.GetService<IServiceF>()?.ServiceE?.ServiceD is null ||
+            provider.GetService<Logger<IServiceG>>() is null)
+        {
+            return -1;
+        }
+
+        int hServices = 0;
+        foreach (IServiceH h in provider.GetServices<IServiceH>())
+        {
+            hServices++;
+            if (h == null)
+            {
+                return -1;
+            }
+        }
+
+        if (hServices != 2)
+        {
+            return -1;
+        }
+
+        return 100;
+    }
+
+    private class ServiceA { }
+    private class ServiceB { }
+    private interface IServiceC { }
+    private class ServiceC : IServiceC { }
+
+    public interface IServiceD { }
+    public interface IServiceE { IServiceD ServiceD { get; } }
+    public interface IServiceF { IServiceE ServiceE { get; } }
+    public class ServiceD : IServiceD
+    {
+    }
+    public class ServiceE : IServiceE
+    {
+        public IServiceD ServiceD { get; }
+        public ServiceE(IServiceD d) { ServiceD = d; }
+    }
+    public class ServiceF : IServiceF
+    {
+        public IServiceE ServiceE { get; }
+        public ServiceF(IServiceE e) { ServiceE = e; }
+    }
+
+    public class Logger<T> { }
+    public interface IServiceG { }
+    public class ServiceG : IServiceG { }
+
+    public interface IServiceH { }
+    public class ServiceH1 : IServiceH { }
+    public class ServiceH2 : IServiceH { }
+}
diff --git a/src/libraries/Microsoft.Extensions.DependencyModel/ref/Microsoft.Extensions.DependencyModel.csproj b/src/libraries/Microsoft.Extensions.DependencyModel/ref/Microsoft.Extensions.DependencyModel.csproj
index 4133d3704eca6f..86069259a9bc94 100644
--- a/src/libraries/Microsoft.Extensions.DependencyModel/ref/Microsoft.Extensions.DependencyModel.csproj
+++ b/src/libraries/Microsoft.Extensions.DependencyModel/ref/Microsoft.Extensions.DependencyModel.csproj
@@ -1,12 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.DependencyModel.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyModel/src/Microsoft.Extensions.DependencyModel.csproj b/src/libraries/Microsoft.Extensions.DependencyModel/src/Microsoft.Extensions.DependencyModel.csproj
index b6794fc1c8e84b..39dbc199219746 100644
--- a/src/libraries/Microsoft.Extensions.DependencyModel/src/Microsoft.Extensions.DependencyModel.csproj
+++ b/src/libraries/Microsoft.Extensions.DependencyModel/src/Microsoft.Extensions.DependencyModel.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
   <PropertyGroup>
@@ -19,16 +18,15 @@
   </ItemGroup>
 
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
     <Reference Include="System.Runtime" />
     <PackageReference Include="System.Runtime.InteropServices.RuntimeInformation" Version="4.3.0" Condition="'$(TargetFramework)' == 'net461'" />
   </ItemGroup>
+
   <ItemGroup>
-    <Reference Include="System.Buffers" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Text.Json" />
-    <Reference Include="System.Text.Encodings.Web" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Json\src\System.Text.Json.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Encodings.Web\src\System.Text.Encodings.Web.csproj" />
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
+
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyModel/tests/DependencyContextLoaderTests.cs b/src/libraries/Microsoft.Extensions.DependencyModel/tests/DependencyContextLoaderTests.cs
index fe4dc14c93d410..8e8070e8a51357 100644
--- a/src/libraries/Microsoft.Extensions.DependencyModel/tests/DependencyContextLoaderTests.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyModel/tests/DependencyContextLoaderTests.cs
@@ -81,7 +81,7 @@ public void LoadCanLoadANonEntryAssembly()
             var loader = new DependencyContextLoader();
             var context = loader.Load(typeof(DependencyContextLoaderTests).Assembly);
 
-            context.RuntimeLibraries.Should().Contain(l => l.Name == "Microsoft.Extensions.DependencyModel");
+            context.RuntimeLibraries.Should().Contain(l => l.Name == "nonentrypointassembly");
         }
 
         [Fact]
diff --git a/src/libraries/Microsoft.Extensions.DependencyModel/tests/Microsoft.Extensions.DependencyModel.Tests.csproj b/src/libraries/Microsoft.Extensions.DependencyModel/tests/Microsoft.Extensions.DependencyModel.Tests.csproj
index fa4e2326a573fb..d9f4d1ebc92b19 100644
--- a/src/libraries/Microsoft.Extensions.DependencyModel/tests/Microsoft.Extensions.DependencyModel.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.DependencyModel/tests/Microsoft.Extensions.DependencyModel.Tests.csproj
@@ -1,21 +1,23 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
+    <DefaultItemExcludes>$(DefaultItemExcludes);nonentrypointassembly\*</DefaultItemExcludes>
     <!-- Needed for .NET Framework. -->
     <GenerateDependencyFile>true</GenerateDependencyFile>
   </PropertyGroup>
 
   <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.DependencyModel" />
-
-    <PackageReference Include="Microsoft.DotNet.InternalAbstractions" Version="1.0.0" />
     <PackageReference Include="FluentAssertions" Version="4.19.4" />
-    <PackageReference Include="Moq" Version="$(MoqVersion)" />
+    <PackageReference Include="Microsoft.DotNet.InternalAbstractions" Version="1.0.0" />
     <PackageReference Include="Microsoft.DotNet.ProjectModel" Version="1.0.0-rc3-003121" />
+    <PackageReference Include="Moq" Version="$(MoqVersion)" />
     <!-- Upgrade the transitive dependency's version to avoid PackageTargetFallback on .NETCoreApp. -->
     <PackageReference Include="Newtonsoft.Json" Version="$(NewtonsoftJsonVersion)" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.DependencyModel.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="nonentrypointassembly\nonentrypointassembly.csproj" />
+
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.DependencyModel/tests/nonentrypointassembly/NonEntryPointClass.cs b/src/libraries/Microsoft.Extensions.DependencyModel/tests/nonentrypointassembly/NonEntryPointClass.cs
new file mode 100644
index 00000000000000..283734eebf5dae
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.DependencyModel/tests/nonentrypointassembly/NonEntryPointClass.cs
@@ -0,0 +1,12 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+namespace nonentrypointassembly
+{
+    public class NonEntryPointClass
+    {
+    }
+}
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests.csproj b/src/libraries/Microsoft.Extensions.DependencyModel/tests/nonentrypointassembly/nonentrypointassembly.csproj
similarity index 61%
rename from src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests.csproj
rename to src/libraries/Microsoft.Extensions.DependencyModel/tests/nonentrypointassembly/nonentrypointassembly.csproj
index 80a382c4ba14e4..0f39283f6e18c1 100644
--- a/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.DependencyModel/tests/nonentrypointassembly/nonentrypointassembly.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
diff --git a/src/libraries/Microsoft.Extensions.FileProviders.Abstractions/ref/Microsoft.Extensions.FileProviders.Abstractions.csproj b/src/libraries/Microsoft.Extensions.FileProviders.Abstractions/ref/Microsoft.Extensions.FileProviders.Abstractions.csproj
index 778d01d8f903b5..32239798f1f1e2 100644
--- a/src/libraries/Microsoft.Extensions.FileProviders.Abstractions/ref/Microsoft.Extensions.FileProviders.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.FileProviders.Abstractions/ref/Microsoft.Extensions.FileProviders.Abstractions.csproj
@@ -1,11 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.FileProviders.Abstractions.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.FileProviders.Abstractions/src/Microsoft.Extensions.FileProviders.Abstractions.csproj b/src/libraries/Microsoft.Extensions.FileProviders.Abstractions/src/Microsoft.Extensions.FileProviders.Abstractions.csproj
index 8c16ef3ce824e5..b55c758da87b2f 100644
--- a/src/libraries/Microsoft.Extensions.FileProviders.Abstractions/src/Microsoft.Extensions.FileProviders.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.FileProviders.Abstractions/src/Microsoft.Extensions.FileProviders.Abstractions.csproj
@@ -2,8 +2,7 @@
 
   <PropertyGroup>
     <RootNamespace>Microsoft.Extensions.FileProviders</RootNamespace>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -13,13 +12,8 @@
   </ItemGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.FileSystemGlobbing" />
-    <Reference Include="Microsoft.Extensions.Primitives" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileSystemGlobbing\src\Microsoft.Extensions.FileSystemGlobbing.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.FileProviders.Composite/ref/Microsoft.Extensions.FileProviders.Composite.csproj b/src/libraries/Microsoft.Extensions.FileProviders.Composite/ref/Microsoft.Extensions.FileProviders.Composite.csproj
index 9c945ef56a7241..bb27ead3394177 100644
--- a/src/libraries/Microsoft.Extensions.FileProviders.Composite/ref/Microsoft.Extensions.FileProviders.Composite.csproj
+++ b/src/libraries/Microsoft.Extensions.FileProviders.Composite/ref/Microsoft.Extensions.FileProviders.Composite.csproj
@@ -1,13 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <RootNamespace>Microsoft.Extensions.FileProviders</RootNamespace>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.FileProviders.Composite.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.FileProviders.Composite/src/Microsoft.Extensions.FileProviders.Composite.csproj b/src/libraries/Microsoft.Extensions.FileProviders.Composite/src/Microsoft.Extensions.FileProviders.Composite.csproj
index 898fe2fbd58c3e..80db265cd682df 100644
--- a/src/libraries/Microsoft.Extensions.FileProviders.Composite/src/Microsoft.Extensions.FileProviders.Composite.csproj
+++ b/src/libraries/Microsoft.Extensions.FileProviders.Composite/src/Microsoft.Extensions.FileProviders.Composite.csproj
@@ -2,19 +2,13 @@
 
   <PropertyGroup>
     <RootNamespace>Microsoft.Extensions.FileProviders</RootNamespace>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.FileProviders.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Primitives" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.FileProviders.Composite/tests/Microsoft.Extensions.FileProviders.Composite.Tests.csproj b/src/libraries/Microsoft.Extensions.FileProviders.Composite/tests/Microsoft.Extensions.FileProviders.Composite.Tests.csproj
index 05183b81816c20..a9e97be7d3663a 100644
--- a/src/libraries/Microsoft.Extensions.FileProviders.Composite/tests/Microsoft.Extensions.FileProviders.Composite.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.FileProviders.Composite/tests/Microsoft.Extensions.FileProviders.Composite.Tests.csproj
@@ -2,12 +2,15 @@
 
   <PropertyGroup>
     <RootNamespace>Microsoft.Extensions.FileProviders.Composite</RootNamespace>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="Moq" Version="$(MoqVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Composite\src\Microsoft.Extensions.FileProviders.Composite.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.FileProviders.Physical/ref/Microsoft.Extensions.FileProviders.Physical.csproj b/src/libraries/Microsoft.Extensions.FileProviders.Physical/ref/Microsoft.Extensions.FileProviders.Physical.csproj
index c6b18a0ac30719..cb4948ba130acb 100644
--- a/src/libraries/Microsoft.Extensions.FileProviders.Physical/ref/Microsoft.Extensions.FileProviders.Physical.csproj
+++ b/src/libraries/Microsoft.Extensions.FileProviders.Physical/ref/Microsoft.Extensions.FileProviders.Physical.csproj
@@ -1,13 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.FileProviders.Physical.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileSystemGlobbing\ref\Microsoft.Extensions.FileSystemGlobbing.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileSystemGlobbing\ref\Microsoft.Extensions.FileSystemGlobbing.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.FileProviders.Physical/src/Microsoft.Extensions.FileProviders.Physical.csproj b/src/libraries/Microsoft.Extensions.FileProviders.Physical/src/Microsoft.Extensions.FileProviders.Physical.csproj
index ba390655fe156c..376c72160f6d4a 100644
--- a/src/libraries/Microsoft.Extensions.FileProviders.Physical/src/Microsoft.Extensions.FileProviders.Physical.csproj
+++ b/src/libraries/Microsoft.Extensions.FileProviders.Physical/src/Microsoft.Extensions.FileProviders.Physical.csproj
@@ -2,17 +2,11 @@
 
   <PropertyGroup>
     <RootNamespace>Microsoft.Extensions.FileProviders</RootNamespace>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
-  <PropertyGroup>
-    <!-- Ensure Assemblies are first resolved via targeting pack when targeting net461 -->
-    <AssemblySearchPaths Condition="'$(TargetFramework)' == 'net461'">$(NuGetPackageRoot)\microsoft.targetingpack.netframework.v4.6.1\1.0.1\lib\net461\;$(AssemblySearchPaths)</AssemblySearchPaths>
-  </PropertyGroup>
-
   <ItemGroup>
     <Compile Include="$(CommonPath)Extensions\EmptyDisposable.cs"
              Link="Common\src\Extensions\EmptyDisposable.cs" />
@@ -21,17 +15,14 @@
   </ItemGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.FileProviders.Abstractions" />
-    <Reference Include="Microsoft.Extensions.FileSystemGlobbing" />
-    <Reference Include="Microsoft.Extensions.Primitives"  />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileSystemGlobbing\src\Microsoft.Extensions.FileSystemGlobbing.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <!-- For IncrementalHash -->
-    <PackageReference Include="System.Security.Cryptography.Algorithms" Version="4.3.1" Condition="'$(TargetFramework)' == 'net461'" />
+  <!-- For IncrementalHash -->
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.Security.Cryptography.Algorithms" Version="$(SystemSecurityCryptographyAlgorithmsVersion)" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.FileProviders.Physical/tests/Microsoft.Extensions.FileProviders.Physical.Tests.csproj b/src/libraries/Microsoft.Extensions.FileProviders.Physical/tests/Microsoft.Extensions.FileProviders.Physical.Tests.csproj
index 11edb64eab6906..2f22d08400baa6 100644
--- a/src/libraries/Microsoft.Extensions.FileProviders.Physical/tests/Microsoft.Extensions.FileProviders.Physical.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.FileProviders.Physical/tests/Microsoft.Extensions.FileProviders.Physical.Tests.csproj
@@ -2,20 +2,18 @@
 
   <PropertyGroup>
     <RootNamespace>Microsoft.Extensions.FileProviders.Physical</RootNamespace>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\xunit\ITestCondition.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\xunit\ITestCondition.cs" />
-    <Compile Include="$(CommonTestPath)Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\TaskExtensions.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\TaskExtensions.cs" />
+    <Compile Include="$(CommonTestPath)System\Threading\Tasks\TaskTimeoutExtensions.cs"
+             Link="Common\System\Threading\Tasks\TaskTimeoutExtensions.cs" />
   </ItemGroup>
 
   <ItemGroup>
     <PackageReference Include="Moq" Version="$(MoqVersion)" />
-    <ReferenceFromRuntime Include="Microsoft.Extensions.FileProviders.Physical" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.FileProviders.Physical.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.FileProviders.Physical/tests/PhysicalFileProviderTests.cs b/src/libraries/Microsoft.Extensions.FileProviders.Physical/tests/PhysicalFileProviderTests.cs
index 819a30a392c8e0..0d9fb9577845c2 100644
--- a/src/libraries/Microsoft.Extensions.FileProviders.Physical/tests/PhysicalFileProviderTests.cs
+++ b/src/libraries/Microsoft.Extensions.FileProviders.Physical/tests/PhysicalFileProviderTests.cs
@@ -6,7 +6,6 @@
 using System.Linq;
 using System.Runtime.InteropServices;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.FileProviders.Internal;
 using Microsoft.Extensions.FileProviders.Physical;
 using Microsoft.Extensions.Primitives;
diff --git a/src/libraries/Microsoft.Extensions.FileSystemGlobbing/ref/Microsoft.Extensions.FileSystemGlobbing.csproj b/src/libraries/Microsoft.Extensions.FileSystemGlobbing/ref/Microsoft.Extensions.FileSystemGlobbing.csproj
index 3b99a60054e95d..b939996a35bcf8 100644
--- a/src/libraries/Microsoft.Extensions.FileSystemGlobbing/ref/Microsoft.Extensions.FileSystemGlobbing.csproj
+++ b/src/libraries/Microsoft.Extensions.FileSystemGlobbing/ref/Microsoft.Extensions.FileSystemGlobbing.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.FileSystemGlobbing.cs" />
diff --git a/src/libraries/Microsoft.Extensions.FileSystemGlobbing/src/Microsoft.Extensions.FileSystemGlobbing.csproj b/src/libraries/Microsoft.Extensions.FileSystemGlobbing/src/Microsoft.Extensions.FileSystemGlobbing.csproj
index ab4b23464b4d31..cf923440da6e9e 100644
--- a/src/libraries/Microsoft.Extensions.FileSystemGlobbing/src/Microsoft.Extensions.FileSystemGlobbing.csproj
+++ b/src/libraries/Microsoft.Extensions.FileSystemGlobbing/src/Microsoft.Extensions.FileSystemGlobbing.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -11,10 +10,4 @@
              Link="Common\src\Extensions\HashCodeCombiner\HashCodeCombiner.cs" />
   </ItemGroup>
 
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-  </ItemGroup>
-
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.FileSystemGlobbing/tests/Microsoft.Extensions.FileSystemGlobbing.Tests.csproj b/src/libraries/Microsoft.Extensions.FileSystemGlobbing/tests/Microsoft.Extensions.FileSystemGlobbing.Tests.csproj
index 80a382c4ba14e4..d871ed685eaa7d 100644
--- a/src/libraries/Microsoft.Extensions.FileSystemGlobbing/tests/Microsoft.Extensions.FileSystemGlobbing.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.FileSystemGlobbing/tests/Microsoft.Extensions.FileSystemGlobbing.Tests.csproj
@@ -1,8 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="..\src\Microsoft.Extensions.FileSystemGlobbing.csproj" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/BuildWebHostInvalidSignature/BuildWebHostInvalidSignature.csproj b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/BuildWebHostInvalidSignature/BuildWebHostInvalidSignature.csproj
index fcc7214c0b5f54..716b25a87281da 100644
--- a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/BuildWebHostInvalidSignature/BuildWebHostInvalidSignature.csproj
+++ b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/BuildWebHostInvalidSignature/BuildWebHostInvalidSignature.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
     <OutputType>Exe</OutputType>
   </PropertyGroup>
diff --git a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/BuildWebHostPatternTestSite/BuildWebHostPatternTestSite.csproj b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/BuildWebHostPatternTestSite/BuildWebHostPatternTestSite.csproj
index fcc7214c0b5f54..716b25a87281da 100644
--- a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/BuildWebHostPatternTestSite/BuildWebHostPatternTestSite.csproj
+++ b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/BuildWebHostPatternTestSite/BuildWebHostPatternTestSite.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
     <OutputType>Exe</OutputType>
   </PropertyGroup>
diff --git a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateHostBuilderInvalidSignature/CreateHostBuilderInvalidSignature.csproj b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateHostBuilderInvalidSignature/CreateHostBuilderInvalidSignature.csproj
index fcc7214c0b5f54..716b25a87281da 100644
--- a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateHostBuilderInvalidSignature/CreateHostBuilderInvalidSignature.csproj
+++ b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateHostBuilderInvalidSignature/CreateHostBuilderInvalidSignature.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
     <OutputType>Exe</OutputType>
   </PropertyGroup>
diff --git a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateHostBuilderPatternTestSite/CreateHostBuilderPatternTestSite.csproj b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateHostBuilderPatternTestSite/CreateHostBuilderPatternTestSite.csproj
index fcc7214c0b5f54..716b25a87281da 100644
--- a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateHostBuilderPatternTestSite/CreateHostBuilderPatternTestSite.csproj
+++ b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateHostBuilderPatternTestSite/CreateHostBuilderPatternTestSite.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
     <OutputType>Exe</OutputType>
   </PropertyGroup>
diff --git a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateWebHostBuilderInvalidSignature/CreateWebHostBuilderInvalidSignature.csproj b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateWebHostBuilderInvalidSignature/CreateWebHostBuilderInvalidSignature.csproj
index fcc7214c0b5f54..716b25a87281da 100644
--- a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateWebHostBuilderInvalidSignature/CreateWebHostBuilderInvalidSignature.csproj
+++ b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateWebHostBuilderInvalidSignature/CreateWebHostBuilderInvalidSignature.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
     <OutputType>Exe</OutputType>
   </PropertyGroup>
diff --git a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateWebHostBuilderPatternTestSite/CreateWebHostBuilderPatternTestSite.csproj b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateWebHostBuilderPatternTestSite/CreateWebHostBuilderPatternTestSite.csproj
index fcc7214c0b5f54..716b25a87281da 100644
--- a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateWebHostBuilderPatternTestSite/CreateWebHostBuilderPatternTestSite.csproj
+++ b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/CreateWebHostBuilderPatternTestSite/CreateWebHostBuilderPatternTestSite.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
     <OutputType>Exe</OutputType>
   </PropertyGroup>
diff --git a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/Microsoft.Extensions.HostFactoryResolver.Tests.csproj b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/Microsoft.Extensions.HostFactoryResolver.Tests.csproj
index ce58ed38bbc1ba..686592b47604cd 100644
--- a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/Microsoft.Extensions.HostFactoryResolver.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/Microsoft.Extensions.HostFactoryResolver.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/MockHostTypes/MockHostTypes.csproj b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/MockHostTypes/MockHostTypes.csproj
index 80a382c4ba14e4..88e03293e6ce4c 100644
--- a/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/MockHostTypes/MockHostTypes.csproj
+++ b/src/libraries/Microsoft.Extensions.HostFactoryResolver/tests/MockHostTypes/MockHostTypes.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
diff --git a/src/libraries/Microsoft.Extensions.Hosting.Abstractions/ref/Microsoft.Extensions.Hosting.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Hosting.Abstractions/ref/Microsoft.Extensions.Hosting.Abstractions.csproj
index cd10bfb2b3810d..e651cdd660c9d1 100644
--- a/src/libraries/Microsoft.Extensions.Hosting.Abstractions/ref/Microsoft.Extensions.Hosting.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Hosting.Abstractions/ref/Microsoft.Extensions.Hosting.Abstractions.csproj
@@ -1,16 +1,19 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net461</TargetFrameworks>
     <NoWarn>$(NoWarn);CS0618</NoWarn>
   </PropertyGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-    <Reference Include="Microsoft.Bcl.AsyncInterfaces"  />
-  </ItemGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Hosting.Abstractions.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        '$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Bcl.AsyncInterfaces\ref\Microsoft.Bcl.AsyncInterfaces.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/Microsoft.Extensions.Hosting.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/Microsoft.Extensions.Hosting.Abstractions.csproj
index 3de7d53d9c9e11..d0f3cc26369a92 100644
--- a/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/Microsoft.Extensions.Hosting.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/Microsoft.Extensions.Hosting.Abstractions.csproj
@@ -1,28 +1,27 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.1;netstandard2.0;net461</TargetFrameworks>
     <RootNamespace>Microsoft.Extensions.Hosting</RootNamespace>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.FileProviders.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.Runtime" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' Or $(TargetFramework.StartsWith('net4'))">
-    <Reference Include="Microsoft.Bcl.AsyncInterfaces" />
-    <Reference Include="System.Threading.Tasks.Extensions" />
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Bcl.AsyncInterfaces\src\Microsoft.Bcl.AsyncInterfaces.csproj" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/ServiceCollectionHostedServiceExtensions.cs b/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/ServiceCollectionHostedServiceExtensions.cs
index f1c39b35279411..5b8092edbd1f14 100644
--- a/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/ServiceCollectionHostedServiceExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/ServiceCollectionHostedServiceExtensions.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Hosting;
 
@@ -15,7 +16,7 @@ public static class ServiceCollectionHostedServiceExtensions
         /// <typeparam name="THostedService">An <see cref="IHostedService"/> to register.</typeparam>
         /// <param name="services">The <see cref="IServiceCollection"/> to register with.</param>
         /// <returns>The original <see cref="IServiceCollection"/>.</returns>
-        public static IServiceCollection AddHostedService<THostedService>(this IServiceCollection services)
+        public static IServiceCollection AddHostedService<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] THostedService>(this IServiceCollection services)
             where THostedService : class, IHostedService
         {
             services.TryAddEnumerable(ServiceDescriptor.Singleton<IHostedService, THostedService>());
diff --git a/src/libraries/Microsoft.Extensions.Hosting/ref/Microsoft.Extensions.Hosting.csproj b/src/libraries/Microsoft.Extensions.Hosting/ref/Microsoft.Extensions.Hosting.csproj
index 8f69092efa8b51..63f62d833dee4b 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/ref/Microsoft.Extensions.Hosting.csproj
+++ b/src/libraries/Microsoft.Extensions.Hosting/ref/Microsoft.Extensions.Hosting.csproj
@@ -1,18 +1,20 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <NoWarn>$(NoWarn);CS0618</NoWarn>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Hosting.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection\ref\Microsoft.Extensions.DependencyInjection.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Hosting.Abstractions\ref\Microsoft.Extensions.Hosting.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.FileProviders.Physical\ref\Microsoft.Extensions.FileProviders.Physical.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\ref\Microsoft.Extensions.DependencyInjection.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Hosting.Abstractions\ref\Microsoft.Extensions.Hosting.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\ref\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Physical\ref\Microsoft.Extensions.FileProviders.Physical.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Hosting/src/Internal/Host.cs b/src/libraries/Microsoft.Extensions.Hosting/src/Internal/Host.cs
index 026727948c0cff..1fcb8fd08fab88 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/src/Internal/Host.cs
+++ b/src/libraries/Microsoft.Extensions.Hosting/src/Internal/Host.cs
@@ -88,11 +88,12 @@ public async Task StopAsync(CancellationToken cancellationToken = default)
                     }
                 }
 
+                // Fire IHostApplicationLifetime.Stopped
+                _applicationLifetime.NotifyStopped();
+
                 token.ThrowIfCancellationRequested();
                 await _hostLifetime.StopAsync(token).ConfigureAwait(false);
 
-                // Fire IHostApplicationLifetime.Stopped
-                _applicationLifetime.NotifyStopped();
 
                 if (exceptions.Count > 0)
                 {
diff --git a/src/libraries/Microsoft.Extensions.Hosting/src/Microsoft.Extensions.Hosting.csproj b/src/libraries/Microsoft.Extensions.Hosting/src/Microsoft.Extensions.Hosting.csproj
index d384aae9cc35d7..13dd4bc402e522 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/src/Microsoft.Extensions.Hosting.csproj
+++ b/src/libraries/Microsoft.Extensions.Hosting/src/Microsoft.Extensions.Hosting.csproj
@@ -1,58 +1,41 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netstandard2.1;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
-  <PropertyGroup>
-    <!-- Ensure Assemblies are first resolved via targeting pack when targeting net461 -->
-    <AssemblySearchPaths Condition="'$(TargetFramework)' == 'net461'">$(NuGetPackageRoot)\microsoft.targetingpack.netframework.v4.6.1\1.0.1\lib\net461\;$(AssemblySearchPaths)</AssemblySearchPaths>
-  </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Hosting.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Configuration" />
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Configuration.Binder" />
-    <Reference Include="Microsoft.Extensions.Configuration.CommandLine" />
-    <Reference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" />
-    <Reference Include="Microsoft.Extensions.Configuration.FileExtensions" />
-    <Reference Include="Microsoft.Extensions.Configuration.Json" />
-    <Reference Include="Microsoft.Extensions.Configuration.UserSecrets" />
-    <Reference Include="Microsoft.Extensions.DependencyInjection" />
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.FileProviders.Physical" />
-    <Reference Include="Microsoft.Extensions.Logging" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging.Console" />
-    <Reference Include="Microsoft.Extensions.Logging.Configuration" />
-    <Reference Include="Microsoft.Extensions.Logging.Debug" />
-    <Reference Include="Microsoft.Extensions.Logging.EventSource" />
-    <Reference Include="Microsoft.Extensions.Logging.EventLog" />
-    <Reference Include="Microsoft.Extensions.Options" />
-    <Reference Include="Microsoft.Extensions.FileProviders.Abstractions" />
-  </ItemGroup>
-
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.Console" />
-    <Reference Include="System.IO.FileSystem" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.InteropServices.RuntimeInformation" />
-    <Reference Include="System.Threading" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.CommandLine\src\Microsoft.Extensions.Configuration.CommandLine.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.EnvironmentVariables\src\Microsoft.Extensions.Configuration.EnvironmentVariables.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.FileExtensions\src\Microsoft.Extensions.Configuration.FileExtensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Json\src\Microsoft.Extensions.Configuration.Json.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.UserSecrets\src\Microsoft.Extensions.Configuration.UserSecrets.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Abstractions\src\Microsoft.Extensions.FileProviders.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.FileProviders.Physical\src\Microsoft.Extensions.FileProviders.Physical.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Hosting.Abstractions\src\Microsoft.Extensions.Hosting.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\src\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Configuration\src\Microsoft.Extensions.Logging.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Console\src\Microsoft.Extensions.Logging.Console.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Debug\src\Microsoft.Extensions.Logging.Debug.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.EventLog\src\Microsoft.Extensions.Logging.EventLog.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.EventSource\src\Microsoft.Extensions.Logging.EventSource.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' OR $(TargetFramework.StartsWith('net4'))">
-    <Reference Include="Microsoft.Bcl.AsyncInterfaces" />
-    <Reference Include="System.Threading.Tasks.Extensions" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Bcl.AsyncInterfaces\src\Microsoft.Bcl.AsyncInterfaces.csproj" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
   </ItemGroup>
 
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
     <Reference Include="System.Runtime" />
     <PackageReference Include="System.Runtime.InteropServices.RuntimeInformation" Version="4.3.0" Condition="'$(TargetFramework)' == 'net461'" />
   </ItemGroup>
diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/SelfHostDeployer.cs b/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/SelfHostDeployer.cs
index b609679863a659..4dd4a4c065714a 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/SelfHostDeployer.cs
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/IntegrationTesting/src/Deployers/SelfHostDeployer.cs
@@ -8,7 +8,6 @@
 using System.Text.RegularExpressions;
 using System.Threading;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Logging;
 
 namespace Microsoft.Extensions.Hosting.IntegrationTesting
diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/Microsoft.Extensions.Hosting.Functional.Tests.csproj b/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/Microsoft.Extensions.Hosting.Functional.Tests.csproj
index fe116dda28fd30..ffd54fef7784b3 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/Microsoft.Extensions.Hosting.Functional.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/Microsoft.Extensions.Hosting.Functional.Tests.csproj
@@ -1,15 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
     <Content Include="testroot\**\*" />
     <Compile Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\tests\Common\TestLoggerBuilder.cs" />
-    <Compile Include="$(LibrariesProjectRoot)Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\TaskExtensions.cs"
-             Link="TestingUtils\Microsoft.AspNetCore.Testing\src\TaskExtensions.cs" />
     <Compile Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\tests\DI.Common\Common\src\LogLevelAttribute.cs"
              Link="tests\DI.Common\Common\src\LogLevelAttribute.cs" />
     <Compile Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\tests\DI.Common\Common\src\LogValuesAssert.cs"
@@ -20,8 +18,17 @@
              Link="tests\DI.Common\Common\src\XunitLoggerProvider.cs" />
   </ItemGroup>
 
+  <ItemGroup>
+    <Compile Include="$(CommonTestPath)System\Threading\Tasks\TaskTimeoutExtensions.cs"
+             Link="Common\System\Threading\Tasks\TaskTimeoutExtensions.cs" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\TestApp\Microsoft.Extensions.Hosting.TestApp.csproj" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.Net.Http" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/ShutdownTests.cs b/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/ShutdownTests.cs
index 50dfdad150e944..c9a4af01e5bc7f 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/ShutdownTests.cs
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/FunctionalTests/ShutdownTests.cs
@@ -6,7 +6,6 @@
 using System.IO;
 using System.Runtime.InteropServices;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Hosting.IntegrationTesting;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Test;
diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/TestApp/Microsoft.Extensions.Hosting.TestApp.csproj b/src/libraries/Microsoft.Extensions.Hosting/tests/TestApp/Microsoft.Extensions.Hosting.TestApp.csproj
index 28b6ff9259f9cc..399232d63b797b 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/tests/TestApp/Microsoft.Extensions.Hosting.TestApp.csproj
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/TestApp/Microsoft.Extensions.Hosting.TestApp.csproj
@@ -1,7 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
     <OutputType>Exe</OutputType>
   </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.CommandLine\src\Microsoft.Extensions.Configuration.CommandLine.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.EnvironmentVariables\src\Microsoft.Extensions.Configuration.EnvironmentVariables.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Hosting\src\Microsoft.Extensions.Hosting.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Console\src\Microsoft.Extensions.Logging.Console.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/TrimmingTests/AddHostedServiceTests.cs b/src/libraries/Microsoft.Extensions.Hosting/tests/TrimmingTests/AddHostedServiceTests.cs
new file mode 100644
index 00000000000000..585eea0a6a07f9
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/TrimmingTests/AddHostedServiceTests.cs
@@ -0,0 +1,34 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using System.Threading;
+using System.Threading.Tasks;
+
+class Program
+{
+    static int Main(string[] args)
+    {
+        IServiceCollection descriptors = new ServiceCollection();
+        descriptors.AddHostedService<MyHost>();
+
+        ServiceProvider provider = descriptors.BuildServiceProvider();
+
+        foreach (IHostedService h in provider.GetServices<IHostedService>())
+        {
+            if (!(h is MyHost))
+            {
+                return -1;
+            }
+        }
+
+        return 100;
+    }
+
+    private class MyHost : IHostedService
+    {
+        public Task StartAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+        public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+    }
+}
diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/TrimmingTests/Microsoft.Extensions.Hosting.TrimmingTests.proj b/src/libraries/Microsoft.Extensions.Hosting/tests/TrimmingTests/Microsoft.Extensions.Hosting.TrimmingTests.proj
new file mode 100644
index 00000000000000..61e8e1a7596653
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/TrimmingTests/Microsoft.Extensions.Hosting.TrimmingTests.proj
@@ -0,0 +1,13 @@
+<Project DefaultTargets="Build">
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props))" />
+
+  <PropertyGroup>
+    <AdditionalProjectReferences>Microsoft.Extensions.Hosting.Abstractions;Microsoft.Extensions.DependencyInjection</AdditionalProjectReferences>
+  </PropertyGroup>
+  
+  <ItemGroup>
+    <TestConsoleAppSourceFiles Include="AddHostedServiceTests.cs" />
+  </ItemGroup>
+
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets))" />
+</Project>
diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/HostBuilderTests.cs b/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/HostBuilderTests.cs
index 07e9c021a57aa1..5c1a3b67d1287c 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/HostBuilderTests.cs
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/HostBuilderTests.cs
@@ -143,7 +143,7 @@ public void DefaultIHostEnvironmentValues()
                     Assert.Equal(Environments.Production, env.EnvironmentName);
 #if NETCOREAPP
                     Assert.NotNull(env.ApplicationName);
-#elif NET472
+#elif NETFRAMEWORK
                     // Note GetEntryAssembly returns null for the net4x console test runner.
                     Assert.Null(env.ApplicationName);
 #else
@@ -159,7 +159,7 @@ public void DefaultIHostEnvironmentValues()
                 Assert.Equal(Environments.Production, env.EnvironmentName);
 #if NETCOREAPP
                 Assert.NotNull(env.ApplicationName);
-#elif NET472
+#elif NETFRAMEWORK
                 // Note GetEntryAssembly returns null for the net4x console test runner.
                 Assert.Null(env.ApplicationName);
 #else
diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/Internal/HostTests.cs b/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/Internal/HostTests.cs
index 092ac4fe8b2c77..d160f022c9aee4 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/Internal/HostTests.cs
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/Internal/HostTests.cs
@@ -839,6 +839,78 @@ public async Task HostedServiceCanInjectApplicationLifetime()
             }
         }
 
+        [Fact]
+        public async Task HostShutdownFiresApplicationLifetimeStoppedBeforeHostLifetimeStopped()
+        {
+            var stoppingCalls = 0;
+            var startedCalls = 0;
+            var disposingCalls = 0;
+
+            FakeHostLifetime fakeHostLifetime = null;
+            ApplicationLifetime applicationLifetime = null;
+
+            using (var host = CreateBuilder()
+                .ConfigureServices((services) =>
+                {
+                    Action started = () =>
+                    {
+                        startedCalls++;
+                    };
+
+                    Action stopping = () =>
+                    {
+                        stoppingCalls++;
+                    };
+
+                    Action disposing = () =>
+                    {
+                        disposingCalls++;
+                    };
+
+                    services.AddSingleton<IHostedService>(_ => new DelegateHostedService(started, stopping, disposing));
+
+                    services.AddSingleton<IHostLifetime>(_ =>
+                    {
+                        fakeHostLifetime = new FakeHostLifetime();
+
+                        fakeHostLifetime.StopAction = () =>
+                        {
+                            Assert.Equal(1, startedCalls);
+                            Assert.Equal(1, stoppingCalls);
+                            Assert.True(applicationLifetime.ApplicationStopped.IsCancellationRequested);
+                        };
+                        return fakeHostLifetime;
+                    }
+                    );
+
+                })
+                .Build())
+            {
+                var lifetime = host.Services.GetRequiredService<IHostApplicationLifetime>();
+                var hostLifetime = host.Services.GetRequiredService<IHostLifetime>();
+                applicationLifetime = lifetime as ApplicationLifetime;
+                Assert.NotNull(applicationLifetime);
+
+                Assert.Equal(0, startedCalls);
+
+                await host.StartAsync();
+                Assert.Equal(1, startedCalls);
+                Assert.Equal(0, stoppingCalls);
+                Assert.Equal(0, disposingCalls);
+
+                Assert.True(lifetime.ApplicationStarted.IsCancellationRequested);
+                Assert.False(lifetime.ApplicationStopping.IsCancellationRequested);
+                Assert.False(lifetime.ApplicationStopped.IsCancellationRequested);
+
+                await host.StopAsync();
+
+                Assert.True(lifetime.ApplicationStopping.IsCancellationRequested);
+                Assert.True(lifetime.ApplicationStopped.IsCancellationRequested);
+                Assert.Equal(1, startedCalls);
+                Assert.Equal(1, stoppingCalls);
+            }
+        }
+
         [Fact]
         public async Task HostStopApplicationFiresStopOnHostedService()
         {
@@ -1215,6 +1287,8 @@ public void Dispose()
             }
         }
 
+
+
         private class DelegateHostedService : IHostedService, IDisposable
         {
             private readonly Action _started;
diff --git a/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/Microsoft.Extensions.Hosting.Unit.Tests.csproj b/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/Microsoft.Extensions.Hosting.Unit.Tests.csproj
index af2ed3b68a5c23..b5365cdda84475 100644
--- a/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/Microsoft.Extensions.Hosting.Unit.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/Microsoft.Extensions.Hosting.Unit.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -12,6 +12,8 @@
 
   <ItemGroup>
     <PackageReference Include="Moq" Version="$(MoqVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Json\src\Microsoft.Extensions.Configuration.Json.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Hosting\src\Microsoft.Extensions.Hosting.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Http/Microsoft.Extensions.Http.sln b/src/libraries/Microsoft.Extensions.Http/Microsoft.Extensions.Http.sln
index 15ace04ecb75d5..ab21d6dff380b8 100644
--- a/src/libraries/Microsoft.Extensions.Http/Microsoft.Extensions.Http.sln
+++ b/src/libraries/Microsoft.Extensions.Http/Microsoft.Extensions.Http.sln
@@ -13,10 +13,10 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Http",
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Http", "src\Microsoft.Extensions.Http.csproj", "{A50C941B-09D7-4AB4-85AF-D02E6F96885A}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Http.Tests", "tests\Microsoft.Extensions.Http.Tests.csproj", "{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7}"
-EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestUtilities", "..\Common\tests\TestUtilities\TestUtilities.csproj", "{92E18BB1-B630-4B03-9B05-47F31D1BF94A}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Http.Tests", "tests\Microsoft.Extensions.Http.Tests\Microsoft.Extensions.Http.Tests.csproj", "{7DADD323-891C-4EA7-8906-6BC4009FA083}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -31,14 +31,14 @@ Global
 		{A50C941B-09D7-4AB4-85AF-D02E6F96885A}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{A50C941B-09D7-4AB4-85AF-D02E6F96885A}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{A50C941B-09D7-4AB4-85AF-D02E6F96885A}.Release|Any CPU.Build.0 = Release|Any CPU
-		{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7}.Release|Any CPU.Build.0 = Release|Any CPU
 		{92E18BB1-B630-4B03-9B05-47F31D1BF94A}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{92E18BB1-B630-4B03-9B05-47F31D1BF94A}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{92E18BB1-B630-4B03-9B05-47F31D1BF94A}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{92E18BB1-B630-4B03-9B05-47F31D1BF94A}.Release|Any CPU.Build.0 = Release|Any CPU
+		{7DADD323-891C-4EA7-8906-6BC4009FA083}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{7DADD323-891C-4EA7-8906-6BC4009FA083}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{7DADD323-891C-4EA7-8906-6BC4009FA083}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{7DADD323-891C-4EA7-8906-6BC4009FA083}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -46,8 +46,8 @@ Global
 	GlobalSection(NestedProjects) = preSolution
 		{183E40F1-33A4-461D-AADF-4CF59FB93CCA} = {B51DC955-13A6-41ED-A6C7-DDAB98911513}
 		{A50C941B-09D7-4AB4-85AF-D02E6F96885A} = {0517D0EB-1ED7-420A-A7D7-9A167C102ED2}
-		{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7} = {9DE482AA-076A-4EB1-821F-EE2A4A230B4A}
 		{92E18BB1-B630-4B03-9B05-47F31D1BF94A} = {9DE482AA-076A-4EB1-821F-EE2A4A230B4A}
+		{7DADD323-891C-4EA7-8906-6BC4009FA083} = {9DE482AA-076A-4EB1-821F-EE2A4A230B4A}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {F300086C-E02A-417C-8659-59AA5139E68A}
diff --git a/src/libraries/Microsoft.Extensions.Http/ref/Microsoft.Extensions.Http.csproj b/src/libraries/Microsoft.Extensions.Http/ref/Microsoft.Extensions.Http.csproj
index c798ddd1c3094f..d0551567b5ec3e 100644
--- a/src/libraries/Microsoft.Extensions.Http/ref/Microsoft.Extensions.Http.csproj
+++ b/src/libraries/Microsoft.Extensions.Http/ref/Microsoft.Extensions.Http.csproj
@@ -1,12 +1,17 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
-<ItemGroup>
+  <ItemGroup>
     <Compile Include="Microsoft.Extensions.Http.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.Net.Http" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Http/src/DefaultTypedHttpClientFactory.cs b/src/libraries/Microsoft.Extensions.Http/src/DefaultTypedHttpClientFactory.cs
index b5d75b0d9ca472..1b0f442d6091bc 100644
--- a/src/libraries/Microsoft.Extensions.Http/src/DefaultTypedHttpClientFactory.cs
+++ b/src/libraries/Microsoft.Extensions.Http/src/DefaultTypedHttpClientFactory.cs
@@ -2,13 +2,15 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Net.Http;
 using System.Threading;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.Extensions.Http
 {
-    internal class DefaultTypedHttpClientFactory<TClient> : ITypedHttpClientFactory<TClient>
+    internal class DefaultTypedHttpClientFactory<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient> :
+        ITypedHttpClientFactory<TClient>
     {
         private readonly Cache _cache;
         private readonly IServiceProvider _services;
diff --git a/src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientBuilderExtensions.cs b/src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientBuilderExtensions.cs
index f1509da93d16c6..8d6ffb703f154a 100644
--- a/src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientBuilderExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientBuilderExtensions.cs
@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Net.Http;
 using System.Threading;
@@ -316,7 +317,8 @@ public static IHttpClientBuilder ConfigureHttpMessageHandlerBuilder(this IHttpCl
         /// scope bound to the message handler, which is managed independently.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddTypedClient<TClient>(this IHttpClientBuilder builder)
+        public static IHttpClientBuilder AddTypedClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IHttpClientBuilder builder)
             where TClient : class
         {
             if (builder == null)
@@ -327,7 +329,8 @@ public static IHttpClientBuilder AddTypedClient<TClient>(this IHttpClientBuilder
             return AddTypedClientCore<TClient>(builder, validateSingleType: false);
         }
 
-        internal static IHttpClientBuilder AddTypedClientCore<TClient>(this IHttpClientBuilder builder, bool validateSingleType)
+        internal static IHttpClientBuilder AddTypedClientCore<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IHttpClientBuilder builder, bool validateSingleType)
             where TClient : class
         {
             ReserveClient(builder, typeof(TClient), builder.Name, validateSingleType);
@@ -375,7 +378,8 @@ internal static IHttpClientBuilder AddTypedClientCore<TClient>(this IHttpClientB
         /// scope bound to the message handler, which is managed independently.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddTypedClient<TClient, TImplementation>(this IHttpClientBuilder builder)
+        public static IHttpClientBuilder AddTypedClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IHttpClientBuilder builder)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -387,7 +391,8 @@ public static IHttpClientBuilder AddTypedClient<TClient, TImplementation>(this I
             return AddTypedClientCore<TClient, TImplementation>(builder, validateSingleType: false);
         }
 
-        internal static IHttpClientBuilder AddTypedClientCore<TClient, TImplementation>(this IHttpClientBuilder builder, bool validateSingleType)
+        internal static IHttpClientBuilder AddTypedClientCore<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IHttpClientBuilder builder, bool validateSingleType)
             where TClient : class
             where TImplementation : class, TClient
         {
diff --git a/src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientFactoryServiceCollectionExtensions.cs b/src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientFactoryServiceCollectionExtensions.cs
index d0f90cf3e1ca56..b0a34b788e4305 100644
--- a/src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientFactoryServiceCollectionExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientFactoryServiceCollectionExtensions.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Net.Http;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Http;
@@ -198,7 +199,8 @@ public static IHttpClientBuilder AddHttpClient(this IServiceCollection services,
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services)
             where TClient : class
         {
             if (services == null)
@@ -240,7 +242,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -282,7 +285,8 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services, string name)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services, string name)
             where TClient : class
         {
             if (services == null)
@@ -332,7 +336,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services, string name)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services, string name)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -376,7 +381,8 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services, Action<HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services, Action<HttpClient> configureClient)
             where TClient : class
         {
             if (services == null)
@@ -421,7 +427,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services, Action<IServiceProvider, HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services, Action<IServiceProvider, HttpClient> configureClient)
             where TClient : class
         {
             if (services == null)
@@ -470,7 +477,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services, Action<HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services, Action<HttpClient> configureClient)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -520,7 +528,8 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services, Action<IServiceProvider, HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services, Action<IServiceProvider, HttpClient> configureClient)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -569,7 +578,8 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services, string name, Action<HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services, string name, Action<HttpClient> configureClient)
             where TClient : class
         {
             if (services == null)
@@ -621,7 +631,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services, string name, Action<IServiceProvider, HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services, string name, Action<IServiceProvider, HttpClient> configureClient)
             where TClient : class
         {
             if (services == null)
@@ -677,7 +688,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services, string name, Action<HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services, string name, Action<HttpClient> configureClient)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -734,7 +746,8 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services, string name, Action<IServiceProvider, HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services, string name, Action<IServiceProvider, HttpClient> configureClient)
             where TClient : class
             where TImplementation : class, TClient
         {
diff --git a/src/libraries/Microsoft.Extensions.Http/src/ITypedHttpClientFactory.cs b/src/libraries/Microsoft.Extensions.Http/src/ITypedHttpClientFactory.cs
index 67ac64c230125f..979f99a43a658e 100644
--- a/src/libraries/Microsoft.Extensions.Http/src/ITypedHttpClientFactory.cs
+++ b/src/libraries/Microsoft.Extensions.Http/src/ITypedHttpClientFactory.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Net.Http;
 using Microsoft.Extensions.DependencyInjection;
 
@@ -96,7 +97,7 @@ namespace Microsoft.Extensions.Http
     /// }
     /// </code>
     /// </example>
-    public interface ITypedHttpClientFactory<TClient>
+    public interface ITypedHttpClientFactory<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>
     {
         /// <summary>
         /// Creates a typed client given an associated <see cref="HttpClient"/>.
diff --git a/src/libraries/Microsoft.Extensions.Http/src/Microsoft.Extensions.Http.csproj b/src/libraries/Microsoft.Extensions.Http/src/Microsoft.Extensions.Http.csproj
index 47eeebc131c9fd..6de909a45f7eaf 100644
--- a/src/libraries/Microsoft.Extensions.Http/src/Microsoft.Extensions.Http.csproj
+++ b/src/libraries/Microsoft.Extensions.Http/src/Microsoft.Extensions.Http.csproj
@@ -1,14 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
-  <PropertyGroup>
-    <!-- Ensure Assemblies are first resolved via targeting pack when targeting net461 -->
-    <AssemblySearchPaths Condition="'$(TargetFramework)' == 'net461'">$(NuGetPackageRoot)\microsoft.targetingpack.netframework.v4.6.1\1.0.1\lib\net461\;$(AssemblySearchPaths)</AssemblySearchPaths>
-  </PropertyGroup>
 
   <ItemGroup>
     <Compile Include="$(CommonPath)Extensions\NonCapturingTimer\NonCapturingTimer.cs"
@@ -17,20 +12,19 @@
              Link="Common\src\Extensions\TypeNameHelper\TypeNameHelper.cs" />
     <Compile Include="$(CommonPath)Extensions\ValueStopwatch\ValueStopwatch.cs"
              Link="Common\src\Extensions\ValueStopwatch\ValueStopwatch.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
   </ItemGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Options" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\src\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj" />
   </ItemGroup>
 
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
     <Reference Include="System.Net.Http" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/DefaultHttpClientFactoryTest.cs b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DefaultHttpClientFactoryTest.cs
similarity index 99%
rename from src/libraries/Microsoft.Extensions.Http/tests/DefaultHttpClientFactoryTest.cs
rename to src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DefaultHttpClientFactoryTest.cs
index a4cc8dee05ccfc..72d89b17f8ab56 100644
--- a/src/libraries/Microsoft.Extensions.Http/tests/DefaultHttpClientFactoryTest.cs
+++ b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DefaultHttpClientFactoryTest.cs
@@ -341,7 +341,7 @@ public async Task Factory_CreateClient_WithExpiry_HandlerCanBeReusedBeforeExpiry
             Assert.NotSame(activeEntry1.Handler, activeEntry2.Handler);
         }
 
-        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported), nameof(PlatformDetection.IsPreciseGcSupported))]
         public async Task Factory_CleanupCycle_DisposesEligibleHandler()
         {
             // Arrange
@@ -411,8 +411,7 @@ private async Task<ExpiredHandlerTrackingEntry> SimulateClientUse_Factory_Cleanu
             return cleanupEntry;
         }
 
-        [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/34023", TestRuntimes.Mono)]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsPreciseGcSupported))]
         public async Task Factory_CleanupCycle_DisposesLiveHandler()
         {
             // Arrange
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/DefaultHttpMessageHandlerBuilderTest.cs b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DefaultHttpMessageHandlerBuilderTest.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Http/tests/DefaultHttpMessageHandlerBuilderTest.cs
rename to src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DefaultHttpMessageHandlerBuilderTest.cs
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/DependencyInjection/HttpClientFactoryServiceCollectionExtensionsTest.cs b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DependencyInjection/HttpClientFactoryServiceCollectionExtensionsTest.cs
similarity index 94%
rename from src/libraries/Microsoft.Extensions.Http/tests/DependencyInjection/HttpClientFactoryServiceCollectionExtensionsTest.cs
rename to src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DependencyInjection/HttpClientFactoryServiceCollectionExtensionsTest.cs
index 6e526dbdad572b..fec6276e6ce26d 100644
--- a/src/libraries/Microsoft.Extensions.Http/tests/DependencyInjection/HttpClientFactoryServiceCollectionExtensionsTest.cs
+++ b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DependencyInjection/HttpClientFactoryServiceCollectionExtensionsTest.cs
@@ -948,6 +948,7 @@ public async Task AddHttpClient_MessageHandler_SingletonDependency()
             var request = new HttpRequestMessage(HttpMethod.Get, "http://example.com/");
             var response = await client.HttpClient.SendAsync(request);
 
+#if NETFRAMEWORK
             Assert.Same(
                 services.GetRequiredService<SingletonService>(),
                 request.Properties[nameof(SingletonService)]);
@@ -955,6 +956,18 @@ public async Task AddHttpClient_MessageHandler_SingletonDependency()
             Assert.Same(
                 client.Service,
                 request.Properties[nameof(SingletonService)]);
+#else
+#nullable enable
+            request.Options.TryGetValue(new HttpRequestOptionsKey<SingletonService>(nameof(SingletonService)), out SingletonService? optService);
+#nullable disable
+            Assert.Same(
+                services.GetRequiredService<SingletonService>(),
+                optService);
+
+            Assert.Same(
+                client.Service,
+                optService);
+#endif
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
@@ -979,6 +992,7 @@ public async Task AddHttpClient_MessageHandler_Scope_SingletonDependency()
                 var request = new HttpRequestMessage(HttpMethod.Get, "http://example.com/");
                 var response = await client.HttpClient.SendAsync(request);
 
+#if NETFRAMEWORK
                 Assert.Same(
                     services.GetRequiredService<SingletonService>(),
                     request.Properties[nameof(SingletonService)]);
@@ -990,6 +1004,23 @@ public async Task AddHttpClient_MessageHandler_Scope_SingletonDependency()
                 Assert.Same(
                     client.Service,
                     request.Properties[nameof(SingletonService)]);
+#else
+#nullable enable
+                request.Options.TryGetValue(new HttpRequestOptionsKey<SingletonService>(nameof(SingletonService)), out SingletonService? optService);
+#nullable disable
+
+                Assert.Same(
+                    services.GetRequiredService<SingletonService>(),
+                    optService);
+
+                Assert.Same(
+                    scope.ServiceProvider.GetRequiredService<SingletonService>(),
+                    optService);
+
+                Assert.Same(
+                    client.Service,
+                    optService);
+#endif
             }
         }
 
@@ -1035,6 +1066,7 @@ public async Task AddHttpClient_MessageHandler_Scope_ScopedDependency()
                 var request = new HttpRequestMessage(HttpMethod.Get, "http://example.com/");
                 var response = await client.HttpClient.SendAsync(request);
 
+#if NETFRAMEWORK
                 Assert.NotSame(
                     scope.ServiceProvider.GetRequiredService<ScopedService>(),
                     request.Properties[nameof(ScopedService)]);
@@ -1046,6 +1078,22 @@ public async Task AddHttpClient_MessageHandler_Scope_ScopedDependency()
                 Assert.NotSame(
                     client.Service,
                     request.Properties[nameof(ScopedService)]);
+#else
+#nullable enable
+                request.Options.TryGetValue(new HttpRequestOptionsKey<ScopedService>(nameof(ScopedService)), out ScopedService? optService);
+#nullable disable
+                Assert.NotSame(
+                    scope.ServiceProvider.GetRequiredService<ScopedService>(),
+                    optService);
+
+                Assert.Same(
+                    scope.ServiceProvider.GetRequiredService<ScopedService>(),
+                    client.Service);
+
+                Assert.NotSame(
+                    client.Service,
+                    optService);
+#endif
             }
         }
 
@@ -1069,6 +1117,7 @@ public async Task AddHttpClient_MessageHandler_TransientDependency()
             var request = new HttpRequestMessage(HttpMethod.Get, "http://example.com/");
             var response = await client.HttpClient.SendAsync(request);
 
+#if NETFRAMEWORK
             Assert.NotSame(
                 services.GetRequiredService<TransientService>(),
                 request.Properties[nameof(TransientService)]);
@@ -1076,6 +1125,18 @@ public async Task AddHttpClient_MessageHandler_TransientDependency()
             Assert.NotSame(
                 client.Service,
                 request.Properties[nameof(TransientService)]);
+#else
+#nullable enable
+            request.Options.TryGetValue(new HttpRequestOptionsKey<TransientService>(nameof(TransientService)), out TransientService? optService);
+#nullable disable
+            Assert.NotSame(
+                services.GetRequiredService<TransientService>(),
+                optService);
+
+            Assert.NotSame(
+                client.Service,
+                optService);
+#endif
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
@@ -1100,6 +1161,7 @@ public async Task AddHttpClient_MessageHandler_Scope_TransientDependency()
                 var request = new HttpRequestMessage(HttpMethod.Get, "http://example.com/");
                 var response = await client.HttpClient.SendAsync(request);
 
+#if NETFRAMEWORK
                 Assert.NotSame(
                     services.GetRequiredService<TransientService>(),
                     request.Properties[nameof(TransientService)]);
@@ -1107,6 +1169,18 @@ public async Task AddHttpClient_MessageHandler_Scope_TransientDependency()
                 Assert.NotSame(
                     client.Service,
                     request.Properties[nameof(TransientService)]);
+#else
+#nullable enable
+            request.Options.TryGetValue(new HttpRequestOptionsKey<TransientService>(nameof(TransientService)), out TransientService? optService);
+#nullable disable
+                Assert.NotSame(
+                    services.GetRequiredService<TransientService>(),
+                    optService);
+
+                Assert.NotSame(
+                    client.Service,
+                    optService);
+#endif
             }
         }
 
@@ -1304,7 +1378,11 @@ public HandlerWithSingletonService(SingletonService service)
 
             protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
             {
+#if NETFRAMEWORK
                 request.Properties[nameof(SingletonService)] = Service;
+#else
+                request.Options.Set(new HttpRequestOptionsKey<SingletonService>(nameof(SingletonService)), Service);
+#endif
                 return Task.FromResult(new HttpResponseMessage());
             }
         }
@@ -1320,7 +1398,11 @@ public HandlerWithScopedService(ScopedService service)
 
             protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
             {
+#if NETFRAMEWORK
                 request.Properties[nameof(ScopedService)] = Service;
+#else                
+                request.Options.Set(new HttpRequestOptionsKey<ScopedService>(nameof(ScopedService)), Service);
+#endif
                 return Task.FromResult(new HttpResponseMessage());
             }
         }
@@ -1336,7 +1418,11 @@ public HandlerWithTransientService(TransientService service)
 
             protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
             {
+#if NETFRAMEWORK
                 request.Properties[nameof(TransientService)] = Service;
+#else
+                request.Options.Set(new HttpRequestOptionsKey<TransientService>(nameof(TransientService)), Service);
+#endif
                 return Task.FromResult(new HttpResponseMessage());
             }
         }
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/DependencyInjection/OtherTestOptions.cs b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DependencyInjection/OtherTestOptions.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Http/tests/DependencyInjection/OtherTestOptions.cs
rename to src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DependencyInjection/OtherTestOptions.cs
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/HttpMessageHandlerBuilderTest.cs b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/HttpMessageHandlerBuilderTest.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Http/tests/HttpMessageHandlerBuilderTest.cs
rename to src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/HttpMessageHandlerBuilderTest.cs
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/ITestTypedClient.cs b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/ITestTypedClient.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Http/tests/ITestTypedClient.cs
rename to src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/ITestTypedClient.cs
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/Logging/HttpHeadersLogValueTest.cs b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/Logging/HttpHeadersLogValueTest.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Http/tests/Logging/HttpHeadersLogValueTest.cs
rename to src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/Logging/HttpHeadersLogValueTest.cs
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/Logging/RedactedLogValueIntegrationTest.cs b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/Logging/RedactedLogValueIntegrationTest.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Http/tests/Logging/RedactedLogValueIntegrationTest.cs
rename to src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/Logging/RedactedLogValueIntegrationTest.cs
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests.csproj b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/Microsoft.Extensions.Http.Tests.csproj
similarity index 73%
rename from src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests.csproj
rename to src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/Microsoft.Extensions.Http.Tests.csproj
index 81926a709d7b33..76700604db8551 100644
--- a/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/Microsoft.Extensions.Http.Tests.csproj
@@ -1,7 +1,7 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -24,7 +24,12 @@
 
   <ItemGroup>
     <PackageReference Include="Moq" Version="$(MoqVersion)" />
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Http" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Http\src\Microsoft.Extensions.Http.csproj" SkipUseReferenceAssembly="true" />
+  	<ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.Net.Http" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/TestTypedClient.cs b/src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/TestTypedClient.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Http/tests/TestTypedClient.cs
rename to src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/TestTypedClient.cs
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/TrimmingTests/AddTypedClientTests.cs b/src/libraries/Microsoft.Extensions.Http/tests/TrimmingTests/AddTypedClientTests.cs
new file mode 100644
index 00000000000000..17bcf13fc5a674
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Http/tests/TrimmingTests/AddTypedClientTests.cs
@@ -0,0 +1,58 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Extensions.DependencyInjection;
+using System.Net.Http;
+
+class Program
+{
+    static int Main(string[] args)
+    {
+        IServiceCollection descriptors = new ServiceCollection();
+        descriptors.AddHttpClient("test1")
+            .AddTypedClient<TypedClientA>()
+            .AddTypedClient<ITypedClientB, TypedClientB>();
+
+        descriptors.AddHttpClient<TypedClientC>("test2");
+        descriptors.AddHttpClient<ITypedClientD, TypedClientD>("test3");
+
+        ServiceProvider provider = descriptors.BuildServiceProvider();
+
+        TypedClientA clientA = provider.GetRequiredService<TypedClientA>();
+        ITypedClientB clientB = provider.GetRequiredService<ITypedClientB>();
+        TypedClientC clientC = provider.GetRequiredService<TypedClientC>();
+        ITypedClientD clientD = provider.GetRequiredService<ITypedClientD>();
+
+        if (clientA == null ||
+            !(clientB is TypedClientB) ||
+            clientC == null ||
+            !(clientD is TypedClientD))
+        {
+            return -1;
+        }
+
+        return 100;
+    }
+
+    class TypedClientA
+    {
+        public TypedClientA(HttpClient httpClient) { }
+    }
+
+    interface ITypedClientB { }
+    class TypedClientB : ITypedClientB
+    {
+        public TypedClientB(HttpClient httpClient) { }
+    }
+
+    class TypedClientC
+    {
+        public TypedClientC(HttpClient httpClient) { }
+    }
+
+    interface ITypedClientD { }
+    class TypedClientD : ITypedClientD
+    {
+        public TypedClientD(HttpClient httpClient) { }
+    }
+}
diff --git a/src/libraries/Microsoft.Extensions.Http/tests/TrimmingTests/Microsoft.Extensions.Http.TrimmingTests.proj b/src/libraries/Microsoft.Extensions.Http/tests/TrimmingTests/Microsoft.Extensions.Http.TrimmingTests.proj
new file mode 100644
index 00000000000000..4d71019770909d
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Http/tests/TrimmingTests/Microsoft.Extensions.Http.TrimmingTests.proj
@@ -0,0 +1,13 @@
+<Project DefaultTargets="Build">
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props))" />
+
+  <PropertyGroup>
+    <AdditionalProjectReferences>Microsoft.Extensions.Http</AdditionalProjectReferences>
+  </PropertyGroup>
+  
+  <ItemGroup>
+    <TestConsoleAppSourceFiles Include="AddTypedClientTests.cs" />
+  </ItemGroup>
+
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets))" />
+</Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.Abstractions/ref/Microsoft.Extensions.Logging.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Logging.Abstractions/ref/Microsoft.Extensions.Logging.Abstractions.csproj
index 805321e4b7090d..905c8b20bbecc3 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Abstractions/ref/Microsoft.Extensions.Logging.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.Abstractions/ref/Microsoft.Extensions.Logging.Abstractions.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Logging.Abstractions.cs" />
diff --git a/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/Microsoft.Extensions.Logging.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/Microsoft.Extensions.Logging.Abstractions.csproj
index 1462166794f388..26c5d1f3329de2 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/Microsoft.Extensions.Logging.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/Microsoft.Extensions.Logging.Abstractions.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -15,9 +14,4 @@
              Link="Common\src\Extensions\Logging\NullScope.cs" />
   </ItemGroup>
 
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
-  </ItemGroup>
-
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.Configuration/ref/Microsoft.Extensions.Logging.Configuration.csproj b/src/libraries/Microsoft.Extensions.Logging.Configuration/ref/Microsoft.Extensions.Logging.Configuration.csproj
index d5e676b199f9c4..880386c22985d2 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Configuration/ref/Microsoft.Extensions.Logging.Configuration.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.Configuration/ref/Microsoft.Extensions.Logging.Configuration.csproj
@@ -1,12 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Logging.Configuration.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Options.ConfigurationExtensions\ref\Microsoft.Extensions.Options.ConfigurationExtensions.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options.ConfigurationExtensions\ref\Microsoft.Extensions.Options.ConfigurationExtensions.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.Configuration/src/Microsoft.Extensions.Logging.Configuration.csproj b/src/libraries/Microsoft.Extensions.Logging.Configuration/src/Microsoft.Extensions.Logging.Configuration.csproj
index 31d6673acd765f..d12a37aa417549 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Configuration/src/Microsoft.Extensions.Logging.Configuration.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.Configuration/src/Microsoft.Extensions.Logging.Configuration.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -11,24 +10,15 @@
              Link="Common\Extensions\ProviderAliasUtilities\ProviderAliasUtilities.cs" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.Runtime" />
-  </ItemGroup>
-
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration" />
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Configuration.Binder" />
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Options" />
-    <Reference Include="Microsoft.Extensions.Options.ConfigurationExtensions" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\src\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options.ConfigurationExtensions\src\Microsoft.Extensions.Options.ConfigurationExtensions.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/Microsoft.Extensions.Logging.Console.sln b/src/libraries/Microsoft.Extensions.Logging.Console/Microsoft.Extensions.Logging.Console.sln
index a7cab36d8df353..24a098f8e6b3c7 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/Microsoft.Extensions.Logging.Console.sln
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/Microsoft.Extensions.Logging.Console.sln
@@ -13,7 +13,7 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Loggin
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{56A299FB-3733-4AF5-AE10-66AB73D6FC13}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Logging.Console.Tests", "tests\Microsoft.Extensions.Logging.Console.Tests.csproj", "{9B344154-013F-4D6B-99A5-77DFA1CB8CC0}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Logging.Console.Tests", "tests\Microsoft.Extensions.Logging.Console.Tests\Microsoft.Extensions.Logging.Console.Tests.csproj", "{A2CFB82A-F553-44CD-8765-97409380EED9}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -29,10 +29,10 @@ Global
 		{CDEDF61A-4D74-4EAA-B31E-AF5CAAA7B974}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{CDEDF61A-4D74-4EAA-B31E-AF5CAAA7B974}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{CDEDF61A-4D74-4EAA-B31E-AF5CAAA7B974}.Release|Any CPU.Build.0 = Release|Any CPU
-		{9B344154-013F-4D6B-99A5-77DFA1CB8CC0}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{9B344154-013F-4D6B-99A5-77DFA1CB8CC0}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{9B344154-013F-4D6B-99A5-77DFA1CB8CC0}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{9B344154-013F-4D6B-99A5-77DFA1CB8CC0}.Release|Any CPU.Build.0 = Release|Any CPU
+		{A2CFB82A-F553-44CD-8765-97409380EED9}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A2CFB82A-F553-44CD-8765-97409380EED9}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A2CFB82A-F553-44CD-8765-97409380EED9}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A2CFB82A-F553-44CD-8765-97409380EED9}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -40,7 +40,7 @@ Global
 	GlobalSection(NestedProjects) = preSolution
 		{6D191D5A-572C-4BFA-B73B-C24AF80E8016} = {A12B6049-11A7-4E2B-857B-620B917B4A46}
 		{CDEDF61A-4D74-4EAA-B31E-AF5CAAA7B974} = {A1F1D16A-5787-45E5-AF85-617702C216C6}
-		{9B344154-013F-4D6B-99A5-77DFA1CB8CC0} = {56A299FB-3733-4AF5-AE10-66AB73D6FC13}
+		{A2CFB82A-F553-44CD-8765-97409380EED9} = {56A299FB-3733-4AF5-AE10-66AB73D6FC13}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {E75E4D9D-8919-409F-8FF1-67DD9C346EA7}
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/ref/Microsoft.Extensions.Logging.Console.cs b/src/libraries/Microsoft.Extensions.Logging.Console/ref/Microsoft.Extensions.Logging.Console.cs
index 13f7dfa6c3bdbc..0ffa7866b5791a 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/ref/Microsoft.Extensions.Logging.Console.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/ref/Microsoft.Extensions.Logging.Console.cs
@@ -12,8 +12,11 @@ public static partial class ConsoleLoggerExtensions
         public static Microsoft.Extensions.Logging.ILoggingBuilder AddConsole(this Microsoft.Extensions.Logging.ILoggingBuilder builder, System.Action<Microsoft.Extensions.Logging.Console.ConsoleLoggerOptions> configure) { throw null; }
         public static Microsoft.Extensions.Logging.ILoggingBuilder AddConsoleFormatter<TFormatter, TOptions>(this Microsoft.Extensions.Logging.ILoggingBuilder builder) where TFormatter : Microsoft.Extensions.Logging.Console.ConsoleFormatter where TOptions : Microsoft.Extensions.Logging.Console.ConsoleFormatterOptions { throw null; }
         public static Microsoft.Extensions.Logging.ILoggingBuilder AddConsoleFormatter<TFormatter, TOptions>(this Microsoft.Extensions.Logging.ILoggingBuilder builder, System.Action<TOptions> configure) where TFormatter : Microsoft.Extensions.Logging.Console.ConsoleFormatter where TOptions : Microsoft.Extensions.Logging.Console.ConsoleFormatterOptions { throw null; }
+        public static Microsoft.Extensions.Logging.ILoggingBuilder AddJsonConsole(this Microsoft.Extensions.Logging.ILoggingBuilder builder) { throw null; }
         public static Microsoft.Extensions.Logging.ILoggingBuilder AddJsonConsole(this Microsoft.Extensions.Logging.ILoggingBuilder builder, System.Action<Microsoft.Extensions.Logging.Console.JsonConsoleFormatterOptions> configure) { throw null; }
+        public static Microsoft.Extensions.Logging.ILoggingBuilder AddSimpleConsole(this Microsoft.Extensions.Logging.ILoggingBuilder builder) { throw null; }
         public static Microsoft.Extensions.Logging.ILoggingBuilder AddSimpleConsole(this Microsoft.Extensions.Logging.ILoggingBuilder builder, System.Action<Microsoft.Extensions.Logging.Console.SimpleConsoleFormatterOptions> configure) { throw null; }
+        public static Microsoft.Extensions.Logging.ILoggingBuilder AddSystemdConsole(this Microsoft.Extensions.Logging.ILoggingBuilder builder) { throw null; }
         public static Microsoft.Extensions.Logging.ILoggingBuilder AddSystemdConsole(this Microsoft.Extensions.Logging.ILoggingBuilder builder, System.Action<Microsoft.Extensions.Logging.Console.ConsoleFormatterOptions> configure) { throw null; }
     }
 }
@@ -47,7 +50,7 @@ public enum ConsoleLoggerFormat
     public partial class ConsoleLoggerOptions
     {
         public ConsoleLoggerOptions() { }
-        [System.ObsoleteAttribute("ConsoleLoggerOptions.DisableColors has been deprecated. Please use SimpleConsoleFormatterOptions.DisableColors instead.", false)]
+        [System.ObsoleteAttribute("ConsoleLoggerOptions.DisableColors has been deprecated. Please use SimpleConsoleFormatterOptions.ColorBehavior instead.", false)]
         public bool DisableColors { get { throw null; } set { } }
         [System.ObsoleteAttribute("ConsoleLoggerOptions.Format has been deprecated. Please use ConsoleLoggerOptions.FormatterName instead.", false)]
         public Microsoft.Extensions.Logging.Console.ConsoleLoggerFormat Format { get { throw null; } set { } }
@@ -74,10 +77,16 @@ public partial class JsonConsoleFormatterOptions : Microsoft.Extensions.Logging.
         public JsonConsoleFormatterOptions() { }
         public System.Text.Json.JsonWriterOptions JsonWriterOptions { get { throw null; } set { } }
     }
+    public enum LoggerColorBehavior
+    {
+        Default = 0,
+        Enabled = 1,
+        Disabled = 2,
+    }
     public partial class SimpleConsoleFormatterOptions : Microsoft.Extensions.Logging.Console.ConsoleFormatterOptions
     {
         public SimpleConsoleFormatterOptions() { }
-        public bool DisableColors { get { throw null; } set { } }
+        public Microsoft.Extensions.Logging.Console.LoggerColorBehavior ColorBehavior { get { throw null; } set { } }
         public bool SingleLine { get { throw null; } set { } }
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/ref/Microsoft.Extensions.Logging.Console.csproj b/src/libraries/Microsoft.Extensions.Logging.Console/ref/Microsoft.Extensions.Logging.Console.csproj
index 0756d569fde5c5..f56ed2cc9d0b1e 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/ref/Microsoft.Extensions.Logging.Console.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/ref/Microsoft.Extensions.Logging.Console.csproj
@@ -1,13 +1,16 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Logging.Console.cs" />
-    <ProjectReference Include="..\..\System.Text.Json\ref\System.Text.Json.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Json\ref\System.Text.Json.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParser.cs b/src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParser.cs
index 665093b4086673..bf2ee5f99c9011 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParser.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParser.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.IO;
+using System.Runtime.CompilerServices;
 
 namespace Microsoft.Extensions.Logging.Console
 {
@@ -47,6 +48,7 @@ public void Parse(string message)
         {
             int startIndex = -1;
             int length = 0;
+            int escapeCode;
             ConsoleColor? foreground = null;
             ConsoleColor? background = null;
             var span = message.AsSpan();
@@ -59,12 +61,10 @@ public void Parse(string message)
                 {
                     if (span[i + 3] == 'm')
                     {
-#if NETCOREAPP
-                        if (ushort.TryParse(span.Slice(i + 2, length: 1), out ushort escapeCode))
-#else
-                        if (ushort.TryParse(span.Slice(i + 2, length: 1).ToString(), out ushort escapeCode))
-#endif
+                        // Example: \x1B[1m
+                        if (IsDigit(span[i + 2]))
                         {
+                            escapeCode = (int)(span[i + 2] - '0');
                             if (startIndex != -1)
                             {
                                 _onParseWrite(message, startIndex, length, background, foreground);
@@ -79,12 +79,10 @@ public void Parse(string message)
                     }
                     else if (span.Length >= i + 5 && span[i + 4] == 'm')
                     {
-#if NETCOREAPP
-                        if (ushort.TryParse(span.Slice(i + 2, length: 2), out ushort escapeCode))
-#else
-                        if (ushort.TryParse(span.Slice(i + 2, length: 2).ToString(), out ushort escapeCode))
-#endif
+                        // Example: \x1B[40m
+                        if (IsDigit(span[i + 2]) && IsDigit(span[i + 3]))
                         {
+                            escapeCode = (int)(span[i + 2] - '0') * 10 + (int)(span[i + 3] - '0');
                             if (startIndex != -1)
                             {
                                 _onParseWrite(message, startIndex, length, background, foreground);
@@ -128,6 +126,9 @@ public void Parse(string message)
             }
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static bool IsDigit(char c) => (uint)(c - '0') <= ('9' - '0');
+
         internal const string DefaultForegroundColor = "\x1B[39m\x1B[22m"; // reset to default foreground color
         internal const string DefaultBackgroundColor = "\x1B[49m"; // reset to the background color
 
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerFactoryExtensions.cs b/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerExtensions.cs
similarity index 80%
rename from src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerFactoryExtensions.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerExtensions.cs
index 9dbea88f9b253d..8cd8a594e359b2 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerFactoryExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerExtensions.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
@@ -49,6 +50,13 @@ public static ILoggingBuilder AddConsole(this ILoggingBuilder builder, Action<Co
             return builder;
         }
 
+        /// <summary>
+        /// Add the default console log formatter named 'simple' to the factory with default properties.
+        /// </summary>
+        /// <param name="builder">The <see cref="ILoggingBuilder"/> to use.</param>
+        public static ILoggingBuilder AddSimpleConsole(this ILoggingBuilder builder) =>
+            builder.AddFormatterWithName(ConsoleFormatterNames.Simple);
+
         /// <summary>
         /// Add and configure a console log formatter named 'simple' to the factory.
         /// </summary>
@@ -59,6 +67,13 @@ public static ILoggingBuilder AddSimpleConsole(this ILoggingBuilder builder, Act
             return builder.AddConsoleWithFormatter<SimpleConsoleFormatterOptions>(ConsoleFormatterNames.Simple, configure);
         }
 
+        /// <summary>
+        /// Add a console log formatter named 'json' to the factory with default properties.
+        /// </summary>
+        /// <param name="builder">The <see cref="ILoggingBuilder"/> to use.</param>
+        public static ILoggingBuilder AddJsonConsole(this ILoggingBuilder builder) =>
+            builder.AddFormatterWithName(ConsoleFormatterNames.Json);
+
         /// <summary>
         /// Add and configure a console log formatter named 'json' to the factory.
         /// </summary>
@@ -79,6 +94,13 @@ public static ILoggingBuilder AddSystemdConsole(this ILoggingBuilder builder, Ac
             return builder.AddConsoleWithFormatter<ConsoleFormatterOptions>(ConsoleFormatterNames.Systemd, configure);
         }
 
+        /// <summary>
+        /// Add a console log formatter named 'systemd' to the factory with default properties.
+        /// </summary>
+        /// <param name="builder">The <see cref="ILoggingBuilder"/> to use.</param>
+        public static ILoggingBuilder AddSystemdConsole(this ILoggingBuilder builder) =>
+            builder.AddFormatterWithName(ConsoleFormatterNames.Systemd);
+
         internal static ILoggingBuilder AddConsoleWithFormatter<TOptions>(this ILoggingBuilder builder, string name, Action<TOptions> configure)
             where TOptions : ConsoleFormatterOptions
         {
@@ -86,17 +108,20 @@ internal static ILoggingBuilder AddConsoleWithFormatter<TOptions>(this ILoggingB
             {
                 throw new ArgumentNullException(nameof(configure));
             }
-            builder.AddConsole((ConsoleLoggerOptions options) => options.FormatterName = name);
+            builder.AddFormatterWithName(name);
             builder.Services.Configure(configure);
 
             return builder;
         }
 
+        private static ILoggingBuilder AddFormatterWithName(this ILoggingBuilder builder, string name) =>
+            builder.AddConsole((ConsoleLoggerOptions options) => options.FormatterName = name);
+
         /// <summary>
         /// Adds a custom console logger formatter 'TFormatter' to be configured with options 'TOptions'.
         /// </summary>
         /// <param name="builder">The <see cref="ILoggingBuilder"/> to use.</param>
-        public static ILoggingBuilder AddConsoleFormatter<TFormatter, TOptions>(this ILoggingBuilder builder)
+        public static ILoggingBuilder AddConsoleFormatter<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TFormatter, TOptions>(this ILoggingBuilder builder)
             where TOptions : ConsoleFormatterOptions
             where TFormatter : ConsoleFormatter
         {
@@ -114,7 +139,7 @@ public static ILoggingBuilder AddConsoleFormatter<TFormatter, TOptions>(this ILo
         /// </summary>
         /// <param name="builder">The <see cref="ILoggingBuilder"/> to use.</param>
         /// <param name="configure">A delegate to configure options 'TOptions' for custom formatter 'TFormatter'.</param>
-        public static ILoggingBuilder AddConsoleFormatter<TFormatter, TOptions>(this ILoggingBuilder builder, Action<TOptions> configure)
+        public static ILoggingBuilder AddConsoleFormatter<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TFormatter, TOptions>(this ILoggingBuilder builder, Action<TOptions> configure)
             where TOptions : ConsoleFormatterOptions
             where TFormatter : ConsoleFormatter
         {
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerOptions.cs b/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerOptions.cs
index cda6f89e52c192..5951124db396d4 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerOptions.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerOptions.cs
@@ -13,7 +13,7 @@ public class ConsoleLoggerOptions
         /// <summary>
         /// Disables colors when <see langword="true" />.
         /// </summary>
-        [System.ObsoleteAttribute("ConsoleLoggerOptions.DisableColors has been deprecated. Please use SimpleConsoleFormatterOptions.DisableColors instead.", false)]
+        [System.ObsoleteAttribute("ConsoleLoggerOptions.DisableColors has been deprecated. Please use SimpleConsoleFormatterOptions.ColorBehavior instead.", false)]
         public bool DisableColors { get; set; }
 
 #pragma warning disable CS0618
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerProvider.cs b/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerProvider.cs
index 4c5c596a4467eb..d5a22520a1e295 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerProvider.cs
@@ -153,7 +153,7 @@ private void UpdateFormatterOptions(ConsoleFormatter formatter, ConsoleLoggerOpt
             {
                 defaultFormatter.FormatterOptions = new SimpleConsoleFormatterOptions()
                 {
-                    DisableColors = deprecatedFromOptions.DisableColors,
+                    ColorBehavior = deprecatedFromOptions.DisableColors ? LoggerColorBehavior.Disabled : LoggerColorBehavior.Enabled,
                     IncludeScopes = deprecatedFromOptions.IncludeScopes,
                     TimestampFormat = deprecatedFromOptions.TimestampFormat,
                     UseUtcTimestamp = deprecatedFromOptions.UseUtcTimestamp,
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/FormatterOptionsMonitor.cs b/src/libraries/Microsoft.Extensions.Logging.Console/src/FormatterOptionsMonitor.cs
index d29376cb9b84b8..00adb44b4b61f4 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/src/FormatterOptionsMonitor.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/FormatterOptionsMonitor.cs
@@ -2,11 +2,14 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.Options;
 
 namespace Microsoft.Extensions.Logging.Console
 {
-    internal class FormatterOptionsMonitor<TOptions> : IOptionsMonitor<TOptions> where TOptions : ConsoleFormatterOptions
+    internal class FormatterOptionsMonitor<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions> :
+        IOptionsMonitor<TOptions>
+        where TOptions : ConsoleFormatterOptions
     {
         private TOptions _options;
         public FormatterOptionsMonitor(TOptions options)
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs b/src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs
index 68aa95a92504fb..3a5aafe0cffe88 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs
@@ -41,14 +41,12 @@ public override void Write<TState>(in LogEntry<TState> logEntry, IExternalScopeP
                 using (var writer = new Utf8JsonWriter(output, FormatterOptions.JsonWriterOptions))
                 {
                     writer.WriteStartObject();
-                    string timestamp = null;
                     var timestampFormat = FormatterOptions.TimestampFormat;
                     if (timestampFormat != null)
                     {
-                        var dateTime = FormatterOptions.UseUtcTimestamp ? DateTime.UtcNow : DateTime.Now;
-                        timestamp = dateTime.ToString(timestampFormat);
+                        DateTimeOffset dateTimeOffset = FormatterOptions.UseUtcTimestamp ? DateTimeOffset.UtcNow : DateTimeOffset.Now;
+                        writer.WriteString("Timestamp", dateTimeOffset.ToString(timestampFormat));
                     }
-                    writer.WriteString("Timestamp", timestamp);
                     writer.WriteNumber(nameof(logEntry.EventId), eventId);
                     writer.WriteString(nameof(logEntry.LogLevel), GetLogLevelString(logLevel));
                     writer.WriteString(nameof(logEntry.Category), category);
@@ -77,12 +75,18 @@ public override void Write<TState>(in LogEntry<TState> logEntry, IExternalScopeP
                         writer.WriteEndObject();
                     }
 
-                    if (logEntry.State is IReadOnlyCollection<KeyValuePair<string, object>> stateDictionary)
+                    if (logEntry.State != null)
                     {
-                        foreach (KeyValuePair<string, object> item in stateDictionary)
+                        writer.WriteStartObject(nameof(logEntry.State));
+                        writer.WriteString("Message", logEntry.State.ToString());
+                        if (logEntry.State is IReadOnlyCollection<KeyValuePair<string, object>> stateProperties)
                         {
-                            writer.WriteString(item.Key, Convert.ToString(item.Value, CultureInfo.InvariantCulture));
+                            foreach (KeyValuePair<string, object> item in stateProperties)
+                            {
+                                writer.WriteString(item.Key, ToInvariantString(item.Value));
+                            }
                         }
+                        writer.WriteEndObject();
                     }
                     WriteScopeInformation(writer, scopeProvider);
                     writer.WriteEndObject();
@@ -115,26 +119,30 @@ private void WriteScopeInformation(Utf8JsonWriter writer, IExternalScopeProvider
         {
             if (FormatterOptions.IncludeScopes && scopeProvider != null)
             {
-                int numScopes = 0;
-                writer.WriteStartObject("Scopes");
+                writer.WriteStartArray("Scopes");
                 scopeProvider.ForEachScope((scope, state) =>
                 {
-                    if (scope is IReadOnlyCollection<KeyValuePair<string, object>> scopeDictionary)
+                    if (scope is IReadOnlyCollection<KeyValuePair<string, object>> scopes)
                     {
-                        foreach (KeyValuePair<string, object> item in scopeDictionary)
+                        state.WriteStartObject();
+                        state.WriteString("Message", scope.ToString());
+                        foreach (KeyValuePair<string, object> item in scopes)
                         {
-                            state.WriteString(item.Key, Convert.ToString(item.Value, CultureInfo.InvariantCulture));
+                            state.WriteString(item.Key, ToInvariantString(item.Value));
                         }
+                        state.WriteEndObject();
                     }
                     else
                     {
-                        state.WriteString(numScopes++.ToString(), scope.ToString());
+                        state.WriteStringValue(ToInvariantString(scope));
                     }
                 }, writer);
-                writer.WriteEndObject();
+                writer.WriteEndArray();
             }
         }
 
+        private static string ToInvariantString(object obj) => Convert.ToString(obj, CultureInfo.InvariantCulture);
+
         internal JsonConsoleFormatterOptions FormatterOptions { get; set; }
 
         private void ReloadLoggerOptions(JsonConsoleFormatterOptions options)
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/LoggerColorBehavior.cs b/src/libraries/Microsoft.Extensions.Logging.Console/src/LoggerColorBehavior.cs
new file mode 100644
index 00000000000000..c38ec1969b43de
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/LoggerColorBehavior.cs
@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.Extensions.Logging.Console
+{
+    /// <summary>
+    /// Determines when to use color when logging messages.
+    /// </summary>
+    public enum LoggerColorBehavior
+    {
+        /// <summary>
+        /// Use the default color behavior, enabling color except when the console output is redirected.
+        /// </summary>
+        /// <remarks>
+        /// Enables color except when the console output is redirected.
+        /// </remarks>
+        Default,
+        /// <summary>
+        /// Enable color for logging
+        /// </summary>
+        Enabled,
+        /// <summary>
+        /// Disable color for logging
+        /// </summary>
+        Disabled,
+    }
+}
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj b/src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj
index 3afd1b9ed232e9..1e8e0f43fa4b75 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj
@@ -1,24 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.0;net461</TargetFrameworks>
+    <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <EnableDefaultItems>true</EnableDefaultItems>
     <Nullable>annotations</Nullable>
     <DefineConstants>$(DefineConstants);NO_SUPPRESS_GC_TRANSITION</DefineConstants>
+    <!-- Use targeting pack references instead of granular ones in the project file. -->
+    <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>
   </PropertyGroup>
-  <PropertyGroup>
-    <!-- Ensure Assemblies are first resolved via targeting pack when targeting net461 -->
-    <AssemblySearchPaths Condition="'$(TargetFramework)' == 'net461'">$(NuGetPackageRoot)\microsoft.targetingpack.netframework.v4.6.1\1.0.1\lib\net461\;$(AssemblySearchPaths)</AssemblySearchPaths>
-  </PropertyGroup>
-
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Collections.Concurrent" />
-    <Reference Include="System.Console" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.InteropServices.RuntimeInformation" />
-    <Reference Include="System.Threading.Thread" />
-  </ItemGroup>
 
   <ItemGroup>
     <Compile Include="$(CommonPath)Extensions\Logging\NullExternalScopeProvider.cs"
@@ -39,33 +29,29 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Buffers" />
-    <Reference Include="Microsoft.Bcl.AsyncInterfaces" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
+  </ItemGroup>
+  
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Bcl.AsyncInterfaces\src\Microsoft.Bcl.AsyncInterfaces.csproj" />
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
   </ItemGroup>
 
   <ItemGroup>
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Text.Json" />
-    <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging.Configuration" />
-    <Reference Include="Microsoft.Extensions.Options" />
-    <Reference Include="Microsoft.Extensions.Options.ConfigurationExtensions" />
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Configuration" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\src\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Configuration\src\Microsoft.Extensions.Logging.Configuration.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Json\src\System.Text.Json.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.ValueTuple" />
-    <Reference Include="System.Runtime" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
     <PackageReference Include="System.Runtime.InteropServices.RuntimeInformation" Version="4.3.0" Condition="'$(TargetFramework)' == 'net461'" />
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" Condition="'$(TargetFramework)' == 'net461'" />
+    <Reference Include="System.Runtime" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs b/src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs
index e92aa0c2784004..bc702ca0438ad1 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs
@@ -53,8 +53,8 @@ public override void Write<TState>(in LogEntry<TState> logEntry, IExternalScopeP
             string timestampFormat = FormatterOptions.TimestampFormat;
             if (timestampFormat != null)
             {
-                DateTime dateTime = GetCurrentDateTime();
-                timestamp = dateTime.ToString(timestampFormat);
+                DateTimeOffset dateTimeOffset = GetCurrentDateTime();
+                timestamp = dateTimeOffset.ToString(timestampFormat);
             }
             if (timestamp != null)
             {
@@ -86,10 +86,6 @@ private void CreateDefaultLogMessage<TState>(TextWriter textWriter, in LogEntry<
 
             // scope information
             WriteScopeInformation(textWriter, scopeProvider, singleLine);
-            if (singleLine)
-            {
-                textWriter.Write(' ');
-            }
             WriteMessage(textWriter, message, singleLine);
 
             // Example:
@@ -112,6 +108,7 @@ private void WriteMessage(TextWriter textWriter, string message, bool singleLine
             {
                 if (singleLine)
                 {
+                    textWriter.Write(' ');
                     WriteReplacing(textWriter, Environment.NewLine, " ", message);
                 }
                 else
@@ -129,9 +126,9 @@ static void WriteReplacing(TextWriter writer, string oldValue, string newValue,
             }
         }
 
-        private DateTime GetCurrentDateTime()
+        private DateTimeOffset GetCurrentDateTime()
         {
-            return FormatterOptions.UseUtcTimestamp ? DateTime.UtcNow : DateTime.Now;
+            return FormatterOptions.UseUtcTimestamp ? DateTimeOffset.UtcNow : DateTimeOffset.Now;
         }
 
         private static string GetLogLevelString(LogLevel logLevel)
@@ -150,7 +147,9 @@ private static string GetLogLevelString(LogLevel logLevel)
 
         private ConsoleColors GetLogLevelConsoleColors(LogLevel logLevel)
         {
-            if (FormatterOptions.DisableColors)
+            bool disableColors = (FormatterOptions.ColorBehavior == LoggerColorBehavior.Disabled) ||
+                (FormatterOptions.ColorBehavior == LoggerColorBehavior.Default && System.Console.IsOutputRedirected);
+            if (disableColors)
             {
                 return new ConsoleColors(null, null);
             }
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatterOptions.cs b/src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatterOptions.cs
index 9ee51c14938911..44aab1edc5ff30 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatterOptions.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatterOptions.cs
@@ -11,9 +11,9 @@ public class SimpleConsoleFormatterOptions : ConsoleFormatterOptions
         public SimpleConsoleFormatterOptions() { }
 
         /// <summary>
-        /// Disables colors when <see langword="true" />.
+        /// Determines when to use color when logging messages.
         /// </summary>
-        public bool DisableColors { get; set; }
+        public LoggerColorBehavior ColorBehavior { get; set; }
 
         /// <summary>
         /// When <see langword="false" />, the entire message gets logged in a single line.
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/src/SystemdConsoleFormatter.cs b/src/libraries/Microsoft.Extensions.Logging.Console/src/SystemdConsoleFormatter.cs
index 0140adf513560f..1916dd2fa04988 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/src/SystemdConsoleFormatter.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/src/SystemdConsoleFormatter.cs
@@ -57,8 +57,8 @@ public override void Write<TState>(in LogEntry<TState> logEntry, IExternalScopeP
             string timestampFormat = FormatterOptions.TimestampFormat;
             if (timestampFormat != null)
             {
-                DateTime dateTime = GetCurrentDateTime();
-                textWriter.Write(dateTime.ToString(timestampFormat));
+                DateTimeOffset dateTimeOffset = GetCurrentDateTime();
+                textWriter.Write(dateTimeOffset.ToString(timestampFormat));
             }
 
             // category and event id
@@ -96,9 +96,9 @@ static void WriteReplacingNewLine(TextWriter writer, string message)
             }
         }
 
-        private DateTime GetCurrentDateTime()
+        private DateTimeOffset GetCurrentDateTime()
         {
-            return FormatterOptions.UseUtcTimestamp ? DateTime.UtcNow : DateTime.Now;
+            return FormatterOptions.UseUtcTimestamp ? DateTimeOffset.UtcNow : DateTimeOffset.Now;
         }
 
         private static string GetSyslogSeverityString(LogLevel logLevel)
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/JsonConsoleFormatterTests.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/JsonConsoleFormatterTests.cs
deleted file mode 100644
index f5e536d94adb7f..00000000000000
--- a/src/libraries/Microsoft.Extensions.Logging.Console/tests/JsonConsoleFormatterTests.cs
+++ /dev/null
@@ -1,48 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Text.Json;
-using Microsoft.Extensions.Logging.Abstractions;
-using Microsoft.Extensions.Logging.Console;
-using Microsoft.Extensions.Logging.Test.Console;
-using Xunit;
-
-namespace Microsoft.Extensions.Logging.Console.Test
-{
-    public class JsonConsoleFormatterTests : ConsoleFormatterTests
-    {
-        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        public void NoLogScope_DoesNotWriteAnyScopeContentToOutput_Json()
-        {
-            // Arrange
-            var t = ConsoleFormatterTests.SetUp(
-                new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Json },
-                new SimpleConsoleFormatterOptions { IncludeScopes = true },
-                new ConsoleFormatterOptions { IncludeScopes = true },
-                new JsonConsoleFormatterOptions {
-                    IncludeScopes = true,
-                    JsonWriterOptions = new JsonWriterOptions() { Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping } 
-                });
-            var logger = t.Logger;
-            var sink = t.Sink;
-
-            // Act
-            using (logger.BeginScope("Scope with named parameter {namedParameter}", 123))
-            using (logger.BeginScope("SimpleScope"))
-                logger.Log(LogLevel.Warning, 0, "Message with {args}", 73, _defaultFormatter);
-
-            // Assert
-            Assert.Equal(1, sink.Writes.Count);
-            var write = sink.Writes[0];
-            Assert.Equal(TestConsole.DefaultBackgroundColor, write.BackgroundColor);
-            Assert.Equal(TestConsole.DefaultForegroundColor, write.ForegroundColor);
-            Assert.Contains("Message with {args}", write.Message);
-            Assert.Contains("73", write.Message);
-            Assert.Contains("{OriginalFormat}", write.Message);
-            Assert.Contains("namedParameter", write.Message);
-            Assert.Contains("123", write.Message);
-            Assert.Contains("SimpleScope", write.Message);
-        }
-    }
-}
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests.csproj b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests.csproj
deleted file mode 100644
index 2524f77b4b469a..00000000000000
--- a/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests.csproj
+++ /dev/null
@@ -1,13 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-
-  <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
-    <TestRuntime>true</TestRuntime>
-    <EnableDefaultItems>true</EnableDefaultItems>
-  </PropertyGroup>
-
-  <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Logging.Console" />
-  </ItemGroup>
-
-</Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/AnsiParserTests.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/AnsiParserTests.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Logging.Console/tests/AnsiParserTests.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/AnsiParserTests.cs
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/Console/ConsoleContext.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/Console/ConsoleContext.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Logging.Console/tests/Console/ConsoleContext.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/Console/ConsoleContext.cs
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/Console/ConsoleSink.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/Console/ConsoleSink.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Logging.Console/tests/Console/ConsoleSink.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/Console/ConsoleSink.cs
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/Console/TestConsole.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/Console/TestConsole.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Logging.Console/tests/Console/TestConsole.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/Console/TestConsole.cs
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/ConsoleFormatterTests.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/ConsoleFormatterTests.cs
similarity index 99%
rename from src/libraries/Microsoft.Extensions.Logging.Console/tests/ConsoleFormatterTests.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/ConsoleFormatterTests.cs
index 580a745a12d8fc..78e17092a5f0e3 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/tests/ConsoleFormatterTests.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/ConsoleFormatterTests.cs
@@ -126,7 +126,7 @@ public void Log_LogsCorrectTimestamp(string formatterName, LogLevel level)
             // Arrange
             var t = SetUp(
                 new ConsoleLoggerOptions { FormatterName = formatterName },
-                new SimpleConsoleFormatterOptions { TimestampFormat = "yyyy-MM-ddTHH:mm:sszz ", UseUtcTimestamp = false },
+                new SimpleConsoleFormatterOptions { TimestampFormat = "yyyy-MM-ddTHH:mm:sszz ", UseUtcTimestamp = false, ColorBehavior = LoggerColorBehavior.Enabled },
                 new ConsoleFormatterOptions { TimestampFormat = "yyyy-MM-ddTHH:mm:sszz ", UseUtcTimestamp = false },
                 new JsonConsoleFormatterOptions {
                     TimestampFormat = "yyyy-MM-ddTHH:mm:sszz ",
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/ConsoleLoggerExtensionsTests.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/ConsoleLoggerExtensionsTests.cs
similarity index 85%
rename from src/libraries/Microsoft.Extensions.Logging.Console/tests/ConsoleLoggerExtensionsTests.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/ConsoleLoggerExtensionsTests.cs
index 85a643012c8298..739978be7d069e 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/tests/ConsoleLoggerExtensionsTests.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/ConsoleLoggerExtensionsTests.cs
@@ -76,7 +76,6 @@ public void AddConsoleFormatter_NullConfigure_Throws()
 
         [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
         [MemberData(nameof(FormatterNames))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
         public void AddConsole_ConsoleLoggerOptionsFromConfigFile_IsReadFromLoggingConfiguration(string formatterName)
         {
             var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
@@ -96,7 +95,6 @@ public void AddConsole_ConsoleLoggerOptionsFromConfigFile_IsReadFromLoggingConfi
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
         public void AddConsoleFormatter_CustomFormatter_IsReadFromLoggingConfiguration()
         {
             var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
@@ -156,11 +154,10 @@ private class CustomOptions : ConsoleFormatterOptions
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
         public void AddSimpleConsole_ChangeProperties_IsReadFromLoggingConfiguration()
         {
             var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
-                new KeyValuePair<string, string>("Console:FormatterOptions:DisableColors", "true"),
+                new KeyValuePair<string, string>("Console:FormatterOptions:ColorBehavior", "Disabled"),
                 new KeyValuePair<string, string>("Console:FormatterOptions:SingleLine", "true"),
                 new KeyValuePair<string, string>("Console:FormatterOptions:TimestampFormat", "HH:mm "),
                 new KeyValuePair<string, string>("Console:FormatterOptions:UseUtcTimestamp", "true"),
@@ -170,7 +167,7 @@ public void AddSimpleConsole_ChangeProperties_IsReadFromLoggingConfiguration()
             var loggerProvider = new ServiceCollection()
                 .AddLogging(builder => builder
                     .AddConfiguration(configuration)
-                    .AddSimpleConsole(o => {})
+                    .AddSimpleConsole()
                 )
                 .BuildServiceProvider()
                 .GetRequiredService<ILoggerProvider>();
@@ -179,7 +176,7 @@ public void AddSimpleConsole_ChangeProperties_IsReadFromLoggingConfiguration()
             var logger = (ConsoleLogger)consoleLoggerProvider.CreateLogger("Category");
             Assert.Equal(ConsoleFormatterNames.Simple, logger.Options.FormatterName);
             var formatter = Assert.IsType<SimpleConsoleFormatter>(logger.Formatter);
-            Assert.True(formatter.FormatterOptions.DisableColors);
+            Assert.Equal(LoggerColorBehavior.Disabled, formatter.FormatterOptions.ColorBehavior);
             Assert.True(formatter.FormatterOptions.SingleLine);
             Assert.Equal("HH:mm ", formatter.FormatterOptions.TimestampFormat);
             Assert.True(formatter.FormatterOptions.UseUtcTimestamp);
@@ -187,7 +184,36 @@ public void AddSimpleConsole_ChangeProperties_IsReadFromLoggingConfiguration()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
+        public void AddSimpleConsole_OutsideConfig_TakesProperty()
+        {
+            var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
+                new KeyValuePair<string, string>("Console:FormatterOptions:TimestampFormat", "HH:mm "),
+                new KeyValuePair<string, string>("Console:FormatterOptions:UseUtcTimestamp", "true"),
+                new KeyValuePair<string, string>("Console:FormatterOptions:IncludeScopes", "false"),
+            }).Build();
+
+            var loggerProvider = new ServiceCollection()
+                .AddLogging(builder => builder
+                    .AddConfiguration(configuration)
+                    .AddSimpleConsole(o => {
+                        o.TimestampFormat = "HH:mm:ss ";
+                        o.IncludeScopes = false;
+                        o.UseUtcTimestamp = true;
+                    })
+                )
+                .BuildServiceProvider()
+                .GetRequiredService<ILoggerProvider>();
+
+            var consoleLoggerProvider = Assert.IsType<ConsoleLoggerProvider>(loggerProvider);
+            var logger = (ConsoleLogger)consoleLoggerProvider.CreateLogger("Category");
+            Assert.Equal(ConsoleFormatterNames.Simple, logger.Options.FormatterName);
+            var formatter = Assert.IsType<SimpleConsoleFormatter>(logger.Formatter);
+            Assert.Equal("HH:mm:ss ", formatter.FormatterOptions.TimestampFormat);
+            Assert.False(formatter.FormatterOptions.IncludeScopes);
+            Assert.True(formatter.FormatterOptions.UseUtcTimestamp);
+        }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
         public void AddSystemdConsole_ChangeProperties_IsReadFromLoggingConfiguration()
         {
             var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
@@ -199,7 +225,7 @@ public void AddSystemdConsole_ChangeProperties_IsReadFromLoggingConfiguration()
             var loggerProvider = new ServiceCollection()
                 .AddLogging(builder => builder
                     .AddConfiguration(configuration)
-                    .AddSystemdConsole(o => {})
+                    .AddSystemdConsole()
                 )
                 .BuildServiceProvider()
                 .GetRequiredService<ILoggerProvider>();
@@ -214,7 +240,36 @@ public void AddSystemdConsole_ChangeProperties_IsReadFromLoggingConfiguration()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
+        public void AddSystemdConsole_OutsideConfig_TakesProperty()
+        {
+            var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
+                new KeyValuePair<string, string>("Console:FormatterOptions:TimestampFormat", "HH:mm "),
+                new KeyValuePair<string, string>("Console:FormatterOptions:UseUtcTimestamp", "true"),
+                new KeyValuePair<string, string>("Console:FormatterOptions:IncludeScopes", "true"),
+            }).Build();
+
+            var loggerProvider = new ServiceCollection()
+                .AddLogging(builder => builder
+                    .AddConfiguration(configuration)
+                    .AddSystemdConsole(o => {
+                        o.TimestampFormat = "HH:mm:ss ";
+                        o.IncludeScopes = false;
+                        o.UseUtcTimestamp = false;
+                    })
+                )
+                .BuildServiceProvider()
+                .GetRequiredService<ILoggerProvider>();
+
+            var consoleLoggerProvider = Assert.IsType<ConsoleLoggerProvider>(loggerProvider);
+            var logger = (ConsoleLogger)consoleLoggerProvider.CreateLogger("Category");
+            Assert.Equal(ConsoleFormatterNames.Systemd, logger.Options.FormatterName);
+            var formatter = Assert.IsType<SystemdConsoleFormatter>(logger.Formatter);
+            Assert.Equal("HH:mm:ss ", formatter.FormatterOptions.TimestampFormat);
+            Assert.False(formatter.FormatterOptions.UseUtcTimestamp);
+            Assert.False(formatter.FormatterOptions.IncludeScopes);
+        }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
         public void AddJsonConsole_ChangeProperties_IsReadFromLoggingConfiguration()
         {
             var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
@@ -227,7 +282,7 @@ public void AddJsonConsole_ChangeProperties_IsReadFromLoggingConfiguration()
             var loggerProvider = new ServiceCollection()
                 .AddLogging(builder => builder
                     .AddConfiguration(configuration)
-                    .AddJsonConsole(o => {})
+                    .AddJsonConsole()
                 )
                 .BuildServiceProvider()
                 .GetRequiredService<ILoggerProvider>();
@@ -243,7 +298,6 @@ public void AddJsonConsole_ChangeProperties_IsReadFromLoggingConfiguration()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
         public void AddJsonConsole_OutsideConfig_TakesProperty()
         {
             var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
@@ -278,7 +332,6 @@ public void AddJsonConsole_OutsideConfig_TakesProperty()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
         public void AddConsole_NullFormatterNameUsingSystemdFormat_AnyDeprecatedPropertiesOverwriteFormatterOptions()
         {
             var configs = new[] {
@@ -304,7 +357,6 @@ public void AddConsole_NullFormatterNameUsingSystemdFormat_AnyDeprecatedProperti
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
         public void AddConsole_NullFormatterName_UsingSystemdFormat_IgnoreFormatterOptionsAndUseDeprecatedInstead()
         {
             var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
@@ -337,7 +389,6 @@ public void AddConsole_NullFormatterName_UsingSystemdFormat_IgnoreFormatterOptio
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
         public void AddConsole_NullFormatterName_UsingDefaultFormat_IgnoreFormatterOptionsAndUseDeprecatedInstead()
         {
             var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
@@ -373,14 +424,13 @@ public void AddConsole_NullFormatterName_UsingDefaultFormat_IgnoreFormatterOptio
             Assert.Equal("HH:mm:ss ", formatter.FormatterOptions.TimestampFormat);  // ignore FormatterOptions, using deprecated one
             Assert.False(formatter.FormatterOptions.UseUtcTimestamp);               // not set anywhere, defaulted to false
             Assert.False(formatter.FormatterOptions.IncludeScopes);                 // setup using lambda wins over config
-            Assert.True(formatter.FormatterOptions.DisableColors);                  // setup using lambda
+            Assert.Equal(LoggerColorBehavior.Disabled, formatter.FormatterOptions.ColorBehavior);                  // setup using lambda
         }
 
         [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
         [InlineData("missingFormatter")]
         [InlineData("simple")]
         [InlineData("Simple")]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
         public void AddConsole_FormatterNameIsSet_UsingDefaultFormat_IgnoreDeprecatedAndUseFormatterOptionsInstead(string formatterName)
         {
             var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
@@ -417,14 +467,13 @@ public void AddConsole_FormatterNameIsSet_UsingDefaultFormat_IgnoreDeprecatedAnd
             Assert.Equal("HH:mm ", formatter.FormatterOptions.TimestampFormat);     // ignore deprecated, using FormatterOptions instead
             Assert.False(formatter.FormatterOptions.UseUtcTimestamp);               // not set anywhere, defaulted to false
             Assert.True(formatter.FormatterOptions.IncludeScopes);                  // ignore deprecated set in lambda use FormatterOptions instead
-            Assert.False(formatter.FormatterOptions.DisableColors);                 // ignore deprecated set in lambda, defaulted to false
+            Assert.Equal(LoggerColorBehavior.Default, formatter.FormatterOptions.ColorBehavior);                 // ignore deprecated set in lambda, defaulted to false
         }
 
         [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
         [InlineData("missingFormatter")]
         [InlineData("systemd")]
         [InlineData("Systemd")]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
         public void AddConsole_FormatterNameIsSet_UsingSystemdFormat_IgnoreDeprecatedAndUseFormatterOptionsInstead(string formatterName)
         {
             var configuration = new ConfigurationBuilder().AddInMemoryCollection(new[] {
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/ConsoleLoggerTest.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/ConsoleLoggerTest.cs
similarity index 99%
rename from src/libraries/Microsoft.Extensions.Logging.Console/tests/ConsoleLoggerTest.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/ConsoleLoggerTest.cs
index 9f6a99f5d7d963..ebe9985a245d27 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/tests/ConsoleLoggerTest.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/ConsoleLoggerTest.cs
@@ -86,7 +86,8 @@ private static void VerifyDeprecatedPropertiesUsedOnNullFormatterName(ConsoleLog
                 Assert.Equal(formatter.FormatterOptions.IncludeScopes, logger.Options.IncludeScopes);
                 Assert.Equal(formatter.FormatterOptions.UseUtcTimestamp, logger.Options.UseUtcTimestamp);
                 Assert.Equal(formatter.FormatterOptions.TimestampFormat, logger.Options.TimestampFormat);
-                Assert.Equal(formatter.FormatterOptions.DisableColors, logger.Options.DisableColors);   
+                Assert.Equal(formatter.FormatterOptions.ColorBehavior, 
+                    logger.Options.DisableColors ? LoggerColorBehavior.Disabled : LoggerColorBehavior.Enabled);   
             }
             else
             {
@@ -102,7 +103,8 @@ private static void UpdateFormatterOptions(ConsoleFormatter formatter, ConsoleLo
             // kept for deprecated apis:
             if (formatter is SimpleConsoleFormatter defaultFormatter)
             {
-                defaultFormatter.FormatterOptions.DisableColors = deprecatedFromOptions.DisableColors;
+                defaultFormatter.FormatterOptions.ColorBehavior = deprecatedFromOptions.DisableColors ? 
+                    LoggerColorBehavior.Disabled : LoggerColorBehavior.Enabled;
                 defaultFormatter.FormatterOptions.IncludeScopes = deprecatedFromOptions.IncludeScopes;
                 defaultFormatter.FormatterOptions.TimestampFormat = deprecatedFromOptions.TimestampFormat;
                 defaultFormatter.FormatterOptions.UseUtcTimestamp = deprecatedFromOptions.UseUtcTimestamp;
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/JsonConsoleFormatterTests.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/JsonConsoleFormatterTests.cs
new file mode 100644
index 00000000000000..09f4050a9ed4be
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/JsonConsoleFormatterTests.cs
@@ -0,0 +1,241 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Text.Json;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Logging.Console;
+using Microsoft.Extensions.Logging.Test.Console;
+using Xunit;
+
+namespace Microsoft.Extensions.Logging.Console.Test
+{
+    public class JsonConsoleFormatterTests : ConsoleFormatterTests
+    {
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        public void NoLogScope_DoesNotWriteAnyScopeContentToOutput_Json()
+        {
+            // Arrange
+            var t = ConsoleFormatterTests.SetUp(
+                new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Json },
+                new SimpleConsoleFormatterOptions { IncludeScopes = true },
+                new ConsoleFormatterOptions { IncludeScopes = true },
+                new JsonConsoleFormatterOptions {
+                    IncludeScopes = true,
+                    JsonWriterOptions = new JsonWriterOptions() { Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping } 
+                });
+            var logger = t.Logger;
+            var sink = t.Sink;
+
+            // Act
+            using (logger.BeginScope("Scope with named parameter {namedParameter}", 123))
+            using (logger.BeginScope("SimpleScope"))
+                logger.Log(LogLevel.Warning, 0, "Message with {args}", 73, _defaultFormatter);
+
+            // Assert
+            Assert.Equal(1, sink.Writes.Count);
+            var write = sink.Writes[0];
+            Assert.Equal(TestConsole.DefaultBackgroundColor, write.BackgroundColor);
+            Assert.Equal(TestConsole.DefaultForegroundColor, write.ForegroundColor);
+            Assert.Contains("Message with {args}", write.Message);
+            Assert.Contains("73", write.Message);
+            Assert.Contains("{OriginalFormat}", write.Message);
+            Assert.Contains("namedParameter", write.Message);
+            Assert.Contains("123", write.Message);
+            Assert.Contains("SimpleScope", write.Message);
+        }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        public void Log_TimestampFormatSet_ContainsTimestamp()
+        {
+            // Arrange
+            var t = SetUp(
+                new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Json },
+                simpleOptions: null,
+                systemdOptions: null,
+                jsonOptions: new JsonConsoleFormatterOptions
+                {
+                    TimestampFormat = "hh:mm:ss ",
+                }
+            );
+            var logger = (ILogger)t.Logger;
+            var sink = t.Sink;
+            var exception = new InvalidOperationException("Invalid value");
+
+            // Act
+            logger.LogCritical(eventId: 0, message: null);
+
+            // Assert
+            Assert.Equal(1, sink.Writes.Count);
+            Assert.Contains(
+                "\"Timestamp\":",
+                GetMessage(sink.Writes.GetRange(0 * t.WritesPerMsg, t.WritesPerMsg)));
+        }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        public void Log_NullMessage_LogsWhenMessageIsNotProvided()
+        {
+            // Arrange
+            var t = SetUp(
+                new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Json },
+                simpleOptions: null,
+                systemdOptions: null,
+                jsonOptions: new JsonConsoleFormatterOptions
+                {
+                    JsonWriterOptions = new JsonWriterOptions() { Indented = false }
+                }
+            );
+            var logger = (ILogger)t.Logger;
+            var sink = t.Sink;
+            var exception = new InvalidOperationException("Invalid value");
+
+            // Act
+            logger.LogCritical(eventId: 0, exception: null, message: null);
+            logger.LogCritical(eventId: 0, message: null);
+            logger.LogCritical(eventId: 0, message: null, exception: exception);
+
+            // Assert
+            Assert.Equal(3, sink.Writes.Count);
+            Assert.Equal(
+                "{\"EventId\":0,\"LogLevel\":\"Critical\",\"Category\":\"test\",\"Message\":\"[null]\""
+                + ",\"State\":{\"Message\":\"[null]\",\"{OriginalFormat}\":\"[null]\"}}"
+                +  Environment.NewLine,
+                GetMessage(sink.Writes.GetRange(0 * t.WritesPerMsg, t.WritesPerMsg)));
+            Assert.Equal(
+                "{\"EventId\":0,\"LogLevel\":\"Critical\",\"Category\":\"test\",\"Message\":\"[null]\""
+                + ",\"State\":{\"Message\":\"[null]\",\"{OriginalFormat}\":\"[null]\"}}"
+                +  Environment.NewLine,
+                GetMessage(sink.Writes.GetRange(1 * t.WritesPerMsg, t.WritesPerMsg)));
+
+            Assert.Equal(
+                "{\"EventId\":0,\"LogLevel\":\"Critical\",\"Category\":\"test\""
+                + ",\"Message\":\"[null]\""
+                + ",\"Exception\":{\"Message\":\"Invalid value\",\"Type\":\"System.InvalidOperationException\",\"StackTrace\":[],\"HResult\":-2146233079}"
+                + ",\"State\":{\"Message\":\"[null]\",\"{OriginalFormat}\":\"[null]\"}}"
+                +  Environment.NewLine,
+                GetMessage(sink.Writes.GetRange(2 * t.WritesPerMsg, t.WritesPerMsg)));
+        }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        public void Log_ExceptionWithMessage_ExtractsInfo()
+        {
+            // Arrange
+            var t = SetUp(
+                new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Json },
+                simpleOptions: null,
+                systemdOptions: null,
+                jsonOptions: new JsonConsoleFormatterOptions
+                {
+                    JsonWriterOptions = new JsonWriterOptions() { Indented = false },
+                    IncludeScopes = true
+                }
+            );
+            var logger = (ILogger)t.Logger;
+            var sink = t.Sink;
+            var exception = new InvalidOperationException("Invalid value");
+
+            // Act
+            logger.LogInformation(exception, "exception message with {0}", "stacktrace");
+            logger.Log(LogLevel.Information, 0, state: "exception message", exception: exception, formatter: (a, b) => a);
+            
+            using (logger.BeginScope("scope1 {name1}", 123))
+            using (logger.BeginScope("scope2 {name1} {name2}", 456, 789))
+                logger.Log(LogLevel.Information, 0, state: "exception message", exception: exception, formatter: (a, b) => a);
+
+            // Assert
+            Assert.Equal(3, sink.Writes.Count);
+            Assert.Equal(
+                "{\"EventId\":0,\"LogLevel\":\"Information\",\"Category\":\"test\""
+                + ",\"Message\":\"exception message with stacktrace\""
+                + ",\"Exception\":{\"Message\":\"Invalid value\",\"Type\":\"System.InvalidOperationException\",\"StackTrace\":[],\"HResult\":-2146233079}"
+                + ",\"State\":{\"Message\":\"exception message with stacktrace\",\"0\":\"stacktrace\",\"{OriginalFormat}\":\"exception message with {0}\"}"
+                + ",\"Scopes\":[]"
+                +"}" +  Environment.NewLine,
+                GetMessage(sink.Writes.GetRange(0 * t.WritesPerMsg, t.WritesPerMsg)));
+            Assert.Equal(
+                "{\"EventId\":0,\"LogLevel\":\"Information\",\"Category\":\"test\""
+                + ",\"Message\":\"exception message\""
+                + ",\"Exception\":{\"Message\":\"Invalid value\",\"Type\":\"System.InvalidOperationException\",\"StackTrace\":[],\"HResult\":-2146233079}"
+                + ",\"State\":{\"Message\":\"exception message\"}"
+                + ",\"Scopes\":[]"
+                +"}" +  Environment.NewLine,
+                GetMessage(sink.Writes.GetRange(1 * t.WritesPerMsg, t.WritesPerMsg)));
+            Assert.Equal(
+                "{\"EventId\":0,\"LogLevel\":\"Information\",\"Category\":\"test\""
+                + ",\"Message\":\"exception message\""
+                + ",\"Exception\":{\"Message\":\"Invalid value\",\"Type\":\"System.InvalidOperationException\",\"StackTrace\":[],\"HResult\":-2146233079}"
+                + ",\"State\":{\"Message\":\"exception message\"}"
+                + ",\"Scopes\":[{\"Message\":\"scope1 123\",\"name1\":\"123\",\"{OriginalFormat}\":\"scope1 {name1}\"},{\"Message\":\"scope2 456 789\",\"name1\":\"456\",\"name2\":\"789\",\"{OriginalFormat}\":\"scope2 {name1} {name2}\"}]"
+                +"}" +  Environment.NewLine,
+                GetMessage(sink.Writes.GetRange(2 * t.WritesPerMsg, t.WritesPerMsg)));
+        }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        public void Log_IncludeScopes_ContainsDuplicateNamedPropertiesInScope_AcceptableJson()
+        {
+            // Arrange
+            var t = SetUp(
+                new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Json },
+                simpleOptions: null,
+                systemdOptions: null,
+                jsonOptions: new JsonConsoleFormatterOptions
+                {
+                    JsonWriterOptions = new JsonWriterOptions() { Indented = false },
+                    IncludeScopes = true
+                }
+            );
+            var logger = (ILogger)t.Logger;
+            var sink = t.Sink;
+
+            // Act
+            using (logger.BeginScope("scope1 {name1}", 123))
+            using (logger.BeginScope("scope2 {name1} {name2}", 456, 789))
+                logger.Log(LogLevel.Information, 0, state: "exception message", exception: null, formatter: (a, b) => a);
+
+            // Assert
+            Assert.Equal(1, sink.Writes.Count);
+            Assert.Equal(
+                "{\"EventId\":0,\"LogLevel\":\"Information\",\"Category\":\"test\""
+                + ",\"Message\":\"exception message\""
+                + ",\"State\":{\"Message\":\"exception message\"}"
+                + ",\"Scopes\":[{\"Message\":\"scope1 123\",\"name1\":\"123\",\"{OriginalFormat}\":\"scope1 {name1}\"},{\"Message\":\"scope2 456 789\",\"name1\":\"456\",\"name2\":\"789\",\"{OriginalFormat}\":\"scope2 {name1} {name2}\"}]"
+                +"}" +  Environment.NewLine,
+                GetMessage(sink.Writes.GetRange(0 * t.WritesPerMsg, t.WritesPerMsg)));
+        }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        public void Log_StateAndScopeAreCollections_IncludesMessageAndCollectionValues()
+        {
+            // Arrange
+            var t = SetUp(
+                new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Json },
+                simpleOptions: null,
+                systemdOptions: null,
+                jsonOptions: new JsonConsoleFormatterOptions
+                {
+                    JsonWriterOptions = new JsonWriterOptions() { Indented = false },
+                    IncludeScopes = true
+                }
+            );
+            var logger = (ILogger)t.Logger;
+            var sink = t.Sink;
+
+            // Act
+            using (logger.BeginScope("{Number}", 2))
+            using (logger.BeginScope("{AnotherNumber}", 3))
+            {
+                logger.LogInformation("{LogEntryNumber}", 1);
+            }
+
+            // Assert
+            Assert.Equal(1, sink.Writes.Count);
+            Assert.Equal(
+                "{\"EventId\":0,\"LogLevel\":\"Information\",\"Category\":\"test\""
+                + ",\"Message\":\"1\""
+                + ",\"State\":{\"Message\":\"1\",\"LogEntryNumber\":\"1\",\"{OriginalFormat}\":\"{LogEntryNumber}\"}"
+                + ",\"Scopes\":[{\"Message\":\"2\",\"Number\":\"2\",\"{OriginalFormat}\":\"{Number}\"},{\"Message\":\"3\",\"AnotherNumber\":\"3\",\"{OriginalFormat}\":\"{AnotherNumber}\"}]"
+                +"}" +  Environment.NewLine,
+                GetMessage(sink.Writes.GetRange(0 * t.WritesPerMsg, t.WritesPerMsg)));
+        }
+    }
+}
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/Microsoft.Extensions.Logging.Console.Tests.csproj b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/Microsoft.Extensions.Logging.Console.Tests.csproj
new file mode 100644
index 00000000000000..6caa09d4a5fa98
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/Microsoft.Extensions.Logging.Console.Tests.csproj
@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
+    <TestRuntime>true</TestRuntime>
+    <EnableDefaultItems>true</EnableDefaultItems>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Console\src\Microsoft.Extensions.Logging.Console.csproj" SkipUseReferenceAssembly="true" />
+  </ItemGroup>
+
+</Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/SimpleConsoleFormatterTests.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/SimpleConsoleFormatterTests.cs
similarity index 54%
rename from src/libraries/Microsoft.Extensions.Logging.Console/tests/SimpleConsoleFormatterTests.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/SimpleConsoleFormatterTests.cs
index d92c8af9514822..3bb1fa491ecea0 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Console/tests/SimpleConsoleFormatterTests.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/SimpleConsoleFormatterTests.cs
@@ -9,13 +9,16 @@ namespace Microsoft.Extensions.Logging.Console.Test
 {
     public class SimpleConsoleFormatterTests : ConsoleFormatterTests
     {
-        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        public void Log_WritingScopes_LogsWithCorrectColors()
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [InlineData(LoggerColorBehavior.Default)]
+        [InlineData(LoggerColorBehavior.Enabled)]
+        [InlineData(LoggerColorBehavior.Disabled)]
+        public void Log_WritingScopes_LogsWithCorrectColorsWhenColorEnabled(LoggerColorBehavior colorBehavior)
         {
             // Arrange
             var t = SetUp(
                 new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Simple },
-                new SimpleConsoleFormatterOptions { IncludeScopes = true }
+                new SimpleConsoleFormatterOptions { IncludeScopes = true, ColorBehavior = colorBehavior }
                 );
             var logger = t.Logger;
             var sink = t.Sink;
@@ -29,13 +32,25 @@ public void Log_WritingScopes_LogsWithCorrectColors()
             }
 
             // Assert
-            Assert.Equal(2, sink.Writes.Count);
-            var write = sink.Writes[0];
-            Assert.Equal(ConsoleColor.Black, write.BackgroundColor);
-            Assert.Equal(ConsoleColor.DarkGreen, write.ForegroundColor);
-            write = sink.Writes[1];
-            Assert.Equal(TestConsole.DefaultBackgroundColor, write.BackgroundColor);
-            Assert.Equal(TestConsole.DefaultForegroundColor, write.ForegroundColor);
+            switch (colorBehavior)
+            {
+                case LoggerColorBehavior.Enabled:
+                    Assert.Equal(2, sink.Writes.Count);
+                    var write = sink.Writes[0];
+                    Assert.Equal(ConsoleColor.Black, write.BackgroundColor);
+                    Assert.Equal(ConsoleColor.DarkGreen, write.ForegroundColor);
+                    write = sink.Writes[1];
+                    Assert.Equal(TestConsole.DefaultBackgroundColor, write.BackgroundColor);
+                    Assert.Equal(TestConsole.DefaultForegroundColor, write.ForegroundColor);
+                    break;
+                case LoggerColorBehavior.Default:
+                case LoggerColorBehavior.Disabled:
+                    Assert.Equal(1, sink.Writes.Count);
+                    write = sink.Writes[0];
+                    Assert.Equal(TestConsole.DefaultBackgroundColor, write.BackgroundColor);
+                    Assert.Equal(TestConsole.DefaultForegroundColor, write.ForegroundColor);
+                    break;
+            }
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
@@ -44,7 +59,7 @@ public void Log_NoLogScope_DoesNotWriteAnyScopeContentToOutput()
             // Arrange
             var t = SetUp(
                 new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Simple },
-                new SimpleConsoleFormatterOptions { IncludeScopes = true }
+                new SimpleConsoleFormatterOptions { IncludeScopes = true, ColorBehavior = LoggerColorBehavior.Enabled }
             );
             var logger = t.Logger;
             var sink = t.Sink;
@@ -68,7 +83,7 @@ public void Log_SingleLine_LogsWhenMessageIsNotProvided()
             // Arrange
             var t = SetUp(
                 new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Simple },
-                new SimpleConsoleFormatterOptions { SingleLine = true }
+                new SimpleConsoleFormatterOptions { SingleLine = true, ColorBehavior = LoggerColorBehavior.Enabled }
             );
             var logger = (ILogger)t.Logger;
             var sink = t.Sink;
@@ -89,8 +104,35 @@ public void Log_SingleLine_LogsWhenMessageIsNotProvided()
                 GetMessage(sink.Writes.GetRange(1 * t.WritesPerMsg, t.WritesPerMsg)));
 
             Assert.Equal(
-                "crit: test[0]" + " " + "[null]" + "System.InvalidOperationException: Invalid value" + Environment.NewLine,
+                "crit: test[0]" + " " + "[null]" + " " + "System.InvalidOperationException: Invalid value" + Environment.NewLine,
                 GetMessage(sink.Writes.GetRange(2 * t.WritesPerMsg, t.WritesPerMsg)));
         }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        public void Log_SingleLine_LogsWhenBothMessageAndExceptionProvided()
+        {
+            // Arrange
+            var t = SetUp(
+                new ConsoleLoggerOptions { FormatterName = ConsoleFormatterNames.Simple },
+                new SimpleConsoleFormatterOptions { SingleLine = true, ColorBehavior = LoggerColorBehavior.Enabled }
+            );
+            var logger = (ILogger)t.Logger;
+            var sink = t.Sink;
+            var exception = new InvalidOperationException("Invalid value");
+
+            // Act
+            logger.LogCritical(eventId: 0, message: "exception happened");
+            logger.LogCritical(eventId: 0, message: "exception happened", exception: exception);
+
+            // Assert
+            Assert.Equal(4, sink.Writes.Count);
+            Assert.Equal(
+                "crit: test[0]" + " " + "exception happened" + Environment.NewLine,
+                GetMessage(sink.Writes.GetRange(0 * t.WritesPerMsg, t.WritesPerMsg)));
+
+            Assert.Equal(
+                "crit: test[0]" + " " + "exception happened" + " " + "System.InvalidOperationException: Invalid value" + Environment.NewLine,
+                GetMessage(sink.Writes.GetRange(1 * t.WritesPerMsg, t.WritesPerMsg)));
+        }
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/TestFormatterOptionsMonitor.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/TestFormatterOptionsMonitor.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Logging.Console/tests/TestFormatterOptionsMonitor.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/TestFormatterOptionsMonitor.cs
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/TextWriterExtensionsTests.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/TextWriterExtensionsTests.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Logging.Console/tests/TextWriterExtensionsTests.cs
rename to src/libraries/Microsoft.Extensions.Logging.Console/tests/Microsoft.Extensions.Logging.Console.Tests/TextWriterExtensionsTests.cs
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/TrimmingTests/AddConsoleFormatterTests.cs b/src/libraries/Microsoft.Extensions.Logging.Console/tests/TrimmingTests/AddConsoleFormatterTests.cs
new file mode 100644
index 00000000000000..e12c7d7797783e
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/tests/TrimmingTests/AddConsoleFormatterTests.cs
@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Logging.Console;
+using System.IO;
+
+class Program
+{
+    private static int ConstructorCallCount = 0;
+    private static int WriteCallCount = 0;
+
+    static int Main(string[] args)
+    {
+        IServiceCollection descriptors = new ServiceCollection();
+        descriptors.AddLogging(builder =>
+        {
+            builder.AddConsoleFormatter<CustomFormatter, CustomOptions>();
+            builder.AddConsole(o => { o.FormatterName = "custom"; });
+        });
+
+        ServiceProvider provider = descriptors.BuildServiceProvider();
+
+        ILoggerProvider logger = provider.GetRequiredService<ILoggerProvider>();
+        logger.CreateLogger("log").LogError("Hello");
+
+        if (ConstructorCallCount != 1 ||
+            WriteCallCount != 1)
+        {
+            return -1;
+        }
+
+        return 100;
+    }
+
+    private class CustomFormatter : ConsoleFormatter
+    {
+        public CustomFormatter() : base("Custom")
+        {
+            ConstructorCallCount++;
+        }
+        public override void Write<TState>(in LogEntry<TState> logEntry, IExternalScopeProvider scopeProvider, TextWriter textWriter)
+        {
+            WriteCallCount++;
+        }
+    }
+
+    private class CustomOptions : ConsoleFormatterOptions { }
+}
diff --git a/src/libraries/Microsoft.Extensions.Logging.Console/tests/TrimmingTests/Microsoft.Extensions.Logging.Console.TrimmingTests.proj b/src/libraries/Microsoft.Extensions.Logging.Console/tests/TrimmingTests/Microsoft.Extensions.Logging.Console.TrimmingTests.proj
new file mode 100644
index 00000000000000..353b9d16635aca
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Logging.Console/tests/TrimmingTests/Microsoft.Extensions.Logging.Console.TrimmingTests.proj
@@ -0,0 +1,13 @@
+<Project DefaultTargets="Build">
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props))" />
+
+  <PropertyGroup>
+    <AdditionalProjectReferences>Microsoft.Extensions.Logging.Console</AdditionalProjectReferences>
+  </PropertyGroup>
+  
+  <ItemGroup>
+    <TestConsoleAppSourceFiles Include="AddConsoleFormatterTests.cs" />
+  </ItemGroup>
+
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets))" />
+</Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.Debug/ref/Microsoft.Extensions.Logging.Debug.csproj b/src/libraries/Microsoft.Extensions.Logging.Debug/ref/Microsoft.Extensions.Logging.Debug.csproj
index 3857ebe8a7bff4..046103224ca355 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Debug/ref/Microsoft.Extensions.Logging.Debug.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.Debug/ref/Microsoft.Extensions.Logging.Debug.csproj
@@ -1,10 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Logging.Debug.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.Debug/src/Microsoft.Extensions.Logging.Debug.csproj b/src/libraries/Microsoft.Extensions.Logging.Debug/src/Microsoft.Extensions.Logging.Debug.csproj
index d1d2c4274e5b2f..a025ca9fc851af 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Debug/src/Microsoft.Extensions.Logging.Debug.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.Debug/src/Microsoft.Extensions.Logging.Debug.csproj
@@ -1,14 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Runtime" />
-  </ItemGroup>
-
   <ItemGroup>
     <Compile Include="$(CommonPath)Extensions\Logging\NullExternalScopeProvider.cs"
              Link="Common\src\Extensions\Logging\NullExternalScopeProvider.cs" />
@@ -17,14 +13,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\src\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.EventLog/ref/Microsoft.Extensions.Logging.EventLog.csproj b/src/libraries/Microsoft.Extensions.Logging.EventLog/ref/Microsoft.Extensions.Logging.EventLog.csproj
index 21d4d4cb730983..41ab6a29cfaf49 100644
--- a/src/libraries/Microsoft.Extensions.Logging.EventLog/ref/Microsoft.Extensions.Logging.EventLog.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.EventLog/ref/Microsoft.Extensions.Logging.EventLog.csproj
@@ -1,11 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Logging.EventLog.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.EventLog/src/Microsoft.Extensions.Logging.EventLog.csproj b/src/libraries/Microsoft.Extensions.Logging.EventLog/src/Microsoft.Extensions.Logging.EventLog.csproj
index fca2aa1bcf1a92..9ae5802d972d1a 100644
--- a/src/libraries/Microsoft.Extensions.Logging.EventLog/src/Microsoft.Extensions.Logging.EventLog.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.EventLog/src/Microsoft.Extensions.Logging.EventLog.csproj
@@ -1,26 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent);net461;netstandard2.0;netstandard2.1</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.ComponentModel.Primitives" />
-    <Reference Include="System.Runtime" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
-
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="System.Diagnostics.EventLog" />
-  </ItemGroup>
-
   <ItemGroup>
     <Compile Include="$(CommonPath)Extensions\Logging\NullExternalScopeProvider.cs"
              Link="Common\src\Extensions\Logging\NullExternalScopeProvider.cs" />
@@ -29,10 +13,14 @@
   </ItemGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Options" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\src\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj" />
+  </ItemGroup>
+  
+  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Diagnostics.EventLog\src\System.Diagnostics.EventLog.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.EventSource/ref/Microsoft.Extensions.Logging.EventSource.csproj b/src/libraries/Microsoft.Extensions.Logging.EventSource/ref/Microsoft.Extensions.Logging.EventSource.csproj
index ecf0ef7df93a7d..fe5b5ee697d378 100644
--- a/src/libraries/Microsoft.Extensions.Logging.EventSource/ref/Microsoft.Extensions.Logging.EventSource.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.EventSource/ref/Microsoft.Extensions.Logging.EventSource.csproj
@@ -1,10 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Logging.EventSource.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.EventSource/src/LoggingEventSource.cs b/src/libraries/Microsoft.Extensions.Logging.EventSource/src/LoggingEventSource.cs
index d62ff6e7fe963b..a8bb222127056c 100644
--- a/src/libraries/Microsoft.Extensions.Logging.EventSource/src/LoggingEventSource.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.EventSource/src/LoggingEventSource.cs
@@ -31,7 +31,9 @@ namespace Microsoft.Extensions.Logging.EventSource
     ///
     /// SPEC =                          // empty spec, same as *
     ///      | NAME                     // Just a name the level is the default level
-    ///      | NAME : LEVEL            // specifies level for a particular logger (can have a * suffix).
+    ///      | NAME : LEVEL             // specifies level for a particular logger (can have a * suffix).
+    ///
+    /// When "UseAppFilters" is specified in the FilterSpecs, it avoids disabling all categories which happens by default otherwise.
     ///
     /// Where Name is the name of a ILoggger (case matters), Name can have a * which acts as a wildcard
     /// AS A SUFFIX.   Thus Net* will match any loggers that start with the 'Net'.
@@ -111,6 +113,7 @@ public static class Keywords
         // having assignment in ctor would overwrite the value
         private LoggerFilterRule[] _filterSpec = Array.Empty<LoggerFilterRule>();
         private CancellationTokenSource _cancellationTokenSource;
+        private const string UseAppFilters = "UseAppFilters";
 
         private LoggingEventSource() : base(EventSourceSettings.EtwSelfDescribingEventFormat)
         {
@@ -336,39 +339,50 @@ private static LoggerFilterRule[] ParseFilterSpec(string filterSpec, LogLevel de
                 return new[] { new LoggerFilterRule(typeof(EventSourceLoggerProvider).FullName, null, defaultLevel, null) };
             }
 
-            var rules = new List<LoggerFilterRule>();
+            if (filterSpec == null)
+            {
+                // All event source loggers are disabled by default
+                return new[] { new LoggerFilterRule(typeof(EventSourceLoggerProvider).FullName, null, LogLevel.None, null) };
+            }
 
-            // All event source loggers are disabled by default
-            rules.Add(new LoggerFilterRule(typeof(EventSourceLoggerProvider).FullName, null, LogLevel.None, null));
+            var rules = new List<LoggerFilterRule>();
+            int ruleStringsStartIndex = 0;
+            string[] ruleStrings = filterSpec.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries);
+            if (ruleStrings.Length > 0 && ruleStrings[0].Equals(UseAppFilters, StringComparison.OrdinalIgnoreCase))
+            {
+                // Avoid adding default rule to disable event source loggers
+                ruleStringsStartIndex = 1;
+            }
+            else
+            {
+                rules.Add(new LoggerFilterRule(typeof(EventSourceLoggerProvider).FullName, null, LogLevel.None, null));
+            }
 
-            if (filterSpec != null)
+            for (int i = ruleStringsStartIndex; i < ruleStrings.Length; i++)
             {
-                string[] ruleStrings = filterSpec.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries);
-                foreach (string rule in ruleStrings)
+                string rule = ruleStrings[i];
+                LogLevel level = defaultLevel;
+                string[] parts = rule.Split(new[] { ':' }, 2);
+                string loggerName = parts[0];
+                if (loggerName.Length == 0)
                 {
-                    LogLevel level = defaultLevel;
-                    string[] parts = rule.Split(new[] { ':' }, 2);
-                    string loggerName = parts[0];
-                    if (loggerName.Length == 0)
-                    {
-                        continue;
-                    }
+                    continue;
+                }
 
-                    if (loggerName[loggerName.Length - 1] == '*')
-                    {
-                        loggerName = loggerName.Substring(0, loggerName.Length - 1);
-                    }
+                if (loggerName[loggerName.Length - 1] == '*')
+                {
+                    loggerName = loggerName.Substring(0, loggerName.Length - 1);
+                }
 
-                    if (parts.Length == 2)
+                if (parts.Length == 2)
+                {
+                    if (!TryParseLevel(defaultLevel, parts[1], out level))
                     {
-                        if (!TryParseLevel(defaultLevel, parts[1], out level))
-                        {
-                            continue;
-                        }
+                        continue;
                     }
-
-                    rules.Add(new LoggerFilterRule(typeof(EventSourceLoggerProvider).FullName, loggerName, level, null));
                 }
+
+                rules.Add(new LoggerFilterRule(typeof(EventSourceLoggerProvider).FullName, loggerName, level, null));
             }
 
             return rules.ToArray();
diff --git a/src/libraries/Microsoft.Extensions.Logging.EventSource/src/Microsoft.Extensions.Logging.EventSource.csproj b/src/libraries/Microsoft.Extensions.Logging.EventSource/src/Microsoft.Extensions.Logging.EventSource.csproj
index d55f53f867f642..b6cd4860ebc8c7 100644
--- a/src/libraries/Microsoft.Extensions.Logging.EventSource/src/Microsoft.Extensions.Logging.EventSource.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.EventSource/src/Microsoft.Extensions.Logging.EventSource.csproj
@@ -1,10 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.0;net461</TargetFrameworks>
+    <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <EnableDefaultItems>true</EnableDefaultItems>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <!-- Use targeting pack references instead of granular ones in the project file. -->
+    <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>
   </PropertyGroup>
 
   <ItemGroup>
@@ -12,32 +14,21 @@
              Link="Common\src\Extensions\Logging\NullExternalScopeProvider.cs" />
     <Compile Include="$(CommonPath)Extensions\Logging\NullScope.cs"
              Link="Common\src\Extensions\Logging\NullScope.cs" />
-
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Options" />
-    <Reference Include="Microsoft.Extensions.Primitives" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
-    <Reference Include="System.Text.Json" />
-  </ItemGroup>
-
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.Diagnostics.Tracing" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Threading" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' OR $(TargetFramework.StartsWith('net4'))">
-    <Reference Include="Microsoft.Bcl.AsyncInterfaces" />
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\src\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Bcl.AsyncInterfaces\src\Microsoft.Bcl.AsyncInterfaces.csproj" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Json\src\System.Text.Json.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.EventSource/tests/EventSourceLoggerTest.cs b/src/libraries/Microsoft.Extensions.Logging.EventSource/tests/EventSourceLoggerTest.cs
index f015f06a05c03b..6c4543c05d4fbe 100644
--- a/src/libraries/Microsoft.Extensions.Logging.EventSource/tests/EventSourceLoggerTest.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.EventSource/tests/EventSourceLoggerTest.cs
@@ -53,6 +53,113 @@ public void IsEnabledReturnsCorrectValue()
             }
         }
 
+        [Fact]
+        public void FilterSpecs_UseAppFilters_IncreaseLoggingLevelForOneCategory_GuaranteesAllRulesRemainAvailable()
+        {
+            using (var testListener = new TestEventListener())
+            {
+                var loggerFactory = LoggerFactory.Create(builder =>
+                    builder
+                        .AddEventSourceLogger()
+                        .AddFilter("Logger1*", LogLevel.Warning)
+                        .AddFilter("Logger2*", LogLevel.Error)
+                        .AddFilter("Logger3*", LogLevel.Critical)
+                        .AddFilter<EventSourceLoggerProvider>("Logger4*", LogLevel.Error)
+                );
+
+                var listenerSettings = new TestEventListener.ListenerSettings();
+                listenerSettings.FilterSpec = "UseAppFilters;Logger3:1";
+                testListener.EnableEvents(listenerSettings);
+
+                var logger = loggerFactory.CreateLogger("Logger1");
+                var logger2 = loggerFactory.CreateLogger("Logger2");
+                var logger3 = loggerFactory.CreateLogger("Logger3");
+                var logger4 = loggerFactory.CreateLogger("Logger4");
+
+                Assert.False(logger.IsEnabled(LogLevel.None));
+                Assert.True(logger.IsEnabled(LogLevel.Critical));
+                Assert.True(logger.IsEnabled(LogLevel.Error));
+                Assert.True(logger.IsEnabled(LogLevel.Warning));
+                Assert.False(logger.IsEnabled(LogLevel.Information));
+                Assert.False(logger.IsEnabled(LogLevel.Debug));
+                Assert.False(logger.IsEnabled(LogLevel.Trace));
+
+                Assert.False(logger2.IsEnabled(LogLevel.None));
+                Assert.True(logger2.IsEnabled(LogLevel.Critical));
+                Assert.True(logger2.IsEnabled(LogLevel.Error));
+                Assert.False(logger2.IsEnabled(LogLevel.Warning));
+                Assert.False(logger2.IsEnabled(LogLevel.Information));
+                Assert.False(logger2.IsEnabled(LogLevel.Debug));
+                Assert.False(logger2.IsEnabled(LogLevel.Trace));
+
+                Assert.False(logger3.IsEnabled(LogLevel.None));
+                Assert.True(logger3.IsEnabled(LogLevel.Critical));
+                Assert.True(logger3.IsEnabled(LogLevel.Error));
+                Assert.True(logger3.IsEnabled(LogLevel.Warning));
+                Assert.True(logger3.IsEnabled(LogLevel.Information));
+                Assert.True(logger3.IsEnabled(LogLevel.Debug));
+                Assert.False(logger3.IsEnabled(LogLevel.Trace));
+
+                Assert.False(logger4.IsEnabled(LogLevel.None));
+                Assert.True(logger4.IsEnabled(LogLevel.Critical));
+                Assert.True(logger4.IsEnabled(LogLevel.Error));
+                Assert.False(logger4.IsEnabled(LogLevel.Warning));
+                Assert.False(logger4.IsEnabled(LogLevel.Information));
+                Assert.False(logger4.IsEnabled(LogLevel.Debug));
+                Assert.False(logger4.IsEnabled(LogLevel.Trace));
+            }
+        }
+
+        [Theory]
+        [InlineData("")]
+        [InlineData("UseAppFilters_StartsThisWay:Debug;")]
+        public void FilterSpecs_IncreaseLoggingLevelForOneCategory_DisablesExistingRulesByDefault(string prefix)
+        {
+            using (var testListener = new TestEventListener())
+            {
+                var loggerFactory = LoggerFactory.Create(builder =>
+                    builder
+                        .AddEventSourceLogger()
+                        .AddFilter("Logger1*", LogLevel.Warning)
+                        .AddFilter("Logger2*", LogLevel.Error)
+                        .AddFilter("Logger3*", LogLevel.Critical)
+                        .AddFilter<EventSourceLoggerProvider>("Logger4*", LogLevel.Error)
+                );
+
+                var listenerSettings = new TestEventListener.ListenerSettings();
+                listenerSettings.FilterSpec = prefix + "Logger3:1";
+                testListener.EnableEvents(listenerSettings);
+
+                var logger = loggerFactory.CreateLogger("Logger1");
+                var logger2 = loggerFactory.CreateLogger("Logger2");
+                var logger3 = loggerFactory.CreateLogger("Logger3");
+                var logger4 = loggerFactory.CreateLogger("Logger4");
+                
+                foreach (LogLevel level in Enum.GetValues(typeof(LogLevel)))
+                {
+                    Assert.False(logger.IsEnabled(LogLevel.None));
+                    Assert.False(logger2.IsEnabled(LogLevel.None));
+                }
+
+                Assert.False(logger3.IsEnabled(LogLevel.None));
+                Assert.True(logger3.IsEnabled(LogLevel.Critical));
+                Assert.True(logger3.IsEnabled(LogLevel.Error));
+                Assert.True(logger3.IsEnabled(LogLevel.Warning));
+                Assert.True(logger3.IsEnabled(LogLevel.Information));
+                Assert.True(logger3.IsEnabled(LogLevel.Debug));
+                Assert.False(logger3.IsEnabled(LogLevel.Trace));
+
+                // Note: default disabling rule does not take precedence on filter rules that specify both a provider and a category
+                Assert.False(logger4.IsEnabled(LogLevel.None));
+                Assert.True(logger4.IsEnabled(LogLevel.Critical));
+                Assert.True(logger4.IsEnabled(LogLevel.Error));
+                Assert.False(logger4.IsEnabled(LogLevel.Warning));
+                Assert.False(logger4.IsEnabled(LogLevel.Information));
+                Assert.False(logger4.IsEnabled(LogLevel.Debug));
+                Assert.False(logger4.IsEnabled(LogLevel.Trace));
+            }
+        }
+
         [Fact]
         public void Logs_AsExpected_WithDefaults()
         {
diff --git a/src/libraries/Microsoft.Extensions.Logging.EventSource/tests/Microsoft.Extensions.Logging.EventSource.Tests.csproj b/src/libraries/Microsoft.Extensions.Logging.EventSource/tests/Microsoft.Extensions.Logging.EventSource.Tests.csproj
index 4fa230c5669f79..ba8087956f5de1 100644
--- a/src/libraries/Microsoft.Extensions.Logging.EventSource/tests/Microsoft.Extensions.Logging.EventSource.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.EventSource/tests/Microsoft.Extensions.Logging.EventSource.Tests.csproj
@@ -1,12 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Logging.EventSource" />
     <PackageReference Include="Newtonsoft.Json" Version="$(NewtonsoftJsonVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Logging.EventSource.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
+
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.TraceSource/ref/Microsoft.Extensions.Logging.TraceSource.csproj b/src/libraries/Microsoft.Extensions.Logging.TraceSource/ref/Microsoft.Extensions.Logging.TraceSource.csproj
index eaa0a981e27ee7..35d85582fedfd7 100644
--- a/src/libraries/Microsoft.Extensions.Logging.TraceSource/ref/Microsoft.Extensions.Logging.TraceSource.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.TraceSource/ref/Microsoft.Extensions.Logging.TraceSource.csproj
@@ -1,10 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Logging.TraceSource.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\ref\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging.TraceSource/src/Microsoft.Extensions.Logging.TraceSource.csproj b/src/libraries/Microsoft.Extensions.Logging.TraceSource/src/Microsoft.Extensions.Logging.TraceSource.csproj
index ca883dd4c7dd0c..89bb3fe1b9e786 100644
--- a/src/libraries/Microsoft.Extensions.Logging.TraceSource/src/Microsoft.Extensions.Logging.TraceSource.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging.TraceSource/src/Microsoft.Extensions.Logging.TraceSource.csproj
@@ -1,27 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Collections.Concurrent" />
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.Diagnostics.TraceSource" />
-    <Reference Include="System.Runtime" />
-  </ItemGroup>
-
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\src\Microsoft.Extensions.Logging.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging/ref/Microsoft.Extensions.Logging.cs b/src/libraries/Microsoft.Extensions.Logging/ref/Microsoft.Extensions.Logging.cs
index d192fa99a48410..fafdc5319da6b6 100644
--- a/src/libraries/Microsoft.Extensions.Logging/ref/Microsoft.Extensions.Logging.cs
+++ b/src/libraries/Microsoft.Extensions.Logging/ref/Microsoft.Extensions.Logging.cs
@@ -14,6 +14,16 @@ public static partial class LoggingServiceCollectionExtensions
 }
 namespace Microsoft.Extensions.Logging
 {
+    [System.FlagsAttribute]
+    public enum ActivityTrackingOptions
+    {
+        None = 0,
+        SpanId = 1,
+        TraceId = 2,
+        ParentId = 4,
+        TraceState = 8,
+        TraceFlags = 16,
+    }
     public static partial class FilterLoggingBuilderExtensions
     {
         public static Microsoft.Extensions.Logging.ILoggingBuilder AddFilter(this Microsoft.Extensions.Logging.ILoggingBuilder builder, System.Func<Microsoft.Extensions.Logging.LogLevel, bool> levelFilter) { throw null; }
@@ -39,21 +49,6 @@ public partial interface ILoggingBuilder
     {
         Microsoft.Extensions.DependencyInjection.IServiceCollection Services { get; }
     }
-    [System.Flags]
-    public enum ActivityTrackingOptions
-    {
-        None        = 0x0000,
-        SpanId      = 0x0001,
-        TraceId     = 0x0002,
-        ParentId    = 0x0004,
-        TraceState  = 0x0008,
-        TraceFlags  = 0x0010
-    }
-    public class LoggerFactoryOptions
-    {
-        public LoggerFactoryOptions() { }
-        public ActivityTrackingOptions ActivityTrackingOptions { get {throw null; } set { throw null; } }
-    }
     public partial class LoggerFactory : Microsoft.Extensions.Logging.ILoggerFactory, System.IDisposable
     {
         public LoggerFactory() { }
@@ -67,6 +62,11 @@ public void AddProvider(Microsoft.Extensions.Logging.ILoggerProvider provider) {
         public Microsoft.Extensions.Logging.ILogger CreateLogger(string categoryName) { throw null; }
         public void Dispose() { }
     }
+    public partial class LoggerFactoryOptions
+    {
+        public LoggerFactoryOptions() { }
+        public Microsoft.Extensions.Logging.ActivityTrackingOptions ActivityTrackingOptions { get { throw null; } set { } }
+    }
     public partial class LoggerFilterOptions
     {
         public LoggerFilterOptions() { }
@@ -87,8 +87,8 @@ public static partial class LoggingBuilderExtensions
     {
         public static Microsoft.Extensions.Logging.ILoggingBuilder AddProvider(this Microsoft.Extensions.Logging.ILoggingBuilder builder, Microsoft.Extensions.Logging.ILoggerProvider provider) { throw null; }
         public static Microsoft.Extensions.Logging.ILoggingBuilder ClearProviders(this Microsoft.Extensions.Logging.ILoggingBuilder builder) { throw null; }
-        public static Microsoft.Extensions.Logging.ILoggingBuilder SetMinimumLevel(this Microsoft.Extensions.Logging.ILoggingBuilder builder, Microsoft.Extensions.Logging.LogLevel level) { throw null; }
         public static Microsoft.Extensions.Logging.ILoggingBuilder Configure(this Microsoft.Extensions.Logging.ILoggingBuilder builder, System.Action<Microsoft.Extensions.Logging.LoggerFactoryOptions> action) { throw null; }
+        public static Microsoft.Extensions.Logging.ILoggingBuilder SetMinimumLevel(this Microsoft.Extensions.Logging.ILoggingBuilder builder, Microsoft.Extensions.Logging.LogLevel level) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class, AllowMultiple=false, Inherited=false)]
     public partial class ProviderAliasAttribute : System.Attribute
diff --git a/src/libraries/Microsoft.Extensions.Logging/ref/Microsoft.Extensions.Logging.csproj b/src/libraries/Microsoft.Extensions.Logging/ref/Microsoft.Extensions.Logging.csproj
index c79d0fdc6128e4..745210c3658269 100644
--- a/src/libraries/Microsoft.Extensions.Logging/ref/Microsoft.Extensions.Logging.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging/ref/Microsoft.Extensions.Logging.csproj
@@ -1,11 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Logging.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\ref\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging/src/Microsoft.Extensions.Logging.csproj b/src/libraries/Microsoft.Extensions.Logging/src/Microsoft.Extensions.Logging.csproj
index 5d4787254c6b8b..49781fe7a45053 100644
--- a/src/libraries/Microsoft.Extensions.Logging/src/Microsoft.Extensions.Logging.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging/src/Microsoft.Extensions.Logging.csproj
@@ -1,9 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.1;netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
+    <!-- Use targeting pack references instead of granular ones in the project file. -->
+    <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>
   </PropertyGroup>
 
   <ItemGroup>
@@ -15,34 +16,21 @@
              Link="Common\src\Extensions\Logging\NullScope.cs" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Threading" />
-  </ItemGroup>
-
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.DependencyInjection" />
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Options" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Diagnostics.DiagnosticSource\src\System.Diagnostics.DiagnosticSource.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' OR $(TargetFramework.StartsWith('net4'))">
-    <Reference Include="Microsoft.Bcl.AsyncInterfaces" />
-  </ItemGroup>
-
-  <ItemGroup>
-    <Reference Include="System.Diagnostics.DiagnosticSource" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Bcl.AsyncInterfaces\src\Microsoft.Bcl.AsyncInterfaces.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.ValueTuple" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging/tests/Common/LoggerFactoryTest.cs b/src/libraries/Microsoft.Extensions.Logging/tests/Common/LoggerFactoryTest.cs
index 8e81ba231909c7..c124f36eaa24c6 100644
--- a/src/libraries/Microsoft.Extensions.Logging/tests/Common/LoggerFactoryTest.cs
+++ b/src/libraries/Microsoft.Extensions.Logging/tests/Common/LoggerFactoryTest.cs
@@ -198,7 +198,6 @@ public void TestActivityIds(ActivityTrackingOptions options)
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38337", TestPlatforms.Browser)]
         public void TestInvalidActivityTrackingOptions()
         {
             Assert.Throws<ArgumentException>(() =>
diff --git a/src/libraries/Microsoft.Extensions.Logging/tests/Common/Microsoft.Extensions.Logging.Tests.csproj b/src/libraries/Microsoft.Extensions.Logging/tests/Common/Microsoft.Extensions.Logging.Tests.csproj
index cec257df2ecaa6..83ceb2b247352b 100644
--- a/src/libraries/Microsoft.Extensions.Logging/tests/Common/Microsoft.Extensions.Logging.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging/tests/Common/Microsoft.Extensions.Logging.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
@@ -18,10 +18,21 @@
              Link="tests\DI.Common\Common\src\TestLogger.cs" />
     <Compile Include="..\DI.Common\Common\src\TestLoggerFactory.cs"
              Link="tests\DI.Common\Common\src\TestLoggerFactory.cs" />
+  </ItemGroup>
+
+  <ItemGroup>
     <PackageReference Include="Moq" Version="$(MoqVersion)" />
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Logging.Abstractions" />
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Logging.Console" />
-    <ReferenceFromRuntime Include="Microsoft.Extensions.Logging.EventLog" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Abstractions\src\Microsoft.Extensions.Logging.Abstractions.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Console\src\Microsoft.Extensions.Logging.Console.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.EventLog\src\Microsoft.Extensions.Logging.EventLog.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Json\src\Microsoft.Extensions.Configuration.Json.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.Debug\src\Microsoft.Extensions.Logging.Debug.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging.TraceSource\src\Microsoft.Extensions.Logging.TraceSource.csproj" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Diagnostics.DiagnosticSource\src\System.Diagnostics.DiagnosticSource.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Logging/tests/Common/TraceSourceLoggerProviderTest.cs b/src/libraries/Microsoft.Extensions.Logging/tests/Common/TraceSourceLoggerProviderTest.cs
index b67ef0e79346b1..80d9e7ab1909a0 100644
--- a/src/libraries/Microsoft.Extensions.Logging/tests/Common/TraceSourceLoggerProviderTest.cs
+++ b/src/libraries/Microsoft.Extensions.Logging/tests/Common/TraceSourceLoggerProviderTest.cs
@@ -1,7 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#if NET472
+#if NETFRAMEWORK
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
diff --git a/src/libraries/Microsoft.Extensions.Logging/tests/Common/TraceSourceScopeTest.cs b/src/libraries/Microsoft.Extensions.Logging/tests/Common/TraceSourceScopeTest.cs
index 6f9255dce6e385..25bd315a8679b0 100644
--- a/src/libraries/Microsoft.Extensions.Logging/tests/Common/TraceSourceScopeTest.cs
+++ b/src/libraries/Microsoft.Extensions.Logging/tests/Common/TraceSourceScopeTest.cs
@@ -8,7 +8,7 @@ namespace Microsoft.Extensions.Logging.Test
 {
     public class TraceSourceScopeTest
     {
-#if NET472
+#if NETFRAMEWORK
         [Fact]
         public static void DiagnosticsScope_PushesAndPops_LogicalOperationStack()
         {
diff --git a/src/libraries/Microsoft.Extensions.Logging/tests/DI.Common/Common/tests/Microsoft.Extensions.Logging.Testing.Tests.csproj b/src/libraries/Microsoft.Extensions.Logging/tests/DI.Common/Common/tests/Microsoft.Extensions.Logging.Testing.Tests.csproj
index 420524704ece84..c729cbe733115d 100644
--- a/src/libraries/Microsoft.Extensions.Logging/tests/DI.Common/Common/tests/Microsoft.Extensions.Logging.Testing.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Logging/tests/DI.Common/Common/tests/Microsoft.Extensions.Logging.Testing.Tests.csproj
@@ -1,12 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Compile Include="..\..\..\..\..\Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\ShortClassNameAttribute.cs"
-             Link="Common\tests\Extensions\TestingUtils\Microsoft.AspNetCore.Testing\src\ShortClassNameAttribute.cs" />
     <Compile Include="..\src\LogLevelAttribute.cs"
              Link="tests\DI.Common\Common\src\LogLevelAttribute.cs" />
     <Compile Include="..\src\LogValuesAssert.cs"
@@ -18,4 +16,9 @@
     <Compile Include="..\src\XunitLoggerProvider.cs"
              Link="tests\DI.Common\Common\src\XunitLoggerProvider.cs" />
   </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Logging\src\Microsoft.Extensions.Logging.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/Microsoft.Extensions.Options.ConfigurationExtensions.sln b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/Microsoft.Extensions.Options.ConfigurationExtensions.sln
index 7628543f319ac0..4782d11b90add0 100644
--- a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/Microsoft.Extensions.Options.ConfigurationExtensions.sln
+++ b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/Microsoft.Extensions.Options.ConfigurationExtensions.sln
@@ -11,6 +11,18 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Option
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Options.ConfigurationExtensions", "src\Microsoft.Extensions.Options.ConfigurationExtensions.csproj", "{D4C213E7-336F-4601-9F92-1D632D082422}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{4CB60D51-6D36-49DB-A3AC-B45664F39EFC}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Options.ConfigurationExtensions.Tests", "tests\Microsoft.Extensions.Options.ConfigurationExtensions.Tests.csproj", "{5F41C8C2-663D-4D57-9211-2F495D7DFACE}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TestUtilities", "..\Common\tests\TestUtilities\TestUtilities.csproj", "{3EFE3DA9-F864-40A3-8892-899D731CC027}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.DependencyInjection", "..\Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj", "{D8AC9F6D-95FA-4377-A867-FF75683393AA}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Configuration", "..\Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj", "{1F88377A-7C91-466E-9351-1B0AE0DF78AB}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Options", "..\Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj", "{D53344C9-58C5-4A2B-8182-74A48763A8FE}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -25,6 +37,26 @@ Global
 		{D4C213E7-336F-4601-9F92-1D632D082422}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{D4C213E7-336F-4601-9F92-1D632D082422}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{D4C213E7-336F-4601-9F92-1D632D082422}.Release|Any CPU.Build.0 = Release|Any CPU
+		{5F41C8C2-663D-4D57-9211-2F495D7DFACE}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{5F41C8C2-663D-4D57-9211-2F495D7DFACE}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{5F41C8C2-663D-4D57-9211-2F495D7DFACE}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{5F41C8C2-663D-4D57-9211-2F495D7DFACE}.Release|Any CPU.Build.0 = Release|Any CPU
+		{3EFE3DA9-F864-40A3-8892-899D731CC027}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{3EFE3DA9-F864-40A3-8892-899D731CC027}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{3EFE3DA9-F864-40A3-8892-899D731CC027}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{3EFE3DA9-F864-40A3-8892-899D731CC027}.Release|Any CPU.Build.0 = Release|Any CPU
+		{D8AC9F6D-95FA-4377-A867-FF75683393AA}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D8AC9F6D-95FA-4377-A867-FF75683393AA}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D8AC9F6D-95FA-4377-A867-FF75683393AA}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{D8AC9F6D-95FA-4377-A867-FF75683393AA}.Release|Any CPU.Build.0 = Release|Any CPU
+		{1F88377A-7C91-466E-9351-1B0AE0DF78AB}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{1F88377A-7C91-466E-9351-1B0AE0DF78AB}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{1F88377A-7C91-466E-9351-1B0AE0DF78AB}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{1F88377A-7C91-466E-9351-1B0AE0DF78AB}.Release|Any CPU.Build.0 = Release|Any CPU
+		{D53344C9-58C5-4A2B-8182-74A48763A8FE}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D53344C9-58C5-4A2B-8182-74A48763A8FE}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D53344C9-58C5-4A2B-8182-74A48763A8FE}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{D53344C9-58C5-4A2B-8182-74A48763A8FE}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -32,6 +64,11 @@ Global
 	GlobalSection(NestedProjects) = preSolution
 		{F0815ADD-0115-4368-886E-2135355BC439} = {9EDF28B3-F998-47FE-B23A-753205641B49}
 		{D4C213E7-336F-4601-9F92-1D632D082422} = {BF3EE9AA-4B66-4410-B1D2-3971169F1E40}
+		{5F41C8C2-663D-4D57-9211-2F495D7DFACE} = {4CB60D51-6D36-49DB-A3AC-B45664F39EFC}
+		{3EFE3DA9-F864-40A3-8892-899D731CC027} = {4CB60D51-6D36-49DB-A3AC-B45664F39EFC}
+		{D8AC9F6D-95FA-4377-A867-FF75683393AA} = {4CB60D51-6D36-49DB-A3AC-B45664F39EFC}
+		{1F88377A-7C91-466E-9351-1B0AE0DF78AB} = {4CB60D51-6D36-49DB-A3AC-B45664F39EFC}
+		{D53344C9-58C5-4A2B-8182-74A48763A8FE} = {4CB60D51-6D36-49DB-A3AC-B45664F39EFC}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {0414F2BB-333F-487E-92AE-530AA983499B}
diff --git a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/ref/Microsoft.Extensions.Options.ConfigurationExtensions.cs b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/ref/Microsoft.Extensions.Options.ConfigurationExtensions.cs
index 938fb6c1bb8556..43e04c4327d585 100644
--- a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/ref/Microsoft.Extensions.Options.ConfigurationExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/ref/Microsoft.Extensions.Options.ConfigurationExtensions.cs
@@ -8,6 +8,7 @@ namespace Microsoft.Extensions.DependencyInjection
 {
     public static partial class OptionsBuilderConfigurationExtensions
     {
+        public static Microsoft.Extensions.Options.OptionsBuilder<TOptions> BindConfiguration<TOptions>(this Microsoft.Extensions.Options.OptionsBuilder<TOptions> optionsBuilder, string configSectionPath, System.Action<Microsoft.Extensions.Configuration.BinderOptions> configureBinder = null) where TOptions : class { throw null; }
         public static Microsoft.Extensions.Options.OptionsBuilder<TOptions> Bind<TOptions>(this Microsoft.Extensions.Options.OptionsBuilder<TOptions> optionsBuilder, Microsoft.Extensions.Configuration.IConfiguration config) where TOptions : class { throw null; }
         public static Microsoft.Extensions.Options.OptionsBuilder<TOptions> Bind<TOptions>(this Microsoft.Extensions.Options.OptionsBuilder<TOptions> optionsBuilder, Microsoft.Extensions.Configuration.IConfiguration config, System.Action<Microsoft.Extensions.Configuration.BinderOptions> configureBinder) where TOptions : class { throw null; }
     }
diff --git a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/ref/Microsoft.Extensions.Options.ConfigurationExtensions.csproj b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/ref/Microsoft.Extensions.Options.ConfigurationExtensions.csproj
index be66538ec516b3..b28dde039c486c 100644
--- a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/ref/Microsoft.Extensions.Options.ConfigurationExtensions.csproj
+++ b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/ref/Microsoft.Extensions.Options.ConfigurationExtensions.csproj
@@ -1,13 +1,15 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Options.ConfigurationExtensions.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Configuration.Binder\ref\Microsoft.Extensions.Configuration.Binder.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\ref\Microsoft.Extensions.Configuration.Binder.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/src/Microsoft.Extensions.Options.ConfigurationExtensions.csproj b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/src/Microsoft.Extensions.Options.ConfigurationExtensions.csproj
index 3d9e3c322e9697..5a43205e7f0c53 100644
--- a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/src/Microsoft.Extensions.Options.ConfigurationExtensions.csproj
+++ b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/src/Microsoft.Extensions.Options.ConfigurationExtensions.csproj
@@ -1,26 +1,16 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.Configuration.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Configuration.Binder" />
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Options" />
-    <Reference Include="Microsoft.Extensions.Primitives" />
-  </ItemGroup>
-
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.Runtime" />
-  </ItemGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Binder\src\Microsoft.Extensions.Configuration.Binder.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/src/OptionsBuilderConfigurationExtensions.cs b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/src/OptionsBuilderConfigurationExtensions.cs
index e1f642676c498b..a102c2b49da4e2 100644
--- a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/src/OptionsBuilderConfigurationExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/src/OptionsBuilderConfigurationExtensions.cs
@@ -40,5 +40,37 @@ public static OptionsBuilder<TOptions> Bind<TOptions>(this OptionsBuilder<TOptio
             optionsBuilder.Services.Configure<TOptions>(optionsBuilder.Name, config, configureBinder);
             return optionsBuilder;
         }
+
+        /// <summary>
+        /// Registers the dependency injection container to bind <typeparamref name="TOptions"/> against
+        /// the <see cref="IConfiguration"/> obtained from the DI service provider.
+        /// </summary>
+        /// <typeparam name="TOptions">The options type to be configured.</typeparam>
+        /// <param name="optionsBuilder">The options builder to add the services to.</param>
+        /// <param name="configSectionPath">The name of the configuration section to bind from.</param>
+        /// <param name="configureBinder">Optional. Used to configure the <see cref="BinderOptions"/>.</param>
+        /// <returns>The <see cref="OptionsBuilder{TOptions}"/> so that additional calls can be chained.</returns>
+        /// <exception cref="ArgumentNullException">
+        /// <paramref name="optionsBuilder"/> or <paramref name="configSectionPath" /> is <see langword="null"/>.
+        /// </exception>
+        /// <seealso cref="Bind{TOptions}(OptionsBuilder{TOptions}, IConfiguration, Action{BinderOptions})"/>
+        public static OptionsBuilder<TOptions> BindConfiguration<TOptions>(
+            this OptionsBuilder<TOptions> optionsBuilder,
+            string configSectionPath,
+            Action<BinderOptions> configureBinder = null)
+            where TOptions : class
+        {
+            _ = optionsBuilder ?? throw new ArgumentNullException(nameof(optionsBuilder));
+            _ = configSectionPath ?? throw new ArgumentNullException(nameof(configSectionPath));
+
+            optionsBuilder.Configure<IConfiguration>((opts, config) =>
+            {
+                IConfiguration section = string.Equals("", configSectionPath, StringComparison.OrdinalIgnoreCase)
+                    ? config
+                    : config.GetSection(configSectionPath);
+                section.Bind(opts, configureBinder);
+            });
+            return optionsBuilder;
+        }
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/FakeOptions.cs b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/FakeOptions.cs
new file mode 100644
index 00000000000000..5a1b3d6144276b
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/FakeOptions.cs
@@ -0,0 +1,7 @@
+namespace Microsoft.Extensions.Options.ConfigurationExtensions.Tests
+{
+    public class FakeOptions
+    {
+        public string? Message { get; set; }
+    }
+}
diff --git a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/Microsoft.Extensions.Options.ConfigurationExtensions.Tests.csproj b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/Microsoft.Extensions.Options.ConfigurationExtensions.Tests.csproj
new file mode 100644
index 00000000000000..91a11d65d3b1af
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/Microsoft.Extensions.Options.ConfigurationExtensions.Tests.csproj
@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <Nullable>enable</Nullable>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
+    <EnableDefaultItems>true</EnableDefaultItems>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj"/>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj"/>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj"/>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\src\Microsoft.Extensions.Options.ConfigurationExtensions.csproj" SkipUseReferenceAssembly="true" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/OptionsBuidlerConfigurationExtensionsTests.cs b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/OptionsBuidlerConfigurationExtensionsTests.cs
new file mode 100644
index 00000000000000..2aa44c5fcd23ef
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/OptionsBuidlerConfigurationExtensionsTests.cs
@@ -0,0 +1,106 @@
+using System;
+using System.Collections.Generic;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+
+namespace Microsoft.Extensions.Options.ConfigurationExtensions.Tests
+{
+    public class OptionsBuidlerConfigurationExtensionsTests
+    {
+        [Fact]
+        public static void BindConfiguration_ThrowsForNullBuilder()
+        {
+            OptionsBuilder<FakeOptions> optionsBuilder = null!;
+
+            Assert.Throws<ArgumentNullException>("optionsBuilder", () =>
+            {
+                optionsBuilder.BindConfiguration("test");
+            });
+        }
+
+        [Fact]
+        public static void BindConfiguration_ThrowsForNullConfigurationSectionPath()
+        {
+            var services = new ServiceCollection();
+            var optionsBuilder = new OptionsBuilder<FakeOptions>(services, Options.DefaultName);
+            string configSectionPath = null!;
+
+            Assert.Throws<ArgumentNullException>("configSectionPath", () =>
+            {
+                optionsBuilder.BindConfiguration(configSectionPath);
+            });
+        }
+
+        [Fact]
+        public static void BindConfiguration_ReturnsSameBuilderInstance()
+        {
+            var services = new ServiceCollection();
+            var optionsBuilder = new OptionsBuilder<FakeOptions>(services, Options.DefaultName);
+
+            var returnedBuilder = optionsBuilder.BindConfiguration("Test");
+
+            Assert.Same(optionsBuilder, returnedBuilder);
+        }
+
+        [Fact]
+        public static void BindConfiguration_OptionsMaterializationThrowsIfNoConfigurationInDI()
+        {
+            var services = new ServiceCollection();
+            var optionsBuilder = services.AddOptions<FakeOptions>();
+
+            _ = optionsBuilder.BindConfiguration("Test");
+            using ServiceProvider serviceProvider = services.BuildServiceProvider();
+
+            Assert.ThrowsAny<InvalidOperationException>(() =>
+            {
+                _ = serviceProvider.GetRequiredService<IOptions<FakeOptions>>();
+            });
+        }
+
+        [Fact]
+        public static void BindConfiguration_UsesConfigurationSectionPath()
+        {
+            const string configSectionName = "Test";
+            const string messageValue = "This is a test";
+            var configEntries = new Dictionary<string, string>
+            {
+                [ConfigurationPath.Combine(configSectionName, nameof(FakeOptions.Message))] = messageValue
+            };
+            var services = new ServiceCollection();
+            services.AddSingleton<IConfiguration>(new ConfigurationBuilder()
+                .AddInMemoryCollection(configEntries)
+                .Build());
+            var optionsBuilder = services.AddOptions<FakeOptions>();
+
+            _ = optionsBuilder.BindConfiguration(configSectionName);
+
+            using ServiceProvider serviceProvider = services.BuildServiceProvider();
+            var options = serviceProvider.GetRequiredService<IOptions<FakeOptions>>().Value;
+
+            Assert.Equal(messageValue, options.Message);
+        }
+
+        [Fact]
+        public static void BindConfiguration_UsesConfigurationRootIfSectionNameIsEmptyString()
+        {
+            const string messageValue = "This is a test";
+            var configEntries = new Dictionary<string, string>
+            {
+                [nameof(FakeOptions.Message)] = messageValue
+            };
+            var services = new ServiceCollection();
+            services.AddSingleton<IConfiguration>(new ConfigurationBuilder()
+                .AddInMemoryCollection(configEntries)
+                .Build());
+            var optionsBuilder = services.AddOptions<FakeOptions>();
+
+            _ = optionsBuilder.BindConfiguration(configSectionPath: "");
+
+            using ServiceProvider serviceProvider = services.BuildServiceProvider();
+            var options = serviceProvider.GetRequiredService<IOptions<FakeOptions>>().Value;
+
+            Assert.Equal(messageValue, options.Message);
+        }
+    }
+}
diff --git a/src/libraries/Microsoft.Extensions.Options.DataAnnotations/ref/Microsoft.Extensions.Options.DataAnnotations.csproj b/src/libraries/Microsoft.Extensions.Options.DataAnnotations/ref/Microsoft.Extensions.Options.DataAnnotations.csproj
index b8dd59bff6fe78..c7fe04287c373d 100644
--- a/src/libraries/Microsoft.Extensions.Options.DataAnnotations/ref/Microsoft.Extensions.Options.DataAnnotations.csproj
+++ b/src/libraries/Microsoft.Extensions.Options.DataAnnotations/ref/Microsoft.Extensions.Options.DataAnnotations.csproj
@@ -1,10 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Options.DataAnnotations.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\ref\Microsoft.Extensions.Options.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Options.DataAnnotations/src/Microsoft.Extensions.Options.DataAnnotations.csproj b/src/libraries/Microsoft.Extensions.Options.DataAnnotations/src/Microsoft.Extensions.Options.DataAnnotations.csproj
index 9adaadcc69d57e..bcf5ce56123e9b 100644
--- a/src/libraries/Microsoft.Extensions.Options.DataAnnotations/src/Microsoft.Extensions.Options.DataAnnotations.csproj
+++ b/src/libraries/Microsoft.Extensions.Options.DataAnnotations/src/Microsoft.Extensions.Options.DataAnnotations.csproj
@@ -1,28 +1,24 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.1;netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Options" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options\src\Microsoft.Extensions.Options.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Reference Include="System.ComponentModel.Annotations" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <PackageReference Include="System.ComponentModel.Annotations" Version="$(SystemComponentModelAnnotationsVersion)" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.Runtime" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.1'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.ComponentModel.Annotations\src\System.ComponentModel.Annotations.csproj" />
   </ItemGroup>
 
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
     <Reference Include="System.ComponentModel.DataAnnotations" />
   </ItemGroup>
 
diff --git a/src/libraries/Microsoft.Extensions.Options/Microsoft.Extensions.Options.sln b/src/libraries/Microsoft.Extensions.Options/Microsoft.Extensions.Options.sln
index b67b0a590f1f11..569f822cf139d6 100644
--- a/src/libraries/Microsoft.Extensions.Options/Microsoft.Extensions.Options.sln
+++ b/src/libraries/Microsoft.Extensions.Options/Microsoft.Extensions.Options.sln
@@ -13,9 +13,9 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Option
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Options", "src\Microsoft.Extensions.Options.csproj", "{0ACF563C-7E53-469A-A61D-B93916DED810}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Options.Tests", "tests\Microsoft.Extensions.Options.Tests.csproj", "{77771F73-3122-49BD-85D8-6D880B9902F3}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TestUtilities", "..\Common\tests\TestUtilities\TestUtilities.csproj", "{A5C2304B-0A92-427A-BD01-C7927EFA8B78}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestUtilities", "..\Common\tests\TestUtilities\TestUtilities.csproj", "{A5C2304B-0A92-427A-BD01-C7927EFA8B78}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Options.Tests", "tests\Microsoft.Extensions.Options.Tests\Microsoft.Extensions.Options.Tests.csproj", "{0905577D-D2A0-4EF1-848B-8A99F12BE3D0}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -31,14 +31,14 @@ Global
 		{0ACF563C-7E53-469A-A61D-B93916DED810}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{0ACF563C-7E53-469A-A61D-B93916DED810}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{0ACF563C-7E53-469A-A61D-B93916DED810}.Release|Any CPU.Build.0 = Release|Any CPU
-		{77771F73-3122-49BD-85D8-6D880B9902F3}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{77771F73-3122-49BD-85D8-6D880B9902F3}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{77771F73-3122-49BD-85D8-6D880B9902F3}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{77771F73-3122-49BD-85D8-6D880B9902F3}.Release|Any CPU.Build.0 = Release|Any CPU
 		{A5C2304B-0A92-427A-BD01-C7927EFA8B78}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{A5C2304B-0A92-427A-BD01-C7927EFA8B78}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{A5C2304B-0A92-427A-BD01-C7927EFA8B78}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{A5C2304B-0A92-427A-BD01-C7927EFA8B78}.Release|Any CPU.Build.0 = Release|Any CPU
+		{0905577D-D2A0-4EF1-848B-8A99F12BE3D0}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{0905577D-D2A0-4EF1-848B-8A99F12BE3D0}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{0905577D-D2A0-4EF1-848B-8A99F12BE3D0}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{0905577D-D2A0-4EF1-848B-8A99F12BE3D0}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -46,8 +46,8 @@ Global
 	GlobalSection(NestedProjects) = preSolution
 		{9F96CC5A-969C-47FA-81DB-7093598A226F} = {5827CC1E-1A61-4799-96B4-AB1052346A52}
 		{0ACF563C-7E53-469A-A61D-B93916DED810} = {9205B11D-A45B-4F2C-BF37-8C5F26FCBDB7}
-		{77771F73-3122-49BD-85D8-6D880B9902F3} = {CAB34510-96B9-422E-904F-C03476004E13}
 		{A5C2304B-0A92-427A-BD01-C7927EFA8B78} = {CAB34510-96B9-422E-904F-C03476004E13}
+		{0905577D-D2A0-4EF1-848B-8A99F12BE3D0} = {CAB34510-96B9-422E-904F-C03476004E13}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {5DE09ECD-4E45-4B08-B44A-327EF5203D1B}
diff --git a/src/libraries/Microsoft.Extensions.Options/ref/Microsoft.Extensions.Options.cs b/src/libraries/Microsoft.Extensions.Options/ref/Microsoft.Extensions.Options.cs
index 32f254eff792eb..d0b8af0aec10d1 100644
--- a/src/libraries/Microsoft.Extensions.Options/ref/Microsoft.Extensions.Options.cs
+++ b/src/libraries/Microsoft.Extensions.Options/ref/Microsoft.Extensions.Options.cs
@@ -13,8 +13,8 @@ public static partial class OptionsServiceCollectionExtensions
         public static Microsoft.Extensions.Options.OptionsBuilder<TOptions> AddOptions<TOptions>(this Microsoft.Extensions.DependencyInjection.IServiceCollection services, string name) where TOptions : class { throw null; }
         public static Microsoft.Extensions.DependencyInjection.IServiceCollection ConfigureAll<TOptions>(this Microsoft.Extensions.DependencyInjection.IServiceCollection services, System.Action<TOptions> configureOptions) where TOptions : class { throw null; }
         public static Microsoft.Extensions.DependencyInjection.IServiceCollection ConfigureOptions(this Microsoft.Extensions.DependencyInjection.IServiceCollection services, object configureInstance) { throw null; }
-        public static Microsoft.Extensions.DependencyInjection.IServiceCollection ConfigureOptions(this Microsoft.Extensions.DependencyInjection.IServiceCollection services, System.Type configureType) { throw null; }
-        public static Microsoft.Extensions.DependencyInjection.IServiceCollection ConfigureOptions<TConfigureOptions>(this Microsoft.Extensions.DependencyInjection.IServiceCollection services) where TConfigureOptions : class { throw null; }
+        public static Microsoft.Extensions.DependencyInjection.IServiceCollection ConfigureOptions(this Microsoft.Extensions.DependencyInjection.IServiceCollection services, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors)] System.Type configureType) { throw null; }
+        public static Microsoft.Extensions.DependencyInjection.IServiceCollection ConfigureOptions<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] TConfigureOptions>(this Microsoft.Extensions.DependencyInjection.IServiceCollection services) where TConfigureOptions : class { throw null; }
         public static Microsoft.Extensions.DependencyInjection.IServiceCollection Configure<TOptions>(this Microsoft.Extensions.DependencyInjection.IServiceCollection services, System.Action<TOptions> configureOptions) where TOptions : class { throw null; }
         public static Microsoft.Extensions.DependencyInjection.IServiceCollection Configure<TOptions>(this Microsoft.Extensions.DependencyInjection.IServiceCollection services, string name, System.Action<TOptions> configureOptions) where TOptions : class { throw null; }
         public static Microsoft.Extensions.DependencyInjection.IServiceCollection PostConfigureAll<TOptions>(this Microsoft.Extensions.DependencyInjection.IServiceCollection services, System.Action<TOptions> configureOptions) where TOptions : class { throw null; }
@@ -106,28 +106,28 @@ public partial interface IOptionsChangeTokenSource<out TOptions>
         string Name { get; }
         Microsoft.Extensions.Primitives.IChangeToken GetChangeToken();
     }
-    public partial interface IOptionsFactory<TOptions> where TOptions : class
+    public partial interface IOptionsFactory<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions> where TOptions : class
     {
         TOptions Create(string name);
     }
-    public partial interface IOptionsMonitorCache<TOptions> where TOptions : class
+    public partial interface IOptionsMonitorCache<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions> where TOptions : class
     {
         void Clear();
         TOptions GetOrAdd(string name, System.Func<TOptions> createOptions);
         bool TryAdd(string name, TOptions options);
         bool TryRemove(string name);
     }
-    public partial interface IOptionsMonitor<out TOptions>
+    public partial interface IOptionsMonitor<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] out TOptions>
     {
         TOptions CurrentValue { get; }
         TOptions Get(string name);
         System.IDisposable OnChange(System.Action<TOptions, string> listener);
     }
-    public partial interface IOptionsSnapshot<out TOptions> : Microsoft.Extensions.Options.IOptions<TOptions> where TOptions : class
+    public partial interface IOptionsSnapshot<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] out TOptions> : Microsoft.Extensions.Options.IOptions<TOptions> where TOptions : class
     {
         TOptions Get(string name);
     }
-    public partial interface IOptions<out TOptions> where TOptions : class
+    public partial interface IOptions<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] out TOptions> where TOptions : class
     {
         TOptions Value { get; }
     }
@@ -142,7 +142,7 @@ public partial interface IValidateOptions<TOptions> where TOptions : class
     public static partial class Options
     {
         public static readonly string DefaultName;
-        public static Microsoft.Extensions.Options.IOptions<TOptions> Create<TOptions>(TOptions options) where TOptions : class { throw null; }
+        public static Microsoft.Extensions.Options.IOptions<TOptions> Create<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions>(TOptions options) where TOptions : class { throw null; }
     }
     public partial class OptionsBuilder<TOptions> where TOptions : class
     {
@@ -174,7 +174,7 @@ public OptionsBuilder(Microsoft.Extensions.DependencyInjection.IServiceCollectio
         public virtual Microsoft.Extensions.Options.OptionsBuilder<TOptions> Validate<TDep1, TDep2, TDep3, TDep4, TDep5>(System.Func<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5, bool> validation) { throw null; }
         public virtual Microsoft.Extensions.Options.OptionsBuilder<TOptions> Validate<TDep1, TDep2, TDep3, TDep4, TDep5>(System.Func<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5, bool> validation, string failureMessage) { throw null; }
     }
-    public partial class OptionsCache<TOptions> : Microsoft.Extensions.Options.IOptionsMonitorCache<TOptions> where TOptions : class
+    public partial class OptionsCache<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions> : Microsoft.Extensions.Options.IOptionsMonitorCache<TOptions> where TOptions : class
     {
         public OptionsCache() { }
         public void Clear() { }
@@ -182,14 +182,14 @@ public void Clear() { }
         public virtual bool TryAdd(string name, TOptions options) { throw null; }
         public virtual bool TryRemove(string name) { throw null; }
     }
-    public partial class OptionsFactory<TOptions> : Microsoft.Extensions.Options.IOptionsFactory<TOptions> where TOptions : class
+    public partial class OptionsFactory<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions> : Microsoft.Extensions.Options.IOptionsFactory<TOptions> where TOptions : class
     {
         public OptionsFactory(System.Collections.Generic.IEnumerable<Microsoft.Extensions.Options.IConfigureOptions<TOptions>> setups, System.Collections.Generic.IEnumerable<Microsoft.Extensions.Options.IPostConfigureOptions<TOptions>> postConfigures) { }
         public OptionsFactory(System.Collections.Generic.IEnumerable<Microsoft.Extensions.Options.IConfigureOptions<TOptions>> setups, System.Collections.Generic.IEnumerable<Microsoft.Extensions.Options.IPostConfigureOptions<TOptions>> postConfigures, System.Collections.Generic.IEnumerable<Microsoft.Extensions.Options.IValidateOptions<TOptions>> validations) { }
         public TOptions Create(string name) { throw null; }
         protected virtual TOptions CreateInstance(string name) { throw null; }
     }
-    public partial class OptionsManager<TOptions> : Microsoft.Extensions.Options.IOptions<TOptions>, Microsoft.Extensions.Options.IOptionsSnapshot<TOptions> where TOptions : class
+    public partial class OptionsManager<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions> : Microsoft.Extensions.Options.IOptions<TOptions>, Microsoft.Extensions.Options.IOptionsSnapshot<TOptions> where TOptions : class
     {
         public OptionsManager(Microsoft.Extensions.Options.IOptionsFactory<TOptions> factory) { }
         public TOptions Value { get { throw null; } }
@@ -197,9 +197,9 @@ public OptionsManager(Microsoft.Extensions.Options.IOptionsFactory<TOptions> fac
     }
     public static partial class OptionsMonitorExtensions
     {
-        public static System.IDisposable OnChange<TOptions>(this Microsoft.Extensions.Options.IOptionsMonitor<TOptions> monitor, System.Action<TOptions> listener) { throw null; }
+        public static System.IDisposable OnChange<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions>(this Microsoft.Extensions.Options.IOptionsMonitor<TOptions> monitor, System.Action<TOptions> listener) { throw null; }
     }
-    public partial class OptionsMonitor<TOptions> : Microsoft.Extensions.Options.IOptionsMonitor<TOptions>, System.IDisposable where TOptions : class
+    public partial class OptionsMonitor<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions> : Microsoft.Extensions.Options.IOptionsMonitor<TOptions>, System.IDisposable where TOptions : class
     {
         public OptionsMonitor(Microsoft.Extensions.Options.IOptionsFactory<TOptions> factory, System.Collections.Generic.IEnumerable<Microsoft.Extensions.Options.IOptionsChangeTokenSource<TOptions>> sources, Microsoft.Extensions.Options.IOptionsMonitorCache<TOptions> cache) { }
         public TOptions CurrentValue { get { throw null; } }
@@ -215,7 +215,7 @@ public OptionsValidationException(string optionsName, System.Type optionsType, S
         public string OptionsName { get { throw null; } }
         public System.Type OptionsType { get { throw null; } }
     }
-    public partial class OptionsWrapper<TOptions> : Microsoft.Extensions.Options.IOptions<TOptions> where TOptions : class
+    public partial class OptionsWrapper<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions> : Microsoft.Extensions.Options.IOptions<TOptions> where TOptions : class
     {
         public OptionsWrapper(TOptions options) { }
         public TOptions Value { get { throw null; } }
diff --git a/src/libraries/Microsoft.Extensions.Options/ref/Microsoft.Extensions.Options.csproj b/src/libraries/Microsoft.Extensions.Options/ref/Microsoft.Extensions.Options.csproj
index a119724225afd6..c441c3ec38a198 100644
--- a/src/libraries/Microsoft.Extensions.Options/ref/Microsoft.Extensions.Options.csproj
+++ b/src/libraries/Microsoft.Extensions.Options/ref/Microsoft.Extensions.Options.csproj
@@ -1,13 +1,17 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net461</TargetFrameworks>
   </PropertyGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-    <Reference Include="System.ComponentModel.Annotations" />
-  </ItemGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Options.cs" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
-    <ProjectReference Include="..\..\Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\ref\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <PackageReference Include="System.ComponentModel.Annotations" Version="$(SystemComponentModelAnnotationsVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Options/src/IOptions.cs b/src/libraries/Microsoft.Extensions.Options/src/IOptions.cs
index de08efd501d2e3..0ceca9fb0c9463 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/IOptions.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/IOptions.cs
@@ -1,13 +1,16 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace Microsoft.Extensions.Options
 {
     /// <summary>
     /// Used to retrieve configured <typeparamref name="TOptions"/> instances.
     /// </summary>
     /// <typeparam name="TOptions">The type of options being requested.</typeparam>
-    public interface IOptions<out TOptions> where TOptions : class
+    public interface IOptions<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] out TOptions>
+        where TOptions : class
     {
         /// <summary>
         /// The default configured <typeparamref name="TOptions"/> instance
diff --git a/src/libraries/Microsoft.Extensions.Options/src/IOptionsFactory.cs b/src/libraries/Microsoft.Extensions.Options/src/IOptionsFactory.cs
index e8d8a17a8476c3..82077f13cef7e5 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/IOptionsFactory.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/IOptionsFactory.cs
@@ -1,13 +1,16 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace Microsoft.Extensions.Options
 {
     /// <summary>
     /// Used to create <typeparamref name="TOptions"/> instances.
     /// </summary>
     /// <typeparam name="TOptions">The type of options being requested.</typeparam>
-    public interface IOptionsFactory<TOptions> where TOptions : class
+    public interface IOptionsFactory<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions>
+        where TOptions : class
     {
         /// <summary>
         /// Returns a configured <typeparamref name="TOptions"/> instance with the given name.
diff --git a/src/libraries/Microsoft.Extensions.Options/src/IOptionsMonitor.cs b/src/libraries/Microsoft.Extensions.Options/src/IOptionsMonitor.cs
index 9f01a495de941a..10c51cba1aac3c 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/IOptionsMonitor.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/IOptionsMonitor.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.Extensions.Options
 {
@@ -9,7 +10,7 @@ namespace Microsoft.Extensions.Options
     /// Used for notifications when <typeparamref name="TOptions"/> instances change.
     /// </summary>
     /// <typeparam name="TOptions">The options type.</typeparam>
-    public interface IOptionsMonitor<out TOptions>
+    public interface IOptionsMonitor<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] out TOptions>
     {
         /// <summary>
         /// Returns the current <typeparamref name="TOptions"/> instance with the <see cref="Options.DefaultName"/>.
diff --git a/src/libraries/Microsoft.Extensions.Options/src/IOptionsMonitorCache.cs b/src/libraries/Microsoft.Extensions.Options/src/IOptionsMonitorCache.cs
index 0706192059d4fb..f06062d3eae000 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/IOptionsMonitorCache.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/IOptionsMonitorCache.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.Extensions.Options
 {
@@ -9,7 +10,8 @@ namespace Microsoft.Extensions.Options
     /// Used by <see cref="IOptionsMonitor{TOptions}"/> to cache <typeparamref name="TOptions"/> instances.
     /// </summary>
     /// <typeparam name="TOptions">The type of options being requested.</typeparam>
-    public interface IOptionsMonitorCache<TOptions> where TOptions : class
+    public interface IOptionsMonitorCache<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions>
+        where TOptions : class
     {
         /// <summary>
         /// Gets a named options instance, or adds a new instance created with <paramref name="createOptions"/>.
diff --git a/src/libraries/Microsoft.Extensions.Options/src/IOptionsSnapshot.cs b/src/libraries/Microsoft.Extensions.Options/src/IOptionsSnapshot.cs
index 603be4b7c857fe..d29a381f0cb5a8 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/IOptionsSnapshot.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/IOptionsSnapshot.cs
@@ -1,13 +1,17 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace Microsoft.Extensions.Options
 {
     /// <summary>
     /// Used to access the value of <typeparamref name="TOptions"/> for the lifetime of a request.
     /// </summary>
     /// <typeparam name="TOptions">Options type.</typeparam>
-    public interface IOptionsSnapshot<out TOptions> : IOptions<TOptions> where TOptions : class
+    public interface IOptionsSnapshot<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] out TOptions> :
+        IOptions<TOptions>
+        where TOptions : class
     {
         /// <summary>
         /// Returns a configured <typeparamref name="TOptions"/> instance with the given name.
diff --git a/src/libraries/Microsoft.Extensions.Options/src/Microsoft.Extensions.Options.csproj b/src/libraries/Microsoft.Extensions.Options/src/Microsoft.Extensions.Options.csproj
index eda46678ac443f..4da5f5e410f283 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/Microsoft.Extensions.Options.csproj
+++ b/src/libraries/Microsoft.Extensions.Options/src/Microsoft.Extensions.Options.csproj
@@ -1,32 +1,28 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
+    <!-- Use targeting pack references instead of granular ones in the project file. -->
+    <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>
   </PropertyGroup>
 
-  <ItemGroup>
-    <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
-    <Reference Include="Microsoft.Extensions.Primitives" />
+  <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)'">
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Collections.Concurrent" />
-    <Reference Include="System.ComponentModel" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Threading" />
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' OR $(TargetFramework.StartsWith('net4'))">
-    <Reference Include="System.ComponentModel.Annotations" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <PackageReference Include="System.ComponentModel.Annotations" Version="$(SystemComponentModelAnnotationsVersion)" />
   </ItemGroup>
 
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
+    <Reference Include="System.ComponentModel.DataAnnotations" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Options/src/Options.cs b/src/libraries/Microsoft.Extensions.Options/src/Options.cs
index bd9ca34ef64310..7c6ea6bc34f6f8 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/Options.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/Options.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace Microsoft.Extensions.Options
 {
     /// <summary>
@@ -8,6 +10,9 @@ namespace Microsoft.Extensions.Options
     /// </summary>
     public static class Options
     {
+        // By default, we're going to keep public, parameterless constructor on any Options class.
+        internal const DynamicallyAccessedMemberTypes DynamicallyAccessedMembers = DynamicallyAccessedMemberTypes.PublicParameterlessConstructor;
+
         /// <summary>
         /// The default name used for options instances: "".
         /// </summary>
@@ -19,7 +24,8 @@ public static class Options
         /// <typeparam name="TOptions">Options type.</typeparam>
         /// <param name="options">Options object.</param>
         /// <returns>Wrapped options object.</returns>
-        public static IOptions<TOptions> Create<TOptions>(TOptions options) where TOptions : class
+        public static IOptions<TOptions> Create<[DynamicallyAccessedMembers(DynamicallyAccessedMembers)] TOptions>(TOptions options)
+            where TOptions : class
         {
             return new OptionsWrapper<TOptions>(options);
         }
diff --git a/src/libraries/Microsoft.Extensions.Options/src/OptionsCache.cs b/src/libraries/Microsoft.Extensions.Options/src/OptionsCache.cs
index 8bf2b3388b2ff6..b4094fe54de20a 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/OptionsCache.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/OptionsCache.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Concurrent;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.Extensions.Options
 {
@@ -10,7 +11,9 @@ namespace Microsoft.Extensions.Options
     /// Used to cache <typeparamref name="TOptions"/> instances.
     /// </summary>
     /// <typeparam name="TOptions">The type of options being requested.</typeparam>
-    public class OptionsCache<TOptions> : IOptionsMonitorCache<TOptions> where TOptions : class
+    public class OptionsCache<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> :
+        IOptionsMonitorCache<TOptions>
+        where TOptions : class
     {
         private readonly ConcurrentDictionary<string, Lazy<TOptions>> _cache = new ConcurrentDictionary<string, Lazy<TOptions>>(StringComparer.Ordinal);
 
diff --git a/src/libraries/Microsoft.Extensions.Options/src/OptionsFactory.cs b/src/libraries/Microsoft.Extensions.Options/src/OptionsFactory.cs
index c20cd9ee3a3743..dec163c398d33b 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/OptionsFactory.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/OptionsFactory.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.Extensions.Options
 {
@@ -10,7 +11,9 @@ namespace Microsoft.Extensions.Options
     /// Implementation of <see cref="IOptionsFactory{TOptions}"/>.
     /// </summary>
     /// <typeparam name="TOptions">The type of options being requested.</typeparam>
-    public class OptionsFactory<TOptions> : IOptionsFactory<TOptions> where TOptions : class
+    public class OptionsFactory<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> :
+        IOptionsFactory<TOptions>
+        where TOptions : class
     {
         private readonly IEnumerable<IConfigureOptions<TOptions>> _setups;
         private readonly IEnumerable<IPostConfigureOptions<TOptions>> _postConfigures;
diff --git a/src/libraries/Microsoft.Extensions.Options/src/OptionsManager.cs b/src/libraries/Microsoft.Extensions.Options/src/OptionsManager.cs
index 20182ab52109ea..71b5a134f35139 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/OptionsManager.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/OptionsManager.cs
@@ -1,13 +1,18 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace Microsoft.Extensions.Options
 {
     /// <summary>
     /// Implementation of <see cref="IOptions{TOptions}"/> and <see cref="IOptionsSnapshot{TOptions}"/>.
     /// </summary>
     /// <typeparam name="TOptions">Options type.</typeparam>
-    public class OptionsManager<TOptions> : IOptions<TOptions>, IOptionsSnapshot<TOptions> where TOptions : class
+    public class OptionsManager<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> :
+        IOptions<TOptions>,
+        IOptionsSnapshot<TOptions>
+        where TOptions : class
     {
         private readonly IOptionsFactory<TOptions> _factory;
         private readonly OptionsCache<TOptions> _cache = new OptionsCache<TOptions>(); // Note: this is a private cache
diff --git a/src/libraries/Microsoft.Extensions.Options/src/OptionsMonitor.cs b/src/libraries/Microsoft.Extensions.Options/src/OptionsMonitor.cs
index 6fe92a3c40f82a..7c43e2864cdf60 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/OptionsMonitor.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/OptionsMonitor.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.Extensions.Options
@@ -11,7 +12,10 @@ namespace Microsoft.Extensions.Options
     /// Implementation of <see cref="IOptionsMonitor{TOptions}"/>.
     /// </summary>
     /// <typeparam name="TOptions">Options type.</typeparam>
-    public class OptionsMonitor<TOptions> : IOptionsMonitor<TOptions>, IDisposable where TOptions : class
+    public class OptionsMonitor<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> :
+        IOptionsMonitor<TOptions>,
+        IDisposable
+        where TOptions : class
     {
         private readonly IOptionsMonitorCache<TOptions> _cache;
         private readonly IOptionsFactory<TOptions> _factory;
diff --git a/src/libraries/Microsoft.Extensions.Options/src/OptionsMonitorExtensions.cs b/src/libraries/Microsoft.Extensions.Options/src/OptionsMonitorExtensions.cs
index aecb3ec75800fe..518a5744f85b82 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/OptionsMonitorExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/OptionsMonitorExtensions.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.Extensions.Options
 {
@@ -16,7 +17,9 @@ public static class OptionsMonitorExtensions
         /// <param name="monitor">The IOptionsMonitor.</param>
         /// <param name="listener">The action to be invoked when <typeparamref name="TOptions"/> has changed.</param>
         /// <returns>An <see cref="IDisposable"/> which should be disposed to stop listening for changes.</returns>
-        public static IDisposable OnChange<TOptions>(this IOptionsMonitor<TOptions> monitor, Action<TOptions> listener)
-            => monitor.OnChange((o, _) => listener(o));
+        public static IDisposable OnChange<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions>(
+            this IOptionsMonitor<TOptions> monitor,
+            Action<TOptions> listener)
+                => monitor.OnChange((o, _) => listener(o));
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Options/src/OptionsServiceCollectionExtensions.cs b/src/libraries/Microsoft.Extensions.Options/src/OptionsServiceCollectionExtensions.cs
index 2a1aec0395ab0c..10341d4e217d58 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/OptionsServiceCollectionExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/OptionsServiceCollectionExtensions.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
@@ -140,8 +141,10 @@ public static IServiceCollection PostConfigureAll<TOptions>(this IServiceCollect
         /// <typeparam name="TConfigureOptions">The type that will configure options.</typeparam>
         /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
         /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
-        public static IServiceCollection ConfigureOptions<TConfigureOptions>(this IServiceCollection services) where TConfigureOptions : class
-            => services.ConfigureOptions(typeof(TConfigureOptions));
+        public static IServiceCollection ConfigureOptions<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TConfigureOptions>(
+            this IServiceCollection services)
+            where TConfigureOptions : class
+                => services.ConfigureOptions(typeof(TConfigureOptions));
 
         private static bool IsAction(Type type)
             => (type.GetTypeInfo().IsGenericType && type.GetGenericTypeDefinition() == typeof(Action<>));
@@ -174,7 +177,9 @@ private static IEnumerable<Type> FindConfigurationServices(Type type)
         /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
         /// <param name="configureType">The type that will configure options.</param>
         /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
-        public static IServiceCollection ConfigureOptions(this IServiceCollection services, Type configureType)
+        public static IServiceCollection ConfigureOptions(
+            this IServiceCollection services,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type configureType)
         {
             services.AddOptions();
             IEnumerable<Type> serviceTypes = FindConfigurationServices(configureType);
diff --git a/src/libraries/Microsoft.Extensions.Options/src/OptionsWrapper.cs b/src/libraries/Microsoft.Extensions.Options/src/OptionsWrapper.cs
index ca47d5e782198b..cdc295802aac1a 100644
--- a/src/libraries/Microsoft.Extensions.Options/src/OptionsWrapper.cs
+++ b/src/libraries/Microsoft.Extensions.Options/src/OptionsWrapper.cs
@@ -1,7 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.Extensions.Options
 {
@@ -9,7 +9,9 @@ namespace Microsoft.Extensions.Options
     /// <see cref="IOptions{TOptions}"/> wrapper that returns the options instance.
     /// </summary>
     /// <typeparam name="TOptions">Options type.</typeparam>
-    public class OptionsWrapper<TOptions> : IOptions<TOptions> where TOptions : class
+    public class OptionsWrapper<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> :
+        IOptions<TOptions>
+        where TOptions : class
     {
         /// <summary>
         /// Intializes the wrapper with the options instance to return.
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/ComplexOptions.cs b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/ComplexOptions.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Options/tests/ComplexOptions.cs
rename to src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/ComplexOptions.cs
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/FakeChangeToken.cs b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/FakeChangeToken.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Options/tests/FakeChangeToken.cs
rename to src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/FakeChangeToken.cs
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/FakeOptions.cs b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/FakeOptions.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Options/tests/FakeOptions.cs
rename to src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/FakeOptions.cs
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/FakeOptionsFactory.cs b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/FakeOptionsFactory.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Options/tests/FakeOptionsFactory.cs
rename to src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/FakeOptionsFactory.cs
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/Microsoft.Extensions.Options.Tests.csproj b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/Microsoft.Extensions.Options.Tests.csproj
new file mode 100644
index 00000000000000..e6fb72af73171f
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/Microsoft.Extensions.Options.Tests.csproj
@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
+    <EnableDefaultItems>true</EnableDefaultItems>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj"/>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection\src\Microsoft.Extensions.DependencyInjection.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options.ConfigurationExtensions\src\Microsoft.Extensions.Options.ConfigurationExtensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Options.DataAnnotations\src\Microsoft.Extensions.Options.DataAnnotations.csproj" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.ComponentModel.DataAnnotations" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/OptionsBuilderTest.cs b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsBuilderTest.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Options/tests/OptionsBuilderTest.cs
rename to src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsBuilderTest.cs
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/OptionsFactoryTests.cs b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsFactoryTests.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Options/tests/OptionsFactoryTests.cs
rename to src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsFactoryTests.cs
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/OptionsMonitorTest.cs b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsMonitorTest.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Options/tests/OptionsMonitorTest.cs
rename to src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsMonitorTest.cs
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/OptionsSnapshotTest.cs b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsSnapshotTest.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Options/tests/OptionsSnapshotTest.cs
rename to src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsSnapshotTest.cs
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/OptionsTest.cs b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsTest.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Options/tests/OptionsTest.cs
rename to src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsTest.cs
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/OptionsValidationTests.cs b/src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsValidationTests.cs
similarity index 100%
rename from src/libraries/Microsoft.Extensions.Options/tests/OptionsValidationTests.cs
rename to src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsValidationTests.cs
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/TrimmingTests/ConfigureTests.cs b/src/libraries/Microsoft.Extensions.Options/tests/TrimmingTests/ConfigureTests.cs
new file mode 100644
index 00000000000000..870b27bbe9e100
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Options/tests/TrimmingTests/ConfigureTests.cs
@@ -0,0 +1,78 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+using System;
+
+class Program
+{
+    static int Main(string[] args)
+    {
+        ServiceCollection services = new ServiceCollection();
+        services.Configure<OptionsA>(o =>
+        {
+            o.OptionValue = 99;
+        });
+        services.ConfigureOptions<OptionsAPostConfigure>();
+        services.AddOptions<OptionsB>()
+            .Configure<IOptions<OptionsA>>((b, a) =>
+            {
+                b.OptionString = a.Value.OptionValue.ToString();
+            });
+
+        ServiceProvider provider = services.BuildServiceProvider();
+
+        OptionsA optionsA = provider.GetService<IOptions<OptionsA>>().Value;
+        OptionsB optionsB = provider.GetService<IOptionsMonitor<OptionsB>>().CurrentValue;
+        OptionsC optionsC = provider.GetService<IOptions<OptionsC>>().Value;
+        OptionsD optionsD = provider.GetService<IOptionsFactory<OptionsD>>().Create(string.Empty);
+
+        if (optionsA.OptionValue != 99 ||
+            optionsA.PostConfigureOption != 101 ||
+            optionsB.OptionString != "99" ||
+            optionsC is null ||
+            optionsD is null)
+        {
+            return -1;
+        }
+
+        return 100;
+    }
+
+    private class OptionsA
+    {
+        public int OptionValue { get; set; }
+        public int PostConfigureOption { get; set; }
+    }
+
+    private class OptionsAPostConfigure : IPostConfigureOptions<OptionsA>
+    {
+        public void PostConfigure(string name, OptionsA options)
+        {
+            if (name.Length != 0)
+            {
+                throw new ArgumentException("name must be empty", nameof(name));
+            }
+
+            options.PostConfigureOption = 101;
+        }
+    }
+
+    private class OptionsB
+    {
+        public string OptionString { get; set; }
+    }
+
+    // Note: OptionsC is never configured
+    private class OptionsC
+    {
+        public string OptionString { get; set; }
+    }
+
+    // Note: OptionsD is never configured
+    private class OptionsD
+    {
+        public string OptionString { get; set; }
+    }
+}
diff --git a/src/libraries/Microsoft.Extensions.Options/tests/TrimmingTests/Microsoft.Extensions.Options.TrimmingTests.proj b/src/libraries/Microsoft.Extensions.Options/tests/TrimmingTests/Microsoft.Extensions.Options.TrimmingTests.proj
new file mode 100644
index 00000000000000..669ac862ad7b16
--- /dev/null
+++ b/src/libraries/Microsoft.Extensions.Options/tests/TrimmingTests/Microsoft.Extensions.Options.TrimmingTests.proj
@@ -0,0 +1,16 @@
+<Project DefaultTargets="Build">
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props))" />
+
+  <PropertyGroup>
+    <AdditionalProjectReferences>
+      Microsoft.Extensions.Options;
+      Microsoft.Extensions.DependencyInjection
+    </AdditionalProjectReferences>
+  </PropertyGroup>
+  
+  <ItemGroup>
+    <TestConsoleAppSourceFiles Include="ConfigureTests.cs" />
+  </ItemGroup>
+
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets))" />
+</Project>
diff --git a/src/libraries/Microsoft.Extensions.Primitives/ref/Microsoft.Extensions.Primitives.csproj b/src/libraries/Microsoft.Extensions.Primitives/ref/Microsoft.Extensions.Primitives.csproj
index a96a2cac069ce3..aee88d8e234935 100644
--- a/src/libraries/Microsoft.Extensions.Primitives/ref/Microsoft.Extensions.Primitives.csproj
+++ b/src/libraries/Microsoft.Extensions.Primitives/ref/Microsoft.Extensions.Primitives.csproj
@@ -1,11 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net461</TargetFrameworks>
   </PropertyGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-    <Reference Include="System.Memory"  />
-  </ItemGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Primitives.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        '$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Primitives/src/Microsoft.Extensions.Primitives.csproj b/src/libraries/Microsoft.Extensions.Primitives/src/Microsoft.Extensions.Primitives.csproj
index bd8c31c27a1398..0472414867b517 100644
--- a/src/libraries/Microsoft.Extensions.Primitives/src/Microsoft.Extensions.Primitives.csproj
+++ b/src/libraries/Microsoft.Extensions.Primitives/src/Microsoft.Extensions.Primitives.csproj
@@ -1,10 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.0;net461</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
+    <!-- Use targeting pack references instead of granular ones in the project file. -->
+    <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>
   </PropertyGroup>
+
   <ItemGroup>
     <Compile Include="$(CommonPath)Extensions\HashCodeCombiner\HashCodeCombiner.cs"
              Link="Common\src\Extensions\HashCodeCombiner\HashCodeCombiner.cs" />
@@ -20,23 +22,11 @@
     <Compile Include="StringValues.cs" />
     <Compile Include="ThrowHelper.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.0' AND !$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Diagnostics.Debug" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Threading" />
-    <Reference Include="System.Threading.Tasks" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' OR $(TargetFramework.StartsWith('net4'))">
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
+
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.CompilerServices.Unsafe\src\System.Runtime.CompilerServices.Unsafe.ilproj" />
   </ItemGroup>
+
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Primitives/tests/Microsoft.Extensions.Primitives.Tests.csproj b/src/libraries/Microsoft.Extensions.Primitives/tests/Microsoft.Extensions.Primitives.Tests.csproj
index d468ddb100262e..5bdba47205fd95 100644
--- a/src/libraries/Microsoft.Extensions.Primitives/tests/Microsoft.Extensions.Primitives.Tests.csproj
+++ b/src/libraries/Microsoft.Extensions.Primitives/tests/Microsoft.Extensions.Primitives.Tests.csproj
@@ -1,12 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);net472</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="Moq" Version="$(MoqVersion)" />
+    <ProjectReference Include="..\src\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/libraries/Microsoft.IO.Redist/Directory.Build.props b/src/libraries/Microsoft.IO.Redist/Directory.Build.props
index 7dcfd0eaa201ba..ba1f965d83cae7 100644
--- a/src/libraries/Microsoft.IO.Redist/Directory.Build.props
+++ b/src/libraries/Microsoft.IO.Redist/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>false</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/Microsoft.IO.Redist/src/Microsoft.IO.Redist.csproj b/src/libraries/Microsoft.IO.Redist/src/Microsoft.IO.Redist.csproj
index 41b1e51a0b5815..b9a0737a28de79 100644
--- a/src/libraries/Microsoft.IO.Redist/src/Microsoft.IO.Redist.csproj
+++ b/src/libraries/Microsoft.IO.Redist/src/Microsoft.IO.Redist.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>Microsoft.IO.Redist</AssemblyName>
-    <TargetFrameworks>$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>net472</TargetFrameworks>
     <DefineConstants>$(DefineConstants);MS_IO_REDIST</DefineConstants>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <ClsCompliant>false</ClsCompliant>
@@ -196,12 +195,8 @@
     <Compile Include="Microsoft\IO\StringExtensions.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.ValueTuple" />
-    <Reference Include="System.Buffers" />
-    <Reference Include="System.Memory" />
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
   <ItemGroup>
     <Folder Include="Microsoft\IO\Enumeration\" />
diff --git a/src/libraries/Microsoft.VisualBasic.Core/Directory.Build.props b/src/libraries/Microsoft.VisualBasic.Core/Directory.Build.props
index 49b11607763d59..df1a195487723b 100644
--- a/src/libraries/Microsoft.VisualBasic.Core/Directory.Build.props
+++ b/src/libraries/Microsoft.VisualBasic.Core/Directory.Build.props
@@ -5,6 +5,5 @@
     <PackageVersion>$(MajorVersion).$(MinorVersion).$(PatchVersion)</PackageVersion>
     <AssemblyVersion>10.0.6.0</AssemblyVersion>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.VisualBasic.Core/ref/Microsoft.VisualBasic.Core.cs b/src/libraries/Microsoft.VisualBasic.Core/ref/Microsoft.VisualBasic.Core.cs
index 7b0bfbcf12dcc4..db978528bf99ee 100644
--- a/src/libraries/Microsoft.VisualBasic.Core/ref/Microsoft.VisualBasic.Core.cs
+++ b/src/libraries/Microsoft.VisualBasic.Core/ref/Microsoft.VisualBasic.Core.cs
@@ -771,9 +771,8 @@ internal Conversions() { }
         public static decimal ToDecimal(string? Value) { throw null; }
         public static double ToDouble(object? Value) { throw null; }
         public static double ToDouble(string? Value) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
         [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNull("Value")]
-        public static T ToGenericParameter<T>(object? Value) { throw null; }
+        public static T? ToGenericParameter<T>(object? Value) { throw null; }
         public static int ToInteger(object? Value) { throw null; }
         public static int ToInteger(string? Value) { throw null; }
         public static long ToLong(object? Value) { throw null; }
diff --git a/src/libraries/Microsoft.VisualBasic.Core/src/Microsoft.VisualBasic.Core.vbproj b/src/libraries/Microsoft.VisualBasic.Core/src/Microsoft.VisualBasic.Core.vbproj
index 3fe68cb9c08710..9d76a13c5fce71 100644
--- a/src/libraries/Microsoft.VisualBasic.Core/src/Microsoft.VisualBasic.Core.vbproj
+++ b/src/libraries/Microsoft.VisualBasic.Core/src/Microsoft.VisualBasic.Core.vbproj
@@ -95,8 +95,8 @@
     <Compile Include="Microsoft\VisualBasic\VBMath.vb" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
-    <Reference Include="Microsoft.Win32.Registry" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.NonGeneric" />
     <Reference Include="System.Collections.Specialized" />
diff --git a/src/libraries/Microsoft.VisualBasic.Core/src/Resources/Strings.resx b/src/libraries/Microsoft.VisualBasic.Core/src/Resources/Strings.resx
index 26d02a1974d368..140af06cdf94f8 100644
--- a/src/libraries/Microsoft.VisualBasic.Core/src/Resources/Strings.resx
+++ b/src/libraries/Microsoft.VisualBasic.Core/src/Resources/Strings.resx
@@ -572,15 +572,6 @@
   <data name="Argument_LCIDNotSupported1" xml:space="preserve">
     <value>Locale id '{0}' is not supported on this system.</value>
   </data>
-  <data name="ProcessNotFound" xml:space="preserve">
-    <value>Process '{0}' was not found.</value>
-  </data>
-  <data name="Array_RankMismatch" xml:space="preserve">
-    <value>'ReDim' cannot change the number of dimensions.</value>
-  </data>
-  <data name="Array_TypeMismatch" xml:space="preserve">
-    <value>'ReDim' can only change the rightmost dimension.</value>
-  </data>
   <data name="InvalidCast_FromTo" xml:space="preserve">
     <value>Conversion from type '{0}' to type '{1}' is not valid.</value>
   </data>
@@ -725,18 +716,6 @@
   <data name="Security_LateBoundCallsNotPermitted" xml:space="preserve">
     <value>Late bound calls to file system methods in the Visual Basic runtime are not permitted.</value>
   </data>
-  <data name="Serialization_MissingCultureInfo" xml:space="preserve">
-    <value>Deserialization data is corrupt.  The CultureInfo for this Collection is missing.</value>
-  </data>
-  <data name="Serialization_MissingKeys" xml:space="preserve">
-    <value>Deserialization data is corrupt.  The keys for this Collection are missing.</value>
-  </data>
-  <data name="Serialization_MissingValues" xml:space="preserve">
-    <value>Deserialization data is corrupt.  The values for this Collection are missing.</value>
-  </data>
-  <data name="Serialization_KeyValueDifferentSizes" xml:space="preserve">
-    <value>Deserialization data is corrupt.  The keys and values arrays have different sizes.</value>
-  </data>
   <data name="MatchArgumentFailure2" xml:space="preserve">
     <value>Method invocation failed because '{0}' cannot be called with these arguments:{1}</value>
   </data>
@@ -839,12 +818,6 @@
   <data name="EmptyPlaceHolderMessage" xml:space="preserve">
     <value>Empty placeholder to adjust for 1-based array.</value>
   </data>
-  <data name="Mouse_NoMouseIsPresent" xml:space="preserve">
-    <value>No mouse is present.</value>
-  </data>
-  <data name="Mouse_NoWheelIsPresent" xml:space="preserve">
-    <value>No mouse wheel is present.</value>
-  </data>
   <data name="IO_SpecialDirectoryNotExist" xml:space="preserve">
     <value>Could not find special directory '{0}'.</value>
   </data>
@@ -920,75 +893,6 @@
   <data name="General_ArgumentEmptyOrNothing_Name" xml:space="preserve">
     <value>Argument '{0}' cannot be an empty string or Nothing.</value>
   </data>
-  <data name="General_PropertyNothing" xml:space="preserve">
-    <value>Property {0} cannot be set to Nothing.</value>
-  </data>
-  <data name="ApplicationLog_FreeSpaceError" xml:space="preserve">
-    <value>Cannot determine the amount of available disk space.</value>
-  </data>
-  <data name="ApplicationLog_FileExceedsMaximumSize" xml:space="preserve">
-    <value>Unable to write to log file because writing to it would cause it to exceed the MaxFileSize value.</value>
-  </data>
-  <data name="ApplicationLog_ReservedSpaceEncroached" xml:space="preserve">
-    <value>Unable to write to log file because writing to it would reduce free disk space below ReservedSpace value.</value>
-  </data>
-  <data name="ApplicationLog_NegativeNumber" xml:space="preserve">
-    <value>The value of {0} must be a positive number.</value>
-  </data>
-  <data name="ApplicationLogBaseNameNull" xml:space="preserve">
-    <value>BaseFileName cannot be Nothing or an empty String.</value>
-  </data>
-  <data name="ApplicationLogNumberTooSmall" xml:space="preserve">
-    <value>The value of {0} must be greater than or equal to 1000.</value>
-  </data>
-  <data name="ApplicationLog_ExhaustedPossibleStreamNames" xml:space="preserve">
-    <value>Unable to obtain a stream for the log.  Potential file names based on {0} are already in use.</value>
-  </data>
-  <data name="Network_InvalidUriString" xml:space="preserve">
-    <value>'{0}' is not a valid remote file address. A valid address should include a protocol, a path and a file name.</value>
-  </data>
-  <data name="Network_BadConnectionTimeout" xml:space="preserve">
-    <value>The ConnectionTimeout must be greater than 0.</value>
-  </data>
-  <data name="Network_NetworkNotAvailable" xml:space="preserve">
-    <value>Unable to ping because a network connection is not available.</value>
-  </data>
-  <data name="Network_UploadAddressNeedsFilename" xml:space="preserve">
-    <value>The address for UploadFile needs to include a file name.</value>
-  </data>
-  <data name="Network_DownloadNeedsFilename" xml:space="preserve">
-    <value>destinationFileName needs to include a file name.</value>
-  </data>
-  <data name="ProgressDialogDownloadingTitle" xml:space="preserve">
-    <value>Downloading {0}</value>
-  </data>
-  <data name="ProgressDialogUploadingTitle" xml:space="preserve">
-    <value>Uploading {0}</value>
-  </data>
-  <data name="ProgressDialogDownloadingLabel" xml:space="preserve">
-    <value>Downloading {0} to {1}</value>
-  </data>
-  <data name="ProgressDialogUploadingLabel" xml:space="preserve">
-    <value>Uploading {0} to {1}</value>
-  </data>
-  <data name="DiagnosticInfo_Memory" xml:space="preserve">
-    <value>Could not obtain memory information due to internal error.</value>
-  </data>
-  <data name="DiagnosticInfo_FullOSName" xml:space="preserve">
-    <value>Could not obtain full operation system name due to internal error. This might be caused by WMI not existing on the current machine.</value>
-  </data>
-  <data name="AppModel_CantGetMemoryMappedFile" xml:space="preserve">
-    <value>An unexpected error has occurred because an operating system resource required for single instance startup cannot be acquired.</value>
-  </data>
-  <data name="AppModel_NoStartupForm" xml:space="preserve">
-    <value>A startup form has not been specified.</value>
-  </data>
-  <data name="AppModel_SingleInstanceCantConnect" xml:space="preserve">
-    <value>This single-instance application could not connect to the original instance.</value>
-  </data>
-  <data name="AppModel_SplashAndMainFormTheSame" xml:space="preserve">
-    <value>Splash screen and main form cannot be the same form.</value>
-  </data>
   <data name="TextFieldParser_NumberOfCharsMustBePositive" xml:space="preserve">
     <value>NumberOfChars must be greater than zero.</value>
   </data>
@@ -1034,24 +938,9 @@
   <data name="TextFieldParser_EndCharsInDelimiter" xml:space="preserve">
     <value>TextFieldParser does not support delimiters that contain end-of-line characters.</value>
   </data>
-  <data name="EnvVarNotFound_Name" xml:space="preserve">
-    <value>Environment variable is not defined: '{0}'.</value>
-  </data>
-  <data name="WinForms_RecursiveFormCreate" xml:space="preserve">
-    <value>The form referred to itself during construction from a default instance, which led to infinite recursion.  Within the Form's constructor refer to the form using 'Me.'</value>
-  </data>
-  <data name="WinForms_SeeInnerException" xml:space="preserve">
-    <value>An error occurred creating the form. See Exception.InnerException for details.  The error is: {0}</value>
-  </data>
-  <data name="WebNotSupportedOnThisSKU" xml:space="preserve">
-    <value>Current target framework does not support web operations.</value>
-  </data>
   <data name="NoShellCopyOrMove" xml:space="preserve">
     <value>UI not available for copy or move</value>
   </data>
-  <data name="NoShellDelete" xml:space="preserve">
-    <value>UI not available for delete</value>
-  </data>
   <data name="MethodRequiresSystemWindowsForms" xml:space="preserve">
     <value>Method requires System.Windows.Forms.</value>
   </data>
diff --git a/src/libraries/Microsoft.VisualBasic.Core/tests/Microsoft.VisualBasic.Core.Tests.csproj b/src/libraries/Microsoft.VisualBasic.Core/tests/Microsoft.VisualBasic.Core.Tests.csproj
index f7ed31e0b036c0..74c7f14cfeeb78 100644
--- a/src/libraries/Microsoft.VisualBasic.Core/tests/Microsoft.VisualBasic.Core.Tests.csproj
+++ b/src/libraries/Microsoft.VisualBasic.Core/tests/Microsoft.VisualBasic.Core.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="AssemblyAttributes.cs" />
@@ -50,4 +50,8 @@
     <Compile Include="UtilsTests.cs" />
     <Compile Include="VBMathTests.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Encoding.CodePages\src\System.Text.Encoding.CodePages.csproj" />
+    <Reference Include="Microsoft.VisualBasic" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Win32.Primitives/Directory.Build.props b/src/libraries/Microsoft.Win32.Primitives/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/Microsoft.Win32.Primitives/Directory.Build.props
+++ b/src/libraries/Microsoft.Win32.Primitives/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Win32.Registry.AccessControl/ref/Microsoft.Win32.Registry.AccessControl.csproj b/src/libraries/Microsoft.Win32.Registry.AccessControl/ref/Microsoft.Win32.Registry.AccessControl.csproj
index ab5061eb5c8d1d..ac6eb1b1d3397e 100644
--- a/src/libraries/Microsoft.Win32.Registry.AccessControl/ref/Microsoft.Win32.Registry.AccessControl.csproj
+++ b/src/libraries/Microsoft.Win32.Registry.AccessControl/ref/Microsoft.Win32.Registry.AccessControl.csproj
@@ -1,16 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Win32.Registry.AccessControl.cs" />
     <Compile Include="Microsoft.Win32.Registry.AccessControl.Forwards.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-  </ItemGroup>
   <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
     <ProjectReference Include="..\..\Microsoft.Win32.Registry\ref\Microsoft.Win32.Registry.csproj" />
     <ProjectReference Include="..\..\System.Security.AccessControl\ref\System.Security.AccessControl.csproj" />
diff --git a/src/libraries/Microsoft.Win32.Registry.AccessControl/src/Microsoft.Win32.Registry.AccessControl.csproj b/src/libraries/Microsoft.Win32.Registry.AccessControl/src/Microsoft.Win32.Registry.AccessControl.csproj
index 9ceaab88111125..f93606b6a96021 100644
--- a/src/libraries/Microsoft.Win32.Registry.AccessControl/src/Microsoft.Win32.Registry.AccessControl.csproj
+++ b/src/libraries/Microsoft.Win32.Registry.AccessControl/src/Microsoft.Win32.Registry.AccessControl.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
-    <TargetFrameworks>netstandard2.0-Windows_NT;netstandard2.0;net461-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0-Windows_NT;netstandard2.0;net461-Windows_NT</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -10,17 +9,11 @@
     <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsWindows)' != 'true'">SR.PlatformNotSupported_RegistryAccessControl</GeneratePlatformNotSupportedAssemblyMessage>
     <OmitResources Condition="$(TargetFramework.StartsWith('net4'))">true</OmitResources>
   </PropertyGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-  </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="Microsoft.Win32.Registry" />
-    <Reference Include="System.Security.AccessControl" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(TargetsWindows)' != 'true'">
-    <Reference Include="System.Resources.ResourceManager" />
-  </ItemGroup>
   <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
     <Compile Include="Microsoft\Win32\RegistryAclExtensions.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\src\System.Security.AccessControl.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Win32.Registry.AccessControl/tests/Microsoft.Win32.Registry.AccessControl.Tests.csproj b/src/libraries/Microsoft.Win32.Registry.AccessControl/tests/Microsoft.Win32.Registry.AccessControl.Tests.csproj
index ee2fa0f75fae07..c7ded4394f3550 100644
--- a/src/libraries/Microsoft.Win32.Registry.AccessControl/tests/Microsoft.Win32.Registry.AccessControl.Tests.csproj
+++ b/src/libraries/Microsoft.Win32.Registry.AccessControl/tests/Microsoft.Win32.Registry.AccessControl.Tests.csproj
@@ -1,8 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="RegistryAclExtensionsTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\Microsoft.Win32.Registry.AccessControl.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Win32.Registry/Directory.Build.props b/src/libraries/Microsoft.Win32.Registry/Directory.Build.props
index 27a4a5522a2778..33e65b7cb46516 100644
--- a/src/libraries/Microsoft.Win32.Registry/Directory.Build.props
+++ b/src/libraries/Microsoft.Win32.Registry/Directory.Build.props
@@ -2,8 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
-    <IsNETCoreAppRef>false</IsNETCoreAppRef>
     <IsWindowsSpecific>true</IsWindowsSpecific>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Win32.Registry/ref/Microsoft.Win32.Registry.cs b/src/libraries/Microsoft.Win32.Registry/ref/Microsoft.Win32.Registry.cs
index f9005e63f44569..ea51db47d32ed7 100644
--- a/src/libraries/Microsoft.Win32.Registry/ref/Microsoft.Win32.Registry.cs
+++ b/src/libraries/Microsoft.Win32.Registry/ref/Microsoft.Win32.Registry.cs
@@ -115,7 +115,6 @@ namespace Microsoft.Win32.SafeHandles
     public sealed partial class SafeRegistryHandle : Microsoft.Win32.SafeHandles.SafeHandleZeroOrMinusOneIsInvalid
     {
         public SafeRegistryHandle(System.IntPtr preexistingHandle, bool ownsHandle) : base (default(bool)) { }
-        public override bool IsInvalid { get { throw null; } }
         protected override bool ReleaseHandle() { throw null; }
     }
 }
diff --git a/src/libraries/Microsoft.Win32.Registry/ref/Microsoft.Win32.Registry.csproj b/src/libraries/Microsoft.Win32.Registry/ref/Microsoft.Win32.Registry.csproj
index b8b7036446b5b0..cdf33b7f09e1e6 100644
--- a/src/libraries/Microsoft.Win32.Registry/ref/Microsoft.Win32.Registry.csproj
+++ b/src/libraries/Microsoft.Win32.Registry/ref/Microsoft.Win32.Registry.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkCurrent);net461</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -10,9 +10,6 @@
   <ItemGroup>
     <Compile Include="Microsoft.Win32.Registry.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-  </ItemGroup>
   <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
     <ProjectReference Include="..\..\System.Security.AccessControl\ref\System.Security.AccessControl.csproj" />
     <ProjectReference Include="..\..\System.Security.Principal.Windows\ref\System.Security.Principal.Windows.csproj" />
diff --git a/src/libraries/Microsoft.Win32.Registry/src/Microsoft.Win32.Registry.csproj b/src/libraries/Microsoft.Win32.Registry/src/Microsoft.Win32.Registry.csproj
index 3030b9a60d1e50..76c93e82be74b0 100644
--- a/src/libraries/Microsoft.Win32.Registry/src/Microsoft.Win32.Registry.csproj
+++ b/src/libraries/Microsoft.Win32.Registry/src/Microsoft.Win32.Registry.csproj
@@ -2,9 +2,8 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DefineConstants>$(DefineConstants);REGISTRY_ASSEMBLY</DefineConstants>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent);$(NetFrameworkCurrent)-Windows_NT;netstandard2.0-Windows_NT;netstandard2.0;net461-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent);netstandard2.0-Windows_NT;netstandard2.0;net461-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <NoWarn>$(NoWarn);CA2249</NoWarn>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -74,10 +73,11 @@
     <Compile Include="Microsoft\Win32\SafeHandles\SafeRegistryHandle.FileSystem.cs" />
     <Compile Include="System\Security\AccessControl\RegistrySecurity.FileSystem.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
+  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\src\System.Security.AccessControl.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
   </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <Reference Include="System.Buffers" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Diagnostics.Debug" />
@@ -87,7 +87,11 @@
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="System.Security.AccessControl" />
-    <Reference Include="System.Security.Principal.Windows" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Permissions\src\System.Security.Permissions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.IO.FileSystem.AccessControl\src\System.IO.FileSystem.AccessControl.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Win32.Registry/tests/Microsoft.Win32.Registry.Tests.csproj b/src/libraries/Microsoft.Win32.Registry/tests/Microsoft.Win32.Registry.Tests.csproj
index 1323c126075885..36f086dad5527c 100644
--- a/src/libraries/Microsoft.Win32.Registry/tests/Microsoft.Win32.Registry.Tests.csproj
+++ b/src/libraries/Microsoft.Win32.Registry/tests/Microsoft.Win32.Registry.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <DefineConstants>$(DefineConstants);REGISTRY_ASSEMBLY</DefineConstants>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Libraries.cs"
@@ -56,4 +56,7 @@
     <Compile Include="TestData.cs" />
     <Compile Include="XunitAssemblyAttributes.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\Microsoft.Win32.Registry.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Win32.SystemEvents/ref/Microsoft.Win32.SystemEvents.csproj b/src/libraries/Microsoft.Win32.SystemEvents/ref/Microsoft.Win32.SystemEvents.csproj
index 00a2bef840b0fc..e0413852fedaf5 100644
--- a/src/libraries/Microsoft.Win32.SystemEvents/ref/Microsoft.Win32.SystemEvents.csproj
+++ b/src/libraries/Microsoft.Win32.SystemEvents/ref/Microsoft.Win32.SystemEvents.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkCurrent);net461</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -10,8 +10,4 @@
   <ItemGroup>
     <Compile Include="Microsoft.Win32.SystemEvents.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Microsoft.Win32.SystemEvents/src/Microsoft.Win32.SystemEvents.csproj b/src/libraries/Microsoft.Win32.SystemEvents/src/Microsoft.Win32.SystemEvents.csproj
index ba2d1c66aa26a6..4cdba1a506ea85 100644
--- a/src/libraries/Microsoft.Win32.SystemEvents/src/Microsoft.Win32.SystemEvents.csproj
+++ b/src/libraries/Microsoft.Win32.SystemEvents/src/Microsoft.Win32.SystemEvents.csproj
@@ -2,9 +2,8 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT;netcoreapp3.0-Windows_NT;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT;netcoreapp3.0-Windows_NT;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -118,14 +117,13 @@
     <Compile Include="$(CoreLibSharedDir)System\Runtime\InteropServices\SuppressGCTransitionAttribute.cs"
              Link="System\Runtime\InteropServices\SuppressGCTransitionAttribute.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or $(TargetFramework.StartsWith('netcoreapp'))">
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or
+                        $(TargetFramework.StartsWith('netcoreapp'))">
     <Reference Include="System.Collections" />
     <Reference Include="System.ComponentModel.EventBasedAsync" />
     <Reference Include="System.ComponentModel.Primitives" />
+    <Reference Include="System.ComponentModel.TypeConverter"
+               Condition="$(TargetFramework.StartsWith('netcoreapp2.0'))" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Diagnostics.Tools" />
     <Reference Include="System.Resources.ResourceManager" />
@@ -135,7 +133,4 @@
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Thread" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('netcoreapp2.0'))">
-    <Reference Include="System.ComponentModel.TypeConverter" />
-  </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Win32.SystemEvents/tests/Microsoft.Win32.SystemEvents.Tests.csproj b/src/libraries/Microsoft.Win32.SystemEvents/tests/Microsoft.Win32.SystemEvents.Tests.csproj
index 3faa8abcdbe7da..dd477165222434 100644
--- a/src/libraries/Microsoft.Win32.SystemEvents/tests/Microsoft.Win32.SystemEvents.Tests.csproj
+++ b/src/libraries/Microsoft.Win32.SystemEvents/tests/Microsoft.Win32.SystemEvents.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Libraries.cs"
@@ -29,4 +29,7 @@
   <ItemGroup>
     <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\Microsoft.Win32.SystemEvents.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.XmlSerializer.Generator/pkg/build/dotnet-Microsoft.XmlSerializer.Generator.runtimeconfig.json b/src/libraries/Microsoft.XmlSerializer.Generator/pkg/build/dotnet-Microsoft.XmlSerializer.Generator.runtimeconfig.json
index a8e41025fa9855..5978b833d31c87 100644
--- a/src/libraries/Microsoft.XmlSerializer.Generator/pkg/build/dotnet-Microsoft.XmlSerializer.Generator.runtimeconfig.json
+++ b/src/libraries/Microsoft.XmlSerializer.Generator/pkg/build/dotnet-Microsoft.XmlSerializer.Generator.runtimeconfig.json
@@ -5,6 +5,6 @@
       "name": "Microsoft.NETCore.App",
       "version": "2.0.0"
     },
-    "rollForward": "Major"
+    "rollForward": "LatestMajor"
   }
 }
\ No newline at end of file
diff --git a/src/libraries/Microsoft.XmlSerializer.Generator/tests/Microsoft.XmlSerializer.Generator.Tests.csproj b/src/libraries/Microsoft.XmlSerializer.Generator/tests/Microsoft.XmlSerializer.Generator.Tests.csproj
index 7109d5ba318037..13024a3e7a7fc8 100644
--- a/src/libraries/Microsoft.XmlSerializer.Generator/tests/Microsoft.XmlSerializer.Generator.Tests.csproj
+++ b/src/libraries/Microsoft.XmlSerializer.Generator/tests/Microsoft.XmlSerializer.Generator.Tests.csproj
@@ -29,11 +29,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ReferenceFromRuntime Include="dotnet-Microsoft.XmlSerializer.Generator">
-      <!-- Copy this to our test output directory and run from there.
-           This is required so that we can stage the application with a custom runtimeconfig that lets it run on the test shared framework. -->
-      <Private>true</Private>
-    </ReferenceFromRuntime>
+    <ProjectReference Include="..\src\Microsoft.XmlSerializer.Generator.csproj" />
   </ItemGroup>
 
   <!-- This target runs before binplacing as it needs to provide a test assembly to binplace, and depends on CopyFilesToOutputDirectory
diff --git a/src/libraries/Native/Unix/CMakeLists.txt b/src/libraries/Native/Unix/CMakeLists.txt
index 6c1c4ea45861bc..3168c7e55c8333 100644
--- a/src/libraries/Native/Unix/CMakeLists.txt
+++ b/src/libraries/Native/Unix/CMakeLists.txt
@@ -1,14 +1,14 @@
-cmake_minimum_required(VERSION 3.14.5)
+cmake_minimum_required(VERSION 3.6.2)
+if(CLR_CMAKE_TARGET_IOS OR CLR_CMAKE_TARGET_TVOS) 
+     # CMake 3.14.5 contains bug fixes for iOS 
+     cmake_minimum_required(VERSION 3.14.5) 
+ endif() 
 cmake_policy(SET CMP0042 NEW)
 
 project(CoreFX C)
 
 include(${CLR_ENG_NATIVE_DIR}/configuretools.cmake)
 
-if(NOT CLR_CMAKE_TARGET_BROWSER)
-    cmake_policy(SET CMP0083 NEW)
-endif(NOT CLR_CMAKE_TARGET_BROWSER)
-
 set(CMAKE_MACOSX_RPATH ON)
 set(CMAKE_INSTALL_PREFIX $ENV{__CMakeBinDir})
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
@@ -161,7 +161,8 @@ if(CLR_CMAKE_TARGET_UNIX)
     if(NOT CLR_CMAKE_TARGET_BROWSER AND NOT CLR_CMAKE_TARGET_IOS AND NOT CLR_CMAKE_TARGET_TVOS)
         if(CLR_CMAKE_TARGET_OSX)
             add_definitions(-DTARGET_OSX)
-            add_link_options(-Wl,-bind_at_load)
+            set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,-bind_at_load")
+            set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-bind_at_load" )
         else()
             add_compile_options($<$<COMPILE_LANGUAGE:ASM>:-Wa,--noexecstack>)
             if(CLR_CMAKE_TARGET_SUNOS)
@@ -169,7 +170,8 @@ if(CLR_CMAKE_TARGET_UNIX)
             else()
                 # -z,now is required for full relro.
                 # see https://www.redhat.com/en/blog/hardening-elf-binaries-using-relocation-read-only-relro
-                add_link_options(-Wl,--build-id=sha1 -Wl,-z,relro,-z,now)
+                set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,--build-id=sha1 -Wl,-z,relro,-z,now")
+                set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--build-id=sha1 -Wl,-z,relro,-z,now" )
             endif()
         endif()
     endif()
diff --git a/src/libraries/Native/Unix/Common/pal_compiler.h b/src/libraries/Native/Unix/Common/pal_compiler.h
index 42e638cef11dfa..c53dc3996fedae 100644
--- a/src/libraries/Native/Unix/Common/pal_compiler.h
+++ b/src/libraries/Native/Unix/Common/pal_compiler.h
@@ -33,3 +33,11 @@
 #define EXTERN_C extern
 #endif // __cplusplus
 #endif // EXTERN_C
+
+#ifndef TYPEOF
+#ifdef __cplusplus
+#define TYPEOF decltype
+#else
+#define TYPEOF __typeof
+#endif // __cplusplus
+#endif // TYPEOF
diff --git a/src/libraries/Native/Unix/System.Globalization.Native/CMakeLists.txt b/src/libraries/Native/Unix/System.Globalization.Native/CMakeLists.txt
index ca9ed1fbe159ed..b426252987059d 100644
--- a/src/libraries/Native/Unix/System.Globalization.Native/CMakeLists.txt
+++ b/src/libraries/Native/Unix/System.Globalization.Native/CMakeLists.txt
@@ -23,12 +23,7 @@ if(CLR_CMAKE_TARGET_UNIX)
         endif()
 
         if(CLR_CMAKE_TARGET_OSX)
-            find_library(ICUCORE icucore)
-            if(ICUCORE STREQUAL ICUCORE-NOTFOUND)
-                message(FATAL_ERROR "Cannot find libicucore, skipping build for System.Globalization.Native. .NET globalization is not expected to function.")
-                return()
-            endif()
-            add_definitions(-DOSX_ICU_LIBRARY_PATH=\"${ICUCORE}\")
+            add_definitions(-DOSX_ICU_LIBRARY_PATH="/usr/lib/libicucore.dylib")
             add_definitions(-DU_DISABLE_RENAMING)
         else()
             find_library(ICUUC icuuc)
@@ -64,6 +59,10 @@ set(NATIVEGLOBALIZATION_SOURCES
     entrypoints.c
 )
 
+if (MSVC)
+    set_source_files_properties(${NATIVEGLOBALIZATION_SOURCES} PROPERTIES LANGUAGE CXX)
+endif()
+
 include_directories("../Common")
 
 if (GEN_SHARED_LIB)
@@ -80,14 +79,15 @@ if (GEN_SHARED_LIB)
     install_with_stripped_symbols (System.Globalization.Native PROGRAMS .)
 endif()
 
-add_library(System.Globalization.Native-Static
+add_library(System.Globalization.Native_obj
     OBJECT
     ${NATIVEGLOBALIZATION_SOURCES}
 )
 
-set_target_properties(System.Globalization.Native-Static PROPERTIES OUTPUT_NAME System.Globalization.Native  CLEAN_DIRECT_OUTPUT 1)
+set_target_properties(System.Globalization.Native_obj PROPERTIES OUTPUT_NAME System.Globalization.Native  CLEAN_DIRECT_OUTPUT 1)
 
-install (TARGETS System.Globalization.Native-Static DESTINATION .)
+add_library(System.Globalization.Native-static INTERFACE)
+target_sources(System.Globalization.Native-static INTERFACE $<TARGET_OBJECTS:System.Globalization.Native_obj>)
 
 if(NOT CLR_CMAKE_TARGET_OSX AND NOT CLR_CMAKE_TARGET_IOS AND NOT CLR_CMAKE_TARGET_TVOS AND NOT CLR_CMAKE_TARGET_ANDROID)
     if (GEN_SHARED_LIB)
diff --git a/src/libraries/Native/Unix/System.Globalization.Native/configure.cmake b/src/libraries/Native/Unix/System.Globalization.Native/configure.cmake
index f0042b1a59c43f..76fac2b7b7e923 100644
--- a/src/libraries/Native/Unix/System.Globalization.Native/configure.cmake
+++ b/src/libraries/Native/Unix/System.Globalization.Native/configure.cmake
@@ -1,4 +1,4 @@
-if(CLR_CMAKE_TARGET_ANDROID)
+if(CLR_CMAKE_TARGET_ANDROID OR CLR_CMAKE_TARGET_OSX)
     set(HAVE_SET_MAX_VARIABLE 1)
     set(HAVE_UDAT_STANDALONE_SHORTER_WEEKDAYS 1)
 else()
@@ -13,11 +13,7 @@ else()
             int main(void) { enum UDateFormatSymbolType e = UDAT_STANDALONE_SHORTER_WEEKDAYS; }
         " HAVE_UDAT_STANDALONE_SHORTER_WEEKDAYS)
 
-        if(CLR_CMAKE_TARGET_OSX)
-            set(CMAKE_REQUIRED_LIBRARIES ${ICUCORE})
-        else()
-            set(CMAKE_REQUIRED_LIBRARIES ${ICUUC} ${ICUI18N})
-        endif()
+        set(CMAKE_REQUIRED_LIBRARIES ${ICUUC} ${ICUI18N})
 
         check_symbol_exists(
             ucol_setMaxVariable
diff --git a/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim.c b/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim.c
index d4780a2c06f5ee..43e1d4fb370bcc 100644
--- a/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim.c
+++ b/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim.c
@@ -19,7 +19,7 @@
 #include "pal_icushim.h"
 
 // Define pointers to all the used ICU functions
-#define PER_FUNCTION_BLOCK(fn, lib) __typeof(fn)* fn##_ptr;
+#define PER_FUNCTION_BLOCK(fn, lib) TYPEOF(fn)* fn##_ptr;
 FOR_ALL_ICU_FUNCTIONS
 #undef PER_FUNCTION_BLOCK
 
@@ -43,7 +43,7 @@ static void* libicui18n = NULL;
 #define PER_FUNCTION_BLOCK(fn, lib) \
     c_static_assert_msg((sizeof(#fn) + MaxICUVersionStringWithSuffixLength + 1) <= sizeof(symbolName), "The symbolName is too small for symbol " #fn); \
     sprintf(symbolName, #fn "%s", symbolVersion); \
-    fn##_ptr = (__typeof(fn)*)dlsym(lib, symbolName); \
+    fn##_ptr = (TYPEOF(fn)*)dlsym(lib, symbolName); \
     if (fn##_ptr == NULL) { fprintf(stderr, "Cannot get symbol %s from " #lib "\nError: %s\n", symbolName, dlerror()); abort(); }
 
 static int FindSymbolVersion(int majorVer, int minorVer, int subVer, char* symbolName, char* symbolVersion, char* suffix)
@@ -90,7 +90,7 @@ static int FindSymbolVersion(int majorVer, int minorVer, int subVer, char* symbo
 
 #define PER_FUNCTION_BLOCK(fn, lib) \
     sprintf_s(symbolName, SYMBOL_NAME_SIZE, #fn "%s", symbolVersion); \
-    fn##_ptr = (__typeof(fn)*)GetProcAddress((HMODULE)lib, symbolName); \
+    fn##_ptr = (TYPEOF(fn)*)GetProcAddress((HMODULE)lib, symbolName); \
     if (fn##_ptr == NULL) { fprintf(stderr, "Cannot get symbol %s from " #lib "\nError: %u\n", symbolName, GetLastError()); abort(); }
 
 static int FindICULibs()
diff --git a/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim_internal.h b/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim_internal.h
index fcb669e0fc6ac4..46d8064b2d1a73 100644
--- a/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim_internal.h
+++ b/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim_internal.h
@@ -46,10 +46,6 @@
 
 #include "icu.h"
 
-#ifndef __typeof
-#define __typeof decltype
-#endif
-
 #define HAVE_SET_MAX_VARIABLE 1
 #define UDAT_STANDALONE_SHORTER_WEEKDAYS 1
 
@@ -180,7 +176,7 @@
     FOR_ALL_OS_CONDITIONAL_ICU_FUNCTIONS
 
 // Declare pointers to all the used ICU functions
-#define PER_FUNCTION_BLOCK(fn, lib) EXTERN_C __typeof(fn)* fn##_ptr;
+#define PER_FUNCTION_BLOCK(fn, lib) EXTERN_C TYPEOF(fn)* fn##_ptr;
 FOR_ALL_ICU_FUNCTIONS
 #undef PER_FUNCTION_BLOCK
 
diff --git a/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim_static.c b/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim_static.c
index 41a1956a2743c8..a2bf312fdee59f 100644
--- a/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim_static.c
+++ b/src/libraries/Native/Unix/System.Globalization.Native/pal_icushim_static.c
@@ -11,6 +11,8 @@
 #include <unicode/localpointer.h>
 #include <unicode/utrace.h>
 
+static int32_t isLoaded = 0;
+
 static void log_icu_error(const char* name, UErrorCode status)
 {
     const char * statusText = u_errorName(status);
@@ -65,7 +67,8 @@ int32_t GlobalizationNative_LoadICU(void)
         log_icu_error("ulocdata_getCLDRVersion", status);
         return 0;
     }
-
+    
+    isLoaded = 1;
     return 1;
 }
 
@@ -76,6 +79,12 @@ void GlobalizationNative_InitICUFunctions(void* icuuc, void* icuin, const char*
 
 int32_t GlobalizationNative_GetICUVersion(void)
 {
+    // this method is only used from our tests
+    // this way we ensure we're testing on the right mode
+    // even though we can call u_getVersion without loading since it is statically linked.
+    if (!isLoaded)
+        return 0;
+
     UVersionInfo versionInfo;
     u_getVersion(versionInfo);
 
diff --git a/src/libraries/Native/Unix/System.Native/pal_networkstatistics.c b/src/libraries/Native/Unix/System.Native/pal_networkstatistics.c
index 142203293c4488..4a7c394109e778 100644
--- a/src/libraries/Native/Unix/System.Native/pal_networkstatistics.c
+++ b/src/libraries/Native/Unix/System.Native/pal_networkstatistics.c
@@ -193,8 +193,8 @@ int32_t SystemNative_GetIcmpv4GlobalStatistics(Icmpv4GlobalStatistics* retStats)
         return -1;
     }
 
-    __typeof(systemStats.icps_inhist[0])* inHist = systemStats.icps_inhist;
-    __typeof(systemStats.icps_outhist[0])* outHist = systemStats.icps_outhist;
+    TYPEOF(systemStats.icps_inhist[0])* inHist = systemStats.icps_inhist;
+    TYPEOF(systemStats.icps_outhist[0])* outHist = systemStats.icps_outhist;
 
     retStats->AddressMaskRepliesReceived = inHist[ICMP_MASKREPLY];
     retStats->AddressMaskRepliesSent = outHist[ICMP_MASKREPLY];
diff --git a/src/libraries/Native/Unix/System.Native/pal_runtimeinformation.c b/src/libraries/Native/Unix/System.Native/pal_runtimeinformation.c
index 0f76fc0b8815b3..56ad9f2a4240b2 100644
--- a/src/libraries/Native/Unix/System.Native/pal_runtimeinformation.c
+++ b/src/libraries/Native/Unix/System.Native/pal_runtimeinformation.c
@@ -41,7 +41,8 @@ int32_t SystemNative_GetUnixVersion(char* version, int* capacity)
  0 - x86
  1 - x64
  2 - ARM
- 3 - ARM64 */
+ 3 - ARM64
+ 4 - WASM */
 int32_t SystemNative_GetOSArchitecture()
 {
 #if defined(TARGET_ARM)
@@ -50,8 +51,10 @@ int32_t SystemNative_GetOSArchitecture()
     return ARCH_ARM64;
 #elif defined(TARGET_AMD64)
     return ARCH_X64;
-#elif defined(TARGET_X86) || defined(TARGET_WASM) // TODO: add arch for WASM
+#elif defined(TARGET_X86)
     return ARCH_X86;
+#elif defined(TARGET_WASM)
+    return ARCH_WASM;
 #else
 #error Unidentified Architecture
 #endif
@@ -61,7 +64,8 @@ int32_t SystemNative_GetOSArchitecture()
 0 - x86
 1 - x64
 2 - ARM
-3 - ARM64 */
+3 - ARM64
+4 - WASM */
 int32_t SystemNative_GetProcessArchitecture()
 {
 #if defined(TARGET_ARM)
@@ -70,8 +74,10 @@ int32_t SystemNative_GetProcessArchitecture()
     return ARCH_ARM64;
 #elif defined(TARGET_AMD64)
     return ARCH_X64;
-#elif defined(TARGET_X86) || defined(TARGET_WASM) // TODO: add arch for WASM
+#elif defined(TARGET_X86)
     return ARCH_X86;
+#elif defined(TARGET_WASM)
+    return ARCH_WASM;
 #else
 #error Unidentified Architecture
 #endif
diff --git a/src/libraries/Native/Unix/System.Native/pal_runtimeinformation.h b/src/libraries/Native/Unix/System.Native/pal_runtimeinformation.h
index f52a01db11c17b..8f233ae1e603b1 100644
--- a/src/libraries/Native/Unix/System.Native/pal_runtimeinformation.h
+++ b/src/libraries/Native/Unix/System.Native/pal_runtimeinformation.h
@@ -21,5 +21,6 @@ enum
     ARCH_X86,
     ARCH_X64,
     ARCH_ARM,
-    ARCH_ARM64
+    ARCH_ARM64,
+    ARCH_WASM
 };
diff --git a/src/libraries/Native/Unix/System.Security.Cryptography.Native/apibridge.c b/src/libraries/Native/Unix/System.Security.Cryptography.Native/apibridge.c
index 066d872d8068ca..b5bab626c7005c 100644
--- a/src/libraries/Native/Unix/System.Security.Cryptography.Native/apibridge.c
+++ b/src/libraries/Native/Unix/System.Security.Cryptography.Native/apibridge.c
@@ -478,6 +478,16 @@ int32_t local_RSA_set0_crt_params(RSA* rsa, BIGNUM* dmp1, BIGNUM* dmq1, BIGNUM*
     return 1;
 }
 
+int32_t local_SSL_CTX_config(SSL_CTX* ctx, const char* name)
+{
+    (void)ctx;
+    (void)name;
+
+    // 1.0.x didn't load config in the same manner as 1.1.x,
+    // so the appropriate answer is "section not found".
+    return 0;
+}
+
 int32_t local_SSL_is_init_finished(const SSL* ssl)
 {
     return SSL_state(ssl) == SSL_ST_OK;
diff --git a/src/libraries/Native/Unix/System.Security.Cryptography.Native/apibridge.h b/src/libraries/Native/Unix/System.Security.Cryptography.Native/apibridge.h
index f2146a08ed748f..52e74314d0760e 100644
--- a/src/libraries/Native/Unix/System.Security.Cryptography.Native/apibridge.h
+++ b/src/libraries/Native/Unix/System.Security.Cryptography.Native/apibridge.h
@@ -26,6 +26,7 @@ int32_t local_RSA_set0_crt_params(RSA* rsa, BIGNUM* dmp1, BIGNUM* dmq1, BIGNUM*
 int32_t local_RSA_set0_factors(RSA* rsa, BIGNUM* p, BIGNUM* q);
 int32_t local_RSA_set0_key(RSA* rsa, BIGNUM* n, BIGNUM* e, BIGNUM* d);
 int32_t local_SSL_is_init_finished(const SSL* ssl);
+int32_t local_SSL_CTX_config(SSL_CTX* ctx, const char* name);
 unsigned long local_SSL_CTX_set_options(SSL_CTX* ctx, unsigned long options);
 void local_SSL_CTX_set_security_level(SSL_CTX* ctx, int32_t level);
 int local_SSL_session_reused(SSL* ssl);
diff --git a/src/libraries/Native/Unix/System.Security.Cryptography.Native/opensslshim.c b/src/libraries/Native/Unix/System.Security.Cryptography.Native/opensslshim.c
index 03e2c59fb7073d..8085b0258ca693 100644
--- a/src/libraries/Native/Unix/System.Security.Cryptography.Native/opensslshim.c
+++ b/src/libraries/Native/Unix/System.Security.Cryptography.Native/opensslshim.c
@@ -11,12 +11,12 @@
 #include "opensslshim.h"
 
 // Define pointers to all the used OpenSSL functions
-#define REQUIRED_FUNCTION(fn) __typeof(fn) fn##_ptr;
-#define NEW_REQUIRED_FUNCTION(fn) __typeof(fn) fn##_ptr;
-#define LIGHTUP_FUNCTION(fn) __typeof(fn) fn##_ptr;
-#define FALLBACK_FUNCTION(fn) __typeof(fn) fn##_ptr;
-#define RENAMED_FUNCTION(fn,oldfn) __typeof(fn) fn##_ptr;
-#define LEGACY_FUNCTION(fn) __typeof(fn) fn##_ptr;
+#define REQUIRED_FUNCTION(fn) TYPEOF(fn) fn##_ptr;
+#define NEW_REQUIRED_FUNCTION(fn) TYPEOF(fn) fn##_ptr;
+#define LIGHTUP_FUNCTION(fn) TYPEOF(fn) fn##_ptr;
+#define FALLBACK_FUNCTION(fn) TYPEOF(fn) fn##_ptr;
+#define RENAMED_FUNCTION(fn,oldfn) TYPEOF(fn) fn##_ptr;
+#define LEGACY_FUNCTION(fn) TYPEOF(fn) fn##_ptr;
 FOR_ALL_OPENSSL_FUNCTIONS
 #undef LEGACY_FUNCTION
 #undef RENAMED_FUNCTION
@@ -131,23 +131,23 @@ static void InitializeOpenSSLShim()
 
     // Get pointers to all the functions that are needed
 #define REQUIRED_FUNCTION(fn) \
-    if (!(fn##_ptr = (__typeof(fn))(dlsym(libssl, #fn)))) { fprintf(stderr, "Cannot get required symbol " #fn " from libssl\n"); abort(); }
+    if (!(fn##_ptr = (TYPEOF(fn))(dlsym(libssl, #fn)))) { fprintf(stderr, "Cannot get required symbol " #fn " from libssl\n"); abort(); }
 
 #define NEW_REQUIRED_FUNCTION(fn) \
-    if (!v1_0_sentinel && !(fn##_ptr = (__typeof(fn))(dlsym(libssl, #fn)))) { fprintf(stderr, "Cannot get required symbol " #fn " from libssl\n"); abort(); }
+    if (!v1_0_sentinel && !(fn##_ptr = (TYPEOF(fn))(dlsym(libssl, #fn)))) { fprintf(stderr, "Cannot get required symbol " #fn " from libssl\n"); abort(); }
 
 #define LIGHTUP_FUNCTION(fn) \
-    fn##_ptr = (__typeof(fn))(dlsym(libssl, #fn));
+    fn##_ptr = (TYPEOF(fn))(dlsym(libssl, #fn));
 
 #define FALLBACK_FUNCTION(fn) \
-    if (!(fn##_ptr = (__typeof(fn))(dlsym(libssl, #fn)))) { fn##_ptr = (__typeof(fn))local_##fn; }
+    if (!(fn##_ptr = (TYPEOF(fn))(dlsym(libssl, #fn)))) { fn##_ptr = (TYPEOF(fn))local_##fn; }
 
 #define RENAMED_FUNCTION(fn,oldfn) \
-    if (!v1_0_sentinel && !(fn##_ptr = (__typeof(fn))(dlsym(libssl, #fn)))) { fprintf(stderr, "Cannot get required symbol " #fn " from libssl\n"); abort(); } \
-    if (v1_0_sentinel && !(fn##_ptr = (__typeof(fn))(dlsym(libssl, #oldfn)))) { fprintf(stderr, "Cannot get required symbol " #oldfn " from libssl\n"); abort(); }
+    if (!v1_0_sentinel && !(fn##_ptr = (TYPEOF(fn))(dlsym(libssl, #fn)))) { fprintf(stderr, "Cannot get required symbol " #fn " from libssl\n"); abort(); } \
+    if (v1_0_sentinel && !(fn##_ptr = (TYPEOF(fn))(dlsym(libssl, #oldfn)))) { fprintf(stderr, "Cannot get required symbol " #oldfn " from libssl\n"); abort(); }
 
 #define LEGACY_FUNCTION(fn) \
-    if (v1_0_sentinel && !(fn##_ptr = (__typeof(fn))(dlsym(libssl, #fn)))) { fprintf(stderr, "Cannot get required symbol " #fn " from libssl\n"); abort(); }
+    if (v1_0_sentinel && !(fn##_ptr = (TYPEOF(fn))(dlsym(libssl, #fn)))) { fprintf(stderr, "Cannot get required symbol " #fn " from libssl\n"); abort(); }
 
     FOR_ALL_OPENSSL_FUNCTIONS
 #undef LEGACY_FUNCTION
diff --git a/src/libraries/Native/Unix/System.Security.Cryptography.Native/opensslshim.h b/src/libraries/Native/Unix/System.Security.Cryptography.Native/opensslshim.h
index 98c4672c5cc0da..825c8845838a9e 100644
--- a/src/libraries/Native/Unix/System.Security.Cryptography.Native/opensslshim.h
+++ b/src/libraries/Native/Unix/System.Security.Cryptography.Native/opensslshim.h
@@ -35,6 +35,7 @@
 #include <openssl/x509v3.h>
 
 #include "pal_crypto_config.h"
+#include "pal_compiler.h"
 #define OPENSSL_VERSION_1_1_1_RTM 0x10101000L
 #define OPENSSL_VERSION_1_1_0_RTM 0x10100000L
 #define OPENSSL_VERSION_1_0_2_RTM 0x10002000L
@@ -148,6 +149,7 @@ int32_t RSA_set0_crt_params(RSA* rsa, BIGNUM* dmp1, BIGNUM* dmq1, BIGNUM* iqmp);
 int32_t RSA_set0_factors(RSA* rsa, BIGNUM* p, BIGNUM* q);
 int32_t RSA_set0_key(RSA* rsa, BIGNUM* n, BIGNUM* e, BIGNUM* d);
 int32_t SSL_is_init_finished(SSL* ssl);
+int SSL_CTX_config(SSL_CTX* ctx, const char* name);
 #undef SSL_CTX_set_options
 unsigned long SSL_CTX_set_options(SSL_CTX* ctx, unsigned long options);
 void SSL_CTX_set_security_level(SSL_CTX* ctx, int32_t level);
@@ -456,6 +458,7 @@ void SSL_get0_alpn_selected(const SSL* ssl, const unsigned char** protocol, unsi
     REQUIRED_FUNCTION(SSL_ctrl) \
     REQUIRED_FUNCTION(SSL_set_quiet_shutdown) \
     REQUIRED_FUNCTION(SSL_CTX_check_private_key) \
+    FALLBACK_FUNCTION(SSL_CTX_config) \
     REQUIRED_FUNCTION(SSL_CTX_ctrl) \
     REQUIRED_FUNCTION(SSL_CTX_free) \
     FALLBACK_FUNCTION(SSL_is_init_finished) \
@@ -474,6 +477,7 @@ void SSL_get0_alpn_selected(const SSL* ssl, const unsigned char** protocol, unsi
     REQUIRED_FUNCTION(SSL_CTX_use_PrivateKey) \
     REQUIRED_FUNCTION(SSL_do_handshake) \
     REQUIRED_FUNCTION(SSL_free) \
+    REQUIRED_FUNCTION(SSL_get_ciphers) \
     REQUIRED_FUNCTION(SSL_get_client_CA_list) \
     REQUIRED_FUNCTION(SSL_get_current_cipher) \
     REQUIRED_FUNCTION(SSL_get_error) \
@@ -576,12 +580,12 @@ void SSL_get0_alpn_selected(const SSL* ssl, const unsigned char** protocol, unsi
     LIGHTUP_FUNCTION(EC_POINT_set_affine_coordinates_GF2m) \
 
 // Declare pointers to all the used OpenSSL functions
-#define REQUIRED_FUNCTION(fn) extern __typeof(fn)* fn##_ptr;
-#define NEW_REQUIRED_FUNCTION(fn) extern __typeof(fn)* fn##_ptr;
-#define LIGHTUP_FUNCTION(fn) extern __typeof(fn)* fn##_ptr;
-#define FALLBACK_FUNCTION(fn) extern __typeof(fn)* fn##_ptr;
-#define RENAMED_FUNCTION(fn,oldfn) extern __typeof(fn)* fn##_ptr;
-#define LEGACY_FUNCTION(fn) extern __typeof(fn)* fn##_ptr;
+#define REQUIRED_FUNCTION(fn) extern TYPEOF(fn)* fn##_ptr;
+#define NEW_REQUIRED_FUNCTION(fn) extern TYPEOF(fn)* fn##_ptr;
+#define LIGHTUP_FUNCTION(fn) extern TYPEOF(fn)* fn##_ptr;
+#define FALLBACK_FUNCTION(fn) extern TYPEOF(fn)* fn##_ptr;
+#define RENAMED_FUNCTION(fn,oldfn) extern TYPEOF(fn)* fn##_ptr;
+#define LEGACY_FUNCTION(fn) extern TYPEOF(fn)* fn##_ptr;
 FOR_ALL_OPENSSL_FUNCTIONS
 #undef LEGACY_FUNCTION
 #undef RENAMED_FUNCTION
@@ -855,6 +859,7 @@ FOR_ALL_OPENSSL_FUNCTIONS
 #define SSL_ctrl SSL_ctrl_ptr
 #define SSL_set_quiet_shutdown SSL_set_quiet_shutdown_ptr
 #define SSL_CTX_check_private_key SSL_CTX_check_private_key_ptr
+#define SSL_CTX_config SSL_CTX_config_ptr
 #define SSL_CTX_ctrl SSL_CTX_ctrl_ptr
 #define SSL_CTX_free SSL_CTX_free_ptr
 #define SSL_CTX_new SSL_CTX_new_ptr
@@ -872,6 +877,7 @@ FOR_ALL_OPENSSL_FUNCTIONS
 #define SSL_CTX_use_PrivateKey SSL_CTX_use_PrivateKey_ptr
 #define SSL_do_handshake SSL_do_handshake_ptr
 #define SSL_free SSL_free_ptr
+#define SSL_get_ciphers SSL_get_ciphers_ptr
 #define SSL_get_client_CA_list SSL_get_client_CA_list_ptr
 #define SSL_get_current_cipher SSL_get_current_cipher_ptr
 #define SSL_get_error SSL_get_error_ptr
@@ -986,6 +992,7 @@ FOR_ALL_OPENSSL_FUNCTIONS
 // type-safe OPENSSL_sk_num
 #define sk_ASN1_OBJECT_num(stack) OPENSSL_sk_num((const OPENSSL_STACK*)(1 ? stack : (const STACK_OF(ASN1_OBJECT)*)0))
 #define sk_GENERAL_NAME_num(stack) OPENSSL_sk_num((const OPENSSL_STACK*)(1 ? stack : (const STACK_OF(GENERAL_NAME)*)0))
+#define sk_SSL_CIPHER_num(stack) OPENSSL_sk_num((const OPENSSL_STACK*)(1 ? stack : (const STACK_OF(SSL_CIPHER)*)0))
 #define sk_X509_NAME_num(stack) OPENSSL_sk_num((const OPENSSL_STACK*)(1 ? stack : (const STACK_OF(X509_NAME)*)0))
 #define sk_X509_num(stack) OPENSSL_sk_num((const OPENSSL_STACK*)(1 ? stack : (const STACK_OF(X509)*)0))
 
diff --git a/src/libraries/Native/Unix/System.Security.Cryptography.Native/pal_ssl.c b/src/libraries/Native/Unix/System.Security.Cryptography.Native/pal_ssl.c
index 89aca2c3a0417d..5167987a1c4ed8 100644
--- a/src/libraries/Native/Unix/System.Security.Cryptography.Native/pal_ssl.c
+++ b/src/libraries/Native/Unix/System.Security.Cryptography.Native/pal_ssl.c
@@ -15,6 +15,19 @@ c_static_assert(PAL_SSL_ERROR_WANT_WRITE == SSL_ERROR_WANT_WRITE);
 c_static_assert(PAL_SSL_ERROR_SYSCALL == SSL_ERROR_SYSCALL);
 c_static_assert(PAL_SSL_ERROR_ZERO_RETURN == SSL_ERROR_ZERO_RETURN);
 
+#define DOTNET_DEFAULT_CIPHERSTRING \
+    "ECDHE-ECDSA-AES256-GCM-SHA384:" \
+    "ECDHE-ECDSA-AES128-GCM-SHA256:" \
+    "ECDHE-RSA-AES256-GCM-SHA384:" \
+    "ECDHE-RSA-AES128-GCM-SHA256:" \
+    "ECDHE-ECDSA-AES256-SHA384:" \
+    "ECDHE-ECDSA-AES128-SHA256:" \
+    "ECDHE-RSA-AES256-SHA384:" \
+    "ECDHE-RSA-AES128-SHA256:" \
+    /* Temporary TLS 1.0/1.1 compat after this line */\
+    "ECDHE-ECDSA-AES256-SHA:" \
+    "ECDHE-RSA-AES256-SHA:" \
+
 int32_t CryptoNative_EnsureOpenSslInitialized(void);
 
 #ifdef NEED_OPENSSL_1_0
@@ -25,6 +38,79 @@ static void EnsureLibSsl10Initialized()
 }
 #endif
 
+static int32_t g_config_specified_ciphersuites = 0;
+
+static void DetectCiphersuiteConfiguration()
+{
+    // This routine will always produce g_config_specified_ciphersuites = 0 on OpenSSL 1.0.x,
+    // so if we're building direct for 1.0.x (the only time NEED_OPENSSL_1_1 is undefined) then
+    // just omit all the code here.
+    //
+    // The method uses OpenSSL 1.0.x API, except for the fallback function SSL_CTX_config, to
+    // make the portable version easier.
+#ifdef NEED_OPENSSL_1_1
+
+    // Check to see if there's a registered default CipherString. If not, we will use our own.
+    SSL_CTX* ctx = SSL_CTX_new(TLS_method());
+    assert(ctx != NULL);
+
+    // SSL_get_ciphers returns a shared pointer, no need to save/free it.
+    // It gets invalidated every time we touch the configuration, so we can't ask just once, either.
+    SSL* ssl = SSL_new(ctx);
+    assert(ssl != NULL);
+    int defaultCount = sk_SSL_CIPHER_num(SSL_get_ciphers(ssl));
+    SSL_free(ssl);
+
+    int rv = SSL_CTX_set_cipher_list(ctx, "ALL");
+    assert(rv);
+
+    ssl = SSL_new(ctx);
+    assert(ssl != NULL);
+    int allCount = sk_SSL_CIPHER_num(SSL_get_ciphers(ssl));
+    SSL_free(ssl);
+
+    // It isn't expected that the default list and the "ALL" list have the same cardinality,
+    // but if that does happen (custom build, config, et cetera) then use the "RSA" list
+    // instead of the "ALL" list. Since the RSA list doesn't include legacy ciphersuites
+    // appropriate for ECDSA server certificates, it should be different than the ALL list.
+    if (allCount == defaultCount)
+    {
+        rv = SSL_CTX_set_cipher_list(ctx, "RSA");
+        assert(rv);
+        ssl = SSL_new(ctx);
+        assert(ssl != NULL);
+        allCount = sk_SSL_CIPHER_num(SSL_get_ciphers(ssl));
+        SSL_free(ssl);
+        // If the implicit default, "ALL", and "RSA" all have the same cardinality, just fail.
+        assert(allCount != defaultCount);
+    }
+
+    if (!SSL_CTX_config(ctx, "system_default"))
+    {
+        // There's no system_default configuration, so no default CipherString.
+        ERR_clear_error();
+    }
+    else
+    {
+        ssl = SSL_new(ctx);
+        assert(ssl != NULL);
+        int after = sk_SSL_CIPHER_num(SSL_get_ciphers(ssl));
+        SSL_free(ssl);
+
+        g_config_specified_ciphersuites = (allCount != after);
+    }
+
+    SSL_CTX_free(ctx);
+
+#elif !defined(FEATURE_DISTRO_AGNOSTIC_SSL) && defined(SSL_SYSTEM_DEFAULT_CIPHER_LIST)
+
+    // The Fedora, RHEL, and CentOS builds replace the normal defaults (with a configuration model).
+    // Consider their non-portable builds to always have specified ciphersuites in config.
+    g_config_specified_ciphersuites = 1;
+
+#endif
+}
+
 void CryptoNative_EnsureLibSslInitialized()
 {
     CryptoNative_EnsureOpenSslInitialized();
@@ -40,6 +126,8 @@ void CryptoNative_EnsureLibSslInitialized()
 #elif OPENSSL_VERSION_NUMBER < OPENSSL_VERSION_1_1_0_RTM
     EnsureLibSsl10Initialized();
 #endif
+
+    DetectCiphersuiteConfiguration();
 }
 
 const SSL_METHOD* CryptoNative_SslV2_3Method()
@@ -57,7 +145,20 @@ SSL_CTX* CryptoNative_SslCtxCreate(SSL_METHOD* method)
     {
         // As of OpenSSL 1.1.0, compression is disabled by default. In case an older build
         // is used, ensure it's disabled.
-        SSL_CTX_set_options(ctx, SSL_OP_NO_COMPRESSION);
+        //
+        // The other .NET platforms are server-preference, and the common consensus seems
+        // to be to use server preference (as of June 2020), so just always assert that.
+        SSL_CTX_set_options(ctx, SSL_OP_NO_COMPRESSION | SSL_OP_CIPHER_SERVER_PREFERENCE);
+
+        // If openssl.cnf doesn't have an opinion for CipherString, then use this value instead
+        if (!g_config_specified_ciphersuites)
+        {
+            if (!SSL_CTX_set_cipher_list(ctx, DOTNET_DEFAULT_CIPHERSTRING))
+            {
+                SSL_CTX_free(ctx);
+                return NULL;
+            }
+        }
     }
 
     return ctx;
diff --git a/src/libraries/Native/build-native.proj b/src/libraries/Native/build-native.proj
index b0551571adf724..28dc8184f01cf0 100644
--- a/src/libraries/Native/build-native.proj
+++ b/src/libraries/Native/build-native.proj
@@ -1,9 +1,4 @@
-<Project>
-  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props))" />
-
-  <!-- Target that builds all the native binaries in the Native folder -->
-  <Target Name="Build" DependsOnTargets="BuildNativeUnix;BuildNativeWindows" />
-
+<Project Sdk="Microsoft.Build.Traversal">
   <PropertyGroup>
     <!-- Hardcode version paths in a global location. -->
     <NativeVersionFile Condition="'$(TargetOS)' == 'Windows_NT'">$(ArtifactsObjDir)_version.h</NativeVersionFile>
@@ -11,9 +6,14 @@
     <_BuildNativeArgs>$(TargetArchitecture) $(Configuration) outconfig $(BuildTargetFramework)-$(TargetOS)-$(Configuration)-$(TargetArchitecture) -os $(TargetOS)</_BuildNativeArgs>
   </PropertyGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="native-binplace.proj"
+                      Condition="'$(BuildingNETCoreAppVertical)' == 'true'" />
+  </ItemGroup>
+
   <Target Name="BuildNativeUnix"
+          BeforeTargets="Build"
           Condition="'$(TargetOS)' != 'Windows_NT'">
-
     <PropertyGroup>
       <!--
         MSBuildNodeCount should a good approximation for how many procs to use for native build, if we find that doesn't work
@@ -32,20 +32,16 @@
       <_BuildNativeUnixArgs>$(_BuildNativeArgs)$(_ProcessCountArg)$(_PortableBuildArg)$(_CrossBuildArg)$(_BuildNativeCompilerArg)$(_CMakeArgs) $(Compiler)</_BuildNativeUnixArgs>
     </PropertyGroup>
 
-    <Message Text="$(MSBuildProjectDirectory)/build-native.sh $(_BuildNativeUnixArgs)" Importance="High"/>
-    <Exec Command="&quot;$(MSBuildProjectDirectory)/build-native.sh&quot; $(_BuildNativeUnixArgs)" />
-
+    <Message Text="$(MSBuildThisFileDirectory)build-native.sh $(_BuildNativeUnixArgs)" Importance="High"/>
+    <Exec Command="&quot;$(MSBuildThisFileDirectory)build-native.sh&quot; $(_BuildNativeUnixArgs)" />
   </Target>
 
-  <!-- We don't have any native components when building for netfx. -->
   <Target Name="BuildNativeWindows"
-          Condition="'$(TargetOS)' == 'Windows_NT' and !$(TargetFramework.StartsWith('net4'))">
-
+          BeforeTargets="Build"
+          Condition="'$(TargetOS)' == 'Windows_NT' and
+                     '$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'">
     <!-- Run script that invokes Cmake to create VS files, and then calls msbuild to compile them -->
-    <Message Text="&quot;$(MSBuildProjectDirectory)\build-native.cmd&quot; $(_BuildNativeArgs)" Importance="High"/>
-    <Exec Command="&quot;$(MSBuildProjectDirectory)\build-native.cmd&quot; $(_BuildNativeArgs)" />
-
+    <Message Text="&quot;$(MSBuildThisFileDirectory)build-native.cmd&quot; $(_BuildNativeArgs)" Importance="High"/>
+    <Exec Command="&quot;$(MSBuildThisFileDirectory)build-native.cmd&quot; $(_BuildNativeArgs)" />
   </Target>
-
-  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets))" />
 </Project>
diff --git a/src/libraries/Native/native-binplace.proj b/src/libraries/Native/native-binplace.proj
index f8a558defe35b0..4c49de39a4b1e1 100644
--- a/src/libraries/Native/native-binplace.proj
+++ b/src/libraries/Native/native-binplace.proj
@@ -2,10 +2,11 @@
   <Import Sdk="Microsoft.NET.Sdk" Project="Sdk.props" />
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <TargetFramework>$(BuildTargetFramework)</TargetFramework>
     <BinPlaceRuntime>false</BinPlaceRuntime>
     <BinPlaceNative>true</BinPlaceNative>
+    <DisableImplicitFrameworkReferences>true</DisableImplicitFrameworkReferences>
   </PropertyGroup>
 
   <Import Sdk="Microsoft.NET.Sdk" Project="Sdk.targets" />
@@ -22,10 +23,6 @@
       <BinPlaceItem Include="$(NativeBinDir)*.dbg" />
       <BinPlaceItem Include="$(NativeBinDir)*.dylib" />
       <BinPlaceItem Include="$(NativeBinDir)*.dwarf" />
-      <BinPlaceItem Condition="'$(TargetOS)' == 'Browser'" Include="$(NativeBinDir)dotnet.js" />
-      <BinPlaceItem Condition="'$(TargetOS)' == 'Browser'" Include="$(NativeBinDir)dotnet.wasm" />
-      <BinPlaceItem Condition="'$(TargetOS)' == 'Browser'" Include="$(NativeBinDir)dotnet.timezones.blat" />
-      <BinPlaceItem Condition="'$(TargetOS)' == 'Browser'" Include="$(NativeBinDir)icudt.dat" />
       <FileWrites Include="@(BinPlaceItem)" />
     </ItemGroup>
   </Target>
diff --git a/src/libraries/NetCoreAppLibrary.props b/src/libraries/NetCoreAppLibrary.props
new file mode 100644
index 00000000000000..0fd6812ef3c1b6
--- /dev/null
+++ b/src/libraries/NetCoreAppLibrary.props
@@ -0,0 +1,163 @@
+<Project>
+  <PropertyGroup>
+    <!-- The trailing semicolon is important for each entry! -->
+    <NetCoreAppLibrary>
+      Microsoft.CSharp;
+      Microsoft.VisualBasic.Core;
+      Microsoft.Win32.Primitives;
+      Microsoft.Win32.Registry;
+      System.AppContext;
+      System.Buffers;
+      System.Collections;
+      System.Collections.Concurrent;
+      System.Collections.Immutable;
+      System.Collections.NonGeneric;
+      System.Collections.Specialized;
+      System.ComponentModel;
+      System.ComponentModel.Annotations;
+      System.ComponentModel.EventBasedAsync;
+      System.ComponentModel.Primitives;
+      System.ComponentModel.TypeConverter;
+      System.Console;
+      System.Data.Common;
+      System.Data.DataSetExtensions;
+      System.Diagnostics.Contracts;
+      System.Diagnostics.Debug;
+      System.Diagnostics.DiagnosticSource;
+      System.Diagnostics.FileVersionInfo;
+      System.Diagnostics.Process;
+      System.Diagnostics.StackTrace;
+      System.Diagnostics.TextWriterTraceListener;
+      System.Diagnostics.Tools;
+      System.Diagnostics.TraceSource;
+      System.Diagnostics.Tracing;
+      System.Drawing.Primitives;
+      System.Dynamic.Runtime;
+      System.Formats.Asn1;
+      System.Globalization;
+      System.Globalization.Calendars;
+      System.Globalization.Extensions;
+      System.IO;
+      System.IO.Compression;
+      System.IO.Compression.Brotli;
+      System.IO.Compression.ZipFile;
+      System.IO.FileSystem;
+      System.IO.FileSystem.AccessControl;
+      System.IO.FileSystem.DriveInfo;
+      System.IO.FileSystem.Primitives;
+      System.IO.FileSystem.Watcher;
+      System.IO.IsolatedStorage;
+      System.IO.MemoryMappedFiles;
+      System.IO.Pipelines;
+      System.IO.Pipes;
+      System.IO.Pipes.AccessControl;
+      System.IO.UnmanagedMemoryStream;
+      System.Linq;
+      System.Linq.Expressions;
+      System.Linq.Parallel;
+      System.Linq.Queryable;
+      System.Memory;
+      System.Net.Connections;
+      System.Net.Http;
+      System.Net.Http.Json;
+      System.Net.HttpListener;
+      System.Net.Mail;
+      System.Net.NameResolution;
+      System.Net.NetworkInformation;
+      System.Net.Ping;
+      System.Net.Primitives;
+      System.Net.Requests;
+      System.Net.Security;
+      System.Net.ServicePoint;
+      System.Net.Sockets;
+      System.Net.WebClient;
+      System.Net.WebHeaderCollection;
+      System.Net.WebProxy;
+      System.Net.WebSockets;
+      System.Net.WebSockets.Client;
+      System.Numerics.Vectors;
+      System.ObjectModel;
+      System.Private.DataContractSerialization;
+      System.Private.Runtime.InteropServices.JavaScript;
+      System.Private.Uri;
+      System.Private.Xml;
+      System.Private.Xml.Linq;
+      System.Reflection;
+      System.Reflection.DispatchProxy;
+      System.Reflection.Emit;
+      System.Reflection.Emit.ILGeneration;
+      System.Reflection.Emit.Lightweight;
+      System.Reflection.Extensions;
+      System.Reflection.Metadata;
+      System.Reflection.Primitives;
+      System.Reflection.TypeExtensions;
+      System.Resources.Reader;
+      System.Resources.ResourceManager;
+      System.Resources.Writer;
+      System.Runtime;
+      System.Runtime.CompilerServices.Unsafe;
+      System.Runtime.CompilerServices.VisualC;
+      System.Runtime.Extensions;
+      System.Runtime.Handles;
+      System.Runtime.InteropServices;
+      System.Runtime.InteropServices.RuntimeInformation;
+      System.Runtime.Intrinsics;
+      System.Runtime.Loader;
+      System.Runtime.Numerics;
+      System.Runtime.Serialization.Formatters;
+      System.Runtime.Serialization.Json;
+      System.Runtime.Serialization.Primitives;
+      System.Runtime.Serialization.Xml;
+      System.Security.AccessControl;
+      System.Security.Claims;
+      System.Security.Cryptography.Algorithms;
+      System.Security.Cryptography.Cng;
+      System.Security.Cryptography.Csp;
+      System.Security.Cryptography.Encoding;
+      System.Security.Cryptography.OpenSsl;
+      System.Security.Cryptography.Primitives;
+      System.Security.Cryptography.X509Certificates;
+      System.Security.Principal;
+      System.Security.Principal.Windows;
+      System.Security.SecureString;
+      System.Text.Encoding;
+      System.Text.Encoding.CodePages;
+      System.Text.Encoding.Extensions;
+      System.Text.Encodings.Web;
+      System.Text.Json;
+      System.Text.RegularExpressions;
+      System.Threading;
+      System.Threading.Channels;
+      System.Threading.Overlapped;
+      System.Threading.Tasks;
+      System.Threading.Tasks.Dataflow;
+      System.Threading.Tasks.Extensions;
+      System.Threading.Tasks.Parallel;
+      System.Threading.Thread;
+      System.Threading.ThreadPool;
+      System.Threading.Timer;
+      System.Transactions.Local;
+      System.ValueTuple;
+      System.Web.HttpUtility;
+      System.Xml.ReaderWriter;
+      System.Xml.XDocument;
+      System.Xml.XmlDocument;
+      System.Xml.XmlSerializer;
+      System.Xml.XPath;
+      System.Xml.XPath.XDocument;
+    </NetCoreAppLibrary>
+    <NetCoreAppLibraryNoReference>
+      Microsoft.Win32.Registry;
+      System.IO.FileSystem.AccessControl;
+      System.IO.Pipes.AccessControl;
+      System.Security.AccessControl;
+      System.Security.Cryptography.Cng;
+      System.Security.Cryptography.OpenSsl;
+      System.Security.Principal.Windows;
+    </NetCoreAppLibraryNoReference>
+  </PropertyGroup>
+  <!-- Make NetCoreAppLibrary available as an item. -->
+  <ItemGroup>
+    <NetCoreAppLibrary Include="$(NetCoreAppLibrary)" />
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/src/libraries/System.AppContext/Directory.Build.props b/src/libraries/System.AppContext/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.AppContext/Directory.Build.props
+++ b/src/libraries/System.AppContext/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.AppContext/src/System.AppContext.csproj b/src/libraries/System.AppContext/src/System.AppContext.csproj
index 0b924ac9f8c370..4f2d15aa3b6a58 100644
--- a/src/libraries/System.AppContext/src/System.AppContext.csproj
+++ b/src/libraries/System.AppContext/src/System.AppContext.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.AppContext</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Buffers/Directory.Build.props b/src/libraries/System.Buffers/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.Buffers/Directory.Build.props
+++ b/src/libraries/System.Buffers/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.CodeDom/ref/System.CodeDom.cs b/src/libraries/System.CodeDom/ref/System.CodeDom.cs
index d25a4aaad0cf0b..fa701a269a54eb 100644
--- a/src/libraries/System.CodeDom/ref/System.CodeDom.cs
+++ b/src/libraries/System.CodeDom/ref/System.CodeDom.cs
@@ -993,7 +993,7 @@ protected virtual void GenerateSnippetCompileUnit(System.CodeDom.CodeSnippetComp
         protected abstract void GenerateSnippetMember(System.CodeDom.CodeSnippetTypeMember e);
         protected virtual void GenerateSnippetStatement(System.CodeDom.CodeSnippetStatement e) { }
         protected void GenerateStatement(System.CodeDom.CodeStatement e) { }
-        protected void GenerateStatements(System.CodeDom.CodeStatementCollection stms) { }
+        protected void GenerateStatements(System.CodeDom.CodeStatementCollection stmts) { }
         protected abstract void GenerateThisReferenceExpression(System.CodeDom.CodeThisReferenceExpression e);
         protected abstract void GenerateThrowExceptionStatement(System.CodeDom.CodeThrowExceptionStatement e);
         protected abstract void GenerateTryCatchFinallyStatement(System.CodeDom.CodeTryCatchFinallyStatement e);
diff --git a/src/libraries/System.CodeDom/ref/System.CodeDom.csproj b/src/libraries/System.CodeDom/ref/System.CodeDom.csproj
index 189b1e64476170..fdc597d599ccd0 100644
--- a/src/libraries/System.CodeDom/ref/System.CodeDom.csproj
+++ b/src/libraries/System.CodeDom/ref/System.CodeDom.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -10,10 +9,6 @@
   <ItemGroup>
     <Compile Include="System.CodeDom.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
   <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
     <ProjectReference Include="..\..\System.Security.Permissions\ref\System.Security.Permissions.csproj" />
   </ItemGroup>
diff --git a/src/libraries/System.CodeDom/src/System.CodeDom.csproj b/src/libraries/System.CodeDom/src/System.CodeDom.csproj
index 7217ca52bc65d7..e3622bd5d65e7e 100644
--- a/src/libraries/System.CodeDom/src/System.CodeDom.csproj
+++ b/src/libraries/System.CodeDom/src/System.CodeDom.csproj
@@ -2,8 +2,7 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DefineConstants>$(DefineConstants);CODEDOM</DefineConstants>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -129,8 +128,4 @@
     <Compile Include="System\Collections\Specialized\FixedStringLookup.cs" />
     <Compile Include="$(CommonPath)System\CSharpHelpers.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.CodeDom/tests/System.CodeDom.Tests.csproj b/src/libraries/System.CodeDom/tests/System.CodeDom.Tests.csproj
index 9e92688da3e9db..f90d915dffa5f0 100644
--- a/src/libraries/System.CodeDom/tests/System.CodeDom.Tests.csproj
+++ b/src/libraries/System.CodeDom/tests/System.CodeDom.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\CodeDom\CodeAttributeDeclarationCollectionTests.cs" />
@@ -110,4 +110,7 @@
     <Compile Include="$(CommonTestPath)System\Runtime\Serialization\Formatters\BinaryFormatterHelpers.cs"
              Link="Common\System\Runtime\Serialization\Formatters\BinaryFormatterHelpers.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <ProjectReference Include="..\src\System.CodeDom.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.CodeDom/tests/System/CodeDom/Compiler/CompilerResultsTests.cs b/src/libraries/System.CodeDom/tests/System/CodeDom/Compiler/CompilerResultsTests.cs
index a88143c34b5540..aa791baa631aa8 100644
--- a/src/libraries/System.CodeDom/tests/System/CodeDom/Compiler/CompilerResultsTests.cs
+++ b/src/libraries/System.CodeDom/tests/System/CodeDom/Compiler/CompilerResultsTests.cs
@@ -31,7 +31,7 @@ public void Ctor_TempFileCollection(TempFileCollection tempFiles)
         [Fact]
         public void CompiledAssembly_GetWithPathToAssemblySet_ReturnsExpectedAssembly()
         {
-            var results = new CompilerResults(null) { PathToAssembly = typeof(CompilerResultsTests).Assembly.Location };
+            var results = new CompilerResults(null) { PathToAssembly = AssemblyPathHelper.GetAssemblyLocation(typeof(CompilerResultsTests).Assembly) };
 
             Assert.NotNull(results.CompiledAssembly);
             Assert.Equal(typeof(CompilerResultsTests).Assembly.FullName, results.CompiledAssembly.FullName);
diff --git a/src/libraries/System.Collections.Concurrent/Directory.Build.props b/src/libraries/System.Collections.Concurrent/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Collections.Concurrent/Directory.Build.props
+++ b/src/libraries/System.Collections.Concurrent/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Collections.Concurrent/ref/System.Collections.Concurrent.cs b/src/libraries/System.Collections.Concurrent/ref/System.Collections.Concurrent.cs
index cef519b39d5bdb..c1a477bb048de4 100644
--- a/src/libraries/System.Collections.Concurrent/ref/System.Collections.Concurrent.cs
+++ b/src/libraries/System.Collections.Concurrent/ref/System.Collections.Concurrent.cs
@@ -33,8 +33,8 @@ void System.Collections.ICollection.CopyTo(System.Array array, int index) { }
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
         public T Take() { throw null; }
         public T Take(System.Threading.CancellationToken cancellationToken) { throw null; }
-        public static int TakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, [System.Diagnostics.CodeAnalysis.MaybeNullAttribute] out T item) { throw null; }
-        public static int TakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, [System.Diagnostics.CodeAnalysis.MaybeNullAttribute] out T item, System.Threading.CancellationToken cancellationToken) { throw null; }
+        public static int TakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, out T? item) { throw null; }
+        public static int TakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, out T? item, System.Threading.CancellationToken cancellationToken) { throw null; }
         public T[] ToArray() { throw null; }
         public bool TryAdd(T item) { throw null; }
         public bool TryAdd(T item, int millisecondsTimeout) { throw null; }
@@ -48,10 +48,10 @@ void System.Collections.ICollection.CopyTo(System.Array array, int index) { }
         public bool TryTake([System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out T item, int millisecondsTimeout) { throw null; }
         public bool TryTake([System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out T item, int millisecondsTimeout, System.Threading.CancellationToken cancellationToken) { throw null; }
         public bool TryTake([System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out T item, System.TimeSpan timeout) { throw null; }
-        public static int TryTakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, [System.Diagnostics.CodeAnalysis.MaybeNullAttribute] out T item) { throw null; }
-        public static int TryTakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, [System.Diagnostics.CodeAnalysis.MaybeNullAttribute] out T item, int millisecondsTimeout) { throw null; }
-        public static int TryTakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, [System.Diagnostics.CodeAnalysis.MaybeNullAttribute] out T item, int millisecondsTimeout, System.Threading.CancellationToken cancellationToken) { throw null; }
-        public static int TryTakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, [System.Diagnostics.CodeAnalysis.MaybeNullAttribute] out T item, System.TimeSpan timeout) { throw null; }
+        public static int TryTakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, out T? item) { throw null; }
+        public static int TryTakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, out T? item, int millisecondsTimeout) { throw null; }
+        public static int TryTakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, out T? item, int millisecondsTimeout, System.Threading.CancellationToken cancellationToken) { throw null; }
+        public static int TryTakeFromAny(System.Collections.Concurrent.BlockingCollection<T>[] collections, out T? item, System.TimeSpan timeout) { throw null; }
     }
     public partial class ConcurrentBag<T> : System.Collections.Concurrent.IProducerConsumerCollection<T>, System.Collections.Generic.IEnumerable<T>, System.Collections.Generic.IReadOnlyCollection<T>, System.Collections.ICollection, System.Collections.IEnumerable
     {
diff --git a/src/libraries/System.Collections.Concurrent/src/System.Collections.Concurrent.csproj b/src/libraries/System.Collections.Concurrent/src/System.Collections.Concurrent.csproj
index 93f3a50fc275c0..0584d13dbe8e72 100644
--- a/src/libraries/System.Collections.Concurrent/src/System.Collections.Concurrent.csproj
+++ b/src/libraries/System.Collections.Concurrent/src/System.Collections.Concurrent.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Collections.Concurrent</AssemblyName>
-    <RootNamespace>System.Collections.Concurrent</RootNamespace>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <Nullable>enable</Nullable>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
@@ -23,8 +21,8 @@
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(CoreLibProject)" />
-    <ProjectReference Include="..\..\System.Collections\src\System.Collections.csproj" />
-    <ProjectReference Include="..\..\System.Diagnostics.Tracing\src\System.Diagnostics.Tracing.csproj" />
-    <ProjectReference Include="..\..\System.Threading\src\System.Threading.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections\src\System.Collections.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Diagnostics.Tracing\src\System.Diagnostics.Tracing.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Threading\src\System.Threading.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/BlockingCollection.cs b/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/BlockingCollection.cs
index ec80b76e754136..a7a74c66c3204b 100644
--- a/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/BlockingCollection.cs
+++ b/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/BlockingCollection.cs
@@ -1169,7 +1169,7 @@ private static int UpdateTimeOut(uint startTime, int originalWaitMillisecondsTim
         /// <exception cref="System.ArgumentOutOfRangeException">The count of <paramref name="collections"/> is greater than the maximum size of
         /// 62 for STA and 63 for MTA.</exception>
         /// <remarks>A call to TakeFromAny may block until an item is available to be removed.</remarks>
-        public static int TakeFromAny(BlockingCollection<T>[] collections, [MaybeNull] out T item)
+        public static int TakeFromAny(BlockingCollection<T>[] collections, out T? item)
         {
             return TakeFromAny(collections, out item, CancellationToken.None);
         }
@@ -1198,7 +1198,7 @@ public static int TakeFromAny(BlockingCollection<T>[] collections, [MaybeNull] o
         /// <exception cref="System.ArgumentOutOfRangeException">The count of <paramref name="collections"/> is greater than the maximum size of
         /// 62 for STA and 63 for MTA.</exception>
         /// <remarks>A call to TakeFromAny may block until an item is available to be removed.</remarks>
-        public static int TakeFromAny(BlockingCollection<T>[] collections, [MaybeNull] out T item, CancellationToken cancellationToken)
+        public static int TakeFromAny(BlockingCollection<T>[] collections, out T? item, CancellationToken cancellationToken)
         {
             int returnValue = TryTakeFromAnyCore(collections, out item, Timeout.Infinite, true, cancellationToken);
             Debug.Assert(returnValue >= 0 && returnValue < collections.Length,
@@ -1226,7 +1226,7 @@ public static int TakeFromAny(BlockingCollection<T>[] collections, [MaybeNull] o
         /// <exception cref="System.ArgumentOutOfRangeException">The count of <paramref name="collections"/> is greater than the maximum size of
         /// 62 for STA and 63 for MTA.</exception>
         /// <remarks>A call to TryTakeFromAny may block until an item is available to be removed.</remarks>
-        public static int TryTakeFromAny(BlockingCollection<T>[] collections, [MaybeNull] out T item)
+        public static int TryTakeFromAny(BlockingCollection<T>[] collections, out T? item)
         {
             return TryTakeFromAny(collections, out item, 0);
         }
@@ -1257,7 +1257,7 @@ public static int TryTakeFromAny(BlockingCollection<T>[] collections, [MaybeNull
         /// <exception cref="System.ArgumentOutOfRangeException">The count of <paramref name="collections"/> is greater than the maximum size of
         /// 62 for STA and 63 for MTA.</exception>
         /// <remarks>A call to TryTakeFromAny may block until an item is available to be removed.</remarks>
-        public static int TryTakeFromAny(BlockingCollection<T>[] collections, [MaybeNull] out T item, TimeSpan timeout)
+        public static int TryTakeFromAny(BlockingCollection<T>[] collections, out T? item, TimeSpan timeout)
         {
             ValidateTimeout(timeout);
             return TryTakeFromAnyCore(collections, out item, (int)timeout.TotalMilliseconds, false, CancellationToken.None);
@@ -1287,7 +1287,7 @@ public static int TryTakeFromAny(BlockingCollection<T>[] collections, [MaybeNull
         /// <exception cref="System.ArgumentOutOfRangeException">The count of <paramref name="collections"/> is greater than the maximum size of
         /// 62 for STA and 63 for MTA.</exception>
         /// <remarks>A call to TryTakeFromAny may block until an item is available to be removed.</remarks>
-        public static int TryTakeFromAny(BlockingCollection<T>[] collections, [MaybeNull] out T item, int millisecondsTimeout)
+        public static int TryTakeFromAny(BlockingCollection<T>[] collections, out T? item, int millisecondsTimeout)
         {
             ValidateMillisecondsTimeout(millisecondsTimeout);
             return TryTakeFromAnyCore(collections, out item, millisecondsTimeout, false, CancellationToken.None);
@@ -1321,7 +1321,7 @@ public static int TryTakeFromAny(BlockingCollection<T>[] collections, [MaybeNull
         /// <exception cref="System.ArgumentOutOfRangeException">The count of <paramref name="collections"/> is greater than the maximum size of
         /// 62 for STA and 63 for MTA.</exception>
         /// <remarks>A call to TryTakeFromAny may block until an item is available to be removed.</remarks>
-        public static int TryTakeFromAny(BlockingCollection<T>[] collections, [MaybeNull] out T item, int millisecondsTimeout, CancellationToken cancellationToken)
+        public static int TryTakeFromAny(BlockingCollection<T>[] collections, out T? item, int millisecondsTimeout, CancellationToken cancellationToken)
         {
             ValidateMillisecondsTimeout(millisecondsTimeout);
             return TryTakeFromAnyCore(collections, out item, millisecondsTimeout, false, cancellationToken);
@@ -1344,7 +1344,7 @@ public static int TryTakeFromAny(BlockingCollection<T>[] collections, [MaybeNull
         /// <exception cref="System.ArgumentException">If the collections argument is a 0-length array or contains a
         /// null element. Also, if at least one of the collections has been marked complete for adds.</exception>
         /// <exception cref="System.ObjectDisposedException">If at least one of the collections has been disposed.</exception>
-        private static int TryTakeFromAnyCore(BlockingCollection<T>[] collections, [MaybeNull] out T item, int millisecondsTimeout, bool isTakeOperation, CancellationToken externalCancellationToken)
+        private static int TryTakeFromAnyCore(BlockingCollection<T>[] collections, out T? item, int millisecondsTimeout, bool isTakeOperation, CancellationToken externalCancellationToken)
         {
             ValidateCollectionsArray(collections, false);
 
@@ -1378,7 +1378,7 @@ private static int TryTakeFromAnyCore(BlockingCollection<T>[] collections, [Mayb
         /// <exception cref="System.ArgumentException">If the collections argument is a 0-length array or contains a
         /// null element. Also, if at least one of the collections has been marked complete for adds.</exception>
         /// <exception cref="System.ObjectDisposedException">If at least one of the collections has been disposed.</exception>
-        private static int TryTakeFromAnyCoreSlow(BlockingCollection<T>[] collections, [MaybeNull] out T item, int millisecondsTimeout, bool isTakeOperation, CancellationToken externalCancellationToken)
+        private static int TryTakeFromAnyCoreSlow(BlockingCollection<T>[] collections, out T? item, int millisecondsTimeout, bool isTakeOperation, CancellationToken externalCancellationToken)
         {
             const int OPERATION_FAILED = -1;
 
diff --git a/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentBag.cs b/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentBag.cs
index e2253548c46a6b..2ac047da258419 100644
--- a/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentBag.cs
+++ b/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentBag.cs
@@ -1089,7 +1089,7 @@ internal enum Operation
         private sealed class Enumerator : IEnumerator<T>
         {
             private readonly T[] _array;
-            [AllowNull] private T _current = default;
+            private T? _current;
             private int _index;
 
             public Enumerator(T[] array)
@@ -1110,7 +1110,7 @@ public bool MoveNext()
                 return false;
             }
 
-            public T Current => _current;
+            public T Current => _current!;
 
             object? IEnumerator.Current
             {
diff --git a/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentDictionary.cs b/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentDictionary.cs
index 6b06c592e38585..affa3bfaa30b57 100644
--- a/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentDictionary.cs
+++ b/src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentDictionary.cs
@@ -344,7 +344,7 @@ public bool TryRemove(KeyValuePair<TKey, TValue> item)
         /// <param name="value">The variable into which the removed value, if found, is stored.</param>
         /// <param name="matchValue">Whether removal of the key is conditional on its value.</param>
         /// <param name="oldValue">The conditional value to compare against if <paramref name="matchValue"/> is true</param>
-        private bool TryRemoveInternal(TKey key, [MaybeNullWhen(false)] out TValue value, bool matchValue, [AllowNull] TValue oldValue)
+        private bool TryRemoveInternal(TKey key, [MaybeNullWhen(false)] out TValue value, bool matchValue, TValue? oldValue)
         {
             IEqualityComparer<TKey>? comparer = _comparer;
             int hashcode = comparer is null ? key.GetHashCode() : comparer.GetHashCode(key);
@@ -375,7 +375,7 @@ private bool TryRemoveInternal(TKey key, [MaybeNullWhen(false)] out TValue value
                                 bool valuesMatch = EqualityComparer<TValue>.Default.Equals(oldValue, curr._value);
                                 if (!valuesMatch)
                                 {
-                                    value = default!;
+                                    value = default;
                                     return false;
                                 }
                             }
diff --git a/src/libraries/System.Collections.Immutable/Directory.Build.props b/src/libraries/System.Collections.Immutable/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Collections.Immutable/Directory.Build.props
+++ b/src/libraries/System.Collections.Immutable/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.cs b/src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.cs
index 403bbf8aff654e..b24217cca9ceb7 100644
--- a/src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.cs
+++ b/src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.cs
@@ -122,9 +122,9 @@ public partial struct ImmutableArray<T> : System.Collections.Generic.ICollection
         public System.ReadOnlyMemory<T> AsMemory() { throw null; }
         public System.ReadOnlySpan<T> AsSpan() { throw null; }
 #endif
-        public System.Collections.Immutable.ImmutableArray<TOther> As<TOther>() where TOther : class { throw null; }
-        public System.Collections.Immutable.ImmutableArray<TOther> CastArray<TOther>() where TOther : class { throw null; }
-        public static System.Collections.Immutable.ImmutableArray<T> CastUp<TDerived>(System.Collections.Immutable.ImmutableArray<TDerived> items) where TDerived : class, T { throw null; }
+        public System.Collections.Immutable.ImmutableArray<TOther> As<TOther>() where TOther : class? { throw null; }
+        public System.Collections.Immutable.ImmutableArray<TOther> CastArray<TOther>() where TOther : class? { throw null; }
+        public static System.Collections.Immutable.ImmutableArray<T> CastUp<TDerived>(System.Collections.Immutable.ImmutableArray<TDerived> items) where TDerived : class?, T { throw null; }
         public System.Collections.Immutable.ImmutableArray<T> Clear() { throw null; }
         public bool Contains(T item) { throw null; }
         public void CopyTo(int sourceIndex, T[] destination, int destinationIndex, int length) { }
@@ -268,8 +268,7 @@ public static partial class ImmutableDictionary
         public static System.Collections.Immutable.ImmutableDictionary<TKey, TValue> Create<TKey, TValue>() where TKey : notnull { throw null; }
         public static System.Collections.Immutable.ImmutableDictionary<TKey, TValue> Create<TKey, TValue>(System.Collections.Generic.IEqualityComparer<TKey>? keyComparer) where TKey : notnull { throw null; }
         public static System.Collections.Immutable.ImmutableDictionary<TKey, TValue> Create<TKey, TValue>(System.Collections.Generic.IEqualityComparer<TKey>? keyComparer, System.Collections.Generic.IEqualityComparer<TValue>? valueComparer) where TKey : notnull { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TValue GetValueOrDefault<TKey, TValue>(this System.Collections.Immutable.IImmutableDictionary<TKey, TValue> dictionary, TKey key) where TKey : notnull { throw null; }
+        public static TValue? GetValueOrDefault<TKey, TValue>(this System.Collections.Immutable.IImmutableDictionary<TKey, TValue> dictionary, TKey key) where TKey : notnull { throw null; }
         public static TValue GetValueOrDefault<TKey, TValue>(this System.Collections.Immutable.IImmutableDictionary<TKey, TValue> dictionary, TKey key, TValue defaultValue) where TKey : notnull { throw null; }
         public static System.Collections.Immutable.ImmutableDictionary<TKey, TValue> ToImmutableDictionary<TKey, TValue>(this System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TValue>> source) where TKey : notnull { throw null; }
         public static System.Collections.Immutable.ImmutableDictionary<TKey, TValue> ToImmutableDictionary<TKey, TValue>(this System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TValue>> source, System.Collections.Generic.IEqualityComparer<TKey>? keyComparer) where TKey : notnull { throw null; }
@@ -367,8 +366,7 @@ public void Clear() { }
             public bool ContainsKey(TKey key) { throw null; }
             public bool ContainsValue(TValue value) { throw null; }
             public System.Collections.Immutable.ImmutableDictionary<TKey, TValue>.Enumerator GetEnumerator() { throw null; }
-            [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-            public TValue GetValueOrDefault(TKey key) { throw null; }
+            public TValue? GetValueOrDefault(TKey key) { throw null; }
             public TValue GetValueOrDefault(TKey key, TValue defaultValue) { throw null; }
             public bool Remove(System.Collections.Generic.KeyValuePair<TKey, TValue> item) { throw null; }
             public bool Remove(TKey key) { throw null; }
@@ -413,7 +411,7 @@ public static partial class ImmutableHashSet
         public static System.Collections.Immutable.ImmutableHashSet<TSource> ToImmutableHashSet<TSource>(this System.Collections.Immutable.ImmutableHashSet<TSource>.Builder builder) { throw null; }
     }
 
-    #if !NETSTANDARD1_0 && !NETSTANDARD1_3 && !NETSTANDARD2_0
+    #if !NETSTANDARD1_0 && !NETSTANDARD1_3 && !NETSTANDARD2_0 && !NETFRAMEWORK
     public sealed partial class ImmutableHashSet<T> : System.Collections.Generic.ICollection<T>, System.Collections.Generic.IEnumerable<T>, System.Collections.Generic.IReadOnlyCollection<T>, System.Collections.Generic.ISet<T>, System.Collections.Generic.IReadOnlySet<T>, System.Collections.ICollection, System.Collections.IEnumerable, System.Collections.Immutable.IImmutableSet<T>
 #else
     public sealed partial class ImmutableHashSet<T> : System.Collections.Generic.ICollection<T>, System.Collections.Generic.IEnumerable<T>, System.Collections.Generic.IReadOnlyCollection<T>, System.Collections.Generic.ISet<T>, System.Collections.ICollection, System.Collections.IEnumerable, System.Collections.Immutable.IImmutableSet<T>
@@ -520,8 +518,8 @@ public static void Push<T>(ref System.Collections.Immutable.ImmutableStack<T> lo
         public static bool TryPop<T>(ref System.Collections.Immutable.ImmutableStack<T> location, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out T value) { throw null; }
         public static bool TryRemove<TKey, TValue>(ref System.Collections.Immutable.ImmutableDictionary<TKey, TValue> location, TKey key, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out TValue value) where TKey : notnull { throw null; }
         public static bool TryUpdate<TKey, TValue>(ref System.Collections.Immutable.ImmutableDictionary<TKey, TValue> location, TKey key, TValue newValue, TValue comparisonValue) where TKey : notnull { throw null; }
-        public static bool Update<T>(ref T location, System.Func<T, T> transformer) where T : class { throw null; }
-        public static bool Update<T, TArg>(ref T location, System.Func<T, TArg, T> transformer, TArg transformerArgument) where T : class { throw null; }
+        public static bool Update<T>(ref T location, System.Func<T, T> transformer) where T : class? { throw null; }
+        public static bool Update<T, TArg>(ref T location, System.Func<T, TArg, T> transformer, TArg transformerArgument) where T : class? { throw null; }
         public static bool Update<T>(ref System.Collections.Immutable.ImmutableArray<T> location, Func<System.Collections.Immutable.ImmutableArray<T>, System.Collections.Immutable.ImmutableArray<T>> transformer) { throw null; }
         public static bool Update<T, TArg>(ref System.Collections.Immutable.ImmutableArray<T> location, Func<System.Collections.Immutable.ImmutableArray<T>, TArg, System.Collections.Immutable.ImmutableArray<T>> transformer, TArg transformerArgument) { throw null; }
     }
@@ -572,14 +570,12 @@ public void CopyTo(int index, T[] array, int arrayIndex, int count) { }
         public void CopyTo(T[] array) { }
         public void CopyTo(T[] array, int arrayIndex) { }
         public bool Exists(System.Predicate<T> match) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T Find(System.Predicate<T> match) { throw null; }
+        public T? Find(System.Predicate<T> match) { throw null; }
         public System.Collections.Immutable.ImmutableList<T> FindAll(System.Predicate<T> match) { throw null; }
         public int FindIndex(int startIndex, int count, System.Predicate<T> match) { throw null; }
         public int FindIndex(int startIndex, System.Predicate<T> match) { throw null; }
         public int FindIndex(System.Predicate<T> match) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T FindLast(System.Predicate<T> match) { throw null; }
+        public T? FindLast(System.Predicate<T> match) { throw null; }
         public int FindLastIndex(int startIndex, int count, System.Predicate<T> match) { throw null; }
         public int FindLastIndex(int startIndex, System.Predicate<T> match) { throw null; }
         public int FindLastIndex(System.Predicate<T> match) { throw null; }
@@ -662,14 +658,12 @@ public void CopyTo(int index, T[] array, int arrayIndex, int count) { }
             public void CopyTo(T[] array) { }
             public void CopyTo(T[] array, int arrayIndex) { }
             public bool Exists(System.Predicate<T> match) { throw null; }
-            [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-            public T Find(System.Predicate<T> match) { throw null; }
+            public T? Find(System.Predicate<T> match) { throw null; }
             public System.Collections.Immutable.ImmutableList<T> FindAll(System.Predicate<T> match) { throw null; }
             public int FindIndex(int startIndex, int count, System.Predicate<T> match) { throw null; }
             public int FindIndex(int startIndex, System.Predicate<T> match) { throw null; }
             public int FindIndex(System.Predicate<T> match) { throw null; }
-            [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-            public T FindLast(System.Predicate<T> match) { throw null; }
+            public T? FindLast(System.Predicate<T> match) { throw null; }
             public int FindLastIndex(int startIndex, int count, System.Predicate<T> match) { throw null; }
             public int FindLastIndex(int startIndex, System.Predicate<T> match) { throw null; }
             public int FindLastIndex(System.Predicate<T> match) { throw null; }
@@ -866,8 +860,7 @@ public void Clear() { }
             public bool ContainsKey(TKey key) { throw null; }
             public bool ContainsValue(TValue value) { throw null; }
             public System.Collections.Immutable.ImmutableSortedDictionary<TKey, TValue>.Enumerator GetEnumerator() { throw null; }
-            [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-            public TValue GetValueOrDefault(TKey key) { throw null; }
+            public TValue? GetValueOrDefault(TKey key) { throw null; }
             public TValue GetValueOrDefault(TKey key, TValue defaultValue) { throw null; }
             public bool Remove(System.Collections.Generic.KeyValuePair<TKey, TValue> item) { throw null; }
             public bool Remove(TKey key) { throw null; }
@@ -916,7 +909,7 @@ public static partial class ImmutableSortedSet
         public static System.Collections.Immutable.ImmutableSortedSet<TSource> ToImmutableSortedSet<TSource>(this System.Collections.Immutable.ImmutableSortedSet<TSource>.Builder builder) { throw null; }
     }
 
-    #if !NETSTANDARD1_0 && !NETSTANDARD1_3 && !NETSTANDARD2_0
+    #if !NETSTANDARD1_0 && !NETSTANDARD1_3 && !NETSTANDARD2_0 && !NETFRAMEWORK
     public sealed partial class ImmutableSortedSet<T> : System.Collections.Generic.ICollection<T>, System.Collections.Generic.IEnumerable<T>, System.Collections.Generic.IList<T>, System.Collections.Generic.IReadOnlyCollection<T>, System.Collections.Generic.IReadOnlyList<T>, System.Collections.Generic.ISet<T>, System.Collections.Generic.IReadOnlySet<T>, System.Collections.ICollection, System.Collections.IEnumerable, System.Collections.IList, System.Collections.Immutable.IImmutableSet<T>
     #else
     public sealed partial class ImmutableSortedSet<T> : System.Collections.Generic.ICollection<T>, System.Collections.Generic.IEnumerable<T>, System.Collections.Generic.IList<T>, System.Collections.Generic.IReadOnlyCollection<T>, System.Collections.Generic.IReadOnlyList<T>, System.Collections.Generic.ISet<T>, System.Collections.ICollection, System.Collections.IEnumerable, System.Collections.IList, System.Collections.Immutable.IImmutableSet<T>
@@ -928,10 +921,8 @@ internal ImmutableSortedSet() { }
         public bool IsEmpty { get { throw null; } }
         public T this[int index] { get { throw null; } }
         public System.Collections.Generic.IComparer<T> KeyComparer { get { throw null; } }
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T Max { get { throw null; } }
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T Min { get { throw null; } }
+        public T? Max { get { throw null; } }
+        public T? Min { get { throw null; } }
         bool System.Collections.Generic.ICollection<T>.IsReadOnly { get { throw null; } }
         T System.Collections.Generic.IList<T>.this[int index] { get { throw null; } set { } }
         bool System.Collections.ICollection.IsSynchronized { get { throw null; } }
@@ -996,10 +987,8 @@ internal Builder() { }
             public int Count { get { throw null; } }
             public T this[int index] { get { throw null; } }
             public System.Collections.Generic.IComparer<T> KeyComparer { get { throw null; } set { } }
-            [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-            public T Max { get { throw null; } }
-            [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-            public T Min { get { throw null; } }
+            public T? Max { get { throw null; } }
+            public T? Min { get { throw null; } }
             bool System.Collections.Generic.ICollection<T>.IsReadOnly { get { throw null; } }
             bool System.Collections.ICollection.IsSynchronized { get { throw null; } }
             object System.Collections.ICollection.SyncRoot { get { throw null; } }
@@ -1083,32 +1072,24 @@ namespace System.Linq
 {
     public static partial class ImmutableArrayExtensions
     {
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T Aggregate<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, T, T> func) { throw null; }
+        public static T? Aggregate<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, T, T> func) { throw null; }
         public static TAccumulate Aggregate<TAccumulate, T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, TAccumulate seed, System.Func<TAccumulate, T, TAccumulate> func) { throw null; }
         public static TResult Aggregate<TAccumulate, TResult, T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, TAccumulate seed, System.Func<TAccumulate, T, TAccumulate> func, System.Func<TAccumulate, TResult> resultSelector) { throw null; }
         public static bool All<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
         public static bool Any<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
         public static bool Any<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
         public static bool Any<T>(this System.Collections.Immutable.ImmutableArray<T>.Builder builder) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T ElementAtOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, int index) { throw null; }
+        public static T? ElementAtOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, int index) { throw null; }
         public static T ElementAt<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, int index) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T FirstOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T FirstOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T FirstOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T>.Builder builder) { throw null; }
+        public static T? FirstOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
+        public static T? FirstOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
+        public static T? FirstOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T>.Builder builder) { throw null; }
         public static T First<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
         public static T First<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
         public static T First<T>(this System.Collections.Immutable.ImmutableArray<T>.Builder builder) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T LastOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T LastOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T LastOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T>.Builder builder) { throw null; }
+        public static T? LastOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
+        public static T? LastOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
+        public static T? LastOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T>.Builder builder) { throw null; }
         public static T Last<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
         public static T Last<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
         public static T Last<T>(this System.Collections.Immutable.ImmutableArray<T>.Builder builder) { throw null; }
@@ -1117,10 +1098,8 @@ public static partial class ImmutableArrayExtensions
         public static bool SequenceEqual<TDerived, TBase>(this System.Collections.Immutable.ImmutableArray<TBase> immutableArray, System.Collections.Generic.IEnumerable<TDerived> items, System.Collections.Generic.IEqualityComparer<TBase>? comparer = null) where TDerived : TBase { throw null; }
         public static bool SequenceEqual<TDerived, TBase>(this System.Collections.Immutable.ImmutableArray<TBase> immutableArray, System.Collections.Immutable.ImmutableArray<TDerived> items, System.Collections.Generic.IEqualityComparer<TBase>? comparer = null) where TDerived : TBase { throw null; }
         public static bool SequenceEqual<TDerived, TBase>(this System.Collections.Immutable.ImmutableArray<TBase> immutableArray, System.Collections.Immutable.ImmutableArray<TDerived> items, System.Func<TBase, TBase, bool> predicate) where TDerived : TBase { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T SingleOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T SingleOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
+        public static T? SingleOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
+        public static T? SingleOrDefault<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
         public static T Single<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
         public static T Single<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray, System.Func<T, bool> predicate) { throw null; }
         public static T[] ToArray<T>(this System.Collections.Immutable.ImmutableArray<T> immutableArray) { throw null; }
diff --git a/src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.csproj b/src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.csproj
index 48e1f0bde560bd..57d3d7cec3d4dd 100644
--- a/src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.csproj
+++ b/src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.0;netstandard1.3;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.0;netstandard1.3;netstandard2.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -12,16 +12,17 @@
     <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
     <ProjectReference Include="..\..\System.Runtime.InteropServices\ref\System.Runtime.InteropServices.csproj" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.0'">
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Collections" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3' or
+                        '$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
+  <!-- Include these transitive dependencies to overrule NuGet's ProjectReference over PackageReferene behavior. -->
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3'">
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Runtime.InteropServices" />
+    <PackageReference Include="System.Runtime.InteropServices" Version="$(SystemRuntimeInteropServicesVersion)" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3' or '$(TargetFramework)' == 'netstandard2.0'">
-    <Reference Include="System.Memory" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3' or '$(TargetFramework)' == 'netstandard1.0'">
+    <PackageReference Include="System.Runtime" Version="$(SystemRuntimeVersion)" />
+    <PackageReference Include="System.Collections" Version="$(SystemCollectionsVersion)" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj b/src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj
index f2fc64f714f3ea..f950c965cac28e 100644
--- a/src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj
+++ b/src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.0;netstandard1.3;netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.0;netstandard1.3;netstandard2.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -88,13 +87,13 @@
     <Compile Include="Validation\ValidatedNotNullAttribute.cs" />
     <Compile Include="$(CommonPath)System\Runtime\Versioning\NonVersionableAttribute.cs"
              Link="Common\System\Runtime\Versioning\NonVersionableAttribute.cs" />
+    <None Include="Interfaces.cd" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.0' or '$(TargetFramework)' == 'netstandard1.3'">
     <Compile Include="$(CommonPath)System\Diagnostics\CodeAnalysis\ExcludeFromCodeCoverageAttribute.cs"
              Link="System\Diagnostics\CodeAnalysis\ExcludeFromCodeCoverageAttribute.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <None Include="Interfaces.cd" />
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <Reference Include="System.Collections" />
     <Reference Include="System.Diagnostics.Contracts" />
     <Reference Include="System.Diagnostics.Debug" />
@@ -104,22 +103,14 @@
     <Reference Include="System.Resources.ResourceManager" />
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Threading" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3'">
-    <Reference Include="System.AppContext" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3' or '$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <Reference Include="System.Runtime.InteropServices" />
+    <Reference Include="System.Threading" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3' or '$(TargetFramework)' == 'netstandard2.0'">
-    <Reference Include="System.Memory" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Memory" />
-    <Reference Include="netstandard" />
-    <Reference Include="System.Core" />
+  <ItemGroup>
+    <PackageReference Include="System.Diagnostics.Contracts" Condition="$(TargetFramework.StartsWith('netstandard1.'))" Version="$(SystemDiagnosticsContractsVersion)" />
+    <PackageReference Include="System.Memory" Condition="'$(TargetFramework)' == 'netstandard1.3' or
+                                                         '$(TargetFramework)' == 'netstandard2.0' or
+                                                         $(TargetFramework.StartsWith('net4'))" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Runtime.InteropServices" Condition="'$(TargetFramework)' == 'netstandard1.3'" Version="$(SystemRuntimeInteropServicesVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/AllocFreeConcurrentStack.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/AllocFreeConcurrentStack.cs
index 3188fce8fe3b43..e44135512ed8e5 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/AllocFreeConcurrentStack.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/AllocFreeConcurrentStack.cs
@@ -31,7 +31,7 @@ public static bool TryTake([MaybeNullWhen(false)] out T item)
                 return true;
             }
 
-            item = default(T)!;
+            item = default;
             return false;
         }
 
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/IImmutableListQueries.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/IImmutableListQueries.cs
index d5decd80e654a7..cb19d186960902 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/IImmutableListQueries.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/IImmutableListQueries.cs
@@ -120,8 +120,7 @@ internal interface IImmutableListQueries<T> : IReadOnlyList<T>
         /// The first element that matches the conditions defined by the specified predicate,
         /// if found; otherwise, the default value for type <typeparamref name="T"/>.
         /// </returns>
-        [return: MaybeNull]
-        T Find(Predicate<T> match);
+        T? Find(Predicate<T> match);
 
         /// <summary>
         /// Retrieves all the elements that match the conditions defined by the specified
@@ -194,8 +193,7 @@ internal interface IImmutableListQueries<T> : IReadOnlyList<T>
         /// The last element that matches the conditions defined by the specified predicate,
         /// if found; otherwise, the default value for type <typeparamref name="T"/>.
         /// </returns>
-        [return: MaybeNull]
-        T FindLast(Predicate<T> match);
+        T? FindLast(Predicate<T> match);
 
         /// <summary>
         /// Searches for an element that matches the conditions defined by the specified
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Minimal.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Minimal.cs
index 93da9008ff8bd4..6210a0a9a1f8a3 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Minimal.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Minimal.cs
@@ -334,7 +334,7 @@ public bool Equals(ImmutableArray<T> other)
         /// <see cref="ImmutableArray{T}.As{TOther}"/>  or <see cref="ImmutableArray{T}.CastArray{TOther}"/>method.
         /// </remarks>
         public static ImmutableArray<T> CastUp<TDerived>(ImmutableArray<TDerived> items)
-            where TDerived : class, T
+            where TDerived : class?, T
         {
             return new ImmutableArray<T>(items.array);
         }
@@ -344,7 +344,7 @@ public static ImmutableArray<T> CastUp<TDerived>(ImmutableArray<TDerived> items)
         /// array to an array of type <typeparam name="TOther"/>.
         /// </summary>
         /// <exception cref="InvalidCastException">Thrown if the cast is illegal.</exception>
-        public ImmutableArray<TOther> CastArray<TOther>() where TOther : class
+        public ImmutableArray<TOther> CastArray<TOther>() where TOther : class?
         {
             return new ImmutableArray<TOther>((TOther[])(object)array!);
         }
@@ -364,9 +364,9 @@ public ImmutableArray<TOther> CastArray<TOther>() where TOther : class
         /// element types to their derived types. However, downcasting is only successful
         /// when it reverses a prior upcasting operation.
         /// </remarks>
-        public ImmutableArray<TOther> As<TOther>() where TOther : class
+        public ImmutableArray<TOther> As<TOther>() where TOther : class?
         {
-            return new ImmutableArray<TOther>((this.array as TOther[])!);
+            return new ImmutableArray<TOther>((this.array as TOther[]));
         }
 
         /// <summary>
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary.cs
index 80d99d4d207a01..53e6a030761e43 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary.cs
@@ -290,8 +290,7 @@ public static bool Contains<TKey, TValue>(this IImmutableDictionary<TKey, TValue
         /// <param name="dictionary">The dictionary to retrieve the value from.</param>
         /// <param name="key">The key to search for.</param>
         /// <returns>The value for the key, or the default value of type <typeparamref name="TValue"/> if no matching key was found.</returns>
-        [return: MaybeNull]
-        public static TValue GetValueOrDefault<TKey, TValue>(this IImmutableDictionary<TKey, TValue> dictionary, TKey key) where TKey : notnull
+        public static TValue? GetValueOrDefault<TKey, TValue>(this IImmutableDictionary<TKey, TValue> dictionary, TKey key) where TKey : notnull
         {
             return GetValueOrDefault(dictionary, key, default(TValue)!);
         }
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.Builder.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.Builder.cs
index a3c7662277719c..eb94a5bfd27c07 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.Builder.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.Builder.cs
@@ -466,8 +466,7 @@ public Enumerator GetEnumerator()
             /// </summary>
             /// <param name="key">The key to search for.</param>
             /// <returns>The value for the key, or the default value of type <typeparamref name="TValue"/> if no matching key was found.</returns>
-            [return: MaybeNull]
-            public TValue GetValueOrDefault(TKey key)
+            public TValue? GetValueOrDefault(TKey key)
             {
                 return this.GetValueOrDefault(key, default(TValue)!);
             }
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.HashBucket.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.HashBucket.cs
index 0f8e7cede69093..77e65ecf25dd5a 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.HashBucket.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.HashBucket.cs
@@ -263,7 +263,7 @@ internal bool TryGetValue(TKey key, Comparers comparers, [MaybeNullWhen(false)]
             {
                 if (this.IsEmpty)
                 {
-                    value = default(TValue)!;
+                    value = default;
                     return false;
                 }
 
@@ -277,7 +277,7 @@ internal bool TryGetValue(TKey key, Comparers comparers, [MaybeNullWhen(false)]
                 var index = _additionalElements.IndexOf(kv, comparers.KeyOnlyComparer);
                 if (index < 0)
                 {
-                    value = default(TValue)!;
+                    value = default;
                     return false;
                 }
 
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.cs
index 504d1202d0757c..346fdc1d1160e3 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary_2.cs
@@ -912,7 +912,7 @@ private static bool TryGetValue(TKey key, MutationInput origin, [MaybeNullWhen(f
                 return bucket.TryGetValue(key, origin.Comparers, out value!);
             }
 
-            value = default(TValue)!;
+            value = default;
             return false;
         }
 
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableInterlocked.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableInterlocked.cs
index 6d3ba1728e6b28..5f99c0624b4941 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableInterlocked.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableInterlocked.cs
@@ -30,7 +30,7 @@ public static class ImmutableInterlocked
         /// <c>false</c> if the location's value remained the same because the last
         /// invocation of <paramref name="transformer"/> returned the existing value.
         /// </returns>
-        public static bool Update<T>(ref T location, Func<T, T> transformer) where T : class
+        public static bool Update<T>(ref T location, Func<T, T> transformer) where T : class?
         {
             Requires.NotNull(transformer, nameof(transformer));
 
@@ -74,7 +74,7 @@ public static bool Update<T>(ref T location, Func<T, T> transformer) where T : c
         /// <c>false</c> if the location's value remained the same because the last
         /// invocation of <paramref name="transformer"/> returned the existing value.
         /// </returns>
-        public static bool Update<T, TArg>(ref T location, Func<T, TArg, T> transformer, TArg transformerArgument) where T : class
+        public static bool Update<T, TArg>(ref T location, Func<T, TArg, T> transformer, TArg transformerArgument) where T : class?
         {
             Requires.NotNull(transformer, nameof(transformer));
 
@@ -525,7 +525,7 @@ public static bool TryPop<T>(ref ImmutableStack<T> location, [MaybeNullWhen(fals
 
                 if (priorCollection.IsEmpty)
                 {
-                    value = default(T)!;
+                    value = default;
                     return false;
                 }
 
@@ -580,7 +580,7 @@ public static bool TryDequeue<T>(ref ImmutableQueue<T> location, [MaybeNullWhen(
 
                 if (priorCollection.IsEmpty)
                 {
-                    value = default(T)!;
+                    value = default;
                     return false;
                 }
 
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Builder.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Builder.cs
index 7d5577d8f2ec51..ee6b888241d255 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Builder.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Builder.cs
@@ -395,8 +395,7 @@ public ImmutableList<TOutput> ConvertAll<TOutput>(Func<T, TOutput> converter)
             /// The first element that matches the conditions defined by the specified predicate,
             /// if found; otherwise, the default value for type T.
             /// </returns>
-            [return: MaybeNull]
-            public T Find(Predicate<T> match) => _root.Find(match);
+            public T? Find(Predicate<T> match) => _root.Find(match);
 
             /// <summary>
             /// Retrieves all the elements that match the conditions defined by the specified
@@ -469,8 +468,7 @@ public ImmutableList<TOutput> ConvertAll<TOutput>(Func<T, TOutput> converter)
             /// The last element that matches the conditions defined by the specified predicate,
             /// if found; otherwise, the default value for type T.
             /// </returns>
-            [return: MaybeNull]
-            public T FindLast(Predicate<T> match) => _root.FindLast(match);
+            public T? FindLast(Predicate<T> match) => _root.FindLast(match);
 
             /// <summary>
             /// Searches for an element that matches the conditions defined by the specified
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Node.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Node.cs
index 9c30a67a6d9072..ef0381384f29ac 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Node.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Node.cs
@@ -998,8 +998,7 @@ internal bool Exists(Predicate<T> match)
             /// The first element that matches the conditions defined by the specified predicate,
             /// if found; otherwise, the default value for type <typeparamref name="T"/>.
             /// </returns>
-            [return: MaybeNull]
-            internal T Find(Predicate<T> match)
+            internal T? Find(Predicate<T> match)
             {
                 Requires.NotNull(match, nameof(match));
 
@@ -1011,7 +1010,7 @@ internal T Find(Predicate<T> match)
                     }
                 }
 
-                return default(T)!;
+                return default;
             }
 
             /// <summary>
@@ -1144,8 +1143,7 @@ internal int FindIndex(int startIndex, int count, Predicate<T> match)
             /// The last element that matches the conditions defined by the specified predicate,
             /// if found; otherwise, the default value for type <typeparamref name="T"/>.
             /// </returns>
-            [return: MaybeNull]
-            internal T FindLast(Predicate<T> match)
+            internal T? FindLast(Predicate<T> match)
             {
                 Requires.NotNull(match, nameof(match));
 
@@ -1160,7 +1158,7 @@ internal T FindLast(Predicate<T> match)
                     }
                 }
 
-                return default(T)!;
+                return default;
             }
 
             /// <summary>
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.cs
index e252d3c5619854..9597b0a98b6ae3 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.cs
@@ -593,8 +593,7 @@ public ImmutableList<TOutput> ConvertAll<TOutput>(Func<T, TOutput> converter)
         /// The first element that matches the conditions defined by the specified predicate,
         /// if found; otherwise, the default value for type <typeparamref name="T"/>.
         /// </returns>
-        [return: MaybeNull]
-        public T Find(Predicate<T> match) => _root.Find(match);
+        public T? Find(Predicate<T> match) => _root.Find(match);
 
         /// <summary>
         /// Retrieves all the elements that match the conditions defined by the specified
@@ -667,8 +666,7 @@ public ImmutableList<TOutput> ConvertAll<TOutput>(Func<T, TOutput> converter)
         /// The last element that matches the conditions defined by the specified predicate,
         /// if found; otherwise, the default value for type <typeparamref name="T"/>.
         /// </returns>
-        [return: MaybeNull]
-        public T FindLast(Predicate<T> match) => _root.FindLast(match);
+        public T? FindLast(Predicate<T> match) => _root.FindLast(match);
 
         /// <summary>
         /// Searches for an element that matches the conditions defined by the specified
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary_2.Builder.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary_2.Builder.cs
index 47da5f071d9bbd..2f8fafe67b298e 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary_2.Builder.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary_2.Builder.cs
@@ -603,8 +603,7 @@ public void RemoveRange(IEnumerable<TKey> keys)
             /// </summary>
             /// <param name="key">The key to search for.</param>
             /// <returns>The value for the key, or the default value for type <typeparamref name="TValue"/> if no matching key was found.</returns>
-            [return: MaybeNull]
-            public TValue GetValueOrDefault(TKey key)
+            public TValue? GetValueOrDefault(TKey key)
             {
                 return this.GetValueOrDefault(key, default(TValue)!);
             }
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary_2.Node.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary_2.Node.cs
index 353fb921136852..99173a5b2715cd 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary_2.Node.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary_2.Node.cs
@@ -362,7 +362,7 @@ internal bool TryGetValue(TKey key, IComparer<TKey> keyComparer, [MaybeNullWhen(
                 var match = this.Search(key, keyComparer);
                 if (match.IsEmpty)
                 {
-                    value = default(TValue)!;
+                    value = default;
                     return false;
                 }
                 else
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.Builder.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.Builder.cs
index 35169818def2af..2a1c606d12aace 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.Builder.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.Builder.cs
@@ -123,8 +123,7 @@ public ref readonly T ItemRef(int index)
             /// Gets the maximum value in the collection, as defined by the comparer.
             /// </summary>
             /// <value>The maximum value in the set.</value>
-            [MaybeNull]
-            public T Max
+            public T? Max
             {
                 get { return _root.Max; }
             }
@@ -133,8 +132,7 @@ public T Max
             /// Gets the minimum value in the collection, as defined by the comparer.
             /// </summary>
             /// <value>The minimum value in the set.</value>
-            [MaybeNull]
-            public T Min
+            public T? Min
             {
                 get { return _root.Min; }
             }
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.Node.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.Node.cs
index 9ff2099a971440..89b044c0ce9793 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.Node.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.Node.cs
@@ -184,14 +184,13 @@ internal T Key
             /// Gets the maximum value in the collection, as defined by the comparer.
             /// </summary>
             /// <value>The maximum value in the set.</value>
-            [MaybeNull]
-            internal T Max
+            internal T? Max
             {
                 get
                 {
                     if (this.IsEmpty)
                     {
-                        return default(T)!;
+                        return default;
                     }
 
                     Node n = this;
@@ -208,14 +207,13 @@ internal T Max
             /// Gets the minimum value in the collection, as defined by the comparer.
             /// </summary>
             /// <value>The minimum value in the set.</value>
-            [MaybeNull]
-            internal T Min
+            internal T? Min
             {
                 get
                 {
                     if (this.IsEmpty)
                     {
-                        return default(T)!;
+                        return default;
                     }
 
                     Node n = this;
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.cs
index c6b8a281f98a4e..b74674d8e2718f 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.cs
@@ -84,8 +84,7 @@ public ImmutableSortedSet<T> Clear()
         /// Gets the maximum value in the collection, as defined by the comparer.
         /// </summary>
         /// <value>The maximum value in the set.</value>
-        [MaybeNull]
-        public T Max
+        public T? Max
         {
             get { return _root.Max; }
         }
@@ -94,8 +93,7 @@ public T Max
         /// Gets the minimum value in the collection, as defined by the comparer.
         /// </summary>
         /// <value>The minimum value in the set.</value>
-        [MaybeNull]
-        public T Min
+        public T? Min
         {
             get { return _root.Min; }
         }
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableStack_1.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableStack_1.cs
index 15b5fbdd68eeda..f8b70a0a230d89 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableStack_1.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableStack_1.cs
@@ -27,8 +27,7 @@ public sealed partial class ImmutableStack<T> : IImmutableStack<T>
         /// <summary>
         /// The element on the top of the stack.
         /// </summary>
-        [MaybeNull]
-        private readonly T _head = default!;
+        private readonly T? _head;
 
         /// <summary>
         /// A stack that contains the rest of the elements (under the top element).
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/SecureObjectPool.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/SecureObjectPool.cs
index 8d3664fe955471..6d194da50e5db8 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/SecureObjectPool.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/SecureObjectPool.cs
@@ -124,7 +124,7 @@ internal bool TryUse<TCaller>(ref TCaller caller, [MaybeNullWhen(false)] out T v
             }
             else
             {
-                value = default(T)!;
+                value = default;
                 return false;
             }
         }
diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/SortedInt32KeyNode.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/SortedInt32KeyNode.cs
index 96ba5622790e00..25cc0638f62f6a 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/SortedInt32KeyNode.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/SortedInt32KeyNode.cs
@@ -34,8 +34,7 @@ internal sealed partial class SortedInt32KeyNode<TValue> : IBinaryTree
         /// <summary>
         /// The value associated with this node.
         /// </summary>
-        [MaybeNull]
-        private readonly TValue _value = default!;
+        private readonly TValue? _value;
 
         /// <summary>
         /// A value indicating whether this node has been frozen (made immutable).
@@ -197,15 +196,14 @@ internal SortedInt32KeyNode<TValue> Remove(int key, out bool mutated)
         /// </summary>
         /// <param name="key">The key.</param>
         /// <returns>The value.</returns>
-        [return: MaybeNull]
-        internal TValue GetValueOrDefault(int key)
+        internal TValue? GetValueOrDefault(int key)
         {
             SortedInt32KeyNode<TValue> node = this;
             while (true)
             {
                 if (node.IsEmpty)
                 {
-                    return default(TValue)!;
+                    return default;
                 }
 
                 if (key == node._key)
@@ -237,7 +235,7 @@ internal bool TryGetValue(int key, [MaybeNullWhen(false)] out TValue value)
             {
                 if (node.IsEmpty)
                 {
-                    value = default(TValue)!;
+                    value = default;
                     return false;
                 }
 
diff --git a/src/libraries/System.Collections.Immutable/src/System/Linq/ImmutableArrayExtensions.cs b/src/libraries/System.Collections.Immutable/src/System/Linq/ImmutableArrayExtensions.cs
index 13109d4c1143ad..2850cc5c1c368d 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Linq/ImmutableArrayExtensions.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Linq/ImmutableArrayExtensions.cs
@@ -253,14 +253,13 @@ public static bool SequenceEqual<TDerived, TBase>(this ImmutableArray<TBase> imm
         /// Applies an accumulator function over a sequence.
         /// </summary>
         /// <typeparam name="T">The type of element contained by the collection.</typeparam>
-        [return: MaybeNull]
-        public static T Aggregate<T>(this ImmutableArray<T> immutableArray, Func<T, T, T> func)
+        public static T? Aggregate<T>(this ImmutableArray<T> immutableArray, Func<T, T, T> func)
         {
             Requires.NotNull(func, nameof(func));
 
             if (immutableArray.Length == 0)
             {
-                return default(T)!;
+                return default;
             }
 
             var result = immutableArray[0];
@@ -316,12 +315,11 @@ public static T ElementAt<T>(this ImmutableArray<T> immutableArray, int index)
         /// Returns the element at a specified index in a sequence or a default value if the index is out of range.
         /// </summary>
         /// <typeparam name="T">The type of element contained by the collection.</typeparam>
-        [return: MaybeNull]
-        public static T ElementAtOrDefault<T>(this ImmutableArray<T> immutableArray, int index)
+        public static T? ElementAtOrDefault<T>(this ImmutableArray<T> immutableArray, int index)
         {
             if (index < 0 || index >= immutableArray.Length)
             {
-                return default(T)!;
+                return default;
             }
 
             return immutableArray[index];
@@ -367,18 +365,16 @@ public static T First<T>(this ImmutableArray<T> immutableArray)
         /// </summary>
         /// <typeparam name="T">The type of element contained by the collection.</typeparam>
         /// <param name="immutableArray"></param>
-        [return: MaybeNull]
-        public static T FirstOrDefault<T>(this ImmutableArray<T> immutableArray)
+        public static T? FirstOrDefault<T>(this ImmutableArray<T> immutableArray)
         {
-            return immutableArray.array!.Length > 0 ? immutableArray.array[0] : default(T)!;
+            return immutableArray.array!.Length > 0 ? immutableArray.array[0] : default;
         }
 
         /// <summary>
         /// Returns the first element of the sequence that satisfies a condition or a default value if no such element is found.
         /// </summary>
         /// <typeparam name="T">The type of element contained by the collection.</typeparam>
-        [return: MaybeNull]
-        public static T FirstOrDefault<T>(this ImmutableArray<T> immutableArray, Func<T, bool> predicate)
+        public static T? FirstOrDefault<T>(this ImmutableArray<T> immutableArray, Func<T, bool> predicate)
         {
             Requires.NotNull(predicate, nameof(predicate));
 
@@ -390,7 +386,7 @@ public static T FirstOrDefault<T>(this ImmutableArray<T> immutableArray, Func<T,
                 }
             }
 
-            return default(T)!;
+            return default;
         }
 
         /// <summary>
@@ -432,8 +428,7 @@ public static T Last<T>(this ImmutableArray<T> immutableArray, Func<T, bool> pre
         /// </summary>
         /// <typeparam name="T">The type of element contained by the collection.</typeparam>
         /// <param name="immutableArray"></param>
-        [return: MaybeNull]
-        public static T LastOrDefault<T>(this ImmutableArray<T> immutableArray)
+        public static T? LastOrDefault<T>(this ImmutableArray<T> immutableArray)
         {
             immutableArray.ThrowNullRefIfNotInitialized();
             return immutableArray.array!.LastOrDefault()!;
@@ -443,8 +438,7 @@ public static T LastOrDefault<T>(this ImmutableArray<T> immutableArray)
         /// Returns the last element of a sequence that satisfies a condition or a default value if no such element is found.
         /// </summary>
         /// <typeparam name="T">The type of element contained by the collection.</typeparam>
-        [return: MaybeNull]
-        public static T LastOrDefault<T>(this ImmutableArray<T> immutableArray, Func<T, bool> predicate)
+        public static T? LastOrDefault<T>(this ImmutableArray<T> immutableArray, Func<T, bool> predicate)
         {
             Requires.NotNull(predicate, nameof(predicate));
 
@@ -456,7 +450,7 @@ public static T LastOrDefault<T>(this ImmutableArray<T> immutableArray, Func<T,
                 }
             }
 
-            return default(T)!;
+            return default;
         }
 
         /// <summary>
@@ -478,8 +472,8 @@ public static T Single<T>(this ImmutableArray<T> immutableArray, Func<T, bool> p
         {
             Requires.NotNull(predicate, nameof(predicate));
 
-            var first = true;
-            var result = default(T)!;
+            bool first = true;
+            T? result = default;
             foreach (var v in immutableArray.array!)
             {
                 if (predicate(v))
@@ -499,7 +493,7 @@ public static T Single<T>(this ImmutableArray<T> immutableArray, Func<T, bool> p
                 Enumerable.Empty<T>().Single(); // throw the same exception as LINQ would
             }
 
-            return result;
+            return result!;
         }
 
         /// <summary>
@@ -507,8 +501,7 @@ public static T Single<T>(this ImmutableArray<T> immutableArray, Func<T, bool> p
         /// </summary>
         /// <typeparam name="T">The type of element contained by the collection.</typeparam>
         /// <param name="immutableArray"></param>
-        [return: MaybeNull]
-        public static T SingleOrDefault<T>(this ImmutableArray<T> immutableArray)
+        public static T? SingleOrDefault<T>(this ImmutableArray<T> immutableArray)
         {
             immutableArray.ThrowNullRefIfNotInitialized();
             return immutableArray.array!.SingleOrDefault()!;
@@ -518,13 +511,12 @@ public static T SingleOrDefault<T>(this ImmutableArray<T> immutableArray)
         /// Returns the only element of a sequence that satisfies a specified condition or a default value if no such element exists; this method throws an exception if more than one element satisfies the condition.
         /// </summary>
         /// <typeparam name="T">The type of element contained by the collection.</typeparam>
-        [return: MaybeNull]
-        public static T SingleOrDefault<T>(this ImmutableArray<T> immutableArray, Func<T, bool> predicate)
+        public static T? SingleOrDefault<T>(this ImmutableArray<T> immutableArray, Func<T, bool> predicate)
         {
             Requires.NotNull(predicate, nameof(predicate));
 
-            var first = true;
-            var result = default(T)!;
+            bool first = true;
+            T? result = default;
             foreach (var v in immutableArray.array!)
             {
                 if (predicate(v))
@@ -657,12 +649,11 @@ public static T First<T>(this ImmutableArray<T>.Builder builder)
         /// <summary>
         /// Returns the first element in the collection, or the default value if the collection is empty.
         /// </summary>
-        [return: MaybeNull]
-        public static T FirstOrDefault<T>(this ImmutableArray<T>.Builder builder)
+        public static T? FirstOrDefault<T>(this ImmutableArray<T>.Builder builder)
         {
             Requires.NotNull(builder, nameof(builder));
 
-            return builder.Any() ? builder[0] : default(T)!;
+            return builder.Any() ? builder[0] : default;
         }
 
         /// <summary>
@@ -684,12 +675,11 @@ public static T Last<T>(this ImmutableArray<T>.Builder builder)
         /// <summary>
         /// Returns the last element in the collection, or the default value if the collection is empty.
         /// </summary>
-        [return: MaybeNull]
-        public static T LastOrDefault<T>(this ImmutableArray<T>.Builder builder)
+        public static T? LastOrDefault<T>(this ImmutableArray<T>.Builder builder)
         {
             Requires.NotNull(builder, nameof(builder));
 
-            return builder.Any() ? builder[builder.Count - 1] : default(T)!;
+            return builder.Any() ? builder[builder.Count - 1] : default;
         }
 
         /// <summary>
diff --git a/src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj b/src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj
index f5130bcc181d61..f71e364a81ea28 100644
--- a/src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj
+++ b/src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj
@@ -1,10 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <NoWarn>0436</NoWarn>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
-    <Compile Include="$(CommonTestPath)System\Collections\DictionaryExtensions.cs" Condition="'$(TargetFramework)' == '$(NetFrameworkCurrent)'"
+    <Compile Include="$(CommonTestPath)System\Collections\DictionaryExtensions.cs" Condition="'$(TargetFramework)' == 'net461'"
              Link="Common\System\Collections\DictionaryExtensions.cs" />
     <Compile Include="BadHasher.cs" />
     <Compile Include="EverythingEqual.cs" />
@@ -77,8 +77,7 @@
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <!-- Some internal types are needed, so we reference the implementation assembly, rather than the reference assembly. -->
-    <DefaultReferenceExclusions Include="System.Collections.Immutable" />
-    <ReferenceFromRuntime Include="System.Collections.Immutable" />
+    <ProjectReference Include="..\src\System.Collections.Immutable.csproj" SkipUseReferenceAssembly="true" />
     <Compile Include="ImmutableListTestBase.cs" />
     <Compile Include="ImmutableListTest.cs" />
     <Compile Include="ImmutableListBuilderTest.cs" />
@@ -96,4 +95,7 @@
     <Compile Include="ImmutableSortedSetBuilderTest.nonnetstandard.cs" />
     <Compile Include="ImmutableSortedDictionaryTest.nonnetstandard.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="..\src\System.Collections.Immutable.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Collections.NonGeneric/Directory.Build.props b/src/libraries/System.Collections.NonGeneric/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Collections.NonGeneric/Directory.Build.props
+++ b/src/libraries/System.Collections.NonGeneric/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Collections.NonGeneric/src/System.Collections.NonGeneric.csproj b/src/libraries/System.Collections.NonGeneric/src/System.Collections.NonGeneric.csproj
index 9ec5c3a1eb93ad..5009669653d115 100644
--- a/src/libraries/System.Collections.NonGeneric/src/System.Collections.NonGeneric.csproj
+++ b/src/libraries/System.Collections.NonGeneric/src/System.Collections.NonGeneric.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RootNamespace>System.Collections.NonGeneric</RootNamespace>
-    <AssemblyName>System.Collections.NonGeneric</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Collections.Specialized/Directory.Build.props b/src/libraries/System.Collections.Specialized/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Collections.Specialized/Directory.Build.props
+++ b/src/libraries/System.Collections.Specialized/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Collections.Specialized/src/System.Collections.Specialized.csproj b/src/libraries/System.Collections.Specialized/src/System.Collections.Specialized.csproj
index 6139444928b2ca..1eff0c5b1da7c4 100644
--- a/src/libraries/System.Collections.Specialized/src/System.Collections.Specialized.csproj
+++ b/src/libraries/System.Collections.Specialized/src/System.Collections.Specialized.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RootNamespace>System.Collections.Specialized</RootNamespace>
-    <AssemblyName>System.Collections.Specialized</AssemblyName>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
diff --git a/src/libraries/System.Collections/Directory.Build.props b/src/libraries/System.Collections/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Collections/Directory.Build.props
+++ b/src/libraries/System.Collections/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Collections/ref/System.Collections.cs b/src/libraries/System.Collections/ref/System.Collections.cs
index b0505e82384992..334a67afad23ea 100644
--- a/src/libraries/System.Collections/ref/System.Collections.cs
+++ b/src/libraries/System.Collections/ref/System.Collections.cs
@@ -43,8 +43,7 @@ namespace System.Collections.Generic
 {
     public static partial class CollectionExtensions
     {
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TValue GetValueOrDefault<TKey, TValue>(this System.Collections.Generic.IReadOnlyDictionary<TKey, TValue> dictionary, TKey key) { throw null; }
+        public static TValue? GetValueOrDefault<TKey, TValue>(this System.Collections.Generic.IReadOnlyDictionary<TKey, TValue> dictionary, TKey key) { throw null; }
         public static TValue GetValueOrDefault<TKey, TValue>(this System.Collections.Generic.IReadOnlyDictionary<TKey, TValue> dictionary, TKey key, TValue defaultValue) { throw null; }
         public static bool Remove<TKey, TValue>(this System.Collections.Generic.IDictionary<TKey, TValue> dictionary, TKey key, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out TValue value) { throw null; }
         public static bool TryAdd<TKey, TValue>(this System.Collections.Generic.IDictionary<TKey, TValue> dictionary, TKey key, TValue value) { throw null; }
@@ -53,7 +52,7 @@ public abstract partial class Comparer<T> : System.Collections.Generic.IComparer
     {
         protected Comparer() { }
         public static System.Collections.Generic.Comparer<T> Default { get { throw null; } }
-        public abstract int Compare([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T x, [System.Diagnostics.CodeAnalysis.AllowNullAttribute] T y);
+        public abstract int Compare(T? x, T? y);
         public static System.Collections.Generic.Comparer<T> Create(System.Comparison<T> comparison) { throw null; }
         int System.Collections.IComparer.Compare(object? x, object? y) { throw null; }
     }
@@ -184,7 +183,7 @@ public abstract partial class EqualityComparer<T> : System.Collections.Generic.I
     {
         protected EqualityComparer() { }
         public static System.Collections.Generic.EqualityComparer<T> Default { get { throw null; } }
-        public abstract bool Equals([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T x, [System.Diagnostics.CodeAnalysis.AllowNullAttribute] T y);
+        public abstract bool Equals(T? x, T? y);
         public abstract int GetHashCode([System.Diagnostics.CodeAnalysis.DisallowNullAttribute] T obj);
         bool System.Collections.IEqualityComparer.Equals(object? x, object? y) { throw null; }
         int System.Collections.IEqualityComparer.GetHashCode(object obj) { throw null; }
@@ -326,14 +325,12 @@ public void CopyTo(int index, T[] array, int arrayIndex, int count) { }
         public void CopyTo(T[] array) { }
         public void CopyTo(T[] array, int arrayIndex) { }
         public bool Exists(System.Predicate<T> match) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T Find(System.Predicate<T> match) { throw null; }
+        public T? Find(System.Predicate<T> match) { throw null; }
         public System.Collections.Generic.List<T> FindAll(System.Predicate<T> match) { throw null; }
         public int FindIndex(int startIndex, int count, System.Predicate<T> match) { throw null; }
         public int FindIndex(int startIndex, System.Predicate<T> match) { throw null; }
         public int FindIndex(System.Predicate<T> match) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T FindLast(System.Predicate<T> match) { throw null; }
+        public T? FindLast(System.Predicate<T> match) { throw null; }
         public int FindLastIndex(int startIndex, int count, System.Predicate<T> match) { throw null; }
         public int FindLastIndex(int startIndex, System.Predicate<T> match) { throw null; }
         public int FindLastIndex(System.Predicate<T> match) { throw null; }
@@ -589,10 +586,8 @@ public SortedSet(System.Collections.Generic.IEnumerable<T> collection, System.Co
         protected SortedSet(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         public System.Collections.Generic.IComparer<T> Comparer { get { throw null; } }
         public int Count { get { throw null; } }
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T Max { get { throw null; } }
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T Min { get { throw null; } }
+        public T? Max { get { throw null; } }
+        public T? Min { get { throw null; } }
         bool System.Collections.Generic.ICollection<T>.IsReadOnly { get { throw null; } }
         bool System.Collections.ICollection.IsSynchronized { get { throw null; } }
         object System.Collections.ICollection.SyncRoot { get { throw null; } }
@@ -607,7 +602,7 @@ public void CopyTo(T[] array, int index, int count) { }
         public void ExceptWith(System.Collections.Generic.IEnumerable<T> other) { }
         public System.Collections.Generic.SortedSet<T>.Enumerator GetEnumerator() { throw null; }
         protected virtual void GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
-        public virtual System.Collections.Generic.SortedSet<T> GetViewBetween(T lowerValue, T upperValue) { throw null; }
+        public virtual System.Collections.Generic.SortedSet<T> GetViewBetween(T? lowerValue, T? upperValue) { throw null; }
         public virtual void IntersectWith(System.Collections.Generic.IEnumerable<T> other) { }
         public bool IsProperSubsetOf(System.Collections.Generic.IEnumerable<T> other) { throw null; }
         public bool IsProperSupersetOf(System.Collections.Generic.IEnumerable<T> other) { throw null; }
diff --git a/src/libraries/System.Collections/src/System.Collections.csproj b/src/libraries/System.Collections/src/System.Collections.csproj
index 7ac500622b248f..9f8e4b8bb6295d 100644
--- a/src/libraries/System.Collections/src/System.Collections.csproj
+++ b/src/libraries/System.Collections/src/System.Collections.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Collections</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Collections/src/System/Collections/Generic/CollectionExtensions.cs b/src/libraries/System.Collections/src/System/Collections/Generic/CollectionExtensions.cs
index 47de3ec036e7f7..39158f2e18cde2 100644
--- a/src/libraries/System.Collections/src/System/Collections/Generic/CollectionExtensions.cs
+++ b/src/libraries/System.Collections/src/System/Collections/Generic/CollectionExtensions.cs
@@ -7,8 +7,7 @@ namespace System.Collections.Generic
 {
     public static class CollectionExtensions
     {
-        [return: MaybeNull]
-        public static TValue GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dictionary, TKey key)
+        public static TValue? GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dictionary, TKey key)
         {
             return dictionary.GetValueOrDefault(key, default!);
         }
@@ -53,7 +52,7 @@ public static bool Remove<TKey, TValue>(this IDictionary<TKey, TValue> dictionar
                 return true;
             }
 
-            value = default(TValue)!;
+            value = default;
             return false;
         }
     }
diff --git a/src/libraries/System.Collections/src/System/Collections/Generic/LinkedList.cs b/src/libraries/System.Collections/src/System/Collections/Generic/LinkedList.cs
index 1694a7cbf651f5..cd2718696213ac 100644
--- a/src/libraries/System.Collections/src/System/Collections/Generic/LinkedList.cs
+++ b/src/libraries/System.Collections/src/System/Collections/Generic/LinkedList.cs
@@ -530,7 +530,7 @@ public struct Enumerator : IEnumerator<T>, IEnumerator, ISerializable, IDeserial
             private readonly LinkedList<T> _list;
             private LinkedListNode<T>? _node;
             private readonly int _version;
-            [AllowNull] private T _current;
+            private T? _current;
             private int _index;
 
             internal Enumerator(LinkedList<T> list)
@@ -542,10 +542,7 @@ internal Enumerator(LinkedList<T> list)
                 _index = 0;
             }
 
-            public T Current
-            {
-                get { return _current; }
-            }
+            public T Current => _current!;
 
             object? IEnumerator.Current
             {
diff --git a/src/libraries/System.Collections/src/System/Collections/Generic/Queue.cs b/src/libraries/System.Collections/src/System/Collections/Generic/Queue.cs
index efd2b1e9a72c94..c468d1663c45c4 100644
--- a/src/libraries/System.Collections/src/System/Collections/Generic/Queue.cs
+++ b/src/libraries/System.Collections/src/System/Collections/Generic/Queue.cs
@@ -395,7 +395,7 @@ public struct Enumerator : IEnumerator<T>,
             private readonly Queue<T> _q;
             private readonly int _version;
             private int _index;   // -1 = not started, -2 = ended/disposed
-            [AllowNull] private T _currentElement;
+            private T? _currentElement;
 
             internal Enumerator(Queue<T> q)
             {
@@ -457,7 +457,7 @@ public T Current
                 {
                     if (_index < 0)
                         ThrowEnumerationNotStartedOrEnded();
-                    return _currentElement;
+                    return _currentElement!;
                 }
             }
 
diff --git a/src/libraries/System.Collections/src/System/Collections/Generic/SortedDictionary.cs b/src/libraries/System.Collections/src/System/Collections/Generic/SortedDictionary.cs
index 8bca75b21f7cda..fd649d52ca3476 100644
--- a/src/libraries/System.Collections/src/System/Collections/Generic/SortedDictionary.cs
+++ b/src/libraries/System.Collections/src/System/Collections/Generic/SortedDictionary.cs
@@ -288,7 +288,7 @@ public bool TryGetValue(TKey key, [MaybeNullWhen(false)] out TValue value)
             TreeSet<KeyValuePair<TKey, TValue>>.Node? node = _set.FindNode(new KeyValuePair<TKey, TValue>(key, default(TValue)!));
             if (node == null)
             {
-                value = default(TValue)!;
+                value = default;
                 return false;
             }
             value = node.Item.Value;
diff --git a/src/libraries/System.Collections/src/System/Collections/Generic/SortedList.cs b/src/libraries/System.Collections/src/System/Collections/Generic/SortedList.cs
index 57192e1a30d149..220de76fca1690 100644
--- a/src/libraries/System.Collections/src/System/Collections/Generic/SortedList.cs
+++ b/src/libraries/System.Collections/src/System/Collections/Generic/SortedList.cs
@@ -526,9 +526,8 @@ void ICollection.CopyTo(Array array, int index)
         private const int MaxArrayLength = 0X7FEFFFFF;
 
         // Ensures that the capacity of this sorted list is at least the given
-        // minimum value. If the current capacity of the list is less than
-        // min, the capacity is increased to twice the current capacity or
-        // to min, whichever is larger.
+        // minimum value. The capacity is increased to twice the current capacity
+        // or to min, whichever is larger.
         private void EnsureCapacity(int min)
         {
             int newCapacity = keys.Length == 0 ? DefaultCapacity : keys.Length * 2;
@@ -686,7 +685,7 @@ public bool TryGetValue(TKey key, [MaybeNullWhen(false)] out TValue value)
                 return true;
             }
 
-            value = default(TValue)!;
+            value = default;
             return false;
         }
 
@@ -762,8 +761,8 @@ private static bool IsCompatibleKey(object key)
         private struct Enumerator : IEnumerator<KeyValuePair<TKey, TValue>>, IDictionaryEnumerator
         {
             private readonly SortedList<TKey, TValue> _sortedList;
-            [AllowNull] private TKey _key;
-            [AllowNull] private TValue _value;
+            private TKey? _key;
+            private TValue? _value;
             private int _index;
             private readonly int _version;
             private readonly int _getEnumeratorRetType;  // What should Enumerator.Current return?
@@ -797,7 +796,7 @@ object IDictionaryEnumerator.Key
                         throw new InvalidOperationException(SR.InvalidOperation_EnumOpCantHappen);
                     }
 
-                    return _key;
+                    return _key!;
                 }
             }
 
@@ -828,17 +827,11 @@ DictionaryEntry IDictionaryEnumerator.Entry
                         throw new InvalidOperationException(SR.InvalidOperation_EnumOpCantHappen);
                     }
 
-                    return new DictionaryEntry(_key, _value);
+                    return new DictionaryEntry(_key!, _value);
                 }
             }
 
-            public KeyValuePair<TKey, TValue> Current
-            {
-                get
-                {
-                    return new KeyValuePair<TKey, TValue>(_key, _value);
-                }
-            }
+            public KeyValuePair<TKey, TValue> Current => new KeyValuePair<TKey, TValue>(_key!, _value!);
 
             object? IEnumerator.Current
             {
@@ -851,11 +844,11 @@ public KeyValuePair<TKey, TValue> Current
 
                     if (_getEnumeratorRetType == DictEntry)
                     {
-                        return new DictionaryEntry(_key, _value);
+                        return new DictionaryEntry(_key!, _value);
                     }
                     else
                     {
-                        return new KeyValuePair<TKey, TValue>(_key, _value);
+                        return new KeyValuePair<TKey, TValue>(_key!, _value!);
                     }
                 }
             }
@@ -891,7 +884,7 @@ private sealed class SortedListKeyEnumerator : IEnumerator<TKey>, IEnumerator
             private readonly SortedList<TKey, TValue> _sortedList;
             private int _index;
             private readonly int _version;
-            [AllowNull] private TKey _currentKey = default!;
+            private TKey? _currentKey;
 
             internal SortedListKeyEnumerator(SortedList<TKey, TValue> sortedList)
             {
@@ -924,13 +917,7 @@ public bool MoveNext()
                 return false;
             }
 
-            public TKey Current
-            {
-                get
-                {
-                    return _currentKey;
-                }
-            }
+            public TKey Current => _currentKey!;
 
             object? IEnumerator.Current
             {
@@ -961,7 +948,7 @@ private sealed class SortedListValueEnumerator : IEnumerator<TValue>, IEnumerato
             private readonly SortedList<TKey, TValue> _sortedList;
             private int _index;
             private readonly int _version;
-            [AllowNull] private TValue _currentValue = default!;
+            private TValue? _currentValue;
 
             internal SortedListValueEnumerator(SortedList<TKey, TValue> sortedList)
             {
@@ -994,13 +981,7 @@ public bool MoveNext()
                 return false;
             }
 
-            public TValue Current
-            {
-                get
-                {
-                    return _currentValue;
-                }
-            }
+            public TValue Current => _currentValue!;
 
             object? IEnumerator.Current
             {
diff --git a/src/libraries/System.Collections/src/System/Collections/Generic/SortedSet.TreeSubSet.cs b/src/libraries/System.Collections/src/System/Collections/Generic/SortedSet.TreeSubSet.cs
index eb116ac0eb45c6..91745e21d058f3 100644
--- a/src/libraries/System.Collections/src/System/Collections/Generic/SortedSet.TreeSubSet.cs
+++ b/src/libraries/System.Collections/src/System/Collections/Generic/SortedSet.TreeSubSet.cs
@@ -16,10 +16,8 @@ public partial class SortedSet<T>
         internal sealed class TreeSubSet : SortedSet<T>, ISerializable, IDeserializationCallback
         {
             private readonly SortedSet<T> _underlying;
-            [MaybeNull, AllowNull]
-            private readonly T _min;
-            [MaybeNull, AllowNull]
-            private readonly T _max;
+            private readonly T? _min;
+            private readonly T? _max;
             // keeps track of whether the count variable is up to date
             // up to date -> _countVersion = _underlying.version
             // not up to date -> _countVersion < _underlying.version
@@ -38,7 +36,7 @@ internal override bool versionUpToDate()
             }
 #endif
 
-            public TreeSubSet(SortedSet<T> Underlying, [AllowNull] T Min, [AllowNull] T Max, bool lowerBoundActive, bool upperBoundActive)
+            public TreeSubSet(SortedSet<T> Underlying, T? Min, T? Max, bool lowerBoundActive, bool upperBoundActive)
                 : base(Underlying.Comparer)
             {
                 _underlying = Underlying;
@@ -129,7 +127,7 @@ internal override T MinInternal
                 get
                 {
                     Node? current = root;
-                    T result = default(T)!;
+                    T? result = default;
 
                     while (current != null)
                     {
@@ -150,7 +148,7 @@ internal override T MinInternal
                         }
                     }
 
-                    return result;
+                    return result!;
                 }
             }
 
@@ -159,7 +157,7 @@ internal override T MaxInternal
                 get
                 {
                     Node? current = root;
-                    T result = default(T)!;
+                    T? result = default;
 
                     while (current != null)
                     {
@@ -179,7 +177,7 @@ internal override T MaxInternal
                         }
                     }
 
-                    return result;
+                    return result!;
                 }
             }
 
@@ -340,7 +338,7 @@ internal override int TotalCount()
             // This passes functionality down to the underlying tree, clipping edges if necessary
             // There's nothing gained by having a nested subset. May as well draw it from the base
             // Cannot increase the bounds of the subset, can only decrease it
-            public override SortedSet<T> GetViewBetween([AllowNull] T lowerValue, [AllowNull] T upperValue)
+            public override SortedSet<T> GetViewBetween(T? lowerValue, T? upperValue)
             {
                 if (_lBoundActive && Comparer.Compare(_min, lowerValue) > 0)
                 {
diff --git a/src/libraries/System.Collections/src/System/Collections/Generic/SortedSet.cs b/src/libraries/System.Collections/src/System/Collections/Generic/SortedSet.cs
index 3cc375c478346b..3d2989a86c8bd6 100644
--- a/src/libraries/System.Collections/src/System/Collections/Generic/SortedSet.cs
+++ b/src/libraries/System.Collections/src/System/Collections/Generic/SortedSet.cs
@@ -755,9 +755,9 @@ internal virtual int InternalIndexOf(T item)
             return -1;
         }
 
-        internal Node? FindRange([AllowNull] T from, [AllowNull]  T to) => FindRange(from, to, lowerBoundActive: true, upperBoundActive: true);
+        internal Node? FindRange(T? from, T? to) => FindRange(from, to, lowerBoundActive: true, upperBoundActive: true);
 
-        internal Node? FindRange([AllowNull] T from, [AllowNull] T to, bool lowerBoundActive, bool upperBoundActive)
+        internal Node? FindRange(T? from, T? to, bool lowerBoundActive, bool upperBoundActive)
         {
             Node? current = root;
             while (current != null)
@@ -1504,17 +1504,15 @@ public int RemoveWhere(Predicate<T> match)
 
         #region ISorted members
 
-        [MaybeNull]
-        public T Min => MinInternal;
+        public T? Min => MinInternal;
 
-        [MaybeNull]
-        internal virtual T MinInternal
+        internal virtual T? MinInternal
         {
             get
             {
                 if (root == null)
                 {
-                    return default(T)!;
+                    return default;
                 }
 
                 Node current = root;
@@ -1527,17 +1525,15 @@ internal virtual T MinInternal
             }
         }
 
-        [MaybeNull]
-        public T Max => MaxInternal;
+        public T? Max => MaxInternal;
 
-        [MaybeNull]
-        internal virtual T MaxInternal
+        internal virtual T? MaxInternal
         {
             get
             {
                 if (root == null)
                 {
-                    return default(T)!;
+                    return default;
                 }
 
                 Node current = root;
@@ -1559,7 +1555,7 @@ public IEnumerable<T> Reverse()
             }
         }
 
-        public virtual SortedSet<T> GetViewBetween([AllowNull] T lowerValue, [AllowNull] T upperValue)
+        public virtual SortedSet<T> GetViewBetween(T? lowerValue, T? upperValue)
         {
             if (Comparer.Compare(lowerValue, upperValue) > 0)
             {
@@ -2074,7 +2070,7 @@ public bool TryGetValue(T equalValue, [MaybeNullWhen(false)] out T actualValue)
                 actualValue = node.Item;
                 return true;
             }
-            actualValue = default(T)!;
+            actualValue = default;
             return false;
         }
 
diff --git a/src/libraries/System.Collections/src/System/Collections/Generic/Stack.cs b/src/libraries/System.Collections/src/System/Collections/Generic/Stack.cs
index dbb41578cade97..8f191eed51e48c 100644
--- a/src/libraries/System.Collections/src/System/Collections/Generic/Stack.cs
+++ b/src/libraries/System.Collections/src/System/Collections/Generic/Stack.cs
@@ -315,7 +315,7 @@ public struct Enumerator : IEnumerator<T>, System.Collections.IEnumerator
             private readonly Stack<T> _stack;
             private readonly int _version;
             private int _index;
-            [AllowNull] private T _currentElement;
+            private T? _currentElement;
 
             internal Enumerator(Stack<T> stack)
             {
@@ -361,7 +361,7 @@ public T Current
                 {
                     if (_index < 0)
                         ThrowEnumerationNotStartedOrEnded();
-                    return _currentElement;
+                    return _currentElement!;
                 }
             }
 
diff --git a/src/libraries/System.Collections/tests/Generic/Dictionary/Dictionary.Generic.Tests.cs b/src/libraries/System.Collections/tests/Generic/Dictionary/Dictionary.Generic.Tests.cs
index 3de72528d02c14..32f277e82b15c4 100644
--- a/src/libraries/System.Collections/tests/Generic/Dictionary/Dictionary.Generic.Tests.cs
+++ b/src/libraries/System.Collections/tests/Generic/Dictionary/Dictionary.Generic.Tests.cs
@@ -3,7 +3,9 @@
 
 using Common.System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Linq;
+using System.Runtime.Serialization;
 using Xunit;
 
 namespace System.Collections.Tests
@@ -610,5 +612,37 @@ public void TrimExcess_Generic_DoesInvalidateEnumeration()
         }
 
         #endregion
+
+        #region Non-randomized comparers
+        [Fact]
+        public void Dictionary_Comparer_NonRandomizedStringComparers()
+        {
+            RunTest(null);
+            RunTest(EqualityComparer<string>.Default);
+            RunTest(StringComparer.Ordinal);
+            RunTest(StringComparer.OrdinalIgnoreCase);
+            RunTest(StringComparer.InvariantCulture);
+            RunTest(StringComparer.InvariantCultureIgnoreCase);
+            RunTest(StringComparer.Create(CultureInfo.InvariantCulture, ignoreCase: false));
+            RunTest(StringComparer.Create(CultureInfo.InvariantCulture, ignoreCase: true));
+
+            void RunTest(IEqualityComparer<string> comparer)
+            {
+                // First, instantiate the dictionary and check its Comparer property
+
+                Dictionary<string, object> dict = new Dictionary<string, object>(comparer);
+                object expected = comparer ?? EqualityComparer<string>.Default;
+
+                Assert.Same(expected, dict.Comparer);
+
+                // Then pretend to serialize the dictionary and check the stored Comparer instance
+
+                SerializationInfo si = new SerializationInfo(typeof(Dictionary<string, object>), new FormatterConverter());
+                dict.GetObjectData(si, new StreamingContext(StreamingContextStates.All));
+
+                Assert.Same(expected, si.GetValue("Comparer", typeof(IEqualityComparer<string>)));
+            }
+        }
+        #endregion
     }
 }
diff --git a/src/libraries/System.Collections/tests/Generic/Dictionary/HashCollisionScenarios/OutOfBoundsRegression.cs b/src/libraries/System.Collections/tests/Generic/Dictionary/HashCollisionScenarios/OutOfBoundsRegression.cs
index bc8308847cda82..934e57aafe4cc3 100644
--- a/src/libraries/System.Collections/tests/Generic/Dictionary/HashCollisionScenarios/OutOfBoundsRegression.cs
+++ b/src/libraries/System.Collections/tests/Generic/Dictionary/HashCollisionScenarios/OutOfBoundsRegression.cs
@@ -2,6 +2,10 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Collections.Generic;
+using System.Numerics;
+using System.Reflection;
+using System.Runtime.InteropServices;
+using System.Runtime.Serialization;
 using Xunit;
 
 namespace System.Collections.Tests
@@ -37,5 +41,238 @@ public static void OutOfBoundsRegression()
                     dictionary.Remove(key);
             }
         }
+
+        [Fact]
+        public static void ComparerImplementations_Dictionary_WithWellKnownStringComparers()
+        {
+            Type nonRandomizedOrdinalComparerType = typeof(object).Assembly.GetType("System.Collections.Generic.NonRandomizedStringEqualityComparer+OrdinalComparer", throwOnError: true);
+            Type nonRandomizedOrdinalIgnoreCaseComparerType = typeof(object).Assembly.GetType("System.Collections.Generic.NonRandomizedStringEqualityComparer+OrdinalIgnoreCaseComparer", throwOnError: true);
+            Type randomizedOrdinalComparerType = typeof(object).Assembly.GetType("System.Collections.Generic.RandomizedStringEqualityComparer+OrdinalComparer", throwOnError: true);
+            Type randomizedOrdinalIgnoreCaseComparerType = typeof(object).Assembly.GetType("System.Collections.Generic.RandomizedStringEqualityComparer+OrdinalIgnoreCaseComparer", throwOnError: true);
+
+            // null comparer
+
+            RunDictionaryTest(
+                equalityComparer: null,
+                expectedInternalComparerBeforeCollisionThreshold: nonRandomizedOrdinalComparerType,
+                expectedPublicComparerBeforeCollisionThreshold: EqualityComparer<string>.Default.GetType(),
+                expectedComparerAfterCollisionThreshold: randomizedOrdinalComparerType);
+
+            // EqualityComparer<string>.Default comparer
+
+            RunDictionaryTest(
+                equalityComparer: EqualityComparer<string>.Default,
+                expectedInternalComparerBeforeCollisionThreshold: nonRandomizedOrdinalComparerType,
+                expectedPublicComparerBeforeCollisionThreshold: EqualityComparer<string>.Default.GetType(),
+                expectedComparerAfterCollisionThreshold: randomizedOrdinalComparerType);
+
+            // Ordinal comparer
+
+            RunDictionaryTest(
+                equalityComparer: StringComparer.Ordinal,
+                expectedInternalComparerBeforeCollisionThreshold: nonRandomizedOrdinalComparerType,
+                expectedPublicComparerBeforeCollisionThreshold: StringComparer.Ordinal.GetType(),
+                expectedComparerAfterCollisionThreshold: randomizedOrdinalComparerType);
+
+            // OrdinalIgnoreCase comparer
+
+            RunDictionaryTest(
+                equalityComparer: StringComparer.OrdinalIgnoreCase,
+                expectedInternalComparerBeforeCollisionThreshold: nonRandomizedOrdinalIgnoreCaseComparerType,
+                expectedPublicComparerBeforeCollisionThreshold: StringComparer.OrdinalIgnoreCase.GetType(),
+                expectedComparerAfterCollisionThreshold: randomizedOrdinalIgnoreCaseComparerType);
+
+            // linguistic comparer (not optimized)
+
+            RunDictionaryTest(
+                equalityComparer: StringComparer.InvariantCulture,
+                expectedInternalComparerBeforeCollisionThreshold: StringComparer.InvariantCulture.GetType(),
+                expectedPublicComparerBeforeCollisionThreshold: StringComparer.InvariantCulture.GetType(),
+                expectedComparerAfterCollisionThreshold: StringComparer.InvariantCulture.GetType());
+
+            static void RunDictionaryTest(
+                IEqualityComparer<string> equalityComparer,
+                Type expectedInternalComparerBeforeCollisionThreshold,
+                Type expectedPublicComparerBeforeCollisionThreshold,
+                Type expectedComparerAfterCollisionThreshold)
+            {
+                RunCollectionTestCommon(
+                    () => new Dictionary<string, object>(equalityComparer),
+                    (dictionary, key) => dictionary.Add(key, null),
+                    (dictionary, key) => dictionary.ContainsKey(key),
+                    dictionary => dictionary.Comparer,
+                    expectedInternalComparerBeforeCollisionThreshold,
+                    expectedPublicComparerBeforeCollisionThreshold,
+                    expectedComparerAfterCollisionThreshold);
+            }
+        }
+
+        [Fact]
+        public static void ComparerImplementations_HashSet_WithWellKnownStringComparers()
+        {
+            Type nonRandomizedOrdinalComparerType = typeof(object).Assembly.GetType("System.Collections.Generic.NonRandomizedStringEqualityComparer+OrdinalComparer", throwOnError: true);
+            Type nonRandomizedOrdinalIgnoreCaseComparerType = typeof(object).Assembly.GetType("System.Collections.Generic.NonRandomizedStringEqualityComparer+OrdinalIgnoreCaseComparer", throwOnError: true);
+            Type randomizedOrdinalComparerType = typeof(object).Assembly.GetType("System.Collections.Generic.RandomizedStringEqualityComparer+OrdinalComparer", throwOnError: true);
+            Type randomizedOrdinalIgnoreCaseComparerType = typeof(object).Assembly.GetType("System.Collections.Generic.RandomizedStringEqualityComparer+OrdinalIgnoreCaseComparer", throwOnError: true);
+
+            // null comparer
+
+            RunHashSetTest(
+                equalityComparer: null,
+                expectedInternalComparerBeforeCollisionThreshold: nonRandomizedOrdinalComparerType,
+                expectedPublicComparerBeforeCollisionThreshold: EqualityComparer<string>.Default.GetType(),
+                expectedComparerAfterCollisionThreshold: randomizedOrdinalComparerType);
+
+            // EqualityComparer<string>.Default comparer
+
+            RunHashSetTest(
+                equalityComparer: EqualityComparer<string>.Default,
+                expectedInternalComparerBeforeCollisionThreshold: nonRandomizedOrdinalComparerType,
+                expectedPublicComparerBeforeCollisionThreshold: EqualityComparer<string>.Default.GetType(),
+                expectedComparerAfterCollisionThreshold: randomizedOrdinalComparerType);
+
+            // Ordinal comparer
+
+            RunHashSetTest(
+                equalityComparer: StringComparer.Ordinal,
+                expectedInternalComparerBeforeCollisionThreshold: nonRandomizedOrdinalComparerType,
+                expectedPublicComparerBeforeCollisionThreshold: StringComparer.Ordinal.GetType(),
+                expectedComparerAfterCollisionThreshold: randomizedOrdinalComparerType);
+
+            // OrdinalIgnoreCase comparer
+
+            RunHashSetTest(
+                equalityComparer: StringComparer.OrdinalIgnoreCase,
+                expectedInternalComparerBeforeCollisionThreshold: nonRandomizedOrdinalIgnoreCaseComparerType,
+                expectedPublicComparerBeforeCollisionThreshold: StringComparer.OrdinalIgnoreCase.GetType(),
+                expectedComparerAfterCollisionThreshold: randomizedOrdinalIgnoreCaseComparerType);
+
+            // linguistic comparer (not optimized)
+
+            RunHashSetTest(
+                equalityComparer: StringComparer.InvariantCulture,
+                expectedInternalComparerBeforeCollisionThreshold: StringComparer.InvariantCulture.GetType(),
+                expectedPublicComparerBeforeCollisionThreshold: StringComparer.InvariantCulture.GetType(),
+                expectedComparerAfterCollisionThreshold: StringComparer.InvariantCulture.GetType());
+
+            static void RunHashSetTest(
+                IEqualityComparer<string> equalityComparer,
+                Type expectedInternalComparerBeforeCollisionThreshold,
+                Type expectedPublicComparerBeforeCollisionThreshold,
+                Type expectedComparerAfterCollisionThreshold)
+            {
+                RunCollectionTestCommon(
+                    () => new HashSet<string>(equalityComparer),
+                    (set, key) => Assert.True(set.Add(key)),
+                    (set, key) => set.Contains(key),
+                    set => set.Comparer,
+                    expectedInternalComparerBeforeCollisionThreshold,
+                    expectedPublicComparerBeforeCollisionThreshold,
+                    expectedComparerAfterCollisionThreshold);
+            }
+        }
+
+        private static void RunCollectionTestCommon<TCollection>(
+            Func<TCollection> collectionFactory,
+            Action<TCollection, string> addKeyCallback,
+            Func<TCollection, string, bool> containsKeyCallback,
+            Func<TCollection, IEqualityComparer<string>> getComparerCallback,
+            Type expectedInternalComparerBeforeCollisionThreshold,
+            Type expectedPublicComparerBeforeCollisionThreshold,
+            Type expectedComparerAfterCollisionThreshold)
+        {
+            TCollection collection = collectionFactory();
+            List<string> allKeys = new List<string>();
+
+            const int StartOfRange = 0xE020; // use the Unicode Private Use range to avoid accidentally creating strings that really do compare as equal OrdinalIgnoreCase
+            const int Stride = 0x40; // to ensure we don't accidentally reset the 0x20 bit of the seed, which is used to negate OrdinalIgnoreCase effects
+
+            // First, go right up to the collision threshold, but don't exceed it.
+
+            for (int i = 0; i < 100; i++)
+            {
+                string newKey = GenerateCollidingString(i * Stride + StartOfRange);
+                Assert.Equal(0, _lazyGetNonRandomizedHashCodeDel.Value(newKey)); // ensure has a zero hash code Ordinal
+                Assert.Equal(0x24716ca0, _lazyGetNonRandomizedOrdinalIgnoreCaseHashCodeDel.Value(newKey)); // ensure has a zero hash code OrdinalIgnoreCase
+
+                addKeyCallback(collection, newKey);
+                allKeys.Add(newKey);
+            }
+
+            FieldInfo internalComparerField = collection.GetType().GetField("_comparer", BindingFlags.NonPublic | BindingFlags.Instance);
+            Assert.NotNull(internalComparerField);
+
+            Assert.Equal(expectedInternalComparerBeforeCollisionThreshold, internalComparerField.GetValue(collection)?.GetType());
+            Assert.Equal(expectedPublicComparerBeforeCollisionThreshold, getComparerCallback(collection).GetType());
+
+            // Now exceed the collision threshold, which should rebucket entries.
+            // Continue adding a few more entries to ensure we didn't corrupt internal state.
+
+            for (int i = 100; i < 110; i++)
+            {
+                string newKey = GenerateCollidingString(i * Stride + StartOfRange);
+                Assert.Equal(0, _lazyGetNonRandomizedHashCodeDel.Value(newKey)); // ensure has a zero hash code Ordinal
+                Assert.Equal(0x24716ca0, _lazyGetNonRandomizedOrdinalIgnoreCaseHashCodeDel.Value(newKey)); // ensure has a zero hash code OrdinalIgnoreCase
+
+                addKeyCallback(collection, newKey);
+                allKeys.Add(newKey);
+            }
+
+            Assert.Equal(expectedComparerAfterCollisionThreshold, internalComparerField.GetValue(collection)?.GetType());
+            Assert.Equal(expectedPublicComparerBeforeCollisionThreshold, getComparerCallback(collection).GetType()); // shouldn't change this return value after collision threshold met
+
+            // And validate that all strings are present in the dictionary.
+
+            foreach (string key in allKeys)
+            {
+                Assert.True(containsKeyCallback(collection, key));
+            }
+
+            // Also make sure we didn't accidentally put the internal comparer in the serialized object data.
+
+            collection = collectionFactory();
+            SerializationInfo si = new SerializationInfo(collection.GetType(), new FormatterConverter());
+            ((ISerializable)collection).GetObjectData(si, new StreamingContext());
+
+            object serializedComparer = si.GetValue("Comparer", typeof(IEqualityComparer<string>));
+            Assert.Equal(expectedPublicComparerBeforeCollisionThreshold, serializedComparer.GetType());
+        }
+
+        private static Lazy<Func<string, int>> _lazyGetNonRandomizedHashCodeDel = new Lazy<Func<string, int>>(
+            () => GetStringHashCodeOpenDelegate("GetNonRandomizedHashCode"));
+
+        private static Lazy<Func<string, int>> _lazyGetNonRandomizedOrdinalIgnoreCaseHashCodeDel = new Lazy<Func<string, int>>(
+            () => GetStringHashCodeOpenDelegate("GetNonRandomizedHashCodeOrdinalIgnoreCase"));
+
+        // Generates a string with a well-known non-randomized hash code:
+        // - string.GetNonRandomizedHashCode returns 0.
+        // - string.GetNonRandomizedHashCodeOrdinalIgnoreCase returns 0x24716ca0.
+        // Provide a different seed to produce a different string.
+        private static string GenerateCollidingString(int seed)
+        {
+            return string.Create(8, seed, (span, seed) =>
+            {
+                Span<byte> asBytes = MemoryMarshal.AsBytes(span);
+
+                uint hash1 = (5381 << 16) + 5381;
+                uint hash2 = BitOperations.RotateLeft(hash1, 5) + hash1;
+
+                MemoryMarshal.Write(asBytes, ref seed);
+                MemoryMarshal.Write(asBytes.Slice(4), ref hash2); // set hash2 := 0 (for Ordinal)
+
+                hash1 = (BitOperations.RotateLeft(hash1, 5) + hash1) ^ (uint)seed;
+                hash1 = (BitOperations.RotateLeft(hash1, 5) + hash1);
+
+                MemoryMarshal.Write(asBytes.Slice(8), ref hash1); // set hash1 := 0 (for Ordinal)
+            });
+        }
+
+        private static Func<string, int> GetStringHashCodeOpenDelegate(string methodName)
+        {
+            MethodInfo method = typeof(string).GetMethod(methodName, BindingFlags.Instance | BindingFlags.NonPublic);
+            Assert.NotNull(method);
+
+            return method.CreateDelegate<Func<string, int>>(target: null); // create open delegate unbound to 'this'
+        }
     }
 }
diff --git a/src/libraries/System.ComponentModel.Annotations/Directory.Build.props b/src/libraries/System.ComponentModel.Annotations/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.ComponentModel.Annotations/Directory.Build.props
+++ b/src/libraries/System.ComponentModel.Annotations/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ComponentModel.Annotations/ref/System.ComponentModel.Annotations.cs b/src/libraries/System.ComponentModel.Annotations/ref/System.ComponentModel.Annotations.cs
index 1747a8cacd99cf..4db1cfdddce9da 100644
--- a/src/libraries/System.ComponentModel.Annotations/ref/System.ComponentModel.Annotations.cs
+++ b/src/libraries/System.ComponentModel.Annotations/ref/System.ComponentModel.Annotations.cs
@@ -6,12 +6,15 @@
 
 namespace System.ComponentModel.DataAnnotations
 {
+// TODO-NULLABLE: Enable after System.ComponentModel.TypeDescriptionProvider is annotated
+#nullable disable
     public partial class AssociatedMetadataTypeTypeDescriptionProvider : System.ComponentModel.TypeDescriptionProvider
     {
         public AssociatedMetadataTypeTypeDescriptionProvider(System.Type type) { }
         public AssociatedMetadataTypeTypeDescriptionProvider(System.Type type, System.Type associatedMetadataType) { }
         public override System.ComponentModel.ICustomTypeDescriptor GetTypeDescriptor(System.Type objectType, object instance) { throw null; }
     }
+#nullable enable
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Property, AllowMultiple=false, Inherited=true)]
     [System.ObsoleteAttribute("This attribute is no longer in use and will be ignored if applied.")]
     public sealed partial class AssociationAttribute : System.Attribute
@@ -29,7 +32,7 @@ public partial class CompareAttribute : System.ComponentModel.DataAnnotations.Va
     {
         public CompareAttribute(string otherProperty) { }
         public string OtherProperty { get { throw null; } }
-        public string OtherPropertyDisplayName { get { throw null; } }
+        public string? OtherPropertyDisplayName { get { throw null; } }
         public override bool RequiresValidationContext { get { throw null; } }
         public override string FormatErrorMessage(string name) { throw null; }
         protected override System.ComponentModel.DataAnnotations.ValidationResult IsValid(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { throw null; }
@@ -43,7 +46,7 @@ public ConcurrencyCheckAttribute() { }
     public sealed partial class CreditCardAttribute : System.ComponentModel.DataAnnotations.DataTypeAttribute
     {
         public CreditCardAttribute() : base (default(System.ComponentModel.DataAnnotations.DataType)) { }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Field | System.AttributeTargets.Method | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=true)]
     public sealed partial class CustomValidationAttribute : System.ComponentModel.DataAnnotations.ValidationAttribute
@@ -52,7 +55,7 @@ public CustomValidationAttribute(System.Type validatorType, string method) { }
         public string Method { get { throw null; } }
         public System.Type ValidatorType { get { throw null; } }
         public override string FormatErrorMessage(string name) { throw null; }
-        protected override System.ComponentModel.DataAnnotations.ValidationResult IsValid(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { throw null; }
+        protected override System.ComponentModel.DataAnnotations.ValidationResult? IsValid(object? value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { throw null; }
     }
     public enum DataType
     {
@@ -79,11 +82,11 @@ public partial class DataTypeAttribute : System.ComponentModel.DataAnnotations.V
     {
         public DataTypeAttribute(System.ComponentModel.DataAnnotations.DataType dataType) { }
         public DataTypeAttribute(string customDataType) { }
-        public string CustomDataType { get { throw null; } }
+        public string? CustomDataType { get { throw null; } }
         public System.ComponentModel.DataAnnotations.DataType DataType { get { throw null; } }
-        public System.ComponentModel.DataAnnotations.DisplayFormatAttribute DisplayFormat { get { throw null; } protected set { } }
+        public System.ComponentModel.DataAnnotations.DisplayFormatAttribute? DisplayFormat { get { throw null; } protected set { } }
         public virtual string GetDataTypeName() { throw null; }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Field | System.AttributeTargets.Method | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=false)]
     public sealed partial class DisplayAttribute : System.Attribute
@@ -91,30 +94,30 @@ public sealed partial class DisplayAttribute : System.Attribute
         public DisplayAttribute() { }
         public bool AutoGenerateField { get { throw null; } set { } }
         public bool AutoGenerateFilter { get { throw null; } set { } }
-        public string Description { get { throw null; } set { } }
-        public string GroupName { get { throw null; } set { } }
-        public string Name { get { throw null; } set { } }
+        public string? Description { get { throw null; } set { } }
+        public string? GroupName { get { throw null; } set { } }
+        public string? Name { get { throw null; } set { } }
         public int Order { get { throw null; } set { } }
-        public string Prompt { get { throw null; } set { } }
-        public System.Type ResourceType { get { throw null; } set { } }
-        public string ShortName { get { throw null; } set { } }
+        public string? Prompt { get { throw null; } set { } }
+        public System.Type? ResourceType { get { throw null; } set { } }
+        public string? ShortName { get { throw null; } set { } }
         public bool? GetAutoGenerateField() { throw null; }
         public bool? GetAutoGenerateFilter() { throw null; }
         public string GetDescription() { throw null; }
-        public string GetGroupName() { throw null; }
-        public string GetName() { throw null; }
+        public string? GetGroupName() { throw null; }
+        public string? GetName() { throw null; }
         public int? GetOrder() { throw null; }
-        public string GetPrompt() { throw null; }
-        public string GetShortName() { throw null; }
+        public string? GetPrompt() { throw null; }
+        public string? GetShortName() { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class, Inherited=true, AllowMultiple=false)]
     public partial class DisplayColumnAttribute : System.Attribute
     {
         public DisplayColumnAttribute(string displayColumn) { }
-        public DisplayColumnAttribute(string displayColumn, string sortColumn) { }
-        public DisplayColumnAttribute(string displayColumn, string sortColumn, bool sortDescending) { }
+        public DisplayColumnAttribute(string displayColumn, string? sortColumn) { }
+        public DisplayColumnAttribute(string displayColumn, string? sortColumn, bool sortDescending) { }
         public string DisplayColumn { get { throw null; } }
-        public string SortColumn { get { throw null; } }
+        public string? SortColumn { get { throw null; } }
         public bool SortDescending { get { throw null; } }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Property, AllowMultiple=false)]
@@ -123,11 +126,11 @@ public partial class DisplayFormatAttribute : System.Attribute
         public DisplayFormatAttribute() { }
         public bool ApplyFormatInEditMode { get { throw null; } set { } }
         public bool ConvertEmptyStringToNull { get { throw null; } set { } }
-        public string DataFormatString { get { throw null; } set { } }
+        public string? DataFormatString { get { throw null; } set { } }
         public bool HtmlEncode { get { throw null; } set { } }
-        public string NullDisplayText { get { throw null; } set { } }
-        public System.Type NullDisplayTextResourceType { get { throw null; } set { } }
-        public string GetNullDisplayText() { throw null; }
+        public string? NullDisplayText { get { throw null; } set { } }
+        public System.Type? NullDisplayTextResourceType { get { throw null; } set { } }
+        public string? GetNullDisplayText() { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Property, AllowMultiple=false, Inherited=true)]
     public sealed partial class EditableAttribute : System.Attribute
@@ -140,14 +143,14 @@ public EditableAttribute(bool allowEdit) { }
     public sealed partial class EmailAddressAttribute : System.ComponentModel.DataAnnotations.DataTypeAttribute
     {
         public EmailAddressAttribute() : base (default(System.ComponentModel.DataAnnotations.DataType)) { }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Method | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=false)]
     public sealed partial class EnumDataTypeAttribute : System.ComponentModel.DataAnnotations.DataTypeAttribute
     {
         public EnumDataTypeAttribute(System.Type enumType) : base (default(System.ComponentModel.DataAnnotations.DataType)) { }
         public System.Type EnumType { get { throw null; } }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=false)]
     public sealed partial class FileExtensionsAttribute : System.ComponentModel.DataAnnotations.DataTypeAttribute
@@ -155,19 +158,19 @@ public sealed partial class FileExtensionsAttribute : System.ComponentModel.Data
         public FileExtensionsAttribute() : base (default(System.ComponentModel.DataAnnotations.DataType)) { }
         public string Extensions { get { throw null; } set { } }
         public override string FormatErrorMessage(string name) { throw null; }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Property, AllowMultiple=false)]
     [System.ObsoleteAttribute("This attribute is no longer in use and will be ignored if applied.")]
     public sealed partial class FilterUIHintAttribute : System.Attribute
     {
         public FilterUIHintAttribute(string filterUIHint) { }
-        public FilterUIHintAttribute(string filterUIHint, string presentationLayer) { }
-        public FilterUIHintAttribute(string filterUIHint, string presentationLayer, params object[] controlParameters) { }
+        public FilterUIHintAttribute(string filterUIHint, string? presentationLayer) { }
+        public FilterUIHintAttribute(string filterUIHint, string? presentationLayer, params object[] controlParameters) { }
         public System.Collections.Generic.IDictionary<string, object> ControlParameters { get { throw null; } }
         public string FilterUIHint { get { throw null; } }
-        public string PresentationLayer { get { throw null; } }
-        public override bool Equals(object obj) { throw null; }
+        public string? PresentationLayer { get { throw null; } }
+        public override bool Equals(object? obj) { throw null; }
         public override int GetHashCode() { throw null; }
     }
     public partial interface IValidatableObject
@@ -186,7 +189,7 @@ public MaxLengthAttribute() { }
         public MaxLengthAttribute(int length) { }
         public int Length { get { throw null; } }
         public override string FormatErrorMessage(string name) { throw null; }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class, AllowMultiple=false)]
     public sealed partial class MetadataTypeAttribute : System.Attribute
@@ -200,13 +203,13 @@ public partial class MinLengthAttribute : System.ComponentModel.DataAnnotations.
         public MinLengthAttribute(int length) { }
         public int Length { get { throw null; } }
         public override string FormatErrorMessage(string name) { throw null; }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=false)]
     public sealed partial class PhoneAttribute : System.ComponentModel.DataAnnotations.DataTypeAttribute
     {
         public PhoneAttribute() : base (default(System.ComponentModel.DataAnnotations.DataType)) { }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=false)]
     public partial class RangeAttribute : System.ComponentModel.DataAnnotations.ValidationAttribute
@@ -220,7 +223,7 @@ public RangeAttribute(System.Type type, string minimum, string maximum) { }
         public System.Type OperandType { get { throw null; } }
         public bool ParseLimitsInInvariantCulture { get { throw null; } set { } }
         public override string FormatErrorMessage(string name) { throw null; }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=false)]
     public partial class RegularExpressionAttribute : System.ComponentModel.DataAnnotations.ValidationAttribute
@@ -229,14 +232,14 @@ public RegularExpressionAttribute(string pattern) { }
         public int MatchTimeoutInMilliseconds { get { throw null; } set { } }
         public string Pattern { get { throw null; } }
         public override string FormatErrorMessage(string name) { throw null; }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=false)]
     public partial class RequiredAttribute : System.ComponentModel.DataAnnotations.ValidationAttribute
     {
         public RequiredAttribute() { }
         public bool AllowEmptyStrings { get { throw null; } set { } }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Property, AllowMultiple=false)]
     public partial class ScaffoldColumnAttribute : System.Attribute
@@ -251,7 +254,7 @@ public StringLengthAttribute(int maximumLength) { }
         public int MaximumLength { get { throw null; } }
         public int MinimumLength { get { throw null; } set { } }
         public override string FormatErrorMessage(string name) { throw null; }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Property, AllowMultiple=false, Inherited=true)]
     public sealed partial class TimestampAttribute : System.Attribute
@@ -262,81 +265,81 @@ public TimestampAttribute() { }
     public partial class UIHintAttribute : System.Attribute
     {
         public UIHintAttribute(string uiHint) { }
-        public UIHintAttribute(string uiHint, string presentationLayer) { }
-        public UIHintAttribute(string uiHint, string presentationLayer, params object[] controlParameters) { }
-        public System.Collections.Generic.IDictionary<string, object> ControlParameters { get { throw null; } }
-        public string PresentationLayer { get { throw null; } }
+        public UIHintAttribute(string uiHint, string? presentationLayer) { }
+        public UIHintAttribute(string uiHint, string? presentationLayer, params object?[]? controlParameters) { }
+        public System.Collections.Generic.IDictionary<string, object?> ControlParameters { get { throw null; } }
+        public string? PresentationLayer { get { throw null; } }
         public string UIHint { get { throw null; } }
-        public override bool Equals(object obj) { throw null; }
+        public override bool Equals(object? obj) { throw null; }
         public override int GetHashCode() { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Field | System.AttributeTargets.Parameter | System.AttributeTargets.Property, AllowMultiple=false)]
     public sealed partial class UrlAttribute : System.ComponentModel.DataAnnotations.DataTypeAttribute
     {
         public UrlAttribute() : base (default(System.ComponentModel.DataAnnotations.DataType)) { }
-        public override bool IsValid(object value) { throw null; }
+        public override bool IsValid(object? value) { throw null; }
     }
     public abstract partial class ValidationAttribute : System.Attribute
     {
         protected ValidationAttribute() { }
         protected ValidationAttribute(System.Func<string> errorMessageAccessor) { }
         protected ValidationAttribute(string errorMessage) { }
-        public string ErrorMessage { get { throw null; } set { } }
-        public string ErrorMessageResourceName { get { throw null; } set { } }
-        public System.Type ErrorMessageResourceType { get { throw null; } set { } }
+        public string? ErrorMessage { get { throw null; } set { } }
+        public string? ErrorMessageResourceName { get { throw null; } set { } }
+        public System.Type? ErrorMessageResourceType { get { throw null; } set { } }
         protected string ErrorMessageString { get { throw null; } }
         public virtual bool RequiresValidationContext { get { throw null; } }
         public virtual string FormatErrorMessage(string name) { throw null; }
-        public System.ComponentModel.DataAnnotations.ValidationResult GetValidationResult(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { throw null; }
-        public virtual bool IsValid(object value) { throw null; }
-        protected virtual System.ComponentModel.DataAnnotations.ValidationResult IsValid(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { throw null; }
-        public void Validate(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { }
-        public void Validate(object value, string name) { }
+        public System.ComponentModel.DataAnnotations.ValidationResult? GetValidationResult(object? value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { throw null; }
+        public virtual bool IsValid(object? value) { throw null; }
+        protected virtual System.ComponentModel.DataAnnotations.ValidationResult IsValid(object? value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { throw null; }
+        public void Validate(object? value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { }
+        public void Validate(object? value, string name) { }
     }
     public sealed partial class ValidationContext : System.IServiceProvider
     {
         public ValidationContext(object instance) { }
-        public ValidationContext(object instance, System.Collections.Generic.IDictionary<object, object> items) { }
-        public ValidationContext(object instance, System.IServiceProvider serviceProvider, System.Collections.Generic.IDictionary<object, object> items) { }
+        public ValidationContext(object instance, System.Collections.Generic.IDictionary<object, object>? items) { }
+        public ValidationContext(object instance, System.IServiceProvider? serviceProvider, System.Collections.Generic.IDictionary<object, object?>? items) { }
         public string DisplayName { get { throw null; } set { } }
-        public System.Collections.Generic.IDictionary<object, object> Items { get { throw null; } }
-        public string MemberName { get { throw null; } set { } }
+        public System.Collections.Generic.IDictionary<object, object?> Items { get { throw null; } }
+        public string? MemberName { get { throw null; } set { } }
         public object ObjectInstance { get { throw null; } }
         public System.Type ObjectType { get { throw null; } }
-        public object GetService(System.Type serviceType) { throw null; }
-        public void InitializeServiceProvider(System.Func<System.Type, object> serviceProvider) { }
+        public object? GetService(System.Type serviceType) { throw null; }
+        public void InitializeServiceProvider(System.Func<System.Type, object?> serviceProvider) { }
     }
     public partial class ValidationException : System.Exception
     {
         public ValidationException() { }
-        public ValidationException(System.ComponentModel.DataAnnotations.ValidationResult validationResult, System.ComponentModel.DataAnnotations.ValidationAttribute validatingAttribute, object value) { }
+        public ValidationException(System.ComponentModel.DataAnnotations.ValidationResult validationResult, System.ComponentModel.DataAnnotations.ValidationAttribute? validatingAttribute, object? value) { }
         protected ValidationException(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
-        public ValidationException(string message) { }
-        public ValidationException(string errorMessage, System.ComponentModel.DataAnnotations.ValidationAttribute validatingAttribute, object value) { }
-        public ValidationException(string message, System.Exception innerException) { }
-        public System.ComponentModel.DataAnnotations.ValidationAttribute ValidationAttribute { get { throw null; } }
+        public ValidationException(string? message) { }
+        public ValidationException(string? errorMessage, System.ComponentModel.DataAnnotations.ValidationAttribute? validatingAttribute, object? value) { }
+        public ValidationException(string? message, System.Exception? innerException) { }
+        public System.ComponentModel.DataAnnotations.ValidationAttribute? ValidationAttribute { get { throw null; } }
         public System.ComponentModel.DataAnnotations.ValidationResult ValidationResult { get { throw null; } }
-        public object Value { get { throw null; } }
+        public object? Value { get { throw null; } }
     }
     public partial class ValidationResult
     {
-        public static readonly System.ComponentModel.DataAnnotations.ValidationResult Success;
+        public static readonly System.ComponentModel.DataAnnotations.ValidationResult? Success;
         protected ValidationResult(System.ComponentModel.DataAnnotations.ValidationResult validationResult) { }
-        public ValidationResult(string errorMessage) { }
-        public ValidationResult(string errorMessage, System.Collections.Generic.IEnumerable<string> memberNames) { }
-        public string ErrorMessage { get { throw null; } set { } }
+        public ValidationResult(string? errorMessage) { }
+        public ValidationResult(string? errorMessage, System.Collections.Generic.IEnumerable<string>? memberNames) { }
+        public string? ErrorMessage { get { throw null; } set { } }
         public System.Collections.Generic.IEnumerable<string> MemberNames { get { throw null; } }
         public override string ToString() { throw null; }
     }
     public static partial class Validator
     {
-        public static bool TryValidateObject(object instance, System.ComponentModel.DataAnnotations.ValidationContext validationContext, System.Collections.Generic.ICollection<System.ComponentModel.DataAnnotations.ValidationResult> validationResults) { throw null; }
-        public static bool TryValidateObject(object instance, System.ComponentModel.DataAnnotations.ValidationContext validationContext, System.Collections.Generic.ICollection<System.ComponentModel.DataAnnotations.ValidationResult> validationResults, bool validateAllProperties) { throw null; }
-        public static bool TryValidateProperty(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext, System.Collections.Generic.ICollection<System.ComponentModel.DataAnnotations.ValidationResult> validationResults) { throw null; }
-        public static bool TryValidateValue(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext, System.Collections.Generic.ICollection<System.ComponentModel.DataAnnotations.ValidationResult> validationResults, System.Collections.Generic.IEnumerable<System.ComponentModel.DataAnnotations.ValidationAttribute> validationAttributes) { throw null; }
+        public static bool TryValidateObject(object instance, System.ComponentModel.DataAnnotations.ValidationContext validationContext, System.Collections.Generic.ICollection<System.ComponentModel.DataAnnotations.ValidationResult>? validationResults) { throw null; }
+        public static bool TryValidateObject(object instance, System.ComponentModel.DataAnnotations.ValidationContext validationContext, System.Collections.Generic.ICollection<System.ComponentModel.DataAnnotations.ValidationResult>? validationResults, bool validateAllProperties) { throw null; }
+        public static bool TryValidateProperty(object? value, System.ComponentModel.DataAnnotations.ValidationContext validationContext, System.Collections.Generic.ICollection<System.ComponentModel.DataAnnotations.ValidationResult>? validationResults) { throw null; }
+        public static bool TryValidateValue(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext, System.Collections.Generic.ICollection<System.ComponentModel.DataAnnotations.ValidationResult>? validationResults, System.Collections.Generic.IEnumerable<System.ComponentModel.DataAnnotations.ValidationAttribute> validationAttributes) { throw null; }
         public static void ValidateObject(object instance, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { }
         public static void ValidateObject(object instance, System.ComponentModel.DataAnnotations.ValidationContext validationContext, bool validateAllProperties) { }
-        public static void ValidateProperty(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { }
+        public static void ValidateProperty(object? value, System.ComponentModel.DataAnnotations.ValidationContext validationContext) { }
         public static void ValidateValue(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext, System.Collections.Generic.IEnumerable<System.ComponentModel.DataAnnotations.ValidationAttribute> validationAttributes) { }
     }
 }
@@ -347,9 +350,10 @@ public partial class ColumnAttribute : System.Attribute
     {
         public ColumnAttribute() { }
         public ColumnAttribute(string name) { }
-        public string Name { get { throw null; } }
+        public string? Name { get { throw null; } }
         public int Order { get { throw null; } set { } }
-        public string TypeName { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.DisallowNullAttribute]
+        public string? TypeName { get { throw null; } set { } }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class, AllowMultiple=false)]
     public partial class ComplexTypeAttribute : System.Attribute
@@ -390,6 +394,7 @@ public partial class TableAttribute : System.Attribute
     {
         public TableAttribute(string name) { }
         public string Name { get { throw null; } }
-        public string Schema { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.DisallowNullAttribute]
+        public string? Schema { get { throw null; } set { } }
     }
 }
diff --git a/src/libraries/System.ComponentModel.Annotations/ref/System.ComponentModel.Annotations.csproj b/src/libraries/System.ComponentModel.Annotations/ref/System.ComponentModel.Annotations.csproj
index 733060bf78e3e2..fdedddfbbdb24b 100644
--- a/src/libraries/System.ComponentModel.Annotations/ref/System.ComponentModel.Annotations.csproj
+++ b/src/libraries/System.ComponentModel.Annotations/ref/System.ComponentModel.Annotations.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>netstandard2.1</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.ComponentModel.Annotations.cs" />
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System.ComponentModel.Annotations.csproj b/src/libraries/System.ComponentModel.Annotations/src/System.ComponentModel.Annotations.csproj
index e871a28c7c0e62..8e376bbde0acda 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System.ComponentModel.Annotations.csproj
+++ b/src/libraries/System.ComponentModel.Annotations/src/System.ComponentModel.Annotations.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>netstandard2.1</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\ComponentModel\DataAnnotations\AssociatedMetadataTypeTypeDescriptor.cs" />
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociatedMetadataTypeTypeDescriptionProvider.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociatedMetadataTypeTypeDescriptionProvider.cs
index b0ca16061661b4..fc7b7e456b9b9c 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociatedMetadataTypeTypeDescriptionProvider.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociatedMetadataTypeTypeDescriptionProvider.cs
@@ -1,6 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+// TODO-NULLABLE: Enable after System.ComponentModel.TypeDescriptionProvider is annotated
+#nullable disable
+
 namespace System.ComponentModel.DataAnnotations
 {
     /// <summary>
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociatedMetadataTypeTypeDescriptor.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociatedMetadataTypeTypeDescriptor.cs
index 7ce7d3aecd9eb2..2bc82d50a6e343 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociatedMetadataTypeTypeDescriptor.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociatedMetadataTypeTypeDescriptor.cs
@@ -1,6 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+// TODO-NULLABLE: Enable after System.ComponentModel.TypeDescriptionProvider is annotated
+#nullable disable
+
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Globalization;
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociationAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociationAttribute.cs
index 2276b3f33f66d1..41078c03f41960 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociationAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/AssociationAttribute.cs
@@ -68,7 +68,7 @@ public AssociationAttribute(string name, string thisKey, string otherKey)
         /// </summary>
         /// <param name="key">The key to parse</param>
         /// <returns>Array of individual key members</returns>
-        private static string[] GetKeyMembers(string key)
+        private static string[] GetKeyMembers(string? key)
         {
             if (key == null)
             {
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CompareAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CompareAttribute.cs
index 5b8ab828f6ee0a..dab56c6018e6e5 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CompareAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CompareAttribute.cs
@@ -17,7 +17,7 @@ public CompareAttribute(string otherProperty) : base(SR.CompareAttribute_MustMat
 
         public string OtherProperty { get; }
 
-        public string OtherPropertyDisplayName { get; internal set; }
+        public string? OtherPropertyDisplayName { get; internal set; }
 
         public override bool RequiresValidationContext => true;
 
@@ -25,7 +25,7 @@ public override string FormatErrorMessage(string name) =>
             string.Format(
                 CultureInfo.CurrentCulture, ErrorMessageString, name, OtherPropertyDisplayName ?? OtherProperty);
 
-        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
+        protected override ValidationResult? IsValid(object? value, ValidationContext validationContext)
         {
             var otherPropertyInfo = validationContext.ObjectType.GetRuntimeProperty(OtherProperty);
             if (otherPropertyInfo == null)
@@ -37,7 +37,7 @@ protected override ValidationResult IsValid(object value, ValidationContext vali
                 throw new ArgumentException(SR.Format(SR.Common_PropertyNotFound, validationContext.ObjectType.FullName, OtherProperty));
             }
 
-            object otherPropertyValue = otherPropertyInfo.GetValue(validationContext.ObjectInstance, null);
+            object? otherPropertyValue = otherPropertyInfo.GetValue(validationContext.ObjectInstance, null);
             if (!Equals(value, otherPropertyValue))
             {
                 if (OtherPropertyDisplayName == null)
@@ -45,7 +45,7 @@ protected override ValidationResult IsValid(object value, ValidationContext vali
                     OtherPropertyDisplayName = GetDisplayNameForProperty(otherPropertyInfo);
                 }
 
-                string[] memberNames = validationContext.MemberName != null
+                string[]? memberNames = validationContext.MemberName != null
                    ? new[] { validationContext.MemberName }
                    : null;
                 return new ValidationResult(FormatErrorMessage(validationContext.DisplayName), memberNames);
@@ -54,12 +54,14 @@ protected override ValidationResult IsValid(object value, ValidationContext vali
             return null;
         }
 
-        private string GetDisplayNameForProperty(PropertyInfo property)
+        private string? GetDisplayNameForProperty(PropertyInfo property)
         {
             var attributes = CustomAttributeExtensions.GetCustomAttributes(property, true);
             var display = attributes.OfType<DisplayAttribute>().FirstOrDefault();
             if (display != null)
             {
+                // TODO-NULLABLE: This will return null if [DisplayName] is specified but no Name has been defined - probably a bug.
+                // Should fall back to OtherProperty in this case instead.
                 return display.GetName();
             }
 
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CreditCardAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CreditCardAttribute.cs
index a9a5aea98dbc10..4715007eaf8b37 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CreditCardAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CreditCardAttribute.cs
@@ -15,7 +15,7 @@ public CreditCardAttribute()
             DefaultErrorMessage = SR.CreditCardAttribute_Invalid;
         }
 
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             if (value == null)
             {
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CustomValidationAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CustomValidationAttribute.cs
index 58b8a01e72a8ea..67c7077102be92 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CustomValidationAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CustomValidationAttribute.cs
@@ -58,12 +58,12 @@ public sealed class CustomValidationAttribute : ValidationAttribute
     {
         #region Member Fields
 
-        private readonly Lazy<string> _malformedErrorMessage;
+        private readonly Lazy<string?> _malformedErrorMessage;
         private bool _isSingleArgumentMethod;
-        private string _lastMessage;
-        private MethodInfo _methodInfo;
-        private Type _firstParameterType;
-        private Tuple<string, Type> _typeId;
+        private string? _lastMessage;
+        private MethodInfo? _methodInfo;
+        private Type? _firstParameterType;
+        private Tuple<string, Type>? _typeId;
 
         #endregion
 
@@ -88,7 +88,7 @@ public CustomValidationAttribute(Type validatorType, string method)
         {
             ValidatorType = validatorType;
             Method = method;
-            _malformedErrorMessage = new Lazy<string>(CheckAttributeWellFormed);
+            _malformedErrorMessage = new Lazy<string?>(CheckAttributeWellFormed);
         }
 
         #endregion
@@ -143,7 +143,7 @@ public override bool RequiresValidationContext
         /// </param>
         /// <returns>Whatever the <see cref="Method" /> in <see cref="ValidatorType" /> returns.</returns>
         /// <exception cref="InvalidOperationException"> is thrown if the current attribute is malformed.</exception>
-        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
+        protected override ValidationResult? IsValid(object? value, ValidationContext validationContext)
         {
             // If attribute is not valid, throw an exception right away to inform the developer
             ThrowIfAttributeNotWellFormed();
@@ -153,7 +153,7 @@ protected override ValidationResult IsValid(object value, ValidationContext vali
             // If the value is not of the correct type and cannot be converted, fail
             // to indicate it is not acceptable.  The convention is that IsValid is merely a probe,
             // and clients are not expecting exceptions.
-            object convertedValue;
+            object? convertedValue;
             if (!TryConvertValue(value, out convertedValue))
             {
                 return new ValidationResult(SR.Format(SR.CustomValidationAttribute_Type_Conversion_Failed,
@@ -171,10 +171,10 @@ protected override ValidationResult IsValid(object value, ValidationContext vali
                 // 1-parameter form is ValidationResult Method(object value)
                 // 2-parameter form is ValidationResult Method(object value, ValidationContext context),
                 var methodParams = _isSingleArgumentMethod
-                    ? new object[] { convertedValue }
+                    ? new object?[] { convertedValue }
                     : new[] { convertedValue, validationContext };
 
-                var result = (ValidationResult)methodInfo.Invoke(null, methodParams);
+                var result = (ValidationResult?)methodInfo!.Invoke(null, methodParams);
 
                 // We capture the message they provide us only in the event of failure,
                 // otherwise we use the normal message supplied via the ctor
@@ -189,7 +189,7 @@ protected override ValidationResult IsValid(object value, ValidationContext vali
             }
             catch (TargetInvocationException tie)
             {
-                throw tie.InnerException;
+                throw tie.InnerException!;
             }
         }
 
@@ -217,13 +217,13 @@ public override string FormatErrorMessage(string name)
         ///     Checks whether the current attribute instance itself is valid for use.
         /// </summary>
         /// <returns>The error message why it is not well-formed, null if it is well-formed.</returns>
-        private string CheckAttributeWellFormed() => ValidateValidatorTypeParameter() ?? ValidateMethodParameter();
+        private string? CheckAttributeWellFormed() => ValidateValidatorTypeParameter() ?? ValidateMethodParameter();
 
         /// <summary>
         ///     Internal helper to determine whether <see cref="ValidatorType" /> is legal for use.
         /// </summary>
         /// <returns><c>null</c> or the appropriate error message.</returns>
-        private string ValidateValidatorTypeParameter()
+        private string? ValidateValidatorTypeParameter()
         {
             if (ValidatorType == null)
             {
@@ -242,7 +242,7 @@ private string ValidateValidatorTypeParameter()
         ///     Internal helper to determine whether <see cref="Method" /> is legal for use.
         /// </summary>
         /// <returns><c>null</c> or the appropriate error message.</returns>
-        private string ValidateMethodParameter()
+        private string? ValidateMethodParameter()
         {
             if (string.IsNullOrEmpty(Method))
             {
@@ -295,7 +295,7 @@ private string ValidateMethodParameter()
         /// </summary>
         private void ThrowIfAttributeNotWellFormed()
         {
-            string errorMessage = _malformedErrorMessage.Value;
+            string? errorMessage = _malformedErrorMessage.Value;
             if (errorMessage != null)
             {
                 throw new InvalidOperationException(errorMessage);
@@ -309,10 +309,10 @@ private void ThrowIfAttributeNotWellFormed()
         /// <param name="value">The value to check/convert.</param>
         /// <param name="convertedValue">If successful, the converted (or copied) value.</param>
         /// <returns><c>true</c> if type value was already correct or was successfully converted.</returns>
-        private bool TryConvertValue(object value, out object convertedValue)
+        private bool TryConvertValue(object? value, out object? convertedValue)
         {
             convertedValue = null;
-            var expectedValueType = _firstParameterType;
+            var expectedValueType = _firstParameterType!;
 
             // Null is permitted for reference types or for Nullable<>'s only
             if (value == null)
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DataTypeAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DataTypeAttribute.cs
index 443b3b777aca03..d6ea70b7c8fdda 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DataTypeAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DataTypeAttribute.cs
@@ -67,12 +67,12 @@ public DataTypeAttribute(string customDataType)
         ///     Gets the string representing a custom data type. Returns a non-null value only if <see cref="DataType" /> is
         ///     DataType.Custom.
         /// </summary>
-        public string CustomDataType { get; }
+        public string? CustomDataType { get; }
 
         /// <summary>
         ///     Gets the default display format that gets used along with this DataType.
         /// </summary>
-        public DisplayFormatAttribute DisplayFormat { get; protected set; }
+        public DisplayFormatAttribute? DisplayFormat { get; protected set; }
 
         /// <summary>
         ///     Return the name of the data type, either using the <see cref="DataType" /> enum or <see cref="CustomDataType" />
@@ -87,7 +87,7 @@ public virtual string GetDataTypeName()
             if (DataType == DataType.Custom)
             {
                 // If it's a custom type string, use it as the template name
-                return CustomDataType;
+                return CustomDataType!;
             }
             // If it's an enum, turn it into a string
             // Use the cached array with enum string values instead of ToString() as the latter is too slow
@@ -101,7 +101,7 @@ public virtual string GetDataTypeName()
         /// <param name="value">The value to validate</param>
         /// <returns>Unconditionally returns <c>true</c></returns>
         /// <exception cref="InvalidOperationException"> is thrown if the current attribute is ill-formed.</exception>
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             EnsureValidDataType();
 
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayAttribute.cs
index 0b6d9a9524384c..2d8b11f00b3162 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayAttribute.cs
@@ -25,7 +25,7 @@ public sealed class DisplayAttribute : Attribute
         private bool? _autoGenerateField;
         private bool? _autoGenerateFilter;
         private int? _order;
-        private Type _resourceType;
+        private Type? _resourceType;
 
         #endregion
 
@@ -54,7 +54,7 @@ public sealed class DisplayAttribute : Attribute
         ///     The short name is generally used as the grid column label for a UI element bound to the member
         ///     bearing this attribute.  A <c>null</c> or empty string is legal, and consumers must allow for that.
         /// </value>
-        public string ShortName
+        public string? ShortName
         {
             get => _shortName.Value;
             set => _shortName.Value = value;
@@ -79,7 +79,7 @@ public string ShortName
         ///     The name is generally used as the field label for a UI element bound to the member
         ///     bearing this attribute.  A <c>null</c> or empty string is legal, and consumers must allow for that.
         /// </value>
-        public string Name
+        public string? Name
         {
             get => _name.Value;
             set => _name.Value = value;
@@ -104,7 +104,7 @@ public string Name
         ///     Description is generally used as a tool tip or description a UI element bound to the member
         ///     bearing this attribute.  A <c>null</c> or empty string is legal, and consumers must allow for that.
         /// </value>
-        public string Description
+        public string? Description
         {
             get => _description.Value;
             set => _description.Value = value;
@@ -129,7 +129,7 @@ public string Description
         ///     A prompt is generally used as a prompt or watermark for a UI element bound to the member
         ///     bearing this attribute.  A <c>null</c> or empty string is legal, and consumers must allow for that.
         /// </value>
-        public string Prompt
+        public string? Prompt
         {
             get => _prompt.Value;
             set => _prompt.Value = value;
@@ -154,7 +154,7 @@ public string Prompt
         ///     A group name is used for grouping fields into the UI.  A <c>null</c> or empty string is legal,
         ///     and consumers must allow for that.
         /// </value>
-        public string GroupName
+        public string? GroupName
         {
             get => _groupName.Value;
             set => _groupName.Value = value;
@@ -167,7 +167,7 @@ public string GroupName
         ///     <see cref="GetName" />, <see cref="GetDescription" />, <see cref="GetPrompt" />, and <see cref="GetGroupName" />
         ///     methods to return localized values.
         /// </summary>
-        public Type ResourceType
+        public Type? ResourceType
         {
             get => _resourceType;
             set
@@ -298,7 +298,7 @@ public int Order
         ///     but a public static property with a name matching the <see cref="ShortName" /> value couldn't be found
         ///     on the <see cref="ResourceType" />.
         /// </exception>
-        public string GetShortName() => _shortName.GetLocalizableValue() ?? GetName();
+        public string? GetShortName() => _shortName.GetLocalizableValue() ?? GetName();
 
         /// <summary>
         ///     Gets the UI display string for Name.
@@ -325,7 +325,7 @@ public int Order
         ///     but a public static property with a name matching the <see cref="Name" /> value couldn't be found
         ///     on the <see cref="ResourceType" />.
         /// </exception>
-        public string GetName() => _name.GetLocalizableValue();
+        public string? GetName() => _name.GetLocalizableValue();
 
         /// <summary>
         ///     Gets the UI display string for Description.
@@ -348,7 +348,7 @@ public int Order
         ///     but a public static property with a name matching the <see cref="Description" /> value couldn't be found
         ///     on the <see cref="ResourceType" />.
         /// </exception>
-        public string GetDescription() => _description.GetLocalizableValue();
+        public string? GetDescription() => _description.GetLocalizableValue();
 
         /// <summary>
         ///     Gets the UI display string for Prompt.
@@ -371,7 +371,7 @@ public int Order
         ///     but a public static property with a name matching the <see cref="Prompt" /> value couldn't be found
         ///     on the <see cref="ResourceType" />.
         /// </exception>
-        public string GetPrompt() => _prompt.GetLocalizableValue();
+        public string? GetPrompt() => _prompt.GetLocalizableValue();
 
         /// <summary>
         ///     Gets the UI display string for GroupName.
@@ -394,7 +394,7 @@ public int Order
         ///     but a public static property with a name matching the <see cref="GroupName" /> value couldn't be found
         ///     on the <see cref="ResourceType" />.
         /// </exception>
-        public string GetGroupName() => _groupName.GetLocalizableValue();
+        public string? GetGroupName() => _groupName.GetLocalizableValue();
 
         /// <summary>
         ///     Gets the value of <see cref="AutoGenerateField" /> if it has been set, or <c>null</c>.
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayColumnAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayColumnAttribute.cs
index 1ed02dfe874596..d13f5cda2268bb 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayColumnAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayColumnAttribute.cs
@@ -15,12 +15,12 @@ public DisplayColumnAttribute(string displayColumn)
         {
         }
 
-        public DisplayColumnAttribute(string displayColumn, string sortColumn)
+        public DisplayColumnAttribute(string displayColumn, string? sortColumn)
             : this(displayColumn, sortColumn, false)
         {
         }
 
-        public DisplayColumnAttribute(string displayColumn, string sortColumn, bool sortDescending)
+        public DisplayColumnAttribute(string displayColumn, string? sortColumn, bool sortDescending)
         {
             DisplayColumn = displayColumn;
             SortColumn = sortColumn;
@@ -29,7 +29,7 @@ public DisplayColumnAttribute(string displayColumn, string sortColumn, bool sort
 
         public string DisplayColumn { get; }
 
-        public string SortColumn { get; }
+        public string? SortColumn { get; }
 
         public bool SortDescending { get; }
     }
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayFormatAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayFormatAttribute.cs
index 76b7a8b525c498..96a82b04120e0e 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayFormatAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DisplayFormatAttribute.cs
@@ -25,7 +25,7 @@ public DisplayFormatAttribute()
         /// <summary>
         ///     Gets or sets the format string
         /// </summary>
-        public string DataFormatString { get; set; }
+        public string? DataFormatString { get; set; }
 
         /// <summary>
         ///     Gets or sets the string to display when the value is null, which may be a resource key string.
@@ -46,7 +46,7 @@ public DisplayFormatAttribute()
         ///     The null display text is generally used as placeholder when the value is not specified.
         ///     A <c>null</c> or empty string is legal, and consumers must allow for that.
         /// </value>
-        public string NullDisplayText
+        public string? NullDisplayText
         {
             get => _nullDisplayText.Value;
             set => _nullDisplayText.Value = value;
@@ -72,7 +72,7 @@ public string NullDisplayText
         ///     Using <see cref="NullDisplayTextResourceType" /> along with <see cref="NullDisplayText" />, allows the <see cref="GetNullDisplayText" />
         ///     method to return localized values.
         /// </summary>
-        public Type NullDisplayTextResourceType
+        public Type? NullDisplayTextResourceType
         {
             get => _nullDisplayText.ResourceType;
             set => _nullDisplayText.ResourceType = value;
@@ -102,6 +102,6 @@ public Type NullDisplayTextResourceType
         ///     but a public static property with a name matching the <see cref="NullDisplayText" /> value couldn't be found
         ///     on the <see cref="NullDisplayTextResourceType" />.
         /// </exception>
-        public string GetNullDisplayText() => _nullDisplayText.GetLocalizableValue();
+        public string? GetNullDisplayText() => _nullDisplayText.GetLocalizableValue();
     }
 }
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/EmailAddressAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/EmailAddressAttribute.cs
index eba694c990e278..2e28b0cb6ac3df 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/EmailAddressAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/EmailAddressAttribute.cs
@@ -15,7 +15,7 @@ public EmailAddressAttribute()
             DefaultErrorMessage = SR.EmailAddressAttribute_Invalid;
         }
 
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             if (value == null)
             {
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/EnumDataTypeAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/EnumDataTypeAttribute.cs
index ba0a48e37c4862..18dd723deb304f 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/EnumDataTypeAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/EnumDataTypeAttribute.cs
@@ -20,7 +20,7 @@ public EnumDataTypeAttribute(Type enumType)
 
         public Type EnumType { get; }
 
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             if (EnumType == null)
             {
@@ -91,8 +91,8 @@ public override bool IsValid(object value)
                 // If it is, the string representation of the enum value will be something like "A, B", while
                 // the string representation of the underlying value will be "3". If the enum value does not
                 // match a valid flag combination, then it would also be something like "3".
-                string underlying = GetUnderlyingTypeValueString(EnumType, convertedValue);
-                string converted = convertedValue.ToString();
+                string underlying = GetUnderlyingTypeValueString(EnumType, convertedValue)!;
+                string? converted = convertedValue.ToString();
                 return !underlying.Equals(converted);
             }
 
@@ -102,7 +102,7 @@ public override bool IsValid(object value)
         private static bool IsEnumTypeInFlagsMode(Type enumType) =>
             enumType.GetCustomAttributes(typeof(FlagsAttribute), false).Any();
 
-        private static string GetUnderlyingTypeValueString(Type enumType, object enumValue) =>
+        private static string? GetUnderlyingTypeValueString(Type enumType, object enumValue) =>
             Convert.ChangeType(enumValue, Enum.GetUnderlyingType(enumType), CultureInfo.InvariantCulture).ToString();
     }
 }
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/FileExtensionsAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/FileExtensionsAttribute.cs
index df2f1fc2add11b..e66e2807e51a36 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/FileExtensionsAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/FileExtensionsAttribute.cs
@@ -12,7 +12,7 @@ namespace System.ComponentModel.DataAnnotations
         AllowMultiple = false)]
     public sealed class FileExtensionsAttribute : DataTypeAttribute
     {
-        private string _extensions;
+        private string? _extensions;
 
         public FileExtensionsAttribute()
             : base(DataType.Upload)
@@ -42,7 +42,7 @@ private IEnumerable<string> ExtensionsParsed
         public override string FormatErrorMessage(string name) =>
             string.Format(CultureInfo.CurrentCulture, ErrorMessageString, name, ExtensionsFormatted);
 
-        public override bool IsValid(object value) =>
+        public override bool IsValid(object? value) =>
             value == null || value is string valueAsString && ValidateExtension(valueAsString);
 
         private bool ValidateExtension(string fileName)
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/FilterUIHintAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/FilterUIHintAttribute.cs
index e30b2838333886..bb5138ef3900ac 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/FilterUIHintAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/FilterUIHintAttribute.cs
@@ -24,14 +24,14 @@ public sealed class FilterUIHintAttribute : Attribute
         /// Gets the name of the presentation layer that supports the control type
         /// in <see cref="FilterUIHint"/>
         /// </summary>
-        public string PresentationLayer => _implementation.PresentationLayer;
+        public string? PresentationLayer => _implementation.PresentationLayer;
 
         /// <summary>
         /// Gets the name-value pairs used as parameters to the control's constructor
         /// </summary>
         /// <exception cref="InvalidOperationException"> is thrown if the current attribute
         /// is ill-formed.</exception>
-        public IDictionary<string, object> ControlParameters => _implementation.ControlParameters;
+        public IDictionary<string, object?> ControlParameters => _implementation.ControlParameters;
 
         /// <summary>
         /// Constructor that accepts the name of the control, without specifying
@@ -50,7 +50,7 @@ public FilterUIHintAttribute(string filterUIHint)
         /// <param name="filterUIHint">The name of the control to use</param>
         /// <param name="presentationLayer">The name of the presentation layer that
         /// supports this control</param>
-        public FilterUIHintAttribute(string filterUIHint, string presentationLayer)
+        public FilterUIHintAttribute(string filterUIHint, string? presentationLayer)
             : this(filterUIHint, presentationLayer, Array.Empty<object>())
         {
         }
@@ -62,8 +62,8 @@ public FilterUIHintAttribute(string filterUIHint, string presentationLayer)
         /// <param name="filterUIHint">The name of the control</param>
         /// <param name="presentationLayer">The presentation layer</param>
         /// <param name="controlParameters">The list of parameters for the control</param>
-        public FilterUIHintAttribute(string filterUIHint, string presentationLayer,
-            params object[] controlParameters)
+        public FilterUIHintAttribute(string filterUIHint, string? presentationLayer,
+            params object?[] controlParameters)
         {
             _implementation = new UIHintAttribute.UIHintImplementation(
                 filterUIHint, presentationLayer, controlParameters);
@@ -82,7 +82,7 @@ public FilterUIHintAttribute(string filterUIHint, string presentationLayer,
         /// <param name="obj">An System.Object.</param>
         /// <returns>true if obj is a FilterUIHintAttribute and its value is the same
         /// as this instance; otherwise, false.</returns>
-        public override bool Equals(object obj) =>
+        public override bool Equals(object? obj) =>
             obj is FilterUIHintAttribute otherAttribute && _implementation.Equals(otherAttribute._implementation);
     }
 }
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/LocalizableString.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/LocalizableString.cs
index a65becde4e6495..5c8dfca6b56d47 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/LocalizableString.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/LocalizableString.cs
@@ -15,9 +15,9 @@ internal class LocalizableString
         #region Member fields
 
         private readonly string _propertyName;
-        private Func<string> _cachedResult;
-        private string _propertyValue;
-        private Type _resourceType;
+        private Func<string?>? _cachedResult;
+        private string? _propertyValue;
+        private Type? _resourceType;
 
         #endregion
 
@@ -46,7 +46,7 @@ public LocalizableString(string propertyName)
         ///     either the literal, non-localized value, or it can be a resource name
         ///     found on the resource type supplied to <see cref="GetLocalizableValue" />.
         /// </summary>
-        public string Value
+        public string? Value
         {
             get => _propertyValue;
             set
@@ -62,7 +62,7 @@ public string Value
         /// <summary>
         ///     Gets or sets the resource type to be used for localization.
         /// </summary>
-        public Type ResourceType
+        public Type? ResourceType
         {
             get => _resourceType;
             set
@@ -108,7 +108,7 @@ private void ClearCache()
         /// <returns>
         ///     Returns the potentially localized value.
         /// </returns>
-        public string GetLocalizableValue()
+        public string? GetLocalizableValue()
         {
             if (_cachedResult == null)
             {
@@ -153,7 +153,7 @@ public string GetLocalizableValue()
                     else
                     {
                         // We have a valid property, so cache the resource
-                        _cachedResult = () => (string)property.GetValue(null, null);
+                        _cachedResult = () => (string?)property!.GetValue(null, null);
                     }
                 }
             }
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/MaxLengthAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/MaxLengthAttribute.cs
index 76d2e7407e7b6b..903112d41fa84f 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/MaxLengthAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/MaxLengthAttribute.cs
@@ -59,7 +59,7 @@ public MaxLengthAttribute()
         ///     <c>true</c> if the value is null or less than or equal to the specified maximum length, otherwise <c>false</c>
         /// </returns>
         /// <exception cref="InvalidOperationException">Length is zero or less than negative one.</exception>
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             // Check the lengths for legality
             EnsureLegalLengths();
@@ -120,10 +120,10 @@ public static bool TryGetCount(object value, out int count)
                 return true;
             }
 
-            PropertyInfo property = value.GetType().GetRuntimeProperty("Count");
+            PropertyInfo? property = value.GetType().GetRuntimeProperty("Count");
             if (property != null && property.CanRead && property.PropertyType == typeof(int))
             {
-                count = (int)property.GetValue(value);
+                count = (int)property.GetValue(value)!;
                 return true;
             }
 
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/MinLengthAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/MinLengthAttribute.cs
index 0b34a5f068c353..7b0e09f659050f 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/MinLengthAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/MinLengthAttribute.cs
@@ -43,7 +43,7 @@ public MinLengthAttribute(int length)
         ///     <c>false</c>
         /// </returns>
         /// <exception cref="InvalidOperationException">Length is less than zero.</exception>
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             // Check the lengths for legality
             EnsureLegalLengths();
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/PhoneAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/PhoneAttribute.cs
index d264e5eeb2f656..cec872c27f4c3c 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/PhoneAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/PhoneAttribute.cs
@@ -20,7 +20,7 @@ public PhoneAttribute()
             DefaultErrorMessage = SR.PhoneAttribute_Invalid;
         }
 
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             if (value == null)
             {
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RangeAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RangeAttribute.cs
index 3e9bb7591d7a94..a3b2e0b96c5119 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RangeAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RangeAttribute.cs
@@ -84,9 +84,9 @@ public RangeAttribute(Type type, string minimum, string maximum)
         /// parameters, for which the invariant culture is always used for any conversions of the validated value.</remarks>
         public bool ConvertValueInInvariantCulture { get; set; }
 
-        private Func<object, object> Conversion { get; set; }
+        private Func<object, object?>? Conversion { get; set; }
 
-        private void Initialize(IComparable minimum, IComparable maximum, Func<object, object> conversion)
+        private void Initialize(IComparable minimum, IComparable maximum, Func<object, object?> conversion)
         {
             if (minimum.CompareTo(maximum) > 0)
             {
@@ -104,7 +104,7 @@ private void Initialize(IComparable minimum, IComparable maximum, Func<object, o
         /// <param name="value">The value to test for validity.</param>
         /// <returns><c>true</c> means the <paramref name="value" /> is valid</returns>
         /// <exception cref="InvalidOperationException"> is thrown if the current attribute is ill-formed.</exception>
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             // Validate our properties and create the conversion function
             SetupConversion();
@@ -115,11 +115,11 @@ public override bool IsValid(object value)
                 return true;
             }
 
-            object convertedValue;
+            object? convertedValue;
 
             try
             {
-                convertedValue = Conversion(value);
+                convertedValue = Conversion!(value);
             }
             catch (FormatException)
             {
@@ -207,7 +207,7 @@ private void SetupConversion()
                         ? converter.ConvertFromInvariantString((string)maximum)
                         : converter.ConvertFromString((string)maximum));
 
-                    Func<object, object> conversion;
+                    Func<object, object?> conversion;
                     if (ConvertValueInInvariantCulture)
                     {
                         conversion = value => value.GetType() == type
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RegularExpressionAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RegularExpressionAttribute.cs
index 79c1a7a945f7f5..e7f4eb1db432e4 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RegularExpressionAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RegularExpressionAttribute.cs
@@ -35,7 +35,7 @@ public RegularExpressionAttribute(string pattern)
         /// </summary>
         public string Pattern { get; }
 
-        private Regex Regex { get; set; }
+        private Regex? Regex { get; set; }
 
         /// <summary>
         ///     Override of <see cref="ValidationAttribute.IsValid(object)" />
@@ -47,12 +47,12 @@ public RegularExpressionAttribute(string pattern)
         /// <returns><c>true</c> if the given value matches the current regular expression pattern</returns>
         /// <exception cref="InvalidOperationException"> is thrown if the current attribute is ill-formed.</exception>
         /// <exception cref="ArgumentException"> is thrown if the <see cref="Pattern" /> is not a valid regular expression.</exception>
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             SetupRegex();
 
             // Convert the value to a string
-            string stringValue = Convert.ToString(value, CultureInfo.CurrentCulture);
+            string? stringValue = Convert.ToString(value, CultureInfo.CurrentCulture);
 
             // Automatically pass if value is null or empty. RequiredAttribute should be used to assert a value is not empty.
             if (string.IsNullOrEmpty(stringValue))
@@ -60,7 +60,7 @@ public override bool IsValid(object value)
                 return true;
             }
 
-            var m = Regex.Match(stringValue);
+            var m = Regex!.Match(stringValue);
 
             // We are looking for an exact match, not just a search hit. This matches what
             // the RegularExpressionValidator control does
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RequiredAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RequiredAttribute.cs
index f7233499f959fe..a5003f0d2d3188 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RequiredAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/RequiredAttribute.cs
@@ -36,7 +36,7 @@ public RequiredAttribute()
         ///     <see cref="RequiredAttribute.AllowEmptyStrings" />
         ///     then <c>false</c> is returned only if <paramref name="value" /> is null.
         /// </returns>
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             if (value == null)
             {
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Schema/ColumnAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Schema/ColumnAttribute.cs
index d1e558389b1261..f871d3d5c09819 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Schema/ColumnAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Schema/ColumnAttribute.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 
 namespace System.ComponentModel.DataAnnotations.Schema
@@ -12,7 +13,7 @@ namespace System.ComponentModel.DataAnnotations.Schema
     public class ColumnAttribute : Attribute
     {
         private int _order = -1;
-        private string _typeName;
+        private string? _typeName;
 
         /// <summary>
         ///     Initializes a new instance of the <see cref="ColumnAttribute" /> class.
@@ -38,7 +39,7 @@ public ColumnAttribute(string name)
         /// <summary>
         ///     The name of the column the property is mapped to.
         /// </summary>
-        public string Name { get; }
+        public string? Name { get; }
 
         /// <summary>
         ///     The zero-based order of the column the property is mapped to.
@@ -60,7 +61,8 @@ public int Order
         /// <summary>
         ///     The database provider specific data type of the column the property is mapped to.
         /// </summary>
-        public string TypeName
+        [DisallowNull]
+        public string? TypeName
         {
             get => _typeName;
             set
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Schema/TableAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Schema/TableAttribute.cs
index 911161490f905e..489bf85830c827 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Schema/TableAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Schema/TableAttribute.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 
 namespace System.ComponentModel.DataAnnotations.Schema
@@ -11,7 +12,7 @@ namespace System.ComponentModel.DataAnnotations.Schema
     [AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
     public class TableAttribute : Attribute
     {
-        private string _schema;
+        private string? _schema;
 
         /// <summary>
         ///     Initializes a new instance of the <see cref="TableAttribute" /> class.
@@ -35,7 +36,8 @@ public TableAttribute(string name)
         /// <summary>
         ///     The schema of the table the class is mapped to.
         /// </summary>
-        public string Schema
+        [DisallowNull]
+        public string? Schema
         {
             get => _schema;
             set
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/StringLengthAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/StringLengthAttribute.cs
index f6cb119e25e6f9..17e39eec4b3c34 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/StringLengthAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/StringLengthAttribute.cs
@@ -42,7 +42,7 @@ public StringLengthAttribute(int maximumLength)
         /// <param name="value">The value to test.</param>
         /// <returns><c>true</c> if the value is null or less than or equal to the set maximum length</returns>
         /// <exception cref="InvalidOperationException"> is thrown if the current attribute is ill-formed.</exception>
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             // Check the lengths for legality
             EnsureLegalLengths();
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/UIHintAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/UIHintAttribute.cs
index 21de33d8d35a81..f92ebaa75c1074 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/UIHintAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/UIHintAttribute.cs
@@ -42,7 +42,7 @@ public UIHintAttribute(string uiHint, string presentationLayer)
         /// <param name="uiHint">The name of the control</param>
         /// <param name="presentationLayer">The presentation layer</param>
         /// <param name="controlParameters">The list of parameters for the control</param>
-        public UIHintAttribute(string uiHint, string presentationLayer, params object[] controlParameters)
+        public UIHintAttribute(string uiHint, string? presentationLayer, params object?[]? controlParameters)
         {
             _implementation = new UIHintImplementation(uiHint, presentationLayer, controlParameters);
         }
@@ -55,25 +55,25 @@ public UIHintAttribute(string uiHint, string presentationLayer, params object[]
         /// <summary>
         ///     Gets the name of the presentation layer that supports the control type in <see cref="UIHint" />
         /// </summary>
-        public string PresentationLayer => _implementation.PresentationLayer;
+        public string? PresentationLayer => _implementation.PresentationLayer;
 
         /// <summary>
         ///     Gets the name-value pairs used as parameters to the control's constructor
         /// </summary>
         /// <exception cref="InvalidOperationException"> is thrown if the current attribute is ill-formed.</exception>
-        public IDictionary<string, object> ControlParameters => _implementation.ControlParameters;
+        public IDictionary<string, object?> ControlParameters => _implementation.ControlParameters;
 
         public override int GetHashCode() => _implementation.GetHashCode();
 
-        public override bool Equals(object obj) =>
+        public override bool Equals(object? obj) =>
             obj is UIHintAttribute otherAttribute && _implementation.Equals(otherAttribute._implementation);
 
         internal class UIHintImplementation
         {
-            private readonly object[] _inputControlParameters;
-            private IDictionary<string, object> _controlParameters;
+            private readonly object?[]? _inputControlParameters;
+            private IDictionary<string, object?>? _controlParameters;
 
-            public UIHintImplementation(string uiHint, string presentationLayer, params object[] controlParameters)
+            public UIHintImplementation(string uiHint, string? presentationLayer, params object?[]? controlParameters)
             {
                 UIHint = uiHint;
                 PresentationLayer = presentationLayer;
@@ -92,12 +92,12 @@ public UIHintImplementation(string uiHint, string presentationLayer, params obje
             /// <summary>
             ///     Gets the name of the presentation layer that supports the control type in <see cref="UIHint" />
             /// </summary>
-            public string PresentationLayer { get; }
+            public string? PresentationLayer { get; }
 
             // Lazy load the dictionary. It's fine if this method executes multiple times in stress scenarios.
             // If the method throws (indicating that the input params are invalid) this property will throw
             // every time it's accessed.
-            public IDictionary<string, object> ControlParameters =>
+            public IDictionary<string, object?> ControlParameters =>
                 _controlParameters ?? (_controlParameters = BuildControlParametersDictionary());
 
             /// <summary>
@@ -118,18 +118,19 @@ public override int GetHashCode()
             /// </summary>
             /// <param name="obj">An System.Object.</param>
             /// <returns>true if obj is a UIHintAttribute and its value is the same as this instance; otherwise, false.</returns>
-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
             {
-                // don't need to perform a type check on obj since this is an internal class
-                var otherImplementation = (UIHintImplementation)obj;
+                var otherImplementation = obj as UIHintImplementation;
 
-                if (UIHint != otherImplementation.UIHint || PresentationLayer != otherImplementation.PresentationLayer)
+                if (otherImplementation is null ||
+                    UIHint != otherImplementation.UIHint ||
+                    PresentationLayer != otherImplementation.PresentationLayer)
                 {
                     return false;
                 }
 
-                IDictionary<string, object> leftParams;
-                IDictionary<string, object> rightParams;
+                IDictionary<string, object?> leftParams;
+                IDictionary<string, object?> rightParams;
 
                 try
                 {
@@ -157,11 +158,11 @@ public override bool Equals(object obj)
             /// <returns>
             ///     Dictionary of control parameters.
             /// </returns>
-            private IDictionary<string, object> BuildControlParametersDictionary()
+            private IDictionary<string, object?> BuildControlParametersDictionary()
             {
-                IDictionary<string, object> controlParameters = new Dictionary<string, object>();
+                IDictionary<string, object?> controlParameters = new Dictionary<string, object?>();
 
-                object[] inputControlParameters = _inputControlParameters;
+                object?[]? inputControlParameters = _inputControlParameters;
 
                 if (inputControlParameters == null || inputControlParameters.Length == 0)
                 {
@@ -174,8 +175,8 @@ private IDictionary<string, object> BuildControlParametersDictionary()
 
                 for (int i = 0; i < inputControlParameters.Length; i += 2)
                 {
-                    object key = inputControlParameters[i];
-                    object value = inputControlParameters[i + 1];
+                    object? key = inputControlParameters[i];
+                    object? value = inputControlParameters[i + 1];
                     if (key == null)
                     {
                         throw new InvalidOperationException(SR.Format(SR.UIHintImplementation_ControlParameterKeyIsNull, i));
@@ -185,7 +186,7 @@ private IDictionary<string, object> BuildControlParametersDictionary()
                     {
                         throw new InvalidOperationException(SR.Format(SR.UIHintImplementation_ControlParameterKeyIsNotAString,
                                                             i,
-                                                            inputControlParameters[i].ToString()));
+                                                            inputControlParameters[i]!.ToString()));
                     }
 
                     if (controlParameters.ContainsKey(keyString))
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/UrlAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/UrlAttribute.cs
index cb11bc4ee5d55d..9913f1883e7636 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/UrlAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/UrlAttribute.cs
@@ -15,7 +15,7 @@ public UrlAttribute()
             DefaultErrorMessage = SR.UrlAttribute_Invalid;
         }
 
-        public override bool IsValid(object value)
+        public override bool IsValid(object? value)
         {
             if (value == null)
             {
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationAttribute.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationAttribute.cs
index 0d7f64cb861e22..01ec012f20de99 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationAttribute.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationAttribute.cs
@@ -22,12 +22,12 @@ public abstract class ValidationAttribute : Attribute
     {
         #region Member Fields
 
-        private string _errorMessage;
-        private Func<string> _errorMessageResourceAccessor;
-        private string _errorMessageResourceName;
-        private Type _errorMessageResourceType;
+        private string? _errorMessage;
+        private Func<string>? _errorMessageResourceAccessor;
+        private string? _errorMessageResourceName;
+        private Type? _errorMessageResourceType;
         private volatile bool _hasBaseIsValid;
-        private string _defaultErrorMessage;
+        private string? _defaultErrorMessage;
         #endregion
 
         #region All Constructors
@@ -76,7 +76,7 @@ protected ValidationAttribute(Func<string> errorMessageAccessor)
         /// This property was added after the public contract for DataAnnotations was created.
         /// It is internal to avoid changing the DataAnnotations contract.
         /// </summary>
-        internal string DefaultErrorMessage
+        internal string? DefaultErrorMessage
         {
             set
             {
@@ -99,7 +99,7 @@ protected string ErrorMessageString
             get
             {
                 SetupResourceAccessor();
-                return _errorMessageResourceAccessor();
+                return _errorMessageResourceAccessor!();
             }
         }
 
@@ -127,7 +127,7 @@ protected string ErrorMessageString
         ///     This property is intended to be used for non-localizable error messages.  Use
         ///     <see cref="ErrorMessageResourceType" /> and <see cref="ErrorMessageResourceName" /> for localizable error messages.
         /// </value>
-        public string ErrorMessage
+        public string? ErrorMessage
         {
             // If _errorMessage is not set, return the default. This is done to preserve
             // behavior prior to the fix where ErrorMessage showed the non-null message to use.
@@ -154,7 +154,7 @@ public string ErrorMessage
         ///     Use this property to set the name of the property within <see cref="ErrorMessageResourceType" />
         ///     that will provide a localized error message.  Use <see cref="ErrorMessage" /> for non-localized error messages.
         /// </value>
-        public string ErrorMessageResourceName
+        public string? ErrorMessageResourceName
         {
             get => _errorMessageResourceName;
             set
@@ -175,7 +175,7 @@ public string ErrorMessageResourceName
         ///         Use <see cref="ErrorMessage" /> instead of this pair if error messages are not localized.
         ///     </para>
         /// </value>
-        public Type ErrorMessageResourceType
+        public Type? ErrorMessageResourceType
         {
             get => _errorMessageResourceType;
             set
@@ -199,7 +199,7 @@ private void SetupResourceAccessor()
         {
             if (_errorMessageResourceAccessor == null)
             {
-                string localErrorMessage = ErrorMessage;
+                string? localErrorMessage = ErrorMessage;
                 bool resourceNameSet = !string.IsNullOrEmpty(_errorMessageResourceName);
                 bool errorMessageSet = !string.IsNullOrEmpty(_errorMessage);
                 bool resourceTypeSet = _errorMessageResourceType != null;
@@ -231,7 +231,7 @@ private void SetupResourceAccessor()
                     // Here if not using resource type/name -- the accessor is just the error message string,
                     // which we know is not empty to have gotten this far.
                     // We captured error message to local in case it changes before accessor runs
-                    _errorMessageResourceAccessor = () => localErrorMessage;
+                    _errorMessageResourceAccessor = () => localErrorMessage!;
                 }
             }
         }
@@ -273,7 +273,9 @@ private void SetResourceAccessorByPropertyLookup()
                                                     _errorMessageResourceType.FullName));
             }
 
-            _errorMessageResourceAccessor = () => (string)property.GetValue(null, null);
+
+            // TODO-NULLABLE: If the user-provided resource returns null, an ArgumentNullException is thrown - should probably throw a better exception
+            _errorMessageResourceAccessor = () => (string)property.GetValue(null, null)!;
         }
 
         #endregion
@@ -321,7 +323,7 @@ public virtual string FormatErrorMessage(string name) =>
         ///     is thrown when neither overload of IsValid has been implemented
         ///     by a derived class.
         /// </exception>
-        public virtual bool IsValid(object value)
+        public virtual bool IsValid(object? value)
         {
             if (!_hasBaseIsValid)
             {
@@ -330,7 +332,10 @@ public virtual bool IsValid(object value)
             }
 
             // call overridden method.
-            return IsValid(value, null) == ValidationResult.Success;
+            // The IsValid method without a validationContext predates the one accepting the context.
+            // This is theoretically unreachable through normal use cases.
+            // Instead, the overload using validationContext should be called.
+            return IsValid(value, null!) == ValidationResult.Success;
         }
 
         /// <summary>
@@ -355,7 +360,7 @@ public virtual bool IsValid(object value)
         ///     is thrown when <see cref="IsValid(object, ValidationContext)" />
         ///     has not been implemented by a derived class.
         /// </exception>
-        protected virtual ValidationResult IsValid(object value, ValidationContext validationContext)
+        protected virtual ValidationResult? IsValid(object? value, ValidationContext validationContext)
         {
             if (_hasBaseIsValid)
             {
@@ -369,8 +374,8 @@ protected virtual ValidationResult IsValid(object value, ValidationContext valid
             // call overridden method.
             if (!IsValid(value))
             {
-                string[] memberNames = validationContext.MemberName != null
-                    ? new string[] { validationContext.MemberName }
+                string[]? memberNames = validationContext.MemberName is { } memberName
+                    ? new[] { memberName }
                     : null;
                 result = new ValidationResult(FormatErrorMessage(validationContext.DisplayName), memberNames);
             }
@@ -404,7 +409,7 @@ protected virtual ValidationResult IsValid(object value, ValidationContext valid
         ///     is thrown when <see cref="IsValid(object, ValidationContext)" />
         ///     has not been implemented by a derived class.
         /// </exception>
-        public ValidationResult GetValidationResult(object value, ValidationContext validationContext)
+        public ValidationResult? GetValidationResult(object? value, ValidationContext validationContext)
         {
             if (validationContext == null)
             {
@@ -445,7 +450,7 @@ public ValidationResult GetValidationResult(object value, ValidationContext vali
         ///     is thrown if <see cref="IsValid(object)" /> returns <c>false</c>.
         /// </exception>
         /// <exception cref="InvalidOperationException"> is thrown if the current attribute is malformed.</exception>
-        public void Validate(object value, string name)
+        public void Validate(object? value, string name)
         {
             if (!IsValid(value))
             {
@@ -474,14 +479,14 @@ public void Validate(object value, string name)
         ///     is thrown when <see cref="IsValid(object, ValidationContext)" />
         ///     has not been implemented by a derived class.
         /// </exception>
-        public void Validate(object value, ValidationContext validationContext)
+        public void Validate(object? value, ValidationContext validationContext)
         {
             if (validationContext == null)
             {
                 throw new ArgumentNullException(nameof(validationContext));
             }
 
-            ValidationResult result = GetValidationResult(value, validationContext);
+            ValidationResult? result = GetValidationResult(value, validationContext);
 
             if (result != null)
             {
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationAttributeStore.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationAttributeStore.cs
index 710bb9d1ebcff2..db3b57bd0be181 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationAttributeStore.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationAttributeStore.cs
@@ -3,6 +3,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Linq;
 using System.Reflection;
@@ -43,7 +44,7 @@ internal IEnumerable<ValidationAttribute> GetTypeValidationAttributes(Validation
         /// </summary>
         /// <param name="validationContext">The context that describes the type.  It cannot be null.</param>
         /// <returns>The display attribute instance, if present.</returns>
-        internal DisplayAttribute GetTypeDisplayAttribute(ValidationContext validationContext)
+        internal DisplayAttribute? GetTypeDisplayAttribute(ValidationContext validationContext)
         {
             EnsureValidationContext(validationContext);
             var item = GetTypeStoreItem(validationContext.ObjectType);
@@ -59,7 +60,7 @@ internal IEnumerable<ValidationAttribute> GetPropertyValidationAttributes(Valida
         {
             EnsureValidationContext(validationContext);
             var typeItem = GetTypeStoreItem(validationContext.ObjectType);
-            var item = typeItem.GetPropertyStoreItem(validationContext.MemberName);
+            var item = typeItem.GetPropertyStoreItem(validationContext.MemberName!);
             return item.ValidationAttributes;
         }
 
@@ -68,11 +69,11 @@ internal IEnumerable<ValidationAttribute> GetPropertyValidationAttributes(Valida
         /// </summary>
         /// <param name="validationContext">The context that describes the property.  It cannot be null.</param>
         /// <returns>The display attribute instance, if present.</returns>
-        internal DisplayAttribute GetPropertyDisplayAttribute(ValidationContext validationContext)
+        internal DisplayAttribute? GetPropertyDisplayAttribute(ValidationContext validationContext)
         {
             EnsureValidationContext(validationContext);
             var typeItem = GetTypeStoreItem(validationContext.ObjectType);
-            var item = typeItem.GetPropertyStoreItem(validationContext.MemberName);
+            var item = typeItem.GetPropertyStoreItem(validationContext.MemberName!);
             return item.DisplayAttribute;
         }
 
@@ -85,7 +86,7 @@ internal Type GetPropertyType(ValidationContext validationContext)
         {
             EnsureValidationContext(validationContext);
             var typeItem = GetTypeStoreItem(validationContext.ObjectType);
-            var item = typeItem.GetPropertyStoreItem(validationContext.MemberName);
+            var item = typeItem.GetPropertyStoreItem(validationContext.MemberName!);
             return item.PropertyType;
         }
 
@@ -100,8 +101,8 @@ internal bool IsPropertyContext(ValidationContext validationContext)
         {
             EnsureValidationContext(validationContext);
             var typeItem = GetTypeStoreItem(validationContext.ObjectType);
-            PropertyStoreItem item;
-            return typeItem.TryGetPropertyStoreItem(validationContext.MemberName, out item);
+            PropertyStoreItem? item;
+            return typeItem.TryGetPropertyStoreItem(validationContext.MemberName!, out item);
         }
 
         /// <summary>
@@ -115,7 +116,7 @@ private TypeStoreItem GetTypeStoreItem(Type type)
 
             lock (_typeStoreItems)
             {
-                if (!_typeStoreItems.TryGetValue(type, out TypeStoreItem item))
+                if (!_typeStoreItems.TryGetValue(type, out TypeStoreItem? item))
                 {
                     // use CustomAttributeExtensions.GetCustomAttributes() to get inherited attributes as well as direct ones
                     var attributes = CustomAttributeExtensions.GetCustomAttributes(type, true);
@@ -158,7 +159,7 @@ internal StoreItem(IEnumerable<Attribute> attributes)
 
             internal IEnumerable<ValidationAttribute> ValidationAttributes { get; }
 
-            internal DisplayAttribute DisplayAttribute { get; }
+            internal DisplayAttribute? DisplayAttribute { get; }
         }
 
         /// <summary>
@@ -168,7 +169,7 @@ private class TypeStoreItem : StoreItem
         {
             private readonly object _syncRoot = new object();
             private readonly Type _type;
-            private Dictionary<string, PropertyStoreItem> _propertyStoreItems;
+            private Dictionary<string, PropertyStoreItem>? _propertyStoreItems;
 
             internal TypeStoreItem(Type type, IEnumerable<Attribute> attributes)
                 : base(attributes)
@@ -178,7 +179,7 @@ internal TypeStoreItem(Type type, IEnumerable<Attribute> attributes)
 
             internal PropertyStoreItem GetPropertyStoreItem(string propertyName)
             {
-                if (!TryGetPropertyStoreItem(propertyName, out PropertyStoreItem item))
+                if (!TryGetPropertyStoreItem(propertyName, out PropertyStoreItem? item))
                 {
                     throw new ArgumentException(SR.Format(SR.AttributeStore_Unknown_Property, _type.Name, propertyName),
                                                 nameof(propertyName));
@@ -187,7 +188,7 @@ internal PropertyStoreItem GetPropertyStoreItem(string propertyName)
                 return item;
             }
 
-            internal bool TryGetPropertyStoreItem(string propertyName, out PropertyStoreItem item)
+            internal bool TryGetPropertyStoreItem(string propertyName, [NotNullWhen(true)] out PropertyStoreItem? item)
             {
                 if (string.IsNullOrEmpty(propertyName))
                 {
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationContext.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationContext.cs
index ba91968f704a68..f12578ac9d6ec8 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationContext.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationContext.cs
@@ -28,9 +28,9 @@ public sealed class ValidationContext
     {
         #region Member Fields
 
-        private readonly Dictionary<object, object> _items;
-        private string _displayName;
-        private Func<Type, object> _serviceProvider;
+        private readonly Dictionary<object, object?> _items;
+        private string? _displayName;
+        private Func<Type, object?>? _serviceProvider;
 
         #endregion
 
@@ -57,7 +57,7 @@ public ValidationContext(object instance)
         ///     new dictionary, preventing consumers from modifying the original dictionary.
         /// </param>
         /// <exception cref="ArgumentNullException">When <paramref name="instance" /> is <c>null</c></exception>
-        public ValidationContext(object instance, IDictionary<object, object> items)
+        public ValidationContext(object instance, IDictionary<object, object?>? items)
             : this(instance, null, items)
         {
         }
@@ -78,7 +78,7 @@ public ValidationContext(object instance, IDictionary<object, object> items)
         ///     new dictionary, preventing consumers from modifying the original dictionary.
         /// </param>
         /// <exception cref="ArgumentNullException">When <paramref name="instance" /> is <c>null</c></exception>
-        public ValidationContext(object instance, IServiceProvider serviceProvider, IDictionary<object, object> items)
+        public ValidationContext(object instance, IServiceProvider? serviceProvider, IDictionary<object, object?>? items)
         {
             if (instance == null)
             {
@@ -90,7 +90,7 @@ public ValidationContext(object instance, IServiceProvider serviceProvider, IDic
                 InitializeServiceProvider(serviceType => serviceProvider.GetService(serviceType));
             }
 
-            _items = items != null ? new Dictionary<object, object>(items) : new Dictionary<object, object>();
+            _items = items != null ? new Dictionary<object, object?>(items) : new Dictionary<object, object?>();
             ObjectInstance = instance;
         }
 
@@ -155,7 +155,7 @@ public string DisplayName
         ///     This name reflects the API name of the member being validated, not a localized name.  It should be set
         ///     only for property or parameter contexts.
         /// </value>
-        public string MemberName { get; set; }
+        public string? MemberName { get; set; }
 
         /// <summary>
         ///     Gets the dictionary of key/value pairs associated with this context.
@@ -164,7 +164,7 @@ public string DisplayName
         ///     This property will never be null, but the dictionary may be empty.  Changes made
         ///     to items in this dictionary will never affect the original dictionary specified in the constructor.
         /// </value>
-        public IDictionary<object, object> Items => _items;
+        public IDictionary<object, object?> Items => _items;
 
         #endregion
 
@@ -174,11 +174,11 @@ public string DisplayName
         ///     Looks up the display name using the DisplayAttribute attached to the respective type or property.
         /// </summary>
         /// <returns>A display-friendly name of the member represented by the <see cref="MemberName" />.</returns>
-        private string GetDisplayName()
+        private string? GetDisplayName()
         {
-            string displayName = null;
+            string? displayName = null;
             ValidationAttributeStore store = ValidationAttributeStore.Instance;
-            DisplayAttribute displayAttribute = null;
+            DisplayAttribute? displayAttribute = null;
 
             if (string.IsNullOrEmpty(MemberName))
             {
@@ -206,7 +206,7 @@ private string GetDisplayName()
         ///     desired <see cref="Type" /> when <see cref="GetService" /> is called.
         ///     If it is <c>null</c>, <see cref="GetService" /> will always return <c>null</c>.
         /// </param>
-        public void InitializeServiceProvider(Func<Type, object> serviceProvider)
+        public void InitializeServiceProvider(Func<Type, object?> serviceProvider)
         {
             _serviceProvider = serviceProvider;
         }
@@ -220,7 +220,7 @@ public void InitializeServiceProvider(Func<Type, object> serviceProvider)
         /// </summary>
         /// <param name="serviceType">The type of the service needed.</param>
         /// <returns>An instance of that service or null if it is not available.</returns>
-        public object GetService(Type serviceType) => _serviceProvider?.Invoke(serviceType);
+        public object? GetService(Type serviceType) => _serviceProvider?.Invoke(serviceType);
 
         #endregion
     }
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationException.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationException.cs
index efb091e055e5ab..fc57b1f10cf6af 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationException.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationException.cs
@@ -12,7 +12,7 @@ namespace System.ComponentModel.DataAnnotations
     [System.Runtime.CompilerServices.TypeForwardedFrom("System.ComponentModel.DataAnnotations, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35")]
     public class ValidationException : Exception
     {
-        private ValidationResult _validationResult;
+        private ValidationResult? _validationResult;
 
         /// <summary>
         ///     Constructor that accepts a structured <see cref="ValidationResult" /> describing the problem.
@@ -20,8 +20,8 @@ public class ValidationException : Exception
         /// <param name="validationResult">The value describing the validation error</param>
         /// <param name="validatingAttribute">The attribute that triggered this exception</param>
         /// <param name="value">The value that caused the validating attribute to trigger the exception</param>
-        public ValidationException(ValidationResult validationResult, ValidationAttribute validatingAttribute,
-            object value)
+        public ValidationException(ValidationResult validationResult, ValidationAttribute? validatingAttribute,
+            object? value)
             : this(validationResult.ErrorMessage, validatingAttribute, value)
         {
             _validationResult = validationResult;
@@ -33,7 +33,7 @@ public ValidationException(ValidationResult validationResult, ValidationAttribut
         /// <param name="errorMessage">The localized error message</param>
         /// <param name="validatingAttribute">The attribute that triggered this exception</param>
         /// <param name="value">The value that caused the validating attribute to trigger the exception</param>
-        public ValidationException(string errorMessage, ValidationAttribute validatingAttribute, object value)
+        public ValidationException(string? errorMessage, ValidationAttribute? validatingAttribute, object? value)
             : base(errorMessage)
         {
             Value = value;
@@ -53,7 +53,7 @@ public ValidationException()
         /// </summary>
         /// <remarks>The long form of this constructor is preferred because it gives better error reporting.</remarks>
         /// <param name="message">The localized message</param>
-        public ValidationException(string message)
+        public ValidationException(string? message)
             : base(message)
         {
         }
@@ -64,7 +64,7 @@ public ValidationException(string message)
         /// <remarks>The long form of this constructor is preferred because it gives better error reporting</remarks>
         /// <param name="message">The localized error message</param>
         /// <param name="innerException">inner exception</param>
-        public ValidationException(string message, Exception innerException)
+        public ValidationException(string? message, Exception? innerException)
             : base(message, innerException)
         {
         }
@@ -82,7 +82,7 @@ protected ValidationException(SerializationInfo info, StreamingContext context)
         /// <summary>
         ///     Gets the <see>ValidationAttribute</see> instance that triggered this exception.
         /// </summary>
-        public ValidationAttribute ValidationAttribute { get; }
+        public ValidationAttribute? ValidationAttribute { get; }
 
         /// <summary>
         ///     Gets the <see cref="ValidationResult" /> instance that describes the validation error.
@@ -96,6 +96,6 @@ protected ValidationException(SerializationInfo info, StreamingContext context)
         /// <summary>
         ///     Gets the value that caused the validating attribute to trigger the exception
         /// </summary>
-        public object Value { get; }
+        public object? Value { get; }
     }
 }
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationResult.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationResult.cs
index 5142f185d53e0f..fa26fd83bd1816 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationResult.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/ValidationResult.cs
@@ -23,7 +23,7 @@ public class ValidationResult
         ///     The <c>null</c> value is used to indicate success.  Consumers of <see cref="ValidationResult" />s
         ///     should compare the values to <see cref="ValidationResult.Success" /> rather than checking for null.
         /// </remarks>
-        public static readonly ValidationResult Success;
+        public static readonly ValidationResult? Success;
 
         #endregion
 
@@ -37,7 +37,7 @@ public class ValidationResult
         ///     The user-visible error message.  If null, <see cref="ValidationAttribute.GetValidationResult" />
         ///     will use <see cref="ValidationAttribute.FormatErrorMessage" /> for its error message.
         /// </param>
-        public ValidationResult(string errorMessage)
+        public ValidationResult(string? errorMessage)
             : this(errorMessage, null)
         {
         }
@@ -54,7 +54,7 @@ public ValidationResult(string errorMessage)
         ///     The list of member names affected by this result.
         ///     This list of member names is meant to be used by presentation layers to indicate which fields are in error.
         /// </param>
-        public ValidationResult(string errorMessage, IEnumerable<string> memberNames)
+        public ValidationResult(string? errorMessage, IEnumerable<string>? memberNames)
         {
             ErrorMessage = errorMessage;
             MemberNames = memberNames ?? Array.Empty<string>();
@@ -88,7 +88,7 @@ protected ValidationResult(ValidationResult validationResult)
         /// <summary>
         ///     Gets the error message for this result.  It may be null.
         /// </summary>
-        public string ErrorMessage { get; set; }
+        public string? ErrorMessage { get; set; }
 
         #endregion
 
@@ -107,7 +107,7 @@ protected ValidationResult(ValidationResult validationResult)
         ///     The <see cref="ErrorMessage" /> property value if specified,
         ///     otherwise, the base <see cref="object.ToString" /> result.
         /// </returns>
-        public override string ToString() => ErrorMessage ?? base.ToString();
+        public override string ToString() => ErrorMessage ?? base.ToString()!;
         #endregion Methods
     }
 }
diff --git a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Validator.cs b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Validator.cs
index a50329ace69826..b6251f53451f37 100644
--- a/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Validator.cs
+++ b/src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/Validator.cs
@@ -3,6 +3,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Linq;
 using System.Reflection;
@@ -46,12 +47,12 @@ public static class Validator
         ///     When the <see cref="ValidationContext.MemberName" /> of <paramref name="validationContext" /> is not a valid
         ///     property.
         /// </exception>
-        public static bool TryValidateProperty(object value, ValidationContext validationContext,
-            ICollection<ValidationResult> validationResults)
+        public static bool TryValidateProperty(object? value, ValidationContext validationContext,
+            ICollection<ValidationResult>? validationResults)
         {
             // Throw if value cannot be assigned to this property.  That is not a validation exception.
             var propertyType = _store.GetPropertyType(validationContext);
-            var propertyName = validationContext.MemberName;
+            var propertyName = validationContext.MemberName!;
             EnsureValidPropertyType(propertyName, propertyType, value);
 
             var result = true;
@@ -92,7 +93,7 @@ public static bool TryValidateProperty(object value, ValidationContext validatio
         ///     <see cref="ValidationContext.ObjectInstance" />on <paramref name="validationContext" />.
         /// </exception>
         public static bool TryValidateObject(
-            object instance, ValidationContext validationContext, ICollection<ValidationResult> validationResults) =>
+            object instance, ValidationContext validationContext, ICollection<ValidationResult>? validationResults) =>
             TryValidateObject(instance, validationContext, validationResults, false /*validateAllProperties*/);
 
         /// <summary>
@@ -129,13 +130,14 @@ public static bool TryValidateObject(
         ///     <see cref="ValidationContext.ObjectInstance" />on <paramref name="validationContext" />.
         /// </exception>
         public static bool TryValidateObject(object instance, ValidationContext validationContext,
-            ICollection<ValidationResult> validationResults, bool validateAllProperties)
+            ICollection<ValidationResult>? validationResults, bool validateAllProperties)
         {
             if (instance == null)
             {
                 throw new ArgumentNullException(nameof(instance));
             }
 
+            // TODO-NULLABLE: null validationContext isn't supported (GetObjectValidationErrors will throw), remove that check
             if (validationContext != null && instance != validationContext.ObjectInstance)
             {
                 throw new ArgumentException(SR.Validator_InstanceMustMatchValidationContextInstance, nameof(instance));
@@ -144,7 +146,7 @@ public static bool TryValidateObject(object instance, ValidationContext validati
             var result = true;
             var breakOnFirstError = (validationResults == null);
 
-            foreach (ValidationError err in GetObjectValidationErrors(instance, validationContext, validateAllProperties, breakOnFirstError))
+            foreach (ValidationError err in GetObjectValidationErrors(instance, validationContext!, validateAllProperties, breakOnFirstError))
             {
                 result = false;
 
@@ -184,7 +186,7 @@ public static bool TryValidateObject(object instance, ValidationContext validati
         /// </param>
         /// <returns><c>true</c> if the object is valid, <c>false</c> if any validation errors are encountered.</returns>
         public static bool TryValidateValue(object value, ValidationContext validationContext,
-            ICollection<ValidationResult> validationResults, IEnumerable<ValidationAttribute> validationAttributes)
+            ICollection<ValidationResult>? validationResults, IEnumerable<ValidationAttribute> validationAttributes)
         {
             var result = true;
             var breakOnFirstError = validationResults == null;
@@ -211,11 +213,11 @@ var err in
         /// </param>
         /// <exception cref="ArgumentNullException">When <paramref name="validationContext" /> is null.</exception>
         /// <exception cref="ValidationException">When <paramref name="value" /> is invalid for this property.</exception>
-        public static void ValidateProperty(object value, ValidationContext validationContext)
+        public static void ValidateProperty(object? value, ValidationContext validationContext)
         {
             // Throw if value cannot be assigned to this property.  That is not a validation exception.
             var propertyType = _store.GetPropertyType(validationContext);
-            EnsureValidPropertyType(validationContext.MemberName, propertyType, value);
+            EnsureValidPropertyType(validationContext.MemberName!, propertyType, value);
 
             var attributes = _store.GetPropertyValidationAttributes(validationContext);
 
@@ -343,7 +345,7 @@ private static ValidationContext CreateValidationContext(object instance, Valida
         /// </param>
         /// <returns><c>true</c> if the assignment is legal.</returns>
         /// <exception cref="ArgumentNullException">When <paramref name="destinationType" /> is null.</exception>
-        private static bool CanBeAssigned(Type destinationType, object value)
+        private static bool CanBeAssigned(Type destinationType, object? value)
         {
             if (value == null)
             {
@@ -364,7 +366,7 @@ private static bool CanBeAssigned(Type destinationType, object value)
         /// <param name="propertyType">The type of the property.</param>
         /// <param name="value">The value.  Null is permitted only if the property will accept it.</param>
         /// <exception cref="ArgumentException"> is thrown if <paramref name="value" /> is the wrong type for this property.</exception>
-        private static void EnsureValidPropertyType(string propertyName, Type propertyType, object value)
+        private static void EnsureValidPropertyType(string propertyName, Type propertyType, object? value)
         {
             if (!CanBeAssigned(propertyType, value))
             {
@@ -476,7 +478,7 @@ private static IEnumerable<ValidationError> GetObjectPropertyValidationErrors(ob
                         var validationResult = reqAttr.GetValidationResult(property.Value, property.Key);
                         if (validationResult != ValidationResult.Success)
                         {
-                            errors.Add(new ValidationError(reqAttr, property.Value, validationResult));
+                            errors.Add(new ValidationError(reqAttr, property.Value, validationResult!));
                         }
                     }
                 }
@@ -500,12 +502,12 @@ private static IEnumerable<ValidationError> GetObjectPropertyValidationErrors(ob
         ///     value.
         /// </returns>
         /// <remarks>Ignores indexed properties.</remarks>
-        private static ICollection<KeyValuePair<ValidationContext, object>> GetPropertyValues(object instance,
+        private static ICollection<KeyValuePair<ValidationContext, object?>> GetPropertyValues(object instance,
             ValidationContext validationContext)
         {
             var properties = instance.GetType().GetRuntimeProperties()
                                 .Where(p => ValidationAttributeStore.IsPublic(p) && !p.GetIndexParameters().Any());
-            var items = new List<KeyValuePair<ValidationContext, object>>(properties.Count());
+            var items = new List<KeyValuePair<ValidationContext, object?>>(properties.Count());
             foreach (var property in properties)
             {
                 var context = CreateValidationContext(instance, validationContext);
@@ -513,7 +515,7 @@ private static ICollection<KeyValuePair<ValidationContext, object>> GetPropertyV
 
                 if (_store.GetPropertyValidationAttributes(context).Any())
                 {
-                    items.Add(new KeyValuePair<ValidationContext, object>(context, property.GetValue(instance, null)));
+                    items.Add(new KeyValuePair<ValidationContext, object?>(context, property.GetValue(instance, null)));
                 }
             }
 
@@ -537,7 +539,7 @@ private static ICollection<KeyValuePair<ValidationContext, object>> GetPropertyV
         /// </param>
         /// <returns>The collection of validation errors.</returns>
         /// <exception cref="ArgumentNullException">When <paramref name="validationContext" /> is null.</exception>
-        private static IEnumerable<ValidationError> GetValidationErrors(object value,
+        private static IEnumerable<ValidationError> GetValidationErrors(object? value,
             ValidationContext validationContext, IEnumerable<ValidationAttribute> attributes, bool breakOnFirstError)
         {
             if (validationContext == null)
@@ -546,7 +548,7 @@ private static IEnumerable<ValidationError> GetValidationErrors(object value,
             }
 
             var errors = new List<ValidationError>();
-            ValidationError validationError;
+            ValidationError? validationError;
 
             // Get the required validator if there is one and test it first, aborting on failure
             var required = attributes.OfType<RequiredAttribute>().FirstOrDefault();
@@ -592,15 +594,15 @@ private static IEnumerable<ValidationError> GetValidationErrors(object value,
         /// </param>
         /// <returns><c>true</c> if the value is valid.</returns>
         /// <exception cref="ArgumentNullException">When <paramref name="validationContext" /> is null.</exception>
-        private static bool TryValidate(object value, ValidationContext validationContext, ValidationAttribute attribute,
-            out ValidationError validationError)
+        private static bool TryValidate(object? value, ValidationContext validationContext, ValidationAttribute attribute,
+            [NotNullWhen(false)] out ValidationError? validationError)
         {
             Debug.Assert(validationContext != null);
 
             var validationResult = attribute.GetValidationResult(value, validationContext);
             if (validationResult != ValidationResult.Success)
             {
-                validationError = new ValidationError(attribute, value, validationResult);
+                validationError = new ValidationError(attribute, value, validationResult!);
                 return false;
             }
 
@@ -614,10 +616,10 @@ private static bool TryValidate(object value, ValidationContext validationContex
         /// </summary>
         private class ValidationError
         {
-            private readonly object _value;
-            private readonly ValidationAttribute _validationAttribute;
+            private readonly object? _value;
+            private readonly ValidationAttribute? _validationAttribute;
 
-            internal ValidationError(ValidationAttribute validationAttribute, object value,
+            internal ValidationError(ValidationAttribute? validationAttribute, object? value,
                 ValidationResult validationResult)
             {
                 _validationAttribute = validationAttribute;
diff --git a/src/libraries/System.ComponentModel.Annotations/tests/System.ComponentModel.Annotations.Tests.csproj b/src/libraries/System.ComponentModel.Annotations/tests/System.ComponentModel.Annotations.Tests.csproj
index 17571c6c8694fe..5c9152f2cd2179 100644
--- a/src/libraries/System.ComponentModel.Annotations/tests/System.ComponentModel.Annotations.Tests.csproj
+++ b/src/libraries/System.ComponentModel.Annotations/tests/System.ComponentModel.Annotations.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\ComponentModel\DataAnnotations\AssociatedMetadataTypeTypeDescriptionProviderTests.cs" />
@@ -42,4 +42,7 @@
     <Compile Include="System\ComponentModel\DataAnnotations\ValidationResultTests.cs" />
     <Compile Include="System\ComponentModel\DataAnnotations\ValidatorTests.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
+    <Reference Include="System.ComponentModel.DataAnnotations" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ComponentModel.Composition.Registration/src/System.ComponentModel.Composition.Registration.csproj b/src/libraries/System.ComponentModel.Composition.Registration/src/System.ComponentModel.Composition.Registration.csproj
index bca38d6e8f46c5..68bae6aecf016c 100644
--- a/src/libraries/System.ComponentModel.Composition.Registration/src/System.ComponentModel.Composition.Registration.csproj
+++ b/src/libraries/System.ComponentModel.Composition.Registration/src/System.ComponentModel.Composition.Registration.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.ComponentModel.Composition.Registration</AssemblyName>
     <TargetFrameworks>netstandard2.1</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
@@ -25,7 +24,7 @@
              Link="Common\System\Composition\Diagnostics\TraceWriter.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.ComponentModel.Composition" />
-    <Reference Include="System.Reflection.Context" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.ComponentModel.Composition\src\System.ComponentModel.Composition.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Reflection.Context\src\System.Reflection.Context.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.ComponentModel.Composition.Registration/tests/System.ComponentModel.Composition.Registration.Tests.csproj b/src/libraries/System.ComponentModel.Composition.Registration/tests/System.ComponentModel.Composition.Registration.Tests.csproj
index 8c0707afe31bbd..56a6770887484c 100644
--- a/src/libraries/System.ComponentModel.Composition.Registration/tests/System.ComponentModel.Composition.Registration.Tests.csproj
+++ b/src/libraries/System.ComponentModel.Composition.Registration/tests/System.ComponentModel.Composition.Registration.Tests.csproj
@@ -19,4 +19,7 @@
     <Compile Include="System\ComponentModel\Composition\Registration\RegistrationBuilderTests.cs" />
     <Compile Include="System\ComponentModel\Composition\Registration\RegistrationContextUnitTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.ComponentModel.Composition.Registration.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ComponentModel.Composition/ref/System.ComponentModel.Composition.cs b/src/libraries/System.ComponentModel.Composition/ref/System.ComponentModel.Composition.cs
index 2b30949c522fbb..f55f6b216d37f9 100644
--- a/src/libraries/System.ComponentModel.Composition/ref/System.ComponentModel.Composition.cs
+++ b/src/libraries/System.ComponentModel.Composition/ref/System.ComponentModel.Composition.cs
@@ -415,16 +415,12 @@ public abstract partial class ExportProvider
         protected ExportProvider() { }
         public event System.EventHandler<System.ComponentModel.Composition.Hosting.ExportsChangeEventArgs>? ExportsChanged { add { } remove { } }
         public event System.EventHandler<System.ComponentModel.Composition.Hosting.ExportsChangeEventArgs>? ExportsChanging { add { } remove { } }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T GetExportedValueOrDefault<T>() { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T GetExportedValueOrDefault<T>(string? contractName) { throw null; }
+        public T? GetExportedValueOrDefault<T>() { throw null; }
+        public T? GetExportedValueOrDefault<T>(string? contractName) { throw null; }
         public System.Collections.Generic.IEnumerable<T> GetExportedValues<T>() { throw null; }
         public System.Collections.Generic.IEnumerable<T> GetExportedValues<T>(string? contractName) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T GetExportedValue<T>() { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T GetExportedValue<T>(string? contractName) { throw null; }
+        public T? GetExportedValue<T>() { throw null; }
+        public T? GetExportedValue<T>(string? contractName) { throw null; }
         public System.Collections.Generic.IEnumerable<System.ComponentModel.Composition.Primitives.Export> GetExports(System.ComponentModel.Composition.Primitives.ImportDefinition definition) { throw null; }
         public System.Collections.Generic.IEnumerable<System.ComponentModel.Composition.Primitives.Export> GetExports(System.ComponentModel.Composition.Primitives.ImportDefinition definition, System.ComponentModel.Composition.Hosting.AtomicComposition? atomicComposition) { throw null; }
         public System.Collections.Generic.IEnumerable<System.Lazy<object, object>> GetExports(System.Type type, System.Type? metadataViewType, string? contractName) { throw null; }
diff --git a/src/libraries/System.ComponentModel.Composition/ref/System.ComponentModel.Composition.csproj b/src/libraries/System.ComponentModel.Composition/ref/System.ComponentModel.Composition.csproj
index cbf8732c35c4d0..543c5c85ca1d35 100644
--- a/src/libraries/System.ComponentModel.Composition/ref/System.ComponentModel.Composition.csproj
+++ b/src/libraries/System.ComponentModel.Composition/ref/System.ComponentModel.Composition.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;_net461</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
diff --git a/src/libraries/System.ComponentModel.Composition/src/System.ComponentModel.Composition.csproj b/src/libraries/System.ComponentModel.Composition/src/System.ComponentModel.Composition.csproj
index 826fc8dd9fa5f1..519abadf0b6608 100644
--- a/src/libraries/System.ComponentModel.Composition/src/System.ComponentModel.Composition.csproj
+++ b/src/libraries/System.ComponentModel.Composition/src/System.ComponentModel.Composition.csproj
@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RootNamespace />
-    <!-- CommonStrings needs RootNamespace to be empty -->
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp2.0;_$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp2.0</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -214,4 +212,4 @@
     <Reference Include="System.Threading.Thread" />
     <Reference Include="System.Text.Encoding.Extensions" />
   </ItemGroup>
-</Project>
+</Project>
\ No newline at end of file
diff --git a/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/CompositionResultOfT.cs b/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/CompositionResultOfT.cs
index 380d2029e1d5f1..9c66e1817b8956 100644
--- a/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/CompositionResultOfT.cs
+++ b/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/CompositionResultOfT.cs
@@ -11,7 +11,7 @@ namespace System.ComponentModel.Composition
     internal struct CompositionResult<T>
     {
         private readonly IEnumerable<CompositionError>? _errors;
-        [AllowNull] private readonly T _value;
+        private readonly T? _value;
 
         public CompositionResult(T value)
             : this(value, null)
@@ -28,7 +28,7 @@ public CompositionResult(IEnumerable<CompositionError>? errors)
         {
         }
 
-        internal CompositionResult([AllowNull] T value, IEnumerable<CompositionError>? errors)
+        internal CompositionResult(T? value, IEnumerable<CompositionError>? errors)
         {
             _errors = errors;
             _value = value;
@@ -53,7 +53,7 @@ public T Value
             {
                 ThrowOnErrors();
 
-                return _value;
+                return _value!;
             }
         }
 
diff --git a/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/Hosting/AtomicComposition.cs b/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/Hosting/AtomicComposition.cs
index d20dac11902058..752d817a0507fd 100644
--- a/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/Hosting/AtomicComposition.cs
+++ b/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/Hosting/AtomicComposition.cs
@@ -295,7 +295,7 @@ private bool TryGetValueInternal<T>(object key, bool localAtomicCompositionOnly,
                 return _outerAtomicComposition.TryGetValueInternal<T>(key, localAtomicCompositionOnly, out value);
             }
 
-            value = default(T)!;
+            value = default;
             return false;
         }
 
diff --git a/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/Hosting/ExportProvider.GetExportOverrides.cs b/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/Hosting/ExportProvider.GetExportOverrides.cs
index 12f0a6a3e418a6..8ddbd6c5368902 100644
--- a/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/Hosting/ExportProvider.GetExportOverrides.cs
+++ b/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/Hosting/ExportProvider.GetExportOverrides.cs
@@ -473,8 +473,7 @@ public IEnumerable<Lazy<T, TMetadataView>> GetExports<T, TMetadataView>(string?
         ///     An error occurred during composition. <see cref="CompositionException.Errors"/> will
         ///     contain a collection of errors that occurred.
         /// </exception>
-        [return: MaybeNull]
-        public T GetExportedValue<T>()
+        public T? GetExportedValue<T>()
         {
             return GetExportedValue<T>((string?)null);
         }
@@ -524,8 +523,7 @@ public T GetExportedValue<T>()
         ///     An error occurred during composition. <see cref="CompositionException.Errors"/> will
         ///     contain a collection of errors that occurred.
         /// </exception>
-        [return: MaybeNull]
-        public T GetExportedValue<T>(string? contractName)
+        public T? GetExportedValue<T>(string? contractName)
         {
             return GetExportedValueCore<T>(contractName, ImportCardinality.ExactlyOne);
         }
@@ -575,8 +573,7 @@ public T GetExportedValue<T>(string? contractName)
         ///     An error occurred during composition. <see cref="CompositionException.Errors"/> will
         ///     contain a collection of errors that occurred.
         /// </exception>
-        [return: MaybeNull]
-        public T GetExportedValueOrDefault<T>()
+        public T? GetExportedValueOrDefault<T>()
         {
             return GetExportedValueOrDefault<T>((string?)null);
         }
@@ -626,8 +623,7 @@ public T GetExportedValueOrDefault<T>()
         ///     An error occurred during composition. <see cref="CompositionException.Errors"/> will
         ///     contain a collection of errors that occurred.
         /// </exception>
-        [return: MaybeNull]
-        public T GetExportedValueOrDefault<T>(string? contractName)
+        public T? GetExportedValueOrDefault<T>(string? contractName)
         {
             return GetExportedValueCore<T>(contractName, ImportCardinality.ZeroOrOne);
         }
@@ -724,8 +720,7 @@ private IEnumerable<T> GetExportedValuesCore<T>(string? contractName)
             return result;
         }
 
-        [return: MaybeNull]
-        private T GetExportedValueCore<T>(string? contractName, ImportCardinality cardinality)
+        private T? GetExportedValueCore<T>(string? contractName, ImportCardinality cardinality)
         {
             if (!cardinality.IsAtMostOne())
             {
@@ -734,7 +729,7 @@ private T GetExportedValueCore<T>(string? contractName, ImportCardinality cardin
 
             Export? export = GetExportsCore(typeof(T), (Type?)null, contractName, cardinality).SingleOrDefault();
 
-            return (export != null) ? ExportServices.GetCastedExportedValue<T>(export) : default(T)!;
+            return (export != null) ? ExportServices.GetCastedExportedValue<T>(export) : default;
         }
 
         private IEnumerable<Lazy<T>> GetExportsCore<T>(string? contractName)
diff --git a/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/MetadataServices.cs b/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/MetadataServices.cs
index b64f990f7950e3..25d362e457d7d4 100644
--- a/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/MetadataServices.cs
+++ b/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/MetadataServices.cs
@@ -26,27 +26,19 @@ internal static class MetadataServices
             return new ReadOnlyDictionary<string, object?>(metadata);
         }
 
-        [return: MaybeNull]
-        public static T GetValue<T>(this IDictionary<string, object?> metadata, string key)
+        public static T? GetValue<T>(this IDictionary<string, object?> metadata, string key)
         {
             if (metadata == null)
             {
                 throw new ArgumentNullException(nameof(metadata));
             }
 
-            if (!metadata.TryGetValue(key, out object? untypedValue))
+            if (metadata.TryGetValue(key, out object? untypedValue) && untypedValue is T t)
             {
-                return default(T)!;
+                return t;
             }
 
-            if (untypedValue is T)
-            {
-                return (T)untypedValue;
-            }
-            else
-            {
-                return default(T)!;
-            }
+            return default;
         }
     }
 }
diff --git a/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/ReflectionModel/LazyMemberInfo.cs b/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/ReflectionModel/LazyMemberInfo.cs
index 983f25d9efc9e9..14124ff46f5cfa 100644
--- a/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/ReflectionModel/LazyMemberInfo.cs
+++ b/src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/ReflectionModel/LazyMemberInfo.cs
@@ -103,7 +103,7 @@ public override int GetHashCode()
                 {
                     throw new Exception(SR.Diagnostic_InternalExceptionMessage);
                 }
-                return MemberType.GetHashCode() ^ _accessors[0]!.GetHashCode(); // TODO-NULLABLE https://github.com/dotnet/roslyn/issues/34644
+                return MemberType.GetHashCode() ^ _accessors[0]!.GetHashCode(); // TODO-NULLABLE: Indexer nullability tracked (https://github.com/dotnet/roslyn/issues/34644)
             }
         }
 
diff --git a/src/libraries/System.ComponentModel.Composition/tests/System.ComponentModel.Composition.Noop.Assembly/System.ComponentModel.Composition.Noop.Assembly.csproj b/src/libraries/System.ComponentModel.Composition/tests/System.ComponentModel.Composition.Noop.Assembly/System.ComponentModel.Composition.Noop.Assembly.csproj
index 6d6060c2a287be..6bf5cb7f9f9ebd 100644
--- a/src/libraries/System.ComponentModel.Composition/tests/System.ComponentModel.Composition.Noop.Assembly/System.ComponentModel.Composition.Noop.Assembly.csproj
+++ b/src/libraries/System.ComponentModel.Composition/tests/System.ComponentModel.Composition.Noop.Assembly/System.ComponentModel.Composition.Noop.Assembly.csproj
@@ -5,4 +5,7 @@
   <ItemGroup>
     <Compile Include="TestClass.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.ComponentModel.Composition\src\System.ComponentModel.Composition.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ComponentModel.Composition/tests/System.ComponentModel.Composition.Tests.csproj b/src/libraries/System.ComponentModel.Composition/tests/System.ComponentModel.Composition.Tests.csproj
index fc7811e645ef99..72e124ecebf0fb 100644
--- a/src/libraries/System.ComponentModel.Composition/tests/System.ComponentModel.Composition.Tests.csproj
+++ b/src/libraries/System.ComponentModel.Composition/tests/System.ComponentModel.Composition.Tests.csproj
@@ -1,14 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
-  <!-- TODO: Add net472 configuration after OOB package bug is fixed: https://github.com/dotnet/runtime/issues/23497 -->
   <PropertyGroup>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
-  <ItemGroup>
-    <!-- Some internal types are needed, so we reference the implementation assembly, rather than the reference assembly. -->
-    <DefaultReferenceExclusions Include="System.ComponentModel.Composition" />
-    <ReferenceFromRuntime Include="System.ComponentModel.Composition" />
-  </ItemGroup>
   <ItemGroup>
     <Compile Include="$(CommonTestPath)System\IO\TempDirectory.cs"
              Link="Common\System\IO\TempDirectory.cs" />
@@ -171,10 +165,11 @@
     <Compile Include="System\UnitTesting\TestServices.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="System.ComponentModel.Composition.Noop.Assembly/System.ComponentModel.Composition.Noop.Assembly.csproj">
-      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
-      <OutputItemType>content</OutputItemType>
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-    </ProjectReference>
+    <ProjectReference Include="System.ComponentModel.Composition.Noop.Assembly/System.ComponentModel.Composition.Noop.Assembly.csproj"
+                      ReferenceOutputAssembly="false"
+                      OutputItemType="content"
+                      CopyToOutputDirectory="PreserveNewest" />
+    <!-- Some internal types are needed, so we reference the implementation assembly, rather than the reference assembly. -->
+    <ProjectReference Include="..\src\System.ComponentModel.Composition.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
-</Project>
\ No newline at end of file
+</Project>
diff --git a/src/libraries/System.ComponentModel.Composition/tests/System/ComponentModel/Composition/Hosting/AssemblyCatalogTests.cs b/src/libraries/System.ComponentModel.Composition/tests/System/ComponentModel/Composition/Hosting/AssemblyCatalogTests.cs
index c8d43e7b10f767..333dd8e473bb6d 100644
--- a/src/libraries/System.ComponentModel.Composition/tests/System/ComponentModel/Composition/Hosting/AssemblyCatalogTests.cs
+++ b/src/libraries/System.ComponentModel.Composition/tests/System/ComponentModel/Composition/Hosting/AssemblyCatalogTests.cs
@@ -36,10 +36,12 @@ public class TestAssemblyFour { }
 
     public class AssemblyCatalogTestsHelper
     {
+#pragma warning disable SYSLIB0012
         protected string GetAttributedAssemblyCodeBase()
         {
             return Assembly.GetExecutingAssembly().CodeBase;
         }
+#pragma warning restore SYSLIB0012
 
         protected Assembly GetAttributedAssembly()
         {
@@ -74,7 +76,9 @@ internal static void Constructor_ValueAsCodebaseArgument_ShouldSetAssemblyProper
 
             foreach (var e in expectations)
             {
+#pragma warning disable SYSLIB0012
                 var catalog = catalogCreator(e.CodeBase);
+#pragma warning restore SYSLIB0012
 
                 Assert.Same(e, catalog.Assembly);
             }
@@ -694,6 +698,7 @@ public void Constructor8_NullReflectionContextArgument_ShouldThrowArgumentNull()
             });
         }
 
+#pragma warning disable SYSLIB0012
         [Fact]
         public void Constructor8_NullDefinitionOriginArgument_ShouldThrowArgumentNull()
         {
@@ -702,6 +707,7 @@ public void Constructor8_NullDefinitionOriginArgument_ShouldThrowArgumentNull()
                 return new AssemblyCatalog(GetAttributedAssembly().CodeBase, new AssemblyCatalogTestsReflectionContext(), dO);
             });
         }
+#pragma warning restore SYSLIB0012
 
         //=========================================================================================================================================
         //  Test cases for Assemblies decorated with the CatalogDiscoveryAttribute
diff --git a/src/libraries/System.ComponentModel.EventBasedAsync/Directory.Build.props b/src/libraries/System.ComponentModel.EventBasedAsync/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.ComponentModel.EventBasedAsync/Directory.Build.props
+++ b/src/libraries/System.ComponentModel.EventBasedAsync/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ComponentModel.EventBasedAsync/src/System.ComponentModel.EventBasedAsync.csproj b/src/libraries/System.ComponentModel.EventBasedAsync/src/System.ComponentModel.EventBasedAsync.csproj
index a33080137075ed..ad8ffe0f0061d1 100644
--- a/src/libraries/System.ComponentModel.EventBasedAsync/src/System.ComponentModel.EventBasedAsync.csproj
+++ b/src/libraries/System.ComponentModel.EventBasedAsync/src/System.ComponentModel.EventBasedAsync.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RootNamespace>System.ComponentModel.EventBasedAsync</RootNamespace>
-    <AssemblyName>System.ComponentModel.EventBasedAsync</AssemblyName>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
diff --git a/src/libraries/System.ComponentModel.EventBasedAsync/tests/BackgroundWorkerTests.cs b/src/libraries/System.ComponentModel.EventBasedAsync/tests/BackgroundWorkerTests.cs
index 8ba0dcb842cd01..7bdfb4d6a34dfc 100644
--- a/src/libraries/System.ComponentModel.EventBasedAsync/tests/BackgroundWorkerTests.cs
+++ b/src/libraries/System.ComponentModel.EventBasedAsync/tests/BackgroundWorkerTests.cs
@@ -327,7 +327,6 @@ public void DisposeTwiceShouldNotThrow()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsPreciseGcSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38283", TestPlatforms.Browser)]
         public void TestFinalization()
         {
             // BackgroundWorker has a finalizer that exists purely for backwards compatibility
diff --git a/src/libraries/System.ComponentModel.Primitives/Directory.Build.props b/src/libraries/System.ComponentModel.Primitives/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.ComponentModel.Primitives/Directory.Build.props
+++ b/src/libraries/System.ComponentModel.Primitives/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ComponentModel.Primitives/ref/System.ComponentModel.Primitives.cs b/src/libraries/System.ComponentModel.Primitives/ref/System.ComponentModel.Primitives.cs
index f7997fb51900ff..77a375bcc40f1e 100644
--- a/src/libraries/System.ComponentModel.Primitives/ref/System.ComponentModel.Primitives.cs
+++ b/src/libraries/System.ComponentModel.Primitives/ref/System.ComponentModel.Primitives.cs
@@ -86,6 +86,20 @@ public DescriptionAttribute(string description) { }
         public override int GetHashCode() { throw null; }
         public override bool IsDefaultAttribute() { throw null; }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Interface, AllowMultiple=true, Inherited=true)]
+    public sealed partial class DesignerAttribute : System.Attribute
+    {
+        public DesignerAttribute(string designerTypeName) { }
+        public DesignerAttribute(string designerTypeName, string designerBaseTypeName) { }
+        public DesignerAttribute(string designerTypeName, System.Type designerBaseType) { }
+        public DesignerAttribute(System.Type designerType) { }
+        public DesignerAttribute(System.Type designerType, System.Type designerBaseType) { }
+        public string DesignerBaseTypeName { get { throw null; } }
+        public string DesignerTypeName { get { throw null; } }
+        public override object TypeId { get { throw null; } }
+        public override bool Equals(object? obj) { throw null; }
+        public override int GetHashCode() { throw null; }
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class, AllowMultiple=false, Inherited=true)]
     public sealed partial class DesignerCategoryAttribute : System.Attribute
     {
@@ -153,6 +167,8 @@ public void AddHandlers(System.ComponentModel.EventHandlerList listToAddFrom) {
         public void Dispose() { }
         public void RemoveHandler(object key, System.Delegate? value) { }
     }
+    [System.ComponentModel.DesignerAttribute("System.ComponentModel.Design.ComponentDesigner, System.Design, Version=4.0.0.0, PublicKeyToken=b03f5f7f11d50a3a")]
+    [System.ComponentModel.DesignerAttribute("System.Windows.Forms.Design.ComponentDocumentDesigner, System.Design, Version=4.0.0.0, PublicKeyToken=b03f5f7f11d50a3a")]
     [System.ComponentModel.TypeConverterAttribute("System.ComponentModel.ComponentConverter, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
     public partial interface IComponent : System.IDisposable
     {
@@ -261,7 +277,7 @@ public sealed partial class ParenthesizePropertyNameAttribute : System.Attribute
         public ParenthesizePropertyNameAttribute() { }
         public ParenthesizePropertyNameAttribute(bool needParenthesis) { }
         public bool NeedParenthesis { get { throw null; } }
-        public override bool Equals(object? o) { throw null; }
+        public override bool Equals(object? obj) { throw null; }
         public override int GetHashCode() { throw null; }
         public override bool IsDefaultAttribute() { throw null; }
     }
@@ -291,7 +307,7 @@ public sealed partial class RefreshPropertiesAttribute : System.Attribute
         public static readonly System.ComponentModel.RefreshPropertiesAttribute Repaint;
         public RefreshPropertiesAttribute(System.ComponentModel.RefreshProperties refresh) { }
         public System.ComponentModel.RefreshProperties RefreshProperties { get { throw null; } }
-        public override bool Equals(object? value) { throw null; }
+        public override bool Equals(object? obj) { throw null; }
         public override int GetHashCode() { throw null; }
         public override bool IsDefaultAttribute() { throw null; }
     }
diff --git a/src/libraries/System.ComponentModel.Primitives/src/System.ComponentModel.Primitives.csproj b/src/libraries/System.ComponentModel.Primitives/src/System.ComponentModel.Primitives.csproj
index 53e44fa05eac16..52c0c07386120e 100644
--- a/src/libraries/System.ComponentModel.Primitives/src/System.ComponentModel.Primitives.csproj
+++ b/src/libraries/System.ComponentModel.Primitives/src/System.ComponentModel.Primitives.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RootNamespace>System.ComponentModel.Primitives</RootNamespace>
-    <AssemblyName>System.ComponentModel.Primitives</AssemblyName>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -12,6 +10,7 @@
     <Compile Include="System\ComponentModel\Component.cs" />
     <Compile Include="System\ComponentModel\ComponentCollection.cs" />
     <Compile Include="System\ComponentModel\DescriptionAttribute.cs" />
+    <Compile Include="System\ComponentModel\DesignerAttribute.cs" />
     <Compile Include="System\ComponentModel\DesignerCategoryAttribute.cs" />
     <Compile Include="System\ComponentModel\DesignerSerializationVisibility.cs" />
     <Compile Include="System\ComponentModel\DesignerSerializationVisibilityAttribute.cs" />
diff --git a/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/DesignerAttribute.cs b/src/libraries/System.ComponentModel.Primitives/src/System/ComponentModel/DesignerAttribute.cs
similarity index 92%
rename from src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/DesignerAttribute.cs
rename to src/libraries/System.ComponentModel.Primitives/src/System/ComponentModel/DesignerAttribute.cs
index 06f34b933759a2..bde0162bbdf0f4 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/DesignerAttribute.cs
+++ b/src/libraries/System.ComponentModel.Primitives/src/System/ComponentModel/DesignerAttribute.cs
@@ -11,7 +11,7 @@ namespace System.ComponentModel
     [AttributeUsage(AttributeTargets.Class | AttributeTargets.Interface, AllowMultiple = true, Inherited = true)]
     public sealed class DesignerAttribute : Attribute
     {
-        private string _typeId;
+        private string? _typeId;
 
         /// <summary>
         /// Initializes a new instance of the <see cref='System.ComponentModel.DesignerAttribute'/> class using the name of the type that
@@ -20,7 +20,7 @@ public sealed class DesignerAttribute : Attribute
         public DesignerAttribute(string designerTypeName)
         {
             DesignerTypeName = designerTypeName ?? throw new ArgumentNullException(nameof(designerTypeName));
-            DesignerBaseTypeName = typeof(IDesigner).FullName;
+            DesignerBaseTypeName = "System.ComponentModel.Design.IDesigner, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089";
         }
 
         /// <summary>
@@ -34,8 +34,8 @@ public DesignerAttribute(Type designerType)
                 throw new ArgumentNullException(nameof(designerType));
             }
 
-            DesignerTypeName = designerType.AssemblyQualifiedName;
-            DesignerBaseTypeName = typeof(IDesigner).FullName;
+            DesignerTypeName = designerType.AssemblyQualifiedName!;
+            DesignerBaseTypeName = "System.ComponentModel.Design.IDesigner, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089";
         }
 
         /// <summary>
@@ -64,7 +64,7 @@ public DesignerAttribute(string designerTypeName, Type designerBaseType)
             }
 
             DesignerTypeName = designerTypeName;
-            DesignerBaseTypeName = designerBaseType.AssemblyQualifiedName;
+            DesignerBaseTypeName = designerBaseType.AssemblyQualifiedName!;
         }
 
         /// <summary>
@@ -82,8 +82,8 @@ public DesignerAttribute(Type designerType, Type designerBaseType)
                 throw new ArgumentNullException(nameof(designerBaseType));
             }
 
-            DesignerTypeName = designerType.AssemblyQualifiedName;
-            DesignerBaseTypeName = designerBaseType.AssemblyQualifiedName;
+            DesignerTypeName = designerType.AssemblyQualifiedName!;
+            DesignerBaseTypeName = designerBaseType.AssemblyQualifiedName!;
         }
 
         /// <summary>
@@ -121,7 +121,7 @@ public override object TypeId
             }
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (obj == this)
             {
diff --git a/src/libraries/System.ComponentModel.Primitives/src/System/ComponentModel/IComponent.cs b/src/libraries/System.ComponentModel.Primitives/src/System/ComponentModel/IComponent.cs
index a94e4f765880e3..bf953543bdd10a 100644
--- a/src/libraries/System.ComponentModel.Primitives/src/System/ComponentModel/IComponent.cs
+++ b/src/libraries/System.ComponentModel.Primitives/src/System/ComponentModel/IComponent.cs
@@ -19,6 +19,8 @@ namespace System.ComponentModel
     /// provided "site".
     /// Provides functionality required by all components.
     /// </summary>
+    [Designer("System.ComponentModel.Design.ComponentDesigner, System.Design, Version=4.0.0.0, PublicKeyToken=b03f5f7f11d50a3a")]
+    [Designer("System.Windows.Forms.Design.ComponentDocumentDesigner, System.Design, Version=4.0.0.0, PublicKeyToken=b03f5f7f11d50a3a")]
     [TypeConverter("System.ComponentModel.ComponentConverter, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
     public interface IComponent : IDisposable
     {
diff --git a/src/libraries/System.ComponentModel.Primitives/tests/System.ComponentModel.Primitives.Tests.csproj b/src/libraries/System.ComponentModel.Primitives/tests/System.ComponentModel.Primitives.Tests.csproj
index 2994d54eb7422c..ab75a03e98333e 100644
--- a/src/libraries/System.ComponentModel.Primitives/tests/System.ComponentModel.Primitives.Tests.csproj
+++ b/src/libraries/System.ComponentModel.Primitives/tests/System.ComponentModel.Primitives.Tests.csproj
@@ -8,6 +8,7 @@
     <Compile Include="System\ComponentModel\ComponentCollectionTests.cs" />
     <Compile Include="System\ComponentModel\ComponentTests.cs" />
     <Compile Include="System\ComponentModel\DescriptionAttributeTests.cs" />
+    <Compile Include="System\ComponentModel\DesignerAttributeTests.cs" />
     <Compile Include="System\ComponentModel\DesignerCategoryAttributeTests.cs" />
     <Compile Include="System\ComponentModel\DesignerSerializationVisibilityAttributeTests.cs" />
     <Compile Include="System\ComponentModel\DesignOnlyAttributeTests.cs" />
diff --git a/src/libraries/System.ComponentModel.TypeConverter/tests/DesignerAttributeTests.cs b/src/libraries/System.ComponentModel.Primitives/tests/System/ComponentModel/DesignerAttributeTests.cs
similarity index 95%
rename from src/libraries/System.ComponentModel.TypeConverter/tests/DesignerAttributeTests.cs
rename to src/libraries/System.ComponentModel.Primitives/tests/System/ComponentModel/DesignerAttributeTests.cs
index fcd64ecbfaf91a..4b7246eadd00dd 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/tests/DesignerAttributeTests.cs
+++ b/src/libraries/System.ComponentModel.Primitives/tests/System/ComponentModel/DesignerAttributeTests.cs
@@ -17,7 +17,7 @@ public void Ctor_String(string designerTypeName)
         {
             var attribute = new DesignerAttribute(designerTypeName);
             Assert.Equal(designerTypeName, attribute.DesignerTypeName);
-            Assert.Equal(typeof(IDesigner).FullName, attribute.DesignerBaseTypeName);
+            Assert.Equal("System.ComponentModel.Design.IDesigner, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089", attribute.DesignerBaseTypeName);
         }
 
         [Theory]
@@ -28,7 +28,7 @@ public void Ctor_Type(Type designerType)
         {
             var attribute = new DesignerAttribute(designerType);
             Assert.Equal(designerType.AssemblyQualifiedName, attribute.DesignerTypeName);
-            Assert.Equal(typeof(IDesigner).FullName, attribute.DesignerBaseTypeName);
+            Assert.Equal("System.ComponentModel.Design.IDesigner, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089", attribute.DesignerBaseTypeName);
         }
 
         [Theory]
diff --git a/src/libraries/System.ComponentModel.TypeConverter/Directory.Build.props b/src/libraries/System.ComponentModel.TypeConverter/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/Directory.Build.props
+++ b/src/libraries/System.ComponentModel.TypeConverter/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ComponentModel.TypeConverter/ref/System.ComponentModel.TypeConverter.Forwards.cs b/src/libraries/System.ComponentModel.TypeConverter/ref/System.ComponentModel.TypeConverter.Forwards.cs
index a789d29492d261..9fa6997506351a 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/ref/System.ComponentModel.TypeConverter.Forwards.cs
+++ b/src/libraries/System.ComponentModel.TypeConverter/ref/System.ComponentModel.TypeConverter.Forwards.cs
@@ -4,9 +4,10 @@
 // Changes to this file must follow the https://aka.ms/api-review process.
 // ------------------------------------------------------------------------------
 
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.ComponentModel.Component))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.ComponentModel.DesignerAttribute))]
 [assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.ComponentModel.InvalidAsynchronousStateException))]
 [assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.ComponentModel.InvalidEnumArgumentException))]
-[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.ComponentModel.Component))]
 [assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.ComponentModel.ISupportInitialize))]
 [assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.ComponentModel.TypeConverterAttribute))]
 [assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.ComponentModel.TypeDescriptionProviderAttribute))]
diff --git a/src/libraries/System.ComponentModel.TypeConverter/ref/System.ComponentModel.TypeConverter.cs b/src/libraries/System.ComponentModel.TypeConverter/ref/System.ComponentModel.TypeConverter.cs
index 74a1e68eade5fc..cfe811bb42dfcb 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/ref/System.ComponentModel.TypeConverter.cs
+++ b/src/libraries/System.ComponentModel.TypeConverter/ref/System.ComponentModel.TypeConverter.cs
@@ -381,20 +381,6 @@ public DefaultPropertyAttribute(string name) { }
         public override bool Equals(object obj) { throw null; }
         public override int GetHashCode() { throw null; }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Interface, AllowMultiple=true, Inherited=true)]
-    public sealed partial class DesignerAttribute : System.Attribute
-    {
-        public DesignerAttribute(string designerTypeName) { }
-        public DesignerAttribute(string designerTypeName, string designerBaseTypeName) { }
-        public DesignerAttribute(string designerTypeName, System.Type designerBaseType) { }
-        public DesignerAttribute(System.Type designerType) { }
-        public DesignerAttribute(System.Type designerType, System.Type designerBaseType) { }
-        public string DesignerBaseTypeName { get { throw null; } }
-        public string DesignerTypeName { get { throw null; } }
-        public override object TypeId { get { throw null; } }
-        public override bool Equals(object obj) { throw null; }
-        public override int GetHashCode() { throw null; }
-    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Interface)]
     public sealed partial class DesignTimeVisibleAttribute : System.Attribute
     {
@@ -833,6 +819,7 @@ public LookupBindingPropertiesAttribute(string dataSource, string displayMember,
         public override bool Equals(object obj) { throw null; }
         public override int GetHashCode() { throw null; }
     }
+    [System.ComponentModel.DesignerAttribute("System.Windows.Forms.Design.ComponentDocumentDesigner, System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", typeof(System.ComponentModel.Design.IRootDesigner))]
     [System.ComponentModel.DesignerCategoryAttribute("Component")]
     [System.ComponentModel.TypeConverterAttribute(typeof(System.ComponentModel.ComponentConverter))]
     public partial class MarshalByValueComponent : System.ComponentModel.IComponent, System.IDisposable, System.IServiceProvider
@@ -1349,9 +1336,9 @@ public sealed partial class TypeDescriptor
         internal TypeDescriptor() { }
         [System.ObsoleteAttribute("This property has been deprecated. Use a type description provider to supply type information for COM types instead. https://go.microsoft.com/fwlink/?linkid=14202")]
         public static System.ComponentModel.IComNativeDescriptorHandler ComNativeDescriptorHandler { get { throw null; } set { } }
-        public static System.Type ComObjectType { get { throw null; } }
+        public static System.Type ComObjectType { [return: System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] get { throw null; } }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Advanced)]
-        public static System.Type InterfaceType { get { throw null; } }
+        public static System.Type InterfaceType { [return: System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] get { throw null; } }
         public static event System.ComponentModel.RefreshEventHandler Refreshed { add { } remove { } }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Advanced)]
         public static System.ComponentModel.TypeDescriptionProvider AddAttributes(object instance, params System.Attribute[] attributes) { throw null; }
diff --git a/src/libraries/System.ComponentModel.TypeConverter/src/System.ComponentModel.TypeConverter.csproj b/src/libraries/System.ComponentModel.TypeConverter/src/System.ComponentModel.TypeConverter.csproj
index f4869cbbb261c8..f102c543163002 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/src/System.ComponentModel.TypeConverter.csproj
+++ b/src/libraries/System.ComponentModel.TypeConverter/src/System.ComponentModel.TypeConverter.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RootNamespace>System.ComponentModel.TypeConverter</RootNamespace>
-    <AssemblyName>System.ComponentModel.TypeConverter</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
@@ -121,7 +119,6 @@
     <Compile Include="System\ComponentModel\DataObjectMethodAttribute.cs" />
     <Compile Include="System\ComponentModel\DataObjectMethodType.cs" />
     <Compile Include="System\ComponentModel\DefaultBindingPropertyAttribute.cs" />
-    <Compile Include="System\ComponentModel\DesignerAttribute.cs" />
     <Compile Include="System\ComponentModel\DesignTimeVisibleAttribute.cs" />
     <Compile Include="System\ComponentModel\Design\IDesigner.cs" />
     <Compile Include="System\ComponentModel\Design\DesignerVerbCollection.cs" />
diff --git a/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/Design/DesigntimeLicenseContext.cs b/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/Design/DesigntimeLicenseContext.cs
index a8d5bb856e9843..c650b38372f750 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/Design/DesigntimeLicenseContext.cs
+++ b/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/Design/DesigntimeLicenseContext.cs
@@ -77,16 +77,12 @@ public override string GetSavedLicenseKey(Type type, Assembly resourceAssembly)
                     // try everything.
                     foreach (Assembly asm in AppDomain.CurrentDomain.GetAssemblies())
                     {
-                        // Though, I could not repro this, we seem to be hitting an AssemblyBuilder
-                        // when walking through all the assemblies in the current app domain. This throws an
-                        // exception on Assembly.CodeBase and we bail out. Catching exceptions here is not a
-                        // bad thing.
-                        if (asm.IsDynamic)
+                        // Assemblies loaded in memory return empty string from Location.
+                        string location = asm.Location;
+                        if (location == string.Empty)
                             continue;
 
-                        // file://fullpath/foo.exe
-                        string fileName = GetLocalPath(asm.EscapedCodeBase);
-                        fileName = new FileInfo(fileName).Name;
+                        string fileName = new FileInfo(location).Name;
 
                         Stream s = asm.GetManifestResourceStream(fileName + ".licenses");
                         if (s == null)
@@ -103,44 +99,43 @@ public override string GetSavedLicenseKey(Type type, Assembly resourceAssembly)
                         }
                     }
                 }
-                else if (!resourceAssembly.IsDynamic)
+                else
                 {
-                    // EscapedCodeBase won't be supported by emitted assemblies anyway
-                    string fileName;
-
-                    fileName = GetLocalPath(resourceAssembly.EscapedCodeBase);
-
-                    fileName = Path.GetFileName(fileName);
-                    string licResourceName = fileName + ".licenses";
-
-                    // First try the filename
-                    Stream s = resourceAssembly.GetManifestResourceStream(licResourceName);
-                    if (s == null)
+                    string location = resourceAssembly.Location;
+                    if (location != string.Empty)
                     {
-                        string resolvedName = null;
-                        CompareInfo comparer = CultureInfo.InvariantCulture.CompareInfo;
-                        string shortAssemblyName = resourceAssembly.GetName().Name;
-                        // If the assembly has been renamed, we try our best to find a good match in the available resources
-                        // by looking at the assembly name (which doesn't change even after a file rename) + ".exe.licenses" or + ".dll.licenses"
-                        foreach (string existingName in resourceAssembly.GetManifestResourceNames())
+                        string fileName = Path.GetFileName(location);
+                        string licResourceName = fileName + ".licenses";
+
+                        // First try the filename
+                        Stream s = resourceAssembly.GetManifestResourceStream(licResourceName);
+                        if (s == null)
                         {
-                            if (comparer.Compare(existingName, licResourceName, CompareOptions.IgnoreCase) == 0 ||
-                             comparer.Compare(existingName, shortAssemblyName + ".exe.licenses", CompareOptions.IgnoreCase) == 0 ||
-                             comparer.Compare(existingName, shortAssemblyName + ".dll.licenses", CompareOptions.IgnoreCase) == 0)
+                            string resolvedName = null;
+                            CompareInfo comparer = CultureInfo.InvariantCulture.CompareInfo;
+                            string shortAssemblyName = resourceAssembly.GetName().Name;
+                            // If the assembly has been renamed, we try our best to find a good match in the available resources
+                            // by looking at the assembly name (which doesn't change even after a file rename) + ".exe.licenses" or + ".dll.licenses"
+                            foreach (string existingName in resourceAssembly.GetManifestResourceNames())
                             {
-                                resolvedName = existingName;
-                                break;
+                                if (comparer.Compare(existingName, licResourceName, CompareOptions.IgnoreCase) == 0 ||
+                                 comparer.Compare(existingName, shortAssemblyName + ".exe.licenses", CompareOptions.IgnoreCase) == 0 ||
+                                 comparer.Compare(existingName, shortAssemblyName + ".dll.licenses", CompareOptions.IgnoreCase) == 0)
+                                {
+                                    resolvedName = existingName;
+                                    break;
+                                }
+                            }
+                            if (resolvedName != null)
+                            {
+                                s = resourceAssembly.GetManifestResourceStream(resolvedName);
                             }
                         }
-                        if (resolvedName != null)
+                        if (s != null)
                         {
-                            s = resourceAssembly.GetManifestResourceStream(resolvedName);
+                            DesigntimeLicenseContextSerializer.Deserialize(s, fileName.ToUpperInvariant(), this);
                         }
                     }
-                    if (s != null)
-                    {
-                        DesigntimeLicenseContextSerializer.Deserialize(s, fileName.ToUpperInvariant(), this);
-                    }
                 }
             }
             return (string)_savedLicenseKeys[type.AssemblyQualifiedName];
diff --git a/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ReflectTypeDescriptionProvider.ReflectedTypeData.cs b/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ReflectTypeDescriptionProvider.ReflectedTypeData.cs
index d2b7d59ef7816c..70c8024c825e06 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ReflectTypeDescriptionProvider.ReflectedTypeData.cs
+++ b/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ReflectTypeDescriptionProvider.ReflectedTypeData.cs
@@ -218,7 +218,7 @@ internal TypeConverter GetConverter(object instance)
                     {
                         // We did not get a converter. Traverse up the base class chain until
                         // we find one in the stock hashtable.
-                        _converter = (TypeConverter)SearchIntrinsicTable(IntrinsicTypeConverters, _type);
+                        _converter = GetIntrinsicTypeConverter(_type);
                         Debug.Assert(_converter != null, "There is no intrinsic setup in the hashtable for the Object type");
                     }
                 }
@@ -348,7 +348,7 @@ internal object GetEditor(object instance, Type editorBaseType)
                     Hashtable intrinsicEditors = GetEditorTable(editorBaseType);
                     if (intrinsicEditors != null)
                     {
-                        editor = SearchIntrinsicTable(intrinsicEditors, _type);
+                        editor = GetIntrinsicTypeEditor(intrinsicEditors, _type);
                     }
 
                     // As a quick sanity check, check to see that the editor we got back is of
diff --git a/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ReflectTypeDescriptionProvider.cs b/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ReflectTypeDescriptionProvider.cs
index ce355d14ac3c64..ff4cd113da6f0c 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ReflectTypeDescriptionProvider.cs
+++ b/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ReflectTypeDescriptionProvider.cs
@@ -5,7 +5,6 @@
 using System.Collections.Generic;
 using System.ComponentModel.Design;
 using System.Diagnostics;
-using System.Drawing;
 using System.Globalization;
 using System.Linq;
 using System.Reflection;
@@ -38,7 +37,7 @@ internal sealed partial class ReflectTypeDescriptionProvider : TypeDescriptionPr
         // This is where we store the various converters, etc for the intrinsic types.
         //
         private static Hashtable s_editorTables;
-        private static Hashtable s_intrinsicTypeConverters;
+        private static Dictionary<object, IntrinsicTypeConverterData> s_intrinsicTypeConverters;
 
         // For converters, etc that are bound to class attribute data, rather than a class
         // type, we have special key sentinel values that we put into the hash table.
@@ -94,44 +93,88 @@ internal ReflectTypeDescriptionProvider()
         private static Hashtable EditorTables => LazyInitializer.EnsureInitialized(ref s_editorTables, () => new Hashtable(4));
 
         /// <summary>
-        /// This is a table we create for intrinsic types.
-        /// There should be entries here ONLY for intrinsic
-        /// types, as all other types we should be able to
-        /// add attributes directly as metadata.
+        /// Provides a way to create <see cref="TypeConverter"/> instances, and cache them where applicable.
         /// </summary>
-        private static Hashtable IntrinsicTypeConverters => LazyInitializer.EnsureInitialized(ref s_intrinsicTypeConverters, () => new Hashtable
+        private class IntrinsicTypeConverterData
+        {
+            private readonly Func<Type, TypeConverter> _constructionFunc;
+
+            private readonly bool _cacheConverterInstance;
+
+            private TypeConverter _converterInstance;
+
+            /// <summary>
+            /// Creates a new instance of <see cref="IntrinsicTypeConverterData"/>.
+            /// </summary>
+            /// <param name="constructionFunc">
+            /// A func that creates a new <see cref="TypeConverter"/> instance.
+            /// </param>
+            /// <param name="cacheConverterInstance">
+            /// Indicates whether to cache created <see cref="TypeConverter"/> instances. This is false when the converter handles multiple types,
+            /// specifically <see cref="EnumConverter"/>, <see cref="NullableConverter"/>, and <see cref="ReferenceConverter"/>.
+            /// </param>
+            public IntrinsicTypeConverterData(Func<Type, TypeConverter> constructionFunc, bool cacheConverterInstance = true)
+            {
+                _constructionFunc = constructionFunc;
+                _cacheConverterInstance = cacheConverterInstance;
+            }
+
+            public TypeConverter GetOrCreateConverterInstance(Type innerType)
+            {
+                if (!_cacheConverterInstance)
+                {
+                    return _constructionFunc(innerType);
+                }
+
+                _converterInstance ??= _constructionFunc(innerType);
+                return _converterInstance;
+            }
+        }
+
+        /// <summary>
+        /// This is a table we create for intrinsic types.There should be entries here ONLY for
+        /// intrinsic types, as all other types we should be able to add attributes directly as metadata.
+        /// </summary>
+        /// <remarks>
+        /// <see cref="Uri"/> and <see cref="CultureInfo"/> are the only types that can be inherited for which
+        /// we have intrinsic converters for. The appropriate converter needs to be fetched when look-ups are done
+        /// for deriving types. When adding to this cache, consider whether the type can be inherited and add the
+        /// appropriate logic to handle this in <see cref="GetIntrinsicTypeConverter(Type)"/> below.
+        /// </remarks>
+        private static Dictionary<object, IntrinsicTypeConverterData> IntrinsicTypeConverters
+            => LazyInitializer.EnsureInitialized(ref s_intrinsicTypeConverters, () => new Dictionary<object, IntrinsicTypeConverterData>(27)
         {
             // Add the intrinsics
             //
-            [typeof(bool)] = typeof(BooleanConverter),
-            [typeof(byte)] = typeof(ByteConverter),
-            [typeof(sbyte)] = typeof(SByteConverter),
-            [typeof(char)] = typeof(CharConverter),
-            [typeof(double)] = typeof(DoubleConverter),
-            [typeof(string)] = typeof(StringConverter),
-            [typeof(int)] = typeof(Int32Converter),
-            [typeof(short)] = typeof(Int16Converter),
-            [typeof(long)] = typeof(Int64Converter),
-            [typeof(float)] = typeof(SingleConverter),
-            [typeof(ushort)] = typeof(UInt16Converter),
-            [typeof(uint)] = typeof(UInt32Converter),
-            [typeof(ulong)] = typeof(UInt64Converter),
-            [typeof(object)] = typeof(TypeConverter),
-            [typeof(void)] = typeof(TypeConverter),
-            [typeof(CultureInfo)] = typeof(CultureInfoConverter),
-            [typeof(DateTime)] = typeof(DateTimeConverter),
-            [typeof(DateTimeOffset)] = typeof(DateTimeOffsetConverter),
-            [typeof(decimal)] = typeof(DecimalConverter),
-            [typeof(TimeSpan)] = typeof(TimeSpanConverter),
-            [typeof(Guid)] = typeof(GuidConverter),
-            [typeof(Uri)] = typeof(UriTypeConverter),
-            [typeof(Version)] = typeof(VersionConverter),
+            [typeof(bool)] = new IntrinsicTypeConverterData((type) => new BooleanConverter()),
+            [typeof(byte)] = new IntrinsicTypeConverterData((type) => new ByteConverter()),
+            [typeof(sbyte)] = new IntrinsicTypeConverterData((type) => new SByteConverter()),
+            [typeof(char)] = new IntrinsicTypeConverterData((type) => new CharConverter()),
+            [typeof(double)] = new IntrinsicTypeConverterData((type) => new DoubleConverter()),
+            [typeof(string)] = new IntrinsicTypeConverterData((type) => new StringConverter()),
+            [typeof(int)] = new IntrinsicTypeConverterData((type) => new Int32Converter()),
+            [typeof(short)] = new IntrinsicTypeConverterData((type) => new Int16Converter()),
+            [typeof(long)] = new IntrinsicTypeConverterData((type) => new Int64Converter()),
+            [typeof(float)] = new IntrinsicTypeConverterData((type) => new SingleConverter()),
+            [typeof(ushort)] = new IntrinsicTypeConverterData((type) => new UInt16Converter()),
+            [typeof(uint)] = new IntrinsicTypeConverterData((type) => new UInt32Converter()),
+            [typeof(ulong)] = new IntrinsicTypeConverterData((type) => new UInt64Converter()),
+            [typeof(object)] = new IntrinsicTypeConverterData((type) => new TypeConverter()),
+            [typeof(CultureInfo)] = new IntrinsicTypeConverterData((type) => new CultureInfoConverter()),
+            [typeof(DateTime)] = new IntrinsicTypeConverterData((type) => new DateTimeConverter()),
+            [typeof(DateTimeOffset)] = new IntrinsicTypeConverterData((type) => new DateTimeOffsetConverter()),
+            [typeof(decimal)] = new IntrinsicTypeConverterData((type) => new DecimalConverter()),
+            [typeof(TimeSpan)] = new IntrinsicTypeConverterData((type) => new TimeSpanConverter()),
+            [typeof(Guid)] = new IntrinsicTypeConverterData((type) => new GuidConverter()),
+            [typeof(Uri)] = new IntrinsicTypeConverterData((type) => new UriTypeConverter()),
+            [typeof(Version)] = new IntrinsicTypeConverterData((type) => new VersionConverter()),
             // Special cases for things that are not bound to a specific type
             //
-            [typeof(Array)] = typeof(ArrayConverter),
-            [typeof(ICollection)] = typeof(CollectionConverter),
-            [typeof(Enum)] = typeof(EnumConverter),
-            [s_intrinsicNullableKey] = typeof(NullableConverter),
+            [typeof(Array)] = new IntrinsicTypeConverterData((type) => new ArrayConverter()),
+            [typeof(ICollection)] = new IntrinsicTypeConverterData((type) => new CollectionConverter()),
+            [typeof(Enum)] = new IntrinsicTypeConverterData((type) => new EnumConverter(type), cacheConverterInstance: false),
+            [s_intrinsicNullableKey] = new IntrinsicTypeConverterData((type) => new NullableConverter(type), cacheConverterInstance: false),
+            [s_intrinsicReferenceKey] = new IntrinsicTypeConverterData((type) => new ReferenceConverter(type), cacheConverterInstance: false),
         });
 
         private static Hashtable PropertyCache => LazyInitializer.EnsureInitialized(ref s_propertyCache, () => new Hashtable());
@@ -1215,14 +1258,14 @@ internal void Refresh(Type type)
 
         /// <summary>
         /// Searches the provided intrinsic hashtable for a match with the object type.
-        /// At the beginning, the hashtable contains types for the various converters.
+        /// At the beginning, the hashtable contains types for the various editors.
         /// As this table is searched, the types for these objects
         /// are replaced with instances, so we only create as needed. This method
         /// does the search up the base class hierarchy and will create instances
         /// for types as needed. These instances are stored back into the table
         /// for the base type, and for the original component type, for fast access.
         /// </summary>
-        private static object SearchIntrinsicTable(Hashtable table, Type callingType)
+        private static object GetIntrinsicTypeEditor(Hashtable table, Type callingType)
         {
             object hashEntry = null;
 
@@ -1337,5 +1380,76 @@ private static object SearchIntrinsicTable(Hashtable table, Type callingType)
 
             return hashEntry;
         }
+
+        /// <summary>
+        /// Searches the intrinsic converter dictionary for a match with the object type.
+        /// The strongly-typed dictionary maps object types to converter data objects which lazily
+        /// creates (and caches for re-use, where applicable) converter instances.
+        /// </summary>
+        private static TypeConverter GetIntrinsicTypeConverter(Type callingType)
+        {
+            TypeConverter converter;
+
+            // We take a lock on this dictionary. Nothing in this code calls out to
+            // other methods that lock, so it should be fairly safe to grab this lock.
+            lock (IntrinsicTypeConverters)
+            {
+                if (!IntrinsicTypeConverters.TryGetValue(callingType, out IntrinsicTypeConverterData converterData))
+                {
+                    if (callingType.IsEnum)
+                    {
+                        converterData = IntrinsicTypeConverters[typeof(Enum)];
+                    }
+                    else if (callingType.IsArray)
+                    {
+                        converterData = IntrinsicTypeConverters[typeof(Array)];
+                    }
+                    else if (callingType.IsGenericType && callingType.GetGenericTypeDefinition() == typeof(Nullable<>))
+                    {
+                        converterData = IntrinsicTypeConverters[s_intrinsicNullableKey];
+                    }
+                    else if (typeof(ICollection).IsAssignableFrom(callingType))
+                    {
+                        converterData = IntrinsicTypeConverters[typeof(ICollection)];
+                    }
+                    else if (callingType.IsInterface)
+                    {
+                        converterData = IntrinsicTypeConverters[s_intrinsicReferenceKey];
+                    }
+                    else
+                    {
+                        // Uri and CultureInfo are the only types that can be derived from for which we have intrinsic converters.
+                        // Check if the calling type derives from either and return the appropriate converter.
+
+                        // We should have fetched converters for these types above.
+                        Debug.Assert(callingType != typeof(Uri) && callingType != typeof(CultureInfo));
+
+                        Type key = null;
+
+                        Type baseType = callingType.BaseType;
+                        while (baseType != null && baseType != typeof(object))
+                        {
+                            if (baseType == typeof(Uri) || baseType == typeof(CultureInfo))
+                            {
+                                key = baseType;
+                                break;
+                            }
+
+                            baseType = baseType.BaseType;
+                        }
+
+                        // Handle other reference and value types. An instance of TypeConverter itself created and returned below.
+                        key ??= typeof(object);
+
+                        converterData = IntrinsicTypeConverters[key];
+                    }
+                }
+
+                // This needs to be done within the lock as the dictionary value may be mutated in the following method call.
+                converter = converterData.GetOrCreateConverterInstance(callingType);
+            }
+
+            return converter;
+        }
     }
 }
diff --git a/src/libraries/System.ComponentModel.TypeConverter/tests/Security/Authentication/ExtendedProtection/ExtendedProtectionPolicyTypeConverterTests.cs b/src/libraries/System.ComponentModel.TypeConverter/tests/Security/Authentication/ExtendedProtection/ExtendedProtectionPolicyTypeConverterTests.cs
index 55bf14930ffd7c..a09110342ff6d3 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/tests/Security/Authentication/ExtendedProtection/ExtendedProtectionPolicyTypeConverterTests.cs
+++ b/src/libraries/System.ComponentModel.TypeConverter/tests/Security/Authentication/ExtendedProtection/ExtendedProtectionPolicyTypeConverterTests.cs
@@ -30,12 +30,14 @@ public void CanConvertTo_PositiveTests()
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Net.Security is not supported on this platform.
         public void ConvertTo_NullTypeTests()
         {
             Assert.Throws<ArgumentNullException>(() => converter.ConvertTo(null, CultureInfo.InvariantCulture, new ExtendedProtectionPolicy(PolicyEnforcement.Never), null));
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Net.Security is not supported on this platform.
         public void ConvertTo_PositiveTests()
         {
             ExtendedProtectionPolicy policy = new ExtendedProtectionPolicy(PolicyEnforcement.Never);
@@ -55,6 +57,7 @@ public void ConvertTo_PositiveTests()
         }
 
         [Theory]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Net.Security is not supported on this platform.
         [InlineData(typeof(int))]
         [InlineData(typeof(ExtendedProtectionPolicy))]
         [InlineData(typeof(bool))]
diff --git a/src/libraries/System.ComponentModel.TypeConverter/tests/System.ComponentModel.TypeConverter.Tests.csproj b/src/libraries/System.ComponentModel.TypeConverter/tests/System.ComponentModel.TypeConverter.Tests.csproj
index eb8dda3696e84e..a7d84bb1ff6c7b 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/tests/System.ComponentModel.TypeConverter.Tests.csproj
+++ b/src/libraries/System.ComponentModel.TypeConverter/tests/System.ComponentModel.TypeConverter.Tests.csproj
@@ -6,14 +6,12 @@
     <AssemblyVersion>9.9.9.9</AssemblyVersion>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+  <ItemGroup>
     <Compile Include="Drawing\ColorConverterTests.cs" />
     <Compile Include="Drawing\PointConverterTests.cs" />
     <Compile Include="Drawing\RectangleConverterTests.cs" />
     <Compile Include="Drawing\SizeConverterTests.cs" />
     <Compile Include="Drawing\SizeFConverterTests.cs" />
-  </ItemGroup>
-  <ItemGroup>
     <Compile Include="Design\Serialization\ComponentSerializationServiceTests.cs" />
     <Compile Include="Design\StandardCommandsTests.cs" />
     <Compile Include="Extensions\EnumeratorExtensions.cs" />
@@ -72,7 +70,6 @@
     <Compile Include="DefaultEventAttributeTests.cs" />
     <Compile Include="EditorAttributeTests.cs" />
     <Compile Include="DesignTimeVisibleAttributeTests.cs" />
-    <Compile Include="DesignerAttributeTests.cs" />
     <Compile Include="DefaultPropertyAttributeTests.cs" />
     <Compile Include="Design\DesignerTransactionCloseEventArgsTests.cs" />
     <Compile Include="Design\DesignerVerbTests.cs" />
diff --git a/src/libraries/System.ComponentModel.TypeConverter/tests/TrimmingTests/TypeConverterTest.cs b/src/libraries/System.ComponentModel.TypeConverter/tests/TrimmingTests/TypeConverterTest.cs
new file mode 100644
index 00000000000000..dca3536084d253
--- /dev/null
+++ b/src/libraries/System.ComponentModel.TypeConverter/tests/TrimmingTests/TypeConverterTest.cs
@@ -0,0 +1,182 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections;
+using System.ComponentModel;
+using System.Globalization;
+
+/// <summary>
+/// Tests that the relevant constructors of intrinsic TypeConverter types are preserved when needed in a trimmed application.
+/// </summary>
+class Program
+{
+    static int Main(string[] args)
+    {
+        if (!RunTest(targetType: typeof(bool), expectedConverterType: typeof(BooleanConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(byte), expectedConverterType: typeof(ByteConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(sbyte), expectedConverterType: typeof(SByteConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(char), expectedConverterType: typeof(CharConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(double), expectedConverterType: typeof(DoubleConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(string), expectedConverterType: typeof(StringConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(short), expectedConverterType: typeof(Int16Converter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(int), expectedConverterType: typeof(Int32Converter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(long), expectedConverterType: typeof(Int64Converter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(float), expectedConverterType: typeof(SingleConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(ushort), expectedConverterType: typeof(UInt16Converter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(uint), expectedConverterType: typeof(UInt32Converter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(ulong), expectedConverterType: typeof(UInt64Converter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(object), expectedConverterType: typeof(TypeConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(DateTime), expectedConverterType: typeof(DateTimeConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(DateTimeOffset), expectedConverterType: typeof(DateTimeOffsetConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(decimal), expectedConverterType: typeof(DecimalConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(TimeSpan), expectedConverterType: typeof(TimeSpanConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(Guid), expectedConverterType: typeof(GuidConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(Array), expectedConverterType: typeof(ArrayConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(ICollection), expectedConverterType: typeof(CollectionConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(Enum), expectedConverterType: typeof(EnumConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(DayOfWeek), expectedConverterType: typeof(EnumConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(SomeValueType?), expectedConverterType: typeof(NullableConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(ClassWithNoConverter), expectedConverterType: typeof(TypeConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(Uri), expectedConverterType: typeof(UriTypeConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(CultureInfo), expectedConverterType: typeof(CultureInfoConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(Version), expectedConverterType: typeof(VersionConverter)))
+        {
+            return -1;
+        }
+
+        if (!RunTest(targetType: typeof(IFooComponent), expectedConverterType: typeof(ReferenceConverter)))
+        {
+            return -1;
+        }
+
+        return 100;
+    }
+
+    private static bool RunTest(Type targetType, Type expectedConverterType)
+    {
+        TypeConverter retrievedConverter = TypeDescriptor.GetConverter(targetType);
+        return retrievedConverter.GetType() == expectedConverterType && retrievedConverter.CanConvertTo(typeof(string));
+    }
+
+    private struct SomeValueType
+    {
+    }
+
+    // TypeDescriptor should default to the TypeConverter in this case.
+    private class ClassWithNoConverter
+    {
+    }
+
+    private interface IFooComponent
+    {
+    }
+}
diff --git a/src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs b/src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs
index 60aeeed511e176..39a37f6bfb3973 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs
+++ b/src/libraries/System.ComponentModel.TypeConverter/tests/TypeDescriptorTests.cs
@@ -469,7 +469,9 @@ public void GetAssociationReturnsDesigner()
         [InlineData(typeof(TimeSpan), typeof(TimeSpanConverter))]
         [InlineData(typeof(Guid), typeof(GuidConverter))]
         [InlineData(typeof(Array), typeof(ArrayConverter))]
+        [InlineData(typeof(int[]), typeof(ArrayConverter))]
         [InlineData(typeof(ICollection), typeof(CollectionConverter))]
+        [InlineData(typeof(Stack), typeof(CollectionConverter))]
         [InlineData(typeof(Enum), typeof(EnumConverter))]
         [InlineData(typeof(SomeEnum), typeof(EnumConverter))]
         [InlineData(typeof(SomeValueType?), typeof(NullableConverter))]
@@ -482,9 +484,14 @@ public void GetAssociationReturnsDesigner()
         [InlineData(typeof(ClassIBase), typeof(IBaseConverter))]
         [InlineData(typeof(ClassIDerived), typeof(IBaseConverter))]
         [InlineData(typeof(Uri), typeof(UriTypeConverter))]
+        [InlineData(typeof(DerivedUri), typeof(UriTypeConverter))]
+        [InlineData(typeof(TwiceDerivedUri), typeof(UriTypeConverter))]
         [InlineData(typeof(CultureInfo), typeof(CultureInfoConverter))]
+        [InlineData(typeof(DerivedCultureInfo), typeof(CultureInfoConverter))]
+        [InlineData(typeof(TwiceDerivedCultureInfo), typeof(CultureInfoConverter))]
         [InlineData(typeof(Version), typeof(VersionConverter))]
         [InlineData(typeof(IComponent), typeof(ComponentConverter))]
+        [InlineData(typeof(IFooComponent), typeof(ReferenceConverter))]
         public static void GetConverter(Type targetType, Type resultConverterType)
         {
             TypeConverter converter = TypeDescriptor.GetConverter(targetType);
@@ -1151,5 +1158,32 @@ class FooBarDerived : FooBarBase
             [Description("Derived")]
             public override int Value { get; set; }
         }
+
+        interface IFooComponent
+        {
+            bool Flag { get; set; }
+        }
+
+        class DerivedUri : Uri
+        {
+            protected DerivedUri() : base("https://hello")
+            {
+            }
+        }
+
+        class TwiceDerivedUri : DerivedUri
+        {
+        }
+
+        class DerivedCultureInfo : CultureInfo
+        {
+            protected DerivedCultureInfo() : base("hello")
+            {
+            }
+        }
+
+        class TwiceDerivedCultureInfo : DerivedCultureInfo
+        {
+        }
     }
 }
diff --git a/src/libraries/System.ComponentModel.TypeConverter/tests/XTypeDescriptionProviderTests.cs b/src/libraries/System.ComponentModel.TypeConverter/tests/XTypeDescriptionProviderTests.cs
index 7dde31b29544f5..2b176d835eca5b 100644
--- a/src/libraries/System.ComponentModel.TypeConverter/tests/XTypeDescriptionProviderTests.cs
+++ b/src/libraries/System.ComponentModel.TypeConverter/tests/XTypeDescriptionProviderTests.cs
@@ -10,6 +10,7 @@
 
 namespace System.Xml.Linq.Tests
 {
+    [ActiveIssue("https://github.com/dotnet/runtime/issues/39709", TestPlatforms.Browser)]
     public class XTypeDescriptionProviderTests
     {
         [Fact]
diff --git a/src/libraries/System.ComponentModel/Directory.Build.props b/src/libraries/System.ComponentModel/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.ComponentModel/Directory.Build.props
+++ b/src/libraries/System.ComponentModel/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.ComponentModel/src/System.ComponentModel.csproj b/src/libraries/System.ComponentModel/src/System.ComponentModel.csproj
index fcaa643da271e7..5b0195df044a11 100644
--- a/src/libraries/System.ComponentModel/src/System.ComponentModel.csproj
+++ b/src/libraries/System.ComponentModel/src/System.ComponentModel.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RootNamespace>System.ComponentModel</RootNamespace>
-    <AssemblyName>System.ComponentModel</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Composition.AttributedModel/src/System.Composition.AttributedModel.csproj b/src/libraries/System.Composition.AttributedModel/src/System.Composition.AttributedModel.csproj
index a39f3494bb05c7..999ec09ad8fc2b 100644
--- a/src/libraries/System.Composition.AttributedModel/src/System.Composition.AttributedModel.csproj
+++ b/src/libraries/System.Composition.AttributedModel/src/System.Composition.AttributedModel.csproj
@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Composition.AttributedModel</AssemblyName>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Composition\Convention\AttributedModelProvider.cs" />
@@ -19,7 +17,4 @@
     <Compile Include="System\Composition\SharedAttribute.cs" />
     <Compile Include="System\Composition\SharingBoundaryAttribute.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition.AttributedModel/tests/System.Composition.AttributeModel.Tests.csproj b/src/libraries/System.Composition.AttributedModel/tests/System.Composition.AttributeModel.Tests.csproj
index 45d5ed3df29f0b..b10127ed9daa0d 100644
--- a/src/libraries/System.Composition.AttributedModel/tests/System.Composition.AttributeModel.Tests.csproj
+++ b/src/libraries/System.Composition.AttributedModel/tests/System.Composition.AttributeModel.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="SharingBoundaryAttributeTests.cs" />
@@ -15,4 +15,10 @@
     <Compile Include="ExportMetadataAttributeTests.cs" />
     <Compile Include="ExportAttributeTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Composition.AttributedModel.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.ComponentModel.Composition\src\System.ComponentModel.Composition.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition.Convention/src/System.Composition.Convention.csproj b/src/libraries/System.Composition.Convention/src/System.Composition.Convention.csproj
index eed8dbc7d09ca0..f954e1930f70c3 100644
--- a/src/libraries/System.Composition.Convention/src/System.Composition.Convention.csproj
+++ b/src/libraries/System.Composition.Convention/src/System.Composition.Convention.csproj
@@ -1,11 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Composition.Convention</AssemblyName>
-    <RootNamespace>
-    </RootNamespace>
-    <!-- CommonStrings needs RootNamespace to be empty -->
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Composition\Convention\ConventionBuilder.cs" />
@@ -26,10 +21,6 @@
              Link="Common\System\Composition\Diagnostics\TraceWriter.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Composition.AttributedModel\src\System.Composition.AttributedModel.csproj" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Composition.AttributedModel\src\System.Composition.AttributedModel.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition.Convention/tests/System.Composition.Convention.Tests.csproj b/src/libraries/System.Composition.Convention/tests/System.Composition.Convention.Tests.csproj
index 376dc6bc76e74c..9474efba0b9599 100644
--- a/src/libraries/System.Composition.Convention/tests/System.Composition.Convention.Tests.csproj
+++ b/src/libraries/System.Composition.Convention/tests/System.Composition.Convention.Tests.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Composition.Convention.Tests</AssemblyName>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="AttributedModelConventionExtensions.cs" />
@@ -16,4 +15,8 @@
     <Compile Include="PartBuilderOfTTests.cs" />
     <Compile Include="PartBuilderTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="../src/System.Composition.Convention.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Composition.TypedParts\src\System.Composition.TypedParts.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition.Hosting/src/System.Composition.Hosting.csproj b/src/libraries/System.Composition.Hosting/src/System.Composition.Hosting.csproj
index 23a9f0f487696d..09ae2efdf03209 100644
--- a/src/libraries/System.Composition.Hosting/src/System.Composition.Hosting.csproj
+++ b/src/libraries/System.Composition.Hosting/src/System.Composition.Hosting.csproj
@@ -1,11 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Composition.Hosting</AssemblyName>
-    <RootNamespace>
-    </RootNamespace>
-    <!-- CommonStrings needs RootNamespace to be empty -->
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Composition\Hosting\CompositionHost.cs" />
@@ -36,12 +31,9 @@
     <Compile Include="System\Composition\Hosting\Util\SmallSparseInitonlyArray.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Composition.Runtime\src\System.Composition.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Composition.Runtime\src\System.Composition.Runtime.csproj" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
-    <Reference Include="System" />
     <Reference Include="System.ComponentModel.Composition" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition.Hosting/tests/System.Composition.Hosting.Tests.csproj b/src/libraries/System.Composition.Hosting/tests/System.Composition.Hosting.Tests.csproj
index 3d7e2480f35102..931a211e151808 100644
--- a/src/libraries/System.Composition.Hosting/tests/System.Composition.Hosting.Tests.csproj
+++ b/src/libraries/System.Composition.Hosting/tests/System.Composition.Hosting.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Composition\Hosting\Core\CompositionDependencyTests.cs" />
@@ -12,4 +12,10 @@
     <Compile Include="System\Composition\Hosting\Core\LifetimeContextTests.cs" />
     <Compile Include="System\Composition\Hosting\Core\ExportDescriptorTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Composition.Hosting.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.ComponentModel.Composition" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/CompositionHostTests.cs b/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/CompositionHostTests.cs
index 0f74a27fdbb11f..f703345120442f 100644
--- a/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/CompositionHostTests.cs
+++ b/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/CompositionHostTests.cs
@@ -10,7 +10,6 @@ namespace System.Composition.Hosting.Core.Tests
     public class CompositionHostTests
     {
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetExport_CompositionContextContract_ReturnsExpected()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -21,7 +20,6 @@ public void GetExport_CompositionContextContract_ReturnsExpected()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetExport_MultipleDependencies_ReturnsExpected()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new MultipleDependency()))
@@ -56,7 +54,6 @@ public override IEnumerable<ExportDescriptorPromise> GetExportDescriptors(Compos
         }
 
         [Theory]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         [InlineData(typeof(int), new Type[] { typeof(int) })]
         [InlineData(typeof(IList<>), new Type[] { typeof(IList<>) })]
         [InlineData(typeof(ICollection<>), new Type[] { typeof(ICollection<>) })]
@@ -86,7 +83,6 @@ public void GetExport_LazyOrExportFactoryContractType_ReturnsExpected(Type type,
         }
 
         [Theory]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         [InlineData(typeof(string[]), new Type[] { typeof(string[]), typeof(string) })]
         [InlineData(typeof(IList<string>), new Type[] { typeof(IList<string>), typeof(string) })]
         [InlineData(typeof(ICollection<string>), new Type[] { typeof(ICollection<string>), typeof(string) })]
@@ -105,7 +101,6 @@ public void GetExport_ImoportManyWithMetadataConstraints_ReturnsExpected(Type co
         }
 
         [Theory]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         [InlineData(typeof(ExportFactory<int>), null, new Type[] { typeof(int), typeof(ExportFactory<int>) })]
         [InlineData(typeof(ExportFactory<int>), new string[] { "1", "2", "3" }, new Type[] { typeof(int), typeof(ExportFactory<int>) })]
         [InlineData(typeof(ExportFactory<int, ParameterlessConstructor>), null, new Type[] { typeof(int), typeof(ExportFactory<int, ParameterlessConstructor>) })]
@@ -134,7 +129,6 @@ public override IEnumerable<ExportDescriptorPromise> GetExportDescriptors(Compos
         }
 
         [Theory]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         [InlineData(typeof(Lazy<int, int>))]
         [InlineData(typeof(Lazy<int, IDictionary<string, string>>))]
         [InlineData(typeof(Lazy<int, PrivateConstructor>))]
@@ -148,7 +142,6 @@ public void GetExport_InvalidMetadata_ThrowsComposititionFailedException(Type ty
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetExport_AbstractMetadata_ThrowsInvalidOperationException()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -158,7 +151,6 @@ public void GetExport_AbstractMetadata_ThrowsInvalidOperationException()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetExport_NullProviderInProviders_ThrowsNullReferenceException()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[] { null }))
@@ -177,7 +169,6 @@ public void TryGetExport_NullContract_ThrowsArgumentNullException()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetExport_MultipleReturns_ThrowsCompositionFailedException()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new MultiplePromises()))
@@ -200,7 +191,6 @@ public override IEnumerable<ExportDescriptorPromise> GetExportDescriptors(Compos
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetExport_FailedDependency_ThrowsCompositionFailedException()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new FailedDependency()))
diff --git a/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/CompositionOperationTests.cs b/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/CompositionOperationTests.cs
index 15c61603be55f4..d66a21c433acbb 100644
--- a/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/CompositionOperationTests.cs
+++ b/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/CompositionOperationTests.cs
@@ -9,7 +9,6 @@ namespace System.Composition.Hosting.Core.Tests
     public class CompositionOperationTests
     {
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void Run_ValidContextAndAction_ReturnsExpected()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -49,7 +48,6 @@ public void Run_NullOutmostContext_ThrowsArgumentNullException()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void Run_NullActivator_ThrowsArgumentNullException()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -62,7 +60,6 @@ public void Run_NullActivator_ThrowsArgumentNullException()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void AddNonPrequisiteAction_NullAction_ThrowsArgumentNullException()
         {
             object Activator(LifetimeContext context, CompositionOperation operation)
@@ -81,7 +78,6 @@ object Activator(LifetimeContext context, CompositionOperation operation)
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void AddPostCompositionAction_NullAction_ThrowsArgumentNullException()
         {
             object Activator(LifetimeContext context, CompositionOperation operation)
diff --git a/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/LifetimeContextTests.cs b/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/LifetimeContextTests.cs
index a7a77d7e25d579..2cc06006ef9651 100644
--- a/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/LifetimeContextTests.cs
+++ b/src/libraries/System.Composition.Hosting/tests/System/Composition/Hosting/Core/LifetimeContextTests.cs
@@ -14,7 +14,6 @@ public void AllocateSharingId_InvokeMultipleTimes_ReturnsDifferentValue()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void AddBoundInstance_NonNullInstance_DisposesInstanceOnDisposal()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -35,7 +34,6 @@ public void AddBoundInstance_NonNullInstance_DisposesInstanceOnDisposal()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void AddBoundInstance_NullInstance_ThrowsNullReferenceExceptionOnDisposal()
         {
             CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]);
@@ -47,7 +45,6 @@ public void AddBoundInstance_NullInstance_ThrowsNullReferenceExceptionOnDisposal
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void AddBoundInstance_Disposed_ThrowsObjectDisposedException()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -61,7 +58,6 @@ public void AddBoundInstance_Disposed_ThrowsObjectDisposedException()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetOrCreate_ValidActivatorDuringInitialization_Success()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -90,7 +86,6 @@ object GetOrCreateActivate(LifetimeContext getOrCreateContext, CompositionOperat
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetOrCreate_ValidActivatorAfterInitialization_Success()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -120,7 +115,6 @@ object Activator(LifetimeContext activatorContext, CompositionOperation activato
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetOrCreate_NullActivator_ThrowsNullReferenceException()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -139,7 +133,6 @@ object Activator(LifetimeContext activatorContext, CompositionOperation activato
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetOrCreate_NullOperation_ThrowsNullReferenceException()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -152,7 +145,6 @@ public void GetOrCreate_NullOperation_ThrowsNullReferenceException()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void FindContextWithin_NullSharingBoundary_ReturnsRoot()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -165,7 +157,6 @@ public void FindContextWithin_NullSharingBoundary_ReturnsRoot()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void FindContextWithin_UnknownSharingBoundary_ThrowsCompositionFailedException()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
@@ -178,7 +169,6 @@ public void FindContextWithin_UnknownSharingBoundary_ThrowsCompositionFailedExce
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ToString_NoParent_ReturnsExpected()
         {
             using (CompositionHost host = CompositionHost.CreateCompositionHost(new ExportDescriptorProvider[0]))
diff --git a/src/libraries/System.Composition.Runtime/src/System.Composition.Runtime.csproj b/src/libraries/System.Composition.Runtime/src/System.Composition.Runtime.csproj
index 25aab756fed343..cdd6654321fe49 100644
--- a/src/libraries/System.Composition.Runtime/src/System.Composition.Runtime.csproj
+++ b/src/libraries/System.Composition.Runtime/src/System.Composition.Runtime.csproj
@@ -1,9 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <RootNamespace>System.Composition</RootNamespace>
-    <AssemblyName>System.Composition.Runtime</AssemblyName>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Composition\CompositionContext.cs" />
@@ -14,9 +12,4 @@
     <Compile Include="System\Composition\Hosting\Core\CompositionContract.cs" />
     <Compile Include="System\Composition\Runtime\Util\Formatters.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
-    <Reference Include="System" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition.Runtime/tests/System.Composition.Runtime.Tests.csproj b/src/libraries/System.Composition.Runtime/tests/System.Composition.Runtime.Tests.csproj
index 8270d6438106e3..83e64920c6c6c4 100644
--- a/src/libraries/System.Composition.Runtime/tests/System.Composition.Runtime.Tests.csproj
+++ b/src/libraries/System.Composition.Runtime/tests/System.Composition.Runtime.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Composition\Hosting\Core\CompositionContractTests.cs" />
@@ -10,4 +10,10 @@
     <Compile Include="System\Composition\ExportFactoryTests.cs" />
     <Compile Include="System\Composition\ExportTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Composition.Runtime.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition.TypedParts/src/System.Composition.TypedParts.csproj b/src/libraries/System.Composition.TypedParts/src/System.Composition.TypedParts.csproj
index 2d6a799248f5d3..7294633de7eb83 100644
--- a/src/libraries/System.Composition.TypedParts/src/System.Composition.TypedParts.csproj
+++ b/src/libraries/System.Composition.TypedParts/src/System.Composition.TypedParts.csproj
@@ -1,9 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <RootNamespace>System.Composition</RootNamespace>
-    <AssemblyName>System.Composition.TypedParts</AssemblyName>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Composition\CompositionContextExtensions.cs" />
@@ -31,12 +29,8 @@
              Link="Common\System\Numerics\Hashing\HashHelpers.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Composition.AttributedModel\src\System.Composition.AttributedModel.csproj" />
-    <ProjectReference Include="..\..\System.Composition.Hosting\src\System.Composition.Hosting.csproj" />
-    <ProjectReference Include="..\..\System.Composition.Runtime\src\System.Composition.Runtime.csproj" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Composition.AttributedModel\src\System.Composition.AttributedModel.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Composition.Hosting\src\System.Composition.Hosting.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Composition.Runtime\src\System.Composition.Runtime.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition.TypedParts/tests/ContainerConfigurationTests.cs b/src/libraries/System.Composition.TypedParts/tests/ContainerConfigurationTests.cs
index 2edd7f7987eb33..480cd9e537f9df 100644
--- a/src/libraries/System.Composition.TypedParts/tests/ContainerConfigurationTests.cs
+++ b/src/libraries/System.Composition.TypedParts/tests/ContainerConfigurationTests.cs
@@ -15,7 +15,6 @@ namespace System.Composition.Hosting.Tests
     public class ContainerConfigurationTests
     {
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WithProvider_ValidProvider_RegistersProvider()
         {
             var configuration = new ContainerConfiguration();
@@ -62,7 +61,6 @@ public void WithProvider_NullProvider_ThrowsArgumentNullException()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WithDefaultConventions_PartWithNoMatchingConvention_Success()
         {
             var conventions = new ConventionBuilder();
@@ -77,7 +75,6 @@ public void WithDefaultConventions_PartWithNoMatchingConvention_Success()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WithDefaultConventions_IEnumerablePartsWithNoMatchingConvention_Success()
         {
             var conventions = new ConventionBuilder();
@@ -92,7 +89,6 @@ public void WithDefaultConventions_IEnumerablePartsWithNoMatchingConvention_Succ
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WithDefaultConventions_PartsArrayWithNoMatchingConvention_Success()
         {
             var conventions = new ConventionBuilder();
@@ -107,7 +103,6 @@ public void WithDefaultConventions_PartsArrayWithNoMatchingConvention_Success()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WithDefaultConventions_PartTNoMatchingConvention_Success()
         {
             var conventions = new ConventionBuilder();
@@ -143,7 +138,6 @@ public void WithDefaultConventions_AlreadyHasDefaultConventions_ThrowsInvalidOpe
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WithPartT_Convention_Success()
         {
             var conventions = new ConventionBuilder();
@@ -157,7 +151,6 @@ public void WithPartT_Convention_Success()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WithPart_Convention_Success()
         {
             var conventions = new ConventionBuilder();
@@ -179,7 +172,6 @@ public void WithPart_NullPartType_ThrowsArgumentNullException()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WithParts_Convention_Success()
         {
             var conventions = new ConventionBuilder();
@@ -262,7 +254,6 @@ public void WithAssemby_Null_ThrowsNullReferenceExceptionOnCreation()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_ExportedSubClass_Success()
         {
             CompositionHost container = new ContainerConfiguration()
@@ -283,7 +274,6 @@ public class Base
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_OpenGenericTypes_Success()
         {
             var conventions = new ConventionBuilder();
@@ -313,7 +303,6 @@ public EFRepository(IContainer test) { }
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_ImportConventionsWithInheritedProperties_Success()
         {
             var conventions = new ConventionBuilder();
@@ -341,7 +330,6 @@ public class BaseWithImport
         public class DerivedFromBaseWithImport : BaseWithImport { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_ExportConventionsWithInheritedProperties_Success()
         {
             var conventions = new ConventionBuilder();
@@ -363,7 +351,6 @@ public class BaseWithExport
         public class DerivedFromBaseWithExport : BaseWithExport { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_ExportsToInheritedProperties_DontInterfereWithBase()
         {
             var conventions = new ConventionBuilder();
@@ -387,7 +374,6 @@ public class BaseWithExport2
         public class DerivedFromBaseWithExport2 : BaseWithExport { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_HasConventions_ClassExportsAreNotInherited()
         {
             CompositionHost container = new ContainerConfiguration()
@@ -397,7 +383,6 @@ public void CreateContainer_HasConventions_ClassExportsAreNotInherited()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_HasConventions_PropertyExportsAreNotInherited()
         {
             CompositionHost container = new ContainerConfiguration()
@@ -420,7 +405,6 @@ public class DerivedFromBaseWithDeclaredExports : BaseWithDeclaredExports { }
         public class CustomExport : ExportAttribute { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_HasConventions_CustomAttributesAreNotInherited()
         {
             CompositionHost container = new ContainerConfiguration()
@@ -435,7 +419,6 @@ public class BaseWithCustomExport { }
         public class DerivedFromBaseWithCustomExport : BaseWithCustomExport { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_OpenGenericTypePart_Success()
         {
             ContainerConfiguration configuration = new ContainerConfiguration().WithParts(typeof(GenericExportedType<>));
@@ -489,7 +472,6 @@ public void CreateContainer_UnassignableType_ThrowsCompositionFailedException()
         public class ContractExportedType { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_AbstractOrStructType_Success()
         {
             ContainerConfiguration configuration = new ContainerConfiguration().WithParts(typeof(AbstractClass), typeof(StructType));
@@ -503,7 +485,6 @@ public abstract class AbstractClass { }
         public struct StructType { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_MetadataProperty_Success()
         {
             ContainerConfiguration configuration = new ContainerConfiguration().WithPart(typeof(MetadataProperty));
@@ -541,7 +522,6 @@ public class MetadataProperty
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreateContainer_MetadataClass_Success()
         {
             ContainerConfiguration configuration = new ContainerConfiguration().WithPart(typeof(MetadataClass));
diff --git a/src/libraries/System.Composition.TypedParts/tests/ReflectionTests.cs b/src/libraries/System.Composition.TypedParts/tests/ReflectionTests.cs
index 5ca91f762aa7d2..291a1e5bbf13a4 100644
--- a/src/libraries/System.Composition.TypedParts/tests/ReflectionTests.cs
+++ b/src/libraries/System.Composition.TypedParts/tests/ReflectionTests.cs
@@ -27,7 +27,6 @@ public class ReflectionTests
         /// revert to a default value during GetExport.
         /// </remarks>
         [ConditionalFact(nameof(HasMultiplerProcessors))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MultiThreadedGetExportsWorkWithImportingConstuctor()
         {
             var errors = new ConcurrentBag<Exception>();
diff --git a/src/libraries/System.Composition.TypedParts/tests/System.Composition.TypedParts.Tests.csproj b/src/libraries/System.Composition.TypedParts/tests/System.Composition.TypedParts.Tests.csproj
index b2a05265bb1e17..5701c13ee3fb59 100644
--- a/src/libraries/System.Composition.TypedParts/tests/System.Composition.TypedParts.Tests.csproj
+++ b/src/libraries/System.Composition.TypedParts/tests/System.Composition.TypedParts.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="ContainerConfigurationTests.cs" />
@@ -8,4 +8,12 @@
              Link="Common\System\Diagnostics\DebuggerAttributes.cs" />
     <Compile Include="ReflectionTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Composition.TypedParts.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Composition.Convention\src\System.Composition.Convention.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <!-- S.C.DataAnnotations targeting .NET Framework isn't live built anymore. -->
+    <Reference Include="System.ComponentModel.DataAnnotations" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition/tests/ActivationEventOrderingTests.cs b/src/libraries/System.Composition/tests/ActivationEventOrderingTests.cs
index d1e172e7672670..f023b805963b7d 100644
--- a/src/libraries/System.Composition/tests/ActivationEventOrderingTests.cs
+++ b/src/libraries/System.Composition/tests/ActivationEventOrderingTests.cs
@@ -31,7 +31,6 @@ public void OnImportsSatisfied()
     public class ActivationEventOrderingTests : ContainerTests
     {
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void OnImportsSatisfiedIsCalledAfterPropertyInjection()
         {
             var cc = CreateContainer(typeof(TracksImportSatisfaction), typeof(Imported));
diff --git a/src/libraries/System.Composition/tests/CardinalityTests.cs b/src/libraries/System.Composition/tests/CardinalityTests.cs
index 76b2b8bb9bcda5..149287cfa8721d 100644
--- a/src/libraries/System.Composition/tests/CardinalityTests.cs
+++ b/src/libraries/System.Composition/tests/CardinalityTests.cs
@@ -31,7 +31,6 @@ public UsesLog(ILog log) { }
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void RequestingOneWhereMultipleArePresentFails()
         {
             var c = CreateContainer(typeof(LogA), typeof(LogB));
@@ -42,7 +41,6 @@ public void RequestingOneWhereMultipleArePresentFails()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ImportingOneWhereMultipleArePresentFails()
         {
             var c = CreateContainer(typeof(LogA), typeof(LogB), typeof(UsesLog));
diff --git a/src/libraries/System.Composition/tests/CircularityTests.cs b/src/libraries/System.Composition/tests/CircularityTests.cs
index 707bdde3f2e6ac..98a4f0b36efdb3 100644
--- a/src/libraries/System.Composition/tests/CircularityTests.cs
+++ b/src/libraries/System.Composition/tests/CircularityTests.cs
@@ -116,7 +116,6 @@ public PrDepB(PrDepA a) { }
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CanHandleDefinitionCircularity()
         {
             var cc = CreateContainer(typeof(ACircular), typeof(BLazy));
@@ -126,7 +125,6 @@ public void CanHandleDefinitionCircularity()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CanHandleDefinitionCircularity2()
         {
             var cc = CreateContainer(typeof(ACircular), typeof(BLazy));
@@ -135,7 +133,6 @@ public void CanHandleDefinitionCircularity2()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void HandlesPropertyPropertyCircularity()
         {
             var cc = CreateContainer(typeof(PropertyPropertyA), typeof(PropertyPropertyB));
@@ -144,7 +141,6 @@ public void HandlesPropertyPropertyCircularity()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void HandlesPropertyPropertyCircularityReversed()
         {
             var cc = CreateContainer(typeof(PropertyPropertyA), typeof(PropertyPropertyB));
@@ -153,7 +149,6 @@ public void HandlesPropertyPropertyCircularityReversed()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void HandlesConstructorPropertyCircularity()
         {
             var cc = CreateContainer(typeof(ConstructorPropertyA), typeof(ConstructorPropertyB));
@@ -162,7 +157,6 @@ public void HandlesConstructorPropertyCircularity()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void HandlesConstructorPropertyCircularityReversed()
         {
             var cc = CreateContainer(typeof(ConstructorPropertyA), typeof(ConstructorPropertyB));
@@ -171,7 +165,6 @@ public void HandlesConstructorPropertyCircularityReversed()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void HandlesMetadataCircularity()
         {
             var cc = CreateContainer(typeof(MetadataCircularityA), typeof(MetadataCircularityB));
@@ -182,7 +175,6 @@ public void HandlesMetadataCircularity()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void SharedPartCanHaveNonPrereqDependencyOnSelf()
         {
             var cc = CreateContainer(typeof(NonPrereqSelfDependency));
@@ -191,7 +183,6 @@ public void SharedPartCanHaveNonPrereqDependencyOnSelf()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void PrerequisiteCircularitiesAreDetected()
         {
             var cc = CreateContainer(typeof(PrDepA), typeof(PrDepB));
diff --git a/src/libraries/System.Composition/tests/CompositionContextExtensionsTests.cs b/src/libraries/System.Composition/tests/CompositionContextExtensionsTests.cs
index 0ed5f7db05758f..6e555c5ab25a8a 100644
--- a/src/libraries/System.Composition/tests/CompositionContextExtensionsTests.cs
+++ b/src/libraries/System.Composition/tests/CompositionContextExtensionsTests.cs
@@ -15,7 +15,6 @@ public class CompositionContextExtensionsTests : ContainerTests
         public interface IUnregistered { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GettingAnOptionalExportThatDoesntExistReturnsNull()
         {
             var c = CreateContainer();
diff --git a/src/libraries/System.Composition/tests/ConcurrencyTests.cs b/src/libraries/System.Composition/tests/ConcurrencyTests.cs
index 8e76ea3b1196fd..6801f55a57d32e 100644
--- a/src/libraries/System.Composition/tests/ConcurrencyTests.cs
+++ b/src/libraries/System.Composition/tests/ConcurrencyTests.cs
@@ -28,7 +28,6 @@ public void OnImportsSatisfied()
         // This does not test the desired behaviour deterministically,
         // but is close enough to be repeatable at least on my machine :)
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void SharedInstancesAreNotVisibleUntilActivationCompletes()
         {
             var c = CreateContainer(typeof(PausesDuringActivation));
diff --git a/src/libraries/System.Composition/tests/ConstraintTests.cs b/src/libraries/System.Composition/tests/ConstraintTests.cs
index 03de969a50bef6..8efacc48748503 100644
--- a/src/libraries/System.Composition/tests/ConstraintTests.cs
+++ b/src/libraries/System.Composition/tests/ConstraintTests.cs
@@ -41,7 +41,6 @@ public class UnrelatedThings<TC, TP> : ObservableCollection<TC>, IUnrelatedThing
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GenericPartDiscoveryIgnoresAPartAndDoesntThrowAnExceptionWhenItsConstraintOnTypeParameterIsNotAssignableFromTheExportTarget()
         {
             var container = CreateContainer(typeof(ThingHandler<>), typeof(BookHandler<>));
@@ -53,7 +52,6 @@ public void GenericPartDiscoveryIgnoresAPartAndDoesntThrowAnExceptionWhenItsCons
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GenericPartDiscoveryIncludesAPartWhenItsConstraintOnTypeParameterIsAssignableFromTheExportTarget()
         {
             var container = CreateContainer(typeof(ThingHandler<>), typeof(BookHandler<>));
@@ -66,7 +64,6 @@ public void GenericPartDiscoveryIncludesAPartWhenItsConstraintOnTypeParameterIsA
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetExport_ComplexConstraint_ExportSuccessful()
         {
             CompositionContext container = CreateContainer(typeof(UnrelatedThings<,>));
@@ -79,7 +76,6 @@ public void GetExport_ComplexConstraint_ExportSuccessful()
 
         [Fact]
         [ActiveIssue("https://github.com/dotnet/runtime/issues/23356")]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetExport_WhereClause_ExportSuccessful()
         {
             CompositionContext container = CreateContainer(typeof(InheritedThings<,>));
diff --git a/src/libraries/System.Composition/tests/CustomerReportedMetadataBug.cs b/src/libraries/System.Composition/tests/CustomerReportedMetadataBug.cs
index bcb84b5e417a2a..5a9f99de980f79 100644
--- a/src/libraries/System.Composition/tests/CustomerReportedMetadataBug.cs
+++ b/src/libraries/System.Composition/tests/CustomerReportedMetadataBug.cs
@@ -37,7 +37,6 @@ public class LooseImporter
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void SampleServicesCorrectlyImported()
         {
             var container = new ContainerConfiguration()
diff --git a/src/libraries/System.Composition/tests/DictionaryImportTests.cs b/src/libraries/System.Composition/tests/DictionaryImportTests.cs
index 30dc2965e86414..8d2b9d0f2b8d54 100644
--- a/src/libraries/System.Composition/tests/DictionaryImportTests.cs
+++ b/src/libraries/System.Composition/tests/DictionaryImportTests.cs
@@ -68,7 +68,6 @@ private CompositionContext CreateContainer(params Type[] types)
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DictionaryImportsKeyedByMetadata()
         {
             var container = CreateContainer(new[] { typeof(ValueA), typeof(ValueB), typeof(Consumer) });
@@ -81,7 +80,6 @@ public void DictionaryImportsKeyedByMetadata()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DictionaryImportsReceiveMetadataFromNestedAdapters()
         {
             var container = CreateContainer(new[] { typeof(ValueA), typeof(ValueB), typeof(LazyConsumer) });
@@ -93,7 +91,6 @@ public void DictionaryImportsReceiveMetadataFromNestedAdapters()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WhenAMetadataKeyIsDuplicatedAnInformativeExceptionIsThrown()
         {
             var container = CreateContainer(typeof(ValueA), typeof(ValueA), typeof(Consumer));
@@ -102,7 +99,6 @@ public void WhenAMetadataKeyIsDuplicatedAnInformativeExceptionIsThrown()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WhenAMetadataKeyIsMissingAnInformativeExceptionIsThrown()
         {
             var container = CreateContainer(typeof(ValueA), typeof(ValueMissing), typeof(Consumer));
@@ -111,7 +107,6 @@ public void WhenAMetadataKeyIsMissingAnInformativeExceptionIsThrown()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WhenAMetadataValueIsOfTheWrongTypeAnInformativeExceptionIsThrown()
         {
             var container = CreateContainer(typeof(ValueA), typeof(NonStringValue), typeof(Consumer));
@@ -120,7 +115,6 @@ public void WhenAMetadataValueIsOfTheWrongTypeAnInformativeExceptionIsThrown()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DictionaryImportsCompatibleWithConventionBuilder()
         {
             var rb = new ConventionBuilder();
diff --git a/src/libraries/System.Composition/tests/DiscoveryTests.cs b/src/libraries/System.Composition/tests/DiscoveryTests.cs
index 2cfc58a60ded61..833001774e4e0b 100644
--- a/src/libraries/System.Composition/tests/DiscoveryTests.cs
+++ b/src/libraries/System.Composition/tests/DiscoveryTests.cs
@@ -40,7 +40,6 @@ public class IncompatibleRuleProperty
         public class NotDiscoverable { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DiscoversCustomExportAttributes()
         {
             var container = CreateContainer(typeof(UnfairRule));
@@ -49,7 +48,6 @@ public void DiscoversCustomExportAttributes()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DiscoversCustomExportAttributesUnderConventions()
         {
             var container = CreateContainer(new ConventionBuilder(), typeof(UnfairRule));
@@ -58,7 +56,6 @@ public void DiscoversCustomExportAttributesUnderConventions()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void InstanceExportsOfIncompatibleContractsAreDetected()
         {
             var x = Assert.Throws<CompositionFailedException>(() => CreateContainer(typeof(IncompatibleRule)));
@@ -66,7 +63,6 @@ public void InstanceExportsOfIncompatibleContractsAreDetected()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void PropertyExportsOfIncompatibleContractsAreDetected()
         {
             var x = Assert.Throws<CompositionFailedException>(() => CreateContainer(typeof(IncompatibleRuleProperty)));
@@ -74,7 +70,6 @@ public void PropertyExportsOfIncompatibleContractsAreDetected()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ANonDiscoverablePartIsIgnored()
         {
             var container = CreateContainer(typeof(NotDiscoverable));
@@ -90,7 +85,6 @@ public class CloudBus : IBus { }
         public class SpecialCloudBus : CloudBus { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DoesNotDiscoverExportAttributesFromBase()
         {
             var container = CreateContainer(typeof(SpecialCloudBus));
@@ -111,7 +105,6 @@ public class HomeController : BaseController
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void SatisfiesImportsAppliedToBase()
         {
             var container = CreateContainer(typeof(HomeController), typeof(CloudBus));
@@ -129,7 +122,6 @@ public class MultipleImportsOnProperty
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MultipleImportAttributesAreDetected()
         {
             var c = new ContainerConfiguration()
diff --git a/src/libraries/System.Composition/tests/ErrorMessageQualityTests.cs b/src/libraries/System.Composition/tests/ErrorMessageQualityTests.cs
index be67604f86647a..f0918e392c29c3 100644
--- a/src/libraries/System.Composition/tests/ErrorMessageQualityTests.cs
+++ b/src/libraries/System.Composition/tests/ErrorMessageQualityTests.cs
@@ -63,7 +63,6 @@ public class RequiresOnlyOne
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MissingTopLevelExportMessageIsInformative()
         {
             var cc = CreateContainer();
@@ -72,7 +71,6 @@ public void MissingTopLevelExportMessageIsInformative()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MissingTopLevelNamedExportMessageIsInformative()
         {
             var cc = CreateContainer();
@@ -81,7 +79,6 @@ public void MissingTopLevelNamedExportMessageIsInformative()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MissingDependencyMessageIsInformative()
         {
             var cc = CreateContainer(typeof(UserOfUnregistered));
@@ -92,7 +89,6 @@ public void MissingDependencyMessageIsInformative()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CycleMessageIsInformative()
         {
             var cc = CreateContainer(typeof(CycleA), typeof(CycleB), typeof(CycleC));
@@ -106,7 +102,6 @@ public void CycleMessageIsInformative()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CardinalityViolationMessageIsInformative()
         {
             var cc = CreateContainer(typeof(ShouldBeOne), typeof(ButThereIsAnother), typeof(RequiresOnlyOne));
diff --git a/src/libraries/System.Composition/tests/ExportDescriptorProviderTests.cs b/src/libraries/System.Composition/tests/ExportDescriptorProviderTests.cs
index a0371ccf9232e2..f0d941b548638e 100644
--- a/src/libraries/System.Composition/tests/ExportDescriptorProviderTests.cs
+++ b/src/libraries/System.Composition/tests/ExportDescriptorProviderTests.cs
@@ -40,7 +40,6 @@ public class ExportsObject
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ProvidersCanLocateImplementationsOfAContractItSupports()
         {
             var container = new ContainerConfiguration()
@@ -53,7 +52,6 @@ public void ProvidersCanLocateImplementationsOfAContractItSupports()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ProvidersCanDetectAbsenceOfAContractItSupports()
         {
             var container = new ContainerConfiguration()
diff --git a/src/libraries/System.Composition/tests/ExportFactoryTests.cs b/src/libraries/System.Composition/tests/ExportFactoryTests.cs
index 385f8b177147f3..ba9b2757e0f401 100644
--- a/src/libraries/System.Composition/tests/ExportFactoryTests.cs
+++ b/src/libraries/System.Composition/tests/ExportFactoryTests.cs
@@ -105,7 +105,6 @@ public void Dispose()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void SharedPartsAreSharedBetweenAllScopes()
         {
             var cc = CreateContainer(typeof(SharedUnbounded), typeof(DataConsistencyBoundaryProvider));
@@ -116,7 +115,6 @@ public void SharedPartsAreSharedBetweenAllScopes()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void TheSameSharedInstanceIsReusedWithinItsSharingBoundary()
         {
             var cc = CreateContainer(typeof(SharedBoundedByDC), typeof(SharedPartConsumer), typeof(DataConsistencyBoundaryProvider));
@@ -130,7 +128,6 @@ public void TheSameSharedInstanceIsReusedWithinItsSharingBoundary()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void NonSharedInstancesCreatedByAnExportFactoryAreControlledByTheirExportLifetimeContext()
         {
             var cc = CreateContainer(typeof(A), typeof(UseExportFactory));
@@ -143,7 +140,6 @@ public void NonSharedInstancesCreatedByAnExportFactoryAreControlledByTheirExport
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DependenciesOfSharedPartsAreResolvedInTheGlobalScope()
         {
             var cc = new ContainerConfiguration()
@@ -159,7 +155,6 @@ public void DependenciesOfSharedPartsAreResolvedInTheGlobalScope()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WhenABoundaryIsPresentBoundedPartsCannotBeCreatedOutsideIt()
         {
             var container = CreateContainer(typeof(DataConsistencyBoundaryProvider), typeof(SharedBoundedByDC));
@@ -167,7 +162,6 @@ public void WhenABoundaryIsPresentBoundedPartsCannotBeCreatedOutsideIt()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void TheProductOfAnExportFactoryCanBeDisposedDuringDisposalOfTheParent()
         {
             var container = new ContainerConfiguration()
@@ -199,7 +193,6 @@ public class AConsumer
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ExportFactoryCanBeComposedWithImportManyAndNames()
         {
             var cc = CreateContainer(typeof(AConsumer), typeof(A1), typeof(A2));
@@ -233,7 +226,6 @@ public class HasFactory
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void WhenReleasingAnExportFromAnExportFactoryItsNonSharedDependenciesAreDisposed()
         {
             var cc = CreateContainer(typeof(Disposable), typeof(HasDisposableDependency), typeof(HasFactory));
diff --git a/src/libraries/System.Composition/tests/ExportMetadataDiscoveryTests.cs b/src/libraries/System.Composition/tests/ExportMetadataDiscoveryTests.cs
index f20437e16474a2..28f7e822a498d5 100644
--- a/src/libraries/System.Composition/tests/ExportMetadataDiscoveryTests.cs
+++ b/src/libraries/System.Composition/tests/ExportMetadataDiscoveryTests.cs
@@ -51,7 +51,6 @@ public class Prioritized {[DefaultValue(0)] public int Priority { get; set; } }
         public class MultipleNames { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DiscoversMetadataSpecifiedUsingMetadataAttributeOnExportAttribute()
         {
             var cc = CreateContainer(typeof(SingleNamedExport));
@@ -60,7 +59,6 @@ public void DiscoversMetadataSpecifiedUsingMetadataAttributeOnExportAttribute()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void IfMetadataIsSpecifiedOnAnExportAttributeOtherExportsDoNotHaveIt()
         {
             var cc = CreateContainer(typeof(MultipleExportsOneNamedAndBothPrioritized));
@@ -70,7 +68,6 @@ public void IfMetadataIsSpecifiedOnAnExportAttributeOtherExportsDoNotHaveIt()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DiscoversStandaloneExportMetadata()
         {
             var cc = CreateContainer(typeof(NamedAndPrioritized));
@@ -79,7 +76,6 @@ public void DiscoversStandaloneExportMetadata()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DiscoversStandaloneExportMetadataUsingMetadataAttributes()
         {
             var cc = CreateContainer(typeof(NamedWithCustomMetadata));
@@ -88,7 +84,6 @@ public void DiscoversStandaloneExportMetadataUsingMetadataAttributes()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void StandaloneExportMetadataAppliesToAllExportsOnAMember()
         {
             var cc = CreateContainer(typeof(MultipleExportsOneNamedAndBothPrioritized));
@@ -98,7 +93,6 @@ public void StandaloneExportMetadataAppliesToAllExportsOnAMember()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MultiplePiecesOfMetadataAreCombinedIntoAnArray()
         {
             var cc = CreateContainer(typeof(MultipleNames));
@@ -119,7 +113,6 @@ public MultipleExportsNonDefaultConstructor(ConstructorImported c) { }
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MultipleExportsCanBeRetrievedWhenANonDefaultConstructorExists()
         {
             var c = CreateContainer(typeof(ConstructorImported), typeof(MultipleExportsNonDefaultConstructor));
diff --git a/src/libraries/System.Composition/tests/ImportManyTests.cs b/src/libraries/System.Composition/tests/ImportManyTests.cs
index 63a4c7674446bd..f9c02063055a6f 100644
--- a/src/libraries/System.Composition/tests/ImportManyTests.cs
+++ b/src/libraries/System.Composition/tests/ImportManyTests.cs
@@ -41,7 +41,6 @@ public ImportManyPropsOfA()
             }
         }
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ImportsMany()
         {
             var cc = CreateContainer(typeof(A), typeof(A2), typeof(ImportManyIA));
@@ -50,7 +49,6 @@ public void ImportsMany()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ImportsManyProperties()
         {
             var cc = CreateContainer(typeof(A), typeof(A2), typeof(ImportManyPropsOfA));
diff --git a/src/libraries/System.Composition/tests/ImportOrderingTests.cs b/src/libraries/System.Composition/tests/ImportOrderingTests.cs
index 717f38b30ba401..0372c95e797bf7 100644
--- a/src/libraries/System.Composition/tests/ImportOrderingTests.cs
+++ b/src/libraries/System.Composition/tests/ImportOrderingTests.cs
@@ -48,7 +48,6 @@ public class HasImportedItems
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CollectionsImportedWithAnOrderingAttributeComeInOrder()
         {
             var container = CreateExtendedContainer(typeof(HasImportedItems), typeof(Item1), typeof(Item4), typeof(Item2), typeof(Item3));
@@ -62,7 +61,6 @@ public void CollectionsImportedWithAnOrderingAttributeComeInOrder()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void IfAnItemIsMissingMetadataAnInformativeExceptionIsThrown()
         {
             var container = CreateExtendedContainer(typeof(HasImportedItems), typeof(Item1), typeof(ItemWithoutOrder));
diff --git a/src/libraries/System.Composition/tests/InheritanceTests.cs b/src/libraries/System.Composition/tests/InheritanceTests.cs
index 79292823345eac..43d1f276723b70 100644
--- a/src/libraries/System.Composition/tests/InheritanceTests.cs
+++ b/src/libraries/System.Composition/tests/InheritanceTests.cs
@@ -25,7 +25,6 @@ public class Base
         public class Derived : Base { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ClassExportsAreNotInherited()
         {
             var cc = CreateContainer(typeof(Derived));
@@ -34,7 +33,6 @@ public void ClassExportsAreNotInherited()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void PropertyExportsAreNotInherited()
         {
             var cc = CreateContainer(typeof(Derived));
@@ -46,7 +44,6 @@ public void PropertyExportsAreNotInherited()
         public class ExportingDerived : Base { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ExportsAtTheClassLevelAreAppliedIgnoringBaseExports()
         {
             var cc = CreateContainer(typeof(ExportingDerived));
@@ -87,7 +84,6 @@ public class OverridingImporter : BaseImporter
         public class NonOverridingImporter : BaseImporter { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ImportsOnOverriddenPropertiesOverrideImportsOnTheBase()
         {
             var c = CreateContainer(typeof(Exporter), typeof(OverridingImporter), typeof(NonOverridingImporter));
@@ -98,7 +94,6 @@ public void ImportsOnOverriddenPropertiesOverrideImportsOnTheBase()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void LooseImportsOnDerivedPropertiesOverrideImportsOnTheBase()
         {
             var c = CreateContainer(typeof(Exporter));
@@ -111,7 +106,6 @@ public void LooseImportsOnDerivedPropertiesOverrideImportsOnTheBase()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ImportsOnBaseAreInherited()
         {
             var c = CreateContainer(typeof(Exporter), typeof(NonOverridingImporter));
@@ -121,7 +115,6 @@ public void ImportsOnBaseAreInherited()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void LooseImportsOnBaseAreInherited()
         {
             var c = CreateContainer(typeof(Exporter));
@@ -137,7 +130,6 @@ public class NotDiscoverableBase { }
         public class DiscoverableDerived : NotDiscoverableBase { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void PartNotDiscoverableAttributeIsNotInherited()
         {
             var c = CreateContainer(typeof(DiscoverableDerived));
@@ -152,7 +144,6 @@ public class SharedBase { }
         public class SharedDerived : SharedBase { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void PartMetadataIsNotInherited()
         {
             var c = CreateContainer(typeof(SharedDerived));
@@ -173,7 +164,6 @@ public class HasImportsSatisfied
         public class InheritsImportsSatisfied : HasImportsSatisfied { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void OnImportsSatisfiedAttributeIsInherited()
         {
             var c = CreateContainer(typeof(InheritsImportsSatisfied));
@@ -192,7 +182,6 @@ public class AHandler : IHandler { }
         public class ABHandler : AHandler { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MetadataIsOnlyDrawnFromTheTypeToWhichItIsApplied()
         {
             var c = CreateContainer(typeof(ABHandler));
@@ -214,7 +203,6 @@ public class DerivedOverrideExporter : BaseVirtualExporter
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ExportsOnOverridePropertiesOverrideExportsOnTheBase()
         {
             var c = CreateContainer(typeof(DerivedOverrideExporter));
diff --git a/src/libraries/System.Composition/tests/LazyTests.cs b/src/libraries/System.Composition/tests/LazyTests.cs
index 0af4972d8a22f1..75899fa7abb010 100644
--- a/src/libraries/System.Composition/tests/LazyTests.cs
+++ b/src/libraries/System.Composition/tests/LazyTests.cs
@@ -35,7 +35,6 @@ public class NamedFred { }
         public class Named { public string Name { get; set; } }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ComposesLazily()
         {
             var cc = CreateContainer(typeof(A), typeof(BLazy));
@@ -44,7 +43,6 @@ public void ComposesLazily()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void SupportsExportMetadata()
         {
             var cc = CreateContainer(typeof(NamedFred));
@@ -53,7 +51,6 @@ public void SupportsExportMetadata()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ReturnsExportMetadataAsADictionary()
         {
             var cc = CreateContainer(typeof(NamedFred));
@@ -75,7 +72,6 @@ public class AConsumer
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void LazyCanBeComposedWithImportManyAndNames()
         {
             var cc = CreateContainer(typeof(AConsumer), typeof(A1), typeof(A2));
diff --git a/src/libraries/System.Composition/tests/LightContainerTests.cs b/src/libraries/System.Composition/tests/LightContainerTests.cs
index 1ce818bf48f789..a7933d5656191f 100644
--- a/src/libraries/System.Composition/tests/LightContainerTests.cs
+++ b/src/libraries/System.Composition/tests/LightContainerTests.cs
@@ -53,7 +53,6 @@ public class HasPropertyA
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CreatesInstanceWithNoDependencies()
         {
             var cc = CreateContainer(typeof(A));
@@ -62,7 +61,6 @@ public void CreatesInstanceWithNoDependencies()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DefaultLifetimeIsNonShared()
         {
             var cc = CreateContainer(typeof(A));
@@ -72,7 +70,6 @@ public void DefaultLifetimeIsNonShared()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void Composes()
         {
             var cc = CreateContainer(typeof(A), typeof(B));
@@ -81,7 +78,6 @@ public void Composes()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CanSpecifyExportsWithConventionBuilder()
         {
             var rb = new ConventionBuilder();
@@ -92,7 +88,6 @@ public void CanSpecifyExportsWithConventionBuilder()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CanSpecifyLifetimeWithConventionBuilder()
         {
             var rb = new ConventionBuilder();
@@ -104,7 +99,6 @@ public void CanSpecifyLifetimeWithConventionBuilder()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void InjectsPropertyImports()
         {
             var rb = new ConventionBuilder();
@@ -115,7 +109,6 @@ public void InjectsPropertyImports()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void VerifyAssemblyNameCanBeUsedWithContainer()
         {
             var test = new ContainerConfiguration()
@@ -127,7 +120,6 @@ public void VerifyAssemblyNameCanBeUsedWithContainer()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void VerifyAssemblyWithTwoBaseTypeWithOnlyOneExportedWorks()
         {
             var test = new ContainerConfiguration()
diff --git a/src/libraries/System.Composition/tests/LooseImportsTests.cs b/src/libraries/System.Composition/tests/LooseImportsTests.cs
index cf7d03bbba2ee6..0dfd80c996eb3b 100644
--- a/src/libraries/System.Composition/tests/LooseImportsTests.cs
+++ b/src/libraries/System.Composition/tests/LooseImportsTests.cs
@@ -23,7 +23,6 @@ public class SaveChangesAttribute
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void SatisfyImportsSetsLooseImportsOnAttributedPart()
         {
             var container = CreateContainer(typeof(Transaction));
diff --git a/src/libraries/System.Composition/tests/MetadataConstraintTests.cs b/src/libraries/System.Composition/tests/MetadataConstraintTests.cs
index 0b95b0dae40be4..4f6429612bf30e 100644
--- a/src/libraries/System.Composition/tests/MetadataConstraintTests.cs
+++ b/src/libraries/System.Composition/tests/MetadataConstraintTests.cs
@@ -31,7 +31,6 @@ public class ManySettingUser
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void AnImportMetadataConstraintMatchesMetadataOnTheExport()
         {
             var cc = CreateContainer(typeof(SomeSetting), typeof(SomeSettingUser));
@@ -40,7 +39,6 @@ public void AnImportMetadataConstraintMatchesMetadataOnTheExport()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void AnImportMetadataConstraintMatchesMetadataOnTheExportEvenIfDiscoveryHasCompletedForTheExport()
         {
             var cc = CreateContainer(typeof(SomeSetting), typeof(SomeSettingUser));
@@ -50,7 +48,6 @@ public void AnImportMetadataConstraintMatchesMetadataOnTheExportEvenIfDiscoveryH
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ImportMetadataConstraintsComposeWithOtherRelationshipTypes()
         {
             var cc = CreateContainer(typeof(SomeSetting), typeof(ManySettingUser));
@@ -62,7 +59,6 @@ public void ImportMetadataConstraintsComposeWithOtherRelationshipTypes()
         public class SomeSetting<T> { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ConstraintsCanBeAppliedToGenerics()
         {
             var contract = new CompositionContract(typeof(SomeSetting<string>), null, new Dictionary<string, object>
@@ -86,7 +82,6 @@ public class Controller
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ItemEqualityIsUsedWhenMatchingMetadataValuesThatAreArrays()
         {
             var c = CreateContainer(typeof(Presenter), typeof(Controller));
diff --git a/src/libraries/System.Composition/tests/MetadataTests.cs b/src/libraries/System.Composition/tests/MetadataTests.cs
index f9740fa56a88d6..77343806aadc83 100644
--- a/src/libraries/System.Composition/tests/MetadataTests.cs
+++ b/src/libraries/System.Composition/tests/MetadataTests.cs
@@ -31,7 +31,6 @@ public class MetadataCircularityB
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void HandlesMetadataCircularity()
         {
             var cc = CreateContainer(typeof(MetadataCircularityA), typeof(MetadataCircularityB));
@@ -90,7 +89,6 @@ public class MultiValuedName { public string[] Name { get; set; } }
         public class Prioritized {[DefaultValue(0)] public int Priority { get; set; } }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MultipleMetadataAttributesWithAPropertyThatReturnsNull()
         {
             var cc = CreateContainer(typeof(NameNullTwiceExport));
@@ -99,7 +97,6 @@ public void MultipleMetadataAttributesWithAPropertyThatReturnsNull()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DiscoversMetadataSpecifiedUsingMetadataAttributeOnExportAttribute()
         {
             var cc = CreateContainer(typeof(SingleNamedExport));
@@ -108,7 +105,6 @@ public void DiscoversMetadataSpecifiedUsingMetadataAttributeOnExportAttribute()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void IfMetadataIsSpecifiedOnAnExportAttributeOtherExportsDoNotHaveIt()
         {
             var cc = CreateContainer(typeof(MultipleExportsOneNamedAndBothPrioritized));
@@ -118,7 +114,6 @@ public void IfMetadataIsSpecifiedOnAnExportAttributeOtherExportsDoNotHaveIt()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DiscoversStandaloneExportMetadata()
         {
             var cc = CreateContainer(typeof(NamedAndPrioritized));
@@ -127,7 +122,6 @@ public void DiscoversStandaloneExportMetadata()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void DiscoversStandaloneExportMetadataUsingMetadataAttributes()
         {
             var cc = CreateContainer(typeof(NamedWithCustomMetadata));
@@ -136,7 +130,6 @@ public void DiscoversStandaloneExportMetadataUsingMetadataAttributes()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void StandaloneExportMetadataAppliesToAllExportsOnAMember()
         {
             var cc = CreateContainer(typeof(MultipleExportsOneNamedAndBothPrioritized));
@@ -146,7 +139,6 @@ public void StandaloneExportMetadataAppliesToAllExportsOnAMember()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MultiplePiecesOfMetadataAreCombinedIntoAnArray()
         {
             var cc = CreateContainer(typeof(MultipleNames));
@@ -160,7 +152,6 @@ public void MultiplePiecesOfMetadataAreCombinedIntoAnArray()
         public class NamedFred { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void SupportsExportMetadata()
         {
             var cc = CreateContainer(typeof(NamedFred));
diff --git a/src/libraries/System.Composition/tests/MetadataViewGenerationTests.cs b/src/libraries/System.Composition/tests/MetadataViewGenerationTests.cs
index a34ab54c1c884d..9786a7db1ae4fc 100644
--- a/src/libraries/System.Composition/tests/MetadataViewGenerationTests.cs
+++ b/src/libraries/System.Composition/tests/MetadataViewGenerationTests.cs
@@ -21,7 +21,6 @@ public class HasNameA { }
         public class Named { public string Name { get; set; } }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void AConcreteTypeWithWritablePropertiesIsAMetadataView()
         {
             var cc = new ContainerConfiguration()
@@ -39,7 +38,6 @@ public class HasNoName { }
         public class OptionallyNamed {[DefaultValue("B")] public string Name { get; set; } }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MetadataViewsCanCarryDefaultValues()
         {
             var cc = new ContainerConfiguration()
@@ -62,7 +60,6 @@ public DictionaryName(IDictionary<string, object> metadata)
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void AConcreteTypeWithDictionaryConstructorIsAMetadataView()
         {
             var cc = new ContainerConfiguration()
@@ -80,7 +77,6 @@ public InvalidConcreteView(string unsupported) { }
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void AConcreteTypeWithUnsupportedConstructorsCannotBeUsedAsAMetadataView()
         {
             var cc = new ContainerConfiguration()
@@ -105,7 +101,6 @@ public class ImportsWithMetadataInterface
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void UnsupportedMetadataViewMessageIsInformative()
         {
             var cc = new ContainerConfiguration().WithParts(typeof(ImportsWithMetadataInterface), typeof(ExportsWithMetadata)).CreateContainer();
@@ -123,7 +118,6 @@ public class ReadonlyNameOrderMetadata
         public class HasOrder { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ReadOnlyPropertiesOnMetadataViewsAreIgnored()
         {
             var c = new ContainerConfiguration()
diff --git a/src/libraries/System.Composition/tests/Microsoft.Composition.Demos.ExtendedCollectionImports/Microsoft.Composition.Demos.ExtendedCollectionImports.csproj b/src/libraries/System.Composition/tests/Microsoft.Composition.Demos.ExtendedCollectionImports/Microsoft.Composition.Demos.ExtendedCollectionImports.csproj
index 83405db2622453..13c75ae1df6f08 100644
--- a/src/libraries/System.Composition/tests/Microsoft.Composition.Demos.ExtendedCollectionImports/Microsoft.Composition.Demos.ExtendedCollectionImports.csproj
+++ b/src/libraries/System.Composition/tests/Microsoft.Composition.Demos.ExtendedCollectionImports/Microsoft.Composition.Demos.ExtendedCollectionImports.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>Microsoft.Composition.Demos.ExtendedCollectionImports</AssemblyName>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Dictionaries\DictionaryExportDescriptorProvider.cs" />
@@ -10,4 +9,7 @@
     <Compile Include="OrderedCollections\OrderedImportManyExportDescriptorProvider.cs" />
     <Compile Include="KeyByMetadataAttribute.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Composition.TypedParts\src\System.Composition.TypedParts.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition/tests/OpenGenericsTests.cs b/src/libraries/System.Composition/tests/OpenGenericsTests.cs
index 22c1c2c10348c5..a7eec57c15b096 100644
--- a/src/libraries/System.Composition/tests/OpenGenericsTests.cs
+++ b/src/libraries/System.Composition/tests/OpenGenericsTests.cs
@@ -64,7 +64,6 @@ private class SomeGenericType<T> { }
         private class ExportsBase<T> : SomeGenericType<T> { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CanExportBasicOpenGeneric()
         {
             var cc = CreateContainer(typeof(BasicRepository<>));
@@ -73,7 +72,6 @@ public void CanExportBasicOpenGeneric()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void OpenGenericProvidesMultipleInstantiations()
         {
             var cc = CreateContainer(typeof(BasicRepository<>));
@@ -83,7 +81,6 @@ public void OpenGenericProvidesMultipleInstantiations()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CanExportOpenGenericProperty()
         {
             var cc = CreateContainer(typeof(RepositoryProperty<>));
@@ -92,7 +89,6 @@ public void CanExportOpenGenericProperty()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ASharedOpenGenericWithTwoExportsIsProvidedByASingleInstance()
         {
             var cc = CreateContainer(typeof(TwoGenericExports<>));
@@ -104,7 +100,6 @@ public void ASharedOpenGenericWithTwoExportsIsProvidedByASingleInstance()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void APartWithMultipleGenericExportsIsOnlyDiscoveredOnce()
         {
             var cc = CreateContainer(typeof(BasicRepository<>), typeof(TwoGenericExports<>));
@@ -118,7 +113,6 @@ public void APartWithMultipleGenericExportsIsOnlyDiscoveredOnce()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MultipleGenericExportsCanBeSpecifiedAtTheClassLevel()
         {
             var cc = CreateContainer(typeof(FirstAndSecond<>));
@@ -129,7 +123,6 @@ public void MultipleGenericExportsCanBeSpecifiedAtTheClassLevel()
         // In future, the set of allowable generic type mappings will be expanded (see
         // ignored tests above).
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void TypesWithMismatchedGenericParameterListsAreDetectedDuringDiscovery()
         {
             var x = Assert.Throws<CompositionFailedException>(() => CreateContainer(typeof(RepositoryWithKey<,>)));
@@ -137,7 +130,6 @@ public void TypesWithMismatchedGenericParameterListsAreDetectedDuringDiscovery()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void TypesWithNonGenericExportsAreDetectedDuringDiscovery()
         {
             var x = Assert.Throws<CompositionFailedException>(() => CreateContainer(typeof(RepositoryWithNonGenericExport<>)));
@@ -145,7 +137,6 @@ public void TypesWithNonGenericExportsAreDetectedDuringDiscovery()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void OpenGenericsCanExportSelf()
         {
             var cc = CreateContainer(typeof(ExportSelf<>));
@@ -154,7 +145,6 @@ public void OpenGenericsCanExportSelf()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void OpenGenericsCanExportBase()
         {
             var cc = CreateContainer(typeof(ExportsBase<>));
diff --git a/src/libraries/System.Composition/tests/OptionalImportTests.cs b/src/libraries/System.Composition/tests/OptionalImportTests.cs
index d2290da93caedb..6db89fb08db287 100644
--- a/src/libraries/System.Composition/tests/OptionalImportTests.cs
+++ b/src/libraries/System.Composition/tests/OptionalImportTests.cs
@@ -54,7 +54,6 @@ public Missing Missing
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MissingOptionalConstructorParametersAreSuppliedTheirDefaultValue()
         {
             var cc = CreateContainer(typeof(Supplied), typeof(HasOptionalConstructorParameter));
@@ -64,7 +63,6 @@ public void MissingOptionalConstructorParametersAreSuppliedTheirDefaultValue()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MissingOptionalPropertyImportsAreIgnored()
         {
             var cc = CreateContainer(typeof(Supplied), typeof(HasOptionalProperty));
diff --git a/src/libraries/System.Composition/tests/PropertyExportTests.cs b/src/libraries/System.Composition/tests/PropertyExportTests.cs
index 4f8af0b674aae8..84e94caed62993 100644
--- a/src/libraries/System.Composition/tests/PropertyExportTests.cs
+++ b/src/libraries/System.Composition/tests/PropertyExportTests.cs
@@ -19,7 +19,6 @@ public class Messenger
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CanExportProperty()
         {
             var cc = CreateContainer(typeof(Messenger));
@@ -44,7 +43,6 @@ public class Selfless
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ExportedPropertiesShareTheSameSharedPartInstance()
         {
             var cc = CreateContainer(typeof(SelfObsessed), typeof(Selfless));
diff --git a/src/libraries/System.Composition/tests/SharingTests.cs b/src/libraries/System.Composition/tests/SharingTests.cs
index 5154a12aca3cc3..826881f349c5df 100644
--- a/src/libraries/System.Composition/tests/SharingTests.cs
+++ b/src/libraries/System.Composition/tests/SharingTests.cs
@@ -318,7 +318,6 @@ public class SharingTest : ContainerTests
         /// we fail only when we create instance of B.. is that correct.
         /// </summary>
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void BoundaryExposedBoundaryButNoneImported()
         {
             try
@@ -338,7 +337,6 @@ public void BoundaryExposedBoundaryButNoneImported()
         /// Needs to be fixed so that specifying boundary would automatically create the shared
         /// </summary>
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void BoundarySharingTest()
         {
             var cc = CreateContainer(typeof(A), typeof(B), typeof(C), typeof(D));
@@ -360,7 +358,6 @@ public void BoundarySharingTest()
         /// CirA root of the composition has to be shared explicitly.
         /// </summary>
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void CircularBoundarySharingTest()
         {
             var cc = CreateContainer(typeof(CirA), typeof(CirB), typeof(CirC));
@@ -377,7 +374,6 @@ public void CircularBoundarySharingTest()
         /// Something is badly busted here.. I am getting a null ref exception
         /// </summary>
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void MultipleBoundarySpecified()
         {
             var cc = CreateContainer(typeof(ProjA), typeof(ProjB), typeof(SolA), typeof(DocA), typeof(DocB), typeof(ColA), typeof(ColB));
@@ -387,7 +383,6 @@ public void MultipleBoundarySpecified()
 
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void SharedPartExportingMultipleContractsSharesAnInstance()
         {
             var cc = CreateContainer(typeof(XY));
@@ -397,7 +392,6 @@ public void SharedPartExportingMultipleContractsSharesAnInstance()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetExportsCreatesInstancedObjectByDefault()
         {
             var cc = CreateContainer(typeof(NonSharedClass));
@@ -407,7 +401,6 @@ public void GetExportsCreatesInstancedObjectByDefault()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetExportsCreatesSharedObjectsWhenSpecified()
         {
             var cc = CreateContainer(typeof(SharedClass));
@@ -422,7 +415,6 @@ public void GetExportsCreatesSharedObjectsWhenSpecified()
         /// verify that On Method call different instances are returned.
         /// </summary>
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ExportFactoryCreatesNewInstances()
         {
             var cc = CreateContainer(typeof(ClassWithExportFactoryShared), typeof(NonSharedClass));
@@ -438,7 +430,6 @@ public void ExportFactoryCreatesNewInstances()
         /// ExportFactory should be importable as a property
         /// </summary>
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ClassWithExportFactoryAsAProperty()
         {
             var cc = CreateContainer(typeof(ClassWithExportFactoryAsAProperty), typeof(NonSharedClass));
@@ -455,7 +446,6 @@ public void ClassWithExportFactoryAsAProperty()
         /// is creating a part which is shared, it will return back the same instance of the part.
         /// </summary>
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ClassWithExportFactoryAndSharedExport()
         {
             var cc = CreateContainer(typeof(ClassWithExportFactoryShared), typeof(SharedClass));
@@ -472,7 +462,6 @@ public void ClassWithExportFactoryAndSharedExport()
         /// Two instances of the root class are created , the part created using export factory should not be shared
         /// </summary>
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ClassWithNonSharedExportFactoryCreatesSharedInstances()
         {
             var cc = CreateContainer(typeof(ClassWithExportFactoryNonShared), typeof(SharedClass));
@@ -488,7 +477,6 @@ public void ClassWithNonSharedExportFactoryCreatesSharedInstances()
         public class ASharedPart { }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void ConsistentResultsAreReturneWhenResolvingLargeNumbersOfSharedParts()
         {
             var config = new ContainerConfiguration();
diff --git a/src/libraries/System.Composition/tests/System.Composition.Tests.csproj b/src/libraries/System.Composition/tests/System.Composition.Tests.csproj
index 412844950a7a4b..2eace5fc8d2abf 100644
--- a/src/libraries/System.Composition/tests/System.Composition.Tests.csproj
+++ b/src/libraries/System.Composition/tests/System.Composition.Tests.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <RootNamespace>System.Composition.Lightweight.UnitTests</RootNamespace>
-    <AssemblyName>System.Composition.Tests</AssemblyName>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="ActivationEventOrderingTests.cs" />
@@ -36,7 +35,11 @@
     <Compile Include="Util\AssertX.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Composition.Convention\src\System.Composition.Convention.csproj" />
     <ProjectReference Include="Microsoft.Composition.Demos.ExtendedCollectionImports\Microsoft.Composition.Demos.ExtendedCollectionImports.csproj" />
     <ProjectReference Include="TestLibrary\TestLibrary.csproj" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.ComponentModel.Composition" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Composition/tests/TestLibrary/TestLibrary.csproj b/src/libraries/System.Composition/tests/TestLibrary/TestLibrary.csproj
index dd2b89535774b6..bc524e4f37f4e5 100644
--- a/src/libraries/System.Composition/tests/TestLibrary/TestLibrary.csproj
+++ b/src/libraries/System.Composition/tests/TestLibrary/TestLibrary.csproj
@@ -1,8 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="TestClass.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Composition.AttributedModel\src\System.Composition.AttributedModel.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Configuration.ConfigurationManager/ref/System.Configuration.ConfigurationManager.cs b/src/libraries/System.Configuration.ConfigurationManager/ref/System.Configuration.ConfigurationManager.cs
index df967acbbdfb20..29527d20cd521a 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/ref/System.Configuration.ConfigurationManager.cs
+++ b/src/libraries/System.Configuration.ConfigurationManager/ref/System.Configuration.ConfigurationManager.cs
@@ -607,7 +607,7 @@ public DictionarySectionHandler() { }
         protected virtual string ValueAttributeName { get { throw null; } }
         public virtual object Create(object parent, object context, System.Xml.XmlNode section) { throw null; }
     }
-    [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+    [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
     public sealed partial class DpapiProtectedConfigurationProvider : System.Configuration.ProtectedConfigurationProvider
     {
         public DpapiProtectedConfigurationProvider() { }
diff --git a/src/libraries/System.Configuration.ConfigurationManager/ref/System.Configuration.ConfigurationManager.csproj b/src/libraries/System.Configuration.ConfigurationManager/ref/System.Configuration.ConfigurationManager.csproj
index d4a6743c14150c..4adc0b2edb5f57 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/ref/System.Configuration.ConfigurationManager.csproj
+++ b/src/libraries/System.Configuration.ConfigurationManager/ref/System.Configuration.ConfigurationManager.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <NoWarn>$(NoWarn);CS0618</NoWarn>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -15,11 +14,6 @@
     <ProjectReference Include="..\..\System.Security.Permissions\ref\System.Security.Permissions.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(IsPartialFacadeAssembly)'  == 'true'">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Reference Include="System.Configuration" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.Drawing" />
-    <Reference Include="System.Xml" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Configuration.ConfigurationManager/src/System.Configuration.ConfigurationManager.csproj b/src/libraries/System.Configuration.ConfigurationManager/src/System.Configuration.ConfigurationManager.csproj
index 2d71eb3b7e3743..574ed1ed373959 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/src/System.Configuration.ConfigurationManager.csproj
+++ b/src/libraries/System.Configuration.ConfigurationManager/src/System.Configuration.ConfigurationManager.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -251,15 +250,10 @@
              Link="Common\System\IO\TempFileCollection.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
-    <Reference Include="System.Security.Cryptography.ProtectedData" />
-    <Reference Include="System.Security.Permissions" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.ProtectedData\src\System.Security.Cryptography.ProtectedData.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Permissions\src\System.Security.Permissions.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(IsPartialFacadeAssembly)' == 'true'">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
     <Reference Include="System.Configuration" />
-    <Reference Include="System.Drawing" />
-    <Reference Include="System.Xml" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/ClientConfigPaths.cs b/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/ClientConfigPaths.cs
index abb97375d82905..087cb3e1f7b6bf 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/ClientConfigPaths.cs
+++ b/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/ClientConfigPaths.cs
@@ -215,22 +215,38 @@ private static string GetTypeAndHashSuffix(string exePath)
                 AssemblyName assemblyName = assembly.GetName();
                 Uri codeBase = new Uri(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, assembly.ManifestModule.Name));
 
-                hash = IdentityHelper.GetNormalizedStrongNameHash(assemblyName);
+                try
+                {
+                    // Certain platforms may not have support for crypto
+                    hash = IdentityHelper.GetNormalizedStrongNameHash(assemblyName);
+                }
+                catch (PlatformNotSupportedException) { }
+
                 if (hash != null)
                 {
                     typeName = StrongNameDesc;
                 }
                 else
                 {
-                    hash = IdentityHelper.GetNormalizedUriHash(codeBase);
-                    typeName = UrlDesc;
+                    try
+                    {
+                        // Certain platforms may not have support for crypto
+                        hash = IdentityHelper.GetNormalizedUriHash(codeBase);
+                        typeName = UrlDesc;
+                    }
+                    catch (PlatformNotSupportedException) { }
                 }
             }
             else if (!string.IsNullOrEmpty(exePath))
             {
-                // Fall back on the exe name
-                hash = IdentityHelper.GetStrongHashSuitableForObjectName(exePath);
-                typeName = PathDesc;
+                try
+                {
+                    // Fall back on the exe name
+                    // Certain platforms may not have support for crypto
+                    hash = IdentityHelper.GetStrongHashSuitableForObjectName(exePath);
+                    typeName = PathDesc;
+                }
+                catch (PlatformNotSupportedException) { }
             }
 
             if (!string.IsNullOrEmpty(hash)) suffix = "_" + typeName + "_" + hash;
diff --git a/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/DpapiProtectedConfigurationProvider.cs b/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/DpapiProtectedConfigurationProvider.cs
index b6ada8acbfefa9..db546c8010316c 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/DpapiProtectedConfigurationProvider.cs
+++ b/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/DpapiProtectedConfigurationProvider.cs
@@ -9,7 +9,7 @@
 
 namespace System.Configuration
 {
-    [MinimumOSPlatform("windows7.0")]
+    [SupportedOSPlatform("windows")]
     public sealed class DpapiProtectedConfigurationProvider : ProtectedConfigurationProvider
     {
         private bool _useMachineProtection = true;
diff --git a/src/libraries/System.Configuration.ConfigurationManager/tests/Mono/GenericEnumConverterTest.cs b/src/libraries/System.Configuration.ConfigurationManager/tests/Mono/GenericEnumConverterTest.cs
index dd15eb2ebc95b0..039d6845e8ebfb 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/tests/Mono/GenericEnumConverterTest.cs
+++ b/src/libraries/System.Configuration.ConfigurationManager/tests/Mono/GenericEnumConverterTest.cs
@@ -49,9 +49,9 @@ public void Ctor_Null()
         }
 
         [Fact]
-        public void Ctor_TypeError()
+        public void Ctor_Object()
         {
-            GenericEnumConverter cv = new GenericEnumConverter(typeof(object));
+            Assert.NotNull(new GenericEnumConverter(typeof(object)));
         }
 
         [Fact]
diff --git a/src/libraries/System.Configuration.ConfigurationManager/tests/System.Configuration.ConfigurationManager.Tests.csproj b/src/libraries/System.Configuration.ConfigurationManager/tests/System.Configuration.ConfigurationManager.Tests.csproj
index e4572e3663fcc8..555d37eb2cb37b 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/tests/System.Configuration.ConfigurationManager.Tests.csproj
+++ b/src/libraries/System.Configuration.ConfigurationManager/tests/System.Configuration.ConfigurationManager.Tests.csproj
@@ -4,7 +4,7 @@
     <TestDisableAppDomain>true</TestDisableAppDomain>
     <TestDisableParallelization>true</TestDisableParallelization>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonTestPath)System\IO\TempDirectory.cs"
@@ -105,4 +105,10 @@
     <Compile Include="System\Configuration\ValidatiorUtilsTests.cs" />
     <Compile Include="System\Drawing\Configuration\SystemDrawingSectionTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Configuration.ConfigurationManager.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.Configuration" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/CallBackValidatorAttributeTests.cs b/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/CallBackValidatorAttributeTests.cs
index 2b400892b389cb..aa3b8f204d357c 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/CallBackValidatorAttributeTests.cs
+++ b/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/CallBackValidatorAttributeTests.cs
@@ -56,7 +56,7 @@ public void SuccessfulCallback_CallTwice()
                 Type = typeof(CallBackValidatorAttributeTests),
                 CallbackMethodName = "CallBackValidatorTestMethod"
             };
-            var response = testCallBackValidatorAttribute.ValidatorInstance;
+            _ = testCallBackValidatorAttribute.ValidatorInstance;
             Assert.IsType<CallbackValidator>(testCallBackValidatorAttribute.ValidatorInstance);
         }
 
diff --git a/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/SettingElementTests.cs b/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/SettingElementTests.cs
index 325c98ef014cc7..5ed74c72148578 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/SettingElementTests.cs
+++ b/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/SettingElementTests.cs
@@ -73,6 +73,9 @@ public void NonDefaultValueHasNonNullHashCode()
                     }
                 }
             };
+
+            // Validate the getting the hash code doesn't throw
+            _ = Element.GetHashCode();
         }
     }
 }
diff --git a/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/StringValidatorTests.cs b/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/StringValidatorTests.cs
index 981d54db02a99f..40cbf78668cfc2 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/StringValidatorTests.cs
+++ b/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/StringValidatorTests.cs
@@ -42,7 +42,7 @@ public void Validate_StringTooSmall()
         public void Validate_StringTooBig()
         {
             StringValidator validator = new StringValidator(5, 10);
-            ArgumentException thrownException = AssertExtensions.Throws<ArgumentException>(null, () => validator.Validate("This is more than ten"));
+            AssertExtensions.Throws<ArgumentException>(null, () => validator.Validate("This is more than ten"));
         }
 
         [Fact]
@@ -58,7 +58,7 @@ public void Validate_EmptyString()
         public void Validate_UsinginvalidCharacters(string stringToValidate)
         {
             StringValidator validator = new StringValidator(1, 20, "_-");
-            ArgumentException result = AssertExtensions.Throws<ArgumentException>(null, () => validator.Validate(stringToValidate));
+            AssertExtensions.Throws<ArgumentException>(null, () => validator.Validate(stringToValidate));
         }
 
         [Fact]
diff --git a/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/TypeUtilTests.cs b/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/TypeUtilTests.cs
index 52da2e86daa70c..d9420fb1c037c9 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/TypeUtilTests.cs
+++ b/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/TypeUtilTests.cs
@@ -46,15 +46,12 @@ public void GetType_NoAssemblyQualifcation(string typeString, Type expectedType)
 
         [Theory,
             // ConfigurationManager types roll forward
+            // ConfigurationManager isn't part of the shared framework and potentially app-local.
+            // https://github.com/dotnet/runtime/issues/12376#issuecomment-479670104 explains why testing the type roll forward behavior doesn't work in such cases.
             InlineData(
                 "System.Configuration.UserSettingsGroup, System.Configuration.ConfigurationManager, Version=1.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51",
-                typeof(UserSettingsGroup)),
-            // Mono doesn't care about the versioning here and will resolve the type back
-            InlineData(
-                "System.Configuration.UserSettingsGroup, System.Configuration.ConfigurationManager, Version=255.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51",
-                null)
+                typeof(UserSettingsGroup))
             ]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38351", TestRuntimes.Mono)]
         public void GetType_ConfigurationManagerTypes(string typeString, Type expectedType)
         {
             Assert.Equal(expectedType, TypeUtil.GetType(typeString, throwOnError: false));
diff --git a/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/UrlPathTests.cs b/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/UrlPathTests.cs
index dbcfea89d0f818..4619bec0f43023 100644
--- a/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/UrlPathTests.cs
+++ b/src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/UrlPathTests.cs
@@ -14,7 +14,7 @@ public class UrlPathTests
         public void GetDirectoryOrRootName_Null()
         {
             string test = UrlPath.GetDirectoryOrRootName(null);
-            Assert.Null(null);
+            Assert.Null(test);
         }
 
         [Fact]
diff --git a/src/libraries/System.Console/Directory.Build.props b/src/libraries/System.Console/Directory.Build.props
index 42c6eafce67ed8..d68d22c1b917f8 100644
--- a/src/libraries/System.Console/Directory.Build.props
+++ b/src/libraries/System.Console/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Console/ref/System.Console.cs b/src/libraries/System.Console/ref/System.Console.cs
index 20b7d335e046ef..6c17987a1b49d0 100644
--- a/src/libraries/System.Console/ref/System.Console.cs
+++ b/src/libraries/System.Console/ref/System.Console.cs
@@ -9,14 +9,14 @@ namespace System
     public static partial class Console
     {
         public static System.ConsoleColor BackgroundColor { get { throw null; } set { } }
-        public static int BufferHeight { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
-        public static int BufferWidth { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        public static int BufferHeight { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
+        public static int BufferWidth { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static bool CapsLock { get { throw null; } }
         public static int CursorLeft { get { throw null; } set { } }
-        public static int CursorSize { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
+        public static int CursorSize { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
         public static int CursorTop { get { throw null; } set { } }
-        public static bool CursorVisible { [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] get { throw null; } set { } }
+        public static bool CursorVisible { [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] get { throw null; } set { } }
         public static System.IO.TextWriter Error { get { throw null; } }
         public static System.ConsoleColor ForegroundColor { get { throw null; } set { } }
         public static System.IO.TextReader In { get { throw null; } }
@@ -27,25 +27,25 @@ public static partial class Console
         public static bool KeyAvailable { get { throw null; } }
         public static int LargestWindowHeight { get { throw null; } }
         public static int LargestWindowWidth { get { throw null; } }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static bool NumberLock { get { throw null; } }
         public static System.IO.TextWriter Out { get { throw null; } }
         public static System.Text.Encoding OutputEncoding { get { throw null; } set { } }
-        public static string Title { [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] get { throw null; } set { } }
+        public static string Title { [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] get { throw null; } set { } }
         public static bool TreatControlCAsInput { get { throw null; } set { } }
-        public static int WindowHeight { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
-        public static int WindowLeft { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
-        public static int WindowTop { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
-        public static int WindowWidth { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
+        public static int WindowHeight { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
+        public static int WindowLeft { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
+        public static int WindowTop { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
+        public static int WindowWidth { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
         public static event System.ConsoleCancelEventHandler? CancelKeyPress { add { } remove { } }
         public static void Beep() { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static void Beep(int frequency, int duration) { }
         public static void Clear() { }
         public static (int Left, int Top) GetCursorPosition() { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static void MoveBufferArea(int sourceLeft, int sourceTop, int sourceWidth, int sourceHeight, int targetLeft, int targetTop) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static void MoveBufferArea(int sourceLeft, int sourceTop, int sourceWidth, int sourceHeight, int targetLeft, int targetTop, char sourceChar, System.ConsoleColor sourceForeColor, System.ConsoleColor sourceBackColor) { }
         public static System.IO.Stream OpenStandardError() { throw null; }
         public static System.IO.Stream OpenStandardError(int bufferSize) { throw null; }
@@ -58,15 +58,15 @@ public static void MoveBufferArea(int sourceLeft, int sourceTop, int sourceWidth
         public static System.ConsoleKeyInfo ReadKey(bool intercept) { throw null; }
         public static string? ReadLine() { throw null; }
         public static void ResetColor() { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static void SetBufferSize(int width, int height) { }
         public static void SetCursorPosition(int left, int top) { }
         public static void SetError(System.IO.TextWriter newError) { }
         public static void SetIn(System.IO.TextReader newIn) { }
         public static void SetOut(System.IO.TextWriter newOut) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static void SetWindowPosition(int left, int top) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static void SetWindowSize(int width, int height) { }
         public static void Write(bool value) { }
         public static void Write(char value) { }
diff --git a/src/libraries/System.Console/src/System/Console.cs b/src/libraries/System.Console/src/System/Console.cs
index ed25ffe8599fad..ec589857c16138 100644
--- a/src/libraries/System.Console/src/System/Console.cs
+++ b/src/libraries/System.Console/src/System/Console.cs
@@ -277,17 +277,17 @@ static StrongBox<bool> EnsureInitialized()
         public static int CursorSize
         {
             get { return ConsolePal.CursorSize; }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set { ConsolePal.CursorSize = value; }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static bool NumberLock
         {
             get { return ConsolePal.NumberLock; }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static bool CapsLock
         {
             get { return ConsolePal.CapsLock; }
@@ -315,18 +315,18 @@ public static void ResetColor()
         public static int BufferWidth
         {
             get { return ConsolePal.BufferWidth; }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set { ConsolePal.BufferWidth = value; }
         }
 
         public static int BufferHeight
         {
             get { return ConsolePal.BufferHeight; }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set { ConsolePal.BufferHeight = value; }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static void SetBufferSize(int width, int height)
         {
             ConsolePal.SetBufferSize(width, height);
@@ -335,38 +335,38 @@ public static void SetBufferSize(int width, int height)
         public static int WindowLeft
         {
             get { return ConsolePal.WindowLeft; }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set { ConsolePal.WindowLeft = value; }
         }
 
         public static int WindowTop
         {
             get { return ConsolePal.WindowTop; }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set { ConsolePal.WindowTop = value; }
         }
 
         public static int WindowWidth
         {
             get { return ConsolePal.WindowWidth; }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set { ConsolePal.WindowWidth = value; }
         }
 
         public static int WindowHeight
         {
             get { return ConsolePal.WindowHeight; }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set { ConsolePal.WindowHeight = value; }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static void SetWindowPosition(int left, int top)
         {
             ConsolePal.SetWindowPosition(left, top);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static void SetWindowSize(int width, int height)
         {
             ConsolePal.SetWindowSize(width, height);
@@ -384,7 +384,7 @@ public static int LargestWindowHeight
 
         public static bool CursorVisible
         {
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             get { return ConsolePal.CursorVisible; }
             set { ConsolePal.CursorVisible = value; }
         }
@@ -413,7 +413,7 @@ public static (int Left, int Top) GetCursorPosition()
 
         public static string Title
         {
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             get { return ConsolePal.Title; }
             set
             {
@@ -426,19 +426,19 @@ public static void Beep()
             ConsolePal.Beep();
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static void Beep(int frequency, int duration)
         {
             ConsolePal.Beep(frequency, duration);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static void MoveBufferArea(int sourceLeft, int sourceTop, int sourceWidth, int sourceHeight, int targetLeft, int targetTop)
         {
             ConsolePal.MoveBufferArea(sourceLeft, sourceTop, sourceWidth, sourceHeight, targetLeft, targetTop, ' ', ConsoleColor.Black, BackgroundColor);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static void MoveBufferArea(int sourceLeft, int sourceTop, int sourceWidth, int sourceHeight, int targetLeft, int targetTop, char sourceChar, ConsoleColor sourceForeColor, ConsoleColor sourceBackColor)
         {
             ConsolePal.MoveBufferArea(sourceLeft, sourceTop, sourceWidth, sourceHeight, targetLeft, targetTop, sourceChar, sourceForeColor, sourceBackColor);
diff --git a/src/libraries/System.Console/src/System/IO/StdInReader.cs b/src/libraries/System.Console/src/System/IO/StdInReader.cs
index c60b0fd1f2a5ee..99ebbd34c61496 100644
--- a/src/libraries/System.Console/src/System/IO/StdInReader.cs
+++ b/src/libraries/System.Console/src/System/IO/StdInReader.cs
@@ -254,11 +254,6 @@ internal ConsoleKey GetKeyFromCharValue(char x, out bool isShift, out bool isCtr
                 case '\r':
                     return ConsoleKey.Enter;
 
-                case '\n':
-                    // Windows compatibility; LF is Ctrl+Enter
-                    isCtrl = true;
-                    return ConsoleKey.Enter;
-
                 case (char)(0x1B):
                     return ConsoleKey.Escape;
 
diff --git a/src/libraries/System.Console/tests/ManualTests/ManualTests.cs b/src/libraries/System.Console/tests/ManualTests/ManualTests.cs
index 4c019a908e2108..43688d799eba0f 100644
--- a/src/libraries/System.Console/tests/ManualTests/ManualTests.cs
+++ b/src/libraries/System.Console/tests/ManualTests/ManualTests.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 using Xunit;
 
@@ -67,17 +69,9 @@ public static void ReadKey()
         }
 
         [ConditionalTheory(nameof(ManualTestsEnabled))]
-        [InlineData('\x01', ConsoleKey.A, ConsoleModifiers.Control)]
-        [InlineData('\x01', ConsoleKey.A, ConsoleModifiers.Control | ConsoleModifiers.Alt)]
-        [InlineData('\r', ConsoleKey.Enter, (ConsoleModifiers)0)]
-        [InlineData('\n', ConsoleKey.Enter, ConsoleModifiers.Control)]
-        public static void ReadKey_KeyChords(char keyChar, ConsoleKey key, ConsoleModifiers modifiers)
+        [MemberData(nameof(GetKeyChords))]
+        public static void ReadKey_KeyChords(ConsoleKeyInfo expected)
         {
-            var expected = new ConsoleKeyInfo(keyChar, key, 
-                control: modifiers.HasFlag(ConsoleModifiers.Control),
-                alt: modifiers.HasFlag(ConsoleModifiers.Alt),
-                shift: modifiers.HasFlag(ConsoleModifiers.Shift));
-
             Console.Write($"Please type key chord {RenderKeyChord(expected)}: ");
             var actual = Console.ReadKey(intercept: true);
             Console.WriteLine();
@@ -96,6 +90,34 @@ static string RenderKeyChord(ConsoleKeyInfo key)
             }
         }
 
+        public static IEnumerable<object[]> GetKeyChords()
+        {
+            yield return MkConsoleKeyInfo('\x01', ConsoleKey.A, ConsoleModifiers.Control);
+            yield return MkConsoleKeyInfo('\x01', ConsoleKey.A, ConsoleModifiers.Control | ConsoleModifiers.Alt);
+            yield return MkConsoleKeyInfo('\r', ConsoleKey.Enter, (ConsoleModifiers)0);
+
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                // windows will report '\n' as 'Ctrl+Enter', which is typically not picked up by Unix terminals
+                yield return MkConsoleKeyInfo('\n', ConsoleKey.Enter, ConsoleModifiers.Control);
+            }
+            else
+            {
+                yield return MkConsoleKeyInfo('\n', ConsoleKey.J, ConsoleModifiers.Control);
+            }
+
+            static object[] MkConsoleKeyInfo (char keyChar, ConsoleKey consoleKey, ConsoleModifiers modifiers)
+            {
+                return new object[]
+                {
+                    new ConsoleKeyInfo(keyChar, consoleKey, 
+                        control: modifiers.HasFlag(ConsoleModifiers.Control),
+                        alt: modifiers.HasFlag(ConsoleModifiers.Alt),
+                        shift: modifiers.HasFlag(ConsoleModifiers.Shift))
+                };
+            }
+        }
+
         [ConditionalFact(nameof(ManualTestsEnabled))]
         public static void OpenStandardInput()
         {
diff --git a/src/libraries/System.Console/tests/ManualTests/Readme.md b/src/libraries/System.Console/tests/ManualTests/Readme.md
index 983015f62203f9..7d77e7fe3e1ee0 100644
--- a/src/libraries/System.Console/tests/ManualTests/Readme.md
+++ b/src/libraries/System.Console/tests/ManualTests/Readme.md
@@ -7,3 +7,20 @@ To run the suite, follow these steps:
 2. Using a terminal, navigate to the current folder.
 3. Enable manual testing by defining the `MANUAL_TESTS` environment variable (e.g. on bash `export MANUAL_TESTS=true`).
 4. Run `dotnet test` and follow the instructions in the command prompt.
+
+## Instructions for Windows testers
+
+VsTest on Windows redirects console input, so in order to properly execute the manual tests, 
+`xunit-console` must be invoked directly. To do this first run
+
+```
+> dotnet build -t:Test
+```
+
+And then copy and execute the commands logged under the `To repro directly:` section of the output logs.
+
+## Instructions for MacOS testers
+
+By default, Alt-Key does not work on the MacOS terminal.
+Before running the tests, navigate to `Terminal > Preferences > Settings > Keyboard`
+and check "Use option as meta key" at the bottom.
diff --git a/src/libraries/System.Data.Common/Directory.Build.props b/src/libraries/System.Data.Common/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Data.Common/Directory.Build.props
+++ b/src/libraries/System.Data.Common/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Data.Common/ref/System.Data.Common.cs b/src/libraries/System.Data.Common/ref/System.Data.Common.cs
index 5d70fda61ec01f..d9df3c0270774c 100644
--- a/src/libraries/System.Data.Common/ref/System.Data.Common.cs
+++ b/src/libraries/System.Data.Common/ref/System.Data.Common.cs
@@ -65,7 +65,7 @@ public sealed partial class ConstraintCollection : System.Data.InternalDataColle
     {
         internal ConstraintCollection() { }
         public System.Data.Constraint this[int index] { get { throw null; } }
-        public System.Data.Constraint this[string name] { get { throw null; } }
+        public System.Data.Constraint? this[string? name] { get { throw null; } }
         protected override System.Collections.ArrayList List { get { throw null; } }
         public event System.ComponentModel.CollectionChangeEventHandler? CollectionChanged { add { } remove { } }
         public void Add(System.Data.Constraint constraint) { }
@@ -167,7 +167,7 @@ internal DataColumnCollection() { }
         public System.Data.DataColumn this[int index] { get { throw null; } }
         public System.Data.DataColumn? this[string name] { get { throw null; } }
         protected override System.Collections.ArrayList List { get { throw null; } }
-        public event System.ComponentModel.CollectionChangeEventHandler CollectionChanged { add { } remove { } }
+        public event System.ComponentModel.CollectionChangeEventHandler? CollectionChanged { add { } remove { } }
         public System.Data.DataColumn Add() { throw null; }
         public void Add(System.Data.DataColumn column) { }
         public System.Data.DataColumn Add(string? columnName) { throw null; }
@@ -261,7 +261,7 @@ public abstract partial class DataRelationCollection : System.Data.InternalDataC
     {
         protected DataRelationCollection() { }
         public abstract System.Data.DataRelation this[int index] { get; }
-        public abstract System.Data.DataRelation? this[string name] { get; }
+        public abstract System.Data.DataRelation? this[string? name] { get; }
         public event System.ComponentModel.CollectionChangeEventHandler? CollectionChanged { add { } remove { } }
         public virtual System.Data.DataRelation Add(System.Data.DataColumn parentColumn, System.Data.DataColumn childColumn) { throw null; }
         public virtual System.Data.DataRelation Add(System.Data.DataColumn[] parentColumns, System.Data.DataColumn[] childColumns) { throw null; }
@@ -274,7 +274,7 @@ protected virtual void AddCore(System.Data.DataRelation relation) { }
         public virtual void AddRange(System.Data.DataRelation[]? relations) { }
         public virtual bool CanRemove(System.Data.DataRelation? relation) { throw null; }
         public virtual void Clear() { }
-        public virtual bool Contains(string name) { throw null; }
+        public virtual bool Contains(string? name) { throw null; }
         public void CopyTo(System.Data.DataRelation[] array, int index) { }
         protected abstract System.Data.DataSet GetDataSet();
         public virtual int IndexOf(System.Data.DataRelation? relation) { throw null; }
@@ -378,8 +378,8 @@ internal DataRowCollection() { }
         public void Add(System.Data.DataRow row) { }
         public System.Data.DataRow Add(params object?[] values) { throw null; }
         public void Clear() { }
-        public bool Contains(object key) { throw null; }
-        public bool Contains(object[] keys) { throw null; }
+        public bool Contains(object? key) { throw null; }
+        public bool Contains(object?[] keys) { throw null; }
         public override void CopyTo(System.Array ar, int index) { }
         public void CopyTo(System.Data.DataRow[] array, int index) { }
         public System.Data.DataRow? Find(object? key) { throw null; }
@@ -403,21 +403,15 @@ internal DataRowComparer() { }
     }
     public static partial class DataRowExtensions
     {
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T Field<T>(this System.Data.DataRow row, System.Data.DataColumn column) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T Field<T>(this System.Data.DataRow row, System.Data.DataColumn column, System.Data.DataRowVersion version) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T Field<T>(this System.Data.DataRow row, int columnIndex) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T Field<T>(this System.Data.DataRow row, int columnIndex, System.Data.DataRowVersion version) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T Field<T>(this System.Data.DataRow row, string columnName) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T Field<T>(this System.Data.DataRow row, string columnName, System.Data.DataRowVersion version) { throw null; }
-        public static void SetField<T>(this System.Data.DataRow row, System.Data.DataColumn column, [System.Diagnostics.CodeAnalysis.AllowNullAttribute] T value) { }
-        public static void SetField<T>(this System.Data.DataRow row, int columnIndex, [System.Diagnostics.CodeAnalysis.AllowNullAttribute] T value) { }
-        public static void SetField<T>(this System.Data.DataRow row, string columnName, [System.Diagnostics.CodeAnalysis.AllowNullAttribute] T value) { }
+        public static T? Field<T>(this System.Data.DataRow row, System.Data.DataColumn column) { throw null; }
+        public static T? Field<T>(this System.Data.DataRow row, System.Data.DataColumn column, System.Data.DataRowVersion version) { throw null; }
+        public static T? Field<T>(this System.Data.DataRow row, int columnIndex) { throw null; }
+        public static T? Field<T>(this System.Data.DataRow row, int columnIndex, System.Data.DataRowVersion version) { throw null; }
+        public static T? Field<T>(this System.Data.DataRow row, string columnName) { throw null; }
+        public static T? Field<T>(this System.Data.DataRow row, string columnName, System.Data.DataRowVersion version) { throw null; }
+        public static void SetField<T>(this System.Data.DataRow row, System.Data.DataColumn column, T? value) { }
+        public static void SetField<T>(this System.Data.DataRow row, int columnIndex, T? value) { }
+        public static void SetField<T>(this System.Data.DataRow row, string columnName, T? value) { }
     }
     [System.FlagsAttribute]
     public enum DataRowState
@@ -477,6 +471,7 @@ public void EndEdit() { }
         object System.ComponentModel.ICustomTypeDescriptor.GetPropertyOwner(System.ComponentModel.PropertyDescriptor pd) { throw null; }
 #nullable enable
     }
+    [System.ComponentModel.DesignerAttribute("Microsoft.VSDesigner.Data.VS.DataSetDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     [System.ComponentModel.DefaultPropertyAttribute("DataSetName")]
     [System.Xml.Serialization.XmlRootAttribute("DataSet")]
     [System.Xml.Serialization.XmlSchemaProviderAttribute("GetDataSetSchema")]
@@ -868,6 +863,7 @@ public override void Close() { }
         public override bool NextResult() { throw null; }
         public override bool Read() { throw null; }
     }
+    [System.ComponentModel.DesignerAttribute("Microsoft.VSDesigner.Data.VS.DataViewDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     [System.ComponentModel.DefaultEventAttribute("PositionChanged")]
     [System.ComponentModel.DefaultPropertyAttribute("Table")]
     public partial class DataView : System.ComponentModel.MarshalByValueComponent, System.Collections.ICollection, System.Collections.IEnumerable, System.Collections.IList, System.ComponentModel.IBindingList, System.ComponentModel.IBindingListView, System.ComponentModel.ISupportInitialize, System.ComponentModel.ISupportInitializeNotification, System.ComponentModel.ITypedList
@@ -965,6 +961,7 @@ void System.ComponentModel.IBindingListView.RemoveFilter() { }
         protected void UpdateIndex() { }
         protected virtual void UpdateIndex(bool force) { }
     }
+    [System.ComponentModel.DesignerAttribute("Microsoft.VSDesigner.Data.VS.DataViewManagerDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public partial class DataViewManager : System.ComponentModel.MarshalByValueComponent, System.Collections.ICollection, System.Collections.IEnumerable, System.Collections.IList, System.ComponentModel.IBindingList, System.ComponentModel.ITypedList
     {
         public DataViewManager() { }
@@ -1054,8 +1051,8 @@ internal DataViewSettingCollection() { }
         [System.ComponentModel.BrowsableAttribute(false)]
         public bool IsSynchronized { get { throw null; } }
         public virtual System.Data.DataViewSetting this[System.Data.DataTable table] { get { throw null; } set { } }
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public virtual System.Data.DataViewSetting this[int index] { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.DisallowNullAttribute]
+        public virtual System.Data.DataViewSetting? this[int index] { get { throw null; } set { } }
         public virtual System.Data.DataViewSetting? this[string tableName] { get { throw null; } }
         [System.ComponentModel.BrowsableAttribute(false)]
         public object SyncRoot { get { throw null; } }
@@ -1560,8 +1557,7 @@ public SyntaxErrorException(string? message, System.Exception? innerException) {
     public static partial class TypedTableBaseExtensions
     {
         public static System.Data.EnumerableRowCollection<TRow> AsEnumerable<TRow>(this System.Data.TypedTableBase<TRow> source) where TRow : System.Data.DataRow { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TRow ElementAtOrDefault<TRow>(this System.Data.TypedTableBase<TRow> source, int index) where TRow : System.Data.DataRow { throw null; }
+        public static TRow? ElementAtOrDefault<TRow>(this System.Data.TypedTableBase<TRow> source, int index) where TRow : System.Data.DataRow { throw null; }
         public static System.Data.OrderedEnumerableRowCollection<TRow> OrderByDescending<TRow, TKey>(this System.Data.TypedTableBase<TRow> source, System.Func<TRow, TKey> keySelector) where TRow : System.Data.DataRow { throw null; }
         public static System.Data.OrderedEnumerableRowCollection<TRow> OrderByDescending<TRow, TKey>(this System.Data.TypedTableBase<TRow> source, System.Func<TRow, TKey> keySelector, System.Collections.Generic.IComparer<TKey> comparer) where TRow : System.Data.DataRow { throw null; }
         public static System.Data.OrderedEnumerableRowCollection<TRow> OrderBy<TRow, TKey>(this System.Data.TypedTableBase<TRow> source, System.Func<TRow, TKey> keySelector) where TRow : System.Data.DataRow { throw null; }
@@ -2079,8 +2075,8 @@ protected DbDataAdapter(System.Data.Common.DbDataAdapter adapter) { }
         public System.Data.Common.DbCommand? UpdateCommand { get { throw null; } set { } }
         protected virtual int AddToBatch(System.Data.IDbCommand command) { throw null; }
         protected virtual void ClearBatch() { }
-        protected virtual System.Data.Common.RowUpdatedEventArgs CreateRowUpdatedEvent(System.Data.DataRow dataRow, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
-        protected virtual System.Data.Common.RowUpdatingEventArgs CreateRowUpdatingEvent(System.Data.DataRow dataRow, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
+        protected virtual System.Data.Common.RowUpdatedEventArgs CreateRowUpdatedEvent(System.Data.DataRow dataRow, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
+        protected virtual System.Data.Common.RowUpdatingEventArgs CreateRowUpdatingEvent(System.Data.DataRow dataRow, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
         protected override void Dispose(bool disposing) { }
         protected virtual int ExecuteBatch() { throw null; }
         public override int Fill(System.Data.DataSet dataSet) { throw null; }
@@ -2441,6 +2437,13 @@ protected virtual void Dispose(bool disposing) { }
         public virtual System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }
         public abstract void Rollback();
         public virtual System.Threading.Tasks.Task RollbackAsync(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        public virtual bool SupportsSavepoints { get { throw null; } }
+        public virtual System.Threading.Tasks.Task SaveAsync(string savepointName, System.Threading.CancellationToken cancellationToken = default) { throw null; }
+        public virtual System.Threading.Tasks.Task RollbackAsync(string savepointName, System.Threading.CancellationToken cancellationToken = default) { throw null; }
+        public virtual System.Threading.Tasks.Task ReleaseAsync(string savepointName, System.Threading.CancellationToken cancellationToken = default) { throw null; }
+        public virtual void Save(string savepointName) { throw null; }
+        public virtual void Rollback(string savepointName) { throw null; }
+        public virtual void Release(string savepointName) { throw null; }
     }
     public enum GroupByBehavior
     {
@@ -2462,8 +2465,8 @@ public enum IdentifierCase
     }
     public partial class RowUpdatedEventArgs : System.EventArgs
     {
-        public RowUpdatedEventArgs(System.Data.DataRow dataRow, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { }
-        public System.Data.IDbCommand Command { get { throw null; } }
+        public RowUpdatedEventArgs(System.Data.DataRow dataRow, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { }
+        public System.Data.IDbCommand? Command { get { throw null; } }
         public System.Exception? Errors { get { throw null; } set { } }
         public int RecordsAffected { get { throw null; } }
         public System.Data.DataRow Row { get { throw null; } }
@@ -2476,7 +2479,7 @@ public void CopyToRows(System.Data.DataRow[] array, int arrayIndex) { }
     }
     public partial class RowUpdatingEventArgs : System.EventArgs
     {
-        public RowUpdatingEventArgs(System.Data.DataRow dataRow, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { }
+        public RowUpdatingEventArgs(System.Data.DataRow dataRow, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { }
         protected virtual System.Data.IDbCommand? BaseCommand { get { throw null; } set { } }
         public System.Data.IDbCommand? Command { get { throw null; } set { } }
         public System.Exception? Errors { get { throw null; } set { } }
diff --git a/src/libraries/System.Data.Common/src/System.Data.Common.csproj b/src/libraries/System.Data.Common/src/System.Data.Common.csproj
index a872f6cefe4519..5e445cebc31df6 100644
--- a/src/libraries/System.Data.Common/src/System.Data.Common.csproj
+++ b/src/libraries/System.Data.Common/src/System.Data.Common.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Data.Common</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Data.Common/src/System/Data/Common/DBCommandBuilder.cs b/src/libraries/System.Data.Common/src/System/Data/Common/DBCommandBuilder.cs
index 72a5d8d51dad68..3fe1c1af3b6abd 100644
--- a/src/libraries/System.Data.Common/src/System/Data/Common/DBCommandBuilder.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/Common/DBCommandBuilder.cs
@@ -169,15 +169,15 @@ private void ApplyProviderSpecificFormat()
             {
                 for (int i = 0; i < _baseParameterNames.Length; i++)
                 {
-                    if (_baseParameterNames[i] is { } baseParameterName)
+                    if (_baseParameterNames[i] is string baseParameterName)
                     {
                         _baseParameterNames[i] = _dbCommandBuilder.GetParameterName(baseParameterName);
                     }
-                    if (_originalParameterNames[i] is { } originalParameterName)
+                    if (_originalParameterNames[i] is string originalParameterName)
                     {
                         _originalParameterNames[i] = _dbCommandBuilder.GetParameterName(originalParameterName);
                     }
-                    if (_nullParameterNames[i] is { } nullParameterName)
+                    if (_nullParameterNames[i] is string nullParameterName)
                     {
                         _nullParameterNames[i] = _dbCommandBuilder.GetParameterName(nullParameterName);
                     }
@@ -228,7 +228,7 @@ internal void GenerateMissingNames(DbSchemaRow?[] schemaRows)
                         _baseParameterNames[i] = GetNextGenericParameterName();
                         _originalParameterNames[i] = GetNextGenericParameterName();
                         // don't bother generating an 'IsNull' name if it's not used
-                        if (schemaRows[i] is { } schemaRow && schemaRow.AllowDBNull)
+                        if (schemaRows[i] is DbSchemaRow schemaRow && schemaRow.AllowDBNull)
                         {
                             _nullParameterNames[i] = GetNextGenericParameterName();
                         }
@@ -633,7 +633,7 @@ private void BuildCache(bool closeConnection, DataRow? dataRow, bool useColumnsF
             string[] srcColumnNames = new string[schemaRows.Length];
             for (int i = 0; i < schemaRows.Length; ++i)
             {
-                if (schemaRows[i] is { } schemaRow)
+                if (schemaRows[i] is DbSchemaRow schemaRow)
                 {
                     srcColumnNames[i] = schemaRow.ColumnName;
                 }
diff --git a/src/libraries/System.Data.Common/src/System/Data/Common/DbDataAdapter.cs b/src/libraries/System.Data.Common/src/System/Data/Common/DbDataAdapter.cs
index e86beec5934404..b1e417ec7d14c2 100644
--- a/src/libraries/System.Data.Common/src/System/Data/Common/DbDataAdapter.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/Common/DbDataAdapter.cs
@@ -254,12 +254,12 @@ private void CloneFrom(DbDataAdapter from)
             return (IDbCommand?)((command is ICloneable) ? ((ICloneable)command).Clone() : null);
         }
 
-        protected virtual RowUpdatedEventArgs CreateRowUpdatedEvent(DataRow dataRow, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        protected virtual RowUpdatedEventArgs CreateRowUpdatedEvent(DataRow dataRow, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         {
             return new RowUpdatedEventArgs(dataRow, command, statementType, tableMapping);
         }
 
-        protected virtual RowUpdatingEventArgs CreateRowUpdatingEvent(DataRow dataRow, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        protected virtual RowUpdatingEventArgs CreateRowUpdatingEvent(DataRow dataRow, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         {
             return new RowUpdatingEventArgs(dataRow, command, statementType, tableMapping);
         }
@@ -1035,7 +1035,7 @@ protected virtual int Update(DataRow[] dataRows, DataTableMapping tableMapping)
                             // TODO: the event may be raised with a null command, but only if the update, but only if
                             // the update attempt fails (because no command was configured). We should not emit the
                             // event in this case.
-                            RowUpdatingEventArgs? rowUpdatingEvent = CreateRowUpdatingEvent(dataRow, dataCommand!, statementType, tableMapping);
+                            RowUpdatingEventArgs? rowUpdatingEvent = CreateRowUpdatingEvent(dataRow, dataCommand, statementType, tableMapping);
 
                             // this try/catch for any exceptions during the parameter initialization
                             try
@@ -1159,7 +1159,7 @@ protected virtual int Update(DataRow[] dataRows, DataTableMapping tableMapping)
                                 if (null != errors)
                                 {
                                     // TODO: See above comment on dataCommand being null
-                                    rowUpdatedEvent = CreateRowUpdatedEvent(dataRow, dataCommand!, StatementType.Batch, tableMapping);
+                                    rowUpdatedEvent = CreateRowUpdatedEvent(dataRow, dataCommand, StatementType.Batch, tableMapping);
                                     rowUpdatedEvent.Errors = errors;
                                     rowUpdatedEvent.Status = UpdateStatus.ErrorsOccurred;
 
@@ -1182,7 +1182,7 @@ protected virtual int Update(DataRow[] dataRows, DataTableMapping tableMapping)
                             }
 
                             // TODO: See above comment on dataCommand being null
-                            rowUpdatedEvent = CreateRowUpdatedEvent(dataRow, dataCommand!, statementType, tableMapping);
+                            rowUpdatedEvent = CreateRowUpdatedEvent(dataRow, dataCommand, statementType, tableMapping);
 
                             // this try/catch for any exceptions during the execution, population, output parameters
                             try
@@ -1280,8 +1280,8 @@ protected virtual int Update(DataRow[] dataRows, DataTableMapping tableMapping)
                         if (1 != maxBatchCommands && 0 < commandCount)
                         {
                             // TODO: See above comment on dataCommand being null
-                            // TODO: DataRow is null because we call AdapterInit below, which populars rows
-                            RowUpdatedEventArgs rowUpdatedEvent = CreateRowUpdatedEvent(null!, dataCommand!, statementType, tableMapping);
+                            // TODO: DataRow is null because we call AdapterInit below, which populates rows
+                            RowUpdatedEventArgs rowUpdatedEvent = CreateRowUpdatedEvent(null!, dataCommand, statementType, tableMapping);
 
                             try
                             {
@@ -1659,7 +1659,7 @@ private int UpdatedRowStatusErrors(RowUpdatedEventArgs rowUpdatedEvent, BatchCom
                 DataRow row = batchCommands[i]._row;
                 Debug.Assert(null != row, "null dataRow?");
 
-                if (batchCommands[i]._errors is { } commandErrors)
+                if (batchCommands[i]._errors is Exception commandErrors)
                 { // will exist if 0 == RecordsAffected
                     string rowMsg = commandErrors.Message;
                     if (string.IsNullOrEmpty(rowMsg))
diff --git a/src/libraries/System.Data.Common/src/System/Data/Common/DbDataReaderExtensions.cs b/src/libraries/System.Data.Common/src/System/Data/Common/DbDataReaderExtensions.cs
index 97e0fafbff1a7d..8b851446d44d45 100644
--- a/src/libraries/System.Data.Common/src/System/Data/Common/DbDataReaderExtensions.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/Common/DbDataReaderExtensions.cs
@@ -30,7 +30,7 @@ private void PopulateFields()
                 BaseSchemaName = GetDbColumnValue<string?>(SchemaTableColumn.BaseSchemaName);
                 BaseServerName = GetDbColumnValue<string?>(SchemaTableOptionalColumn.BaseServerName);
                 BaseTableName = GetDbColumnValue<string?>(SchemaTableColumn.BaseTableName);
-                ColumnName = GetDbColumnValue<string>(SchemaTableColumn.ColumnName);
+                ColumnName = GetDbColumnValue<string>(SchemaTableColumn.ColumnName)!;
                 ColumnOrdinal = GetDbColumnValue<int?>(SchemaTableColumn.ColumnOrdinal);
                 ColumnSize = GetDbColumnValue<int?>(SchemaTableColumn.ColumnSize);
                 IsAliased = GetDbColumnValue<bool?>(SchemaTableColumn.IsAliased);
@@ -49,8 +49,7 @@ private void PopulateFields()
                 DataTypeName = GetDbColumnValue<string?>("DataTypeName");
             }
 
-            // The following may return null, but local methods can't be annotated for that yet ([MaybeNull])
-            private T GetDbColumnValue<T>(string columnName) => _schemaColumns.Contains(columnName) && _schemaRow[columnName] is T value ? value : default!;
+            private T? GetDbColumnValue<T>(string columnName) => _schemaColumns.Contains(columnName) && _schemaRow[columnName] is T value ? value : default;
         }
 
         public static ReadOnlyCollection<DbColumn> GetColumnSchema(this DbDataReader reader)
diff --git a/src/libraries/System.Data.Common/src/System/Data/Common/DbTransaction.cs b/src/libraries/System.Data.Common/src/System/Data/Common/DbTransaction.cs
index fe357a63413c83..8728590fedebbc 100644
--- a/src/libraries/System.Data.Common/src/System/Data/Common/DbTransaction.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/Common/DbTransaction.cs
@@ -67,5 +67,121 @@ public virtual Task RollbackAsync(CancellationToken cancellationToken = default)
                 return Task.FromException(e);
             }
         }
+
+        #region Savepoints
+
+        /// <summary>
+        /// Gets a value that indicates whether this <see cref="DbTransaction" /> instance supports database savepoints.
+        /// If <see langword="false" />, the methods <see cref="SaveAsync" />,
+        /// <see cref="RollbackAsync(string, System.Threading.CancellationToken)"/> and <see cref="ReleaseAsync" /> as
+        /// well as their synchronous counterparts are expected to throw <see cref="NotSupportedException" />.
+        /// </summary>
+        /// <returns>
+        /// <see langword="true" /> if this <see cref="DbTransaction"/> instance supports database savepoints; otherwise,
+        /// <see langword="false" />.
+        /// </returns>
+        public virtual bool SupportsSavepoints => false;
+
+        /// <summary>
+        /// Creates a savepoint in the transaction. This allows all commands that are executed after the savepoint was
+        /// established to be rolled back, restoring the transaction state to what it was at the time of the savepoint.
+        /// </summary>
+        /// <param name="savepointName">The name of the savepoint to be created.</param>
+        /// <param name="cancellationToken">
+        /// An optional token to cancel the asynchronous operation. The default value is <see cref="CancellationToken.None" />.
+        /// </param>
+        /// <returns>A <see cref="Task " /> representing the asynchronous operation.</returns>
+        public virtual Task SaveAsync(string savepointName, CancellationToken cancellationToken = default)
+        {
+            if (cancellationToken.IsCancellationRequested)
+            {
+                return Task.FromCanceled(cancellationToken);
+            }
+
+            try
+            {
+                Save(savepointName);
+                return Task.CompletedTask;
+            }
+            catch (Exception e)
+            {
+                return Task.FromException(e);
+            }
+        }
+
+        /// <summary>
+        /// Rolls back all commands that were executed after the specified savepoint was established.
+        /// </summary>
+        /// <param name="savepointName">The name of the savepoint to roll back to.</param>
+        /// <param name="cancellationToken">
+        /// An optional token to cancel the asynchronous operation. The default value is <see cref="CancellationToken.None" />.
+        /// </param>
+        /// <returns>A <see cref="Task " /> representing the asynchronous operation.</returns>
+        public virtual Task RollbackAsync(string savepointName, CancellationToken cancellationToken = default)
+        {
+            if (cancellationToken.IsCancellationRequested)
+            {
+                return Task.FromCanceled(cancellationToken);
+            }
+
+            try
+            {
+                Rollback(savepointName);
+                return Task.CompletedTask;
+            }
+            catch (Exception e)
+            {
+                return Task.FromException(e);
+            }
+        }
+
+        /// <summary>
+        /// Destroys a savepoint previously defined in the current transaction. This allows the system to
+        /// reclaim some resources before the transaction ends.
+        /// </summary>
+        /// <param name="savepointName">The name of the savepoint to release.</param>
+        /// <param name="cancellationToken">
+        /// An optional token to cancel the asynchronous operation. The default value is <see cref="CancellationToken.None" />.
+        /// </param>
+        /// <returns>A <see cref="Task " /> representing the asynchronous operation.</returns>
+        public virtual Task ReleaseAsync(string savepointName, CancellationToken cancellationToken = default)
+        {
+            if (cancellationToken.IsCancellationRequested)
+            {
+                return Task.FromCanceled(cancellationToken);
+            }
+
+            try
+            {
+                Release(savepointName);
+                return Task.CompletedTask;
+            }
+            catch (Exception e)
+            {
+                return Task.FromException(e);
+            }
+        }
+
+        /// <summary>
+        /// Creates a savepoint in the transaction. This allows all commands that are executed after the savepoint was
+        /// established to be rolled back, restoring the transaction state to what it was at the time of the savepoint.
+        /// </summary>
+        /// <param name="savepointName">The name of the savepoint to be created.</param>
+        public virtual void Save(string savepointName) => throw new NotSupportedException();
+
+        /// <summary>
+        /// Rolls back all commands that were executed after the specified savepoint was established.
+        /// </summary>
+        /// <param name="savepointName">The name of the savepoint to roll back to.</param>
+        public virtual void Rollback(string savepointName) => throw new NotSupportedException();
+
+        /// <summary>
+        /// Destroys a savepoint previously defined in the current transaction. This allows the system to
+        /// reclaim some resources before the transaction ends.
+        /// </summary>
+        /// <param name="savepointName">The name of the savepoint to release.</param>
+        public virtual void Release(string savepointName) {}
+
+        #endregion
     }
 }
diff --git a/src/libraries/System.Data.Common/src/System/Data/Common/RowUpdatedEventArgs.cs b/src/libraries/System.Data.Common/src/System/Data/Common/RowUpdatedEventArgs.cs
index a2ef4bf0ced60a..261a68ad56cc54 100644
--- a/src/libraries/System.Data.Common/src/System/Data/Common/RowUpdatedEventArgs.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/Common/RowUpdatedEventArgs.cs
@@ -9,7 +9,7 @@ namespace System.Data.Common
 
     public class RowUpdatedEventArgs : EventArgs
     {
-        private readonly IDbCommand _command;
+        private readonly IDbCommand? _command;
         private StatementType _statementType;
         private readonly DataTableMapping _tableMapping;
         private Exception? _errors;
@@ -20,7 +20,7 @@ public class RowUpdatedEventArgs : EventArgs
         private UpdateStatus _status; // UpdateStatus.Continue; /*0*/
         private int _recordsAffected;
 
-        public RowUpdatedEventArgs(DataRow dataRow, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        public RowUpdatedEventArgs(DataRow dataRow, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         {
             switch (statementType)
             {
@@ -39,7 +39,7 @@ public RowUpdatedEventArgs(DataRow dataRow, IDbCommand command, StatementType st
             _tableMapping = tableMapping;
         }
 
-        public IDbCommand Command
+        public IDbCommand? Command
         {
             get
             {
diff --git a/src/libraries/System.Data.Common/src/System/Data/Common/SQLTypes/SQLInt64Storage.cs b/src/libraries/System.Data.Common/src/System/Data/Common/SQLTypes/SQLInt64Storage.cs
index 2c9fa58f854d75..e469f3218b5b1c 100644
--- a/src/libraries/System.Data.Common/src/System/Data/Common/SQLTypes/SQLInt64Storage.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/Common/SQLTypes/SQLInt64Storage.cs
@@ -12,7 +12,7 @@ namespace System.Data.Common
 {
     internal sealed class SqlInt64Storage : DataStorage
     {
-        private SqlInt64[] _values = default!;
+        private SqlInt64[] _values = default!; // Late-initialized
 
         public SqlInt64Storage(DataColumn column)
         : base(column, typeof(SqlInt64), SqlInt64.Null, SqlInt64.Null, StorageType.SqlInt64)
diff --git a/src/libraries/System.Data.Common/src/System/Data/ConstraintCollection.cs b/src/libraries/System.Data.Common/src/System/Data/ConstraintCollection.cs
index 806bab3e90b009..aabcde99fe0323 100644
--- a/src/libraries/System.Data.Common/src/System/Data/ConstraintCollection.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/ConstraintCollection.cs
@@ -87,7 +87,7 @@ internal void Add(Constraint constraint, bool addUniqueWhenAddingForeign)
             }
 
             // It is an error if we find an equivalent constraint already in collection
-            if (FindConstraint(constraint) is { } matchedConstraint)
+            if (FindConstraint(constraint) is Constraint matchedConstraint)
             {
                 throw ExceptionBuilder.DuplicateConstraint(matchedConstraint.ConstraintName);
             }
diff --git a/src/libraries/System.Data.Common/src/System/Data/DataRow.cs b/src/libraries/System.Data.Common/src/System/Data/DataRow.cs
index 084cbd242f48c0..1a1c4d70f2b72c 100644
--- a/src/libraries/System.Data.Common/src/System/Data/DataRow.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/DataRow.cs
@@ -450,7 +450,7 @@ public object?[] ItemArray
                 for (int i = 0; i < value.Length; ++i)
                 {
                     // Empty means don't change the row.
-                    if (value[i] is { } item)
+                    if (value[i] is object item)
                     {
                         // may throw exception if user removes column from table during event
                         DataColumn column = _columns[i];
diff --git a/src/libraries/System.Data.Common/src/System/Data/DataRowExtensions.cs b/src/libraries/System.Data.Common/src/System/Data/DataRowExtensions.cs
index afa65a31f7eefd..3ebbdc113527fd 100644
--- a/src/libraries/System.Data.Common/src/System/Data/DataRowExtensions.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/DataRowExtensions.cs
@@ -19,8 +19,7 @@ public static class DataRowExtensions
         /// <param name="row">The input DataRow</param>
         /// <param name="columnName">The input column name specifying which row value to retrieve.</param>
         /// <returns>The DataRow value for the column specified.</returns>
-        [return: MaybeNull]
-        public static T Field<T>(this DataRow row, string columnName)
+        public static T? Field<T>(this DataRow row, string columnName)
         {
             DataSetUtil.CheckArgumentNull(row, nameof(row));
             return UnboxT<T>.s_unbox(row[columnName]);
@@ -35,8 +34,7 @@ public static T Field<T>(this DataRow row, string columnName)
         /// <param name="row">The input DataRow</param>
         /// <param name="column">The input DataColumn specifying which row value to retrieve.</param>
         /// <returns>The DataRow value for the column specified.</returns>
-        [return: MaybeNull]
-        public static T Field<T>(this DataRow row, DataColumn column)
+        public static T? Field<T>(this DataRow row, DataColumn column)
         {
             DataSetUtil.CheckArgumentNull(row, nameof(row));
             return UnboxT<T>.s_unbox(row[column]);
@@ -51,8 +49,7 @@ public static T Field<T>(this DataRow row, DataColumn column)
         /// <param name="row">The input DataRow</param>
         /// <param name="columnIndex">The input ordinal specifying which row value to retrieve.</param>
         /// <returns>The DataRow value for the column specified.</returns>
-        [return: MaybeNull]
-        public static T Field<T>(this DataRow row, int columnIndex)
+        public static T? Field<T>(this DataRow row, int columnIndex)
         {
             DataSetUtil.CheckArgumentNull(row, nameof(row));
             return UnboxT<T>.s_unbox(row[columnIndex]);
@@ -68,8 +65,7 @@ public static T Field<T>(this DataRow row, int columnIndex)
         /// <param name="columnIndex">The input ordinal specifying which row value to retrieve.</param>
         /// <param name="version">The DataRow version for which row value to retrieve.</param>
         /// <returns>The DataRow value for the column specified.</returns>
-        [return: MaybeNull]
-        public static T Field<T>(this DataRow row, int columnIndex, DataRowVersion version)
+        public static T? Field<T>(this DataRow row, int columnIndex, DataRowVersion version)
         {
             DataSetUtil.CheckArgumentNull(row, nameof(row));
             return UnboxT<T>.s_unbox(row[columnIndex, version]);
@@ -85,8 +81,7 @@ public static T Field<T>(this DataRow row, int columnIndex, DataRowVersion versi
         /// <param name="columnName">The input column name specifying which row value to retrieve.</param>
         /// <param name="version">The DataRow version for which row value to retrieve.</param>
         /// <returns>The DataRow value for the column specified.</returns>
-        [return: MaybeNull]
-        public static T Field<T>(this DataRow row, string columnName, DataRowVersion version)
+        public static T? Field<T>(this DataRow row, string columnName, DataRowVersion version)
         {
             DataSetUtil.CheckArgumentNull(row, nameof(row));
             return UnboxT<T>.s_unbox(row[columnName, version]);
@@ -102,8 +97,7 @@ public static T Field<T>(this DataRow row, string columnName, DataRowVersion ver
         /// <param name="column">The input DataColumn specifying which row value to retrieve.</param>
         /// <param name="version">The DataRow version for which row value to retrieve.</param>
         /// <returns>The DataRow value for the column specified.</returns>
-        [return: MaybeNull]
-        public static T Field<T>(this DataRow row, DataColumn column, DataRowVersion version)
+        public static T? Field<T>(this DataRow row, DataColumn column, DataRowVersion version)
         {
             DataSetUtil.CheckArgumentNull(row, nameof(row));
             return UnboxT<T>.s_unbox(row[column, version]);
@@ -115,7 +109,7 @@ public static T Field<T>(this DataRow row, DataColumn column, DataRowVersion ver
         /// <param name="row">The input DataRow.</param>
         /// <param name="columnIndex">The input ordinal specifying which row value to set.</param>
         /// <param name="value">The new row value for the specified column.</param>
-        public static void SetField<T>(this DataRow row, int columnIndex, [AllowNull] T value)
+        public static void SetField<T>(this DataRow row, int columnIndex, T? value)
         {
             DataSetUtil.CheckArgumentNull(row, nameof(row));
             row[columnIndex] = (object?)value ?? DBNull.Value;
@@ -127,7 +121,7 @@ public static void SetField<T>(this DataRow row, int columnIndex, [AllowNull] T
         /// <param name="row">The input DataRow.</param>
         /// <param name="columnName">The input column name specifying which row value to retrieve.</param>
         /// <param name="value">The new row value for the specified column.</param>
-        public static void SetField<T>(this DataRow row, string columnName, [AllowNull] T value)
+        public static void SetField<T>(this DataRow row, string columnName, T? value)
         {
             DataSetUtil.CheckArgumentNull(row, nameof(row));
             row[columnName] = (object?)value ?? DBNull.Value;
@@ -139,7 +133,7 @@ public static void SetField<T>(this DataRow row, string columnName, [AllowNull]
         /// <param name="row">The input DataRow.</param>
         /// <param name="column">The input DataColumn specifying which row value to retrieve.</param>
         /// <param name="value">The new row value for the specified column.</param>
-        public static void SetField<T>(this DataRow row, DataColumn column, [AllowNull] T value)
+        public static void SetField<T>(this DataRow row, DataColumn column, T? value)
         {
             DataSetUtil.CheckArgumentNull(row, nameof(row));
             row[column] = (object?)value ?? DBNull.Value;
@@ -147,9 +141,9 @@ public static void SetField<T>(this DataRow row, DataColumn column, [AllowNull]
 
         private static class UnboxT<T>
         {
-            internal static readonly Converter<object, T> s_unbox = Create();
+            internal static readonly Converter<object, T?> s_unbox = Create();
 
-            private static Converter<object, T> Create()
+            private static Converter<object, T?> Create()
             {
                 if (typeof(T).IsValueType)
                 {
@@ -165,8 +159,7 @@ private static Converter<object, T> Create()
                 return ReferenceField;
             }
 
-            [return: MaybeNull]
-            private static T ReferenceField(object value)
+            private static T? ReferenceField(object value)
                 => value == DBNull.Value ? default : (T)value;
 
             private static T ValueField(object value)
@@ -174,7 +167,6 @@ private static T ValueField(object value)
                     ? throw DataSetUtil.InvalidCast(SR.Format(SR.DataSetLinq_NonNullableCast, typeof(T)))
                     : (T)value;
 
-            [return: MaybeNull]
             private static Nullable<TElem> NullableField<TElem>(object value) where TElem : struct
                 => value == DBNull.Value ? default : new Nullable<TElem>((TElem)value);
         }
diff --git a/src/libraries/System.Data.Common/src/System/Data/DataSet.cs b/src/libraries/System.Data.Common/src/System/Data/DataSet.cs
index 10e27f30cbbc71..20af21299567af 100644
--- a/src/libraries/System.Data.Common/src/System/Data/DataSet.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/DataSet.cs
@@ -23,6 +23,7 @@ namespace System.Data
     /// <summary>
     /// Represents an in-memory cache of data.
     /// </summary>
+    [Designer("Microsoft.VSDesigner.Data.VS.DataSetDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     [DefaultProperty(nameof(DataSetName))]
     [Serializable]
     [XmlSchemaProvider(nameof(GetDataSetSchema))]
diff --git a/src/libraries/System.Data.Common/src/System/Data/DataTable.cs b/src/libraries/System.Data.Common/src/System/Data/DataTable.cs
index 851ac8900f7031..ff8af676e92c9f 100644
--- a/src/libraries/System.Data.Common/src/System/Data/DataTable.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/DataTable.cs
@@ -2431,8 +2431,8 @@ private DataTable CloneTo(DataTable clone, DataSet? cloneDS, bool skipExpression
                 {
                     if (foreign.Table == foreign.RelatedTable)
                     {
-                        if (foreign.Clone(clone) is { } clonedConstraint &&
-                            clone.Constraints.FindConstraint(clonedConstraint) is { } oldConstraint)
+                        if (foreign.Clone(clone) is ForeignKeyConstraint clonedConstraint &&
+                            clone.Constraints.FindConstraint(clonedConstraint) is Constraint oldConstraint)
                         {
                             oldConstraint.ConstraintName = Constraints[j].ConstraintName;
                         }
@@ -2440,8 +2440,8 @@ private DataTable CloneTo(DataTable clone, DataSet? cloneDS, bool skipExpression
                 }
                 else if (unique != null)
                 {
-                    if (unique.Clone(clone) is { } clonedConstraint &&
-                        clone.Constraints.FindConstraint(clonedConstraint) is { } oldConstraint)
+                    if (unique.Clone(clone) is UniqueConstraint clonedConstraint &&
+                        clone.Constraints.FindConstraint(clonedConstraint) is Constraint oldConstraint)
                     {
                         oldConstraint.ConstraintName = Constraints[j].ConstraintName;
                         foreach (object key in clonedConstraint.ExtendedProperties.Keys)
@@ -2462,7 +2462,7 @@ private DataTable CloneTo(DataTable clone, DataSet? cloneDS, bool skipExpression
                     if (foreign != null)
                     {
                         if (foreign.Table == foreign.RelatedTable &&
-                            foreign.Clone(clone) is { } newforeign)
+                            foreign.Clone(clone) is ForeignKeyConstraint newforeign)
                         {
                             // we cant make sure that we recieve a cloned FKC,since it depends if table and relatedtable be the same
                             clone.Constraints.Add(newforeign);
@@ -3375,7 +3375,7 @@ internal int NewRecordFromArray(object?[] value)
             {
                 for (int i = 0; i < value.Length; i++)
                 {
-                    if (value[i] is { } v)
+                    if (value[i] is object v)
                     {
                         _columnCollection[i][record] = v;
                     }
diff --git a/src/libraries/System.Data.Common/src/System/Data/DataView.cs b/src/libraries/System.Data.Common/src/System/Data/DataView.cs
index 931f1ebd5fe67c..aa750a44d74194 100644
--- a/src/libraries/System.Data.Common/src/System/Data/DataView.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/DataView.cs
@@ -15,6 +15,7 @@ namespace System.Data
     /// Represents a databindable, customized view of a <see cref='System.Data.DataTable'/>
     /// for sorting, filtering, searching, editing, and navigation.
     /// </summary>
+    [Designer("Microsoft.VSDesigner.Data.VS.DataViewDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     [DefaultProperty(nameof(Table))]
     [DefaultEvent("PositionChanged")]
     public class DataView : MarshalByValueComponent, IBindingListView, System.ComponentModel.ITypedList, ISupportInitializeNotification
diff --git a/src/libraries/System.Data.Common/src/System/Data/DataViewManager.cs b/src/libraries/System.Data.Common/src/System/Data/DataViewManager.cs
index e10db2488dc450..0f76e3d604c85f 100644
--- a/src/libraries/System.Data.Common/src/System/Data/DataViewManager.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/DataViewManager.cs
@@ -10,6 +10,7 @@
 
 namespace System.Data
 {
+    [Designer("Microsoft.VSDesigner.Data.VS.DataViewManagerDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public class DataViewManager : MarshalByValueComponent, IBindingList, System.ComponentModel.ITypedList
     {
         private DataViewSettingCollection _dataViewSettingsCollection;
diff --git a/src/libraries/System.Data.Common/src/System/Data/DataViewSettingCollection.cs b/src/libraries/System.Data.Common/src/System/Data/DataViewSettingCollection.cs
index dc059c1a3e3bea..62b9fb6e470c4a 100644
--- a/src/libraries/System.Data.Common/src/System/Data/DataViewSettingCollection.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/DataViewSettingCollection.cs
@@ -84,8 +84,8 @@ public virtual DataViewSetting? this[string tableName]
             }
         }
 
-        [MaybeNull]
-        public virtual DataViewSetting this[int index]
+        [DisallowNull]
+        public virtual DataViewSetting? this[int index]
         {
             get
             {
diff --git a/src/libraries/System.Data.Common/src/System/Data/ProviderBase/SchemaMapping.cs b/src/libraries/System.Data.Common/src/System/Data/ProviderBase/SchemaMapping.cs
index 1fedea0de8b3e9..849908991e48a8 100644
--- a/src/libraries/System.Data.Common/src/System/Data/ProviderBase/SchemaMapping.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/ProviderBase/SchemaMapping.cs
@@ -217,7 +217,7 @@ internal void ApplyToDataRow(DataRow dataRow)
 
                     for (int i = 0; i < mapped.Length; ++i)
                     {
-                        if (mapped[i] is { } m)
+                        if (mapped[i] is object m)
                         {
                             dataRow[i] = m;
                         }
diff --git a/src/libraries/System.Data.Common/src/System/Data/RbTree.cs b/src/libraries/System.Data.Common/src/System/Data/RbTree.cs
index 4c40476ca3857c..a5f75b089899bc 100644
--- a/src/libraries/System.Data.Common/src/System/Data/RbTree.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/RbTree.cs
@@ -96,8 +96,8 @@ internal abstract class RBTree<K> : IEnumerable
         internal const int DefaultPageSize = 32; /* 512 = 2^9 32 million nodes*/
         internal const int NIL = 0;                  // 0th page, 0th slot for each tree till CLR static & generics issue is fixed
 
-        private TreePage?[] _pageTable = default!; // initial size 4, then doubles (grows) - it never shrinks. Late-initialized to non-null in InitTree.
-        private int[] _pageTableMap = default!; // Late-initialized to non-null in InitTree
+        private TreePage?[] _pageTable; // initial size 4, then doubles (grows) - it never shrinks.
+        private int[] _pageTableMap;
         private int _inUsePageCount;    // contains count of allocated pages per tree, its <= the capacity of  pageTable
         private int _nextFreePageLine;   // used for keeping track of position of last used free page in pageTable
         public int root;
@@ -107,8 +107,8 @@ internal abstract class RBTree<K> : IEnumerable
         private int _inUseSatelliteTreeCount; // total number of satellite associated with this tree.
         private readonly TreeAccessMethod _accessMethod;
 
-        protected abstract int CompareNode([AllowNull] K record1, [AllowNull] K record2);
-        protected abstract int CompareSateliteTreeNode([AllowNull] K record1, [AllowNull] K record2);
+        protected abstract int CompareNode(K? record1, K? record2);
+        protected abstract int CompareSateliteTreeNode(K? record1, K? record2);
 
         protected RBTree(TreeAccessMethod accessMethod)
         {
@@ -116,6 +116,8 @@ protected RBTree(TreeAccessMethod accessMethod)
             InitTree();
         }
 
+        [MemberNotNull(nameof(_pageTable))]
+        [MemberNotNull(nameof(_pageTableMap))]
         private void InitTree()
         {
             root = NIL;
@@ -337,7 +339,7 @@ public bool HasDuplicates
          * Use bitmap associated with page to allocate a slot.
          * mark the slot as used and return its index.
          */
-        private int GetNewNode([AllowNull] K key)
+        private int GetNewNode(K? key)
         {
             // find page with free slots, if none, allocate a new page
             TreePage? page = null;
@@ -1205,7 +1207,7 @@ private int RBDeleteFixup(int root_id, int x_id, int px_id /* px is parent of x
             return root_id;
         }
 
-        private int SearchSubTree(int root_id, [AllowNull] K key)
+        private int SearchSubTree(int root_id, K? key)
         {
             if (root_id != NIL && _accessMethod != TreeAccessMethod.KEY_SEARCH_AND_INDEX)
             {
@@ -1556,7 +1558,7 @@ public int Insert(K item)
 
         // Begin: List of methods for making it easy to work with ArrayList
 
-        public int Add([AllowNull] K item) //Insert (int record)
+        public int Add(K? item) //Insert (int record)
         {
             int nodeId = GetNewNode(item);
             RBInsert(NIL, nodeId, NIL, -1, false);
@@ -1875,8 +1877,7 @@ private struct Node
             internal int _parentId;
             internal int _nextId;      // multiple records associated with same key
             internal int _subTreeSize;     // number of nodes in subtree rooted at the current node
-            [AllowNull, MaybeNull]
-            internal K _keyOfNode;
+            internal K? _keyOfNode;
             internal NodeColor _nodeColor;
         }
 
@@ -2042,8 +2043,7 @@ internal struct RBTreeEnumerator : IEnumerator<K>, IEnumerator
             private readonly RBTree<K> _tree;
             private readonly int _version;
             private int _index, _mainTreeNodeId;
-            [AllowNull, MaybeNull]
-            private K _current;
+            private K? _current;
 
             internal RBTreeEnumerator(RBTree<K> tree)
             {
diff --git a/src/libraries/System.Data.Common/src/System/Data/RecordManager.cs b/src/libraries/System.Data.Common/src/System/Data/RecordManager.cs
index daa5cc158b141d..dfffcc6e52c216 100644
--- a/src/libraries/System.Data.Common/src/System/Data/RecordManager.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/RecordManager.cs
@@ -168,7 +168,7 @@ internal void Clear(bool clearAll)
                 _freeRecordList.Capacity = _freeRecordList.Count + _table.Rows.Count;
                 for (int record = 0; record < _recordCapacity; ++record)
                 {
-                    if (_rows[record] is { } row && row.rowID != -1)
+                    if (_rows[record] is DataRow row && row.rowID != -1)
                     {
                         int tempRecord = record;
                         FreeRecord(ref tempRecord);
diff --git a/src/libraries/System.Data.Common/src/System/Data/Select.cs b/src/libraries/System.Data.Common/src/System/Data/Select.cs
index 8dbd298e1bca63..97fbb80c7b08fc 100644
--- a/src/libraries/System.Data.Common/src/System/Data/Select.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/Select.cs
@@ -491,7 +491,7 @@ private void BuildLinearExpression()
                 {
                     if (!_candidateColumns[i].flag)
                     {
-                        if (_candidateColumns[i].expr is { } expr)
+                        if (_candidateColumns[i].expr is BinaryNode expr)
                         {
                             _linearExpression = (_linearExpression == null ? _candidateColumns[i].expr : new BinaryNode(_table, Operators.And, expr, _linearExpression));
                         }
diff --git a/src/libraries/System.Data.Common/src/System/Data/SortExpressionBuilder.cs b/src/libraries/System.Data.Common/src/System/Data/SortExpressionBuilder.cs
index 2889e2445b9cbb..c5304d94ef346a 100644
--- a/src/libraries/System.Data.Common/src/System/Data/SortExpressionBuilder.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/SortExpressionBuilder.cs
@@ -92,7 +92,7 @@ public List<object> Select(T row)
         /// Note: Comparison is done in the order it was Added.
         /// </summary>
         /// <returns>Comparison result of the combined Sort comparer expression</returns>
-        public int Compare([AllowNull] List<object> a, [AllowNull] List<object> b)
+        public int Compare(List<object>? a, List<object>? b)
         {
             Debug.Assert(a != null && b != null && a.Count == Count);
 
diff --git a/src/libraries/System.Data.Common/src/System/Data/TypedTableBaseExtensions.cs b/src/libraries/System.Data.Common/src/System/Data/TypedTableBaseExtensions.cs
index 91535113670d4e..ccdd59352c9fb9 100644
--- a/src/libraries/System.Data.Common/src/System/Data/TypedTableBaseExtensions.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/TypedTableBaseExtensions.cs
@@ -92,8 +92,7 @@ public static EnumerableRowCollection<TRow> AsEnumerable<TRow>(this TypedTableBa
             return new EnumerableRowCollection<TRow>(source as DataTable);
         }
 
-        [return: MaybeNull]
-        public static TRow ElementAtOrDefault<TRow>(this TypedTableBase<TRow> source, int index) where TRow : DataRow
+        public static TRow? ElementAtOrDefault<TRow>(this TypedTableBase<TRow> source, int index) where TRow : DataRow
         {
             if ((index >= 0) && (index < source.Rows.Count))
             {
diff --git a/src/libraries/System.Data.Common/src/System/Data/xmlsaver.cs b/src/libraries/System.Data.Common/src/System/Data/xmlsaver.cs
index 959cebbcfc51ce..0d5f4952a27713 100644
--- a/src/libraries/System.Data.Common/src/System/Data/xmlsaver.cs
+++ b/src/libraries/System.Data.Common/src/System/Data/xmlsaver.cs
@@ -6,6 +6,7 @@
 using System.Data.SqlTypes;
 using System.Data.Common;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.IO;
 using System.Text;
@@ -2250,7 +2251,7 @@ internal sealed class NewDiffgramGen
         internal XmlWriter _xmlw = default!; // Late-initialized
         private bool _fBefore;
         private bool _fErrors;
-        internal Hashtable _rowsOrder = default!; // Always initialized in DoAssignments
+        internal Hashtable _rowsOrder;
         private readonly ArrayList _tables = new ArrayList();
         private readonly bool _writeHierarchy;
 
@@ -2297,7 +2298,7 @@ private void CreateTableHierarchy(DataTable dt)
             }
         }
 
-
+        [MemberNotNull(nameof(_rowsOrder))]
         private void DoAssignments(ArrayList tables)
         {
             int rows = 0;
diff --git a/src/libraries/System.Data.Common/tests/System.Data.Common.Tests.csproj b/src/libraries/System.Data.Common/tests/System.Data.Common.Tests.csproj
index 75ae4978aa7cdb..3eff311a0a4bf8 100644
--- a/src/libraries/System.Data.Common/tests/System.Data.Common.Tests.csproj
+++ b/src/libraries/System.Data.Common/tests/System.Data.Common.Tests.csproj
@@ -119,6 +119,7 @@
     <Compile Include="$(CommonTestPath)System\Runtime\Serialization\Formatters\BinaryFormatterHelpers.cs"
              Link="Common\System\Runtime\Serialization\Formatters\BinaryFormatterHelpers.cs" />
   </ItemGroup>
+  <!-- S.D.SqlClient isn't live built anymore. -->
   <ItemGroup>
     <PackageReference Include="System.Data.SqlClient" Version="$(SystemDataSqlClientVersion)" />
   </ItemGroup>
diff --git a/src/libraries/System.Data.Common/tests/System/Data/Common/DbProviderFactoriesTests.cs b/src/libraries/System.Data.Common/tests/System/Data/Common/DbProviderFactoriesTests.cs
index 8862a85e5c377f..2537fb30e95dba 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/Common/DbProviderFactoriesTests.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/Common/DbProviderFactoriesTests.cs
@@ -15,6 +15,7 @@ public sealed class TestProviderFactory : DbProviderFactory
         private TestProviderFactory() { }
     }
 
+    [PlatformSpecific(~TestPlatforms.Browser)]
     public class DbProviderFactoriesTests
     {
         [Fact]
diff --git a/src/libraries/System.Data.Common/tests/System/Data/Common/DbProviderFactoryTest.cs b/src/libraries/System.Data.Common/tests/System/Data/Common/DbProviderFactoryTest.cs
index 9393016bc51f91..b810686ab4f72d 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/Common/DbProviderFactoryTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/Common/DbProviderFactoryTest.cs
@@ -6,6 +6,7 @@
 
 namespace System.Data.Tests.Common
 {
+    [PlatformSpecific(~TestPlatforms.Browser)]
     public class DbProviderFactoryTest
     {
         [Fact]
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataRowTest2.cs b/src/libraries/System.Data.Common/tests/System/Data/DataRowTest2.cs
index 7369c858866949..bfb22d111550f0 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataRowTest2.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataRowTest2.cs
@@ -1894,7 +1894,7 @@ public void IsNull_ByIndex()
             Assert.True(dr.IsNull(1));
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void IsNull_ByName()
         {
             DataTable dt = new DataTable();
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataSetInferXmlSchemaTest.cs b/src/libraries/System.Data.Common/tests/System/Data/DataSetInferXmlSchemaTest.cs
index b953a5d3616c65..5bf2ef00533a81 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataSetInferXmlSchemaTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataSetInferXmlSchemaTest.cs
@@ -246,7 +246,7 @@ public void SimpleElementTable()
             DataSetAssertion.AssertDataColumn("col3", dt.Columns[2], "col3", true, false, 0, 1, "col3", MappingType.Element, typeof(string), DBNull.Value, string.Empty, -1, string.Empty, 2, string.Empty, false, false);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void SimpleDataSet()
         {
             DataSet ds = GetDataSet(_xml8, null);
@@ -337,7 +337,7 @@ public void SignificantWhitespaceIgnored2()
             DataSetAssertion.AssertDataSet("pure_whitespace", ds, "root", 0, 0);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TwoElementTable()
         {
             // FIXME: Also test ReadXml (, XmlReadMode.InferSchema) and
@@ -356,7 +356,7 @@ public void TwoElementTable()
             DataSetAssertion.AssertDataColumn("col2_2", dt.Columns[1], "col2_2", true, false, 0, 1, "col2_2", MappingType.Element, typeof(string), DBNull.Value, string.Empty, -1, string.Empty, 1, string.Empty, false, false);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ConflictSimpleComplexColumns()
         {
             DataSet ds = GetDataSet(_xml18, null);
@@ -377,7 +377,7 @@ public void ConflictSimpleComplexColumns()
             DataSetAssertion.AssertForeignKeyConstraint("fkey", dr.ChildKeyConstraint, "table_col", AcceptRejectRule.None, Rule.Cascade, Rule.Cascade, new string[] { "table_Id" }, new string[] { "table_Id" });
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ConflictColumnTable()
         {
             DataSet ds = GetDataSet(_xml19, null);
@@ -398,7 +398,7 @@ public void ConflictColumnTable()
             DataSetAssertion.AssertForeignKeyConstraint("fkey", dr.ChildKeyConstraint, "table_col", AcceptRejectRule.None, Rule.Cascade, Rule.Cascade, new string[] { "table_Id" }, new string[] { "table_Id" });
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ConflictColumnTableAttribute()
         {
             // Conflicts between a column and a table, additionally an attribute.
@@ -421,7 +421,7 @@ public void ConflictColumnTableAttribute()
             DataSetAssertion.AssertForeignKeyConstraint("fkey", dr.ChildKeyConstraint, "table_col", AcceptRejectRule.None, Rule.Cascade, Rule.Cascade, new string[] { "table_Id" }, new string[] { "table_Id" });
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ConflictAttributeDataTable()
         {
             Assert.Throws<DataException>(() =>
@@ -433,7 +433,7 @@ public void ConflictAttributeDataTable()
            });
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ConflictExistingPrimaryKey()
         {
             Assert.Throws<ConstraintException>(() =>
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataSetReadXmlSchemaTest.cs b/src/libraries/System.Data.Common/tests/System/Data/DataSetReadXmlSchemaTest.cs
index 4c1bfa8ca081b1..de1c0685bb05e8 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataSetReadXmlSchemaTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataSetReadXmlSchemaTest.cs
@@ -52,7 +52,7 @@ private DataSet CreateTestSet()
             return ds;
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void SingleElementTreatmentDifference()
         {
             // This is one of the most complicated case. When the content
@@ -149,7 +149,7 @@ public void SingleElementTreatmentDifference()
             DataSetAssertion.AssertDataTable("complex", ds.Tables[0], "Root", 1, 0, 0, 0, 0, 0);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void SuspiciousDataSetElement()
         {
             string schema = @"<?xml version='1.0'?>
@@ -174,7 +174,7 @@ public void SuspiciousDataSetElement()
             DataSetAssertion.AssertDataTable("table", ds.Tables[0], "elem", 2, 0, 0, 0, 0, 0);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void UnusedComplexTypesIgnored()
         {
             string xs = @"<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' id='hoge'>
@@ -213,7 +213,7 @@ public void SimpleTypeComponentsIgnored()
             DataSetAssertion.AssertDataSet("ds", ds, "NewDataSet", 0, 0);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void IsDataSetAndTypeIgnored()
         {
             string xsbase = @"<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' xmlns:msdata='urn:schemas-microsoft-com:xml-msdata'>
@@ -243,7 +243,7 @@ public void IsDataSetAndTypeIgnored()
             DataSetAssertion.AssertDataSet("ds", ds, "NewDataSet", 1, 0);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void NestedReferenceNotAllowed()
         {
             string xs = @"<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' xmlns:msdata='urn:schemas-microsoft-com:xml-msdata'>
@@ -272,7 +272,7 @@ public void NestedReferenceNotAllowed()
            });
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void IsDataSetOnLocalElementIgnored()
         {
             string xsbase = @"<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' xmlns:msdata='urn:schemas-microsoft-com:xml-msdata'>
@@ -294,7 +294,7 @@ public void IsDataSetOnLocalElementIgnored()
             DataSetAssertion.AssertDataSet("ds", ds, "NewDataSet", 1, 0);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void LocaleOnRootWithoutIsDataSet()
         {
             using (new ThreadCultureChange("fi-FI"))
@@ -323,7 +323,7 @@ public void LocaleOnRootWithoutIsDataSet()
         }
 
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ElementHasIdentityConstraint()
         {
             string constraints = @"
@@ -381,7 +381,7 @@ public void ElementHasIdentityConstraint()
             Assert.Equal(0, ds.Relations.Count);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void PrefixedTargetNS()
         {
             string xs = @"<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' xmlns:msdata='urn:schemas-microsoft-com:xml-msdata' xmlns:x='urn:foo' targetNamespace='urn:foo' elementFormDefault='qualified'>
@@ -477,7 +477,7 @@ private void ReadTest1Check(DataSet ds)
                 new string[] { "Column1_3" });
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         // 001-004
         public void TestSampleFileNoTables()
         {
@@ -510,7 +510,7 @@ public void TestSampleFileNoTables()
             DataSetAssertion.AssertDataSet("004", ds, "NewDataSet", 0, 0);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TestSampleFileSimpleTables()
         {
             var ds = new DataSet();
@@ -547,7 +547,7 @@ public void TestSampleFileSimpleTables()
             DataSetAssertion.AssertDataColumn("att2", dt.Columns["att2"], "att2", true, false, 0, 1, "att2", MappingType.Attribute, typeof(int), 2, string.Empty, -1, string.Empty, /*1*/-1, string.Empty, false, false);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TestSampleFileComplexTables()
         {
             // Nested simple type element
@@ -608,7 +608,7 @@ public void TestSampleFileComplexTables()
             DataSetAssertion.AssertDataColumn("id", dt.Columns[1], "uno_Id", true, false, 0, 1, "uno_Id", MappingType.Hidden, typeof(int), DBNull.Value, string.Empty, -1, string.Empty, 1, string.Empty, false, false);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TestSampleFileComplexTables3()
         {
             var ds = new DataSet();
@@ -639,7 +639,7 @@ public void TestSampleFileComplexTables3()
             DataSetAssertion.AssertDataColumn("simple", dt.Columns[1], "e_text", false, false, 0, 1, "e_text", MappingType.SimpleContent, typeof(decimal), DBNull.Value, string.Empty, -1, string.Empty, 1, string.Empty, false, false);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TestSampleFileXPath()
         {
             var ds = new DataSet();
@@ -681,7 +681,7 @@ public void TestSampleFileXPath()
                     </xs:schema>"));
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TestAnnotatedRelation1()
         {
             var ds = new DataSet();
@@ -732,7 +732,7 @@ public void TestAnnotatedRelation1()
             DataSetAssertion.AssertDataRelation("rel", ds.Relations[0], "rel", false, new string[] { "pk" }, new string[] { "fk" }, false, false);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TestAnnotatedRelation2()
         {
             var ds = new DataSet();
@@ -783,7 +783,7 @@ public void TestAnnotatedRelation2()
             DataSetAssertion.AssertDataRelation("rel", ds.Relations[0], "rel", true, new string[] { "pk" }, new string[] { "fk" }, false, false);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void RepeatableSimpleElement()
         {
             var ds = new DataSet();
@@ -811,7 +811,7 @@ public void RepeatableSimpleElement()
             DataSetAssertion.AssertDataRelation("rel", ds.Relations[0], "Foo_Bar", true, new string[] { "Foo_Id" }, new string[] { "Foo_Id" }, true, true);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TestMoreThanOneRepeatableColumns()
         {
             var ds = new DataSet();
@@ -861,7 +861,7 @@ public void AutoIncrementStep()
             Assert.True(ds.GetXmlSchema().IndexOf("AutoIncrementStep") > 0);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadConstraints()
         {
             var ds = new DataSet();
@@ -904,7 +904,7 @@ public void ReadConstraints()
             Assert.Equal("fk1", ds.Tables[1].Constraints[0].ConstraintName);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadAnnotatedRelations_MultipleColumns()
         {
             var ds = new DataSet();
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataSetReadXmlTest.cs b/src/libraries/System.Data.Common/tests/System/Data/DataSetReadXmlTest.cs
index 0bf6fd54914338..fa45aa582875a8 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataSetReadXmlTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataSetReadXmlTest.cs
@@ -65,7 +65,7 @@ public class DataSetReadXmlTest
 </xs:schema>";
         private const string schema2 = schema1 + xml8;
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadSimpleAuto()
         {
             DataSet ds;
@@ -285,7 +285,7 @@ public void ReadSimpleIgnoreSchema()
                 "NewDataSet", 0);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadSimpleInferSchema()
         {
             DataSet ds;
@@ -606,7 +606,7 @@ public void SequentialRead2()
             DataSetAssertion.AssertDataTable("#3", ds.Tables[0], "root", 1, 2, 0, 0, 0, 0);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadComplexElementDocument()
         {
             var ds = new DataSet();
@@ -639,7 +639,7 @@ public void IgnoreSchemaShouldFillData()
             Assert.Equal(0, dt.Rows.Count);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void NameConflictDSAndTable()
         {
             string xml = @"<PriceListDetails>
@@ -657,7 +657,7 @@ public void NameConflictDSAndTable()
             Assert.NotNull(ds.Tables["PriceListDetails"]);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ColumnOrder()
         {
             string xml = "<?xml version=\"1.0\" standalone=\"yes\"?>" +
@@ -690,7 +690,7 @@ public void ColumnOrder()
             Assert.Equal(3, ds.Tables[0].Columns[3].Ordinal);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void XmlSpace()
         {
             string xml = "<?xml version=\"1.0\" standalone=\"yes\"?>" +
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataSetTest.cs b/src/libraries/System.Data.Common/tests/System/Data/DataSetTest.cs
index bd35d061c0dd41..4c2e8b38b4e5f3 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataSetTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataSetTest.cs
@@ -367,7 +367,7 @@ public void OwnWriteXmlSchema()
             Assert.Equal("</xs:schema>", TextString);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadWriteXml()
         {
             var ds = new DataSet();
@@ -424,7 +424,7 @@ public void ReadWriteXml()
             Assert.Equal("</Root>", TextString);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadWriteXmlDiffGram()
         {
             var ds = new DataSet();
@@ -507,7 +507,7 @@ public void ReadWriteXmlDiffGram()
             Assert.Equal("</diffgr:diffgram>", TextString);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void WriteXmlSchema()
         {
             using (new ThreadCultureChange("fi-FI"))
@@ -989,7 +989,7 @@ public void WriteNestedTableXml()
             Assert.Equal(sw.ToString().Replace("\r\n", "\n"), xml.Replace("\r\n", "\n"));
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void WriteXmlToStream()
         {
             string xml = "<set><table1><col1>sample text</col1><col2/></table1><table2 attr='value'><col3>sample text 2</col3></table2></set>";
@@ -1028,7 +1028,7 @@ public void WtiteXmlEncodedXml()
             Assert.Equal(sw.ToString().Replace("\r\n", "\n"), xml.Replace("\r\n", "\n"));
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadWriteXml2()
         {
             string xml = "<FullTextResponse><Domains><AvailResponse info='y' name='novell-ximian-group' /><AvailResponse info='n' name='ximian' /></Domains></FullTextResponse>";
@@ -1046,7 +1046,7 @@ public void ReadWriteXml2()
             Assert.Equal(xml, sw.ToString());
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadWriteXml3()
         {
             string input = @"<FullTextResponse>
@@ -1559,7 +1559,7 @@ public void WriteXmlModeSchema()
             Assert.Equal(result.Replace("\r\n", "\n"), xml.Replace("\r\n", "\n"));
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void WriteXmlModeSchema1()
         {
             // Keeping the brackets as the test otherwise starts to fail.
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataSetTest2.cs b/src/libraries/System.Data.Common/tests/System/Data/DataSetTest2.cs
index aec8467dbc6094..d5943b3da388c7 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataSetTest2.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataSetTest2.cs
@@ -540,7 +540,7 @@ public void HasErrors()
 
         #region test namespaces
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_BasicXml()
         {
             StringBuilder sb = new StringBuilder();
@@ -572,7 +572,7 @@ public void InferXmlSchema_BasicXml()
             Assert.Equal("Discontinued", ds.Tables[1].Columns[2].ColumnName);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_WithoutIgnoreNameSpaces()
         {
             StringBuilder sb = new StringBuilder();
@@ -597,7 +597,7 @@ public void InferXmlSchema_WithoutIgnoreNameSpaces()
             Assert.Equal(8, ds.Tables.Count);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_IgnoreNameSpace()
         {
             StringBuilder sb = new StringBuilder();
@@ -637,7 +637,7 @@ public void InferXmlSchema_IgnoreNameSpace()
             Assert.Equal("Discontinued", ds.Tables[2].Columns["Discontinued"].ColumnName);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_IgnoreNameSpaces() //Ignoring 2 namespaces
         {
             StringBuilder sb = new StringBuilder();
@@ -667,7 +667,7 @@ public void InferXmlSchema_IgnoreNameSpaces() //Ignoring 2 namespaces
         #endregion
 
         #region inferringTables
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_inferringTables1()
         {
             //According to the msdn documantaion :
@@ -691,7 +691,7 @@ public void InferXmlSchema_inferringTables1()
             Assert.Equal("Element1_Text", ds.Tables[0].Columns["Element1_Text"].ColumnName);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_inferringTables2()
         {
             //According to the msdn documantaion :
@@ -741,7 +741,7 @@ public void InferXmlSchema_inferringTables3()
             Assert.Equal("Element2", ds.Tables[0].Columns["Element2"].ColumnName);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_inferringTables4()
         {
             //According to the msdn documantaion :
@@ -766,7 +766,7 @@ public void InferXmlSchema_inferringTables4()
             Assert.Equal("attr2", ds.Tables[0].Columns["attr2"].ColumnName);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_inferringTables5()
         {
             //According to the msdn documantaion :
@@ -791,7 +791,7 @@ public void InferXmlSchema_inferringTables5()
         #endregion
 
         #region inferringColumns
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_inferringColumns1()
         {
             //ms-help://MS.MSDNQTR.2003FEB.1033/cpguide/html/cpconinferringcolumns.htm
@@ -815,7 +815,7 @@ public void InferXmlSchema_inferringColumns1()
             Assert.Equal(typeof(string), ds.Tables[0].Columns["attr2"].DataType);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_inferringColumns2()
         {
             //ms-help://MS.MSDNQTR.2003FEB.1033/cpguide/html/cpconinferringcolumns.htm
@@ -850,7 +850,7 @@ public void InferXmlSchema_inferringColumns2()
 
         #region Inferring Relationships
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_inferringRelationships1()
         {
             //ms-help://MS.MSDNQTR.2003FEB.1033/cpguide/html/cpconinferringrelationships.htm
@@ -914,7 +914,7 @@ public void InferXmlSchema_inferringRelationships1()
 
         #region Inferring Element Text
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_elementText1()
         {
             //ms-help://MS.MSDNQTR.2003FEB.1033/cpguide/html/cpconinferringelementtext.htm
@@ -942,7 +942,7 @@ public void InferXmlSchema_elementText1()
             Assert.Equal(typeof(string), ds.Tables["Element1"].Columns["Element1_Text"].DataType);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void InferXmlSchema_elementText2()
         {
             //ms-help://MS.MSDNQTR.2003FEB.1033/cpguide/html/cpconinferringelementtext.htm
@@ -988,7 +988,7 @@ public void Locale()
             Assert.Equal(culInfo, ds.Locale);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void DataSetSpecificCulture()
         {
             using (new ThreadCultureChange("cs-CZ"))
@@ -2235,7 +2235,7 @@ public void ReadXml_Strm2()
             // Tables[2] ParentRelations[0] name
             Assert.Equal("Stock_Price", ds.Tables[2].ParentRelations[0].RelationName);
         }
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadXml_Strm3()
         {
             DataSet ds = new DataSet("TestDataSet");
@@ -2264,7 +2264,7 @@ public void ReadXml_Strm3()
             Assert.Equal(MappingType.Hidden, ds.Tables["Price"].Columns["Stock_Id"].ColumnMapping);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadXml_Strm4()
         {
             _ds = new DataSet("Stocks");
@@ -2365,7 +2365,7 @@ private void privateTestCase(string name, string toTable, string toTestSelect, s
             Assert.Equal(_ds.Tables[toTable].Select(toTestSelect)[0]["Stock_Id"], _ds.Tables[toCompareTable].Select(toCompareSelect)[0]["Stock_Id"]);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadXml_Strm5()
         {
             string xmlData;
@@ -2589,7 +2589,7 @@ private string dataSetDescription(DataSet ds)
             return desc;
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadXml_Strm6()
         {
             // TC1
@@ -2608,7 +2608,7 @@ public void ReadXml_Strm6()
             Assert.Equal(3, ds.Tables["c"].Rows.Count);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadXmlSchema_2()
         {
             var ds = new DataSet();
@@ -3070,7 +3070,7 @@ private void CheckNode(string description, string xPath, int expectedNodesCout,
             Assert.Equal(expectedNodesCout, actualNodeCount);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void WriteXml_Stream()
         {
             {
@@ -3515,7 +3515,7 @@ private void AssertDataTableValues(DataTable dt)
             Assert.Equal("data8", dt.Rows[0]["&ID"]);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void Bug537229_BinFormatSerializer_Test()
         {
             DataSet ds = new DataSet();
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataSetTypedDataSetTest.cs b/src/libraries/System.Data.Common/tests/System/Data/DataSetTypedDataSetTest.cs
index cc5d61cdac4a73..856b779e8c11a6 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataSetTypedDataSetTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataSetTypedDataSetTest.cs
@@ -40,7 +40,7 @@ public class DataSetTypedDataSetTest
     {
         private string _eventStatus = string.Empty;
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TypedDataSet()
         {
             int i = 0;
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataTableExtensionsTest.cs b/src/libraries/System.Data.Common/tests/System/Data/DataTableExtensionsTest.cs
index e3f53fe429ab63..8608ba7bd645de 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataTableExtensionsTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataTableExtensionsTest.cs
@@ -5,6 +5,7 @@
 
 namespace System.Data.Tests
 {
+    [PlatformSpecific(~TestPlatforms.Browser)]
     public class DataTableExtensionsTest
     {
         private DataTable _dt;
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataTableReadXmlSchemaTest.cs b/src/libraries/System.Data.Common/tests/System/Data/DataTableReadXmlSchemaTest.cs
index 59191f5226fea4..17bb95df00d1ae 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataTableReadXmlSchemaTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataTableReadXmlSchemaTest.cs
@@ -53,7 +53,7 @@ private DataSet CreateTestSet()
             return ds;
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void SuspiciousDataSetElement()
         {
             string schema = @"<?xml version='1.0'?>
@@ -108,7 +108,7 @@ public void UnusedComplexTypesIgnored()
             });
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void IsDataSetAndTypeIgnored()
         {
             string xsbase = @"<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' xmlns:msdata='urn:schemas-microsoft-com:xml-msdata'>
@@ -140,7 +140,7 @@ public void IsDataSetAndTypeIgnored()
             });
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void NestedReferenceNotAllowed()
         {
             string xs = @"<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' xmlns:msdata='urn:schemas-microsoft-com:xml-msdata'>
@@ -194,7 +194,7 @@ public void LocaleOnRootWithoutIsDataSet()
             DataSetAssertion.AssertDataColumn("col2", dt.Columns[1], "Child", false, false, 0, 1, "Child", MappingType.Element, typeof(string), DBNull.Value, string.Empty, -1, string.Empty, 1, string.Empty, false, false);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void PrefixedTargetNS()
         {
             string xs = @"<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' xmlns:msdata='urn:schemas-microsoft-com:xml-msdata' xmlns:x='urn:foo' targetNamespace='urn:foo' elementFormDefault='qualified'>
@@ -308,7 +308,7 @@ public void TestSampleFileSimpleTables()
             DataSetAssertion.AssertDataColumn("att2", dt.Columns["att2"], "att2", true, false, 0, 1, "att2", MappingType.Attribute, typeof(int), 2, string.Empty, -1, string.Empty, /*1*/-1, string.Empty, false, false);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TestSampleFileComplexTables3()
         {
             var ds = new DataSet();
@@ -338,7 +338,7 @@ public void TestSampleFileComplexTables3()
             DataSetAssertion.AssertDataColumn("simple", dt.Columns[1], "e_text", false, false, 0, 1, "e_text", MappingType.SimpleContent, typeof(decimal), DBNull.Value, string.Empty, -1, string.Empty, 1, string.Empty, false, false);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void TestSampleFileXPath()
         {
             var ds = new DataSet();
@@ -428,7 +428,7 @@ public void ReadConstraints()
             Assert.Equal("Constraint1", ds.Tables[0].Constraints[0].ConstraintName);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void XsdSchemaSerializationIgnoresLocale()
         {
             var serializer = new BinaryFormatter();
@@ -475,7 +475,7 @@ public void XsdSchemaSerializationIgnoresLocale()
             Assert.DoesNotContain("()2", rawSchemaXML);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework, ".NET Framework does not have the fix for this bug")]
         public void XsdSchemaDeserializationIgnoresLocale()
         {
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataTableTest.cs b/src/libraries/System.Data.Common/tests/System/Data/DataTableTest.cs
index 2202651e330ebd..df8276d0aac4eb 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataTableTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataTableTest.cs
@@ -375,7 +375,7 @@ public void SelectOperators()
 
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void DataColumnTypeSerialization()
         {
             DataTable dt = new DataTable("MyTable");
@@ -1767,7 +1767,7 @@ public void TestWriteXmlSchema3()
             Assert.Equal("</xs:schema>", textString);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void Serialize()
         {
             // Create an array with multiple elements refering to
@@ -2887,7 +2887,7 @@ public void ReadXmlSchema()
             Assert.True(column3.Unique);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void ReadXmlSchema_2()
         {
             DataTable dt = new DataTable();
@@ -3111,7 +3111,7 @@ public void ReadXmlSchema_ByXmlReader()
             Assert.Equal(0, dt2.Rows.Count);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void WriteXmlSchema()
         {
             using (new ThreadCultureChange("en-GB"))
diff --git a/src/libraries/System.Data.Common/tests/System/Data/DataTableTest4.cs b/src/libraries/System.Data.Common/tests/System/Data/DataTableTest4.cs
index 4fa0a6308fa764..da6cabc4ecd1be 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/DataTableTest4.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/DataTableTest4.cs
@@ -870,7 +870,7 @@ public void XmlTest7()
             Assert.Equal(3, row["ParentID"]);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void XmlTest8()
         {
             MakeParentTable1();
@@ -910,7 +910,7 @@ public void XmlTest8()
             Assert.Equal("3", row["DepartmentID"]);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void XmlTest9()
         {
             MakeParentTable1();
diff --git a/src/libraries/System.Data.Common/tests/System/Data/FacadeTest.cs b/src/libraries/System.Data.Common/tests/System/Data/FacadeTest.cs
index 49540efe7a7eb6..f8eba45d7f5c48 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/FacadeTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/FacadeTest.cs
@@ -10,6 +10,7 @@ public class FacadeTest
         [Theory]
         [InlineData("Microsoft.SqlServer.Server.SqlMetaData")] // Type from System.Data.SqlClient
         [InlineData("System.Data.SqlTypes.SqlBytes")] // Type from System.Data.Common
+        [PlatformSpecific(~TestPlatforms.Browser)]
         public void TestSystemData(string typeName)
         {
             // Verify that the type can be loaded via .NET Framework compat facade
diff --git a/src/libraries/System.Data.Common/tests/System/Data/SqlTypes/SqlStringSortingTest.cs b/src/libraries/System.Data.Common/tests/System/Data/SqlTypes/SqlStringSortingTest.cs
index 1f6fb8536ea458..0cae8f7a40409e 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/SqlTypes/SqlStringSortingTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/SqlTypes/SqlStringSortingTest.cs
@@ -37,7 +37,7 @@ public static class SqlStringSortingTest
 
         private static readonly UnicodeEncoding s_unicodeEncoding = new UnicodeEncoding(bigEndian: false, byteOrderMark: false, throwOnInvalidBytes: true);
 
-        [ConditionalTheory]
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         [InlineData("ja-JP", 0x0411)] // Japanese - Japan
         [InlineData("ar-SA", 0x0401)] // Arabic - Saudi Arabia
         [InlineData("de-DE", 0x0407)] // German - Germany
diff --git a/src/libraries/System.Data.Common/tests/System/Data/SqlTypes/SqlStringTest.cs b/src/libraries/System.Data.Common/tests/System/Data/SqlTypes/SqlStringTest.cs
index d123a60bf4e0b6..86a4b1683c4c92 100644
--- a/src/libraries/System.Data.Common/tests/System/Data/SqlTypes/SqlStringTest.cs
+++ b/src/libraries/System.Data.Common/tests/System/Data/SqlTypes/SqlStringTest.cs
@@ -62,7 +62,7 @@ public void Constructor_Value_Success()
             ValidateProperties(value, CultureInfo.CurrentCulture, new SqlString(value));
         }
 
-        [Theory]
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         [InlineData(1033, "en-US")]
         [InlineData(1036, "fr-FR")]
         public void Constructor_ValueLcid_Success(int lcid, string name)
@@ -97,35 +97,38 @@ public void Create()
             SqlString testString = new SqlString("Test");
             Assert.Equal("Test", testString.Value);
 
-            // SqlString (String, int)
-            testString = new SqlString("Test", 2057);
-            Assert.Equal(2057, testString.LCID);
-
-            // SqlString (int, SqlCompareOptions, byte[])
-            testString = new SqlString(2057,
-                SqlCompareOptions.BinarySort | SqlCompareOptions.IgnoreCase,
-                new byte[2] { 123, 221 });
-            Assert.Equal(2057, testString.CompareInfo.LCID);
-
-            // SqlString(string, int, SqlCompareOptions)
-            testString = new SqlString("Test", 2057, SqlCompareOptions.IgnoreNonSpace);
-            Assert.False(testString.IsNull);
-
-            // SqlString (int, SqlCompareOptions, byte[], bool)
-            testString = new SqlString(2057, SqlCompareOptions.BinarySort, new byte[4] { 100, 100, 200, 45 }, true);
-            Assert.Equal((byte)63, testString.GetNonUnicodeBytes()[0]);
-            testString = new SqlString(2057, SqlCompareOptions.BinarySort, new byte[2] { 113, 100 }, false);
-            Assert.Equal("qd", testString.Value);
-
-            // SqlString (int, SqlCompareOptions, byte[], int, int)
-            testString = new SqlString(2057, SqlCompareOptions.BinarySort, new byte[2] { 113, 100 }, 0, 2);
-            Assert.False(testString.IsNull);
-
-            // SqlString (int, SqlCompareOptions, byte[], int, int, bool)
-            testString = new SqlString(2057, SqlCompareOptions.IgnoreCase, new byte[3] { 100, 111, 50 }, 1, 2, false);
-            Assert.Equal("o2", testString.Value);
-            testString = new SqlString(2057, SqlCompareOptions.IgnoreCase, new byte[3] { 123, 111, 222 }, 1, 2, true);
-            Assert.False(testString.IsNull);
+            if (PlatformDetection.IsNotInvariantGlobalization)
+            {
+                // SqlString (String, int)
+                testString = new SqlString("Test", 2057);
+                Assert.Equal(2057, testString.LCID);
+
+                // SqlString (int, SqlCompareOptions, byte[])
+                testString = new SqlString(2057,
+                    SqlCompareOptions.BinarySort | SqlCompareOptions.IgnoreCase,
+                    new byte[2] { 123, 221 });
+                Assert.Equal(2057, testString.CompareInfo.LCID);
+
+                // SqlString(string, int, SqlCompareOptions)
+                testString = new SqlString("Test", 2057, SqlCompareOptions.IgnoreNonSpace);
+                Assert.False(testString.IsNull);
+
+                // SqlString (int, SqlCompareOptions, byte[], bool)
+                testString = new SqlString(2057, SqlCompareOptions.BinarySort, new byte[4] { 100, 100, 200, 45 }, true);
+                Assert.Equal((byte)63, testString.GetNonUnicodeBytes()[0]);
+                testString = new SqlString(2057, SqlCompareOptions.BinarySort, new byte[2] { 113, 100 }, false);
+                Assert.Equal("qd", testString.Value);
+
+                // SqlString (int, SqlCompareOptions, byte[], int, int)
+                testString = new SqlString(2057, SqlCompareOptions.BinarySort, new byte[2] { 113, 100 }, 0, 2);
+                Assert.False(testString.IsNull);
+
+                // SqlString (int, SqlCompareOptions, byte[], int, int, bool)
+                testString = new SqlString(2057, SqlCompareOptions.IgnoreCase, new byte[3] { 100, 111, 50 }, 1, 2, false);
+                Assert.Equal("o2", testString.Value);
+                testString = new SqlString(2057, SqlCompareOptions.IgnoreCase, new byte[3] { 123, 111, 222 }, 1, 2, true);
+                Assert.False(testString.IsNull);
+            }
         }
 
         [Fact]
@@ -170,7 +173,7 @@ public void PublicFields()
         }
 
         // Test properties
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void Properties()
         {
             using (new ThreadCultureChange("en-AU"))
@@ -207,7 +210,7 @@ public void CompareToArgumentException()
             AssertExtensions.Throws<ArgumentException>(null, () => _test1.CompareTo(test));
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void CompareToSqlTypeException()
         {
             SqlString t1 = new SqlString("test", 2057, SqlCompareOptions.IgnoreCase);
@@ -215,7 +218,7 @@ public void CompareToSqlTypeException()
             Assert.Throws<SqlTypeException>(() => t1.CompareTo(t2));
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotInvariantGlobalization))]
         public void CompareTo()
         {
             Assert.True(_test1.CompareTo(_test3) < 0);
diff --git a/src/libraries/System.Data.DataSetExtensions/Directory.Build.props b/src/libraries/System.Data.DataSetExtensions/Directory.Build.props
index 46a67e8e603423..bfb6ea882438b6 100644
--- a/src/libraries/System.Data.DataSetExtensions/Directory.Build.props
+++ b/src/libraries/System.Data.DataSetExtensions/Directory.Build.props
@@ -4,6 +4,5 @@
     <!-- AssemblyVersion is frozen to that which originally shipped in 2.1 -->
     <AssemblyVersion>4.0.0.0</AssemblyVersion>
     <StrongNameKeyId>ECMA</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Data.DataSetExtensions/ref/System.Data.DataSetExtensions.csproj b/src/libraries/System.Data.DataSetExtensions/ref/System.Data.DataSetExtensions.csproj
index 08914f651d1b80..d1d4624ffde4c0 100644
--- a/src/libraries/System.Data.DataSetExtensions/ref/System.Data.DataSetExtensions.csproj
+++ b/src/libraries/System.Data.DataSetExtensions/ref/System.Data.DataSetExtensions.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Data.DataSetExtensions.Forwards.cs" />
diff --git a/src/libraries/System.Data.DataSetExtensions/src/System.Data.DataSetExtensions.csproj b/src/libraries/System.Data.DataSetExtensions/src/System.Data.DataSetExtensions.csproj
index 03a9ccaaf1a79c..3dd6d9ffcab9be 100644
--- a/src/libraries/System.Data.DataSetExtensions/src/System.Data.DataSetExtensions.csproj
+++ b/src/libraries/System.Data.DataSetExtensions/src/System.Data.DataSetExtensions.csproj
@@ -1,8 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Data.DataSetExtensions</AssemblyName>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup>
   </PropertyGroup>
diff --git a/src/libraries/System.Data.Odbc/ref/System.Data.Odbc.cs b/src/libraries/System.Data.Odbc/ref/System.Data.Odbc.cs
index d755e6d29560cf..858ecbf6e8fe04 100644
--- a/src/libraries/System.Data.Odbc/ref/System.Data.Odbc.cs
+++ b/src/libraries/System.Data.Odbc/ref/System.Data.Odbc.cs
@@ -6,20 +6,22 @@
 
 namespace System.Data.Odbc
 {
+    [System.ComponentModel.DesignerAttribute("Microsoft.VSDesigner.Data.VS.OdbcCommandDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public sealed partial class OdbcCommand : System.Data.Common.DbCommand, System.ICloneable
     {
         public OdbcCommand() { }
-        public OdbcCommand(string cmdText) { }
-        public OdbcCommand(string cmdText, System.Data.Odbc.OdbcConnection connection) { }
-        public OdbcCommand(string cmdText, System.Data.Odbc.OdbcConnection connection, System.Data.Odbc.OdbcTransaction transaction) { }
+        public OdbcCommand(string? cmdText) { }
+        public OdbcCommand(string? cmdText, System.Data.Odbc.OdbcConnection? connection) { }
+        public OdbcCommand(string? cmdText, System.Data.Odbc.OdbcConnection? connection, System.Data.Odbc.OdbcTransaction? transaction) { }
+        [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public override string CommandText { get { throw null; } set { } }
         public override int CommandTimeout { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute(System.Data.CommandType.Text)]
         public override System.Data.CommandType CommandType { get { throw null; } set { } }
-        public new System.Data.Odbc.OdbcConnection Connection { get { throw null; } set { } }
-        protected override System.Data.Common.DbConnection DbConnection { get { throw null; } set { } }
+        public new System.Data.Odbc.OdbcConnection? Connection { get { throw null; } set { } }
+        protected override System.Data.Common.DbConnection? DbConnection { get { throw null; } set { } }
         protected override System.Data.Common.DbParameterCollection DbParameterCollection { get { throw null; } }
-        protected override System.Data.Common.DbTransaction DbTransaction { get { throw null; } set { } }
+        protected override System.Data.Common.DbTransaction? DbTransaction { get { throw null; } set { } }
         [System.ComponentModel.BrowsableAttribute(false)]
         [System.ComponentModel.DefaultValueAttribute(true)]
         [System.ComponentModel.DesignOnlyAttribute(true)]
@@ -29,7 +31,7 @@ public OdbcCommand(string cmdText, System.Data.Odbc.OdbcConnection connection, S
         public new System.Data.Odbc.OdbcParameterCollection Parameters { get { throw null; } }
         [System.ComponentModel.BrowsableAttribute(false)]
         [System.ComponentModel.DesignerSerializationVisibilityAttribute(System.ComponentModel.DesignerSerializationVisibility.Hidden)]
-        public new System.Data.Odbc.OdbcTransaction Transaction { get { throw null; } set { } }
+        public new System.Data.Odbc.OdbcTransaction? Transaction { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute(System.Data.UpdateRowSource.Both)]
         public override System.Data.UpdateRowSource UpdatedRowSource { get { throw null; } set { } }
         public override void Cancel() { }
@@ -40,16 +42,16 @@ protected override void Dispose(bool disposing) { }
         public override int ExecuteNonQuery() { throw null; }
         public new System.Data.Odbc.OdbcDataReader ExecuteReader() { throw null; }
         public new System.Data.Odbc.OdbcDataReader ExecuteReader(System.Data.CommandBehavior behavior) { throw null; }
-        public override object ExecuteScalar() { throw null; }
+        public override object? ExecuteScalar() { throw null; }
         public override void Prepare() { }
         public void ResetCommandTimeout() { }
-        object System.ICloneable.Clone() { throw null; }
+        object? System.ICloneable.Clone() { throw null; }
     }
     public sealed partial class OdbcCommandBuilder : System.Data.Common.DbCommandBuilder
     {
         public OdbcCommandBuilder() { }
-        public OdbcCommandBuilder(System.Data.Odbc.OdbcDataAdapter adapter) { }
-        public new System.Data.Odbc.OdbcDataAdapter DataAdapter { get { throw null; } set { } }
+        public OdbcCommandBuilder(System.Data.Odbc.OdbcDataAdapter? adapter) { }
+        public new System.Data.Odbc.OdbcDataAdapter? DataAdapter { get { throw null; } set { } }
         protected override void ApplyParameterInfo(System.Data.Common.DbParameter parameter, System.Data.DataRow datarow, System.Data.StatementType statementType, bool whereClause) { }
         public static void DeriveParameters(System.Data.Odbc.OdbcCommand command) { }
         public new System.Data.Odbc.OdbcCommand GetDeleteCommand() { throw null; }
@@ -62,15 +64,16 @@ public static void DeriveParameters(System.Data.Odbc.OdbcCommand command) { }
         public new System.Data.Odbc.OdbcCommand GetUpdateCommand() { throw null; }
         public new System.Data.Odbc.OdbcCommand GetUpdateCommand(bool useColumnsForParameterNames) { throw null; }
         public override string QuoteIdentifier(string unquotedIdentifier) { throw null; }
-        public string QuoteIdentifier(string unquotedIdentifier, System.Data.Odbc.OdbcConnection connection) { throw null; }
+        public string QuoteIdentifier(string unquotedIdentifier, System.Data.Odbc.OdbcConnection? connection) { throw null; }
         protected override void SetRowUpdatingHandler(System.Data.Common.DbDataAdapter adapter) { }
         public override string UnquoteIdentifier(string quotedIdentifier) { throw null; }
-        public string UnquoteIdentifier(string quotedIdentifier, System.Data.Odbc.OdbcConnection connection) { throw null; }
+        public string UnquoteIdentifier(string quotedIdentifier, System.Data.Odbc.OdbcConnection? connection) { throw null; }
     }
     public sealed partial class OdbcConnection : System.Data.Common.DbConnection, System.ICloneable
     {
         public OdbcConnection() { }
-        public OdbcConnection(string connectionString) { }
+        public OdbcConnection(string? connectionString) { }
+        [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public override string ConnectionString { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute(15)]
         [System.ComponentModel.DesignerSerializationVisibilityAttribute(System.ComponentModel.DesignerSerializationVisibility.Hidden)]
@@ -89,7 +92,7 @@ public OdbcConnection(string connectionString) { }
         [System.ComponentModel.BrowsableAttribute(false)]
         [System.ComponentModel.DesignerSerializationVisibilityAttribute(System.ComponentModel.DesignerSerializationVisibility.Hidden)]
         public override System.Data.ConnectionState State { get { throw null; } }
-        public event System.Data.Odbc.OdbcInfoMessageEventHandler InfoMessage { add { } remove { } }
+        public event System.Data.Odbc.OdbcInfoMessageEventHandler? InfoMessage { add { } remove { } }
         protected override System.Data.Common.DbTransaction BeginDbTransaction(System.Data.IsolationLevel isolationLevel) { throw null; }
         public new System.Data.Odbc.OdbcTransaction BeginTransaction() { throw null; }
         public new System.Data.Odbc.OdbcTransaction BeginTransaction(System.Data.IsolationLevel isolevel) { throw null; }
@@ -100,7 +103,7 @@ public override void Close() { }
         protected override void Dispose(bool disposing) { }
         public override System.Data.DataTable GetSchema() { throw null; }
         public override System.Data.DataTable GetSchema(string collectionName) { throw null; }
-        public override System.Data.DataTable GetSchema(string collectionName, string[] restrictionValues) { throw null; }
+        public override System.Data.DataTable GetSchema(string collectionName, string?[]? restrictionValues) { throw null; }
         public override void Open() { }
         public static void ReleaseObjectPool() { }
         object System.ICloneable.Clone() { throw null; }
@@ -108,39 +111,41 @@ public static void ReleaseObjectPool() { }
     public sealed partial class OdbcConnectionStringBuilder : System.Data.Common.DbConnectionStringBuilder
     {
         public OdbcConnectionStringBuilder() { }
-        public OdbcConnectionStringBuilder(string connectionString) { }
+        public OdbcConnectionStringBuilder(string? connectionString) { }
         [System.ComponentModel.DisplayNameAttribute("Driver")]
         public string Driver { get { throw null; } set { } }
         [System.ComponentModel.DisplayNameAttribute("Dsn")]
         public string Dsn { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public override object this[string keyword] { get { throw null; } set { } }
         public override System.Collections.ICollection Keys { get { throw null; } }
         public override void Clear() { }
         public override bool ContainsKey(string keyword) { throw null; }
         public override bool Remove(string keyword) { throw null; }
-        public override bool TryGetValue(string keyword, out object value) { throw null; }
+        public override bool TryGetValue(string keyword, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out object? value) { throw null; }
     }
+    [System.ComponentModel.DesignerAttribute("Microsoft.VSDesigner.Data.VS.OdbcDataAdapterDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public sealed partial class OdbcDataAdapter : System.Data.Common.DbDataAdapter, System.Data.IDataAdapter, System.Data.IDbDataAdapter, System.ICloneable
     {
         public OdbcDataAdapter() { }
-        public OdbcDataAdapter(System.Data.Odbc.OdbcCommand selectCommand) { }
-        public OdbcDataAdapter(string selectCommandText, System.Data.Odbc.OdbcConnection selectConnection) { }
-        public OdbcDataAdapter(string selectCommandText, string selectConnectionString) { }
-        public new System.Data.Odbc.OdbcCommand DeleteCommand { get { throw null; } set { } }
-        public new System.Data.Odbc.OdbcCommand InsertCommand { get { throw null; } set { } }
-        public new System.Data.Odbc.OdbcCommand SelectCommand { get { throw null; } set { } }
-        System.Data.IDbCommand System.Data.IDbDataAdapter.DeleteCommand { get { throw null; } set { } }
-        System.Data.IDbCommand System.Data.IDbDataAdapter.InsertCommand { get { throw null; } set { } }
-        System.Data.IDbCommand System.Data.IDbDataAdapter.SelectCommand { get { throw null; } set { } }
-        System.Data.IDbCommand System.Data.IDbDataAdapter.UpdateCommand { get { throw null; } set { } }
-        public new System.Data.Odbc.OdbcCommand UpdateCommand { get { throw null; } set { } }
-        public event System.Data.Odbc.OdbcRowUpdatedEventHandler RowUpdated { add { } remove { } }
-        public event System.Data.Odbc.OdbcRowUpdatingEventHandler RowUpdating { add { } remove { } }
-        protected override System.Data.Common.RowUpdatedEventArgs CreateRowUpdatedEvent(System.Data.DataRow dataRow, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
-        protected override System.Data.Common.RowUpdatingEventArgs CreateRowUpdatingEvent(System.Data.DataRow dataRow, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
+        public OdbcDataAdapter(System.Data.Odbc.OdbcCommand? selectCommand) { }
+        public OdbcDataAdapter(string? selectCommandText, System.Data.Odbc.OdbcConnection? selectConnection) { }
+        public OdbcDataAdapter(string? selectCommandText, string? selectConnectionString) { }
+        public new System.Data.Odbc.OdbcCommand? DeleteCommand { get { throw null; } set { } }
+        public new System.Data.Odbc.OdbcCommand? InsertCommand { get { throw null; } set { } }
+        public new System.Data.Odbc.OdbcCommand? SelectCommand { get { throw null; } set { } }
+        System.Data.IDbCommand? System.Data.IDbDataAdapter.DeleteCommand { get { throw null; } set { } }
+        System.Data.IDbCommand? System.Data.IDbDataAdapter.InsertCommand { get { throw null; } set { } }
+        System.Data.IDbCommand? System.Data.IDbDataAdapter.SelectCommand { get { throw null; } set { } }
+        System.Data.IDbCommand? System.Data.IDbDataAdapter.UpdateCommand { get { throw null; } set { } }
+        public new System.Data.Odbc.OdbcCommand? UpdateCommand { get { throw null; } set { } }
+        public event System.Data.Odbc.OdbcRowUpdatedEventHandler? RowUpdated { add { } remove { } }
+        public event System.Data.Odbc.OdbcRowUpdatingEventHandler? RowUpdating { add { } remove { } }
+        protected override System.Data.Common.RowUpdatedEventArgs CreateRowUpdatedEvent(System.Data.DataRow dataRow, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
+        protected override System.Data.Common.RowUpdatingEventArgs CreateRowUpdatingEvent(System.Data.DataRow dataRow, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
         protected override void OnRowUpdated(System.Data.Common.RowUpdatedEventArgs value) { }
         protected override void OnRowUpdating(System.Data.Common.RowUpdatingEventArgs value) { }
-        object System.ICloneable.Clone() { throw null; }
+        object? System.ICloneable.Clone() { throw null; }
     }
     public sealed partial class OdbcDataReader : System.Data.Common.DbDataReader
     {
@@ -156,9 +161,9 @@ public override void Close() { }
         protected override void Dispose(bool disposing) { }
         public override bool GetBoolean(int i) { throw null; }
         public override byte GetByte(int i) { throw null; }
-        public override long GetBytes(int i, long dataIndex, byte[] buffer, int bufferIndex, int length) { throw null; }
+        public override long GetBytes(int i, long dataIndex, byte[]? buffer, int bufferIndex, int length) { throw null; }
         public override char GetChar(int i) { throw null; }
-        public override long GetChars(int i, long dataIndex, char[] buffer, int bufferIndex, int length) { throw null; }
+        public override long GetChars(int i, long dataIndex, char[]? buffer, int bufferIndex, int length) { throw null; }
         public override string GetDataTypeName(int i) { throw null; }
         public System.DateTime GetDate(int i) { throw null; }
         public override System.DateTime GetDateTime(int i) { throw null; }
@@ -247,31 +252,33 @@ public static partial class OdbcMetaDataColumnNames
     public sealed partial class OdbcParameter : System.Data.Common.DbParameter, System.Data.IDataParameter, System.Data.IDbDataParameter, System.ICloneable
     {
         public OdbcParameter() { }
-        public OdbcParameter(string name, System.Data.Odbc.OdbcType type) { }
-        public OdbcParameter(string name, System.Data.Odbc.OdbcType type, int size) { }
+        public OdbcParameter(string? name, System.Data.Odbc.OdbcType type) { }
+        public OdbcParameter(string? name, System.Data.Odbc.OdbcType type, int size) { }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Advanced)]
-        public OdbcParameter(string parameterName, System.Data.Odbc.OdbcType odbcType, int size, System.Data.ParameterDirection parameterDirection, bool isNullable, byte precision, byte scale, string srcColumn, System.Data.DataRowVersion srcVersion, object value) { }
+        public OdbcParameter(string? parameterName, System.Data.Odbc.OdbcType odbcType, int size, System.Data.ParameterDirection parameterDirection, bool isNullable, byte precision, byte scale, string? srcColumn, System.Data.DataRowVersion srcVersion, object? value) { }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Advanced)]
-        public OdbcParameter(string parameterName, System.Data.Odbc.OdbcType odbcType, int size, System.Data.ParameterDirection parameterDirection, byte precision, byte scale, string sourceColumn, System.Data.DataRowVersion sourceVersion, bool sourceColumnNullMapping, object value) { }
-        public OdbcParameter(string name, System.Data.Odbc.OdbcType type, int size, string sourcecolumn) { }
-        public OdbcParameter(string name, object value) { }
+        public OdbcParameter(string? parameterName, System.Data.Odbc.OdbcType odbcType, int size, System.Data.ParameterDirection parameterDirection, byte precision, byte scale, string? sourceColumn, System.Data.DataRowVersion sourceVersion, bool sourceColumnNullMapping, object? value) { }
+        public OdbcParameter(string? name, System.Data.Odbc.OdbcType type, int size, string? sourcecolumn) { }
+        public OdbcParameter(string? name, object? value) { }
         public override System.Data.DbType DbType { get { throw null; } set { } }
         public override System.Data.ParameterDirection Direction { get { throw null; } set { } }
         public override bool IsNullable { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute(System.Data.Odbc.OdbcType.NChar)]
         [System.Data.Common.DbProviderSpecificTypePropertyAttribute(true)]
         public System.Data.Odbc.OdbcType OdbcType { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public override string ParameterName { get { throw null; } set { } }
         public new byte Precision { get { throw null; } set { } }
         public new byte Scale { get { throw null; } set { } }
         public override int Size { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public override string SourceColumn { get { throw null; } set { } }
         public override bool SourceColumnNullMapping { get { throw null; } set { } }
         public override System.Data.DataRowVersion SourceVersion { get { throw null; } set { } }
-        public override object Value { get { throw null; } set { } }
+        public override object? Value { get { throw null; } set { } }
         public override void ResetDbType() { }
         public void ResetOdbcType() { }
-        object System.ICloneable.Clone() { throw null; }
+        object? System.ICloneable.Clone() { throw null; }
         public override string ToString() { throw null; }
     }
     public sealed partial class OdbcParameterCollection : System.Data.Common.DbParameterCollection
@@ -290,15 +297,15 @@ internal OdbcParameterCollection() { }
         public override object SyncRoot { get { throw null; } }
         public System.Data.Odbc.OdbcParameter Add(System.Data.Odbc.OdbcParameter value) { throw null; }
         public override int Add(object value) { throw null; }
-        public System.Data.Odbc.OdbcParameter Add(string parameterName, System.Data.Odbc.OdbcType odbcType) { throw null; }
-        public System.Data.Odbc.OdbcParameter Add(string parameterName, System.Data.Odbc.OdbcType odbcType, int size) { throw null; }
-        public System.Data.Odbc.OdbcParameter Add(string parameterName, System.Data.Odbc.OdbcType odbcType, int size, string sourceColumn) { throw null; }
+        public System.Data.Odbc.OdbcParameter Add(string? parameterName, System.Data.Odbc.OdbcType odbcType) { throw null; }
+        public System.Data.Odbc.OdbcParameter Add(string? parameterName, System.Data.Odbc.OdbcType odbcType, int size) { throw null; }
+        public System.Data.Odbc.OdbcParameter Add(string? parameterName, System.Data.Odbc.OdbcType odbcType, int size, string? sourceColumn) { throw null; }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         [System.ObsoleteAttribute("Add(String parameterName, Object value) has been deprecated.  Use AddWithValue(String parameterName, Object value).  https://go.microsoft.com/fwlink/?linkid=14202", false)]
-        public System.Data.Odbc.OdbcParameter Add(string parameterName, object value) { throw null; }
+        public System.Data.Odbc.OdbcParameter Add(string? parameterName, object? value) { throw null; }
         public override void AddRange(System.Array values) { }
         public void AddRange(System.Data.Odbc.OdbcParameter[] values) { }
-        public System.Data.Odbc.OdbcParameter AddWithValue(string parameterName, object value) { throw null; }
+        public System.Data.Odbc.OdbcParameter AddWithValue(string? parameterName, object? value) { throw null; }
         public override void Clear() { }
         public bool Contains(System.Data.Odbc.OdbcParameter value) { throw null; }
         public override bool Contains(object value) { throw null; }
@@ -322,22 +329,22 @@ protected override void SetParameter(string parameterName, System.Data.Common.Db
     }
     public sealed partial class OdbcRowUpdatedEventArgs : System.Data.Common.RowUpdatedEventArgs
     {
-        public OdbcRowUpdatedEventArgs(System.Data.DataRow row, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) : base (default(System.Data.DataRow), default(System.Data.IDbCommand), default(System.Data.StatementType), default(System.Data.Common.DataTableMapping)) { }
-        public new System.Data.Odbc.OdbcCommand Command { get { throw null; } }
+        public OdbcRowUpdatedEventArgs(System.Data.DataRow row, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) : base (default(System.Data.DataRow), default(System.Data.IDbCommand), default(System.Data.StatementType), default(System.Data.Common.DataTableMapping)) { }
+        public new System.Data.Odbc.OdbcCommand? Command { get { throw null; } }
     }
     public delegate void OdbcRowUpdatedEventHandler(object sender, System.Data.Odbc.OdbcRowUpdatedEventArgs e);
     public sealed partial class OdbcRowUpdatingEventArgs : System.Data.Common.RowUpdatingEventArgs
     {
-        public OdbcRowUpdatingEventArgs(System.Data.DataRow row, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) : base (default(System.Data.DataRow), default(System.Data.IDbCommand), default(System.Data.StatementType), default(System.Data.Common.DataTableMapping)) { }
-        protected override System.Data.IDbCommand BaseCommand { get { throw null; } set { } }
-        public new System.Data.Odbc.OdbcCommand Command { get { throw null; } set { } }
+        public OdbcRowUpdatingEventArgs(System.Data.DataRow row, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) : base (default(System.Data.DataRow), default(System.Data.IDbCommand), default(System.Data.StatementType), default(System.Data.Common.DataTableMapping)) { }
+        protected override System.Data.IDbCommand? BaseCommand { get { throw null; } set { } }
+        public new System.Data.Odbc.OdbcCommand? Command { get { throw null; } set { } }
     }
     public delegate void OdbcRowUpdatingEventHandler(object sender, System.Data.Odbc.OdbcRowUpdatingEventArgs e);
     public sealed partial class OdbcTransaction : System.Data.Common.DbTransaction
     {
         internal OdbcTransaction() { }
-        public new System.Data.Odbc.OdbcConnection Connection { get { throw null; } }
-        protected override System.Data.Common.DbConnection DbConnection { get { throw null; } }
+        public new System.Data.Odbc.OdbcConnection? Connection { get { throw null; } }
+        protected override System.Data.Common.DbConnection? DbConnection { get { throw null; } }
         public override System.Data.IsolationLevel IsolationLevel { get { throw null; } }
         public override void Commit() { }
         protected override void Dispose(bool disposing) { }
diff --git a/src/libraries/System.Data.Odbc/ref/System.Data.Odbc.csproj b/src/libraries/System.Data.Odbc/ref/System.Data.Odbc.csproj
index 1aa56e780adbeb..a36f4ed64a8b06 100644
--- a/src/libraries/System.Data.Odbc/ref/System.Data.Odbc.csproj
+++ b/src/libraries/System.Data.Odbc/ref/System.Data.Odbc.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkCurrent);net461</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -9,9 +10,4 @@
   <ItemGroup>
     <Compile Include="System.Data.Odbc.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Data" />
-  </ItemGroup>
-</Project>
\ No newline at end of file
+</Project>
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/AdapterUtil.Odbc.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/AdapterUtil.Odbc.cs
index de295724ab8a47..60eda2401f9896 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/AdapterUtil.Odbc.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/AdapterUtil.Odbc.cs
@@ -18,7 +18,7 @@ internal static string GetString(string value)
             return value;
         }
 
-        internal static string GetString(string format, params object[] args)
+        internal static string GetString(string format, params object?[] args)
         {
             return SR.Format(format, args);
         }
@@ -59,7 +59,7 @@ internal static TimeoutException TimeoutException(string error)
             TraceExceptionAsReturnValue(e);
             return e;
         }
-        internal static InvalidOperationException InvalidOperation(string error, Exception inner)
+        internal static InvalidOperationException InvalidOperation(string error, Exception? inner)
         {
             InvalidOperationException e = new InvalidOperationException(error, inner);
             TraceExceptionAsReturnValue(e);
@@ -193,7 +193,7 @@ internal static InvalidOperationException InvalidDataDirectory()
         {
             return ADP.InvalidOperation(SR.GetString(SR.ADP_InvalidDataDirectory));
         }
-        internal static ArgumentException InvalidKeyname(string parameterName)
+        internal static ArgumentException InvalidKeyname(string? parameterName)
         {
             return Argument(SR.GetString(SR.ADP_InvalidKey), parameterName);
         }
@@ -272,7 +272,7 @@ internal static Exception OpenReaderExists()
             return OpenReaderExists(null);
         }
 
-        internal static Exception OpenReaderExists(Exception e)
+        internal static Exception OpenReaderExists(Exception? e)
         {
             return InvalidOperation(SR.GetString(SR.ADP_OpenReaderExists), e);
         }
@@ -313,7 +313,7 @@ internal static InvalidOperationException QuotePrefixNotSet(string method)
         //
         // : ConnectionUtil
         //
-        internal static Exception ConnectionIsDisabled(Exception InnerException)
+        internal static Exception ConnectionIsDisabled(Exception? InnerException)
         {
             return InvalidOperation(SR.GetString(SR.ADP_ConnectionIsDisabled), InnerException);
         }
@@ -367,7 +367,7 @@ internal static ArgumentException InvalidDataType(TypeCode typecode)
         }
         internal static ArgumentException UnknownDataType(Type dataType)
         {
-            return Argument(SR.GetString(SR.ADP_UnknownDataType, dataType.FullName));
+            return Argument(SR.GetString(SR.ADP_UnknownDataType, dataType.FullName!));
         }
         internal static ArgumentException DbTypeNotSupported(System.Data.DbType type, Type enumtype)
         {
@@ -375,7 +375,7 @@ internal static ArgumentException DbTypeNotSupported(System.Data.DbType type, Ty
         }
         internal static ArgumentException UnknownDataTypeCode(Type dataType, TypeCode typeCode)
         {
-            return Argument(SR.GetString(SR.ADP_UnknownDataTypeCode, ((int)typeCode).ToString(CultureInfo.InvariantCulture), dataType.FullName));
+            return Argument(SR.GetString(SR.ADP_UnknownDataTypeCode, ((int)typeCode).ToString(CultureInfo.InvariantCulture), dataType.FullName!));
         }
         internal static ArgumentException InvalidOffsetValue(int value)
         {
@@ -477,7 +477,7 @@ internal static Exception IncorrectNumberOfDataSourceInformationRows()
             return Argument(SR.GetString(SR.MDF_IncorrectNumberOfDataSourceInformationRows));
         }
 
-        internal static ArgumentException InvalidRestrictionValue(string collectionName, string restrictionName, string restrictionValue)
+        internal static ArgumentException InvalidRestrictionValue(string collectionName, string restrictionName, string? restrictionValue)
         {
             return ADP.Argument(SR.GetString(SR.MDF_InvalidRestrictionValue, collectionName, restrictionName, restrictionValue));
         }
@@ -572,7 +572,7 @@ internal static Exception UnsupportedVersion(string collectionName)
         internal static readonly IntPtr PtrZero = new IntPtr(0); // IntPtr.Zero
         internal static readonly int PtrSize = IntPtr.Size;
 
-        internal static Delegate FindBuilder(MulticastDelegate mcd)
+        internal static Delegate? FindBuilder(MulticastDelegate mcd)
         { // V1.2.3300
             if (null != mcd)
             {
@@ -651,7 +651,7 @@ internal static string GetFullPath(string filename)
             return Path.GetFullPath(filename);
         }
 
-        internal static int StringLength(string inputString)
+        internal static int StringLength(string? inputString)
         {
             return ((null != inputString) ? inputString.Length : 0);
         }
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DBConnectionString.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DBConnectionString.cs
index cf901dd7a13ef6..dba3fdbbc37e47 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DBConnectionString.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DBConnectionString.cs
@@ -26,17 +26,17 @@ private static class KEY
         private readonly string _encryptedUsersConnectionString;
 
         // hash of unique keys to values
-        private readonly Dictionary<string, string> _parsetable;
+        private readonly Dictionary<string, string?> _parsetable;
 
         // a linked list of key/value and their length in _encryptedUsersConnectionString
-        private readonly NameValuePair _keychain;
+        private readonly NameValuePair? _keychain;
 
         // track the existance of "password" or "pwd" in the connection string
         // not used for anything anymore but must keep it set correct for V1.1 serialization
         private readonly bool _hasPassword;
 
-        private readonly string[] _restrictionValues;
-        private readonly string _restrictions;
+        private readonly string[]? _restrictionValues;
+        private readonly string? _restrictions;
 
         private readonly KeyRestrictionBehavior _behavior;
 
@@ -44,7 +44,7 @@ private static class KEY
 #pragma warning disable CA1823
         // this field is no longer used, hence the warning was disabled
         // however, it can not be removed or it will break serialization with V1.1
-        private readonly string _encryptedActualConnectionString;
+        private readonly string? _encryptedActualConnectionString;
 #pragma warning restore CA1823
 #pragma warning restore CS0169
 
@@ -56,13 +56,13 @@ internal DBConnectionString(string value, string restrictions, KeyRestrictionBeh
         }
 
         internal DBConnectionString(DbConnectionOptions connectionOptions)
-            : this(connectionOptions, (string)null, KeyRestrictionBehavior.AllowOnly, null, true)
+            : this(connectionOptions, null, KeyRestrictionBehavior.AllowOnly, null, true)
         {
             // used by DBDataPermission to convert from DbConnectionOptions to DBConnectionString
             // since backward compatability requires Everett level classes
         }
 
-        private DBConnectionString(DbConnectionOptions connectionOptions, string restrictions, KeyRestrictionBehavior behavior, Dictionary<string, string> synonyms, bool mustCloneDictionary)
+        private DBConnectionString(DbConnectionOptions connectionOptions, string? restrictions, KeyRestrictionBehavior behavior, Dictionary<string, string>? synonyms, bool mustCloneDictionary)
         { // used by DBDataPermission
             Debug.Assert(null != connectionOptions, "null connectionOptions");
             switch (behavior)
@@ -89,7 +89,7 @@ private DBConnectionString(DbConnectionOptions connectionOptions, string restric
                 {
                     // clone the hashtable to replace user's password/pwd value with "*"
                     // we only need to clone if coming from DbConnectionOptions and password exists
-                    _parsetable = new Dictionary<string, string>(_parsetable);
+                    _parsetable = new Dictionary<string, string?>(_parsetable);
                 }
 
                 // different than Everett in that instead of removing password/pwd from
@@ -117,7 +117,7 @@ private DBConnectionString(DbConnectionOptions connectionOptions, string restric
             }
         }
 
-        private DBConnectionString(DBConnectionString connectionString, string[] restrictionValues, KeyRestrictionBehavior behavior)
+        private DBConnectionString(DBConnectionString connectionString, string[]? restrictionValues, KeyRestrictionBehavior behavior)
         {
             // used by intersect for two equal connection strings with different restrictions
             _encryptedUsersConnectionString = connectionString._encryptedUsersConnectionString;
@@ -147,7 +147,7 @@ internal bool IsEmpty
             get { return (null == _keychain); }
         }
 
-        internal NameValuePair KeyChain
+        internal NameValuePair? KeyChain
         {
             get { return _keychain; }
         }
@@ -156,10 +156,10 @@ internal string Restrictions
         {
             get
             {
-                string restrictions = _restrictions;
+                string? restrictions = _restrictions;
                 if (null == restrictions)
                 {
-                    string[] restrictionValues = _restrictionValues;
+                    string[]? restrictionValues = _restrictionValues;
                     if ((null != restrictionValues) && (0 < restrictionValues.Length))
                     {
                         StringBuilder builder = new StringBuilder();
@@ -184,9 +184,9 @@ internal string Restrictions
             }
         }
 
-        internal string this[string keyword]
+        internal string? this[string keyword]
         {
-            get { return (string)_parsetable[keyword]; }
+            get { return _parsetable[keyword]; }
         }
 
         internal bool ContainsKey(string keyword)
@@ -194,10 +194,10 @@ internal bool ContainsKey(string keyword)
             return _parsetable.ContainsKey(keyword);
         }
 
-        internal DBConnectionString Intersect(DBConnectionString entry)
+        internal DBConnectionString Intersect(DBConnectionString? entry)
         {
             KeyRestrictionBehavior behavior = _behavior;
-            string[] restrictionValues = null;
+            string[]? restrictionValues = null;
 
             if (null == entry)
             {
@@ -294,7 +294,7 @@ internal DBConnectionString Intersect(DBConnectionString entry)
         }
 
         [Conditional("DEBUG")]
-        private void ValidateCombinedSet(DBConnectionString componentSet, DBConnectionString combinedSet)
+        private void ValidateCombinedSet(DBConnectionString? componentSet, DBConnectionString combinedSet)
         {
             Debug.Assert(combinedSet != null, "The combined connection string should not be null");
             if ((componentSet != null) && (combinedSet._restrictionValues != null) && (componentSet._restrictionValues != null))
@@ -362,7 +362,7 @@ internal bool IsSupersetOf(DBConnectionString entry)
                 case KeyRestrictionBehavior.AllowOnly:
                     // every key must either be in the resticted connection string or in the allowed keywords
                     // keychain may contain duplicates, but it is better than GetEnumerator on _parsetable.Keys
-                    for (NameValuePair current = entry.KeyChain; null != current; current = current.Next)
+                    for (NameValuePair? current = entry.KeyChain; null != current; current = current.Next)
                     {
                         if (!ContainsKey(current.Name) && IsRestrictedKeyword(current.Name))
                         {
@@ -390,9 +390,9 @@ internal bool IsSupersetOf(DBConnectionString entry)
             return true;
         }
 
-        private static string[] NewRestrictionAllowOnly(string[] allowonly, string[] preventusage)
+        private static string[]? NewRestrictionAllowOnly(string[] allowonly, string[] preventusage)
         {
-            List<string> newlist = null;
+            List<string>? newlist = null;
             for (int i = 0; i < allowonly.Length; ++i)
             {
                 if (0 > Array.BinarySearch(preventusage, allowonly[i], StringComparer.Ordinal))
@@ -404,7 +404,7 @@ private static string[] NewRestrictionAllowOnly(string[] allowonly, string[] pre
                     newlist.Add(allowonly[i]);
                 }
             }
-            string[] restrictionValues = null;
+            string[]? restrictionValues = null;
             if (null != newlist)
             {
                 restrictionValues = newlist.ToArray();
@@ -413,9 +413,9 @@ private static string[] NewRestrictionAllowOnly(string[] allowonly, string[] pre
             return restrictionValues;
         }
 
-        private static string[] NewRestrictionIntersect(string[] a, string[] b)
+        private static string[]? NewRestrictionIntersect(string[] a, string[] b)
         {
-            List<string> newlist = null;
+            List<string>? newlist = null;
             for (int i = 0; i < a.Length; ++i)
             {
                 if (0 <= Array.BinarySearch(b, a[i], StringComparer.Ordinal))
@@ -427,7 +427,7 @@ private static string[] NewRestrictionIntersect(string[] a, string[] b)
                     newlist.Add(a[i]);
                 }
             }
-            string[] restrictionValues = null;
+            string[]? restrictionValues = null;
             if (newlist != null)
             {
                 restrictionValues = newlist.ToArray();
@@ -462,7 +462,7 @@ private static string[] NoDuplicateUnion(string[] a, string[] b)
             return restrictionValues;
         }
 
-        private static string[] ParseRestrictions(string restrictions, Dictionary<string, string> synonyms)
+        private static string[]? ParseRestrictions(string restrictions, Dictionary<string, string>? synonyms)
         {
             List<string> restrictionValues = new List<string>();
             StringBuilder buffer = new StringBuilder(restrictions.Length);
@@ -473,7 +473,7 @@ private static string[] ParseRestrictions(string restrictions, Dictionary<string
             {
                 int startPosition = nextStartPosition;
 
-                string keyname, keyvalue; // since parsing restrictions ignores values, it doesn't matter if we use ODBC rules or OLEDB rules
+                string? keyname, keyvalue; // since parsing restrictions ignores values, it doesn't matter if we use ODBC rules or OLEDB rules
                 nextStartPosition = DbConnectionOptions.GetKeyValuePair(restrictions, startPosition, buffer, false, out keyname, out keyvalue);
                 if (!string.IsNullOrEmpty(keyname))
                 {
@@ -488,7 +488,7 @@ private static string[] ParseRestrictions(string restrictions, Dictionary<string
             return RemoveDuplicates(restrictionValues.ToArray());
         }
 
-        internal static string[] RemoveDuplicates(string[] restrictions)
+        internal static string[] RemoveDuplicates(string?[] restrictions)
         {
             int count = restrictions.Length;
             if (0 < count)
@@ -497,14 +497,14 @@ internal static string[] RemoveDuplicates(string[] restrictions)
 
                 for (int i = 1; i < restrictions.Length; ++i)
                 {
-                    string prev = restrictions[i - 1];
+                    string prev = restrictions[i - 1]!;
                     if ((0 == prev.Length) || (prev == restrictions[i]))
                     {
                         restrictions[i - 1] = null;
                         count--;
                     }
                 }
-                if (0 == restrictions[restrictions.Length - 1].Length)
+                if (0 == restrictions[restrictions.Length - 1]!.Length)
                 {
                     restrictions[restrictions.Length - 1] = null;
                     count--;
@@ -515,20 +515,20 @@ internal static string[] RemoveDuplicates(string[] restrictions)
                     count = 0;
                     for (int i = 0; i < restrictions.Length; ++i)
                     {
-                        if (null != restrictions[i])
+                        if (restrictions[i] is string restriction)
                         {
-                            tmp[count++] = restrictions[i];
+                            tmp[count++] = restriction;
                         }
                     }
                     restrictions = tmp;
                 }
             }
             Verify(restrictions);
-            return restrictions;
+            return restrictions!;
         }
 
         [ConditionalAttribute("DEBUG")]
-        private static void Verify(string[] restrictionValues)
+        private static void Verify(string?[]? restrictionValues)
         {
             if (null != restrictionValues)
             {
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DbConnectionOptions.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DbConnectionOptions.cs
index 7131fb2e2973a2..893a3e2084a4c6 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DbConnectionOptions.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DbConnectionOptions.cs
@@ -41,10 +41,10 @@ public DbConnectionOptions(string connectionString)
 
         // synonyms hashtable is meant to be read-only translation of parsed string
         // keywords/synonyms to a known keyword string
-        public DbConnectionOptions(string connectionString, Dictionary<string, string> synonyms, bool useOdbcRules)
+        public DbConnectionOptions(string connectionString, Dictionary<string, string>? synonyms, bool useOdbcRules)
         {
             _useOdbcRules = useOdbcRules;
-            _parsetable = new Dictionary<string, string>();
+            _parsetable = new Dictionary<string, string?>();
             _usersConnectionString = ((null != connectionString) ? connectionString : "");
 
             // first pass on parsing, initial syntax check
@@ -79,16 +79,16 @@ internal bool HasBlankPassword
                 {
                     if (_parsetable.ContainsKey(KEY.Password))
                     {
-                        return string.IsNullOrEmpty((string)_parsetable[KEY.Password]);
+                        return string.IsNullOrEmpty(_parsetable[KEY.Password]);
                     }
                     else
                     if (_parsetable.ContainsKey(SYNONYM.Pwd))
                     {
-                        return string.IsNullOrEmpty((string)_parsetable[SYNONYM.Pwd]); // MDAC 83097
+                        return string.IsNullOrEmpty(_parsetable[SYNONYM.Pwd]); // MDAC 83097
                     }
                     else
                     {
-                        return ((_parsetable.ContainsKey(KEY.User_ID) && !string.IsNullOrEmpty((string)_parsetable[KEY.User_ID])) || (_parsetable.ContainsKey(SYNONYM.UID) && !string.IsNullOrEmpty((string)_parsetable[SYNONYM.UID])));
+                        return ((_parsetable.ContainsKey(KEY.User_ID) && !string.IsNullOrEmpty(_parsetable[KEY.User_ID])) || (_parsetable.ContainsKey(SYNONYM.UID) && !string.IsNullOrEmpty(_parsetable[SYNONYM.UID])));
                     }
                 }
                 return false;
@@ -100,7 +100,7 @@ public bool IsEmpty
             get { return (null == _keyChain); }
         }
 
-        internal Dictionary<string, string> Parsetable
+        internal Dictionary<string, string?> Parsetable
         {
             get { return _parsetable; }
         }
@@ -110,12 +110,12 @@ public ICollection Keys
             get { return _parsetable.Keys; }
         }
 
-        public string this[string keyword]
+        public string? this[string keyword]
         {
-            get { return (string)_parsetable[keyword]; }
+            get { return _parsetable[keyword]; }
         }
 
-        internal static void AppendKeyValuePairBuilder(StringBuilder builder, string keyName, string keyValue, bool useOdbcRules)
+        internal static void AppendKeyValuePairBuilder(StringBuilder builder, string keyName, string? keyValue, bool useOdbcRules)
         {
             ADP.CheckArgumentNull(builder, nameof(builder));
             ADP.CheckArgumentLength(keyName, nameof(keyName));
@@ -193,7 +193,7 @@ internal static void AppendKeyValuePairBuilder(StringBuilder builder, string key
         // same as Boolean, but with SSPI thrown in as valid yes
         public bool ConvertValueToIntegratedSecurity()
         {
-            object value = _parsetable[KEY.Integrated_Security];
+            object? value = _parsetable[KEY.Integrated_Security];
             if (null == value)
             {
                 return false;
@@ -223,7 +223,7 @@ internal bool ConvertValueToIntegratedSecurityInternal(string stringValue)
 
         public int ConvertValueToInt32(string keyName, int defaultValue)
         {
-            object value = _parsetable[keyName];
+            object? value = _parsetable[keyName];
             if (null == value)
             {
                 return defaultValue;
@@ -249,7 +249,7 @@ internal static int ConvertToInt32Internal(string keyname, string stringValue)
 
         public string ConvertValueToString(string keyName, string defaultValue)
         {
-            string value = (string)_parsetable[keyName];
+            string? value = _parsetable[keyName];
             return ((null != value) ? value : defaultValue);
         }
 
@@ -262,16 +262,16 @@ public bool ContainsKey(string keyword)
         // * this method queries "DataDirectory" value from the current AppDomain.
         //   This string is used for to replace "!DataDirectory!" values in the connection string, it is not considered as an "exposed resource".
         // * This method uses GetFullPath to validate that root path is valid, the result is not exposed out.
-        internal static string ExpandDataDirectory(string keyword, string value, ref string datadir)
+        internal static string? ExpandDataDirectory(string keyword, string? value, ref string? datadir)
         {
-            string fullPath = null;
+            string? fullPath = null;
             if ((null != value) && value.StartsWith(DataDirectory, StringComparison.OrdinalIgnoreCase))
             {
-                string rootFolderPath = datadir;
+                string? rootFolderPath = datadir;
                 if (null == rootFolderPath)
                 {
                     // find the replacement path
-                    object rootFolderObject = AppDomain.CurrentDomain.GetData("DataDirectory");
+                    object? rootFolderObject = AppDomain.CurrentDomain.GetData("DataDirectory");
                     rootFolderPath = (rootFolderObject as string);
                     if ((null != rootFolderObject) && (null == rootFolderPath))
                     {
@@ -320,16 +320,16 @@ internal static string ExpandDataDirectory(string keyword, string value, ref str
             return fullPath;
         }
 
-        internal string ExpandDataDirectories(ref string filename, ref int position)
+        internal string? ExpandDataDirectories(ref string? filename, ref int position)
         {
-            string value = null;
+            string? value = null;
             StringBuilder builder = new StringBuilder(_usersConnectionString.Length);
-            string datadir = null;
+            string? datadir = null;
 
             int copyPosition = 0;
             bool expanded = false;
 
-            for (NameValuePair current = _keyChain; null != current; current = current.Next)
+            for (NameValuePair? current = _keyChain; null != current; current = current.Next)
             {
                 value = current.Value;
 
@@ -420,7 +420,7 @@ internal string ExpandKeyword(string keyword, string replacementValue)
             int copyPosition = 0;
 
             StringBuilder builder = new StringBuilder(_usersConnectionString.Length);
-            for (NameValuePair current = _keyChain; null != current; current = current.Next)
+            for (NameValuePair? current = _keyChain; null != current; current = current.Next)
             {
                 if ((current.Name == keyword) && (current.Value == this[keyword]))
                 {
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DbConnectionStringCommon.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DbConnectionStringCommon.cs
index d133e16d0f941f..7c7c32497976d0 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DbConnectionStringCommon.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/DbConnectionStringCommon.cs
@@ -155,7 +155,7 @@ internal static class DbConnectionStringBuilderUtil
         internal static bool ConvertToBoolean(object value)
         {
             Debug.Assert(null != value, "ConvertToBoolean(null)");
-            string svalue = (value as string);
+            string? svalue = (value as string);
             if (null != svalue)
             {
                 if (StringComparer.OrdinalIgnoreCase.Equals(svalue, "true") || StringComparer.OrdinalIgnoreCase.Equals(svalue, "yes"))
@@ -194,7 +194,7 @@ internal static bool ConvertToBoolean(object value)
         internal static bool ConvertToIntegratedSecurity(object value)
         {
             Debug.Assert(null != value, "ConvertToIntegratedSecurity(null)");
-            string svalue = (value as string);
+            string? svalue = (value as string);
             if (null != svalue)
             {
                 if (StringComparer.OrdinalIgnoreCase.Equals(svalue, "sspi") || StringComparer.OrdinalIgnoreCase.Equals(svalue, "true") || StringComparer.OrdinalIgnoreCase.Equals(svalue, "yes"))
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/NameValuePermission.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/NameValuePermission.cs
index c57ae936b006a5..004fcd7832fa7a 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/NameValuePermission.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/Common/NameValuePermission.cs
@@ -11,23 +11,23 @@ internal sealed class NameValuePermission : IComparable
         // reused as both key and value nodes
         // key nodes link to value nodes
         // value nodes link to key nodes
-        private readonly string _value;
+        private readonly string? _value;
 
         // value node with (null != _restrictions) are allowed to match connection strings
-        private DBConnectionString _entry;
+        private DBConnectionString? _entry;
 
-        private NameValuePermission[] _tree; // with branches
+        private NameValuePermission[]? _tree; // with branches
 
         internal NameValuePermission()
         { // root node
         }
 
-        private NameValuePermission(string keyword)
+        private NameValuePermission(string? keyword)
         {
             _value = keyword;
         }
 
-        private NameValuePermission(string value, DBConnectionString entry)
+        private NameValuePermission(string? value, DBConnectionString? entry)
         {
             _value = value;
             _entry = entry;
@@ -40,7 +40,7 @@ private NameValuePermission(NameValuePermission permit)
             _tree = permit._tree;
             if (null != _tree)
             {
-                NameValuePermission[] tree = (_tree.Clone() as NameValuePermission[]);
+                NameValuePermission[] tree = (_tree.Clone() as NameValuePermission[])!;
                 for (int i = 0; i < tree.Length; ++i)
                 {
                     if (null != tree[i])
@@ -52,9 +52,9 @@ private NameValuePermission(NameValuePermission permit)
             }
         }
 
-        int IComparable.CompareTo(object a)
+        int IComparable.CompareTo(object? a)
         {
-            return StringComparer.Ordinal.Compare(_value, ((NameValuePermission)a)._value);
+            return StringComparer.Ordinal.Compare(_value, ((NameValuePermission?)a)?._value);
         }
 
         internal static void AddEntry(NameValuePermission kvtree, ArrayList entries, DBConnectionString entry)
@@ -63,9 +63,9 @@ internal static void AddEntry(NameValuePermission kvtree, ArrayList entries, DBC
 
             if (null != entry.KeyChain)
             {
-                for (NameValuePair keychain = entry.KeyChain; null != keychain; keychain = keychain.Next)
+                for (NameValuePair? keychain = entry.KeyChain; null != keychain; keychain = keychain.Next)
                 {
-                    NameValuePermission kv;
+                    NameValuePermission? kv;
 
                     kv = kvtree.CheckKeyForValue(keychain.Name);
                     if (null == kv)
@@ -78,7 +78,7 @@ internal static void AddEntry(NameValuePermission kvtree, ArrayList entries, DBC
                     kv = kvtree.CheckKeyForValue(keychain.Value);
                     if (null == kv)
                     {
-                        DBConnectionString insertValue = ((null != keychain.Next) ? null : entry);
+                        DBConnectionString? insertValue = ((null != keychain.Next) ? null : entry);
                         kv = new NameValuePermission(keychain.Value, insertValue);
                         kvtree.Add(kv); // add directly into live tree
                         if (null != insertValue)
@@ -105,7 +105,7 @@ internal static void AddEntry(NameValuePermission kvtree, ArrayList entries, DBC
             }
             else
             { // global restrictions, MDAC 84443
-                DBConnectionString kentry = kvtree._entry;
+                DBConnectionString? kentry = kvtree._entry;
                 if (null != kentry)
                 {
                     Debug.Assert(entries.Contains(kentry), "entries doesn't contain entry");
@@ -146,14 +146,14 @@ internal void Intersect(ArrayList entries, NameValuePermission target)
                     int count = _tree.Length;
                     for (int i = 0; i < _tree.Length; ++i)
                     {
-                        NameValuePermission kvtree = target.CheckKeyForValue(_tree[i]._value);
+                        NameValuePermission? kvtree = target.CheckKeyForValue(_tree[i]._value);
                         if (null != kvtree)
                         { // does target tree contain our value
                             _tree[i].Intersect(entries, kvtree);
                         }
                         else
                         {
-                            _tree[i] = null;
+                            _tree[i] = null!; // Temporary, removed below
                             --count;
                         }
                     }
@@ -179,12 +179,12 @@ internal void Intersect(ArrayList entries, NameValuePermission target)
 
         private void Add(NameValuePermission permit)
         {
-            NameValuePermission[] tree = _tree;
+            NameValuePermission[]? tree = _tree;
             int length = ((null != tree) ? tree.Length : 0);
             NameValuePermission[] newtree = new NameValuePermission[1 + length];
             for (int i = 0; i < newtree.Length - 1; ++i)
             {
-                newtree[i] = tree[i];
+                newtree[i] = tree![i];
             }
             newtree[length] = permit;
             Array.Sort(newtree);
@@ -198,7 +198,7 @@ internal bool CheckValueForKeyPermit(DBConnectionString parsetable)
                 return false;
             }
             bool hasMatch = false;
-            NameValuePermission[] keytree = _tree; // _tree won't mutate but Add will replace it
+            NameValuePermission[]? keytree = _tree; // _tree won't mutate but Add will replace it
             if (null != keytree)
             {
                 hasMatch = parsetable.IsEmpty; // MDAC 86773
@@ -210,16 +210,16 @@ internal bool CheckValueForKeyPermit(DBConnectionString parsetable)
                         NameValuePermission permitKey = keytree[i];
                         if (null != permitKey)
                         {
-                            string keyword = permitKey._value;
+                            string keyword = permitKey._value!;
 #if DEBUG
                             Debug.Assert(null == permitKey._entry, "key member has no restrictions");
 #endif
                             if (parsetable.ContainsKey(keyword))
                             {
-                                string valueInQuestion = (string)parsetable[keyword];
+                                string? valueInQuestion = parsetable[keyword];
 
                                 // keyword is restricted to certain values
-                                NameValuePermission permitValue = permitKey.CheckKeyForValue(valueInQuestion);
+                                NameValuePermission? permitValue = permitKey.CheckKeyForValue(valueInQuestion);
                                 if (null != permitValue)
                                 {
                                     //value does match - continue the chain down that branch
@@ -248,7 +248,7 @@ internal bool CheckValueForKeyPermit(DBConnectionString parsetable)
                 // partial chain match, either leaf-node by shorter chain or fail mid-chain if (null == _restrictions)
             }
 
-            DBConnectionString entry = _entry;
+            DBConnectionString? entry = _entry;
             if (null != entry)
             {
                 // also checking !hasMatch is tempting, but wrong
@@ -261,9 +261,9 @@ internal bool CheckValueForKeyPermit(DBConnectionString parsetable)
             return hasMatch; // mid-chain failure
         }
 
-        private NameValuePermission CheckKeyForValue(string keyInQuestion)
+        private NameValuePermission? CheckKeyForValue(string? keyInQuestion)
         {
-            NameValuePermission[] valuetree = _tree; // _tree won't mutate but Add will replace it
+            NameValuePermission[]? valuetree = _tree; // _tree won't mutate but Add will replace it
             if (null != valuetree)
             {
                 for (int i = 0; i < valuetree.Length; ++i)
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbBuffer.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbBuffer.cs
index 61b550a5e6b4ef..e885ac9380b67e 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbBuffer.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbBuffer.cs
@@ -60,7 +60,7 @@ internal string PtrToStringUni(int offset)
             Validate(offset, 2);
             Debug.Assert(0 == offset % ADP.PtrSize, "invalid alignment");
 
-            string value = null;
+            string? value = null;
             bool mustRelease = false;
 
             try
@@ -69,7 +69,7 @@ internal string PtrToStringUni(int offset)
 
                 IntPtr ptr = ADP.IntPtrOffset(DangerousGetHandle(), offset);
                 value = Marshal.PtrToStringUni(ptr);
-                Validate(offset, (2 * (value.Length + 1)));
+                Validate(offset, (2 * (value!.Length + 1)));
             }
             finally
             {
@@ -88,7 +88,7 @@ internal string PtrToStringUni(int offset, int length)
             Validate(offset, 2 * length);
             Debug.Assert(0 == offset % ADP.PtrSize, "invalid alignment");
 
-            string value = null;
+            string? value = null;
             bool mustRelease = false;
 
             try
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionFactory.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionFactory.cs
index 9b05f5b6d0e35a..5e37564f0710fc 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionFactory.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionFactory.cs
@@ -10,12 +10,12 @@ namespace System.Data.ProviderBase
 {
     internal abstract partial class DbConnectionFactory
     {
-        internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, out DbConnectionInternal connection)
+        internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions, DbConnectionInternal? oldConnection, out DbConnectionInternal? connection)
         {
             Debug.Assert(null != owningConnection, "null owningConnection?");
 
             DbConnectionPoolGroup poolGroup;
-            DbConnectionPool connectionPool;
+            DbConnectionPool? connectionPool;
             connection = null;
 
             //  Work around race condition with clearing the pool between GetConnectionPool obtaining pool
@@ -32,7 +32,7 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
 
             do
             {
-                poolGroup = GetConnectionPoolGroup(owningConnection);
+                poolGroup = GetConnectionPoolGroup(owningConnection)!;
                 // Doing this on the callers thread is important because it looks up the WindowsIdentity from the thread.
                 connectionPool = GetConnectionPool(owningConnection, poolGroup);
                 if (null == connectionPool)
@@ -40,7 +40,7 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
                     // If GetConnectionPool returns null, we can be certain that
                     // this connection should not be pooled via DbConnectionPool
                     // or have a disabled pool entry.
-                    poolGroup = GetConnectionPoolGroup(owningConnection); // previous entry have been disabled
+                    poolGroup = GetConnectionPoolGroup(owningConnection)!; // previous entry have been disabled
 
                     if (retry != null)
                     {
@@ -76,6 +76,7 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
 
                             // now that we have an antecedent task, schedule our work when it is completed.
                             // If it is a new slot or a completed task, this continuation will start right away.
+                            // TODO: newTask needs to be over non-nullable DbConnection (see below), there may be a bug here
                             newTask = s_pendingOpenNonPooled[idx].ContinueWith((_) =>
                             {
                                 var newConnection = CreateNonPooledConnection(owningConnection, poolGroup, userOptions);
@@ -85,10 +86,10 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
                                     oldConnection.Dispose();
                                 }
                                 return newConnection;
-                            }, cancellationTokenSource.Token, TaskContinuationOptions.LongRunning, TaskScheduler.Default);
+                            }, cancellationTokenSource.Token, TaskContinuationOptions.LongRunning, TaskScheduler.Default)!;
 
                             // Place this new task in the slot so any future work will be queued behind it
-                            s_pendingOpenNonPooled[idx] = newTask;
+                            s_pendingOpenNonPooled[idx] = newTask!;
                         }
 
                         // Set up the timeout (if needed)
@@ -108,7 +109,7 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
                             }
                             else if (task.IsFaulted)
                             {
-                                retry.TrySetException(task.Exception.InnerException);
+                                retry.TrySetException(task.Exception!.InnerException!);
                             }
                             else
                             {
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionInternal.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionInternal.cs
index 2ab7701a42f241..09d49bb131d68e 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionInternal.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionInternal.cs
@@ -79,12 +79,12 @@ internal virtual void CloseConnection(DbConnection owningObject, DbConnectionFac
                 // Lock to prevent race condition with cancellation
                 lock (this)
                 {
-                    object lockToken = ObtainAdditionalLocksForClose();
+                    object? lockToken = ObtainAdditionalLocksForClose();
                     try
                     {
                         PrepareForCloseConnection();
 
-                        DbConnectionPool connectionPool = Pool;
+                        DbConnectionPool? connectionPool = Pool;
 
 
                         // The singleton closed classes won't have owners and
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPool.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPool.cs
index 835dcf219aba6c..ab2d89be6121ac 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPool.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPool.cs
@@ -22,7 +22,7 @@ private enum State
 
         private sealed class PendingGetConnection
         {
-            public PendingGetConnection(long dueTime, DbConnection owner, TaskCompletionSource<DbConnectionInternal> completion, DbConnectionOptions userOptions)
+            public PendingGetConnection(long dueTime, DbConnection owner, TaskCompletionSource<DbConnectionInternal> completion, DbConnectionOptions? userOptions)
             {
                 DueTime = dueTime;
                 Owner = owner;
@@ -31,7 +31,7 @@ public PendingGetConnection(long dueTime, DbConnection owner, TaskCompletionSour
             public long DueTime { get; private set; }
             public DbConnection Owner { get; private set; }
             public TaskCompletionSource<DbConnectionInternal> Completion { get; private set; }
-            public DbConnectionOptions UserOptions { get; private set; }
+            public DbConnectionOptions? UserOptions { get; private set; }
         }
 
 
@@ -97,12 +97,12 @@ internal WaitHandle[] GetHandles(bool withCreate)
         private static readonly Random s_random = new Random(5101977); // Value obtained from Dave Driver
 
         private readonly int _cleanupWait;
-        private readonly DbConnectionPoolIdentity _identity;
+        private readonly DbConnectionPoolIdentity? _identity;
 
         private readonly DbConnectionFactory _connectionFactory;
         private readonly DbConnectionPoolGroup _connectionPoolGroup;
         private readonly DbConnectionPoolGroupOptions _connectionPoolGroupOptions;
-        private readonly DbConnectionPoolProviderInfo _connectionPoolProviderInfo;
+        private readonly DbConnectionPoolProviderInfo? _connectionPoolProviderInfo;
 
         private State _state;
 
@@ -117,13 +117,13 @@ internal WaitHandle[] GetHandles(bool withCreate)
         private int _waitCount;
         private readonly PoolWaitHandles _waitHandles;
 
-        private Exception _resError;
+        private Exception? _resError;
         private volatile bool _errorOccurred;
 
         private int _errorWait;
-        private Timer _errorTimer;
+        private Timer? _errorTimer;
 
-        private Timer _cleanupTimer;
+        private Timer? _cleanupTimer;
 
 
         private readonly List<DbConnectionInternal> _objectList;
@@ -135,7 +135,7 @@ internal DbConnectionPool(
                             DbConnectionFactory connectionFactory,
                             DbConnectionPoolGroup connectionPoolGroup,
                             DbConnectionPoolIdentity identity,
-                            DbConnectionPoolProviderInfo connectionPoolProviderInfo)
+                            DbConnectionPoolProviderInfo? connectionPoolProviderInfo)
         {
             Debug.Assert(null != connectionPoolGroup, "null connectionPoolGroup");
 
@@ -220,7 +220,7 @@ private bool NeedToReplenish
             }
         }
 
-        internal DbConnectionPoolIdentity Identity
+        internal DbConnectionPoolIdentity? Identity
         {
             get { return _identity; }
         }
@@ -251,7 +251,7 @@ internal DbConnectionPoolGroupOptions PoolGroupOptions
             get { return _connectionPoolGroupOptions; }
         }
 
-        internal DbConnectionPoolProviderInfo ProviderInfo
+        internal DbConnectionPoolProviderInfo? ProviderInfo
         {
             get { return _connectionPoolProviderInfo; }
         }
@@ -266,7 +266,7 @@ private bool UsingIntegrateSecurity
             get { return (null != _identity && DbConnectionPoolIdentity.NoIdentity != _identity); }
         }
 
-        private void CleanupCallback(object state)
+        private void CleanupCallback(object? state)
         {
             // Called when the cleanup-timer ticks over.
 
@@ -294,7 +294,7 @@ private void CleanupCallback(object state)
                 if (_waitHandles.PoolSemaphore.WaitOne(0))
                 {
                     // We obtained a objects from the semaphore.
-                    DbConnectionInternal obj;
+                    DbConnectionInternal? obj;
 
                     if (_stackOld.TryPop(out obj))
                     {
@@ -323,7 +323,7 @@ private void CleanupCallback(object state)
             {
                 while (true)
                 {
-                    DbConnectionInternal obj;
+                    DbConnectionInternal? obj;
 
                     if (!_stackNew.TryPop(out obj))
                         break;
@@ -345,7 +345,7 @@ private void CleanupCallback(object state)
 
         internal void Clear()
         {
-            DbConnectionInternal obj;
+            DbConnectionInternal? obj;
 
             // First, quickly doom everything.
             lock (_objectList)
@@ -387,9 +387,9 @@ private Timer CreateCleanupTimer()
                 _cleanupWait,
                 _cleanupWait);
 
-        private DbConnectionInternal CreateObject(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection)
+        private DbConnectionInternal CreateObject(DbConnection? owningObject, DbConnectionOptions? userOptions, DbConnectionInternal? oldConnection)
         {
-            DbConnectionInternal newObj = null;
+            DbConnectionInternal? newObj = null;
 
             try
             {
@@ -571,13 +571,13 @@ internal void DestroyObject(DbConnectionInternal obj)
             obj.Dispose();
         }
 
-        private void ErrorCallback(object state)
+        private void ErrorCallback(object? state)
         {
             _errorOccurred = false;
             _waitHandles.ErrorEvent.Reset();
 
             // the error state is cleaned, destroy the timer to avoid periodic invocation
-            Timer t = _errorTimer;
+            Timer? t = _errorTimer;
             _errorTimer = null;
             if (t != null)
             {
@@ -588,14 +588,14 @@ private void ErrorCallback(object state)
 
         // TODO: move this to src/Common and integrate with SqlClient
         // Note: Odbc connections are not passing through this code
-        private Exception TryCloneCachedException()
+        private Exception? TryCloneCachedException()
         {
             return _resError;
         }
 
         private void WaitForPendingOpen()
         {
-            PendingGetConnection next;
+            PendingGetConnection? next;
 
             do
             {
@@ -631,9 +631,9 @@ private void WaitForPendingOpen()
                             delay = (uint)Math.Max(ADP.TimerRemainingMilliseconds(next.DueTime), 0);
                         }
 
-                        DbConnectionInternal connection = null;
+                        DbConnectionInternal? connection = null;
                         bool timeout = false;
-                        Exception caughtException = null;
+                        Exception? caughtException = null;
 
                         try
                         {
@@ -675,7 +675,7 @@ private void WaitForPendingOpen()
             } while (!_pendingOpens.IsEmpty);
         }
 
-        internal bool TryGetConnection(DbConnection owningObject, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions, out DbConnectionInternal connection)
+        internal bool TryGetConnection(DbConnection owningObject, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions, out DbConnectionInternal? connection)
         {
             uint waitForMultipleObjectsTimeout = 0;
             bool allowCreate = false;
@@ -728,9 +728,9 @@ internal bool TryGetConnection(DbConnection owningObject, TaskCompletionSource<D
             return false;
         }
 
-        private bool TryGetConnection(DbConnection owningObject, uint waitForMultipleObjectsTimeout, bool allowCreate, bool onlyOneCheckConnection, DbConnectionOptions userOptions, out DbConnectionInternal connection)
+        private bool TryGetConnection(DbConnection owningObject, uint waitForMultipleObjectsTimeout, bool allowCreate, bool onlyOneCheckConnection, DbConnectionOptions? userOptions, out DbConnectionInternal? connection)
         {
-            DbConnectionInternal obj = null;
+            DbConnectionInternal? obj = null;
             if (null == obj)
             {
                 Interlocked.Increment(ref _waitCount);
@@ -764,7 +764,7 @@ private bool TryGetConnection(DbConnection owningObject, uint waitForMultipleObj
                             case ERROR_HANDLE:
                                 // Throw the error that PoolCreateRequest stashed.
                                 Interlocked.Decrement(ref _waitCount);
-                                throw TryCloneCachedException();
+                                throw TryCloneCachedException()!;
 
                             case CREATION_HANDLE:
 
@@ -892,9 +892,9 @@ private void PrepareConnection(DbConnection owningObject, DbConnectionInternal o
         /// <param name="userOptions">Options used to create the new connection</param>
         /// <param name="oldConnection">Inner connection that will be replaced</param>
         /// <returns>A new inner connection that is attached to the <paramref name="owningObject"/></returns>
-        internal DbConnectionInternal ReplaceConnection(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection)
+        internal DbConnectionInternal? ReplaceConnection(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection)
         {
-            DbConnectionInternal newConnection = UserCreateRequest(owningObject, userOptions, oldConnection);
+            DbConnectionInternal? newConnection = UserCreateRequest(owningObject, userOptions, oldConnection);
 
             if (newConnection != null)
             {
@@ -907,9 +907,9 @@ internal DbConnectionInternal ReplaceConnection(DbConnection owningObject, DbCon
             return newConnection;
         }
 
-        private DbConnectionInternal GetFromGeneralPool()
+        private DbConnectionInternal? GetFromGeneralPool()
         {
-            DbConnectionInternal obj = null;
+            DbConnectionInternal? obj = null;
 
             if (!_stackNew.TryPop(out obj))
             {
@@ -938,7 +938,7 @@ private DbConnectionInternal GetFromGeneralPool()
             return (obj);
         }
 
-        private void PoolCreateRequest(object state)
+        private void PoolCreateRequest(object? state)
         {
             // called by pooler to ensure pool requests are currently being satisfied -
             // creation mutex has not been obtained
@@ -968,7 +968,7 @@ private void PoolCreateRequest(object state)
                         // since either Open will fail or we will open a object for this pool that does
                         // not belong in this pool.  The side effect of this is that if using integrated
                         // security min pool size cannot be guaranteed.
-                        if (UsingIntegrateSecurity && !_identity.Equals(DbConnectionPoolIdentity.GetCurrent()))
+                        if (UsingIntegrateSecurity && !_identity!.Equals(DbConnectionPoolIdentity.GetCurrent()))
                         {
                             return;
                         }
@@ -1147,7 +1147,7 @@ internal void Shutdown()
             _state = State.ShuttingDown;
 
             // deactivate timer callbacks
-            Timer t = _cleanupTimer;
+            Timer? t = _cleanupTimer;
             _cleanupTimer = null;
             if (null != t)
             {
@@ -1156,15 +1156,15 @@ internal void Shutdown()
         }
 
 
-        private DbConnectionInternal UserCreateRequest(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection = null)
+        private DbConnectionInternal? UserCreateRequest(DbConnection owningObject, DbConnectionOptions? userOptions, DbConnectionInternal? oldConnection = null)
         {
             // called by user when they were not able to obtain a free object but
             // instead obtained creation mutex
 
-            DbConnectionInternal obj = null;
+            DbConnectionInternal? obj = null;
             if (ErrorOccurred)
             {
-                throw TryCloneCachedException();
+                throw TryCloneCachedException()!;
             }
             else
             {
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPoolGroupProviderInfo.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPoolGroupProviderInfo.cs
index 911720230d2133..44c2fd1a379e96 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPoolGroupProviderInfo.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPoolGroupProviderInfo.cs
@@ -5,9 +5,9 @@ namespace System.Data.ProviderBase
 {
     internal class DbConnectionPoolGroupProviderInfo
     {
-        private DbConnectionPoolGroup _poolGroup;
+        private DbConnectionPoolGroup? _poolGroup;
 
-        internal DbConnectionPoolGroup PoolGroup
+        internal DbConnectionPoolGroup? PoolGroup
         {
             get
             {
diff --git a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPoolIdentity.cs b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPoolIdentity.cs
index 7e1e6f9932dc51..62112312ff01bc 100644
--- a/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPoolIdentity.cs
+++ b/src/libraries/System.Data.Odbc/src/Common/System/Data/ProviderBase/DbConnectionPoolIdentity.cs
@@ -30,7 +30,7 @@ internal static DbConnectionPoolIdentity GetCurrent()
             throw new PlatformNotSupportedException();
         }
 
-        public override bool Equals(object value)
+        public override bool Equals(object? value)
         {
             bool result = ((this == NoIdentity) || (this == value));
             if (!result && (null != value))
diff --git a/src/libraries/System.Data.Odbc/src/System.Data.Odbc.csproj b/src/libraries/System.Data.Odbc/src/System.Data.Odbc.csproj
index 0592f1dd00be60..b9c72520b7ea80 100644
--- a/src/libraries/System.Data.Odbc/src/System.Data.Odbc.csproj
+++ b/src/libraries/System.Data.Odbc/src/System.Data.Odbc.csproj
@@ -1,10 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-FreeBSD;$(NetCoreAppCurrent)-illumos;$(NetCoreAppCurrent)-Solaris;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS;$(NetCoreAppCurrent);netcoreapp2.0-FreeBSD;netcoreapp2.0-Linux;netcoreapp2.0-OSX;netcoreapp2.0-Windows_NT;netstandard2.0;net461-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-FreeBSD;$(NetCoreAppCurrent)-illumos;$(NetCoreAppCurrent)-Solaris;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS;$(NetCoreAppCurrent);netcoreapp2.0-FreeBSD;netcoreapp2.0-Linux;netcoreapp2.0-OSX;netcoreapp2.0-Windows_NT;netstandard2.0;net461-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <NoWarn>$(NoWarn);CA2249</NoWarn>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -126,12 +126,16 @@
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Libraries.cs"
              Link="Common\Interop\Windows\Interop.Libraries.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' == 'true'">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Data" />
+  <ItemGroup>
+    <EmbeddedResource Include="Resources\System.Data.Odbc.OdbcMetaData.xml">
+      <LogicalName>System.Data.Odbc.OdbcMetaData.xml</LogicalName>
+    </EmbeddedResource>
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="DatabaseSetupInstructions.md" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
-    <Reference Include="Microsoft.Win32.Registry" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or
+                        $(TargetFramework.StartsWith('netcoreapp2.0'))">
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
     <Reference Include="System.Collections.Specialized" />
@@ -148,10 +152,9 @@
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
+    <Reference Include="System.Runtime.InteropServices.RuntimeInformation" />
     <Reference Include="System.Security.Claims" />
     <Reference Include="System.Security.Principal" />
-    <Reference Include="System.Security.Principal.Windows" />
-    <Reference Include="System.Text.Encoding.CodePages" />
     <Reference Include="System.Text.Encoding.Extensions" />
     <Reference Include="System.Text.RegularExpressions" />
     <Reference Include="System.Threading" />
@@ -160,18 +163,13 @@
     <Reference Include="System.Threading.ThreadPool" />
     <Reference Include="System.Threading.Timer" />
     <Reference Include="System.Transactions" />
-    <Reference Include="System.Xml.ReaderWriter" />
-    <Reference Include="System.Runtime.InteropServices.RuntimeInformation" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or $(TargetFramework.StartsWith('netcoreapp2.0'))">
     <Reference Include="System.Transactions.Local" />
+    <Reference Include="System.Xml.ReaderWriter" />
   </ItemGroup>
-  <ItemGroup>
-    <EmbeddedResource Include="Resources\System.Data.Odbc.OdbcMetaData.xml">
-      <LogicalName>System.Data.Odbc.OdbcMetaData.xml</LogicalName>
-    </EmbeddedResource>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <Reference Include="System.Text.Encoding.CodePages" />
   </ItemGroup>
-  <ItemGroup>
-    <None Include="DatabaseSetupInstructions.md" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netcoreapp2.0'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Encoding.CodePages\src\System.Text.Encoding.CodePages.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/DbDataRecord.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/DbDataRecord.cs
index 65887bf7984cde..7b4887893f6277 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/DbDataRecord.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/DbDataRecord.cs
@@ -9,9 +9,9 @@ internal DbSchemaInfo()
         {
         }
 
-        internal string _name;
-        internal string _typename;
-        internal Type _type;
+        internal string? _name;
+        internal string? _typename;
+        internal Type? _type;
         internal ODBC32.SQL_TYPE? _dbtype;
     }
 
@@ -19,9 +19,9 @@ internal DbSchemaInfo()
     // Cache
     //
     //  This is a on-demand cache, only caching what the user requests.
-    //  The reational is that for ForwardOnly access (the default and LCD of drivers)
+    //  The rationale is that for ForwardOnly access (the default and LCD of drivers)
     //  we cannot obtain the data more than once, and even GetData(0) (to determine is-null)
-    //  still obtains data for fixed lenght types.
+    //  still obtains data for fixed length types.
 
     //  So simple code like:
     //      if (!rReader.IsDBNull(i))
@@ -39,8 +39,8 @@ internal sealed class DbCache
         //Data
 
         private readonly bool[] _isBadValue;
-        private DbSchemaInfo[] _schema;
-        private readonly object[] _values;
+        private DbSchemaInfo?[]? _schema;
+        private readonly object?[] _values;
         private readonly OdbcDataReader _record;
         internal int _count;
         internal bool _randomaccess = true;
@@ -56,13 +56,13 @@ internal DbCache(OdbcDataReader record, int count)
         }
 
         //Accessor
-        internal object this[int i]
+        internal object? this[int i]
         {
             get
             {
                 if (_isBadValue[i])
                 {
-                    OverflowException innerException = (OverflowException)Values[i];
+                    OverflowException innerException = (OverflowException)Values[i]!;
                     throw new OverflowException(innerException.Message, innerException);
                 }
                 return Values[i];
@@ -87,7 +87,7 @@ internal void InvalidateValue(int i)
             _isBadValue[i] = true;
         }
 
-        internal object[] Values
+        internal object?[] Values
         {
             get
             {
@@ -95,7 +95,7 @@ internal object[] Values
             }
         }
 
-        internal object AccessIndex(int i)
+        internal object? AccessIndex(int i)
         {
             //Note: We could put this directly in this[i], instead of having an explicit overload.
             //However that means that EVERY access into the cache takes the hit of checking, so
@@ -106,7 +106,7 @@ internal object AccessIndex(int i)
             //      ....
             //  return cache[i];
 
-            object[] values = this.Values;
+            object?[] values = this.Values;
             if (_randomaccess)
             {
                 //Random
@@ -130,11 +130,8 @@ internal DbSchemaInfo GetSchema(int i)
             {
                 _schema = new DbSchemaInfo[Count];
             }
-            if (_schema[i] == null)
-            {
-                _schema[i] = new DbSchemaInfo();
-            }
-            return _schema[i];
+
+            return _schema[i] ??= new DbSchemaInfo();
         }
 
         internal void FlushValues()
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/Odbc32.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/Odbc32.cs
index 1fed607d524db2..6c326926ba576e 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/Odbc32.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/Odbc32.cs
@@ -116,7 +116,7 @@ internal static void TraceODBC(int level, string method, ODBC32.RetCode retcode)
         {
         }
 
-        internal static short ShortStringLength(string inputString)
+        internal static short ShortStringLength(string? inputString)
         {
             return checked((short)ADP.StringLength(inputString));
         }
@@ -716,14 +716,14 @@ internal enum SQL_SPECIALCOLUMNSET : short
         internal const short SQL_RESULT_COL = 3;
 
         // Helpers
-        internal static OdbcErrorCollection GetDiagErrors(string source, OdbcHandle hrHandle, RetCode retcode)
+        internal static OdbcErrorCollection GetDiagErrors(string? source, OdbcHandle hrHandle, RetCode retcode)
         {
             OdbcErrorCollection errors = new OdbcErrorCollection();
             GetDiagErrors(errors, source, hrHandle, retcode);
             return errors;
         }
 
-        internal static void GetDiagErrors(OdbcErrorCollection errors, string source, OdbcHandle hrHandle, RetCode retcode)
+        internal static void GetDiagErrors(OdbcErrorCollection errors, string? source, OdbcHandle hrHandle, RetCode retcode)
         {
             Debug.Assert(retcode != ODBC32.RetCode.INVALID_HANDLE, "retcode must never be ODBC32.RetCode.INVALID_HANDLE");
             if (RetCode.SUCCESS != retcode)
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcCommand.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcCommand.cs
index be558f4ac9dda3..ca88997ebdbd1a 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcCommand.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcCommand.cs
@@ -4,6 +4,7 @@
 using System.ComponentModel;            //Component
 using System.Data.Common;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 
 // todo:
@@ -15,26 +16,27 @@
 
 namespace System.Data.Odbc
 {
+    [Designer("Microsoft.VSDesigner.Data.VS.OdbcCommandDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public sealed class OdbcCommand : DbCommand, ICloneable
     {
         private static int s_objectTypeCount; // Bid counter
         internal readonly int ObjectID = System.Threading.Interlocked.Increment(ref s_objectTypeCount);
 
-        private string _commandText;
+        private string? _commandText;
         private CommandType _commandType;
         private int _commandTimeout = ADP.DefaultCommandTimeout;
         private UpdateRowSource _updatedRowSource = UpdateRowSource.Both;
         private bool _designTimeInvisible;
         private bool _isPrepared;                        // true if the command is prepared
 
-        private OdbcConnection _connection;
-        private OdbcTransaction _transaction;
+        private OdbcConnection? _connection;
+        private OdbcTransaction? _transaction;
 
-        private WeakReference _weakDataReaderReference;
+        private WeakReference? _weakDataReaderReference;
 
-        private CMDWrapper _cmdWrapper;
+        private CMDWrapper? _cmdWrapper;
 
-        private OdbcParameterCollection _parameterCollection;   // Parameter collection
+        private OdbcParameterCollection? _parameterCollection;   // Parameter collection
 
         private ConnectionState _cmdState;
 
@@ -43,20 +45,20 @@ public OdbcCommand() : base()
             GC.SuppressFinalize(this);
         }
 
-        public OdbcCommand(string cmdText) : this()
+        public OdbcCommand(string? cmdText) : this()
         {
             // note: arguments are assigned to properties so we do not have to trace them.
             // We still need to include them into the argument list of the definition!
             CommandText = cmdText;
         }
 
-        public OdbcCommand(string cmdText, OdbcConnection connection) : this()
+        public OdbcCommand(string? cmdText, OdbcConnection? connection) : this()
         {
             CommandText = cmdText;
             Connection = connection;
         }
 
-        public OdbcCommand(string cmdText, OdbcConnection connection, OdbcTransaction transaction) : this()
+        public OdbcCommand(string? cmdText, OdbcConnection? connection, OdbcTransaction? transaction) : this()
         {
             CommandText = cmdText;
             Connection = connection;
@@ -83,7 +85,7 @@ private void DisposeDataReader()
         {
             if (null != _weakDataReaderReference)
             {
-                IDisposable reader = (IDisposable)_weakDataReaderReference.Target;
+                IDisposable? reader = (IDisposable?)_weakDataReaderReference.Target;
                 if ((null != reader) && _weakDataReaderReference.IsAlive)
                 {
                     ((IDisposable)reader).Dispose();
@@ -95,11 +97,11 @@ private void DisposeDataReader()
         internal void DisconnectFromDataReaderAndConnection()
         {
             // get a reference to the datareader if it is alive
-            OdbcDataReader liveReader = null;
+            OdbcDataReader? liveReader = null;
             if (_weakDataReaderReference != null)
             {
-                OdbcDataReader reader;
-                reader = (OdbcDataReader)_weakDataReaderReference.Target;
+                OdbcDataReader? reader;
+                reader = (OdbcDataReader?)_weakDataReaderReference.Target;
                 if (_weakDataReaderReference.IsAlive)
                 {
                     liveReader = reader;
@@ -149,15 +151,16 @@ internal bool Canceling
         {
             get
             {
-                return _cmdWrapper.Canceling;
+                return _cmdWrapper!.Canceling;
             }
         }
 
+        [AllowNull]
         public override string CommandText
         {
             get
             {
-                string value = _commandText;
+                string? value = _commandText;
                 return ((null != value) ? value : string.Empty);
             }
             set
@@ -231,7 +234,7 @@ public override CommandType CommandType
             }
         }
 
-        public new OdbcConnection Connection
+        public new OdbcConnection? Connection
         {
             get
             {
@@ -250,7 +253,7 @@ public override CommandType CommandType
             }
         }
 
-        protected override DbConnection DbConnection
+        protected override DbConnection? DbConnection
         { // V1.2.3300
             get
             {
@@ -258,7 +261,7 @@ protected override DbConnection DbConnection
             }
             set
             {
-                Connection = (OdbcConnection)value;
+                Connection = (OdbcConnection?)value;
             }
         }
 
@@ -270,7 +273,7 @@ protected override DbParameterCollection DbParameterCollection
             }
         }
 
-        protected override DbTransaction DbTransaction
+        protected override DbTransaction? DbTransaction
         { // V1.2.3300
             get
             {
@@ -278,7 +281,7 @@ protected override DbTransaction DbTransaction
             }
             set
             {
-                Transaction = (OdbcTransaction)value;
+                Transaction = (OdbcTransaction?)value;
             }
         }
 
@@ -332,7 +335,7 @@ internal bool HasParameters
         Browsable(false),
         DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden),
         ]
-        public new OdbcTransaction Transaction
+        public new OdbcTransaction? Transaction
         {
             get
             {
@@ -379,7 +382,7 @@ public override UpdateRowSource UpdatedRowSource
 
         internal OdbcDescriptorHandle GetDescriptorHandle(ODBC32.SQL_ATTR attribute)
         {
-            return _cmdWrapper.GetDescriptorHandle(attribute);
+            return _cmdWrapper!.GetDescriptorHandle(attribute);
         }
 
 
@@ -398,7 +401,7 @@ internal CMDWrapper GetStatementHandle()
             //
             if (_cmdWrapper == null)
             {
-                _cmdWrapper = new CMDWrapper(_connection);
+                _cmdWrapper = new CMDWrapper(_connection!);
 
                 Debug.Assert(null != _connection, "GetStatementHandle without connection?");
                 _connection.AddWeakReference(this, OdbcReferenceCollection.CommandTag);
@@ -431,11 +434,11 @@ internal CMDWrapper GetStatementHandle()
 
         public override void Cancel()
         {
-            CMDWrapper wrapper = _cmdWrapper;
+            CMDWrapper? wrapper = _cmdWrapper;
             if (null != wrapper)
             {
                 wrapper.Canceling = true;
-                OdbcStatementHandle stmt = wrapper.StatementHandle;
+                OdbcStatementHandle? stmt = wrapper.StatementHandle;
                 if (null != stmt)
                 {
                     lock (stmt)
@@ -451,7 +454,7 @@ public override void Cancel()
                                 // don't fire info message events on cancel
                                 break;
                             default:
-                                throw wrapper.Connection.HandleErrorNoThrow(stmt, retcode);
+                                throw wrapper.Connection.HandleErrorNoThrow(stmt, retcode)!;
                         }
                     }
                 }
@@ -488,7 +491,7 @@ internal bool RecoverFromConnection()
 
         private void CloseCommandWrapper()
         {
-            CMDWrapper wrapper = _cmdWrapper;
+            CMDWrapper? wrapper = _cmdWrapper;
             if (null != wrapper)
             {
                 try
@@ -560,7 +563,7 @@ public override int ExecuteNonQuery()
             return ExecuteReaderObject(behavior, ADP.ExecuteReader, true);
         }
 
-        internal OdbcDataReader ExecuteReaderFromSQLMethod(object[] methodArguments,
+        internal OdbcDataReader ExecuteReaderFromSQLMethod(object?[]? methodArguments,
                                                             ODBC32.SQL_API method)
         {
             return ExecuteReaderObject(CommandBehavior.Default, method.ToString(), true, methodArguments, method);
@@ -579,10 +582,10 @@ private OdbcDataReader ExecuteReaderObject(CommandBehavior behavior, string meth
         private OdbcDataReader ExecuteReaderObject(CommandBehavior behavior,
                                                    string method,
                                                    bool needReader,
-                                                   object[] methodArguments,
+                                                   object?[]? methodArguments,
                                                    ODBC32.SQL_API odbcApiMethod)
         { // MDAC 68324
-            OdbcDataReader localReader = null;
+            OdbcDataReader? localReader = null;
             try
             {
                 DisposeDeadDataReader();    // this is a no-op if cmdState is not Fetching
@@ -596,14 +599,14 @@ private OdbcDataReader ExecuteReaderObject(CommandBehavior behavior,
 
                 ODBC32.RetCode retcode;
 
-                OdbcStatementHandle stmt = GetStatementHandle().StatementHandle;
-                _cmdWrapper.Canceling = false;
+                OdbcStatementHandle stmt = GetStatementHandle().StatementHandle!;
+                _cmdWrapper!.Canceling = false;
 
                 if (null != _weakDataReaderReference)
                 {
                     if (_weakDataReaderReference.IsAlive)
                     {
-                        object target = _weakDataReaderReference.Target;
+                        object? target = _weakDataReaderReference.Target;
                         if (null != target && _weakDataReaderReference.IsAlive)
                         {
                             if (!((OdbcDataReader)target).IsClosed)
@@ -617,7 +620,7 @@ private OdbcDataReader ExecuteReaderObject(CommandBehavior behavior,
 
                 //Set command properties
                 //Not all drivers support timeout. So fail silently if error
-                if (!Connection.ProviderInfo.NoQueryTimeout)
+                if (!Connection!.ProviderInfo.NoQueryTimeout)
                 {
                     TrySetStatementAttribute(stmt,
                         ODBC32.SQL_ATTR.QUERY_TIMEOUT,
@@ -668,12 +671,12 @@ private OdbcDataReader ExecuteReaderObject(CommandBehavior behavior,
 
                     if (ODBC32.RetCode.SUCCESS != retcode)
                     {
-                        _connection.HandleError(stmt, retcode);
+                        _connection!.HandleError(stmt, retcode);
                     }
                 }
 
                 bool mustRelease = false;
-                CNativeBuffer parameterBuffer = _cmdWrapper._nativeParameterBuffer;
+                CNativeBuffer? parameterBuffer = _cmdWrapper._nativeParameterBuffer;
 
                 try
                 {
@@ -727,7 +730,7 @@ private OdbcDataReader ExecuteReaderObject(CommandBehavior behavior,
                             else
                             {
                                 // any other returncode indicates an error
-                                _connection.HandleError(stmt, retcode);
+                                _connection!.HandleError(stmt, retcode);
                             }
                         }
 
@@ -754,42 +757,42 @@ private OdbcDataReader ExecuteReaderObject(CommandBehavior behavior,
                                 break;
 
                             case ODBC32.SQL_API.SQLTABLES:
-                                retcode = stmt.Tables((string)methodArguments[0],  //TableCatalog
-                                    (string)methodArguments[1],  //TableSchema,
-                                    (string)methodArguments[2],  //TableName
-                                    (string)methodArguments[3]); //TableType
+                                retcode = stmt.Tables((string)methodArguments![0]!,  //TableCatalog
+                                    (string)methodArguments[1]!,  //TableSchema,
+                                    (string)methodArguments[2]!,  //TableName
+                                    (string)methodArguments[3]!); //TableType
                                 break;
 
                             case ODBC32.SQL_API.SQLCOLUMNS:
-                                retcode = stmt.Columns((string)methodArguments[0],  //TableCatalog
-                                    (string)methodArguments[1],  //TableSchema
-                                    (string)methodArguments[2],  //TableName
-                                    (string)methodArguments[3]); //ColumnName
+                                retcode = stmt.Columns((string)methodArguments![0]!,  //TableCatalog
+                                    (string)methodArguments[1]!,  //TableSchema
+                                    (string)methodArguments[2]!,  //TableName
+                                    (string)methodArguments[3]!); //ColumnName
                                 break;
 
                             case ODBC32.SQL_API.SQLPROCEDURES:
-                                retcode = stmt.Procedures((string)methodArguments[0],  //ProcedureCatalog
-                                    (string)methodArguments[1],  //ProcedureSchema
-                                    (string)methodArguments[2]); //procedureName
+                                retcode = stmt.Procedures((string)methodArguments![0]!,  //ProcedureCatalog
+                                    (string)methodArguments[1]!,  //ProcedureSchema
+                                    (string)methodArguments[2]!); //procedureName
                                 break;
 
                             case ODBC32.SQL_API.SQLPROCEDURECOLUMNS:
-                                retcode = stmt.ProcedureColumns((string)methodArguments[0],  //ProcedureCatalog
-                                    (string)methodArguments[1],  //ProcedureSchema
-                                    (string)methodArguments[2],  //procedureName
-                                    (string)methodArguments[3]); //columnName
+                                retcode = stmt.ProcedureColumns((string)methodArguments![0]!,  //ProcedureCatalog
+                                    (string)methodArguments[1]!,  //ProcedureSchema
+                                    (string)methodArguments[2]!,  //procedureName
+                                    (string)methodArguments[3]!); //columnName
                                 break;
 
                             case ODBC32.SQL_API.SQLSTATISTICS:
-                                retcode = stmt.Statistics((string)methodArguments[0],  //TableCatalog
-                                    (string)methodArguments[1],  //TableSchema
-                                    (string)methodArguments[2],  //TableName
-                                    (short)methodArguments[3],   //IndexTrpe
-                                    (short)methodArguments[4]);  //Accuracy
+                                retcode = stmt.Statistics((string)methodArguments![0]!,  //TableCatalog
+                                    (string)methodArguments[1]!,  //TableSchema
+                                    (string)methodArguments[2]!,  //TableName
+                                    (short)methodArguments[3]!,   //IndexTrpe
+                                    (short)methodArguments[4]!);  //Accuracy
                                 break;
 
                             case ODBC32.SQL_API.SQLGETTYPEINFO:
-                                retcode = stmt.GetTypeInfo((short)methodArguments[0]);  //SQL Type
+                                retcode = stmt.GetTypeInfo((short)methodArguments![0]!);  //SQL Type
                                 break;
 
                             default:
@@ -801,7 +804,7 @@ private OdbcDataReader ExecuteReaderObject(CommandBehavior behavior,
                         //Note: Execute will return NO_DATA for Update/Delete non-row returning queries
                         if ((ODBC32.RetCode.SUCCESS != retcode) && (ODBC32.RetCode.NO_DATA != retcode))
                         {
-                            _connection.HandleError(stmt, retcode);
+                            _connection!.HandleError(stmt, retcode);
                         }
                     } // end SchemaOnly
                 }
@@ -809,7 +812,7 @@ private OdbcDataReader ExecuteReaderObject(CommandBehavior behavior,
                 {
                     if (mustRelease)
                     {
-                        parameterBuffer.DangerousRelease();
+                        parameterBuffer!.DangerousRelease();
                     }
                 }
 
@@ -843,12 +846,12 @@ private OdbcDataReader ExecuteReaderObject(CommandBehavior behavior,
                     }
                 }
             }
-            return localReader;
+            return localReader!;
         }
 
-        public override object ExecuteScalar()
+        public override object? ExecuteScalar()
         {
-            object value = null;
+            object? value = null;
             using (IDataReader reader = ExecuteReaderObject(0, ADP.ExecuteScalar, false))
             {
                 if (reader.Read() && (0 < reader.FieldCount))
@@ -862,7 +865,7 @@ public override object ExecuteScalar()
 
         internal string GetDiagSqlState()
         {
-            return _cmdWrapper.GetDiagSqlState();
+            return _cmdWrapper!.GetDiagSqlState();
         }
 
         private void PropertyChanging()
@@ -886,7 +889,7 @@ public override void Prepare()
 
             ValidateOpenConnection(ADP.Prepare);
 
-            if (0 != (ConnectionState.Fetching & _connection.InternalState))
+            if (0 != (ConnectionState.Fetching & _connection!.InternalState))
             {
                 throw ADP.OpenReaderExists();
             }
@@ -899,7 +902,7 @@ public override void Prepare()
             DisposeDeadDataReader();
             GetStatementHandle();
 
-            OdbcStatementHandle stmt = _cmdWrapper.StatementHandle;
+            OdbcStatementHandle stmt = _cmdWrapper!.StatementHandle!;
 
             retcode = stmt.Prepare(CommandText);
 
@@ -927,7 +930,7 @@ private void TrySetStatementAttribute(OdbcStatementHandle stmt, ODBC32.SQL_ATTR
 
                 if ((sqlState == "HYC00") || (sqlState == "HY092"))
                 {
-                    Connection.FlagUnsupportedStmtAttr(stmtAttribute);
+                    Connection!.FlagUnsupportedStmtAttr(stmtAttribute);
                 }
                 else
                 {
@@ -939,7 +942,7 @@ private void TrySetStatementAttribute(OdbcStatementHandle stmt, ODBC32.SQL_ATTR
         private void ValidateOpenConnection(string methodName)
         {
             // see if we have a connection
-            OdbcConnection connection = Connection;
+            OdbcConnection? connection = Connection;
 
             if (null == connection)
             {
@@ -967,15 +970,15 @@ private void ValidateConnectionAndTransaction(string method)
     }
     internal sealed class CMDWrapper
     {
-        private OdbcStatementHandle _stmt;                  // hStmt
-        private OdbcStatementHandle _keyinfostmt;           // hStmt for keyinfo
+        private OdbcStatementHandle? _stmt;                  // hStmt
+        private OdbcStatementHandle? _keyinfostmt;           // hStmt for keyinfo
 
-        internal OdbcDescriptorHandle _hdesc;              // hDesc
+        internal OdbcDescriptorHandle? _hdesc;              // hDesc
 
-        internal CNativeBuffer _nativeParameterBuffer;      // Native memory for internal memory management
+        internal CNativeBuffer? _nativeParameterBuffer;      // Native memory for internal memory management
         // (Performance optimization)
 
-        internal CNativeBuffer _dataReaderBuf;         // Reusable DataReader buffer
+        internal CNativeBuffer? _dataReaderBuf;         // Reusable DataReader buffer
 
         private readonly OdbcConnection _connection;        // Connection
         private bool _canceling;             // true if the command is canceling
@@ -1019,12 +1022,12 @@ internal bool HasBoundColumns
             }
         }
 
-        internal OdbcStatementHandle StatementHandle
+        internal OdbcStatementHandle? StatementHandle
         {
             get { return _stmt; }
         }
 
-        internal OdbcStatementHandle KeyInfoStatement
+        internal OdbcStatementHandle? KeyInfoStatement
         {
             get
             {
@@ -1053,7 +1056,7 @@ internal void Dispose()
             }
             DisposeStatementHandle();
 
-            CNativeBuffer buffer = _nativeParameterBuffer;
+            CNativeBuffer? buffer = _nativeParameterBuffer;
             _nativeParameterBuffer = null;
             if (null != buffer)
             {
@@ -1065,7 +1068,7 @@ internal void Dispose()
 
         private void DisposeDescriptorHandle()
         {
-            OdbcDescriptorHandle handle = _hdesc;
+            OdbcDescriptorHandle? handle = _hdesc;
             if (null != handle)
             {
                 _hdesc = null;
@@ -1077,7 +1080,7 @@ internal void DisposeStatementHandle()
             DisposeKeyInfoStatementHandle();
             DisposeDescriptorHandle();
 
-            OdbcStatementHandle handle = _stmt;
+            OdbcStatementHandle? handle = _stmt;
             if (null != handle)
             {
                 _stmt = null;
@@ -1087,7 +1090,7 @@ internal void DisposeStatementHandle()
 
         internal void DisposeKeyInfoStatementHandle()
         {
-            OdbcStatementHandle handle = _keyinfostmt;
+            OdbcStatementHandle? handle = _keyinfostmt;
             if (null != handle)
             {
                 _keyinfostmt = null;
@@ -1099,7 +1102,7 @@ internal void FreeStatementHandle(ODBC32.STMT stmt)
         {
             DisposeDescriptorHandle();
 
-            OdbcStatementHandle handle = _stmt;
+            OdbcStatementHandle? handle = _stmt;
             if (null != handle)
             {
                 try
@@ -1124,7 +1127,7 @@ internal void FreeStatementHandle(ODBC32.STMT stmt)
 
         internal void FreeKeyInfoStatementHandle(ODBC32.STMT stmt)
         {
-            OdbcStatementHandle handle = _keyinfostmt;
+            OdbcStatementHandle? handle = _keyinfostmt;
             if (null != handle)
             {
                 try
@@ -1149,10 +1152,10 @@ internal void FreeKeyInfoStatementHandle(ODBC32.STMT stmt)
         //
         internal OdbcDescriptorHandle GetDescriptorHandle(ODBC32.SQL_ATTR attribute)
         {
-            OdbcDescriptorHandle hdesc = _hdesc;
-            if (null == _hdesc)
+            OdbcDescriptorHandle? hdesc = _hdesc;
+            if (null == hdesc)
             {
-                _hdesc = hdesc = new OdbcDescriptorHandle(_stmt, attribute);
+                _hdesc = hdesc = new OdbcDescriptorHandle(_stmt!, attribute);
             }
             return hdesc;
         }
@@ -1160,7 +1163,7 @@ internal OdbcDescriptorHandle GetDescriptorHandle(ODBC32.SQL_ATTR attribute)
         internal string GetDiagSqlState()
         {
             string sqlstate;
-            _stmt.GetDiagnosticField(out sqlstate);
+            _stmt!.GetDiagnosticField(out sqlstate);
             return sqlstate;
         }
 
@@ -1170,10 +1173,10 @@ internal void StatementErrorHandler(ODBC32.RetCode retcode)
             {
                 case ODBC32.RetCode.SUCCESS:
                 case ODBC32.RetCode.SUCCESS_WITH_INFO:
-                    _connection.HandleErrorNoThrow(_stmt, retcode);
+                    _connection.HandleErrorNoThrow(_stmt!, retcode);
                     break;
                 default:
-                    throw _connection.HandleErrorNoThrow(_stmt, retcode);
+                    throw _connection.HandleErrorNoThrow(_stmt!, retcode)!;
             }
         }
 
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcCommandBuilder.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcCommandBuilder.cs
index a855418b9e2fe6..55a1fd1c208ee9 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcCommandBuilder.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcCommandBuilder.cs
@@ -14,12 +14,12 @@ public OdbcCommandBuilder() : base()
             GC.SuppressFinalize(this);
         }
 
-        public OdbcCommandBuilder(OdbcDataAdapter adapter) : this()
+        public OdbcCommandBuilder(OdbcDataAdapter? adapter) : this()
         {
             DataAdapter = adapter;
         }
 
-        public new OdbcDataAdapter DataAdapter
+        public new OdbcDataAdapter? DataAdapter
         {
             get
             {
@@ -123,7 +123,7 @@ public static void DeriveParameters(OdbcCommand command)
                 throw ADP.CommandTextRequired(ADP.DeriveParameters);
             }
 
-            OdbcConnection connection = command.Connection;
+            OdbcConnection? connection = command.Connection;
 
             if (null == connection)
             {
@@ -166,7 +166,7 @@ private static OdbcParameter[] DeriveParametersFromStoredProcedure(OdbcConnectio
 
             // following call ensures that the command has a statement handle allocated
             CMDWrapper cmdWrapper = command.GetStatementHandle();
-            OdbcStatementHandle hstmt = cmdWrapper.StatementHandle;
+            OdbcStatementHandle hstmt = cmdWrapper.StatementHandle!;
             int cColsAffected;
 
             // maps an enforced 4-part qualified string as follows
@@ -176,7 +176,7 @@ private static OdbcParameter[] DeriveParametersFromStoredProcedure(OdbcConnectio
             // parts[3] = ProcedureName
             //
             string quote = connection.QuoteChar(ADP.DeriveParameters);
-            string[] parts = MultipartIdentifier.ParseMultipartIdentifier(command.CommandText, quote, quote, '.', 4, true, SR.ODBC_ODBCCommandText, false);
+            string?[] parts = MultipartIdentifier.ParseMultipartIdentifier(command.CommandText, quote, quote, '.', 4, true, SR.ODBC_ODBCCommandText, false);
             if (null == parts[3])
             { // match Everett behavior, if the commandtext is nothing but whitespace set the command text to the whitespace
                 parts[3] = command.CommandText;
@@ -251,7 +251,7 @@ public override string QuoteIdentifier(string unquotedIdentifier)
             return QuoteIdentifier(unquotedIdentifier, null /* use DataAdapter.SelectCommand.Connection if available */);
         }
 
-        public string QuoteIdentifier(string unquotedIdentifier, OdbcConnection connection)
+        public string QuoteIdentifier(string unquotedIdentifier, OdbcConnection? connection)
         {
             ADP.CheckArgumentNull(unquotedIdentifier, nameof(unquotedIdentifier));
 
@@ -306,11 +306,11 @@ public override string UnquoteIdentifier(string quotedIdentifier)
             return UnquoteIdentifier(quotedIdentifier, null /* use DataAdapter.SelectCommand.Connection if available */);
         }
 
-        public string UnquoteIdentifier(string quotedIdentifier, OdbcConnection connection)
+        public string UnquoteIdentifier(string quotedIdentifier, OdbcConnection? connection)
         {
             ADP.CheckArgumentNull(quotedIdentifier, nameof(quotedIdentifier));
 
-            // if the user has specificed a prefix use the user specified  prefix and suffix
+            // if the user has specified a prefix use the user specified  prefix and suffix
             // otherwise get them from the provider
             string quotePrefix = QuotePrefix;
             string quoteSuffix = QuoteSuffix;
@@ -330,7 +330,7 @@ public string UnquoteIdentifier(string quotedIdentifier, OdbcConnection connecti
                 quoteSuffix = quotePrefix;
             }
 
-            string unquotedIdentifier;
+            string? unquotedIdentifier;
             // by the ODBC spec "If the data source does not support quoted identifiers, a blank is returned."
             // So if a blank is returned the string is returned unchanged. Otherwise the returned string is used
             // to unquote the string
@@ -344,7 +344,7 @@ public string UnquoteIdentifier(string quotedIdentifier, OdbcConnection connecti
             {
                 unquotedIdentifier = quotedIdentifier;
             }
-            return unquotedIdentifier;
+            return unquotedIdentifier!;
         }
     }
 }
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnection.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnection.cs
index 4b7ec8fa72de42..9841dd7790662c 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnection.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnection.cs
@@ -16,12 +16,12 @@ public sealed partial class OdbcConnection : DbConnection, ICloneable
     {
         private int _connectionTimeout = ADP.DefaultConnectionTimeout;
 
-        private OdbcInfoMessageEventHandler _infoMessageEventHandler;
-        private WeakReference _weakTransaction;
+        private OdbcInfoMessageEventHandler? _infoMessageEventHandler;
+        private WeakReference? _weakTransaction;
 
-        private OdbcConnectionHandle _connectionHandle;
+        private OdbcConnectionHandle? _connectionHandle;
 
-        public OdbcConnection(string connectionString) : this()
+        public OdbcConnection(string? connectionString) : this()
         {
             ConnectionString = connectionString;
         }
@@ -32,7 +32,7 @@ private OdbcConnection(OdbcConnection connection) : this()
             _connectionTimeout = connection._connectionTimeout;
         }
 
-        internal OdbcConnectionHandle ConnectionHandle
+        internal OdbcConnectionHandle? ConnectionHandle
         {
             get
             {
@@ -45,6 +45,7 @@ internal OdbcConnectionHandle ConnectionHandle
             }
         }
 
+        [AllowNull]
         public override string ConnectionString
         {
             get
@@ -110,7 +111,7 @@ public override string DataSource
                     // note: This will return an empty string if the driver keyword was used to connect
                     // see ODBC3.0 Programmers Reference, SQLGetInfo
                     //
-                    return GetInfoStringUnhandled(ODBC32.SQL_INFO.SERVER_NAME, true);
+                    return GetInfoStringUnhandled(ODBC32.SQL_INFO.SERVER_NAME, true)!;
                 }
                 return string.Empty;
             }
@@ -145,7 +146,7 @@ internal OdbcConnectionPoolGroupProviderInfo ProviderInfo
             get
             {
                 Debug.Assert(null != this.PoolGroup, "PoolGroup must never be null when accessing ProviderInfo");
-                return (OdbcConnectionPoolGroupProviderInfo)this.PoolGroup.ProviderInfo;
+                return (OdbcConnectionPoolGroupProviderInfo)this.PoolGroup.ProviderInfo!;
             }
         }
 
@@ -165,14 +166,14 @@ internal bool IsOpen
             }
         }
 
-        internal OdbcTransaction LocalTransaction
+        internal OdbcTransaction? LocalTransaction
         {
             get
             {
-                OdbcTransaction result = null;
+                OdbcTransaction? result = null;
                 if (null != _weakTransaction)
                 {
-                    result = ((OdbcTransaction)_weakTransaction.Target);
+                    result = ((OdbcTransaction?)_weakTransaction.Target);
                 }
                 return result;
             }
@@ -200,7 +201,7 @@ public string Driver
                 {
                     if (ProviderInfo.DriverName == null)
                     {
-                        ProviderInfo.DriverName = GetInfoStringUnhandled(ODBC32.SQL_INFO.DRIVER_NAME);
+                        ProviderInfo.DriverName = GetInfoStringUnhandled(ODBC32.SQL_INFO.DRIVER_NAME)!;
                     }
                     return ProviderInfo.DriverName;
                 }
@@ -237,7 +238,7 @@ internal bool IsV3Driver
             }
         }
 
-        public event OdbcInfoMessageEventHandler InfoMessage
+        public event OdbcInfoMessageEventHandler? InfoMessage
         {
             add
             {
@@ -255,7 +256,7 @@ internal char EscapeChar(string method)
             if (!ProviderInfo.HasEscapeChar)
             {
                 string escapeCharString;
-                escapeCharString = GetInfoStringUnhandled(ODBC32.SQL_INFO.SEARCH_PATTERN_ESCAPE);
+                escapeCharString = GetInfoStringUnhandled(ODBC32.SQL_INFO.SEARCH_PATTERN_ESCAPE)!;
                 Debug.Assert((escapeCharString.Length <= 1), "Can't handle multichar quotes");
                 ProviderInfo.EscapeChar = (escapeCharString.Length == 1) ? escapeCharString[0] : QuoteChar(method)[0];
             }
@@ -268,7 +269,7 @@ internal string QuoteChar(string method)
             if (!ProviderInfo.HasQuoteChar)
             {
                 string quoteCharString;
-                quoteCharString = GetInfoStringUnhandled(ODBC32.SQL_INFO.IDENTIFIER_QUOTE_CHAR);
+                quoteCharString = GetInfoStringUnhandled(ODBC32.SQL_INFO.IDENTIFIER_QUOTE_CHAR)!;
                 Debug.Assert((quoteCharString.Length <= 1), "Can't handle multichar quotes");
                 ProviderInfo.QuoteChar = (1 == quoteCharString.Length) ? quoteCharString : "\0";
             }
@@ -287,11 +288,11 @@ internal string QuoteChar(string method)
 
         private void RollbackDeadTransaction()
         {
-            WeakReference weak = _weakTransaction;
+            WeakReference? weak = _weakTransaction;
             if ((null != weak) && !weak.IsAlive)
             {
                 _weakTransaction = null;
-                ConnectionHandle.CompleteTransaction(ODBC32.SQL_ROLLBACK);
+                ConnectionHandle!.CompleteTransaction(ODBC32.SQL_ROLLBACK);
             }
         }
 
@@ -315,7 +316,7 @@ object ICloneable.Clone()
             return clone;
         }
 
-        internal bool ConnectionIsAlive(Exception innerException)
+        internal bool ConnectionIsAlive(Exception? innerException)
         {
             if (IsOpen)
             {
@@ -348,18 +349,18 @@ public override void Close()
         {
             InnerConnection.CloseConnection(this, ConnectionFactory);
 
-            OdbcConnectionHandle connectionHandle = _connectionHandle;
+            OdbcConnectionHandle? connectionHandle = _connectionHandle;
 
             if (null != connectionHandle)
             {
                 _connectionHandle = null;
 
                 // If there is a pending transaction, automatically rollback.
-                WeakReference weak = _weakTransaction;
+                WeakReference? weak = _weakTransaction;
                 if (null != weak)
                 {
                     _weakTransaction = null;
-                    IDisposable transaction = weak.Target as OdbcTransaction;
+                    IDisposable? transaction = weak.Target as OdbcTransaction;
                     if ((null != transaction) && weak.IsAlive)
                     {
                         transaction.Dispose();
@@ -379,7 +380,7 @@ internal string GetConnectAttrString(ODBC32.SQL_ATTR attribute)
             string value = "";
             int cbActual = 0;
             byte[] buffer = new byte[100];
-            OdbcConnectionHandle connectionHandle = ConnectionHandle;
+            OdbcConnectionHandle? connectionHandle = ConnectionHandle;
             if (null != connectionHandle)
             {
                 ODBC32.RetCode retcode = connectionHandle.GetConnectionAttribute(attribute, buffer, out cbActual);
@@ -412,7 +413,7 @@ internal int GetConnectAttr(ODBC32.SQL_ATTR attribute, ODBC32.HANDLER handler)
             int retval = -1;
             int cbActual = 0;
             byte[] buffer = new byte[4];
-            OdbcConnectionHandle connectionHandle = ConnectionHandle;
+            OdbcConnectionHandle? connectionHandle = ConnectionHandle;
             if (null != connectionHandle)
             {
                 ODBC32.RetCode retcode = connectionHandle.GetConnectionAttribute(attribute, buffer, out cbActual);
@@ -442,7 +443,7 @@ internal int GetConnectAttr(ODBC32.SQL_ATTR attribute, ODBC32.HANDLER handler)
 
         private string GetDiagSqlState()
         {
-            OdbcConnectionHandle connectionHandle = ConnectionHandle;
+            OdbcConnectionHandle connectionHandle = ConnectionHandle!;
             string sqlstate;
             connectionHandle.GetDiagnosticField(out sqlstate);
             return sqlstate;
@@ -451,7 +452,7 @@ private string GetDiagSqlState()
         internal ODBC32.RetCode GetInfoInt16Unhandled(ODBC32.SQL_INFO info, out short resultValue)
         {
             byte[] buffer = new byte[2];
-            ODBC32.RetCode retcode = ConnectionHandle.GetInfo1(info, buffer);
+            ODBC32.RetCode retcode = ConnectionHandle!.GetInfo1(info, buffer);
             resultValue = BitConverter.ToInt16(buffer, 0);
             return retcode;
         }
@@ -459,7 +460,7 @@ internal ODBC32.RetCode GetInfoInt16Unhandled(ODBC32.SQL_INFO info, out short re
         internal ODBC32.RetCode GetInfoInt32Unhandled(ODBC32.SQL_INFO info, out int resultValue)
         {
             byte[] buffer = new byte[4];
-            ODBC32.RetCode retcode = ConnectionHandle.GetInfo1(info, buffer);
+            ODBC32.RetCode retcode = ConnectionHandle!.GetInfo1(info, buffer);
             resultValue = BitConverter.ToInt32(buffer, 0);
             return retcode;
         }
@@ -467,22 +468,22 @@ internal ODBC32.RetCode GetInfoInt32Unhandled(ODBC32.SQL_INFO info, out int resu
         private int GetInfoInt32Unhandled(ODBC32.SQL_INFO infotype)
         {
             byte[] buffer = new byte[4];
-            ConnectionHandle.GetInfo1(infotype, buffer);
+            ConnectionHandle!.GetInfo1(infotype, buffer);
             return BitConverter.ToInt32(buffer, 0);
         }
 
-        internal string GetInfoStringUnhandled(ODBC32.SQL_INFO info)
+        internal string? GetInfoStringUnhandled(ODBC32.SQL_INFO info)
         {
             return GetInfoStringUnhandled(info, false);
         }
 
-        private string GetInfoStringUnhandled(ODBC32.SQL_INFO info, bool handleError)
+        private string? GetInfoStringUnhandled(ODBC32.SQL_INFO info, bool handleError)
         {
             //SQLGetInfo
-            string value = null;
+            string? value = null;
             short cbActual = 0;
             byte[] buffer = new byte[100];
-            OdbcConnectionHandle connectionHandle = ConnectionHandle;
+            OdbcConnectionHandle? connectionHandle = ConnectionHandle;
             if (null != connectionHandle)
             {
                 ODBC32.RetCode retcode = connectionHandle.GetInfo2(info, buffer, out cbActual);
@@ -499,7 +500,7 @@ private string GetInfoStringUnhandled(ODBC32.SQL_INFO info, bool handleError)
                 }
                 else if (handleError)
                 {
-                    this.HandleError(ConnectionHandle, retcode);
+                    this.HandleError(connectionHandle, retcode);
                 }
             }
             else if (handleError)
@@ -510,7 +511,7 @@ private string GetInfoStringUnhandled(ODBC32.SQL_INFO info, bool handleError)
         }
 
         // non-throwing HandleError
-        internal Exception HandleErrorNoThrow(OdbcHandle hrHandle, ODBC32.RetCode retcode)
+        internal Exception? HandleErrorNoThrow(OdbcHandle hrHandle, ODBC32.RetCode retcode)
         {
             Debug.Assert(retcode != ODBC32.RetCode.INVALID_HANDLE, "retcode must never be ODBC32.RetCode.INVALID_HANDLE");
 
@@ -537,14 +538,14 @@ internal Exception HandleErrorNoThrow(OdbcHandle hrHandle, ODBC32.RetCode retcod
                         e.Errors.SetSource(this.Driver);
                     }
                     ConnectionIsAlive(e);        // this will close and throw if the connection is dead
-                    return (Exception)e;
+                    return e;
             }
             return null;
         }
 
         internal void HandleError(OdbcHandle hrHandle, ODBC32.RetCode retcode)
         {
-            Exception e = HandleErrorNoThrow(hrHandle, retcode);
+            Exception? e = HandleErrorNoThrow(hrHandle, retcode);
             switch (retcode)
             {
                 case ODBC32.RetCode.SUCCESS:
@@ -601,11 +602,11 @@ public static void ReleaseObjectPool()
             OdbcEnvironment.ReleaseObjectPool();
         }
 
-        internal OdbcTransaction SetStateExecuting(string method, OdbcTransaction transaction)
+        internal OdbcTransaction? SetStateExecuting(string method, OdbcTransaction? transaction)
         { // MDAC 69003
             if (null != _weakTransaction)
             { // transaction may exist
-                OdbcTransaction weak = (_weakTransaction.Target as OdbcTransaction);
+                OdbcTransaction? weak = (_weakTransaction.Target as OdbcTransaction);
                 if (transaction != weak)
                 { // transaction doesn't exist
                     if (null == transaction)
@@ -778,7 +779,7 @@ internal bool SQLGetFunctions(ODBC32.SQL_API odbcFunction)
             ODBC32.RetCode retcode;
             short fExists;
             Debug.Assert((short)odbcFunction != 0, "SQL_API_ALL_FUNCTIONS is not supported");
-            OdbcConnectionHandle connectionHandle = ConnectionHandle;
+            OdbcConnectionHandle? connectionHandle = ConnectionHandle;
             if (null != connectionHandle)
             {
                 retcode = connectionHandle.GetFunctions(odbcFunction, out fExists);
@@ -921,7 +922,7 @@ internal OdbcTransaction Open_BeginTransaction(IsolationLevel isolevel)
             };
 
             //Start the transaction
-            OdbcConnectionHandle connectionHandle = ConnectionHandle;
+            OdbcConnectionHandle connectionHandle = ConnectionHandle!;
             ODBC32.RetCode retcode = connectionHandle.BeginTransaction(ref isolevel);
             if (retcode == ODBC32.RetCode.ERROR)
             {
@@ -948,7 +949,7 @@ internal void Open_ChangeDatabase(string value)
             RollbackDeadTransaction();
 
             //Set the database
-            OdbcConnectionHandle connectionHandle = ConnectionHandle;
+            OdbcConnectionHandle connectionHandle = ConnectionHandle!;
             ODBC32.RetCode retcode = connectionHandle.SetConnectionAttribute3(ODBC32.SQL_ATTR.CURRENT_CATALOG, value, checked((int)value.Length * 2));
 
             if (retcode != ODBC32.RetCode.SUCCESS)
@@ -957,7 +958,7 @@ internal void Open_ChangeDatabase(string value)
             }
         }
 
-        internal string Open_GetServerVersion()
+        internal string? Open_GetServerVersion()
         {
             //SQLGetInfo - SQL_DBMS_VER
             return GetInfoStringUnhandled(ODBC32.SQL_INFO.DBMS_VER, true);
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionFactory.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionFactory.cs
index 0bdd4b432cd907..d9d35950a2e612 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionFactory.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionFactory.cs
@@ -5,6 +5,7 @@
 using System.Data.Common;
 using System.Data.ProviderBase;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 
 namespace System.Data.Odbc
@@ -26,20 +27,21 @@ public override DbProviderFactory ProviderFactory
             }
         }
 
-        protected override DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningObject)
+        protected override DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool? pool, DbConnection? owningObject)
         {
-            DbConnectionInternal result = new OdbcConnectionOpen(owningObject as OdbcConnection, options as OdbcConnectionString);
+            // TODO: owningObject may actually be null (see DbConnectionPool.CreateObject), in which case this will throw...
+            DbConnectionInternal result = new OdbcConnectionOpen((owningObject as OdbcConnection)!, (options as OdbcConnectionString)!);
             return result;
         }
 
-        protected override DbConnectionOptions CreateConnectionOptions(string connectionString, DbConnectionOptions previous)
+        protected override DbConnectionOptions CreateConnectionOptions(string connectionString, DbConnectionOptions? previous)
         {
             Debug.Assert(!string.IsNullOrEmpty(connectionString), "empty connectionString");
             OdbcConnectionString result = new OdbcConnectionString(connectionString, (null != previous));
             return result;
         }
 
-        protected override DbConnectionPoolGroupOptions CreateConnectionPoolGroupOptions(DbConnectionOptions connectionOptions)
+        protected override DbConnectionPoolGroupOptions? CreateConnectionPoolGroupOptions(DbConnectionOptions connectionOptions)
         {
             // At this time, the ODBC provider only supports native pooling so we
             // simply return NULL to indicate that.
@@ -60,20 +62,20 @@ protected override DbMetaDataFactory CreateMetaDataFactory(DbConnectionInternal
             Debug.Assert(odbcOuterConnection != null, "outer connection may not be null.");
 
             // get the DBMS Name
-            object driverName = null;
-            string stringValue = odbcOuterConnection.GetInfoStringUnhandled(ODBC32.SQL_INFO.DRIVER_NAME);
+            object? driverName = null;
+            string? stringValue = odbcOuterConnection.GetInfoStringUnhandled(ODBC32.SQL_INFO.DRIVER_NAME);
             if (stringValue != null)
             {
                 driverName = stringValue;
             }
 
-            Stream XMLStream = System.Reflection.Assembly.GetExecutingAssembly().GetManifestResourceStream("System.Data.Odbc.OdbcMetaData.xml");
+            Stream? XMLStream = System.Reflection.Assembly.GetExecutingAssembly().GetManifestResourceStream("System.Data.Odbc.OdbcMetaData.xml");
             cacheMetaDataFactory = true;
 
 
             Debug.Assert(XMLStream != null, "XMLstream may not be null.");
 
-            string versionString = odbcOuterConnection.GetInfoStringUnhandled(ODBC32.SQL_INFO.DBMS_VER);
+            string versionString = odbcOuterConnection.GetInfoStringUnhandled(ODBC32.SQL_INFO.DBMS_VER)!;
 
             return new OdbcMetaDataFactory(XMLStream,
                                             versionString,
@@ -81,9 +83,9 @@ protected override DbMetaDataFactory CreateMetaDataFactory(DbConnectionInternal
                                             odbcOuterConnection);
         }
 
-        internal override DbConnectionPoolGroup GetConnectionPoolGroup(DbConnection connection)
+        internal override DbConnectionPoolGroup? GetConnectionPoolGroup(DbConnection? connection)
         {
-            OdbcConnection c = (connection as OdbcConnection);
+            OdbcConnection? c = (connection as OdbcConnection);
             if (null != c)
             {
                 return c.PoolGroup;
@@ -91,9 +93,9 @@ internal override DbConnectionPoolGroup GetConnectionPoolGroup(DbConnection conn
             return null;
         }
 
-        internal override DbConnectionInternal GetInnerConnection(DbConnection connection)
+        internal override DbConnectionInternal? GetInnerConnection(DbConnection connection)
         {
-            OdbcConnection c = (connection as OdbcConnection);
+            OdbcConnection? c = (connection as OdbcConnection);
             if (null != c)
             {
                 return c.InnerConnection;
@@ -103,7 +105,7 @@ internal override DbConnectionInternal GetInnerConnection(DbConnection connectio
 
         internal override void PermissionDemand(DbConnection outerConnection)
         {
-            OdbcConnection c = (outerConnection as OdbcConnection);
+            OdbcConnection? c = (outerConnection as OdbcConnection);
             if (null != c)
             {
                 c.PermissionDemand();
@@ -112,7 +114,7 @@ internal override void PermissionDemand(DbConnection outerConnection)
 
         internal override void SetConnectionPoolGroup(DbConnection outerConnection, DbConnectionPoolGroup poolGroup)
         {
-            OdbcConnection c = (outerConnection as OdbcConnection);
+            OdbcConnection? c = (outerConnection as OdbcConnection);
             if (null != c)
             {
                 c.PoolGroup = poolGroup;
@@ -121,7 +123,7 @@ internal override void SetConnectionPoolGroup(DbConnection outerConnection, DbCo
 
         internal override void SetInnerConnectionEvent(DbConnection owningObject, DbConnectionInternal to)
         {
-            OdbcConnection c = (owningObject as OdbcConnection);
+            OdbcConnection? c = (owningObject as OdbcConnection);
             if (null != c)
             {
                 c.SetInnerConnectionEvent(to);
@@ -130,7 +132,7 @@ internal override void SetInnerConnectionEvent(DbConnection owningObject, DbConn
 
         internal override bool SetInnerConnectionFrom(DbConnection owningObject, DbConnectionInternal to, DbConnectionInternal from)
         {
-            OdbcConnection c = (owningObject as OdbcConnection);
+            OdbcConnection? c = (owningObject as OdbcConnection);
             if (null != c)
             {
                 return c.SetInnerConnectionFrom(to, from);
@@ -140,7 +142,7 @@ internal override bool SetInnerConnectionFrom(DbConnection owningObject, DbConne
 
         internal override void SetInnerConnectionTo(DbConnection owningObject, DbConnectionInternal to)
         {
-            OdbcConnection c = (owningObject as OdbcConnection);
+            OdbcConnection? c = (owningObject as OdbcConnection);
             if (null != c)
             {
                 c.SetInnerConnectionTo(to);
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionHelper.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionHelper.cs
index 90e755ecd37c04..a84658b4b543f5 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionHelper.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionHelper.cs
@@ -12,8 +12,8 @@ public sealed partial class OdbcConnection : DbConnection
     {
         private static readonly DbConnectionFactory s_connectionFactory = OdbcConnectionFactory.SingletonInstance;
 
-        private DbConnectionOptions _userConnectionOptions;
-        private DbConnectionPoolGroup _poolGroup;
+        private DbConnectionOptions? _userConnectionOptions;
+        private DbConnectionPoolGroup? _poolGroup;
         private DbConnectionInternal _innerConnection;
         private int _closeCount;
 
@@ -60,11 +60,11 @@ internal DbConnectionFactory ConnectionFactory
             }
         }
 
-        internal DbConnectionOptions ConnectionOptions
+        internal DbConnectionOptions? ConnectionOptions
         {
             get
             {
-                System.Data.ProviderBase.DbConnectionPoolGroup poolGroup = PoolGroup;
+                System.Data.ProviderBase.DbConnectionPoolGroup? poolGroup = PoolGroup;
                 return ((null != poolGroup) ? poolGroup.ConnectionOptions : null);
             }
         }
@@ -72,11 +72,11 @@ internal DbConnectionOptions ConnectionOptions
         private string ConnectionString_Get()
         {
             bool hidePassword = InnerConnection.ShouldHidePassword;
-            DbConnectionOptions connectionOptions = UserConnectionOptions;
+            DbConnectionOptions? connectionOptions = UserConnectionOptions;
             return ((null != connectionOptions) ? connectionOptions.UsersConnectionString(hidePassword) : "");
         }
 
-        private void ConnectionString_Set(string value)
+        private void ConnectionString_Set(string? value)
         {
             DbConnectionPoolKey key = new DbConnectionPoolKey(value);
 
@@ -85,8 +85,8 @@ private void ConnectionString_Set(string value)
 
         private void ConnectionString_Set(DbConnectionPoolKey key)
         {
-            DbConnectionOptions connectionOptions = null;
-            System.Data.ProviderBase.DbConnectionPoolGroup poolGroup = ConnectionFactory.GetConnectionPoolGroup(key, null, ref connectionOptions);
+            DbConnectionOptions? connectionOptions = null;
+            System.Data.ProviderBase.DbConnectionPoolGroup? poolGroup = ConnectionFactory.GetConnectionPoolGroup(key, null, ref connectionOptions);
             DbConnectionInternal connectionInternal = InnerConnection;
             bool flag = connectionInternal.AllowSetConnectionString;
             if (flag)
@@ -113,7 +113,7 @@ internal DbConnectionInternal InnerConnection
             }
         }
 
-        internal System.Data.ProviderBase.DbConnectionPoolGroup PoolGroup
+        internal System.Data.ProviderBase.DbConnectionPoolGroup? PoolGroup
         {
             get
             {
@@ -127,7 +127,7 @@ internal System.Data.ProviderBase.DbConnectionPoolGroup PoolGroup
         }
 
 
-        internal DbConnectionOptions UserConnectionOptions
+        internal DbConnectionOptions? UserConnectionOptions
         {
             get
             {
@@ -152,9 +152,8 @@ internal void AddWeakReference(object value, int tag)
 
         protected override DbCommand CreateDbCommand()
         {
-            DbCommand command = null;
             DbProviderFactory providerFactory = ConnectionFactory.ProviderFactory;
-            command = providerFactory.CreateCommand();
+            DbCommand command = providerFactory.CreateCommand()!;
             command.Connection = this;
             return command;
         }
@@ -184,11 +183,11 @@ public override DataTable GetSchema(string collectionName)
             return this.GetSchema(collectionName, null);
         }
 
-        public override DataTable GetSchema(string collectionName, string[] restrictionValues)
+        public override DataTable GetSchema(string collectionName, string?[]? restrictionValues)
         {
             // NOTE: This is virtual because not all providers may choose to support
             //       returning schema data
-            return InnerConnection.GetSchema(ConnectionFactory, PoolGroup, this, collectionName, restrictionValues);
+            return InnerConnection.GetSchema(ConnectionFactory, PoolGroup!, this, collectionName, restrictionValues);
         }
 
         internal void NotifyWeakReference(int message)
@@ -199,13 +198,13 @@ internal void NotifyWeakReference(int message)
         internal void PermissionDemand()
         {
             Debug.Assert(DbConnectionClosedConnecting.SingletonInstance == _innerConnection, "not connecting");
-            System.Data.ProviderBase.DbConnectionPoolGroup poolGroup = PoolGroup;
-            DbConnectionOptions connectionOptions = ((null != poolGroup) ? poolGroup.ConnectionOptions : null);
+            System.Data.ProviderBase.DbConnectionPoolGroup? poolGroup = PoolGroup;
+            DbConnectionOptions? connectionOptions = ((null != poolGroup) ? poolGroup.ConnectionOptions : null);
             if ((null == connectionOptions) || connectionOptions.IsEmpty)
             {
                 throw ADP.NoConnectionString();
             }
-            DbConnectionOptions userConnectionOptions = UserConnectionOptions;
+            DbConnectionOptions? userConnectionOptions = UserConnectionOptions;
             Debug.Assert(null != userConnectionOptions, "null UserConnectionOptions");
         }
 
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionOpen.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionOpen.cs
index 2c6f7c71487e10..008facb51311e3 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionOpen.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionOpen.cs
@@ -19,7 +19,7 @@ internal OdbcConnection OuterConnection
         {
             get
             {
-                OdbcConnection outerConnection = (OdbcConnection)Owner;
+                OdbcConnection? outerConnection = (OdbcConnection?)Owner;
 
                 if (null == outerConnection)
                     throw ODBC.OpenConnectionNoOwner();
@@ -32,7 +32,9 @@ public override string ServerVersion
         {
             get
             {
-                return OuterConnection.Open_GetServerVersion();
+                // TODO-NULLABLE: This seems like it returns null if the connection is open, whereas the docs say it should throw
+                // InvalidOperationException
+                return OuterConnection.Open_GetServerVersion()!;
             }
         }
 
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionPoolProviderInfo.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionPoolProviderInfo.cs
index e498e985858528..b49f953fecdb81 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionPoolProviderInfo.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionPoolProviderInfo.cs
@@ -2,14 +2,15 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Data.ProviderBase;
+using System.Diagnostics;
 
 namespace System.Data.Odbc
 {
     internal sealed class OdbcConnectionPoolGroupProviderInfo : DbConnectionPoolGroupProviderInfo
     {
-        private string _driverName;
-        private string _driverVersion;
-        private string _quoteChar;
+        private string? _driverName;
+        private string? _driverVersion;
+        private string? _quoteChar;
 
         private char _escapeChar;
         private bool _hasQuoteChar;
@@ -35,7 +36,7 @@ internal sealed class OdbcConnectionPoolGroupProviderInfo : DbConnectionPoolGrou
         // flags for unsupported Functions
         private bool _noSqlPrimaryKeys;
 
-        internal string DriverName
+        internal string? DriverName
         {
             get
             {
@@ -47,7 +48,7 @@ internal string DriverName
             }
         }
 
-        internal string DriverVersion
+        internal string? DriverVersion
         {
             get
             {
@@ -82,6 +83,7 @@ internal string QuoteChar
         {
             get
             {
+                Debug.Assert(_quoteChar != null, "QuoteChar getter called but no quote char was set");
                 return _quoteChar;
             }
             set
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionString.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionString.cs
index e17edacb232233..74790e05ac1f2a 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionString.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionString.cs
@@ -12,13 +12,13 @@ internal sealed class OdbcConnectionString : DbConnectionOptions
         // used by pooling classes so it is much easier to verify correctness
         // when not worried about the class being modified during execution
 
-        private readonly string _expandedConnectionString;
+        private readonly string? _expandedConnectionString;
 
         internal OdbcConnectionString(string connectionString, bool validate) : base(connectionString, null, true)
         {
             if (!validate)
             {
-                string filename = null;
+                string? filename = null;
                 int position = 0;
                 _expandedConnectionString = ExpandDataDirectories(ref filename, ref position);
             }
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionStringbuilder.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionStringbuilder.cs
index 877275e2b865cc..ae68e130447fec 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionStringbuilder.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcConnectionStringbuilder.cs
@@ -7,6 +7,7 @@
 using System.ComponentModel;
 using System.Data.Common;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Data.Odbc
 {
@@ -30,16 +31,16 @@ private enum Keywords
             { DbConnectionStringKeywords.Dsn, Keywords.Dsn }
         };
 
-        private string[] _knownKeywords;
+        private string[]? _knownKeywords;
 
         private string _dsn = DbConnectionStringDefaults.Dsn;
         private string _driver = DbConnectionStringDefaults.Driver;
 
-        public OdbcConnectionStringBuilder() : this((string)null)
+        public OdbcConnectionStringBuilder() : this(null)
         {
         }
 
-        public OdbcConnectionStringBuilder(string connectionString) : base(true)
+        public OdbcConnectionStringBuilder(string? connectionString) : base(true)
         {
             if (!string.IsNullOrEmpty(connectionString))
             {
@@ -47,6 +48,7 @@ public OdbcConnectionStringBuilder(string connectionString) : base(true)
             }
         }
 
+        [AllowNull]
         public override object this[string keyword]
         {
             get
@@ -119,7 +121,7 @@ public override ICollection Keys
         {
             get
             {
-                string[] knownKeywords = _knownKeywords;
+                string[]? knownKeywords = _knownKeywords;
                 if (null == knownKeywords)
                 {
                     knownKeywords = s_validKeywords;
@@ -245,7 +247,7 @@ private void SetValue(string keyword, string value)
             base[keyword] = value;
         }
 
-        public override bool TryGetValue(string keyword, out object value)
+        public override bool TryGetValue(string keyword, [NotNullWhen(true)] out object? value)
         {
             ADP.CheckArgumentNull(keyword, nameof(keyword));
             Keywords index;
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcDataAdapter.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcDataAdapter.cs
index 2235d13909b1a2..77630d1f286938 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcDataAdapter.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcDataAdapter.cs
@@ -1,33 +1,35 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.ComponentModel;
 using System.Data.Common;
 
 namespace System.Data.Odbc
 {
+    [Designer("Microsoft.VSDesigner.Data.VS.OdbcDataAdapterDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public sealed class OdbcDataAdapter : DbDataAdapter, IDbDataAdapter, ICloneable
     {
         private static readonly object s_eventRowUpdated = new object();
         private static readonly object s_eventRowUpdating = new object();
 
-        private OdbcCommand _deleteCommand, _insertCommand, _selectCommand, _updateCommand;
+        private OdbcCommand? _deleteCommand, _insertCommand, _selectCommand, _updateCommand;
 
         public OdbcDataAdapter() : base()
         {
             GC.SuppressFinalize(this);
         }
 
-        public OdbcDataAdapter(OdbcCommand selectCommand) : this()
+        public OdbcDataAdapter(OdbcCommand? selectCommand) : this()
         {
             SelectCommand = selectCommand;
         }
 
-        public OdbcDataAdapter(string selectCommandText, OdbcConnection selectConnection) : this()
+        public OdbcDataAdapter(string? selectCommandText, OdbcConnection? selectConnection) : this()
         {
             SelectCommand = new OdbcCommand(selectCommandText, selectConnection);
         }
 
-        public OdbcDataAdapter(string selectCommandText, string selectConnectionString) : this()
+        public OdbcDataAdapter(string? selectCommandText, string? selectConnectionString) : this()
         {
             OdbcConnection connection = new OdbcConnection(selectConnectionString);
             SelectCommand = new OdbcCommand(selectCommandText, connection);
@@ -38,55 +40,55 @@ private OdbcDataAdapter(OdbcDataAdapter from) : base(from)
             GC.SuppressFinalize(this);
         }
 
-        public new OdbcCommand DeleteCommand
+        public new OdbcCommand? DeleteCommand
         {
             get { return _deleteCommand; }
             set { _deleteCommand = value; }
         }
 
-        IDbCommand IDbDataAdapter.DeleteCommand
+        IDbCommand? IDbDataAdapter.DeleteCommand
         {
             get { return _deleteCommand; }
-            set { _deleteCommand = (OdbcCommand)value; }
+            set { _deleteCommand = (OdbcCommand?)value; }
         }
 
-        public new OdbcCommand InsertCommand
+        public new OdbcCommand? InsertCommand
         {
             get { return _insertCommand; }
             set { _insertCommand = value; }
         }
 
-        IDbCommand IDbDataAdapter.InsertCommand
+        IDbCommand? IDbDataAdapter.InsertCommand
         {
             get { return _insertCommand; }
-            set { _insertCommand = (OdbcCommand)value; }
+            set { _insertCommand = (OdbcCommand?)value; }
         }
 
-        public new OdbcCommand SelectCommand
+        public new OdbcCommand? SelectCommand
         {
             get { return _selectCommand; }
             set { _selectCommand = value; }
         }
 
-        IDbCommand IDbDataAdapter.SelectCommand
+        IDbCommand? IDbDataAdapter.SelectCommand
         {
             get { return _selectCommand; }
-            set { _selectCommand = (OdbcCommand)value; }
+            set { _selectCommand = (OdbcCommand?)value; }
         }
 
-        public new OdbcCommand UpdateCommand
+        public new OdbcCommand? UpdateCommand
         {
             get { return _updateCommand; }
             set { _updateCommand = value; }
         }
 
-        IDbCommand IDbDataAdapter.UpdateCommand
+        IDbCommand? IDbDataAdapter.UpdateCommand
         {
             get { return _updateCommand; }
-            set { _updateCommand = (OdbcCommand)value; }
+            set { _updateCommand = (OdbcCommand?)value; }
         }
 
-        public event OdbcRowUpdatedEventHandler RowUpdated
+        public event OdbcRowUpdatedEventHandler? RowUpdated
         {
             add
             {
@@ -98,18 +100,18 @@ public event OdbcRowUpdatedEventHandler RowUpdated
             }
         }
 
-        public event OdbcRowUpdatingEventHandler RowUpdating
+        public event OdbcRowUpdatingEventHandler? RowUpdating
         {
             add
             {
-                OdbcRowUpdatingEventHandler handler = (OdbcRowUpdatingEventHandler)Events[s_eventRowUpdating];
+                OdbcRowUpdatingEventHandler? handler = (OdbcRowUpdatingEventHandler?)Events[s_eventRowUpdating];
 
                 // MDAC 58177, 64513
                 // prevent someone from registering two different command builders on the adapter by
                 // silently removing the old one
-                if ((null != handler) && (value.Target is OdbcCommandBuilder))
+                if ((null != handler) && (value!.Target is OdbcCommandBuilder))
                 {
-                    OdbcRowUpdatingEventHandler d = (OdbcRowUpdatingEventHandler)ADP.FindBuilder(handler);
+                    OdbcRowUpdatingEventHandler? d = (OdbcRowUpdatingEventHandler?)ADP.FindBuilder(handler);
                     if (null != d)
                     {
                         Events.RemoveHandler(s_eventRowUpdating, d);
@@ -129,19 +131,19 @@ object ICloneable.Clone()
             return new OdbcDataAdapter(this);
         }
 
-        protected override RowUpdatedEventArgs CreateRowUpdatedEvent(DataRow dataRow, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        protected override RowUpdatedEventArgs CreateRowUpdatedEvent(DataRow dataRow, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         {
             return new OdbcRowUpdatedEventArgs(dataRow, command, statementType, tableMapping);
         }
 
-        protected override RowUpdatingEventArgs CreateRowUpdatingEvent(DataRow dataRow, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        protected override RowUpdatingEventArgs CreateRowUpdatingEvent(DataRow dataRow, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         {
             return new OdbcRowUpdatingEventArgs(dataRow, command, statementType, tableMapping);
         }
 
         protected override void OnRowUpdated(RowUpdatedEventArgs value)
         {
-            OdbcRowUpdatedEventHandler handler = (OdbcRowUpdatedEventHandler)Events[s_eventRowUpdated];
+            OdbcRowUpdatedEventHandler? handler = (OdbcRowUpdatedEventHandler?)Events[s_eventRowUpdated];
             if ((null != handler) && (value is OdbcRowUpdatedEventArgs))
             {
                 handler(this, (OdbcRowUpdatedEventArgs)value);
@@ -151,7 +153,7 @@ protected override void OnRowUpdated(RowUpdatedEventArgs value)
 
         protected override void OnRowUpdating(RowUpdatingEventArgs value)
         {
-            OdbcRowUpdatingEventHandler handler = (OdbcRowUpdatingEventHandler)Events[s_eventRowUpdating];
+            OdbcRowUpdatingEventHandler? handler = (OdbcRowUpdatingEventHandler?)Events[s_eventRowUpdating];
             if ((null != handler) && (value is OdbcRowUpdatingEventArgs))
             {
                 handler(this, (OdbcRowUpdatingEventArgs)value);
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcDataReader.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcDataReader.cs
index d66f5f28a6a068..87c0e9238ab25b 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcDataReader.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcDataReader.cs
@@ -15,12 +15,12 @@ namespace System.Data.Odbc
 {
     public sealed class OdbcDataReader : DbDataReader
     {
-        private OdbcCommand _command;
+        private OdbcCommand? _command;
 
         private int _recordAffected = -1;
-        private FieldNameLookup _fieldNameLookup;
+        private FieldNameLookup? _fieldNameLookup;
 
-        private DbCache _dataCache;
+        private DbCache? _dataCache;
         private enum HasRowsStatus
         {
             DontKnow = 0,
@@ -51,10 +51,10 @@ private enum HasRowsStatus
         // the DataReader must not free the statement handle. this is done by the command
         //
 
-        private MetaData[] _metadata;
-        private DataTable _schemaTable; // MDAC 68336
+        private MetaData[]? _metadata;
+        private DataTable? _schemaTable; // MDAC 68336
         private readonly string _cmdText;    // get a copy in case the command text on the command is changed ...
-        private CMDWrapper _cmdWrapper;
+        private CMDWrapper? _cmdWrapper;
 
         internal OdbcDataReader(OdbcCommand command, CMDWrapper cmdWrapper, CommandBehavior commandbehavior)
         {
@@ -69,7 +69,7 @@ private CNativeBuffer Buffer
         {
             get
             {
-                CNativeBuffer value = _cmdWrapper._dataReaderBuf;
+                CNativeBuffer? value = _cmdWrapper!._dataReaderBuf;
                 if (null == value)
                 {
                     Debug.Fail("object is disposed");
@@ -79,7 +79,7 @@ private CNativeBuffer Buffer
             }
         }
 
-        private OdbcConnection Connection
+        private OdbcConnection? Connection
         {
             get
             {
@@ -94,7 +94,7 @@ private OdbcConnection Connection
             }
         }
 
-        internal OdbcCommand Command
+        internal OdbcCommand? Command
         {
             get
             {
@@ -110,13 +110,13 @@ private OdbcStatementHandle StatementHandle
         {
             get
             {
-                return _cmdWrapper.StatementHandle;
+                return _cmdWrapper!.StatementHandle!;
             }
         }
 
         private OdbcStatementHandle KeyInfoStatementHandle
         {
-            get { return _cmdWrapper.KeyInfoStatement; }
+            get { return _cmdWrapper!.KeyInfoStatement!; }
         }
 
         internal bool IsBehavior(CommandBehavior behavior)
@@ -178,7 +178,7 @@ public override int FieldCount
                     ODBC32.RetCode retcode = this.FieldCountNoThrow(out cColsAffected);
                     if (retcode != ODBC32.RetCode.SUCCESS)
                     {
-                        Connection.HandleError(StatementHandle, retcode);
+                        Connection!.HandleError(StatementHandle, retcode);
                     }
                 }
                 return ((null != _dataCache) ? _dataCache._count : 0);
@@ -224,7 +224,7 @@ internal ODBC32.RetCode FieldCountNoThrow(out short cColsAffected)
                 {
                     // we need to search for the first hidden column
                     //
-                    if (!Connection.ProviderInfo.NoSqlSoptSSNoBrowseTable && !Connection.ProviderInfo.NoSqlSoptSSHiddenColumns)
+                    if (!Connection!.ProviderInfo.NoSqlSoptSSNoBrowseTable && !Connection.ProviderInfo.NoSqlSoptSSHiddenColumns)
                     {
                         for (int i = 0; i < cColsAffected; i++)
                         {
@@ -317,9 +317,9 @@ public override void Close()
 
         private void Close(bool disposing)
         {
-            Exception error = null;
+            Exception? error = null;
 
-            CMDWrapper wrapper = _cmdWrapper;
+            CMDWrapper? wrapper = _cmdWrapper;
             if (null != wrapper && wrapper.StatementHandle != null)
             {
                 // disposing
@@ -339,7 +339,7 @@ private void Close(bool disposing)
                         {
                             // Output Parameters are not guareenteed to be returned until all the data
                             // from any restssets are read, so we do this after the above NextResult call(s)
-                            _command.Parameters.GetOutputValues(_cmdWrapper);
+                            _command.Parameters.GetOutputValues(_cmdWrapper!);
                         }
                         wrapper.FreeStatementHandle(ODBC32.STMT.CLOSE);
                         _command.CloseFromDataReader();
@@ -407,7 +407,10 @@ public override string GetDataTypeName(int i)
                 {
                     info._typename = GetColAttributeStr(i, ODBC32.SQL_DESC.TYPE_NAME, ODBC32.SQL_COLUMN.TYPE_NAME, ODBC32.HANDLER.THROW);
                 }
+// TODO-NULLABLE: Behavior change probably needed here - when there's no data type, we mostly probably need to throw instead of returning null.
+#nullable disable
                 return info._typename;
+#nullable enable
             }
             throw ADP.DataReaderNoData();
         }
@@ -545,7 +548,7 @@ internal object GetValue(int i, TypeMap typemap)
                     //will work), and then query for a speicial SQLServer specific attribute.
                     if (_isRead)
                     {
-                        if (_dataCache.AccessIndex(i) == null)
+                        if (_dataCache!.AccessIndex(i) == null)
                         {
                             int dummy;
                             bool isNotDbNull = QueryFieldInfo(i, ODBC32.SQL_C.BINARY, out dummy);
@@ -557,7 +560,7 @@ internal object GetValue(int i, TypeMap typemap)
                                 return GetValue(i, TypeMap.FromSqlType(subtype));
                             }
                         }
-                        return _dataCache[i];
+                        return _dataCache[i]!;
                     }
                     throw ADP.DataReaderNoData();
 
@@ -573,11 +576,11 @@ public override object GetValue(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     _dataCache[i] = GetValue(i, GetSqlType(i));
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -601,7 +604,7 @@ private TypeMap GetSqlType(int i)
             //Note: Types are always returned (advertised) from ODBC as SQL_TYPEs, and
             //are always bound by the user as SQL_C types.
             TypeMap typeMap;
-            DbSchemaInfo info = _dataCache.GetSchema(i);
+            DbSchemaInfo info = _dataCache!.GetSchema(i);
             if (!info._dbtype.HasValue)
             {
                 info._dbtype = unchecked((ODBC32.SQL_TYPE)(int)GetColAttribute(i, ODBC32.SQL_DESC.CONCISE_TYPE, ODBC32.SQL_COLUMN.TYPE, ODBC32.HANDLER.THROW));
@@ -617,14 +620,14 @@ private TypeMap GetSqlType(int i)
             {
                 typeMap = TypeMap.FromSqlType(info._dbtype.Value);
             }
-            Connection.SetSupportedType(info._dbtype.Value);
+            Connection!.SetSupportedType(info._dbtype.Value);
             return typeMap;
         }
 
         public override bool IsDBNull(int i)
         {
-            //  Note: ODBC SQLGetData doesn't allow retriving the column value twice.
-            //  The reational is that for ForwardOnly access (the default and LCD of drivers)
+            //  Note: ODBC SQLGetData doesn't allow retrieving the column value twice.
+            //  The rationale is that for ForwardOnly access (the default and LCD of drivers)
             //  we cannot obtain the data more than once, and even GetData(0) (to determine is-null)
             //  still obtains data for fixed length types.
 
@@ -650,7 +653,7 @@ public override bool IsDBNull(int i)
             // But, to minimize regressions, we will continue caching the fixed-size values (case 2), even with SequentialAccess
             // only in case of SequentialAccess with variable length data types (case 3), we will use GetData with zero length.
 
-            object cachedObj = _dataCache[i];
+            object? cachedObj = _dataCache![i];
             if (cachedObj != null)
             {
                 // case 4 - if cached object was created before, use it
@@ -686,14 +689,14 @@ private object internalGetByte(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.UTINYINT))
                     {
                         _dataCache[i] = Buffer.ReadByte(0);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -706,14 +709,14 @@ private object internalGetChar(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.WCHAR))
                     {
                         _dataCache[i] = Buffer.ReadChar(0);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -726,14 +729,14 @@ private object internalGetInt16(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.SSHORT))
                     {
                         _dataCache[i] = Buffer.ReadInt16(0);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -746,14 +749,14 @@ private object internalGetInt32(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.SLONG))
                     {
                         _dataCache[i] = Buffer.ReadInt32(0);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -773,7 +776,7 @@ private object internalGetInt64(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.WCHAR))
                     {
@@ -781,7 +784,7 @@ private object internalGetInt64(int i)
                         _dataCache[i] = long.Parse(value, CultureInfo.InvariantCulture);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -794,14 +797,14 @@ private object internalGetBoolean(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.BIT))
                     {
                         _dataCache[i] = Buffer.MarshalToManaged(0, ODBC32.SQL_C.BIT, -1);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -814,14 +817,14 @@ private object internalGetFloat(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.REAL))
                     {
                         _dataCache[i] = Buffer.ReadSingle(0);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -835,14 +838,14 @@ private object internalGetDate(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.TYPE_DATE))
                     {
                         _dataCache[i] = Buffer.MarshalToManaged(0, ODBC32.SQL_C.TYPE_DATE, -1);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -856,14 +859,14 @@ private object internalGetDateTime(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.TYPE_TIMESTAMP))
                     {
                         _dataCache[i] = Buffer.MarshalToManaged(0, ODBC32.SQL_C.TYPE_TIMESTAMP, -1);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -884,11 +887,11 @@ private object internalGetDecimal(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.WCHAR))
                     {
-                        string s = null;
+                        string? s = null;
                         try
                         {
                             s = (string)Buffer.MarshalToManaged(0, ODBC32.SQL_C.WCHAR, ODBC32.SQL_NTS);
@@ -901,7 +904,7 @@ private object internalGetDecimal(int i)
                         }
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -914,14 +917,14 @@ private object internalGetDouble(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.DOUBLE))
                     {
                         _dataCache[i] = Buffer.ReadDouble(0);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -935,14 +938,14 @@ private object internalGetGuid(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.GUID))
                     {
                         _dataCache[i] = Buffer.ReadGuid(0);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -956,7 +959,7 @@ private object internalGetString(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     // Obtain _ALL_ the characters
                     // Note: We can bind directly as WCHAR in ODBC and the DM will convert to and
@@ -1049,7 +1052,7 @@ private object internalGetString(int i)
                         _dataCache[i] = builder.ToString();
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -1063,14 +1066,14 @@ private object internalGetTime(int i)
         {
             if (_isRead)
             {
-                if (_dataCache.AccessIndex(i) == null)
+                if (_dataCache!.AccessIndex(i) == null)
                 {
                     if (GetData(i, ODBC32.SQL_C.TYPE_TIME))
                     {
                         _dataCache[i] = Buffer.MarshalToManaged(0, ODBC32.SQL_C.TYPE_TIME, -1);
                     }
                 }
-                return _dataCache[i];
+                return _dataCache[i]!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -1087,17 +1090,17 @@ private void SetCurrentRowColumnInfo(int row, int column)
             }
         }
 
-        public override long GetBytes(int i, long dataIndex, byte[] buffer, int bufferIndex, int length)
+        public override long GetBytes(int i, long dataIndex, byte[]? buffer, int bufferIndex, int length)
         {
             return GetBytesOrChars(i, dataIndex, buffer, false /* bytes buffer */, bufferIndex, length);
         }
-        public override long GetChars(int i, long dataIndex, char[] buffer, int bufferIndex, int length)
+        public override long GetChars(int i, long dataIndex, char[]? buffer, int bufferIndex, int length)
         {
             return GetBytesOrChars(i, dataIndex, buffer, true /* chars buffer */, bufferIndex, length);
         }
 
         // unify the implementation of GetChars and GetBytes to prevent code duplicate
-        private long GetBytesOrChars(int i, long dataIndex, Array buffer, bool isCharsBuffer, int bufferIndex, int length)
+        private long GetBytesOrChars(int i, long dataIndex, Array? buffer, bool isCharsBuffer, int bufferIndex, int length)
         {
             if (IsClosed)
             {
@@ -1133,13 +1136,13 @@ private long GetBytesOrChars(int i, long dataIndex, Array buffer, bool isCharsBu
             //                       use the cache - preserve the original behavior to minimize regression risk
             // 4. sequential access, no cache: (fixed now) user reads the bytes/chars in sequential order (no cache)
 
-            object cachedObj = null;                 // The cached object (if there is one)
+            object? cachedObj = null;                 // The cached object (if there is one)
 
             // Get cached object, ensure the correct type using explicit cast, to preserve same behavior as before
             if (isCharsBuffer)
-                cachedObj = (string)_dataCache[i];
+                cachedObj = (string?)_dataCache![i];
             else
-                cachedObj = (byte[])_dataCache[i];
+                cachedObj = (byte[]?)_dataCache![i];
 
             bool isRandomAccess = !IsCommandBehavior(CommandBehavior.SequentialAccess);
 
@@ -1354,7 +1357,7 @@ private long GetBytesOrChars(int i, long dataIndex, Array buffer, bool isCharsBu
 
         // fill the user's buffer (char[] or byte[], depending on isCharsBuffer)
         // if buffer is null, just skip the bytesOrCharsLength bytes or chars
-        private int readBytesOrCharsSequentialAccess(int i, Array buffer, bool isCharsBuffer, int bufferIndex, long bytesOrCharsLength)
+        private int readBytesOrCharsSequentialAccess(int i, Array? buffer, bool isCharsBuffer, int bufferIndex, long bytesOrCharsLength)
         {
             Debug.Assert(bufferIndex >= 0, "Negative buffer index");
             Debug.Assert(bytesOrCharsLength >= 0, "Negative number of bytes or chars to read");
@@ -1477,7 +1480,7 @@ private int readBytesOrCharsSequentialAccess(int i, Array buffer, bool isCharsBu
 
         private object internalGetBytes(int i)
         {
-            if (_dataCache.AccessIndex(i) == null)
+            if (_dataCache!.AccessIndex(i) == null)
             {
                 // Obtain _ALL_ the bytes...
                 // The first time GetData returns the true length (so we have to min it).
@@ -1536,7 +1539,7 @@ private object internalGetBytes(int i)
                     _dataCache[i] = rgBytes;
                 }
             }
-            return _dataCache[i];
+            return _dataCache[i]!;
         }
 
         // GetColAttribute
@@ -1555,7 +1558,7 @@ private SQLLEN GetColAttribute(int iColumn, ODBC32.SQL_DESC v3FieldId, ODBC32.SQ
             ODBC32.RetCode retcode;
 
             // protect against dead connection, dead or canceling command.
-            if ((Connection == null) || _cmdWrapper.Canceling)
+            if ((Connection == null) || _cmdWrapper!.Canceling)
             {
                 return -1;
             }
@@ -1578,7 +1581,7 @@ private SQLLEN GetColAttribute(int iColumn, ODBC32.SQL_DESC v3FieldId, ODBC32.SQ
             {
                 if (retcode == ODBC32.RetCode.ERROR)
                 {
-                    if ("HY091" == Command.GetDiagSqlState())
+                    if ("HY091" == Command!.GetDiagSqlState())
                     {
                         Connection.FlagUnsupportedColAttr(v3FieldId, v2FieldId);
                     }
@@ -1601,7 +1604,7 @@ private SQLLEN GetColAttribute(int iColumn, ODBC32.SQL_DESC v3FieldId, ODBC32.SQ
         // returns the stringvalue of the FieldIdentifier field of the column
         // or null if the string returned was empty or if the FieldIdentifier wasn't supported by the driver
         //
-        private string GetColAttributeStr(int i, ODBC32.SQL_DESC v3FieldId, ODBC32.SQL_COLUMN v2FieldId, ODBC32.HANDLER handler)
+        private string? GetColAttributeStr(int i, ODBC32.SQL_DESC v3FieldId, ODBC32.SQL_COLUMN v2FieldId, ODBC32.HANDLER handler)
         {
             ODBC32.RetCode retcode;
             short cchNameLength = 0;
@@ -1609,10 +1612,10 @@ private string GetColAttributeStr(int i, ODBC32.SQL_DESC v3FieldId, ODBC32.SQL_C
             CNativeBuffer buffer = Buffer;
             buffer.WriteInt16(0, 0);
 
-            OdbcStatementHandle stmt = StatementHandle;
+            OdbcStatementHandle? stmt = StatementHandle;
 
             // protect against dead connection
-            if (Connection == null || _cmdWrapper.Canceling || stmt == null)
+            if (Connection == null || _cmdWrapper!.Canceling || stmt == null)
             {
                 return "";
             }
@@ -1633,7 +1636,7 @@ private string GetColAttributeStr(int i, ODBC32.SQL_DESC v3FieldId, ODBC32.SQL_C
             {
                 if (retcode == ODBC32.RetCode.ERROR)
                 {
-                    if ("HY091" == Command.GetDiagSqlState())
+                    if ("HY091" == Command!.GetDiagSqlState())
                     {
                         Connection.FlagUnsupportedColAttr(v3FieldId, v2FieldId);
                     }
@@ -1651,12 +1654,12 @@ private string GetColAttributeStr(int i, ODBC32.SQL_DESC v3FieldId, ODBC32.SQL_C
         // todo: Another 3.0 only attribute that is guaranteed to fail on V2 driver.
         // need to special case this for V2 drivers.
         //
-        private string GetDescFieldStr(int i, ODBC32.SQL_DESC attribute, ODBC32.HANDLER handler)
+        private string? GetDescFieldStr(int i, ODBC32.SQL_DESC attribute, ODBC32.HANDLER handler)
         {
             int numericAttribute = 0;
 
             // protect against dead connection, dead or canceling command.
-            if ((Connection == null) || _cmdWrapper.Canceling)
+            if ((Connection == null) || _cmdWrapper!.Canceling)
             {
                 return "";
             }
@@ -1684,7 +1687,7 @@ private string GetDescFieldStr(int i, ODBC32.SQL_DESC attribute, ODBC32.HANDLER
                 {
                     if (retcode == ODBC32.RetCode.ERROR)
                     {
-                        if ("HY091" == Command.GetDiagSqlState())
+                        if ("HY091" == Command!.GetDiagSqlState())
                         {
                             Connection.FlagUnsupportedColAttr(attribute, (ODBC32.SQL_COLUMN)0);
                         }
@@ -1786,7 +1789,7 @@ private bool GetData(int i, ODBC32.SQL_C sqlctype, int cb, out int cbLengthOrInd
                     // Thus, ignore NO_DATA for variable length data, but raise exception for fixed-size types
                     if (sqlctype != ODBC32.SQL_C.WCHAR && sqlctype != ODBC32.SQL_C.BINARY)
                     {
-                        Connection.HandleError(StatementHandle, retcode);
+                        Connection!.HandleError(StatementHandle, retcode);
                     }
 
                     if (cbActual == (IntPtr)ODBC32.SQL_NO_TOTAL)
@@ -1797,7 +1800,7 @@ private bool GetData(int i, ODBC32.SQL_C sqlctype, int cb, out int cbLengthOrInd
                     break;
 
                 default:
-                    Connection.HandleError(StatementHandle, retcode);
+                    Connection!.HandleError(StatementHandle, retcode);
                     break;
             }
 
@@ -1810,7 +1813,7 @@ private bool GetData(int i, ODBC32.SQL_C sqlctype, int cb, out int cbLengthOrInd
                 // Store the DBNull value in cache. Note that if we need to do it, because second call into the SQLGetData returns NO_DATA, which means
                 // we already consumed the value (see above) and the NULL information is lost. By storing the null in cache, we avoid second call into the driver
                 // for the same row/column.
-                _dataCache[i] = DBNull.Value;
+                _dataCache![i] = DBNull.Value;
                 // the indicator is never -1 (and it should not actually be used if the data is DBNull)
                 cbLengthOrIndicator = 0;
                 return false;
@@ -1864,7 +1867,7 @@ public override bool Read()
             switch (retcode)
             {
                 case ODBC32.RetCode.SUCCESS_WITH_INFO:
-                    Connection.HandleErrorNoThrow(StatementHandle, retcode);
+                    Connection!.HandleErrorNoThrow(StatementHandle, retcode);
                     _hasRows = HasRowsStatus.HasRows;
                     _isRead = true;
                     break;
@@ -1880,11 +1883,11 @@ public override bool Read()
                     }
                     break;
                 default:
-                    Connection.HandleError(StatementHandle, retcode);
+                    Connection!.HandleError(StatementHandle, retcode);
                     break;
             }
             //Null out previous cached row values.
-            _dataCache.FlushValues();
+            _dataCache!.FlushValues();
 
             // if CommandBehavior == SingleRow we set _noMoreResults to true so that following reads will fail
             if (IsCommandBehavior(CommandBehavior.SingleRow))
@@ -1961,7 +1964,7 @@ private bool NextResult(bool disposing, bool allresults)
             _schemaTable = null;
 
             int loop = 0; // infinite loop protection, max out after 2000 consecutive failed results
-            OdbcErrorCollection errors = null; // SQLBU 342112
+            OdbcErrorCollection? errors = null; // SQLBU 342112
             do
             {
                 _isValidResult = false;
@@ -1971,7 +1974,7 @@ private bool NextResult(bool disposing, bool allresults)
 
                 if (retcode == ODBC32.RetCode.SUCCESS_WITH_INFO)
                 {
-                    Connection.HandleErrorNoThrow(StatementHandle, retcode);
+                    Connection!.HandleErrorNoThrow(StatementHandle, retcode);
                 }
                 else if (!disposing && (retcode != ODBC32.RetCode.NO_DATA) && (ODBC32.RetCode.SUCCESS != retcode))
                 {
@@ -2010,7 +2013,7 @@ private bool NextResult(bool disposing, bool allresults)
             if (null != errors)
             {
                 Debug.Assert(!disposing, "errors while disposing");
-                errors.SetSource(Connection.Driver);
+                errors.SetSource(Connection!.Driver);
                 OdbcException exception = OdbcException.CreateException(errors, firstRetCode);
                 Connection.ConnectionIsAlive(exception);
                 throw exception;
@@ -2022,7 +2025,7 @@ private void BuildMetaDataInfo()
         {
             int count = FieldCount;
             MetaData[] metaInfos = new MetaData[count];
-            List<string> qrytables;
+            List<string>? qrytables;
             bool needkeyinfo = IsCommandBehavior(CommandBehavior.KeyInfo);
             bool isKeyColumn;
             bool isHidden;
@@ -2094,7 +2097,7 @@ private void BuildMetaDataInfo()
                     // Note: Following two attributes are SQL Server specific (hence _SS in the name)
 
                     // SSS_WARNINGS_OFF
-                    if (!Connection.ProviderInfo.NoSqlCASSColumnKey)
+                    if (!Connection!.ProviderInfo.NoSqlCASSColumnKey)
                     {
                         isKeyColumn = GetColAttribute(i, (ODBC32.SQL_DESC)ODBC32.SQL_CA_SS.COLUMN_KEY, (ODBC32.SQL_COLUMN)(-1), ODBC32.HANDLER.IGNORE) == 1;
                         if (isKeyColumn)
@@ -2113,22 +2116,22 @@ private void BuildMetaDataInfo()
 
                     if (Connection.IsV3Driver)
                     {
-                        if ((metaInfos[i].baseTableName == null) || (metaInfos[i].baseTableName.Length == 0))
+                        if (string.IsNullOrEmpty(metaInfos[i].baseTableName))
                         {
                             // Driver didn't return the necessary information from GetColAttributeStr.
                             // Try GetDescField()
                             metaInfos[i].baseTableName = GetDescFieldStr(i, ODBC32.SQL_DESC.BASE_TABLE_NAME, ODBC32.HANDLER.IGNORE);
                         }
-                        if ((metaInfos[i].baseColumnName == null) || (metaInfos[i].baseColumnName.Length == 0))
+                        if (string.IsNullOrEmpty(metaInfos[i].baseColumnName))
                         {
                             // Driver didn't return the necessary information from GetColAttributeStr.
                             // Try GetDescField()
                             metaInfos[i].baseColumnName = GetDescFieldStr(i, ODBC32.SQL_DESC.BASE_COLUMN_NAME, ODBC32.HANDLER.IGNORE);
                         }
                     }
-                    if ((metaInfos[i].baseTableName != null) && !(qrytables.Contains(metaInfos[i].baseTableName)))
+                    if ((metaInfos[i].baseTableName is string baseTableName) && !(qrytables!.Contains(baseTableName)))
                     {
-                        qrytables.Add(metaInfos[i].baseTableName);
+                        qrytables.Add(baseTableName);
                     }
                 }
 
@@ -2143,7 +2146,7 @@ private void BuildMetaDataInfo()
             // now loop over the hidden columns (if any)
 
             // SSS_WARNINGS_OFF
-            if (!Connection.ProviderInfo.NoSqlCASSColumnKey)
+            if (!Connection!.ProviderInfo.NoSqlCASSColumnKey)
             {
                 for (int i = count; i < count + _hiddenColumns; i++)
                 {
@@ -2250,7 +2253,10 @@ public override DataTable GetSchemaTable()
             }
             if (_noMoreResults)
             {
+// TODO-NULLABLE: Behavior change (https://github.com/dotnet/runtime/issues/509)
+#nullable disable
                 return null;                                            // no more results
+#nullable enable
             }
             if (null != _schemaTable)
             {
@@ -2269,24 +2275,24 @@ public override DataTable GetSchemaTable()
                 BuildMetaDataInfo();
             }
 
-            DataColumn columnName = schematable.Columns["ColumnName"];
-            DataColumn columnOrdinal = schematable.Columns["ColumnOrdinal"];
-            DataColumn columnSize = schematable.Columns["ColumnSize"];
-            DataColumn numericPrecision = schematable.Columns["NumericPrecision"];
-            DataColumn numericScale = schematable.Columns["NumericScale"];
-            DataColumn dataType = schematable.Columns["DataType"];
-            DataColumn providerType = schematable.Columns["ProviderType"];
-            DataColumn isLong = schematable.Columns["IsLong"];
-            DataColumn allowDBNull = schematable.Columns["AllowDBNull"];
-            DataColumn isReadOnly = schematable.Columns["IsReadOnly"];
-            DataColumn isRowVersion = schematable.Columns["IsRowVersion"];
-            DataColumn isUnique = schematable.Columns["IsUnique"];
-            DataColumn isKey = schematable.Columns["IsKey"];
-            DataColumn isAutoIncrement = schematable.Columns["IsAutoIncrement"];
-            DataColumn baseSchemaName = schematable.Columns["BaseSchemaName"];
-            DataColumn baseCatalogName = schematable.Columns["BaseCatalogName"];
-            DataColumn baseTableName = schematable.Columns["BaseTableName"];
-            DataColumn baseColumnName = schematable.Columns["BaseColumnName"];
+            DataColumn columnName = schematable.Columns["ColumnName"]!;
+            DataColumn columnOrdinal = schematable.Columns["ColumnOrdinal"]!;
+            DataColumn columnSize = schematable.Columns["ColumnSize"]!;
+            DataColumn numericPrecision = schematable.Columns["NumericPrecision"]!;
+            DataColumn numericScale = schematable.Columns["NumericScale"]!;
+            DataColumn dataType = schematable.Columns["DataType"]!;
+            DataColumn providerType = schematable.Columns["ProviderType"]!;
+            DataColumn isLong = schematable.Columns["IsLong"]!;
+            DataColumn allowDBNull = schematable.Columns["AllowDBNull"]!;
+            DataColumn isReadOnly = schematable.Columns["IsReadOnly"]!;
+            DataColumn isRowVersion = schematable.Columns["IsRowVersion"]!;
+            DataColumn isUnique = schematable.Columns["IsUnique"]!;
+            DataColumn isKey = schematable.Columns["IsKey"]!;
+            DataColumn isAutoIncrement = schematable.Columns["IsAutoIncrement"]!;
+            DataColumn baseSchemaName = schematable.Columns["BaseSchemaName"]!;
+            DataColumn baseCatalogName = schematable.Columns["BaseCatalogName"]!;
+            DataColumn baseTableName = schematable.Columns["BaseTableName"]!;
+            DataColumn baseColumnName = schematable.Columns["BaseColumnName"]!;
 
 
             //Populate the rows (1 row for each column)
@@ -2297,7 +2303,7 @@ public override DataTable GetSchemaTable()
 
                 row[columnName] = GetName(i);        //ColumnName
                 row[columnOrdinal] = i;                 //ColumnOrdinal
-                row[columnSize] = unchecked((int)Math.Min(Math.Max(int.MinValue, _metadata[i].size.ToInt64()), int.MaxValue));
+                row[columnSize] = unchecked((int)Math.Min(Math.Max(int.MinValue, _metadata![i].size.ToInt64()), int.MaxValue));
                 row[numericPrecision] = (short)_metadata[i].precision;
                 row[numericScale] = (short)_metadata[i].scale;
                 row[dataType] = _metadata[i].typemap._type;          //DataType
@@ -2328,6 +2334,8 @@ public override DataTable GetSchemaTable()
 
         internal int RetrieveKeyInfo(bool needkeyinfo, QualifiedTableName qualifiedTableName, bool quoted)
         {
+            Debug.Assert(_metadata != null);
+
             ODBC32.RetCode retcode;
             string columnname;
             int ordinal;
@@ -2350,13 +2358,13 @@ internal int RetrieveKeyInfo(bool needkeyinfo, QualifiedTableName qualifiedTable
 
                 if (needkeyinfo)
                 {
-                    if (!Connection.ProviderInfo.NoSqlPrimaryKeys)
+                    if (!Connection!.ProviderInfo.NoSqlPrimaryKeys)
                     {
                         // Get the primary keys
                         retcode = KeyInfoStatementHandle.PrimaryKeys(
                                     qualifiedTableName.Catalog,
                                     qualifiedTableName.Schema,
-                                    qualifiedTableName.GetTable(quoted));
+                                    qualifiedTableName.GetTable(quoted)!);
 
                         if ((retcode == ODBC32.RetCode.SUCCESS) || (retcode == ODBC32.RetCode.SUCCESS_WITH_INFO))
                         {
@@ -2419,7 +2427,7 @@ internal int RetrieveKeyInfo(bool needkeyinfo, QualifiedTableName qualifiedTable
                         }
                         else
                         {
-                            if ("IM001" == Command.GetDiagSqlState())
+                            if ("IM001" == Command!.GetDiagSqlState())
                             {
                                 Connection.ProviderInfo.NoSqlPrimaryKeys = true;
                             }
@@ -2436,7 +2444,7 @@ internal int RetrieveKeyInfo(bool needkeyinfo, QualifiedTableName qualifiedTable
                 }
 
                 // Get the special columns for version
-                retcode = KeyInfoStatementHandle.SpecialColumns(qualifiedTableName.GetTable(quoted));
+                retcode = KeyInfoStatementHandle.SpecialColumns(qualifiedTableName.GetTable(quoted)!);
 
                 if ((retcode == ODBC32.RetCode.SUCCESS) || (retcode == ODBC32.RetCode.SUCCESS_WITH_INFO))
                 {
@@ -2496,6 +2504,8 @@ internal int RetrieveKeyInfo(bool needkeyinfo, QualifiedTableName qualifiedTable
         // Uses SQLStatistics to retrieve key information for a table
         private int RetrieveKeyInfoFromStatistics(QualifiedTableName qualifiedTableName, bool quoted)
         {
+            Debug.Assert(_metadata != null);
+
             ODBC32.RetCode retcode;
             string columnname = string.Empty;
             string indexname = string.Empty;
@@ -2514,7 +2524,7 @@ private int RetrieveKeyInfoFromStatistics(QualifiedTableName qualifiedTableName,
             // devnote: this test is already done by calling method ...
             // if (IsClosed) return;   // protect against dead connection
 
-            string tablename1 = qualifiedTableName.GetTable(quoted);
+            string tablename1 = qualifiedTableName.GetTable(quoted)!;
 
             // Select only unique indexes
             retcode = KeyInfoStatementHandle.Statistics(tablename1);
@@ -2670,7 +2680,7 @@ private int RetrieveKeyInfoFromStatistics(QualifiedTableName qualifiedTableName,
                     }
                 }
                 // Unbind the columns
-                _cmdWrapper.FreeKeyInfoStatementHandle(ODBC32.STMT.UNBIND);
+                _cmdWrapper!.FreeKeyInfoStatementHandle(ODBC32.STMT.UNBIND);
             }
             finally
             {
@@ -2694,12 +2704,12 @@ internal bool SameIndexColumn(string currentindexname, string indexname, int ord
             return false;
         }
 
-        internal int GetOrdinalFromBaseColName(string columnname)
+        internal int GetOrdinalFromBaseColName(string? columnname)
         {
             return GetOrdinalFromBaseColName(columnname, null);
         }
 
-        internal int GetOrdinalFromBaseColName(string columnname, string tablename)
+        internal int GetOrdinalFromBaseColName(string? columnname, string? tablename)
         {
             if (string.IsNullOrEmpty(columnname))
             {
@@ -2737,7 +2747,7 @@ internal int GetOrdinalFromBaseColName(string columnname, string tablename)
         // we can't handle multiple tablenames (JOIN)
         // only the first tablename will be returned
 
-        internal string GetTableNameFromCommandText()
+        internal string? GetTableNameFromCommandText()
         {
             if (_command == null)
             {
@@ -2750,7 +2760,7 @@ internal string GetTableNameFromCommandText()
             }
             string tablename;
             int idx;
-            CStringTokenizer tokenstmt = new CStringTokenizer(localcmdtext, Connection.QuoteChar(ADP.GetSchemaTable)[0], Connection.EscapeChar(ADP.GetSchemaTable));
+            CStringTokenizer tokenstmt = new CStringTokenizer(localcmdtext, Connection!.QuoteChar(ADP.GetSchemaTable)[0], Connection.EscapeChar(ADP.GetSchemaTable));
 
             if (tokenstmt.StartsWith("select") == true)
             {
@@ -2800,7 +2810,7 @@ internal void SetBaseTableNames(QualifiedTableName qualifiedTableName)
 
             for (int i = 0; i < count; i++)
             {
-                if (_metadata[i].baseTableName == null)
+                if (_metadata![i].baseTableName == null)
                 {
                     _metadata[i].baseTableName = qualifiedTableName.Table;
                     _metadata[i].baseSchemaName = qualifiedTableName.Schema;
@@ -2812,13 +2822,13 @@ internal void SetBaseTableNames(QualifiedTableName qualifiedTableName)
 
         internal sealed class QualifiedTableName
         {
-            private readonly string _catalogName;
-            private readonly string _schemaName;
-            private string _tableName;
-            private string _quotedTableName;
+            private readonly string? _catalogName;
+            private readonly string? _schemaName;
+            private string? _tableName;
+            private string? _quotedTableName;
             private readonly string _quoteChar;
 
-            internal string Catalog
+            internal string? Catalog
             {
                 get
                 {
@@ -2826,7 +2836,7 @@ internal string Catalog
                 }
             }
 
-            internal string Schema
+            internal string? Schema
             {
                 get
                 {
@@ -2834,7 +2844,7 @@ internal string Schema
                 }
             }
 
-            internal string Table
+            internal string? Table
             {
                 get
                 {
@@ -2846,14 +2856,14 @@ internal string Table
                     _tableName = UnQuote(value);
                 }
             }
-            internal string QuotedTable
+            internal string? QuotedTable
             {
                 get
                 {
                     return _quotedTableName;
                 }
             }
-            internal string GetTable(bool flag)
+            internal string? GetTable(bool flag)
             {
                 return (flag ? QuotedTable : Table);
             }
@@ -2861,18 +2871,18 @@ internal QualifiedTableName(string quoteChar)
             {
                 _quoteChar = quoteChar;
             }
-            internal QualifiedTableName(string quoteChar, string qualifiedname)
+            internal QualifiedTableName(string quoteChar, string? qualifiedname)
             {
                 _quoteChar = quoteChar;
 
-                string[] names = ParseProcedureName(qualifiedname, quoteChar, quoteChar);
+                string?[] names = ParseProcedureName(qualifiedname, quoteChar, quoteChar);
                 _catalogName = UnQuote(names[1]);
                 _schemaName = UnQuote(names[2]);
                 _quotedTableName = names[3];
                 _tableName = UnQuote(names[3]);
             }
 
-            private string UnQuote(string str)
+            private string? UnQuote(string? str)
             {
                 if ((str != null) && (str.Length > 0))
                 {
@@ -2893,7 +2903,7 @@ private string UnQuote(string str)
             // Note: copy-and pasted from internal DbCommandBuilder implementation
             // Note: Per definition (ODBC reference) the CatalogSeparator comes before and after the
             // catalog name, the SchemaSeparator is undefined. Does it come between Schema and Table?
-            internal static string[] ParseProcedureName(string name, string quotePrefix, string quoteSuffix)
+            internal static string?[] ParseProcedureName(string? name, string? quotePrefix, string? quoteSuffix)
             {
                 // Procedure may consist of up to four parts:
                 // 0) Server
@@ -2906,7 +2916,7 @@ internal static string[] ParseProcedureName(string name, string quotePrefix, str
                 //
                 const string Separator = ".";
 
-                string[] qualifiers = new string[4];
+                string?[] qualifiers = new string[4];
                 if (!string.IsNullOrEmpty(name))
                 {
                     bool useQuotes = !string.IsNullOrEmpty(quotePrefix) && !string.IsNullOrEmpty(quoteSuffix);
@@ -2917,8 +2927,10 @@ internal static string[] ParseProcedureName(string name, string quotePrefix, str
                         int startPos = currentPos;
 
                         // does the part begin with a quotePrefix?
-                        if (useQuotes && (name.IndexOf(quotePrefix, currentPos, quotePrefix.Length, StringComparison.Ordinal) == currentPos))
+                        if (useQuotes && (name.IndexOf(quotePrefix!, currentPos, quotePrefix!.Length, StringComparison.Ordinal) == currentPos))
                         {
+                            Debug.Assert(quotePrefix != null && quoteSuffix != null);
+
                             currentPos += quotePrefix.Length; // move past the quotePrefix
 
                             // search for the quoteSuffix (or end of string)
@@ -2978,7 +2990,7 @@ internal static string[] ParseProcedureName(string name, string quotePrefix, str
         private sealed class MetaData
         {
             internal int ordinal;
-            internal TypeMap typemap;
+            internal TypeMap typemap = null!; // Lazy-initialized
 
             internal SQLLEN size;
             internal byte precision;
@@ -2992,10 +3004,10 @@ private sealed class MetaData
             internal bool isLong;
 
             internal bool isKeyColumn;
-            internal string baseSchemaName;
-            internal string baseCatalogName;
-            internal string baseTableName;
-            internal string baseColumnName;
+            internal string? baseSchemaName;
+            internal string? baseCatalogName;
+            internal string? baseTableName;
+            internal string? baseColumnName;
         }
     }
 }
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcEnvironment.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcEnvironment.cs
index 76f363e30effd8..f6c0538764f74f 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcEnvironment.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcEnvironment.cs
@@ -7,14 +7,14 @@ namespace System.Data.Odbc
 {
     internal sealed class OdbcEnvironment
     {
-        private static object s_globalEnvironmentHandle;
+        private static object? s_globalEnvironmentHandle;
         private static readonly object s_globalEnvironmentHandleLock = new object();
 
         private OdbcEnvironment() { }  // default const.
 
         internal static OdbcEnvironmentHandle GetGlobalEnvironmentHandle()
         {
-            OdbcEnvironmentHandle globalEnvironmentHandle = s_globalEnvironmentHandle as OdbcEnvironmentHandle;
+            OdbcEnvironmentHandle? globalEnvironmentHandle = s_globalEnvironmentHandle as OdbcEnvironmentHandle;
             if (null == globalEnvironmentHandle)
             {
                 lock (s_globalEnvironmentHandleLock)
@@ -32,10 +32,10 @@ internal static OdbcEnvironmentHandle GetGlobalEnvironmentHandle()
 
         internal static void ReleaseObjectPool()
         {
-            object globalEnvironmentHandle = Interlocked.Exchange(ref s_globalEnvironmentHandle, null);
+            object? globalEnvironmentHandle = Interlocked.Exchange(ref s_globalEnvironmentHandle, null);
             if (null != globalEnvironmentHandle)
             {
-                (globalEnvironmentHandle as OdbcEnvironmentHandle).Dispose(); // internally refcounted so will happen correctly
+                ((OdbcEnvironmentHandle)globalEnvironmentHandle).Dispose(); // internally refcounted so will happen correctly
             }
         }
     }
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcError.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcError.cs
index 44a0f01712084b..564089c6904647 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcError.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcError.cs
@@ -11,9 +11,9 @@ public sealed class OdbcError
         internal string _message;
         internal string _state;
         internal int _nativeerror;
-        internal string _source;
+        internal string? _source;
 
-        internal OdbcError(string source, string message, string state, int nativeerror)
+        internal OdbcError(string? source, string message, string state, int nativeerror)
         {
             _source = source;
             _message = message;
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcErrorCollection.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcErrorCollection.cs
index 60bbf1b525f720..a94643cfba18b2 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcErrorCollection.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcErrorCollection.cs
@@ -37,7 +37,7 @@ public OdbcError this[int i]
         {
             get
             {
-                return (OdbcError)_items[i];
+                return (OdbcError)_items[i]!;
             }
         }
 
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcException.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcException.cs
index 4725546e407232..7a2f87ef4e1103 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcException.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcException.cs
@@ -37,7 +37,7 @@ internal OdbcException(string message, OdbcErrorCollection errors) : base(messag
         private OdbcException(SerializationInfo si, StreamingContext sc) : base(si, sc)
         {
             // Ignoring ODBC32.RETCODE
-            _odbcErrors = (OdbcErrorCollection)si.GetValue("odbcErrors", typeof(OdbcErrorCollection));
+            _odbcErrors = (OdbcErrorCollection)si.GetValue("odbcErrors", typeof(OdbcErrorCollection))!;
             HResult = HResults.OdbcException;
         }
 
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcHandle.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcHandle.cs
index 4936464cb100bd..77900ae013f17f 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcHandle.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcHandle.cs
@@ -12,9 +12,9 @@ namespace System.Data.Odbc
     internal abstract class OdbcHandle : SafeHandle
     {
         private readonly ODBC32.SQL_HANDLE _handleType;
-        private OdbcHandle _parentHandle;
+        private OdbcHandle? _parentHandle;
 
-        protected OdbcHandle(ODBC32.SQL_HANDLE handleType, OdbcHandle parentHandle) : base(IntPtr.Zero, true)
+        protected OdbcHandle(ODBC32.SQL_HANDLE handleType, OdbcHandle? parentHandle) : base(IntPtr.Zero, true)
         {
             _handleType = handleType;
 
@@ -61,7 +61,7 @@ protected OdbcHandle(ODBC32.SQL_HANDLE handleType, OdbcHandle parentHandle) : ba
                             else
                             {
                                 // without a handle, ReleaseHandle may not be called
-                                parentHandle.DangerousRelease();
+                                parentHandle!.DangerousRelease();
                             }
                             break;
                     }
@@ -164,7 +164,7 @@ protected override bool ReleaseHandle()
 
             // If we ended up getting released, then we have to release
             // our reference on our parent.
-            OdbcHandle parentHandle = _parentHandle;
+            OdbcHandle? parentHandle = _parentHandle;
             _parentHandle = null;
             if (null != parentHandle)
             {
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcMetaDataFactory.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcMetaDataFactory.cs
index f56a53cd6fe40b..f8eefe7edb6687 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcMetaDataFactory.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcMetaDataFactory.cs
@@ -49,7 +49,7 @@ internal OdbcMetaDataFactory(Stream XMLStream,
                 new SchemaFunctionName(OdbcMetaDataCollectionNames.Views, ODBC32.SQL_API.SQLTABLES)};
 
             // verify the existance of the table in the data set
-            DataTable metaDataCollectionsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
+            DataTable? metaDataCollectionsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
             if (metaDataCollectionsTable == null)
             {
                 throw ADP.UnableToBuildCollection(DbMetaDataCollectionNames.MetaDataCollections);
@@ -59,7 +59,7 @@ internal OdbcMetaDataFactory(Stream XMLStream,
             metaDataCollectionsTable = CloneAndFilterCollection(DbMetaDataCollectionNames.MetaDataCollections, null);
 
             // verify the existance of the table in the data set
-            DataTable restrictionsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.Restrictions];
+            DataTable? restrictionsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.Restrictions];
             if (restrictionsTable != null)
             {
                 // copy the table filtering out any rows that don't apply to the current version of the provider
@@ -72,13 +72,14 @@ internal OdbcMetaDataFactory(Stream XMLStream,
             // 3) the provider does not support the necessary odbc function
 
 
-            DataColumn populationMechanism = metaDataCollectionsTable.Columns[_populationMechanism];
-            DataColumn collectionName = metaDataCollectionsTable.Columns[_collectionName];
-            DataColumn restrictionCollectionName = null;
+            DataColumn populationMechanism = metaDataCollectionsTable.Columns[_populationMechanism]!;
+            DataColumn collectionName = metaDataCollectionsTable.Columns[_collectionName]!;
+            DataColumn? restrictionCollectionName = null;
             if (restrictionsTable != null)
             {
                 restrictionCollectionName = restrictionsTable.Columns[_collectionName];
             }
+            Debug.Assert(restrictionCollectionName != null);
 
             foreach (DataRow collection in metaDataCollectionsTable.Rows)
             {
@@ -123,12 +124,12 @@ internal OdbcMetaDataFactory(Stream XMLStream,
 
             // replace the original table with the updated one
             metaDataCollectionsTable.AcceptChanges();
-            CollectionDataSet.Tables.Remove(CollectionDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections]);
+            CollectionDataSet.Tables.Remove(CollectionDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections]!);
             CollectionDataSet.Tables.Add(metaDataCollectionsTable);
 
             if (restrictionsTable != null)
             {
-                CollectionDataSet.Tables.Remove(CollectionDataSet.Tables[DbMetaDataCollectionNames.Restrictions]);
+                CollectionDataSet.Tables.Remove(CollectionDataSet.Tables[DbMetaDataCollectionNames.Restrictions]!);
                 CollectionDataSet.Tables.Add(restrictionsTable);
             }
         }
@@ -180,7 +181,7 @@ private DataTable DataTableFromDataReader(IDataReader reader, string tableName)
 
         private void DataTableFromDataReaderDataTypes(DataTable dataTypesTable, OdbcDataReader dataReader, OdbcConnection connection)
         {
-            DataTable schemaTable = null;
+            DataTable? schemaTable = null;
             //
 
             // Build a DataTable from the reader
@@ -195,25 +196,25 @@ private void DataTableFromDataReaderDataTypes(DataTable dataTypesTable, OdbcData
             object[] getTypeInfoValues = new object[schemaTable.Rows.Count];
             DataRow dataTypesRow;
 
-            DataColumn typeNameColumn = dataTypesTable.Columns[DbMetaDataColumnNames.TypeName];
-            DataColumn providerDbTypeColumn = dataTypesTable.Columns[DbMetaDataColumnNames.ProviderDbType];
-            DataColumn columnSizeColumn = dataTypesTable.Columns[DbMetaDataColumnNames.ColumnSize];
-            DataColumn createParametersColumn = dataTypesTable.Columns[DbMetaDataColumnNames.CreateParameters];
-            DataColumn dataTypeColumn = dataTypesTable.Columns[DbMetaDataColumnNames.DataType];
-            DataColumn isAutoIncermentableColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsAutoIncrementable];
-            DataColumn isCaseSensitiveColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsCaseSensitive];
-            DataColumn isFixedLengthColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsFixedLength];
-            DataColumn isFixedPrecisionScaleColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsFixedPrecisionScale];
-            DataColumn isLongColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsLong];
-            DataColumn isNullableColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsNullable];
-            DataColumn isSearchableColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsSearchable];
-            DataColumn isSearchableWithLikeColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsSearchableWithLike];
-            DataColumn isUnsignedColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsUnsigned];
-            DataColumn maximumScaleColumn = dataTypesTable.Columns[DbMetaDataColumnNames.MaximumScale];
-            DataColumn minimumScaleColumn = dataTypesTable.Columns[DbMetaDataColumnNames.MinimumScale];
-            DataColumn literalPrefixColumn = dataTypesTable.Columns[DbMetaDataColumnNames.LiteralPrefix];
-            DataColumn literalSuffixColumn = dataTypesTable.Columns[DbMetaDataColumnNames.LiteralSuffix];
-            DataColumn SQLTypeNameColumn = dataTypesTable.Columns[OdbcMetaDataColumnNames.SQLType];
+            DataColumn typeNameColumn = dataTypesTable.Columns[DbMetaDataColumnNames.TypeName]!;
+            DataColumn providerDbTypeColumn = dataTypesTable.Columns[DbMetaDataColumnNames.ProviderDbType]!;
+            DataColumn columnSizeColumn = dataTypesTable.Columns[DbMetaDataColumnNames.ColumnSize]!;
+            DataColumn createParametersColumn = dataTypesTable.Columns[DbMetaDataColumnNames.CreateParameters]!;
+            DataColumn dataTypeColumn = dataTypesTable.Columns[DbMetaDataColumnNames.DataType]!;
+            DataColumn isAutoIncermentableColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsAutoIncrementable]!;
+            DataColumn isCaseSensitiveColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsCaseSensitive]!;
+            DataColumn isFixedLengthColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsFixedLength]!;
+            DataColumn isFixedPrecisionScaleColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsFixedPrecisionScale]!;
+            DataColumn isLongColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsLong]!;
+            DataColumn isNullableColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsNullable]!;
+            DataColumn isSearchableColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsSearchable]!;
+            DataColumn isSearchableWithLikeColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsSearchableWithLike]!;
+            DataColumn isUnsignedColumn = dataTypesTable.Columns[DbMetaDataColumnNames.IsUnsigned]!;
+            DataColumn maximumScaleColumn = dataTypesTable.Columns[DbMetaDataColumnNames.MaximumScale]!;
+            DataColumn minimumScaleColumn = dataTypesTable.Columns[DbMetaDataColumnNames.MinimumScale]!;
+            DataColumn literalPrefixColumn = dataTypesTable.Columns[DbMetaDataColumnNames.LiteralPrefix]!;
+            DataColumn literalSuffixColumn = dataTypesTable.Columns[DbMetaDataColumnNames.LiteralSuffix]!;
+            DataColumn SQLTypeNameColumn = dataTypesTable.Columns[OdbcMetaDataColumnNames.SQLType]!;
 
 
             const int indexTYPE_NAME = 0;
@@ -234,7 +235,7 @@ private void DataTableFromDataReaderDataTypes(DataTable dataTypesTable, OdbcData
             const int SQL_DATE_V2 = 9;
             const int SQL_TIME_V2 = 10;
 
-            TypeMap typeMap;
+            TypeMap? typeMap;
 
 
             while (dataReader.Read())
@@ -247,11 +248,9 @@ private void DataTableFromDataReaderDataTypes(DataTable dataTypesTable, OdbcData
                 dataTypesRow[typeNameColumn] = getTypeInfoValues[indexTYPE_NAME];
                 dataTypesRow[SQLTypeNameColumn] = getTypeInfoValues[indexDATA_TYPE];
 
-                sqlType = (ODBC32.SQL_TYPE)(int)Convert.ChangeType(getTypeInfoValues[indexDATA_TYPE],
-                                                                      typeof(int),
-                                                                      (System.IFormatProvider)null);
+                sqlType = (ODBC32.SQL_TYPE)(int)Convert.ChangeType(getTypeInfoValues[indexDATA_TYPE], typeof(int), null);
                 // if the driver is pre version 3 and it returned the v2 SQL_DATE or SQL_TIME types they need
-                // to be mapped to thier v3 equlivants
+                // to be mapped to their v3 equivalent
                 if (connection.IsV3Driver == false)
                 {
                     if ((int)sqlType == SQL_DATE_V2)
@@ -428,7 +427,7 @@ private void DataTableFromDataReaderDataTypes(DataTable dataTypesTable, OdbcData
 
         private DataTable DataTableFromDataReaderIndex(IDataReader reader,
                                                        string tableName,
-                                                       string restrictionIndexName)
+                                                       string? restrictionIndexName)
         {
             // set up the column structure of the data table from the reader
             object[] values;
@@ -499,7 +498,7 @@ private DataTable DataTableFromDataReaderProcedures(IDataReader reader, string t
             return resultTable;
         }
 
-        private void FillOutRestrictions(int restrictionsCount, string[] restrictions, object[] allRestrictions, string collectionName)
+        private void FillOutRestrictions(int restrictionsCount, string?[]? restrictions, object?[] allRestrictions, string collectionName)
         {
             Debug.Assert(allRestrictions.Length >= restrictionsCount);
 
@@ -530,11 +529,11 @@ private void FillOutRestrictions(int restrictionsCount, string[] restrictions, o
         }
 
 
-        private DataTable GetColumnsCollection(string[] restrictions, OdbcConnection connection)
+        private DataTable GetColumnsCollection(string?[]? restrictions, OdbcConnection connection)
         {
-            OdbcCommand command = null;
-            OdbcDataReader dataReader = null;
-            DataTable resultTable = null;
+            OdbcCommand? command = null;
+            OdbcDataReader? dataReader = null;
+            DataTable? resultTable = null;
             const int columnsRestrictionsCount = 4;
 
             try
@@ -563,7 +562,7 @@ private DataTable GetColumnsCollection(string[] restrictions, OdbcConnection con
         }
 
 
-        private DataTable GetDataSourceInformationCollection(string[] restrictions,
+        private DataTable GetDataSourceInformationCollection(string?[]? restrictions,
                                                              OdbcConnection connection)
         {
             if (ADP.IsEmptyArray(restrictions) == false)
@@ -572,7 +571,7 @@ private DataTable GetDataSourceInformationCollection(string[] restrictions,
             }
 
             // verify that the data source information table is in the data set
-            DataTable dataSourceInformationTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.DataSourceInformation];
+            DataTable? dataSourceInformationTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.DataSourceInformation];
             if (dataSourceInformationTable == null)
             {
                 throw ADP.UnableToBuildCollection(DbMetaDataCollectionNames.DataSourceInformation);
@@ -588,7 +587,7 @@ private DataTable GetDataSourceInformationCollection(string[] restrictions,
             }
             DataRow dataSourceInformation = dataSourceInformationTable.Rows[0];
 
-            string stringValue;
+            string? stringValue;
             short int16Value;
             int int32Value;
             ODBC32.RetCode retcode;
@@ -724,7 +723,7 @@ private DataTable GetDataSourceInformationCollection(string[] restrictions,
             }
 
             // build the QuotedIdentifierPattern using the quote prefix and suffix from the provider and
-            // assuming that the quote suffix is escaped via repetion (i.e " becomes "")
+            // assuming that the quote suffix is escaped via repetition (i.e " becomes "")
             stringValue = connection.QuoteChar(ADP.GetSchema);
 
             if (stringValue != null)
@@ -733,7 +732,7 @@ private DataTable GetDataSourceInformationCollection(string[] restrictions,
                 // quoted identifiers
                 if (stringValue != " ")
                 {
-                    // only know how to build the parttern if the quote characters is 1 character
+                    // only know how to build the pattern if the quote characters is 1 character
                     // in all other cases just leave the field null
                     if (stringValue.Length == 1)
                     {
@@ -782,7 +781,7 @@ private DataTable GetDataSourceInformationCollection(string[] restrictions,
         }
 
 
-        private DataTable GetDataTypesCollection(string[] restrictions, OdbcConnection connection)
+        private DataTable GetDataTypesCollection(string?[]? restrictions, OdbcConnection connection)
         {
             if (ADP.IsEmptyArray(restrictions) == false)
             {
@@ -792,7 +791,7 @@ private DataTable GetDataTypesCollection(string[] restrictions, OdbcConnection c
 
 
             // verify the existance of the table in the data set
-            DataTable dataTypesTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.DataTypes];
+            DataTable? dataTypesTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.DataTypes];
             if (dataTypesTable == null)
             {
                 throw ADP.UnableToBuildCollection(DbMetaDataCollectionNames.DataTypes);
@@ -801,8 +800,8 @@ private DataTable GetDataTypesCollection(string[] restrictions, OdbcConnection c
             // copy the data table it
             dataTypesTable = CloneAndFilterCollection(DbMetaDataCollectionNames.DataTypes, null);
 
-            OdbcCommand command = null;
-            OdbcDataReader dataReader = null;
+            OdbcCommand? command = null;
+            OdbcDataReader? dataReader = null;
             object[] allArguments = new object[1];
             allArguments[0] = ODBC32.SQL_ALL_TYPES;
 
@@ -831,11 +830,11 @@ private DataTable GetDataTypesCollection(string[] restrictions, OdbcConnection c
             return dataTypesTable;
         }
 
-        private DataTable GetIndexCollection(string[] restrictions, OdbcConnection connection)
+        private DataTable GetIndexCollection(string?[]? restrictions, OdbcConnection connection)
         {
-            OdbcCommand command = null;
-            OdbcDataReader dataReader = null;
-            DataTable resultTable = null;
+            OdbcCommand? command = null;
+            OdbcDataReader? dataReader = null;
+            DataTable? resultTable = null;
             const int nativeRestrictionsCount = 5;
             const int indexRestrictionsCount = 4;
             const int indexOfTableName = 2;
@@ -857,7 +856,7 @@ private DataTable GetIndexCollection(string[] restrictions, OdbcConnection conne
 
                 dataReader = command.ExecuteReaderFromSQLMethod(allRestrictions, ODBC32.SQL_API.SQLSTATISTICS);
 
-                string indexName = null;
+                string? indexName = null;
                 if (restrictions != null)
                 {
                     if (restrictions.Length >= indexOfIndexName + 1)
@@ -885,11 +884,11 @@ private DataTable GetIndexCollection(string[] restrictions, OdbcConnection conne
             return resultTable;
         }
 
-        private DataTable GetProcedureColumnsCollection(string[] restrictions, OdbcConnection connection, bool isColumns)
+        private DataTable GetProcedureColumnsCollection(string?[]? restrictions, OdbcConnection connection, bool isColumns)
         {
-            OdbcCommand command = null;
-            OdbcDataReader dataReader = null;
-            DataTable resultTable = null;
+            OdbcCommand? command = null;
+            OdbcDataReader? dataReader = null;
+            DataTable? resultTable = null;
             const int procedureColumnsRestrictionsCount = 4;
 
             try
@@ -928,18 +927,18 @@ private DataTable GetProcedureColumnsCollection(string[] restrictions, OdbcConne
             return resultTable;
         }
 
-        private DataTable GetProceduresCollection(string[] restrictions, OdbcConnection connection)
+        private DataTable GetProceduresCollection(string?[]? restrictions, OdbcConnection connection)
         {
-            OdbcCommand command = null;
-            OdbcDataReader dataReader = null;
-            DataTable resultTable = null;
+            OdbcCommand? command = null;
+            OdbcDataReader? dataReader = null;
+            DataTable? resultTable = null;
             const int columnsRestrictionsCount = 4;
             const int indexOfProcedureType = 3;
 
             try
             {
                 command = GetCommand(connection);
-                string[] allRestrictions = new string[columnsRestrictionsCount];
+                string?[] allRestrictions = new string[columnsRestrictionsCount];
                 FillOutRestrictions(columnsRestrictionsCount, restrictions, allRestrictions, OdbcMetaDataCollectionNames.Procedures);
 
 
@@ -952,7 +951,7 @@ private DataTable GetProceduresCollection(string[] restrictions, OdbcConnection
                 else
                 {
                     short procedureType;
-                    if ((restrictions[indexOfProcedureType] == "SQL_PT_UNKNOWN") ||
+                    if ((restrictions![indexOfProcedureType] == "SQL_PT_UNKNOWN") ||
                             (restrictions[indexOfProcedureType] == "0" /*ODBC32.SQL_PROCEDURETYPE.UNKNOWN*/))
                     {
                         procedureType = (short)ODBC32.SQL_PROCEDURETYPE.UNKNOWN;
@@ -990,7 +989,7 @@ private DataTable GetProceduresCollection(string[] restrictions, OdbcConnection
             return resultTable;
         }
 
-        private DataTable GetReservedWordsCollection(string[] restrictions, OdbcConnection connection)
+        private DataTable GetReservedWordsCollection(string?[]? restrictions, OdbcConnection connection)
         {
             if (ADP.IsEmptyArray(restrictions) == false)
             {
@@ -998,7 +997,7 @@ private DataTable GetReservedWordsCollection(string[] restrictions, OdbcConnecti
             }
 
             // verify the existance of the table in the data set
-            DataTable reservedWordsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.ReservedWords];
+            DataTable? reservedWordsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.ReservedWords];
             if (reservedWordsTable == null)
             {
                 throw ADP.UnableToBuildCollection(DbMetaDataCollectionNames.ReservedWords);
@@ -1007,13 +1006,13 @@ private DataTable GetReservedWordsCollection(string[] restrictions, OdbcConnecti
             // copy the table filtering out any rows that don't apply to tho current version of the prrovider
             reservedWordsTable = CloneAndFilterCollection(DbMetaDataCollectionNames.ReservedWords, null);
 
-            DataColumn reservedWordColumn = reservedWordsTable.Columns[DbMetaDataColumnNames.ReservedWord];
+            DataColumn? reservedWordColumn = reservedWordsTable.Columns[DbMetaDataColumnNames.ReservedWord];
             if (reservedWordColumn == null)
             {
                 throw ADP.UnableToBuildCollection(DbMetaDataCollectionNames.ReservedWords);
             }
 
-            string keywords = connection.GetInfoStringUnhandled(ODBC32.SQL_INFO.KEYWORDS);
+            string? keywords = connection.GetInfoStringUnhandled(ODBC32.SQL_INFO.KEYWORDS);
 
             if (null != keywords)
             {
@@ -1031,11 +1030,11 @@ private DataTable GetReservedWordsCollection(string[] restrictions, OdbcConnecti
             return reservedWordsTable;
         }
 
-        private DataTable GetTablesCollection(string[] restrictions, OdbcConnection connection, bool isTables)
+        private DataTable GetTablesCollection(string?[]? restrictions, OdbcConnection connection, bool isTables)
         {
-            OdbcCommand command = null;
-            OdbcDataReader dataReader = null;
-            DataTable resultTable = null;
+            OdbcCommand? command = null;
+            OdbcDataReader? dataReader = null;
+            DataTable? resultTable = null;
             const int tablesRestrictionsCount = 3;
             const string includedTableTypesTables = "TABLE,SYSTEM TABLE";
             const string includedTableTypesViews = "VIEW";
@@ -1081,7 +1080,7 @@ private DataTable GetTablesCollection(string[] restrictions, OdbcConnection conn
         }
 
         private bool IncludeIndexRow(object rowIndexName,
-                                        string restrictionIndexName,
+                                        string? restrictionIndexName,
                                         short rowIndexType)
         {
             // never include table statictics rows
@@ -1112,9 +1111,9 @@ private DataTable NewDataTableFromReader(IDataReader reader, out object[] values
             return resultTable;
         }
 
-        protected override DataTable PrepareCollection(string collectionName, string[] restrictions, DbConnection connection)
+        protected override DataTable PrepareCollection(string collectionName, string?[]? restrictions, DbConnection connection)
         {
-            DataTable resultTable = null;
+            DataTable? resultTable = null;
             OdbcConnection odbcConnection = (OdbcConnection)connection;
 
             if (collectionName == OdbcMetaDataCollectionNames.Tables)
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameter.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameter.cs
index 23d65eb394a827..08c95dc69d086f 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameter.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameter.cs
@@ -5,6 +5,7 @@
 using System.Data.Common;
 using System.Data.SqlTypes;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Runtime.InteropServices;
 using System.Text;
@@ -32,10 +33,10 @@ public sealed partial class OdbcParameter : DbParameter, ICloneable, IDataParame
         // Bind:            Bind may change _bindtype if the type is not supported through the driver
         //
 
-        private TypeMap _typemap;
-        private TypeMap _bindtype;
+        private TypeMap? _typemap;
+        private TypeMap? _bindtype;
 
-        private string _parameterName;
+        private string? _parameterName;
         private byte _precision;
         private byte _scale;
         private bool _hasScale;
@@ -47,7 +48,7 @@ public sealed partial class OdbcParameter : DbParameter, ICloneable, IDataParame
         private int _boundScale;
         private IntPtr _boundBuffer;
         private IntPtr _boundIntbuffer;
-        private TypeMap _originalbindtype;         // the original type in case we had to change the bindtype
+        private TypeMap? _originalbindtype;         // the original type in case we had to change the bindtype
                                                    // (e.g. decimal to string)
         private byte _internalPrecision;
         private bool _internalShouldSerializeSize;
@@ -56,12 +57,12 @@ public sealed partial class OdbcParameter : DbParameter, ICloneable, IDataParame
         private byte _internalScale;
         private int _internalOffset;
         internal bool _internalUserSpecifiedType;
-        private object _internalValue;
+        private object? _internalValue;
 
         private int _preparedOffset;
         private int _preparedSize;
         private int _preparedBufferSize;
-        private object _preparedValue;
+        private object? _preparedValue;
         private int _preparedIntOffset;
         private int _preparedValueOffset;
 
@@ -72,26 +73,26 @@ public OdbcParameter() : base()
             // uses System.Threading!
         }
 
-        public OdbcParameter(string name, object value) : this()
+        public OdbcParameter(string? name, object? value) : this()
         {
             ParameterName = name;
             Value = value;
         }
 
-        public OdbcParameter(string name, OdbcType type) : this()
+        public OdbcParameter(string? name, OdbcType type) : this()
         {
             ParameterName = name;
             OdbcType = type;
         }
 
-        public OdbcParameter(string name, OdbcType type, int size) : this()
+        public OdbcParameter(string? name, OdbcType type, int size) : this()
         {
             ParameterName = name;
             OdbcType = type;
             Size = size;
         }
 
-        public OdbcParameter(string name, OdbcType type, int size, string sourcecolumn) : this()
+        public OdbcParameter(string? name, OdbcType type, int size, string? sourcecolumn) : this()
         {
             ParameterName = name;
             OdbcType = type;
@@ -101,16 +102,16 @@ public OdbcParameter(string name, OdbcType type, int size, string sourcecolumn)
 
 
         [EditorBrowsableAttribute(EditorBrowsableState.Advanced)] // MDAC 69508
-        public OdbcParameter(string parameterName,
+        public OdbcParameter(string? parameterName,
                              OdbcType odbcType,
                              int size,
                              ParameterDirection parameterDirection,
                              bool isNullable,
                              byte precision,
                              byte scale,
-                             string srcColumn,
+                             string? srcColumn,
                              DataRowVersion srcVersion,
-                             object value
+                             object? value
                              ) : this()
         { // V1.0 everything
             this.ParameterName = parameterName;
@@ -126,12 +127,12 @@ object value
         }
 
         [EditorBrowsableAttribute(EditorBrowsableState.Advanced)] // MDAC 69508
-        public OdbcParameter(string parameterName,
+        public OdbcParameter(string? parameterName,
                                  OdbcType odbcType, int size,
                                  ParameterDirection parameterDirection,
                                  byte precision, byte scale,
-                                 string sourceColumn, DataRowVersion sourceVersion, bool sourceColumnNullMapping,
-                                 object value) : this()
+                                 string? sourceColumn, DataRowVersion sourceVersion, bool sourceColumnNullMapping,
+                                 object? value) : this()
         { // V2.0 everything - round trip all browsable properties + precision/scale
             this.ParameterName = parameterName;
             this.OdbcType = odbcType;
@@ -151,7 +152,7 @@ public override System.Data.DbType DbType
             {
                 if (_userSpecifiedType)
                 {
-                    return _typemap._dbType;
+                    return _typemap!._dbType;
                 }
                 return TypeMap._NVarChar._dbType; // default type
             }
@@ -181,7 +182,7 @@ public OdbcType OdbcType
             {
                 if (_userSpecifiedType)
                 {
-                    return _typemap._odbcType;
+                    return _typemap!._odbcType;
                 }
                 return TypeMap._NVarChar._odbcType; // default type
             }
@@ -219,11 +220,12 @@ internal bool UserSpecifiedType
             }
         }
 
+        [AllowNull]
         public override string ParameterName
         { // V1.2.3300, XXXParameter V1.0.3300
             get
             {
-                string parameterName = _parameterName;
+                string? parameterName = _parameterName;
                 return ((null != parameterName) ? parameterName : string.Empty);
             }
             set
@@ -314,16 +316,16 @@ private bool ShouldSerializeScale(byte scale)
         }
 
         // returns the count of bytes for the data (ColumnSize argument to SqlBindParameter)
-        private int GetColumnSize(object value, int offset, int ordinal)
+        private int GetColumnSize(object? value, int offset, int ordinal)
         {
-            if ((ODBC32.SQL_C.NUMERIC == _bindtype._sql_c) && (0 != _internalPrecision))
+            if ((ODBC32.SQL_C.NUMERIC == _bindtype!._sql_c) && (0 != _internalPrecision))
             {
                 return Math.Min((int)_internalPrecision, ADP.DecimalMaxPrecision);
             }
             int cch = _bindtype._columnSize;
             if (0 >= cch)
             {
-                if (ODBC32.SQL_C.NUMERIC == _typemap._sql_c)
+                if (ODBC32.SQL_C.NUMERIC == _typemap!._sql_c)
                 {
                     cch = 62;  // (DecimalMaxPrecision+sign+terminator)*BytesPerUnicodeCharacter
                 }
@@ -414,9 +416,9 @@ private int GetColumnSize(object value, int offset, int ordinal)
 
         // Return the count of bytes for the data (size in bytes for the native buffer)
         //
-        private int GetValueSize(object value, int offset)
+        private int GetValueSize(object? value, int offset)
         {
-            if ((ODBC32.SQL_C.NUMERIC == _bindtype._sql_c) && (0 != _internalPrecision))
+            if ((ODBC32.SQL_C.NUMERIC == _bindtype!._sql_c) && (0 != _internalPrecision))
             {
                 return Math.Min((int)_internalPrecision, ADP.DecimalMaxPrecision);
             }
@@ -457,12 +459,12 @@ private int GetValueSize(object value, int offset)
 
         // return the count of bytes for the data, used for SQLBindParameter
         //
-        private int GetParameterSize(object value, int offset, int ordinal)
+        private int GetParameterSize(object? value, int offset, int ordinal)
         {
-            int ccb = _bindtype._bufferSize;
+            int ccb = _bindtype!._bufferSize;
             if (0 >= ccb)
             {
-                if (ODBC32.SQL_C.NUMERIC == _typemap._sql_c)
+                if (ODBC32.SQL_C.NUMERIC == _typemap!._sql_c)
                 {
                     ccb = 518; // _bindtype would be VarChar ([0-9]?{255} + '-' + '.') * 2
                 }
@@ -529,7 +531,7 @@ private int GetParameterSize(object value, int offset, int ordinal)
             return ccb;
         }
 
-        private byte GetParameterPrecision(object value)
+        private byte GetParameterPrecision(object? value)
         {
             if (0 != _internalPrecision && value is decimal)
             {
@@ -556,7 +558,7 @@ private byte GetParameterPrecision(object value)
         }
 
 
-        private byte GetParameterScale(object value)
+        private byte GetParameterScale(object? value)
         {
             // For any value that is not decimal simply return the Scale
             //
@@ -618,11 +620,13 @@ internal void ClearBinding()
 
         internal void PrepareForBind(OdbcCommand command, short ordinal, ref int parameterBufferSize)
         {
+            Debug.Assert(command.Connection != null);
+
             // make a snapshot of the current properties. Properties may change while we work on them
             //
             CopyParameterInternal();
 
-            object value = ProcessAndGetParameterValue();
+            object? value = ProcessAndGetParameterValue();
             int offset = _internalOffset;
             int size = _internalSize;
             ODBC32.SQL_C sql_c_type;
@@ -663,7 +667,7 @@ internal void PrepareForBind(OdbcCommand command, short ordinal, ref int paramet
 
             // type support verification for certain data types
             //
-            switch (_bindtype._sql_type)
+            switch (_bindtype!._sql_type)
             {
                 case ODBC32.SQL_TYPE.DECIMAL:
                 case ODBC32.SQL_TYPE.NUMERIC:
@@ -703,7 +707,7 @@ internal void PrepareForBind(OdbcCommand command, short ordinal, ref int paramet
                 case ODBC32.SQL_TYPE.WLONGVARCHAR:
                     if (value is char)
                     {
-                        value = value.ToString();
+                        value = value.ToString()!;
                         size = ((string)value).Length;
                         offset = 0;
                     }
@@ -739,7 +743,7 @@ internal void PrepareForBind(OdbcCommand command, short ordinal, ref int paramet
                             int lcid = System.Globalization.CultureInfo.CurrentCulture.LCID;
                             CultureInfo culInfo = new CultureInfo(lcid);
                             Encoding cpe = System.Text.Encoding.GetEncoding(culInfo.TextInfo.ANSICodePage);
-                            value = cpe.GetBytes(value.ToString());
+                            value = cpe.GetBytes(value.ToString()!);
                             size = ((byte[])value).Length;
                         }
                     }
@@ -786,13 +790,15 @@ internal void PrepareForBind(OdbcCommand command, short ordinal, ref int paramet
 
         internal void Bind(OdbcStatementHandle hstmt, OdbcCommand command, short ordinal, CNativeBuffer parameterBuffer, bool allowReentrance)
         {
+            Debug.Assert(command.Connection != null);
+
             ODBC32.RetCode retcode;
             ODBC32.SQL_C sql_c_type = _prepared_Sql_C_Type;
             ODBC32.SQL_PARAM sqldirection = SqlDirectionFromParameterDirection();
 
             int offset = _preparedOffset;
             int size = _preparedSize;
-            object value = _preparedValue;
+            object? value = _preparedValue;
             int cbValueSize = GetValueSize(value, offset);             // count of bytes for the data
             int cchSize = GetColumnSize(value, offset, ordinal);   // count of bytes for the data, used to allocate the buffer length
             byte precision = GetParameterPrecision(value);
@@ -843,7 +849,7 @@ internal void Bind(OdbcStatementHandle hstmt, OdbcCommand command, short ordinal
 
             if (!_hasChanged
                 && (_boundSqlCType == sql_c_type)
-                && (_boundParameterType == _bindtype._sql_type)
+                && (_boundParameterType == _bindtype!._sql_type)
                 && (_boundSize == cchSize)
                 && (_boundScale == scale)
                 && (_boundBuffer == valueBuffer.Handle)
@@ -858,7 +864,7 @@ internal void Bind(OdbcStatementHandle hstmt, OdbcCommand command, short ordinal
                                     ordinal,                    // Parameter Number
                                     (short)sqldirection,        // InputOutputType
                                     sql_c_type,                 // ValueType
-                                    _bindtype._sql_type,        // ParameterType
+                                    _bindtype!._sql_type,        // ParameterType
                                     (IntPtr)cchSize,            // ColumnSize
                                     (IntPtr)scale,              // DecimalDigits
                                     valueBuffer,                // ParameterValuePtr
@@ -968,7 +974,7 @@ internal void GetOutputValue(CNativeBuffer parameterBuffer)
                         }
                     }
 
-                    if ((typemap != _typemap) && (null != Value) && !Convert.IsDBNull(Value) && (Value.GetType() != _typemap._type))
+                    if ((typemap != _typemap) && (null != Value) && !Convert.IsDBNull(Value) && (Value.GetType() != _typemap!._type))
                     {
                         Debug.Assert(ODBC32.SQL_C.NUMERIC == _typemap._sql_c, "unexpected");
                         Value = decimal.Parse((string)Value, System.Globalization.CultureInfo.CurrentCulture);
@@ -977,9 +983,9 @@ internal void GetOutputValue(CNativeBuffer parameterBuffer)
             }
         }
 
-        private object ProcessAndGetParameterValue()
+        private object? ProcessAndGetParameterValue()
         {
-            object value = _internalValue;
+            object? value = _internalValue;
             if (_internalUserSpecifiedType)
             {
                 if ((null != value) && !Convert.IsDBNull(value))
@@ -987,11 +993,11 @@ private object ProcessAndGetParameterValue()
                     Type valueType = value.GetType();
                     if (!valueType.IsArray)
                     {
-                        if (valueType != _typemap._type)
+                        if (valueType != _typemap!._type)
                         {
                             try
                             {
-                                value = Convert.ChangeType(value, _typemap._type, (System.IFormatProvider)null);
+                                value = Convert.ChangeType(value, _typemap._type, null);
                             }
                             catch (Exception e)
                             {
@@ -1040,7 +1046,7 @@ private void PropertyTypeChanging()
             //CoercedValue = null;
         }
 
-        internal void SetInputValue(object value, ODBC32.SQL_C sql_c_type, int cbsize, int sizeorprecision, int offset, CNativeBuffer parameterBuffer)
+        internal void SetInputValue(object? value, ODBC32.SQL_C sql_c_type, int cbsize, int sizeorprecision, int offset, CNativeBuffer parameterBuffer)
         { //Handle any input params
             if ((ParameterDirection.Input == _internalDirection) || (ParameterDirection.InputOutput == _internalDirection))
             {
@@ -1105,7 +1111,7 @@ private ODBC32.SQL_PARAM SqlDirectionFromParameterDirection()
             }
         }
 
-        public override object Value
+        public override object? Value
         { // V1.2.3300, XXXParameter V1.0.3300
             get
             {
@@ -1118,17 +1124,17 @@ public override object Value
             }
         }
 
-        private byte ValuePrecision(object value)
+        private byte ValuePrecision(object? value)
         {
             return ValuePrecisionCore(value);
         }
 
-        private byte ValueScale(object value)
+        private byte ValueScale(object? value)
         {
             return ValueScaleCore(value);
         }
 
-        private int ValueSize(object value)
+        private int ValueSize(object? value)
         {
             return ValueSizeCore(value);
         }
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterCollection.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterCollection.cs
index b84fac3863057e..d86b6d323f2603 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterCollection.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterCollection.cs
@@ -63,29 +63,29 @@ public OdbcParameter Add(OdbcParameter value)
 
         [EditorBrowsableAttribute(EditorBrowsableState.Never)]
         [ObsoleteAttribute("Add(String parameterName, Object value) has been deprecated.  Use AddWithValue(String parameterName, Object value).  https://go.microsoft.com/fwlink/?linkid=14202", false)] // 79027
-        public OdbcParameter Add(string parameterName, object value)
+        public OdbcParameter Add(string? parameterName, object? value)
         {
             // MDAC 59206
             return Add(new OdbcParameter(parameterName, value));
         }
 
-        public OdbcParameter AddWithValue(string parameterName, object value)
+        public OdbcParameter AddWithValue(string? parameterName, object? value)
         {
             // MDAC 79027
             return Add(new OdbcParameter(parameterName, value));
         }
 
-        public OdbcParameter Add(string parameterName, OdbcType odbcType)
+        public OdbcParameter Add(string? parameterName, OdbcType odbcType)
         {
             return Add(new OdbcParameter(parameterName, odbcType));
         }
 
-        public OdbcParameter Add(string parameterName, OdbcType odbcType, int size)
+        public OdbcParameter Add(string? parameterName, OdbcType odbcType, int size)
         {
             return Add(new OdbcParameter(parameterName, odbcType, size));
         }
 
-        public OdbcParameter Add(string parameterName, OdbcType odbcType, int size, string sourceColumn)
+        public OdbcParameter Add(string? parameterName, OdbcType odbcType, int size, string? sourceColumn)
         {
             return Add(new OdbcParameter(parameterName, odbcType, size, sourceColumn));
         }
@@ -102,7 +102,7 @@ internal void Bind(OdbcCommand command, CMDWrapper cmdWrapper, CNativeBuffer par
         {
             for (int i = 0; i < Count; ++i)
             {
-                this[i].Bind(cmdWrapper.StatementHandle, command, checked((short)(i + 1)), parameterBuffer, true);
+                this[i].Bind(cmdWrapper.StatementHandle!, command, checked((short)(i + 1)), parameterBuffer, true);
             }
             _rebindCollection = false;
         }
@@ -160,7 +160,7 @@ internal void GetOutputValues(CMDWrapper cmdWrapper)
             // mdac 88542 - we will not read out the parameters if the collection has changed
             if (!_rebindCollection)
             {
-                CNativeBuffer parameterBuffer = cmdWrapper._nativeParameterBuffer;
+                CNativeBuffer parameterBuffer = cmdWrapper._nativeParameterBuffer!;
                 for (int i = 0; i < Count; ++i)
                 {
                     this[i].GetOutputValue(parameterBuffer);
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterCollectionHelper.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterCollectionHelper.cs
index 668a4ae3cedb6a..671b50959b9e6e 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterCollectionHelper.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterCollectionHelper.cs
@@ -10,7 +10,7 @@ namespace System.Data.Odbc
 {
     public sealed partial class OdbcParameterCollection : DbParameterCollection
     {
-        private List<OdbcParameter> _items;
+        private List<OdbcParameter>? _items;
 
         public override int Count
         {
@@ -24,7 +24,7 @@ private List<OdbcParameter> InnerList
         {
             get
             {
-                List<OdbcParameter> items = _items;
+                List<OdbcParameter>? items = _items;
 
                 if (null == items)
                 {
@@ -297,7 +297,7 @@ private void Validate(int index, object value)
                 throw ADP.ParameterNull(nameof(value), this, s_itemType);
             }
 
-            object parent = ((OdbcParameter)value).CompareExchangeParent(this, null);
+            object? parent = ((OdbcParameter)value).CompareExchangeParent(this, null);
             if (null != parent)
             {
                 if (this != parent)
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterHelper.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterHelper.cs
index 0173da3e45db52..60634ace151211 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterHelper.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcParameterHelper.cs
@@ -2,25 +2,26 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Data.Common;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Data.Odbc
 {
     public sealed partial class OdbcParameter : DbParameter
     {
-        private object _value;
+        private object? _value;
 
-        private object _parent;
+        private object? _parent;
 
         private ParameterDirection _direction;
         private int _size;
         private int _offset;
-        private string _sourceColumn;
+        private string? _sourceColumn;
         private DataRowVersion _sourceVersion;
         private bool _sourceColumnNullMapping;
 
         private bool _isNullable;
 
-        private object _coercedValue;
+        private object? _coercedValue;
 
         private OdbcParameter(OdbcParameter source) : this() // V1.2.3300, Clone
         {
@@ -28,14 +29,13 @@ private OdbcParameter(OdbcParameter source) : this() // V1.2.3300, Clone
 
             source.CloneHelper(this);
 
-            ICloneable cloneable = (_value as ICloneable);
-            if (null != cloneable)
+            if (_value is ICloneable cloneable)
             { // MDAC 49322
                 _value = cloneable.Clone();
             }
         }
 
-        private object CoercedValue
+        private object? CoercedValue
         {
             get
             {
@@ -134,11 +134,12 @@ private bool ShouldSerializeSize()
             return (0 != _size);
         }
 
+        [AllowNull]
         public override string SourceColumn
         {
             get
             {
-                string sourceColumn = _sourceColumn;
+                string? sourceColumn = _sourceColumn;
                 return ((null != sourceColumn) ? sourceColumn : string.Empty);
             }
             set
@@ -195,9 +196,9 @@ private void CloneHelperCore(OdbcParameter destination)
             destination._isNullable = _isNullable;
         }
 
-        internal object CompareExchangeParent(object value, object comparand)
+        internal object? CompareExchangeParent(object? value, object? comparand)
         {
-            object parent = _parent;
+            object? parent = _parent;
             if (comparand == parent)
             {
                 _parent = value;
@@ -215,7 +216,7 @@ public override string ToString()
             return ParameterName;
         }
 
-        private byte ValuePrecisionCore(object value)
+        private byte ValuePrecisionCore(object? value)
         {
             if (value is decimal)
             {
@@ -224,7 +225,7 @@ private byte ValuePrecisionCore(object value)
             return 0;
         }
 
-        private byte ValueScaleCore(object value)
+        private byte ValueScaleCore(object? value)
         {
             if (value is decimal)
             {
@@ -233,29 +234,19 @@ private byte ValueScaleCore(object value)
             return 0;
         }
 
-        private int ValueSizeCore(object value)
+        private int ValueSizeCore(object? value)
         {
             if (!ADP.IsNull(value))
             {
-                string svalue = (value as string);
-                if (null != svalue)
+                return value switch
                 {
-                    return svalue.Length;
-                }
-                byte[] bvalue = (value as byte[]);
-                if (null != bvalue)
-                {
-                    return bvalue.Length;
-                }
-                char[] cvalue = (value as char[]);
-                if (null != cvalue)
-                {
-                    return cvalue.Length;
-                }
-                if ((value is byte) || (value is char))
-                {
-                    return 1;
-                }
+                    string svalue => svalue.Length,
+                    byte[] bvalue => bvalue.Length,
+                    char[] cvalue => cvalue.Length,
+                    byte _ => 1,
+                    char _ => 1,
+                    _ => 0
+                };
             }
             return 0;
         }
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcRowUpdatingEvent.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcRowUpdatingEvent.cs
index 61da7ce32a4fc6..05f6e51b4c4a55 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcRowUpdatingEvent.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcRowUpdatingEvent.cs
@@ -19,12 +19,12 @@ namespace System.Data.Odbc
     /////////////////////////////////////////////////////////////////////////
     public sealed class OdbcRowUpdatingEventArgs : RowUpdatingEventArgs
     {
-        public OdbcRowUpdatingEventArgs(DataRow row, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        public OdbcRowUpdatingEventArgs(DataRow row, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         : base(row, command, statementType, tableMapping)
         {
         }
 
-        public new OdbcCommand Command
+        public new OdbcCommand? Command
         {
             get { return (base.Command as OdbcCommand); }
             set
@@ -33,7 +33,7 @@ public OdbcRowUpdatingEventArgs(DataRow row, IDbCommand command, StatementType s
             }
         }
 
-        protected override IDbCommand BaseCommand
+        protected override IDbCommand? BaseCommand
         {
             get { return base.BaseCommand; }
             set { base.BaseCommand = (value as OdbcCommand); }
@@ -46,14 +46,14 @@ protected override IDbCommand BaseCommand
     /////////////////////////////////////////////////////////////////////////
     public sealed class OdbcRowUpdatedEventArgs : RowUpdatedEventArgs
     {
-        public OdbcRowUpdatedEventArgs(DataRow row, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        public OdbcRowUpdatedEventArgs(DataRow row, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         : base(row, command, statementType, tableMapping)
         {
         }
 
-        public new OdbcCommand Command
+        public new OdbcCommand? Command
         {
-            get { return (OdbcCommand)base.Command; }
+            get { return (OdbcCommand?)base.Command; }
         }
     }
 }
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcStatementHandle.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcStatementHandle.cs
index dba62ed2026054..11d970c8518806 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcStatementHandle.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcStatementHandle.cs
@@ -62,7 +62,7 @@ public unsafe long ToInt64()
 
     internal sealed class OdbcStatementHandle : OdbcHandle
     {
-        internal OdbcStatementHandle(OdbcConnectionHandle connectionHandle) : base(ODBC32.SQL_HANDLE.STMT, connectionHandle)
+        internal OdbcStatementHandle(OdbcConnectionHandle? connectionHandle) : base(ODBC32.SQL_HANDLE.STMT, connectionHandle)
         {
         }
 
@@ -215,7 +215,7 @@ internal ODBC32.RetCode Prepare(string commandText)
             return retcode;
         }
 
-        internal ODBC32.RetCode PrimaryKeys(string catalogName, string schemaName, string tableName)
+        internal ODBC32.RetCode PrimaryKeys(string? catalogName, string? schemaName, string tableName)
         {
             ODBC32.RetCode retcode = Interop.Odbc.SQLPrimaryKeysW(this,
                             catalogName, ODBC.ShortStringLength(catalogName),          // CatalogName
@@ -242,10 +242,10 @@ internal ODBC32.RetCode Procedures(string procedureCatalog,
             return retcode;
         }
 
-        internal ODBC32.RetCode ProcedureColumns(string procedureCatalog,
-                                                 string procedureSchema,
-                                                 string procedureName,
-                                                 string columnName)
+        internal ODBC32.RetCode ProcedureColumns(string? procedureCatalog,
+                                                 string? procedureSchema,
+                                                 string? procedureName,
+                                                 string? columnName)
         {
             ODBC32.RetCode retcode = Interop.Odbc.SQLProcedureColumnsW(this,
                                                                               procedureCatalog,
@@ -287,8 +287,8 @@ internal ODBC32.RetCode SpecialColumns(string quotedTable)
             return retcode;
         }
 
-        internal ODBC32.RetCode Statistics(string tableCatalog,
-                                           string tableSchema,
+        internal ODBC32.RetCode Statistics(string? tableCatalog,
+                                           string? tableSchema,
                                            string tableName,
                                            short unique,
                                            short accuracy)
diff --git a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcTransaction.cs b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcTransaction.cs
index 38ae74d0ca594e..aceee7efbe499a 100644
--- a/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcTransaction.cs
+++ b/src/libraries/System.Data.Odbc/src/System/Data/Odbc/OdbcTransaction.cs
@@ -7,9 +7,9 @@ namespace System.Data.Odbc
 {
     public sealed class OdbcTransaction : DbTransaction
     {
-        private OdbcConnection _connection;
+        private OdbcConnection? _connection;
         private IsolationLevel _isolevel = IsolationLevel.Unspecified;
-        private OdbcConnectionHandle _handle;
+        private OdbcConnectionHandle? _handle;
 
         internal OdbcTransaction(OdbcConnection connection, IsolationLevel isolevel, OdbcConnectionHandle handle)
         {
@@ -18,7 +18,7 @@ internal OdbcTransaction(OdbcConnection connection, IsolationLevel isolevel, Odb
             _handle = handle;
         }
 
-        public new OdbcConnection Connection
+        public new OdbcConnection? Connection
         { // MDAC 66655
             get
             {
@@ -26,7 +26,7 @@ internal OdbcTransaction(OdbcConnection connection, IsolationLevel isolevel, Odb
             }
         }
 
-        protected override DbConnection DbConnection
+        protected override DbConnection? DbConnection
         { // MDAC 66655
             get
             {
@@ -38,7 +38,7 @@ public override IsolationLevel IsolationLevel
         {
             get
             {
-                OdbcConnection connection = _connection;
+                OdbcConnection? connection = _connection;
                 if (null == connection)
                 {
                     throw ADP.TransactionZombied(this);
@@ -67,7 +67,7 @@ public override IsolationLevel IsolationLevel
 
         public override void Commit()
         {
-            OdbcConnection connection = _connection;
+            OdbcConnection? connection = _connection;
             if (null == connection)
             {
                 throw ADP.TransactionZombied(this);
@@ -76,7 +76,7 @@ public override void Commit()
             connection.CheckState(ADP.CommitTransaction); // MDAC 68289
 
             //Note: SQLEndTran success if not actually in a transaction, so we have to throw
-            //since the IDbTransaciton spec indicates this is an error for the managed packages
+            //since the IDbTransaction spec indicates this is an error for the managed packages
             if (null == _handle)
             {
                 throw ODBC.NotInTransaction();
@@ -100,7 +100,7 @@ protected override void Dispose(bool disposing)
         {
             if (disposing)
             {
-                OdbcConnectionHandle handle = _handle;
+                OdbcConnectionHandle? handle = _handle;
                 _handle = null;
                 if (null != handle)
                 {
@@ -112,7 +112,7 @@ protected override void Dispose(bool disposing)
                             //don't throw an exception here, but trace it so it can be logged
                             if (_connection != null)
                             {
-                                Exception e = _connection.HandleErrorNoThrow(handle, retcode);
+                                Exception e = _connection.HandleErrorNoThrow(handle, retcode)!;
                                 ADP.TraceExceptionWithoutRethrow(e);
                             }
                         }
@@ -141,7 +141,7 @@ protected override void Dispose(bool disposing)
 
         public override void Rollback()
         {
-            OdbcConnection connection = _connection;
+            OdbcConnection? connection = _connection;
             if (null == connection)
             {
                 throw ADP.TransactionZombied(this);
@@ -149,7 +149,7 @@ public override void Rollback()
             connection.CheckState(ADP.RollbackTransaction); // MDAC 68289
 
             //Note: SQLEndTran success if not actually in a transaction, so we have to throw
-            //since the IDbTransaciton spec indicates this is an error for the managed packages
+            //since the IDbTransaction spec indicates this is an error for the managed packages
             if (null == _handle)
             {
                 throw ODBC.NotInTransaction();
diff --git a/src/libraries/System.Data.Odbc/tests/OdbcParameterTests.cs b/src/libraries/System.Data.Odbc/tests/OdbcParameterTests.cs
index 0264246c1a80ca..369bd2a07b609c 100644
--- a/src/libraries/System.Data.Odbc/tests/OdbcParameterTests.cs
+++ b/src/libraries/System.Data.Odbc/tests/OdbcParameterTests.cs
@@ -1,7 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System.Data.SqlClient;
 using System.Text;
 using Xunit;
 
diff --git a/src/libraries/System.Data.Odbc/tests/System.Data.Odbc.Tests.csproj b/src/libraries/System.Data.Odbc/tests/System.Data.Odbc.Tests.csproj
index 95c97d667a0ae9..208f6a4ab831b8 100644
--- a/src/libraries/System.Data.Odbc/tests/System.Data.Odbc.Tests.csproj
+++ b/src/libraries/System.Data.Odbc/tests/System.Data.Odbc.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <DefineConstants Condition="'$(TargetsWindows)' == 'true'">$(DefineConstants);TargetsWindows</DefineConstants>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-FreeBSD;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-FreeBSD;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="DependencyCheckTest.cs" />
@@ -39,4 +39,7 @@
   <ItemGroup Condition="'$(TargetsWindows)' != 'true'">
     <Compile Include="ConnectionStrings.Unix.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="..\src\System.Data.Odbc.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Data.OleDb/ref/System.Data.OleDb.cs b/src/libraries/System.Data.OleDb/ref/System.Data.OleDb.cs
index 76a78d3defd12b..eaaff8244c5913 100644
--- a/src/libraries/System.Data.OleDb/ref/System.Data.OleDb.cs
+++ b/src/libraries/System.Data.OleDb/ref/System.Data.OleDb.cs
@@ -6,24 +6,25 @@
 
 namespace System.Data.OleDb
 {
+    [System.ComponentModel.DesignerAttribute("Microsoft.VSDesigner.Data.VS.OleDbCommandDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public sealed partial class OleDbCommand : System.Data.Common.DbCommand, System.Data.IDbCommand, System.ICloneable, System.IDisposable
     {
         public OleDbCommand() { }
-        public OleDbCommand(string cmdText) { }
-        public OleDbCommand(string cmdText, System.Data.OleDb.OleDbConnection connection) { }
-        public OleDbCommand(string cmdText, System.Data.OleDb.OleDbConnection connection, System.Data.OleDb.OleDbTransaction transaction) { }
+        public OleDbCommand(string? cmdText) { }
+        public OleDbCommand(string? cmdText, System.Data.OleDb.OleDbConnection? connection) { }
+        public OleDbCommand(string? cmdText, System.Data.OleDb.OleDbConnection? connection, System.Data.OleDb.OleDbTransaction? transaction) { }
         [System.ComponentModel.DefaultValueAttribute("")]
         [System.ComponentModel.RefreshPropertiesAttribute(System.ComponentModel.RefreshProperties.All)]
-        public override string CommandText { get { throw null; } set { } }
+        public override string? CommandText { get { throw null; } set { } }
         public override int CommandTimeout { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute(System.Data.CommandType.Text)]
         [System.ComponentModel.RefreshPropertiesAttribute(System.ComponentModel.RefreshProperties.All)]
         public override System.Data.CommandType CommandType { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute(null)]
-        public new System.Data.OleDb.OleDbConnection Connection { get { throw null; } set { } }
-        protected override System.Data.Common.DbConnection DbConnection { get { throw null; } set { } }
+        public new System.Data.OleDb.OleDbConnection? Connection { get { throw null; } set { } }
+        protected override System.Data.Common.DbConnection? DbConnection { get { throw null; } set { } }
         protected override System.Data.Common.DbParameterCollection DbParameterCollection { get { throw null; } }
-        protected override System.Data.Common.DbTransaction DbTransaction { get { throw null; } set { } }
+        protected override System.Data.Common.DbTransaction? DbTransaction { get { throw null; } set { } }
         [System.ComponentModel.BrowsableAttribute(false)]
         [System.ComponentModel.DefaultValueAttribute(true)]
         [System.ComponentModel.DesignOnlyAttribute(true)]
@@ -32,7 +33,7 @@ public OleDbCommand(string cmdText, System.Data.OleDb.OleDbConnection connection
         public new System.Data.OleDb.OleDbParameterCollection Parameters { get { throw null; } }
         [System.ComponentModel.BrowsableAttribute(false)]
         [System.ComponentModel.DesignerSerializationVisibilityAttribute(System.ComponentModel.DesignerSerializationVisibility.Hidden)]
-        public new System.Data.OleDb.OleDbTransaction Transaction { get { throw null; } set { } }
+        public new System.Data.OleDb.OleDbTransaction? Transaction { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute(System.Data.UpdateRowSource.Both)]
         public override System.Data.UpdateRowSource UpdatedRowSource { get { throw null; } set { } }
         public override void Cancel() { }
@@ -44,7 +45,7 @@ protected override void Dispose(bool disposing) { }
         public override int ExecuteNonQuery() { throw null; }
         public new System.Data.OleDb.OleDbDataReader ExecuteReader() { throw null; }
         public new System.Data.OleDb.OleDbDataReader ExecuteReader(System.Data.CommandBehavior behavior) { throw null; }
-        public override object ExecuteScalar() { throw null; }
+        public override object? ExecuteScalar() { throw null; }
         public override void Prepare() { }
         public void ResetCommandTimeout() { }
         System.Data.IDataReader System.Data.IDbCommand.ExecuteReader() { throw null; }
@@ -54,9 +55,9 @@ public void ResetCommandTimeout() { }
     public sealed partial class OleDbCommandBuilder : System.Data.Common.DbCommandBuilder
     {
         public OleDbCommandBuilder() { }
-        public OleDbCommandBuilder(System.Data.OleDb.OleDbDataAdapter adapter) { }
+        public OleDbCommandBuilder(System.Data.OleDb.OleDbDataAdapter? adapter) { }
         [System.ComponentModel.DefaultValueAttribute(null)]
-        public new System.Data.OleDb.OleDbDataAdapter DataAdapter { get { throw null; } set { } }
+        public new System.Data.OleDb.OleDbDataAdapter? DataAdapter { get { throw null; } set { } }
         protected override void ApplyParameterInfo(System.Data.Common.DbParameter parameter, System.Data.DataRow datarow, System.Data.StatementType statementType, bool whereClause) { }
         public static void DeriveParameters(System.Data.OleDb.OleDbCommand command) { }
         public new System.Data.OleDb.OleDbCommand GetDeleteCommand() { throw null; }
@@ -78,11 +79,12 @@ protected override void SetRowUpdatingHandler(System.Data.Common.DbDataAdapter a
     public sealed partial class OleDbConnection : System.Data.Common.DbConnection, System.Data.IDbConnection, System.ICloneable, System.IDisposable
     {
         public OleDbConnection() { }
-        public OleDbConnection(string connectionString) { }
+        public OleDbConnection(string? connectionString) { }
         [System.ComponentModel.DefaultValueAttribute("")]
         [System.ComponentModel.RecommendedAsConfigurableAttribute(true)]
         [System.ComponentModel.RefreshPropertiesAttribute(System.ComponentModel.RefreshProperties.All)]
         [System.ComponentModel.SettingsBindableAttribute(true)]
+        [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public override string ConnectionString { get { throw null; } set { } }
         [System.ComponentModel.DesignerSerializationVisibilityAttribute(System.ComponentModel.DesignerSerializationVisibility.Hidden)]
         public override int ConnectionTimeout { get { throw null; } }
@@ -97,7 +99,7 @@ public OleDbConnection(string connectionString) { }
         [System.ComponentModel.BrowsableAttribute(false)]
         [System.ComponentModel.DesignerSerializationVisibilityAttribute(System.ComponentModel.DesignerSerializationVisibility.Hidden)]
         public override System.Data.ConnectionState State { get { throw null; } }
-        public event System.Data.OleDb.OleDbInfoMessageEventHandler InfoMessage { add { } remove { } }
+        public event System.Data.OleDb.OleDbInfoMessageEventHandler? InfoMessage { add { } remove { } }
         protected override System.Data.Common.DbTransaction BeginDbTransaction(System.Data.IsolationLevel isolationLevel) { throw null; }
         public new System.Data.OleDb.OleDbTransaction BeginTransaction() { throw null; }
         public new System.Data.OleDb.OleDbTransaction BeginTransaction(System.Data.IsolationLevel isolationLevel) { throw null; }
@@ -106,11 +108,11 @@ public override void Close() { }
         public new System.Data.OleDb.OleDbCommand CreateCommand() { throw null; }
         protected override System.Data.Common.DbCommand CreateDbCommand() { throw null; }
         protected override void Dispose(bool disposing) { }
-        public override void EnlistTransaction(System.Transactions.Transaction transaction) { }
-        public System.Data.DataTable GetOleDbSchemaTable(System.Guid schema, object[] restrictions) { throw null; }
+        public override void EnlistTransaction(System.Transactions.Transaction? transaction) { }
+        public System.Data.DataTable? GetOleDbSchemaTable(System.Guid schema, object?[]? restrictions) { throw null; }
         public override System.Data.DataTable GetSchema() { throw null; }
         public override System.Data.DataTable GetSchema(string collectionName) { throw null; }
-        public override System.Data.DataTable GetSchema(string collectionName, string[] restrictionValues) { throw null; }
+        public override System.Data.DataTable GetSchema(string collectionName, string?[]? restrictionValues) { throw null; }
         public override void Open() { }
         public static void ReleaseObjectPool() { }
         public void ResetState() { }
@@ -121,13 +123,14 @@ public void ResetState() { }
     public sealed partial class OleDbConnectionStringBuilder : System.Data.Common.DbConnectionStringBuilder
     {
         public OleDbConnectionStringBuilder() { }
-        public OleDbConnectionStringBuilder(string connectionString) { }
+        public OleDbConnectionStringBuilder(string? connectionString) { }
         [System.ComponentModel.DisplayNameAttribute("Data Source")]
         [System.ComponentModel.RefreshPropertiesAttribute(System.ComponentModel.RefreshProperties.All)]
         public string DataSource { get { throw null; } set { } }
         [System.ComponentModel.DisplayNameAttribute("File Name")]
         [System.ComponentModel.RefreshPropertiesAttribute(System.ComponentModel.RefreshProperties.All)]
         public string FileName { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public override object this[string keyword] { get { throw null; } set { } }
         public override System.Collections.ICollection Keys { get { throw null; } }
         [System.ComponentModel.DisplayNameAttribute("Persist Security Info")]
@@ -136,35 +139,36 @@ public OleDbConnectionStringBuilder(string connectionString) { }
         public override void Clear() { }
         public override bool ContainsKey(string keyword) { throw null; }
         public override bool Remove(string keyword) { throw null; }
-        public override bool TryGetValue(string keyword, out object value) { throw null; }
+        public override bool TryGetValue(string keyword, [System.Diagnostics.CodeAnalysis.NotNullWhen(true)] out object? value) { throw null; }
     }
+    [System.ComponentModel.DesignerAttribute("Microsoft.VSDesigner.Data.VS.OleDbDataAdapterDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public sealed partial class OleDbDataAdapter : System.Data.Common.DbDataAdapter, System.Data.IDataAdapter, System.Data.IDbDataAdapter, System.ICloneable
     {
         public OleDbDataAdapter() { }
-        public OleDbDataAdapter(System.Data.OleDb.OleDbCommand selectCommand) { }
-        public OleDbDataAdapter(string selectCommandText, System.Data.OleDb.OleDbConnection selectConnection) { }
-        public OleDbDataAdapter(string selectCommandText, string selectConnectionString) { }
+        public OleDbDataAdapter(System.Data.OleDb.OleDbCommand? selectCommand) { }
+        public OleDbDataAdapter(string? selectCommandText, System.Data.OleDb.OleDbConnection? selectConnection) { }
+        public OleDbDataAdapter(string? selectCommandText, string? selectConnectionString) { }
         [System.ComponentModel.DefaultValueAttribute(null)]
-        public new System.Data.OleDb.OleDbCommand DeleteCommand { get { throw null; } set { } }
+        public new System.Data.OleDb.OleDbCommand? DeleteCommand { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute(null)]
-        public new System.Data.OleDb.OleDbCommand InsertCommand { get { throw null; } set { } }
+        public new System.Data.OleDb.OleDbCommand? InsertCommand { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute(null)]
-        public new System.Data.OleDb.OleDbCommand SelectCommand { get { throw null; } set { } }
-        System.Data.IDbCommand System.Data.IDbDataAdapter.DeleteCommand { get { throw null; } set { } }
-        System.Data.IDbCommand System.Data.IDbDataAdapter.InsertCommand { get { throw null; } set { } }
-        System.Data.IDbCommand System.Data.IDbDataAdapter.SelectCommand { get { throw null; } set { } }
-        System.Data.IDbCommand System.Data.IDbDataAdapter.UpdateCommand { get { throw null; } set { } }
+        public new System.Data.OleDb.OleDbCommand? SelectCommand { get { throw null; } set { } }
+        System.Data.IDbCommand? System.Data.IDbDataAdapter.DeleteCommand { get { throw null; } set { } }
+        System.Data.IDbCommand? System.Data.IDbDataAdapter.InsertCommand { get { throw null; } set { } }
+        System.Data.IDbCommand? System.Data.IDbDataAdapter.SelectCommand { get { throw null; } set { } }
+        System.Data.IDbCommand? System.Data.IDbDataAdapter.UpdateCommand { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute(null)]
-        public new System.Data.OleDb.OleDbCommand UpdateCommand { get { throw null; } set { } }
-        public event System.Data.OleDb.OleDbRowUpdatedEventHandler RowUpdated { add { } remove { } }
-        public event System.Data.OleDb.OleDbRowUpdatingEventHandler RowUpdating { add { } remove { } }
-        protected override System.Data.Common.RowUpdatedEventArgs CreateRowUpdatedEvent(System.Data.DataRow dataRow, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
-        protected override System.Data.Common.RowUpdatingEventArgs CreateRowUpdatingEvent(System.Data.DataRow dataRow, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
+        public new System.Data.OleDb.OleDbCommand? UpdateCommand { get { throw null; } set { } }
+        public event System.Data.OleDb.OleDbRowUpdatedEventHandler? RowUpdated { add { } remove { } }
+        public event System.Data.OleDb.OleDbRowUpdatingEventHandler? RowUpdating { add { } remove { } }
+        protected override System.Data.Common.RowUpdatedEventArgs CreateRowUpdatedEvent(System.Data.DataRow dataRow, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
+        protected override System.Data.Common.RowUpdatingEventArgs CreateRowUpdatingEvent(System.Data.DataRow dataRow, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) { throw null; }
         public int Fill(System.Data.DataSet dataSet, object ADODBRecordSet, string srcTable) { throw null; }
         public int Fill(System.Data.DataTable dataTable, object ADODBRecordSet) { throw null; }
         protected override void OnRowUpdated(System.Data.Common.RowUpdatedEventArgs value) { }
         protected override void OnRowUpdating(System.Data.Common.RowUpdatingEventArgs value) { }
-        object System.ICloneable.Clone() { throw null; }
+        object? System.ICloneable.Clone() { throw null; }
     }
     public sealed partial class OleDbDataReader : System.Data.Common.DbDataReader
     {
@@ -180,9 +184,9 @@ internal OleDbDataReader() { }
         public override void Close() { }
         public override bool GetBoolean(int ordinal) { throw null; }
         public override byte GetByte(int ordinal) { throw null; }
-        public override long GetBytes(int ordinal, long dataIndex, byte[] buffer, int bufferIndex, int length) { throw null; }
+        public override long GetBytes(int ordinal, long dataIndex, byte[]? buffer, int bufferIndex, int length) { throw null; }
         public override char GetChar(int ordinal) { throw null; }
-        public override long GetChars(int ordinal, long dataIndex, char[] buffer, int bufferIndex, int length) { throw null; }
+        public override long GetChars(int ordinal, long dataIndex, char[]? buffer, int bufferIndex, int length) { throw null; }
         public new System.Data.OleDb.OleDbDataReader GetData(int ordinal) { throw null; }
         public override string GetDataTypeName(int index) { throw null; }
         public override System.DateTime GetDateTime(int ordinal) { throw null; }
@@ -259,7 +263,7 @@ internal OleDbInfoMessageEventArgs() { }
         public int ErrorCode { get { throw null; } }
         public System.Data.OleDb.OleDbErrorCollection Errors { get { throw null; } }
         public string Message { get { throw null; } }
-        public string Source { get { throw null; } }
+        public string? Source { get { throw null; } }
         public override string ToString() { throw null; }
     }
     public delegate void OleDbInfoMessageEventHandler(object sender, System.Data.OleDb.OleDbInfoMessageEventArgs e);
@@ -319,12 +323,12 @@ public static partial class OleDbMetaDataColumnNames
     public sealed partial class OleDbParameter : System.Data.Common.DbParameter, System.Data.IDataParameter, System.Data.IDbDataParameter, System.ICloneable
     {
         public OleDbParameter() { }
-        public OleDbParameter(string name, System.Data.OleDb.OleDbType dataType) { }
-        public OleDbParameter(string name, System.Data.OleDb.OleDbType dataType, int size) { }
-        public OleDbParameter(string parameterName, System.Data.OleDb.OleDbType dbType, int size, System.Data.ParameterDirection direction, bool isNullable, byte precision, byte scale, string srcColumn, System.Data.DataRowVersion srcVersion, object value) { }
-        public OleDbParameter(string parameterName, System.Data.OleDb.OleDbType dbType, int size, System.Data.ParameterDirection direction, byte precision, byte scale, string sourceColumn, System.Data.DataRowVersion sourceVersion, bool sourceColumnNullMapping, object value) { }
-        public OleDbParameter(string name, System.Data.OleDb.OleDbType dataType, int size, string srcColumn) { }
-        public OleDbParameter(string name, object value) { }
+        public OleDbParameter(string? name, System.Data.OleDb.OleDbType dataType) { }
+        public OleDbParameter(string? name, System.Data.OleDb.OleDbType dataType, int size) { }
+        public OleDbParameter(string? parameterName, System.Data.OleDb.OleDbType dbType, int size, System.Data.ParameterDirection direction, bool isNullable, byte precision, byte scale, string? srcColumn, System.Data.DataRowVersion srcVersion, object? value) { }
+        public OleDbParameter(string? parameterName, System.Data.OleDb.OleDbType dbType, int size, System.Data.ParameterDirection direction, byte precision, byte scale, string? sourceColumn, System.Data.DataRowVersion sourceVersion, bool sourceColumnNullMapping, object? value) { }
+        public OleDbParameter(string? name, System.Data.OleDb.OleDbType dataType, int size, string? srcColumn) { }
+        public OleDbParameter(string? name, object? value) { }
         public override System.Data.DbType DbType { get { throw null; } set { } }
         [System.ComponentModel.RefreshPropertiesAttribute(System.ComponentModel.RefreshProperties.All)]
         public override System.Data.ParameterDirection Direction { get { throw null; } set { } }
@@ -332,21 +336,23 @@ public OleDbParameter(string name, object value) { }
         [System.ComponentModel.RefreshPropertiesAttribute(System.ComponentModel.RefreshProperties.All)]
         [System.Data.Common.DbProviderSpecificTypePropertyAttribute(true)]
         public System.Data.OleDb.OleDbType OleDbType { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public override string ParameterName { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute((byte)0)]
         public new byte Precision { get { throw null; } set { } }
         [System.ComponentModel.DefaultValueAttribute((byte)0)]
         public new byte Scale { get { throw null; } set { } }
         public override int Size { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public override string SourceColumn { get { throw null; } set { } }
         public override bool SourceColumnNullMapping { get { throw null; } set { } }
         public override System.Data.DataRowVersion SourceVersion { get { throw null; } set { } }
         [System.ComponentModel.RefreshPropertiesAttribute(System.ComponentModel.RefreshProperties.All)]
         [System.ComponentModel.TypeConverterAttribute(typeof(System.ComponentModel.StringConverter))]
-        public override object Value { get { throw null; } set { } }
+        public override object? Value { get { throw null; } set { } }
         public override void ResetDbType() { }
         public void ResetOleDbType() { }
-        object System.ICloneable.Clone() { throw null; }
+        object? System.ICloneable.Clone() { throw null; }
         public override string ToString() { throw null; }
     }
     public sealed partial class OleDbParameterCollection : System.Data.Common.DbParameterCollection
@@ -365,13 +371,13 @@ internal OleDbParameterCollection() { }
         public override object SyncRoot { get { throw null; } }
         public System.Data.OleDb.OleDbParameter Add(System.Data.OleDb.OleDbParameter value) { throw null; }
         public override int Add(object value) { throw null; }
-        public System.Data.OleDb.OleDbParameter Add(string parameterName, System.Data.OleDb.OleDbType oleDbType) { throw null; }
-        public System.Data.OleDb.OleDbParameter Add(string parameterName, System.Data.OleDb.OleDbType oleDbType, int size) { throw null; }
-        public System.Data.OleDb.OleDbParameter Add(string parameterName, System.Data.OleDb.OleDbType oleDbType, int size, string sourceColumn) { throw null; }
-        public System.Data.OleDb.OleDbParameter Add(string parameterName, object value) { throw null; }
+        public System.Data.OleDb.OleDbParameter Add(string? parameterName, System.Data.OleDb.OleDbType oleDbType) { throw null; }
+        public System.Data.OleDb.OleDbParameter Add(string? parameterName, System.Data.OleDb.OleDbType oleDbType, int size) { throw null; }
+        public System.Data.OleDb.OleDbParameter Add(string? parameterName, System.Data.OleDb.OleDbType oleDbType, int size, string? sourceColumn) { throw null; }
+        public System.Data.OleDb.OleDbParameter Add(string? parameterName, object? value) { throw null; }
         public override void AddRange(System.Array values) { }
         public void AddRange(System.Data.OleDb.OleDbParameter[] values) { }
-        public System.Data.OleDb.OleDbParameter AddWithValue(string parameterName, object value) { throw null; }
+        public System.Data.OleDb.OleDbParameter AddWithValue(string? parameterName, object? value) { throw null; }
         public override void Clear() { }
         public bool Contains(System.Data.OleDb.OleDbParameter value) { throw null; }
         public override bool Contains(object value) { throw null; }
@@ -395,15 +401,15 @@ protected override void SetParameter(string parameterName, System.Data.Common.Db
     }
     public sealed partial class OleDbRowUpdatedEventArgs : System.Data.Common.RowUpdatedEventArgs
     {
-        public OleDbRowUpdatedEventArgs(System.Data.DataRow dataRow, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) : base (default(System.Data.DataRow), default(System.Data.IDbCommand), default(System.Data.StatementType), default(System.Data.Common.DataTableMapping)) { }
-        public new System.Data.OleDb.OleDbCommand Command { get { throw null; } }
+        public OleDbRowUpdatedEventArgs(System.Data.DataRow dataRow, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) : base (default(System.Data.DataRow), default(System.Data.IDbCommand), default(System.Data.StatementType), default(System.Data.Common.DataTableMapping)) { }
+        public new System.Data.OleDb.OleDbCommand? Command { get { throw null; } }
     }
     public delegate void OleDbRowUpdatedEventHandler(object sender, System.Data.OleDb.OleDbRowUpdatedEventArgs e);
     public sealed partial class OleDbRowUpdatingEventArgs : System.Data.Common.RowUpdatingEventArgs
     {
-        public OleDbRowUpdatingEventArgs(System.Data.DataRow dataRow, System.Data.IDbCommand command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) : base (default(System.Data.DataRow), default(System.Data.IDbCommand), default(System.Data.StatementType), default(System.Data.Common.DataTableMapping)) { }
-        protected override System.Data.IDbCommand BaseCommand { get { throw null; } set { } }
-        public new System.Data.OleDb.OleDbCommand Command { get { throw null; } set { } }
+        public OleDbRowUpdatingEventArgs(System.Data.DataRow dataRow, System.Data.IDbCommand? command, System.Data.StatementType statementType, System.Data.Common.DataTableMapping tableMapping) : base (default(System.Data.DataRow), default(System.Data.IDbCommand), default(System.Data.StatementType), default(System.Data.Common.DataTableMapping)) { }
+        protected override System.Data.IDbCommand? BaseCommand { get { throw null; } set { } }
+        public new System.Data.OleDb.OleDbCommand? Command { get { throw null; } set { } }
     }
     public delegate void OleDbRowUpdatingEventHandler(object sender, System.Data.OleDb.OleDbRowUpdatingEventArgs e);
     public sealed partial class OleDbSchemaGuid
@@ -450,8 +456,8 @@ public OleDbSchemaGuid() { }
     public sealed partial class OleDbTransaction : System.Data.Common.DbTransaction
     {
         internal OleDbTransaction() { }
-        public new System.Data.OleDb.OleDbConnection Connection { get { throw null; } }
-        protected override System.Data.Common.DbConnection DbConnection { get { throw null; } }
+        public new System.Data.OleDb.OleDbConnection? Connection { get { throw null; } }
+        protected override System.Data.Common.DbConnection? DbConnection { get { throw null; } }
         public override System.Data.IsolationLevel IsolationLevel { get { throw null; } }
         public System.Data.OleDb.OleDbTransaction Begin() { throw null; }
         public System.Data.OleDb.OleDbTransaction Begin(System.Data.IsolationLevel isolevel) { throw null; }
diff --git a/src/libraries/System.Data.OleDb/ref/System.Data.OleDb.csproj b/src/libraries/System.Data.OleDb/ref/System.Data.OleDb.csproj
index 445fc32cff3d7a..912dfa3acf23f7 100644
--- a/src/libraries/System.Data.OleDb/ref/System.Data.OleDb.csproj
+++ b/src/libraries/System.Data.OleDb/ref/System.Data.OleDb.csproj
@@ -1,8 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <NoWarn>$(NoWarn);0618</NoWarn>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -13,9 +13,6 @@
     <Compile Condition="!$(TargetFramework.StartsWith('net4'))" Include="System.Data.OleDb.Manual.cs" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Data" />
     <Reference Include="System.Transactions" />
   </ItemGroup>
   <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
diff --git a/src/libraries/System.Data.OleDb/src/AdapterSwitches.cs b/src/libraries/System.Data.OleDb/src/AdapterSwitches.cs
index d8a0ac64092cdc..4ffe04c40f74af 100644
--- a/src/libraries/System.Data.OleDb/src/AdapterSwitches.cs
+++ b/src/libraries/System.Data.OleDb/src/AdapterSwitches.cs
@@ -9,13 +9,13 @@ namespace System.Data.Common
 {
     internal static class AdapterSwitches
     {
-        private static TraceSwitch _dataSchema;
+        private static TraceSwitch? _dataSchema;
 
         internal static TraceSwitch DataSchema
         {
             get
             {
-                TraceSwitch dataSchema = _dataSchema;
+                TraceSwitch? dataSchema = _dataSchema;
                 if (null == dataSchema)
                 {
                     _dataSchema = dataSchema = new TraceSwitch("Data.Schema", "Enable tracing for schema actions.");
diff --git a/src/libraries/System.Data.OleDb/src/ColumnBinding.cs b/src/libraries/System.Data.OleDb/src/ColumnBinding.cs
index 322e30c24cb30f..34334156e3e1fb 100644
--- a/src/libraries/System.Data.OleDb/src/ColumnBinding.cs
+++ b/src/libraries/System.Data.OleDb/src/ColumnBinding.cs
@@ -19,14 +19,14 @@ internal sealed class ColumnBinding
         private readonly Bindings _bindings;
 
         // unique to this ColumnBinding
-        private readonly OleDbParameter _parameter; // output value
+        private readonly OleDbParameter? _parameter; // output value
         private readonly int _parameterChangeID;
         private readonly int _offsetStatus;
         private readonly int _offsetLength;
         private readonly int _offsetValue;
 
         // Delegate ad hoc created 'Marshal.GetIDispatchForObject' reflection object cache
-        private static Func<object, IntPtr> s_getIDispatchForObject;
+        private static Func<object, IntPtr>? s_getIDispatchForObject;
 
         private readonly int _ordinal;
         private readonly int _maxLen;
@@ -42,15 +42,15 @@ internal sealed class ColumnBinding
         // unique per current input value
         private int _valueBindingOffset;
         private int _valueBindingSize;
-        internal StringMemHandle _sptr;
+        internal StringMemHandle? _sptr;
         private GCHandle _pinnedBuffer;
 
         // value is cached via property getters so the original may be released
         // for Value, ValueByteArray, ValueString, ValueVariant
-        private object _value;
+        private object? _value;
 
         internal ColumnBinding(OleDbDataReader dataReader, int index, int indexForAccessor, int indexWithinAccessor,
-                                OleDbParameter parameter, RowBinding rowbinding, Bindings bindings, tagDBBINDING binding, int offset,
+                                OleDbParameter? parameter, RowBinding rowbinding, Bindings bindings, tagDBBINDING binding, int offset,
                                 bool ifIRowsetElseIRow)
         {
             Debug.Assert(null != rowbinding, "null rowbinding");
@@ -123,7 +123,7 @@ private short DbType
 
         private Type ExpectedType
         {
-            get { return NativeDBType.FromDBType(DbType, false, false).dataType; }
+            get { return NativeDBType.FromDBType(DbType, false, false).dataType!; }
         }
 
         internal int Index
@@ -203,7 +203,7 @@ internal void ResetValue()
         {
             _value = null;
 
-            StringMemHandle sptr = _sptr;
+            StringMemHandle? sptr = _sptr;
             _sptr = null;
 
             if (null != sptr)
@@ -274,8 +274,8 @@ private void SetValueEmpty()
 
         internal object Value()
         {
-            object value = _value;
-            if (null == value)
+            object value;
+            if (null == _value)
             {
                 switch (StatusValue())
                 {
@@ -433,9 +433,9 @@ internal object Value()
                 }
                 _value = value;
             }
-            return value;
+            return _value!;
         }
-        internal void Value(object value)
+        internal void Value(object? value)
         {
             if (null == value)
             {
@@ -663,7 +663,7 @@ private byte[] Value_ByRefBYTES()
         {
             Debug.Assert(((NativeDBType.BYREF | NativeDBType.BYTES) == DbType), "Value_ByRefBYTES");
             Debug.Assert((DBStatus.S_OK == StatusValue()), "Value_ByRefBYTES");
-            byte[] value = null;
+            byte[]? value = null;
             RowBinding bindings = RowBinding;
             bool mustRelease = false;
             RuntimeHelpers.PrepareConstrainedRegions();
@@ -948,7 +948,8 @@ internal OleDbDataReader Value_HCHAPTER()
             Debug.Assert(NativeDBType.HCHAPTER == DbType, "Value_HCHAPTER");
             Debug.Assert(DBStatus.S_OK == StatusValue(), "Value_HCHAPTER");
 
-            return DataReader().ResetChapter(IndexForAccessor, IndexWithinAccessor, RowBinding, ValueOffset);
+            // TODO-NULLABLE: This shouldn't return null
+            return DataReader().ResetChapter(IndexForAccessor, IndexWithinAccessor, RowBinding, ValueOffset)!;
         }
 
         private sbyte Value_I1()
@@ -1042,15 +1043,15 @@ private void Value_IDISPATCH(object value)
             // lazy init reflection objects
             if (s_getIDispatchForObject == null)
             {
-                object delegateInstance = null;
-                MethodInfo mi = typeof(Marshal).GetMethod("GetIDispatchForObject", BindingFlags.Public | BindingFlags.Static);
+                object? delegateInstance = null;
+                MethodInfo? mi = typeof(Marshal).GetMethod("GetIDispatchForObject", BindingFlags.Public | BindingFlags.Static);
                 if (mi == null)
                 {
                     throw new NotSupportedException(SR.PlatformNotSupported_GetIDispatchForObject);
                 }
                 Volatile.Write(ref delegateInstance, mi.CreateDelegate(typeof(Func<object, IntPtr>)));
                 s_getIDispatchForObject = delegateInstance as Func<object, IntPtr>;
-                ptr = s_getIDispatchForObject(value);
+                ptr = s_getIDispatchForObject!(value);
             }
             RowBinding.WriteIntPtr(ValueOffset, ptr);
         }
@@ -1272,7 +1273,7 @@ internal bool ValueBoolean()
 
         internal byte[] ValueByteArray()
         {
-            byte[] value = (byte[])_value;
+            byte[]? value = (byte[]?)_value;
             if (null == value)
             {
                 switch (StatusValue())
@@ -1340,7 +1341,7 @@ internal byte ValueByte()
 
         internal OleDbDataReader ValueChapter()
         {
-            OleDbDataReader value = (OleDbDataReader)_value;
+            OleDbDataReader? value = (OleDbDataReader?)_value;
             if (null == value)
             {
                 switch (StatusValue())
@@ -1605,7 +1606,7 @@ internal double ValueDouble()
 
         internal string ValueString()
         {
-            string value = (string)_value;
+            string? value = (string?)_value;
             if (null == value)
             {
                 switch (StatusValue())
@@ -1652,7 +1653,7 @@ internal string ValueString()
 
         private object ValueVariant()
         {
-            object value = _value;
+            object? value = _value;
             if (null == value)
             {
                 value = Value_VARIANT();
diff --git a/src/libraries/System.Data.OleDb/src/DbBindings.cs b/src/libraries/System.Data.OleDb/src/DbBindings.cs
index 512985e4bbba72..c3802812854454 100644
--- a/src/libraries/System.Data.OleDb/src/DbBindings.cs
+++ b/src/libraries/System.Data.OleDb/src/DbBindings.cs
@@ -9,16 +9,16 @@ namespace System.Data.OleDb
 {
     internal sealed class Bindings
     {
-        private readonly tagDBPARAMBINDINFO[] _bindInfo;
+        private readonly tagDBPARAMBINDINFO[]? _bindInfo;
         private readonly tagDBBINDING[] _dbbindings;
         private readonly tagDBCOLUMNACCESS[] _dbcolumns;
 
-        private OleDbParameter[] _parameters;
+        private OleDbParameter[]? _parameters;
         private readonly int _collectionChangeID;
 
-        private OleDbDataReader _dataReader;
-        private ColumnBinding[] _columnBindings;
-        private RowBinding _rowBinding;
+        private OleDbDataReader? _dataReader;
+        private ColumnBinding[]? _columnBindings;
+        private RowBinding? _rowBinding;
 
         private int _index;
         private readonly int _count;
@@ -53,7 +53,7 @@ internal Bindings(OleDbDataReader dataReader, bool ifIRowsetElseIRow, int count)
             _ifIRowsetElseIRow = ifIRowsetElseIRow;
         }
 
-        internal tagDBPARAMBINDINFO[] BindInfo
+        internal tagDBPARAMBINDINFO[]? BindInfo
         {
             get { return _bindInfo; }
         }
@@ -84,7 +84,7 @@ internal OleDbParameter[] Parameters()
             return _parameters;
         }
 
-        internal RowBinding RowBinding()
+        internal RowBinding? RowBinding()
         {
             //Debug.Assert(null != _rowBinding, "null RowBinding");
             return _rowBinding;
@@ -102,7 +102,7 @@ internal IntPtr DataSourceType
             //get { return _bindInfo[_index].pwszDataSourceType; }
             set
             {
-                _bindInfo[_index].pwszDataSourceType = value;
+                _bindInfo![_index].pwszDataSourceType = value;
             }
         }
         internal IntPtr Name
@@ -110,7 +110,7 @@ internal IntPtr Name
             //get { return _bindInfo[_index].pwszName; }
             set
             {
-                _bindInfo[_index].pwszName = value;
+                _bindInfo![_index].pwszName = value;
             }
         }
         internal IntPtr ParamSize
@@ -125,7 +125,7 @@ internal IntPtr ParamSize
             }
             set
             {
-                _bindInfo[_index].ulParamSize = value;
+                _bindInfo![_index].ulParamSize = value;
             }
         }
         internal int Flags
@@ -133,7 +133,7 @@ internal int Flags
             //get { return _bindInfo[_index].dwFlag; }
             set
             {
-                _bindInfo[_index].dwFlags = value;
+                _bindInfo![_index].dwFlags = value;
             }
         }
 
@@ -246,7 +246,7 @@ internal byte Scale
             }
         }
 
-        internal int AllocateForAccessor(OleDbDataReader dataReader, int indexStart, int indexForAccessor)
+        internal int AllocateForAccessor(OleDbDataReader? dataReader, int indexStart, int indexForAccessor)
         {
             Debug.Assert(null == _rowBinding, "row binding already allocated");
             Debug.Assert(null == _columnBindings, "column bindings already allocated");
@@ -283,7 +283,7 @@ internal void ApplyInputParameters()
             ColumnBinding[] columnBindings = this.ColumnBindings();
             OleDbParameter[] parameters = this.Parameters();
 
-            RowBinding().StartDataBlock();
+            RowBinding()!.StartDataBlock();
             for (int i = 0; i < parameters.Length; ++i)
             {
                 if (ADP.IsDirection(parameters[i], ParameterDirection.Input))
@@ -345,7 +345,7 @@ internal bool AreParameterBindingsInvalid(OleDbParameterCollection collection)
 
         internal void CleanupBindings()
         {
-            RowBinding rowBinding = this.RowBinding();
+            RowBinding? rowBinding = this.RowBinding();
             if (null != rowBinding)
             {
                 rowBinding.ResetValues();
@@ -384,7 +384,7 @@ public void Dispose()
             _dataReader = null;
             _columnBindings = null;
 
-            RowBinding rowBinding = _rowBinding;
+            RowBinding? rowBinding = _rowBinding;
             _rowBinding = null;
             if (null != rowBinding)
             {
diff --git a/src/libraries/System.Data.OleDb/src/DbConnectionOptions.cs b/src/libraries/System.Data.OleDb/src/DbConnectionOptions.cs
index aa42ab2cb8a8fd..11c5e01bb4b5ff 100644
--- a/src/libraries/System.Data.OleDb/src/DbConnectionOptions.cs
+++ b/src/libraries/System.Data.OleDb/src/DbConnectionOptions.cs
@@ -3,6 +3,7 @@
 
 using System.Collections;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Runtime.Versioning;
 using System.Text;
@@ -96,7 +97,7 @@ private static class SYNONYM
 
         private readonly string _usersConnectionString;
         private readonly Hashtable _parsetable;
-        internal readonly NameValuePair KeyChain;
+        internal readonly NameValuePair? KeyChain;
         internal readonly bool HasPasswordKeyword;
         internal readonly bool HasUserIdKeyword;
 
@@ -117,14 +118,14 @@ private static class SYNONYM
         internal readonly bool UseOdbcRules;
 
         // called by derived classes that may cache based on connectionString
-        public DbConnectionOptions(string connectionString)
+        public DbConnectionOptions(string? connectionString)
             : this(connectionString, null, false)
         {
         }
 
         // synonyms hashtable is meant to be read-only translation of parsed string
         // keywords/synonyms to a known keyword string
-        public DbConnectionOptions(string connectionString, Hashtable synonyms, bool useOdbcRules)
+        public DbConnectionOptions(string? connectionString, Hashtable? synonyms, bool useOdbcRules)
         {
             UseOdbcRules = useOdbcRules;
             _parsetable = new Hashtable();
@@ -171,12 +172,12 @@ public bool IsEmpty
             get { return (null == KeyChain); }
         }
 
-        public string this[string keyword]
+        public string? this[string keyword]
         {
-            get { return (string)_parsetable[keyword]; }
+            get { return (string?)_parsetable[keyword]; }
         }
 
-        internal static void AppendKeyValuePairBuilder(StringBuilder builder, string keyName, string keyValue, bool useOdbcRules)
+        internal static void AppendKeyValuePairBuilder(StringBuilder builder, string keyName, string? keyValue, bool useOdbcRules)
         {
             ADP.CheckArgumentNull(builder, "builder");
             ADP.CheckArgumentLength(keyName, "keyName");
@@ -251,7 +252,7 @@ internal static void AppendKeyValuePairBuilder(StringBuilder builder, string key
 
         public bool ConvertValueToBoolean(string keyName, bool defaultValue)
         {
-            object value = _parsetable[keyName];
+            object? value = _parsetable[keyName];
             if (null == value)
             {
                 return defaultValue;
@@ -281,7 +282,7 @@ internal static bool ConvertValueToBooleanInternal(string keyName, string string
 
         public int ConvertValueToInt32(string keyName, int defaultValue)
         {
-            object value = _parsetable[keyName];
+            object? value = _parsetable[keyName];
             if (null == value)
             {
                 return defaultValue;
@@ -305,9 +306,9 @@ internal static int ConvertToInt32Internal(string keyname, string stringValue)
             }
         }
 
-        public string ConvertValueToString(string keyName, string defaultValue)
+        public string? ConvertValueToString(string keyName, string? defaultValue)
         {
-            string value = (string)_parsetable[keyName];
+            string? value = (string?)_parsetable[keyName];
             return ((null != value) ? value : defaultValue);
         }
 
@@ -330,16 +331,16 @@ protected internal virtual string Expand()
         // * this method queries "DataDirectory" value from the current AppDomain.
         //   This string is used for to replace "!DataDirectory!" values in the connection string, it is not considered as an "exposed resource".
         // * This method uses GetFullPath to validate that root path is valid, the result is not exposed out.
-        internal static string ExpandDataDirectory(string keyword, string value, ref string datadir)
+        internal static string? ExpandDataDirectory(string keyword, string? value, ref string? datadir)
         {
-            string fullPath = null;
+            string? fullPath = null;
             if ((null != value) && value.StartsWith(DataDirectory, StringComparison.OrdinalIgnoreCase))
             {
-                string rootFolderPath = datadir;
+                string? rootFolderPath = datadir;
                 if (null == rootFolderPath)
                 {
                     // find the replacement path
-                    object rootFolderObject = AppDomain.CurrentDomain.GetData("DataDirectory");
+                    object? rootFolderObject = AppDomain.CurrentDomain.GetData("DataDirectory");
                     rootFolderPath = (rootFolderObject as string);
                     if ((null != rootFolderObject) && (null == rootFolderPath))
                     {
@@ -388,16 +389,16 @@ internal static string ExpandDataDirectory(string keyword, string value, ref str
             return fullPath;
         }
 
-        internal string ExpandDataDirectories(ref string filename, ref int position)
+        internal string? ExpandDataDirectories(ref string? filename, ref int position)
         {
-            string value = null;
+            string? value = null;
             StringBuilder builder = new StringBuilder(_usersConnectionString.Length);
-            string datadir = null;
+            string? datadir = null;
 
             int copyPosition = 0;
             bool expanded = false;
 
-            for (NameValuePair current = KeyChain; null != current; current = current.Next)
+            for (NameValuePair? current = KeyChain; null != current; current = current.Next)
             {
                 value = current.Value;
 
@@ -481,11 +482,11 @@ internal string ExpandDataDirectories(ref string filename, ref int position)
         }
 
         [System.Diagnostics.Conditional("DEBUG")]
-        private static void DebugTraceKeyValuePair(string keyname, string keyvalue, Hashtable synonyms)
+        private static void DebugTraceKeyValuePair(string keyname, string? keyvalue, Hashtable? synonyms)
         {
             Debug.Assert(keyname == keyname.ToLowerInvariant(), "missing ToLower");
 
-            string realkeyname = ((null != synonyms) ? (string)synonyms[keyname] : keyname);
+            string? realkeyname = ((null != synonyms) ? (string)synonyms[keyname]! : keyname);
             if ((KEY.Password != realkeyname) && (SYNONYM.Pwd != realkeyname))
             { // don't trace passwords ever!
                 if (null != keyvalue)
@@ -543,7 +544,7 @@ private enum ParserState
             NullTermination,
         };
 
-        internal static int GetKeyValuePair(string connectionString, int currentPosition, StringBuilder buffer, bool useOdbcRules, out string keyname, out string keyvalue)
+        internal static int GetKeyValuePair(string connectionString, int currentPosition, StringBuilder buffer, bool useOdbcRules, out string? keyname, out string? keyvalue)
         {
             int startposition = currentPosition;
 
@@ -747,7 +748,7 @@ internal static int GetKeyValuePair(string connectionString, int currentPosition
             return currentPosition;
         }
 
-        private static bool IsValueValidInternal(string keyvalue)
+        private static bool IsValueValidInternal(string? keyvalue)
         {
             if (null != keyvalue)
             {
@@ -760,7 +761,7 @@ private static bool IsValueValidInternal(string keyvalue)
             return true;
         }
 
-        private static bool IsKeyNameValid(string keyname)
+        private static bool IsKeyNameValid([NotNullWhen(true)] string? keyname)
         {
             if (null != keyname)
             {
@@ -774,7 +775,7 @@ private static bool IsKeyNameValid(string keyname)
         }
 
 #if DEBUG
-        private static Hashtable SplitConnectionString(string connectionString, Hashtable synonyms, bool firstKey)
+        private static Hashtable SplitConnectionString(string connectionString, Hashtable? synonyms, bool firstKey)
         {
             Hashtable parsetable = new Hashtable();
             Regex parser = (firstKey ? ConnectionStringRegexOdbc : ConnectionStringRegex);
@@ -795,7 +796,7 @@ private static Hashtable SplitConnectionString(string connectionString, Hashtabl
                 foreach (Capture keypair in match.Groups[KeyIndex].Captures)
                 {
                     string keyname = (firstKey ? keypair.Value : keypair.Value.Replace("==", "=")).ToLowerInvariant();
-                    string keyvalue = keyvalues[indexValue++].Value;
+                    string? keyvalue = keyvalues[indexValue++].Value;
                     if (0 < keyvalue.Length)
                     {
                         if (!firstKey)
@@ -819,7 +820,7 @@ private static Hashtable SplitConnectionString(string connectionString, Hashtabl
                     }
                     DebugTraceKeyValuePair(keyname, keyvalue, synonyms);
 
-                    string realkeyname = ((null != synonyms) ? (string)synonyms[keyname] : keyname);
+                    string? realkeyname = ((null != synonyms) ? (string)synonyms[keyname]! : keyname);
                     if (!IsKeyNameValid(realkeyname))
                     {
                         throw ADP.KeywordNotSupported(keyname);
@@ -833,7 +834,7 @@ private static Hashtable SplitConnectionString(string connectionString, Hashtabl
             return parsetable;
         }
 
-        private static void ParseComparison(Hashtable parsetable, string connectionString, Hashtable synonyms, bool firstKey, Exception e)
+        private static void ParseComparison(Hashtable parsetable, string connectionString, Hashtable? synonyms, bool firstKey, Exception? e)
         {
             try
             {
@@ -841,8 +842,8 @@ private static void ParseComparison(Hashtable parsetable, string connectionStrin
                 foreach (DictionaryEntry entry in parsedvalues)
                 {
                     string keyname = (string)entry.Key;
-                    string value1 = (string)entry.Value;
-                    string value2 = (string)parsetable[keyname];
+                    string? value1 = (string?)entry.Value;
+                    string? value2 = (string?)parsetable[keyname];
                     Debug.Assert(parsetable.Contains(keyname), "ParseInternal code vs. regex mismatch keyname <" + keyname + ">");
                     Debug.Assert(value1 == value2, "ParseInternal code vs. regex mismatch keyvalue <" + value1 + "> <" + value2 + ">");
                 }
@@ -884,11 +885,11 @@ private static void ParseComparison(Hashtable parsetable, string connectionStrin
             }
         }
 #endif
-        private static NameValuePair ParseInternal(Hashtable parsetable, string connectionString, bool buildChain, Hashtable synonyms, bool firstKey)
+        private static NameValuePair? ParseInternal(Hashtable parsetable, string connectionString, bool buildChain, Hashtable? synonyms, bool firstKey)
         {
             Debug.Assert(null != connectionString, "null connectionstring");
             StringBuilder buffer = new StringBuilder();
-            NameValuePair localKeychain = null, keychain = null;
+            NameValuePair? localKeychain = null, keychain = null;
 #if DEBUG
             try
             {
@@ -899,7 +900,7 @@ private static NameValuePair ParseInternal(Hashtable parsetable, string connecti
                 {
                     int startPosition = nextStartPosition;
 
-                    string keyname, keyvalue;
+                    string? keyname, keyvalue;
                     nextStartPosition = GetKeyValuePair(connectionString, startPosition, buffer, firstKey, out keyname, out keyvalue);
                     if (ADP.IsEmpty(keyname))
                     {
@@ -912,7 +913,7 @@ private static NameValuePair ParseInternal(Hashtable parsetable, string connecti
                     Debug.Assert(IsKeyNameValid(keyname), "ParseFailure, invalid keyname");
                     Debug.Assert(IsValueValidInternal(keyvalue), "parse failure, invalid keyvalue");
 #endif
-                    string realkeyname = ((null != synonyms) ? (string)synonyms[keyname] : keyname);
+                    string? realkeyname = ((null != synonyms) ? (string)synonyms[keyname]! : keyname);
                     if (!IsKeyNameValid(realkeyname))
                     {
                         throw ADP.KeywordNotSupported(keyname);
@@ -943,13 +944,13 @@ private static NameValuePair ParseInternal(Hashtable parsetable, string connecti
             return keychain;
         }
 
-        internal NameValuePair ReplacePasswordPwd(out string constr, bool fakePassword)
+        internal NameValuePair? ReplacePasswordPwd(out string constr, bool fakePassword)
         {
             bool expanded = false;
             int copyPosition = 0;
-            NameValuePair head = null, tail = null, next = null;
+            NameValuePair? head = null, tail = null, next = null;
             StringBuilder builder = new StringBuilder(_usersConnectionString.Length);
-            for (NameValuePair current = KeyChain; null != current; current = current.Next)
+            for (NameValuePair? current = KeyChain; null != current; current = current.Next)
             {
                 if ((KEY.Password != current.Name) && (SYNONYM.Pwd != current.Name))
                 {
diff --git a/src/libraries/System.Data.OleDb/src/DbConnectionStringCommon.cs b/src/libraries/System.Data.OleDb/src/DbConnectionStringCommon.cs
index 9ee6aded022f6d..9477bb47b6cb11 100644
--- a/src/libraries/System.Data.OleDb/src/DbConnectionStringCommon.cs
+++ b/src/libraries/System.Data.OleDb/src/DbConnectionStringCommon.cs
@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 
 namespace System.Data.Common
@@ -111,7 +112,7 @@ public K Current
                 }
             }
 
-            object System.Collections.IEnumerator.Current
+            object? System.Collections.IEnumerator.Current
             {
                 get
                 {
@@ -131,7 +132,7 @@ internal static class DbConnectionStringBuilderUtil
         internal static bool ConvertToBoolean(object value)
         {
             Debug.Assert(null != value, "ConvertToBoolean(null)");
-            string svalue = (value as string);
+            string? svalue = (value as string);
             if (null != svalue)
             {
                 if (StringComparer.OrdinalIgnoreCase.Equals(svalue, "true") || StringComparer.OrdinalIgnoreCase.Equals(svalue, "yes"))
diff --git a/src/libraries/System.Data.OleDb/src/DbParameterHelper.cs b/src/libraries/System.Data.OleDb/src/DbParameterHelper.cs
index a78b359f304a8d..a89572d1f606a0 100644
--- a/src/libraries/System.Data.OleDb/src/DbParameterHelper.cs
+++ b/src/libraries/System.Data.OleDb/src/DbParameterHelper.cs
@@ -3,24 +3,25 @@
 
 using System.ComponentModel;
 using System.Data.Common;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Data.OleDb
 {
     public sealed partial class OleDbParameter : DbParameter
     { // V1.2.3300
-        private object _value;
+        private object? _value;
 
-        private object _parent;
+        private object? _parent;
 
         private ParameterDirection _direction;
         private int _size;
-        private string _sourceColumn;
+        private string? _sourceColumn;
         private DataRowVersion _sourceVersion;
         private bool _sourceColumnNullMapping;
 
         private bool _isNullable;
 
-        private object _coercedValue;
+        private object? _coercedValue;
 
         private OleDbParameter(OleDbParameter source) : this()
         { // V1.2.3300, Clone
@@ -28,14 +29,14 @@ private OleDbParameter(OleDbParameter source) : this()
 
             source.CloneHelper(this);
 
-            ICloneable cloneable = (_value as ICloneable);
+            ICloneable? cloneable = (_value as ICloneable);
             if (null != cloneable)
             {
                 _value = cloneable.Clone();
             }
         }
 
-        private object CoercedValue
+        private object? CoercedValue
         { // V1.2.3300
             get
             {
@@ -134,11 +135,12 @@ private bool ShouldSerializeSize()
             return (0 != _size);
         }
 
+        [AllowNull]
         public override string SourceColumn
         { // V1.2.3300, XXXParameter V1.0.3300
             get
             {
-                string sourceColumn = _sourceColumn;
+                string? sourceColumn = _sourceColumn;
                 return ((null != sourceColumn) ? sourceColumn : string.Empty);
             }
             set
@@ -200,13 +202,13 @@ internal void CopyTo(DbParameter destination)
             CloneHelper((OleDbParameter)destination);
         }
 
-        internal object CompareExchangeParent(object value, object comparand)
+        internal object? CompareExchangeParent(object? value, object? comparand)
         {
             // the interlock guarantees same parameter won't belong to multiple collections
             // at the same time, but to actually occur the user must really try
             // since we never declared thread safety, we don't care at this time
             //return System.Threading.Interlocked.CompareExchange(ref _parent, value, comparand);
-            object parent = _parent;
+            object? parent = _parent;
             if (comparand == parent)
             {
                 _parent = value;
@@ -224,7 +226,7 @@ public override string ToString()
             return ParameterName;
         }
 
-        private byte ValuePrecisionCore(object value)
+        private byte ValuePrecisionCore(object? value)
         { // V1.2.3300
             if (value is decimal)
             {
@@ -233,7 +235,7 @@ private byte ValuePrecisionCore(object value)
             return 0;
         }
 
-        private byte ValueScaleCore(object value)
+        private byte ValueScaleCore(object? value)
         { // V1.2.3300
             if (value is decimal)
             {
@@ -242,21 +244,21 @@ private byte ValueScaleCore(object value)
             return 0;
         }
 
-        private int ValueSizeCore(object value)
+        private int ValueSizeCore(object? value)
         { // V1.2.3300
             if (!ADP.IsNull(value))
             {
-                string svalue = (value as string);
+                string? svalue = (value as string);
                 if (null != svalue)
                 {
                     return svalue.Length;
                 }
-                byte[] bvalue = (value as byte[]);
+                byte[]? bvalue = (value as byte[]);
                 if (null != bvalue)
                 {
                     return bvalue.Length;
                 }
-                char[] cvalue = (value as char[]);
+                char[]? cvalue = (value as char[]);
                 if (null != cvalue)
                 {
                     return cvalue.Length;
diff --git a/src/libraries/System.Data.OleDb/src/DbPropSet.cs b/src/libraries/System.Data.OleDb/src/DbPropSet.cs
index b4fb008c499f12..30935b1c6f80dd 100644
--- a/src/libraries/System.Data.OleDb/src/DbPropSet.cs
+++ b/src/libraries/System.Data.OleDb/src/DbPropSet.cs
@@ -14,7 +14,7 @@ internal sealed class DBPropSet : SafeHandle
         private readonly int propertySetCount;
 
         // stores the exception with last error.HRESULT from IDBProperties.GetProperties
-        private Exception lastErrorFromProvider;
+        private Exception? lastErrorFromProvider;
 
         private DBPropSet() : base(IntPtr.Zero, true)
         {
@@ -42,7 +42,7 @@ internal DBPropSet(int propertysetCount) : this()
             }
         }
 
-        internal DBPropSet(UnsafeNativeMethods.IDBProperties properties, PropertyIDSet propidset, out OleDbHResult hr) : this()
+        internal DBPropSet(UnsafeNativeMethods.IDBProperties properties, PropertyIDSet? propidset, out OleDbHResult hr) : this()
         {
             Debug.Assert(null != properties, "null IDBProperties");
 
@@ -60,7 +60,7 @@ internal DBPropSet(UnsafeNativeMethods.IDBProperties properties, PropertyIDSet p
             }
         }
 
-        internal DBPropSet(UnsafeNativeMethods.IRowsetInfo properties, PropertyIDSet propidset, out OleDbHResult hr) : this()
+        internal DBPropSet(UnsafeNativeMethods.IRowsetInfo properties, PropertyIDSet? propidset, out OleDbHResult hr) : this()
         {
             Debug.Assert(null != properties, "null IRowsetInfo");
 
@@ -78,7 +78,7 @@ internal DBPropSet(UnsafeNativeMethods.IRowsetInfo properties, PropertyIDSet pro
             }
         }
 
-        internal DBPropSet(UnsafeNativeMethods.ICommandProperties properties, PropertyIDSet propidset, out OleDbHResult hr) : this()
+        internal DBPropSet(UnsafeNativeMethods.ICommandProperties properties, PropertyIDSet? propidset, out OleDbHResult hr) : this()
         {
             Debug.Assert(null != properties, "null ICommandProperties");
 
@@ -99,7 +99,7 @@ internal DBPropSet(UnsafeNativeMethods.ICommandProperties properties, PropertyID
         private void SetLastErrorInfo(OleDbHResult lastErrorHr)
         {
             // note: OleDbHResult is actually a simple wrapper over HRESULT with OLEDB-specific codes
-            UnsafeNativeMethods.IErrorInfo errorInfo = null;
+            UnsafeNativeMethods.IErrorInfo? errorInfo = null;
             string message = string.Empty;
 
             OleDbHResult errorInfoHr = UnsafeNativeMethods.GetErrorInfo(0, out errorInfo);  // 0 - IErrorInfo exists, 1 - no IErrorInfo
@@ -172,7 +172,7 @@ internal ItagDBPROP[] GetPropertySet(int index, out Guid propertyset)
             }
 
             tagDBPROPSET propset = new tagDBPROPSET();
-            ItagDBPROP[] properties = null;
+            ItagDBPROP[]? properties = null;
 
             bool mustRelease = false;
             RuntimeHelpers.PrepareConstrainedRegions();
diff --git a/src/libraries/System.Data.OleDb/src/NativeMethods.cs b/src/libraries/System.Data.OleDb/src/NativeMethods.cs
index 871ae1bb7de9b6..6592ed5df3b5a3 100644
--- a/src/libraries/System.Data.OleDb/src/NativeMethods.cs
+++ b/src/libraries/System.Data.OleDb/src/NativeMethods.cs
@@ -27,7 +27,7 @@ internal interface ITransactionJoin
             int GetOptionsObject(IntPtr ppOptions);
 
             void JoinTransaction(
-                [In, MarshalAs(UnmanagedType.Interface)] object punkTransactionCoord,
+                [In, MarshalAs(UnmanagedType.Interface)] object? punkTransactionCoord,
                 [In] int isoLevel,
                 [In] int isoFlags,
                 [In] IntPtr pOtherOptions);
diff --git a/src/libraries/System.Data.OleDb/src/OleDbCommand.cs b/src/libraries/System.Data.OleDb/src/OleDbCommand.cs
index ced289c042f768..458335b605ac28 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbCommand.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbCommand.cs
@@ -4,6 +4,7 @@
 using System.ComponentModel;
 using System.Data.Common;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Text;
@@ -11,27 +12,28 @@
 
 namespace System.Data.OleDb
 {
+    [Designer("Microsoft.VSDesigner.Data.VS.OleDbCommandDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public sealed class OleDbCommand : DbCommand, ICloneable, IDbCommand
     {
         // command data
-        private string _commandText;
+        private string? _commandText;
         private CommandType _commandType;
         private int _commandTimeout = ADP.DefaultCommandTimeout;
         private UpdateRowSource _updatedRowSource = UpdateRowSource.Both;
         private bool _designTimeInvisible;
-        private OleDbConnection _connection;
-        private OleDbTransaction _transaction;
+        private OleDbConnection? _connection;
+        private OleDbTransaction? _transaction;
 
-        private OleDbParameterCollection _parameters;
+        private OleDbParameterCollection? _parameters;
 
         // native information
-        private UnsafeNativeMethods.ICommandText _icommandText;
+        private UnsafeNativeMethods.ICommandText? _icommandText;
 
         // if executing with a different CommandBehavior.KeyInfo behavior
         // original ICommandText must be released and a new ICommandText generated
         private CommandBehavior commandBehavior;
 
-        private Bindings _dbBindings;
+        private Bindings? _dbBindings;
 
         internal bool canceling;
         private bool _isPrepared;
@@ -48,18 +50,18 @@ public OleDbCommand() : base()
             GC.SuppressFinalize(this);
         }
 
-        public OleDbCommand(string cmdText) : this()
+        public OleDbCommand(string? cmdText) : this()
         {
             CommandText = cmdText;
         }
 
-        public OleDbCommand(string cmdText, OleDbConnection connection) : this()
+        public OleDbCommand(string? cmdText, OleDbConnection? connection) : this()
         {
             CommandText = cmdText;
             Connection = connection;
         }
 
-        public OleDbCommand(string cmdText, OleDbConnection connection, OleDbTransaction transaction) : this()
+        public OleDbCommand(string? cmdText, OleDbConnection? connection, OleDbTransaction? transaction) : this()
         {
             CommandText = cmdText;
             Connection = connection;
@@ -79,11 +81,11 @@ private OleDbCommand(OleDbCommand from) : this()
             OleDbParameterCollection parameters = Parameters;
             foreach (object parameter in from.Parameters)
             {
-                parameters.Add((parameter is ICloneable) ? (parameter as ICloneable).Clone() : parameter);
+                parameters.Add(parameter is ICloneable cloneableParameter ? cloneableParameter.Clone() : parameter);
             }
         }
 
-        private Bindings ParameterBindings
+        private Bindings? ParameterBindings
         {
             get
             {
@@ -91,7 +93,7 @@ private Bindings ParameterBindings
             }
             set
             {
-                Bindings bindings = _dbBindings;
+                Bindings? bindings = _dbBindings;
                 _dbBindings = value;
                 if ((null != bindings) && (value != bindings))
                 {
@@ -102,11 +104,12 @@ private Bindings ParameterBindings
 
         [DefaultValue("")]
         [RefreshProperties(RefreshProperties.All)]
+        [AllowNull]
         public override string CommandText
         {
             get
             {
-                string value = _commandText;
+                string? value = _commandText;
                 return ((null != value) ? value : string.Empty);
             }
             set
@@ -174,7 +177,7 @@ public override CommandType CommandType
         }
 
         [DefaultValue(null)]
-        public new OleDbConnection Connection
+        public new OleDbConnection? Connection
         {
             get
             {
@@ -182,7 +185,7 @@ public override CommandType CommandType
             }
             set
             {
-                OleDbConnection connection = _connection;
+                OleDbConnection? connection = _connection;
                 if (value != connection)
                 {
                     PropertyChanging();
@@ -200,7 +203,7 @@ public override CommandType CommandType
 
         private void ResetConnection()
         {
-            OleDbConnection connection = _connection;
+            OleDbConnection? connection = _connection;
             if (null != connection)
             {
                 PropertyChanging();
@@ -214,7 +217,7 @@ private void ResetConnection()
             _connection = null;
         }
 
-        protected override DbConnection DbConnection
+        protected override DbConnection? DbConnection
         { // V1.2.3300
             get
             {
@@ -222,7 +225,7 @@ protected override DbConnection DbConnection
             }
             set
             {
-                Connection = (OleDbConnection)value;
+                Connection = (OleDbConnection?)value;
             }
         }
 
@@ -234,7 +237,7 @@ protected override DbParameterCollection DbParameterCollection
             }
         }
 
-        protected override DbTransaction DbTransaction
+        protected override DbTransaction? DbTransaction
         { // V1.2.3300
             get
             {
@@ -242,7 +245,7 @@ protected override DbTransaction DbTransaction
             }
             set
             {
-                Transaction = (OleDbTransaction)value;
+                Transaction = (OleDbTransaction?)value;
             }
         }
 
@@ -276,7 +279,7 @@ public override bool DesignTimeVisible
         {
             get
             {
-                OleDbParameterCollection value = _parameters;
+                OleDbParameterCollection? value = _parameters;
                 if (null == value)
                 {
                     // delay the creation of the OleDbParameterCollection
@@ -290,7 +293,7 @@ public override bool DesignTimeVisible
 
         private bool HasParameters()
         {
-            OleDbParameterCollection value = _parameters;
+            OleDbParameterCollection? value = _parameters;
             return (null != value) && (0 < value.Count);
         }
 
@@ -298,13 +301,13 @@ private bool HasParameters()
         Browsable(false),
         DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden),
         ]
-        public new OleDbTransaction Transaction
+        public new OleDbTransaction? Transaction
         {
             get
             {
                 // find the last non-zombied local transaction object, but not transactions
                 // that may have been started after the current local transaction
-                OleDbTransaction transaction = _transaction;
+                OleDbTransaction? transaction = _transaction;
                 while ((null != transaction) && (null == transaction.Connection))
                 {
                     transaction = transaction.Parent;
@@ -358,20 +361,20 @@ internal UnsafeNativeMethods.ICommandProperties ICommandProperties()
         }
 
         // optional interface, unsafe cast
-        private UnsafeNativeMethods.ICommandPrepare ICommandPrepare()
+        private UnsafeNativeMethods.ICommandPrepare? ICommandPrepare()
         {
             Debug.Assert(null != _icommandText, "ICommandPrepare: null ICommandText");
-            return (_icommandText as UnsafeNativeMethods.ICommandPrepare);
+            return _icommandText as UnsafeNativeMethods.ICommandPrepare;
         }
 
         // optional interface, unsafe cast
         private UnsafeNativeMethods.ICommandWithParameters ICommandWithParameters()
         {
             Debug.Assert(null != _icommandText, "ICommandWithParameters: null ICommandText");
-            UnsafeNativeMethods.ICommandWithParameters value = (_icommandText as UnsafeNativeMethods.ICommandWithParameters);
+            UnsafeNativeMethods.ICommandWithParameters? value = (_icommandText as UnsafeNativeMethods.ICommandWithParameters);
             if (null == value)
             {
-                throw ODB.NoProviderSupportForParameters(_connection.Provider, (Exception)null);
+                throw ODB.NoProviderSupportForParameters(_connection!.Provider, null);
             }
             return value;
         }
@@ -385,7 +388,7 @@ private void CreateAccessor()
             // do this first in-case the command doesn't support parameters
             UnsafeNativeMethods.ICommandWithParameters commandWithParameters = ICommandWithParameters();
 
-            OleDbParameterCollection collection = _parameters;
+            OleDbParameterCollection collection = _parameters!;
             OleDbParameter[] parameters = new OleDbParameter[collection.Count];
             collection.CopyTo(parameters, 0);
 
@@ -399,7 +402,7 @@ private void CreateAccessor()
 
             bindings.AllocateForAccessor(null, 0, 0);
 
-            ApplyParameterBindings(commandWithParameters, bindings.BindInfo);
+            ApplyParameterBindings(commandWithParameters, bindings.BindInfo!);
 
             UnsafeNativeMethods.IAccessor iaccessor = IAccessor();
             OleDbHResult hr = bindings.CreateAccessor(iaccessor, ODB.DBACCESSOR_PARAMETERDATA);
@@ -454,7 +457,7 @@ public override void Cancel()
             unchecked
             { _changeID++; }
 
-            UnsafeNativeMethods.ICommandText icmdtxt = _icommandText;
+            UnsafeNativeMethods.ICommandText? icmdtxt = _icommandText;
             if (null != icmdtxt)
             {
                 OleDbHResult hr = OleDbHResult.S_OK;
@@ -516,7 +519,7 @@ internal void CloseInternal()
         // may be called from either
         //      OleDbDataReader.Close/Dispose
         //      via OleDbCommand.Dispose or OleDbConnection.Close
-        internal void CloseFromDataReader(Bindings bindings)
+        internal void CloseFromDataReader(Bindings? bindings)
         {
             if (null != bindings)
             {
@@ -541,7 +544,7 @@ private void CloseInternalCommand()
             this.commandBehavior = CommandBehavior.Default;
             _isPrepared = false;
 
-            UnsafeNativeMethods.ICommandText ict = Interlocked.Exchange<UnsafeNativeMethods.ICommandText>(ref _icommandText, null);
+            UnsafeNativeMethods.ICommandText? ict = Interlocked.Exchange(ref _icommandText, null);
             if (null != ict)
             {
                 lock (ict)
@@ -554,7 +557,7 @@ private void CloseInternalCommand()
         private void CloseInternalParameters()
         {
             Debug.Assert(null != _connection, "no connection, CloseInternalParameters");
-            Bindings bindings = _dbBindings;
+            Bindings? bindings = _dbBindings;
             _dbBindings = null;
             if (null != bindings)
             {
@@ -606,7 +609,7 @@ IDataReader IDbCommand.ExecuteReader()
         public new OleDbDataReader ExecuteReader(CommandBehavior behavior)
         {
             _executeQuery = true;
-            return ExecuteReaderInternal(behavior, ADP.ExecuteReader);
+            return ExecuteReaderInternal(behavior, ADP.ExecuteReader)!;
         }
 
         IDataReader IDbCommand.ExecuteReader(CommandBehavior behavior)
@@ -619,10 +622,10 @@ protected override DbDataReader ExecuteDbDataReader(CommandBehavior behavior)
             return ExecuteReader(behavior);
         }
 
-        private OleDbDataReader ExecuteReaderInternal(CommandBehavior behavior, string method)
+        private OleDbDataReader? ExecuteReaderInternal(CommandBehavior behavior, string method)
         {
-            OleDbDataReader dataReader = null;
-            OleDbException nextResultsFailure = null;
+            OleDbDataReader? dataReader = null;
+            OleDbException? nextResultsFailure = null;
             int state = ODB.InternalStateClosed;
             try
             {
@@ -634,7 +637,7 @@ private OleDbDataReader ExecuteReaderInternal(CommandBehavior behavior, string m
                     behavior |= CommandBehavior.SingleResult;
                 }
 
-                object executeResult;
+                object? executeResult;
                 int resultType;
 
                 switch (CommandType)
@@ -657,7 +660,7 @@ private OleDbDataReader ExecuteReaderInternal(CommandBehavior behavior, string m
                 {
                     try
                     {
-                        dataReader = new OleDbDataReader(_connection, this, 0, this.commandBehavior);
+                        dataReader = new OleDbDataReader(_connection!, this, 0, this.commandBehavior);
 
                         switch (resultType)
                         {
@@ -679,7 +682,7 @@ private OleDbDataReader ExecuteReaderInternal(CommandBehavior behavior, string m
                                 {
                                     PrepareCommandText(2);
                                 }
-                                OleDbDataReader.GenerateSchemaTable(dataReader, _icommandText, behavior);
+                                OleDbDataReader.GenerateSchemaTable(dataReader, _icommandText!, behavior);
                                 break;
                             default:
                                 Debug.Assert(false, "ExecuteReaderInternal: unknown result type");
@@ -687,7 +690,7 @@ private OleDbDataReader ExecuteReaderInternal(CommandBehavior behavior, string m
                         }
                         executeResult = null;
                         _hasDataReader = true;
-                        _connection.AddWeakReference(dataReader, OleDbReferenceCollection.DataReaderTag);
+                        _connection!.AddWeakReference(dataReader, OleDbReferenceCollection.DataReaderTag);
 
                         // command stays in the executing state until the connection
                         // has a datareader to track for it being closed
@@ -713,10 +716,10 @@ private OleDbDataReader ExecuteReaderInternal(CommandBehavior behavior, string m
                     {
                         if (ODB.ExecutedIMultipleResults == resultType)
                         {
-                            UnsafeNativeMethods.IMultipleResults multipleResults = (UnsafeNativeMethods.IMultipleResults)executeResult;
+                            UnsafeNativeMethods.IMultipleResults? multipleResults = (UnsafeNativeMethods.IMultipleResults?)executeResult;
 
                             // may cause a Connection.ResetState which closes connection
-                            nextResultsFailure = OleDbDataReader.NextResults(multipleResults, _connection, this, out _recordsAffected);
+                            nextResultsFailure = OleDbDataReader.NextResults(multipleResults, _connection!, this, out _recordsAffected);
                         }
                     }
                     finally
@@ -782,7 +785,7 @@ private OleDbDataReader ExecuteReaderInternal(CommandBehavior behavior, string m
             return dataReader;
         }
 
-        private int ExecuteCommand(CommandBehavior behavior, out object executeResult)
+        private int ExecuteCommand(CommandBehavior behavior, out object? executeResult)
         {
             if (InitializeCommand(behavior, false))
             {
@@ -802,19 +805,20 @@ private int ExecuteCommand(CommandBehavior behavior, out object executeResult)
         private int ExecuteCommandText(out object executeResult)
         {
             int retcode;
-            tagDBPARAMS dbParams = null;
-            RowBinding rowbinding = null;
-            Bindings bindings = ParameterBindings;
+            tagDBPARAMS? dbParams = null;
+            RowBinding? rowbinding = null;
+            Bindings? bindings = ParameterBindings;
             bool mustRelease = false;
 
             RuntimeHelpers.PrepareConstrainedRegions();
             try
             {
+                // TODO-NULLABLE: Code below seems to assume that bindings will always be non-null
                 if (null != bindings)
                 { // parameters may be suppressed
                     rowbinding = bindings.RowBinding();
 
-                    rowbinding.DangerousAddRef(ref mustRelease);
+                    rowbinding!.DangerousAddRef(ref mustRelease);
 
                     // bindings can't be released until after last rowset is released
                     // that is when output parameters are populated
@@ -826,24 +830,24 @@ private int ExecuteCommandText(out object executeResult)
                     dbParams.cParamSets = 1;
                     dbParams.hAccessor = rowbinding.DangerousGetAccessorHandle();
                 }
-                if ((0 == (CommandBehavior.SingleResult & this.commandBehavior)) && _connection.SupportMultipleResults())
+                if ((0 == (CommandBehavior.SingleResult & this.commandBehavior)) && _connection!.SupportMultipleResults())
                 {
-                    retcode = ExecuteCommandTextForMultpleResults(dbParams, out executeResult);
+                    retcode = ExecuteCommandTextForMultpleResults(dbParams!, out executeResult);
                 }
                 else if (0 == (CommandBehavior.SingleRow & this.commandBehavior) || !_executeQuery)
                 {
-                    retcode = ExecuteCommandTextForSingleResult(dbParams, out executeResult);
+                    retcode = ExecuteCommandTextForSingleResult(dbParams!, out executeResult);
                 }
                 else
                 {
-                    retcode = ExecuteCommandTextForSingleRow(dbParams, out executeResult);
+                    retcode = ExecuteCommandTextForSingleRow(dbParams!, out executeResult);
                 }
             }
             finally
             {
                 if (mustRelease)
                 {
-                    rowbinding.DangerousRelease();
+                    rowbinding!.DangerousRelease();
                 }
             }
             return retcode;
@@ -853,7 +857,7 @@ private int ExecuteCommandTextForMultpleResults(tagDBPARAMS dbParams, out object
         {
             Debug.Assert(0 == (CommandBehavior.SingleRow & this.commandBehavior), "SingleRow implies SingleResult");
             OleDbHResult hr;
-            hr = _icommandText.Execute(ADP.PtrZero, ref ODB.IID_IMultipleResults, dbParams, out _recordsAffected, out executeResult);
+            hr = _icommandText!.Execute(ADP.PtrZero, ref ODB.IID_IMultipleResults, dbParams, out _recordsAffected, out executeResult);
 
             if (OleDbHResult.E_NOINTERFACE != hr)
             {
@@ -871,11 +875,11 @@ private int ExecuteCommandTextForSingleResult(tagDBPARAMS dbParams, out object e
             // (Microsoft.Jet.OLEDB.4.0 returns 0 for recordsAffected instead of -1)
             if (_executeQuery)
             {
-                hr = _icommandText.Execute(ADP.PtrZero, ref ODB.IID_IRowset, dbParams, out _recordsAffected, out executeResult);
+                hr = _icommandText!.Execute(ADP.PtrZero, ref ODB.IID_IRowset, dbParams, out _recordsAffected, out executeResult);
             }
             else
             {
-                hr = _icommandText.Execute(ADP.PtrZero, ref ODB.IID_NULL, dbParams, out _recordsAffected, out executeResult);
+                hr = _icommandText!.Execute(ADP.PtrZero, ref ODB.IID_NULL, dbParams, out _recordsAffected, out executeResult);
             }
             ExecuteCommandTextErrorHandling(hr);
             return ODB.ExecutedIRowset;
@@ -885,10 +889,10 @@ private int ExecuteCommandTextForSingleRow(tagDBPARAMS dbParams, out object exec
         {
             Debug.Assert(_executeQuery, "ExecuteNonQuery should always use ExecuteCommandTextForSingleResult");
 
-            if (_connection.SupportIRow(this))
+            if (_connection!.SupportIRow(this))
             {
                 OleDbHResult hr;
-                hr = _icommandText.Execute(ADP.PtrZero, ref ODB.IID_IRow, dbParams, out _recordsAffected, out executeResult);
+                hr = _icommandText!.Execute(ADP.PtrZero, ref ODB.IID_IRow, dbParams, out _recordsAffected, out executeResult);
 
                 if (OleDbHResult.DB_E_NOTFOUND == hr)
                 {
@@ -907,7 +911,7 @@ private int ExecuteCommandTextForSingleRow(tagDBPARAMS dbParams, out object exec
 
         private void ExecuteCommandTextErrorHandling(OleDbHResult hr)
         {
-            Exception e = OleDbConnection.ProcessResults(hr, _connection, this);
+            Exception? e = OleDbConnection.ProcessResults(hr, _connection, this);
             if (null != e)
             {
                 e = ExecuteCommandTextSpecialErrorHandling(hr, e);
@@ -927,7 +931,7 @@ private Exception ExecuteCommandTextSpecialErrorHandling(OleDbHResult hr, Except
                 Debug.Assert(null != e, "missing inner exception");
 
                 StringBuilder builder = new StringBuilder();
-                ParameterBindings.ParameterStatus(builder);
+                ParameterBindings!.ParameterStatus(builder);
                 e = ODB.CommandParameterStatus(builder.ToString(), e);
             }
             return e;
@@ -940,11 +944,11 @@ public override int ExecuteNonQuery()
             return ADP.IntPtrToInt32(_recordsAffected);
         }
 
-        public override object ExecuteScalar()
+        public override object? ExecuteScalar()
         {
-            object value = null;
+            object? value = null;
             _executeQuery = true;
-            using (OleDbDataReader reader = ExecuteReaderInternal(CommandBehavior.Default, ADP.ExecuteScalar))
+            using (OleDbDataReader reader = ExecuteReaderInternal(CommandBehavior.Default, ADP.ExecuteScalar)!)
             {
                 if (reader.Read() && (0 < reader.FieldCount))
                 {
@@ -954,14 +958,14 @@ public override object ExecuteScalar()
             return value;
         }
 
-        private int ExecuteTableDirect(CommandBehavior behavior, out object executeResult)
+        private int ExecuteTableDirect(CommandBehavior behavior, out object? executeResult)
         {
             this.commandBehavior = behavior;
             executeResult = null;
 
             OleDbHResult hr = OleDbHResult.S_OK;
 
-            StringMemHandle sptr = null;
+            StringMemHandle? sptr = null;
             bool mustReleaseStringHandle = false;
 
             RuntimeHelpers.PrepareConstrainedRegions();
@@ -978,9 +982,9 @@ private int ExecuteTableDirect(CommandBehavior behavior, out object executeResul
                     tableID.eKind = ODB.DBKIND_NAME;
                     tableID.ulPropid = sptr.DangerousGetHandle();
 
-                    using (IOpenRowsetWrapper iopenRowset = _connection.IOpenRowset())
+                    using (IOpenRowsetWrapper iopenRowset = _connection!.IOpenRowset())
                     {
-                        using (DBPropSet propSet = CommandPropertySets())
+                        using (DBPropSet? propSet = CommandPropertySets())
                         {
                             if (null != propSet)
                             {
@@ -1016,7 +1020,7 @@ private int ExecuteTableDirect(CommandBehavior behavior, out object executeResul
             {
                 if (mustReleaseStringHandle)
                 {
-                    sptr.DangerousRelease();
+                    sptr!.DangerousRelease();
                 }
             }
             ProcessResults(hr);
@@ -1118,7 +1122,7 @@ private string ExpandStoredProcedureToText(string sproctext)
 
         private void ParameterCleanup()
         {
-            Bindings bindings = ParameterBindings;
+            Bindings? bindings = ParameterBindings;
             if (null != bindings)
             {
                 bindings.CleanupBindings();
@@ -1143,7 +1147,7 @@ private bool InitializeCommand(CommandBehavior behavior, bool throwifnotsupporte
                 return false;
             }
 
-            if ((null != _dbBindings) && _dbBindings.AreParameterBindingsInvalid(_parameters))
+            if ((null != _dbBindings) && _dbBindings.AreParameterBindingsInvalid(_parameters!))
             {
                 CloseInternalParameters();
             }
@@ -1163,7 +1167,7 @@ private bool InitializeCommand(CommandBehavior behavior, bool throwifnotsupporte
 
                 string commandText = ExpandCommandText();
 
-                hr = _icommandText.SetCommandText(ref ODB.DBGUID_DEFAULT, commandText);
+                hr = _icommandText!.SetCommandText(ref ODB.DBGUID_DEFAULT, commandText);
 
                 if (hr < 0)
                 {
@@ -1199,7 +1203,7 @@ public override void Prepare()
 
         private void PrepareCommandText(int expectedExecutionCount)
         {
-            OleDbParameterCollection parameters = _parameters;
+            OleDbParameterCollection? parameters = _parameters;
             if (null != parameters)
             {
                 foreach (OleDbParameter parameter in parameters)
@@ -1213,7 +1217,7 @@ private void PrepareCommandText(int expectedExecutionCount)
                     }
                 }
             }
-            UnsafeNativeMethods.ICommandPrepare icommandPrepare = ICommandPrepare();
+            UnsafeNativeMethods.ICommandPrepare? icommandPrepare = ICommandPrepare();
             if (null != icommandPrepare)
             {
                 OleDbHResult hr;
@@ -1228,19 +1232,19 @@ private void PrepareCommandText(int expectedExecutionCount)
 
         private void ProcessResults(OleDbHResult hr)
         {
-            Exception e = OleDbConnection.ProcessResults(hr, _connection, this);
+            Exception? e = OleDbConnection.ProcessResults(hr, _connection, this);
             if (null != e)
             { throw e; }
         }
 
         private void ProcessResultsNoReset(OleDbHResult hr)
         {
-            Exception e = OleDbConnection.ProcessResults(hr, null, this);
+            Exception? e = OleDbConnection.ProcessResults(hr, null, this);
             if (null != e)
             { throw e; }
         }
 
-        internal object GetPropertyValue(Guid propertySet, int propertyID)
+        internal object? GetPropertyValue(Guid propertySet, int propertyID)
         {
             if (null != _icommandText)
             {
@@ -1272,6 +1276,8 @@ internal object GetPropertyValue(Guid propertySet, int propertyID)
 
         private bool PropertiesOnCommand(bool throwNotSupported)
         {
+            Debug.Assert(_connection != null);
+
             if (null != _icommandText)
             {
                 return true;
@@ -1279,10 +1285,7 @@ private bool PropertiesOnCommand(bool throwNotSupported)
             Debug.Assert(!_isPrepared, "null command isPrepared");
 
             OleDbConnection connection = _connection;
-            if (null == connection)
-            {
-                connection.CheckStateOpen(ODB.Properties);
-            }
+            connection.CheckStateOpen(ODB.Properties);
             if (!_trackingForClose)
             {
                 _trackingForClose = true;
@@ -1299,7 +1302,7 @@ private bool PropertiesOnCommand(bool throwNotSupported)
                 return false;
             }
 
-            using (DBPropSet propSet = CommandPropertySets())
+            using (DBPropSet? propSet = CommandPropertySets())
             {
                 if (null != propSet)
                 {
@@ -1315,9 +1318,9 @@ private bool PropertiesOnCommand(bool throwNotSupported)
             return true;
         }
 
-        private DBPropSet CommandPropertySets()
+        private DBPropSet? CommandPropertySets()
         {
-            DBPropSet propSet = null;
+            DBPropSet? propSet = null;
 
             bool keyInfo = (0 != (CommandBehavior.KeyInfo & this.commandBehavior));
 
@@ -1351,9 +1354,9 @@ private DBPropSet CommandPropertySets()
             return propSet;
         }
 
-        internal Bindings TakeBindingOwnerShip()
+        internal Bindings? TakeBindingOwnerShip()
         {
-            Bindings bindings = _dbBindings;
+            Bindings? bindings = _dbBindings;
             _dbBindings = null;
             return bindings;
         }
@@ -1382,7 +1385,7 @@ private void ValidateConnection(string method)
         private void ValidateConnectionAndTransaction(string method)
         {
             ValidateConnection(method);
-            _transaction = _connection.ValidateTransaction(Transaction, method);
+            _transaction = _connection!.ValidateTransaction(Transaction, method);
             this.canceling = false;
         }
     }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbCommandBuilder.cs b/src/libraries/System.Data.OleDb/src/OleDbCommandBuilder.cs
index a421943730c96d..7eeabb87487d03 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbCommandBuilder.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbCommandBuilder.cs
@@ -15,13 +15,13 @@ public OleDbCommandBuilder() : base()
             GC.SuppressFinalize(this);
         }
 
-        public OleDbCommandBuilder(OleDbDataAdapter adapter) : this()
+        public OleDbCommandBuilder(OleDbDataAdapter? adapter) : this()
         {
             DataAdapter = adapter;
         }
 
         [DefaultValue(null)]
-        public new OleDbDataAdapter DataAdapter
+        public new OleDbDataAdapter? DataAdapter
         {
             get
             {
@@ -122,7 +122,7 @@ public static void DeriveParameters(OleDbCommand command)
             {
                 throw ADP.CommandTextRequired(ADP.DeriveParameters);
             }
-            OleDbConnection connection = command.Connection;
+            OleDbConnection? connection = command.Connection;
             if (null == connection)
             {
                 throw ADP.ConnectionRequired(ADP.DeriveParameters);
@@ -155,13 +155,13 @@ private static OleDbParameter[] DeriveParametersFromStoredProcedure(OleDbConnect
                 string quotePrefix, quoteSuffix;
                 connection.GetLiteralQuotes(ADP.DeriveParameters, out quotePrefix, out quoteSuffix);
 
-                object[] parsed = MultipartIdentifier.ParseMultipartIdentifier(command.CommandText, quotePrefix, quoteSuffix, '.', 4, true, SR.OLEDB_OLEDBCommandText, false);
+                object?[] parsed = MultipartIdentifier.ParseMultipartIdentifier(command.CommandText, quotePrefix, quoteSuffix, '.', 4, true, SR.OLEDB_OLEDBCommandText, false);
                 if (null == parsed[3])
                 {
                     throw ADP.NoStoredProcedureExists(command.CommandText);
                 }
 
-                object[] restrictions = new object[4];
+                object?[] restrictions = new object[4];
                 object value;
 
                 // Parse returns an enforced 4 part array
@@ -182,19 +182,19 @@ private static OleDbParameter[] DeriveParametersFromStoredProcedure(OleDbConnect
                 //if (cmdConnection.IsServer_msdaora) {
                 //    restrictions[1] = Convert.ToString(cmdConnection.UserId).ToUpper();
                 //}
-                DataTable table = connection.GetSchemaRowset(OleDbSchemaGuid.Procedure_Parameters, restrictions);
+                DataTable? table = connection.GetSchemaRowset(OleDbSchemaGuid.Procedure_Parameters, restrictions);
 
                 if (null != table)
                 {
                     DataColumnCollection columns = table.Columns;
 
-                    DataColumn parameterName = null;
-                    DataColumn parameterDirection = null;
-                    DataColumn dataType = null;
-                    DataColumn maxLen = null;
-                    DataColumn numericPrecision = null;
-                    DataColumn numericScale = null;
-                    DataColumn backendtype = null;
+                    DataColumn? parameterName = null;
+                    DataColumn? parameterDirection = null;
+                    DataColumn? dataType = null;
+                    DataColumn? maxLen = null;
+                    DataColumn? numericPrecision = null;
+                    DataColumn? numericScale = null;
+                    DataColumn? backendtype = null;
 
                     int index = columns.IndexOf(ODB.PARAMETER_NAME);
                     if (-1 != index)
@@ -235,7 +235,7 @@ private static OleDbParameter[] DeriveParametersFromStoredProcedure(OleDbConnect
                         if ((null != parameterName) && !dataRow.IsNull(parameterName, DataRowVersion.Default))
                         {
                             // $CONSIDER - not trimming the @ from the beginning but to left the designer do that
-                            parameter.ParameterName = Convert.ToString(dataRow[parameterName, DataRowVersion.Default], CultureInfo.InvariantCulture).TrimStart(new char[] { '@', ' ', ':' });
+                            parameter.ParameterName = Convert.ToString(dataRow[parameterName, DataRowVersion.Default], CultureInfo.InvariantCulture)!.TrimStart(new char[] { '@', ' ', ':' });
                         }
                         if ((null != parameterDirection) && !dataRow.IsNull(parameterDirection, DataRowVersion.Default))
                         {
@@ -271,7 +271,7 @@ private static OleDbParameter[] DeriveParametersFromStoredProcedure(OleDbConnect
                             case OleDbType.VarBinary:
                             case OleDbType.VarChar:
                             case OleDbType.VarWChar:
-                                value = dataRow[backendtype, DataRowVersion.Default];
+                                value = dataRow[backendtype!, DataRowVersion.Default];
                                 if (value is string)
                                 {
                                     string backendtypename = ((string)value).ToLowerInvariant();
@@ -316,8 +316,8 @@ private static OleDbParameter[] DeriveParametersFromStoredProcedure(OleDbConnect
                 }
                 if ((0 == plist.Length) && connection.SupportSchemaRowset(OleDbSchemaGuid.Procedures))
                 {
-                    restrictions = new object[4] { null, null, command.CommandText, null };
-                    table = connection.GetSchemaRowset(OleDbSchemaGuid.Procedures, restrictions);
+                    restrictions = new object?[4] { null, null, command.CommandText, null };
+                    table = connection.GetSchemaRowset(OleDbSchemaGuid.Procedures, restrictions)!;
                     if (0 == table.Rows.Count)
                     {
                         throw ADP.NoStoredProcedureExists(command.CommandText);
@@ -326,8 +326,8 @@ private static OleDbParameter[] DeriveParametersFromStoredProcedure(OleDbConnect
             }
             else if (connection.SupportSchemaRowset(OleDbSchemaGuid.Procedures))
             {
-                object[] restrictions = new object[4] { null, null, command.CommandText, null };
-                DataTable table = connection.GetSchemaRowset(OleDbSchemaGuid.Procedures, restrictions);
+                object?[] restrictions = new object?[4] { null, null, command.CommandText, null };
+                DataTable table = connection.GetSchemaRowset(OleDbSchemaGuid.Procedures, restrictions)!;
                 if (0 == table.Rows.Count)
                 {
                     throw ADP.NoStoredProcedureExists(command.CommandText);
@@ -356,7 +356,7 @@ public override string QuoteIdentifier(string unquotedIdentifier)
         {
             return QuoteIdentifier(unquotedIdentifier, null /* use DataAdapter.SelectCommand.Connection if available */);
         }
-        public string QuoteIdentifier(string unquotedIdentifier, OleDbConnection connection)
+        public string QuoteIdentifier(string unquotedIdentifier, OleDbConnection? connection)
         {
             ADP.CheckArgumentNull(unquotedIdentifier, "unquotedIdentifier");
 
@@ -406,7 +406,7 @@ public override string UnquoteIdentifier(string quotedIdentifier)
             return UnquoteIdentifier(quotedIdentifier, null /* use DataAdapter.SelectCommand.Connection if available */);
         }
 
-        public string UnquoteIdentifier(string quotedIdentifier, OleDbConnection connection)
+        public string UnquoteIdentifier(string quotedIdentifier, OleDbConnection? connection)
         {
             ADP.CheckArgumentNull(quotedIdentifier, "quotedIdentifier");
 
@@ -435,13 +435,11 @@ public string UnquoteIdentifier(string quotedIdentifier, OleDbConnection connect
                 }
             }
 
-            string unquotedIdentifier;
+            string? unquotedIdentifier;
             // ignoring the return value because it is acceptable for the quotedString to not be quoted in this
             // context.
             ADP.RemoveStringQuotes(quotePrefix, quoteSuffix, quotedIdentifier, out unquotedIdentifier);
-            return unquotedIdentifier;
-
+            return unquotedIdentifier!;
         }
-
     }
 }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbConnection.cs b/src/libraries/System.Data.OleDb/src/OleDbConnection.cs
index fef98bef3407aa..06963692ec1d83 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbConnection.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbConnection.cs
@@ -25,7 +25,7 @@ public sealed partial class OleDbConnection : DbConnection, ICloneable, IDbConne
     {
         private static readonly object EventInfoMessage = new object();
 
-        public OleDbConnection(string connectionString) : this()
+        public OleDbConnection(string? connectionString) : this()
         {
             ConnectionString = connectionString;
         }
@@ -42,6 +42,7 @@ private OleDbConnection(OleDbConnection connection) : this()
 #pragma warning restore 618
         SettingsBindable(true),
         RefreshProperties(RefreshProperties.All),
+        AllowNull
         ]
         public override string ConnectionString
         {
@@ -55,9 +56,9 @@ public override string ConnectionString
             }
         }
 
-        private OleDbConnectionString OleDbConnectionStringValue
+        private OleDbConnectionString? OleDbConnectionStringValue
         {
-            get { return (OleDbConnectionString)ConnectionOptions; }
+            get { return (OleDbConnectionString?)ConnectionOptions; }
         }
 
         [
@@ -67,14 +68,14 @@ public override int ConnectionTimeout
         {
             get
             {
-                object value = null;
+                object? value = null;
                 if (IsOpen)
                 {
                     value = GetDataSourceValue(OleDbPropertySetGuid.DBInit, ODB.DBPROP_INIT_TIMEOUT);
                 }
                 else
                 {
-                    OleDbConnectionString constr = this.OleDbConnectionStringValue;
+                    OleDbConnectionString? constr = this.OleDbConnectionStringValue;
                     value = (null != constr) ? constr.ConnectTimeout : ADP.DefaultConnectionTimeout;
                 }
                 if (null != value)
@@ -93,8 +94,8 @@ public override string Database
         {
             get
             {
-                OleDbConnectionString constr = (OleDbConnectionString)UserConnectionOptions;
-                object value = (null != constr) ? constr.InitialCatalog : string.Empty;
+                OleDbConnectionString? constr = (OleDbConnectionString?)UserConnectionOptions;
+                object? value = (null != constr) ? constr.InitialCatalog : string.Empty;
                 if ((null != value) && !((string)value).StartsWith(DbConnectionOptions.DataDirectory, StringComparison.OrdinalIgnoreCase))
                 {
                     OleDbConnectionInternal connection = GetOpenConnection();
@@ -115,7 +116,7 @@ public override string Database
                         value = (null != constr) ? constr.InitialCatalog : string.Empty;
                     }
                 }
-                return Convert.ToString(value, CultureInfo.InvariantCulture);
+                return Convert.ToString(value, CultureInfo.InvariantCulture)!;
             }
         }
 
@@ -126,14 +127,14 @@ public override string DataSource
         {
             get
             {
-                OleDbConnectionString constr = (OleDbConnectionString)UserConnectionOptions;
-                object value = (null != constr) ? constr.DataSource : string.Empty;
+                OleDbConnectionString? constr = (OleDbConnectionString?)UserConnectionOptions;
+                object? value = (null != constr) ? constr.DataSource : string.Empty;
                 if ((null != value) && !((string)value).StartsWith(DbConnectionOptions.DataDirectory, StringComparison.OrdinalIgnoreCase))
                 {
                     if (IsOpen)
                     {
                         value = GetDataSourceValue(OleDbPropertySetGuid.DBInit, ODB.DBPROP_INIT_DATASOURCE);
-                        if ((null == value) || ((value is string) && (0 == (value as string).Length)))
+                        if ((null == value) || ((value is string) && (0 == (value as string)!.Length)))
                         {
                             value = GetDataSourceValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_DATASOURCENAME);
                         }
@@ -144,7 +145,7 @@ public override string DataSource
                         value = (null != constr) ? constr.DataSource : string.Empty;
                     }
                 }
-                return Convert.ToString(value, CultureInfo.InvariantCulture);
+                return Convert.ToString(value, CultureInfo.InvariantCulture)!;
             }
         }
 
@@ -153,7 +154,7 @@ internal bool IsOpen
             get { return (null != GetOpenConnection()); }
         }
 
-        internal OleDbTransaction LocalTransaction
+        internal OleDbTransaction? LocalTransaction
         {
             set
             {
@@ -174,8 +175,8 @@ public string Provider
         {
             get
             {
-                OleDbConnectionString constr = this.OleDbConnectionStringValue;
-                string value = ((null != constr) ? constr.ConvertValueToString(ODB.Provider, null) : null);
+                OleDbConnectionString? constr = this.OleDbConnectionStringValue;
+                string? value = ((null != constr) ? constr.ConvertValueToString(ODB.Provider, null) : null);
                 return ((null != value) ? value : string.Empty);
             }
         }
@@ -184,7 +185,8 @@ internal OleDbConnectionPoolGroupProviderInfo ProviderInfo
         {
             get
             {
-                return (OleDbConnectionPoolGroupProviderInfo)PoolGroup.ProviderInfo;
+                Debug.Assert(null != this.PoolGroup, "PoolGroup must never be null when accessing ProviderInfo");
+                return (OleDbConnectionPoolGroupProviderInfo)PoolGroup!.ProviderInfo!;
             }
         }
 
@@ -214,7 +216,7 @@ public void ResetState()
         {
             if (IsOpen)
             {
-                object value = GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_CONNECTIONSTATUS);
+                object? value = GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_CONNECTIONSTATUS);
                 if (value is int)
                 {
                     int connectionStatus = (int)value;
@@ -238,7 +240,7 @@ public void ResetState()
             }
         }
 
-        public event OleDbInfoMessageEventHandler InfoMessage
+        public event OleDbInfoMessageEventHandler? InfoMessage
         {
             add
             {
@@ -250,7 +252,7 @@ public event OleDbInfoMessageEventHandler InfoMessage
             }
         }
 
-        internal UnsafeNativeMethods.ICommandText ICommandText()
+        internal UnsafeNativeMethods.ICommandText? ICommandText()
         {
             Debug.Assert(null != GetOpenConnection(), "ICommandText closed");
             return GetOpenConnection().ICommandText();
@@ -291,7 +293,7 @@ internal int QuotedIdentifierCase()
             Debug.Assert(null != this.OleDbConnectionStringValue, "no OleDbConnectionString QuotedIdentifierCase");
 
             int quotedIdentifierCase;
-            object value = GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_QUOTEDIDENTIFIERCASE);
+            object? value = GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_QUOTEDIDENTIFIERCASE);
             if (value is int)
             {// not OleDbPropertyStatus
                 quotedIdentifierCase = (int)value;
@@ -379,15 +381,15 @@ protected override DbTransaction BeginDbTransaction(IsolationLevel isolationLeve
             return transaction;
         }
 
-        internal object GetDataSourcePropertyValue(Guid propertySet, int propertyID)
+        internal object? GetDataSourcePropertyValue(Guid propertySet, int propertyID)
         {
             OleDbConnectionInternal connection = GetOpenConnection();
             return connection.GetDataSourcePropertyValue(propertySet, propertyID);
         }
 
-        internal object GetDataSourceValue(Guid propertySet, int propertyID)
+        internal object? GetDataSourceValue(Guid propertySet, int propertyID)
         {
-            object value = GetDataSourcePropertyValue(propertySet, propertyID);
+            object? value = GetDataSourcePropertyValue(propertySet, propertyID);
             if ((value is OleDbPropertyStatus) || Convert.IsDBNull(value))
             {
                 value = null;
@@ -398,7 +400,7 @@ internal object GetDataSourceValue(Guid propertySet, int propertyID)
         private OleDbConnectionInternal GetOpenConnection()
         {
             DbConnectionInternal innerConnection = InnerConnection;
-            return (innerConnection as OleDbConnectionInternal);
+            return (innerConnection as OleDbConnectionInternal)!;
         }
 
         internal void GetLiteralQuotes(string method, out string quotePrefix, out string quoteSuffix)
@@ -407,27 +409,19 @@ internal void GetLiteralQuotes(string method, out string quotePrefix, out string
             OleDbConnectionPoolGroupProviderInfo info = ProviderInfo;
             if (info.HasQuoteFix)
             {
-                quotePrefix = info.QuotePrefix;
-                quoteSuffix = info.QuoteSuffix;
+                quotePrefix = info.QuotePrefix!;
+                quoteSuffix = info.QuoteSuffix!;
             }
             else
             {
                 OleDbConnectionInternal connection = GetOpenConnection();
-                quotePrefix = connection.GetLiteralInfo(ODB.DBLITERAL_QUOTE_PREFIX);
-                quoteSuffix = connection.GetLiteralInfo(ODB.DBLITERAL_QUOTE_SUFFIX);
-                if (null == quotePrefix)
-                {
-                    quotePrefix = "";
-                }
-                if (null == quoteSuffix)
-                {
-                    quoteSuffix = quotePrefix;
-                }
+                quotePrefix = connection.GetLiteralInfo(ODB.DBLITERAL_QUOTE_PREFIX) ?? "";
+                quoteSuffix = connection.GetLiteralInfo(ODB.DBLITERAL_QUOTE_SUFFIX) ?? "";
                 info.SetQuoteFix(quotePrefix, quoteSuffix);
             }
         }
 
-        public DataTable GetOleDbSchemaTable(Guid schema, object[] restrictions)
+        public DataTable? GetOleDbSchemaTable(Guid schema, object?[]? restrictions)
         {
             CheckStateOpen(ADP.GetOleDbSchemaTable);
             OleDbConnectionInternal connection = GetOpenConnection();
@@ -474,7 +468,7 @@ public DataTable GetOleDbSchemaTable(Guid schema, object[] restrictions)
             }
         }
 
-        internal DataTable GetSchemaRowset(Guid schema, object[] restrictions)
+        internal DataTable? GetSchemaRowset(Guid schema, object?[] restrictions)
         {
             Debug.Assert(null != GetOpenConnection(), "GetSchemaRowset closed");
             return GetOpenConnection().GetSchemaRowset(schema, restrictions);
@@ -494,7 +488,7 @@ internal bool HasLiveReader(OleDbCommand cmd)
 
         internal void OnInfoMessage(UnsafeNativeMethods.IErrorInfo errorInfo, OleDbHResult errorCode)
         {
-            OleDbInfoMessageEventHandler handler = (OleDbInfoMessageEventHandler)Events[EventInfoMessage];
+            OleDbInfoMessageEventHandler? handler = (OleDbInfoMessageEventHandler?)Events[EventInfoMessage];
             if (null != handler)
             {
                 try
@@ -522,7 +516,7 @@ public override void Open()
 
             // need to manually enlist in some cases, because
             // native OLE DB doesn't know about SysTx transactions.
-            if ((0 != (ODB.DBPROPVAL_OS_TXNENLISTMENT & ((OleDbConnectionString)(this.ConnectionOptions)).OleDbServices))
+            if ((0 != (ODB.DBPROPVAL_OS_TXNENLISTMENT & ((OleDbConnectionString)(this.ConnectionOptions!)).OleDbServices))
                         && ADP.NeedManualEnlistment())
             {
                 GetOpenConnection().EnlistTransactionInternal(SysTx.Transaction.Current);
@@ -541,7 +535,7 @@ internal void SetDataSourcePropertyValue(Guid propertySet, int propertyID, strin
 
                     if (hr < 0)
                     {
-                        Exception e = OleDbConnection.ProcessResults(hr, null, this);
+                        Exception? e = OleDbConnection.ProcessResults(hr, null, this);
                         if (OleDbHResult.DB_E_ERRORSOCCURRED == hr)
                         {
                             StringBuilder builder = new StringBuilder();
@@ -552,7 +546,7 @@ internal void SetDataSourcePropertyValue(Guid propertySet, int propertyID, strin
 
                             ODB.PropsetSetFailure(builder, description, dbprops[0].dwStatus);
 
-                            e = ODB.PropsetSetFailure(builder.ToString(), e);
+                            e = ODB.PropsetSetFailure(builder.ToString(), e!);
                         }
                         if (null != e)
                         {
@@ -572,12 +566,12 @@ internal bool SupportSchemaRowset(Guid schema)
             return GetOpenConnection().SupportSchemaRowset(schema);
         }
 
-        internal OleDbTransaction ValidateTransaction(OleDbTransaction transaction, string method)
+        internal OleDbTransaction? ValidateTransaction(OleDbTransaction? transaction, string method)
         {
             return GetOpenConnection().ValidateTransaction(transaction, method);
         }
 
-        internal static Exception ProcessResults(OleDbHResult hresult, OleDbConnection connection, object src)
+        internal static Exception? ProcessResults(OleDbHResult hresult, OleDbConnection? connection, object? src)
         {
             if ((0 <= (int)hresult) && ((null == connection) || (null == connection.Events[EventInfoMessage])))
             {
@@ -586,8 +580,8 @@ internal static Exception ProcessResults(OleDbHResult hresult, OleDbConnection c
             }
 
             // ErrorInfo object is to be checked regardless the hresult returned by the function called
-            Exception e = null;
-            UnsafeNativeMethods.IErrorInfo errorInfo = null;
+            Exception? e = null;
+            UnsafeNativeMethods.IErrorInfo? errorInfo = null;
             OleDbHResult hr = UnsafeNativeMethods.GetErrorInfo(0, out errorInfo);  // 0 - IErrorInfo exists, 1 - no IErrorInfo
             if ((OleDbHResult.S_OK == hr) && (null != errorInfo))
             {
@@ -643,7 +637,7 @@ public static void ReleaseObjectPool()
             OleDbConnectionFactory.SingletonInstance.ClearAllPools();
         }
 
-        private static void ResetState(OleDbConnection connection)
+        private static void ResetState(OleDbConnection? connection)
         {
             if (null != connection)
             {
diff --git a/src/libraries/System.Data.OleDb/src/OleDbConnectionFactory.cs b/src/libraries/System.Data.OleDb/src/OleDbConnectionFactory.cs
index a6ab9fda124e8c..9b1a7cd366424a 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbConnectionFactory.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbConnectionFactory.cs
@@ -31,13 +31,14 @@ public override DbProviderFactory ProviderFactory
             }
         }
 
-        protected override DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningObject)
+        protected override DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool? pool, DbConnection? owningObject)
         {
-            DbConnectionInternal result = new OleDbConnectionInternal((OleDbConnectionString)options, (OleDbConnection)owningObject);
+            // TODO-NULLABLE: owningObject may actually be null (see DbConnectionPool.CreateObject), in which case this will throw...
+            DbConnectionInternal result = new OleDbConnectionInternal((OleDbConnectionString)options, (OleDbConnection)owningObject!);
             return result;
         }
 
-        protected override DbConnectionOptions CreateConnectionOptions(string connectionString, DbConnectionOptions previous)
+        protected override DbConnectionOptions CreateConnectionOptions(string connectionString, DbConnectionOptions? previous)
         {
             Debug.Assert(!ADP.IsEmpty(connectionString), "null connectionString");
             OleDbConnectionString result = new OleDbConnectionString(connectionString, (null != previous));
@@ -50,17 +51,17 @@ protected override DbMetaDataFactory CreateMetaDataFactory(DbConnectionInternal
             cacheMetaDataFactory = false;
 
             OleDbConnectionInternal oleDbInternalConnection = (OleDbConnectionInternal)internalConnection;
-            OleDbConnection oleDbOuterConnection = oleDbInternalConnection.Connection;
+            OleDbConnection? oleDbOuterConnection = oleDbInternalConnection.Connection;
             Debug.Assert(oleDbOuterConnection != null, "outer connection may not be null.");
 
             NameValueCollection settings = (NameValueCollection)ConfigurationManager.GetSection("system.data.oledb");
-            Stream XMLStream = null;
-            string providerFileName = oleDbOuterConnection.GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_PROVIDERFILENAME) as string;
+            Stream? XMLStream = null;
+            string? providerFileName = oleDbOuterConnection.GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_PROVIDERFILENAME) as string;
 
             if (settings != null)
             {
-                string[] values = null;
-                string metaDataXML = null;
+                string[]? values = null;
+                string? metaDataXML = null;
                 // first try to get the provider specific xml
 
                 // if providerfilename is not supported we can't build the settings key needed to
@@ -81,7 +82,7 @@ protected override DbMetaDataFactory CreateMetaDataFactory(DbConnectionInternal
                 // If there is new XML get it
                 if (values != null)
                 {
-                    XMLStream = ADP.GetXmlStreamFromValues(values, metaDataXML);
+                    XMLStream = ADP.GetXmlStreamFromValues(values, metaDataXML!);
                 }
             }
 
@@ -103,7 +104,7 @@ protected override DbMetaDataFactory CreateMetaDataFactory(DbConnectionInternal
                                              oleDbInternalConnection.GetSchemaRowsetInformation());
         }
 
-        protected override DbConnectionPoolGroupOptions CreateConnectionPoolGroupOptions(DbConnectionOptions connectionOptions)
+        protected override DbConnectionPoolGroupOptions? CreateConnectionPoolGroupOptions(DbConnectionOptions connectionOptions)
         {
             return null;
         }
@@ -113,9 +114,9 @@ internal override DbConnectionPoolGroupProviderInfo CreateConnectionPoolGroupPro
             return new OleDbConnectionPoolGroupProviderInfo();
         }
 
-        internal override DbConnectionPoolGroup GetConnectionPoolGroup(DbConnection connection)
+        internal override DbConnectionPoolGroup? GetConnectionPoolGroup(DbConnection connection)
         {
-            OleDbConnection c = (connection as OleDbConnection);
+            OleDbConnection? c = (connection as OleDbConnection);
             if (null != c)
             {
                 return c.PoolGroup;
@@ -125,7 +126,7 @@ internal override DbConnectionPoolGroup GetConnectionPoolGroup(DbConnection conn
 
         internal override void PermissionDemand(DbConnection outerConnection)
         {
-            OleDbConnection c = (outerConnection as OleDbConnection);
+            OleDbConnection? c = (outerConnection as OleDbConnection);
             if (null != c)
             {
                 c.PermissionDemand();
@@ -134,7 +135,7 @@ internal override void PermissionDemand(DbConnection outerConnection)
 
         internal override void SetConnectionPoolGroup(DbConnection outerConnection, DbConnectionPoolGroup poolGroup)
         {
-            OleDbConnection c = (outerConnection as OleDbConnection);
+            OleDbConnection? c = (outerConnection as OleDbConnection);
             if (null != c)
             {
                 c.PoolGroup = poolGroup;
@@ -143,7 +144,7 @@ internal override void SetConnectionPoolGroup(DbConnection outerConnection, DbCo
 
         internal override void SetInnerConnectionEvent(DbConnection owningObject, DbConnectionInternal to)
         {
-            OleDbConnection c = (owningObject as OleDbConnection);
+            OleDbConnection? c = (owningObject as OleDbConnection);
             if (null != c)
             {
                 c.SetInnerConnectionEvent(to);
@@ -152,7 +153,7 @@ internal override void SetInnerConnectionEvent(DbConnection owningObject, DbConn
 
         internal override bool SetInnerConnectionFrom(DbConnection owningObject, DbConnectionInternal to, DbConnectionInternal from)
         {
-            OleDbConnection c = (owningObject as OleDbConnection);
+            OleDbConnection? c = (owningObject as OleDbConnection);
             if (null != c)
             {
                 return c.SetInnerConnectionFrom(to, from);
@@ -162,7 +163,7 @@ internal override bool SetInnerConnectionFrom(DbConnection owningObject, DbConne
 
         internal override void SetInnerConnectionTo(DbConnection owningObject, DbConnectionInternal to)
         {
-            OleDbConnection c = (owningObject as OleDbConnection);
+            OleDbConnection? c = (owningObject as OleDbConnection);
             if (null != c)
             {
                 c.SetInnerConnectionTo(to);
diff --git a/src/libraries/System.Data.OleDb/src/OleDbConnectionInternal.cs b/src/libraries/System.Data.OleDb/src/OleDbConnectionInternal.cs
index e4d1e502238327..09ab6982105b5e 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbConnectionInternal.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbConnectionInternal.cs
@@ -15,7 +15,7 @@ namespace System.Data.OleDb
 
     internal sealed class OleDbConnectionInternal : DbConnectionInternal, IDisposable
     {
-        private static volatile OleDbServicesWrapper idataInitialize;
+        private static volatile OleDbServicesWrapper? idataInitialize;
         private static readonly object dataInitializeLock = new object();
 
         internal readonly OleDbConnectionString ConnectionString; // parsed connection string attributes
@@ -50,18 +50,18 @@ internal sealed class OleDbConnectionInternal : DbConnectionInternal, IDisposabl
         // offered much better performance.
 
         // the "Data Source object".
-        private readonly DataSourceWrapper _datasrcwrp;
+        private readonly DataSourceWrapper? _datasrcwrp;
 
         // the "Session object".
-        private readonly SessionWrapper _sessionwrp;
+        private readonly SessionWrapper? _sessionwrp;
 
-        private WeakReference weakTransaction;
+        private WeakReference? weakTransaction;
 
         // When set to true the current connection is enlisted in a transaction that must be
         // un-enlisted during Deactivate.
         private bool _unEnlistDuringDeactivate;
 
-        internal OleDbConnectionInternal(OleDbConnectionString constr, OleDbConnection connection) : base()
+        internal OleDbConnectionInternal(OleDbConnectionString constr, OleDbConnection? connection) : base()
         {
             Debug.Assert((null != constr) && !constr.IsEmpty, "empty connectionstring");
             ConnectionString = constr;
@@ -100,7 +100,7 @@ internal OleDbConnectionInternal(OleDbConnectionString constr, OleDbConnection c
                     }
                     else
                     {
-                        Exception e = OleDbConnection.ProcessResults(hr, null, null);
+                        Exception? e = OleDbConnection.ProcessResults(hr, null, null);
                         Debug.Assert(null != e, "CreateSessionError");
                         throw e;
                     }
@@ -123,11 +123,11 @@ internal OleDbConnectionInternal(OleDbConnectionString constr, OleDbConnection c
             }
         }
 
-        internal OleDbConnection Connection
+        internal OleDbConnection? Connection
         {
             get
             {
-                return (OleDbConnection)Owner;
+                return (OleDbConnection?)Owner;
             }
         }
 
@@ -139,14 +139,14 @@ internal bool HasSession
             }
         }
 
-        internal OleDbTransaction LocalTransaction
+        internal OleDbTransaction? LocalTransaction
         {
             get
             {
-                OleDbTransaction result = null;
+                OleDbTransaction? result = null;
                 if (null != weakTransaction)
                 {
-                    result = ((OleDbTransaction)weakTransaction.Target);
+                    result = ((OleDbTransaction?)weakTransaction.Target);
                 }
                 return result;
             }
@@ -171,8 +171,8 @@ public override string ServerVersion
             // consider making a method, not a property
             get
             {
-                object value = GetDataSourceValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_DBMSVER);
-                return Convert.ToString(value, CultureInfo.InvariantCulture);
+                object value = GetDataSourceValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_DBMSVER)!;
+                return Convert.ToString(value, CultureInfo.InvariantCulture)!;
             }
         }
 
@@ -218,12 +218,12 @@ internal ITransactionJoinWrapper ITransactionJoin()
         }
 
         // optional interface, unsafe cast
-        internal UnsafeNativeMethods.ICommandText ICommandText()
+        internal UnsafeNativeMethods.ICommandText? ICommandText()
         {
             Debug.Assert(null != _datasrcwrp, "IDBCreateCommand: null datasource");
             Debug.Assert(null != _sessionwrp, "IDBCreateCommand: null session");
 
-            object icommandText = null;
+            object? icommandText = null;
             OleDbHResult hr = _sessionwrp.CreateCommand(ref icommandText);
 
             Debug.Assert((0 <= hr) || (null == icommandText), "CreateICommandText: error with ICommandText");
@@ -238,23 +238,23 @@ internal UnsafeNativeMethods.ICommandText ICommandText()
                     SafeNativeMethods.Wrapper.ClearErrorInfo();
                 }
             }
-            return (UnsafeNativeMethods.ICommandText)icommandText;
+            return (UnsafeNativeMethods.ICommandText?)icommandText;
         }
 
-        protected override void Activate(SysTx.Transaction transaction)
+        protected override void Activate(SysTx.Transaction? transaction)
         {
             throw ADP.NotSupported();
         }
 
         public override DbTransaction BeginTransaction(IsolationLevel isolationLevel)
         {
-            OleDbConnection outerConnection = Connection;
+            OleDbConnection outerConnection = Connection!;
             if (null != LocalTransaction)
             {
                 throw ADP.ParallelTransactionsNotSupported(outerConnection);
             }
 
-            object unknown = null;
+            object? unknown = null;
             OleDbTransaction transaction;
             try
             {
@@ -262,10 +262,10 @@ public override DbTransaction BeginTransaction(IsolationLevel isolationLevel)
                 Debug.Assert(null != _datasrcwrp, "ITransactionLocal: null datasource");
                 Debug.Assert(null != _sessionwrp, "ITransactionLocal: null session");
                 unknown = _sessionwrp.ComWrapper();
-                UnsafeNativeMethods.ITransactionLocal value = (unknown as UnsafeNativeMethods.ITransactionLocal);
+                UnsafeNativeMethods.ITransactionLocal? value = (unknown as UnsafeNativeMethods.ITransactionLocal);
                 if (null == value)
                 {
-                    throw ODB.TransactionsNotSupported(Provider, (Exception)null);
+                    throw ODB.TransactionsNotSupported(Provider, null);
                 }
                 transaction.BeginInternal(value);
             }
@@ -294,7 +294,7 @@ protected override void Deactivate()
                 // Un-enlist transaction as OLEDB connection pool is unaware of managed transactions.
                 EnlistTransactionInternal(null);
             }
-            OleDbTransaction transaction = LocalTransaction;
+            OleDbTransaction? transaction = LocalTransaction;
             if (null != transaction)
             {
                 LocalTransaction = null;
@@ -318,7 +318,7 @@ public override void Dispose()
             base.Dispose();
         }
 
-        public override void EnlistTransaction(SysTx.Transaction transaction)
+        public override void EnlistTransaction(SysTx.Transaction? transaction)
         {
             if (null != LocalTransaction)
             {
@@ -327,15 +327,15 @@ public override void EnlistTransaction(SysTx.Transaction transaction)
             EnlistTransactionInternal(transaction);
         }
 
-        internal void EnlistTransactionInternal(SysTx.Transaction transaction)
+        internal void EnlistTransactionInternal(SysTx.Transaction? transaction)
         {
-            SysTx.IDtcTransaction oleTxTransaction = ADP.GetOletxTransaction(transaction);
+            SysTx.IDtcTransaction? oleTxTransaction = ADP.GetOletxTransaction(transaction);
 
             using (ITransactionJoinWrapper transactionJoin = ITransactionJoin())
             {
                 if (null == transactionJoin.Value)
                 {
-                    throw ODB.TransactionsNotSupported(Provider, (Exception)null);
+                    throw ODB.TransactionsNotSupported(Provider, null);
                 }
                 transactionJoin.Value.JoinTransaction(oleTxTransaction, (int)IsolationLevel.Unspecified, 0, IntPtr.Zero);
                 _unEnlistDuringDeactivate = (null != transaction);
@@ -343,9 +343,9 @@ internal void EnlistTransactionInternal(SysTx.Transaction transaction)
             EnlistedTransaction = transaction;
         }
 
-        internal object GetDataSourceValue(Guid propertySet, int propertyID)
+        internal object? GetDataSourceValue(Guid propertySet, int propertyID)
         {
-            object value = GetDataSourcePropertyValue(propertySet, propertyID);
+            object? value = GetDataSourcePropertyValue(propertySet, propertyID);
             if ((value is OleDbPropertyStatus) || Convert.IsDBNull(value))
             {
                 value = null;
@@ -353,7 +353,7 @@ internal object GetDataSourceValue(Guid propertySet, int propertyID)
             return value;
         }
 
-        internal object GetDataSourcePropertyValue(Guid propertySet, int propertyID)
+        internal object? GetDataSourcePropertyValue(Guid propertySet, int propertyID)
         {
             OleDbHResult hr;
             ItagDBPROP[] dbprops;
@@ -380,11 +380,12 @@ internal object GetDataSourcePropertyValue(Guid propertySet, int propertyID)
             return dbprops[0].dwStatus;
         }
 
-        internal DataTable BuildInfoLiterals()
+        internal DataTable? BuildInfoLiterals()
         {
             using (IDBInfoWrapper wrapper = IDBInfo())
             {
                 UnsafeNativeMethods.IDBInfo dbInfo = wrapper.Value;
+                // TODO-NULLABLE: check may not be necessary (and thus method may return non-nullable)
                 if (null == dbInfo)
                 {
                     return null;
@@ -445,9 +446,9 @@ internal DataTable BuildInfoLiterals()
             }
         }
 
-        internal DataTable BuildInfoKeywords()
+        internal DataTable? BuildInfoKeywords()
         {
-            DataTable table = new DataTable(ODB.DbInfoKeywords);
+            DataTable? table = new DataTable(ODB.DbInfoKeywords);
             table.Locale = CultureInfo.InvariantCulture;
             DataColumn keyword = new DataColumn(ODB.Keyword, typeof(string));
             table.Columns.Add(keyword);
@@ -506,7 +507,7 @@ internal DataTable BuildSchemaGuids()
             table.Columns.Add(schemaGuid);
             table.Columns.Add(restrictionSupport);
 
-            SchemaSupport[] supportedSchemas = GetSchemaRowsetInformation();
+            SchemaSupport[]? supportedSchemas = GetSchemaRowsetInformation();
 
             if (null != supportedSchemas)
             {
@@ -523,7 +524,7 @@ internal DataTable BuildSchemaGuids()
             return table;
         }
 
-        internal string GetLiteralInfo(int literal)
+        internal string? GetLiteralInfo(int literal)
         {
             using (IDBInfoWrapper wrapper = IDBInfo())
             {
@@ -532,7 +533,7 @@ internal string GetLiteralInfo(int literal)
                 {
                     return null;
                 }
-                string literalValue = null;
+                string? literalValue = null;
                 IntPtr literalInfo = ADP.PtrZero;
                 int literalCount = 0;
                 OleDbHResult hr;
@@ -560,17 +561,17 @@ internal string GetLiteralInfo(int literal)
             }
         }
 
-        internal SchemaSupport[] GetSchemaRowsetInformation()
+        internal SchemaSupport[]? GetSchemaRowsetInformation()
         {
             OleDbConnectionString constr = ConnectionString;
-            SchemaSupport[] supportedSchemas = constr.SchemaSupport;
+            SchemaSupport[]? supportedSchemas = constr.SchemaSupport;
             if (null != supportedSchemas)
             {
                 return supportedSchemas;
             }
             using (IDBSchemaRowsetWrapper wrapper = IDBSchemaRowset())
             {
-                UnsafeNativeMethods.IDBSchemaRowset dbSchemaRowset = wrapper.Value;
+                UnsafeNativeMethods.IDBSchemaRowset? dbSchemaRowset = wrapper.Value;
                 if (null == dbSchemaRowset)
                 {
                     return null; // IDBSchemaRowset not supported
@@ -595,7 +596,7 @@ internal SchemaSupport[] GetSchemaRowsetInformation()
                         for (int i = 0, offset = 0; i < supportedSchemas.Length; ++i, offset += ODB.SizeOf_Guid)
                         {
                             IntPtr ptr = ADP.IntPtrOffset(schemaGuids, i * ODB.SizeOf_Guid);
-                            supportedSchemas[i]._schemaRowset = (Guid)Marshal.PtrToStructure(ptr, typeof(Guid));
+                            supportedSchemas[i]._schemaRowset = (Guid)Marshal.PtrToStructure(ptr, typeof(Guid))!;
                         }
                     }
                     if (ADP.PtrZero != schemaRestrictions)
@@ -611,13 +612,13 @@ internal SchemaSupport[] GetSchemaRowsetInformation()
             }
         }
 
-        internal DataTable GetSchemaRowset(Guid schema, object[] restrictions)
+        internal DataTable? GetSchemaRowset(Guid schema, object?[]? restrictions)
         {
             if (null == restrictions)
             {
                 restrictions = Array.Empty<object>();
             }
-            DataTable dataTable = null;
+            DataTable? dataTable = null;
             using (IDBSchemaRowsetWrapper wrapper = IDBSchemaRowset())
             {
                 UnsafeNativeMethods.IDBSchemaRowset dbSchemaRowset = wrapper.Value;
@@ -626,7 +627,7 @@ internal DataTable GetSchemaRowset(Guid schema, object[] restrictions)
                     throw ODB.SchemaRowsetsNotSupported(Provider);
                 }
 
-                UnsafeNativeMethods.IRowset rowset = null;
+                UnsafeNativeMethods.IRowset? rowset = null;
                 OleDbHResult hr;
                 hr = dbSchemaRowset.GetRowset(ADP.PtrZero, ref schema, restrictions.Length, restrictions, ref ODB.IID_IRowset, 0, ADP.PtrZero, out rowset);
 
@@ -656,7 +657,7 @@ internal DataTable GetSchemaRowset(Guid schema, object[] restrictions)
         // returns true if there is an active data reader on the specified command
         internal bool HasLiveReader(OleDbCommand cmd)
         {
-            OleDbDataReader reader = null;
+            OleDbDataReader? reader = null;
 
             if (null != ReferenceCollection)
             {
@@ -668,15 +669,15 @@ internal bool HasLiveReader(OleDbCommand cmd)
 
         private void ProcessResults(OleDbHResult hr)
         {
-            OleDbConnection connection = Connection; // get value from weakref only once
-            Exception e = OleDbConnection.ProcessResults(hr, connection, connection);
+            OleDbConnection? connection = Connection; // get value from weakref only once
+            Exception? e = OleDbConnection.ProcessResults(hr, connection, connection);
             if (null != e)
             { throw e; }
         }
 
         internal bool SupportSchemaRowset(Guid schema)
         {
-            SchemaSupport[] schemaSupport = GetSchemaRowsetInformation();
+            SchemaSupport[]? schemaSupport = GetSchemaRowsetInformation();
             if (null != schemaSupport)
             {
                 for (int i = 0; i < schemaSupport.Length; ++i)
@@ -692,8 +693,8 @@ internal bool SupportSchemaRowset(Guid schema)
 
         private static object CreateInstanceDataLinks()
         {
-            Type datalink = Type.GetTypeFromCLSID(ODB.CLSID_DataLinks, true);
-            return Activator.CreateInstance(datalink, System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance, null, null, CultureInfo.InvariantCulture, null);
+            Type datalink = Type.GetTypeFromCLSID(ODB.CLSID_DataLinks, true)!;
+            return Activator.CreateInstance(datalink, System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance, null, null, CultureInfo.InvariantCulture, null)!;
         }
 
         // @devnote: should be multithread safe access to OleDbConnection.idataInitialize,
@@ -701,7 +702,7 @@ private static object CreateInstanceDataLinks()
         // OLE DB will ensure I'll work with just the single pool
         private static OleDbServicesWrapper GetObjectPool()
         {
-            OleDbServicesWrapper wrapper = OleDbConnectionInternal.idataInitialize;
+            OleDbServicesWrapper? wrapper = OleDbConnectionInternal.idataInitialize;
             if (null == wrapper)
             {
                 lock (dataInitializeLock)
@@ -764,11 +765,11 @@ public static void ReleaseObjectPool()
             OleDbConnectionInternal.idataInitialize = null;
         }
 
-        internal OleDbTransaction ValidateTransaction(OleDbTransaction transaction, string method)
+        internal OleDbTransaction? ValidateTransaction(OleDbTransaction? transaction, string method)
         {
             if (null != this.weakTransaction)
             {
-                OleDbTransaction head = (OleDbTransaction)this.weakTransaction.Target;
+                OleDbTransaction? head = (OleDbTransaction?)this.weakTransaction.Target;
                 if ((null != head) && this.weakTransaction.IsAlive)
                 {
                     head = OleDbTransaction.TransactionUpdate(head);
@@ -817,9 +818,9 @@ internal OleDbTransaction ValidateTransaction(OleDbTransaction transaction, stri
             return null;
         }
 
-        internal Dictionary<string, OleDbPropertyInfo> GetPropertyInfo(Guid[] propertySets)
+        internal Dictionary<string, OleDbPropertyInfo>? GetPropertyInfo(Guid[] propertySets)
         {
-            Dictionary<string, OleDbPropertyInfo> properties = null;
+            Dictionary<string, OleDbPropertyInfo>? properties = null;
 
             if (null == propertySets)
             {
diff --git a/src/libraries/System.Data.OleDb/src/OleDbConnectionPoolGroupProviderInfo.cs b/src/libraries/System.Data.OleDb/src/OleDbConnectionPoolGroupProviderInfo.cs
index fc472aa109d048..594f0db3f6a0bb 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbConnectionPoolGroupProviderInfo.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbConnectionPoolGroupProviderInfo.cs
@@ -8,7 +8,7 @@ namespace System.Data.OleDb
     internal sealed class OleDbConnectionPoolGroupProviderInfo : DbConnectionPoolGroupProviderInfo
     {
         private bool _hasQuoteFix;
-        private string _quotePrefix, _quoteSuffix;
+        private string? _quotePrefix, _quoteSuffix;
 
         internal OleDbConnectionPoolGroupProviderInfo()
         {
@@ -18,11 +18,11 @@ internal bool HasQuoteFix
         {
             get { return _hasQuoteFix; }
         }
-        internal string QuotePrefix
+        internal string? QuotePrefix
         {
             get { return _quotePrefix; }
         }
-        internal string QuoteSuffix
+        internal string? QuoteSuffix
         {
             get { return _quoteSuffix; }
         }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbConnectionString.cs b/src/libraries/System.Data.OleDb/src/OleDbConnectionString.cs
index 665421f8ba40b4..7f3946291684b3 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbConnectionString.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbConnectionString.cs
@@ -50,7 +50,7 @@ private static class UDL
             internal static volatile bool _PoolSizeInit;
             internal static int _PoolSize;
 
-            internal static volatile Dictionary<string, string> _Pool;
+            internal static volatile Dictionary<string, string>? _Pool;
             internal static object _PoolLock = new object();
         }
 
@@ -61,11 +61,11 @@ private static class VALUES
 
         // set during ctor
         internal readonly bool PossiblePrompt;
-        internal readonly string ActualConnectionString; // cached value passed to GetDataSource
+        internal readonly string? ActualConnectionString; // cached value passed to GetDataSource
 
-        private readonly string _expandedConnectionString;
+        private readonly string? _expandedConnectionString;
 
-        internal SchemaSupport[] _schemaSupport;
+        internal SchemaSupport[]? _schemaSupport;
 
         internal int _sqlSupport;
         internal bool _supportMultipleResults;
@@ -76,10 +76,10 @@ private static class VALUES
         private int _oledbServices;
 
         // these are cached delegates (per unique connectionstring)
-        internal UnsafeNativeMethods.IUnknownQueryInterface DangerousDataSourceIUnknownQueryInterface;
-        internal UnsafeNativeMethods.IDBInitializeInitialize DangerousIDBInitializeInitialize;
-        internal UnsafeNativeMethods.IDBCreateSessionCreateSession DangerousIDBCreateSessionCreateSession;
-        internal UnsafeNativeMethods.IDBCreateCommandCreateCommand DangerousIDBCreateCommandCreateCommand;
+        internal UnsafeNativeMethods.IUnknownQueryInterface? DangerousDataSourceIUnknownQueryInterface;
+        internal UnsafeNativeMethods.IDBInitializeInitialize? DangerousIDBInitializeInitialize;
+        internal UnsafeNativeMethods.IDBCreateSessionCreateSession? DangerousIDBCreateSessionCreateSession;
+        internal UnsafeNativeMethods.IDBCreateCommandCreateCommand? DangerousIDBCreateCommandCreateCommand;
 
         // since IDBCreateCommand interface may not be supported for a particular provider (only IOpenRowset)
         // we cache that fact rather than call QueryInterface on every call to Open
@@ -89,17 +89,17 @@ private static class VALUES
         // from the UDL file. The UDL file is opened as FileMode.Open, FileAccess.Read, FileShare.Read, allowing concurrent access to it.
         internal OleDbConnectionString(string connectionString, bool validate) : base(connectionString)
         {
-            string prompt = this[KEY.Prompt];
+            string? prompt = this[KEY.Prompt];
             PossiblePrompt = ((!ADP.IsEmpty(prompt) && (0 != string.Compare(prompt, VALUES.NoPrompt, StringComparison.OrdinalIgnoreCase)))
                               || !ADP.IsEmpty(this[KEY.WindowHandle]));
 
             if (!IsEmpty)
             {
-                string udlConnectionString = null;
+                string? udlConnectionString = null;
                 if (!validate)
                 {
                     int position = 0;
-                    string udlFileName = null;
+                    string? udlFileName = null;
                     _expandedConnectionString = ExpandDataDirectories(ref udlFileName, ref position);
 
                     if (!ADP.IsEmpty(udlFileName))
@@ -112,7 +112,7 @@ internal OleDbConnectionString(string connectionString, bool validate) : base(co
 
                         if (!ADP.IsEmpty(udlConnectionString))
                         {
-                            _expandedConnectionString = _expandedConnectionString.Substring(0, position) + udlConnectionString + ';' + _expandedConnectionString.Substring(position);
+                            _expandedConnectionString = _expandedConnectionString!.Substring(0, position) + udlConnectionString + ';' + _expandedConnectionString.Substring(position);
                         }
                     }
                 }
@@ -130,12 +130,12 @@ internal int ConnectTimeout
 
         internal string DataSource
         {
-            get { return base.ConvertValueToString(KEY.Data_Source, string.Empty); }
+            get { return base.ConvertValueToString(KEY.Data_Source, string.Empty)!; }
         }
 
         internal string InitialCatalog
         {
-            get { return base.ConvertValueToString(KEY.Initial_Catalog, string.Empty); }
+            get { return base.ConvertValueToString(KEY.Initial_Catalog, string.Empty)!; }
         }
 
         internal string Provider
@@ -143,7 +143,7 @@ internal string Provider
             get
             {
                 Debug.Assert(!ADP.IsEmpty(this[KEY.Provider]), "no Provider");
-                return this[KEY.Provider];
+                return this[KEY.Provider]!;
             }
         }
 
@@ -155,7 +155,7 @@ internal int OleDbServices
             }
         }
 
-        internal SchemaSupport[] SchemaSupport
+        internal SchemaSupport[]? SchemaSupport
         { // OleDbConnection.GetSchemaRowsetInformation
             get { return _schemaSupport; }
             set { _schemaSupport = value; }
@@ -178,7 +178,7 @@ internal int GetSqlSupport(OleDbConnection connection)
             int sqlSupport = _sqlSupport;
             if (!_hasSqlSupport)
             {
-                object value = connection.GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_SQLSUPPORT);
+                object? value = connection.GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_SQLSUPPORT);
                 if (value is int)
                 { // not OleDbPropertyStatus
                     sqlSupport = (int)value;
@@ -194,7 +194,7 @@ internal bool GetSupportIRow(OleDbConnection connection, OleDbCommand command)
             bool supportIRow = _supportIRow;
             if (!_hasSupportIRow)
             {
-                object value = command.GetPropertyValue(OleDbPropertySetGuid.Rowset, ODB.DBPROP_IRow);
+                object? value = command.GetPropertyValue(OleDbPropertySetGuid.Rowset, ODB.DBPROP_IRow);
 
                 // SQLOLEDB always returns VARIANT_FALSE for DBPROP_IROW, so base the answer on existance
                 supportIRow = !(value is OleDbPropertyStatus);
@@ -209,7 +209,7 @@ internal bool GetSupportMultipleResults(OleDbConnection connection)
             bool supportMultipleResults = _supportMultipleResults;
             if (!_hasSupportMultipleResults)
             {
-                object value = connection.GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_MULTIPLERESULTS);
+                object? value = connection.GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_MULTIPLERESULTS);
                 if (value is int)
                 {// not OleDbPropertyStatus
                     supportMultipleResults = (ODB.DBPROPVAL_MR_NOTSUPPORTED != (int)value);
@@ -228,7 +228,7 @@ private static int UdlPoolSize
                 int poolsize = UDL._PoolSize;
                 if (!UDL._PoolSizeInit)
                 {
-                    object value = ADP.LocalMachineRegistryValue(UDL.Location, UDL.Pooling);
+                    object? value = ADP.LocalMachineRegistryValue(UDL.Location, UDL.Pooling);
                     if (value is int)
                     {
                         poolsize = (int)value;
@@ -241,10 +241,10 @@ private static int UdlPoolSize
             }
         }
 
-        private static string LoadStringFromStorage(string udlfilename)
+        private static string? LoadStringFromStorage(string udlfilename)
         {
-            string udlConnectionString = null;
-            Dictionary<string, string> udlcache = UDL._Pool;
+            string? udlConnectionString = null;
+            Dictionary<string, string>? udlcache = UDL._Pool;
 
             if ((null == udlcache) || !udlcache.TryGetValue(udlfilename, out udlConnectionString))
             {
@@ -295,8 +295,8 @@ private static string LoadStringFromFileStorage(string udlfilename)
             //  [oledb]
             //  ; Everything after this line is an OLE DB initstring
             //
-            string connectionString = null;
-            Exception failure = null;
+            string? connectionString = null;
+            Exception? failure = null;
             try
             {
                 int hdrlength = ADP.CharSize * UDL.Header.Length;
@@ -342,7 +342,7 @@ private static string LoadStringFromFileStorage(string udlfilename)
             {
                 throw failure;
             }
-            return connectionString.Trim();
+            return connectionString!.Trim();
         }
 
         private string ValidateConnectionString(string connectionString)
@@ -358,7 +358,7 @@ private string ValidateConnectionString(string connectionString)
                 throw ADP.InvalidConnectTimeoutValue();
             }
 
-            string progid = ConvertValueToString(KEY.Data_Provider, null);
+            string? progid = ConvertValueToString(KEY.Data_Provider, null);
             if (null != progid)
             {
                 progid = progid.Trim();
@@ -376,7 +376,7 @@ private string ValidateConnectionString(string connectionString)
                     ValidateProvider(progid);
                 }
             }
-            progid = ConvertValueToString(KEY.Provider, string.Empty).Trim();
+            progid = ConvertValueToString(KEY.Provider, string.Empty)!.Trim();
             ValidateProvider(progid); // will fail on empty 'Provider' value
 
             // initialize to default
@@ -385,10 +385,10 @@ private string ValidateConnectionString(string connectionString)
             // our default is -13, we turn off ODB.DBPROPVAL_OS_AGR_AFTERSESSION and ODB.DBPROPVAL_OS_CLIENTCURSOR flags
             _oledbServices = DbConnectionStringDefaults.OleDbServices;
 
-            bool hasOleDBServices = (base.ContainsKey(KEY.Ole_DB_Services) && !ADP.IsEmpty((string)base[KEY.Ole_DB_Services]));
+            bool hasOleDBServices = (base.ContainsKey(KEY.Ole_DB_Services) && !ADP.IsEmpty((string?)base[KEY.Ole_DB_Services]));
             if (!hasOleDBServices)
             { // don't touch registry if they have OLE DB Services
-                string classid = (string)ADP.ClassesRootRegistryValue(progid + "\\CLSID", string.Empty);
+                string? classid = (string?)ADP.ClassesRootRegistryValue(progid + "\\CLSID", string.Empty);
                 if ((null != classid) && (0 < classid.Length))
                 {
                     // CLSID detection of 'Microsoft OLE DB Provider for ODBC Drivers'
@@ -397,7 +397,7 @@ private string ValidateConnectionString(string connectionString)
                     {
                         throw ODB.MSDASQLNotSupported();
                     }
-                    object tmp = ADP.ClassesRootRegistryValue("CLSID\\{" + classidProvider.ToString("D", CultureInfo.InvariantCulture) + "}", ODB.OLEDB_SERVICES);
+                    object? tmp = ADP.ClassesRootRegistryValue("CLSID\\{" + classidProvider.ToString("D", CultureInfo.InvariantCulture) + "}", ODB.OLEDB_SERVICES);
                     if (null != tmp)
                     {
                         // @devnote: some providers like MSDataShape don't have the OLEDB_SERVICES value
diff --git a/src/libraries/System.Data.OleDb/src/OleDbConnectionStringBuilder.cs b/src/libraries/System.Data.OleDb/src/OleDbConnectionStringBuilder.cs
index 0ffb80427fc5f2..91e07a35389d99 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbConnectionStringBuilder.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbConnectionStringBuilder.cs
@@ -6,6 +6,7 @@
 using System.ComponentModel;
 using System.Data.Common;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Text;
 
@@ -41,8 +42,8 @@ private enum Keywords
             { DbConnectionStringKeywords.OleDbServices, Keywords.OleDbServices },
         };
 
-        private string[] _knownKeywords;
-        private Dictionary<string, OleDbPropertyInfo> _propertyInfo;
+        private string[]? _knownKeywords;
+        private Dictionary<string, OleDbPropertyInfo>? _propertyInfo;
 
         private string _fileName = DbConnectionStringDefaults.FileName;
 
@@ -58,7 +59,7 @@ public OleDbConnectionStringBuilder() : this(null)
             _knownKeywords = s_validKeywords;
         }
 
-        public OleDbConnectionStringBuilder(string connectionString) : base()
+        public OleDbConnectionStringBuilder(string? connectionString) : base()
         {
             if (!ADP.IsEmpty(connectionString))
             {
@@ -66,12 +67,13 @@ public OleDbConnectionStringBuilder(string connectionString) : base()
             }
         }
 
+        [AllowNull]
         public override object this[string keyword]
         {
             get
             {
                 ADP.CheckArgumentNull(keyword, "keyword");
-                object value;
+                object? value;
                 Keywords index;
                 if (s_keywords.TryGetValue(keyword, out index))
                 {
@@ -81,7 +83,7 @@ public override object this[string keyword]
                 {
                     Dictionary<string, OleDbPropertyInfo> dynamic = GetProviderInfo(Provider);
                     OleDbPropertyInfo info = dynamic[keyword];
-                    value = info._defaultValue;
+                    value = info._defaultValue!;
                 }
                 return value;
             }
@@ -199,7 +201,7 @@ public override ICollection Keys
         {
             get
             {
-                string[] knownKeywords = _knownKeywords;
+                string[]? knownKeywords = _knownKeywords;
                 if (null == knownKeywords)
                 {
                     Dictionary<string, OleDbPropertyInfo> dynamic = GetProviderInfo(Provider);
@@ -369,11 +371,11 @@ private void RestartProvider()
 
         private void SetValue(string keyword, bool value)
         {
-            base[keyword] = value.ToString((System.IFormatProvider)null);
+            base[keyword] = value.ToString(null);
         }
         private void SetValue(string keyword, int value)
         {
-            base[keyword] = value.ToString((System.IFormatProvider)null);
+            base[keyword] = value.ToString((System.IFormatProvider?)null);
         }
         private void SetValue(string keyword, string value)
         {
@@ -381,7 +383,7 @@ private void SetValue(string keyword, string value)
             base[keyword] = value;
         }
 
-        public override bool TryGetValue(string keyword, out object value)
+        public override bool TryGetValue(string keyword, [NotNullWhen(true)] out object? value)
         {
             ADP.CheckArgumentNull(keyword, "keyword");
             Keywords index;
@@ -393,10 +395,10 @@ public override bool TryGetValue(string keyword, out object value)
             else if (!base.TryGetValue(keyword, out value))
             {
                 Dictionary<string, OleDbPropertyInfo> dynamic = GetProviderInfo(Provider);
-                OleDbPropertyInfo info;
+                OleDbPropertyInfo? info;
                 if (dynamic.TryGetValue(keyword, out info))
                 {
-                    value = info._defaultValue;
+                    value = info._defaultValue!;
                     return true;
                 }
                 return false;
@@ -406,13 +408,13 @@ public override bool TryGetValue(string keyword, out object value)
 
         private Dictionary<string, OleDbPropertyInfo> GetProviderInfo(string provider)
         {
-            Dictionary<string, OleDbPropertyInfo> providerInfo = _propertyInfo;
+            Dictionary<string, OleDbPropertyInfo>? providerInfo = _propertyInfo;
             if (null == providerInfo)
             {
                 providerInfo = new Dictionary<string, OleDbPropertyInfo>(StringComparer.OrdinalIgnoreCase);
                 if (!ADP.IsEmpty(provider))
                 {
-                    Dictionary<string, OleDbPropertyInfo> hash = null;
+                    Dictionary<string, OleDbPropertyInfo>? hash = null;
                     try
                     {
                         StringBuilder builder = new StringBuilder();
@@ -420,15 +422,15 @@ private Dictionary<string, OleDbPropertyInfo> GetProviderInfo(string provider)
                         OleDbConnectionString constr = new OleDbConnectionString(builder.ToString(), true);
 
                         // load provider without calling Initialize or CreateDataSource
-                        using (OleDbConnectionInternal connection = new OleDbConnectionInternal(constr, (OleDbConnection)null))
+                        using (OleDbConnectionInternal connection = new OleDbConnectionInternal(constr, null))
                         {
                             // get all the init property information for the provider
-                            hash = connection.GetPropertyInfo(new Guid[] { OleDbPropertySetGuid.DBInitAll });
+                            hash = connection.GetPropertyInfo(new Guid[] { OleDbPropertySetGuid.DBInitAll })!;
                             foreach (KeyValuePair<string, OleDbPropertyInfo> entry in hash)
                             {
                                 Keywords index;
                                 OleDbPropertyInfo info = entry.Value;
-                                if (!s_keywords.TryGetValue(info._description, out index))
+                                if (!s_keywords.TryGetValue(info._description!, out index))
                                 {
                                     if ((OleDbPropertySetGuid.DBInit == info._propertySet) &&
                                             ((ODB.DBPROP_INIT_ASYNCH == info._propertyID) ||
@@ -437,7 +439,7 @@ private Dictionary<string, OleDbPropertyInfo> GetProviderInfo(string provider)
                                     {
                                         continue; // skip this keyword
                                     }
-                                    providerInfo[info._description] = info;
+                                    providerInfo[info._description!] = info;
                                 }
                             }
 
@@ -529,7 +531,7 @@ private sealed class OleDbProviderConverter : StringConverter
             private const int DBSOURCETYPE_DATASOURCE_TDP = 1;
             private const int DBSOURCETYPE_DATASOURCE_MDP = 3;
 
-            private StandardValuesCollection _standardValues;
+            private StandardValuesCollection? _standardValues;
 
             // converter classes should have public ctor
             public OleDbProviderConverter()
@@ -546,16 +548,16 @@ public override bool GetStandardValuesExclusive(ITypeDescriptorContext context)
                 return false;
             }
 
-            public override StandardValuesCollection GetStandardValues(ITypeDescriptorContext context)
+            public override StandardValuesCollection? GetStandardValues(ITypeDescriptorContext context)
             {
-                StandardValuesCollection dataSourceNames = _standardValues;
+                StandardValuesCollection? dataSourceNames = _standardValues;
                 if (null == _standardValues)
                 {
                     // Get the sources rowset for the SQLOLEDB enumerator
                     DataTable table = (new OleDbEnumerator()).GetElements();
 
-                    DataColumn column2 = table.Columns["SOURCES_NAME"];
-                    DataColumn column5 = table.Columns["SOURCES_TYPE"];
+                    DataColumn column2 = table.Columns["SOURCES_NAME"]!;
+                    DataColumn column5 = table.Columns["SOURCES_TYPE"]!;
                     //DataColumn column4 = table.Columns["SOURCES_DESCRIPTION"];
 
                     System.Collections.Generic.List<string> providerNames = new System.Collections.Generic.List<string>(table.Rows.Count);
@@ -597,7 +599,7 @@ internal enum OleDbServiceValues : int
 
         internal sealed class OleDbServicesConverter : TypeConverter
         {
-            private StandardValuesCollection _standardValues;
+            private StandardValuesCollection? _standardValues;
 
             // converter classes should have public ctor
             public OleDbServicesConverter() : base()
@@ -612,7 +614,7 @@ public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceT
 
             public override object ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value)
             {
-                string svalue = (value as string);
+                string? svalue = (value as string);
                 if (null != svalue)
                 {
                     int services;
@@ -631,7 +633,6 @@ public override object ConvertFrom(ITypeDescriptorContext context, System.Global
                                 convertedValue |= (int)(OleDbServiceValues)Enum.Parse(typeof(OleDbServiceValues), v, true);
                             }
                             return (int)convertedValue;
-                            ;
                         }
                         else
                         {
@@ -669,7 +670,7 @@ public override bool GetStandardValuesExclusive(ITypeDescriptorContext context)
 
             public override StandardValuesCollection GetStandardValues(ITypeDescriptorContext context)
             {
-                StandardValuesCollection standardValues = _standardValues;
+                StandardValuesCollection? standardValues = _standardValues;
                 if (null == standardValues)
                 {
                     Array objValues = Enum.GetValues(typeof(OleDbServiceValues));
@@ -711,7 +712,7 @@ public override object ConvertTo(ITypeDescriptorContext context, CultureInfo cul
                 }
                 if (typeof(System.ComponentModel.Design.Serialization.InstanceDescriptor) == destinationType)
                 {
-                    OleDbConnectionStringBuilder obj = (value as OleDbConnectionStringBuilder);
+                    OleDbConnectionStringBuilder? obj = (value as OleDbConnectionStringBuilder);
                     if (null != obj)
                     {
                         return ConvertToInstanceDescriptor(obj);
@@ -724,7 +725,7 @@ private System.ComponentModel.Design.Serialization.InstanceDescriptor ConvertToI
             {
                 Type[] ctorParams = new Type[] { typeof(string) };
                 object[] ctorValues = new object[] { options.ConnectionString };
-                System.Reflection.ConstructorInfo ctor = typeof(OleDbConnectionStringBuilder).GetConstructor(ctorParams);
+                System.Reflection.ConstructorInfo ctor = typeof(OleDbConnectionStringBuilder).GetConstructor(ctorParams)!;
                 return new System.ComponentModel.Design.Serialization.InstanceDescriptor(ctor, ctorValues);
             }
         }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbDataAdapter.cs b/src/libraries/System.Data.OleDb/src/OleDbDataAdapter.cs
index 6b772f1a30fb62..e4e7ba472378ae 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbDataAdapter.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbDataAdapter.cs
@@ -8,30 +8,31 @@
 
 namespace System.Data.OleDb
 {
+    [Designer("Microsoft.VSDesigner.Data.VS.OleDbDataAdapterDesigner, Microsoft.VSDesigner, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public sealed class OleDbDataAdapter : DbDataAdapter, IDbDataAdapter, ICloneable
     {
         private static readonly object EventRowUpdated = new object();
         private static readonly object EventRowUpdating = new object();
 
-        private OleDbCommand _deleteCommand, _insertCommand, _selectCommand, _updateCommand;
+        private OleDbCommand? _deleteCommand, _insertCommand, _selectCommand, _updateCommand;
 
         public OleDbDataAdapter() : base()
         {
             GC.SuppressFinalize(this);
         }
 
-        public OleDbDataAdapter(OleDbCommand selectCommand) : this()
+        public OleDbDataAdapter(OleDbCommand? selectCommand) : this()
         {
             SelectCommand = selectCommand;
         }
 
-        public OleDbDataAdapter(string selectCommandText, string selectConnectionString) : this()
+        public OleDbDataAdapter(string? selectCommandText, string? selectConnectionString) : this()
         {
             OleDbConnection connection = new OleDbConnection(selectConnectionString);
             SelectCommand = new OleDbCommand(selectCommandText, connection);
         }
 
-        public OleDbDataAdapter(string selectCommandText, OleDbConnection selectConnection) : this()
+        public OleDbDataAdapter(string? selectCommandText, OleDbConnection? selectConnection) : this()
         {
             SelectCommand = new OleDbCommand(selectCommandText, selectConnection);
         }
@@ -44,80 +45,80 @@ private OleDbDataAdapter(OleDbDataAdapter from) : base(from)
         [
         DefaultValue(null),
         ]
-        public new OleDbCommand DeleteCommand
+        public new OleDbCommand? DeleteCommand
         {
             get { return _deleteCommand; }
             set { _deleteCommand = value; }
         }
 
-        IDbCommand IDbDataAdapter.DeleteCommand
+        IDbCommand? IDbDataAdapter.DeleteCommand
         {
             get { return _deleteCommand; }
-            set { _deleteCommand = (OleDbCommand)value; }
+            set { _deleteCommand = (OleDbCommand?)value; }
         }
 
         [
         DefaultValue(null)
         ]
-        public new OleDbCommand InsertCommand
+        public new OleDbCommand? InsertCommand
         {
             get { return _insertCommand; }
             set { _insertCommand = value; }
         }
 
-        IDbCommand IDbDataAdapter.InsertCommand
+        IDbCommand? IDbDataAdapter.InsertCommand
         {
             get { return _insertCommand; }
-            set { _insertCommand = (OleDbCommand)value; }
+            set { _insertCommand = (OleDbCommand?)value; }
         }
 
         [
         DefaultValue(null)
         ]
-        public new OleDbCommand SelectCommand
+        public new OleDbCommand? SelectCommand
         {
             get { return _selectCommand; }
             set { _selectCommand = value; }
         }
 
-        IDbCommand IDbDataAdapter.SelectCommand
+        IDbCommand? IDbDataAdapter.SelectCommand
         {
             get { return _selectCommand; }
-            set { _selectCommand = (OleDbCommand)value; }
+            set { _selectCommand = (OleDbCommand?)value; }
         }
 
         [
         DefaultValue(null)
         ]
-        public new OleDbCommand UpdateCommand
+        public new OleDbCommand? UpdateCommand
         {
             get { return _updateCommand; }
             set { _updateCommand = value; }
         }
 
-        IDbCommand IDbDataAdapter.UpdateCommand
+        IDbCommand? IDbDataAdapter.UpdateCommand
         {
             get { return _updateCommand; }
-            set { _updateCommand = (OleDbCommand)value; }
+            set { _updateCommand = (OleDbCommand?)value; }
         }
 
-        public event OleDbRowUpdatedEventHandler RowUpdated
+        public event OleDbRowUpdatedEventHandler? RowUpdated
         {
             add { Events.AddHandler(EventRowUpdated, value); }
             remove { Events.RemoveHandler(EventRowUpdated, value); }
         }
 
-        public event OleDbRowUpdatingEventHandler RowUpdating
+        public event OleDbRowUpdatingEventHandler? RowUpdating
         {
             add
             {
-                OleDbRowUpdatingEventHandler handler = (OleDbRowUpdatingEventHandler)Events[EventRowUpdating];
+                OleDbRowUpdatingEventHandler? handler = (OleDbRowUpdatingEventHandler?)Events[EventRowUpdating];
 
                 // prevent someone from registering two different command builders on the adapter by
                 // silently removing the old one
                 if ((null != handler) && (value.Target is DbCommandBuilder))
                 {
-                    OleDbRowUpdatingEventHandler d = (OleDbRowUpdatingEventHandler)ADP.FindBuilder(handler);
+                    OleDbRowUpdatingEventHandler? d = (OleDbRowUpdatingEventHandler?)ADP.FindBuilder(handler);
                     if (null != d)
                     {
                         Events.RemoveHandler(EventRowUpdating, d);
@@ -133,12 +134,12 @@ object ICloneable.Clone()
             return new OleDbDataAdapter(this);
         }
 
-        protected override RowUpdatedEventArgs CreateRowUpdatedEvent(DataRow dataRow, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        protected override RowUpdatedEventArgs CreateRowUpdatedEvent(DataRow dataRow, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         {
             return new OleDbRowUpdatedEventArgs(dataRow, command, statementType, tableMapping);
         }
 
-        protected override RowUpdatingEventArgs CreateRowUpdatingEvent(DataRow dataRow, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        protected override RowUpdatingEventArgs CreateRowUpdatingEvent(DataRow dataRow, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         {
             return new OleDbRowUpdatingEventArgs(dataRow, command, statementType, tableMapping);
         }
@@ -179,7 +180,7 @@ public int Fill(DataSet dataSet, object ADODBRecordSet, string srcTable)
             return FillFromADODB((object)dataSet, ADODBRecordSet, srcTable, true);
         }
 
-        private int FillFromADODB(object data, object adodb, string srcTable, bool multipleResults)
+        private int FillFromADODB(object data, object adodb, string? srcTable, bool multipleResults)
         {
             Debug.Assert(null != data, "FillFromADODB: null data object");
             Debug.Assert(null != adodb, "FillFromADODB: null ADODB");
@@ -200,8 +201,8 @@ private int FillFromADODB(object data, object adodb, string srcTable, bool multi
             */
 
             bool closeRecordset = multipleResults;
-            UnsafeNativeMethods.ADORecordsetConstruction recordset = (adodb as UnsafeNativeMethods.ADORecordsetConstruction);
-            UnsafeNativeMethods.ADORecordConstruction record = null;
+            UnsafeNativeMethods.ADORecordsetConstruction? recordset = (adodb as UnsafeNativeMethods.ADORecordsetConstruction);
+            UnsafeNativeMethods.ADORecordConstruction? record = null;
 
             if (null != recordset)
             {
@@ -237,10 +238,10 @@ record = (adodb as UnsafeNativeMethods.ADORecordConstruction);
 
                 do
                 {
-                    string tmp = null;
+                    string? tmp = null;
                     if (data is DataSet)
                     {
-                        tmp = GetSourceTableName(srcTable, resultCount);
+                        tmp = GetSourceTableName(srcTable!, resultCount);
                     }
                     results += FillFromRecordset(data, recordset, tmp, out incrementResultCount);
 
@@ -257,7 +258,7 @@ record = (adodb as UnsafeNativeMethods.ADORecordConstruction);
                             // Current provider does not support returning multiple recordsets from a single execution.
                             if (ODB.ADODB_NextResultError != (int)hr)
                             {
-                                UnsafeNativeMethods.IErrorInfo errorInfo = null;
+                                UnsafeNativeMethods.IErrorInfo? errorInfo = null;
                                 UnsafeNativeMethods.GetErrorInfo(0, out errorInfo);
 
                                 string message = string.Empty;
@@ -287,7 +288,7 @@ record = (adodb as UnsafeNativeMethods.ADORecordConstruction);
             }
             else if (null != record)
             {
-                results = FillFromRecord(data, record, srcTable);
+                results = FillFromRecord(data, record, srcTable!);
                 if (closeRecordset)
                 {
                     FillClose(false, record);
@@ -304,12 +305,12 @@ record = (adodb as UnsafeNativeMethods.ADORecordConstruction);
         //    return base.Fill(dataTable, dataReader);
         //}
 
-        private int FillFromRecordset(object data, UnsafeNativeMethods.ADORecordsetConstruction recordset, string srcTable, out bool incrementResultCount)
+        private int FillFromRecordset(object data, UnsafeNativeMethods.ADORecordsetConstruction recordset, string? srcTable, out bool incrementResultCount)
         {
             incrementResultCount = false;
 
             IntPtr chapter; /*ODB.DB_NULL_HCHAPTER*/
-            object result = null;
+            object? result = null;
             try
             {
                 result = recordset.get_Rowset();
@@ -331,7 +332,7 @@ private int FillFromRecordset(object data, UnsafeNativeMethods.ADORecordsetConst
                 CommandBehavior behavior = (MissingSchemaAction.AddWithKey != MissingSchemaAction) ? 0 : CommandBehavior.KeyInfo;
                 behavior |= CommandBehavior.SequentialAccess;
 
-                OleDbDataReader dataReader = null;
+                OleDbDataReader? dataReader = null;
                 try
                 {
                     // intialized with chapter only since we don't want ReleaseChapter called for this chapter handle
@@ -350,7 +351,7 @@ private int FillFromRecordset(object data, UnsafeNativeMethods.ADORecordsetConst
                         }
                         else
                         {
-                            return base.Fill((DataSet)data, srcTable, dataReader, 0, 0);
+                            return base.Fill((DataSet)data, srcTable!, dataReader, 0, 0);
                         }
                     }
                 }
@@ -367,7 +368,7 @@ private int FillFromRecordset(object data, UnsafeNativeMethods.ADORecordsetConst
 
         private int FillFromRecord(object data, UnsafeNativeMethods.ADORecordConstruction record, string srcTable)
         {
-            object result = null;
+            object? result = null;
             try
             {
                 result = record.get_Row();
@@ -388,7 +389,7 @@ private int FillFromRecord(object data, UnsafeNativeMethods.ADORecordConstructio
                 CommandBehavior behavior = (MissingSchemaAction.AddWithKey != MissingSchemaAction) ? 0 : CommandBehavior.KeyInfo;
                 behavior |= CommandBehavior.SequentialAccess | CommandBehavior.SingleRow;
 
-                OleDbDataReader dataReader = null;
+                OleDbDataReader? dataReader = null;
                 try
                 {
                     dataReader = new OleDbDataReader(null, null, 0, behavior);
@@ -428,7 +429,7 @@ private void FillClose(bool isrecordset, object value)
             }
             if ((0 < (int)hr) && (ODB.ADODB_AlreadyClosedError != (int)hr))
             {
-                UnsafeNativeMethods.IErrorInfo errorInfo = null;
+                UnsafeNativeMethods.IErrorInfo? errorInfo = null;
                 UnsafeNativeMethods.GetErrorInfo(0, out errorInfo);
                 string message = string.Empty;
                 throw new COMException(message, (int)hr);
@@ -437,7 +438,7 @@ private void FillClose(bool isrecordset, object value)
 
         protected override void OnRowUpdated(RowUpdatedEventArgs value)
         {
-            OleDbRowUpdatedEventHandler handler = (OleDbRowUpdatedEventHandler)Events[EventRowUpdated];
+            OleDbRowUpdatedEventHandler? handler = (OleDbRowUpdatedEventHandler?)Events[EventRowUpdated];
             if ((null != handler) && (value is OleDbRowUpdatedEventArgs))
             {
                 handler(this, (OleDbRowUpdatedEventArgs)value);
@@ -447,7 +448,7 @@ protected override void OnRowUpdated(RowUpdatedEventArgs value)
 
         protected override void OnRowUpdating(RowUpdatingEventArgs value)
         {
-            OleDbRowUpdatingEventHandler handler = (OleDbRowUpdatingEventHandler)Events[EventRowUpdating];
+            OleDbRowUpdatingEventHandler? handler = (OleDbRowUpdatingEventHandler?)Events[EventRowUpdating];
             if ((null != handler) && (value is OleDbRowUpdatingEventArgs))
             {
                 handler(this, (OleDbRowUpdatingEventArgs)value);
diff --git a/src/libraries/System.Data.OleDb/src/OleDbDataReader.cs b/src/libraries/System.Data.OleDb/src/OleDbDataReader.cs
index 5560f3f0e956c8..cf0a8ef67023b8 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbDataReader.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbDataReader.cs
@@ -18,17 +18,17 @@ public sealed class OleDbDataReader : DbDataReader
         private readonly CommandBehavior _commandBehavior;
 
         // object model interaction
-        private OleDbConnection _connection;
-        private OleDbCommand _command;
+        private OleDbConnection? _connection;
+        private OleDbCommand? _command;
 
         // DataReader owns the parameter bindings until CloseDataReader
         // this allows OleDbCommand.Dispose to not require OleDbDataReader.Dispose
-        private Bindings _parameterBindings;
+        private Bindings? _parameterBindings;
 
         // OLEDB interfaces
-        private UnsafeNativeMethods.IMultipleResults _imultipleResults;
-        private UnsafeNativeMethods.IRowset _irowset;
-        private UnsafeNativeMethods.IRow _irow;
+        private UnsafeNativeMethods.IMultipleResults? _imultipleResults;
+        private UnsafeNativeMethods.IRowset? _irowset;
+        private UnsafeNativeMethods.IRow? _irow;
 
         private ChapterHandle _chapterHandle = ChapterHandle.DB_NULL_HCHAPTER;
 
@@ -38,7 +38,7 @@ public sealed class OleDbDataReader : DbDataReader
         private long _sequentialBytesRead;
         private int _sequentialOrdinal;
 
-        private Bindings[] _bindings; // _metdata contains the ColumnBinding
+        private Bindings?[]? _bindings; // _metdata contains the ColumnBinding
 
         // do we need to jump to the next accessor
         private int _nextAccessorForRetrieval;
@@ -55,20 +55,20 @@ public sealed class OleDbDataReader : DbDataReader
 
         // cached information for Reading (rowhandles/status)
         private IntPtr _rowHandleFetchCount; // (>1 fails against jet)
-        private RowHandleBuffer _rowHandleNativeBuffer;
+        private RowHandleBuffer? _rowHandleNativeBuffer;
 
         private IntPtr _rowFetchedCount;
         private int _currentRow;
 
-        private DataTable _dbSchemaTable;
+        private DataTable? _dbSchemaTable;
 
         private int _visibleFieldCount;
-        private MetaData[] _metadata;
-        private FieldNameLookup _fieldNameLookup;
+        private MetaData[]? _metadata;
+        private FieldNameLookup? _fieldNameLookup;
 
         // ctor for an ICommandText, IMultipleResults, IRowset, IRow
         // ctor for an ADODB.Recordset, ADODB.Record or Hierarchial resultset
-        internal OleDbDataReader(OleDbConnection connection, OleDbCommand command, int depth, CommandBehavior commandBehavior)
+        internal OleDbDataReader(OleDbConnection? connection, OleDbCommand? command, int depth, CommandBehavior commandBehavior)
         {
             _connection = connection;
             _command = command;
@@ -92,12 +92,12 @@ private void Initialize()
             }
         }
 
-        internal void InitializeIMultipleResults(object result)
+        internal void InitializeIMultipleResults(object? result)
         {
             Initialize();
-            _imultipleResults = (UnsafeNativeMethods.IMultipleResults)result; // maybe null if no results
+            _imultipleResults = (UnsafeNativeMethods.IMultipleResults?)result; // maybe null if no results
         }
-        internal void InitializeIRowset(object result, ChapterHandle chapterHandle, IntPtr recordsAffected)
+        internal void InitializeIRowset(object? result, ChapterHandle chapterHandle, IntPtr recordsAffected)
         {
             // if from ADODB, connection will be null
             if ((null == _connection) || (ChapterHandle.DB_NULL_HCHAPTER != chapterHandle))
@@ -107,21 +107,21 @@ internal void InitializeIRowset(object result, ChapterHandle chapterHandle, IntP
 
             Initialize();
             _recordsAffected = recordsAffected;
-            _irowset = (UnsafeNativeMethods.IRowset)result; // maybe null if no results
+            _irowset = (UnsafeNativeMethods.IRowset?)result; // maybe null if no results
             _chapterHandle = chapterHandle;
         }
 
-        internal void InitializeIRow(object result, IntPtr recordsAffected)
+        internal void InitializeIRow(object? result, IntPtr recordsAffected)
         {
             Initialize();
             Debug.Assert(_singleRow, "SingleRow not already set");
             _singleRow = true;
             _recordsAffected = recordsAffected;
-            _irow = (UnsafeNativeMethods.IRow)result; // maybe null if no results
+            _irow = (UnsafeNativeMethods.IRow?)result; // maybe null if no results
             _hasRows = (null != _irow);
         }
 
-        internal OleDbCommand Command
+        internal OleDbCommand? Command
         {
             get
             {
@@ -149,7 +149,7 @@ public override int FieldCount
                 {
                     throw ADP.DataReaderClosed("FieldCount");
                 }
-                MetaData[] metadata = MetaData;
+                MetaData[]? metadata = MetaData;
                 return ((null != metadata) ? metadata.Length : 0);
             }
         }
@@ -178,7 +178,7 @@ public override bool IsClosed
             }
         }
 
-        private MetaData[] MetaData
+        private MetaData[]? MetaData
         {
             get { return _metadata; }
         }
@@ -232,7 +232,7 @@ private UnsafeNativeMethods.IRowsetInfo IRowsetInfo()
 
         private UnsafeNativeMethods.IRowset IRowset()
         {
-            UnsafeNativeMethods.IRowset irowset = _irowset;
+            UnsafeNativeMethods.IRowset? irowset = _irowset;
             if (null == irowset)
             {
                 Debug.Assert(false, "object is disposed");
@@ -243,7 +243,7 @@ private UnsafeNativeMethods.IRowset IRowset()
 
         private UnsafeNativeMethods.IRow IRow()
         {
-            UnsafeNativeMethods.IRow irow = _irow;
+            UnsafeNativeMethods.IRow? irow = _irow;
             if (null == irow)
             {
                 Debug.Assert(false, "object is disposed");
@@ -254,10 +254,10 @@ private UnsafeNativeMethods.IRow IRow()
 
         public override DataTable GetSchemaTable()
         {
-            DataTable schemaTable = _dbSchemaTable;
+            DataTable? schemaTable = _dbSchemaTable;
             if (null == schemaTable)
             {
-                MetaData[] metadata = MetaData;
+                MetaData[]? metadata = MetaData;
                 if ((null != metadata) && (0 < metadata.Length))
                 {
                     if ((0 < metadata.Length) && _useIColumnsRowset && (null != _connection))
@@ -273,7 +273,10 @@ public override DataTable GetSchemaTable()
                 //GetSchemaTable() is defined to return null after NextResult returns false
                 //throw ADP.DataReaderNoData();
             }
+// TODO-NULLABLE: Behavior change (https://github.com/dotnet/runtime/issues/509)
+#nullable disable
             return schemaTable;
+#nullable enable
         }
 
         internal void BuildMetaInfo()
@@ -451,7 +454,7 @@ private void BuildSchemaTableInfo(object handle, bool filterITypeInfo, bool filt
             Debug.Assert(null == _dbSchemaTable, "non-null SchemaTable");
             Debug.Assert(null == _metadata, "non-null metadata");
             Debug.Assert(null != handle, "unexpected null rowset");
-            UnsafeNativeMethods.IColumnsInfo icolumnsInfo = (handle as UnsafeNativeMethods.IColumnsInfo);
+            UnsafeNativeMethods.IColumnsInfo? icolumnsInfo = (handle as UnsafeNativeMethods.IColumnsInfo);
             if (null == icolumnsInfo)
             {
                 _dbSchemaTable = null;
@@ -606,11 +609,11 @@ private void BuildSchemaTableRowset(object handle)
         {
             Debug.Assert(null == _dbSchemaTable, "BuildSchemaTableRowset - non-null SchemaTable");
             Debug.Assert(null != handle, "BuildSchemaTableRowset(object) - unexpected null handle");
-            UnsafeNativeMethods.IColumnsRowset icolumnsRowset = (handle as UnsafeNativeMethods.IColumnsRowset);
+            UnsafeNativeMethods.IColumnsRowset? icolumnsRowset = (handle as UnsafeNativeMethods.IColumnsRowset);
 
             if (null != icolumnsRowset)
             {
-                UnsafeNativeMethods.IRowset rowset = null;
+                UnsafeNativeMethods.IRowset? rowset = null;
                 IntPtr cOptColumns;
                 OleDbHResult hr;
 
@@ -643,11 +646,11 @@ private void BuildSchemaTableRowset(object handle)
 
         public override void Close()
         {
-            OleDbConnection con = _connection;
-            OleDbCommand cmd = _command;
-            Bindings bindings = _parameterBindings;
-            _connection = null;
-            _command = null;
+            OleDbConnection? con = _connection;
+            OleDbCommand? cmd = _command;
+            Bindings? bindings = _parameterBindings;
+            _connection = null!;
+            _command = null!;
             _parameterBindings = null;
 
             _isClosed = true;
@@ -667,7 +670,7 @@ public override void Close()
             }
             else
             {
-                UnsafeNativeMethods.IMultipleResults multipleResults = _imultipleResults;
+                UnsafeNativeMethods.IMultipleResults? multipleResults = _imultipleResults;
                 _imultipleResults = null;
 
                 if (null != multipleResults)
@@ -682,7 +685,7 @@ public override void Close()
                         if ((null != cmd) && !cmd.canceling)
                         {
                             IntPtr affected = IntPtr.Zero;
-                            OleDbException nextResultsFailure = NextResults(multipleResults, null, cmd, out affected);
+                            OleDbException? nextResultsFailure = NextResults(multipleResults, null, cmd, out affected);
                             _recordsAffected = AddRecordsAffected(_recordsAffected, affected);
                             if (null != nextResultsFailure)
                             {
@@ -718,7 +721,7 @@ public override void Close()
             }
 
             // release unmanaged objects
-            RowHandleBuffer rowHandleNativeBuffer = _rowHandleNativeBuffer;
+            RowHandleBuffer? rowHandleNativeBuffer = _rowHandleNativeBuffer;
             _rowHandleNativeBuffer = null;
             if (null != rowHandleNativeBuffer)
             {
@@ -738,7 +741,7 @@ internal void CloseReaderFromConnection(bool canceling)
 
             // called from the connection which will remove this from its ReferenceCollection
             // we want the NextResult behavior, but no errors
-            _connection = null;
+            _connection = null!;
 
             Close();
         }
@@ -754,16 +757,16 @@ private void DisposeManagedRowset()
             _nextAccessorForRetrieval = 0;
             _nextValueForRetrieval = 0;
 
-            Bindings[] bindings = _bindings;
+            Bindings?[]? bindings = _bindings;
             _bindings = null;
 
             if (null != bindings)
             {
                 for (int i = 0; i < bindings.Length; ++i)
                 {
-                    if (null != bindings[i])
+                    if (bindings[i] is Bindings binding)
                     {
-                        bindings[i].Dispose();
+                        binding.Dispose();
                     }
                 }
             }
@@ -779,7 +782,7 @@ private void DisposeManagedRowset()
 
         private void DisposeNativeMultipleResults()
         {
-            UnsafeNativeMethods.IMultipleResults imultipleResults = _imultipleResults;
+            UnsafeNativeMethods.IMultipleResults? imultipleResults = _imultipleResults;
             _imultipleResults = null;
 
             if (null != imultipleResults)
@@ -790,7 +793,7 @@ private void DisposeNativeMultipleResults()
 
         private void DisposeNativeRowset()
         {
-            UnsafeNativeMethods.IRowset irowset = _irowset;
+            UnsafeNativeMethods.IRowset? irowset = _irowset;
             _irowset = null;
 
             ChapterHandle chapter = _chapterHandle;
@@ -809,7 +812,7 @@ private void DisposeNativeRowset()
 
         private void DisposeNativeRow()
         {
-            UnsafeNativeMethods.IRow irow = _irow;
+            UnsafeNativeMethods.IRow? irow = _irow;
             _irow = null;
 
             if (null != irow)
@@ -860,7 +863,7 @@ private ColumnBinding DoSequentialCheck(int ordinal, long dataIndex, string meth
             return binding;
         }
 
-        public override long GetBytes(int ordinal, long dataIndex, byte[] buffer, int bufferIndex, int length)
+        public override long GetBytes(int ordinal, long dataIndex, byte[]? buffer, int bufferIndex, int length)
         {
             ColumnBinding binding = DoSequentialCheck(ordinal, dataIndex, ADP.GetBytes);
             byte[] value = binding.ValueByteArray();
@@ -896,7 +899,7 @@ public override long GetBytes(int ordinal, long dataIndex, byte[] buffer, int bu
             return byteCount;
         }
 
-        public override long GetChars(int ordinal, long dataIndex, char[] buffer, int bufferIndex, int length)
+        public override long GetChars(int ordinal, long dataIndex, char[]? buffer, int bufferIndex, int length)
         {
             ColumnBinding binding = DoSequentialCheck(ordinal, dataIndex, ADP.GetChars);
             string value = binding.ValueString();
@@ -951,21 +954,22 @@ protected override DbDataReader GetDbDataReader(int ordinal)
             return GetData(ordinal);
         }
 
-        internal OleDbDataReader ResetChapter(int bindingIndex, int index, RowBinding rowbinding, int valueOffset)
+        internal OleDbDataReader? ResetChapter(int bindingIndex, int index, RowBinding rowbinding, int valueOffset)
         {
-            return GetDataForReader(_metadata[bindingIndex + index].ordinal, rowbinding, valueOffset);
+            return GetDataForReader(_metadata![bindingIndex + index].ordinal, rowbinding, valueOffset);
         }
 
-        private OleDbDataReader GetDataForReader(IntPtr ordinal, RowBinding rowbinding, int valueOffset)
+        private OleDbDataReader? GetDataForReader(IntPtr ordinal, RowBinding rowbinding, int valueOffset)
         {
             UnsafeNativeMethods.IRowsetInfo rowsetInfo = IRowsetInfo();
-            UnsafeNativeMethods.IRowset result;
+            UnsafeNativeMethods.IRowset? result;
             OleDbHResult hr;
             hr = rowsetInfo.GetReferencedRowset((IntPtr)ordinal, ref ODB.IID_IRowset, out result);
 
             ProcessResults(hr);
 
-            OleDbDataReader reader = null;
+            OleDbDataReader? reader = null;
+            // TODO: Not sure if GetReferenceRowset above actually returns null, calling code seems to assume it doesn't
             if (null != result)
             {
                 // only when the first datareader is closed will the connection close
@@ -1021,7 +1025,8 @@ public override Type GetFieldType(int index)
         {
             if (null != _metadata)
             {
-                return _metadata[index].type.dataType;
+                // TODO-NULLABLE: Should throw if null (empty), though it probably doesn't happen
+                return _metadata[index].type.dataType!;
             }
             throw ADP.DataReaderNoData();
         }
@@ -1102,7 +1107,7 @@ private MetaData DoValueCheck(int ordinal)
                 throw ADP.NonSequentialColumnAccess(ordinal, _nextValueForRetrieval);
             }
             // @usernote: user may encounter the IndexOutOfRangeException
-            MetaData info = _metadata[ordinal];
+            MetaData info = _metadata![ordinal];
             return info;
         }
 
@@ -1127,7 +1132,7 @@ private ColumnBinding GetValueBinding(MetaData info)
                 {
                     if (_nextValueForRetrieval != binding.Index)
                     { // release old value
-                        _metadata[_nextValueForRetrieval].columnBinding.ResetValue();
+                        _metadata![_nextValueForRetrieval].columnBinding.ResetValue();
                     }
                     _nextAccessorForRetrieval = binding.IndexForAccessor;
                 }
@@ -1166,7 +1171,7 @@ public override int GetValues(object[] values)
             }
             DoValueCheck(0);
             int count = Math.Min(values.Length, _visibleFieldCount);
-            for (int i = 0; (i < _metadata.Length) && (i < count); ++i)
+            for (int i = 0; (i < _metadata!.Length) && (i < count); ++i)
             {
                 ColumnBinding binding = GetValueBinding(_metadata[i]);
                 values[i] = binding.Value();
@@ -1187,7 +1192,7 @@ public override bool IsDBNull(int ordinal)
 
         private void ProcessResults(OleDbHResult hr)
         {
-            Exception e;
+            Exception? e;
             if (null != _command)
             {
                 e = OleDbConnection.ProcessResults(hr, _connection, _command);
@@ -1249,10 +1254,10 @@ internal void HasRowsRead()
             _isRead = false;
         }
 
-        internal static OleDbException NextResults(UnsafeNativeMethods.IMultipleResults imultipleResults, OleDbConnection connection, OleDbCommand command, out IntPtr recordsAffected)
+        internal static OleDbException? NextResults(UnsafeNativeMethods.IMultipleResults? imultipleResults, OleDbConnection? connection, OleDbCommand command, out IntPtr recordsAffected)
         {
             recordsAffected = ADP.RecordsUnaffected;
-            List<OleDbException> exceptions = null;
+            List<OleDbException>? exceptions = null;
             if (null != imultipleResults)
             {
                 object result;
@@ -1278,10 +1283,10 @@ internal static OleDbException NextResults(UnsafeNativeMethods.IMultipleResults
                     }
                     if (null != connection)
                     {
-                        Exception e = OleDbConnection.ProcessResults(hr, connection, command);
+                        Exception? e = OleDbConnection.ProcessResults(hr, connection, command);
                         if (null != e)
                         {
-                            OleDbException excep = (e as OleDbException);
+                            OleDbException? excep = (e as OleDbException);
                             if (null != excep)
                             {
                                 if (null == exceptions)
@@ -1337,8 +1342,8 @@ public override bool NextResult()
             }
             _fieldNameLookup = null;
 
-            OleDbCommand command = _command;
-            UnsafeNativeMethods.IMultipleResults imultipleResults = _imultipleResults;
+            OleDbCommand? command = _command;
+            UnsafeNativeMethods.IMultipleResults? imultipleResults = _imultipleResults;
             if (null != imultipleResults)
             {
                 DisposeOpenResults();
@@ -1349,7 +1354,7 @@ public override bool NextResult()
                     Debug.Assert(null == _irow, "NextResult: row loop check");
                     Debug.Assert(null == _irowset, "NextResult: rowset loop check");
 
-                    object result = null;
+                    object? result = null;
                     OleDbHResult hr;
                     IntPtr affected;
 
@@ -1394,7 +1399,7 @@ public override bool NextResult()
         public override bool Read()
         {
             bool retflag = false;
-            OleDbCommand command = _command;
+            OleDbCommand? command = _command;
             if ((null != command) && command.canceling)
             {
                 DisposeOpenResults();
@@ -1439,7 +1444,7 @@ private bool ReadRow()
             else
             {
                 _isRead = true;
-                return (0 < _metadata.Length);
+                return (0 < _metadata!.Length);
             }
             return false;
         }
@@ -1447,7 +1452,7 @@ private bool ReadRow()
         private bool ReadRowset()
         {
             Debug.Assert(null != _irowset, "ReadRow: null IRowset");
-            Debug.Assert(0 <= _metadata.Length, "incorrect state for fieldCount");
+            Debug.Assert(0 <= _metadata!.Length, "incorrect state for fieldCount");
 
             // releases bindings as necessary
             // bumps current row, else resets it back to initial state
@@ -1477,11 +1482,11 @@ private void ReleaseCurrentRow()
             if (0 < (int)_rowFetchedCount)
             {
                 // release the data in the current row
-                Bindings[] bindings = _bindings;
+                Bindings?[]? bindings = _bindings;
                 Debug.Assert(null != bindings, "ReleaseCurrentRow: null dbBindings");
                 for (int i = 0; (i < bindings.Length) && (i < _nextAccessorForRetrieval); ++i)
                 {
-                    bindings[i].CleanupBindings();
+                    bindings[i]!.CleanupBindings();
                 }
                 _nextAccessorForRetrieval = 0;
                 _nextValueForRetrieval = 0;
@@ -1516,7 +1521,7 @@ private void CreateAccessors(bool allowMultipleAccessor)
             {
                 _rowHandleFetchCount = new IntPtr(1);
 
-                object maxRows = GetPropertyValue(ODB.DBPROP_MAXROWS);
+                object? maxRows = GetPropertyValue(ODB.DBPROP_MAXROWS);
                 if (maxRows is int)
                 {
                     _rowHandleFetchCount = new IntPtr((int)maxRows);
@@ -1545,7 +1550,7 @@ private Bindings[] CreateBindingsFromMetaData(bool allowMultipleAccessor)
             int bindingCount = 0;
             int currentBindingIndex = 0;
 
-            MetaData[] metadata = _metadata;
+            MetaData[] metadata = _metadata!;
 
             int[] indexToBinding = new int[metadata.Length];
             int[] indexWithinBinding = new int[metadata.Length];
@@ -1723,7 +1728,7 @@ private void GetRowHandles(/*int skipCount*/)
 
             OleDbHResult hr = 0;
 
-            RowHandleBuffer rowHandleBuffer = _rowHandleNativeBuffer;
+            RowHandleBuffer rowHandleBuffer = _rowHandleNativeBuffer!;
             bool mustRelease = false;
 
             RuntimeHelpers.PrepareConstrainedRegions();
@@ -1777,7 +1782,7 @@ private void GetRowDataFromHandle()
 
             IntPtr rowHandle = _rowHandleNativeBuffer.GetRowHandle(_currentRow);
 
-            RowBinding rowBinding = _bindings[_nextAccessorForRetrieval].RowBinding();
+            RowBinding rowBinding = _bindings[_nextAccessorForRetrieval]!.RowBinding()!;
             IntPtr accessorHandle = rowBinding.DangerousGetAccessorHandle();
 
             bool mustRelease = false;
@@ -1811,7 +1816,7 @@ private void ReleaseRowHandles()
 
             OleDbHResult hr;
             UnsafeNativeMethods.IRowset irowset = IRowset();
-            hr = irowset.ReleaseRows(_rowFetchedCount, _rowHandleNativeBuffer, ADP.PtrZero, ADP.PtrZero, ADP.PtrZero);
+            hr = irowset.ReleaseRows(_rowFetchedCount, _rowHandleNativeBuffer!, ADP.PtrZero, ADP.PtrZero, ADP.PtrZero);
 
             if (hr < 0)
             {
@@ -1824,7 +1829,7 @@ private void ReleaseRowHandles()
             _isRead = false;
         }
 
-        private object GetPropertyValue(int propertyId)
+        private object? GetPropertyValue(int propertyId)
         {
             if (null != _irowset)
             {
@@ -1837,7 +1842,7 @@ private object GetPropertyValue(int propertyId)
             return OleDbPropertyStatus.NotSupported;
         }
 
-        private object GetPropertyOnRowset(Guid propertySet, int propertyID)
+        private object? GetPropertyOnRowset(Guid propertySet, int propertyID)
         {
             OleDbHResult hr;
             ItagDBPROP[] dbprops;
@@ -1868,14 +1873,14 @@ private void GetRowValue()
             Debug.Assert(null != _irow, "GetRowValue: null IRow");
             Debug.Assert(null != _metadata, "GetRowValue: null MetaData");
 
-            Bindings bindings = _bindings[_nextAccessorForRetrieval];
+            Bindings bindings = _bindings![_nextAccessorForRetrieval]!;
             ColumnBinding[] columnBindings = bindings.ColumnBindings();
-            RowBinding rowBinding = bindings.RowBinding();
+            RowBinding rowBinding = bindings.RowBinding()!;
             Debug.Assert(_nextValueForRetrieval <= columnBindings[0].Index, "backwards retrieval");
 
             bool mustReleaseBinding = false;
             bool[] mustRelease = new bool[columnBindings.Length];
-            StringMemHandle[] sptr = new StringMemHandle[columnBindings.Length];
+            StringMemHandle?[] sptr = new StringMemHandle[columnBindings.Length];
 
             RuntimeHelpers.PrepareConstrainedRegions();
             try
@@ -1892,9 +1897,9 @@ private void GetRowValue()
                         columnBindings[i]._sptr = sptr[i];
                     }
 
-                    sptr[i].DangerousAddRef(ref mustRelease[i]);
+                    sptr[i]!.DangerousAddRef(ref mustRelease[i]);
 
-                    IntPtr ulPropid = ((null != sptr[i]) ? sptr[i].DangerousGetHandle() : info.propid);
+                    IntPtr ulPropid = ((null != sptr[i]) ? sptr[i]!.DangerousGetHandle() : info.propid);
                     bindings.GuidKindName(info.guid, info.kind, ulPropid);
                 }
 
@@ -1917,7 +1922,7 @@ private void GetRowValue()
                 {
                     if (mustRelease[i])
                     {
-                        sptr[i].DangerousRelease();
+                        sptr[i]!.DangerousRelease();
                     }
                 }
             }
@@ -1927,7 +1932,7 @@ private void GetRowValue()
         private int IndexOf(Hashtable hash, string name)
         {
             // via case sensitive search, first match with lowest ordinal matches
-            object index = hash[name];
+            object? index = hash[name];
             if (null != index)
             {
                 return (int)index; // match via case-insensitive or by chance lowercase
@@ -1963,7 +1968,7 @@ private void AppendSchemaInfo()
             }
 
             string schemaName, catalogName; // enforce single table
-            string baseSchemaName = null, baseCatalogName = null, baseTableName = null;
+            string? baseSchemaName = null, baseCatalogName = null, baseTableName = null;
             for (int i = 0; i < _metadata.Length; ++i)
             {
                 MetaData info = _metadata[i];
@@ -2005,7 +2010,7 @@ private void AppendSchemaInfo()
             {
                 if (ODB.DBPROPVAL_IC_SENSITIVE == _connection.QuotedIdentifierCase())
                 {
-                    string p = null, s = null;
+                    string? p = null, s = null;
                     _connection.GetLiteralQuotes(ADP.GetSchemaTable, out s, out p);
                     if (null == s)
                     {
@@ -2023,7 +2028,7 @@ private void AppendSchemaInfo()
 
             for (int i = _metadata.Length - 1; 0 <= i; --i)
             {
-                string basecolumname = _metadata[i].baseColumnName;
+                string? basecolumname = _metadata[i].baseColumnName;
                 if (!ADP.IsEmpty(basecolumname))
                 {
                     baseColumnNames[basecolumname] = i;
@@ -2031,7 +2036,7 @@ private void AppendSchemaInfo()
             }
             for (int i = 0; i < _metadata.Length; ++i)
             {
-                string basecolumname = _metadata[i].baseColumnName;
+                string? basecolumname = _metadata[i].baseColumnName;
                 if (!ADP.IsEmpty(basecolumname))
                 {
                     basecolumname = basecolumname.ToLowerInvariant();
@@ -2043,9 +2048,9 @@ private void AppendSchemaInfo()
             }
 
             // look for primary keys in the table
-            if (_connection.SupportSchemaRowset(OleDbSchemaGuid.Primary_Keys))
+            if (_connection!.SupportSchemaRowset(OleDbSchemaGuid.Primary_Keys))
             {
-                object[] restrictions = new object[] { baseCatalogName, baseSchemaName, baseTableName };
+                object?[] restrictions = new object?[] { baseCatalogName, baseSchemaName, baseTableName };
                 keyCount = AppendSchemaPrimaryKey(baseColumnNames, restrictions);
             }
             if (0 != keyCount)
@@ -2056,19 +2061,19 @@ private void AppendSchemaInfo()
             // look for a single unique contraint that can be upgraded
             if (_connection.SupportSchemaRowset(OleDbSchemaGuid.Indexes))
             {
-                object[] restrictions = new object[] { baseCatalogName, baseSchemaName, null, null, baseTableName };
+                object?[] restrictions = new object?[] { baseCatalogName, baseSchemaName, null, null, baseTableName };
                 AppendSchemaUniqueIndexAsKey(baseColumnNames, restrictions);
             }
         }
 
-        private int AppendSchemaPrimaryKey(Hashtable baseColumnNames, object[] restrictions)
+        private int AppendSchemaPrimaryKey(Hashtable baseColumnNames, object?[] restrictions)
         {
             int keyCount = 0;
             bool partialPrimaryKey = false;
-            DataTable table = null;
+            DataTable? table = null;
             try
             {
-                table = _connection.GetSchemaRowset(OleDbSchemaGuid.Primary_Keys, restrictions);
+                table = _connection!.GetSchemaRowset(OleDbSchemaGuid.Primary_Keys, restrictions);
             }
             catch (Exception e)
             {
@@ -2095,7 +2100,7 @@ private int AppendSchemaPrimaryKey(Hashtable baseColumnNames, object[] restricti
                         int metaindex = IndexOf(baseColumnNames, name);
                         if (0 <= metaindex)
                         {
-                            MetaData info = _metadata[metaindex];
+                            MetaData info = _metadata![metaindex];
                             info.isKeyColumn = true;
                             info.flags &= ~ODB.DBCOLUMNFLAGS_ISNULLABLE;
                             keyCount++;
@@ -2116,7 +2121,7 @@ private int AppendSchemaPrimaryKey(Hashtable baseColumnNames, object[] restricti
             }
             if (partialPrimaryKey)
             { // partial primary key detected
-                for (int i = 0; i < _metadata.Length; ++i)
+                for (int i = 0; i < _metadata!.Length; ++i)
                 {
                     _metadata[i].isKeyColumn = false;
                 }
@@ -2125,13 +2130,13 @@ private int AppendSchemaPrimaryKey(Hashtable baseColumnNames, object[] restricti
             return keyCount;
         }
 
-        private void AppendSchemaUniqueIndexAsKey(Hashtable baseColumnNames, object[] restrictions)
+        private void AppendSchemaUniqueIndexAsKey(Hashtable baseColumnNames, object?[] restrictions)
         {
             bool partialPrimaryKey = false;
-            DataTable table = null;
+            DataTable? table = null;
             try
             {
-                table = _connection.GetSchemaRowset(OleDbSchemaGuid.Indexes, restrictions);
+                table = _connection!.GetSchemaRowset(OleDbSchemaGuid.Indexes, restrictions);
             }
             catch (Exception e)
             {
@@ -2159,11 +2164,11 @@ private void AppendSchemaUniqueIndexAsKey(Hashtable baseColumnNames, object[] re
                     DataColumn pkeyColumn = dataColumns[pkeyIndex];
                     DataColumn uniqCOlumn = dataColumns[uniqIndex];
                     DataColumn nameColumn = dataColumns[nameIndex];
-                    DataColumn nulls = ((-1 != nullIndex) ? dataColumns[nullIndex] : null);
+                    DataColumn? nulls = ((-1 != nullIndex) ? dataColumns[nullIndex] : null);
 
-                    bool[] keys = new bool[_metadata.Length];
-                    bool[] uniq = new bool[_metadata.Length];
-                    string uniqueIndexName = null;
+                    bool[] keys = new bool[_metadata!.Length];
+                    bool[]? uniq = new bool[_metadata.Length];
+                    string? uniqueIndexName = null;
 
                     // match pkey name BaseColumnName
                     foreach (DataRow dataRow in table.Rows)
@@ -2257,21 +2262,22 @@ private void AppendSchemaUniqueIndexAsKey(Hashtable baseColumnNames, object[] re
             }
         }
 
-        private MetaData FindMetaData(string name)
+        private MetaData? FindMetaData(string name)
         {
-            int index = _fieldNameLookup.IndexOfName(name);
-            return ((-1 != index) ? _metadata[index] : null);
+            int index = _fieldNameLookup!.IndexOfName(name);
+            return ((-1 != index) ? _metadata![index] : null);
         }
 
-        internal void DumpToSchemaTable(UnsafeNativeMethods.IRowset rowset)
+        internal void DumpToSchemaTable(UnsafeNativeMethods.IRowset? rowset)
         {
             List<MetaData> metainfo = new List<MetaData>();
 
-            object hiddenColumns = null;
+            object? hiddenColumns = null;
             using (OleDbDataReader dataReader = new OleDbDataReader(_connection, _command, int.MinValue, 0))
             {
                 dataReader.InitializeIRowset(rowset, ChapterHandle.DB_NULL_HCHAPTER, IntPtr.Zero);
-                dataReader.BuildSchemaTableInfo(rowset, true, false);
+                // TODO-NULLABLE: BuildSchemaTableInfo asserts that rowset isn't null, but doesn't do anything with it
+                dataReader.BuildSchemaTableInfo(rowset!, true, false);
 
                 hiddenColumns = GetPropertyValue(ODB.DBPROP_HIDDENCOLUMNS);
                 if (0 == dataReader.FieldCount)
@@ -2286,24 +2292,24 @@ internal void DumpToSchemaTable(UnsafeNativeMethods.IRowset rowset)
                 // This column, together with the DBCOLUMN_GUID and DBCOLUMN_PROPID
                 // columns, forms the ID of the column. One or more (but not all) of these columns
                 // will be NULL, depending on which elements of the DBID structure the provider uses.
-                MetaData columnidname = dataReader.FindMetaData(ODB.DBCOLUMN_IDNAME);
-                MetaData columnguid = dataReader.FindMetaData(ODB.DBCOLUMN_GUID);
-                MetaData columnpropid = dataReader.FindMetaData(ODB.DBCOLUMN_PROPID);
-
-                MetaData columnname = dataReader.FindMetaData(ODB.DBCOLUMN_NAME);
-                MetaData columnordinal = dataReader.FindMetaData(ODB.DBCOLUMN_NUMBER);
-                MetaData dbtype = dataReader.FindMetaData(ODB.DBCOLUMN_TYPE);
-                MetaData columnsize = dataReader.FindMetaData(ODB.DBCOLUMN_COLUMNSIZE);
-                MetaData numericprecision = dataReader.FindMetaData(ODB.DBCOLUMN_PRECISION);
-                MetaData numericscale = dataReader.FindMetaData(ODB.DBCOLUMN_SCALE);
-                MetaData columnflags = dataReader.FindMetaData(ODB.DBCOLUMN_FLAGS);
-                MetaData baseschemaname = dataReader.FindMetaData(ODB.DBCOLUMN_BASESCHEMANAME);
-                MetaData basecatalogname = dataReader.FindMetaData(ODB.DBCOLUMN_BASECATALOGNAME);
-                MetaData basetablename = dataReader.FindMetaData(ODB.DBCOLUMN_BASETABLENAME);
-                MetaData basecolumnname = dataReader.FindMetaData(ODB.DBCOLUMN_BASECOLUMNNAME);
-                MetaData isautoincrement = dataReader.FindMetaData(ODB.DBCOLUMN_ISAUTOINCREMENT);
-                MetaData isunique = dataReader.FindMetaData(ODB.DBCOLUMN_ISUNIQUE);
-                MetaData iskeycolumn = dataReader.FindMetaData(ODB.DBCOLUMN_KEYCOLUMN);
+                MetaData columnidname = dataReader.FindMetaData(ODB.DBCOLUMN_IDNAME)!;
+                MetaData columnguid = dataReader.FindMetaData(ODB.DBCOLUMN_GUID)!;
+                MetaData columnpropid = dataReader.FindMetaData(ODB.DBCOLUMN_PROPID)!;
+
+                MetaData columnname = dataReader.FindMetaData(ODB.DBCOLUMN_NAME)!;
+                MetaData columnordinal = dataReader.FindMetaData(ODB.DBCOLUMN_NUMBER)!;
+                MetaData dbtype = dataReader.FindMetaData(ODB.DBCOLUMN_TYPE)!;
+                MetaData columnsize = dataReader.FindMetaData(ODB.DBCOLUMN_COLUMNSIZE)!;
+                MetaData numericprecision = dataReader.FindMetaData(ODB.DBCOLUMN_PRECISION)!;
+                MetaData numericscale = dataReader.FindMetaData(ODB.DBCOLUMN_SCALE)!;
+                MetaData columnflags = dataReader.FindMetaData(ODB.DBCOLUMN_FLAGS)!;
+                MetaData baseschemaname = dataReader.FindMetaData(ODB.DBCOLUMN_BASESCHEMANAME)!;
+                MetaData basecatalogname = dataReader.FindMetaData(ODB.DBCOLUMN_BASECATALOGNAME)!;
+                MetaData basetablename = dataReader.FindMetaData(ODB.DBCOLUMN_BASETABLENAME)!;
+                MetaData basecolumnname = dataReader.FindMetaData(ODB.DBCOLUMN_BASECOLUMNNAME)!;
+                MetaData isautoincrement = dataReader.FindMetaData(ODB.DBCOLUMN_ISAUTOINCREMENT)!;
+                MetaData isunique = dataReader.FindMetaData(ODB.DBCOLUMN_ISUNIQUE)!;
+                MetaData iskeycolumn = dataReader.FindMetaData(ODB.DBCOLUMN_KEYCOLUMN)!;
 
                 // @devnote: because we want to use the DBACCESSOR_OPTIMIZED bit,
                 // we are required to create the accessor before fetching any rows
@@ -2517,7 +2523,7 @@ internal void DumpToSchemaTable(UnsafeNativeMethods.IRowset rowset)
 #if DEBUG
                     if (AdapterSwitches.DataSchema.TraceVerbose)
                     {
-                        Debug.WriteLine("Filtered Column: DBCOLUMN_FLAGS=" + info.flags.ToString("X8", (System.IFormatProvider)null) + " DBCOLUMN_NAME=" + info.columnName);
+                        Debug.WriteLine("Filtered Column: DBCOLUMN_FLAGS=" + info.flags.ToString("X8", null) + " DBCOLUMN_NAME=" + info.columnName);
                     }
 #endif
                     info.isHidden = true;
@@ -2542,7 +2548,7 @@ internal static void GenerateSchemaTable(OleDbDataReader dataReader, object hand
             {
                 dataReader.BuildSchemaTableInfo(handle, false, false); // only tries IColumnsInfo
             }
-            MetaData[] metadata = dataReader.MetaData;
+            MetaData[]? metadata = dataReader.MetaData;
             if ((null != metadata) && (0 < metadata.Length))
             {
                 dataReader.BuildSchemaTable(metadata);
@@ -2581,17 +2587,17 @@ private static bool IsReadOnly(int flags)
 
     internal sealed class MetaData : IComparable
     {
-        internal Bindings bindings;
-        internal ColumnBinding columnBinding;
+        internal Bindings? bindings;
+        internal ColumnBinding columnBinding = null!; // Late-initialized
 
-        internal string columnName;
+        internal string columnName = null!; // Late-initialized
 
         internal Guid guid;
         internal int kind;
         internal IntPtr propid;
-        internal string idname;
+        internal string? idname;
 
-        internal NativeDBType type;
+        internal NativeDBType type = null!; // Late-initialized
 
         internal IntPtr ordinal;
         internal int size;
@@ -2606,22 +2612,22 @@ internal sealed class MetaData : IComparable
         internal bool isKeyColumn;
         internal bool isHidden;
 
-        internal string baseSchemaName;
-        internal string baseCatalogName;
-        internal string baseTableName;
-        internal string baseColumnName;
+        internal string? baseSchemaName;
+        internal string? baseCatalogName;
+        internal string? baseTableName;
+        internal string? baseColumnName;
 
-        int IComparable.CompareTo(object obj)
+        int IComparable.CompareTo(object? obj)
         {
-            if (isHidden == (obj as MetaData).isHidden)
+            if (isHidden == (obj as MetaData)!.isHidden)
             {
                 if (ODB.IsRunningOnX86)
                 {
-                    return ((int)ordinal - (int)(obj as MetaData).ordinal);
+                    return ((int)ordinal - (int)(obj as MetaData)!.ordinal);
                 }
                 else
                 {
-                    long v = ((long)ordinal - (long)(obj as MetaData).ordinal);
+                    long v = ((long)ordinal - (long)(obj as MetaData)!.ordinal);
                     return ((0 < v) ? 1 : ((v < 0) ? -1 : 0));
                 }
             }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbEnumerator.cs b/src/libraries/System.Data.OleDb/src/OleDbEnumerator.cs
index 8b78d5618d2363..03ddf25741551c 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbEnumerator.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbEnumerator.cs
@@ -28,17 +28,17 @@ public static OleDbDataReader GetEnumerator(Type type)
 
         internal static OleDbDataReader GetEnumeratorFromType(Type type)
         {
-            object value = Activator.CreateInstance(type, System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance, null, null, CultureInfo.InvariantCulture, null);
+            object? value = Activator.CreateInstance(type, System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance, null, null, CultureInfo.InvariantCulture, null);
             return GetEnumeratorReader(value);
         }
 
-        private static OleDbDataReader GetEnumeratorReader(object value)
+        private static OleDbDataReader GetEnumeratorReader(object? value)
         {
-            NativeMethods.ISourcesRowset srcrowset = null;
+            NativeMethods.ISourcesRowset? srcrowset = null;
 
             try
             {
-                srcrowset = (NativeMethods.ISourcesRowset)value;
+                srcrowset = (NativeMethods.ISourcesRowset?)value;
             }
             catch (InvalidCastException)
             {
@@ -54,7 +54,7 @@ private static OleDbDataReader GetEnumeratorReader(object value)
             IntPtr propSets = ADP.PtrZero;
             OleDbHResult hr = srcrowset.GetSourcesRowset(ADP.PtrZero, ODB.IID_IRowset, propCount, propSets, out value);
 
-            Exception f = OleDbConnection.ProcessResults(hr, null, null);
+            Exception? f = OleDbConnection.ProcessResults(hr, null, null);
             if (null != f)
             {
                 throw f;
@@ -72,7 +72,7 @@ public static OleDbDataReader GetRootEnumerator()
             //readonly Guid CLSID_MSDAENUM = new Guid(0xc8b522d0,0x5cf3,0x11ce,0xad,0xe5,0x00,0xaa,0x00,0x44,0x77,0x3d);
             //Type msdaenum = Type.GetTypeFromCLSID(CLSID_MSDAENUM, true);
             const string PROGID_MSDAENUM = "MSDAENUM";
-            Type msdaenum = Type.GetTypeFromProgID(PROGID_MSDAENUM, true);
+            Type msdaenum = Type.GetTypeFromProgID(PROGID_MSDAENUM, true)!;
             return GetEnumeratorFromType(msdaenum);
         }
     }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbError.cs b/src/libraries/System.Data.OleDb/src/OleDbError.cs
index d578a50da63750..333cdb3128a795 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbError.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbError.cs
@@ -8,9 +8,9 @@ namespace System.Data.OleDb
 {
     public sealed class OleDbError
     {
-        private readonly string message;
-        private readonly string source;
-        private readonly string sqlState;
+        private readonly string? message;
+        private readonly string? source;
+        private readonly string? sqlState;
         private readonly int nativeError;
 
         internal OleDbError(UnsafeNativeMethods.IErrorRecords errorRecords, int index)
@@ -56,7 +56,7 @@ internal OleDbError(UnsafeNativeMethods.IErrorRecords errorRecords, int index)
                     {
                         this.source = ODB.FailedGetSource(hr);
                     }
-                    Marshal.ReleaseComObject(errorInfo);
+                    Marshal.ReleaseComObject(errorInfo!);
                 }
             }
 
@@ -74,7 +74,7 @@ public string Message
         {
             get
             {
-                string message = this.message;
+                string? message = this.message;
                 return ((null != message) ? message : string.Empty);
             }
         }
@@ -91,7 +91,7 @@ public string Source
         {
             get
             {
-                string source = this.source;
+                string? source = this.source;
                 return ((null != source) ? source : string.Empty);
             }
         }
@@ -100,7 +100,7 @@ public string SQLState
         {
             get
             {
-                string sqlState = this.sqlState;
+                string? sqlState = this.sqlState;
                 return ((null != sqlState) ? sqlState : string.Empty);
             }
         }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbErrorCollection.cs b/src/libraries/System.Data.OleDb/src/OleDbErrorCollection.cs
index 72e47b72705c79..d6a16448755966 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbErrorCollection.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbErrorCollection.cs
@@ -12,10 +12,10 @@ public sealed class OleDbErrorCollection : System.Collections.ICollection
     {
         private readonly ArrayList items;
 
-        internal OleDbErrorCollection(UnsafeNativeMethods.IErrorInfo errorInfo)
+        internal OleDbErrorCollection(UnsafeNativeMethods.IErrorInfo? errorInfo)
         {
             ArrayList items = new ArrayList();
-            UnsafeNativeMethods.IErrorRecords errorRecords = (errorInfo as UnsafeNativeMethods.IErrorRecords);
+            UnsafeNativeMethods.IErrorRecords? errorRecords = (errorInfo as UnsafeNativeMethods.IErrorRecords);
             if (null != errorRecords)
             {
                 int recordCount = errorRecords.GetRecordCount();
@@ -52,7 +52,7 @@ public OleDbError this[int index]
         {
             get
             {
-                return (this.items[index] as OleDbError);
+                return (this.items[index] as OleDbError)!;
             }
         }
 
diff --git a/src/libraries/System.Data.OleDb/src/OleDbException.cs b/src/libraries/System.Data.OleDb/src/OleDbException.cs
index 563099230061ad..410e9cb33da820 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbException.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbException.cs
@@ -15,19 +15,19 @@ public sealed class OleDbException : System.Data.Common.DbException
     {
         private readonly OleDbErrorCollection oledbErrors;
 
-        internal OleDbException(string message, OleDbHResult errorCode, Exception inner) : base(message, inner)
+        internal OleDbException(string? message, OleDbHResult errorCode, Exception? inner) : base(message, inner)
         {
             HResult = (int)errorCode;
             this.oledbErrors = new OleDbErrorCollection(null);
         }
 
-        internal OleDbException(OleDbException previous, Exception inner) : base(previous.Message, inner)
+        internal OleDbException(OleDbException previous, Exception? inner) : base(previous.Message, inner)
         {
             HResult = previous.ErrorCode;
             this.oledbErrors = previous.oledbErrors;
         }
 
-        private OleDbException(string message, Exception inner, string source, OleDbHResult errorCode, OleDbErrorCollection errors) : base(message, inner)
+        private OleDbException(string? message, Exception? inner, string? source, OleDbHResult errorCode, OleDbErrorCollection errors) : base(message, inner)
         {
             Debug.Assert(null != errors, "OleDbException without OleDbErrorCollection");
             Source = source;
@@ -64,11 +64,11 @@ public OleDbErrorCollection Errors
             }
         }
 
-        internal static OleDbException CreateException(UnsafeNativeMethods.IErrorInfo errorInfo, OleDbHResult errorCode, Exception inner)
+        internal static OleDbException CreateException(UnsafeNativeMethods.IErrorInfo errorInfo, OleDbHResult errorCode, Exception? inner)
         {
             OleDbErrorCollection errors = new OleDbErrorCollection(errorInfo);
-            string message = null;
-            string source = null;
+            string? message = null;
+            string? source = null;
             OleDbHResult hr = 0;
 
             if (null != errorInfo)
diff --git a/src/libraries/System.Data.OleDb/src/OleDbInfoMessageEvent.cs b/src/libraries/System.Data.OleDb/src/OleDbInfoMessageEvent.cs
index c9f7444a3bc1d4..e082c8f5c53c1c 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbInfoMessageEvent.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbInfoMessageEvent.cs
@@ -39,7 +39,7 @@ public string Message
             }
         }
 
-        public string Source
+        public string? Source
         {
             get
             {
diff --git a/src/libraries/System.Data.OleDb/src/OleDbMetaDataFactory.cs b/src/libraries/System.Data.OleDb/src/OleDbMetaDataFactory.cs
index d5d32870a35745..e978419c2f8369 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbMetaDataFactory.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbMetaDataFactory.cs
@@ -33,7 +33,7 @@ internal SchemaRowsetName(string schemaName, Guid schemaRowset)
         internal OleDbMetaDataFactory(Stream XMLStream,
                                     string serverVersion,
                                     string serverVersionNormalized,
-                                    SchemaSupport[] schemaSupport) :
+                                    SchemaSupport[]? schemaSupport) :
             base(XMLStream, serverVersion, serverVersionNormalized)
         {
             // set up the colletion mane schema rowset guid mapping
@@ -50,7 +50,7 @@ internal OleDbMetaDataFactory(Stream XMLStream,
                  new SchemaRowsetName(OleDbMetaDataCollectionNames.Views, OleDbSchemaGuid.Views)};
 
             // verify the existance of the table in the data set
-            DataTable metaDataCollectionsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
+            DataTable? metaDataCollectionsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
             if (metaDataCollectionsTable == null)
             {
                 throw ADP.UnableToBuildCollection(DbMetaDataCollectionNames.MetaDataCollections);
@@ -60,7 +60,7 @@ internal OleDbMetaDataFactory(Stream XMLStream,
             metaDataCollectionsTable = CloneAndFilterCollection(DbMetaDataCollectionNames.MetaDataCollections, null);
 
             // verify the existance of the table in the data set
-            DataTable restrictionsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.Restrictions];
+            DataTable? restrictionsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.Restrictions];
             if (restrictionsTable != null)
             {
                 // copy the table filtering out any rows that don't apply to the current version of the provider
@@ -72,17 +72,17 @@ internal OleDbMetaDataFactory(Stream XMLStream,
             // 2) it is in the collection to schema rowset mapping above
             // 3) the provider does not support the necessary schema rowset
 
-            DataColumn populationMechanism = metaDataCollectionsTable.Columns[_populationMechanism];
+            DataColumn? populationMechanism = metaDataCollectionsTable.Columns[_populationMechanism];
             if ((null == populationMechanism) || (typeof(string) != populationMechanism.DataType))
             {
                 throw ADP.InvalidXmlMissingColumn(DbMetaDataCollectionNames.MetaDataCollections, _populationMechanism);
             }
-            DataColumn collectionName = metaDataCollectionsTable.Columns[_collectionName];
+            DataColumn? collectionName = metaDataCollectionsTable.Columns[_collectionName];
             if ((null == collectionName) || (typeof(string) != collectionName.DataType))
             {
                 throw ADP.InvalidXmlMissingColumn(DbMetaDataCollectionNames.MetaDataCollections, _collectionName);
             }
-            DataColumn restrictionCollectionName = null;
+            DataColumn? restrictionCollectionName = null;
             if (restrictionsTable != null)
             {
                 restrictionCollectionName = restrictionsTable.Columns[_collectionName];
@@ -94,12 +94,12 @@ internal OleDbMetaDataFactory(Stream XMLStream,
 
             foreach (DataRow collection in metaDataCollectionsTable.Rows)
             {
-                string populationMechanismValue = collection[populationMechanism] as string;
+                string? populationMechanismValue = collection[populationMechanism] as string;
                 if (ADP.IsEmpty(populationMechanismValue))
                 {
                     throw ADP.InvalidXmlInvalidValue(DbMetaDataCollectionNames.MetaDataCollections, _populationMechanism);
                 }
-                string collectionNameValue = collection[collectionName] as string;
+                string? collectionNameValue = collection[collectionName] as string;
                 if (ADP.IsEmpty(collectionNameValue))
                 {
                     throw ADP.InvalidXmlInvalidValue(DbMetaDataCollectionNames.MetaDataCollections, _collectionName);
@@ -144,7 +144,7 @@ internal OleDbMetaDataFactory(Stream XMLStream,
                         {
                             foreach (DataRow restriction in restrictionsTable.Rows)
                             {
-                                string restrictionCollectionNameValue = restriction[restrictionCollectionName] as string;
+                                string? restrictionCollectionNameValue = restriction[restrictionCollectionName!] as string;
                                 if (ADP.IsEmpty(restrictionCollectionNameValue))
                                 {
                                     throw ADP.InvalidXmlInvalidValue(DbMetaDataCollectionNames.Restrictions, _collectionName);
@@ -164,12 +164,12 @@ internal OleDbMetaDataFactory(Stream XMLStream,
 
             // replace the original table with the updated one
             metaDataCollectionsTable.AcceptChanges();
-            CollectionDataSet.Tables.Remove(CollectionDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections]);
+            CollectionDataSet.Tables.Remove(CollectionDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections]!);
             CollectionDataSet.Tables.Add(metaDataCollectionsTable);
 
             if (restrictionsTable != null)
             {
-                CollectionDataSet.Tables.Remove(CollectionDataSet.Tables[DbMetaDataCollectionNames.Restrictions]);
+                CollectionDataSet.Tables.Remove(CollectionDataSet.Tables[DbMetaDataCollectionNames.Restrictions]!);
                 CollectionDataSet.Tables.Add(restrictionsTable);
             }
 
@@ -189,7 +189,7 @@ private string BuildRegularExpression(string invalidChars, string invalidStartin
         private DataTable GetDataSourceInformationTable(OleDbConnection connection, OleDbConnectionInternal internalConnection)
         {
             // verify that the data source information table is in the data set
-            DataTable dataSourceInformationTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.DataSourceInformation];
+            DataTable? dataSourceInformationTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.DataSourceInformation];
             if (dataSourceInformationTable == null)
             {
                 throw ADP.UnableToBuildCollection(DbMetaDataCollectionNames.DataSourceInformation);
@@ -206,8 +206,8 @@ private DataTable GetDataSourceInformationTable(OleDbConnection connection, OleD
             DataRow dataSourceInformation = dataSourceInformationTable.Rows[0];
 
             // update the identifier separator
-            string catalogSeparatorPattern = internalConnection.GetLiteralInfo(ODB.DBLITERAL_CATALOG_SEPARATOR);
-            string schemaSeparatorPattern = internalConnection.GetLiteralInfo(ODB.DBLITERAL_SCHEMA_SEPARATOR);
+            string? catalogSeparatorPattern = internalConnection.GetLiteralInfo(ODB.DBLITERAL_CATALOG_SEPARATOR);
+            string? schemaSeparatorPattern = internalConnection.GetLiteralInfo(ODB.DBLITERAL_SCHEMA_SEPARATOR);
 
             if (catalogSeparatorPattern != null)
             {
@@ -233,7 +233,7 @@ private DataTable GetDataSourceInformationTable(OleDbConnection connection, OleD
             }
 
             // update the DataSourceProductName
-            object property;
+            object? property;
             property = connection.GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, ODB.DBPROP_DBMSNAME);
             if (property != null)
             {
@@ -283,7 +283,7 @@ private DataTable GetDataSourceInformationTable(OleDbConnection connection, OleD
                 dataSourceInformation[DbMetaDataColumnNames.OrderByColumnsInSelect] = (bool)property;
             }
 
-            DataTable infoLiterals = internalConnection.BuildInfoLiterals();
+            DataTable? infoLiterals = internalConnection.BuildInfoLiterals();
             if (infoLiterals != null)
             {
                 DataRow[] tableNameRow = infoLiterals.Select("Literal = " + ODB.DBLITERAL_TABLE_NAME.ToString(CultureInfo.InvariantCulture));
@@ -353,7 +353,7 @@ private DataTable GetDataSourceInformationTable(OleDbConnection connection, OleD
         private DataTable GetDataTypesTable(OleDbConnection connection)
         {
             // verify the existance of the table in the data set
-            DataTable dataTypesTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.DataTypes];
+            DataTable? dataTypesTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.DataTypes];
             if (dataTypesTable == null)
             {
                 throw ADP.UnableToBuildCollection(DbMetaDataCollectionNames.DataTypes);
@@ -362,9 +362,9 @@ private DataTable GetDataTypesTable(OleDbConnection connection)
             // copy the table filtering out any rows that don't apply to tho current version of the prrovider
             dataTypesTable = CloneAndFilterCollection(DbMetaDataCollectionNames.DataTypes, null);
 
-            DataTable providerTypesTable = connection.GetOleDbSchemaTable(OleDbSchemaGuid.Provider_Types, null);
+            DataTable providerTypesTable = connection.GetOleDbSchemaTable(OleDbSchemaGuid.Provider_Types, null)!;
 
-            DataColumn[] targetColumns = new DataColumn[] {
+            DataColumn?[] targetColumns = new DataColumn?[] {
                 dataTypesTable.Columns[DbMetaDataColumnNames.TypeName],
                 dataTypesTable.Columns[DbMetaDataColumnNames.ColumnSize],
                 dataTypesTable.Columns[DbMetaDataColumnNames.CreateParameters],
@@ -381,7 +381,7 @@ private DataTable GetDataTypesTable(OleDbConnection connection)
                 dataTypesTable.Columns[DbMetaDataColumnNames.LiteralSuffix],
                 dataTypesTable.Columns[OleDbMetaDataColumnNames.NativeDataType]};
 
-            DataColumn[] sourceColumns = new DataColumn[] {
+            DataColumn?[] sourceColumns = new DataColumn?[] {
                 providerTypesTable.Columns["TYPE_NAME"],
                 providerTypesTable.Columns["COLUMN_SIZE"],
                 providerTypesTable.Columns["CREATE_PARAMS"],
@@ -400,31 +400,31 @@ private DataTable GetDataTypesTable(OleDbConnection connection)
 
             Debug.Assert(sourceColumns.Length == targetColumns.Length);
 
-            DataColumn isSearchable = dataTypesTable.Columns[DbMetaDataColumnNames.IsSearchable];
-            DataColumn isSearchableWithLike = dataTypesTable.Columns[DbMetaDataColumnNames.IsSearchableWithLike];
-            DataColumn providerDbType = dataTypesTable.Columns[DbMetaDataColumnNames.ProviderDbType];
-            DataColumn clrType = dataTypesTable.Columns[DbMetaDataColumnNames.DataType];
-            DataColumn isLong = dataTypesTable.Columns[DbMetaDataColumnNames.IsLong];
-            DataColumn isFixed = dataTypesTable.Columns[DbMetaDataColumnNames.IsFixedLength];
-            DataColumn sourceOleDbType = providerTypesTable.Columns["DATA_TYPE"];
+            DataColumn isSearchable = dataTypesTable.Columns[DbMetaDataColumnNames.IsSearchable]!;
+            DataColumn isSearchableWithLike = dataTypesTable.Columns[DbMetaDataColumnNames.IsSearchableWithLike]!;
+            DataColumn providerDbType = dataTypesTable.Columns[DbMetaDataColumnNames.ProviderDbType]!;
+            DataColumn clrType = dataTypesTable.Columns[DbMetaDataColumnNames.DataType]!;
+            DataColumn isLong = dataTypesTable.Columns[DbMetaDataColumnNames.IsLong]!;
+            DataColumn isFixed = dataTypesTable.Columns[DbMetaDataColumnNames.IsFixedLength]!;
+            DataColumn sourceOleDbType = providerTypesTable.Columns["DATA_TYPE"]!;
 
-            DataColumn searchable = providerTypesTable.Columns["SEARCHABLE"];
+            DataColumn searchable = providerTypesTable.Columns["SEARCHABLE"]!;
 
             foreach (DataRow sourceRow in providerTypesTable.Rows)
             {
                 DataRow newRow = dataTypesTable.NewRow();
                 for (int i = 0; i < sourceColumns.Length; i++)
                 {
-                    if ((sourceColumns[i] != null) && (targetColumns[i] != null))
+                    if ((sourceColumns[i] is DataColumn sourceColumn) && (targetColumns[i] is DataColumn targetColumn))
                     {
-                        newRow[targetColumns[i]] = sourceRow[sourceColumns[i]];
+                        newRow[targetColumn] = sourceRow[sourceColumn];
                     }
                 }
 
                 short nativeDataType = (short)Convert.ChangeType(sourceRow[sourceOleDbType], typeof(short), CultureInfo.InvariantCulture);
                 NativeDBType nativeType = NativeDBType.FromDBType(nativeDataType, (bool)newRow[isLong], (bool)newRow[isFixed]);
 
-                newRow[clrType] = nativeType.dataType.FullName;
+                newRow[clrType] = nativeType.dataType!.FullName;
                 newRow[providerDbType] = nativeType.enumOleDbType;
 
                 // searchable has to be special cased becasue it is not an eaxct mapping
@@ -472,7 +472,7 @@ private DataTable GetDataTypesTable(OleDbConnection connection)
         private DataTable GetReservedWordsTable(OleDbConnectionInternal internalConnection)
         {
             // verify the existance of the table in the data set
-            DataTable reservedWordsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.ReservedWords];
+            DataTable? reservedWordsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.ReservedWords];
             if (null == reservedWordsTable)
             {
                 throw ADP.UnableToBuildCollection(DbMetaDataCollectionNames.ReservedWords);
@@ -481,7 +481,7 @@ private DataTable GetReservedWordsTable(OleDbConnectionInternal internalConnecti
             // copy the table filtering out any rows that don't apply to tho current version of the prrovider
             reservedWordsTable = CloneAndFilterCollection(DbMetaDataCollectionNames.ReservedWords, null);
 
-            DataColumn reservedWordColumn = reservedWordsTable.Columns[DbMetaDataColumnNames.ReservedWord];
+            DataColumn? reservedWordColumn = reservedWordsTable.Columns[DbMetaDataColumnNames.ReservedWord];
             if (null == reservedWordColumn)
             {
                 throw ADP.UnableToBuildCollection(DbMetaDataCollectionNames.ReservedWords);
@@ -495,11 +495,11 @@ private DataTable GetReservedWordsTable(OleDbConnectionInternal internalConnecti
             return reservedWordsTable;
         }
 
-        protected override DataTable PrepareCollection(string collectionName, string[] restrictions, DbConnection connection)
+        protected override DataTable PrepareCollection(string collectionName, string?[]? restrictions, DbConnection connection)
         {
             OleDbConnection oleDbConnection = (OleDbConnection)connection;
             OleDbConnectionInternal oleDbInternalConnection = (OleDbConnectionInternal)(oleDbConnection.InnerConnection);
-            DataTable resultTable = null;
+            DataTable? resultTable = null;
             if (collectionName == DbMetaDataCollectionNames.DataSourceInformation)
             {
                 if (ADP.IsEmptyArray(restrictions) == false)
@@ -532,12 +532,12 @@ protected override DataTable PrepareCollection(string collectionName, string[] r
                     {
                         // need to special case the oledb schema rowset restrictions on columns that are not
                         // string tpyes
-                        object[] mungedRestrictions = restrictions;
+                        object?[]? mungedRestrictions = restrictions;
                         ;
                         if (restrictions != null)
                         {
                             //verify that there are not too many restrictions
-                            DataTable metaDataCollectionsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
+                            DataTable metaDataCollectionsTable = CollectionDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections]!;
                             int numberOfSupportedRestictions = -1;
                             // prepare colletion is called with the exact collection name so
                             // we can do an exact string comparision here
@@ -595,7 +595,7 @@ protected override DataTable PrepareCollection(string collectionName, string[] r
                                 }
                                 else
                                 {
-                                    throw ADP.InvalidRestrictionValue(collectionName, "TYPE", restrictions[indexRestrictionTypeSlot]);
+                                    throw ADP.InvalidRestrictionValue(collectionName, "TYPE", restrictions[indexRestrictionTypeSlot]!);
                                 }
 
                                 mungedRestrictions[indexRestrictionTypeSlot] = indexTypeValue;
@@ -634,7 +634,7 @@ protected override DataTable PrepareCollection(string collectionName, string[] r
                                 }
                                 else
                                 {
-                                    throw ADP.InvalidRestrictionValue(collectionName, "PROCEDURE_TYPE", restrictions[procedureRestrictionTypeSlot]);
+                                    throw ADP.InvalidRestrictionValue(collectionName, "PROCEDURE_TYPE", restrictions[procedureRestrictionTypeSlot]!);
                                 }
 
                                 mungedRestrictions[procedureRestrictionTypeSlot] = procedureTypeValue;
@@ -658,7 +658,7 @@ protected override DataTable PrepareCollection(string collectionName, string[] r
 
         private void SetIdentifierCase(string columnName, int propertyID, DataRow row, OleDbConnection connection)
         {
-            object property = connection.GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, propertyID);
+            object? property = connection.GetDataSourcePropertyValue(OleDbPropertySetGuid.DataSourceInfo, propertyID);
             IdentifierCase identifierCase = IdentifierCase.Unknown;
             if (property != null)
             {
diff --git a/src/libraries/System.Data.OleDb/src/OleDbParameter.cs b/src/libraries/System.Data.OleDb/src/OleDbParameter.cs
index 169c660ad73fc4..61053ad7c31908 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbParameter.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbParameter.cs
@@ -4,6 +4,7 @@
 using System.ComponentModel;
 using System.Data.Common;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 
 namespace System.Data.OleDb
@@ -11,21 +12,21 @@ namespace System.Data.OleDb
     [TypeConverter(typeof(OleDbParameter.OleDbParameterConverter))]
     public sealed partial class OleDbParameter : DbParameter, ICloneable, IDbDataParameter
     {
-        private NativeDBType _metaType;
+        private NativeDBType? _metaType;
         private int _changeID;
 
-        private string _parameterName;
+        private string? _parameterName;
         private byte _precision;
         private byte _scale;
         private bool _hasScale;
 
-        private NativeDBType _coerceMetaType;
+        private NativeDBType? _coerceMetaType;
 
         public OleDbParameter() : base()
         { // V1.0 nothing
         }
 
-        public OleDbParameter(string name, object value) : this()
+        public OleDbParameter(string? name, object? value) : this()
         {
             Debug.Assert(!(value is OleDbType), "use OleDbParameter(string, OleDbType)");
             Debug.Assert(!(value is SqlDbType), "use OleDbParameter(string, OleDbType)");
@@ -34,20 +35,20 @@ public OleDbParameter(string name, object value) : this()
             Value = value;
         }
 
-        public OleDbParameter(string name, OleDbType dataType) : this()
+        public OleDbParameter(string? name, OleDbType dataType) : this()
         {
             ParameterName = name;
             OleDbType = dataType;
         }
 
-        public OleDbParameter(string name, OleDbType dataType, int size) : this()
+        public OleDbParameter(string? name, OleDbType dataType, int size) : this()
         {
             ParameterName = name;
             OleDbType = dataType;
             Size = size;
         }
 
-        public OleDbParameter(string name, OleDbType dataType, int size, string srcColumn) : this()
+        public OleDbParameter(string? name, OleDbType dataType, int size, string? srcColumn) : this()
         {
             ParameterName = name;
             OleDbType = dataType;
@@ -56,12 +57,12 @@ public OleDbParameter(string name, OleDbType dataType, int size, string srcColum
         }
 
         [EditorBrowsable(EditorBrowsableState.Advanced)]
-        public OleDbParameter(string parameterName,
+        public OleDbParameter(string? parameterName,
                               OleDbType dbType, int size,
                               ParameterDirection direction, bool isNullable,
                               byte precision, byte scale,
-                              string srcColumn, DataRowVersion srcVersion,
-                              object value) : this()
+                              string? srcColumn, DataRowVersion srcVersion,
+                              object? value) : this()
         { // V1.0 everything
             ParameterName = parameterName;
             OleDbType = dbType;
@@ -76,12 +77,12 @@ public OleDbParameter(string parameterName,
         }
 
         [EditorBrowsable(EditorBrowsableState.Advanced)]
-        public OleDbParameter(string parameterName,
+        public OleDbParameter(string? parameterName,
                               OleDbType dbType, int size,
                               ParameterDirection direction,
                               byte precision, byte scale,
-                              string sourceColumn, DataRowVersion sourceVersion, bool sourceColumnNullMapping,
-                              object value) : this()
+                              string? sourceColumn, DataRowVersion sourceVersion, bool sourceColumnNullMapping,
+                              object? value) : this()
         { // V2.0 everything - round trip all browsable properties + precision/scale
             ParameterName = parameterName;
             OleDbType = dbType;
@@ -111,7 +112,7 @@ public override DbType DbType
             }
             set
             {
-                NativeDBType dbtype = _metaType;
+                NativeDBType? dbtype = _metaType;
                 if ((null == dbtype) || (dbtype.enumDbType != value))
                 {
                     PropertyTypeChanging();
@@ -137,7 +138,7 @@ public OleDbType OleDbType
             }
             set
             {
-                NativeDBType dbtype = _metaType;
+                NativeDBType? dbtype = _metaType;
                 if ((null == dbtype) || (dbtype.enumOleDbType != value))
                 {
                     PropertyTypeChanging();
@@ -160,11 +161,12 @@ public void ResetOleDbType()
             }
         }
 
+        [AllowNull]
         public override string ParameterName
         { // V1.2.3300, XXXParameter V1.0.3300
             get
             {
-                string parameterName = _parameterName;
+                string? parameterName = _parameterName;
                 return ((null != parameterName) ? parameterName : string.Empty);
             }
             set
@@ -289,7 +291,7 @@ private void PropertyTypeChanging()
         internal bool BindParameter(int index, Bindings bindings)
         {
             int changeID = _changeID;
-            object value = Value;
+            object? value = Value;
 
             NativeDBType dbtype = GetBindType(value);
             if (OleDbType.Empty == dbtype.enumOleDbType)
@@ -357,7 +359,7 @@ internal bool BindParameter(int index, Bindings bindings)
             { // variable length data (varbinary, varchar, nvarchar)
                 if (!ShouldSerializeSize() && ADP.IsDirection(this, ParameterDirection.Output))
                 {
-                    throw ADP.UninitializedParameterSize(index, _coerceMetaType.dataType);
+                    throw ADP.UninitializedParameterSize(index, _coerceMetaType.dataType!);
                 }
 
                 bool computedSize;
@@ -460,7 +462,7 @@ internal bool BindParameter(int index, Bindings bindings)
             return IsParameterComputed();
         }
 
-        private static object CoerceValue(object value, NativeDBType destinationType)
+        private static object? CoerceValue(object? value, NativeDBType destinationType)
         {
             Debug.Assert(null != destinationType, "null destinationType");
             if ((null != value) && (DBNull.Value != value) && (typeof(object) != destinationType.dataType))
@@ -475,11 +477,11 @@ private static object CoerceValue(object value, NativeDBType destinationType)
                         }
                         else if ((NativeDBType.CY == destinationType.dbType) && (typeof(string) == currentType))
                         {
-                            value = decimal.Parse((string)value, NumberStyles.Currency, (IFormatProvider)null);
+                            value = decimal.Parse((string)value, NumberStyles.Currency, null);
                         }
                         else
                         {
-                            value = Convert.ChangeType(value, destinationType.dataType, (IFormatProvider)null);
+                            value = Convert.ChangeType(value, destinationType.dataType!, null);
                         }
                     }
                     catch (Exception e)
@@ -490,16 +492,16 @@ private static object CoerceValue(object value, NativeDBType destinationType)
                             throw;
                         }
 
-                        throw ADP.ParameterConversionFailed(value, destinationType.dataType, e);
+                        throw ADP.ParameterConversionFailed(value, destinationType.dataType!, e);
                     }
                 }
             }
             return value;
         }
 
-        private NativeDBType GetBindType(object value)
+        private NativeDBType GetBindType(object? value)
         {
-            NativeDBType dbtype = _metaType;
+            NativeDBType? dbtype = _metaType;
             if (null == dbtype)
             {
                 if (ADP.IsNull(value))
@@ -514,12 +516,12 @@ private NativeDBType GetBindType(object value)
             return dbtype;
         }
 
-        internal object GetCoercedValue()
+        internal object? GetCoercedValue()
         {
-            object value = CoercedValue; // will also be set during binding, will rebind everytime if _metaType not set
+            object? value = CoercedValue; // will also be set during binding, will rebind everytime if _metaType not set
             if (null == value)
             {
-                value = CoerceValue(Value, _coerceMetaType);
+                value = CoerceValue(Value, _coerceMetaType!);
                 CoercedValue = value;
             }
             return value;
@@ -527,7 +529,7 @@ internal object GetCoercedValue()
 
         internal bool IsParameterComputed()
         {
-            NativeDBType metaType = _metaType;
+            NativeDBType? metaType = _metaType;
             return ((null == metaType)
                     || (!ShouldSerializeSize() && metaType.IsVariableLength)
                     || ((NativeDBType.DECIMAL == metaType.dbType) || (NativeDBType.NUMERIC == metaType.dbType)
@@ -560,7 +562,7 @@ internal void Prepare(OleDbCommand cmd)
         RefreshProperties(RefreshProperties.All),
         TypeConverter(typeof(StringConverter)),
         ]
-        public override object Value
+        public override object? Value
         { // V1.2.3300, XXXParameter V1.0.3300
             get
             {
@@ -573,17 +575,17 @@ public override object Value
             }
         }
 
-        private byte ValuePrecision(object value)
+        private byte ValuePrecision(object? value)
         {
             return ValuePrecisionCore(value);
         }
 
-        private byte ValueScale(object value)
+        private byte ValueScale(object? value)
         {
             return ValueScaleCore(value);
         }
 
-        private int ValueSize(object value)
+        private int ValueSize(object? value)
         {
             return ValueSizeCore(value);
         }
@@ -641,9 +643,9 @@ public override object ConvertTo(ITypeDescriptorContext context, CultureInfo cul
                 {
                     throw ADP.ArgumentNull("destinationType");
                 }
-                if ((typeof(System.ComponentModel.Design.Serialization.InstanceDescriptor) == destinationType) && (value is OleDbParameter))
+                if ((typeof(System.ComponentModel.Design.Serialization.InstanceDescriptor) == destinationType) && (value is OleDbParameter parameter))
                 {
-                    return ConvertToInstanceDescriptor(value as OleDbParameter);
+                    return ConvertToInstanceDescriptor(parameter);
                 }
                 return base.ConvertTo(context, culture, value, destinationType);
             }
@@ -680,7 +682,7 @@ private System.ComponentModel.Design.Serialization.InstanceDescriptor ConvertToI
                 }
 
                 Type[] ctorParams;
-                object[] ctorValues;
+                object?[] ctorValues;
                 switch (flags)
                 {
                     case 0: // ParameterName
@@ -702,7 +704,7 @@ private System.ComponentModel.Design.Serialization.InstanceDescriptor ConvertToI
                         break;
                     case 8: // Value
                         ctorParams = new Type[] { typeof(string), typeof(object) };
-                        ctorValues = new object[] { p.ParameterName, p.Value };
+                        ctorValues = new object?[] { p.ParameterName, p.Value };
                         break;
                     default: // everything else
                         if (0 == (32 & flags))
@@ -711,7 +713,7 @@ private System.ComponentModel.Design.Serialization.InstanceDescriptor ConvertToI
                             typeof(string), typeof(OleDbType), typeof(int), typeof(ParameterDirection),
                             typeof(bool), typeof(byte), typeof(byte), typeof(string),
                             typeof(DataRowVersion), typeof(object) };
-                            ctorValues = new object[] {
+                            ctorValues = new object?[] {
                             p.ParameterName, p.OleDbType,  p.Size, p.Direction,
                             p.IsNullable, p.PrecisionInternal, p.ScaleInternal, p.SourceColumn,
                             p.SourceVersion, p.Value };
@@ -723,7 +725,7 @@ private System.ComponentModel.Design.Serialization.InstanceDescriptor ConvertToI
                             typeof(byte), typeof(byte),
                             typeof(string), typeof(DataRowVersion), typeof(bool),
                             typeof(object) };
-                            ctorValues = new object[] {
+                            ctorValues = new object?[] {
                             p.ParameterName, p.OleDbType,  p.Size, p.Direction,
                             p.PrecisionInternal, p.ScaleInternal,
                             p.SourceColumn, p.SourceVersion, p.SourceColumnNullMapping,
@@ -731,7 +733,7 @@ private System.ComponentModel.Design.Serialization.InstanceDescriptor ConvertToI
                         }
                         break;
                 }
-                System.Reflection.ConstructorInfo ctor = typeof(OleDbParameter).GetConstructor(ctorParams);
+                System.Reflection.ConstructorInfo ctor = typeof(OleDbParameter).GetConstructor(ctorParams)!;
                 return new System.ComponentModel.Design.Serialization.InstanceDescriptor(ctor, ctorValues);
             }
         }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbParameterCollection.cs b/src/libraries/System.Data.OleDb/src/OleDbParameterCollection.cs
index 393e1cc494d630..3f540656e000d3 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbParameterCollection.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbParameterCollection.cs
@@ -64,27 +64,27 @@ public OleDbParameter Add(OleDbParameter value)
 
         [EditorBrowsable(EditorBrowsableState.Never)]
         [Obsolete("Add(String parameterName, Object value) has been deprecated.  Use AddWithValue(String parameterName, Object value).  https://go.microsoft.com/fwlink/?linkid=14202", false)]
-        public OleDbParameter Add(string parameterName, object value)
+        public OleDbParameter Add(string? parameterName, object? value)
         {
             return Add(new OleDbParameter(parameterName, value));
         }
 
-        public OleDbParameter AddWithValue(string parameterName, object value)
+        public OleDbParameter AddWithValue(string? parameterName, object? value)
         {
             return Add(new OleDbParameter(parameterName, value));
         }
 
-        public OleDbParameter Add(string parameterName, OleDbType oleDbType)
+        public OleDbParameter Add(string? parameterName, OleDbType oleDbType)
         {
             return Add(new OleDbParameter(parameterName, oleDbType));
         }
 
-        public OleDbParameter Add(string parameterName, OleDbType oleDbType, int size)
+        public OleDbParameter Add(string? parameterName, OleDbType oleDbType, int size)
         {
             return Add(new OleDbParameter(parameterName, oleDbType, size));
         }
 
-        public OleDbParameter Add(string parameterName, OleDbType oleDbType, int size, string sourceColumn)
+        public OleDbParameter Add(string? parameterName, OleDbType oleDbType, int size, string? sourceColumn)
         {
             return Add(new OleDbParameter(parameterName, oleDbType, size, sourceColumn));
         }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbParameterCollectionHelper.cs b/src/libraries/System.Data.OleDb/src/OleDbParameterCollectionHelper.cs
index 3470271878fdf7..9f0f898c5c300f 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbParameterCollectionHelper.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbParameterCollectionHelper.cs
@@ -11,7 +11,7 @@ namespace System.Data.OleDb
 {
     public sealed partial class OleDbParameterCollection : DbParameterCollection
     {
-        private List<OleDbParameter> _items;
+        private List<OleDbParameter>? _items;
 
         public override int Count
         {
@@ -25,7 +25,7 @@ private List<OleDbParameter> InnerList
         {
             get
             {
-                List<OleDbParameter> items = _items;
+                List<OleDbParameter>? items = _items;
 
                 if (null == items)
                 {
@@ -298,7 +298,7 @@ private void Validate(int index, object value)
                 throw ADP.ParameterNull(nameof(value), this, s_itemType);
             }
 
-            object parent = ((OleDbParameter)value).CompareExchangeParent(this, null);
+            object? parent = ((OleDbParameter)value).CompareExchangeParent(this, null);
             if (null != parent)
             {
                 if (this != parent)
diff --git a/src/libraries/System.Data.OleDb/src/OleDbRowUpdatedEvent.cs b/src/libraries/System.Data.OleDb/src/OleDbRowUpdatedEvent.cs
index 07e5a442fac452..99c2db066904b2 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbRowUpdatedEvent.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbRowUpdatedEvent.cs
@@ -7,16 +7,16 @@ namespace System.Data.OleDb
 {
     public sealed class OleDbRowUpdatedEventArgs : RowUpdatedEventArgs
     {
-        public OleDbRowUpdatedEventArgs(DataRow dataRow, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        public OleDbRowUpdatedEventArgs(DataRow dataRow, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         : base(dataRow, command, statementType, tableMapping)
         {
         }
 
-        public new OleDbCommand Command
+        public new OleDbCommand? Command
         {
             get
             {
-                return (OleDbCommand)base.Command;
+                return (OleDbCommand?)base.Command;
             }
         }
     }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbRowUpdatingEvent.cs b/src/libraries/System.Data.OleDb/src/OleDbRowUpdatingEvent.cs
index 6233b2f6d60750..d9f38ddea44fa5 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbRowUpdatingEvent.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbRowUpdatingEvent.cs
@@ -7,18 +7,18 @@ namespace System.Data.OleDb
 {
     public sealed class OleDbRowUpdatingEventArgs : RowUpdatingEventArgs
     {
-        public OleDbRowUpdatingEventArgs(DataRow dataRow, IDbCommand command, StatementType statementType, DataTableMapping tableMapping)
+        public OleDbRowUpdatingEventArgs(DataRow dataRow, IDbCommand? command, StatementType statementType, DataTableMapping tableMapping)
         : base(dataRow, command, statementType, tableMapping)
         {
         }
 
-        public new OleDbCommand Command
+        public new OleDbCommand? Command
         {
             get { return (base.Command as OleDbCommand); }
             set { base.Command = value; }
         }
 
-        protected override IDbCommand BaseCommand
+        protected override IDbCommand? BaseCommand
         {
             get { return base.BaseCommand; }
             set { base.BaseCommand = (value as OleDbCommand); }
diff --git a/src/libraries/System.Data.OleDb/src/OleDbStruct.cs b/src/libraries/System.Data.OleDb/src/OleDbStruct.cs
index 638b0973586efe..69a0e4807db783 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbStruct.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbStruct.cs
@@ -248,13 +248,13 @@ typedef struct tagDBLITERALINFO {
     internal sealed class tagDBLITERALINFO
     {
         [MarshalAs(UnmanagedType.LPWStr)]
-        internal string pwszLiteralValue = null;
+        internal string? pwszLiteralValue = null;
 
         [MarshalAs(UnmanagedType.LPWStr)]
-        internal string pwszInvalidChars = null;
+        internal string? pwszInvalidChars = null;
 
         [MarshalAs(UnmanagedType.LPWStr)]
-        internal string pwszInvalidStartingChars = null;
+        internal string? pwszInvalidStartingChars = null;
 
         internal int it;
 
@@ -309,7 +309,7 @@ typedef struct tagDBPROP {
     internal interface ItagDBPROP
     {
         OleDbPropertyStatus dwStatus { get; }
-        object vValue { get; }
+        object? vValue { get; }
         int dwPropertyID { get; }
     }
 
@@ -318,7 +318,7 @@ internal sealed class tagDBPROP_x86 : ItagDBPROP
     {
         OleDbPropertyStatus ItagDBPROP.dwStatus => this.dwStatus;
 
-        object ItagDBPROP.vValue => this.vValue;
+        object? ItagDBPROP.vValue => this.vValue;
 
         int ItagDBPROP.dwPropertyID => this.dwPropertyID;
 
@@ -329,7 +329,7 @@ internal sealed class tagDBPROP_x86 : ItagDBPROP
         internal tagDBIDX columnid;
 
         // Variant
-        [MarshalAs(UnmanagedType.Struct)] internal object vValue;
+        [MarshalAs(UnmanagedType.Struct)] internal object? vValue;
 
         internal tagDBPROP_x86()
         {
@@ -348,7 +348,7 @@ internal sealed class tagDBPROP : ItagDBPROP
     {
         OleDbPropertyStatus ItagDBPROP.dwStatus => this.dwStatus;
 
-        object ItagDBPROP.vValue => this.vValue;
+        object? ItagDBPROP.vValue => this.vValue;
 
         int ItagDBPROP.dwPropertyID => this.dwPropertyID;
         internal int dwPropertyID;
@@ -358,7 +358,7 @@ internal sealed class tagDBPROP : ItagDBPROP
         internal tagDBIDX columnid;
 
         // Variant
-        [MarshalAs(UnmanagedType.Struct)] internal object vValue;
+        [MarshalAs(UnmanagedType.Struct)] internal object? vValue;
 
         internal tagDBPROP()
         {
@@ -416,7 +416,7 @@ typedef struct tagDBCOLUMNINFO {
     internal sealed class tagDBCOLUMNINFO
     {
         [MarshalAs(UnmanagedType.LPWStr)]
-        internal string pwszName = null;
+        internal string? pwszName = null;
 
         //[MarshalAs(UnmanagedType.Interface)]
         internal IntPtr pTypeInfo = (IntPtr)0;
@@ -493,8 +493,8 @@ internal interface ItagDBPROPINFO
         int dwPropertyID { get; }
         int dwFlags { get; }
         int vtType { get; }
-        object vValue { get; }
-        string pwszDescription { get; }
+        object? vValue { get; }
+        string? pwszDescription { get; }
     }
 
     [StructLayout(LayoutKind.Sequential, Pack = 2)]
@@ -506,18 +506,18 @@ internal sealed class tagDBPROPINFO_x86 : ItagDBPROPINFO
 
         int ItagDBPROPINFO.vtType => this.vtType;
 
-        object ItagDBPROPINFO.vValue => this.vValue;
+        object? ItagDBPROPINFO.vValue => this.vValue;
 
-        string ItagDBPROPINFO.pwszDescription => this.pwszDescription;
+        string? ItagDBPROPINFO.pwszDescription => this.pwszDescription;
 
-        [MarshalAs(UnmanagedType.LPWStr)] internal string pwszDescription;
+        [MarshalAs(UnmanagedType.LPWStr)] internal string? pwszDescription;
 
         internal int dwPropertyID;
         internal int dwFlags;
 
         internal short vtType;
 
-        [MarshalAs(UnmanagedType.Struct)] internal object vValue;
+        [MarshalAs(UnmanagedType.Struct)] internal object? vValue;
 
         internal tagDBPROPINFO_x86()
         {
@@ -533,17 +533,17 @@ internal sealed class tagDBPROPINFO : ItagDBPROPINFO
 
         int ItagDBPROPINFO.vtType => this.vtType;
 
-        object ItagDBPROPINFO.vValue => this.vValue;
+        object? ItagDBPROPINFO.vValue => this.vValue;
 
-        string ItagDBPROPINFO.pwszDescription => this.pwszDescription;
-        [MarshalAs(UnmanagedType.LPWStr)] internal string pwszDescription;
+        string? ItagDBPROPINFO.pwszDescription => this.pwszDescription;
+        [MarshalAs(UnmanagedType.LPWStr)] internal string? pwszDescription;
 
         internal int dwPropertyID;
         internal int dwFlags;
 
         internal short vtType;
 
-        [MarshalAs(UnmanagedType.Struct)] internal object vValue;
+        [MarshalAs(UnmanagedType.Struct)] internal object? vValue;
 
         internal tagDBPROPINFO()
         {
diff --git a/src/libraries/System.Data.OleDb/src/OleDbTransaction.cs b/src/libraries/System.Data.OleDb/src/OleDbTransaction.cs
index 9dbd11d705a2f7..d8712488698e67 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbTransaction.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbTransaction.cs
@@ -11,11 +11,11 @@ namespace System.Data.OleDb
 {
     public sealed class OleDbTransaction : DbTransaction
     {
-        private readonly OleDbTransaction _parentTransaction; // strong reference to keep parent alive
+        private readonly OleDbTransaction? _parentTransaction; // strong reference to keep parent alive
         private readonly System.Data.IsolationLevel _isolationLevel;
 
-        private WeakReference _nestedTransaction; // child transactions
-        private WrappedTransaction _transaction;
+        private WeakReference? _nestedTransaction; // child transactions
+        private WrappedTransaction? _transaction;
 
         internal OleDbConnection _parentConnection;
 
@@ -114,7 +114,7 @@ protected override bool ReleaseHandle()
             }
         }
 
-        internal OleDbTransaction(OleDbConnection connection, OleDbTransaction transaction, IsolationLevel isolevel)
+        internal OleDbTransaction(OleDbConnection connection, OleDbTransaction? transaction, IsolationLevel isolevel)
         {
             _parentConnection = connection;
             _parentTransaction = transaction;
@@ -165,7 +165,7 @@ public override IsolationLevel IsolationLevel
             }
         }
 
-        internal OleDbTransaction Parent
+        internal OleDbTransaction? Parent
         {
             get
             {
@@ -188,7 +188,7 @@ public OleDbTransaction Begin(IsolationLevel isolevel)
             OleDbTransaction transaction = new OleDbTransaction(_parentConnection, this, isolevel);
             _nestedTransaction = new WeakReference(transaction, false);
 
-            UnsafeNativeMethods.ITransactionLocal wrapper = null;
+            UnsafeNativeMethods.ITransactionLocal? wrapper = null;
             try
             {
                 wrapper = (UnsafeNativeMethods.ITransactionLocal)_transaction.ComWrapper();
@@ -238,7 +238,7 @@ private void CommitInternal()
             }
             if (null != _nestedTransaction)
             {
-                OleDbTransaction transaction = (OleDbTransaction)_nestedTransaction.Target;
+                OleDbTransaction? transaction = (OleDbTransaction?)_nestedTransaction.Target;
                 if ((null != transaction) && _nestedTransaction.IsAlive)
                 {
                     transaction.CommitInternal();
@@ -291,12 +291,12 @@ private void DisposeManaged()
             {
                 _parentConnection.LocalTransaction = null;
             }
-            _parentConnection = null;
+            _parentConnection = null!;
         }
 
         private void ProcessResults(OleDbHResult hr)
         {
-            Exception e = OleDbConnection.ProcessResults(hr, _parentConnection, this);
+            Exception? e = OleDbConnection.ProcessResults(hr, _parentConnection, this);
             if (null != e)
             { throw e; }
         }
@@ -319,7 +319,7 @@ internal OleDbHResult RollbackInternal(bool exceptionHandling)
             {
                 if (null != _nestedTransaction)
                 {
-                    OleDbTransaction transaction = (OleDbTransaction)_nestedTransaction.Target;
+                    OleDbTransaction? transaction = (OleDbTransaction?)_nestedTransaction.Target;
                     if ((null != transaction) && _nestedTransaction.IsAlive)
                     {
                         hr = transaction.RollbackInternal(exceptionHandling);
@@ -353,7 +353,7 @@ internal static OleDbTransaction TransactionLast(OleDbTransaction head)
         {
             if (null != head._nestedTransaction)
             {
-                OleDbTransaction current = (OleDbTransaction)head._nestedTransaction.Target;
+                OleDbTransaction? current = (OleDbTransaction?)head._nestedTransaction.Target;
                 if ((null != current) && head._nestedTransaction.IsAlive)
                 {
                     return TransactionLast(current);
@@ -362,7 +362,7 @@ internal static OleDbTransaction TransactionLast(OleDbTransaction head)
             return head;
         }
 
-        internal static OleDbTransaction TransactionUpdate(OleDbTransaction transaction)
+        internal static OleDbTransaction? TransactionUpdate(OleDbTransaction? transaction)
         {
             if ((null != transaction) && (null == transaction._transaction))
             {
diff --git a/src/libraries/System.Data.OleDb/src/OleDbWrapper.cs b/src/libraries/System.Data.OleDb/src/OleDbWrapper.cs
index 19e66808fd2550..23ef6c6b0d4954 100644
--- a/src/libraries/System.Data.OleDb/src/OleDbWrapper.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDbWrapper.cs
@@ -17,10 +17,10 @@ internal sealed class OleDbServicesWrapper : WrappedIUnknown
 
         // since we only have one DataLinks object, caching the delegate here is valid as long we
         // maintain an AddRef which is also the lifetime of this class instance
-        private readonly UnsafeNativeMethods.IDataInitializeGetDataSource DangerousIDataInitializeGetDataSource;
+        private readonly UnsafeNativeMethods.IDataInitializeGetDataSource? DangerousIDataInitializeGetDataSource;
 
         // DataLinks (the unknown parameter) is created via Activator.CreateInstance outside of the SafeHandle
-        internal OleDbServicesWrapper(object unknown) : base()
+        internal OleDbServicesWrapper(object? unknown) : base()
         {
             if (null != unknown)
             {
@@ -44,7 +44,7 @@ internal OleDbServicesWrapper(object unknown) : base()
         internal void GetDataSource(OleDbConnectionString constr, ref DataSourceWrapper datasrcWrapper)
         {
             OleDbHResult hr;
-            UnsafeNativeMethods.IDataInitializeGetDataSource GetDataSource = DangerousIDataInitializeGetDataSource;
+            UnsafeNativeMethods.IDataInitializeGetDataSource GetDataSource = DangerousIDataInitializeGetDataSource!;
             bool mustRelease = false;
             RuntimeHelpers.PrepareConstrainedRegions();
             try
@@ -52,7 +52,7 @@ internal void GetDataSource(OleDbConnectionString constr, ref DataSourceWrapper
                 DangerousAddRef(ref mustRelease);
 
                 // this is the string that DataLinks / OLE DB Services will use to create the provider
-                string connectionString = constr.ActualConnectionString;
+                string connectionString = constr.ActualConnectionString!;
 
                 // base.handle is the 'this' pointer for making the COM call to GetDataSource
                 // the datasrcWrapper will store the IID_IDBInitialize pointer
@@ -72,7 +72,7 @@ internal void GetDataSource(OleDbConnectionString constr, ref DataSourceWrapper
                 {
                     throw ODB.ProviderUnavailable(constr.Provider, null);
                 }
-                Exception e = OleDbConnection.ProcessResults(hr, null, null);
+                Exception? e = OleDbConnection.ProcessResults(hr, null, null);
                 Debug.Assert(null != e, "CreateProviderError");
                 throw e;
             }
@@ -113,7 +113,7 @@ internal OleDbHResult InitializeAndCreateSession(OleDbConnectionString constr, r
                 IntPtr method = Marshal.ReadIntPtr(vtable, 0);
 
                 // we cache the QueryInterface delegate to prevent recreating it on every call
-                UnsafeNativeMethods.IUnknownQueryInterface QueryInterface = constr.DangerousDataSourceIUnknownQueryInterface;
+                UnsafeNativeMethods.IUnknownQueryInterface? QueryInterface = constr.DangerousDataSourceIUnknownQueryInterface;
 
                 // since the delegate lifetime is longer than the original instance used to create it
                 // we double check before each usage to verify the delegates function pointer
@@ -130,7 +130,7 @@ internal OleDbHResult InitializeAndCreateSession(OleDbConnectionString constr, r
                 method = Marshal.ReadIntPtr(vtable, 3 * IntPtr.Size);  // Initialize is the 4'th vtable entry
 
                 // we cache the Initialize delegate to prevent recreating it on every call
-                UnsafeNativeMethods.IDBInitializeInitialize Initialize = constr.DangerousIDBInitializeInitialize;
+                UnsafeNativeMethods.IDBInitializeInitialize? Initialize = constr.DangerousIDBInitializeInitialize;
 
                 // since the delegate lifetime is longer than the original instance used to create it
                 // we double check before each usage to verify the delegates function pointer
@@ -156,7 +156,7 @@ internal OleDbHResult InitializeAndCreateSession(OleDbConnectionString constr, r
                         vtable = Marshal.ReadIntPtr(idbCreateSession, 0);
                         method = Marshal.ReadIntPtr(vtable, 3 * IntPtr.Size);  // CreateSession is the 4'th vtable entry
 
-                        UnsafeNativeMethods.IDBCreateSessionCreateSession CreateSession = constr.DangerousIDBCreateSessionCreateSession;
+                        UnsafeNativeMethods.IDBCreateSessionCreateSession? CreateSession = constr.DangerousIDBCreateSessionCreateSession;
 
                         // since the delegate lifetime is longer than the original instance used to create it
                         // we double check before each usage to verify the delegates function pointer
@@ -227,7 +227,7 @@ internal sealed class SessionWrapper : WrappedIUnknown
 
         // we cache the DangerousIDBCreateCommandCreateCommand (expecting base.handle to be IDBCreateCommand)
         // since we maintain an AddRef on IDBCreateCommand it is safe to use the delegate without rechecking its function pointer
-        private UnsafeNativeMethods.IDBCreateCommandCreateCommand DangerousIDBCreateCommandCreateCommand;
+        private UnsafeNativeMethods.IDBCreateCommandCreateCommand? DangerousIDBCreateCommandCreateCommand;
 
         internal SessionWrapper() : base()
         {
@@ -319,11 +319,11 @@ internal void VerifyIDBCreateCommand(OleDbConnectionString constr)
             DangerousIDBCreateCommandCreateCommand = CreateCommand;
         }
 
-        internal OleDbHResult CreateCommand(ref object icommandText)
+        internal OleDbHResult CreateCommand(ref object? icommandText)
         {
             // if (null == CreateCommand), the IDBCreateCommand isn't supported - aka E_NOINTERFACE
             OleDbHResult hr = OleDbHResult.E_NOINTERFACE;
-            UnsafeNativeMethods.IDBCreateCommandCreateCommand CreateCommand = DangerousIDBCreateCommandCreateCommand;
+            UnsafeNativeMethods.IDBCreateCommandCreateCommand? CreateCommand = DangerousIDBCreateCommandCreateCommand;
             if (null != CreateCommand)
             {
                 bool mustRelease = false;
@@ -362,7 +362,7 @@ internal ITransactionJoinWrapper ITransactionJoin(OleDbConnectionInternal connec
         }
     }
 
-    // unable to use generics bacause (unknown as T) doesn't compile
+    // unable to use generics because (unknown as T) doesn't compile
     internal struct IDBInfoWrapper : IDisposable
     {
         // _unknown must be tracked because the _value may not exist,
@@ -373,7 +373,7 @@ internal struct IDBInfoWrapper : IDisposable
         internal IDBInfoWrapper(object unknown)
         {
             _unknown = unknown;
-            _value = (unknown as UnsafeNativeMethods.IDBInfo);
+            _value = (unknown as UnsafeNativeMethods.IDBInfo)!;
         }
 
         internal UnsafeNativeMethods.IDBInfo Value
@@ -387,8 +387,8 @@ internal UnsafeNativeMethods.IDBInfo Value
         public void Dispose()
         {
             object unknown = _unknown;
-            _unknown = null;
-            _value = null;
+            _unknown = null!;
+            _value = null!;
             if (null != unknown)
             {
                 Marshal.ReleaseComObject(unknown);
@@ -404,7 +404,7 @@ internal struct IDBPropertiesWrapper : IDisposable
         internal IDBPropertiesWrapper(object unknown)
         {
             _unknown = unknown;
-            _value = (unknown as UnsafeNativeMethods.IDBProperties);
+            _value = (unknown as UnsafeNativeMethods.IDBProperties)!;
             Debug.Assert(null != _value, "null IDBProperties");
         }
 
@@ -420,8 +420,8 @@ internal UnsafeNativeMethods.IDBProperties Value
         public void Dispose()
         {
             object unknown = _unknown;
-            _unknown = null;
-            _value = null;
+            _unknown = null!;
+            _value = null!;
             if (null != unknown)
             {
                 Marshal.ReleaseComObject(unknown);
@@ -437,7 +437,7 @@ internal struct IDBSchemaRowsetWrapper : IDisposable
         internal IDBSchemaRowsetWrapper(object unknown)
         {
             _unknown = unknown;
-            _value = (unknown as UnsafeNativeMethods.IDBSchemaRowset);
+            _value = (unknown as UnsafeNativeMethods.IDBSchemaRowset)!;
         }
 
         internal UnsafeNativeMethods.IDBSchemaRowset Value
@@ -451,8 +451,8 @@ internal UnsafeNativeMethods.IDBSchemaRowset Value
         public void Dispose()
         {
             object unknown = _unknown;
-            _unknown = null;
-            _value = null;
+            _unknown = null!;
+            _value = null!;
             if (null != unknown)
             {
                 Marshal.ReleaseComObject(unknown);
@@ -468,7 +468,7 @@ internal struct IOpenRowsetWrapper : IDisposable
         internal IOpenRowsetWrapper(object unknown)
         {
             _unknown = unknown;
-            _value = (unknown as UnsafeNativeMethods.IOpenRowset);
+            _value = (unknown as UnsafeNativeMethods.IOpenRowset)!;
             Debug.Assert(null != _value, "null IOpenRowsetWrapper");
         }
 
@@ -484,8 +484,8 @@ internal UnsafeNativeMethods.IOpenRowset Value
         public void Dispose()
         {
             object unknown = _unknown;
-            _unknown = null;
-            _value = null;
+            _unknown = null!;
+            _value = null!;
             if (null != unknown)
             {
                 Marshal.ReleaseComObject(unknown);
@@ -501,7 +501,7 @@ internal struct ITransactionJoinWrapper : IDisposable
         internal ITransactionJoinWrapper(object unknown)
         {
             _unknown = unknown;
-            _value = (unknown as NativeMethods.ITransactionJoin);
+            _value = (unknown as NativeMethods.ITransactionJoin)!;
         }
 
         internal NativeMethods.ITransactionJoin Value
@@ -515,8 +515,8 @@ internal NativeMethods.ITransactionJoin Value
         public void Dispose()
         {
             object unknown = _unknown;
-            _unknown = null;
-            _value = null;
+            _unknown = null!;
+            _value = null!;
             if (null != unknown)
             {
                 Marshal.ReleaseComObject(unknown);
diff --git a/src/libraries/System.Data.OleDb/src/OleDb_Enum.cs b/src/libraries/System.Data.OleDb/src/OleDb_Enum.cs
index e2e4915014881c..b1c7664c3c58e5 100644
--- a/src/libraries/System.Data.OleDb/src/OleDb_Enum.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDb_Enum.cs
@@ -178,7 +178,7 @@ internal sealed class NativeDBType
         internal readonly DbType enumDbType;    // enum System.Data.DbType
         internal readonly short dbType;        // OLE DB DBTYPE_
         internal readonly short wType;         // OLE DB DBTYPE_ we ask OleDB Provider to bind as
-        internal readonly Type dataType;      // CLR Type
+        internal readonly Type? dataType;      // CLR Type
 
         internal readonly int dbPart;    // the DBPart w or w/out length
         internal readonly bool isfixed;   // IsFixedLength
@@ -189,7 +189,7 @@ internal sealed class NativeDBType
         internal readonly string dataSourceType; // ICommandWithParameters.SetParameterInfo standard type name
         internal readonly StringMemHandle dbString;  // ptr to native allocated memory for dataSourceType string
 
-        private NativeDBType(byte maxpre, int fixlen, bool isfixed, bool islong, OleDbType enumOleDbType, short dbType, string dbstring, Type dataType, short wType, DbType enumDbType)
+        private NativeDBType(byte maxpre, int fixlen, bool isfixed, bool islong, OleDbType enumOleDbType, short dbType, string dbstring, Type? dataType, short wType, DbType enumDbType)
         {
             this.enumOleDbType = enumOleDbType;
             this.dbType = dbType;
@@ -265,7 +265,7 @@ internal static NativeDBType FromDataType(OleDbType enumOleDbType) =>
 
         internal static NativeDBType FromSystemType(object value)
         {
-            IConvertible ic = (value as IConvertible);
+            IConvertible? ic = (value as IConvertible);
             if (null != ic)
             {
                 return ic.GetTypeCode() switch
diff --git a/src/libraries/System.Data.OleDb/src/OleDb_Util.cs b/src/libraries/System.Data.OleDb/src/OleDb_Util.cs
index 5d125952f19494..b0a39dea96c734 100644
--- a/src/libraries/System.Data.OleDb/src/OleDb_Util.cs
+++ b/src/libraries/System.Data.OleDb/src/OleDb_Util.cs
@@ -92,7 +92,7 @@ internal static Exception BadStatus_ParamAcc(int index, DBBindStatus status)
         {
             return ADP.DataAdapter(SR.Format(SR.OleDb_BadStatus_ParamAcc, index.ToString(CultureInfo.InvariantCulture), status.ToString()));
         }
-        internal static Exception NoProviderSupportForParameters(string provider, Exception inner)
+        internal static Exception NoProviderSupportForParameters(string provider, Exception? inner)
         {
             return ADP.DataAdapter(SR.Format(SR.OleDb_NoProviderSupportForParameters, provider), inner);
         }
@@ -174,7 +174,7 @@ internal static ArgumentException SchemaRowsetsNotSupported(string provider)
         {
             return ADP.Argument(SR.Format(SR.OleDb_SchemaRowsetsNotSupported, "IDBSchemaRowset", provider));
         }
-        internal static OleDbException NoErrorInformation(string provider, OleDbHResult hr, Exception inner)
+        internal static OleDbException NoErrorInformation(string? provider, OleDbHResult hr, Exception? inner)
         {
             OleDbException e;
             if (!ADP.IsEmpty(provider))
@@ -188,7 +188,7 @@ internal static OleDbException NoErrorInformation(string provider, OleDbHResult
             ADP.TraceExceptionAsReturnValue(e);
             return e;
         }
-        internal static InvalidOperationException MDACNotAvailable(Exception inner)
+        internal static InvalidOperationException MDACNotAvailable(Exception? inner)
         {
             return ADP.DataAdapter(SR.Format(SR.OleDb_MDACNotAvailable), inner);
         }
@@ -196,7 +196,7 @@ internal static ArgumentException MSDASQLNotSupported()
         {
             return ADP.Argument(SR.Format(SR.OleDb_MSDASQLNotSupported));
         }
-        internal static InvalidOperationException CommandTextNotSupported(string provider, Exception inner)
+        internal static InvalidOperationException CommandTextNotSupported(string provider, Exception? inner)
         {
             return ADP.DataAdapter(SR.Format(SR.OleDb_CommandTextNotSupported, provider), inner);
         }
@@ -204,12 +204,12 @@ internal static InvalidOperationException PossiblePromptNotUserInteractive()
         {
             return ADP.DataAdapter(SR.Format(SR.OleDb_PossiblePromptNotUserInteractive));
         }
-        internal static InvalidOperationException ProviderUnavailable(string provider, Exception inner)
+        internal static InvalidOperationException ProviderUnavailable(string provider, Exception? inner)
         {
             //return new OleDbException(SR.Format(SR.OleDb_ProviderUnavailable, provider), (int)OleDbHResult.CO_E_CLASSSTRING, inner);
             return ADP.DataAdapter(SR.Format(SR.OleDb_ProviderUnavailable, provider), inner);
         }
-        internal static InvalidOperationException TransactionsNotSupported(string provider, Exception inner)
+        internal static InvalidOperationException TransactionsNotSupported(string provider, Exception? inner)
         {
             return ADP.DataAdapter(SR.Format(SR.OleDb_TransactionsNotSupported, provider), inner);
         }
@@ -707,7 +707,7 @@ internal static string ELookup(OleDbHResult hr)
         private static readonly Hashtable g_wlookpup = new Hashtable();
         internal static string WLookup(short id)
         {
-            string value = (string)g_wlookpup[id];
+            string? value = (string?)g_wlookpup[id];
             if (null == value)
             {
                 value = "0x" + ((short)id).ToString("X2", CultureInfo.InvariantCulture) + " " + ((short)id);
diff --git a/src/libraries/System.Data.OleDb/src/PropertyInfoSet.cs b/src/libraries/System.Data.OleDb/src/PropertyInfoSet.cs
index 60690d084bbece..60b44bab7de48c 100644
--- a/src/libraries/System.Data.OleDb/src/PropertyInfoSet.cs
+++ b/src/libraries/System.Data.OleDb/src/PropertyInfoSet.cs
@@ -13,15 +13,15 @@ internal sealed class OleDbPropertyInfo
     {
         public Guid _propertySet;
         public int _propertyID;
-        public string _description;
-        public string _lowercase;
-        public Type _type;
+        public string? _description;
+        public string? _lowercase;
+        public Type? _type;
 
         public int _flags;
         public int _vtype;
-        public object _supportedValues;
+        public object? _supportedValues;
 
-        public object _defaultValue;
+        public object? _defaultValue;
     }
 
     internal sealed class PropertyInfoSet : SafeHandle
@@ -54,9 +54,9 @@ public override bool IsInvalid
             }
         }
 
-        internal Dictionary<string, OleDbPropertyInfo> GetValues()
+        internal Dictionary<string, OleDbPropertyInfo>? GetValues()
         {
-            Dictionary<string, OleDbPropertyInfo> propertyLookup = null;
+            Dictionary<string, OleDbPropertyInfo>? propertyLookup = null;
 
             bool mustRelease = false;
             RuntimeHelpers.PrepareConstrainedRegions();
@@ -88,7 +88,7 @@ internal Dictionary<string, OleDbPropertyInfo> GetValues()
                             propertyInfo._vtype = propinfo.vtType;
                             propertyInfo._supportedValues = propinfo.vValue;
                             propertyInfo._description = propinfo.pwszDescription;
-                            propertyInfo._lowercase = propinfo.pwszDescription.ToLowerInvariant();
+                            propertyInfo._lowercase = propinfo.pwszDescription!.ToLowerInvariant();
                             propertyInfo._type = PropertyInfoSet.FromVtType(propinfo.vtType);
 
                             propertyLookup[propertyInfo._lowercase] = propertyInfo;
@@ -142,7 +142,7 @@ protected override bool ReleaseHandle()
             return true;
         }
 
-        internal static Type FromVtType(int vartype) =>
+        internal static Type? FromVtType(int vartype) =>
             (VarEnum)vartype switch
             {
                 VarEnum.VT_EMPTY => null,
diff --git a/src/libraries/System.Data.OleDb/src/RowBinding.cs b/src/libraries/System.Data.OleDb/src/RowBinding.cs
index fbbd2515465117..7f94bf563d5f13 100644
--- a/src/libraries/System.Data.OleDb/src/RowBinding.cs
+++ b/src/libraries/System.Data.OleDb/src/RowBinding.cs
@@ -15,7 +15,7 @@ internal sealed class RowBinding : System.Data.ProviderBase.DbBuffer
         private readonly int _dataLength;
         private readonly int _emptyStringOffset;
 
-        private UnsafeNativeMethods.IAccessor _iaccessor;
+        private UnsafeNativeMethods.IAccessor? _iaccessor;
         private IntPtr _accessorHandle;
 
         private readonly bool _needToReset;
@@ -117,9 +117,9 @@ internal OleDbHResult CreateAccessor(UnsafeNativeMethods.IAccessor iaccessor, in
             return hr;
         }
 
-        internal ColumnBinding[] SetBindings(OleDbDataReader dataReader, Bindings bindings,
+        internal ColumnBinding[] SetBindings(OleDbDataReader? dataReader, Bindings bindings,
                                              int indexStart, int indexForAccessor,
-                                             OleDbParameter[] parameters, tagDBBINDING[] dbbindings, bool ifIRowsetElseIRow)
+                                             OleDbParameter[]? parameters, tagDBBINDING[] dbbindings, bool ifIRowsetElseIRow)
         {
             Debug.Assert(null != bindings, "null bindings");
             Debug.Assert(dbbindings.Length == BindingCount(), "count mismatch");
@@ -150,9 +150,9 @@ internal ColumnBinding[] SetBindings(OleDbDataReader dataReader, Bindings bindin
             for (int indexWithinAccessor = 0; indexWithinAccessor < columns.Length; ++indexWithinAccessor)
             {
                 int index = indexStart + indexWithinAccessor;
-                OleDbParameter parameter = ((null != parameters) ? parameters[index] : null);
+                OleDbParameter? parameter = ((null != parameters) ? parameters[index] : null);
                 columns[indexWithinAccessor] = new ColumnBinding(
-                    dataReader, index, indexForAccessor, indexWithinAccessor,
+                    dataReader!, index, indexForAccessor, indexWithinAccessor,
                     parameter, this, bindings, dbbindings[indexWithinAccessor], _headerLength,
                     ifIRowsetElseIRow);
             }
@@ -172,7 +172,7 @@ internal object GetVariantValue(int offset)
             Debug.Assert(0 == offset % 8, "invalid alignment");
             ValidateCheck(offset, 2 * ODB.SizeOf_Variant);
 
-            object value = null;
+            object? value = null;
             bool mustRelease = false;
             RuntimeHelpers.PrepareConstrainedRegions();
             try
@@ -320,7 +320,7 @@ internal void CloseFromConnection()
         {
             ResetValues();
 
-            UnsafeNativeMethods.IAccessor iaccessor = _iaccessor;
+            UnsafeNativeMethods.IAccessor? iaccessor = _iaccessor;
             IntPtr accessorHandle = _accessorHandle;
 
             _iaccessor = null;
@@ -393,7 +393,7 @@ internal void ResetValues()
 #endif
         }
 
-        private unsafe void ResetValues(IntPtr buffer, object iaccessor)
+        private unsafe void ResetValues(IntPtr buffer, object? iaccessor)
         {
             Debug.Assert(ADP.PtrZero != buffer && _needToReset && _haveData, "shouldn't be calling ResetValues");
             for (int i = 0; i < _bindingCount; ++i)
@@ -473,7 +473,7 @@ private static void FreeChapter(IntPtr buffer, int valueOffset, object iaccessor
         {
             Debug.Assert(0 == valueOffset % 8, "unexpected unaligned ptr offset");
 
-            UnsafeNativeMethods.IChapteredRowset chapteredRowset = (iaccessor as UnsafeNativeMethods.IChapteredRowset);
+            UnsafeNativeMethods.IChapteredRowset chapteredRowset = (iaccessor as UnsafeNativeMethods.IChapteredRowset)!;
             IntPtr chapter = SafeNativeMethods.InterlockedExchangePointer(ADP.IntPtrOffset(buffer, valueOffset), ADP.PtrZero);
             if (ODB.DB_NULL_HCHAPTER != chapter)
             {
diff --git a/src/libraries/System.Data.OleDb/src/SafeHandles.cs b/src/libraries/System.Data.OleDb/src/SafeHandles.cs
index bd26b91d9d3b8f..185712be565c7b 100644
--- a/src/libraries/System.Data.OleDb/src/SafeHandles.cs
+++ b/src/libraries/System.Data.OleDb/src/SafeHandles.cs
@@ -21,7 +21,7 @@ private DualCoTaskMem() : base(IntPtr.Zero, true)
         }
 
         // IDBInfo.GetLiteralInfo
-        internal DualCoTaskMem(UnsafeNativeMethods.IDBInfo dbInfo, int[] literals, out int literalCount, out IntPtr literalInfo, out OleDbHResult hr) : this()
+        internal DualCoTaskMem(UnsafeNativeMethods.IDBInfo dbInfo, int[]? literals, out int literalCount, out IntPtr literalInfo, out OleDbHResult hr) : this()
         {
             int count = (null != literals) ? literals.Length : 0;
             hr = dbInfo.GetLiteralInfo(count, literals, out literalCount, out base.handle, out this.handle2);
@@ -93,7 +93,7 @@ internal IntPtr GetRowHandle(int index)
 
     internal sealed class StringMemHandle : DbBuffer
     {
-        internal StringMemHandle(string value) : base((null != value) ? checked(2 + 2 * value.Length) : 0)
+        internal StringMemHandle(string? value) : base((null != value) ? checked(2 + 2 * value.Length) : 0)
         {
             if (null != value)
             {
@@ -128,7 +128,7 @@ internal static ChapterHandle CreateChapterHandle(IntPtr chapter)
         }
 
         // from ADODBRecordSetConstruction we do not want to release the initial chapter handle
-        private ChapterHandle(IntPtr chapter) : base((object)null)
+        private ChapterHandle(IntPtr chapter) : base((object?)null)
         {
             _chapterHandle = chapter;
         }
@@ -665,7 +665,7 @@ internal static unsafe OleDbHResult IChapteredRowsetReleaseChapter(System.IntPtr
         {
             OleDbHResult hr = OleDbHResult.E_UNEXPECTED;
             IntPtr hchapter = chapter;
-            System.Data.Common.UnsafeNativeMethods.IChapteredRowset chapteredRowset = null;
+            System.Data.Common.UnsafeNativeMethods.IChapteredRowset? chapteredRowset = null;
             RuntimeHelpers.PrepareConstrainedRegions();
             try
             { }
@@ -687,7 +687,7 @@ internal static unsafe OleDbHResult IChapteredRowsetReleaseChapter(System.IntPtr
         internal static unsafe OleDbHResult ITransactionAbort(System.IntPtr ptr)
         {
             OleDbHResult hr = OleDbHResult.E_UNEXPECTED;
-            ITransactionLocal transactionLocal = null;
+            ITransactionLocal? transactionLocal = null;
             RuntimeHelpers.PrepareConstrainedRegions();
             try
             { }
@@ -709,7 +709,7 @@ internal static unsafe OleDbHResult ITransactionAbort(System.IntPtr ptr)
         internal static unsafe OleDbHResult ITransactionCommit(System.IntPtr ptr)
         {
             OleDbHResult hr = OleDbHResult.E_UNEXPECTED;
-            ITransactionLocal transactionLocal = null;
+            ITransactionLocal? transactionLocal = null;
             RuntimeHelpers.PrepareConstrainedRegions();
             try
             { }
diff --git a/src/libraries/System.Data.OleDb/src/System.Data.OleDb.csproj b/src/libraries/System.Data.OleDb/src/System.Data.OleDb.csproj
index 1ab198757c5dfd..d3029f06d56d3e 100644
--- a/src/libraries/System.Data.OleDb/src/System.Data.OleDb.csproj
+++ b/src/libraries/System.Data.OleDb/src/System.Data.OleDb.csproj
@@ -1,9 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>netstandard2.0-Windows_NT;netstandard2.0;net461-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0-Windows_NT;netstandard2.0;net461-Windows_NT</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -96,15 +96,11 @@
       <LogicalName>System.Data.OleDb.OleDbMetaData.xml</LogicalName>
     </EmbeddedResource>
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Data" />
-  </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="Microsoft.Win32.Registry" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Configuration.ConfigurationManager" />
-    <Reference Include="System.Diagnostics.PerformanceCounter" />
-    <Reference Include="System.Security.Principal.Windows" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard'))">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Configuration.ConfigurationManager\src\System.Configuration.ConfigurationManager.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Diagnostics.PerformanceCounter\src\System.Diagnostics.PerformanceCounter.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/Common/AdapterUtil.cs b/src/libraries/System.Data.OleDb/src/System/Data/Common/AdapterUtil.cs
index 2bb8e85534f719..f5bacfd6239170 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/Common/AdapterUtil.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/Common/AdapterUtil.cs
@@ -6,6 +6,7 @@
 using System.Configuration;
 using System.Data.SqlTypes;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.IO;
 using System.Runtime.Versioning;
@@ -66,13 +67,13 @@ internal static ArgumentException Argument(string error)
             TraceExceptionAsReturnValue(e);
             return e;
         }
-        internal static ArgumentException Argument(string error, Exception inner)
+        internal static ArgumentException Argument(string error, Exception? inner)
         {
             ArgumentException e = new ArgumentException(error, inner);
             TraceExceptionAsReturnValue(e);
             return e;
         }
-        internal static ArgumentException Argument(string error, string parameter)
+        internal static ArgumentException Argument(string error, string? parameter)
         {
             ArgumentException e = new ArgumentException(error, parameter);
             TraceExceptionAsReturnValue(e);
@@ -118,7 +119,7 @@ internal static InvalidCastException InvalidCast(string error)
         {
             return InvalidCast(error, null);
         }
-        internal static InvalidCastException InvalidCast(string error, Exception inner)
+        internal static InvalidCastException InvalidCast(string error, Exception? inner)
         {
             InvalidCastException e = new InvalidCastException(error, inner);
             TraceExceptionAsReturnValue(e);
@@ -136,7 +137,7 @@ internal static TimeoutException TimeoutException(string error)
             TraceExceptionAsReturnValue(e);
             return e;
         }
-        internal static InvalidOperationException InvalidOperation(string error, Exception inner)
+        internal static InvalidOperationException InvalidOperation(string error, Exception? inner)
         {
             InvalidOperationException e = new InvalidOperationException(error, inner);
             TraceExceptionAsReturnValue(e);
@@ -158,7 +159,7 @@ internal static InvalidOperationException DataAdapter(string error)
         {
             return InvalidOperation(error);
         }
-        internal static InvalidOperationException DataAdapter(string error, Exception inner)
+        internal static InvalidOperationException DataAdapter(string error, Exception? inner)
         {
             return InvalidOperation(error, inner);
         }
@@ -366,7 +367,7 @@ internal static InvalidOperationException InvalidDataDirectory()
         {
             return ADP.InvalidOperation(SR.GetString(SR.ADP_InvalidDataDirectory));
         }
-        internal static ArgumentException InvalidKeyname(string parameterName)
+        internal static ArgumentException InvalidKeyname(string? parameterName)
         {
             return Argument(SR.GetString(SR.ADP_InvalidKey), parameterName);
         }
@@ -376,7 +377,7 @@ internal static ArgumentException InvalidValue(string parameterName)
         }
         internal static ArgumentException ConvertFailed(Type fromType, Type toType, Exception innerException)
         {
-            return ADP.Argument(SR.GetString(SR.SqlConvert_ConvertFailed, fromType.FullName, toType.FullName), innerException);
+            return ADP.Argument(SR.GetString(SR.SqlConvert_ConvertFailed, fromType.FullName!, toType.FullName!), innerException);
         }
 
         //
@@ -424,7 +425,7 @@ internal static Exception InvalidConnectionOptionValue(string key)
         {
             return InvalidConnectionOptionValue(key, null);
         }
-        internal static Exception InvalidConnectionOptionValue(string key, Exception inner)
+        internal static Exception InvalidConnectionOptionValue(string key, Exception? inner)
         {
             return Argument(SR.GetString(SR.ADP_InvalidConnectionOptionValue, key), inner);
         }
@@ -509,7 +510,7 @@ internal static Exception OpenReaderExists()
             return OpenReaderExists(null);
         }
 
-        internal static Exception OpenReaderExists(Exception e)
+        internal static Exception OpenReaderExists(Exception? e)
         {
             return InvalidOperation(SR.GetString(SR.ADP_OpenReaderExists), e);
         }
@@ -698,7 +699,7 @@ internal static ArgumentException DbTypeNotSupported(System.Data.DbType type, Ty
         }
         internal static ArgumentException UnknownDataTypeCode(Type dataType, TypeCode typeCode)
         {
-            return Argument(SR.GetString(SR.ADP_UnknownDataTypeCode, ((int)typeCode).ToString(CultureInfo.InvariantCulture), dataType.FullName));
+            return Argument(SR.GetString(SR.ADP_UnknownDataTypeCode, ((int)typeCode).ToString(CultureInfo.InvariantCulture), dataType.FullName!));
         }
         internal static ArgumentException InvalidOffsetValue(int value)
         {
@@ -909,7 +910,7 @@ internal static bool CompareInsensitiveInvariant(string strvalue, string strcons
             return (0 == CultureInfo.InvariantCulture.CompareInfo.Compare(strvalue, strconst, CompareOptions.IgnoreCase));
         }
 
-        internal static Delegate FindBuilder(MulticastDelegate mcd)
+        internal static Delegate? FindBuilder(MulticastDelegate? mcd)
         { // V1.2.3300
             if (null != mcd)
             {
@@ -927,20 +928,20 @@ internal static Delegate FindBuilder(MulticastDelegate mcd)
         internal static readonly bool IsWindowsNT = (PlatformID.Win32NT == Environment.OSVersion.Platform);
         internal static readonly bool IsPlatformNT5 = (ADP.IsWindowsNT && (Environment.OSVersion.Version.Major >= 5));
 
-        internal static SysTx.Transaction GetCurrentTransaction()
+        internal static SysTx.Transaction? GetCurrentTransaction()
         {
-            SysTx.Transaction transaction = SysTx.Transaction.Current;
+            SysTx.Transaction? transaction = SysTx.Transaction.Current;
             return transaction;
         }
 
-        internal static void SetCurrentTransaction(SysTx.Transaction transaction)
+        internal static void SetCurrentTransaction(SysTx.Transaction? transaction)
         {
             SysTx.Transaction.Current = transaction;
         }
 
-        internal static SysTx.IDtcTransaction GetOletxTransaction(SysTx.Transaction transaction)
+        internal static SysTx.IDtcTransaction? GetOletxTransaction(SysTx.Transaction? transaction)
         {
-            SysTx.IDtcTransaction oleTxTransaction = null;
+            SysTx.IDtcTransaction? oleTxTransaction = null;
 
             if (null != transaction)
             {
@@ -1092,11 +1093,11 @@ internal static Stream GetXmlStream(string value, string errorString)
 
         }
 
-        internal static object ClassesRootRegistryValue(string subkey, string queryvalue)
+        internal static object? ClassesRootRegistryValue(string subkey, string queryvalue)
         {
             try
             {
-                using (RegistryKey key = Registry.ClassesRoot.OpenSubKey(subkey, false))
+                using (RegistryKey? key = Registry.ClassesRoot.OpenSubKey(subkey, false))
                 {
                     return ((null != key) ? key.GetValue(queryvalue) : null);
                 }
@@ -1110,11 +1111,11 @@ internal static object ClassesRootRegistryValue(string subkey, string queryvalue
             }
         }
 
-        internal static object LocalMachineRegistryValue(string subkey, string queryvalue)
+        internal static object? LocalMachineRegistryValue(string subkey, string queryvalue)
         {
             try
             {
-                using (RegistryKey key = Registry.LocalMachine.OpenSubKey(subkey, false))
+                using (RegistryKey? key = Registry.LocalMachine.OpenSubKey(subkey, false))
                 {
                     return ((null != key) ? key.GetValue(queryvalue) : null);
                 }
@@ -1132,14 +1133,14 @@ internal static object LocalMachineRegistryValue(string subkey, string queryvalu
         internal static void CheckVersionMDAC(bool ifodbcelseoledb)
         {
             int major, minor, build;
-            string version;
+            string? version;
 
             try
             {
-                version = (string)ADP.LocalMachineRegistryValue("Software\\Microsoft\\DataAccess", "FullInstallVer");
+                version = (string?)ADP.LocalMachineRegistryValue("Software\\Microsoft\\DataAccess", "FullInstallVer");
                 if (ADP.IsEmpty(version))
                 {
-                    string filename = (string)ADP.ClassesRootRegistryValue(System.Data.OleDb.ODB.DataLinks_CLSID, string.Empty);
+                    string filename = (string)ADP.ClassesRootRegistryValue(System.Data.OleDb.ODB.DataLinks_CLSID, string.Empty)!;
                     FileVersionInfo versionInfo = ADP.GetVersionInfo(filename);
                     major = versionInfo.FileMajorPart;
                     minor = versionInfo.FileMinorPart;
@@ -1183,7 +1184,7 @@ internal static void CheckVersionMDAC(bool ifodbcelseoledb)
 
         // the return value is true if the string was quoted and false if it was not
         // this allows the caller to determine if it is an error or not for the quotedString to not be quoted
-        internal static bool RemoveStringQuotes(string quotePrefix, string quoteSuffix, string quotedString, out string unquotedString)
+        internal static bool RemoveStringQuotes(string? quotePrefix, string? quoteSuffix, string? quotedString, out string? unquotedString)
         {
             int prefixLength;
             if (quotePrefix == null)
@@ -1229,7 +1230,7 @@ internal static bool RemoveStringQuotes(string quotePrefix, string quoteSuffix,
             // is the prefix present?
             if (prefixLength > 0)
             {
-                if (quotedString.StartsWith(quotePrefix, StringComparison.Ordinal) == false)
+                if (quotedString.StartsWith(quotePrefix!, StringComparison.Ordinal) == false)
                 {
                     unquotedString = quotedString;
                     return false;
@@ -1239,7 +1240,7 @@ internal static bool RemoveStringQuotes(string quotePrefix, string quoteSuffix,
             // is the suffix present?
             if (suffixLength > 0)
             {
-                if (quotedString.EndsWith(quoteSuffix, StringComparison.Ordinal) == false)
+                if (quotedString.EndsWith(quoteSuffix!, StringComparison.Ordinal) == false)
                 {
                     unquotedString = quotedString;
                     return false;
@@ -1279,12 +1280,12 @@ internal static int IntPtrToInt32(IntPtr value)
         }
 
         // TODO: are those names appropriate for common code?
-        internal static int SrcCompare(string strA, string strB)
+        internal static int SrcCompare(string? strA, string? strB)
         { // this is null safe
             return ((strA == strB) ? 0 : 1);
         }
 
-        internal static int DstCompare(string strA, string strB)
+        internal static int DstCompare(string? strA, string? strB)
         { // this is null safe
             return CultureInfo.CurrentCulture.CompareInfo.Compare(strA, strB, ADP.compareOptions);
         }
@@ -1312,23 +1313,23 @@ private static void IsDirectionValid(ParameterDirection value)
         }
 #endif
 
-        internal static bool IsEmpty(string str)
+        internal static bool IsEmpty([NotNullWhen(false)] string? str)
         {
             return ((null == str) || (0 == str.Length));
         }
 
-        internal static bool IsEmptyArray(string[] array)
+        internal static bool IsEmptyArray([NotNullWhen(false)] string?[]? array)
         {
             return ((null == array) || (0 == array.Length));
         }
 
-        internal static bool IsNull(object value)
+        internal static bool IsNull([NotNullWhen(false)] object? value)
         {
             if ((null == value) || (DBNull.Value == value))
             {
                 return true;
             }
-            INullable nullable = (value as INullable);
+            INullable? nullable = (value as INullable);
             return ((null != nullable) && nullable.IsNull);
         }
     }
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/Common/DbConnectionPoolKey.cs b/src/libraries/System.Data.OleDb/src/System/Data/Common/DbConnectionPoolKey.cs
index 011e9d871a0ac2..80252bde49e876 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/Common/DbConnectionPoolKey.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/Common/DbConnectionPoolKey.cs
@@ -10,9 +10,9 @@ namespace System.Data.Common
     //  Only connection string is used as a key
     internal class DbConnectionPoolKey : ICloneable
     {
-        private string _connectionString;
+        private string? _connectionString;
 
-        internal DbConnectionPoolKey(string connectionString)
+        internal DbConnectionPoolKey(string? connectionString)
         {
             _connectionString = connectionString;
         }
@@ -27,7 +27,7 @@ object ICloneable.Clone()
             return new DbConnectionPoolKey(this);
         }
 
-        internal virtual string ConnectionString
+        internal virtual string? ConnectionString
         {
             get
             {
@@ -40,14 +40,14 @@ internal virtual string ConnectionString
             }
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (obj == null || obj.GetType() != typeof(DbConnectionPoolKey))
             {
                 return false;
             }
 
-            DbConnectionPoolKey key = obj as DbConnectionPoolKey;
+            DbConnectionPoolKey? key = obj as DbConnectionPoolKey;
 
             return (key != null && _connectionString == key._connectionString);
         }
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/Common/FieldNameLookup.cs b/src/libraries/System.Data.OleDb/src/System/Data/Common/FieldNameLookup.cs
index 32a4c27e59d8ef..918c3304fe6090 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/Common/FieldNameLookup.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/Common/FieldNameLookup.cs
@@ -12,14 +12,14 @@ internal sealed class FieldNameLookup
     { // V1.2.3300
 
         // hashtable stores the index into the _fieldNames, match via case-sensitive
-        private Hashtable _fieldNameLookup;
+        private Hashtable? _fieldNameLookup;
 
         // original names for linear searches when exact matches fail
         private readonly string[] _fieldNames;
 
         // if _defaultLocaleID is -1 then _compareInfo is initialized with InvariantCulture CompareInfo
         // otherwise it is specified by the server? for the correct compare info
-        private CompareInfo _compareInfo;
+        private CompareInfo? _compareInfo;
         private readonly int _defaultLocaleID;
 
         public FieldNameLookup(IDataRecord reader, int defaultLocaleID)
@@ -57,7 +57,7 @@ public int IndexOfName(string fieldName)
                 GenerateLookup();
             }
             // via case sensitive search, first match with lowest ordinal matches
-            object value = _fieldNameLookup[fieldName];
+            object? value = _fieldNameLookup![fieldName];
             return ((null != value) ? (int)value : -1);
         }
 
@@ -68,7 +68,7 @@ public int IndexOf(string fieldName)
                 GenerateLookup();
             }
             int index;
-            object value = _fieldNameLookup[fieldName];
+            object? value = _fieldNameLookup![fieldName];
             if (null != value)
             {
                 // via case sensitive search, first match with lowest ordinal matches
@@ -89,7 +89,7 @@ public int IndexOf(string fieldName)
 
         private int LinearIndexOf(string fieldName, CompareOptions compareOptions)
         {
-            CompareInfo compareInfo = _compareInfo;
+            CompareInfo? compareInfo = _compareInfo;
             if (null == compareInfo)
             {
                 if (-1 != _defaultLocaleID)
@@ -107,7 +107,7 @@ private int LinearIndexOf(string fieldName, CompareOptions compareOptions)
             {
                 if (0 == compareInfo.Compare(fieldName, _fieldNames[i], compareOptions))
                 {
-                    _fieldNameLookup[fieldName] = i; // add an exact match for the future
+                    _fieldNameLookup![fieldName] = i; // add an exact match for the future
                     return i;
                 }
             }
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/Common/NameValuePair.cs b/src/libraries/System.Data.OleDb/src/System/Data/Common/NameValuePair.cs
index 6b7887034b40d6..09ec22615fca61 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/Common/NameValuePair.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/Common/NameValuePair.cs
@@ -8,11 +8,11 @@ namespace System.Data.Common
     internal sealed class NameValuePair
     {
         private readonly string _name;
-        private readonly string _value;
+        private readonly string? _value;
         private readonly int _length;
-        private NameValuePair _next;
+        private NameValuePair? _next;
 
-        internal NameValuePair(string name, string value, int length)
+        internal NameValuePair(string name, string? value, int length)
         {
             Debug.Assert(!string.IsNullOrEmpty(name), "empty keyname");
             _name = name;
@@ -30,9 +30,9 @@ internal int Length
         }
 
         internal string Name => _name;
-        internal string Value => _value;
+        internal string? Value => _value;
 
-        internal NameValuePair Next
+        internal NameValuePair? Next
         {
             get { return _next; }
             set
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/Common/SR.cs b/src/libraries/System.Data.OleDb/src/System/Data/Common/SR.cs
index 4212e8d0b1f162..b89c3c7c1ff4ff 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/Common/SR.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/Common/SR.cs
@@ -10,7 +10,7 @@ internal static string GetString(string value)
             return value;
         }
 
-        internal static string GetString(string format, params object[] args)
+        internal static string GetString(string format, params object?[] args)
         {
             return SR.Format(format, args);
         }
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbBuffer.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbBuffer.cs
index b849aa34e3fa64..dc0db72fa5c6cd 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbBuffer.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbBuffer.cs
@@ -71,7 +71,7 @@ internal string PtrToStringUni(int offset, int length)
             Validate(offset, 2 * length);
             Debug.Assert(0 == offset % ADP.PtrSize, "invalid alignment");
 
-            string value = null;
+            string? value = null;
             bool mustRelease = false;
             RuntimeHelpers.PrepareConstrainedRegions();
             try
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionClosed.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionClosed.cs
index 8fd14e20d6ba25..0d89234d92bc34 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionClosed.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionClosed.cs
@@ -23,7 +23,7 @@ public override string ServerVersion
             }
         }
 
-        protected override void Activate(SysTx.Transaction transaction)
+        protected override void Activate(SysTx.Transaction? transaction)
         {
             throw ADP.ClosedConnectionError();
         }
@@ -43,12 +43,12 @@ protected override void Deactivate()
             throw ADP.ClosedConnectionError();
         }
 
-        public override void EnlistTransaction(SysTx.Transaction transaction)
+        public override void EnlistTransaction(SysTx.Transaction? transaction)
         {
             throw ADP.ClosedConnectionError();
         }
 
-        protected internal override DataTable GetSchema(DbConnectionFactory factory, DbConnectionPoolGroup poolGroup, DbConnection outerConnection, string collectionName, string[] restrictions)
+        protected internal override DataTable GetSchema(DbConnectionFactory factory, DbConnectionPoolGroup poolGroup, DbConnection outerConnection, string collectionName, string?[]? restrictions)
         {
             throw ADP.ClosedConnectionError();
         }
@@ -58,7 +58,7 @@ protected override DbReferenceCollection CreateReferenceCollection()
             throw ADP.ClosedConnectionError();
         }
 
-        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
         {
             return base.TryOpenConnectionInternal(outerConnection, connectionFactory, retry, userOptions);
         }
@@ -70,7 +70,7 @@ protected DbConnectionBusy(ConnectionState state) : base(state, true, false)
         {
         }
 
-        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
         {
             throw ADP.ConnectionAlreadyOpen(State);
         }
@@ -111,7 +111,7 @@ internal override void CloseConnection(DbConnection owningObject, DbConnectionFa
             connectionFactory.SetInnerConnectionTo(owningObject, DbConnectionClosedPreviouslyOpened.SingletonInstance);
         }
 
-        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal override bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
         {
             if (retry == null || !retry.Task.IsCompleted)
             {
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionFactory.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionFactory.cs
index 539ef470492f00..d096b432bc808d 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionFactory.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionFactory.cs
@@ -23,8 +23,8 @@ internal abstract class DbConnectionFactory
         // s_pendingOpenNonPooled is an array of tasks used to throttle creation of non-pooled connections to
         // a maximum of Environment.ProcessorCount at a time.
         private static int s_pendingOpenNonPooledNext;
-        private static readonly Task<DbConnectionInternal>[] s_pendingOpenNonPooled = new Task<DbConnectionInternal>[Environment.ProcessorCount];
-        private static Task<DbConnectionInternal> s_completedTask;
+        private static readonly Task<DbConnectionInternal?>[] s_pendingOpenNonPooled = new Task<DbConnectionInternal?>[Environment.ProcessorCount];
+        private static Task<DbConnectionInternal?>? s_completedTask;
 
         protected DbConnectionFactory() : this(DbConnectionPoolCountersNoCounters.SingletonInstance) { }
 
@@ -68,13 +68,13 @@ protected virtual DbMetaDataFactory CreateMetaDataFactory(DbConnectionInternal i
             throw ADP.NotSupported();
         }
 
-        internal DbConnectionInternal CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup, DbConnectionOptions userOptions)
+        internal DbConnectionInternal? CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup, DbConnectionOptions? userOptions)
         {
             Debug.Assert(null != owningConnection, "null owningConnection?");
             Debug.Assert(null != poolGroup, "null poolGroup?");
 
             DbConnectionOptions connectionOptions = poolGroup.ConnectionOptions;
-            DbConnectionPoolGroupProviderInfo poolGroupProviderInfo = poolGroup.ProviderInfo;
+            DbConnectionPoolGroupProviderInfo poolGroupProviderInfo = poolGroup.ProviderInfo!;
             DbConnectionPoolKey poolKey = poolGroup.PoolKey;
 
             DbConnectionInternal newConnection = CreateConnection(connectionOptions, poolKey, poolGroupProviderInfo, null, owningConnection, userOptions);
@@ -86,10 +86,10 @@ internal DbConnectionInternal CreateNonPooledConnection(DbConnection owningConne
             return newConnection;
         }
 
-        internal DbConnectionInternal CreatePooledConnection(DbConnectionPool pool, DbConnection owningObject, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions userOptions)
+        internal DbConnectionInternal? CreatePooledConnection(DbConnectionPool pool, DbConnection? owningObject, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions? userOptions)
         {
             Debug.Assert(null != pool, "null pool?");
-            DbConnectionPoolGroupProviderInfo poolGroupProviderInfo = pool.PoolGroup.ProviderInfo;
+            DbConnectionPoolGroupProviderInfo poolGroupProviderInfo = pool.PoolGroup.ProviderInfo!;
 
             DbConnectionInternal newConnection = CreateConnection(options, poolKey, poolGroupProviderInfo, pool, owningObject, userOptions);
             if (null != newConnection)
@@ -100,7 +100,7 @@ internal DbConnectionInternal CreatePooledConnection(DbConnectionPool pool, DbCo
             return newConnection;
         }
 
-        internal virtual DbConnectionPoolGroupProviderInfo CreateConnectionPoolGroupProviderInfo(DbConnectionOptions connectionOptions)
+        internal virtual DbConnectionPoolGroupProviderInfo? CreateConnectionPoolGroupProviderInfo(DbConnectionOptions connectionOptions)
         {
             return null;
         }
@@ -112,23 +112,23 @@ private Timer CreatePruningTimer()
         }
 
         // GetCompletedTask must be called from within s_pendingOpenPooled lock
-        private static Task<DbConnectionInternal> GetCompletedTask()
+        private static Task<DbConnectionInternal?> GetCompletedTask()
         {
             if (s_completedTask == null)
             {
-                TaskCompletionSource<DbConnectionInternal> source = new TaskCompletionSource<DbConnectionInternal>();
+                TaskCompletionSource<DbConnectionInternal?> source = new TaskCompletionSource<DbConnectionInternal?>();
                 source.SetResult(null);
                 s_completedTask = source.Task;
             }
             return s_completedTask;
         }
 
-        internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, out DbConnectionInternal connection)
+        internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions, DbConnectionInternal? oldConnection, out DbConnectionInternal? connection)
         {
             Debug.Assert(null != owningConnection, "null owningConnection?");
 
             DbConnectionPoolGroup poolGroup;
-            DbConnectionPool connectionPool;
+            DbConnectionPool? connectionPool;
             connection = null;
 
             //  Work around race condition with clearing the pool between GetConnectionPool obtaining pool
@@ -145,7 +145,7 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
 
             do
             {
-                poolGroup = GetConnectionPoolGroup(owningConnection);
+                poolGroup = GetConnectionPoolGroup(owningConnection)!;
                 // Doing this on the callers thread is important because it looks up the WindowsIdentity from the thread.
                 connectionPool = GetConnectionPool(owningConnection, poolGroup);
                 if (null == connectionPool)
@@ -153,7 +153,7 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
                     // If GetConnectionPool returns null, we can be certain that
                     // this connection should not be pooled via DbConnectionPool
                     // or have a disabled pool entry.
-                    poolGroup = GetConnectionPoolGroup(owningConnection); // previous entry have been disabled
+                    poolGroup = GetConnectionPoolGroup(owningConnection)!; // previous entry have been disabled
 
                     if (retry != null)
                     {
@@ -190,7 +190,7 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
                             // than intended.
                             newTask = s_pendingOpenNonPooled[idx].ContinueWith((_) =>
                             {
-                                Transactions.Transaction originalTransaction = ADP.GetCurrentTransaction();
+                                Transactions.Transaction? originalTransaction = ADP.GetCurrentTransaction();
                                 try
                                 {
                                     ADP.SetCurrentTransaction(retry.Task.AsyncState as Transactions.Transaction);
@@ -206,10 +206,10 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
                                 {
                                     ADP.SetCurrentTransaction(originalTransaction);
                                 }
-                            }, cancellationTokenSource.Token, TaskContinuationOptions.LongRunning, TaskScheduler.Default);
+                            }, cancellationTokenSource.Token, TaskContinuationOptions.LongRunning, TaskScheduler.Default)!;
 
                             // Place this new task in the slot so any future work will be queued behind it
-                            s_pendingOpenNonPooled[idx] = newTask;
+                            s_pendingOpenNonPooled[idx] = newTask!;
                         }
 
                         // Set up the timeout (if needed)
@@ -229,7 +229,7 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
                             }
                             else if (task.IsFaulted)
                             {
-                                retry.TrySetException(task.Exception.InnerException);
+                                retry.TrySetException(task.Exception!.InnerException!);
                             }
                             else
                             {
@@ -298,7 +298,7 @@ internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSour
             return true;
         }
 
-        private DbConnectionPool GetConnectionPool(DbConnection owningObject, DbConnectionPoolGroup connectionPoolGroup)
+        private DbConnectionPool? GetConnectionPool(DbConnection owningObject, DbConnectionPoolGroup connectionPoolGroup)
         {
             // if poolgroup is disabled, it will be replaced with a new entry
 
@@ -320,25 +320,25 @@ private DbConnectionPool GetConnectionPool(DbConnection owningObject, DbConnecti
                 DbConnectionPoolGroupOptions poolOptions = connectionPoolGroup.PoolGroupOptions;
 
                 // get the string to hash on again
-                DbConnectionOptions connectionOptions = connectionPoolGroup.ConnectionOptions;
+                DbConnectionOptions? connectionOptions = connectionPoolGroup.ConnectionOptions;
                 Debug.Assert(null != connectionOptions, "prevent expansion of connectionString");
 
-                connectionPoolGroup = GetConnectionPoolGroup(connectionPoolGroup.PoolKey, poolOptions, ref connectionOptions);
+                connectionPoolGroup = GetConnectionPoolGroup(connectionPoolGroup.PoolKey, poolOptions, ref connectionOptions)!;
                 Debug.Assert(null != connectionPoolGroup, "null connectionPoolGroup?");
                 SetConnectionPoolGroup(owningObject, connectionPoolGroup);
             }
-            DbConnectionPool connectionPool = connectionPoolGroup.GetConnectionPool(this);
+            DbConnectionPool? connectionPool = connectionPoolGroup.GetConnectionPool(this);
             return connectionPool;
         }
 
-        internal DbConnectionPoolGroup GetConnectionPoolGroup(DbConnectionPoolKey key, DbConnectionPoolGroupOptions poolOptions, ref DbConnectionOptions userConnectionOptions)
+        internal DbConnectionPoolGroup? GetConnectionPoolGroup(DbConnectionPoolKey key, DbConnectionPoolGroupOptions? poolOptions, ref DbConnectionOptions? userConnectionOptions)
         {
             if (ADP.IsEmpty(key.ConnectionString))
             {
-                return (DbConnectionPoolGroup)null;
+                return null;
             }
 
-            DbConnectionPoolGroup connectionPoolGroup;
+            DbConnectionPoolGroup? connectionPoolGroup;
             Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> connectionPoolGroups = _connectionPoolGroups;
             if (!connectionPoolGroups.TryGetValue(key, out connectionPoolGroup) || (connectionPoolGroup.IsDisabled && (null != connectionPoolGroup.PoolGroupOptions)))
             {
@@ -389,7 +389,7 @@ internal DbConnectionPoolGroup GetConnectionPoolGroup(DbConnectionPoolKey key, D
                     connectionPoolGroups = _connectionPoolGroups;
                     if (!connectionPoolGroups.TryGetValue(key, out connectionPoolGroup))
                     {
-                        DbConnectionPoolGroup newConnectionPoolGroup = new DbConnectionPoolGroup(connectionOptions, key, poolOptions);
+                        DbConnectionPoolGroup newConnectionPoolGroup = new DbConnectionPoolGroup(connectionOptions, key, poolOptions!);
                         newConnectionPoolGroup.ProviderInfo = CreateConnectionPoolGroupProviderInfo(connectionOptions);
 
                         // build new dictionary with space for new connection string
@@ -426,7 +426,7 @@ internal DbMetaDataFactory GetMetaDataFactory(DbConnectionPoolGroup connectionPo
 
             // get the matadatafactory from the pool entry. If it does not already have one
             // create one and save it on the pool entry
-            DbMetaDataFactory metaDataFactory = connectionPoolGroup.MetaDataFactory;
+            DbMetaDataFactory? metaDataFactory = connectionPoolGroup.MetaDataFactory;
 
             // consider serializing this so we don't construct multiple metadata factories
             // if two threads happen to hit this at the same time.  One will be GC'd
@@ -442,7 +442,7 @@ internal DbMetaDataFactory GetMetaDataFactory(DbConnectionPoolGroup connectionPo
             return metaDataFactory;
         }
 
-        private void PruneConnectionPoolGroups(object state)
+        private void PruneConnectionPoolGroups(object? state)
         {
             // when debugging this method, expect multiple threads at the same time
             // First, walk the pool release list and attempt to clear each
@@ -559,18 +559,18 @@ internal void QueuePoolGroupForRelease(DbConnectionPoolGroup poolGroup)
             PerformanceCounters.NumberOfInactiveConnectionPoolGroups.Increment();
         }
 
-        protected virtual DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions)
+        protected virtual DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool? pool, DbConnection? owningConnection, DbConnectionOptions? userOptions)
         {
             return CreateConnection(options, poolKey, poolGroupProviderInfo, pool, owningConnection);
         }
 
-        protected abstract DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection);
+        protected abstract DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool? pool, DbConnection? owningConnection);
 
-        protected abstract DbConnectionOptions CreateConnectionOptions(string connectionString, DbConnectionOptions previous);
+        protected abstract DbConnectionOptions CreateConnectionOptions(string connectionString, DbConnectionOptions? previous);
 
-        protected abstract DbConnectionPoolGroupOptions CreateConnectionPoolGroupOptions(DbConnectionOptions options);
+        protected abstract DbConnectionPoolGroupOptions? CreateConnectionPoolGroupOptions(DbConnectionOptions options);
 
-        internal abstract DbConnectionPoolGroup GetConnectionPoolGroup(DbConnection connection);
+        internal abstract DbConnectionPoolGroup? GetConnectionPoolGroup(DbConnection connection);
         internal abstract void PermissionDemand(DbConnection outerConnection);
 
         internal abstract void SetConnectionPoolGroup(DbConnection outerConnection, DbConnectionPoolGroup poolGroup);
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionHelper.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionHelper.cs
index 51a21ee365490d..c7cacdaf6cabbb 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionHelper.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionHelper.cs
@@ -14,8 +14,8 @@ public sealed partial class OleDbConnection : DbConnection
     {
         private static readonly DbConnectionFactory _connectionFactory = OleDbConnectionFactory.SingletonInstance;
 
-        private DbConnectionOptions _userConnectionOptions;
-        private DbConnectionPoolGroup _poolGroup;
+        private DbConnectionOptions? _userConnectionOptions;
+        private DbConnectionPoolGroup? _poolGroup;
         private DbConnectionInternal _innerConnection;
         private int _closeCount;          // used to distinguish between different uses of this object, so we don't have to maintain a list of it's children
 
@@ -52,11 +52,11 @@ internal DbConnectionFactory ConnectionFactory
             }
         }
 
-        internal DbConnectionOptions ConnectionOptions
+        internal DbConnectionOptions? ConnectionOptions
         {
             get
             {
-                System.Data.ProviderBase.DbConnectionPoolGroup poolGroup = PoolGroup;
+                System.Data.ProviderBase.DbConnectionPoolGroup? poolGroup = PoolGroup;
                 return ((null != poolGroup) ? poolGroup.ConnectionOptions : null);
             }
         }
@@ -64,11 +64,11 @@ internal DbConnectionOptions ConnectionOptions
         private string ConnectionString_Get()
         {
             bool hidePassword = InnerConnection.ShouldHidePassword;
-            DbConnectionOptions connectionOptions = UserConnectionOptions;
+            DbConnectionOptions? connectionOptions = UserConnectionOptions;
             return ((null != connectionOptions) ? connectionOptions.UsersConnectionString(hidePassword) : "");
         }
 
-        private void ConnectionString_Set(string value)
+        private void ConnectionString_Set(string? value)
         {
             DbConnectionPoolKey key = new DbConnectionPoolKey(value);
 
@@ -77,8 +77,8 @@ private void ConnectionString_Set(string value)
 
         private void ConnectionString_Set(DbConnectionPoolKey key)
         {
-            DbConnectionOptions connectionOptions = null;
-            System.Data.ProviderBase.DbConnectionPoolGroup poolGroup = ConnectionFactory.GetConnectionPoolGroup(key, null, ref connectionOptions);
+            DbConnectionOptions? connectionOptions = null;
+            System.Data.ProviderBase.DbConnectionPoolGroup? poolGroup = ConnectionFactory.GetConnectionPoolGroup(key, null, ref connectionOptions);
             DbConnectionInternal connectionInternal = InnerConnection;
             bool flag = connectionInternal.AllowSetConnectionString;
             if (flag)
@@ -115,7 +115,7 @@ internal DbConnectionInternal InnerConnection
             }
         }
 
-        internal System.Data.ProviderBase.DbConnectionPoolGroup PoolGroup
+        internal System.Data.ProviderBase.DbConnectionPoolGroup? PoolGroup
         {
             get
             {
@@ -129,7 +129,7 @@ internal System.Data.ProviderBase.DbConnectionPoolGroup PoolGroup
             }
         }
 
-        internal DbConnectionOptions UserConnectionOptions
+        internal DbConnectionOptions? UserConnectionOptions
         {
             get
             {
@@ -144,10 +144,10 @@ internal void AddWeakReference(object value, int tag)
 
         protected override DbCommand CreateDbCommand()
         {
-            DbCommand command = null;
+            DbCommand? command = null;
 
             DbProviderFactory providerFactory = ConnectionFactory.ProviderFactory;
-            command = providerFactory.CreateCommand();
+            command = providerFactory.CreateCommand()!;
             command.Connection = this;
             return command;
         }
@@ -189,7 +189,7 @@ protected override void Dispose(bool disposing)
         //    GC.KeepAlive(this);
         //}
 
-        public override void EnlistTransaction(SysTx.Transaction transaction)
+        public override void EnlistTransaction(SysTx.Transaction? transaction)
         {
             // If we're currently enlisted in a transaction and we were called
             // on the EnlistTransaction method (Whidbey) we're not allowed to
@@ -200,7 +200,7 @@ public override void EnlistTransaction(SysTx.Transaction transaction)
             // NOTE: since transaction enlistment involves round trips to the
             // server, we don't want to lock here, we'll handle the race conditions
             // elsewhere.
-            SysTx.Transaction enlistedTransaction = innerConnection.EnlistedTransaction;
+            SysTx.Transaction? enlistedTransaction = innerConnection.EnlistedTransaction;
             if (enlistedTransaction != null)
             {
                 // Allow calling enlist if already enlisted (no-op)
@@ -235,11 +235,11 @@ public override DataTable GetSchema(string collectionName)
             return this.GetSchema(collectionName, null);
         }
 
-        public override DataTable GetSchema(string collectionName, string[] restrictionValues)
+        public override DataTable GetSchema(string collectionName, string?[]? restrictionValues)
         {
             // NOTE: This is virtual because not all providers may choose to support
             //       returning schema data
-            return InnerConnection.GetSchema(ConnectionFactory, PoolGroup, this, collectionName, restrictionValues);
+            return InnerConnection.GetSchema(ConnectionFactory, PoolGroup!, this, collectionName, restrictionValues);
         }
 
         internal void NotifyWeakReference(int message)
@@ -251,14 +251,14 @@ internal void PermissionDemand()
         {
             Debug.Assert(DbConnectionClosedConnecting.SingletonInstance == _innerConnection, "not connecting");
 
-            System.Data.ProviderBase.DbConnectionPoolGroup poolGroup = PoolGroup;
-            DbConnectionOptions connectionOptions = ((null != poolGroup) ? poolGroup.ConnectionOptions : null);
+            System.Data.ProviderBase.DbConnectionPoolGroup? poolGroup = PoolGroup;
+            DbConnectionOptions? connectionOptions = ((null != poolGroup) ? poolGroup.ConnectionOptions : null);
             if ((null == connectionOptions) || connectionOptions.IsEmpty)
             {
                 throw ADP.NoConnectionString();
             }
 
-            DbConnectionOptions userConnectionOptions = UserConnectionOptions;
+            DbConnectionOptions? userConnectionOptions = UserConnectionOptions;
             Debug.Assert(null != userConnectionOptions, "null UserConnectionOptions");
         }
 
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionInternal.Shared.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionInternal.Shared.cs
index 802248ca51b4ee..7aa55a95e73d61 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionInternal.Shared.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionInternal.Shared.cs
@@ -20,9 +20,9 @@ internal abstract partial class DbConnectionInternal // V1.1.3300
 
         private readonly WeakReference _owningObject = new WeakReference(null, false);  // [usage must be thread safe] the owning object, when not in the pool. (both Pooled and Non-Pooled connections)
 
-        private DbConnectionPool _connectionPool;           // the pooler that the connection came from (Pooled connections only)
-        private DbConnectionPoolCounters _performanceCounters;      // the performance counters we're supposed to update
-        private DbReferenceCollection _referenceCollection;      // collection of objects that we need to notify in some way when we're being deactivated
+        private DbConnectionPool? _connectionPool;           // the pooler that the connection came from (Pooled connections only)
+        private DbConnectionPoolCounters? _performanceCounters;      // the performance counters we're supposed to update
+        private DbReferenceCollection? _referenceCollection;      // collection of objects that we need to notify in some way when we're being deactivated
         private int _pooledCount;              // [usage must be thread safe] the number of times this object has been pushed into the pool less the number of times it's been popped (0 != inPool)
 
         private bool _connectionIsDoomed;       // true when the connection should no longer be used.
@@ -31,13 +31,13 @@ internal abstract partial class DbConnectionInternal // V1.1.3300
 
         private DateTime _createTime;               // when the connection was created.
 
-        private SysTx.Transaction _enlistedTransaction;      // [usage must be thread-safe] the transaction that we're enlisted in, either manually or automatically
+        private SysTx.Transaction? _enlistedTransaction;      // [usage must be thread-safe] the transaction that we're enlisted in, either manually or automatically
 
         // _enlistedTransaction is a clone, so that transaction information can be queried even if the original transaction object is disposed.
         // However, there are times when we need to know if the original transaction object was disposed, so we keep a reference to it here.
         // This field should only be assigned a value at the same time _enlistedTransaction is updated.
         // Also, this reference should not be disposed, since we aren't taking ownership of it.
-        private SysTx.Transaction _enlistedTransactionOriginal;
+        private SysTx.Transaction? _enlistedTransactionOriginal;
 
 #if DEBUG
         private int _activateCount;            // debug only counter to verify activate/deactivates are in sync.
@@ -72,7 +72,7 @@ internal bool CanBePooled
             }
         }
 
-        protected internal SysTx.Transaction EnlistedTransaction
+        protected internal SysTx.Transaction? EnlistedTransaction
         {
             get
             {
@@ -80,7 +80,7 @@ protected internal SysTx.Transaction EnlistedTransaction
             }
             set
             {
-                SysTx.Transaction currentEnlistedTransaction = _enlistedTransaction;
+                SysTx.Transaction? currentEnlistedTransaction = _enlistedTransaction;
                 if (((null == currentEnlistedTransaction) && (null != value))
                     || ((null != currentEnlistedTransaction) && !currentEnlistedTransaction.Equals(value)))
                 {
@@ -92,8 +92,8 @@ protected internal SysTx.Transaction EnlistedTransaction
                     // we need to use a clone of the transaction
                     // when we store it, or we'll end up keeping it past the
                     // duration of the using block of the TransactionScope
-                    SysTx.Transaction valueClone = null;
-                    SysTx.Transaction previousTransactionClone = null;
+                    SysTx.Transaction? valueClone = null;
+                    SysTx.Transaction? previousTransactionClone = null;
                     try
                     {
                         if (null != value)
@@ -231,17 +231,17 @@ internal bool IsEmancipated
             }
         }
 
-        protected internal object Owner
+        protected internal object? Owner
         {
             // We use a weak reference to the owning object so we can identify when
-            // it has been garbage collected without thowing exceptions.
+            // it has been garbage collected without throwing exceptions.
             get
             {
                 return _owningObject.Target;
             }
         }
 
-        internal DbConnectionPool Pool
+        internal DbConnectionPool? Pool
         {
             get
             {
@@ -249,14 +249,14 @@ internal DbConnectionPool Pool
             }
         }
 
-        protected DbConnectionPoolCounters PerformanceCounters
+        protected DbConnectionPoolCounters? PerformanceCounters
         {
             get
             {
                 return _performanceCounters;
             }
         }
-        protected internal DbReferenceCollection ReferenceCollection
+        protected internal DbReferenceCollection? ReferenceCollection
         {
             get
             {
@@ -285,7 +285,7 @@ public ConnectionState State
             }
         }
 
-        protected abstract void Activate(SysTx.Transaction transaction);
+        protected abstract void Activate(SysTx.Transaction? transaction);
 
         internal void AddWeakReference(object value, int tag)
         {
@@ -312,12 +312,12 @@ protected virtual void PrepareForCloseConnection()
             // By default, there is no preperation required
         }
 
-        protected virtual object ObtainAdditionalLocksForClose()
+        protected virtual object? ObtainAdditionalLocksForClose()
         {
             return null; // no additional locks in default implementation
         }
 
-        protected virtual void ReleaseAdditionalLocksForClose(object lockToken)
+        protected virtual void ReleaseAdditionalLocksForClose(object? lockToken)
         {
             // no additional locks in default implementation
         }
@@ -343,7 +343,7 @@ internal void DeactivateConnection()
                 PerformanceCounters.NumberOfActiveConnections.Decrement();
             }
 
-            if (!_connectionIsDoomed && Pool.UseLoadBalancing)
+            if (!_connectionIsDoomed && Pool!.UseLoadBalancing)
             {
                 // If we're not already doomed, check the connection's lifetime and
                 // doom it if it's lifetime has elapsed.
@@ -377,7 +377,7 @@ internal virtual void DelegatedTransactionEnded()
 
                 Deactivate(); // call it one more time just in case
 
-                DbConnectionPool pool = Pool;
+                DbConnectionPool? pool = Pool;
 
                 if (null == pool)
                 {
@@ -399,7 +399,7 @@ internal virtual void DelegatedTransactionEnded()
                 // once and for all, or the server will have fits about us
                 // leaving connections open until the client-side GC kicks
                 // in.
-                PerformanceCounters.NumberOfNonPooledConnections.Decrement();
+                PerformanceCounters!.NumberOfNonPooledConnections.Decrement();
                 Dispose();
             }
             // When _pooledCount is 0, the connection is a pooled connection
@@ -419,9 +419,9 @@ protected internal void DoomThisConnection()
             _connectionIsDoomed = true;
         }
 
-        public abstract void EnlistTransaction(SysTx.Transaction transaction);
+        public abstract void EnlistTransaction(SysTx.Transaction? transaction);
 
-        protected internal virtual DataTable GetSchema(DbConnectionFactory factory, DbConnectionPoolGroup poolGroup, DbConnection outerConnection, string collectionName, string[] restrictions)
+        protected internal virtual DataTable GetSchema(DbConnectionFactory factory, DbConnectionPoolGroup poolGroup, DbConnection outerConnection, string collectionName, string?[]? restrictions)
         {
             Debug.Assert(outerConnection != null, "outerConnection may not be null.");
 
@@ -456,7 +456,7 @@ internal void MakePooledConnection(DbConnectionPool connectionPool)
 
         internal void NotifyWeakReference(int message)
         {
-            DbReferenceCollection referenceCollection = ReferenceCollection;
+            DbReferenceCollection? referenceCollection = ReferenceCollection;
             if (null != referenceCollection)
             {
                 referenceCollection.Notify(message);
@@ -476,17 +476,17 @@ internal virtual void OpenConnection(DbConnection outerConnection, DbConnectionF
         /// override this and do the correct thing.</devdoc>
         // User code should either override DbConnectionInternal.Activate when it comes out of the pool
         // or override DbConnectionFactory.CreateConnection when the connection is created for non-pooled connections
-        internal virtual bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        internal virtual bool TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
         {
             throw ADP.ConnectionAlreadyOpen(State);
         }
 
-        protected bool TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions)
+        protected bool TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions)
         {
             // ?->Connecting: prevent set_ConnectionString during Open
             if (connectionFactory.SetInnerConnectionFrom(outerConnection, DbConnectionClosedConnecting.SingletonInstance, this))
             {
-                DbConnectionInternal openConnection = null;
+                DbConnectionInternal? openConnection = null;
                 try
                 {
                     connectionFactory.PermissionDemand(outerConnection);
@@ -512,7 +512,7 @@ protected bool TryOpenConnectionInternal(DbConnection outerConnection, DbConnect
             return true;
         }
 
-        internal void PrePush(object expectedOwner)
+        internal void PrePush(object? expectedOwner)
         {
             // Called by DbConnectionPool when we're about to be put into it's pool, we
             // take this opportunity to ensure ownership and pool counts are legit.
@@ -581,7 +581,7 @@ internal void PostPop(object newOwner)
 
         internal void RemoveWeakReference(object value)
         {
-            DbReferenceCollection referenceCollection = ReferenceCollection;
+            DbReferenceCollection? referenceCollection = ReferenceCollection;
             if (null != referenceCollection)
             {
                 referenceCollection.Remove(value);
@@ -590,7 +590,7 @@ internal void RemoveWeakReference(object value)
 
         internal void DetachCurrentTransactionIfEnded()
         {
-            SysTx.Transaction enlistedTransaction = EnlistedTransaction;
+            SysTx.Transaction? enlistedTransaction = EnlistedTransaction;
             if (enlistedTransaction != null)
             {
                 bool transactionIsDead;
@@ -619,10 +619,10 @@ internal void DetachTransaction(SysTx.Transaction transaction, bool isExplicitly
             lock (this)
             {
                 // Detach if detach-on-end behavior, or if outer connection was closed
-                DbConnection owner = (DbConnection)Owner;
+                DbConnection? owner = (DbConnection?)Owner;
                 if (isExplicitlyReleasing || UnbindOnTransactionCompletion || null == owner)
                 {
-                    SysTx.Transaction currentEnlistedTransaction = _enlistedTransaction;
+                    SysTx.Transaction? currentEnlistedTransaction = _enlistedTransaction;
                     if (currentEnlistedTransaction != null && transaction.Equals(currentEnlistedTransaction))
                     {
                         EnlistedTransaction = null;
@@ -639,12 +639,12 @@ internal void DetachTransaction(SysTx.Transaction transaction, bool isExplicitly
         internal void SetInStasis()
         {
             _isInStasis = true;
-            PerformanceCounters.NumberOfStasisConnections.Increment();
+            PerformanceCounters!.NumberOfStasisConnections.Increment();
         }
 
         private void TerminateStasis(bool returningToPool)
         {
-            PerformanceCounters.NumberOfStasisConnections.Decrement();
+            PerformanceCounters!.NumberOfStasisConnections.Decrement();
             _isInStasis = false;
         }
 
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionInternal.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionInternal.cs
index 2f63a7a8498728..f98d94b4ba044e 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionInternal.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionInternal.cs
@@ -11,7 +11,7 @@ namespace System.Data.ProviderBase
 {
     internal abstract partial class DbConnectionInternal
     {
-        internal void ActivateConnection(SysTx.Transaction transaction)
+        internal void ActivateConnection(SysTx.Transaction? transaction)
         {
             // Internal method called from the connection pooler so we don't expose
             // the Activate method publicly.
@@ -22,7 +22,7 @@ internal void ActivateConnection(SysTx.Transaction transaction)
 
             Activate(transaction);
 
-            PerformanceCounters.NumberOfActiveConnections.Increment();
+            PerformanceCounters!.NumberOfActiveConnections.Increment();
         }
 
         internal virtual void CloseConnection(DbConnection owningObject, DbConnectionFactory connectionFactory)
@@ -76,12 +76,12 @@ internal virtual void CloseConnection(DbConnection owningObject, DbConnectionFac
                 // Lock to prevent race condition with cancellation
                 lock (this)
                 {
-                    object lockToken = ObtainAdditionalLocksForClose();
+                    object? lockToken = ObtainAdditionalLocksForClose();
                     try
                     {
                         PrepareForCloseConnection();
 
-                        DbConnectionPool connectionPool = Pool;
+                        DbConnectionPool? connectionPool = Pool;
 
                         // Detach from enlisted transactions that are no longer active on close
                         DetachCurrentTransactionIfEnded();
@@ -100,7 +100,7 @@ internal virtual void CloseConnection(DbConnection owningObject, DbConnectionFac
                         {
                             Deactivate();   // ensure we de-activate non-pooled connections, or the data readers and transactions may not get cleaned up...
 
-                            PerformanceCounters.HardDisconnectsPerSecond.Increment();
+                            PerformanceCounters!.HardDisconnectsPerSecond.Increment();
 
                             // To prevent an endless recursion, we need to clear
                             // the owning object before we call dispose so that
@@ -143,7 +143,7 @@ public virtual void Dispose()
             // Dispose of the _enlistedTransaction since it is a clone
             // of the original reference.
             // _enlistedTransaction can be changed by another thread (TX end event)
-            SysTx.Transaction enlistedTransaction = Interlocked.Exchange(ref _enlistedTransaction, null);
+            SysTx.Transaction? enlistedTransaction = Interlocked.Exchange(ref _enlistedTransaction, null);
             if (enlistedTransaction != null)
             {
                 enlistedTransaction.Dispose();
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPool.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPool.cs
index 5809fc7a5f78e0..e411fc550101fb 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPool.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPool.cs
@@ -47,7 +47,7 @@ internal void Dispose()
 
         private sealed class PendingGetConnection
         {
-            public PendingGetConnection(long dueTime, DbConnection owner, TaskCompletionSource<DbConnectionInternal> completion, DbConnectionOptions userOptions)
+            public PendingGetConnection(long dueTime, DbConnection owner, TaskCompletionSource<DbConnectionInternal> completion, DbConnectionOptions? userOptions)
             {
                 DueTime = dueTime;
                 Owner = owner;
@@ -56,7 +56,7 @@ public PendingGetConnection(long dueTime, DbConnection owner, TaskCompletionSour
             public long DueTime { get; private set; }
             public DbConnection Owner { get; private set; }
             public TaskCompletionSource<DbConnectionInternal> Completion { get; private set; }
-            public DbConnectionOptions UserOptions { get; private set; }
+            public DbConnectionOptions? UserOptions { get; private set; }
         }
 
         private sealed class TransactedConnectionPool
@@ -81,13 +81,13 @@ internal DbConnectionPool Pool
                 }
             }
 
-            internal DbConnectionInternal GetTransactedObject(SysTx.Transaction transaction)
+            internal DbConnectionInternal? GetTransactedObject(SysTx.Transaction transaction)
             {
                 Debug.Assert(null != transaction, "null transaction?");
 
-                DbConnectionInternal transactedObject = null;
+                DbConnectionInternal? transactedObject = null;
 
-                TransactedConnectionList connections;
+                TransactedConnectionList? connections;
                 bool txnFound = false;
 
                 lock (_transactedCxns)
@@ -126,7 +126,7 @@ internal void PutTransactedObject(SysTx.Transaction transaction, DbConnectionInt
                 Debug.Assert(null != transaction, "null transaction?");
                 Debug.Assert(null != transactedObject, "null transactedObject?");
 
-                TransactedConnectionList connections;
+                TransactedConnectionList? connections;
                 bool txnFound = false;
 
                 // NOTE: because TransactionEnded is an asynchronous notification, there's no guarantee
@@ -155,8 +155,8 @@ internal void PutTransactedObject(SysTx.Transaction transaction, DbConnectionInt
                 {
                     // create the transacted pool, making sure to clone the associated transaction
                     //   for use as a key in our internal dictionary of transactions and connections
-                    SysTx.Transaction transactionClone = null;
-                    TransactedConnectionList newConnections = null;
+                    SysTx.Transaction? transactionClone = null;
+                    TransactedConnectionList? newConnections = null;
 
                     try
                     {
@@ -339,7 +339,7 @@ protected override bool ReleaseHandle()
         private static readonly Random _random = new Random(5101977); // Value obtained from Dave Driver
 
         private readonly int _cleanupWait;
-        private readonly DbConnectionPoolIdentity _identity;
+        private readonly DbConnectionPoolIdentity? _identity;
 
         private readonly DbConnectionFactory _connectionFactory;
         private readonly DbConnectionPoolGroup _connectionPoolGroup;
@@ -357,15 +357,15 @@ protected override bool ReleaseHandle()
         private int _waitCount;
         private readonly PoolWaitHandles _waitHandles;
 
-        private Exception _resError;
+        private Exception? _resError;
         private volatile bool _errorOccurred;
 
         private int _errorWait;
-        private Timer _errorTimer;
+        private Timer? _errorTimer;
 
-        private Timer _cleanupTimer;
+        private Timer? _cleanupTimer;
 
-        private readonly TransactedConnectionPool _transactedConnectionPool;
+        private readonly TransactedConnectionPool? _transactedConnectionPool;
 
         private readonly List<DbConnectionInternal> _objectList;
         private int _totalObjects;
@@ -508,7 +508,7 @@ private bool UsingIntegrateSecurity
             get { return (null != _identity && DbConnectionPoolIdentity.NoIdentity != _identity); }
         }
 
-        private void CleanupCallback(object state)
+        private void CleanupCallback(object? state)
         {
             // Called when the cleanup-timer ticks over.
 
@@ -536,7 +536,7 @@ private void CleanupCallback(object state)
                 if (_waitHandles.PoolSemaphore.WaitOne(0, false) /* != WAIT_TIMEOUT */)
                 {
                     // We obtained a objects from the semaphore.
-                    DbConnectionInternal obj;
+                    DbConnectionInternal? obj;
 
                     if (_stackOld.TryPop(out obj))
                     {
@@ -595,7 +595,7 @@ private void CleanupCallback(object state)
             {
                 while (true)
                 {
-                    DbConnectionInternal obj;
+                    DbConnectionInternal? obj;
 
                     if (!_stackNew.TryPop(out obj))
                         break;
@@ -616,7 +616,7 @@ private void CleanupCallback(object state)
 
         internal void Clear()
         {
-            DbConnectionInternal obj;
+            DbConnectionInternal? obj;
 
             // First, quickly doom everything.
             lock (_objectList)
@@ -660,9 +660,9 @@ private Timer CreateCleanupTimer()
 
         private bool IsBlockingPeriodEnabled() => true;
 
-        private DbConnectionInternal CreateObject(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection)
+        private DbConnectionInternal CreateObject(DbConnection? owningObject, DbConnectionOptions? userOptions, DbConnectionInternal? oldConnection)
         {
-            DbConnectionInternal newObj = null;
+            DbConnectionInternal? newObj = null;
 
             try
             {
@@ -821,7 +821,7 @@ private void DeactivateObject(DbConnectionInternal obj)
                             // the transaction asyncronously completing on a second
                             // thread.
 
-                            SysTx.Transaction transaction = obj.EnlistedTransaction;
+                            SysTx.Transaction? transaction = obj.EnlistedTransaction;
                             if (null != transaction)
                             {
                                 // NOTE: we're not locking on _state, so it's possible that its
@@ -921,13 +921,13 @@ internal void DestroyObject(DbConnectionInternal obj)
             }
         }
 
-        private void ErrorCallback(object state)
+        private void ErrorCallback(object? state)
         {
             _errorOccurred = false;
             _waitHandles.ErrorEvent.Reset();
 
             // the error state is cleaned, destroy the timer to avoid periodic invocation
-            Timer t = _errorTimer;
+            Timer? t = _errorTimer;
             _errorTimer = null;
             if (t != null)
             {
@@ -937,7 +937,7 @@ private void ErrorCallback(object state)
 
         // TODO: move this to src/Common and integrate with SqlClient
         // Note: OleDb connections are not passing through this code
-        private Exception TryCloneCachedException()
+        private Exception? TryCloneCachedException()
         {
             return _resError;
         }
@@ -946,7 +946,7 @@ private void WaitForPendingOpen()
         {
             Debug.Assert(!Thread.CurrentThread.IsThreadPoolThread, "This thread may block for a long time.  Threadpool threads should not be used.");
 
-            PendingGetConnection next;
+            PendingGetConnection? next;
 
             do
             {
@@ -985,9 +985,9 @@ private void WaitForPendingOpen()
                             delay = (uint)Math.Max(ADP.TimerRemainingMilliseconds(next.DueTime), 0);
                         }
 
-                        DbConnectionInternal connection = null;
+                        DbConnectionInternal? connection = null;
                         bool timeout = false;
-                        Exception caughtException = null;
+                        Exception? caughtException = null;
 
                         RuntimeHelpers.PrepareConstrainedRegions();
                         try
@@ -1050,7 +1050,7 @@ private void WaitForPendingOpen()
             } while (_pendingOpens.TryPeek(out next));
         }
 
-        internal bool TryGetConnection(DbConnection owningObject, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions, out DbConnectionInternal connection)
+        internal bool TryGetConnection(DbConnection owningObject, TaskCompletionSource<DbConnectionInternal>? retry, DbConnectionOptions? userOptions, out DbConnectionInternal? connection)
         {
             uint waitForMultipleObjectsTimeout = 0;
             bool allowCreate = false;
@@ -1103,10 +1103,10 @@ internal bool TryGetConnection(DbConnection owningObject, TaskCompletionSource<D
             return false;
         }
 
-        private bool TryGetConnection(DbConnection owningObject, uint waitForMultipleObjectsTimeout, bool allowCreate, bool onlyOneCheckConnection, DbConnectionOptions userOptions, out DbConnectionInternal connection)
+        private bool TryGetConnection(DbConnection owningObject, uint waitForMultipleObjectsTimeout, bool allowCreate, bool onlyOneCheckConnection, DbConnectionOptions? userOptions, out DbConnectionInternal? connection)
         {
-            DbConnectionInternal obj = null;
-            SysTx.Transaction transaction = null;
+            DbConnectionInternal? obj = null;
+            SysTx.Transaction? transaction = null;
 
             PerformanceCounters.SoftConnectsPerSecond.Increment();
 
@@ -1168,7 +1168,7 @@ private bool TryGetConnection(DbConnection owningObject, uint waitForMultipleObj
                             case ERROR_HANDLE:
                                 // Throw the error that PoolCreateRequest stashed.
                                 Interlocked.Decrement(ref _waitCount);
-                                throw TryCloneCachedException();
+                                throw TryCloneCachedException()!;
 
                             case CREATION_HANDLE:
 
@@ -1301,7 +1301,7 @@ private bool TryGetConnection(DbConnection owningObject, uint waitForMultipleObj
             return true;
         }
 
-        private void PrepareConnection(DbConnection owningObject, DbConnectionInternal obj, SysTx.Transaction transaction)
+        private void PrepareConnection(DbConnection owningObject, DbConnectionInternal obj, SysTx.Transaction? transaction)
         {
             lock (obj)
             {   // Protect against Clear and ReclaimEmancipatedObjects, which call IsEmancipated, which is affected by PrePush and PostPop
@@ -1327,15 +1327,15 @@ private void PrepareConnection(DbConnection owningObject, DbConnectionInternal o
         /// <param name="userOptions">Options used to create the new connection</param>
         /// <param name="oldConnection">Inner connection that will be replaced</param>
         /// <returns>A new inner connection that is attached to the <paramref name="owningObject"/></returns>
-        internal DbConnectionInternal ReplaceConnection(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection)
+        internal DbConnectionInternal? ReplaceConnection(DbConnection owningObject, DbConnectionOptions? userOptions, DbConnectionInternal? oldConnection)
         {
             PerformanceCounters.SoftConnectsPerSecond.Increment();
 
-            DbConnectionInternal newConnection = UserCreateRequest(owningObject, userOptions, oldConnection);
+            DbConnectionInternal? newConnection = UserCreateRequest(owningObject, userOptions, oldConnection);
 
             if (newConnection != null)
             {
-                PrepareConnection(owningObject, newConnection, oldConnection.EnlistedTransaction);
+                PrepareConnection(owningObject, newConnection, oldConnection!.EnlistedTransaction);
                 oldConnection.PrepareForReplaceConnection();
                 oldConnection.DeactivateConnection();
                 oldConnection.Dispose();
@@ -1344,9 +1344,9 @@ internal DbConnectionInternal ReplaceConnection(DbConnection owningObject, DbCon
             return newConnection;
         }
 
-        private DbConnectionInternal GetFromGeneralPool()
+        private DbConnectionInternal? GetFromGeneralPool()
         {
-            DbConnectionInternal obj = null;
+            DbConnectionInternal? obj = null;
 
             if (!_stackNew.TryPop(out obj))
             {
@@ -1377,10 +1377,10 @@ private DbConnectionInternal GetFromGeneralPool()
             return (obj);
         }
 
-        private DbConnectionInternal GetFromTransactedPool(out SysTx.Transaction transaction)
+        private DbConnectionInternal? GetFromTransactedPool(out SysTx.Transaction? transaction)
         {
             transaction = ADP.GetCurrentTransaction();
-            DbConnectionInternal obj = null;
+            DbConnectionInternal? obj = null;
 
             if (null != transaction && null != _transactedConnectionPool)
             {
@@ -1412,7 +1412,7 @@ private DbConnectionInternal GetFromTransactedPool(out SysTx.Transaction transac
             return obj;
         }
 
-        private void PoolCreateRequest(object state)
+        private void PoolCreateRequest(object? state)
         {
             // called by pooler to ensure pool requests are currently being satisfied -
             // creation mutex has not been obtained
@@ -1442,7 +1442,7 @@ private void PoolCreateRequest(object state)
                         // since either Open will fail or we will open a object for this pool that does
                         // not belong in this pool.  The side effect of this is that if using integrated
                         // security min pool size cannot be guaranteed.
-                        if (UsingIntegrateSecurity && !_identity.Equals(DbConnectionPoolIdentity.GetCurrent()))
+                        if (UsingIntegrateSecurity && !_identity!.Equals(DbConnectionPoolIdentity.GetCurrent()))
                         {
                             return;
                         }
@@ -1686,7 +1686,7 @@ internal void Shutdown()
             _state = State.ShuttingDown;
 
             // deactivate timer callbacks
-            Timer t = _cleanupTimer;
+            Timer? t = _cleanupTimer;
             _cleanupTimer = null;
             if (null != t)
             {
@@ -1694,15 +1694,15 @@ internal void Shutdown()
             }
         }
 
-        private DbConnectionInternal UserCreateRequest(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection = null)
+        private DbConnectionInternal? UserCreateRequest(DbConnection owningObject, DbConnectionOptions? userOptions, DbConnectionInternal? oldConnection = null)
         {
             // called by user when they were not able to obtain a free object but
             // instead obtained creation mutex
 
-            DbConnectionInternal obj = null;
+            DbConnectionInternal? obj = null;
             if (ErrorOccurred)
             {
-                throw TryCloneCachedException();
+                throw TryCloneCachedException()!;
             }
             else
             {
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolCounters.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolCounters.cs
index df6f363cf6f3a0..e1c2f3bfca2bbd 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolCounters.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolCounters.cs
@@ -90,9 +90,9 @@ private static class CreationData
 
         internal sealed class Counter
         {
-            private PerformanceCounter _instance;
+            private PerformanceCounter? _instance;
 
-            internal Counter(string categoryName, string instanceName, string counterName, PerformanceCounterType counterType)
+            internal Counter(string? categoryName, string? instanceName, string counterName, PerformanceCounterType counterType)
             {
                 if (ADP.IsPlatformNT5)
                 {
@@ -120,7 +120,7 @@ internal Counter(string categoryName, string instanceName, string counterName, P
 
             internal void Decrement()
             {
-                PerformanceCounter instance = _instance;
+                PerformanceCounter? instance = _instance;
                 if (null != instance)
                 {
                     instance.Decrement();
@@ -129,7 +129,7 @@ internal void Decrement()
 
             internal void Dispose()
             { // TODO: race condition, Dispose at the same time as Increment/Decrement
-                PerformanceCounter instance = _instance;
+                PerformanceCounter? instance = _instance;
                 _instance = null;
                 if (null != instance)
                 {
@@ -142,7 +142,7 @@ internal void Dispose()
 
             internal void Increment()
             {
-                PerformanceCounter instance = _instance;
+                PerformanceCounter? instance = _instance;
                 if (null != instance)
                 {
                     instance.Increment();
@@ -171,13 +171,13 @@ protected DbConnectionPoolCounters() : this(null, null)
         {
         }
 
-        protected DbConnectionPoolCounters(string categoryName, string categoryHelp)
+        protected DbConnectionPoolCounters(string? categoryName, string? categoryHelp)
         {
             AppDomain.CurrentDomain.DomainUnload += new EventHandler(this.UnloadEventHandler);
             AppDomain.CurrentDomain.ProcessExit += new EventHandler(this.ExitEventHandler);
             AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(this.ExceptionEventHandler);
 
-            string instanceName = null;
+            string? instanceName = null;
 
             if (!ADP.IsEmpty(categoryName))
             {
@@ -188,7 +188,7 @@ protected DbConnectionPoolCounters(string categoryName, string categoryHelp)
             }
 
             // level 0-3: hard connects/disconnects, plus basic pool/pool entry statistics
-            string basicCategoryName = categoryName;
+            string? basicCategoryName = categoryName;
             HardConnectsPerSecond = new Counter(basicCategoryName, instanceName, CreationData.HardConnectsPerSecond.CounterName, CreationData.HardConnectsPerSecond.CounterType);
             HardDisconnectsPerSecond = new Counter(basicCategoryName, instanceName, CreationData.HardDisconnectsPerSecond.CounterName, CreationData.HardDisconnectsPerSecond.CounterType);
             NumberOfNonPooledConnections = new Counter(basicCategoryName, instanceName, CreationData.NumberOfNonPooledConnections.CounterName, CreationData.NumberOfNonPooledConnections.CounterType);
@@ -201,7 +201,7 @@ protected DbConnectionPoolCounters(string categoryName, string categoryHelp)
             NumberOfReclaimedConnections = new Counter(basicCategoryName, instanceName, CreationData.NumberOfReclaimedConnections.CounterName, CreationData.NumberOfReclaimedConnections.CounterType);
 
             // level 4: expensive stuff
-            string verboseCategoryName = null;
+            string? verboseCategoryName = null;
             if (!ADP.IsEmpty(categoryName))
             {
                 // don't load TraceSwitch if no categoryName so that Odbc/OleDb have a chance of not loading TraceSwitch
@@ -217,12 +217,12 @@ protected DbConnectionPoolCounters(string categoryName, string categoryHelp)
             NumberOfActiveConnections = new Counter(verboseCategoryName, instanceName, CreationData.NumberOfActiveConnections.CounterName, CreationData.NumberOfActiveConnections.CounterType);
             NumberOfFreeConnections = new Counter(verboseCategoryName, instanceName, CreationData.NumberOfFreeConnections.CounterName, CreationData.NumberOfFreeConnections.CounterType);
         }
-        private string GetAssemblyName()
+        private string? GetAssemblyName()
         {
-            string result = null;
+            string? result = null;
 
             // First try GetEntryAssembly name, then AppDomain.FriendlyName.
-            Assembly assembly = Assembly.GetEntryAssembly();
+            Assembly? assembly = Assembly.GetEntryAssembly();
 
             if (null != assembly)
             {
@@ -239,9 +239,9 @@ private string GetAssemblyName()
         // TODO: remove the Resource* attributes if you do not use GetCurrentProcessId after the fix
         private string GetInstanceName()
         {
-            string result = null;
+            string? result = null;
 
-            string instanceName = GetAssemblyName(); // instance perfcounter name
+            string? instanceName = GetAssemblyName(); // instance perfcounter name
 
             if (ADP.IsEmpty(instanceName))
             {
@@ -259,7 +259,7 @@ private string GetInstanceName()
             // to PERFMON.  They recommend that we translate them as shown below, to
             // prevent problems.
 
-            result = string.Format((IFormatProvider)null, "{0}[{1}]", instanceName, pid);
+            result = string.Format(null, "{0}[{1}]", instanceName, pid);
             result = result.Replace('(', '[').Replace(')', ']').Replace('#', '_').Replace('/', '_').Replace('\\', '_');
 
             // counter instance name cannot be greater than 127
@@ -272,13 +272,13 @@ private string GetInstanceName()
                 const string insertString = "[...]";
                 int firstPartLength = (CounterInstanceNameMaxLength - insertString.Length) / 2;
                 int lastPartLength = CounterInstanceNameMaxLength - firstPartLength - insertString.Length;
-                result = string.Format((IFormatProvider)null, "{0}{1}{2}",
+                result = string.Format(null, "{0}{1}{2}",
                     result.Substring(0, firstPartLength),
                     insertString,
                     result.Substring(result.Length - lastPartLength, lastPartLength));
 
                 Debug.Assert(result.Length == CounterInstanceNameMaxLength,
-                    string.Format((IFormatProvider)null, "wrong calculation of the instance name: expected {0}, actual: {1}", CounterInstanceNameMaxLength, result.Length));
+                    string.Format(null, "wrong calculation of the instance name: expected {0}, actual: {1}", CounterInstanceNameMaxLength, result.Length));
             }
 
             return result;
@@ -319,12 +319,12 @@ private void ExceptionEventHandler(object sender, UnhandledExceptionEventArgs e)
             }
         }
 
-        private void ExitEventHandler(object sender, EventArgs e)
+        private void ExitEventHandler(object? sender, EventArgs e)
         {
             Dispose();
         }
 
-        private void UnloadEventHandler(object sender, EventArgs e)
+        private void UnloadEventHandler(object? sender, EventArgs e)
         {
             Dispose();
         }
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolGroup.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolGroup.cs
index 0f9320b122ce98..792f6e7bc2d4b8 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolGroup.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolGroup.cs
@@ -33,8 +33,8 @@ internal sealed class DbConnectionPoolGroup
 
         private int _state;          // see PoolGroupState* below
 
-        private DbConnectionPoolGroupProviderInfo _providerInfo;
-        private DbMetaDataFactory _metaDataFactory;
+        private DbConnectionPoolGroupProviderInfo? _providerInfo;
+        private DbMetaDataFactory? _metaDataFactory;
 
         // always lock this before changing _state, we don't want to move out of the 'Disabled' state
         // PoolGroupStateUninitialized = 0;
@@ -49,7 +49,7 @@ internal DbConnectionPoolGroup(DbConnectionOptions connectionOptions, DbConnecti
 
             _connectionOptions = connectionOptions;
             _poolKey = key;
-            _poolGroupOptions = poolGroupOptions;
+            _poolGroupOptions = poolGroupOptions!;
 
             // always lock this object before changing state
             // HybridDictionary does not create any sub-objects until add
@@ -75,7 +75,7 @@ internal DbConnectionPoolKey PoolKey
             }
         }
 
-        internal DbConnectionPoolGroupProviderInfo ProviderInfo
+        internal DbConnectionPoolGroupProviderInfo? ProviderInfo
         {
             get
             {
@@ -86,7 +86,7 @@ internal DbConnectionPoolGroupProviderInfo ProviderInfo
                 _providerInfo = value;
                 if (null != value)
                 {
-                    _providerInfo.PoolGroup = this;
+                    _providerInfo!.PoolGroup = this;
                 }
             }
         }
@@ -107,7 +107,7 @@ internal DbConnectionPoolGroupOptions PoolGroupOptions
             }
         }
 
-        internal DbMetaDataFactory MetaDataFactory
+        internal DbMetaDataFactory? MetaDataFactory
         {
             get
             {
@@ -126,7 +126,7 @@ internal int Clear()
             // will return the number of connections in the group after clearing has finished
 
             // First, note the old collection and create a new collection to be used
-            ConcurrentDictionary<DbConnectionPoolIdentity, DbConnectionPool> oldPoolCollection = null;
+            ConcurrentDictionary<DbConnectionPoolIdentity, DbConnectionPool>? oldPoolCollection = null;
             lock (this)
             {
                 if (_poolCollection.Count > 0)
@@ -162,7 +162,7 @@ internal int Clear()
             return _poolCollection.Count;
         }
 
-        internal DbConnectionPool GetConnectionPool(DbConnectionFactory connectionFactory)
+        internal DbConnectionPool? GetConnectionPool(DbConnectionFactory connectionFactory)
         {
             // When this method returns null it indicates that the connection
             // factory should not use pooling.
@@ -171,12 +171,12 @@ internal DbConnectionPool GetConnectionPool(DbConnectionFactory connectionFactor
             // many of the APIs we require.
             // PoolGroupOptions will only be null when we're not supposed to pool
             // connections.
-            DbConnectionPool pool = null;
+            DbConnectionPool? pool = null;
             if (null != _poolGroupOptions)
             {
                 Debug.Assert(ADP.IsWindowsNT, "should not be pooling on Win9x");
 
-                DbConnectionPoolIdentity currentIdentity = DbConnectionPoolIdentity.NoIdentity;
+                DbConnectionPoolIdentity? currentIdentity = DbConnectionPoolIdentity.NoIdentity;
                 if (_poolGroupOptions.PoolByIdentity)
                 {
                     // if we're pooling by identity (because integrated security is
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolGroupProviderInfo.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolGroupProviderInfo.cs
index 911720230d2133..44c2fd1a379e96 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolGroupProviderInfo.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolGroupProviderInfo.cs
@@ -5,9 +5,9 @@ namespace System.Data.ProviderBase
 {
     internal class DbConnectionPoolGroupProviderInfo
     {
-        private DbConnectionPoolGroup _poolGroup;
+        private DbConnectionPoolGroup? _poolGroup;
 
-        internal DbConnectionPoolGroup PoolGroup
+        internal DbConnectionPoolGroup? PoolGroup
         {
             get
             {
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolIdentity.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolIdentity.cs
index a7d839b8c2e2ae..9fe3910b372a24 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolIdentity.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbConnectionPoolIdentity.cs
@@ -58,7 +58,7 @@ private static byte[] CreateWellKnownSid(WellKnownSidType sidType)
             return resultSid;
         }
 
-        public override bool Equals(object value)
+        public override bool Equals(object? value)
         {
             bool result = ((this == NoIdentity) || (this == value));
             if (!result && (null != value))
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbMetaDataFactory.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbMetaDataFactory.cs
index 24e665052e8aa7..68892d670c3c16 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbMetaDataFactory.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbMetaDataFactory.cs
@@ -38,7 +38,8 @@ public DbMetaDataFactory(Stream xmlStream, string serverVersion, string normaliz
             ADP.CheckArgumentNull(serverVersion, "serverVersion");
             ADP.CheckArgumentNull(normalizedServerVersion, "normalizedServerVersion");
 
-            LoadDataSetFromXml(xmlStream);
+            _metaDataCollectionsDataSet = new DataSet { Locale = CultureInfo.InvariantCulture };
+            _metaDataCollectionsDataSet.ReadXml(xmlStream);
 
             _serverVersionString = serverVersion;
             _normalizedServerVersion = normalizedServerVersion;
@@ -68,9 +69,9 @@ protected string ServerVersionNormalized
             }
         }
 
-        protected DataTable CloneAndFilterCollection(string collectionName, string[] hiddenColumnNames)
+        protected DataTable CloneAndFilterCollection(string collectionName, string[]? hiddenColumnNames)
         {
-            DataTable sourceTable;
+            DataTable? sourceTable;
             DataTable destinationTable;
             DataColumn[] filteredSourceColumns;
             DataColumnCollection destinationColumns;
@@ -115,28 +116,28 @@ protected virtual void Dispose(bool disposing)
         {
             if (disposing)
             {
-                _normalizedServerVersion = null;
-                _serverVersionString = null;
+                _normalizedServerVersion = null!;
+                _serverVersionString = null!;
                 _metaDataCollectionsDataSet.Dispose();
             }
         }
 
-        private DataTable ExecuteCommand(DataRow requestedCollectionRow, string[] restrictions, DbConnection connection)
+        private DataTable ExecuteCommand(DataRow requestedCollectionRow, string?[]? restrictions, DbConnection connection)
         {
-            DataTable metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
-            DataColumn populationStringColumn = metaDataCollectionsTable.Columns[_populationString];
-            DataColumn numberOfRestrictionsColumn = metaDataCollectionsTable.Columns[_numberOfRestrictions];
-            DataColumn collectionNameColumn = metaDataCollectionsTable.Columns[_collectionName];
+            DataTable metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections]!;
+            DataColumn populationStringColumn = metaDataCollectionsTable.Columns[_populationString]!;
+            DataColumn numberOfRestrictionsColumn = metaDataCollectionsTable.Columns[_numberOfRestrictions]!;
+            DataColumn collectionNameColumn = metaDataCollectionsTable.Columns[_collectionName]!;
             //DataColumn  restrictionNameColumn = metaDataCollectionsTable.Columns[_restrictionName];
 
-            DataTable resultTable = null;
-            DbCommand command = null;
-            DataTable schemaTable = null;
+            DataTable? resultTable = null;
+            DbCommand? command = null;
+            DataTable? schemaTable = null;
 
             Debug.Assert(requestedCollectionRow != null);
-            string sqlCommand = requestedCollectionRow[populationStringColumn, DataRowVersion.Current] as string;
+            string sqlCommand = (requestedCollectionRow[populationStringColumn, DataRowVersion.Current] as string)!;
             int numberOfRestrictions = (int)requestedCollectionRow[numberOfRestrictionsColumn, DataRowVersion.Current];
-            string collectionName = requestedCollectionRow[collectionNameColumn, DataRowVersion.Current] as string;
+            string collectionName = (requestedCollectionRow[collectionNameColumn, DataRowVersion.Current] as string)!;
 
             if ((restrictions != null) && (restrictions.Length > numberOfRestrictions))
             {
@@ -167,7 +168,7 @@ private DataTable ExecuteCommand(DataRow requestedCollectionRow, string[] restri
                 command.Parameters.Add(restrictionParameter);
             }
 
-            DbDataReader reader = null;
+            DbDataReader? reader = null;
             try
             {
                 try
@@ -212,11 +213,11 @@ private DataTable ExecuteCommand(DataRow requestedCollectionRow, string[] restri
             return resultTable;
         }
 
-        private DataColumn[] FilterColumns(DataTable sourceTable, string[] hiddenColumnNames, DataColumnCollection destinationColumns)
+        private DataColumn[] FilterColumns(DataTable sourceTable, string[]? hiddenColumnNames, DataColumnCollection destinationColumns)
         {
             DataColumn newDestinationColumn;
             int currentColumn;
-            DataColumn[] filteredSourceColumns = null;
+            DataColumn[]? filteredSourceColumns = null;
 
             int columnCount = 0;
             foreach (DataColumn sourceColumn in sourceTable.Columns)
@@ -253,23 +254,23 @@ internal DataRow FindMetaDataCollectionRow(string collectionName)
             bool versionFailure;
             bool haveExactMatch;
             bool haveMultipleInexactMatches;
-            string candidateCollectionName;
+            string? candidateCollectionName;
 
-            DataTable metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
+            DataTable? metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
             if (metaDataCollectionsTable == null)
             {
                 throw ADP.InvalidXml();
             }
 
-            DataColumn collectionNameColumn = metaDataCollectionsTable.Columns[DbMetaDataColumnNames.CollectionName];
+            DataColumn? collectionNameColumn = metaDataCollectionsTable.Columns[DbMetaDataColumnNames.CollectionName];
 
             if ((null == collectionNameColumn) || (typeof(string) != collectionNameColumn.DataType))
             {
                 throw ADP.InvalidXmlMissingColumn(DbMetaDataCollectionNames.MetaDataCollections, DbMetaDataColumnNames.CollectionName);
             }
 
-            DataRow requestedCollectionRow = null;
-            string exactCollectionName = null;
+            DataRow? requestedCollectionRow = null;
+            string? exactCollectionName = null;
 
             // find the requested collection
             versionFailure = false;
@@ -341,8 +342,8 @@ internal DataRow FindMetaDataCollectionRow(string collectionName)
         private void FixUpVersion(DataTable dataSourceInfoTable)
         {
             Debug.Assert(dataSourceInfoTable.TableName == DbMetaDataCollectionNames.DataSourceInformation);
-            DataColumn versionColumn = dataSourceInfoTable.Columns[_dataSourceProductVersion];
-            DataColumn normalizedVersionColumn = dataSourceInfoTable.Columns[_dataSourceProductVersionNormalized];
+            DataColumn? versionColumn = dataSourceInfoTable.Columns[_dataSourceProductVersion];
+            DataColumn? normalizedVersionColumn = dataSourceInfoTable.Columns[_dataSourceProductVersionNormalized];
 
             if ((versionColumn == null) || (normalizedVersionColumn == null))
             {
@@ -363,14 +364,14 @@ private void FixUpVersion(DataTable dataSourceInfoTable)
 
         private string GetParameterName(string neededCollectionName, int neededRestrictionNumber)
         {
-            DataTable restrictionsTable = null;
-            DataColumnCollection restrictionColumns = null;
-            DataColumn collectionName = null;
-            DataColumn parameterName = null;
-            DataColumn restrictionName = null;
-            DataColumn restrictionNumber = null;
+            DataTable? restrictionsTable = null;
+            DataColumnCollection? restrictionColumns = null;
+            DataColumn? collectionName = null;
+            DataColumn? parameterName = null;
+            DataColumn? restrictionName = null;
+            DataColumn? restrictionNumber = null;
             ;
-            string result = null;
+            string? result = null;
 
             restrictionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.Restrictions];
             if (restrictionsTable != null)
@@ -390,7 +391,7 @@ private string GetParameterName(string neededCollectionName, int neededRestricti
                 throw ADP.MissingRestrictionColumn();
             }
 
-            foreach (DataRow restriction in restrictionsTable.Rows)
+            foreach (DataRow restriction in restrictionsTable!.Rows)
             {
                 if (((string)restriction[collectionName] == neededCollectionName) &&
                     ((int)restriction[restrictionNumber] == neededRestrictionNumber) &&
@@ -410,26 +411,26 @@ private string GetParameterName(string neededCollectionName, int neededRestricti
 
         }
 
-        public virtual DataTable GetSchema(DbConnection connection, string collectionName, string[] restrictions)
+        public virtual DataTable GetSchema(DbConnection connection, string collectionName, string?[]? restrictions)
         {
             Debug.Assert(_metaDataCollectionsDataSet != null);
 
-            DataTable metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections];
-            DataColumn populationMechanismColumn = metaDataCollectionsTable.Columns[_populationMechanism];
-            DataColumn collectionNameColumn = metaDataCollectionsTable.Columns[DbMetaDataColumnNames.CollectionName];
-            DataRow requestedCollectionRow = null;
-            DataTable requestedSchema = null;
-            string[] hiddenColumns;
-            string exactCollectionName = null;
+            DataTable metaDataCollectionsTable = _metaDataCollectionsDataSet.Tables[DbMetaDataCollectionNames.MetaDataCollections]!;
+            DataColumn populationMechanismColumn = metaDataCollectionsTable.Columns[_populationMechanism]!;
+            DataColumn collectionNameColumn = metaDataCollectionsTable.Columns[DbMetaDataColumnNames.CollectionName]!;
+            DataRow? requestedCollectionRow = null;
+            DataTable? requestedSchema = null;
+            string[]? hiddenColumns;
+            string? exactCollectionName = null;
 
             requestedCollectionRow = FindMetaDataCollectionRow(collectionName);
-            exactCollectionName = requestedCollectionRow[collectionNameColumn, DataRowVersion.Current] as string;
+            exactCollectionName = (requestedCollectionRow[collectionNameColumn, DataRowVersion.Current] as string)!;
 
             if (ADP.IsEmptyArray(restrictions) == false)
             {
-                for (int i = 0; i < restrictions.Length; i++)
+                for (int i = 0; i < restrictions!.Length; i++)
                 {
-                    if ((restrictions[i] != null) && (restrictions[i].Length > 4096))
+                    if ((restrictions[i]?.Length > 4096))
                     {
                         // use a non-specific error because no new beta 2 error messages are allowed
                         // TODO: will add a more descriptive error in RTM
@@ -438,7 +439,7 @@ public virtual DataTable GetSchema(DbConnection connection, string collectionNam
                 }
             }
 
-            string populationMechanism = requestedCollectionRow[populationMechanismColumn, DataRowVersion.Current] as string;
+            string populationMechanism = (requestedCollectionRow[populationMechanismColumn, DataRowVersion.Current] as string)!;
             switch (populationMechanism)
             {
                 case _dataTable:
@@ -485,7 +486,7 @@ public virtual DataTable GetSchema(DbConnection connection, string collectionNam
             return requestedSchema;
         }
 
-        private bool IncludeThisColumn(DataColumn sourceColumn, string[] hiddenColumnNames)
+        private bool IncludeThisColumn(DataColumn sourceColumn, string[]? hiddenColumnNames)
         {
             bool result = true;
             string sourceColumnName = sourceColumn.ColumnName;
@@ -516,14 +517,7 @@ private bool IncludeThisColumn(DataColumn sourceColumn, string[] hiddenColumnNam
             return result;
         }
 
-        private void LoadDataSetFromXml(Stream XmlStream)
-        {
-            _metaDataCollectionsDataSet = new DataSet();
-            _metaDataCollectionsDataSet.Locale = System.Globalization.CultureInfo.InvariantCulture;
-            _metaDataCollectionsDataSet.ReadXml(XmlStream);
-        }
-
-        protected virtual DataTable PrepareCollection(string collectionName, string[] restrictions, DbConnection connection)
+        protected virtual DataTable PrepareCollection(string collectionName, string?[]? restrictions, DbConnection connection)
         {
             throw ADP.NotSupported();
         }
@@ -532,7 +526,7 @@ private bool SupportedByCurrentVersion(DataRow requestedCollectionRow)
         {
             bool result = true;
             DataColumnCollection tableColumns = requestedCollectionRow.Table.Columns;
-            DataColumn versionColumn;
+            DataColumn? versionColumn;
             object version;
 
             // check the minimum version first
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbReferenceCollection.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbReferenceCollection.cs
index c08b3436a640ee..02e526676ca374 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbReferenceCollection.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/DbReferenceCollection.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 
 namespace System.Data.ProviderBase
@@ -51,7 +52,7 @@ public int Tag
                 }
             }
 
-            public object Target
+            public object? Target
             {
                 get
                 {
@@ -132,7 +133,7 @@ protected void AddItem(object value, int tag)
             }
         }
 
-        internal T FindItem<T>(int tag, Func<T, bool> filterMethod) where T : class
+        internal T? FindItem<T>(int tag, Func<T, bool> filterMethod) where T : class
         {
             bool lockObtained = false;
             try
@@ -150,11 +151,11 @@ internal T FindItem<T>(int tag, Func<T, bool> filterMethod) where T : class
                             {
                                 // NOTE: Check if the returned value is null twice may seem wasteful, but this if for performance
                                 // Since checking for null twice is cheaper than calling both HasTarget and Target OR always attempting to typecast
-                                object value = _items[counter].Target;
+                                object? value = _items[counter].Target;
                                 if (value != null)
                                 {
                                     // Make sure the item has the correct type and passes the filtering
-                                    T tempItem = value as T;
+                                    T? tempItem = value as T;
                                     if ((tempItem != null) && (filterMethod(tempItem)))
                                     {
                                         return tempItem;
@@ -191,7 +192,7 @@ public void Notify(int message)
                         {
                             for (int index = 0; index <= _lastItemIndex; ++index)
                             {
-                                object value = _items[index].Target; // checks tag & gets target
+                                object? value = _items[index].Target; // checks tag & gets target
                                 if (null != value)
                                 {
                                     NotifyItem(message, _items[index].Tag, value);
diff --git a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/WrappedIUnknown.cs b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/WrappedIUnknown.cs
index 66ba0d16fb291d..a45f38e06111aa 100644
--- a/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/WrappedIUnknown.cs
+++ b/src/libraries/System.Data.OleDb/src/System/Data/ProviderBase/WrappedIUnknown.cs
@@ -18,7 +18,7 @@ internal WrappedIUnknown() : base(IntPtr.Zero, true)
         {
         }
 
-        internal WrappedIUnknown(object unknown) : this()
+        internal WrappedIUnknown(object? unknown) : this()
         {
             if (null != unknown)
             {
@@ -44,7 +44,7 @@ internal object ComWrapper()
         {
             // NOTE: Method, instead of property, to avoid being evaluated at
             // runtime in the debugger.
-            object value = null;
+            object? value = null;
             bool mustRelease = false;
             RuntimeHelpers.PrepareConstrainedRegions();
             try
diff --git a/src/libraries/System.Data.OleDb/src/UnsafeNativeMethods.cs b/src/libraries/System.Data.OleDb/src/UnsafeNativeMethods.cs
index b6e203b43ae538..4f6717007d3e3b 100644
--- a/src/libraries/System.Data.OleDb/src/UnsafeNativeMethods.cs
+++ b/src/libraries/System.Data.OleDb/src/UnsafeNativeMethods.cs
@@ -337,7 +337,7 @@ HRESULT GetProperties(
             [PreserveSig]
             System.Data.OleDb.OleDbHResult GetProperties(
                 [In] int cPropertyIDSets,
-                [In] SafeHandle rgPropertyIDSets,
+                [In] SafeHandle? rgPropertyIDSets,
                 [Out] out int pcPropertySets,
                 [Out] out IntPtr prgPropertySets);
 
@@ -372,7 +372,7 @@ HRESULT Execute(
             System.Data.OleDb.OleDbHResult Execute(
                 [In] IntPtr pUnkOuter,
                 [In] ref Guid riid,
-                [In] System.Data.OleDb.tagDBPARAMS pDBParams,
+                [In] System.Data.OleDb.tagDBPARAMS? pDBParams,
                 [Out] out IntPtr pcRowsAffected,
                 [Out, MarshalAs(UnmanagedType.Interface)] out object ppRowset);
 
@@ -436,7 +436,7 @@ [out] OLECHAR ** ppCharBuffer
             [PreserveSig]
             System.Data.OleDb.OleDbHResult GetLiteralInfo(
                 [In] int cLiterals,
-                [In, MarshalAs(UnmanagedType.LPArray)] int[] rgLiterals,
+                [In, MarshalAs(UnmanagedType.LPArray)] int[]? rgLiterals,
                 [Out] out int pcLiteralInfo,
                 [Out] out IntPtr prgLiteralInfo,
                 [Out] out IntPtr ppCharBuffer);
@@ -455,7 +455,7 @@ HRESULT GetProperties(
             [PreserveSig]
             System.Data.OleDb.OleDbHResult GetProperties(
                 [In] int cPropertyIDSets,
-                [In] SafeHandle rgPropertyIDSets,
+                [In] SafeHandle? rgPropertyIDSets,
                 [Out] out int pcPropertySets,
                 [Out] out IntPtr prgPropertySets);
 
@@ -492,7 +492,7 @@ System.Data.OleDb.OleDbHResult GetRowset(
                 [In] IntPtr pUnkOuter,
                 [In] ref Guid rguidSchema,
                 [In] int cRestrictions,
-                [In, MarshalAs(UnmanagedType.LPArray)] object[] rgRestrictions,
+                [In, MarshalAs(UnmanagedType.LPArray)] object?[] rgRestrictions,
                 [In] ref Guid riid,
                 [In] int cPropertySets,
                 [In] IntPtr rgPropertySets,
@@ -715,7 +715,7 @@ HRESULT GetProperties(
             [PreserveSig]
             System.Data.OleDb.OleDbHResult GetProperties(
                 [In] int cPropertyIDSets,
-                [In] SafeHandle rgPropertyIDSets,
+                [In] SafeHandle? rgPropertyIDSets,
                 [Out] out int pcPropertySets,
                 [Out] out IntPtr prgPropertySets);
 
@@ -811,7 +811,7 @@ internal delegate System.Data.OleDb.OleDbHResult IDBCreateCommandCreateCommand(
                 IntPtr pThis, // first parameter is always the 'this' value, must use use result from QI
                 IntPtr pUnkOuter,
                 ref Guid riid,
-                [MarshalAs(UnmanagedType.Interface)] ref object ppCommand);
+                [MarshalAs(UnmanagedType.Interface)] ref object? ppCommand);
 
         //
         // Advapi32.dll Integrated security functions
@@ -840,7 +840,7 @@ internal Trustee(string name)
         [DllImport(Interop.Libraries.Advapi32, EntryPoint = "CreateWellKnownSid", SetLastError = true, CharSet = CharSet.Unicode)]
         internal static extern int CreateWellKnownSid(
             int sidType,
-            byte[] domainSid,
+            byte[]? domainSid,
             [Out] byte[] resultSid,
             ref uint resultSidLength);
     }
diff --git a/src/libraries/System.Data.OleDb/tests/System.Data.OleDb.Tests.csproj b/src/libraries/System.Data.OleDb/tests/System.Data.OleDb.Tests.csproj
index 268d99b2c716bf..d4874a8727ff33 100644
--- a/src/libraries/System.Data.OleDb/tests/System.Data.OleDb.Tests.csproj
+++ b/src/libraries/System.Data.OleDb/tests/System.Data.OleDb.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Helpers.cs" />
@@ -12,4 +12,11 @@
     <Compile Include="OleDbDataReaderTests.cs" />
     <Compile Include="OleDbParameterTests.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="..\src\System.Data.OleDb.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net461'))">
+    <Reference Include="Microsoft.CSharp" />
+    <Reference Include="System.Data.DataSetExtensions" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.Contracts/Directory.Build.props b/src/libraries/System.Diagnostics.Contracts/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Diagnostics.Contracts/Directory.Build.props
+++ b/src/libraries/System.Diagnostics.Contracts/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Diagnostics.Contracts/src/System.Diagnostics.Contracts.csproj b/src/libraries/System.Diagnostics.Contracts/src/System.Diagnostics.Contracts.csproj
index 2e459ec3a069a0..dd3dc2940a54b1 100644
--- a/src/libraries/System.Diagnostics.Contracts/src/System.Diagnostics.Contracts.csproj
+++ b/src/libraries/System.Diagnostics.Contracts/src/System.Diagnostics.Contracts.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Diagnostics.Contracts</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Diagnostics.Debug/Directory.Build.props b/src/libraries/System.Diagnostics.Debug/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Diagnostics.Debug/Directory.Build.props
+++ b/src/libraries/System.Diagnostics.Debug/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.Debug/src/System.Diagnostics.Debug.csproj b/src/libraries/System.Diagnostics.Debug/src/System.Diagnostics.Debug.csproj
index b7a84d2aed1749..dd3dc2940a54b1 100644
--- a/src/libraries/System.Diagnostics.Debug/src/System.Diagnostics.Debug.csproj
+++ b/src/libraries/System.Diagnostics.Debug/src/System.Diagnostics.Debug.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Diagnostics.Debug</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Diagnostics.Debug/tests/System.Diagnostics.Debug.Tests.csproj b/src/libraries/System.Diagnostics.Debug/tests/System.Diagnostics.Debug.Tests.csproj
index 4d90da957da24a..96893aa3faa277 100644
--- a/src/libraries/System.Diagnostics.Debug/tests/System.Diagnostics.Debug.Tests.csproj
+++ b/src/libraries/System.Diagnostics.Debug/tests/System.Diagnostics.Debug.Tests.csproj
@@ -3,15 +3,16 @@
     <RootNamespace>System.Diagnostics.Tests</RootNamespace>
     <IgnoreArchitectureMismatches>true</IgnoreArchitectureMismatches>
     <ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>None</ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>
-    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix</TargetFrameworks>
     <TestRuntime>true</TestRuntime>
   </PropertyGroup>
   <ItemGroup>
-    <DefaultReferenceExclusions Include="System.Diagnostics.Debug" />
-    <DefaultReferenceExclusions Include="System.Runtime.Extensions" />
-    <ProjectReference Include="$(CoreLibProject)" Private="false" />
-    <ReferenceFromRuntime Include="System.Runtime" />
-    <ReferenceFromRuntime Include="System.Threading" />
+    <DefaultReferenceExclusion Include="System.Diagnostics.Debug" />
+    <DefaultReferenceExclusion Include="System.Runtime.Extensions" />
+    <ProjectReference Include="$(CoreLibProject)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\src\System.Runtime.csproj;
+                               $(LibrariesProjectRoot)System.Threading\src\System.Threading.csproj"
+                      SkipUseReferenceAssembly="true" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="DebugTests.cs" />
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/Directory.Build.props b/src/libraries/System.Diagnostics.DiagnosticSource/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/Directory.Build.props
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSource.csproj b/src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSource.csproj
index 1766bbf5625361..e34e24c6fbf3bb 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSource.csproj
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSource.csproj
@@ -1,9 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard1.1;netstandard1.3;net45;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;netstandard1.1;netstandard1.3;net45</TargetFrameworks>
     <CLSCompliant>false</CLSCompliant>
     <Nullable>enable</Nullable>
+    <AvoidRestoreCycleOnSelfReference>true</AvoidRestoreCycleOnSelfReference>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -15,21 +15,9 @@
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' != 'netstandard1.1'">
     <Compile Include="System.Diagnostics.DiagnosticSourceActivity.cs" />
-    <Reference Include="System.Memory" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'net45' or '$(TargetFramework)' == '$(NetFrameworkCurrent)'">
-    <Reference Include="mscorlib" />
-  </ItemGroup>
-
   <ItemGroup Condition="'$(TargetFramework)' == 'net45'">
     <Reference Include="System.Runtime" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetFrameworkCurrent)'">
-    <Reference Include="netstandard" />
-  </ItemGroup>
-
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.1' or '$(TargetFramework)' == 'netstandard1.3'">
-    <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="System.Runtime" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSourceActivity.cs b/src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSourceActivity.cs
index f0b93c82b4075a..8e0f944e09cf6f 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSourceActivity.cs
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSourceActivity.cs
@@ -210,6 +210,8 @@ public readonly struct ActivityEvent
         public System.Diagnostics.ActivityTraceFlags TraceFlags  { get { throw null; } }
         public string? TraceState  { get { throw null; } }
         public bool IsRemote { get { throw null; } }
+        public static bool TryParse(string traceParent, string? traceState, out System.Diagnostics.ActivityContext context) { throw null; }
+        public static System.Diagnostics.ActivityContext Parse(string traceParent, string? traceState) { throw null; }
         public static bool operator ==(System.Diagnostics.ActivityContext left, System.Diagnostics.ActivityContext right) { throw null; }
         public static bool operator !=(System.Diagnostics.ActivityContext left, System.Diagnostics.ActivityContext right) { throw null; }
         public bool Equals(System.Diagnostics.ActivityContext value) { throw null; }
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/src/Resources/Strings.resx b/src/libraries/System.Diagnostics.DiagnosticSource/src/Resources/Strings.resx
index 52df21c79f1eea..76242301beb3db 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/src/Resources/Strings.resx
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/src/Resources/Strings.resx
@@ -156,4 +156,7 @@
   <data name="KeyAlreadyExist" xml:space="preserve">
     <value>"The collection already contains item with same key '{0}''"</value>
   </data>
+  <data name="InvalidTraceParent" xml:space="preserve">
+    <value>"Invalid trace parent."</value>
+  </data>
 </root>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj b/src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj
index 0745b28f5a9542..275bebeb1fece5 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj
@@ -4,8 +4,8 @@
     <CLSCompliant>false</CLSCompliant>
     <NoWarn>$(NoWarn);SA1205</NoWarn>
     <Nullable>enable</Nullable>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.1;netstandard1.3;net45;net46;netstandard2.0;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.1;netstandard1.3;net45;net46;netstandard2.0</TargetFrameworks>
+    <AvoidRestoreCycleOnSelfReference>true</AvoidRestoreCycleOnSelfReference>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -45,8 +45,6 @@
     <Compile Include="System\Diagnostics\ActivityListener.cs" />
     <Compile Include="System\Diagnostics\ActivitySource.cs" />
     <Compile Include="System\Diagnostics\DiagnosticSourceActivity.cs" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
     <None Include="ActivityUserGuide.md" />
   </ItemGroup>
   <ItemGroup Condition=" '$(TargetFramework)' == '$(NetCoreAppCurrent)'">
@@ -60,8 +58,6 @@
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'net45'">
     <Compile Include="System\Diagnostics\Activity.Current.net45.cs" />
-    <TargetingPackReference Include="System" />
-    <TargetingPackReference Include="System.Runtime.Remoting" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or '$(TargetFramework)' == 'netstandard1.1' or '$(TargetFramework)' == 'netstandard1.3' or '$(TargetFramework)' == 'netstandard2.0'">
     <Compile Include="System\Diagnostics\Activity.DateTime.corefx.cs" />
@@ -78,26 +74,24 @@
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
     <Compile Include="System\Diagnostics\HttpHandlerDiagnosticListener.cs" />
+    <Compile Include="AssemblyInfo.netfx.cs" />
+    <Compile Include="System\Diagnostics\Activity.DateTime.netfx.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' != '$(NetFrameworkCurrent)'">
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Diagnostics.Tracing" />
+    <Reference Include="System.Memory" />
     <Reference Include="System.Reflection" />
     <Reference Include="System.Runtime" />
+    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Resources.ResourceManager" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3'">
-    <Reference Include="System.AppContext" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Compile Include="AssemblyInfo.netfx.cs" />
-    <Compile Include="System\Diagnostics\Activity.DateTime.netfx.cs" />
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
+  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard1.1' and '$(TargetFramework)' != '$(NetCoreAppCurrent)'">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Activity.cs b/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Activity.cs
index 5cb992426c36a6..23834958a4f4cb 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Activity.cs
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Activity.cs
@@ -3,8 +3,10 @@
 
 using System.Buffers.Binary;
 using System.Buffers.Text;
+using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Concurrent;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Text;
@@ -33,6 +35,7 @@ public partial class Activity : IDisposable
     {
 #pragma warning disable CA1825 // Array.Empty<T>() doesn't exist in all configurations
         private static readonly IEnumerable<KeyValuePair<string, string?>> s_emptyBaggageTags = new KeyValuePair<string, string?>[0];
+        private static readonly IEnumerable<KeyValuePair<string, object?>> s_emptyTagObjects = new KeyValuePair<string, object?>[0];
         private static readonly IEnumerable<ActivityLink> s_emptyLinks = new ActivityLink[0];
         private static readonly IEnumerable<ActivityEvent> s_emptyEvents = new ActivityEvent[0];
 #pragma warning restore CA1825
@@ -255,7 +258,7 @@ public string? RootId
 #if ALLOW_PARTIALLY_TRUSTED_CALLERS
         [System.Security.SecuritySafeCriticalAttribute]
 #endif
-            get => _tags?.Enumerate() ?? Unsafe.As<IEnumerable<KeyValuePair<string, object?>>>(s_emptyBaggageTags);
+            get => _tags ?? s_emptyTagObjects;
         }
 
         /// <summary>
@@ -264,7 +267,7 @@ public string? RootId
         /// </summary>
         public IEnumerable<ActivityEvent> Events
         {
-            get => _events != null ? _events.Enumerate() : s_emptyEvents;
+            get => _events ?? s_emptyEvents;
         }
 
         /// <summary>
@@ -273,7 +276,7 @@ public IEnumerable<ActivityEvent> Events
         /// </summary>
         public IEnumerable<ActivityLink> Links
         {
-            get => _links != null ? _links.Enumerate() : s_emptyLinks;
+            get => _links ?? s_emptyLinks;
         }
 
         /// <summary>
@@ -839,24 +842,29 @@ private static bool IsW3CId(string id)
 #if ALLOW_PARTIALLY_TRUSTED_CALLERS
         [System.Security.SecuritySafeCriticalAttribute]
 #endif
-        internal static bool TryConvertIdToContext(string id, out ActivityContext context)
+        internal static bool TryConvertIdToContext(string traceParent, string? traceState, out ActivityContext context)
         {
             context = default;
-            if (!IsW3CId(id))
+            if (!IsW3CId(traceParent))
             {
                 return false;
             }
 
-            ReadOnlySpan<char> traceIdSpan = id.AsSpan(3,  32);
-            ReadOnlySpan<char> spanIdSpan  = id.AsSpan(36, 16);
+            ReadOnlySpan<char> traceIdSpan = traceParent.AsSpan(3,  32);
+            ReadOnlySpan<char> spanIdSpan  = traceParent.AsSpan(36, 16);
 
             if (!ActivityTraceId.IsLowerCaseHexAndNotAllZeros(traceIdSpan) || !ActivityTraceId.IsLowerCaseHexAndNotAllZeros(spanIdSpan) ||
-                !HexConverter.IsHexLowerChar(id[53]) || !HexConverter.IsHexLowerChar(id[54]))
+                !HexConverter.IsHexLowerChar(traceParent[53]) || !HexConverter.IsHexLowerChar(traceParent[54]))
             {
                 return false;
             }
 
-            context = new ActivityContext(new ActivityTraceId(traceIdSpan.ToString()), new ActivitySpanId(spanIdSpan.ToString()), (ActivityTraceFlags) ActivityTraceId.HexByteFromChars(id[53], id[54]));
+            context = new ActivityContext(
+                            new ActivityTraceId(traceIdSpan.ToString()),
+                            new ActivitySpanId(spanIdSpan.ToString()),
+                            (ActivityTraceFlags) ActivityTraceId.HexByteFromChars(traceParent[53], traceParent[54]),
+                            traceState);
+
             return true;
         }
 
@@ -986,7 +994,7 @@ internal static Activity CreateAndStart(ActivitySource source, string name, Acti
                 }
             }
 
-            activity.StartTimeUtc = startTime == default ? DateTime.UtcNow : startTime.DateTime;
+            activity.StartTimeUtc = startTime == default ? DateTime.UtcNow : startTime.UtcDateTime;
 
             activity.IsAllDataRequested = request == ActivityDataRequest.AllData || request == ActivityDataRequest.AllDataAndRecorded;
 
@@ -1233,7 +1241,7 @@ private partial class LinkedListNode<T>
         }
 
         // We are not using the public LinkedList<T> because we need to ensure thread safety operation on the list.
-        private class LinkedList<T>
+        private class LinkedList<T> : IEnumerable<T>
         {
             private LinkedListNode<T> _first;
             private LinkedListNode<T> _last;
@@ -1264,18 +1272,12 @@ public void Add(T value)
                 }
             }
 
-            public IEnumerable<T> Enumerate()
-            {
-                LinkedListNode<T>? current = _first;
-                do
-                {
-                    yield return current.Value;
-                    current = current.Next;
-                } while (current != null);
-            }
+            public Enumerator<T> GetEnumerator() => new Enumerator<T>(_first);
+            IEnumerator<T> IEnumerable<T>.GetEnumerator() => new Enumerator<T>(_first);
+            IEnumerator IEnumerable.GetEnumerator() => new Enumerator<T>(_first);
         }
 
-        private class TagsLinkedList
+        private class TagsLinkedList : IEnumerable<KeyValuePair<string, object?>>
         {
             private LinkedListNode<KeyValuePair<string, object?>>? _first;
             private LinkedListNode<KeyValuePair<string, object?>>? _last;
@@ -1377,6 +1379,10 @@ public void Set(KeyValuePair<string, object?> value)
                 }
             }
 
+            public Enumerator<KeyValuePair<string, object?>> GetEnumerator() => new Enumerator<KeyValuePair<string, object?>>(_first);
+            IEnumerator<KeyValuePair<string, object?>> IEnumerable<KeyValuePair<string, object?>>.GetEnumerator() => new Enumerator<KeyValuePair<string, object?>>(_first);
+            IEnumerator IEnumerable.GetEnumerator() => new Enumerator<KeyValuePair<string, object?>>(_first);
+
             public IEnumerable<KeyValuePair<string, string?>> EnumerateStringValues()
             {
                 LinkedListNode<KeyValuePair<string, object?>>? current = _first;
@@ -1385,22 +1391,47 @@ public void Set(KeyValuePair<string, object?> value)
                 {
                     if (current.Value.Value is string || current.Value.Value == null)
                     {
-                        yield return new KeyValuePair<string, string?>(current.Value.Key, (string?) current.Value.Value);
+                        yield return new KeyValuePair<string, string?>(current.Value.Key, (string?)current.Value.Value);
                     }
 
                     current = current.Next;
                 };
             }
+        }
+
+        private struct Enumerator<T> : IEnumerator<T>
+        {
+            private readonly LinkedListNode<T>? _head;
+            private LinkedListNode<T>? _nextNode;
+            [AllowNull, MaybeNull] private T _currentItem;
 
-            public IEnumerable<KeyValuePair<string, object?>> Enumerate()
+            public Enumerator(LinkedListNode<T>? head)
             {
-                LinkedListNode<KeyValuePair<string, object?>>? current = _first;
+                _nextNode = _head = head;
+                _currentItem = default;
+            }
 
-                while (current != null)
+            public T Current => _currentItem!;
+
+            object? IEnumerator.Current => Current;
+
+            public bool MoveNext()
+            {
+                if (_nextNode == null)
                 {
-                    yield return current.Value;
-                    current = current.Next;
-                };
+                    _currentItem = default;
+                    return false;
+                }
+
+                _currentItem = _nextNode.Value;
+                _nextNode = _nextNode.Next;
+                return true;
+            }
+
+            public void Reset() => _nextNode = _head;
+
+            public void Dispose()
+            {
             }
         }
 
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivityContext.cs b/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivityContext.cs
index 454eba3ab0c60c..0522cbfb7dce89 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivityContext.cs
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivityContext.cs
@@ -59,7 +59,41 @@ public ActivityContext(ActivityTraceId traceId, ActivitySpanId spanId, ActivityT
         /// </remarks>
         public bool IsRemote { get; }
 
-        public bool Equals(ActivityContext value) =>  SpanId.Equals(value.SpanId) && TraceId.Equals(value.TraceId) && TraceFlags == value.TraceFlags && TraceState == value.TraceState;
+        /// <summary>
+        /// Parse W3C trace context headers to ActivityContext object.
+        /// </summary>
+        /// <param name="traceParent">W3C trace parent header.</param>
+        /// <param name="traceState">W3C trace state.</param>
+        /// <param name="context">The ActivityContext object created from the parsing operation.</param>
+        public static bool TryParse(string traceParent, string? traceState, out ActivityContext context)
+        {
+            if (traceParent == null)
+            {
+                throw new ArgumentNullException(nameof(traceParent));
+            }
+
+            return Activity.TryConvertIdToContext(traceParent, traceState, out context);
+        }
+
+        /// <summary>
+        /// Parse W3C trace context headers to ActivityContext object.
+        /// </summary>
+        /// <param name="traceParent">W3C trace parent header.</param>
+        /// <param name="traceState">Trace state.</param>
+        /// <returns>
+        /// The ActivityContext object created from the parsing operation.
+        /// </returns>
+        public static ActivityContext Parse(string traceParent, string? traceState)
+        {
+            if (!TryParse(traceParent, traceState, out ActivityContext context))
+            {
+                throw new ArgumentException(SR.InvalidTraceParent);
+            }
+
+            return context;
+        }
+
+        public bool Equals(ActivityContext value) =>  SpanId.Equals(value.SpanId) && TraceId.Equals(value.TraceId) && TraceFlags == value.TraceFlags && TraceState == value.TraceState && IsRemote == value.IsRemote;
 
         public override bool Equals(object? obj) => (obj is ActivityContext context) ? Equals(context) : false;
         public static bool operator ==(ActivityContext left, ActivityContext right) => left.Equals(right);
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivitySource.cs b/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivitySource.cs
index a89068f6c11bb2..ac110fd590e524 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivitySource.cs
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivitySource.cs
@@ -145,7 +145,7 @@ public bool HasListeners()
                         {
                             if (!canUseContext.HasValue)
                             {
-                                canUseContext = Activity.TryConvertIdToContext(parentId, out ActivityContext ctx);
+                                canUseContext = Activity.TryConvertIdToContext(parentId, traceState: null, out ActivityContext ctx);
                                 if (canUseContext.Value)
                                 {
                                     dataWithContext = new ActivityCreationOptions<ActivityContext>(data.Source, data.Name, ctx, data.Kind, data.Tags, data.Links);
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/tests/ActivitySourceTests.cs b/src/libraries/System.Diagnostics.DiagnosticSource/tests/ActivitySourceTests.cs
index 2f3be9de49579b..99bafcd319d504 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/tests/ActivitySourceTests.cs
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/tests/ActivitySourceTests.cs
@@ -323,12 +323,15 @@ public void TestActivityCreationProperties()
                 attributes.Add(new KeyValuePair<string, object>("tag2", "tagValue2"));
                 attributes.Add(new KeyValuePair<string, object>("tag3", "tagValue3"));
 
-                using (Activity activity = source.StartActivity("a1", ActivityKind.Client, ctx, attributes, links))
+                DateTimeOffset startTime = DateTimeOffset.UtcNow;
+
+                using (Activity activity = source.StartActivity("a1", ActivityKind.Client, ctx, attributes, links, startTime))
                 {
                     Assert.NotNull(activity);
                     Assert.Equal("a1", activity.OperationName);
                     Assert.Equal("a1", activity.DisplayName);
                     Assert.Equal(ActivityKind.Client, activity.Kind);
+                    Assert.Equal(startTime, activity.StartTimeUtc);
 
                     Assert.Equal(ctx.TraceId, activity.TraceId);
                     Assert.Equal(ctx.SpanId, activity.ParentSpanId);
@@ -379,6 +382,32 @@ public void TestDefaultParentContext()
             }).Dispose();
         }
 
+        [Fact]
+        public void TestActivityContextParsing()
+        {
+            const string w3cId = "00-99d43cb30a4cdb4fbeee3a19c29201b0-e82825765f051b47-01";
+            Assert.True(ActivityContext.TryParse(w3cId, "k=v", out ActivityContext context));
+            Assert.Equal("99d43cb30a4cdb4fbeee3a19c29201b0", context.TraceId.ToHexString());
+            Assert.Equal("e82825765f051b47", context.SpanId.ToHexString());
+            Assert.Equal(ActivityTraceFlags.Recorded, context.TraceFlags);
+            Assert.Equal("k=v", context.TraceState);
+
+            context = ActivityContext.Parse(w3cId, "k=v");
+            Assert.Equal("99d43cb30a4cdb4fbeee3a19c29201b0", context.TraceId.ToHexString());
+            Assert.Equal("e82825765f051b47", context.SpanId.ToHexString());
+            Assert.Equal(ActivityTraceFlags.Recorded, context.TraceFlags);
+            Assert.Equal("k=v", context.TraceState);
+
+            context = ActivityContext.Parse(w3cId, null);
+            Assert.Null(context.TraceState);
+
+            Assert.Throws<ArgumentNullException>(() => ActivityContext.TryParse(null, "k=v", out context));
+            Assert.Throws<ArgumentNullException>(() => ActivityContext.Parse(null, null));
+            Assert.Throws<ArgumentException>(() => ActivityContext.Parse("BadW3C", null));
+
+            const string invalidW3CContext = "00-Z9d43cb30a4cdb4fbeee3a19c29201b0-e82825765f051b47-01";
+            Assert.False(ActivityContext.TryParse(invalidW3CContext, null, out context));
+        }
 
         [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
         public void TestCreatingActivityUsingDifferentParentIds()
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/tests/System.Diagnostics.DiagnosticSource.Tests.csproj b/src/libraries/System.Diagnostics.DiagnosticSource/tests/System.Diagnostics.DiagnosticSource.Tests.csproj
index d06639f76f9c60..8cc016a37866b0 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/tests/System.Diagnostics.DiagnosticSource.Tests.csproj
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/tests/System.Diagnostics.DiagnosticSource.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net48-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
     <Compile Include="DiagnosticSourceEventSourceBridgeTests.cs" />
@@ -18,4 +18,8 @@
     <Compile Include="$(CommonTestPath)System\Net\Configuration.cs" Link="Common\System\Net\Configuration.cs" />
     <Compile Include="$(CommonTestPath)System\Net\Configuration.Http.cs" Link="Common\System\Net\Configuration.Http.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="..\src\System.Diagnostics.DiagnosticSource.csproj" />
+    <Reference Include="System.Net.Http" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestCollectionFixture.cs b/src/libraries/System.Diagnostics.DiagnosticSource/tests/TestWithConfigSwitches/AssemblyInfo.cs
similarity index 50%
rename from src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestCollectionFixture.cs
rename to src/libraries/System.Diagnostics.DiagnosticSource/tests/TestWithConfigSwitches/AssemblyInfo.cs
index 7fed04272adf10..7fe77fb2043e78 100644
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestCollectionFixture.cs
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/tests/TestWithConfigSwitches/AssemblyInfo.cs
@@ -1,10 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-namespace Microsoft.AspNetCore.Testing
-{
-    public class TestCollectionFixture
-    {
-        public int Count { get; set; }
-    }
-}
+using Xunit;
+
+[assembly: ActiveIssue("https://github.com/dotnet/runtime/issues/38433", TestPlatforms.Browser)]
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.DiagnosticSource/tests/TestWithConfigSwitches/System.Diagnostics.DiagnosticSource.Switches.Tests.csproj b/src/libraries/System.Diagnostics.DiagnosticSource/tests/TestWithConfigSwitches/System.Diagnostics.DiagnosticSource.Switches.Tests.csproj
index 04a992f8cd81cc..1d596d074a3ad4 100644
--- a/src/libraries/System.Diagnostics.DiagnosticSource/tests/TestWithConfigSwitches/System.Diagnostics.DiagnosticSource.Switches.Tests.csproj
+++ b/src/libraries/System.Diagnostics.DiagnosticSource/tests/TestWithConfigSwitches/System.Diagnostics.DiagnosticSource.Switches.Tests.csproj
@@ -2,8 +2,10 @@
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <TestRuntime>true</TestRuntime>
+    <IgnoreForCI Condition="'$(TargetOS)' == 'Browser'">true</IgnoreForCI>
   </PropertyGroup>
   <ItemGroup>
+    <Compile Include="AssemblyInfo.cs" />
     <Compile Include="ActivityTests.cs" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.EventLog/ref/System.Diagnostics.EventLog.csproj b/src/libraries/System.Diagnostics.EventLog/ref/System.Diagnostics.EventLog.csproj
index 4a6216abc116c6..3413c45fda3e0c 100644
--- a/src/libraries/System.Diagnostics.EventLog/ref/System.Diagnostics.EventLog.csproj
+++ b/src/libraries/System.Diagnostics.EventLog/ref/System.Diagnostics.EventLog.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetFrameworkCurrent);net461;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -11,13 +11,6 @@
   </ItemGroup>
   <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
     <ProjectReference Include="..\..\System.Security.Permissions\ref\System.Security.Permissions.csproj" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-  </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
     <ProjectReference Include="..\..\System.Security.Principal.Windows\ref\System.Security.Principal.Windows.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.EventLog/src/System.Diagnostics.EventLog.csproj b/src/libraries/System.Diagnostics.EventLog/src/System.Diagnostics.EventLog.csproj
index db056eb6bf9843..42937d19fb5815 100644
--- a/src/libraries/System.Diagnostics.EventLog/src/System.Diagnostics.EventLog.csproj
+++ b/src/libraries/System.Diagnostics.EventLog/src/System.Diagnostics.EventLog.csproj
@@ -1,9 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netcoreapp2.0-Windows_NT;net461;netstandard2.0;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netcoreapp2.0-Windows_NT;net461;netstandard2.0</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -99,14 +98,11 @@
     <Compile Include="$(CommonPath)System\Diagnostics\NetFrameworkUtils.cs"
              Link="Common\System\Diagnostics\NetFrameworkUtils.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-  </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or
+                        $(TargetFramework.StartsWith('netcoreapp2.0'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Threading.AccessControl\src\System.Threading.AccessControl.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
-    <Reference Include="Microsoft.Win32.Registry" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Specialized" />
     <Reference Include="System.ComponentModel" />
@@ -121,12 +117,13 @@
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Threading" />
-    <Reference Include="System.Threading.AccessControl" />
     <Reference Include="System.Threading.Tasks" />
     <Reference Include="System.Threading.Thread" />
     <Reference Include="System.Threading.ThreadPool" />
     <Reference Include="System.Threading.Overlapped" />
   </ItemGroup>
+  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.EventLog/tests/System.Diagnostics.EventLog.Tests.csproj b/src/libraries/System.Diagnostics.EventLog/tests/System.Diagnostics.EventLog.Tests.csproj
index efb0b608cbcd0c..8ebc945c1214b1 100644
--- a/src/libraries/System.Diagnostics.EventLog/tests/System.Diagnostics.EventLog.Tests.csproj
+++ b/src/libraries/System.Diagnostics.EventLog/tests/System.Diagnostics.EventLog.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="EventInstanceTests.cs" />
@@ -22,4 +22,7 @@
     <Compile Include="System\Diagnostics\Reader\EventLogWatcherTests.cs" /> 
     <Compile Include="System\Diagnostics\Reader\ProviderMetadataTests.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="..\src\System.Diagnostics.EventLog.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.FileVersionInfo/Directory.Build.props b/src/libraries/System.Diagnostics.FileVersionInfo/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Diagnostics.FileVersionInfo/Directory.Build.props
+++ b/src/libraries/System.Diagnostics.FileVersionInfo/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.FileVersionInfo/src/System.Diagnostics.FileVersionInfo.csproj b/src/libraries/System.Diagnostics.FileVersionInfo/src/System.Diagnostics.FileVersionInfo.csproj
index e2c079b60206e5..06ae2e9836a557 100644
--- a/src/libraries/System.Diagnostics.FileVersionInfo/src/System.Diagnostics.FileVersionInfo.csproj
+++ b/src/libraries/System.Diagnostics.FileVersionInfo/src/System.Diagnostics.FileVersionInfo.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Diagnostics.FileVersionInfo</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
@@ -47,8 +46,7 @@
     <Reference Include="System.Runtime.InteropServices" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
-    <ProjectReference Include="../../System.Reflection.Metadata/src/System.Reflection.Metadata.csproj" />
     <Reference Include="System.Collections.Immutable" />
-    <Reference Include="System.Runtime.Extensions" />
+    <Reference Include="System.Reflection.Metadata" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Diagnostics.FileVersionInfo/tests/System.Diagnostics.FileVersionInfo.TestAssembly/System.Diagnostics.FileVersionInfo.TestAssembly.csproj b/src/libraries/System.Diagnostics.FileVersionInfo/tests/System.Diagnostics.FileVersionInfo.TestAssembly/System.Diagnostics.FileVersionInfo.TestAssembly.csproj
index 74112e70a89699..2067fee50c5965 100644
--- a/src/libraries/System.Diagnostics.FileVersionInfo/tests/System.Diagnostics.FileVersionInfo.TestAssembly/System.Diagnostics.FileVersionInfo.TestAssembly.csproj
+++ b/src/libraries/System.Diagnostics.FileVersionInfo/tests/System.Diagnostics.FileVersionInfo.TestAssembly/System.Diagnostics.FileVersionInfo.TestAssembly.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetExt>.dll</TargetExt>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
diff --git a/src/libraries/System.Diagnostics.PerformanceCounter/ref/System.Diagnostics.PerformanceCounter.csproj b/src/libraries/System.Diagnostics.PerformanceCounter/ref/System.Diagnostics.PerformanceCounter.csproj
index d7a3700fc963ce..7a9aa75f8c3e86 100644
--- a/src/libraries/System.Diagnostics.PerformanceCounter/ref/System.Diagnostics.PerformanceCounter.csproj
+++ b/src/libraries/System.Diagnostics.PerformanceCounter/ref/System.Diagnostics.PerformanceCounter.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -10,9 +10,4 @@
   <ItemGroup>
     <Compile Include="System.Diagnostics.PerformanceCounter.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.PerformanceCounter/src/System.Diagnostics.PerformanceCounter.csproj b/src/libraries/System.Diagnostics.PerformanceCounter/src/System.Diagnostics.PerformanceCounter.csproj
index 5c19edbe2729b6..225439e4973207 100644
--- a/src/libraries/System.Diagnostics.PerformanceCounter/src/System.Diagnostics.PerformanceCounter.csproj
+++ b/src/libraries/System.Diagnostics.PerformanceCounter/src/System.Diagnostics.PerformanceCounter.csproj
@@ -1,10 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netcoreapp2.0-Windows_NT;netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netcoreapp2.0-Windows_NT;netstandard2.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -123,20 +121,16 @@
     <Compile Include="$(CommonPath)System\Diagnostics\NetFrameworkUtils.cs"
              Link="Common\System\Diagnostics\NetFrameworkUtils.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-  </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="Microsoft.Win32.Registry" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or $(TargetFramework.StartsWith('netcoreapp2.0'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Configuration.ConfigurationManager\src\System.Configuration.ConfigurationManager.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Buffers" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.NonGeneric" />
     <Reference Include="System.ComponentModel.Primitives" />
     <Reference Include="System.ComponentModel.TypeConverter" />
-    <Reference Include="System.Configuration.ConfigurationManager" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Diagnostics.Process" />
     <Reference Include="System.Diagnostics.Tools" />
@@ -148,9 +142,12 @@
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Security.Claims" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Security.Principal" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Thread" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or $(TargetFramework.StartsWith('netcoreapp2.0'))">
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.PerformanceCounter/tests/System.Diagnostics.PerformanceCounter.Tests.csproj b/src/libraries/System.Diagnostics.PerformanceCounter/tests/System.Diagnostics.PerformanceCounter.Tests.csproj
index 18c5796f93d27c..0ddd69a7a648eb 100644
--- a/src/libraries/System.Diagnostics.PerformanceCounter/tests/System.Diagnostics.PerformanceCounter.Tests.csproj
+++ b/src/libraries/System.Diagnostics.PerformanceCounter/tests/System.Diagnostics.PerformanceCounter.Tests.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <Win32Resource>provider.res</Win32Resource>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="PerformanceCounterTests.cs" />
@@ -18,9 +17,10 @@
     <Compile Include="PerformanceDataTests.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Content Include="provider.man">
-      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
-    </Content>
+    <Content Include="provider.man" CopyToOutputDirectory="Always" />
     <None Include="provider.res" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="..\src\System.Diagnostics.PerformanceCounter.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.Process/Directory.Build.props b/src/libraries/System.Diagnostics.Process/Directory.Build.props
index 42c6eafce67ed8..d68d22c1b917f8 100644
--- a/src/libraries/System.Diagnostics.Process/Directory.Build.props
+++ b/src/libraries/System.Diagnostics.Process/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.Process/ref/System.Diagnostics.Process.cs b/src/libraries/System.Diagnostics.Process/ref/System.Diagnostics.Process.cs
index 60808eea784a9a..74fa2a149c4d8d 100644
--- a/src/libraries/System.Diagnostics.Process/ref/System.Diagnostics.Process.cs
+++ b/src/libraries/System.Diagnostics.Process/ref/System.Diagnostics.Process.cs
@@ -26,6 +26,7 @@ public partial class MonitoringDescriptionAttribute : System.ComponentModel.Desc
         public MonitoringDescriptionAttribute(string description) { }
         public override string Description { get { throw null; } }
     }
+    [System.ComponentModel.DesignerAttribute("System.Diagnostics.Design.ProcessDesigner, System.Design, Version=4.0.0.0, PublicKeyToken=b03f5f7f11d50a3a")]
     public partial class Process : System.ComponentModel.Component, System.IDisposable
     {
         public Process() { }
@@ -41,8 +42,8 @@ public Process() { }
         public System.Diagnostics.ProcessModule? MainModule { get { throw null; } }
         public System.IntPtr MainWindowHandle { get { throw null; } }
         public string MainWindowTitle { get { throw null; } }
-        public System.IntPtr MaxWorkingSet { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
-        public System.IntPtr MinWorkingSet { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
+        public System.IntPtr MaxWorkingSet { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
+        public System.IntPtr MinWorkingSet { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
         public System.Diagnostics.ProcessModuleCollection Modules { get { throw null; } }
         [System.ObsoleteAttribute("This property has been deprecated.  Please use System.Diagnostics.Process.NonpagedSystemMemorySize64 instead.  https://go.microsoft.com/fwlink/?linkid=14202")]
         public int NonpagedSystemMemorySize { get { throw null; } }
@@ -116,18 +117,19 @@ public void Refresh() { }
         public static System.Diagnostics.Process Start(string fileName) { throw null; }
         public static System.Diagnostics.Process Start(string fileName, string arguments) { throw null; }
         [System.CLSCompliantAttribute(false)]
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
-        public static System.Diagnostics.Process Start(string fileName, string userName, System.Security.SecureString password, string domain) { throw null; }
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
+        public static System.Diagnostics.Process? Start(string fileName, string userName, System.Security.SecureString password, string domain) { throw null; }
         [System.CLSCompliantAttribute(false)]
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
-        public static System.Diagnostics.Process Start(string fileName, string arguments, string userName, System.Security.SecureString password, string domain) { throw null; }
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
+        public static System.Diagnostics.Process? Start(string fileName, string arguments, string userName, System.Security.SecureString password, string domain) { throw null; }
         public override string ToString() { throw null; }
         public void WaitForExit() { }
         public bool WaitForExit(int milliseconds) { throw null; }
-        public System.Threading.Tasks.Task WaitForExitAsync(System.Threading.CancellationToken cancellationToken = default) { throw null; }
+        public System.Threading.Tasks.Task WaitForExitAsync(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public bool WaitForInputIdle() { throw null; }
         public bool WaitForInputIdle(int milliseconds) { throw null; }
     }
+    [System.ComponentModel.DesignerAttribute("System.Diagnostics.Design.ProcessModuleDesigner, System.Design, Version=4.0.0.0, PublicKeyToken=b03f5f7f11d50a3a")]
     public partial class ProcessModule : System.ComponentModel.Component
     {
         internal ProcessModule() { }
@@ -165,19 +167,19 @@ public ProcessStartInfo(string fileName, string arguments) { }
         public System.Collections.ObjectModel.Collection<string> ArgumentList { get { throw null; } }
         public string Arguments { get { throw null; } set { } }
         public bool CreateNoWindow { get { throw null; } set { } }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public string Domain { get { throw null; } set { } }
         public System.Collections.Generic.IDictionary<string, string?> Environment { get { throw null; } }
         public System.Collections.Specialized.StringDictionary EnvironmentVariables { get { throw null; } }
         public bool ErrorDialog { get { throw null; } set { } }
         public System.IntPtr ErrorDialogParentHandle { get { throw null; } set { } }
         public string FileName { get { throw null; } set { } }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public bool LoadUserProfile { get { throw null; } set { } }
         [System.CLSCompliantAttribute(false)]
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public System.Security.SecureString? Password { get { throw null; } set { } }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public string? PasswordInClearText { get { throw null; } set { } }
         public bool RedirectStandardError { get { throw null; } set { } }
         public bool RedirectStandardInput { get { throw null; } set { } }
@@ -194,6 +196,7 @@ public ProcessStartInfo(string fileName, string arguments) { }
         public System.Diagnostics.ProcessWindowStyle WindowStyle { get { throw null; } set { } }
         public string WorkingDirectory { get { throw null; } set { } }
     }
+    [System.ComponentModel.DesignerAttribute("System.Diagnostics.Design.ProcessThreadDesigner, System.Design, Version=4.0.0.0, PublicKeyToken=b03f5f7f11d50a3a")]
     public partial class ProcessThread : System.ComponentModel.Component
     {
         internal ProcessThread() { }
@@ -202,9 +205,9 @@ internal ProcessThread() { }
         public int Id { get { throw null; } }
         public int IdealProcessor { set { } }
         public bool PriorityBoostEnabled { get { throw null; } set { } }
-        public System.Diagnostics.ThreadPriorityLevel PriorityLevel { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
+        public System.Diagnostics.ThreadPriorityLevel PriorityLevel { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
         public System.TimeSpan PrivilegedProcessorTime { get { throw null; } }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public System.IntPtr ProcessorAffinity { set { } }
         public System.IntPtr StartAddress { get { throw null; } }
         public System.DateTime StartTime { get { throw null; } }
diff --git a/src/libraries/System.Diagnostics.Process/src/Resources/Strings.resx b/src/libraries/System.Diagnostics.Process/src/Resources/Strings.resx
index 5d52fa2a50123b..6aa5781a15250b 100644
--- a/src/libraries/System.Diagnostics.Process/src/Resources/Strings.resx
+++ b/src/libraries/System.Diagnostics.Process/src/Resources/Strings.resx
@@ -246,7 +246,7 @@
     <value>The {0} property is not supported on this platform.</value>
   </data>
   <data name="Process_PlatformNotSupported" xml:space="preserve">
-    <value>System.Diagnostics.Process is not supported on this platform</value>
+    <value>System.Diagnostics.Process is not supported on this platform.</value>
   </data>
   <data name="RUsageFailure" xml:space="preserve">
     <value>Failed to set or retrieve rusage information. See the error code for OS-specific error information.</value>
diff --git a/src/libraries/System.Diagnostics.Process/src/System.Diagnostics.Process.csproj b/src/libraries/System.Diagnostics.Process/src/System.Diagnostics.Process.csproj
index 7c759f49f81a37..947d0f2a1bb0ca 100644
--- a/src/libraries/System.Diagnostics.Process/src/System.Diagnostics.Process.csproj
+++ b/src/libraries/System.Diagnostics.Process/src/System.Diagnostics.Process.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
     <DefineConstants>$(DefineConstants);FEATURE_REGISTRY</DefineConstants>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-FreeBSD;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent);$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS</TargetFrameworks>
@@ -325,8 +324,8 @@
     <Compile Include="System\Diagnostics\ProcessThread.UnknownUnix.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
-    <Reference Include="Microsoft.Win32.Registry" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
     <Reference Include="System.Collections.NonGeneric" />
diff --git a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs
index 845c054930dd1c..fee92705d93102 100644
--- a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs
+++ b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs
@@ -42,14 +42,14 @@ public static void LeaveDebugMode()
         }
 
         [CLSCompliant(false)]
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static Process Start(string fileName, string userName, SecureString password, string domain)
         {
             throw new PlatformNotSupportedException(SR.ProcessStartWithPasswordAndDomainNotSupported);
         }
 
         [CLSCompliant(false)]
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static Process Start(string fileName, string arguments, string userName, SecureString password, string domain)
         {
             throw new PlatformNotSupportedException(SR.ProcessStartWithPasswordAndDomainNotSupported);
diff --git a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Windows.cs b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Windows.cs
index f56571300ceac1..af02b8a2b6141f 100644
--- a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Windows.cs
+++ b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Windows.cs
@@ -47,7 +47,7 @@ public static Process[] GetProcessesByName(string? processName, string machineNa
         }
 
         [CLSCompliant(false)]
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static Process? Start(string fileName, string userName, SecureString password, string domain)
         {
             ProcessStartInfo startInfo = new ProcessStartInfo(fileName);
@@ -59,7 +59,7 @@ public static Process[] GetProcessesByName(string? processName, string machineNa
         }
 
         [CLSCompliant(false)]
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static Process? Start(string fileName, string arguments, string userName, SecureString password, string domain)
         {
             ProcessStartInfo startInfo = new ProcessStartInfo(fileName, arguments);
diff --git a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.cs b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.cs
index 17b665eb5dd05e..7349b3112e405b 100644
--- a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.cs
+++ b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.cs
@@ -20,6 +20,7 @@ namespace System.Diagnostics
     ///       processes. Enables you to start and stop system processes.
     ///    </para>
     /// </devdoc>
+    [Designer("System.Diagnostics.Design.ProcessDesigner, System.Design, Version=4.0.0.0, PublicKeyToken=b03f5f7f11d50a3a")]
     public partial class Process : Component
     {
         private bool _haveProcessId;
@@ -265,7 +266,7 @@ public IntPtr MaxWorkingSet
                 EnsureWorkingSetLimits();
                 return _maxWorkingSet;
             }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 SetWorkingSetLimits(null, value);
@@ -285,7 +286,7 @@ public IntPtr MinWorkingSet
                 EnsureWorkingSetLimits();
                 return _minWorkingSet;
             }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 SetWorkingSetLimits(value, null);
diff --git a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessModule.cs b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessModule.cs
index 4d6f5aadad27ae..b2abe8263bc8e9 100644
--- a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessModule.cs
+++ b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessModule.cs
@@ -10,6 +10,7 @@ namespace System.Diagnostics
     ///     a particular process.  Using this component, you can determine
     ///     information about the module.
     /// </devdoc>
+    [Designer("System.Diagnostics.Design.ProcessModuleDesigner, System.Design, Version=4.0.0.0, PublicKeyToken=b03f5f7f11d50a3a")]
     public class ProcessModule : Component
     {
         private FileVersionInfo? _fileVersionInfo;
diff --git a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.Unix.cs b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.Unix.cs
index 1af5bb923dc9cb..4c674caef0b1d3 100644
--- a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.Unix.cs
+++ b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.Unix.cs
@@ -14,21 +14,21 @@ public sealed partial class ProcessStartInfo
     {
         private const bool CaseSensitiveEnvironmentVariables = true;
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public string PasswordInClearText
         {
             get { throw new PlatformNotSupportedException(SR.Format(SR.ProcessStartSingleFeatureNotSupported, nameof(PasswordInClearText))); }
             set { throw new PlatformNotSupportedException(SR.Format(SR.ProcessStartSingleFeatureNotSupported, nameof(PasswordInClearText))); }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public string Domain
         {
             get { throw new PlatformNotSupportedException(SR.Format(SR.ProcessStartSingleFeatureNotSupported, nameof(Domain))); }
             set { throw new PlatformNotSupportedException(SR.Format(SR.ProcessStartSingleFeatureNotSupported, nameof(Domain))); }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public bool LoadUserProfile
         {
             get { throw new PlatformNotSupportedException(SR.Format(SR.ProcessStartSingleFeatureNotSupported, nameof(LoadUserProfile))); }
@@ -40,7 +40,7 @@ public bool LoadUserProfile
         public string[] Verbs => Array.Empty<string>();
 
         [CLSCompliant(false)]
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public SecureString Password
         {
             get { throw new PlatformNotSupportedException(SR.Format(SR.ProcessStartSingleFeatureNotSupported, nameof(Password))); }
diff --git a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.Windows.cs b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.Windows.cs
index 5545b0590f4c74..f786a0055eb883 100644
--- a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.Windows.cs
+++ b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.Windows.cs
@@ -12,21 +12,21 @@ public sealed partial class ProcessStartInfo
 
         private const bool CaseSensitiveEnvironmentVariables = false;
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public string? PasswordInClearText { get; set; }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public string Domain
         {
             get => _domain ?? string.Empty;
             set => _domain = value;
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public bool LoadUserProfile { get; set; }
 
         [CLSCompliant(false)]
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public SecureString? Password { get; set; }
     }
 }
diff --git a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.Unix.cs b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.Unix.cs
index ac65c2dffb871e..ccee750841cd71 100644
--- a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.Unix.cs
+++ b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.Unix.cs
@@ -41,7 +41,7 @@ private bool PriorityBoostEnabledCore
         /// two, etc.  For example, the value 1 means run on processor one, 2 means run on
         /// processor two, 3 means run on processor one or two.
         /// </summary>
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public IntPtr ProcessorAffinity
         {
             set { throw new PlatformNotSupportedException(); } // No ability to change the affinity of a thread in an arbitrary process
diff --git a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.Windows.cs b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.Windows.cs
index 450a1d77edf3d8..f46fd604e5e21a 100644
--- a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.Windows.cs
+++ b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.Windows.cs
@@ -100,7 +100,7 @@ private ThreadPriorityLevel PriorityLevelCore
         /// two, etc.  For example, the value 1 means run on processor one, 2 means run on
         /// processor two, 3 means run on processor one or two.
         /// </summary>
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public IntPtr ProcessorAffinity
         {
             set
diff --git a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.cs b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.cs
index b4ad10f029c53e..6ff4cafba84986 100644
--- a/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.cs
+++ b/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessThread.cs
@@ -13,6 +13,7 @@ namespace System.Diagnostics
     ///       returned from the System.Diagnostics.Process.ProcessThread property of the System.Diagnostics.Process component.
     ///    </para>
     /// </devdoc>
+    [Designer("System.Diagnostics.Design.ProcessThreadDesigner, System.Design, Version=4.0.0.0, PublicKeyToken=b03f5f7f11d50a3a")]
     public partial class ProcessThread : Component
     {
         private readonly bool _isRemoteMachine;
@@ -95,7 +96,7 @@ public ThreadPriorityLevel PriorityLevel
                 }
                 return _priorityLevel.Value;
             }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 PriorityLevelCore = value;
diff --git a/src/libraries/System.Diagnostics.Process/tests/ProcessStartInfoTests.cs b/src/libraries/System.Diagnostics.Process/tests/ProcessStartInfoTests.cs
index 09eea0aba6576f..ced27b832ab369 100644
--- a/src/libraries/System.Diagnostics.Process/tests/ProcessStartInfoTests.cs
+++ b/src/libraries/System.Diagnostics.Process/tests/ProcessStartInfoTests.cs
@@ -354,6 +354,7 @@ public void TestWorkingDirectoryPropertyInChildProcess()
                 [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported)), PlatformSpecific(TestPlatforms.Windows), OuterLoop] // Uses P/Invokes, Requires admin privileges
         public void TestUserCredentialsPropertiesOnWindows()
         {
+            // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy credentials.")]
             string username = "test", password = "PassWord123!!";
             try
             {
diff --git a/src/libraries/System.Diagnostics.Process/tests/System.Diagnostics.Process.Tests.csproj b/src/libraries/System.Diagnostics.Process/tests/System.Diagnostics.Process.Tests.csproj
index 83b129811ed289..091c18cdbb75ce 100644
--- a/src/libraries/System.Diagnostics.Process/tests/System.Diagnostics.Process.Tests.csproj
+++ b/src/libraries/System.Diagnostics.Process/tests/System.Diagnostics.Process.Tests.csproj
@@ -18,7 +18,6 @@
     <Compile Include="DelegateSynchronizeInvoke.cs" />
     <Compile Include="Helpers.cs" />
     <Compile Include="Interop.cs" />
-    <Compile Include="Interop.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="ProcessCollectionTests.cs" />
     <Compile Include="ProcessModuleTests.cs" />
     <Compile Include="ProcessStandardConsoleTests.cs" />
@@ -39,9 +38,14 @@
              Link="System\PasteArguments.Windows.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)' == 'true' or '$(TargetsBrowser)' == 'true'">
+    <Compile Include="Interop.Unix.cs" />
     <Compile Include="ProcessTests.Unix.cs" />
     <Compile Include="ProcessThreadTests.Unix.cs" />
     <Compile Include="$(CoreLibSharedDir)System\PasteArguments.Unix.cs"
              Link="System\PasteArguments.Unix.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices\src\System.DirectoryServices.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Diagnostics.StackTrace/Directory.Build.props b/src/libraries/System.Diagnostics.StackTrace/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Diagnostics.StackTrace/Directory.Build.props
+++ b/src/libraries/System.Diagnostics.StackTrace/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.StackTrace/ref/System.Diagnostics.StackTrace.cs b/src/libraries/System.Diagnostics.StackTrace/ref/System.Diagnostics.StackTrace.cs
index 3696fe37c4218a..46fd6d68b0ce72 100644
--- a/src/libraries/System.Diagnostics.StackTrace/ref/System.Diagnostics.StackTrace.cs
+++ b/src/libraries/System.Diagnostics.StackTrace/ref/System.Diagnostics.StackTrace.cs
@@ -10,9 +10,9 @@ public partial class StackFrame
     {
         public const int OFFSET_UNKNOWN = -1;
         public StackFrame() { }
-        public StackFrame(bool fNeedFileInfo) { }
+        public StackFrame(bool needFileInfo) { }
         public StackFrame(int skipFrames) { }
-        public StackFrame(int skipFrames, bool fNeedFileInfo) { }
+        public StackFrame(int skipFrames, bool needFileInfo) { }
         public StackFrame(string? fileName, int lineNumber) { }
         public StackFrame(string? fileName, int lineNumber, int colNumber) { }
         public virtual int GetFileColumnNumber() { throw null; }
diff --git a/src/libraries/System.Diagnostics.StackTrace/src/System.Diagnostics.StackTrace.csproj b/src/libraries/System.Diagnostics.StackTrace/src/System.Diagnostics.StackTrace.csproj
index 0b3dadaa19cf4a..4c218b7212f8d1 100644
--- a/src/libraries/System.Diagnostics.StackTrace/src/System.Diagnostics.StackTrace.csproj
+++ b/src/libraries/System.Diagnostics.StackTrace/src/System.Diagnostics.StackTrace.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Diagnostics.StackTrace</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <Nullable>enable</Nullable>
@@ -23,15 +22,13 @@
     <Compile Include="System\Diagnostics\SymbolStore\SymLanguageType.cs" />
     <Compile Include="System\Diagnostics\SymbolStore\SymLanguageVendor.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.IO.FileSystem" />
-    <ProjectReference Include="..\..\System.Collections.Concurrent\src\System.Collections.Concurrent.csproj" />
-    <ProjectReference Include="..\..\System.Runtime\src\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Runtime.Extensions\src\System.Runtime.Extensions.csproj" />
-    <ProjectReference Include="..\..\System.Reflection.Metadata\src\System.Reflection.Metadata.csproj" />
-    <ProjectReference Include="..\..\System.Collections.Immutable\src\System.Collections.Immutable.csproj" />
-  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(CoreLibProject)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.Concurrent\src\System.Collections.Concurrent.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.Immutable\src\System.Collections.Immutable.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Reflection.Metadata\src\System.Reflection.Metadata.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.Extensions\src\System.Runtime.Extensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\src\System.Runtime.csproj" />
+    <Reference Include="System.IO.FileSystem" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Diagnostics.StackTrace/tests/StackFrameExtensionsTests.cs b/src/libraries/System.Diagnostics.StackTrace/tests/StackFrameExtensionsTests.cs
index aaecae6e7fb2fe..a8572840bfacde 100644
--- a/src/libraries/System.Diagnostics.StackTrace/tests/StackFrameExtensionsTests.cs
+++ b/src/libraries/System.Diagnostics.StackTrace/tests/StackFrameExtensionsTests.cs
@@ -6,7 +6,6 @@
 
 namespace System.Diagnostics.Tests
 {
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/39223", TestPlatforms.Browser)]
     public class StackFrameExtensionsTests
     {
         public static IEnumerable<object[]> StackFrame_TestData()
diff --git a/src/libraries/System.Diagnostics.StackTrace/tests/StackFrameTests.cs b/src/libraries/System.Diagnostics.StackTrace/tests/StackFrameTests.cs
index 445ae86ca6f1c7..e80c6b950960f7 100644
--- a/src/libraries/System.Diagnostics.StackTrace/tests/StackFrameTests.cs
+++ b/src/libraries/System.Diagnostics.StackTrace/tests/StackFrameTests.cs
@@ -8,7 +8,6 @@
 
 namespace System.Diagnostics.Tests
 {
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/39223", TestPlatforms.Browser)]
     public class StackFrameTests
     {
         [Fact]
diff --git a/src/libraries/System.Diagnostics.StackTrace/tests/StackTraceSymbolsTests.cs b/src/libraries/System.Diagnostics.StackTrace/tests/StackTraceSymbolsTests.cs
index ba291aeb1d958c..47eb6f07b700fe 100644
--- a/src/libraries/System.Diagnostics.StackTrace/tests/StackTraceSymbolsTests.cs
+++ b/src/libraries/System.Diagnostics.StackTrace/tests/StackTraceSymbolsTests.cs
@@ -7,13 +7,12 @@
 
 namespace System.Diagnostics.SymbolStore.Tests
 {
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/39223", TestPlatforms.Browser)]
     public class StackTraceSymbolsTests
     {
         [Fact]
         public void StackTraceSymbolsDoNotLockFile()
         {
-            var asmPath = typeof(StackTraceSymbolsTests).Assembly.Location;
+            var asmPath = AssemblyPathHelper.GetAssemblyLocation(typeof(StackTraceSymbolsTests).Assembly);
             var pdbPath = Path.ChangeExtension(asmPath, ".pdb");
 
             Assert.True(File.Exists(pdbPath));
diff --git a/src/libraries/System.Diagnostics.StackTrace/tests/StackTraceTests.cs b/src/libraries/System.Diagnostics.StackTrace/tests/StackTraceTests.cs
index 67119f9799cf34..894374ba29b4dc 100644
--- a/src/libraries/System.Diagnostics.StackTrace/tests/StackTraceTests.cs
+++ b/src/libraries/System.Diagnostics.StackTrace/tests/StackTraceTests.cs
@@ -29,7 +29,6 @@ public static StackTrace MethodWithException()
 
 namespace System.Diagnostics.Tests
 {
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/39223", TestPlatforms.Browser)]
     public class StackTraceTests
     {
         [Fact]
diff --git a/src/libraries/System.Diagnostics.StackTrace/tests/System.Diagnostics.StackTrace.Tests.csproj b/src/libraries/System.Diagnostics.StackTrace/tests/System.Diagnostics.StackTrace.Tests.csproj
index 0290d8432c8ffb..b112648c183634 100644
--- a/src/libraries/System.Diagnostics.StackTrace/tests/System.Diagnostics.StackTrace.Tests.csproj
+++ b/src/libraries/System.Diagnostics.StackTrace/tests/System.Diagnostics.StackTrace.Tests.csproj
@@ -13,4 +13,8 @@
     <Compile Include="SymLanguageVendorTests.cs" />
     <Compile Include="SymbolTokenTests.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
+    <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />
+    <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).pdb" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.TextWriterTraceListener/Directory.Build.props b/src/libraries/System.Diagnostics.TextWriterTraceListener/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Diagnostics.TextWriterTraceListener/Directory.Build.props
+++ b/src/libraries/System.Diagnostics.TextWriterTraceListener/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.Tools/Directory.Build.props b/src/libraries/System.Diagnostics.Tools/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Diagnostics.Tools/Directory.Build.props
+++ b/src/libraries/System.Diagnostics.Tools/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.Tools/src/System.Diagnostics.Tools.csproj b/src/libraries/System.Diagnostics.Tools/src/System.Diagnostics.Tools.csproj
index 7e813184ea81e9..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Diagnostics.Tools/src/System.Diagnostics.Tools.csproj
+++ b/src/libraries/System.Diagnostics.Tools/src/System.Diagnostics.Tools.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Diagnostics.Tools</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Diagnostics.TraceSource/Directory.Build.props b/src/libraries/System.Diagnostics.TraceSource/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Diagnostics.TraceSource/Directory.Build.props
+++ b/src/libraries/System.Diagnostics.TraceSource/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.TraceSource/src/System.Diagnostics.TraceSource.csproj b/src/libraries/System.Diagnostics.TraceSource/src/System.Diagnostics.TraceSource.csproj
index 7baa10ff2bb9e4..7b62f85f073baa 100644
--- a/src/libraries/System.Diagnostics.TraceSource/src/System.Diagnostics.TraceSource.csproj
+++ b/src/libraries/System.Diagnostics.TraceSource/src/System.Diagnostics.TraceSource.csproj
@@ -28,17 +28,15 @@
     <Compile Include="System\Diagnostics\SwitchAttribute.cs" />
     <Compile Include="System\Diagnostics\SwitchLevelAttribute.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.IO.FileSystem" />
-    <ProjectReference Include="..\..\System.Collections\src\System.Collections.csproj" />
-    <ProjectReference Include="..\..\System.Collections.NonGeneric\src\System.Collections.NonGeneric.csproj" />
-    <ProjectReference Include="..\..\System.Collections.Specialized\src\System.Collections.Specialized.csproj " />
-    <ProjectReference Include="..\..\System.ComponentModel.Primitives\src\System.ComponentModel.Primitives.csproj " />
-    <ProjectReference Include="..\..\System.Runtime\src\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Runtime.Extensions\src\System.Runtime.Extensions.csproj" />
-    <ProjectReference Include="..\..\System.Threading\src\System.Threading.csproj" />
-  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(CoreLibProject)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections\src\System.Collections.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.NonGeneric\src\System.Collections.NonGeneric.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.Specialized\src\System.Collections.Specialized.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.ComponentModel.Primitives\src\System.ComponentModel.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\src\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.Extensions\src\System.Runtime.Extensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Threading\src\System.Threading.csproj" />
+    <Reference Include="System.IO.FileSystem" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Diagnostics.TraceSource/tests/TraceEventCacheClassTests.cs b/src/libraries/System.Diagnostics.TraceSource/tests/TraceEventCacheClassTests.cs
index 680f8b620a1201..6933d0323daee2 100644
--- a/src/libraries/System.Diagnostics.TraceSource/tests/TraceEventCacheClassTests.cs
+++ b/src/libraries/System.Diagnostics.TraceSource/tests/TraceEventCacheClassTests.cs
@@ -48,7 +48,6 @@ public void TimestampTest()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/39223", TestPlatforms.Browser)]
         public void CallstackTest_NotEmpty()
         {
             var cache = new TraceEventCache();
@@ -56,7 +55,6 @@ public void CallstackTest_NotEmpty()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/39223", TestPlatforms.Browser)]
         public void CallstackTest_ContainsExpectedFrames()
         {
             var cache = new TraceEventCache();
diff --git a/src/libraries/System.Diagnostics.TraceSource/tests/TraceListenerClassTests.cs b/src/libraries/System.Diagnostics.TraceSource/tests/TraceListenerClassTests.cs
index fbe1193514260d..08668fdd732106 100644
--- a/src/libraries/System.Diagnostics.TraceSource/tests/TraceListenerClassTests.cs
+++ b/src/libraries/System.Diagnostics.TraceSource/tests/TraceListenerClassTests.cs
@@ -313,7 +313,6 @@ public void WriteFooterTest(TraceOptions opts, int flagCount)
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/39223", TestPlatforms.Browser)]
         [MethodImpl(MethodImplOptions.NoInlining)]
         public void WriteFooterTest_Callstack()
         {
diff --git a/src/libraries/System.Diagnostics.Tracing/Directory.Build.props b/src/libraries/System.Diagnostics.Tracing/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Diagnostics.Tracing/Directory.Build.props
+++ b/src/libraries/System.Diagnostics.Tracing/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Diagnostics.Tracing/src/System.Diagnostics.Tracing.csproj b/src/libraries/System.Diagnostics.Tracing/src/System.Diagnostics.Tracing.csproj
index bae87cb23cbb5b..dd3dc2940a54b1 100644
--- a/src/libraries/System.Diagnostics.Tracing/src/System.Diagnostics.Tracing.csproj
+++ b/src/libraries/System.Diagnostics.Tracing/src/System.Diagnostics.Tracing.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Diagnostics.Tracing</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.DirectoryServices.AccountManagement/src/System.DirectoryServices.AccountManagement.csproj b/src/libraries/System.DirectoryServices.AccountManagement/src/System.DirectoryServices.AccountManagement.csproj
index 04288a7c8775c5..adbd9aecb5211e 100644
--- a/src/libraries/System.DirectoryServices.AccountManagement/src/System.DirectoryServices.AccountManagement.csproj
+++ b/src/libraries/System.DirectoryServices.AccountManagement/src/System.DirectoryServices.AccountManagement.csproj
@@ -3,7 +3,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DefineConstants>$(DefineConstants);FLAVOR_WHIDBEY;PAPI_AD;PAPI_REGSAM;USE_CTX_CACHE</DefineConstants>
     <IncludeDllSafeSearchPathAttribute>true</IncludeDllSafeSearchPathAttribute>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT;_$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <NoWarn>$(NoWarn);CA2249</NoWarn>
   </PropertyGroup>
@@ -91,24 +91,26 @@
              Link="Common\Interop\Windows\Advapi32\Interop.LookupAccountSid.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.DirectoryServices" />
-    <Reference Include="System.DirectoryServices.Protocols" />
-    <Reference Include="System.Configuration.ConfigurationManager" />
-    <Reference Include="System.IO.FileSystem.AccessControl" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Security.AccessControl" />
-    <Reference Include="System.Security.Principal.Windows" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Configuration.ConfigurationManager\src\System.Configuration.ConfigurationManager.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices\src\System.DirectoryServices.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices.Protocols\src\System.DirectoryServices.Protocols.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.IO.FileSystem.AccessControl\src\System.IO.FileSystem.AccessControl.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\src\System.Security.AccessControl.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.NonGeneric" />
     <Reference Include="System.Collections.Specialized" />
     <Reference Include="System.ComponentModel.Primitives" />
+    <Reference Include="System.ComponentModel.TypeConverter"
+               Condition="'$(TargetFramework)' == 'netcoreapp2.0'" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Net.Primitives" />
     <Reference Include="System.Net.Security" />
     <Reference Include="System.Resources.ResourceManager" />
+    <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Security.Claims" />
@@ -119,7 +121,4 @@
     <Reference Include="System.Threading.Thread" />
     <Reference Include="System.Xml.ReaderWriter" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp2.0'">
-    <Reference Include="System.ComponentModel.TypeConverter" />
-  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.DirectoryServices.AccountManagement/src/System/DirectoryServices/AccountManagement/constants.cs b/src/libraries/System.DirectoryServices.AccountManagement/src/System/DirectoryServices/AccountManagement/constants.cs
index 8662ef2bf3ca7e..93c5e6f23c771d 100644
--- a/src/libraries/System.DirectoryServices.AccountManagement/src/System/DirectoryServices/AccountManagement/constants.cs
+++ b/src/libraries/System.DirectoryServices.AccountManagement/src/System/DirectoryServices/AccountManagement/constants.cs
@@ -95,6 +95,7 @@ private PropertyNames() { }
 
         // these two are not publicly exposed properties, but are used internally to track ResetPassword/ExpirePasswordNow
         // operations against unpersisted principals, so that they can be performed once the principal has been Saved
+        // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Not a password.")]
         internal const string PwdInfoPassword = "AuthenticablePrincipal.PasswordInfo.Password";
         internal const string PwdInfoExpireImmediately = "AuthenticablePrincipal.PasswordInfo.ExpireImmediately";
     }
diff --git a/src/libraries/System.DirectoryServices.AccountManagement/tests/PrincipalTest.cs b/src/libraries/System.DirectoryServices.AccountManagement/tests/PrincipalTest.cs
index b46ceab58626c8..7b91de75941bec 100644
--- a/src/libraries/System.DirectoryServices.AccountManagement/tests/PrincipalTest.cs
+++ b/src/libraries/System.DirectoryServices.AccountManagement/tests/PrincipalTest.cs
@@ -15,8 +15,8 @@ public abstract class PrincipalTest : IDisposable
 
         private void RefreshContext()
         {
-            string username = "Administrator";
-            string password = "Adrumble@6";
+            // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy credentials.")]
+            string username = "Administrator", password = "Adrumble@6";
 
             string OU = "Tests";
             string baseDomain = WindowsIdentity.GetCurrent().Name.Split(new char[] { '\\' })[1] + "-TEST";
diff --git a/src/libraries/System.DirectoryServices.AccountManagement/tests/System.DirectoryServices.AccountManagement.Tests.csproj b/src/libraries/System.DirectoryServices.AccountManagement/tests/System.DirectoryServices.AccountManagement.Tests.csproj
index f896e5f1babd14..ff681406c78e1c 100644
--- a/src/libraries/System.DirectoryServices.AccountManagement/tests/System.DirectoryServices.AccountManagement.Tests.csproj
+++ b/src/libraries/System.DirectoryServices.AccountManagement/tests/System.DirectoryServices.AccountManagement.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="ComputerPrincipalTest.cs" />
@@ -18,4 +18,14 @@
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="..\src\System.DirectoryServices.AccountManagement.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices\src\System.DirectoryServices.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices.Protocols\src\System.DirectoryServices.Protocols.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
+    <Reference Include="System.DirectoryServices" />
+    <Reference Include="System.DirectoryServices.AccountManagement" />
+    <Reference Include="System.DirectoryServices.Protocols" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.DirectoryServices.AccountManagement/tests/UserPrincipalTest.cs b/src/libraries/System.DirectoryServices.AccountManagement/tests/UserPrincipalTest.cs
index 73d1a92107478e..22fa3f7053b3b9 100644
--- a/src/libraries/System.DirectoryServices.AccountManagement/tests/UserPrincipalTest.cs
+++ b/src/libraries/System.DirectoryServices.AccountManagement/tests/UserPrincipalTest.cs
@@ -31,8 +31,8 @@ public void UserPrincipalConstructorTest()
 
         public void ComputedUACCheck()
         {
-            string username = "Administrator";
-            string password = "Adrumble@6";
+            // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy credentials.")]
+            string username = "Administrator", password = "Adrumble@6";
             //TODO: don't assume it exists, create it if its not
             string OU = "TestNull";
             string baseDomain =WindowsIdentity.GetCurrent().Name.Split(new char[] { '\\' })[1] + "-TEST";
diff --git a/src/libraries/System.DirectoryServices.Protocols/src/System.DirectoryServices.Protocols.csproj b/src/libraries/System.DirectoryServices.Protocols/src/System.DirectoryServices.Protocols.csproj
index 8ac014eba2d53b..c37e4da51fa4bd 100644
--- a/src/libraries/System.DirectoryServices.Protocols/src/System.DirectoryServices.Protocols.csproj
+++ b/src/libraries/System.DirectoryServices.Protocols/src/System.DirectoryServices.Protocols.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IncludeDllSafeSearchPathAttribute>true</IncludeDllSafeSearchPathAttribute>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netcoreapp2.0-Windows_NT;$(NetCoreAppCurrent)-OSX;netcoreapp2.0-OSX;$(NetCoreAppCurrent)-Linux;netcoreapp2.0-Linux;netstandard2.0;_$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netcoreapp2.0-Windows_NT;$(NetCoreAppCurrent)-OSX;netcoreapp2.0-OSX;$(NetCoreAppCurrent)-Linux;netcoreapp2.0-Linux;netstandard2.0</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -81,13 +81,13 @@
     </Compile>
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.Security.AccessControl" />
-    <Reference Include="System.Security.Principal.Windows" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.NonGeneric" />
     <Reference Include="System.Collections.Specialized" />
+    <Reference Include="System.ComponentModel.Primitives" />
     <Reference Include="System.ComponentModel.TypeConverter" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Net.Primitives" />
@@ -103,7 +103,4 @@
     <Reference Include="System.Threading.Tasks.Extensions" />
     <Reference Include="System.Xml.ReaderWriter" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.ComponentModel.Primitives" />
-  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.DirectoryServices.Protocols/tests/System.DirectoryServices.Protocols.Tests.csproj b/src/libraries/System.DirectoryServices.Protocols/tests/System.DirectoryServices.Protocols.Tests.csproj
index 682e1a9711a766..1175b1d42159f4 100644
--- a/src/libraries/System.DirectoryServices.Protocols/tests/System.DirectoryServices.Protocols.Tests.csproj
+++ b/src/libraries/System.DirectoryServices.Protocols/tests/System.DirectoryServices.Protocols.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent)-OSX;net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="BerConverterTests.cs" />
@@ -56,4 +56,12 @@
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices\src\System.DirectoryServices.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices.Protocols\src\System.DirectoryServices.Protocols.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
+    <Reference Include="System.DirectoryServices" />
+    <Reference Include="System.DirectoryServices.Protocols" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.csproj b/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.csproj
index 3df27100b060d6..68593ef6e13ebe 100644
--- a/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.csproj
+++ b/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;_$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.DirectoryServices.cs" />
diff --git a/src/libraries/System.DirectoryServices/src/System.DirectoryServices.csproj b/src/libraries/System.DirectoryServices/src/System.DirectoryServices.csproj
index fcbbc47ff8df2a..fe5b6232d96ab5 100644
--- a/src/libraries/System.DirectoryServices/src/System.DirectoryServices.csproj
+++ b/src/libraries/System.DirectoryServices/src/System.DirectoryServices.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT;_$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -137,18 +137,18 @@
     <Compile Include="Interop\UnsafeNativeMethods.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Permissions\src\System.Security.Permissions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\src\System.Security.AccessControl.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.IO.FileSystem.AccessControl\src\System.IO.FileSystem.AccessControl.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.NonGeneric" />
     <Reference Include="System.ComponentModel.TypeConverter" />
-    <Reference Include="System.IO.FileSystem.AccessControl" />
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="System.Security.AccessControl" />
-    <Reference Include="System.Security.Permissions" />
-    <Reference Include="System.Security.Principal.Windows" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections.Specialized" />
     <Reference Include="System.ComponentModel" />
diff --git a/src/libraries/System.DirectoryServices/tests/System.DirectoryServices.Tests.csproj b/src/libraries/System.DirectoryServices/tests/System.DirectoryServices.Tests.csproj
index 53be1a5cb23a6a..f71b684f686bd6 100644
--- a/src/libraries/System.DirectoryServices/tests/System.DirectoryServices.Tests.csproj
+++ b/src/libraries/System.DirectoryServices/tests/System.DirectoryServices.Tests.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <!-- SYSLIB0003: CAS is obsolete, but we still have tests referencing it -->
     <NoWarn>$(NoWarn);SYSLIB0003</NoWarn>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\DirectoryServices\ActiveDirectorySecurityTests.cs" />
@@ -31,4 +31,10 @@
     <Compile Include="System\DirectoryServices\DirectoryServicesTests.Windows.cs" />
     <Compile Include="System\DirectoryServices\ActiveDirectoryComInterop.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="..\src\System.DirectoryServices.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
+    <Reference Include="System.DirectoryServices" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Drawing.Common/ref/System.Drawing.Common.cs b/src/libraries/System.Drawing.Common/ref/System.Drawing.Common.cs
index 9f54ee11672f92..463ccfd5d00e00 100644
--- a/src/libraries/System.Drawing.Common/ref/System.Drawing.Common.cs
+++ b/src/libraries/System.Drawing.Common/ref/System.Drawing.Common.cs
@@ -207,7 +207,6 @@ public sealed partial class BufferedGraphics : System.IDisposable
         internal BufferedGraphics() { }
         public System.Drawing.Graphics Graphics { get { throw null; } }
         public void Dispose() { }
-        ~BufferedGraphics() { }
         public void Render() { }
         public void Render(System.Drawing.Graphics? target) { }
         public void Render(System.IntPtr targetDC) { }
@@ -657,7 +656,7 @@ public void Dispose() { }
         ~Icon() { }
         public static System.Drawing.Icon FromHandle(System.IntPtr handle) { throw null; }
         public void Save(System.IO.Stream outputStream) { }
-        void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
+        void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo si, System.Runtime.Serialization.StreamingContext context) { }
         public System.Drawing.Bitmap ToBitmap() { throw null; }
         public override string ToString() { throw null; }
     }
@@ -731,7 +730,7 @@ public void SaveAdd(System.Drawing.Image image, System.Drawing.Imaging.EncoderPa
         public void SaveAdd(System.Drawing.Imaging.EncoderParameters? encoderParams) { }
         public int SelectActiveFrame(System.Drawing.Imaging.FrameDimension dimension, int frameIndex) { throw null; }
         public void SetPropertyItem(System.Drawing.Imaging.PropertyItem propitem) { }
-        void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
+        void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo si, System.Runtime.Serialization.StreamingContext context) { }
         public delegate bool GetThumbnailImageAbort();
     }
     public sealed partial class ImageAnimator
@@ -2096,17 +2095,17 @@ public sealed partial class Encoder
     {
         public static readonly System.Drawing.Imaging.Encoder ChrominanceTable;
         public static readonly System.Drawing.Imaging.Encoder ColorDepth;
+        public static readonly System.Drawing.Imaging.Encoder ColorSpace;
         public static readonly System.Drawing.Imaging.Encoder Compression;
+        public static readonly System.Drawing.Imaging.Encoder ImageItems;
         public static readonly System.Drawing.Imaging.Encoder LuminanceTable;
         public static readonly System.Drawing.Imaging.Encoder Quality;
         public static readonly System.Drawing.Imaging.Encoder RenderMethod;
+        public static readonly System.Drawing.Imaging.Encoder SaveAsCmyk;
         public static readonly System.Drawing.Imaging.Encoder SaveFlag;
         public static readonly System.Drawing.Imaging.Encoder ScanMethod;
         public static readonly System.Drawing.Imaging.Encoder Transformation;
         public static readonly System.Drawing.Imaging.Encoder Version;
-        public static readonly System.Drawing.Imaging.Encoder ColorSpace;
-        public static readonly System.Drawing.Imaging.Encoder ImageItems;
-        public static readonly System.Drawing.Imaging.Encoder SaveAsCmyk;
         public Encoder(System.Guid guid) { }
         public System.Guid Guid { get { throw null; } }
     }
@@ -2718,8 +2717,8 @@ public virtual void OnEndPrint(System.Drawing.Printing.PrintDocument document, S
         public virtual System.Drawing.Graphics? OnStartPage(System.Drawing.Printing.PrintDocument document, System.Drawing.Printing.PrintPageEventArgs e) { throw null; }
         public virtual void OnStartPrint(System.Drawing.Printing.PrintDocument document, System.Drawing.Printing.PrintEventArgs e) { }
     }
-    [System.ComponentModel.DefaultPropertyAttribute("DocumentName")]
     [System.ComponentModel.DefaultEventAttribute("PrintPage")]
+    [System.ComponentModel.DefaultPropertyAttribute("DocumentName")]
     public partial class PrintDocument : System.ComponentModel.Component
     {
         public PrintDocument() { }
diff --git a/src/libraries/System.Drawing.Common/src/System.Drawing.Common.csproj b/src/libraries/System.Drawing.Common/src/System.Drawing.Common.csproj
index 0a20f12215117d..a2a3625642527b 100644
--- a/src/libraries/System.Drawing.Common/src/System.Drawing.Common.csproj
+++ b/src/libraries/System.Drawing.Common/src/System.Drawing.Common.csproj
@@ -347,10 +347,11 @@
       <LogicalName>placeholder.ico</LogicalName>
     </EmbeddedResource>
   </ItemGroup>
-  <!-- References -->
+  <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.SystemEvents\src\Microsoft.Win32.SystemEvents.csproj" />  
+  </ItemGroup>
   <ItemGroup>
     <Reference Include="Microsoft.Win32.Primitives" />
-    <Reference Condition="'$(TargetsWindows)' == 'true'" Include="Microsoft.Win32.SystemEvents" />
     <Reference Include="System.Buffers" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.NonGeneric" />
diff --git a/src/libraries/System.Drawing.Common/tests/BufferedGraphicsTests.cs b/src/libraries/System.Drawing.Common/tests/BufferedGraphicsTests.cs
index bdb250e0bb4668..de5d15ed02cb94 100644
--- a/src/libraries/System.Drawing.Common/tests/BufferedGraphicsTests.cs
+++ b/src/libraries/System.Drawing.Common/tests/BufferedGraphicsTests.cs
@@ -72,8 +72,6 @@ public void Render_ParameterlessWithTargetGraphics_Success()
         [ConditionalFact(Helpers.IsDrawingSupported)]
         public void Render_ParameterlessWithNullTargetGraphics_Success()
         {
-            Color color = Color.FromArgb(255, 0, 0, 0);
-
             using (var context = new BufferedGraphicsContext())
             using (var image = new Bitmap(3, 3))
             using (Graphics graphics = Graphics.FromImage(image))
diff --git a/src/libraries/System.Drawing.Common/tests/Drawing2D/GraphicsPathIteratorTests.cs b/src/libraries/System.Drawing.Common/tests/Drawing2D/GraphicsPathIteratorTests.cs
index 4e820c12115525..45ae21bbe2ec1c 100644
--- a/src/libraries/System.Drawing.Common/tests/Drawing2D/GraphicsPathIteratorTests.cs
+++ b/src/libraries/System.Drawing.Common/tests/Drawing2D/GraphicsPathIteratorTests.cs
@@ -251,7 +251,6 @@ public void Rewind_Success()
                 gp.StartFigure();
                 gp.AddLine(20, 21, 22, 23);
                 gp.AddBezier(5, 6, 7, 8, 9, 10, 11, 12);
-                byte[] types = new byte[] { 0, 3, 3, 3, 1, 33, 0, 1 };
 
                 using (GraphicsPathIterator gpi = new GraphicsPathIterator(gp))
                 {
diff --git a/src/libraries/System.Drawing.Common/tests/FontTests.cs b/src/libraries/System.Drawing.Common/tests/FontTests.cs
index c314b21c6708d0..067ff89a7be6e8 100644
--- a/src/libraries/System.Drawing.Common/tests/FontTests.cs
+++ b/src/libraries/System.Drawing.Common/tests/FontTests.cs
@@ -714,7 +714,7 @@ public void FromLogFont_UnblittableStruct()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     var logFont = new UnblittableLOGFONT
diff --git a/src/libraries/System.Drawing.Common/tests/GraphicsTests.cs b/src/libraries/System.Drawing.Common/tests/GraphicsTests.cs
index 5b558c7dad251d..ea823989bceb6e 100644
--- a/src/libraries/System.Drawing.Common/tests/GraphicsTests.cs
+++ b/src/libraries/System.Drawing.Common/tests/GraphicsTests.cs
@@ -63,7 +63,7 @@ public void GetHdc_NotReleased_ThrowsInvalidOperationException()
             using (var bitmap = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(bitmap))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.GetHdc());
@@ -416,7 +416,7 @@ public void CompositingMode_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.CompositingMode);
@@ -510,7 +510,7 @@ public void CompositingQuality_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.CompositingQuality);
@@ -573,7 +573,7 @@ public void DpiX_GetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DpiX);
@@ -604,7 +604,7 @@ public void DpiY_GetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DpiX);
@@ -656,7 +656,7 @@ public void Flush_Busy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.Flush());
@@ -730,7 +730,7 @@ public void InterpolationMode_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.InterpolationMode);
@@ -792,7 +792,7 @@ public void PageScale_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.PageScale);
@@ -864,7 +864,7 @@ public void PageUnit_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.PageUnit);
@@ -935,7 +935,7 @@ public void PixelOffsetMode_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.PixelOffsetMode);
@@ -1004,7 +1004,6 @@ public static IEnumerable<object[]> RenderingOrigin_TestData()
         [MemberData(nameof(RenderingOrigin_TestData))]
         public void RenderingOrigin_SetToCustom_RendersExpected(Point renderingOrigin, Color[][] expectedRendering)
         {
-            Color empty = Color.FromArgb(255, 0, 0, 0);
             Color red = Color.FromArgb(Color.Red.ToArgb());
 
             using (var image = new Bitmap(3, 3))
@@ -1026,7 +1025,7 @@ public void RenderingOrigin_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.RenderingOrigin);
@@ -1097,7 +1096,7 @@ public void SmoothingMode_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.SmoothingMode);
@@ -1156,7 +1155,7 @@ public void TextContrast_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.TextContrast);
@@ -1218,7 +1217,7 @@ public void TextRenderingHint_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.TextRenderingHint);
@@ -1315,7 +1314,7 @@ public void Transform_GetSetWhenBusy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var matrix = new Matrix())
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.Transform);
@@ -1364,7 +1363,7 @@ public void ResetTransform_Busy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.ResetTransform());
@@ -1483,7 +1482,7 @@ public void MultiplyTransform_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var matrix = new Matrix())
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.MultiplyTransform(matrix));
@@ -1570,7 +1569,7 @@ public void TranslateTransform_Busy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.TranslateTransform(0, 0));
@@ -1664,7 +1663,7 @@ public void ScaleTransform_Busy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.ScaleTransform(0, 0));
@@ -1751,7 +1750,7 @@ public void RotateTransform_Busy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.RotateTransform(0));
@@ -1814,8 +1813,6 @@ public void CopyFromScreen_OutOfRange_DoesNotAffectGraphics(int sourceX, int sou
         [InlineData(1, 1, 2, 2, 3, 3)]
         public void CopyFromScreen_ValidRange_AffectsGraphics(int sourceX, int sourceY, int destinationX, int destinationY, int width, int height)
         {
-            Size screenSize = Helpers.GetHWndRect(IntPtr.Zero).Size;
-
             Color color = Color.FromArgb(2, 3, 4);
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
@@ -1934,7 +1931,7 @@ public void CopyFromScreen_Busy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.CopyFromScreen(0, 0, 0, 0, Size.Empty));
@@ -2198,7 +2195,7 @@ public void TransformPoints_Busy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.TransformPoints(CoordinateSpace.Page, CoordinateSpace.Page, new Point[] { Point.Empty }));
@@ -2250,7 +2247,7 @@ public void GetNearestColor_Busy_ThrowsInvalidOperationException()
             using (var image = new Bitmap(10, 10))
             using (Graphics graphics = Graphics.FromImage(image))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.GetNearestColor(Color.Red));
@@ -2344,7 +2341,7 @@ public void DrawArc_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawArc(pen, new Rectangle(0, 0, 1, 1), 0, 90));
@@ -2412,7 +2409,7 @@ public void DrawRectangle_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawRectangle(pen, new Rectangle(0, 0, 1, 1)));
@@ -2498,7 +2495,7 @@ public void DrawRectangles_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawRectangles(pen, new Rectangle[2]));
@@ -2563,7 +2560,7 @@ public void DrawEllipse_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawEllipse(pen, new Rectangle(0, 0, 1, 1)));
@@ -2661,7 +2658,7 @@ public void DrawPie_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawPie(pen, new Rectangle(0, 0, 1, 1), 0, 90));
@@ -2751,7 +2748,7 @@ public void DrawPolygon_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawPolygon(pen, new Point[2]));
@@ -2837,7 +2834,7 @@ public void DrawPath_Busy_ThrowsInvalidOperationException()
             using (var pen = new Pen(Color.Red))
             using (var graphicsPath = new GraphicsPath())
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawPath(pen, graphicsPath));
@@ -2961,7 +2958,7 @@ public void DrawCurve_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawCurve(pen, new Point[2]));
@@ -3066,7 +3063,7 @@ public void DrawClosedCurve_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawClosedCurve(pen, new Point[3]));
@@ -3125,7 +3122,7 @@ public void Clear_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.Clear(Color.Red));
diff --git a/src/libraries/System.Drawing.Common/tests/Graphics_DrawBezierTests.cs b/src/libraries/System.Drawing.Common/tests/Graphics_DrawBezierTests.cs
index ea8d68a3533444..c822db2a9d15b2 100644
--- a/src/libraries/System.Drawing.Common/tests/Graphics_DrawBezierTests.cs
+++ b/src/libraries/System.Drawing.Common/tests/Graphics_DrawBezierTests.cs
@@ -101,7 +101,7 @@ public void DrawBezier_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawBezier(pen, 1, 2, 3, 4, 5, 6, 7, 8));
@@ -190,7 +190,7 @@ public void DrawBeziers_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawBeziers(pen, new Point[2]));
diff --git a/src/libraries/System.Drawing.Common/tests/Graphics_DrawLineTests.cs b/src/libraries/System.Drawing.Common/tests/Graphics_DrawLineTests.cs
index aa5da3fca26bad..e25d506eb84b99 100644
--- a/src/libraries/System.Drawing.Common/tests/Graphics_DrawLineTests.cs
+++ b/src/libraries/System.Drawing.Common/tests/Graphics_DrawLineTests.cs
@@ -76,7 +76,7 @@ public void DrawLine_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawLine(pen, Point.Empty, Point.Empty));
@@ -166,7 +166,7 @@ public void DrawLines_Busy_ThrowsInvalidOperationException()
             using (Graphics graphics = Graphics.FromImage(image))
             using (var pen = new Pen(Color.Red))
             {
-                IntPtr hdc = graphics.GetHdc();
+                graphics.GetHdc();
                 try
                 {
                     Assert.Throws<InvalidOperationException>(() => graphics.DrawLines(pen, new Point[2]));
diff --git a/src/libraries/System.Drawing.Common/tests/Imaging/ColorMatrixTests.cs b/src/libraries/System.Drawing.Common/tests/Imaging/ColorMatrixTests.cs
index cf12d3f1825431..35d706af8fda4b 100644
--- a/src/libraries/System.Drawing.Common/tests/Imaging/ColorMatrixTests.cs
+++ b/src/libraries/System.Drawing.Common/tests/Imaging/ColorMatrixTests.cs
@@ -155,7 +155,7 @@ public void AccessToNotExistingElement_ThrowsIndexOutOfRangeException()
                 new float[] { 4.0f, 4.1f, 4.2f, 4.3f, 4.4f, 4.5f },
                 new float[] { 5.0f, 5.1f, 5.2f, 5.3f, 5.4f, 5.5f }
             });
-            Assert.Throws<IndexOutOfRangeException>(() => { var x = cm[5, 5]; });
+            Assert.Throws<IndexOutOfRangeException>(() => _ = cm[5, 5]);
         }
 
         [ConditionalFact(Helpers.IsDrawingSupported)]
diff --git a/src/libraries/System.Drawing.Common/tests/System.Drawing.Common.Tests.csproj b/src/libraries/System.Drawing.Common/tests/System.Drawing.Common.Tests.csproj
index 0b1354728a100f..5537f87099e4ad 100644
--- a/src/libraries/System.Drawing.Common/tests/System.Drawing.Common.Tests.csproj
+++ b/src/libraries/System.Drawing.Common/tests/System.Drawing.Common.Tests.csproj
@@ -2,8 +2,7 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
-    <IgnoreForCI Condition="'$(TargetOS)' == 'Browser'">true</IgnoreForCI>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="AssemblyInfo.cs" />
@@ -106,4 +105,10 @@
       <LogicalName>System.Drawing.Tests.Icon_toolboxBitmapAttributeTest</LogicalName>
     </EmbeddedResource>
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.SystemEvents\src\Microsoft.Win32.SystemEvents.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="..\src\System.Drawing.Common.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Drawing.Common/tests/mono/System.Drawing/BitmapTests.cs b/src/libraries/System.Drawing.Common/tests/mono/System.Drawing/BitmapTests.cs
index e48c366b75565c..4fecd70d8a0d2f 100644
--- a/src/libraries/System.Drawing.Common/tests/mono/System.Drawing/BitmapTests.cs
+++ b/src/libraries/System.Drawing.Common/tests/mono/System.Drawing/BitmapTests.cs
@@ -528,8 +528,6 @@ public void Rotate()
         [PlatformSpecific(TestPlatforms.AnyUnix)]
         public void Rotate1bit4bit(string file, RotateFlipType type, string md5)
         {
-            StringBuilder md5s = new StringBuilder();
-
             using (Bitmap bmp = new Bitmap(Helpers.GetTestBitmapPath(file)))
             {
                 Assert.Equal(md5, RotateIndexedBmp(bmp, type));
@@ -887,20 +885,6 @@ public void BmpDataStride1()
             }
         }
 
-        private Stream Serialize(object o)
-        {
-            MemoryStream ms = new MemoryStream();
-            IFormatter formatter = new BinaryFormatter();
-            formatter.Serialize(ms, o);
-            ms.Position = 0;
-            return ms;
-        }
-
-        private object Deserialize(Stream s)
-        {
-            return new BinaryFormatter().Deserialize(s);
-        }
-
         static int[] palette1 = {
             -16777216,
             -1,
diff --git a/src/libraries/System.Drawing.Common/tests/mono/System.Drawing/GraphicsTests.cs b/src/libraries/System.Drawing.Common/tests/mono/System.Drawing/GraphicsTests.cs
index ac36387e5b0335..756e860a2a644e 100644
--- a/src/libraries/System.Drawing.Common/tests/mono/System.Drawing/GraphicsTests.cs
+++ b/src/libraries/System.Drawing.Common/tests/mono/System.Drawing/GraphicsTests.cs
@@ -687,15 +687,6 @@ public void Clip_RotateTransform_BoundsChange()
             }
         }
 
-        private void CheckBoundsInt(string msg, RectangleF bounds, int x, int y, int w, int h)
-        {
-            // currently bounds are rounded at 8 pixels (FIXME - we can go down to 1 pixel)
-            AssertEquals(msg + ".X", x, bounds.X, -1);
-            AssertEquals(msg + ".Y", y, bounds.Y, -1);
-            AssertEquals(msg + ".Width", w, bounds.Width, -1);
-            AssertEquals(msg + ".Height", h, bounds.Height, -1);
-        }
-
         [ConditionalFact(Helpers.IsDrawingSupported)]
         public void Clip_ScaleTransform_NoBoundsChange()
         {
@@ -777,7 +768,6 @@ public void TranslateTransform_Order()
             }
         }
 
-        static Point[] SmallCurve = new Point[3] { new Point(0, 0), new Point(15, 5), new Point(5, 15) };
         static PointF[] SmallCurveF = new PointF[3] { new PointF(0, 0), new PointF(15, 5), new PointF(5, 15) };
 
         static Point[] TooSmallCurve = new Point[2] { new Point(0, 0), new Point(15, 5) };
diff --git a/src/libraries/System.Drawing.Primitives/Directory.Build.props b/src/libraries/System.Drawing.Primitives/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Drawing.Primitives/Directory.Build.props
+++ b/src/libraries/System.Drawing.Primitives/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Drawing.Primitives/src/System.Drawing.Primitives.csproj b/src/libraries/System.Drawing.Primitives/src/System.Drawing.Primitives.csproj
index be4e03afc7445d..fd17cd2352c3f9 100644
--- a/src/libraries/System.Drawing.Primitives/src/System.Drawing.Primitives.csproj
+++ b/src/libraries/System.Drawing.Primitives/src/System.Drawing.Primitives.csproj
@@ -1,21 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <OutputType>Library</OutputType>
     <RootNamespace>System.Drawing</RootNamespace>
-    <AssemblyName>System.Drawing.Primitives</AssemblyName>
     <DefineConstants Condition="'$(TargetsWindows)' == 'true'">$(DefineConstants);FEATURE_WINDOWS_SYSTEM_COLORS</DefineConstants>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
-  <ItemGroup>
-    <Reference Include="System.Collections" />
-    <Reference Include="System.ObjectModel" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="System.ComponentModel.Primitives" />
-    <Reference Include="Microsoft.Win32.SystemEvents" />
-  </ItemGroup>
   <ItemGroup>
     <Compile Include="System\Drawing\KnownColorNames.cs" />
     <Compile Include="System\Drawing\Point.cs" />
@@ -46,4 +35,13 @@
     <Compile Include="$(CommonPath)Interop\Windows\User32\Interop.Win32SystemColors.cs"
              Link="Common\Interop\Windows\User32\Interop.Win32SystemColors.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.SystemEvents\src\Microsoft.Win32.SystemEvents.csproj" />
+    <Reference Include="System.Collections" />
+    <Reference Include="System.ComponentModel.Primitives" />
+    <Reference Include="System.ObjectModel" />
+    <Reference Include="System.Runtime" />
+    <Reference Include="System.Runtime.Extensions" />
+    <Reference Include="System.Runtime.InteropServices" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Dynamic.Runtime/Directory.Build.props b/src/libraries/System.Dynamic.Runtime/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Dynamic.Runtime/Directory.Build.props
+++ b/src/libraries/System.Dynamic.Runtime/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Dynamic.Runtime/src/System.Dynamic.Runtime.csproj b/src/libraries/System.Dynamic.Runtime/src/System.Dynamic.Runtime.csproj
index 2fb5c055bf30ff..152b87d25dd610 100644
--- a/src/libraries/System.Dynamic.Runtime/src/System.Dynamic.Runtime.csproj
+++ b/src/libraries/System.Dynamic.Runtime/src/System.Dynamic.Runtime.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Dynamic.Runtime</AssemblyName>
-    <RootNamespace>System.Dynamic.Runtime</RootNamespace>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Formats.Asn1/Directory.Build.props b/src/libraries/System.Formats.Asn1/Directory.Build.props
index 749d7fc1c6b56d..ba1f965d83cae7 100644
--- a/src/libraries/System.Formats.Asn1/Directory.Build.props
+++ b/src/libraries/System.Formats.Asn1/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Formats.Asn1/ref/System.Formats.Asn1.csproj b/src/libraries/System.Formats.Asn1/ref/System.Formats.Asn1.csproj
index 7715f692f9c04b..ee0ebfbfe10401 100644
--- a/src/libraries/System.Formats.Asn1/ref/System.Formats.Asn1.csproj
+++ b/src/libraries/System.Formats.Asn1/ref/System.Formats.Asn1.csproj
@@ -1,12 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Formats.Asn1.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.Memory" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Formats.Asn1/src/System.Formats.Asn1.csproj b/src/libraries/System.Formats.Asn1/src/System.Formats.Asn1.csproj
index 501a4f5ad368d3..f9fdc8c95a08ce 100644
--- a/src/libraries/System.Formats.Asn1/src/System.Formats.Asn1.csproj
+++ b/src/libraries/System.Formats.Asn1/src/System.Formats.Asn1.csproj
@@ -2,8 +2,7 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonPath)System\Security\Cryptography\CryptoPool.cs">
@@ -48,13 +47,11 @@
     <Compile Include="System\Formats\Asn1\UniversalTagNumber.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.Buffers" />
-    <Reference Include="System.Memory" />
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Reference Include="System.Numerics" />
-    <Reference Include="System.ValueTuple" />
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" Condition="'$(TargetFramework)' == 'net461'" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Formats.Asn1/tests/System.Formats.Asn1.Tests.csproj b/src/libraries/System.Formats.Asn1/tests/System.Formats.Asn1.Tests.csproj
index beb4397ba6c512..1c4965e48777ee 100644
--- a/src/libraries/System.Formats.Asn1/tests/System.Formats.Asn1.Tests.csproj
+++ b/src/libraries/System.Formats.Asn1/tests/System.Formats.Asn1.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Asn1TagTests.cs" />
@@ -52,4 +52,8 @@
       <Link>CommonTest\System\Security\Cryptography\ByteUtils.cs</Link>
     </Compile>
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="..\src\System.Formats.Asn1.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Reflection.Metadata\src\System.Reflection.Metadata.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Formats.Cbor/System.Formats.Cbor.sln b/src/libraries/System.Formats.Cbor/System.Formats.Cbor.sln
index baed5dfb19566d..31f26813ae83a3 100644
--- a/src/libraries/System.Formats.Cbor/System.Formats.Cbor.sln
+++ b/src/libraries/System.Formats.Cbor/System.Formats.Cbor.sln
@@ -14,6 +14,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "System.Formats.Cbor", "ref\
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "System.Formats.Cbor.Tests", "tests\System.Formats.Cbor.Tests.csproj", "{1C84C43C-69A8-493E-AC11-0DA9C22BFB46}"
 EndProject
+Project("{6EC3EE1D-3C4E-46DD-8F32-0CC8E7565705}") = "System.Formats.Cbor.Tests.DataModel", "tests\CborDocument\System.Formats.Cbor.Tests.DataModel.fsproj", "{3BF538B4-0985-4918-90A7-8F15BA9E661C}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -32,6 +34,10 @@ Global
 		{1C84C43C-69A8-493E-AC11-0DA9C22BFB46}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{1C84C43C-69A8-493E-AC11-0DA9C22BFB46}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{1C84C43C-69A8-493E-AC11-0DA9C22BFB46}.Release|Any CPU.Build.0 = Release|Any CPU
+		{3BF538B4-0985-4918-90A7-8F15BA9E661C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{3BF538B4-0985-4918-90A7-8F15BA9E661C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{3BF538B4-0985-4918-90A7-8F15BA9E661C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{3BF538B4-0985-4918-90A7-8F15BA9E661C}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -40,6 +46,7 @@ Global
 		{57B5AD1E-D0BA-4811-9276-9BBAFF44AB31} = {59B37ECC-D5BB-488A-9571-1E239EDF19A9}
 		{B17130D2-0A75-464A-A3E7-67123C567CAF} = {B3417D0B-D64E-4CC8-AEAA-F0C7C963248F}
 		{1C84C43C-69A8-493E-AC11-0DA9C22BFB46} = {00675670-C8E7-4428-A16F-9E6B933586A8}
+		{3BF538B4-0985-4918-90A7-8F15BA9E661C} = {00675670-C8E7-4428-A16F-9E6B933586A8}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {36EE2FB8-4CD8-4A12-8FD5-9FDF3D0F6D40}
diff --git a/src/libraries/System.Formats.Cbor/ref/System.Formats.Cbor.csproj b/src/libraries/System.Formats.Cbor/ref/System.Formats.Cbor.csproj
index db6640ae50f777..574a834fd1ed9e 100644
--- a/src/libraries/System.Formats.Cbor/ref/System.Formats.Cbor.csproj
+++ b/src/libraries/System.Formats.Cbor/ref/System.Formats.Cbor.csproj
@@ -7,7 +7,7 @@
     <Compile Include="System.Formats.Cbor.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Runtime.Numerics\ref\System.Runtime.Numerics.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.Numerics\ref\System.Runtime.Numerics.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Formats.Cbor/src/Resources/Strings.resx b/src/libraries/System.Formats.Cbor/src/Resources/Strings.resx
index 996d2f89e0d38d..4fde1bed0fd72c 100644
--- a/src/libraries/System.Formats.Cbor/src/Resources/Strings.resx
+++ b/src/libraries/System.Formats.Cbor/src/Resources/Strings.resx
@@ -121,7 +121,7 @@
     <value>The destination is too small to hold the encoded value.</value>
   </data>
   <data name="Cbor_PopMajorTypeMismatch" xml:space="preserve">
-    <value>Cannot perform the requested operation, the current context is '{0}'.</value>
+    <value>Cannot perform the requested operation, the current major type context is '{0}'.</value>
   </data>
   <data name="Cbor_NotAtEndOfDefiniteLengthDataItem" xml:space="preserve">
     <value>Not at end of the definite-length data item.</value>
@@ -246,4 +246,4 @@
   <data name="CborContentException_DefaultMessage" xml:space="preserve">
     <value>The CBOR encoding is invalid.</value>
   </data>
-</root>
\ No newline at end of file
+</root>
diff --git a/src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs b/src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs
index 5ba1c400afc780..9e5b0376265a50 100644
--- a/src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs
+++ b/src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs
@@ -292,6 +292,7 @@ private void PushDataItem(CborMajorType newMajorType, int? definiteLength)
             _keysRequireSorting = false;
             _keyEncodingRanges = null;
             _keyValuePairEncodingRanges = null;
+            _isTagContext = false;
         }
 
         private void PopDataItem(CborMajorType typeToPop)
@@ -313,7 +314,7 @@ private void PopDataItem(CborMajorType typeToPop)
 
             if (_isTagContext)
             {
-                // writer expecting value after a tag data item , cannot pop the current context
+                // writer expecting value after a tag data item, cannot pop the current context
                 throw new InvalidOperationException(SR.Format(SR.Cbor_PopMajorTypeMismatch, (int)CborMajorType.Tag));
             }
 
diff --git a/src/libraries/System.Formats.Cbor/tests/CborDocument/CborDocument.fs b/src/libraries/System.Formats.Cbor/tests/CborDocument/CborDocument.fs
new file mode 100644
index 00000000000000..7e63f401de2018
--- /dev/null
+++ b/src/libraries/System.Formats.Cbor/tests/CborDocument/CborDocument.fs
@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Formats.Cbor.Tests.DataModel
+
+open System
+
+// --
+// Models a CBOR document type using a discriminated union.
+// Discriminated unions have structural equality for free
+// and random instances can be generated using FsCheck.
+//
+// The type and serialization helpers are used by the
+// property tests in the main test project.
+//
+
+type CborDocument =
+    // Major type 0
+    | UnsignedInteger of uint64
+    // Major type 1
+    | NegativeInteger of uint64
+    // Major type 2
+    | ByteString of byte[]
+    | ByteStringIndefiniteLength of byte[][]
+    // Major type 3
+    | TextString of string
+    | TextStringIndefiniteLength of string[]
+    // Major type 4
+    | Array of isDefiniteLength:bool * CborDocument[]
+    // Major type 5
+    | Map of isDefiniteLength:bool * Map<CborDocument, CborDocument>
+    // Major type 6
+    | Tag of tag:uint64 * CborDocument
+    | SemanticValue of CborSemanticValue
+    // Major type 7
+    | Double of double
+    | SimpleValue of value:byte
+
+// Defines a set of semantic values drawing either from the CBOR spec
+// or invented here for the purposes of this test.
+and CborSemanticValue =
+    | Null
+    | Bool of bool
+    | Int32 of int
+    | Int64 of int64
+    | Half of Half
+    | Single of single
+    | DateTimeOffset of DateTimeOffset
+    | UnixTimeSeconds of seconds:int64
+    | BigInt of bigint
+    | Decimal of decimal
diff --git a/src/libraries/System.Formats.Cbor/tests/CborDocument/CborDocumentSerializer.fs b/src/libraries/System.Formats.Cbor/tests/CborDocument/CborDocumentSerializer.fs
new file mode 100644
index 00000000000000..44728b426ed7f1
--- /dev/null
+++ b/src/libraries/System.Formats.Cbor/tests/CborDocument/CborDocumentSerializer.fs
@@ -0,0 +1,185 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+module rec System.Formats.Cbor.Tests.DataModel.CborDocumentSerializer
+
+open System
+open System.Formats.Cbor
+open System.Formats.Cbor.Tests.DataModel
+
+let createWriter (context : CborPropertyTestContext) =
+    new CborWriter(
+        conformanceMode = context.ConformanceMode,
+        convertIndefiniteLengthEncodings = context.ConvertIndefiniteLengthItems,
+        allowMultipleRootLevelValues = (context.RootDocuments.Length > 1))
+
+let createReader (context : CborPropertyTestContext) (encoding : byte[]) =
+    new CborReader(
+        data = ReadOnlyMemory<byte>.op_Implicit encoding,
+        conformanceMode = context.ConformanceMode,
+        allowMultipleRootLevelValues = (context.RootDocuments.Length > 1))
+
+let encode (context : CborPropertyTestContext) =
+    let writer = createWriter context
+    for doc in context.RootDocuments do
+        write writer doc
+    writer.Encode()
+
+let decode (context : CborPropertyTestContext) (data : byte[]) =
+    let reader = createReader context data
+    let values = new System.Collections.Generic.List<_>()
+    while reader.PeekState() <> CborReaderState.Finished do
+        values.Add(read reader)
+    values.ToArray()
+
+let rec write (writer : CborWriter) (doc : CborDocument) =
+    match doc with
+    | UnsignedInteger i -> writer.WriteUInt64 i
+    | NegativeInteger i -> writer.WriteCborNegativeIntegerRepresentation i
+    | ByteString bs -> writer.WriteByteString bs
+    | TextString ts -> writer.WriteTextString ts
+    | ByteStringIndefiniteLength bss ->
+        writer.WriteStartIndefiniteLengthByteString()
+        for bs in bss do
+            writer.WriteByteString bs
+        writer.WriteEndIndefiniteLengthByteString()
+
+    | TextStringIndefiniteLength tss ->
+        writer.WriteStartIndefiniteLengthTextString()
+        for ts in tss do
+            writer.WriteTextString ts
+        writer.WriteEndIndefiniteLengthTextString()
+
+    | Array (isDefiniteLength, elements) ->
+        writer.WriteStartArray (if isDefiniteLength then Nullable elements.Length else Nullable())
+        for elem in elements do
+            write writer elem
+        writer.WriteEndArray()
+
+    | Map (isDefiniteLength, pairs) ->
+        writer.WriteStartMap (if isDefiniteLength then Nullable pairs.Count else Nullable())
+        for kv in pairs do
+            write writer kv.Key ; write writer kv.Value
+        writer.WriteEndMap()
+
+    | Tag (tag, nested) ->
+        writer.WriteTag (LanguagePrimitives.EnumOfValue tag)
+        write writer nested
+
+    | Double d -> writer.WriteDouble d
+    | SimpleValue v -> writer.WriteSimpleValue(LanguagePrimitives.EnumOfValue v)
+
+    | SemanticValue value ->
+        writer.WriteTag CborTagExt.SemValueGuard
+        writeSemanticValue writer value
+
+let private writeSemanticValue (writer : CborWriter) (s : CborSemanticValue) =
+    match s with
+    | Null -> writer.WriteTag CborTagExt.Null; writer.WriteNull()
+    | Bool b -> writer.WriteTag CborTagExt.Bool; writer.WriteBoolean b
+    | Int32 i -> writer.WriteTag CborTagExt.Int32; writer.WriteInt32 i
+    | Int64 i -> writer.WriteTag CborTagExt.Int64; writer.WriteInt64 i
+    | Half f -> writer.WriteTag CborTagExt.Half; writer.WriteHalf f
+    | Single f -> writer.WriteTag CborTagExt.Single; writer.WriteSingle f
+    | DateTimeOffset d -> writer.WriteDateTimeOffset d
+    | UnixTimeSeconds s -> writer.WriteUnixTimeSeconds s
+    | BigInt i -> writer.WriteBigInteger i
+    | Decimal d -> writer.WriteDecimal d
+
+let rec read (reader : CborReader) : CborDocument =
+    match reader.PeekState() with
+    | CborReaderState.UnsignedInteger -> UnsignedInteger(reader.ReadUInt64())
+    | CborReaderState.NegativeInteger -> NegativeInteger(reader.ReadCborNegativeIntegerRepresentation())
+    | CborReaderState.ByteString -> ByteString(reader.ReadByteString())
+    | CborReaderState.TextString -> TextString(reader.ReadTextString())
+    | CborReaderState.StartArray ->
+        let length = reader.ReadStartArray()
+        if length.HasValue then
+            let results = Array.zeroCreate<CborDocument> length.Value
+            for i = 0 to results.Length - 1 do
+                results.[i] <- read reader
+
+            reader.ReadEndArray()
+            Array(true, results)
+        else
+            let results = new System.Collections.Generic.List<_>()
+            while reader.PeekState() <> CborReaderState.EndArray do
+                results.Add(read reader)
+
+            reader.ReadEndArray()
+            Array(false, results.ToArray())
+
+    | CborReaderState.StartIndefiniteLengthByteString ->
+        reader.ReadStartIndefiniteLengthByteString()
+        let chunks = new System.Collections.Generic.List<byte[]>()
+        while reader.PeekState() <> CborReaderState.EndIndefiniteLengthByteString do
+            chunks.Add(reader.ReadByteString())
+        reader.ReadEndIndefiniteLengthByteString()
+        ByteStringIndefiniteLength(chunks.ToArray())
+
+    | CborReaderState.StartIndefiniteLengthTextString ->
+        reader.ReadStartIndefiniteLengthTextString()
+        let chunks = new System.Collections.Generic.List<string>()
+        while reader.PeekState() <> CborReaderState.EndIndefiniteLengthTextString do
+            chunks.Add(reader.ReadTextString())
+        reader.ReadEndIndefiniteLengthTextString()
+        TextStringIndefiniteLength(chunks.ToArray())
+
+    | CborReaderState.StartMap ->
+        let length = reader.ReadStartMap()
+        if length.HasValue then
+            let results = Array.zeroCreate<CborDocument * CborDocument> length.Value
+            for i = 0 to results.Length - 1 do
+                results.[i] <- (read reader, read reader)
+            reader.ReadEndMap()
+            Map(true, Map.ofArray results)
+        else
+            let results = new System.Collections.Generic.List<_>()
+            while reader.PeekState() <> CborReaderState.EndMap do
+                results.Add(read reader, read reader)
+            reader.ReadEndMap()
+            Map(false, Map.ofSeq results)
+
+    | CborReaderState.Tag ->
+        let tag = reader.ReadTag()
+        if tag = CborTagExt.SemValueGuard then SemanticValue(readSemanticValue reader)
+        else Tag (LanguagePrimitives.EnumToValue tag, read reader)
+
+    | CborReaderState.HalfPrecisionFloat
+    | CborReaderState.SinglePrecisionFloat
+    | CborReaderState.DoublePrecisionFloat -> Double (reader.ReadDouble())
+
+    | CborReaderState.Null
+    | CborReaderState.Boolean
+    | CborReaderState.SimpleValue ->
+        let value = reader.ReadSimpleValue()
+        SimpleValue(LanguagePrimitives.EnumToValue value)
+
+    | state -> failwithf "Unrecognized reader state %O" state
+
+let private readSemanticValue (reader : CborReader) : CborSemanticValue =
+    match reader.PeekTag() with
+    | CborTagExt.Null -> let _ = reader.ReadTag() in reader.ReadNull(); Null
+    | CborTagExt.Bool -> let _ = reader.ReadTag() in Bool(reader.ReadBoolean())
+    | CborTagExt.Int32 -> let _ = reader.ReadTag() in Int32(reader.ReadInt32())
+    | CborTagExt.Int64 -> let _ = reader.ReadTag() in Int64(reader.ReadInt64())
+    | CborTagExt.Half -> let _ = reader.ReadTag() in Half(reader.ReadHalf())
+    | CborTagExt.Single -> let _ = reader.ReadTag() in Single(reader.ReadSingle())
+    | CborTag.DateTimeString -> DateTimeOffset(reader.ReadDateTimeOffset())
+    | CborTag.UnixTimeSeconds -> let dto = reader.ReadUnixTimeSeconds() in UnixTimeSeconds(dto.ToUnixTimeSeconds())
+    | CborTag.UnsignedBigNum
+    | CborTag.NegativeBigNum -> BigInt(reader.ReadBigInteger())
+    | CborTag.DecimalFraction -> Decimal(reader.ReadDecimal())
+    | tag -> failwithf "Unrecognized tag %O" tag
+
+// defines a set of custom CBOR tags for semantic value encodings
+module private CborTagExt =
+
+    let [<Literal>] SemValueGuard : CborTag = LanguagePrimitives.EnumOfValue 50015001uL
+
+    let [<Literal>] Null : CborTag = LanguagePrimitives.EnumOfValue 5001uL
+    let [<Literal>] Bool : CborTag = LanguagePrimitives.EnumOfValue 5002uL
+    let [<Literal>] Int32 : CborTag = LanguagePrimitives.EnumOfValue 5003uL
+    let [<Literal>] Int64 : CborTag = LanguagePrimitives.EnumOfValue 5004uL
+    let [<Literal>] Half : CborTag = LanguagePrimitives.EnumOfValue 5005uL
+    let [<Literal>] Single : CborTag = LanguagePrimitives.EnumOfValue 5006uL
diff --git a/src/libraries/System.Formats.Cbor/tests/CborDocument/CborPropertyTestContext.fs b/src/libraries/System.Formats.Cbor/tests/CborDocument/CborPropertyTestContext.fs
new file mode 100644
index 00000000000000..921000f3ef5151
--- /dev/null
+++ b/src/libraries/System.Formats.Cbor/tests/CborDocument/CborPropertyTestContext.fs
@@ -0,0 +1,106 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Formats.Cbor.Tests.DataModel
+
+open System.Formats.Cbor
+open System.Formats.Cbor.Tests.DataModel
+
+/// Randomly generated record containing parameters for a CBOR property-based test
+[<CLIMutable>]
+type CborPropertyTestContext =
+    {
+        RootDocuments : CborDocument[]
+        ConformanceMode : CborConformanceMode
+        ConvertIndefiniteLengthItems : bool
+    }
+
+module rec CborPropertyTestContextHelper =
+
+    /// Identifies & transforms documents that might not be accepted under the supplied conformance mode
+    let create (mode : CborConformanceMode) (convertIndefiniteLengthItems : bool) (docs : CborDocument[]) =
+        {
+            RootDocuments = Array.map (normalize mode convertIndefiniteLengthItems) docs
+            ConvertIndefiniteLengthItems = convertIndefiniteLengthItems
+            ConformanceMode = mode
+        }
+
+    /// Gets the expected value that we would expected to see after a full serialization/deserialization roundtrip
+    let getExpectedRoundtripValues (context : CborPropertyTestContext) =
+        Array.map (getExpectedRoundtripValue context.ConvertIndefiniteLengthItems) context.RootDocuments
+
+    /// Identifies & transforms documents that might not be accepted under the supplied conformance mode
+    let private normalize (mode : CborConformanceMode) (convertIndefiniteLengthItems : bool) (doc : CborDocument) =
+        // normalization can lead to collisions in conformance modes that require field uniqueness
+        // mitigate by wrapping with a unique CBOR node
+        let mutable counter = 19000uL
+        let createUniqueWrapper (doc : CborDocument) =
+            counter <- counter + 1uL
+            Array(true, [|UnsignedInteger counter; doc|])
+
+        // not accepted by strict & canonical conformance modes
+        let trimNonCanonicalSimpleValue doc =
+            match doc with
+            | SimpleValue value when value >= 24uy && value < 32uy -> createUniqueWrapper(SimpleValue 0uy)
+            | _ -> doc
+
+        // completely replace indefinite-length nodes in canonical conformance modes
+        let trimIndefiniteLengthNode doc =
+            match doc with
+            | ByteStringIndefiniteLength bss -> createUniqueWrapper(ByteString (Array.concat bss))
+            | TextStringIndefiniteLength tss -> createUniqueWrapper(TextString (String.concat "" tss))
+            | Array(false, elems) -> createUniqueWrapper(Array(true, elems))
+            | Map(false, fields) -> createUniqueWrapper(Map(true, fields))
+            | _ -> doc
+
+        // CTAP2 does not allow major type 6, at all
+        let trimTagNode doc =
+            match doc with
+            | Tag (tag, doc) -> Array(true, [| UnsignedInteger (uint64 tag) ; doc|])
+            | SemanticValue _ -> createUniqueWrapper(UnsignedInteger 0uL)
+            | _ -> doc
+
+        match mode with
+        | CborConformanceMode.Lax -> doc
+        | CborConformanceMode.Strict
+        | CborConformanceMode.Canonical -> map (trimNonCanonicalSimpleValue << trimIndefiniteLengthNode) doc
+        | CborConformanceMode.Ctap2Canonical -> map (trimNonCanonicalSimpleValue << trimIndefiniteLengthNode << trimTagNode) doc
+        | _ -> doc
+
+    /// Gets the expected value that we would expected to see after a full serialization/deserialization roundtrip
+    let private getExpectedRoundtripValue (convertIndefiniteLengthItems : bool) (doc : CborDocument) =
+        if not convertIndefiniteLengthItems then doc else
+
+        let trimIndefiniteLengthNode doc =
+            match doc with
+            | ByteStringIndefiniteLength bss -> ByteString (Array.concat bss)
+            | TextStringIndefiniteLength tss -> TextString (String.concat "" tss)
+            | Array(false, elems) -> Array(true, elems)
+            | Map(false, fields) -> Map(true, fields)
+            | _ -> doc
+
+        map trimIndefiniteLengthNode doc
+
+    /// Depth-first application of update function on a CBOR doc tree
+    let rec private map (updater : CborDocument -> CborDocument) (doc : CborDocument) =
+        match updater doc with
+        | UnsignedInteger _
+        | NegativeInteger _
+        | ByteString _
+        | ByteStringIndefiniteLength _
+        | TextString _
+        | TextStringIndefiniteLength _
+        | SemanticValue _
+        | SimpleValue _
+        | Double _ as updated -> updated
+
+        | Tag(tag, value) -> Tag(tag, map updater value)
+        | Array(isDefiniteLength, elems) -> Array(isDefiniteLength, Array.map (map updater) elems)
+        | Map(isDefiniteLength, fields) ->
+            let updatedFields =
+                fields
+                |> Map.toSeq
+                |> Seq.map (fun (k,v) -> map updater k, map updater v)
+                |> Map.ofSeq
+
+            Map(isDefiniteLength, updatedFields)
diff --git a/src/libraries/System.Formats.Cbor/tests/CborDocument/System.Formats.Cbor.Tests.DataModel.fsproj b/src/libraries/System.Formats.Cbor/tests/CborDocument/System.Formats.Cbor.Tests.DataModel.fsproj
new file mode 100644
index 00000000000000..94a84ccfa46132
--- /dev/null
+++ b/src/libraries/System.Formats.Cbor/tests/CborDocument/System.Formats.Cbor.Tests.DataModel.fsproj
@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="CborDocument.fs" />
+    <Compile Include="CborPropertyTestContext.fs" />
+    <Compile Include="CborDocumentSerializer.fs" />
+  </ItemGroup>
+
+  <ItemGroup>
+      <ProjectReference Include="..\..\src\System.Formats.Cbor.csproj" />
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/src/libraries/System.Formats.Cbor/tests/CborRoundtripTests.cs b/src/libraries/System.Formats.Cbor/tests/CborRoundtripTests.cs
deleted file mode 100644
index 1e410d77a99aaf..00000000000000
--- a/src/libraries/System.Formats.Cbor/tests/CborRoundtripTests.cs
+++ /dev/null
@@ -1,180 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-using System.Linq;
-using Test.Cryptography;
-using Xunit;
-#if CBOR_PROPERTY_TESTS 
-using FsCheck.Xunit;
-#endif
-
-namespace System.Formats.Cbor.Tests
-{
-    public partial class CborRoundtripTests
-    {
-
-#if CBOR_PROPERTY_TESTS
-        private const string ReplaySeed = "(0,0)"; // set a seed for deterministic runs
-        private const int MaxTests = 10_000;
-#endif
-
-#if CBOR_PROPERTY_TESTS
-        [Property(Replay = ReplaySeed, MaxTest = MaxTests)]
-#else
-        [Theory]
-        [InlineData(0)]
-        [InlineData(1)]
-        [InlineData(10)]
-        [InlineData(23)]
-        [InlineData(24)]
-        [InlineData(25)]
-        [InlineData(100)]
-        [InlineData(1000)]
-        [InlineData(1000000)]
-        [InlineData(1000000000000)]
-        [InlineData(-1)]
-        [InlineData(-10)]
-        [InlineData(-100)]
-        [InlineData(-1000)]
-        [InlineData(byte.MaxValue)]
-        [InlineData(byte.MaxValue + 1)]
-        [InlineData(-1 - byte.MaxValue)]
-        [InlineData(-2 - byte.MaxValue)]
-        [InlineData(ushort.MaxValue)]
-        [InlineData(ushort.MaxValue + 1)]
-        [InlineData(-1 - ushort.MaxValue)]
-        [InlineData(-2 - ushort.MaxValue)]
-        [InlineData(uint.MaxValue)]
-        [InlineData((long)uint.MaxValue + 1)]
-        [InlineData(-1 - uint.MaxValue)]
-        [InlineData(-2 - uint.MaxValue)]
-        [InlineData(long.MinValue)]
-        [InlineData(long.MaxValue)]
-#endif
-        public static void Roundtrip_Int64(long input)
-        {
-            var writer = new CborWriter();
-            writer.WriteInt64(input);
-            byte[] encoding = writer.Encode();
-
-            var reader = new CborReader(encoding);
-            long result = reader.ReadInt64();
-            Assert.Equal(input, result);
-        }
-
-#if CBOR_PROPERTY_TESTS
-        [Property(Replay = ReplaySeed, MaxTest = MaxTests)]
-#else
-        [Theory]
-        [InlineData(0)]
-        [InlineData(1)]
-        [InlineData(10)]
-        [InlineData(23)]
-        [InlineData(24)]
-        [InlineData(25)]
-        [InlineData(100)]
-        [InlineData(1000)]
-        [InlineData(1000000)]
-        [InlineData(1000000000000)]
-        [InlineData(byte.MaxValue)]
-        [InlineData(byte.MaxValue + 1)]
-        [InlineData(ushort.MaxValue)]
-        [InlineData(ushort.MaxValue + 1)]
-        [InlineData(uint.MaxValue)]
-        [InlineData((long)uint.MaxValue + 1)]
-        [InlineData(long.MaxValue)]
-        [InlineData(ulong.MaxValue)]
-#endif
-        public static void Roundtrip_UInt64(ulong input)
-        {
-            var writer = new CborWriter();
-            writer.WriteUInt64(input);
-            byte[] encoding = writer.Encode();
-
-            var reader = new CborReader(encoding);
-            ulong result = reader.ReadUInt64();
-            Assert.Equal(input, result);
-        }
-
-#if CBOR_PROPERTY_TESTS
-        [Property(Replay = ReplaySeed, MaxTest = MaxTests)]
-        public static void Roundtrip_ByteString(byte[] input)
-        {
-#else
-        [Theory]
-        [InlineData("")]
-        [InlineData("01020304")]
-        [InlineData("ffffffffffffffffffffffffffff")]
-        public static void Roundtrip_ByteString(string hexInput)
-        {
-            byte[] input = hexInput.HexToByteArray();
-#endif
-            var writer = new CborWriter();
-            writer.WriteByteString(input);
-            byte[] encoding = writer.Encode();
-
-            var reader = new CborReader(encoding);
-            byte[] result = reader.ReadByteString();
-            AssertHelper.HexEqual(input ?? Array.Empty<byte>(), result);
-        }
-
-#if CBOR_PROPERTY_TESTS
-        [Property(Replay = ReplaySeed, MaxTest = MaxTests)]
-#else
-        [Theory]
-        [InlineData("")]
-        [InlineData("a")]
-        [InlineData("IETF")]
-        [InlineData("\"\\")]
-        [InlineData("\u00fc")]
-        [InlineData("\u6c34")]
-        [InlineData("\ud800\udd51")]
-#endif
-        public static void Roundtrip_TextString(string input)
-        {
-            var writer = new CborWriter();
-            writer.WriteTextString(input);
-            byte[] encoding = writer.Encode();
-
-            var reader = new CborReader(encoding);
-            string result = reader.ReadTextString();
-            Assert.Equal(input ?? "", result);
-        }
-
-#if CBOR_PROPERTY_TESTS
-        [Property(Replay = ReplaySeed, MaxTest = MaxTests)]
-        public static void ByteString_Encoding_ShouldContainInputBytes(byte[] input)
-        {
-#else
-        [Theory]
-        [InlineData("")]
-        [InlineData("01020304")]
-        [InlineData("ffffffffffffffffffffffffffff")]
-        public static void ByteString_Encoding_ShouldContainInputBytes(string hexInput)
-        {
-            byte[] input = hexInput.HexToByteArray();
-#endif
-            var writer = new CborWriter();
-            writer.WriteByteString(input);
-            byte[] encoding = writer.Encode();
-
-            int length = input?.Length ?? 0;
-            int lengthEncodingLength = GetLengthEncodingLength(length);
-
-            Assert.Equal(lengthEncodingLength + length, encoding.Length);
-            AssertHelper.HexEqual(input ?? Array.Empty<byte>(), encoding.Skip(lengthEncodingLength).ToArray());
-
-            static int GetLengthEncodingLength(int length)
-            {
-                return length switch
-                {
-                    _ when (length < 24) => 1,
-                    _ when (length < byte.MaxValue) => 1 + sizeof(byte),
-                    _ when (length < ushort.MaxValue) => 1 + sizeof(ushort),
-                    _ => 1 + sizeof(uint)
-                };
-            }
-        }
-    }
-}
diff --git a/src/libraries/System.Formats.Cbor/tests/PropertyTests/CborPropertyTests.cs b/src/libraries/System.Formats.Cbor/tests/PropertyTests/CborPropertyTests.cs
new file mode 100644
index 00000000000000..d265baec831d56
--- /dev/null
+++ b/src/libraries/System.Formats.Cbor/tests/PropertyTests/CborPropertyTests.cs
@@ -0,0 +1,219 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Formats.Cbor.Tests.DataModel;
+using System.Linq;
+using FsCheck;
+using FsCheck.Xunit;
+using Xunit;
+
+namespace System.Formats.Cbor.Tests
+{
+    public static class CborPropertyTests
+    {
+        private const string? ReplaySeed = "(42,42)"; // set a seed for deterministic runs, null for randomized runs
+        private const int MaxTests = 100; // FsCheck default is 100
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void Roundtrip_Int64(CborConformanceMode mode, long input)
+        {
+            var writer = new CborWriter(mode);
+            writer.WriteInt64(input);
+            byte[] encoding = writer.Encode();
+
+            var reader = new CborReader(encoding, mode);
+            long result = reader.ReadInt64();
+            Assert.Equal(input, result);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void Roundtrip_UInt64(CborConformanceMode mode, ulong input)
+        {
+            var writer = new CborWriter(mode);
+            writer.WriteUInt64(input);
+            byte[] encoding = writer.Encode();
+
+            var reader = new CborReader(encoding, mode);
+            ulong result = reader.ReadUInt64();
+            Assert.Equal(input, result);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void Roundtrip_NegativeInteger(CborConformanceMode mode, ulong input)
+        {
+            var writer = new CborWriter(mode);
+            writer.WriteCborNegativeIntegerRepresentation(input);
+            byte[] encoding = writer.Encode();
+
+            var reader = new CborReader(encoding, mode);
+            ulong result = reader.ReadCborNegativeIntegerRepresentation();
+            Assert.Equal(input, result);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void Roundtrip_ByteString(CborConformanceMode mode, byte[] input)
+        {
+            var writer = new CborWriter(mode);
+            writer.WriteByteString(input);
+            byte[] encoding = writer.Encode();
+
+            var reader = new CborReader(encoding, mode);
+            byte[] result = reader.ReadByteString();
+            AssertHelper.HexEqual(input, result);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void Roundtrip_TextString(CborConformanceMode mode, string input)
+        {
+            var writer = new CborWriter(mode);
+            writer.WriteTextString(input);
+            byte[] encoding = writer.Encode();
+
+            var reader = new CborReader(encoding, mode);
+            string result = reader.ReadTextString();
+            Assert.Equal(input, result);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void Roundtrip_IndefiniteByteString(CborConformanceMode mode, byte[][] chunks)
+        {
+            bool convertIndefiniteLengthEncodings = mode is CborConformanceMode.Canonical or CborConformanceMode.Ctap2Canonical;
+            var writer = new CborWriter(convertIndefiniteLengthEncodings: convertIndefiniteLengthEncodings);
+
+            writer.WriteStartIndefiniteLengthByteString();
+            foreach (byte[] chunk in chunks)
+            {
+                writer.WriteByteString(chunk);
+            }
+            writer.WriteEndIndefiniteLengthByteString();
+
+            byte[] encoding = writer.Encode();
+
+            var reader = new CborReader(encoding);
+            byte[] expected = chunks.SelectMany(ch => ch).ToArray();
+            byte[] result = reader.ReadByteString();
+            AssertHelper.HexEqual(expected, result);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void Roundtrip_IndefiniteTextString(CborConformanceMode mode, string[] chunks)
+        {
+            bool convertIndefiniteLengthEncodings = mode is CborConformanceMode.Canonical or CborConformanceMode.Ctap2Canonical;
+            var writer = new CborWriter(convertIndefiniteLengthEncodings: convertIndefiniteLengthEncodings);
+
+            writer.WriteStartIndefiniteLengthTextString();
+            foreach (string chunk in chunks)
+            {
+                writer.WriteTextString(chunk);
+            }
+            writer.WriteEndIndefiniteLengthTextString();
+
+            byte[] encoding = writer.Encode();
+
+            var reader = new CborReader(encoding);
+            string expected = String.Concat(chunks);
+            string result = reader.ReadTextString();
+            Assert.Equal(expected, result);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void Roundtrip_Half(CborConformanceMode mode, Half input)
+        {
+            var writer = new CborWriter(mode);
+            writer.WriteHalf(input);
+            byte[] encoding = writer.Encode();
+
+            var reader = new CborReader(encoding, mode);
+            Half result = reader.ReadHalf();
+            Assert.Equal(input, result);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void Roundtrip_Double(CborConformanceMode mode, double input)
+        {
+            var writer = new CborWriter();
+            writer.WriteDouble(input);
+            byte[] encoding = writer.Encode();
+
+            var reader = new CborReader(encoding);
+            double result = reader.ReadDouble();
+            Assert.Equal(input, result);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void Roundtrip_Decimal(CborConformanceMode mode, decimal input)
+        {
+            var writer = new CborWriter();
+            writer.WriteDecimal(input);
+            byte[] encoding = writer.Encode();
+
+            var reader = new CborReader(encoding);
+            decimal result = reader.ReadDecimal();
+            Assert.Equal(input, result);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void ByteString_Encoding_ShouldContainInputBytes(CborConformanceMode mode, byte[] input)
+        {
+            var writer = new CborWriter(mode);
+            writer.WriteByteString(input);
+            byte[] encoding = writer.Encode();
+
+            int length = input?.Length ?? 0;
+            int lengthEncodingLength = GetLengthEncodingLength(length);
+
+            Assert.Equal(lengthEncodingLength + length, encoding.Length);
+            AssertHelper.HexEqual(input ?? Array.Empty<byte>(), encoding.Skip(lengthEncodingLength).ToArray());
+
+            static int GetLengthEncodingLength(int length)
+            {
+                return length switch
+                {
+                    _ when (length < 24) => 1,
+                    _ when (length < byte.MaxValue) => 1 + sizeof(byte),
+                    _ when (length < ushort.MaxValue) => 1 + sizeof(ushort),
+                    _ => 1 + sizeof(uint)
+                };
+            }
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void CborDocument_Roundtrip(CborPropertyTestContext input)
+        {
+            byte[] encoding = CborDocumentSerializer.encode(input);
+
+            CborDocument[] expectedResults = CborPropertyTestContextHelper.getExpectedRoundtripValues(input);
+            CborDocument[] roundtrippedDocuments = CborDocumentSerializer.decode(input, encoding);
+            Assert.Equal(expectedResults, roundtrippedDocuments);
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void CborDocument_SkipValue(CborPropertyTestContext input)
+        {
+            int length = input.RootDocuments.Length;
+            input.RootDocuments = new[] { CborDocument.NewArray(_isDefiniteLength: true, input.RootDocuments) };
+            byte[] encoding = CborDocumentSerializer.encode(input);
+
+            CborReader reader = CborDocumentSerializer.createReader(input, encoding);
+            reader.ReadStartArray();
+            for (int i = 0; i < length; i++)
+            {
+                reader.SkipValue();
+            }
+            reader.ReadEndArray();
+            Assert.Equal(CborReaderState.Finished, reader.PeekState());
+        }
+
+        [Property(Replay = ReplaySeed, MaxTest = MaxTests, Arbitrary = new[] { typeof(CborRandomGenerators) })]
+        public static void CborDocument_SkipToParent(CborPropertyTestContext input)
+        {
+            input.RootDocuments = new[] { CborDocument.NewArray(_isDefiniteLength: true, input.RootDocuments) };
+            byte[] encoding = CborDocumentSerializer.encode(input);
+
+            CborReader reader = CborDocumentSerializer.createReader(input, encoding);
+            reader.ReadStartArray();
+            reader.SkipToParent();
+            Assert.Equal(CborReaderState.Finished, reader.PeekState());
+        }
+    }
+}
diff --git a/src/libraries/System.Formats.Cbor/tests/PropertyTests/CborRandomGenerators.cs b/src/libraries/System.Formats.Cbor/tests/PropertyTests/CborRandomGenerators.cs
new file mode 100644
index 00000000000000..2cf77cf39d97f9
--- /dev/null
+++ b/src/libraries/System.Formats.Cbor/tests/PropertyTests/CborRandomGenerators.cs
@@ -0,0 +1,68 @@
+using System.Collections.Generic;
+using System.Formats.Cbor.Tests.DataModel;
+using System.Linq;
+using FsCheck;
+
+namespace System.Formats.Cbor.Tests
+{
+    public static class CborRandomGenerators
+    {
+        public static Arbitrary<CborPropertyTestContext> PropertyTestInput()
+        {
+            Arbitrary<NonEmptyArray<CborDocument>> documentArb = Arb.Default.NonEmptyArray<CborDocument>();
+            Arbitrary<bool> convertArb = Arb.Default.Bool();
+            Gen<CborConformanceMode> conformanceModes = Gen.Elements(
+                CborConformanceMode.Lax,
+                CborConformanceMode.Strict,
+                CborConformanceMode.Canonical,
+                CborConformanceMode.Ctap2Canonical);
+
+            Gen<CborPropertyTestContext> inputGen =
+                from docs in documentArb.Generator
+                from convert in convertArb.Generator
+                from mode in conformanceModes
+                select CborPropertyTestContextHelper.create(mode, convert, docs.Get);
+
+            IEnumerable<CborPropertyTestContext> Shrinker(CborPropertyTestContext input)
+            {
+                var nonEmptyArrayInput = NonEmptyArray<CborDocument>.NewNonEmptyArray(input.RootDocuments);
+
+                foreach (NonEmptyArray<CborDocument> shrunkDoc in documentArb.Shrinker(nonEmptyArrayInput))
+                {
+                    yield return CborPropertyTestContextHelper.create(input.ConformanceMode, input.ConvertIndefiniteLengthItems, input.RootDocuments);
+                }
+            }
+
+            return Arb.From(inputGen, Shrinker);
+        }
+
+        // Do not generate null strings and byte arrays
+        public static Arbitrary<string> String() => Arb.Default.String().Filter(s => s is not null);
+        public static Arbitrary<byte[]> ByteArray() => Arb.Default.Array<byte>().Filter(s => s is not null);
+
+        // forgo NaN value generation in order to simplify equality checks
+        public static Arbitrary<float> Single() => Arb.Default.Float32().Filter(s => !float.IsNaN(s));
+        public static Arbitrary<double> Double() => Arb.Default.Float().Filter(s => !double.IsNaN(s));
+
+        // FsCheck has no built-in System.Half generator, define one here
+        public static Arbitrary<Half> Half()
+        {
+            Arbitrary<float> singleArb = Arb.Default.Float32();
+
+            Gen<Half> generator =
+                from f in singleArb.Generator
+                where !float.IsNaN(f)
+                select (Half)f;
+
+            IEnumerable<Half> Shrinker(Half h)
+            {
+                foreach (float shrunk in singleArb.Shrinker((float)h))
+                {
+                    yield return (Half)shrunk;
+                }
+            }
+
+            return Arb.From(generator, Shrinker);
+        }
+    }
+}
diff --git a/src/libraries/System.Formats.Cbor/tests/System.Formats.Cbor.Tests.csproj b/src/libraries/System.Formats.Cbor/tests/System.Formats.Cbor.Tests.csproj
index f1c45bd8a8e570..c2211d72e5b198 100644
--- a/src/libraries/System.Formats.Cbor/tests/System.Formats.Cbor.Tests.csproj
+++ b/src/libraries/System.Formats.Cbor/tests/System.Formats.Cbor.Tests.csproj
@@ -2,11 +2,15 @@
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <nullable>enable</nullable>
+    <!-- Referenced assembly 'FsCheck' does not have a strong name.-->
+    <NoWarn>CS8002</NoWarn>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonTestPath)System\Security\Cryptography\ByteUtils.cs">
       <Link>CommonTest\System\Security\Cryptography\ByteUtils.cs</Link>
     </Compile>
+    <Compile Include="PropertyTests\CborPropertyTests.cs" />
+    <Compile Include="PropertyTests\CborRandomGenerators.cs" />
     <Compile Include="Reader\CborReaderTests.cs" />
     <Compile Include="Reader\CborReaderTests.ByteString.cs" />
     <Compile Include="Reader\CborReaderTests.TextString.cs" />
@@ -26,7 +30,13 @@
     <Compile Include="Writer\CborWriterTests.Integer.cs" />
     <Compile Include="Writer\CborWriterTests.ByteString.cs" />
     <Compile Include="Writer\CborWriterTests.TextString.cs" />
-    <Compile Include="CborRoundtripTests.cs" />
     <Compile Include="CoseKeyHelpers.cs" />
   </ItemGroup>
+  
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Formats.Cbor.csproj" />
+    <ProjectReference Include="CborDocument\System.Formats.Cbor.Tests.DataModel.fsproj" />
+    <PackageReference Include="FsCheck" Version="$(FsCheckVersion)" />
+    <PackageReference Include="FsCheck.Xunit" Version="$(FsCheckVersion)" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Formats.Cbor/tests/Writer/CborWriterTests.Map.cs b/src/libraries/System.Formats.Cbor/tests/Writer/CborWriterTests.Map.cs
index 78d663d672a4ec..a6b9133a80f866 100644
--- a/src/libraries/System.Formats.Cbor/tests/Writer/CborWriterTests.Map.cs
+++ b/src/libraries/System.Formats.Cbor/tests/Writer/CborWriterTests.Map.cs
@@ -101,15 +101,15 @@ public static void WriteMap_IndefiniteLength_WithPatching_NestedValues_HappyPath
         [InlineData(new object[] { Map, "a", "A", -1, 2, new byte[] { }, new byte[] { 1 } }, "a3200240410161616141")]
         [InlineData(new object[] { Map, new object[] { Map, 3, 4, 1, 2 }, 0, new object[] { 1, 2, 3 }, 0, new string[] { "a", "b" }, 0, new string[] { Hex, "ab", "" }, 00 }, "a441ab00626162008301020300a20102030400")]
         public static void WriteMap_IndefiniteLength_WithPatching_Ctap2Sorting_HappyPath(object[] values, string expectedHexEncoding)
-    {
-        byte[] expectedEncoding = expectedHexEncoding.HexToByteArray();
-        var writer = new CborWriter(CborConformanceMode.Ctap2Canonical, convertIndefiniteLengthEncodings: true);
-        Helpers.WriteMap(writer, values, useDefiniteLengthCollections: false);
-        byte[] actualEncoding = writer.Encode();
-        AssertHelper.HexEqual(expectedEncoding, actualEncoding);
-    }
+        {
+            byte[] expectedEncoding = expectedHexEncoding.HexToByteArray();
+            var writer = new CborWriter(CborConformanceMode.Ctap2Canonical, convertIndefiniteLengthEncodings: true);
+            Helpers.WriteMap(writer, values, useDefiniteLengthCollections: false);
+            byte[] actualEncoding = writer.Encode();
+            AssertHelper.HexEqual(expectedEncoding, actualEncoding);
+        }
 
-    [Theory]
+        [Theory]
         [InlineData(new object[] { Map, "a", 1, "b", new object[] { 2, 3 } }, "a26161016162820203")]
         [InlineData(new object[] { Map, "a", new object[] { 2, 3, "b", new object[] { Map, "x", -1, "y", new object[] { "z", 0 } } } }, "a161618402036162a2617820617982617a00")]
         [InlineData(new object[] { "a", new object[] { Map, "b", "c" } }, "826161a161626163")]
@@ -384,5 +384,18 @@ public static void WriteStartMap_IndefiniteLength_NoPatching_UnsupportedConforma
             var writer = new CborWriter(conformanceMode, convertIndefiniteLengthEncodings: false);
             Assert.Throws<InvalidOperationException>(() => writer.WriteStartMap(null));
         }
+
+        [Fact]
+        public static void Write_TaggedEmptyMap_ShouldSucceed()
+        {
+            var writer = new CborWriter();
+
+            writer.WriteTag(CborTag.DateTimeString);
+            writer.WriteStartMap(0);
+            writer.WriteEndMap();
+
+            byte[] encoding = writer.Encode();
+            Assert.Equal("C0A0", encoding.ByteArrayToHex());
+        }
     }
 }
diff --git a/src/libraries/System.Globalization.Calendars/Directory.Build.props b/src/libraries/System.Globalization.Calendars/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Globalization.Calendars/Directory.Build.props
+++ b/src/libraries/System.Globalization.Calendars/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Globalization.Calendars/src/System.Globalization.Calendars.csproj b/src/libraries/System.Globalization.Calendars/src/System.Globalization.Calendars.csproj
index c251f69ea9e3ab..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Globalization.Calendars/src/System.Globalization.Calendars.csproj
+++ b/src/libraries/System.Globalization.Calendars/src/System.Globalization.Calendars.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Globalization.Calendars</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Globalization.Extensions/Directory.Build.props b/src/libraries/System.Globalization.Extensions/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Globalization.Extensions/Directory.Build.props
+++ b/src/libraries/System.Globalization.Extensions/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Globalization/Directory.Build.props b/src/libraries/System.Globalization/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Globalization/Directory.Build.props
+++ b/src/libraries/System.Globalization/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Globalization/src/System.Globalization.csproj b/src/libraries/System.Globalization/src/System.Globalization.csproj
index 4dacec6ff437c5..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Globalization/src/System.Globalization.csproj
+++ b/src/libraries/System.Globalization/src/System.Globalization.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Globalization</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Globalization/tests/CultureInfo/CultureInfoEnglishName.cs b/src/libraries/System.Globalization/tests/CultureInfo/CultureInfoEnglishName.cs
index 23c2032c51cd41..fdb6e4b189fcee 100644
--- a/src/libraries/System.Globalization/tests/CultureInfo/CultureInfoEnglishName.cs
+++ b/src/libraries/System.Globalization/tests/CultureInfo/CultureInfoEnglishName.cs
@@ -11,8 +11,18 @@ public class CultureInfoEnglishName
         public static IEnumerable<object[]> EnglishName_TestData()
         {
             yield return new object[] { CultureInfo.CurrentCulture.Name, CultureInfo.CurrentCulture.EnglishName };
-            yield return new object[] { "en-US", "English (United States)" };
-            yield return new object[] { "fr-FR", "French (France)" };
+
+            if (PlatformDetection.IsNotBrowser)
+            {
+                yield return new object[] { "en-US", "English (United States)" };
+                yield return new object[] { "fr-FR", "French (France)" };
+            }
+            else
+            {
+                // Browser's ICU doesn't contain CultureInfo.EnglishName
+                yield return new object[] { "en-US", "en (US)" };
+                yield return new object[] { "fr-FR", "fr (FR)" };
+            }
         }
 
         [Theory]
diff --git a/src/libraries/System.Globalization/tests/CultureInfo/CultureInfoNativeName.cs b/src/libraries/System.Globalization/tests/CultureInfo/CultureInfoNativeName.cs
index b97a645b8b2a57..58429b132138cc 100644
--- a/src/libraries/System.Globalization/tests/CultureInfo/CultureInfoNativeName.cs
+++ b/src/libraries/System.Globalization/tests/CultureInfo/CultureInfoNativeName.cs
@@ -11,8 +11,18 @@ public class CultureInfoNativeName
         public static IEnumerable<object[]> NativeName_TestData()
         {
             yield return new object[] { CultureInfo.CurrentCulture.Name, CultureInfo.CurrentCulture.NativeName };
-            yield return new object[] { "en-US", "English (United States)" };
-            yield return new object[] { "en-CA", "English (Canada)" };
+            
+            if (PlatformDetection.IsNotBrowser)
+            {
+                yield return new object[] { "en-US", "English (United States)" };
+                yield return new object[] { "en-CA", "English (Canada)" };
+            }
+            else
+            {
+                // Browser's ICU doesn't contain CultureInfo.NativeName
+                yield return new object[] { "en-US", "en (US)" };
+                yield return new object[] { "en-CA", "en (CA)" };
+            }
         }
 
         [Theory]
diff --git a/src/libraries/System.Globalization/tests/DateTimeFormatInfo/DateTimeFormatInfoTests.cs b/src/libraries/System.Globalization/tests/DateTimeFormatInfo/DateTimeFormatInfoTests.cs
index 1689c9e312d2db..90c94defe96a9e 100644
--- a/src/libraries/System.Globalization/tests/DateTimeFormatInfo/DateTimeFormatInfoTests.cs
+++ b/src/libraries/System.Globalization/tests/DateTimeFormatInfo/DateTimeFormatInfoTests.cs
@@ -66,7 +66,12 @@ public void NativeCalendarName_Get_ReturnsExpected(DateTimeFormatInfo dtfi, Cale
             try
             {
                 dtfi.Calendar = calendar;
-                Assert.Equal(nativeCalendarName, dtfi.NativeCalendarName);
+
+                if (PlatformDetection.IsNotBrowser)
+                {
+                    // Browser's ICU doesn't contain NativeCalendarName,
+                    Assert.Equal(nativeCalendarName, dtfi.NativeCalendarName);
+                }
             }
             catch
             {
@@ -182,5 +187,27 @@ public void TestFirstYearOfJapaneseEra()
                         $"Parsing '{formattedDateWithGannen}' result should match if '{formattedDate}' has Gan-nen symbol"
             );
         }
+
+        [Fact]
+        public void JapaneseAbbreviatedEnglishEraNamesTest()
+        {
+            string [] eraNames = { "M", "T", "S", "H", "R" };
+
+            var ci = new CultureInfo("ja-JP") { DateTimeFormat = { Calendar = new JapaneseCalendar() }};
+
+            int eraNumber = ci.DateTimeFormat.GetEra("Q");
+            if (eraNumber == 4 || eraNumber == 5)
+            {
+                // Skip the test on Windows versions which have wrong Japanese Era information.
+                // Windows at some point used "Q" as fake era name before getting the official name.
+                return;
+            }
+
+            int numberOfErasToTest = Math.Min(eraNames.Length, ci.DateTimeFormat.Calendar.Eras.Length);
+            for (int i = 0; i < numberOfErasToTest; i++)
+            {
+                Assert.Equal(i + 1, ci.DateTimeFormat.GetEra(eraNames[i]));
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Globalization/tests/Invariant/Invariant.Tests.csproj b/src/libraries/System.Globalization/tests/Invariant/Invariant.Tests.csproj
index 1de762de1564b5..6979cd759d0ec1 100644
--- a/src/libraries/System.Globalization/tests/Invariant/Invariant.Tests.csproj
+++ b/src/libraries/System.Globalization/tests/Invariant/Invariant.Tests.csproj
@@ -3,6 +3,7 @@
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <TestRuntime>true</TestRuntime>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <InvariantGlobalization>true</InvariantGlobalization>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="InvariantMode.cs" />
diff --git a/src/libraries/System.Globalization/tests/NumberFormatInfo/NumberFormatInfoNumberGroupSizes.cs b/src/libraries/System.Globalization/tests/NumberFormatInfo/NumberFormatInfoNumberGroupSizes.cs
index 045d3e0b585be7..62ae02d3aa4a4c 100644
--- a/src/libraries/System.Globalization/tests/NumberFormatInfo/NumberFormatInfoNumberGroupSizes.cs
+++ b/src/libraries/System.Globalization/tests/NumberFormatInfo/NumberFormatInfoNumberGroupSizes.cs
@@ -13,8 +13,8 @@ public static IEnumerable<object[]> NumberGroupSizes_TestData()
             yield return new object[] { NumberFormatInfo.InvariantInfo, new int[] { 3 } };
             yield return new object[] { CultureInfo.GetCultureInfo("en-US").NumberFormat, new int[] { 3 } };
 
-            // Culture does not exist on Windows 7
-            if (!PlatformDetection.IsWindows7)
+            // Culture does not exist on Windows 7 and in Browser's ICU
+            if (!PlatformDetection.IsWindows7 && PlatformDetection.IsNotBrowser)
             {
                 yield return new object[] { CultureInfo.GetCultureInfo("ur-IN").NumberFormat, NumberFormatInfoData.UrINNumberGroupSizes() };
             }
diff --git a/src/libraries/System.Globalization/tests/System/Globalization/RegionInfoTests.cs b/src/libraries/System.Globalization/tests/System/Globalization/RegionInfoTests.cs
index dd99a40e94ca83..84cc05e356276a 100644
--- a/src/libraries/System.Globalization/tests/System/Globalization/RegionInfoTests.cs
+++ b/src/libraries/System.Globalization/tests/System/Globalization/RegionInfoTests.cs
@@ -79,6 +79,24 @@ public void CurrentRegion_Windows()
             }).Dispose();
         }
 
+
+        [ConditionalTheory(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        // We are testing with "no" as it match a neutral culture name. We want ensure this not conflict with region name.
+        [InlineData("no")]
+        [InlineData("No")]
+        [InlineData("NO")]
+        public void ValidateUsingCasedRegionName(string regionName)
+        {
+            RemoteExecutor.Invoke(name =>
+            {
+                // It is important to do this test in the following order because we have internal cache for regions.
+                // creating the region with the original input name should be the first to do to ensure not cached before.
+                string resultedName = new RegionInfo(name).Name;
+                string expectedName = new RegionInfo(name.ToUpperInvariant()).Name;
+                Assert.Equal(expectedName, resultedName);
+            }, regionName).Dispose();
+        }
+
         [Theory]
         [InlineData("en-US", "United States")]
         [OuterLoop("May fail on machines with multiple language packs installed")] // see https://github.com/dotnet/runtime/issues/30132
@@ -90,20 +108,51 @@ public void DisplayName(string name, string expected)
             }
         }
 
+        public static IEnumerable<object[]> NativeName_TestData()
+        {
+            if (PlatformDetection.IsNotBrowser)
+            {
+                yield return new object[] { "GB", "United Kingdom" };
+                yield return new object[] { "SE", "Sverige" };
+                yield return new object[] { "FR", "France" };
+            }
+            else
+            {
+                // Browser's ICU doesn't contain RegionInfo.NativeName
+                yield return new object[] { "GB", "GB" };
+                yield return new object[] { "SE", "SE" };
+                yield return new object[] { "FR", "FR" };
+            }
+        }
+
         [Theory]
-        [InlineData("GB", "United Kingdom")]
-        [InlineData("SE", "Sverige")]
-        [InlineData("FR", "France")]
+        [MemberData(nameof(NativeName_TestData))]
         public void NativeName(string name, string expected)
         {
             Assert.Equal(expected, new RegionInfo(name).NativeName);
         }
 
+        public static IEnumerable<object[]> EnglishName_TestData()
+        {
+            if (PlatformDetection.IsNotBrowser)
+            {
+                yield return new object[] { "en-US", new string[] { "United States" } };
+                yield return new object[] { "US", new string[] { "United States" } };
+                yield return new object[] { "zh-CN", new string[] { "China", "People's Republic of China", "China mainland" }};
+                yield return new object[] { "CN", new string[] { "China", "People's Republic of China", "China mainland" } };
+            }
+            else
+            {
+                // Browser's ICU doesn't contain RegionInfo.EnglishName
+                yield return new object[] { "en-US", new string[] { "US" } };
+                yield return new object[] { "US", new string[] { "US" } };
+                yield return new object[] { "zh-CN", new string[] { "CN" }};
+                yield return new object[] { "CN", new string[] { "CN" } };
+            }
+        }
+
         [Theory]
-        [InlineData("en-US", new string[] { "United States" })]
-        [InlineData("US", new string[] { "United States" })]
-        [InlineData("zh-CN", new string[] { "China", "People's Republic of China", "China mainland" })]
-        [InlineData("CN", new string[] { "China", "People's Republic of China", "China mainland" })]
+        [MemberData(nameof(EnglishName_TestData))]
         public void EnglishName(string name, string[] expected)
         {
             string result = new RegionInfo(name).EnglishName;
diff --git a/src/libraries/System.Globalization/tests/System/Globalization/TextInfoTests.cs b/src/libraries/System.Globalization/tests/System/Globalization/TextInfoTests.cs
index 099f9c24fb4226..3ab4461d0176a9 100644
--- a/src/libraries/System.Globalization/tests/System/Globalization/TextInfoTests.cs
+++ b/src/libraries/System.Globalization/tests/System/Globalization/TextInfoTests.cs
@@ -171,7 +171,7 @@ public void EqualsTest(TextInfo textInfo, object obj, bool expected)
             }
         }
 
-        private static readonly string [] s_cultureNames = new string[] { "", "en-US", "fr", "fr-FR" };
+        private static readonly string [] s_cultureNames = new string[] { "en-US", "fr", "fr-FR" };
 
         // ToLower_TestData_netcore has the data which is specific to netcore framework
         public static IEnumerable<object[]> ToLower_TestData_netcore()
@@ -181,6 +181,11 @@ public static IEnumerable<object[]> ToLower_TestData_netcore()
                 // DESERT CAPITAL LETTER LONG I has a lower case variant (but not on Windows 7).
                 yield return new object[] { cultureName, "\U00010400", PlatformDetection.IsWindows7 ? "\U00010400" : "\U00010428" };
             }
+
+            if (!PlatformDetection.IsNlsGlobalization)
+            {
+                yield return new object[] { "", "\U00010400", PlatformDetection.IsWindows7 ? "\U00010400" : "\U00010428" };
+            }
         }
 
         public static IEnumerable<string> GetTestLocales()
diff --git a/src/libraries/System.IO.Compression.Brotli/Directory.Build.props b/src/libraries/System.IO.Compression.Brotli/Directory.Build.props
index aa25926ea66cf9..8cda5782c1d130 100644
--- a/src/libraries/System.IO.Compression.Brotli/Directory.Build.props
+++ b/src/libraries/System.IO.Compression.Brotli/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>ECMA</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Compression.Brotli/src/System.IO.Compression.Brotli.csproj b/src/libraries/System.IO.Compression.Brotli/src/System.IO.Compression.Brotli.csproj
index 40101d08ad9808..bdb837e5ef95e0 100644
--- a/src/libraries/System.IO.Compression.Brotli/src/System.IO.Compression.Brotli.csproj
+++ b/src/libraries/System.IO.Compression.Brotli/src/System.IO.Compression.Brotli.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.IO.Compression.Brotli</AssemblyName>
-    <OutputType>Library</OutputType>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.IO.Compression.ZipFile/Directory.Build.props b/src/libraries/System.IO.Compression.ZipFile/Directory.Build.props
index aa25926ea66cf9..8cda5782c1d130 100644
--- a/src/libraries/System.IO.Compression.ZipFile/Directory.Build.props
+++ b/src/libraries/System.IO.Compression.ZipFile/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>ECMA</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Compression.ZipFile/src/System.IO.Compression.ZipFile.csproj b/src/libraries/System.IO.Compression.ZipFile/src/System.IO.Compression.ZipFile.csproj
index ca1e0b34350237..366de34f8b92df 100644
--- a/src/libraries/System.IO.Compression.ZipFile/src/System.IO.Compression.ZipFile.csproj
+++ b/src/libraries/System.IO.Compression.ZipFile/src/System.IO.Compression.ZipFile.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.IO.Compression.ZipFile</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.IO.Compression/Directory.Build.props b/src/libraries/System.IO.Compression/Directory.Build.props
index aa25926ea66cf9..8cda5782c1d130 100644
--- a/src/libraries/System.IO.Compression/Directory.Build.props
+++ b/src/libraries/System.IO.Compression/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>ECMA</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Compression/src/System.IO.Compression.csproj b/src/libraries/System.IO.Compression/src/System.IO.Compression.csproj
index 8ec233ee5dec9c..e22bba9c0c1000 100644
--- a/src/libraries/System.IO.Compression/src/System.IO.Compression.csproj
+++ b/src/libraries/System.IO.Compression/src/System.IO.Compression.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.IO.Compression</AssemblyName>
-    <OutputType>Library</OutputType>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.IO.FileSystem.AccessControl/Directory.Build.props b/src/libraries/System.IO.FileSystem.AccessControl/Directory.Build.props
index 27a4a5522a2778..33e65b7cb46516 100644
--- a/src/libraries/System.IO.FileSystem.AccessControl/Directory.Build.props
+++ b/src/libraries/System.IO.FileSystem.AccessControl/Directory.Build.props
@@ -2,8 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
-    <IsNETCoreAppRef>false</IsNETCoreAppRef>
     <IsWindowsSpecific>true</IsWindowsSpecific>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.FileSystem.AccessControl/ref/System.IO.FileSystem.AccessControl.csproj b/src/libraries/System.IO.FileSystem.AccessControl/ref/System.IO.FileSystem.AccessControl.csproj
index ed7f15c6b99034..33c93c6d81950e 100644
--- a/src/libraries/System.IO.FileSystem.AccessControl/ref/System.IO.FileSystem.AccessControl.csproj
+++ b/src/libraries/System.IO.FileSystem.AccessControl/ref/System.IO.FileSystem.AccessControl.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkCurrent);net461</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -11,9 +10,6 @@
   <ItemGroup>
     <Compile Include="System.IO.FileSystem.AccessControl.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-  </ItemGroup>
   <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
     <ProjectReference Include="..\..\System.Security.AccessControl\ref\System.Security.AccessControl.csproj" />
     <ProjectReference Include="..\..\System.Security.Principal.Windows\ref\System.Security.Principal.Windows.csproj" />
diff --git a/src/libraries/System.IO.FileSystem.AccessControl/src/System.IO.FileSystem.AccessControl.csproj b/src/libraries/System.IO.FileSystem.AccessControl/src/System.IO.FileSystem.AccessControl.csproj
index 3d496a69c3f217..e7f893498e48a3 100644
--- a/src/libraries/System.IO.FileSystem.AccessControl/src/System.IO.FileSystem.AccessControl.csproj
+++ b/src/libraries/System.IO.FileSystem.AccessControl/src/System.IO.FileSystem.AccessControl.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netstandard2.0-Windows_NT;net461-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netstandard2.0-Windows_NT;net461-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -99,27 +98,26 @@
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
     <Compile Include="System\IO\FileSystemAclExtensions.net46.cs" />
   </ItemGroup>
-  <!-- Reference includes -->
-  <ItemGroup Condition="'$(TargetsWindows)' == 'true' and !$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="System.Buffers" />
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="System.Threading.Tasks" />
+  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\src\System.Security.AccessControl.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Runtime" />
-  </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <Reference Include="System.Buffers" Condition="'$(TargetsWindows)' == 'true'" />
+    <Reference Include="System.Collections" Condition="'$(TargetsWindows)' == 'true'" />
     <Reference Include="System.Collections.NonGeneric" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.IO.FileSystem" />
+    <Reference Include="System.Memory" Condition="'$(TargetsWindows)' == 'true'" />
     <Reference Include="System.Resources.ResourceManager" />
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.Handles" />
-    <Reference Include="System.Security.AccessControl" />
-    <Reference Include="System.Security.Principal.Windows" />
+    <Reference Include="System.Runtime.InteropServices" Condition="'$(TargetsWindows)' == 'true'" />
+    <Reference Include="System.Threading.Tasks" Condition="'$(TargetsWindows)' == 'true'" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard'))">
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.IO.FileSystem.AccessControl/tests/DirectoryObjectSecurityTests.cs b/src/libraries/System.IO.FileSystem.AccessControl/tests/DirectoryObjectSecurityTests.cs
index 7f8998a27ca1bf..fd14735f299a57 100644
--- a/src/libraries/System.IO.FileSystem.AccessControl/tests/DirectoryObjectSecurityTests.cs
+++ b/src/libraries/System.IO.FileSystem.AccessControl/tests/DirectoryObjectSecurityTests.cs
@@ -67,7 +67,6 @@ public void ObjectInitialization_InvalidSecurityDescriptor()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/23972", TargetFrameworkMonikers.NetFramework)]
         public void GetAccessRules_InvalidTargetType()
         {
             var activeDirectorySecurity = new ActiveDirectorySecurity();
diff --git a/src/libraries/System.IO.FileSystem.AccessControl/tests/FileSystemAclExtensionsTests.cs b/src/libraries/System.IO.FileSystem.AccessControl/tests/FileSystemAclExtensionsTests.cs
index b5dd1f492fd588..431e8e4154e22c 100644
--- a/src/libraries/System.IO.FileSystem.AccessControl/tests/FileSystemAclExtensionsTests.cs
+++ b/src/libraries/System.IO.FileSystem.AccessControl/tests/FileSystemAclExtensionsTests.cs
@@ -478,7 +478,7 @@ public void DirectorySecurity_CreateDirectory_DirectoryAlreadyExists()
             string path = Path.Combine(directory.Path, "createMe");
 
             DirectorySecurity basicSecurity = new DirectorySecurity();
-            DirectoryInfo basicDirInfo = basicSecurity.CreateDirectory(path);
+            basicSecurity.CreateDirectory(path);
 
             Assert.True(Directory.Exists(path));
 
@@ -534,7 +534,7 @@ private void Verify_DirectorySecurity_CreateDirectory(DirectorySecurity expected
             using var directory = new TempDirectory();
             string path = Path.Combine(directory.Path, "createMe");
 
-            DirectoryInfo createdInfo = expectedSecurity.CreateDirectory(path);
+            expectedSecurity.CreateDirectory(path);
 
             Assert.True(Directory.Exists(path));
 
diff --git a/src/libraries/System.IO.FileSystem.AccessControl/tests/FileSystemSecurityTests.cs b/src/libraries/System.IO.FileSystem.AccessControl/tests/FileSystemSecurityTests.cs
index 922604febf6991..b2730208c0e8f7 100644
--- a/src/libraries/System.IO.FileSystem.AccessControl/tests/FileSystemSecurityTests.cs
+++ b/src/libraries/System.IO.FileSystem.AccessControl/tests/FileSystemSecurityTests.cs
@@ -423,7 +423,7 @@ public void DirNotFound_DirectorySecurity()
             // - NetCore: a valid name because long paths are correctly handled, and non-existent, as expected
             AssertExtensions.Throws<DirectoryNotFoundException, ArgumentException>(() =>
             {
-                var security = new DirectorySecurity(longDir, AccessControlSections.Owner);
+                new DirectorySecurity(longDir, AccessControlSections.Owner);
             });
             
         }
@@ -440,7 +440,7 @@ public void FileNotFound_FileSecurity()
             // - NetCore: a valid name because long paths are correctly handled, and non-existent, as expected
             AssertExtensions.Throws<FileNotFoundException, ArgumentException>(() =>
             {
-                var security = new FileSecurity(filePath, AccessControlSections.Owner);
+                new FileSecurity(filePath, AccessControlSections.Owner);
             });
         }
 
diff --git a/src/libraries/System.IO.FileSystem.AccessControl/tests/System.IO.FileSystem.AccessControl.Tests.csproj b/src/libraries/System.IO.FileSystem.AccessControl/tests/System.IO.FileSystem.AccessControl.Tests.csproj
index 2130178404f347..663ab486f555bc 100644
--- a/src/libraries/System.IO.FileSystem.AccessControl/tests/System.IO.FileSystem.AccessControl.Tests.csproj
+++ b/src/libraries/System.IO.FileSystem.AccessControl/tests/System.IO.FileSystem.AccessControl.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="DirectoryObjectSecurityTests.cs" />
@@ -14,4 +14,13 @@
     <Compile Include="FileSystemSecurityTests.cs" />
     <Compile Include="Helpers.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.IO.FileSystem.AccessControl.csproj" SkipUseReferenceAssembly="true" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices\src\System.DirectoryServices.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.DirectoryServices" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.IO.FileSystem.DriveInfo/Directory.Build.props b/src/libraries/System.IO.FileSystem.DriveInfo/Directory.Build.props
index 42c6eafce67ed8..d68d22c1b917f8 100644
--- a/src/libraries/System.IO.FileSystem.DriveInfo/Directory.Build.props
+++ b/src/libraries/System.IO.FileSystem.DriveInfo/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.FileSystem.DriveInfo/ref/System.IO.FileSystem.DriveInfo.cs b/src/libraries/System.IO.FileSystem.DriveInfo/ref/System.IO.FileSystem.DriveInfo.cs
index cc5e3b7735695a..19e8f51412b35f 100644
--- a/src/libraries/System.IO.FileSystem.DriveInfo/ref/System.IO.FileSystem.DriveInfo.cs
+++ b/src/libraries/System.IO.FileSystem.DriveInfo/ref/System.IO.FileSystem.DriveInfo.cs
@@ -18,7 +18,7 @@ public DriveInfo(string driveName) { }
         public long TotalFreeSpace { get { throw null; } }
         public long TotalSize { get { throw null; } }
         [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
-        public string VolumeLabel { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
+        public string VolumeLabel { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
         public static System.IO.DriveInfo[] GetDrives() { throw null; }
         void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         public override string ToString() { throw null; }
diff --git a/src/libraries/System.IO.FileSystem.DriveInfo/src/System/IO/DriveInfo.UnixOrBrowser.cs b/src/libraries/System.IO.FileSystem.DriveInfo/src/System/IO/DriveInfo.UnixOrBrowser.cs
index 89ac3ae7ad5ff0..51892986a5df68 100644
--- a/src/libraries/System.IO.FileSystem.DriveInfo/src/System/IO/DriveInfo.UnixOrBrowser.cs
+++ b/src/libraries/System.IO.FileSystem.DriveInfo/src/System/IO/DriveInfo.UnixOrBrowser.cs
@@ -42,7 +42,7 @@ public string VolumeLabel
             {
                 return Name;
             }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 throw new PlatformNotSupportedException();
diff --git a/src/libraries/System.IO.FileSystem.DriveInfo/src/System/IO/DriveInfo.Windows.cs b/src/libraries/System.IO.FileSystem.DriveInfo/src/System/IO/DriveInfo.Windows.cs
index df7eadd5e1e5da..d361611377ed15 100644
--- a/src/libraries/System.IO.FileSystem.DriveInfo/src/System/IO/DriveInfo.Windows.cs
+++ b/src/libraries/System.IO.FileSystem.DriveInfo/src/System/IO/DriveInfo.Windows.cs
@@ -59,7 +59,7 @@ public long AvailableFreeSpace
                 finally
                 {
                     if (success)
-                        Interop.Kernel32.SetThreadErrorMode(oldMode, out oldMode);
+                        Interop.Kernel32.SetThreadErrorMode(oldMode, out _);
                 }
                 return userBytes;
             }
@@ -81,7 +81,7 @@ public long TotalFreeSpace
                 finally
                 {
                     if (success)
-                        Interop.Kernel32.SetThreadErrorMode(oldMode, out oldMode);
+                        Interop.Kernel32.SetThreadErrorMode(oldMode, out _);
                 }
                 return freeBytes;
             }
@@ -95,7 +95,7 @@ public long TotalSize
                 // or other various removable media drives.
                 long userBytes, totalBytes, freeBytes;
                 uint oldMode;
-                bool success = Interop.Kernel32.SetThreadErrorMode(Interop.Kernel32.SEM_FAILCRITICALERRORS, out oldMode);
+                Interop.Kernel32.SetThreadErrorMode(Interop.Kernel32.SEM_FAILCRITICALERRORS, out oldMode);
                 try
                 {
                     bool r = Interop.Kernel32.GetDiskFreeSpaceEx(Name, out userBytes, out totalBytes, out freeBytes);
@@ -104,7 +104,7 @@ public long TotalSize
                 }
                 finally
                 {
-                    Interop.Kernel32.SetThreadErrorMode(oldMode, out oldMode);
+                    Interop.Kernel32.SetThreadErrorMode(oldMode, out _);
                 }
                 return totalBytes;
             }
@@ -139,7 +139,7 @@ public unsafe string VolumeLabel
 
                 return new string(volumeName);
             }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 uint oldMode;
@@ -159,7 +159,7 @@ public unsafe string VolumeLabel
                 finally
                 {
                     if (success)
-                        Interop.Kernel32.SetThreadErrorMode(oldMode, out oldMode);
+                        Interop.Kernel32.SetThreadErrorMode(oldMode, out _);
                 }
             }
         }
diff --git a/src/libraries/System.IO.FileSystem.Primitives/Directory.Build.props b/src/libraries/System.IO.FileSystem.Primitives/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.IO.FileSystem.Primitives/Directory.Build.props
+++ b/src/libraries/System.IO.FileSystem.Primitives/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.FileSystem.Primitives/src/System.IO.FileSystem.Primitives.csproj b/src/libraries/System.IO.FileSystem.Primitives/src/System.IO.FileSystem.Primitives.csproj
index 3297291a29533c..94d0c640130480 100644
--- a/src/libraries/System.IO.FileSystem.Primitives/src/System.IO.FileSystem.Primitives.csproj
+++ b/src/libraries/System.IO.FileSystem.Primitives/src/System.IO.FileSystem.Primitives.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.IO.FileSystem.Primitives</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.IO.FileSystem.Watcher/Directory.Build.props b/src/libraries/System.IO.FileSystem.Watcher/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.IO.FileSystem.Watcher/Directory.Build.props
+++ b/src/libraries/System.IO.FileSystem.Watcher/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.FileSystem.Watcher/src/Resources/Strings.resx b/src/libraries/System.IO.FileSystem.Watcher/src/Resources/Strings.resx
index 1a3a137fe01272..c16582a79cc7f3 100644
--- a/src/libraries/System.IO.FileSystem.Watcher/src/Resources/Strings.resx
+++ b/src/libraries/System.IO.FileSystem.Watcher/src/Resources/Strings.resx
@@ -192,6 +192,6 @@
     <value>The path '{0}' is too long, or a component of the specified path is too long.</value>
   </data>
   <data name="FileSystemWatcher_PlatformNotSupported" xml:space="preserve">
-    <value>System.IO.FileSystem.Watcher is not supported on Browser.</value>
+    <value>System.IO.FileSystem.Watcher is not supported on this platform.</value>
   </data>
 </root>
diff --git a/src/libraries/System.IO.FileSystem/Directory.Build.props b/src/libraries/System.IO.FileSystem/Directory.Build.props
index 42c6eafce67ed8..d68d22c1b917f8 100644
--- a/src/libraries/System.IO.FileSystem/Directory.Build.props
+++ b/src/libraries/System.IO.FileSystem/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.FileSystem/ref/System.IO.FileSystem.cs b/src/libraries/System.IO.FileSystem/ref/System.IO.FileSystem.cs
index 953c048a7943c3..e6fbef2727e0ba 100644
--- a/src/libraries/System.IO.FileSystem/ref/System.IO.FileSystem.cs
+++ b/src/libraries/System.IO.FileSystem/ref/System.IO.FileSystem.cs
@@ -121,10 +121,10 @@ public static void Copy(string sourceFileName, string destFileName, bool overwri
         public static System.IO.FileStream Create(string path, int bufferSize) { throw null; }
         public static System.IO.FileStream Create(string path, int bufferSize, System.IO.FileOptions options) { throw null; }
         public static System.IO.StreamWriter CreateText(string path) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static void Decrypt(string path) { }
         public static void Delete(string path) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static void Encrypt(string path) { }
         public static bool Exists(string? path) { throw null; }
         public static System.IO.FileAttributes GetAttributes(string path) { throw null; }
diff --git a/src/libraries/System.IO.FileSystem/src/System.IO.FileSystem.csproj b/src/libraries/System.IO.FileSystem/src/System.IO.FileSystem.csproj
index df5ddd614c29f2..f7d2d0c5499a70 100644
--- a/src/libraries/System.IO.FileSystem/src/System.IO.FileSystem.csproj
+++ b/src/libraries/System.IO.FileSystem/src/System.IO.FileSystem.csproj
@@ -1,11 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.IO.FileSystem</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
+  <PropertyGroup Condition="'$(TargetsBrowser)' == 'true'">
+    <DefineConstants>$(DefineConstants);TARGET_BROWSER</DefineConstants>
+  </PropertyGroup>
   <ItemGroup>
     <!-- System.IO.Enumeration.FileSystemEntry is not correctly parsed by CsharpAnalyser so we are skipping this type from autogenerated typeforwards file.  -->
     <GenFacadesIgnoreMissingType Include="System.IO.Enumeration.FileSystemEntry" />
@@ -178,8 +180,6 @@
              Link="Interop\Unix\Interop.Errors.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.IOErrors.cs"
              Link="Interop\Unix\Interop.IOErrors.cs" />
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetEUid.cs"
-             Link="Common\Interop\Unix\Interop.GetEUid.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.MountPoints.cs"
              Link="Common\Interop\Unix\Interop.MountPoints.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.Permissions.cs"
@@ -193,7 +193,9 @@
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.Unlink.cs"
              Link="Common\Interop\Unix\Interop.Unlink.cs" />
     <Compile Include="$(CoreLibSharedDir)System\IO\DriveInfoInternal.Unix.cs"
-             Link="Common\System\IO\DriveInfoInternal.Unix.cs" />
+             Link="Common\System\IO\DriveInfoInternal.Unix.cs" Condition="'$(TargetsBrowser)' != 'true'" />
+    <Compile Include="$(CoreLibSharedDir)System\IO\DriveInfoInternal.Browser.cs"
+             Link="Common\System\IO\DriveInfoInternal.Browser.cs" Condition="'$(TargetsBrowser)' == 'true'" />
     <Compile Include="$(CoreLibSharedDir)System\IO\PathInternal.Unix.cs"
              Link="System\IO\PathInternal.Unix.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Libraries.cs"
@@ -202,8 +204,6 @@
              Link="Common\Interop\Unix\Interop.ChMod.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.CopyFile.cs"
              Link="Common\Interop\Unix\Interop.CopyFile.cs" />
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetEGid.cs"
-             Link="Common\Interop\Unix\Interop.GetEGid.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.LChflags.cs"
              Link="Common\Interop\Unix\Interop.LChflags.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.Link.cs"
@@ -227,6 +227,12 @@
     <Compile Include="System\IO\FileSystem.Unix.cs" />
     <Compile Include="System\IO\FileSystemInfo.Unix.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetEUid.cs"
+             Link="Common\Interop\Unix\Interop.GetEUid.cs" />
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetEGid.cs"
+             Link="Common\Interop\Unix\Interop.GetEGid.cs" />
+  </ItemGroup>
   <!-- Unix references -->
   <ItemGroup Condition="'$(TargetsUnix)' == 'true' or '$(TargetsBrowser)' == 'true'">
     <Reference Include="System.Threading" />
diff --git a/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.Unix.cs b/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.Unix.cs
index 029f9cd895360e..95bb53f43ba8f6 100644
--- a/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.Unix.cs
+++ b/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.Unix.cs
@@ -25,7 +25,7 @@ public unsafe abstract partial class FileSystemEnumerator<TResult> : CriticalFin
         private Queue<string>? _pending;
 
         private Interop.Sys.DirectoryEntry _entry;
-        private TResult _current = default!;
+        private TResult? _current;
 
         // Used for creating full paths
         private char[]? _pathBuffer;
diff --git a/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.Windows.cs b/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.Windows.cs
index 69084acc3d6bc3..32fd206ea897df 100644
--- a/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.Windows.cs
+++ b/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.Windows.cs
@@ -31,7 +31,7 @@ public unsafe abstract partial class FileSystemEnumerator<TResult> : CriticalFin
         private readonly object _lock = new object();
 
         private Interop.NtDll.FILE_FULL_DIR_INFORMATION* _entry;
-        private TResult _current = default!;
+        private TResult? _current;
 
         private IntPtr _buffer;
         private int _bufferLength;
diff --git a/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.cs b/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.cs
index c3d4a978066c3e..b5168eb1ab059a 100644
--- a/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.cs
+++ b/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerator.cs
@@ -69,7 +69,7 @@ protected virtual void OnDirectoryFinished(ReadOnlySpan<char> directory) { }
         /// <param name="error">The native error code.</param>
         protected virtual bool ContinueOnError(int error) => false;
 
-        public TResult Current => _current;
+        public TResult Current => _current!;
 
         object? IEnumerator.Current => Current;
 
diff --git a/src/libraries/System.IO.FileSystem/src/System/IO/File.cs b/src/libraries/System.IO.FileSystem/src/System/IO/File.cs
index 2e5909c15a03d3..1b089a91ffc883 100644
--- a/src/libraries/System.IO.FileSystem/src/System/IO/File.cs
+++ b/src/libraries/System.IO.FileSystem/src/System/IO/File.cs
@@ -328,7 +328,7 @@ public static void WriteAllText(string path, string? contents, Encoding encoding
         public static byte[] ReadAllBytes(string path)
         {
             // bufferSize == 1 used to avoid unnecessary buffer in FileStream
-            using (FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize: 1))
+            using (FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize: 1, FileOptions.SequentialScan))
             {
                 long fileLength = fs.Length;
                 if (fileLength > int.MaxValue)
@@ -646,13 +646,13 @@ public static void Move(string sourceFileName, string destFileName, bool overwri
             FileSystem.MoveFile(fullSourceFileName, fullDestFileName, overwrite);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static void Encrypt(string path)
         {
             FileSystem.Encrypt(path ?? throw new ArgumentNullException(nameof(path)));
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static void Decrypt(string path)
         {
             FileSystem.Decrypt(path ?? throw new ArgumentNullException(nameof(path)));
diff --git a/src/libraries/System.IO.FileSystem/src/System/IO/FileStatus.Unix.cs b/src/libraries/System.IO.FileSystem/src/System/IO/FileStatus.Unix.cs
index 086c09039f02e6..e32d3a1c54dfdb 100644
--- a/src/libraries/System.IO.FileSystem/src/System/IO/FileStatus.Unix.cs
+++ b/src/libraries/System.IO.FileSystem/src/System/IO/FileStatus.Unix.cs
@@ -39,7 +39,12 @@ internal static void Initialize(
         internal bool IsReadOnly(ReadOnlySpan<char> path, bool continueOnError = false)
         {
             EnsureStatInitialized(path, continueOnError);
+#if TARGET_BROWSER
+            const Interop.Sys.Permissions readBit = Interop.Sys.Permissions.S_IRUSR;
+            const Interop.Sys.Permissions writeBit = Interop.Sys.Permissions.S_IWUSR;
+#else
             Interop.Sys.Permissions readBit, writeBit;
+
             if (_fileStatus.Uid == Interop.Sys.GetEUid())
             {
                 // User effectively owns the file
@@ -58,6 +63,7 @@ internal bool IsReadOnly(ReadOnlySpan<char> path, bool continueOnError = false)
                 readBit = Interop.Sys.Permissions.S_IROTH;
                 writeBit = Interop.Sys.Permissions.S_IWOTH;
             }
+#endif
 
             return ((_fileStatus.Mode & (int)readBit) != 0 && // has read permission
                 (_fileStatus.Mode & (int)writeBit) == 0);     // but not write permission
diff --git a/src/libraries/System.IO.FileSystem/src/System/IO/FileSystem.Unix.cs b/src/libraries/System.IO.FileSystem/src/System/IO/FileSystem.Unix.cs
index cb39fcb7e03047..df790a51b8d9f6 100644
--- a/src/libraries/System.IO.FileSystem/src/System/IO/FileSystem.Unix.cs
+++ b/src/libraries/System.IO.FileSystem/src/System/IO/FileSystem.Unix.cs
@@ -381,6 +381,19 @@ public static void MoveDirectory(string sourceFullPath, string destFullPath)
                 throw new IOException(SR.Format(SR.IO_AlreadyExists_Name, destFullPath));
             }
 
+#if TARGET_BROWSER
+            // renaming a file doesn't return correct error code on emscripten if one of the parent paths does not exist,
+            // manually workaround it for now (https://github.com/dotnet/runtime/issues/40305)
+            if (!Directory.Exists(Path.GetDirectoryName(sourceFullPath)))
+            {
+                throw new DirectoryNotFoundException(SR.Format(SR.IO_PathNotFound_Path, sourceFullPath));
+            }
+            if (!Directory.Exists(Path.GetDirectoryName(destFullPath)))
+            {
+                throw new DirectoryNotFoundException(SR.Format(SR.IO_PathNotFound_Path, destFullPath));
+            }
+#endif
+
             if (Interop.Sys.Rename(sourceFullPath, destFullPath) < 0)
             {
                 Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
diff --git a/src/libraries/System.IO.FileSystem/src/System/IO/Iterator.cs b/src/libraries/System.IO.FileSystem/src/System/IO/Iterator.cs
index 49c4b4cfd378e5..09bf15d98a4724 100644
--- a/src/libraries/System.IO.FileSystem/src/System/IO/Iterator.cs
+++ b/src/libraries/System.IO.FileSystem/src/System/IO/Iterator.cs
@@ -14,18 +14,14 @@ internal abstract class Iterator<TSource> : IEnumerable<TSource>, IEnumerator<TS
     {
         private readonly int _threadId;
         internal int state;
-        [MaybeNull, AllowNull]
-        internal TSource current = default;
+        internal TSource? current;
 
         public Iterator()
         {
             _threadId = Environment.CurrentManagedThreadId;
         }
 
-        public TSource Current
-        {
-            get { return current!; }
-        }
+        public TSource Current => current!;
 
         protected abstract Iterator<TSource> Clone();
 
@@ -37,7 +33,7 @@ public void Dispose()
 
         protected virtual void Dispose(bool disposing)
         {
-            current = default(TSource)!;
+            current = default;
             state = -1;
         }
 
diff --git a/src/libraries/System.IO.FileSystem/tests/Directory/EnumerableAPIs.cs b/src/libraries/System.IO.FileSystem/tests/Directory/EnumerableAPIs.cs
index c160e3e989069f..76e5a440b764fd 100644
--- a/src/libraries/System.IO.FileSystem/tests/Directory/EnumerableAPIs.cs
+++ b/src/libraries/System.IO.FileSystem/tests/Directory/EnumerableAPIs.cs
@@ -94,8 +94,8 @@ public void Clone_Enumerator_Trimmed_SearchPattern()
         public void Delete_Directory_After_Creating_Enumerable()
         {
             DirectoryInfo testDir = Directory.CreateDirectory(GetTestFilePath());
-            DirectoryInfo subDir1 = Directory.CreateDirectory(Path.Combine(testDir.FullName, "a"));
-            DirectoryInfo subDir2 = Directory.CreateDirectory(Path.Combine(testDir.FullName, "b"));
+            Directory.CreateDirectory(Path.Combine(testDir.FullName, "a"));
+            Directory.CreateDirectory(Path.Combine(testDir.FullName, "b"));
             var enumerator = Directory.EnumerateDirectories(testDir.FullName);
             foreach (var dir in enumerator)
             {
@@ -110,8 +110,8 @@ public void Trailing_Slash_Adds_Trailing_Star()
         {
             // A searchpattern of c:\temp\ will become c:\temp\* internally
             DirectoryInfo testDir = Directory.CreateDirectory(GetTestFilePath());
-            DirectoryInfo subDir1 = Directory.CreateDirectory(Path.Combine(testDir.FullName, "a"));
-            DirectoryInfo subDir2 = Directory.CreateDirectory(Path.Combine(testDir.FullName, "b"));
+            Directory.CreateDirectory(Path.Combine(testDir.FullName, "a"));
+            Directory.CreateDirectory(Path.Combine(testDir.FullName, "b"));
             var enumerator = Directory.EnumerateDirectories(testDir.FullName, "a" + Path.DirectorySeparatorChar);
             Assert.Equal(0, enumerator.ToArray().Length);
         }
diff --git a/src/libraries/System.IO.FileSystem/tests/Directory/Exists.cs b/src/libraries/System.IO.FileSystem/tests/Directory/Exists.cs
index 248d0b3c218783..cfe5834f53d375 100644
--- a/src/libraries/System.IO.FileSystem/tests/Directory/Exists.cs
+++ b/src/libraries/System.IO.FileSystem/tests/Directory/Exists.cs
@@ -44,7 +44,7 @@ public void NonExistentValidPath_ReturnsFalse(string path)
         public void ValidPathExists_ReturnsTrue(string component)
         {
             string path = Path.Combine(TestDirectory, component);
-            DirectoryInfo testDir = Directory.CreateDirectory(path);
+            Directory.CreateDirectory(path);
             Assert.True(Exists(path));
         }
 
@@ -73,7 +73,7 @@ public void PathAlreadyExistsAsFile()
         public void PathAlreadyExistsAsDirectory()
         {
             string path = GetTestFilePath();
-            DirectoryInfo testDir = Directory.CreateDirectory(path);
+            Directory.CreateDirectory(path);
 
             Assert.True(Exists(IOServices.RemoveTrailingSlash(path)));
             Assert.True(Exists(IOServices.RemoveTrailingSlash(IOServices.RemoveTrailingSlash(path))));
@@ -177,7 +177,7 @@ public void SymlinkToNewDirectory()
         public void ValidExtendedPathExists_ReturnsTrue(string component)
         {
             string path = IOInputs.ExtendedPrefix + Path.Combine(TestDirectory, "extended", component);
-            DirectoryInfo testDir = Directory.CreateDirectory(path);
+            Directory.CreateDirectory(path);
             Assert.True(Exists(path));
         }
 
@@ -198,7 +198,7 @@ public void ExtendedPathAlreadyExistsAsFile()
         public void ExtendedPathAlreadyExistsAsDirectory()
         {
             string path = IOInputs.ExtendedPrefix + GetTestFilePath();
-            DirectoryInfo testDir = Directory.CreateDirectory(path);
+            Directory.CreateDirectory(path);
 
             Assert.True(Exists(IOServices.RemoveTrailingSlash(path)));
             Assert.True(Exists(IOServices.RemoveTrailingSlash(IOServices.RemoveTrailingSlash(path))));
@@ -278,7 +278,7 @@ public void TrailingSpaceExists(string component)
         {
             // Windows trims spaces
             string path = GetTestFilePath();
-            DirectoryInfo testDir = Directory.CreateDirectory(path + component);
+            Directory.CreateDirectory(path + component);
             Assert.True(Exists(path), "can find without space");
             Assert.True(Exists(path + component), "can find with space");
         }
diff --git a/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str.cs b/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str.cs
index a9fbc242833c29..642439142ac000 100644
--- a/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str.cs
+++ b/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str.cs
@@ -208,7 +208,7 @@ public void InvalidPath_Core()
         {
             foreach (char invalid in Path.GetInvalidFileNameChars())
             {
-                string badPath = string.Format($"{TestDirectory}{Path.DirectorySeparatorChar}te{invalid}st");
+                string badPath = $"{TestDirectory}{Path.DirectorySeparatorChar}te{invalid}st";
                 switch (invalid)
                 {
                     case '/':
diff --git a/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str_str.cs b/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str_str.cs
index 6e557c5874df60..5a8c5150fd09f1 100644
--- a/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str_str.cs
+++ b/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str_str.cs
@@ -682,7 +682,7 @@ public virtual void WindowsSearchPatternQuestionMarks()
         {
             string testDir1Str = GetTestFileName();
             DirectoryInfo testDir = new DirectoryInfo(TestDirectory);
-            DirectoryInfo testDir1 = testDir.CreateSubdirectory(testDir1Str);
+            testDir.CreateSubdirectory(testDir1Str);
 
             using (File.Create(Path.Combine(TestDirectory, testDir1Str, GetTestFileName())))
             using (File.Create(Path.Combine(TestDirectory, GetTestFileName())))
diff --git a/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str_str_so.cs b/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str_str_so.cs
index 7410d20492f77a..c18f14e5bc4836 100644
--- a/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str_str_so.cs
+++ b/src/libraries/System.IO.FileSystem/tests/Directory/GetFileSystemEntries_str_str_so.cs
@@ -32,7 +32,7 @@ public override void WindowsSearchPatternQuestionMarks()
         {
             string testDir1Str = GetTestFileName();
             DirectoryInfo testDir = new DirectoryInfo(TestDirectory);
-            DirectoryInfo testDir1 = testDir.CreateSubdirectory(testDir1Str);
+            testDir.CreateSubdirectory(testDir1Str);
 
             using (File.Create(Path.Combine(TestDirectory, testDir1Str, GetTestFileName())))
             using (File.Create(Path.Combine(TestDirectory, GetTestFileName())))
diff --git a/src/libraries/System.IO.FileSystem/tests/Directory/SetCurrentDirectory.cs b/src/libraries/System.IO.FileSystem/tests/Directory/SetCurrentDirectory.cs
index 04e636582d7e24..16287ef7b3f455 100644
--- a/src/libraries/System.IO.FileSystem/tests/Directory/SetCurrentDirectory.cs
+++ b/src/libraries/System.IO.FileSystem/tests/Directory/SetCurrentDirectory.cs
@@ -64,8 +64,6 @@ public void SetToPathContainingSymLink()
                     Assert.True(Directory.Exists(linkPath), "linkPath should exist");
 
                     // Set Current Directory to symlink
-                    string currentDir = Directory.GetCurrentDirectory();
-
                     Directory.SetCurrentDirectory(linkPath);
                     if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
                     {
diff --git a/src/libraries/System.IO.FileSystem/tests/Enumeration/ErrorHandlingTests.cs b/src/libraries/System.IO.FileSystem/tests/Enumeration/ErrorHandlingTests.cs
index e6858057bf4f60..2c330cb0b2e708 100644
--- a/src/libraries/System.IO.FileSystem/tests/Enumeration/ErrorHandlingTests.cs
+++ b/src/libraries/System.IO.FileSystem/tests/Enumeration/ErrorHandlingTests.cs
@@ -73,8 +73,11 @@ public void NotFoundErrorIsExpected()
             // Make sure we're returning the native error as expected (and not the PAL error on Unix)
             using (LastError le = new LastError(Path.GetRandomFileName()))
             {
-                // Conveniently ERROR_FILE_NOT_FOUND and ENOENT are both 0x2
-                Assert.Equal(2, le.Error);
+                // while ERROR_FILE_NOT_FOUND/ENOENT have predictable values on Windows, Linux and Mac,
+                //  we can't rely on ENOENT having the same value on other platforms. Instead, assert
+                //  that we didn't get the PAL error because we know its value.
+                const int PAL_Error_ENOENT = 0x1002D;
+                Assert.NotEqual(PAL_Error_ENOENT, le.Error);
             }
         }
 
diff --git a/src/libraries/System.IO.FileSystem/tests/File/Exists.cs b/src/libraries/System.IO.FileSystem/tests/File/Exists.cs
index 9263b48e4b6c20..40d5ebce3d4b77 100644
--- a/src/libraries/System.IO.FileSystem/tests/File/Exists.cs
+++ b/src/libraries/System.IO.FileSystem/tests/File/Exists.cs
@@ -104,7 +104,7 @@ public void PathEndsInAltTrailingSlash_AndExists_Windows()
         public void PathAlreadyExistsAsDirectory()
         {
             string path = GetTestFilePath();
-            DirectoryInfo testDir = Directory.CreateDirectory(path);
+            Directory.CreateDirectory(path);
 
             Assert.False(Exists(IOServices.RemoveTrailingSlash(path)));
             Assert.False(Exists(IOServices.RemoveTrailingSlash(IOServices.RemoveTrailingSlash(path))));
diff --git a/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllBytes.cs b/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllBytes.cs
index 46d2e87437355d..33c10d40b84784 100644
--- a/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllBytes.cs
+++ b/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllBytes.cs
@@ -22,7 +22,6 @@ public void NullParameters()
         [Fact]
         public void InvalidParameters()
         {
-            string path = GetTestFilePath();
             Assert.Throws<ArgumentException>(() => File.WriteAllBytes(string.Empty, new byte[0]));
             Assert.Throws<ArgumentException>(() => File.ReadAllBytes(string.Empty));
         }
diff --git a/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllBytesAsync.cs b/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllBytesAsync.cs
index 11779d7de3f1ae..30fc35e97b1e7a 100644
--- a/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllBytesAsync.cs
+++ b/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllBytesAsync.cs
@@ -24,7 +24,6 @@ public async Task NullParametersAsync()
         [Fact]
         public async Task InvalidParametersAsync()
         {
-            string path = GetTestFilePath();
             await Assert.ThrowsAsync<ArgumentException>("path", async () => await File.WriteAllBytesAsync(string.Empty, new byte[0]));
             await Assert.ThrowsAsync<ArgumentException>("path", async () => await File.ReadAllBytesAsync(string.Empty));
         }
diff --git a/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllText.cs b/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllText.cs
index 1062036adfe551..152858cc92388a 100644
--- a/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllText.cs
+++ b/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllText.cs
@@ -28,7 +28,6 @@ protected virtual string Read(string path)
         [Fact]
         public void NullParameters()
         {
-            string path = GetTestFilePath();
             Assert.Throws<ArgumentNullException>(() => Write(null, "Text"));
             Assert.Throws<ArgumentNullException>(() => Read(null));
         }
@@ -58,7 +57,6 @@ public void EmptyStringContent_CreatesFile()
         [Fact]
         public void InvalidParameters()
         {
-            string path = GetTestFilePath();
             Assert.Throws<ArgumentException>(() => Write(string.Empty, "Text"));
             Assert.Throws<ArgumentException>(() => Read(""));
         }
diff --git a/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllTextAsync.cs b/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllTextAsync.cs
index 8b8134462c8959..3d2f1d9d8da6c3 100644
--- a/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllTextAsync.cs
+++ b/src/libraries/System.IO.FileSystem/tests/File/ReadWriteAllTextAsync.cs
@@ -26,7 +26,6 @@ public class File_ReadWriteAllTextAsync : FileSystemTest
         [Fact]
         public async Task NullParametersAsync()
         {
-            string path = GetTestFilePath();
             await Assert.ThrowsAsync<ArgumentNullException>("path", async () => await WriteAsync(null, "Text"));
             await Assert.ThrowsAsync<ArgumentNullException>("path", async () => await ReadAsync(null));
         }
@@ -54,7 +53,6 @@ public async Task EmptyStringContent_CreatesFileAsync()
         [Fact]
         public async Task InvalidParametersAsync()
         {
-            string path = GetTestFilePath();
             await Assert.ThrowsAsync<ArgumentException>("path", async () => await WriteAsync(string.Empty, "Text"));
             await Assert.ThrowsAsync<ArgumentException>("path", async () => await ReadAsync(""));
         }
diff --git a/src/libraries/System.IO.FileSystem/tests/FileInfo/GetSetTimes.cs b/src/libraries/System.IO.FileSystem/tests/FileInfo/GetSetTimes.cs
index 2c92d0c57e60c2..b27adf59f27c85 100644
--- a/src/libraries/System.IO.FileSystem/tests/FileInfo/GetSetTimes.cs
+++ b/src/libraries/System.IO.FileSystem/tests/FileInfo/GetSetTimes.cs
@@ -186,13 +186,10 @@ public void CopyToMillisecondPresent_HFS()
         public void DeleteAfterEnumerate_TimesStillSet()
         {
             // When enumerating we populate the state as we already have it.
-            DateTime beforeTime = DateTime.UtcNow.AddSeconds(-1);
             string filePath = GetTestFilePath();
             File.Create(filePath).Dispose();
             FileInfo info = new DirectoryInfo(TestDirectory).EnumerateFiles().First();
 
-            DateTime afterTime = DateTime.UtcNow.AddSeconds(1);
-
             info.Delete();
             Assert.Equal(DateTime.FromFileTimeUtc(0), info.LastAccessTimeUtc);
         }
diff --git a/src/libraries/System.IO.FileSystem/tests/FileStream/CopyToAsync.cs b/src/libraries/System.IO.FileSystem/tests/FileStream/CopyToAsync.cs
index 20179f5e9e1ca4..da7145719b90d1 100644
--- a/src/libraries/System.IO.FileSystem/tests/FileStream/CopyToAsync.cs
+++ b/src/libraries/System.IO.FileSystem/tests/FileStream/CopyToAsync.cs
@@ -104,7 +104,7 @@ public async Task File_AllDataCopied(
                 // If configured to expose the handle, do so.  This influences the stream's need to ensure the position is in sync.
                 if (exposeHandle)
                 {
-                    var ignored = src.SafeFileHandle;
+                    _ = src.SafeFileHandle;
                 }
 
                 // If configured to "preWrite", do a write before we start reading.
diff --git a/src/libraries/System.IO.FileSystem/tests/FileStream/Dispose.cs b/src/libraries/System.IO.FileSystem/tests/FileStream/Dispose.cs
index 1285c31fad147e..c87ac78705838b 100644
--- a/src/libraries/System.IO.FileSystem/tests/FileStream/Dispose.cs
+++ b/src/libraries/System.IO.FileSystem/tests/FileStream/Dispose.cs
@@ -193,7 +193,7 @@ public void Finalizer_CallsVirtualDispose_FalseArg()
 
             Action act = () => // separate method to avoid JIT lifetime-extension issues
             {
-                var fs2 = new MyFileStream(GetTestFilePath(), FileMode.Create)
+                new MyFileStream(GetTestFilePath(), FileMode.Create)
                 {
                     DisposeMethod = (disposing) =>
                     {
diff --git a/src/libraries/System.IO.FileSystem/tests/FileStream/SafeFileHandle.cs b/src/libraries/System.IO.FileSystem/tests/FileStream/SafeFileHandle.cs
index 00aac7d9b670fc..03b3353931724a 100644
--- a/src/libraries/System.IO.FileSystem/tests/FileStream/SafeFileHandle.cs
+++ b/src/libraries/System.IO.FileSystem/tests/FileStream/SafeFileHandle.cs
@@ -52,7 +52,7 @@ public void AccessFlushesFileClosesHandle()
                 // other handle doesn't yet see the change
                 Assert.Equal(0, fsr.Length);
 
-                SafeFileHandle handle = fs.SafeFileHandle;
+                _ = fs.SafeFileHandle;
 
                 // expect the handle to be flushed
                 Assert.Equal(TestBuffer.Length, fsr.Length);
diff --git a/src/libraries/System.IO.FileSystem/tests/FileStream/WriteAsync.cs b/src/libraries/System.IO.FileSystem/tests/FileStream/WriteAsync.cs
index 47bea8be293cfd..2710edcbf31068 100644
--- a/src/libraries/System.IO.FileSystem/tests/FileStream/WriteAsync.cs
+++ b/src/libraries/System.IO.FileSystem/tests/FileStream/WriteAsync.cs
@@ -311,7 +311,7 @@ public async Task ManyConcurrentWriteAsyncs_OuterLoop(
                 }
                 if (exposeHandle)
                 {
-                    var ignored = fs.SafeFileHandle;
+                    _ = fs.SafeFileHandle;
                 }
 
                 Task[] writes = new Task[numWrites];
diff --git a/src/libraries/System.IO.FileSystem/tests/PortedCommon/CommonUtilities.cs b/src/libraries/System.IO.FileSystem/tests/PortedCommon/CommonUtilities.cs
index f807ab97739926..03737fa30d4255 100644
--- a/src/libraries/System.IO.FileSystem/tests/PortedCommon/CommonUtilities.cs
+++ b/src/libraries/System.IO.FileSystem/tests/PortedCommon/CommonUtilities.cs
@@ -262,9 +262,6 @@ private void CreateFileSystem()
         //we will not include this directory
         //        m_listOfAllDirs.Add(m_startDir);
 
-        string currentWorkingDir = _startDir;
-        string parentDir = _startDir;
-
         _allDirs = new Dictionary<int, Dictionary<string, List<string>>>();
         //        List<String> dirsForOneLevel = new List<String>();
         //        List<String> tempDirsForOneLevel;
@@ -386,72 +383,4 @@ static TestInfo()
     }
 
     public static string CurrentDirectory { get; set; }
-
-    private delegate void ExceptionCode();
-
-    private void DeleteFile(string fileName)
-    {
-        if (File.Exists(fileName))
-            File.Delete(fileName);
-    }
-
-
-    //Checks for error
-    private static bool Eval(bool expression, string msg, params object[] values)
-    {
-        return Eval(expression, string.Format(msg, values));
-    }
-
-    private static bool Eval<T>(T actual, T expected, string errorMsg)
-    {
-        bool retValue = expected == null ? actual == null : expected.Equals(actual);
-
-        if (!retValue)
-            Eval(retValue, errorMsg +
-            " Expected:" + (null == expected ? "<null>" : expected.ToString()) +
-            " Actual:" + (null == actual ? "<null>" : actual.ToString()));
-
-        return retValue;
-    }
-
-    private static bool Eval(bool expression, string msg)
-    {
-        if (!expression)
-        {
-            Console.WriteLine(msg);
-        }
-        return expression;
-    }
-
-    //Checks for a particular type of exception
-    private static void CheckException<E>(ExceptionCode test, string error)
-    {
-        CheckException<E>(test, error, null);
-    }
-
-    //Checks for a particular type of exception and an Exception msg
-    private static void CheckException<E>(ExceptionCode test, string error, string msgExpected)
-    {
-        bool exception = false;
-        try
-        {
-            test();
-            error = string.Format("{0} Exception NOT thrown ", error);
-        }
-        catch (Exception e)
-        {
-            if (e.GetType() == typeof(E))
-            {
-                exception = true;
-                if (System.Globalization.CultureInfo.CurrentUICulture.Name == "en-US" && msgExpected != null && e.Message != msgExpected)
-                {
-                    exception = false;
-                    error = string.Format("{0} Message Different: <{1}>", error, e.Message);
-                }
-            }
-            else
-                error = string.Format("{0} Exception type: {1}", error, e.GetType().Name);
-        }
-        Eval(exception, error);
-    }
 }
diff --git a/src/libraries/System.IO.IsolatedStorage/Directory.Build.props b/src/libraries/System.IO.IsolatedStorage/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.IO.IsolatedStorage/Directory.Build.props
+++ b/src/libraries/System.IO.IsolatedStorage/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.IsolatedStorage/ref/System.IO.IsolatedStorage.cs b/src/libraries/System.IO.IsolatedStorage/ref/System.IO.IsolatedStorage.cs
index b8d23578d7b0d5..776534a95f04f7 100644
--- a/src/libraries/System.IO.IsolatedStorage/ref/System.IO.IsolatedStorage.cs
+++ b/src/libraries/System.IO.IsolatedStorage/ref/System.IO.IsolatedStorage.cs
@@ -63,7 +63,6 @@ public void DeleteFile(string file) { }
         public bool DirectoryExists(string path) { throw null; }
         public void Dispose() { }
         public bool FileExists(string path) { throw null; }
-        ~IsolatedStorageFile() { }
         public System.DateTimeOffset GetCreationTime(string path) { throw null; }
         public string[] GetDirectoryNames() { throw null; }
         public string[] GetDirectoryNames(string searchPattern) { throw null; }
@@ -111,8 +110,8 @@ public partial class IsolatedStorageFileStream : System.IO.FileStream
         public override long Length { get { throw null; } }
         public override long Position { get { throw null; } set { } }
         public override Microsoft.Win32.SafeHandles.SafeFileHandle SafeFileHandle { get { throw null; } }
-        public override System.IAsyncResult BeginRead(byte[] buffer, int offset, int numBytes, System.AsyncCallback? userCallback, object? stateObject) { throw null; }
-        public override System.IAsyncResult BeginWrite(byte[] buffer, int offset, int numBytes, System.AsyncCallback? userCallback, object? stateObject) { throw null; }
+        public override System.IAsyncResult BeginRead(byte[] array, int offset, int numBytes, System.AsyncCallback? userCallback, object? stateObject) { throw null; }
+        public override System.IAsyncResult BeginWrite(byte[] array, int offset, int numBytes, System.AsyncCallback? userCallback, object? stateObject) { throw null; }
         protected override void Dispose(bool disposing) { }
         public override System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }
         public override int EndRead(System.IAsyncResult asyncResult) { throw null; }
diff --git a/src/libraries/System.IO.IsolatedStorage/src/System.IO.IsolatedStorage.csproj b/src/libraries/System.IO.IsolatedStorage/src/System.IO.IsolatedStorage.csproj
index 75bb5e2176c738..066018d64f7c0a 100644
--- a/src/libraries/System.IO.IsolatedStorage/src/System.IO.IsolatedStorage.csproj
+++ b/src/libraries/System.IO.IsolatedStorage/src/System.IO.IsolatedStorage.csproj
@@ -36,8 +36,8 @@
     <Reference Include="System.Runtime" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
-    <Reference Include="System.IO.FileSystem.AccessControl" />
-    <Reference Include="System.Security.AccessControl" />
-    <Reference Include="System.Security.Principal.Windows" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.IO.FileSystem.AccessControl\src\System.IO.FileSystem.AccessControl.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\src\System.Security.AccessControl.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.IO.IsolatedStorage/src/System/IO/IsolatedStorage/Helper.Win32Unix.cs b/src/libraries/System.IO.IsolatedStorage/src/System/IO/IsolatedStorage/Helper.Win32Unix.cs
index 692ddc1d7766c4..33e611115fa28e 100644
--- a/src/libraries/System.IO.IsolatedStorage/src/System/IO/IsolatedStorage/Helper.Win32Unix.cs
+++ b/src/libraries/System.IO.IsolatedStorage/src/System/IO/IsolatedStorage/Helper.Win32Unix.cs
@@ -54,7 +54,9 @@ internal static void GetDefaultIdentityAndHash(out object identity, out string h
                 throw new IsolatedStorageException(SR.IsolatedStorage_Init);
 
             AssemblyName assemblyName = assembly.GetName();
+#pragma warning disable SYSLIB0012
             Uri codeBase = new Uri(assembly.CodeBase!);
+#pragma warning restore SYSLIB0012
 
             hash = IdentityHelper.GetNormalizedStrongNameHash(assemblyName)!;
             if (hash != null)
diff --git a/src/libraries/System.IO.IsolatedStorage/tests/System.IO.IsolatedStorage.Tests.csproj b/src/libraries/System.IO.IsolatedStorage/tests/System.IO.IsolatedStorage.Tests.csproj
index 47504a43fde6a8..57f315d8850619 100644
--- a/src/libraries/System.IO.IsolatedStorage/tests/System.IO.IsolatedStorage.Tests.csproj
+++ b/src/libraries/System.IO.IsolatedStorage/tests/System.IO.IsolatedStorage.Tests.csproj
@@ -52,4 +52,7 @@
     <Compile Include="System\IO\IsolatedStorage\TestHelper.cs" />
     <Compile Include="System\IO\IsolatedStorage\RemoveTests.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices\src\System.DirectoryServices.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.IO.MemoryMappedFiles/Directory.Build.props b/src/libraries/System.IO.MemoryMappedFiles/Directory.Build.props
index 42c6eafce67ed8..d68d22c1b917f8 100644
--- a/src/libraries/System.IO.MemoryMappedFiles/Directory.Build.props
+++ b/src/libraries/System.IO.MemoryMappedFiles/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.MemoryMappedFiles/ref/System.IO.MemoryMappedFiles.cs b/src/libraries/System.IO.MemoryMappedFiles/ref/System.IO.MemoryMappedFiles.cs
index 4748d3acb85b18..e112060f78498d 100644
--- a/src/libraries/System.IO.MemoryMappedFiles/ref/System.IO.MemoryMappedFiles.cs
+++ b/src/libraries/System.IO.MemoryMappedFiles/ref/System.IO.MemoryMappedFiles.cs
@@ -33,11 +33,11 @@ internal MemoryMappedFile() { }
         public static System.IO.MemoryMappedFiles.MemoryMappedFile CreateNew(string? mapName, long capacity) { throw null; }
         public static System.IO.MemoryMappedFiles.MemoryMappedFile CreateNew(string? mapName, long capacity, System.IO.MemoryMappedFiles.MemoryMappedFileAccess access) { throw null; }
         public static System.IO.MemoryMappedFiles.MemoryMappedFile CreateNew(string? mapName, long capacity, System.IO.MemoryMappedFiles.MemoryMappedFileAccess access, System.IO.MemoryMappedFiles.MemoryMappedFileOptions options, System.IO.HandleInheritability inheritability) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.IO.MemoryMappedFiles.MemoryMappedFile CreateOrOpen(string mapName, long capacity) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.IO.MemoryMappedFiles.MemoryMappedFile CreateOrOpen(string mapName, long capacity, System.IO.MemoryMappedFiles.MemoryMappedFileAccess access) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.IO.MemoryMappedFiles.MemoryMappedFile CreateOrOpen(string mapName, long capacity, System.IO.MemoryMappedFiles.MemoryMappedFileAccess access, System.IO.MemoryMappedFiles.MemoryMappedFileOptions options, System.IO.HandleInheritability inheritability) { throw null; }
         public System.IO.MemoryMappedFiles.MemoryMappedViewAccessor CreateViewAccessor() { throw null; }
         public System.IO.MemoryMappedFiles.MemoryMappedViewAccessor CreateViewAccessor(long offset, long size) { throw null; }
@@ -47,11 +47,11 @@ internal MemoryMappedFile() { }
         public System.IO.MemoryMappedFiles.MemoryMappedViewStream CreateViewStream(long offset, long size, System.IO.MemoryMappedFiles.MemoryMappedFileAccess access) { throw null; }
         public void Dispose() { }
         protected virtual void Dispose(bool disposing) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.IO.MemoryMappedFiles.MemoryMappedFile OpenExisting(string mapName) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.IO.MemoryMappedFiles.MemoryMappedFile OpenExisting(string mapName, System.IO.MemoryMappedFiles.MemoryMappedFileRights desiredAccessRights) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.IO.MemoryMappedFiles.MemoryMappedFile OpenExisting(string mapName, System.IO.MemoryMappedFiles.MemoryMappedFileRights desiredAccessRights, System.IO.HandleInheritability inheritability) { throw null; }
     }
     public enum MemoryMappedFileAccess
diff --git a/src/libraries/System.IO.MemoryMappedFiles/src/Microsoft/Win32/SafeMemoryMappedFileHandle.Windows.cs b/src/libraries/System.IO.MemoryMappedFiles/src/Microsoft/Win32/SafeMemoryMappedFileHandle.Windows.cs
index 29a6916bebd9e0..bd0f7ebb13a389 100644
--- a/src/libraries/System.IO.MemoryMappedFiles/src/Microsoft/Win32/SafeMemoryMappedFileHandle.Windows.cs
+++ b/src/libraries/System.IO.MemoryMappedFiles/src/Microsoft/Win32/SafeMemoryMappedFileHandle.Windows.cs
@@ -14,5 +14,7 @@ protected override bool ReleaseHandle()
         {
             return Interop.Kernel32.CloseHandle(handle);
         }
+
+        public override bool IsInvalid => base.IsInvalid;
     }
 }
diff --git a/src/libraries/System.IO.MemoryMappedFiles/src/System.IO.MemoryMappedFiles.csproj b/src/libraries/System.IO.MemoryMappedFiles/src/System.IO.MemoryMappedFiles.csproj
index 587c8045111468..875e392be70807 100644
--- a/src/libraries/System.IO.MemoryMappedFiles/src/System.IO.MemoryMappedFiles.csproj
+++ b/src/libraries/System.IO.MemoryMappedFiles/src/System.IO.MemoryMappedFiles.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.IO.MemoryMappedFiles</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
diff --git a/src/libraries/System.IO.MemoryMappedFiles/src/System/IO/MemoryMappedFiles/MemoryMappedFile.cs b/src/libraries/System.IO.MemoryMappedFiles/src/System/IO/MemoryMappedFiles/MemoryMappedFile.cs
index aed549229ae1db..d2f04e84d27ef9 100644
--- a/src/libraries/System.IO.MemoryMappedFiles/src/System/IO/MemoryMappedFiles/MemoryMappedFile.cs
+++ b/src/libraries/System.IO.MemoryMappedFiles/src/System/IO/MemoryMappedFiles/MemoryMappedFile.cs
@@ -44,19 +44,19 @@ private MemoryMappedFile(SafeMemoryMappedFileHandle handle, FileStream fileStrea
         // the first override of this method.  Note: having ReadWrite access to the object does not mean that we
         // have ReadWrite access to the pages mapping the file.  The OS will check against the access on the pages
         // when a view is created.
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static MemoryMappedFile OpenExisting(string mapName)
         {
             return OpenExisting(mapName, MemoryMappedFileRights.ReadWrite, HandleInheritability.None);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static MemoryMappedFile OpenExisting(string mapName, MemoryMappedFileRights desiredAccessRights)
         {
             return OpenExisting(mapName, desiredAccessRights, HandleInheritability.None);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static MemoryMappedFile OpenExisting(string mapName, MemoryMappedFileRights desiredAccessRights,
                                                                     HandleInheritability inheritability)
         {
@@ -295,21 +295,21 @@ public static MemoryMappedFile CreateNew(string? mapName, long capacity, MemoryM
         // memory mapped file if one exists with the same name.  The capacity, options, and
         // memoryMappedFileSecurity arguments will be ignored in the case of the later.
         // This is ideal for P2P style IPC.
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static MemoryMappedFile CreateOrOpen(string mapName, long capacity)
         {
             return CreateOrOpen(mapName, capacity, MemoryMappedFileAccess.ReadWrite,
                 MemoryMappedFileOptions.None, HandleInheritability.None);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static MemoryMappedFile CreateOrOpen(string mapName, long capacity,
                                                     MemoryMappedFileAccess access)
         {
             return CreateOrOpen(mapName, capacity, access, MemoryMappedFileOptions.None, HandleInheritability.None);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static MemoryMappedFile CreateOrOpen(string mapName, long capacity,
                                                     MemoryMappedFileAccess access, MemoryMappedFileOptions options,
                                                     HandleInheritability inheritability)
diff --git a/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFilesTestsBase.Unix.cs b/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFilesTestsBase.Unix.cs
index c754fcb8daaf15..86cc494976bbd5 100644
--- a/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFilesTestsBase.Unix.cs
+++ b/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFilesTestsBase.Unix.cs
@@ -14,7 +14,7 @@ public abstract partial class MemoryMappedFilesTestBase : FileCleanupTestBase
         /// <summary>Gets the system's page size.</summary>
         protected static Lazy<int> s_pageSize = new Lazy<int>(() =>
         {
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.Browser))
+            if (OperatingSystem.IsBrowser())
                 return Environment.SystemPageSize;
 
             int pageSize;
diff --git a/src/libraries/System.IO.Packaging/ref/System.IO.Packaging.csproj b/src/libraries/System.IO.Packaging/ref/System.IO.Packaging.csproj
index 56941538f8b06c..bb30574d28d8d7 100644
--- a/src/libraries/System.IO.Packaging/ref/System.IO.Packaging.csproj
+++ b/src/libraries/System.IO.Packaging/ref/System.IO.Packaging.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard1.3;net46;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;netstandard1.3;net46</TargetFrameworks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -15,15 +14,7 @@
     <Compile Include="System.IO.Packaging.Serialization.cs" />
     <Compile Include="System.IO.Packaging.PackUriScheme.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetFrameworkCurrent)' or '$(TargetFramework)' == 'net46'">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
     <Reference Include="WindowsBase" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.IO" />
-    <Reference Include="System.IO.FileSystem.Primitives" />
-    <Reference Include="System.Runtime" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Packaging/src/System.IO.Packaging.csproj b/src/libraries/System.IO.Packaging/src/System.IO.Packaging.csproj
index 44240d763755f3..d8d6ce3f3da356 100644
--- a/src/libraries/System.IO.Packaging/src/System.IO.Packaging.csproj
+++ b/src/libraries/System.IO.Packaging/src/System.IO.Packaging.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>netstandard2.0;net46;netstandard1.3;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net46;netstandard1.3</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -10,22 +9,6 @@
     <DefineConstants Condition="'$(TargetFramework)' != 'netstandard1.3'">$(DefineConstants);FEATURE_SERIALIZATION</DefineConstants>
     <IsPartialFacadeAssembly Condition="$(TargetFramework.StartsWith('net4'))">true</IsPartialFacadeAssembly>
   </PropertyGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3'">
-    <Reference Include="System.AppContext" />
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Diagnostics.Debug" />
-    <Reference Include="System.Globalization" />
-    <Reference Include="System.IO" />
-    <Reference Include="System.IO.Compression" />
-    <Reference Include="System.IO.FileSystem" />
-    <Reference Include="System.IO.FileSystem.Primitives" />
-    <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Threading.Tasks" />
-    <Reference Include="System.Text.Encoding" />
-    <Reference Include="System.Xml.ReaderWriter" />
-  </ItemGroup>
   <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
     <Compile Include="System\IO\Packaging\CompressionOption.cs" />
     <Compile Include="System\IO\Packaging\ContentType.cs" />
@@ -57,7 +40,6 @@
     <Compile Condition="'$(TargetFramework)' != 'netstandard1.3'" Include="System\IO\Packaging\PackUriHelper.PackUriScheme.cs" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
     <Reference Include="WindowsBase" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Packaging/tests/System.IO.Packaging.Tests.csproj b/src/libraries/System.IO.Packaging/tests/System.IO.Packaging.Tests.csproj
index 611983cc55b0ab..41d84a25961145 100644
--- a/src/libraries/System.IO.Packaging/tests/System.IO.Packaging.Tests.csproj
+++ b/src/libraries/System.IO.Packaging/tests/System.IO.Packaging.Tests.csproj
@@ -1,11 +1,15 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net48-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Tests.cs" />
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="System.IO.Packaging.TestData" Version="$(SystemIOPackagingTestDataVersion)" />
+    <ProjectReference Include="..\src\System.IO.Packaging.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net48'))">
+    <Reference Include="WindowsBase" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Pipelines/pkg/System.IO.Pipelines.pkgproj b/src/libraries/System.IO.Pipelines/pkg/System.IO.Pipelines.pkgproj
index da675e50fc194f..9b454d0d07b4b5 100644
--- a/src/libraries/System.IO.Pipelines/pkg/System.IO.Pipelines.pkgproj
+++ b/src/libraries/System.IO.Pipelines/pkg/System.IO.Pipelines.pkgproj
@@ -11,6 +11,12 @@
     </ProjectReference>
     <ProjectReference Include="..\src\System.IO.Pipelines.csproj" />
     <HarvestIncludePaths Include="lib/netstandard1.3" />
+
+    <!-- Even though this library is inbox we want to treat it as out
+         of box in the package so that we can continue to evolve it. -->
+    <ValidatePackageSuppression Include="TreatAsOutOfBox">
+      <Value>.NETCoreApp</Value>
+    </ValidatePackageSuppression>
   </ItemGroup>
   <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets))" />
 </Project>
diff --git a/src/libraries/System.IO.Pipelines/ref/System.IO.Pipelines.csproj b/src/libraries/System.IO.Pipelines/ref/System.IO.Pipelines.csproj
index 2af41b5283fb69..7cb28689989ffa 100644
--- a/src/libraries/System.IO.Pipelines/ref/System.IO.Pipelines.csproj
+++ b/src/libraries/System.IO.Pipelines/ref/System.IO.Pipelines.csproj
@@ -1,17 +1,23 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
+    <ExcludeFromPackage Condition="'$(TargetFramework)' == 'net461'">true</ExcludeFromPackage>
     <!-- We only plan to use this ref in netcoreapp. For all other netstandard compatible frameworks
     we should use the lib asset instead. -->
     <PackageTargetFramework>netcoreapp2.0</PackageTargetFramework>
+    <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.IO.Pipelines.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.Buffers" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Threading.Tasks.Extensions" />
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="..\..\System.Memory\ref\System.Memory.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)'">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.IO.Pipelines/src/System.IO.Pipelines.csproj b/src/libraries/System.IO.Pipelines/src/System.IO.Pipelines.csproj
index 545a857a9515fc..f5e9a5531f5e3a 100644
--- a/src/libraries/System.IO.Pipelines/src/System.IO.Pipelines.csproj
+++ b/src/libraries/System.IO.Pipelines/src/System.IO.Pipelines.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp3.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp3.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -46,11 +45,14 @@
     <Compile Include="System\IO\Pipelines\ThreadPoolScheduler.netstandard.cs" />
     <Compile Include="System\IO\Pipelines\CancellationTokenExtensions.netstandard.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
+   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                         $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
   </ItemGroup>
-  <ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or
+                        '$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="System.Buffers" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Diagnostics.Debug" />
diff --git a/src/libraries/System.IO.Pipelines/tests/System.IO.Pipelines.Tests.csproj b/src/libraries/System.IO.Pipelines/tests/System.IO.Pipelines.Tests.csproj
index 0e9b268811fcf8..5c0a2a305f4fee 100644
--- a/src/libraries/System.IO.Pipelines/tests/System.IO.Pipelines.Tests.csproj
+++ b/src/libraries/System.IO.Pipelines/tests/System.IO.Pipelines.Tests.csproj
@@ -1,13 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <!-- Some internal types are needed, so we reference the implementation assembly, rather than the reference assembly. -->
-    <DefaultReferenceExclusions Include="System.IO.Pipelines" />
-    <ReferenceFromRuntime Include="System.IO.Pipelines" />
-  </ItemGroup>
   <ItemGroup>
     <Compile Include="Infrastructure\HeapBufferPool.cs" />
     <Compile Include="Infrastructure\DisposeTrackingBufferPool.cs" />
@@ -49,4 +44,11 @@
     <Compile Include="PipeWriterStreamTests.nonnetstandard.cs" />
     <Compile Include="PipeReaderStreamTests.nonnetstandard.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <!-- Some internal types are needed, so we reference the implementation assembly, rather than the reference assembly. -->
+    <ProjectReference Include="..\src\System.IO.Pipelines.csproj" SkipUseReferenceAssembly="true" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="..\src\System.IO.Pipelines.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Pipes.AccessControl/Directory.Build.props b/src/libraries/System.IO.Pipes.AccessControl/Directory.Build.props
index 27a4a5522a2778..33e65b7cb46516 100644
--- a/src/libraries/System.IO.Pipes.AccessControl/Directory.Build.props
+++ b/src/libraries/System.IO.Pipes.AccessControl/Directory.Build.props
@@ -2,8 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
-    <IsNETCoreAppRef>false</IsNETCoreAppRef>
     <IsWindowsSpecific>true</IsWindowsSpecific>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Pipes.AccessControl/src/System.IO.Pipes.AccessControl.csproj b/src/libraries/System.IO.Pipes.AccessControl/src/System.IO.Pipes.AccessControl.csproj
index aa09673b2ed72c..81ac8d687ca3f0 100644
--- a/src/libraries/System.IO.Pipes.AccessControl/src/System.IO.Pipes.AccessControl.csproj
+++ b/src/libraries/System.IO.Pipes.AccessControl/src/System.IO.Pipes.AccessControl.csproj
@@ -1,25 +1,26 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.IO.Pipes.AccessControl</AssemblyName>
-    <IncludeDefaultReferences>false</IncludeDefaultReferences>
-    <IsPartialFacadeAssembly Condition="'$(TargetsWindows)' == 'true'">true</IsPartialFacadeAssembly>
-    <OmitResources Condition="'$(TargetsWindows)' == 'true'">true</OmitResources>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsWindows)' != 'true'">SR.PlatformNotSupported_AccessControl</GeneratePlatformNotSupportedAssemblyMessage>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
+  <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsWindows)' != 'true'">SR.PlatformNotSupported_AccessControl</GeneratePlatformNotSupportedAssemblyMessage>
+    <OmitResources Condition="'$(TargetsWindows)' == 'true'">true</OmitResources>
+    <IsPartialFacadeAssembly Condition="'$(TargetsWindows)' == 'true'">true</IsPartialFacadeAssembly>
   </PropertyGroup>
   <ItemGroup>
     <Reference Include="System.Runtime" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
-    <ProjectReference Include="..\..\System.IO.Pipes\src\System.IO.Pipes.csproj" />
-    <ProjectReference Include="..\..\System.Security.AccessControl\src\System.Security.AccessControl.csproj" />
+  <!-- Include src projects during restore as TargetsWindows isn't set. -->
+  <ItemGroup Condition="'$(TargetsWindows)' == 'true' or '$(MSBuildRestoreSessionId)' != ''">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.IO.Pipes\src\System.IO.Pipes.csproj" SkipUseReferenceAssembly="true" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\src\System.Security.AccessControl.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsWindows)' != 'true'">
+    <!-- Referencing the ref project directly as the src project doesn't have a RID less configuration. -->
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\ref\System.Security.AccessControl.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\ref\System.Security.Principal.Windows.csproj" />
     <Reference Include="System.IO.Pipes" />
-    <Reference Include="System.Security.AccessControl" />
-    <Reference Include="System.Security.Principal.Windows" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.IO.Pipes.AccessControl/tests/System.IO.Pipes.AccessControl.Tests.csproj b/src/libraries/System.IO.Pipes.AccessControl/tests/System.IO.Pipes.AccessControl.Tests.csproj
index 21202e86f0e700..57015e7b67883a 100644
--- a/src/libraries/System.IO.Pipes.AccessControl/tests/System.IO.Pipes.AccessControl.Tests.csproj
+++ b/src/libraries/System.IO.Pipes.AccessControl/tests/System.IO.Pipes.AccessControl.Tests.csproj
@@ -15,4 +15,7 @@
     <Compile Include="PipeTest.AclExtensions.cs" />
     <Compile Include="..\..\System.IO.Pipes\tests\PipeTestBase.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.IO.Pipes.AccessControl.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Pipes/Directory.Build.props b/src/libraries/System.IO.Pipes/Directory.Build.props
index 42c6eafce67ed8..d68d22c1b917f8 100644
--- a/src/libraries/System.IO.Pipes/Directory.Build.props
+++ b/src/libraries/System.IO.Pipes/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Pipes/ref/System.IO.Pipes.cs b/src/libraries/System.IO.Pipes/ref/System.IO.Pipes.cs
index 8ef9f9f5b06477..8dfe980c49fba9 100644
--- a/src/libraries/System.IO.Pipes/ref/System.IO.Pipes.cs
+++ b/src/libraries/System.IO.Pipes/ref/System.IO.Pipes.cs
@@ -48,7 +48,7 @@ public sealed partial class NamedPipeClientStream : System.IO.Pipes.PipeStream
         public NamedPipeClientStream(string serverName, string pipeName, System.IO.Pipes.PipeDirection direction, System.IO.Pipes.PipeOptions options) : base (default(System.IO.Pipes.PipeDirection), default(int)) { }
         public NamedPipeClientStream(string serverName, string pipeName, System.IO.Pipes.PipeDirection direction, System.IO.Pipes.PipeOptions options, System.Security.Principal.TokenImpersonationLevel impersonationLevel) : base (default(System.IO.Pipes.PipeDirection), default(int)) { }
         public NamedPipeClientStream(string serverName, string pipeName, System.IO.Pipes.PipeDirection direction, System.IO.Pipes.PipeOptions options, System.Security.Principal.TokenImpersonationLevel impersonationLevel, System.IO.HandleInheritability inheritability) : base (default(System.IO.Pipes.PipeDirection), default(int)) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public int NumberOfServerInstances { get { throw null; } }
         protected internal override void CheckPipePropertyOperations() { }
         public void Connect() { }
@@ -129,7 +129,7 @@ protected void InitializeHandle(Microsoft.Win32.SafeHandles.SafePipeHandle? hand
         public override int ReadByte() { throw null; }
         public override long Seek(long offset, System.IO.SeekOrigin origin) { throw null; }
         public override void SetLength(long value) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public void WaitForPipeDrain() { }
         public override void Write(byte[] buffer, int offset, int count) { }
         public override void Write(System.ReadOnlySpan<byte> buffer) { }
@@ -141,7 +141,7 @@ public override void WriteByte(byte value) { }
     public enum PipeTransmissionMode
     {
         Byte = 0,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         Message = 1,
     }
 }
diff --git a/src/libraries/System.IO.Pipes/src/Resources/Strings.resx b/src/libraries/System.IO.Pipes/src/Resources/Strings.resx
index e4777e219890c6..5b1a648e56a50a 100644
--- a/src/libraries/System.IO.Pipes/src/Resources/Strings.resx
+++ b/src/libraries/System.IO.Pipes/src/Resources/Strings.resx
@@ -292,6 +292,6 @@
     <value>'pipeSecurity' must be null when 'options' contains 'PipeOptions.CurrentUserOnly'. </value>
   </data>
   <data name="Pipes_PlatformNotSupported" xml:space="preserve">
-    <value>System.IO.Pipes is not supported on this platform</value>
+    <value>System.IO.Pipes is not supported on this platform.</value>
   </data>
 </root>
diff --git a/src/libraries/System.IO.Pipes/src/System.IO.Pipes.csproj b/src/libraries/System.IO.Pipes/src/System.IO.Pipes.csproj
index becae30a11a9db..2016c93b4c0436 100644
--- a/src/libraries/System.IO.Pipes/src/System.IO.Pipes.csproj
+++ b/src/libraries/System.IO.Pipes/src/System.IO.Pipes.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.IO.Pipes</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <OmitTransitiveCompileReferences>true</OmitTransitiveCompileReferences>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)</TargetFrameworks>
@@ -183,10 +182,11 @@
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Overlapped" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
+  <!-- Include src projects during restore as TargetsWindows isn't set. -->
+  <ItemGroup Condition="'$(TargetsWindows)' == 'true' or '$(MSBuildRestoreSessionId)' != ''">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\src\System.Security.AccessControl.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
     <Reference Include="System.Collections.NonGeneric" />
-    <Reference Include="System.Security.AccessControl" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Security.Claims" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)' == 'true' or '$(TargetsBrowser)' == 'true'">
diff --git a/src/libraries/System.IO.Pipes/src/System/IO/Pipes/NamedPipeClientStream.Unix.cs b/src/libraries/System.IO.Pipes/src/System/IO/Pipes/NamedPipeClientStream.Unix.cs
index dfb09b40cfed2c..42fe518e0012e3 100644
--- a/src/libraries/System.IO.Pipes/src/System/IO/Pipes/NamedPipeClientStream.Unix.cs
+++ b/src/libraries/System.IO.Pipes/src/System/IO/Pipes/NamedPipeClientStream.Unix.cs
@@ -67,7 +67,7 @@ private bool TryConnect(int timeout, CancellationToken cancellationToken)
             return true;
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public int NumberOfServerInstances
         {
             get
diff --git a/src/libraries/System.IO.Pipes/src/System/IO/Pipes/NamedPipeClientStream.Windows.cs b/src/libraries/System.IO.Pipes/src/System/IO/Pipes/NamedPipeClientStream.Windows.cs
index 730f1eab530eea..a082a3da863972 100644
--- a/src/libraries/System.IO.Pipes/src/System/IO/Pipes/NamedPipeClientStream.Windows.cs
+++ b/src/libraries/System.IO.Pipes/src/System/IO/Pipes/NamedPipeClientStream.Windows.cs
@@ -108,7 +108,7 @@ private bool TryConnect(int timeout, CancellationToken cancellationToken)
             return true;
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public unsafe int NumberOfServerInstances
         {
             get
diff --git a/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeStream.Unix.cs b/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeStream.Unix.cs
index 502829f49daab6..6e6fa8a5c1385f 100644
--- a/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeStream.Unix.cs
+++ b/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeStream.Unix.cs
@@ -220,7 +220,7 @@ private IOException GetIOExceptionForSocketException(SocketException e)
         }
 
         // Blocks until the other end of the pipe has read in all written buffer.
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public void WaitForPipeDrain()
         {
             CheckWriteOperations();
diff --git a/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeStream.Windows.cs b/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeStream.Windows.cs
index 030f769a762bd7..b221c9880b6cfa 100644
--- a/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeStream.Windows.cs
+++ b/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeStream.Windows.cs
@@ -179,7 +179,7 @@ private Task WriteAsyncCore(ReadOnlyMemory<byte> buffer, CancellationToken cance
         }
 
         // Blocks until the other end of the pipe has read in all written buffer.
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public void WaitForPipeDrain()
         {
             CheckWriteOperations();
diff --git a/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeTransmissionMode.cs b/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeTransmissionMode.cs
index fbfd0ccf85ec05..c4d8f0956c0431 100644
--- a/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeTransmissionMode.cs
+++ b/src/libraries/System.IO.Pipes/src/System/IO/Pipes/PipeTransmissionMode.cs
@@ -8,7 +8,7 @@ namespace System.IO.Pipes
     public enum PipeTransmissionMode
     {
         Byte = 0,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         Message = 1,
     }
 }
diff --git a/src/libraries/System.IO.Pipes/tests/AnonymousPipeTests/AnonymousPipeTest.Specific.cs b/src/libraries/System.IO.Pipes/tests/AnonymousPipeTests/AnonymousPipeTest.Specific.cs
index 4dd10185ecd8c5..f7ef3d6afa8f73 100644
--- a/src/libraries/System.IO.Pipes/tests/AnonymousPipeTests/AnonymousPipeTest.Specific.cs
+++ b/src/libraries/System.IO.Pipes/tests/AnonymousPipeTests/AnonymousPipeTest.Specific.cs
@@ -85,7 +85,7 @@ public static void Linux_BufferSizeRoundtrips()
             // On Linux, setting the buffer size of the server will also set the buffer size of the
             // client, regardless of the direction of the flow
 
-            int desiredBufferSize = 4096;
+            int desiredBufferSize = Environment.SystemPageSize;
             using (var server = new AnonymousPipeServerStream(PipeDirection.Out, HandleInheritability.None, desiredBufferSize))
             {
                 Assert.Equal(desiredBufferSize, server.OutBufferSize);
diff --git a/src/libraries/System.IO.Pipes/tests/System.IO.Pipes.Tests.csproj b/src/libraries/System.IO.Pipes/tests/System.IO.Pipes.Tests.csproj
index d3759ed22d1c82..ead46c1faaa2e1 100644
--- a/src/libraries/System.IO.Pipes/tests/System.IO.Pipes.Tests.csproj
+++ b/src/libraries/System.IO.Pipes/tests/System.IO.Pipes.Tests.csproj
@@ -59,4 +59,8 @@
     <Compile Include="NamedPipeTests\NamedPipeTest.RunAsClient.Unix.cs" />
     <Compile Include="NativeOverlapped.unix.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices\src\System.DirectoryServices.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices.AccountManagement\src\System.DirectoryServices.AccountManagement.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.IO.Ports/ref/System.IO.Ports.csproj b/src/libraries/System.IO.Ports/ref/System.IO.Ports.csproj
index fba4e13b90477f..bb26f9be9a0897 100644
--- a/src/libraries/System.IO.Ports/ref/System.IO.Ports.csproj
+++ b/src/libraries/System.IO.Ports/ref/System.IO.Ports.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -10,8 +9,4 @@
   <ItemGroup>
     <Compile Include="System.IO.Ports.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.Ports/src/System.IO.Ports.csproj b/src/libraries/System.IO.Ports/src/System.IO.Ports.csproj
index 307aa3bf4b4549..595800abe83860 100644
--- a/src/libraries/System.IO.Ports/src/System.IO.Ports.csproj
+++ b/src/libraries/System.IO.Ports/src/System.IO.Ports.csproj
@@ -4,8 +4,7 @@
     <DefineConstants>$(DefineConstants);NOSPAN;SERIAL_PORTS</DefineConstants>
     <IncludeDllSafeSearchPathAttribute>true</IncludeDllSafeSearchPathAttribute>
     <Nullable>annotations</Nullable>
-    <TargetFrameworks>netstandard2.0-Windows_NT;netstandard2.0-Linux;netstandard2.0-OSX;netstandard2.0;net461-Windows_NT;netstandard2.0-FreeBSD;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0-Windows_NT;netstandard2.0-Linux;netstandard2.0-OSX;netstandard2.0;net461-Windows_NT;netstandard2.0-FreeBSD</TargetFrameworks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -134,28 +133,8 @@
     <Compile Include="$(CommonPath)System\Threading\Tasks\TaskToApm.cs"
              Link="Common\System\Threading\Tasks\TaskToApm.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="Microsoft.Win32.Registry" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Threading.Tasks" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(TargetsLinux)' == 'true' or '$(TargetsOSX)' == 'true'">
-    <Reference Include="Microsoft.Win32.Primitives" />
-    <Reference Include="System.Collections" />
-    <Reference Include="System.ComponentModel.Primitives" />
-    <Reference Include="System.Diagnostics.Debug" />
-    <Reference Include="System.Diagnostics.Tools" />
-    <Reference Include="System.IO.FileSystem" />
-    <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="System.Text.Encoding.Extensions" />
-    <Reference Include="System.Threading" />
-    <Reference Include="System.Threading.Thread" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard'))">
+    <ProjectReference Condition="'$(TargetsWindows)' == 'true'" Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.IO.Ports/tests/SerialPort/BaudRate.cs b/src/libraries/System.IO.Ports/tests/SerialPort/BaudRate.cs
index 1dee6e9e3688fe..2735d9dc0470fa 100644
--- a/src/libraries/System.IO.Ports/tests/SerialPort/BaudRate.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialPort/BaudRate.cs
@@ -260,7 +260,6 @@ private void VerifyBaudRate(SerialPort com1)
             using (SerialPort com2 = new SerialPort(TCSupport.LocalMachineSerialInfo.SecondAvailablePortName))
             {
                 double expectedTime, actualTime, percentageDifference;
-                int numBytes = 0;
 
                 //Generate some random byte to read/write at this baudrate
                 for (int i = 0; i < xmitBytes.Length; i++)
@@ -316,7 +315,7 @@ private void VerifyBaudRate(SerialPort com1)
                 if (MAX_ACCEPTABLE_PERCENTAGE_DIFFERENCE < percentageDifference)
                 {
                     Assert.True(false, string.Format("ERROR!!! BuadRate not used Expected time:{0}, actual time:{1} percentageDifference:{2}",
-                        expectedTime, actualTime, percentageDifference, numBytes));
+                        expectedTime, actualTime, percentageDifference));
                 }
 
                 com2.Read(rcvBytes, 0, rcvBytes.Length);
diff --git a/src/libraries/System.IO.Ports/tests/SerialPort/Encoding.cs b/src/libraries/System.IO.Ports/tests/SerialPort/Encoding.cs
index 0380848d84320a..88fd4f2391f7b7 100644
--- a/src/libraries/System.IO.Ports/tests/SerialPort/Encoding.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialPort/Encoding.cs
@@ -175,7 +175,7 @@ private void VerifyExceptionAtOpen(SerialPort com, Encoding encoding, ThrowAt th
                 if (ThrowAt.Open == throwAt)
                     com.Open();
 
-                object myEncoding = com.Encoding;
+                _ = com.Encoding;
 
                 com.Encoding = origEncoding;
 
diff --git a/src/libraries/System.IO.Ports/tests/SerialPort/Handshake.cs b/src/libraries/System.IO.Ports/tests/SerialPort/Handshake.cs
index 7bb7b1ac4981c4..a9c80e3e76ca60 100644
--- a/src/libraries/System.IO.Ports/tests/SerialPort/Handshake.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialPort/Handshake.cs
@@ -591,7 +591,6 @@ private void VerirfyRTSBufferFull(SerialPort com1, SerialPort com2)
         {
             int com1BaudRate = com1.BaudRate;
             int com2BaudRate = com2.BaudRate;
-            int com1ReadBufferSize = com1.ReadBufferSize;
             int bufferSize = com1.ReadBufferSize;
             int upperLimit = (3 * bufferSize) / 4;
             int lowerLimit = bufferSize / 4;
@@ -695,7 +694,6 @@ private void VerirfyXOnXOffBufferFull(SerialPort com1, SerialPort com2)
         {
             int com1BaudRate = com1.BaudRate;
             int com2BaudRate = com2.BaudRate;
-            int com1ReadBufferSize = com1.ReadBufferSize;
             bool com2RtsEnable = com2.RtsEnable;
             int bufferSize = com1.ReadBufferSize;
             int upperLimit = bufferSize - 1024;
diff --git a/src/libraries/System.IO.Ports/tests/SerialPort/ReadBufferSize.cs b/src/libraries/System.IO.Ports/tests/SerialPort/ReadBufferSize.cs
index 733253fa9f9831..4ec9ea9cd41de7 100644
--- a/src/libraries/System.IO.Ports/tests/SerialPort/ReadBufferSize.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialPort/ReadBufferSize.cs
@@ -299,7 +299,6 @@ private void VerifyReadBufferSize(SerialPort com1)
                 SerialPortProperties serPortProp = new SerialPortProperties();
                 Random rndGen = new Random(-55);
                 int bytesToRead = readBufferSize < 4096 ? 4096 : readBufferSize;
-                int origBaudRate = com1.BaudRate;
                 int origReadTimeout = com1.ReadTimeout;
                 int bytesRead;
 
diff --git a/src/libraries/System.IO.Ports/tests/SerialPort/Read_char_int_int_Generic.cs b/src/libraries/System.IO.Ports/tests/SerialPort/Read_char_int_int_Generic.cs
index ba3f3dede8753a..817b38e1daeb6c 100644
--- a/src/libraries/System.IO.Ports/tests/SerialPort/Read_char_int_int_Generic.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialPort/Read_char_int_int_Generic.cs
@@ -276,8 +276,6 @@ public void BytesToRead_1_Buffer_Size()
         [ConditionalFact(nameof(HasNullModem))]
         public void BytesToRead_Equal_Buffer_Size()
         {
-            Random rndGen = new Random(-55);
-
             VerifyBytesToRead(numRndBytesToRead);
         }
         #endregion
diff --git a/src/libraries/System.IO.Ports/tests/SerialPort/RtsEnable.cs b/src/libraries/System.IO.Ports/tests/SerialPort/RtsEnable.cs
index bd347c42cced61..23cbbe7a5304c2 100644
--- a/src/libraries/System.IO.Ports/tests/SerialPort/RtsEnable.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialPort/RtsEnable.cs
@@ -190,7 +190,7 @@ public void RtsEnable_Get_Handshake_RequestToSend()
 
                 Assert.Throws<InvalidOperationException>(() =>
                 {
-                    bool rtsEnable = com1.RtsEnable;
+                    _ = com1.RtsEnable;
                 });
             }
         }
@@ -208,7 +208,7 @@ public void RtsEnable_Get_Handshake_RequestToSendXOnXOff()
 
                 Assert.Throws<InvalidOperationException>(() =>
                 {
-                    bool rtsEnable = com1.RtsEnable;
+                    _ = com1.RtsEnable;
                 });
             }
         }
diff --git a/src/libraries/System.IO.Ports/tests/SerialPort/WriteLine.cs b/src/libraries/System.IO.Ports/tests/SerialPort/WriteLine.cs
index 9a690ae6cf4710..9cb5b700d022d7 100644
--- a/src/libraries/System.IO.Ports/tests/SerialPort/WriteLine.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialPort/WriteLine.cs
@@ -29,35 +29,35 @@ public class WriteLine : PortsTest
 
         #region Test Cases
         [ConditionalFact(nameof(HasLoopbackOrNullModem))]
-        private void ASCIIEncoding()
+        public void ASCIIEncoding()
         {
             Debug.WriteLine("Verifying write method with ASCIIEncoding");
             VerifyWrite(new ASCIIEncoding(), ENCODING_STRING_SIZE, GenRandomNewLine(true));
         }
 
         [ConditionalFact(nameof(HasLoopbackOrNullModem))]
-        private void UTF8Encoding()
+        public void UTF8Encoding()
         {
             Debug.WriteLine("Verifying write method with UTF8Encoding");
             VerifyWrite(new UTF8Encoding(), ENCODING_STRING_SIZE, GenRandomNewLine(false));
         }
 
         [ConditionalFact(nameof(HasLoopbackOrNullModem))]
-        private void UTF32Encoding()
+        public void UTF32Encoding()
         {
             Debug.WriteLine("Verifying write method with UTF32Encoding");
             VerifyWrite(new UTF32Encoding(), ENCODING_STRING_SIZE, GenRandomNewLine(false));
         }
 
         [ConditionalFact(nameof(HasLoopbackOrNullModem))]
-        private void UnicodeEncoding()
+        public void UnicodeEncoding()
         {
             Debug.WriteLine("Verifying write method with UnicodeEncoding");
             VerifyWrite(new UnicodeEncoding(), ENCODING_STRING_SIZE, GenRandomNewLine(false));
         }
 
         [ConditionalFact(nameof(HasOneSerialPort))]
-        private void NullString()
+        public void NullString()
         {
             using (SerialPort com = new SerialPort(TCSupport.LocalMachineSerialInfo.FirstAvailablePortName))
             {
@@ -75,7 +75,7 @@ private void NullString()
         }
 
         [ConditionalFact(nameof(HasLoopbackOrNullModem))]
-        private void EmptyString()
+        public void EmptyString()
         {
             using (SerialPort com1 = TCSupport.InitFirstSerialPort())
             using (SerialPort com2 = TCSupport.InitSecondSerialPort(com1))
@@ -92,7 +92,7 @@ private void EmptyString()
         }
 
         [ConditionalFact(nameof(HasLoopbackOrNullModem))]
-        private void String_Null_Char()
+        public void String_Null_Char()
         {
             using (SerialPort com1 = TCSupport.InitFirstSerialPort())
             using (SerialPort com2 = TCSupport.InitSecondSerialPort(com1))
@@ -110,7 +110,7 @@ private void String_Null_Char()
         }
 
         [ConditionalFact(nameof(HasLoopbackOrNullModem))]
-        private void LargeString()
+        public void LargeString()
         {
             Debug.WriteLine("Verifying write method with a large string size");
             VerifyWrite(new UnicodeEncoding(), LARGE_STRING_SIZE, DEFAULT_NEW_LINE, 1);
@@ -118,7 +118,7 @@ private void LargeString()
 
 
         [ConditionalFact(nameof(HasLoopbackOrNullModem))]
-        private void StrContains_NewLine_RND()
+        public void StrContains_NewLine_RND()
         {
             using (SerialPort com1 = TCSupport.InitFirstSerialPort())
             using (SerialPort com2 = TCSupport.InitSecondSerialPort(com1))
@@ -145,7 +145,7 @@ private void StrContains_NewLine_RND()
         }
 
         [ConditionalFact(nameof(HasLoopbackOrNullModem))]
-        private void StrContains_NewLine_CRLF()
+        public void StrContains_NewLine_CRLF()
         {
             using (SerialPort com1 = TCSupport.InitFirstSerialPort())
             using (SerialPort com2 = TCSupport.InitSecondSerialPort(com1))
@@ -172,7 +172,7 @@ private void StrContains_NewLine_CRLF()
         }
 
         [ConditionalFact(nameof(HasLoopbackOrNullModem))]
-        private void StrContains_NewLine_null()
+        public void StrContains_NewLine_null()
         {
             using (SerialPort com1 = TCSupport.InitFirstSerialPort())
             using (SerialPort com2 = TCSupport.InitSecondSerialPort(com1))
@@ -239,7 +239,6 @@ private void VerifyWriteLine(SerialPort com1, SerialPort com2, string stringToWr
             int byteRead;
             int index = 0;
             int numNewLineBytes;
-            char[] newLineChars = com1.NewLine.ToCharArray();
             StringBuilder expectedStrBldr = new StringBuilder();
             string expectedString;
 
diff --git a/src/libraries/System.IO.Ports/tests/SerialPort/Write_byte_int_int.cs b/src/libraries/System.IO.Ports/tests/SerialPort/Write_byte_int_int.cs
index 1574766ca620dc..6357e341c419ee 100644
--- a/src/libraries/System.IO.Ports/tests/SerialPort/Write_byte_int_int.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialPort/Write_byte_int_int.cs
@@ -134,7 +134,6 @@ public void OffsetCount_EQ_Length()
             int bufferLength = rndGen.Next(1, MAX_BUFFER_SIZE);
             int offset = rndGen.Next(0, bufferLength - 1);
             int count = bufferLength - offset;
-            Type expectedException = typeof(ArgumentException);
 
             VerifyWrite(new byte[bufferLength], offset, count);
         }
@@ -146,7 +145,6 @@ public void Offset_EQ_Length_Minus_1()
             int bufferLength = rndGen.Next(1, MAX_BUFFER_SIZE);
             int offset = bufferLength - 1;
             int count = 1;
-            Type expectedException = typeof(ArgumentException);
 
             VerifyWrite(new byte[bufferLength], offset, count);
         }
@@ -158,7 +156,6 @@ public void Count_EQ_Length()
             int bufferLength = rndGen.Next(1, MAX_BUFFER_SIZE);
             int offset = 0;
             int count = bufferLength;
-            Type expectedException = typeof(ArgumentException);
 
             VerifyWrite(new byte[bufferLength], offset, count);
         }
@@ -300,12 +297,6 @@ private void VerifyWrite(byte[] buffer, int offset, int count, Encoding encoding
             }
         }
 
-        private void VerifyWriteByteArray(byte[] buffer, int offset, int count, SerialPort com1, SerialPort com2)
-        {
-            VerifyWriteByteArray(buffer, offset, count, com1, com2, DEFAULT_NUM_WRITES);
-        }
-
-
         private void VerifyWriteByteArray(byte[] buffer, int offset, int count, SerialPort com1, SerialPort com2, int numWrites)
         {
             byte[] oldBuffer, expectedBytes, actualBytes;
diff --git a/src/libraries/System.IO.Ports/tests/SerialStream/BeginRead_Generic.cs b/src/libraries/System.IO.Ports/tests/SerialStream/BeginRead_Generic.cs
index 9967eba360b628..fac360dcfb2549 100644
--- a/src/libraries/System.IO.Ports/tests/SerialStream/BeginRead_Generic.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialStream/BeginRead_Generic.cs
@@ -13,13 +13,6 @@ namespace System.IO.Ports.Tests
 {
     public class SerialStream_BeginRead_Generic : PortsTest
     {
-        // Set bounds fore random timeout values.
-        // If the min is to low read will not timeout accurately and the testcase will fail
-        private const int minRandomTimeout = 250;
-
-        // If the max is to large then the testcase will take forever to run
-        private const int maxRandomTimeout = 2000;
-
         // If the percentage difference between the expected timeout and the actual timeout
         // found through Stopwatch is greater then 10% then the timeout value was not correctly
         // to the read method and the testcase fails.
@@ -39,10 +32,6 @@ public class SerialStream_BeginRead_Generic : PortsTest
         // byte array used in this situation
         private const int defaultByteArraySize = 1;
 
-        private const int NUM_TRYS = 5;
-
-        private const int MAX_WAIT_THREAD = 1000;
-
         #region Test Cases
 
         [ConditionalFact(nameof(HasOneSerialPort))]
@@ -102,25 +91,6 @@ public void TimeoutIsIgnoredForBeginRead()
             }
         }
 
-        private void WriteToCom1()
-        {
-            using (var com2 = new SerialPort(TCSupport.LocalMachineSerialInfo.SecondAvailablePortName))
-            {
-                var rndGen = new Random(-55);
-                var xmitBuffer = new byte[1];
-                int sleepPeriod = rndGen.Next(minRandomTimeout, maxRandomTimeout / 2);
-
-                // Sleep some random period with of a maximum duration of half the largest possible timeout value for a read method on COM1
-                Thread.Sleep(sleepPeriod);
-
-                com2.Open();
-                com2.Write(xmitBuffer, 0, xmitBuffer.Length);
-
-                if (com2.IsOpen)
-                    com2.Close();
-            }
-        }
-
         [KnownFailure]
         [ConditionalFact(nameof(HasNullModem))]
         public void DefaultParityReplaceByte()
@@ -236,8 +206,6 @@ public void BytesToRead_1_Buffer_Size()
         [ConditionalFact(nameof(HasNullModem))]
         public void BytesToRead_Equal_Buffer_Size()
         {
-            var rndGen = new Random(-55);
-
             VerifyBytesToRead(numRndBytesToRead, new UTF8Encoding());
         }
         #endregion
diff --git a/src/libraries/System.IO.Ports/tests/SerialStream/Length.cs b/src/libraries/System.IO.Ports/tests/SerialStream/Length.cs
index 3372b371ac4da8..e634d51f29a7e7 100644
--- a/src/libraries/System.IO.Ports/tests/SerialStream/Length.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialStream/Length.cs
@@ -64,7 +64,7 @@ private void VerifyLengthException(Stream serialStream, Type expectedException)
         {
             Assert.Throws(expectedException, () =>
             {
-                long lengthTest = serialStream.Length;
+                _ = serialStream.Length;
             });
         }
         #endregion
diff --git a/src/libraries/System.IO.Ports/tests/SerialStream/Position.cs b/src/libraries/System.IO.Ports/tests/SerialStream/Position.cs
index 265f55a688896d..36b8d1d005ef27 100644
--- a/src/libraries/System.IO.Ports/tests/SerialStream/Position.cs
+++ b/src/libraries/System.IO.Ports/tests/SerialStream/Position.cs
@@ -78,7 +78,7 @@ private void VerifyPositionException(Stream serialStream, long value, Type expec
             Assert.Throws(expectedException, () => serialStream.Position = value);
             Assert.Throws(expectedException, () =>
             {
-                long positionTest = serialStream.Position;
+                _ = serialStream.Position;
             });
         }
         #endregion
diff --git a/src/libraries/System.IO.Ports/tests/System.IO.Ports.Tests.csproj b/src/libraries/System.IO.Ports/tests/System.IO.Ports.Tests.csproj
index 67de446f54719c..d0797175561fb1 100644
--- a/src/libraries/System.IO.Ports/tests/System.IO.Ports.Tests.csproj
+++ b/src/libraries/System.IO.Ports/tests/System.IO.Ports.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-FreeBSD;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-FreeBSD;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="AssemblyInfo.cs" />
@@ -117,4 +117,11 @@
   <ItemGroup>
     <Folder Include="Legacy\Manual\" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
+    <ProjectReference Include="..\src\System.IO.Ports.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Encoding.CodePages\src\System.Text.Encoding.CodePages.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.UnmanagedMemoryStream/Directory.Build.props b/src/libraries/System.IO.UnmanagedMemoryStream/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.IO.UnmanagedMemoryStream/Directory.Build.props
+++ b/src/libraries/System.IO.UnmanagedMemoryStream/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO.UnmanagedMemoryStream/src/System.IO.UnmanagedMemoryStream.csproj b/src/libraries/System.IO.UnmanagedMemoryStream/src/System.IO.UnmanagedMemoryStream.csproj
index af6feb1057856a..4f2d15aa3b6a58 100644
--- a/src/libraries/System.IO.UnmanagedMemoryStream/src/System.IO.UnmanagedMemoryStream.csproj
+++ b/src/libraries/System.IO.UnmanagedMemoryStream/src/System.IO.UnmanagedMemoryStream.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.IO.UnmanagedMemoryStream</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.IO/Directory.Build.props b/src/libraries/System.IO/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.IO/Directory.Build.props
+++ b/src/libraries/System.IO/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.IO/src/System.IO.csproj b/src/libraries/System.IO/src/System.IO.csproj
index d7effb020f5cb3..3b108d6826762c 100644
--- a/src/libraries/System.IO/src/System.IO.csproj
+++ b/src/libraries/System.IO/src/System.IO.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.IO</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Linq.Expressions/Directory.Build.props b/src/libraries/System.Linq.Expressions/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Linq.Expressions/Directory.Build.props
+++ b/src/libraries/System.Linq.Expressions/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Linq.Expressions/src/System.Linq.Expressions.csproj b/src/libraries/System.Linq.Expressions/src/System.Linq.Expressions.csproj
index 07d0cebd1746ed..7972cdb54f1fa7 100644
--- a/src/libraries/System.Linq.Expressions/src/System.Linq.Expressions.csproj
+++ b/src/libraries/System.Linq.Expressions/src/System.Linq.Expressions.csproj
@@ -3,8 +3,6 @@
     <FeatureInterpret>true</FeatureInterpret>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
-  </PropertyGroup>
-  <PropertyGroup>
     <IsInterpreting>false</IsInterpreting>
     <DefineConstants> $(DefineConstants);FEATURE_DLG_INVOKE;FEATURE_FAST_CREATE</DefineConstants>
     <DefineConstants Condition=" '$(IsInterpreting)' != 'true' ">$(DefineConstants);FEATURE_COMPILE</DefineConstants>
diff --git a/src/libraries/System.Linq.Expressions/src/System/Dynamic/Utils/CacheDict.cs b/src/libraries/System.Linq.Expressions/src/System/Dynamic/Utils/CacheDict.cs
index 50b6cf2e1e303d..9c9a3bddcc7382 100644
--- a/src/libraries/System.Linq.Expressions/src/System/Dynamic/Utils/CacheDict.cs
+++ b/src/libraries/System.Linq.Expressions/src/System/Dynamic/Utils/CacheDict.cs
@@ -77,7 +77,7 @@ internal bool TryGetValue(TKey key, [MaybeNullWhen(false)] out TValue value)
                 return true;
             }
 
-            value = default(TValue)!;
+            value = default;
             return false;
         }
 
diff --git a/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Compiler/LambdaCompiler.cs b/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Compiler/LambdaCompiler.cs
index 7365e1025b2956..c647214c170d9a 100644
--- a/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Compiler/LambdaCompiler.cs
+++ b/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Compiler/LambdaCompiler.cs
@@ -286,7 +286,7 @@ private MemberExpression CreateLazyInitializedField<T>(string name)
             Debug.Assert(_method is DynamicMethod);
 #endif
             {
-                return Expression.Field(Expression.Constant(new StrongBox<T>(default(T)!)), "Value");
+                return Expression.Field(Expression.Constant(new StrongBox<T>()), "Value");
             }
 #if FEATURE_COMPILE_TO_METHODBUILDER
             else
diff --git a/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Interpreter/Utilities.cs b/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Interpreter/Utilities.cs
index 618557728ce153..7b757e955d2322 100644
--- a/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Interpreter/Utilities.cs
+++ b/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Interpreter/Utilities.cs
@@ -192,7 +192,7 @@ public bool TryGetValue(TKey key, [MaybeNullWhen(false)] out TValue value)
                     }
                 }
             }
-            value = default(TValue)!;
+            value = default;
             return false;
         }
 
diff --git a/src/libraries/System.Linq.Expressions/tests/System.Linq.Expressions.Tests.csproj b/src/libraries/System.Linq.Expressions/tests/System.Linq.Expressions.Tests.csproj
index 48bc8a57cc68ae..ea477dc9d04e57 100644
--- a/src/libraries/System.Linq.Expressions/tests/System.Linq.Expressions.Tests.csproj
+++ b/src/libraries/System.Linq.Expressions/tests/System.Linq.Expressions.Tests.csproj
@@ -6,10 +6,6 @@
     <DefineConstants Condition=" '$(FeatureInterpret)' == 'true' ">$(DefineConstants);FEATURE_INTERPRET</DefineConstants>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
-  <ItemGroup>
-    <DefaultReferenceExclusions Include="System.Linq.Expressions" />
-    <ReferenceFromRuntime Include="System.Linq.Expressions" />
-  </ItemGroup>
   <ItemGroup>
     <AssembliesBeingTested Include="Microsoft.CSharp" />
   </ItemGroup>
@@ -246,5 +242,6 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="xunit.extensibility.execution" Version="$(XUnitVersion)" />
+    <ProjectReference Include="..\src\System.Linq.Expressions.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Linq.Parallel/Directory.Build.props b/src/libraries/System.Linq.Parallel/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Linq.Parallel/Directory.Build.props
+++ b/src/libraries/System.Linq.Parallel/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Linq.Parallel/ref/System.Linq.Parallel.cs b/src/libraries/System.Linq.Parallel/ref/System.Linq.Parallel.cs
index 837bf534b8ba77..e8ab5c078ef00c 100644
--- a/src/libraries/System.Linq.Parallel/ref/System.Linq.Parallel.cs
+++ b/src/libraries/System.Linq.Parallel/ref/System.Linq.Parallel.cs
@@ -61,8 +61,7 @@ public static partial class ParallelEnumerable
         public static System.Linq.ParallelQuery<TSource> DefaultIfEmpty<TSource>(this System.Linq.ParallelQuery<TSource> source, TSource defaultValue) { throw null; }
         public static System.Linq.ParallelQuery<TSource> Distinct<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
         public static System.Linq.ParallelQuery<TSource> Distinct<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource ElementAtOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source, int index) { throw null; }
+        public static TSource? ElementAtOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source, int index) { throw null; }
         public static TSource ElementAt<TSource>(this System.Linq.ParallelQuery<TSource> source, int index) { throw null; }
         public static System.Linq.ParallelQuery<TResult> Empty<TResult>() { throw null; }
         [System.ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
@@ -71,10 +70,8 @@ public static partial class ParallelEnumerable
         public static System.Linq.ParallelQuery<TSource> Except<TSource>(this System.Linq.ParallelQuery<TSource> first, System.Collections.Generic.IEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
         public static System.Linq.ParallelQuery<TSource> Except<TSource>(this System.Linq.ParallelQuery<TSource> first, System.Linq.ParallelQuery<TSource> second) { throw null; }
         public static System.Linq.ParallelQuery<TSource> Except<TSource>(this System.Linq.ParallelQuery<TSource> first, System.Linq.ParallelQuery<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource FirstOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource FirstOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
+        public static TSource? FirstOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
+        public static TSource? FirstOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static TSource First<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
         public static TSource First<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static void ForAll<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Action<TSource> action) { }
@@ -104,10 +101,8 @@ public static void ForAll<TSource>(this System.Linq.ParallelQuery<TSource> sourc
         public static System.Linq.ParallelQuery<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Linq.ParallelQuery<TOuter> outer, System.Collections.Generic.IEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer) { throw null; }
         public static System.Linq.ParallelQuery<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Linq.ParallelQuery<TOuter> outer, System.Linq.ParallelQuery<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector) { throw null; }
         public static System.Linq.ParallelQuery<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Linq.ParallelQuery<TOuter> outer, System.Linq.ParallelQuery<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource LastOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource LastOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
+        public static TSource? LastOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
+        public static TSource? LastOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static TSource Last<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
         public static TSource Last<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static long LongCount<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
@@ -122,8 +117,7 @@ public static void ForAll<TSource>(this System.Linq.ParallelQuery<TSource> sourc
         public static long? Max(this System.Linq.ParallelQuery<long?> source) { throw null; }
         public static float? Max(this System.Linq.ParallelQuery<float?> source) { throw null; }
         public static float Max(this System.Linq.ParallelQuery<float> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource Max<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
+        public static TSource? Max<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
         public static decimal Max<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, decimal> selector) { throw null; }
         public static double Max<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, double> selector) { throw null; }
         public static int Max<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, int> selector) { throw null; }
@@ -134,8 +128,7 @@ public static void ForAll<TSource>(this System.Linq.ParallelQuery<TSource> sourc
         public static long? Max<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, long?> selector) { throw null; }
         public static float? Max<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, float?> selector) { throw null; }
         public static float Max<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, float> selector) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TResult Max<TSource, TResult>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, TResult> selector) { throw null; }
+        public static TResult? Max<TSource, TResult>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, TResult> selector) { throw null; }
         public static decimal Min(this System.Linq.ParallelQuery<decimal> source) { throw null; }
         public static double Min(this System.Linq.ParallelQuery<double> source) { throw null; }
         public static int Min(this System.Linq.ParallelQuery<int> source) { throw null; }
@@ -146,8 +139,7 @@ public static void ForAll<TSource>(this System.Linq.ParallelQuery<TSource> sourc
         public static long? Min(this System.Linq.ParallelQuery<long?> source) { throw null; }
         public static float? Min(this System.Linq.ParallelQuery<float?> source) { throw null; }
         public static float Min(this System.Linq.ParallelQuery<float> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource Min<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
+        public static TSource? Min<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
         public static decimal Min<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, decimal> selector) { throw null; }
         public static double Min<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, double> selector) { throw null; }
         public static int Min<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, int> selector) { throw null; }
@@ -158,8 +150,7 @@ public static void ForAll<TSource>(this System.Linq.ParallelQuery<TSource> sourc
         public static long? Min<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, long?> selector) { throw null; }
         public static float? Min<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, float?> selector) { throw null; }
         public static float Min<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, float> selector) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TResult Min<TSource, TResult>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, TResult> selector) { throw null; }
+        public static TResult? Min<TSource, TResult>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, TResult> selector) { throw null; }
         public static System.Linq.ParallelQuery<TResult> OfType<TResult>(this System.Linq.ParallelQuery source) { throw null; }
         public static System.Linq.OrderedParallelQuery<TSource> OrderByDescending<TSource, TKey>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, TKey> keySelector) { throw null; }
         public static System.Linq.OrderedParallelQuery<TSource> OrderByDescending<TSource, TKey>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, TKey> keySelector, System.Collections.Generic.IComparer<TKey>? comparer) { throw null; }
@@ -180,10 +171,8 @@ public static void ForAll<TSource>(this System.Linq.ParallelQuery<TSource> sourc
         public static bool SequenceEqual<TSource>(this System.Linq.ParallelQuery<TSource> first, System.Collections.Generic.IEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
         public static bool SequenceEqual<TSource>(this System.Linq.ParallelQuery<TSource> first, System.Linq.ParallelQuery<TSource> second) { throw null; }
         public static bool SequenceEqual<TSource>(this System.Linq.ParallelQuery<TSource> first, System.Linq.ParallelQuery<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource SingleOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource SingleOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
+        public static TSource? SingleOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
+        public static TSource? SingleOrDefault<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static TSource Single<TSource>(this System.Linq.ParallelQuery<TSource> source) { throw null; }
         public static TSource Single<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static System.Linq.ParallelQuery<TSource> SkipWhile<TSource>(this System.Linq.ParallelQuery<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
diff --git a/src/libraries/System.Linq.Parallel/src/System.Linq.Parallel.csproj b/src/libraries/System.Linq.Parallel/src/System.Linq.Parallel.csproj
index f2c2c5627ed0e9..c04ba4bf4e3832 100644
--- a/src/libraries/System.Linq.Parallel/src/System.Linq.Parallel.csproj
+++ b/src/libraries/System.Linq.Parallel/src/System.Linq.Parallel.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Linq.Parallel</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
 	<Nullable>enable</Nullable>
diff --git a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Enumerables/AggregationMinMaxHelpers.cs b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Enumerables/AggregationMinMaxHelpers.cs
index 7a5fa88fdeebe0..746c1a5b7496af 100644
--- a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Enumerables/AggregationMinMaxHelpers.cs
+++ b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Enumerables/AggregationMinMaxHelpers.cs
@@ -20,8 +20,7 @@ internal static class AggregationMinMaxHelpers<T>
         // Helper method to find the minimum or maximum element in the source.
         //
 
-        [return: MaybeNull]
-        private static T Reduce(IEnumerable<T> source, int sign)
+        private static T? Reduce(IEnumerable<T> source, int sign)
         {
             Debug.Assert(source != null);
             Debug.Assert(sign == -1 || sign == 1);
@@ -41,8 +40,7 @@ private static T Reduce(IEnumerable<T> source, int sign)
         // Helper method to find the minimum element in the source.
         //
 
-        [return: MaybeNull]
-        internal static T ReduceMin(IEnumerable<T> source)
+        internal static T? ReduceMin(IEnumerable<T> source)
         {
             return Reduce(source, -1);
         }
@@ -51,8 +49,7 @@ internal static T ReduceMin(IEnumerable<T> source)
         // Helper method to find the maximum element in the source.
         //
 
-        [return: MaybeNull]
-        internal static T ReduceMax(IEnumerable<T> source)
+        internal static T? ReduceMax(IEnumerable<T> source)
         {
             return Reduce(source, 1);
         }
diff --git a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Enumerables/EmptyEnumerable.cs b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Enumerables/EmptyEnumerable.cs
index 4ad52acb80606f..d4e21e184902ac 100644
--- a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Enumerables/EmptyEnumerable.cs
+++ b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Enumerables/EmptyEnumerable.cs
@@ -56,7 +56,7 @@ public override IEnumerator<T> GetEnumerator()
         }
     }
 
-    internal class EmptyEnumerator<T> : QueryOperatorEnumerator<T, int>, IEnumerator<T>
+    internal sealed class EmptyEnumerator<T> : QueryOperatorEnumerator<T, int>, IEnumerator<T>
     {
         internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref T currentElement, ref int currentKey)
         {
diff --git a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Helpers.cs b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Helpers.cs
index 746887d4965e1f..54494258c2ed71 100644
--- a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Helpers.cs
+++ b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Helpers.cs
@@ -133,7 +133,7 @@ internal struct Slot
         {
             internal int hashCode;
             internal int next;
-            [MaybeNull, AllowNull] internal TElement value;
+            internal TElement? value;
         }
     }
 }
diff --git a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Merging/AsynchronousChannelMergeEnumerator.cs b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Merging/AsynchronousChannelMergeEnumerator.cs
index e741ac506b35cf..3432a14aef671a 100644
--- a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Merging/AsynchronousChannelMergeEnumerator.cs
+++ b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Merging/AsynchronousChannelMergeEnumerator.cs
@@ -32,7 +32,7 @@ internal sealed class AsynchronousChannelMergeEnumerator<T> : MergeEnumerator<T>
         private IntValueEvent? _consumerEvent; // The consumer event.
         private readonly bool[] _done;       // Tracks which channels are done.
         private int _channelIndex;  // The next channel from which we'll dequeue.
-        [MaybeNull, AllowNull] private T _currentElement = default;  // The remembered element from the previous MoveNext.
+        private T? _currentElement;  // The remembered element from the previous MoveNext.
 
         //-----------------------------------------------------------------------------------
         // Allocates a new enumerator over a set of one-to-one channels.
diff --git a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Merging/SynchronousChannelMergeEnumerator.cs b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Merging/SynchronousChannelMergeEnumerator.cs
index bb0c023d95543d..ba10ef68646219 100644
--- a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Merging/SynchronousChannelMergeEnumerator.cs
+++ b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Merging/SynchronousChannelMergeEnumerator.cs
@@ -24,7 +24,7 @@ internal sealed class SynchronousChannelMergeEnumerator<T> : MergeEnumerator<T>
     {
         private readonly SynchronousChannel<T>[] _channels; // The channel array we will enumerate, from left-to-right.
         private int _channelIndex; // The current channel index. This moves through the array as we enumerate.
-        private T _currentElement = default!; // The last element remembered during enumeration.
+        private T? _currentElement; // The last element remembered during enumeration.
 
         //-----------------------------------------------------------------------------------
         // Instantiates a new enumerator for a set of channels.
@@ -61,7 +61,7 @@ public override T Current
                     throw new InvalidOperationException(SR.PLINQ_CommonEnumerator_Current_NotStarted);
                 }
 
-                return _currentElement;
+                return _currentElement!;
             }
         }
 
diff --git a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Binary/ConcatQueryOperator.cs b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Binary/ConcatQueryOperator.cs
index faa7e1afb76dcc..f6b4b72099dc4e 100644
--- a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Binary/ConcatQueryOperator.cs
+++ b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Binary/ConcatQueryOperator.cs
@@ -296,10 +296,8 @@ internal override TSource GetElement(int index)
 
     internal struct ConcatKey<TLeftKey, TRightKey>
     {
-        [MaybeNull, AllowNull]
-        private readonly TLeftKey _leftKey;
-        [MaybeNull, AllowNull]
-        private readonly TRightKey _rightKey;
+        private readonly TLeftKey? _leftKey;
+        private readonly TRightKey? _rightKey;
         private readonly bool _isLeft;
 
         private ConcatKey([AllowNull] TLeftKey leftKey, [AllowNull] TRightKey rightKey, bool isLeft)
diff --git a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Utils/ReverseComparer.cs b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Utils/ReverseComparer.cs
index f949814c9c5922..229b5244acb104 100644
--- a/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Utils/ReverseComparer.cs
+++ b/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Utils/ReverseComparer.cs
@@ -26,7 +26,7 @@ internal ReverseComparer(IComparer<T> comparer)
             _comparer = comparer;
         }
 
-        public int Compare([AllowNull] T x, [AllowNull] T y)
+        public int Compare(T? x, T? y)
         {
             return _comparer.Compare(y, x);
         }
diff --git a/src/libraries/System.Linq.Parallel/src/System/Linq/ParallelEnumerable.cs b/src/libraries/System.Linq.Parallel/src/System/Linq/ParallelEnumerable.cs
index 17a378e8037731..f4f870c316423a 100644
--- a/src/libraries/System.Linq.Parallel/src/System/Linq/ParallelEnumerable.cs
+++ b/src/libraries/System.Linq.Parallel/src/System/Linq/ParallelEnumerable.cs
@@ -2659,8 +2659,7 @@ public static decimal Min(this ParallelQuery<decimal> source)
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TSource Min<TSource>(this ParallelQuery<TSource> source)
+        public static TSource? Min<TSource>(this ParallelQuery<TSource> source)
         {
             if (source == null) throw new ArgumentNullException(nameof(source));
             return AggregationMinMaxHelpers<TSource>.ReduceMin(source);
@@ -2922,8 +2921,7 @@ public static decimal Min<TSource>(this ParallelQuery<TSource> source, Func<TSou
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TResult Min<TSource, TResult>(this ParallelQuery<TSource> source, Func<TSource, TResult> selector)
+        public static TResult? Min<TSource, TResult>(this ParallelQuery<TSource> source, Func<TSource, TResult> selector)
         {
             return source.Select<TSource, TResult>(selector).Min<TResult>();
         }
@@ -3164,8 +3162,7 @@ public static decimal Max(this ParallelQuery<decimal> source)
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TSource Max<TSource>(this ParallelQuery<TSource> source)
+        public static TSource? Max<TSource>(this ParallelQuery<TSource> source)
         {
             if (source == null) throw new ArgumentNullException(nameof(source));
             return AggregationMinMaxHelpers<TSource>.ReduceMax(source);
@@ -3427,8 +3424,7 @@ public static decimal Max<TSource>(this ParallelQuery<TSource> source, Func<TSou
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TResult Max<TSource, TResult>(this ParallelQuery<TSource> source, Func<TSource, TResult> selector)
+        public static TResult? Max<TSource, TResult>(this ParallelQuery<TSource> source, Func<TSource, TResult> selector)
         {
             return source.Select<TSource, TResult>(selector).Max<TResult>();
         }
@@ -5289,8 +5285,7 @@ public static ParallelQuery<TResult> Cast<TResult>(this ParallelQuery source)
         //     defaultIfEmpty - whether to return a default value (true) or throw an
         //                      exception if the output of the query operator is empty
         //
-        [return: MaybeNull]
-        private static TSource GetOneWithPossibleDefault<TSource>(
+        private static TSource? GetOneWithPossibleDefault<TSource>(
             QueryOperator<TSource> queryOp, bool throwIfTwo, bool defaultIfEmpty)
         {
             Debug.Assert(queryOp != null, "expected query operator");
@@ -5321,7 +5316,7 @@ private static TSource GetOneWithPossibleDefault<TSource>(
 
             if (defaultIfEmpty)
             {
-                return default(TSource)!;
+                return default;
             }
             else
             {
@@ -5436,8 +5431,7 @@ public static TSource First<TSource>(this ParallelQuery<TSource> source, Func<TS
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TSource FirstOrDefault<TSource>(this ParallelQuery<TSource> source)
+        public static TSource? FirstOrDefault<TSource>(this ParallelQuery<TSource> source)
         {
             if (source == null) throw new ArgumentNullException(nameof(source));
 
@@ -5483,8 +5477,7 @@ public static TSource FirstOrDefault<TSource>(this ParallelQuery<TSource> source
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TSource FirstOrDefault<TSource>(this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
+        public static TSource? FirstOrDefault<TSource>(this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
         {
             if (source == null) throw new ArgumentNullException(nameof(source));
             if (predicate == null) throw new ArgumentNullException(nameof(predicate));
@@ -5616,8 +5609,7 @@ public static TSource Last<TSource>(this ParallelQuery<TSource> source, Func<TSo
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TSource LastOrDefault<TSource>(this ParallelQuery<TSource> source)
+        public static TSource? LastOrDefault<TSource>(this ParallelQuery<TSource> source)
         {
             // @PERF: optimize for seekable data sources.  E.g. if an array, we can
             //     seek directly to the last element.
@@ -5659,8 +5651,7 @@ public static TSource LastOrDefault<TSource>(this ParallelQuery<TSource> source)
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TSource LastOrDefault<TSource>(this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
+        public static TSource? LastOrDefault<TSource>(this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
         {
             if (source == null) throw new ArgumentNullException(nameof(source));
             if (predicate == null) throw new ArgumentNullException(nameof(predicate));
@@ -5764,8 +5755,7 @@ public static TSource Single<TSource>(this ParallelQuery<TSource> source, Func<T
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TSource SingleOrDefault<TSource>(this ParallelQuery<TSource> source)
+        public static TSource? SingleOrDefault<TSource>(this ParallelQuery<TSource> source)
         {
             // @PERF: optimize for ICollection-typed data sources, i.e. we can just
             //     check the Count property and avoid costly fork/join/synchronization.
@@ -5795,8 +5785,7 @@ public static TSource SingleOrDefault<TSource>(this ParallelQuery<TSource> sourc
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TSource SingleOrDefault<TSource>(this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
+        public static TSource? SingleOrDefault<TSource>(this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
         {
             if (source == null) throw new ArgumentNullException(nameof(source));
             if (predicate == null) throw new ArgumentNullException(nameof(predicate));
@@ -5821,9 +5810,9 @@ public static TSource SingleOrDefault<TSource>(this ParallelQuery<TSource> sourc
         /// <exception cref="System.ArgumentNullException">
         /// <paramref name="source"/> is a null reference (Nothing in Visual Basic).
         /// </exception>
-        public static ParallelQuery<TSource> DefaultIfEmpty<TSource>(this ParallelQuery<TSource> source)
+        public static ParallelQuery<TSource?> DefaultIfEmpty<TSource>(this ParallelQuery<TSource> source)
         {
-            return DefaultIfEmpty<TSource>(source, default!);
+            return DefaultIfEmpty<TSource>(source, default!)!;
         }
 
         /// <summary>
@@ -5909,8 +5898,7 @@ public static TSource ElementAt<TSource>(this ParallelQuery<TSource> source, int
         /// <exception cref="System.OperationCanceledException">
         /// The query was canceled.
         /// </exception>
-        [return: MaybeNull]
-        public static TSource ElementAtOrDefault<TSource>(this ParallelQuery<TSource> source, int index)
+        public static TSource? ElementAtOrDefault<TSource>(this ParallelQuery<TSource> source, int index)
         {
             if (source == null) throw new ArgumentNullException(nameof(source));
 
@@ -5928,7 +5916,7 @@ public static TSource ElementAtOrDefault<TSource>(this ParallelQuery<TSource> so
                 }
             }
 
-            return default(TSource)!;
+            return default;
         }
     }
 }
diff --git a/src/libraries/System.Linq.Parallel/tests/QueryOperators/ZipTests.cs b/src/libraries/System.Linq.Parallel/tests/QueryOperators/ZipTests.cs
index 9e6446f538ed7e..c952169b8c37f2 100644
--- a/src/libraries/System.Linq.Parallel/tests/QueryOperators/ZipTests.cs
+++ b/src/libraries/System.Linq.Parallel/tests/QueryOperators/ZipTests.cs
@@ -56,15 +56,27 @@ public static void Zip_Unordered(int leftCount, int rightCount)
         {
             ParallelQuery<int> leftQuery = UnorderedSources.Default(leftCount);
             ParallelQuery<int> rightQuery = UnorderedSources.Default(leftCount, rightCount);
-            IntegerRangeSet seen = new IntegerRangeSet(0, Math.Min(leftCount, rightCount));
+            IntegerRangeSet seen_left = new IntegerRangeSet(0, leftCount);
+            IntegerRangeSet seen_right = new IntegerRangeSet(leftCount, rightCount);
+            var expected_seen = Math.Min(leftCount, rightCount);
             foreach (var pair in leftQuery.Zip(rightQuery, (x, y) => KeyValuePair.Create(x, y)))
             {
-                // For unordered collections the pairing isn't actually guaranteed, but an effect of the implementation.
-                // If this test starts failing it should be updated, and possibly mentioned in release notes.
-                Assert.Equal(pair.Key + leftCount, pair.Value);
-                seen.Add(pair.Key);
+                // Can only validate about whether the elements have been previously seen, not anything about the order.
+                seen_left.Add(pair.Key);
+                seen_right.Add(pair.Value);
+            }
+
+            // Zip truncates the longer collection, but which elements it leaves off is undefined when unordered.
+            Assert.Equal(expected_seen, seen_left.Count(kv => kv.Value));
+            Assert.Equal(expected_seen, seen_right.Count(kv => kv.Value));
+            if (leftCount <= rightCount)
+            {
+                seen_left.AssertComplete();
+            }
+            if (rightCount <= leftCount)
+            {
+                seen_right.AssertComplete();
             }
-            seen.AssertComplete();
         }
 
         [Fact]
@@ -106,16 +118,28 @@ public static void Zip_Unordered_NotPipelined(int leftCount, int rightCount)
         {
             ParallelQuery<int> leftQuery = UnorderedSources.Default(leftCount);
             ParallelQuery<int> rightQuery = UnorderedSources.Default(leftCount, rightCount);
-            IntegerRangeSet seen = new IntegerRangeSet(0, Math.Min(leftCount, rightCount));
+            IntegerRangeSet seen_left = new IntegerRangeSet(0, leftCount);
+            IntegerRangeSet seen_right = new IntegerRangeSet(leftCount, rightCount);
+            var expected_seen = Math.Min(leftCount, rightCount);
             Assert.All(leftQuery.Zip(rightQuery, (x, y) => KeyValuePair.Create(x, y)).ToList(),
                 pair =>
                 {
-                    // For unordered collections the pairing isn't actually guaranteed, but an effect of the implementation.
-                    // If this test starts failing it should be updated, and possibly mentioned in release notes.
-                    Assert.Equal(pair.Key + leftCount, pair.Value);
-                    seen.Add(pair.Key);
+                    // Can only validate about whether the elements have been previously seen, not anything about the order.
+                    seen_left.Add(pair.Key);
+                    seen_right.Add(pair.Value);
                 });
-            seen.AssertComplete();
+
+            // Zip truncates the longer collection, but which elements it leaves off is undefined when unordered.
+            Assert.Equal(expected_seen, seen_left.Count(kv => kv.Value));
+            Assert.Equal(expected_seen, seen_right.Count(kv => kv.Value));
+            if (leftCount <= rightCount)
+            {
+                seen_left.AssertComplete();
+            }
+            if (rightCount <= leftCount)
+            {
+                seen_right.AssertComplete();
+            }
         }
 
         [Fact]
diff --git a/src/libraries/System.Linq.Queryable/Directory.Build.props b/src/libraries/System.Linq.Queryable/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Linq.Queryable/Directory.Build.props
+++ b/src/libraries/System.Linq.Queryable/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Linq.Queryable/ref/System.Linq.Queryable.cs b/src/libraries/System.Linq.Queryable/ref/System.Linq.Queryable.cs
index 91d264afdb8b33..c3253aada63af5 100644
--- a/src/libraries/System.Linq.Queryable/ref/System.Linq.Queryable.cs
+++ b/src/libraries/System.Linq.Queryable/ref/System.Linq.Queryable.cs
@@ -74,15 +74,12 @@ public static partial class Queryable
         public static System.Linq.IQueryable<TSource> DefaultIfEmpty<TSource>(this System.Linq.IQueryable<TSource> source, TSource defaultValue) { throw null; }
         public static System.Linq.IQueryable<TSource> Distinct<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
         public static System.Linq.IQueryable<TSource> Distinct<TSource>(this System.Linq.IQueryable<TSource> source, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource ElementAtOrDefault<TSource>(this System.Linq.IQueryable<TSource> source, int index) { throw null; }
+        public static TSource? ElementAtOrDefault<TSource>(this System.Linq.IQueryable<TSource> source, int index) { throw null; }
         public static TSource ElementAt<TSource>(this System.Linq.IQueryable<TSource> source, int index) { throw null; }
         public static System.Linq.IQueryable<TSource> Except<TSource>(this System.Linq.IQueryable<TSource> source1, System.Collections.Generic.IEnumerable<TSource> source2) { throw null; }
         public static System.Linq.IQueryable<TSource> Except<TSource>(this System.Linq.IQueryable<TSource> source1, System.Collections.Generic.IEnumerable<TSource> source2, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource FirstOrDefault<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource FirstOrDefault<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) { throw null; }
+        public static TSource? FirstOrDefault<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
+        public static TSource? FirstOrDefault<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) { throw null; }
         public static TSource First<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
         public static TSource First<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) { throw null; }
         public static System.Linq.IQueryable<System.Linq.IGrouping<TKey, TSource>> GroupBy<TSource, TKey>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, TKey>> keySelector) { throw null; }
@@ -99,22 +96,16 @@ public static partial class Queryable
         public static System.Linq.IQueryable<TSource> Intersect<TSource>(this System.Linq.IQueryable<TSource> source1, System.Collections.Generic.IEnumerable<TSource> source2, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
         public static System.Linq.IQueryable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Linq.IQueryable<TOuter> outer, System.Collections.Generic.IEnumerable<TInner> inner, System.Linq.Expressions.Expression<System.Func<TOuter, TKey>> outerKeySelector, System.Linq.Expressions.Expression<System.Func<TInner, TKey>> innerKeySelector, System.Linq.Expressions.Expression<System.Func<TOuter, TInner, TResult>> resultSelector) { throw null; }
         public static System.Linq.IQueryable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Linq.IQueryable<TOuter> outer, System.Collections.Generic.IEnumerable<TInner> inner, System.Linq.Expressions.Expression<System.Func<TOuter, TKey>> outerKeySelector, System.Linq.Expressions.Expression<System.Func<TInner, TKey>> innerKeySelector, System.Linq.Expressions.Expression<System.Func<TOuter, TInner, TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource LastOrDefault<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource LastOrDefault<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) { throw null; }
+        public static TSource? LastOrDefault<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
+        public static TSource? LastOrDefault<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) { throw null; }
         public static TSource Last<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
         public static TSource Last<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) { throw null; }
         public static long LongCount<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
         public static long LongCount<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource Max<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TResult Max<TSource, TResult>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, TResult>> selector) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource Min<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TResult Min<TSource, TResult>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, TResult>> selector) { throw null; }
+        public static TSource? Max<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
+        public static TResult? Max<TSource, TResult>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, TResult>> selector) { throw null; }
+        public static TSource? Min<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
+        public static TResult? Min<TSource, TResult>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, TResult>> selector) { throw null; }
         public static System.Linq.IQueryable<TResult> OfType<TResult>(this System.Linq.IQueryable source) { throw null; }
         public static System.Linq.IOrderedQueryable<TSource> OrderByDescending<TSource, TKey>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, TKey>> keySelector) { throw null; }
         public static System.Linq.IOrderedQueryable<TSource> OrderByDescending<TSource, TKey>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, TKey>> keySelector, System.Collections.Generic.IComparer<TKey>? comparer) { throw null; }
@@ -130,10 +121,8 @@ public static partial class Queryable
         public static System.Linq.IQueryable<TResult> Select<TSource, TResult>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, TResult>> selector) { throw null; }
         public static bool SequenceEqual<TSource>(this System.Linq.IQueryable<TSource> source1, System.Collections.Generic.IEnumerable<TSource> source2) { throw null; }
         public static bool SequenceEqual<TSource>(this System.Linq.IQueryable<TSource> source1, System.Collections.Generic.IEnumerable<TSource> source2, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource SingleOrDefault<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TSource SingleOrDefault<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) { throw null; }
+        public static TSource? SingleOrDefault<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
+        public static TSource? SingleOrDefault<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) { throw null; }
         public static TSource Single<TSource>(this System.Linq.IQueryable<TSource> source) { throw null; }
         public static TSource Single<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) { throw null; }
         public static System.Linq.IQueryable<TSource> SkipLast<TSource>(this System.Linq.IQueryable<TSource> source, int count) { throw null; }
diff --git a/src/libraries/System.Linq.Queryable/src/System.Linq.Queryable.csproj b/src/libraries/System.Linq.Queryable/src/System.Linq.Queryable.csproj
index a531c2e8494096..d3def1d1063a46 100644
--- a/src/libraries/System.Linq.Queryable/src/System.Linq.Queryable.csproj
+++ b/src/libraries/System.Linq.Queryable/src/System.Linq.Queryable.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Linq.Queryable</AssemblyName>
-    <RootNamespace>System.Linq.Queryable</RootNamespace>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
diff --git a/src/libraries/System.Linq.Queryable/src/System/Linq/CachedReflection.cs b/src/libraries/System.Linq.Queryable/src/System/Linq/CachedReflection.cs
index 91e37ff906b2cf..8f345d0a86bb4f 100644
--- a/src/libraries/System.Linq.Queryable/src/System/Linq/CachedReflection.cs
+++ b/src/libraries/System.Linq.Queryable/src/System/Linq/CachedReflection.cs
@@ -262,7 +262,7 @@ public static MethodInfo ElementAt_TSource_2(Type TSource) =>
 
         public static MethodInfo ElementAtOrDefault_TSource_2(Type TSource) =>
              (s_ElementAtOrDefault_TSource_2 ??
-             (s_ElementAtOrDefault_TSource_2 = new Func<IQueryable<object>, int, object>(Queryable.ElementAtOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_ElementAtOrDefault_TSource_2 = new Func<IQueryable<object>, int, object?>(Queryable.ElementAtOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource);
 
         private static MethodInfo? s_Except_TSource_2;
@@ -297,14 +297,14 @@ public static MethodInfo First_TSource_2(Type TSource) =>
 
         public static MethodInfo FirstOrDefault_TSource_1(Type TSource) =>
              (s_FirstOrDefault_TSource_1 ??
-             (s_FirstOrDefault_TSource_1 = new Func<IQueryable<object>, object>(Queryable.FirstOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_FirstOrDefault_TSource_1 = new Func<IQueryable<object>, object?>(Queryable.FirstOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource);
 
         private static MethodInfo? s_FirstOrDefault_TSource_2;
 
         public static MethodInfo FirstOrDefault_TSource_2(Type TSource) =>
              (s_FirstOrDefault_TSource_2 ??
-             (s_FirstOrDefault_TSource_2 = new Func<IQueryable<object>, Expression<Func<object, bool>>, object>(Queryable.FirstOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_FirstOrDefault_TSource_2 = new Func<IQueryable<object>, Expression<Func<object, bool>>, object?>(Queryable.FirstOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource);
 
         private static MethodInfo? s_GroupBy_TSource_TKey_2;
@@ -423,14 +423,14 @@ public static MethodInfo Last_TSource_2(Type TSource) =>
 
         public static MethodInfo LastOrDefault_TSource_1(Type TSource) =>
              (s_LastOrDefault_TSource_1 ??
-             (s_LastOrDefault_TSource_1 = new Func<IQueryable<object>, object>(Queryable.LastOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_LastOrDefault_TSource_1 = new Func<IQueryable<object>, object?>(Queryable.LastOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource);
 
         private static MethodInfo? s_LastOrDefault_TSource_2;
 
         public static MethodInfo LastOrDefault_TSource_2(Type TSource) =>
              (s_LastOrDefault_TSource_2 ??
-             (s_LastOrDefault_TSource_2 = new Func<IQueryable<object>, Expression<Func<object, bool>>, object>(Queryable.LastOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_LastOrDefault_TSource_2 = new Func<IQueryable<object>, Expression<Func<object, bool>>, object?>(Queryable.LastOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource);
 
         private static MethodInfo? s_LongCount_TSource_1;
@@ -451,28 +451,28 @@ public static MethodInfo LongCount_TSource_2(Type TSource) =>
 
         public static MethodInfo Max_TSource_1(Type TSource) =>
              (s_Max_TSource_1 ??
-             (s_Max_TSource_1 = new Func<IQueryable<object>, object>(Queryable.Max).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_Max_TSource_1 = new Func<IQueryable<object>, object?>(Queryable.Max).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource);
 
         private static MethodInfo? s_Max_TSource_TResult_2;
 
         public static MethodInfo Max_TSource_TResult_2(Type TSource, Type TResult) =>
              (s_Max_TSource_TResult_2 ??
-             (s_Max_TSource_TResult_2 = new Func<IQueryable<object>, Expression<Func<object, object>>, object>(Queryable.Max).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_Max_TSource_TResult_2 = new Func<IQueryable<object>, Expression<Func<object, object>>, object?>(Queryable.Max).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource, TResult);
 
         private static MethodInfo? s_Min_TSource_1;
 
         public static MethodInfo Min_TSource_1(Type TSource) =>
              (s_Min_TSource_1 ??
-             (s_Min_TSource_1 = new Func<IQueryable<object>, object>(Queryable.Min).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_Min_TSource_1 = new Func<IQueryable<object>, object?>(Queryable.Min).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource);
 
         private static MethodInfo? s_Min_TSource_TResult_2;
 
         public static MethodInfo Min_TSource_TResult_2(Type TSource, Type TResult) =>
              (s_Min_TSource_TResult_2 ??
-             (s_Min_TSource_TResult_2 = new Func<IQueryable<object>, Expression<Func<object, object>>, object>(Queryable.Min).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_Min_TSource_TResult_2 = new Func<IQueryable<object>, Expression<Func<object, object>>, object?>(Queryable.Min).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource, TResult);
 
         private static MethodInfo? s_OfType_TResult_1;
@@ -591,14 +591,14 @@ public static MethodInfo Single_TSource_2(Type TSource) =>
 
         public static MethodInfo SingleOrDefault_TSource_1(Type TSource) =>
              (s_SingleOrDefault_TSource_1 ??
-             (s_SingleOrDefault_TSource_1 = new Func<IQueryable<object>, object>(Queryable.SingleOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_SingleOrDefault_TSource_1 = new Func<IQueryable<object>, object?>(Queryable.SingleOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource);
 
         private static MethodInfo? s_SingleOrDefault_TSource_2;
 
         public static MethodInfo SingleOrDefault_TSource_2(Type TSource) =>
              (s_SingleOrDefault_TSource_2 ??
-             (s_SingleOrDefault_TSource_2 = new Func<IQueryable<object>, Expression<Func<object, bool>>, object>(Queryable.SingleOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
+             (s_SingleOrDefault_TSource_2 = new Func<IQueryable<object>, Expression<Func<object, bool>>, object?>(Queryable.SingleOrDefault).GetMethodInfo().GetGenericMethodDefinition()))
               .MakeGenericMethod(TSource);
 
         private static MethodInfo? s_Skip_TSource_2;
diff --git a/src/libraries/System.Linq.Queryable/src/System/Linq/Queryable.cs b/src/libraries/System.Linq.Queryable/src/System/Linq/Queryable.cs
index e3ed64c4f1916e..902474b9eedfe4 100644
--- a/src/libraries/System.Linq.Queryable/src/System/Linq/Queryable.cs
+++ b/src/libraries/System.Linq.Queryable/src/System/Linq/Queryable.cs
@@ -740,8 +740,7 @@ public static TSource First<TSource>(this IQueryable<TSource> source, Expression
                     ));
         }
 
-        [return: MaybeNull]
-        public static TSource FirstOrDefault<TSource>(this IQueryable<TSource> source)
+        public static TSource? FirstOrDefault<TSource>(this IQueryable<TSource> source)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
@@ -751,8 +750,7 @@ public static TSource FirstOrDefault<TSource>(this IQueryable<TSource> source)
                     CachedReflectionInfo.FirstOrDefault_TSource_1(typeof(TSource)), source.Expression));
         }
 
-        [return: MaybeNull]
-        public static TSource FirstOrDefault<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
+        public static TSource? FirstOrDefault<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
@@ -790,8 +788,7 @@ public static TSource Last<TSource>(this IQueryable<TSource> source, Expression<
                     ));
         }
 
-        [return: MaybeNull]
-        public static TSource LastOrDefault<TSource>(this IQueryable<TSource> source)
+        public static TSource? LastOrDefault<TSource>(this IQueryable<TSource> source)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
@@ -801,8 +798,7 @@ public static TSource LastOrDefault<TSource>(this IQueryable<TSource> source)
                     CachedReflectionInfo.LastOrDefault_TSource_1(typeof(TSource)), source.Expression));
         }
 
-        [return: MaybeNull]
-        public static TSource LastOrDefault<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
+        public static TSource? LastOrDefault<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
@@ -840,8 +836,7 @@ public static TSource Single<TSource>(this IQueryable<TSource> source, Expressio
                     ));
         }
 
-        [return: MaybeNull]
-        public static TSource SingleOrDefault<TSource>(this IQueryable<TSource> source)
+        public static TSource? SingleOrDefault<TSource>(this IQueryable<TSource> source)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
@@ -851,8 +846,7 @@ public static TSource SingleOrDefault<TSource>(this IQueryable<TSource> source)
                     CachedReflectionInfo.SingleOrDefault_TSource_1(typeof(TSource)), source.Expression));
         }
 
-        [return: MaybeNull]
-        public static TSource SingleOrDefault<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
+        public static TSource? SingleOrDefault<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
@@ -880,8 +874,7 @@ public static TSource ElementAt<TSource>(this IQueryable<TSource> source, int in
                     ));
         }
 
-        [return: MaybeNull]
-        public static TSource ElementAtOrDefault<TSource>(this IQueryable<TSource> source, int index)
+        public static TSource? ElementAtOrDefault<TSource>(this IQueryable<TSource> source, int index)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
@@ -1065,8 +1058,7 @@ public static long LongCount<TSource>(this IQueryable<TSource> source, Expressio
                     ));
         }
 
-        [return: MaybeNull]
-        public static TSource Min<TSource>(this IQueryable<TSource> source)
+        public static TSource? Min<TSource>(this IQueryable<TSource> source)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
@@ -1076,8 +1068,7 @@ public static TSource Min<TSource>(this IQueryable<TSource> source)
                     CachedReflectionInfo.Min_TSource_1(typeof(TSource)), source.Expression));
         }
 
-        [return: MaybeNull]
-        public static TResult Min<TSource, TResult>(this IQueryable<TSource> source, Expression<Func<TSource, TResult>> selector)
+        public static TResult? Min<TSource, TResult>(this IQueryable<TSource> source, Expression<Func<TSource, TResult>> selector)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
@@ -1091,8 +1082,7 @@ public static TResult Min<TSource, TResult>(this IQueryable<TSource> source, Exp
                     ));
         }
 
-        [return: MaybeNull]
-        public static TSource Max<TSource>(this IQueryable<TSource> source)
+        public static TSource? Max<TSource>(this IQueryable<TSource> source)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
@@ -1102,8 +1092,7 @@ public static TSource Max<TSource>(this IQueryable<TSource> source)
                     CachedReflectionInfo.Max_TSource_1(typeof(TSource)), source.Expression));
         }
 
-        [return: MaybeNull]
-        public static TResult Max<TSource, TResult>(this IQueryable<TSource> source, Expression<Func<TSource, TResult>> selector)
+        public static TResult? Max<TSource, TResult>(this IQueryable<TSource> source, Expression<Func<TSource, TResult>> selector)
         {
             if (source == null)
                 throw Error.ArgumentNull(nameof(source));
diff --git a/src/libraries/System.Linq/Directory.Build.props b/src/libraries/System.Linq/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Linq/Directory.Build.props
+++ b/src/libraries/System.Linq/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Linq/ref/System.Linq.cs b/src/libraries/System.Linq/ref/System.Linq.cs
index bf41a28033ca9b..91d5432e2b5a3a 100644
--- a/src/libraries/System.Linq/ref/System.Linq.cs
+++ b/src/libraries/System.Linq/ref/System.Linq.cs
@@ -42,17 +42,17 @@ public static partial class Enumerable
         public static bool Contains<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, TSource value, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
         public static int Count<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
         public static int Count<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
-        public static System.Collections.Generic.IEnumerable<TSource> DefaultIfEmpty<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
+        public static System.Collections.Generic.IEnumerable<TSource?> DefaultIfEmpty<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
         public static System.Collections.Generic.IEnumerable<TSource> DefaultIfEmpty<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, TSource defaultValue) { throw null; }
         public static System.Collections.Generic.IEnumerable<TSource> Distinct<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
         public static System.Collections.Generic.IEnumerable<TSource> Distinct<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TSource ElementAtOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, int index) { throw null; }
+        public static TSource? ElementAtOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, int index) { throw null; }
         public static TSource ElementAt<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, int index) { throw null; }
         public static System.Collections.Generic.IEnumerable<TResult> Empty<TResult>() { throw null; }
         public static System.Collections.Generic.IEnumerable<TSource> Except<TSource>(this System.Collections.Generic.IEnumerable<TSource> first, System.Collections.Generic.IEnumerable<TSource> second) { throw null; }
         public static System.Collections.Generic.IEnumerable<TSource> Except<TSource>(this System.Collections.Generic.IEnumerable<TSource> first, System.Collections.Generic.IEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TSource FirstOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TSource FirstOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
+        public static TSource? FirstOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
+        public static TSource? FirstOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static TSource First<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
         public static TSource First<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static System.Collections.Generic.IEnumerable<System.Linq.IGrouping<TKey, TSource>> GroupBy<TSource, TKey>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, TKey> keySelector) { throw null; }
@@ -69,8 +69,8 @@ public static partial class Enumerable
         public static System.Collections.Generic.IEnumerable<TSource> Intersect<TSource>(this System.Collections.Generic.IEnumerable<TSource> first, System.Collections.Generic.IEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
         public static System.Collections.Generic.IEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IEnumerable<TOuter> outer, System.Collections.Generic.IEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector) { throw null; }
         public static System.Collections.Generic.IEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IEnumerable<TOuter> outer, System.Collections.Generic.IEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TSource LastOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TSource LastOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
+        public static TSource? LastOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
+        public static TSource? LastOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static TSource Last<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
         public static TSource Last<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static long LongCount<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
@@ -85,7 +85,7 @@ public static partial class Enumerable
         public static long? Max(this System.Collections.Generic.IEnumerable<long?> source) { throw null; }
         public static float? Max(this System.Collections.Generic.IEnumerable<float?> source) { throw null; }
         public static float Max(this System.Collections.Generic.IEnumerable<float> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TSource Max<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
+        public static TSource? Max<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
         public static decimal Max<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, decimal> selector) { throw null; }
         public static double Max<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, double> selector) { throw null; }
         public static int Max<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, int> selector) { throw null; }
@@ -96,7 +96,7 @@ public static partial class Enumerable
         public static long? Max<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, long?> selector) { throw null; }
         public static float? Max<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, float?> selector) { throw null; }
         public static float Max<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, float> selector) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TResult Max<TSource, TResult>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, TResult> selector) { throw null; }
+        public static TResult? Max<TSource, TResult>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, TResult> selector) { throw null; }
         public static decimal Min(this System.Collections.Generic.IEnumerable<decimal> source) { throw null; }
         public static double Min(this System.Collections.Generic.IEnumerable<double> source) { throw null; }
         public static int Min(this System.Collections.Generic.IEnumerable<int> source) { throw null; }
@@ -107,7 +107,7 @@ public static partial class Enumerable
         public static long? Min(this System.Collections.Generic.IEnumerable<long?> source) { throw null; }
         public static float? Min(this System.Collections.Generic.IEnumerable<float?> source) { throw null; }
         public static float Min(this System.Collections.Generic.IEnumerable<float> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TSource Min<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
+        public static TSource? Min<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
         public static decimal Min<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, decimal> selector) { throw null; }
         public static double Min<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, double> selector) { throw null; }
         public static int Min<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, int> selector) { throw null; }
@@ -118,7 +118,7 @@ public static partial class Enumerable
         public static long? Min<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, long?> selector) { throw null; }
         public static float? Min<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, float?> selector) { throw null; }
         public static float Min<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, float> selector) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TResult Min<TSource, TResult>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, TResult> selector) { throw null; }
+        public static TResult? Min<TSource, TResult>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, TResult> selector) { throw null; }
         public static System.Collections.Generic.IEnumerable<TResult> OfType<TResult>(this System.Collections.IEnumerable source) { throw null; }
         public static System.Linq.IOrderedEnumerable<TSource> OrderByDescending<TSource, TKey>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, TKey> keySelector) { throw null; }
         public static System.Linq.IOrderedEnumerable<TSource> OrderByDescending<TSource, TKey>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, TKey> keySelector, System.Collections.Generic.IComparer<TKey>? comparer) { throw null; }
@@ -136,8 +136,8 @@ public static partial class Enumerable
         public static System.Collections.Generic.IEnumerable<TResult> Select<TSource, TResult>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, TResult> selector) { throw null; }
         public static bool SequenceEqual<TSource>(this System.Collections.Generic.IEnumerable<TSource> first, System.Collections.Generic.IEnumerable<TSource> second) { throw null; }
         public static bool SequenceEqual<TSource>(this System.Collections.Generic.IEnumerable<TSource> first, System.Collections.Generic.IEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TSource SingleOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute] public static TSource SingleOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
+        public static TSource? SingleOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
+        public static TSource? SingleOrDefault<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static TSource Single<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
         public static TSource Single<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, bool> predicate) { throw null; }
         public static System.Collections.Generic.IEnumerable<TSource> SkipLast<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, int count) { throw null; }
diff --git a/src/libraries/System.Linq/src/System.Linq.csproj b/src/libraries/System.Linq/src/System.Linq.csproj
index a9caa2e36d3ea9..ea585685f3e609 100644
--- a/src/libraries/System.Linq/src/System.Linq.csproj
+++ b/src/libraries/System.Linq/src/System.Linq.csproj
@@ -1,15 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Linq</AssemblyName>
-    <RootNamespace>System.Linq</RootNamespace>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
-  <ItemGroup>
-    <ContractProject Include="..\ref\System.Linq.csproj">
-      <BuildTargetFramework>$(NetCoreAppCurrent)</BuildTargetFramework>
-    </ContractProject>
-  </ItemGroup>
   <ItemGroup> <!-- Optimize for speed -->
     <Compile Include="System\Linq\AppendPrepend.SpeedOpt.cs" />
     <Compile Include="System\Linq\Concat.SpeedOpt.cs" />
diff --git a/src/libraries/System.Linq/src/System/Linq/DefaultIfEmpty.cs b/src/libraries/System.Linq/src/System/Linq/DefaultIfEmpty.cs
index e358538081c0a5..a513a6eb7fe33a 100644
--- a/src/libraries/System.Linq/src/System/Linq/DefaultIfEmpty.cs
+++ b/src/libraries/System.Linq/src/System/Linq/DefaultIfEmpty.cs
@@ -8,7 +8,7 @@ namespace System.Linq
 {
     public static partial class Enumerable
     {
-        public static IEnumerable<TSource> DefaultIfEmpty<TSource>(this IEnumerable<TSource> source) =>
+        public static IEnumerable<TSource?> DefaultIfEmpty<TSource>(this IEnumerable<TSource> source) =>
             DefaultIfEmpty(source, default!);
 
         public static IEnumerable<TSource> DefaultIfEmpty<TSource>(this IEnumerable<TSource> source, TSource defaultValue)
diff --git a/src/libraries/System.Linq/src/System/Linq/ElementAt.cs b/src/libraries/System.Linq/src/System/Linq/ElementAt.cs
index a857819b290d80..da8dc8f9287646 100644
--- a/src/libraries/System.Linq/src/System/Linq/ElementAt.cs
+++ b/src/libraries/System.Linq/src/System/Linq/ElementAt.cs
@@ -51,8 +51,7 @@ public static TSource ElementAt<TSource>(this IEnumerable<TSource> source, int i
             return default;
         }
 
-        [return: MaybeNull]
-        public static TSource ElementAtOrDefault<TSource>(this IEnumerable<TSource> source, int index)
+        public static TSource? ElementAtOrDefault<TSource>(this IEnumerable<TSource> source, int index)
         {
             if (source == null)
             {
@@ -90,7 +89,7 @@ public static TSource ElementAtOrDefault<TSource>(this IEnumerable<TSource> sour
                 }
             }
 
-            return default!;
+            return default;
         }
     }
 }
diff --git a/src/libraries/System.Linq/src/System/Linq/First.cs b/src/libraries/System.Linq/src/System/Linq/First.cs
index 6ebeb804463f8e..295acb5e4d4150 100644
--- a/src/libraries/System.Linq/src/System/Linq/First.cs
+++ b/src/libraries/System.Linq/src/System/Linq/First.cs
@@ -30,16 +30,13 @@ public static TSource First<TSource>(this IEnumerable<TSource> source, Func<TSou
             return first!;
         }
 
-        [return: MaybeNull]
-        public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source) =>
+        public static TSource? FirstOrDefault<TSource>(this IEnumerable<TSource> source) =>
             source.TryGetFirst(out bool _);
 
-        [return: MaybeNull]
-        public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) =>
+        public static TSource? FirstOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) =>
             source.TryGetFirst(predicate, out bool _);
 
-        [return: MaybeNull]
-        private static TSource TryGetFirst<TSource>(this IEnumerable<TSource> source, out bool found)
+        private static TSource? TryGetFirst<TSource>(this IEnumerable<TSource> source, out bool found)
         {
             if (source == null)
             {
@@ -72,11 +69,10 @@ private static TSource TryGetFirst<TSource>(this IEnumerable<TSource> source, ou
             }
 
             found = false;
-            return default!;
+            return default;
         }
 
-        [return: MaybeNull]
-        private static TSource TryGetFirst<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate, out bool found)
+        private static TSource? TryGetFirst<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate, out bool found)
         {
             if (source == null)
             {
@@ -98,7 +94,7 @@ private static TSource TryGetFirst<TSource>(this IEnumerable<TSource> source, Fu
             }
 
             found = false;
-            return default!;
+            return default;
         }
     }
 }
diff --git a/src/libraries/System.Linq/src/System/Linq/IPartition.cs b/src/libraries/System.Linq/src/System/Linq/IPartition.cs
index d1c5e2e102b769..68b676f0948fa6 100644
--- a/src/libraries/System.Linq/src/System/Linq/IPartition.cs
+++ b/src/libraries/System.Linq/src/System/Linq/IPartition.cs
@@ -30,23 +30,20 @@ internal interface IPartition<TElement> : IIListProvider<TElement>
         /// <param name="index">The 0-based index to access.</param>
         /// <param name="found"><c>true</c> if the sequence contains an element at that index, <c>false</c> otherwise.</param>
         /// <returns>The element if <paramref name="found"/> is <c>true</c>, otherwise, the default value of <typeparamref name="TElement"/>.</returns>
-        [return: MaybeNull]
-        TElement TryGetElementAt(int index, out bool found);
+        TElement? TryGetElementAt(int index, out bool found);
 
         /// <summary>
         /// Gets the first item in this sequence.
         /// </summary>
         /// <param name="found"><c>true</c> if the sequence contains an element, <c>false</c> otherwise.</param>
         /// <returns>The element if <paramref name="found"/> is <c>true</c>, otherwise, the default value of <typeparamref name="TElement"/>.</returns>
-        [return: MaybeNull]
-        TElement TryGetFirst(out bool found);
+        TElement? TryGetFirst(out bool found);
 
         /// <summary>
         /// Gets the last item in this sequence.
         /// </summary>
         /// <param name="found"><c>true</c> if the sequence contains an element, <c>false</c> otherwise.</param>
         /// <returns>The element if <paramref name="found"/> is <c>true</c>, otherwise, the default value of <typeparamref name="TElement"/>.</returns>
-        [return: MaybeNull]
-        TElement TryGetLast(out bool found);
+        TElement? TryGetLast(out bool found);
     }
 }
diff --git a/src/libraries/System.Linq/src/System/Linq/Last.cs b/src/libraries/System.Linq/src/System/Linq/Last.cs
index d08bbf96682fe3..d7819614ab0753 100644
--- a/src/libraries/System.Linq/src/System/Linq/Last.cs
+++ b/src/libraries/System.Linq/src/System/Linq/Last.cs
@@ -30,16 +30,13 @@ public static TSource Last<TSource>(this IEnumerable<TSource> source, Func<TSour
             return last!;
         }
 
-        [return: MaybeNull]
-        public static TSource LastOrDefault<TSource>(this IEnumerable<TSource> source) =>
+        public static TSource? LastOrDefault<TSource>(this IEnumerable<TSource> source) =>
             source.TryGetLast(out bool _);
 
-        [return: MaybeNull]
-        public static TSource LastOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) =>
+        public static TSource? LastOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) =>
             source.TryGetLast(predicate, out bool _);
 
-        [return: MaybeNull]
-        private static TSource TryGetLast<TSource>(this IEnumerable<TSource> source, out bool found)
+        private static TSource? TryGetLast<TSource>(this IEnumerable<TSource> source, out bool found)
         {
             if (source == null)
             {
@@ -80,11 +77,10 @@ private static TSource TryGetLast<TSource>(this IEnumerable<TSource> source, out
             }
 
             found = false;
-            return default!;
+            return default;
         }
 
-        [return: MaybeNull]
-        private static TSource TryGetLast<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate, out bool found)
+        private static TSource? TryGetLast<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate, out bool found)
         {
             if (source == null)
             {
@@ -139,7 +135,7 @@ private static TSource TryGetLast<TSource>(this IEnumerable<TSource> source, Fun
             }
 
             found = false;
-            return default!;
+            return default;
         }
     }
 }
diff --git a/src/libraries/System.Linq/src/System/Linq/Max.cs b/src/libraries/System.Linq/src/System/Linq/Max.cs
index 21e1f8d890bf95..9dc4c92cd1f865 100644
--- a/src/libraries/System.Linq/src/System/Linq/Max.cs
+++ b/src/libraries/System.Linq/src/System/Linq/Max.cs
@@ -441,8 +441,7 @@ public static decimal Max(this IEnumerable<decimal> source)
             return value;
         }
 
-        [return: MaybeNull]
-        public static TSource Max<TSource>(this IEnumerable<TSource> source)
+        public static TSource? Max<TSource>(this IEnumerable<TSource> source)
         {
             if (source == null)
             {
@@ -450,7 +449,7 @@ public static TSource Max<TSource>(this IEnumerable<TSource> source)
             }
 
             Comparer<TSource> comparer = Comparer<TSource>.Default;
-            TSource value = default!;
+            TSource? value = default;
             if (value == null)
             {
                 using (IEnumerator<TSource> e = source.GetEnumerator())
@@ -983,8 +982,7 @@ public static decimal Max<TSource>(this IEnumerable<TSource> source, Func<TSourc
             return value;
         }
 
-        [return: MaybeNull]
-        public static TResult Max<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)
+        public static TResult? Max<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)
         {
             if (source == null)
             {
@@ -997,7 +995,7 @@ public static TResult Max<TSource, TResult>(this IEnumerable<TSource> source, Fu
             }
 
             Comparer<TResult> comparer = Comparer<TResult>.Default;
-            TResult value = default!;
+            TResult? value = default;
             if (value == null)
             {
                 using (IEnumerator<TSource> e = source.GetEnumerator())
diff --git a/src/libraries/System.Linq/src/System/Linq/Min.cs b/src/libraries/System.Linq/src/System/Linq/Min.cs
index b3a7e62d5b7f8b..9958c8468bec44 100644
--- a/src/libraries/System.Linq/src/System/Linq/Min.cs
+++ b/src/libraries/System.Linq/src/System/Linq/Min.cs
@@ -399,8 +399,7 @@ public static decimal Min(this IEnumerable<decimal> source)
             return value;
         }
 
-        [return: MaybeNull]
-        public static TSource Min<TSource>(this IEnumerable<TSource> source)
+        public static TSource? Min<TSource>(this IEnumerable<TSource> source)
         {
             if (source == null)
             {
@@ -408,7 +407,7 @@ public static TSource Min<TSource>(this IEnumerable<TSource> source)
             }
 
             Comparer<TSource> comparer = Comparer<TSource>.Default;
-            TSource value = default!;
+            TSource? value = default;
             if (value == null)
             {
                 using (IEnumerator<TSource> e = source.GetEnumerator())
@@ -899,8 +898,7 @@ public static decimal Min<TSource>(this IEnumerable<TSource> source, Func<TSourc
             return value;
         }
 
-        [return: MaybeNull]
-        public static TResult Min<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)
+        public static TResult? Min<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)
         {
             if (source == null)
             {
@@ -913,7 +911,7 @@ public static TResult Min<TSource, TResult>(this IEnumerable<TSource> source, Fu
             }
 
             Comparer<TResult> comparer = Comparer<TResult>.Default;
-            TResult value = default!;
+            TResult? value = default;
             if (value == null)
             {
                 using (IEnumerator<TSource> e = source.GetEnumerator())
diff --git a/src/libraries/System.Linq/src/System/Linq/OrderedEnumerable.SpeedOpt.cs b/src/libraries/System.Linq/src/System/Linq/OrderedEnumerable.SpeedOpt.cs
index 5d3946e14299c4..b90dbf28a9537b 100644
--- a/src/libraries/System.Linq/src/System/Linq/OrderedEnumerable.SpeedOpt.cs
+++ b/src/libraries/System.Linq/src/System/Linq/OrderedEnumerable.SpeedOpt.cs
@@ -138,8 +138,7 @@ internal int GetCount(int minIdx, int maxIdx, bool onlyIfCheap)
 
         public IPartition<TElement> Take(int count) => new OrderedPartition<TElement>(this, 0, count - 1);
 
-        [return: MaybeNull]
-        public TElement TryGetElementAt(int index, out bool found)
+        public TElement? TryGetElementAt(int index, out bool found)
         {
             if (index == 0)
             {
@@ -158,11 +157,10 @@ public TElement TryGetElementAt(int index, out bool found)
             }
 
             found = false;
-            return default!;
+            return default;
         }
 
-        [return: MaybeNull]
-        public TElement TryGetFirst(out bool found)
+        public TElement? TryGetFirst(out bool found)
         {
             CachingComparer<TElement> comparer = GetComparer();
             using (IEnumerator<TElement> e = _source.GetEnumerator())
@@ -170,7 +168,7 @@ public TElement TryGetFirst(out bool found)
                 if (!e.MoveNext())
                 {
                     found = false;
-                    return default!;
+                    return default;
                 }
 
                 TElement value = e.Current;
@@ -189,15 +187,14 @@ public TElement TryGetFirst(out bool found)
             }
         }
 
-        [return: MaybeNull]
-        public TElement TryGetLast(out bool found)
+        public TElement? TryGetLast(out bool found)
         {
             using (IEnumerator<TElement> e = _source.GetEnumerator())
             {
                 if (!e.MoveNext())
                 {
                     found = false;
-                    return default!;
+                    return default;
                 }
 
                 CachingComparer<TElement> comparer = GetComparer();
@@ -217,15 +214,14 @@ public TElement TryGetLast(out bool found)
             }
         }
 
-        [return: MaybeNull]
-        public TElement TryGetLast(int minIdx, int maxIdx, out bool found)
+        public TElement? TryGetLast(int minIdx, int maxIdx, out bool found)
         {
             Buffer<TElement> buffer = new Buffer<TElement>(_source);
             int count = buffer._count;
             if (minIdx >= count)
             {
                 found = false;
-                return default!;
+                return default;
             }
 
             found = true;
diff --git a/src/libraries/System.Linq/src/System/Linq/OrderedEnumerable.cs b/src/libraries/System.Linq/src/System/Linq/OrderedEnumerable.cs
index 8f985a4469fb37..2c8cf01f941d62 100644
--- a/src/libraries/System.Linq/src/System/Linq/OrderedEnumerable.cs
+++ b/src/libraries/System.Linq/src/System/Linq/OrderedEnumerable.cs
@@ -72,8 +72,7 @@ internal IEnumerator<TElement> GetEnumerator(int minIdx, int maxIdx)
         IOrderedEnumerable<TElement> IOrderedEnumerable<TElement>.CreateOrderedEnumerable<TKey>(Func<TElement, TKey> keySelector, IComparer<TKey>? comparer, bool descending) =>
             new OrderedEnumerable<TElement, TKey>(_source, keySelector, comparer, @descending, this);
 
-        [return: MaybeNull]
-        public TElement TryGetLast(Func<TElement, bool> predicate, out bool found)
+        public TElement? TryGetLast(Func<TElement, bool> predicate, out bool found)
         {
             CachingComparer<TElement> comparer = GetComparer();
             using (IEnumerator<TElement> e = _source.GetEnumerator())
@@ -84,7 +83,7 @@ public TElement TryGetLast(Func<TElement, bool> predicate, out bool found)
                     if (!e.MoveNext())
                     {
                         found = false;
-                        return default!;
+                        return default;
                     }
 
                     value = e.Current;
@@ -176,7 +175,7 @@ internal class CachingComparer<TElement, TKey> : CachingComparer<TElement>
         protected readonly Func<TElement, TKey> _keySelector;
         protected readonly IComparer<TKey> _comparer;
         protected readonly bool _descending;
-        [MaybeNull] protected TKey _lastKey = default!;
+        protected TKey? _lastKey;
 
         public CachingComparer(Func<TElement, TKey> keySelector, IComparer<TKey> comparer, bool descending)
         {
diff --git a/src/libraries/System.Linq/src/System/Linq/Partition.SpeedOpt.cs b/src/libraries/System.Linq/src/System/Linq/Partition.SpeedOpt.cs
index f2f39c02bead89..c46465f82547b3 100644
--- a/src/libraries/System.Linq/src/System/Linq/Partition.SpeedOpt.cs
+++ b/src/libraries/System.Linq/src/System/Linq/Partition.SpeedOpt.cs
@@ -38,7 +38,6 @@ private EmptyPartition()
         public TElement Current => default!;
 
         [ExcludeFromCodeCoverage(Justification = "Shouldn't be called, and as undefined can return or throw anything anyway")]
-        [MaybeNull]
         object IEnumerator.Current => default!;
 
         void IEnumerator.Reset()
@@ -55,25 +54,22 @@ void IDisposable.Dispose()
 
         public IPartition<TElement> Take(int count) => this;
 
-        [return: MaybeNull]
-        public TElement TryGetElementAt(int index, out bool found)
+        public TElement? TryGetElementAt(int index, out bool found)
         {
             found = false;
-            return default!;
+            return default;
         }
 
-        [return: MaybeNull]
-        public TElement TryGetFirst(out bool found)
+        public TElement? TryGetFirst(out bool found)
         {
             found = false;
-            return default!;
+            return default;
         }
 
-        [return: MaybeNull]
-        public TElement TryGetLast(out bool found)
+        public TElement? TryGetLast(out bool found)
         {
             found = false;
-            return default!;
+            return default;
         }
 
         public TElement[] ToArray() => Array.Empty<TElement>();
@@ -117,8 +113,7 @@ public IPartition<TElement> Take(int count)
             return new OrderedPartition<TElement>(_source, _minIndexInclusive, maxIndex);
         }
 
-        [return: MaybeNull]
-        public TElement TryGetElementAt(int index, out bool found)
+        public TElement? TryGetElementAt(int index, out bool found)
         {
             if (unchecked((uint)index <= (uint)(_maxIndexInclusive - _minIndexInclusive)))
             {
@@ -126,14 +121,12 @@ public TElement TryGetElementAt(int index, out bool found)
             }
 
             found = false;
-            return default!;
+            return default;
         }
 
-        [return: MaybeNull]
-        public TElement TryGetFirst(out bool found) => _source.TryGetElementAt(_minIndexInclusive, out found);
+        public TElement? TryGetFirst(out bool found) => _source.TryGetElementAt(_minIndexInclusive, out found);
 
-        [return: MaybeNull]
-        public TElement TryGetLast(out bool found) =>
+        public TElement? TryGetLast(out bool found) =>
             _source.TryGetLast(_minIndexInclusive, _maxIndexInclusive, out found);
 
         public TElement[] ToArray() => _source.ToArray(_minIndexInclusive, _maxIndexInclusive);
@@ -201,8 +194,7 @@ public IPartition<TSource> Take(int count)
                 return unchecked((uint)maxIndex >= (uint)_maxIndexInclusive) ? this : new ListPartition<TSource>(_source, _minIndexInclusive, maxIndex);
             }
 
-            [return: MaybeNull]
-            public TSource TryGetElementAt(int index, out bool found)
+            public TSource? TryGetElementAt(int index, out bool found)
             {
                 if (unchecked((uint)index <= (uint)(_maxIndexInclusive - _minIndexInclusive) && index < _source.Count - _minIndexInclusive))
                 {
@@ -211,11 +203,10 @@ public TSource TryGetElementAt(int index, out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
-            [return: MaybeNull]
-            public TSource TryGetFirst(out bool found)
+            public TSource? TryGetFirst(out bool found)
             {
                 if (_source.Count > _minIndexInclusive)
                 {
@@ -224,11 +215,10 @@ public TSource TryGetFirst(out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
-            [return: MaybeNull]
-            public TSource TryGetLast(out bool found)
+            public TSource? TryGetLast(out bool found)
             {
                 int lastIndex = _source.Count - 1;
                 if (lastIndex >= _minIndexInclusive)
@@ -238,7 +228,7 @@ public TSource TryGetLast(out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
             private int Count
@@ -480,8 +470,7 @@ public IPartition<TSource> Take(int count)
                 return new EnumerablePartition<TSource>(_source, _minIndexInclusive, maxIndex);
             }
 
-            [return: MaybeNull]
-            public TSource TryGetElementAt(int index, out bool found)
+            public TSource? TryGetElementAt(int index, out bool found)
             {
                 // If the index is negative or >= our max count, return early.
                 if (index >= 0 && (!HasLimit || index < Limit))
@@ -499,11 +488,10 @@ public TSource TryGetElementAt(int index, out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
-            [return: MaybeNull]
-            public TSource TryGetFirst(out bool found)
+            public TSource? TryGetFirst(out bool found)
             {
                 using (IEnumerator<TSource> en = _source.GetEnumerator())
                 {
@@ -515,11 +503,10 @@ public TSource TryGetFirst(out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
-            [return: MaybeNull]
-            public TSource TryGetLast(out bool found)
+            public TSource? TryGetLast(out bool found)
             {
                 using (IEnumerator<TSource> en = _source.GetEnumerator())
                 {
@@ -542,7 +529,7 @@ public TSource TryGetLast(out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
             public TSource[] ToArray()
diff --git a/src/libraries/System.Linq/src/System/Linq/Repeat.SpeedOpt.cs b/src/libraries/System.Linq/src/System/Linq/Repeat.SpeedOpt.cs
index 7cc12d6678e099..3840acd81340a5 100644
--- a/src/libraries/System.Linq/src/System/Linq/Repeat.SpeedOpt.cs
+++ b/src/libraries/System.Linq/src/System/Linq/Repeat.SpeedOpt.cs
@@ -62,8 +62,7 @@ public IPartition<TResult> Take(int count)
                 return new RepeatIterator<TResult>(_current, count);
             }
 
-            [return: MaybeNull]
-            public TResult TryGetElementAt(int index, out bool found)
+            public TResult? TryGetElementAt(int index, out bool found)
             {
                 if ((uint)index < (uint)_count)
                 {
@@ -72,7 +71,7 @@ public TResult TryGetElementAt(int index, out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
             public TResult TryGetFirst(out bool found)
diff --git a/src/libraries/System.Linq/src/System/Linq/Select.SpeedOpt.cs b/src/libraries/System.Linq/src/System/Linq/Select.SpeedOpt.cs
index 530f92b0b1fb7b..e23cbd49f32238 100644
--- a/src/libraries/System.Linq/src/System/Linq/Select.SpeedOpt.cs
+++ b/src/libraries/System.Linq/src/System/Linq/Select.SpeedOpt.cs
@@ -133,8 +133,7 @@ public IPartition<TResult> Take(int count)
                     new SelectListPartitionIterator<TSource, TResult>(_source, _selector, 0, count - 1);
             }
 
-            [return: MaybeNull]
-            public TResult TryGetElementAt(int index, out bool found)
+            public TResult? TryGetElementAt(int index, out bool found)
             {
                 if (unchecked((uint)index < (uint)_source.Length))
                 {
@@ -143,7 +142,7 @@ public TResult TryGetElementAt(int index, out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
             public TResult TryGetFirst(out bool found)
@@ -262,8 +261,7 @@ public IPartition<TResult> Take(int count)
                 return new SelectRangeIterator<TResult>(_start, _start + count, _selector);
             }
 
-            [return: MaybeNull]
-            public TResult TryGetElementAt(int index, out bool found)
+            public TResult? TryGetElementAt(int index, out bool found)
             {
                 if ((uint)index < (uint)(_end - _start))
                 {
@@ -272,7 +270,7 @@ public TResult TryGetElementAt(int index, out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
             public TResult TryGetFirst(out bool found)
@@ -351,8 +349,7 @@ public IPartition<TResult> Take(int count)
                 return new SelectListPartitionIterator<TSource, TResult>(_source, _selector, 0, count - 1);
             }
 
-            [return: MaybeNull]
-            public TResult TryGetElementAt(int index, out bool found)
+            public TResult? TryGetElementAt(int index, out bool found)
             {
                 if (unchecked((uint)index < (uint)_source.Count))
                 {
@@ -361,11 +358,10 @@ public TResult TryGetElementAt(int index, out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
-            [return: MaybeNull]
-            public TResult TryGetFirst(out bool found)
+            public TResult? TryGetFirst(out bool found)
             {
                 if (_source.Count != 0)
                 {
@@ -374,11 +370,10 @@ public TResult TryGetFirst(out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
-            [return: MaybeNull]
-            public TResult TryGetLast(out bool found)
+            public TResult? TryGetLast(out bool found)
             {
                 int len = _source.Count;
                 if (len != 0)
@@ -388,7 +383,7 @@ public TResult TryGetLast(out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
         }
 
@@ -453,8 +448,7 @@ public IPartition<TResult> Take(int count)
                 return new SelectListPartitionIterator<TSource, TResult>(_source, _selector, 0, count - 1);
             }
 
-            [return: MaybeNull]
-            public TResult TryGetElementAt(int index, out bool found)
+            public TResult? TryGetElementAt(int index, out bool found)
             {
                 if (unchecked((uint)index < (uint)_source.Count))
                 {
@@ -463,11 +457,10 @@ public TResult TryGetElementAt(int index, out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
-            [return: MaybeNull]
-            public TResult TryGetFirst(out bool found)
+            public TResult? TryGetFirst(out bool found)
             {
                 if (_source.Count != 0)
                 {
@@ -476,11 +469,10 @@ public TResult TryGetFirst(out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
-            [return: MaybeNull]
-            public TResult TryGetLast(out bool found)
+            public TResult? TryGetLast(out bool found)
             {
                 int len = _source.Count;
                 if (len != 0)
@@ -490,7 +482,7 @@ public TResult TryGetLast(out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
         }
 
@@ -565,8 +557,7 @@ public IPartition<TResult> Take(int count)
                 return new SelectIPartitionIterator<TSource, TResult>(_source.Take(count), _selector);
             }
 
-            [return: MaybeNull]
-            public TResult TryGetElementAt(int index, out bool found)
+            public TResult? TryGetElementAt(int index, out bool found)
             {
                 bool sourceFound;
                 TSource input = _source.TryGetElementAt(index, out sourceFound);
@@ -574,8 +565,7 @@ public TResult TryGetElementAt(int index, out bool found)
                 return sourceFound ? _selector(input!) : default!;
             }
 
-            [return: MaybeNull]
-            public TResult TryGetFirst(out bool found)
+            public TResult? TryGetFirst(out bool found)
             {
                 bool sourceFound;
                 TSource input = _source.TryGetFirst(out sourceFound);
@@ -583,8 +573,7 @@ public TResult TryGetFirst(out bool found)
                 return sourceFound ? _selector(input!) : default!;
             }
 
-            [return: MaybeNull]
-            public TResult TryGetLast(out bool found)
+            public TResult? TryGetLast(out bool found)
             {
                 bool sourceFound;
                 TSource input = _source.TryGetLast(out sourceFound);
@@ -739,8 +728,7 @@ public IPartition<TResult> Take(int count)
                 return (uint)maxIndex >= (uint)_maxIndexInclusive ? this : new SelectListPartitionIterator<TSource, TResult>(_source, _selector, _minIndexInclusive, maxIndex);
             }
 
-            [return: MaybeNull]
-            public TResult TryGetElementAt(int index, out bool found)
+            public TResult? TryGetElementAt(int index, out bool found)
             {
                 if ((uint)index <= (uint)(_maxIndexInclusive - _minIndexInclusive) && index < _source.Count - _minIndexInclusive)
                 {
@@ -749,11 +737,10 @@ public TResult TryGetElementAt(int index, out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
-            [return: MaybeNull]
-            public TResult TryGetFirst(out bool found)
+            public TResult? TryGetFirst(out bool found)
             {
                 if (_source.Count > _minIndexInclusive)
                 {
@@ -762,11 +749,10 @@ public TResult TryGetFirst(out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
-            [return: MaybeNull]
-            public TResult TryGetLast(out bool found)
+            public TResult? TryGetLast(out bool found)
             {
                 int lastIndex = _source.Count - 1;
                 if (lastIndex >= _minIndexInclusive)
@@ -776,7 +762,7 @@ public TResult TryGetLast(out bool found)
                 }
 
                 found = false;
-                return default!;
+                return default;
             }
 
             private int Count
diff --git a/src/libraries/System.Linq/src/System/Linq/Single.cs b/src/libraries/System.Linq/src/System/Linq/Single.cs
index 7640bc7c864653..913405d502c2f7 100644
--- a/src/libraries/System.Linq/src/System/Linq/Single.cs
+++ b/src/libraries/System.Linq/src/System/Linq/Single.cs
@@ -83,8 +83,7 @@ public static TSource Single<TSource>(this IEnumerable<TSource> source, Func<TSo
             return default;
         }
 
-        [return: MaybeNull]
-        public static TSource SingleOrDefault<TSource>(this IEnumerable<TSource> source)
+        public static TSource? SingleOrDefault<TSource>(this IEnumerable<TSource> source)
         {
             if (source == null)
             {
@@ -96,7 +95,7 @@ public static TSource SingleOrDefault<TSource>(this IEnumerable<TSource> source)
                 switch (list.Count)
                 {
                     case 0:
-                        return default!;
+                        return default;
                     case 1:
                         return list[0];
                 }
@@ -107,7 +106,7 @@ public static TSource SingleOrDefault<TSource>(this IEnumerable<TSource> source)
                 {
                     if (!e.MoveNext())
                     {
-                        return default!;
+                        return default;
                     }
 
                     TSource result = e.Current;
@@ -122,8 +121,7 @@ public static TSource SingleOrDefault<TSource>(this IEnumerable<TSource> source)
             return default;
         }
 
-        [return: MaybeNull]
-        public static TSource SingleOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
+        public static TSource? SingleOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
         {
             if (source == null)
             {
@@ -155,7 +153,7 @@ public static TSource SingleOrDefault<TSource>(this IEnumerable<TSource> source,
                 }
             }
 
-            return default!;
+            return default;
         }
     }
 }
diff --git a/src/libraries/System.Management/src/System.Management.csproj b/src/libraries/System.Management/src/System.Management.csproj
index ac50cd7a9b1bfa..c91da1b9c5b693 100644
--- a/src/libraries/System.Management/src/System.Management.csproj
+++ b/src/libraries/System.Management/src/System.Management.csproj
@@ -3,7 +3,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <NoWarn>$(NoWarn);0618</NoWarn>
     <IncludeDllSafeSearchPathAttribute>true</IncludeDllSafeSearchPathAttribute>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT;_$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -60,11 +60,11 @@
     <Compile Include="System\Management\InteropClasses\WMIInterop.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="Microsoft.Win32.Primitives" />
-    <Reference Include="Microsoft.Win32.Registry" />
-    <Reference Include="System.CodeDom" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.CodeDom\src\System.CodeDom.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Win32.Registry\src\Microsoft.Win32.Registry.csproj" />
+    <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections.NonGeneric" />
     <Reference Include="System.Collections.Specialized" />
     <Reference Include="System.ComponentModel.Primitives" />
diff --git a/src/libraries/System.Management/src/System/Management/InteropClasses/WMIInterop.cs b/src/libraries/System.Management/src/System/Management/InteropClasses/WMIInterop.cs
index 8ba6b71bed8bbf..b2de37af52c1a2 100644
--- a/src/libraries/System.Management/src/System/Management/InteropClasses/WMIInterop.cs
+++ b/src/libraries/System.Management/src/System/Management/InteropClasses/WMIInterop.cs
@@ -74,58 +74,6 @@ private void Dispose_(bool finalization)
             Dispose_(true);
         }
 
-        private void DeserializeFromBlob(byte[] rg)
-        {
-            IntPtr hGlobal = IntPtr.Zero;
-            System.Runtime.InteropServices.ComTypes.IStream stream = null;
-            try
-            {
-                // If something goes wrong, we want to make sure the object is invalidated
-                pWbemClassObject = IntPtr.Zero;
-
-                hGlobal = Marshal.AllocHGlobal(rg.Length);
-                Marshal.Copy(rg, 0, hGlobal, rg.Length);
-                stream = Interop.Ole32.CreateStreamOnHGlobal(hGlobal, false);
-                pWbemClassObject = Interop.Ole32.CoUnmarshalInterface(stream, IID_IWbemClassObject);
-            }
-            finally
-            {
-                if (stream != null)
-                    Marshal.ReleaseComObject(stream);
-                if (hGlobal != IntPtr.Zero)
-                    Marshal.FreeHGlobal(hGlobal);
-            }
-        }
-
-        private byte[] SerializeToBlob()
-        {
-            byte[] rg = null;
-            System.Runtime.InteropServices.ComTypes.IStream stream = null;
-            IntPtr pData = IntPtr.Zero;
-            try
-            {
-                // Stream will own the HGlobal
-                stream = Interop.Ole32.CreateStreamOnHGlobal(IntPtr.Zero, true);
-
-                Interop.Ole32.CoMarshalInterface(stream, IID_IWbemClassObject, pWbemClassObject, (uint)MSHCTX.MSHCTX_DIFFERENTMACHINE, IntPtr.Zero, (uint)MSHLFLAGS.MSHLFLAGS_TABLEWEAK);
-
-                System.Runtime.InteropServices.ComTypes.STATSTG statstg;
-                stream.Stat(out statstg, (int)STATFLAG.STATFLAG_DEFAULT);
-                rg = new byte[statstg.cbSize];
-                pData = Interop.Kernel32.GlobalLock(Interop.Ole32.GetHGlobalFromStream(stream));
-                Marshal.Copy(pData, rg, 0, (int)statstg.cbSize);
-            }
-            finally
-            {
-                if (pData != IntPtr.Zero)
-                    Interop.Kernel32.GlobalUnlock(pData);
-                if (stream != null)
-                    Marshal.ReleaseComObject(stream);
-            }
-            GC.KeepAlive(this);
-            return rg;
-        }
-
         // Interface methods
         public int GetQualifierSet_(out IWbemQualifierSetFreeThreaded ppQualSet)
         {
diff --git a/src/libraries/System.Management/src/System/Management/ManagementObject.cs b/src/libraries/System.Management/src/System/Management/ManagementObject.cs
index 9bf0b10a974e35..bd551dcee66c96 100644
--- a/src/libraries/System.Management/src/System/Management/ManagementObject.cs
+++ b/src/libraries/System.Management/src/System/Management/ManagementObject.cs
@@ -2304,8 +2304,6 @@ public ManagementBaseObject InvokeMethod(
             {
                 Initialize(false);
                 InvokeMethodOptions o = (null != options) ? options : new InvokeMethodOptions();
-                IWbemServices wbemServices = scope.GetIWbemServices();
-
                 SecurityHandler securityHandler = null;
                 int status = (int)ManagementStatus.NoError;
 
diff --git a/src/libraries/System.Management/src/System/Management/ManagementScope.cs b/src/libraries/System.Management/src/System/Management/ManagementScope.cs
index aa6201a195ab0e..95f18ca6b06609 100644
--- a/src/libraries/System.Management/src/System/Management/ManagementScope.cs
+++ b/src/libraries/System.Management/src/System/Management/ManagementScope.cs
@@ -969,8 +969,6 @@ internal void Initialize()
         private void InitializeGuts(object o)
         {
             ManagementScope threadParam = (ManagementScope)o;
-            IWbemLocator loc = (IWbemLocator)new WbemLocator();
-            IntPtr punk = IntPtr.Zero;
 
             if (null == threadParam.options)
             {
@@ -986,8 +984,7 @@ private void InitializeGuts(object o)
                 // path here as we do NOT want to trigger an
                 // IdentifierChanged event as a result of this set
 
-                bool bUnused;
-                nsPath = threadParam.prvpath.SetNamespacePath(ManagementPath.DefaultPath.Path, out bUnused);
+                nsPath = threadParam.prvpath.SetNamespacePath(ManagementPath.DefaultPath.Path, out _);
             }
 
             int status = (int)ManagementStatus.NoError;
diff --git a/src/libraries/System.Management/src/System/Management/WMIGenerator.cs b/src/libraries/System.Management/src/System/Management/WMIGenerator.cs
index 38453159239d80..56a515ca09cb90 100644
--- a/src/libraries/System.Management/src/System/Management/WMIGenerator.cs
+++ b/src/libraries/System.Management/src/System/Management/WMIGenerator.cs
@@ -3036,7 +3036,7 @@ private void GenerateMethods()
                                 {
                                     CodeTypeReference dateType = cmm.ReturnType;
                                     // Check if it is Time interval and if so change the type to Time Interval
-                                    bool isRetTypeTimeInterval = GetDateTimeType(prop, ref dateType);
+                                    GetDateTimeType(prop, ref dateType);
                                     cmm.ReturnType = dateType;
                                 }
                                 retRefType = cmm.ReturnType;
@@ -6116,7 +6116,6 @@ private void AddCommentsForEmbeddedProperties()
         private bool GetDateTimeType(PropertyData prop, ref CodeTypeReference codeType)
         {
             bool isTimeInterval = false;
-            codeType = null;
             if (prop.IsArray)
             {
                 codeType = new CodeTypeReference("System.DateTime", 1);
@@ -7339,11 +7338,6 @@ private void ToDMTFDateHelper(string dateTimeMember, CodeMemberMethod cmmdt, str
             cmie2.Parameters.Add(new CodePrimitiveExpression(2));
             cmie2.Parameters.Add(new CodePrimitiveExpression('0'));
 
-            CodeMethodInvokeExpression cmie3 = GenerateConcatStrings(cmie, cmie2);
-            /*                new CodeMethodInvokeExpression();
-                        cmie3.Method = new CodeMethodReferenceExpression(cmie,"Concat");
-                        cmie3.Parameters.Add(cmie2); */
-
             cmmdt.Statements.Add(new CodeAssignStatement(new CodeVariableReferenceExpression(dmtfDateTime),
                 GenerateConcatStrings(new CodeVariableReferenceExpression(dmtfDateTime),
                 cmie2)));
diff --git a/src/libraries/System.Management/tests/System.Management.Tests.csproj b/src/libraries/System.Management/tests/System.Management.Tests.csproj
index d71c4999db1a97..dfa032993bcd74 100644
--- a/src/libraries/System.Management/tests/System.Management.Tests.csproj
+++ b/src/libraries/System.Management/tests/System.Management.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="MofHelpers\MofCollection.cs" />
@@ -23,4 +23,10 @@
       <LogicalName>CleanUp.mof</LogicalName>
     </EmbeddedResource>
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="..\src\System.Management.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
+    <Reference Include="System.Management" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Memory/Directory.Build.props b/src/libraries/System.Memory/Directory.Build.props
index 749d7fc1c6b56d..ba1f965d83cae7 100644
--- a/src/libraries/System.Memory/Directory.Build.props
+++ b/src/libraries/System.Memory/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Memory/ref/System.Memory.cs b/src/libraries/System.Memory/ref/System.Memory.cs
index ec2eec1d2a4f11..fc29a53017de0e 100644
--- a/src/libraries/System.Memory/ref/System.Memory.cs
+++ b/src/libraries/System.Memory/ref/System.Memory.cs
@@ -283,7 +283,7 @@ public void Rewind(long count) { }
         public bool TryReadTo(out System.Buffers.ReadOnlySequence<T> sequence, System.ReadOnlySpan<T> delimiter, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadTo(out System.Buffers.ReadOnlySequence<T> sequence, T delimiter, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadTo(out System.Buffers.ReadOnlySequence<T> sequence, T delimiter, T delimiterEscape, bool advancePastDelimiter = true) { throw null; }
-        public bool TryReadTo(out System.ReadOnlySpan<T> sequence, System.ReadOnlySpan<T> delimiter, bool advancePastDelimiter = true) { throw null; }
+        public bool TryReadTo(out System.ReadOnlySpan<T> span, System.ReadOnlySpan<T> delimiter, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadTo(out System.ReadOnlySpan<T> span, T delimiter, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadTo(out System.ReadOnlySpan<T> span, T delimiter, T delimiterEscape, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadToAny(out System.Buffers.ReadOnlySequence<T> sequence, System.ReadOnlySpan<T> delimiters, bool advancePastDelimiter = true) { throw null; }
diff --git a/src/libraries/System.Memory/src/System/Buffers/ReadOnlySequence.cs b/src/libraries/System.Memory/src/System/Buffers/ReadOnlySequence.cs
index 273a9702c8ca78..7fd6b1372c127a 100644
--- a/src/libraries/System.Memory/src/System/Buffers/ReadOnlySequence.cs
+++ b/src/libraries/System.Memory/src/System/Buffers/ReadOnlySequence.cs
@@ -17,8 +17,8 @@ namespace System.Buffers
     public readonly partial struct ReadOnlySequence<T>
     {
         // The data is essentially two SequencePositions, however the Start and End SequencePositions are deconstructed to improve packing.
-        [AllowNull] private readonly object? _startObject;
-        [AllowNull] private readonly object? _endObject;
+        private readonly object? _startObject;
+        private readonly object? _endObject;
         private readonly int _startInteger;
         private readonly int _endInteger;
 
diff --git a/src/libraries/System.Memory/tests/Span/Reflection.cs b/src/libraries/System.Memory/tests/Span/Reflection.cs
index 3da4f54013fe6e..dbdcc7dbdcd336 100644
--- a/src/libraries/System.Memory/tests/Span/Reflection.cs
+++ b/src/libraries/System.Memory/tests/Span/Reflection.cs
@@ -40,7 +40,6 @@ public static void MemoryExtensions_StaticWithSpanArguments()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/39311", TestPlatforms.Browser)]
         public static void BinaryPrimitives_StaticWithSpanArgument()
         {
             Type type = typeof(BinaryPrimitives);
diff --git a/src/libraries/System.Memory/tests/System.Memory.Tests.csproj b/src/libraries/System.Memory/tests/System.Memory.Tests.csproj
index 1b310ee36a434c..d0508aaa6c78aa 100644
--- a/src/libraries/System.Memory/tests/System.Memory.Tests.csproj
+++ b/src/libraries/System.Memory/tests/System.Memory.Tests.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <IncludePartialFacadeTests>true</IncludePartialFacadeTests>
     <TestRuntime>true</TestRuntime>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Net.Connections/Directory.Build.props b/src/libraries/System.Net.Connections/Directory.Build.props
new file mode 100644
index 00000000000000..63f02a0f817ef2
--- /dev/null
+++ b/src/libraries/System.Net.Connections/Directory.Build.props
@@ -0,0 +1,6 @@
+<Project>
+  <Import Project="..\Directory.Build.props" />
+  <PropertyGroup>
+    <StrongNameKeyId>Microsoft</StrongNameKeyId>
+  </PropertyGroup>
+</Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Connections/System.Net.Connections.sln b/src/libraries/System.Net.Connections/System.Net.Connections.sln
new file mode 100644
index 00000000000000..a325eb24b97132
--- /dev/null
+++ b/src/libraries/System.Net.Connections/System.Net.Connections.sln
@@ -0,0 +1,50 @@
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.30310.162
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "System.Net.Connections", "src\System.Net.Connections.csproj", "{1D422B1D-D7C4-41B9-862D-EB3D98DF37DE}"
+	ProjectSection(ProjectDependencies) = postProject
+		{132BF813-FC40-4D39-8B6F-E55D7633F0ED} = {132BF813-FC40-4D39-8B6F-E55D7633F0ED}
+	EndProjectSection
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "System.Net.Connections", "ref\System.Net.Connections.csproj", "{132BF813-FC40-4D39-8B6F-E55D7633F0ED}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{E107E9C1-E893-4E87-987E-04EF0DCEAEFD}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "ref", "ref", "{2E666815-2EDB-464B-9DF6-380BF4789AD4}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{E0983BCC-F93B-4FFF-A4E4-EA874908783F}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "System.Net.Connections.Tests", "tests\System.Net.Connections.Tests\System.Net.Connections.Tests.csproj", "{A4DB505A-FFD8-4A7B-B31A-12AD623E7AD9}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{1D422B1D-D7C4-41B9-862D-EB3D98DF37DE}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{1D422B1D-D7C4-41B9-862D-EB3D98DF37DE}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{1D422B1D-D7C4-41B9-862D-EB3D98DF37DE}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{1D422B1D-D7C4-41B9-862D-EB3D98DF37DE}.Release|Any CPU.Build.0 = Release|Any CPU
+		{132BF813-FC40-4D39-8B6F-E55D7633F0ED}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{132BF813-FC40-4D39-8B6F-E55D7633F0ED}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{132BF813-FC40-4D39-8B6F-E55D7633F0ED}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{132BF813-FC40-4D39-8B6F-E55D7633F0ED}.Release|Any CPU.Build.0 = Release|Any CPU
+		{A4DB505A-FFD8-4A7B-B31A-12AD623E7AD9}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A4DB505A-FFD8-4A7B-B31A-12AD623E7AD9}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A4DB505A-FFD8-4A7B-B31A-12AD623E7AD9}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A4DB505A-FFD8-4A7B-B31A-12AD623E7AD9}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(NestedProjects) = preSolution
+		{1D422B1D-D7C4-41B9-862D-EB3D98DF37DE} = {E107E9C1-E893-4E87-987E-04EF0DCEAEFD}
+		{132BF813-FC40-4D39-8B6F-E55D7633F0ED} = {2E666815-2EDB-464B-9DF6-380BF4789AD4}
+		{A4DB505A-FFD8-4A7B-B31A-12AD623E7AD9} = {E0983BCC-F93B-4FFF-A4E4-EA874908783F}
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {5100F629-0FAB-4C6F-9A54-95AE9565EE0D}
+	EndGlobalSection
+EndGlobal
diff --git a/src/libraries/System.Net.Connections/ref/System.Net.Connections.cs b/src/libraries/System.Net.Connections/ref/System.Net.Connections.cs
new file mode 100644
index 00000000000000..6eaa384fdc7eea
--- /dev/null
+++ b/src/libraries/System.Net.Connections/ref/System.Net.Connections.cs
@@ -0,0 +1,74 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// ------------------------------------------------------------------------------
+// Changes to this file must follow the https://aka.ms/api-review process.
+// ------------------------------------------------------------------------------
+
+namespace System.Net.Connections
+{
+    public abstract partial class Connection : System.Net.Connections.ConnectionBase
+    {
+        protected Connection() { }
+        public System.IO.Pipelines.IDuplexPipe Pipe { get { throw null; } }
+        public System.IO.Stream Stream { get { throw null; } }
+        protected virtual System.IO.Pipelines.IDuplexPipe CreatePipe() { throw null; }
+        protected virtual System.IO.Stream CreateStream() { throw null; }
+        public static System.Net.Connections.Connection FromPipe(System.IO.Pipelines.IDuplexPipe pipe, bool leaveOpen = false, System.Net.Connections.IConnectionProperties? properties = null, System.Net.EndPoint? localEndPoint = null, System.Net.EndPoint? remoteEndPoint = null) { throw null; }
+        public static System.Net.Connections.Connection FromStream(System.IO.Stream stream, bool leaveOpen = false, System.Net.Connections.IConnectionProperties? properties = null, System.Net.EndPoint? localEndPoint = null, System.Net.EndPoint? remoteEndPoint = null) { throw null; }
+    }
+    public abstract partial class ConnectionBase : System.IAsyncDisposable, System.IDisposable
+    {
+        protected ConnectionBase() { }
+        public abstract System.Net.Connections.IConnectionProperties ConnectionProperties { get; }
+        public abstract System.Net.EndPoint? LocalEndPoint { get; }
+        public abstract System.Net.EndPoint? RemoteEndPoint { get; }
+        public System.Threading.Tasks.ValueTask CloseAsync(System.Net.Connections.ConnectionCloseMethod method = System.Net.Connections.ConnectionCloseMethod.GracefulShutdown, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        protected abstract System.Threading.Tasks.ValueTask CloseAsyncCore(System.Net.Connections.ConnectionCloseMethod method, System.Threading.CancellationToken cancellationToken);
+        public void Dispose() { }
+        public System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }
+    }
+    public enum ConnectionCloseMethod
+    {
+        GracefulShutdown = 0,
+        Abort = 1,
+        Immediate = 2,
+    }
+    public static partial class ConnectionExtensions
+    {
+        public static System.Net.Connections.ConnectionFactory Filter(this System.Net.Connections.ConnectionFactory factory, System.Func<System.Net.Connections.Connection, System.Net.Connections.IConnectionProperties?, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<System.Net.Connections.Connection>> filter) { throw null; }
+        public static bool TryGet<T>(this System.Net.Connections.IConnectionProperties properties, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out T property) { throw null; }
+    }
+    public abstract partial class ConnectionFactory : System.IAsyncDisposable, System.IDisposable
+    {
+        protected ConnectionFactory() { }
+        public abstract System.Threading.Tasks.ValueTask<System.Net.Connections.Connection> ConnectAsync(System.Net.EndPoint? endPoint, System.Net.Connections.IConnectionProperties? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken));
+        public void Dispose() { }
+        protected virtual void Dispose(bool disposing) { }
+        public System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }
+        protected virtual System.Threading.Tasks.ValueTask DisposeAsyncCore() { throw null; }
+    }
+    public abstract partial class ConnectionListener : System.IAsyncDisposable, System.IDisposable
+    {
+        protected ConnectionListener() { }
+        public abstract System.Net.Connections.IConnectionProperties ListenerProperties { get; }
+        public abstract System.Net.EndPoint? LocalEndPoint { get; }
+        public abstract System.Threading.Tasks.ValueTask<System.Net.Connections.Connection> AcceptAsync(System.Net.Connections.IConnectionProperties? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken));
+        public void Dispose() { }
+        protected virtual void Dispose(bool disposing) { }
+        public System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }
+        protected virtual System.Threading.Tasks.ValueTask DisposeAsyncCore() { throw null; }
+    }
+    public abstract partial class ConnectionListenerFactory : System.IAsyncDisposable, System.IDisposable
+    {
+        protected ConnectionListenerFactory() { }
+        public abstract System.Threading.Tasks.ValueTask<System.Net.Connections.ConnectionListener> ListenAsync(System.Net.EndPoint? endPoint, System.Net.Connections.IConnectionProperties? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken));
+        public void Dispose() { }
+        protected virtual void Dispose(bool disposing) { }
+        public System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }
+        protected virtual System.Threading.Tasks.ValueTask DisposeAsyncCore() { throw null; }
+    }
+    public partial interface IConnectionProperties
+    {
+        bool TryGet(System.Type propertyKey, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out object? property);
+    }
+}
diff --git a/src/libraries/System.Net.Connections/ref/System.Net.Connections.csproj b/src/libraries/System.Net.Connections/ref/System.Net.Connections.csproj
new file mode 100644
index 00000000000000..b239637616b4fd
--- /dev/null
+++ b/src/libraries/System.Net.Connections/ref/System.Net.Connections.csproj
@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="System.Net.Connections.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="..\..\System.Net.Primitives\ref\System.Net.Primitives.csproj" />
+    <ProjectReference Include="..\..\System.IO.Pipelines\ref\System.IO.Pipelines.csproj" />
+  </ItemGroup>
+</Project>
diff --git a/src/libraries/System.Net.Connections/src/Resources/Strings.resx b/src/libraries/System.Net.Connections/src/Resources/Strings.resx
new file mode 100644
index 00000000000000..004c0da9c84926
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/Resources/Strings.resx
@@ -0,0 +1,138 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <!-- 
+    Microsoft ResX Schema 
+    
+    Version 2.0
+    
+    The primary goals of this format is to allow a simple XML format 
+    that is mostly human readable. The generation and parsing of the 
+    various data types are done through the TypeConverter classes 
+    associated with the data types.
+    
+    Example:
+    
+    ... ado.net/XML headers & schema ...
+    <resheader name="resmimetype">text/microsoft-resx</resheader>
+    <resheader name="version">2.0</resheader>
+    <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>
+    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>
+    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>
+    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>
+    <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">
+        <value>[base64 mime encoded serialized .NET Framework object]</value>
+    </data>
+    <data name="Icon1" type="System.Drawing.Icon, System.Drawing" mimetype="application/x-microsoft.net.object.bytearray.base64">
+        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
+        <comment>This is a comment</comment>
+    </data>
+                
+    There are any number of "resheader" rows that contain simple 
+    name/value pairs.
+    
+    Each data row contains a name, and value. The row also contains a 
+    type or mimetype. Type corresponds to a .NET class that support 
+    text/value conversion through the TypeConverter architecture. 
+    Classes that don't support this are serialized and stored with the 
+    mimetype set.
+    
+    The mimetype is used for serialized objects, and tells the 
+    ResXResourceReader how to depersist the object. This is currently not 
+    extensible. For a given mimetype the value must be set accordingly:
+    
+    Note - application/x-microsoft.net.object.binary.base64 is the format 
+    that the ResXResourceWriter will generate, however the reader can 
+    read any of the formats listed below.
+    
+    mimetype: application/x-microsoft.net.object.binary.base64
+    value   : The object must be serialized with 
+            : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
+            : and then encoded with base64 encoding.
+    
+    mimetype: application/x-microsoft.net.object.soap.base64
+    value   : The object must be serialized with 
+            : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
+            : and then encoded with base64 encoding.
+
+    mimetype: application/x-microsoft.net.object.bytearray.base64
+    value   : The object must be serialized into a byte array 
+            : using a System.ComponentModel.TypeConverter
+            : and then encoded with base64 encoding.
+    -->
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />
+    <xsd:element name="root" msdata:IsDataSet="true">
+      <xsd:complexType>
+        <xsd:choice maxOccurs="unbounded">
+          <xsd:element name="metadata">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" />
+              </xsd:sequence>
+              <xsd:attribute name="name" use="required" type="xsd:string" />
+              <xsd:attribute name="type" type="xsd:string" />
+              <xsd:attribute name="mimetype" type="xsd:string" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="assembly">
+            <xsd:complexType>
+              <xsd:attribute name="alias" type="xsd:string" />
+              <xsd:attribute name="name" type="xsd:string" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="data">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />
+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />
+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="resheader">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" />
+            </xsd:complexType>
+          </xsd:element>
+        </xsd:choice>
+      </xsd:complexType>
+    </xsd:element>
+  </xsd:schema>
+  <resheader name="resmimetype">
+    <value>text/microsoft-resx</value>
+  </resheader>
+  <resheader name="version">
+    <value>2.0</value>
+  </resheader>
+  <resheader name="reader">
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <resheader name="writer">
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <data name="net_connections_createpipe_null" xml:space="preserve">
+    <value>The CreatePipe implementation returned null; a valid reference was expected.</value>
+  </data>
+  <data name="net_connections_createstream_null" xml:space="preserve">
+    <value>The CreateStream implementation returned null; a valid reference was expected.</value>
+  </data>
+  <data name="net_connections_no_create_overrides" xml:space="preserve">
+    <value>One of CreatePipe or CreateStream must be implemented</value>
+  </data>
+  <data name="net_connections_pipe_use_after_stream" xml:space="preserve">
+    <value>The Connection's Pipe may not be accessed after Stream has been accessed.</value>
+  </data>
+  <data name="net_connections_stream_use_after_pipe" xml:space="preserve">
+    <value>The Connection's Stream may not be accessed after Pipe has been accessed.</value>
+  </data>
+  <data name="net_connections_zero_byte_pipe_read" xml:space="preserve">
+    <value>The PipeReader returned a zero-length  read.</value>
+  </data>
+</root>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Connections/src/System.Net.Connections.csproj b/src/libraries/System.Net.Connections/src/System.Net.Connections.csproj
new file mode 100644
index 00000000000000..c53e55947afb47
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/System.Net.Connections.csproj
@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(CommonPath)System\Threading\Tasks\TaskToApm.cs" Link="Common\System\Threading\Tasks\TaskToApm.cs" />
+    <Compile Include="System\Net\Connections\ConnectionBase.cs" />
+    <Compile Include="System\Net\Connections\ConnectionCloseMethod.cs" />
+    <Compile Include="System\Net\Connections\ConnectionExtensions.cs" />
+    <Compile Include="System\Net\Connections\ConnectionListenerFactory.cs" />
+    <Compile Include="System\Net\Connections\Connection.cs" />
+    <Compile Include="System\Net\Connections\DuplexPipeStream.cs" />
+    <Compile Include="System\Net\Connections\ConnectionFactory.cs" />
+    <Compile Include="System\Net\Connections\ConnectionListener.cs" />
+    <Compile Include="System\Net\Connections\IConnectionProperties.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <Reference Include="System.Runtime" />
+    <Reference Include="System.Memory" />
+    <Reference Include="System.Net.Primitives" />
+    <Reference Include="System.Threading" />
+    <Reference Include="System.Threading.Tasks" />
+    <Reference Include="System.IO.Pipelines" />
+  </ItemGroup>
+</Project>
diff --git a/src/libraries/System.Net.Connections/src/System/Net/Connections/Connection.cs b/src/libraries/System.Net.Connections/src/System/Net/Connections/Connection.cs
new file mode 100644
index 00000000000000..8f7d479ce2a1a5
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/System/Net/Connections/Connection.cs
@@ -0,0 +1,265 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+using System.IO;
+using System.IO.Pipelines;
+using System.Runtime.ExceptionServices;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections
+{
+    /// <summary>
+    /// A connection.
+    /// </summary>
+    public abstract class Connection : ConnectionBase
+    {
+        private Stream? _stream;
+        private IDuplexPipe? _pipe;
+        private bool _initializing;
+
+        /// <summary>
+        /// The connection's <see cref="Stream"/>.
+        /// </summary>
+        public Stream Stream =>
+            _stream != null ? _stream :
+            _pipe != null ? throw new InvalidOperationException(SR.net_connections_stream_use_after_pipe) :
+            (_stream = CreateStream() ?? throw new InvalidOperationException(SR.net_connections_createstream_null));
+
+        /// <summary>
+        /// The connection's <see cref="IDuplexPipe"/>.
+        /// </summary>
+        public IDuplexPipe Pipe =>
+            _pipe != null ? _pipe :
+            _stream != null ? throw new InvalidOperationException(SR.net_connections_pipe_use_after_stream) :
+            (_pipe = CreatePipe() ?? throw new InvalidOperationException(SR.net_connections_createpipe_null));
+
+        /// <summary>
+        /// Initializes the <see cref="Stream"/> for the <see cref="Connection"/>.
+        /// </summary>
+        /// <returns>A <see cref="Stream"/>.</returns>
+        /// <remarks>
+        /// At least one of <see cref="CreateStream"/> and <see cref="CreatePipe"/> must be overridden.
+        /// If only <see cref="CreateStream"/> is overridden, a user accessing <see cref="Pipe"/> will get a <see cref="IDuplexPipe"/> wrapping the <see cref="Stream"/>.
+        /// </remarks>
+        protected virtual Stream CreateStream()
+        {
+            if (_initializing) throw new InvalidOperationException(SR.net_connections_no_create_overrides);
+
+            try
+            {
+                _initializing = true;
+
+                IDuplexPipe pipe = CreatePipe();
+                if (pipe == null) throw new InvalidOperationException(SR.net_connections_createpipe_null);
+
+                return new DuplexPipeStream(pipe);
+            }
+            finally
+            {
+                _initializing = false;
+            }
+        }
+
+        /// <summary>
+        /// Initializes the <see cref="Pipe"/> for the <see cref="Connection"/>.
+        /// </summary>
+        /// <returns>An <see cref="IDuplexPipe"/>.</returns>
+        /// <remarks>
+        /// At least one of <see cref="CreateStream"/> and <see cref="CreatePipe"/> must be overridden.
+        /// If only <see cref="CreatePipe"/> is overridden, a user accessing <see cref="Stream"/> will get a <see cref="Stream"/> wrapping the <see cref="Pipe"/>.
+        /// </remarks>
+        protected virtual IDuplexPipe CreatePipe()
+        {
+            if (_initializing) throw new InvalidOperationException(SR.net_connections_no_create_overrides);
+
+            try
+            {
+                _initializing = true;
+
+                Stream stream = CreateStream();
+                if (stream == null) throw new InvalidOperationException(SR.net_connections_createstream_null);
+
+                return new DuplexStreamPipe(stream);
+            }
+            finally
+            {
+                _initializing = false;
+            }
+        }
+
+        private sealed class DuplexStreamPipe : IDuplexPipe
+        {
+            private static readonly StreamPipeReaderOptions s_readerOpts = new StreamPipeReaderOptions(leaveOpen: true);
+            private static readonly StreamPipeWriterOptions s_writerOpts = new StreamPipeWriterOptions(leaveOpen: true);
+
+            public DuplexStreamPipe(Stream stream)
+            {
+                Input = PipeReader.Create(stream, s_readerOpts);
+                Output = PipeWriter.Create(stream, s_writerOpts);
+            }
+
+            public PipeReader Input { get; }
+
+            public PipeWriter Output { get; }
+        }
+
+        /// <summary>
+        /// Creates a connection for a <see cref="Stream"/>.
+        /// </summary>
+        /// <param name="stream">The connection's <see cref="Connection.Stream"/>.</param>
+        /// <param name="leaveOpen">If false, the <paramref name="stream"/> will be disposed of once the connection has been closed.</param>
+        /// <param name="properties">The connection's <see cref="ConnectionBase.ConnectionProperties"/>.</param>
+        /// <param name="localEndPoint">The connection's <see cref="ConnectionBase.LocalEndPoint"/>.</param>
+        /// <param name="remoteEndPoint">The connection's <see cref="ConnectionBase.RemoteEndPoint"/>.</param>
+        /// <returns>A new <see cref="Connection"/>.</returns>
+        public static Connection FromStream(Stream stream, bool leaveOpen = false, IConnectionProperties? properties = null, EndPoint? localEndPoint = null, EndPoint? remoteEndPoint = null)
+        {
+            if (stream == null) throw new ArgumentNullException(nameof(stream));
+            return new ConnectionFromStream(stream, leaveOpen, properties, localEndPoint, remoteEndPoint);
+        }
+
+        /// <summary>
+        /// Creates a connection for an <see cref="IDuplexPipe"/>.
+        /// </summary>
+        /// <param name="pipe">The connection's <see cref="Connection.Pipe"/>.</param>
+        /// <param name="leaveOpen">If false and the <paramref name="pipe"/> implements <see cref="IAsyncDisposable"/> or <see cref="IDisposable"/>, it will be disposed of once the connection has been closed.</param>
+        /// <param name="properties">The connection's <see cref="ConnectionBase.ConnectionProperties"/>.</param>
+        /// <param name="localEndPoint">The connection's <see cref="ConnectionBase.LocalEndPoint"/>.</param>
+        /// <param name="remoteEndPoint">The connection's <see cref="ConnectionBase.RemoteEndPoint"/>.</param>
+        /// <returns>A new <see cref="Connection"/>.</returns>
+        public static Connection FromPipe(IDuplexPipe pipe, bool leaveOpen = false, IConnectionProperties? properties = null, EndPoint? localEndPoint = null, EndPoint? remoteEndPoint = null)
+        {
+            if (pipe == null) throw new ArgumentNullException(nameof(pipe));
+            return new ConnectionFromPipe(pipe, leaveOpen, properties, localEndPoint, remoteEndPoint);
+        }
+
+        private sealed class ConnectionFromStream : Connection, IConnectionProperties
+        {
+            private Stream? _originalStream;
+            private IConnectionProperties? _properties;
+            private readonly bool _leaveOpen;
+
+            public override IConnectionProperties ConnectionProperties => _properties ?? this;
+
+            public override EndPoint? LocalEndPoint { get; }
+
+            public override EndPoint? RemoteEndPoint { get; }
+
+            public ConnectionFromStream(Stream stream, bool leaveOpen, IConnectionProperties? properties, EndPoint? localEndPoint, EndPoint? remoteEndPoint)
+            {
+                _originalStream = stream;
+                _leaveOpen = leaveOpen;
+                _properties = properties;
+                LocalEndPoint = localEndPoint;
+                RemoteEndPoint = remoteEndPoint;
+            }
+
+            protected override Stream CreateStream() => _originalStream ?? throw new ObjectDisposedException(nameof(Connection));
+
+            protected override async ValueTask CloseAsyncCore(ConnectionCloseMethod method, CancellationToken cancellationToken)
+            {
+                if (_originalStream == null)
+                {
+                    return;
+                }
+
+                if (method == ConnectionCloseMethod.GracefulShutdown)
+                {
+                    await _originalStream.FlushAsync(cancellationToken).ConfigureAwait(false);
+                }
+
+                if (!_leaveOpen)
+                {
+                    await _originalStream.DisposeAsync().ConfigureAwait(false);
+                }
+
+                _originalStream = null;
+            }
+
+            bool IConnectionProperties.TryGet(Type propertyKey, [NotNullWhen(true)] out object? property)
+            {
+                property = null;
+                return false;
+            }
+        }
+
+        private sealed class ConnectionFromPipe : Connection, IConnectionProperties
+        {
+            private IDuplexPipe? _originalPipe;
+            private IConnectionProperties? _properties;
+            private readonly bool _leaveOpen;
+
+            public override IConnectionProperties ConnectionProperties => _properties ?? this;
+
+            public override EndPoint? LocalEndPoint { get; }
+
+            public override EndPoint? RemoteEndPoint { get; }
+
+            public ConnectionFromPipe(IDuplexPipe pipe, bool leaveOpen, IConnectionProperties? properties, EndPoint? localEndPoint, EndPoint? remoteEndPoint)
+            {
+                _originalPipe = pipe;
+                _leaveOpen = leaveOpen;
+                _properties = properties;
+                LocalEndPoint = localEndPoint;
+                RemoteEndPoint = remoteEndPoint;
+            }
+
+            protected override IDuplexPipe CreatePipe() => _originalPipe ?? throw new ObjectDisposedException(nameof(Connection));
+
+            protected override async ValueTask CloseAsyncCore(ConnectionCloseMethod method, CancellationToken cancellationToken)
+            {
+                if (_originalPipe == null)
+                {
+                    return;
+                }
+
+                Exception? inputException, outputException;
+
+                if (method == ConnectionCloseMethod.GracefulShutdown)
+                {
+                    // Flush happens implicitly from CompleteAsync(null), so only flush here if we need cancellation.
+                    if (cancellationToken.CanBeCanceled)
+                    {
+                        FlushResult r = await _originalPipe.Output.FlushAsync(cancellationToken).ConfigureAwait(false);
+                        if (r.IsCanceled) cancellationToken.ThrowIfCancellationRequested();
+                    }
+
+                    inputException = null;
+                    outputException = null;
+                }
+                else
+                {
+                    inputException = ExceptionDispatchInfo.SetCurrentStackTrace(new ObjectDisposedException(nameof(Connection)));
+                    outputException = ExceptionDispatchInfo.SetCurrentStackTrace(new ObjectDisposedException(nameof(Connection)));
+                }
+
+                await _originalPipe.Input.CompleteAsync(inputException).ConfigureAwait(false);
+                await _originalPipe.Output.CompleteAsync(outputException).ConfigureAwait(false);
+
+                if (!_leaveOpen)
+                {
+                    switch (_originalPipe)
+                    {
+                        case IAsyncDisposable d:
+                            await d.DisposeAsync().ConfigureAwait(false);
+                            break;
+                        case IDisposable d:
+                            d.Dispose();
+                            break;
+                    }
+                }
+
+                _originalPipe = null;
+            }
+
+            bool IConnectionProperties.TryGet(Type propertyKey, [NotNullWhen(true)] out object? property)
+            {
+                property = null;
+                return false;
+            }
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionBase.cs b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionBase.cs
new file mode 100644
index 00000000000000..027431babe2a8a
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionBase.cs
@@ -0,0 +1,80 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections
+{
+    /// <summary>
+    /// Provides base functionality shared between singular (e.g. TCP) and multiplexed (e.g. QUIC) connections.
+    /// </summary>
+    public abstract class ConnectionBase : IDisposable, IAsyncDisposable
+    {
+        private bool _disposed;
+
+        /// <summary>
+        /// Properties exposed by this connection.
+        /// </summary>
+        public abstract IConnectionProperties ConnectionProperties { get; }
+
+        /// <summary>
+        /// The local endpoint of this connection, if any.
+        /// </summary>
+        public abstract EndPoint? LocalEndPoint { get; }
+
+        /// <summary>
+        /// The remote endpoint of this connection, if any.
+        /// </summary>
+        public abstract EndPoint? RemoteEndPoint { get; }
+
+        /// <summary>
+        /// Closes the connection.
+        /// </summary>
+        /// <param name="method">The method to use when closing the connection.</param>
+        /// <param name="cancellationToken">A cancellation token for the asynchronous operation.</param>
+        /// <returns>A <see cref="ValueTask"/> for the asynchronous operation.</returns>
+        public async ValueTask CloseAsync(ConnectionCloseMethod method = ConnectionCloseMethod.GracefulShutdown, CancellationToken cancellationToken = default)
+        {
+            if (!_disposed)
+            {
+                await CloseAsyncCore(method, cancellationToken).ConfigureAwait(false);
+                _disposed = true;
+            }
+            GC.SuppressFinalize(this);
+        }
+
+        /// <summary>
+        /// Closes the connection.
+        /// </summary>
+        /// <param name="method">The method to use when closing the connection.</param>
+        /// <param name="cancellationToken">A cancellation token for the asynchronous operation.</param>
+        /// <returns>A <see cref="ValueTask"/> for the asynchronous operation.</returns>
+        protected abstract ValueTask CloseAsyncCore(ConnectionCloseMethod method, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Disposes of the connection.
+        /// </summary>
+        /// <remarks>
+        /// This is equivalent to calling <see cref="CloseAsync(ConnectionCloseMethod, CancellationToken)"/> with the method <see cref="ConnectionCloseMethod.GracefulShutdown"/>, and calling GetAwaiter().GetResult() on the resulting task.
+        /// To increase likelihood of synchronous completion, call <see cref="CloseAsync(ConnectionCloseMethod, CancellationToken)"/> directly with the method <see cref="ConnectionCloseMethod.Immediate"/>.
+        /// </remarks>
+        public void Dispose()
+        {
+            ValueTask t = CloseAsync(ConnectionCloseMethod.GracefulShutdown, CancellationToken.None);
+
+            if (t.IsCompleted) t.GetAwaiter().GetResult();
+            else t.AsTask().GetAwaiter().GetResult();
+        }
+
+        /// <summary>
+        /// Disposes of the connection.
+        /// </summary>
+        /// <returns>A <see cref="ValueTask"/> for the asynchronous operation.</returns>
+        /// <remarks>This is equivalent to calling <see cref="CloseAsync(ConnectionCloseMethod, CancellationToken)"/> with the method <see cref="ConnectionCloseMethod.GracefulShutdown"/>.</remarks>
+        public ValueTask DisposeAsync()
+        {
+            return CloseAsync(ConnectionCloseMethod.GracefulShutdown, CancellationToken.None);
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionCloseMethod.cs b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionCloseMethod.cs
new file mode 100644
index 00000000000000..6b5a0792f4a46b
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionCloseMethod.cs
@@ -0,0 +1,26 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Net.Connections
+{
+    /// <summary>
+    /// Methods for closing a connection.
+    /// </summary>
+    public enum ConnectionCloseMethod
+    {
+        /// <summary>
+        /// The connection should be flushed and closed.
+        /// </summary>
+        GracefulShutdown,
+
+        /// <summary>
+        /// The connection should be aborted gracefully, performing any I/O needed to notify the other side of the connection that it has been aborted.
+        /// </summary>
+        Abort,
+
+        /// <summary>
+        /// The connection should be aborted immediately, avoiding any I/O needed to notify the other side of the connection that it has been aborted.
+        /// </summary>
+        Immediate
+    }
+}
diff --git a/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionExtensions.cs b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionExtensions.cs
new file mode 100644
index 00000000000000..6850247f36067d
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionExtensions.cs
@@ -0,0 +1,87 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics.CodeAnalysis;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections
+{
+    /// <summary>
+    /// Extension methods for working with the System.Net.Connections types.
+    /// </summary>
+    public static class ConnectionExtensions
+    {
+        /// <summary>
+        /// Retrieves a Type-based property from an <see cref="IConnectionProperties"/>, if it exists.
+        /// </summary>
+        /// <typeparam name="T">The type of the property to retrieve.</typeparam>
+        /// <param name="properties">The connection properties to retrieve a property from.</param>
+        /// <param name="property">If <paramref name="properties"/> contains a property of type <typeparamref name="T"/>, receives the property. Otherwise, default.</param>
+        /// <returns>If <paramref name="properties"/> contains a property of type <typeparamref name="T"/>, true. Otherwise, false.</returns>
+        public static bool TryGet<T>(this IConnectionProperties properties, [MaybeNullWhen(false)] out T property)
+        {
+            if (properties == null) throw new ArgumentNullException(nameof(properties));
+
+            if (properties.TryGet(typeof(T), out object? obj) && obj is T propertyValue)
+            {
+                property = propertyValue;
+                return true;
+            }
+            else
+            {
+                property = default;
+                return false;
+            }
+        }
+
+        /// <summary>
+        /// Creates a connection-level filter on top of a <see cref="ConnectionFactory"/>.
+        /// </summary>
+        /// <param name="factory">The factory to be filtered.</param>
+        /// <param name="filter">The connection-level filter to apply on top of <paramref name="factory"/>.</param>
+        /// <returns>A new filtered <see cref="ConnectionFactory"/>.</returns>
+        public static ConnectionFactory Filter(this ConnectionFactory factory, Func<Connection, IConnectionProperties?, CancellationToken, ValueTask<Connection>> filter)
+        {
+            if (factory == null) throw new ArgumentNullException(nameof(factory));
+            if (filter == null) throw new ArgumentNullException(nameof(filter));
+            return new ConnectionFilteringFactory(factory, filter);
+        }
+
+        private sealed class ConnectionFilteringFactory : ConnectionFactory
+        {
+            private readonly ConnectionFactory _baseFactory;
+            private readonly Func<Connection, IConnectionProperties?, CancellationToken, ValueTask<Connection>> _filter;
+
+            public ConnectionFilteringFactory(ConnectionFactory baseFactory, Func<Connection, IConnectionProperties?, CancellationToken, ValueTask<Connection>> filter)
+            {
+                _baseFactory = baseFactory;
+                _filter = filter;
+            }
+
+            public override async ValueTask<Connection> ConnectAsync(EndPoint? endPoint, IConnectionProperties? options = null, CancellationToken cancellationToken = default)
+            {
+                Connection con = await _baseFactory.ConnectAsync(endPoint, options, cancellationToken).ConfigureAwait(false);
+                try
+                {
+                    return await _filter(con, options, cancellationToken).ConfigureAwait(false);
+                }
+                catch
+                {
+                    await con.CloseAsync(ConnectionCloseMethod.Abort, cancellationToken).ConfigureAwait(false);
+                    throw;
+                }
+            }
+
+            protected override void Dispose(bool disposing)
+            {
+                if (disposing) _baseFactory.Dispose();
+            }
+
+            protected override ValueTask DisposeAsyncCore()
+            {
+                return _baseFactory.DisposeAsync();
+            }
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionFactory.cs b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionFactory.cs
new file mode 100644
index 00000000000000..812f78a6ae6ed6
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionFactory.cs
@@ -0,0 +1,53 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections
+{
+    /// <summary>
+    /// A factory for opening outgoing connections.
+    /// </summary>
+    public abstract class ConnectionFactory : IAsyncDisposable, IDisposable
+    {
+        /// <summary>
+        /// Opens a new <see cref="Connection"/>.
+        /// </summary>
+        /// <param name="endPoint">The <see cref="EndPoint"/> to connect to, if any.</param>
+        /// <param name="options">Options used to create the connection, if any.</param>
+        /// <param name="cancellationToken">A token used to cancel the asynchronous operation.</param>
+        /// <returns>A <see cref="ValueTask{TResult}"/> for the <see cref="Connection"/>.</returns>
+        public abstract ValueTask<Connection> ConnectAsync(EndPoint? endPoint, IConnectionProperties? options = null, CancellationToken cancellationToken = default);
+
+        public void Dispose()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+
+        public async ValueTask DisposeAsync()
+        {
+            await DisposeAsyncCore().ConfigureAwait(false);
+            GC.SuppressFinalize(this);
+        }
+
+        /// <summary>
+        /// Disposes the <see cref="ConnectionFactory"/>.
+        /// </summary>
+        /// <param name="disposing">If true, the <see cref="ConnectionFactory"/> is being disposed. If false, the <see cref="ConnectionFactory"/> is being finalized.</param>
+        protected virtual void Dispose(bool disposing)
+        {
+        }
+
+        /// <summary>
+        /// Asynchronously disposes the <see cref="ConnectionFactory"/>.
+        /// </summary>
+        /// <returns>A <see cref="ValueTask"/> representing the asynchronous dispose operation.</returns>
+        protected virtual ValueTask DisposeAsyncCore()
+        {
+            Dispose(true);
+            return default;
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionListener.cs b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionListener.cs
new file mode 100644
index 00000000000000..299ba0d66350a3
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionListener.cs
@@ -0,0 +1,62 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections
+{
+    /// <summary>
+    /// A listener to accept incoming connections.
+    /// </summary>
+    public abstract class ConnectionListener : IAsyncDisposable, IDisposable
+    {
+        /// <summary>
+        /// Properties exposed by this listener.
+        /// </summary>
+        public abstract IConnectionProperties ListenerProperties { get; }
+
+        /// <summary>
+        /// The local endpoint of this connection, if any.
+        /// </summary>
+        public abstract EndPoint? LocalEndPoint { get; }
+
+        /// <summary>
+        /// Accepts an incoming connection.
+        /// </summary>
+        /// <param name="options">Options used to create the connection, if any.</param>
+        /// <param name="cancellationToken">A token used to cancel the asynchronous operation.</param>
+        /// <returns>A <see cref="ValueTask{TResult}"/> for the <see cref="Connection"/>.</returns>
+        public abstract ValueTask<Connection> AcceptAsync(IConnectionProperties? options = null, CancellationToken cancellationToken = default);
+
+        public void Dispose()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+
+        public async ValueTask DisposeAsync()
+        {
+            await DisposeAsyncCore().ConfigureAwait(false);
+            GC.SuppressFinalize(this);
+        }
+
+        /// <summary>
+        /// Disposes the <see cref="ConnectionFactory"/>.
+        /// </summary>
+        /// <param name="disposing">If true, the <see cref="ConnectionFactory"/> is being disposed. If false, the <see cref="ConnectionFactory"/> is being finalized.</param>
+        protected virtual void Dispose(bool disposing)
+        {
+        }
+
+        /// <summary>
+        /// Asynchronously disposes the <see cref="ConnectionFactory"/>.
+        /// </summary>
+        /// <returns>A <see cref="ValueTask"/> representing the asynchronous dispose operation.</returns>
+        protected virtual ValueTask DisposeAsyncCore()
+        {
+            Dispose(true);
+            return default;
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionListenerFactory.cs b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionListenerFactory.cs
new file mode 100644
index 00000000000000..7e6339d9d67787
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/System/Net/Connections/ConnectionListenerFactory.cs
@@ -0,0 +1,46 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections
+{
+    /// <summary>
+    /// A factory for creating connection listeners, to accept incoming connections.
+    /// </summary>
+    public abstract class ConnectionListenerFactory : IAsyncDisposable, IDisposable
+    {
+        public abstract ValueTask<ConnectionListener> ListenAsync(EndPoint? endPoint, IConnectionProperties? options = null, CancellationToken cancellationToken = default);
+
+        public void Dispose()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+
+        public async ValueTask DisposeAsync()
+        {
+            await DisposeAsyncCore().ConfigureAwait(false);
+            GC.SuppressFinalize(this);
+        }
+
+        /// <summary>
+        /// Disposes the <see cref="ConnectionFactory"/>.
+        /// </summary>
+        /// <param name="disposing">If true, the <see cref="ConnectionFactory"/> is being disposed. If false, the <see cref="ConnectionFactory"/> is being finalized.</param>
+        protected virtual void Dispose(bool disposing)
+        {
+        }
+
+        /// <summary>
+        /// Asynchronously disposes the <see cref="ConnectionFactory"/>.
+        /// </summary>
+        /// <returns>A <see cref="ValueTask"/> representing the asynchronous dispose operation.</returns>
+        protected virtual ValueTask DisposeAsyncCore()
+        {
+            Dispose(true);
+            return default;
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/src/System/Net/Connections/DuplexPipeStream.cs b/src/libraries/System.Net.Connections/src/System/Net/Connections/DuplexPipeStream.cs
new file mode 100644
index 00000000000000..3319c972b58287
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/System/Net/Connections/DuplexPipeStream.cs
@@ -0,0 +1,166 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Buffers;
+using System.IO;
+using System.IO.Pipelines;
+using System.Runtime.ExceptionServices;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections
+{
+    internal sealed class DuplexPipeStream : Stream
+    {
+        private readonly PipeReader _reader;
+        private readonly PipeWriter _writer;
+
+        public override bool CanRead => true;
+        public override bool CanSeek => false;
+        public override bool CanWrite => true;
+        public override long Length => throw new NotSupportedException();
+        public override long Position { get => throw new NotSupportedException(); set => throw new NotSupportedException(); }
+
+        public DuplexPipeStream(IDuplexPipe pipe)
+        {
+            _reader = pipe.Input;
+            _writer = pipe.Output;
+        }
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                _reader.Complete();
+                _writer.Complete();
+            }
+            base.Dispose(disposing);
+        }
+
+        public override async ValueTask DisposeAsync()
+        {
+            await _reader.CompleteAsync().ConfigureAwait(false);
+            await _writer.CompleteAsync().ConfigureAwait(false);
+        }
+
+        public override void Flush()
+        {
+            FlushAsync().GetAwaiter().GetResult();
+        }
+
+        public override async Task FlushAsync(CancellationToken cancellationToken)
+        {
+            FlushResult r = await _writer.FlushAsync(cancellationToken).ConfigureAwait(false);
+            if (r.IsCanceled) throw new OperationCanceledException(cancellationToken);
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            if (buffer == null) throw new ArgumentNullException(nameof(buffer));
+
+            ValueTask<int> t = ReadAsync(buffer.AsMemory(offset, count));
+            return
+                t.IsCompleted ? t.GetAwaiter().GetResult() :
+                t.AsTask().GetAwaiter().GetResult();
+        }
+
+        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        {
+            if (buffer == null) return Task.FromException<int>(ExceptionDispatchInfo.SetCurrentStackTrace(new ArgumentNullException(nameof(buffer))));
+            return ReadAsync(buffer.AsMemory(offset, count), cancellationToken).AsTask();
+        }
+
+        public override async ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken = default)
+        {
+            ReadResult result = await _reader.ReadAsync(cancellationToken).ConfigureAwait(false);
+
+            if (result.IsCanceled)
+            {
+                throw new OperationCanceledException();
+            }
+
+            ReadOnlySequence<byte> sequence = result.Buffer;
+            long bufferLength = sequence.Length;
+            SequencePosition consumed = sequence.Start;
+
+            try
+            {
+                if (bufferLength != 0)
+                {
+                    int actual = (int)Math.Min(bufferLength, buffer.Length);
+
+                    ReadOnlySequence<byte> slice = actual == bufferLength ? sequence : sequence.Slice(0, actual);
+                    consumed = slice.End;
+                    slice.CopyTo(buffer.Span);
+
+                    return actual;
+                }
+
+                if (result.IsCompleted)
+                {
+                    return 0;
+                }
+            }
+            finally
+            {
+                _reader.AdvanceTo(consumed);
+            }
+
+            // This is a buggy PipeReader implementation that returns 0 byte reads even though the PipeReader
+            // isn't completed or canceled.
+            throw new InvalidOperationException(SR.net_connections_zero_byte_pipe_read);
+        }
+
+        public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback? callback, object? state)
+        {
+            return TaskToApm.Begin(ReadAsync(buffer, offset, count), callback, state);
+        }
+
+        public override int EndRead(IAsyncResult asyncResult)
+        {
+            return TaskToApm.End<int>(asyncResult);
+        }
+
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            throw new NotSupportedException();
+        }
+
+        public override void SetLength(long value)
+        {
+            throw new NotSupportedException();
+        }
+
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            WriteAsync(buffer, offset, count, CancellationToken.None).GetAwaiter().GetResult();
+        }
+
+        public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        {
+            return WriteAsync(buffer.AsMemory(offset, count), cancellationToken).AsTask();
+        }
+
+        public override async ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default)
+        {
+            FlushResult r = await _writer.WriteAsync(buffer, cancellationToken).ConfigureAwait(false);
+            if (r.IsCanceled) throw new OperationCanceledException(cancellationToken);
+        }
+
+        public override IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback? callback, object? state)
+        {
+            return TaskToApm.Begin(WriteAsync(buffer, offset, count), callback, state);
+        }
+
+        public override void EndWrite(IAsyncResult asyncResult)
+        {
+            TaskToApm.End(asyncResult);
+        }
+
+        public override Task CopyToAsync(Stream destination, int bufferSize, CancellationToken cancellationToken)
+        {
+            return _reader.CopyToAsync(destination, cancellationToken);
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/src/System/Net/Connections/IConnectionProperties.cs b/src/libraries/System.Net.Connections/src/System/Net/Connections/IConnectionProperties.cs
new file mode 100644
index 00000000000000..ce89dd97a216b1
--- /dev/null
+++ b/src/libraries/System.Net.Connections/src/System/Net/Connections/IConnectionProperties.cs
@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics.CodeAnalysis;
+
+namespace System.Net.Connections
+{
+    /// <summary>
+    /// A container for connection properties.
+    /// </summary>
+    public interface IConnectionProperties
+    {
+        /// <summary>
+        /// Retrieves a connection property, if it exists.
+        /// </summary>
+        /// <param name="propertyKey">The key of the property to retrieve.</param>
+        /// <param name="property">If the property was found, retrieves the property. Otherwise, null.</param>
+        /// <returns>If the property was found, true. Otherwise, false.</returns>
+        bool TryGet(Type propertyKey, [NotNullWhen(true)] out object? property);
+    }
+}
diff --git a/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/ConnectionBaseTest.cs b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/ConnectionBaseTest.cs
new file mode 100644
index 00000000000000..66cc4a2352bc6b
--- /dev/null
+++ b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/ConnectionBaseTest.cs
@@ -0,0 +1,81 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Threading.Tasks;
+using Xunit;
+
+namespace System.Net.Connections.Tests
+{
+    public class ConnectionBaseTest
+    {
+        [Fact]
+        public void Dispose_CallsClose_Success()
+        {
+            ConnectionCloseMethod? method = null;
+
+            var con = new MockConnection();
+            con.OnCloseAsyncCore = (m, t) =>
+            {
+                method = m;
+                return default(ValueTask);
+            };
+
+            con.Dispose();
+
+            Assert.Equal(ConnectionCloseMethod.GracefulShutdown, method);
+        }
+
+        [Fact]
+        public async Task DisposeAsync_CallsClose_Success()
+        {
+            ConnectionCloseMethod? method = null;
+
+            var con = new MockConnection();
+            con.OnCloseAsyncCore = (m, t) =>
+            {
+                method = m;
+                return default(ValueTask);
+            };
+
+            await con.DisposeAsync();
+
+            Assert.Equal(ConnectionCloseMethod.GracefulShutdown, method);
+        }
+
+        [Fact]
+        public void Dispose_CalledOnce_Success()
+        {
+            int callCount = 0;
+
+            var con = new MockConnection();
+            con.OnCloseAsyncCore = delegate
+            {
+                ++callCount;
+                return default(ValueTask);
+            };
+
+            con.Dispose();
+            con.Dispose();
+
+            Assert.Equal(1, callCount);
+        }
+
+        [Fact]
+        public async Task DisposeAsync_CalledOnce_Success()
+        {
+            int callCount = 0;
+
+            var con = new MockConnection();
+            con.OnCloseAsyncCore = delegate
+            {
+                ++callCount;
+                return default(ValueTask);
+            };
+
+            await con.DisposeAsync();
+            await con.DisposeAsync();
+
+            Assert.Equal(1, callCount);
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/ConnectionTest.cs b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/ConnectionTest.cs
new file mode 100644
index 00000000000000..ad16e45fc6cf31
--- /dev/null
+++ b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/ConnectionTest.cs
@@ -0,0 +1,264 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Buffers;
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+using System.IO;
+using System.IO.Pipelines;
+using System.Linq;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace System.Net.Connections.Tests
+{
+    public class ConnectionTest
+    {
+        [Fact]
+        public void CreateStream_CalledOnce_Success()
+        {
+            int callCount = 0;
+
+            var con = new MockConnection();
+            con.OnCreateStream = () =>
+            {
+                ++callCount;
+                return new MemoryStream();
+            };
+
+            _ = con.Stream;
+            _ = con.Stream;
+
+            Assert.Equal(1, callCount);
+        }
+
+        [Fact]
+        public void CreatePipe_CalledOnce_Success()
+        {
+            int callCount = 0;
+
+            var con = new MockConnection();
+            con.OnCreatePipe = () =>
+            {
+                ++callCount;
+                return new MockPipe();
+            };
+
+            _ = con.Pipe;
+            _ = con.Pipe;
+
+            Assert.Equal(1, callCount);
+        }
+
+        [Fact]
+        public void AccessStream_AccessPipe_Fail()
+        {
+            var con = new MockConnection();
+            con.OnCreateStream = () => new MemoryStream();
+
+            _ = con.Stream;
+            Assert.Throws<InvalidOperationException>(() => _ = con.Pipe);
+        }
+
+        [Fact]
+        public void AccessPipe_AccessStream_Fail()
+        {
+            var con = new MockConnection();
+            con.OnCreatePipe = () => new MockPipe();
+
+            _ = con.Pipe;
+            Assert.Throws<InvalidOperationException>(() => _ = con.Stream);
+        }
+
+        [Fact]
+        public void AccessStream_NoOverloads_Fail()
+        {
+            var con = new ConnectionWithoutStreamOrPipe();
+            Assert.Throws<InvalidOperationException>(() => _ = con.Stream);
+        }
+
+        [Fact]
+        public void AccessPipe_NoOverloads_Fail()
+        {
+            var con = new ConnectionWithoutStreamOrPipe();
+            Assert.Throws<InvalidOperationException>(() => _ = con.Pipe);
+        }
+
+        [Fact]
+        public async Task WrappedStream_Success()
+        {
+            var bytesA = Encoding.ASCII.GetBytes("foo");
+            var bytesB = Encoding.ASCII.GetBytes("bar");
+
+            var stream = new MemoryStream();
+            stream.Write(bytesA);
+            stream.Position = 0;
+
+            var con = new MockConnection();
+            con.OnCreateStream = () => stream;
+
+            IDuplexPipe pipe = con.Pipe;
+
+            ReadResult res = await pipe.Input.ReadAsync();
+            Assert.Equal(bytesA, res.Buffer.ToArray());
+
+            await pipe.Output.WriteAsync(bytesB);
+            Assert.Equal(bytesA.Concat(bytesB).ToArray(), stream.ToArray());
+        }
+
+        [Fact]
+        public async Task WrappedPipe_Success()
+        {
+            var bytesA = Encoding.ASCII.GetBytes("foo");
+            var bytesB = Encoding.ASCII.GetBytes("bar");
+
+            var stream = new MemoryStream();
+            stream.Write(bytesA);
+            stream.Position = 0;
+
+            var pipe = new MockPipe
+            {
+                Input = PipeReader.Create(stream),
+                Output = PipeWriter.Create(stream)
+            };
+
+            var con = new MockConnection();
+            con.OnCreatePipe = () => pipe;
+
+            Stream s = con.Stream;
+
+            var readBuffer = new byte[4];
+            int len = await s.ReadAsync(readBuffer);
+            Assert.Equal(3, len);
+            Assert.Equal(bytesA, readBuffer.AsSpan(0, len).ToArray());
+
+            await s.WriteAsync(bytesB);
+            Assert.Equal(bytesA.Concat(bytesB).ToArray(), stream.ToArray());
+        }
+
+        [Theory]
+        [InlineData(ConnectionCloseMethod.GracefulShutdown, true)]
+        [InlineData(ConnectionCloseMethod.Abort, false)]
+        [InlineData(ConnectionCloseMethod.Immediate, false)]
+        public async Task FromStream_CloseMethod_Flushed(ConnectionCloseMethod method, bool shouldFlush)
+        {
+            bool streamFlushed = false;
+
+            var stream = new MockStream
+            {
+                OnFlushAsync = _ => { streamFlushed = true; return Task.CompletedTask; }
+            };
+
+            var con = Connection.FromStream(stream, leaveOpen: true);
+
+            await con.CloseAsync(method);
+            Assert.Equal(shouldFlush, streamFlushed);
+        }
+
+        [Theory]
+        [InlineData(ConnectionCloseMethod.GracefulShutdown, true)]
+        [InlineData(ConnectionCloseMethod.Abort, false)]
+        [InlineData(ConnectionCloseMethod.Immediate, false)]
+        public async Task FromPipe_CloseMethod_Flushed(ConnectionCloseMethod method, bool shouldFlush)
+        {
+            bool pipeFlushed = false;
+
+            var pipe = new MockPipe
+            {
+                Input = new MockPipeReader()
+                {
+                    OnCompleteAsync = _ => default
+                },
+                Output = new MockPipeWriter()
+                {
+                    OnFlushAsync = _ => { pipeFlushed = true; return default; },
+                    OnCompleteAsync = _ => default
+                }
+            };
+
+            var con = Connection.FromPipe(pipe);
+
+            await con.CloseAsync(method, new CancellationTokenSource().Token);
+            Assert.Equal(shouldFlush, pipeFlushed);
+        }
+
+        [Theory]
+        [InlineData(true, false)]
+        [InlineData(false, true)]
+        public async Task FromStream_LeaveOpen_StreamDisposed(bool leaveOpen, bool shouldDispose)
+        {
+            bool streamDisposed = false;
+
+            var stream = new MockStream();
+            stream.OnDisposeAsync = delegate { streamDisposed = true; return default; };
+
+            var con = Connection.FromStream(stream, leaveOpen);
+
+            await con.CloseAsync(ConnectionCloseMethod.Immediate);
+            Assert.Equal(shouldDispose, streamDisposed);
+        }
+
+        [Theory]
+        [InlineData(true, false)]
+        [InlineData(false, true)]
+        public async Task FromPipe_LeaveOpen_PipeDisposed(bool leaveOpen, bool shouldDispose)
+        {
+            bool pipeDisposed = false;
+
+            var pipe = new MockPipe
+            {
+                OnDisposeAsync = () => { pipeDisposed = true; return default; },
+                Input = new MockPipeReader()
+                {
+                    OnCompleteAsync = _ => default
+                },
+                Output = new MockPipeWriter()
+                {
+                    OnFlushAsync = _ => default,
+                    OnCompleteAsync = _ => default
+                }
+            };
+
+            var con = Connection.FromPipe(pipe, leaveOpen);
+
+            await con.CloseAsync(ConnectionCloseMethod.Immediate);
+            Assert.Equal(shouldDispose, pipeDisposed);
+        }
+
+        [Fact]
+        public void FromStream_PropertiesInitialized()
+        {
+            var properties = new DummyConnectionProperties();
+            var localEndPoint = new IPEndPoint(IPAddress.Any, 1);
+            var remoteEndPoint = new IPEndPoint(IPAddress.Any, 2);
+
+            Connection c = Connection.FromStream(new MockStream(), leaveOpen: false, properties, localEndPoint, remoteEndPoint);
+            Assert.Same(properties, c.ConnectionProperties);
+            Assert.Same(localEndPoint, c.LocalEndPoint);
+            Assert.Same(remoteEndPoint, c.RemoteEndPoint);
+        }
+
+        [Fact]
+        public void FromPipe_PropertiesInitialized()
+        {
+            var properties = new DummyConnectionProperties();
+            var localEndPoint = new IPEndPoint(IPAddress.Any, 1);
+            var remoteEndPoint = new IPEndPoint(IPAddress.Any, 2);
+
+            Connection c = Connection.FromPipe(new MockPipe(), leaveOpen: false, properties, localEndPoint, remoteEndPoint);
+            Assert.Same(properties, c.ConnectionProperties);
+            Assert.Same(localEndPoint, c.LocalEndPoint);
+            Assert.Same(remoteEndPoint, c.RemoteEndPoint);
+        }
+
+        private sealed class DummyConnectionProperties : IConnectionProperties
+        {
+            public bool TryGet(Type propertyKey, [NotNullWhen(true)] out object property)
+            {
+                throw new NotImplementedException();
+            }
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/ConnectionWithoutStreamOrPipe.cs b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/ConnectionWithoutStreamOrPipe.cs
new file mode 100644
index 00000000000000..16e52387b1d6a5
--- /dev/null
+++ b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/ConnectionWithoutStreamOrPipe.cs
@@ -0,0 +1,22 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections.Tests
+{
+    internal class ConnectionWithoutStreamOrPipe : Connection
+    {
+        public override IConnectionProperties ConnectionProperties => throw new NotImplementedException();
+
+        public override EndPoint LocalEndPoint => throw new NotImplementedException();
+
+        public override EndPoint RemoteEndPoint => throw new NotImplementedException();
+
+        protected override ValueTask CloseAsyncCore(ConnectionCloseMethod method, CancellationToken cancellationToken)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockConnection.cs b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockConnection.cs
new file mode 100644
index 00000000000000..f1acf758fef8bb
--- /dev/null
+++ b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockConnection.cs
@@ -0,0 +1,33 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO;
+using System.IO.Pipelines;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections.Tests
+{
+    internal class MockConnection : Connection
+    {
+        public Func<IConnectionProperties> OnConnectionProperties { get; set; }
+        public Func<EndPoint> OnLocalEndPoint { get; set; }
+        public Func<EndPoint> OnRemoteEndPoint { get; set; }
+        public Func<ConnectionCloseMethod, CancellationToken, ValueTask> OnCloseAsyncCore { get; set; }
+        public Func<IDuplexPipe> OnCreatePipe { get; set; }
+        public Func<Stream> OnCreateStream { get; set; }
+
+        public override IConnectionProperties ConnectionProperties => OnConnectionProperties();
+
+        public override EndPoint LocalEndPoint => OnLocalEndPoint();
+
+        public override EndPoint RemoteEndPoint => OnRemoteEndPoint();
+
+        protected override ValueTask CloseAsyncCore(ConnectionCloseMethod method, CancellationToken cancellationToken) =>
+            OnCloseAsyncCore(method, cancellationToken);
+
+        protected override IDuplexPipe CreatePipe() => OnCreatePipe != null ? OnCreatePipe() : base.CreatePipe();
+
+        protected override Stream CreateStream() => OnCreateStream != null ? OnCreateStream() : base.CreateStream();
+    }
+}
diff --git a/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockPipe.cs b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockPipe.cs
new file mode 100644
index 00000000000000..6abbb9a7cc6224
--- /dev/null
+++ b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockPipe.cs
@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO.Pipelines;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections.Tests
+{
+    internal class MockPipe : IDuplexPipe, IAsyncDisposable
+    {
+        public Func<ValueTask> OnDisposeAsync { get; set; }
+        public PipeReader Input { get; set; }
+
+        public PipeWriter Output { get; set; }
+
+        public ValueTask DisposeAsync()
+        {
+            return OnDisposeAsync?.Invoke() ?? default;
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockPipeReader.cs b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockPipeReader.cs
new file mode 100644
index 00000000000000..2413bf10a77df7
--- /dev/null
+++ b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockPipeReader.cs
@@ -0,0 +1,44 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO.Pipelines;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections.Tests
+{
+    internal class MockPipeReader : PipeReader
+    {
+        public Action<SequencePosition, SequencePosition> OnAdvanceTo { get; set; }
+        public Action OnCancelPendingRead { get; set; }
+        public Action<Exception> OnComplete { get; set; }
+        public Func<Exception,ValueTask> OnCompleteAsync { get; set; }
+        public Func<CancellationToken, ValueTask<ReadResult>> OnReadAsync { get; set; }
+        public Func<ReadResult?> OnTryRead { get; set; }
+
+        public override void AdvanceTo(SequencePosition consumed)
+            => OnAdvanceTo(consumed, consumed);
+
+        public override void AdvanceTo(SequencePosition consumed, SequencePosition examined)
+            => OnAdvanceTo(consumed, examined);
+
+        public override void CancelPendingRead()
+            => OnCancelPendingRead();
+
+        public override void Complete(Exception exception = null)
+            => OnComplete(exception);
+
+        public override ValueTask<ReadResult> ReadAsync(CancellationToken cancellationToken = default)
+            => OnReadAsync(cancellationToken);
+
+        public override bool TryRead(out ReadResult result)
+        {
+            ReadResult? r = OnTryRead();
+            result = r.GetValueOrDefault();
+            return r.HasValue;
+        }
+
+        public override ValueTask CompleteAsync(Exception exception = null)
+            => OnCompleteAsync(exception);
+    }
+}
diff --git a/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockPipeWriter.cs b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockPipeWriter.cs
new file mode 100644
index 00000000000000..7c35e19a0ae51a
--- /dev/null
+++ b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockPipeWriter.cs
@@ -0,0 +1,40 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO.Pipelines;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections.Tests
+{
+    internal class MockPipeWriter : PipeWriter
+    {
+        public Action<int> OnAdvance { get; set; }
+        public Action OnCancelPendingFlush { get; set; }
+        public Action<Exception> OnComplete { get; set; }
+        public Func<Exception,ValueTask> OnCompleteAsync { get; set; }
+        public Func<CancellationToken,ValueTask<FlushResult>> OnFlushAsync { get; set; }
+        public Func<int, Memory<byte>> OnGetMemory { get; set; }
+
+        public override void Advance(int bytes)
+            => OnAdvance(bytes);
+
+        public override void CancelPendingFlush()
+            => OnCancelPendingFlush();
+
+        public override void Complete(Exception exception = null)
+            => OnComplete(exception);
+
+        public override ValueTask CompleteAsync(Exception exception = null)
+            => OnCompleteAsync(exception);
+
+        public override ValueTask<FlushResult> FlushAsync(CancellationToken cancellationToken = default)
+            => OnFlushAsync(cancellationToken);
+
+        public override Memory<byte> GetMemory(int sizeHint = 0)
+            => OnGetMemory(sizeHint);
+
+        public override Span<byte> GetSpan(int sizeHint = 0)
+            => GetMemory(sizeHint).Span;
+    }
+}
diff --git a/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockStream.cs b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockStream.cs
new file mode 100644
index 00000000000000..50dbc31ab11c75
--- /dev/null
+++ b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/MockStream.cs
@@ -0,0 +1,107 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections.Tests
+{
+    internal class MockStream : Stream
+    {
+        public Func<Memory<byte>, CancellationToken, ValueTask<int>> OnReadAsync { get; set; }
+        public Func<ReadOnlyMemory<byte>, CancellationToken, ValueTask> OnWriteAsync { get; set; }
+        public Func<CancellationToken, Task> OnFlushAsync { get; set; }
+        public Func<ValueTask> OnDisposeAsync { get; set; }
+
+        public override bool CanRead => true;
+
+        public override bool CanSeek => false;
+
+        public override bool CanWrite => true;
+
+        public override long Length => throw new NotImplementedException();
+
+        public override long Position { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing) DisposeAsync().AsTask().GetAwaiter().GetResult();
+        }
+
+        public override ValueTask DisposeAsync()
+        {
+            return OnDisposeAsync();
+        }
+
+        public override void Flush()
+        {
+            FlushAsync().GetAwaiter().GetResult();
+        }
+
+        public override Task FlushAsync(CancellationToken cancellationToken)
+        {
+            return OnFlushAsync(cancellationToken);
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            return ReadAsync(buffer, offset, count).GetAwaiter().GetResult();
+        }
+
+        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        {
+            return ReadAsync(buffer.AsMemory(offset, count), cancellationToken).AsTask();
+        }
+
+        public override ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken = default)
+        {
+            return OnReadAsync(buffer, cancellationToken);
+        }
+
+        public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback callback, object state)
+        {
+            return TaskToApm.Begin(ReadAsync(buffer, offset, count), callback, state);
+        }
+
+        public override int EndRead(IAsyncResult asyncResult)
+        {
+            return TaskToApm.End<int>(asyncResult);
+        }
+
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override void SetLength(long value)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            WriteAsync(buffer, offset, count).GetAwaiter().GetResult();
+        }
+
+        public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        {
+            return WriteAsync(buffer.AsMemory(offset, count), cancellationToken).AsTask();
+        }
+
+        public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default)
+        {
+            return OnWriteAsync(buffer, cancellationToken);
+        }
+
+        public override IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback callback, object state)
+        {
+            return TaskToApm.Begin(WriteAsync(buffer, offset, count), callback, state);
+        }
+
+        public override void EndWrite(IAsyncResult asyncResult)
+        {
+            TaskToApm.End(asyncResult);
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/System.Net.Connections.Tests.csproj b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/System.Net.Connections.Tests.csproj
new file mode 100644
index 00000000000000..9aa01126533b0b
--- /dev/null
+++ b/src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/System.Net.Connections.Tests.csproj
@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="$(CommonPath)System\Threading\Tasks\TaskToApm.cs" Link="Common\System\Threading\Tasks\TaskToApm.cs" />
+    <Compile Include="ConnectionBaseTest.cs" />
+    <Compile Include="ConnectionTest.cs" />
+    <Compile Include="ConnectionWithoutStreamOrPipe.cs" />
+    <Compile Include="MockConnection.cs" />
+    <Compile Include="MockPipe.cs" />
+    <Compile Include="MockPipeReader.cs" />
+    <Compile Include="MockPipeWriter.cs" />
+    <Compile Include="MockStream.cs" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/libraries/System.Net.Http.Json/Directory.Build.props b/src/libraries/System.Net.Http.Json/Directory.Build.props
index 749d7fc1c6b56d..ba1f965d83cae7 100644
--- a/src/libraries/System.Net.Http.Json/Directory.Build.props
+++ b/src/libraries/System.Net.Http.Json/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Net.Http.Json/ref/System.Net.Http.Json.cs b/src/libraries/System.Net.Http.Json/ref/System.Net.Http.Json.cs
index c8d7a3c7c9b431..34e35f78833990 100644
--- a/src/libraries/System.Net.Http.Json/ref/System.Net.Http.Json.cs
+++ b/src/libraries/System.Net.Http.Json/ref/System.Net.Http.Json.cs
@@ -12,10 +12,10 @@ public static partial class HttpClientJsonExtensions
         public static System.Threading.Tasks.Task<object?> GetFromJsonAsync(this System.Net.Http.HttpClient client, string? requestUri, System.Type type, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public static System.Threading.Tasks.Task<object?> GetFromJsonAsync(this System.Net.Http.HttpClient client, System.Uri? requestUri, System.Type type, System.Text.Json.JsonSerializerOptions? options, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public static System.Threading.Tasks.Task<object?> GetFromJsonAsync(this System.Net.Http.HttpClient client, System.Uri? requestUri, System.Type type, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
-        public static System.Threading.Tasks.Task<TValue> GetFromJsonAsync<TValue>(this System.Net.Http.HttpClient client, string? requestUri, System.Text.Json.JsonSerializerOptions? options, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
-        public static System.Threading.Tasks.Task<TValue> GetFromJsonAsync<TValue>(this System.Net.Http.HttpClient client, string? requestUri, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
-        public static System.Threading.Tasks.Task<TValue> GetFromJsonAsync<TValue>(this System.Net.Http.HttpClient client, System.Uri? requestUri, System.Text.Json.JsonSerializerOptions? options, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
-        public static System.Threading.Tasks.Task<TValue> GetFromJsonAsync<TValue>(this System.Net.Http.HttpClient client, System.Uri? requestUri, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        public static System.Threading.Tasks.Task<TValue?> GetFromJsonAsync<TValue>(this System.Net.Http.HttpClient client, string? requestUri, System.Text.Json.JsonSerializerOptions? options, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        public static System.Threading.Tasks.Task<TValue?> GetFromJsonAsync<TValue>(this System.Net.Http.HttpClient client, string? requestUri, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        public static System.Threading.Tasks.Task<TValue?> GetFromJsonAsync<TValue>(this System.Net.Http.HttpClient client, System.Uri? requestUri, System.Text.Json.JsonSerializerOptions? options, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        public static System.Threading.Tasks.Task<TValue?> GetFromJsonAsync<TValue>(this System.Net.Http.HttpClient client, System.Uri? requestUri, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public static System.Threading.Tasks.Task<System.Net.Http.HttpResponseMessage> PostAsJsonAsync<TValue>(this System.Net.Http.HttpClient client, string? requestUri, TValue value, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public static System.Threading.Tasks.Task<System.Net.Http.HttpResponseMessage> PostAsJsonAsync<TValue>(this System.Net.Http.HttpClient client, string? requestUri, TValue value, System.Threading.CancellationToken cancellationToken) { throw null; }
         public static System.Threading.Tasks.Task<System.Net.Http.HttpResponseMessage> PostAsJsonAsync<TValue>(this System.Net.Http.HttpClient client, System.Uri? requestUri, TValue value, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
@@ -28,7 +28,7 @@ public static partial class HttpClientJsonExtensions
     public static partial class HttpContentJsonExtensions
     {
         public static System.Threading.Tasks.Task<object?> ReadFromJsonAsync(this System.Net.Http.HttpContent content, System.Type type, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
-        public static System.Threading.Tasks.Task<T> ReadFromJsonAsync<T>(this System.Net.Http.HttpContent content, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        public static System.Threading.Tasks.Task<T?> ReadFromJsonAsync<T>(this System.Net.Http.HttpContent content, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
     }
     public sealed partial class JsonContent : System.Net.Http.HttpContent
     {
diff --git a/src/libraries/System.Net.Http.Json/ref/System.Net.Http.Json.csproj b/src/libraries/System.Net.Http.Json/ref/System.Net.Http.Json.csproj
index af8add8a69fa8f..37e96e45e22573 100644
--- a/src/libraries/System.Net.Http.Json/ref/System.Net.Http.Json.csproj
+++ b/src/libraries/System.Net.Http.Json/ref/System.Net.Http.Json.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
@@ -15,4 +15,7 @@
   <ItemGroup>
     <ProjectReference Include="..\..\System.Text.Json\ref\System.Text.Json.csproj" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.Net.Http" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.Http.Json/src/System.Net.Http.Json.csproj b/src/libraries/System.Net.Http.Json/src/System.Net.Http.Json.csproj
index ee6e5c6a9af48c..031e3a30153c4c 100644
--- a/src/libraries/System.Net.Http.Json/src/System.Net.Http.Json.csproj
+++ b/src/libraries/System.Net.Http.Json/src/System.Net.Http.Json.csproj
@@ -1,13 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetCoreAppCurrent);net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
-  <PropertyGroup>
-    <!-- Ensure Assemblies are first resolved via targeting pack when targeting net461 -->
-    <AssemblySearchPaths Condition="'$(TargetFramework)' == 'net461'">$(NuGetPackageRoot)\microsoft.targetingpack.netframework.v4.6.1\1.0.1\lib\net461\;$(AssemblySearchPaths)</AssemblySearchPaths>
-  </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Net\Http\Json\HttpClientJsonExtensions.Get.cs" />
     <Compile Include="System\Net\Http\Json\HttpClientJsonExtensions.Post.cs" />
@@ -18,26 +13,31 @@
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <Compile Include="System\Net\Http\Json\HttpContentJsonExtensions.netcoreapp.cs" />
     <Compile Include="System\Net\Http\Json\JsonContent.netcoreapp.cs" />
-    <Reference Include="System.Net.Mail" />
-    <Reference Include="System.Net.Http" />
-    <Reference Include="System.Net.Primitives" />
-    <Reference Include="System.Runtime" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' OR $(TargetFramework.StartsWith('net4'))">
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
     <Compile Include="System\ArraySegmentExtensions.netstandard.cs" />
     <Compile Include="System\Net\Http\Json\HttpContentJsonExtensions.netstandard.cs" />
     <Compile Include="System\Net\Http\Json\TranscodingReadStream.cs" />
     <Compile Include="System\Net\Http\Json\TranscodingWriteStream.cs" />
-    <Reference Include="System.Buffers" />
   </ItemGroup>
-  <ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <Reference Include="System.Memory" />
+    <Reference Include="System.Net.Mail" />
+    <Reference Include="System.Net.Http" />
+    <Reference Include="System.Net.Primitives" />
+    <Reference Include="System.Runtime" />
     <Reference Include="System.Text.Json" />
     <Reference Include="System.Threading.Tasks.Extensions" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Json\src\System.Text.Json.csproj" />
+  </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Reference Include="System.Net.Http" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.Http.Json/src/System/Net/Http/Json/HttpClientJsonExtensions.Get.cs b/src/libraries/System.Net.Http.Json/src/System/Net/Http/Json/HttpClientJsonExtensions.Get.cs
index dd50490e26d399..908b5bc1566786 100644
--- a/src/libraries/System.Net.Http.Json/src/System/Net/Http/Json/HttpClientJsonExtensions.Get.cs
+++ b/src/libraries/System.Net.Http.Json/src/System/Net/Http/Json/HttpClientJsonExtensions.Get.cs
@@ -34,7 +34,7 @@ public static partial class HttpClientJsonExtensions
             return GetFromJsonAsyncCore(taskResponse, type, options, cancellationToken);
         }
 
-        public static Task<TValue> GetFromJsonAsync<TValue>(this HttpClient client, string? requestUri, JsonSerializerOptions? options, CancellationToken cancellationToken = default)
+        public static Task<TValue?> GetFromJsonAsync<TValue>(this HttpClient client, string? requestUri, JsonSerializerOptions? options, CancellationToken cancellationToken = default)
         {
             if (client == null)
             {
@@ -45,7 +45,7 @@ public static Task<TValue> GetFromJsonAsync<TValue>(this HttpClient client, stri
             return GetFromJsonAsyncCore<TValue>(taskResponse, options, cancellationToken);
         }
 
-        public static Task<TValue> GetFromJsonAsync<TValue>(this HttpClient client, Uri? requestUri, JsonSerializerOptions? options, CancellationToken cancellationToken = default)
+        public static Task<TValue?> GetFromJsonAsync<TValue>(this HttpClient client, Uri? requestUri, JsonSerializerOptions? options, CancellationToken cancellationToken = default)
         {
             if (client == null)
             {
@@ -62,10 +62,10 @@ public static Task<TValue> GetFromJsonAsync<TValue>(this HttpClient client, Uri?
         public static Task<object?> GetFromJsonAsync(this HttpClient client, Uri? requestUri, Type type, CancellationToken cancellationToken = default)
             => client.GetFromJsonAsync(requestUri, type, options: null, cancellationToken);
 
-        public static Task<TValue> GetFromJsonAsync<TValue>(this HttpClient client, string? requestUri, CancellationToken cancellationToken = default)
+        public static Task<TValue?> GetFromJsonAsync<TValue>(this HttpClient client, string? requestUri, CancellationToken cancellationToken = default)
             => client.GetFromJsonAsync<TValue>(requestUri, options: null, cancellationToken);
 
-        public static Task<TValue> GetFromJsonAsync<TValue>(this HttpClient client, Uri? requestUri, CancellationToken cancellationToken = default)
+        public static Task<TValue?> GetFromJsonAsync<TValue>(this HttpClient client, Uri? requestUri, CancellationToken cancellationToken = default)
             => client.GetFromJsonAsync<TValue>(requestUri, options: null, cancellationToken);
 
         private static async Task<object?> GetFromJsonAsyncCore(Task<HttpResponseMessage> taskResponse, Type type, JsonSerializerOptions? options, CancellationToken cancellationToken)
@@ -80,7 +80,7 @@ public static Task<TValue> GetFromJsonAsync<TValue>(this HttpClient client, Uri?
             }
         }
 
-        private static async Task<T> GetFromJsonAsyncCore<T>(Task<HttpResponseMessage> taskResponse, JsonSerializerOptions? options, CancellationToken cancellationToken)
+        private static async Task<T?> GetFromJsonAsyncCore<T>(Task<HttpResponseMessage> taskResponse, JsonSerializerOptions? options, CancellationToken cancellationToken)
         {
             using (HttpResponseMessage response = await taskResponse.ConfigureAwait(false))
             {
diff --git a/src/libraries/System.Net.Http.Json/src/System/Net/Http/Json/HttpContentJsonExtensions.cs b/src/libraries/System.Net.Http.Json/src/System/Net/Http/Json/HttpContentJsonExtensions.cs
index 753c0315583c03..e73c6fb49d73e0 100644
--- a/src/libraries/System.Net.Http.Json/src/System/Net/Http/Json/HttpContentJsonExtensions.cs
+++ b/src/libraries/System.Net.Http.Json/src/System/Net/Http/Json/HttpContentJsonExtensions.cs
@@ -21,7 +21,7 @@ public static partial class HttpContentJsonExtensions
             return ReadFromJsonAsyncCore(content, type, sourceEncoding, options, cancellationToken);
         }
 
-        public static Task<T> ReadFromJsonAsync<T>(this HttpContent content, JsonSerializerOptions? options = null, CancellationToken cancellationToken = default)
+        public static Task<T?> ReadFromJsonAsync<T>(this HttpContent content, JsonSerializerOptions? options = null, CancellationToken cancellationToken = default)
         {
             ValidateContent(content);
             Debug.Assert(content.Headers.ContentType != null);
@@ -46,7 +46,7 @@ public static Task<T> ReadFromJsonAsync<T>(this HttpContent content, JsonSeriali
             }
         }
 
-        private static async Task<T> ReadFromJsonAsyncCore<T>(HttpContent content, Encoding? sourceEncoding, JsonSerializerOptions? options, CancellationToken cancellationToken)
+        private static async Task<T?> ReadFromJsonAsyncCore<T>(HttpContent content, Encoding? sourceEncoding, JsonSerializerOptions? options, CancellationToken cancellationToken)
         {
             Stream contentStream = await ReadHttpContentStreamAsync(content, cancellationToken).ConfigureAwait(false);
 
diff --git a/src/libraries/System.Net.Http.Json/tests/FunctionalTests/System.Net.Http.Json.Functional.Tests.csproj b/src/libraries/System.Net.Http.Json/tests/FunctionalTests/System.Net.Http.Json.Functional.Tests.csproj
index 2653fcb9dc5247..81605d947b365c 100644
--- a/src/libraries/System.Net.Http.Json/tests/FunctionalTests/System.Net.Http.Json.Functional.Tests.csproj
+++ b/src/libraries/System.Net.Http.Json/tests/FunctionalTests/System.Net.Http.Json.Functional.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="HttpClientJsonExtensionsTests.cs" />
@@ -29,4 +29,8 @@
     <Compile Include="$(CommonTestPath)System\Threading\Tasks\TaskTimeoutExtensions.cs"
              Link="Common\System\Threading\Tasks\TaskTimeoutExtensions.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
+    <Reference Include="System.Net.Http" />
+    <ProjectReference Include="..\..\src\System.Net.Http.Json.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.Http.Json/tests/UnitTests/System.Net.Http.Json.Unit.Tests.csproj b/src/libraries/System.Net.Http.Json/tests/UnitTests/System.Net.Http.Json.Unit.Tests.csproj
index 0f09eb18d9f7a9..0997a1c96f77dd 100644
--- a/src/libraries/System.Net.Http.Json/tests/UnitTests/System.Net.Http.Json.Unit.Tests.csproj
+++ b/src/libraries/System.Net.Http.Json/tests/UnitTests/System.Net.Http.Json.Unit.Tests.csproj
@@ -1,12 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="TranscodingReadStreamTests.cs" />
     <Compile Include="TranscodingWriteStreamTests.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetFrameworkCurrent)'">
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
     <Compile Include="..\..\src\System\ArraySegmentExtensions.netstandard.cs"
              Link="ProductionCode\System\ArraySegmentExtensions.netstandard.cs" />
   </ItemGroup>
@@ -16,4 +16,7 @@
     <Compile Include="..\..\src\System\Net\Http\Json\TranscodingWriteStream.cs"
              Link="ProductionCode\System\Net\Http\Json\TranscodingWriteStream.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="..\..\src\System.Net.Http.Json.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.Http.WinHttpHandler/ref/System.Net.Http.WinHttpHandler.cs b/src/libraries/System.Net.Http.WinHttpHandler/ref/System.Net.Http.WinHttpHandler.cs
index 4236046359d6f7..7339effba4e25d 100644
--- a/src/libraries/System.Net.Http.WinHttpHandler/ref/System.Net.Http.WinHttpHandler.cs
+++ b/src/libraries/System.Net.Http.WinHttpHandler/ref/System.Net.Http.WinHttpHandler.cs
@@ -30,11 +30,11 @@ public WinHttpHandler() { }
         public System.Net.CookieContainer? CookieContainer { get { throw null; } set { } }
         public System.Net.Http.CookieUsePolicy CookieUsePolicy { get { throw null; } set { } }
         public System.Net.ICredentials? DefaultProxyCredentials { get { throw null; } set { } }
+        public bool EnableMultipleHttp2Connections { get { throw null; } set { } }
         public int MaxAutomaticRedirections { get { throw null; } set { } }
         public int MaxConnectionsPerServer { get { throw null; } set { } }
         public int MaxResponseDrainSize { get { throw null; } set { } }
         public int MaxResponseHeadersLength { get { throw null; } set { } }
-        public bool EnableMultipleHttp2Connections { get { throw null; } set { } }
         public bool PreAuthenticate { get { throw null; } set { } }
         public System.Collections.Generic.IDictionary<string, object> Properties { get { throw null; } }
         public System.Net.IWebProxy? Proxy { get { throw null; } set { } }
diff --git a/src/libraries/System.Net.Http.WinHttpHandler/ref/System.Net.Http.WinHttpHandler.csproj b/src/libraries/System.Net.Http.WinHttpHandler/ref/System.Net.Http.WinHttpHandler.csproj
index 69bfc2c5a79bc5..806d5504734c7e 100644
--- a/src/libraries/System.Net.Http.WinHttpHandler/ref/System.Net.Http.WinHttpHandler.csproj
+++ b/src/libraries/System.Net.Http.WinHttpHandler/ref/System.Net.Http.WinHttpHandler.csproj
@@ -1,19 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
-  <PropertyGroup>
-    <!-- Ensure Assemblies are first resolved via targeting pack when targeting net461 -->
-    <AssemblySearchPaths Condition="'$(TargetFramework)' == 'net461'">$(NuGetPackageRoot)\microsoft.targetingpack.netframework.v4.6.1\1.0.1\lib\net461\;$(AssemblySearchPaths)</AssemblySearchPaths>
-  </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Net.Http.WinHttpHandler.cs" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Reference Include="System.Net.Http" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Http.WinHttpHandler/src/System.Net.Http.WinHttpHandler.csproj b/src/libraries/System.Net.Http.WinHttpHandler/src/System.Net.Http.WinHttpHandler.csproj
index 8c06bc26a682f8..71f4b005c6b4d7 100644
--- a/src/libraries/System.Net.Http.WinHttpHandler/src/System.Net.Http.WinHttpHandler.csproj
+++ b/src/libraries/System.Net.Http.WinHttpHandler/src/System.Net.Http.WinHttpHandler.csproj
@@ -1,9 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
     <IncludeDllSafeSearchPathAttribute>true</IncludeDllSafeSearchPathAttribute>
-    <TargetFrameworks>netstandard2.0-Windows_NT;netstandard2.0;net461-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0-Windows_NT;netstandard2.0;net461-Windows_NT</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DefineConstants>$(DefineConstants);WINHTTPHANDLER_DLL</DefineConstants>
     <Nullable>enable</Nullable>
@@ -17,6 +15,20 @@
   <ItemGroup Condition="'$(TargetsWindows)' == 'true'" >
     <Compile Include="$(CommonPath)\Interop\Windows\Interop.Libraries.cs"
              Link="Common\Interop\Windows\Interop.Libraries.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_ALGORITHM_IDENTIFIER.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_ALGORITHM_IDENTIFIER.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_BIT_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_BIT_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.DATA_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.DATA_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.MsgEncodingType.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.MsgEncodingType.cs" />
     <Compile Include="$(CommonPath)\Interop\Windows\Crypt32\Interop.CertEnumCertificatesInStore.cs"
              Link="Common\Interop\Windows\Crypt32\Interop.CertEnumCertificatesInStore.cs" />
     <Compile Include="$(CommonPath)\Interop\Windows\Crypt32\Interop.certificates_types.cs"
@@ -87,14 +99,10 @@
              Link="Common\System\Net\Logging\NetEventSource.Common.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.Buffers" />
-    <Reference Include="System.Diagnostics.DiagnosticSource" />
-    <Reference Include="System.Memory" />
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Reference Include="System.Net.Http" />
-    <Reference Include="netstandard" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.Http.WinHttpHandler/tests/FunctionalTests/HttpClientHandlerTestBase.WinHttpHandler.cs b/src/libraries/System.Net.Http.WinHttpHandler/tests/FunctionalTests/HttpClientHandlerTestBase.WinHttpHandler.cs
index 179cf30e9105e7..0896bbd7b5b08a 100644
--- a/src/libraries/System.Net.Http.WinHttpHandler/tests/FunctionalTests/HttpClientHandlerTestBase.WinHttpHandler.cs
+++ b/src/libraries/System.Net.Http.WinHttpHandler/tests/FunctionalTests/HttpClientHandlerTestBase.WinHttpHandler.cs
@@ -25,5 +25,11 @@ protected static WinHttpClientHandler CreateHttpClientHandler(Version useVersion
 
             return handler;
         }
+
+        protected static HttpRequestMessage CreateRequest(HttpMethod method, Uri uri, Version version, bool exactVersion = false) =>
+            new HttpRequestMessage(method, uri)
+            {
+                Version = version
+            };
     }
 }
diff --git a/src/libraries/System.Net.Http.WinHttpHandler/tests/FunctionalTests/System.Net.Http.WinHttpHandler.Functional.Tests.csproj b/src/libraries/System.Net.Http.WinHttpHandler/tests/FunctionalTests/System.Net.Http.WinHttpHandler.Functional.Tests.csproj
index 98985ef8fc344b..1d0dceca18b31c 100644
--- a/src/libraries/System.Net.Http.WinHttpHandler/tests/FunctionalTests/System.Net.Http.WinHttpHandler.Functional.Tests.csproj
+++ b/src/libraries/System.Net.Http.WinHttpHandler/tests/FunctionalTests/System.Net.Http.WinHttpHandler.Functional.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net48-Windows_NT</TargetFrameworks>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
     <DefineConstants>$(DefineConstants);WINHTTPHANDLER_TEST</DefineConstants>
     <LangVersion>8.0</LangVersion>
@@ -129,6 +129,8 @@
              Link="Common\System\Net\Http\SchSendAuxRecordHttpTest.cs" />
     <Compile Include="$(CommonTestPath)System\Net\Http\SyncBlockingContent.cs"
              Link="Common\System\Net\Http\SyncBlockingContent.cs" />
+    <Compile Include="$(CommonTestPath)System\Net\Http\ThrowingContent.cs"
+             Link="Common\System\Net\Http\ThrowingContent.cs" />
     <Compile Include="$(CommonTestPath)System\Threading\Tasks\TaskTimeoutExtensions.cs"
              Link="Common\System\Threading\Tasks\TaskTimeoutExtensions.cs" />
     <Compile Include="$(CommonTestPath)System\Threading\TrackingSynchronizationContext.cs"
@@ -141,5 +143,14 @@
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="$(NewtonsoftJsonVersion)" />
     <PackageReference Include="System.Net.TestData" Version="$(SystemNetTestDataVersion)" />
+    <ProjectReference Include="..\..\src\System.Net.Http.WinHttpHandler.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices.Protocols\src\System.DirectoryServices.Protocols.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net48'))">
+    <Reference Include="System.DirectoryServices.Protocols" />
+    <Reference Include="System.Net.Http" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Net.Http.Json\src\System.Net.Http.Json.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/ClientCertificateHelper.cs b/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/ClientCertificateHelper.cs
index b0e144992937c4..c284d2be592538 100644
--- a/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/ClientCertificateHelper.cs
+++ b/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/ClientCertificateHelper.cs
@@ -13,6 +13,7 @@ public class ClientCertificateHelper
         private readonly X509Certificate2 _cert_KeyUsageIncludesDigitalSignature_EKUIncludesClientAuth_PrivateKey =
             new X509Certificate2(
                 Convert.FromBase64String(
+                  // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Dummy certificate for testing.")]
                   @"MIIKTgIBAzCCCgoGCSqGSIb3DQEHAaCCCfsEggn3MIIJ8zCCBgwGCSqGSIb3DQEHAaCCBf0EggX5
                     MIIF9TCCBfEGCyqGSIb3DQEMCgECoIIE/jCCBPowHAYKKoZIhvcNAQwBAzAOBAiHDatvDr8QBQIC
                     B9AEggTYv1r4ckwt7o6f6DCMHlb/zv4t7rPju+PP0PjoJ8kzPfj419aSeyPuE+65YH9WFDqafJed
@@ -65,6 +66,7 @@ public class ClientCertificateHelper
         private readonly X509Certificate2 _cert_KeyUsageMissingDigitalSignature_EKUIncludesClientAuth_PrivateKey =
             new X509Certificate2(
                 Convert.FromBase64String(
+                  // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Dummy certificate for testing.")]
                   @"MIIKTgIBAzCCCgoGCSqGSIb3DQEHAaCCCfsEggn3MIIJ8zCCBgwGCSqGSIb3DQEHAaCCBf0EggX5
                     MIIF9TCCBfEGCyqGSIb3DQEMCgECoIIE/jCCBPowHAYKKoZIhvcNAQwBAzAOBAiSNi65ZF5ZTQIC
                     B9AEggTYRTivDtzHOWRR+MobtGFEUu6d1PiIlF1Ic84FWvmFCcJShkBmg3cBqDilqtamAkDkga4h
@@ -117,6 +119,7 @@ public class ClientCertificateHelper
         private readonly X509Certificate2 _cert_KeyUsageIncludesDigitalSignature_EKUMissingClientAuth_PrivateKey =
             new X509Certificate2(
                 Convert.FromBase64String(
+                  // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Dummy certificate for testing.")]
                   @"MIIKRgIBAzCCCgIGCSqGSIb3DQEHAaCCCfMEggnvMIIJ6zCCBgQGCSqGSIb3DQEHAaCCBfUEggXx
                     MIIF7TCCBekGCyqGSIb3DQEMCgECoIIE9jCCBPIwHAYKKoZIhvcNAQwBAzAOBAhCUuNQ0RqfZQIC
                     B9AEggTQHCQRSiCiNI7egTvUaI1Z3tfeLwFWvG7B/za5v9fb97MExoyVQSDmUyUDTlVEcg3gVqJZ
@@ -169,6 +172,7 @@ public class ClientCertificateHelper
         private readonly X509Certificate2 _cert_KeyUsageIncludesDigitalSignature_NoEKU_PrivateKey =
             new X509Certificate2(
                 Convert.FromBase64String(
+                  // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Dummy certificate for testing.")]
                   @"MIIKPgIBAzCCCfoGCSqGSIb3DQEHAaCCCesEggnnMIIJ4zCCBgwGCSqGSIb3DQEHAaCCBf0EggX5
                     MIIF9TCCBfEGCyqGSIb3DQEMCgECoIIE/jCCBPowHAYKKoZIhvcNAQwBAzAOBAijQh1kbOZOYQIC
                     B9AEggTY+wDp3V31Lh7f8YrsqEsyGZ+GlYvFhLWvDASjisYJi5NlQ0ONbf0KOXHVSvBj3tVyuHm4
@@ -221,6 +225,7 @@ public class ClientCertificateHelper
         private readonly X509Certificate2 _cert_KeyUsageIncludesDigitalSignature_EKUIncludesClientAuth_NoPrivateKey =
             new X509Certificate2(
                 Convert.FromBase64String(
+                  // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Dummy certificate for testing.")]
                   @"MIIDFjCCAf6gAwIBAgIQTm8+EF94L4FJ0nBFl5LICzANBgkqhkiG9w0BAQsFADAb
                     MRkwFwYDVQQDDBB1c2VyQGV4YW1wbGUuY29tMCAXDTE1MTAwNTEwMDMwMFoYDzIx
                     MTUxMDA1MTAwMzAwWjAbMRkwFwYDVQQDDBB1c2VyQGV4YW1wbGUuY29tMIIBIjAN
diff --git a/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/FakeInterop.cs b/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/FakeInterop.cs
index d043adbda35647..728aacd3eb27c9 100644
--- a/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/FakeInterop.cs
+++ b/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/FakeInterop.cs
@@ -20,6 +20,34 @@ internal static partial class Interop
 {
     internal static partial class Crypt32
     {
+        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
+        internal unsafe struct CERT_CHAIN_POLICY_PARA
+        {
+            public uint cbSize;
+            public uint dwFlags;
+            public void* pvExtraPolicyPara;
+        }
+
+        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
+        internal unsafe struct CERT_CHAIN_POLICY_STATUS
+        {
+            public uint cbSize;
+            public uint dwError;
+            public int lChainIndex;
+            public int lElementIndex;
+            public void* pvExtraPolicyStatus;
+        }
+
+        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
+        internal struct CERT_CONTEXT
+        {
+            internal uint dwCertEncodingType;
+            internal IntPtr pbCertEncoded;
+            internal uint cbCertEncoded;
+            internal IntPtr pCertInfo;
+            internal IntPtr hCertStore;
+        }
+
         public static bool CertFreeCertificateContext(IntPtr certContext)
         {
             return true;
@@ -33,6 +61,7 @@ public static bool CertVerifyCertificateChainPolicy(
         {
             return true;
         }
+
     }
 
     internal static partial class Kernel32
diff --git a/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/FakeX509Certificates.cs b/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/FakeX509Certificates.cs
index 69739185cf1de7..6af1b365bd2fa8 100644
--- a/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/FakeX509Certificates.cs
+++ b/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/FakeX509Certificates.cs
@@ -3,8 +3,27 @@
 
 using System.Diagnostics;
 using System.Net.Http.WinHttpHandlerUnitTests;
+using System.Net.Security;
 using System.Security.Cryptography.X509Certificates;
 
+namespace System.Net.Http
+{
+    internal static class WinHttpCertificateHelper
+    {
+        public static void BuildChain(
+            X509Certificate2 certificate,
+            X509Certificate2Collection remoteCertificateStore,
+            string hostName,
+            bool checkCertificateRevocationList,
+            out X509Chain chain,
+            out SslPolicyErrors sslPolicyErrors)
+        {
+            chain = null;
+            sslPolicyErrors = SslPolicyErrors.None;
+        }
+    }
+}
+
 namespace System.Security.Cryptography.X509Certificates
 {
     public class X509Store : IDisposable
diff --git a/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/System.Net.Http.WinHttpHandler.Unit.Tests.csproj b/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/System.Net.Http.WinHttpHandler.Unit.Tests.csproj
index 502c0cc8e46e8c..0c3e0d0e6f185e 100644
--- a/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/System.Net.Http.WinHttpHandler.Unit.Tests.csproj
+++ b/src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/System.Net.Http.WinHttpHandler.Unit.Tests.csproj
@@ -8,7 +8,7 @@
     <Nullable>annotations</Nullable>
   </PropertyGroup>
   <ItemGroup>
-    <DefaultReferenceExclusions Include="System.Net.Http.WinHttpHandler" />
+    <DefaultReferenceExclusion Include="System.Net.Http.WinHttpHandler" />
   </ItemGroup>
   <ItemGroup Condition=" '$(TargetsWindows)' == 'true' ">
     <Compile Include="$(CommonTestPath)System\Net\SslProtocolSupport.cs"
@@ -17,8 +17,6 @@
              Link="Common\Interop\Windows\Interop.Libraries.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CertEnumCertificatesInStore.cs"
              Link="Common\Interop\Windows\Crypt32\Interop.CertEnumCertificatesInStore.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.certificates_types.cs"
-             Link="Common\Interop\Windows\Crypt32\Interop.certificates_types.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.HRESULT_FROM_WIN32.cs"
              Link="Common\Interop\Windows\Interop.HRESULT_FROM_WIN32.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\SChannel\UnmanagedCertificateContext.IntPtr.cs"
@@ -65,8 +63,6 @@
              Link="ProductionCode\NoWriteNoSeekStreamContent.cs" />
     <Compile Include="..\..\src\System\Net\Http\WinHttpAuthHelper.cs"
              Link="ProductionCode\WinHttpAuthHelper.cs" />
-    <Compile Include="..\..\src\System\Net\Http\WinHttpCertificateHelper.cs"
-             Link="ProductionCode\WinHttpCertificateHelper.cs" />
     <Compile Include="..\..\src\System\Net\Http\WinHttpChannelBinding.cs"
              Link="ProductionCode\WinHttpChannelBinding.cs" />
     <Compile Include="..\..\src\System\Net\Http\WinHttpCookieContainerAdapter.cs"
diff --git a/src/libraries/System.Net.Http/Directory.Build.props b/src/libraries/System.Net.Http/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Net.Http/Directory.Build.props
+++ b/src/libraries/System.Net.Http/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Http/ref/System.Net.Http.cs b/src/libraries/System.Net.Http/ref/System.Net.Http.cs
index dc1e77f19d7fb2..415a52f71b17ad 100644
--- a/src/libraries/System.Net.Http/ref/System.Net.Http.cs
+++ b/src/libraries/System.Net.Http/ref/System.Net.Http.cs
@@ -4,6 +4,8 @@
 // Changes to this file must follow the https://aka.ms/api-review process.
 // ------------------------------------------------------------------------------
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace System.Net.Http
 {
     public partial class ByteArrayContent : System.Net.Http.HttpContent
@@ -37,6 +39,7 @@ public partial class FormUrlEncodedContent : System.Net.Http.ByteArrayContent
         public FormUrlEncodedContent(System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string?, string?>> nameValueCollection) : base (default(byte[])) { }
         protected override System.Threading.Tasks.Task SerializeToStreamAsync(System.IO.Stream stream, System.Net.TransportContext? context, System.Threading.CancellationToken cancellationToken) { throw null; }
     }
+    public delegate System.Text.Encoding? HeaderEncodingSelector<TContext>(string headerName, TContext context);
     public partial class HttpClient : System.Net.Http.HttpMessageInvoker
     {
         public HttpClient() : base (default(System.Net.Http.HttpMessageHandler)) { }
@@ -212,13 +215,44 @@ public HttpRequestMessage(System.Net.Http.HttpMethod method, System.Uri? request
         public System.Net.Http.HttpContent? Content { get { throw null; } set { } }
         public System.Net.Http.Headers.HttpRequestHeaders Headers { get { throw null; } }
         public System.Net.Http.HttpMethod Method { get { throw null; } set { } }
+        [Obsolete("Use Options instead.")]
         public System.Collections.Generic.IDictionary<string, object?> Properties { get { throw null; } }
+        public HttpRequestOptions Options { get { throw null; } }
         public System.Uri? RequestUri { get { throw null; } set { } }
         public System.Version Version { get { throw null; } set { } }
         public void Dispose() { }
         protected virtual void Dispose(bool disposing) { }
         public override string ToString() { throw null; }
     }
+
+    public readonly struct HttpRequestOptionsKey<TValue>
+    {
+        public HttpRequestOptionsKey(string key) {}
+        public string Key { get { throw null; } }
+    }
+
+    public sealed class HttpRequestOptions : System.Collections.Generic.IDictionary<string, object?>
+    {
+        void System.Collections.Generic.IDictionary<string, object?>.Add(string key, object? value) { throw null; }
+        System.Collections.Generic.ICollection<string> System.Collections.Generic.IDictionary<string, object?>.Keys { get { throw null; } }
+        System.Collections.Generic.ICollection<object?> System.Collections.Generic.IDictionary<string, object?>.Values { get { throw null; } }
+        bool System.Collections.Generic.IDictionary<string, object?>.Remove(string key) { throw null; }
+        bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<string, object?>>.Remove(System.Collections.Generic.KeyValuePair<string, object?> item) { throw null; }
+        bool System.Collections.Generic.IDictionary<string, object?>.TryGetValue(string key, out object? value) { throw null; }
+        object? System.Collections.Generic.IDictionary<string, object?>.this[string key] { get { throw null; } set { } }
+        void System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<string, object?>>.Add(System.Collections.Generic.KeyValuePair<string, object?> item) { throw null; }
+        void System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<string, object?>>.Clear() { throw null; }
+        bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<string, object?>>.Contains(System.Collections.Generic.KeyValuePair<string, object?> item) { throw null; }
+        bool System.Collections.Generic.IDictionary<string, object?>.ContainsKey(string key) { throw null; }
+        void System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<string, object?>>.CopyTo(System.Collections.Generic.KeyValuePair<string, object?>[] array, int arrayIndex) { throw null; }
+        int System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<string, object?>>.Count { get { throw null; } }
+        bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<string, object?>>.IsReadOnly { get { throw null; } }
+        System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string, object?>> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, object?>>.GetEnumerator() { throw null; }
+        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
+        public bool TryGetValue<TValue>(HttpRequestOptionsKey<TValue> key, [MaybeNullWhen(false)] out TValue value) { throw null; }
+        public void Set<TValue>(HttpRequestOptionsKey<TValue> key, TValue value) { throw null; }
+    }
+
     public partial class HttpResponseMessage : System.IDisposable
     {
         public HttpResponseMessage() { }
@@ -251,6 +285,7 @@ public partial class MultipartContent : System.Net.Http.HttpContent, System.Coll
         public MultipartContent() { }
         public MultipartContent(string subtype) { }
         public MultipartContent(string subtype, string boundary) { }
+        public System.Net.Http.HeaderEncodingSelector<System.Net.Http.HttpContent>? HeaderEncodingSelector { get { throw null; } set { } }
         public virtual void Add(System.Net.Http.HttpContent content) { }
         protected override System.IO.Stream CreateContentReadStream(System.Threading.CancellationToken cancellationToken) { throw null; }
         protected override System.Threading.Tasks.Task<System.IO.Stream> CreateContentReadStreamAsync() { throw null; }
@@ -282,11 +317,22 @@ protected override void SerializeToStream(System.IO.Stream stream, System.Net.Tr
         protected override System.Threading.Tasks.Task SerializeToStreamAsync(System.IO.Stream stream, System.Net.TransportContext? context, System.Threading.CancellationToken cancellationToken) { throw null; }
         protected internal override bool TryComputeLength(out long length) { throw null; }
     }
+    public partial class SocketsHttpConnectionFactory : System.Net.Connections.ConnectionFactory
+    {
+        public SocketsHttpConnectionFactory() { }
+        public sealed override System.Threading.Tasks.ValueTask<System.Net.Connections.Connection> ConnectAsync(System.Net.EndPoint? endPoint, System.Net.Connections.IConnectionProperties? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        public virtual System.Net.Sockets.Socket CreateSocket(System.Net.Http.HttpRequestMessage message, System.Net.EndPoint? endPoint, System.Net.Connections.IConnectionProperties options) { throw null; }
+        protected override void Dispose(bool disposing) { }
+        protected override System.Threading.Tasks.ValueTask DisposeAsyncCore() { throw null; }
+        public virtual System.Threading.Tasks.ValueTask<System.Net.Connections.Connection> EstablishConnectionAsync(System.Net.Http.HttpRequestMessage message, System.Net.EndPoint? endPoint, System.Net.Connections.IConnectionProperties options, System.Threading.CancellationToken cancellationToken) { throw null; }
+    }
     public sealed partial class SocketsHttpHandler : System.Net.Http.HttpMessageHandler
     {
         public SocketsHttpHandler() { }
+        public static bool IsSupported { get { throw null; } }
         public bool AllowAutoRedirect { get { throw null; } set { } }
         public System.Net.DecompressionMethods AutomaticDecompression { get { throw null; } set { } }
+        public System.Net.Connections.ConnectionFactory? ConnectionFactory { get { throw null; } set { } }
         public System.TimeSpan ConnectTimeout { get { throw null; } set { } }
         [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public System.Net.CookieContainer CookieContainer { get { throw null; } set { } }
@@ -297,12 +343,15 @@ public SocketsHttpHandler() { }
         public int MaxConnectionsPerServer { get { throw null; } set { } }
         public int MaxResponseDrainSize { get { throw null; } set { } }
         public int MaxResponseHeadersLength { get { throw null; } set { } }
+        public System.Func<System.Net.Http.HttpRequestMessage, System.Net.Connections.Connection, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<System.Net.Connections.Connection>>? PlaintextFilter { get { throw null; } set { } }
         public System.TimeSpan PooledConnectionIdleTimeout { get { throw null; } set { } }
         public System.TimeSpan PooledConnectionLifetime { get { throw null; } set { } }
         public bool PreAuthenticate { get { throw null; } set { } }
         public System.Collections.Generic.IDictionary<string, object?> Properties { get { throw null; } }
         public System.Net.IWebProxy? Proxy { get { throw null; } set { } }
+        public System.Net.Http.HeaderEncodingSelector<System.Net.Http.HttpRequestMessage>? RequestHeaderEncodingSelector { get { throw null; } set { } }
         public System.TimeSpan ResponseDrainTimeout { get { throw null; } set { } }
+        public System.Net.Http.HeaderEncodingSelector<System.Net.Http.HttpRequestMessage>? ResponseHeaderEncodingSelector { get { throw null; } set { } }
         [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public System.Net.Security.SslClientAuthenticationOptions SslOptions { get { throw null; } set { } }
         public bool UseCookies { get { throw null; } set { } }
@@ -310,6 +359,7 @@ public SocketsHttpHandler() { }
         protected override void Dispose(bool disposing) { }
         protected internal override System.Net.Http.HttpResponseMessage Send(System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) { throw null; }
         protected internal override System.Threading.Tasks.Task<System.Net.Http.HttpResponseMessage> SendAsync(System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) { throw null; }
+        public bool EnableMultipleHttp2Connections { get { throw null; } set { } }
     }
     public partial class StreamContent : System.Net.Http.HttpContent
     {
diff --git a/src/libraries/System.Net.Http/ref/System.Net.Http.csproj b/src/libraries/System.Net.Http/ref/System.Net.Http.csproj
index 9f96fca1d9e605..296b6c0cdb1b55 100644
--- a/src/libraries/System.Net.Http/ref/System.Net.Http.csproj
+++ b/src/libraries/System.Net.Http/ref/System.Net.Http.csproj
@@ -9,6 +9,8 @@
   <ItemGroup>
     <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
     <ProjectReference Include="..\..\System.Net.Primitives\ref\System.Net.Primitives.csproj" />
+    <ProjectReference Include="..\..\System.Net.Sockets\ref\System.Net.Sockets.csproj" />
+    <ProjectReference Include="..\..\System.Net.Connections\ref\System.Net.Connections.csproj" />
     <ProjectReference Include="..\..\System.Net.Security\ref\System.Net.Security.csproj" />
     <ProjectReference Include="..\..\System.Security.Cryptography.X509Certificates\ref\System.Security.Cryptography.X509Certificates.csproj" />
     <ProjectReference Include="..\..\System.Text.Encoding\ref\System.Text.Encoding.csproj" />
diff --git a/src/libraries/System.Net.Http/src/ILLink/ILLink.Substitutions.xml b/src/libraries/System.Net.Http/src/ILLink/ILLink.Substitutions.xml
index 5715e75fc8303a..5e70f6fbb5d7d5 100644
--- a/src/libraries/System.Net.Http/src/ILLink/ILLink.Substitutions.xml
+++ b/src/libraries/System.Net.Http/src/ILLink/ILLink.Substitutions.xml
@@ -1,7 +1,7 @@
 <linker>
   <assembly fullname="System.Net.Http">
     <type fullname="System.Net.Http.DiagnosticsHandler">
-      <method signature="System.Boolean IsEnabled()" body="stub" value="false" feature="System.Net.Http.EnableActivityPropagation" featurevalue="false" />
+      <method signature="System.Boolean IsGloballyEnabled()" body="stub" value="false" feature="System.Net.Http.EnableActivityPropagation" featurevalue="false" />
     </type>
   </assembly>
 </linker>
diff --git a/src/libraries/System.Net.Http/src/Resources/Strings.resx b/src/libraries/System.Net.Http/src/Resources/Strings.resx
index 8848ecf6794897..0ac22a4bf44cd3 100644
--- a/src/libraries/System.Net.Http/src/Resources/Strings.resx
+++ b/src/libraries/System.Net.Http/src/Resources/Strings.resx
@@ -435,6 +435,9 @@
   <data name="net_http_http2_stream_error" xml:space="preserve">
     <value>The HTTP/2 server reset the stream. HTTP/2 error code '{0}' (0x{1}).</value>
   </data>
+  <data name="net_http_http2_connection_not_established" xml:space="preserve">
+    <value>An HTTP/2 connection could not be established because the server did not complete the HTTP/2 handshake.</value>
+  </data>
   <data name="net_MethodNotImplementedException" xml:space="preserve">
     <value>This method is not implemented by this class.</value>
   </data>
diff --git a/src/libraries/System.Net.Http/src/System.Net.Http.csproj b/src/libraries/System.Net.Http/src/System.Net.Http.csproj
index 65d63c045bbf58..420af9b298b7fc 100644
--- a/src/libraries/System.Net.Http/src/System.Net.Http.csproj
+++ b/src/libraries/System.Net.Http/src/System.Net.Http.csproj
@@ -1,7 +1,5 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <OutputType>Library</OutputType>
-    <AssemblyName>System.Net.Http</AssemblyName>
     <WindowsRID>win</WindowsRID>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DefineConstants>$(DefineConstants);HTTP_DLL</DefineConstants>
@@ -31,6 +29,7 @@
     <Compile Include="System\Net\Http\EmptyContent.cs" />
     <Compile Include="System\Net\Http\EmptyReadStream.cs" />
     <Compile Include="System\Net\Http\FormUrlEncodedContent.cs" />
+    <Compile Include="System\Net\Http\HeaderEncodingSelector.cs" />
     <Compile Include="System\Net\Http\Headers\AltSvcHeaderParser.cs" />
     <Compile Include="System\Net\Http\Headers\AltSvcHeaderValue.cs" />
     <Compile Include="System\Net\Http\Headers\KnownHeader.cs" />
@@ -47,6 +46,8 @@
     <Compile Include="System\Net\Http\HttpParseResult.cs" />
     <Compile Include="System\Net\Http\HttpRequestException.cs" />
     <Compile Include="System\Net\Http\HttpRequestMessage.cs" />
+    <Compile Include="System\Net\Http\HttpRequestOptions.cs" />
+    <Compile Include="System\Net\Http\HttpRequestOptionsKey.cs" />
     <Compile Include="System\Net\Http\HttpResponseMessage.cs" />
     <Compile Include="System\Net\Http\HttpRuleParser.cs" />
     <Compile Include="System\Net\Http\HttpTelemetry.cs" />
@@ -108,6 +109,8 @@
              Link="Common\System\IO\StreamHelpers.CopyValidation.cs" />
     <Compile Include="$(CommonPath)System\Net\Security\SslClientAuthenticationOptionsExtensions.cs"
              Link="Common\System\Net\Security\SslClientAuthenticationOptionsExtensions.cs" />
+    <Compile Include="$(CommonPath)System\Net\NetworkErrorHelper.cs"
+             Link="Common\System\Net\NetworkErrorHelper.cs" />
     <Compile Include="$(CommonPath)System\IO\DelegatingStream.cs"
              Link="Common\System\IO\DelegatingStream.cs" />
     <Compile Include="$(CommonPath)System\IO\ReadOnlyMemoryStream.cs"
@@ -171,6 +174,10 @@
     <Compile Include="System\Net\Http\SocketsHttpHandler\RedirectHandler.cs" />
     <Compile Include="System\Net\Http\SocketsHttpHandler\SocketsHttpHandler.cs" />
     <Compile Include="System\Net\Http\SocketsHttpHandler\SystemProxyInfo.cs" />
+    <Compile Include="System\Net\Http\SocketsHttpHandler\Connections\SocketConnection.cs" />
+    <Compile Include="System\Net\Http\SocketsHttpHandler\Connections\TaskSocketAsyncEventArgs.cs" />
+    <Compile Include="System\Net\Http\SocketsHttpHandler\DnsEndPointWithProperties.cs" />
+    <Compile Include="System\Net\Http\SocketsHttpHandler\SocketsHttpConnectionFactory.cs" />
     <Compile Include="$(CommonPath)System\Net\NTAuthentication.Common.cs"
              Link="Common\System\Net\NTAuthentication.Common.cs" />
     <Compile Include="$(CommonPath)System\Net\ContextFlagsPal.cs"
@@ -431,20 +438,28 @@
              Link="Common\Interop\Windows\Interop.Libraries.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.UNICODE_STRING.cs"
             Link="Common\Interop\Windows\Interop.UNICODE_STRING.cs" />
-    <Compile Include="$(CommonPath)\Interop\Windows\Crypt32\Interop.CertEnumCertificatesInStore.cs"
-             Link="Common\Interop\Windows\Crypt32\Interop.CertEnumCertificatesInStore.cs" />
-    <Compile Include="$(CommonPath)\Interop\Windows\Crypt32\Interop.certificates_types.cs"
-             Link="Common\Interop\Windows\Crypt32\Interop.certificates_types.cs" />
-    <Compile Include="$(CommonPath)\Interop\Windows\Crypt32\Interop.certificates.cs"
-             Link="Common\Interop\Windows\Crypt32\Interop.certificates.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_ALGORITHM_IDENTIFIER.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_ALGORITHM_IDENTIFIER.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_BIT_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_BIT_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.DATA_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.DATA_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.MsgEncodingType.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.MsgEncodingType.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CertFreeCertificateContext.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CertFreeCertificateContext.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.FormatMessage.cs"
              Link="Common\Interop\Windows\Kernel32\Interop.FormatMessage.cs" />
     <Compile Include="$(CommonPath)\Interop\Windows\Kernel32\Interop.GetModuleHandle.cs"
              Link="Common\Interop\Windows\Kernel32\Interop.GetModuleHandle.cs" />
     <Compile Include="$(CommonPath)\Interop\Windows\Interop.HRESULT_FROM_WIN32.cs"
              Link="Common\Interop\Windows\Interop.HRESULT_FROM_WIN32.cs" />
-    <Compile Include="$(CommonPath)\Interop\Windows\SChannel\UnmanagedCertificateContext.IntPtr.cs"
-             Link="Common\Interop\Windows\SChannel\UnmanagedCertificateContext.IntPtr.cs" />
     <Compile Include="$(CommonPath)\Interop\Windows\WinHttp\Interop.SafeWinHttpHandle.cs"
              Link="Common\Interop\Windows\WinHttp\Interop.SafeWinHttpHandle.cs" />
     <Compile Include="$(CommonPath)\Interop\Windows\WinHttp\Interop.winhttp_types.cs"
@@ -473,12 +488,8 @@
              Link="Common\System\Net\Security\CertificateHelper.Windows.cs" />
     <Compile Include="$(CommonPath)\System\Runtime\ExceptionServices\ExceptionStackTrace.cs"
              Link="Common\System\Runtime\ExceptionServices\ExceptionStackTrace.cs" />
-    <Compile Include="$(CommonPath)\System\Threading\Tasks\RendezvousAwaitable.cs"
-             Link="Common\System\Threading\Tasks\RendezvousAwaitable.cs" />
     <Compile Include="$(CommonPath)System\Threading\Tasks\TaskToApm.cs"
              Link="Common\System\Threading\Tasks\TaskToApm.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\SChannel\Interop.SecPkgContext_ApplicationProtocol.cs"
-             Link="Common\Interop\Windows\SChannel\Interop.SecPkgContext_ApplicationProtocol.cs" />
     <Compile Include="$(CommonPath)System\Net\Security\SecurityBuffer.Windows.cs"
              Link="Common\System\Net\Security\SecurityBuffer.Windows.cs" />
     <Compile Include="$(CommonPath)System\Net\Security\SecurityBufferType.Windows.cs"
@@ -505,8 +516,6 @@
              Link="Common\Interop\Windows\SspiCli\SecPkgContext_NegotiationInfoW.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\SspiCli\NegotiationInfoClass.cs"
              Link="Common\Interop\Windows\SspiCli\NegotiationInfoClass.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\SChannel\SecPkgContext_ConnectionInfo.cs"
-             Link="Common\Interop\Windows\SChannel\SecPkgContext_ConnectionInfo.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\SChannel\SecPkgContext_CipherInfo.cs"
              Link="Common\Interop\Windows\SChannel\SecPkgContext_CipherInfo.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\SspiCli\SSPISecureChannelType.cs"
@@ -663,9 +672,11 @@
     <Compile Include="System\Net\Http\SocketsHttpHandler\HttpNoProxy.cs" />
     <Compile Include="System\Net\Http\BrowserHttpHandler\SystemProxyInfo.Browser.cs" />
     <Compile Include="System\Net\Http\BrowserHttpHandler\SocketsHttpHandler.cs" />
+    <Compile Include="System\Net\Http\BrowserHttpHandler\SocketsHttpConnectionFactory.cs" />
     <Compile Include="System\Net\Http\BrowserHttpHandler\BrowserHttpHandler.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
@@ -673,7 +684,9 @@
     <Reference Include="System.Diagnostics.DiagnosticSource" />
     <Reference Include="System.Diagnostics.Tracing" />
     <Reference Include="System.IO.Compression" />
+    <Reference Include="System.IO.Pipelines" />
     <Reference Include="System.Memory" />
+    <Reference Include="System.Net.Connections" />
     <Reference Include="System.Net.NameResolution" />
     <Reference Include="System.Net.NetworkInformation" />
     <Reference Include="System.Net.Primitives" />
@@ -690,20 +703,22 @@
     <Reference Include="System.Security.Cryptography.Primitives" />
     <Reference Include="System.Security.Cryptography.X509Certificates" />
     <Reference Include="System.Security.Principal" Condition="'$(TargetsWindows)' == 'true'" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Channels" />
     <Reference Include="System.IO.Compression.Brotli" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.OpenSsl\src\System.Security.Cryptography.OpenSsl.csproj" />
     <Reference Include="System.Console" Condition="'$(Configuration)' == 'Debug'" />
     <Reference Include="System.Diagnostics.StackTrace" />
     <Reference Include="System.IO.FileSystem" />
     <Reference Include="System.Security.Cryptography.Algorithms" />
     <Reference Include="System.Security.Cryptography.Encoding" />
-    <Reference Include="System.Security.Cryptography.OpenSsl" />
     <Reference Include="System.Security.Cryptography.Primitives" />
   </ItemGroup>
+  <ItemGroup Condition=" '$(TargetsBrowser)' == 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Runtime.InteropServices.JavaScript\src\System.Private.Runtime.InteropServices.JavaScript.csproj" />
+  </ItemGroup>
   <ItemGroup>
     <Content Include="msquic.dll" Condition="Exists('msquic.dll')">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
@@ -721,7 +736,4 @@
   <ItemGroup>
     <None Include="Resources\SR.resx" />
   </ItemGroup>
-  <ItemGroup Condition=" '$(TargetsBrowser)' == 'true'">
-    <ProjectReference Include="..\..\System.Runtime.InteropServices.JavaScript/src/System.Runtime.InteropServices.JavaScript.csproj" />
-  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/BrowserHttpHandler.cs b/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/BrowserHttpHandler.cs
index eb577324faa16f..5b026591ab5ca9 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/BrowserHttpHandler.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/BrowserHttpHandler.cs
@@ -32,6 +32,9 @@ internal sealed class BrowserHttpHandler : HttpMessageHandler
         private static readonly JSObject? s_fetch = (JSObject)System.Runtime.InteropServices.JavaScript.Runtime.GetGlobalObject("fetch");
         private static readonly JSObject? s_window = (JSObject)System.Runtime.InteropServices.JavaScript.Runtime.GetGlobalObject("window");
 
+        private static readonly HttpRequestOptionsKey<bool> EnableStreamingResponse = new HttpRequestOptionsKey<bool>("WebAssemblyEnableStreamingResponse");
+        private static readonly HttpRequestOptionsKey<IDictionary<string, object>> FetchOptions = new HttpRequestOptionsKey<IDictionary<string, object>>("WebAssemblyFetchOptions");
+
         /// <summary>
         /// Gets whether the current Browser supports streaming responses
         /// </summary>
@@ -120,6 +123,10 @@ public SslClientAuthenticationOptions SslOptions
             set => throw new PlatformNotSupportedException();
         }
 
+        public bool SupportsAutomaticDecompression => false;
+        public bool SupportsProxy => false;
+        public bool SupportsRedirectConfiguration => false;
+
         private Dictionary<string, object?>? _properties;
         public IDictionary<string, object?> Properties => _properties ??= new Dictionary<string, object?>();
 
@@ -129,8 +136,7 @@ protected internal override async Task<HttpResponseMessage> SendAsync(HttpReques
             {
                 var requestObject = new JSObject();
 
-                if (request.Properties.TryGetValue("WebAssemblyFetchOptions", out object? fetchOptionsValue) &&
-                    fetchOptionsValue is IDictionary<string, object> fetchOptions)
+                if (request.Options.TryGetValue(FetchOptions, out IDictionary<string, object>? fetchOptions))
                 {
                     foreach (KeyValuePair<string, object> item in fetchOptions)
                     {
@@ -221,9 +227,13 @@ protected internal override async Task<HttpResponseMessage> SendAsync(HttpReques
 
                 HttpResponseMessage httpResponse = new HttpResponseMessage((HttpStatusCode)status.Status);
 
-                bool streamingEnabled = request.Properties.TryGetValue("WebAssemblyEnableStreamingResponse", out object? streamingEnabledValue) && (bool)(streamingEnabledValue ?? false);
+                bool streamingEnabled = false;
+                if (StreamingSupported)
+                {
+                    request.Options.TryGetValue(EnableStreamingResponse, out streamingEnabled);
+                }
 
-                httpResponse.Content = StreamingSupported && streamingEnabled
+                httpResponse.Content = streamingEnabled
                     ? new StreamContent(wasmHttpReadStream = new WasmHttpReadStream(status))
                     : (HttpContent)new BrowserHttpContent(status);
 
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/SocketsHttpConnectionFactory.cs b/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/SocketsHttpConnectionFactory.cs
new file mode 100644
index 00000000000000..664de02694ba64
--- /dev/null
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/SocketsHttpConnectionFactory.cs
@@ -0,0 +1,19 @@
+using System.Threading;
+using System.Threading.Tasks;
+using System.Net.Connections;
+using System.Net.Sockets;
+
+namespace System.Net.Http
+{
+    public class SocketsHttpConnectionFactory : ConnectionFactory
+    {
+        public sealed override ValueTask<Connection> ConnectAsync(EndPoint? endPoint, IConnectionProperties? options = null, CancellationToken cancellationToken = default)
+            => throw new NotImplementedException();
+
+        public virtual Socket CreateSocket(HttpRequestMessage message, EndPoint? endPoint, IConnectionProperties options)
+            => throw new NotImplementedException();
+
+        public virtual ValueTask<Connection> EstablishConnectionAsync(HttpRequestMessage message, EndPoint? endPoint, IConnectionProperties options, CancellationToken cancellationToken)
+            => throw new NotImplementedException();
+    }
+}
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/SocketsHttpHandler.cs b/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/SocketsHttpHandler.cs
index 6f474758b89701..2a1d63d35b15f6 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/SocketsHttpHandler.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/SocketsHttpHandler.cs
@@ -6,11 +6,14 @@
 using System.Threading;
 using System.Threading.Tasks;
 using System.Diagnostics.CodeAnalysis;
+using System.Net.Connections;
 
 namespace System.Net.Http
 {
     public sealed class SocketsHttpHandler : HttpMessageHandler
     {
+        public static bool IsSupported => false;
+
         public bool UseCookies
         {
             get => throw new PlatformNotSupportedException();
@@ -127,9 +130,39 @@ public TimeSpan Expect100ContinueTimeout
             set => throw new PlatformNotSupportedException();
         }
 
+        public ConnectionFactory? ConnectionFactory
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        public Func<HttpRequestMessage, Connection, CancellationToken, ValueTask<Connection>>? PlaintextFilter
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
         public IDictionary<string, object?> Properties => throw new PlatformNotSupportedException();
 
+        public HeaderEncodingSelector<HttpRequestMessage>? RequestHeaderEncodingSelector
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
+        public HeaderEncodingSelector<HttpRequestMessage>? ResponseHeaderEncodingSelector
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
         protected internal override Task<HttpResponseMessage> SendAsync(
             HttpRequestMessage request, CancellationToken cancellationToken) => throw new PlatformNotSupportedException();
+
+        public bool EnableMultipleHttp2Connections
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
     }
 }
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/DiagnosticsHandler.cs b/src/libraries/System.Net.Http/src/System/Net/Http/DiagnosticsHandler.cs
index f69d5ff2f77789..47f260eec04b03 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/DiagnosticsHandler.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/DiagnosticsHandler.cs
@@ -27,7 +27,12 @@ internal static bool IsEnabled()
         {
             // check if there is a parent Activity (and propagation is not suppressed)
             // or if someone listens to HttpHandlerDiagnosticListener
-            return Settings.s_activityPropagationEnabled && (Activity.Current != null || Settings.s_diagnosticListener.IsEnabled());
+            return IsGloballyEnabled() && (Activity.Current != null || Settings.s_diagnosticListener.IsEnabled());
+        }
+
+        internal static bool IsGloballyEnabled()
+        {
+            return Settings.s_activityPropagationEnabled;
         }
 
         // SendAsyncCore returns already completed ValueTask for when async: false is passed.
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/HeaderEncodingSelector.cs b/src/libraries/System.Net.Http/src/System/Net/Http/HeaderEncodingSelector.cs
new file mode 100644
index 00000000000000..cb984b838cb5c3
--- /dev/null
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/HeaderEncodingSelector.cs
@@ -0,0 +1,15 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Text;
+
+namespace System.Net.Http
+{
+    /// <summary>
+    /// Represents a method that specifies the <see cref="Encoding"/> to use when interpreting header values.
+    /// </summary>
+    /// <param name="headerName">Name of the header to specify the <see cref="Encoding"/> for.</param>
+    /// <param name="context">The <typeparamref name="TContext"/> we are enoding/decoding the headers for.</param>
+    /// <returns><see cref="Encoding"/> to use or <see langword="null"/> to use the default behavior.</returns>
+    public delegate Encoding? HeaderEncodingSelector<TContext>(string headerName, TContext context);
+}
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/AltSvcHeaderValue.cs b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/AltSvcHeaderValue.cs
index c4400b63b7456e..ce534b0e1d5425 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/AltSvcHeaderValue.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/AltSvcHeaderValue.cs
@@ -1,6 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Globalization;
+using System.Text;
+
 namespace System.Net.Http.Headers
 {
     /// <remarks>
@@ -44,5 +47,30 @@ public AltSvcHeaderValue(string alpnProtocolName, string? host, int port, TimeSp
         /// </summary>
         /// <remarks>TODO: if made public, this should be made internal as Persist is left open-ended and can be non-boolean in the future.</remarks>
         public bool Persist { get; }
+
+        public override string ToString()
+        {
+            StringBuilder sb = StringBuilderCache.Acquire(capacity: AlpnProtocolName.Length + (Host?.Length ?? 0) + 64);
+
+            sb.Append(AlpnProtocolName);
+            sb.Append("=\"");
+            if (Host != null) sb.Append(Host);
+            sb.Append(':');
+            sb.Append(Port.ToString(CultureInfo.InvariantCulture));
+            sb.Append('"');
+
+            if (MaxAge != TimeSpan.FromTicks(AltSvcHeaderParser.DefaultMaxAgeTicks))
+            {
+                sb.Append("; ma=");
+                sb.Append((MaxAge.Ticks / TimeSpan.TicksPerSecond).ToString(CultureInfo.InvariantCulture));
+            }
+
+            if (Persist)
+            {
+                sb.Append("; persist=1");
+            }
+
+            return StringBuilderCache.GetStringAndRelease(sb);
+        }
     }
 }
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HeaderDescriptor.cs b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HeaderDescriptor.cs
index 8970f78f166411..229490b5432dd9 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HeaderDescriptor.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HeaderDescriptor.cs
@@ -4,6 +4,7 @@
 using System.Buffers;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
+using System.Text;
 using System.Text.Unicode;
 
 namespace System.Net.Http.Headers
@@ -116,7 +117,7 @@ public HeaderDescriptor AsCustomHeader()
             return new HeaderDescriptor(_knownHeader.Name);
         }
 
-        public string GetHeaderValue(ReadOnlySpan<byte> headerValue)
+        public string GetHeaderValue(ReadOnlySpan<byte> headerValue, Encoding? valueEncoding)
         {
             if (headerValue.Length == 0)
             {
@@ -156,7 +157,7 @@ public string GetHeaderValue(ReadOnlySpan<byte> headerValue)
                 }
             }
 
-            return HttpRuleParser.DefaultHttpEncoding.GetString(headerValue);
+            return (valueEncoding ?? HttpRuleParser.DefaultHttpEncoding).GetString(headerValue);
         }
 
         internal static string? GetKnownContentType(ReadOnlySpan<byte> contentTypeValue)
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpRequestHeaders.cs b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpRequestHeaders.cs
index 9f837133de0a9b..b2eacbfd619f00 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpRequestHeaders.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpRequestHeaders.cs
@@ -35,16 +35,16 @@ private T GetSpecializedCollection<T>(int slot, Func<HttpRequestHeaders, T> crea
         }
 
         public HttpHeaderValueCollection<MediaTypeWithQualityHeaderValue> Accept =>
-            GetSpecializedCollection(AcceptSlot, thisRef => new HttpHeaderValueCollection<MediaTypeWithQualityHeaderValue>(KnownHeaders.Accept.Descriptor, thisRef));
+            GetSpecializedCollection(AcceptSlot, static thisRef => new HttpHeaderValueCollection<MediaTypeWithQualityHeaderValue>(KnownHeaders.Accept.Descriptor, thisRef));
 
         public HttpHeaderValueCollection<StringWithQualityHeaderValue> AcceptCharset =>
-            GetSpecializedCollection(AcceptCharsetSlot, thisRef => new HttpHeaderValueCollection<StringWithQualityHeaderValue>(KnownHeaders.AcceptCharset.Descriptor, thisRef));
+            GetSpecializedCollection(AcceptCharsetSlot, static thisRef => new HttpHeaderValueCollection<StringWithQualityHeaderValue>(KnownHeaders.AcceptCharset.Descriptor, thisRef));
 
         public HttpHeaderValueCollection<StringWithQualityHeaderValue> AcceptEncoding =>
-            GetSpecializedCollection(AcceptEncodingSlot, thisRef => new HttpHeaderValueCollection<StringWithQualityHeaderValue>(KnownHeaders.AcceptEncoding.Descriptor, thisRef));
+            GetSpecializedCollection(AcceptEncodingSlot, static thisRef => new HttpHeaderValueCollection<StringWithQualityHeaderValue>(KnownHeaders.AcceptEncoding.Descriptor, thisRef));
 
         public HttpHeaderValueCollection<StringWithQualityHeaderValue> AcceptLanguage =>
-            GetSpecializedCollection(AcceptLanguageSlot, thisRef => new HttpHeaderValueCollection<StringWithQualityHeaderValue>(KnownHeaders.AcceptLanguage.Descriptor, thisRef));
+            GetSpecializedCollection(AcceptLanguageSlot, static thisRef => new HttpHeaderValueCollection<StringWithQualityHeaderValue>(KnownHeaders.AcceptLanguage.Descriptor, thisRef));
 
         public AuthenticationHeaderValue? Authorization
         {
@@ -130,7 +130,7 @@ public string? Host
         }
 
         public HttpHeaderValueCollection<EntityTagHeaderValue> IfMatch =>
-            GetSpecializedCollection(IfMatchSlot, thisRef => new HttpHeaderValueCollection<EntityTagHeaderValue>(KnownHeaders.IfMatch.Descriptor, thisRef));
+            GetSpecializedCollection(IfMatchSlot, static thisRef => new HttpHeaderValueCollection<EntityTagHeaderValue>(KnownHeaders.IfMatch.Descriptor, thisRef));
 
         public DateTimeOffset? IfModifiedSince
         {
@@ -139,7 +139,7 @@ public DateTimeOffset? IfModifiedSince
         }
 
         public HttpHeaderValueCollection<EntityTagHeaderValue> IfNoneMatch =>
-            GetSpecializedCollection(IfNoneMatchSlot, thisRef => new HttpHeaderValueCollection<EntityTagHeaderValue>(KnownHeaders.IfNoneMatch.Descriptor, thisRef));
+            GetSpecializedCollection(IfNoneMatchSlot, static thisRef => new HttpHeaderValueCollection<EntityTagHeaderValue>(KnownHeaders.IfNoneMatch.Descriptor, thisRef));
 
         public RangeConditionHeaderValue? IfRange
         {
@@ -187,10 +187,10 @@ public Uri? Referrer
         }
 
         public HttpHeaderValueCollection<TransferCodingWithQualityHeaderValue> TE =>
-            GetSpecializedCollection(TransferEncodingSlot, thisRef => new HttpHeaderValueCollection<TransferCodingWithQualityHeaderValue>(KnownHeaders.TE.Descriptor, thisRef));
+            GetSpecializedCollection(TransferEncodingSlot, static thisRef => new HttpHeaderValueCollection<TransferCodingWithQualityHeaderValue>(KnownHeaders.TE.Descriptor, thisRef));
 
         public HttpHeaderValueCollection<ProductInfoHeaderValue> UserAgent =>
-            GetSpecializedCollection(UserAgentSlot, thisRef => new HttpHeaderValueCollection<ProductInfoHeaderValue>(KnownHeaders.UserAgent.Descriptor, thisRef));
+            GetSpecializedCollection(UserAgentSlot, static thisRef => new HttpHeaderValueCollection<ProductInfoHeaderValue>(KnownHeaders.UserAgent.Descriptor, thisRef));
 
         private HttpHeaderValueCollection<NameValueWithParametersHeaderValue> ExpectCore =>
             _expect ??= new HttpHeaderValueCollection<NameValueWithParametersHeaderValue>(KnownHeaders.Expect.Descriptor, this, HeaderUtilities.ExpectContinue);
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpResponseHeaders.cs b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpResponseHeaders.cs
index fd8557f758ccef..2c03f00acf7972 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpResponseHeaders.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpResponseHeaders.cs
@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
-using System.Diagnostics.CodeAnalysis;
 
 namespace System.Net.Http.Headers
 {
@@ -36,7 +35,7 @@ private T GetSpecializedCollection<T>(int slot, Func<HttpResponseHeaders, T> cre
         }
 
         public HttpHeaderValueCollection<string> AcceptRanges =>
-            GetSpecializedCollection(AcceptRangesSlot, thisRef => new HttpHeaderValueCollection<string>(KnownHeaders.AcceptRanges.Descriptor, thisRef, HeaderUtilities.TokenValidator));
+            GetSpecializedCollection(AcceptRangesSlot, static thisRef => new HttpHeaderValueCollection<string>(KnownHeaders.AcceptRanges.Descriptor, thisRef, HeaderUtilities.TokenValidator));
 
         public TimeSpan? Age
         {
@@ -57,7 +56,7 @@ public Uri? Location
         }
 
         public HttpHeaderValueCollection<AuthenticationHeaderValue> ProxyAuthenticate =>
-            GetSpecializedCollection(ProxyAuthenticateSlot, thisRef => new HttpHeaderValueCollection<AuthenticationHeaderValue>(KnownHeaders.ProxyAuthenticate.Descriptor, thisRef));
+            GetSpecializedCollection(ProxyAuthenticateSlot, static thisRef => new HttpHeaderValueCollection<AuthenticationHeaderValue>(KnownHeaders.ProxyAuthenticate.Descriptor, thisRef));
 
         public RetryConditionHeaderValue? RetryAfter
         {
@@ -66,13 +65,13 @@ public RetryConditionHeaderValue? RetryAfter
         }
 
         public HttpHeaderValueCollection<ProductInfoHeaderValue> Server =>
-            GetSpecializedCollection(ServerSlot, thisRef => new HttpHeaderValueCollection<ProductInfoHeaderValue>(KnownHeaders.Server.Descriptor, thisRef));
+            GetSpecializedCollection(ServerSlot, static thisRef => new HttpHeaderValueCollection<ProductInfoHeaderValue>(KnownHeaders.Server.Descriptor, thisRef));
 
         public HttpHeaderValueCollection<string> Vary =>
-            GetSpecializedCollection(VarySlot, thisRef => new HttpHeaderValueCollection<string>(KnownHeaders.Vary.Descriptor, thisRef, HeaderUtilities.TokenValidator));
+            GetSpecializedCollection(VarySlot, static thisRef => new HttpHeaderValueCollection<string>(KnownHeaders.Vary.Descriptor, thisRef, HeaderUtilities.TokenValidator));
 
         public HttpHeaderValueCollection<AuthenticationHeaderValue> WwwAuthenticate =>
-            GetSpecializedCollection(WwwAuthenticateSlot, thisRef => new HttpHeaderValueCollection<AuthenticationHeaderValue>(KnownHeaders.WWWAuthenticate.Descriptor, thisRef));
+            GetSpecializedCollection(WwwAuthenticateSlot, static thisRef => new HttpHeaderValueCollection<AuthenticationHeaderValue>(KnownHeaders.WWWAuthenticate.Descriptor, thisRef));
 
         #endregion
 
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/MediaTypeHeaderParser.cs b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/MediaTypeHeaderParser.cs
index ab8d0a6cd288de..42e4cf3f043fc5 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/MediaTypeHeaderParser.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/MediaTypeHeaderParser.cs
@@ -10,12 +10,9 @@ internal class MediaTypeHeaderParser : BaseHeaderParser
         private readonly bool _supportsMultipleValues;
         private readonly Func<MediaTypeHeaderValue> _mediaTypeCreator;
 
-        internal static readonly MediaTypeHeaderParser SingleValueParser = new MediaTypeHeaderParser(false,
-            CreateMediaType);
-        internal static readonly MediaTypeHeaderParser SingleValueWithQualityParser = new MediaTypeHeaderParser(false,
-            CreateMediaTypeWithQuality);
-        internal static readonly MediaTypeHeaderParser MultipleValuesParser = new MediaTypeHeaderParser(true,
-            CreateMediaTypeWithQuality);
+        internal static readonly MediaTypeHeaderParser SingleValueParser = new MediaTypeHeaderParser(false, CreateMediaType);
+        internal static readonly MediaTypeHeaderParser SingleValueWithQualityParser = new MediaTypeHeaderParser(false, CreateMediaTypeWithQuality);
+        internal static readonly MediaTypeHeaderParser MultipleValuesParser = new MediaTypeHeaderParser(true, CreateMediaTypeWithQuality);
 
         private MediaTypeHeaderParser(bool supportsMultipleValues, Func<MediaTypeHeaderValue> mediaTypeCreator)
             : base(supportsMultipleValues)
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/HttpClientHandler.cs b/src/libraries/System.Net.Http/src/System/Net/Http/HttpClientHandler.cs
index ec2e729113b18b..5540ba7f642cd9 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/HttpClientHandler.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/HttpClientHandler.cs
@@ -18,7 +18,7 @@ public partial class HttpClientHandler : HttpMessageHandler
 #else
         private readonly SocketsHttpHandler _underlyingHandler;
 #endif
-        private readonly DiagnosticsHandler _diagnosticsHandler;
+        private readonly DiagnosticsHandler? _diagnosticsHandler;
         private ClientCertificateOption _clientCertificateOptions;
 
         private volatile bool _disposed;
@@ -30,7 +30,10 @@ public HttpClientHandler()
 #else
             _underlyingHandler = new SocketsHttpHandler();
 #endif
-            _diagnosticsHandler = new DiagnosticsHandler(_underlyingHandler);
+            if (DiagnosticsHandler.IsGloballyEnabled())
+            {
+                _diagnosticsHandler = new DiagnosticsHandler(_underlyingHandler);
+            }
             ClientCertificateOptions = ClientCertificateOption.Manual;
         }
 
@@ -45,9 +48,9 @@ protected override void Dispose(bool disposing)
             base.Dispose(disposing);
         }
 
-        public virtual bool SupportsAutomaticDecompression => true;
-        public virtual bool SupportsProxy => true;
-        public virtual bool SupportsRedirectConfiguration => true;
+        public virtual bool SupportsAutomaticDecompression => _underlyingHandler.SupportsAutomaticDecompression;
+        public virtual bool SupportsProxy => _underlyingHandler.SupportsProxy;
+        public virtual bool SupportsRedirectConfiguration => _underlyingHandler.SupportsRedirectConfiguration;
 
         public bool UseCookies
         {
@@ -273,7 +276,7 @@ public SslProtocols SslProtocols
         protected internal override HttpResponseMessage Send(HttpRequestMessage request,
             CancellationToken cancellationToken)
         {
-            return DiagnosticsHandler.IsEnabled() ?
+            return DiagnosticsHandler.IsEnabled() && _diagnosticsHandler != null ?
                 _diagnosticsHandler.Send(request, cancellationToken) :
                 _underlyingHandler.Send(request, cancellationToken);
         }
@@ -281,7 +284,7 @@ protected internal override HttpResponseMessage Send(HttpRequestMessage request,
         protected internal override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
             CancellationToken cancellationToken)
         {
-            return DiagnosticsHandler.IsEnabled() ?
+            return DiagnosticsHandler.IsEnabled() && _diagnosticsHandler != null ?
                 _diagnosticsHandler.SendAsync(request, cancellationToken) :
                 _underlyingHandler.SendAsync(request, cancellationToken);
         }
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/HttpContent.cs b/src/libraries/System.Net.Http/src/System/Net/Http/HttpContent.cs
index 0ec9f1ab0a39a5..7ceae4eeacccea 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/HttpContent.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/HttpContent.cs
@@ -155,7 +155,7 @@ public Task<string> ReadAsStringAsync() =>
         public Task<string> ReadAsStringAsync(CancellationToken cancellationToken)
         {
             CheckDisposed();
-            return WaitAndReturnAsync(LoadIntoBufferAsync(cancellationToken), this, s => s.ReadBufferedContentAsString());
+            return WaitAndReturnAsync(LoadIntoBufferAsync(cancellationToken), this, static s => s.ReadBufferedContentAsString());
         }
 
         private string ReadBufferedContentAsString()
@@ -240,7 +240,7 @@ public Task<byte[]> ReadAsByteArrayAsync() =>
         public Task<byte[]> ReadAsByteArrayAsync(CancellationToken cancellationToken)
         {
             CheckDisposed();
-            return WaitAndReturnAsync(LoadIntoBufferAsync(cancellationToken), this, s => s.ReadBufferedContentAsByteArray());
+            return WaitAndReturnAsync(LoadIntoBufferAsync(cancellationToken), this, static s => s.ReadBufferedContentAsByteArray());
         }
 
         internal byte[] ReadBufferedContentAsByteArray()
@@ -457,7 +457,7 @@ internal void LoadIntoBuffer(long maxBufferSize, CancellationToken cancellationT
             // We're only comfortable disposing of the HttpContent instance like this because LoadIntoBuffer is internal and
             // we're only using it on content instances we get back from a handler's Send call that haven't been given out to the user yet.
             // If we were to ever make LoadIntoBuffer public, we'd need to rethink this.
-            CancellationTokenRegistration cancellationRegistration = cancellationToken.Register(s => ((HttpContent)s!).Dispose(), this);
+            CancellationTokenRegistration cancellationRegistration = cancellationToken.Register(static s => ((HttpContent)s!).Dispose(), this);
 
             try
             {
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestMessage.cs b/src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestMessage.cs
index 3cbb1d058c3987..83ee09fd178103 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestMessage.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestMessage.cs
@@ -24,7 +24,7 @@ public class HttpRequestMessage : IDisposable
         private Version _version;
         private HttpContent? _content;
         private bool _disposed;
-        private IDictionary<string, object?>? _properties;
+        private HttpRequestOptions? _options;
 
         public Version Version
         {
@@ -111,17 +111,10 @@ public HttpRequestHeaders Headers
 
         internal bool HasHeaders => _headers != null;
 
-        public IDictionary<string, object?> Properties
-        {
-            get
-            {
-                if (_properties == null)
-                {
-                    _properties = new Dictionary<string, object?>();
-                }
-                return _properties;
-            }
-        }
+        [Obsolete("Use Options instead.")]
+        public IDictionary<string, object?> Properties => Options;
+
+        public HttpRequestOptions Options => _options ??= new HttpRequestOptions();
 
         public HttpRequestMessage()
             : this(HttpMethod.Get, (Uri?)null)
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestOptions.cs b/src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestOptions.cs
new file mode 100644
index 00000000000000..195eb0d10fe621
--- /dev/null
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestOptions.cs
@@ -0,0 +1,56 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+
+namespace System.Net.Http
+{
+    public sealed class HttpRequestOptions : IDictionary<string, object?>
+    {
+        private Dictionary<string, object?> Options { get; } = new Dictionary<string, object?>();
+        object? IDictionary<string, object?>.this[string key]
+        {
+            get
+            {
+                return Options[key];
+            }
+            set
+            {
+                Options[key] = value;
+            }
+        }
+        ICollection<string> IDictionary<string, object?>.Keys => Options.Keys;
+        ICollection<object?> IDictionary<string, object?>.Values => Options.Values;
+        int ICollection<KeyValuePair<string, object?>>.Count => Options.Count;
+        bool ICollection<KeyValuePair<string, object?>>.IsReadOnly => ((IDictionary<string, object?>)Options).IsReadOnly;
+        void IDictionary<string, object?>.Add(string key, object? value) => Options.Add(key, value);
+        void ICollection<KeyValuePair<string, object?>>.Add(KeyValuePair<string, object?> item) => ((IDictionary<string, object?>)Options).Add(item);
+        void ICollection<KeyValuePair<string, object?>>.Clear() => Options.Clear();
+        bool ICollection<KeyValuePair<string, object?>>.Contains(KeyValuePair<string, object?> item) => ((IDictionary<string, object?>)Options).Contains(item);
+        bool IDictionary<string, object?>.ContainsKey(string key) => Options.ContainsKey(key);
+        void ICollection<KeyValuePair<string, object?>>.CopyTo(KeyValuePair<string, object?>[] array, int arrayIndex) =>
+            ((IDictionary<string, object?>)Options).CopyTo(array, arrayIndex);
+        IEnumerator<KeyValuePair<string, object?>> IEnumerable<KeyValuePair<string, object?>>.GetEnumerator() => Options.GetEnumerator();
+        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => ((System.Collections.IEnumerable)Options).GetEnumerator();
+        bool IDictionary<string, object?>.Remove(string key) => Options.Remove(key);
+        bool ICollection<KeyValuePair<string, object?>>.Remove(KeyValuePair<string, object?> item) => ((IDictionary<string, object?>)Options).Remove(item);
+        bool IDictionary<string, object?>.TryGetValue(string key, out object? value) => Options.TryGetValue(key, out value);
+        public bool TryGetValue<TValue>(HttpRequestOptionsKey<TValue> key, [MaybeNullWhen(false)] out TValue value)
+        {
+            if (Options.TryGetValue(key.Key, out object? _value) && _value is TValue tvalue)
+            {
+                value = tvalue;
+                return true;
+            }
+
+            value = default(TValue);
+            return false;
+        }
+
+        public void Set<TValue>(HttpRequestOptionsKey<TValue> key, TValue value)
+        {
+            Options[key.Key] = value;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestOptionsKey.cs b/src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestOptionsKey.cs
new file mode 100644
index 00000000000000..f51f8ebf162fe7
--- /dev/null
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestOptionsKey.cs
@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+namespace System.Net.Http
+{
+    public readonly struct HttpRequestOptionsKey<TValue>
+    {
+        public string Key { get; }
+        public HttpRequestOptionsKey(string key)
+        {
+            Key = key;
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/MessageProcessingHandler.cs b/src/libraries/System.Net.Http/src/System/Net/Http/MessageProcessingHandler.cs
index dff8ab9db0f524..f903186995e70c 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/MessageProcessingHandler.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/MessageProcessingHandler.cs
@@ -63,7 +63,7 @@ protected internal sealed override Task<HttpResponseMessage> SendAsync(HttpReque
 
                 // We schedule a continuation task once the inner handler completes in order to trigger the response
                 // processing method. ProcessResponse() is only called if the task wasn't canceled before.
-                sendAsyncTask.ContinueWithStandard(tcs, (task, state) =>
+                sendAsyncTask.ContinueWithStandard(tcs, static (task, state) =>
                 {
                     var sendState = (SendState)state!;
                     MessageProcessingHandler self = sendState._handler;
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/MultipartContent.cs b/src/libraries/System.Net.Http/src/System/Net/Http/MultipartContent.cs
index 4f1a1dd23acf64..7ea8eb232f0397 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/MultipartContent.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/MultipartContent.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Buffers;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
@@ -18,10 +19,10 @@ public class MultipartContent : HttpContent, IEnumerable<HttpContent>
 
         private const string CrLf = "\r\n";
 
-        private static readonly int s_crlfLength = GetEncodedLength(CrLf);
-        private static readonly int s_dashDashLength = GetEncodedLength("--");
-        private static readonly int s_colonSpaceLength = GetEncodedLength(": ");
-        private static readonly int s_commaSpaceLength = GetEncodedLength(", ");
+        private const int CrLfLength = 2;
+        private const int DashDashLength = 2;
+        private const int ColonSpaceLength = 2;
+        private const int CommaSpaceLength = 2;
 
         private readonly List<HttpContent> _nestedContent;
         private readonly string _boundary;
@@ -157,6 +158,12 @@ Collections.IEnumerator Collections.IEnumerable.GetEnumerator()
 
         #region Serialization
 
+        /// <summary>
+        /// Gets or sets a callback that returns the <see cref="Encoding"/> to decode the value for the specified response header name,
+        /// or <see langword="null"/> to use the default behavior.
+        /// </summary>
+        public HeaderEncodingSelector<HttpContent>? HeaderEncodingSelector { get; set; }
+
         // for-each content
         //   write "--" + boundary
         //   for-each content header
@@ -171,20 +178,19 @@ protected override void SerializeToStream(Stream stream, TransportContext? conte
             try
             {
                 // Write start boundary.
-                EncodeStringToStream(stream, "--" + _boundary + CrLf);
+                WriteToStream(stream, "--" + _boundary + CrLf);
 
                 // Write each nested content.
-                var output = new StringBuilder();
                 for (int contentIndex = 0; contentIndex < _nestedContent.Count; contentIndex++)
                 {
                     // Write divider, headers, and content.
                     HttpContent content = _nestedContent[contentIndex];
-                    EncodeStringToStream(stream, SerializeHeadersToString(output, contentIndex, content));
+                    SerializeHeadersToStream(stream, content, writeDivider: contentIndex != 0);
                     content.CopyTo(stream, context, cancellationToken);
                 }
 
                 // Write footer boundary.
-                EncodeStringToStream(stream, CrLf + "--" + _boundary + "--" + CrLf);
+                WriteToStream(stream, CrLf + "--" + _boundary + "--" + CrLf);
             }
             catch (Exception ex)
             {
@@ -219,12 +225,17 @@ private protected async Task SerializeToStreamAsyncCore(Stream stream, Transport
                 await EncodeStringToStreamAsync(stream, "--" + _boundary + CrLf, cancellationToken).ConfigureAwait(false);
 
                 // Write each nested content.
-                var output = new StringBuilder();
+                var output = new MemoryStream();
                 for (int contentIndex = 0; contentIndex < _nestedContent.Count; contentIndex++)
                 {
                     // Write divider, headers, and content.
                     HttpContent content = _nestedContent[contentIndex];
-                    await EncodeStringToStreamAsync(stream, SerializeHeadersToString(output, contentIndex, content), cancellationToken).ConfigureAwait(false);
+
+                    output.SetLength(0);
+                    SerializeHeadersToStream(output, content, writeDivider: contentIndex != 0);
+                    output.Position = 0;
+                    await output.CopyToAsync(stream, cancellationToken).ConfigureAwait(false);
+
                     await content.CopyToAsync(stream, context, cancellationToken).ConfigureAwait(false);
                 }
 
@@ -259,7 +270,6 @@ private async ValueTask<Stream> CreateContentReadStreamAsyncCore(bool async, Can
             try
             {
                 var streams = new Stream[2 + (_nestedContent.Count * 2)];
-                var scratch = new StringBuilder();
                 int streamIndex = 0;
 
                 // Start boundary.
@@ -271,7 +281,7 @@ private async ValueTask<Stream> CreateContentReadStreamAsyncCore(bool async, Can
                     cancellationToken.ThrowIfCancellationRequested();
 
                     HttpContent nestedContent = _nestedContent[contentIndex];
-                    streams[streamIndex++] = EncodeStringToNewStream(SerializeHeadersToString(scratch, contentIndex, nestedContent));
+                    streams[streamIndex++] = EncodeHeadersToNewStream(nestedContent, writeDivider: contentIndex != 0);
 
                     Stream readStream;
                     if (async)
@@ -312,43 +322,35 @@ private async ValueTask<Stream> CreateContentReadStreamAsyncCore(bool async, Can
             }
         }
 
-        private string SerializeHeadersToString(StringBuilder scratch, int contentIndex, HttpContent content)
+        private void SerializeHeadersToStream(Stream stream, HttpContent content, bool writeDivider)
         {
-            scratch.Clear();
-
             // Add divider.
-            if (contentIndex != 0) // Write divider for all but the first content.
+            if (writeDivider) // Write divider for all but the first content.
             {
-                scratch.Append(CrLf + "--"); // const strings
-                scratch.Append(_boundary);
-                scratch.Append(CrLf);
+                WriteToStream(stream, CrLf + "--"); // const strings
+                WriteToStream(stream, _boundary);
+                WriteToStream(stream, CrLf);
             }
 
             // Add headers.
             foreach (KeyValuePair<string, IEnumerable<string>> headerPair in content.Headers)
             {
-                scratch.Append(headerPair.Key);
-                scratch.Append(": ");
+                Encoding headerValueEncoding = HeaderEncodingSelector?.Invoke(headerPair.Key, content) ?? HttpRuleParser.DefaultHttpEncoding;
+
+                WriteToStream(stream, headerPair.Key);
+                WriteToStream(stream, ": ");
                 string delim = string.Empty;
                 foreach (string value in headerPair.Value)
                 {
-                    scratch.Append(delim);
-                    scratch.Append(value);
+                    WriteToStream(stream, delim);
+                    WriteToStream(stream, value, headerValueEncoding);
                     delim = ", ";
                 }
-                scratch.Append(CrLf);
+                WriteToStream(stream, CrLf);
             }
 
             // Extra CRLF to end headers (even if there are no headers).
-            scratch.Append(CrLf);
-
-            return scratch.ToString();
-        }
-
-        private static void EncodeStringToStream(Stream stream, string input)
-        {
-            byte[] buffer = HttpRuleParser.DefaultHttpEncoding.GetBytes(input);
-            stream.Write(buffer);
+            WriteToStream(stream, CrLf);
         }
 
         private static ValueTask EncodeStringToStreamAsync(Stream stream, string input, CancellationToken cancellationToken)
@@ -362,55 +364,55 @@ private static Stream EncodeStringToNewStream(string input)
             return new MemoryStream(HttpRuleParser.DefaultHttpEncoding.GetBytes(input), writable: false);
         }
 
+        private Stream EncodeHeadersToNewStream(HttpContent content, bool writeDivider)
+        {
+            var stream = new MemoryStream();
+            SerializeHeadersToStream(stream, content, writeDivider);
+            stream.Position = 0;
+            return stream;
+        }
+
         internal override bool AllowDuplex => false;
 
         protected internal override bool TryComputeLength(out long length)
         {
-            int boundaryLength = GetEncodedLength(_boundary);
-
-            long currentLength = 0;
-            long internalBoundaryLength = s_crlfLength + s_dashDashLength + boundaryLength + s_crlfLength;
-
             // Start Boundary.
-            currentLength += s_dashDashLength + boundaryLength + s_crlfLength;
+            long currentLength = DashDashLength + _boundary.Length + CrLfLength;
 
-            bool first = true;
-            foreach (HttpContent content in _nestedContent)
+            if (_nestedContent.Count > 1)
             {
-                if (first)
-                {
-                    first = false; // First boundary already written.
-                }
-                else
-                {
-                    // Internal Boundary.
-                    currentLength += internalBoundaryLength;
-                }
+                // Internal boundaries
+                currentLength += (_nestedContent.Count - 1) * (CrLfLength + DashDashLength + _boundary.Length + CrLfLength);
+            }
 
+            foreach (HttpContent content in _nestedContent)
+            {
                 // Headers.
                 foreach (KeyValuePair<string, IEnumerable<string>> headerPair in content.Headers)
                 {
-                    currentLength += GetEncodedLength(headerPair.Key) + s_colonSpaceLength;
+                    currentLength += headerPair.Key.Length + ColonSpaceLength;
+
+                    Encoding headerValueEncoding = HeaderEncodingSelector?.Invoke(headerPair.Key, content) ?? HttpRuleParser.DefaultHttpEncoding;
 
                     int valueCount = 0;
                     foreach (string value in headerPair.Value)
                     {
-                        currentLength += GetEncodedLength(value);
+                        currentLength += headerValueEncoding.GetByteCount(value);
                         valueCount++;
                     }
+
                     if (valueCount > 1)
                     {
-                        currentLength += (valueCount - 1) * s_commaSpaceLength;
+                        currentLength += (valueCount - 1) * CommaSpaceLength;
                     }
 
-                    currentLength += s_crlfLength;
+                    currentLength += CrLfLength;
                 }
 
-                currentLength += s_crlfLength;
+                currentLength += CrLfLength;
 
                 // Content.
-                long tempContentLength = 0;
-                if (!content.TryComputeLength(out tempContentLength))
+                if (!content.TryComputeLength(out long tempContentLength))
                 {
                     length = 0;
                     return false;
@@ -419,17 +421,12 @@ protected internal override bool TryComputeLength(out long length)
             }
 
             // Terminating boundary.
-            currentLength += s_crlfLength + s_dashDashLength + boundaryLength + s_dashDashLength + s_crlfLength;
+            currentLength += CrLfLength + DashDashLength + _boundary.Length + DashDashLength + CrLfLength;
 
             length = currentLength;
             return true;
         }
 
-        private static int GetEncodedLength(string input)
-        {
-            return HttpRuleParser.DefaultHttpEncoding.GetByteCount(input);
-        }
-
         private sealed class ContentReadStream : Stream
         {
             private readonly Stream[] _streams;
@@ -671,6 +668,36 @@ public override void Flush() { }
             public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken) { throw new NotSupportedException(); }
             public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default) { throw new NotSupportedException(); }
         }
+
+
+        private static void WriteToStream(Stream stream, string content) =>
+            WriteToStream(stream, content, HttpRuleParser.DefaultHttpEncoding);
+
+        private static void WriteToStream(Stream stream, string content, Encoding encoding)
+        {
+            const int StackallocThreshold = 1024;
+
+            int maxLength = encoding.GetMaxByteCount(content.Length);
+
+            byte[]? rentedBuffer = null;
+            Span<byte> buffer = maxLength <= StackallocThreshold
+                ? stackalloc byte[StackallocThreshold]
+                : (rentedBuffer = ArrayPool<byte>.Shared.Rent(maxLength));
+
+            try
+            {
+                int written = encoding.GetBytes(content, buffer);
+                stream.Write(buffer.Slice(0, written));
+            }
+            finally
+            {
+                if (rentedBuffer != null)
+                {
+                    ArrayPool<byte>.Shared.Return(rentedBuffer);
+                }
+            }
+        }
+
         #endregion Serialization
     }
 }
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/RequestRetryType.cs b/src/libraries/System.Net.Http/src/System/Net/Http/RequestRetryType.cs
index 4456e4fa64054b..f2e29c4726d553 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/RequestRetryType.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/RequestRetryType.cs
@@ -26,6 +26,10 @@ internal enum RequestRetryType
         /// <summary>
         /// The proxy failed, so the request should be retried on the next proxy.
         /// </summary>
-        RetryOnNextProxy
+        RetryOnNextProxy,
+
+        /// The HTTP/2 connection reached the maximum number of streams and
+        /// another HTTP/2 connection must be created or found to serve the request.
+        RetryOnNextConnection
     }
 }
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ChunkedEncodingReadStream.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ChunkedEncodingReadStream.cs
index 7cef2961ed160f..d747bd8ba233ad 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ChunkedEncodingReadStream.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ChunkedEncodingReadStream.cs
@@ -468,7 +468,7 @@ public override async ValueTask<bool> DrainAsync(int maxDrainBytes)
                             if (drainTime != Timeout.InfiniteTimeSpan)
                             {
                                 cts = new CancellationTokenSource((int)drainTime.TotalMilliseconds);
-                                ctr = cts.Token.Register(s => ((HttpConnection)s!).Dispose(), _connection);
+                                ctr = cts.Token.Register(static s => ((HttpConnection)s!).Dispose(), _connection);
                             }
                         }
 
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ConnectHelper.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ConnectHelper.cs
index ab6047ec43ce4a..467e813c49ac58 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ConnectHelper.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ConnectHelper.cs
@@ -3,11 +3,10 @@
 
 using System.Diagnostics;
 using System.IO;
+using System.Net.Connections;
 using System.Net.Quic;
 using System.Net.Security;
 using System.Net.Sockets;
-using System.Runtime.CompilerServices;
-using System.Runtime.ExceptionServices;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
@@ -33,58 +32,23 @@ public CertificateCallbackMapper(Func<HttpRequestMessage, X509Certificate2?, X50
             }
         }
 
-        public static ValueTask<Stream> ConnectAsync(string host, int port, bool async, CancellationToken cancellationToken)
+        public static async ValueTask<Connection> ConnectAsync(ConnectionFactory factory, DnsEndPoint endPoint, IConnectionProperties? options, CancellationToken cancellationToken)
         {
-            return async ? ConnectAsync(host, port, cancellationToken) : new ValueTask<Stream>(Connect(host, port, cancellationToken));
-        }
-
-        private static async ValueTask<Stream> ConnectAsync(string host, int port, CancellationToken cancellationToken)
-        {
-            // Rather than creating a new Socket and calling ConnectAsync on it, we use the static
-            // Socket.ConnectAsync with a SocketAsyncEventArgs, as we can then use Socket.CancelConnectAsync
-            // to cancel it if needed.
-            var saea = new ConnectEventArgs();
             try
             {
-                saea.Initialize(cancellationToken);
-
-                // Configure which server to which to connect.
-                saea.RemoteEndPoint = new DnsEndPoint(host, port);
-
-                // Initiate the connection.
-                if (Socket.ConnectAsync(SocketType.Stream, ProtocolType.Tcp, saea))
-                {
-                    // Connect completing asynchronously. Enable it to be canceled and wait for it.
-                    using (cancellationToken.UnsafeRegister(s => Socket.CancelConnectAsync((SocketAsyncEventArgs)s!), saea))
-                    {
-                        await saea.Builder.Task.ConfigureAwait(false);
-                    }
-                }
-                else if (saea.SocketError != SocketError.Success)
-                {
-                    // Connect completed synchronously but unsuccessfully.
-                    throw new SocketException((int)saea.SocketError);
-                }
-
-                Debug.Assert(saea.SocketError == SocketError.Success, $"Expected Success, got {saea.SocketError}.");
-                Debug.Assert(saea.ConnectSocket != null, "Expected non-null socket");
-
-                // Configure the socket and return a stream for it.
-                Socket socket = saea.ConnectSocket;
-                socket.NoDelay = true;
-                return new NetworkStream(socket, ownsSocket: true);
+                return await factory.ConnectAsync(endPoint, options, cancellationToken).ConfigureAwait(false);
             }
-            catch (Exception error) when (!(error is OperationCanceledException))
+            catch (OperationCanceledException ex) when (ex.CancellationToken == cancellationToken)
             {
-                throw CreateWrappedException(error, host, port, cancellationToken);
+                throw CancellationHelper.CreateOperationCanceledException(innerException: null, cancellationToken);
             }
-            finally
+            catch (Exception ex)
             {
-                saea.Dispose();
+                throw CreateWrappedException(ex, endPoint.Host, endPoint.Port, cancellationToken);
             }
         }
 
-        private static Stream Connect(string host, int port, CancellationToken cancellationToken)
+        public static Connection Connect(string host, int port, CancellationToken cancellationToken)
         {
             // For synchronous connections, we can just create a socket and make the connection.
             cancellationToken.ThrowIfCancellationRequested();
@@ -92,7 +56,7 @@ private static Stream Connect(string host, int port, CancellationToken cancellat
             try
             {
                 socket.NoDelay = true;
-                using (cancellationToken.UnsafeRegister(s => ((Socket)s!).Dispose(), socket))
+                using (cancellationToken.UnsafeRegister(static s => ((Socket)s!).Dispose(), socket))
                 {
                     socket.Connect(new DnsEndPoint(host, port));
                 }
@@ -103,52 +67,7 @@ private static Stream Connect(string host, int port, CancellationToken cancellat
                 throw CreateWrappedException(e, host, port, cancellationToken);
             }
 
-            return new NetworkStream(socket, ownsSocket: true);
-        }
-
-        /// <summary>SocketAsyncEventArgs that carries with it additional state for a Task builder and a CancellationToken.</summary>
-        private sealed class ConnectEventArgs : SocketAsyncEventArgs
-        {
-            internal ConnectEventArgs() :
-                // The OnCompleted callback serves just to complete a task that's awaited in ConnectAsync,
-                // so we don't need to also flow ExecutionContext again into the OnCompleted callback.
-                base(unsafeSuppressExecutionContextFlow: true)
-            {
-            }
-
-            public AsyncTaskMethodBuilder Builder { get; private set; }
-            public CancellationToken CancellationToken { get; private set; }
-
-            public void Initialize(CancellationToken cancellationToken)
-            {
-                CancellationToken = cancellationToken;
-                AsyncTaskMethodBuilder b = default;
-                _ = b.Task; // force initialization
-                Builder = b;
-            }
-
-            protected override void OnCompleted(SocketAsyncEventArgs _)
-            {
-                switch (SocketError)
-                {
-                    case SocketError.Success:
-                        Builder.SetResult();
-                        break;
-
-                    case SocketError.OperationAborted:
-                    case SocketError.ConnectionAborted:
-                        if (CancellationToken.IsCancellationRequested)
-                        {
-                            Builder.SetException(ExceptionDispatchInfo.SetCurrentStackTrace(CancellationHelper.CreateOperationCanceledException(null, CancellationToken)));
-                            break;
-                        }
-                        goto default;
-
-                    default:
-                        Builder.SetException(ExceptionDispatchInfo.SetCurrentStackTrace(new SocketException((int)SocketError)));
-                        break;
-                }
-            }
+            return new SocketConnection(socket);
         }
 
         public static ValueTask<SslStream> EstablishSslConnectionAsync(SslClientAuthenticationOptions sslOptions, HttpRequestMessage request, bool async, Stream stream, CancellationToken cancellationToken)
@@ -186,7 +105,7 @@ private static async ValueTask<SslStream> EstablishSslConnectionAsyncCore(bool a
                 }
                 else
                 {
-                    using (cancellationToken.UnsafeRegister(s => ((Stream)s!).Dispose(), stream))
+                    using (cancellationToken.UnsafeRegister(static s => ((Stream)s!).Dispose(), stream))
                     {
                         sslStream.AuthenticateAsClient(sslOptions);
                     }
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Connections/SocketConnection.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Connections/SocketConnection.cs
new file mode 100644
index 00000000000000..130cf634ec2990
--- /dev/null
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Connections/SocketConnection.cs
@@ -0,0 +1,71 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics.CodeAnalysis;
+using System.IO;
+using System.Net.Http;
+using System.Net.Sockets;
+using System.Runtime.ExceptionServices;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Connections
+{
+    internal sealed class SocketConnection : Connection, IConnectionProperties
+    {
+        private readonly NetworkStream _stream;
+
+        public override EndPoint? RemoteEndPoint => _stream.Socket.RemoteEndPoint;
+        public override EndPoint? LocalEndPoint => _stream.Socket.LocalEndPoint;
+        public override IConnectionProperties ConnectionProperties => this;
+
+        public SocketConnection(Socket socket)
+        {
+            _stream = new NetworkStream(socket, ownsSocket: true);
+        }
+
+        protected override ValueTask CloseAsyncCore(ConnectionCloseMethod method, CancellationToken cancellationToken)
+        {
+            if (cancellationToken.IsCancellationRequested)
+            {
+                return ValueTask.FromCanceled(cancellationToken);
+            }
+
+            try
+            {
+                if (method != ConnectionCloseMethod.GracefulShutdown)
+                {
+                    // Dispose must be called first in order to cause a connection reset,
+                    // as NetworkStream.Dispose() will call Shutdown(Both).
+                    _stream.Socket.Dispose();
+                }
+
+                _stream.Dispose();
+            }
+            catch (SocketException socketException)
+            {
+                return ValueTask.FromException(ExceptionDispatchInfo.SetCurrentStackTrace(NetworkErrorHelper.MapSocketException(socketException)));
+            }
+            catch (Exception ex)
+            {
+                return ValueTask.FromException(ex);
+            }
+
+            return default;
+        }
+
+        protected override Stream CreateStream() => _stream;
+
+        bool IConnectionProperties.TryGet(Type propertyKey, [NotNullWhen(true)] out object? property)
+        {
+            if (propertyKey == typeof(Socket))
+            {
+                property = _stream.Socket;
+                return true;
+            }
+
+            property = null;
+            return false;
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Connections/TaskSocketAsyncEventArgs.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Connections/TaskSocketAsyncEventArgs.cs
new file mode 100644
index 00000000000000..7bf8947215a404
--- /dev/null
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Connections/TaskSocketAsyncEventArgs.cs
@@ -0,0 +1,32 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Net.Sockets;
+using System.Threading.Tasks;
+using System.Threading.Tasks.Sources;
+
+namespace System.Net.Connections
+{
+    internal sealed class TaskSocketAsyncEventArgs : SocketAsyncEventArgs, IValueTaskSource
+    {
+        private ManualResetValueTaskSourceCore<int> _valueTaskSource;
+
+        public void ResetTask() => _valueTaskSource.Reset();
+        public ValueTask Task => new ValueTask(this, _valueTaskSource.Version);
+
+        public void GetResult(short token) => _valueTaskSource.GetResult(token);
+        public ValueTaskSourceStatus GetStatus(short token) => _valueTaskSource.GetStatus(token);
+        public void OnCompleted(Action<object?> continuation, object? state, short token, ValueTaskSourceOnCompletedFlags flags) => _valueTaskSource.OnCompleted(continuation, state, token, flags);
+        public void Complete() => _valueTaskSource.SetResult(0);
+
+        public TaskSocketAsyncEventArgs()
+            : base(unsafeSuppressExecutionContextFlow: true)
+        {
+        }
+
+        protected override void OnCompleted(SocketAsyncEventArgs e)
+        {
+            _valueTaskSource.SetResult(0);
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ContentLengthReadStream.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ContentLengthReadStream.cs
index ca0e0033d57366..f6f7b44da3e196 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ContentLengthReadStream.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ContentLengthReadStream.cs
@@ -218,7 +218,7 @@ public override async ValueTask<bool> DrainAsync(int maxDrainBytes)
                 if (drainTime != Timeout.InfiniteTimeSpan)
                 {
                     cts = new CancellationTokenSource((int)drainTime.TotalMilliseconds);
-                    ctr = cts.Token.Register(s => ((HttpConnection)s!).Dispose(), _connection);
+                    ctr = cts.Token.Register(static s => ((HttpConnection)s!).Dispose(), _connection);
                 }
                 try
                 {
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/CreditManager.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/CreditManager.cs
index 0439b51c85b7f0..1174a85996974e 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/CreditManager.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/CreditManager.cs
@@ -28,6 +28,8 @@ public CreditManager(IHttpTrace owner, string name, int initialCredit)
             _current = initialCredit;
         }
 
+        public bool IsCreditAvailable => Volatile.Read(ref _current) > 0;
+
         private object SyncObject
         {
             // Generally locking on "this" is considered poor form, but this type is internal,
@@ -35,32 +37,30 @@ private object SyncObject
             get => this;
         }
 
-        public ValueTask<int> RequestCreditAsync(int amount, CancellationToken cancellationToken)
+        public bool TryRequestCreditNoWait(int amount)
         {
             lock (SyncObject)
             {
-                if (_disposed)
-                {
-                    throw new ObjectDisposedException($"{nameof(CreditManager)}:{_owner.GetType().Name}:{_name}");
-                }
+                return TryRequestCreditNoLock(amount) > 0;
+            }
+        }
 
+        public ValueTask<int> RequestCreditAsync(int amount, CancellationToken cancellationToken)
+        {
+            lock (SyncObject)
+            {
                 // If we can satisfy the request with credit already available, do so synchronously.
-                if (_current > 0)
-                {
-                    Debug.Assert(_waitersTail is null, "Shouldn't have waiters when credit is available");
+                int granted = TryRequestCreditNoLock(amount);
 
-                    int granted = Math.Min(amount, _current);
-                    if (NetEventSource.Log.IsEnabled()) _owner.Trace($"{_name}. requested={amount}, current={_current}, granted={granted}");
-                    _current -= granted;
+                if (granted > 0)
+                {
                     return new ValueTask<int>(granted);
                 }
 
                 if (NetEventSource.Log.IsEnabled()) _owner.Trace($"{_name}. requested={amount}, no credit available.");
 
                 // Otherwise, create a new waiter.
-                CreditWaiter waiter = cancellationToken.CanBeCanceled ?
-                    new CancelableCreditWaiter(SyncObject, cancellationToken) :
-                    new CreditWaiter();
+                var waiter = new CreditWaiter(cancellationToken);
                 waiter.Amount = amount;
 
                 // Add the waiter at the tail of the queue.
@@ -155,5 +155,26 @@ public void Dispose()
                 }
             }
         }
+
+        private int TryRequestCreditNoLock(int amount)
+        {
+            Debug.Assert(Monitor.IsEntered(SyncObject), "Shouldn't be called outside lock.");
+
+            if (_disposed)
+            {
+                throw new ObjectDisposedException($"{nameof(CreditManager)}:{_owner.GetType().Name}:{_name}");
+            }
+
+            if (_current > 0)
+            {
+                Debug.Assert(_waitersTail is null, "Shouldn't have waiters when credit is available");
+
+                int granted = Math.Min(amount, _current);
+                if (NetEventSource.Log.IsEnabled()) _owner.Trace($"{_name}. requested={amount}, current={_current}, granted={granted}");
+                _current -= granted;
+                return granted;
+            }
+            return 0;
+        }
     }
 }
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/CreditWaiter.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/CreditWaiter.cs
index 430d92a6543160..43a8d86d71a7cb 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/CreditWaiter.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/CreditWaiter.cs
@@ -1,7 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System.Diagnostics;
 using System.Runtime.ExceptionServices;
 using System.Threading;
 using System.Threading.Tasks;
@@ -10,21 +9,65 @@
 namespace System.Net.Http
 {
     /// <summary>Represents a waiter for credit.</summary>
-    internal class CreditWaiter : IValueTaskSource<int>
+    internal sealed class CreditWaiter : IValueTaskSource<int>
     {
+        // State for the implementation of the CreditWaiter. Note that neither _cancellationToken nor
+        // _registration are zero'd out upon completion, because they're used for synchronization
+        // between successful completion and cancellation.  This means an instance may end up
+        // referencing the underlying CancellationTokenSource even after the await operation has completed.
+
+        /// <summary>Cancellation token for the current wait operation.</summary>
+        private CancellationToken _cancellationToken;
+        /// <summary>Cancellation registration for the current wait operation.</summary>
+        private CancellationTokenRegistration _registration;
+        /// <summary><see cref="IValueTaskSource"/> implementation.</summary>
+        private ManualResetValueTaskSourceCore<int> _source;
+
+        // State carried with the waiter for the consumer to use; these aren't used at all in the implementation.
+
+        /// <summary>Amount of credit desired by this waiter.</summary>
         public int Amount;
+        /// <summary>Next waiter in a list of waiters.</summary>
         public CreditWaiter? Next;
-        protected ManualResetValueTaskSourceCore<int> _source;
 
-        public CreditWaiter() => _source.RunContinuationsAsynchronously = true;
+        /// <summary>Initializes a waiter for a credit wait operation.</summary>
+        /// <param name="cancellationToken">The cancellation token for this wait operation.</param>
+        public CreditWaiter(CancellationToken cancellationToken)
+        {
+            _source.RunContinuationsAsynchronously = true;
+            RegisterCancellation(cancellationToken);
+        }
 
-        public ValueTask<int> AsValueTask() => new ValueTask<int>(this, _source.Version);
+        /// <summary>Re-initializes a waiter for a credit wait operation.</summary>
+        /// <param name="cancellationToken">The cancellation token for this wait operation.</param>
+        public void ResetForAwait(CancellationToken cancellationToken)
+        {
+            _source.Reset();
+            RegisterCancellation(cancellationToken);
+        }
 
-        public bool IsPending => _source.GetStatus(_source.Version) == ValueTaskSourceStatus.Pending;
+        /// <summary>Registers with the cancellation token to transition the source to a canceled state.</summary>
+        /// <param name="cancellationToken">The cancellation token with which to register.</param>
+        private void RegisterCancellation(CancellationToken cancellationToken)
+        {
+            _cancellationToken = cancellationToken;
+            _registration = cancellationToken.UnsafeRegister(static s =>
+            {
+                // The callback will only fire if cancellation owns the right to complete the instance.
+                var thisRef = (CreditWaiter)s!;
+                thisRef._source.SetException(ExceptionDispatchInfo.SetCurrentStackTrace(new OperationCanceledException(thisRef._cancellationToken)));
+            }, this);
+        }
 
+        /// <summary>Wraps the instance as a <see cref="ValueTask{TResult}"/> to make it awaitable.</summary>
+        public ValueTask<int> AsValueTask() => new ValueTask<int>(this, _source.Version);
+
+        /// <summary>Completes the instance with the specified result.</summary>
+        /// <param name="result">The result value.</param>
+        /// <returns>true if the instance was successfully completed; false if it was or is being canceled.</returns>
         public bool TrySetResult(int result)
         {
-            if (IsPending)
+            if (UnregisterAndOwnCompletion())
             {
                 _source.SetResult(result);
                 return true;
@@ -33,17 +76,25 @@ public bool TrySetResult(int result)
             return false;
         }
 
-        public virtual void CleanUp() { }
-
+        /// <summary>Disposes the instance, failing any outstanding wait.</summary>
         public void Dispose()
         {
-            CleanUp();
-            if (IsPending)
+            if (UnregisterAndOwnCompletion())
             {
                 _source.SetException(ExceptionDispatchInfo.SetCurrentStackTrace(new ObjectDisposedException(nameof(CreditManager), SR.net_http_disposed_while_in_use)));
             }
         }
 
+        /// <summary>Unregisters the cancellation callback.</summary>
+        /// <returns>true if the non-cancellation caller has the right to complete the instance; false if the instance was or is being completed by cancellation.</returns>
+        private bool UnregisterAndOwnCompletion() =>
+            // Unregister the cancellation callback.  If Unregister returns true, then the cancellation callback was successfully removed,
+            // meaning it hasn't run and won't ever run.  If it returns false, a) cancellation already occurred or is occurring and thus
+            // the callback couldn't be removed, b) cancellation occurred prior to the UnsafeRegister call such that _registration was
+            // set to a default value (or hasn't been set yet), or c) a default CancellationToken was used.  (a) and (b) are effectively
+            // the same, and (c) can be checked via CanBeCanceled.
+            _registration.Unregister() || !_cancellationToken.CanBeCanceled;
+
         int IValueTaskSource<int>.GetResult(short token) =>
             _source.GetResult(token);
         ValueTaskSourceStatus IValueTaskSource<int>.GetStatus(short token) =>
@@ -51,56 +102,4 @@ ValueTaskSourceStatus IValueTaskSource<int>.GetStatus(short token) =>
         void IValueTaskSource<int>.OnCompleted(Action<object?> continuation, object? state, short token, ValueTaskSourceOnCompletedFlags flags) =>
             _source.OnCompleted(continuation, state, token, flags);
     }
-
-    /// <summary>Represents a cancelable waiter for credit.</summary>
-    internal sealed class CancelableCreditWaiter : CreditWaiter
-    {
-        private readonly object _syncObj;
-        private CancellationTokenRegistration _registration;
-
-        public CancelableCreditWaiter(object syncObj, CancellationToken cancellationToken)
-        {
-            _syncObj = syncObj;
-            RegisterCancellation(cancellationToken);
-        }
-
-        public void ResetForAwait(CancellationToken cancellationToken)
-        {
-            Debug.Assert(Monitor.IsEntered(_syncObj));
-            Debug.Assert(!IsPending);
-            Debug.Assert(Next is null);
-            Debug.Assert(_registration == default);
-
-            _source.Reset();
-            RegisterCancellation(cancellationToken);
-        }
-
-        public override void CleanUp()
-        {
-            Monitor.IsEntered(_syncObj);
-            _registration.Dispose();
-            _registration = default;
-        }
-
-        private void RegisterCancellation(CancellationToken cancellationToken)
-        {
-            _registration = cancellationToken.UnsafeRegister(s =>
-            {
-                CancelableCreditWaiter thisRef = (CancelableCreditWaiter)s!;
-                lock (thisRef._syncObj)
-                {
-                    if (thisRef.IsPending)
-                    {
-                        thisRef._registration = default; // benign race with setting in the ctor
-                        thisRef._source.SetException(ExceptionDispatchInfo.SetCurrentStackTrace(new OperationCanceledException(thisRef._registration.Token)));
-
-                        // We don't remove it from the list as we lack a prev pointer that would enable us to do so correctly,
-                        // and it's not worth adding a prev pointer for the rare case of cancellation.  We instead just
-                        // check when completing a waiter whether it's already been canceled.  As such, we also do not
-                        // dispose it here.
-                    }
-                }
-            }, this);
-        }
-    }
 }
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/DnsEndPointWithProperties.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/DnsEndPointWithProperties.cs
new file mode 100644
index 00000000000000..b99801c1fac156
--- /dev/null
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/DnsEndPointWithProperties.cs
@@ -0,0 +1,31 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics.CodeAnalysis;
+using System.Net.Connections;
+
+namespace System.Net.Http
+{
+    // Passed to a connection factory, merges allocations for the DnsEndPoint and connection properties.
+    internal sealed class DnsEndPointWithProperties : DnsEndPoint, IConnectionProperties
+    {
+        public HttpRequestMessage InitialRequest { get; }
+
+        public DnsEndPointWithProperties(string host, int port, HttpRequestMessage initialRequest) : base(host, port)
+        {
+            InitialRequest = initialRequest;
+        }
+
+        bool IConnectionProperties.TryGet(Type propertyKey, [NotNullWhen(true)] out object? property)
+        {
+            if (propertyKey == typeof(DnsEndPointWithProperties))
+            {
+                property = this;
+                return true;
+            }
+
+            property = null;
+            return false;
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs
index e34219aac41739..289fd7a1cb770e 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Connection.cs
@@ -6,6 +6,7 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.IO;
+using System.Net.Connections;
 using System.Net.Http.Headers;
 using System.Net.Http.HPack;
 using System.Net.Security;
@@ -21,6 +22,7 @@ internal sealed partial class Http2Connection : HttpConnectionBase, IDisposable
     {
         private readonly HttpConnectionPool _pool;
         private readonly Stream _stream;
+        private readonly Connection _connection;
 
         // NOTE: These are mutable structs; do not make these readonly.
         private ArrayBuffer _incomingBuffer;
@@ -94,10 +96,11 @@ internal sealed partial class Http2Connection : HttpConnectionBase, IDisposable
         // Channel options for creating _writeChannel
         private static readonly UnboundedChannelOptions s_channelOptions = new UnboundedChannelOptions() { SingleReader = true };
 
-        public Http2Connection(HttpConnectionPool pool, Stream stream)
+        public Http2Connection(HttpConnectionPool pool, Connection connection)
         {
             _pool = pool;
-            _stream = stream;
+            _stream = connection.Stream;
+            _connection = connection;
             _incomingBuffer = new ArrayBuffer(InitialConnectionBufferSize);
             _outgoingBuffer = new ArrayBuffer(InitialConnectionBufferSize);
 
@@ -114,12 +117,15 @@ public Http2Connection(HttpConnectionPool pool, Stream stream)
             _initialWindowSize = DefaultInitialWindowSize;
             _maxConcurrentStreams = int.MaxValue;
             _pendingWindowUpdate = 0;
+            _idleSinceTickCount = Environment.TickCount64;
 
-            if (NetEventSource.Log.IsEnabled()) TraceConnection(stream);
+            if (NetEventSource.Log.IsEnabled()) TraceConnection(_stream);
         }
 
         private object SyncObject => _httpStreams;
 
+        public bool CanAddNewStream => _concurrentStreams.IsCreditAvailable;
+
         public async ValueTask SetupAsync()
         {
             _outgoingBuffer.EnsureAvailableSpace(s_http2ConnectionPreface.Length +
@@ -185,7 +191,17 @@ private async ValueTask<FrameHeader> ReadFrameAsync(bool initialFrame = false)
                 {
                     int bytesRead = await _stream.ReadAsync(_incomingBuffer.AvailableMemory).ConfigureAwait(false);
                     _incomingBuffer.Commit(bytesRead);
-                    if (bytesRead == 0) ThrowPrematureEOF(FrameHeader.Size);
+                    if (bytesRead == 0)
+                    {
+                        if (_incomingBuffer.ActiveLength == 0)
+                        {
+                            ThrowMissingFrame();
+                        }
+                        else
+                        {
+                            ThrowPrematureEOF(FrameHeader.Size);
+                        }
+                    }
                 }
                 while (_incomingBuffer.ActiveLength < FrameHeader.Size);
             }
@@ -223,33 +239,44 @@ private async ValueTask<FrameHeader> ReadFrameAsync(bool initialFrame = false)
 
             void ThrowPrematureEOF(int requiredBytes) =>
                 throw new IOException(SR.Format(SR.net_http_invalid_response_premature_eof_bytecount, requiredBytes - _incomingBuffer.ActiveLength));
+
+            void ThrowMissingFrame() =>
+                throw new IOException(SR.net_http_invalid_response_missing_frame);
+
         }
 
         private async Task ProcessIncomingFramesAsync()
         {
             try
             {
-                // Read the initial settings frame.
-                FrameHeader frameHeader = await ReadFrameAsync(initialFrame: true).ConfigureAwait(false);
-                if (frameHeader.Type != FrameType.Settings || frameHeader.AckFlag)
+                FrameHeader frameHeader;
+                try
                 {
-                    ThrowProtocolError();
-                }
-                if (NetEventSource.Log.IsEnabled()) Trace($"Frame 0: {frameHeader}.");
+                    // Read the initial settings frame.
+                    frameHeader = await ReadFrameAsync(initialFrame: true).ConfigureAwait(false);
+                    if (frameHeader.Type != FrameType.Settings || frameHeader.AckFlag)
+                    {
+                        ThrowProtocolError();
+                    }
 
-                // Process the initial SETTINGS frame. This will send an ACK.
-                ProcessSettingsFrame(frameHeader);
+                    if (NetEventSource.Log.IsEnabled()) Trace($"Frame 0: {frameHeader}.");
+
+                    // Process the initial SETTINGS frame. This will send an ACK.
+                    ProcessSettingsFrame(frameHeader);
+                }
+                catch (IOException e)
+                {
+                    throw new IOException(SR.net_http_http2_connection_not_established, e);
+                }
 
                 // Keep processing frames as they arrive.
                 for (long frameNum = 1; ; frameNum++)
                 {
-                    // We could just call ReadFrameAsync here, but we add this code before it for two reasons:
-                    // 1. To provide a better error message when we're unable to read another frame.  We otherwise
-                    //    generally output an error message that's relatively obscure.
-                    // 2. To avoid another state machine allocation in the relatively common case where we
-                    //    currently don't have enough data buffered and issuing a read for the frame header
-                    //    completes asynchronously, but that read ends up also reading enough data to fulfill
-                    //    the entire frame's needs (not just the header).
+                    // We could just call ReadFrameAsync here, but we add this code
+                    // to avoid another state machine allocation in the relatively common case where we
+                    // currently don't have enough data buffered and issuing a read for the frame header
+                    // completes asynchronously, but that read ends up also reading enough data to fulfill
+                    // the entire frame's needs (not just the header).
                     if (_incomingBuffer.ActiveLength < FrameHeader.Size)
                     {
                         _incomingBuffer.EnsureAvailableSpace(FrameHeader.Size - _incomingBuffer.ActiveLength);
@@ -260,10 +287,8 @@ private async Task ProcessIncomingFramesAsync()
                             _incomingBuffer.Commit(bytesRead);
                             if (bytesRead == 0)
                             {
-                                string message = _incomingBuffer.ActiveLength == 0 ?
-                                    SR.net_http_invalid_response_missing_frame :
-                                    SR.Format(SR.net_http_invalid_response_premature_eof_bytecount, FrameHeader.Size - _incomingBuffer.ActiveLength);
-                                throw new IOException(message);
+                                // ReadFrameAsync below will detect that the frame is incomplete and throw the appropriate error.
+                                break;
                             }
                         }
                         while (_incomingBuffer.ActiveLength < FrameHeader.Size);
@@ -465,7 +490,7 @@ private void ProcessAltSvcFrame(FrameHeader frameHeader)
                 //  - On stream 0, the origin will be specified. HTTP/2 can service multiple origins per connection, and so the server can report origins other than what our pool is using.
                 //  - Otherwise, the origin is implicitly defined by the request stream and must be of length 0.
 
-                if ((frameHeader.StreamId != 0 && originLength == 0) || (frameHeader.StreamId == 0 && span.Length >= originLength && span.Slice(originLength).SequenceEqual(_pool.Http2AltSvcOriginUri)))
+                if ((frameHeader.StreamId != 0 && originLength == 0) || (frameHeader.StreamId == 0 && span.Length >= originLength && span.Slice(0, originLength).SequenceEqual(_pool.Http2AltSvcOriginUri)))
                 {
                     span = span.Slice(originLength);
 
@@ -765,7 +790,7 @@ private void ProcessGoAwayFrame(FrameHeader frameHeader)
         }
 
         internal Task FlushAsync(CancellationToken cancellationToken) =>
-            PerformWriteAsync(0, 0, (_, __) => true, cancellationToken);
+            PerformWriteAsync(0, 0, static (_, __) => true, cancellationToken);
 
         private abstract class WriteQueueEntry : TaskCompletionSource
         {
@@ -778,7 +803,7 @@ public WriteQueueEntry(int writeBytes, CancellationToken cancellationToken)
                 WriteBytes = writeBytes;
 
                 _cancellationToken = cancellationToken;
-                _cancellationRegistration = cancellationToken.UnsafeRegister(s => ((WriteQueueEntry)s!).OnCancellation(), this);
+                _cancellationRegistration = cancellationToken.UnsafeRegister(static s => ((WriteQueueEntry)s!).OnCancellation(), this);
             }
 
             public int WriteBytes { get; }
@@ -901,7 +926,7 @@ private async Task ProcessOutgoingFramesAsync()
         }
 
         private Task SendSettingsAckAsync() =>
-            PerformWriteAsync(FrameHeader.Size, this, (thisRef, writeBuffer) =>
+            PerformWriteAsync(FrameHeader.Size, this, static (thisRef, writeBuffer) =>
             {
                 if (NetEventSource.Log.IsEnabled()) thisRef.Trace("Started writing.");
 
@@ -912,7 +937,7 @@ private Task SendSettingsAckAsync() =>
 
         /// <param name="pingContent">The 8-byte ping content to send, read as a big-endian integer.</param>
         private Task SendPingAckAsync(long pingContent) =>
-            PerformWriteAsync(FrameHeader.Size + FrameHeader.PingLength, (thisRef: this, pingContent), (state, writeBuffer) =>
+            PerformWriteAsync(FrameHeader.Size + FrameHeader.PingLength, (thisRef: this, pingContent), static (state, writeBuffer) =>
             {
                 if (NetEventSource.Log.IsEnabled()) state.thisRef.Trace("Started writing.");
 
@@ -926,7 +951,7 @@ private Task SendPingAckAsync(long pingContent) =>
             });
 
         private Task SendRstStreamAsync(int streamId, Http2ProtocolErrorCode errorCode) =>
-            PerformWriteAsync(FrameHeader.Size + FrameHeader.RstStreamLength, (thisRef: this, streamId, errorCode), (s, writeBuffer) =>
+            PerformWriteAsync(FrameHeader.Size + FrameHeader.RstStreamLength, (thisRef: this, streamId, errorCode), static (s, writeBuffer) =>
             {
                 if (NetEventSource.Log.IsEnabled()) s.thisRef.Trace(s.streamId, $"Started writing. {nameof(s.errorCode)}={s.errorCode}");
 
@@ -968,12 +993,12 @@ private void WriteIndexedHeader(int index, string value, ref ArrayBuffer headerB
             headerBuffer.Commit(bytesWritten);
         }
 
-        private void WriteLiteralHeader(string name, ReadOnlySpan<string> values, ref ArrayBuffer headerBuffer)
+        private void WriteLiteralHeader(string name, ReadOnlySpan<string> values, Encoding? valueEncoding, ref ArrayBuffer headerBuffer)
         {
             if (NetEventSource.Log.IsEnabled()) Trace($"{nameof(name)}={name}, {nameof(values)}={string.Join(", ", values.ToArray())}");
 
             int bytesWritten;
-            while (!HPackEncoder.EncodeLiteralHeaderFieldWithoutIndexingNewName(name, values, HttpHeaderParser.DefaultSeparator, headerBuffer.AvailableSpan, out bytesWritten))
+            while (!HPackEncoder.EncodeLiteralHeaderFieldWithoutIndexingNewName(name, values, HttpHeaderParser.DefaultSeparator, valueEncoding, headerBuffer.AvailableSpan, out bytesWritten))
             {
                 headerBuffer.EnsureAvailableSpace(headerBuffer.AvailableLength + 1);
             }
@@ -981,12 +1006,12 @@ private void WriteLiteralHeader(string name, ReadOnlySpan<string> values, ref Ar
             headerBuffer.Commit(bytesWritten);
         }
 
-        private void WriteLiteralHeaderValues(ReadOnlySpan<string> values, string? separator, ref ArrayBuffer headerBuffer)
+        private void WriteLiteralHeaderValues(ReadOnlySpan<string> values, string? separator, Encoding? valueEncoding, ref ArrayBuffer headerBuffer)
         {
             if (NetEventSource.Log.IsEnabled()) Trace($"{nameof(values)}={string.Join(separator, values.ToArray())}");
 
             int bytesWritten;
-            while (!HPackEncoder.EncodeStringLiterals(values, separator, headerBuffer.AvailableSpan, out bytesWritten))
+            while (!HPackEncoder.EncodeStringLiterals(values, separator, valueEncoding, headerBuffer.AvailableSpan, out bytesWritten))
             {
                 headerBuffer.EnsureAvailableSpace(headerBuffer.AvailableLength + 1);
             }
@@ -994,12 +1019,12 @@ private void WriteLiteralHeaderValues(ReadOnlySpan<string> values, string? separ
             headerBuffer.Commit(bytesWritten);
         }
 
-        private void WriteLiteralHeaderValue(string value, ref ArrayBuffer headerBuffer)
+        private void WriteLiteralHeaderValue(string value, Encoding? valueEncoding, ref ArrayBuffer headerBuffer)
         {
             if (NetEventSource.Log.IsEnabled()) Trace($"{nameof(value)}={value}");
 
             int bytesWritten;
-            while (!HPackEncoder.EncodeStringLiteral(value, headerBuffer.AvailableSpan, out bytesWritten))
+            while (!HPackEncoder.EncodeStringLiteral(value, valueEncoding, headerBuffer.AvailableSpan, out bytesWritten))
             {
                 headerBuffer.EnsureAvailableSpace(headerBuffer.AvailableLength + 1);
             }
@@ -1020,7 +1045,7 @@ private void WriteBytes(ReadOnlySpan<byte> bytes, ref ArrayBuffer headerBuffer)
             headerBuffer.Commit(bytes.Length);
         }
 
-        private void WriteHeaderCollection(HttpHeaders headers, ref ArrayBuffer headerBuffer)
+        private void WriteHeaderCollection(HttpRequestMessage request, HttpHeaders headers, ref ArrayBuffer headerBuffer)
         {
             if (NetEventSource.Log.IsEnabled()) Trace("");
 
@@ -1029,6 +1054,8 @@ private void WriteHeaderCollection(HttpHeaders headers, ref ArrayBuffer headerBu
                 return;
             }
 
+            HeaderEncodingSelector<HttpRequestMessage>? encodingSelector = _pool.Settings._requestHeaderEncodingSelector;
+
             ref string[]? tmpHeaderValuesArray = ref t_headerValues;
             foreach (KeyValuePair<HeaderDescriptor, object> header in headers.HeaderStore)
             {
@@ -1036,6 +1063,8 @@ private void WriteHeaderCollection(HttpHeaders headers, ref ArrayBuffer headerBu
                 Debug.Assert(headerValuesCount > 0, "No values for header??");
                 ReadOnlySpan<string> headerValues = tmpHeaderValuesArray.AsSpan(0, headerValuesCount);
 
+                Encoding? valueEncoding = encodingSelector?.Invoke(header.Key.Name, request);
+
                 KnownHeader? knownHeader = header.Key.KnownHeader;
                 if (knownHeader != null)
                 {
@@ -1052,7 +1081,7 @@ private void WriteHeaderCollection(HttpHeaders headers, ref ArrayBuffer headerBu
                                 if (string.Equals(value, "trailers", StringComparison.OrdinalIgnoreCase))
                                 {
                                     WriteBytes(knownHeader.Http2EncodedName, ref headerBuffer);
-                                    WriteLiteralHeaderValue(value, ref headerBuffer);
+                                    WriteLiteralHeaderValue(value, valueEncoding, ref headerBuffer);
                                     break;
                                 }
                             }
@@ -1075,13 +1104,13 @@ private void WriteHeaderCollection(HttpHeaders headers, ref ArrayBuffer headerBu
                             }
                         }
 
-                        WriteLiteralHeaderValues(headerValues, separator, ref headerBuffer);
+                        WriteLiteralHeaderValues(headerValues, separator, valueEncoding, ref headerBuffer);
                     }
                 }
                 else
                 {
                     // The header is not known: fall back to just encoding the header name and value(s).
-                    WriteLiteralHeader(header.Key.Name, headerValues, ref headerBuffer);
+                    WriteLiteralHeader(header.Key.Name, headerValues, valueEncoding, ref headerBuffer);
                 }
             }
         }
@@ -1136,7 +1165,7 @@ private void WriteHeaders(HttpRequestMessage request, ref ArrayBuffer headerBuff
 
             if (request.HasHeaders)
             {
-                WriteHeaderCollection(request.Headers, ref headerBuffer);
+                WriteHeaderCollection(request, request.Headers, ref headerBuffer);
             }
 
             // Determine cookies to send.
@@ -1146,7 +1175,9 @@ private void WriteHeaders(HttpRequestMessage request, ref ArrayBuffer headerBuff
                 if (cookiesFromContainer != string.Empty)
                 {
                     WriteBytes(KnownHeaders.Cookie.Http2EncodedName, ref headerBuffer);
-                    WriteLiteralHeaderValue(cookiesFromContainer, ref headerBuffer);
+
+                    Encoding? cookieEncoding = _pool.Settings._requestHeaderEncodingSelector?.Invoke(KnownHeaders.Cookie.Name, request);
+                    WriteLiteralHeaderValue(cookiesFromContainer, cookieEncoding, ref headerBuffer);
                 }
             }
 
@@ -1157,12 +1188,12 @@ private void WriteHeaders(HttpRequestMessage request, ref ArrayBuffer headerBuff
                 if (normalizedMethod.MustHaveRequestBody)
                 {
                     WriteBytes(KnownHeaders.ContentLength.Http2EncodedName, ref headerBuffer);
-                    WriteLiteralHeaderValue("0", ref headerBuffer);
+                    WriteLiteralHeaderValue("0", valueEncoding: null, ref headerBuffer);
                 }
             }
             else
             {
-                WriteHeaderCollection(request.Content.Headers, ref headerBuffer);
+                WriteHeaderCollection(request, request.Content.Headers, ref headerBuffer);
             }
         }
 
@@ -1203,7 +1234,17 @@ private async ValueTask<Http2Stream> SendHeadersAsync(HttpRequestMessage request
             // in order to avoid consuming resources in potentially many requests waiting for access.
             try
             {
-                await _concurrentStreams.RequestCreditAsync(1, cancellationToken).ConfigureAwait(false);
+                if (_pool.EnableMultipleHttp2Connections)
+                {
+                    if (!_concurrentStreams.TryRequestCreditNoWait(1))
+                    {
+                        throw new HttpRequestException(null, null, RequestRetryType.RetryOnNextConnection);
+                    }
+                }
+                else
+                {
+                    await _concurrentStreams.RequestCreditAsync(1, cancellationToken).ConfigureAwait(false);
+                }
             }
             catch (ObjectDisposedException)
             {
@@ -1249,7 +1290,7 @@ private async ValueTask<Http2Stream> SendHeadersAsync(HttpRequestMessage request
                 // Start the write.  This serializes access to write to the connection, and ensures that HEADERS
                 // and CONTINUATION frames stay together, as they must do. We use the lock as well to ensure new
                 // streams are created and started in order.
-                await PerformWriteAsync(totalSize, (thisRef: this, http2Stream, headerBytes, endStream: (request.Content == null), mustFlush), (s, writeBuffer) =>
+                await PerformWriteAsync(totalSize, (thisRef: this, http2Stream, headerBytes, endStream: (request.Content == null), mustFlush), static (s, writeBuffer) =>
                 {
                     if (NetEventSource.Log.IsEnabled()) s.thisRef.Trace(s.http2Stream.StreamId, $"Started writing. Total header bytes={s.headerBytes.Length}");
 
@@ -1269,7 +1310,7 @@ await PerformWriteAsync(totalSize, (thisRef: this, http2Stream, headerBytes, end
                         // assigning the stream ID to ensure only one stream gets an ID, and it must be held
                         // across setting the initial window size (available credit) and storing the stream into
                         // collection such that window size updates are able to atomically affect all known streams.
-                        s.http2Stream.Initialize(s.thisRef._nextStream, _initialWindowSize);
+                        s.http2Stream.Initialize(s.thisRef._nextStream, s.thisRef._initialWindowSize);
 
                         // Client-initiated streams are always odd-numbered, so increase by 2.
                         s.thisRef._nextStream += 2;
@@ -1337,7 +1378,7 @@ private async Task SendStreamDataAsync(int streamId, ReadOnlyMemory<byte> buffer
                 (current, remaining) = SplitBuffer(remaining, frameSize);
                 try
                 {
-                    await PerformWriteAsync(FrameHeader.Size + current.Length, (thisRef: this, streamId, current), (s, writeBuffer) =>
+                    await PerformWriteAsync(FrameHeader.Size + current.Length, (thisRef: this, streamId, current), static (s, writeBuffer) =>
                     {
                         // Invoked while holding the lock:
                         if (NetEventSource.Log.IsEnabled()) s.thisRef.Trace(s.streamId, $"Started writing. {nameof(writeBuffer.Length)}={writeBuffer.Length}");
@@ -1358,7 +1399,7 @@ await PerformWriteAsync(FrameHeader.Size + current.Length, (thisRef: this, strea
         }
 
         private Task SendEndStreamAsync(int streamId) =>
-            PerformWriteAsync(FrameHeader.Size, (thisRef: this, streamId), (s, writeBuffer) =>
+            PerformWriteAsync(FrameHeader.Size, (thisRef: this, streamId), static (s, writeBuffer) =>
             {
                 if (NetEventSource.Log.IsEnabled()) s.thisRef.Trace(s.streamId, "Started writing.");
 
@@ -1371,7 +1412,7 @@ private Task SendWindowUpdateAsync(int streamId, int amount)
         {
             // We update both the connection-level and stream-level windows at the same time
             Debug.Assert(amount > 0);
-            return PerformWriteAsync(FrameHeader.Size + FrameHeader.WindowUpdateLength, (thisRef: this, streamId, amount), (s, writeBuffer) =>
+            return PerformWriteAsync(FrameHeader.Size + FrameHeader.WindowUpdateLength, (thisRef: this, streamId, amount), static (s, writeBuffer) =>
             {
                 if (NetEventSource.Log.IsEnabled()) s.thisRef.Trace(s.streamId, $"Started writing. {nameof(s.amount)}={s.amount}");
 
@@ -1572,7 +1613,7 @@ private void CheckForShutdown()
             }
 
             // Do shutdown.
-            _stream.Close();
+            _connection.Dispose();
 
             _connectionWindow.Dispose();
             _concurrentStreams.Dispose();
@@ -1734,7 +1775,8 @@ public sealed override async Task<HttpResponseMessage> SendAsync(HttpRequestMess
                 if (requestBodyTask.IsCompleted ||
                     duplex == false ||
                     await Task.WhenAny(requestBodyTask, responseHeadersTask).ConfigureAwait(false) == requestBodyTask ||
-                    requestBodyTask.IsCompleted)
+                    requestBodyTask.IsCompleted ||
+                    http2Stream.SendRequestFinished)
                 {
                     // The sending of the request body completed before receiving all of the request headers (or we're
                     // ok waiting for the request body even if it hasn't completed, e.g. because we're not doing duplex).
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Stream.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Stream.cs
index eb866134c06212..0635de4df9b93f 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Stream.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http2Stream.cs
@@ -36,7 +36,7 @@ private sealed class Http2Stream : IValueTaskSource, IHttpHeadersHandler, IHttpT
 
             private ArrayBuffer _responseBuffer; // mutable struct, do not make this readonly
             private int _pendingWindowUpdate;
-            private CancelableCreditWaiter? _creditWaiter;
+            private CreditWaiter? _creditWaiter;
             private int _availableCredit;
 
             private StreamCompletionState _requestCompletionState;
@@ -145,6 +145,8 @@ public void Initialize(int streamId, int initialWindowSize)
 
             public int StreamId { get; private set; }
 
+            public bool SendRequestFinished => _requestCompletionState != StreamCompletionState.InProgress;
+
             public HttpResponseMessage GetAndClearResponse()
             {
                 // Once SendAsync completes, the Http2Stream should no longer hold onto the response message.
@@ -300,8 +302,8 @@ public async ValueTask<bool> WaitFor100ContinueAsync(CancellationToken cancellat
                 // We await the created Timer's disposal so that we ensure any work associated with it has quiesced prior to this method
                 // returning, just in case this object is pooled and potentially reused for another operation in the future.
                 TaskCompletionSource<bool> waiter = _expect100ContinueWaiter!;
-                using (cancellationToken.UnsafeRegister(s => ((TaskCompletionSource<bool>)s!).TrySetResult(false), waiter))
-                await using (new Timer(s =>
+                using (cancellationToken.UnsafeRegister(static s => ((TaskCompletionSource<bool>)s!).TrySetResult(false), waiter))
+                await using (new Timer(static s =>
                 {
                     var thisRef = (Http2Stream)s!;
                     if (NetEventSource.Log.IsEnabled()) thisRef.Trace($"100-Continue timer expired.");
@@ -424,7 +426,7 @@ public void OnWindowUpdate(int amount)
                 lock (SyncObject)
                 {
                     _availableCredit = checked(_availableCredit + amount);
-                    if (_availableCredit > 0 && _creditWaiter != null && _creditWaiter.IsPending)
+                    if (_availableCredit > 0 && _creditWaiter != null)
                     {
                         int granted = Math.Min(_availableCredit, _creditWaiter.Amount);
                         if (_creditWaiter.TrySetResult(granted))
@@ -540,24 +542,26 @@ public void OnHeader(ReadOnlySpan<byte> name, ReadOnlySpan<byte> value)
                             throw new HttpRequestException(SR.Format(SR.net_http_invalid_response_header_name, Encoding.ASCII.GetString(name)));
                         }
 
+                        Encoding? valueEncoding = _connection._pool.Settings._responseHeaderEncodingSelector?.Invoke(descriptor.Name, _request);
+
                         // Note we ignore the return value from TryAddWithoutValidation;
                         // if the header can't be added, we silently drop it.
                         if (_responseProtocolState == ResponseProtocolState.ExpectingTrailingHeaders)
                         {
                             Debug.Assert(_trailers != null);
-                            string headerValue = descriptor.GetHeaderValue(value);
+                            string headerValue = descriptor.GetHeaderValue(value, valueEncoding);
                             _trailers.TryAddWithoutValidation((descriptor.HeaderType & HttpHeaderType.Request) == HttpHeaderType.Request ? descriptor.AsCustomHeader() : descriptor, headerValue);
                         }
                         else if ((descriptor.HeaderType & HttpHeaderType.Content) == HttpHeaderType.Content)
                         {
                             Debug.Assert(_response != null && _response.Content != null);
-                            string headerValue = descriptor.GetHeaderValue(value);
+                            string headerValue = descriptor.GetHeaderValue(value, valueEncoding);
                             _response.Content.Headers.TryAddWithoutValidation(descriptor, headerValue);
                         }
                         else
                         {
                             Debug.Assert(_response != null);
-                            string headerValue = _connection.GetResponseHeaderValueWithCaching(descriptor, value);
+                            string headerValue = _connection.GetResponseHeaderValueWithCaching(descriptor, value, valueEncoding);
                             _response.Headers.TryAddWithoutValidation((descriptor.HeaderType & HttpHeaderType.Request) == HttpHeaderType.Request ? descriptor.AsCustomHeader() : descriptor, headerValue);
                         }
                     }
@@ -1096,11 +1100,10 @@ private async ValueTask SendDataAsync(ReadOnlyMemory<byte> buffer, CancellationT
                             {
                                 if (_creditWaiter is null)
                                 {
-                                    _creditWaiter = new CancelableCreditWaiter(SyncObject, _requestBodyCancellationSource.Token);
+                                    _creditWaiter = new CreditWaiter(_requestBodyCancellationSource.Token);
                                 }
                                 else
                                 {
-                                    Debug.Assert(!_creditWaiter.IsPending);
                                     _creditWaiter.ResetForAwait(_requestBodyCancellationSource.Token);
                                 }
                                 _creditWaiter.Amount = buffer.Length;
@@ -1109,9 +1112,9 @@ private async ValueTask SendDataAsync(ReadOnlyMemory<byte> buffer, CancellationT
 
                         if (sendSize == -1)
                         {
+                            // Logically this is part of the else block above, but we can't await while holding the lock.
                             Debug.Assert(_creditWaiter != null);
                             sendSize = await _creditWaiter.AsValueTask().ConfigureAwait(false);
-                            _creditWaiter.CleanUp();
                         }
 
                         ReadOnlyMemory<byte> current;
@@ -1149,7 +1152,7 @@ private void CloseResponseBody()
             }
 
             private CancellationTokenRegistration RegisterRequestBodyCancellation(CancellationToken cancellationToken) =>
-                cancellationToken.UnsafeRegister(s => ((CancellationTokenSource)s!).Cancel(), _requestBodyCancellationSource);
+                cancellationToken.UnsafeRegister(static s => ((CancellationTokenSource)s!).Cancel(), _requestBodyCancellationSource);
 
             // This object is itself usable as a backing source for ValueTask.  Since there's only ever one awaiter
             // for this object's state transitions at a time, we allow the object to be awaited directly. All functionality
@@ -1191,7 +1194,7 @@ private ValueTask WaitForDataAsync(CancellationToken cancellationToken)
                 // However, this could still be non-cancelable if HttpMessageInvoker was used, at which point this will only be
                 // cancelable if the caller's token was cancelable.
 
-                _waitSourceCancellation = cancellationToken.UnsafeRegister(s =>
+                _waitSourceCancellation = cancellationToken.UnsafeRegister(static s =>
                 {
                     var thisRef = (Http2Stream)s!;
 
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3Connection.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3Connection.cs
index 54fe0e9c8bb74c..9ee2bdf910b83e 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3Connection.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3Connection.cs
@@ -9,11 +9,16 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Net.Http.Headers;
+using System.Net.Security;
 
 namespace System.Net.Http
 {
     internal sealed class Http3Connection : HttpConnectionBase, IDisposable
     {
+        // TODO: once HTTP/3 is standardized, create APIs for these.
+        public static readonly Version HttpVersion30 = new Version(3, 0);
+        public static readonly SslApplicationProtocol Http3ApplicationProtocol = new SslApplicationProtocol("h3");
+
         /// <summary>
         /// If we receive a settings frame larger than this, tear down the connection with an error.
         /// </summary>
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3RequestStream.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3RequestStream.cs
index 52f2363700b70f..b5afcb5f9d8f39 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3RequestStream.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/Http3RequestStream.cs
@@ -12,8 +12,6 @@
 using System.Runtime.CompilerServices;
 using System.Net.Http.QPack;
 using System.Runtime.ExceptionServices;
-using System.Buffers;
-using System.Diagnostics.CodeAnalysis;
 
 namespace System.Net.Http
 {
@@ -292,11 +290,9 @@ public async Task<HttpResponseMessage> SendAsync(CancellationToken cancellationT
         /// <summary>
         /// Waits for the initial response headers to be completed, including e.g. Expect 100 Continue.
         /// </summary>
-        /// <param name="cancellationToken"></param>
-        /// <returns></returns>
         private async Task ReadResponseAsync(CancellationToken cancellationToken)
         {
-            Debug.Assert(_response != null);
+            Debug.Assert(_response == null);
             do
             {
                 _headerState = HeaderState.StatusHeader;
@@ -313,6 +309,7 @@ private async Task ReadResponseAsync(CancellationToken cancellationToken)
                 }
 
                 await ReadHeadersAsync(payloadLength, cancellationToken).ConfigureAwait(false);
+                Debug.Assert(_response != null);
             }
             while ((int)_response.StatusCode < 200);
 
@@ -331,10 +328,8 @@ private async Task SendContentAsync(HttpContent content, CancellationToken cance
                 {
                     if (_connection.Pool.Settings._expect100ContinueTimeout != Timeout.InfiniteTimeSpan)
                     {
-                        timer = new Timer(o =>
-                        {
-                            ((Http3RequestStream)o!)._expect100ContinueCompletionSource!.TrySetResult(true);
-                        }, this, _connection.Pool.Settings._expect100ContinueTimeout, Timeout.InfiniteTimeSpan);
+                        timer = new Timer(static o => ((Http3RequestStream)o!)._expect100ContinueCompletionSource!.TrySetResult(true),
+                            this, _connection.Pool.Settings._expect100ContinueTimeout, Timeout.InfiniteTimeSpan);
                     }
 
                     if (!await _expect100ContinueCompletionSource.Task.ConfigureAwait(false))
@@ -550,7 +545,8 @@ private void BufferHeaders(HttpRequestMessage request)
                 string cookiesFromContainer = _connection.Pool.Settings._cookieContainer!.GetCookieHeader(request.RequestUri);
                 if (cookiesFromContainer != string.Empty)
                 {
-                    BufferLiteralHeaderWithStaticNameReference(H3StaticTable.Cookie, cookiesFromContainer);
+                    Encoding? valueEncoding = _connection.Pool.Settings._requestHeaderEncodingSelector?.Invoke(HttpKnownHeaderNames.Cookie, request);
+                    BufferLiteralHeaderWithStaticNameReference(H3StaticTable.Cookie, cookiesFromContainer, valueEncoding);
                 }
             }
 
@@ -592,12 +588,16 @@ private void BufferHeaderCollection(HttpHeaders headers)
                 return;
             }
 
+            HeaderEncodingSelector<HttpRequestMessage>? encodingSelector = _connection.Pool.Settings._requestHeaderEncodingSelector;
+
             foreach (KeyValuePair<HeaderDescriptor, object> header in headers.HeaderStore)
             {
                 int headerValuesCount = HttpHeaders.GetValuesAsStrings(header.Key, header.Value, ref _headerValues);
                 Debug.Assert(headerValuesCount > 0, "No values for header??");
                 ReadOnlySpan<string> headerValues = _headerValues.AsSpan(0, headerValuesCount);
 
+                Encoding? valueEncoding = encodingSelector?.Invoke(header.Key.Name, _request);
+
                 KnownHeader? knownHeader = header.Key.KnownHeader;
                 if (knownHeader != null)
                 {
@@ -614,7 +614,7 @@ private void BufferHeaderCollection(HttpHeaders headers)
                             {
                                 if (string.Equals(value, "trailers", StringComparison.OrdinalIgnoreCase))
                                 {
-                                    BufferLiteralHeaderWithoutNameReference("TE", value);
+                                    BufferLiteralHeaderWithoutNameReference("TE", value, valueEncoding);
                                     break;
                                 }
                             }
@@ -637,13 +637,13 @@ private void BufferHeaderCollection(HttpHeaders headers)
                             }
                         }
 
-                        BufferLiteralHeaderValues(headerValues, separator);
+                        BufferLiteralHeaderValues(headerValues, separator, valueEncoding);
                     }
                 }
                 else
                 {
                     // The header is not known: fall back to just encoding the header name and value(s).
-                    BufferLiteralHeaderWithoutNameReference(header.Key.Name, headerValues, ", ");
+                    BufferLiteralHeaderWithoutNameReference(header.Key.Name, headerValues, HttpHeaderParser.DefaultSeparator, valueEncoding);
                 }
             }
         }
@@ -658,40 +658,40 @@ private void BufferIndexedHeader(int index)
             _sendBuffer.Commit(bytesWritten);
         }
 
-        private void BufferLiteralHeaderWithStaticNameReference(int nameIndex, string value)
+        private void BufferLiteralHeaderWithStaticNameReference(int nameIndex, string value, Encoding? valueEncoding = null)
         {
             int bytesWritten;
-            while (!QPackEncoder.EncodeLiteralHeaderFieldWithStaticNameReference(nameIndex, value, _sendBuffer.AvailableSpan, out bytesWritten))
+            while (!QPackEncoder.EncodeLiteralHeaderFieldWithStaticNameReference(nameIndex, value, valueEncoding, _sendBuffer.AvailableSpan, out bytesWritten))
             {
                 _sendBuffer.Grow();
             }
             _sendBuffer.Commit(bytesWritten);
         }
 
-        private void BufferLiteralHeaderWithoutNameReference(string name, ReadOnlySpan<string> values, string separator)
+        private void BufferLiteralHeaderWithoutNameReference(string name, ReadOnlySpan<string> values, string separator, Encoding? valueEncoding)
         {
             int bytesWritten;
-            while (!QPackEncoder.EncodeLiteralHeaderFieldWithoutNameReference(name, values, separator, _sendBuffer.AvailableSpan, out bytesWritten))
+            while (!QPackEncoder.EncodeLiteralHeaderFieldWithoutNameReference(name, values, separator, valueEncoding, _sendBuffer.AvailableSpan, out bytesWritten))
             {
                 _sendBuffer.Grow();
             }
             _sendBuffer.Commit(bytesWritten);
         }
 
-        private void BufferLiteralHeaderWithoutNameReference(string name, string value)
+        private void BufferLiteralHeaderWithoutNameReference(string name, string value, Encoding? valueEncoding)
         {
             int bytesWritten;
-            while (!QPackEncoder.EncodeLiteralHeaderFieldWithoutNameReference(name, value, _sendBuffer.AvailableSpan, out bytesWritten))
+            while (!QPackEncoder.EncodeLiteralHeaderFieldWithoutNameReference(name, value, valueEncoding, _sendBuffer.AvailableSpan, out bytesWritten))
             {
                 _sendBuffer.Grow();
             }
             _sendBuffer.Commit(bytesWritten);
         }
 
-        private void BufferLiteralHeaderValues(ReadOnlySpan<string> values, string? separator)
+        private void BufferLiteralHeaderValues(ReadOnlySpan<string> values, string? separator, Encoding? valueEncoding)
         {
             int bytesWritten;
-            while (!QPackEncoder.EncodeValueString(values, separator, _sendBuffer.AvailableSpan, out bytesWritten))
+            while (!QPackEncoder.EncodeValueString(values, separator, valueEncoding, _sendBuffer.AvailableSpan, out bytesWritten))
             {
                 _sendBuffer.Grow();
             }
@@ -883,7 +883,7 @@ private void OnHeader(int? staticIndex, HeaderDescriptor descriptor, string? sta
 
                 _response = new HttpResponseMessage()
                 {
-                    Version = HttpVersion.Version30,
+                    Version = Http3Connection.HttpVersion30,
                     RequestMessage = _request,
                     Content = new HttpConnectionResponseContent(),
                     StatusCode = (HttpStatusCode)statusCode
@@ -919,7 +919,13 @@ private void OnHeader(int? staticIndex, HeaderDescriptor descriptor, string? sta
             }
             else
             {
-                string headerValue = staticValue ?? _connection.GetResponseHeaderValueWithCaching(descriptor, literalValue);
+                string? headerValue = staticValue;
+
+                if (headerValue is null)
+                {
+                    Encoding? encoding = _connection.Pool.Settings._responseHeaderEncodingSelector?.Invoke(descriptor.Name, _request);
+                    headerValue = _connection.GetResponseHeaderValueWithCaching(descriptor, literalValue, encoding);
+                }
 
                 switch (_headerState)
                 {
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpAuthority.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpAuthority.cs
index de4a6a5b93238a..43a4181aa60c0f 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpAuthority.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpAuthority.cs
@@ -31,8 +31,7 @@ public HttpAuthority(string host, int port)
 
         public bool Equals(HttpAuthority? other)
         {
-            Debug.Assert(other != null);
-            return string.Equals(IdnHost, other.IdnHost) && Port == other.Port;
+            return other != null && string.Equals(IdnHost, other.IdnHost) && Port == other.Port;
         }
 
         public override bool Equals(object? obj)
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnection.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnection.cs
index 943eb017d23cac..131af80227ee72 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnection.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnection.cs
@@ -10,6 +10,7 @@
 using System.Net.Http.Headers;
 using System.Net.Security;
 using System.Net.Sockets;
+using System.Net.Connections;
 using System.Runtime.CompilerServices;
 using System.Text;
 using System.Threading;
@@ -45,6 +46,7 @@ internal partial class HttpConnection : HttpConnectionBase, IDisposable
         private readonly HttpConnectionPool _pool;
         private readonly Socket? _socket; // used for polling; _stream should be used for all reading/writing. _stream owns disposal.
         private readonly Stream _stream;
+        private readonly Connection _connection;
         private readonly TransportContext? _transportContext;
         private readonly WeakReference<HttpConnection> _weakThisRef;
 
@@ -68,16 +70,16 @@ internal partial class HttpConnection : HttpConnectionBase, IDisposable
 
         public HttpConnection(
             HttpConnectionPool pool,
-            Socket? socket,
-            Stream stream,
+            Connection connection,
             TransportContext? transportContext)
         {
             Debug.Assert(pool != null);
-            Debug.Assert(stream != null);
+            Debug.Assert(connection != null);
 
             _pool = pool;
-            _socket = socket; // may be null in cases where we couldn't easily get the underlying socket
-            _stream = stream;
+            connection.ConnectionProperties.TryGet(out _socket); // may be null in cases where we couldn't easily get the underlying socket
+            _stream = connection.Stream;
+            _connection = connection;
             _transportContext = transportContext;
 
             _writeBuffer = new byte[InitialWriteBufferSize];
@@ -101,7 +103,7 @@ protected void Dispose(bool disposing)
                 if (disposing)
                 {
                     GC.SuppressFinalize(this);
-                    _stream.Dispose();
+                    _connection.Dispose();
 
                     // Eat any exceptions from the read-ahead task.  We don't need to log, as we expect
                     // failures from this task due to closing the connection while a read is in progress.
@@ -195,6 +197,8 @@ private void ConsumeFromRemainingBuffer(int bytesToConsume)
 
         private async ValueTask WriteHeadersAsync(HttpHeaders headers, string? cookiesFromContainer, bool async)
         {
+            Debug.Assert(_currentRequest != null);
+
             if (headers.HeaderStore != null)
             {
                 foreach (KeyValuePair<HeaderDescriptor, object> header in headers.HeaderStore)
@@ -213,12 +217,14 @@ private async ValueTask WriteHeadersAsync(HttpHeaders headers, string? cookiesFr
                     Debug.Assert(headerValuesCount > 0, "No values for header??");
                     if (headerValuesCount > 0)
                     {
-                        await WriteStringAsync(_headerValues[0], async).ConfigureAwait(false);
+                        Encoding? valueEncoding = _pool.Settings._requestHeaderEncodingSelector?.Invoke(header.Key.Name, _currentRequest);
+
+                        await WriteStringAsync(_headerValues[0], async, valueEncoding).ConfigureAwait(false);
 
                         if (cookiesFromContainer != null && header.Key.KnownHeader == KnownHeaders.Cookie)
                         {
                             await WriteTwoBytesAsync((byte)';', (byte)' ', async).ConfigureAwait(false);
-                            await WriteStringAsync(cookiesFromContainer, async).ConfigureAwait(false);
+                            await WriteStringAsync(cookiesFromContainer, async, valueEncoding).ConfigureAwait(false);
 
                             cookiesFromContainer = null;
                         }
@@ -236,7 +242,7 @@ private async ValueTask WriteHeadersAsync(HttpHeaders headers, string? cookiesFr
                             for (int i = 1; i < headerValuesCount; i++)
                             {
                                 await WriteAsciiStringAsync(separator, async).ConfigureAwait(false);
-                                await WriteStringAsync(_headerValues[i], async).ConfigureAwait(false);
+                                await WriteStringAsync(_headerValues[i], async, valueEncoding).ConfigureAwait(false);
                             }
                         }
                     }
@@ -249,7 +255,10 @@ private async ValueTask WriteHeadersAsync(HttpHeaders headers, string? cookiesFr
             {
                 await WriteAsciiStringAsync(HttpKnownHeaderNames.Cookie, async).ConfigureAwait(false);
                 await WriteTwoBytesAsync((byte)':', (byte)' ', async).ConfigureAwait(false);
-                await WriteStringAsync(cookiesFromContainer, async).ConfigureAwait(false);
+
+                Encoding? valueEncoding = _pool.Settings._requestHeaderEncodingSelector?.Invoke(HttpKnownHeaderNames.Cookie, _currentRequest);
+                await WriteStringAsync(cookiesFromContainer, async, valueEncoding).ConfigureAwait(false);
+
                 await WriteTwoBytesAsync((byte)'\r', (byte)'\n', async).ConfigureAwait(false);
             }
         }
@@ -457,7 +466,7 @@ public async Task<HttpResponseMessage> SendAsyncCore(HttpRequestMessage request,
                         // Then kick off the request.  The TCS' result indicates whether content should be sent or not.
                         allowExpect100ToContinue = new TaskCompletionSource<bool>();
                         var expect100Timer = new Timer(
-                            s => ((TaskCompletionSource<bool>)s!).TrySetResult(true),
+                            static s => ((TaskCompletionSource<bool>)s!).TrySetResult(true),
                             allowExpect100ToContinue, _pool.Settings._expect100ContinueTimeout, Timeout.InfiniteTimeSpan);
                         sendRequestContentTask = SendRequestContentWithExpect100ContinueAsync(
                             request, allowExpect100ToContinue.Task, CreateRequestContentStream(request), expect100Timer, async, cancellationToken);
@@ -692,6 +701,21 @@ public async Task<HttpResponseMessage> SendAsyncCore(HttpRequestMessage request,
                 // hook up a continuation that will log it.
                 if (sendRequestContentTask != null && !sendRequestContentTask.IsCompletedSuccessfully)
                 {
+                    // In case the connection is disposed, it's most probable that
+                    // expect100Continue timer expired and request content sending failed.
+                    // We're awaiting the task to propagate the exception in this case.
+                    if (Volatile.Read(ref _disposed) == 1)
+                    {
+                        if (async)
+                        {
+                            await sendRequestContentTask.ConfigureAwait(false);
+                        }
+                        else
+                        {
+                            // No way around it here if we want to get the exception from the task.
+                            sendRequestContentTask.GetAwaiter().GetResult();
+                        }
+                    }
                     LogExceptions(sendRequestContentTask);
                 }
 
@@ -755,7 +779,7 @@ private CancellationTokenRegistration RegisterCancellation(CancellationToken can
             //   request and prioritize that over other exceptions, wrapping the actual exception as an inner of an OCE.
             // - A weak reference to this HttpConnection is stored in the cancellation token, to prevent the token from
             //   artificially keeping this connection alive.
-            return cancellationToken.Register(s =>
+            return cancellationToken.Register(static s =>
             {
                 var weakThisRef = (WeakReference<HttpConnection>)s!;
                 if (weakThisRef.TryGetTarget(out HttpConnection? strongThisRef))
@@ -793,7 +817,8 @@ private async ValueTask SendRequestContentAsync(HttpRequestMessage request, Http
         }
 
         private async Task SendRequestContentWithExpect100ContinueAsync(
-            HttpRequestMessage request, Task<bool> allowExpect100ToContinueTask, HttpContentWriteStream stream, Timer expect100Timer, bool async, CancellationToken cancellationToken)
+            HttpRequestMessage request, Task<bool> allowExpect100ToContinueTask,
+            HttpContentWriteStream stream, Timer expect100Timer, bool async, CancellationToken cancellationToken)
         {
             // Wait until we receive a trigger notification that it's ok to continue sending content.
             // This will come either when the timer fires or when we receive a response status line from the server.
@@ -806,7 +831,17 @@ private async Task SendRequestContentWithExpect100ContinueAsync(
             if (sendRequestContent)
             {
                 if (NetEventSource.Log.IsEnabled()) Trace($"Sending request content for Expect: 100-continue.");
-                await SendRequestContentAsync(request, stream, async, cancellationToken).ConfigureAwait(false);
+                try
+                {
+                    await SendRequestContentAsync(request, stream, async, cancellationToken).ConfigureAwait(false);
+                }
+                catch
+                {
+                    // Tear down the connection if called from the timer thread because caller's thread will wait for server status line indefinitely
+                    // or till HttpClient.Timeout tear the connection itself.
+                    Dispose();
+                    throw;
+                }
             }
             else
             {
@@ -956,22 +991,25 @@ private static void ParseHeaderNameValue(HttpConnection connection, ReadOnlySpan
                 pos++;
             }
 
+            Debug.Assert(response.RequestMessage != null);
+            Encoding? valueEncoding = connection._pool.Settings._responseHeaderEncodingSelector?.Invoke(descriptor.Name, response.RequestMessage);
+
             // Note we ignore the return value from TryAddWithoutValidation. If the header can't be added, we silently drop it.
             ReadOnlySpan<byte> value = line.Slice(pos);
             if (isFromTrailer)
             {
-                string headerValue = descriptor.GetHeaderValue(value);
+                string headerValue = descriptor.GetHeaderValue(value, valueEncoding);
                 response.TrailingHeaders.TryAddWithoutValidation((descriptor.HeaderType & HttpHeaderType.Request) == HttpHeaderType.Request ? descriptor.AsCustomHeader() : descriptor, headerValue);
             }
             else if ((descriptor.HeaderType & HttpHeaderType.Content) == HttpHeaderType.Content)
             {
-                string headerValue = descriptor.GetHeaderValue(value);
+                string headerValue = descriptor.GetHeaderValue(value, valueEncoding);
                 response.Content!.Headers.TryAddWithoutValidation(descriptor, headerValue);
             }
             else
             {
                 // Request headers returned on the response must be treated as custom headers.
-                string headerValue = connection.GetResponseHeaderValueWithCaching(descriptor, value);
+                string headerValue = connection.GetResponseHeaderValueWithCaching(descriptor, value, valueEncoding);
                 response.Headers.TryAddWithoutValidation(
                     (descriptor.HeaderType & HttpHeaderType.Request) == HttpHeaderType.Request ? descriptor.AsCustomHeader() : descriptor,
                     headerValue);
@@ -1154,23 +1192,23 @@ private Task WriteBytesAsync(byte[] bytes, bool async)
                 _writeOffset += bytes.Length;
                 return Task.CompletedTask;
             }
-            return WriteBytesSlowAsync(bytes, async);
+            return WriteBytesSlowAsync(bytes, bytes.Length, async);
         }
 
-        private async Task WriteBytesSlowAsync(byte[] bytes, bool async)
+        private async Task WriteBytesSlowAsync(byte[] bytes, int length, bool async)
         {
             int offset = 0;
             while (true)
             {
-                int remaining = bytes.Length - offset;
+                int remaining = length - offset;
                 int toCopy = Math.Min(remaining, _writeBuffer.Length - _writeOffset);
                 Buffer.BlockCopy(bytes, offset, _writeBuffer, _writeOffset, toCopy);
                 _writeOffset += toCopy;
                 offset += toCopy;
 
-                Debug.Assert(offset <= bytes.Length, $"Expected {nameof(offset)} to be <= {bytes.Length}, got {offset}");
+                Debug.Assert(offset <= length, $"Expected {nameof(offset)} to be <= {length}, got {offset}");
                 Debug.Assert(_writeOffset <= _writeBuffer.Length, $"Expected {nameof(_writeOffset)} to be <= {_writeBuffer.Length}, got {_writeOffset}");
-                if (offset == bytes.Length)
+                if (offset == length)
                 {
                     break;
                 }
@@ -1207,6 +1245,43 @@ private Task WriteStringAsync(string s, bool async)
             return WriteStringAsyncSlow(s, async);
         }
 
+        private Task WriteStringAsync(string s, bool async, Encoding? encoding)
+        {
+            if (encoding is null)
+            {
+                return WriteStringAsync(s, async);
+            }
+
+            // If there's enough space in the buffer to just copy all of the string's bytes, do so.
+            if (encoding.GetMaxByteCount(s.Length) <= _writeBuffer.Length - _writeOffset)
+            {
+                _writeOffset += encoding.GetBytes(s, _writeBuffer.AsSpan(_writeOffset));
+                return Task.CompletedTask;
+            }
+
+            // Otherwise, fall back to doing a normal slow string write
+            return WriteStringWithEncodingAsyncSlow(s, async, encoding);
+        }
+
+        private async Task WriteStringWithEncodingAsyncSlow(string s, bool async, Encoding encoding)
+        {
+            // Avoid calculating the length if the rented array would be small anyway
+            int length = s.Length <= 512
+                ? encoding.GetMaxByteCount(s.Length)
+                : encoding.GetByteCount(s);
+
+            byte[] rentedBuffer = ArrayPool<byte>.Shared.Rent(length);
+            try
+            {
+                int written = encoding.GetBytes(s, rentedBuffer);
+                await WriteBytesSlowAsync(rentedBuffer, written, async).ConfigureAwait(false);
+            }
+            finally
+            {
+                ArrayPool<byte>.Shared.Return(rentedBuffer);
+            }
+        }
+
         private Task WriteAsciiStringAsync(string s, bool async)
         {
             // If there's enough space in the buffer to just copy all of the string's bytes, do so.
@@ -1891,7 +1966,7 @@ public sealed override void Trace(string message, [CallerMemberName] string? mem
 
     internal sealed class HttpConnectionWithFinalizer : HttpConnection
     {
-        public HttpConnectionWithFinalizer(HttpConnectionPool pool, Socket? socket, Stream stream, TransportContext? transportContext) : base(pool, socket, stream, transportContext) { }
+        public HttpConnectionWithFinalizer(HttpConnectionPool pool, Connection connection, TransportContext? transportContext) : base(pool, connection, transportContext) { }
 
         // This class is separated from HttpConnection so we only pay the price of having a finalizer
         // when it's actually needed, e.g. when MaxConnectionsPerServer is enabled.
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionBase.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionBase.cs
index c96f56b2906543..df8191b7402784 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionBase.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionBase.cs
@@ -7,6 +7,7 @@
 using System.Net.Http.Headers;
 using System.Net.Security;
 using System.Runtime.CompilerServices;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -20,19 +21,19 @@ internal abstract class HttpConnectionBase : IHttpTrace
         private string? _lastServerHeaderValue;
 
         /// <summary>Uses <see cref="HeaderDescriptor.GetHeaderValue"/>, but first special-cases several known headers for which we can use caching.</summary>
-        public string GetResponseHeaderValueWithCaching(HeaderDescriptor descriptor, ReadOnlySpan<byte> value)
+        public string GetResponseHeaderValueWithCaching(HeaderDescriptor descriptor, ReadOnlySpan<byte> value, Encoding? valueEncoding)
         {
             return
-                ReferenceEquals(descriptor.KnownHeader, KnownHeaders.Date) ? GetOrAddCachedValue(ref _lastDateHeaderValue, descriptor, value) :
-                ReferenceEquals(descriptor.KnownHeader, KnownHeaders.Server) ? GetOrAddCachedValue(ref _lastServerHeaderValue, descriptor, value) :
-                descriptor.GetHeaderValue(value);
+                ReferenceEquals(descriptor.KnownHeader, KnownHeaders.Date) ? GetOrAddCachedValue(ref _lastDateHeaderValue, descriptor, value, valueEncoding) :
+                ReferenceEquals(descriptor.KnownHeader, KnownHeaders.Server) ? GetOrAddCachedValue(ref _lastServerHeaderValue, descriptor, value, valueEncoding) :
+                descriptor.GetHeaderValue(value, valueEncoding);
 
-            static string GetOrAddCachedValue([NotNull] ref string? cache, HeaderDescriptor descriptor, ReadOnlySpan<byte> value)
+            static string GetOrAddCachedValue([NotNull] ref string? cache, HeaderDescriptor descriptor, ReadOnlySpan<byte> value, Encoding? encoding)
             {
                 string? lastValue = cache;
                 if (lastValue is null || !ByteArrayHelpers.EqualsOrdinalAscii(lastValue, value))
                 {
-                    cache = lastValue = descriptor.GetHeaderValue(value);
+                    cache = lastValue = descriptor.GetHeaderValue(value, encoding);
                 }
                 return lastValue;
             }
@@ -111,7 +112,7 @@ internal static void IgnoreExceptions(ValueTask<int> task)
             }
             else
             {
-                task.AsTask().ContinueWith(t => _ = t.Exception,
+                task.AsTask().ContinueWith(static t => _ = t.Exception,
                     CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously | TaskContinuationOptions.OnlyOnFaulted, TaskScheduler.Default);
             }
         }
@@ -128,7 +129,7 @@ internal void LogExceptions(Task task)
             }
             else
             {
-                task.ContinueWith((t, state) => LogFaulted((HttpConnectionBase)state!, t), this,
+                task.ContinueWith(static (t, state) => LogFaulted((HttpConnectionBase)state!, t), this,
                     CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously | TaskContinuationOptions.OnlyOnFaulted, TaskScheduler.Default);
             }
 
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs
index 94989785eb4cee..e2c2e366424871 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs
@@ -6,6 +6,7 @@
 using System.Diagnostics;
 using System.Globalization;
 using System.IO;
+using System.Net.Connections;
 using System.Net.Http.Headers;
 using System.Net.Http.HPack;
 using System.Net.Http.QPack;
@@ -66,7 +67,8 @@ internal sealed class HttpConnectionPool : IDisposable
         private readonly int _maxConnections;
 
         private bool _http2Enabled;
-        private Http2Connection? _http2Connection;
+        // This array must be treated as immutable. It can only be replaced with a new value in AddHttp2Connection method.
+        private volatile Http2Connection[]? _http2Connections;
         private SemaphoreSlim? _http2ConnectionCreateLock;
         private byte[]? _http2AltSvcOriginUri;
         internal readonly byte[]? _http2EncodedAuthorityHostHeader;
@@ -122,7 +124,7 @@ public HttpConnectionPool(HttpConnectionPoolManager poolManager, HttpConnectionK
             }
 
             _http2Enabled = _poolManager.Settings._maxHttpVersion >= HttpVersion.Version20;
-            _http3Enabled = _poolManager.Settings._maxHttpVersion >= HttpVersion.Version30;
+            _http3Enabled = _poolManager.Settings._maxHttpVersion >= Http3Connection.HttpVersion30;
 
             switch (kind)
             {
@@ -257,7 +259,7 @@ public HttpConnectionPool(HttpConnectionPoolManager poolManager, HttpConnectionK
             if (NetEventSource.Log.IsEnabled()) Trace($"{this}");
         }
 
-        private static readonly List<SslApplicationProtocol> s_http3ApplicationProtocols = new List<SslApplicationProtocol>() { SslApplicationProtocol.Http3 };
+        private static readonly List<SslApplicationProtocol> s_http3ApplicationProtocols = new List<SslApplicationProtocol>() { Http3Connection.Http3ApplicationProtocol };
         private static readonly List<SslApplicationProtocol> s_http2ApplicationProtocols = new List<SslApplicationProtocol>() { SslApplicationProtocol.Http2, SslApplicationProtocol.Http11 };
 
         private static SslClientAuthenticationOptions ConstructSslOptions(HttpConnectionPoolManager poolManager, string sslHostName)
@@ -329,6 +331,8 @@ public byte[] Http2AltSvcOriginUri
             }
         }
 
+        public bool EnableMultipleHttp2Connections => _poolManager.Settings.EnableMultipleHttp2Connections;
+
         /// <summary>Object used to synchronize access to state in the pool.</summary>
         private object SyncObj => _idleConnections;
 
@@ -483,24 +487,14 @@ public byte[] Http2AltSvcOriginUri
             Debug.Assert(_kind == HttpConnectionKind.Https || _kind == HttpConnectionKind.SslProxyTunnel || _kind == HttpConnectionKind.Http);
 
             // See if we have an HTTP2 connection
-            Http2Connection? http2Connection = _http2Connection;
+            Http2Connection? http2Connection = GetExistingHttp2Connection();
 
             if (http2Connection != null)
             {
-                TimeSpan pooledConnectionLifetime = _poolManager.Settings._pooledConnectionLifetime;
-                if (http2Connection.LifetimeExpired(Environment.TickCount64, pooledConnectionLifetime))
-                {
-                    // Connection expired.
-                    http2Connection.Dispose();
-                    InvalidateHttp2Connection(http2Connection);
-                }
-                else
-                {
-                    // Connection exist and it is still good to use.
-                    if (NetEventSource.Log.IsEnabled()) Trace("Using existing HTTP2 connection.");
-                    _usedSinceLastCleanup = true;
-                    return (http2Connection, false, null);
-                }
+                // Connection exists and it is still good to use.
+                if (NetEventSource.Log.IsEnabled()) Trace("Using existing HTTP2 connection.");
+                _usedSinceLastCleanup = true;
+                return (http2Connection, false, null);
             }
 
             // Ensure that the connection creation semaphore is created
@@ -516,7 +510,7 @@ public byte[] Http2AltSvcOriginUri
             }
 
             // Try to establish an HTTP2 connection
-            Socket? socket = null;
+            Connection? connection = null;
             SslStream? sslStream = null;
             TransportContext? transportContext = null;
 
@@ -524,16 +518,10 @@ public byte[] Http2AltSvcOriginUri
             await _http2ConnectionCreateLock.WaitAsync(cancellationToken).ConfigureAwait(false);
             try
             {
-                if (_http2Connection != null)
+                http2Connection = GetExistingHttp2Connection();
+                if (http2Connection != null)
                 {
-                    // Someone beat us to it
-
-                    if (NetEventSource.Log.IsEnabled())
-                    {
-                        Trace("Using existing HTTP2 connection.");
-                    }
-
-                    return (_http2Connection, false, null);
+                    return (http2Connection, false, null);
                 }
 
                 // Recheck if HTTP2 has been disabled by a previous attempt.
@@ -544,32 +532,42 @@ public byte[] Http2AltSvcOriginUri
                         Trace("Attempting new HTTP2 connection.");
                     }
 
-                    Stream? stream;
                     HttpResponseMessage? failureResponse;
-                    (socket, stream, transportContext, failureResponse) =
+
+                    (connection, transportContext, failureResponse) =
                         await ConnectAsync(request, async, true, cancellationToken).ConfigureAwait(false);
+
                     if (failureResponse != null)
                     {
                         return (null, true, failureResponse);
                     }
 
+                    Debug.Assert(connection != null);
+
+                    sslStream = connection.Stream as SslStream;
+
+                    if (Settings._plaintextFilter != null)
+                    {
+                        connection = await Settings._plaintextFilter(request, connection, cancellationToken).ConfigureAwait(false);
+                    }
+
                     if (_kind == HttpConnectionKind.Http)
                     {
-                        http2Connection = new Http2Connection(this, stream!);
+                        http2Connection = new Http2Connection(this, connection);
                         await http2Connection.SetupAsync().ConfigureAwait(false);
 
-                        Debug.Assert(_http2Connection == null);
-                        _http2Connection = http2Connection;
+                        AddHttp2Connection(http2Connection);
 
                         if (NetEventSource.Log.IsEnabled())
                         {
                             Trace("New unencrypted HTTP2 connection established.");
                         }
 
-                        return (_http2Connection, true, null);
+                        return (http2Connection, true, null);
                     }
 
-                    sslStream = (SslStream)stream!;
+                    Debug.Assert(sslStream != null);
+
                     if (sslStream.NegotiatedApplicationProtocol == SslApplicationProtocol.Http2)
                     {
                         // The server accepted our request for HTTP2.
@@ -579,18 +577,17 @@ public byte[] Http2AltSvcOriginUri
                             throw new HttpRequestException(SR.Format(SR.net_ssl_http2_requires_tls12, sslStream.SslProtocol));
                         }
 
-                        http2Connection = new Http2Connection(this, sslStream);
+                        http2Connection = new Http2Connection(this, connection);
                         await http2Connection.SetupAsync().ConfigureAwait(false);
 
-                        Debug.Assert(_http2Connection == null);
-                        _http2Connection = http2Connection;
+                        AddHttp2Connection(http2Connection);
 
                         if (NetEventSource.Log.IsEnabled())
                         {
                             Trace("New HTTP2 connection established.");
                         }
 
-                        return (_http2Connection, true, null);
+                        return (http2Connection, true, null);
                     }
                 }
             }
@@ -631,7 +628,7 @@ public byte[] Http2AltSvcOriginUri
 
                 if (canUse)
                 {
-                    return (ConstructHttp11Connection(socket, sslStream, transportContext), true, null);
+                    return (ConstructHttp11Connection(connection!, transportContext), true, null);
                 }
                 else
                 {
@@ -640,7 +637,7 @@ public byte[] Http2AltSvcOriginUri
                         Trace("Discarding downgraded HTTP/1.1 connection because connection limit is exceeded");
                     }
 
-                    sslStream.Close();
+                    await connection!.CloseAsync(ConnectionCloseMethod.GracefulShutdown, cancellationToken).ConfigureAwait(false);
                 }
             }
 
@@ -648,6 +645,53 @@ public byte[] Http2AltSvcOriginUri
             return await GetHttpConnectionAsync(request, async, cancellationToken).ConfigureAwait(false);
         }
 
+        private Http2Connection? GetExistingHttp2Connection()
+        {
+            Http2Connection[]? localConnections = _http2Connections;
+
+            if (localConnections == null)
+            {
+                return null;
+            }
+
+            for (int i = 0; i < localConnections.Length; i++)
+            {
+                Http2Connection http2Connection = localConnections[i];
+
+                TimeSpan pooledConnectionLifetime = _poolManager.Settings._pooledConnectionLifetime;
+                if (http2Connection.LifetimeExpired(Environment.TickCount64, pooledConnectionLifetime))
+                {
+                    // Connection expired.
+                    http2Connection.Dispose();
+                    InvalidateHttp2Connection(http2Connection);
+                }
+                else if (!EnableMultipleHttp2Connections || http2Connection.CanAddNewStream)
+                {
+                    return http2Connection;
+                }
+            }
+
+            return null;
+        }
+
+        private void AddHttp2Connection(Http2Connection newConnection)
+        {
+            lock (SyncObj)
+            {
+                Http2Connection[]? localHttp2Connections = _http2Connections;
+                int newCollectionSize = localHttp2Connections == null ? 1 : localHttp2Connections.Length + 1;
+                Http2Connection[] newHttp2Connections = new Http2Connection[newCollectionSize];
+                newHttp2Connections[0] = newConnection;
+
+                if (localHttp2Connections != null)
+                {
+                    Array.Copy(localHttp2Connections, 0, newHttp2Connections, 1, localHttp2Connections.Length);
+                }
+
+                _http2Connections = newHttp2Connections;
+            }
+        }
+
         private async ValueTask<(HttpConnectionBase? connection, bool isNewConnection, HttpResponseMessage? failureResponse)>
             GetHttp3ConnectionAsync(HttpRequestMessage request, HttpAuthority authority, CancellationToken cancellationToken)
         {
@@ -794,6 +838,16 @@ public async ValueTask<HttpResponseMessage> SendWithRetryAsync(HttpRequestMessag
                     // Eat exception and try again.
                     continue;
                 }
+                catch (HttpRequestException e) when (e.AllowRetry == RequestRetryType.RetryOnNextConnection)
+                {
+                    if (NetEventSource.Log.IsEnabled())
+                    {
+                        Trace($"Retrying request on another HTTP/2 connection after active streams limit is reached on existing one: {e}");
+                    }
+
+                    // Eat exception and try again.
+                    continue;
+                }
 
                 // Check for the Alt-Svc header, to upgrade to HTTP/3.
                 if (_altSvcEnabled && response.Headers.TryGetValues(KnownHeaders.AltSvc.Descriptor, out IEnumerable<string>? altSvcHeaderValues))
@@ -829,7 +883,7 @@ internal void HandleAltSvc(IEnumerable<string> altSvcHeaderValues, TimeSpan? res
             {
                 int parseIdx = 0;
 
-                while (AltSvcHeaderParser.Parser.TryParseValue(altSvcHeaderValue, null, ref parseIdx, out object? parsedValue))
+                if (AltSvcHeaderParser.Parser.TryParseValue(altSvcHeaderValue, null, ref parseIdx, out object? parsedValue))
                 {
                     var value = (AltSvcHeaderValue?)parsedValue;
 
@@ -900,7 +954,7 @@ internal void HandleAltSvc(IEnumerable<string> altSvcHeaderValues, TimeSpan? res
                                 restoreFlow = true;
                             }
 
-                            _authorityExpireTimer = new Timer(o =>
+                            _authorityExpireTimer = new Timer(static o =>
                             {
                                 var wr = (WeakReference<HttpConnectionPool>)o!;
                                 if (wr.TryGetTarget(out HttpConnectionPool? @this))
@@ -1082,7 +1136,7 @@ public ValueTask<HttpResponseMessage> SendAsync(HttpRequestMessage request, bool
             return SendWithProxyAuthAsync(request, async, doRequestAuth, cancellationToken);
         }
 
-        private async ValueTask<(Socket?, Stream?, TransportContext?, HttpResponseMessage?)> ConnectAsync(HttpRequestMessage request, bool async, bool allowHttp2, CancellationToken cancellationToken)
+        private async ValueTask<(Connection?, TransportContext?, HttpResponseMessage?)> ConnectAsync(HttpRequestMessage request, bool async, bool allowHttp2, CancellationToken cancellationToken)
         {
             // If a non-infinite connect timeout has been set, create and use a new CancellationToken that will be canceled
             // when either the original token is canceled or a connect timeout occurs.
@@ -1096,44 +1150,44 @@ public ValueTask<HttpResponseMessage> SendAsync(HttpRequestMessage request, bool
 
             try
             {
-                Stream? stream = null;
+                Connection? connection = null;
                 switch (_kind)
                 {
                     case HttpConnectionKind.Http:
                     case HttpConnectionKind.Https:
                     case HttpConnectionKind.ProxyConnect:
                         Debug.Assert(_originAuthority != null);
-                        stream = await ConnectHelper.ConnectAsync(_originAuthority.IdnHost, _originAuthority.Port, async, cancellationToken).ConfigureAwait(false);
+                        connection = await ConnectToTcpHostAsync(_originAuthority.IdnHost, _originAuthority.Port, request, async, cancellationToken).ConfigureAwait(false);
                         break;
 
                     case HttpConnectionKind.Proxy:
-                        stream = await ConnectHelper.ConnectAsync(_proxyUri!.IdnHost, _proxyUri.Port, async, cancellationToken).ConfigureAwait(false);
+                        connection = await ConnectToTcpHostAsync(_proxyUri!.IdnHost, _proxyUri.Port, request, async, cancellationToken).ConfigureAwait(false);
                         break;
 
                     case HttpConnectionKind.ProxyTunnel:
                     case HttpConnectionKind.SslProxyTunnel:
                         HttpResponseMessage? response;
-                        (stream, response) = await EstablishProxyTunnel(async, request.HasHeaders ? request.Headers : null, cancellationToken).ConfigureAwait(false);
+                        (connection, response) = await EstablishProxyTunnel(async, request.HasHeaders ? request.Headers : null, cancellationToken).ConfigureAwait(false);
                         if (response != null)
                         {
                             // Return non-success response from proxy.
                             response.RequestMessage = request;
-                            return (null, null, null, response);
+                            return (null, null, response);
                         }
                         break;
                 }
 
-                Socket? socket = (stream as NetworkStream)?.Socket;
+                Debug.Assert(connection != null);
 
                 TransportContext? transportContext = null;
                 if (_kind == HttpConnectionKind.Https || _kind == HttpConnectionKind.SslProxyTunnel)
                 {
-                    SslStream sslStream = await ConnectHelper.EstablishSslConnectionAsync(allowHttp2 ? _sslOptionsHttp2! : _sslOptionsHttp11!, request, async, stream!, cancellationToken).ConfigureAwait(false);
-                    stream = sslStream;
+                    SslStream sslStream = await ConnectHelper.EstablishSslConnectionAsync(allowHttp2 ? _sslOptionsHttp2! : _sslOptionsHttp11!, request, async, connection.Stream, cancellationToken).ConfigureAwait(false);
+                    connection = Connection.FromStream(sslStream, leaveOpen: false, connection.ConnectionProperties, connection.LocalEndPoint, connection.RemoteEndPoint);
                     transportContext = sslStream.TransportContext;
                 }
 
-                return (socket, stream, transportContext, null);
+                return (connection, transportContext, null);
             }
             finally
             {
@@ -1141,9 +1195,37 @@ public ValueTask<HttpResponseMessage> SendAsync(HttpRequestMessage request, bool
             }
         }
 
+        private ValueTask<Connection> ConnectToTcpHostAsync(string host, int port, HttpRequestMessage initialRequest, bool async, CancellationToken cancellationToken)
+        {
+            if (async)
+            {
+                ConnectionFactory connectionFactory = Settings._connectionFactory ?? SocketsHttpConnectionFactory.Default;
+
+                var endPoint = new DnsEndPointWithProperties(host, port, initialRequest);
+                return ConnectHelper.ConnectAsync(connectionFactory, endPoint, endPoint, cancellationToken);
+            }
+
+            // Synchronous path.
+
+            if (Settings._connectionFactory != null)
+            {
+                // connection factories only support async.
+                throw new HttpRequestException();
+            }
+
+            try
+            {
+                return new ValueTask<Connection>(ConnectHelper.Connect(host, port, cancellationToken));
+            }
+            catch (Exception ex)
+            {
+                return ValueTask.FromException<Connection>(ex);
+            }
+        }
+
         internal async ValueTask<(HttpConnection?, HttpResponseMessage?)> CreateHttp11ConnectionAsync(HttpRequestMessage request, bool async, CancellationToken cancellationToken)
         {
-            (Socket? socket, Stream? stream, TransportContext? transportContext, HttpResponseMessage? failureResponse) =
+            (Connection? connection, TransportContext? transportContext, HttpResponseMessage? failureResponse) =
                 await ConnectAsync(request, async, false, cancellationToken).ConfigureAwait(false);
 
             if (failureResponse != null)
@@ -1151,18 +1233,18 @@ public ValueTask<HttpResponseMessage> SendAsync(HttpRequestMessage request, bool
                 return (null, failureResponse);
             }
 
-            return (ConstructHttp11Connection(socket, stream!, transportContext), null);
+            return (ConstructHttp11Connection(connection!, transportContext), null);
         }
 
-        private HttpConnection ConstructHttp11Connection(Socket? socket, Stream stream, TransportContext? transportContext)
+        private HttpConnection ConstructHttp11Connection(Connection connection, TransportContext? transportContext)
         {
             return _maxConnections == int.MaxValue ?
-                new HttpConnection(this, socket, stream, transportContext) :
-                new HttpConnectionWithFinalizer(this, socket, stream, transportContext); // finalizer needed to signal the pool when a connection is dropped
+                new HttpConnection(this, connection, transportContext) :
+                new HttpConnectionWithFinalizer(this, connection, transportContext); // finalizer needed to signal the pool when a connection is dropped
         }
 
         // Returns the established stream or an HttpResponseMessage from the proxy indicating failure.
-        private async ValueTask<(Stream?, HttpResponseMessage?)> EstablishProxyTunnel(bool async, HttpRequestHeaders? headers, CancellationToken cancellationToken)
+        private async ValueTask<(Connection?, HttpResponseMessage?)> EstablishProxyTunnel(bool async, HttpRequestHeaders? headers, CancellationToken cancellationToken)
         {
             Debug.Assert(_originAuthority != null);
             // Send a CONNECT request to the proxy server to establish a tunnel.
@@ -1181,7 +1263,12 @@ private HttpConnection ConstructHttp11Connection(Socket? socket, Stream stream,
                 return (null, tunnelResponse);
             }
 
-            return (tunnelResponse.Content!.ReadAsStream(cancellationToken), null);
+            Stream stream = tunnelResponse.Content.ReadAsStream(cancellationToken);
+            EndPoint remoteEndPoint = new DnsEndPoint(_originAuthority.IdnHost, _originAuthority.Port);
+
+            // TODO: the Socket from the response can be funneled into a connection property here.
+
+            return (Connection.FromStream(stream, remoteEndPoint: remoteEndPoint), null);
         }
 
         /// <summary>Enqueues a waiter to the waiters list.</summary>
@@ -1355,9 +1442,39 @@ public void InvalidateHttp2Connection(Http2Connection connection)
         {
             lock (SyncObj)
             {
-                if (_http2Connection == connection)
+                Http2Connection[]? localHttp2Connections = _http2Connections;
+
+                if (localHttp2Connections == null)
+                {
+                    return;
+                }
+
+                if (localHttp2Connections.Length == 1)
+                {
+                    // Fast shortcut for the most common case.
+                    if (localHttp2Connections[0] == connection)
+                    {
+                        _http2Connections = null;
+                    }
+                    return;
+                }
+
+                int invalidatedIndex = Array.IndexOf(localHttp2Connections, connection);
+                if (invalidatedIndex >= 0)
                 {
-                    _http2Connection = null;
+                    Http2Connection[] newHttp2Connections = new Http2Connection[localHttp2Connections.Length - 1];
+
+                    if (invalidatedIndex > 0)
+                    {
+                        Array.Copy(localHttp2Connections, newHttp2Connections, invalidatedIndex);
+                    }
+
+                    if (invalidatedIndex < localHttp2Connections.Length - 1)
+                    {
+                        Array.Copy(localHttp2Connections, invalidatedIndex + 1, newHttp2Connections, invalidatedIndex, newHttp2Connections.Length - invalidatedIndex);
+                    }
+
+                    _http2Connections = newHttp2Connections;
                 }
             }
         }
@@ -1389,10 +1506,13 @@ public void Dispose()
                     list.ForEach(c => c._connection.Dispose());
                     list.Clear();
 
-                    if (_http2Connection != null)
+                    if (_http2Connections != null)
                     {
-                        _http2Connection.Dispose();
-                        _http2Connection = null;
+                        for (int i = 0; i < _http2Connections.Length; i++)
+                        {
+                            _http2Connections[i].Dispose();
+                        }
+                        _http2Connections = null;
                     }
 
                     if (_authorityExpireTimer != null)
@@ -1436,15 +1556,51 @@ public bool CleanCacheAndDisposeIfUnused()
                 // Get the current time.  This is compared against each connection's last returned
                 // time to determine whether a connection is too old and should be closed.
                 long nowTicks = Environment.TickCount64;
-                Http2Connection? http2Connection = _http2Connection;
+                // Copy the reference to a local variable to simplify the removal logic below.
+                Http2Connection[]? localHttp2Connections = _http2Connections;
 
-                if (http2Connection != null)
+                if (localHttp2Connections != null)
                 {
-                    if (http2Connection.IsExpired(nowTicks, pooledConnectionLifetime, pooledConnectionIdleTimeout))
+                    Http2Connection[]? newHttp2Connections = null;
+                    int newIndex = 0;
+                    for (int i = 0; i < localHttp2Connections.Length; i++)
                     {
-                        http2Connection.Dispose();
-                        // We can set _http2Connection directly while holding lock instead of calling InvalidateHttp2Connection().
-                        _http2Connection = null;
+                        Http2Connection http2Connection = localHttp2Connections[i];
+                        if (http2Connection.IsExpired(nowTicks, pooledConnectionLifetime, pooledConnectionIdleTimeout))
+                        {
+                            http2Connection.Dispose();
+
+                            if (newHttp2Connections == null)
+                            {
+                                newHttp2Connections = new Http2Connection[localHttp2Connections.Length];
+                                if (i > 0)
+                                {
+                                    // Copy valid connections residing at the beggining of the current collection.
+                                    Array.Copy(localHttp2Connections, newHttp2Connections, i);
+                                    newIndex = i;
+                                }
+                            }
+                        }
+                        else if (newHttp2Connections != null)
+                        {
+                            newHttp2Connections[newIndex] = localHttp2Connections[i];
+                            newIndex++;
+                        }
+                    }
+
+                    if (newHttp2Connections != null)
+                    {
+                        //Some connections have been removed, so _http2Connections must be replaced.
+                        if (newIndex > 0)
+                        {
+                            Array.Resize(ref newHttp2Connections, newIndex);
+                            _http2Connections = newHttp2Connections;
+                        }
+                        else
+                        {
+                            // All connections expired.
+                            _http2Connections = null;
+                        }
                     }
                 }
 
@@ -1493,7 +1649,7 @@ public bool CleanCacheAndDisposeIfUnused()
                     // if a pool was used since the last time we cleaned up, give it another chance. New pools
                     // start out saying they've recently been used, to give them a bit of breathing room and time
                     // for the initial collection to be added to it.
-                    if (_associatedConnectionCount == 0 && !_usedSinceLastCleanup && _http2Connection == null)
+                    if (_associatedConnectionCount == 0 && !_usedSinceLastCleanup && _http2Connections == null)
                     {
                         Debug.Assert(list.Count == 0, $"Expected {nameof(list)}.{nameof(list.Count)} == 0");
                         _disposed = true;
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPoolManager.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPoolManager.cs
index e01950ed8d0e49..67906139abd503 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPoolManager.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPoolManager.cs
@@ -102,7 +102,7 @@ public HttpConnectionPoolManager(HttpConnectionSettings settings)
                     // Create the timer.  Ensure the Timer has a weak reference to this manager; otherwise, it
                     // can introduce a cycle that keeps the HttpConnectionPoolManager rooted by the Timer
                     // implementation until the handler is Disposed (or indefinitely if it's not).
-                    _cleaningTimer = new Timer(s =>
+                    _cleaningTimer = new Timer(static s =>
                     {
                         var wr = (WeakReference<HttpConnectionPoolManager>)s!;
                         if (wr.TryGetTarget(out HttpConnectionPoolManager? thisRef))
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionSettings.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionSettings.cs
index 959f82ba83f4b4..42b67aabc31ac3 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionSettings.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionSettings.cs
@@ -2,7 +2,10 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Collections.Generic;
+using System.Net.Connections;
 using System.Net.Security;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace System.Net.Http
 {
@@ -43,6 +46,9 @@ internal sealed class HttpConnectionSettings
         internal TimeSpan _expect100ContinueTimeout = HttpHandlerDefaults.DefaultExpect100ContinueTimeout;
         internal TimeSpan _connectTimeout = HttpHandlerDefaults.DefaultConnectTimeout;
 
+        internal HeaderEncodingSelector<HttpRequestMessage>? _requestHeaderEncodingSelector;
+        internal HeaderEncodingSelector<HttpRequestMessage>? _responseHeaderEncodingSelector;
+
         internal Version _maxHttpVersion;
 
         internal bool _allowUnencryptedHttp2;
@@ -52,13 +58,18 @@ internal sealed class HttpConnectionSettings
 
         internal SslClientAuthenticationOptions? _sslOptions;
 
+        internal bool _enableMultipleHttp2Connections;
+
+        internal ConnectionFactory? _connectionFactory;
+        internal Func<HttpRequestMessage, Connection, CancellationToken, ValueTask<Connection>>? _plaintextFilter;
+
         internal IDictionary<string, object?>? _properties;
 
         public HttpConnectionSettings()
         {
             bool allowHttp2 = AllowHttp2;
             _maxHttpVersion =
-                AllowDraftHttp3 && allowHttp2 ? HttpVersion.Version30 :
+                AllowDraftHttp3 && allowHttp2 ? Http3Connection.HttpVersion30 :
                 allowHttp2 ? HttpVersion.Version20 :
                 HttpVersion.Version11;
             _allowUnencryptedHttp2 = allowHttp2 && AllowUnencryptedHttp2;
@@ -101,7 +112,12 @@ public HttpConnectionSettings CloneAndNormalize()
                 _useCookies = _useCookies,
                 _useProxy = _useProxy,
                 _allowUnencryptedHttp2 = _allowUnencryptedHttp2,
-                _assumePrenegotiatedHttp3ForTesting = _assumePrenegotiatedHttp3ForTesting
+                _assumePrenegotiatedHttp3ForTesting = _assumePrenegotiatedHttp3ForTesting,
+                _requestHeaderEncodingSelector = _requestHeaderEncodingSelector,
+                _responseHeaderEncodingSelector = _responseHeaderEncodingSelector,
+                _enableMultipleHttp2Connections = _enableMultipleHttp2Connections,
+                _connectionFactory = _connectionFactory,
+                _plaintextFilter = _plaintextFilter
             };
         }
 
@@ -183,6 +199,8 @@ private static bool AllowDraftHttp3
             }
         }
 
+        public bool EnableMultipleHttp2Connections => _enableMultipleHttp2Connections;
+
         private byte[]? _http3SettingsFrame;
         internal byte[] Http3SettingsFrame => _http3SettingsFrame ??= Http3Connection.BuildSettingsFrame(this);
     }
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocketsHttpConnectionFactory.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocketsHttpConnectionFactory.cs
new file mode 100644
index 00000000000000..34018a14170aca
--- /dev/null
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocketsHttpConnectionFactory.cs
@@ -0,0 +1,94 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Net.Connections;
+using System.Net.Sockets;
+using System.Runtime.ExceptionServices;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Http
+{
+    /// <summary>
+    /// The default connection factory used by <see cref="SocketsHttpHandler"/>, opening TCP connections.
+    /// </summary>
+    public class SocketsHttpConnectionFactory : ConnectionFactory
+    {
+        internal static SocketsHttpConnectionFactory Default { get; } = new SocketsHttpConnectionFactory();
+
+        /// <inheritdoc/>
+        public sealed override ValueTask<Connection> ConnectAsync(EndPoint? endPoint, IConnectionProperties? options = null, CancellationToken cancellationToken = default)
+        {
+            if (options == null || !options.TryGet(out DnsEndPointWithProperties? httpOptions))
+            {
+                return ValueTask.FromException<Connection>(ExceptionDispatchInfo.SetCurrentStackTrace(new HttpRequestException($"{nameof(SocketsHttpConnectionFactory)} requires a {nameof(DnsEndPointWithProperties)} property.")));
+            }
+
+            return EstablishConnectionAsync(httpOptions!.InitialRequest, endPoint, options, cancellationToken);
+        }
+
+        /// <summary>
+        /// Creates the socket to be used for a request.
+        /// </summary>
+        /// <param name="message">The request causing this socket to be opened. Once opened, it may be reused for many subsequent requests.</param>
+        /// <param name="endPoint">The EndPoint this socket will be connected to.</param>
+        /// <param name="options">Properties, if any, that might change how the socket is initialized.</param>
+        /// <returns>A new unconnected socket.</returns>
+        public virtual Socket CreateSocket(HttpRequestMessage message, EndPoint? endPoint, IConnectionProperties options)
+        {
+            return new Socket(SocketType.Stream, ProtocolType.Tcp);
+        }
+
+        /// <summary>
+        /// Establishes a new connection for a request.
+        /// </summary>
+        /// <param name="message">The request causing this connection to be established. Once connected, it may be reused for many subsequent requests.</param>
+        /// <param name="endPoint">The EndPoint to connect to.</param>
+        /// <param name="options">Properties, if any, that might change how the connection is made.</param>
+        /// <param name="cancellationToken">A cancellation token for the asynchronous operation.</param>
+        /// <returns>A new open connection.</returns>
+        public virtual async ValueTask<Connection> EstablishConnectionAsync(HttpRequestMessage message, EndPoint? endPoint, IConnectionProperties options, CancellationToken cancellationToken)
+        {
+            if (message == null) throw new ArgumentNullException(nameof(message));
+            if (endPoint == null) throw new ArgumentNullException(nameof(endPoint));
+
+            Socket socket = CreateSocket(message, endPoint, options);
+
+            try
+            {
+                using var args = new TaskSocketAsyncEventArgs();
+                args.RemoteEndPoint = endPoint;
+
+                if (socket.ConnectAsync(args))
+                {
+                    using (cancellationToken.UnsafeRegister(o => Socket.CancelConnectAsync((SocketAsyncEventArgs)o!), args))
+                    {
+                        await args.Task.ConfigureAwait(false);
+                    }
+                }
+
+                if (args.SocketError != SocketError.Success)
+                {
+                    Exception ex = args.SocketError == SocketError.OperationAborted && cancellationToken.IsCancellationRequested
+                        ? (Exception)new OperationCanceledException(cancellationToken)
+                        : new SocketException((int)args.SocketError);
+
+                    throw ex;
+                }
+
+                socket.NoDelay = true;
+                return new SocketConnection(socket);
+            }
+            catch (SocketException socketException)
+            {
+                socket.Dispose();
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
+            catch
+            {
+                socket.Dispose();
+                throw;
+            }
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocketsHttpHandler.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocketsHttpHandler.cs
index 294b0c1734b76e..73c1c3493af040 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocketsHttpHandler.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocketsHttpHandler.cs
@@ -3,10 +3,12 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Net.Connections;
 using System.Net.Security;
 using System.Threading;
 using System.Threading.Tasks;
 using System.Diagnostics.CodeAnalysis;
+using System.Text;
 
 namespace System.Net.Http
 {
@@ -33,6 +35,11 @@ private void CheckDisposedOrStarted()
             }
         }
 
+        /// <summary>
+        /// Gets a value that indicates whether the handler is supported on the current platform.
+        /// </summary>
+        public static bool IsSupported => true;
+
         public bool UseCookies
         {
             get => _settings._useCookies;
@@ -273,9 +280,83 @@ public TimeSpan Expect100ContinueTimeout
             }
         }
 
+        /// <summary>
+        /// Gets or sets a value that indicates whether additional HTTP/2 connections can be established to the same server
+        /// when the maximum of concurrent streams is reached on all existing connections.
+        /// </summary>
+        public bool EnableMultipleHttp2Connections
+        {
+            get => _settings._enableMultipleHttp2Connections;
+            set
+            {
+                CheckDisposedOrStarted();
+
+                _settings._enableMultipleHttp2Connections = value;
+            }
+        }
+
+        internal bool SupportsAutomaticDecompression => true;
+        internal bool SupportsProxy => true;
+        internal bool SupportsRedirectConfiguration => true;
+
+        /// <summary>
+        /// When non-null, a custom factory used to open new TCP connections.
+        /// When null, a <see cref="SocketsHttpConnectionFactory"/> will be used.
+        /// </summary>
+        public ConnectionFactory? ConnectionFactory
+        {
+            get => _settings._connectionFactory;
+            set
+            {
+                CheckDisposedOrStarted();
+                _settings._connectionFactory = value;
+            }
+        }
+
+        /// <summary>
+        /// When non-null, a connection filter that is applied prior to any TLS encryption.
+        /// </summary>
+        public Func<HttpRequestMessage, Connection, CancellationToken, ValueTask<Connection>>? PlaintextFilter
+        {
+            get => _settings._plaintextFilter;
+            set
+            {
+                CheckDisposedOrStarted();
+                _settings._plaintextFilter = value;
+            }
+        }
+
         public IDictionary<string, object?> Properties =>
             _settings._properties ?? (_settings._properties = new Dictionary<string, object?>());
 
+        /// <summary>
+        /// Gets or sets a callback that returns the <see cref="Encoding"/> to encode the value for the specified request header name,
+        /// or <see langword="null"/> to use the default behavior.
+        /// </summary>
+        public HeaderEncodingSelector<HttpRequestMessage>? RequestHeaderEncodingSelector
+        {
+            get => _settings._requestHeaderEncodingSelector;
+            set
+            {
+                CheckDisposedOrStarted();
+                _settings._requestHeaderEncodingSelector = value;
+            }
+        }
+
+        /// <summary>
+        /// Gets or sets a callback that returns the <see cref="Encoding"/> to decode the value for the specified response header name,
+        /// or <see langword="null"/> to use the default behavior.
+        /// </summary>
+        public HeaderEncodingSelector<HttpRequestMessage>? ResponseHeaderEncodingSelector
+        {
+            get => _settings._responseHeaderEncodingSelector;
+            set
+            {
+                CheckDisposedOrStarted();
+                _settings._responseHeaderEncodingSelector = value;
+            }
+        }
+
         protected override void Dispose(bool disposing)
         {
             if (disposing && !_disposed)
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.AltSvc.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.AltSvc.cs
index b09815bcee6b81..7fcd9372198dde 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.AltSvc.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.AltSvc.cs
@@ -20,43 +20,59 @@ public HttpClientHandler_AltSvc_Test(ITestOutputHelper output) : base(output)
         /// </summary>
         protected override HttpClient CreateHttpClient()
         {
-            HttpClientHandler handler = CreateHttpClientHandler(HttpVersion.Version30);
+            bool http3Enabled = (bool)typeof(SocketsHttpHandler)
+                .Assembly
+                .GetType("System.Net.Http.HttpConnectionSettings", throwOnError: true)
+                .GetProperty("AllowDraftHttp3", Reflection.BindingFlags.Static | Reflection.BindingFlags.NonPublic)
+                .GetValue(null);
+
+            Assert.True(http3Enabled, "HTTP/3 draft support must be enabled for this test.");
+
+            HttpClientHandler handler = CreateHttpClientHandler(HttpVersion30);
             SetUsePrenegotiatedHttp3(handler, usePrenegotiatedHttp3: false);
 
             return CreateHttpClient(handler);
         }
 
-        [Fact]
-        public async Task AltSvc_Header_UpgradeFrom11_Success()
+        [Theory]
+        [MemberData(nameof(AltSvcHeaderUpgradeVersions))]
+        public async Task AltSvc_Header_Upgrade_Success(Version fromVersion)
         {
-            await AltSvc_Header_Upgrade_Success(HttpVersion.Version11).ConfigureAwait(false);
-        }
+            // The test makes a request to a HTTP/1 or HTTP/2 server first, which supplies an Alt-Svc header pointing to the second server.
+            using GenericLoopbackServer firstServer =
+                fromVersion.Major switch
+                {
+                    1 => new LoopbackServer(new LoopbackServer.Options { UseSsl = true }),
+                    2 => Http2LoopbackServer.CreateServer(),
+                    _ => throw new Exception("Unknown HTTP version.")
+                };
+
+            // The second request is expected to come in on this HTTP/3 server.
+            using var secondServer = new Http3LoopbackServer();
 
-        [Fact]
-        public async Task AltSvc_Header_UpgradeFrom20_Success()
-        {
-            await AltSvc_Header_Upgrade_Success(HttpVersion.Version20).ConfigureAwait(false);
-        }
-
-        private async Task AltSvc_Header_Upgrade_Success(Version fromVersion)
-        {
-            using GenericLoopbackServer firstServer = GetFactoryForVersion(fromVersion).CreateServer();
-            using Http3LoopbackServer secondServer = new Http3LoopbackServer();
             using HttpClient client = CreateHttpClient();
 
             Task<HttpResponseMessage> firstResponseTask = client.GetAsync(firstServer.Address);
-
-            await firstServer.AcceptConnectionSendResponseAndCloseAsync(additionalHeaders: new[]
+            Task serverTask = firstServer.AcceptConnectionSendResponseAndCloseAsync(additionalHeaders: new[]
             {
-                new HttpHeaderData("Alt-Svc", $"h3={secondServer.Address.IdnHost}:{secondServer.Address.Port}")
+                new HttpHeaderData("Alt-Svc", $"h3=\"{secondServer.Address.IdnHost}:{secondServer.Address.Port}\"")
             });
 
-            HttpResponseMessage firstResponse = await firstResponseTask;
+            await new[] { firstResponseTask, serverTask }.WhenAllOrAnyFailed(30_000);
+
+            using HttpResponseMessage firstResponse = firstResponseTask.Result;
             Assert.True(firstResponse.IsSuccessStatusCode);
 
             await AltSvc_Upgrade_Success(firstServer, secondServer, client);
         }
 
+        public static TheoryData<Version> AltSvcHeaderUpgradeVersions =>
+            new TheoryData<Version>
+            {
+                { HttpVersion.Version11 },
+                { HttpVersion.Version20 }
+            };
+
         [Fact]
         public async Task AltSvc_ConnectionFrame_UpgradeFrom20_Success()
         {
@@ -65,15 +81,18 @@ public async Task AltSvc_ConnectionFrame_UpgradeFrom20_Success()
             using HttpClient client = CreateHttpClient();
 
             Task<HttpResponseMessage> firstResponseTask = client.GetAsync(firstServer.Address);
-
-            using (Http2LoopbackConnection connection = await firstServer.EstablishConnectionAsync())
+            Task serverTask = Task.Run(async () =>
             {
+                using Http2LoopbackConnection connection = await firstServer.EstablishConnectionAsync();
+
                 int streamId = await connection.ReadRequestHeaderAsync();
+                await connection.WriteFrameAsync(new AltSvcFrame($"https://{firstServer.Address.IdnHost}:{firstServer.Address.Port}", $"h3=\"{secondServer.Address.IdnHost}:{secondServer.Address.Port}\"", streamId: 0));
                 await connection.SendDefaultResponseAsync(streamId);
-                await connection.WriteFrameAsync(new AltSvcFrame($"https://{firstServer.Address.IdnHost}:{firstServer.Address.Port}", $"h3={secondServer.Address.IdnHost}:{secondServer.Address.Port}", 0));
-            }
+            });
+
+            await new[] { firstResponseTask, serverTask }.WhenAllOrAnyFailed(30_000);
 
-            HttpResponseMessage firstResponse = await firstResponseTask;
+            HttpResponseMessage firstResponse = firstResponseTask.Result;
             Assert.True(firstResponse.IsSuccessStatusCode);
 
             await AltSvc_Upgrade_Success(firstServer, secondServer, client);
@@ -87,16 +106,19 @@ public async Task AltSvc_ResponseFrame_UpgradeFrom20_Success()
             using HttpClient client = CreateHttpClient();
 
             Task<HttpResponseMessage> firstResponseTask = client.GetAsync(firstServer.Address);
-
-            using (Http2LoopbackConnection connection = await firstServer.EstablishConnectionAsync())
+            Task serverTask = Task.Run(async () =>
             {
+                using Http2LoopbackConnection connection = await firstServer.EstablishConnectionAsync();
+
                 int streamId = await connection.ReadRequestHeaderAsync();
                 await connection.SendDefaultResponseHeadersAsync(streamId);
-                await connection.WriteFrameAsync(new AltSvcFrame("", $"h3={secondServer.Address.IdnHost}:{secondServer.Address.Port}", streamId));
+                await connection.WriteFrameAsync(new AltSvcFrame("", $"h3=\"{secondServer.Address.IdnHost}:{secondServer.Address.Port}\"", streamId));
                 await connection.SendResponseDataAsync(streamId, Array.Empty<byte>(), true);
-            }
+            });
+
+            await new[] { firstResponseTask, serverTask }.WhenAllOrAnyFailed(30_000);
 
-            HttpResponseMessage firstResponse = await firstResponseTask;
+            HttpResponseMessage firstResponse = firstResponseTask.Result;
             Assert.True(firstResponse.IsSuccessStatusCode);
 
             await AltSvc_Upgrade_Success(firstServer, secondServer, client);
@@ -105,12 +127,15 @@ public async Task AltSvc_ResponseFrame_UpgradeFrom20_Success()
         private async Task AltSvc_Upgrade_Success(GenericLoopbackServer firstServer, Http3LoopbackServer secondServer, HttpClient client)
         {
             Task<HttpResponseMessage> secondResponseTask = client.GetAsync(firstServer.Address);
+            Task<HttpRequestData> secondRequestTask = secondServer.AcceptConnectionSendResponseAndCloseAsync();
+
+            await new[] { (Task)secondResponseTask, secondRequestTask }.WhenAllOrAnyFailed(30_000);
+
+            HttpRequestData secondRequest = secondRequestTask.Result;
+            using HttpResponseMessage secondResponse = secondResponseTask.Result;
 
-            HttpRequestData secondRequest = await secondServer.AcceptConnectionSendResponseAndCloseAsync();
             string altUsed = secondRequest.GetSingleHeaderValue("Alt-Used");
             Assert.Equal($"{secondServer.Address.IdnHost}:{secondServer.Address.Port}", altUsed);
-
-            HttpResponseMessage secondResponse = await secondResponseTask;
             Assert.True(secondResponse.IsSuccessStatusCode);
         }
     }
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Headers.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Headers.cs
index afffb680a94266..3ed0f554fc06f9 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Headers.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Headers.cs
@@ -6,6 +6,7 @@
 using System.Linq;
 using System.Net.Http.Headers;
 using System.Net.Test.Common;
+using System.Text;
 using System.Threading.Tasks;
 
 using Xunit;
@@ -332,5 +333,132 @@ await server.HandleRequestAsync(headers: new[]
                     });
                 });
         }
+
+        private static readonly (string Name, Encoding ValueEncoding, string[] Values)[] s_nonAsciiHeaders = new[]
+        {
+            ("foo",             Encoding.ASCII,     new[] { "bar" }),
+            ("header-0",        Encoding.UTF8,      new[] { "\uD83D\uDE03", "\uD83D\uDE48\uD83D\uDE49\uD83D\uDE4A" }),
+            ("Cache-Control",   Encoding.UTF8,      new[] { "no-cache" }),
+            ("header-1",        Encoding.UTF8,      new[] { "\uD83D\uDE03" }),
+            ("Some-Header1",    Encoding.Latin1,    new[] { "\uD83D\uDE03", "UTF8-best-fit-to-latin1" }),
+            ("Some-Header2",    Encoding.Latin1,    new[] { "\u00FF", "\u00C4nd", "Ascii\u00A9" }),
+            ("Some-Header3",    Encoding.ASCII,     new[] { "\u00FF", "\u00C4nd", "Ascii\u00A9", "Latin1-best-fit-to-ascii" }),
+            ("header-2",        Encoding.UTF8,      new[] { "\uD83D\uDE48\uD83D\uDE49\uD83D\uDE4A" }),
+            ("header-3",        Encoding.UTF8,      new[] { "\uFFFD" }),
+            ("header-4",        Encoding.UTF8,      new[] { "\uD83D\uDE48\uD83D\uDE49\uD83D\uDE4A", "\uD83D\uDE03" }),
+            ("Cookie",          Encoding.UTF8,      new[] { "Cookies", "\uD83C\uDF6A", "everywhere" }),
+            ("Set-Cookie",      Encoding.UTF8,      new[] { "\uD83C\uDDF8\uD83C\uDDEE" }),
+            ("header-5",        Encoding.UTF8,      new[] { "\uD83D\uDE48\uD83D\uDE49\uD83D\uDE4A", "foo", "\uD83D\uDE03", "bar" }),
+            ("bar",             Encoding.UTF8,      new[] { "foo" })
+        };
+
+        [Fact]
+        public async Task SendAsync_CustomRequestEncodingSelector_CanSendNonAsciiHeaderValues()
+        {
+            await LoopbackServerFactory.CreateClientAndServerAsync(
+                async uri =>
+                {
+                    var requestMessage = new HttpRequestMessage(HttpMethod.Get, uri)
+                    {
+                        Version = UseVersion
+                    };
+
+                    foreach ((string name, _, string[] values) in s_nonAsciiHeaders)
+                    {
+                        requestMessage.Headers.Add(name, values);
+                    }
+
+                    List<string> seenHeaderNames = new List<string>();
+
+                    using HttpClientHandler handler = CreateHttpClientHandler();
+                    var underlyingHandler = (SocketsHttpHandler)GetUnderlyingSocketsHttpHandler(handler);
+
+                    underlyingHandler.RequestHeaderEncodingSelector = (name, request) =>
+                    {
+                        Assert.NotNull(name);
+                        Assert.Same(request, requestMessage);
+                        seenHeaderNames.Add(name);
+                        return Assert.Single(s_nonAsciiHeaders, h => h.Name.Equals(name, StringComparison.OrdinalIgnoreCase)).ValueEncoding;
+                    };
+
+                    using HttpClient client = CreateHttpClient(handler);
+
+                    await client.SendAsync(requestMessage);
+
+                    foreach ((string name, _, _) in s_nonAsciiHeaders)
+                    {
+                        Assert.Contains(name, seenHeaderNames);
+                    }
+                },
+                async server =>
+                {
+                    HttpRequestData requestData = await server.HandleRequestAsync();
+
+                    Assert.All(requestData.Headers,
+                        h => Assert.False(h.HuffmanEncoded, "Expose raw decoded bytes once HuffmanEncoding is supported"));
+
+                    foreach ((string name, Encoding valueEncoding, string[] values) in s_nonAsciiHeaders)
+                    {
+                        byte[] valueBytes = valueEncoding.GetBytes(string.Join(", ", values));
+                        Assert.Single(requestData.Headers,
+                            h => h.Name.Equals(name, StringComparison.OrdinalIgnoreCase) && h.Raw.AsSpan().IndexOf(valueBytes) != -1);
+                    }
+                });
+        }
+
+        [Fact]
+        public async Task SendAsync_CustomResponseEncodingSelector_CanReceiveNonAsciiHeaderValues()
+        {
+            await LoopbackServerFactory.CreateClientAndServerAsync(
+                async uri =>
+                {
+                    var requestMessage = new HttpRequestMessage(HttpMethod.Get, uri)
+                    {
+                        Version = UseVersion
+                    };
+
+                    List<string> seenHeaderNames = new List<string>();
+
+                    using HttpClientHandler handler = CreateHttpClientHandler();
+                    var underlyingHandler = (SocketsHttpHandler)GetUnderlyingSocketsHttpHandler(handler);
+
+                    underlyingHandler.ResponseHeaderEncodingSelector = (name, request) =>
+                    {
+                        Assert.NotNull(name);
+                        Assert.Same(request, requestMessage);
+                        seenHeaderNames.Add(name);
+
+                        if (s_nonAsciiHeaders.Any(h => h.Name.Equals(name, StringComparison.OrdinalIgnoreCase)))
+                        {
+                            return Assert.Single(s_nonAsciiHeaders, h => h.Name.Equals(name, StringComparison.OrdinalIgnoreCase)).ValueEncoding;
+                        }
+
+                        // Not one of our custom headers
+                        return null;
+                    };
+
+                    using HttpClient client = CreateHttpClient(handler);
+
+                    using HttpResponseMessage response = await client.SendAsync(requestMessage);
+
+                    foreach ((string name, Encoding valueEncoding, string[] values) in s_nonAsciiHeaders)
+                    {
+                        Assert.Contains(name, seenHeaderNames);
+                        IEnumerable<string> receivedValues = Assert.Single(response.Headers, h => h.Key.Equals(name, StringComparison.OrdinalIgnoreCase)).Value;
+                        string value = Assert.Single(receivedValues);
+
+                        string expected = valueEncoding.GetString(valueEncoding.GetBytes(string.Join(", ", values)));
+                        Assert.Equal(expected, value, StringComparer.OrdinalIgnoreCase);
+                    }
+                },
+                async server =>
+                {
+                    List<HttpHeaderData> headerData = s_nonAsciiHeaders
+                        .Select(h => new HttpHeaderData(h.Name, string.Join(", ", h.Values), valueEncoding: h.ValueEncoding))
+                        .ToList();
+
+                    await server.HandleRequestAsync(headers: headerData);
+                });
+        }
     }
 }
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Http2.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Http2.cs
index a0cfd9a88d0465..defa4719d64fd7 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Http2.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Http2.cs
@@ -78,7 +78,7 @@ public async Task Http2_ClientPreface_Sent()
 
                 string connectionPreface = (await server.AcceptConnectionAsync()).PrefixString;
 
-                Assert.Equal("PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n", connectionPreface);
+                Assert.Equal(Http2LoopbackConnection.Http2Prefix, connectionPreface);
             }
         }
 
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Http3.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Http3.cs
index 145ecd06a11dc5..27d4b77c536a14 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Http3.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Http3.cs
@@ -19,7 +19,7 @@ namespace System.Net.Http.Functional.Tests
 {
     public abstract class HttpClientHandlerTest_Http3 : HttpClientHandlerTestBase
     {
-        protected override Version UseVersion => HttpVersion.Version30;
+        protected override Version UseVersion => HttpVersion30;
 
         public static bool SupportsAlpn => PlatformDetection.SupportsAlpn;
 
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTestBase.SocketsHttpHandler.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTestBase.SocketsHttpHandler.cs
index 90fa26e8fe75e8..bc718b29d66787 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTestBase.SocketsHttpHandler.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTestBase.SocketsHttpHandler.cs
@@ -22,7 +22,7 @@ protected static HttpClientHandler CreateHttpClientHandler(Version useVersion =
                 handler.ServerCertificateCustomValidationCallback = TestHelper.AllowAllCertificates;
             }
 
-            if (useVersion == HttpVersion.Version30)
+            if (useVersion == HttpVersion30)
             {
                 SetUsePrenegotiatedHttp3(handler, usePrenegotiatedHttp3: true);
             }
@@ -45,5 +45,11 @@ protected static object GetUnderlyingSocketsHttpHandler(HttpClientHandler handle
             FieldInfo field = typeof(HttpClientHandler).GetField("_underlyingHandler", BindingFlags.Instance | BindingFlags.NonPublic);
             return field?.GetValue(handler);
         }
+
+        protected static HttpRequestMessage CreateRequest(HttpMethod method, Uri uri, Version version, bool exactVersion = false) =>
+            new HttpRequestMessage(method, uri)
+            {
+                Version = version,
+            };
     }
 }
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientMiniStressTest.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientMiniStressTest.cs
index 8a316d0a97393a..5c89f6969e08ef 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientMiniStressTest.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientMiniStressTest.cs
@@ -35,7 +35,7 @@ public void CreateAndDestroyManyClients(int numClients)
     public sealed class SocketsHttpHandler_HttpClientMiniStress_Http3 : HttpClientMiniStress
     {
         public SocketsHttpHandler_HttpClientMiniStress_Http3(ITestOutputHelper output) : base(output) { }
-        protected override Version UseVersion => HttpVersion.Version30;
+        protected override Version UseVersion => HttpVersion30;
     }
 
     public sealed class SocketsHttpHandler_HttpClientMiniStress_Http2 : HttpClientMiniStress
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientTest.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientTest.cs
index 5a23a73ef5f246..0074a06bc65725 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientTest.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientTest.cs
@@ -873,6 +873,7 @@ await server.AcceptConnectionAsync(async connection =>
 
         [Fact]
         [OuterLoop]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/39056")]
         public async Task Send_TimeoutRequestContent_Throws()
         {
             await LoopbackServer.CreateClientAndServerAsync(
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpRequestMessageTest.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpRequestMessageTest.cs
index 5e8928b7db9f25..8f5ff80d998d27 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/HttpRequestMessageTest.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/HttpRequestMessageTest.cs
@@ -154,7 +154,7 @@ public void Properties_SetPropertiesAndGetTheirValue_MatchingValues()
             Assert.Equal(version, rm.Version);
 
             Assert.NotNull(rm.Headers);
-            Assert.NotNull(rm.Properties);
+            Assert.NotNull(rm.Options);
         }
 
         [Fact]
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/MsQuicTests.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/MsQuicTests.cs
index a8a5b93855a4bb..76fe3c5277e749 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/MsQuicTests.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/MsQuicTests.cs
@@ -215,42 +215,76 @@ public async Task MultipleStreamsOnSingleConnection()
             await (new[] { listenTask, clientTask }).WhenAllOrAnyFailed(millisecondsTimeout: 60000);
         }
 
+        [Fact]
+        public async Task TestConnect()
+        {
+            SslServerAuthenticationOptions serverOpts = GetSslServerAuthenticationOptions();
+
+            using QuicListener listener = new QuicListener(
+                QuicImplementationProviders.MsQuic,
+                new IPEndPoint(IPAddress.Loopback, 0),
+                serverOpts);
+
+            listener.Start();
+            IPEndPoint listenEndPoint = listener.ListenEndPoint;
+            Assert.NotEqual(0, listenEndPoint.Port);
+
+            using QuicConnection clientConnection = new QuicConnection(
+                QuicImplementationProviders.MsQuic,
+                listenEndPoint,
+                GetSslClientAuthenticationOptions());
+
+            Assert.False(clientConnection.Connected);
+            Assert.Equal(listenEndPoint, clientConnection.RemoteEndPoint);
+
+            ValueTask connectTask = clientConnection.ConnectAsync();
+            QuicConnection serverConnection = await listener.AcceptConnectionAsync();
+            await connectTask;
+
+            Assert.True(clientConnection.Connected);
+            Assert.True(serverConnection.Connected);
+            Assert.Equal(listenEndPoint, serverConnection.LocalEndPoint);
+            Assert.Equal(listenEndPoint, clientConnection.RemoteEndPoint);
+            Assert.Equal(clientConnection.LocalEndPoint, serverConnection.RemoteEndPoint);
+            Assert.Equal(serverOpts.ApplicationProtocols[0].ToString(), clientConnection.NegotiatedApplicationProtocol.ToString());
+            Assert.Equal(serverOpts.ApplicationProtocols[0].ToString(), serverConnection.NegotiatedApplicationProtocol.ToString());
+        }
+
         [Fact]
         public async Task TestStreams()
         {
-            using (QuicListener listener = new QuicListener(
+            using QuicListener listener = new QuicListener(
                 QuicImplementationProviders.MsQuic,
                 new IPEndPoint(IPAddress.Loopback, 0),
-                GetSslServerAuthenticationOptions()))
-            {
-                listener.Start();
-                IPEndPoint listenEndPoint = listener.ListenEndPoint;
+                GetSslServerAuthenticationOptions());
 
-                using (QuicConnection clientConnection = new QuicConnection(
-                    QuicImplementationProviders.MsQuic,
-                    listenEndPoint,
-                    sslClientAuthenticationOptions: new SslClientAuthenticationOptions { ApplicationProtocols = new List<SslApplicationProtocol>() { new SslApplicationProtocol("quictest") } }))
-                {
-                    Assert.False(clientConnection.Connected);
-                    Assert.Equal(listenEndPoint, clientConnection.RemoteEndPoint);
-
-                    ValueTask connectTask = clientConnection.ConnectAsync();
-                    QuicConnection serverConnection = await listener.AcceptConnectionAsync();
-                    await connectTask;
-
-                    Assert.True(clientConnection.Connected);
-                    Assert.True(serverConnection.Connected);
-                    Assert.Equal(listenEndPoint, serverConnection.LocalEndPoint);
-                    Assert.Equal(listenEndPoint, clientConnection.RemoteEndPoint);
-                    Assert.Equal(clientConnection.LocalEndPoint, serverConnection.RemoteEndPoint);
-
-                    await CreateAndTestBidirectionalStream(clientConnection, serverConnection);
-                    await CreateAndTestBidirectionalStream(serverConnection, clientConnection);
-                    await CreateAndTestUnidirectionalStream(serverConnection, clientConnection);
-                    await CreateAndTestUnidirectionalStream(clientConnection, serverConnection);
-                    await clientConnection.CloseAsync(errorCode: 0);
-                }
-            }
+            listener.Start();
+            IPEndPoint listenEndPoint = listener.ListenEndPoint;
+            Assert.NotEqual(0, listenEndPoint.Port);
+
+            using QuicConnection clientConnection = new QuicConnection(
+                QuicImplementationProviders.MsQuic,
+                listenEndPoint,
+                GetSslClientAuthenticationOptions());
+
+            Assert.False(clientConnection.Connected);
+            Assert.Equal(listenEndPoint, clientConnection.RemoteEndPoint);
+
+            ValueTask connectTask = clientConnection.ConnectAsync();
+            QuicConnection serverConnection = await listener.AcceptConnectionAsync();
+            await connectTask;
+
+            Assert.True(clientConnection.Connected);
+            Assert.True(serverConnection.Connected);
+            Assert.Equal(listenEndPoint, serverConnection.LocalEndPoint);
+            Assert.Equal(listenEndPoint, clientConnection.RemoteEndPoint);
+            Assert.Equal(clientConnection.LocalEndPoint, serverConnection.RemoteEndPoint);
+
+            await CreateAndTestBidirectionalStream(clientConnection, serverConnection);
+            await CreateAndTestBidirectionalStream(serverConnection, clientConnection);
+            await CreateAndTestUnidirectionalStream(serverConnection, clientConnection);
+            await CreateAndTestUnidirectionalStream(clientConnection, serverConnection);
+            await clientConnection.CloseAsync(errorCode: 0);
         }
 
         [Fact]
@@ -336,36 +370,31 @@ public async Task GetStreamIdWithoutStartWorks()
 
         private static async Task CreateAndTestBidirectionalStream(QuicConnection c1, QuicConnection c2)
         {
-            using (QuicStream s1 = c1.OpenBidirectionalStream())
-            {
-                Assert.True(s1.CanRead);
-                Assert.True(s1.CanWrite);
+            using QuicStream s1 = c1.OpenBidirectionalStream();
+            Assert.True(s1.CanRead);
+            Assert.True(s1.CanWrite);
 
-                ValueTask writeTask = s1.WriteAsync(s_data);
-                using (QuicStream s2 = await c2.AcceptStreamAsync())
-                {
-                    await ReceiveDataAsync(s_data, s2);
-                    await writeTask;
-                    await TestBidirectionalStream(s1, s2);
-                }
-            }
+            ValueTask writeTask = s1.WriteAsync(s_data);
+
+            using QuicStream s2 = await c2.AcceptStreamAsync();
+            await ReceiveDataAsync(s_data, s2);
+            await writeTask;
+            await TestBidirectionalStream(s1, s2);
         }
 
         private static async Task CreateAndTestUnidirectionalStream(QuicConnection c1, QuicConnection c2)
         {
-            using (QuicStream s1 = c1.OpenUnidirectionalStream())
-            {
-                Assert.False(s1.CanRead);
-                Assert.True(s1.CanWrite);
+            using QuicStream s1 = c1.OpenUnidirectionalStream();
 
-                ValueTask writeTask = s1.WriteAsync(s_data);
-                using (QuicStream s2 = await c2.AcceptStreamAsync())
-                {
-                    await ReceiveDataAsync(s_data, s2);
-                    await writeTask;
-                    await TestUnidirectionalStream(s1, s2);
-                }
-            }
+            Assert.False(s1.CanRead);
+            Assert.True(s1.CanWrite);
+
+            ValueTask writeTask = s1.WriteAsync(s_data);
+
+            using QuicStream s2 = await c2.AcceptStreamAsync();
+            await ReceiveDataAsync(s_data, s2);
+            await writeTask;
+            await TestUnidirectionalStream(s1, s2);
         }
 
         private static async Task TestBidirectionalStream(QuicStream s1, QuicStream s2)
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/MultipartContentTest.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/MultipartContentTest.cs
index 7565e5b698314e..a945cc3db3ea97 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/MultipartContentTest.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/MultipartContentTest.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.IO;
+using System.Linq;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -387,6 +388,122 @@ public void ReadAsStream_CreateContentReadStreamThrows()
             Assert.Throws<NotImplementedException>(() => mc.ReadAsStream());
         }
 
+        [Theory]
+        [InlineData(true)]
+        [InlineData(false)]
+        public async Task ReadAsStreamAsync_CustomEncodingSelector_SelectorIsCalledWithCustomState(bool async)
+        {
+            var mc = new MultipartContent();
+
+            var stringContent = new StringContent("foo");
+            stringContent.Headers.Add("StringContent", "foo");
+            mc.Add(stringContent);
+
+            var byteArrayContent = new ByteArrayContent(Encoding.ASCII.GetBytes("foo"));
+            byteArrayContent.Headers.Add("ByteArrayContent", "foo");
+            mc.Add(byteArrayContent);
+
+            bool seenStringContent = false, seenByteArrayContent = false;
+
+            mc.HeaderEncodingSelector = (name, content) =>
+            {
+                if (ReferenceEquals(content, stringContent) && name == "StringContent")
+                {
+                    seenStringContent = true;
+                }
+
+                if (ReferenceEquals(content, byteArrayContent) && name == "ByteArrayContent")
+                {
+                    seenByteArrayContent = true;
+                }
+
+                return null;
+            };
+
+            var dummy = new MemoryStream();
+            if (async)
+            {
+                await (await mc.ReadAsStreamAsync()).CopyToAsync(dummy);
+            }
+            else
+            {
+                mc.ReadAsStream().CopyTo(dummy);
+            }
+
+            Assert.True(seenStringContent);
+            Assert.True(seenByteArrayContent);
+        }
+
+        [Theory]
+        [InlineData(true)]
+        [InlineData(false)]
+        public async Task ReadAsStreamAsync_CustomEncodingSelector_CustomEncodingIsUsed(bool async)
+        {
+            var mc = new MultipartContent("subtype", "fooBoundary");
+
+            var stringContent = new StringContent("bar1");
+            stringContent.Headers.Add("latin1", "\uD83D\uDE00");
+            mc.Add(stringContent);
+
+            var byteArrayContent = new ByteArrayContent(Encoding.ASCII.GetBytes("bar2"));
+            byteArrayContent.Headers.Add("utf8", "\uD83D\uDE00");
+            mc.Add(byteArrayContent);
+
+            byteArrayContent = new ByteArrayContent(Encoding.ASCII.GetBytes("bar3"));
+            byteArrayContent.Headers.Add("ascii", "\uD83D\uDE00");
+            mc.Add(byteArrayContent);
+
+            byteArrayContent = new ByteArrayContent(Encoding.ASCII.GetBytes("bar4"));
+            byteArrayContent.Headers.Add("default", "\uD83D\uDE00");
+            mc.Add(byteArrayContent);
+
+            mc.HeaderEncodingSelector = (name, _) => name switch
+            {
+                "latin1" => Encoding.Latin1,
+                "utf8" => Encoding.UTF8,
+                "ascii" => Encoding.ASCII,
+                _ => null
+            };
+
+            var ms = new MemoryStream();
+            if (async)
+            {
+                await (await mc.ReadAsStreamAsync()).CopyToAsync(ms);
+            }
+            else
+            {
+                mc.ReadAsStream().CopyTo(ms);
+            }
+
+            byte[] expected = Concat(
+                Encoding.Latin1.GetBytes("--fooBoundary\r\n"),
+                Encoding.Latin1.GetBytes("Content-Type: text/plain; charset=utf-8\r\n"),
+                Encoding.Latin1.GetBytes("latin1: "),
+                Encoding.Latin1.GetBytes("\uD83D\uDE00"),
+                Encoding.Latin1.GetBytes("\r\n\r\n"),
+                Encoding.Latin1.GetBytes("bar1"),
+                Encoding.Latin1.GetBytes("\r\n--fooBoundary\r\n"),
+                Encoding.Latin1.GetBytes("utf8: "),
+                Encoding.UTF8.GetBytes("\uD83D\uDE00"),
+                Encoding.Latin1.GetBytes("\r\n\r\n"),
+                Encoding.Latin1.GetBytes("bar2"),
+                Encoding.Latin1.GetBytes("\r\n--fooBoundary\r\n"),
+                Encoding.Latin1.GetBytes("ascii: "),
+                Encoding.ASCII.GetBytes("\uD83D\uDE00"),
+                Encoding.Latin1.GetBytes("\r\n\r\n"),
+                Encoding.Latin1.GetBytes("bar3"),
+                Encoding.Latin1.GetBytes("\r\n--fooBoundary\r\n"),
+                Encoding.Latin1.GetBytes("default: "),
+                Encoding.Latin1.GetBytes("\uD83D\uDE00"),
+                Encoding.Latin1.GetBytes("\r\n\r\n"),
+                Encoding.Latin1.GetBytes("bar4"),
+                Encoding.Latin1.GetBytes("\r\n--fooBoundary--\r\n"));
+
+            Assert.Equal(expected, ms.ToArray());
+
+            static byte[] Concat(params byte[][] arrays) => arrays.SelectMany(b => b).ToArray();
+        }
+
         #region Helpers
 
         private static async Task<string> MultipartContentToStringAsync(MultipartContent content, MultipartContentToStringMode mode, bool async)
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.cs
index a60e509ba7fd17..551ce4e96b63c9 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.cs
@@ -5,6 +5,7 @@
 using System.Diagnostics;
 using System.IO;
 using System.Linq;
+using System.Net.Connections;
 using System.Net.Quic;
 using System.Net.Security;
 using System.Net.Sockets;
@@ -105,6 +106,72 @@ private sealed class SetOnFinalized
         }
     }
 
+    public class SocketsHttpHandler_ConnectionFactoryTest : HttpClientHandlerTestBase
+    {
+        public SocketsHttpHandler_ConnectionFactoryTest(ITestOutputHelper output) : base(output) { }
+
+        [Fact]
+        public async Task CustomConnectionFactory_AsyncRequest_Success()
+        {
+            await using ConnectionListenerFactory listenerFactory = new VirtualNetworkConnectionListenerFactory();
+            await using ConnectionListener listener = await listenerFactory.ListenAsync(endPoint: null);
+            await using ConnectionFactory connectionFactory = VirtualNetworkConnectionListenerFactory.GetConnectionFactory(listener);
+
+            var options = new GenericLoopbackOptions();
+
+            Task serverTask = Task.Run(async () =>
+            {
+                await using Connection serverConnection = await listener.AcceptAsync();
+                using GenericLoopbackConnection loopbackConnection = await LoopbackServerFactory.CreateConnectionAsync(socket: null, serverConnection.Stream, options);
+
+                await loopbackConnection.InitializeConnectionAsync();
+
+                HttpRequestData requestData = await loopbackConnection.ReadRequestDataAsync();
+                await loopbackConnection.SendResponseAsync(content: "foo");
+
+                Assert.Equal("/foo", requestData.Path);
+            });
+
+            Task clientTask = Task.Run(async () =>
+            {
+                using HttpClientHandler handler = CreateHttpClientHandler();
+                handler.ServerCertificateCustomValidationCallback = TestHelper.AllowAllCertificates;
+                
+                var socketsHandler = (SocketsHttpHandler)GetUnderlyingSocketsHttpHandler(handler);
+                socketsHandler.ConnectionFactory = connectionFactory;
+
+                using HttpClient client = CreateHttpClient(handler);
+
+                string response = await client.GetStringAsync($"{(options.UseSsl ? "https" : "http")}://{Guid.NewGuid():N}.com/foo");
+                Assert.Equal("foo", response);
+            });
+
+            await new[] { serverTask, clientTask }.WhenAllOrAnyFailed(60_000);
+        }
+
+        [Fact]
+        public async Task CustomConnectionFactory_SyncRequest_Fails()
+        {
+            await using ConnectionFactory connectionFactory = new SocketsHttpConnectionFactory();
+            using SocketsHttpHandler handler = new SocketsHttpHandler
+            {
+                ConnectionFactory = connectionFactory
+            };
+
+            using HttpClient client = CreateHttpClient(handler);
+
+            HttpRequestException e = await Assert.ThrowsAnyAsync<HttpRequestException>(() => client.GetStringAsync($"http://{Guid.NewGuid():N}.com/foo"));
+            NetworkException networkException = Assert.IsType<NetworkException>(e.InnerException);
+            Assert.Equal(NetworkError.HostNotFound, networkException.NetworkError);
+        }
+    }
+
+    public sealed class SocketsHttpHandler_ConnectionFactoryTest_Http2 : SocketsHttpHandler_ConnectionFactoryTest
+    {
+        public SocketsHttpHandler_ConnectionFactoryTest_Http2(ITestOutputHelper output) : base(output) { }
+        protected override Version UseVersion => HttpVersion.Version20;
+    }
+
     public sealed class SocketsHttpHandler_HttpProtocolTests : HttpProtocolTests
     {
         public SocketsHttpHandler_HttpProtocolTests(ITestOutputHelper output) : base(output) { }
@@ -663,6 +730,7 @@ await TestHelper.WhenAllCompletedOrAnyFailed(
 
         [Theory]
         [InlineData("Age", "1")]
+        // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy authorisation header.")]
         [InlineData("Authorization", "Basic YWxhZGRpbjpvcGVuc2VzYW1l")]
         [InlineData("Cache-Control", "no-cache")]
         [InlineData("Content-Encoding", "gzip")]
@@ -1519,7 +1587,7 @@ public async Task ProxyAuth_SameConnection_Succeeds()
 
                 using  (var handler = new HttpClientHandler())
                 {
-                    handler.Proxy = new UseSpecifiedUriWebProxy(proxyUrl, new NetworkCredential("abc", "def"));
+                    handler.Proxy = new UseSpecifiedUriWebProxy(proxyUrl, new NetworkCredential("abc", "password"));
 
                     using (HttpClient client = CreateHttpClient(handler))
                     {
@@ -1924,6 +1992,300 @@ private static byte[] PreperateResponseWithRedirect(byte[] location)
     public sealed class SocketsHttpHandlerTest_Http2 : HttpClientHandlerTest_Http2
     {
         public SocketsHttpHandlerTest_Http2(ITestOutputHelper output) : base(output) { }
+
+        [ConditionalFact(nameof(SupportsAlpn))]
+        public async Task Http2_MultipleConnectionsEnabled_ConnectionLimitNotReached_ConcurrentRequestsSuccessfullyHandled()
+        {
+            const int MaxConcurrentStreams = 2;
+            using Http2LoopbackServer server = Http2LoopbackServer.CreateServer();
+            using SocketsHttpHandler handler = CreateHandler();
+            using (HttpClient client = CreateHttpClient(handler))
+            {
+                server.AllowMultipleConnections = true;
+                List<Task<HttpResponseMessage>> sendTasks = new List<Task<HttpResponseMessage>>();
+                List<Http2LoopbackConnection> connections = new List<Http2LoopbackConnection>();
+                List<int> acceptedStreams = new List<int>();
+                for (int i = 0; i < 3; i++)
+                {
+                    Http2LoopbackConnection connection = await PrepareConnection(server, client, MaxConcurrentStreams).ConfigureAwait(false);
+                    AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+                    connections.Add(connection);
+                    int prevAcceptedStreamCount = acceptedStreams.Count;
+                    acceptedStreams.AddRange(await AcceptRequests(connection, MaxConcurrentStreams).ConfigureAwait(false));
+                    Assert.Equal(prevAcceptedStreamCount + MaxConcurrentStreams, acceptedStreams.Count);
+                }
+
+                int responseIndex = 0;
+                List<Task> responseTasks = new List<Task>();
+                foreach (Http2LoopbackConnection connection in connections)
+                {
+                    for (int i = 0; i < MaxConcurrentStreams; i++)
+                    {
+                        int streamId = acceptedStreams[responseIndex++];
+                        responseTasks.Add(connection.SendDefaultResponseAsync(streamId));
+                    }
+                }
+
+                await Task.WhenAll(responseTasks).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds).ConfigureAwait(false);
+                await Task.WhenAll(sendTasks).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds).ConfigureAwait(false);
+
+                await VerifySendTasks(sendTasks).ConfigureAwait(false);
+            }
+        }
+
+        [ConditionalFact(nameof(SupportsAlpn))]
+        public async Task Http2_MultipleConnectionsEnabled_InfiniteRequestsCompletelyBlockOneConnection_RemaningRequestsAreHandledByNewConnection()
+        {
+            const int MaxConcurrentStreams = 2;
+            using Http2LoopbackServer server = Http2LoopbackServer.CreateServer();
+            using SocketsHttpHandler handler = CreateHandler();
+            using (HttpClient client = CreateHttpClient(handler))
+            {
+                server.AllowMultipleConnections = true;
+                List<Task<HttpResponseMessage>> sendTasks = new List<Task<HttpResponseMessage>>();
+                Http2LoopbackConnection connection0 = await PrepareConnection(server, client, MaxConcurrentStreams).ConfigureAwait(false);
+                AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+
+                // Block the first connection on infinite requests.
+                List<int> blockedStreamIds = await AcceptRequests(connection0, MaxConcurrentStreams).ConfigureAwait(false);
+                Assert.Equal(MaxConcurrentStreams, blockedStreamIds.Count);
+
+                Http2LoopbackConnection connection1 = await PrepareConnection(server, client, MaxConcurrentStreams).ConfigureAwait(false);
+                AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+
+                int handledRequestCount = (await HandleAllPendingRequests(connection1, MaxConcurrentStreams).ConfigureAwait(false)).Count;
+
+                Assert.Equal(MaxConcurrentStreams, handledRequestCount);
+
+                //Complete inifinite requests.
+                handledRequestCount = await SendResponses(connection0, blockedStreamIds);
+
+                Assert.Equal(MaxConcurrentStreams, handledRequestCount);
+
+                await Task.WhenAll(sendTasks).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds).ConfigureAwait(false);
+
+                await VerifySendTasks(sendTasks).ConfigureAwait(false);
+            }
+        }
+
+        [ConditionalFact(nameof(SupportsAlpn))]
+        public async Task Http2_MultipleConnectionsEnabled_OpenAndCloseMultipleConnections_Success()
+        {
+            const int MaxConcurrentStreams = 2;
+            using Http2LoopbackServer server = Http2LoopbackServer.CreateServer();
+            using SocketsHttpHandler handler = CreateHandler();
+            using (HttpClient client = CreateHttpClient(handler))
+            {
+                server.AllowMultipleConnections = true;
+                List<Task<HttpResponseMessage>> sendTasks = new List<Task<HttpResponseMessage>>();
+                Http2LoopbackConnection connection0 = await PrepareConnection(server, client, MaxConcurrentStreams).ConfigureAwait(false);
+                AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+                Http2LoopbackConnection connection1 = await PrepareConnection(server, client, MaxConcurrentStreams).ConfigureAwait(false);
+                AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+                Http2LoopbackConnection connection2 = await PrepareConnection(server, client, MaxConcurrentStreams).ConfigureAwait(false);
+                AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+
+                Task<(int Count, int LastStreamId)>[] handleRequestTasks = new[] {
+                    HandleAllPendingRequests(connection0, sendTasks.Count),
+                    HandleAllPendingRequests(connection1, sendTasks.Count),
+                    HandleAllPendingRequests(connection2, sendTasks.Count)
+                };
+
+                await Task.WhenAll(handleRequestTasks).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds).ConfigureAwait(false);
+
+                Assert.Equal(handleRequestTasks[0].Result.Count, MaxConcurrentStreams);
+                Assert.Equal(handleRequestTasks[1].Result.Count, MaxConcurrentStreams);
+                Assert.Equal(handleRequestTasks[2].Result.Count, MaxConcurrentStreams);
+
+                await connection0.ShutdownIgnoringErrorsAsync(handleRequestTasks[0].Result.LastStreamId).ConfigureAwait(false);
+                await connection2.ShutdownIgnoringErrorsAsync(handleRequestTasks[2].Result.LastStreamId).ConfigureAwait(false);
+
+                //Fill all connection1's stream slots
+                AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+
+                Http2LoopbackConnection connection3 = await PrepareConnection(server, client, MaxConcurrentStreams).ConfigureAwait(false);
+                AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+                Http2LoopbackConnection connection4 = await PrepareConnection(server, client, MaxConcurrentStreams).ConfigureAwait(false);
+                AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+
+                Task<(int Count, int LastStreamId)>[] finalHandleTasks = new[] {
+                    HandleAllPendingRequests(connection1, sendTasks.Count),
+                    HandleAllPendingRequests(connection3, sendTasks.Count),
+                    HandleAllPendingRequests(connection4, sendTasks.Count)
+                };
+
+                await Task.WhenAll(finalHandleTasks).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds).ConfigureAwait(false);
+
+                Assert.Equal(finalHandleTasks[0].Result.Count, MaxConcurrentStreams);
+                Assert.Equal(finalHandleTasks[1].Result.Count, MaxConcurrentStreams);
+                Assert.Equal(finalHandleTasks[2].Result.Count, MaxConcurrentStreams);
+
+                await Task.WhenAll(sendTasks).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds).ConfigureAwait(false);
+
+                await VerifySendTasks(sendTasks).ConfigureAwait(false);
+            }
+        }
+
+        [ConditionalFact(nameof(SupportsAlpn))]
+        public async Task Http2_MultipleConnectionsEnabled_IdleConnectionTimeoutExpired_ConnectionRemovedAndNewCreated()
+        {
+            const int MaxConcurrentStreams = 2;
+            using Http2LoopbackServer server = Http2LoopbackServer.CreateServer();
+            using SocketsHttpHandler handler = CreateHandler();
+            handler.PooledConnectionIdleTimeout = TimeSpan.FromSeconds(20);
+            using (HttpClient client = CreateHttpClient(handler))
+            {
+                server.AllowMultipleConnections = true;
+                List<Task<HttpResponseMessage>> sendTasks = new List<Task<HttpResponseMessage>>();
+                Http2LoopbackConnection connection0 = await PrepareConnection(server, client, MaxConcurrentStreams).ConfigureAwait(false);
+                AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+                List<int> acceptedStreamIds = await AcceptRequests(connection0, MaxConcurrentStreams).ConfigureAwait(false);
+                Assert.Equal(MaxConcurrentStreams, acceptedStreamIds.Count);
+
+                List<Task<HttpResponseMessage>> connection1SendTasks = new List<Task<HttpResponseMessage>>();
+                Http2LoopbackConnection connection1 = await PrepareConnection(server, client, MaxConcurrentStreams, readTimeout: 30).ConfigureAwait(false);
+                AcquireAllStreamSlots(server, client, connection1SendTasks, MaxConcurrentStreams);
+                int handledRequests1 = (await HandleAllPendingRequests(connection1, MaxConcurrentStreams).ConfigureAwait(false)).Count;
+
+                Assert.Equal(MaxConcurrentStreams, handledRequests1);
+
+                // Complete all the requests.
+                await Task.WhenAll(connection1SendTasks).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds).ConfigureAwait(false);
+                await VerifySendTasks(connection1SendTasks).ConfigureAwait(false);
+                connection1SendTasks.ForEach(t => t.Result.Dispose());
+
+                // Wait until the idle connection timeout expires.
+                await connection1.WaitForClientDisconnectAsync(false).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds).ConfigureAwait(false);
+                // Client connection might be still alive, so send an extra request which will either land on the shutting down connection or on a new one.
+                try
+                {
+                    await client.GetAsync(server.Address).TimeoutAfter(handler.PooledConnectionIdleTimeout).ConfigureAwait(false);
+                }
+                catch (Exception)
+                {
+                    // Suppress all exceptions.
+                }
+
+                Assert.True(connection1.IsInvalid);
+                Assert.False(connection0.IsInvalid);
+
+                Http2LoopbackConnection connection2 = await PrepareConnection(server, client, MaxConcurrentStreams, readTimeout: 15, expectedWarpUpTasks:2).ConfigureAwait(false);
+
+                AcquireAllStreamSlots(server, client, sendTasks, MaxConcurrentStreams);
+
+                int handledRequests2 = (await HandleAllPendingRequests(connection2, MaxConcurrentStreams).ConfigureAwait(false)).Count;
+                Assert.Equal(MaxConcurrentStreams, handledRequests2);
+
+                //Make sure connection0 is still alive.
+                int handledRequests0 = await SendResponses(connection0, acceptedStreamIds).ConfigureAwait(false);
+                Assert.Equal(MaxConcurrentStreams, handledRequests0);
+
+                await Task.WhenAll(sendTasks).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds).ConfigureAwait(false);
+
+                await VerifySendTasks(sendTasks).ConfigureAwait(false);
+            }
+        }
+
+        private async Task VerifySendTasks(IReadOnlyList<Task<HttpResponseMessage>> sendTasks)
+        {
+            foreach (Task<HttpResponseMessage> sendTask in sendTasks)
+            {
+                HttpResponseMessage response = await sendTask.ConfigureAwait(false);
+                Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            }
+        }
+
+        private static SocketsHttpHandler CreateHandler() => new SocketsHttpHandler
+        {
+            EnableMultipleHttp2Connections = true,
+            PooledConnectionIdleTimeout = TimeSpan.FromHours(1),
+            PooledConnectionLifetime = TimeSpan.FromHours(1),
+            SslOptions = { RemoteCertificateValidationCallback = delegate { return true; } }
+        };
+
+        private async Task<Http2LoopbackConnection> PrepareConnection(Http2LoopbackServer server, HttpClient client, uint maxConcurrentStreams, int readTimeout = 3, int expectedWarpUpTasks = 1)
+        {
+            Task<HttpResponseMessage> warmUpTask = client.GetAsync(server.Address);
+            Http2LoopbackConnection connection = await GetConnection(server, maxConcurrentStreams, readTimeout).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds * 2).ConfigureAwait(false);
+            // Wait until the client confirms MaxConcurrentStreams setting took into effect.
+            Task settingAckReceived = connection.SettingAckWaiter;
+            while (true)
+            {
+                Task handleRequestTask = HandleAllPendingRequests(connection, expectedWarpUpTasks);
+                await Task.WhenAll(warmUpTask, handleRequestTask).TimeoutAfter(TestHelper.PassingTestTimeoutMilliseconds * 2).ConfigureAwait(false);
+                Assert.True(warmUpTask.Result.IsSuccessStatusCode);
+                warmUpTask.Result.Dispose();
+                if (settingAckReceived.IsCompleted)
+                {
+                    break;
+                }
+
+                warmUpTask = client.GetAsync(server.Address);
+            }
+            return connection;
+        }
+
+        private static void AcquireAllStreamSlots(Http2LoopbackServer server, HttpClient client, List<Task<HttpResponseMessage>> sendTasks, uint maxConcurrentStreams)
+        {
+            for (int i = 0; i < maxConcurrentStreams; i++)
+            {
+                sendTasks.Add(client.GetAsync(server.Address));
+            }
+        }
+
+        private static async Task<Http2LoopbackConnection> GetConnection(Http2LoopbackServer server, uint maxConcurrentStreams, int readTimeout) =>
+            await server.EstablishConnectionAsync(TimeSpan.FromSeconds(readTimeout), TimeSpan.FromSeconds(10), new SettingsEntry { SettingId = SettingId.MaxConcurrentStreams, Value = maxConcurrentStreams }).ConfigureAwait(false);
+
+        private async Task<(int Count, int LastStreamId)> HandleAllPendingRequests(Http2LoopbackConnection connection, int totalRequestCount)
+        {
+            int streamId = -1;
+            for (int i = 0; i < totalRequestCount; i++)
+            {
+                try
+                {
+                    // Exact number of requests sent over the given connection is unknown,
+                    // so we keep reading headers and sending response while there are available requests.
+                    streamId = await connection.ReadRequestHeaderAsync().ConfigureAwait(false);
+                    await connection.SendDefaultResponseAsync(streamId).ConfigureAwait(false);
+                }
+                catch (OperationCanceledException)
+                {
+                    return (i, streamId);
+                }
+            }
+
+            return (totalRequestCount, streamId);
+        }
+
+        private async Task<List<int>> AcceptRequests(Http2LoopbackConnection connection, int maxRequests = int.MaxValue)
+        {
+            List<int> streamIds = new List<int>();
+            for (int i = 0; i < maxRequests; i++)
+            {
+                try
+                {
+                    streamIds.Add(await connection.ReadRequestHeaderAsync().ConfigureAwait(false));
+                }
+                catch (OperationCanceledException)
+                {
+                    return streamIds;
+                }
+            }
+
+            return streamIds;
+        }
+
+        private async Task<int> SendResponses(Http2LoopbackConnection connection, IEnumerable<int> streamIds)
+        {
+            int count = 0;
+            foreach (int streamId in streamIds)
+            {
+                count++;
+                await connection.SendDefaultResponseAsync(streamId).ConfigureAwait(false);
+            }
+
+            return count;
+        }
     }
 
     [ConditionalClass(typeof(PlatformDetection), nameof(PlatformDetection.SupportsAlpn))]
@@ -1963,7 +2325,7 @@ public SocketsHttpHandler_HttpClientHandler_Cancellation_Test_Http2(ITestOutputH
     public sealed class SocketsHttpHandler_HttpClientHandler_Finalization_Http3_Test : HttpClientHandler_Finalization_Test
     {
         public SocketsHttpHandler_HttpClientHandler_Finalization_Http3_Test(ITestOutputHelper output) : base(output) { }
-        protected override Version UseVersion => HttpVersion.Version30;
+        protected override Version UseVersion => HttpVersion30;
     }
 
     [ConditionalClass(typeof(QuicConnection), nameof(QuicConnection.IsQuicSupported))]
@@ -1976,34 +2338,34 @@ public SocketsHttpHandlerTest_Http3(ITestOutputHelper output) : base(output) { }
     public sealed class SocketsHttpHandlerTest_Cookies_Http3 : HttpClientHandlerTest_Cookies
     {
         public SocketsHttpHandlerTest_Cookies_Http3(ITestOutputHelper output) : base(output) { }
-        protected override Version UseVersion => HttpVersion.Version30;
+        protected override Version UseVersion => HttpVersion30;
     }
 
     [ConditionalClass(typeof(QuicConnection), nameof(QuicConnection.IsQuicSupported))]
     public sealed class SocketsHttpHandlerTest_HttpClientHandlerTest_Http3 : HttpClientHandlerTest
     {
         public SocketsHttpHandlerTest_HttpClientHandlerTest_Http3(ITestOutputHelper output) : base(output) { }
-        protected override Version UseVersion => HttpVersion.Version30;
+        protected override Version UseVersion => HttpVersion30;
     }
 
     [ConditionalClass(typeof(QuicConnection), nameof(QuicConnection.IsQuicSupported))]
     public sealed class SocketsHttpHandlerTest_HttpClientHandlerTest_Headers_Http3 : HttpClientHandlerTest_Headers
     {
         public SocketsHttpHandlerTest_HttpClientHandlerTest_Headers_Http3(ITestOutputHelper output) : base(output) { }
-        protected override Version UseVersion => HttpVersion.Version30;
+        protected override Version UseVersion => HttpVersion30;
     }
 
     [ConditionalClass(typeof(QuicConnection), nameof(QuicConnection.IsQuicSupported))]
     public sealed class SocketsHttpHandler_HttpClientHandler_Cancellation_Test_Http3 : HttpClientHandler_Cancellation_Test
     {
         public SocketsHttpHandler_HttpClientHandler_Cancellation_Test_Http3(ITestOutputHelper output) : base(output) { }
-        protected override Version UseVersion => HttpVersion.Version30;
+        protected override Version UseVersion => HttpVersion30;
     }
 
     [ConditionalClass(typeof(QuicConnection), nameof(QuicConnection.IsQuicSupported))]
     public sealed class SocketsHttpHandler_HttpClientHandler_AltSvc_Test_Http3 : HttpClientHandler_AltSvc_Test
     {
         public SocketsHttpHandler_HttpClientHandler_AltSvc_Test_Http3(ITestOutputHelper output) : base(output) { }
-        protected override Version UseVersion => HttpVersion.Version30;
+        protected override Version UseVersion => HttpVersion30;
     }
 }
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/System.Net.Http.Functional.Tests.csproj b/src/libraries/System.Net.Http/tests/FunctionalTests/System.Net.Http.Functional.Tests.csproj
index 01fafd5a6ff7ac..2c97dd43097e8d 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/System.Net.Http.Functional.Tests.csproj
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/System.Net.Http.Functional.Tests.csproj
@@ -120,6 +120,8 @@
              Link="Common\System\Net\TestWebProxies.cs" />
     <Compile Include="$(CommonTestPath)System\Net\VerboseTestLogging.cs"
              Link="Common\System\Net\VerboseTestLogging.cs" />
+    <Compile Include="$(CommonTestPath)System\Net\Http\HttpAgnosticLoopbackServer.cs"
+             Link="Common\System\Net\Http\HttpAgnosticLoopbackServer.cs" />
     <Compile Include="$(CommonTestPath)System\Net\Http\LoopbackProxyServer.cs"
              Link="Common\System\Net\Http\LoopbackProxyServer.cs" />
     <Compile Include="$(CommonTestPath)System\Net\Http\LoopbackServer.cs"
@@ -179,7 +181,6 @@
     <Compile Include="$(CommonTestPath)System\Net\Http\HttpClientHandlerTest.Proxy.cs"
              Link="Common\System\Net\Http\HttpClientHandlerTest.Proxy.cs" />
     <Compile Include="HttpClientHandlerTest.Http3.cs" />
-
     <Compile Include="HttpClientHandlerTest.ResponseDrain.cs" />
     <Compile Include="$(CommonTestPath)System\Net\Http\HttpClientHandlerTest.ServerCertificates.cs"
              Link="Common\System\Net\Http\HttpClientHandlerTest.ServerCertificates.cs" />
@@ -227,8 +228,13 @@
              Link="Common\System\Net\Http\SyncBlockingContent.cs" />
     <Compile Include="$(CommonTestPath)System\Net\Http\DefaultCredentialsTest.cs"
              Link="Common\System\Net\Http\DefaultCredentialsTest.cs" />
-    <Compile Include="ThrowingContent.cs" />
+    <Compile Include="$(CommonTestPath)System\Net\Http\ThrowingContent.cs"
+             Link="Common\System\Net\Http\ThrowingContent.cs" />
+    <Compile Include="ThrowingContent.netcore.cs" />
     <Compile Include="Watchdog.cs" />
+    <Compile Include="$(CommonTestPath)System\Net\VirtualNetwork\VirtualNetwork.cs" Link="Common\System\Net\VirtualNetwork\VirtualNetwork.cs" />
+    <Compile Include="$(CommonTestPath)System\Net\VirtualNetwork\VirtualNetworkStream.cs" Link="Common\System\Net\VirtualNetwork\VirtualNetworkStream.cs" />
+    <Compile Include="$(CommonTestPath)System\Net\VirtualNetwork\VirtualNetworkConnectionListenerFactory.cs" Link="Common\System\Net\VirtualNetwork\VirtualNetworkConnectionListenerFactory.cs" />
   </ItemGroup>
   <!-- Windows specific files -->
   <ItemGroup Condition=" '$(TargetsWindows)' == 'true'">
@@ -281,12 +287,13 @@
     <Compile Include="$(CommonTestPath)System\Net\Http\HuffmanEncoder.cs"
              Link="Common\System\Net\Http\HuffmanEncoder.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <PackageReference Include="System.Net.TestData" Version="$(SystemNetTestDataVersion)" />
-  </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="SelectedSitesTest.txt">
       <Link>SelectedSitesTest.txt</Link>
     </EmbeddedResource>
   </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="System.Net.TestData" Version="$(SystemNetTestDataVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices.Protocols\src\System.DirectoryServices.Protocols.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/ThrowingContent.netcore.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/ThrowingContent.netcore.cs
new file mode 100644
index 00000000000000..8f4fd472477034
--- /dev/null
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/ThrowingContent.netcore.cs
@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Net.Http.Functional.Tests
+{
+    public partial class ThrowingContent : HttpContent
+    {
+        protected override void SerializeToStream(Stream stream, TransportContext context, CancellationToken cancellationToken)
+        {
+            throw _exnFactory();
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Http/tests/StressTests/HttpStress/StressClient.cs b/src/libraries/System.Net.Http/tests/StressTests/HttpStress/StressClient.cs
index 415ccbdc5145b8..9e1b3a3b18a787 100644
--- a/src/libraries/System.Net.Http/tests/StressTests/HttpStress/StressClient.cs
+++ b/src/libraries/System.Net.Http/tests/StressTests/HttpStress/StressClient.cs
@@ -452,7 +452,7 @@ public void PrintFailureTypes()
 
         private class StructuralEqualityComparer<T> : IEqualityComparer<T> where T : IStructuralEquatable
         {
-            public bool Equals([AllowNull] T left, [AllowNull] T right) => left != null && left.Equals(right, StructuralComparisons.StructuralEqualityComparer);
+            public bool Equals(T? left, T? right) => left != null && left.Equals(right, StructuralComparisons.StructuralEqualityComparer);
             public int GetHashCode(T value) => value.GetHashCode(StructuralComparisons.StructuralEqualityComparer);
         }
     }
diff --git a/src/libraries/System.Net.Http/tests/StressTests/HttpStress/StressServer.cs b/src/libraries/System.Net.Http/tests/StressTests/HttpStress/StressServer.cs
index 91bee1c33866a1..6bf834b8ef970f 100644
--- a/src/libraries/System.Net.Http/tests/StressTests/HttpStress/StressServer.cs
+++ b/src/libraries/System.Net.Http/tests/StressTests/HttpStress/StressServer.cs
@@ -198,8 +198,7 @@ private static void MapRoutes(IEndpointRouteBuilder endpoints)
             });
             endpoints.MapGet("/variables", async context =>
             {
-                string queryString = context.Request.QueryString.Value;
-                NameValueCollection nameValueCollection = HttpUtility.ParseQueryString(queryString);
+                NameValueCollection nameValueCollection = HttpUtility.ParseQueryString(context.Request.QueryString.Value!);
 
                 StringBuilder sb = new StringBuilder();
                 for (int i = 0; i < nameValueCollection.Count; i++)
diff --git a/src/libraries/System.Net.Http/tests/UnitTests/HPack/HPackRoundtripTests.cs b/src/libraries/System.Net.Http/tests/UnitTests/HPack/HPackRoundtripTests.cs
index 730cab367c4b97..3fd84d6a4abbee 100644
--- a/src/libraries/System.Net.Http/tests/UnitTests/HPack/HPackRoundtripTests.cs
+++ b/src/libraries/System.Net.Http/tests/UnitTests/HPack/HPackRoundtripTests.cs
@@ -14,25 +14,35 @@ namespace System.Net.Http.Unit.Tests.HPack
 {
     public class HPackRoundtripTests
     {
-
         public static IEnumerable<object[]> TestHeaders()
         {
-            yield return new object[] { new HttpRequestHeaders() { { "header", "value" } } };
-            yield return new object[] { new HttpRequestHeaders() { { "header", new[] { "value1", "value2" } } } };
+            yield return new object[] { new HttpRequestHeaders() { { "header", "value" } }, null };
+            yield return new object[] { new HttpRequestHeaders() { { "header", "value" } }, Encoding.ASCII };
+            yield return new object[] { new HttpRequestHeaders() { { "header", new[] { "value1", "value2" } } }, null };
+            yield return new object[] { new HttpRequestHeaders() { { "header", new[] { "value1", "value2" } } }, Encoding.ASCII };
             yield return new object[] { new HttpRequestHeaders()
             {
                 { "header-0", new[] { "value1", "value2" } },
                 { "header-0", "value3" },
                 { "header-1", "value1" },
                 { "header-2", new[] { "value1", "value2" } },
-            } };
+            }, null };
+            yield return new object[] { new HttpRequestHeaders() { { "header", "foo" } }, Encoding.UTF8 };
+            yield return new object[] { new HttpRequestHeaders() { { "header", "\uD83D\uDE03" } }, Encoding.UTF8 };
+            yield return new object[] { new HttpRequestHeaders()
+            {
+                { "header-0", new[] { "\uD83D\uDE03", "\uD83D\uDE48\uD83D\uDE49\uD83D\uDE4A" } },
+                { "header-1", "\uD83D\uDE03" },
+                { "header-2", "\uD83D\uDE48\uD83D\uDE49\uD83D\uDE4A" },
+                { "header-3", new[] { "\uD83D\uDE03", "\uD83D\uDE48\uD83D\uDE49\uD83D\uDE4A" } }
+            }, Encoding.UTF8 };
         }
 
         [Theory, MemberData(nameof(TestHeaders))]
-        public void HPack_HeaderEncodeDecodeRoundtrip_ShouldMatchOriginalInput(HttpHeaders headers)
+        public void HPack_HeaderEncodeDecodeRoundtrip_ShouldMatchOriginalInput(HttpHeaders headers, Encoding? valueEncoding)
         {
-            Memory<byte> encoding = HPackEncode(headers);
-            HttpHeaders decodedHeaders = HPackDecode(encoding);
+            Memory<byte> encoding = HPackEncode(headers, valueEncoding);
+            HttpHeaders decodedHeaders = HPackDecode(encoding, valueEncoding);
 
             // Assert: decoded headers are structurally equal to original headers
             Assert.Equal(headers.Count(), decodedHeaders.Count());
@@ -44,7 +54,7 @@ public void HPack_HeaderEncodeDecodeRoundtrip_ShouldMatchOriginalInput(HttpHeade
         }
 
         // adapted from Header serialization code in Http2Connection.cs
-        private static Memory<byte> HPackEncode(HttpHeaders headers)
+        private static Memory<byte> HPackEncode(HttpHeaders headers, Encoding? valueEncoding)
         {
             var buffer = new ArrayBuffer(4);
             FillAvailableSpaceWithOnes(buffer);
@@ -101,7 +111,7 @@ void WriteBytes(ReadOnlySpan<byte> bytes)
             void WriteLiteralHeaderValues(ReadOnlySpan<string> values, string separator)
             {
                 int bytesWritten;
-                while (!HPackEncoder.EncodeStringLiterals(values, separator, buffer.AvailableSpan, out bytesWritten))
+                while (!HPackEncoder.EncodeStringLiterals(values, separator, valueEncoding, buffer.AvailableSpan, out bytesWritten))
                 {
                     buffer.EnsureAvailableSpace(buffer.AvailableLength + 1);
                     FillAvailableSpaceWithOnes(buffer);
@@ -113,7 +123,7 @@ void WriteLiteralHeaderValues(ReadOnlySpan<string> values, string separator)
             void WriteLiteralHeader(string name, ReadOnlySpan<string> values)
             {
                 int bytesWritten;
-                while (!HPackEncoder.EncodeLiteralHeaderFieldWithoutIndexingNewName(name, values, HttpHeaderParser.DefaultSeparator, buffer.AvailableSpan, out bytesWritten))
+                while (!HPackEncoder.EncodeLiteralHeaderFieldWithoutIndexingNewName(name, values, HttpHeaderParser.DefaultSeparator, valueEncoding, buffer.AvailableSpan, out bytesWritten))
                 {
                     buffer.EnsureAvailableSpace(buffer.AvailableLength + 1);
                     FillAvailableSpaceWithOnes(buffer);
@@ -127,12 +137,12 @@ void WriteLiteralHeader(string name, ReadOnlySpan<string> values)
         }
 
         // adapted from header deserialization code in Http2Connection.cs
-        private static HttpHeaders HPackDecode(Memory<byte> memory)
+        private static HttpHeaders HPackDecode(Memory<byte> memory, Encoding? valueEncoding)
         {
             var header = new HttpRequestHeaders();
             var hpackDecoder = new HPackDecoder(maxDynamicTableSize: 0, maxHeadersLength: HttpHandlerDefaults.DefaultMaxResponseHeadersLength * 1024);
 
-            hpackDecoder.Decode(memory.Span, true, new HeaderHandler(header));
+            hpackDecoder.Decode(memory.Span, true, new HeaderHandler(header, valueEncoding));
 
             return header;
         }
@@ -140,9 +150,12 @@ private static HttpHeaders HPackDecode(Memory<byte> memory)
         private class HeaderHandler : IHttpHeadersHandler
         {
             HttpRequestHeaders _headers;
-            public HeaderHandler(HttpRequestHeaders headers)
+            Encoding? _valueEncoding;
+
+            public HeaderHandler(HttpRequestHeaders headers, Encoding? valueEncoding)
             {
                 _headers = headers;
+                _valueEncoding = valueEncoding;
             }
 
             public void OnHeader(ReadOnlySpan<byte> name, ReadOnlySpan<byte> value)
@@ -152,7 +165,7 @@ public void OnHeader(ReadOnlySpan<byte> name, ReadOnlySpan<byte> value)
                     throw new HttpRequestException(SR.Format(SR.net_http_invalid_response_header_name, Encoding.ASCII.GetString(name)));
                 }
 
-                string headerValue = descriptor.GetHeaderValue(value);
+                string headerValue = descriptor.GetHeaderValue(value, _valueEncoding);
 
                 _headers.TryAddWithoutValidation(descriptor, headerValue.Split(',').Select(x => x.Trim()));
             }
diff --git a/src/libraries/System.Net.Http/tests/UnitTests/Headers/HeaderEncodingTest.cs b/src/libraries/System.Net.Http/tests/UnitTests/Headers/HeaderEncodingTest.cs
new file mode 100644
index 00000000000000..d7f41e0deeee61
--- /dev/null
+++ b/src/libraries/System.Net.Http/tests/UnitTests/Headers/HeaderEncodingTest.cs
@@ -0,0 +1,37 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Net.Http.Headers;
+using System.Text;
+using Xunit;
+
+namespace System.Net.Http.Tests
+{
+    public class HeaderEncodingTest
+    {
+        [Theory]
+        [InlineData("")]
+        [InlineData("foo")]
+        [InlineData("\uD83D\uDE03")]
+        [InlineData("\0")]
+        [InlineData("\x01")]
+        [InlineData("\xFF")]
+        [InlineData("\uFFFF")]
+        [InlineData("\uFFFD")]
+        [InlineData("\uD83D\uDE48\uD83D\uDE49\uD83D\uDE4A")]
+        public void RoundTripsUtf8(string input)
+        {
+            byte[] encoded = Encoding.UTF8.GetBytes(input);
+
+            Assert.True(HeaderDescriptor.TryGet("custom-header", out HeaderDescriptor descriptor));
+            Assert.Null(descriptor.KnownHeader);
+            string roundtrip = descriptor.GetHeaderValue(encoded, Encoding.UTF8);
+            Assert.Equal(input, roundtrip);
+
+            Assert.True(HeaderDescriptor.TryGet("Cache-Control", out descriptor));
+            Assert.NotNull(descriptor.KnownHeader);
+            roundtrip = descriptor.GetHeaderValue(encoded, Encoding.UTF8);
+            Assert.Equal(input, roundtrip);
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Http/tests/UnitTests/Headers/KnownHeadersTest.cs b/src/libraries/System.Net.Http/tests/UnitTests/Headers/KnownHeadersTest.cs
index a87760246048c6..78fada7218b4ac 100644
--- a/src/libraries/System.Net.Http/tests/UnitTests/Headers/KnownHeadersTest.cs
+++ b/src/libraries/System.Net.Http/tests/UnitTests/Headers/KnownHeadersTest.cs
@@ -222,11 +222,11 @@ static void Validate(KnownHeader knownHeader, string value)
             {
                 Assert.NotNull(knownHeader);
 
-                string v1 = knownHeader.Descriptor.GetHeaderValue(value.Select(c => (byte)c).ToArray());
+                string v1 = knownHeader.Descriptor.GetHeaderValue(value.Select(c => (byte)c).ToArray(), valueEncoding: null);
                 Assert.NotNull(v1);
                 Assert.Equal(value, v1, StringComparer.OrdinalIgnoreCase);
 
-                string v2 = knownHeader.Descriptor.GetHeaderValue(value.Select(c => (byte)c).ToArray());
+                string v2 = knownHeader.Descriptor.GetHeaderValue(value.Select(c => (byte)c).ToArray(), valueEncoding: null);
                 Assert.Same(v1, v2);
             }
         }
@@ -239,8 +239,8 @@ public void GetKnownHeaderValue_Unknown_NotFound(string name, string value)
             KnownHeader knownHeader = KnownHeaders.TryGetKnownHeader(name);
             Assert.NotNull(knownHeader);
 
-            string v1 = knownHeader.Descriptor.GetHeaderValue(value.Select(c => (byte)c).ToArray());
-            string v2 = knownHeader.Descriptor.GetHeaderValue(value.Select(c => (byte)c).ToArray());
+            string v1 = knownHeader.Descriptor.GetHeaderValue(value.Select(c => (byte)c).ToArray(), valueEncoding: null);
+            string v2 = knownHeader.Descriptor.GetHeaderValue(value.Select(c => (byte)c).ToArray(), valueEncoding: null);
             Assert.Equal(value, v1);
             Assert.Equal(value, v2);
             Assert.NotSame(v1, v2);
diff --git a/src/libraries/System.Net.Http/tests/UnitTests/Headers/MultipartContentTest.cs b/src/libraries/System.Net.Http/tests/UnitTests/Headers/MultipartContentTest.cs
new file mode 100644
index 00000000000000..e89d38c204bfdb
--- /dev/null
+++ b/src/libraries/System.Net.Http/tests/UnitTests/Headers/MultipartContentTest.cs
@@ -0,0 +1,86 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace System.Net.Http.Tests
+{
+    public class MultipartContentTest
+    {
+        public static IEnumerable<object[]> MultipartContent_TestData()
+        {
+            var multipartContents = new List<MultipartContent>();
+
+            var complexContent = new MultipartContent();
+
+            var stringContent = new StringContent("bar1");
+            stringContent.Headers.Add("latin1", "\uD83D\uDE00");
+            complexContent.Add(stringContent);
+
+            var byteArrayContent = new ByteArrayContent(Encoding.ASCII.GetBytes("bar2"));
+            byteArrayContent.Headers.Add("utf8", "\uD83D\uDE00");
+            complexContent.Add(byteArrayContent);
+
+            byteArrayContent = new ByteArrayContent(Encoding.ASCII.GetBytes("bar3"));
+            byteArrayContent.Headers.Add("ascii", "\uD83D\uDE00");
+            complexContent.Add(byteArrayContent);
+
+            byteArrayContent = new ByteArrayContent(Encoding.ASCII.GetBytes("bar4"));
+            byteArrayContent.Headers.Add("default", "\uD83D\uDE00");
+            complexContent.Add(byteArrayContent);
+
+            stringContent = new StringContent("bar5");
+            stringContent.Headers.Add("foo", "bar");
+            complexContent.Add(stringContent);
+
+            multipartContents.Add(complexContent);
+            multipartContents.Add(new MultipartContent());
+            multipartContents.Add(new MultipartFormDataContent());
+
+            var encodingSelectors = new HeaderEncodingSelector<HttpContent>[]
+            {
+                (_, _) => null,
+                (_, _) => Encoding.ASCII,
+                (_, _) => Encoding.Latin1,
+                (_, _) => Encoding.UTF8,
+                (name, _) => name switch
+                {
+                    "latin1" => Encoding.Latin1,
+                    "utf8" => Encoding.UTF8,
+                    "ascii" => Encoding.ASCII,
+                    _ => null
+                }
+            };
+
+            foreach (MultipartContent multipartContent in multipartContents)
+            {
+                foreach (HeaderEncodingSelector<HttpContent> encodingSelector in encodingSelectors)
+                {
+                    multipartContent.HeaderEncodingSelector = encodingSelector;
+                    yield return new object[] { multipartContent };
+                }
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(MultipartContent_TestData))]
+        public async Task MultipartContent_TryComputeLength_ReturnsSameLengthAsCopyToAsync(MultipartContent multipartContent)
+        {
+            Assert.True(multipartContent.TryComputeLength(out long length));
+
+            var copyToStream = new MemoryStream();
+            multipartContent.CopyTo(copyToStream, context: null, cancellationToken: default);
+            Assert.Equal(length, copyToStream.Length);
+
+            var copyToAsyncStream = new MemoryStream();
+            await multipartContent.CopyToAsync(copyToAsyncStream, context: null, cancellationToken: default);
+            Assert.Equal(length, copyToAsyncStream.Length);
+
+            Assert.Equal(copyToStream.ToArray(), copyToAsyncStream.ToArray());
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Http/tests/UnitTests/System.Net.Http.Unit.Tests.csproj b/src/libraries/System.Net.Http/tests/UnitTests/System.Net.Http.Unit.Tests.csproj
index 9ca98181f81fbb..19de137c6434a3 100644
--- a/src/libraries/System.Net.Http/tests/UnitTests/System.Net.Http.Unit.Tests.csproj
+++ b/src/libraries/System.Net.Http/tests/UnitTests/System.Net.Http.Unit.Tests.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <StringResourcesPath>../../src/Resources/Strings.resx</StringResourcesPath>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
@@ -8,8 +8,8 @@
   </PropertyGroup>
   <!-- Do not reference these assemblies from the TargetingPack since we are building part of the source code for tests. -->
   <ItemGroup>
-    <DefaultReferenceExclusions Include="System.Net.Http" />
-    <DefaultReferenceExclusions Include="System.Net.Mail" />
+    <DefaultReferenceExclusion Include="System.Net.Http" />
+    <DefaultReferenceExclusion Include="System.Net.Mail" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="$(CommonPath)System\HexConverter.cs"
@@ -90,6 +90,8 @@
          Link="ProductionCode\System\Net\Http\EmptyReadStream.cs" />
     <Compile Include="..\..\src\System\Net\Http\FormUrlEncodedContent.cs"
              Link="ProductionCode\System\Net\Http\FormUrlEncodedContent.cs" />
+    <Compile Include="..\..\src\System\Net\Http\HeaderEncodingSelector.cs"
+             Link="ProductionCode\System\Net\Http\HeaderEncodingSelector.cs" />
     <Compile Include="..\..\src\System\Net\Http\Headers\AltSvcHeaderParser.cs"
              Link="ProductionCode\System\Net\Http\Headers\AltSvcHeaderParser.cs" />
     <Compile Include="..\..\src\System\Net\Http\Headers\AltSvcHeaderValue.cs"
@@ -206,6 +208,10 @@
              Link="ProductionCode\System\Net\Http\RequestRetryType.cs" />
     <Compile Include="..\..\src\System\Net\Http\HttpRequestMessage.cs"
              Link="ProductionCode\System\Net\Http\HttpRequestMessage.cs" />
+   <Compile Include="..\..\src\System\Net\Http\HttpRequestOptions.cs"
+             Link="ProductionCode\System\Net\Http\HttpRequestOptions.cs" />
+   <Compile Include="..\..\src\System\Net\Http\HttpRequestOptionsKey.cs"
+             Link="ProductionCode\System\Net\Http\HttpRequestOptionsKey.cs" />
     <Compile Include="..\..\src\System\Net\Http\HttpResponseMessage.cs"
              Link="ProductionCode\System\Net\Http\HttpResponseMessage.cs" />
     <Compile Include="..\..\src\System\Net\Http\HttpRuleParser.cs"
@@ -269,6 +275,7 @@
     <Compile Include="Headers\GenericHeaderParserTest\TokenListParserTest.cs" />
     <Compile Include="Headers\GenericHeaderParserTest\ViaParserTest.cs" />
     <Compile Include="Headers\GenericHeaderParserTest\WarningParserTest.cs" />
+    <Compile Include="Headers\HeaderEncodingTest.cs" />
     <Compile Include="Headers\HeaderUtilitiesTest.cs" />
     <Compile Include="Headers\HttpContentHeadersTest.cs" />
     <Compile Include="Headers\HttpHeadersTest.cs" />
@@ -281,6 +288,7 @@
     <Compile Include="Headers\MediaTypeHeaderParserTest.cs" />
     <Compile Include="Headers\MediaTypeHeaderValueTest.cs" />
     <Compile Include="Headers\MediaTypeWithQualityHeaderValueTest.cs" />
+    <Compile Include="Headers\MultipartContentTest.cs" />
     <Compile Include="Headers\NameValueHeaderValueTest.cs" />
     <Compile Include="Headers\NameValueWithParametersHeaderValueTest.cs" />
     <Compile Include="Headers\ObjectCollectionTest.cs" />
@@ -332,10 +340,6 @@
              Link="ProductionCode\System\Net\Http\WinHttpTraceHelper.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Libraries.cs"
              Link="ProductionCode\Common\Interop\Windows\Interop.Libraries.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CertEnumCertificatesInStore.cs"
-             Link="ProductionCode\Common\Interop\Windows\Crypt32\Interop.CertEnumCertificatesInStore.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.certificates_types.cs"
-             Link="ProductionCode\Common\Interop\Windows\Crypt32\Interop.certificates_types.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.HRESULT_FROM_WIN32.cs"
              Link="ProductionCode\Common\Interop\Windows\Interop.HRESULT_FROM_WIN32.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\WinHttp\Interop.SafeWinHttpHandle.cs"
diff --git a/src/libraries/System.Net.HttpListener/Directory.Build.props b/src/libraries/System.Net.HttpListener/Directory.Build.props
index e912bb862bfa60..1db5968484c1ec 100644
--- a/src/libraries/System.Net.HttpListener/Directory.Build.props
+++ b/src/libraries/System.Net.HttpListener/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.HttpListener/ref/System.Net.HttpListener.cs b/src/libraries/System.Net.HttpListener/ref/System.Net.HttpListener.cs
index 3e867fd5a07b3b..27f33aac7a2aa2 100644
--- a/src/libraries/System.Net.HttpListener/ref/System.Net.HttpListener.cs
+++ b/src/libraries/System.Net.HttpListener/ref/System.Net.HttpListener.cs
@@ -139,11 +139,11 @@ public partial class HttpListenerTimeoutManager
     {
         internal HttpListenerTimeoutManager() { }
         public System.TimeSpan DrainEntityBody { get { throw null; } set { } }
-        public System.TimeSpan EntityBody { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
-        public System.TimeSpan HeaderWait { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
+        public System.TimeSpan EntityBody { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
+        public System.TimeSpan HeaderWait { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
         public System.TimeSpan IdleConnection { get { throw null; } set { } }
-        public long MinSendBytesPerSecond { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
-        public System.TimeSpan RequestQueue { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
+        public long MinSendBytesPerSecond { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
+        public System.TimeSpan RequestQueue { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
     }
 }
 namespace System.Net.WebSockets
diff --git a/src/libraries/System.Net.HttpListener/src/System.Net.HttpListener.csproj b/src/libraries/System.Net.HttpListener/src/System.Net.HttpListener.csproj
index 8f6ce68838a676..6948d70ef10db6 100644
--- a/src/libraries/System.Net.HttpListener/src/System.Net.HttpListener.csproj
+++ b/src/libraries/System.Net.HttpListener/src/System.Net.HttpListener.csproj
@@ -6,6 +6,7 @@
     <Nullable>annotations</Nullable>
   </PropertyGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.NonGeneric" />
@@ -28,14 +29,10 @@
     <Reference Include="System.Security.Cryptography.Primitives" />
     <Reference Include="System.Security.Cryptography.X509Certificates" />
     <Reference Include="System.Security.Principal" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Text.Encoding.Extensions" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Overlapped" />
   </ItemGroup>
-  <ItemGroup Condition=" '$(TargetsWindows)' == 'true'">
-    <Reference Include="System.Memory" />
-  </ItemGroup>
   <ItemGroup>
     <Compile Include="System\Net\BoundaryType.cs" />
     <Compile Include="System\Net\EntitySendFormat.cs" />
@@ -119,8 +116,6 @@
              Link="Common\Interop\Windows\Interop.Libraries.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.UNICODE_STRING.cs"
              Link="Common\Interop\Windows\Interop.UNICODE_STRING.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\SChannel\Interop.SecPkgContext_ApplicationProtocol.cs"
-             Link="Common\Interop\Windows\SChannel\Interop.SecPkgContext_ApplicationProtocol.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.BOOL.cs"
              Link="Common\Interop\Windows\Interop.BOOL.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\WebSocket\Interop.Structs.cs"
@@ -197,10 +192,22 @@
              Link="Common\System\Net\Security\NegotiateStreamPal.Windows.cs" />
     <Compile Include="$(CommonPath)System\Net\Security\NetEventSource.Security.Windows.cs"
              Link="Common\System\Net\Security\NetEventSource.Security.Windows.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.certificates_types.cs"
-             Link="Common\Interop\Windows\Crypt32\Interop.certificates_types.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.certificates.cs"
-             Link="Common\Interop\Windows\Crypt32\Interop.certificates.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CertFreeCertificateContext.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CertFreeCertificateContext.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_ALGORITHM_IDENTIFIER.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_ALGORITHM_IDENTIFIER.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_BIT_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_BIT_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.DATA_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.DATA_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.MsgEncodingType.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.MsgEncodingType.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\SspiCli\SecPkgContext_Bindings.cs"
              Link="Common\Interop\Windows\SspiCli\SecPkgContext_Bindings.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\SChannel\Interop.SECURITY_STATUS.cs"
diff --git a/src/libraries/System.Net.HttpListener/src/System/Net/Managed/HttpListenerTimeoutManager.Managed.cs b/src/libraries/System.Net.HttpListener/src/System/Net/Managed/HttpListenerTimeoutManager.Managed.cs
index fbb9d1718db8dc..8dda7441040797 100644
--- a/src/libraries/System.Net.HttpListener/src/System/Net/Managed/HttpListenerTimeoutManager.Managed.cs
+++ b/src/libraries/System.Net.HttpListener/src/System/Net/Managed/HttpListenerTimeoutManager.Managed.cs
@@ -39,7 +39,7 @@ public TimeSpan IdleConnection
         public TimeSpan EntityBody
         {
             get => TimeSpan.Zero;
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 ValidateTimeout(value);
@@ -50,7 +50,7 @@ public TimeSpan EntityBody
         public TimeSpan HeaderWait
         {
             get => TimeSpan.Zero;
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 ValidateTimeout(value);
@@ -61,7 +61,7 @@ public TimeSpan HeaderWait
         public long MinSendBytesPerSecond
         {
             get => 0;
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 if (value < 0 || value > uint.MaxValue)
@@ -75,7 +75,7 @@ public long MinSendBytesPerSecond
         public TimeSpan RequestQueue
         {
             get => TimeSpan.Zero;
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 ValidateTimeout(value);
diff --git a/src/libraries/System.Net.HttpListener/src/System/Net/Windows/HttpListenerTimeoutManager.Windows.cs b/src/libraries/System.Net.HttpListener/src/System/Net/Windows/HttpListenerTimeoutManager.Windows.cs
index 3de078196d9e9a..a1af5b35b71a84 100644
--- a/src/libraries/System.Net.HttpListener/src/System/Net/Windows/HttpListenerTimeoutManager.Windows.cs
+++ b/src/libraries/System.Net.HttpListener/src/System/Net/Windows/HttpListenerTimeoutManager.Windows.cs
@@ -83,7 +83,7 @@ public TimeSpan EntityBody
             {
                 return GetTimeout(Interop.HttpApi.HTTP_TIMEOUT_TYPE.EntityBody);
             }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 SetTimespanTimeout(Interop.HttpApi.HTTP_TIMEOUT_TYPE.EntityBody, value);
@@ -121,7 +121,7 @@ public TimeSpan RequestQueue
             {
                 return GetTimeout(Interop.HttpApi.HTTP_TIMEOUT_TYPE.RequestQueue);
             }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 SetTimespanTimeout(Interop.HttpApi.HTTP_TIMEOUT_TYPE.RequestQueue, value);
@@ -157,7 +157,7 @@ public TimeSpan HeaderWait
             {
                 return GetTimeout(Interop.HttpApi.HTTP_TIMEOUT_TYPE.HeaderWait);
             }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 SetTimespanTimeout(Interop.HttpApi.HTTP_TIMEOUT_TYPE.HeaderWait, value);
@@ -177,7 +177,7 @@ public long MinSendBytesPerSecond
                 //
                 return _minSendBytesPerSecond;
             }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 //
diff --git a/src/libraries/System.Net.HttpListener/tests/System.Net.HttpListener.Tests.csproj b/src/libraries/System.Net.HttpListener/tests/System.Net.HttpListener.Tests.csproj
index ea16d78ce8d380..9da20596f8144d 100644
--- a/src/libraries/System.Net.HttpListener/tests/System.Net.HttpListener.Tests.csproj
+++ b/src/libraries/System.Net.HttpListener/tests/System.Net.HttpListener.Tests.csproj
@@ -27,7 +27,4 @@
     <Compile Include="$(CommonTestPath)System\Threading\Tasks\TaskTimeoutExtensions.cs"
              Link="Common\System\Threading\Tasks\TaskTimeoutExtensions.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetsOSX)'=='true'">
-    <TestCommandLines Include="ulimit -n 7000" />
-  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.Mail/Directory.Build.props b/src/libraries/System.Net.Mail/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.Net.Mail/Directory.Build.props
+++ b/src/libraries/System.Net.Mail/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Mail/src/Resources/Strings.resx b/src/libraries/System.Net.Mail/src/Resources/Strings.resx
index dd4d31fb2a9cb0..b04e8c6d8d1e27 100644
--- a/src/libraries/System.Net.Mail/src/Resources/Strings.resx
+++ b/src/libraries/System.Net.Mail/src/Resources/Strings.resx
@@ -334,7 +334,7 @@
   <data name="SmtpGetIisPickupDirectoryNotSupported" xml:space="preserve">
     <value>IIS delivery is not supported.</value>
   </data>
-  <data name="SystemNetMailNotSupported" xml:space="preserve">
+  <data name="SystemNetMail_PlatformNotSupported" xml:space="preserve">
     <value>System.Net.Mail is not supported on this platform.</value>
   </data>
 </root>
diff --git a/src/libraries/System.Net.Mail/src/System.Net.Mail.csproj b/src/libraries/System.Net.Mail/src/System.Net.Mail.csproj
index 27a9633849037c..0bc8b1c63c4608 100644
--- a/src/libraries/System.Net.Mail/src/System.Net.Mail.csproj
+++ b/src/libraries/System.Net.Mail/src/System.Net.Mail.csproj
@@ -6,7 +6,7 @@
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemNetMailNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemNetMail_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
     <Compile Include="System\Net\Base64Stream.cs" />
@@ -161,8 +161,6 @@
   </ItemGroup>
   <!-- Windows specific files -->
   <ItemGroup Condition="'$(TargetsWindows)'=='true'">
-    <Compile Include="$(CommonPath)Interop\Windows\SChannel\Interop.SecPkgContext_ApplicationProtocol.cs"
-             Link="Common\Interop\Windows\SChannel\Interop.SecPkgContext_ApplicationProtocol.cs" />
     <Compile Include="$(CommonPath)System\Net\Security\SecurityBuffer.Windows.cs"
              Link="Common\System\Net\Security\SecurityBuffer.Windows.cs" />
     <Compile Include="$(CommonPath)System\Net\Security\SecurityBufferType.Windows.cs"
@@ -179,10 +177,22 @@
              Link="Common\System\Net\Security\NegotiateStreamPal.Windows.cs" />
     <Compile Include="$(CommonPath)System\Net\Security\NetEventSource.Security.Windows.cs"
              Link="Common\System\Net\Security\NetEventSource.Security.Windows.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.certificates_types.cs"
-             Link="Common\Interop\Windows\Crypt32\Interop.certificates_types.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.certificates.cs"
-             Link="Common\Interop\Windows\Crypt32\Interop.certificates.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CertFreeCertificateContext.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CertFreeCertificateContext.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_ALGORITHM_IDENTIFIER.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_ALGORITHM_IDENTIFIER.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_BIT_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_BIT_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.DATA_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.DATA_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.MsgEncodingType.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.MsgEncodingType.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Libraries.cs"
              Link="Common\Interop\Windows\Interop.Libraries.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\SspiCli\SecPkgContext_Bindings.cs"
@@ -225,6 +235,7 @@
              Link="Common\Interop\Windows\SspiCli\SSPIWrapper.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.NonGeneric" />
@@ -244,10 +255,6 @@
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Security.Claims" />
     <Reference Include="System.Security.Cryptography.X509Certificates" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Threading" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
-    <Reference Include="System.Memory" />
-  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.Mail/tests/Functional/SmtpClientTest.cs b/src/libraries/System.Net.Mail/tests/Functional/SmtpClientTest.cs
index 8a6f58093f4d28..3d55574f0cab38 100644
--- a/src/libraries/System.Net.Mail/tests/Functional/SmtpClientTest.cs
+++ b/src/libraries/System.Net.Mail/tests/Functional/SmtpClientTest.cs
@@ -293,7 +293,7 @@ public void TestMailDelivery()
         {
             using var server = new LoopbackSmtpServer();
             using SmtpClient client = server.CreateClient();
-            client.Credentials = new NetworkCredential("Foo", "Bar");
+            client.Credentials = new NetworkCredential("foo", "bar");
             MailMessage msg = new MailMessage("foo@example.com", "bar@example.com", "hello", "howdydoo");
 
             client.Send(msg);
@@ -303,8 +303,8 @@ public void TestMailDelivery()
             Assert.Equal("hello", server.Message.Subject);
             Assert.Equal("howdydoo", server.Message.Body);
             Assert.Equal(GetClientDomain(), server.ClientDomain);
-            Assert.Equal("Foo", server.Username);
-            Assert.Equal("Bar", server.Password);
+            Assert.Equal("foo", server.Username);
+            Assert.Equal("bar", server.Password);
             Assert.Equal("LOGIN", server.AuthMethodUsed, StringComparer.OrdinalIgnoreCase);
         }
 
diff --git a/src/libraries/System.Net.Mail/tests/Functional/System.Net.Mail.Functional.Tests.csproj b/src/libraries/System.Net.Mail/tests/Functional/System.Net.Mail.Functional.Tests.csproj
index 9ceee73590e4f8..83bb83a34f4d20 100644
--- a/src/libraries/System.Net.Mail/tests/Functional/System.Net.Mail.Functional.Tests.csproj
+++ b/src/libraries/System.Net.Mail/tests/Functional/System.Net.Mail.Functional.Tests.csproj
@@ -31,7 +31,4 @@
     <Compile Include="$(CommonTestPath)System\Threading\Tasks\TaskTimeoutExtensions.cs"
              Link="Common\System\Threading\Tasks\TaskTimeoutExtensions.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.Net.NetworkInformation" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Mail/tests/Unit/System.Net.Mail.Unit.Tests.csproj b/src/libraries/System.Net.Mail/tests/Unit/System.Net.Mail.Unit.Tests.csproj
index 6b9e7bd1dfa49d..79709820e29b91 100644
--- a/src/libraries/System.Net.Mail/tests/Unit/System.Net.Mail.Unit.Tests.csproj
+++ b/src/libraries/System.Net.Mail/tests/Unit/System.Net.Mail.Unit.Tests.csproj
@@ -23,10 +23,6 @@
     <Compile Include="SmtpDateTimeTest.cs" />
     <Compile Include="WriteStateInfoTest.cs" />
   </ItemGroup>
-  <!-- Do not reference these assemblies from the TargetingPack since we are building part of the source code for tests. -->
-  <ItemGroup>
-    <DefaultReferenceExclusions Include="System.Net.Mail" />
-  </ItemGroup>
   <ItemGroup>
     <Compile Include="..\..\src\System\Net\Base64Stream.cs"
              Link="ProductionCode\Base64Stream.cs" />
@@ -217,10 +213,22 @@
              Link="Common\System\Net\Security\NegotiateStreamPal.Windows.cs" />
     <Compile Include="$(CommonPath)System\Net\Security\NetEventSource.Security.Windows.cs"
              Link="Common\System\Net\Security\NetEventSource.Security.Windows.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.certificates_types.cs"
-             Link="Common\Interop\Windows\Crypt32\Interop.certificates_types.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.certificates.cs"
-             Link="Common\Interop\Windows\Crypt32\Interop.certificates.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_ALGORITHM_IDENTIFIER.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_ALGORITHM_IDENTIFIER.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_BIT_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_BIT_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.DATA_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.DATA_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.MsgEncodingType.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.MsgEncodingType.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CertFreeCertificateContext.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CertFreeCertificateContext.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Libraries.cs"
              Link="Common\Interop\Windows\Interop.Libraries.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\SspiCli\SecPkgContext_Bindings.cs"
@@ -264,4 +272,9 @@
     <Compile Include="$(CommonPath)Interop\Windows\Interop.UNICODE_STRING.cs"
              Link="Common\Interop\Windows\Interop.UNICODE_STRING.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <!-- Do not reference these assemblies from the TargetingPack since we are building part of the source code for tests. -->
+    <DefaultReferenceExclusion Include="System.Net.Mail" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.NameResolution/Directory.Build.props b/src/libraries/System.Net.NameResolution/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Net.NameResolution/Directory.Build.props
+++ b/src/libraries/System.Net.NameResolution/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.NameResolution/src/Resources/Strings.resx b/src/libraries/System.Net.NameResolution/src/Resources/Strings.resx
index 578cb9c5e2fb7d..ab9add73ea9554 100644
--- a/src/libraries/System.Net.NameResolution/src/Resources/Strings.resx
+++ b/src/libraries/System.Net.NameResolution/src/Resources/Strings.resx
@@ -72,7 +72,7 @@
   <data name="net_invalid_ip_addr" xml:space="preserve">
     <value>IPv4 address 0.0.0.0 and IPv6 address ::0 are unspecified addresses that cannot be used as a target address.</value>
   </data>
-  <data name="NameResolution_PlatformNotSupported" xml:space="preserve">
+  <data name="SystemNetNameResolution_PlatformNotSupported" xml:space="preserve">
     <value>System.Net.NameResolution is not supported on this platform.</value>
   </data>
 </root>
\ No newline at end of file
diff --git a/src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csproj b/src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csproj
index 9dd965698c5dff..27f4e9570af9ec 100644
--- a/src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csproj
+++ b/src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csproj
@@ -1,12 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Net.NameResolution</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.NameResolution_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemNetNameResolution_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
     <GeneratePlatformNotSupportedAdditionalParameters Condition="'$(TargetsBrowser)' == 'true'">--exclude-api-list ExcludeApiList.PNSE.Browser.txt</GeneratePlatformNotSupportedAdditionalParameters>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
@@ -113,6 +112,7 @@
     <Compile Include="System\Net\Dns.Browser.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Diagnostics.Tracing" />
@@ -123,7 +123,6 @@
     <Reference Include="System.Runtime.Handles" />
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Security.Claims" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Overlapped" />
     <Reference Include="System.Threading.ThreadPool" />
diff --git a/src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.cs b/src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.cs
index c216dcbf96db52..81cc5f62597c39 100644
--- a/src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.cs
+++ b/src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.cs
@@ -1,6 +1,5 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
 
 using System.Diagnostics;
 using System.Diagnostics.Tracing;
diff --git a/src/libraries/System.Net.NameResolution/tests/PalTests/System.Net.NameResolution.Pal.Tests.csproj b/src/libraries/System.Net.NameResolution/tests/PalTests/System.Net.NameResolution.Pal.Tests.csproj
index 66a902b68b37c0..3d260d337f6c9e 100644
--- a/src/libraries/System.Net.NameResolution/tests/PalTests/System.Net.NameResolution.Pal.Tests.csproj
+++ b/src/libraries/System.Net.NameResolution/tests/PalTests/System.Net.NameResolution.Pal.Tests.csproj
@@ -8,7 +8,7 @@
   </PropertyGroup>
   <!-- Do not reference these assemblies from the TargetingPack since we are building part of the source code for tests. -->
   <ItemGroup>
-    <DefaultReferenceExclusions Include="System.Net.NameResolution" />
+    <DefaultReferenceExclusion Include="System.Net.NameResolution" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="..\..\src\System\Net\IPHostEntry.cs"
diff --git a/src/libraries/System.Net.NameResolution/tests/UnitTests/System.Net.NameResolution.Unit.Tests.csproj b/src/libraries/System.Net.NameResolution/tests/UnitTests/System.Net.NameResolution.Unit.Tests.csproj
index 7e3f969094b870..747b30730e03ef 100644
--- a/src/libraries/System.Net.NameResolution/tests/UnitTests/System.Net.NameResolution.Unit.Tests.csproj
+++ b/src/libraries/System.Net.NameResolution/tests/UnitTests/System.Net.NameResolution.Unit.Tests.csproj
@@ -10,7 +10,7 @@
   </PropertyGroup>
   <!-- Do not reference these assemblies from the TargetingPack since we are building part of the source code for tests. -->
   <ItemGroup>
-    <DefaultReferenceExclusions Include="System.Net.NameResolution" />
+    <DefaultReferenceExclusion Include="System.Net.NameResolution" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="..\..\src\System\Net\IPHostEntry.cs"
diff --git a/src/libraries/System.Net.NetworkInformation/Directory.Build.props b/src/libraries/System.Net.NetworkInformation/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Net.NetworkInformation/Directory.Build.props
+++ b/src/libraries/System.Net.NetworkInformation/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.NetworkInformation/src/Resources/Strings.resx b/src/libraries/System.Net.NetworkInformation/src/Resources/Strings.resx
index 3f86a8ff7d6289..e2064ff2bfebab 100644
--- a/src/libraries/System.Net.NetworkInformation/src/Resources/Strings.resx
+++ b/src/libraries/System.Net.NetworkInformation/src/Resources/Strings.resx
@@ -90,7 +90,7 @@
   <data name="net_PInvokeError" xml:space="preserve">
     <value>An error was encountered while querying information from the operating system.</value>
   </data>
-  <data name="net_NetworkInformation_PlatformNotSupported" xml:space="preserve">
+  <data name="SystemNetNetworkInformation_PlatformNotSupported" xml:space="preserve">
     <value>System.Net.NetworkInformation is not supported on this platform.</value>
   </data>
 </root>
diff --git a/src/libraries/System.Net.NetworkInformation/src/System.Net.NetworkInformation.csproj b/src/libraries/System.Net.NetworkInformation/src/System.Net.NetworkInformation.csproj
index 6f973f7559deb9..3bb0644d9947ad 100644
--- a/src/libraries/System.Net.NetworkInformation/src/System.Net.NetworkInformation.csproj
+++ b/src/libraries/System.Net.NetworkInformation/src/System.Net.NetworkInformation.csproj
@@ -1,13 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Net.NetworkInformation</AssemblyName>
-    <OutputType>Library</OutputType>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent)-Browser;$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS;$(NetCoreAppCurrent)-FreeBSD</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.net_NetworkInformation_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemNetNetworkInformation_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
     <Compile Include="System\Net\NetworkInformation\DuplicateAddressDetectionState.cs" />
@@ -193,6 +191,7 @@
     <Compile Include="System\Net\NetworkInformation\NetworkAddressChange.UnknownUnix.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Diagnostics.Tracing" />
@@ -203,7 +202,6 @@
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Security.Claims" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Overlapped" />
     <Reference Include="System.Threading.ThreadPool" />
diff --git a/src/libraries/System.Net.Ping/Directory.Build.props b/src/libraries/System.Net.Ping/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Net.Ping/Directory.Build.props
+++ b/src/libraries/System.Net.Ping/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Ping/src/Resources/Strings.resx b/src/libraries/System.Net.Ping/src/Resources/Strings.resx
index 7b96fe56921ce6..1ad9023082ef59 100644
--- a/src/libraries/System.Net.Ping/src/Resources/Strings.resx
+++ b/src/libraries/System.Net.Ping/src/Resources/Strings.resx
@@ -87,7 +87,7 @@
   <data name="net_ping_not_supported_uwp" xml:space="preserve">
     <value>Ping functionality is not currently supported in UWP.</value>
   </data>
-  <data name="Ping_PlatformNotSupported" xml:space="preserve">
+  <data name="SystemNetPing_PlatformNotSupported" xml:space="preserve">
     <value>System.Net.Ping is not supported on this platform.</value>
   </data>
 </root>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Ping/src/System.Net.Ping.csproj b/src/libraries/System.Net.Ping/src/System.Net.Ping.csproj
index fd4c98b1521a07..b817ebac3ef979 100644
--- a/src/libraries/System.Net.Ping/src/System.Net.Ping.csproj
+++ b/src/libraries/System.Net.Ping/src/System.Net.Ping.csproj
@@ -1,12 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Net.Ping</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.Ping_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemNetPing_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
     <Compile Include="System\Net\NetworkInformation\IPStatus.cs" />
diff --git a/src/libraries/System.Net.Primitives/Directory.Build.props b/src/libraries/System.Net.Primitives/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Net.Primitives/Directory.Build.props
+++ b/src/libraries/System.Net.Primitives/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Primitives/ref/System.Net.Primitives.cs b/src/libraries/System.Net.Primitives/ref/System.Net.Primitives.cs
index bce36a86ce6259..9127d1bf3ca59c 100644
--- a/src/libraries/System.Net.Primitives/ref/System.Net.Primitives.cs
+++ b/src/libraries/System.Net.Primitives/ref/System.Net.Primitives.cs
@@ -208,7 +208,6 @@ public static partial class HttpVersion
         public static readonly System.Version Version10;
         public static readonly System.Version Version11;
         public static readonly System.Version Version20;
-        public static readonly System.Version Version30;
     }
     public partial interface ICredentials
     {
@@ -253,11 +252,11 @@ public IPAddress(System.ReadOnlySpan<byte> address, long scopeid) { }
         public static short NetworkToHostOrder(short network) { throw null; }
         public static int NetworkToHostOrder(int network) { throw null; }
         public static long NetworkToHostOrder(long network) { throw null; }
-        public static System.Net.IPAddress Parse(System.ReadOnlySpan<char> ipString) { throw null; }
+        public static System.Net.IPAddress Parse(System.ReadOnlySpan<char> ipSpan) { throw null; }
         public static System.Net.IPAddress Parse(string ipString) { throw null; }
         public override string ToString() { throw null; }
         public bool TryFormat(System.Span<char> destination, out int charsWritten) { throw null; }
-        public static bool TryParse(System.ReadOnlySpan<char> ipString, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.Net.IPAddress? address) { throw null; }
+        public static bool TryParse(System.ReadOnlySpan<char> ipSpan, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.Net.IPAddress? address) { throw null; }
         public static bool TryParse([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] string? ipString, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.Net.IPAddress? address) { throw null; }
         public bool TryWriteBytes(System.Span<byte> destination, out int bytesWritten) { throw null; }
     }
@@ -305,7 +304,7 @@ public NetworkCredential(string? userName, string? password, string? domain) { }
         [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public string UserName { get { throw null; } set { } }
         public System.Net.NetworkCredential GetCredential(string? host, int port, string? authenticationType) { throw null; }
-        public System.Net.NetworkCredential GetCredential(System.Uri? uri, string? authType) { throw null; }
+        public System.Net.NetworkCredential GetCredential(System.Uri? uri, string? authenticationType) { throw null; }
     }
     public partial class SocketAddress
     {
@@ -323,6 +322,23 @@ public abstract partial class TransportContext
         protected TransportContext() { }
         public abstract System.Security.Authentication.ExtendedProtection.ChannelBinding? GetChannelBinding(System.Security.Authentication.ExtendedProtection.ChannelBindingKind kind);
     }
+    public enum NetworkError : int
+    {
+        Unknown = 0,
+        EndPointInUse,
+        HostNotFound,
+        ConnectionRefused,
+        OperationAborted,
+        ConnectionAborted,
+        ConnectionReset,
+    }
+    public class NetworkException : System.IO.IOException
+    {
+        public NetworkException(NetworkError error, Exception? innerException = null) { }
+        public NetworkException(string message, NetworkError error, Exception? innerException = null) { }
+        protected NetworkException(System.Runtime.Serialization.SerializationInfo serializationInfo, System.Runtime.Serialization.StreamingContext streamingContext) { }
+        public NetworkError NetworkError { get { throw null; } }
+    }
 }
 namespace System.Net.Cache
 {
diff --git a/src/libraries/System.Net.Primitives/src/Resources/Strings.resx b/src/libraries/System.Net.Primitives/src/Resources/Strings.resx
index d95ea7484aace1..d0dbe85701a4cd 100644
--- a/src/libraries/System.Net.Primitives/src/Resources/Strings.resx
+++ b/src/libraries/System.Net.Primitives/src/Resources/Strings.resx
@@ -114,4 +114,25 @@
   <data name="bad_endpoint_string" xml:space="preserve">
     <value>An invalid IPEndPoint was specified.</value>
   </data>
+  <data name="networkerror_unknown" xml:space="preserve">
+    <value>An unknown network error occurred.</value>
+  </data>
+  <data name="networkerror_addressinuse" xml:space="preserve">
+    <value>The requested EndPoint is already in use.</value>
+  </data>
+  <data name="networkerror_connectionrefused" xml:space="preserve">
+    <value>No connection could be made because the remote host actively refused it.</value>
+  </data>
+  <data name="networkerror_hostnotfound" xml:space="preserve">
+    <value>No such host is known.</value>
+  </data>
+  <data name="networkerror_operationaborted" xml:space="preserve">
+    <value>The operation was aborted by the user.</value>
+  </data>
+  <data name="networkerror_connectionaborted" xml:space="preserve">
+    <value>The connection was aborted by the local host.</value>
+  </data>
+  <data name="networkerror_connectionreset" xml:space="preserve">
+    <value>The connection was forcibly closed by the remote host.</value>
+  </data>
 </root>
diff --git a/src/libraries/System.Net.Primitives/src/System.Net.Primitives.csproj b/src/libraries/System.Net.Primitives/src/System.Net.Primitives.csproj
index 8c5c2d9924eaee..413d76f6925cb6 100644
--- a/src/libraries/System.Net.Primitives/src/System.Net.Primitives.csproj
+++ b/src/libraries/System.Net.Primitives/src/System.Net.Primitives.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Net.Primitives</AssemblyName>
-    <OutputType>Library</OutputType>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <ILLinkKeepDepAttributes>false</ILLinkKeepDepAttributes> <!-- See comments in Cookie.cs -->
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
@@ -36,6 +34,8 @@
     <Compile Include="System\Net\IWebProxy.cs" />
     <Compile Include="System\Net\NetEventSource.Primitives.cs" />
     <Compile Include="System\Net\NetworkCredential.cs" />
+    <Compile Include="System\Net\NetworkException.cs" />
+    <Compile Include="System\Net\NetworkError.cs" />
     <Compile Include="System\Net\TransportContext.cs" />
     <Compile Include="System\Net\SocketException.cs" />
     <Compile Include="System\Net\SecureProtocols\NegotiateEnumTypes.cs" />
@@ -117,14 +117,22 @@
     <Compile Include="System\Net\SocketException.Unix.cs" />
     <Compile Include="$(CommonPath)System\Net\SocketAddressPal.Unix.cs"
              Link="Common\System\Net\SocketAddressPal.Unix.cs" />
-    <Compile Include="$(CommonPath)System\Net\NetworkInformation\HostInformationPal.Unix.cs"
-             Link="Common\System\Net\NetworkInformation\HostInformationPal.Unix.cs" />
     <Compile Include="$(CommonPath)System\Net\Sockets\SocketErrorPal.Unix.cs"
              Link="Common\System\Net\Sockets\SocketErrorPal.Unix.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Errors.cs"
              Link="Common\Interop\Unix\Interop.Errors.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Libraries.cs"
              Link="Common\Interop\Unix\Interop.Libraries.cs" />
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.IPAddress.cs"
+             Link="Common\Interop\Unix\System.Native\Interop.IPAddress.cs" />
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.SocketAddress.cs"
+             Link="Common\Interop\Unix\System.Native\Interop.SocketAddress.cs" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
+    <Compile Include="$(CommonPath)System\Net\NetworkInformation\HostInformationPal.Unix.cs"
+             Link="Common\System\Net\NetworkInformation\HostInformationPal.Unix.cs" />
+    <Compile Include="$(CommonPath)System\Net\NetworkInformation\InterfaceInfoPal.Unix.cs"
+             Link="Common\System\Net\NetworkInformation\InterfaceInfoPal.Unix.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetDomainName.cs"
              Link="Common\Interop\Unix\System.Native\Interop.GetDomainName.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetHostName.cs"
@@ -133,14 +141,14 @@
              Link="Common\Interop\Unix\System.Native\Interop.GetNameInfo.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.HostEntry.cs"
              Link="Common\Interop\Unix\System.Native\Interop.HostEntry.cs" />
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.IPAddress.cs"
-             Link="Common\Interop\Unix\System.Native\Interop.IPAddress.cs" />
-    <Compile Include="$(CommonPath)System\Net\NetworkInformation\InterfaceInfoPal.Unix.cs"
-             Link="Common\System\Net\NetworkInformation\InterfaceInfoPal.Unix.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.InterfaceNameToIndex.cs"
              Link="Common\Interop\Unix\System.Native\Interop.InterfaceNameToIndex.cs" />
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.SocketAddress.cs"
-             Link="Common\Interop\Unix\System.Native\Interop.SocketAddress.cs" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetsBrowser)' == 'true'">
+    <Compile Include="$(CommonPath)System\Net\NetworkInformation\HostInformationPal.Browser.cs"
+             Link="Common\System\Net\NetworkInformation\HostInformationPal.Browser.cs" />
+    <Compile Include="$(CommonPath)System\Net\NetworkInformation\InterfaceInfoPal.Browser.cs"
+             Link="Common\System\Net\NetworkInformation\InterfaceInfoPal.Browser.cs" />
   </ItemGroup>
   <ItemGroup>
     <Reference Include="Microsoft.Win32.Primitives" />
diff --git a/src/libraries/System.Net.Primitives/src/System/Net/Cookie.cs b/src/libraries/System.Net.Primitives/src/System/Net/Cookie.cs
index c953ef2b89731e..dc694bc09ecde7 100644
--- a/src/libraries/System.Net.Primitives/src/System/Net/Cookie.cs
+++ b/src/libraries/System.Net.Primitives/src/System/Net/Cookie.cs
@@ -414,14 +414,6 @@ internal bool VerifySetDefaults(CookieVariant variant, Uri uri, bool isLocalDoma
                     // Domain must start with '.' if set explicitly.
                     if (domain[0] != '.')
                     {
-                        if (!(variant == CookieVariant.Rfc2965 || variant == CookieVariant.Plain))
-                        {
-                            if (shouldThrow)
-                            {
-                                throw new CookieException(SR.Format(SR.net_cookie_attribute, CookieFields.DomainAttributeName, m_domain));
-                            }
-                            return false;
-                        }
                         domain = '.' + domain;
                     }
 
@@ -498,7 +490,24 @@ internal bool VerifySetDefaults(CookieVariant variant, Uri uri, bool isLocalDoma
                 switch (m_cookieVariant)
                 {
                     case CookieVariant.Plain:
-                        m_path = path;
+                        // As per RFC6265 5.1.4. (https://tools.ietf.org/html/rfc6265#section-5.1.4):
+                        // | 2. If the uri-path is empty or if the first character of the uri-
+                        // |    path is not a %x2F ("/") character, output %x2F ("/") and skip
+                        // |    the remaining steps.
+                        // | 3. If the uri-path contains no more than one %x2F ("/") character,
+                        // |    output %x2F ("/") and skip the remaining step.
+                        // Note: Normally Uri.AbsolutePath contains at least one "/" after parsing,
+                        //       but it's possible construct Uri with an empty path using a custom UriParser
+                        int lastSlash;
+                        if (path.Length == 0 || path[0] != '/' || (lastSlash = path.LastIndexOf('/')) == 0)
+                        {
+                            m_path = "/";
+                            break;
+                        }
+
+                        // | 4. Output the characters of the uri-path from the first character up
+                        // |    to, but not including, the right-most %x2F ("/").
+                        m_path = path.Substring(0, lastSlash);
                         break;
                     case CookieVariant.Rfc2109:
                         m_path = path.Substring(0, path.LastIndexOf('/')); // May be empty
@@ -511,18 +520,6 @@ internal bool VerifySetDefaults(CookieVariant variant, Uri uri, bool isLocalDoma
                         break;
                 }
             }
-            else
-            {
-                // Check current path (implicit/explicit) against given URI.
-                if (!path.StartsWith(CookieParser.CheckQuoted(m_path), StringComparison.Ordinal))
-                {
-                    if (shouldThrow)
-                    {
-                        throw new CookieException(SR.Format(SR.net_cookie_attribute, CookieFields.PathAttributeName, m_path));
-                    }
-                    return false;
-                }
-            }
 
             // Set the default port if Port attribute was present but had no value.
             if (setDefault && (m_port_implicit == false && m_port.Length == 0))
diff --git a/src/libraries/System.Net.Primitives/src/System/Net/CookieContainer.cs b/src/libraries/System.Net.Primitives/src/System/Net/CookieContainer.cs
index c381399b43c9cd..9728030b8cd4d6 100644
--- a/src/libraries/System.Net.Primitives/src/System/Net/CookieContainer.cs
+++ b/src/libraries/System.Net.Primitives/src/System/Net/CookieContainer.cs
@@ -6,6 +6,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+using System.Linq;
 using System.Net.NetworkInformation;
 using System.Text;
 
@@ -885,7 +886,7 @@ private void BuildCookieCollectionFromDomainMatches(Uri uri, bool isSecure, int
                     for (int e = 0; e < listCount; e++)
                     {
                         string path = (string)list.GetKey(e);
-                        if (uri.AbsolutePath.StartsWith(CookieParser.CheckQuoted(path), StringComparison.Ordinal))
+                        if (PathMatch(uri.AbsolutePath, path))
                         {
                             CookieCollection cc = (CookieCollection)list.GetByIndex(e)!;
                             cc.TimeStamp(CookieCollection.Stamp.Set);
@@ -905,6 +906,26 @@ private void BuildCookieCollectionFromDomainMatches(Uri uri, bool isSecure, int
             }
         }
 
+        // Implement path-matching according to https://tools.ietf.org/html/rfc6265#section-5.1.4:
+        // | A request-path path-matches a given cookie-path if at least one of the following conditions holds:
+        // | - The cookie-path and the request-path are identical.
+        // | - The cookie-path is a prefix of the request-path, and the last character of the cookie-path is %x2F ("/").
+        // | - The cookie-path is a prefix of the request-path, and the first character of the request-path that is not included in the cookie-path is a %x2F ("/") character.
+        // The latter conditions are needed to make sure that
+        // PathMatch("/fooBar, "/foo") == false
+        // but:
+        // PathMatch("/foo/bar", "/foo") == true, PathMatch("/foo/bar", "/foo/") == true
+        private static bool PathMatch(string requestPath, string cookiePath)
+        {
+            cookiePath = CookieParser.CheckQuoted(cookiePath);
+
+            if (!requestPath.StartsWith(cookiePath, StringComparison.Ordinal))
+                return false;
+            return requestPath.Length == cookiePath.Length ||
+                   cookiePath.Length > 0 && cookiePath[^1] == '/' ||
+                   requestPath[cookiePath.Length] == '/';
+        }
+
         private void MergeUpdateCollections(ref CookieCollection? destination, CookieCollection source, int port, bool isSecure, bool isPlainOnly)
         {
             lock (source)
diff --git a/src/libraries/System.Net.Primitives/src/System/Net/HttpVersion.cs b/src/libraries/System.Net.Primitives/src/System/Net/HttpVersion.cs
index f293df83da617c..55a2b50ad25581 100644
--- a/src/libraries/System.Net.Primitives/src/System/Net/HttpVersion.cs
+++ b/src/libraries/System.Net.Primitives/src/System/Net/HttpVersion.cs
@@ -9,6 +9,5 @@ public static class HttpVersion
         public static readonly Version Version10 = new Version(1, 0);
         public static readonly Version Version11 = new Version(1, 1);
         public static readonly Version Version20 = new Version(2, 0);
-        public static readonly Version Version30 = new Version(3, 0);
     }
 }
diff --git a/src/libraries/System.Net.Primitives/src/System/Net/NetworkError.cs b/src/libraries/System.Net.Primitives/src/System/Net/NetworkError.cs
new file mode 100644
index 00000000000000..44bcac8678a289
--- /dev/null
+++ b/src/libraries/System.Net.Primitives/src/System/Net/NetworkError.cs
@@ -0,0 +1,30 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Net
+{
+    /// <summary>Defines a set of error codes for use with <see cref='System.Net.NetworkException'/>.</summary>
+    public enum NetworkError : int
+    {
+        /// <summary>An unknown network error occurred.</summary>
+        Unknown = 0,
+
+        /// <summary>The requested EndPoint is already in use.</summary>
+        EndPointInUse,
+
+        /// <summary>No such host is known.</summary>
+        HostNotFound,
+
+        /// <summary>No connection could be made because the remote host actively refused it.</summary>
+        ConnectionRefused,
+
+        /// <summary>The operation was aborted by the user.</summary>
+        OperationAborted,
+
+        /// <summary>The connection was aborted by the local host.</summary>
+        ConnectionAborted,
+
+        /// <summary>The connection was forcibly closed by the remote host.</summary>
+        ConnectionReset,
+    }
+}
diff --git a/src/libraries/System.Net.Primitives/src/System/Net/NetworkException.cs b/src/libraries/System.Net.Primitives/src/System/Net/NetworkException.cs
new file mode 100644
index 00000000000000..7b1b48f9379142
--- /dev/null
+++ b/src/libraries/System.Net.Primitives/src/System/Net/NetworkException.cs
@@ -0,0 +1,52 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO;
+using System.Runtime.Serialization;
+
+namespace System.Net
+{
+    /// <summary>Provides socket exceptions to the application.</summary>
+    [Serializable]
+    public class NetworkException : IOException
+    {
+        /// <summary>Creates a new instance of the <see cref='System.Net.NetworkException'/> class with the specified error code.</summary>
+        public NetworkException(NetworkError error, Exception? innerException = null)
+            : this(GetExceptionMessage(error), error, innerException) {}
+
+        /// <summary>Creates a new instance of the <see cref='System.Net.NetworkException'/> class with the specified error code and message.</summary>
+        public NetworkException(string message, NetworkError error, Exception? innerException = null)
+            : base(message, innerException)
+        {
+            NetworkError = error;
+        }
+
+        /// <summary>Creates a new instance of the <see cref='System.Net.NetworkException'/> from serialized data.</summary>
+        protected NetworkException(SerializationInfo serializationInfo, StreamingContext streamingContext)
+            : base(serializationInfo, streamingContext)
+        {
+            NetworkError = (NetworkError)serializationInfo.GetInt32("NetworkError");
+        }
+
+        /// <summary>Populates the serialization data for this object.</summary>
+        public override void GetObjectData(SerializationInfo serializationInfo, StreamingContext streamingContext)
+        {
+            base.GetObjectData(serializationInfo, streamingContext);
+            serializationInfo.AddValue("NetworkError", (int)NetworkError);
+        }
+
+        /// <summary>Returns the specific kind of error.</summary>
+        public NetworkError NetworkError { get; }
+
+        private static string GetExceptionMessage(NetworkError error) => error switch
+        {
+            NetworkError.EndPointInUse => SR.networkerror_addressinuse,
+            NetworkError.HostNotFound => SR.networkerror_hostnotfound,
+            NetworkError.ConnectionRefused => SR.networkerror_connectionrefused,
+            NetworkError.ConnectionAborted => SR.networkerror_connectionaborted,
+            NetworkError.ConnectionReset => SR.networkerror_connectionreset,
+            NetworkError.OperationAborted => SR.networkerror_operationaborted,
+            _ => SR.networkerror_unknown
+        };
+    }
+}
diff --git a/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieContainerTest.cs b/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieContainerTest.cs
index 6b45b096ccab7e..da3bd1f6e909f4 100644
--- a/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieContainerTest.cs
+++ b/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieContainerTest.cs
@@ -140,7 +140,6 @@ public static IEnumerable<object[]> SetCookiesInvalidData()
             yield return new object[] { u5, "$=value" }; // Invalid name
             yield return new object[] { new Uri("http://url.com"), "na\tme=value; domain=.domain.com" }; // Invalid name
             yield return new object[] { new Uri("http://url.com"), "name=value; domain=.domain.com" }; // Domain not the same
-            yield return new object[] { new Uri("http://url.com/path"), "name=value; domain=.url.com; path=/root" }; // Path not the same
             yield return new object[] { new Uri("http://url.com:90"), "name=value; port=\"80\"" }; // Port not the same
             yield return new object[] { new Uri("http://url.com"), "name=value; domain=" }; // Empty domain
             yield return new object[] { u6, "name11=value11; version=invalidversion" }; // Invalid version
diff --git a/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieTest/CookieContainerTest.cs b/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieTest/CookieContainerTest.cs
index 621bc1d371054c..ca5086386b14e4 100644
--- a/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieTest/CookieContainerTest.cs
+++ b/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieTest/CookieContainerTest.cs
@@ -13,7 +13,7 @@ public partial class CookieContainerTest
         private const string CookieValue2 = "CookieValue2";
 
         [Fact]
-        public void Add_CookieVersion1AndRootDomainWithNoLeadingDot_ThrowsCookieException()
+        public void Add_CookieVersion1AndRootDomainWithNoLeadingDot_Success()
         {
             const string SchemePrefix = "http://";
             const string OriginalDomain = "contoso.com";
@@ -21,7 +21,8 @@ public void Add_CookieVersion1AndRootDomainWithNoLeadingDot_ThrowsCookieExceptio
             var container = new CookieContainer();
             var cookie = new Cookie(CookieName1, CookieValue1) { Version = 1, Domain = OriginalDomain };
             var uri = new Uri(SchemePrefix + OriginalDomain);
-            Assert.Throws<CookieException>(() => container.Add(uri, cookie));
+            container.Add(uri, cookie);
+            Assert.Equal(1, container.GetCookies(uri).Count);
         }
 
         [Fact]
diff --git a/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieTest/CookiePortTest.cs b/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieTest/CookiePortTest.cs
index d7a3428507674f..5ed895d050d1f4 100644
--- a/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieTest/CookiePortTest.cs
+++ b/src/libraries/System.Net.Primitives/tests/FunctionalTests/CookieTest/CookiePortTest.cs
@@ -13,65 +13,65 @@ public class CookiePortTest
         public CookiePortTest()
         {
             _cc = new CookieContainer();
-            _cookie = new Cookie("name", "value1", "/path", "localhost");
+            _cookie = new Cookie("name", "value1", "/path", "example.com");
             // use both space and comma as delimiter
             _cookie.Port = "\"80 110,1050, 1090 ,1100\"";
-            _cc.Add(new Uri("http://localhost/path"), _cookie);
+            _cc.Add(new Uri("http://example.com/path"), _cookie);
         }
 
         [Fact]
         public void Port_SetMultiplePorts_Port1Set()
         {
-            CookieCollection cookies = _cc.GetCookies(new Uri("http://localhost:80/path"));
+            CookieCollection cookies = _cc.GetCookies(new Uri("http://example.com:80/path"));
             Assert.Equal(1, cookies.Count);
         }
 
         [Fact]
         public void Port_SpaceDelimiter_PortSet()
         {
-            CookieCollection cookies = _cc.GetCookies(new Uri("http://localhost:110/path"));
+            CookieCollection cookies = _cc.GetCookies(new Uri("http://example.com:110/path"));
             Assert.Equal(1, cookies.Count);
         }
 
         [Fact]
         public void Port_CommaDelimiter_PortSet()
         {
-            CookieCollection cookies = _cc.GetCookies(new Uri("http://localhost:1050/path"));
+            CookieCollection cookies = _cc.GetCookies(new Uri("http://example.com:1050/path"));
             Assert.Equal(1, cookies.Count);
         }
 
         [Fact]
         public void Port_CommaSpaceDelimiter_PortSet()
         {
-            CookieCollection cookies = _cc.GetCookies(new Uri("http://localhost:1090/path"));
+            CookieCollection cookies = _cc.GetCookies(new Uri("http://example.com:1090/path"));
             Assert.Equal(1, cookies.Count);
         }
 
         [Fact]
         public void Port_SpaceCommaDelimiter_PortSet()
         {
-            CookieCollection cookies = _cc.GetCookies(new Uri("http://localhost:1100/path"));
+            CookieCollection cookies = _cc.GetCookies(new Uri("http://example.com:1100/path"));
             Assert.Equal(1, cookies.Count);
         }
 
         [Fact]
         public void Port_SetMultiplePorts_NoPortMatch()
         {
-            CookieCollection cookies = _cc.GetCookies(new Uri("http://localhost:1000/path"));
+            CookieCollection cookies = _cc.GetCookies(new Uri("http://example.com:1000/path"));
             Assert.Equal(0, cookies.Count);
         }
 
         [Fact]
         public void Port_SetMultiplePorts_NoPathMatch()
         {
-            CookieCollection cookies = _cc.GetCookies(new Uri("http://localhost:1050"));
+            CookieCollection cookies = _cc.GetCookies(new Uri("http://example.com:1050"));
             Assert.Equal(0, cookies.Count);
         }
 
         [Fact]
         public void Port_NoPortSpecified_ReturnsCookies()
         {
-            CookieCollection cookies = _cc.GetCookies(new Uri("http://localhost/path"));
+            CookieCollection cookies = _cc.GetCookies(new Uri("http://example.com/path"));
             Assert.Equal(1, cookies.Count);
         }
     }
diff --git a/src/libraries/System.Net.Primitives/tests/FunctionalTests/NetworkExceptionTest.cs b/src/libraries/System.Net.Primitives/tests/FunctionalTests/NetworkExceptionTest.cs
new file mode 100644
index 00000000000000..a7f60c9de1624b
--- /dev/null
+++ b/src/libraries/System.Net.Primitives/tests/FunctionalTests/NetworkExceptionTest.cs
@@ -0,0 +1,34 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Xunit;
+
+namespace System.Net.Primitives.Functional.Tests
+{
+    public static class NetworkExceptionTest
+    {
+        [Fact]
+        public static void Create_AllErrorCodes_Success()
+        {
+            foreach (NetworkError error in Enum.GetValues(typeof(NetworkError)))
+            {
+                NetworkException e = new NetworkException(error);
+                Assert.Equal(error, e.NetworkError);
+                Assert.Null(e.InnerException);
+                Assert.NotNull(e.Message);
+            }
+        }
+
+        [Fact]
+        public static void Create_InnerExceptionAndMessage_Success()
+        {
+            const string Message = "Hello";
+            Exception inner = new Exception();
+
+            NetworkException e = new NetworkException(Message, NetworkError.Unknown, inner);
+
+            Assert.Equal(inner, e.InnerException);
+            Assert.Equal(Message, e.Message);
+        }
+    }
+}
diff --git a/src/libraries/System.Net.Primitives/tests/FunctionalTests/SocketAddressTest.cs b/src/libraries/System.Net.Primitives/tests/FunctionalTests/SocketAddressTest.cs
index a4ce20f12fbd92..af2a89c4807a50 100644
--- a/src/libraries/System.Net.Primitives/tests/FunctionalTests/SocketAddressTest.cs
+++ b/src/libraries/System.Net.Primitives/tests/FunctionalTests/SocketAddressTest.cs
@@ -98,7 +98,7 @@ public static void ToString_LegacyUnknownFamily_Success(AddressFamily family)
         [Theory]
         [InlineData(AddressFamily.Packet)]
         [InlineData(AddressFamily.ControllerAreaNetwork)]
-        [PlatformSpecific(~TestPlatforms.Linux)]
+        [PlatformSpecific(~(TestPlatforms.Linux | TestPlatforms.Browser))]
         public static void ToString_UnsupportedFamily_Throws(AddressFamily family)
         {
             Assert.Throws<PlatformNotSupportedException>(() => new SocketAddress(family));
diff --git a/src/libraries/System.Net.Primitives/tests/FunctionalTests/System.Net.Primitives.Functional.Tests.csproj b/src/libraries/System.Net.Primitives/tests/FunctionalTests/System.Net.Primitives.Functional.Tests.csproj
index 7dca1982f9e4e3..215b3411c287d8 100644
--- a/src/libraries/System.Net.Primitives/tests/FunctionalTests/System.Net.Primitives.Functional.Tests.csproj
+++ b/src/libraries/System.Net.Primitives/tests/FunctionalTests/System.Net.Primitives.Functional.Tests.csproj
@@ -20,6 +20,7 @@
     <Compile Include="IPEndPointParsing.cs" />
     <Compile Include="IPEndPointTest.cs" />
     <Compile Include="NetworkCredentialTest.cs" />
+    <Compile Include="NetworkExceptionTest.cs" />
     <Compile Include="SocketAddressTest.cs" />
     <Compile Include="LoggingTest.cs" />
     <Compile Include="RequestCachePolicyTest.cs" />
@@ -27,7 +28,4 @@
     <Compile Include="$(CommonTestPath)System\Diagnostics\Tracing\TestEventListener.cs"
              Link="Common\System\Diagnostics\Tracing\TestEventListener.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.Memory" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Primitives/tests/PalTests/System.Net.Primitives.Pal.Tests.csproj b/src/libraries/System.Net.Primitives/tests/PalTests/System.Net.Primitives.Pal.Tests.csproj
index 38a9e23817f92b..26647c83c7f1ad 100644
--- a/src/libraries/System.Net.Primitives/tests/PalTests/System.Net.Primitives.Pal.Tests.csproj
+++ b/src/libraries/System.Net.Primitives/tests/PalTests/System.Net.Primitives.Pal.Tests.csproj
@@ -11,7 +11,7 @@
   </PropertyGroup>
   <!-- Do not reference these assemblies from the TargetingPack since we are building part of the source code for tests. -->
   <ItemGroup>
-    <DefaultReferenceExclusions Include="System.Net.Primitives" />
+    <DefaultReferenceExclusion Include="System.Net.Primitives" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="..\..\src\System\Net\Sockets\AddressFamily.cs"
@@ -85,8 +85,6 @@
   <ItemGroup Condition="'$(TargetsUnix)' == 'true' or '$(TargetsBrowser)' == 'true'">
     <Compile Include="..\..\src\System\Net\SocketException.Unix.cs"
              Link="ProductionCode\System\Net\SocketException.Unix.cs" />
-    <Compile Include="$(CommonPath)System\Net\NetworkInformation\HostInformationPal.Unix.cs"
-             Link="Common\System\Net\NetworkInformation\HostInformationPal.Unix.cs" />
     <Compile Include="$(CommonPath)System\Net\SocketAddressPal.Unix.cs"
              Link="Common\System\Net\SocketAddressPal.Unix.cs" />
     <Compile Include="$(CommonPath)System\Net\Sockets\SocketErrorPal.Unix.cs"
@@ -97,21 +95,31 @@
              Link="ProductionCode\Interop\Unix\Interop.Errors.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Libraries.cs"
              Link="ProductionCode\Common\Interop\Unix\Interop.Libraries.cs" />
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetDomainName.cs"
-             Link="ProductionCode\Common\Interop\Unix\System.Native\Interop.GetDomainName.cs" />
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetHostName.cs"
-             Link="ProductionCode\Common\Interop\Unix\System.Native\Interop.GetHostName.cs" />
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetNameInfo.cs"
-             Link="ProductionCode\Common\Interop\Unix\System.Native\Interop.GetNameInfo.cs" />
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.HostEntry.cs"
-             Link="ProductionCode\Common\Interop\Unix\System.Native\Interop.HostEntry.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.IPAddress.cs"
              Link="ProductionCode\Common\Interop\Unix\System.Native\Interop.IPAddress.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.SocketAddress.cs"
              Link="ProductionCode\Common\Interop\Unix\System.Native\Interop.SocketAddress.cs" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
+    <Compile Include="$(CommonPath)System\Net\NetworkInformation\HostInformationPal.Unix.cs"
+             Link="Common\System\Net\NetworkInformation\HostInformationPal.Unix.cs" />
     <Compile Include="$(CommonPath)System\Net\NetworkInformation\InterfaceInfoPal.Unix.cs"
-             Link="ProductionCode\Common\System\Net\NetworkInformation\InterfaceInfoPal.Unix.cs" />
+             Link="Common\System\Net\NetworkInformation\InterfaceInfoPal.Unix.cs" />
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetDomainName.cs"
+             Link="Common\Interop\Unix\System.Native\Interop.GetDomainName.cs" />
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetHostName.cs"
+             Link="Common\Interop\Unix\System.Native\Interop.GetHostName.cs" />
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetNameInfo.cs"
+             Link="Common\Interop\Unix\System.Native\Interop.GetNameInfo.cs" />
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.HostEntry.cs"
+             Link="Common\Interop\Unix\System.Native\Interop.HostEntry.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.InterfaceNameToIndex.cs"
-             Link="ProductionCode\Common\Interop\Unix\System.Native\Interop.InterfaceNameToIndex.cs" />
+             Link="Common\Interop\Unix\System.Native\Interop.InterfaceNameToIndex.cs" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetsBrowser)' == 'true'">
+    <Compile Include="$(CommonPath)System\Net\NetworkInformation\HostInformationPal.Browser.cs"
+             Link="Common\System\Net\NetworkInformation\HostInformationPal.Browser.cs" />
+    <Compile Include="$(CommonPath)System\Net\NetworkInformation\InterfaceInfoPal.Browser.cs"
+             Link="ProductionCode\Common\System\Net\NetworkInformation\InterfaceInfoPal.Browser.cs" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Primitives/tests/UnitTests/CookieContainerTest.cs b/src/libraries/System.Net.Primitives/tests/UnitTests/CookieContainerTest.cs
index ec97b807714d6c..6daad6860a7b2a 100644
--- a/src/libraries/System.Net.Primitives/tests/UnitTests/CookieContainerTest.cs
+++ b/src/libraries/System.Net.Primitives/tests/UnitTests/CookieContainerTest.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Net;
 using System.Threading.Tasks;
 
@@ -36,6 +37,18 @@ public class CookieContainerTest
         private const string CookieValue1 = "CookieValue1";
         private const string CookieValue2 = "CookieValue2";
 
+        // Creates cookies as following:
+        // c1  | .url1.com     | name1=value
+        // c2  | .url1.com     | name2=value; Secure=True
+        // c3  | .url1.com     | name3=value; $Version=1;  $Domain=.url1.com; $Port="80, 90, 100, 443"
+        // c4  | 127.0.0.1     | name4=value
+        // c5  | 127.0.0.1     | name4=value; Path=/path
+        // c6  | .url3.com     | name6=value
+        // c7  | .url3.com     | name7=value
+        // c8  | url4.com      | name8=value
+        // c9  | url4.com      | name9=value
+        // c10 | url5.com/path | name10=value
+        // c11 | url5.com/path | name11=value; $Version=1;  $Port="80, 90, 100"
         private CookieContainer CreateCount11Container()
         {
             CookieContainer cc1 = new CookieContainer();
@@ -100,9 +113,9 @@ public static IEnumerable<object[]> SetCookiesData()
                 new Cookie[]
                 {
                     c10,
+                    c11,
                     new Cookie("name98", "value98"),
                     new Cookie("name99", "value99"),
-                    c11
                 }
             }; // Simple
 
@@ -364,7 +377,7 @@ public void SetCookies_Success(Uri uri, string cookieHeader, Cookie[] expected)
         }
 
         [Fact]
-        public void Add_CookieVersion1AndRootDomainWithNoLeadingDot_ThrowsCookieException()
+        public void Add_CookieVersion1AndRootDomainWithNoLeadingDot_Success()
         {
             const string SchemePrefix = "http://";
             const string OriginalDomain = "contoso.com";
@@ -372,7 +385,8 @@ public void Add_CookieVersion1AndRootDomainWithNoLeadingDot_ThrowsCookieExceptio
             var container = new CookieContainer();
             var cookie = new Cookie(CookieName1, CookieValue1) { Version = 1, Domain = OriginalDomain };
             var uri = new Uri(SchemePrefix + OriginalDomain);
-            Assert.Throws<CookieException>(() => container.Add(uri, cookie));
+            container.Add(uri, cookie);
+            Assert.Equal(1, container.GetCookies(uri).Count);
         }
 
         [Fact]
@@ -636,7 +650,7 @@ public void GetCookies_DifferentPaths_GetsMatchedPathsIncludingEmptyPath()
         {
             // Internally, paths are stored alphabetically sorted - so expect a cookie collection sorted by the path of each cookie
             // This test ensures that all cookies with paths (that the path specified by the uri starts with) are returned
-            Cookie c1 = new Cookie("name1", "value", "/aa", ".url.com");
+            Cookie c1 = new Cookie("name1", "value", "/a/a", ".url.com");
             Cookie c2 = new Cookie("name2", "value", "/a", ".url.com");
             Cookie c3 = new Cookie("name3", "value", "/b", ".url.com"); // Should be ignored - no match with the URL's path
             Cookie c4 = new Cookie("name4", "value", "/", ".url.com"); // Should NOT be ignored (has no path specified)
@@ -647,7 +661,7 @@ public void GetCookies_DifferentPaths_GetsMatchedPathsIncludingEmptyPath()
             cc1.Add(c3);
             cc1.Add(c4);
 
-            CookieCollection cc2 = cc1.GetCookies(new Uri("http://url.com/aaa"));
+            CookieCollection cc2 = cc1.GetCookies(new Uri("http://url.com/a/a/a"));
             Assert.Equal(3, cc2.Count);
             Assert.Equal(c1, cc2[0]);
             Assert.Equal(c2, cc2[1]);
@@ -762,5 +776,156 @@ private void VerifyGetCookies(CookieContainer cc1, Uri uri, Cookie[] expected)
                 Assert.Equal(c1.Value, c2.Value);
             }
         }
+
+        public static IEnumerable<object[]> DomainCheckIgnoresVersionData()
+        {
+            string[] hosts = { "localhost", "example.com", "test.example.com" };
+            int?[] ports = { null, 5000 };
+            int?[] versions = { null, 0, 1, 100 };
+
+            foreach (string host in hosts)
+            {
+                foreach (int? port in ports)
+                {
+                    string url = $"http://{host}" + (port != null ? $":{port}" : "");
+                    string domainWithLeadingDot = "." + host;
+
+                    foreach (int? version in versions)
+                    {
+                        // domain with leading dot
+                        yield return new object[] { url, domainWithLeadingDot, version };
+
+                        // domain without leading dot
+                        yield return new object[] { url, host, version };
+                    }
+                }
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(DomainCheckIgnoresVersionData))]
+        public void SetCookies_DomainCheckSuccess_IgnoresVersion(string url, string domain, int? version)
+        {
+            var uri = new Uri(url);
+
+            string cookie = $"my_cookie=my_value; Domain={domain}" + (version != null ? $"; Version = {version}" : "");
+            CookieContainer container = new CookieContainer();
+
+            container.SetCookies(uri, cookie);
+
+            CookieCollection acceptedCookies = container.GetCookies(uri);
+            Assert.Equal(1, acceptedCookies.Count);
+            Assert.Equal(domain, acceptedCookies[0].Domain);
+        }
+
+        [Theory]
+        [InlineData(".example.com")]
+        [InlineData("example.com")]
+        [InlineData(".test.example.com")]
+        [InlineData("test.example.com")]
+        public void SetCookies_DomainCheckSuccess_IgnoresAbsenceOfLeadingDot(string domain)
+        {
+            var uri = new Uri("http://test.example.com");
+
+            string cookie = $"my_cookie=my_value; Domain={domain}";
+            CookieContainer container = new CookieContainer();
+
+            container.SetCookies(uri, cookie);
+
+            CookieCollection acceptedCookies = container.GetCookies(uri);
+            Assert.Equal(1, acceptedCookies.Count);
+            Assert.Equal(domain, acceptedCookies[0].Domain);
+        }
+
+        [Theory]
+        [InlineData(".other.example.com")]
+        [InlineData("other.example.com")]
+        [InlineData(".xample.com")]
+        [InlineData("xample.com")]
+        public void SetCookies_DomainCheckFailure_IgnoresAbsenceOfLeadingDot(string domain)
+        {
+            var uri = new Uri("http://test.example.com");
+
+            string cookie = $"my_cookie=my_value; Domain={domain}";
+            CookieContainer container = new CookieContainer();
+
+            Assert.Throws<CookieException>(() => container.SetCookies(uri, cookie));
+        }
+
+        // Test default-path calculation as defined in
+        // https://tools.ietf.org/html/rfc6265#section-5.1.4
+        public static readonly TheoryData<string, string> DefaultPathData = new TheoryData<string, string>()
+        {
+            {"http://url1.com", "/"},
+            {"http://url1.com/abc", "/"},
+            {"http://url1.com/abc/xy", "/abc"},
+            {"http://url1.com/abc/xy/foo", "/abc/xy"},
+            {"http://127.0.0.1", "/"},
+            {"http://127.0.0.1/a/s/d/f", "/a/s/d"},
+        };
+
+        [Theory]
+        [MemberData(nameof(DefaultPathData))]
+        public void GetCookies_DefaultPathCalculationFollowsRfc6265(string uriString, string expectedPath)
+        {
+            Cookie cookie = new Cookie("n", "v");
+            Uri uri = new Uri(uriString);
+
+            CookieContainer container = new CookieContainer();
+            container.Add(uri, cookie);
+
+            Cookie actualCookie = container.GetCookies(uri).Single();
+            Assert.Equal(expectedPath, actualCookie.Path);
+        }
+
+        // Test path-match as defined in
+        // https://tools.ietf.org/html/rfc6265#section-5.1.4
+        public static readonly TheoryData<bool, string[], string, int> PathMatchData = new TheoryData<bool, string[], string, int>
+        {
+            {false, new [] {"/"}, "/", 1},
+            {false, new [] {"/asd/fg/hjk/l", "/x"}, "/asd/fg/hjk/l", 1},
+            {false, new [] {"/a", "/x"}, "/a/hello", 1},
+            {false, new [] {"/a/foo", "/a/lol"}, "/a/foo/1/2/3", 1},
+            {false, new [] {"/a/", "/x"}, "/a/hello", 1},
+            {false, new [] {"", "/x"}, "/y", 1},
+            {false, new [] {"//"}, "/", 0},
+            {false, new [] {"//"}, "//", 1},
+            {false, new [] {"", "/", "//", "///"}, "///", 4},
+
+            // Should not match the second half of the criteria:
+            // "The cookie-path is a prefix of the request-path, and the first
+            // character of the request-path that is not included in the cookie-
+            // path is a %x2F ("/") character."
+            {false, new [] {"/a/foo", "/x"}, "/a/foo123", 0},
+
+            {true, new [] {"/"}, "/", 1},
+            {true, new [] {"/a/b", "/a/c", "/x/y"}, "/a/hello", 2},
+            {true, new [] {"/a/foo/b", "/a/foo/c", "/a/foo/42", "/a/lol/42"}, "/a/foo/hello", 3},
+        };
+
+        [Theory]
+        [MemberData(nameof(PathMatchData))]
+        public void GetCookies_PathMatchingFollowsRfc6265(bool useDefaultPath, string[] cookiePaths, string requestPath, int expectedMatches)
+        {
+            CookieContainer container = new CookieContainer();
+
+            int i = 0;
+            foreach (string cookiePath in cookiePaths)
+            {
+                if (useDefaultPath)
+                {
+                    container.Add(new Uri("http://test.com" + cookiePath), new Cookie($"c{i}", "value"));
+                }
+                else
+                {
+                    container.Add(new Uri("http://test.com"), new Cookie($"c{i}", "value", cookiePath));
+                }
+                i++;
+            }
+
+            Uri requestUri = new Uri("http://test.com" + requestPath);
+            CookieCollection collection = container.GetCookies(requestUri);
+            Assert.Equal(expectedMatches, collection.Count);
+        }
     }
 }
diff --git a/src/libraries/System.Net.Primitives/tests/UnitTests/System.Net.Primitives.UnitTests.Tests.csproj b/src/libraries/System.Net.Primitives/tests/UnitTests/System.Net.Primitives.UnitTests.Tests.csproj
index aefbc4c814fa58..4619f2a57ad2fe 100644
--- a/src/libraries/System.Net.Primitives/tests/UnitTests/System.Net.Primitives.UnitTests.Tests.csproj
+++ b/src/libraries/System.Net.Primitives/tests/UnitTests/System.Net.Primitives.UnitTests.Tests.csproj
@@ -12,7 +12,7 @@
   </PropertyGroup>
   <!-- Do not reference these assemblies from the TargetingPack since we are building part of the source code for tests. -->
   <ItemGroup>
-    <DefaultReferenceExclusions Include="System.Net.Primitives" />
+    <DefaultReferenceExclusion Include="System.Net.Primitives" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="CookieInternalTest.cs" />
diff --git a/src/libraries/System.Net.Requests/Directory.Build.props b/src/libraries/System.Net.Requests/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Net.Requests/Directory.Build.props
+++ b/src/libraries/System.Net.Requests/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Requests/src/Resources/Strings.resx b/src/libraries/System.Net.Requests/src/Resources/Strings.resx
index cb28aec1a43a20..5240ec2908eec6 100644
--- a/src/libraries/System.Net.Requests/src/Resources/Strings.resx
+++ b/src/libraries/System.Net.Requests/src/Resources/Strings.resx
@@ -267,4 +267,7 @@
   <data name="net_invalid_host" xml:space="preserve">
     <value>The specified value is not a valid Host header string.</value>
   </data>
+  <data name="SystemNetRequests_PlatformNotSupported" xml:space="preserve">
+    <value>System.Net.Requests is not supported on this platform.</value>
+  </data>
 </root>
diff --git a/src/libraries/System.Net.Requests/src/System.Net.Requests.csproj b/src/libraries/System.Net.Requests/src/System.Net.Requests.csproj
index 9db098574bbd4f..b21e3f4132676e 100644
--- a/src/libraries/System.Net.Requests/src/System.Net.Requests.csproj
+++ b/src/libraries/System.Net.Requests/src/System.Net.Requests.csproj
@@ -1,12 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RootNamespace>System.Net.Requests</RootNamespace>
-    <AssemblyName>System.Net.Requests</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
-  <ItemGroup>
+  <PropertyGroup>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemNetRequests_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <NoWarn Condition="'$(GeneratePlatformNotSupportedAssemblyMessage)' != ''">$(NoWarn);CS0809</NoWarn>
+  </PropertyGroup>
+  <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
     <Compile Include="System\Net\AuthenticationManager.cs" />
     <Compile Include="System\Net\Authorization.cs" />
     <Compile Include="System\Net\FileWebRequest.cs" />
@@ -79,12 +81,13 @@
              Link="Common\System\Net\ContextAwareResult.Windows.cs" />
     <Compile Include="System\Net\WebExceptionPal.Windows.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetsUnix)' == 'true' or '$(TargetsBrowser)' == 'true' ">
+  <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
     <Compile Include="$(CommonPath)System\Net\ContextAwareResult.Unix.cs"
              Link="Common\System\Net\ContextAwareResult.Unix.cs" />
     <Compile Include="System\Net\WebExceptionPal.Unix.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.NonGeneric" />
@@ -103,7 +106,6 @@
     <Reference Include="System.Security.Claims" />
     <Reference Include="System.Security.Cryptography.X509Certificates" />
     <Reference Include="System.Security.Principal" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Thread" />
   </ItemGroup>
diff --git a/src/libraries/System.Net.Requests/src/System/Net/FtpControlStream.cs b/src/libraries/System.Net.Requests/src/System/Net/FtpControlStream.cs
index 5ddcd417e9b2b9..4fb863569a6b65 100644
--- a/src/libraries/System.Net.Requests/src/System/Net/FtpControlStream.cs
+++ b/src/libraries/System.Net.Requests/src/System/Net/FtpControlStream.cs
@@ -499,6 +499,7 @@ protected override PipelineEntry[] BuildCommandsList(WebRequest req)
                 if (domainUserName.Length == 0 && password.Length == 0)
                 {
                     domainUserName = "anonymous";
+                    // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Anonymous FTP credential in production code.")]
                     password = "anonymous@";
                 }
 
diff --git a/src/libraries/System.Net.Requests/src/System/Net/FtpWebRequest.cs b/src/libraries/System.Net.Requests/src/System/Net/FtpWebRequest.cs
index b95ba4b49d1092..dacc4b7cf96219 100644
--- a/src/libraries/System.Net.Requests/src/System/Net/FtpWebRequest.cs
+++ b/src/libraries/System.Net.Requests/src/System/Net/FtpWebRequest.cs
@@ -220,6 +220,7 @@ public sealed class FtpWebRequest : WebRequest
         private LazyAsyncResult? _readAsyncResult;
         private LazyAsyncResult? _requestCompleteAsyncResult;
 
+        // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Anonymous FTP credential in production code.")]
         private static readonly NetworkCredential s_defaultFtpNetworkCredential = new NetworkCredential("anonymous", "anonymous@", string.Empty);
         private const int s_DefaultTimeout = 100000;  // 100 seconds
         private static readonly TimerThread.Queue s_DefaultTimerQueue = TimerThread.GetOrCreateQueue(s_DefaultTimeout);
diff --git a/src/libraries/System.Net.Requests/tests/AssemblyInfo.cs b/src/libraries/System.Net.Requests/tests/AssemblyInfo.cs
index 527dabb9c3cdc4..67d13a0af274a1 100644
--- a/src/libraries/System.Net.Requests/tests/AssemblyInfo.cs
+++ b/src/libraries/System.Net.Requests/tests/AssemblyInfo.cs
@@ -4,4 +4,4 @@
 using Xunit;
 
 [assembly: ActiveIssue("https://github.com/dotnet/runtime/issues/34690", TestPlatforms.Windows, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
-[assembly: ActiveIssue("https://github.com/dotnet/runtime/issues/38283", TestPlatforms.Browser)]
+[assembly: SkipOnMono("System.Net.Requests is not supported on Browser.", TestPlatforms.Browser)]
diff --git a/src/libraries/System.Net.Requests/tests/HttpWebRequestTest.cs b/src/libraries/System.Net.Requests/tests/HttpWebRequestTest.cs
index c09a28538162bd..32903adbbe8741 100644
--- a/src/libraries/System.Net.Requests/tests/HttpWebRequestTest.cs
+++ b/src/libraries/System.Net.Requests/tests/HttpWebRequestTest.cs
@@ -109,7 +109,7 @@ public static IEnumerable<object[]> MixedWebRequestParameters()
             yield return new object[] {new HttpWebRequestParameters { AllowAutoRedirect = true, AutomaticDecompression = DecompressionMethods.GZip,
                 MaximumAutomaticRedirections = 2, MaximumResponseHeadersLength = 100, PreAuthenticate = true, SslProtocols = SecurityProtocolType.Tls12, Timeout = 100000}, true};
             yield return new object[] {new HttpWebRequestParameters { AllowAutoRedirect = false, AutomaticDecompression = DecompressionMethods.GZip,
-                MaximumAutomaticRedirections = 2, MaximumResponseHeadersLength = 100, PreAuthenticate = true, SslProtocols = SecurityProtocolType.Tls12, Timeout = 10000,
+                MaximumAutomaticRedirections = 2, MaximumResponseHeadersLength = 100, PreAuthenticate = true, SslProtocols = SecurityProtocolType.Tls12, Timeout = 100000,
                 NewServerCertificateValidationCallback = true }, false};
             yield return new object[] {new HttpWebRequestParameters { AllowAutoRedirect = true, AutomaticDecompression = DecompressionMethods.GZip,
                 MaximumAutomaticRedirections = 2, MaximumResponseHeadersLength = 100, PreAuthenticate = true, SslProtocols = SecurityProtocolType.Tls12, Timeout = 100000,
@@ -1688,62 +1688,60 @@ public void GetResponseAsync_ParametersAreNotCachable_CreateNewClient(HttpWebReq
         public void GetResponseAsync_ParametersAreCachableButDifferent_CreateNewClient()
         {
             RemoteExecutor.Invoke(async (async) =>
-             {
-                 using (var listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
-                 {
-                     listener.Bind(new IPEndPoint(IPAddress.Loopback, 0));
-                     listener.Listen(1);
-                     var ep = (IPEndPoint)listener.LocalEndPoint;
-                     var uri = new Uri($"http://{ep.Address}:{ep.Port}/");
-
-                     var referenceParameters = new HttpWebRequestParameters
-                     {
-                         AllowAutoRedirect = true,
-                         AutomaticDecompression = DecompressionMethods.GZip,
-                         MaximumAutomaticRedirections = 2,
-                         MaximumResponseHeadersLength = 100,
-                         PreAuthenticate = true,
-                         SslProtocols = SecurityProtocolType.Tls12,
-                         Timeout = 100000
-                     };
-                     HttpWebRequest firstRequest = WebRequest.CreateHttp(uri);
-                     referenceParameters.Configure(firstRequest);
-                     firstRequest.Method = HttpMethod.Get.Method;
-
-                     string responseContent = "Test response.";
-
-                     Task<WebResponse> firstResponseTask = bool.Parse(async) ? firstRequest.GetResponseAsync() : Task.Run(() => firstRequest.GetResponse());
-                     using (Socket server = await listener.AcceptAsync())
-                     using (var serverStream = new NetworkStream(server, ownsSocket: false))
-                     using (var serverReader = new StreamReader(serverStream))
-                     {
-                         await ReplyToClient(responseContent, server, serverReader);
-                         await VerifyResponse(responseContent, firstResponseTask);
-
-                         foreach (object[] caseRow in CachableWebRequestParameters())
-                         {
-                             var currentParameters = (HttpWebRequestParameters)caseRow[0];
-                             bool connectionReused = (bool)caseRow[1];
-                             Task<Socket> secondAccept = listener.AcceptAsync();
-
-                             HttpWebRequest currentRequest = WebRequest.CreateHttp(uri);
-                             currentParameters.Configure(currentRequest);
-
-                             Task<WebResponse> currentResponseTask = bool.Parse(async) ? currentRequest.GetResponseAsync() : Task.Run(() => currentRequest.GetResponse());
-                             if (connectionReused)
-                             {
-                                 await ReplyToClient(responseContent, server, serverReader);
-                                 Assert.False(secondAccept.IsCompleted);
-                                 await VerifyResponse(responseContent, currentResponseTask);
-                             }
-                             else
-                             {
-                                 await VerifyNewConnection(responseContent, secondAccept, currentResponseTask);
-                             }
-                         }
-                     }
-                 }
-             }, (this is HttpWebRequestTest_Async).ToString()).Dispose();
+            {
+                using (var listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
+                {
+                    listener.Bind(new IPEndPoint(IPAddress.Loopback, 0));
+                    listener.Listen(1);
+                    var ep = (IPEndPoint)listener.LocalEndPoint;
+                    var uri = new Uri($"http://{ep.Address}:{ep.Port}/");
+                    var referenceParameters = new HttpWebRequestParameters
+                    {
+                        AllowAutoRedirect = true,
+                        AutomaticDecompression = DecompressionMethods.GZip,
+                        MaximumAutomaticRedirections = 2,
+                        MaximumResponseHeadersLength = 100,
+                        PreAuthenticate = true,
+                        SslProtocols = SecurityProtocolType.Tls12,
+                        Timeout = 100000
+                    };
+                    HttpWebRequest firstRequest = WebRequest.CreateHttp(uri);
+                    referenceParameters.Configure(firstRequest);
+                    firstRequest.Method = HttpMethod.Get.Method;
+
+                    string responseContent = "Test response.";
+                    Task<WebResponse> firstResponseTask = bool.Parse(async) ? firstRequest.GetResponseAsync() : Task.Run(() => firstRequest.GetResponse());
+                    using (Socket server = await listener.AcceptAsync())
+                    using (var serverStream = new NetworkStream(server, ownsSocket: false))
+                    using (var serverReader = new StreamReader(serverStream))
+                    {
+                        await ReplyToClient(responseContent, server, serverReader);
+                        await VerifyResponse(responseContent, firstResponseTask);
+
+                        foreach (object[] caseRow in CachableWebRequestParameters())
+                        {
+                            var currentParameters = (HttpWebRequestParameters)caseRow[0];
+                            bool connectionReused = (bool)caseRow[1];
+                            Task<Socket> secondAccept = listener.AcceptAsync();
+
+                            HttpWebRequest currentRequest = WebRequest.CreateHttp(uri);
+                            currentParameters.Configure(currentRequest);
+
+                            Task<WebResponse> currentResponseTask = bool.Parse(async) ? currentRequest.GetResponseAsync() : Task.Run(() => currentRequest.GetResponse());
+                            if (connectionReused)
+                            {
+                                await ReplyToClient(responseContent, server, serverReader);
+                                Assert.False(secondAccept.IsCompleted);
+                                await VerifyResponse(responseContent, currentResponseTask);
+                            }
+                            else
+                            {
+                                await VerifyNewConnection(responseContent, secondAccept, currentResponseTask);
+                            }
+                        }
+                    }
+                }
+            }, (this is HttpWebRequestTest_Async).ToString()).Dispose();
         }
 
         [Fact]
diff --git a/src/libraries/System.Net.Requests/tests/System.Net.Requests.Tests.csproj b/src/libraries/System.Net.Requests/tests/System.Net.Requests.Tests.csproj
index e0c47d0262bdbf..ecb8a780af90ce 100644
--- a/src/libraries/System.Net.Requests/tests/System.Net.Requests.Tests.csproj
+++ b/src/libraries/System.Net.Requests/tests/System.Net.Requests.Tests.csproj
@@ -4,6 +4,7 @@
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <DefineConstants>$(DefineConstants);NETSTANDARD</DefineConstants>
+    <IgnoreForCI Condition="'$(TargetOS)' == 'Browser'">true</IgnoreForCI>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="AssemblyInfo.cs" />
diff --git a/src/libraries/System.Net.Security/Directory.Build.props b/src/libraries/System.Net.Security/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Net.Security/Directory.Build.props
+++ b/src/libraries/System.Net.Security/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Security/ref/System.Net.Security.cs b/src/libraries/System.Net.Security/ref/System.Net.Security.cs
index 3ef7ad8ab16fdb..9092eb24326eb6 100644
--- a/src/libraries/System.Net.Security/ref/System.Net.Security.cs
+++ b/src/libraries/System.Net.Security/ref/System.Net.Security.cs
@@ -119,7 +119,6 @@ public readonly struct SslClientHelloInfo
         private readonly int _dummyPrimitive;
         public static readonly System.Net.Security.SslApplicationProtocol Http11;
         public static readonly System.Net.Security.SslApplicationProtocol Http2;
-        public static readonly System.Net.Security.SslApplicationProtocol Http3;
         public SslApplicationProtocol(byte[] protocol) { throw null; }
         public SslApplicationProtocol(string protocol) { throw null; }
         public System.ReadOnlyMemory<byte> Protocol { get { throw null; } }
diff --git a/src/libraries/System.Net.Security/ref/System.Net.Security.csproj b/src/libraries/System.Net.Security/ref/System.Net.Security.csproj
index 6e4bace9eb569f..f5519a69b6028f 100644
--- a/src/libraries/System.Net.Security/ref/System.Net.Security.csproj
+++ b/src/libraries/System.Net.Security/ref/System.Net.Security.csproj
@@ -9,12 +9,10 @@
   <ItemGroup>
     <ProjectReference Include="..\..\System.Collections.NonGeneric\ref\System.Collections.NonGeneric.csproj" />
     <ProjectReference Include="..\..\System.Collections\ref\System.Collections.csproj" />
+    <ProjectReference Include="..\..\System.Memory\ref\System.Memory.csproj" />
     <ProjectReference Include="..\..\System.Net.Primitives\ref\System.Net.Primitives.csproj" />
     <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
     <ProjectReference Include="..\..\System.Security.Cryptography.X509Certificates\ref\System.Security.Cryptography.X509Certificates.csproj" />
     <ProjectReference Include="..\..\System.Security.Principal\ref\System.Security.Principal.csproj" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.Memory" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Security/src/System.Net.Security.csproj b/src/libraries/System.Net.Security/src/System.Net.Security.csproj
index 1c423af89c5e33..9c5b528027f2fb 100644
--- a/src/libraries/System.Net.Security/src/System.Net.Security.csproj
+++ b/src/libraries/System.Net.Security/src/System.Net.Security.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Net.Security</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser;$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS</TargetFrameworks>
     <!-- This is needed so that code for TlsCipherSuite will have no namespace (causes compile errors) when used within T4 template  -->
@@ -152,16 +151,28 @@
              Link="Common\Interop\Windows\Interop.Libraries.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Interop.UNICODE_STRING.cs"
              Link="Common\Interop\Windows\Interop.UNICODE_STRING.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_CONTEXT.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.CERT_PUBLIC_KEY_INFO.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_ALGORITHM_IDENTIFIER.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_ALGORITHM_IDENTIFIER.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CRYPT_BIT_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.CRYPT_BIT_BLOB.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.DATA_BLOB.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.DATA_BLOB.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.certificates.cs"
              Link="Common\Interop\Windows\Crypt32\Interop.certificates.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.certificates_types.cs"
              Link="Common\Interop\Windows\Crypt32\Interop.certificates_types.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.CertEnumCertificatesInStore.cs"
              Link="Common\Interop\Windows\Crypt32\Interop.CertEnumCertificatesInStore.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Crypt32\Interop.MsgEncodingType.cs"
+             Link="Common\Interop\Windows\Crypt32\Interop.Interop.MsgEncodingType.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.CloseHandle.cs"
              Link="Common\Interop\Windows\Kernel32\Interop.CloseHandle.cs" />
-    <Compile Include="$(CommonPath)Interop\Windows\NtDll\Interop.RtlGetVersion.cs"
-             Link="Common\Interop\Windows\NtDll\Interop.RtlGetVersion.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\SChannel\Interop.Alerts.cs"
              Link="Common\Interop\Windows\SChannel\Interop.Alerts.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\SChannel\Interop.SchProtocols.cs"
@@ -345,6 +356,7 @@
     <Compile Include="System\Net\Security\CipherSuitesPolicyPal.OSX.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
@@ -361,15 +373,14 @@
     <Reference Include="System.Security.Cryptography.Encoding" />
     <Reference Include="System.Security.Cryptography.X509Certificates" />
     <Reference Include="System.Security.Principal" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.ThreadPool" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.OpenSsl\src\System.Security.Cryptography.OpenSsl.csproj" />
     <Reference Include="System.Console" Condition="'$(Configuration)' == 'Debug'" />
     <Reference Include="System.Diagnostics.StackTrace" />
     <Reference Include="System.Security.Cryptography.Algorithms" />
-    <Reference Include="System.Security.Cryptography.OpenSsl" />
     <Reference Include="System.Security.Cryptography.Primitives" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.Security/src/System/Net/BufferAsyncResult.cs b/src/libraries/System.Net.Security/src/System/Net/BufferAsyncResult.cs
deleted file mode 100644
index 456ca9a9b47eb1..00000000000000
--- a/src/libraries/System.Net.Security/src/System/Net/BufferAsyncResult.cs
+++ /dev/null
@@ -1,64 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Diagnostics;
-
-namespace System.Net
-{
-    //
-    // Preserve the original request buffer & sizes for user IO requests.
-    // This is returned as an IAsyncResult to the application.
-    //
-    internal sealed class BufferAsyncResult : LazyAsyncResult
-    {
-        /// <summary>Stored into LazyAsyncResult.Result to indicate a completed result.</summary>
-        public static readonly object ResultSentinal = nameof(BufferAsyncResult) + "." + nameof(ResultSentinal);
-        /// <summary>Stores the input count or the output result of the operation.</summary>
-        private int _countOrResult;
-#if DEBUG
-        /// <summary>true if <see cref="_countOrResult"/> backs <see cref="Int32Result"/>, false if <see cref="Count"/>.</summary>
-        private bool _countOrResultIsResult;
-#endif
-
-        public BufferAsyncResult(object asyncObject, byte[] buffer, int offset, int count, object? asyncState, AsyncCallback? asyncCallback)
-            : base(asyncObject, asyncState, asyncCallback)
-        {
-            Buffer = buffer;
-            Offset = offset;
-            _countOrResult = count;
-        }
-
-        public byte[] Buffer { get; }
-        public int Offset { get; }
-        public int Count
-        {
-            get
-            {
-#if DEBUG
-                Debug.Assert(!_countOrResultIsResult, "Trying to get count after it's already the result");
-#endif
-                return _countOrResult;
-            }
-        }
-
-        public int Int32Result // Int32Result to differentiate from the base's "object Result"
-        {
-            get
-            {
-#if DEBUG
-                Debug.Assert(_countOrResultIsResult, "Still represents the count, not the result");
-                Debug.Assert(ReferenceEquals(Result, ResultSentinal), "Expected the base object Result to be the sentinel");
-#endif
-                return _countOrResult;
-            }
-            set
-            {
-#if DEBUG
-                Debug.Assert(!_countOrResultIsResult, "Should only be set when result hasn't yet been set");
-                _countOrResultIsResult = true;
-#endif
-                _countOrResult = value;
-            }
-        }
-    }
-}
diff --git a/src/libraries/System.Net.Security/src/System/Net/HelperAsyncResults.cs b/src/libraries/System.Net.Security/src/System/Net/HelperAsyncResults.cs
deleted file mode 100644
index 0280f57c0ea902..00000000000000
--- a/src/libraries/System.Net.Security/src/System/Net/HelperAsyncResults.cs
+++ /dev/null
@@ -1,121 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Diagnostics;
-using System.Threading;
-
-namespace System.Net
-{
-    // The callback type used with below AsyncProtocolRequest class
-    internal delegate void AsyncProtocolCallback(AsyncProtocolRequest asyncRequest);
-
-    //
-    // The class mimics LazyAsyncResult although it does not need to be thread safe nor it does need an Event.
-    // We use this to implement iterative protocol logic:
-    // 1) It can be reused for handshake-like or multi-IO request protocols.
-    // 2) It won't block async IO since there is NO event handler exposed.
-    //
-    // UserAsyncResult property is a link into original user IO request (could be a BufferAsyncResult).
-    //
-    internal class AsyncProtocolRequest
-    {
-        private AsyncProtocolCallback? _callback;
-        private int _completionStatus;
-
-        private const int StatusNotStarted = 0;
-        private const int StatusCompleted = 1;
-        private const int StatusCheckedOnSyncCompletion = 2;
-
-        public LazyAsyncResult UserAsyncResult;
-        public int Result;
-        public readonly CancellationToken CancellationToken;
-
-        public byte[]? Buffer; // Temporary buffer reused by a protocol.
-        public int Offset;
-        public int Count;
-
-        public AsyncProtocolRequest(LazyAsyncResult userAsyncResult, CancellationToken cancellationToken = default)
-        {
-            if (userAsyncResult == null)
-            {
-                NetEventSource.Fail(this, "userAsyncResult == null");
-            }
-            if (userAsyncResult!.InternalPeekCompleted)
-            {
-                NetEventSource.Fail(this, "userAsyncResult is already completed.");
-            }
-            UserAsyncResult = userAsyncResult;
-            CancellationToken = cancellationToken;
-        }
-
-        public void SetNextRequest(byte[]? buffer, int offset, int count, AsyncProtocolCallback? callback)
-        {
-            if (_completionStatus != StatusNotStarted)
-            {
-                throw new InternalException(_completionStatus); // Pending operation is in progress.
-            }
-
-            Buffer = buffer;
-            Offset = offset;
-            Count = count;
-            _callback = callback;
-        }
-
-        internal object? AsyncObject => UserAsyncResult.AsyncObject;
-
-        //
-        // Notify protocol so a next stage could be started.
-        //
-        internal void CompleteRequest(int result)
-        {
-            Result = result;
-            int status = Interlocked.Exchange(ref _completionStatus, StatusCompleted);
-            if (status == StatusCompleted)
-            {
-                throw new InternalException(); // Only allow one call.
-            }
-
-            if (status == StatusCheckedOnSyncCompletion)
-            {
-                _completionStatus = StatusNotStarted;
-                _callback!(this);
-            }
-        }
-
-        public bool MustCompleteSynchronously
-        {
-            get
-            {
-                int status = Interlocked.Exchange(ref _completionStatus, StatusCheckedOnSyncCompletion);
-                if (status == StatusCheckedOnSyncCompletion)
-                {
-                    throw new InternalException(); // Only allow one call.
-                }
-
-                if (status == StatusCompleted)
-                {
-                    _completionStatus = StatusNotStarted;
-                    return true;
-                }
-                return false;
-            }
-        }
-
-        //
-        // Important: This will abandon _Callback and directly notify UserAsyncResult.
-        //
-        internal void CompleteUserWithError(Exception e) => UserAsyncResult.InvokeCallback(e);
-
-        internal void CompleteUser() => UserAsyncResult.InvokeCallback();
-
-        internal void CompleteUser(int userResult)
-        {
-            Debug.Assert(UserAsyncResult is BufferAsyncResult, "CompleteUser(int) may only be used with a BufferAsyncResult");
-            var bar = (BufferAsyncResult)UserAsyncResult;
-            bar.Int32Result = userResult;
-            bar.InvokeCallback(BufferAsyncResult.ResultSentinal);
-        }
-
-        internal bool IsUserCompleted => UserAsyncResult.InternalPeekCompleted;
-    }
-}
diff --git a/src/libraries/System.Net.Security/src/System/Net/Security/SslApplicationProtocol.cs b/src/libraries/System.Net.Security/src/System/Net/Security/SslApplicationProtocol.cs
index 0c1e3239160a9d..6b1a912588065f 100644
--- a/src/libraries/System.Net.Security/src/System/Net/Security/SslApplicationProtocol.cs
+++ b/src/libraries/System.Net.Security/src/System/Net/Security/SslApplicationProtocol.cs
@@ -10,13 +10,10 @@ namespace System.Net.Security
     public readonly struct SslApplicationProtocol : IEquatable<SslApplicationProtocol>
     {
         private static readonly Encoding s_utf8 = Encoding.GetEncoding(Encoding.UTF8.CodePage, EncoderFallback.ExceptionFallback, DecoderFallback.ExceptionFallback);
-        private static readonly byte[] s_http3Utf8 = new byte[] { 0x68, 0x33 }; // "h3"
         private static readonly byte[] s_http2Utf8 = new byte[] { 0x68, 0x32 }; // "h2"
         private static readonly byte[] s_http11Utf8 = new byte[] { 0x68, 0x74, 0x74, 0x70, 0x2f, 0x31, 0x2e, 0x31 }; // "http/1.1"
 
         // Refer to IANA on ApplicationProtocols: https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml#alpn-protocol-ids
-        // h3
-        public static readonly SslApplicationProtocol Http3 = new SslApplicationProtocol(s_http3Utf8, copy: false);
         // h2
         public static readonly SslApplicationProtocol Http2 = new SslApplicationProtocol(s_http2Utf8, copy: false);
         // http/1.1
diff --git a/src/libraries/System.Net.Security/src/System/Net/Security/SslStream.Implementation.cs b/src/libraries/System.Net.Security/src/System/Net/Security/SslStream.Implementation.cs
index afda3eb1de5e75..5f3c5cdff31eb8 100644
--- a/src/libraries/System.Net.Security/src/System/Net/Security/SslStream.Implementation.cs
+++ b/src/libraries/System.Net.Security/src/System/Net/Security/SslStream.Implementation.cs
@@ -15,8 +15,6 @@ namespace System.Net.Security
 {
     public partial class SslStream
     {
-        private static int s_uniqueNameInteger = 123;
-
         private SslAuthenticationOptions? _sslAuthenticationOptions;
 
         private int _nestedAuth;
@@ -66,10 +64,6 @@ private void ValidateCreateContext(SslClientAuthenticationOptions sslClientAuthe
             try
             {
                 _sslAuthenticationOptions = new SslAuthenticationOptions(sslClientAuthenticationOptions, remoteCallback, localCallback);
-                if (_sslAuthenticationOptions.TargetHost!.Length == 0)
-                {
-                    _sslAuthenticationOptions.TargetHost = "?" + Interlocked.Increment(ref s_uniqueNameInteger).ToString(NumberFormatInfo.InvariantInfo);
-                }
                 _context = new SecureChannel(_sslAuthenticationOptions, this);
             }
             catch (Win32Exception e)
@@ -420,12 +414,15 @@ private async ValueTask<ProtocolToken> ReceiveBlobAsync<TIOAdapter>(TIOAdapter a
                     if (_lastFrame.HandshakeType == TlsHandshakeType.ClientHello)
                     {
                         // SNI if it exist. Even if we could not parse the hello, we can fall-back to default certificate.
-                        _sslAuthenticationOptions!.TargetHost = _lastFrame.TargetName;
+                        if (_lastFrame.TargetName != null)
+                        {
+                            _sslAuthenticationOptions!.TargetHost = _lastFrame.TargetName;
+                        }
 
                         if (_sslAuthenticationOptions.ServerOptionDelegate != null)
                         {
                             SslServerAuthenticationOptions userOptions =
-                                await _sslAuthenticationOptions.ServerOptionDelegate(this, new SslClientHelloInfo(_lastFrame.TargetName, _lastFrame.SupportedVersions),
+                                await _sslAuthenticationOptions.ServerOptionDelegate(this, new SslClientHelloInfo(_sslAuthenticationOptions.TargetHost, _lastFrame.SupportedVersions),
                                                                                     _sslAuthenticationOptions.UserState, adapter.CancellationToken).ConfigureAwait(false);
                             _sslAuthenticationOptions.UpdateOptions(userOptions);
                         }
diff --git a/src/libraries/System.Net.Security/src/System/Net/Security/SslStreamPal.Windows.cs b/src/libraries/System.Net.Security/src/System/Net/Security/SslStreamPal.Windows.cs
index 1056c21ec711ed..5e72e6b553b0d9 100644
--- a/src/libraries/System.Net.Security/src/System/Net/Security/SslStreamPal.Windows.cs
+++ b/src/libraries/System.Net.Security/src/System/Net/Security/SslStreamPal.Windows.cs
@@ -120,7 +120,7 @@ public static SafeFreeCredentials AcquireCredentialsHandle(X509Certificate? cert
 
         // This is legacy crypto API used on .NET Framework and older Windows versions.
         // It only supports TLS up to 1.2
-        public static SafeFreeCredentials AcquireCredentialsHandleSchannelCred(X509Certificate? certificate, SslProtocols protocols, EncryptionPolicy policy, bool isServer)
+        public static unsafe SafeFreeCredentials AcquireCredentialsHandleSchannelCred(X509Certificate? certificate, SslProtocols protocols, EncryptionPolicy policy, bool isServer)
         {
             int protocolFlags = GetProtocolFlagsFromSslProtocols(protocols, isServer);
             Interop.SspiCli.SCHANNEL_CRED.Flags flags;
@@ -150,13 +150,19 @@ public static SafeFreeCredentials AcquireCredentialsHandleSchannelCred(X509Certi
 
             if (NetEventSource.Log.IsEnabled()) NetEventSource.Info($"flags=({flags}), ProtocolFlags=({protocolFlags}), EncryptionPolicy={policy}");
             Interop.SspiCli.SCHANNEL_CRED secureCredential = CreateSecureCredential(
-                Interop.SspiCli.SCHANNEL_CRED.CurrentVersion,
-                certificate,
                 flags,
                 protocolFlags,
                 policy);
 
-            return AcquireCredentialsHandle(direction, secureCredential);
+            Interop.Crypt32.CERT_CONTEXT* certificateHandle = null;
+            if (certificate != null)
+            {
+                secureCredential.cCreds = 1;
+                certificateHandle = (Interop.Crypt32.CERT_CONTEXT*)certificate.Handle;
+                secureCredential.paCred = &certificateHandle;
+            }
+
+            return AcquireCredentialsHandle(direction, &secureCredential);
         }
 
         // This function uses new crypto API to support TLS 1.3 and beyond.
@@ -202,11 +208,11 @@ public static unsafe SafeFreeCredentials AcquireCredentialsHandleSchCredentials(
             credential.dwVersion = Interop.SspiCli.SCH_CREDENTIALS.CurrentVersion;
             credential.dwFlags = flags;
 
-            IntPtr certificateHandle = IntPtr.Zero;
+            Interop.Crypt32.CERT_CONTEXT *certificateHandle = null;
             if (certificate != null)
             {
                 credential.cCreds = 1;
-                certificateHandle = certificate.Handle;
+                certificateHandle = (Interop.Crypt32.CERT_CONTEXT *)certificate.Handle;
                 credential.paCred = &certificateHandle;
             }
 
@@ -442,8 +448,6 @@ private static int GetProtocolFlagsFromSslProtocols(SslProtocols protocols, bool
         }
 
         private static Interop.SspiCli.SCHANNEL_CRED CreateSecureCredential(
-            int version,
-            X509Certificate? certificate,
             Interop.SspiCli.SCHANNEL_CRED.Flags flags,
             int protocols, EncryptionPolicy policy)
         {
@@ -452,12 +456,13 @@ private static Interop.SspiCli.SCHANNEL_CRED CreateSecureCredential(
                 hRootStore = IntPtr.Zero,
                 aphMappers = IntPtr.Zero,
                 palgSupportedAlgs = IntPtr.Zero,
-                paCred = IntPtr.Zero,
+                paCred = null,
                 cCreds = 0,
                 cMappers = 0,
                 cSupportedAlgs = 0,
                 dwSessionLifespan = 0,
-                reserved = 0
+                reserved = 0,
+                dwVersion = Interop.SspiCli.SCHANNEL_CRED.CurrentVersion
             };
 
             if (policy == EncryptionPolicy.RequireEncryption)
@@ -483,14 +488,8 @@ private static Interop.SspiCli.SCHANNEL_CRED CreateSecureCredential(
                 throw new ArgumentException(SR.Format(SR.net_invalid_enum, "EncryptionPolicy"), nameof(policy));
             }
 
-            credential.dwVersion = version;
             credential.dwFlags = flags;
             credential.grbitEnabledProtocols = protocols;
-            if (certificate != null)
-            {
-                credential.paCred = certificate.Handle;
-                credential.cCreds = 1;
-            }
 
             return credential;
         }
@@ -498,7 +497,7 @@ private static Interop.SspiCli.SCHANNEL_CRED CreateSecureCredential(
         //
         // Security: we temporarily reset thread token to open the handle under process account.
         //
-        private static SafeFreeCredentials AcquireCredentialsHandle(Interop.SspiCli.CredentialUse credUsage, Interop.SspiCli.SCHANNEL_CRED secureCredential)
+        private static unsafe SafeFreeCredentials AcquireCredentialsHandle(Interop.SspiCli.CredentialUse credUsage, Interop.SspiCli.SCHANNEL_CRED* secureCredential)
         {
             // First try without impersonation, if it fails, then try the process account.
             // I.E. We don't know which account the certificate context was created under.
diff --git a/src/libraries/System.Net.Security/src/System/Net/Security/TlsFrameHelper.cs b/src/libraries/System.Net.Security/src/System/Net/Security/TlsFrameHelper.cs
index e3657030abecdb..7140fea2cf554b 100644
--- a/src/libraries/System.Net.Security/src/System/Net/Security/TlsFrameHelper.cs
+++ b/src/libraries/System.Net.Security/src/System/Net/Security/TlsFrameHelper.cs
@@ -111,7 +111,6 @@ public enum ApplicationProtocolInfo
             None = 0,
             Http11 = 1,
             Http2 = 2,
-            Http3 = 4,
             Other = 128
         }
 
@@ -673,10 +672,6 @@ private static bool TryGetApplicationProtocolsFromExtension(ReadOnlySpan<byte> e
                     {
                         alpn |= ApplicationProtocolInfo.Http2;
                     }
-                    else if (protocol.SequenceEqual(SslApplicationProtocol.Http3.Protocol.Span))
-                    {
-                        alpn |= ApplicationProtocolInfo.Http3;
-                    }
                     else
                     {
                         alpn |= ApplicationProtocolInfo.Other;
diff --git a/src/libraries/System.Net.Security/src/System/Security/Authentication/ExtendedProtection/ServiceNameCollection.cs b/src/libraries/System.Net.Security/src/System/Security/Authentication/ExtendedProtection/ServiceNameCollection.cs
index 7bfa4f7863ed61..8797f31cf589e6 100644
--- a/src/libraries/System.Net.Security/src/System/Security/Authentication/ExtendedProtection/ServiceNameCollection.cs
+++ b/src/libraries/System.Net.Security/src/System/Security/Authentication/ExtendedProtection/ServiceNameCollection.cs
@@ -133,7 +133,7 @@ private void AddIfNew(IList serviceNames)
         /// <summary>
         /// Normalize, check for duplicates, and add if the value is unique.
         /// </summary>
-        private void AddIfNew([MaybeNull]string serviceName)
+        private void AddIfNew(string serviceName)
         {
             if (string.IsNullOrEmpty(serviceName))
             {
@@ -164,6 +164,7 @@ private static int GetCountOrOne(IEnumerable collection)
         // prefix/host:port
         // prefix/host/DistinguishedName
         // prefix/host:port/DistinguishedName
+        [return: NotNullIfNotNull("inputServiceName")]
         private static string? NormalizeServiceName(string? inputServiceName)
         {
             if (string.IsNullOrWhiteSpace(inputServiceName))
diff --git a/src/libraries/System.Net.Security/tests/FunctionalTests/ServerAsyncAuthenticateTest.cs b/src/libraries/System.Net.Security/tests/FunctionalTests/ServerAsyncAuthenticateTest.cs
index 1518cfc3fa545e..6695fc966ae5ab 100644
--- a/src/libraries/System.Net.Security/tests/FunctionalTests/ServerAsyncAuthenticateTest.cs
+++ b/src/libraries/System.Net.Security/tests/FunctionalTests/ServerAsyncAuthenticateTest.cs
@@ -23,8 +23,6 @@ public class ServerAsyncAuthenticateTest : IDisposable
         private readonly ITestOutputHelper _logVerbose;
         private readonly X509Certificate2 _serverCertificate;
 
-        public static bool IsNotWindows7 => !PlatformDetection.IsWindows7;
-
         public ServerAsyncAuthenticateTest(ITestOutputHelper output)
         {
             _log = output;
@@ -99,9 +97,8 @@ public async Task ServerAsyncAuthenticate_SimpleSniOptions_Success()
             }
         }
 
-        [ConditionalTheory(nameof(IsNotWindows7))]
-        [InlineData(SslProtocols.Tls11)]
-        [InlineData(SslProtocols.Tls12)]
+        [Theory]
+        [MemberData(nameof(SupportedProtocolData))]
         public async Task ServerAsyncAuthenticate_SniSetVersion_Success(SslProtocols version)
         {
             var serverOptions = new SslServerAuthenticationOptions() { ServerCertificate = _serverCertificate, EnabledSslProtocols = version };
@@ -247,6 +244,18 @@ public static IEnumerable<object[]> ProtocolMismatchData()
             yield return new object[] { SslProtocols.Tls12, SslProtocols.Tls11, typeof(AuthenticationException) };
         }
 
+        public static IEnumerable<Object[]> SupportedProtocolData()
+        {
+            if (PlatformDetection.SupportsTls11)
+            {
+                yield return new object[] { SslProtocols.Tls11 };
+            }
+
+            if (PlatformDetection.SupportsTls12)
+            {
+                yield return new object[] { SslProtocols.Tls12 };
+            }
+        }
         #region Helpers
 
         private async Task ServerAsyncSslHelper(
diff --git a/src/libraries/System.Net.Security/tests/FunctionalTests/SslStreamNetworkStreamTest.cs b/src/libraries/System.Net.Security/tests/FunctionalTests/SslStreamNetworkStreamTest.cs
index fffc62a5a36ee2..46345ba49d4262 100644
--- a/src/libraries/System.Net.Security/tests/FunctionalTests/SslStreamNetworkStreamTest.cs
+++ b/src/libraries/System.Net.Security/tests/FunctionalTests/SslStreamNetworkStreamTest.cs
@@ -205,7 +205,7 @@ public async Task SslStream_NestedAuth_Throws()
         [InlineData(true)]
         public async Task SslStream_TargetHostName_Succeeds(bool useEmptyName)
         {
-            string tagetName = useEmptyName ? string.Empty : Guid.NewGuid().ToString("N");
+            string targetName = useEmptyName ? string.Empty : Guid.NewGuid().ToString("N");
 
             (Stream clientStream, Stream serverStream) = TestHelper.GetConnectedStreams();
             using (clientStream)
@@ -218,19 +218,12 @@ public async Task SslStream_TargetHostName_Succeeds(bool useEmptyName)
                 Assert.Equal(string.Empty, client.TargetHostName);
                 Assert.Equal(string.Empty, server.TargetHostName);
 
-                SslClientAuthenticationOptions clientOptions = new SslClientAuthenticationOptions() { TargetHost = tagetName };
+                SslClientAuthenticationOptions clientOptions = new SslClientAuthenticationOptions() { TargetHost = targetName };
                 clientOptions.RemoteCertificateValidationCallback =
                     (sender, certificate, chain, sslPolicyErrors) =>
                     {
                         SslStream stream = (SslStream)sender;
-                        if (useEmptyName)
-                        {
-                            Assert.Equal('?', stream.TargetHostName[0]);
-                        }
-                        else
-                        {
-                            Assert.Equal(tagetName, stream.TargetHostName);
-                        }
+                        Assert.Equal(targetName, stream.TargetHostName);
 
                         return true;
                     };
@@ -240,14 +233,7 @@ public async Task SslStream_TargetHostName_Succeeds(bool useEmptyName)
                     (sender, name) =>
                     {
                         SslStream stream = (SslStream)sender;
-                        if (useEmptyName)
-                        {
-                            Assert.Equal('?', stream.TargetHostName[0]);
-                        }
-                        else
-                        {
-                            Assert.Equal(tagetName, stream.TargetHostName);
-                        }
+                        Assert.Equal(targetName, stream.TargetHostName);
 
                         return certificate;
                     };
@@ -255,16 +241,8 @@ public async Task SslStream_TargetHostName_Succeeds(bool useEmptyName)
                 await TestConfiguration.WhenAllOrAnyFailedWithTimeout(
                                 client.AuthenticateAsClientAsync(clientOptions),
                                 server.AuthenticateAsServerAsync(serverOptions));
-                if (useEmptyName)
-                {
-                    Assert.Equal('?', client.TargetHostName[0]);
-                    Assert.Equal('?', server.TargetHostName[0]);
-                }
-                else
-                {
-                    Assert.Equal(tagetName, client.TargetHostName);
-                    Assert.Equal(tagetName, server.TargetHostName);
-                }
+                Assert.Equal(targetName, client.TargetHostName);
+                Assert.Equal(targetName, server.TargetHostName);
             }
         }
 
diff --git a/src/libraries/System.Net.Security/tests/FunctionalTests/System.Net.Security.Tests.csproj b/src/libraries/System.Net.Security/tests/FunctionalTests/System.Net.Security.Tests.csproj
index 3845b272ae6aed..84bada8bc9ffed 100644
--- a/src/libraries/System.Net.Security/tests/FunctionalTests/System.Net.Security.Tests.csproj
+++ b/src/libraries/System.Net.Security/tests/FunctionalTests/System.Net.Security.Tests.csproj
@@ -108,5 +108,6 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="System.Net.TestData" Version="$(SystemNetTestDataVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.Security/tests/UnitTests/System.Net.Security.Unit.Tests.csproj b/src/libraries/System.Net.Security/tests/UnitTests/System.Net.Security.Unit.Tests.csproj
index 8379fd48c4792a..1d83e45035d666 100644
--- a/src/libraries/System.Net.Security/tests/UnitTests/System.Net.Security.Unit.Tests.csproj
+++ b/src/libraries/System.Net.Security/tests/UnitTests/System.Net.Security.Unit.Tests.csproj
@@ -76,11 +76,4 @@
     <Compile Include="$(CommonPath)System\Net\InternalException.cs"
              Link="ProductionCode\Common\System\Net\InternalException.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="System.Threading" />
-  </ItemGroup>
-</Project>
+</Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.ServicePoint/Directory.Build.props b/src/libraries/System.Net.ServicePoint/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.Net.ServicePoint/Directory.Build.props
+++ b/src/libraries/System.Net.ServicePoint/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Sockets/Directory.Build.props b/src/libraries/System.Net.Sockets/Directory.Build.props
index 42c6eafce67ed8..d68d22c1b917f8 100644
--- a/src/libraries/System.Net.Sockets/Directory.Build.props
+++ b/src/libraries/System.Net.Sockets/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Sockets/ref/System.Net.Sockets.cs b/src/libraries/System.Net.Sockets/ref/System.Net.Sockets.cs
index 0917f00c68e002..11d3309cf116df 100644
--- a/src/libraries/System.Net.Sockets/ref/System.Net.Sockets.cs
+++ b/src/libraries/System.Net.Sockets/ref/System.Net.Sockets.cs
@@ -8,70 +8,70 @@ namespace System.Net.Sockets
 {
     public enum IOControlCode : long
     {
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         EnableCircularQueuing = (long)671088642,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         Flush = (long)671088644,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         AddressListChange = (long)671088663,
         DataToRead = (long)1074030207,
         OobDataRead = (long)1074033415,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         GetBroadcastAddress = (long)1207959557,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         AddressListQuery = (long)1207959574,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         QueryTargetPnpHandle = (long)1207959576,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         AsyncIO = (long)2147772029,
         NonBlockingIO = (long)2147772030,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         AssociateHandle = (long)2281701377,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         MultipointLoopback = (long)2281701385,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         MulticastScope = (long)2281701386,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         SetQos = (long)2281701387,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         SetGroupQos = (long)2281701388,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         RoutingInterfaceChange = (long)2281701397,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         NamespaceChange = (long)2281701401,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         ReceiveAll = (long)2550136833,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         ReceiveAllMulticast = (long)2550136834,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         ReceiveAllIgmpMulticast = (long)2550136835,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         KeepAliveValues = (long)2550136836,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         AbsorbRouterAlert = (long)2550136837,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         UnicastInterface = (long)2550136838,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         LimitBroadcasts = (long)2550136839,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         BindToInterface = (long)2550136840,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         MulticastInterface = (long)2550136841,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         AddMulticastGroupOnInterface = (long)2550136842,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         DeleteMulticastGroupFromInterface = (long)2550136843,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         GetExtensionFunctionPointer = (long)3355443206,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         GetQos = (long)3355443207,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         GetGroupQos = (long)3355443208,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         TranslateHandle = (long)3355443213,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         RoutingInterfaceQuery = (long)3355443220,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         AddressListSort = (long)3355443225,
     }
     public partial struct IPPacketInformation
@@ -254,6 +254,7 @@ public partial class Socket : System.IDisposable
     {
         public Socket(System.Net.Sockets.SafeSocketHandle handle) { }
         public Socket(System.Net.Sockets.AddressFamily addressFamily, System.Net.Sockets.SocketType socketType, System.Net.Sockets.ProtocolType protocolType) { }
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public Socket(System.Net.Sockets.SocketInformation socketInformation) { }
         public Socket(System.Net.Sockets.SocketType socketType, System.Net.Sockets.ProtocolType protocolType) { }
         public System.Net.Sockets.AddressFamily AddressFamily { get { throw null; } }
@@ -325,10 +326,10 @@ public void Disconnect(bool reuseSocket) { }
         public bool DisconnectAsync(System.Net.Sockets.SocketAsyncEventArgs e) { throw null; }
         public void Dispose() { }
         protected virtual void Dispose(bool disposing) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public System.Net.Sockets.SocketInformation DuplicateAndClose(int targetProcessId) { throw null; }
-        public System.Net.Sockets.Socket EndAccept(out byte[]? buffer, System.IAsyncResult asyncResult) { throw null; }
-        public System.Net.Sockets.Socket EndAccept(out byte[]? buffer, out int bytesTransferred, System.IAsyncResult asyncResult) { throw null; }
+        public System.Net.Sockets.Socket EndAccept(out byte[] buffer, System.IAsyncResult asyncResult) { throw null; }
+        public System.Net.Sockets.Socket EndAccept(out byte[] buffer, out int bytesTransferred, System.IAsyncResult asyncResult) { throw null; }
         public System.Net.Sockets.Socket EndAccept(System.IAsyncResult asyncResult) { throw null; }
         public void EndConnect(System.IAsyncResult asyncResult) { }
         public void EndDisconnect(System.IAsyncResult asyncResult) { }
@@ -390,7 +391,7 @@ public void SendFile(string? fileName, byte[]? preBuffer, byte[]? postBuffer, Sy
         public int SendTo(byte[] buffer, System.Net.EndPoint remoteEP) { throw null; }
         public int SendTo(byte[] buffer, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEP) { throw null; }
         public bool SendToAsync(System.Net.Sockets.SocketAsyncEventArgs e) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public void SetIPProtectionLevel(System.Net.Sockets.IPProtectionLevel level) { }
         public void SetRawSocketOption(int optionLevel, int optionName, System.ReadOnlySpan<byte> optionValue) { }
         public void SetSocketOption(System.Net.Sockets.SocketOptionLevel optionLevel, System.Net.Sockets.SocketOptionName optionName, bool optionValue) { }
@@ -625,7 +626,7 @@ public TcpListener(System.Net.IPEndPoint localEP) { }
         public System.Threading.Tasks.Task<System.Net.Sockets.Socket> AcceptSocketAsync() { throw null; }
         public System.Net.Sockets.TcpClient AcceptTcpClient() { throw null; }
         public System.Threading.Tasks.Task<System.Net.Sockets.TcpClient> AcceptTcpClientAsync() { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public void AllowNatTraversal(bool allowed) { }
         public System.IAsyncResult BeginAcceptSocket(System.AsyncCallback? callback, object? state) { throw null; }
         public System.IAsyncResult BeginAcceptTcpClient(System.AsyncCallback? callback, object? state) { throw null; }
@@ -643,11 +644,11 @@ public enum TransmitFileOptions
         UseDefaultWorkerThread = 0,
         Disconnect = 1,
         ReuseSocket = 2,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         WriteBehind = 4,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         UseSystemThread = 16,
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         UseKernelApc = 32,
     }
     public partial class UdpClient : System.IDisposable
@@ -666,7 +667,7 @@ public UdpClient(string hostname, int port) { }
         public bool ExclusiveAddressUse { get { throw null; } set { } }
         public bool MulticastLoopback { get { throw null; } set { } }
         public short Ttl { get { throw null; } set { } }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public void AllowNatTraversal(bool allowed) { }
         public System.IAsyncResult BeginReceive(System.AsyncCallback? requestCallback, object? state) { throw null; }
         public System.IAsyncResult BeginSend(byte[] datagram, int bytes, System.AsyncCallback? requestCallback, object? state) { throw null; }
diff --git a/src/libraries/System.Net.Sockets/src/Resources/Strings.resx b/src/libraries/System.Net.Sockets/src/Resources/Strings.resx
index c2b2e397211ba5..87af48e42174e6 100644
--- a/src/libraries/System.Net.Sockets/src/Resources/Strings.resx
+++ b/src/libraries/System.Net.Sockets/src/Resources/Strings.resx
@@ -262,7 +262,10 @@
   <data name="InvalidNullArgument" xml:space="preserve">
     <value>Null is not a valid value for {0}.</value>
   </data>
-  <data name="Sockets_PlatformNotSupported" xml:space="preserve">
+  <data name="SystemNetSockets_PlatformNotSupported" xml:space="preserve">
     <value>System.Net.Sockets is not supported on this platform.</value>
   </data>
-</root>
+  <data name="net_sockets_accept_receive_apm_notsupported" xml:space="preserve">
+    <value>This platform does not support receiving data with Socket.BeginAccept/EndAccept.  Instead, make a separate call to ReceiveAsync or BeginReceive/EndReceive.</value>
+  </data>
+</root>
\ No newline at end of file
diff --git a/src/libraries/System.Net.Sockets/src/System.Net.Sockets.csproj b/src/libraries/System.Net.Sockets/src/System.Net.Sockets.csproj
index 211dd8a0eafd5e..4d39c2d94a77bb 100644
--- a/src/libraries/System.Net.Sockets/src/System.Net.Sockets.csproj
+++ b/src/libraries/System.Net.Sockets/src/System.Net.Sockets.csproj
@@ -1,12 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Net.Sockets</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.Sockets_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemNetSockets_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <PropertyGroup>
     <!-- SYSTEM_NET_SOCKETS_DLL is required to allow source-level code sharing for types defined within the
@@ -81,6 +80,8 @@
              Link="Common\System\Net\SocketAddress.cs" />
     <Compile Include="$(CommonPath)System\Net\TcpValidationHelpers.cs"
              Link="Common\System\Net\TcpValidationHelpers.cs" />
+    <Compile Include="$(CommonPath)System\Threading\Tasks\TaskToApm.cs"
+             Link="Common\System\Threading\Tasks\TaskToApm.cs" />
     <!-- System.Net.Internals -->
     <Compile Include="$(CommonPath)System\Net\Internals\IPEndPointExtensions.cs"
              Link="Common\System\Net\Internals\IPEndPointExtensions.cs" />
@@ -94,6 +95,8 @@
              Link="Common\System\Net\Sockets\ProtocolType.cs" />
     <Compile Include="$(CommonPath)System\Net\Sockets\SocketType.cs"
              Link="Common\System\Net\Sockets\SocketType.cs" />
+    <Compile Include="$(CommonPath)System\Net\NetworkErrorHelper.cs"
+             Link="Common\System\Net\NetworkErrorHelper.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
     <!-- Windows: CoreCLR -->
@@ -216,8 +219,6 @@
              Link="Common\System\Net\SocketProtocolSupportPal.Unix" />
     <Compile Include="$(CommonPath)System\Net\Sockets\SocketErrorPal.Unix.cs"
              Link="Common\System\Net\Sockets\SocketErrorPal.Unix" />
-    <Compile Include="$(CommonPath)System\Threading\Tasks\TaskToApm.cs"
-             Link="Common\System\Threading\Tasks\TaskToApm.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Errors.cs"
              Link="Common\Interop\Unix\Interop.Errors.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Libraries.cs"
@@ -302,6 +303,7 @@
              Link="Common\Interop\Unix\System.Native\Interop.Write.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
@@ -315,7 +317,6 @@
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Runtime.InteropServices.RuntimeInformation" />
     <Reference Include="System.Security.Claims" />
-    <Reference Include="System.Security.Principal.Windows" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Overlapped" />
     <Reference Include="System.Threading.ThreadPool" />
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/IOControlCode.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/IOControlCode.cs
index fc1d69159bab31..0039c85553c3dd 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/IOControlCode.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/IOControlCode.cs
@@ -7,70 +7,70 @@ namespace System.Net.Sockets
 {
     public enum IOControlCode : long
     {
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         AsyncIO = 0x8004667D,
         NonBlockingIO = 0x8004667E,  // fionbio
         DataToRead = 0x4004667F,  // fionread
         OobDataRead = 0x40047307,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         AssociateHandle = 0x88000001,  // SIO_ASSOCIATE_HANDLE
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         EnableCircularQueuing = 0x28000002,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         Flush = 0x28000004,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         GetBroadcastAddress = 0x48000005,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         GetExtensionFunctionPointer = 0xC8000006,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         GetQos = 0xC8000007,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         GetGroupQos = 0xC8000008,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         MultipointLoopback = 0x88000009,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         MulticastScope = 0x8800000A,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         SetQos = 0x8800000B,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         SetGroupQos = 0x8800000C,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         TranslateHandle = 0xC800000D,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         RoutingInterfaceQuery = 0xC8000014,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         RoutingInterfaceChange = 0x88000015,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         AddressListQuery = 0x48000016,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         AddressListChange = 0x28000017,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         QueryTargetPnpHandle = 0x48000018,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         NamespaceChange = 0x88000019,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         AddressListSort = 0xC8000019,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         ReceiveAll = 0x98000001,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         ReceiveAllMulticast = 0x98000002,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         ReceiveAllIgmpMulticast = 0x98000003,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         KeepAliveValues = 0x98000004,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         AbsorbRouterAlert = 0x98000005,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         UnicastInterface = 0x98000006,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         LimitBroadcasts = 0x98000007,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         BindToInterface = 0x98000008,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         MulticastInterface = 0x98000009,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         AddMulticastGroupOnInterface = 0x9800000A,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         DeleteMulticastGroupFromInterface = 0x9800000B
     }
 }
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/NetworkStream.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/NetworkStream.cs
index d6fa0458bdc579..e2a3ac6fff45d3 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/NetworkStream.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/NetworkStream.cs
@@ -50,15 +50,15 @@ public NetworkStream(Socket socket, FileAccess access, bool ownsSocket)
                 // allowing non-blocking sockets could result in non-deterministic failures from those
                 // operations. A developer that requires using NetworkStream with a non-blocking socket can
                 // temporarily flip Socket.Blocking as a workaround.
-                throw new IOException(SR.net_sockets_blocking);
+                throw GetCustomNetworkException(SR.net_sockets_blocking);
             }
             if (!socket.Connected)
             {
-                throw new IOException(SR.net_notconnected);
+                throw GetCustomNetworkException(SR.net_notconnected);
             }
             if (socket.SocketType != SocketType.Stream)
             {
-                throw new IOException(SR.net_notstream);
+                throw GetCustomNetworkException(SR.net_notstream);
             }
 
             _streamSocket = socket;
@@ -241,11 +241,13 @@ public override int Read(byte[] buffer, int offset, int size)
             {
                 return _streamSocket.Receive(buffer, offset, size, 0);
             }
+            catch (SocketException socketException)
+            {
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
             catch (Exception exception) when (!(exception is OutOfMemoryException))
             {
-                // Some sort of error occurred on the socket call,
-                // set the SocketException as InnerException and throw.
-                throw new IOException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
+                throw GetCustomNetworkException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
             }
         }
 
@@ -266,7 +268,7 @@ public override int Read(Span<byte> buffer)
             if (errorCode != SocketError.Success)
             {
                 var exception = new SocketException((int)errorCode);
-                throw new IOException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
+                throw NetworkErrorHelper.MapSocketException(exception);
             }
             return bytesRead;
         }
@@ -322,11 +324,13 @@ public override void Write(byte[] buffer, int offset, int size)
                 // after ALL the requested number of bytes was transferred.
                 _streamSocket.Send(buffer, offset, size, SocketFlags.None);
             }
+            catch (SocketException socketException)
+            {
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
             catch (Exception exception) when (!(exception is OutOfMemoryException))
             {
-                // Some sort of error occurred on the socket call,
-                // set the SocketException as InnerException and throw.
-                throw new IOException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
+                throw GetCustomNetworkException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
             }
         }
 
@@ -348,7 +352,7 @@ public override void Write(ReadOnlySpan<byte> buffer)
             if (errorCode != SocketError.Success)
             {
                 var exception = new SocketException((int)errorCode);
-                throw new IOException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
+                throw NetworkErrorHelper.MapSocketException(exception);
             }
         }
 
@@ -443,11 +447,13 @@ public override IAsyncResult BeginRead(byte[] buffer, int offset, int size, Asyn
                         callback,
                         state);
             }
+            catch (SocketException socketException)
+            {
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
             catch (Exception exception) when (!(exception is OutOfMemoryException))
             {
-                // Some sort of error occurred on the socket call,
-                // set the SocketException as InnerException and throw.
-                throw new IOException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
+                throw GetCustomNetworkException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
             }
         }
 
@@ -473,11 +479,13 @@ public override int EndRead(IAsyncResult asyncResult)
             {
                 return _streamSocket.EndReceive(asyncResult);
             }
+            catch (SocketException socketException)
+            {
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
             catch (Exception exception) when (!(exception is OutOfMemoryException))
             {
-                // Some sort of error occurred on the socket call,
-                // set the SocketException as InnerException and throw.
-                throw new IOException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
+                throw GetCustomNetworkException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
             }
         }
 
@@ -529,11 +537,13 @@ public override IAsyncResult BeginWrite(byte[] buffer, int offset, int size, Asy
                         callback,
                         state);
             }
+            catch (SocketException socketException)
+            {
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
             catch (Exception exception) when (!(exception is OutOfMemoryException))
             {
-                // Some sort of error occurred on the socket call,
-                // set the SocketException as InnerException and throw.
-                throw new IOException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
+                throw GetCustomNetworkException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
             }
         }
 
@@ -555,11 +565,13 @@ public override void EndWrite(IAsyncResult asyncResult)
             {
                 _streamSocket.EndSend(asyncResult);
             }
+            catch (SocketException socketException)
+            {
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
             catch (Exception exception) when (!(exception is OutOfMemoryException))
             {
-                // Some sort of error occurred on the socket call,
-                // set the SocketException as InnerException and throw.
-                throw new IOException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
+                throw GetCustomNetworkException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
             }
         }
 
@@ -609,11 +621,13 @@ public override Task<int> ReadAsync(byte[] buffer, int offset, int size, Cancell
                     fromNetworkStream: true,
                     cancellationToken).AsTask();
             }
+            catch (SocketException socketException)
+            {
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
             catch (Exception exception) when (!(exception is OutOfMemoryException))
             {
-                // Some sort of error occurred on the socket call,
-                // set the SocketException as InnerException and throw.
-                throw new IOException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
+                throw GetCustomNetworkException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
             }
         }
 
@@ -634,11 +648,13 @@ public override ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken
                     fromNetworkStream: true,
                     cancellationToken: cancellationToken);
             }
+            catch (SocketException socketException)
+            {
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
             catch (Exception exception) when (!(exception is OutOfMemoryException))
             {
-                // Some sort of error occurred on the socket call,
-                // set the SocketException as InnerException and throw.
-                throw new IOException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
+                throw GetCustomNetworkException(SR.Format(SR.net_io_readfailure, exception.Message), exception);
             }
         }
 
@@ -687,11 +703,13 @@ public override Task WriteAsync(byte[] buffer, int offset, int size, Cancellatio
                     SocketFlags.None,
                     cancellationToken).AsTask();
             }
+            catch (SocketException socketException)
+            {
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
             catch (Exception exception) when (!(exception is OutOfMemoryException))
             {
-                // Some sort of error occurred on the socket call,
-                // set the SocketException as InnerException and throw.
-                throw new IOException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
+                throw GetCustomNetworkException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
             }
         }
 
@@ -711,11 +729,13 @@ public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationTo
                     SocketFlags.None,
                     cancellationToken);
             }
+            catch (SocketException socketException)
+            {
+                throw NetworkErrorHelper.MapSocketException(socketException);
+            }
             catch (Exception exception) when (!(exception is OutOfMemoryException))
             {
-                // Some sort of error occurred on the socket call,
-                // set the SocketException as InnerException and throw.
-                throw new IOException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
+                throw GetCustomNetworkException(SR.Format(SR.net_io_writefailure, exception.Message), exception);
             }
         }
 
@@ -772,5 +792,10 @@ private void ThrowIfDisposed()
 
             void ThrowObjectDisposedException() => throw new ObjectDisposedException(GetType().FullName);
         }
+
+        private static NetworkException GetCustomNetworkException(string message, Exception? innerException = null)
+        {
+            return new NetworkException(message, NetworkError.Unknown, innerException);
+        }
     }
 }
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Tasks.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Tasks.cs
index 7e995116b8779e..75a226949d933e 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Tasks.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Tasks.cs
@@ -154,7 +154,7 @@ internal ValueTask<int> ReceiveAsync(Memory<byte> buffer, SocketFlags socketFlag
             Debug.Assert(saea.BufferList == null);
             saea.SetBuffer(buffer);
             saea.SocketFlags = socketFlags;
-            saea.WrapExceptionsInIOExceptions = fromNetworkStream;
+            saea.WrapExceptionsInNetworkExceptions = fromNetworkStream;
             return saea.ReceiveAsync(this, cancellationToken);
         }
 
@@ -237,7 +237,7 @@ internal ValueTask<int> SendAsync(ReadOnlyMemory<byte> buffer, SocketFlags socke
             Debug.Assert(saea.BufferList == null);
             saea.SetBuffer(MemoryMarshal.AsMemory(buffer));
             saea.SocketFlags = socketFlags;
-            saea.WrapExceptionsInIOExceptions = false;
+            saea.WrapExceptionsInNetworkExceptions = false;
             return saea.SendAsync(this, cancellationToken);
         }
 
@@ -255,7 +255,7 @@ internal ValueTask SendAsyncForNetworkStream(ReadOnlyMemory<byte> buffer, Socket
             Debug.Assert(saea.BufferList == null);
             saea.SetBuffer(MemoryMarshal.AsMemory(buffer));
             saea.SocketFlags = socketFlags;
-            saea.WrapExceptionsInIOExceptions = true;
+            saea.WrapExceptionsInNetworkExceptions = true;
             return saea.SendAsyncForNetworkStream(this, cancellationToken);
         }
 
@@ -577,7 +577,7 @@ public AwaitableSocketAsyncEventArgs(Socket owner, bool isReceiveForCaching) :
                 _isReadForCaching = isReceiveForCaching;
             }
 
-            public bool WrapExceptionsInIOExceptions { get; set; }
+            public bool WrapExceptionsInNetworkExceptions { get; set; }
 
             private void Release()
             {
@@ -885,8 +885,8 @@ private Exception CreateException(SocketError error, bool forAsyncThrow = true)
                     e = ExceptionDispatchInfo.SetCurrentStackTrace(e);
                 }
 
-                return WrapExceptionsInIOExceptions ?
-                    new IOException(SR.Format(SR.net_io_readfailure, e.Message), e) :
+                return WrapExceptionsInNetworkExceptions ?
+                    NetworkErrorHelper.MapSocketException((SocketException)e) :
                     e;
             }
         }
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Unix.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Unix.cs
index 0886dbff4ccc35..fd9a6c80fcf417 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Unix.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Unix.cs
@@ -10,7 +10,7 @@ namespace System.Net.Sockets
 {
     public partial class Socket
     {
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public Socket(SocketInformation socketInformation)
         {
             // This constructor works in conjunction with DuplicateAndClose, which is not supported on Unix.
@@ -18,7 +18,7 @@ public Socket(SocketInformation socketInformation)
             throw new PlatformNotSupportedException(SR.net_sockets_duplicateandclose_notsupported);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public SocketInformation DuplicateAndClose(int targetProcessId)
         {
             // DuplicateAndClose is not supported on Unix, since passing file descriptors between processes
@@ -27,6 +27,26 @@ public SocketInformation DuplicateAndClose(int targetProcessId)
             throw new PlatformNotSupportedException(SR.net_sockets_duplicateandclose_notsupported);
         }
 
+        public IAsyncResult BeginAccept(int receiveSize, AsyncCallback? callback, object? state)
+        {
+            throw new PlatformNotSupportedException(SR.net_sockets_accept_receive_apm_notsupported);
+        }
+
+        public IAsyncResult BeginAccept(Socket? acceptSocket, int receiveSize, AsyncCallback? callback, object? state)
+        {
+            throw new PlatformNotSupportedException(SR.net_sockets_accept_receive_apm_notsupported);
+        }
+
+        public Socket EndAccept(out byte[] buffer, IAsyncResult asyncResult)
+        {
+            throw new PlatformNotSupportedException(SR.net_sockets_accept_receive_apm_notsupported);
+        }
+
+        public Socket EndAccept(out byte[] buffer, out int bytesTransferred, IAsyncResult asyncResult)
+        {
+            throw new PlatformNotSupportedException(SR.net_sockets_accept_receive_apm_notsupported);
+        }
+
         internal bool PreferInlineCompletions
         {
             get => _handle.PreferInlineCompletions;
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Windows.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Windows.cs
index d9c64a5471278d..a8cb83dc651f8d 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Windows.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Windows.cs
@@ -17,7 +17,7 @@ public partial class Socket
 
         internal void ReplaceHandleIfNecessaryAfterFailedConnect() { /* nop on Windows */ }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public Socket(SocketInformation socketInformation)
         {
             InitializeSockets();
@@ -106,7 +106,7 @@ private unsafe void LoadSocketTypeFromHandle(
             blocking = true;
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public SocketInformation DuplicateAndClose(int targetProcessId)
         {
             ThrowIfDisposed();
@@ -127,6 +127,30 @@ public SocketInformation DuplicateAndClose(int targetProcessId)
             return info;
         }
 
+        public IAsyncResult BeginAccept(int receiveSize, AsyncCallback? callback, object? state)
+        {
+            return BeginAccept(acceptSocket: null, receiveSize, callback, state);
+        }
+
+        // This is the truly async version that uses AcceptEx.
+        public IAsyncResult BeginAccept(Socket? acceptSocket, int receiveSize, AsyncCallback? callback, object? state)
+        {
+            return BeginAcceptCommon(acceptSocket, receiveSize, callback, state);
+        }
+
+        public Socket EndAccept(out byte[] buffer, IAsyncResult asyncResult)
+        {
+            Socket socket = EndAccept(out byte[] innerBuffer, out int bytesTransferred, asyncResult);
+            buffer = new byte[bytesTransferred];
+            Buffer.BlockCopy(innerBuffer, 0, buffer, 0, bytesTransferred);
+            return socket;
+        }
+
+        public Socket EndAccept(out byte[] buffer, out int bytesTransferred, IAsyncResult asyncResult)
+        {
+            return EndAcceptCommon(out buffer!, out bytesTransferred, asyncResult);
+        }
+
         private void EnsureDynamicWinsockMethods()
         {
             if (_dynamicWinsockMethods == null)
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs
index a874c7f60dc427..9fbc3c4c9a28b6 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs
@@ -1087,6 +1087,8 @@ public Socket Accept()
                     IPEndPointExtensions.Serialize(_rightEndPoint) :
                     new Internals.SocketAddress(_addressFamily, SocketPal.MaximumAddressSize); // may be different size.
 
+            if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptStart(socketAddress);
+
             // This may throw ObjectDisposedException.
             SafeSocketHandle acceptedSocketHandle;
             SocketError errorCode = SocketPal.Accept(
@@ -1098,10 +1100,16 @@ public Socket Accept()
             // Throw an appropriate SocketException if the native call fails.
             if (errorCode != SocketError.Success)
             {
+                if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptFailedAndStop(errorCode, null);
+
                 Debug.Assert(acceptedSocketHandle.IsInvalid);
                 UpdateAcceptSocketErrorForDisposed(ref errorCode);
                 UpdateStatusAfterSocketErrorAndThrowException(errorCode);
             }
+            else
+            {
+                if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptStop();
+            }
 
             Debug.Assert(!acceptedSocketHandle.IsInvalid);
 
@@ -1169,8 +1177,14 @@ public int Send(IList<ArraySegment<byte>> buffers, SocketFlags socketFlags, out
                 // Update the internal state of this socket according to the error before throwing.
                 UpdateStatusAfterSocketError(errorCode);
                 if (NetEventSource.Log.IsEnabled()) NetEventSource.Error(this, new SocketException((int)errorCode));
+                // Don't log transfered byte count in case of a failure.
                 return 0;
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesSent(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramSent();
+            }
 
             return bytesTransferred;
         }
@@ -1222,6 +1236,11 @@ public int Send(byte[] buffer, int offset, int size, SocketFlags socketFlags, ou
                 if (NetEventSource.Log.IsEnabled()) NetEventSource.Error(this, new SocketException((int)errorCode));
                 return 0;
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesSent(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramSent();
+            }
 
             if (NetEventSource.Log.IsEnabled())
             {
@@ -1258,6 +1277,11 @@ public int Send(ReadOnlySpan<byte> buffer, SocketFlags socketFlags, out SocketEr
                 if (NetEventSource.Log.IsEnabled()) NetEventSource.Error(this, new SocketException((int)errorCode));
                 bytesTransferred = 0;
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesSent(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramSent();
+            }
 
             return bytesTransferred;
         }
@@ -1322,6 +1346,11 @@ public int SendTo(byte[] buffer, int offset, int size, SocketFlags socketFlags,
 
                 UpdateStatusAfterSocketErrorAndThrowException(errorCode);
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesSent(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramSent();
+            }
 
             if (_rightEndPoint == null)
             {
@@ -1410,6 +1439,11 @@ public int Receive(byte[] buffer, int offset, int size, SocketFlags socketFlags,
                 if (NetEventSource.Log.IsEnabled()) NetEventSource.Error(this, new SocketException((int)errorCode));
                 return 0;
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesReceived(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramReceived();
+            }
 
             if (NetEventSource.Log.IsEnabled()) NetEventSource.DumpBuffer(this, buffer, offset, bytesTransferred);
 
@@ -1442,6 +1476,11 @@ public int Receive(Span<byte> buffer, SocketFlags socketFlags, out SocketError e
                 if (NetEventSource.Log.IsEnabled()) NetEventSource.Error(this, new SocketException((int)errorCode));
                 bytesTransferred = 0;
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesReceived(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramReceived();
+            }
 
             return bytesTransferred;
         }
@@ -1482,6 +1521,7 @@ public int Receive(IList<ArraySegment<byte>> buffers, SocketFlags socketFlags, o
 
             int bytesTransferred;
             errorCode = SocketPal.Receive(_handle, buffers, socketFlags, out bytesTransferred);
+
             UpdateReceiveSocketErrorForDisposed(ref errorCode, bytesTransferred);
 
             if (errorCode != SocketError.Success)
@@ -1491,6 +1531,11 @@ public int Receive(IList<ArraySegment<byte>> buffers, SocketFlags socketFlags, o
                 if (NetEventSource.Log.IsEnabled()) NetEventSource.Error(this, new SocketException((int)errorCode));
                 return 0;
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesReceived(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramReceived();
+            }
 
             return bytesTransferred;
         }
@@ -1544,12 +1589,16 @@ public int ReceiveMessageFrom(byte[] buffer, int offset, int size, ref SocketFla
             SocketError errorCode = SocketPal.ReceiveMessageFrom(this, _handle, buffer, offset, size, ref socketFlags, socketAddress, out receiveAddress, out ipPacketInformation, out bytesTransferred);
 
             UpdateReceiveSocketErrorForDisposed(ref errorCode, bytesTransferred);
-
             // Throw an appropriate SocketException if the native call fails.
             if (errorCode != SocketError.Success && errorCode != SocketError.MessageSize)
             {
                 UpdateStatusAfterSocketErrorAndThrowException(errorCode);
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesReceived(bytesTransferred);
+                if (errorCode == SocketError.Success && SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramReceived();
+            }
 
             if (!socketAddressOriginal.Equals(receiveAddress))
             {
@@ -1620,7 +1669,6 @@ public int ReceiveFrom(byte[] buffer, int offset, int size, SocketFlags socketFl
             SocketError errorCode = SocketPal.ReceiveFrom(_handle, buffer, offset, size, socketFlags, socketAddress.Buffer, ref socketAddress.InternalSize, out bytesTransferred);
 
             UpdateReceiveSocketErrorForDisposed(ref errorCode, bytesTransferred);
-
             // If the native call fails we'll throw a SocketException.
             SocketException? socketException = null;
             if (errorCode != SocketError.Success)
@@ -1634,6 +1682,11 @@ public int ReceiveFrom(byte[] buffer, int offset, int size, SocketFlags socketFl
                     throw socketException;
                 }
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesReceived(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramReceived();
+            }
 
             if (!socketAddressOriginal.Equals(socketAddress))
             {
@@ -1936,7 +1989,7 @@ public int GetRawSocketOption(int optionLevel, int optionName, Span<byte> option
             return realOptionLength;
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public void SetIPProtectionLevel(IPProtectionLevel level)
         {
             if (level == IPProtectionLevel.Unspecified)
@@ -2578,6 +2631,7 @@ public int EndSend(IAsyncResult asyncResult, out SocketError errorCode)
 
             // Throw an appropriate SocketException if the native call failed asynchronously.
             errorCode = (SocketError)castedAsyncResult.ErrorCode;
+
             if (errorCode != SocketError.Success)
             {
                 UpdateSendSocketErrorForDisposed(ref errorCode);
@@ -2586,6 +2640,11 @@ public int EndSend(IAsyncResult asyncResult, out SocketError errorCode)
                 if (NetEventSource.Log.IsEnabled()) NetEventSource.Error(this, new SocketException((int)errorCode));
                 return 0;
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesSent(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramSent();
+            }
 
             return bytesTransferred;
         }
@@ -2761,6 +2820,11 @@ public int EndSendTo(IAsyncResult asyncResult)
                 UpdateSendSocketErrorForDisposed(ref errorCode);
                 UpdateStatusAfterSocketErrorAndThrowException(errorCode);
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesSent(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramSent();
+            }
 
             return bytesTransferred;
         }
@@ -2997,6 +3061,11 @@ public int EndReceive(IAsyncResult asyncResult, out SocketError errorCode)
                 if (NetEventSource.Log.IsEnabled()) NetEventSource.Error(this, new SocketException((int)errorCode));
                 return 0;
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesReceived(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramReceived();
+            }
             return bytesTransferred;
         }
 
@@ -3165,6 +3234,11 @@ public int EndReceiveMessageFrom(IAsyncResult asyncResult, ref SocketFlags socke
             {
                 UpdateStatusAfterSocketErrorAndThrowException(errorCode);
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesReceived(bytesTransferred);
+                if (errorCode == SocketError.Success && SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramReceived();
+            }
 
             socketFlags = castedAsyncResult.SocketFlags;
             ipPacketInformation = castedAsyncResult.IPPacketInformation;
@@ -3368,6 +3442,11 @@ public int EndReceiveFrom(IAsyncResult asyncResult, ref EndPoint endPoint)
             {
                 UpdateStatusAfterSocketErrorAndThrowException(errorCode);
             }
+            else if (SocketsTelemetry.Log.IsEnabled())
+            {
+                SocketsTelemetry.Log.BytesReceived(bytesTransferred);
+                if (SocketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramReceived();
+            }
             return bytesTransferred;
         }
 
@@ -3393,7 +3472,7 @@ public IAsyncResult BeginAccept(AsyncCallback? callback, object? state)
         {
             if (!_isDisconnected)
             {
-                return BeginAccept(0, callback, state);
+                return BeginAcceptCommon(acceptSocket: null, receiveSize: 0, callback, state);
             }
 
             Debug.Assert(Disposed);
@@ -3401,13 +3480,7 @@ public IAsyncResult BeginAccept(AsyncCallback? callback, object? state)
             return null; // unreachable
         }
 
-        public IAsyncResult BeginAccept(int receiveSize, AsyncCallback? callback, object? state)
-        {
-            return BeginAccept(null, receiveSize, callback, state);
-        }
-
-        // This is the truly async version that uses AcceptEx.
-        public IAsyncResult BeginAccept(Socket? acceptSocket, int receiveSize, AsyncCallback? callback, object? state)
+        private IAsyncResult BeginAcceptCommon(Socket? acceptSocket, int receiveSize, AsyncCallback? callback, object? state)
         {
             ThrowIfDisposed();
 
@@ -3422,16 +3495,6 @@ public IAsyncResult BeginAccept(Socket? acceptSocket, int receiveSize, AsyncCall
             asyncResult.StartPostingAsyncOp(false);
 
             // Start the accept.
-            DoBeginAccept(acceptSocket, receiveSize, asyncResult);
-
-            // Finish the flow capture, maybe complete here.
-            asyncResult.FinishPostingAsyncOp(ref Caches.AcceptClosureCache);
-
-            return asyncResult;
-        }
-
-        private void DoBeginAccept(Socket? acceptSocket, int receiveSize, AcceptOverlappedAsyncResult asyncResult)
-        {
             if (_rightEndPoint == null)
             {
                 throw new InvalidOperationException(SR.net_sockets_mustbind);
@@ -3446,6 +3509,7 @@ private void DoBeginAccept(Socket? acceptSocket, int receiveSize, AcceptOverlapp
             asyncResult.AcceptSocket = GetOrCreateAcceptSocket(acceptSocket, false, nameof(acceptSocket), out acceptHandle);
 
             if (NetEventSource.Log.IsEnabled()) NetEventSource.Info(this, $"AcceptSocket:{acceptSocket}");
+            if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptStart(_rightEndPoint);
 
             int socketAddressSize = GetAddressSize(_rightEndPoint);
             SocketError errorCode = SocketPal.AcceptAsync(this, _handle, acceptHandle, receiveSize, socketAddressSize, asyncResult);
@@ -3455,9 +3519,18 @@ private void DoBeginAccept(Socket? acceptSocket, int receiveSize, AcceptOverlapp
             // Throw an appropriate SocketException if the native call fails synchronously.
             if (!CheckErrorAndUpdateStatus(errorCode))
             {
+                if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptFailedAndStop(errorCode, null);
+
                 UpdateAcceptSocketErrorForDisposed(ref errorCode);
                 throw new SocketException((int)errorCode);
             }
+
+            if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptStop();
+
+            // Finish the flow capture, maybe complete here.
+            asyncResult.FinishPostingAsyncOp(ref Caches.AcceptClosureCache);
+
+            return asyncResult;
         }
 
         // Routine Description:
@@ -3475,24 +3548,9 @@ private void DoBeginAccept(Socket? acceptSocket, int receiveSize, AcceptOverlapp
         //    Socket - a valid socket if successful
         public Socket EndAccept(IAsyncResult asyncResult)
         {
-            int bytesTransferred;
-            byte[]? buffer;
-            return EndAccept(out buffer, out bytesTransferred, asyncResult);
+            return EndAcceptCommon(out _, out _, asyncResult);
         }
-
-        public Socket EndAccept(out byte[]? buffer, IAsyncResult asyncResult)
-        {
-            int bytesTransferred;
-            byte[]? innerBuffer;
-
-            Socket socket = EndAccept(out innerBuffer, out bytesTransferred, asyncResult);
-            buffer = new byte[bytesTransferred];
-            // https://github.com/dotnet/runtime/issues/32633 - this throws on Unix
-            Buffer.BlockCopy(innerBuffer!, 0, buffer, 0, bytesTransferred);
-            return socket;
-        }
-
-        public Socket EndAccept(out byte[]? buffer, out int bytesTransferred, IAsyncResult asyncResult)
+        private Socket EndAcceptCommon(out byte[]? buffer, out int bytesTransferred, IAsyncResult asyncResult)
         {
             ThrowIfDisposed();
 
@@ -3521,9 +3579,15 @@ public Socket EndAccept(out byte[]? buffer, out int bytesTransferred, IAsyncResu
             SocketError errorCode = (SocketError)castedAsyncResult.ErrorCode;
             if (errorCode != SocketError.Success)
             {
+                if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptFailedAndStop(errorCode, null);
+
                 UpdateAcceptSocketErrorForDisposed(ref errorCode);
                 UpdateStatusAfterSocketErrorAndThrowException(errorCode);
             }
+            else
+            {
+                if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptStop();
+            }
 
             if (NetEventSource.Log.IsEnabled()) NetEventSource.Accepted(socket, socket.RemoteEndPoint, socket.LocalEndPoint);
             return socket;
@@ -4073,6 +4137,7 @@ private CacheSet Caches
         #endregion
 
         #region Internal and private methods
+
         internal static void GetIPProtocolInformation(AddressFamily addressFamily, Internals.SocketAddress socketAddress, out bool isIPv4, out bool isIPv6)
         {
             bool isIPv4MappedToIPv6 = socketAddress.Family == AddressFamily.InterNetworkV6 && socketAddress.GetIPAddress().IsIPv4MappedToIPv6;
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.Windows.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.Windows.cs
index 0c4b0fce6a8643..6368666ec6bf43 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.Windows.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.Windows.cs
@@ -486,13 +486,13 @@ internal unsafe SocketError DoOperationReceiveMessageFrom(Socket socket, SafeSoc
             bool ipv4 = (_currentSocket!.AddressFamily == AddressFamily.InterNetwork || (ipAddress != null && ipAddress.IsIPv4MappedToIPv6)); // DualMode
             bool ipv6 = _currentSocket.AddressFamily == AddressFamily.InterNetworkV6;
 
-            if (ipv4 && (_controlBufferPinned == null || _controlBufferPinned.Length != sizeof(Interop.Winsock.ControlData)))
+            if (ipv6 && (_controlBufferPinned == null || _controlBufferPinned.Length != sizeof(Interop.Winsock.ControlDataIPv6)))
             {
-                _controlBufferPinned = GC.AllocateUninitializedArray<byte>(sizeof(Interop.Winsock.ControlData), pinned: true);
+                _controlBufferPinned = GC.AllocateUninitializedArray<byte>(sizeof(Interop.Winsock.ControlDataIPv6), pinned: true);
             }
-            else if (ipv6 && (_controlBufferPinned == null || _controlBufferPinned.Length != sizeof(Interop.Winsock.ControlDataIPv6)))
+            else if (ipv4 && (_controlBufferPinned == null || _controlBufferPinned.Length != sizeof(Interop.Winsock.ControlData)))
             {
-                _controlBufferPinned = GC.AllocateUninitializedArray<byte>(sizeof(Interop.Winsock.ControlDataIPv6), pinned: true);
+                _controlBufferPinned = GC.AllocateUninitializedArray<byte>(sizeof(Interop.Winsock.ControlData), pinned: true);
             }
 
             // If single buffer we need a single element WSABuffer.
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.cs
index 213cb30909b99a..114a65d256d70d 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.cs
@@ -547,6 +547,8 @@ internal void StartOperationAccept()
                     _acceptBuffer = new byte[_acceptAddressBufferCount];
                 }
             }
+
+            if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptStart(_currentSocket!._rightEndPoint!);
         }
 
         internal void StartOperationConnect(MultipleConnectAsync? multipleConnect, bool userSocket)
@@ -587,9 +589,10 @@ internal void FinishOperationSyncFailure(SocketError socketError, int bytesTrans
         {
             SetResults(socketError, bytesTransferred, flags);
 
-            if (SocketsTelemetry.Log.IsEnabled() && _multipleConnect == null && _completedOperation == SocketAsyncOperation.Connect)
+            if (SocketsTelemetry.Log.IsEnabled())
             {
-                SocketsTelemetry.Log.ConnectFailedAndStop(socketError, null);
+                if (_multipleConnect == null && _completedOperation == SocketAsyncOperation.Connect) SocketsTelemetry.Log.ConnectFailedAndStop(socketError, null);
+                if (_completedOperation == SocketAsyncOperation.Accept) SocketsTelemetry.Log.AcceptFailedAndStop(socketError, null);
             }
 
             // This will be null if we're doing a static ConnectAsync to a DnsEndPoint with AddressFamily.Unspecified;
@@ -615,6 +618,8 @@ internal void FinishOperationSyncFailure(SocketError socketError, int bytesTrans
                     break;
             }
 
+            // Don't log transfered byte count in case of a failure.
+
             Complete();
         }
 
@@ -665,6 +670,8 @@ internal void FinishWrapperConnectSuccess(Socket? connectSocket, int bytesTransf
             _currentSocket = connectSocket;
             _connectSocket = connectSocket;
 
+            if (SocketsTelemetry.Log.IsEnabled()) LogBytesTransferEvents(connectSocket?.SocketType, SocketAsyncOperation.Connect, bytesTransferred);
+
             // Complete the operation and raise the event.
             ExecutionContext? context = _context; // store context before it's cleared as part of completing the operation
             Complete();
@@ -708,9 +715,13 @@ internal void FinishOperationSyncSuccess(int bytesTransferred, SocketFlags flags
                             }
                             catch (ObjectDisposedException) { }
                         }
+
+                        if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptStop();
                     }
                     else
                     {
+                        if (SocketsTelemetry.Log.IsEnabled()) SocketsTelemetry.Log.AcceptFailedAndStop(socketError, null);
+
                         SetResults(socketError, bytesTransferred, flags);
                         _acceptSocket = null;
                         _currentSocket.UpdateStatusAfterSocketError(socketError);
@@ -789,6 +800,8 @@ internal void FinishOperationSyncSuccess(int bytesTransferred, SocketFlags flags
                     break;
             }
 
+            if (SocketsTelemetry.Log.IsEnabled()) LogBytesTransferEvents(_currentSocket?.SocketType, _completedOperation, bytesTransferred);
+
             Complete();
         }
 
@@ -822,5 +835,26 @@ private void FinishOperationSync(SocketError socketError, int bytesTransferred,
                 FinishOperationSyncFailure(socketError, bytesTransferred, flags);
             }
         }
+
+        private static void LogBytesTransferEvents(SocketType? socketType, SocketAsyncOperation operation, int bytesTransferred)
+        {
+            switch (operation)
+            {
+                case SocketAsyncOperation.Receive:
+                case SocketAsyncOperation.ReceiveFrom:
+                case SocketAsyncOperation.ReceiveMessageFrom:
+                case SocketAsyncOperation.Accept:
+                    SocketsTelemetry.Log.BytesReceived(bytesTransferred);
+                    if (socketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramReceived();
+                    break;
+                case SocketAsyncOperation.Send:
+                case SocketAsyncOperation.SendTo:
+                case SocketAsyncOperation.SendPackets:
+                case SocketAsyncOperation.Connect:
+                    SocketsTelemetry.Log.BytesSent(bytesTransferred);
+                    if (socketType == SocketType.Dgram) SocketsTelemetry.Log.DatagramSent();
+                    break;
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Windows.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Windows.cs
index d68f47cf377709..1d7947523b12ef 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Windows.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Windows.cs
@@ -436,6 +436,12 @@ public static unsafe IPPacketInformation GetIPPacketInformation(Interop.Winsock.
 
         public static unsafe IPPacketInformation GetIPPacketInformation(Interop.Winsock.ControlDataIPv6* controlBuffer)
         {
+            if (controlBuffer->length == (UIntPtr)sizeof(Interop.Winsock.ControlData))
+            {
+                // IPv4 client connectiong to dual mode socket.
+                return GetIPPacketInformation((Interop.Winsock.ControlData*)controlBuffer);
+            }
+
             IPAddress address = controlBuffer->length != UIntPtr.Zero ?
                 new IPAddress(new ReadOnlySpan<byte>(controlBuffer->address, Interop.Winsock.IPv6AddressLength)) :
                 IPAddress.IPv6None;
@@ -451,7 +457,6 @@ public static unsafe SocketError ReceiveMessageFrom(Socket socket, SafeSocketHan
             bytesTransferred = 0;
             receiveAddress = socketAddress;
             ipPacketInformation = default(IPPacketInformation);
-
             fixed (byte* ptrBuffer = buffer)
             fixed (byte* ptrSocketAddress = socketAddress.Buffer)
             {
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketsTelemetry.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketsTelemetry.cs
index 7f0e2a78eb749a..f3430e7b7ed7d3 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketsTelemetry.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketsTelemetry.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics.Tracing;
+using System.Threading;
 
 namespace System.Net.Sockets
 {
@@ -10,9 +11,24 @@ internal sealed class SocketsTelemetry : EventSource
     {
         public static readonly SocketsTelemetry Log = new SocketsTelemetry();
 
+        private PollingCounter? _outgoingConnectionsEstablishedCounter;
+        private PollingCounter? _incomingConnectionsEstablishedCounter;
+        private PollingCounter? _bytesReceivedCounter;
+        private PollingCounter? _bytesSentCounter;
+        private PollingCounter? _datagramsReceivedCounter;
+        private PollingCounter? _datagramsSentCounter;
+
+        private long _outgoingConnectionsEstablished;
+        private long _incomingConnectionsEstablished;
+        private long _bytesReceived;
+        private long _bytesSent;
+        private long _datagramsReceived;
+        private long _datagramsSent;
+
         [Event(1, Level = EventLevel.Informational)]
         public void ConnectStart(string? address)
         {
+            Interlocked.Increment(ref _outgoingConnectionsEstablished);
             if (IsEnabled(EventLevel.Informational, EventKeywords.All))
             {
                 WriteEvent(eventId: 1, address ?? "");
@@ -46,6 +62,34 @@ public void ConnectCanceled()
             }
         }
 
+        [Event(5, Level = EventLevel.Informational)]
+        public void AcceptStart(string? address)
+        {
+            Interlocked.Increment(ref _incomingConnectionsEstablished);
+            if (IsEnabled(EventLevel.Informational, EventKeywords.All))
+            {
+                WriteEvent(eventId: 5, address ?? "");
+            }
+        }
+
+        [Event(6, Level = EventLevel.Informational)]
+        public void AcceptStop()
+        {
+            if (IsEnabled(EventLevel.Informational, EventKeywords.All))
+            {
+                WriteEvent(eventId: 6);
+            }
+        }
+
+        [Event(7, Level = EventLevel.Error)]
+        public void AcceptFailed(SocketError error, string? exceptionMessage)
+        {
+            if (IsEnabled(EventLevel.Error, EventKeywords.All))
+            {
+                WriteEvent(eventId: 7, (int)error, exceptionMessage ?? string.Empty);
+            }
+        }
+
         [NonEvent]
         public void ConnectStart(Internals.SocketAddress address)
         {
@@ -71,5 +115,81 @@ public void ConnectFailedAndStop(SocketError error, string? exceptionMessage)
             ConnectFailed(error, exceptionMessage);
             ConnectStop();
         }
+
+        [NonEvent]
+        public void AcceptStart(Internals.SocketAddress address)
+        {
+            AcceptStart(address.ToString());
+        }
+
+        [NonEvent]
+        public void AcceptStart(EndPoint address)
+        {
+            AcceptStart(address.ToString());
+        }
+
+        [NonEvent]
+        public void AcceptFailedAndStop(SocketError error, string? exceptionMessage)
+        {
+            AcceptFailed(error, exceptionMessage);
+            AcceptStop();
+        }
+
+        [NonEvent]
+        public void BytesReceived(int count)
+        {
+            Interlocked.Add(ref _bytesReceived, count);
+        }
+
+        [NonEvent]
+        public void BytesSent(int count)
+        {
+            Interlocked.Add(ref _bytesSent, count);
+        }
+
+        [NonEvent]
+        public void DatagramReceived()
+        {
+            Interlocked.Increment(ref _datagramsReceived);
+        }
+
+        [NonEvent]
+        public void DatagramSent()
+        {
+            Interlocked.Increment(ref _datagramsSent);
+        }
+
+        protected override void OnEventCommand(EventCommandEventArgs command)
+        {
+            if (command.Command == EventCommand.Enable)
+            {
+                // This is the convention for initializing counters in the RuntimeEventSource (lazily on the first enable command).
+
+                _outgoingConnectionsEstablishedCounter ??= new PollingCounter("outgoing-connections-established", this, () => Interlocked.Read(ref _outgoingConnectionsEstablished))
+                {
+                    DisplayName = "Outgoing Connections Established",
+                };
+                _incomingConnectionsEstablishedCounter ??= new PollingCounter("incoming-connections-established", this, () => Interlocked.Read(ref _incomingConnectionsEstablished))
+                {
+                    DisplayName = "Incoming Connections Established",
+                };
+                _bytesReceivedCounter ??= new PollingCounter("bytes-received", this, () => Interlocked.Read(ref _bytesReceived))
+                {
+                    DisplayName = "Bytes Received",
+                };
+                _bytesSentCounter ??= new PollingCounter("bytes-sent", this, () => Interlocked.Read(ref _bytesSent))
+                {
+                    DisplayName = "Bytes Sent",
+                };
+                _datagramsReceivedCounter ??= new PollingCounter("datagrams-received", this, () => Interlocked.Read(ref _datagramsReceived))
+                {
+                    DisplayName = "Datagrams Received",
+                };
+                _datagramsSentCounter ??= new PollingCounter("datagrams-sent", this, () => Interlocked.Read(ref _datagramsSent))
+                {
+                    DisplayName = "Datagrams Sent",
+                };
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TCPListener.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TCPListener.cs
index df906c11b4d022..6c623fec1cfb99 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TCPListener.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TCPListener.cs
@@ -112,7 +112,7 @@ public bool ExclusiveAddressUse
             }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public void AllowNatTraversal(bool allowed)
         {
             if (_active)
@@ -207,40 +207,17 @@ public TcpClient AcceptTcpClient()
             return new TcpClient(acceptedSocket);
         }
 
-        public IAsyncResult BeginAcceptSocket(AsyncCallback? callback, object? state)
-        {
-
-            if (!_active)
-            {
-                throw new InvalidOperationException(SR.net_stopped);
-            }
-
-            return _serverSocket!.BeginAccept(callback, state);
-        }
+        public IAsyncResult BeginAcceptSocket(AsyncCallback? callback, object? state) =>
+            TaskToApm.Begin(AcceptSocketAsync(), callback, state);
 
-        public Socket EndAcceptSocket(IAsyncResult asyncResult)
-        {
-            if (asyncResult == null)
-            {
-                throw new ArgumentNullException(nameof(asyncResult));
-            }
-
-            LazyAsyncResult? lazyResult = asyncResult as LazyAsyncResult;
-            Socket? asyncSocket = lazyResult == null ? null : lazyResult.AsyncObject as Socket;
-            if (asyncSocket == null)
-            {
-                throw new ArgumentException(SR.net_io_invalidasyncresult, nameof(asyncResult));
-            }
-
-            // This will throw ObjectDisposedException if Stop() has been called.
-            return asyncSocket.EndAccept(asyncResult);
-        }
+        public Socket EndAcceptSocket(IAsyncResult asyncResult) =>
+            TaskToApm.End<Socket>(asyncResult);
 
         public IAsyncResult BeginAcceptTcpClient(AsyncCallback? callback, object? state) =>
-            BeginAcceptSocket(callback, state);
+            TaskToApm.Begin(AcceptTcpClientAsync(), callback, state);
 
         public TcpClient EndAcceptTcpClient(IAsyncResult asyncResult) =>
-            new TcpClient(EndAcceptSocket(asyncResult));
+            TaskToApm.End<TcpClient>(asyncResult);
 
         public Task<Socket> AcceptSocketAsync()
         {
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TransmitFileOptions.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TransmitFileOptions.cs
index cc1d42c633f00e..32b69e7e53ca64 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TransmitFileOptions.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TransmitFileOptions.cs
@@ -11,11 +11,11 @@ public enum TransmitFileOptions
         UseDefaultWorkerThread = 0x00,
         Disconnect = 0x01,
         ReuseSocket = 0x02,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         WriteBehind = 0x04,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         UseSystemThread = 0x10,
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         UseKernelApc = 0x20,
     };
 }
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/UDPClient.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/UDPClient.cs
index e5b9074bb4cf66..e27a77da1f81db 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/UDPClient.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/UDPClient.cs
@@ -193,7 +193,7 @@ public bool ExclusiveAddressUse
             }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public void AllowNatTraversal(bool allowed)
         {
             _clientSocket.SetIPProtectionLevel(allowed ? IPProtectionLevel.Unrestricted : IPProtectionLevel.EdgeRestricted);
diff --git a/src/libraries/System.Net.Sockets/tests/FunctionalTests/Accept.cs b/src/libraries/System.Net.Sockets/tests/FunctionalTests/Accept.cs
index ec453a0781f338..7f0dc3adc14a41 100644
--- a/src/libraries/System.Net.Sockets/tests/FunctionalTests/Accept.cs
+++ b/src/libraries/System.Net.Sockets/tests/FunctionalTests/Accept.cs
@@ -345,6 +345,49 @@ await RetryHelper.ExecuteAsync(async () =>
                 }
             }, maxAttempts: 10);
         }
+
+        [Fact]
+        [PlatformSpecific(TestPlatforms.Windows)]
+        public async Task AcceptReceive_Windows_Success()
+        {
+            if (!SupportsAcceptReceive)
+            {
+                // Currently only supported by APM and EAP
+                return;
+            }
+
+            using Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+            int port = listener.BindToAnonymousPort(IPAddress.Loopback);
+            IPEndPoint listenerEndpoint = new IPEndPoint(IPAddress.Loopback, port);
+            listener.Listen(100);
+
+            var acceptTask = AcceptAsync(listener, 1);
+
+            using Socket sender = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+            sender.Connect(listenerEndpoint);
+            sender.Send(new byte[] { 42 });
+
+            (_, byte[] recvBuffer) = await acceptTask;
+            Assert.Equal(new byte[] { 42 }, recvBuffer);
+        }
+
+        [Fact]
+        [PlatformSpecific(TestPlatforms.AnyUnix)]
+        public void AcceptReceive_Unix_ThrowsPlatformNotSupportedException()
+        {
+            if (!SupportsAcceptReceive)
+            {
+                // Currently only supported by APM and EAP
+                return;
+            }
+
+            using Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+            int port = listener.BindToAnonymousPort(IPAddress.Loopback);
+            IPEndPoint listenerEndpoint = new IPEndPoint(IPAddress.Loopback, port);
+            listener.Listen(100);
+
+            Assert.ThrowsAsync<PlatformNotSupportedException>(() => AcceptAsync(listener, 1) );
+        }
     }
 
     public sealed class AcceptSync : Accept<SocketHelperArraySync>
@@ -360,6 +403,22 @@ public AcceptSyncForceNonBlocking(ITestOutputHelper output) : base(output) {}
     public sealed class AcceptApm : Accept<SocketHelperApm>
     {
         public AcceptApm(ITestOutputHelper output) : base(output) {}
+
+        [Fact]
+        [PlatformSpecific(TestPlatforms.AnyUnix)]
+        public void EndAccept_AcceptReceiveUnix_ThrowsPlatformNotSupportedException()
+        {
+            using Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+
+            // Creating a fake IAsyncResult:
+            int port = listener.BindToAnonymousPort(IPAddress.Loopback);
+            IPEndPoint listenerEndpoint = new IPEndPoint(IPAddress.Loopback, port);
+            listener.Listen(100);
+            IAsyncResult iar = listener.BeginAccept(callback: null, state: null);
+
+            Assert.Throws<PlatformNotSupportedException>(() => listener.EndAccept(out _, iar));
+            Assert.Throws<PlatformNotSupportedException>(() => listener.EndAccept(out _, out _, iar));
+        }
     }
 
     public sealed class AcceptTask : Accept<SocketHelperTask>
diff --git a/src/libraries/System.Net.Sockets/tests/FunctionalTests/DualModeSocketTest.cs b/src/libraries/System.Net.Sockets/tests/FunctionalTests/DualModeSocketTest.cs
index fa81b0194b599c..38ea1a28c1087c 100644
--- a/src/libraries/System.Net.Sockets/tests/FunctionalTests/DualModeSocketTest.cs
+++ b/src/libraries/System.Net.Sockets/tests/FunctionalTests/DualModeSocketTest.cs
@@ -1947,6 +1947,60 @@ public void ReceiveMessageFromV4BoundToAnyV6_Success()
             ReceiveMessageFrom_Helper(IPAddress.IPv6Any, IPAddress.Loopback);
         }
 
+        [Theory]
+        [InlineData(true)]
+        [InlineData(false)]
+        [PlatformSpecific(~TestPlatforms.OSX)]  // ReceiveMessageFrom not supported on OSX
+        public void ReceiveMessageFromAsync_SocketAsyncEventArgs_Success(bool ipv4)
+        {
+            const int DataLength = 10;
+            AddressFamily family = ipv4 ? AddressFamily.InterNetwork : AddressFamily.InterNetworkV6;
+            IPAddress loopback = ipv4 ? IPAddress.Loopback : IPAddress.Loopback.MapToIPv6();
+            IPAddress clientAddress = ipv4 ? IPAddress.Loopback : IPAddress.IPv6Loopback;
+
+            var completed = new ManualResetEventSlim(false);
+            using (var sender = new Socket(family, SocketType.Dgram, ProtocolType.Udp))
+            using (var receiver = new Socket(AddressFamily.InterNetworkV6, SocketType.Dgram, ProtocolType.Udp))
+            {
+                receiver.DualMode = true;
+                receiver.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.PacketInformation, true);
+                receiver.SetSocketOption(SocketOptionLevel.IPv6, SocketOptionName.PacketInformation, true);
+                int receiverPort = receiver.BindToAnonymousPort(IPAddress.IPv6Any);
+
+                if (!ipv4)
+                {
+                    sender.DualMode = true;
+                }
+
+                int senderPort = sender.BindToAnonymousPort(loopback);
+                var expectedEP = new IPEndPoint(IPAddress.Loopback.MapToIPv6(), senderPort);
+
+                var args = new SocketAsyncEventArgs() { RemoteEndPoint = new IPEndPoint(IPAddress.IPv6Any, 0) };
+                args.Completed += (s, e) => { Console.WriteLine("Got 1 packet {0} {1}", e.RemoteEndPoint, e.ReceiveMessageFromPacketInfo.Address); completed.Set(); };
+                args.SetBuffer(new byte[DataLength], 0, DataLength);
+
+                var ep = new IPEndPoint(loopback, receiverPort);
+                for (int iters = 0; iters < 5; iters++)
+                {
+                    for (int i = 0; i < TestSettings.UDPRedundancy; i++)
+                    {
+                        sender.SendTo(new byte[DataLength], ep);
+                    }
+
+                    if (!receiver.ReceiveMessageFromAsync(args))
+                    {
+                        completed.Set();
+                    }
+                    Assert.True(completed.Wait(TestSettings.PassingTestTimeout), "Timeout while waiting for connection");
+                    completed.Reset();
+
+                    Assert.Equal(DataLength, args.BytesTransferred);
+                    Assert.Equal(expectedEP, args.RemoteEndPoint);
+                    Assert.True(args.ReceiveMessageFromPacketInfo.Address.Equals(IPAddress.Loopback) || args.ReceiveMessageFromPacketInfo.Address.Equals(IPAddress.Loopback.MapToIPv6()));
+                }
+            }
+        }
+
         private void ReceiveMessageFrom_Helper(IPAddress listenOn, IPAddress connectTo, bool expectedToTimeout = false)
         {
             using (Socket serverSocket = new Socket(SocketType.Dgram, ProtocolType.Udp))
diff --git a/src/libraries/System.Net.Sockets/tests/FunctionalTests/NetworkStreamTest.cs b/src/libraries/System.Net.Sockets/tests/FunctionalTests/NetworkStreamTest.cs
index f7b0e83e44a762..fb293859854186 100644
--- a/src/libraries/System.Net.Sockets/tests/FunctionalTests/NetworkStreamTest.cs
+++ b/src/libraries/System.Net.Sockets/tests/FunctionalTests/NetworkStreamTest.cs
@@ -25,25 +25,25 @@ public void Ctor_NullSocket_ThrowsArgumentNullExceptions()
         }
 
         [Fact]
-        public void Ctor_NotConnected_ThrowsIOException()
+        public void Ctor_NotConnected_ThrowsNetworkException()
         {
-            Assert.Throws<IOException>(() => new NetworkStream(new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)));
+            Assert.Throws<NetworkException>(() => new NetworkStream(new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)));
         }
 
         [Fact]
-        public async Task Ctor_NotStream_ThrowsIOException()
+        public async Task Ctor_NotStream_ThrowsNetworkException()
         {
             using (Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
             using (Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
             {
                 listener.Bind(new IPEndPoint(IPAddress.Loopback, 0));
                 await client.ConnectAsync(new IPEndPoint(IPAddress.Loopback, ((IPEndPoint)listener.LocalEndPoint).Port));
-                Assert.Throws<IOException>(() => new NetworkStream(client));
+                Assert.Throws<NetworkException>(() => new NetworkStream(client));
             }
         }
 
         [Fact]
-        public async Task Ctor_NonBlockingSocket_ThrowsIOException()
+        public async Task Ctor_NonBlockingSocket_ThrowsNetworkException()
         {
             using (Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
             using (Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
@@ -56,7 +56,7 @@ public async Task Ctor_NonBlockingSocket_ThrowsIOException()
                 using (Socket server = await acceptTask)
                 {
                     server.Blocking = false;
-                    Assert.Throws<IOException>(() => new NetworkStream(server));
+                    Assert.Throws<NetworkException>(() => new NetworkStream(server));
                 }
             }
         }
@@ -186,7 +186,7 @@ public async Task Ctor_SocketBool_CanReadAndWrite(bool ownsSocket)
                         }
                         else if (ownsSocket)
                         {
-                            Assert.IsType<IOException>(e);
+                            Assert.IsType<NetworkException>(e);
                         }
                         else
                         {
@@ -302,7 +302,7 @@ await RunWithConnectedNetworkStreamsAsync((server, _) =>
         }
 
         [Fact]
-        public async Task DisposeSocketDirectly_ReadWriteThrowIOException()
+        public async Task DisposeSocketDirectly_ReadWriteThrowNetworkException()
         {
             using (Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
             using (Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
@@ -317,14 +317,14 @@ public async Task DisposeSocketDirectly_ReadWriteThrowIOException()
                 {
                     serverSocket.Dispose();
 
-                    Assert.Throws<IOException>(() => server.Read(new byte[1], 0, 1));
-                    Assert.Throws<IOException>(() => server.Write(new byte[1], 0, 1));
+                    Assert.Throws<NetworkException>(() => server.Read(new byte[1], 0, 1));
+                    Assert.Throws<NetworkException>(() => server.Write(new byte[1], 0, 1));
 
-                    Assert.Throws<IOException>(() => server.BeginRead(new byte[1], 0, 1, null, null));
-                    Assert.Throws<IOException>(() => server.BeginWrite(new byte[1], 0, 1, null, null));
+                    Assert.Throws<NetworkException>(() => server.BeginRead(new byte[1], 0, 1, null, null));
+                    Assert.Throws<NetworkException>(() => server.BeginWrite(new byte[1], 0, 1, null, null));
 
-                    Assert.Throws<IOException>(() => { server.ReadAsync(new byte[1], 0, 1); });
-                    Assert.Throws<IOException>(() => { server.WriteAsync(new byte[1], 0, 1); });
+                    Assert.Throws<NetworkException>(() => { server.ReadAsync(new byte[1], 0, 1); });
+                    Assert.Throws<NetworkException>(() => { server.WriteAsync(new byte[1], 0, 1); });
                 }
             }
         }
@@ -334,8 +334,8 @@ public async Task InvalidIAsyncResult_EndReadWriteThrows()
         {
             await RunWithConnectedNetworkStreamsAsync((server, _) =>
             {
-                Assert.Throws<IOException>(() => server.EndRead(Task.CompletedTask));
-                Assert.Throws<IOException>(() => server.EndWrite(Task.CompletedTask));
+                Assert.Throws<NetworkException>(() => server.EndRead(Task.CompletedTask));
+                Assert.Throws<NetworkException>(() => server.EndWrite(Task.CompletedTask));
                 return Task.CompletedTask;
             });
         }
@@ -586,7 +586,7 @@ await RunWithConnectedNetworkStreamsAsync((server, client) =>
                 Assert.Equal(-1, server.ReadTimeout);
 
                 server.ReadTimeout = 1;
-                Assert.ThrowsAny<IOException>(() => server.Read(new byte[1], 0, 1));
+                Assert.ThrowsAny<NetworkException>(() => server.Read(new byte[1], 0, 1));
 
                 return Task.CompletedTask;
             });
@@ -713,8 +713,8 @@ await RunWithConnectedNetworkStreamsAsync(async (stream, _) =>
                 // before that takes effect, it may also complete as aborted.
                 bool isWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
                 Assert.True(
-                    (isWindows && e is IOException) ||
-                    (!isWindows && (e == null || e is IOException)),
+                    (isWindows && e is NetworkException) ||
+                    (!isWindows && (e == null || e is NetworkException)),
                     $"Got unexpected exception: {e?.ToString() ?? "(null)"}");
 
                 // Copying after disposing the stream
diff --git a/src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketTestHelper.cs b/src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketTestHelper.cs
index 836422aa1e758f..307c7c505f60b0 100644
--- a/src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketTestHelper.cs
+++ b/src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketTestHelper.cs
@@ -19,6 +19,7 @@ public partial class NoParallelTests { }
     public abstract class SocketHelperBase
     {
         public abstract Task<Socket> AcceptAsync(Socket s);
+        public abstract Task<(Socket socket, byte[] buffer)> AcceptAsync(Socket s, int receiveSize);
         public abstract Task<Socket> AcceptAsync(Socket s, Socket acceptSocket);
         public abstract Task ConnectAsync(Socket s, EndPoint endPoint);
         public abstract Task MultiConnectAsync(Socket s, IPAddress[] addresses, int port);
@@ -37,13 +38,15 @@ public abstract Task<SocketReceiveFromResult> ReceiveFromAsync(
         public virtual bool ConnectAfterDisconnectResultsInInvalidOperationException => false;
         public virtual bool SupportsMultiConnect => true;
         public virtual bool SupportsAcceptIntoExistingSocket => true;
-        public virtual void Listen(Socket s, int backlog)  { s.Listen(backlog); }
+        public virtual bool SupportsAcceptReceive => false;
+        public virtual void Listen(Socket s, int backlog) { s.Listen(backlog); }
     }
 
     public class SocketHelperArraySync : SocketHelperBase
     {
         public override Task<Socket> AcceptAsync(Socket s) =>
             Task.Run(() => s.Accept());
+        public override Task<(Socket socket, byte[] buffer)> AcceptAsync(Socket s, int receiveSize) => throw new NotSupportedException();
         public override Task<Socket> AcceptAsync(Socket s, Socket acceptSocket) => throw new NotSupportedException();
         public override Task ConnectAsync(Socket s, EndPoint endPoint) =>
             Task.Run(() => s.Connect(endPoint));
@@ -92,8 +95,20 @@ public override void Listen(Socket s, int backlog)
     public sealed class SocketHelperApm : SocketHelperBase
     {
         public override bool DisposeDuringOperationResultsInDisposedException => true;
+        public override bool SupportsAcceptReceive => true;
+
         public override Task<Socket> AcceptAsync(Socket s) =>
             Task.Factory.FromAsync(s.BeginAccept, s.EndAccept, null);
+        public override async Task<(Socket socket, byte[] buffer)> AcceptAsync(Socket s, int receiveSize)
+        {
+            byte[] buffer = null;
+
+            IAsyncResult BeginAccept(AsyncCallback callback, object state) => s.BeginAccept(receiveSize, callback, state);
+            Socket EndAccept(IAsyncResult iar) => s.EndAccept(out buffer, iar);
+
+            Socket socket = await Task.Factory.FromAsync(BeginAccept, EndAccept, null);
+            return (socket, buffer);
+        }
         public override Task<Socket> AcceptAsync(Socket s, Socket acceptSocket) =>
             Task.Factory.FromAsync(s.BeginAccept, s.EndAccept, acceptSocket, 0, null);
         public override Task ConnectAsync(Socket s, EndPoint endPoint) =>
@@ -142,6 +157,8 @@ public class SocketHelperTask : SocketHelperBase
     {
         public override Task<Socket> AcceptAsync(Socket s) =>
             s.AcceptAsync();
+        public override Task<(Socket socket, byte[] buffer)> AcceptAsync(Socket s, int receiveSize)
+            => throw new NotSupportedException();
         public override Task<Socket> AcceptAsync(Socket s, Socket acceptSocket) =>
             s.AcceptAsync(acceptSocket);
         public override Task ConnectAsync(Socket s, EndPoint endPoint) =>
@@ -165,9 +182,24 @@ public override Task<int> SendToAsync(Socket s, ArraySegment<byte> buffer, EndPo
     public sealed class SocketHelperEap : SocketHelperBase
     {
         public override bool ValidatesArrayArguments => false;
+        public override bool SupportsAcceptReceive => true;
 
         public override Task<Socket> AcceptAsync(Socket s) =>
             InvokeAsync(s, e => e.AcceptSocket, e => s.AcceptAsync(e));
+        public override Task<(Socket socket, byte[] buffer)> AcceptAsync(Socket s, int receiveSize) =>
+            InvokeAsync(s, e =>
+            {
+                byte[] buffer = new byte[receiveSize];
+                Array.Copy(e.Buffer, buffer, receiveSize);
+                return (e.AcceptSocket, buffer);
+            }, e =>
+            {
+                // The buffer needs to be large enough for the two special sockaddr buffers that AcceptEx requires
+                // see comments SocketAsyncEventArgs.StartOperationAccept()
+                int bufferLength = receiveSize + 2 * (72 + 16); // 2 * (IPV6 size + 16)
+                e.SetBuffer(new byte[bufferLength], 0, bufferLength);
+                return s.AcceptAsync(e);
+            });
         public override Task<Socket> AcceptAsync(Socket s, Socket acceptSocket) =>
             InvokeAsync(s, e => e.AcceptSocket, e =>
             {
@@ -261,6 +293,7 @@ public SocketTestHelperBase(ITestOutputHelper output)
         //
 
         public Task<Socket> AcceptAsync(Socket s) => _socketHelper.AcceptAsync(s);
+        public Task<(Socket socket, byte[] buffer)> AcceptAsync(Socket s, int receiveSize) => _socketHelper.AcceptAsync(s, receiveSize);
         public Task<Socket> AcceptAsync(Socket s, Socket acceptSocket) => _socketHelper.AcceptAsync(s, acceptSocket);
         public Task ConnectAsync(Socket s, EndPoint endPoint) => _socketHelper.ConnectAsync(s, endPoint);
         public Task MultiConnectAsync(Socket s, IPAddress[] addresses, int port) => _socketHelper.MultiConnectAsync(s, addresses, port);
@@ -279,6 +312,7 @@ public Task<SocketReceiveFromResult> ReceiveFromAsync(
         public bool ConnectAfterDisconnectResultsInInvalidOperationException => _socketHelper.ConnectAfterDisconnectResultsInInvalidOperationException;
         public bool SupportsMultiConnect => _socketHelper.SupportsMultiConnect;
         public bool SupportsAcceptIntoExistingSocket => _socketHelper.SupportsAcceptIntoExistingSocket;
+        public bool SupportsAcceptReceive => _socketHelper.SupportsAcceptReceive;
         public void Listen(Socket s, int backlog) => _socketHelper.Listen(s, backlog);
     }
 
diff --git a/src/libraries/System.Net.Sockets/tests/FunctionalTests/TelemetryTest.cs b/src/libraries/System.Net.Sockets/tests/FunctionalTests/TelemetryTest.cs
index 33529f980d225f..783fbf52e133e8 100644
--- a/src/libraries/System.Net.Sockets/tests/FunctionalTests/TelemetryTest.cs
+++ b/src/libraries/System.Net.Sockets/tests/FunctionalTests/TelemetryTest.cs
@@ -1,8 +1,13 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Collections;
 using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Diagnostics;
 using System.Diagnostics.Tracing;
+using System.Linq;
+using System.Threading.Tasks;
 using Microsoft.DotNet.RemoteExecutor;
 using Xunit;
 using Xunit.Abstractions;
@@ -36,32 +41,60 @@ public void EventSource_EventsRaisedAsExpected()
         {
             RemoteExecutor.Invoke(() =>
             {
-                using (var listener = new TestEventListener("System.Net.Sockets", EventLevel.Verbose))
+                using (var listener = new TestEventListener("System.Net.Sockets", EventLevel.Verbose, 0.1))
                 {
                     var events = new ConcurrentQueue<EventWrittenEventArgs>();
-                    listener.RunWithCallback(events.Enqueue, () =>
+                    listener.RunWithCallbackAsync(events.Enqueue, async () =>
                     {
                         // Invoke several tests to execute code paths while tracing is enabled
 
-                        new SendReceiveSync(null).SendRecv_Stream_TCP(IPAddress.Loopback, false).GetAwaiter();
-                        new SendReceiveSync(null).SendRecv_Stream_TCP(IPAddress.Loopback, true).GetAwaiter();
+                        await new SendReceiveSync(null).SendRecv_Stream_TCP(IPAddress.Loopback, false).ConfigureAwait(false);
+                        await new SendReceiveSync(null).SendRecv_Stream_TCP(IPAddress.Loopback, true).ConfigureAwait(false);
 
-                        new SendReceiveTask(null).SendRecv_Stream_TCP(IPAddress.Loopback, false).GetAwaiter();
-                        new SendReceiveTask(null).SendRecv_Stream_TCP(IPAddress.Loopback, true).GetAwaiter();
+                        await new SendReceiveTask(null).SendRecv_Stream_TCP(IPAddress.Loopback, false).ConfigureAwait(false);
+                        await new SendReceiveTask(null).SendRecv_Stream_TCP(IPAddress.Loopback, true).ConfigureAwait(false);
 
-                        new SendReceiveEap(null).SendRecv_Stream_TCP(IPAddress.Loopback, false).GetAwaiter();
-                        new SendReceiveEap(null).SendRecv_Stream_TCP(IPAddress.Loopback, true).GetAwaiter();
+                        await new SendReceiveEap(null).SendRecv_Stream_TCP(IPAddress.Loopback, false).ConfigureAwait(false);
+                        await new SendReceiveEap(null).SendRecv_Stream_TCP(IPAddress.Loopback, true).ConfigureAwait(false);
 
-                        new SendReceiveApm(null).SendRecv_Stream_TCP(IPAddress.Loopback, false).GetAwaiter();
-                        new SendReceiveApm(null).SendRecv_Stream_TCP(IPAddress.Loopback, true).GetAwaiter();
+                        await new SendReceiveApm(null).SendRecv_Stream_TCP(IPAddress.Loopback, false).ConfigureAwait(false);
+                        await new SendReceiveApm(null).SendRecv_Stream_TCP(IPAddress.Loopback, true).ConfigureAwait(false);
 
-                        new NetworkStreamTest().CopyToAsync_AllDataCopied(4096, true).GetAwaiter().GetResult();
-                        new NetworkStreamTest().Timeout_ValidData_Roundtrips().GetAwaiter().GetResult();
-                    });
+                        await new SendReceiveUdpClient().SendToRecvFromAsync_Datagram_UDP_UdpClient(IPAddress.Loopback).ConfigureAwait(false);
+                        await new SendReceiveUdpClient().SendToRecvFromAsync_Datagram_UDP_UdpClient(IPAddress.Loopback).ConfigureAwait(false);
+
+                        await new NetworkStreamTest().CopyToAsync_AllDataCopied(4096, true).ConfigureAwait(false);
+                        await new NetworkStreamTest().Timeout_ValidData_Roundtrips().ConfigureAwait(false);
+                        await Task.Delay(300).ConfigureAwait(false);
+                    }).Wait();
                     Assert.DoesNotContain(events, ev => ev.EventId == 0); // errors from the EventSource itself
-                    Assert.InRange(events.Count, 1, int.MaxValue);
+                    VerifyEvents(events, "ConnectStart", 10);
+                    VerifyEvents(events, "ConnectStop", 10);
+
+                    Dictionary<string, double> eventCounters = events.Where(e => e.EventName == "EventCounters").Select(e => (IDictionary<string, object>) e.Payload.Single())
+                        .GroupBy(d => (string)d["Name"], d => (double)d["Mean"], (k, v) => new { Name = k, Value = v.Sum() })
+                        .ToDictionary(p => p.Name, p => p.Value);
+
+                    VerifyEventCounter("incoming-connections-established", eventCounters);
+                    VerifyEventCounter("outgoing-connections-established", eventCounters);
+                    VerifyEventCounter("bytes-received", eventCounters);
+                    VerifyEventCounter("bytes-sent", eventCounters);
+                    VerifyEventCounter("datagrams-received", eventCounters);
+                    VerifyEventCounter("datagrams-sent", eventCounters);
                 }
             }).Dispose();
         }
+
+        private static void VerifyEvents(IEnumerable<EventWrittenEventArgs> events, string eventName, int expectedCount)
+        {
+            EventWrittenEventArgs[] starts = events.Where(e => e.EventName == eventName).ToArray();
+            Assert.Equal(expectedCount, starts.Length);
+        }
+
+        private static void VerifyEventCounter(string name, Dictionary<string, double> eventCounters)
+        {
+            Assert.True(eventCounters.ContainsKey(name));
+            Assert.True(eventCounters[name] > 0);
+        }
     }
 }
diff --git a/src/libraries/System.Net.WebClient/Directory.Build.props b/src/libraries/System.Net.WebClient/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.Net.WebClient/Directory.Build.props
+++ b/src/libraries/System.Net.WebClient/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.WebClient/src/Resources/Strings.resx b/src/libraries/System.Net.WebClient/src/Resources/Strings.resx
index 02970f254ffb8f..fb5f49f1167af7 100644
--- a/src/libraries/System.Net.WebClient/src/Resources/Strings.resx
+++ b/src/libraries/System.Net.WebClient/src/Resources/Strings.resx
@@ -75,7 +75,7 @@
   <data name="net_webstatus_MessageLengthLimitExceeded" xml:space="preserve">
     <value>The message length limit was exceeded</value>
   </data>
-  <data name="net_webclient_PlatformNotSupported" xml:space="preserve">
+  <data name="SystemNetWebClient_PlatformNotSupported" xml:space="preserve">
     <value>System.Net.WebClient is not supported on this platform. Use System.Net.Http.HttpClient instead.</value>
   </data>
 </root>
diff --git a/src/libraries/System.Net.WebClient/src/System.Net.WebClient.csproj b/src/libraries/System.Net.WebClient/src/System.Net.WebClient.csproj
index 097c4ff9ff3e4e..8f7d3b5c98891b 100644
--- a/src/libraries/System.Net.WebClient/src/System.Net.WebClient.csproj
+++ b/src/libraries/System.Net.WebClient/src/System.Net.WebClient.csproj
@@ -5,7 +5,7 @@
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.net_webclient_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemNetWebClient_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
     <Compile Include="System\Net\WebClient.cs" />
diff --git a/src/libraries/System.Net.WebHeaderCollection/Directory.Build.props b/src/libraries/System.Net.WebHeaderCollection/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Net.WebHeaderCollection/Directory.Build.props
+++ b/src/libraries/System.Net.WebHeaderCollection/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.WebHeaderCollection/src/System.Net.WebHeaderCollection.csproj b/src/libraries/System.Net.WebHeaderCollection/src/System.Net.WebHeaderCollection.csproj
index d97d8456081bae..3d060d6ebc3c68 100644
--- a/src/libraries/System.Net.WebHeaderCollection/src/System.Net.WebHeaderCollection.csproj
+++ b/src/libraries/System.Net.WebHeaderCollection/src/System.Net.WebHeaderCollection.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Net.WebHeaderCollection</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Net.WebProxy/Directory.Build.props b/src/libraries/System.Net.WebProxy/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.Net.WebProxy/Directory.Build.props
+++ b/src/libraries/System.Net.WebProxy/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.WebSockets.Client/Directory.Build.props b/src/libraries/System.Net.WebSockets.Client/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Net.WebSockets.Client/Directory.Build.props
+++ b/src/libraries/System.Net.WebSockets.Client/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.WebSockets.Client/src/System.Net.WebSockets.Client.csproj b/src/libraries/System.Net.WebSockets.Client/src/System.Net.WebSockets.Client.csproj
index 83b4c5a2a91bcd..b74f3d8962be63 100644
--- a/src/libraries/System.Net.WebSockets.Client/src/System.Net.WebSockets.Client.csproj
+++ b/src/libraries/System.Net.WebSockets.Client/src/System.Net.WebSockets.Client.csproj
@@ -38,7 +38,7 @@
     <Reference Include="System.Security.Cryptography.Primitives" />
     <Reference Include="System.Threading.Channels" Condition="'$(TargetsBrowser)' == 'true'" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetsBrowser)' == 'true'" >
-    <ProjectReference Include="..\..\System.Runtime.InteropServices.JavaScript\src\System.Runtime.InteropServices.JavaScript.csproj" />
-  </ItemGroup>  
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Runtime.InteropServices.JavaScript\src\System.Private.Runtime.InteropServices.JavaScript.csproj" Condition="'$(TargetsBrowser)' == 'true'" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.WebSockets.Client/tests/ConnectTest.cs b/src/libraries/System.Net.WebSockets.Client/tests/ConnectTest.cs
index 20d1cc5fdb1968..6d4d63a730f1ea 100644
--- a/src/libraries/System.Net.WebSockets.Client/tests/ConnectTest.cs
+++ b/src/libraries/System.Net.WebSockets.Client/tests/ConnectTest.cs
@@ -214,6 +214,7 @@ await LoopbackServer.CreateClientAndServerAsync(async uri =>
                 using (var clientSocket = new ClientWebSocket())
                 using (var cts = new CancellationTokenSource(TimeOutMilliseconds))
                 {
+                    // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy authorisation header.")]
                     clientSocket.Options.SetRequestHeader("Authorization", "AWS4-HMAC-SHA256 Credential= AKIAXXXXXXXXXXXYSZA /20190301/us-east-2/neptune-db/aws4_request, SignedHeaders=host;x-amz-date, Signature=b8155de54d9faab00000000000000000000000000a07e0d7dda49902e4d9202");
                     await clientSocket.ConnectAsync(uri, cts.Token);
                 }
diff --git a/src/libraries/System.Net.WebSockets.Client/tests/System.Net.WebSockets.Client.Tests.csproj b/src/libraries/System.Net.WebSockets.Client/tests/System.Net.WebSockets.Client.Tests.csproj
index 413be9b039fd8f..248546468d0fa0 100644
--- a/src/libraries/System.Net.WebSockets.Client/tests/System.Net.WebSockets.Client.Tests.csproj
+++ b/src/libraries/System.Net.WebSockets.Client/tests/System.Net.WebSockets.Client.Tests.csproj
@@ -6,7 +6,7 @@
   </PropertyGroup>
   <!-- Do not reference these assemblies from the TargetingPack since we are building part of the source code for tests. -->
   <ItemGroup>
-    <DefaultReferenceExclusions Include="System.Configuration" />
+    <DefaultReferenceExclusion Include="System.Configuration" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="$(CommonTestPath)System\Net\Capability.Security.cs"
diff --git a/src/libraries/System.Net.WebSockets.WebSocketProtocol/ref/System.Net.WebSockets.WebSocketProtocol.csproj b/src/libraries/System.Net.WebSockets.WebSocketProtocol/ref/System.Net.WebSockets.WebSocketProtocol.csproj
index 4c1d519edd7c3c..7a11f13532cd39 100644
--- a/src/libraries/System.Net.WebSockets.WebSocketProtocol/ref/System.Net.WebSockets.WebSocketProtocol.csproj
+++ b/src/libraries/System.Net.WebSockets.WebSocketProtocol/ref/System.Net.WebSockets.WebSocketProtocol.csproj
@@ -1,12 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Net.WebSockets.WebSocketProtocol.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.Memory" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.WebSockets.WebSocketProtocol/src/System.Net.WebSockets.WebSocketProtocol.csproj b/src/libraries/System.Net.WebSockets.WebSocketProtocol/src/System.Net.WebSockets.WebSocketProtocol.csproj
index 189e51596d37ec..092e7a753fab41 100644
--- a/src/libraries/System.Net.WebSockets.WebSocketProtocol/src/System.Net.WebSockets.WebSocketProtocol.csproj
+++ b/src/libraries/System.Net.WebSockets.WebSocketProtocol/src/System.Net.WebSockets.WebSocketProtocol.csproj
@@ -1,9 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Net.WebSockets.WebSocketProtocol</AssemblyName>
     <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp2.1;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp2.1;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -21,27 +19,30 @@
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' Or $(TargetFramework.StartsWith('net4'))">
     <Compile Include="System\Net\WebSockets\ManagedWebSocketExtensions.netstandard.cs" />
-    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.Memory" />
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or
+                        '$(TargetFramework)' == 'netcoreapp2.1'">
     <Reference Include="Microsoft.Win32.Primitives" />
-    <Reference Include="System.Security.Cryptography.Algorithms" />
-    <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Buffers" />
+    <Reference Include="System.Diagnostics.Debug" />
+    <Reference Include="System.Memory" />
     <Reference Include="System.Net.WebSockets" />
     <Reference Include="System.Numerics.Vectors" />
     <Reference Include="System.Resources.ResourceManager" />
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
+    <Reference Include="System.Security.Cryptography.Algorithms" />
     <Reference Include="System.Text.Encoding.Extensions" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Tasks" />
     <Reference Include="System.Threading.Tasks.Extensions" />
     <Reference Include="System.Threading.Timer" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Numerics.Vectors" Version="$(SystemNumericsVectorsVersion)" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.WebSockets.WebSocketProtocol/tests/System.Net.WebSockets.WebSocketProtocol.Tests.csproj b/src/libraries/System.Net.WebSockets.WebSocketProtocol/tests/System.Net.WebSockets.WebSocketProtocol.Tests.csproj
index eb4d89c4de15c4..16b078941bfc88 100644
--- a/src/libraries/System.Net.WebSockets.WebSocketProtocol/tests/System.Net.WebSockets.WebSocketProtocol.Tests.csproj
+++ b/src/libraries/System.Net.WebSockets.WebSocketProtocol/tests/System.Net.WebSockets.WebSocketProtocol.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonTestPath)System\Net\WebSockets\WebSocketCreateTest.cs"
@@ -13,4 +13,7 @@
              Link="Common\System\Net\HttpKnownHeaderNames.cs" />
     <Compile Include="WebSocketProtocolTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Net.WebSockets.WebSocketProtocol.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Net.WebSockets.WebSocketProtocol/tests/WebSocketProtocolTests.cs b/src/libraries/System.Net.WebSockets.WebSocketProtocol/tests/WebSocketProtocolTests.cs
index 7266ac96e287ca..1d8aecbda9db2f 100644
--- a/src/libraries/System.Net.WebSockets.WebSocketProtocol/tests/WebSocketProtocolTests.cs
+++ b/src/libraries/System.Net.WebSockets.WebSocketProtocol/tests/WebSocketProtocolTests.cs
@@ -6,7 +6,6 @@
 
 namespace System.Net.WebSockets.Tests
 {
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/38807", TestPlatforms.Browser)]
     public sealed class WebSocketProtocolCreateTests : WebSocketCreateTest
     {
         protected override WebSocket CreateFromStream(Stream stream, bool isServer, string subProtocol, TimeSpan keepAliveInterval) =>
diff --git a/src/libraries/System.Net.WebSockets/Directory.Build.props b/src/libraries/System.Net.WebSockets/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Net.WebSockets/Directory.Build.props
+++ b/src/libraries/System.Net.WebSockets/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Net.WebSockets/src/System.Net.WebSockets.csproj b/src/libraries/System.Net.WebSockets/src/System.Net.WebSockets.csproj
index c39977d0064453..212dea7f6eb91f 100644
--- a/src/libraries/System.Net.WebSockets/src/System.Net.WebSockets.csproj
+++ b/src/libraries/System.Net.WebSockets/src/System.Net.WebSockets.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Net.WebSockets</AssemblyName>
     <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Net.WebSockets/tests/WebSocketTests.cs b/src/libraries/System.Net.WebSockets/tests/WebSocketTests.cs
index 892404f040d94a..ad738a00ec8645 100644
--- a/src/libraries/System.Net.WebSockets/tests/WebSocketTests.cs
+++ b/src/libraries/System.Net.WebSockets/tests/WebSocketTests.cs
@@ -6,7 +6,6 @@
 
 namespace System.Net.WebSockets.Tests
 {
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/38807", TestPlatforms.Browser)]
     public sealed class WebSocketTests : WebSocketCreateTest
     {
         protected override WebSocket CreateFromStream(Stream stream, bool isServer, string subProtocol, TimeSpan keepAliveInterval) =>
diff --git a/src/libraries/System.Numerics.Tensors/ref/System.Numerics.Tensors.csproj b/src/libraries/System.Numerics.Tensors/ref/System.Numerics.Tensors.csproj
index 3bffad18351b10..c3ce692b4dfecc 100644
--- a/src/libraries/System.Numerics.Tensors/ref/System.Numerics.Tensors.csproj
+++ b/src/libraries/System.Numerics.Tensors/ref/System.Numerics.Tensors.csproj
@@ -1,22 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard1.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard1.1;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
-  </PropertyGroup>
-    <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
-  <PropertyGroup>
-    <ExcludeFromPackage Condition="'$(TargetFramework)' == 'netstandard2.0'">true</ExcludeFromPackage>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Numerics.Tensors.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Diagnostics.Debug" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Runtime.InteropServices" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Numerics.Tensors/src/System.Numerics.Tensors.csproj b/src/libraries/System.Numerics.Tensors/src/System.Numerics.Tensors.csproj
index b9e1821c6d4f55..655b63c2765596 100644
--- a/src/libraries/System.Numerics.Tensors/src/System.Numerics.Tensors.csproj
+++ b/src/libraries/System.Numerics.Tensors/src/System.Numerics.Tensors.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>netstandard2.0;netstandard1.1;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;netstandard1.1;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -19,18 +18,6 @@
     <Compile Include="System\Numerics\Tensors\Tensor.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Diagnostics.Debug" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Runtime.InteropServices" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Numerics.Tensors/tests/System.Numerics.Tensors.Tests.csproj b/src/libraries/System.Numerics.Tensors/tests/System.Numerics.Tensors.Tests.csproj
index ecbee24629149a..669b0084f4ab4b 100644
--- a/src/libraries/System.Numerics.Tensors/tests/System.Numerics.Tensors.Tests.csproj
+++ b/src/libraries/System.Numerics.Tensors/tests/System.Numerics.Tensors.Tests.csproj
@@ -1,9 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
-  </PropertyGroup>
-  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="NativeMemory.cs" />
@@ -34,8 +32,7 @@
   </ItemGroup>
   <ItemGroup>
     <!-- Some internal types are needed, so we reference the implementation assembly, rather than the reference assembly. -->
-    <DefaultReferenceExclusions Include="System.Numerics.Tensors" />
-    <ReferenceFromRuntime Include="System.Numerics.Tensors" />
+    <ProjectReference Include="..\src\System.Numerics.Tensors.csproj" SkipUseReferenceAssembly="true" />
   </ItemGroup>
   <ItemGroup>
     <!-- enable the TextTemplating extension -->
diff --git a/src/libraries/System.Numerics.Tensors/tests/TensorArithmetic.cs b/src/libraries/System.Numerics.Tensors/tests/TensorArithmetic.cs
index f904c8adbe342a..6dae2ec6854252 100644
--- a/src/libraries/System.Numerics.Tensors/tests/TensorArithmetic.cs
+++ b/src/libraries/System.Numerics.Tensors/tests/TensorArithmetic.cs
@@ -1231,7 +1231,6 @@ public void Decrement(DenseTensor<byte> tensor, DenseTensor<byte> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -1426,7 +1425,6 @@ public void Increment(DenseTensor<byte> tensor, DenseTensor<byte> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -2610,7 +2608,6 @@ public void Decrement(DenseTensor<char> tensor, DenseTensor<char> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -2805,7 +2802,6 @@ public void Increment(DenseTensor<char> tensor, DenseTensor<char> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -3870,7 +3866,6 @@ public void Decrement(DenseTensor<decimal> tensor, DenseTensor<decimal> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -4065,7 +4060,6 @@ public void Increment(DenseTensor<decimal> tensor, DenseTensor<decimal> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -4946,7 +4940,6 @@ public void Decrement(DenseTensor<double> tensor, DenseTensor<double> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -5141,7 +5134,6 @@ public void Increment(DenseTensor<double> tensor, DenseTensor<double> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -6022,7 +6014,6 @@ public void Decrement(DenseTensor<float> tensor, DenseTensor<float> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -6217,7 +6208,6 @@ public void Increment(DenseTensor<float> tensor, DenseTensor<float> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -7217,7 +7207,6 @@ public void Decrement(DenseTensor<int> tensor, DenseTensor<int> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -7412,7 +7401,6 @@ public void Increment(DenseTensor<int> tensor, DenseTensor<int> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -8596,7 +8584,6 @@ public void Decrement(DenseTensor<long> tensor, DenseTensor<long> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -8791,7 +8778,6 @@ public void Increment(DenseTensor<long> tensor, DenseTensor<long> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -9975,7 +9961,6 @@ public void Decrement(DenseTensor<sbyte> tensor, DenseTensor<sbyte> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -10170,7 +10155,6 @@ public void Increment(DenseTensor<sbyte> tensor, DenseTensor<sbyte> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -11354,7 +11338,6 @@ public void Decrement(DenseTensor<short> tensor, DenseTensor<short> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -11549,7 +11532,6 @@ public void Increment(DenseTensor<short> tensor, DenseTensor<short> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -12726,7 +12708,6 @@ public void Decrement(DenseTensor<uint> tensor, DenseTensor<uint> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -12921,7 +12902,6 @@ public void Increment(DenseTensor<uint> tensor, DenseTensor<uint> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -14069,7 +14049,6 @@ public void Decrement(DenseTensor<ulong> tensor, DenseTensor<ulong> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -14264,7 +14243,6 @@ public void Increment(DenseTensor<ulong> tensor, DenseTensor<ulong> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
@@ -15412,7 +15390,6 @@ public void Decrement(DenseTensor<ushort> tensor, DenseTensor<ushort> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]--;
@@ -15607,7 +15584,6 @@ public void Increment(DenseTensor<ushort> tensor, DenseTensor<ushort> result)
         {
 
             var resultSpan = result.Buffer.Span;
-            var tensorSpan = tensor.Buffer.Span;
             for (int i = 0; i < resultSpan.Length; i++)
             {
                 resultSpan[i]++;
diff --git a/src/libraries/System.Numerics.Tensors/tests/TensorOperations.cs b/src/libraries/System.Numerics.Tensors/tests/TensorOperations.cs
index 0502151e4455e6..009ad006b88c53 100644
--- a/src/libraries/System.Numerics.Tensors/tests/TensorOperations.cs
+++ b/src/libraries/System.Numerics.Tensors/tests/TensorOperations.cs
@@ -286,7 +286,7 @@ internal static Tensor<T> And<T>(Tensor<T> tensor, T scalar)
 
         internal static void Contract<T>(Tensor<T> left, Tensor<T> right, int[] leftAxes, int[] rightAxes, Tensor<T> result)
         {
-            var resultDimensions = ValidateContractArgs(left, right, leftAxes, rightAxes, result);
+            ValidateContractArgs(left, right, leftAxes, rightAxes, result);
 
             TensorArithmetic<T>.Instance.Contract(left, right, leftAxes, rightAxes, result);
         }
diff --git a/src/libraries/System.Numerics.Vectors/Directory.Build.props b/src/libraries/System.Numerics.Vectors/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Numerics.Vectors/Directory.Build.props
+++ b/src/libraries/System.Numerics.Vectors/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Numerics.Vectors/ref/System.Numerics.Vectors.cs b/src/libraries/System.Numerics.Vectors/ref/System.Numerics.Vectors.cs
index 9793bb2e37a2ab..ea873ba3cecd75 100644
--- a/src/libraries/System.Numerics.Vectors/ref/System.Numerics.Vectors.cs
+++ b/src/libraries/System.Numerics.Vectors/ref/System.Numerics.Vectors.cs
@@ -208,6 +208,8 @@ public static partial class Vector
         public static System.Numerics.Vector<System.UInt64> AsVectorUInt64<T>(System.Numerics.Vector<T> value) where T : struct { throw null; }
         public static System.Numerics.Vector<T> BitwiseAnd<T>(System.Numerics.Vector<T> left, System.Numerics.Vector<T> right) where T : struct { throw null; }
         public static System.Numerics.Vector<T> BitwiseOr<T>(System.Numerics.Vector<T> left, System.Numerics.Vector<T> right) where T : struct { throw null; }
+        public static System.Numerics.Vector<System.Double> Ceiling(System.Numerics.Vector<System.Double> value) { throw null; }
+        public static System.Numerics.Vector<System.Single> Ceiling(System.Numerics.Vector<System.Single> value) { throw null; }
         public static System.Numerics.Vector<System.Single> ConditionalSelect(System.Numerics.Vector<System.Int32> condition, System.Numerics.Vector<System.Single> left, System.Numerics.Vector<System.Single> right) { throw null; }
         public static System.Numerics.Vector<System.Double> ConditionalSelect(System.Numerics.Vector<System.Int64> condition, System.Numerics.Vector<System.Double> left, System.Numerics.Vector<System.Double> right) { throw null; }
         public static System.Numerics.Vector<T> ConditionalSelect<T>(System.Numerics.Vector<T> condition, System.Numerics.Vector<T> left, System.Numerics.Vector<T> right) where T : struct { throw null; }
@@ -232,6 +234,8 @@ public static partial class Vector
         public static bool EqualsAll<T>(System.Numerics.Vector<T> left, System.Numerics.Vector<T> right) where T : struct { throw null; }
         public static bool EqualsAny<T>(System.Numerics.Vector<T> left, System.Numerics.Vector<T> right) where T : struct { throw null; }
         public static System.Numerics.Vector<T> Equals<T>(System.Numerics.Vector<T> left, System.Numerics.Vector<T> right) where T : struct { throw null; }
+        public static System.Numerics.Vector<System.Double> Floor(System.Numerics.Vector<System.Double> value) { throw null; }
+        public static System.Numerics.Vector<System.Single> Floor(System.Numerics.Vector<System.Single> value) { throw null; }
         public static System.Numerics.Vector<System.Int64> GreaterThan(System.Numerics.Vector<System.Double> left, System.Numerics.Vector<System.Double> right) { throw null; }
         public static System.Numerics.Vector<System.Int32> GreaterThan(System.Numerics.Vector<System.Int32> left, System.Numerics.Vector<System.Int32> right) { throw null; }
         public static System.Numerics.Vector<System.Int64> GreaterThan(System.Numerics.Vector<System.Int64> left, System.Numerics.Vector<System.Int64> right) { throw null; }
@@ -292,10 +296,6 @@ public static partial class Vector
         [System.CLSCompliantAttribute(false)]
         public static void Widen(System.Numerics.Vector<System.UInt32> source, out System.Numerics.Vector<System.UInt64> dest1, out System.Numerics.Vector<System.UInt64> dest2) { throw null; }
         public static System.Numerics.Vector<T> Xor<T>(System.Numerics.Vector<T> left, System.Numerics.Vector<T> right) where T : struct { throw null; }
-        public static System.Numerics.Vector<System.Single> Ceiling(System.Numerics.Vector<System.Single> value) { throw null; }
-        public static System.Numerics.Vector<System.Double> Ceiling(System.Numerics.Vector<System.Double> value) { throw null; }
-        public static System.Numerics.Vector<System.Single> Floor(System.Numerics.Vector<System.Single> value) { throw null; }
-        public static System.Numerics.Vector<System.Double> Floor(System.Numerics.Vector<System.Double> value) { throw null; }
     }
     public partial struct Vector2 : System.IEquatable<System.Numerics.Vector2>, System.IFormattable
     {
diff --git a/src/libraries/System.ObjectModel/Directory.Build.props b/src/libraries/System.ObjectModel/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.ObjectModel/Directory.Build.props
+++ b/src/libraries/System.ObjectModel/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ObjectModel/ref/System.ObjectModel.cs b/src/libraries/System.ObjectModel/ref/System.ObjectModel.cs
index 6761a3092a6b64..150918a7990084 100644
--- a/src/libraries/System.ObjectModel/ref/System.ObjectModel.cs
+++ b/src/libraries/System.ObjectModel/ref/System.ObjectModel.cs
@@ -50,12 +50,12 @@ public ReadOnlyDictionary(System.Collections.Generic.IDictionary<TKey, TValue> d
         protected System.Collections.Generic.IDictionary<TKey, TValue> Dictionary { get { throw null; } }
         public TValue this[TKey key] { get { throw null; } }
         public System.Collections.ObjectModel.ReadOnlyDictionary<TKey, TValue>.KeyCollection Keys { get { throw null; } }
-        bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>.IsReadOnly { get { throw null; } }
-        TValue System.Collections.Generic.IDictionary<TKey,TValue>.this[TKey key] { get { throw null; } set { } }
-        System.Collections.Generic.ICollection<TKey> System.Collections.Generic.IDictionary<TKey,TValue>.Keys { get { throw null; } }
-        System.Collections.Generic.ICollection<TValue> System.Collections.Generic.IDictionary<TKey,TValue>.Values { get { throw null; } }
-        System.Collections.Generic.IEnumerable<TKey> System.Collections.Generic.IReadOnlyDictionary<TKey,TValue>.Keys { get { throw null; } }
-        System.Collections.Generic.IEnumerable<TValue> System.Collections.Generic.IReadOnlyDictionary<TKey,TValue>.Values { get { throw null; } }
+        bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>.IsReadOnly { get { throw null; } }
+        TValue System.Collections.Generic.IDictionary<TKey, TValue>.this[TKey key] { get { throw null; } set { } }
+        System.Collections.Generic.ICollection<TKey> System.Collections.Generic.IDictionary<TKey, TValue>.Keys { get { throw null; } }
+        System.Collections.Generic.ICollection<TValue> System.Collections.Generic.IDictionary<TKey, TValue>.Values { get { throw null; } }
+        System.Collections.Generic.IEnumerable<TKey> System.Collections.Generic.IReadOnlyDictionary<TKey, TValue>.Keys { get { throw null; } }
+        System.Collections.Generic.IEnumerable<TValue> System.Collections.Generic.IReadOnlyDictionary<TKey, TValue>.Values { get { throw null; } }
         bool System.Collections.ICollection.IsSynchronized { get { throw null; } }
         object System.Collections.ICollection.SyncRoot { get { throw null; } }
         bool System.Collections.IDictionary.IsFixedSize { get { throw null; } }
@@ -66,13 +66,13 @@ public ReadOnlyDictionary(System.Collections.Generic.IDictionary<TKey, TValue> d
         public System.Collections.ObjectModel.ReadOnlyDictionary<TKey, TValue>.ValueCollection Values { get { throw null; } }
         public bool ContainsKey(TKey key) { throw null; }
         public System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<TKey, TValue>> GetEnumerator() { throw null; }
-        void System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>.Add(System.Collections.Generic.KeyValuePair<TKey, TValue> item) { }
-        void System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>.Clear() { }
-        bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>.Contains(System.Collections.Generic.KeyValuePair<TKey, TValue> item) { throw null; }
-        void System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>.CopyTo(System.Collections.Generic.KeyValuePair<TKey, TValue>[] array, int arrayIndex) { }
-        bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>.Remove(System.Collections.Generic.KeyValuePair<TKey, TValue> item) { throw null; }
-        void System.Collections.Generic.IDictionary<TKey,TValue>.Add(TKey key, TValue value) { }
-        bool System.Collections.Generic.IDictionary<TKey,TValue>.Remove(TKey key) { throw null; }
+        void System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>.Add(System.Collections.Generic.KeyValuePair<TKey, TValue> item) { }
+        void System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>.Clear() { }
+        bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>.Contains(System.Collections.Generic.KeyValuePair<TKey, TValue> item) { throw null; }
+        void System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>.CopyTo(System.Collections.Generic.KeyValuePair<TKey, TValue>[] array, int arrayIndex) { }
+        bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>.Remove(System.Collections.Generic.KeyValuePair<TKey, TValue> item) { throw null; }
+        void System.Collections.Generic.IDictionary<TKey, TValue>.Add(TKey key, TValue value) { }
+        bool System.Collections.Generic.IDictionary<TKey, TValue>.Remove(TKey key) { throw null; }
         void System.Collections.ICollection.CopyTo(System.Array array, int index) { }
         void System.Collections.IDictionary.Add(object key, object? value) { }
         void System.Collections.IDictionary.Clear() { }
@@ -198,8 +198,9 @@ public sealed partial class TypeConverterAttribute : System.Attribute
     {
         public static readonly System.ComponentModel.TypeConverterAttribute Default;
         public TypeConverterAttribute() { }
-        public TypeConverterAttribute(string typeName) { }
-        public TypeConverterAttribute(System.Type type) { }
+        public TypeConverterAttribute([System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] string typeName) { }
+        public TypeConverterAttribute([System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] System.Type type) { }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
         public string ConverterTypeName { get { throw null; } }
         public override bool Equals(object? obj) { throw null; }
         public override int GetHashCode() { throw null; }
@@ -207,8 +208,9 @@ public TypeConverterAttribute(System.Type type) { }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class, Inherited=true)]
     public sealed partial class TypeDescriptionProviderAttribute : System.Attribute
     {
-        public TypeDescriptionProviderAttribute(string typeName) { }
-        public TypeDescriptionProviderAttribute(System.Type type) { }
+        public TypeDescriptionProviderAttribute([System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] string typeName) { }
+        public TypeDescriptionProviderAttribute([System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] System.Type type) { }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]
         public string TypeName { get { throw null; } }
     }
 }
diff --git a/src/libraries/System.ObjectModel/src/System.ObjectModel.csproj b/src/libraries/System.ObjectModel/src/System.ObjectModel.csproj
index b531e567ae7cac..89776eac649a5b 100644
--- a/src/libraries/System.ObjectModel/src/System.ObjectModel.csproj
+++ b/src/libraries/System.ObjectModel/src/System.ObjectModel.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.ObjectModel</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.ObjectModel/src/System/Collections/ObjectModel/KeyedCollection.cs b/src/libraries/System.ObjectModel/src/System/Collections/ObjectModel/KeyedCollection.cs
index 93cd10b6ffd0b5..3c0c0a4068a755 100644
--- a/src/libraries/System.ObjectModel/src/System/Collections/ObjectModel/KeyedCollection.cs
+++ b/src/libraries/System.ObjectModel/src/System/Collections/ObjectModel/KeyedCollection.cs
@@ -114,7 +114,7 @@ public bool TryGetValue(TKey key, [MaybeNullWhen(false)] out TItem item)
                 }
             }
 
-            item = default(TItem)!;
+            item = default;
             return false;
         }
 
diff --git a/src/libraries/System.ObjectModel/src/System/ComponentModel/TypeConverterAttribute.cs b/src/libraries/System.ObjectModel/src/System/ComponentModel/TypeConverterAttribute.cs
index 0d44850745f7c4..df6569a283a73a 100644
--- a/src/libraries/System.ObjectModel/src/System/ComponentModel/TypeConverterAttribute.cs
+++ b/src/libraries/System.ObjectModel/src/System/ComponentModel/TypeConverterAttribute.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace System.ComponentModel
 {
     /// <summary>
@@ -30,7 +32,7 @@ public TypeConverterAttribute()
         /// class, using the specified type as the data converter for the object this attribute
         /// is bound to.
         /// </summary>
-        public TypeConverterAttribute(Type type)
+        public TypeConverterAttribute([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type type)
         {
             if (type == null)
             {
@@ -45,7 +47,7 @@ public TypeConverterAttribute(Type type)
         /// class, using the specified type name as the data converter for the object this attribute
         /// is bound to.
         /// </summary>
-        public TypeConverterAttribute(string typeName)
+        public TypeConverterAttribute([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] string typeName)
         {
             if (typeName == null)
             {
@@ -59,6 +61,7 @@ public TypeConverterAttribute(string typeName)
         /// Gets the fully qualified type name of the <see cref='System.Type'/> to use as a
         /// converter for the object this attribute is bound to.
         /// </summary>
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)]
         public string ConverterTypeName { get; }
 
         public override bool Equals(object? obj)
diff --git a/src/libraries/System.ObjectModel/tests/KeyedCollection/Serialization.cs b/src/libraries/System.ObjectModel/tests/KeyedCollection/Serialization.cs
index a43c4f08d496af..1c14406006779d 100644
--- a/src/libraries/System.ObjectModel/tests/KeyedCollection/Serialization.cs
+++ b/src/libraries/System.ObjectModel/tests/KeyedCollection/Serialization.cs
@@ -16,7 +16,7 @@ public static IEnumerable<object[]> SerializeDeserialize_Roundtrips_MemberData()
             yield return new object[] { new TestCollection() { "hello", "world" } };
         }
 
-        [Theory]
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported))]
         [MemberData(nameof(SerializeDeserialize_Roundtrips_MemberData))]
         public void SerializeDeserialize_Roundtrips(TestCollection c)
         {
diff --git a/src/libraries/System.ObjectModel/tests/ObservableCollection/ObservableCollection_Serialization.cs b/src/libraries/System.ObjectModel/tests/ObservableCollection/ObservableCollection_Serialization.cs
index 1d2875576e4176..65d5694a93a8f3 100644
--- a/src/libraries/System.ObjectModel/tests/ObservableCollection/ObservableCollection_Serialization.cs
+++ b/src/libraries/System.ObjectModel/tests/ObservableCollection/ObservableCollection_Serialization.cs
@@ -17,7 +17,7 @@ public static IEnumerable<object[]> SerializeDeserialize_Roundtrips_MemberData()
             yield return new object[] { new ObservableCollection<int>() { 1, 5, 3, 4, 2 } };
         }
 
-        [Theory]
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported))]
         [MemberData(nameof(SerializeDeserialize_Roundtrips_MemberData))]
         public void SerializeDeserialize_Roundtrips(ObservableCollection<int> c)
         {
diff --git a/src/libraries/System.ObjectModel/tests/ReadOnlyDictionary/ReadOnlyDictionary_SerializationTests.cs b/src/libraries/System.ObjectModel/tests/ReadOnlyDictionary/ReadOnlyDictionary_SerializationTests.cs
index af7aec630bbd26..d0bb38d21623eb 100644
--- a/src/libraries/System.ObjectModel/tests/ReadOnlyDictionary/ReadOnlyDictionary_SerializationTests.cs
+++ b/src/libraries/System.ObjectModel/tests/ReadOnlyDictionary/ReadOnlyDictionary_SerializationTests.cs
@@ -16,7 +16,7 @@ public static IEnumerable<object[]> SerializeDeserialize_Roundtrips_MemberData()
             yield return new object[] { new ReadOnlyDictionary<string, string>(new Dictionary<string, string>() { { "a", "b" }, { "c", "d" } }) };
         }
 
-        [Theory]
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported))]
         [MemberData(nameof(SerializeDeserialize_Roundtrips_MemberData))]
         public void SerializeDeserialize_Roundtrips(ReadOnlyDictionary<string, string> d)
         {
diff --git a/src/libraries/System.ObjectModel/tests/ReadOnlyObservableCollection/ReadOnlyObservableCollection_SerializationTests.cs b/src/libraries/System.ObjectModel/tests/ReadOnlyObservableCollection/ReadOnlyObservableCollection_SerializationTests.cs
index b2e102dd64b2a3..ed818b6a619818 100644
--- a/src/libraries/System.ObjectModel/tests/ReadOnlyObservableCollection/ReadOnlyObservableCollection_SerializationTests.cs
+++ b/src/libraries/System.ObjectModel/tests/ReadOnlyObservableCollection/ReadOnlyObservableCollection_SerializationTests.cs
@@ -17,7 +17,7 @@ public static IEnumerable<object[]> SerializeDeserialize_Roundtrips_MemberData()
             yield return new object[] { new ReadOnlyObservableCollection<int>(new ObservableCollection<int>() { 1, 2, 3 }) };
         }
 
-        [Theory]
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported))]
         [MemberData(nameof(SerializeDeserialize_Roundtrips_MemberData))]
         public void SerializeDeserialize_Roundtrips(ReadOnlyObservableCollection<int> c)
         {
diff --git a/src/libraries/System.ObjectModel/tests/TrimmingTests/TypeConverterAttributeStringArgCtorTest.cs b/src/libraries/System.ObjectModel/tests/TrimmingTests/TypeConverterAttributeStringArgCtorTest.cs
new file mode 100644
index 00000000000000..4803dce6b7c544
--- /dev/null
+++ b/src/libraries/System.ObjectModel/tests/TrimmingTests/TypeConverterAttributeStringArgCtorTest.cs
@@ -0,0 +1,40 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.ComponentModel;
+using System.Globalization;
+
+namespace TypeConverterAttributeTest
+{
+    /// <summary>
+    /// Tests that the public constructors of types passed into System.ComponentModel.TypeConverterAttribute
+    /// are not trimmed out when needed in a trimmed application.
+    /// </summary>
+    class Program
+    {
+        static int Main(string[] args)
+        {
+            // String-based TypeConverterAttribute ctor overload, ensure public parameterless ctor of TypeConverter type is preserved.
+            TypeDescriptor.AddAttributes(typeof(string), new TypeConverterAttribute("TypeConverterAttributeTest.MyStringConverter, project, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"));
+            var attribute = new DefaultValueAttribute(typeof(string), "Hello, world!");
+            return (string)attribute.Value == "Hello, world!trivia" ? 100 : -1;
+        }
+    }
+
+    internal class MyStringConverter : StringConverter
+    {
+        /// <summary>
+        /// Converts the specified value object to a string object.
+        /// </summary>
+        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        {
+            if (value is string str)
+            {
+                return str + "trivia";
+            }
+
+            throw new NotSupportedException();
+        }
+    }
+}
diff --git a/src/libraries/System.ObjectModel/tests/TrimmingTests/TypeConverterAttributeTypeArgCtorTest.cs b/src/libraries/System.ObjectModel/tests/TrimmingTests/TypeConverterAttributeTypeArgCtorTest.cs
new file mode 100644
index 00000000000000..bfa67ddf27a332
--- /dev/null
+++ b/src/libraries/System.ObjectModel/tests/TrimmingTests/TypeConverterAttributeTypeArgCtorTest.cs
@@ -0,0 +1,47 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.ComponentModel;
+using System.Globalization;
+
+namespace TypeConverterAttributeTest
+{
+    /// <summary>
+    /// Tests that the public constructors of types passed into System.ComponentModel.TypeConverterAttribute
+    /// are not trimmed out when needed in a trimmed application.
+    /// </summary>
+    class Program
+    {
+        static int Main(string[] args)
+        {
+            // Type-based TypeConverterAttribute ctor overload, ensure public parameterized ctor of TypeConverter type is preserved.
+            TypeDescriptor.AddAttributes(typeof(DayOfWeek), new TypeConverterAttribute(typeof(MyDayOfWeekConverter)));
+            var attribute = new DefaultValueAttribute(typeof(DayOfWeek), "Friday");
+            return (DayOfWeek)attribute.Value == DayOfWeek.Monday ? 100 : -1;
+        }
+    }
+
+    internal class MyDayOfWeekConverter : TypeConverter
+    {
+        private readonly Type _type;
+
+        public MyDayOfWeekConverter(Type type)
+        {
+            _type = type;
+        }
+
+        /// <summary>
+        /// Converts the specified value object to a DayOfWeek value.
+        /// </summary>
+        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        {
+            if (_type == typeof(DayOfWeek) && value is string str && str == "Friday")
+            {
+                return DayOfWeek.Monday;
+            }
+
+            throw new NotSupportedException();
+        }
+    }
+}
diff --git a/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.LinkAttributes.Shared.xml b/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.LinkAttributes.Shared.xml
index d864e916300538..8df05e609708b6 100644
--- a/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.LinkAttributes.Shared.xml
+++ b/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.LinkAttributes.Shared.xml
@@ -29,12 +29,25 @@
     <type fullname="System.Diagnostics.DebuggerVisualizerAttribute">
       <attribute internal="RemoveAttributeInstances" />
     </type>
+  </assembly>
 
-    <!-- Attributes used during pretty stack trace printing -->
-    <type fullname="System.Diagnostics.StackTraceHiddenAttribute">
+  <assembly fullname="System.Private.CoreLib" feature="System.Diagnostics.Tracing.EventSource.IsSupported" featurevalue="false">
+    <type fullname="System.Diagnostics.Tracing.EventSourceAttribute">
+      <attribute internal="RemoveAttributeInstances" />
+    </type>
+    <type fullname="System.Diagnostics.Tracing.EventAttribute">
+      <attribute internal="RemoveAttributeInstances" />
+    </type>
+    <type fullname="System.Diagnostics.Tracing.EventDataAttribute">
+      <attribute internal="RemoveAttributeInstances" />
+    </type>
+    <type fullname="System.Diagnostics.Tracing.EventFieldAttribute">
+      <attribute internal="RemoveAttributeInstances" />
+    </type>
+    <type fullname="System.Diagnostics.Tracing.EventIgnoreAttribute">
       <attribute internal="RemoveAttributeInstances" />
     </type>
-    <type fullname="System.Runtime.CompilerServices.CompilerGeneratedAttribute">
+    <type fullname="System.Diagnostics.Tracing.NonEventAttribute">
       <attribute internal="RemoveAttributeInstances" />
     </type>
   </assembly>
diff --git a/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Substitutions.Shared.xml b/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Substitutions.Shared.xml
index 81e98c3f71b58b..9831ce9b6e2d2b 100644
--- a/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Substitutions.Shared.xml
+++ b/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Substitutions.Shared.xml
@@ -15,5 +15,8 @@
     <type fullname="System.Resources.ResourceReader">
       <method signature="System.Boolean InitializeBinaryFormatter()" body="stub" value="false" feature="System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization" featurevalue="false" />
     </type>
+    <type fullname="System.Threading.Tasks.Task" feature="System.Diagnostics.Debugger.IsSupported" featurevalue="false">
+      <field name="s_asyncDebuggingEnabled" value="false" initialize="false" />
+    </type>
   </assembly>
 </linker>
diff --git a/src/libraries/System.Private.CoreLib/src/Resources/Strings.resx b/src/libraries/System.Private.CoreLib/src/Resources/Strings.resx
index 982f0b8e4a2100..5628d08e87fd3b 100644
--- a/src/libraries/System.Private.CoreLib/src/Resources/Strings.resx
+++ b/src/libraries/System.Private.CoreLib/src/Resources/Strings.resx
@@ -3766,6 +3766,9 @@
   <data name="Arg_MustBeHalf" xml:space="preserve">
     <value>Object must be of type Half.</value>
   </data>
+  <data name="Arg_MustBeRune" xml:space="preserve">
+    <value>Object must be of type Rune.</value>
+  </data>
   <data name="BinaryFormatter_SerializationDisallowed" xml:space="preserve">
     <value>BinaryFormatter serialization and deserialization are disabled within this application. See https://aka.ms/binaryformatter for more information.</value>
   </data>
diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index b217b4289df669..27bccfced38f4b 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -15,6 +15,17 @@
     <SupportsX86Intrinsics Condition="'$(Platform)' == 'x64' or ('$(Platform)' == 'x86' and '$(TargetsUnix)' != 'true')">true</SupportsX86Intrinsics>
     <ILLinkSharedDirectory>$(MSBuildThisFileDirectory)ILLink\</ILLinkSharedDirectory>
   </PropertyGroup>
+  <PropertyGroup>
+    <DefineConstants Condition="'$(TargetsUnix)' == 'true'">$(DefineConstants);TARGET_UNIX</DefineConstants>
+    <DefineConstants Condition="'$(TargetsWindows)' == 'true'">$(DefineConstants);TARGET_WINDOWS</DefineConstants>
+    <DefineConstants Condition="'$(TargetsOSX)' == 'true'">$(DefineConstants);TARGET_OSX</DefineConstants>
+    <DefineConstants Condition="'$(TargetsiOS)' == 'true'">$(DefineConstants);TARGET_IOS</DefineConstants>
+    <DefineConstants Condition="'$(TargetstvOS)' == 'true'">$(DefineConstants);TARGET_TVOS</DefineConstants>
+    <DefineConstants Condition="'$(TargetsBrowser)' == 'true'">$(DefineConstants);TARGET_BROWSER</DefineConstants>
+    <DefineConstants Condition="'$(TargetsAndroid)' == 'true'">$(DefineConstants);TARGET_ANDROID</DefineConstants>
+    <DefineConstants Condition="'$(TargetsLinux)' == 'true'">$(DefineConstants);TARGET_LINUX</DefineConstants>
+    <DefineConstants Condition="'$(TargetsFreeBSD)' == 'true'">$(DefineConstants);TARGET_FREEBSD</DefineConstants>
+  </PropertyGroup>
   <ItemGroup>
     <ILLinkSubstitutionsXmls Include="$(ILLinkSharedDirectory)ILLink.Substitutions.Shared.xml" />
     <!-- TODO: Enable these substitutions files for more platforms once https://github.com/mono/linker/issues/1260 is fixed -->
@@ -47,7 +58,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Activator.RuntimeType.cs" Condition="'$(TargetsCoreRT)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\AggregateException.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\AppContext.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\AppContext.Browser.cs" Condition="'$(TargetsBrowser)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\AppContext.AnyOS.cs" Condition="'$(TargetsBrowser)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\AppDomain.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\AppDomainSetup.cs" />
@@ -170,6 +180,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\IEnumerable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\IEnumerator.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\IEqualityComparer.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\IInternalStringEqualityComparer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\IList.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\InsertionBehavior.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\IReadOnlyCollection.cs" />
@@ -180,6 +191,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\KeyNotFoundException.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\KeyValuePair.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\List.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\RandomizedStringEqualityComparer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\NonRandomizedStringEqualityComparer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\Generic\ValueListBuilder.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Collections\HashHelpers.cs" />
@@ -1170,7 +1182,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\Tracing\NativeRuntimeEventSource.cs" Condition="'$(FeaturePerfTracing)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\Tracing\PollingCounter.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\Tracing\RuntimeEventSource.cs" Condition="'$(FeaturePerfTracing)' == 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\Tracing\StubEnvironment.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\Tracing\Winmeta.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\Tracing\TraceLogging\ArrayTypeInfo.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Diagnostics\Tracing\TraceLogging\ConcurrentSet.cs" />
@@ -1709,18 +1720,9 @@
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetCwd.cs">
       <Link>Common\Interop\Unix\System.Native\Interop.GetCwd.cs</Link>
     </Compile>
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetEUid.cs">
-      <Link>Common\Interop\Unix\System.Native\Interop.GetEUid.cs</Link>
-    </Compile>
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetHostName.cs">
       <Link>Common\Interop\Unix\System.Native\Interop.GetHostName.cs</Link>
     </Compile>
-    <Compile Include="$(CommonPath)\Interop\Unix\System.Native\Interop.GetPid.cs">
-      <Link>Common\Interop\Unix\System.Native\Interop.GetPid.cs</Link>
-    </Compile>
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetPwUid.cs">
-      <Link>Common\Interop\Unix\System.Native\Interop.GetPwUid.cs</Link>
-    </Compile>
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetRandomBytes.cs">
       <Link>Common\Interop\Unix\System.Native\Interop.GetRandomBytes.cs</Link>
     </Compile>
@@ -1798,7 +1800,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Environment.NoRegistry.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Environment.UnixOrBrowser.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Environment.OSVersion.OSX.cs" Condition="'$(IsOSXLike)' == 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Environment.OSVersion.Unix.cs" Condition="'$(IsOSXLike)' != 'true' and '$(TargetsBrowser)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Environment.GetFolderPathCore.Unix.cs" Condition="'$(TargetsiOS)' != 'true' and '$(TargetstvOS)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Globalization\CalendarData.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Globalization\CultureData.Unix.cs" />
@@ -1806,13 +1807,11 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Globalization\GlobalizationMode.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Globalization\HijriCalendar.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Guid.Unix.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\IO\DriveInfoInternal.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\FileStream.Lock.OSX.cs" Condition="'$(IsOSXLike)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\FileStream.Lock.Unix.cs" Condition="'$(IsOSXLike)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\FileStream.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\Path.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\PathInternal.Unix.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\IO\PersistedFiles.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IO\PersistedFiles.Names.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\PasteArguments.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\Loader\LibraryNameVariation.Unix.cs" />
@@ -1825,11 +1824,26 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\TimeZoneInfo.Unix.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetEUid.cs">
+      <Link>Common\Interop\Unix\System.Native\Interop.GetEUid.cs</Link>
+    </Compile>
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetPwUid.cs">
+      <Link>Common\Interop\Unix\System.Native\Interop.GetPwUid.cs</Link>
+    </Compile>
+    <Compile Include="$(CommonPath)\Interop\Unix\System.Native\Interop.GetPid.cs">
+      <Link>Common\Interop\Unix\System.Native\Interop.GetPid.cs</Link>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)System\Environment.Unix.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Environment.OSVersion.Unix.cs" Condition="'$(IsOSXLike)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\TimeZoneInfo.GetDisplayName.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\IO\DriveInfoInternal.Unix.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\IO\PersistedFiles.Unix.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' == 'true'">
+    <Compile Include="$(MSBuildThisFileDirectory)System\AppContext.Browser.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Environment.Browser.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\IO\DriveInfoInternal.Browser.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\IO\PersistedFiles.Browser.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\TimeZoneInfo.GetDisplayName.Invariant.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(IsOSXLike)' == 'true'">
diff --git a/src/libraries/System.Private.CoreLib/src/System/Action.cs b/src/libraries/System.Private.CoreLib/src/System/Action.cs
index 539e5fd9ce5817..dacc4fa7cc5b7b 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Action.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Action.cs
@@ -23,7 +23,10 @@ namespace System
     public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14, in T15>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12, T13 arg13, T14 arg14, T15 arg15);
     public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14, in T15, in T16>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9, T10 arg10, T11 arg11, T12 arg12, T13 arg13, T14 arg14, T15 arg15, T16 arg16);
 
-    public delegate int Comparison<in T>([AllowNull] T x, [AllowNull] T y);
+    // This should probably technically be T? rather than T to match `IComparer<T>`.  However, the use cases are generally different,
+    // with Comparison<T> typically being used via a lambda, with the T inferred from the type of the collection being sorted,
+    // and forcing nullable warnings onto all such usage leads to many spurious warnings.
+    public delegate int Comparison<in T>(T x, T y);
 
     public delegate TOutput Converter<in TInput, out TOutput>(TInput input);
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Array.cs b/src/libraries/System.Private.CoreLib/src/System/Array.cs
index 030e8e23d6586c..1e0fca689b40c3 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Array.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Array.cs
@@ -752,8 +752,7 @@ public static void Fill<T>(T[] array, T value, int startIndex, int count)
             }
         }
 
-        [return: MaybeNull]
-        public static T Find<T>(T[] array, Predicate<T> match)
+        public static T? Find<T>(T[] array, Predicate<T> match)
         {
             if (array == null)
             {
@@ -772,7 +771,7 @@ public static T Find<T>(T[] array, Predicate<T> match)
                     return array[i];
                 }
             }
-            return default!;
+            return default;
         }
 
         public static T[] FindAll<T>(T[] array, Predicate<T> match)
@@ -849,8 +848,7 @@ public static int FindIndex<T>(T[] array, int startIndex, int count, Predicate<T
             return -1;
         }
 
-        [return: MaybeNull]
-        public static T FindLast<T>(T[] array, Predicate<T> match)
+        public static T? FindLast<T>(T[] array, Predicate<T> match)
         {
             if (array == null)
             {
@@ -869,7 +867,7 @@ public static T FindLast<T>(T[] array, Predicate<T> match)
                     return array[i];
                 }
             }
-            return default!;
+            return default;
         }
 
         public static int FindLastIndex<T>(T[] array, Predicate<T> match)
diff --git a/src/libraries/System.Private.CoreLib/src/System/BitConverter.cs b/src/libraries/System.Private.CoreLib/src/System/BitConverter.cs
index fe03da6ec47be9..4a06da0807f530 100644
--- a/src/libraries/System.Private.CoreLib/src/System/BitConverter.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/BitConverter.cs
@@ -382,7 +382,7 @@ public static string ToString(byte[] value, int startIndex, int length)
                 throw new ArgumentOutOfRangeException(nameof(length), SR.Format(SR.ArgumentOutOfRange_LengthTooLarge, int.MaxValue / 3));
             }
 
-            return string.Create(length * 3 - 1, (value, startIndex, length), (dst, state) =>
+            return string.Create(length * 3 - 1, (value, startIndex, length), static (dst, state) =>
             {
                 var src = new ReadOnlySpan<byte>(state.value, state.startIndex, state.length);
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueue.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueue.cs
index 76f0ea24755337..08eb093d54f922 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueue.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueue.cs
@@ -689,7 +689,7 @@ private bool TryDequeueSlow([MaybeNullWhen(false)] out T item)
                 // check and this check, another item could have arrived).
                 if (head._nextSegment == null)
                 {
-                    item = default!;
+                    item = default;
                     return false;
                 }
 
@@ -783,7 +783,7 @@ private bool TryPeek([MaybeNullWhen(false)] out T result, bool resultUsed)
                 // and we'll traverse to that segment.
             }
 
-            result = default!;
+            result = default;
             return false;
         }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueueSegment.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueueSegment.cs
index 56a758e2cf9b60..1cd82352ae1754 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueueSegment.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueueSegment.cs
@@ -173,7 +173,7 @@ public bool TryDequeue([MaybeNullWhen(false)] out T item)
                     int currentTail = Volatile.Read(ref _headAndTail.Tail);
                     if (currentTail - currentHead <= 0 || (frozen && (currentTail - FreezeOffset - currentHead <= 0)))
                     {
-                        item = default!;
+                        item = default;
                         return false;
                     }
 
@@ -234,7 +234,7 @@ public bool TryPeek([MaybeNullWhen(false)] out T result, bool resultUsed)
                     int currentTail = Volatile.Read(ref _headAndTail.Tail);
                     if (currentTail - currentHead <= 0 || (frozen && (currentTail - FreezeOffset - currentHead <= 0)))
                     {
-                        result = default!;
+                        result = default;
                         return false;
                     }
 
@@ -311,7 +311,7 @@ public bool TryEnqueue(T item)
         internal struct Slot
         {
             /// <summary>The item.</summary>
-            [AllowNull, MaybeNull] public T Item; // SOS's ThreadPool command depends on this being at the beginning of the struct when T is a reference type
+            public T? Item; // SOS's ThreadPool command depends on this being at the beginning of the struct when T is a reference type
             /// <summary>The sequence number for this slot, used to synchronize between enqueuers and dequeuers.</summary>
             public int SequenceNumber;
         }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/Comparer.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/Comparer.cs
index 0b4f12d9e038ee..2ee414aa62791f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/Comparer.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/Comparer.cs
@@ -21,7 +21,7 @@ public static Comparer<T> Create(Comparison<T> comparison)
             return new ComparisonComparer<T>(comparison);
         }
 
-        public abstract int Compare([AllowNull] T x, [AllowNull] T y);
+        public abstract int Compare(T? x, T? y);
 
         int IComparer.Compare(object? x, object? y)
         {
@@ -42,10 +42,7 @@ public ComparisonComparer(Comparison<T> comparison)
             _comparison = comparison;
         }
 
-        public override int Compare([AllowNull] T x, [AllowNull] T y)
-        {
-            return _comparison(x, y);
-        }
+        public override int Compare(T? x, T? y) => _comparison(x!, y!);
     }
 
     // Note: although there is a lot of shared code in the following
@@ -58,7 +55,7 @@ public override int Compare([AllowNull] T x, [AllowNull] T y)
     // Needs to be public to support binary serialization compatibility
     public sealed partial class GenericComparer<T> : Comparer<T> where T : IComparable<T>
     {
-        public override int Compare([AllowNull] T x, [AllowNull] T y)
+        public override int Compare(T? x, T? y)
         {
             if (x != null)
             {
@@ -106,7 +103,7 @@ public override int GetHashCode() =>
     // Needs to be public to support binary serialization compatibility
     public sealed partial class ObjectComparer<T> : Comparer<T>
     {
-        public override int Compare([AllowNull] T x, [AllowNull] T y)
+        public override int Compare(T? x, T? y)
         {
             return System.Collections.Comparer.Default.Compare(x, y);
         }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/Dictionary.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/Dictionary.cs
index ac4fd58338dfe7..39245df47cce77 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/Dictionary.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/Dictionary.cs
@@ -59,10 +59,24 @@ public Dictionary(int capacity, IEqualityComparer<TKey>? comparer)
                 _comparer = comparer;
             }
 
-            if (typeof(TKey) == typeof(string) && _comparer == null)
+            // Special-case EqualityComparer<string>.Default, StringComparer.Ordinal, and StringComparer.OrdinalIgnoreCase.
+            // We use a non-randomized comparer for improved perf, falling back to a randomized comparer if the
+            // hash buckets become unbalanced.
+
+            if (typeof(TKey) == typeof(string))
             {
-                // To start, move off default comparer for string which is randomised
-                _comparer = (IEqualityComparer<TKey>)NonRandomizedStringEqualityComparer.Default;
+                if (_comparer is null)
+                {
+                    _comparer = (IEqualityComparer<TKey>)NonRandomizedStringEqualityComparer.WrappedAroundDefaultComparer;
+                }
+                else if (ReferenceEquals(_comparer, StringComparer.Ordinal))
+                {
+                    _comparer = (IEqualityComparer<TKey>)NonRandomizedStringEqualityComparer.WrappedAroundStringComparerOrdinal;
+                }
+                else if (ReferenceEquals(_comparer, StringComparer.OrdinalIgnoreCase))
+                {
+                    _comparer = (IEqualityComparer<TKey>)NonRandomizedStringEqualityComparer.WrappedAroundStringComparerOrdinalIgnoreCase;
+                }
             }
         }
 
@@ -125,10 +139,20 @@ protected Dictionary(SerializationInfo info, StreamingContext context)
             HashHelpers.SerializationInfoTable.Add(this, info);
         }
 
-        public IEqualityComparer<TKey> Comparer =>
-            (_comparer == null || _comparer is NonRandomizedStringEqualityComparer) ?
-                EqualityComparer<TKey>.Default :
-                _comparer;
+        public IEqualityComparer<TKey> Comparer
+        {
+            get
+            {
+                if (typeof(TKey) == typeof(string))
+                {
+                    return (IEqualityComparer<TKey>)IInternalStringEqualityComparer.GetUnderlyingEqualityComparer((IEqualityComparer<string?>?)_comparer);
+                }
+                else
+                {
+                    return _comparer ?? EqualityComparer<TKey>.Default;
+                }
+            }
+        }
 
         public int Count => _count - _freeCount;
 
@@ -299,7 +323,7 @@ public virtual void GetObjectData(SerializationInfo info, StreamingContext conte
             }
 
             info.AddValue(VersionName, _version);
-            info.AddValue(ComparerName, _comparer ?? EqualityComparer<TKey>.Default, typeof(IEqualityComparer<TKey>));
+            info.AddValue(ComparerName, Comparer, typeof(IEqualityComparer<TKey>));
             info.AddValue(HashSizeName, _buckets == null ? 0 : _buckets.Length); // This is the length of the bucket array
 
             if (_buckets != null)
@@ -633,7 +657,6 @@ private bool TryInsert(TKey key, TValue value, InsertionBehavior behavior)
             {
                 // If we hit the collision threshold we'll need to switch to the comparer which is using randomized string hashing
                 // i.e. EqualityComparer<string>.Default.
-                _comparer = null;
                 Resize(entries.Length, true);
             }
 
@@ -702,14 +725,21 @@ private void Resize(int newSize, bool forceNewHashCodes)
 
             if (!typeof(TKey).IsValueType && forceNewHashCodes)
             {
+                Debug.Assert(_comparer is NonRandomizedStringEqualityComparer);
+                _comparer = (IEqualityComparer<TKey>)((NonRandomizedStringEqualityComparer)_comparer).GetRandomizedEqualityComparer();
+
                 for (int i = 0; i < count; i++)
                 {
                     if (entries[i].next >= -1)
                     {
-                        Debug.Assert(_comparer == null);
-                        entries[i].hashCode = (uint)entries[i].key.GetHashCode();
+                        entries[i].hashCode = (uint)_comparer.GetHashCode(entries[i].key);
                     }
                 }
+
+                if (ReferenceEquals(_comparer, EqualityComparer<TKey>.Default))
+                {
+                    _comparer = null;
+                }
             }
 
             // Assign member variables after both arrays allocated to guard against corruption from OOM if second fails
@@ -1431,7 +1461,7 @@ public struct Enumerator : IEnumerator<TKey>, IEnumerator
                 private readonly Dictionary<TKey, TValue> _dictionary;
                 private int _index;
                 private readonly int _version;
-                [AllowNull, MaybeNull] private TKey _currentKey;
+                private TKey? _currentKey;
 
                 internal Enumerator(Dictionary<TKey, TValue> dictionary)
                 {
@@ -1623,7 +1653,7 @@ public struct Enumerator : IEnumerator<TValue>, IEnumerator
                 private readonly Dictionary<TKey, TValue> _dictionary;
                 private int _index;
                 private readonly int _version;
-                [AllowNull, MaybeNull] private TValue _currentValue;
+                private TValue? _currentValue;
 
                 internal Enumerator(Dictionary<TKey, TValue> dictionary)
                 {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/EqualityComparer.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/EqualityComparer.cs
index 6b6830e6425df6..180bea6ddf9ddb 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/EqualityComparer.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/EqualityComparer.cs
@@ -13,7 +13,7 @@ public abstract partial class EqualityComparer<T> : IEqualityComparer, IEquality
     {
         // public static EqualityComparer<T> Default is runtime-specific
 
-        public abstract bool Equals([AllowNull] T x, [AllowNull] T y);
+        public abstract bool Equals(T? x, T? y);
         public abstract int GetHashCode([DisallowNull] T obj);
 
         int IEqualityComparer.GetHashCode(object? obj)
@@ -42,7 +42,7 @@ bool IEqualityComparer.Equals(object? x, object? y)
     public sealed partial class GenericEqualityComparer<T> : EqualityComparer<T> where T : IEquatable<T>
     {
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public override bool Equals([AllowNull] T x, [AllowNull] T y)
+        public override bool Equals(T? x, T? y)
         {
             if (x != null)
             {
@@ -100,7 +100,7 @@ public override int GetHashCode() =>
     public sealed partial class ObjectEqualityComparer<T> : EqualityComparer<T>
     {
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public override bool Equals([AllowNull] T x, [AllowNull] T y)
+        public override bool Equals(T? x, T? y)
         {
             if (x != null)
             {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/HashSet.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/HashSet.cs
index f86c16fb8e71c4..394b0ff6fa625b 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/HashSet.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/HashSet.cs
@@ -60,10 +60,24 @@ public HashSet(IEqualityComparer<T>? comparer)
                 _comparer = comparer;
             }
 
-            if (typeof(T) == typeof(string) && _comparer == null)
+            // Special-case EqualityComparer<string>.Default, StringComparer.Ordinal, and StringComparer.OrdinalIgnoreCase.
+            // We use a non-randomized comparer for improved perf, falling back to a randomized comparer if the
+            // hash buckets become unbalanced.
+
+            if (typeof(T) == typeof(string))
             {
-                // To start, move off default comparer for string which is randomized.
-                _comparer = (IEqualityComparer<T>)NonRandomizedStringEqualityComparer.Default;
+                if (_comparer is null)
+                {
+                    _comparer = (IEqualityComparer<T>)NonRandomizedStringEqualityComparer.WrappedAroundDefaultComparer;
+                }
+                else if (ReferenceEquals(_comparer, StringComparer.Ordinal))
+                {
+                    _comparer = (IEqualityComparer<T>)NonRandomizedStringEqualityComparer.WrappedAroundStringComparerOrdinal;
+                }
+                else if (ReferenceEquals(_comparer, StringComparer.OrdinalIgnoreCase))
+                {
+                    _comparer = (IEqualityComparer<T>)NonRandomizedStringEqualityComparer.WrappedAroundStringComparerOrdinalIgnoreCase;
+                }
             }
         }
 
@@ -380,7 +394,7 @@ public virtual void GetObjectData(SerializationInfo info, StreamingContext conte
             }
 
             info.AddValue(VersionName, _version); // need to serialize version to avoid problems with serializing while enumerating
-            info.AddValue(ComparerName, _comparer ?? EqualityComparer<T>.Default, typeof(IEqualityComparer<T>));
+            info.AddValue(ComparerName, Comparer, typeof(IEqualityComparer<T>));
             info.AddValue(CapacityName, _buckets == null ? 0 : _buckets.Length);
 
             if (_buckets != null)
@@ -912,10 +926,20 @@ public int RemoveWhere(Predicate<T> match)
         }
 
         /// <summary>Gets the <see cref="IEqualityComparer"/> object that is used to determine equality for the values in the set.</summary>
-        public IEqualityComparer<T> Comparer =>
-            (_comparer == null || _comparer is NonRandomizedStringEqualityComparer) ?
-                EqualityComparer<T>.Default :
-                _comparer;
+        public IEqualityComparer<T> Comparer
+        {
+            get
+            {
+                if (typeof(T) == typeof(string))
+                {
+                    return (IEqualityComparer<T>)IInternalStringEqualityComparer.GetUnderlyingEqualityComparer((IEqualityComparer<string?>?)_comparer);
+                }
+                else
+                {
+                    return _comparer ?? EqualityComparer<T>.Default;
+                }
+            }
+        }
 
         /// <summary>Ensures that this hash set can hold the specified number of elements without growing.</summary>
         public int EnsureCapacity(int capacity)
@@ -957,15 +981,22 @@ private void Resize(int newSize, bool forceNewHashCodes)
 
             if (!typeof(T).IsValueType && forceNewHashCodes)
             {
+                Debug.Assert(_comparer is NonRandomizedStringEqualityComparer);
+                _comparer = (IEqualityComparer<T>)((NonRandomizedStringEqualityComparer)_comparer).GetRandomizedEqualityComparer();
+
                 for (int i = 0; i < count; i++)
                 {
                     ref Entry entry = ref entries[i];
                     if (entry.Next >= -1)
                     {
-                        Debug.Assert(_comparer == null);
-                        entry.HashCode = entry.Value != null ? entry.Value!.GetHashCode() : 0;
+                        entry.HashCode = entry.Value != null ? _comparer!.GetHashCode(entry.Value) : 0;
                     }
                 }
+
+                if (ReferenceEquals(_comparer, EqualityComparer<T>.Default))
+                {
+                    _comparer = null;
+                }
             }
 
             // Assign member variables after both arrays allocated to guard against corruption from OOM if second fails
@@ -1185,7 +1216,6 @@ private bool AddIfNotPresent(T value, out int location)
             {
                 // If we hit the collision threshold we'll need to switch to the comparer which is using randomized string hashing
                 // i.e. EqualityComparer<string>.Default.
-                _comparer = null;
                 Resize(entries.Length, forceNewHashCodes: true);
                 location = FindItemIndex(value);
                 Debug.Assert(location >= 0);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IComparer.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IComparer.cs
index 82394ef20b9ef0..59a9b90d9f534a 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IComparer.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IComparer.cs
@@ -14,6 +14,6 @@ public interface IComparer<in T>
         // value less than zero if x is less than y, zero if x is equal to y, or a
         // value greater than zero if x is greater than y.
         //
-        int Compare([AllowNull] T x, [AllowNull] T y);
+        int Compare(T? x, T? y);
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IEqualityComparer.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IEqualityComparer.cs
index b83b54ee749fbd..19545c6bbdd40e 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IEqualityComparer.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IEqualityComparer.cs
@@ -10,7 +10,7 @@ namespace System.Collections.Generic
     // It is used in Dictionary class.
     public interface IEqualityComparer<in T>
     {
-        bool Equals([AllowNull] T x, [AllowNull] T y);
+        bool Equals(T? x, T? y);
         int GetHashCode([DisallowNull] T obj);
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IInternalStringEqualityComparer.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IInternalStringEqualityComparer.cs
new file mode 100644
index 00000000000000..28c2ab9a07c9d8
--- /dev/null
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IInternalStringEqualityComparer.cs
@@ -0,0 +1,36 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Collections.Generic
+{
+    /// <summary>
+    /// Represents an <see cref="IEqualityComparer{String}"/> that's meant for internal
+    /// use only and isn't intended to be serialized or returned back to the user.
+    /// Use the <see cref="GetUnderlyingEqualityComparer"/> method to get the object
+    /// that should actually be returned to the caller.
+    /// </summary>
+    internal interface IInternalStringEqualityComparer : IEqualityComparer<string?>
+    {
+        IEqualityComparer<string?> GetUnderlyingEqualityComparer();
+
+        /// <summary>
+        /// Unwraps the internal equality comparer, if proxied.
+        /// Otherwise returns the equality comparer itself or its default equivalent.
+        /// </summary>
+        internal static IEqualityComparer<string?> GetUnderlyingEqualityComparer(IEqualityComparer<string?>? outerComparer)
+        {
+            if (outerComparer is null)
+            {
+                return EqualityComparer<string?>.Default;
+            }
+            else if (outerComparer is IInternalStringEqualityComparer internalComparer)
+            {
+                return internalComparer.GetUnderlyingEqualityComparer();
+            }
+            else
+            {
+                return outerComparer;
+            }
+        }
+    }
+}
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/List.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/List.cs
index 13ab166e8d326c..6da36e0f57bf4f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/List.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/List.cs
@@ -412,8 +412,7 @@ private void EnsureCapacity(int min)
         public bool Exists(Predicate<T> match)
             => FindIndex(match) != -1;
 
-        [return: MaybeNull]
-        public T Find(Predicate<T> match)
+        public T? Find(Predicate<T> match)
         {
             if (match == null)
             {
@@ -427,7 +426,7 @@ public T Find(Predicate<T> match)
                     return _items[i];
                 }
             }
-            return default!;
+            return default;
         }
 
         public List<T> FindAll(Predicate<T> match)
@@ -479,8 +478,7 @@ public int FindIndex(int startIndex, int count, Predicate<T> match)
             return -1;
         }
 
-        [return: MaybeNull]
-        public T FindLast(Predicate<T> match)
+        public T? FindLast(Predicate<T> match)
         {
             if (match == null)
             {
@@ -494,7 +492,7 @@ public T FindLast(Predicate<T> match)
                     return _items[i];
                 }
             }
-            return default!;
+            return default;
         }
 
         public int FindLastIndex(Predicate<T> match)
@@ -1077,7 +1075,7 @@ public struct Enumerator : IEnumerator<T>, IEnumerator
             private readonly List<T> _list;
             private int _index;
             private readonly int _version;
-            [AllowNull, MaybeNull] private T _current;
+            private T? _current;
 
             internal Enumerator(List<T> list)
             {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/NonRandomizedStringEqualityComparer.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/NonRandomizedStringEqualityComparer.cs
index b75ebd52e38bd4..0ec1a501d56f75 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/NonRandomizedStringEqualityComparer.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/NonRandomizedStringEqualityComparer.cs
@@ -1,7 +1,10 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
+using System.Globalization;
 using System.Runtime.Serialization;
+using Internal.Runtime.CompilerServices;
 
 namespace System.Collections.Generic
 {
@@ -11,23 +14,100 @@ namespace System.Collections.Generic
     // randomized string hashing.
     [Serializable] // Required for compatibility with .NET Core 2.0 as we exposed the NonRandomizedStringEqualityComparer inside the serialization blob
     // Needs to be public to support binary serialization compatibility
-    public sealed class NonRandomizedStringEqualityComparer : EqualityComparer<string?>, ISerializable
+    public class NonRandomizedStringEqualityComparer : IEqualityComparer<string?>, IInternalStringEqualityComparer, ISerializable
     {
-        internal static new IEqualityComparer<string?> Default { get; } = new NonRandomizedStringEqualityComparer();
+        // Dictionary<...>.Comparer and similar methods need to return the original IEqualityComparer
+        // that was passed in to the ctor. The caller chooses one of these singletons so that the
+        // GetUnderlyingEqualityComparer method can return the correct value.
 
-        private NonRandomizedStringEqualityComparer() { }
+        internal static readonly NonRandomizedStringEqualityComparer WrappedAroundDefaultComparer = new OrdinalComparer(EqualityComparer<string?>.Default);
+        internal static readonly NonRandomizedStringEqualityComparer WrappedAroundStringComparerOrdinal = new OrdinalComparer(StringComparer.Ordinal);
+        internal static readonly NonRandomizedStringEqualityComparer WrappedAroundStringComparerOrdinalIgnoreCase = new OrdinalIgnoreCaseComparer(StringComparer.OrdinalIgnoreCase);
+
+        private readonly IEqualityComparer<string?> _underlyingComparer;
+
+        private NonRandomizedStringEqualityComparer(IEqualityComparer<string?> underlyingComparer)
+        {
+            Debug.Assert(underlyingComparer != null);
+            _underlyingComparer = underlyingComparer;
+        }
 
         // This is used by the serialization engine.
-        private NonRandomizedStringEqualityComparer(SerializationInfo information, StreamingContext context) { }
+        protected NonRandomizedStringEqualityComparer(SerializationInfo information, StreamingContext context)
+            : this(EqualityComparer<string?>.Default)
+        {
+        }
+
+        public virtual bool Equals(string? x, string? y)
+        {
+            // This instance may have been deserialized into a class that doesn't guarantee
+            // these parameters are non-null. Can't short-circuit the null checks.
+
+            return string.Equals(x, y);
+        }
+
+        public virtual int GetHashCode(string? obj)
+        {
+            // This instance may have been deserialized into a class that doesn't guarantee
+            // these parameters are non-null. Can't short-circuit the null checks.
+
+            return obj?.GetNonRandomizedHashCode() ?? 0;
+        }
 
-        public sealed override bool Equals(string? x, string? y) => string.Equals(x, y);
+        internal virtual RandomizedStringEqualityComparer GetRandomizedEqualityComparer()
+        {
+            return RandomizedStringEqualityComparer.Create(_underlyingComparer, ignoreCase: false);
+        }
 
-        public sealed override int GetHashCode(string? obj) => obj?.GetNonRandomizedHashCode() ?? 0;
+        // Gets the comparer that should be returned back to the caller when querying the
+        // ICollection.Comparer property. Also used for serialization purposes.
+        public virtual IEqualityComparer<string?> GetUnderlyingEqualityComparer() => _underlyingComparer;
 
-        public void GetObjectData(SerializationInfo info, StreamingContext context)
+        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
         {
             // We are doing this to stay compatible with .NET Framework.
+            // Our own collection types will never call this (since this type is a wrapper),
+            // but perhaps third-party collection types could try serializing an instance
+            // of this.
             info.SetType(typeof(GenericEqualityComparer<string>));
         }
+
+        private sealed class OrdinalComparer : NonRandomizedStringEqualityComparer
+        {
+            internal OrdinalComparer(IEqualityComparer<string?> wrappedComparer)
+                : base(wrappedComparer)
+            {
+            }
+
+            public override bool Equals(string? x, string? y) => string.Equals(x, y);
+
+            public override int GetHashCode(string? obj)
+            {
+                Debug.Assert(obj != null, "This implementation is only called from first-party collection types that guarantee non-null parameters.");
+                return obj.GetNonRandomizedHashCode();
+            }
+
+        }
+
+        private sealed class OrdinalIgnoreCaseComparer : NonRandomizedStringEqualityComparer
+        {
+            internal OrdinalIgnoreCaseComparer(IEqualityComparer<string?> wrappedComparer)
+                : base(wrappedComparer)
+            {
+            }
+
+            public override bool Equals(string? x, string? y) => string.EqualsOrdinalIgnoreCase(x, y);
+
+            public override int GetHashCode(string? obj)
+            {
+                Debug.Assert(obj != null, "This implementation is only called from first-party collection types that guarantee non-null parameters.");
+                return obj.GetNonRandomizedHashCodeOrdinalIgnoreCase();
+            }
+
+            internal override RandomizedStringEqualityComparer GetRandomizedEqualityComparer()
+            {
+                return RandomizedStringEqualityComparer.Create(_underlyingComparer, ignoreCase: true);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/RandomizedStringEqualityComparer.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/RandomizedStringEqualityComparer.cs
new file mode 100644
index 00000000000000..168959d83386a2
--- /dev/null
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/RandomizedStringEqualityComparer.cs
@@ -0,0 +1,124 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Internal.Runtime.CompilerServices;
+
+namespace System.Collections.Generic
+{
+    /// <summary>
+    /// A randomized <see cref="EqualityComparer{String}"/> which uses a different seed on each
+    /// construction as a general good hygiene + defense-in-depth mechanism. This implementation
+    /// *does not* need to stay in sync with <see cref="string.GetHashCode"/>, which for stability
+    /// is required to use an app-global seed.
+    /// </summary>
+    internal abstract class RandomizedStringEqualityComparer : EqualityComparer<string?>, IInternalStringEqualityComparer
+    {
+        private readonly MarvinSeed _seed;
+        private readonly IEqualityComparer<string?> _underlyingComparer;
+
+        private unsafe RandomizedStringEqualityComparer(IEqualityComparer<string?> underlyingComparer)
+        {
+            _underlyingComparer = underlyingComparer;
+
+            fixed (MarvinSeed* seed = &_seed)
+            {
+                Interop.GetRandomBytes((byte*)seed, sizeof(MarvinSeed));
+            }
+        }
+
+        internal static RandomizedStringEqualityComparer Create(IEqualityComparer<string?> underlyingComparer, bool ignoreCase)
+        {
+            if (!ignoreCase)
+            {
+                return new OrdinalComparer(underlyingComparer);
+            }
+            else
+            {
+                return new OrdinalIgnoreCaseComparer(underlyingComparer);
+            }
+        }
+
+        public IEqualityComparer<string?> GetUnderlyingEqualityComparer() => _underlyingComparer;
+
+        private struct MarvinSeed
+        {
+            internal uint p0;
+            internal uint p1;
+        }
+
+        private sealed class OrdinalComparer : RandomizedStringEqualityComparer
+        {
+            internal OrdinalComparer(IEqualityComparer<string?> wrappedComparer)
+                : base(wrappedComparer)
+            {
+            }
+
+            public override bool Equals(string? x, string? y) => string.Equals(x, y);
+
+            public override int GetHashCode(string? obj)
+            {
+                if (obj is null)
+                {
+                    return 0;
+                }
+
+                // The Ordinal version of Marvin32 operates over bytes.
+                // The multiplication from # chars -> # bytes will never integer overflow.
+                return Marvin.ComputeHash32(
+                    ref Unsafe.As<char, byte>(ref obj.GetRawStringData()),
+                    (uint)obj.Length * 2,
+                    _seed.p0, _seed.p1);
+            }
+        }
+
+        private sealed class OrdinalIgnoreCaseComparer : RandomizedStringEqualityComparer
+        {
+            internal OrdinalIgnoreCaseComparer(IEqualityComparer<string?> wrappedComparer)
+                : base(wrappedComparer)
+            {
+            }
+
+            public override bool Equals(string? x, string? y) => string.EqualsOrdinalIgnoreCase(x, y);
+
+            public override int GetHashCode(string? obj)
+            {
+                if (obj is null)
+                {
+                    return 0;
+                }
+
+                // The Ordinal version of Marvin32 operates over bytes, so convert
+                // char count -> byte count. Guaranteed not to integer overflow.
+                return Marvin.ComputeHash32(
+                    ref Unsafe.As<char, byte>(ref obj.GetRawStringData()),
+                    (uint)obj.Length * sizeof(char),
+                    _seed.p0, _seed.p1);
+            }
+        }
+
+        private sealed class RandomizedOrdinalIgnoreCaseComparer : RandomizedStringEqualityComparer
+        {
+            internal RandomizedOrdinalIgnoreCaseComparer(IEqualityComparer<string?> underlyingComparer)
+                : base(underlyingComparer)
+            {
+            }
+
+            public override bool Equals(string? x, string? y) => string.EqualsOrdinalIgnoreCase(x, y);
+
+            public override int GetHashCode(string? obj)
+            {
+                if (obj is null)
+                {
+                    return 0;
+                }
+
+                // The OrdinalIgnoreCase version of Marvin32 operates over chars,
+                // so pass in the char count directly.
+                return Marvin.ComputeHash32OrdinalIgnoreCase(
+                    ref obj.GetRawStringData(),
+                    obj.Length,
+                    _seed.p0, _seed.p1);
+            }
+        }
+    }
+}
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/ObjectModel/Collection.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/ObjectModel/Collection.cs
index 2f2676a2cbaa42..fcafafed633f6d 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/ObjectModel/Collection.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/ObjectModel/Collection.cs
@@ -244,7 +244,7 @@ void ICollection.CopyTo(Array array, int index)
             {
                 ThrowHelper.IfNullAndNullsAreIllegalThenThrow<T>(value, ExceptionArgument.value);
 
-                T item = default!;
+                T? item = default;
 
                 try
                 {
@@ -285,7 +285,7 @@ int IList.Add(object? value)
             }
             ThrowHelper.IfNullAndNullsAreIllegalThenThrow<T>(value, ExceptionArgument.value);
 
-            T item = default!;
+            T? item = default;
 
             try
             {
@@ -327,7 +327,7 @@ void IList.Insert(int index, object? value)
             }
             ThrowHelper.IfNullAndNullsAreIllegalThenThrow<T>(value, ExceptionArgument.value);
 
-            T item = default!;
+            T? item = default;
 
             try
             {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/UnconditionalSuppressMessageAttribute.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/UnconditionalSuppressMessageAttribute.cs
index eefc9c442925bb..2d82ed0c0e7f50 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/UnconditionalSuppressMessageAttribute.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/UnconditionalSuppressMessageAttribute.cs
@@ -13,7 +13,12 @@ namespace System.Diagnostics.CodeAnalysis
     /// <see cref="ConditionalAttribute"/>. So it is always preserved in the compiled assembly.
     /// </remarks>
     [AttributeUsage(AttributeTargets.All, Inherited = false, AllowMultiple = true)]
-    public sealed class UnconditionalSuppressMessageAttribute : Attribute
+#if SYSTEM_PRIVATE_CORELIB
+    public
+#else
+    internal
+#endif
+    sealed class UnconditionalSuppressMessageAttribute : Attribute
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="UnconditionalSuppressMessageAttribute"/>
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/ActivityTracker.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/ActivityTracker.cs
index c98e76352fca25..e3f6632f59fb45 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/ActivityTracker.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/ActivityTracker.cs
@@ -227,10 +227,8 @@ public void Enable()
                 }
                 catch (NotImplementedException)
                 {
-#if (!ES_BUILD_PCL)
                     // send message to debugger without delay
                     System.Diagnostics.Debugger.Log(0, null, "Activity Enabled() called but AsyncLocals Not Supported (pre V4.6).  Ignoring Enable");
-#endif
                 }
             }
         }
@@ -511,7 +509,7 @@ private static unsafe int AddIdToGuid(Guid* outPtr, int whereToAddId, uint id, b
                 uint* sumPtr = (uint*)outPtr;
                 // We set the last DWORD the sum of the first 3 DWORDS in the GUID.   This
                 // This last number is a random number (it identifies us as us)  the process ID to make it unique per process.
-                sumPtr[3] = (sumPtr[0] + sumPtr[1] + sumPtr[2] + 0x599D99AD) ^ EventSource.s_currentPid;
+                sumPtr[3] = (sumPtr[0] + sumPtr[1] + sumPtr[2] + 0x599D99AD) ^ (uint)Environment.ProcessId;
 
                 return (int)(ptr - ((byte*)outPtr));
             }
@@ -636,27 +634,4 @@ public class Keywords
         public void SetActivityId(Guid Id) { WriteEvent(3, Id); }
     }
 #endif
-
-#if ES_BUILD_AGAINST_DOTNET_V35 || ES_BUILD_PCL || NO_ASYNC_LOCAL
-    // In these cases we don't have any Async local support.   Do nothing.
-    internal sealed class AsyncLocalValueChangedArgs<T>
-    {
-        public T PreviousValue { get { return default(T); } }
-        public T CurrentValue { get { return default(T); } }
-
-    }
-
-    internal sealed class AsyncLocal<T>
-    {
-        public AsyncLocal(Action<AsyncLocalValueChangedArgs<T>> valueChangedHandler) {
-            throw new NotImplementedException("AsyncLocal only available on V4.6 and above");
-        }
-        public T Value
-        {
-            get { return default(T); }
-            set { }
-        }
-    }
-#endif
-
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventDescriptor.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventDescriptor.cs
index d687d41b42e747..5bdde239895add 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventDescriptor.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventDescriptor.cs
@@ -1,10 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#if ES_BUILD_STANDALONE
 using System;
-using Environment = Microsoft.Diagnostics.Tracing.Internal.Environment;
-#endif
 using System.Runtime.InteropServices;
 
 #if ES_BUILD_STANDALONE
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventProvider.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventProvider.cs
index 919927f4ebaaff..6ed62d08290a8f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventProvider.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventProvider.cs
@@ -1,22 +1,20 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#if ES_BUILD_STANDALONE
-using Microsoft.Win32;
 using System;
 using System.Diagnostics;
-using System.Security.Permissions;
-using BitOperations = Microsoft.Diagnostics.Tracing.Internal.BitOperations;
-#endif
 using System.Collections.Generic;
 using System.Globalization;
 using System.Numerics;
 using System.Runtime.InteropServices;
-#if (CORECLR || MONO) && TARGET_WINDOWS
-using Internal.Win32;
+
+#if ES_BUILD_STANDALONE
+using Microsoft.Win32;
+using System.Security.Permissions;
 #endif
-#if ES_BUILD_AGAINST_DOTNET_V35
-using Microsoft.Internal;       // for Tuple (can't define alias for open generic types so we "use" the whole namespace)
+
+#if !ES_BUILD_STANDALONE && TARGET_WINDOWS
+using Internal.Win32;
 #endif
 
 #if ES_BUILD_STANDALONE
@@ -521,7 +519,7 @@ private unsafe void GetSessionInfo(SessionInfoCallback action, ref List<SessionI
                 }
             }
 #else
-#if !ES_BUILD_PCL && TARGET_WINDOWS  // TODO command arguments don't work on PCL builds...
+#if TARGET_WINDOWS
             // This code is only used in the Nuget Package Version of EventSource.  because
             // the code above is using APIs baned from UWP apps.
             //
@@ -609,7 +607,7 @@ private unsafe bool GetDataFromController(int etwSessionId,
             dataStart = 0;
             if (filterData == null)
             {
-#if (!ES_BUILD_PCL && TARGET_WINDOWS)
+#if TARGET_WINDOWS
                 string regKey = @"\Microsoft\Windows\CurrentVersion\Winevt\Publishers\{" + m_providerId + "}";
                 if (IntPtr.Size == 8)
                     regKey = @"Software\Wow6432Node" + regKey;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventSource.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventSource.cs
index 02b84bcd18ff83..6085322e18d3fd 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventSource.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventSource.cs
@@ -163,17 +163,10 @@
 // opportunity to expose this format to EventListeners in the future.
 //
 
-#if ES_BUILD_STANDALONE
 using System;
-using System.Diagnostics;
-using System.Security.Permissions;
-using EventDescriptor = Microsoft.Diagnostics.Tracing.EventDescriptor;
-using BitOperations = Microsoft.Diagnostics.Tracing.Internal.BitOperations;
-#else
-using System.Threading.Tasks;
-#endif
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Numerics;
@@ -181,7 +174,11 @@
 using System.Resources;
 using System.Text;
 using System.Threading;
-using Microsoft.Reflection;
+using System.Threading.Tasks;
+
+#if ES_BUILD_STANDALONE
+using System.Security.Permissions;
+#endif
 
 #if ES_BUILD_STANDALONE
 namespace Microsoft.Diagnostics.Tracing
@@ -312,13 +309,8 @@ public static Guid GetGuid(Type eventSourceType)
             {
                 if (attrib.Guid != null)
                 {
-#if !ES_BUILD_AGAINST_DOTNET_V35
                     if (Guid.TryParse(attrib.Guid, out Guid g))
                         return g;
-#else
-                    try { return new Guid(attrib.Guid); }
-                    catch (Exception) { }
-#endif
                 }
 
                 if (attrib.Name != null)
@@ -1371,14 +1363,14 @@ protected virtual void Dispose(bool disposing)
                 if (m_etwProvider != null)
                 {
                     m_etwProvider.Dispose();
-                    m_etwProvider = null!; // TODO-NULLABLE: Avoid nulling out in Dispose
+                    m_etwProvider = null!;
                 }
 #endif
 #if FEATURE_PERFTRACING
                 if (m_eventPipeProvider != null)
                 {
                     m_eventPipeProvider.Dispose();
-                    m_eventPipeProvider = null!; // TODO-NULLABLE: Avoid nulling out in Dispose
+                    m_eventPipeProvider = null!;
                 }
 #endif
             }
@@ -1869,7 +1861,7 @@ private static Guid GenerateGuidFromName(string name)
                 {
                     m_EventSourceInDecodeObject = true;
 
-                    if (dataType.IsEnum())
+                    if (dataType.IsEnum)
                     {
                         dataType = Enum.GetUnderlyingType(dataType);
 
@@ -2843,14 +2835,6 @@ private void EnsureDescriptorsInitialized()
                 DefineEventPipeEvents();
 #endif
             }
-            if (s_currentPid == 0)
-            {
-#if ES_BUILD_STANDALONE
-                // for non-BCL EventSource we must assert SecurityPermission
-                new SecurityPermission(PermissionState.Unrestricted).Assert();
-#endif
-                s_currentPid = Interop.GetCurrentProcessId();
-            }
         }
 
         // Send out the ETW manifest XML out to ETW
@@ -2928,13 +2912,6 @@ private unsafe void SendManifest(byte[]? rawManifest)
 #endif // FEATURE_MANAGED_ETW
         }
 
-#if (ES_BUILD_PCL)
-        internal static Attribute GetCustomAttributeHelper(Type type, Type attributeType, EventManifestOptions flags = EventManifestOptions.None)
-        {
-            return GetCustomAttributeHelper(type.GetTypeInfo(), attributeType, flags);
-        }
-#endif
-
         // Helper to deal with the fact that the type we are reflecting over might be loaded in the ReflectionOnly context.
         // When that is the case, we have the build the custom assemblies on a member by hand.
         internal static Attribute? GetCustomAttributeHelper(
@@ -2947,7 +2924,7 @@ internal static Attribute GetCustomAttributeHelper(Type type, Type attributeType
         {
             // AllowEventSourceOverride is an option that allows either Microsoft.Diagnostics.Tracing or
             // System.Diagnostics.Tracing EventSource to be considered valid.  This should not mattter anywhere but in Microsoft.Diagnostics.Tracing (nuget package).
-            if (!member.Module.Assembly.ReflectionOnly() && (flags & EventManifestOptions.AllowEventSourceOverride) == 0)
+            if (!member.Module.Assembly.ReflectionOnly && (flags & EventManifestOptions.AllowEventSourceOverride) == 0)
             {
                 // Let the runtime to the work for us, since we can execute code in this context.
                 Attribute? firstAttribute = null;
@@ -2959,7 +2936,6 @@ internal static Attribute GetCustomAttributeHelper(Type type, Type attributeType
                 return firstAttribute;
             }
 
-#if (!ES_BUILD_PCL)
             foreach (CustomAttributeData data in CustomAttributeData.GetCustomAttributes(member))
             {
                 if (AttributeTypeNamesMatch(attributeType, data.Constructor.ReflectedType!))
@@ -2999,10 +2975,6 @@ internal static Attribute GetCustomAttributeHelper(Type type, Type attributeType
             }
 
             return null;
-#else // ES_BUILD_PCL
-            // Don't use nameof here because the resource doesn't exist on some platforms, which results in a compilation error.
-            throw new ArgumentException("EventSource_PCLPlatformNotSupportedReflection", "EventSource");
-#endif
         }
 
         /// <summary>
@@ -3037,15 +3009,15 @@ private static bool AttributeTypeNamesMatch(Type attributeType, Type reflectedAt
             Type? ret = eventSourceType;
 
             // return false for "object" and interfaces
-            if (ret.BaseType() == null)
+            if (ret.BaseType == null)
                 return null;
 
             // now go up the inheritance chain until hitting a concrete type ("object" at worse)
             do
             {
-                ret = ret.BaseType();
+                ret = ret.BaseType;
             }
-            while (ret != null && ret.IsAbstract());
+            while (ret != null && ret.IsAbstract);
 
             if (ret != null)
             {
@@ -3082,7 +3054,7 @@ private static bool AttributeTypeNamesMatch(Type attributeType, Type reflectedAt
             Exception? exception = null; // exception that might get raised during validation b/c we couldn't/didn't recover from a previous error
             byte[]? res = null;
 
-            if (eventSourceType.IsAbstract() && (flags & EventManifestOptions.Strict) == 0)
+            if (eventSourceType.IsAbstract && (flags & EventManifestOptions.Strict) == 0)
                 return null;
 
             try
@@ -3102,7 +3074,7 @@ private static bool AttributeTypeNamesMatch(Type attributeType, Type reflectedAt
                 ResourceManager? resources = null;
                 EventSourceAttribute? eventSourceAttrib = (EventSourceAttribute?)GetCustomAttributeHelper(eventSourceType, typeof(EventSourceAttribute), flags);
                 if (eventSourceAttrib != null && eventSourceAttrib.LocalizationResources != null)
-                    resources = new ResourceManager(eventSourceAttrib.LocalizationResources, eventSourceType.Assembly());
+                    resources = new ResourceManager(eventSourceAttrib.LocalizationResources, eventSourceType.Assembly);
 
                 manifest = new ManifestBuilder(GetName(eventSourceType, flags), GetGuid(eventSourceType), eventSourceDllName,
                                                resources, flags);
@@ -3115,13 +3087,13 @@ private static bool AttributeTypeNamesMatch(Type attributeType, Type reflectedAt
                 // eventSourceType must be sealed and must derive from this EventSource
                 if ((flags & EventManifestOptions.Strict) != 0)
                 {
-                    bool typeMatch = GetEventSourceBaseType(eventSourceType, (flags & EventManifestOptions.AllowEventSourceOverride) != 0, eventSourceType.Assembly().ReflectionOnly()) != null;
+                    bool typeMatch = GetEventSourceBaseType(eventSourceType, (flags & EventManifestOptions.AllowEventSourceOverride) != 0, eventSourceType.Assembly.ReflectionOnly) != null;
 
                     if (!typeMatch)
                     {
                         manifest.ManifestError(SR.EventSource_TypeMustDeriveFromEventSource);
                     }
-                    if (!eventSourceType.IsAbstract() && !eventSourceType.IsSealed())
+                    if (!eventSourceType.IsAbstract && !eventSourceType.IsSealed)
                     {
                         manifest.ManifestError(SR.EventSource_TypeMustBeSealedOrAbstract);
                     }
@@ -3137,7 +3109,7 @@ private static bool AttributeTypeNamesMatch(Type attributeType, Type reflectedAt
                     Type? nestedType = eventSourceType.GetNestedType(providerEnumKind);
                     if (nestedType != null)
                     {
-                        if (eventSourceType.IsAbstract())
+                        if (eventSourceType.IsAbstract)
                         {
                             manifest.ManifestError(SR.Format(SR.EventSource_AbstractMustNotDeclareKTOC, nestedType.Name));
                         }
@@ -3178,7 +3150,7 @@ private static bool AttributeTypeNamesMatch(Type attributeType, Type reflectedAt
                             continue;
                         }
 
-                        if (eventSourceType.IsAbstract())
+                        if (eventSourceType.IsAbstract)
                         {
                             if (eventAttribute != null)
                             {
@@ -3329,7 +3301,7 @@ private static bool AttributeTypeNamesMatch(Type attributeType, Type reflectedAt
                 }
 
                 // if this is an abstract event source we've already performed all the validation we can
-                if (!eventSourceType.IsAbstract() && (source == null || !source.SelfDescribingEvents))
+                if (!eventSourceType.IsAbstract && (source == null || !source.SelfDescribingEvents))
                 {
                     bNeedsManifest = (flags & EventManifestOptions.OnlyIfNeededForRegistration) == 0
 #if FEATURE_MANAGED_ETW_CHANNELS
@@ -3363,7 +3335,7 @@ private static bool AttributeTypeNamesMatch(Type attributeType, Type reflectedAt
                     foreach (string error in manifest.Errors)
                     {
                         if (!firstError)
-                            msg += Environment.NewLine;
+                            msg += System.Environment.NewLine;
                         firstError = false;
                         msg += error;
                     }
@@ -3397,7 +3369,7 @@ private static bool RemoveFirstArgIfRelatedActivityId(ref ParameterInfo[] args)
         // to the manifest.
         private static void AddProviderEnumKind(ManifestBuilder manifest, FieldInfo staticField, string providerEnumKind)
         {
-            bool reflectionOnly = staticField.Module.Assembly.ReflectionOnly();
+            bool reflectionOnly = staticField.Module.Assembly.ReflectionOnly;
             Type staticFieldType = staticField.FieldType;
             if (!reflectionOnly && (staticFieldType == typeof(EventOpcode)) || AttributeTypeNamesMatch(staticFieldType, typeof(EventOpcode)))
             {
@@ -3594,7 +3566,6 @@ private static void DebugCheckEvent(ref Dictionary<string, string>? eventsByName
         /// <returns>The literal value or -1 if the value could not be determined. </returns>
         private static int GetHelperCallFirstArg(MethodInfo method)
         {
-#if (!ES_BUILD_PCL)
             // Currently searches for the following pattern
             //
             // ...     // CAN ONLY BE THE INSTRUCTIONS BELOW
@@ -3711,7 +3682,6 @@ private static int GetHelperCallFirstArg(MethodInfo method)
                 }
                 idx++;
             }
-#endif
             return -1;
         }
 
@@ -3723,10 +3693,8 @@ internal void ReportOutOfBandMessage(string msg)
         {
             try
             {
-#if (!ES_BUILD_PCL)
                 // send message to debugger without delay
-                System.Diagnostics.Debugger.Log(0, null, string.Format("EventSource Error: {0}{1}", msg, Environment.NewLine));
-#endif
+                System.Diagnostics.Debugger.Log(0, null, string.Format("EventSource Error: {0}{1}", msg, System.Environment.NewLine));
 
                 // Send it to all listeners.
                 if (m_outOfBandMessageCount < 16 - 1)     // Note this is only if size byte
@@ -3807,7 +3775,6 @@ private bool SelfDescribingEvents
 
         private string[]? m_traits;                      // Used to implement GetTraits
 
-        internal static uint s_currentPid;              // current process id, used in synthesizing quasi-GUIDs
         [ThreadStatic]
         private static byte m_EventSourceExceptionRecurenceCount; // current recursion count inside ThrowEventSourceException
 
@@ -5432,7 +5399,7 @@ public void AddEventParameter(Type type, string name)
                 templates.Append(" length=\"").Append(name).Append("Size\"");
             }
             // ETW does not support 64-bit value maps, so we don't specify these as ETW maps
-            if (type.IsEnum() && Enum.GetUnderlyingType(type) != typeof(ulong) && Enum.GetUnderlyingType(type) != typeof(long))
+            if (type.IsEnum && Enum.GetUnderlyingType(type) != typeof(ulong) && Enum.GetUnderlyingType(type) != typeof(long))
             {
                 templates.Append(" map=\"").Append(type.Name).Append('"');
                 mapsTab ??= new Dictionary<string, Type>();
@@ -5924,14 +5891,14 @@ private string GetKeywords(ulong keywords, string eventName)
 
         private string GetTypeName(Type type)
         {
-            if (type.IsEnum())
+            if (type.IsEnum)
             {
                 FieldInfo[] fields = type.GetFields(BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance);
                 string typeName = GetTypeName(fields[0].FieldType);
                 return typeName.Replace("win:Int", "win:UInt"); // ETW requires enums to be unsigned.
             }
 
-            switch (type.GetTypeCode())
+            switch (Type.GetTypeCode(type))
             {
                 case TypeCode.Boolean:
                     return "win:Boolean";
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventSourceException.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventSourceException.cs
index 67f70c747e2cc7..638bb05b9eb9b3 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventSourceException.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventSourceException.cs
@@ -1,10 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#if ES_BUILD_STANDALONE
 using System;
-using Environment = Microsoft.Diagnostics.Tracing.Internal.Environment;
-#endif
 using System.Runtime.Serialization;
 
 #if ES_BUILD_STANDALONE
@@ -16,9 +13,7 @@ namespace System.Diagnostics.Tracing
     /// <summary>
     /// Exception that is thrown when an error occurs during EventSource operation.
     /// </summary>
-#if !ES_BUILD_PCL
     [Serializable]
-#endif
     public class EventSourceException : Exception
     {
         /// <summary>
@@ -38,12 +33,10 @@ public EventSourceException(string? message) : base(message) { }
         /// </summary>
         public EventSourceException(string? message, Exception? innerException) : base(message, innerException) { }
 
-#if !ES_BUILD_PCL
         /// <summary>
         /// Initializes a new instance of the EventSourceException class with serialized data.
         /// </summary>
         protected EventSourceException(SerializationInfo info, StreamingContext context) : base(info, context) { }
-#endif
 
         internal EventSourceException(Exception? innerException) :
             base(SR.EventSource_ListenerWriteFailure, innerException) { }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/RuntimeEventSource.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/RuntimeEventSource.cs
index d5f1c745ff1c58..eecca7780c4c33 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/RuntimeEventSource.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/RuntimeEventSource.cs
@@ -26,6 +26,7 @@ internal sealed class RuntimeEventSource : EventSource
         private IncrementingPollingCounter? _completedItemsCounter;
         private IncrementingPollingCounter? _allocRateCounter;
         private PollingCounter? _timerCounter;
+        private PollingCounter? _fragmentationCounter;
 
 #if !MONO
         private IncrementingPollingCounter? _exceptionCounter;
@@ -70,6 +71,10 @@ protected override void OnEventCommand(EventCommandEventArgs command)
                 _completedItemsCounter ??= new IncrementingPollingCounter("threadpool-completed-items-count", this, () => ThreadPool.CompletedWorkItemCount) { DisplayName = "ThreadPool Completed Work Item Count", DisplayRateTimeScale = new TimeSpan(0, 0, 1) };
                 _allocRateCounter ??= new IncrementingPollingCounter("alloc-rate", this, () => GC.GetTotalAllocatedBytes()) { DisplayName = "Allocation Rate", DisplayUnits = "B", DisplayRateTimeScale = new TimeSpan(0, 0, 1) };
                 _timerCounter ??= new PollingCounter("active-timer-count", this, () => Timer.ActiveCount) { DisplayName = "Number of Active Timers" };
+                _fragmentationCounter ??= new PollingCounter("gc-fragmentation", this, () => {
+                    var gcInfo = GC.GetGCMemoryInfo();
+                    return gcInfo.FragmentedBytes * 100d / gcInfo.HeapSizeBytes;
+                 }) { DisplayName = "GC Fragmentation", DisplayUnits = "%" };
 #if !MONO
                 _exceptionCounter ??= new IncrementingPollingCounter("exception-count", this, () => Exception.GetExceptionCount()) { DisplayName = "Exception Count", DisplayRateTimeScale = new TimeSpan(0, 0, 1) };
                 _gcTimeCounter ??= new PollingCounter("time-in-gc", this, () => GC.GetLastGCPercentTimeInGC()) { DisplayName = "% Time in GC since last GC", DisplayUnits = "%" };
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/StubEnvironment.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/StubEnvironment.cs
deleted file mode 100644
index 9f08d0ca304b40..00000000000000
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/StubEnvironment.cs
+++ /dev/null
@@ -1,371 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System;
-#if ES_BUILD_PCL
-using System.Collections.Generic;
-#endif
-using System.Reflection;
-#if ES_BUILD_STANDALONE
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-using System.Security;
-#endif
-#if ES_BUILD_AGAINST_DOTNET_V35
-using Microsoft.Internal;
-#endif
-using Microsoft.Reflection;
-
-#if ES_BUILD_STANDALONE
-namespace Microsoft.Diagnostics.Tracing.Internal
-#else
-namespace System.Diagnostics.Tracing.Internal
-#endif
-{
-    internal static class Environment
-    {
-        public static readonly string NewLine = System.Environment.NewLine;
-
-        public static int TickCount => System.Environment.TickCount;
-
-        public static string GetResourceString(string key, params object?[] args)
-        {
-            string? fmt = rm.GetString(key);
-            if (fmt != null)
-                return string.Format(fmt, args);
-
-            string sargs = string.Join(", ", args);
-
-            return key + " (" + sargs + ")";
-        }
-
-        public static string GetRuntimeResourceString(string key, params object?[] args)
-        {
-            return GetResourceString(key, args);
-        }
-
-        private static readonly System.Resources.ResourceManager rm = new System.Resources.ResourceManager("Microsoft.Diagnostics.Tracing.Messages", typeof(Environment).Assembly());
-    }
-
-#if ES_BUILD_STANDALONE
-    internal static class BitOperations
-    {
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static uint RotateLeft(uint value, int offset)
-            => (value << offset) | (value >> (32 - offset));
-
-        public static int PopCount(uint value)
-        {
-            const uint c1 = 0x_55555555u;
-            const uint c2 = 0x_33333333u;
-            const uint c3 = 0x_0F0F0F0Fu;
-            const uint c4 = 0x_01010101u;
-
-            value = value - ((value >> 1) & c1);
-            value = (value & c2) + ((value >> 2) & c2);
-            value = (((value + (value >> 4)) & c3) * c4) >> 24;
-
-            return (int)value;
-        }
-
-        public static int TrailingZeroCount(uint value)
-        {
-            if (value == 0)
-                return 32;
-
-            int count = 0;
-            while ((value & 1) == 0)
-            {
-                value >>= 1;
-                count++;
-            }
-            return count;
-        }
-    }
-#endif
-}
-
-#if ES_BUILD_AGAINST_DOTNET_V35
-
-namespace Microsoft.Internal
-{
-    using System.Text;
-
-    internal static class Tuple
-    {
-        public static Tuple<T1> Create<T1>(T1 item1)
-        {
-            return new Tuple<T1>(item1);
-        }
-
-        public static Tuple<T1, T2> Create<T1, T2>(T1 item1, T2 item2)
-        {
-            return new Tuple<T1, T2>(item1, item2);
-        }
-    }
-
-    [Serializable]
-    internal class Tuple<T1>
-    {
-        private readonly T1 m_Item1;
-
-        public T1 Item1 { get { return m_Item1; } }
-
-        public Tuple(T1 item1)
-        {
-            m_Item1 = item1;
-        }
-
-        public override string ToString()
-        {
-            StringBuilder sb = new StringBuilder();
-            sb.Append('(');
-            sb.Append(m_Item1);
-            sb.Append(')');
-            return sb.ToString();
-        }
-
-        int Size
-        {
-            get
-            {
-                return 1;
-            }
-        }
-    }
-
-    [Serializable]
-    public class Tuple<T1, T2>
-    {
-        private readonly T1 m_Item1;
-        private readonly T2 m_Item2;
-
-        public T1 Item1 { get { return m_Item1; } }
-        public T2 Item2 { get { return m_Item2; } }
-
-        public Tuple(T1 item1, T2 item2)
-        {
-            m_Item1 = item1;
-            m_Item2 = item2;
-        }
-
-        public override string ToString()
-        {
-            StringBuilder sb = new StringBuilder();
-            sb.Append('(');
-            sb.Append(m_Item1);
-            sb.Append(", ");
-            sb.Append(m_Item2);
-            sb.Append(')');
-            return sb.ToString();
-        }
-
-        int Size
-        {
-            get
-            {
-                return 2;
-            }
-        }
-    }
-}
-
-#endif
-
-namespace Microsoft.Reflection
-{
-#if ES_BUILD_PCL
-    [Flags]
-    public enum BindingFlags
-    {
-        DeclaredOnly = 0x02,        // Only look at the members declared on the Type
-        Instance     = 0x04,        // Include Instance members in search
-        Static       = 0x08,        // Include Static members in search
-        Public       = 0x10,        // Include Public members in search
-        NonPublic    = 0x20,        // Include Non-Public members in search
-    }
-
-    public enum TypeCode {
-        Empty = 0,                  // Null reference
-        Object = 1,                 // Instance that isn't a value
-        DBNull = 2,                 // Database null value
-        Boolean = 3,                // Boolean
-        Char = 4,                   // Unicode character
-        SByte = 5,                  // Signed 8-bit integer
-        Byte = 6,                   // Unsigned 8-bit integer
-        Int16 = 7,                  // Signed 16-bit integer
-        UInt16 = 8,                 // Unsigned 16-bit integer
-        Int32 = 9,                  // Signed 32-bit integer
-        UInt32 = 10,                // Unsigned 32-bit integer
-        Int64 = 11,                 // Signed 64-bit integer
-        UInt64 = 12,                // Unsigned 64-bit integer
-        Single = 13,                // IEEE 32-bit float
-        Double = 14,                // IEEE 64-bit double
-        Decimal = 15,               // Decimal
-        DateTime = 16,              // DateTime
-        String = 18,                // Unicode character string
-    }
-#endif
-    internal static class ReflectionExtensions
-    {
-#if (!ES_BUILD_PCL)
-
-        //
-        // Type extension methods
-        //
-        public static bool IsEnum(this Type type) { return type.IsEnum; }
-        public static bool IsAbstract(this Type type) { return type.IsAbstract; }
-        public static bool IsSealed(this Type type) { return type.IsSealed; }
-        public static bool IsValueType(this Type type) { return type.IsValueType; }
-        public static bool IsGenericType(this Type type) { return type.IsGenericType; }
-        public static Type? BaseType(this Type type) { return type.BaseType; }
-        public static Assembly Assembly(this Type type) { return type.Assembly; }
-        public static TypeCode GetTypeCode(this Type type) { return Type.GetTypeCode(type); }
-
-        public static bool ReflectionOnly(this Assembly assm) { return assm.ReflectionOnly; }
-
-#else
-
-        //
-        // Type extension methods
-        //
-        public static bool IsEnum(this Type type) { return type.GetTypeInfo().IsEnum; }
-        public static bool IsAbstract(this Type type) { return type.GetTypeInfo().IsAbstract; }
-        public static bool IsSealed(this Type type) { return type.GetTypeInfo().IsSealed; }
-        public static bool IsValueType(this Type type) { return type.GetTypeInfo().IsValueType; }
-        public static bool IsGenericType(this Type type) { return type.IsConstructedGenericType; }
-        public static Type? BaseType(this Type type) { return type.GetTypeInfo().BaseType; }
-        public static Assembly Assembly(this Type type) { return type.GetTypeInfo().Assembly; }
-        public static IEnumerable<PropertyInfo> GetProperties(this Type type)
-        {
-            return type.GetRuntimeProperties();
-        }
-        public static MethodInfo? GetGetMethod(this PropertyInfo propInfo) { return propInfo.GetMethod; }
-        public static Type[] GetGenericArguments(this Type type) { return type.GenericTypeArguments; }
-
-        public static MethodInfo[] GetMethods(this Type type, BindingFlags flags)
-        {
-            // Minimal implementation to cover only the cases we need
-            System.Diagnostics.Debug.Assert((flags & BindingFlags.DeclaredOnly) != 0);
-            System.Diagnostics.Debug.Assert((flags & ~(BindingFlags.DeclaredOnly|BindingFlags.Instance|BindingFlags.Static|BindingFlags.Public|BindingFlags.NonPublic)) == 0);
-            Func<MethodInfo, bool> visFilter;
-            Func<MethodInfo, bool> instFilter;
-            switch (flags & (BindingFlags.Public | BindingFlags.NonPublic))
-            {
-                case 0: visFilter = mi => false; break;
-                case BindingFlags.Public: visFilter = mi => mi.IsPublic; break;
-                case BindingFlags.NonPublic: visFilter = mi => !mi.IsPublic; break;
-                default: visFilter = mi => true; break;
-            }
-            switch (flags & (BindingFlags.Instance | BindingFlags.Static))
-            {
-                case 0: instFilter = mi => false; break;
-                case BindingFlags.Instance: instFilter = mi => !mi.IsStatic; break;
-                case BindingFlags.Static: instFilter = mi => mi.IsStatic; break;
-                default: instFilter = mi => true; break;
-            }
-            List<MethodInfo> methodInfos = new List<MethodInfo>();
-            foreach (var declaredMethod in type.GetTypeInfo().DeclaredMethods)
-            {
-                if (visFilter(declaredMethod) && instFilter(declaredMethod))
-                    methodInfos.Add(declaredMethod);
-            }
-            return methodInfos.ToArray();
-        }
-        public static FieldInfo[] GetFields(this Type type, BindingFlags flags)
-        {
-            // Minimal implementation to cover only the cases we need
-            System.Diagnostics.Debug.Assert((flags & BindingFlags.DeclaredOnly) != 0);
-            System.Diagnostics.Debug.Assert((flags & ~(BindingFlags.DeclaredOnly | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic)) == 0);
-            Func<FieldInfo, bool> visFilter;
-            Func<FieldInfo, bool> instFilter;
-            switch (flags & (BindingFlags.Public | BindingFlags.NonPublic))
-            {
-                case 0: visFilter = fi => false; break;
-                case BindingFlags.Public: visFilter = fi => fi.IsPublic; break;
-                case BindingFlags.NonPublic: visFilter = fi => !fi.IsPublic; break;
-                default: visFilter = fi => true; break;
-            }
-            switch (flags & (BindingFlags.Instance | BindingFlags.Static))
-            {
-                case 0: instFilter = fi => false; break;
-                case BindingFlags.Instance: instFilter = fi => !fi.IsStatic; break;
-                case BindingFlags.Static: instFilter = fi => fi.IsStatic; break;
-                default: instFilter = fi => true; break;
-            }
-            List<FieldInfo> fieldInfos = new List<FieldInfo>();
-            foreach (var declaredField in type.GetTypeInfo().DeclaredFields)
-            {
-                if (visFilter(declaredField) && instFilter(declaredField))
-                    fieldInfos.Add(declaredField);
-            }
-            return fieldInfos.ToArray();
-        }
-        public static Type? GetNestedType(this Type type, string nestedTypeName)
-        {
-            TypeInfo? ti = null;
-            foreach (var nt in type.GetTypeInfo().DeclaredNestedTypes)
-            {
-                if (nt.Name == nestedTypeName)
-                {
-                    ti = nt;
-                    break;
-                }
-            }
-            return ti == null ? null : ti.AsType();
-        }
-        public static TypeCode GetTypeCode(this Type type)
-        {
-            if (type == typeof(bool)) return TypeCode.Boolean;
-            else if (type == typeof(byte)) return TypeCode.Byte;
-            else if (type == typeof(char)) return TypeCode.Char;
-            else if (type == typeof(ushort)) return TypeCode.UInt16;
-            else if (type == typeof(uint)) return TypeCode.UInt32;
-            else if (type == typeof(ulong)) return TypeCode.UInt64;
-            else if (type == typeof(sbyte)) return TypeCode.SByte;
-            else if (type == typeof(short)) return TypeCode.Int16;
-            else if (type == typeof(int)) return TypeCode.Int32;
-            else if (type == typeof(long)) return TypeCode.Int64;
-            else if (type == typeof(string)) return TypeCode.String;
-            else if (type == typeof(float)) return TypeCode.Single;
-            else if (type == typeof(double)) return TypeCode.Double;
-            else if (type == typeof(DateTime)) return TypeCode.DateTime;
-            else if (type == (typeof(decimal))) return TypeCode.Decimal;
-            else return TypeCode.Object;
-        }
-
-        //
-        // FieldInfo extension methods
-        //
-        public static object? GetRawConstantValue(this FieldInfo fi)
-        { return fi.GetValue(null); }
-
-        //
-        // Assembly extension methods
-        //
-        public static bool ReflectionOnly(this Assembly assm)
-        {
-            // In PCL we can't load in reflection-only context
-            return false;
-        }
-
-#endif
-    }
-}
-
-#if ES_BUILD_STANDALONE
-internal static partial class Interop
-{
-    [SuppressUnmanagedCodeSecurityAttribute]
-    internal static partial class Kernel32
-    {
-        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
-        internal static extern int GetCurrentThreadId();
-
-        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
-        internal static extern uint GetCurrentProcessId();
-    }
-
-    internal static uint GetCurrentProcessId() => Kernel32.GetCurrentProcessId();
-}
-#endif
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/DataCollector.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/DataCollector.cs
index da5a4e1807bfef..19bf2e01fdc03f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/DataCollector.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/DataCollector.cs
@@ -1,11 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#if ES_BUILD_STANDALONE
 using System;
 using System.Diagnostics;
-using Environment = Microsoft.Diagnostics.Tracing.Internal.Environment;
-#endif
 using System.Runtime.InteropServices;
 
 #if ES_BUILD_STANDALONE
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/FieldMetadata.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/FieldMetadata.cs
index 47fc5b3fb32a39..cd5db860c31a90 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/FieldMetadata.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/FieldMetadata.cs
@@ -1,14 +1,11 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#if ES_BUILD_STANDALONE
 using System;
 using System.Diagnostics;
-#endif
 using System.Text;
 
 #if ES_BUILD_STANDALONE
-using Environment = Microsoft.Diagnostics.Tracing.Internal.Environment;
 namespace Microsoft.Diagnostics.Tracing
 #else
 namespace System.Diagnostics.Tracing
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/PropertyValue.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/PropertyValue.cs
index 35e9c2da510223..31ce1d6d85a97b 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/PropertyValue.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/PropertyValue.cs
@@ -217,7 +217,7 @@ public override Func<PropertyValue, PropertyValue> GetPropertyGetter(PropertyInf
             {
                 Type type = property.PropertyType;
 
-                if (!Statics.IsValueType(type))
+                if (!type.IsValueType)
                 {
                     var getter = (Func<TContainer, object?>)GetGetMethod(property, type);
                     return container => new PropertyValue(getter((TContainer)container.ReferenceValue!));
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/Statics.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/Statics.cs
index dd3920ba73d09f..b7ad6be87d6bfa 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/Statics.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/Statics.cs
@@ -1,15 +1,11 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#if ES_BUILD_STANDALONE
 using System;
-using Environment = Microsoft.Diagnostics.Tracing.Internal.Environment;
-#endif
 using System.Collections.Generic;
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Text;
-using Microsoft.Reflection;
 
 #if ES_BUILD_STANDALONE
 namespace Microsoft.Diagnostics.Tracing
@@ -321,87 +317,22 @@ public static TraceLoggingDataType FormatPtr(
 
         #region Reflection helpers
 
-        /*
-        All TraceLogging use of reflection APIs should go through wrappers here.
-        This helps with portability, and it also makes it easier to audit what
-        kinds of reflection operations are being done.
-        */
-
-        public static object? CreateInstance(Type type, params object?[]? parameters)
-        {
-            return Activator.CreateInstance(type, parameters);
-        }
-
-        public static bool IsValueType(Type type)
-        {
-            bool result = type.IsValueType();
-            return result;
-        }
-
-        public static bool IsEnum(Type type)
-        {
-            bool result = type.IsEnum();
-            return result;
-        }
-
-        public static IEnumerable<PropertyInfo> GetProperties(Type type)
-        {
-            IEnumerable<PropertyInfo> result = type.GetProperties();
-            return result;
-        }
-
-        public static MethodInfo? GetGetMethod(PropertyInfo propInfo)
-        {
-            MethodInfo? result = propInfo.GetGetMethod();
-            return result;
-        }
-
-        public static MethodInfo? GetDeclaredStaticMethod(Type declaringType, string name)
-        {
-            MethodInfo? result;
-#if (ES_BUILD_PCL)
-            result = declaringType.GetTypeInfo().GetDeclaredMethod(name);
-#else
-            result = declaringType.GetMethod(
-                name,
-                BindingFlags.DeclaredOnly | BindingFlags.Static | BindingFlags.NonPublic);
-#endif
-            return result;
-        }
-
         public static bool HasCustomAttribute(
             PropertyInfo propInfo,
             Type attributeType)
         {
-            bool result;
-#if (ES_BUILD_PCL)
-            result = propInfo.IsDefined(attributeType);
-#else
-            object[] attributes = propInfo.GetCustomAttributes(
-                attributeType,
-                false);
-            result = attributes.Length != 0;
-#endif
-            return result;
+            return propInfo.IsDefined(attributeType, false);
         }
 
         public static AttributeType? GetCustomAttribute<AttributeType>(PropertyInfo propInfo)
             where AttributeType : Attribute
         {
             AttributeType? result = null;
-#if (ES_BUILD_PCL)
-            foreach (var attrib in propInfo.GetCustomAttributes<AttributeType>(false))
-            {
-                result = attrib;
-                break;
-            }
-#else
             object[] attributes = propInfo.GetCustomAttributes(typeof(AttributeType), false);
             if (attributes.Length != 0)
             {
                 result = (AttributeType)attributes[0];
             }
-#endif
             return result;
         }
 
@@ -409,52 +340,28 @@ public static bool HasCustomAttribute(
             where AttributeType : Attribute
         {
             AttributeType? result = null;
-#if (ES_BUILD_PCL)
-            foreach (var attrib in type.GetTypeInfo().GetCustomAttributes<AttributeType>(false))
-            {
-                result = attrib;
-                break;
-            }
-#else
             object[] attributes = type.GetCustomAttributes(typeof(AttributeType), false);
             if (attributes.Length != 0)
             {
                 result = (AttributeType)attributes[0];
             }
-#endif
             return result;
         }
 
-        public static Type[] GetGenericArguments(Type type)
-        {
-            return type.GetGenericArguments();
-        }
-
         public static Type? FindEnumerableElementType(Type type)
         {
             Type? elementType = null;
 
             if (IsGenericMatch(type, typeof(IEnumerable<>)))
             {
-                elementType = GetGenericArguments(type)[0];
+                elementType = type.GetGenericArguments()[0];
             }
             else
             {
-#if (ES_BUILD_PCL)
-                IEnumerable<Type> ifaceTypes = type.GetTypeInfo().ImplementedInterfaces;
-#else
                 Type[] ifaceTypes = type.FindInterfaces(IsGenericMatch, typeof(IEnumerable<>));
-#endif
 
                 foreach (Type ifaceType in ifaceTypes)
                 {
-#if (ES_BUILD_PCL)
-                    if (!IsGenericMatch(ifaceType, typeof(IEnumerable<>)))
-                    {
-                        continue;
-                    }
-#endif
-
                     if (elementType != null)
                     {
                         // ambiguous match. report no match at all.
@@ -462,7 +369,7 @@ public static Type[] GetGenericArguments(Type type)
                         break;
                     }
 
-                    elementType = GetGenericArguments(ifaceType)[0];
+                    elementType = ifaceType.GetGenericArguments()[0];
                 }
             }
 
@@ -471,21 +378,7 @@ public static Type[] GetGenericArguments(Type type)
 
         public static bool IsGenericMatch(Type type, object? openType)
         {
-            return type.IsGenericType() && type.GetGenericTypeDefinition() == (Type?)openType;
-        }
-
-        public static Delegate CreateDelegate(Type delegateType, MethodInfo methodInfo)
-        {
-            Delegate result;
-#if (ES_BUILD_PCL)
-            result = methodInfo.CreateDelegate(
-                delegateType);
-#else
-            result = Delegate.CreateDelegate(
-                delegateType,
-                methodInfo);
-#endif
-            return result;
+            return type.IsGenericType && type.GetGenericTypeDefinition() == (Type?)openType;
         }
 
         public static TraceLoggingTypeInfo CreateDefaultTypeInfo(
@@ -579,7 +472,7 @@ public static TraceLoggingTypeInfo CreateDefaultTypeInfo(
             }
             else
             {
-                if (Statics.IsEnum(dataType))
+                if (dataType.IsEnum)
                     dataType = Enum.GetUnderlyingType(dataType);
 
                 if (dataType == typeof(string))
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TraceLoggingEventSource.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TraceLoggingEventSource.cs
index cabafa707239ef..c6127beeb4cd08 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TraceLoggingEventSource.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TraceLoggingEventSource.cs
@@ -13,14 +13,10 @@
 // #define FEATURE_ADVANCED_MANAGED_ETW_CHANNELS
 #endif
 
-#if ES_BUILD_STANDALONE
 using System;
-using System.Diagnostics;
-using Environment = Microsoft.Diagnostics.Tracing.Internal.Environment;
-using EventDescriptor = Microsoft.Diagnostics.Tracing.EventDescriptor;
-#endif
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Diagnostics;
 using System.Runtime.InteropServices;
 using System.Text;
 
@@ -440,7 +436,7 @@ private unsafe void WriteMultiMergeInner(
                 descriptors[1].SetMetadata(pMetadata1, nameInfo.nameMetadata.Length, 1);
                 descriptors[2].SetMetadata(pMetadata2, eventTypes.typeMetadata.Length, 1);
 
-#if (!ES_BUILD_PCL && !NETCOREAPP)
+#if ES_BUILD_STANDALONE
                 System.Runtime.CompilerServices.RuntimeHelpers.PrepareConstrainedRegions();
 #endif
                 try
@@ -624,7 +620,7 @@ private unsafe void WriteImpl(
                         descriptors[2].SetMetadata(pMetadata2, eventTypes.typeMetadata.Length, 1);
 #endif // FEATURE_MANAGED_ETW
 
-#if (!ES_BUILD_PCL && !NETCOREAPP)
+#if ES_BUILD_STANDALONE
                         System.Runtime.CompilerServices.RuntimeHelpers.PrepareConstrainedRegions();
 #endif
                         EventOpcode opcode = (EventOpcode)descriptor.Opcode;
@@ -731,7 +727,7 @@ private unsafe void WriteToAllListeners(string? eventName, ref EventDescriptor e
             DispatchToAllListeners(-1, eventCallbackArgs);
         }
 
-#if (!ES_BUILD_PCL && !NETCOREAPP)
+#if ES_BUILD_STANDALONE
         [System.Runtime.ConstrainedExecution.ReliabilityContract(
             System.Runtime.ConstrainedExecution.Consistency.WillNotCorruptState,
             System.Runtime.ConstrainedExecution.Cer.Success)]
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TraceLoggingMetadataCollector.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TraceLoggingMetadataCollector.cs
index d50140fef4ccda..e0f2943cbce757 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TraceLoggingMetadataCollector.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TraceLoggingMetadataCollector.cs
@@ -1,10 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#if ES_BUILD_STANDALONE
 using System;
-using Environment = Microsoft.Diagnostics.Tracing.Internal.Environment;
-#endif
 using System.Collections.Generic;
 
 #if ES_BUILD_STANDALONE
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TypeAnalysis.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TypeAnalysis.cs
index df3a61ff2fbf37..0324f31563bba9 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TypeAnalysis.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/TypeAnalysis.cs
@@ -30,10 +30,9 @@ public TypeAnalysis(
             EventDataAttribute? eventAttrib,
             List<Type> recursionCheck)
         {
-            IEnumerable<PropertyInfo> propertyInfos = Statics.GetProperties(dataType);
             var propertyList = new List<PropertyAnalysis>();
 
-            foreach (PropertyInfo propertyInfo in propertyInfos)
+            foreach (PropertyInfo propertyInfo in dataType.GetProperties())
             {
                 if (Statics.HasCustomAttribute(propertyInfo, typeof(EventIgnoreAttribute)))
                 {
@@ -46,7 +45,7 @@ public TypeAnalysis(
                     continue;
                 }
 
-                MethodInfo? getterInfo = Statics.GetGetMethod(propertyInfo);
+                MethodInfo? getterInfo = propertyInfo.GetGetMethod();
                 if (getterInfo == null)
                 {
                     continue;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Environment.Browser.cs b/src/libraries/System.Private.CoreLib/src/System/Environment.Browser.cs
index 9ef90da4762d60..07ad3b8b31c75b 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Environment.Browser.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Environment.Browser.cs
@@ -1,12 +1,14 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.IO;
+
 namespace System
 {
     public static partial class Environment
     {
         // Emscripten VFS mounts at / and is the only drive
-        public static string[] GetLogicalDrives() => new string[] { "/" };
+        public static string[] GetLogicalDrives() => DriveInfoInternal.GetLogicalDrives();
 
         // In the mono runtime, this maps to gethostname, which returns 'emscripten'.
         // Returning the value here allows us to exclude more of the runtime.
@@ -22,5 +24,7 @@ private static OperatingSystem GetOSVersion()
         {
             return new OperatingSystem(PlatformID.Other, new Version(1, 0, 0, 0));
         }
+
+        private static int GetCurrentProcessId() => 42;
     }
-}
\ No newline at end of file
+}
diff --git a/src/libraries/System.Private.CoreLib/src/System/Environment.GetFolderPathCore.Unix.cs b/src/libraries/System.Private.CoreLib/src/System/Environment.GetFolderPathCore.Unix.cs
index 255717538ffada..10374813d6660d 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Environment.GetFolderPathCore.Unix.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Environment.GetFolderPathCore.Unix.cs
@@ -41,7 +41,7 @@ private static string GetFolderPathCore(SpecialFolder folder, SpecialFolderOptio
             {
                 Debug.Assert(option == SpecialFolderOption.Create);
 
-                Func<string, object> createDirectory = LazyInitializer.EnsureInitialized(ref s_directoryCreateDirectory, () =>
+                Func<string, object> createDirectory = LazyInitializer.EnsureInitialized(ref s_directoryCreateDirectory, static () =>
                 {
                     Type dirType = Type.GetType("System.IO.Directory, System.IO.FileSystem, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", throwOnError: true)!;
                     MethodInfo mi = dirType.GetTypeInfo().GetDeclaredMethod("CreateDirectory")!;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Environment.Unix.cs b/src/libraries/System.Private.CoreLib/src/System/Environment.Unix.cs
index 87306e7b741afa..9b5ff6ac417cd9 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Environment.Unix.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Environment.Unix.cs
@@ -110,5 +110,7 @@ private static unsafe bool TryGetUserNameFromPasswd(byte* buf, int bufLen, out s
             // Otherwise, fail.
             throw new IOException(errorInfo.GetErrorMessage(), errorInfo.RawErrno);
         }
+
+        private static int GetCurrentProcessId() => Interop.Sys.GetPid();
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Environment.UnixOrBrowser.cs b/src/libraries/System.Private.CoreLib/src/System/Environment.UnixOrBrowser.cs
index cddf1b929e63f2..588e1dbf57d180 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Environment.UnixOrBrowser.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Environment.UnixOrBrowser.cs
@@ -48,8 +48,6 @@ private static string ExpandEnvironmentVariablesCore(string name)
 
         private static bool Is64BitOperatingSystemWhen32BitProcess => false;
 
-        private static int GetCurrentProcessId() => Interop.Sys.GetPid();
-
         internal const string NewLineConst = "\n";
 
         public static string SystemDirectory => GetFolderPathCore(SpecialFolder.System, SpecialFolderOption.None);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Icu.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Icu.cs
index e5425f8d0a31b3..af5db2379c4dbc 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Icu.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Icu.cs
@@ -3,6 +3,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 using System.Text;
 using Internal.Runtime.CompilerServices;
 
@@ -121,7 +122,7 @@ private static unsafe bool GetCalendarInfo(string localeName, CalendarId calenda
             Debug.Assert(!GlobalizationMode.Invariant);
 
             return Interop.CallStringMethod(
-                (buffer, locale, id, type) =>
+                static (buffer, locale, id, type) =>
                 {
                     fixed (char* bufferPtr = buffer)
                     {
@@ -422,24 +423,12 @@ internal static bool EnumCalendarInfo(string localeName, CalendarId calendarId,
             return result;
         }
 
-#if !TARGET_BROWSER
         private static unsafe bool EnumCalendarInfo(string localeName, CalendarId calendarId, CalendarDataType dataType, ref IcuEnumCalendarsData callbackContext)
         {
-            return Interop.Globalization.EnumCalendarInfo(EnumCalendarInfoCallback, localeName, calendarId, dataType, (IntPtr)Unsafe.AsPointer(ref callbackContext));
-        }
-#else
-        private static unsafe bool EnumCalendarInfo(string localeName, CalendarId calendarId, CalendarDataType dataType, ref IcuEnumCalendarsData callbackContext)
-        {
-            // Temp workaround for pinvoke callbacks for Mono-Wasm-Interpreter
-            // https://github.com/dotnet/runtime/issues/39100
-            var calendarInfoCallback = new Interop.Globalization.EnumCalendarInfoCallback(EnumCalendarInfoCallback);
-            return Interop.Globalization.EnumCalendarInfo(
-                System.Runtime.InteropServices.Marshal.GetFunctionPointerForDelegate(calendarInfoCallback),
-                localeName, calendarId, dataType, (IntPtr)Unsafe.AsPointer(ref callbackContext));
+            return Interop.Globalization.EnumCalendarInfo(&EnumCalendarInfoCallback, localeName, calendarId, dataType, (IntPtr)Unsafe.AsPointer(ref callbackContext));
         }
 
-        [Mono.MonoPInvokeCallback(typeof(Interop.Globalization.EnumCalendarInfoCallback))]
-#endif
+        [UnmanagedCallersOnly]
         private static unsafe void EnumCalendarInfoCallback(char* calendarStringPtr, IntPtr context)
         {
             try
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Nls.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Nls.cs
index b95aca903dcafc..ea0bcbb8026955 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Nls.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Nls.cs
@@ -3,6 +3,7 @@
 
 using System.Diagnostics;
 using System.Collections.Generic;
+using System.Runtime.InteropServices;
 using Internal.Runtime.CompilerServices;
 
 namespace System.Globalization
@@ -69,7 +70,7 @@ private struct EnumData
         }
 
         // EnumCalendarInfoExEx callback itself.
-        // [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvStdcall) })]
+        [UnmanagedCallersOnly]
         private static unsafe Interop.BOOL EnumCalendarInfoCallback(char* lpCalendarInfoString, uint calendar, IntPtr pReserved, void* lParam)
         {
             ref EnumData context = ref Unsafe.As<byte, EnumData>(ref *(byte*)lParam);
@@ -101,7 +102,7 @@ public struct NlsEnumCalendarsData
             public List<int> calendars;      // list of calendars found so far
         }
 
-        // [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvStdcall) })]
+        [UnmanagedCallersOnly]
         private static unsafe Interop.BOOL EnumCalendarsCallback(char* lpCalendarInfoString, uint calendar, IntPtr reserved, void* lParam)
         {
             ref NlsEnumCalendarsData context = ref Unsafe.As<byte, NlsEnumCalendarsData>(ref *(byte*)lParam);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Windows.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Windows.cs
index 0147bed7e2d46d..8f89619276ffa5 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Windows.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CalendarData.Windows.cs
@@ -266,7 +266,7 @@ private static unsafe bool CallEnumCalendarInfo(string localeName, CalendarId ca
             }
 
             // Now call the enumeration API. Work is done by our callback function
-            Interop.Kernel32.EnumCalendarInfoExEx(EnumCalendarInfoCallback, localeName, (uint)calendar, null, calType, Unsafe.AsPointer(ref context));
+            Interop.Kernel32.EnumCalendarInfoExEx(&EnumCalendarInfoCallback, localeName, (uint)calendar, null, calType, Unsafe.AsPointer(ref context));
 
             // Now we have a list of data, fail if we didn't find anything.
             Debug.Assert(context.strings != null);
@@ -418,7 +418,7 @@ private static int NlsGetCalendars(string localeName, bool useUserOverride, Cale
 
             unsafe
             {
-                Interop.Kernel32.EnumCalendarInfoExEx(EnumCalendarsCallback, localeName, ENUM_ALL_CALENDARS, null, CAL_ICALINTVALUE, Unsafe.AsPointer(ref data));
+                Interop.Kernel32.EnumCalendarInfoExEx(&EnumCalendarsCallback, localeName, ENUM_ALL_CALENDARS, null, CAL_ICALINTVALUE, Unsafe.AsPointer(ref data));
             }
 
             // Copy to the output array
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Nls.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Nls.cs
index 41734e6f0d50f6..9738d5a289464d 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Nls.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Nls.cs
@@ -117,7 +117,7 @@ private int NlsGetFirstDayOfWeek()
 
             unsafe
             {
-                Interop.Kernel32.EnumSystemLocalesEx(EnumSystemLocalesProc, Interop.Kernel32.LOCALE_SPECIFICDATA | Interop.Kernel32.LOCALE_SUPPLEMENTAL, Unsafe.AsPointer(ref context), IntPtr.Zero);
+                Interop.Kernel32.EnumSystemLocalesEx(&EnumSystemLocalesProc, Interop.Kernel32.LOCALE_SPECIFICDATA | Interop.Kernel32.LOCALE_SUPPLEMENTAL, Unsafe.AsPointer(ref context), IntPtr.Zero);
             }
 
             if (context.cultureName != null)
@@ -338,7 +338,7 @@ private struct EnumLocaleData
         }
 
         // EnumSystemLocaleEx callback.
-        // [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvStdcall) })]
+        [UnmanagedCallersOnly]
         private static unsafe Interop.BOOL EnumSystemLocalesProc(char* lpLocaleString, uint flags, void* contextHandle)
         {
             ref EnumLocaleData context = ref Unsafe.As<byte, EnumLocaleData>(ref *(byte*)contextHandle);
@@ -361,7 +361,7 @@ private static unsafe Interop.BOOL EnumSystemLocalesProc(char* lpLocaleString, u
         }
 
         // EnumSystemLocaleEx callback.
-        // [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvStdcall) })]
+        [UnmanagedCallersOnly]
         private static unsafe Interop.BOOL EnumAllSystemLocalesProc(char* lpLocaleString, uint flags, void* contextHandle)
         {
             ref EnumData context = ref Unsafe.As<byte, EnumData>(ref *(byte*)contextHandle);
@@ -383,7 +383,7 @@ private struct EnumData
         }
 
         // EnumTimeFormatsEx callback itself.
-        // [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvStdcall) })]
+        [UnmanagedCallersOnly]
         private static unsafe Interop.BOOL EnumTimeCallback(char* lpTimeFormatString, void* lParam)
         {
             ref EnumData context = ref Unsafe.As<byte, EnumData>(ref *(byte*)lParam);
@@ -404,7 +404,7 @@ private static unsafe Interop.BOOL EnumTimeCallback(char* lpTimeFormatString, vo
             data.strings = new List<string>();
 
             // Now call the enumeration API. Work is done by our callback function
-            Interop.Kernel32.EnumTimeFormatsEx(EnumTimeCallback, localeName, dwFlags, Unsafe.AsPointer(ref data));
+            Interop.Kernel32.EnumTimeFormatsEx(&EnumTimeCallback, localeName, dwFlags, Unsafe.AsPointer(ref data));
 
             if (data.strings.Count > 0)
             {
@@ -490,7 +490,7 @@ private static CultureInfo[] NlsEnumCultures(CultureTypes types)
 
             unsafe
             {
-                Interop.Kernel32.EnumSystemLocalesEx(EnumAllSystemLocalesProc, flags, Unsafe.AsPointer(ref context), IntPtr.Zero);
+                Interop.Kernel32.EnumSystemLocalesEx(&EnumAllSystemLocalesProc, flags, Unsafe.AsPointer(ref context), IntPtr.Zero);
             }
 
             CultureInfo[] cultures = new CultureInfo[context.strings.Count];
@@ -518,7 +518,7 @@ internal bool NlsIsReplacementCulture
 
                 unsafe
                 {
-                    Interop.Kernel32.EnumSystemLocalesEx(EnumAllSystemLocalesProc, Interop.Kernel32.LOCALE_REPLACEMENT, Unsafe.AsPointer(ref context), IntPtr.Zero);
+                    Interop.Kernel32.EnumSystemLocalesEx(&EnumAllSystemLocalesProc, Interop.Kernel32.LOCALE_REPLACEMENT, Unsafe.AsPointer(ref context), IntPtr.Zero);
                 }
 
                 for (int i = 0; i < context.strings.Count; i++)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
index 6c0dbe16879782..939c16e4d8d9a6 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
@@ -152,7 +152,7 @@ internal partial class CultureData
         /// </remarks>
         private static Dictionary<string, string> RegionNames =>
             s_regionNames ??=
-            new Dictionary<string, string>(257 /* prime */)
+            new Dictionary<string, string>(257 /* prime */, StringComparer.OrdinalIgnoreCase)
             {
                 { "001", "en-001" },
                 { "029", "en-029" },
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/GregorianCalendar.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/GregorianCalendar.cs
index 1aa2b0247a56c8..4f7bf1c3184dab 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/GregorianCalendar.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/GregorianCalendar.cs
@@ -35,7 +35,7 @@ public class GregorianCalendar : Calendar
         public override CalendarAlgorithmType AlgorithmType => CalendarAlgorithmType.SolarCalendar;
 
         /// <summary>
-        /// Internal method to provide a default intance of GregorianCalendar.
+        /// Internal method to provide a default instance of GregorianCalendar.
         /// Used by NLS+ implementation
         /// </summary>
         internal static Calendar GetDefaultInstance() => s_defaultInstance ??= new GregorianCalendar();
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/JapaneseCalendar.Icu.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/JapaneseCalendar.Icu.cs
index cfc47d72da678d..5ac43a99e56c0c 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/JapaneseCalendar.Icu.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/JapaneseCalendar.Icu.cs
@@ -8,6 +8,8 @@ namespace System.Globalization
 {
     public partial class JapaneseCalendar : Calendar
     {
+        private static readonly string [] s_abbreviatedEnglishEraNames = { "M", "T", "S", "H", "R" };
+
         private static EraInfo[]? IcuGetJapaneseEras()
         {
             if (GlobalizationMode.Invariant)
@@ -23,16 +25,11 @@ public partial class JapaneseCalendar : Calendar
                 return null;
             }
 
-            string[]? abbrevEnglishEraNames;
-            if (!CalendarData.EnumCalendarInfo("en", CalendarId.JAPAN, CalendarDataType.AbbrevEraNames, out abbrevEnglishEraNames))
-            {
-                return null;
-            }
-
             List<EraInfo> eras = new List<EraInfo>();
             int lastMaxYear = GregorianCalendar.MaxYear;
 
             int latestEra = Interop.Globalization.GetLatestJapaneseEra();
+
             for (int i = latestEra; i >= 0; i--)
             {
                 DateTime dt;
@@ -47,16 +44,40 @@ public partial class JapaneseCalendar : Calendar
                     break;
                 }
 
-                eras.Add(new EraInfo(i, dt.Year, dt.Month, dt.Day, dt.Year - 1, 1, lastMaxYear - dt.Year + 1,
-                    eraNames![i], GetAbbreviatedEraName(eraNames, i), abbrevEnglishEraNames![i]));
+                eras.Add(new EraInfo(i, dt.Year, dt.Month, dt.Day, dt.Year - 1, 1, lastMaxYear - dt.Year + 1, eraNames![i], GetAbbreviatedEraName(eraNames, i), ""));
 
                 lastMaxYear = dt.Year;
             }
 
+            string[] abbrevEnglishEraNames;
+            if (!CalendarData.EnumCalendarInfo("ja", CalendarId.JAPAN, CalendarDataType.AbbrevEraNames, out abbrevEnglishEraNames!))
+            {
+                // Failed to get English names. fallback to hardcoded data.
+                abbrevEnglishEraNames = s_abbreviatedEnglishEraNames;
+            }
+
+            // Check if we are getting the English Name at the end of the returned list.
+            // ICU usually return long list including all Era names written in Japanese characters except the recent eras which actually we support will be returned in English.
+            // We have the following check as older ICU versions doesn't carry the English names (e.g. ICU version 50).
+            if (abbrevEnglishEraNames[abbrevEnglishEraNames.Length - 1].Length == 0 || abbrevEnglishEraNames[abbrevEnglishEraNames.Length - 1][0] > '\u007F')
+            {
+                // Couldn't get English names.
+                abbrevEnglishEraNames = s_abbreviatedEnglishEraNames;
+            }
+
+            int startIndex = abbrevEnglishEraNames == s_abbreviatedEnglishEraNames ? eras.Count - 1 : abbrevEnglishEraNames.Length - 1;
+
+            Debug.Assert(abbrevEnglishEraNames == s_abbreviatedEnglishEraNames || eras.Count <= abbrevEnglishEraNames.Length);
+
             // remap the Era numbers, now that we know how many there will be
             for (int i = 0; i < eras.Count; i++)
             {
                 eras[i].era = eras.Count - i;
+                if (startIndex < abbrevEnglishEraNames.Length)
+                {
+                    eras[i].englishEraName = abbrevEnglishEraNames[startIndex];
+                }
+                startIndex--;
             }
 
             return eras.ToArray();
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/JapaneseCalendar.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/JapaneseCalendar.cs
index b147247faf3278..ba6b3087cd82b1 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/JapaneseCalendar.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/JapaneseCalendar.cs
@@ -5,17 +5,17 @@ namespace System.Globalization
 {
     /// <summary>
     /// JapaneseCalendar is based on Gregorian calendar.  The month and day values are the same as
-    /// Gregorian calendar.  However, the year value is an offset to the Gregorian
+    /// Gregorian calendar. However, the year value is an offset to the Gregorian
     /// year based on the era.
     ///
     /// This system is adopted by Emperor Meiji in 1868. The year value is counted based on the reign of an emperor,
     /// and the era begins on the day an emperor ascends the throne and continues until his death.
     /// The era changes at 12:00AM.
     ///
-    /// For example, the current era is Reiwa.  It started on 2019/5/1 A.D.  Therefore, Gregorian year 2019 is also Reiwa 1st.
+    /// For example, the current era is Reiwa. It started on 2019/5/1 A.D.  Therefore, Gregorian year 2019 is also Reiwa 1st.
     /// 2019/5/1 A.D. is also Reiwa 1st 5/1.
     ///
-    /// Any date in the year during which era is changed can be reckoned in either era.  For example,
+    /// Any date in the year during which era is changed can be reckoned in either era. For example,
     /// 2019/1/1 can be 1/1 Reiwa 1st year or 1/1 Heisei 31st year.
     ///
     /// Note:
@@ -50,7 +50,7 @@ public partial class JapaneseCalendar : Calendar
         //
         // We know about 4 built-in eras, however users may add additional era(s) from the
         // registry, by adding values to HKLM\SYSTEM\CurrentControlSet\Control\Nls\Calendars\Japanese\Eras
-        // we don't read the registry and instead we call WinRT to get the needed informatio
+        // we don't read the registry and instead we call WinRT to get the needed information
         //
         // Registry values look like:
         //      yyyy.mm.dd=era_abbrev_english_englishabbrev
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/TextInfo.Nls.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/TextInfo.Nls.cs
index 656385a41a7d5d..ca6689f4cef534 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/TextInfo.Nls.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/TextInfo.Nls.cs
@@ -18,6 +18,8 @@ private unsafe void NlsChangeCase(char* pSource, int pSourceLen, char* pResult,
             Debug.Assert(pSourceLen <= pResultLen);
 
             // Check for Invariant to avoid A/V in LCMapStringEx
+            // We don't specify LCMAP_LINGUISTIC_CASING for Invariant because it will enable Turkish-I behavior too which is not
+            // right for Invariant.
             uint linguisticCasing = IsInvariantLocale(_textInfoName) ? 0 : LCMAP_LINGUISTIC_CASING;
 
             int ret = Interop.Kernel32.LCMapStringEx(_sortHandle != IntPtr.Zero ? null : _textInfoName,
diff --git a/src/libraries/System.Private.CoreLib/src/System/Half.cs b/src/libraries/System.Private.CoreLib/src/System/Half.cs
index d124d7a8992df8..34adab5856cb67 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Half.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Half.cs
@@ -116,7 +116,7 @@ private ushort Significand
                 // says they should be equal, even if the signs differ.
                 return leftIsNegative && !AreZero(left, right);
             }
-            return (short)(left._value) < (short)(right._value);
+            return (left._value < right._value) ^ leftIsNegative;
         }
 
         public static bool operator >(Half left, Half right)
@@ -141,7 +141,7 @@ private ushort Significand
                 // says they should be equal, even if the signs differ.
                 return leftIsNegative || AreZero(left, right);
             }
-            return (short)(left._value) <= (short)(right._value);
+            return (left._value <= right._value) ^ leftIsNegative;
         }
 
         public static bool operator >=(Half left, Half right)
diff --git a/src/libraries/System.Private.CoreLib/src/System/IComparable.cs b/src/libraries/System.Private.CoreLib/src/System/IComparable.cs
index 3c0f50b23fa935..3599bbdf9ded64 100644
--- a/src/libraries/System.Private.CoreLib/src/System/IComparable.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/IComparable.cs
@@ -33,6 +33,6 @@ public interface IComparable<in T>
         // if this is equal to object, or a value greater than zero
         // if this is greater than object.
         //
-        int CompareTo([AllowNull] T other);
+        int CompareTo(T? other);
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/IEquatable.cs b/src/libraries/System.Private.CoreLib/src/System/IEquatable.cs
index 1edba4472c91de..89f0771802a1b9 100644
--- a/src/libraries/System.Private.CoreLib/src/System/IEquatable.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/IEquatable.cs
@@ -7,6 +7,6 @@ namespace System
 {
     public interface IEquatable<T> // invariant due to questionable semantics around equality and inheritance
     {
-        bool Equals([AllowNull] T other);
+        bool Equals(T? other);
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/IO/DriveInfoInternal.Browser.cs b/src/libraries/System.Private.CoreLib/src/System/IO/DriveInfoInternal.Browser.cs
new file mode 100644
index 00000000000000..858a56228216cd
--- /dev/null
+++ b/src/libraries/System.Private.CoreLib/src/System/IO/DriveInfoInternal.Browser.cs
@@ -0,0 +1,11 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.IO
+{
+    /// <summary>Contains internal volume helpers that are shared between many projects.</summary>
+    internal static partial class DriveInfoInternal
+    {
+        internal static string[] GetLogicalDrives() => new string[] { "/" };
+    }
+}
diff --git a/src/libraries/System.Private.CoreLib/src/System/IO/FileStream.Unix.cs b/src/libraries/System.Private.CoreLib/src/System/IO/FileStream.Unix.cs
index 1adc48377db072..8d823b5362fb8f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/IO/FileStream.Unix.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/IO/FileStream.Unix.cs
@@ -290,7 +290,7 @@ public override ValueTask DisposeAsync()
             // override may already exist on a derived type.
             if (_useAsyncIO && _writePos > 0)
             {
-                return new ValueTask(Task.Factory.StartNew(s => ((FileStream)s!).Dispose(), this,
+                return new ValueTask(Task.Factory.StartNew(static s => ((FileStream)s!).Dispose(), this,
                     CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default));
             }
 
@@ -364,7 +364,7 @@ private Task FlushAsyncInternal(CancellationToken cancellationToken)
             if (CanWrite)
             {
                 return Task.Factory.StartNew(
-                    state => ((FileStream)state!).FlushOSBuffer(),
+                    static state => ((FileStream)state!).FlushOSBuffer(),
                     this,
                     cancellationToken,
                     TaskCreationOptions.DenyChildAttach,
@@ -556,7 +556,7 @@ private unsafe int ReadNative(Span<byte> buffer)
             // Otherwise, issue the whole request asynchronously.
             synchronousResult = 0;
             _asyncState.Memory = destination;
-            return waitTask.ContinueWith((t, s) =>
+            return waitTask.ContinueWith(static (t, s) =>
             {
                 // The options available on Unix for writing asynchronously to an arbitrary file
                 // handle typically amount to just using another thread to do the synchronous write,
@@ -715,7 +715,7 @@ private ValueTask WriteAsyncInternal(ReadOnlyMemory<byte> source, CancellationTo
 
             // Otherwise, issue the whole request asynchronously.
             _asyncState.ReadOnlyMemory = source;
-            return new ValueTask(waitTask.ContinueWith((t, s) =>
+            return new ValueTask(waitTask.ContinueWith(static (t, s) =>
             {
                 // The options available on Unix for writing asynchronously to an arbitrary file
                 // handle typically amount to just using another thread to do the synchronous write,
diff --git a/src/libraries/System.Private.CoreLib/src/System/IO/FileStream.Windows.cs b/src/libraries/System.Private.CoreLib/src/System/IO/FileStream.Windows.cs
index b97fc5251fde22..3cfdf8de38f0b9 100644
--- a/src/libraries/System.Private.CoreLib/src/System/IO/FileStream.Windows.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/IO/FileStream.Windows.cs
@@ -1325,7 +1325,7 @@ private async Task AsyncModeCopyToAsync(Stream destination, int bufferSize, Canc
                 // in the read/write copy loop.
                 if (cancellationToken.CanBeCanceled)
                 {
-                    cancellationReg = cancellationToken.UnsafeRegister(s =>
+                    cancellationReg = cancellationToken.UnsafeRegister(static s =>
                     {
                         Debug.Assert(s is AsyncCopyToAwaitable);
                         var innerAwaitable = (AsyncCopyToAwaitable)s;
diff --git a/src/libraries/System.Private.CoreLib/src/System/IO/Path.cs b/src/libraries/System.Private.CoreLib/src/System/IO/Path.cs
index ce912c51cc47ad..5e3e2096d5869e 100644
--- a/src/libraries/System.Private.CoreLib/src/System/IO/Path.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/IO/Path.cs
@@ -655,7 +655,7 @@ private static unsafe string JoinInternal(ReadOnlySpan<char> first, ReadOnlySpan
 #endif
                     first.Length + second.Length + (hasSeparator ? 0 : 1),
                     (First: (IntPtr)f, FirstLength: first.Length, Second: (IntPtr)s, SecondLength: second.Length, HasSeparator: hasSeparator),
-                    (destination, state) =>
+                    static (destination, state) =>
                     {
                         new Span<char>((char*)state.First, state.FirstLength).CopyTo(destination);
                         if (!state.HasSeparator)
@@ -684,7 +684,7 @@ private static unsafe string JoinInternal(ReadOnlySpan<char> first, ReadOnlySpan
                     first.Length + second.Length + third.Length + (firstHasSeparator ? 0 : 1) + (thirdHasSeparator ? 0 : 1),
                     (First: (IntPtr)f, FirstLength: first.Length, Second: (IntPtr)s, SecondLength: second.Length,
                         Third: (IntPtr)t, ThirdLength: third.Length, FirstHasSeparator: firstHasSeparator, ThirdHasSeparator: thirdHasSeparator),
-                    (destination, state) =>
+                    static (destination, state) =>
                     {
                         new Span<char>((char*)state.First, state.FirstLength).CopyTo(destination);
                         if (!state.FirstHasSeparator)
@@ -719,7 +719,7 @@ private static unsafe string JoinInternal(ReadOnlySpan<char> first, ReadOnlySpan
                     (First: (IntPtr)f, FirstLength: first.Length, Second: (IntPtr)s, SecondLength: second.Length,
                         Third: (IntPtr)t, ThirdLength: third.Length, Fourth: (IntPtr)u, FourthLength: fourth.Length,
                         FirstHasSeparator: firstHasSeparator, ThirdHasSeparator: thirdHasSeparator, FourthHasSeparator: fourthHasSeparator),
-                    (destination, state) =>
+                    static (destination, state) =>
                     {
                         new Span<char>((char*)state.First, state.FirstLength).CopyTo(destination);
                         if (!state.FirstHasSeparator)
diff --git a/src/libraries/System.Private.CoreLib/src/System/IO/PersistedFiles.Browser.cs b/src/libraries/System.Private.CoreLib/src/System/IO/PersistedFiles.Browser.cs
new file mode 100644
index 00000000000000..06b606ac29d345
--- /dev/null
+++ b/src/libraries/System.Private.CoreLib/src/System/IO/PersistedFiles.Browser.cs
@@ -0,0 +1,10 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.IO
+{
+    internal static partial class PersistedFiles
+    {
+        internal static string? GetHomeDirectory() => Environment.GetEnvironmentVariable("HOME");
+    }
+}
diff --git a/src/libraries/System.Private.CoreLib/src/System/IO/Stream.cs b/src/libraries/System.Private.CoreLib/src/System/IO/Stream.cs
index dfde3d55c3e983..79388280125786 100644
--- a/src/libraries/System.Private.CoreLib/src/System/IO/Stream.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/IO/Stream.cs
@@ -235,7 +235,7 @@ public Task FlushAsync()
 
         public virtual Task FlushAsync(CancellationToken cancellationToken)
         {
-            return Task.Factory.StartNew(state => ((Stream)state!).Flush(), this,
+            return Task.Factory.StartNew(static state => ((Stream)state!).Flush(), this,
                 cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
@@ -488,7 +488,7 @@ private void RunReadWriteTaskWhenReady(Task asyncWaiter, ReadWriteTask readWrite
             }
             else  // Otherwise, wait for our turn, and then run the task.
             {
-                asyncWaiter.ContinueWith((t, state) =>
+                asyncWaiter.ContinueWith(static (t, state) =>
                 {
                     Debug.Assert(t.IsCompletedSuccessfully, "The semaphore wait should always complete successfully.");
                     var rwt = (ReadWriteTask)state!;
diff --git a/src/libraries/System.Private.CoreLib/src/System/IO/TextReader.cs b/src/libraries/System.Private.CoreLib/src/System/IO/TextReader.cs
index d64625bbff956f..8321c525d2a2ed 100644
--- a/src/libraries/System.Private.CoreLib/src/System/IO/TextReader.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/IO/TextReader.cs
@@ -204,7 +204,7 @@ public virtual int ReadBlock(Span<char> buffer)
 
         #region Task based Async APIs
         public virtual Task<string?> ReadLineAsync() =>
-            Task<string?>.Factory.StartNew(state => ((TextReader)state!).ReadLine(), this,
+            Task<string?>.Factory.StartNew(static state => ((TextReader)state!).ReadLine(), this,
                 CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
 
         public virtual async Task<string> ReadToEndAsync()
@@ -247,7 +247,7 @@ public virtual Task<int> ReadAsync(char[] buffer, int index, int count)
         public virtual ValueTask<int> ReadAsync(Memory<char> buffer, CancellationToken cancellationToken = default) =>
             new ValueTask<int>(MemoryMarshal.TryGetArray(buffer, out ArraySegment<char> array) ?
                 ReadAsync(array.Array!, array.Offset, array.Count) :
-                Task<int>.Factory.StartNew(state =>
+                Task<int>.Factory.StartNew(static state =>
                 {
                     var t = (Tuple<TextReader, Memory<char>>)state!;
                     return t.Item1.Read(t.Item2.Span);
@@ -256,7 +256,7 @@ public virtual ValueTask<int> ReadAsync(Memory<char> buffer, CancellationToken c
         internal virtual ValueTask<int> ReadAsyncInternal(Memory<char> buffer, CancellationToken cancellationToken)
         {
             var tuple = new Tuple<TextReader, Memory<char>>(this, buffer);
-            return new ValueTask<int>(Task<int>.Factory.StartNew(state =>
+            return new ValueTask<int>(Task<int>.Factory.StartNew(static state =>
             {
                 var t = (Tuple<TextReader, Memory<char>>)state!;
                 return t.Item1.Read(t.Item2.Span);
@@ -285,7 +285,7 @@ public virtual Task<int> ReadBlockAsync(char[] buffer, int index, int count)
         public virtual ValueTask<int> ReadBlockAsync(Memory<char> buffer, CancellationToken cancellationToken = default) =>
             new ValueTask<int>(MemoryMarshal.TryGetArray(buffer, out ArraySegment<char> array) ?
                 ReadBlockAsync(array.Array!, array.Offset, array.Count) :
-                Task<int>.Factory.StartNew(state =>
+                Task<int>.Factory.StartNew(static state =>
                 {
                     var t = (Tuple<TextReader, Memory<char>>)state!;
                     return t.Item1.ReadBlock(t.Item2.Span);
diff --git a/src/libraries/System.Private.CoreLib/src/System/IO/TextWriter.cs b/src/libraries/System.Private.CoreLib/src/System/IO/TextWriter.cs
index 15baed8be2f9cb..d969ee23a919c7 100644
--- a/src/libraries/System.Private.CoreLib/src/System/IO/TextWriter.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/IO/TextWriter.cs
@@ -541,7 +541,7 @@ public virtual void WriteLine(string format, params object?[] arg)
         public virtual Task WriteAsync(char value)
         {
             var tuple = new Tuple<TextWriter, char>(this, value);
-            return Task.Factory.StartNew(state =>
+            return Task.Factory.StartNew(static state =>
             {
                 var t = (Tuple<TextWriter, char>)state!;
                 t.Item1.Write(t.Item2);
@@ -552,7 +552,7 @@ public virtual Task WriteAsync(char value)
         public virtual Task WriteAsync(string? value)
         {
             var tuple = new Tuple<TextWriter, string?>(this, value);
-            return Task.Factory.StartNew(state =>
+            return Task.Factory.StartNew(static state =>
             {
                 var t = (Tuple<TextWriter, string?>)state!;
                 t.Item1.Write(t.Item2);
@@ -595,7 +595,7 @@ public Task WriteAsync(char[]? buffer)
         public virtual Task WriteAsync(char[] buffer, int index, int count)
         {
             var tuple = new Tuple<TextWriter, char[], int, int>(this, buffer, index, count);
-            return Task.Factory.StartNew(state =>
+            return Task.Factory.StartNew(static state =>
             {
                 var t = (Tuple<TextWriter, char[], int, int>)state!;
                 t.Item1.Write(t.Item2, t.Item3, t.Item4);
@@ -607,7 +607,7 @@ public virtual Task WriteAsync(ReadOnlyMemory<char> buffer, CancellationToken ca
             cancellationToken.IsCancellationRequested ? Task.FromCanceled(cancellationToken) :
             MemoryMarshal.TryGetArray(buffer, out ArraySegment<char> array) ?
                 WriteAsync(array.Array!, array.Offset, array.Count) :
-                Task.Factory.StartNew(state =>
+                Task.Factory.StartNew(static state =>
                 {
                     var t = (Tuple<TextWriter, ReadOnlyMemory<char>>)state!;
                     t.Item1.Write(t.Item2.Span);
@@ -616,7 +616,7 @@ public virtual Task WriteAsync(ReadOnlyMemory<char> buffer, CancellationToken ca
         public virtual Task WriteLineAsync(char value)
         {
             var tuple = new Tuple<TextWriter, char>(this, value);
-            return Task.Factory.StartNew(state =>
+            return Task.Factory.StartNew(static state =>
             {
                 var t = (Tuple<TextWriter, char>)state!;
                 t.Item1.WriteLine(t.Item2);
@@ -627,7 +627,7 @@ public virtual Task WriteLineAsync(char value)
         public virtual Task WriteLineAsync(string? value)
         {
             var tuple = new Tuple<TextWriter, string?>(this, value);
-            return Task.Factory.StartNew(state =>
+            return Task.Factory.StartNew(static state =>
             {
                 var t = (Tuple<TextWriter, string?>)state!;
                 t.Item1.WriteLine(t.Item2);
@@ -671,7 +671,7 @@ public Task WriteLineAsync(char[]? buffer)
         public virtual Task WriteLineAsync(char[] buffer, int index, int count)
         {
             var tuple = new Tuple<TextWriter, char[], int, int>(this, buffer, index, count);
-            return Task.Factory.StartNew(state =>
+            return Task.Factory.StartNew(static state =>
             {
                 var t = (Tuple<TextWriter, char[], int, int>)state!;
                 t.Item1.WriteLine(t.Item2, t.Item3, t.Item4);
@@ -683,7 +683,7 @@ public virtual Task WriteLineAsync(ReadOnlyMemory<char> buffer, CancellationToke
             cancellationToken.IsCancellationRequested ? Task.FromCanceled(cancellationToken) :
             MemoryMarshal.TryGetArray(buffer, out ArraySegment<char> array) ?
                 WriteLineAsync(array.Array!, array.Offset, array.Count) :
-                Task.Factory.StartNew(state =>
+                Task.Factory.StartNew(static state =>
                 {
                     var t = (Tuple<TextWriter, ReadOnlyMemory<char>>)state!;
                     t.Item1.WriteLine(t.Item2.Span);
@@ -696,7 +696,7 @@ public virtual Task WriteLineAsync()
 
         public virtual Task FlushAsync()
         {
-            return Task.Factory.StartNew(state => ((TextWriter)state!).Flush(), this,
+            return Task.Factory.StartNew(static state => ((TextWriter)state!).Flush(), this,
                 CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
         #endregion
diff --git a/src/libraries/System.Private.CoreLib/src/System/Lazy.cs b/src/libraries/System.Private.CoreLib/src/System/Lazy.cs
index 918682fa86ced8..ac676de6c4c561 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Lazy.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Lazy.cs
@@ -195,7 +195,7 @@ public class Lazy<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.Pub
         private Func<T>? _factory;
 
         // _value eventually stores the lazily created value. It is valid when _state = null.
-        private T _value = default!;
+        private T? _value;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="System.Lazy{T}"/> class that
@@ -447,14 +447,13 @@ private T CreateValue()
         }
 
         /// <summary>Gets the value of the Lazy&lt;T&gt; for debugging display purposes.</summary>
-        [MaybeNull]
-        internal T ValueForDebugDisplay
+        internal T? ValueForDebugDisplay
         {
             get
             {
                 if (!IsValueCreated)
                 {
-                    return default!;
+                    return default;
                 }
                 return _value;
             }
@@ -503,12 +502,12 @@ internal T ValueForDebugDisplay
         /// from initialization delegate.
         /// </remarks>
         [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-        public T Value => _state == null ? _value : CreateValue();
+        public T Value => _state == null ? _value! : CreateValue();
     }
 
     /// <summary>A debugger view of the Lazy&lt;T&gt; to surface additional debugging properties and
     /// to ensure that the Lazy&lt;T&gt; does not become initialized if it was not already.</summary>
-    internal sealed class LazyDebugView<T>
+    internal sealed class LazyDebugView<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>
     {
         // The Lazy object being viewed.
         private readonly Lazy<T> _lazy;
@@ -524,8 +523,7 @@ public LazyDebugView(Lazy<T> lazy)
         public bool IsValueCreated => _lazy.IsValueCreated;
 
         /// <summary>Returns the value of the Lazy object.</summary>
-        [MaybeNull]
-        public T Value => _lazy.ValueForDebugDisplay;
+        public T? Value => _lazy.ValueForDebugDisplay;
 
         /// <summary>Returns the execution mode of the Lazy object</summary>
         public LazyThreadSafetyMode? Mode => _lazy.Mode;
diff --git a/src/libraries/System.Private.CoreLib/src/System/OperatingSystem.cs b/src/libraries/System.Private.CoreLib/src/System/OperatingSystem.cs
index 718f67cc9096f5..6b3a5b5682f48b 100644
--- a/src/libraries/System.Private.CoreLib/src/System/OperatingSystem.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/OperatingSystem.cs
@@ -8,6 +8,10 @@ namespace System
 {
     public sealed class OperatingSystem : ISerializable, ICloneable
     {
+#if TARGET_UNIX && !TARGET_OSX
+        private static readonly string s_osPlatformName = Interop.Sys.GetUnixName();
+#endif
+
         private readonly Version _version;
         private readonly PlatformID _platform;
         private readonly string? _servicePack;
@@ -79,5 +83,193 @@ public string VersionString
                 return _versionString;
             }
         }
+
+        /// <summary>
+        /// Indicates whether the current application is running on the specified platform.
+        /// </summary>
+        /// <param name="platform">Case-insensitive platform name. Examples: Browser, Linux, FreeBSD, Android, iOS, macOS, tvOS, watchOS, Windows.</param>
+        public static bool IsOSPlatform(string platform)
+        {
+            if (platform == null)
+            {
+                throw new ArgumentNullException(nameof(platform));
+            }
+
+#if TARGET_BROWSER
+            return platform.Equals("BROWSER", StringComparison.OrdinalIgnoreCase);
+#elif TARGET_WINDOWS
+            return platform.Equals("WINDOWS", StringComparison.OrdinalIgnoreCase);
+#elif TARGET_OSX
+            return platform.Equals("OSX", StringComparison.OrdinalIgnoreCase) || platform.Equals("MACOS", StringComparison.OrdinalIgnoreCase);
+#elif TARGET_UNIX
+            return platform.Equals(s_osPlatformName, StringComparison.OrdinalIgnoreCase);
+#else
+#error Unknown OS
+#endif
+        }
+
+        /// <summary>
+        /// Check for the OS with a >= version comparison. Used to guard APIs that were added in the given OS release.
+        /// </summary>
+        /// <param name="platform">Case-insensitive platform name. Examples: Browser, Linux, FreeBSD, Android, iOS, macOS, tvOS, watchOS, Windows.</param>
+        /// <param name="major">Major OS version number.</param>
+        /// <param name="minor">Minor OS version number (optional).</param>
+        /// <param name="build">Build OS version number (optional).</param>
+        /// <param name="revision">Revision OS version number (optional).</param>
+        public static bool IsOSPlatformVersionAtLeast(string platform, int major, int minor = 0, int build = 0, int revision = 0)
+            => IsOSPlatform(platform) && IsOSVersionAtLeast(major, minor, build, revision);
+
+        /// <summary>
+        /// Indicates whether the current application is running as WASM in a Browser.
+        /// </summary>
+        public static bool IsBrowser() =>
+#if TARGET_BROWSER
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Indicates whether the current application is running on Linux.
+        /// </summary>
+        public static bool IsLinux() =>
+#if TARGET_LINUX
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Indicates whether the current application is running on FreeBSD.
+        /// </summary>
+        public static bool IsFreeBSD() =>
+#if TARGET_FREEBSD
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the FreeBSD version (returned by 'uname') with a >= version comparison. Used to guard APIs that were added in the given FreeBSD release.
+        /// </summary>
+        public static bool IsFreeBSDVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0)
+            => IsFreeBSD() && IsOSVersionAtLeast(major, minor, build, revision);
+
+        /// <summary>
+        /// Indicates whether the current application is running on Android.
+        /// </summary>
+        public static bool IsAndroid() =>
+#if TARGET_ANDROID
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the Android version (returned by 'uname') with a >= version comparison. Used to guard APIs that were added in the given Android release.
+        /// </summary>
+        public static bool IsAndroidVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0)
+            => IsAndroid() && IsOSVersionAtLeast(major, minor, build, revision);
+
+        /// <summary>
+        /// Indicates whether the current application is running on iOS.
+        /// </summary>
+        public static bool IsIOS() =>
+#if TARGET_IOS
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the iOS version (returned by 'libobjc.get_operatingSystemVersion') with a >= version comparison. Used to guard APIs that were added in the given iOS release.
+        /// </summary>
+        public static bool IsIOSVersionAtLeast(int major, int minor = 0, int build = 0)
+            => IsIOS() && IsOSVersionAtLeast(major, minor, build, 0);
+
+        /// <summary>
+        /// Indicates whether the current application is running on macOS.
+        /// </summary>
+        public static bool IsMacOS() =>
+#if TARGET_OSX
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the macOS version (returned by 'libobjc.get_operatingSystemVersion') with a >= version comparison. Used to guard APIs that were added in the given macOS release.
+        /// </summary>
+        public static bool IsMacOSVersionAtLeast(int major, int minor = 0, int build = 0)
+            => IsMacOS() && IsOSVersionAtLeast(major, minor, build, 0);
+
+        /// <summary>
+        /// Indicates whether the current application is running on tvOS.
+        /// </summary>
+        public static bool IsTvOS() =>
+#if TARGET_TVOS
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the tvOS version (returned by 'libobjc.get_operatingSystemVersion') with a >= version comparison. Used to guard APIs that were added in the given tvOS release.
+        /// </summary>
+        public static bool IsTvOSVersionAtLeast(int major, int minor = 0, int build = 0)
+            => IsTvOS() && IsOSVersionAtLeast(major, minor, build, 0);
+
+        /// <summary>
+        /// Indicates whether the current application is running on watchOS.
+        /// </summary>
+        public static bool IsWatchOS() =>
+#if TARGET_WATCHOS
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the watchOS version (returned by 'libobjc.get_operatingSystemVersion') with a >= version comparison. Used to guard APIs that were added in the given watchOS release.
+        /// </summary>
+        public static bool IsWatchOSVersionAtLeast(int major, int minor = 0, int build = 0)
+            => IsWatchOS() && IsOSVersionAtLeast(major, minor, build, 0);
+
+        /// <summary>
+        /// Indicates whether the current application is running on Windows.
+        /// </summary>
+        public static bool IsWindows() =>
+#if TARGET_WINDOWS
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the Windows version (returned by 'RtlGetVersion') with a >= version comparison. Used to guard APIs that were added in the given Windows release.
+        /// </summary>
+        public static bool IsWindowsVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0)
+            => IsWindows() && IsOSVersionAtLeast(major, minor, build, revision);
+
+        private static bool IsOSVersionAtLeast(int major, int minor, int build, int revision)
+        {
+            Version current = Environment.OSVersion.Version;
+
+            if (current.Major != major)
+            {
+                return current.Major > major;
+            }
+            if (current.Minor != minor)
+            {
+                return current.Minor > minor;
+            }
+            if (current.Build != build)
+            {
+                return current.Build > build;
+            }
+
+            return current.Revision >= revision
+                || (current.Revision == -1 && revision == 0); // it is unavailable on OSX and Environment.OSVersion.Version.Revision returns -1
+        }
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Reflection/IReflect.cs b/src/libraries/System.Private.CoreLib/src/System/Reflection/IReflect.cs
index e46a69c432fd5c..b7e1786d3e9bf5 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Reflection/IReflect.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Reflection/IReflect.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 
 namespace System.Reflection
@@ -10,39 +11,49 @@ public interface IReflect
         // Return the requested method if it is implemented by the Reflection object.  The
         // match is based upon the name and DescriptorInfo which describes the signature
         // of the method.
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         MethodInfo? GetMethod(string name, BindingFlags bindingAttr, Binder? binder, Type[] types, ParameterModifier[]? modifiers);
 
         // Return the requested method if it is implemented by the Reflection object.  The
         // match is based upon the name of the method.  If the object implementes multiple methods
         // with the same name an AmbiguousMatchException is thrown.
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         MethodInfo? GetMethod(string name, BindingFlags bindingAttr);
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         MethodInfo[] GetMethods(BindingFlags bindingAttr);
 
         // Return the requestion field if it is implemented by the Reflection object.  The
         // match is based upon a name.  There cannot be more than a single field with
         // a name.
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         FieldInfo? GetField(string name, BindingFlags bindingAttr);
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         FieldInfo[] GetFields(BindingFlags bindingAttr);
 
         // Return the property based upon name.  If more than one property has the given
         // name an AmbiguousMatchException will be thrown.  Returns null if no property
         // is found.
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         PropertyInfo? GetProperty(string name, BindingFlags bindingAttr);
 
         // Return the property based upon the name and Descriptor info describing the property
         // indexing.  Return null if no property is found.
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         PropertyInfo? GetProperty(string name, BindingFlags bindingAttr, Binder? binder, Type? returnType, Type[] types, ParameterModifier[]? modifiers);
 
         // Returns an array of PropertyInfos for all the properties defined on
         // the Reflection object.
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         PropertyInfo[] GetProperties(BindingFlags bindingAttr);
 
         // Return an array of members which match the passed in name.
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         MemberInfo[] GetMember(string name, BindingFlags bindingAttr);
 
         // Return an array of all of the members defined for this object.
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         MemberInfo[] GetMembers(BindingFlags bindingAttr);
 
         // Description of the Binding Process.
@@ -66,6 +77,7 @@ public interface IReflect
         // For the default binder, the most specific method will be selected.
         //
         // This will invoke a specific member...
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         object? InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target, object?[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters);
 
         // Return the underlying Type that represents the IReflect Object.  For expando object,
diff --git a/src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureType.cs b/src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureType.cs
index f84668ecf55cdb..b8e5e18462c4e4 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureType.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureType.cs
@@ -97,31 +97,79 @@ public sealed override Type MakeArrayType(int rank)
         public sealed override Guid GUID => throw new NotSupportedException(SR.NotSupported_SignatureType);
         protected sealed override TypeCode GetTypeCodeImpl() => throw new NotSupportedException(SR.NotSupported_SignatureType);
         protected sealed override TypeAttributes GetAttributeFlagsImpl() => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public sealed override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public sealed override EventInfo GetEvent(string name, BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public sealed override EventInfo[] GetEvents(BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public sealed override FieldInfo GetField(string name, BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public sealed override FieldInfo[] GetFields(BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public sealed override MemberInfo[] GetMembers(BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public sealed override MethodInfo[] GetMethods(BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public sealed override Type GetNestedType(string name, BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public sealed override Type[] GetNestedTypes(BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public sealed override PropertyInfo[] GetProperties(BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public sealed override object InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target, object?[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected sealed override MethodInfo GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder, CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected sealed override MethodInfo GetMethodImpl(string name, int genericParameterCount, BindingFlags bindingAttr, Binder? binder, CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected sealed override PropertyInfo GetPropertyImpl(string name, BindingFlags bindingAttr, Binder? binder, Type? returnType, Type[]? types, ParameterModifier[]? modifiers) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public sealed override MemberInfo[] FindMembers(MemberTypes memberType, BindingFlags bindingAttr, MemberFilter? filter, object? filterCriteria) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public sealed override MemberInfo[] GetMember(string name, BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public sealed override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(
+            DynamicallyAccessedMemberTypes.PublicFields
+            | DynamicallyAccessedMemberTypes.PublicMethods
+            | DynamicallyAccessedMemberTypes.PublicEvents
+            | DynamicallyAccessedMemberTypes.PublicProperties
+            | DynamicallyAccessedMemberTypes.PublicConstructors
+            | DynamicallyAccessedMemberTypes.PublicNestedTypes)]
         public sealed override MemberInfo[] GetDefaultMembers() => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents)]
         public sealed override EventInfo[] GetEvents() => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
         public sealed override object[] GetCustomAttributes(bool inherit) => throw new NotSupportedException(SR.NotSupported_SignatureType);
         public sealed override object[] GetCustomAttributes(Type attributeType, bool inherit) => throw new NotSupportedException(SR.NotSupported_SignatureType);
         public sealed override bool IsDefined(Type attributeType, bool inherit) => throw new NotSupportedException(SR.NotSupported_SignatureType);
         public sealed override IList<CustomAttributeData> GetCustomAttributesData() => throw new NotSupportedException(SR.NotSupported_SignatureType);
         public sealed override Type GetInterface(string name, bool ignoreCase) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected sealed override ConstructorInfo GetConstructorImpl(BindingFlags bindingAttr, Binder? binder, CallingConventions callConvention, Type[] types, ParameterModifier[]? modifiers) => throw new NotSupportedException(SR.NotSupported_SignatureType);
+
         protected sealed override bool IsCOMObjectImpl() => throw new NotSupportedException(SR.NotSupported_SignatureType);
         protected sealed override bool IsPrimitiveImpl() => throw new NotSupportedException(SR.NotSupported_SignatureType);
         public sealed override IEnumerable<CustomAttributeData> CustomAttributes => throw new NotSupportedException(SR.NotSupported_SignatureType);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureTypeExtensions.cs b/src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureTypeExtensions.cs
index f79b42ea5fd05e..06b391696060e8 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureTypeExtensions.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureTypeExtensions.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace System.Reflection
 {
 #if CORERT
@@ -108,6 +110,8 @@ internal static bool MatchesExactly(this SignatureType pattern, Type actual)
             return signatureType.TryResolve(genericMethod.GetGenericArguments());
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2006:UnrecognizedReflectionPattern",
+            Justification = "Used to find matching method overloads. Only used for assignability checks.")]
         private static Type? TryResolve(this SignatureType signatureType, Type[] genericMethodParameters)
         {
             if (signatureType.IsSZArray)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Reflection/TypeDelegator.cs b/src/libraries/System.Private.CoreLib/src/System/Reflection/TypeDelegator.cs
index 5461da5198959c..9c0cf16aa5c5af 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Reflection/TypeDelegator.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Reflection/TypeDelegator.cs
@@ -38,6 +38,7 @@ public TypeDelegator([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.
         public override Guid GUID => typeImpl.GUID;
         public override int MetadataToken => typeImpl.MetadataToken;
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target,
             object?[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters)
         {
@@ -53,14 +54,17 @@ public TypeDelegator([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.
         public override string? AssemblyQualifiedName => typeImpl.AssemblyQualifiedName;
         public override Type? BaseType => typeImpl.BaseType;
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo? GetConstructorImpl(BindingFlags bindingAttr, Binder? binder,
                 CallingConventions callConvention, Type[] types, ParameterModifier[]? modifiers)
         {
             return typeImpl.GetConstructor(bindingAttr, binder, callConvention, types, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr) => typeImpl.GetConstructors(bindingAttr);
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo? GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder,
                 CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers)
         {
@@ -72,19 +76,26 @@ public TypeDelegator([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.
                 return typeImpl.GetMethod(name, bindingAttr, binder, callConvention, types, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr) => typeImpl.GetMethods(bindingAttr);
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo? GetField(string name, BindingFlags bindingAttr) => typeImpl.GetField(name, bindingAttr);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr) => typeImpl.GetFields(bindingAttr);
 
         public override Type? GetInterface(string name, bool ignoreCase) => typeImpl.GetInterface(name, ignoreCase);
 
         public override Type[] GetInterfaces() => typeImpl.GetInterfaces();
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo? GetEvent(string name, BindingFlags bindingAttr) => typeImpl.GetEvent(name, bindingAttr);
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents)]
         public override EventInfo[] GetEvents() => typeImpl.GetEvents();
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo? GetPropertyImpl(string name, BindingFlags bindingAttr, Binder? binder,
                         Type? returnType, Type[]? types, ParameterModifier[]? modifiers)
         {
@@ -94,11 +105,22 @@ public TypeDelegator([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.
                 return typeImpl.GetProperty(name, bindingAttr, binder, returnType, types!, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr) => typeImpl.GetProperties(bindingAttr);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr) => typeImpl.GetEvents(bindingAttr);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr) => typeImpl.GetNestedTypes(bindingAttr);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type? GetNestedType(string name, BindingFlags bindingAttr) => typeImpl.GetNestedType(name, bindingAttr);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr) => typeImpl.GetMember(name, type, bindingAttr);
+
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr) => typeImpl.GetMembers(bindingAttr);
 
         protected override TypeAttributes GetAttributeFlagsImpl() => typeImpl.Attributes;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Reflection/TypeInfo.cs b/src/libraries/System.Private.CoreLib/src/System/Reflection/TypeInfo.cs
index 5786aa4d9d02cc..3487f2aab00c4c 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Reflection/TypeInfo.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Reflection/TypeInfo.cs
@@ -33,11 +33,16 @@ protected TypeInfo() { }
         [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public virtual IEnumerable<MethodInfo> GetDeclaredMethods(string name)
         {
-            foreach (MethodInfo method in GetMethods(TypeInfo.DeclaredOnlyLookup))
+            foreach (MethodInfo method in GetDeclaredOnlyMethods(this))
             {
                 if (method.Name == name)
                     yield return method;
             }
+
+            [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2006:UnrecognizedReflectionPattern",
+                Justification = "The yield return state machine doesn't propagate annotations")]
+            static MethodInfo[] GetDeclaredOnlyMethods(
+                Type type) => type.GetMethods(TypeInfo.DeclaredOnlyLookup);
         }
 
         public virtual IEnumerable<ConstructorInfo> DeclaredConstructors
@@ -75,10 +80,15 @@ public virtual IEnumerable<System.Reflection.TypeInfo> DeclaredNestedTypes
             [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
             get
             {
-                foreach (Type t in GetNestedTypes(TypeInfo.DeclaredOnlyLookup))
+                foreach (Type t in GetDeclaredOnlyNestedTypes(this))
                 {
                     yield return t.GetTypeInfo();
                 }
+
+                [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2006:UnrecognizedReflectionPattern",
+                    Justification = "The yield return state machine doesn't propagate annotations")]
+                static Type[] GetDeclaredOnlyNestedTypes(
+                    Type type) => type.GetNestedTypes(TypeInfo.DeclaredOnlyLookup);
             }
         }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceManager.cs b/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceManager.cs
index 2334103d055ff5..16c585d4fe6345 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceManager.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceManager.cs
@@ -306,7 +306,9 @@ public virtual void ReleaseAllResources()
             }
         }
 
-        public static ResourceManager CreateFileBasedResourceManager(string baseName, string resourceDir, Type? usingResourceSet)
+        public static ResourceManager CreateFileBasedResourceManager(string baseName, string resourceDir,
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
+            Type? usingResourceSet)
         {
             return new ResourceManager(baseName, resourceDir, usingResourceSet);
         }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceReader.Core.cs b/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceReader.Core.cs
index 880f21c1b98bff..bb2cea4df74978 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceReader.Core.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceReader.Core.cs
@@ -78,11 +78,11 @@ private bool InitializeBinaryFormatter()
             // If BinaryFormatter support is disabled for the app, the linker will replace this entire
             // method body with "return false;", skipping all reflection code below.
 
-            LazyInitializer.EnsureInitialized(ref s_binaryFormatterType, () =>
+            LazyInitializer.EnsureInitialized(ref s_binaryFormatterType, static () =>
                 Type.GetType("System.Runtime.Serialization.Formatters.Binary.BinaryFormatter, System.Runtime.Serialization.Formatters, Version=0.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a",
                 throwOnError: true)!);
 
-            LazyInitializer.EnsureInitialized(ref s_deserializeMethod, () =>
+            LazyInitializer.EnsureInitialized(ref s_deserializeMethod, static () =>
             {
                 MethodInfo binaryFormatterDeserialize = s_binaryFormatterType!.GetMethod("Deserialize", new Type[] { typeof(Stream) })!;
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceReader.cs b/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceReader.cs
index baf733b3678bde..c43899c5243131 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceReader.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceReader.cs
@@ -157,11 +157,11 @@ private unsafe void Dispose(bool disposing)
                     // Close the stream in a thread-safe way.  This fix means
                     // that we may call Close n times, but that's safe.
                     BinaryReader copyOfStore = _store;
-                    _store = null!; // TODO-NULLABLE: Avoid nulling out in Dispose
+                    _store = null!;
                     if (copyOfStore != null)
                         copyOfStore.Close();
                 }
-                _store = null!; // TODO-NULLABLE: Avoid nulling out in Dispose
+                _store = null!;
                 _namePositions = null;
                 _nameHashes = null;
                 _ums = null;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceSet.cs b/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceSet.cs
index 0a42533351b55e..6ad05b68692935 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceSet.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Resources/ResourceSet.cs
@@ -14,6 +14,7 @@
 
 using System.Collections;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Reflection;
 
@@ -28,7 +29,7 @@ namespace System.Resources
     public class ResourceSet : IDisposable, IEnumerable
     {
         protected IResourceReader Reader = null!;
-        internal Hashtable? Table; // TODO-NULLABLE: Avoid nulling out in Dispose
+        internal Hashtable? Table;
 
         private Hashtable? _caseInsensitiveTable;  // For case-insensitive lookups.
 
@@ -89,11 +90,11 @@ protected virtual void Dispose(bool disposing)
             {
                 // Close the Reader in a thread-safe way.
                 IResourceReader? copyOfReader = Reader;
-                Reader = null!; // TODO-NULLABLE: Avoid nulling out in Dispose
+                Reader = null!;
                 if (copyOfReader != null)
                     copyOfReader.Close();
             }
-            Reader = null!; // TODO-NULLABLE: Avoid nulling out in Dispose
+            Reader = null!;
             _caseInsensitiveTable = null;
             Table = null;
         }
@@ -114,10 +115,11 @@ public virtual Type GetDefaultReader()
         // Returns the preferred IResourceWriter class for this kind of ResourceSet.
         // Subclasses of ResourceSet using their own Readers &; should override
         // GetDefaultReader and GetDefaultWriter.
+        // TODO: https://github.com/mono/linker/issues/943
+        [DynamicDependency(DynamicallyAccessedMemberTypes.PublicConstructors, "System.Resources.ResourceWriter", "System.Resources.Writer")]
         public virtual Type GetDefaultWriter()
         {
-            Assembly resourceWriterAssembly = Assembly.Load("System.Resources.Writer, Version=4.0.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a");
-            return resourceWriterAssembly.GetType("System.Resources.ResourceWriter", throwOnError: true)!;
+            return Type.GetType("System.Resources.ResourceWriter, System.Resources.Writer", throwOnError: true)!;
         }
 
         public virtual IDictionaryEnumerator GetEnumerator()
diff --git a/src/libraries/System.Private.CoreLib/src/System/Resources/RuntimeResourceSet.cs b/src/libraries/System.Private.CoreLib/src/System/Resources/RuntimeResourceSet.cs
index c00ebb2b04a457..f6de75e7e3e98a 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Resources/RuntimeResourceSet.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Resources/RuntimeResourceSet.cs
@@ -175,12 +175,12 @@ sealed class RuntimeResourceSet : ResourceSet, IEnumerable
         // for arbitrarily long times, since the object is usually a string
         // literal that will live for the lifetime of the appdomain.  The
         // value is a ResourceLocator instance, which might cache the object.
-        private Dictionary<string, ResourceLocator>? _resCache; // TODO-NULLABLE: Avoid nulling out in Dispose
+        private Dictionary<string, ResourceLocator>? _resCache;
 
 
         // For our special load-on-demand reader, cache the cast.  The
         // RuntimeResourceSet's implementation knows how to treat this reader specially.
-        private ResourceReader? _defaultReader; // TODO-NULLABLE: Avoid nulling out in Dispose
+        private ResourceReader? _defaultReader;
 
         // This is a lookup table for case-insensitive lookups, and may be null.
         // Consider always using a case-insensitive resource cache, as we don't
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncTaskCache.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncTaskCache.cs
index 363371f7e7b727..1c654cd79c3705 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncTaskCache.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncTaskCache.cs
@@ -45,7 +45,7 @@ private static int GetPoolAsyncValueTasksLimitValue() =>
         /// <typeparam name="TResult">Specifies the result type.</typeparam>
         /// <param name="result">The result for the task.</param>
         /// <returns>The cacheable task.</returns>
-        internal static Task<TResult> CreateCacheableTask<TResult>([AllowNull] TResult result) =>
+        internal static Task<TResult> CreateCacheableTask<TResult>(TResult? result) =>
             new Task<TResult>(false, result, (TaskCreationOptions)InternalTaskOptions.DoNotDispose, default);
 
         /// <summary>Creates an array of cached tasks for the values in the range [INCLUSIVE_MIN,EXCLUSIVE_MAX).</summary>
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncTaskMethodBuilderT.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncTaskMethodBuilderT.cs
index 4a3d1dfed13b8f..70ac433630decc 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncTaskMethodBuilderT.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncTaskMethodBuilderT.cs
@@ -292,8 +292,7 @@ private static void ExecutionContextCallback(object? s)
             /// <summary>A delegate to the <see cref="MoveNext()"/> method.</summary>
             private Action? _moveNextAction;
             /// <summary>The state machine itself.</summary>
-            [AllowNull, MaybeNull]
-            public TStateMachine StateMachine = default; // mutable struct; do not make this readonly. SOS DumpAsync command depends on this name.
+            public TStateMachine? StateMachine; // mutable struct; do not make this readonly. SOS DumpAsync command depends on this name.
             /// <summary>Captured ExecutionContext with which to invoke <see cref="MoveNextAction"/>; may be null.</summary>
             public ExecutionContext? Context;
 
@@ -428,7 +427,7 @@ public void SetResult(TResult result)
         /// <summary>Completes the already initialized task with the specified result.</summary>
         /// <param name="result">The result to use to complete the task.</param>
         /// <param name="task">The task to complete.</param>
-        internal static void SetExistingTaskResult(Task<TResult> task, [AllowNull] TResult result)
+        internal static void SetExistingTaskResult(Task<TResult> task, TResult? result)
         {
             Debug.Assert(task != null, "Expected non-null task");
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncValueTaskMethodBuilderT.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncValueTaskMethodBuilderT.cs
index 1c88475eae7d63..846c64999c3003 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncValueTaskMethodBuilderT.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncValueTaskMethodBuilderT.cs
@@ -364,8 +364,7 @@ private sealed class StateMachineBox<TStateMachine> :
             /// <summary>If this box is stored in the cache, the next box in the cache.</summary>
             private StateMachineBox<TStateMachine>? _next;
             /// <summary>The state machine itself.</summary>
-            [AllowNull, MaybeNull]
-            public TStateMachine StateMachine = default;
+            public TStateMachine? StateMachine;
 
             /// <summary>Gets a box object to use for an operation.  This may be a reused, pooled object, or it may be new.</summary>
             [MethodImpl(MethodImplOptions.AggressiveInlining)] // only one caller
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ConditionalWeakTable.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ConditionalWeakTable.cs
index 8d3b9adb0f3bc8..d5caca5098f087 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ConditionalWeakTable.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ConditionalWeakTable.cs
@@ -552,7 +552,7 @@ internal bool TryGetEntry(int index, [NotNullWhen(true)] out TKey? key, [MaybeNu
                 }
 
                 key = default;
-                value = default!;
+                value = default;
                 return false;
             }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/TaskAwaiter.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/TaskAwaiter.cs
index b14e8432eb3faf..e5eddb76ee9db0 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/TaskAwaiter.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/TaskAwaiter.cs
@@ -270,7 +270,7 @@ private static Action OutputWaitEtwEvents(Task task, Action continuation)
             // is enabled, and in doing so it allows us to pass the awaited task's information into the end event
             // in a purely pay-for-play manner (the alternatively would be to increase the size of TaskAwaiter
             // just for this ETW purpose, not pay-for-play, since GetResult would need to know whether a real yield occurred).
-            return AsyncMethodBuilderCore.CreateContinuationWrapper(continuation, (innerContinuation, innerTask) =>
+            return AsyncMethodBuilderCore.CreateContinuationWrapper(continuation, static (innerContinuation, innerTask) =>
             {
                 if (Task.s_asyncDebuggingEnabled)
                 {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ValueTaskAwaiter.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ValueTaskAwaiter.cs
index 4cf0714e3a5372..68675a82f0afc9 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ValueTaskAwaiter.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ValueTaskAwaiter.cs
@@ -14,7 +14,7 @@ namespace System.Runtime.CompilerServices
     public readonly struct ValueTaskAwaiter : ICriticalNotifyCompletion, IStateMachineBoxAwareAwaiter
     {
         /// <summary>Shim used to invoke an <see cref="Action"/> passed as the state argument to a <see cref="Action{Object}"/>.</summary>
-        internal static readonly Action<object?> s_invokeActionDelegate = state =>
+        internal static readonly Action<object?> s_invokeActionDelegate = static state =>
         {
             if (!(state is Action action))
             {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/YieldAwaitable.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/YieldAwaitable.cs
index 45a73ad88c5aa8..7500cba3d4e303 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/YieldAwaitable.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/YieldAwaitable.cs
@@ -129,7 +129,7 @@ void IStateMachineBoxAwareAwaiter.AwaitUnsafeOnCompleted(IAsyncStateMachineBox b
                 SynchronizationContext? syncCtx = SynchronizationContext.Current;
                 if (syncCtx != null && syncCtx.GetType() != typeof(SynchronizationContext))
                 {
-                    syncCtx.Post(s => ((IAsyncStateMachineBox)s!).MoveNext(), box);
+                    syncCtx.Post(static s => ((IAsyncStateMachineBox)s!).MoveNext(), box);
                 }
                 else
                 {
@@ -140,7 +140,7 @@ void IStateMachineBoxAwareAwaiter.AwaitUnsafeOnCompleted(IAsyncStateMachineBox b
                     }
                     else
                     {
-                        Task.Factory.StartNew(s => ((IAsyncStateMachineBox)s!).MoveNext(), box, default, TaskCreationOptions.PreferFairness, scheduler);
+                        Task.Factory.StartNew(static s => ((IAsyncStateMachineBox)s!).MoveNext(), box, default, TaskCreationOptions.PreferFairness, scheduler);
                     }
                 }
             }
@@ -156,7 +156,7 @@ private static Action OutputCorrelationEtwEvent(Action continuation)
                 // fire the correlation ETW event
                 TplEventSource.Log.AwaitTaskContinuationScheduled(TaskScheduler.Current.Id, (currentTask != null) ? currentTask.Id : 0, continuationId);
 
-                return AsyncMethodBuilderCore.CreateContinuationWrapper(continuation, (innerContinuation, continuationIdTask) =>
+                return AsyncMethodBuilderCore.CreateContinuationWrapper(continuation, static (innerContinuation, continuationIdTask) =>
                 {
                     TplEventSource log = TplEventSource.Log;
                     log.TaskWaitContinuationStarted(((Task<int>)continuationIdTask).Result);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/AllowReversePInvokeCallsAttribute.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/AllowReversePInvokeCallsAttribute.cs
index 5b14e88c4beec7..99b3a57a3dbbdb 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/AllowReversePInvokeCallsAttribute.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/AllowReversePInvokeCallsAttribute.cs
@@ -3,8 +3,8 @@
 
 namespace System.Runtime.InteropServices
 {
-    // To be used on methods that sink reverse P/Invoke calls.
-    // This attribute was a Silverlight security measure, currently ignored.
+    // This attribute was a Silverlight security measure and is no longer respected.
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
     [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = false)]
     public sealed class AllowReversePInvokeCallsAttribute : Attribute
     {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/DispatchWrapper.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/DispatchWrapper.cs
index 5be89fc0062308..740d69aefde6b7 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/DispatchWrapper.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/DispatchWrapper.cs
@@ -22,7 +22,7 @@ public DispatchWrapper(object? obj)
             }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public object? WrappedObject { get; }
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.NoCom.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.NoCom.cs
index 2e7c3b36b4e6a9..ed7d4928c250a8 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.NoCom.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.NoCom.cs
@@ -15,7 +15,7 @@ public static int GetHRForException(Exception? e)
             return e?.HResult ?? 0;
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static int AddRef(IntPtr pUnk)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
@@ -23,13 +23,13 @@ public static int AddRef(IntPtr pUnk)
 
         public static bool AreComObjectsAvailableForCleanup() => false;
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static IntPtr CreateAggregatedObject(IntPtr pOuter, object o)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static object BindToMoniker(string monikerName)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
@@ -39,55 +39,55 @@ public static void CleanupUnusedObjectsInCurrentContext()
         {
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static IntPtr CreateAggregatedObject<T>(IntPtr pOuter, T o) where T : notnull
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static object? CreateWrapperOfType(object? o, Type t)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
-        public static TWrapper CreateWrapperOfType<T, TWrapper>([AllowNull] T o)
+        [SupportedOSPlatform("windows")]
+        public static TWrapper CreateWrapperOfType<T, TWrapper>(T? o)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static void ChangeWrapperHandleStrength(object otp, bool fIsWeak)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static int FinalReleaseComObject(object o)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static IntPtr GetComInterfaceForObject(object o, Type T)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static IntPtr GetComInterfaceForObject(object o, Type T, CustomQueryInterfaceMode mode)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static IntPtr GetComInterfaceForObject<T, TInterface>([DisallowNull] T o)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static object? GetComObjectData(object obj, object key)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
@@ -103,92 +103,91 @@ public static IntPtr GetHINSTANCE(Module m)
             return (IntPtr)(-1);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static IntPtr GetIDispatchForObject(object o)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static IntPtr GetIUnknownForObject(object o)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static void GetNativeVariantForObject(object? obj, IntPtr pDstNativeVariant)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
-        public static void GetNativeVariantForObject<T>([AllowNull] T obj, IntPtr pDstNativeVariant)
+        [SupportedOSPlatform("windows")]
+        public static void GetNativeVariantForObject<T>(T? obj, IntPtr pDstNativeVariant)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static object GetTypedObjectForIUnknown(IntPtr pUnk, Type t)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static object GetObjectForIUnknown(IntPtr pUnk)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static object? GetObjectForNativeVariant(IntPtr pSrcNativeVariant)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
-        [return: MaybeNull]
-        public static T GetObjectForNativeVariant<T>(IntPtr pSrcNativeVariant)
+        [SupportedOSPlatform("windows")]
+        public static T? GetObjectForNativeVariant<T>(IntPtr pSrcNativeVariant)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static object?[] GetObjectsForNativeVariants(IntPtr aSrcNativeVariant, int cVars)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static T[] GetObjectsForNativeVariants<T>(IntPtr aSrcNativeVariant, int cVars)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static int GetStartComSlot(Type t)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static int GetEndComSlot(Type t)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static Type? GetTypeFromCLSID(Guid clsid)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static string GetTypeInfoName(ITypeInfo typeInfo)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static object GetUniqueObjectForIUnknown(IntPtr unknown)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
@@ -213,25 +212,25 @@ public static bool IsTypeVisibleFromCom(Type t)
             return false;
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static int QueryInterface(IntPtr pUnk, ref Guid iid, out IntPtr ppv)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static int Release(IntPtr pUnk)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static int ReleaseComObject(object o)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static bool SetComObjectData(object obj, object key, object? data)
         {
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_ComInterop);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.cs
index 40c0396c2ac080..7a2e976c92af53 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.cs
@@ -572,8 +572,7 @@ public static void PtrToStructure<T>(IntPtr ptr, [DisallowNull] T structure)
             PtrToStructure(ptr, (object)structure!);
         }
 
-        [return: MaybeNull]
-        public static T PtrToStructure<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]T>(IntPtr ptr) => (T)PtrToStructure(ptr, typeof(T))!;
+        public static T? PtrToStructure<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]T>(IntPtr ptr) => (T)PtrToStructure(ptr, typeof(T))!;
 
         public static void DestroyStructure<T>(IntPtr ptr) => DestroyStructure(ptr, typeof(T));
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Arm/AdvSimd.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Arm/AdvSimd.PlatformNotSupported.cs
index 748ba26f67d522..2fcc2efcfc9cad 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Arm/AdvSimd.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Arm/AdvSimd.PlatformNotSupported.cs
@@ -9,12 +9,12 @@ namespace System.Runtime.Intrinsics.Arm
     /// This class provides access to the ARM AdvSIMD hardware instructions via intrinsics
     /// </summary>
     [CLSCompliant(false)]
-#if USE_INTERNAL_ACCESSIBILITY
-    internal
-#else
+#if SYSTEM_PRIVATE_CORELIB
     public
+#else
+    internal
 #endif
-        abstract class AdvSimd : ArmBase
+    abstract class AdvSimd : ArmBase
     {
         internal AdvSimd() { }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Arm/ArmBase.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Arm/ArmBase.PlatformNotSupported.cs
index ad356ade45adde..48bafcb0489f19 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Arm/ArmBase.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Arm/ArmBase.PlatformNotSupported.cs
@@ -10,12 +10,12 @@ namespace System.Runtime.Intrinsics.Arm
     /// This class provides access to the ARM base hardware instructions via intrinsics
     /// </summary>
     [CLSCompliant(false)]
-#if USE_INTERNAL_ACCESSIBILITY
-    internal
-#else
+#if SYSTEM_PRIVATE_CORELIB
     public
+#else
+    internal
 #endif
-        abstract class ArmBase
+    abstract class ArmBase
     {
         internal ArmBase() { }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi1.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi1.PlatformNotSupported.cs
index 045a8a273b6da2..56ff44adb7d9c1 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi1.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi1.PlatformNotSupported.cs
@@ -11,17 +11,17 @@ namespace System.Runtime.Intrinsics.X86
     /// This class provides access to Intel BMI1 hardware instructions via intrinsics
     /// </summary>
     [CLSCompliant(false)]
-    public abstract class Bmi1 // : X86Base
+    public abstract class Bmi1 : X86Base
     {
         internal Bmi1() { }
 
-        public static bool IsSupported { [Intrinsic] get { return false; } }
+        public static new bool IsSupported { [Intrinsic] get { return false; } }
 
-        public abstract class X64 // : X86Base.X64
+        public new abstract class X64 : X86Base.X64
         {
             internal X64() { }
 
-            public static bool IsSupported { [Intrinsic] get { return false; } }
+            public static new bool IsSupported { [Intrinsic] get { return false; } }
 
             /// <summary>
             /// unsigned __int64 _andn_u64 (unsigned __int64 a, unsigned __int64 b)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi1.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi1.cs
index 535d5f775720e2..82e501ca97deaa 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi1.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi1.cs
@@ -10,18 +10,18 @@ namespace System.Runtime.Intrinsics.X86
     /// </summary>
     [Intrinsic]
     [CLSCompliant(false)]
-    public abstract class Bmi1 // : X86Base
+    public abstract class Bmi1 : X86Base
     {
         internal Bmi1() { }
 
-        public static bool IsSupported { get => IsSupported; }
+        public static new bool IsSupported { get => IsSupported; }
 
         [Intrinsic]
-        public abstract class X64 // : X86Base.X64
+        public new abstract class X64 : X86Base.X64
         {
             internal X64() { }
 
-            public static bool IsSupported { get => IsSupported; }
+            public static new bool IsSupported { get => IsSupported; }
 
             /// <summary>
             /// unsigned __int64 _andn_u64 (unsigned __int64 a, unsigned __int64 b)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi2.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi2.PlatformNotSupported.cs
index 08a4204301a5bb..8c1a66ec970672 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi2.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi2.PlatformNotSupported.cs
@@ -11,17 +11,17 @@ namespace System.Runtime.Intrinsics.X86
     /// This class provides access to Intel BMI2 hardware instructions via intrinsics
     /// </summary>
     [CLSCompliant(false)]
-    public abstract class Bmi2 // : X86Base
+    public abstract class Bmi2 : X86Base
     {
         internal Bmi2() { }
 
-        public static bool IsSupported { [Intrinsic] get { return false; } }
+        public static new bool IsSupported { [Intrinsic] get { return false; } }
 
-        public abstract class X64 // : X86Base.X64
+        public new abstract class X64 : X86Base.X64
         {
             internal X64() { }
 
-            public static bool IsSupported { [Intrinsic] get { return false; } }
+            public static new bool IsSupported { [Intrinsic] get { return false; } }
 
             /// <summary>
             /// unsigned __int64 _bzhi_u64 (unsigned __int64 a, unsigned int index)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi2.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi2.cs
index 81dff57da5a0eb..95104e6d2b92e4 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi2.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Bmi2.cs
@@ -10,18 +10,18 @@ namespace System.Runtime.Intrinsics.X86
     /// </summary>
     [Intrinsic]
     [CLSCompliant(false)]
-    public abstract class Bmi2 // : X86Base
+    public abstract class Bmi2 : X86Base
     {
         internal Bmi2() { }
 
-        public static bool IsSupported { get => IsSupported; }
+        public static new bool IsSupported { get => IsSupported; }
 
         [Intrinsic]
-        public abstract class X64 // : X86Base.X64
+        public new abstract class X64 : X86Base.X64
         {
             internal X64() { }
 
-            public static bool IsSupported { get => IsSupported; }
+            public static new bool IsSupported { get => IsSupported; }
 
             /// <summary>
             /// unsigned __int64 _bzhi_u64 (unsigned __int64 a, unsigned int index)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Lzcnt.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Lzcnt.PlatformNotSupported.cs
index a800021bbab42a..1c2eed20a3c87a 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Lzcnt.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Lzcnt.PlatformNotSupported.cs
@@ -10,17 +10,17 @@ namespace System.Runtime.Intrinsics.X86
     /// This class provides access to Intel LZCNT hardware instructions via intrinsics
     /// </summary>
     [CLSCompliant(false)]
-    public abstract class Lzcnt // : X86Base
+    public abstract class Lzcnt : X86Base
     {
         internal Lzcnt() { }
 
-        public static bool IsSupported { [Intrinsic] get { return false; } }
+        public static new bool IsSupported { [Intrinsic] get { return false; } }
 
-        public abstract class X64 // : X86Base.X64
+        public new abstract class X64 : X86Base.X64
         {
             internal X64() { }
 
-            public static bool IsSupported { [Intrinsic] get { return false; } }
+            public static new bool IsSupported { [Intrinsic] get { return false; } }
 
             /// <summary>
             /// unsigned __int64 _lzcnt_u64 (unsigned __int64 a)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Lzcnt.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Lzcnt.cs
index d6d278c5d4c2f8..55e8f737de8f1a 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Lzcnt.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Lzcnt.cs
@@ -10,18 +10,18 @@ namespace System.Runtime.Intrinsics.X86
     /// </summary>
     [Intrinsic]
     [CLSCompliant(false)]
-    public abstract class Lzcnt // : X86Base
+    public abstract class Lzcnt : X86Base
     {
         internal Lzcnt() { }
 
-        public static bool IsSupported { get => IsSupported; }
+        public static new bool IsSupported { get => IsSupported; }
 
         [Intrinsic]
-        public abstract class X64 // : X86Base.X64
+        public new abstract class X64 : X86Base.X64
         {
             internal X64() { }
 
-            public static bool IsSupported { get => IsSupported; }
+            public static new bool IsSupported { get => IsSupported; }
 
             /// <summary>
             /// unsigned __int64 _lzcnt_u64 (unsigned __int64 a)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Sse.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Sse.PlatformNotSupported.cs
index 00d3c684294ff8..1d92f91621b66a 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Sse.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Sse.PlatformNotSupported.cs
@@ -11,17 +11,17 @@ namespace System.Runtime.Intrinsics.X86
     /// This class provides access to Intel SSE hardware instructions via intrinsics
     /// </summary>
     [CLSCompliant(false)]
-    public abstract class Sse // : X86Base
+    public abstract class Sse : X86Base
     {
         internal Sse() { }
 
-        public static bool IsSupported { [Intrinsic] get { return false; } }
+        public static new bool IsSupported { [Intrinsic] get { return false; } }
 
-        public abstract class X64 // : X86Base.X64
+        public new abstract class X64 : X86Base.X64
         {
             internal X64() { }
 
-            public static bool IsSupported { [Intrinsic] get { return false; } }
+            public static new bool IsSupported { [Intrinsic] get { return false; } }
 
             /// <summary>
             /// __int64 _mm_cvtss_si64 (__m128 a)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Sse.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Sse.cs
index 1e88751c368709..129f2ecbd09a1f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Sse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/Sse.cs
@@ -10,18 +10,18 @@ namespace System.Runtime.Intrinsics.X86
     /// </summary>
     [Intrinsic]
     [CLSCompliant(false)]
-    public abstract class Sse // : X86Base
+    public abstract class Sse : X86Base
     {
         internal Sse() { }
 
-        public static bool IsSupported { get => IsSupported; }
+        public static new bool IsSupported { get => IsSupported; }
 
         [Intrinsic]
-        public abstract class X64 // : X86Base.X64
+        public new abstract class X64 : X86Base.X64
         {
             internal X64() { }
 
-            public static bool IsSupported { get => IsSupported; }
+            public static new bool IsSupported { get => IsSupported; }
 
             /// <summary>
             /// __int64 _mm_cvtss_si64 (__m128 a)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.PlatformNotSupported.cs
index a0e0e68fbd0326..261ac82076ecb4 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.PlatformNotSupported.cs
@@ -9,13 +9,13 @@ namespace System.Runtime.Intrinsics.X86
     /// <summary>
     /// This class provides access to the x86 base hardware instructions via intrinsics
     /// </summary>
-    internal abstract class X86Base
+    public abstract partial class X86Base
     {
         internal X86Base() { }
 
         public static bool IsSupported { [Intrinsic] get => false; }
 
-        internal abstract class X64
+        public abstract class X64
         {
             internal X64() { }
 
@@ -65,5 +65,11 @@ internal X64() { }
         /// Its functionality is exposed in the public <see cref="System.Numerics.BitOperations" /> class.
         /// </remarks>
         internal static uint BitScanReverse(uint value) { throw new PlatformNotSupportedException(); }
+
+        /// <summary>
+        /// void __cpuidex(int cpuInfo[4], int function_id, int subfunction_id);
+        ///   CPUID
+        /// </summary>
+        public static (int Eax, int Ebx, int Ecx, int Edx) CpuId(int functionId, int subFunctionId) { throw new PlatformNotSupportedException(); }
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.cs
index de49813d9de0aa..7f7576be50ad25 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 
 namespace System.Runtime.Intrinsics.X86
 {
@@ -9,13 +10,17 @@ namespace System.Runtime.Intrinsics.X86
     /// This class provides access to the x86 base hardware instructions via intrinsics
     /// </summary>
     [Intrinsic]
-    internal abstract class X86Base
+    public abstract partial class X86Base
     {
+        internal X86Base() { }
+
         public static bool IsSupported { get => IsSupported; }
 
         [Intrinsic]
-        internal abstract class X64
+        public abstract class X64
         {
+            internal X64() { }
+
             public static bool IsSupported { get => IsSupported; }
 
             /// <summary>
@@ -62,5 +67,16 @@ internal abstract class X64
         /// Its functionality is exposed in the public <see cref="System.Numerics.BitOperations" /> class.
         /// </remarks>
         internal static uint BitScanReverse(uint value) => BitScanReverse(value);
+
+        /// <summary>
+        /// void __cpuidex(int cpuInfo[4], int function_id, int subfunction_id);
+        ///   CPUID
+        /// </summary>
+        public static unsafe (int Eax, int Ebx, int Ecx, int Edx) CpuId(int functionId, int subFunctionId)
+        {
+            int* cpuInfo = stackalloc int[4];
+            __cpuidex(cpuInfo, functionId, subFunctionId);
+            return (cpuInfo[0], cpuInfo[1], cpuInfo[2], cpuInfo[3]);
+        }
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/PlatformAttributes.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/PlatformAttributes.cs
index c230113c9b0f2f..0f99e4475a43a0 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/PlatformAttributes.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/PlatformAttributes.cs
@@ -45,7 +45,7 @@ public TargetPlatformAttribute(string platformName) : base(platformName)
     /// applied to indicate support on multiple operating systems.
     /// </summary>
     /// <remarks>
-    /// Callers can apply a <see cref="System.Runtime.Versioning.MinimumOSPlatformAttribute" />
+    /// Callers can apply a <see cref="System.Runtime.Versioning.SupportedOSPlatformAttribute " />
     /// or use guards to prevent calls to APIs on unsupported operating systems.
     ///
     /// A given platform should only be specified once.
@@ -66,9 +66,9 @@ public TargetPlatformAttribute(string platformName) : base(platformName)
 #else
     internal
 #endif
-        sealed class MinimumOSPlatformAttribute : OSPlatformAttribute
+        sealed class SupportedOSPlatformAttribute  : OSPlatformAttribute
     {
-        public MinimumOSPlatformAttribute(string platformName) : base(platformName)
+        public SupportedOSPlatformAttribute (string platformName) : base(platformName)
         {
         }
     }
@@ -133,9 +133,9 @@ public ObsoletedInOSPlatformAttribute(string platformName, string message) : bas
 #else
     internal
 #endif
-        sealed class RemovedInOSPlatformAttribute : OSPlatformAttribute
+        sealed class UnsupportedOSPlatformAttribute : OSPlatformAttribute
     {
-        public RemovedInOSPlatformAttribute(string platformName) : base(platformName)
+        public UnsupportedOSPlatformAttribute(string platformName) : base(platformName)
         {
         }
     }
diff --git a/src/libraries/System.Private.CoreLib/src/System/SpanHelpers.BinarySearch.cs b/src/libraries/System.Private.CoreLib/src/System/SpanHelpers.BinarySearch.cs
index 2da00f975d23c8..4b8c9127cd23f8 100644
--- a/src/libraries/System.Private.CoreLib/src/System/SpanHelpers.BinarySearch.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/SpanHelpers.BinarySearch.cs
@@ -75,7 +75,7 @@ public ComparerComparable(T value, TComparer comparer)
             }
 
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            public int CompareTo([AllowNull] T other) => _comparer.Compare(_value, other);
+            public int CompareTo(T? other) => _comparer.Compare(_value, other);
         }
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/String.Comparison.cs b/src/libraries/System.Private.CoreLib/src/System/String.Comparison.cs
index d93701185fa6c4..40f63176236c5c 100644
--- a/src/libraries/System.Private.CoreLib/src/System/String.Comparison.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/String.Comparison.cs
@@ -42,7 +42,27 @@ private static int CompareOrdinalHelper(string strA, int indexA, int countA, str
             return SpanHelpers.SequenceCompareTo(ref Unsafe.Add(ref strA.GetRawStringData(), indexA), countA, ref Unsafe.Add(ref strB.GetRawStringData(), indexB), countB);
         }
 
-        private static bool EqualsOrdinalIgnoreCase(string strA, string strB)
+        internal static bool EqualsOrdinalIgnoreCase(string? strA, string? strB)
+        {
+            if (ReferenceEquals(strA, strB))
+            {
+                return true;
+            }
+
+            if (strA is null || strB is null)
+            {
+                return false;
+            }
+
+            if (strA.Length != strB.Length)
+            {
+                return false;
+            }
+
+            return EqualsOrdinalIgnoreCaseNoLengthCheck(strA, strB);
+        }
+
+        private static bool EqualsOrdinalIgnoreCaseNoLengthCheck(string strA, string strB)
         {
             Debug.Assert(strA.Length == strB.Length);
 
@@ -645,7 +665,7 @@ public bool Equals(string? value, StringComparison comparisonType)
                     if (this.Length != value.Length)
                         return false;
 
-                    return EqualsOrdinalIgnoreCase(this, value);
+                    return EqualsOrdinalIgnoreCaseNoLengthCheck(this, value);
 
                 default:
                     throw new ArgumentException(SR.NotSupported_StringComparison, nameof(comparisonType));
@@ -701,7 +721,7 @@ public static bool Equals(string? a, string? b, StringComparison comparisonType)
                     if (a.Length != b.Length)
                         return false;
 
-                    return EqualsOrdinalIgnoreCase(a, b);
+                    return EqualsOrdinalIgnoreCaseNoLengthCheck(a, b);
 
                 default:
                     throw new ArgumentException(SR.NotSupported_StringComparison, nameof(comparisonType));
@@ -811,6 +831,46 @@ internal unsafe int GetNonRandomizedHashCode()
             }
         }
 
+        // Use this if and only if 'Denial of Service' attacks are not a concern (i.e. never used for free-form user input),
+        // or are otherwise mitigated
+        internal unsafe int GetNonRandomizedHashCodeOrdinalIgnoreCase()
+        {
+            fixed (char* src = &_firstChar)
+            {
+                Debug.Assert(src[this.Length] == '\0', "src[this.Length] == '\\0'");
+                Debug.Assert(((int)src) % 4 == 0, "Managed string should start at 4 bytes boundary");
+
+                uint hash1 = (5381 << 16) + 5381;
+                uint hash2 = hash1;
+
+                uint* ptr = (uint*)src;
+                int length = this.Length;
+
+                // We "normalize to lowercase" every char by ORing with 0x0020. This casts
+                // a very wide net because it will change, e.g., '^' to '~'. But that should
+                // be ok because we expect this to be very rare in practice.
+
+                const uint NormalizeToLowercase = 0x0020_0020u; // valid both for big-endian and for little-endian
+
+                while (length > 2)
+                {
+                    length -= 4;
+                    // Where length is 4n-1 (e.g. 3,7,11,15,19) this additionally consumes the null terminator
+                    hash1 = (BitOperations.RotateLeft(hash1, 5) + hash1) ^ (ptr[0] | NormalizeToLowercase);
+                    hash2 = (BitOperations.RotateLeft(hash2, 5) + hash2) ^ (ptr[1] | NormalizeToLowercase);
+                    ptr += 2;
+                }
+
+                if (length > 0)
+                {
+                    // Where length is 4n-3 (e.g. 1,5,9,13,17) this additionally consumes the null terminator
+                    hash2 = (BitOperations.RotateLeft(hash2, 5) + hash2) ^ (ptr[0] | NormalizeToLowercase);
+                }
+
+                return (int)(hash1 + (hash2 * 1566083941));
+            }
+        }
+
         // Determines whether a specified string is a prefix of the current instance
         //
         public bool StartsWith(string value)
diff --git a/src/libraries/System.Private.CoreLib/src/System/String.cs b/src/libraries/System.Private.CoreLib/src/System/String.cs
index 49af25beb49c3b..54333a3c215d9a 100644
--- a/src/libraries/System.Private.CoreLib/src/System/String.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/String.cs
@@ -611,6 +611,7 @@ public StringRuneEnumerator EnumerateRunes()
         internal static unsafe int wcslen(char* ptr)
         {
             // IndexOf processes memory in aligned chunks, and thus it won't crash even if it accesses memory beyond the null terminator.
+            // This IndexOf behavior is an implementation detail of the runtime and callers outside System.Private.CoreLib must not depend on it.
             int length = SpanHelpers.IndexOf(ref *ptr, '\0', int.MaxValue);
             if (length < 0)
             {
@@ -624,6 +625,7 @@ internal static unsafe int wcslen(char* ptr)
         internal static unsafe int strlen(byte* ptr)
         {
             // IndexOf processes memory in aligned chunks, and thus it won't crash even if it accesses memory beyond the null terminator.
+            // This IndexOf behavior is an implementation detail of the runtime and callers outside System.Private.CoreLib must not depend on it.
             int length = SpanHelpers.IndexOf(ref *ptr, (byte)'\0', int.MaxValue);
             if (length < 0)
             {
diff --git a/src/libraries/System.Private.CoreLib/src/System/StringComparer.cs b/src/libraries/System.Private.CoreLib/src/System/StringComparer.cs
index e935c3d33163f4..39791cf55a61cf 100644
--- a/src/libraries/System.Private.CoreLib/src/System/StringComparer.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/StringComparer.cs
@@ -12,14 +12,9 @@ namespace System
     [System.Runtime.CompilerServices.TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
     public abstract class StringComparer : IComparer, IEqualityComparer, IComparer<string?>, IEqualityComparer<string?>
     {
-        private static readonly CultureAwareComparer s_invariantCulture = new CultureAwareComparer(CultureInfo.InvariantCulture, CompareOptions.None);
-        private static readonly CultureAwareComparer s_invariantCultureIgnoreCase = new CultureAwareComparer(CultureInfo.InvariantCulture, CompareOptions.IgnoreCase);
-        private static readonly OrdinalCaseSensitiveComparer s_ordinal = new OrdinalCaseSensitiveComparer();
-        private static readonly OrdinalIgnoreCaseComparer s_ordinalIgnoreCase = new OrdinalIgnoreCaseComparer();
+        public static StringComparer InvariantCulture => CultureAwareComparer.InvariantCaseSensitiveInstance;
 
-        public static StringComparer InvariantCulture => s_invariantCulture;
-
-        public static StringComparer InvariantCultureIgnoreCase => s_invariantCultureIgnoreCase;
+        public static StringComparer InvariantCultureIgnoreCase => CultureAwareComparer.InvariantIgnoreCaseInstance;
 
         public static StringComparer CurrentCulture =>
             new CultureAwareComparer(CultureInfo.CurrentCulture, CompareOptions.None);
@@ -27,9 +22,9 @@ public abstract class StringComparer : IComparer, IEqualityComparer, IComparer<s
         public static StringComparer CurrentCultureIgnoreCase =>
             new CultureAwareComparer(CultureInfo.CurrentCulture, CompareOptions.IgnoreCase);
 
-        public static StringComparer Ordinal => s_ordinal;
+        public static StringComparer Ordinal => OrdinalCaseSensitiveComparer.Instance;
 
-        public static StringComparer OrdinalIgnoreCase => s_ordinalIgnoreCase;
+        public static StringComparer OrdinalIgnoreCase => OrdinalIgnoreCaseComparer.Instance;
 
         // Convert a StringComparison to a StringComparer
         public static StringComparer FromComparison(StringComparison comparisonType)
@@ -128,6 +123,9 @@ public int GetHashCode(object obj)
     [System.Runtime.CompilerServices.TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
     public sealed class CultureAwareComparer : StringComparer, ISerializable
     {
+        internal static readonly CultureAwareComparer InvariantCaseSensitiveInstance = new CultureAwareComparer(CompareInfo.Invariant, CompareOptions.None);
+        internal static readonly CultureAwareComparer InvariantIgnoreCaseInstance = new CultureAwareComparer(CompareInfo.Invariant, CompareOptions.IgnoreCase);
+
         private const CompareOptions ValidCompareMaskOffFlags = ~(CompareOptions.IgnoreCase | CompareOptions.IgnoreSymbols | CompareOptions.IgnoreNonSpace | CompareOptions.IgnoreWidth | CompareOptions.IgnoreKanaType | CompareOptions.StringSort);
 
         private readonly CompareInfo _compareInfo; // Do not rename (binary serialization)
@@ -286,7 +284,9 @@ public override int GetHashCode()
     [Serializable]
     internal sealed class OrdinalCaseSensitiveComparer : OrdinalComparer, ISerializable
     {
-        public OrdinalCaseSensitiveComparer() : base(false)
+        internal static readonly OrdinalCaseSensitiveComparer Instance = new OrdinalCaseSensitiveComparer();
+
+        private OrdinalCaseSensitiveComparer() : base(false)
         {
         }
 
@@ -313,7 +313,9 @@ public void GetObjectData(SerializationInfo info, StreamingContext context)
     [Serializable]
     internal sealed class OrdinalIgnoreCaseComparer : OrdinalComparer, ISerializable
     {
-        public OrdinalIgnoreCaseComparer() : base(true)
+        internal static readonly OrdinalIgnoreCaseComparer Instance = new OrdinalIgnoreCaseComparer();
+
+        private OrdinalIgnoreCaseComparer() : base(true)
         {
         }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/ASCIIUtility.cs b/src/libraries/System.Private.CoreLib/src/System/Text/ASCIIUtility.cs
index 7628f6f89b45e8..76075a5e66dc48 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/ASCIIUtility.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/ASCIIUtility.cs
@@ -1003,6 +1003,16 @@ private static void NarrowFourUtf16CharsToAsciiAndWriteToBuffer(ref byte outputB
                 Vector128<uint> vecNarrow = Sse2.PackUnsignedSaturate(vecWide, vecWide).AsUInt32();
                 Unsafe.WriteUnaligned<uint>(ref outputBuffer, Sse2.ConvertToUInt32(vecNarrow));
             }
+            else if (AdvSimd.IsSupported)
+            {
+                // Narrows a vector of words [ w0 w1 w2 w3 ] to a vector of bytes
+                // [ b0 b1 b2 b3 * * * * ], then writes 4 bytes (32 bits) to the destination.
+
+                Vector128<short> vecWide = Vector128.CreateScalarUnsafe(value).AsInt16();
+                Vector64<byte> lower = AdvSimd.ExtractNarrowingSaturateUnsignedLower(vecWide);
+                Unsafe.WriteUnaligned<uint>(ref outputBuffer, lower.AsUInt32().ToScalar());
+            }
+
             else
             {
                 if (BitConverter.IsLittleEndian)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Latin1Encoding.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Latin1Encoding.cs
index 5ba1d6a902aa9e..01f6710a9632f5 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/Latin1Encoding.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/Latin1Encoding.cs
@@ -542,7 +542,7 @@ public unsafe override string GetString(byte[] bytes)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.bytes);
             }
 
-            return string.Create(bytes.Length, (encoding: this, bytes), (chars, args) =>
+            return string.Create(bytes.Length, (encoding: this, bytes), static (chars, args) =>
             {
                 Debug.Assert(chars.Length == args.bytes.Length);
 
@@ -577,7 +577,7 @@ public unsafe override string GetString(byte[] bytes, int index, int count)
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.bytes, ExceptionResource.ArgumentOutOfRange_IndexCountBuffer);
             }
 
-            return string.Create(count, (encoding: this, bytes, index), (chars, args) =>
+            return string.Create(count, (encoding: this, bytes, index), static (chars, args) =>
             {
                 fixed (byte* pBytes = args.bytes)
                 fixed (char* pChars = chars)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Rune.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Rune.cs
index f7dfd4c2c595d6..f2e1aa0c14acb2 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/Rune.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/Rune.cs
@@ -17,7 +17,7 @@ namespace System.Text
     /// assuming that the underlying <see cref="Rune"/> instance is well-formed.
     /// </remarks>
     [DebuggerDisplay("{DebuggerDisplay,nq}")]
-    public readonly struct Rune : IComparable<Rune>, IEquatable<Rune>
+    public readonly struct Rune : IComparable, IComparable<Rune>, IEquatable<Rune>
     {
         internal const int MaxUtf16CharsPerRune = 2; // supplementary plane code points are encoded as 2 UTF-16 code units
         internal const int MaxUtf8BytesPerRune = 4; // supplementary plane code points are encoded as 4 UTF-8 code units
@@ -269,7 +269,7 @@ private static Rune ChangeCaseCultureAware(Rune rune, CultureInfo culture, bool
         }
 #endif
 
-        public int CompareTo(Rune other) => _value.CompareTo(other._value);
+        public int CompareTo(Rune other) => this.Value - other.Value; // values don't span entire 32-bit domain; won't integer overflow
 
         /// <summary>
         /// Decodes the <see cref="Rune"/> at the beginning of the provided UTF-16 source buffer.
@@ -1437,5 +1437,21 @@ public static Rune ToUpperInvariant(Rune value)
             return ChangeCaseCultureAware(value, CultureInfo.InvariantCulture, toUpper: true);
 #endif
         }
+
+        /// <inheritdoc cref="IComparable.CompareTo" />
+        int IComparable.CompareTo(object? obj)
+        {
+            if (obj is null)
+            {
+                return 1; // non-null ("this") always sorts after null
+            }
+
+            if (obj is Rune other)
+            {
+                return this.CompareTo(other);
+            }
+
+            throw new ArgumentException(SR.Arg_MustBeRune);
+        }
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/StringBuilder.cs b/src/libraries/System.Private.CoreLib/src/System/Text/StringBuilder.cs
index 9e368e45e76f55..dfdf689194d0b0 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/StringBuilder.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/StringBuilder.cs
@@ -795,7 +795,6 @@ public StringBuilder Append(char[]? value, int startIndex, int charCount)
             }
         }
 
-
         /// <summary>
         /// Appends a string to the end of this builder.
         /// </summary>
@@ -808,9 +807,8 @@ public StringBuilder Append(string? value)
                 char[] chunkChars = m_ChunkChars;
                 int chunkLength = m_ChunkLength;
                 int valueLen = value.Length;
-                int newCurrentIndex = chunkLength + valueLen;
 
-                if (newCurrentIndex < chunkChars.Length) // Use strictly < to avoid issues if count == 0, newIndex == length
+                if (((uint)chunkLength + (uint)valueLen) < (uint)chunkChars.Length) // Use strictly < to avoid issues if count == 0, newIndex == length
                 {
                     if (valueLen <= 2)
                     {
@@ -835,7 +833,7 @@ public StringBuilder Append(string? value)
                         }
                     }
 
-                    m_ChunkLength = newCurrentIndex;
+                    m_ChunkLength = chunkLength + valueLen;
                 }
                 else
                 {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf16Utility.Validation.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf16Utility.Validation.cs
index cd4e6627d84455..f2df0ccdf53c42 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf16Utility.Validation.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf16Utility.Validation.cs
@@ -87,6 +87,11 @@ static Utf16Utility()
                     Vector128<ushort> vectorA800 = Vector128.Create((ushort)0xA800);
                     Vector128<short> vector8800 = Vector128.Create(unchecked((short)0x8800));
                     Vector128<ushort> vectorZero = Vector128<ushort>.Zero;
+
+                    Vector128<byte> bitMask128 = BitConverter.IsLittleEndian ?
+                        Vector128.Create(0x80402010_08040201).AsByte() :
+                        Vector128.Create(0x01020408_10204080).AsByte();
+
                     do
                     {
                         Vector128<ushort> utf16Data;
@@ -127,7 +132,7 @@ static Utf16Utility()
                         uint debugMask;
                         if (AdvSimd.Arm64.IsSupported)
                         {
-                            debugMask = GetNonAsciiBytes(charIsNonAscii.AsByte());
+                            debugMask = GetNonAsciiBytes(charIsNonAscii.AsByte(), bitMask128);
                         }
                         else
                         {
@@ -145,7 +150,7 @@ static Utf16Utility()
                         if (AdvSimd.IsSupported)
                         {
                             charIsThreeByteUtf8Encoded = AdvSimd.Subtract(vectorZero, AdvSimd.ShiftRightLogical(utf16Data, 11));
-                            mask = GetNonAsciiBytes(AdvSimd.Or(charIsNonAscii, charIsThreeByteUtf8Encoded).AsByte());
+                            mask = GetNonAsciiBytes(AdvSimd.Or(charIsNonAscii, charIsThreeByteUtf8Encoded).AsByte(), bitMask128);
                         }
                         else
                         {
@@ -185,7 +190,7 @@ static Utf16Utility()
                         if (AdvSimd.Arm64.IsSupported)
                         {
                             utf16Data = AdvSimd.Add(utf16Data, vectorA800);
-                            mask = GetNonAsciiBytes(AdvSimd.CompareLessThan(utf16Data.AsInt16(), vector8800).AsByte());
+                            mask = GetNonAsciiBytes(AdvSimd.CompareLessThan(utf16Data.AsInt16(), vector8800).AsByte(), bitMask128);
                         }
                         else
                         {
@@ -219,7 +224,7 @@ static Utf16Utility()
                             uint mask2;
                             if (AdvSimd.Arm64.IsSupported)
                             {
-                                mask2 = GetNonAsciiBytes(AdvSimd.ShiftRightLogical(utf16Data, 3).AsByte());
+                                mask2 = GetNonAsciiBytes(AdvSimd.ShiftRightLogical(utf16Data, 3).AsByte(), bitMask128);
                             }
                             else
                             {
@@ -480,17 +485,13 @@ static Utf16Utility()
             return pInputBuffer;
         }
 
-        private static readonly Vector128<byte> s_bitMask128 = BitConverter.IsLittleEndian ?
-                                                Vector128.Create(0x80402010_08040201).AsByte() :
-                                                Vector128.Create(0x01020408_10204080).AsByte();
-
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static uint GetNonAsciiBytes(Vector128<byte> value)
+        private static uint GetNonAsciiBytes(Vector128<byte> value, Vector128<byte> bitMask128)
         {
             Debug.Assert(AdvSimd.Arm64.IsSupported);
 
             Vector128<byte> mostSignificantBitIsSet = AdvSimd.ShiftRightArithmetic(value.AsSByte(), 7).AsByte();
-            Vector128<byte> extractedBits = AdvSimd.And(mostSignificantBitIsSet, s_bitMask128);
+            Vector128<byte> extractedBits = AdvSimd.And(mostSignificantBitIsSet, bitMask128);
 
             // self-pairwise add until all flags have moved to the first two bytes of the vector
             extractedBits = AdvSimd.Arm64.AddPairwise(extractedBits, extractedBits);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs
index ee9f789a40fab0..b0c1376611b9e7 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs
@@ -6,6 +6,7 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.Arm;
 using System.Runtime.Intrinsics.X86;
 
 #if SYSTEM_PRIVATE_CORELIB
@@ -882,7 +883,7 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
             // is not enabled.
 
             Unsafe.SkipInit(out Vector128<short> nonAsciiUtf16DataMask);
-            if (Sse41.X64.IsSupported)
+            if (Sse41.X64.IsSupported || (AdvSimd.Arm64.IsSupported && BitConverter.IsLittleEndian))
             {
                 nonAsciiUtf16DataMask = Vector128.Create(unchecked((short)0xFF80)); // mask of non-ASCII bits in a UTF-16 char
             }
@@ -940,10 +941,8 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
                     uint inputCharsRemaining = (uint)(pFinalPosWhereCanReadDWordFromInputBuffer - pInputBuffer) + 2;
                     uint minElementsRemaining = (uint)Math.Min(inputCharsRemaining, outputBytesRemaining);
 
-                    if (Sse41.X64.IsSupported)
+                    if (Sse41.X64.IsSupported || (AdvSimd.Arm64.IsSupported && BitConverter.IsLittleEndian))
                     {
-                        Debug.Assert(BitConverter.IsLittleEndian, "SSE41 requires little-endian.");
-
                         // Try reading and writing 8 elements per iteration.
                         uint maxIters = minElementsRemaining / 8;
                         ulong possibleNonAsciiQWord;
@@ -952,14 +951,30 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
                         for (i = 0; (uint)i < maxIters; i++)
                         {
                             utf16Data = Unsafe.ReadUnaligned<Vector128<short>>(pInputBuffer);
-                            if (!Sse41.TestZ(utf16Data, nonAsciiUtf16DataMask))
+
+                            if (AdvSimd.IsSupported)
                             {
-                                goto LoopTerminatedDueToNonAsciiDataInVectorLocal;
-                            }
+                                Vector128<short> isUtf16DataNonAscii = AdvSimd.CompareTest(utf16Data, nonAsciiUtf16DataMask);
+                                bool hasNonAsciiDataInVector = AdvSimd.Arm64.MinPairwise(isUtf16DataNonAscii, isUtf16DataNonAscii).AsUInt64().ToScalar() != 0;
 
-                            // narrow and write
+                                if (hasNonAsciiDataInVector)
+                                {
+                                    goto LoopTerminatedDueToNonAsciiDataInVectorLocal;
+                                }
 
-                            Sse2.StoreScalar((ulong*)pOutputBuffer /* unaligned */, Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt64());
+                                Vector64<byte> lower = AdvSimd.ExtractNarrowingSaturateUnsignedLower(utf16Data);
+                                AdvSimd.Store(pOutputBuffer, lower);
+                            }
+                            else
+                            {
+                                if (!Sse41.TestZ(utf16Data, nonAsciiUtf16DataMask))
+                                {
+                                    goto LoopTerminatedDueToNonAsciiDataInVectorLocal;
+                                }
+
+                                // narrow and write
+                                Sse2.StoreScalar((ulong*)pOutputBuffer /* unaligned */, Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt64());
+                            }
 
                             pInputBuffer += 8;
                             pOutputBuffer += 8;
@@ -978,7 +993,16 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
                             }
 
                             utf16Data = Vector128.CreateScalarUnsafe(possibleNonAsciiQWord).AsInt16();
-                            Unsafe.WriteUnaligned<uint>(pOutputBuffer, Sse2.ConvertToUInt32(Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt32()));
+
+                            if (AdvSimd.IsSupported)
+                            {
+                                Vector64<byte> lower = AdvSimd.ExtractNarrowingSaturateUnsignedLower(utf16Data);
+                                AdvSimd.StoreSelectedScalar((uint*)pOutputBuffer, lower.AsUInt32(), 0);
+                            }
+                            else
+                            {
+                                Unsafe.WriteUnaligned<uint>(pOutputBuffer, Sse2.ConvertToUInt32(Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt32()));
+                            }
 
                             pInputBuffer += 4;
                             pOutputBuffer += 4;
@@ -990,7 +1014,15 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
                     LoopTerminatedDueToNonAsciiDataInVectorLocal:
 
                         outputBytesRemaining -= 8 * i;
-                        possibleNonAsciiQWord = Sse2.X64.ConvertToUInt64(utf16Data.AsUInt64());
+
+                        if (Sse2.X64.IsSupported)
+                        {
+                            possibleNonAsciiQWord = Sse2.X64.ConvertToUInt64(utf16Data.AsUInt64());
+                        }
+                        else
+                        {
+                            possibleNonAsciiQWord = utf16Data.AsUInt64().ToScalar();
+                        }
 
                         // Temporarily set 'possibleNonAsciiQWord' to be the low 64 bits of the vector,
                         // then check whether it's all-ASCII. If so, narrow and write to the destination
@@ -1000,7 +1032,15 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
 
                         if (Utf16Utility.AllCharsInUInt64AreAscii(possibleNonAsciiQWord)) // all chars in first QWORD are ASCII
                         {
-                            Unsafe.WriteUnaligned<uint>(pOutputBuffer, Sse2.ConvertToUInt32(Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt32()));
+                            if (AdvSimd.IsSupported)
+                            {
+                                Vector64<byte> lower = AdvSimd.ExtractNarrowingSaturateUnsignedLower(utf16Data);
+                                AdvSimd.StoreSelectedScalar((uint*)pOutputBuffer, lower.AsUInt32(), 0);
+                            }
+                            else
+                            {
+                                Unsafe.WriteUnaligned<uint>(pOutputBuffer, Sse2.ConvertToUInt32(Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt32()));
+                            }
                             pInputBuffer += 4;
                             pOutputBuffer += 4;
                             outputBytesRemaining -= 4;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Validation.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Validation.cs
index 33e5181363920b..7730708030ebaf 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Validation.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Validation.cs
@@ -4,6 +4,8 @@
 using System.Diagnostics;
 using System.Numerics;
 using System.Runtime.CompilerServices;
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.Arm;
 using System.Runtime.Intrinsics.X86;
 
 #if SYSTEM_PRIVATE_CORELIB
@@ -117,22 +119,35 @@ internal static unsafe partial class Utf8Utility
                         // the alignment check consumes at most a single DWORD.)
 
                         byte* pInputBufferFinalPosAtWhichCanSafelyLoop = pFinalPosWhereCanReadDWordFromInputBuffer - 3 * sizeof(uint); // can safely read 4 DWORDs here
-                        uint mask;
+                        nuint trailingZeroCount;
+
+                        Vector128<byte> bitMask128 = BitConverter.IsLittleEndian ?
+                            Vector128.Create((ushort)0x1001).AsByte() :
+                            Vector128.Create((ushort)0x0110).AsByte();
 
                         do
                         {
-                            if (Sse2.IsSupported)
+                            // pInputBuffer is 32-bit aligned but not necessary 128-bit aligned, so we're
+                            // going to perform an unaligned load. We don't necessarily care about aligning
+                            // this because we pessimistically assume we'll encounter non-ASCII data at some
+                            // point in the not-too-distant future (otherwise we would've stayed entirely
+                            // within the all-ASCII vectorized code at the entry to this method).
+                            if (AdvSimd.Arm64.IsSupported && BitConverter.IsLittleEndian)
                             {
-                                // pInputBuffer is 32-bit aligned but not necessary 128-bit aligned, so we're
-                                // going to perform an unaligned load. We don't necessarily care about aligning
-                                // this because we pessimistically assume we'll encounter non-ASCII data at some
-                                // point in the not-too-distant future (otherwise we would've stayed entirely
-                                // within the all-ASCII vectorized code at the entry to this method).
-
-                                mask = (uint)Sse2.MoveMask(Sse2.LoadVector128((byte*)pInputBuffer));
+                                ulong mask = GetNonAsciiBytes(AdvSimd.LoadVector128(pInputBuffer), bitMask128);
+                                if (mask != 0)
+                                {
+                                    trailingZeroCount = (nuint)BitOperations.TrailingZeroCount(mask) >> 2;
+                                    goto LoopTerminatedEarlyDueToNonAsciiData;
+                                }
+                            }
+                            else if (Sse2.IsSupported)
+                            {
+                                uint mask = (uint)Sse2.MoveMask(Sse2.LoadVector128(pInputBuffer));
                                 if (mask != 0)
                                 {
-                                    goto Sse2LoopTerminatedEarlyDueToNonAsciiData;
+                                    trailingZeroCount = (nuint)BitOperations.TrailingZeroCount(mask);
+                                    goto LoopTerminatedEarlyDueToNonAsciiData;
                                 }
                             }
                             else
@@ -153,19 +168,20 @@ internal static unsafe partial class Utf8Utility
 
                         continue; // need to perform a bounds check because we might be running out of data
 
-                    Sse2LoopTerminatedEarlyDueToNonAsciiData:
+                    LoopTerminatedEarlyDueToNonAsciiData:
+                        // x86 can only be little endian, while ARM can be big or little endian
+                        // so if we reached this label we need to check both combinations are supported
+                        Debug.Assert((AdvSimd.Arm64.IsSupported && BitConverter.IsLittleEndian) || Sse2.IsSupported);
 
-                        Debug.Assert(BitConverter.IsLittleEndian);
-                        Debug.Assert(Sse2.IsSupported);
 
                         // The 'mask' value will have a 0 bit for each ASCII byte we saw and a 1 bit
-                        // for each non-ASCII byte we saw. We can count the number of ASCII bytes,
+                        // for each non-ASCII byte we saw. trailingZeroCount will count the number of ASCII bytes,
                         // bump our input counter by that amount, and resume processing from the
                         // "the first byte is no longer ASCII" portion of the main loop.
+                        // We should not expect a total number of zeroes equal or larger than 16.
+                        Debug.Assert(trailingZeroCount < 16);
 
-                        Debug.Assert(mask != 0);
-
-                        pInputBuffer += BitOperations.TrailingZeroCount(mask);
+                        pInputBuffer += trailingZeroCount;
                         if (pInputBuffer > pFinalPosWhereCanReadDWordFromInputBuffer)
                         {
                             goto ProcessRemainingBytesSlow;
@@ -719,5 +735,19 @@ internal static unsafe partial class Utf8Utility
             scalarCountAdjustment = tempScalarCountAdjustment;
             return pInputBuffer;
         }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static ulong GetNonAsciiBytes(Vector128<byte> value, Vector128<byte> bitMask128)
+        {
+            if (!AdvSimd.Arm64.IsSupported || !BitConverter.IsLittleEndian)
+            {
+                throw new PlatformNotSupportedException();
+            }
+
+            Vector128<byte> mostSignificantBitIsSet = AdvSimd.ShiftRightArithmetic(value.AsSByte(), 7).AsByte();
+            Vector128<byte> extractedBits = AdvSimd.And(mostSignificantBitIsSet, bitMask128);
+            extractedBits = AdvSimd.Arm64.AddPairwise(extractedBits, extractedBits);
+            return extractedBits.AsUInt64().ToScalar();
+        }
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Utf8Span.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Utf8Span.cs
index 83beddeff2e362..fcd6d4f92cb230 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/Utf8Span.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/Utf8Span.cs
@@ -275,7 +275,7 @@ internal unsafe string ToStringNoReplacement()
 
 #if (!NETSTANDARD2_0 && !NETFRAMEWORK)
                 // TODO_UTF8STRING: Can we call string.FastAllocate directly?
-                return string.Create(utf16CharCount, (pbData: (IntPtr)pData, cbData: Length), (chars, state) =>
+                return string.Create(utf16CharCount, (pbData: (IntPtr)pData, cbData: Length), static (chars, state) =>
                 {
                     OperationStatus status = Utf8.ToUtf16(new ReadOnlySpan<byte>((byte*)state.pbData, state.cbData), chars, out _, out _, replaceInvalidSequences: false);
                     Debug.Assert(status == OperationStatus.Done, "Did somebody mutate this Utf8String instance unexpectedly?");
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/AsyncLocal.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/AsyncLocal.cs
index 1a81b1dbc4227e..288ffbd32e6903 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/AsyncLocal.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/AsyncLocal.cs
@@ -86,8 +86,8 @@ internal interface IAsyncLocal
 
     public readonly struct AsyncLocalValueChangedArgs<T>
     {
-        [MaybeNull] public T PreviousValue { get; }
-        [MaybeNull] public T CurrentValue { get; }
+        public T? PreviousValue { get; }
+        public T? CurrentValue { get; }
 
         //
         // If the value changed because we changed to a different ExecutionContext, this is true.  If it changed
@@ -95,7 +95,7 @@ public readonly struct AsyncLocalValueChangedArgs<T>
         //
         public bool ThreadContextChanged { get; }
 
-        internal AsyncLocalValueChangedArgs([AllowNull] T previousValue, [AllowNull] T currentValue, bool contextChanged)
+        internal AsyncLocalValueChangedArgs(T? previousValue, T? currentValue, bool contextChanged)
         {
             PreviousValue = previousValue!;
             CurrentValue = currentValue!;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/CancellationTokenSource.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/CancellationTokenSource.cs
index b15c39dd93d1bc..d439fd3c29ec62 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/CancellationTokenSource.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/CancellationTokenSource.cs
@@ -681,7 +681,7 @@ private void ExecuteCallbackHandlers(bool throwOnFirstException)
                             if (node.SynchronizationContext != null)
                             {
                                 // Transition to the target syncContext and continue there.
-                                node.SynchronizationContext.Send(s =>
+                                node.SynchronizationContext.Send(static s =>
                                 {
                                     var n = (CallbackNode)s!;
                                     n.Partition.Source.ThreadIDExecutingCallbacks = Environment.CurrentManagedThreadId;
@@ -819,7 +819,7 @@ internal ValueTask WaitForCallbackToCompleteAsync(long id)
             // unfortunate thing to do.  However, we expect this to be a rare case (disposing while the associated
             // callback is running), and brief when it happens (so the polling will be minimal), and making
             // this work with a callback mechanism will add additional cost to other more common cases.
-            return new ValueTask(Task.Factory.StartNew(s =>
+            return new ValueTask(Task.Factory.StartNew(static s =>
             {
                 Debug.Assert(s is Tuple<CancellationTokenSource, long>);
                 var state = (Tuple<CancellationTokenSource, long>)s;
@@ -874,7 +874,7 @@ protected override void Dispose(bool disposing)
 
         private sealed class LinkedNCancellationTokenSource : CancellationTokenSource
         {
-            internal static readonly Action<object?> s_linkedTokenCancelDelegate = s =>
+            internal static readonly Action<object?> s_linkedTokenCancelDelegate = static s =>
             {
                 Debug.Assert(s is CancellationTokenSource, $"Expected {typeof(CancellationTokenSource)}, got {s}");
                 ((CancellationTokenSource)s).NotifyCancellation(throwOnFirstException: false); // skip ThrowIfDisposed() check in Cancel()
@@ -1028,7 +1028,7 @@ public void ExecuteCallback()
                 ExecutionContext? context = ExecutionContext;
                 if (context != null)
                 {
-                    ExecutionContext.RunInternal(context, s =>
+                    ExecutionContext.RunInternal(context, static s =>
                     {
                         Debug.Assert(s is CallbackNode, $"Expected {typeof(CallbackNode)}, got {s}");
                         CallbackNode n = (CallbackNode)s;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/EventWaitHandle.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/EventWaitHandle.cs
index 6d95be79f6ce3a..f17eaddb5d132b 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/EventWaitHandle.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/EventWaitHandle.cs
@@ -28,7 +28,7 @@ public EventWaitHandle(bool initialState, EventResetMode mode, string? name, out
             CreateEventCore(initialState, mode, name, out createdNew);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static EventWaitHandle OpenExisting(string name)
         {
             switch (OpenExistingWorker(name, out EventWaitHandle? result))
@@ -45,7 +45,7 @@ public static EventWaitHandle OpenExisting(string name)
             }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static bool TryOpenExisting(string name, [NotNullWhen(true)] out EventWaitHandle? result) =>
             OpenExistingWorker(name, out result!) == OpenExistingResult.Success;
     }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Semaphore.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Semaphore.cs
index 40555cc8dfda65..fb386e9e8be9d0 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Semaphore.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Semaphore.cs
@@ -33,7 +33,7 @@ public Semaphore(int initialCount, int maximumCount, string? name, out bool crea
             CreateSemaphoreCore(initialCount, maximumCount, name, out createdNew);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static Semaphore OpenExisting(string name)
         {
             switch (OpenExistingWorker(name, out Semaphore? result))
@@ -50,7 +50,7 @@ public static Semaphore OpenExisting(string name)
             }
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public static bool TryOpenExisting(string name, [NotNullWhen(true)] out Semaphore? result) =>
             OpenExistingWorker(name, out result!) == OpenExistingResult.Success;
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/SemaphoreSlim.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/SemaphoreSlim.cs
index f4fa69d1c2ec55..7b13c93c0b5592 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/SemaphoreSlim.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/SemaphoreSlim.cs
@@ -728,7 +728,7 @@ private async Task<bool> WaitUntilCountOrTimeoutAsync(TaskNode asyncWaiter, int
             {
                 // Wait until either the task is completed or cancellation is requested.
                 var cancellationTask = new Task(null, TaskCreationOptions.RunContinuationsAsynchronously, promiseStyle: true);
-                using (cancellationToken.UnsafeRegister(s => ((Task)s!).TrySetResult(), cancellationTask))
+                using (cancellationToken.UnsafeRegister(static s => ((Task)s!).TrySetResult(), cancellationTask))
                 {
                     if (asyncWaiter == await Task.WhenAny(asyncWaiter, cancellationTask).ConfigureAwait(false))
                     {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/SynchronizationContext.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/SynchronizationContext.cs
index cce3668bd58431..b3ed9d1b9691f9 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/SynchronizationContext.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/SynchronizationContext.cs
@@ -19,7 +19,7 @@ public SynchronizationContext()
 
         public virtual void Send(SendOrPostCallback d, object? state) => d(state);
 
-        public virtual void Post(SendOrPostCallback d, object? state) => ThreadPool.QueueUserWorkItem(s => s.d(s.state), (d, state), preferLocal: false);
+        public virtual void Post(SendOrPostCallback d, object? state) => ThreadPool.QueueUserWorkItem(static s => s.d(s.state), (d, state), preferLocal: false);
 
         /// <summary>
         ///     Optional override for subclasses, for responding to notification that operation is starting.
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
index 8537465a43bc1d..cec1ef48a1c090 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
@@ -197,7 +197,7 @@ private void CompleteTaskAsync()
             if (!cs.m_completionQueued)
             {
                 cs.m_completionQueued = true;
-                ThreadPool.QueueUserWorkItem(state =>
+                ThreadPool.QueueUserWorkItem(static state =>
                 {
                     Debug.Assert(state is ConcurrentExclusiveSchedulerPair);
                     var localThis = (ConcurrentExclusiveSchedulerPair)state;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Future.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Future.cs
index b993f263cc28a5..32dceb94def788 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Future.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Future.cs
@@ -59,7 +59,7 @@ namespace System.Threading.Tasks
     public class Task<TResult> : Task
     {
         // The value itself, if set.
-        [MaybeNull, AllowNull] internal TResult m_result = default!;
+        internal TResult? m_result;
 
         private static readonly TaskFactory<TResult> s_Factory = new TaskFactory<TResult>();
 
@@ -93,7 +93,7 @@ internal Task(TResult result) :
             m_result = result;
         }
 
-        internal Task(bool canceled, [AllowNull] TResult result, TaskCreationOptions creationOptions, CancellationToken ct)
+        internal Task(bool canceled, TResult? result, TaskCreationOptions creationOptions, CancellationToken ct)
             : base(canceled, creationOptions, ct)
         {
             if (!canceled)
@@ -364,7 +364,7 @@ internal static Task<TResult> StartNew(Task? parent, Func<object?, TResult> func
 
 
         // internal helper function breaks out logic used by TaskCompletionSource
-        internal bool TrySetResult([AllowNull] TResult result)
+        internal bool TrySetResult(TResult? result)
         {
             Debug.Assert(m_action == null, "Task<T>.TrySetResult(): non-null m_action");
 
@@ -1357,7 +1357,7 @@ public SystemThreadingTasks_FutureDebugView(Task<TResult> task)
             m_task = task;
         }
 
-        [MaybeNull] public TResult Result => m_task.Status == TaskStatus.RanToCompletion ? m_task.Result : default!;
+        public TResult? Result => m_task.Status == TaskStatus.RanToCompletion ? m_task.Result : default;
         public object? AsyncState => m_task.AsyncState;
         public TaskCreationOptions CreationOptions => m_task.CreationOptions;
         public Exception? Exception => m_task.Exception;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/FutureFactory.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/FutureFactory.cs
index 8049fd764b904f..b2ca3898176ce8 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/FutureFactory.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/FutureFactory.cs
@@ -1670,7 +1670,7 @@ internal static Task<TResult> ContinueWhenAllImpl(Task[] tasks,
             if (continuationFunction != null)
             {
                 return starter.ContinueWith(
-                    (completedTasks, state) =>
+                    static (completedTasks, state) =>
                     {
                         completedTasks.NotifyDebuggerOfWaitCompletionIfNecessary();
                         Debug.Assert(state is Func<Task[], TResult>);
@@ -1682,7 +1682,7 @@ internal static Task<TResult> ContinueWhenAllImpl(Task[] tasks,
             {
                 Debug.Assert(continuationAction != null);
                 return starter.ContinueWith<TResult>(
-                   (completedTasks, state) =>
+                   static (completedTasks, state) =>
                    {
                        completedTasks.NotifyDebuggerOfWaitCompletionIfNecessary();
                        Debug.Assert(state is Action<Task[]>);
@@ -1992,7 +1992,7 @@ internal static Task<TResult> ContinueWhenAnyImpl(Task[] tasks,
             if (continuationFunction != null)
             {
                 return starter.ContinueWith(
-                     (completedTask, state) =>
+                     static (completedTask, state) =>
                      {
                          Debug.Assert(state is Func<Task, TResult>);
                          return ((Func<Task, TResult>)state)(completedTask.Result);
@@ -2003,7 +2003,7 @@ internal static Task<TResult> ContinueWhenAnyImpl(Task[] tasks,
             {
                 Debug.Assert(continuationAction != null);
                 return starter.ContinueWith<TResult>(
-                    (completedTask, state) =>
+                    static (completedTask, state) =>
                     {
                         Debug.Assert(state is Action<Task>);
                         ((Action<Task>)state)(completedTask.Result);
@@ -2063,7 +2063,7 @@ internal static class GenericDelegateCache<TAntecedentResult, TResult>
     {
         // ContinueWith delegate for TaskFactory<TResult>.ContinueWhenAnyImpl<TAntecedentResult>(non-null continuationFunction)
         internal static Func<Task<Task>, object?, TResult> CWAnyFuncDelegate =
-            (Task<Task> wrappedWinner, object? state) =>
+            static (Task<Task> wrappedWinner, object? state) =>
             {
                 Debug.Assert(state is Func<Task<TAntecedentResult>, TResult>);
                 var func = (Func<Task<TAntecedentResult>, TResult>)state;
@@ -2073,7 +2073,7 @@ internal static class GenericDelegateCache<TAntecedentResult, TResult>
 
         // ContinueWith delegate for TaskFactory<TResult>.ContinueWhenAnyImpl<TAntecedentResult>(non-null continuationAction)
         internal static Func<Task<Task>, object?, TResult> CWAnyActionDelegate =
-            (Task<Task> wrappedWinner, object? state) =>
+            static (Task<Task> wrappedWinner, object? state) =>
             {
                 Debug.Assert(state is Action<Task<TAntecedentResult>>);
                 var action = (Action<Task<TAntecedentResult>>)state;
@@ -2084,7 +2084,7 @@ internal static class GenericDelegateCache<TAntecedentResult, TResult>
 
         // ContinueWith delegate for TaskFactory<TResult>.ContinueWhenAllImpl<TAntecedentResult>(non-null continuationFunction)
         internal static Func<Task<Task<TAntecedentResult>[]>, object?, TResult> CWAllFuncDelegate =
-            (Task<Task<TAntecedentResult>[]> wrappedAntecedents, object? state) =>
+            static (Task<Task<TAntecedentResult>[]> wrappedAntecedents, object? state) =>
             {
                 wrappedAntecedents.NotifyDebuggerOfWaitCompletionIfNecessary();
                 Debug.Assert(state is Func<Task<TAntecedentResult>[], TResult>);
@@ -2094,7 +2094,7 @@ internal static class GenericDelegateCache<TAntecedentResult, TResult>
 
         // ContinueWith delegate for TaskFactory<TResult>.ContinueWhenAllImpl<TAntecedentResult>(non-null continuationAction)
         internal static Func<Task<Task<TAntecedentResult>[]>, object?, TResult> CWAllActionDelegate =
-            (Task<Task<TAntecedentResult>[]> wrappedAntecedents, object? state) =>
+            static (Task<Task<TAntecedentResult>[]> wrappedAntecedents, object? state) =>
             {
                 wrappedAntecedents.NotifyDebuggerOfWaitCompletionIfNecessary();
                 Debug.Assert(state is Action<Task<TAntecedentResult>[]>);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ProducerConsumerQueues.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ProducerConsumerQueues.cs
index f067ffd44eb226..b1ef1c1b0339b6 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ProducerConsumerQueues.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ProducerConsumerQueues.cs
@@ -239,7 +239,7 @@ private bool TryDequeueSlow(ref Segment segment, ref T[] array, [MaybeNullWhen(f
 
             if (first == segment.m_state.m_last)
             {
-                result = default!;
+                result = default;
                 return false;
             }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Sources/ManualResetValueTaskSourceCore.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Sources/ManualResetValueTaskSourceCore.cs
index 734c1a605cedee..b9caa5392bcecb 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Sources/ManualResetValueTaskSourceCore.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Sources/ManualResetValueTaskSourceCore.cs
@@ -31,7 +31,7 @@ public struct ManualResetValueTaskSourceCore<TResult>
         /// <summary>Whether the current operation has completed.</summary>
         private bool _completed;
         /// <summary>The result with which the operation succeeded, or the default value if it hasn't yet completed or failed.</summary>
-        [AllowNull, MaybeNull] private TResult _result;
+        private TResult? _result;
         /// <summary>The exception with which the operation failed, or null if it hasn't yet completed or completed successfully.</summary>
         private ExceptionDispatchInfo? _error;
         /// <summary>The current version of this value, used to help prevent misuse.</summary>
@@ -98,7 +98,7 @@ public TResult GetResult(short token)
             }
 
             _error?.Throw();
-            return _result;
+            return _result!;
         }
 
         /// <summary>Schedules the continuation action for this operation.</summary>
@@ -173,7 +173,7 @@ public void OnCompleted(Action<object?> continuation, object? state, short token
                         break;
 
                     case SynchronizationContext sc:
-                        sc.Post(s =>
+                        sc.Post(static s =>
                         {
                             var tuple = (Tuple<Action<object?>, object?>)s!;
                             tuple.Item1(tuple.Item2);
@@ -318,7 +318,7 @@ private void InvokeSchedulerContinuation()
             switch (_capturedContext)
             {
                 case SynchronizationContext sc:
-                    sc.Post(s =>
+                    sc.Post(static s =>
                     {
                         var state = (Tuple<Action<object?>, object?>)s!;
                         state.Item1(state.Item2);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs
index fbf12c5cc4c488..3b34af008a2b85 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs
@@ -619,7 +619,7 @@ private void AssignCancellationToken(CancellationToken cancellationToken, Task?
                         if (antecedent == null)
                         {
                             // if no antecedent was specified, use this task's reference as the cancellation state object
-                            ctr = cancellationToken.UnsafeRegister(t => ((Task)t!).InternalCancel(), this);
+                            ctr = cancellationToken.UnsafeRegister(static t => ((Task)t!).InternalCancel(), this);
                         }
                         else
                         {
@@ -628,7 +628,7 @@ private void AssignCancellationToken(CancellationToken cancellationToken, Task?
                             // If an antecedent was specified, pack this task, its antecedent and the TaskContinuation together as a tuple
                             // and use it as the cancellation state object. This will be unpacked in the cancellation callback so that
                             // antecedent.RemoveCancellation(continuation) can be invoked.
-                            ctr = cancellationToken.UnsafeRegister(t =>
+                            ctr = cancellationToken.UnsafeRegister(static t =>
                             {
                                 var tuple = (Tuple<Task, Task, TaskContinuation>)t!;
 
@@ -1880,7 +1880,7 @@ internal static void ThrowAsync(Exception exception, SynchronizationContext? tar
                 try
                 {
                     // Post the throwing of the exception to that context, and return.
-                    targetContext.Post(state => ((ExceptionDispatchInfo)state!).Throw(), edi);
+                    targetContext.Post(static state => ((ExceptionDispatchInfo)state!).Throw(), edi);
                     return;
                 }
                 catch (Exception postException)
@@ -1895,7 +1895,7 @@ internal static void ThrowAsync(Exception exception, SynchronizationContext? tar
             RuntimeExceptionHelpers.ReportUnhandledException(edi.SourceException);
 #else
             // Propagate the exception(s) on the ThreadPool
-            ThreadPool.QueueUserWorkItem(state => ((ExceptionDispatchInfo)state!).Throw(), edi);
+            ThreadPool.QueueUserWorkItem(static state => ((ExceptionDispatchInfo)state!).Throw(), edi);
 
 #endif // CORERT
         }
@@ -5420,7 +5420,7 @@ internal DelayPromiseWithCancellation(int millisecondsDelay, CancellationToken t
                 Debug.Assert(token.CanBeCanceled);
 
                 _token = token;
-                _registration = token.UnsafeRegister(state => ((DelayPromiseWithCancellation)state!).CompleteCanceled(), this);
+                _registration = token.UnsafeRegister(static state => ((DelayPromiseWithCancellation)state!).CompleteCanceled(), this);
             }
 
             private void CompleteCanceled()
@@ -6590,7 +6590,7 @@ private void InvokeCoreAsync(Task completingTask)
             // there's a high liklihood this thread is going to be doing lots more work before
             // returning to the thread pool (at the very least unwinding through thousands of
             // stack frames).  So we queue to the global queue.
-            ThreadPool.UnsafeQueueUserWorkItem(state =>
+            ThreadPool.UnsafeQueueUserWorkItem(static state =>
             {
                 // InvokeCore(completingTask);
                 var tuple = (Tuple<UnwrapPromise<TResult>, Task>)state!;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TaskContinuation.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TaskContinuation.cs
index 9136bad1024087..f6a1627450597a 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TaskContinuation.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TaskContinuation.cs
@@ -364,7 +364,7 @@ internal override void Run(Task completedTask, bool canInlineContinuationTask)
     internal sealed class SynchronizationContextAwaitTaskContinuation : AwaitTaskContinuation
     {
         /// <summary>SendOrPostCallback delegate to invoke the action.</summary>
-        private static readonly SendOrPostCallback s_postCallback = state =>
+        private static readonly SendOrPostCallback s_postCallback = static state =>
         {
             Debug.Assert(state is Action);
             ((Action)state)();
@@ -490,7 +490,7 @@ internal sealed override void Run(Task ignored, bool canInlineContinuationTask)
 
                 // Create the continuation task task. If we're allowed to inline, try to do so.
                 // The target scheduler may still deny us from executing on this thread, in which case this'll be queued.
-                Task task = CreateTask(state =>
+                Task task = CreateTask(static state =>
                 {
                     try
                     {
@@ -664,7 +664,7 @@ void IThreadPoolWorkItem.Execute()
         }
 
         /// <summary>Cached delegate that invokes an Action passed as an object parameter.</summary>
-        private static readonly ContextCallback s_invokeContextCallback = (state) =>
+        private static readonly ContextCallback s_invokeContextCallback = static (state) =>
         {
             Debug.Assert(state is Action);
             ((Action)state)();
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TaskScheduler.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TaskScheduler.cs
index fce90d7289f372..e416fe36519957 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TaskScheduler.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TaskScheduler.cs
@@ -600,7 +600,7 @@ protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQu
         public override int MaximumConcurrencyLevel => 1;
 
         // preallocated SendOrPostCallback delegate
-        private static readonly SendOrPostCallback s_postCallback = s =>
+        private static readonly SendOrPostCallback s_postCallback = static s =>
         {
             Debug.Assert(s is Task);
             ((Task)s).ExecuteEntry(); // with double-execute check because SC could be buggy
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ThreadPoolTaskScheduler.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ThreadPoolTaskScheduler.cs
index d7e806bdcedbd0..dd502abd95f21b 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ThreadPoolTaskScheduler.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ThreadPoolTaskScheduler.cs
@@ -29,7 +29,7 @@ internal ThreadPoolTaskScheduler()
         }
 
         // static delegate for threads allocated to handle LongRunning tasks.
-        private static readonly ParameterizedThreadStart s_longRunningThreadWork = s =>
+        private static readonly ParameterizedThreadStart s_longRunningThreadWork = static s =>
         {
             Debug.Assert(s is Task);
             ((Task)s).ExecuteEntryUnsafe(threadPoolThread: null);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TplEventSource.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TplEventSource.cs
index 9b89c9ecf19b54..ea85eab23cfeea 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TplEventSource.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TplEventSource.cs
@@ -556,7 +556,7 @@ internal static Guid CreateGuidForTaskID(int taskID)
             // using the taskGuid, the appdomain ID, and 8 bytes of 'randomization' chosen by
             // using the last 8 bytes  as the provider GUID for this provider.
             // These were generated by CreateGuid, and are reasonably random (and thus unlikely to collide
-            uint pid = EventSource.s_currentPid;
+            int pid = Environment.ProcessId;
             return new Guid(taskID,
                             (short)DefaultAppDomainID, (short)(DefaultAppDomainID >> 16),
                             (byte)pid, (byte)(pid >> 8), (byte)(pid >> 16), (byte)(pid >> 24),
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ValueTask.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ValueTask.cs
index fbfecd11b13888..afc8f5a00f3a00 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ValueTask.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ValueTask.cs
@@ -231,7 +231,7 @@ private Task GetTaskForValueTaskSource(IValueTaskSource t)
         /// <summary>Type used to create a <see cref="Task"/> to represent a <see cref="IValueTaskSource"/>.</summary>
         private sealed class ValueTaskSourceAsTask : Task
         {
-            private static readonly Action<object?> s_completionAction = state =>
+            private static readonly Action<object?> s_completionAction = static state =>
             {
                 if (!(state is ValueTaskSourceAsTask vtst) ||
                     !(vtst._source is IValueTaskSource source))
@@ -445,7 +445,7 @@ public ConfiguredValueTaskAwaitable ConfigureAwait(bool continueOnCapturedContex
         /// <summary>null if <see cref="_result"/> has the result, otherwise a <see cref="Task{TResult}"/> or a <see cref="IValueTaskSource{TResult}"/>.</summary>
         internal readonly object? _obj;
         /// <summary>The result to be used if the operation completed successfully synchronously.</summary>
-        [AllowNull] internal readonly TResult _result;
+        internal readonly TResult? _result;
         /// <summary>Opaque value passed through to the <see cref="IValueTaskSource{TResult}"/>.</summary>
         internal readonly short _token;
         /// <summary>true to continue on the captured context; otherwise, false.</summary>
@@ -508,7 +508,7 @@ public ValueTask(IValueTaskSource<TResult> source, short token)
         /// <param name="token">The token.</param>
         /// <param name="continueOnCapturedContext">true to continue on captured context; otherwise, false.</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private ValueTask(object? obj, TResult result, short token, bool continueOnCapturedContext)
+        private ValueTask(object? obj, TResult? result, short token, bool continueOnCapturedContext)
         {
             _obj = obj;
             _result = result;
@@ -556,7 +556,7 @@ public Task<TResult> AsTask()
 
             if (obj == null)
             {
-                return AsyncTaskMethodBuilder<TResult>.GetTaskForResult(_result);
+                return AsyncTaskMethodBuilder<TResult>.GetTaskForResult(_result!);
             }
 
             if (obj is Task<TResult> t)
@@ -623,7 +623,7 @@ private Task<TResult> GetTaskForValueTaskSource(IValueTaskSource<TResult> t)
         /// <summary>Type used to create a <see cref="Task{TResult}"/> to represent a <see cref="IValueTaskSource{TResult}"/>.</summary>
         private sealed class ValueTaskSourceAsTask : Task<TResult>
         {
-            private static readonly Action<object?> s_completionAction = state =>
+            private static readonly Action<object?> s_completionAction = static state =>
             {
                 if (!(state is ValueTaskSourceAsTask vtst) ||
                     !(vtst._source is IValueTaskSource<TResult> source))
@@ -781,7 +781,7 @@ public TResult Result
 
                 if (obj == null)
                 {
-                    return _result;
+                    return _result!;
                 }
 
                 if (obj is Task<TResult> t)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Thread.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Thread.cs
index f468e6cab13a8e..ba36c3f14fa307 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Thread.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Thread.cs
@@ -227,7 +227,7 @@ public ApartmentState ApartmentState
             set => TrySetApartmentState(value);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public void SetApartmentState(ApartmentState state)
         {
             if (!TrySetApartmentState(state))
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadLocal.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadLocal.cs
index 2d0c67cc605e02..4d7188e8580692 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadLocal.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadLocal.cs
@@ -305,8 +305,7 @@ public T Value
             }
         }
 
-        [return: MaybeNull]
-        private T GetValueSlow()
+        private T? GetValueSlow()
         {
             // If the object has been disposed, the id will be -1.
             int id = ~_idComplement;
@@ -538,8 +537,7 @@ public bool IsValueCreated
 
         /// <summary>Gets the value of the ThreadLocal&lt;T&gt; for debugging display purposes. It takes care of getting
         /// the value for the current thread in the ThreadLocal mode.</summary>
-        [MaybeNull]
-        internal T ValueForDebugDisplay
+        internal T? ValueForDebugDisplay
         {
             get
             {
@@ -548,7 +546,7 @@ internal T ValueForDebugDisplay
 
                 LinkedSlot? slot;
                 if (slotArray == null || id >= slotArray.Length || (slot = slotArray[id].Value) == null || !_initialized)
-                    return default!;
+                    return default;
                 return slot._value;
             }
         }
@@ -672,7 +670,7 @@ internal LinkedSlot(LinkedSlotVolatile[]? slotArray)
             internal volatile LinkedSlotVolatile[]? _slotArray;
 
             // The value for this slot.
-            [AllowNull, MaybeNull] internal T _value = default;
+            internal T? _value;
         }
 
         /// <summary>
@@ -804,8 +802,7 @@ public SystemThreading_ThreadLocalDebugView(ThreadLocal<T> tlocal)
         public bool IsValueCreated => _tlocal.IsValueCreated;
 
         /// <summary>Returns the value of the ThreadLocal object.</summary>
-        [MaybeNull]
-        public T Value => _tlocal.ValueForDebugDisplay;
+        public T? Value => _tlocal.ValueForDebugDisplay;
 
         /// <summary>Return all values for all threads that have accessed this instance.</summary>
         public List<T>? Values => _tlocal.ValuesForDebugDisplay;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPool.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPool.cs
index 4ff85f148998e1..4bcf665b9a6ca3 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPool.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPool.cs
@@ -938,7 +938,7 @@ public static partial class ThreadPool
         internal static readonly ThreadPoolWorkQueue s_workQueue = new ThreadPoolWorkQueue();
 
         /// <summary>Shim used to invoke <see cref="IAsyncStateMachineBox.MoveNext"/> of the supplied <see cref="IAsyncStateMachineBox"/>.</summary>
-        internal static readonly Action<object?> s_invokeAsyncStateMachineBox = state =>
+        internal static readonly Action<object?> s_invokeAsyncStateMachineBox = static state =>
         {
             if (!(state is IAsyncStateMachineBox box))
             {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Timer.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Timer.cs
index 95c146de38b0cf..6486053794a5f5 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Timer.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Timer.cs
@@ -639,7 +639,7 @@ internal void CallCallback(bool isThreadPool)
             }
         }
 
-        private static readonly ContextCallback s_callCallbackInContext = state =>
+        private static readonly ContextCallback s_callCallbackInContext = static state =>
         {
             Debug.Assert(state is TimerQueueTimer);
             var t = (TimerQueueTimer)state;
diff --git a/src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs b/src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs
index 9d43ddf5d5139c..b9b2d3831bb2c4 100644
--- a/src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs
@@ -796,7 +796,7 @@ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones()
                     }
 
                     // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
-                    list.Sort((x, y) =>
+                    list.Sort(static (x, y) =>
                     {
                         // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
                         int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Type.Helpers.cs b/src/libraries/System.Private.CoreLib/src/System/Type.Helpers.cs
index 491f7ac437cf14..d28dcd8b0b07a6 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Type.Helpers.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Type.Helpers.cs
@@ -304,7 +304,7 @@ public virtual MemberInfo[] FindMembers(MemberTypes memberType, BindingFlags bin
             {
                 for (i = 0; i < e.Length; i++)
                     if (e[i] != null)
-                        ret[cnt++] = e[i]!;  // TODO-NULLABLE: Indexer nullability tracked (https://github.com/dotnet/roslyn/issues/34644)
+                        ret[cnt++] = e[i]!; // TODO-NULLABLE: Indexer nullability tracked (https://github.com/dotnet/roslyn/issues/34644)
             }
 
             // Copy the Types
@@ -312,7 +312,7 @@ public virtual MemberInfo[] FindMembers(MemberTypes memberType, BindingFlags bin
             {
                 for (i = 0; i < t.Length; i++)
                     if (t[i] != null)
-                        ret[cnt++] = t[i]!;  // TODO-NULLABLE: Indexer nullability tracked (https://github.com/dotnet/roslyn/issues/34644)
+                        ret[cnt++] = t[i]!; // TODO-NULLABLE: Indexer nullability tracked (https://github.com/dotnet/roslyn/issues/34644)
             }
 
             return ret;
diff --git a/src/libraries/System.Private.DataContractSerialization/Directory.Build.props b/src/libraries/System.Private.DataContractSerialization/Directory.Build.props
index 8c72c62fd5932e..63f02a0f817ef2 100644
--- a/src/libraries/System.Private.DataContractSerialization/Directory.Build.props
+++ b/src/libraries/System.Private.DataContractSerialization/Directory.Build.props
@@ -2,7 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
-    <IsNETCoreAppRef>false</IsNETCoreAppRef>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Private.DataContractSerialization/src/System.Private.DataContractSerialization.csproj b/src/libraries/System.Private.DataContractSerialization/src/System.Private.DataContractSerialization.csproj
index 2252cd2cdc1216..7ab4ab7cd8d07f 100644
--- a/src/libraries/System.Private.DataContractSerialization/src/System.Private.DataContractSerialization.csproj
+++ b/src/libraries/System.Private.DataContractSerialization/src/System.Private.DataContractSerialization.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Private.DataContractSerialization</AssemblyName>
-    <RootNamespace>System.Private.DataContractSerialization</RootNamespace>
     <NoWarn>$(NoWarn);1634;1691;649</NoWarn>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DebugSymbols>true</DebugSymbols>
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/Directory.Build.props b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/Directory.Build.props
similarity index 80%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/Directory.Build.props
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/Directory.Build.props
+++ b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/System.Runtime.InteropServices.JavaScript.sln b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/System.Private.Runtime.InteropServices.JavaScript.sln
similarity index 89%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/System.Runtime.InteropServices.JavaScript.sln
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/System.Private.Runtime.InteropServices.JavaScript.sln
index 1a0db563634ee7..eacf0032df3a19 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/System.Runtime.InteropServices.JavaScript.sln
+++ b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/System.Private.Runtime.InteropServices.JavaScript.sln
@@ -6,12 +6,12 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{1A2F9F4A
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{E107E9C1-E893-4E87-987E-04EF0DCEAEFD}"
 EndProject
-Project("{9344BDBB-3E7F-41FC-A0DD-8665D75EE146}") = "System.Runtime.InteropServices.JavaScript.Tests", "tests\System.Runtime.InteropServices.JavaScript.Tests.csproj", "{4F753464-0719-4559-9E0F-86175CECA903}"
+Project("{9344BDBB-3E7F-41FC-A0DD-8665D75EE146}") = "System.Private.Runtime.InteropServices.JavaScript.Tests", "tests\System.Private.Runtime.InteropServices.JavaScript.Tests.csproj", "{4F753464-0719-4559-9E0F-86175CECA903}"
 	ProjectSection(ProjectDependencies) = postProject
 		{644FCC7F-1478-4D30-BF66-40E0ADF8723C} = {644FCC7F-1478-4D30-BF66-40E0ADF8723C}
 	EndProjectSection
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "System.Runtime.InteropServices.JavaScript", "src\System.Runtime.InteropServices.JavaScript.csproj", "{644FCC7F-1478-4D30-BF66-40E0ADF8723C}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "System.Private.Runtime.InteropServices.JavaScript", "src\System.Private.Runtime.InteropServices.JavaScript.csproj", "{644FCC7F-1478-4D30-BF66-40E0ADF8723C}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/ILLinkTrim.xml b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/ILLinkTrim.xml
similarity index 60%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/ILLinkTrim.xml
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/ILLinkTrim.xml
index 67f100eb7747ff..7587cdc31bb9c4 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/ILLinkTrim.xml
+++ b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/ILLinkTrim.xml
@@ -1,5 +1,5 @@
 <linker>
-    <assembly fullname="System.Runtime.InteropServices.JavaScript">
+    <assembly fullname="System.Private.Runtime.InteropServices.JavaScript">
         <type fullname="System.Runtime.InteropServices.JavaScript.Runtime" />
     </assembly>
 </linker>
diff --git a/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/Resources/Strings.resx b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/Resources/Strings.resx
new file mode 100644
index 00000000000000..8d3b3f1694f092
--- /dev/null
+++ b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/Resources/Strings.resx
@@ -0,0 +1,123 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <!-- 
+    Microsoft ResX Schema 
+    
+    Version 2.0
+    
+    The primary goals of this format is to allow a simple XML format 
+    that is mostly human readable. The generation and parsing of the 
+    various data types are done through the TypeConverter classes 
+    associated with the data types.
+    
+    Example:
+    
+    ... ado.net/XML headers & schema ...
+    <resheader name="resmimetype">text/microsoft-resx</resheader>
+    <resheader name="version">2.0</resheader>
+    <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>
+    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>
+    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>
+    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>
+    <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">
+        <value>[base64 mime encoded serialized .NET Framework object]</value>
+    </data>
+    <data name="Icon1" type="System.Drawing.Icon, System.Drawing" mimetype="application/x-microsoft.net.object.bytearray.base64">
+        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
+        <comment>This is a comment</comment>
+    </data>
+                
+    There are any number of "resheader" rows that contain simple 
+    name/value pairs.
+    
+    Each data row contains a name, and value. The row also contains a 
+    type or mimetype. Type corresponds to a .NET class that support 
+    text/value conversion through the TypeConverter architecture. 
+    Classes that don't support this are serialized and stored with the 
+    mimetype set.
+    
+    The mimetype is used for serialized objects, and tells the 
+    ResXResourceReader how to depersist the object. This is currently not 
+    extensible. For a given mimetype the value must be set accordingly:
+    
+    Note - application/x-microsoft.net.object.binary.base64 is the format 
+    that the ResXResourceWriter will generate, however the reader can 
+    read any of the formats listed below.
+    
+    mimetype: application/x-microsoft.net.object.binary.base64
+    value   : The object must be serialized with 
+            : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
+            : and then encoded with base64 encoding.
+    
+    mimetype: application/x-microsoft.net.object.soap.base64
+    value   : The object must be serialized with 
+            : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
+            : and then encoded with base64 encoding.
+
+    mimetype: application/x-microsoft.net.object.bytearray.base64
+    value   : The object must be serialized into a byte array 
+            : using a System.ComponentModel.TypeConverter
+            : and then encoded with base64 encoding.
+    -->
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />
+    <xsd:element name="root" msdata:IsDataSet="true">
+      <xsd:complexType>
+        <xsd:choice maxOccurs="unbounded">
+          <xsd:element name="metadata">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" />
+              </xsd:sequence>
+              <xsd:attribute name="name" use="required" type="xsd:string" />
+              <xsd:attribute name="type" type="xsd:string" />
+              <xsd:attribute name="mimetype" type="xsd:string" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="assembly">
+            <xsd:complexType>
+              <xsd:attribute name="alias" type="xsd:string" />
+              <xsd:attribute name="name" type="xsd:string" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="data">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />
+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />
+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="resheader">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" />
+            </xsd:complexType>
+          </xsd:element>
+        </xsd:choice>
+      </xsd:complexType>
+    </xsd:element>
+  </xsd:schema>
+  <resheader name="resmimetype">
+    <value>text/microsoft-resx</value>
+  </resheader>
+  <resheader name="version">
+    <value>2.0</value>
+  </resheader>
+  <resheader name="reader">
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <resheader name="writer">
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <data name="SystemRuntimeInteropServicesJavaScript_PlatformNotSupported" xml:space="preserve">
+    <value>System.Private.Runtime.InteropServices.JavaScript is not supported on this platform.</value>
+  </data>
+</root>
\ No newline at end of file
diff --git a/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System.Private.Runtime.InteropServices.JavaScript.csproj b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System.Private.Runtime.InteropServices.JavaScript.csproj
new file mode 100644
index 00000000000000..778b0ec31bf687
--- /dev/null
+++ b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System.Private.Runtime.InteropServices.JavaScript.csproj
@@ -0,0 +1,49 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <Nullable>enable</Nullable>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Browser</TargetFrameworks>
+  </PropertyGroup>
+  <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
+  <PropertyGroup Condition="'$(TargetsBrowser)' == 'true'">
+    <!-- The Browser build currently doesn't use any strings from SR, so don't include it until it does. -->
+    <OmitResources>true</OmitResources>
+    <GenerateResourcesSubstitutions>false</GenerateResourcesSubstitutions>
+  </PropertyGroup>
+  <ItemGroup Condition="'$(TargetsBrowser)' == 'true'">
+    <Compile Include="$(CommonPath)Interop\Browser\Interop.Runtime.cs" Link="Common\Interop\Browser\Interop.Runtime.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Runtime.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\JSException.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\JSObject.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\DataView.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Float32Array.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Float64Array.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Int8Array.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Int16Array.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Int32Array.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Uint8Array.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Uint16Array.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Uint32Array.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Uint8ClampedArray.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\TypedArray.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Array.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\ArrayBuffer.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\SharedArrayBuffer.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Map.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\CoreObject.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\HostObject.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Function.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\AnyRef.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <Reference Include="System.Runtime" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetsBrowser)' == 'true'">
+    <Reference Include="System.Collections" />
+    <Reference Include="System.Memory" />
+    <Reference Include="System.Net.Primitives" />
+    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
+    <Reference Include="System.Runtime.InteropServices" />
+    <Reference Include="System.Threading" />
+  </ItemGroup>
+</Project>
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/AnyRef.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/AnyRef.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/AnyRef.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/AnyRef.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Array.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Array.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Array.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Array.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/ArrayBuffer.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/ArrayBuffer.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/ArrayBuffer.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/ArrayBuffer.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/CoreObject.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/CoreObject.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/CoreObject.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/CoreObject.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/DataView.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/DataView.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/DataView.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/DataView.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Float32Array.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Float32Array.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Float32Array.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Float32Array.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Float64Array.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Float64Array.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Float64Array.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Float64Array.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Function.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Function.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Function.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Function.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/HostObject.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/HostObject.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/HostObject.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/HostObject.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int16Array.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int16Array.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int16Array.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int16Array.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int32Array.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int32Array.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int32Array.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int32Array.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int8Array.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int8Array.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int8Array.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Int8Array.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSException.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSException.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSException.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSException.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSObject.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSObject.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSObject.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSObject.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Map.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Map.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Map.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Map.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Runtime.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Runtime.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Runtime.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Runtime.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/SharedArrayBuffer.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/SharedArrayBuffer.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/SharedArrayBuffer.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/SharedArrayBuffer.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/TypedArray.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/TypedArray.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/TypedArray.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/TypedArray.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint16Array.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint16Array.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint16Array.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint16Array.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint32Array.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint32Array.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint32Array.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint32Array.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint8Array.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint8Array.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint8Array.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint8Array.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint8ClampedArray.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint8ClampedArray.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint8ClampedArray.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Uint8ClampedArray.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/AssemblyInfo.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/AssemblyInfo.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/tests/AssemblyInfo.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/AssemblyInfo.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.Tests.csproj b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System.Private.Runtime.InteropServices.JavaScript.Tests.csproj
similarity index 69%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.Tests.csproj
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System.Private.Runtime.InteropServices.JavaScript.Tests.csproj
index 0bb06264f93e83..20ae0d4a72159d 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.Tests.csproj
+++ b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System.Private.Runtime.InteropServices.JavaScript.Tests.csproj
@@ -1,13 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppCurrent)-Browser</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Browser</TargetFrameworks>
     <TestRuntime>true</TestRuntime>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="AssemblyInfo.cs" />
   </ItemGroup>
-  <ItemGroup Condition=" '$(TargetsBrowser)' == 'true'">
+  <ItemGroup>
     <Compile Include="System\Runtime\InteropServices\JavaScript\JavaScriptTests.cs" />
     <Compile Include="System\Runtime\InteropServices\JavaScript\DataViewTests.cs" />
     <Compile Include="System\Runtime\InteropServices\JavaScript\TypedArrayTests.cs" />
@@ -15,5 +15,10 @@
     <!-- <Compile Include="System\Runtime\InteropServices\JavaScript\MapTests.cs" /> -->
     <Compile Include="System\Runtime\InteropServices\JavaScript\MarshalTests.cs" />
     <Compile Include="System\Runtime\InteropServices\JavaScript\HelperMarshal.cs" />
+    <Compile Include="System\Runtime\InteropServices\JavaScript\Http\HttpRequestMessageTest.cs" />    
+  </ItemGroup>
+  <ItemGroup>
+    <!-- Part of the shared framework but not exposed. -->
+    <ProjectReference Include="..\src\System.Private.Runtime.InteropServices.JavaScript.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/ArrayTests.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/ArrayTests.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/ArrayTests.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/ArrayTests.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/DataViewTests.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/DataViewTests.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/DataViewTests.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/DataViewTests.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/HelperMarshal.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/HelperMarshal.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/HelperMarshal.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/HelperMarshal.cs
diff --git a/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/Http/HttpRequestMessageTest.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/Http/HttpRequestMessageTest.cs
new file mode 100644
index 00000000000000..80a8cd126f1562
--- /dev/null
+++ b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/Http/HttpRequestMessageTest.cs
@@ -0,0 +1,376 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Generic;
+using System.IO;
+using System.Net.Http.Headers;
+using System.Net.Http;
+using System.Net;
+using System.Threading.Tasks;
+
+using Xunit;
+using Xunit.Abstractions;
+
+namespace System.Runtime.InteropServices.JavaScript.Http.Tests
+{
+    public class HttpRequestMessageTest
+    {
+        private readonly Version _expectedRequestMessageVersion = HttpVersion.Version11;
+        private HttpRequestOptionsKey<bool> EnableStreamingResponse = new HttpRequestOptionsKey<bool>("WebAssemblyEnableStreamingResponse");
+#nullable enable        
+        private HttpRequestOptionsKey<IDictionary<string, object?>> FetchOptions = new HttpRequestOptionsKey<IDictionary<string, object?>>("WebAssemblyFetchOptions");
+#nullable disable
+
+        [Fact]
+        public void Ctor_Default_CorrectDefaults()
+        {
+            var rm = new HttpRequestMessage();
+
+            Assert.Equal(HttpMethod.Get, rm.Method);
+            Assert.Null(rm.Content);
+            Assert.Null(rm.RequestUri);
+        }
+
+        [Fact]
+        public void Ctor_RelativeStringUri_CorrectValues()
+        {
+            var rm = new HttpRequestMessage(HttpMethod.Post, "/relative");
+
+            Assert.Equal(HttpMethod.Post, rm.Method);
+            Assert.Equal(_expectedRequestMessageVersion, rm.Version);
+            Assert.Null(rm.Content);
+            Assert.Equal(new Uri("/relative", UriKind.Relative), rm.RequestUri);
+        }
+
+        [Fact]
+        public void Ctor_AbsoluteStringUri_CorrectValues()
+        {
+            var rm = new HttpRequestMessage(HttpMethod.Post, "http://host/absolute/");
+
+            Assert.Equal(HttpMethod.Post, rm.Method);
+            Assert.Equal(_expectedRequestMessageVersion, rm.Version);
+            Assert.Null(rm.Content);
+            Assert.Equal(new Uri("http://host/absolute/"), rm.RequestUri);
+        }
+
+        [Fact]
+        public void Ctor_NullStringUri_Accepted()
+        {
+            var rm = new HttpRequestMessage(HttpMethod.Put, (string)null);
+
+            Assert.Null(rm.RequestUri);
+            Assert.Equal(HttpMethod.Put, rm.Method);
+            Assert.Equal(_expectedRequestMessageVersion, rm.Version);
+            Assert.Null(rm.Content);
+        }
+
+        [Fact]
+        public void Ctor_RelativeUri_CorrectValues()
+        {
+            var uri = new Uri("/relative", UriKind.Relative);
+            var rm = new HttpRequestMessage(HttpMethod.Post, uri);
+
+            Assert.Equal(HttpMethod.Post, rm.Method);
+            Assert.Equal(_expectedRequestMessageVersion, rm.Version);
+            Assert.Null(rm.Content);
+            Assert.Equal(uri, rm.RequestUri);
+        }
+
+        [Fact]
+        public void Ctor_AbsoluteUri_CorrectValues()
+        {
+            var uri = new Uri("http://host/absolute/");
+            var rm = new HttpRequestMessage(HttpMethod.Post, uri);
+
+            Assert.Equal(HttpMethod.Post, rm.Method);
+            Assert.Equal(_expectedRequestMessageVersion, rm.Version);
+            Assert.Null(rm.Content);
+            Assert.Equal(uri, rm.RequestUri);
+        }
+
+        [Fact]
+        public void Ctor_NullUri_Accepted()
+        {
+            var rm = new HttpRequestMessage(HttpMethod.Put, (Uri)null);
+
+            Assert.Null(rm.RequestUri);
+            Assert.Equal(HttpMethod.Put, rm.Method);
+            Assert.Equal(_expectedRequestMessageVersion, rm.Version);
+            Assert.Null(rm.Content);
+        }
+
+        [Fact]
+        public void Ctor_NullMethod_ThrowsArgumentNullException()
+        {
+            Assert.Throws<ArgumentNullException>(() => new HttpRequestMessage(null, "http://example.com"));
+        }
+
+        [Fact]
+        public void Ctor_NonHttpUri_ThrowsArgumentException()
+        {
+            AssertExtensions.Throws<ArgumentException>("requestUri", () => new HttpRequestMessage(HttpMethod.Put, "ftp://example.com"));
+        }
+
+        [Fact]
+        public void Dispose_DisposeObject_ContentGetsDisposedAndSettersWillThrowButGettersStillWork()
+        {
+            var rm = new HttpRequestMessage(HttpMethod.Get, "http://example.com");
+            var content = new MockContent();
+            rm.Content = content;
+            Assert.False(content.IsDisposed);
+
+            rm.Dispose();
+            rm.Dispose(); // Multiple calls don't throw.
+
+            Assert.True(content.IsDisposed);
+            Assert.Throws<ObjectDisposedException>(() => { rm.Method = HttpMethod.Put; });
+            Assert.Throws<ObjectDisposedException>(() => { rm.RequestUri = null; });
+            Assert.Throws<ObjectDisposedException>(() => { rm.Version = new Version(1, 0); });
+            Assert.Throws<ObjectDisposedException>(() => { rm.Content = null; });
+
+            // Property getters should still work after disposing.
+            Assert.Equal(HttpMethod.Get, rm.Method);
+            Assert.Equal(new Uri("http://example.com"), rm.RequestUri);
+            Assert.Equal(_expectedRequestMessageVersion, rm.Version);
+            Assert.Equal(content, rm.Content);
+        }
+
+        [Fact]
+        public void Properties_SetOptionsAndGetTheirValue_MatchingValues()
+        {
+            var rm = new HttpRequestMessage();
+
+            var content = new MockContent();
+            var uri = new Uri("https://example.com");
+            var version = new Version(1, 0);
+            var method = new HttpMethod("custom");
+
+            rm.Content = content;
+            rm.Method = method;
+            rm.RequestUri = uri;
+            rm.Version = version;
+
+            Assert.Equal(content, rm.Content);
+            Assert.Equal(uri, rm.RequestUri);
+            Assert.Equal(method, rm.Method);
+            Assert.Equal(version, rm.Version);
+
+            Assert.NotNull(rm.Headers);
+            Assert.NotNull(rm.Options);
+        }
+
+#nullable enable
+        [Fact]
+        public void Properties_SetOptionsAndGetTheirValue_Set_FetchOptions()
+        {
+            var rm = new HttpRequestMessage();
+
+            var content = new MockContent();
+            var uri = new Uri("https://example.com");
+            var version = new Version(1, 0);
+            var method = new HttpMethod("custom");
+
+            rm.Content = content;
+            rm.Method = method;
+            rm.RequestUri = uri;
+            rm.Version = version;
+            
+            var fetchme = new Dictionary<string, object?>();
+            fetchme.Add("hic", null);
+            fetchme.Add("sunt", 4444);
+            fetchme.Add("dracones", new List<string>());
+            rm.Options.Set(FetchOptions, fetchme);
+
+            Assert.Equal(content, rm.Content);
+            Assert.Equal(uri, rm.RequestUri);
+            Assert.Equal(method, rm.Method);
+            Assert.Equal(version, rm.Version);
+
+            Assert.NotNull(rm.Headers);
+            Assert.NotNull(rm.Options);
+
+            rm.Options.TryGetValue(FetchOptions, out IDictionary<string, object?>? fetchOptionsValue);
+            Assert.NotNull(fetchOptionsValue);
+            if (fetchOptionsValue != null)
+            {
+                foreach (var item in fetchOptionsValue)
+                {
+                    Assert.True(fetchme.ContainsKey(item.Key));
+                }
+            }
+        }
+#nullable disable
+
+#nullable enable
+        [Fact]
+        public void Properties_SetOptionsAndGetTheirValue_NotSet_FetchOptions()
+        {
+            var rm = new HttpRequestMessage();
+
+            var content = new MockContent();
+            var uri = new Uri("https://example.com");
+            var version = new Version(1, 0);
+            var method = new HttpMethod("custom");
+
+            rm.Content = content;
+            rm.Method = method;
+            rm.RequestUri = uri;
+            rm.Version = version;
+
+            Assert.Equal(content, rm.Content);
+            Assert.Equal(uri, rm.RequestUri);
+            Assert.Equal(method, rm.Method);
+            Assert.Equal(version, rm.Version);
+
+            Assert.NotNull(rm.Headers);
+            Assert.NotNull(rm.Options);
+
+            rm.Options.TryGetValue(FetchOptions, out IDictionary<string, object?>? fetchOptionsValue);
+            Assert.Null(fetchOptionsValue);
+        }
+#nullable disable
+
+        [Fact]
+        public void Properties_SetOptionsAndGetTheirValue_Set_EnableStreamingResponse()
+        {
+            var rm = new HttpRequestMessage();
+
+            var content = new MockContent();
+            var uri = new Uri("https://example.com");
+            var version = new Version(1, 0);
+            var method = new HttpMethod("custom");
+
+            rm.Content = content;
+            rm.Method = method;
+            rm.RequestUri = uri;
+            rm.Version = version;
+            
+            rm.Options.Set(EnableStreamingResponse, true);
+
+            Assert.Equal(content, rm.Content);
+            Assert.Equal(uri, rm.RequestUri);
+            Assert.Equal(method, rm.Method);
+            Assert.Equal(version, rm.Version);
+
+            Assert.NotNull(rm.Headers);
+            Assert.NotNull(rm.Options);
+
+            rm.Options.TryGetValue(EnableStreamingResponse, out bool streamingEnabledValue);
+            Assert.True(streamingEnabledValue);
+        }
+
+        [Fact]
+        public void Properties_SetOptionsAndGetTheirValue_NotSet_EnableStreamingResponse()
+        {
+            var rm = new HttpRequestMessage();
+
+            var content = new MockContent();
+            var uri = new Uri("https://example.com");
+            var version = new Version(1, 0);
+            var method = new HttpMethod("custom");
+
+            rm.Content = content;
+            rm.Method = method;
+            rm.RequestUri = uri;
+            rm.Version = version;
+            
+            Assert.Equal(content, rm.Content);
+            Assert.Equal(uri, rm.RequestUri);
+            Assert.Equal(method, rm.Method);
+            Assert.Equal(version, rm.Version);
+
+            Assert.NotNull(rm.Headers);
+            Assert.NotNull(rm.Options);
+
+            rm.Options.TryGetValue(EnableStreamingResponse, out bool streamingEnabledValue);
+            Assert.False(streamingEnabledValue);
+        }
+
+        [Fact]
+        public void RequestUri_SetNonHttpUri_ThrowsArgumentException()
+        {
+            var rm = new HttpRequestMessage();
+            AssertExtensions.Throws<ArgumentException>("value", () => { rm.RequestUri = new Uri("ftp://example.com"); });
+        }
+
+        [Fact]
+        public void Version_SetToNull_ThrowsArgumentNullException()
+        {
+            var rm = new HttpRequestMessage();
+            Assert.Throws<ArgumentNullException>(() => { rm.Version = null; });
+        }
+
+        [Fact]
+        public void Method_SetToNull_ThrowsArgumentNullException()
+        {
+            var rm = new HttpRequestMessage();
+            Assert.Throws<ArgumentNullException>(() => { rm.Method = null; });
+        }
+
+        [Fact]
+        public void ToString_DefaultAndNonDefaultInstance_DumpAllFields()
+        {
+            var rm = new HttpRequestMessage();
+            string expected =
+                    "Method: GET, RequestUri: '<null>', Version: " +
+                    _expectedRequestMessageVersion.ToString(2) +
+                    $", Content: <null>, Headers:{Environment.NewLine}{{{Environment.NewLine}}}";
+            Assert.Equal(expected, rm.ToString());
+
+            rm.Method = HttpMethod.Put;
+            rm.RequestUri = new Uri("http://a.com/");
+            rm.Version = new Version(1, 0);
+            rm.Content = new StringContent("content");
+
+            // Note that there is no Content-Length header: The reason is that the value for Content-Length header
+            // doesn't get set by StringContent..ctor, but only if someone actually accesses the ContentLength property.
+            Assert.Equal(
+                "Method: PUT, RequestUri: 'http://a.com/', Version: 1.0, Content: " + typeof(StringContent).ToString() + ", Headers:" + Environment.NewLine +
+                $"{{{Environment.NewLine}" +
+                "  Content-Type: text/plain; charset=utf-8" + Environment.NewLine +
+                "}", rm.ToString());
+
+            rm.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("text/plain", 0.2));
+            rm.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("text/xml", 0.1));
+            rm.Headers.Add("Custom-Request-Header", "value1");
+            rm.Content.Headers.Add("Custom-Content-Header", "value2");
+
+            Assert.Equal(
+                "Method: PUT, RequestUri: 'http://a.com/', Version: 1.0, Content: " + typeof(StringContent).ToString() + ", Headers:" + Environment.NewLine +
+                "{" + Environment.NewLine +
+                "  Accept: text/plain; q=0.2" + Environment.NewLine +
+                "  Accept: text/xml; q=0.1" + Environment.NewLine +
+                "  Custom-Request-Header: value1" + Environment.NewLine +
+                "  Content-Type: text/plain; charset=utf-8" + Environment.NewLine +
+                "  Custom-Content-Header: value2" + Environment.NewLine +
+                "}", rm.ToString());
+        }
+
+        #region Helper methods
+
+        private class MockContent : HttpContent
+        {
+            public bool IsDisposed { get; private set; }
+
+            protected override bool TryComputeLength(out long length)
+            {
+                throw new NotImplementedException();
+            }
+
+#nullable enable
+            protected override Task SerializeToStreamAsync(Stream stream, TransportContext? context)
+            {
+#nullable disable                
+                throw new NotImplementedException();
+            }
+
+            protected override void Dispose(bool disposing)
+            {
+                IsDisposed = true;
+                base.Dispose(disposing);
+            }
+        }
+
+        #endregion
+    }
+}
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/JavaScriptTests.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/JavaScriptTests.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/JavaScriptTests.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/JavaScriptTests.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/MapTests.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/MapTests.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/MapTests.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/MapTests.cs
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/MarshalTests.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/MarshalTests.cs
similarity index 99%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/MarshalTests.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/MarshalTests.cs
index 68f16e673f194d..b9f4ed73cfb803 100644
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/MarshalTests.cs
+++ b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/MarshalTests.cs
@@ -7,6 +7,7 @@
 
 namespace System.Runtime.InteropServices.JavaScript.Tests
 {
+    [ActiveIssue("https://github.com/dotnet/runtime/issues/40112")]
     public static class MarshalTests
     {
         [Fact]
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/TypedArrayTests.cs b/src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/TypedArrayTests.cs
similarity index 100%
rename from src/libraries/System.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/TypedArrayTests.cs
rename to src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System/Runtime/InteropServices/JavaScript/TypedArrayTests.cs
diff --git a/src/libraries/System.Private.Uri/Directory.Build.props b/src/libraries/System.Private.Uri/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Private.Uri/Directory.Build.props
+++ b/src/libraries/System.Private.Uri/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Private.Uri/src/System.Private.Uri.csproj b/src/libraries/System.Private.Uri/src/System.Private.Uri.csproj
index a639777cb80029..731f081a11eb9c 100644
--- a/src/libraries/System.Private.Uri/src/System.Private.Uri.csproj
+++ b/src/libraries/System.Private.Uri/src/System.Private.Uri.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Private.Uri</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Private.Xml.Linq/Directory.Build.props b/src/libraries/System.Private.Xml.Linq/Directory.Build.props
index 05cc2bde64e551..bdcfca3b543cbb 100644
--- a/src/libraries/System.Private.Xml.Linq/Directory.Build.props
+++ b/src/libraries/System.Private.Xml.Linq/Directory.Build.props
@@ -2,7 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
-    <IsNETCoreAppRef>false</IsNETCoreAppRef>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Private.Xml.Linq/src/System.Private.Xml.Linq.csproj b/src/libraries/System.Private.Xml.Linq/src/System.Private.Xml.Linq.csproj
index a24010636c271a..4db38b8700d29d 100644
--- a/src/libraries/System.Private.Xml.Linq/src/System.Private.Xml.Linq.csproj
+++ b/src/libraries/System.Private.Xml.Linq/src/System.Private.Xml.Linq.csproj
@@ -1,11 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Private.Xml.Linq</AssemblyName>
     <RootNamespace>System.Xml</RootNamespace>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Private.Xml\src\System.Private.Xml.csproj" />
     <Compile Include="$(CommonPath)System\Collections\Generic\EnumerableHelpers.cs"
              Link="Common\System\Collections\Generic\EnumerableHelpers.cs" />
     <Compile Include="$(CommonPath)System\Text\StringBuilderCache.cs"
@@ -43,6 +41,7 @@
     <Compile Include="System\Xml\XPath\XObjectExtensions.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Xml\src\System.Private.Xml.csproj" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Linq" />
     <Reference Include="System.ObjectModel" />
diff --git a/src/libraries/System.Private.Xml/Directory.Build.props b/src/libraries/System.Private.Xml/Directory.Build.props
index 05cc2bde64e551..bdcfca3b543cbb 100644
--- a/src/libraries/System.Private.Xml/Directory.Build.props
+++ b/src/libraries/System.Private.Xml/Directory.Build.props
@@ -2,7 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
-    <IsNETCoreAppRef>false</IsNETCoreAppRef>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Private.Xml/src/System.Private.Xml.csproj b/src/libraries/System.Private.Xml/src/System.Private.Xml.csproj
index 01dcb093e6e2d0..c3b7f512fce2c4 100644
--- a/src/libraries/System.Private.Xml/src/System.Private.Xml.csproj
+++ b/src/libraries/System.Private.Xml/src/System.Private.Xml.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Private.Xml</AssemblyName>
     <RootNamespace>System.Xml</RootNamespace>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DefineConstants>$(DefineConstants);FEATURE_COMPILED_XSL</DefineConstants>
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/BinaryXml/XmlBinaryReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/BinaryXml/XmlBinaryReader.cs
index 664014a754e414..c7d02fafc8397c 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/BinaryXml/XmlBinaryReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/BinaryXml/XmlBinaryReader.cs
@@ -670,7 +670,7 @@ public override int AttributeCount
             }
         }
 
-        public override string? GetAttribute(string name, string ns)
+        public override string? GetAttribute(string name, string? ns)
         {
             if (ScanState.XmlText == _state)
             {
@@ -721,7 +721,7 @@ public override string GetAttribute(int i)
             }
         }
 
-        public override bool MoveToAttribute(string name, string ns)
+        public override bool MoveToAttribute(string name, string? ns)
         {
             if (ScanState.XmlText == _state)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentBuilder.cs b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentBuilder.cs
index ff09876f0d29b8..34c4fcc8722702 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentBuilder.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentBuilder.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Globalization;
 using System.IO;
@@ -11,6 +12,7 @@
 using System.Diagnostics;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 
 namespace MS.Internal.Xml.Cache
 {
@@ -40,21 +42,21 @@ internal sealed class XPathDocumentBuilder : XmlRawWriter
         private readonly Stack<XPathNodeRef> _stkNmsp;    // In-scope namespaces
         private XPathNodeInfoTable _infoTable;   // Atomization table for shared node information
         private XPathDocument _doc;              // Currently building document
-        private IXmlLineInfo _lineInfo;          // Line information provider
+        private IXmlLineInfo? _lineInfo;          // Line information provider
         private XmlNameTable _nameTable;         // Atomization table for all names in the document
         private bool _atomizeNames;              // True if all names should be atomized (false if they are pre-atomized)
 
         private XPathNode[] _pageNmsp;           // Page of last in-scope namespace node
         private int _idxNmsp;                    // Page index of last in-scope namespace node
-        private XPathNode[] _pageParent;         // Page of last parent-type node (Element or Root)
+        private XPathNode[]? _pageParent;         // Page of last parent-type node (Element or Root)
         private int _idxParent;                  // Page index of last parent-type node (Element or Root)
-        private XPathNode[] _pageSibling;        // Page of previous sibling node (may be null if no previous sibling)
+        private XPathNode[]? _pageSibling;        // Page of previous sibling node (may be null if no previous sibling)
         private int _idxSibling;                 // Page index of previous sibling node
         private int _lineNumBase;                // Line number from which offsets are computed
         private int _linePosBase;                // Line position from which offsets are computed
 
-        private XmlQualifiedName _idAttrName;    // Cached name of an ID attribute
-        private Hashtable _elemIdMap;            // Map from element name to ID attribute name
+        private XmlQualifiedName? _idAttrName;    // Cached name of an ID attribute
+        private Hashtable? _elemIdMap;            // Map from element name to ID attribute name
         private XPathNodeRef[] _elemNameIndex;   // Elements with the same name are linked together so that they can be searched quickly
 
         private const int ElementIndexSize = 64;
@@ -62,7 +64,7 @@ internal sealed class XPathDocumentBuilder : XmlRawWriter
         /// <summary>
         /// Create a new XPathDocumentBuilder which creates nodes in "doc".
         /// </summary>
-        public XPathDocumentBuilder(XPathDocument doc, IXmlLineInfo lineInfo, string baseUri, XPathDocument.LoadFlags flags)
+        public XPathDocumentBuilder(XPathDocument doc, IXmlLineInfo? lineInfo, string? baseUri, XPathDocument.LoadFlags flags)
         {
             // Allocate the initial node (for non-namespaces) page, and the initial namespace page
             _nodePageFact.Init(256);
@@ -77,7 +79,12 @@ public XPathDocumentBuilder(XPathDocument doc, IXmlLineInfo lineInfo, string bas
         /// Start construction of a new document.  This must be called before any other methods are called.
         /// It may also be called after Close(), in order to build further documents.
         /// </summary>
-        public void Initialize(XPathDocument doc, IXmlLineInfo lineInfo, string baseUri, XPathDocument.LoadFlags flags)
+        [MemberNotNull(nameof(_doc))]
+        [MemberNotNull(nameof(_elemNameIndex))]
+        [MemberNotNull(nameof(_infoTable))]
+        [MemberNotNull(nameof(_nameTable))]
+        [MemberNotNull(nameof(_pageNmsp))]
+        public void Initialize(XPathDocument doc, IXmlLineInfo? lineInfo, string? baseUri, XPathDocument.LoadFlags flags)
         {
             XPathNode[] page;
             int idx;
@@ -126,14 +133,14 @@ public void Initialize(XPathDocument doc, IXmlLineInfo lineInfo, string baseUri,
         /// <summary>
         /// XPathDocument ignores the DocType information.
         /// </summary>
-        public override void WriteDocType(string name, string pubid, string sysid, string subset)
+        public override void WriteDocType(string name, string? pubid, string? sysid, string? subset)
         {
         }
 
         /// <summary>
         /// Shortcut for calling WriteStartElement with elemType == null.
         /// </summary>
-        public override void WriteStartElement(string prefix, string localName, string ns)
+        public override void WriteStartElement(string? prefix, string localName, string? ns)
         {
             this.WriteStartElement(prefix, localName, ns, string.Empty);
         }
@@ -141,7 +148,7 @@ public override void WriteStartElement(string prefix, string localName, string n
         /// <summary>
         /// Build an element node and attach it to its parent, if one exists.  Make the element the new parent node.
         /// </summary>
-        public void WriteStartElement(string prefix, string localName, string ns, string baseUri)
+        public void WriteStartElement(string? prefix, string localName, string? ns, string? baseUri)
         {
             int hash;
             Debug.Assert(prefix != null && localName != null && ns != null && localName.Length != 0 && baseUri != null);
@@ -164,7 +171,7 @@ public void WriteStartElement(string prefix, string localName, string ns, string
 
             // If elements within this document might have IDs, then cache the name of the ID attribute, if one exists
             if (_elemIdMap != null)
-                _idAttrName = (XmlQualifiedName)_elemIdMap[new XmlQualifiedName(localName, prefix)];
+                _idAttrName = (XmlQualifiedName?)_elemIdMap[new XmlQualifiedName(localName, prefix)];
         }
 
         /// <summary>
@@ -205,7 +212,7 @@ internal override void WriteFullEndElement(string prefix, string localName, stri
         public void WriteEndElement(bool allowShortcutTag)
         {
             XPathNodeRef nodeRef;
-            Debug.Assert(_pageParent[_idxParent].NodeType == XPathNodeType.Element);
+            Debug.Assert(_pageParent != null && _pageParent[_idxParent].NodeType == XPathNodeType.Element);
 
             // If element has no content-typed children except for the one about to be added, then
             // its value is the same as its only text child's.
@@ -277,11 +284,12 @@ public void WriteEndElement(bool allowShortcutTag)
         /// <summary>
         /// Shortcut for calling WriteStartAttribute with attrfType == null.
         /// </summary>
-        public override void WriteStartAttribute(string prefix, string localName, string namespaceName)
+        public override void WriteStartAttribute(string? prefix, string localName, string? namespaceName)
         {
-            Debug.Assert(!prefix.Equals("xmlns"));
-            Debug.Assert(_idxParent == 0 || _pageParent[_idxParent].NodeType == XPathNodeType.Element);
-            Debug.Assert(_idxSibling == 0 || _pageSibling[_idxSibling].NodeType == XPathNodeType.Attribute);
+            Debug.Assert(namespaceName != null);
+            Debug.Assert(prefix != null && !prefix.Equals("xmlns"));
+            Debug.Assert(_idxParent == 0 || (_pageParent != null && _pageParent[_idxParent].NodeType == XPathNodeType.Element));
+            Debug.Assert(_idxSibling == 0 || (_pageSibling != null && _pageSibling[_idxSibling].NodeType == XPathNodeType.Attribute));
 
             if (_atomizeNames)
             {
@@ -298,6 +306,7 @@ public override void WriteStartAttribute(string prefix, string localName, string
         /// </summary>
         public override void WriteEndAttribute()
         {
+            Debug.Assert(_pageSibling != null);
             Debug.Assert(_pageSibling[_idxSibling].NodeType == XPathNodeType.Attribute);
 
             _pageSibling[_idxSibling].SetValue(_textBldr.ReadText());
@@ -309,8 +318,10 @@ public override void WriteEndAttribute()
                     _pageSibling[_idxSibling].Prefix == _idAttrName.Namespace)
                 {
                     // Then add its value to the idValueMap map
-                    Debug.Assert(_idxParent != 0, "ID attribute must have an element parent");
-                    _doc.AddIdElement(_pageSibling[_idxSibling].Value, _pageParent, _idxParent);
+                    Debug.Assert(_idxParent != 0 && _pageParent != null, "ID attribute must have an element parent");
+                    string? id = _pageSibling[_idxSibling].Value;
+                    Debug.Assert(id != null);
+                    _doc.AddIdElement(id, _pageParent, _idxParent);
                 }
             }
         }
@@ -318,7 +329,7 @@ public override void WriteEndAttribute()
         /// <summary>
         /// Map CData text into regular text.
         /// </summary>
-        public override void WriteCData(string text)
+        public override void WriteCData(string? text)
         {
             WriteString(text, TextBlockType.Text);
         }
@@ -326,7 +337,7 @@ public override void WriteCData(string text)
         /// <summary>
         /// Construct comment node.
         /// </summary>
-        public override void WriteComment(string text)
+        public override void WriteComment(string? text)
         {
             AddSibling(XPathNodeType.Comment, string.Empty, string.Empty, string.Empty, string.Empty);
             _pageSibling[_idxSibling].SetValue(text);
@@ -335,7 +346,7 @@ public override void WriteComment(string text)
         /// <summary>
         /// Shortcut for calling WriteProcessingInstruction with baseUri = string.Empty.
         /// </summary>
-        public override void WriteProcessingInstruction(string name, string text)
+        public override void WriteProcessingInstruction(string name, string? text)
         {
             this.WriteProcessingInstruction(name, text, string.Empty);
         }
@@ -343,7 +354,7 @@ public override void WriteProcessingInstruction(string name, string text)
         /// <summary>
         /// Construct pi node.
         /// </summary>
-        public void WriteProcessingInstruction(string name, string text, string baseUri)
+        public void WriteProcessingInstruction(string name, string? text, string? baseUri)
         {
             if (_atomizeNames)
                 name = _nameTable.Add(name);
@@ -355,7 +366,7 @@ public void WriteProcessingInstruction(string name, string text, string baseUri)
         /// <summary>
         /// Write a whitespace text block.
         /// </summary>
-        public override void WriteWhitespace(string ws)
+        public override void WriteWhitespace(string? ws)
         {
             WriteString(ws, TextBlockType.Whitespace);
         }
@@ -363,7 +374,7 @@ public override void WriteWhitespace(string ws)
         /// <summary>
         /// Write an attribute or element text block.
         /// </summary>
-        public override void WriteString(string text)
+        public override void WriteString(string? text)
         {
             WriteString(text, TextBlockType.Text);
         }
@@ -389,7 +400,7 @@ public override void WriteRaw(char[] buffer, int index, int count)
         /// <summary>
         /// Write an element text block with the specified text type (whitespace, significant whitespace, or text).
         /// </summary>
-        public void WriteString(string text, TextBlockType textType)
+        public void WriteString(string? text, TextBlockType textType)
         {
             _textBldr.WriteTextBlock(text, textType);
         }
@@ -424,7 +435,7 @@ public override void WriteSurrogateCharEntity(char lowChar, char highChar)
         /// </summary>
         public override void Close()
         {
-            XPathNode[] page;
+            XPathNode[]? page;
             int idx;
 
             // If cached text exists, then create a text node at the top-level
@@ -470,7 +481,7 @@ internal override void WriteXmlDeclaration(string xmldecl)
         /// </summary>
         internal override void StartElementContent()
         {
-            Debug.Assert(_pageParent[_idxParent].NodeType == XPathNodeType.Element);
+            Debug.Assert(_pageParent != null && _pageParent[_idxParent].NodeType == XPathNodeType.Element);
         }
 
         /// <summary>
@@ -479,12 +490,13 @@ internal override void StartElementContent()
         /// </summary>
         internal override void WriteNamespaceDeclaration(string prefix, string namespaceName)
         {
-            XPathNode[] pageTemp, pageOverride, pageNew, pageOrig, pageCopy;
+            XPathNode[] pageTemp, pageNew, pageCopy;
+            XPathNode[]? pageOverride, pageOrig;
             int idxTemp, idxOverride, idxNew, idxOrig, idxCopy;
-            Debug.Assert(_idxSibling == 0 || _pageSibling[_idxSibling].NodeType == XPathNodeType.Attribute);
+            Debug.Assert(_idxSibling == 0 || (_pageSibling != null && _pageSibling[_idxSibling].NodeType == XPathNodeType.Attribute));
             Debug.Assert(!prefix.Equals("xmlns") && !namespaceName.Equals(XmlReservedNs.NsXmlNs));
             Debug.Assert(_idxParent == 0 || _idxNmsp != 0);
-            Debug.Assert(_idxParent == 0 || _pageParent[_idxParent].NodeType == XPathNodeType.Element);
+            Debug.Assert(_idxParent == 0 || (_pageParent != null && _pageParent[_idxParent].NodeType == XPathNodeType.Element));
 
             if (_atomizeNames)
                 prefix = _nameTable.Add(prefix);
@@ -496,7 +508,7 @@ internal override void WriteNamespaceDeclaration(string prefix, string namespace
             idxOverride = _idxNmsp;
             while (idxOverride != 0)
             {
-                if ((object)pageOverride[idxOverride].LocalName == (object)prefix)
+                if ((object)pageOverride![idxOverride].LocalName == (object)prefix)
                 {
                     // Need to clone all namespaces up until the overridden node in order to bypass it
                     break;
@@ -517,8 +529,9 @@ internal override void WriteNamespaceDeclaration(string prefix, string namespace
 
                 while (idxOrig != idxOverride || pageOrig != pageOverride)
                 {
+                    Debug.Assert(pageOrig != null);
                     // Make a copy of the original namespace node
-                    idxTemp = pageOrig[idxOrig].GetParent(out pageTemp);
+                    idxTemp = pageOrig[idxOrig].GetParent(out pageTemp!);
                     idxTemp = NewNamespaceNode(out pageTemp, pageOrig[idxOrig].LocalName, pageOrig[idxOrig].Value, pageTemp, idxTemp);
 
                     // Attach copy to chain of copied nodes
@@ -533,10 +546,10 @@ internal override void WriteNamespaceDeclaration(string prefix, string namespace
                 }
 
                 // Link farther up in the original chain, just past the last overridden node
-                idxOverride = pageOverride[idxOverride].GetSibling(out pageOverride);
+                idxOverride = pageOverride![idxOverride].GetSibling(out pageOverride);
 
                 if (idxOverride != 0)
-                    pageCopy[idxCopy].SetSibling(_infoTable, pageOverride, idxOverride);
+                    pageCopy[idxCopy].SetSibling(_infoTable, pageOverride!, idxOverride);
                 else
                     Debug.Assert(prefix.Equals("xml"), "xmlns:xml namespace declaration should always be present in the list.");
             }
@@ -553,6 +566,7 @@ internal override void WriteNamespaceDeclaration(string prefix, string namespace
 
             if (_idxParent != 0)
             {
+                Debug.Assert(_pageParent != null);
                 // If this is the first namespace on the current element,
                 if (!_pageParent[_idxParent].HasNamespaceDecls)
                 {
@@ -582,7 +596,7 @@ public void CreateIdTables(IDtdInfo dtdInfo)
             // Extract the elements which has attribute defined as ID from the element declarations
             foreach (IDtdAttributeListInfo attrList in dtdInfo.GetAttributeLists())
             {
-                IDtdAttributeInfo idAttribute = attrList.LookupIdAttribute();
+                IDtdAttributeInfo? idAttribute = attrList.LookupIdAttribute();
                 if (idAttribute != null)
                 {
                     if (_elemIdMap == null)
@@ -612,7 +626,7 @@ private XPathNodeRef LinkSimilarElements(XPathNode[] pagePrev, int idxPrev, XPat
         /// <summary>
         /// Helper method that constructs a new Namespace XPathNode.
         /// </summary>
-        private int NewNamespaceNode(out XPathNode[] page, string prefix, string namespaceUri, XPathNode[] pageElem, int idxElem)
+        private int NewNamespaceNode(out XPathNode[] page, string prefix, string? namespaceUri, XPathNode[]? pageElem, int idxElem)
         {
             XPathNode[] pageNode;
             int idxNode, lineNumOffset, linePosOffset;
@@ -642,7 +656,7 @@ private int NewNamespaceNode(out XPathNode[] page, string prefix, string namespa
         /// <summary>
         /// Helper method that constructs a new XPathNode.
         /// </summary>
-        private int NewNode(out XPathNode[] page, XPathNodeType xptyp, string localName, string namespaceUri, string prefix, string baseUri)
+        private int NewNode(out XPathNode[] page, XPathNodeType xptyp, string localName, string namespaceUri, string prefix, string? baseUri)
         {
             XPathNode[] pageNode;
             int idxNode, lineNumOffset, linePosOffset;
@@ -714,7 +728,8 @@ private void ComputeLineInfo(bool isTextNode, out int lineNumOffset, out int lin
         /// Add a sibling node.  If no previous sibling exists, add the node as the first child of the parent.
         /// If no parent exists, make this node the root of the document.
         /// </summary>
-        private void AddSibling(XPathNodeType xptyp, string localName, string namespaceUri, string prefix, string baseUri)
+        [MemberNotNull(nameof(_pageSibling))]
+        private void AddSibling(XPathNodeType xptyp, string localName, string namespaceUri, string prefix, string? baseUri)
         {
             XPathNode[] pageNew;
             int idxNew;
@@ -728,6 +743,7 @@ private void AddSibling(XPathNodeType xptyp, string localName, string namespaceU
             // this.idxParent is only 0 for the top-most node
             if (_idxParent != 0)
             {
+                Debug.Assert(_pageParent != null);
                 // Set properties on parent
                 _pageParent[_idxParent].SetParentProperties(xptyp);
 
@@ -738,6 +754,7 @@ private void AddSibling(XPathNodeType xptyp, string localName, string namespaceU
                 }
                 else
                 {
+                    Debug.Assert(_pageSibling != null);
                     // There is already a previous sibling
                     _pageSibling[_idxSibling].SetSibling(_infoTable, pageNew, idxNew);
                 }
@@ -750,12 +767,13 @@ private void AddSibling(XPathNodeType xptyp, string localName, string namespaceU
         /// <summary>
         /// Creates a text node from cached text parts.
         /// </summary>
+        [MemberNotNull(nameof(_pageSibling))]
         private void CachedTextNode()
         {
             TextBlockType textType;
             string text;
             Debug.Assert(_textBldr.HasText || (_idxSibling == 0 && _idxParent == 0), "Cannot create empty text node unless it's a top-level text node.");
-            Debug.Assert(_idxSibling == 0 || !_pageSibling[_idxSibling].IsText, "Cannot create adjacent text nodes.");
+            Debug.Assert(_idxSibling == 0 || (_pageSibling != null && !_pageSibling[_idxSibling].IsText), "Cannot create adjacent text nodes.");
 
             // Create a text node
             textType = _textBldr.TextType;
@@ -833,7 +851,7 @@ public void AllocateSlot(out XPathNode[] page, out int idx)
         /// </summary>
         private struct TextBlockBuilder
         {
-            private IXmlLineInfo _lineInfo;
+            private IXmlLineInfo? _lineInfo;
             private TextBlockType _textType;
             private string _text;
             private int _lineNum, _linePos;
@@ -841,7 +859,7 @@ private struct TextBlockBuilder
             /// <summary>
             /// Constructor.
             /// </summary>
-            public void Initialize(IXmlLineInfo lineInfo)
+            public void Initialize(IXmlLineInfo? lineInfo)
             {
                 _lineInfo = lineInfo;
                 _textType = TextBlockType.None;
@@ -882,12 +900,12 @@ public int LinePosition
             /// <summary>
             /// Append a text block with the specified type.
             /// </summary>
-            public void WriteTextBlock(string text, TextBlockType textType)
+            public void WriteTextBlock(string? text, TextBlockType textType)
             {
                 Debug.Assert((int)XPathNodeType.Text < (int)XPathNodeType.SignificantWhitespace);
                 Debug.Assert((int)XPathNodeType.SignificantWhitespace < (int)XPathNodeType.Whitespace);
 
-                if (text.Length != 0)
+                if (!string.IsNullOrEmpty(text))
                 {
                     if (_textType == TextBlockType.None)
                     {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentIterator.cs
index af2d3d91484a18..bcdaaabb7af0c2 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Xml.XPath;
 
@@ -54,7 +55,8 @@ public override int CurrentPosition
     /// </summary>
     internal class XPathDocumentElementChildIterator : XPathDocumentBaseIterator
     {
-        private readonly string _localName, _namespaceUri;
+        private readonly string? _localName;
+        private readonly string _namespaceUri;
 
         /// <summary>
         /// Create an iterator that ranges over all element children of "parent" having the specified QName.
@@ -164,8 +166,9 @@ public override bool MoveNext()
     /// </summary>
     internal class XPathDocumentElementDescendantIterator : XPathDocumentBaseIterator
     {
-        private readonly XPathDocumentNavigator _end;
-        private readonly string _localName, _namespaceUri;
+        private readonly XPathDocumentNavigator? _end;
+        private readonly string? _localName;
+        private readonly string _namespaceUri;
         private bool _matchSelf;
 
         /// <summary>
@@ -236,7 +239,7 @@ public override bool MoveNext()
     /// </summary>
     internal class XPathDocumentKindDescendantIterator : XPathDocumentBaseIterator
     {
-        private readonly XPathDocumentNavigator _end;
+        private readonly XPathDocumentNavigator? _end;
         private readonly XPathNodeType _typ;
         private bool _matchSelf;
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentNavigator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentNavigator.cs
index 51b98d48d4387d..18a32e7923c630 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentNavigator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathDocumentNavigator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Text;
 using System.Xml;
@@ -15,10 +16,10 @@ namespace MS.Internal.Xml.Cache
     internal sealed class XPathDocumentNavigator : XPathNavigator, IXmlLineInfo
     {
         private XPathNode[] _pageCurrent;
-        private XPathNode[] _pageParent;
+        private XPathNode[]? _pageParent;
         private int _idxCurrent;
         private int _idxParent;
-        private string _atomizedLocalName;
+        private string? _atomizedLocalName;
 
 
         //-----------------------------------------------
@@ -29,7 +30,7 @@ internal sealed class XPathDocumentNavigator : XPathNavigator, IXmlLineInfo
         /// Create a new navigator positioned on the specified current node.  If the current node is a namespace or a collapsed
         /// text node, then the parent is a virtualized parent (may be different than .Parent on the current node).
         /// </summary>
-        public XPathDocumentNavigator(XPathNode[] pageCurrent, int idxCurrent, XPathNode[] pageParent, int idxParent)
+        public XPathDocumentNavigator(XPathNode[]? pageCurrent, int idxCurrent, XPathNode[]? pageParent, int idxParent)
         {
             Debug.Assert(pageCurrent != null && idxCurrent != 0);
             Debug.Assert((pageParent == null) == (idxParent == 0));
@@ -62,8 +63,9 @@ public override string Value
         {
             get
             {
-                string value;
-                XPathNode[] page, pageEnd;
+                string? value;
+                XPathNode[] page;
+                XPathNode[]? pageEnd;
                 int idx, idxEnd;
 
                 // Try to get the pre-computed string value of the node
@@ -82,7 +84,7 @@ public override string Value
                         break;
 
                     case XPathNodeType.Text:
-                        Debug.Assert(_idxParent != 0 && _pageParent[_idxParent].HasCollapsedText,
+                        Debug.Assert(_idxParent != 0 && _pageParent![_idxParent].HasCollapsedText,
                                      "ReadStringValue() should have taken care of anything but collapsed text.");
                         break;
                 }
@@ -92,12 +94,16 @@ public override string Value
                 if (_idxParent != 0)
                 {
                     Debug.Assert(_pageCurrent[_idxCurrent].NodeType == XPathNodeType.Text);
-                    return _pageParent[_idxParent].Value;
+
+                    value = _pageParent![_idxParent].Value;
+                    Debug.Assert(value != null);
+
+                    return value;
                 }
 
                 // Must be node with complex content, so concatenate the string values of all text descendants
                 string s = string.Empty;
-                StringBuilder bldr = null;
+                StringBuilder? bldr = null;
 
                 // Get all text nodes which follow the current node in document order, but which are still descendants
                 page = pageEnd = _pageCurrent;
@@ -111,10 +117,12 @@ public override string Value
                 while (XPathNodeHelper.GetTextFollowing(ref page, ref idx, pageEnd, idxEnd))
                 {
                     Debug.Assert(page[idx].NodeType == XPathNodeType.Element || page[idx].IsText);
+                    value = page[idx].Value;
+                    Debug.Assert(value != null);
 
                     if (s.Length == 0)
                     {
-                        s = page[idx].Value;
+                        s = value;
                     }
                     else
                     {
@@ -123,7 +131,7 @@ public override string Value
                             bldr = new StringBuilder();
                             bldr.Append(s);
                         }
-                        bldr.Append(page[idx].Value);
+                        bldr.Append(value);
                     }
                 }
 
@@ -191,13 +199,13 @@ public override string BaseURI
         {
             get
             {
-                XPathNode[] page;
+                XPathNode[]? page;
                 int idx;
 
                 if (_idxParent != 0)
                 {
                     // Get BaseUri of parent for attribute, namespace, and collapsed text nodes
-                    page = _pageParent;
+                    page = _pageParent!;
                     idx = _idxParent;
                 }
                 else
@@ -208,7 +216,7 @@ public override string BaseURI
 
                 do
                 {
-                    switch (page[idx].NodeType)
+                    switch (page![idx].NodeType)
                     {
                         case XPathNodeType.Element:
                         case XPathNodeType.Root:
@@ -285,12 +293,12 @@ public override bool HasAttributes
         /// attribute can be found, return false.  Don't assume the name parts are atomized with respect
         /// to this document.
         /// </summary>
-        public override bool MoveToAttribute(string localName, string namespaceURI)
+        public override bool MoveToAttribute(string? localName, string namespaceURI)
         {
             XPathNode[] page = _pageCurrent;
             int idx = _idxCurrent;
 
-            if ((object)localName != (object)_atomizedLocalName)
+            if ((object?)localName != (object?)_atomizedLocalName)
                 _atomizedLocalName = (localName != null) ? NameTable.Get(localName) : null;
 
             if (XPathNodeHelper.GetAttribute(ref _pageCurrent, ref _idxCurrent, _atomizedLocalName, namespaceURI))
@@ -310,7 +318,7 @@ public override bool MoveToAttribute(string localName, string namespaceURI)
         /// </summary>
         public override bool MoveToFirstNamespace(XPathNamespaceScope namespaceScope)
         {
-            XPathNode[] page;
+            XPathNode[]? page;
             int idx;
 
             if (namespaceScope == XPathNamespaceScope.Local)
@@ -327,11 +335,11 @@ public override bool MoveToFirstNamespace(XPathNamespaceScope namespaceScope)
             while (idx != 0)
             {
                 // Don't include the xmlns:xml namespace node if scope is ExcludeXml
-                if (namespaceScope != XPathNamespaceScope.ExcludeXml || !page[idx].IsXmlNamespaceNode)
+                if (namespaceScope != XPathNamespaceScope.ExcludeXml || !page![idx].IsXmlNamespaceNode)
                 {
                     _pageParent = _pageCurrent;
                     _idxParent = _idxCurrent;
-                    _pageCurrent = page;
+                    _pageCurrent = page!;
                     _idxCurrent = idx;
                     return true;
                 }
@@ -349,7 +357,7 @@ public override bool MoveToFirstNamespace(XPathNamespaceScope namespaceScope)
         /// </summary>
         public override bool MoveToNextNamespace(XPathNamespaceScope scope)
         {
-            XPathNode[] page = _pageCurrent, pageParent;
+            XPathNode[]? page = _pageCurrent, pageParent;
             int idx = _idxCurrent, idxParent;
 
             // If current node is not a namespace node, return false
@@ -365,12 +373,13 @@ public override bool MoveToNextNamespace(XPathNamespaceScope scope)
                 if (idx == 0)
                     return false;
 
+                Debug.Assert(page != null);
                 switch (scope)
                 {
                     case XPathNamespaceScope.Local:
                         // Once parent changes, there are no longer any local namespaces
                         idxParent = page[idx].GetParent(out pageParent);
-                        if (idxParent != _idxParent || (object)pageParent != (object)_pageParent)
+                        if (idxParent != _idxParent || (object?)pageParent != (object?)_pageParent)
                             return false;
                         break;
 
@@ -424,7 +433,8 @@ public override bool MoveToFirstChild()
                 // Virtualize collapsed text nodes
                 _pageParent = _pageCurrent;
                 _idxParent = _idxCurrent;
-                _idxCurrent = _pageCurrent[_idxCurrent].Document.GetCollapsedTextNode(out _pageCurrent);
+                _idxCurrent = _pageCurrent[_idxCurrent].Document.GetCollapsedTextNode(out _pageCurrent!);
+                Debug.Assert(_pageCurrent != null);
                 return true;
             }
 
@@ -461,7 +471,7 @@ public override bool MoveToParent()
         /// </summary>
         public override bool MoveTo(XPathNavigator other)
         {
-            XPathDocumentNavigator that = other as XPathDocumentNavigator;
+            XPathDocumentNavigator? that = other as XPathDocumentNavigator;
             if (that != null)
             {
                 _pageCurrent = that._pageCurrent;
@@ -478,12 +488,13 @@ public override bool MoveTo(XPathNavigator other)
         /// </summary>
         public override bool MoveToId(string id)
         {
-            XPathNode[] page;
+            XPathNode[]? page;
             int idx;
 
             idx = _pageCurrent[_idxCurrent].Document.LookupIdElement(id, out page);
             if (idx != 0)
             {
+                Debug.Assert(page != null);
                 // Move to ID element and clear parent state
                 Debug.Assert(page[idx].NodeType == XPathNodeType.Element);
                 _pageCurrent = page;
@@ -502,7 +513,7 @@ public override bool MoveToId(string id)
         /// </summary>
         public override bool IsSamePosition(XPathNavigator other)
         {
-            XPathDocumentNavigator that = other as XPathDocumentNavigator;
+            XPathDocumentNavigator? that = other as XPathDocumentNavigator;
             if (that != null)
             {
                 return _idxCurrent == that._idxCurrent && _pageCurrent == that._pageCurrent &&
@@ -537,9 +548,9 @@ public override void MoveToRoot()
         /// Move to the first element child of the current node with the specified name.  Return false
         /// if the current node has no matching element children.
         /// </summary>
-        public override bool MoveToChild(string localName, string namespaceURI)
+        public override bool MoveToChild(string? localName, string namespaceURI)
         {
-            if ((object)localName != (object)_atomizedLocalName)
+            if ((object?)localName != (object?)_atomizedLocalName)
                 _atomizedLocalName = (localName != null) ? NameTable.Get(localName) : null;
 
             return XPathNodeHelper.GetElementChild(ref _pageCurrent, ref _idxCurrent, _atomizedLocalName, namespaceURI);
@@ -549,9 +560,9 @@ public override bool MoveToChild(string localName, string namespaceURI)
         /// Move to the first element sibling of the current node with the specified name.  Return false
         /// if the current node has no matching element siblings.
         /// </summary>
-        public override bool MoveToNext(string localName, string namespaceURI)
+        public override bool MoveToNext(string? localName, string namespaceURI)
         {
-            if ((object)localName != (object)_atomizedLocalName)
+            if ((object?)localName != (object?)_atomizedLocalName)
                 _atomizedLocalName = (localName != null) ? NameTable.Get(localName) : null;
 
             return XPathNodeHelper.GetElementSibling(ref _pageCurrent, ref _idxCurrent, _atomizedLocalName, namespaceURI);
@@ -572,7 +583,8 @@ public override bool MoveToChild(XPathNodeType type)
                 // Virtualize collapsed text nodes
                 _pageParent = _pageCurrent;
                 _idxParent = _idxCurrent;
-                _idxCurrent = _pageCurrent[_idxCurrent].Document.GetCollapsedTextNode(out _pageCurrent);
+                _idxCurrent = _pageCurrent[_idxCurrent].Document.GetCollapsedTextNode(out _pageCurrent!);
+                Debug.Assert(_pageCurrent != null);
                 return true;
             }
 
@@ -595,12 +607,12 @@ public override bool MoveToNext(XPathNodeType type)
         ///   3. Has the specified QName
         /// Return false if the current node has no matching following elements.
         /// </summary>
-        public override bool MoveToFollowing(string localName, string namespaceURI, XPathNavigator end)
+        public override bool MoveToFollowing(string? localName, string namespaceURI, XPathNavigator? end)
         {
-            XPathNode[] pageEnd;
+            XPathNode[]? pageEnd;
             int idxEnd;
 
-            if ((object)localName != (object)_atomizedLocalName)
+            if ((object?)localName != (object?)_atomizedLocalName)
                 _atomizedLocalName = (localName != null) ? NameTable.Get(localName) : null;
 
             // Get node on which scan ends (null if rest of document should be scanned)
@@ -609,7 +621,7 @@ public override bool MoveToFollowing(string localName, string namespaceURI, XPat
             // If this navigator is positioned on a virtual node, then compute following of parent
             if (_idxParent != 0)
             {
-                if (!XPathNodeHelper.GetElementFollowing(ref _pageParent, ref _idxParent, pageEnd, idxEnd, _atomizedLocalName, namespaceURI))
+                if (!XPathNodeHelper.GetElementFollowing(ref _pageParent!, ref _idxParent, pageEnd, idxEnd, _atomizedLocalName, namespaceURI))
                     return false;
 
                 _pageCurrent = _pageParent;
@@ -629,10 +641,11 @@ public override bool MoveToFollowing(string localName, string namespaceURI, XPat
         ///   3. Has the specified XPathNodeType
         /// Return false if the current node has no matching following nodes.
         /// </summary>
-        public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
+        public override bool MoveToFollowing(XPathNodeType type, XPathNavigator? end)
         {
-            XPathDocumentNavigator endTiny = end as XPathDocumentNavigator;
-            XPathNode[] page, pageEnd;
+            XPathDocumentNavigator? endTiny = end as XPathDocumentNavigator;
+            XPathNode[] page;
+            XPathNode[]? pageEnd;
             int idx, idxEnd;
 
             // If searching for text, make sure to handle collapsed text nodes correctly
@@ -649,7 +662,8 @@ public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
 
                     _pageParent = _pageCurrent;
                     _idxParent = _idxCurrent;
-                    _idxCurrent = _pageCurrent[_idxCurrent].Document.GetCollapsedTextNode(out _pageCurrent);
+                    _idxCurrent = _pageCurrent[_idxCurrent].Document.GetCollapsedTextNode(out _pageCurrent!);
+                    Debug.Assert(_pageCurrent != null);
                     return true;
                 }
 
@@ -661,7 +675,7 @@ public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
                     // If this navigator is positioned on a virtual node, then compute following of parent
                     if (_idxParent != 0)
                     {
-                        page = _pageParent;
+                        page = _pageParent!;
                         idx = _idxParent;
                     }
                     else
@@ -682,7 +696,8 @@ public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
                     {
                         // Virtualize collapsed text nodes
                         Debug.Assert(page[idx].HasCollapsedText);
-                        _idxCurrent = page[idx].Document.GetCollapsedTextNode(out _pageCurrent);
+                        _idxCurrent = page[idx].Document.GetCollapsedTextNode(out _pageCurrent!);
+                        Debug.Assert(_pageCurrent != null);
                         _pageParent = page;
                         _idxParent = idx;
                     }
@@ -705,7 +720,7 @@ public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
             // If this navigator is positioned on a virtual node, then compute following of parent
             if (_idxParent != 0)
             {
-                if (!XPathNodeHelper.GetContentFollowing(ref _pageParent, ref _idxParent, pageEnd, idxEnd, type))
+                if (!XPathNodeHelper.GetContentFollowing(ref _pageParent!, ref _idxParent, pageEnd, idxEnd, type))
                     return false;
 
                 _pageCurrent = _pageParent;
@@ -732,7 +747,7 @@ public override XPathNodeIterator SelectChildren(XPathNodeType type)
         public override XPathNodeIterator SelectChildren(string name, string namespaceURI)
         {
             // If local name is wildcard, then call XPathNavigator.SelectChildren
-            if (name == null || name.Length == 0)
+            if (name.Length == 0)
                 return base.SelectChildren(name, namespaceURI);
 
             return new XPathDocumentElementChildIterator(this, name, namespaceURI);
@@ -754,7 +769,7 @@ public override XPathNodeIterator SelectDescendants(XPathNodeType type, bool mat
         public override XPathNodeIterator SelectDescendants(string name, string namespaceURI, bool matchSelf)
         {
             // If local name is wildcard, then call XPathNavigator.SelectDescendants
-            if (name == null || name.Length == 0)
+            if (name.Length == 0)
                 return base.SelectDescendants(name, namespaceURI, matchSelf);
 
             return new XPathDocumentElementDescendantIterator(this, name, namespaceURI, matchSelf);
@@ -770,9 +785,9 @@ public override XPathNodeIterator SelectDescendants(string name, string namespac
         ///                           in document order.
         ///     XmlNodeOrder.Same -- This navigator is positioned on the same node as the "other" navigator.
         /// </summary>
-        public override XmlNodeOrder ComparePosition(XPathNavigator other)
+        public override XmlNodeOrder ComparePosition(XPathNavigator? other)
         {
-            XPathDocumentNavigator that = other as XPathDocumentNavigator;
+            XPathDocumentNavigator? that = other as XPathDocumentNavigator;
             if (that != null)
             {
                 XPathDocument thisDoc = _pageCurrent[_idxCurrent].Document;
@@ -799,18 +814,18 @@ public override XmlNodeOrder ComparePosition(XPathNavigator other)
         /// <summary>
         /// Return true if the "other" navigator's current node is a descendant of this navigator's current node.
         /// </summary>
-        public override bool IsDescendant(XPathNavigator other)
+        public override bool IsDescendant(XPathNavigator? other)
         {
-            XPathDocumentNavigator that = other as XPathDocumentNavigator;
+            XPathDocumentNavigator? that = other as XPathDocumentNavigator;
             if (that != null)
             {
-                XPathNode[] pageThat;
+                XPathNode[]? pageThat;
                 int idxThat;
 
                 // If that current node's parent is virtualized, then start with the virtual parent
                 if (that._idxParent != 0)
                 {
-                    pageThat = that._pageParent;
+                    pageThat = that._pageParent!;
                     idxThat = that._idxParent;
                 }
                 else
@@ -822,7 +837,7 @@ public override bool IsDescendant(XPathNavigator other)
                 {
                     if (idxThat == _idxCurrent && pageThat == _pageCurrent)
                         return true;
-                    idxThat = pageThat[idxThat].GetParent(out pageThat);
+                    idxThat = pageThat![idxThat].GetParent(out pageThat);
                 }
             }
             return false;
@@ -844,7 +859,7 @@ private int GetPrimaryLocation()
             }
 
             // Yes, so primary location should be derived from parent node
-            return XPathNodeHelper.GetLocation(_pageParent, _idxParent);
+            return XPathNodeHelper.GetLocation(_pageParent!, _idxParent);
         }
 
         /// <summary>
@@ -893,7 +908,7 @@ internal override string UniqueId
                 // If the current node is virtualized, code its parent
                 if (_idxParent != 0)
                 {
-                    loc = (_pageParent[0].PageInfo.PageNumber - 1) << 16 | (_idxParent - 1);
+                    loc = (_pageParent![0].PageInfo!.PageNumber - 1) << 16 | (_idxParent - 1);
                     do
                     {
                         buf[idx++] = UniqueIdTbl[loc & 0x1f];
@@ -903,7 +918,7 @@ internal override string UniqueId
                 }
 
                 // Code the node itself
-                loc = (_pageCurrent[0].PageInfo.PageNumber - 1) << 16 | (_idxCurrent - 1);
+                loc = (_pageCurrent[0].PageInfo!.PageNumber - 1) << 16 | (_idxCurrent - 1);
                 do
                 {
                     buf[idx++] = UniqueIdTbl[loc & 0x1f];
@@ -947,7 +962,7 @@ public int LineNumber
             {
                 // If the current node is a collapsed text node, then return parent element's line number
                 if (_idxParent != 0 && NodeType == XPathNodeType.Text)
-                    return _pageParent[_idxParent].LineNumber;
+                    return _pageParent![_idxParent].LineNumber;
 
                 return _pageCurrent[_idxCurrent].LineNumber;
             }
@@ -962,7 +977,7 @@ public int LinePosition
             {
                 // If the current node is a collapsed text node, then get position from parent element
                 if (_idxParent != 0 && NodeType == XPathNodeType.Text)
-                    return _pageParent[_idxParent].CollapsedLinePosition;
+                    return _pageParent![_idxParent].CollapsedLinePosition;
 
                 return _pageCurrent[_idxCurrent].LinePosition;
             }
@@ -984,9 +999,9 @@ public int GetPositionHashCode()
         /// <summary>
         /// Return true if navigator is positioned to an element having the specified name.
         /// </summary>
-        public bool IsElementMatch(string localName, string namespaceURI)
+        public bool IsElementMatch(string? localName, string namespaceURI)
         {
-            if ((object)localName != (object)_atomizedLocalName)
+            if ((object?)localName != (object?)_atomizedLocalName)
                 _atomizedLocalName = (localName != null) ? NameTable.Get(localName) : null;
 
             // Cannot be an element if parent is stored
@@ -1011,7 +1026,7 @@ public bool IsKindMatch(XPathNodeType typ)
         ///    1. If useParentOfVirtual is true, then return the page and index of the virtual node's parent
         ///    2. If useParentOfVirtual is false, then return the page and index of the virtual node's parent + 1.
         /// </summary>
-        private int GetFollowingEnd(XPathDocumentNavigator end, bool useParentOfVirtual, out XPathNode[] pageEnd)
+        private int GetFollowingEnd(XPathDocumentNavigator? end, bool useParentOfVirtual, out XPathNode[]? pageEnd)
         {
             // If ending navigator is positioned to a node in another document, then return null
             if (end != null && _pageCurrent[_idxCurrent].Document == end._pageCurrent[end._idxCurrent].Document)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNode.cs b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNode.cs
index 75ab1647c227ce..e8c1dd592c72c2 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNode.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNode.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Diagnostics;
 using System.Xml.XPath;
@@ -33,7 +34,7 @@ internal struct XPathNode
         private ushort _idxSimilar;                     // Page index of next node in document order that has local name with same hashcode
         private ushort _posOffset;                      // Line position offset of node (added to LinePositionBase)
         private uint _props;                          // Node properties (broken down into bits below)
-        private string _value;                          // String value of node
+        private string? _value;                          // String value of node
 
         private const uint NodeTypeMask = 0xF;
         private const uint HasAttributeBit = 0x10;
@@ -124,7 +125,7 @@ public XPathDocument Document
         /// </summary>
         public string BaseUri
         {
-            get { return _info.BaseUri; }
+            get { return _info.BaseUri ?? string.Empty; }
         }
 
         /// <summary>
@@ -159,7 +160,7 @@ public int CollapsedLinePosition
         /// <summary>
         /// Returns information about the node page.  Only the 0th node on each page has this property defined.
         /// </summary>
-        public XPathNodePageInfo PageInfo
+        public XPathNodePageInfo? PageInfo
         {
             get { return _info.PageInfo; }
         }
@@ -169,13 +170,15 @@ public XPathNodePageInfo PageInfo
         /// </summary>
         public int GetRoot(out XPathNode[] pageNode)
         {
-            return _info.Document.GetRootNode(out pageNode);
+            int idx = _info.Document.GetRootNode(out pageNode!);
+            Debug.Assert(pageNode != null);
+            return idx;
         }
 
         /// <summary>
         /// Returns the parent of this node.  If this node has no parent, then 0 is returned.
         /// </summary>
-        public int GetParent(out XPathNode[] pageNode)
+        public int GetParent(out XPathNode[]? pageNode)
         {
             pageNode = _info.ParentPage;
             return _idxParent;
@@ -184,7 +187,7 @@ public int GetParent(out XPathNode[] pageNode)
         /// <summary>
         /// Returns the next sibling of this node.  If this node has no next sibling, then 0 is returned.
         /// </summary>
-        public int GetSibling(out XPathNode[] pageNode)
+        public int GetSibling(out XPathNode[]? pageNode)
         {
             pageNode = _info.SiblingPage;
             return _idxSibling;
@@ -194,7 +197,7 @@ public int GetSibling(out XPathNode[] pageNode)
         /// Returns the next element in document order that has the same local name hashcode as this element.
         /// If there are no similar elements, then 0 is returned.
         /// </summary>
-        public int GetSimilarElement(out XPathNode[] pageNode)
+        public int GetSimilarElement(out XPathNode[]? pageNode)
         {
             pageNode = _info.SimilarElementPage;
             return _idxSimilar;
@@ -204,11 +207,11 @@ public int GetSimilarElement(out XPathNode[] pageNode)
         /// Returns true if this node's name matches the specified localName and namespaceName.  Assume
         /// that localName has been atomized, but namespaceName has not.
         /// </summary>
-        public bool NameMatch(string localName, string namespaceName)
+        public bool NameMatch(string? localName, string namespaceName)
         {
-            Debug.Assert(localName == null || (object)Document.NameTable.Get(localName) == (object)localName, "localName must be atomized.");
+            Debug.Assert(localName == null || (object?)Document.NameTable.Get(localName) == (object)localName, "localName must be atomized.");
 
-            return (object)_info.LocalName == (object)localName &&
+            return (object)_info.LocalName == (object?)localName &&
                    _info.NamespaceUri == namespaceName;
         }
 
@@ -216,12 +219,12 @@ public bool NameMatch(string localName, string namespaceName)
         /// Returns true if this is an Element node with a name that matches the specified localName and
         /// namespaceName.  Assume that localName has been atomized, but namespaceName has not.
         /// </summary>
-        public bool ElementMatch(string localName, string namespaceName)
+        public bool ElementMatch(string? localName, string namespaceName)
         {
-            Debug.Assert(localName == null || (object)Document.NameTable.Get(localName) == (object)localName, "localName must be atomized.");
+            Debug.Assert(localName == null || (object?)Document.NameTable.Get(localName) == (object)localName, "localName must be atomized.");
 
             return NodeType == XPathNodeType.Element &&
-                   (object)_info.LocalName == (object)localName &&
+                   (object)_info.LocalName == (object?)localName &&
                    _info.NamespaceUri == namespaceName;
         }
 
@@ -333,7 +336,7 @@ public int LocalNameHashCode
         /// <summary>
         /// Return the precomputed String value of this node (null if no value exists, i.e. document node, element node with complex content, etc).
         /// </summary>
-        public string Value
+        public string? Value
         {
             get { return _value; }
         }
@@ -385,7 +388,7 @@ public void SetCollapsedLineInfoOffset(int posOffset)
         /// <summary>
         /// Set this node's value.
         /// </summary>
-        public void SetValue(string value)
+        public void SetValue(string? value)
         {
             _value = value;
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNodeHelper.cs b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNodeHelper.cs
index dd477325605fe4..aaea5e0b5a29de 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNodeHelper.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNodeHelper.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Diagnostics;
 using System.Xml.XPath;
@@ -18,7 +19,7 @@ internal abstract class XPathNodeHelper
         /// parent is this node).  Subsequent nodes may not have the same node as parent, so the caller will
         /// need to test the parent in order to terminate a search that processes only local namespaces.
         /// </summary>
-        public static int GetLocalNamespaces(XPathNode[] pageElem, int idxElem, out XPathNode[] pageNmsp)
+        public static int GetLocalNamespaces(XPathNode[] pageElem, int idxElem, out XPathNode[]? pageNmsp)
         {
             if (pageElem[idxElem].HasNamespaceDecls)
             {
@@ -35,7 +36,7 @@ public static int GetLocalNamespaces(XPathNode[] pageElem, int idxElem, out XPat
         /// have this element as their parent.  Since the xmlns:xml namespace node is always in scope, this
         /// method will never return 0 if the specified node is an element.
         /// </summary>
-        public static int GetInScopeNamespaces(XPathNode[] pageElem, int idxElem, out XPathNode[] pageNmsp)
+        public static int GetInScopeNamespaces(XPathNode[] pageElem, int idxElem, out XPathNode[]? pageNmsp)
         {
             XPathDocument doc;
 
@@ -47,7 +48,7 @@ public static int GetInScopeNamespaces(XPathNode[] pageElem, int idxElem, out XP
                 // Walk ancestors, looking for an ancestor that has at least one namespace declaration
                 while (!pageElem[idxElem].HasNamespaceDecls)
                 {
-                    idxElem = pageElem[idxElem].GetParent(out pageElem);
+                    idxElem = pageElem[idxElem].GetParent(out pageElem!);
                     if (idxElem == 0)
                     {
                         // There are no namespace nodes declared on ancestors, so return xmlns:xml node
@@ -84,12 +85,12 @@ public static bool GetFirstAttribute(ref XPathNode[] pageNode, ref int idxNode)
         /// </summary>
         public static bool GetNextAttribute(ref XPathNode[] pageNode, ref int idxNode)
         {
-            XPathNode[] page;
+            XPathNode[]? page;
             int idx;
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
 
             idx = pageNode[idxNode].GetSibling(out page);
-            if (idx != 0 && page[idx].NodeType == XPathNodeType.Attribute)
+            if (idx != 0 && page![idx].NodeType == XPathNodeType.Attribute)
             {
                 pageNode = page;
                 idxNode = idx;
@@ -104,7 +105,7 @@ public static bool GetNextAttribute(ref XPathNode[] pageNode, ref int idxNode)
         /// </summary>
         public static bool GetContentChild(ref XPathNode[] pageNode, ref int idxNode)
         {
-            XPathNode[] page = pageNode;
+            XPathNode[]? page = pageNode;
             int idx = idxNode;
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
 
@@ -117,6 +118,7 @@ public static bool GetContentChild(ref XPathNode[] pageNode, ref int idxNode)
                 {
                     idx = page[idx].GetSibling(out page);
                     Debug.Assert(idx != 0);
+                    Debug.Assert(page != null);
                 }
 
                 pageNode = page;
@@ -132,7 +134,7 @@ public static bool GetContentChild(ref XPathNode[] pageNode, ref int idxNode)
         /// </summary>
         public static bool GetContentSibling(ref XPathNode[] pageNode, ref int idxNode)
         {
-            XPathNode[] page = pageNode;
+            XPathNode[]? page = pageNode;
             int idx = idxNode;
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
 
@@ -141,7 +143,7 @@ public static bool GetContentSibling(ref XPathNode[] pageNode, ref int idxNode)
                 idx = page[idx].GetSibling(out page);
                 if (idx != 0)
                 {
-                    pageNode = page;
+                    pageNode = page!;
                     idxNode = idx;
                     return true;
                 }
@@ -155,14 +157,14 @@ public static bool GetContentSibling(ref XPathNode[] pageNode, ref int idxNode)
         /// </summary>
         public static bool GetParent(ref XPathNode[] pageNode, ref int idxNode)
         {
-            XPathNode[] page = pageNode;
+            XPathNode[]? page = pageNode;
             int idx = idxNode;
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
 
             idx = page[idx].GetParent(out page);
             if (idx != 0)
             {
-                pageNode = page;
+                pageNode = page!;
                 idxNode = idx;
                 return true;
             }
@@ -177,8 +179,8 @@ public static int GetLocation(XPathNode[] pageNode, int idxNode)
         {
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
             Debug.Assert(idxNode <= ushort.MaxValue);
-            Debug.Assert(pageNode[0].PageInfo.PageNumber <= short.MaxValue);
-            return (pageNode[0].PageInfo.PageNumber << 16) | idxNode;
+            Debug.Assert(pageNode[0].PageInfo!.PageNumber <= short.MaxValue);
+            return (pageNode[0].PageInfo!.PageNumber << 16) | idxNode;
         }
 
         /// <summary>
@@ -186,9 +188,9 @@ public static int GetLocation(XPathNode[] pageNode, int idxNode)
         /// then do not set pageNode or idxNode and return false.  Assume that the localName has been atomized with respect
         /// to this document's name table, but not the namespaceName.
         /// </summary>
-        public static bool GetElementChild(ref XPathNode[] pageNode, ref int idxNode, string localName, string namespaceName)
+        public static bool GetElementChild(ref XPathNode[] pageNode, ref int idxNode, string? localName, string namespaceName)
         {
-            XPathNode[] page = pageNode;
+            XPathNode[]? page = pageNode;
             int idx = idxNode;
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
 
@@ -201,7 +203,7 @@ public static bool GetElementChild(ref XPathNode[] pageNode, ref int idxNode, st
                 // Find element with specified localName and namespaceName
                 do
                 {
-                    if (page[idx].ElementMatch(localName, namespaceName))
+                    if (page![idx].ElementMatch(localName, namespaceName))
                     {
                         pageNode = page;
                         idxNode = idx;
@@ -220,9 +222,9 @@ public static bool GetElementChild(ref XPathNode[] pageNode, ref int idxNode, st
         /// return false.  Assume that the localName has been atomized with respect to this document's name table,
         /// but not the namespaceName.
         /// </summary>
-        public static bool GetElementSibling(ref XPathNode[] pageNode, ref int idxNode, string localName, string namespaceName)
+        public static bool GetElementSibling(ref XPathNode[] pageNode, ref int idxNode, string? localName, string namespaceName)
         {
-            XPathNode[] page = pageNode;
+            XPathNode[]? page = pageNode;
             int idx = idxNode;
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
 
@@ -236,7 +238,7 @@ public static bool GetElementSibling(ref XPathNode[] pageNode, ref int idxNode,
                     if (idx == 0)
                         break;
 
-                    if (page[idx].ElementMatch(localName, namespaceName))
+                    if (page![idx].ElementMatch(localName, namespaceName))
                     {
                         pageNode = page;
                         idxNode = idx;
@@ -254,7 +256,7 @@ public static bool GetElementSibling(ref XPathNode[] pageNode, ref int idxNode,
         /// </summary>
         public static bool GetContentChild(ref XPathNode[] pageNode, ref int idxNode, XPathNodeType typ)
         {
-            XPathNode[] page = pageNode;
+            XPathNode[]? page = pageNode;
             int idx = idxNode;
             int mask;
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
@@ -267,7 +269,7 @@ public static bool GetContentChild(ref XPathNode[] pageNode, ref int idxNode, XP
                 GetChild(ref page, ref idx);
                 do
                 {
-                    if (((1 << (int)page[idx].NodeType) & mask) != 0)
+                    if (((1 << (int)page![idx].NodeType) & mask) != 0)
                     {
                         // Never return attributes, as Attribute is not a content type
                         if (typ == XPathNodeType.Attribute)
@@ -292,7 +294,7 @@ public static bool GetContentChild(ref XPathNode[] pageNode, ref int idxNode, XP
         /// </summary>
         public static bool GetContentSibling(ref XPathNode[] pageNode, ref int idxNode, XPathNodeType typ)
         {
-            XPathNode[] page = pageNode;
+            XPathNode[]? page = pageNode;
             int idx = idxNode;
             int mask = XPathNavigator.GetContentKindMask(typ);
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
@@ -306,7 +308,7 @@ public static bool GetContentSibling(ref XPathNode[] pageNode, ref int idxNode,
                     if (idx == 0)
                         break;
 
-                    if (((1 << (int)page[idx].NodeType) & mask) != 0)
+                    if (((1 << (int)page![idx].NodeType) & mask) != 0)
                     {
                         Debug.Assert(typ != XPathNodeType.Attribute && typ != XPathNodeType.Namespace);
                         pageNode = page;
@@ -325,7 +327,7 @@ public static bool GetContentSibling(ref XPathNode[] pageNode, ref int idxNode,
         /// </summary>
         public static bool GetPreviousContentSibling(ref XPathNode[] pageNode, ref int idxNode)
         {
-            XPathNode[] pageParent = pageNode, pagePrec, pageAnc;
+            XPathNode[]? pageParent, pagePrec, pageAnc;
             int idxParent = idxNode, idxPrec, idxAnc;
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
             Debug.Assert(pageNode[idxNode].NodeType != XPathNodeType.Attribute);
@@ -336,14 +338,15 @@ public static bool GetPreviousContentSibling(ref XPathNode[] pageNode, ref int i
             //   3. Get node that immediately precedes the current node in document order
             //   4. If preceding node is parent, then there is no previous sibling, so return false
             //   5. Walk ancestors of preceding node, until parent of current node is found
-            idxParent = pageParent[idxParent].GetParent(out pageParent);
+            idxParent = pageNode[idxParent].GetParent(out pageParent);
             if (idxParent != 0)
             {
                 idxPrec = idxNode - 1;
                 if (idxPrec == 0)
                 {
                     // Need to get previous page
-                    pagePrec = pageNode[0].PageInfo.PreviousPage;
+                    pagePrec = pageNode[0].PageInfo!.PreviousPage;
+                    Debug.Assert(pagePrec != null);
                     idxPrec = pagePrec.Length - 1;
                 }
                 else
@@ -385,9 +388,9 @@ public static bool GetPreviousContentSibling(ref XPathNode[] pageNode, ref int i
         /// then do not set pageNode or idxNode and return false.  Assume that the localName has been atomized with respect
         /// to this document's name table, but not the namespaceName.
         /// </summary>
-        public static bool GetAttribute(ref XPathNode[] pageNode, ref int idxNode, string localName, string namespaceName)
+        public static bool GetAttribute(ref XPathNode[] pageNode, ref int idxNode, string? localName, string namespaceName)
         {
-            XPathNode[] page = pageNode;
+            XPathNode[]? page = pageNode;
             int idx = idxNode;
             Debug.Assert(pageNode != null && idxNode != 0, "Cannot pass null argument(s)");
 
@@ -405,7 +408,7 @@ public static bool GetAttribute(ref XPathNode[] pageNode, ref int idxNode, strin
                     }
                     idx = page[idx].GetSibling(out page);
                 }
-                while (idx != 0 && page[idx].NodeType == XPathNodeType.Attribute);
+                while (idx != 0 && page![idx].NodeType == XPathNodeType.Attribute);
             }
 
             return false;
@@ -419,14 +422,14 @@ public static bool GetAttribute(ref XPathNode[] pageNode, ref int idxNode, strin
         /// If no such element exists, then do not set pageCurrent or idxCurrent and return false.
         /// Assume that the localName has been atomized with respect to this document's name table, but not the namespaceName.
         /// </summary>
-        public static bool GetElementFollowing(ref XPathNode[] pageCurrent, ref int idxCurrent, XPathNode[] pageEnd, int idxEnd, string localName, string namespaceName)
+        public static bool GetElementFollowing(ref XPathNode[] pageCurrent, ref int idxCurrent, XPathNode[]? pageEnd, int idxEnd, string? localName, string namespaceName)
         {
-            XPathNode[] page = pageCurrent;
+            XPathNode[]? page = pageCurrent;
             int idx = idxCurrent;
             Debug.Assert(pageCurrent != null && idxCurrent != 0, "Cannot pass null argument(s)");
 
             // If current node is an element having a matching name,
-            if (page[idx].NodeType == XPathNodeType.Element && (object)page[idx].LocalName == (object)localName)
+            if (page[idx].NodeType == XPathNodeType.Element && (object)page[idx].LocalName == (object?)localName)
             {
                 // Then follow similar element name pointers
                 int idxPageEnd = 0;
@@ -434,8 +437,8 @@ public static bool GetElementFollowing(ref XPathNode[] pageCurrent, ref int idxC
 
                 if (pageEnd != null)
                 {
-                    idxPageEnd = pageEnd[0].PageInfo.PageNumber;
-                    idxPageCurrent = page[0].PageInfo.PageNumber;
+                    idxPageEnd = pageEnd[0].PageInfo!.PageNumber;
+                    idxPageCurrent = page[0].PageInfo!.PageNumber;
 
                     // If ending node is <= starting node in document order, then scan to end of document
                     if (idxPageCurrent > idxPageEnd || (idxPageCurrent == idxPageEnd && idx >= idxEnd))
@@ -449,10 +452,12 @@ public static bool GetElementFollowing(ref XPathNode[] pageCurrent, ref int idxC
                     if (idx == 0)
                         break;
 
+                    Debug.Assert(page != null);
+
                     // Only scan to ending node
                     if (pageEnd != null)
                     {
-                        idxPageCurrent = page[0].PageInfo.PageNumber;
+                        idxPageCurrent = page[0].PageInfo!.PageNumber;
                         if (idxPageCurrent > idxPageEnd)
                             break;
 
@@ -472,7 +477,7 @@ public static bool GetElementFollowing(ref XPathNode[] pageCurrent, ref int idxC
             idx++;
             do
             {
-                if ((object)page == (object)pageEnd && idx <= idxEnd)
+                if ((object)page == (object?)pageEnd && idx <= idxEnd)
                 {
                     // Only scan to termination point
                     while (idx != idxEnd)
@@ -486,7 +491,7 @@ public static bool GetElementFollowing(ref XPathNode[] pageCurrent, ref int idxC
                 else
                 {
                     // Scan all nodes in the page
-                    while (idx < page[0].PageInfo.NodeCount)
+                    while (idx < page[0].PageInfo!.NodeCount)
                     {
                         if (page[idx].ElementMatch(localName, namespaceName))
                             goto FoundNode;
@@ -494,7 +499,7 @@ public static bool GetElementFollowing(ref XPathNode[] pageCurrent, ref int idxC
                     }
                 }
 
-                page = page[0].PageInfo.NextPage;
+                page = page[0].PageInfo!.NextPage;
                 idx = 1;
             }
             while (page != null);
@@ -515,9 +520,9 @@ public static bool GetElementFollowing(ref XPathNode[] pageCurrent, ref int idxC
         ///   3. Has the specified XPathNodeType (but Attributes and Namespaces never match)
         /// If no such node exists, then do not set pageCurrent or idxCurrent and return false.
         /// </summary>
-        public static bool GetContentFollowing(ref XPathNode[] pageCurrent, ref int idxCurrent, XPathNode[] pageEnd, int idxEnd, XPathNodeType typ)
+        public static bool GetContentFollowing(ref XPathNode[] pageCurrent, ref int idxCurrent, XPathNode[]? pageEnd, int idxEnd, XPathNodeType typ)
         {
-            XPathNode[] page = pageCurrent;
+            XPathNode[]? page = pageCurrent;
             int idx = idxCurrent;
             int mask = XPathNavigator.GetContentKindMask(typ);
             Debug.Assert(pageCurrent != null && idxCurrent != 0, "Cannot pass null argument(s)");
@@ -529,7 +534,7 @@ public static bool GetContentFollowing(ref XPathNode[] pageCurrent, ref int idxC
             idx++;
             do
             {
-                if ((object)page == (object)pageEnd && idx <= idxEnd)
+                if ((object)page == (object?)pageEnd && idx <= idxEnd)
                 {
                     // Only scan to termination point
                     while (idx != idxEnd)
@@ -543,7 +548,7 @@ public static bool GetContentFollowing(ref XPathNode[] pageCurrent, ref int idxC
                 else
                 {
                     // Scan all nodes in the page
-                    while (idx < page[0].PageInfo.NodeCount)
+                    while (idx < page[0].PageInfo!.NodeCount)
                     {
                         if (((1 << (int)page[idx].NodeType) & mask) != 0)
                             goto FoundNode;
@@ -551,7 +556,7 @@ public static bool GetContentFollowing(ref XPathNode[] pageCurrent, ref int idxC
                     }
                 }
 
-                page = page[0].PageInfo.NextPage;
+                page = page[0].PageInfo!.NextPage;
                 idx = 1;
             }
             while (page != null);
@@ -574,9 +579,9 @@ public static bool GetContentFollowing(ref XPathNode[] pageCurrent, ref int idxC
         ///   2. Non-collapsed text nodes
         /// If no such node exists, then do not set pageCurrent or idxCurrent and return false.
         /// </summary>
-        public static bool GetTextFollowing(ref XPathNode[] pageCurrent, ref int idxCurrent, XPathNode[] pageEnd, int idxEnd)
+        public static bool GetTextFollowing(ref XPathNode[] pageCurrent, ref int idxCurrent, XPathNode[]? pageEnd, int idxEnd)
         {
-            XPathNode[] page = pageCurrent;
+            XPathNode[]? page = pageCurrent;
             int idx = idxCurrent;
             Debug.Assert(pageCurrent != null && idxCurrent != 0, "Cannot pass null argument(s)");
             Debug.Assert(!page[idx].IsAttrNmsp, "Current node should never be an attribute or namespace--caller should handle this case.");
@@ -586,7 +591,7 @@ public static bool GetTextFollowing(ref XPathNode[] pageCurrent, ref int idxCurr
             idx++;
             do
             {
-                if ((object)page == (object)pageEnd && idx <= idxEnd)
+                if ((object)page == (object?)pageEnd && idx <= idxEnd)
                 {
                     // Only scan to termination point
                     while (idx != idxEnd)
@@ -600,7 +605,7 @@ public static bool GetTextFollowing(ref XPathNode[] pageCurrent, ref int idxCurr
                 else
                 {
                     // Scan all nodes in the page
-                    while (idx < page[0].PageInfo.NodeCount)
+                    while (idx < page[0].PageInfo!.NodeCount)
                     {
                         if (page[idx].IsText || (page[idx].NodeType == XPathNodeType.Element && page[idx].HasCollapsedText))
                             goto FoundNode;
@@ -608,7 +613,7 @@ public static bool GetTextFollowing(ref XPathNode[] pageCurrent, ref int idxCurr
                     }
                 }
 
-                page = page[0].PageInfo.NextPage;
+                page = page[0].PageInfo!.NextPage;
                 idx = 1;
             }
             while (page != null);
@@ -628,18 +633,18 @@ public static bool GetTextFollowing(ref XPathNode[] pageCurrent, ref int idxCurr
         /// </summary>
         public static bool GetNonDescendant(ref XPathNode[] pageNode, ref int idxNode)
         {
-            XPathNode[] page = pageNode;
+            XPathNode[]? page = pageNode;
             int idx = idxNode;
 
             // Get page, idx at which to end sequential scan of nodes
             do
             {
                 // If the current node has a sibling,
-                if (page[idx].HasSibling)
+                if (page![idx].HasSibling)
                 {
                     // Then that is the first non-descendant
                     pageNode = page;
-                    idxNode = page[idx].GetSibling(out pageNode);
+                    idxNode = page[idx].GetSibling(out pageNode!);
                     return true;
                 }
 
@@ -662,7 +667,8 @@ private static void GetChild(ref XPathNode[] pageNode, ref int idxNode)
             if (++idxNode >= pageNode.Length)
             {
                 // Child is first node on next page
-                pageNode = pageNode[0].PageInfo.NextPage;
+                pageNode = pageNode[0].PageInfo!.NextPage!;
+                Debug.Assert(pageNode != null);
                 idxNode = 1;
             }
             // Else child is next node on this page
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNodeInfoAtom.cs b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNodeInfoAtom.cs
index 001844076683ec..4396a832e33851 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNodeInfoAtom.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Cache/XPathNodeInfoAtom.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Diagnostics;
 using System.Text;
@@ -17,13 +18,13 @@ internal sealed class XPathNodePageInfo
     {
         private readonly int _pageNum;
         private int _nodeCount;
-        private readonly XPathNode[] _pagePrev;
-        private XPathNode[] _pageNext;
+        private readonly XPathNode[]? _pagePrev;
+        private XPathNode[]? _pageNext;
 
         /// <summary>
         /// Constructor.
         /// </summary>
-        public XPathNodePageInfo(XPathNode[] pagePrev, int pageNum)
+        public XPathNodePageInfo(XPathNode[]? pagePrev, int pageNum)
         {
             _pagePrev = pagePrev;
             _pageNum = pageNum;
@@ -50,7 +51,7 @@ public int NodeCount
         /// <summary>
         /// Return the previous node page in the document.
         /// </summary>
-        public XPathNode[] PreviousPage
+        public XPathNode[]? PreviousPage
         {
             get { return _pagePrev; }
         }
@@ -58,7 +59,7 @@ public XPathNode[] PreviousPage
         /// <summary>
         /// Return the next node page in the document.
         /// </summary>
-        public XPathNode[] NextPage
+        public XPathNode[]? NextPage
         {
             get { return _pageNext; }
             set { _pageNext = value; }
@@ -77,20 +78,20 @@ public XPathNode[] NextPage
     /// </summary>
     internal sealed class XPathNodeInfoAtom : IEquatable<XPathNodeInfoAtom>
     {
-        private string _localName;
-        private string _namespaceUri;
-        private string _prefix;
-        private string _baseUri;
-        private XPathNode[] _pageParent;
-        private XPathNode[] _pageSibling;
-        private XPathNode[] _pageSimilar;
-        private XPathDocument _doc;
+        private string _localName = null!;
+        private string _namespaceUri = null!;
+        private string _prefix = null!;
+        private string? _baseUri;
+        private XPathNode[]? _pageParent;
+        private XPathNode[]? _pageSibling;
+        private XPathNode[]? _pageSimilar;
+        private XPathDocument _doc = null!;
         private int _lineNumBase;
         private int _linePosBase;
         private int _hashCode;
         private int _localNameHash;
-        private XPathNodeInfoAtom _next;
-        private XPathNodePageInfo _pageInfo;
+        private XPathNodeInfoAtom? _next;
+        private XPathNodePageInfo? _pageInfo;
 
 
         /// <summary>
@@ -105,8 +106,8 @@ public XPathNodeInfoAtom(XPathNodePageInfo pageInfo)
         /// <summary>
         /// Construct a new shared information atom.  This method should only be used by the XNodeInfoTable.
         /// </summary>
-        public XPathNodeInfoAtom(string localName, string namespaceUri, string prefix, string baseUri,
-                                         XPathNode[] pageParent, XPathNode[] pageSibling, XPathNode[] pageSimilar,
+        public XPathNodeInfoAtom(string localName, string namespaceUri, string prefix, string? baseUri,
+                                         XPathNode[]? pageParent, XPathNode[]? pageSibling, XPathNode[]? pageSimilar,
                                          XPathDocument doc, int lineNumBase, int linePosBase)
         {
             Init(localName, namespaceUri, prefix, baseUri, pageParent, pageSibling, pageSimilar, doc, lineNumBase, linePosBase);
@@ -115,8 +116,8 @@ public XPathNodeInfoAtom(string localName, string namespaceUri, string prefix, s
         /// <summary>
         /// Initialize an existing shared information atom.  This method should only be used by the XNodeInfoTable.
         /// </summary>
-        public void Init(string localName, string namespaceUri, string prefix, string baseUri,
-                         XPathNode[] pageParent, XPathNode[] pageSibling, XPathNode[] pageSimilar,
+        public void Init(string localName, string namespaceUri, string prefix, string? baseUri,
+                         XPathNode[]? pageParent, XPathNode[]? pageSibling, XPathNode[]? pageSimilar,
                          XPathDocument doc, int lineNumBase, int linePosBase)
         {
             Debug.Assert(localName != null && namespaceUri != null && prefix != null && doc != null);
@@ -143,7 +144,7 @@ public void Init(string localName, string namespaceUri, string prefix, string ba
         /// <summary>
         /// Returns information about the node page.  Only the 0th node on each page has this property defined.
         /// </summary>
-        public XPathNodePageInfo PageInfo
+        public XPathNodePageInfo? PageInfo
         {
             get { return _pageInfo; }
         }
@@ -175,7 +176,7 @@ public string Prefix
         /// <summary>
         /// Return the base Uri of nodes that share this information atom.
         /// </summary>
-        public string BaseUri
+        public string? BaseUri
         {
             get { return _baseUri; }
         }
@@ -183,7 +184,7 @@ public string BaseUri
         /// <summary>
         /// Return the page containing the next sibling of nodes that share this information atom.
         /// </summary>
-        public XPathNode[] SiblingPage
+        public XPathNode[]? SiblingPage
         {
             get { return _pageSibling; }
         }
@@ -191,7 +192,7 @@ public XPathNode[] SiblingPage
         /// <summary>
         /// Return the page containing the next element having a name which has same hashcode as this element.
         /// </summary>
-        public XPathNode[] SimilarElementPage
+        public XPathNode[]? SimilarElementPage
         {
             get { return _pageSimilar; }
         }
@@ -199,7 +200,7 @@ public XPathNode[] SimilarElementPage
         /// <summary>
         /// Return the page containing the parent of nodes that share this information atom.
         /// </summary>
-        public XPathNode[] ParentPage
+        public XPathNode[]? ParentPage
         {
             get { return _pageParent; }
         }
@@ -239,7 +240,7 @@ public int LocalNameHashCode
         /// <summary>
         /// Link together InfoAtoms that hash to the same hashtable bucket (should only be used by XPathNodeInfoTable)
         /// </summary>
-        public XPathNodeInfoAtom Next
+        public XPathNodeInfoAtom? Next
         {
             get { return _next; }
             set { _next = value; }
@@ -261,13 +262,13 @@ public override int GetHashCode()
                 unchecked
                 {
                     if (_pageSibling != null)
-                        hashCode += (hashCode << 7) ^ _pageSibling[0].PageInfo.PageNumber;
+                        hashCode += (hashCode << 7) ^ _pageSibling[0].PageInfo!.PageNumber;
 
                     if (_pageParent != null)
-                        hashCode += (hashCode << 7) ^ _pageParent[0].PageInfo.PageNumber;
+                        hashCode += (hashCode << 7) ^ _pageParent[0].PageInfo!.PageNumber;
 
                     if (_pageSimilar != null)
-                        hashCode += (hashCode << 7) ^ _pageSimilar[0].PageInfo.PageNumber;
+                        hashCode += (hashCode << 7) ^ _pageSimilar[0].PageInfo!.PageNumber;
                 }
 
                 // Save hashcode.  Don't save 0, so that it won't ever be recomputed.
@@ -280,27 +281,27 @@ public override int GetHashCode()
         /// <summary>
         /// Return true if this InfoAtom has the same values as another InfoAtom.
         /// </summary>
-        public override bool Equals(object other)
+        public override bool Equals(object? other)
         {
             return Equals(other as XPathNodeInfoAtom);
         }
 
-        public bool Equals(XPathNodeInfoAtom other)
+        public bool Equals(XPathNodeInfoAtom? other)
         {
             Debug.Assert(other != null);
-            Debug.Assert((object)_doc == (object)other._doc);
+            Debug.Assert((object?)_doc == (object?)other._doc);
             Debug.Assert(_pageInfo == null);
 
             // Assume that name parts are atomized
             if (this.GetHashCode() == other.GetHashCode())
             {
-                if ((object)_localName == (object)other._localName &&
-                    (object)_pageSibling == (object)other._pageSibling &&
-                    (object)_namespaceUri == (object)other._namespaceUri &&
-                    (object)_pageParent == (object)other._pageParent &&
-                    (object)_pageSimilar == (object)other._pageSimilar &&
-                    (object)_prefix == (object)other._prefix &&
-                    (object)_baseUri == (object)other._baseUri &&
+                if ((object?)_localName == (object?)other._localName &&
+                    (object?)_pageSibling == (object?)other._pageSibling &&
+                    (object?)_namespaceUri == (object?)other._namespaceUri &&
+                    (object?)_pageParent == (object?)other._pageParent &&
+                    (object?)_pageSimilar == (object?)other._pageSimilar &&
+                    (object?)_prefix == (object?)other._prefix &&
+                    (object?)_baseUri == (object?)other._baseUri &&
                     _lineNumBase == other._lineNumBase &&
                     _linePosBase == other._linePosBase)
                 {
@@ -322,12 +323,14 @@ public override string ToString()
             bldr.Append(GetHashCode());
             bldr.Append(", ");
 
+            Debug.Assert(_localName != null);
             if (_localName.Length != 0)
             {
                 bldr.Append('{');
                 bldr.Append(_namespaceUri);
                 bldr.Append('}');
 
+                Debug.Assert(_prefix != null);
                 if (_prefix.Length != 0)
                 {
                     bldr.Append(_prefix);
@@ -341,21 +344,21 @@ public override string ToString()
             if (_pageParent != null)
             {
                 bldr.Append("parent=");
-                bldr.Append(_pageParent[0].PageInfo.PageNumber);
+                bldr.Append(_pageParent[0].PageInfo!.PageNumber);
                 bldr.Append(", ");
             }
 
             if (_pageSibling != null)
             {
                 bldr.Append("sibling=");
-                bldr.Append(_pageSibling[0].PageInfo.PageNumber);
+                bldr.Append(_pageSibling[0].PageInfo!.PageNumber);
                 bldr.Append(", ");
             }
 
             if (_pageSimilar != null)
             {
                 bldr.Append("similar=");
-                bldr.Append(_pageSimilar[0].PageInfo.PageNumber);
+                bldr.Append(_pageSimilar[0].PageInfo!.PageNumber);
                 bldr.Append(", ");
             }
 
@@ -378,7 +381,7 @@ internal sealed class XPathNodeInfoTable
     {
         private XPathNodeInfoAtom[] _hashTable;
         private int _sizeTable;
-        private XPathNodeInfoAtom _infoCached;
+        private XPathNodeInfoAtom? _infoCached;
 
 #if DEBUG
         private const int DefaultTableSize = 2;
@@ -398,8 +401,8 @@ public XPathNodeInfoTable()
         /// <summary>
         /// Create a new XNodeInfoAtom and ensure it is atomized in the table.
         /// </summary>
-        public XPathNodeInfoAtom Create(string localName, string namespaceUri, string prefix, string baseUri,
-                                          XPathNode[] pageParent, XPathNode[] pageSibling, XPathNode[] pageSimilar,
+        public XPathNodeInfoAtom Create(string localName, string namespaceUri, string prefix, string? baseUri,
+                                          XPathNode[]? pageParent, XPathNode[]? pageSibling, XPathNode[]? pageSimilar,
                                           XPathDocument doc, int lineNumBase, int linePosBase)
         {
             XPathNodeInfoAtom info;
@@ -434,7 +437,7 @@ public XPathNodeInfoAtom Create(string localName, string namespaceUri, string pr
         /// </summary>
         private XPathNodeInfoAtom Atomize(XPathNodeInfoAtom info)
         {
-            XPathNodeInfoAtom infoNew, infoNext;
+            XPathNodeInfoAtom? infoNew, infoNext;
 
             // Search for existing XNodeInfoAtom in the table
             infoNew = _hashTable[info.GetHashCode() & (_hashTable.Length - 1)];
@@ -492,7 +495,7 @@ private void AddInfo(XPathNodeInfoAtom info)
         public override string ToString()
         {
             StringBuilder bldr = new StringBuilder();
-            XPathNodeInfoAtom infoAtom;
+            XPathNodeInfoAtom? infoAtom;
 
             for (int i = 0; i < _hashTable.Length; i++)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/IDtdParser.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/IDtdParser.cs
index c9ddb2b5780460..3f771d8f91a60e 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/IDtdParser.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/IDtdParser.cs
@@ -10,6 +10,6 @@ namespace System.Xml
     internal partial interface IDtdParser
     {
         IDtdInfo ParseInternalDtd(IDtdParserAdapter adapter, bool saveInternalSubset);
-        IDtdInfo ParseFreeFloatingDtd(string baseUri, string docTypeName, string publicId, string systemId, string internalSubset, IDtdParserAdapter adapter);
+        IDtdInfo ParseFreeFloatingDtd(string baseUri, string docTypeName, string? publicId, string? systemId, string? internalSubset, IDtdParserAdapter adapter);
     }
 }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/IRemovableWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/IRemovableWriter.cs
index b3e837f56cac37..c74dc523513304 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/IRemovableWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/IRemovableWriter.cs
@@ -17,6 +17,6 @@ namespace System.Xml
     /// </summary>
     internal interface IRemovableWriter
     {
-        OnRemoveWriter OnRemoveWriterEvent { get; set; }
+        OnRemoveWriter? OnRemoveWriterEvent { get; set; }
     }
 }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/IValidationEventHandling.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/IValidationEventHandling.cs
index a19645a8fbb10a..57ce91b8a129a6 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/IValidationEventHandling.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/IValidationEventHandling.cs
@@ -10,7 +10,7 @@ namespace System.Xml
     internal interface IValidationEventHandling
     {
         // This is a ValidationEventHandler, but it is not strongly typed due to dependencies on System.Xml.Schema
-        object EventHandler { get; }
+        object? EventHandler { get; }
 
         // The exception is XmlSchemaException, but it is not strongly typed due to dependencies on System.Xml.Schema
         void SendEvent(Exception exception, XmlSeverityType severity);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/QueryOutputWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/QueryOutputWriter.cs
index 9c631ed9d5a344..6cced37f2300bf 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/QueryOutputWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/QueryOutputWriter.cs
@@ -31,7 +31,7 @@ internal class QueryOutputWriter : XmlRawWriter
         private readonly bool _checkWellFormedDoc;
         private bool _hasDocElem;
         private bool _inAttr;
-        private readonly string _systemId, _publicId;
+        private readonly string? _systemId, _publicId;
         private int _depth;
 
         public QueryOutputWriter(XmlRawWriter writer, XmlWriterSettings settings)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/QueryOutputWriterV1.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/QueryOutputWriterV1.cs
index 8dd3f70992b2a7..527c893952fdfa 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/QueryOutputWriterV1.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/QueryOutputWriterV1.cs
@@ -29,7 +29,7 @@ internal class QueryOutputWriterV1 : XmlWriter
         private readonly BitStack? _bitsCData;
         private readonly XmlQualifiedName? _qnameCData;
         private bool _outputDocType, _inAttr;
-        private readonly string _systemId, _publicId;
+        private readonly string? _systemId, _publicId;
 
         public QueryOutputWriterV1(XmlWriter writer, XmlWriterSettings settings)
         {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/ValidatingReaderNodeData.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/ValidatingReaderNodeData.cs
index 89c7c608ca7893..c58e0ec9f40b31 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/ValidatingReaderNodeData.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/ValidatingReaderNodeData.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.IO;
 using System.Text;
@@ -8,6 +9,7 @@
 using System.Xml.Schema;
 using System.Diagnostics;
 using System.Globalization;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml
 {
@@ -16,12 +18,12 @@ internal class ValidatingReaderNodeData
         private string _localName;
         private string _namespaceUri;
         private string _prefix;
-        private string _nameWPrefix;
+        private string? _nameWPrefix;
 
         private string _rawValue;
-        private string _originalStringValue;  // Original value
+        private string? _originalStringValue;  // Original value
         private int _depth;
-        private AttributePSVIInfo _attributePSVIInfo;  //Used only for default attributes
+        private AttributePSVIInfo? _attributePSVIInfo;  //Used only for default attributes
         private XmlNodeType _nodeType;
 
         private int _lineNo;
@@ -86,6 +88,7 @@ public string GetAtomizedNameWPrefix(XmlNameTable nameTable)
                     _nameWPrefix = nameTable.Add(string.Concat(_prefix, ":", _localName));
                 }
             }
+
             return _nameWPrefix;
         }
 
@@ -113,7 +116,7 @@ public string RawValue
             }
         }
 
-        public string OriginalStringValue
+        public string? OriginalStringValue
         {
             get
             {
@@ -137,7 +140,7 @@ public XmlNodeType NodeType
             }
         }
 
-        public AttributePSVIInfo AttInfo
+        public AttributePSVIInfo? AttInfo
         {
             get
             {
@@ -165,6 +168,10 @@ public int LinePosition
             }
         }
 
+        [MemberNotNull(nameof(_localName))]
+        [MemberNotNull(nameof(_prefix))]
+        [MemberNotNull(nameof(_namespaceUri))]
+        [MemberNotNull(nameof(_rawValue))]
         internal void Clear(XmlNodeType nodeType)
         {
             _nodeType = nodeType;
@@ -172,10 +179,12 @@ internal void Clear(XmlNodeType nodeType)
             _prefix = string.Empty;
             _namespaceUri = string.Empty;
             _rawValue = string.Empty;
+
             if (_attributePSVIInfo != null)
             {
                 _attributePSVIInfo.Reset();
             }
+
             _nameWPrefix = null;
             _lineNo = 0;
             _linePos = 0;
@@ -187,7 +196,7 @@ internal void SetLineInfo(int lineNo, int linePos)
             _linePos = linePos;
         }
 
-        internal void SetLineInfo(IXmlLineInfo lineInfo)
+        internal void SetLineInfo(IXmlLineInfo? lineInfo)
         {
             if (lineInfo != null)
             {
@@ -210,7 +219,7 @@ internal void SetItemData(string value)
             SetItemData(value, value);
         }
 
-        internal void SetItemData(string value, string originalStringValue)
+        internal void SetItemData(string value, string? originalStringValue)
         {
             _rawValue = value;
             _originalStringValue = originalStringValue;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAsyncCheckReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAsyncCheckReader.cs
index 1531deab96ac16..752e156d1a2303 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAsyncCheckReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAsyncCheckReader.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Threading.Tasks;
@@ -64,7 +65,7 @@ public override XmlReaderSettings Settings
         {
             get
             {
-                XmlReaderSettings settings = _coreReader.Settings;
+                XmlReaderSettings? settings = _coreReader.Settings;
                 if (null != settings)
                 {
                     settings = settings.Clone();
@@ -151,7 +152,7 @@ public override int Depth
             }
         }
 
-        public override string BaseURI
+        public override string? BaseURI
         {
             get
             {
@@ -205,7 +206,7 @@ public override string XmlLang
             }
         }
 
-        public override IXmlSchemaInfo SchemaInfo
+        public override IXmlSchemaInfo? SchemaInfo
         {
             get
             {
@@ -418,13 +419,13 @@ public override int AttributeCount
             }
         }
 
-        public override string GetAttribute(string name)
+        public override string? GetAttribute(string name)
         {
             CheckAsync();
             return _coreReader.GetAttribute(name);
         }
 
-        public override string GetAttribute(string name, string namespaceURI)
+        public override string? GetAttribute(string name, string? namespaceURI)
         {
             CheckAsync();
             return _coreReader.GetAttribute(name, namespaceURI);
@@ -445,7 +446,7 @@ public override string this[int i]
             }
         }
 
-        public override string this[string name]
+        public override string? this[string name]
         {
             get
             {
@@ -460,7 +461,7 @@ public override bool MoveToAttribute(string name)
             return _coreReader.MoveToAttribute(name);
         }
 
-        public override bool MoveToAttribute(string name, string ns)
+        public override bool MoveToAttribute(string name, string? ns)
         {
             CheckAsync();
             return _coreReader.MoveToAttribute(name, ns);
@@ -541,7 +542,7 @@ public override XmlNameTable NameTable
             }
         }
 
-        public override string LookupNamespace(string prefix)
+        public override string? LookupNamespace(string prefix)
         {
             CheckAsync();
             return _coreReader.LookupNamespace(prefix);
@@ -754,7 +755,7 @@ protected override void Dispose(bool disposing)
             _coreReader.Dispose();
         }
 
-        internal override XmlNamespaceManager NamespaceManager
+        internal override XmlNamespaceManager? NamespaceManager
         {
             get
             {
@@ -763,7 +764,7 @@ internal override XmlNamespaceManager NamespaceManager
             }
         }
 
-        internal override IDtdInfo DtdInfo
+        internal override IDtdInfo? DtdInfo
         {
             get
             {
@@ -930,12 +931,12 @@ IDictionary<string, string> IXmlNamespaceResolver.GetNamespacesInScope(XmlNamesp
             return _readerAsIXmlNamespaceResolver.GetNamespacesInScope(scope);
         }
 
-        string IXmlNamespaceResolver.LookupNamespace(string prefix)
+        string? IXmlNamespaceResolver.LookupNamespace(string prefix)
         {
             return _readerAsIXmlNamespaceResolver.LookupNamespace(prefix);
         }
 
-        string IXmlNamespaceResolver.LookupPrefix(string namespaceName)
+        string? IXmlNamespaceResolver.LookupPrefix(string namespaceName)
         {
             return _readerAsIXmlNamespaceResolver.LookupPrefix(namespaceName);
         }
@@ -992,12 +993,12 @@ IDictionary<string, string> IXmlNamespaceResolver.GetNamespacesInScope(XmlNamesp
             return _readerAsIXmlNamespaceResolver.GetNamespacesInScope(scope);
         }
 
-        string IXmlNamespaceResolver.LookupNamespace(string prefix)
+        string? IXmlNamespaceResolver.LookupNamespace(string prefix)
         {
             return _readerAsIXmlNamespaceResolver.LookupNamespace(prefix);
         }
 
-        string IXmlNamespaceResolver.LookupPrefix(string namespaceName)
+        string? IXmlNamespaceResolver.LookupPrefix(string namespaceName)
         {
             return _readerAsIXmlNamespaceResolver.LookupPrefix(namespaceName);
         }
@@ -1014,7 +1015,6 @@ public XmlAsyncCheckReaderWithLineInfoNSSchema(XmlReader reader)
             _readerAsIXmlSchemaInfo = (IXmlSchemaInfo)reader;
         }
 
-
         #region IXmlSchemaInfo members
 
         XmlSchemaValidity IXmlSchemaInfo.Validity
@@ -1041,7 +1041,7 @@ bool IXmlSchemaInfo.IsNil
             }
         }
 
-        XmlSchemaSimpleType IXmlSchemaInfo.MemberType
+        XmlSchemaSimpleType? IXmlSchemaInfo.MemberType
         {
             get
             {
@@ -1049,7 +1049,7 @@ XmlSchemaSimpleType IXmlSchemaInfo.MemberType
             }
         }
 
-        XmlSchemaType IXmlSchemaInfo.SchemaType
+        XmlSchemaType? IXmlSchemaInfo.SchemaType
         {
             get
             {
@@ -1057,7 +1057,7 @@ XmlSchemaType IXmlSchemaInfo.SchemaType
             }
         }
 
-        XmlSchemaElement IXmlSchemaInfo.SchemaElement
+        XmlSchemaElement? IXmlSchemaInfo.SchemaElement
         {
             get
             {
@@ -1065,7 +1065,7 @@ XmlSchemaElement IXmlSchemaInfo.SchemaElement
             }
         }
 
-        XmlSchemaAttribute IXmlSchemaInfo.SchemaAttribute
+        XmlSchemaAttribute? IXmlSchemaInfo.SchemaAttribute
         {
             get
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAsyncCheckWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAsyncCheckWriter.cs
index 666fd5487a1783..84990c82955ed0 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAsyncCheckWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAsyncCheckWriter.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Threading.Tasks;
 using System.Xml.XPath;
 
@@ -38,7 +39,7 @@ public override XmlWriterSettings Settings
         {
             get
             {
-                XmlWriterSettings settings = _coreWriter.Settings;
+                XmlWriterSettings? settings = _coreWriter.Settings;
 
                 if (null != settings)
                 {
@@ -74,13 +75,13 @@ public override void WriteEndDocument()
             _coreWriter.WriteEndDocument();
         }
 
-        public override void WriteDocType(string name, string pubid, string sysid, string subset)
+        public override void WriteDocType(string name, string? pubid, string? sysid, string? subset)
         {
             CheckAsync();
             _coreWriter.WriteDocType(name, pubid, sysid, subset);
         }
 
-        public override void WriteStartElement(string prefix, string localName, string ns)
+        public override void WriteStartElement(string? prefix, string localName, string? ns)
         {
             CheckAsync();
             _coreWriter.WriteStartElement(prefix, localName, ns);
@@ -98,7 +99,7 @@ public override void WriteFullEndElement()
             _coreWriter.WriteFullEndElement();
         }
 
-        public override void WriteStartAttribute(string prefix, string localName, string ns)
+        public override void WriteStartAttribute(string? prefix, string localName, string? ns)
         {
             CheckAsync();
             _coreWriter.WriteStartAttribute(prefix, localName, ns);
@@ -110,19 +111,19 @@ public override void WriteEndAttribute()
             _coreWriter.WriteEndAttribute();
         }
 
-        public override void WriteCData(string text)
+        public override void WriteCData(string? text)
         {
             CheckAsync();
             _coreWriter.WriteCData(text);
         }
 
-        public override void WriteComment(string text)
+        public override void WriteComment(string? text)
         {
             CheckAsync();
             _coreWriter.WriteComment(text);
         }
 
-        public override void WriteProcessingInstruction(string name, string text)
+        public override void WriteProcessingInstruction(string name, string? text)
         {
             CheckAsync();
             _coreWriter.WriteProcessingInstruction(name, text);
@@ -140,13 +141,13 @@ public override void WriteCharEntity(char ch)
             _coreWriter.WriteCharEntity(ch);
         }
 
-        public override void WriteWhitespace(string ws)
+        public override void WriteWhitespace(string? ws)
         {
             CheckAsync();
             _coreWriter.WriteWhitespace(ws);
         }
 
-        public override void WriteString(string text)
+        public override void WriteString(string? text)
         {
             CheckAsync();
             _coreWriter.WriteString(text);
@@ -209,7 +210,7 @@ public override void Flush()
             _coreWriter.Flush();
         }
 
-        public override string LookupPrefix(string ns)
+        public override string? LookupPrefix(string ns)
         {
             CheckAsync();
             return _coreWriter.LookupPrefix(ns);
@@ -224,7 +225,7 @@ public override XmlSpace XmlSpace
             }
         }
 
-        public override string XmlLang
+        public override string? XmlLang
         {
             get
             {
@@ -245,7 +246,7 @@ public override void WriteName(string name)
             _coreWriter.WriteName(name);
         }
 
-        public override void WriteQualifiedName(string localName, string ns)
+        public override void WriteQualifiedName(string localName, string? ns)
         {
             CheckAsync();
             _coreWriter.WriteQualifiedName(localName, ns);
@@ -257,7 +258,7 @@ public override void WriteValue(object value)
             _coreWriter.WriteValue(value);
         }
 
-        public override void WriteValue(string value)
+        public override void WriteValue(string? value)
         {
             CheckAsync();
             _coreWriter.WriteValue(value);
@@ -368,7 +369,7 @@ public override Task WriteEndDocumentAsync()
             return task;
         }
 
-        public override Task WriteDocTypeAsync(string name, string pubid, string sysid, string subset)
+        public override Task WriteDocTypeAsync(string name, string? pubid, string? sysid, string? subset)
         {
             CheckAsync();
             var task = _coreWriter.WriteDocTypeAsync(name, pubid, sysid, subset);
@@ -376,7 +377,7 @@ public override Task WriteDocTypeAsync(string name, string pubid, string sysid,
             return task;
         }
 
-        public override Task WriteStartElementAsync(string prefix, string localName, string ns)
+        public override Task WriteStartElementAsync(string? prefix, string localName, string? ns)
         {
             CheckAsync();
             var task = _coreWriter.WriteStartElementAsync(prefix, localName, ns);
@@ -400,7 +401,7 @@ public override Task WriteFullEndElementAsync()
             return task;
         }
 
-        protected internal override Task WriteStartAttributeAsync(string prefix, string localName, string ns)
+        protected internal override Task WriteStartAttributeAsync(string? prefix, string localName, string? ns)
         {
             CheckAsync();
             var task = _coreWriter.WriteStartAttributeAsync(prefix, localName, ns);
@@ -416,7 +417,7 @@ protected internal override Task WriteEndAttributeAsync()
             return task;
         }
 
-        public override Task WriteCDataAsync(string text)
+        public override Task WriteCDataAsync(string? text)
         {
             CheckAsync();
             var task = _coreWriter.WriteCDataAsync(text);
@@ -424,7 +425,7 @@ public override Task WriteCDataAsync(string text)
             return task;
         }
 
-        public override Task WriteCommentAsync(string text)
+        public override Task WriteCommentAsync(string? text)
         {
             CheckAsync();
             var task = _coreWriter.WriteCommentAsync(text);
@@ -456,7 +457,7 @@ public override Task WriteCharEntityAsync(char ch)
             return task;
         }
 
-        public override Task WriteWhitespaceAsync(string ws)
+        public override Task WriteWhitespaceAsync(string? ws)
         {
             CheckAsync();
             var task = _coreWriter.WriteWhitespaceAsync(ws);
@@ -464,7 +465,7 @@ public override Task WriteWhitespaceAsync(string ws)
             return task;
         }
 
-        public override Task WriteStringAsync(string text)
+        public override Task WriteStringAsync(string? text)
         {
             CheckAsync();
             var task = _coreWriter.WriteStringAsync(text);
@@ -544,7 +545,7 @@ public override Task WriteNameAsync(string name)
             return task;
         }
 
-        public override Task WriteQualifiedNameAsync(string localName, string ns)
+        public override Task WriteQualifiedNameAsync(string localName, string? ns)
         {
             CheckAsync();
             var task = _coreWriter.WriteQualifiedNameAsync(localName, ns);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAutoDetectWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAutoDetectWriter.cs
index c4cf2e9da9ca0e..c3aa8c0d97bd95 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAutoDetectWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlAutoDetectWriter.cs
@@ -1,10 +1,12 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     using System;
     using System.Diagnostics;
+    using System.Diagnostics.CodeAnalysis;
     using System.IO;
     using System.Text;
     using System.Xml;
@@ -17,12 +19,12 @@ namespace System.Xml
     /// </summary>
     internal class XmlAutoDetectWriter : XmlRawWriter, IRemovableWriter
     {
-        private XmlRawWriter _wrapped;
-        private OnRemoveWriter _onRemove;
+        private XmlRawWriter? _wrapped;
+        private OnRemoveWriter? _onRemove;
         private readonly XmlWriterSettings _writerSettings;
         private readonly XmlEventCache _eventCache;           // Cache up events until first StartElement is encountered
-        private readonly TextWriter _textWriter;
-        private readonly Stream _strm;
+        private readonly TextWriter? _textWriter;
+        private readonly Stream? _strm;
 
         //-----------------------------------------------
         // Constructors
@@ -59,7 +61,7 @@ public XmlAutoDetectWriter(Stream strm, XmlWriterSettings writerSettings)
         /// <summary>
         /// This writer will raise this event once it has determined whether to replace itself with the Html or Xml writer.
         /// </summary>
-        public OnRemoveWriter OnRemoveWriterEvent
+        public OnRemoveWriter? OnRemoveWriterEvent
         {
             get { return _onRemove; }
             set { _onRemove = value; }
@@ -75,26 +77,27 @@ public override XmlWriterSettings Settings
             get { return _writerSettings; }
         }
 
-        public override void WriteDocType(string name, string pubid, string sysid, string subset)
+        public override void WriteDocType(string name, string? pubid, string? sysid, string? subset)
         {
             EnsureWrappedWriter(XmlOutputMethod.Xml);
             _wrapped.WriteDocType(name, pubid, sysid, subset);
         }
 
-        public override void WriteStartElement(string prefix, string localName, string ns)
+        public override void WriteStartElement(string? prefix, string localName, string? ns)
         {
             if (_wrapped == null)
             {
                 // This is the first time WriteStartElement has been called, so create the Xml or Html writer
-                if (ns.Length == 0 && IsHtmlTag(localName))
+                if (ns!.Length == 0 && IsHtmlTag(localName))
                     CreateWrappedWriter(XmlOutputMethod.Html);
                 else
                     CreateWrappedWriter(XmlOutputMethod.Xml);
             }
+
             _wrapped.WriteStartElement(prefix, localName, ns);
         }
 
-        public override void WriteStartAttribute(string prefix, string localName, string ns)
+        public override void WriteStartAttribute(string? prefix, string localName, string? ns)
         {
             EnsureWrappedWriter(XmlOutputMethod.Xml);
             _wrapped.WriteStartAttribute(prefix, localName, ns);
@@ -106,7 +109,7 @@ public override void WriteEndAttribute()
             _wrapped.WriteEndAttribute();
         }
 
-        public override void WriteCData(string text)
+        public override void WriteCData(string? text)
         {
             if (TextBlockCreatesWriter(text))
                 _wrapped.WriteCData(text);
@@ -114,7 +117,7 @@ public override void WriteCData(string text)
                 _eventCache.WriteCData(text);
         }
 
-        public override void WriteComment(string text)
+        public override void WriteComment(string? text)
         {
             if (_wrapped == null)
                 _eventCache.WriteComment(text);
@@ -122,7 +125,7 @@ public override void WriteComment(string text)
                 _wrapped.WriteComment(text);
         }
 
-        public override void WriteProcessingInstruction(string name, string text)
+        public override void WriteProcessingInstruction(string name, string? text)
         {
             if (_wrapped == null)
                 _eventCache.WriteProcessingInstruction(name, text);
@@ -130,7 +133,7 @@ public override void WriteProcessingInstruction(string name, string text)
                 _wrapped.WriteProcessingInstruction(name, text);
         }
 
-        public override void WriteWhitespace(string ws)
+        public override void WriteWhitespace(string? ws)
         {
             if (_wrapped == null)
                 _eventCache.WriteWhitespace(ws);
@@ -138,7 +141,7 @@ public override void WriteWhitespace(string ws)
                 _wrapped.WriteWhitespace(ws);
         }
 
-        public override void WriteString(string text)
+        public override void WriteString(string? text)
         {
             if (TextBlockCreatesWriter(text))
                 _wrapped.WriteString(text);
@@ -214,7 +217,7 @@ public override void WriteValue(object value)
             _wrapped.WriteValue(value);
         }
 
-        public override void WriteValue(string value)
+        public override void WriteValue(string? value)
         {
             EnsureWrappedWriter(XmlOutputMethod.Xml);
             _wrapped.WriteValue(value);
@@ -272,7 +275,7 @@ public override void WriteValue(long value)
         // XmlRawWriter interface
         //-----------------------------------------------
 
-        internal override IXmlNamespaceResolver NamespaceResolver
+        internal override IXmlNamespaceResolver? NamespaceResolver
         {
             get
             {
@@ -331,7 +334,7 @@ internal override bool SupportsNamespaceDeclarationInChunks
         {
             get
             {
-                return _wrapped.SupportsNamespaceDeclarationInChunks;
+                return _wrapped!.SupportsNamespaceDeclarationInChunks;
             }
         }
 
@@ -343,7 +346,7 @@ internal override void WriteStartNamespaceDeclaration(string prefix)
 
         internal override void WriteEndNamespaceDeclaration()
         {
-            _wrapped.WriteEndNamespaceDeclaration();
+            _wrapped!.WriteEndNamespaceDeclaration();
         }
 
         //-----------------------------------------------
@@ -376,6 +379,7 @@ private static bool IsHtmlTag(string tagName)
         /// <summary>
         /// If a wrapped writer has not yet been created, create one.
         /// </summary>
+        [MemberNotNull(nameof(_wrapped))]
         private void EnsureWrappedWriter(XmlOutputMethod outMethod)
         {
             if (_wrapped == null)
@@ -387,7 +391,8 @@ private void EnsureWrappedWriter(XmlOutputMethod outMethod)
         /// force the creation of a wrapped writer.  Otherwise, create a wrapped writer if one has not yet been
         /// created and return true.
         /// </summary>
-        private bool TextBlockCreatesWriter(string textBlock)
+        [MemberNotNullWhen(true, nameof(_wrapped))]
+        private bool TextBlockCreatesWriter(string? textBlock)
         {
             if (_wrapped == null)
             {
@@ -407,6 +412,7 @@ private bool TextBlockCreatesWriter(string textBlock)
         /// <summary>
         /// Create either the Html or Xml writer and send any cached events to it.
         /// </summary>
+        [MemberNotNull(nameof(_wrapped))]
         private void CreateWrappedWriter(XmlOutputMethod outMethod)
         {
             Debug.Assert(_wrapped == null);
@@ -422,9 +428,9 @@ private void CreateWrappedWriter(XmlOutputMethod outMethod)
             _writerSettings.ReadOnly = true;
 
             if (_textWriter != null)
-                _wrapped = ((XmlWellFormedWriter)XmlWriter.Create(_textWriter, _writerSettings)).RawWriter;
+                _wrapped = ((XmlWellFormedWriter)XmlWriter.Create(_textWriter, _writerSettings)).RawWriter!;
             else
-                _wrapped = ((XmlWellFormedWriter)XmlWriter.Create(_strm, _writerSettings)).RawWriter;
+                _wrapped = ((XmlWellFormedWriter)XmlWriter.Create(_strm!, _writerSettings)).RawWriter!;
 
             // Send cached events to the new writer
             _eventCache.EndEvents();
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingReader.cs
index 7dadd488d0dfc0..ca0ce55d013b95 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingReader.cs
@@ -119,7 +119,7 @@ public override bool MoveToAttribute(string name)
             return base.reader.MoveToAttribute(name);
         }
 
-        public override bool MoveToAttribute(string name, string ns)
+        public override bool MoveToAttribute(string name, string? ns)
         {
             if (_state == State.InReadBinary)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingReaderAsync.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingReaderAsync.cs
index 387d182dc21c06..68f79ba17a167f 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingReaderAsync.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingReaderAsync.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Xml;
 using System.Diagnostics;
@@ -162,8 +163,7 @@ public override async Task<bool> ReadAsync()
                             ValidateQName(base.reader.Name);
                             CheckCharacters(base.reader.Value);
 
-                            string str;
-                            str = base.reader.GetAttribute("SYSTEM");
+                            string? str = base.reader.GetAttribute("SYSTEM");
                             if (str != null)
                             {
                                 CheckCharacters(str);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingWriter.cs
index e8f8fad0707361..2fa82a671869db 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingWriter.cs
@@ -1,12 +1,14 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.IO;
 using System.Text;
 using System.Xml.Schema;
 using System.Collections;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml
 {
@@ -50,30 +52,33 @@ public override XmlWriterSettings Settings
         {
             get
             {
-                XmlWriterSettings s = base.writer.Settings;
+                XmlWriterSettings? s = base.writer.Settings;
                 s = (s != null) ? (XmlWriterSettings)s.Clone() : new XmlWriterSettings();
 
                 if (_checkValues)
                 {
                     s.CheckCharacters = true;
                 }
+
                 if (_replaceNewLines)
                 {
                     s.NewLineHandling = NewLineHandling.Replace;
                     s.NewLineChars = _newLineChars;
                 }
+
                 s.ReadOnly = true;
                 return s;
             }
         }
 
 
-        public override void WriteDocType(string name, string pubid, string sysid, string subset)
+        public override void WriteDocType(string name, string? pubid, string? sysid, string? subset)
         {
             if (_checkNames)
             {
                 ValidateQName(name);
             }
+
             if (_checkValues)
             {
                 if (pubid != null)
@@ -84,25 +89,29 @@ public override void WriteDocType(string name, string pubid, string sysid, strin
                         throw XmlConvert.CreateInvalidCharException(pubid, i);
                     }
                 }
+
                 if (sysid != null)
                 {
                     CheckCharacters(sysid);
                 }
+
                 if (subset != null)
                 {
                     CheckCharacters(subset);
                 }
             }
+
             if (_replaceNewLines)
             {
                 sysid = ReplaceNewLines(sysid);
                 pubid = ReplaceNewLines(pubid);
                 subset = ReplaceNewLines(subset);
             }
+
             writer.WriteDocType(name, pubid, sysid, subset);
         }
 
-        public override void WriteStartElement(string prefix, string localName, string ns)
+        public override void WriteStartElement(string? prefix, string localName, string? ns)
         {
             if (_checkNames)
             {
@@ -110,6 +119,7 @@ public override void WriteStartElement(string prefix, string localName, string n
                 {
                     throw new ArgumentException(SR.Xml_EmptyLocalName);
                 }
+
                 ValidateNCName(localName);
 
                 if (prefix != null && prefix.Length > 0)
@@ -117,10 +127,11 @@ public override void WriteStartElement(string prefix, string localName, string n
                     ValidateNCName(prefix);
                 }
             }
+
             writer.WriteStartElement(prefix, localName, ns);
         }
 
-        public override void WriteStartAttribute(string prefix, string localName, string ns)
+        public override void WriteStartAttribute(string? prefix, string localName, string? ns)
         {
             if (_checkNames)
             {
@@ -128,6 +139,7 @@ public override void WriteStartAttribute(string prefix, string localName, string
                 {
                     throw new ArgumentException(SR.Xml_EmptyLocalName);
                 }
+
                 ValidateNCName(localName);
 
                 if (prefix != null && prefix.Length > 0)
@@ -135,10 +147,11 @@ public override void WriteStartAttribute(string prefix, string localName, string
                     ValidateNCName(prefix);
                 }
             }
+
             writer.WriteStartAttribute(prefix, localName, ns);
         }
 
-        public override void WriteCData(string text)
+        public override void WriteCData(string? text)
         {
             if (text != null)
             {
@@ -146,10 +159,12 @@ public override void WriteCData(string text)
                 {
                     CheckCharacters(text);
                 }
+
                 if (_replaceNewLines)
                 {
                     text = ReplaceNewLines(text);
                 }
+
                 int i;
                 while ((i = text.IndexOf("]]>", StringComparison.Ordinal)) >= 0)
                 {
@@ -160,7 +175,7 @@ public override void WriteCData(string text)
             writer.WriteCData(text);
         }
 
-        public override void WriteComment(string text)
+        public override void WriteComment(string? text)
         {
             if (text != null)
             {
@@ -169,20 +184,23 @@ public override void WriteComment(string text)
                     CheckCharacters(text);
                     text = InterleaveInvalidChars(text, '-', '-');
                 }
+
                 if (_replaceNewLines)
                 {
                     text = ReplaceNewLines(text);
                 }
             }
+
             writer.WriteComment(text);
         }
 
-        public override void WriteProcessingInstruction(string name, string text)
+        public override void WriteProcessingInstruction(string name, string? text)
         {
             if (_checkNames)
             {
                 ValidateNCName(name);
             }
+
             if (text != null)
             {
                 if (_checkValues)
@@ -190,11 +208,13 @@ public override void WriteProcessingInstruction(string name, string text)
                     CheckCharacters(text);
                     text = InterleaveInvalidChars(text, '?', '>');
                 }
+
                 if (_replaceNewLines)
                 {
                     text = ReplaceNewLines(text);
                 }
             }
+
             writer.WriteProcessingInstruction(name, text);
         }
 
@@ -204,15 +224,17 @@ public override void WriteEntityRef(string name)
             {
                 ValidateQName(name);
             }
+
             writer.WriteEntityRef(name);
         }
 
-        public override void WriteWhitespace(string ws)
+        public override void WriteWhitespace(string? ws)
         {
             if (ws == null)
             {
                 ws = string.Empty;
             }
+
             // "checkNames" is intentional here; if false, the whitespace is checked in XmlWellformedWriter
             if (_checkNames)
             {
@@ -222,14 +244,16 @@ public override void WriteWhitespace(string ws)
                     throw new ArgumentException(SR.Format(SR.Xml_InvalidWhitespaceCharacter, XmlException.BuildCharExceptionArgs(ws, i)));
                 }
             }
+
             if (_replaceNewLines)
             {
                 ws = ReplaceNewLines(ws);
             }
+
             writer.WriteWhitespace(ws);
         }
 
-        public override void WriteString(string text)
+        public override void WriteString(string? text)
         {
             if (text != null)
             {
@@ -242,6 +266,7 @@ public override void WriteString(string text)
                     text = ReplaceNewLines(text);
                 }
             }
+
             writer.WriteString(text);
         }
 
@@ -273,15 +298,17 @@ public override void WriteChars(char[] buffer, int index, int count)
             {
                 CheckCharacters(buffer, index, count);
             }
+
             if (_replaceNewLines && WriteState != WriteState.Attribute)
             {
-                string text = ReplaceNewLines(buffer, index, count);
+                string? text = ReplaceNewLines(buffer, index, count);
                 if (text != null)
                 {
                     WriteString(text);
                     return;
                 }
             }
+
             writer.WriteChars(buffer, index, count);
         }
 
@@ -293,8 +320,10 @@ public override void WriteNmToken(string name)
                 {
                     throw new ArgumentException(SR.Xml_EmptyName);
                 }
+
                 XmlConvert.VerifyNMTOKEN(name);
             }
+
             writer.WriteNmToken(name);
         }
 
@@ -304,15 +333,17 @@ public override void WriteName(string name)
             {
                 XmlConvert.VerifyQName(name, ExceptionType.XmlException);
             }
+
             writer.WriteName(name);
         }
 
-        public override void WriteQualifiedName(string localName, string ns)
+        public override void WriteQualifiedName(string localName, string? ns)
         {
             if (_checkNames)
             {
                 ValidateNCName(localName);
             }
+
             writer.WriteQualifiedName(localName, ns);
         }
 
@@ -349,6 +380,7 @@ private void ValidateQName(string name)
             {
                 throw new ArgumentException(SR.Xml_EmptyName);
             }
+
             int colonPos;
             int len = ValidateNames.ParseQName(name, 0, out colonPos);
             if (len != name.Length)
@@ -358,14 +390,15 @@ private void ValidateQName(string name)
             }
         }
 
-        private string ReplaceNewLines(string str)
+        [return: NotNullIfNotNull("str")]
+        private string? ReplaceNewLines(string? str)
         {
             if (str == null)
             {
                 return null;
             }
 
-            StringBuilder sb = null;
+            StringBuilder? sb = null;
             int start = 0;
             int i;
             for (i = 0; i < str.Length; i++)
@@ -396,10 +429,12 @@ private string ReplaceNewLines(string str)
                             i++;
                             continue;
                         }
+
                         if (sb == null)
                         {
                             sb = new StringBuilder(str.Length + 5);
                         }
+
                         sb.Append(str, start, i - start);
                         i++;
                     }
@@ -409,10 +444,12 @@ private string ReplaceNewLines(string str)
                         {
                             continue;
                         }
+
                         if (sb == null)
                         {
                             sb = new StringBuilder(str.Length + 5);
                         }
+
                         sb.Append(str, start, i - start);
                     }
                 }
@@ -435,14 +472,14 @@ private string ReplaceNewLines(string str)
             }
         }
 
-        private string ReplaceNewLines(char[] data, int offset, int len)
+        private string? ReplaceNewLines(char[]? data, int offset, int len)
         {
             if (data == null)
             {
                 return null;
             }
 
-            StringBuilder sb = null;
+            StringBuilder? sb = null;
             int start = offset;
             int endPos = offset + len;
             int i;
@@ -453,16 +490,19 @@ private string ReplaceNewLines(char[] data, int offset, int len)
                 {
                     continue;
                 }
+
                 if (ch == '\n')
                 {
                     if (_newLineChars == "\n")
                     {
                         continue;
                     }
+
                     if (sb == null)
                     {
                         sb = new StringBuilder(len + 5);
                     }
+
                     sb.Append(data, start, i - start);
                 }
                 else if (ch == '\r')
@@ -474,10 +514,12 @@ private string ReplaceNewLines(char[] data, int offset, int len)
                             i++;
                             continue;
                         }
+
                         if (sb == null)
                         {
                             sb = new StringBuilder(len + 5);
                         }
+
                         sb.Append(data, start, i - start);
                         i++;
                     }
@@ -487,10 +529,12 @@ private string ReplaceNewLines(char[] data, int offset, int len)
                         {
                             continue;
                         }
+
                         if (sb == null)
                         {
                             sb = new StringBuilder(len + 5);
                         }
+
                         sb.Append(data, start, i - start);
                     }
                 }
@@ -498,6 +542,7 @@ private string ReplaceNewLines(char[] data, int offset, int len)
                 {
                     continue;
                 }
+
                 sb.Append(_newLineChars);
                 start = i + 1;
             }
@@ -518,7 +563,7 @@ private string ReplaceNewLines(char[] data, int offset, int len)
         // Any "?>" in PI value must be replaced with "? >".
         private string InterleaveInvalidChars(string text, char invChar1, char invChar2)
         {
-            StringBuilder sb = null;
+            StringBuilder? sb = null;
             int start = 0;
             int i;
             for (i = 0; i < text.Length; i++)
@@ -533,6 +578,7 @@ private string InterleaveInvalidChars(string text, char invChar1, char invChar2)
                     {
                         sb = new StringBuilder(text.Length + 5);
                     }
+
                     sb.Append(text, start, i - start);
                     sb.Append(' ');
                     start = i;
@@ -551,6 +597,7 @@ private string InterleaveInvalidChars(string text, char invChar1, char invChar2)
                 {
                     sb.Append(' ');
                 }
+
                 return sb.ToString();
             }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingWriterAsync.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingWriterAsync.cs
index 722d1d7226cbd0..4b5a0e961fbf3c 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingWriterAsync.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlCharCheckingWriterAsync.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.IO;
 using System.Text;
@@ -17,12 +18,13 @@ namespace System.Xml
     //
     internal partial class XmlCharCheckingWriter : XmlWrappingWriter
     {
-        public override Task WriteDocTypeAsync(string name, string pubid, string sysid, string subset)
+        public override Task WriteDocTypeAsync(string name, string? pubid, string? sysid, string? subset)
         {
             if (_checkNames)
             {
                 ValidateQName(name);
             }
+
             if (_checkValues)
             {
                 if (pubid != null)
@@ -33,25 +35,29 @@ public override Task WriteDocTypeAsync(string name, string pubid, string sysid,
                         throw XmlConvert.CreateInvalidCharException(pubid, i);
                     }
                 }
+
                 if (sysid != null)
                 {
                     CheckCharacters(sysid);
                 }
+
                 if (subset != null)
                 {
                     CheckCharacters(subset);
                 }
             }
+
             if (_replaceNewLines)
             {
                 sysid = ReplaceNewLines(sysid);
                 pubid = ReplaceNewLines(pubid);
                 subset = ReplaceNewLines(subset);
             }
+
             return writer.WriteDocTypeAsync(name, pubid, sysid, subset);
         }
 
-        public override Task WriteStartElementAsync(string prefix, string localName, string ns)
+        public override Task WriteStartElementAsync(string? prefix, string localName, string? ns)
         {
             if (_checkNames)
             {
@@ -59,6 +65,7 @@ public override Task WriteStartElementAsync(string prefix, string localName, str
                 {
                     throw new ArgumentException(SR.Xml_EmptyLocalName);
                 }
+
                 ValidateNCName(localName);
 
                 if (prefix != null && prefix.Length > 0)
@@ -69,7 +76,7 @@ public override Task WriteStartElementAsync(string prefix, string localName, str
             return writer.WriteStartElementAsync(prefix, localName, ns);
         }
 
-        protected internal override Task WriteStartAttributeAsync(string prefix, string localName, string ns)
+        protected internal override Task WriteStartAttributeAsync(string? prefix, string localName, string? ns)
         {
             if (_checkNames)
             {
@@ -77,6 +84,7 @@ protected internal override Task WriteStartAttributeAsync(string prefix, string
                 {
                     throw new ArgumentException(SR.Xml_EmptyLocalName);
                 }
+
                 ValidateNCName(localName);
 
                 if (prefix != null && prefix.Length > 0)
@@ -84,10 +92,11 @@ protected internal override Task WriteStartAttributeAsync(string prefix, string
                     ValidateNCName(prefix);
                 }
             }
+
             return writer.WriteStartAttributeAsync(prefix, localName, ns);
         }
 
-        public override async Task WriteCDataAsync(string text)
+        public override async Task WriteCDataAsync(string? text)
         {
             if (text != null)
             {
@@ -95,10 +104,12 @@ public override async Task WriteCDataAsync(string text)
                 {
                     CheckCharacters(text);
                 }
+
                 if (_replaceNewLines)
                 {
                     text = ReplaceNewLines(text);
                 }
+
                 int i;
                 while ((i = text.IndexOf("]]>", StringComparison.Ordinal)) >= 0)
                 {
@@ -106,10 +117,11 @@ public override async Task WriteCDataAsync(string text)
                     text = text.Substring(i + 2);
                 }
             }
+
             await writer.WriteCDataAsync(text).ConfigureAwait(false);
         }
 
-        public override Task WriteCommentAsync(string text)
+        public override Task WriteCommentAsync(string? text)
         {
             if (text != null)
             {
@@ -132,6 +144,7 @@ public override Task WriteProcessingInstructionAsync(string name, string text)
             {
                 ValidateNCName(name);
             }
+
             if (text != null)
             {
                 if (_checkValues)
@@ -144,7 +157,8 @@ public override Task WriteProcessingInstructionAsync(string name, string text)
                     text = ReplaceNewLines(text);
                 }
             }
-            return writer.WriteProcessingInstructionAsync(name, text);
+
+            return writer.WriteProcessingInstructionAsync(name, text!);
         }
 
         public override Task WriteEntityRefAsync(string name)
@@ -156,12 +170,13 @@ public override Task WriteEntityRefAsync(string name)
             return writer.WriteEntityRefAsync(name);
         }
 
-        public override Task WriteWhitespaceAsync(string ws)
+        public override Task WriteWhitespaceAsync(string? ws)
         {
             if (ws == null)
             {
                 ws = string.Empty;
             }
+
             // "checkNames" is intentional here; if false, the whitespace is checked in XmlWellformedWriter
             if (_checkNames)
             {
@@ -171,14 +186,16 @@ public override Task WriteWhitespaceAsync(string ws)
                     throw new ArgumentException(SR.Format(SR.Xml_InvalidWhitespaceCharacter, XmlException.BuildCharExceptionArgs(ws, i)));
                 }
             }
+
             if (_replaceNewLines)
             {
                 ws = ReplaceNewLines(ws);
             }
+
             return writer.WriteWhitespaceAsync(ws);
         }
 
-        public override Task WriteStringAsync(string text)
+        public override Task WriteStringAsync(string? text)
         {
             if (text != null)
             {
@@ -186,11 +203,13 @@ public override Task WriteStringAsync(string text)
                 {
                     CheckCharacters(text);
                 }
+
                 if (_replaceNewLines && WriteState != WriteState.Attribute)
                 {
                     text = ReplaceNewLines(text);
                 }
             }
+
             return writer.WriteStringAsync(text);
         }
 
@@ -222,14 +241,16 @@ public override Task WriteCharsAsync(char[] buffer, int index, int count)
             {
                 CheckCharacters(buffer, index, count);
             }
+
             if (_replaceNewLines && WriteState != WriteState.Attribute)
             {
-                string text = ReplaceNewLines(buffer, index, count);
+                string? text = ReplaceNewLines(buffer, index, count);
                 if (text != null)
                 {
                     return WriteStringAsync(text);
                 }
             }
+
             return writer.WriteCharsAsync(buffer, index, count);
         }
 
@@ -255,12 +276,13 @@ public override Task WriteNameAsync(string name)
             return writer.WriteNameAsync(name);
         }
 
-        public override Task WriteQualifiedNameAsync(string localName, string ns)
+        public override Task WriteQualifiedNameAsync(string localName, string? ns)
         {
             if (_checkNames)
             {
                 ValidateNCName(localName);
             }
+
             return writer.WriteQualifiedNameAsync(localName, ns);
         }
     }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlRawWriterAsync.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlRawWriterAsync.cs
index 7456b4457e1640..fe8091cc64eb84 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlRawWriterAsync.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlRawWriterAsync.cs
@@ -107,7 +107,7 @@ public override Task WriteQualifiedNameAsync(string localName, string? ns)
         }
 
         // Forward call to WriteString(string).
-        public override Task WriteCDataAsync(string text)
+        public override Task WriteCDataAsync(string? text)
         {
             return WriteStringAsync(text);
         }
@@ -126,7 +126,7 @@ public override Task WriteSurrogateCharEntityAsync(char lowChar, char highChar)
         }
 
         // Forward call to WriteString(string).
-        public override Task WriteWhitespaceAsync(string ws)
+        public override Task WriteWhitespaceAsync(string? ws)
         {
             return WriteStringAsync(ws);
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlReader.cs
index 258f4b5bcb5418..36abf85f126cf5 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlReader.cs
@@ -620,7 +620,7 @@ public virtual object ReadElementContentAs(Type returnType, IXmlNamespaceResolve
         public abstract string? GetAttribute(string name);
 
         // Gets the value of the attribute with the LocalName and NamespaceURI
-        public abstract string? GetAttribute(string name, string namespaceURI);
+        public abstract string? GetAttribute(string name, string? namespaceURI);
 
         // Gets the value of the attribute with the specified index.
         public abstract string GetAttribute(int i);
@@ -644,7 +644,7 @@ public virtual string? this[string name]
         }
 
         // Gets the value of the attribute with the LocalName and NamespaceURI
-        public virtual string? this[string name, string namespaceURI]
+        public virtual string? this[string name, string? namespaceURI]
         {
             get
             {
@@ -656,7 +656,7 @@ public virtual string? this[string name]
         public abstract bool MoveToAttribute(string name);
 
         // Moves to the attribute with the specified LocalName and NamespaceURI.
-        public abstract bool MoveToAttribute(string name, string ns);
+        public abstract bool MoveToAttribute(string name, string? ns);
 
         // Moves to the attribute with the specified index.
         public virtual void MoveToAttribute(int i)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlSubtreeReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlSubtreeReader.cs
index 5d7f5dbf79f22e..d00bc27d68c69b 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlSubtreeReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlSubtreeReader.cs
@@ -265,7 +265,7 @@ public override int AttributeCount
             return null;
         }
 
-        public override string? GetAttribute(string name, string namespaceURI)
+        public override string? GetAttribute(string name, string? namespaceURI)
         {
             if (!InAttributeActiveState)
             {
@@ -334,7 +334,7 @@ public override bool MoveToAttribute(string name)
             return false;
         }
 
-        public override bool MoveToAttribute(string name, string ns)
+        public override bool MoveToAttribute(string name, string? ns)
         {
             if (!InAttributeActiveState)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextReader.cs
index 5e1b4d9e003d92..48598298580f09 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextReader.cs
@@ -83,13 +83,13 @@ public XmlTextReader(string url, TextReader input, XmlNameTable nt)
             _impl.OuterReader = this;
         }
 
-        public XmlTextReader(Stream xmlFragment, XmlNodeType fragType, XmlParserContext context)
+        public XmlTextReader(Stream xmlFragment, XmlNodeType fragType, XmlParserContext? context)
         {
             _impl = new XmlTextReaderImpl(xmlFragment, fragType, context);
             _impl.OuterReader = this;
         }
 
-        public XmlTextReader(string xmlFragment, XmlNodeType fragType, XmlParserContext context)
+        public XmlTextReader(string xmlFragment, XmlNodeType fragType, XmlParserContext? context)
         {
             _impl = new XmlTextReaderImpl(xmlFragment, fragType, context);
             _impl.OuterReader = this;
@@ -203,7 +203,7 @@ public override bool MoveToAttribute(string name)
             return _impl.MoveToAttribute(name);
         }
 
-        public override bool MoveToAttribute(string localName, string namespaceURI)
+        public override bool MoveToAttribute(string localName, string? namespaceURI)
         {
             return _impl.MoveToAttribute(localName, namespaceURI);
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextReaderImpl.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextReaderImpl.cs
index 4a959c251118b5..32c82f72dc7e57 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextReaderImpl.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextReaderImpl.cs
@@ -506,7 +506,7 @@ internal XmlTextReaderImpl(string? url, TextReader input, XmlNameTable nt) : thi
         // Initializes a new instance of XmlTextReaderImpl class for parsing fragments with the specified stream, fragment type and parser context
         // This constructor is used when creating XmlTextReaderImpl for V1 XmlTextReader
         // SxS: The method resolves URI but does not expose the resolved value up the stack hence Resource Exposure scope is None.
-        internal XmlTextReaderImpl(Stream xmlFragment, XmlNodeType fragType, XmlParserContext context)
+        internal XmlTextReaderImpl(Stream xmlFragment, XmlNodeType fragType, XmlParserContext? context)
             : this((context != null && context.NameTable != null) ? context.NameTable : new NameTable())
         {
             Encoding? enc = (context != null) ? context.Encoding : null;
@@ -529,7 +529,7 @@ internal XmlTextReaderImpl(Stream xmlFragment, XmlNodeType fragType, XmlParserCo
 
         // Initializes a new instance of XmlTextRreaderImpl class for parsing fragments with the specified string, fragment type and parser context
         // This constructor is used when creating XmlTextReaderImpl for V1 XmlTextReader
-        internal XmlTextReaderImpl(string xmlFragment, XmlNodeType fragType, XmlParserContext context)
+        internal XmlTextReaderImpl(string xmlFragment, XmlNodeType fragType, XmlParserContext? context)
             : this(null == context || null == context.NameTable ? new NameTable() : context.NameTable)
         {
             if (xmlFragment == null)
@@ -556,7 +556,7 @@ internal XmlTextReaderImpl(string xmlFragment, XmlNodeType fragType, XmlParserCo
         // "innerXml" of an XmlDecl is. This internal function is required by DOM. When(if) we handle/allow
         // all nodetypes in InnerXml then we should support them as part of fragment constructor as well.
         // Until then, this internal function will have to do.
-        internal XmlTextReaderImpl(string xmlFragment, XmlParserContext context)
+        internal XmlTextReaderImpl(string xmlFragment, XmlParserContext? context)
             : this(null == context || null == context.NameTable ? new NameTable() : context.NameTable)
         {
             InitStringInput((context == null) ? string.Empty : context.BaseURI, Encoding.Unicode, string.Concat("<?xml ", xmlFragment, "?>"));
@@ -821,7 +821,7 @@ private void FinishInitTextReader()
 
         // Initializes a new instance of the XmlTextReaderImpl class for fragment parsing.
         // This constructor is used by XmlBinaryReader for nested text XML
-        internal XmlTextReaderImpl(string xmlFragment, XmlParserContext context, XmlReaderSettings settings)
+        internal XmlTextReaderImpl(string xmlFragment, XmlParserContext? context, XmlReaderSettings settings)
             : this(null, settings, context)
         {
             Debug.Assert(xmlFragment != null);
@@ -9247,7 +9247,7 @@ internal void SetDtdInfo(IDtdInfo newDtdInfo)
         // Validation support
         //
 
-        internal IValidationEventHandling ValidationEventHandling
+        internal IValidationEventHandling? ValidationEventHandling
         {
             set
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextWriter.cs
index 38e7b8640ad88f..a50f7dafc3dd3b 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextWriter.cs
@@ -293,7 +293,7 @@ public XmlTextWriter(Stream w, Encoding? encoding) : this()
         }
 
         // Creates an instance of the XmlTextWriter class using the specified file.
-        public XmlTextWriter(string filename, Encoding encoding)
+        public XmlTextWriter(string filename, Encoding? encoding)
         : this(new FileStream(filename, FileMode.Create,
                               FileAccess.Write, FileShare.Read), encoding)
         {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReader.cs
index c0c9b77fa40efc..a3911c8e47bae8 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReader.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.IO;
 using System.Text;
@@ -17,6 +18,7 @@ public class XmlValidatingReader : XmlReader, IXmlLineInfo, IXmlNamespaceResolve
         // Member fields
         //
         private readonly XmlValidatingReaderImpl _impl;
+
         //
         // Constructors
         //
@@ -32,6 +34,7 @@ public XmlValidatingReader(string xmlFragment, XmlNodeType fragType, XmlParserCo
             {
                 throw new ArgumentNullException(nameof(xmlFragment));
             }
+
             _impl = new XmlValidatingReaderImpl(xmlFragment, fragType, context);
             _impl.OuterReader = this;
         }
@@ -89,7 +92,7 @@ public override int Depth
             get { return _impl.Depth; }
         }
 
-        public override string BaseURI
+        public override string? BaseURI
         {
             get { return _impl.BaseURI; }
         }
@@ -123,12 +126,12 @@ public override string XmlLang
 
         public override int AttributeCount { get { return _impl.AttributeCount; } }
 
-        public override string GetAttribute(string name)
+        public override string? GetAttribute(string name)
         {
             return _impl.GetAttribute(name);
         }
 
-        public override string GetAttribute(string localName, string namespaceURI)
+        public override string? GetAttribute(string localName, string? namespaceURI)
         {
             return _impl.GetAttribute(localName, namespaceURI);
         }
@@ -143,7 +146,7 @@ public override bool MoveToAttribute(string name)
             return _impl.MoveToAttribute(name);
         }
 
-        public override bool MoveToAttribute(string localName, string namespaceURI)
+        public override bool MoveToAttribute(string localName, string? namespaceURI)
         {
             return _impl.MoveToAttribute(localName, namespaceURI);
         }
@@ -198,13 +201,14 @@ public override XmlNameTable NameTable
             get { return _impl.NameTable; }
         }
 
-        public override string LookupNamespace(string prefix)
+        public override string? LookupNamespace(string prefix)
         {
-            string ns = _impl.LookupNamespace(prefix);
+            string? ns = _impl.LookupNamespace(prefix);
             if (ns != null && ns.Length == 0)
             {
                 ns = null;
             }
+
             return ns;
         }
 
@@ -269,12 +273,12 @@ IDictionary<string, string> IXmlNamespaceResolver.GetNamespacesInScope(XmlNamesp
             return _impl.GetNamespacesInScope(scope);
         }
 
-        string IXmlNamespaceResolver.LookupNamespace(string prefix)
+        string? IXmlNamespaceResolver.LookupNamespace(string prefix)
         {
             return _impl.LookupNamespace(prefix);
         }
 
-        string IXmlNamespaceResolver.LookupPrefix(string namespaceName)
+        string? IXmlNamespaceResolver.LookupPrefix(string namespaceName)
         {
             return _impl.LookupPrefix(namespaceName);
         }
@@ -288,7 +292,7 @@ public event ValidationEventHandler ValidationEventHandler
             remove { _impl.ValidationEventHandler -= value; }
         }
 
-        public object SchemaType
+        public object? SchemaType
         {
             get { return _impl.SchemaType; }
         }
@@ -326,12 +330,12 @@ public bool Namespaces
             set { _impl.Namespaces = value; }
         }
 
-        public object ReadTypedValue()
+        public object? ReadTypedValue()
         {
             return _impl.ReadTypedValue();
         }
 
-        public Encoding Encoding
+        public Encoding? Encoding
         {
             get { return _impl.Encoding; }
         }
@@ -343,7 +347,7 @@ internal XmlValidatingReaderImpl Impl
             get { return _impl; }
         }
 
-        internal override IDtdInfo DtdInfo
+        internal override IDtdInfo? DtdInfo
         {
             get { return _impl.DtdInfo; }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReaderImpl.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReaderImpl.cs
index e8a69444016fa0..239b854adba7f2 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReaderImpl.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReaderImpl.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.IO;
 using System.Text;
@@ -10,6 +11,7 @@
 using System.Globalization;
 using System.Collections.Generic;
 using System.Runtime.Versioning;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml
 {
@@ -35,7 +37,7 @@ internal class ValidationEventHandling : IValidationEventHandling
         {
             // Fields
             private readonly XmlValidatingReaderImpl _reader;
-            private ValidationEventHandler _eventHandler;
+            private ValidationEventHandler? _eventHandler;
 
             // Constructor
             internal ValidationEventHandling(XmlValidatingReaderImpl reader)
@@ -45,7 +47,7 @@ internal ValidationEventHandling(XmlValidatingReaderImpl reader)
 
             // IValidationEventHandling interface
             #region IValidationEventHandling interface
-            object IValidationEventHandling.EventHandler
+            object? IValidationEventHandling.EventHandler
             {
                 get { return _eventHandler; }
             }
@@ -81,7 +83,7 @@ internal void RemoveHandler(ValidationEventHandler handler)
         // core text reader
         private readonly XmlReader _coreReader;
         private readonly XmlTextReaderImpl _coreReaderImpl;
-        private readonly IXmlNamespaceResolver _coreReaderNSResolver;
+        private readonly IXmlNamespaceResolver? _coreReaderNSResolver;
 
         // validation
         private ValidationType _validationType;
@@ -99,10 +101,10 @@ internal void RemoveHandler(ValidationEventHandler handler)
         private readonly ValidationEventHandling _eventHandling;
 
         // misc
-        private readonly XmlParserContext _parserContext;
+        private readonly XmlParserContext? _parserContext;
 
         // helper for Read[Element]ContentAs{Base64,BinHex} methods
-        private ReadContentAsBinaryHelper _readBinaryHelper;
+        private ReadContentAsBinaryHelper? _readBinaryHelper;
 
         // Outer XmlReader exposed to the user - either XmlValidatingReader or XmlValidatingReaderImpl (when created via XmlReader.Create).
         // Virtual methods called from within XmlValidatingReaderImpl must be called on the outer reader so in case the user overrides
@@ -116,27 +118,30 @@ internal void RemoveHandler(ValidationEventHandler handler)
         // This constructor is used when creating XmlValidatingReaderImpl for V1 XmlValidatingReader
         internal XmlValidatingReaderImpl(XmlReader reader)
         {
-            XmlAsyncCheckReader asyncCheckReader = reader as XmlAsyncCheckReader;
+            XmlAsyncCheckReader? asyncCheckReader = reader as XmlAsyncCheckReader;
             if (asyncCheckReader != null)
             {
                 reader = asyncCheckReader.CoreReader;
             }
+
             _outerReader = this;
             _coreReader = reader;
             _coreReaderNSResolver = reader as IXmlNamespaceResolver;
-            _coreReaderImpl = reader as XmlTextReaderImpl;
+            _coreReaderImpl = (reader as XmlTextReaderImpl)!;
             if (_coreReaderImpl == null)
             {
-                XmlTextReader tr = reader as XmlTextReader;
+                XmlTextReader? tr = reader as XmlTextReader;
                 if (tr != null)
                 {
                     _coreReaderImpl = tr.Impl;
                 }
             }
+
             if (_coreReaderImpl == null)
             {
                 throw new ArgumentException(SR.Arg_ExpectingXmlTextReader, nameof(reader));
             }
+
             _coreReaderImpl.EntityHandling = EntityHandling.ExpandEntities;
             _coreReaderImpl.XmlValidatingReaderCompatibilityMode = true;
             _processIdentityConstraints = true;
@@ -152,18 +157,17 @@ internal XmlValidatingReaderImpl(XmlReader reader)
             _validationType = ValidationType.Auto;
             SetupValidation(ValidationType.Auto);
 #pragma warning restore 618
-
         }
 
         // Initializes a new instance of XmlValidatingReaderImpl class for parsing fragments with the specified string, fragment type and parser context
         // This constructor is used when creating XmlValidatingReaderImpl for V1 XmlValidatingReader
         // SxS: This method resolves an Uri but does not expose it to the caller. It's OK to suppress the SxS warning.
-        internal XmlValidatingReaderImpl(string xmlFragment, XmlNodeType fragType, XmlParserContext context)
+        internal XmlValidatingReaderImpl(string xmlFragment, XmlNodeType fragType, XmlParserContext? context)
             : this(new XmlTextReader(xmlFragment, fragType, context))
         {
-            if (_coreReader.BaseURI.Length > 0)
+            if (_coreReader.BaseURI!.Length > 0)
             {
-                _validator.BaseUri = GetResolver().ResolveUri(null, _coreReader.BaseURI);
+                _validator.BaseUri = GetResolver()!.ResolveUri(null, _coreReader.BaseURI);
             }
 
             if (context != null)
@@ -176,12 +180,12 @@ internal XmlValidatingReaderImpl(string xmlFragment, XmlNodeType fragType, XmlPa
         // Initializes a new instance of XmlValidatingReaderImpl class for parsing fragments with the specified stream, fragment type and parser context
         // This constructor is used when creating XmlValidatingReaderImpl for V1 XmlValidatingReader
         // SxS: This method resolves an Uri but does not expose it to the caller. It's OK to suppress the SxS warning.
-        internal XmlValidatingReaderImpl(Stream xmlFragment, XmlNodeType fragType, XmlParserContext context)
+        internal XmlValidatingReaderImpl(Stream xmlFragment, XmlNodeType fragType, XmlParserContext? context)
             : this(new XmlTextReader(xmlFragment, fragType, context))
         {
-            if (_coreReader.BaseURI.Length > 0)
+            if (_coreReader.BaseURI!.Length > 0)
             {
-                _validator.BaseUri = GetResolver().ResolveUri(null, _coreReader.BaseURI);
+                _validator.BaseUri = GetResolver()!.ResolveUri(null, _coreReader.BaseURI);
             }
 
             if (context != null)
@@ -193,28 +197,31 @@ internal XmlValidatingReaderImpl(Stream xmlFragment, XmlNodeType fragType, XmlPa
 
         // Initializes a new instance of XmlValidatingReaderImpl class with the specified arguments.
         // This constructor is used when creating XmlValidatingReaderImpl reader via "XmlReader.Create(..)"
-        internal XmlValidatingReaderImpl(XmlReader reader, ValidationEventHandler settingsEventHandler, bool processIdentityConstraints)
+        internal XmlValidatingReaderImpl(XmlReader reader, ValidationEventHandler? settingsEventHandler, bool processIdentityConstraints)
         {
-            XmlAsyncCheckReader asyncCheckReader = reader as XmlAsyncCheckReader;
+            XmlAsyncCheckReader? asyncCheckReader = reader as XmlAsyncCheckReader;
             if (asyncCheckReader != null)
             {
                 reader = asyncCheckReader.CoreReader;
             }
+
             _outerReader = this;
             _coreReader = reader;
-            _coreReaderImpl = reader as XmlTextReaderImpl;
+            _coreReaderImpl = (reader as XmlTextReaderImpl)!;
             if (_coreReaderImpl == null)
             {
-                XmlTextReader tr = reader as XmlTextReader;
+                XmlTextReader? tr = reader as XmlTextReader;
                 if (tr != null)
                 {
                     _coreReaderImpl = tr.Impl;
                 }
             }
+
             if (_coreReaderImpl == null)
             {
                 throw new ArgumentException(SR.Arg_ExpectingXmlTextReader, nameof(reader));
             }
+
             _coreReaderImpl.XmlValidatingReaderCompatibilityMode = true;
             _coreReaderNSResolver = reader as IXmlNamespaceResolver;
             _processIdentityConstraints = processIdentityConstraints;
@@ -243,11 +250,11 @@ internal XmlValidatingReaderImpl(XmlReader reader, ValidationEventHandler settin
         // XmlReader members
         //
         // Returns the current settings of the reader
-        public override XmlReaderSettings Settings
+        public override XmlReaderSettings? Settings
         {
             get
             {
-                XmlReaderSettings settings;
+                XmlReaderSettings? settings;
                 if (_coreReaderImpl.V1Compat)
                 {
                     settings = null;
@@ -256,6 +263,7 @@ public override XmlReaderSettings Settings
                 {
                     settings = _coreReader.Settings;
                 }
+
                 if (settings != null)
                 {
                     settings = settings.Clone();
@@ -264,11 +272,13 @@ public override XmlReaderSettings Settings
                 {
                     settings = new XmlReaderSettings();
                 }
+
                 settings.ValidationType = ValidationType.DTD;
                 if (!_processIdentityConstraints)
                 {
                     settings.ValidationFlags &= ~XmlSchemaValidationFlags.ProcessIdentityConstraints;
                 }
+
                 settings.ReadOnly = true;
                 return settings;
             }
@@ -347,7 +357,7 @@ public override int Depth
         }
 
         // Returns the base URI of the current node.
-        public override string BaseURI
+        public override string? BaseURI
         {
             get
             {
@@ -428,7 +438,7 @@ public override XmlNameTable NameTable
         }
 
         // Returns encoding of the XML document
-        internal Encoding Encoding
+        internal Encoding? Encoding
         {
             get
             {
@@ -446,13 +456,13 @@ public override int AttributeCount
         }
 
         // Returns value of an attribute with the specified Name
-        public override string GetAttribute(string name)
+        public override string? GetAttribute(string name)
         {
             return _coreReader.GetAttribute(name);
         }
 
         // Returns value of an attribute with the specified LocalName and NamespaceURI
-        public override string GetAttribute(string localName, string namespaceURI)
+        public override string? GetAttribute(string localName, string? namespaceURI)
         {
             return _coreReader.GetAttribute(localName, namespaceURI);
         }
@@ -475,7 +485,7 @@ public override bool MoveToAttribute(string name)
         }
 
         // Moves to an attribute with the specified LocalName and NamespceURI
-        public override bool MoveToAttribute(string localName, string namespaceURI)
+        public override bool MoveToAttribute(string localName, string? namespaceURI)
         {
             if (!_coreReader.MoveToAttribute(localName, namespaceURI))
             {
@@ -565,7 +575,7 @@ public override bool Read()
                     goto case ParsingFunction.Read;
                 case ParsingFunction.InReadBinaryContent:
                     _parsingFunction = ParsingFunction.Read;
-                    _readBinaryHelper.Finish();
+                    _readBinaryHelper!.Finish();
                     goto case ParsingFunction.Read;
                 default:
                     Debug.Fail($"Unexpected parsing function {_parsingFunction}");
@@ -581,7 +591,7 @@ public override void Close()
         }
 
         // Returns NamespaceURI associated with the specified prefix in the current namespace scope.
-        public override string LookupNamespace(string prefix)
+        public override string? LookupNamespace(string prefix)
         {
             return _coreReaderImpl.LookupNamespace(prefix);
         }
@@ -592,7 +602,7 @@ public override bool ReadAttributeValue()
             if (_parsingFunction == ParsingFunction.InReadBinaryContent)
             {
                 _parsingFunction = ParsingFunction.Read;
-                _readBinaryHelper.Finish();
+                _readBinaryHelper!.Finish();
             }
             if (!_coreReader.ReadAttributeValue())
             {
@@ -627,7 +637,7 @@ public override int ReadContentAsBase64(byte[] buffer, int index, int count)
             _parsingFunction = ParsingFunction.Read;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadContentAsBase64(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadContentAsBase64(buffer, index, count);
 
             // setup parsingFunction
             _parsingFunction = ParsingFunction.InReadBinaryContent;
@@ -651,7 +661,7 @@ public override int ReadContentAsBinHex(byte[] buffer, int index, int count)
             _parsingFunction = ParsingFunction.Read;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadContentAsBinHex(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadContentAsBinHex(buffer, index, count);
 
             // setup parsingFunction
             _parsingFunction = ParsingFunction.InReadBinaryContent;
@@ -675,7 +685,7 @@ public override int ReadElementContentAsBase64(byte[] buffer, int index, int cou
             _parsingFunction = ParsingFunction.Read;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadElementContentAsBase64(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadElementContentAsBase64(buffer, index, count);
 
             // setup parsingFunction
             _parsingFunction = ParsingFunction.InReadBinaryContent;
@@ -699,7 +709,7 @@ public override int ReadElementContentAsBinHex(byte[] buffer, int index, int cou
             _parsingFunction = ParsingFunction.Read;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadElementContentAsBinHex(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadElementContentAsBinHex(buffer, index, count);
 
             // setup parsingFunction
             _parsingFunction = ParsingFunction.InReadBinaryContent;
@@ -791,12 +801,12 @@ IDictionary<string, string> IXmlNamespaceResolver.GetNamespacesInScope(XmlNamesp
             return this.GetNamespacesInScope(scope);
         }
 
-        string IXmlNamespaceResolver.LookupNamespace(string prefix)
+        string? IXmlNamespaceResolver.LookupNamespace(string prefix)
         {
             return this.LookupNamespace(prefix);
         }
 
-        string IXmlNamespaceResolver.LookupPrefix(string namespaceName)
+        string? IXmlNamespaceResolver.LookupPrefix(string namespaceName)
         {
             return this.LookupPrefix(namespaceName);
         }
@@ -804,12 +814,12 @@ string IXmlNamespaceResolver.LookupPrefix(string namespaceName)
         // Internal IXmlNamespaceResolver methods
         internal IDictionary<string, string> GetNamespacesInScope(XmlNamespaceScope scope)
         {
-            return _coreReaderNSResolver.GetNamespacesInScope(scope);
+            return _coreReaderNSResolver!.GetNamespacesInScope(scope);
         }
 
-        internal string LookupPrefix(string namespaceName)
+        internal string? LookupPrefix(string namespaceName)
         {
-            return _coreReaderNSResolver.LookupPrefix(namespaceName);
+            return _coreReaderNSResolver!.LookupPrefix(namespaceName);
         }
 
         //
@@ -829,17 +839,18 @@ internal event ValidationEventHandler ValidationEventHandler
         }
 
         // returns the schema type of the current node
-        internal object SchemaType
+        internal object? SchemaType
         {
             get
             {
                 if (_validationType != ValidationType.None)
                 {
-                    XmlSchemaType schemaTypeObj = _coreReaderImpl.InternalSchemaType as XmlSchemaType;
+                    XmlSchemaType? schemaTypeObj = _coreReaderImpl.InternalSchemaType as XmlSchemaType;
                     if (schemaTypeObj != null && schemaTypeObj.QualifiedName.Namespace == XmlReservedNs.NsXs)
                     {
                         return schemaTypeObj.Datatype;
                     }
+
                     return _coreReaderImpl.InternalSchemaType;
                 }
                 else
@@ -932,7 +943,7 @@ internal bool Namespaces
         }
 
         // Returns typed value of the current node (based on the type specified by schema)
-        public object ReadTypedValue()
+        public object? ReadTypedValue()
         {
             if (_validationType == ValidationType.None)
             {
@@ -948,7 +959,8 @@ public object ReadTypedValue()
                     {
                         return null;
                     }
-                    XmlSchemaDatatype dtype = (SchemaType is XmlSchemaDatatype) ? (XmlSchemaDatatype)SchemaType : ((XmlSchemaType)SchemaType).Datatype;
+
+                    XmlSchemaDatatype? dtype = (SchemaType is XmlSchemaDatatype) ? (XmlSchemaDatatype)SchemaType : ((XmlSchemaType)SchemaType).Datatype;
                     if (dtype != null)
                     {
                         if (!_outerReader.IsEmptyElement)
@@ -959,6 +971,7 @@ public object ReadTypedValue()
                                 {
                                     throw new InvalidOperationException(SR.Xml_InvalidOperation);
                                 }
+
                                 XmlNodeType type = _outerReader.NodeType;
                                 if (type != XmlNodeType.CDATA && type != XmlNodeType.Text &&
                                     type != XmlNodeType.Whitespace && type != XmlNodeType.SignificantWhitespace &&
@@ -967,6 +980,7 @@ public object ReadTypedValue()
                                     break;
                                 }
                             }
+
                             if (_outerReader.NodeType != XmlNodeType.EndElement)
                             {
                                 throw new XmlException(SR.Xml_InvalidNodeType, _outerReader.NodeType.ToString());
@@ -1016,7 +1030,7 @@ private void ParseDtdFromParserContext()
 
         private void ValidateDtd()
         {
-            IDtdInfo dtdInfo = _coreReaderImpl.DtdInfo;
+            IDtdInfo? dtdInfo = _coreReaderImpl.DtdInfo;
             if (dtdInfo != null)
             {
                 switch (_validationType)
@@ -1043,26 +1057,28 @@ private void ResolveEntityInternally()
         }
 
         // SxS: This method resolves an Uri but does not expose it to caller. It's OK to suppress the SxS warning.
+        [MemberNotNull(nameof(_validator))]
         private void SetupValidation(ValidationType valType)
         {
-            _validator = BaseValidator.CreateInstance(valType, this, _schemaCollection, _eventHandling, _processIdentityConstraints);
+            _validator = BaseValidator.CreateInstance(valType, this, _schemaCollection, _eventHandling, _processIdentityConstraints)!;
 
-            XmlResolver resolver = GetResolver();
+            XmlResolver? resolver = GetResolver();
             _validator.XmlResolver = resolver;
 
-            if (_outerReader.BaseURI.Length > 0)
+            if (_outerReader.BaseURI!.Length > 0)
             {
                 _validator.BaseUri = (resolver == null) ? new Uri(_outerReader.BaseURI, UriKind.RelativeOrAbsolute) : resolver.ResolveUri(null, _outerReader.BaseURI);
             }
+
             _coreReaderImpl.ValidationEventHandling = (_validationType == ValidationType.None) ? null : _eventHandling;
         }
 
-        private static XmlResolver s_tempResolver;
+        private static XmlResolver? s_tempResolver;
 
         // This is needed because we can't have the setter for XmlResolver public and with internal getter.
-        private XmlResolver GetResolver()
+        private XmlResolver? GetResolver()
         {
-            XmlResolver tempResolver = _coreReaderImpl.GetResolver();
+            XmlResolver? tempResolver = _coreReaderImpl.GetResolver();
 
             if (tempResolver == null && !_coreReaderImpl.IsResolverSet)
             {
@@ -1117,7 +1133,7 @@ internal BaseValidator Validator
             }
         }
 
-        internal override XmlNamespaceManager NamespaceManager
+        internal override XmlNamespaceManager? NamespaceManager
         {
             get
             {
@@ -1133,7 +1149,7 @@ internal bool StandAlone
             }
         }
 
-        internal object SchemaTypeObject
+        internal object? SchemaTypeObject
         {
             set
             {
@@ -1141,7 +1157,7 @@ internal object SchemaTypeObject
             }
         }
 
-        internal object TypedValueObject
+        internal object? TypedValueObject
         {
             get
             {
@@ -1158,24 +1174,25 @@ internal bool AddDefaultAttribute(SchemaAttDef attdef)
             return _coreReaderImpl.AddDefaultAttributeNonDtd(attdef);
         }
 
-        internal override IDtdInfo DtdInfo
+        internal override IDtdInfo? DtdInfo
         {
             get { return _coreReaderImpl.DtdInfo; }
         }
 
         internal void ValidateDefaultAttributeOnUse(IDtdDefaultAttributeInfo defaultAttribute, XmlTextReaderImpl coreReader)
         {
-            SchemaAttDef attdef = defaultAttribute as SchemaAttDef;
+            SchemaAttDef? attdef = defaultAttribute as SchemaAttDef;
             if (attdef == null)
             {
                 return;
             }
 
-            SchemaInfo schemaInfo = coreReader.DtdInfo as SchemaInfo;
+            SchemaInfo? schemaInfo = coreReader.DtdInfo as SchemaInfo;
             if (schemaInfo == null)
             {
                 return;
             }
+
             DtdValidator.CheckDefaultValue(attdef, schemaInfo, _eventHandling, coreReader.BaseURI);
         }
     }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReaderImplAsync.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReaderImplAsync.cs
index 7f23a0959cb300..3b917610d63e80 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReaderImplAsync.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlValidatingReaderImplAsync.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.IO;
 using System.Text;
@@ -63,7 +64,7 @@ public override async Task<bool> ReadAsync()
                     goto case ParsingFunction.Read;
                 case ParsingFunction.InReadBinaryContent:
                     _parsingFunction = ParsingFunction.Read;
-                    await _readBinaryHelper.FinishAsync().ConfigureAwait(false);
+                    await _readBinaryHelper!.FinishAsync().ConfigureAwait(false);
                     goto case ParsingFunction.Read;
                 default:
                     Debug.Fail($"Unexpected parsing function {_parsingFunction}");
@@ -88,7 +89,7 @@ public override async Task<int> ReadContentAsBase64Async(byte[] buffer, int inde
             _parsingFunction = ParsingFunction.Read;
 
             // call to the helper
-            int readCount = await _readBinaryHelper.ReadContentAsBase64Async(buffer, index, count).ConfigureAwait(false);
+            int readCount = await _readBinaryHelper!.ReadContentAsBase64Async(buffer, index, count).ConfigureAwait(false);
 
             // setup parsingFunction
             _parsingFunction = ParsingFunction.InReadBinaryContent;
@@ -112,7 +113,7 @@ public override async Task<int> ReadContentAsBinHexAsync(byte[] buffer, int inde
             _parsingFunction = ParsingFunction.Read;
 
             // call to the helper
-            int readCount = await _readBinaryHelper.ReadContentAsBinHexAsync(buffer, index, count).ConfigureAwait(false);
+            int readCount = await _readBinaryHelper!.ReadContentAsBinHexAsync(buffer, index, count).ConfigureAwait(false);
 
             // setup parsingFunction
             _parsingFunction = ParsingFunction.InReadBinaryContent;
@@ -136,7 +137,7 @@ public override async Task<int> ReadElementContentAsBase64Async(byte[] buffer, i
             _parsingFunction = ParsingFunction.Read;
 
             // call to the helper
-            int readCount = await _readBinaryHelper.ReadElementContentAsBase64Async(buffer, index, count).ConfigureAwait(false);
+            int readCount = await _readBinaryHelper!.ReadElementContentAsBase64Async(buffer, index, count).ConfigureAwait(false);
 
             // setup parsingFunction
             _parsingFunction = ParsingFunction.InReadBinaryContent;
@@ -160,7 +161,7 @@ public override async Task<int> ReadElementContentAsBinHexAsync(byte[] buffer, i
             _parsingFunction = ParsingFunction.Read;
 
             // call to the helper
-            int readCount = await _readBinaryHelper.ReadElementContentAsBinHexAsync(buffer, index, count).ConfigureAwait(false);
+            int readCount = await _readBinaryHelper!.ReadElementContentAsBinHexAsync(buffer, index, count).ConfigureAwait(false);
 
             // setup parsingFunction
             _parsingFunction = ParsingFunction.InReadBinaryContent;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriter.cs
index 1487069cc9102a..738ff3c7c3a3e6 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriter.cs
@@ -1343,7 +1343,7 @@ public override XmlSpace XmlSpace
             }
         }
 
-        public override string XmlLang
+        public override string? XmlLang
         {
             get
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterAsync.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterAsync.cs
index c5ca77b776fe5e..75248f3b473789 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterAsync.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterAsync.cs
@@ -770,7 +770,7 @@ private async Task WriteEndAttributeAsync_SepcialAtt()
             }
         }
 
-        public override async Task WriteCDataAsync(string text)
+        public override async Task WriteCDataAsync(string? text)
         {
             try
             {
@@ -778,6 +778,7 @@ public override async Task WriteCDataAsync(string text)
                 {
                     text = string.Empty;
                 }
+
                 await AdvanceStateAsync(Token.CData).ConfigureAwait(false);
                 await _writer.WriteCDataAsync(text).ConfigureAwait(false);
             }
@@ -788,7 +789,7 @@ public override async Task WriteCDataAsync(string text)
             }
         }
 
-        public override async Task WriteCommentAsync(string text)
+        public override async Task WriteCommentAsync(string? text)
         {
             try
             {
@@ -796,6 +797,7 @@ public override async Task WriteCommentAsync(string text)
                 {
                     text = string.Empty;
                 }
+
                 await AdvanceStateAsync(Token.Comment).ConfigureAwait(false);
                 await _writer.WriteCommentAsync(text).ConfigureAwait(false);
             }
@@ -938,7 +940,7 @@ public override async Task WriteSurrogateCharEntityAsync(char lowChar, char high
             }
         }
 
-        public override async Task WriteWhitespaceAsync(string ws)
+        public override async Task WriteWhitespaceAsync(string? ws)
         {
             try
             {
@@ -946,6 +948,7 @@ public override async Task WriteWhitespaceAsync(string ws)
                 {
                     ws = string.Empty;
                 }
+
                 if (!XmlCharType.Instance.IsOnlyWhitespace(ws))
                 {
                     throw new ArgumentException(SR.Xml_NonWhitespace);
@@ -968,7 +971,7 @@ public override async Task WriteWhitespaceAsync(string ws)
             }
         }
 
-        public override Task WriteStringAsync(string text)
+        public override Task WriteStringAsync(string? text)
         {
             try
             {
@@ -1460,6 +1463,7 @@ private async Task StartElementContentAsync_WithNS()
                     await _nsStack[i].WriteDeclAsync(_writer, _rawWriter).ConfigureAwait(false);
                 }
             }
+
             if (_rawWriter != null)
             {
                 _rawWriter.StartElementContent();
@@ -1477,6 +1481,7 @@ private Task StartElementContentAsync()
             {
                 _rawWriter.StartElementContent();
             }
+
             return Task.CompletedTask;
         }
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterHelpers.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterHelpers.cs
index de07e0ec772eb7..09ab72796797ab 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterHelpers.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterHelpers.cs
@@ -1,10 +1,12 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Text;
 using System.Diagnostics;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml
 {
@@ -26,12 +28,12 @@ IDictionary<string, string> IXmlNamespaceResolver.GetNamespacesInScope(XmlNamesp
             {
                 throw new NotImplementedException();
             }
-            string IXmlNamespaceResolver.LookupNamespace(string prefix)
+            string? IXmlNamespaceResolver.LookupNamespace(string prefix)
             {
                 return _wfWriter.LookupNamespace(prefix);
             }
 
-            string IXmlNamespaceResolver.LookupPrefix(string namespaceName)
+            string? IXmlNamespaceResolver.LookupPrefix(string namespaceName)
             {
                 return _wfWriter.LookupPrefix(namespaceName);
             }
@@ -44,7 +46,7 @@ private partial struct ElementScope
             internal string localName;
             internal string namespaceUri;
             internal XmlSpace xmlSpace;
-            internal string xmlLang;
+            internal string? xmlLang;
 
             internal void Set(string prefix, string localName, string namespaceUri, int prevNSTop)
             {
@@ -90,7 +92,7 @@ internal void Set(string prefix, string namespaceUri, NamespaceKind kind)
                 this.prevNsIndex = -1;
             }
 
-            internal void WriteDecl(XmlWriter writer, XmlRawWriter rawWriter)
+            internal void WriteDecl(XmlWriter writer, XmlRawWriter? rawWriter)
             {
                 Debug.Assert(kind == NamespaceKind.NeedToWrite);
                 if (null != rawWriter)
@@ -107,6 +109,7 @@ internal void WriteDecl(XmlWriter writer, XmlRawWriter rawWriter)
                     {
                         writer.WriteStartAttribute("xmlns", prefix, XmlReservedNs.NsXmlNs);
                     }
+
                     writer.WriteString(namespaceUri);
                     writer.WriteEndAttribute();
                 }
@@ -164,8 +167,13 @@ private class Item
                 internal ItemType type;
                 internal object data;
 
-                internal Item() { }
+                internal Item(ItemType type, object data)
+                {
+                    Set(type, data);
+                }
 
+                [MemberNotNull(nameof(type))]
+                [MemberNotNull(nameof(data))]
                 internal void Set(ItemType type, object data)
                 {
                     this.type = type;
@@ -188,8 +196,8 @@ internal BufferChunk(char[] buffer, int index, int count)
             }
 
             private StringBuilder _stringValue = new StringBuilder();
-            private string _singleStringValue; // special-case for a single WriteString call
-            private Item[] _items;
+            private string? _singleStringValue; // special-case for a single WriteString call
+            private Item[]? _items;
             private int _firstItem;
             private int _lastItem = -1;
 
@@ -344,7 +352,7 @@ internal void Replay(XmlWriter writer)
                 BufferChunk bufChunk;
                 for (int i = _firstItem; i <= _lastItem; i++)
                 {
-                    Item item = _items[i];
+                    Item item = _items![i];
                     switch (item.type)
                     {
                         case ItemType.EntityRef:
@@ -408,7 +416,7 @@ internal void Trim()
                 int i = _firstItem;
                 while (i == _firstItem && i <= _lastItem)
                 {
-                    Item item = _items[i];
+                    Item item = _items![i];
                     switch (item.type)
                     {
                         case ItemType.Whitespace:
@@ -433,11 +441,13 @@ internal void Trim()
                                 bufChunk.index++;
                                 bufChunk.count--;
                             }
+
                             if (bufChunk.index == endIndex)
                             {
                                 // no characters left -> move the firstItem index to exclude it from the Replay
                                 _firstItem++;
                             }
+
                             break;
                     }
                     i++;
@@ -447,7 +457,7 @@ internal void Trim()
                 i = _lastItem;
                 while (i == _lastItem && i >= _firstItem)
                 {
-                    Item item = _items[i];
+                    Item item = _items![i];
                     switch (item.type)
                     {
                         case ItemType.Whitespace:
@@ -470,13 +480,16 @@ internal void Trim()
                             {
                                 bufChunk.count--;
                             }
+
                             if (bufChunk.count == 0)
                             {
                                 // no characters left -> move the lastItem index to exclude it from the Replay
                                 _lastItem--;
                             }
+
                             break;
                     }
+
                     i--;
                 }
             }
@@ -513,11 +526,16 @@ private void AddItem(ItemType type, object data)
                     Array.Copy(_items, newItems, newItemIndex);
                     _items = newItems;
                 }
+
                 if (_items[newItemIndex] == null)
                 {
-                    _items[newItemIndex] = new Item();
+                    _items[newItemIndex] = new Item(type, data);
+                }
+                else
+                {
+                    _items[newItemIndex].Set(type, data);
                 }
-                _items[newItemIndex].Set(type, data);
+
                 _lastItem = newItemIndex;
             }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterHelpersAsync.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterHelpersAsync.cs
index ff243e0025ef14..9b70772408c59c 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterHelpersAsync.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWellFormedWriterHelpersAsync.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Text;
 using System.Diagnostics;
@@ -27,7 +28,7 @@ internal Task WriteFullEndElementAsync(XmlRawWriter rawWriter)
 
         private partial struct Namespace
         {
-            internal async Task WriteDeclAsync(XmlWriter writer, XmlRawWriter rawWriter)
+            internal async Task WriteDeclAsync(XmlWriter writer, XmlRawWriter? rawWriter)
             {
                 Debug.Assert(kind == NamespaceKind.NeedToWrite);
                 if (null != rawWriter)
@@ -63,7 +64,7 @@ internal async Task ReplayAsync(XmlWriter writer)
                 BufferChunk bufChunk;
                 for (int i = _firstItem; i <= _lastItem; i++)
                 {
-                    Item item = _items[i];
+                    Item item = _items![i];
                     switch (item.type)
                     {
                         case ItemType.EntityRef:
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingReader.cs
index 68d844c51a6671..62636bdeef7bc4 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingReader.cs
@@ -61,7 +61,7 @@ internal XmlWrappingReader(XmlReader baseReader)
             return reader.GetAttribute(name);
         }
 
-        public override string? GetAttribute(string name, string namespaceURI)
+        public override string? GetAttribute(string name, string? namespaceURI)
         {
             return reader.GetAttribute(name, namespaceURI);
         }
@@ -76,7 +76,7 @@ public override bool MoveToAttribute(string name)
             return reader.MoveToAttribute(name);
         }
 
-        public override bool MoveToAttribute(string name, string ns)
+        public override bool MoveToAttribute(string name, string? ns)
         {
             return reader.MoveToAttribute(name, ns);
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingWriter.cs
index 217447edeadd53..3f334dcfdae0bd 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingWriter.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Xml.Schema;
 using System.Collections;
@@ -27,10 +28,10 @@ internal XmlWrappingWriter(XmlWriter baseWriter)
         //
         // XmlWriter implementation
         //
-        public override XmlWriterSettings Settings { get { return writer.Settings; } }
+        public override XmlWriterSettings? Settings { get { return writer.Settings; } }
         public override WriteState WriteState { get { return writer.WriteState; } }
         public override XmlSpace XmlSpace { get { return writer.XmlSpace; } }
-        public override string XmlLang { get { return writer.XmlLang; } }
+        public override string? XmlLang { get { return writer.XmlLang; } }
 
 
         public override void WriteStartDocument()
@@ -48,12 +49,12 @@ public override void WriteEndDocument()
             writer.WriteEndDocument();
         }
 
-        public override void WriteDocType(string name, string pubid, string sysid, string subset)
+        public override void WriteDocType(string name, string? pubid, string? sysid, string? subset)
         {
             writer.WriteDocType(name, pubid, sysid, subset);
         }
 
-        public override void WriteStartElement(string prefix, string localName, string ns)
+        public override void WriteStartElement(string? prefix, string localName, string? ns)
         {
             writer.WriteStartElement(prefix, localName, ns);
         }
@@ -68,7 +69,7 @@ public override void WriteFullEndElement()
             writer.WriteFullEndElement();
         }
 
-        public override void WriteStartAttribute(string prefix, string localName, string ns)
+        public override void WriteStartAttribute(string? prefix, string localName, string? ns)
         {
             writer.WriteStartAttribute(prefix, localName, ns);
         }
@@ -78,17 +79,17 @@ public override void WriteEndAttribute()
             writer.WriteEndAttribute();
         }
 
-        public override void WriteCData(string text)
+        public override void WriteCData(string? text)
         {
             writer.WriteCData(text);
         }
 
-        public override void WriteComment(string text)
+        public override void WriteComment(string? text)
         {
             writer.WriteComment(text);
         }
 
-        public override void WriteProcessingInstruction(string name, string text)
+        public override void WriteProcessingInstruction(string name, string? text)
         {
             writer.WriteProcessingInstruction(name, text);
         }
@@ -103,12 +104,12 @@ public override void WriteCharEntity(char ch)
             writer.WriteCharEntity(ch);
         }
 
-        public override void WriteWhitespace(string ws)
+        public override void WriteWhitespace(string? ws)
         {
             writer.WriteWhitespace(ws);
         }
 
-        public override void WriteString(string text)
+        public override void WriteString(string? text)
         {
             writer.WriteString(text);
         }
@@ -148,7 +149,7 @@ public override void Flush()
             writer.Flush();
         }
 
-        public override string LookupPrefix(string ns)
+        public override string? LookupPrefix(string ns)
         {
             return writer.LookupPrefix(ns);
         }
@@ -158,7 +159,7 @@ public override void WriteValue(object value)
             writer.WriteValue(value);
         }
 
-        public override void WriteValue(string value)
+        public override void WriteValue(string? value)
         {
             writer.WriteValue(value);
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingWriterAsync.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingWriterAsync.cs
index 53dcf5860f2fc4..46c2d673390d7b 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingWriterAsync.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWrappingWriterAsync.cs
@@ -59,12 +59,12 @@ protected internal override Task WriteEndAttributeAsync()
             return writer.WriteEndAttributeAsync();
         }
 
-        public override Task WriteCDataAsync(string text)
+        public override Task WriteCDataAsync(string? text)
         {
             return writer.WriteCDataAsync(text);
         }
 
-        public override Task WriteCommentAsync(string text)
+        public override Task WriteCommentAsync(string? text)
         {
             return writer.WriteCommentAsync(text);
         }
@@ -84,12 +84,12 @@ public override Task WriteCharEntityAsync(char ch)
             return writer.WriteCharEntityAsync(ch);
         }
 
-        public override Task WriteWhitespaceAsync(string ws)
+        public override Task WriteWhitespaceAsync(string? ws)
         {
             return writer.WriteWhitespaceAsync(ws);
         }
 
-        public override Task WriteStringAsync(string text)
+        public override Task WriteStringAsync(string? text)
         {
             return writer.WriteStringAsync(text);
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriter.cs
index 8c15b6def4e150..90c848747ad40b 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriter.cs
@@ -490,7 +490,7 @@ public virtual void WriteNode(XPathNavigator navigator, bool defattr)
                         {
                             do
                             {
-                                IXmlSchemaInfo schemaInfo = navigator.SchemaInfo;
+                                IXmlSchemaInfo? schemaInfo = navigator.SchemaInfo;
                                 if (defattr || (schemaInfo == null || !schemaInfo.IsDefault))
                                 {
                                     WriteStartAttribute(navigator.Prefix, navigator.LocalName, navigator.NamespaceURI);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriterAsync.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriterAsync.cs
index 22baf19d7c977c..703d0e101a680b 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriterAsync.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriterAsync.cs
@@ -107,14 +107,14 @@ protected internal virtual Task WriteEndAttributeAsync()
 
         // Writes out a <![CDATA[...]]>; block containing the specified text.
 
-        public virtual Task WriteCDataAsync(string text)
+        public virtual Task WriteCDataAsync(string? text)
         {
             throw new NotImplementedException();
         }
 
         // Writes out a comment <!--...-->; containing the specified text.
 
-        public virtual Task WriteCommentAsync(string text)
+        public virtual Task WriteCommentAsync(string? text)
         {
             throw new NotImplementedException();
         }
@@ -142,14 +142,14 @@ public virtual Task WriteCharEntityAsync(char ch)
 
         // Writes out the given whitespace.
 
-        public virtual Task WriteWhitespaceAsync(string ws)
+        public virtual Task WriteWhitespaceAsync(string? ws)
         {
             throw new NotImplementedException();
         }
 
         // Writes out the specified text content.
 
-        public virtual Task WriteStringAsync(string text)
+        public virtual Task WriteStringAsync(string? text)
         {
             throw new NotImplementedException();
         }
@@ -466,7 +466,7 @@ public virtual async Task WriteNodeAsync(XPathNavigator navigator, bool defattr)
                         {
                             do
                             {
-                                IXmlSchemaInfo schemaInfo = navigator.SchemaInfo;
+                                IXmlSchemaInfo? schemaInfo = navigator.SchemaInfo;
                                 if (defattr || (schemaInfo == null || !schemaInfo.IsDefault))
                                 {
                                     await WriteStartAttributeAsync(navigator.Prefix, navigator.LocalName, navigator.NamespaceURI).ConfigureAwait(false);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriterSettings.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriterSettings.cs
index f0ff98e5a39e0d..5cde9f0b33230c 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriterSettings.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlWriterSettings.cs
@@ -1,11 +1,13 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
 using System.Text;
 using System.Runtime.Versioning;
+using System.Diagnostics.CodeAnalysis;
 
 #if !HIDE_XSL
 using System.Xml.Xsl.Runtime;
@@ -72,9 +74,9 @@ public sealed class XmlWriterSettings
         private List<XmlQualifiedName> _cdataSections = new List<XmlQualifiedName>();
         private bool _doNotEscapeUriAttributes;
         private bool _mergeCDataSections;
-        private string _mediaType;
-        private string _docTypeSystem;
-        private string _docTypePublic;
+        private string? _mediaType;
+        private string? _docTypeSystem;
+        private string? _docTypePublic;
         private XmlStandalone _standalone;
         private bool _autoXmlDecl;
 
@@ -113,6 +115,7 @@ public Encoding Encoding
             {
                 return _encoding;
             }
+            [MemberNotNull(nameof(_encoding))]
             set
             {
                 CheckReadOnly(nameof(Encoding));
@@ -149,6 +152,7 @@ public NewLineHandling NewLineHandling
                 {
                     throw new ArgumentOutOfRangeException(nameof(value));
                 }
+
                 _newLineHandling = value;
             }
         }
@@ -160,6 +164,7 @@ public string NewLineChars
             {
                 return _newLineChars;
             }
+            [MemberNotNull(nameof(_newLineChars))]
             set
             {
                 CheckReadOnly(nameof(NewLineChars));
@@ -168,6 +173,7 @@ public string NewLineChars
                 {
                     throw new ArgumentNullException(nameof(value));
                 }
+
                 _newLineChars = value;
             }
         }
@@ -193,6 +199,7 @@ public string IndentChars
             {
                 return _indentChars;
             }
+            [MemberNotNull(nameof(_indentChars))]
             set
             {
                 CheckReadOnly(nameof(IndentChars));
@@ -201,6 +208,7 @@ public string IndentChars
                 {
                     throw new ArgumentNullException(nameof(value));
                 }
+
                 _indentChars = value;
             }
         }
@@ -326,7 +334,7 @@ public void Reset()
         // can now be set independently of each other.
         public XmlWriterSettings Clone()
         {
-            XmlWriterSettings clonedSettings = MemberwiseClone() as XmlWriterSettings;
+            XmlWriterSettings clonedSettings = (MemberwiseClone() as XmlWriterSettings)!;
 
             // Deep clone shared settings that are not immutable
             clonedSettings._cdataSections = new List<XmlQualifiedName>(_cdataSections);
@@ -376,7 +384,7 @@ internal bool MergeCDataSections
         }
 
         // Used in Html writer when writing Meta element.  Null denotes the default media type.
-        internal string MediaType
+        internal string? MediaType
         {
             get
             {
@@ -390,7 +398,7 @@ internal string MediaType
         }
 
         // System Id in doc-type declaration.  Null denotes the absence of the system Id.
-        internal string DocTypeSystem
+        internal string? DocTypeSystem
         {
             get
             {
@@ -404,7 +412,7 @@ internal string DocTypeSystem
         }
 
         // Public Id in doc-type declaration.  Null denotes the absence of the public Id.
-        internal string DocTypePublic
+        internal string? DocTypePublic
         {
             get
             {
@@ -483,7 +491,7 @@ internal XmlWriter CreateWriter(string outputFileName)
                 newSettings.CloseOutput = true;
             }
 
-            FileStream fs = null;
+            FileStream? fs = null;
             try
             {
                 // open file stream
@@ -705,6 +713,9 @@ private void CheckReadOnly(string propertyName)
         //
         // Private methods
         //
+        [MemberNotNull(nameof(_encoding))]
+        [MemberNotNull(nameof(_newLineChars))]
+        [MemberNotNull(nameof(_indentChars))]
         private void Initialize()
         {
             _encoding = Encoding.UTF8;
@@ -736,7 +747,7 @@ private void Initialize()
         private XmlWriter AddConformanceWrapper(XmlWriter baseWriter)
         {
             ConformanceLevel confLevel = ConformanceLevel.Auto;
-            XmlWriterSettings baseWriterSettings = baseWriter.Settings;
+            XmlWriterSettings? baseWriterSettings = baseWriter.Settings;
             bool checkValues = false;
             bool checkNames = false;
             bool replaceNewLines = false;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdCachingReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdCachingReader.cs
index ade65358775ee4..119604e0b84703 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdCachingReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdCachingReader.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.IO;
 using System.Text;
 using System.Xml.Schema;
@@ -8,6 +9,7 @@
 using System.Diagnostics;
 using System.Globalization;
 using System.Collections;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml
 {
@@ -29,7 +31,7 @@ private enum CachingReaderState
         private ValidatingReaderNodeData[] _contentEvents;
         private ValidatingReaderNodeData[] _attributeEvents;
 
-        private ValidatingReaderNodeData _cachedNode;
+        private ValidatingReaderNodeData? _cachedNode;
 
         private CachingReaderState _cacheState;
         private int _contentIndex;
@@ -45,17 +47,17 @@ private enum CachingReaderState
         private bool _readAhead;
 
         //Lineinfo
-        private readonly IXmlLineInfo _lineInfo;
+        private readonly IXmlLineInfo? _lineInfo;
 
         //ReadAttributeValue TextNode
-        private ValidatingReaderNodeData _textNode;
+        private ValidatingReaderNodeData? _textNode;
 
         //Constants
         private const int InitialAttributeCount = 8;
         private const int InitialContentCount = 4;
 
         //Constructor
-        internal XsdCachingReader(XmlReader reader, IXmlLineInfo lineInfo, CachingEventHandler handlerMethod)
+        internal XsdCachingReader(XmlReader reader, IXmlLineInfo? lineInfo, CachingEventHandler handlerMethod)
         {
             _coreReader = reader;
             _lineInfo = lineInfo;
@@ -65,6 +67,7 @@ internal XsdCachingReader(XmlReader reader, IXmlLineInfo lineInfo, CachingEventH
             Init();
         }
 
+        [MemberNotNull(nameof(_coreReaderNameTable))]
         private void Init()
         {
             _coreReaderNameTable = _coreReader.NameTable;
@@ -92,7 +95,7 @@ internal void Reset(XmlReader reader)
         }
 
         // Settings
-        public override XmlReaderSettings Settings
+        public override XmlReaderSettings? Settings
         {
             get
             {
@@ -107,7 +110,7 @@ public override XmlNodeType NodeType
         {
             get
             {
-                return _cachedNode.NodeType;
+                return _cachedNode!.NodeType;
             }
         }
 
@@ -116,7 +119,7 @@ public override string Name
         {
             get
             {
-                return _cachedNode.GetAtomizedNameWPrefix(_coreReaderNameTable);
+                return _cachedNode!.GetAtomizedNameWPrefix(_coreReaderNameTable);
             }
         }
 
@@ -125,7 +128,7 @@ public override string LocalName
         {
             get
             {
-                return _cachedNode.LocalName;
+                return _cachedNode!.LocalName;
             }
         }
 
@@ -134,7 +137,7 @@ public override string NamespaceURI
         {
             get
             {
-                return _cachedNode.Namespace;
+                return _cachedNode!.Namespace;
             }
         }
 
@@ -143,7 +146,7 @@ public override string Prefix
         {
             get
             {
-                return _cachedNode.Prefix;
+                return _cachedNode!.Prefix;
             }
         }
 
@@ -152,7 +155,7 @@ public override bool HasValue
         {
             get
             {
-                return XmlReader.HasValueInternal(_cachedNode.NodeType);
+                return XmlReader.HasValueInternal(_cachedNode!.NodeType);
             }
         }
 
@@ -161,7 +164,7 @@ public override string Value
         {
             get
             {
-                return _returnOriginalStringValues ? _cachedNode.OriginalStringValue : _cachedNode.RawValue;
+                return _returnOriginalStringValues ? _cachedNode!.OriginalStringValue! : _cachedNode!.RawValue;
             }
         }
 
@@ -170,12 +173,12 @@ public override int Depth
         {
             get
             {
-                return _cachedNode.Depth;
+                return _cachedNode!.Depth;
             }
         }
 
         // Gets the base URI of the current node.
-        public override string BaseURI
+        public override string? BaseURI
         {
             get
             {
@@ -241,7 +244,7 @@ public override int AttributeCount
         }
 
         // Gets the value of the attribute with the specified Name.
-        public override string GetAttribute(string name)
+        public override string? GetAttribute(string name)
         {
             int i;
             if (!name.Contains(':'))
@@ -252,23 +255,25 @@ public override string GetAttribute(string name)
             {
                 i = GetAttributeIndexWithPrefix(name);
             }
+
             return (i >= 0) ? _attributeEvents[i].RawValue : null;
         }
 
         // Gets the value of the attribute with the specified LocalName and NamespaceURI.
-        public override string GetAttribute(string name, string namespaceURI)
+        public override string? GetAttribute(string name, string? namespaceURI)
         {
             namespaceURI = (namespaceURI == null) ? string.Empty : _coreReaderNameTable.Get(namespaceURI);
-            name = _coreReaderNameTable.Get(name);
+            string? atomizedName = _coreReaderNameTable.Get(name);
             ValidatingReaderNodeData attribute;
             for (int i = 0; i < _attributeCount; i++)
             {
                 attribute = _attributeEvents[i];
-                if (Ref.Equal(attribute.LocalName, name) && Ref.Equal(attribute.Namespace, namespaceURI))
+                if (Ref.Equal(attribute.LocalName, atomizedName) && Ref.Equal(attribute.Namespace, namespaceURI))
                 {
                     return attribute.RawValue;
                 }
             }
+
             return null;
         }
 
@@ -279,6 +284,7 @@ public override string GetAttribute(int i)
             {
                 throw new ArgumentOutOfRangeException(nameof(i));
             }
+
             return _attributeEvents[i].RawValue;
         }
 
@@ -292,7 +298,7 @@ public override string this[int i]
         }
 
         // Gets the value of the attribute with the specified LocalName and NamespaceURI.
-        public override string this[string name, string namespaceURI]
+        public override string? this[string name, string? namespaceURI]
         {
             get
             {
@@ -326,15 +332,15 @@ public override bool MoveToAttribute(string name)
         }
 
         // Moves to the attribute with the specified LocalName and NamespaceURI
-        public override bool MoveToAttribute(string name, string ns)
+        public override bool MoveToAttribute(string name, string? ns)
         {
             ns = (ns == null) ? string.Empty : _coreReaderNameTable.Get(ns);
-            name = _coreReaderNameTable.Get(name);
+            string? atomizedName = _coreReaderNameTable.Get(name);
             ValidatingReaderNodeData attribute;
             for (int i = 0; i < _attributeCount; i++)
             {
                 attribute = _attributeEvents[i];
-                if (Ref.Equal(attribute.LocalName, name) &&
+                if (Ref.Equal(attribute.LocalName, atomizedName) &&
                      Ref.Equal(attribute.Namespace, ns))
                 {
                     _currentAttrIndex = i;
@@ -342,6 +348,7 @@ public override bool MoveToAttribute(string name, string ns)
                     return true;
                 }
             }
+
             return false;
         }
 
@@ -382,10 +389,11 @@ public override bool MoveToNextAttribute()
         // Moves to the element that contains the current attribute node.
         public override bool MoveToElement()
         {
-            if (_cacheState != CachingReaderState.Replay || _cachedNode.NodeType != XmlNodeType.Attribute)
+            if (_cacheState != CachingReaderState.Replay || _cachedNode!.NodeType != XmlNodeType.Attribute)
             {
                 return false;
             }
+
             _currentContentIndex = 0;
             _currentAttrIndex = -1;
             Read();
@@ -402,7 +410,7 @@ public override bool Read()
                     goto case CachingReaderState.Record;
 
                 case CachingReaderState.Record:
-                    ValidatingReaderNodeData recordedNode = null;
+                    ValidatingReaderNodeData? recordedNode = null;
                     if (_coreReader.Read())
                     {
                         switch (_coreReader.NodeType)
@@ -466,7 +474,7 @@ public override bool Read()
             }
         }
 
-        internal ValidatingReaderNodeData RecordTextNode(string textValue, string originalStringValue, int depth, int lineNo, int linePos)
+        internal ValidatingReaderNodeData RecordTextNode(string textValue, string? originalStringValue, int depth, int lineNo, int linePos)
         {
             ValidatingReaderNodeData textNode = AddContent(XmlNodeType.Text);
             textNode.SetItemData(textValue, originalStringValue);
@@ -475,7 +483,7 @@ internal ValidatingReaderNodeData RecordTextNode(string textValue, string origin
             return textNode;
         }
 
-        internal void SwitchTextNodeAndEndElement(string textValue, string originalStringValue)
+        internal void SwitchTextNodeAndEndElement(string textValue, string? originalStringValue)
         {
             Debug.Assert(_coreReader.NodeType == XmlNodeType.EndElement || (_coreReader.NodeType == XmlNodeType.Element && _coreReader.IsEmptyElement));
 
@@ -536,7 +544,7 @@ public override ReadState ReadState
         public override void Skip()
         {
             //Skip on caching reader should move to the end of the subtree, past all cached events
-            switch (_cachedNode.NodeType)
+            switch (_cachedNode!.NodeType)
             {
                 case XmlNodeType.Element:
                     if (_coreReader.NodeType != XmlNodeType.EndElement && !_readAhead)
@@ -571,7 +579,7 @@ public override XmlNameTable NameTable
         }
 
         // Resolves a namespace prefix in the current element's scope.
-        public override string LookupNamespace(string prefix)
+        public override string? LookupNamespace(string prefix)
         {
             return _coreReader.LookupNamespace(prefix);
         }
@@ -586,10 +594,11 @@ public override void ResolveEntity()
         public override bool ReadAttributeValue()
         {
             Debug.Assert(_cacheState == CachingReaderState.Replay);
-            if (_cachedNode.NodeType != XmlNodeType.Attribute)
+            if (_cachedNode!.NodeType != XmlNodeType.Attribute)
             {
                 return false;
             }
+
             _cachedNode = CreateDummyTextNode(_cachedNode.RawValue, _cachedNode.Depth + 1);
             return true;
         }
@@ -607,7 +616,7 @@ int IXmlLineInfo.LineNumber
         {
             get
             {
-                return _cachedNode.LineNumber;
+                return _cachedNode!.LineNumber;
             }
         }
 
@@ -615,7 +624,7 @@ int IXmlLineInfo.LinePosition
         {
             get
             {
-                return _cachedNode.LinePosition;
+                return _cachedNode!.LinePosition;
             }
         }
 
@@ -633,7 +642,7 @@ internal XmlReader GetCoreReader()
             return _coreReader;
         }
 
-        internal IXmlLineInfo GetLineInfo()
+        internal IXmlLineInfo? GetLineInfo()
         {
             return _lineInfo;
         }
@@ -716,16 +725,17 @@ private void RecordAttributes()
 
         private int GetAttributeIndexWithoutPrefix(string name)
         {
-            name = _coreReaderNameTable.Get(name);
-            if (name == null)
+            string? atomizedName = _coreReaderNameTable.Get(name);
+            if (atomizedName == null)
             {
                 return -1;
             }
+
             ValidatingReaderNodeData attribute;
             for (int i = 0; i < _attributeCount; i++)
             {
                 attribute = _attributeEvents[i];
-                if (Ref.Equal(attribute.LocalName, name) && attribute.Prefix.Length == 0)
+                if (Ref.Equal(attribute.LocalName, atomizedName) && attribute.Prefix.Length == 0)
                 {
                     return i;
                 }
@@ -735,8 +745,8 @@ private int GetAttributeIndexWithoutPrefix(string name)
 
         private int GetAttributeIndexWithPrefix(string name)
         {
-            name = _coreReaderNameTable.Get(name);
-            if (name == null)
+            string? atomizedName = _coreReaderNameTable.Get(name);
+            if (atomizedName == null)
             {
                 return -1;
             }
@@ -744,11 +754,12 @@ private int GetAttributeIndexWithPrefix(string name)
             for (int i = 0; i < _attributeCount; i++)
             {
                 attribute = _attributeEvents[i];
-                if (Ref.Equal(attribute.GetAtomizedNameWPrefix(_coreReaderNameTable), name))
+                if (Ref.Equal(attribute.GetAtomizedNameWPrefix(_coreReaderNameTable), atomizedName))
                 {
                     return i;
                 }
             }
+
             return -1;
         }
 
@@ -758,6 +769,7 @@ private ValidatingReaderNodeData CreateDummyTextNode(string attributeValue, int
             {
                 _textNode = new ValidatingReaderNodeData(XmlNodeType.Text);
             }
+
             _textNode.Depth = depth;
             _textNode.RawValue = attributeValue;
             return _textNode;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdCachingReaderAsync.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdCachingReaderAsync.cs
index 914e5ffb277f38..9abcb8104bd4cd 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdCachingReaderAsync.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdCachingReaderAsync.cs
@@ -21,11 +21,11 @@ public override Task<string> GetValueAsync()
         {
             if (_returnOriginalStringValues)
             {
-                return Task.FromResult(_cachedNode.OriginalStringValue);
+                return Task.FromResult(_cachedNode!.OriginalStringValue!);
             }
             else
             {
-                return Task.FromResult(_cachedNode.RawValue);
+                return Task.FromResult(_cachedNode!.RawValue);
             }
         }
 
@@ -107,7 +107,7 @@ public override async Task<bool> ReadAsync()
         public override async Task SkipAsync()
         {
             //Skip on caching reader should move to the end of the subtree, past all cached events
-            switch (_cachedNode.NodeType)
+            switch (_cachedNode!.NodeType)
             {
                 case XmlNodeType.Element:
                     if (_coreReader.NodeType != XmlNodeType.EndElement && !_readAhead)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdValidatingReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdValidatingReader.cs
index a6ce8d9fbaa4b0..cc0b4053e85d9d 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdValidatingReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XsdValidatingReader.cs
@@ -1135,7 +1135,7 @@ public override int AttributeCount
         }
 
         // Gets the value of the attribute with the specified LocalName and NamespaceURI.
-        public override string? GetAttribute(string name, string namespaceURI)
+        public override string? GetAttribute(string name, string? namespaceURI)
         {
             string? attValue = _coreReader.GetAttribute(name, namespaceURI);
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentSchemaValidator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentSchemaValidator.cs
index deb041cebb6d54..a7c1c2d3b462f7 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentSchemaValidator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentSchemaValidator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Text;
 using System.Collections;
@@ -18,31 +19,31 @@ namespace System.Xml
 {
     internal sealed class DocumentSchemaValidator : IXmlNamespaceResolver
     {
-        private XmlSchemaValidator _validator;
+        private XmlSchemaValidator? _validator;
         private readonly XmlSchemaSet _schemas;
 
         private readonly XmlNamespaceManager _nsManager;
         private readonly XmlNameTable _nameTable;
 
         //Attributes
-        private ArrayList _defaultAttributes;
+        private ArrayList? _defaultAttributes;
         private readonly XmlValueGetter _nodeValueGetter;
-        private XmlSchemaInfo _attributeSchemaInfo;
+        private XmlSchemaInfo? _attributeSchemaInfo;
 
         //Element PSVI
-        private XmlSchemaInfo _schemaInfo;
+        private XmlSchemaInfo? _schemaInfo;
 
         //Event Handler
-        private readonly ValidationEventHandler _eventHandler;
+        private readonly ValidationEventHandler? _eventHandler;
         private readonly ValidationEventHandler _internalEventHandler;
 
         //Store nodes
-        private XmlNode _startNode;
-        private XmlNode _currentNode;
+        private XmlNode? _startNode;
+        private XmlNode? _currentNode;
         private readonly XmlDocument _document;
 
         //List of nodes for partial validation tree walk
-        private XmlNode[] _nodeSequenceToValidate;
+        private XmlNode?[]? _nodeSequenceToValidate;
         private bool _isPartialTreeValid;
 
         private bool _psviAugmentation;
@@ -54,7 +55,7 @@ internal sealed class DocumentSchemaValidator : IXmlNamespaceResolver
         private readonly string _xsiType;
         private readonly string _xsiNil;
 
-        public DocumentSchemaValidator(XmlDocument ownerDocument, XmlSchemaSet schemas, ValidationEventHandler eventHandler)
+        public DocumentSchemaValidator(XmlDocument ownerDocument, XmlSchemaSet schemas, ValidationEventHandler? eventHandler)
         {
             _schemas = schemas;
             _eventHandler = eventHandler;
@@ -84,7 +85,7 @@ public bool PsviAugmentation
 
         public bool Validate(XmlNode nodeToValidate)
         {
-            XmlSchemaObject partialValidationType = null;
+            XmlSchemaObject? partialValidationType = null;
             XmlSchemaValidationFlags validationFlags = XmlSchemaValidationFlags.AllowXmlAttributes;
             Debug.Assert(nodeToValidate.SchemaInfo != null);
 
@@ -100,7 +101,7 @@ public bool Validate(XmlNode nodeToValidate)
 
                 case XmlNodeType.Element: //Validate children of this element
                     IXmlSchemaInfo schemaInfo = nodeToValidate.SchemaInfo;
-                    XmlSchemaElement schemaElement = schemaInfo.SchemaElement;
+                    XmlSchemaElement? schemaElement = schemaInfo.SchemaElement;
                     if (schemaElement != null)
                     {
                         if (!schemaElement.RefName.IsEmpty)
@@ -120,14 +121,14 @@ public bool Validate(XmlNode nodeToValidate)
 
                         if (partialValidationType == null)
                         { //Validated against xs:any with pc= lax or skip or undeclared / not validated element
-                            if (nodeToValidate.ParentNode.NodeType == XmlNodeType.Document)
+                            if (nodeToValidate.ParentNode!.NodeType == XmlNodeType.Document)
                             {
                                 //If this is the documentElement and it has not been validated at all
                                 nodeToValidate = nodeToValidate.ParentNode;
                             }
                             else
                             {
-                                partialValidationType = FindSchemaInfo(nodeToValidate as XmlElement);
+                                partialValidationType = FindSchemaInfo((nodeToValidate as XmlElement)!);
                                 if (partialValidationType == null)
                                 {
                                     throw new XmlSchemaValidationException(SR.XmlDocument_NoNodeSchemaInfo, null, nodeToValidate);
@@ -142,7 +143,7 @@ public bool Validate(XmlNode nodeToValidate)
                     partialValidationType = nodeToValidate.SchemaInfo.SchemaAttribute;
                     if (partialValidationType == null)
                     { //Validated against xs:anyAttribute with pc = lax or skip / undeclared attribute
-                        partialValidationType = FindSchemaInfo(nodeToValidate as XmlAttribute);
+                        partialValidationType = FindSchemaInfo((nodeToValidate as XmlAttribute)!);
                         if (partialValidationType == null)
                         {
                             throw new XmlSchemaValidationException(SR.XmlDocument_NoNodeSchemaInfo, null, nodeToValidate);
@@ -164,7 +165,7 @@ public bool Validate(XmlNode nodeToValidate)
                 _attributeSchemaInfo = new XmlSchemaInfo();
             }
             ValidateNode(nodeToValidate);
-            _validator.EndValidation();
+            _validator!.EndValidation();
             return _isValid;
         }
 
@@ -173,7 +174,7 @@ public IDictionary<string, string> GetNamespacesInScope(XmlNamespaceScope scope)
             IDictionary<string, string> dictionary = _nsManager.GetNamespacesInScope(scope);
             if (scope != XmlNamespaceScope.Local)
             {
-                XmlNode node = _startNode;
+                XmlNode? node = _startNode;
                 while (node != null)
                 {
                     switch (node.NodeType)
@@ -221,23 +222,25 @@ public IDictionary<string, string> GetNamespacesInScope(XmlNamespaceScope scope)
             return dictionary;
         }
 
-        public string LookupNamespace(string prefix)
+        public string? LookupNamespace(string prefix)
         {
-            string namespaceName = _nsManager.LookupNamespace(prefix);
+            string? namespaceName = _nsManager.LookupNamespace(prefix);
             if (namespaceName == null)
             {
-                namespaceName = _startNode.GetNamespaceOfPrefixStrict(prefix);
+                namespaceName = _startNode!.GetNamespaceOfPrefixStrict(prefix);
             }
+
             return namespaceName;
         }
 
-        public string LookupPrefix(string namespaceName)
+        public string? LookupPrefix(string namespaceName)
         {
-            string prefix = _nsManager.LookupPrefix(namespaceName);
+            string? prefix = _nsManager.LookupPrefix(namespaceName);
             if (prefix == null)
             {
-                prefix = _startNode.GetPrefixOfNamespaceStrict(namespaceName);
+                prefix = _startNode!.GetPrefixOfNamespaceStrict(namespaceName);
             }
+
             return prefix;
         }
 
@@ -245,15 +248,16 @@ private IXmlNamespaceResolver NamespaceResolver
         {
             get
             {
-                if ((object)_startNode == (object)_document)
+                if ((object?)_startNode == (object?)_document)
                 {
                     return _nsManager;
                 }
+
                 return this;
             }
         }
 
-        private void CreateValidator(XmlSchemaObject partialValidationType, XmlSchemaValidationFlags validationFlags)
+        private void CreateValidator(XmlSchemaObject? partialValidationType, XmlSchemaValidationFlags validationFlags)
         {
             _validator = new XmlSchemaValidator(_nameTable, _schemas, NamespaceResolver, validationFlags);
             _validator.SourceUri = XmlConvert.ToUri(_document.BaseURI);
@@ -277,20 +281,22 @@ private void ValidateNode(XmlNode node)
             switch (_currentNode.NodeType)
             {
                 case XmlNodeType.Document:
-                    XmlElement docElem = ((XmlDocument)node).DocumentElement;
+                    XmlElement? docElem = ((XmlDocument)node).DocumentElement;
                     if (docElem == null)
                     {
                         throw new InvalidOperationException(SR.Format(SR.Xml_InvalidXmlDocument, SR.Xdom_NoRootEle));
                     }
+
                     ValidateNode(docElem);
                     break;
 
                 case XmlNodeType.DocumentFragment:
                 case XmlNodeType.EntityReference:
-                    for (XmlNode child = node.FirstChild; child != null; child = child.NextSibling)
+                    for (XmlNode? child = node.FirstChild; child != null; child = child.NextSibling)
                     {
                         ValidateNode(child);
                     }
+
                     break;
 
                 case XmlNodeType.Element:
@@ -298,8 +304,8 @@ private void ValidateNode(XmlNode node)
                     break;
 
                 case XmlNodeType.Attribute: //Top-level attribute
-                    XmlAttribute attr = _currentNode as XmlAttribute;
-                    _validator.ValidateAttribute(attr.LocalName, attr.NamespaceURI, _nodeValueGetter, _attributeSchemaInfo);
+                    XmlAttribute attr = (_currentNode as XmlAttribute)!;
+                    _validator!.ValidateAttribute(attr.LocalName, attr.NamespaceURI, _nodeValueGetter, _attributeSchemaInfo);
                     if (_psviAugmentation)
                     {
                         attr.XmlName = _document.AddAttrXmlName(attr.Prefix, attr.LocalName, attr.NamespaceURI, _attributeSchemaInfo);
@@ -307,16 +313,16 @@ private void ValidateNode(XmlNode node)
                     break;
 
                 case XmlNodeType.Text:
-                    _validator.ValidateText(_nodeValueGetter);
+                    _validator!.ValidateText(_nodeValueGetter);
                     break;
 
                 case XmlNodeType.CDATA:
-                    _validator.ValidateText(_nodeValueGetter);
+                    _validator!.ValidateText(_nodeValueGetter);
                     break;
 
                 case XmlNodeType.Whitespace:
                 case XmlNodeType.SignificantWhitespace:
-                    _validator.ValidateWhitespace(_nodeValueGetter);
+                    _validator!.ValidateWhitespace(_nodeValueGetter);
                     break;
 
                 case XmlNodeType.Comment:
@@ -331,15 +337,15 @@ private void ValidateNode(XmlNode node)
         private void ValidateElement()
         {
             _nsManager.PushScope();
-            XmlElement elementNode = _currentNode as XmlElement;
+            XmlElement? elementNode = _currentNode as XmlElement;
             Debug.Assert(elementNode != null);
 
             XmlAttributeCollection attributes = elementNode.Attributes;
-            XmlAttribute attr = null;
+            XmlAttribute? attr = null;
 
             //Find Xsi attributes that need to be processed before validating the element
-            string xsiNil = null;
-            string xsiType = null;
+            string? xsiNil = null;
+            string? xsiType = null;
 
             for (int i = 0; i < attributes.Count; i++)
             {
@@ -365,15 +371,17 @@ private void ValidateElement()
                     _nsManager.AddNamespace(attr.Prefix.Length == 0 ? string.Empty : attr.LocalName, attr.Value);
                 }
             }
-            _validator.ValidateElement(elementNode.LocalName, elementNode.NamespaceURI, _schemaInfo, xsiType, xsiNil, null, null);
+
+            _validator!.ValidateElement(elementNode.LocalName, elementNode.NamespaceURI, _schemaInfo, xsiType, xsiNil, null, null);
             ValidateAttributes(elementNode);
-            _validator.ValidateEndOfAttributes(_schemaInfo);
+            _validator!.ValidateEndOfAttributes(_schemaInfo);
 
             //If element has children, drill down
-            for (XmlNode child = elementNode.FirstChild; child != null; child = child.NextSibling)
+            for (XmlNode? child = elementNode.FirstChild; child != null; child = child.NextSibling)
             {
                 ValidateNode(child);
             }
+
             //Validate end of element
             _currentNode = elementNode; //Reset current Node for validation call back
             _validator.ValidateEndElement(_schemaInfo);
@@ -381,9 +389,9 @@ private void ValidateElement()
             if (_psviAugmentation)
             {
                 elementNode.XmlName = _document.AddXmlName(elementNode.Prefix, elementNode.LocalName, elementNode.NamespaceURI, _schemaInfo);
-                if (_schemaInfo.IsDefault)
+                if (_schemaInfo!.IsDefault)
                 { //the element has a default value
-                    XmlText textNode = _document.CreateTextNode(_schemaInfo.SchemaElement.ElementDecl.DefaultValueRaw);
+                    XmlText textNode = _document.CreateTextNode(_schemaInfo.SchemaElement!.ElementDecl!.DefaultValueRaw);
                     elementNode.AppendChild(textNode);
                 }
             }
@@ -394,7 +402,7 @@ private void ValidateElement()
         private void ValidateAttributes(XmlElement elementNode)
         {
             XmlAttributeCollection attributes = elementNode.Attributes;
-            XmlAttribute attr = null;
+            XmlAttribute? attr = null;
 
             for (int i = 0; i < attributes.Count; i++)
             {
@@ -404,7 +412,7 @@ private void ValidateAttributes(XmlElement elementNode)
                 { //Do not validate namespace decls
                     continue;
                 }
-                _validator.ValidateAttribute(attr.LocalName, attr.NamespaceURI, _nodeValueGetter, _attributeSchemaInfo);
+                _validator!.ValidateAttribute(attr.LocalName, attr.NamespaceURI, _nodeValueGetter, _attributeSchemaInfo);
                 if (_psviAugmentation)
                 {
                     attr.XmlName = _document.AddAttrXmlName(attr.Prefix, attr.LocalName, attr.NamespaceURI, _attributeSchemaInfo);
@@ -422,21 +430,20 @@ private void ValidateAttributes(XmlElement elementNode)
                 {
                     _defaultAttributes.Clear();
                 }
-                _validator.GetUnspecifiedDefaultAttributes(_defaultAttributes);
-                XmlSchemaAttribute schemaAttribute = null;
+                _validator!.GetUnspecifiedDefaultAttributes(_defaultAttributes);
                 XmlQualifiedName attrQName;
                 attr = null;
                 for (int i = 0; i < _defaultAttributes.Count; i++)
                 {
-                    schemaAttribute = _defaultAttributes[i] as XmlSchemaAttribute;
+                    XmlSchemaAttribute schemaAttribute = (_defaultAttributes[i] as XmlSchemaAttribute)!;
                     attrQName = schemaAttribute.QualifiedName;
                     Debug.Assert(schemaAttribute != null);
                     attr = _document.CreateDefaultAttribute(GetDefaultPrefix(attrQName.Namespace), attrQName.Name, attrQName.Namespace);
                     SetDefaultAttributeSchemaInfo(schemaAttribute);
                     attr.XmlName = _document.AddAttrXmlName(attr.Prefix, attr.LocalName, attr.NamespaceURI, _attributeSchemaInfo);
-                    attr.AppendChild(_document.CreateTextNode(schemaAttribute.AttDef.DefaultValueRaw));
+                    attr.AppendChild(_document.CreateTextNode(schemaAttribute.AttDef!.DefaultValueRaw));
                     attributes.Append(attr);
-                    XmlUnspecifiedAttribute defAttr = attr as XmlUnspecifiedAttribute;
+                    XmlUnspecifiedAttribute? defAttr = attr as XmlUnspecifiedAttribute;
                     if (defAttr != null)
                     {
                         defAttr.SetSpecified(false);
@@ -455,20 +462,20 @@ private void SetDefaultAttributeSchemaInfo(XmlSchemaAttribute schemaAttribute)
             _attributeSchemaInfo.SchemaAttribute = schemaAttribute;
 
             //Get memberType for default attribute
-            SchemaAttDef attributeDef = schemaAttribute.AttDef;
+            SchemaAttDef attributeDef = schemaAttribute.AttDef!;
             if (attributeDef.Datatype.Variety == XmlSchemaDatatypeVariety.Union)
             {
-                XsdSimpleValue simpleValue = attributeDef.DefaultValueTyped as XsdSimpleValue;
+                XsdSimpleValue? simpleValue = attributeDef.DefaultValueTyped as XsdSimpleValue;
                 Debug.Assert(simpleValue != null);
                 _attributeSchemaInfo.MemberType = simpleValue.XmlType;
             }
             _attributeSchemaInfo.Validity = XmlSchemaValidity.Valid;
         }
 
-        private string GetDefaultPrefix(string attributeNS)
+        private string? GetDefaultPrefix(string attributeNS)
         {
             IDictionary<string, string> namespaceDecls = NamespaceResolver.GetNamespacesInScope(XmlNamespaceScope.All);
-            string defaultPrefix = null;
+            string? defaultPrefix = null;
             string defaultNS;
             attributeNS = _nameTable.Add(attributeNS); //atomize ns
 
@@ -484,43 +491,44 @@ private string GetDefaultPrefix(string attributeNS)
                     }
                 }
             }
+
             return defaultPrefix;
         }
 
-        private object GetNodeValue()
+        private object? GetNodeValue()
         {
-            return _currentNode.Value;
+            return _currentNode!.Value;
         }
 
         //Code for finding type during partial validation
-        private XmlSchemaObject FindSchemaInfo(XmlElement elementToValidate)
+        private XmlSchemaObject? FindSchemaInfo(XmlElement elementToValidate)
         {
             _isPartialTreeValid = true;
-            Debug.Assert(elementToValidate.ParentNode.NodeType != XmlNodeType.Document); //Handle if it is the documentElement separately
+            Debug.Assert(elementToValidate.ParentNode!.NodeType != XmlNodeType.Document); //Handle if it is the documentElement separately
 
             //Create nodelist to navigate down again
             XmlNode currentNode = elementToValidate;
-            IXmlSchemaInfo parentSchemaInfo = null;
+            IXmlSchemaInfo? parentSchemaInfo = null;
             int nodeIndex = 0;
 
             //Check common case of parent node first
-            XmlNode parentNode = currentNode.ParentNode;
+            XmlNode? parentNode = currentNode.ParentNode;
             do
             {
-                parentSchemaInfo = parentNode.SchemaInfo;
+                parentSchemaInfo = parentNode!.SchemaInfo;
                 if (parentSchemaInfo.SchemaElement != null || parentSchemaInfo.SchemaType != null)
                 {
                     break; //Found ancestor with schemaInfo
                 }
                 CheckNodeSequenceCapacity(nodeIndex);
-                _nodeSequenceToValidate[nodeIndex++] = parentNode;
+                _nodeSequenceToValidate![nodeIndex++] = parentNode;
                 parentNode = parentNode.ParentNode;
             } while (parentNode != null);
 
             if (parentNode == null)
             { //Did not find any type info all the way to the root, currentNode is Document || DocumentFragment
                 nodeIndex = nodeIndex - 1; //Subtract the one for document and set the node to null
-                _nodeSequenceToValidate[nodeIndex] = null;
+                _nodeSequenceToValidate![nodeIndex] = null;
                 return GetTypeFromAncestors(elementToValidate, null, nodeIndex);
             }
             else
@@ -528,8 +536,8 @@ private XmlSchemaObject FindSchemaInfo(XmlElement elementToValidate)
                 //Start validating down from the parent or ancestor that has schema info and shallow validate all previous siblings
                 //to correctly ascertain particle for current node
                 CheckNodeSequenceCapacity(nodeIndex);
-                _nodeSequenceToValidate[nodeIndex++] = parentNode;
-                XmlSchemaObject ancestorSchemaObject = parentSchemaInfo.SchemaElement;
+                _nodeSequenceToValidate![nodeIndex++] = parentNode;
+                XmlSchemaObject? ancestorSchemaObject = parentSchemaInfo.SchemaElement;
                 if (ancestorSchemaObject == null)
                 {
                     ancestorSchemaObject = parentSchemaInfo.SchemaType;
@@ -563,23 +571,24 @@ private void CheckNodeSequenceCapacity(int currentIndex)
             }
         }
 
-        private XmlSchemaAttribute FindSchemaInfo(XmlAttribute attributeToValidate)
+        private XmlSchemaAttribute? FindSchemaInfo(XmlAttribute attributeToValidate)
         {
-            XmlElement parentElement = attributeToValidate.OwnerElement;
-            XmlSchemaObject schemaObject = FindSchemaInfo(parentElement);
-            XmlSchemaComplexType elementSchemaType = GetComplexType(schemaObject);
+            XmlElement parentElement = attributeToValidate.OwnerElement!;
+            XmlSchemaObject? schemaObject = FindSchemaInfo(parentElement);
+            XmlSchemaComplexType? elementSchemaType = GetComplexType(schemaObject);
             if (elementSchemaType == null)
             {
                 return null;
             }
+
             XmlQualifiedName attName = new XmlQualifiedName(attributeToValidate.LocalName, attributeToValidate.NamespaceURI);
-            XmlSchemaAttribute schemaAttribute = elementSchemaType.AttributeUses[attName] as XmlSchemaAttribute;
+            XmlSchemaAttribute? schemaAttribute = elementSchemaType.AttributeUses[attName] as XmlSchemaAttribute;
             if (schemaAttribute == null)
             {
-                XmlSchemaAnyAttribute anyAttribute = elementSchemaType.AttributeWildcard;
+                XmlSchemaAnyAttribute? anyAttribute = elementSchemaType.AttributeWildcard;
                 if (anyAttribute != null)
                 {
-                    if (anyAttribute.NamespaceList.Allows(attName))
+                    if (anyAttribute.NamespaceList!.Allows(attName))
                     { //Match wildcard against global attribute
                         schemaAttribute = _schemas.GlobalAttributes[attName] as XmlSchemaAttribute;
                     }
@@ -588,7 +597,7 @@ private XmlSchemaAttribute FindSchemaInfo(XmlAttribute attributeToValidate)
             return schemaAttribute;
         }
 
-        private XmlSchemaObject GetTypeFromAncestors(XmlElement elementToValidate, XmlSchemaObject ancestorType, int ancestorsCount)
+        private XmlSchemaObject? GetTypeFromAncestors(XmlElement elementToValidate, XmlSchemaObject? ancestorType, int ancestorsCount)
         {
             //schemaInfo is currentNode's schemaInfo
             _validator = CreateTypeFinderValidator(ancestorType);
@@ -600,8 +609,8 @@ private XmlSchemaObject GetTypeFromAncestors(XmlElement elementToValidate, XmlSc
             bool ancestorHasWildCard = AncestorTypeHasWildcard(ancestorType);
             for (int i = startIndex; i >= 0; i--)
             {
-                XmlNode node = _nodeSequenceToValidate[i];
-                XmlElement currentElement = node as XmlElement;
+                XmlNode node = _nodeSequenceToValidate![i]!;
+                XmlElement currentElement = (node as XmlElement)!;
                 ValidateSingleElement(currentElement, false, _schemaInfo);
                 if (!ancestorHasWildCard)
                 { //store type if ancestor does not have wildcard in its content model
@@ -613,7 +622,7 @@ private XmlSchemaObject GetTypeFromAncestors(XmlElement elementToValidate, XmlSc
                 _validator.ValidateEndOfAttributes(null);
                 if (i > 0)
                 {
-                    ValidateChildrenTillNextAncestor(node, _nodeSequenceToValidate[i - 1]);
+                    ValidateChildrenTillNextAncestor(node, _nodeSequenceToValidate[i - 1]!);
                 }
                 else
                 { //i == 0
@@ -621,11 +630,11 @@ private XmlSchemaObject GetTypeFromAncestors(XmlElement elementToValidate, XmlSc
                 }
             }
 
-            Debug.Assert(_nodeSequenceToValidate[0] == elementToValidate.ParentNode);
+            Debug.Assert(_nodeSequenceToValidate![0] == elementToValidate.ParentNode);
             //validate element whose type is needed,
             ValidateSingleElement(elementToValidate, false, _schemaInfo);
 
-            XmlSchemaObject schemaInfoFound = null;
+            XmlSchemaObject? schemaInfoFound = null;
             if (_schemaInfo.SchemaElement != null)
             {
                 schemaInfoFound = _schemaInfo.SchemaElement;
@@ -651,24 +660,26 @@ private XmlSchemaObject GetTypeFromAncestors(XmlElement elementToValidate, XmlSc
             return schemaInfoFound;
         }
 
-        private bool AncestorTypeHasWildcard(XmlSchemaObject ancestorType)
+        private bool AncestorTypeHasWildcard(XmlSchemaObject? ancestorType)
         {
-            XmlSchemaComplexType ancestorSchemaType = GetComplexType(ancestorType);
+            XmlSchemaComplexType? ancestorSchemaType = GetComplexType(ancestorType);
             if (ancestorType != null)
             {
-                return ancestorSchemaType.HasWildCard;
+                return ancestorSchemaType!.HasWildCard;
             }
+
             return false;
         }
 
-        private XmlSchemaComplexType GetComplexType(XmlSchemaObject schemaObject)
+        private XmlSchemaComplexType? GetComplexType(XmlSchemaObject? schemaObject)
         {
             if (schemaObject == null)
             {
                 return null;
             }
-            XmlSchemaElement schemaElement = schemaObject as XmlSchemaElement;
-            XmlSchemaComplexType complexType = null;
+
+            XmlSchemaElement? schemaElement = schemaObject as XmlSchemaElement;
+            XmlSchemaComplexType? complexType = null;
             if (schemaElement != null)
             {
                 complexType = schemaElement.ElementSchemaType as XmlSchemaComplexType;
@@ -677,20 +688,21 @@ private XmlSchemaComplexType GetComplexType(XmlSchemaObject schemaObject)
             {
                 complexType = schemaObject as XmlSchemaComplexType;
             }
+
             return complexType;
         }
 
-        private void ValidateSingleElement(XmlElement elementNode, bool skipToEnd, XmlSchemaInfo newSchemaInfo)
+        private void ValidateSingleElement(XmlElement elementNode, bool skipToEnd, XmlSchemaInfo? newSchemaInfo)
         {
             _nsManager.PushScope();
             Debug.Assert(elementNode != null);
 
             XmlAttributeCollection attributes = elementNode.Attributes;
-            XmlAttribute attr = null;
+            XmlAttribute? attr = null;
 
             //Find Xsi attributes that need to be processed before validating the element
-            string xsiNil = null;
-            string xsiType = null;
+            string? xsiNil = null;
+            string? xsiType = null;
 
             for (int i = 0; i < attributes.Count; i++)
             {
@@ -716,19 +728,20 @@ private void ValidateSingleElement(XmlElement elementNode, bool skipToEnd, XmlSc
                     _nsManager.AddNamespace(attr.Prefix.Length == 0 ? string.Empty : attr.LocalName, attr.Value);
                 }
             }
-            _validator.ValidateElement(elementNode.LocalName, elementNode.NamespaceURI, newSchemaInfo, xsiType, xsiNil, null, null);
+
+            _validator!.ValidateElement(elementNode.LocalName, elementNode.NamespaceURI, newSchemaInfo, xsiType, xsiNil, null, null);
             //Validate end of element
             if (skipToEnd)
             {
-                _validator.ValidateEndOfAttributes(newSchemaInfo);
-                _validator.SkipToEndElement(newSchemaInfo);
+                _validator!.ValidateEndOfAttributes(newSchemaInfo);
+                _validator!.SkipToEndElement(newSchemaInfo);
                 _nsManager.PopScope(); //Pop current namespace scope
             }
         }
 
         private void ValidateChildrenTillNextAncestor(XmlNode parentNode, XmlNode childToStopAt)
         {
-            XmlNode child;
+            XmlNode? child;
 
             for (child = parentNode.FirstChild; child != null; child = child.NextSibling)
             {
@@ -736,6 +749,7 @@ private void ValidateChildrenTillNextAncestor(XmlNode parentNode, XmlNode childT
                 {
                     break;
                 }
+
                 switch (child.NodeType)
                 {
                     case XmlNodeType.EntityReference:
@@ -743,17 +757,17 @@ private void ValidateChildrenTillNextAncestor(XmlNode parentNode, XmlNode childT
                         break;
 
                     case XmlNodeType.Element: //Flat validation, do not drill down into children
-                        ValidateSingleElement(child as XmlElement, true, null);
+                        ValidateSingleElement((child as XmlElement)!, true, null);
                         break;
 
                     case XmlNodeType.Text:
                     case XmlNodeType.CDATA:
-                        _validator.ValidateText(child.Value);
+                        _validator!.ValidateText(child.Value!);
                         break;
 
                     case XmlNodeType.Whitespace:
                     case XmlNodeType.SignificantWhitespace:
-                        _validator.ValidateWhitespace(child.Value);
+                        _validator!.ValidateWhitespace(child.Value!);
                         break;
 
                     case XmlNodeType.Comment:
@@ -761,13 +775,14 @@ private void ValidateChildrenTillNextAncestor(XmlNode parentNode, XmlNode childT
                         break;
 
                     default:
-                        throw new InvalidOperationException(SR.Format(SR.Xml_UnexpectedNodeType, _currentNode.NodeType));
+                        throw new InvalidOperationException(SR.Format(SR.Xml_UnexpectedNodeType, _currentNode!.NodeType));
                 }
             }
+
             Debug.Assert(child == childToStopAt);
         }
 
-        private XmlSchemaValidator CreateTypeFinderValidator(XmlSchemaObject partialValidationType)
+        private XmlSchemaValidator CreateTypeFinderValidator(XmlSchemaObject? partialValidationType)
         {
             XmlSchemaValidator findTypeValidator = new XmlSchemaValidator(_document.NameTable, _document.Schemas, _nsManager, XmlSchemaValidationFlags.None);
             findTypeValidator.ValidationEventHandler += new ValidationEventHandler(TypeFinderCallBack);
@@ -779,10 +794,11 @@ private XmlSchemaValidator CreateTypeFinderValidator(XmlSchemaObject partialVali
             { //If we walked up to the root and no schemaInfo was there, start validating from root
                 findTypeValidator.Initialize();
             }
+
             return findTypeValidator;
         }
 
-        private void TypeFinderCallBack(object sender, ValidationEventArgs arg)
+        private void TypeFinderCallBack(object? sender, ValidationEventArgs arg)
         {
             if (arg.Severity == XmlSeverityType.Error)
             {
@@ -790,13 +806,13 @@ private void TypeFinderCallBack(object sender, ValidationEventArgs arg)
             }
         }
 
-        private void InternalValidationCallBack(object sender, ValidationEventArgs arg)
+        private void InternalValidationCallBack(object? sender, ValidationEventArgs arg)
         {
             if (arg.Severity == XmlSeverityType.Error)
             {
                 _isValid = false;
             }
-            XmlSchemaValidationException ex = arg.Exception as XmlSchemaValidationException;
+            XmlSchemaValidationException? ex = arg.Exception as XmlSchemaValidationException;
             Debug.Assert(ex != null);
             ex.SetSourceObject(_currentNode);
             if (_eventHandler != null)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentXPathNavigator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentXPathNavigator.cs
index 2b9f90a9523e30..c9c16dda81cd7c 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentXPathNavigator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentXPathNavigator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -8,6 +9,7 @@
 using System.Xml.Schema;
 using System.Xml.XPath;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml
 {
@@ -16,7 +18,7 @@ internal sealed class DocumentXPathNavigator : XPathNavigator, IHasXmlNode
         private readonly XmlDocument _document; // owner document
         private XmlNode _source; // navigator position
         private int _attributeIndex; // index in attribute collection for attribute
-        private XmlElement _namespaceParent; // parent for namespace
+        private XmlElement? _namespaceParent; // parent for namespace
 
         public DocumentXPathNavigator(XmlDocument document, XmlNode node)
         {
@@ -70,7 +72,7 @@ public override void SetValue(string value)
                         {
                             throw new InvalidOperationException(SR.Xdom_Node_Modify_ReadOnly);
                         }
-                        DeleteToFollowingSibling(node.NextSibling, end);
+                        DeleteToFollowingSibling(node.NextSibling!, end);
                     }
                     goto case XmlNodeType.Element;
                 case XmlNodeType.Element:
@@ -113,8 +115,7 @@ public override string NamespaceURI
         {
             get
             {
-                XmlAttribute attribute = _source as XmlAttribute;
-                if (attribute != null
+                if (_source is XmlAttribute attribute
                     && attribute.IsNamespace)
                 {
                     return string.Empty;
@@ -153,8 +154,7 @@ public override string Prefix
         {
             get
             {
-                XmlAttribute attribute = _source as XmlAttribute;
-                if (attribute != null
+                if (_source is XmlAttribute attribute
                     && attribute.IsNamespace)
                 {
                     return string.Empty;
@@ -180,6 +180,11 @@ public override string Value
                     case XmlNodeType.SignificantWhitespace:
                         return ValueText;
                     default:
+                        Debug.Assert(_source.Value != null);
+                        // TODO-NULLABLE: Consider switching this.Value to nullable even if that implies switching it in the base type.
+                        // Also consider the following:
+                        //   * this.SetValue() does not accept null.
+                        //   * _source.Value is nullable.
                         return _source.Value;
                 }
             }
@@ -189,7 +194,7 @@ private string ValueDocument
         {
             get
             {
-                XmlElement element = _document.DocumentElement;
+                XmlElement? element = _document.DocumentElement;
                 if (element != null)
                 {
                     return element.InnerText;
@@ -204,8 +209,8 @@ private string ValueText
             {
                 CalibrateText();
 
-                string value = _source.Value;
-                XmlNode nextSibling = NextSibling(_source);
+                string? value = _source.Value;
+                XmlNode? nextSibling = NextSibling(_source);
                 if (nextSibling != null
                     && nextSibling.IsText)
                 {
@@ -219,6 +224,9 @@ private string ValueText
                            && nextSibling.IsText);
                     value = builder.ToString();
                 }
+                // TODO-NULLABLE: Consider making this nullable given that _source.Value is nullable,
+                // OR we could change this getter to return string.Empty if _source.Value == null.
+                Debug.Assert(value != null);
                 return value;
             }
         }
@@ -235,8 +243,7 @@ public override bool IsEmptyElement
         {
             get
             {
-                XmlElement element = _source as XmlElement;
-                if (element != null)
+                if (_source is XmlElement element)
                 {
                     return element.IsEmpty;
                 }
@@ -266,8 +273,7 @@ public override bool HasAttributes
         {
             get
             {
-                XmlElement element = _source as XmlElement;
-                if (element != null
+                if (_source is XmlElement element
                     && element.HasAttributes)
                 {
                     XmlAttributeCollection attributes = element.Attributes;
@@ -291,8 +297,7 @@ public override string GetAttribute(string localName, string namespaceURI)
 
         public override bool MoveToAttribute(string localName, string namespaceURI)
         {
-            XmlElement element = _source as XmlElement;
-            if (element != null
+            if (_source is XmlElement element
                 && element.HasAttributes)
             {
                 XmlAttributeCollection attributes = element.Attributes;
@@ -320,8 +325,7 @@ public override bool MoveToAttribute(string localName, string namespaceURI)
 
         public override bool MoveToFirstAttribute()
         {
-            XmlElement element = _source as XmlElement;
-            if (element != null
+            if (_source is XmlElement element
                 && element.HasAttributes)
             {
                 XmlAttributeCollection attributes = element.Attributes;
@@ -341,13 +345,12 @@ public override bool MoveToFirstAttribute()
 
         public override bool MoveToNextAttribute()
         {
-            XmlAttribute attribute = _source as XmlAttribute;
-            if (attribute == null
+            if (!(_source is XmlAttribute attribute)
                 || attribute.IsNamespace)
             {
                 return false;
             }
-            XmlAttributeCollection attributes;
+            XmlAttributeCollection? attributes;
             if (!CheckAttributePosition(attribute, out attributes, _attributeIndex)
                 && !ResetAttributePosition(attribute, attributes, out _attributeIndex))
             {
@@ -368,12 +371,11 @@ public override bool MoveToNextAttribute()
 
         public override string GetNamespace(string name)
         {
-            XmlNode node = _source;
+            XmlNode? node = _source;
             while (node != null
                    && node.NodeType != XmlNodeType.Element)
             {
-                XmlAttribute attribute = node as XmlAttribute;
-                if (attribute != null)
+                if (node is XmlAttribute attribute)
                 {
                     node = attribute.OwnerElement;
                 }
@@ -383,7 +385,7 @@ public override string GetNamespace(string name)
                 }
             }
 
-            XmlElement element = node as XmlElement;
+            XmlElement? element = node as XmlElement;
             if (element != null)
             {
                 string localName;
@@ -400,7 +402,7 @@ public override string GetNamespace(string name)
 
                 do
                 {
-                    XmlAttribute attribute = element.GetAttributeNode(localName, namespaceUri);
+                    XmlAttribute? attribute = element.GetAttributeNode(localName, namespaceUri);
                     if (attribute != null)
                     {
                         return attribute.Value;
@@ -427,7 +429,7 @@ public override bool MoveToNamespace(string name)
             {
                 return false;
             }
-            XmlElement element = _source as XmlElement;
+            XmlElement? element = _source as XmlElement;
             if (element != null)
             {
                 string localName;
@@ -444,7 +446,7 @@ public override bool MoveToNamespace(string name)
 
                 do
                 {
-                    XmlAttribute attribute = element.GetAttributeNode(localName, namespaceUri);
+                    XmlAttribute? attribute = element.GetAttributeNode(localName, namespaceUri);
                     if (attribute != null)
                     {
                         _namespaceParent = (XmlElement)_source;
@@ -467,8 +469,7 @@ public override bool MoveToNamespace(string name)
 
         public override bool MoveToFirstNamespace(XPathNamespaceScope scope)
         {
-            XmlElement element = _source as XmlElement;
-            if (element == null)
+            if (!(_source is XmlElement element))
             {
                 return false;
             }
@@ -553,7 +554,7 @@ private static bool MoveToFirstNamespaceGlobal(ref XmlAttributeCollection attrib
             }
 
             Debug.Assert(attributes != null && attributes.parent != null);
-            XmlElement element = attributes.parent.ParentNode as XmlElement;
+            XmlElement? element = attributes.parent.ParentNode as XmlElement;
             while (element != null)
             {
                 if (element.HasAttributes)
@@ -571,13 +572,12 @@ private static bool MoveToFirstNamespaceGlobal(ref XmlAttributeCollection attrib
 
         public override bool MoveToNextNamespace(XPathNamespaceScope scope)
         {
-            XmlAttribute attribute = _source as XmlAttribute;
-            if (attribute == null
+            if (!(_source is XmlAttribute attribute)
                 || !attribute.IsNamespace)
             {
                 return false;
             }
-            XmlAttributeCollection attributes;
+            XmlAttributeCollection? attributes;
             int index = _attributeIndex;
             if (!CheckAttributePosition(attribute, out attributes, index)
                 && !ResetAttributePosition(attribute, attributes, out index))
@@ -668,7 +668,7 @@ private static bool MoveToNextNamespaceGlobal(ref XmlAttributeCollection attribu
             }
 
             Debug.Assert(attributes != null && attributes.parent != null);
-            XmlElement element = attributes.parent.ParentNode as XmlElement;
+            XmlElement? element = attributes.parent.ParentNode as XmlElement;
             while (element != null)
             {
                 if (element.HasAttributes)
@@ -684,25 +684,26 @@ private static bool MoveToNextNamespaceGlobal(ref XmlAttributeCollection attribu
             return false;
         }
 
-        private bool PathHasDuplicateNamespace(XmlElement top, XmlElement bottom, string localName)
+        private bool PathHasDuplicateNamespace(XmlElement? top, XmlElement bottom, string localName)
         {
+            XmlElement? current = bottom;
             string namespaceUri = _document.strReservedXmlns;
-            while (bottom != null
-                   && bottom != top)
+            while (current != null
+                   && current != top)
             {
-                XmlAttribute attribute = bottom.GetAttributeNode(localName, namespaceUri);
+                XmlAttribute? attribute = current.GetAttributeNode(localName, namespaceUri);
                 if (attribute != null)
                 {
                     return true;
                 }
-                bottom = bottom.ParentNode as XmlElement;
+                current = current.ParentNode as XmlElement;
             }
             return false;
         }
 
-        public override string LookupNamespace(string prefix)
+        public override string? LookupNamespace(string prefix)
         {
-            string ns = base.LookupNamespace(prefix);
+            string? ns = base.LookupNamespace(prefix);
             if (ns != null)
             {
                 ns = this.NameTable.Add(ns);
@@ -712,7 +713,7 @@ public override string LookupNamespace(string prefix)
 
         public override bool MoveToNext()
         {
-            XmlNode sibling = NextSibling(_source);
+            XmlNode? sibling = NextSibling(_source);
             if (sibling == null)
             {
                 return false;
@@ -728,7 +729,7 @@ public override bool MoveToNext()
                     }
                 }
             }
-            XmlNode parent = ParentNode(sibling);
+            XmlNode? parent = ParentNode(sibling);
             Debug.Assert(parent != null);
             while (!IsValidChild(parent, sibling))
             {
@@ -744,7 +745,7 @@ public override bool MoveToNext()
 
         public override bool MoveToPrevious()
         {
-            XmlNode sibling = PreviousSibling(_source);
+            XmlNode? sibling = PreviousSibling(_source);
             if (sibling == null)
             {
                 return false;
@@ -764,7 +765,7 @@ public override bool MoveToPrevious()
                     sibling = TextStart(sibling);
                 }
             }
-            XmlNode parent = ParentNode(sibling);
+            XmlNode? parent = ParentNode(sibling);
             Debug.Assert(parent != null);
             while (!IsValidChild(parent, sibling))
             {
@@ -787,12 +788,12 @@ public override bool MoveToFirst()
             {
                 return false;
             }
-            XmlNode parent = ParentNode(_source);
+            XmlNode? parent = ParentNode(_source);
             if (parent == null)
             {
                 return false;
             }
-            XmlNode sibling = FirstChild(parent);
+            XmlNode? sibling = FirstChild(parent);
             Debug.Assert(sibling != null);
             while (!IsValidChild(parent, sibling))
             {
@@ -808,7 +809,7 @@ public override bool MoveToFirst()
 
         public override bool MoveToFirstChild()
         {
-            XmlNode child;
+            XmlNode? child;
             switch (_source.NodeType)
             {
                 case XmlNodeType.Element:
@@ -843,14 +844,13 @@ public override bool MoveToFirstChild()
 
         public override bool MoveToParent()
         {
-            XmlNode parent = ParentNode(_source);
+            XmlNode? parent = ParentNode(_source);
             if (parent != null)
             {
                 _source = parent;
                 return true;
             }
-            XmlAttribute attribute = _source as XmlAttribute;
-            if (attribute != null)
+            if (_source is XmlAttribute attribute)
             {
                 parent = attribute.IsNamespace ? _namespaceParent : attribute.OwnerElement;
                 if (parent != null)
@@ -867,11 +867,10 @@ public override void MoveToRoot()
         {
             while (true)
             {
-                XmlNode parent = _source.ParentNode;
+                XmlNode? parent = _source.ParentNode;
                 if (parent == null)
                 {
-                    XmlAttribute attribute = _source as XmlAttribute;
-                    if (attribute == null)
+                    if (!(_source is XmlAttribute attribute))
                     {
                         break;
                     }
@@ -888,8 +887,7 @@ public override void MoveToRoot()
 
         public override bool MoveTo(XPathNavigator other)
         {
-            DocumentXPathNavigator that = other as DocumentXPathNavigator;
-            if (that != null
+            if (other is DocumentXPathNavigator that
                 && _document == that._document)
             {
                 _source = that._source;
@@ -902,7 +900,7 @@ public override bool MoveTo(XPathNavigator other)
 
         public override bool MoveToId(string id)
         {
-            XmlElement element = _document.GetElementById(id);
+            XmlElement? element = _document.GetElementById(id);
             if (element != null)
             {
                 _source = element;
@@ -919,7 +917,7 @@ public override bool MoveToChild(string localName, string namespaceUri)
                 return false;
             }
 
-            XmlNode child = FirstChild(_source);
+            XmlNode? child = FirstChild(_source);
             if (child != null)
             {
                 do
@@ -945,7 +943,7 @@ public override bool MoveToChild(XPathNodeType type)
                 return false;
             }
 
-            XmlNode child = FirstChild(_source);
+            XmlNode? child = FirstChild(_source);
             if (child != null)
             {
                 int mask = GetContentKindMask(type);
@@ -967,11 +965,10 @@ public override bool MoveToChild(XPathNodeType type)
             return false;
         }
 
-        public override bool MoveToFollowing(string localName, string namespaceUri, XPathNavigator end)
+        public override bool MoveToFollowing(string localName, string namespaceUri, XPathNavigator? end)
         {
-            XmlNode pastFollowing = null;
-            DocumentXPathNavigator that = end as DocumentXPathNavigator;
-            if (that != null)
+            XmlNode? pastFollowing = null;
+            if (end is DocumentXPathNavigator that)
             {
                 if (_document != that._document)
                 {
@@ -990,7 +987,7 @@ public override bool MoveToFollowing(string localName, string namespaceUri, XPat
                 pastFollowing = that._source;
             }
 
-            XmlNode following = _source;
+            XmlNode? following = _source;
             if (following.NodeType == XmlNodeType.Attribute)
             {
                 following = ((XmlAttribute)following).OwnerElement;
@@ -1001,7 +998,7 @@ public override bool MoveToFollowing(string localName, string namespaceUri, XPat
             }
             do
             {
-                XmlNode firstChild = following.FirstChild;
+                XmlNode? firstChild = following.FirstChild;
                 if (firstChild != null)
                 {
                     following = firstChild;
@@ -1010,7 +1007,7 @@ public override bool MoveToFollowing(string localName, string namespaceUri, XPat
                 {
                     while (true)
                     {
-                        XmlNode nextSibling = following.NextSibling;
+                        XmlNode? nextSibling = following.NextSibling;
                         if (nextSibling != null)
                         {
                             following = nextSibling;
@@ -1018,7 +1015,7 @@ public override bool MoveToFollowing(string localName, string namespaceUri, XPat
                         }
                         else
                         {
-                            XmlNode parent = following.ParentNode;
+                            XmlNode? parent = following.ParentNode;
                             if (parent != null)
                             {
                                 following = parent;
@@ -1043,11 +1040,10 @@ public override bool MoveToFollowing(string localName, string namespaceUri, XPat
             return true;
         }
 
-        public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
+        public override bool MoveToFollowing(XPathNodeType type, XPathNavigator? end)
         {
-            XmlNode pastFollowing = null;
-            DocumentXPathNavigator that = end as DocumentXPathNavigator;
-            if (that != null)
+            XmlNode? pastFollowing = null;
+            if (end is DocumentXPathNavigator that)
             {
                 if (_document != that._document)
                 {
@@ -1071,7 +1067,7 @@ public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
             {
                 return false;
             }
-            XmlNode following = _source;
+            XmlNode? following = _source;
             switch (following.NodeType)
             {
                 case XmlNodeType.Attribute:
@@ -1090,7 +1086,7 @@ public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
             }
             do
             {
-                XmlNode firstChild = following.FirstChild;
+                XmlNode? firstChild = following.FirstChild;
                 if (firstChild != null)
                 {
                     following = firstChild;
@@ -1099,7 +1095,7 @@ public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
                 {
                     while (true)
                     {
-                        XmlNode nextSibling = following.NextSibling;
+                        XmlNode? nextSibling = following.NextSibling;
                         if (nextSibling != null)
                         {
                             following = nextSibling;
@@ -1107,7 +1103,7 @@ public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
                         }
                         else
                         {
-                            XmlNode parent = following.ParentNode;
+                            XmlNode? parent = following.ParentNode;
                             if (parent != null)
                             {
                                 following = parent;
@@ -1132,7 +1128,7 @@ public override bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
 
         public override bool MoveToNext(string localName, string namespaceUri)
         {
-            XmlNode sibling = NextSibling(_source);
+            XmlNode? sibling = NextSibling(_source);
             if (sibling == null)
             {
                 return false;
@@ -1154,7 +1150,7 @@ public override bool MoveToNext(string localName, string namespaceUri)
 
         public override bool MoveToNext(XPathNodeType type)
         {
-            XmlNode sibling = NextSibling(_source);
+            XmlNode? sibling = NextSibling(_source);
             if (sibling == null)
             {
                 return false;
@@ -1191,7 +1187,7 @@ public override bool HasChildren
         {
             get
             {
-                XmlNode child;
+                XmlNode? child;
                 switch (_source.NodeType)
                 {
                     case XmlNodeType.Element:
@@ -1225,8 +1221,7 @@ public override bool HasChildren
 
         public override bool IsSamePosition(XPathNavigator other)
         {
-            DocumentXPathNavigator that = other as DocumentXPathNavigator;
-            if (that != null)
+            if (other is DocumentXPathNavigator that)
             {
                 this.CalibrateText();
                 that.CalibrateText();
@@ -1237,10 +1232,9 @@ public override bool IsSamePosition(XPathNavigator other)
             return false;
         }
 
-        public override bool IsDescendant(XPathNavigator other)
+        public override bool IsDescendant(XPathNavigator? other)
         {
-            DocumentXPathNavigator that = other as DocumentXPathNavigator;
-            if (that != null)
+            if (other is DocumentXPathNavigator that)
             {
                 return IsDescendant(_source, that._source);
             }
@@ -1257,7 +1251,7 @@ public override IXmlSchemaInfo SchemaInfo
 
         public override bool CheckValidity(XmlSchemaSet schemas, ValidationEventHandler validationEventHandler)
         {
-            XmlDocument ownerDocument;
+            XmlDocument? ownerDocument;
 
             if (_source.NodeType == XmlNodeType.Document)
             {
@@ -1282,20 +1276,21 @@ public override bool CheckValidity(XmlSchemaSet schemas, ValidationEventHandler
                 throw new InvalidOperationException(SR.XmlDocument_NoSchemaInfo);
             }
 
+            // DocumentSchemaValidator assumes that ownedDocument can never be null.
+            Debug.Assert(ownerDocument != null);
             DocumentSchemaValidator validator = new DocumentSchemaValidator(ownerDocument, schemas, validationEventHandler);
             validator.PsviAugmentation = false;
             return validator.Validate(_source);
         }
 
-        private static XmlNode OwnerNode(XmlNode node)
+        private static XmlNode? OwnerNode(XmlNode node)
         {
-            XmlNode parent = node.ParentNode;
+            XmlNode? parent = node.ParentNode;
             if (parent != null)
             {
                 return parent;
             }
-            XmlAttribute attribute = node as XmlAttribute;
-            if (attribute != null)
+            if (node is XmlAttribute attribute)
             {
                 return attribute.OwnerElement;
             }
@@ -1305,7 +1300,7 @@ private static XmlNode OwnerNode(XmlNode node)
         private static int GetDepth(XmlNode node)
         {
             int depth = 0;
-            XmlNode owner = OwnerNode(node);
+            XmlNode? owner = OwnerNode(node);
             while (owner != null)
             {
                 depth++;
@@ -1327,7 +1322,8 @@ private XmlNodeOrder Compare(XmlNode node1, XmlNode node2)
             {
                 if (node2.XPNodeType == XPathNodeType.Attribute)
                 {
-                    XmlElement element = ((XmlAttribute)node1).OwnerElement;
+                    XmlElement? element = ((XmlAttribute)node1).OwnerElement;
+                    Debug.Assert(element != null);
                     if (element.HasAttributes)
                     {
                         XmlAttributeCollection attributes = element.Attributes;
@@ -1357,7 +1353,7 @@ private XmlNodeOrder Compare(XmlNode node1, XmlNode node2)
             }
 
             //neither of the node is Namespace node or Attribute node
-            XmlNode nextNode = node1.NextSibling;
+            XmlNode? nextNode = node1.NextSibling;
             while (nextNode != null && nextNode != node2)
                 nextNode = nextNode.NextSibling;
             if (nextNode == null)
@@ -1368,10 +1364,9 @@ private XmlNodeOrder Compare(XmlNode node1, XmlNode node2)
                 return XmlNodeOrder.Before;
         }
 
-        public override XmlNodeOrder ComparePosition(XPathNavigator other)
+        public override XmlNodeOrder ComparePosition(XPathNavigator? other)
         {
-            DocumentXPathNavigator that = other as DocumentXPathNavigator;
-            if (that == null)
+            if (!(other is DocumentXPathNavigator that))
             {
                 return XmlNodeOrder.Unknown;
             }
@@ -1391,11 +1386,11 @@ public override XmlNodeOrder ComparePosition(XPathNavigator other)
                 return base.ComparePosition(other);
             }
 
-            XmlNode node1 = _source;
-            XmlNode node2 = that._source;
+            XmlNode? node1 = _source;
+            XmlNode? node2 = that._source;
 
-            XmlNode parent1 = OwnerNode(node1);
-            XmlNode parent2 = OwnerNode(node2);
+            XmlNode? parent1 = OwnerNode(node1);
+            XmlNode? parent2 = OwnerNode(node2);
             if (parent1 == parent2)
             {
                 if (parent1 == null)
@@ -1423,6 +1418,7 @@ public override XmlNodeOrder ComparePosition(XPathNavigator other)
                 {
                     return XmlNodeOrder.Before;
                 }
+                Debug.Assert(node2 != null);
                 parent2 = OwnerNode(node2);
             }
             else if (depth1 > depth2)
@@ -1437,6 +1433,7 @@ public override XmlNodeOrder ComparePosition(XPathNavigator other)
                 {
                     return XmlNodeOrder.After;
                 }
+                Debug.Assert(node1 != null);
                 parent1 = OwnerNode(node1);
             }
 
@@ -1461,13 +1458,13 @@ public override XmlNodeOrder ComparePosition(XPathNavigator other)
 
         public override XPathNodeIterator SelectDescendants(string localName, string namespaceURI, bool matchSelf)
         {
-            string nsAtom = _document.NameTable.Get(namespaceURI);
+            string? nsAtom = _document.NameTable.Get(namespaceURI);
             if (nsAtom == null || _source.NodeType == XmlNodeType.Attribute)
                 return new DocumentXPathNodeIterator_Empty(this);
 
             Debug.Assert(this.NodeType != XPathNodeType.Attribute && this.NodeType != XPathNodeType.Namespace && this.NodeType != XPathNodeType.All);
 
-            string localNameAtom = _document.NameTable.Get(localName);
+            string? localNameAtom = _document.NameTable.Get(localName);
             if (localNameAtom == null)
                 return new DocumentXPathNodeIterator_Empty(this);
 
@@ -1606,8 +1603,7 @@ public override XmlWriter CreateAttributes()
 
         public override XmlWriter ReplaceRange(XPathNavigator lastSiblingToReplace)
         {
-            DocumentXPathNavigator that = lastSiblingToReplace as DocumentXPathNavigator;
-            if (that == null)
+            if (!(lastSiblingToReplace is DocumentXPathNavigator that))
             {
                 if (lastSiblingToReplace == null)
                 {
@@ -1664,8 +1660,7 @@ public override XmlWriter ReplaceRange(XPathNavigator lastSiblingToReplace)
 
         public override void DeleteRange(XPathNavigator lastSiblingToDelete)
         {
-            DocumentXPathNavigator that = lastSiblingToDelete as DocumentXPathNavigator;
-            if (that == null)
+            if (!(lastSiblingToDelete is DocumentXPathNavigator that))
             {
                 if (lastSiblingToDelete == null)
                 {
@@ -1693,7 +1688,7 @@ public override void DeleteRange(XPathNavigator lastSiblingToDelete)
                         {
                             goto default;
                         }
-                        XmlNode parent = OwnerNode(attribute);
+                        XmlNode? parent = OwnerNode(attribute);
                         DeleteAttribute(attribute, _attributeIndex);
                         if (parent != null)
                         {
@@ -1730,7 +1725,7 @@ public override void DeleteRange(XPathNavigator lastSiblingToDelete)
                 {
                     throw new InvalidOperationException(SR.Xpn_BadPosition);
                 }
-                XmlNode parent = OwnerNode(node);
+                XmlNode? parent = OwnerNode(node);
                 DeleteToFollowingSibling(node, end);
                 if (parent != null)
                 {
@@ -1752,7 +1747,7 @@ public override void DeleteSelf()
                     {
                         goto default;
                     }
-                    XmlNode parent = OwnerNode(attribute);
+                    XmlNode? parent = OwnerNode(attribute);
                     DeleteAttribute(attribute, _attributeIndex);
                     if (parent != null)
                     {
@@ -1785,7 +1780,7 @@ public override void DeleteSelf()
 
         private static void DeleteAttribute(XmlAttribute attribute, int index)
         {
-            XmlAttributeCollection attributes;
+            XmlAttributeCollection? attributes;
 
             if (!CheckAttributePosition(attribute, out attributes, index)
                 && !ResetAttributePosition(attribute, attributes, out index))
@@ -1801,7 +1796,7 @@ private static void DeleteAttribute(XmlAttribute attribute, int index)
 
         internal static void DeleteToFollowingSibling(XmlNode node, XmlNode end)
         {
-            XmlNode parent = node.ParentNode;
+            XmlNode? parent = node.ParentNode;
 
             if (parent == null)
             {
@@ -1814,22 +1809,22 @@ internal static void DeleteToFollowingSibling(XmlNode node, XmlNode end)
             }
             while (node != end)
             {
+                Debug.Assert(node != null, "This method needs to be called with the beforehand check of NextSibling being not null from node to end");
                 XmlNode temp = node;
-                node = node.NextSibling;
+                node = node.NextSibling!;
                 parent.RemoveChild(temp);
             }
             parent.RemoveChild(node);
         }
 
-        private static XmlNamespaceManager GetNamespaceManager(XmlNode node, XmlDocument document)
+        private static XmlNamespaceManager GetNamespaceManager(XmlNode? node, XmlDocument document)
         {
             XmlNamespaceManager namespaceManager = new XmlNamespaceManager(document.NameTable);
             List<XmlElement> elements = new List<XmlElement>();
 
             while (node != null)
             {
-                XmlElement element = node as XmlElement;
-                if (element != null
+                if (node is XmlElement element
                     && element.HasAttributes)
                 {
                     elements.Add(element);
@@ -1853,15 +1848,15 @@ private static XmlNamespaceManager GetNamespaceManager(XmlNode node, XmlDocument
             return namespaceManager;
         }
 
+        [MemberNotNull(nameof(_source))]
         internal void ResetPosition(XmlNode node)
         {
             Debug.Assert(node != null, "Undefined navigator position");
             Debug.Assert(node == _document || node.OwnerDocument == _document, "Navigator switched documents");
             _source = node;
-            XmlAttribute attribute = node as XmlAttribute;
-            if (attribute != null)
+            if (node is XmlAttribute attribute)
             {
-                XmlElement element = attribute.OwnerElement;
+                XmlElement? element = attribute.OwnerElement;
                 if (element != null)
                 {
                     ResetAttributePosition(attribute, element.Attributes, out _attributeIndex);
@@ -1873,7 +1868,7 @@ internal void ResetPosition(XmlNode node)
             }
         }
 
-        private static bool ResetAttributePosition(XmlAttribute attribute, XmlAttributeCollection attributes, out int index)
+        private static bool ResetAttributePosition(XmlAttribute attribute, [NotNullWhen(true)] XmlAttributeCollection? attributes, out int index)
         {
             if (attributes != null)
             {
@@ -1890,9 +1885,9 @@ private static bool ResetAttributePosition(XmlAttribute attribute, XmlAttributeC
             return false;
         }
 
-        private static bool CheckAttributePosition(XmlAttribute attribute, out XmlAttributeCollection attributes, int index)
+        private static bool CheckAttributePosition(XmlAttribute attribute, [NotNullWhen(true)] out XmlAttributeCollection? attributes, int index)
         {
-            XmlElement element = attribute.OwnerElement;
+            XmlElement? element = attribute.OwnerElement;
             if (element != null)
             {
                 attributes = element.Attributes;
@@ -1912,7 +1907,7 @@ private static bool CheckAttributePosition(XmlAttribute attribute, out XmlAttrib
 
         private void CalibrateText()
         {
-            XmlNode text = PreviousText(_source);
+            XmlNode? text = PreviousText(_source);
             while (text != null)
             {
                 ResetPosition(text);
@@ -1920,9 +1915,9 @@ private void CalibrateText()
             }
         }
 
-        private XmlNode ParentNode(XmlNode node)
+        private XmlNode? ParentNode(XmlNode node)
         {
-            XmlNode parent = node.ParentNode;
+            XmlNode? parent = node.ParentNode;
 
             if (!_document.HasEntityReferences)
             {
@@ -1931,7 +1926,7 @@ private XmlNode ParentNode(XmlNode node)
             return ParentNodeTail(parent);
         }
 
-        private XmlNode ParentNodeTail(XmlNode parent)
+        private XmlNode? ParentNodeTail(XmlNode? parent)
         {
             while (parent != null
                    && parent.NodeType == XmlNodeType.EntityReference)
@@ -1941,9 +1936,9 @@ private XmlNode ParentNodeTail(XmlNode parent)
             return parent;
         }
 
-        private XmlNode FirstChild(XmlNode node)
+        private XmlNode? FirstChild(XmlNode node)
         {
-            XmlNode child = node.FirstChild;
+            XmlNode? child = node.FirstChild;
 
             if (!_document.HasEntityReferences)
             {
@@ -1952,7 +1947,7 @@ private XmlNode FirstChild(XmlNode node)
             return FirstChildTail(child);
         }
 
-        private XmlNode FirstChildTail(XmlNode child)
+        private XmlNode? FirstChildTail(XmlNode? child)
         {
             while (child != null
                    && child.NodeType == XmlNodeType.EntityReference)
@@ -1962,9 +1957,9 @@ private XmlNode FirstChildTail(XmlNode child)
             return child;
         }
 
-        private XmlNode NextSibling(XmlNode node)
+        private XmlNode? NextSibling(XmlNode node)
         {
-            XmlNode sibling = node.NextSibling;
+            XmlNode? sibling = node.NextSibling;
 
             if (!_document.HasEntityReferences)
             {
@@ -1973,17 +1968,18 @@ private XmlNode NextSibling(XmlNode node)
             return NextSiblingTail(node, sibling);
         }
 
-        private XmlNode NextSiblingTail(XmlNode node, XmlNode sibling)
+        private XmlNode? NextSiblingTail(XmlNode node, XmlNode? sibling)
         {
+            XmlNode? current = node;
             while (sibling == null)
             {
-                node = node.ParentNode;
-                if (node == null
-                    || node.NodeType != XmlNodeType.EntityReference)
+                current = current.ParentNode;
+                if (current == null
+                    || current.NodeType != XmlNodeType.EntityReference)
                 {
                     return null;
                 }
-                sibling = node.NextSibling;
+                sibling = current.NextSibling;
             }
             while (sibling != null
                    && sibling.NodeType == XmlNodeType.EntityReference)
@@ -1993,9 +1989,9 @@ private XmlNode NextSiblingTail(XmlNode node, XmlNode sibling)
             return sibling;
         }
 
-        private XmlNode PreviousSibling(XmlNode node)
+        private XmlNode? PreviousSibling(XmlNode node)
         {
-            XmlNode sibling = node.PreviousSibling;
+            XmlNode? sibling = node.PreviousSibling;
 
             if (!_document.HasEntityReferences)
             {
@@ -2004,17 +2000,18 @@ private XmlNode PreviousSibling(XmlNode node)
             return PreviousSiblingTail(node, sibling);
         }
 
-        private XmlNode PreviousSiblingTail(XmlNode node, XmlNode sibling)
+        private XmlNode? PreviousSiblingTail(XmlNode node, XmlNode? sibling)
         {
+            XmlNode? current = node;
             while (sibling == null)
             {
-                node = node.ParentNode;
-                if (node == null
-                    || node.NodeType != XmlNodeType.EntityReference)
+                current = current.ParentNode;
+                if (current == null
+                    || current.NodeType != XmlNodeType.EntityReference)
                 {
                     return null;
                 }
-                sibling = node.PreviousSibling;
+                sibling = current.PreviousSibling;
             }
             while (sibling != null
                    && sibling.NodeType == XmlNodeType.EntityReference)
@@ -2024,9 +2021,9 @@ private XmlNode PreviousSiblingTail(XmlNode node, XmlNode sibling)
             return sibling;
         }
 
-        private XmlNode PreviousText(XmlNode node)
+        private XmlNode? PreviousText(XmlNode node)
         {
-            XmlNode text = node.PreviousText;
+            XmlNode? text = node.PreviousText;
 
             if (!_document.HasEntityReferences)
             {
@@ -2035,7 +2032,7 @@ private XmlNode PreviousText(XmlNode node)
             return PreviousTextTail(node, text);
         }
 
-        private XmlNode PreviousTextTail(XmlNode node, XmlNode text)
+        private XmlNode? PreviousTextTail(XmlNode node, XmlNode? text)
         {
             if (text != null)
             {
@@ -2045,16 +2042,17 @@ private XmlNode PreviousTextTail(XmlNode node, XmlNode text)
             {
                 return null;
             }
-            XmlNode sibling = node.PreviousSibling;
+            XmlNode? sibling = node.PreviousSibling;
+            XmlNode? current = node;
             while (sibling == null)
             {
-                node = node.ParentNode;
-                if (node == null
-                    || node.NodeType != XmlNodeType.EntityReference)
+                current = current.ParentNode;
+                if (current == null
+                    || current.NodeType != XmlNodeType.EntityReference)
                 {
                     return null;
                 }
-                sibling = node.PreviousSibling;
+                sibling = current.PreviousSibling;
             }
             while (sibling != null)
             {
@@ -2075,16 +2073,17 @@ private XmlNode PreviousTextTail(XmlNode node, XmlNode text)
             return null;
         }
 
-        internal static bool IsFollowingSibling(XmlNode left, XmlNode right)
+        internal static bool IsFollowingSibling(XmlNode left, [NotNullWhen(true)] XmlNode? right)
         {
+            XmlNode? currentLeft = left;
             while (true)
             {
-                left = left.NextSibling;
-                if (left == null)
+                currentLeft = currentLeft.NextSibling;
+                if (currentLeft == null)
                 {
                     break;
                 }
-                if (left == right)
+                if (currentLeft == right)
                 {
                     return true;
                 }
@@ -2096,11 +2095,10 @@ private static bool IsDescendant(XmlNode top, XmlNode bottom)
         {
             while (true)
             {
-                XmlNode parent = bottom.ParentNode;
+                XmlNode? parent = bottom.ParentNode;
                 if (parent == null)
                 {
-                    XmlAttribute attribute = bottom as XmlAttribute;
-                    if (attribute == null)
+                    if (!(bottom is XmlAttribute attribute))
                     {
                         break;
                     }
@@ -2156,28 +2154,30 @@ private static bool IsValidChild(XmlNode parent, XmlNode child)
         private XmlNode TextStart(XmlNode node)
         {
             XmlNode start;
+            XmlNode? current = node;
 
             do
             {
-                start = node;
-                node = PreviousSibling(node);
+                start = current;
+                current = PreviousSibling(current);
             }
-            while (node != null
-                   && node.IsText);
+            while (current != null
+                   && current.IsText);
             return start;
         }
 
         private XmlNode TextEnd(XmlNode node)
         {
             XmlNode end;
+            XmlNode? current = node;
 
             do
             {
-                end = node;
-                node = NextSibling(node);
+                end = current;
+                current = NextSibling(current);
             }
-            while (node != null
-                   && node.IsText);
+            while (current != null
+                   && current.IsText);
             return end;
         }
     }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentXmlWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentXmlWriter.cs
index ee8b229b33f0a9..5019c9bdf9e93e 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentXmlWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/DocumentXmlWriter.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -57,13 +58,13 @@ private enum Method
         private readonly DocumentXmlWriterType _type; // writer type
         private readonly XmlNode _start; // context node
         private readonly XmlDocument _document; // context document
-        private XmlNamespaceManager _namespaceManager; // context namespace manager
+        private XmlNamespaceManager? _namespaceManager; // context namespace manager
         private State _state; // current state
-        private XmlNode _write; // current node
+        private XmlNode? _write; // current node
         private readonly List<XmlNode> _fragment; // top level node cache
         private readonly XmlWriterSettings _settings; // wrapping writer settings
-        private DocumentXPathNavigator _navigator; // context for replace
-        private XmlNode _end; // context for replace
+        private DocumentXPathNavigator? _navigator; // context for replace
+        private XmlNode? _end; // context for replace
 
         public DocumentXmlWriter(DocumentXmlWriterType type, XmlNode start, XmlDocument document)
         {
@@ -81,7 +82,7 @@ public DocumentXmlWriter(DocumentXmlWriterType type, XmlNode start, XmlDocument
             _settings.ReadOnly = true;
         }
 
-        public XmlNamespaceManager NamespaceManager
+        public XmlNamespaceManager? NamespaceManager
         {
             set
             {
@@ -97,7 +98,7 @@ public override XmlWriterSettings Settings
             }
         }
 
-        public DocumentXPathNavigator Navigator
+        public DocumentXPathNavigator? Navigator
         {
             set
             {
@@ -126,9 +127,9 @@ internal override void WriteXmlDeclaration(XmlStandalone standalone)
         internal override void WriteXmlDeclaration(string xmldecl)
         {
             VerifyState(Method.WriteXmlDeclaration);
-            string version, encoding, standalone;
+            string? version, encoding, standalone;
             XmlLoader.ParseXmlDeclarationValue(xmldecl, out version, out encoding, out standalone);
-            XmlNode node = _document.CreateXmlDeclaration(version, encoding, standalone);
+            XmlNode node = _document.CreateXmlDeclaration(version!, encoding, standalone);
             AddChild(node, _write);
         }
 
@@ -147,14 +148,14 @@ public override void WriteEndDocument()
             VerifyState(Method.WriteEndDocument);
         }
 
-        public override void WriteDocType(string name, string pubid, string sysid, string subset)
+        public override void WriteDocType(string name, string? pubid, string? sysid, string? subset)
         {
             VerifyState(Method.WriteDocType);
             XmlNode node = _document.CreateDocumentType(name, pubid, sysid, subset);
             AddChild(node, _write);
         }
 
-        public override void WriteStartElement(string prefix, string localName, string ns)
+        public override void WriteStartElement(string? prefix, string localName, string? ns)
         {
             VerifyState(Method.WriteStartElement);
             XmlNode node = _document.CreateElement(prefix, localName, ns);
@@ -169,6 +170,7 @@ public override void WriteEndElement()
             {
                 throw new InvalidOperationException();
             }
+
             _write = _write.ParentNode;
         }
 
@@ -180,11 +182,12 @@ internal override void WriteEndElement(string prefix, string localName, string n
         public override void WriteFullEndElement()
         {
             VerifyState(Method.WriteFullEndElement);
-            XmlElement elem = _write as XmlElement;
+            XmlElement? elem = _write as XmlElement;
             if (elem == null)
             {
                 throw new InvalidOperationException();
             }
+
             elem.IsEmpty = false;
             _write = elem.ParentNode;
         }
@@ -199,7 +202,7 @@ internal override void StartElementContent()
             // nop
         }
 
-        public override void WriteStartAttribute(string prefix, string localName, string ns)
+        public override void WriteStartAttribute(string? prefix, string localName, string? ns)
         {
             VerifyState(Method.WriteStartAttribute);
             XmlAttribute attr = _document.CreateAttribute(prefix, localName, ns);
@@ -210,16 +213,18 @@ public override void WriteStartAttribute(string prefix, string localName, string
         public override void WriteEndAttribute()
         {
             VerifyState(Method.WriteEndAttribute);
-            XmlAttribute attr = _write as XmlAttribute;
+            XmlAttribute? attr = _write as XmlAttribute;
             if (attr == null)
             {
                 throw new InvalidOperationException();
             }
+
             if (!attr.HasChildNodes)
             {
                 XmlNode node = _document.CreateTextNode(string.Empty);
                 AddChild(node, attr);
             }
+
             _write = attr.OwnerElement;
         }
 
@@ -250,6 +255,7 @@ internal override void WriteStartNamespaceDeclaration(string prefix)
             {
                 attr = _document.CreateAttribute(_document.strXmlns, prefix, _document.strReservedXmlns);
             }
+
             AddAttribute(attr, _write);
             _write = attr;
         }
@@ -257,20 +263,22 @@ internal override void WriteStartNamespaceDeclaration(string prefix)
         internal override void WriteEndNamespaceDeclaration()
         {
             VerifyState(Method.WriteEndNamespaceDeclaration);
-            XmlAttribute attr = _write as XmlAttribute;
+            XmlAttribute? attr = _write as XmlAttribute;
             if (attr == null)
             {
                 throw new InvalidOperationException();
             }
+
             if (!attr.HasChildNodes)
             {
                 XmlNode node = _document.CreateTextNode(string.Empty);
                 AddChild(node, attr);
             }
+
             _write = attr.OwnerElement;
         }
 
-        public override void WriteCData(string text)
+        public override void WriteCData(string? text)
         {
             VerifyState(Method.WriteCData);
             XmlConvert.VerifyCharData(text, ExceptionType.ArgumentException);
@@ -278,7 +286,7 @@ public override void WriteCData(string text)
             AddChild(node, _write);
         }
 
-        public override void WriteComment(string text)
+        public override void WriteComment(string? text)
         {
             VerifyState(Method.WriteComment);
             XmlConvert.VerifyCharData(text, ExceptionType.ArgumentException);
@@ -286,11 +294,11 @@ public override void WriteComment(string text)
             AddChild(node, _write);
         }
 
-        public override void WriteProcessingInstruction(string name, string text)
+        public override void WriteProcessingInstruction(string name, string? text)
         {
             VerifyState(Method.WriteProcessingInstruction);
             XmlConvert.VerifyCharData(text, ExceptionType.ArgumentException);
-            XmlNode node = _document.CreateProcessingInstruction(name, text);
+            XmlNode node = _document.CreateProcessingInstruction(name, text!);
             AddChild(node, _write);
         }
 
@@ -307,7 +315,7 @@ public override void WriteCharEntity(char ch)
             WriteString(char.ToString(ch));
         }
 
-        public override void WriteWhitespace(string text)
+        public override void WriteWhitespace(string? text)
         {
             VerifyState(Method.WriteWhitespace);
             XmlConvert.VerifyCharData(text, ExceptionType.ArgumentException);
@@ -318,7 +326,7 @@ public override void WriteWhitespace(string text)
             }
         }
 
-        public override void WriteString(string text)
+        public override void WriteString(string? text)
         {
             VerifyState(Method.WriteString);
             XmlConvert.VerifyCharData(text, ExceptionType.ArgumentException);
@@ -363,15 +371,17 @@ internal override void Close(WriteState currentState)
                 switch (_type)
                 {
                     case DocumentXmlWriterType.InsertSiblingAfter:
-                        XmlNode parent = _start.ParentNode;
+                        XmlNode? parent = _start.ParentNode;
                         if (parent == null)
                         {
                             throw new InvalidOperationException(SR.Xpn_MissingParent);
                         }
+
                         for (int i = _fragment.Count - 1; i >= 0; i--)
                         {
                             parent.InsertAfter(_fragment[i], _start);
                         }
+
                         break;
                     case DocumentXmlWriterType.InsertSiblingBefore:
                         parent = _start.ParentNode;
@@ -379,22 +389,26 @@ internal override void Close(WriteState currentState)
                         {
                             throw new InvalidOperationException(SR.Xpn_MissingParent);
                         }
+
                         for (int i = 0; i < _fragment.Count; i++)
                         {
                             parent.InsertBefore(_fragment[i], _start);
                         }
+
                         break;
                     case DocumentXmlWriterType.PrependChild:
                         for (int i = _fragment.Count - 1; i >= 0; i--)
                         {
                             _start.PrependChild(_fragment[i]);
                         }
+
                         break;
                     case DocumentXmlWriterType.AppendChild:
                         for (int i = 0; i < _fragment.Count; i++)
                         {
                             _start.AppendChild(_fragment[i]);
                         }
+
                         break;
                     case DocumentXmlWriterType.AppendAttribute:
                         CloseWithAppendAttribute();
@@ -404,6 +418,7 @@ internal override void Close(WriteState currentState)
                         {
                             throw new InvalidOperationException(SR.Xpn_NoContent);
                         }
+
                         CloseWithReplaceToFollowingSibling();
                         break;
                 }
@@ -416,12 +431,12 @@ internal override void Close(WriteState currentState)
 
         private void CloseWithAppendAttribute()
         {
-            XmlElement elem = _start as XmlElement;
+            XmlElement? elem = _start as XmlElement;
             Debug.Assert(elem != null);
             XmlAttributeCollection attrs = elem.Attributes;
             for (int i = 0; i < _fragment.Count; i++)
             {
-                XmlAttribute attr = _fragment[i] as XmlAttribute;
+                XmlAttribute? attr = _fragment[i] as XmlAttribute;
                 Debug.Assert(attr != null);
                 int offset = attrs.FindNodeOffsetNS(attr);
                 if (offset != -1
@@ -432,7 +447,7 @@ private void CloseWithAppendAttribute()
             }
             for (int i = 0; i < _fragment.Count; i++)
             {
-                XmlAttribute attr = _fragment[i] as XmlAttribute;
+                XmlAttribute? attr = _fragment[i] as XmlAttribute;
                 Debug.Assert(attr != null);
                 attrs.Append(attr);
             }
@@ -440,11 +455,12 @@ private void CloseWithAppendAttribute()
 
         private void CloseWithReplaceToFollowingSibling()
         {
-            XmlNode parent = _start.ParentNode;
+            XmlNode? parent = _start.ParentNode;
             if (parent == null)
             {
                 throw new InvalidOperationException(SR.Xpn_MissingParent);
             }
+
             if (_start != _end)
             {
                 if (!DocumentXPathNavigator.IsFollowingSibling(_start, _end))
@@ -455,15 +471,18 @@ private void CloseWithReplaceToFollowingSibling()
                 {
                     throw new InvalidOperationException(SR.Xdom_Node_Modify_ReadOnly);
                 }
-                DocumentXPathNavigator.DeleteToFollowingSibling(_start.NextSibling, _end);
+
+                DocumentXPathNavigator.DeleteToFollowingSibling(_start.NextSibling!, _end);
             }
+
             XmlNode fragment0 = _fragment[0];
             parent.ReplaceChild(fragment0, _start);
             for (int i = _fragment.Count - 1; i >= 1; i--)
             {
                 parent.InsertAfter(_fragment[i], fragment0);
             }
-            _navigator.ResetPosition(fragment0);
+
+            _navigator!.ResetPosition(fragment0);
         }
 
         public override void Flush()
@@ -473,20 +492,20 @@ public override void Flush()
 
         IDictionary<string, string> IXmlNamespaceResolver.GetNamespacesInScope(XmlNamespaceScope scope)
         {
-            return _namespaceManager.GetNamespacesInScope(scope);
+            return _namespaceManager!.GetNamespacesInScope(scope);
         }
 
-        string IXmlNamespaceResolver.LookupNamespace(string prefix)
+        string? IXmlNamespaceResolver.LookupNamespace(string prefix)
         {
-            return _namespaceManager.LookupNamespace(prefix);
+            return _namespaceManager!.LookupNamespace(prefix);
         }
 
-        string IXmlNamespaceResolver.LookupPrefix(string namespaceName)
+        string? IXmlNamespaceResolver.LookupPrefix(string namespaceName)
         {
-            return _namespaceManager.LookupPrefix(namespaceName);
+            return _namespaceManager!.LookupPrefix(namespaceName);
         }
 
-        private void AddAttribute(XmlAttribute attr, XmlNode parent)
+        private void AddAttribute(XmlAttribute attr, XmlNode? parent)
         {
             if (parent == null)
             {
@@ -494,16 +513,17 @@ private void AddAttribute(XmlAttribute attr, XmlNode parent)
             }
             else
             {
-                XmlElement elem = parent as XmlElement;
+                XmlElement? elem = parent as XmlElement;
                 if (elem == null)
                 {
                     throw new InvalidOperationException();
                 }
+
                 elem.Attributes.Append(attr);
             }
         }
 
-        private void AddChild(XmlNode node, XmlNode parent)
+        private void AddChild(XmlNode node, XmlNode? parent)
         {
             if (parent == null)
             {
@@ -523,11 +543,12 @@ private State StartState()
             {
                 case DocumentXmlWriterType.InsertSiblingAfter:
                 case DocumentXmlWriterType.InsertSiblingBefore:
-                    XmlNode parent = _start.ParentNode;
+                    XmlNode? parent = _start.ParentNode;
                     if (parent != null)
                     {
                         nodeType = parent.NodeType;
                     }
+
                     if (nodeType == XmlNodeType.Document)
                     {
                         return State.Prolog;
@@ -536,6 +557,7 @@ private State StartState()
                     {
                         return State.Fragment;
                     }
+
                     break;
                 case DocumentXmlWriterType.PrependChild:
                 case DocumentXmlWriterType.AppendChild:
@@ -548,6 +570,7 @@ private State StartState()
                     {
                         return State.Fragment;
                     }
+
                     break;
                 case DocumentXmlWriterType.AppendAttribute:
                     return State.Attribute;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/DomNameTable.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/DomNameTable.cs
index 593cae97e43d3b..6e187954537731 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/DomNameTable.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/DomNameTable.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Diagnostics;
 using System.Xml.Schema;
@@ -26,7 +27,7 @@ public DomNameTable(XmlDocument document)
             Debug.Assert((_entries.Length & _mask) == 0);  // entries.Length must be a power of two
         }
 
-        public XmlName GetName(string prefix, string localName, string ns, IXmlSchemaInfo schemaInfo)
+        public XmlName? GetName(string? prefix, string localName, string? ns, IXmlSchemaInfo? schemaInfo)
         {
             if (prefix == null)
             {
@@ -56,7 +57,7 @@ public XmlName GetName(string prefix, string localName, string ns, IXmlSchemaInf
             return null;
         }
 
-        public XmlName AddName(string prefix, string localName, string ns, IXmlSchemaInfo schemaInfo)
+        public XmlName AddName(string? prefix, string localName, string? ns, IXmlSchemaInfo? schemaInfo)
         {
             if (prefix == null)
             {
@@ -118,6 +119,7 @@ private void Grow()
                     name = tmp;
                 }
             }
+
             _entries = newEntries;
             _mask = newMask;
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XPathNodeList.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XPathNodeList.cs
index ccc26c0fd8dc5f..4a0ffa3f53c581 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XPathNodeList.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XPathNodeList.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     using System.Xml.XPath;
@@ -10,14 +11,14 @@ namespace System.Xml
 
     internal class XPathNodeList : XmlNodeList
     {
-        private readonly List<XmlNode> _list;
+        private readonly List<XmlNode?> _list;
         private readonly XPathNodeIterator _nodeIterator;
         private bool _done;
 
         public XPathNodeList(XPathNodeIterator nodeIterator)
         {
             _nodeIterator = nodeIterator;
-            _list = new List<XmlNode>();
+            _list = new List<XmlNode?>();
             _done = false;
         }
 
@@ -33,7 +34,7 @@ public override int Count
             }
         }
 
-        private XmlNode GetNode(XPathNavigator n)
+        private XmlNode? GetNode(XPathNavigator n)
         {
             IHasXmlNode iHasNode = (IHasXmlNode)n;
             return iHasNode.GetNode();
@@ -46,7 +47,8 @@ internal int ReadUntil(int index)
             {
                 if (_nodeIterator.MoveNext())
                 {
-                    XmlNode n = GetNode(_nodeIterator.Current);
+                    Debug.Assert(_nodeIterator.Current != null);
+                    XmlNode? n = GetNode(_nodeIterator.Current);
                     if (n != null)
                     {
                         _list.Add(n);
@@ -62,7 +64,7 @@ internal int ReadUntil(int index)
             return count;
         }
 
-        public override XmlNode Item(int index)
+        public override XmlNode? Item(int index)
         {
             if (_list.Count <= index)
             {
@@ -72,6 +74,7 @@ public override XmlNode Item(int index)
             {
                 return null;
             }
+
             return _list[index];
         }
 
@@ -111,7 +114,7 @@ public bool MoveNext()
             return _valid;
         }
 
-        public object Current
+        public object? Current
         {
             get
             {
@@ -119,6 +122,7 @@ public object Current
                 {
                     return _list[_index];
                 }
+
                 return null;
             }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlAttribute.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlAttribute.cs
index a8d6230e876376..24e11bda6ed953 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlAttribute.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlAttribute.cs
@@ -1,10 +1,12 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Xml.Schema;
 using System.Xml.XPath;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml
 {
@@ -13,7 +15,7 @@ namespace System.Xml
     public class XmlAttribute : XmlNode
     {
         private XmlName _name;
-        private XmlLinkedNode _lastChild;
+        private XmlLinkedNode? _lastChild;
 
         internal XmlAttribute(XmlName name, XmlDocument doc) : base(doc)
         {
@@ -35,7 +37,7 @@ internal int LocalNameHash
             get { return _name.HashCode; }
         }
 
-        protected internal XmlAttribute(string prefix, string localName, string namespaceURI, XmlDocument doc)
+        protected internal XmlAttribute(string? prefix, string localName, string? namespaceURI, XmlDocument doc)
         : this(doc.AddAttrXmlName(prefix, localName, namespaceURI, null), doc)
         {
         }
@@ -58,7 +60,7 @@ public override XmlNode CloneNode(bool deep)
         }
 
         // Gets the parent of this node (for nodes that can have parents).
-        public override XmlNode ParentNode
+        public override XmlNode? ParentNode
         {
             get { return null; }
         }
@@ -104,10 +106,11 @@ public override XmlDocument OwnerDocument
         }
 
         // Gets or sets the value of the node.
+        [AllowNull]
         public override string Value
         {
             get { return InnerText; }
-            set { InnerText = value; } //use InnerText which has perf optimization
+            set { InnerText = value!; } //use InnerText which has perf optimization
         }
 
         public override IXmlSchemaInfo SchemaInfo
@@ -140,18 +143,19 @@ internal bool PrepareOwnerElementInElementIdAttrMap()
             XmlDocument ownerDocument = OwnerDocument;
             if (ownerDocument.DtdSchemaInfo != null)
             { // DTD exists
-                XmlElement ownerElement = OwnerElement;
+                XmlElement? ownerElement = OwnerElement;
                 if (ownerElement != null)
                 {
                     return ownerElement.Attributes.PrepareParentInElementIdAttrMap(Prefix, LocalName);
                 }
             }
+
             return false;
         }
 
         internal void ResetOwnerElementInElementIdAttrMap(string oldInnerText)
         {
-            XmlElement ownerElement = OwnerElement;
+            XmlElement? ownerElement = OwnerElement;
             if (ownerElement != null)
             {
                 ownerElement.Attributes.ResetParentInElementIdAttrMap(oldInnerText, InnerText);
@@ -166,7 +170,7 @@ internal override bool IsContainer
         //the function is provided only at Load time to speed up Load process
         internal override XmlNode AppendChildForLoad(XmlNode newChild, XmlDocument doc)
         {
-            XmlNodeChangedEventArgs args = doc.GetInsertEventArgsForLoad(newChild, this);
+            XmlNodeChangedEventArgs? args = doc.GetInsertEventArgsForLoad(newChild, this);
 
             if (args != null)
                 doc.BeforeEvent(args);
@@ -202,7 +206,7 @@ internal override XmlNode AppendChildForLoad(XmlNode newChild, XmlDocument doc)
             return newNode;
         }
 
-        internal override XmlLinkedNode LastNode
+        internal override XmlLinkedNode? LastNode
         {
             get { return _lastChild; }
             set { _lastChild = value; }
@@ -219,12 +223,12 @@ public virtual bool Specified
             get { return true; }
         }
 
-        public override XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
+        public override XmlNode? InsertBefore(XmlNode newChild, XmlNode? refChild)
         {
-            XmlNode node;
+            XmlNode? node;
             if (PrepareOwnerElementInElementIdAttrMap())
             {
-                string innerText = InnerText;
+                string? innerText = InnerText;
                 node = base.InsertBefore(newChild, refChild);
                 ResetOwnerElementInElementIdAttrMap(innerText);
             }
@@ -232,15 +236,16 @@ public override XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
             {
                 node = base.InsertBefore(newChild, refChild);
             }
+
             return node;
         }
 
-        public override XmlNode InsertAfter(XmlNode newChild, XmlNode refChild)
+        public override XmlNode? InsertAfter(XmlNode newChild, XmlNode? refChild)
         {
-            XmlNode node;
+            XmlNode? node;
             if (PrepareOwnerElementInElementIdAttrMap())
             {
-                string innerText = InnerText;
+                string? innerText = InnerText;
                 node = base.InsertAfter(newChild, refChild);
                 ResetOwnerElementInElementIdAttrMap(innerText);
             }
@@ -248,6 +253,7 @@ public override XmlNode InsertAfter(XmlNode newChild, XmlNode refChild)
             {
                 node = base.InsertAfter(newChild, refChild);
             }
+
             return node;
         }
 
@@ -256,7 +262,7 @@ public override XmlNode ReplaceChild(XmlNode newChild, XmlNode oldChild)
             XmlNode node;
             if (PrepareOwnerElementInElementIdAttrMap())
             {
-                string innerText = InnerText;
+                string? innerText = InnerText;
                 node = base.ReplaceChild(newChild, oldChild);
                 ResetOwnerElementInElementIdAttrMap(innerText);
             }
@@ -272,7 +278,7 @@ public override XmlNode RemoveChild(XmlNode oldChild)
             XmlNode node;
             if (PrepareOwnerElementInElementIdAttrMap())
             {
-                string innerText = InnerText;
+                string? innerText = InnerText;
                 node = base.RemoveChild(oldChild);
                 ResetOwnerElementInElementIdAttrMap(innerText);
             }
@@ -283,12 +289,12 @@ public override XmlNode RemoveChild(XmlNode oldChild)
             return node;
         }
 
-        public override XmlNode PrependChild(XmlNode newChild)
+        public override XmlNode? PrependChild(XmlNode newChild)
         {
-            XmlNode node;
+            XmlNode? node;
             if (PrepareOwnerElementInElementIdAttrMap())
             {
-                string innerText = InnerText;
+                string? innerText = InnerText;
                 node = base.PrependChild(newChild);
                 ResetOwnerElementInElementIdAttrMap(innerText);
             }
@@ -296,15 +302,16 @@ public override XmlNode PrependChild(XmlNode newChild)
             {
                 node = base.PrependChild(newChild);
             }
+
             return node;
         }
 
-        public override XmlNode AppendChild(XmlNode newChild)
+        public override XmlNode? AppendChild(XmlNode newChild)
         {
-            XmlNode node;
+            XmlNode? node;
             if (PrepareOwnerElementInElementIdAttrMap())
             {
-                string innerText = InnerText;
+                string? innerText = InnerText;
                 node = base.AppendChild(newChild);
                 ResetOwnerElementInElementIdAttrMap(innerText);
             }
@@ -312,13 +319,14 @@ public override XmlNode AppendChild(XmlNode newChild)
             {
                 node = base.AppendChild(newChild);
             }
+
             return node;
         }
 
         // DOM Level 2
 
         // Gets the XmlElement node that contains this attribute.
-        public virtual XmlElement OwnerElement
+        public virtual XmlElement? OwnerElement
         {
             get
             {
@@ -348,7 +356,7 @@ public override void WriteTo(XmlWriter w)
         // Saves all the children of the node to the specified XmlWriter.
         public override void WriteContentTo(XmlWriter w)
         {
-            for (XmlNode node = FirstChild; node != null; node = node.NextSibling)
+            for (XmlNode? node = FirstChild; node != null; node = node.NextSibling)
             {
                 node.WriteTo(w);
             }
@@ -364,7 +372,7 @@ public override string BaseURI
             }
         }
 
-        internal override void SetParent(XmlNode node)
+        internal override void SetParent(XmlNode? node)
         {
             this.parentNode = node;
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlAttributeCollection.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlAttributeCollection.cs
index 6273f18640c5a0..b2fd07dfb225b2 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlAttributeCollection.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlAttributeCollection.cs
@@ -1,8 +1,10 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml
 {
@@ -32,7 +34,7 @@ public XmlAttribute this[int i]
 
         // Gets the attribute with the specified name.
         [System.Runtime.CompilerServices.IndexerName("ItemOf")]
-        public XmlAttribute this[string name]
+        public XmlAttribute? this[string name]
         {
             get
             {
@@ -55,7 +57,7 @@ public XmlAttribute this[string name]
 
         // Gets the attribute with the specified LocalName and NamespaceUri.
         [System.Runtime.CompilerServices.IndexerName("ItemOf")]
-        public XmlAttribute this[string localName, string namespaceURI]
+        public XmlAttribute? this[string localName, string? namespaceURI]
         {
             get
             {
@@ -90,6 +92,7 @@ internal int FindNodeOffset(XmlAttribute node)
                     return i;
                 }
             }
+
             return -1;
         }
 
@@ -109,7 +112,8 @@ internal int FindNodeOffsetNS(XmlAttribute node)
         }
 
         // Adds a XmlNode using its Name property
-        public override XmlNode SetNamedItem(XmlNode node)
+        [return: NotNullIfNotNull("node")]
+        public override XmlNode? SetNamedItem(XmlNode? node)
         {
             if (node == null)
                 return null;
@@ -170,7 +174,7 @@ public XmlAttribute Append(XmlAttribute node)
         }
 
         // Inserts the specified attribute immediately before the specified reference attribute.
-        public XmlAttribute InsertBefore(XmlAttribute newNode, XmlAttribute refNode)
+        public XmlAttribute InsertBefore(XmlAttribute newNode, XmlAttribute? refNode)
         {
             if (newNode == refNode)
                 return newNode;
@@ -199,7 +203,7 @@ public XmlAttribute InsertBefore(XmlAttribute newNode, XmlAttribute refNode)
         }
 
         // Inserts the specified attribute immediately after the specified reference attribute.
-        public XmlAttribute InsertAfter(XmlAttribute newNode, XmlAttribute refNode)
+        public XmlAttribute InsertAfter(XmlAttribute newNode, XmlAttribute? refNode)
         {
             if (newNode == refNode)
                 return newNode;
@@ -228,7 +232,7 @@ public XmlAttribute InsertAfter(XmlAttribute newNode, XmlAttribute refNode)
         }
 
         // Removes the specified attribute node from the map.
-        public XmlAttribute Remove(XmlAttribute node)
+        public XmlAttribute? Remove(XmlAttribute? node)
         {
             int cNodes = nodes.Count;
             for (int offset = 0; offset < cNodes; offset++)
@@ -239,11 +243,12 @@ public XmlAttribute Remove(XmlAttribute node)
                     return node;
                 }
             }
+
             return null;
         }
 
         // Removes the attribute node with the specified index from the map.
-        public XmlAttribute RemoveAt(int i)
+        public XmlAttribute? RemoveAt(int i)
         {
             if (i < 0 || i >= Count)
                 return null;
@@ -315,26 +320,28 @@ internal override XmlNode RemoveNodeAt(int i)
             Debug.Assert(retNode is XmlAttribute);
             RemoveParentFromElementIdAttrMap((XmlAttribute)retNode);
             // after remove the attribute, we need to check if a default attribute node should be created and inserted into the tree
-            XmlAttribute defattr = parent.OwnerDocument.GetDefaultAttribute((XmlElement)parent, retNode.Prefix, retNode.LocalName, retNode.NamespaceURI);
+            XmlAttribute? defattr = parent.OwnerDocument!.GetDefaultAttribute((XmlElement)parent, retNode.Prefix, retNode.LocalName, retNode.NamespaceURI);
             if (defattr != null)
                 InsertNodeAt(i, defattr);
+
             return retNode;
         }
 
         internal void Detach(XmlAttribute attr)
         {
-            attr.OwnerElement.Attributes.Remove(attr);
+            attr.OwnerElement!.Attributes.Remove(attr);
         }
 
         //insert the parent element node into the map
         internal void InsertParentIntoElementIdAttrMap(XmlAttribute attr)
         {
-            XmlElement parentElem = parent as XmlElement;
+            XmlElement? parentElem = parent as XmlElement;
             if (parentElem != null)
             {
                 if (parent.OwnerDocument == null)
                     return;
-                XmlName attrname = parent.OwnerDocument.GetIDInfoByElement(parentElem.XmlName);
+
+                XmlName? attrname = parent.OwnerDocument.GetIDInfoByElement(parentElem.XmlName);
                 if (attrname != null && attrname.Prefix == attr.XmlName.Prefix && attrname.LocalName == attr.XmlName.LocalName)
                 {
                     parent.OwnerDocument.AddElementWithId(attr.Value, parentElem); //add the element into the hashtable
@@ -345,12 +352,13 @@ internal void InsertParentIntoElementIdAttrMap(XmlAttribute attr)
         //remove the parent element node from the map when the ID attribute is removed
         internal void RemoveParentFromElementIdAttrMap(XmlAttribute attr)
         {
-            XmlElement parentElem = parent as XmlElement;
+            XmlElement? parentElem = parent as XmlElement;
             if (parentElem != null)
             {
                 if (parent.OwnerDocument == null)
                     return;
-                XmlName attrname = parent.OwnerDocument.GetIDInfoByElement(parentElem.XmlName);
+
+                XmlName? attrname = parent.OwnerDocument.GetIDInfoByElement(parentElem.XmlName);
                 if (attrname != null && attrname.Prefix == attr.XmlName.Prefix && attrname.LocalName == attr.XmlName.LocalName)
                 {
                     parent.OwnerDocument.RemoveElementWithId(attr.Value, parentElem); //remove the element from the hashtable
@@ -375,25 +383,26 @@ internal int RemoveDuplicateAttribute(XmlAttribute attr)
 
         internal bool PrepareParentInElementIdAttrMap(string attrPrefix, string attrLocalName)
         {
-            XmlElement parentElem = parent as XmlElement;
+            XmlElement? parentElem = parent as XmlElement;
             Debug.Assert(parentElem != null);
-            XmlDocument doc = parent.OwnerDocument;
+            XmlDocument? doc = parent.OwnerDocument;
             Debug.Assert(doc != null);
             //The returned attrname if not null is the name with namespaceURI being set to string.Empty
             //Because DTD doesn't support namespaceURI so all comparisons are based on no namespaceURI (string.Empty);
-            XmlName attrname = doc.GetIDInfoByElement(parentElem.XmlName);
+            XmlName? attrname = doc.GetIDInfoByElement(parentElem.XmlName);
             if (attrname != null && attrname.Prefix == attrPrefix && attrname.LocalName == attrLocalName)
             {
                 return true;
             }
+
             return false;
         }
 
         internal void ResetParentInElementIdAttrMap(string oldVal, string newVal)
         {
-            XmlElement parentElem = parent as XmlElement;
+            XmlElement? parentElem = parent as XmlElement;
             Debug.Assert(parentElem != null);
-            XmlDocument doc = parent.OwnerDocument;
+            XmlDocument? doc = parent.OwnerDocument;
             Debug.Assert(doc != null);
             doc.RemoveElementWithId(oldVal, parentElem); //add the element into the hashtable
             doc.AddElementWithId(newVal, parentElem);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlCDataSection.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlCDataSection.cs
index b2f52d52186d2d..86f65d649bc928 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlCDataSection.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlCDataSection.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 
@@ -10,7 +11,7 @@ namespace System.Xml
     // interpreted as markup language.
     public class XmlCDataSection : XmlCharacterData
     {
-        protected internal XmlCDataSection(string data, XmlDocument doc) : base(data, doc)
+        protected internal XmlCDataSection(string? data, XmlDocument doc) : base(data, doc)
         {
         }
 
@@ -19,7 +20,7 @@ public override string Name
         {
             get
             {
-                return OwnerDocument.strCDataSectionName;
+                return OwnerDocument!.strCDataSectionName;
             }
         }
 
@@ -28,7 +29,7 @@ public override string LocalName
         {
             get
             {
-                return OwnerDocument.strCDataSectionName;
+                return OwnerDocument!.strCDataSectionName;
             }
         }
 
@@ -41,11 +42,11 @@ public override XmlNodeType NodeType
             }
         }
 
-        public override XmlNode ParentNode
+        public override XmlNode? ParentNode
         {
             get
             {
-                switch (parentNode.NodeType)
+                switch (parentNode!.NodeType)
                 {
                     case XmlNodeType.Document:
                         return null;
@@ -53,11 +54,12 @@ public override XmlNode ParentNode
                     case XmlNodeType.CDATA:
                     case XmlNodeType.Whitespace:
                     case XmlNodeType.SignificantWhitespace:
-                        XmlNode parent = parentNode.parentNode;
+                        XmlNode parent = parentNode.parentNode!;
                         while (parent.IsText)
                         {
-                            parent = parent.parentNode;
+                            parent = parent.parentNode!;
                         }
+
                         return parent;
                     default:
                         return parentNode;
@@ -100,14 +102,15 @@ internal override bool IsText
             }
         }
 
-        public override XmlNode PreviousText
+        public override XmlNode? PreviousText
         {
             get
             {
-                if (parentNode.IsText)
+                if (parentNode != null && parentNode.IsText)
                 {
                     return parentNode;
                 }
+
                 return null;
             }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlCharacterData.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlCharacterData.cs
index c03e0e290e36b4..f5d7f610c5d386 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlCharacterData.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlCharacterData.cs
@@ -1,7 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Text;
 using System.Xml.XPath;
 
@@ -10,16 +12,16 @@ namespace System.Xml
     // Provides text-manipulation methods that are used by several classes.
     public abstract class XmlCharacterData : XmlLinkedNode
     {
-        private string _data;
+        private string? _data;
 
         //base(doc) will throw exception if doc is null.
-        protected internal XmlCharacterData(string data, XmlDocument doc) : base(doc)
+        protected internal XmlCharacterData(string? data, XmlDocument doc) : base(doc)
         {
             _data = data;
         }
 
         // Gets or sets the value of the node.
-        public override string Value
+        public override string? Value
         {
             get { return Data; }
             set { Data = value; }
@@ -29,11 +31,12 @@ public override string Value
         // all its children.
         public override string InnerText
         {
-            get { return Value; }
+            get { return Value!; }
             set { Value = value; }
         }
 
         // Contains this node's data.
+        [AllowNull]
         public virtual string Data
         {
             get
@@ -50,8 +53,8 @@ public virtual string Data
 
             set
             {
-                XmlNode parent = ParentNode;
-                XmlNodeChangedEventArgs args = GetEventArgs(this, parent, parent, _data, value, XmlNodeChangedAction.Change);
+                XmlNode? parent = ParentNode;
+                XmlNodeChangedEventArgs? args = GetEventArgs(this, parent, parent, _data, value, XmlNodeChangedAction.Change);
 
                 if (args != null)
                     BeforeEvent(args);
@@ -86,20 +89,21 @@ public virtual string Substring(int offset, int count)
                 {
                     count = len - offset;
                 }
-                return _data.Substring(offset, count);
+
+                return _data!.Substring(offset, count);
             }
             return string.Empty;
         }
 
         // Appends the specified string to the end of the character
         // data of the node.
-        public virtual void AppendData(string strData)
+        public virtual void AppendData(string? strData)
         {
-            XmlNode parent = ParentNode;
+            XmlNode? parent = ParentNode;
             int capacity = _data != null ? _data.Length : 0;
             if (strData != null) capacity += strData.Length;
             string newValue = new StringBuilder(capacity).Append(_data).Append(strData).ToString();
-            XmlNodeChangedEventArgs args = GetEventArgs(this, parent, parent, _data, newValue, XmlNodeChangedAction.Change);
+            XmlNodeChangedEventArgs? args = GetEventArgs(this, parent, parent, _data, newValue, XmlNodeChangedAction.Change);
 
             if (args != null)
                 BeforeEvent(args);
@@ -111,13 +115,13 @@ public virtual void AppendData(string strData)
         }
 
         // Insert the specified string at the specified character offset.
-        public virtual void InsertData(int offset, string strData)
+        public virtual void InsertData(int offset, string? strData)
         {
-            XmlNode parent = ParentNode;
+            XmlNode? parent = ParentNode;
             int capacity = _data != null ? _data.Length : 0;
             if (strData != null) capacity += strData.Length;
             string newValue = new StringBuilder(capacity).Append(_data).Insert(offset, strData).ToString();
-            XmlNodeChangedEventArgs args = GetEventArgs(this, parent, parent, _data, newValue, XmlNodeChangedAction.Change);
+            XmlNodeChangedEventArgs? args = GetEventArgs(this, parent, parent, _data, newValue, XmlNodeChangedAction.Change);
             if (args != null)
                 BeforeEvent(args);
 
@@ -142,8 +146,8 @@ public virtual void DeleteData(int offset, int count)
             }
 
             string newValue = new StringBuilder(_data).Remove(offset, count).ToString();
-            XmlNode parent = ParentNode;
-            XmlNodeChangedEventArgs args = GetEventArgs(this, parent, parent, _data, newValue, XmlNodeChangedAction.Change);
+            XmlNode? parent = ParentNode;
+            XmlNodeChangedEventArgs? args = GetEventArgs(this, parent, parent, _data, newValue, XmlNodeChangedAction.Change);
 
             if (args != null)
                 BeforeEvent(args);
@@ -156,7 +160,7 @@ public virtual void DeleteData(int offset, int count)
 
         // Replace the specified number of characters starting at the specified offset with the
         // specified string.
-        public virtual void ReplaceData(int offset, int count, string strData)
+        public virtual void ReplaceData(int offset, int count, string? strData)
         {
             int len = _data != null ? _data.Length : 0;
             if (len > 0)
@@ -170,8 +174,8 @@ public virtual void ReplaceData(int offset, int count, string strData)
             StringBuilder temp = new StringBuilder(_data).Remove(offset, count);
             string newValue = temp.Insert(offset, strData).ToString();
 
-            XmlNode parent = ParentNode;
-            XmlNodeChangedEventArgs args = GetEventArgs(this, parent, parent, _data, newValue, XmlNodeChangedAction.Change);
+            XmlNode? parent = ParentNode;
+            XmlNodeChangedEventArgs? args = GetEventArgs(this, parent, parent, _data, newValue, XmlNodeChangedAction.Change);
 
             if (args != null)
                 BeforeEvent(args);
@@ -182,7 +186,7 @@ public virtual void ReplaceData(int offset, int count, string strData)
                 AfterEvent(args);
         }
 
-        internal bool CheckOnData(string data)
+        internal bool CheckOnData(string? data)
         {
             return XmlCharType.Instance.IsOnlyWhitespace(data);
         }
@@ -194,10 +198,11 @@ internal bool DecideXPNodeTypeForTextNodes(XmlNode node, ref XPathNodeType xnt)
             //changes according to the siblings nodetype and will contain the correct
             //nodetype when it returns.
 
-            Debug.Assert(XmlDocument.IsTextNode(node.NodeType) || (node.ParentNode != null && node.ParentNode.NodeType == XmlNodeType.EntityReference));
-            while (node != null)
+            XmlNode? n = node;
+            Debug.Assert(XmlDocument.IsTextNode(n.NodeType) || (n.ParentNode != null && n.ParentNode.NodeType == XmlNodeType.EntityReference));
+            while (n != null)
             {
-                switch (node.NodeType)
+                switch (n.NodeType)
                 {
                     case XmlNodeType.Whitespace:
                         break;
@@ -209,7 +214,7 @@ internal bool DecideXPNodeTypeForTextNodes(XmlNode node, ref XPathNodeType xnt)
                         xnt = XPathNodeType.Text;
                         return false;
                     case XmlNodeType.EntityReference:
-                        if (!DecideXPNodeTypeForTextNodes(node.FirstChild, ref xnt))
+                        if (!DecideXPNodeTypeForTextNodes(n.FirstChild!, ref xnt))
                         {
                             return false;
                         }
@@ -217,7 +222,7 @@ internal bool DecideXPNodeTypeForTextNodes(XmlNode node, ref XPathNodeType xnt)
                     default:
                         return false;
                 }
-                node = node.NextSibling;
+                n = n.NextSibling;
             }
             return true;
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlChildEnumerator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlChildEnumerator.cs
index a5011a9de6dcf5..463b96689ca321 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlChildEnumerator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlChildEnumerator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections;
 
 namespace System.Xml
@@ -8,7 +9,7 @@ namespace System.Xml
     internal sealed class XmlChildEnumerator : IEnumerator
     {
         internal XmlNode container;
-        internal XmlNode child;
+        internal XmlNode? child;
         internal bool isFirst;
 
         internal XmlChildEnumerator(XmlNode container)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlChildNodes.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlChildNodes.cs
index 39bf493c22814a..865f5b13b42075 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlChildNodes.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlChildNodes.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections;
 
 namespace System.Xml
@@ -14,16 +15,18 @@ public XmlChildNodes(XmlNode container)
             _container = container;
         }
 
-        public override XmlNode Item(int i)
+        public override XmlNode? Item(int i)
         {
             // Out of range indexes return a null XmlNode
             if (i < 0)
                 return null;
-            for (XmlNode n = _container.FirstChild; n != null; n = n.NextSibling, i--)
+
+            for (XmlNode? n = _container.FirstChild; n != null; n = n.NextSibling, i--)
             {
                 if (i == 0)
                     return n;
             }
+
             return null;
         }
 
@@ -32,10 +35,11 @@ public override int Count
             get
             {
                 int c = 0;
-                for (XmlNode n = _container.FirstChild; n != null; n = n.NextSibling)
+                for (XmlNode? n = _container.FirstChild; n != null; n = n.NextSibling)
                 {
                     c++;
                 }
+
                 return c;
             }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlComment.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlComment.cs
index 2f5252476a5bb6..d9ea593dc87b57 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlComment.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlComment.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 
@@ -9,20 +10,20 @@ namespace System.Xml
     // Represents the content of an XML comment.
     public class XmlComment : XmlCharacterData
     {
-        protected internal XmlComment(string comment, XmlDocument doc) : base(comment, doc)
+        protected internal XmlComment(string? comment, XmlDocument doc) : base(comment, doc)
         {
         }
 
         // Gets the name of the node.
         public override string Name
         {
-            get { return OwnerDocument.strCommentName; }
+            get { return OwnerDocument!.strCommentName; }
         }
 
         // Gets the name of the current node without the namespace prefix.
         public override string LocalName
         {
-            get { return OwnerDocument.strCommentName; }
+            get { return OwnerDocument!.strCommentName; }
         }
 
         // Gets the type of the current node.
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDeclaration.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDeclaration.cs
index b4e9251448aebc..4544ca733cb718 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDeclaration.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDeclaration.cs
@@ -1,7 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Text;
 
@@ -17,7 +19,7 @@ public class XmlDeclaration : XmlLinkedNode
         private string _encoding;
         private string _standalone;
 
-        protected internal XmlDeclaration(string version, string encoding, string standalone, XmlDocument doc) : base(doc)
+        protected internal XmlDeclaration(string version, string? encoding, string? standalone, XmlDocument doc) : base(doc)
         {
             if (!IsValidXmlVersion(version))
                 throw new ArgumentException(SR.Xdom_Version);
@@ -34,21 +36,26 @@ protected internal XmlDeclaration(string version, string encoding, string standa
         public string Version
         {
             get { return _version; }
+            [MemberNotNull(nameof(_version))]
             internal set { _version = value; }
         }
 
         // Specifies the value of the encoding attribute, as for
         // <?xml version= '1.0' encoding= 'UTF-8' ?>
+        [AllowNull]
         public string Encoding
         {
             get { return _encoding; }
+            [MemberNotNull(nameof(_encoding))]
             set { _encoding = ((value == null) ? string.Empty : value); }
         }
 
         // Specifies the value of the standalone attribute.
+        [AllowNull]
         public string Standalone
         {
             get { return _standalone; }
+            [MemberNotNull(nameof(_standalone))]
             set
             {
                 if (value == null)
@@ -60,10 +67,10 @@ public string Standalone
             }
         }
 
-        public override string Value
+        public override string? Value
         {
             get { return InnerText; }
-            set { InnerText = value; }
+            set { InnerText = value!; }
         }
 
 
@@ -89,17 +96,18 @@ public override string InnerText
                     strb.Append(Standalone);
                     strb.Append('"');
                 }
+
                 return StringBuilderCache.GetStringAndRelease(strb);
             }
 
             set
             {
-                string tempVersion = null;
-                string tempEncoding = null;
-                string tempStandalone = null;
+                string? tempVersion = null;
+                string? tempEncoding = null;
+                string? tempStandalone = null;
                 string orgEncoding = this.Encoding;
                 string orgStandalone = this.Standalone;
-                string orgVersion = this.Version;
+                string? orgVersion = this.Version;
 
                 XmlLoader.ParseXmlDeclarationValue(value, out tempVersion, out tempEncoding, out tempStandalone);
 
@@ -107,7 +115,7 @@ public override string InnerText
                 {
                     if (tempVersion != null && !IsValidXmlVersion(tempVersion))
                         throw new ArgumentException(SR.Xdom_Version);
-                    Version = tempVersion;
+                    Version = tempVersion!;
 
                     if (tempEncoding != null)
                         Encoding = tempEncoding;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocument.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocument.cs
index 7ced05fdb20572..a254bee81f1da3 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocument.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocument.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -12,6 +13,7 @@
 using System.Security;
 using System.Globalization;
 using System.Runtime.Versioning;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml
 {
@@ -72,24 +74,24 @@ private static readonly (string key, int hash)[] s_nameTableSeeds = new[]
 
         private readonly XmlImplementation _implementation;
         private readonly DomNameTable _domNameTable; // hash table of XmlName
-        private XmlLinkedNode _lastChild;
-        private XmlNamedNodeMap _entities;
-        private Hashtable _htElementIdMap;
-        private Hashtable _htElementIDAttrDecl; //key: id; object: the ArrayList of the elements that have the same id (connected or disconnected)
-        private SchemaInfo _schemaInfo;
-        private XmlSchemaSet _schemas; // schemas associated with the cache
+        private XmlLinkedNode? _lastChild;
+        private XmlNamedNodeMap? _entities;
+        private Hashtable? _htElementIdMap;
+        private Hashtable? _htElementIDAttrDecl; //key: id; object: the ArrayList of the elements that have the same id (connected or disconnected)
+        private SchemaInfo? _schemaInfo;
+        private XmlSchemaSet? _schemas; // schemas associated with the cache
         private bool _reportValidity;
         //This variable represents the actual loading status. Since, IsLoading will
         //be manipulated sometimes for adding content to EntityReference this variable
         //has been added which would always represent the loading status of document.
         private bool _actualLoadingStatus;
 
-        private XmlNodeChangedEventHandler _onNodeInsertingDelegate;
-        private XmlNodeChangedEventHandler _onNodeInsertedDelegate;
-        private XmlNodeChangedEventHandler _onNodeRemovingDelegate;
-        private XmlNodeChangedEventHandler _onNodeRemovedDelegate;
-        private XmlNodeChangedEventHandler _onNodeChangingDelegate;
-        private XmlNodeChangedEventHandler _onNodeChangedDelegate;
+        private XmlNodeChangedEventHandler? _onNodeInsertingDelegate;
+        private XmlNodeChangedEventHandler? _onNodeInsertedDelegate;
+        private XmlNodeChangedEventHandler? _onNodeRemovingDelegate;
+        private XmlNodeChangedEventHandler? _onNodeRemovedDelegate;
+        private XmlNodeChangedEventHandler? _onNodeChangingDelegate;
+        private XmlNodeChangedEventHandler? _onNodeChangedDelegate;
 
         // false if there are no ent-ref present, true if ent-ref nodes are or were present (i.e. if all ent-ref were removed, the doc will not clear this flag)
         internal bool fEntRefNodesPresent;
@@ -118,11 +120,11 @@ private static readonly (string key, int hash)[] s_nameTableSeeds = new[]
 
         internal string baseURI;
 
-        private XmlResolver _resolver;
+        private XmlResolver? _resolver;
         internal bool bSetResolver;
         internal object objLock;
 
-        private XmlAttribute _namespaceXml;
+        private XmlAttribute? _namespaceXml;
 
         internal static EmptyEnumerator EmptyEnumerator = new EmptyEnumerator();
         internal static IXmlSchemaInfo NotKnownSchemaInfo = new XmlSchemaInfo(XmlSchemaValidity.NotKnown);
@@ -194,7 +196,7 @@ protected internal XmlDocument(XmlImplementation imp) : base()
             }
         }
 
-        internal SchemaInfo DtdSchemaInfo
+        internal SchemaInfo? DtdSchemaInfo
         {
             get { return _schemaInfo; }
             set { _schemaInfo = value; }
@@ -210,7 +212,7 @@ internal static void CheckName(string name)
             }
         }
 
-        internal XmlName AddXmlName(string prefix, string localName, string namespaceURI, IXmlSchemaInfo schemaInfo)
+        internal XmlName AddXmlName(string? prefix, string localName, string? namespaceURI, IXmlSchemaInfo? schemaInfo)
         {
             XmlName n = _domNameTable.AddName(prefix, localName, namespaceURI, schemaInfo);
             Debug.Assert((prefix == null) ? (n.Prefix.Length == 0) : (prefix == n.Prefix));
@@ -219,16 +221,16 @@ internal XmlName AddXmlName(string prefix, string localName, string namespaceURI
             return n;
         }
 
-        internal XmlName GetXmlName(string prefix, string localName, string namespaceURI, IXmlSchemaInfo schemaInfo)
+        internal XmlName? GetXmlName(string? prefix, string localName, string? namespaceURI, IXmlSchemaInfo? schemaInfo)
         {
-            XmlName n = _domNameTable.GetName(prefix, localName, namespaceURI, schemaInfo);
+            XmlName? n = _domNameTable.GetName(prefix, localName, namespaceURI, schemaInfo);
             Debug.Assert(n == null || ((prefix == null) ? (n.Prefix.Length == 0) : (prefix == n.Prefix)));
             Debug.Assert(n == null || n.LocalName == localName);
             Debug.Assert(n == null || ((namespaceURI == null) ? (n.NamespaceURI.Length == 0) : (n.NamespaceURI == namespaceURI)));
             return n;
         }
 
-        internal XmlName AddAttrXmlName(string prefix, string localName, string namespaceURI, IXmlSchemaInfo schemaInfo)
+        internal XmlName AddAttrXmlName(string? prefix, string localName, string? namespaceURI, IXmlSchemaInfo? schemaInfo)
         {
             XmlName xmlName = AddXmlName(prefix, localName, namespaceURI, schemaInfo);
             Debug.Assert((prefix == null) ? (xmlName.Prefix.Length == 0) : (prefix == xmlName.Prefix));
@@ -262,20 +264,20 @@ internal bool AddIdInfo(XmlName eleName, XmlName attrName)
             return false;
         }
 
-        private XmlName GetIDInfoByElement_(XmlName eleName)
+        private XmlName? GetIDInfoByElement_(XmlName eleName)
         {
             //When XmlDocument is getting the IDAttribute for a given element,
             //we need only compare the prefix and localname of element.XmlName with
             //the registered htElementIDAttrDecl.
-            XmlName newName = GetXmlName(eleName.Prefix, eleName.LocalName, string.Empty, null);
+            XmlName? newName = GetXmlName(eleName.Prefix, eleName.LocalName, string.Empty, null);
             if (newName != null)
             {
-                return (XmlName)(_htElementIDAttrDecl[newName]);
+                return (XmlName?)(_htElementIDAttrDecl![newName]);
             }
             return null;
         }
 
-        internal XmlName GetIDInfoByElement(XmlName eleName)
+        internal XmlName? GetIDInfoByElement(XmlName eleName)
         {
             if (_htElementIDAttrDecl == null)
                 return null;
@@ -283,7 +285,7 @@ internal XmlName GetIDInfoByElement(XmlName eleName)
                 return GetIDInfoByElement_(eleName);
         }
 
-        private WeakReference GetElement(ArrayList elementList, XmlElement elem)
+        private WeakReference? GetElement(ArrayList elementList, XmlElement elem)
         {
             ArrayList gcElemRefs = new ArrayList();
             foreach (WeakReference elemRef in elementList)
@@ -293,7 +295,7 @@ private WeakReference GetElement(ArrayList elementList, XmlElement elem)
                     gcElemRefs.Add(elemRef);
                 else
                 {
-                    if ((XmlElement)(elemRef.Target) == elem)
+                    if ((XmlElement?)(elemRef.Target) == elem)
                         return elemRef;
                 }
             }
@@ -316,7 +318,7 @@ internal void AddElementWithId(string id, XmlElement elem)
             else
             {
                 // there are other element(s) that has the same id
-                ArrayList elementList = (ArrayList)(_htElementIdMap[id]);
+                ArrayList elementList = (ArrayList)(_htElementIdMap[id]!);
                 if (GetElement(elementList, elem) == null)
                     elementList.Add(new WeakReference(elem));
             }
@@ -326,8 +328,8 @@ internal void RemoveElementWithId(string id, XmlElement elem)
         {
             if (_htElementIdMap != null && _htElementIdMap.Contains(id))
             {
-                ArrayList elementList = (ArrayList)(_htElementIdMap[id]);
-                WeakReference elemRef = GetElement(elementList, elem);
+                ArrayList elementList = (ArrayList)(_htElementIdMap[id]!);
+                WeakReference? elemRef = GetElement(elementList, elem);
                 if (elemRef != null)
                 {
                     elementList.Remove(elemRef);
@@ -355,24 +357,24 @@ public override XmlNodeType NodeType
             get { return XmlNodeType.Document; }
         }
 
-        public override XmlNode ParentNode
+        public override XmlNode? ParentNode
         {
             get { return null; }
         }
 
         // Gets the node for the DOCTYPE declaration.
-        public virtual XmlDocumentType DocumentType
+        public virtual XmlDocumentType? DocumentType
         {
-            get { return (XmlDocumentType)FindChild(XmlNodeType.DocumentType); }
+            get { return (XmlDocumentType?)FindChild(XmlNodeType.DocumentType); }
         }
 
-        internal virtual XmlDeclaration Declaration
+        internal virtual XmlDeclaration? Declaration
         {
             get
             {
                 if (HasChildNodes)
                 {
-                    XmlDeclaration dec = FirstChild as XmlDeclaration;
+                    XmlDeclaration? dec = FirstChild as XmlDeclaration;
                     return dec;
                 }
                 return null;
@@ -398,9 +400,9 @@ public override string LocalName
         }
 
         // Gets the root XmlElement for the document.
-        public XmlElement DocumentElement
+        public XmlElement? DocumentElement
         {
-            get { return (XmlElement)FindChild(XmlNodeType.Element); }
+            get { return (XmlElement?)FindChild(XmlNodeType.Element); }
         }
 
         internal override bool IsContainer
@@ -408,14 +410,14 @@ internal override bool IsContainer
             get { return true; }
         }
 
-        internal override XmlLinkedNode LastNode
+        internal override XmlLinkedNode? LastNode
         {
             get { return _lastChild; }
             set { _lastChild = value; }
         }
 
         // Gets the XmlDocument that contains this node.
-        public override XmlDocument OwnerDocument
+        public override XmlDocument? OwnerDocument
         {
             get { return null; }
         }
@@ -447,7 +449,7 @@ internal bool HasSetResolver
             get { return bSetResolver; }
         }
 
-        internal XmlResolver GetResolver()
+        internal XmlResolver? GetResolver()
         {
             return _resolver;
         }
@@ -460,7 +462,7 @@ public virtual XmlResolver XmlResolver
                 if (!bSetResolver)
                     bSetResolver = true;
 
-                XmlDocumentType dtd = this.DocumentType;
+                XmlDocumentType? dtd = this.DocumentType;
                 if (dtd != null)
                 {
                     dtd.DtdSchemaInfo = null;
@@ -498,12 +500,12 @@ internal override bool IsValidChildType(XmlNodeType type)
         }
         // the function examines all the siblings before the refNode
         //  if any of the nodes has type equals to "nt", return true; otherwise, return false;
-        private bool HasNodeTypeInPrevSiblings(XmlNodeType nt, XmlNode refNode)
+        private bool HasNodeTypeInPrevSiblings(XmlNodeType nt, XmlNode? refNode)
         {
             if (refNode == null)
                 return false;
 
-            XmlNode node = null;
+            XmlNode? node = null;
             if (refNode.ParentNode != null)
                 node = refNode.ParentNode.FirstChild;
             while (node != null)
@@ -519,9 +521,9 @@ private bool HasNodeTypeInPrevSiblings(XmlNodeType nt, XmlNode refNode)
 
         // the function examines all the siblings after the refNode
         //  if any of the nodes has the type equals to "nt", return true; otherwise, return false;
-        private bool HasNodeTypeInNextSiblings(XmlNodeType nt, XmlNode refNode)
+        private bool HasNodeTypeInNextSiblings(XmlNodeType nt, XmlNode? refNode)
         {
-            XmlNode node = refNode;
+            XmlNode? node = refNode;
             while (node != null)
             {
                 if (node.NodeType == nt)
@@ -531,7 +533,7 @@ private bool HasNodeTypeInNextSiblings(XmlNodeType nt, XmlNode refNode)
             return false;
         }
 
-        internal override bool CanInsertBefore(XmlNode newChild, XmlNode refChild)
+        internal override bool CanInsertBefore(XmlNode newChild, XmlNode? refChild)
         {
             if (refChild == null)
                 refChild = FirstChild;
@@ -574,7 +576,7 @@ internal override bool CanInsertBefore(XmlNode newChild, XmlNode refChild)
             return false;
         }
 
-        internal override bool CanInsertAfter(XmlNode newChild, XmlNode refChild)
+        internal override bool CanInsertAfter(XmlNode newChild, XmlNode? refChild)
         {
             if (refChild == null)
                 refChild = LastChild;
@@ -633,20 +635,20 @@ internal void SetDefaultNamespace(string prefix, string localName, ref string na
         }
 
         // Creates a XmlCDataSection containing the specified data.
-        public virtual XmlCDataSection CreateCDataSection(string data)
+        public virtual XmlCDataSection CreateCDataSection(string? data)
         {
             fCDataNodesPresent = true;
             return new XmlCDataSection(data, this);
         }
 
         // Creates an XmlComment containing the specified data.
-        public virtual XmlComment CreateComment(string data)
+        public virtual XmlComment CreateComment(string? data)
         {
             return new XmlComment(data, this);
         }
 
         // Returns a new XmlDocumentType object.
-        public virtual XmlDocumentType CreateDocumentType(string name, string publicId, string systemId, string internalSubset)
+        public virtual XmlDocumentType CreateDocumentType(string name, string? publicId, string? systemId, string? internalSubset)
         {
             return new XmlDocumentType(name, publicId, systemId, internalSubset, this);
         }
@@ -669,8 +671,8 @@ public XmlElement CreateElement(string name)
 
         internal void AddDefaultAttributes(XmlElement elem)
         {
-            SchemaInfo schInfo = DtdSchemaInfo;
-            SchemaElementDecl ed = GetSchemaElementDecl(elem);
+            SchemaInfo? schInfo = DtdSchemaInfo;
+            SchemaElementDecl? ed = GetSchemaElementDecl(elem);
             if (ed != null && ed.AttDefs != null)
             {
                 foreach (KeyValuePair<XmlQualifiedName, SchemaAttDef> attrDefs in ed.AttDefs)
@@ -683,7 +685,7 @@ internal void AddDefaultAttributes(XmlElement elem)
                         string attrPrefix;
                         string attrLocalname = attdef.Name.Name;
                         string attrNamespaceURI = string.Empty;
-                        if (schInfo.SchemaType == SchemaType.DTD)
+                        if (schInfo!.SchemaType == SchemaType.DTD)
                         {
                             attrPrefix = attdef.Name.Namespace;
                         }
@@ -699,15 +701,15 @@ internal void AddDefaultAttributes(XmlElement elem)
             }
         }
 
-        private SchemaElementDecl GetSchemaElementDecl(XmlElement elem)
+        private SchemaElementDecl? GetSchemaElementDecl(XmlElement elem)
         {
-            SchemaInfo schInfo = DtdSchemaInfo;
+            SchemaInfo? schInfo = DtdSchemaInfo;
             if (schInfo != null)
             {
                 //build XmlQualifiedName used to identify the element schema declaration
                 XmlQualifiedName qname = new XmlQualifiedName(elem.LocalName, schInfo.SchemaType == SchemaType.DTD ? elem.Prefix : elem.NamespaceURI);
                 //get the schema info for the element
-                SchemaElementDecl elemDecl;
+                SchemaElementDecl? elemDecl;
                 if (schInfo.ElementDecls.TryGetValue(qname, out elemDecl))
                 {
                     return elemDecl;
@@ -724,7 +726,7 @@ private XmlAttribute PrepareDefaultAttribute(SchemaAttDef attdef, string attrPre
             //parsing the default value for the default attribute
             defattr.InnerXml = attdef.DefaultValueRaw;
             //during the expansion of the tree, the flag could be set to true, we need to set it back.
-            XmlUnspecifiedAttribute unspAttr = defattr as XmlUnspecifiedAttribute;
+            XmlUnspecifiedAttribute? unspAttr = defattr as XmlUnspecifiedAttribute;
             if (unspAttr != null)
             {
                 unspAttr.SetSpecified(false);
@@ -746,32 +748,32 @@ public virtual XmlProcessingInstruction CreateProcessingInstruction(string targe
         }
 
         // Creates a XmlDeclaration node with the specified values.
-        public virtual XmlDeclaration CreateXmlDeclaration(string version, string encoding, string standalone)
+        public virtual XmlDeclaration CreateXmlDeclaration(string version, string? encoding, string? standalone)
         {
             return new XmlDeclaration(version, encoding, standalone, this);
         }
 
         // Creates an XmlText with the specified text.
-        public virtual XmlText CreateTextNode(string text)
+        public virtual XmlText CreateTextNode(string? text)
         {
             return new XmlText(text, this);
         }
 
         // Creates a XmlSignificantWhitespace node.
-        public virtual XmlSignificantWhitespace CreateSignificantWhitespace(string text)
+        public virtual XmlSignificantWhitespace CreateSignificantWhitespace(string? text)
         {
             return new XmlSignificantWhitespace(text, this);
         }
 
-        public override XPathNavigator CreateNavigator()
+        public override XPathNavigator? CreateNavigator()
         {
             return CreateNavigator(this);
         }
 
-        protected internal virtual XPathNavigator CreateNavigator(XmlNode node)
+        protected internal virtual XPathNavigator? CreateNavigator(XmlNode node)
         {
             XmlNodeType nodeType = node.NodeType;
-            XmlNode parent;
+            XmlNode? parent;
             XmlNodeType parentType;
 
             switch (nodeType)
@@ -806,7 +808,7 @@ protected internal virtual XPathNavigator CreateNavigator(XmlNode node)
                         }
                         while (parent != null);
                     }
-                    node = NormalizeText(node);
+                    node = NormalizeText(node)!;
                     break;
                 case XmlNodeType.Whitespace:
                     parent = node.ParentNode;
@@ -831,7 +833,7 @@ protected internal virtual XPathNavigator CreateNavigator(XmlNode node)
                         }
                         while (parent != null);
                     }
-                    node = NormalizeText(node);
+                    node = NormalizeText(node)!;
                     break;
                 default:
                     break;
@@ -853,9 +855,11 @@ internal static bool IsTextNode(XmlNodeType nt)
             }
         }
 
-        private XmlNode NormalizeText(XmlNode n)
+        private XmlNode? NormalizeText(XmlNode node)
         {
-            XmlNode retnode = null;
+            XmlNode? retnode = null;
+            XmlNode? n = node;
+
             while (IsTextNode(n.NodeType))
             {
                 retnode = n;
@@ -887,16 +891,18 @@ private XmlNode NormalizeText(XmlNode n)
 
                 if (n == null)
                     break;
+
                 while (n.NodeType == XmlNodeType.EntityReference)
                 {
-                    n = n.LastChild;
+                    n = n.LastChild!;
                 }
             }
+
             return retnode;
         }
 
         // Creates a XmlWhitespace node.
-        public virtual XmlWhitespace CreateWhitespace(string text)
+        public virtual XmlWhitespace CreateWhitespace(string? text)
         {
             return new XmlWhitespace(text, this);
         }
@@ -912,7 +918,7 @@ public virtual XmlNodeList GetElementsByTagName(string name)
 
         // Creates an XmlAttribute with the specified LocalName
         // and NamespaceURI.
-        public XmlAttribute CreateAttribute(string qualifiedName, string namespaceURI)
+        public XmlAttribute CreateAttribute(string qualifiedName, string? namespaceURI)
         {
             string prefix = string.Empty;
             string localName = string.Empty;
@@ -923,7 +929,7 @@ public XmlAttribute CreateAttribute(string qualifiedName, string namespaceURI)
 
         // Creates an XmlElement with the specified LocalName and
         // NamespaceURI.
-        public XmlElement CreateElement(string qualifiedName, string namespaceURI)
+        public XmlElement CreateElement(string qualifiedName, string? namespaceURI)
         {
             string prefix = string.Empty;
             string localName = string.Empty;
@@ -939,16 +945,16 @@ public virtual XmlNodeList GetElementsByTagName(string localName, string namespa
         }
 
         // Returns the XmlElement with the specified ID.
-        public virtual XmlElement GetElementById(string elementId)
+        public virtual XmlElement? GetElementById(string elementId)
         {
             if (_htElementIdMap != null)
             {
-                ArrayList elementList = (ArrayList)(_htElementIdMap[elementId]);
+                ArrayList? elementList = (ArrayList?)(_htElementIdMap[elementId]);
                 if (elementList != null)
                 {
                     foreach (WeakReference elemRef in elementList)
                     {
-                        XmlElement elem = (XmlElement)elemRef.Target;
+                        XmlElement? elem = (XmlElement?)elemRef.Target;
                         if (elem != null
                             && elem.IsConnected())
                             return elem;
@@ -966,14 +972,14 @@ public virtual XmlNode ImportNode(XmlNode node, bool deep)
 
         private XmlNode ImportNodeInternal(XmlNode node, bool deep)
         {
-            XmlNode newNode = null;
-
             if (node == null)
             {
                 throw new InvalidOperationException(SR.Xdom_Import_NullNode);
             }
             else
             {
+                XmlNode newNode;
+
                 switch (node.NodeType)
                 {
                     case XmlNodeType.Element:
@@ -996,7 +1002,7 @@ private XmlNode ImportNodeInternal(XmlNode node, bool deep)
                         newNode = CreateComment(node.Value);
                         break;
                     case XmlNodeType.ProcessingInstruction:
-                        newNode = CreateProcessingInstruction(node.Name, node.Value);
+                        newNode = CreateProcessingInstruction(node.Name, node.Value!);
                         break;
                     case XmlNodeType.XmlDeclaration:
                         XmlDeclaration decl = (XmlDeclaration)node;
@@ -1032,25 +1038,25 @@ private XmlNode ImportNodeInternal(XmlNode node, bool deep)
                     default:
                         throw new InvalidOperationException(SR.Format(CultureInfo.InvariantCulture, SR.Xdom_Import, node.NodeType));
                 }
-            }
 
-            return newNode;
+                return newNode;
+            }
         }
 
         private void ImportAttributes(XmlNode fromElem, XmlNode toElem)
         {
-            int cAttr = fromElem.Attributes.Count;
+            int cAttr = fromElem.Attributes!.Count;
             for (int iAttr = 0; iAttr < cAttr; iAttr++)
             {
                 if (fromElem.Attributes[iAttr].Specified)
-                    toElem.Attributes.SetNamedItem(ImportNodeInternal(fromElem.Attributes[iAttr], true));
+                    toElem.Attributes!.SetNamedItem(ImportNodeInternal(fromElem.Attributes[iAttr], true));
             }
         }
 
         private void ImportChildren(XmlNode fromNode, XmlNode toNode, bool deep)
         {
             Debug.Assert(toNode.NodeType != XmlNodeType.EntityReference);
-            for (XmlNode n = fromNode.FirstChild; n != null; n = n.NextSibling)
+            for (XmlNode? n = fromNode.FirstChild; n != null; n = n.NextSibling)
             {
                 toNode.AppendChild(ImportNodeInternal(n, deep));
             }
@@ -1067,17 +1073,17 @@ public XmlNameTable NameTable
 
         // Creates a XmlAttribute with the specified Prefix, LocalName,
         // and NamespaceURI.
-        public virtual XmlAttribute CreateAttribute(string prefix, string localName, string namespaceURI)
+        public virtual XmlAttribute CreateAttribute(string? prefix, string localName, string? namespaceURI)
         {
             return new XmlAttribute(AddAttrXmlName(prefix, localName, namespaceURI, null), this);
         }
 
-        protected internal virtual XmlAttribute CreateDefaultAttribute(string prefix, string localName, string namespaceURI)
+        protected internal virtual XmlAttribute CreateDefaultAttribute(string? prefix, string localName, string? namespaceURI)
         {
             return new XmlUnspecifiedAttribute(prefix, localName, namespaceURI, this);
         }
 
-        public virtual XmlElement CreateElement(string prefix, string localName, string namespaceURI)
+        public virtual XmlElement CreateElement(string? prefix, string localName, string? namespaceURI)
         {
             XmlElement elem = new XmlElement(AddXmlName(prefix, localName, namespaceURI, null), true, this);
             if (!IsLoading)
@@ -1123,7 +1129,7 @@ internal bool ActualLoadingStatus
 
 
         // Creates a XmlNode with the specified XmlNodeType, Prefix, Name, and NamespaceURI.
-        public virtual XmlNode CreateNode(XmlNodeType type, string prefix, string name, string namespaceURI)
+        public virtual XmlNode CreateNode(XmlNodeType type, string? prefix, string name, string? namespaceURI)
         {
             switch (type)
             {
@@ -1179,23 +1185,23 @@ public virtual XmlNode CreateNode(XmlNodeType type, string prefix, string name,
 
         // Creates an XmlNode with the specified node type, Name, and
         // NamespaceURI.
-        public virtual XmlNode CreateNode(string nodeTypeString, string name, string namespaceURI)
+        public virtual XmlNode CreateNode(string nodeTypeString, string name, string? namespaceURI)
         {
             return CreateNode(ConvertToNodeType(nodeTypeString), name, namespaceURI);
         }
 
         // Creates an XmlNode with the specified XmlNodeType, Name, and
         // NamespaceURI.
-        public virtual XmlNode CreateNode(XmlNodeType type, string name, string namespaceURI)
+        public virtual XmlNode CreateNode(XmlNodeType type, string name, string? namespaceURI)
         {
             return CreateNode(type, null, name, namespaceURI);
         }
 
         // Creates an XmlNode object based on the information in the XmlReader.
         // The reader must be positioned on a node or attribute.
-        public virtual XmlNode ReadNode(XmlReader reader)
+        public virtual XmlNode? ReadNode(XmlReader reader)
         {
-            XmlNode node = null;
+            XmlNode? node = null;
             try
             {
                 IsLoading = true;
@@ -1206,6 +1212,7 @@ public virtual XmlNode ReadNode(XmlReader reader)
             {
                 IsLoading = false;
             }
+
             return node;
         }
 
@@ -1361,7 +1368,7 @@ public virtual void LoadXml(string xml)
         }
 
         //TextEncoding is the one from XmlDeclaration if there is any
-        internal Encoding TextEncoding
+        internal Encoding? TextEncoding
         {
             get
             {
@@ -1377,6 +1384,7 @@ internal Encoding TextEncoding
             }
         }
 
+        [AllowNull]
         public override string InnerText
         {
             set
@@ -1445,14 +1453,14 @@ public virtual void Save(TextWriter writer)
         //that of textwriter's encoding
         public virtual void Save(XmlWriter w)
         {
-            XmlNode n = this.FirstChild;
+            XmlNode? n = this.FirstChild;
             if (n == null)
                 return;
             if (w.WriteState == WriteState.Start)
             {
                 if (n is XmlDeclaration)
                 {
-                    if (Standalone.Length == 0)
+                    if (Standalone!.Length == 0)
                         w.WriteStartDocument();
                     else if (Standalone == "yes")
                         w.WriteStartDocument(true);
@@ -1492,12 +1500,12 @@ public override void WriteContentTo(XmlWriter xw)
             }
         }
 
-        public void Validate(ValidationEventHandler validationEventHandler)
+        public void Validate(ValidationEventHandler? validationEventHandler)
         {
             Validate(validationEventHandler, this);
         }
 
-        public void Validate(ValidationEventHandler validationEventHandler, XmlNode nodeToValidate)
+        public void Validate(ValidationEventHandler? validationEventHandler, XmlNode nodeToValidate)
         {
             if (_schemas == null || _schemas.Count == 0)
             { //Should we error
@@ -1592,7 +1600,7 @@ public event XmlNodeChangedEventHandler NodeChanged
             }
         }
 
-        internal override XmlNodeChangedEventArgs GetEventArgs(XmlNode node, XmlNode oldParent, XmlNode newParent, string oldValue, string newValue, XmlNodeChangedAction action)
+        internal override XmlNodeChangedEventArgs? GetEventArgs(XmlNode node, XmlNode? oldParent, XmlNode? newParent, string? oldValue, string? newValue, XmlNodeChangedAction action)
         {
             _reportValidity = false;
 
@@ -1620,13 +1628,13 @@ internal override XmlNodeChangedEventArgs GetEventArgs(XmlNode node, XmlNode old
             return new XmlNodeChangedEventArgs(node, oldParent, newParent, oldValue, newValue, action);
         }
 
-        internal XmlNodeChangedEventArgs GetInsertEventArgsForLoad(XmlNode node, XmlNode newParent)
+        internal XmlNodeChangedEventArgs? GetInsertEventArgsForLoad(XmlNode node, XmlNode newParent)
         {
             if (_onNodeInsertingDelegate == null && _onNodeInsertedDelegate == null)
             {
                 return null;
             }
-            string nodeValue = node.Value;
+            string? nodeValue = node.Value;
             return new XmlNodeChangedEventArgs(node, null, newParent, nodeValue, nodeValue, XmlNodeChangedAction.Insert);
         }
 
@@ -1682,10 +1690,10 @@ internal override void AfterEvent(XmlNodeChangedEventArgs args)
         // If so, return the newly created default attribute (with children tree);
         // Otherwise, return null.
 
-        internal XmlAttribute GetDefaultAttribute(XmlElement elem, string attrPrefix, string attrLocalname, string attrNamespaceURI)
+        internal XmlAttribute? GetDefaultAttribute(XmlElement elem, string attrPrefix, string attrLocalname, string attrNamespaceURI)
         {
-            SchemaInfo schInfo = DtdSchemaInfo;
-            SchemaElementDecl ed = GetSchemaElementDecl(elem);
+            SchemaInfo? schInfo = DtdSchemaInfo;
+            SchemaElementDecl? ed = GetSchemaElementDecl(elem);
             if (ed != null && ed.AttDefs != null)
             {
                 foreach (KeyValuePair<XmlQualifiedName, SchemaAttDef> attrDefs in ed.AttDefs)
@@ -1696,7 +1704,7 @@ internal XmlAttribute GetDefaultAttribute(XmlElement elem, string attrPrefix, st
                     {
                         if (attdef.Name.Name == attrLocalname)
                         {
-                            if ((schInfo.SchemaType == SchemaType.DTD && attdef.Name.Namespace == attrPrefix) ||
+                            if ((schInfo!.SchemaType == SchemaType.DTD && attdef.Name.Namespace == attrPrefix) ||
                                  (schInfo.SchemaType != SchemaType.DTD && attdef.Name.Namespace == attrNamespaceURI))
                             {
                                 //find a def attribute with the same name, build a default attribute and return
@@ -1710,46 +1718,46 @@ internal XmlAttribute GetDefaultAttribute(XmlElement elem, string attrPrefix, st
             return null;
         }
 
-        internal string Version
+        internal string? Version
         {
             get
             {
-                XmlDeclaration decl = Declaration;
+                XmlDeclaration? decl = Declaration;
                 if (decl != null)
                     return decl.Version;
                 return null;
             }
         }
 
-        internal string Encoding
+        internal string? Encoding
         {
             get
             {
-                XmlDeclaration decl = Declaration;
+                XmlDeclaration? decl = Declaration;
                 if (decl != null)
                     return decl.Encoding;
                 return null;
             }
         }
 
-        internal string Standalone
+        internal string? Standalone
         {
             get
             {
-                XmlDeclaration decl = Declaration;
+                XmlDeclaration? decl = Declaration;
                 if (decl != null)
                     return decl.Standalone;
                 return null;
             }
         }
 
-        internal XmlEntity GetEntityNode(string name)
+        internal XmlEntity? GetEntityNode(string name)
         {
             if (DocumentType != null)
             {
                 XmlNamedNodeMap entites = DocumentType.Entities;
                 if (entites != null)
-                    return (XmlEntity)(entites.GetNamedItem(name));
+                    return (XmlEntity?)(entites.GetNamedItem(name));
             }
             return null;
         }
@@ -1760,7 +1768,7 @@ public override IXmlSchemaInfo SchemaInfo
             {
                 if (_reportValidity)
                 {
-                    XmlElement documentElement = DocumentElement;
+                    XmlElement? documentElement = DocumentElement;
                     if (documentElement != null)
                     {
                         switch (documentElement.SchemaInfo.Validity)
@@ -1796,7 +1804,7 @@ internal override XmlNode AppendChildForLoad(XmlNode newChild, XmlDocument doc)
             if (!CanInsertAfter(newChild, LastChild))
                 throw new InvalidOperationException(SR.Xdom_Node_Insert_Location);
 
-            XmlNodeChangedEventArgs args = GetInsertEventArgsForLoad(newChild, this);
+            XmlNodeChangedEventArgs? args = GetInsertEventArgsForLoad(newChild, this);
 
             if (args != null)
                 BeforeEvent(args);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocumentFragment.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocumentFragment.cs
index 9010ff103dcb8d..ae0345450628dd 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocumentFragment.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocumentFragment.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 
@@ -43,25 +44,26 @@ namespace System.Xml
     // such as <code>insertBefore()</code> and  <code>appendChild()</code>.
     public class XmlDocumentFragment : XmlNode
     {
-        private XmlLinkedNode _lastChild;
+        private XmlLinkedNode? _lastChild;
 
         protected internal XmlDocumentFragment(XmlDocument ownerDocument) : base()
         {
             if (ownerDocument == null)
                 throw new ArgumentException(SR.Xdom_Node_Null_Doc);
+
             parentNode = ownerDocument;
         }
 
         // Gets the name of the node.
         public override string Name
         {
-            get { return OwnerDocument.strDocumentFragmentName; }
+            get { return OwnerDocument!.strDocumentFragmentName; }
         }
 
         // Gets the name of the current node without the namespace prefix.
         public override string LocalName
         {
-            get { return OwnerDocument.strDocumentFragmentName; }
+            get { return OwnerDocument!.strDocumentFragmentName; }
         }
 
         // Gets the type of the current node.
@@ -71,7 +73,7 @@ public override XmlNodeType NodeType
         }
 
         // Gets the parent of this node (for nodes that can have parents).
-        public override XmlNode ParentNode
+        public override XmlNode? ParentNode
         {
             get { return null; }
         }
@@ -81,7 +83,7 @@ public override XmlDocument OwnerDocument
         {
             get
             {
-                return (XmlDocument)parentNode;
+                return (XmlDocument)parentNode!;
             }
         }
 
@@ -118,7 +120,7 @@ internal override bool IsContainer
             get { return true; }
         }
 
-        internal override XmlLinkedNode LastNode
+        internal override XmlLinkedNode? LastNode
         {
             get { return _lastChild; }
             set { _lastChild = value; }
@@ -140,7 +142,7 @@ internal override bool IsValidChildType(XmlNodeType type)
 
                 case XmlNodeType.XmlDeclaration:
                     //if there is an XmlDeclaration node, it has to be the first node;
-                    XmlNode firstNode = FirstChild;
+                    XmlNode? firstNode = FirstChild;
                     if (firstNode == null || firstNode.NodeType != XmlNodeType.XmlDeclaration)
                         return true;
                     else
@@ -149,7 +151,7 @@ internal override bool IsValidChildType(XmlNodeType type)
                     return false;
             }
         }
-        internal override bool CanInsertAfter(XmlNode newChild, XmlNode refChild)
+        internal override bool CanInsertAfter(XmlNode newChild, XmlNode? refChild)
         {
             Debug.Assert(newChild != null); //should be checked that newChild is not null before this function call
             if (newChild.NodeType == XmlNodeType.XmlDeclaration)
@@ -165,7 +167,7 @@ internal override bool CanInsertAfter(XmlNode newChild, XmlNode refChild)
             return true;
         }
 
-        internal override bool CanInsertBefore(XmlNode newChild, XmlNode refChild)
+        internal override bool CanInsertBefore(XmlNode newChild, XmlNode? refChild)
         {
             Debug.Assert(newChild != null); //should be checked that newChild is not null before this function call
             if (newChild.NodeType == XmlNodeType.XmlDeclaration)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocumentType.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocumentType.cs
index 9601322214b3b4..ab166f91a00e70 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocumentType.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDocumentType.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.Schema;
 
@@ -10,17 +11,17 @@ namespace System.Xml
     public class XmlDocumentType : XmlLinkedNode
     {
         private readonly string _name;
-        private readonly string _publicId;
-        private readonly string _systemId;
-        private readonly string _internalSubset;
+        private readonly string? _publicId;
+        private readonly string? _systemId;
+        private readonly string? _internalSubset;
         private bool _namespaces;
-        private XmlNamedNodeMap _entities;
-        private XmlNamedNodeMap _notations;
+        private XmlNamedNodeMap? _entities;
+        private XmlNamedNodeMap? _notations;
 
         // parsed DTD
-        private SchemaInfo _schemaInfo;
+        private SchemaInfo? _schemaInfo;
 
-        protected internal XmlDocumentType(string name, string publicId, string systemId, string internalSubset, XmlDocument doc) : base(doc)
+        protected internal XmlDocumentType(string name, string? publicId, string? systemId, string? internalSubset, XmlDocument doc) : base(doc)
         {
             _name = name;
             _publicId = publicId;
@@ -104,21 +105,21 @@ public XmlNamedNodeMap Notations
         //
 
         // Gets the value of the public identifier on the DOCTYPE declaration.
-        public string PublicId
+        public string? PublicId
         {
             get { return _publicId; }
         }
 
         // Gets the value of
         // the system identifier on the DOCTYPE declaration.
-        public string SystemId
+        public string? SystemId
         {
             get { return _systemId; }
         }
 
         // Gets the entire value of the DTD internal subset
         // on the DOCTYPE declaration.
-        public string InternalSubset
+        public string? InternalSubset
         {
             get { return _internalSubset; }
         }
@@ -141,7 +142,7 @@ public override void WriteContentTo(XmlWriter w)
             // Intentionally do nothing
         }
 
-        internal SchemaInfo DtdSchemaInfo
+        internal SchemaInfo? DtdSchemaInfo
         {
             get
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDomTextWriter.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDomTextWriter.cs
index 72ebd83447d0a1..9697b4945b30d4 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDomTextWriter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlDomTextWriter.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.IO;
 using System.Text;
 
@@ -11,11 +12,11 @@ namespace System.Xml
     // This is not possible with XmlTextWriter. But this class inherits XmlTextWriter.
     internal class XmlDOMTextWriter : XmlTextWriter
     {
-        public XmlDOMTextWriter(Stream w, Encoding encoding) : base(w, encoding)
+        public XmlDOMTextWriter(Stream w, Encoding? encoding) : base(w, encoding)
         {
         }
 
-        public XmlDOMTextWriter(string filename, Encoding encoding) : base(filename, encoding)
+        public XmlDOMTextWriter(string filename, Encoding? encoding) : base(filename, encoding)
         {
         }
 
@@ -25,20 +26,20 @@ public XmlDOMTextWriter(TextWriter w) : base(w)
 
         // Overrides the baseclass implementation so that emptystring prefixes do
         // do not fail if namespace is not specified.
-        public override void WriteStartElement(string prefix, string localName, string ns)
+        public override void WriteStartElement(string? prefix, string localName, string? ns)
         {
-            if ((ns.Length == 0) && (prefix.Length != 0))
-                prefix = "";
+            if (string.IsNullOrEmpty(ns) && !string.IsNullOrEmpty(prefix))
+                prefix = string.Empty;
 
             base.WriteStartElement(prefix, localName, ns);
         }
 
         // Overrides the baseclass implementation so that emptystring prefixes do
         // do not fail if namespace is not specified.
-        public override void WriteStartAttribute(string prefix, string localName, string ns)
+        public override void WriteStartAttribute(string? prefix, string localName, string? ns)
         {
-            if ((ns.Length == 0) && (prefix.Length != 0))
-                prefix = "";
+            if (string.IsNullOrEmpty(ns) && !string.IsNullOrEmpty(prefix))
+                prefix = string.Empty;
 
             base.WriteStartAttribute(prefix, localName, ns);
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlElement.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlElement.cs
index 97250574574fdc..60016007054002 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlElement.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlElement.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Xml.Schema;
 using System.Xml.XPath;
@@ -14,8 +15,8 @@ namespace System.Xml
     public class XmlElement : XmlLinkedNode
     {
         private XmlName _name;
-        private XmlAttributeCollection _attributes;
-        private XmlLinkedNode _lastChild; // == this for empty elements otherwise it is the last child
+        private XmlAttributeCollection? _attributes;
+        private XmlLinkedNode? _lastChild; // == this for empty elements otherwise it is the last child
 
         internal XmlElement(XmlName name, bool empty, XmlDocument doc) : base(doc)
         {
@@ -28,6 +29,7 @@ internal XmlElement(XmlName name, bool empty, XmlDocument doc) : base(doc)
             }
             if (name.LocalName.Length == 0)
                 throw new ArgumentException(SR.Xdom_Empty_LocalName);
+
             _name = name;
             if (empty)
             {
@@ -35,7 +37,7 @@ internal XmlElement(XmlName name, bool empty, XmlDocument doc) : base(doc)
             }
         }
 
-        protected internal XmlElement(string prefix, string localName, string namespaceURI, XmlDocument doc)
+        protected internal XmlElement(string prefix, string localName, string? namespaceURI, XmlDocument doc)
         : this(doc.AddXmlName(prefix, localName, namespaceURI, null), true, doc)
         {
         }
@@ -63,7 +65,7 @@ public override XmlNode CloneNode(bool deep)
                 foreach (XmlAttribute attr in Attributes)
                 {
                     XmlAttribute newAttr = (XmlAttribute)(attr.CloneNode(true));
-                    XmlUnspecifiedAttribute unspecAttr = newAttr as XmlUnspecifiedAttribute;
+                    XmlUnspecifiedAttribute? unspecAttr = newAttr as XmlUnspecifiedAttribute;
                     if (unspecAttr != null && attr.Specified == false)
                     {
                         unspecAttr.SetSpecified(false);
@@ -71,6 +73,7 @@ public override XmlNode CloneNode(bool deep)
                     element.Attributes.InternalAppendAttribute(newAttr);
                 }
             }
+
             if (deep)
                 element.CopyChildren(doc, this, deep);
 
@@ -108,7 +111,7 @@ public override XmlNodeType NodeType
             get { return XmlNodeType.Element; }
         }
 
-        public override XmlNode ParentNode
+        public override XmlNode? ParentNode
         {
             get
             {
@@ -133,7 +136,7 @@ internal override bool IsContainer
         //the function is provided only at Load time to speed up Load process
         internal override XmlNode AppendChildForLoad(XmlNode newChild, XmlDocument doc)
         {
-            XmlNodeChangedEventArgs args = doc.GetInsertEventArgsForLoad(newChild, this);
+            XmlNodeChangedEventArgs? args = doc.GetInsertEventArgsForLoad(newChild, this);
 
             if (args != null)
                 doc.BeforeEvent(args);
@@ -198,13 +201,12 @@ public bool IsEmpty
             }
         }
 
-        internal override XmlLinkedNode LastNode
+        internal override XmlLinkedNode? LastNode
         {
             get
             {
                 return _lastChild == this ? null : _lastChild;
             }
-
             set
             {
                 _lastChild = value;
@@ -267,9 +269,10 @@ public virtual bool HasAttributes
         // Returns the value for the attribute with the specified name.
         public virtual string GetAttribute(string name)
         {
-            XmlAttribute attr = GetAttributeNode(name);
+            XmlAttribute? attr = GetAttributeNode(name);
             if (attr != null)
                 return attr.Value;
+
             return string.Empty;
         }
 
@@ -277,7 +280,7 @@ public virtual string GetAttribute(string name)
         // with the specified name.
         public virtual void SetAttribute(string name, string value)
         {
-            XmlAttribute attr = GetAttributeNode(name);
+            XmlAttribute? attr = GetAttributeNode(name);
             if (attr == null)
             {
                 attr = OwnerDocument.CreateAttribute(name);
@@ -298,7 +301,7 @@ public virtual void RemoveAttribute(string name)
         }
 
         // Returns the XmlAttribute with the specified name.
-        public virtual XmlAttribute GetAttributeNode(string name)
+        public virtual XmlAttribute? GetAttributeNode(string name)
         {
             if (HasAttributes)
                 return Attributes[name];
@@ -310,14 +313,15 @@ public virtual XmlAttribute SetAttributeNode(XmlAttribute newAttr)
         {
             if (newAttr.OwnerElement != null)
                 throw new InvalidOperationException(SR.Xdom_Attr_InUse);
+
             return (XmlAttribute)Attributes.SetNamedItem(newAttr);
         }
 
         // Removes the specified XmlAttribute.
-        public virtual XmlAttribute RemoveAttributeNode(XmlAttribute oldAttr)
+        public virtual XmlAttribute? RemoveAttributeNode(XmlAttribute oldAttr)
         {
             if (HasAttributes)
-                return (XmlAttribute)Attributes.Remove(oldAttr);
+                return (XmlAttribute?)Attributes.Remove(oldAttr);
             return null;
         }
 
@@ -333,19 +337,20 @@ public virtual XmlNodeList GetElementsByTagName(string name)
         //
 
         // Returns the value for the attribute with the specified LocalName and NamespaceURI.
-        public virtual string GetAttribute(string localName, string namespaceURI)
+        public virtual string GetAttribute(string localName, string? namespaceURI)
         {
-            XmlAttribute attr = GetAttributeNode(localName, namespaceURI);
+            XmlAttribute? attr = GetAttributeNode(localName, namespaceURI);
             if (attr != null)
                 return attr.Value;
+
             return string.Empty;
         }
 
         // Sets the value of the attribute with the specified name
         // and namespace.
-        public virtual string SetAttribute(string localName, string namespaceURI, string value)
+        public virtual string SetAttribute(string localName, string? namespaceURI, string value)
         {
-            XmlAttribute attr = GetAttributeNode(localName, namespaceURI);
+            XmlAttribute? attr = GetAttributeNode(localName, namespaceURI);
             if (attr == null)
             {
                 attr = OwnerDocument.CreateAttribute(string.Empty, localName, namespaceURI);
@@ -361,13 +366,13 @@ public virtual string SetAttribute(string localName, string namespaceURI, string
         }
 
         // Removes an attribute specified by LocalName and NamespaceURI.
-        public virtual void RemoveAttribute(string localName, string namespaceURI)
+        public virtual void RemoveAttribute(string localName, string? namespaceURI)
         {
             RemoveAttributeNode(localName, namespaceURI);
         }
 
         // Returns the XmlAttribute with the specified LocalName and NamespaceURI.
-        public virtual XmlAttribute GetAttributeNode(string localName, string namespaceURI)
+        public virtual XmlAttribute? GetAttributeNode(string localName, string? namespaceURI)
         {
             if (HasAttributes)
                 return Attributes[localName, namespaceURI];
@@ -375,26 +380,28 @@ public virtual XmlAttribute GetAttributeNode(string localName, string namespaceU
         }
 
         // Adds the specified XmlAttribute.
-        public virtual XmlAttribute SetAttributeNode(string localName, string namespaceURI)
+        public virtual XmlAttribute SetAttributeNode(string localName, string? namespaceURI)
         {
-            XmlAttribute attr = GetAttributeNode(localName, namespaceURI);
+            XmlAttribute? attr = GetAttributeNode(localName, namespaceURI);
             if (attr == null)
             {
                 attr = OwnerDocument.CreateAttribute(string.Empty, localName, namespaceURI);
                 Attributes.InternalAppendAttribute(attr);
             }
+
             return attr;
         }
 
         // Removes the XmlAttribute specified by LocalName and NamespaceURI.
-        public virtual XmlAttribute RemoveAttributeNode(string localName, string namespaceURI)
+        public virtual XmlAttribute? RemoveAttributeNode(string localName, string? namespaceURI)
         {
             if (HasAttributes)
             {
-                XmlAttribute attr = GetAttributeNode(localName, namespaceURI);
+                XmlAttribute? attr = GetAttributeNode(localName, namespaceURI);
                 Attributes.Remove(attr);
                 return attr;
             }
+
             return null;
         }
 
@@ -413,7 +420,7 @@ public virtual bool HasAttribute(string name)
 
         // Determines whether the current node has the specified
         // attribute from the specified namespace.
-        public virtual bool HasAttribute(string localName, string namespaceURI)
+        public virtual bool HasAttribute(string localName, string? namespaceURI)
         {
             return GetAttributeNode(localName, namespaceURI) != null;
         }
@@ -444,10 +451,11 @@ public override void WriteTo(XmlWriter w)
         }
 
         // This method is copied from System.Xml.Linq.ElementWriter.WriteElement but adapted to DOM
-        private static void WriteElementTo(XmlWriter writer, XmlElement e)
+        private static void WriteElementTo(XmlWriter writer, XmlElement el)
         {
+            XmlElement? e = el;
             XmlNode root = e;
-            XmlNode n = e;
+            XmlNode? n = e;
             while (true)
             {
                 e = n as XmlElement;
@@ -480,15 +488,18 @@ private static void WriteElementTo(XmlWriter writer, XmlElement e)
                     // Use virtual dispatch (might recurse)
                     n.WriteTo(writer);
                 }
+
                 // Go back to the parent after writing the last child
-                while (n != root && n == n.ParentNode.LastChild)
+                while (n != root && n == n.ParentNode!.LastChild)
                 {
                     n = n.ParentNode;
                     Debug.Assert(n != null);
                     writer.WriteFullEndElement();
                 }
+
                 if (n == root)
                     break;
+
                 n = n.NextSibling;
                 Debug.Assert(n != null);
             }
@@ -513,17 +524,18 @@ private void WriteStartElement(XmlWriter w)
         // Saves all the children of the node to the specified XmlWriter.
         public override void WriteContentTo(XmlWriter w)
         {
-            for (XmlNode node = FirstChild; node != null; node = node.NextSibling)
+            for (XmlNode? node = FirstChild; node != null; node = node.NextSibling)
             {
                 node.WriteTo(w);
             }
         }
 
         // Removes the attribute node with the specified index from the attribute collection.
-        public virtual XmlNode RemoveAttributeAt(int i)
+        public virtual XmlNode? RemoveAttributeAt(int i)
         {
             if (HasAttributes)
-                return _attributes.RemoveAt(i);
+                return _attributes!.RemoveAt(i);
+
             return null;
         }
 
@@ -532,7 +544,7 @@ public virtual void RemoveAllAttributes()
         {
             if (HasAttributes)
             {
-                _attributes.RemoveAll();
+                _attributes!.RemoveAll();
             }
         }
 
@@ -585,7 +597,7 @@ public override string InnerText
             }
             set
             {
-                XmlLinkedNode linkedNode = LastNode;
+                XmlLinkedNode? linkedNode = LastNode;
                 if (linkedNode != null && //there is one child
                     linkedNode.NodeType == XmlNodeType.Text && //which is text node
                     linkedNode.next == linkedNode) // and it is the only child
@@ -601,18 +613,19 @@ public override string InnerText
             }
         }
 
-        public override XmlNode NextSibling
+        public override XmlNode? NextSibling
         {
             get
             {
                 if (this.parentNode != null
                     && this.parentNode.LastNode != this)
                     return next;
+
                 return null;
             }
         }
 
-        internal override void SetParent(XmlNode node)
+        internal override void SetParent(XmlNode? node)
         {
             this.parentNode = node;
         }
@@ -624,10 +637,12 @@ internal override void SetParent(XmlNode node)
         internal override string GetXPAttribute(string localName, string ns)
         {
             if (ns == OwnerDocument.strReservedXmlns)
-                return null;
-            XmlAttribute attr = GetAttributeNode(localName, ns);
+                return string.Empty;
+
+            XmlAttribute? attr = GetAttributeNode(localName, ns);
             if (attr != null)
                 return attr.Value;
+
             return string.Empty;
         }
     }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlElementList.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlElementList.cs
index 3892576db3c425..02211d6d21aa39 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlElementList.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlElementList.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections;
 using System.Diagnostics;
 
@@ -8,12 +9,12 @@ namespace System.Xml
 {
     internal class XmlElementList : XmlNodeList
     {
-        private readonly string _asterisk;
+        private readonly string _asterisk = null!;
         private int _changeCount; //recording the total number that the dom tree has been changed ( insertion and deletion )
         //the member vars below are saved for further reconstruction
-        private readonly string _name;         //only one of 2 string groups will be initialized depends on which constructor is called.
-        private string _localName;
-        private string _namespaceURI;
+        private readonly string? _name;         //only one of 2 string groups will be initialized depends on which constructor is called.
+        private string? _localName;
+        private string? _namespaceURI;
         private readonly XmlNode _rootNode;
         // the member vars below serves the optimization of accessing of the elements in the list
         private int _curInd;       // -1 means the starting point for a new search round
@@ -22,7 +23,7 @@ internal class XmlElementList : XmlNodeList
         private bool _atomized;     //whether the localname and namespaceuri are atomized
         private int _matchCount;   // cached list count. -1 means it needs reconstruction
 
-        private WeakReference _listener;   // XmlElementListListener
+        private WeakReference? _listener;   // XmlElementListListener
 
         private XmlElementList(XmlNode parent)
         {
@@ -50,11 +51,12 @@ internal void ConcurrencyCheck(XmlNodeChangedEventArgs args)
             if (_atomized == false)
             {
                 XmlNameTable nameTable = _rootNode.Document.NameTable;
-                _localName = nameTable.Add(_localName);
-                _namespaceURI = nameTable.Add(_namespaceURI);
+                _localName = nameTable.Add(_localName!);
+                _namespaceURI = nameTable.Add(_namespaceURI!);
                 _atomized = true;
             }
-            if (IsMatch(args.Node))
+
+            if (IsMatch(args.Node!))
             {
                 _changeCount++;
                 _curInd = -1;
@@ -62,6 +64,7 @@ internal void ConcurrencyCheck(XmlNodeChangedEventArgs args)
                 if (args.Action == XmlNodeChangedAction.Insert)
                     _empty = false;
             }
+
             _matchCount = -1;
         }
 
@@ -91,6 +94,7 @@ internal XmlElementList(XmlNode parent, string localName, string namespaceURI) :
                 _localName = localName;
                 _namespaceURI = namespaceURI;
             }
+
             _name = null;
         }
 
@@ -100,11 +104,11 @@ internal int ChangeCount
         }
 
         // return the next element node that is in PreOrder
-        private XmlNode NextElemInPreOrder(XmlNode curNode)
+        private XmlNode? NextElemInPreOrder(XmlNode curNode)
         {
             Debug.Assert(curNode != null);
             //For preorder walking, first try its child
-            XmlNode retNode = curNode.FirstChild;
+            XmlNode? retNode = curNode.FirstChild;
             if (retNode == null)
             {
                 //if no child, the next node forward will the be the NextSibling of the first ancestor which has NextSibling
@@ -127,11 +131,11 @@ private XmlNode NextElemInPreOrder(XmlNode curNode)
         }
 
         // return the previous element node that is in PreOrder
-        private XmlNode PrevElemInPreOrder(XmlNode curNode)
+        private XmlNode? PrevElemInPreOrder(XmlNode curNode)
         {
             Debug.Assert(curNode != null);
             //For preorder walking, the previous node will be the right-most node in the tree of PreviousSibling of the curNode
-            XmlNode retNode = curNode.PreviousSibling;
+            XmlNode? retNode = curNode.PreviousSibling;
             // so if the PreviousSibling is not null, going through the tree down to find the right-most node
             while (retNode != null)
             {
@@ -172,10 +176,10 @@ private bool IsMatch(XmlNode curNode)
             return false;
         }
 
-        private XmlNode GetMatchingNode(XmlNode n, bool bNext)
+        private XmlNode? GetMatchingNode(XmlNode n, bool bNext)
         {
             Debug.Assert(n != null);
-            XmlNode node = n;
+            XmlNode? node = n;
             do
             {
                 if (bNext)
@@ -186,21 +190,22 @@ private XmlNode GetMatchingNode(XmlNode n, bool bNext)
             return node;
         }
 
-        private XmlNode GetNthMatchingNode(XmlNode n, bool bNext, int nCount)
+        private XmlNode? GetNthMatchingNode(XmlNode n, bool bNext, int nCount)
         {
             Debug.Assert(n != null);
-            XmlNode node = n;
+            XmlNode? node = n;
             for (int ind = 0; ind < nCount; ind++)
             {
                 node = GetMatchingNode(node, bNext);
                 if (node == null)
                     return null;
             }
+
             return node;
         }
 
         //the function is for the enumerator to find out the next available matching element node
-        public XmlNode GetNextNode(XmlNode n)
+        public XmlNode? GetNextNode(XmlNode? n)
         {
             if (_empty == true)
                 return null;
@@ -208,7 +213,7 @@ public XmlNode GetNextNode(XmlNode n)
             return GetMatchingNode(node, true);
         }
 
-        public override XmlNode Item(int index)
+        public override XmlNode? Item(int index)
         {
             if (_rootNode == null || index < 0)
                 return null;
@@ -221,13 +226,15 @@ public override XmlNode Item(int index)
             bool bForward = (nDiff > 0);
             if (nDiff < 0)
                 nDiff = -nDiff;
-            XmlNode node;
+
+            XmlNode? node;
             if ((node = GetNthMatchingNode(_curElem, bForward, nDiff)) != null)
             {
                 _curInd = index;
                 _curElem = node;
                 return _curElem;
             }
+
             return null;
         }
 
@@ -237,21 +244,25 @@ public override int Count
             {
                 if (_empty == true)
                     return 0;
+
                 if (_matchCount < 0)
                 {
                     int currMatchCount = 0;
                     int currChangeCount = _changeCount;
-                    XmlNode node = _rootNode;
+                    XmlNode? node = _rootNode;
                     while ((node = GetMatchingNode(node, true)) != null)
                     {
                         currMatchCount++;
                     }
+
                     if (currChangeCount != _changeCount)
                     {
                         return currMatchCount;
                     }
+
                     _matchCount = currMatchCount;
                 }
+
                 return _matchCount;
             }
         }
@@ -259,7 +270,8 @@ public override int Count
         public override IEnumerator GetEnumerator()
         {
             if (_empty == true)
-                return new XmlEmptyElementListEnumerator(this); ;
+                return new XmlEmptyElementListEnumerator(this);
+
             return new XmlElementListEnumerator(this);
         }
 
@@ -273,11 +285,12 @@ protected virtual void Dispose(bool disposing)
         {
             if (_listener != null)
             {
-                XmlElementListListener listener = (XmlElementListListener)_listener.Target;
+                XmlElementListListener? listener = (XmlElementListListener?)_listener.Target;
                 if (listener != null)
                 {
                     listener.Unregister();
                 }
+
                 _listener = null;
             }
         }
@@ -286,7 +299,7 @@ protected virtual void Dispose(bool disposing)
     internal class XmlElementListEnumerator : IEnumerator
     {
         private readonly XmlElementList _list;
-        private XmlNode _curElem;
+        private XmlNode? _curElem;
         private int _changeCount; //save the total number that the dom tree has been changed ( insertion and deletion ) when this enumerator is created
 
         public XmlElementListEnumerator(XmlElementList list)
@@ -317,7 +330,7 @@ public void Reset()
             _changeCount = _list.ChangeCount;
         }
 
-        public object Current
+        public object? Current
         {
             get { return _curElem; }
         }
@@ -338,7 +351,7 @@ public void Reset()
         {
         }
 
-        public object Current
+        public object? Current
         {
             get { return null; }
         }
@@ -346,7 +359,7 @@ public object Current
 
     internal class XmlElementListListener
     {
-        private WeakReference _elemList;
+        private WeakReference? _elemList;
         private readonly XmlDocument _doc;
         private readonly XmlNodeChangedEventHandler _nodeChangeHandler;
 
@@ -365,7 +378,7 @@ private void OnListChanged(object sender, XmlNodeChangedEventArgs args)
             {
                 if (_elemList != null)
                 {
-                    XmlElementList el = (XmlElementList)_elemList.Target;
+                    XmlElementList? el = (XmlElementList?)_elemList.Target;
                     if (null != el)
                     {
                         el.ConcurrencyCheck(args);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEntity.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEntity.cs
index cc8523fb3db02e..636bae90881d31 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEntity.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEntity.cs
@@ -1,20 +1,21 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     // Represents a parsed or unparsed entity in the XML document.
     public class XmlEntity : XmlNode
     {
-        private readonly string _publicId;
-        private readonly string _systemId;
-        private readonly string _notationName;
+        private readonly string? _publicId;
+        private readonly string? _systemId;
+        private readonly string? _notationName;
         private readonly string _name;
-        private string _baseURI;
-        private XmlLinkedNode _lastChild;
+        private string _baseURI = string.Empty;
+        private XmlLinkedNode? _lastChild;
         private bool _childrenFoliating;
 
-        internal XmlEntity(string name, string strdata, string publicId, string systemId, string notationName, XmlDocument doc) : base(doc)
+        internal XmlEntity(string name, string? strdata, string? publicId, string? systemId, string? notationName, XmlDocument doc) : base(doc)
         {
             _name = doc.NameTable.Add(name);
             _publicId = publicId;
@@ -71,7 +72,7 @@ internal override bool IsContainer
             get { return true; }
         }
 
-        internal override XmlLinkedNode LastNode
+        internal override XmlLinkedNode? LastNode
         {
             get
             {
@@ -106,20 +107,20 @@ public override XmlNodeType NodeType
         }
 
         // Gets the value of the public identifier on the entity declaration.
-        public string PublicId
+        public string? PublicId
         {
             get { return _publicId; }
         }
 
         // Gets the value of the system identifier on the entity declaration.
-        public string SystemId
+        public string? SystemId
         {
             get { return _systemId; }
         }
 
         // Gets the name of the optional NDATA attribute on the
         // entity declaration.
-        public string NotationName
+        public string? NotationName
         {
             get { return _notationName; }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEntityReference.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEntityReference.cs
index 0d73a247a1af5b..59d7c595e88695 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEntityReference.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEntityReference.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 
 namespace System.Xml
@@ -30,7 +31,7 @@ namespace System.Xml
     public class XmlEntityReference : XmlLinkedNode
     {
         private readonly string _name;
-        private XmlLinkedNode _lastChild;
+        private XmlLinkedNode? _lastChild;
 
         protected internal XmlEntityReference(string name, XmlDocument doc) : base(doc)
         {
@@ -41,6 +42,7 @@ protected internal XmlEntityReference(string name, XmlDocument doc) : base(doc)
                     throw new ArgumentException(SR.Xdom_InvalidCharacter_EntityReference);
                 }
             }
+
             _name = doc.NameTable.Add(name);
             doc.fEntRefNodesPresent = true;
         }
@@ -58,7 +60,7 @@ public override string LocalName
         }
 
         // Gets or sets the value of the node.
-        public override string Value
+        public override string? Value
         {
             get
             {
@@ -103,7 +105,7 @@ internal override bool IsContainer
             get { return true; }
         }
 
-        internal override void SetParent(XmlNode node)
+        internal override void SetParent(XmlNode? node)
         {
             base.SetParent(node);
             if (LastNode == null && node != null && node != OwnerDocument)
@@ -119,7 +121,7 @@ internal override void SetParentForLoad(XmlNode node)
             this.SetParent(node);
         }
 
-        internal override XmlLinkedNode LastNode
+        internal override XmlLinkedNode? LastNode
         {
             get
             {
@@ -174,7 +176,7 @@ public override string BaseURI
         {
             get
             {
-                return OwnerDocument.BaseURI;
+                return OwnerDocument!.BaseURI;
             }
         }
 
@@ -197,7 +199,7 @@ internal string ChildBaseURI
             get
             {
                 //get the associate entity and return its baseUri
-                XmlEntity ent = OwnerDocument.GetEntityNode(_name);
+                XmlEntity? ent = OwnerDocument!.GetEntityNode(_name);
                 if (ent != null)
                 {
                     if (!string.IsNullOrEmpty(ent.SystemId))
@@ -205,6 +207,7 @@ internal string ChildBaseURI
                     else
                         return ent.BaseURI;
                 }
+
                 return string.Empty;
             }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEventChangedAction.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEventChangedAction.cs
index 1cf0a0c7fe00ff..59c2540fce2afc 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEventChangedAction.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlEventChangedAction.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     // Specifies the type of node change
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlImplementation.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlImplementation.cs
index 395c4ef29bb879..5dfbecc1f156e8 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlImplementation.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlImplementation.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     // Provides methods for performing operations that are independent of any
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlLinkedNode.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlLinkedNode.cs
index 7a88926f3366f1..41ae4635e1d05f 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlLinkedNode.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlLinkedNode.cs
@@ -1,12 +1,13 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     // Gets the node immediately preceding or following this node.
     public abstract class XmlLinkedNode : XmlNode
     {
-        internal XmlLinkedNode next;
+        internal XmlLinkedNode? next;
 
         internal XmlLinkedNode(XmlDocument doc) : base(doc)
         {
@@ -14,40 +15,44 @@ internal XmlLinkedNode(XmlDocument doc) : base(doc)
         }
 
         // Gets the node immediately preceding this node.
-        public override XmlNode PreviousSibling
+        public override XmlNode? PreviousSibling
         {
             get
             {
-                XmlNode parent = ParentNode;
+                XmlNode? parent = ParentNode;
                 if (parent != null)
                 {
-                    XmlNode node = parent.FirstChild;
+                    XmlNode? node = parent.FirstChild;
                     while (node != null)
                     {
-                        XmlNode nextSibling = node.NextSibling;
+                        XmlNode? nextSibling = node.NextSibling;
                         if (nextSibling == this)
                         {
                             break;
                         }
+
                         node = nextSibling;
                     }
+
                     return node;
                 }
+
                 return null;
             }
         }
 
         // Gets the node immediately following this node.
-        public override XmlNode NextSibling
+        public override XmlNode? NextSibling
         {
             get
             {
-                XmlNode parent = ParentNode;
+                XmlNode? parent = ParentNode;
                 if (parent != null)
                 {
                     if (next != parent.FirstChild)
                         return next;
                 }
+
                 return null;
             }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlLoader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlLoader.cs
index 71191ddd154fde..05e28484d44902 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlLoader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlLoader.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.IO;
 using System.Diagnostics;
 using System.Globalization;
@@ -12,11 +13,10 @@ namespace System.Xml
 {
     internal class XmlLoader
     {
-        private XmlDocument _doc;
-        private XmlReader _reader;
+        private XmlDocument? _doc;
+        private XmlReader? _reader;
         private bool _preserveWhitespace;
 
-
         public XmlLoader()
         {
         }
@@ -38,7 +38,7 @@ internal void Load(XmlDocument doc, XmlReader reader, bool preserveWhitespace)
                 throw new ArgumentException(SR.Xdom_Load_NoDocument);
             if (reader == null)
                 throw new ArgumentException(SR.Xdom_Load_NoReader);
-            doc.SetBaseURI(reader.BaseURI);
+            doc.SetBaseURI(reader.BaseURI!);
             if (reader.Settings != null
                 && reader.Settings.ValidationType == ValidationType.Schema)
             {
@@ -57,7 +57,7 @@ private void LoadDocSequence(XmlDocument parentDoc)
         {
             Debug.Assert(_reader != null);
             Debug.Assert(parentDoc != null);
-            XmlNode node = null;
+            XmlNode? node = null;
             while ((node = LoadNode(true)) != null)
             {
                 parentDoc.AppendChildForLoad(node, parentDoc);
@@ -66,7 +66,7 @@ private void LoadDocSequence(XmlDocument parentDoc)
             }
         }
 
-        internal XmlNode ReadCurrentNode(XmlDocument doc, XmlReader reader)
+        internal XmlNode? ReadCurrentNode(XmlDocument doc, XmlReader reader)
         {
             _doc = doc;
             _reader = reader;
@@ -83,7 +83,7 @@ internal XmlNode ReadCurrentNode(XmlDocument doc, XmlReader reader)
             }
             if (reader.ReadState == ReadState.Interactive)
             {
-                XmlNode n = LoadNode(true);
+                XmlNode n = LoadNode(true)!;
 
                 // Move to the next node
                 if (n.NodeType != XmlNodeType.Attribute)
@@ -91,23 +91,24 @@ internal XmlNode ReadCurrentNode(XmlDocument doc, XmlReader reader)
 
                 return n;
             }
+
             return null;
         }
 
-        private XmlNode LoadNode(bool skipOverWhitespace)
+        private XmlNode? LoadNode(bool skipOverWhitespace)
         {
-            XmlReader r = _reader;
-            XmlNode parent = null;
-            XmlElement element;
-            IXmlSchemaInfo schemaInfo;
+            XmlReader r = _reader!;
+            XmlNode? parent = null;
+            XmlElement? element;
+            IXmlSchemaInfo? schemaInfo;
             do
             {
-                XmlNode node = null;
+                XmlNode? node = null;
                 switch (r.NodeType)
                 {
                     case XmlNodeType.Element:
                         bool fEmptyElement = r.IsEmptyElement;
-                        element = _doc.CreateElement(r.Prefix, r.LocalName, r.NamespaceURI);
+                        element = _doc!.CreateElement(r.Prefix, r.LocalName, r.NamespaceURI);
                         element.IsEmpty = fEmptyElement;
 
                         if (r.MoveToFirstAttribute())
@@ -155,7 +156,7 @@ private XmlNode LoadNode(bool skipOverWhitespace)
                             element = parent as XmlElement;
                             if (element != null)
                             {
-                                element.XmlName = _doc.AddXmlName(element.Prefix, element.LocalName, element.NamespaceURI, schemaInfo);
+                                element.XmlName = _doc!.AddXmlName(element.Prefix, element.LocalName, element.NamespaceURI, schemaInfo);
                             }
                         }
                         if (parent.ParentNode == null)
@@ -178,17 +179,17 @@ private XmlNode LoadNode(bool skipOverWhitespace)
                         break;
 
                     case XmlNodeType.Text:
-                        node = _doc.CreateTextNode(r.Value);
+                        node = _doc!.CreateTextNode(r.Value);
                         break;
 
                     case XmlNodeType.SignificantWhitespace:
-                        node = _doc.CreateSignificantWhitespace(r.Value);
+                        node = _doc!.CreateSignificantWhitespace(r.Value);
                         break;
 
                     case XmlNodeType.Whitespace:
                         if (_preserveWhitespace)
                         {
-                            node = _doc.CreateWhitespace(r.Value);
+                            node = _doc!.CreateWhitespace(r.Value);
                             break;
                         }
                         else if (parent == null && !skipOverWhitespace)
@@ -201,7 +202,7 @@ private XmlNode LoadNode(bool skipOverWhitespace)
                             continue;
                         }
                     case XmlNodeType.CDATA:
-                        node = _doc.CreateCDataSection(r.Value);
+                        node = _doc!.CreateCDataSection(r.Value);
                         break;
 
 
@@ -210,11 +211,11 @@ private XmlNode LoadNode(bool skipOverWhitespace)
                         break;
 
                     case XmlNodeType.ProcessingInstruction:
-                        node = _doc.CreateProcessingInstruction(r.Name, r.Value);
+                        node = _doc!.CreateProcessingInstruction(r.Name, r.Value);
                         break;
 
                     case XmlNodeType.Comment:
-                        node = _doc.CreateComment(r.Value);
+                        node = _doc!.CreateComment(r.Value);
                         break;
 
                     case XmlNodeType.DocumentType:
@@ -228,7 +229,7 @@ private XmlNode LoadNode(bool skipOverWhitespace)
                 Debug.Assert(node != null);
                 if (parent != null)
                 {
-                    parent.AppendChildForLoad(node, _doc);
+                    parent.AppendChildForLoad(node, _doc!);
                 }
                 else
                 {
@@ -245,12 +246,13 @@ private XmlNode LoadNode(bool skipOverWhitespace)
                     parent = parent.ParentNode;
                 }
             }
+
             return parent;
         }
 
         private XmlAttribute LoadAttributeNode()
         {
-            Debug.Assert(_reader.NodeType == XmlNodeType.Attribute);
+            Debug.Assert(_reader!.NodeType == XmlNodeType.Attribute);
 
             XmlReader r = _reader;
             if (r.IsDefault)
@@ -258,12 +260,13 @@ private XmlAttribute LoadAttributeNode()
                 return LoadDefaultAttribute();
             }
 
-            XmlAttribute attr = _doc.CreateAttribute(r.Prefix, r.LocalName, r.NamespaceURI);
-            IXmlSchemaInfo schemaInfo = r.SchemaInfo;
+            XmlAttribute attr = _doc!.CreateAttribute(r.Prefix, r.LocalName, r.NamespaceURI);
+            IXmlSchemaInfo? schemaInfo = r.SchemaInfo;
             if (schemaInfo != null)
             {
                 attr.XmlName = _doc.AddAttrXmlName(attr.Prefix, attr.LocalName, attr.NamespaceURI, schemaInfo);
             }
+
             while (r.ReadAttributeValue())
             {
                 XmlNode node;
@@ -289,6 +292,7 @@ private XmlAttribute LoadAttributeNode()
                     default:
                         throw UnexpectedNodeType(r.NodeType);
                 }
+
                 Debug.Assert(node != null);
                 attr.AppendChildForLoad(node, _doc);
             }
@@ -298,11 +302,11 @@ private XmlAttribute LoadAttributeNode()
 
         private XmlAttribute LoadDefaultAttribute()
         {
-            Debug.Assert(_reader.IsDefault);
+            Debug.Assert(_reader!.IsDefault);
 
             XmlReader r = _reader;
-            XmlAttribute attr = _doc.CreateDefaultAttribute(r.Prefix, r.LocalName, r.NamespaceURI);
-            IXmlSchemaInfo schemaInfo = r.SchemaInfo;
+            XmlAttribute attr = _doc!.CreateDefaultAttribute(r.Prefix, r.LocalName, r.NamespaceURI);
+            IXmlSchemaInfo? schemaInfo = r.SchemaInfo;
             if (schemaInfo != null)
             {
                 attr.XmlName = _doc.AddAttrXmlName(attr.Prefix, attr.LocalName, attr.NamespaceURI, schemaInfo);
@@ -310,7 +314,7 @@ private XmlAttribute LoadDefaultAttribute()
 
             LoadAttributeValue(attr, false);
 
-            XmlUnspecifiedAttribute defAttr = attr as XmlUnspecifiedAttribute;
+            XmlUnspecifiedAttribute? defAttr = attr as XmlUnspecifiedAttribute;
             // If user overrides CreateDefaultAttribute, then attr will NOT be a XmlUnspecifiedAttribute instance.
             if (defAttr != null)
                 defAttr.SetSpecified(false);
@@ -320,19 +324,19 @@ private XmlAttribute LoadDefaultAttribute()
 
         private void LoadAttributeValue(XmlNode parent, bool direct)
         {
-            XmlReader r = _reader;
+            XmlReader r = _reader!;
             while (r.ReadAttributeValue())
             {
                 XmlNode node;
                 switch (r.NodeType)
                 {
                     case XmlNodeType.Text:
-                        node = direct ? new XmlText(r.Value, _doc) : _doc.CreateTextNode(r.Value);
+                        node = direct ? new XmlText(r.Value, _doc!) : _doc!.CreateTextNode(r.Value);
                         break;
                     case XmlNodeType.EndEntity:
                         return;
                     case XmlNodeType.EntityReference:
-                        node = direct ? new XmlEntityReference(_reader.LocalName, _doc) : _doc.CreateEntityReference(_reader.LocalName);
+                        node = direct ? new XmlEntityReference(_reader!.LocalName, _doc!) : _doc!.CreateEntityReference(_reader!.LocalName);
                         if (r.CanResolveEntity)
                         {
                             r.ResolveEntity();
@@ -341,7 +345,7 @@ private void LoadAttributeValue(XmlNode parent, bool direct)
                             // if the reader does not present any children for the ent-ref
                             if (node.FirstChild == null)
                             {
-                                node.AppendChildForLoad(direct ? new XmlText(string.Empty) : _doc.CreateTextNode(string.Empty), _doc);
+                                node.AppendChildForLoad(direct ? new XmlText(string.Empty) : _doc!.CreateTextNode(string.Empty), _doc!);
                             }
                         }
                         break;
@@ -349,42 +353,42 @@ private void LoadAttributeValue(XmlNode parent, bool direct)
                         throw UnexpectedNodeType(r.NodeType);
                 }
                 Debug.Assert(node != null);
-                parent.AppendChildForLoad(node, _doc);
+                parent.AppendChildForLoad(node, _doc!);
             }
             return;
         }
 
         private XmlEntityReference LoadEntityReferenceNode(bool direct)
         {
-            Debug.Assert(_reader.NodeType == XmlNodeType.EntityReference);
-            XmlEntityReference eref = direct ? new XmlEntityReference(_reader.Name, _doc) : _doc.CreateEntityReference(_reader.Name);
+            Debug.Assert(_reader!.NodeType == XmlNodeType.EntityReference);
+            XmlEntityReference eref = direct ? new XmlEntityReference(_reader.Name, _doc!) : _doc!.CreateEntityReference(_reader.Name);
             if (_reader.CanResolveEntity)
             {
                 _reader.ResolveEntity();
                 while (_reader.Read() && _reader.NodeType != XmlNodeType.EndEntity)
                 {
-                    XmlNode node = direct ? LoadNodeDirect() : LoadNode(false);
+                    XmlNode? node = direct ? LoadNodeDirect() : LoadNode(false);
                     if (node != null)
                     {
-                        eref.AppendChildForLoad(node, _doc);
+                        eref.AppendChildForLoad(node, _doc!);
                     }
                 }
                 // Code internally relies on the fact that an EntRef nodes has at least one child (even an empty text node). Ensure that this holds true,
                 // if the reader does not present any children for the ent-ref
                 if (eref.LastChild == null)
-                    eref.AppendChildForLoad(_doc.CreateTextNode(string.Empty), _doc);
+                    eref.AppendChildForLoad(_doc!.CreateTextNode(string.Empty), _doc);
             }
             return eref;
         }
 
         private XmlDeclaration LoadDeclarationNode()
         {
-            Debug.Assert(_reader.NodeType == XmlNodeType.XmlDeclaration);
+            Debug.Assert(_reader!.NodeType == XmlNodeType.XmlDeclaration);
 
             //parse data
-            string version = null;
-            string encoding = null;
-            string standalone = null;
+            string? version = null;
+            string? encoding = null;
+            string? standalone = null;
 
             // Try first to use the reader to get the xml decl "attributes". Since not all readers are required to support this, it is possible to have
             // implementations that do nothing
@@ -412,15 +416,15 @@ private XmlDeclaration LoadDeclarationNode()
             if (version == null)
                 ParseXmlDeclarationValue(_reader.Value, out version, out encoding, out standalone);
 
-            return _doc.CreateXmlDeclaration(version, encoding, standalone);
+            return _doc!.CreateXmlDeclaration(version!, encoding, standalone);
         }
 
         private XmlDocumentType LoadDocumentTypeNode()
         {
-            Debug.Assert(_reader.NodeType == XmlNodeType.DocumentType);
+            Debug.Assert(_reader!.NodeType == XmlNodeType.DocumentType);
 
-            string publicId = null;
-            string systemId = null;
+            string? publicId = null;
+            string? systemId = null;
             string internalSubset = _reader.Value;
             string localName = _reader.LocalName;
             while (_reader.MoveToNextAttribute())
@@ -436,9 +440,9 @@ private XmlDocumentType LoadDocumentTypeNode()
                 }
             }
 
-            XmlDocumentType dtNode = _doc.CreateDocumentType(localName, publicId, systemId, internalSubset);
+            XmlDocumentType dtNode = _doc!.CreateDocumentType(localName, publicId, systemId, internalSubset);
 
-            IDtdInfo dtdInfo = _reader.DtdInfo;
+            IDtdInfo? dtdInfo = _reader.DtdInfo;
             if (dtdInfo != null)
                 LoadDocumentType(dtdInfo, dtNode);
             else
@@ -454,18 +458,18 @@ private XmlDocumentType LoadDocumentTypeNode()
         // because we do not want to let users extend these (if we would allow this, XmlDataDocument would have a problem, because
         // they do not know that those nodes should not be mapped). It can be also used for an optimized load path when if the
         // XmlDocument is not extended if XmlDocumentType and XmlDeclaration handling is added.
-        private XmlNode LoadNodeDirect()
+        private XmlNode? LoadNodeDirect()
         {
-            XmlReader r = _reader;
-            XmlNode parent = null;
+            XmlReader r = _reader!;
+            XmlNode? parent = null;
             do
             {
-                XmlNode node = null;
+                XmlNode? node = null;
                 switch (r.NodeType)
                 {
                     case XmlNodeType.Element:
-                        bool fEmptyElement = _reader.IsEmptyElement;
-                        XmlElement element = new XmlElement(_reader.Prefix, _reader.LocalName, _reader.NamespaceURI, _doc);
+                        bool fEmptyElement = _reader!.IsEmptyElement;
+                        XmlElement element = new XmlElement(_reader.Prefix, _reader.LocalName, _reader.NamespaceURI, _doc!);
                         element.IsEmpty = fEmptyElement;
 
                         if (_reader.MoveToFirstAttribute())
@@ -481,7 +485,7 @@ private XmlNode LoadNodeDirect()
                         // recursively load all children.
                         if (!fEmptyElement)
                         {
-                            parent.AppendChildForLoad(element, _doc);
+                            parent!.AppendChildForLoad(element, _doc!);
                             parent = element;
                             continue;
                         }
@@ -492,11 +496,12 @@ private XmlNode LoadNodeDirect()
                         }
 
                     case XmlNodeType.EndElement:
-                        Debug.Assert(parent.NodeType == XmlNodeType.Element);
+                        Debug.Assert(parent!.NodeType == XmlNodeType.Element);
                         if (parent.ParentNode == null)
                         {
                             return parent;
                         }
+
                         parent = parent.ParentNode;
                         continue;
 
@@ -512,13 +517,13 @@ private XmlNode LoadNodeDirect()
                         break;
 
                     case XmlNodeType.SignificantWhitespace:
-                        node = new XmlSignificantWhitespace(_reader.Value, _doc);
+                        node = new XmlSignificantWhitespace(_reader!.Value, _doc!);
                         break;
 
                     case XmlNodeType.Whitespace:
                         if (_preserveWhitespace)
                         {
-                            node = new XmlWhitespace(_reader.Value, _doc);
+                            node = new XmlWhitespace(_reader!.Value, _doc!);
                         }
                         else
                         {
@@ -527,29 +532,29 @@ private XmlNode LoadNodeDirect()
                         break;
 
                     case XmlNodeType.Text:
-                        node = new XmlText(_reader.Value, _doc);
+                        node = new XmlText(_reader!.Value, _doc!);
                         break;
 
                     case XmlNodeType.CDATA:
-                        node = new XmlCDataSection(_reader.Value, _doc);
+                        node = new XmlCDataSection(_reader!.Value, _doc!);
                         break;
 
                     case XmlNodeType.ProcessingInstruction:
-                        node = new XmlProcessingInstruction(_reader.Name, _reader.Value, _doc);
+                        node = new XmlProcessingInstruction(_reader!.Name, _reader.Value, _doc!);
                         break;
 
                     case XmlNodeType.Comment:
-                        node = new XmlComment(_reader.Value, _doc);
+                        node = new XmlComment(_reader!.Value, _doc!);
                         break;
 
                     default:
-                        throw UnexpectedNodeType(_reader.NodeType);
+                        throw UnexpectedNodeType(_reader!.NodeType);
                 }
 
                 Debug.Assert(node != null);
                 if (parent != null)
                 {
-                    parent.AppendChildForLoad(node, _doc);
+                    parent.AppendChildForLoad(node, _doc!);
                 }
                 else
                 {
@@ -563,18 +568,18 @@ private XmlNode LoadNodeDirect()
 
         private XmlAttribute LoadAttributeNodeDirect()
         {
-            XmlReader r = _reader;
+            XmlReader r = _reader!;
             XmlAttribute attr;
             if (r.IsDefault)
             {
-                XmlUnspecifiedAttribute defattr = new XmlUnspecifiedAttribute(r.Prefix, r.LocalName, r.NamespaceURI, _doc);
+                XmlUnspecifiedAttribute defattr = new XmlUnspecifiedAttribute(r.Prefix, r.LocalName, r.NamespaceURI, _doc!);
                 LoadAttributeValue(defattr, true);
                 defattr.SetSpecified(false);
                 return defattr;
             }
             else
             {
-                attr = new XmlAttribute(r.Prefix, r.LocalName, r.NamespaceURI, _doc);
+                attr = new XmlAttribute(r.Prefix, r.LocalName, r.NamespaceURI, _doc!);
                 LoadAttributeValue(attr, true);
                 return attr;
             }
@@ -582,7 +587,7 @@ private XmlAttribute LoadAttributeNodeDirect()
 
         internal void ParseDocumentType(XmlDocumentType dtNode)
         {
-            XmlDocument doc = dtNode.OwnerDocument;
+            XmlDocument doc = dtNode.OwnerDocument!;
             //if xmlresolver is set on doc, use that one, otherwise use the default one being created by xmlvalidatingreader
             if (doc.HasSetResolver)
                 ParseDocumentType(dtNode, true, doc.GetResolver());
@@ -590,10 +595,10 @@ internal void ParseDocumentType(XmlDocumentType dtNode)
                 ParseDocumentType(dtNode, false, null);
         }
 
-        private void ParseDocumentType(XmlDocumentType dtNode, bool bUseResolver, XmlResolver resolver)
+        private void ParseDocumentType(XmlDocumentType dtNode, bool bUseResolver, XmlResolver? resolver)
         {
             _doc = dtNode.OwnerDocument;
-            XmlParserContext pc = new XmlParserContext(null, new XmlNamespaceManager(_doc.NameTable), null, null, null, null, _doc.BaseURI, string.Empty, XmlSpace.None);
+            XmlParserContext pc = new XmlParserContext(null, new XmlNamespaceManager(_doc!.NameTable), null, null, null, null, _doc.BaseURI, string.Empty, XmlSpace.None);
             XmlTextReaderImpl tr = new XmlTextReaderImpl("", XmlNodeType.Element, pc);
             tr.Namespaces = dtNode.ParseWithNamespaces;
             if (bUseResolver)
@@ -610,7 +615,7 @@ private void ParseDocumentType(XmlDocumentType dtNode, bool bUseResolver, XmlRes
 
         private void LoadDocumentType(IDtdInfo dtdInfo, XmlDocumentType dtNode)
         {
-            SchemaInfo schInfo = dtdInfo as SchemaInfo;
+            SchemaInfo? schInfo = dtdInfo as SchemaInfo;
             if (schInfo == null)
             {
                 throw new XmlException(SR.Xml_InternalError, string.Empty);
@@ -620,7 +625,7 @@ private void LoadDocumentType(IDtdInfo dtdInfo, XmlDocumentType dtNode)
             if (schInfo != null)
             {
                 //set the schema information into the document
-                _doc.DtdSchemaInfo = schInfo;
+                _doc!.DtdSchemaInfo = schInfo;
 
                 // Notation hashtable
                 if (schInfo.Notations != null)
@@ -677,11 +682,11 @@ private void LoadDocumentType(IDtdInfo dtdInfo, XmlDocumentType dtNode)
         }
 #pragma warning restore 618
 
-        private XmlParserContext GetContext(XmlNode node)
+        private XmlParserContext GetContext(XmlNode? node)
         {
-            string lang = null;
+            string? lang = null;
             XmlSpace spaceMode = XmlSpace.None;
-            XmlDocumentType docType = _doc.DocumentType;
+            XmlDocumentType? docType = _doc!.DocumentType;
             string baseURI = _doc.BaseURI;
             //constructing xmlnamespace
             HashSet<string> prefixes = new HashSet<string>();
@@ -692,7 +697,7 @@ private XmlParserContext GetContext(XmlNode node)
             // Process all xmlns, xmlns:prefix, xml:space and xml:lang attributes
             while (node != null && node != _doc)
             {
-                XmlElement element = node as XmlElement;
+                XmlElement? element = node as XmlElement;
                 if (element != null && element.HasAttributes)
                 {
                     mgr.PushScope();
@@ -725,6 +730,7 @@ private XmlParserContext GetContext(XmlNode node)
                         }
                     }
                 }
+
                 node = node.ParentNode;
             }
             return new XmlParserContext(
@@ -758,7 +764,7 @@ internal XmlNamespaceManager ParsePartialContent(XmlNode parentNode, string inne
 
                 if (nt == XmlNodeType.Entity)
                 {
-                    XmlNode node = null;
+                    XmlNode? node = null;
                     while (_reader.Read() && (node = LoadNodeDirect()) != null)
                     {
                         parentNode.AppendChildForLoad(node, _doc);
@@ -766,19 +772,21 @@ internal XmlNamespaceManager ParsePartialContent(XmlNode parentNode, string inne
                 }
                 else
                 {
-                    XmlNode node = null;
+                    XmlNode? node = null;
                     while (_reader.Read() && (node = LoadNode(true)) != null)
                     {
                         parentNode.AppendChildForLoad(node, _doc);
                     }
                 }
+
                 _doc.IsLoading = bOrigLoading;
             }
             finally
             {
                 _reader.Close();
             }
-            return pc.NamespaceManager;
+
+            return pc.NamespaceManager!;
         }
 
         internal void LoadInnerXmlElement(XmlElement node, string innerxmltext)
@@ -807,9 +815,9 @@ private void RemoveDuplicateNamespace(XmlElement elem, XmlNamespaceManager mgr,
                 for (int i = cAttrs - 1; i >= 0; --i)
                 {
                     XmlAttribute attr = attrs[i];
-                    if (attr.Prefix == _doc.strXmlns)
+                    if (attr.Prefix == _doc!.strXmlns)
                     {
-                        string nsUri = mgr.LookupNamespace(attr.LocalName);
+                        string? nsUri = mgr.LookupNamespace(attr.LocalName);
                         if (nsUri != null)
                         {
                             if (attr.Value == nsUri)
@@ -844,14 +852,15 @@ private void RemoveDuplicateNamespace(XmlElement elem, XmlNamespaceManager mgr,
                 }
             }
             //now recursively remove the duplicate attributes on the children
-            XmlNode child = elem.FirstChild;
+            XmlNode? child = elem.FirstChild;
             while (child != null)
             {
-                XmlElement childElem = child as XmlElement;
+                XmlElement? childElem = child as XmlElement;
                 if (childElem != null)
                     RemoveDuplicateNamespace(childElem, mgr, true);
                 child = child.NextSibling;
             }
+
             mgr.PopScope();
         }
 
@@ -871,7 +880,7 @@ internal void ExpandEntityReference(XmlEntityReference eref)
         {
             //when the ent ref is not associated w/ an entity, append an empty string text node as child
             _doc = eref.OwnerDocument;
-            bool bOrigLoadingState = _doc.IsLoading;
+            bool bOrigLoadingState = _doc!.IsLoading;
             _doc.IsLoading = true;
             switch (eref.Name)
             {
@@ -939,7 +948,7 @@ private XmlReader CreateInnerXmlReader(string xmlFragment, XmlNodeType nt, XmlPa
             }
             Debug.Assert(tr.EntityHandling == EntityHandling.ExpandCharEntities);
 
-            XmlDocumentType dtdNode = doc.DocumentType;
+            XmlDocumentType? dtdNode = doc.DocumentType;
             if (dtdNode != null)
             {
                 tr.Namespaces = dtdNode.ParseWithNamespaces;
@@ -968,12 +977,12 @@ private XmlReader CreateInnerXmlReader(string xmlFragment, XmlNodeType nt, XmlPa
         }
 #pragma warning restore 618
 
-        internal static void ParseXmlDeclarationValue(string strValue, out string version, out string encoding, out string standalone)
+        internal static void ParseXmlDeclarationValue(string strValue, out string? version, out string? encoding, out string? standalone)
         {
             version = null;
             encoding = null;
             standalone = null;
-            XmlTextReaderImpl tempreader = new XmlTextReaderImpl(strValue, (XmlParserContext)null);
+            XmlTextReaderImpl tempreader = new XmlTextReaderImpl(strValue, (XmlParserContext?)null);
             try
             {
                 tempreader.Read();
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlName.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlName.cs
index eeefd61f1988cf..504245a91df73c 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlName.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlName.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     using System.Text;
@@ -12,12 +13,12 @@ internal class XmlName : IXmlSchemaInfo
         private readonly string _prefix;
         private readonly string _localName;
         private readonly string _ns;
-        private string _name;
+        private string? _name;
         private readonly int _hashCode;
         internal XmlDocument ownerDoc;
         internal XmlName next;
 
-        public static XmlName Create(string prefix, string localName, string ns, int hashCode, XmlDocument ownerDoc, XmlName next, IXmlSchemaInfo schemaInfo)
+        public static XmlName Create(string prefix, string localName, string ns, int hashCode, XmlDocument ownerDoc, XmlName next, IXmlSchemaInfo? schemaInfo)
         {
             if (schemaInfo == null)
             {
@@ -139,7 +140,7 @@ public virtual bool IsNil
             }
         }
 
-        public virtual XmlSchemaSimpleType MemberType
+        public virtual XmlSchemaSimpleType? MemberType
         {
             get
             {
@@ -147,7 +148,7 @@ public virtual XmlSchemaSimpleType MemberType
             }
         }
 
-        public virtual XmlSchemaType SchemaType
+        public virtual XmlSchemaType? SchemaType
         {
             get
             {
@@ -155,7 +156,7 @@ public virtual XmlSchemaType SchemaType
             }
         }
 
-        public virtual XmlSchemaElement SchemaElement
+        public virtual XmlSchemaElement? SchemaElement
         {
             get
             {
@@ -163,7 +164,7 @@ public virtual XmlSchemaElement SchemaElement
             }
         }
 
-        public virtual XmlSchemaAttribute SchemaAttribute
+        public virtual XmlSchemaAttribute? SchemaAttribute
         {
             get
             {
@@ -171,7 +172,7 @@ public virtual XmlSchemaAttribute SchemaAttribute
             }
         }
 
-        public virtual bool Equals(IXmlSchemaInfo schemaInfo)
+        public virtual bool Equals(IXmlSchemaInfo? schemaInfo)
         {
             return schemaInfo == null;
         }
@@ -190,9 +191,9 @@ public static int GetHashCode(string name)
     internal sealed class XmlNameEx : XmlName
     {
         private byte _flags;
-        private readonly XmlSchemaSimpleType _memberType;
-        private readonly XmlSchemaType _schemaType;
-        private readonly object _decl;
+        private readonly XmlSchemaSimpleType? _memberType;
+        private readonly XmlSchemaType? _schemaType;
+        private readonly object? _decl;
 
         // flags
         // 0,1  : Validity
@@ -211,7 +212,7 @@ internal XmlNameEx(string prefix, string localName, string ns, int hashCode, Xml
             _schemaType = schemaInfo.SchemaType;
             _decl = schemaInfo.SchemaElement != null
                    ? (object)schemaInfo.SchemaElement
-                   : (object)schemaInfo.SchemaAttribute;
+                   : (object?)schemaInfo.SchemaAttribute;
         }
 
         public override XmlSchemaValidity Validity
@@ -238,7 +239,7 @@ public override bool IsNil
             }
         }
 
-        public override XmlSchemaSimpleType MemberType
+        public override XmlSchemaSimpleType? MemberType
         {
             get
             {
@@ -246,7 +247,7 @@ public override XmlSchemaSimpleType MemberType
             }
         }
 
-        public override XmlSchemaType SchemaType
+        public override XmlSchemaType? SchemaType
         {
             get
             {
@@ -254,7 +255,7 @@ public override XmlSchemaType SchemaType
             }
         }
 
-        public override XmlSchemaElement SchemaElement
+        public override XmlSchemaElement? SchemaElement
         {
             get
             {
@@ -262,7 +263,7 @@ public override XmlSchemaElement SchemaElement
             }
         }
 
-        public override XmlSchemaAttribute SchemaAttribute
+        public override XmlSchemaAttribute? SchemaAttribute
         {
             get
             {
@@ -287,16 +288,16 @@ public void SetIsNil(bool value)
             else _flags = (byte)(_flags & ~IsNilBit);
         }
 
-        public override bool Equals(IXmlSchemaInfo schemaInfo)
+        public override bool Equals(IXmlSchemaInfo? schemaInfo)
         {
             if (schemaInfo != null
                 && schemaInfo.Validity == (XmlSchemaValidity)(_flags & ValidityMask)
                 && schemaInfo.IsDefault == ((_flags & IsDefaultBit) != 0)
                 && schemaInfo.IsNil == ((_flags & IsNilBit) != 0)
-                && (object)schemaInfo.MemberType == (object)_memberType
-                && (object)schemaInfo.SchemaType == (object)_schemaType
-                && (object)schemaInfo.SchemaElement == (object)(_decl as XmlSchemaElement)
-                && (object)schemaInfo.SchemaAttribute == (object)(_decl as XmlSchemaAttribute))
+                && (object?)schemaInfo.MemberType == (object?)_memberType
+                && (object?)schemaInfo.SchemaType == (object?)_schemaType
+                && (object?)schemaInfo.SchemaElement == (object?)(_decl as XmlSchemaElement)
+                && (object?)schemaInfo.SchemaAttribute == (object?)(_decl as XmlSchemaAttribute))
             {
                 return true;
             }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNamedNodeMap.SmallXmlNodeList.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNamedNodeMap.SmallXmlNodeList.cs
index 6c738e031aaf9a..a57403419940a1 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNamedNodeMap.SmallXmlNodeList.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNamedNodeMap.SmallXmlNodeList.cs
@@ -1,8 +1,10 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics;
 
 namespace System.Xml
 {
@@ -16,7 +18,7 @@ internal struct SmallXmlNodeList
             // object.
             // Otherwise, field is an List<object>. Once the field upgrades to an List<object>, it
             // never degrades back, even if all elements are removed.
-            private object _field;
+            private object? _field;
 
             public int Count
             {
@@ -25,7 +27,7 @@ public int Count
                     if (_field == null)
                         return 0;
 
-                    List<object> list = _field as List<object>;
+                    List<object>? list = _field as List<object>;
                     if (list != null)
                         return list.Count;
 
@@ -40,7 +42,7 @@ public object this[int index]
                     if (_field == null)
                         throw new ArgumentOutOfRangeException(nameof(index));
 
-                    List<object> list = _field as List<object>;
+                    List<object>? list = _field as List<object>;
                     if (list != null)
                         return list[index];
 
@@ -57,10 +59,11 @@ public void Add(object value)
                 {
                     if (value == null)
                     {
+                        Debug.Fail("Null was added to the collection which didn't expect it");
                         // If a single null value needs to be stored, then
                         // upgrade to an ArrayList
                         List<object> temp = new List<object>();
-                        temp.Add(null);
+                        temp.Add(null!);
                         _field = temp;
                     }
                     else
@@ -69,7 +72,7 @@ public void Add(object value)
                     return;
                 }
 
-                List<object> list = _field as List<object>;
+                List<object>? list = _field as List<object>;
                 if (list != null)
                 {
                     list.Add(value);
@@ -88,7 +91,7 @@ public void RemoveAt(int index)
                 if (_field == null)
                     throw new ArgumentOutOfRangeException(nameof(index));
 
-                List<object> list = _field as List<object>;
+                List<object?>? list = _field as List<object?>;
                 if (list != null)
                 {
                     list.RemoveAt(index);
@@ -111,7 +114,7 @@ public void Insert(int index, object value)
                     return;
                 }
 
-                List<object> list = _field as List<object>;
+                List<object>? list = _field as List<object>;
                 if (list != null)
                 {
                     list.Insert(index, value);
@@ -156,6 +159,7 @@ public object Current
                         {
                             throw new InvalidOperationException();
                         }
+
                         return _loneValue;
                     }
                 }
@@ -167,6 +171,7 @@ public bool MoveNext()
                         _position = 0;
                         return true;
                     }
+
                     _position = 1;
                     return false;
                 }
@@ -184,7 +189,7 @@ public IEnumerator GetEnumerator()
                     return XmlDocument.EmptyEnumerator;
                 }
 
-                List<object> list = _field as List<object>;
+                List<object>? list = _field as List<object>;
                 if (list != null)
                 {
                     return list.GetEnumerator();
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNamedNodemap.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNamedNodemap.cs
index 2ffb6900ff65cc..54b0c64ce4a348 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNamedNodemap.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNamedNodemap.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections;
 
 namespace System.Xml
@@ -17,16 +18,17 @@ internal XmlNamedNodeMap(XmlNode parent)
         }
 
         // Retrieves a XmlNode specified by name.
-        public virtual XmlNode GetNamedItem(string name)
+        public virtual XmlNode? GetNamedItem(string name)
         {
             int offset = FindNodeOffset(name);
             if (offset >= 0)
                 return (XmlNode)nodes[offset];
+
             return null;
         }
 
         // Adds a XmlNode using its Name property
-        public virtual XmlNode SetNamedItem(XmlNode node)
+        public virtual XmlNode? SetNamedItem(XmlNode? node)
         {
             if (node == null)
                 return null;
@@ -44,13 +46,14 @@ public virtual XmlNode SetNamedItem(XmlNode node)
         }
 
         // Removes the node specified by name.
-        public virtual XmlNode RemoveNamedItem(string name)
+        public virtual XmlNode? RemoveNamedItem(string name)
         {
             int offset = FindNodeOffset(name);
             if (offset >= 0)
             {
                 return RemoveNodeAt(offset);
             }
+
             return null;
         }
 
@@ -64,7 +67,7 @@ public virtual int Count
         }
 
         // Retrieves the node at the specified index in this XmlNamedNodeMap.
-        public virtual XmlNode Item(int index)
+        public virtual XmlNode? Item(int index)
         {
             if (index < 0 || index >= nodes.Count)
                 return null;
@@ -83,22 +86,24 @@ public virtual XmlNode Item(int index)
         //
 
         // Retrieves a node specified by LocalName and NamespaceURI.
-        public virtual XmlNode GetNamedItem(string localName, string namespaceURI)
+        public virtual XmlNode? GetNamedItem(string localName, string? namespaceURI)
         {
             int offset = FindNodeOffset(localName, namespaceURI);
             if (offset >= 0)
                 return (XmlNode)nodes[offset];
+
             return null;
         }
 
         // Removes a node specified by local name and namespace URI.
-        public virtual XmlNode RemoveNamedItem(string localName, string namespaceURI)
+        public virtual XmlNode? RemoveNamedItem(string localName, string? namespaceURI)
         {
             int offset = FindNodeOffset(localName, namespaceURI);
             if (offset >= 0)
             {
                 return RemoveNodeAt(offset);
             }
+
             return null;
         }
 
@@ -121,7 +126,7 @@ internal int FindNodeOffset(string name)
             return -1;
         }
 
-        internal int FindNodeOffset(string localName, string namespaceURI)
+        internal int FindNodeOffset(string localName, string? namespaceURI)
         {
             int c = this.Count;
             for (int i = 0; i < c; i++)
@@ -137,13 +142,14 @@ internal int FindNodeOffset(string localName, string namespaceURI)
 
         internal virtual XmlNode AddNode(XmlNode node)
         {
-            XmlNode oldParent;
+            XmlNode? oldParent;
             if (node.NodeType == XmlNodeType.Attribute)
                 oldParent = ((XmlAttribute)node).OwnerElement;
             else
                 oldParent = node.ParentNode;
-            string nodeValue = node.Value;
-            XmlNodeChangedEventArgs args = parent.GetEventArgs(node, oldParent, parent, nodeValue, nodeValue, XmlNodeChangedAction.Insert);
+
+            string? nodeValue = node.Value;
+            XmlNodeChangedEventArgs? args = parent.GetEventArgs(node, oldParent, parent, nodeValue, nodeValue, XmlNodeChangedAction.Insert);
 
             if (args != null)
                 parent.BeforeEvent(args);
@@ -159,17 +165,19 @@ internal virtual XmlNode AddNode(XmlNode node)
 
         internal virtual XmlNode AddNodeForLoad(XmlNode node, XmlDocument doc)
         {
-            XmlNodeChangedEventArgs args = doc.GetInsertEventArgsForLoad(node, parent);
+            XmlNodeChangedEventArgs? args = doc.GetInsertEventArgsForLoad(node, parent);
             if (args != null)
             {
                 doc.BeforeEvent(args);
             }
+
             nodes.Add(node);
             node.SetParent(parent);
             if (args != null)
             {
                 doc.AfterEvent(args);
             }
+
             return node;
         }
 
@@ -177,8 +185,8 @@ internal virtual XmlNode RemoveNodeAt(int i)
         {
             XmlNode oldNode = (XmlNode)nodes[i];
 
-            string oldNodeValue = oldNode.Value;
-            XmlNodeChangedEventArgs args = parent.GetEventArgs(oldNode, parent, null, oldNodeValue, oldNodeValue, XmlNodeChangedAction.Remove);
+            string? oldNodeValue = oldNode.Value;
+            XmlNodeChangedEventArgs? args = parent.GetEventArgs(oldNode, parent, null, oldNodeValue, oldNodeValue, XmlNodeChangedAction.Remove);
 
             if (args != null)
                 parent.BeforeEvent(args);
@@ -201,14 +209,14 @@ internal XmlNode ReplaceNodeAt(int i, XmlNode node)
 
         internal virtual XmlNode InsertNodeAt(int i, XmlNode node)
         {
-            XmlNode oldParent;
+            XmlNode? oldParent;
             if (node.NodeType == XmlNodeType.Attribute)
                 oldParent = ((XmlAttribute)node).OwnerElement;
             else
                 oldParent = node.ParentNode;
 
-            string nodeValue = node.Value;
-            XmlNodeChangedEventArgs args = parent.GetEventArgs(node, oldParent, parent, nodeValue, nodeValue, XmlNodeChangedAction.Insert);
+            string? nodeValue = node.Value;
+            XmlNodeChangedEventArgs? args = parent.GetEventArgs(node, oldParent, parent, nodeValue, nodeValue, XmlNodeChangedAction.Insert);
 
             if (args != null)
                 parent.BeforeEvent(args);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNode.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNode.cs
index a2e7c57a2e3897..c31e084a6e2e08 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNode.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNode.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.IO;
 using System.Collections;
@@ -10,6 +11,7 @@
 using System.Xml.XPath;
 using MS.Internal.Xml.XPath;
 using System.Globalization;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml
 {
@@ -17,7 +19,7 @@ namespace System.Xml
     [DebuggerDisplay("{debuggerDisplayProxy}")]
     public abstract class XmlNode : ICloneable, IEnumerable, IXPathNavigable
     {
-        internal XmlNode parentNode; //this pointer is reused to save the userdata information, need to prevent internal user access the pointer directly.
+        internal XmlNode? parentNode; //this pointer is reused to save the userdata information, need to prevent internal user access the pointer directly.
 
         internal XmlNode()
         {
@@ -27,61 +29,66 @@ internal XmlNode(XmlDocument doc)
         {
             if (doc == null)
                 throw new ArgumentException(SR.Xdom_Node_Null_Doc);
+
             this.parentNode = doc;
         }
 
-        public virtual XPathNavigator CreateNavigator()
+        public virtual XPathNavigator? CreateNavigator()
         {
-            XmlDocument thisAsDoc = this as XmlDocument;
+            XmlDocument? thisAsDoc = this as XmlDocument;
             if (thisAsDoc != null)
             {
                 return thisAsDoc.CreateNavigator(this);
             }
-            XmlDocument doc = OwnerDocument;
+
+            XmlDocument? doc = OwnerDocument;
             Debug.Assert(doc != null);
             return doc.CreateNavigator(this);
         }
 
         // Selects the first node that matches the xpath expression
-        public XmlNode SelectSingleNode(string xpath)
+        public XmlNode? SelectSingleNode(string xpath)
         {
-            XmlNodeList list = SelectNodes(xpath);
+            XmlNodeList? list = SelectNodes(xpath);
             // SelectNodes returns null for certain node types
             return list != null ? list[0] : null;
         }
 
         // Selects the first node that matches the xpath expression and given namespace context.
-        public XmlNode SelectSingleNode(string xpath, XmlNamespaceManager nsmgr)
+        public XmlNode? SelectSingleNode(string xpath, XmlNamespaceManager nsmgr)
         {
-            XPathNavigator xn = (this).CreateNavigator();
+            XPathNavigator? xn = (this).CreateNavigator();
             //if the method is called on node types like DocType, Entity, XmlDeclaration,
             //the navigator returned is null. So just return null from here for those node types.
             if (xn == null)
                 return null;
+
             XPathExpression exp = xn.Compile(xpath);
             exp.SetContext(nsmgr);
             return new XPathNodeList(xn.Select(exp))[0];
         }
 
         // Selects all nodes that match the xpath expression
-        public XmlNodeList SelectNodes(string xpath)
+        public XmlNodeList? SelectNodes(string xpath)
         {
-            XPathNavigator n = (this).CreateNavigator();
+            XPathNavigator? n = (this).CreateNavigator();
             //if the method is called on node types like DocType, Entity, XmlDeclaration,
             //the navigator returned is null. So just return null from here for those node types.
             if (n == null)
                 return null;
+
             return new XPathNodeList(n.Select(xpath));
         }
 
         // Selects all nodes that match the xpath expression and given namespace context.
-        public XmlNodeList SelectNodes(string xpath, XmlNamespaceManager nsmgr)
+        public XmlNodeList? SelectNodes(string xpath, XmlNamespaceManager nsmgr)
         {
-            XPathNavigator xn = (this).CreateNavigator();
+            XPathNavigator? xn = (this).CreateNavigator();
             //if the method is called on node types like DocType, Entity, XmlDeclaration,
             //the navigator returned is null. So just return null from here for those node types.
             if (xn == null)
                 return null;
+
             XPathExpression exp = xn.Compile(xpath);
             exp.SetContext(nsmgr);
             return new XPathNodeList(xn.Select(exp));
@@ -94,7 +101,7 @@ public abstract string Name
         }
 
         // Gets or sets the value of the node.
-        public virtual string Value
+        public virtual string? Value
         {
             get { return null; }
             set { throw new InvalidOperationException(SR.Format(CultureInfo.InvariantCulture, SR.Xdom_Node_SetVal, NodeType.ToString())); }
@@ -107,7 +114,7 @@ public abstract XmlNodeType NodeType
         }
 
         // Gets the parent of this node (for nodes that can have parents).
-        public virtual XmlNode ParentNode
+        public virtual XmlNode? ParentNode
         {
             get
             {
@@ -119,21 +126,23 @@ public virtual XmlNode ParentNode
                 }
 
                 // Linear lookup through the children of the document
-                XmlLinkedNode firstChild = parentNode.FirstChild as XmlLinkedNode;
+                XmlLinkedNode? firstChild = parentNode.FirstChild as XmlLinkedNode;
                 if (firstChild != null)
                 {
-                    XmlLinkedNode node = firstChild;
+                    XmlLinkedNode? node = firstChild;
                     do
                     {
                         if (node == this)
                         {
                             return parentNode;
                         }
+
                         node = node.next;
                     }
                     while (node != null
                            && node != firstChild);
                 }
+
                 return null;
             }
         }
@@ -145,26 +154,26 @@ public virtual XmlNodeList ChildNodes
         }
 
         // Gets the node immediately preceding this node.
-        public virtual XmlNode PreviousSibling
+        public virtual XmlNode? PreviousSibling
         {
             get { return null; }
         }
 
         // Gets the node immediately following this node.
-        public virtual XmlNode NextSibling
+        public virtual XmlNode? NextSibling
         {
             get { return null; }
         }
 
         // Gets a XmlAttributeCollection containing the attributes
         // of this node.
-        public virtual XmlAttributeCollection Attributes
+        public virtual XmlAttributeCollection? Attributes
         {
             get { return null; }
         }
 
         // Gets the XmlDocument that contains this node.
-        public virtual XmlDocument OwnerDocument
+        public virtual XmlDocument? OwnerDocument
         {
             get
             {
@@ -176,11 +185,11 @@ public virtual XmlDocument OwnerDocument
         }
 
         // Gets the first child of this node.
-        public virtual XmlNode FirstChild
+        public virtual XmlNode? FirstChild
         {
             get
             {
-                XmlLinkedNode linkedNode = LastNode;
+                XmlLinkedNode? linkedNode = LastNode;
                 if (linkedNode != null)
                     return linkedNode.next;
 
@@ -189,7 +198,7 @@ public virtual XmlNode FirstChild
         }
 
         // Gets the last child of this node.
-        public virtual XmlNode LastChild
+        public virtual XmlNode? LastChild
         {
             get { return LastNode; }
         }
@@ -199,7 +208,7 @@ internal virtual bool IsContainer
             get { return false; }
         }
 
-        internal virtual XmlLinkedNode LastNode
+        internal virtual XmlLinkedNode? LastNode
         {
             get { return null; }
             set { }
@@ -207,7 +216,7 @@ internal virtual XmlLinkedNode LastNode
 
         internal bool AncestorNode(XmlNode node)
         {
-            XmlNode n = this.ParentNode;
+            XmlNode? n = this.ParentNode;
 
             while (n != null && n != this)
             {
@@ -222,14 +231,14 @@ internal bool AncestorNode(XmlNode node)
         //trace to the top to find out its parent node.
         internal bool IsConnected()
         {
-            XmlNode parent = ParentNode;
+            XmlNode? parent = ParentNode;
             while (parent != null && !(parent.NodeType == XmlNodeType.Document))
                 parent = parent.ParentNode;
             return parent != null;
         }
 
         // Inserts the specified node immediately before the specified reference node.
-        public virtual XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
+        public virtual XmlNode? InsertBefore(XmlNode newChild, XmlNode? refChild)
         {
             if (this == newChild || AncestorNode(newChild))
                 throw new ArgumentException(SR.Xdom_Node_Insert_Child);
@@ -246,8 +255,8 @@ public virtual XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
             if (newChild == refChild)
                 return newChild;
 
-            XmlDocument childDoc = newChild.OwnerDocument;
-            XmlDocument thisDoc = OwnerDocument;
+            XmlDocument? childDoc = newChild.OwnerDocument;
+            XmlDocument? thisDoc = OwnerDocument;
             if (childDoc != null && childDoc != thisDoc && childDoc != this)
                 throw new ArgumentException(SR.Xdom_Node_Insert_Context);
 
@@ -260,8 +269,8 @@ public virtual XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
             // special case for doc-fragment.
             if (newChild.NodeType == XmlNodeType.DocumentFragment)
             {
-                XmlNode first = newChild.FirstChild;
-                XmlNode node = first;
+                XmlNode? first = newChild.FirstChild;
+                XmlNode? node = first;
                 if (node != null)
                 {
                     newChild.RemoveChild(node);
@@ -269,6 +278,7 @@ public virtual XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
                     // insert the rest of the children after this one.
                     InsertAfter(newChild, node);
                 }
+
                 return first;
             }
 
@@ -278,8 +288,8 @@ public virtual XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
             XmlLinkedNode newNode = (XmlLinkedNode)newChild;
             XmlLinkedNode refNode = (XmlLinkedNode)refChild;
 
-            string newChildValue = newChild.Value;
-            XmlNodeChangedEventArgs args = GetEventArgs(newChild, newChild.ParentNode, this, newChildValue, newChildValue, XmlNodeChangedAction.Insert);
+            string? newChildValue = newChild.Value;
+            XmlNodeChangedEventArgs? args = GetEventArgs(newChild, newChild.ParentNode, this, newChildValue, newChildValue, XmlNodeChangedAction.Insert);
 
             if (args != null)
                 BeforeEvent(args);
@@ -287,7 +297,7 @@ public virtual XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
             if (refNode == FirstChild)
             {
                 newNode.next = refNode;
-                LastNode.next = newNode;
+                LastNode!.next = newNode;
                 newNode.SetParent(this);
 
                 if (newNode.IsText)
@@ -300,7 +310,7 @@ public virtual XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
             }
             else
             {
-                XmlLinkedNode prevNode = (XmlLinkedNode)refNode.PreviousSibling;
+                XmlLinkedNode prevNode = (XmlLinkedNode)refNode.PreviousSibling!;
 
                 newNode.next = refNode;
                 prevNode.next = newNode;
@@ -343,7 +353,7 @@ public virtual XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
         }
 
         // Inserts the specified node immediately after the specified reference node.
-        public virtual XmlNode InsertAfter(XmlNode newChild, XmlNode refChild)
+        public virtual XmlNode? InsertAfter(XmlNode newChild, XmlNode? refChild)
         {
             if (this == newChild || AncestorNode(newChild))
                 throw new ArgumentException(SR.Xdom_Node_Insert_Child);
@@ -360,8 +370,8 @@ public virtual XmlNode InsertAfter(XmlNode newChild, XmlNode refChild)
             if (newChild == refChild)
                 return newChild;
 
-            XmlDocument childDoc = newChild.OwnerDocument;
-            XmlDocument thisDoc = OwnerDocument;
+            XmlDocument? childDoc = newChild.OwnerDocument;
+            XmlDocument? thisDoc = OwnerDocument;
             if (childDoc != null && childDoc != thisDoc && childDoc != this)
                 throw new ArgumentException(SR.Xdom_Node_Insert_Context);
 
@@ -375,11 +385,11 @@ public virtual XmlNode InsertAfter(XmlNode newChild, XmlNode refChild)
             if (newChild.NodeType == XmlNodeType.DocumentFragment)
             {
                 XmlNode last = refChild;
-                XmlNode first = newChild.FirstChild;
-                XmlNode node = first;
+                XmlNode? first = newChild.FirstChild;
+                XmlNode? node = first;
                 while (node != null)
                 {
-                    XmlNode next = node.NextSibling;
+                    XmlNode? next = node.NextSibling;
                     newChild.RemoveChild(node);
                     InsertAfter(node, last);
                     last = node;
@@ -394,8 +404,8 @@ public virtual XmlNode InsertAfter(XmlNode newChild, XmlNode refChild)
             XmlLinkedNode newNode = (XmlLinkedNode)newChild;
             XmlLinkedNode refNode = (XmlLinkedNode)refChild;
 
-            string newChildValue = newChild.Value;
-            XmlNodeChangedEventArgs args = GetEventArgs(newChild, newChild.ParentNode, this, newChildValue, newChildValue, XmlNodeChangedAction.Insert);
+            string? newChildValue = newChild.Value;
+            XmlNodeChangedEventArgs? args = GetEventArgs(newChild, newChild.ParentNode, this, newChildValue, newChildValue, XmlNodeChangedAction.Insert);
 
             if (args != null)
                 BeforeEvent(args);
@@ -417,7 +427,7 @@ public virtual XmlNode InsertAfter(XmlNode newChild, XmlNode refChild)
             }
             else
             {
-                XmlLinkedNode nextNode = refNode.next;
+                XmlLinkedNode nextNode = refNode.next!;
 
                 newNode.next = nextNode;
                 refNode.next = newNode;
@@ -463,9 +473,9 @@ public virtual XmlNode InsertAfter(XmlNode newChild, XmlNode refChild)
         // Replaces the child node oldChild with newChild node.
         public virtual XmlNode ReplaceChild(XmlNode newChild, XmlNode oldChild)
         {
-            XmlNode nextNode = oldChild.NextSibling;
+            XmlNode? nextNode = oldChild.NextSibling;
             RemoveChild(oldChild);
-            XmlNode node = InsertBefore(newChild, nextNode);
+            XmlNode? node = InsertBefore(newChild, nextNode);
             return oldChild;
         }
 
@@ -480,13 +490,13 @@ public virtual XmlNode RemoveChild(XmlNode oldChild)
 
             XmlLinkedNode oldNode = (XmlLinkedNode)oldChild;
 
-            string oldNodeValue = oldNode.Value;
-            XmlNodeChangedEventArgs args = GetEventArgs(oldNode, this, null, oldNodeValue, oldNodeValue, XmlNodeChangedAction.Remove);
+            string? oldNodeValue = oldNode.Value;
+            XmlNodeChangedEventArgs? args = GetEventArgs(oldNode, this, null, oldNodeValue, oldNodeValue, XmlNodeChangedAction.Remove);
 
             if (args != null)
                 BeforeEvent(args);
 
-            XmlLinkedNode lastNode = LastNode;
+            XmlLinkedNode? lastNode = LastNode;
 
             if (oldNode == FirstChild)
             {
@@ -498,7 +508,7 @@ public virtual XmlNode RemoveChild(XmlNode oldChild)
                 }
                 else
                 {
-                    XmlLinkedNode nextNode = oldNode.next;
+                    XmlLinkedNode nextNode = oldNode.next!;
 
                     if (nextNode.IsText)
                     {
@@ -508,7 +518,7 @@ public virtual XmlNode RemoveChild(XmlNode oldChild)
                         }
                     }
 
-                    lastNode.next = nextNode;
+                    lastNode!.next = nextNode;
                     oldNode.next = null;
                     oldNode.SetParent(null);
                 }
@@ -517,7 +527,7 @@ public virtual XmlNode RemoveChild(XmlNode oldChild)
             {
                 if (oldNode == lastNode)
                 {
-                    XmlLinkedNode prevNode = (XmlLinkedNode)oldNode.PreviousSibling;
+                    XmlLinkedNode prevNode = (XmlLinkedNode)oldNode.PreviousSibling!;
                     prevNode.next = oldNode.next;
                     LastNode = prevNode;
                     oldNode.next = null;
@@ -525,8 +535,8 @@ public virtual XmlNode RemoveChild(XmlNode oldChild)
                 }
                 else
                 {
-                    XmlLinkedNode prevNode = (XmlLinkedNode)oldNode.PreviousSibling;
-                    XmlLinkedNode nextNode = oldNode.next;
+                    XmlLinkedNode prevNode = (XmlLinkedNode)oldNode.PreviousSibling!;
+                    XmlLinkedNode nextNode = oldNode.next!;
 
                     if (nextNode.IsText)
                     {
@@ -556,15 +566,15 @@ public virtual XmlNode RemoveChild(XmlNode oldChild)
         }
 
         // Adds the specified node to the beginning of the list of children of this node.
-        public virtual XmlNode PrependChild(XmlNode newChild)
+        public virtual XmlNode? PrependChild(XmlNode newChild)
         {
             return InsertBefore(newChild, FirstChild);
         }
 
         // Adds the specified node to the end of the list of children of this node.
-        public virtual XmlNode AppendChild(XmlNode newChild)
+        public virtual XmlNode? AppendChild(XmlNode newChild)
         {
-            XmlDocument thisDoc = OwnerDocument;
+            XmlDocument? thisDoc = OwnerDocument;
             if (thisDoc == null)
             {
                 thisDoc = this as XmlDocument;
@@ -578,22 +588,23 @@ public virtual XmlNode AppendChild(XmlNode newChild)
             if (newChild.ParentNode != null)
                 newChild.ParentNode.RemoveChild(newChild);
 
-            XmlDocument childDoc = newChild.OwnerDocument;
+            XmlDocument? childDoc = newChild.OwnerDocument;
             if (childDoc != null && childDoc != thisDoc && childDoc != this)
                 throw new ArgumentException(SR.Xdom_Node_Insert_Context);
 
             // special case for doc-fragment.
             if (newChild.NodeType == XmlNodeType.DocumentFragment)
             {
-                XmlNode first = newChild.FirstChild;
-                XmlNode node = first;
+                XmlNode? first = newChild.FirstChild;
+                XmlNode? node = first;
                 while (node != null)
                 {
-                    XmlNode next = node.NextSibling;
+                    XmlNode? next = node.NextSibling;
                     newChild.RemoveChild(node);
                     AppendChild(node);
                     node = next;
                 }
+
                 return first;
             }
 
@@ -604,13 +615,13 @@ public virtual XmlNode AppendChild(XmlNode newChild)
             if (!CanInsertAfter(newChild, LastChild))
                 throw new InvalidOperationException(SR.Xdom_Node_Insert_Location);
 
-            string newChildValue = newChild.Value;
-            XmlNodeChangedEventArgs args = GetEventArgs(newChild, newChild.ParentNode, this, newChildValue, newChildValue, XmlNodeChangedAction.Insert);
+            string? newChildValue = newChild.Value;
+            XmlNodeChangedEventArgs? args = GetEventArgs(newChild, newChild.ParentNode, this, newChildValue, newChildValue, XmlNodeChangedAction.Insert);
 
             if (args != null)
                 BeforeEvent(args);
 
-            XmlLinkedNode refNode = LastNode;
+            XmlLinkedNode? refNode = LastNode;
             XmlLinkedNode newNode = (XmlLinkedNode)newChild;
 
             if (refNode == null)
@@ -644,12 +655,12 @@ public virtual XmlNode AppendChild(XmlNode newChild)
         //the function is provided only at Load time to speed up Load process
         internal virtual XmlNode AppendChildForLoad(XmlNode newChild, XmlDocument doc)
         {
-            XmlNodeChangedEventArgs args = doc.GetInsertEventArgsForLoad(newChild, this);
+            XmlNodeChangedEventArgs? args = doc.GetInsertEventArgsForLoad(newChild, this);
 
             if (args != null)
                 doc.BeforeEvent(args);
 
-            XmlLinkedNode refNode = LastNode;
+            XmlLinkedNode? refNode = LastNode;
             XmlLinkedNode newNode = (XmlLinkedNode)newChild;
 
             if (refNode == null)
@@ -685,12 +696,12 @@ internal virtual bool IsValidChildType(XmlNodeType type)
             return false;
         }
 
-        internal virtual bool CanInsertBefore(XmlNode newChild, XmlNode refChild)
+        internal virtual bool CanInsertBefore(XmlNode newChild, XmlNode? refChild)
         {
             return true;
         }
 
-        internal virtual bool CanInsertAfter(XmlNode newChild, XmlNode refChild)
+        internal virtual bool CanInsertAfter(XmlNode newChild, XmlNode? refChild)
         {
             return true;
         }
@@ -706,7 +717,7 @@ public virtual bool HasChildNodes
 
         internal virtual void CopyChildren(XmlDocument doc, XmlNode container, bool deep)
         {
-            for (XmlNode child = container.FirstChild; child != null; child = child.NextSibling)
+            for (XmlNode? child = container.FirstChild; child != null; child = child.NextSibling)
             {
                 AppendChildForLoad(child.CloneNode(deep), doc);
             }
@@ -721,11 +732,11 @@ internal virtual void CopyChildren(XmlDocument doc, XmlNode container, bool deep
         // are no adjacent XmlText nodes.
         public virtual void Normalize()
         {
-            XmlNode firstChildTextLikeNode = null;
+            XmlNode? firstChildTextLikeNode = null;
             StringBuilder sb = StringBuilderCache.Acquire();
-            for (XmlNode crtChild = this.FirstChild; crtChild != null;)
+            for (XmlNode? crtChild = this.FirstChild; crtChild != null;)
             {
-                XmlNode nextChild = crtChild.NextSibling;
+                XmlNode? nextChild = crtChild.NextSibling;
                 switch (crtChild.NodeType)
                 {
                     case XmlNodeType.Text:
@@ -733,7 +744,7 @@ public virtual void Normalize()
                     case XmlNodeType.SignificantWhitespace:
                         {
                             sb.Append(crtChild.Value);
-                            XmlNode winner = NormalizeWinner(firstChildTextLikeNode, crtChild);
+                            XmlNode? winner = NormalizeWinner(firstChildTextLikeNode, crtChild);
                             if (winner == firstChildTextLikeNode)
                             {
                                 this.RemoveChild(crtChild);
@@ -744,6 +755,7 @@ public virtual void Normalize()
                                     this.RemoveChild(firstChildTextLikeNode);
                                 firstChildTextLikeNode = crtChild;
                             }
+
                             break;
                         }
                     case XmlNodeType.Element:
@@ -758,6 +770,7 @@ public virtual void Normalize()
                                 firstChildTextLikeNode.Value = sb.ToString();
                                 firstChildTextLikeNode = null;
                             }
+
                             sb.Remove(0, sb.Length);
                             break;
                         }
@@ -770,7 +783,7 @@ public virtual void Normalize()
             StringBuilderCache.Release(sb);
         }
 
-        private XmlNode NormalizeWinner(XmlNode firstNode, XmlNode secondNode)
+        private XmlNode? NormalizeWinner(XmlNode? firstNode, XmlNode secondNode)
         {
             //first node has the priority
             if (firstNode == null)
@@ -834,12 +847,12 @@ public virtual bool IsReadOnly
         {
             get
             {
-                XmlDocument doc = OwnerDocument;
+                XmlDocument? doc = OwnerDocument;
                 return HasReadOnlyParent(this);
             }
         }
 
-        internal static bool HasReadOnlyParent(XmlNode n)
+        internal static bool HasReadOnlyParent(XmlNode? n)
         {
             while (n != null)
             {
@@ -886,7 +899,7 @@ public IEnumerator GetEnumerator()
 
         private void AppendChildText(StringBuilder builder)
         {
-            for (XmlNode child = FirstChild; child != null; child = child.NextSibling)
+            for (XmlNode? child = FirstChild; child != null; child = child.NextSibling)
             {
                 if (child.FirstChild == null)
                 {
@@ -907,7 +920,7 @@ public virtual string InnerText
         {
             get
             {
-                XmlNode fc = FirstChild;
+                XmlNode? fc = FirstChild;
                 if (fc == null)
                 {
                     return string.Empty;
@@ -921,9 +934,10 @@ public virtual string InnerText
                         case XmlNodeType.CDATA:
                         case XmlNodeType.Whitespace:
                         case XmlNodeType.SignificantWhitespace:
-                            return fc.Value;
+                            return fc.Value!;
                     }
                 }
+
                 StringBuilder builder = StringBuilderCache.Acquire();
                 AppendChildText(builder);
                 return StringBuilderCache.GetStringAndRelease(builder);
@@ -931,7 +945,7 @@ public virtual string InnerText
 
             set
             {
-                XmlNode firstChild = FirstChild;
+                XmlNode? firstChild = FirstChild;
                 if (firstChild != null  //there is one child
                     && firstChild.NextSibling == null // and exactly one
                     && firstChild.NodeType == XmlNodeType.Text)//which is a text node
@@ -942,7 +956,7 @@ public virtual string InnerText
                 else
                 {
                     RemoveAll();
-                    AppendChild(OwnerDocument.CreateTextNode(value));
+                    AppendChild(OwnerDocument!.CreateTextNode(value));
                 }
             }
         }
@@ -1002,7 +1016,7 @@ public virtual string BaseURI
         {
             get
             {
-                XmlNode curNode = this.ParentNode; //save one while loop since if going to here, the nodetype of this node can't be document, entity and entityref
+                XmlNode? curNode = this.ParentNode; //save one while loop since if going to here, the nodetype of this node can't be document, entity and entityref
                 while (curNode != null)
                 {
                     XmlNodeType nt = curNode.NodeType;
@@ -1030,8 +1044,8 @@ public virtual string BaseURI
         // of the current node.
         public virtual void RemoveAll()
         {
-            XmlNode child = FirstChild;
-            XmlNode sibling = null;
+            XmlNode? child = FirstChild;
+            XmlNode? sibling = null;
 
             while (child != null)
             {
@@ -1047,7 +1061,7 @@ internal XmlDocument Document
             {
                 if (NodeType == XmlNodeType.Document)
                     return (XmlDocument)this;
-                return OwnerDocument;
+                return OwnerDocument!;
             }
         }
 
@@ -1056,20 +1070,22 @@ internal XmlDocument Document
         // the namespace URI in the declaration.
         public virtual string GetNamespaceOfPrefix(string prefix)
         {
-            string namespaceName = GetNamespaceOfPrefixStrict(prefix);
-            return namespaceName != null ? namespaceName : string.Empty;
+            string? namespaceName = GetNamespaceOfPrefixStrict(prefix);
+            return namespaceName ?? string.Empty;
         }
 
-        internal string GetNamespaceOfPrefixStrict(string prefix)
+        internal string? GetNamespaceOfPrefixStrict(string prefix)
         {
             XmlDocument doc = Document;
+            string? pref = prefix;
+
             if (doc != null)
             {
-                prefix = doc.NameTable.Get(prefix);
-                if (prefix == null)
+                pref = doc.NameTable.Get(pref);
+                if (pref == null)
                     return null;
 
-                XmlNode node = this;
+                XmlNode? node = this;
                 while (node != null)
                 {
                     if (node.NodeType == XmlNodeType.Element)
@@ -1078,7 +1094,7 @@ internal string GetNamespaceOfPrefixStrict(string prefix)
                         if (elem.HasAttributes)
                         {
                             XmlAttributeCollection attrs = elem.Attributes;
-                            if (prefix.Length == 0)
+                            if (pref.Length == 0)
                             {
                                 for (int iAttr = 0; iAttr < attrs.Count; iAttr++)
                                 {
@@ -1099,19 +1115,19 @@ internal string GetNamespaceOfPrefixStrict(string prefix)
                                     XmlAttribute attr = attrs[iAttr];
                                     if (Ref.Equal(attr.Prefix, doc.strXmlns))
                                     {
-                                        if (Ref.Equal(attr.LocalName, prefix))
+                                        if (Ref.Equal(attr.LocalName, pref))
                                         {
                                             return attr.Value; // found xmlns:prefix
                                         }
                                     }
-                                    else if (Ref.Equal(attr.Prefix, prefix))
+                                    else if (Ref.Equal(attr.Prefix, pref))
                                     {
                                         return attr.NamespaceURI; // found prefix:attr
                                     }
                                 }
                             }
                         }
-                        if (Ref.Equal(node.Prefix, prefix))
+                        if (Ref.Equal(node.Prefix, pref))
                         {
                             return node.NamespaceURI;
                         }
@@ -1126,15 +1142,16 @@ internal string GetNamespaceOfPrefixStrict(string prefix)
                         node = node.ParentNode;
                     }
                 }
-                if (Ref.Equal(doc.strXml, prefix))
+                if (Ref.Equal(doc.strXml, pref))
                 { // xmlns:xml
                     return doc.strReservedXml;
                 }
-                else if (Ref.Equal(doc.strXmlns, prefix))
+                else if (Ref.Equal(doc.strXmlns, pref))
                 { // xmlns:xmlns
                     return doc.strReservedXmlns;
                 }
             }
+
             return null;
         }
 
@@ -1143,18 +1160,18 @@ internal string GetNamespaceOfPrefixStrict(string prefix)
         // the prefix defined in that declaration.
         public virtual string GetPrefixOfNamespace(string namespaceURI)
         {
-            string prefix = GetPrefixOfNamespaceStrict(namespaceURI);
+            string? prefix = GetPrefixOfNamespaceStrict(namespaceURI);
             return prefix != null ? prefix : string.Empty;
         }
 
-        internal string GetPrefixOfNamespaceStrict(string namespaceURI)
+        internal string? GetPrefixOfNamespaceStrict(string namespaceURI)
         {
             XmlDocument doc = Document;
             if (doc != null)
             {
                 namespaceURI = doc.NameTable.Add(namespaceURI);
 
-                XmlNode node = this;
+                XmlNode? node = this;
                 while (node != null)
                 {
                     if (node.NodeType == XmlNodeType.Element)
@@ -1214,39 +1231,42 @@ internal string GetPrefixOfNamespaceStrict(string namespaceURI)
                     return doc.strXmlns;
                 }
             }
+
             return null;
         }
 
         // Retrieves the first child element with the specified name.
-        public virtual XmlElement this[string name]
+        public virtual XmlElement? this[string name]
         {
             get
             {
-                for (XmlNode n = FirstChild; n != null; n = n.NextSibling)
+                for (XmlNode? n = FirstChild; n != null; n = n.NextSibling)
                 {
                     if (n.NodeType == XmlNodeType.Element && n.Name == name)
                         return (XmlElement)n;
                 }
+
                 return null;
             }
         }
 
         // Retrieves the first child element with the specified LocalName and
         // NamespaceURI.
-        public virtual XmlElement this[string localname, string ns]
+        public virtual XmlElement? this[string localname, string ns]
         {
             get
             {
-                for (XmlNode n = FirstChild; n != null; n = n.NextSibling)
+                for (XmlNode? n = FirstChild; n != null; n = n.NextSibling)
                 {
                     if (n.NodeType == XmlNodeType.Element && n.LocalName == localname && n.NamespaceURI == ns)
                         return (XmlElement)n;
                 }
+
                 return null;
             }
         }
 
-        internal virtual void SetParent(XmlNode node)
+        internal virtual void SetParent(XmlNode? node)
         {
             if (node == null)
             {
@@ -1278,21 +1298,22 @@ internal static void SplitName(string name, out string prefix, out string localN
             }
         }
 
-        internal virtual XmlNode FindChild(XmlNodeType type)
+        internal virtual XmlNode? FindChild(XmlNodeType type)
         {
-            for (XmlNode child = FirstChild; child != null; child = child.NextSibling)
+            for (XmlNode? child = FirstChild; child != null; child = child.NextSibling)
             {
                 if (child.NodeType == type)
                 {
                     return child;
                 }
             }
+
             return null;
         }
 
-        internal virtual XmlNodeChangedEventArgs GetEventArgs(XmlNode node, XmlNode oldParent, XmlNode newParent, string oldValue, string newValue, XmlNodeChangedAction action)
+        internal virtual XmlNodeChangedEventArgs? GetEventArgs(XmlNode node, XmlNode? oldParent, XmlNode? newParent, string? oldValue, string? newValue, XmlNodeChangedAction action)
         {
-            XmlDocument doc = OwnerDocument;
+            XmlDocument? doc = OwnerDocument;
             if (doc != null)
             {
                 if (!doc.IsLoading)
@@ -1300,29 +1321,31 @@ internal virtual XmlNodeChangedEventArgs GetEventArgs(XmlNode node, XmlNode oldP
                     if (((newParent != null && newParent.IsReadOnly) || (oldParent != null && oldParent.IsReadOnly)))
                         throw new InvalidOperationException(SR.Xdom_Node_Modify_ReadOnly);
                 }
+
                 return doc.GetEventArgs(node, oldParent, newParent, oldValue, newValue, action);
             }
+
             return null;
         }
 
         internal virtual void BeforeEvent(XmlNodeChangedEventArgs args)
         {
             if (args != null)
-                OwnerDocument.BeforeEvent(args);
+                OwnerDocument!.BeforeEvent(args);
         }
 
         internal virtual void AfterEvent(XmlNodeChangedEventArgs args)
         {
             if (args != null)
-                OwnerDocument.AfterEvent(args);
+                OwnerDocument!.AfterEvent(args);
         }
 
         internal virtual XmlSpace XmlSpace
         {
             get
             {
-                XmlNode node = this;
-                XmlElement elem = null;
+                XmlNode? node = this;
+                XmlElement? elem = null;
                 do
                 {
                     elem = node as XmlElement;
@@ -1339,9 +1362,10 @@ internal virtual XmlSpace XmlSpace
                                 break;
                         }
                     }
+
                     node = node.ParentNode;
-                }
-                while (node != null);
+                } while (node != null);
+
                 return XmlSpace.None;
             }
         }
@@ -1350,8 +1374,8 @@ internal virtual string XmlLang
         {
             get
             {
-                XmlNode node = this;
-                XmlElement elem = null;
+                XmlNode? node = this;
+                XmlElement? elem = null;
                 do
                 {
                     elem = node as XmlElement;
@@ -1360,8 +1384,10 @@ internal virtual string XmlLang
                         if (elem.HasAttribute("xml:lang"))
                             return elem.GetAttribute("xml:lang");
                     }
+
                     node = node.ParentNode;
                 } while (node != null);
+
                 return string.Empty;
             }
         }
@@ -1395,7 +1421,7 @@ internal virtual bool IsText
             }
         }
 
-        public virtual XmlNode PreviousText
+        public virtual XmlNode? PreviousText
         {
             get
             {
@@ -1443,7 +1469,7 @@ public override string ToString()
                         break;
                     case XmlNodeType.Attribute:
                     case XmlNodeType.ProcessingInstruction:
-                        result += ", Name=\"" + _node.Name + "\", Value=\"" + XmlConvert.EscapeValueForDebuggerDisplay(_node.Value) + "\"";
+                        result += ", Name=\"" + _node.Name + "\", Value=\"" + XmlConvert.EscapeValueForDebuggerDisplay(_node.Value!) + "\"";
                         break;
                     case XmlNodeType.Text:
                     case XmlNodeType.CDATA:
@@ -1451,11 +1477,11 @@ public override string ToString()
                     case XmlNodeType.Whitespace:
                     case XmlNodeType.SignificantWhitespace:
                     case XmlNodeType.XmlDeclaration:
-                        result += ", Value=\"" + XmlConvert.EscapeValueForDebuggerDisplay(_node.Value) + "\"";
+                        result += ", Value=\"" + XmlConvert.EscapeValueForDebuggerDisplay(_node.Value!) + "\"";
                         break;
                     case XmlNodeType.DocumentType:
                         XmlDocumentType documentType = (XmlDocumentType)_node;
-                        result += ", Name=\"" + documentType.Name + "\", SYSTEM=\"" + documentType.SystemId + "\", PUBLIC=\"" + documentType.PublicId + "\", Value=\"" + XmlConvert.EscapeValueForDebuggerDisplay(documentType.InternalSubset) + "\"";
+                        result += ", Name=\"" + documentType.Name + "\", SYSTEM=\"" + documentType.SystemId + "\", PUBLIC=\"" + documentType.PublicId + "\", Value=\"" + XmlConvert.EscapeValueForDebuggerDisplay(documentType.InternalSubset!) + "\"";
                         break;
                     default:
                         break;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeChangedEventArgs.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeChangedEventArgs.cs
index 6ab108ff526428..d89ed2ffb1e40a 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeChangedEventArgs.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeChangedEventArgs.cs
@@ -1,18 +1,19 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     public class XmlNodeChangedEventArgs : EventArgs
     {
         private readonly XmlNodeChangedAction _action;
-        private readonly XmlNode _node;
-        private readonly XmlNode _oldParent;
-        private readonly XmlNode _newParent;
-        private readonly string _oldValue;
-        private readonly string _newValue;
+        private readonly XmlNode? _node;
+        private readonly XmlNode? _oldParent;
+        private readonly XmlNode? _newParent;
+        private readonly string? _oldValue;
+        private readonly string? _newValue;
 
-        public XmlNodeChangedEventArgs(XmlNode node, XmlNode oldParent, XmlNode newParent, string oldValue, string newValue, XmlNodeChangedAction action)
+        public XmlNodeChangedEventArgs(XmlNode? node, XmlNode? oldParent, XmlNode? newParent, string? oldValue, string? newValue, XmlNodeChangedAction action)
         {
             _node = node;
             _oldParent = oldParent;
@@ -24,14 +25,14 @@ public XmlNodeChangedEventArgs(XmlNode node, XmlNode oldParent, XmlNode newParen
 
         public XmlNodeChangedAction Action { get { return _action; } }
 
-        public XmlNode Node { get { return _node; } }
+        public XmlNode? Node { get { return _node; } }
 
-        public XmlNode OldParent { get { return _oldParent; } }
+        public XmlNode? OldParent { get { return _oldParent; } }
 
-        public XmlNode NewParent { get { return _newParent; } }
+        public XmlNode? NewParent { get { return _newParent; } }
 
-        public string OldValue { get { return _oldValue; } }
+        public string? OldValue { get { return _oldValue; } }
 
-        public string NewValue { get { return _newValue; } }
+        public string? NewValue { get { return _newValue; } }
     }
 }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeChangedEventHandler.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeChangedEventHandler.cs
index b63ac819cf4f02..d106ceacf243ae 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeChangedEventHandler.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeChangedEventHandler.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     public delegate void XmlNodeChangedEventHandler(object sender, XmlNodeChangedEventArgs e);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeList.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeList.cs
index 2c14561a41ce82..0565f5203a9279 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeList.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeList.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections;
 
 namespace System.Xml
@@ -9,7 +10,7 @@ namespace System.Xml
     public abstract class XmlNodeList : IEnumerable, IDisposable
     {
         // Retrieves a node at the given index.
-        public abstract XmlNode Item(int index);
+        public abstract XmlNode? Item(int index);
 
         // Gets the number of nodes in this XmlNodeList.
         public abstract int Count { get; }
@@ -20,7 +21,7 @@ public abstract class XmlNodeList : IEnumerable, IDisposable
 
         // Retrieves a node at the given index.
         [System.Runtime.CompilerServices.IndexerName("ItemOf")]
-        public virtual XmlNode this[int i] { get { return Item(i); } }
+        public virtual XmlNode? this[int i] { get { return Item(i); } }
 
         void IDisposable.Dispose()
         {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeReader.cs
index 4ed38db85abff1..b3a255cd467985 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNodeReader.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     using System;
@@ -15,7 +16,7 @@ namespace System.Xml
     internal class XmlNodeReaderNavigator
     {
         private XmlNode _curNode;
-        private XmlNode _elemNode;
+        private XmlNode? _elemNode;
         private XmlNode _logNode;
         private int _attrIndex;
         private int _logAttrIndex;
@@ -45,10 +46,10 @@ internal class XmlNodeReaderNavigator
 
         internal struct VirtualAttribute
         {
-            internal string name;
-            internal string value;
+            internal string? name;
+            internal string? value;
 
-            internal VirtualAttribute(string name, string value)
+            internal VirtualAttribute(string? name, string? value)
             {
                 this.name = name;
                 this.value = value;
@@ -89,7 +90,8 @@ public XmlNodeReaderNavigator(XmlNode node)
             if (nt == XmlNodeType.Document)
                 _doc = (XmlDocument)_curNode;
             else
-                _doc = node.OwnerDocument;
+                _doc = node.OwnerDocument!;
+
             _nameTable = _doc.NameTable;
             _nAttrInd = -1;
             //initialize the caching variables
@@ -134,9 +136,9 @@ public string Name
                     {
                         Debug.Assert(_nAttrInd >= 0 && _nAttrInd < AttributeCount);
                         if (_curNode.NodeType == XmlNodeType.XmlDeclaration)
-                            return decNodeAttributes[_nAttrInd].name;
+                            return decNodeAttributes[_nAttrInd].name!;
                         else
-                            return docTypeNodeAttributes[_nAttrInd].name;
+                            return docTypeNodeAttributes[_nAttrInd].name!;
                     }
                 }
                 if (IsLocalNameEmpty(_curNode.NodeType))
@@ -225,7 +227,7 @@ public string Value
             //See comments in HasValue
             get
             {
-                string retValue = null;
+                string? retValue = null;
                 XmlNodeType nt = _curNode.NodeType;
                 if (_nAttrInd != -1)
                 {
@@ -233,9 +235,9 @@ public string Value
                     Debug.Assert(nt == XmlNodeType.XmlDeclaration || nt == XmlNodeType.DocumentType);
                     Debug.Assert(_nAttrInd >= 0 && _nAttrInd < AttributeCount);
                     if (_curNode.NodeType == XmlNodeType.XmlDeclaration)
-                        return decNodeAttributes[_nAttrInd].value;
+                        return decNodeAttributes[_nAttrInd].value!;
                     else
-                        return docTypeNodeAttributes[_nAttrInd].value;
+                        return docTypeNodeAttributes[_nAttrInd].value!;
                 }
                 if (nt == XmlNodeType.DocumentType)
                     retValue = ((XmlDocumentType)_curNode).InternalSubset; //in this case nav.Value will be null
@@ -321,7 +323,7 @@ public int AttributeCount
                     return ((XmlElement)_curNode).Attributes.Count;
                 else if (nt == XmlNodeType.Attribute
                         || (_bOnAttrVal && nt != XmlNodeType.XmlDeclaration && nt != XmlNodeType.DocumentType))
-                    return _elemNode.Attributes.Count;
+                    return _elemNode!.Attributes!.Count;
                 else if (nt == XmlNodeType.XmlDeclaration)
                 {
                     if (_nDeclarationAttrCount != -1)
@@ -352,7 +354,7 @@ private void CheckIndexCondition(int attributeIndex)
         private void InitDecAttr()
         {
             int i = 0;
-            string strTemp = _doc.Version;
+            string? strTemp = _doc.Version;
             if (strTemp != null && strTemp.Length != 0)
             {
                 decNodeAttributes[i].name = strVersion;
@@ -376,7 +378,7 @@ private void InitDecAttr()
             _nDeclarationAttrCount = i;
         }
 
-        public string GetDeclarationAttr(XmlDeclaration decl, string name)
+        public string? GetDeclarationAttr(XmlDeclaration decl, string name)
         {
             //PreCondition: curNode is pointing at Declaration node or one of its virtual attributes
             if (name == strVersion)
@@ -388,7 +390,7 @@ public string GetDeclarationAttr(XmlDeclaration decl, string name)
             return null;
         }
 
-        public string GetDeclarationAttr(int i)
+        public string? GetDeclarationAttr(int i)
         {
             if (_nDeclarationAttrCount == -1)
                 InitDecAttr();
@@ -410,19 +412,21 @@ public int GetDecAttrInd(string name)
         private void InitDocTypeAttr()
         {
             int i = 0;
-            XmlDocumentType docType = _doc.DocumentType;
+            XmlDocumentType? docType = _doc.DocumentType;
             if (docType == null)
             {
                 _nDocTypeAttrCount = 0;
                 return;
             }
-            string strTemp = docType.PublicId;
+
+            string? strTemp = docType.PublicId;
             if (strTemp != null)
             {
                 docTypeNodeAttributes[i].name = strPublicID;
                 docTypeNodeAttributes[i].value = strTemp;
                 i++;
             }
+
             strTemp = docType.SystemId;
             if (strTemp != null)
             {
@@ -430,10 +434,11 @@ private void InitDocTypeAttr()
                 docTypeNodeAttributes[i].value = strTemp;
                 i++;
             }
+
             _nDocTypeAttrCount = i;
         }
 
-        public string GetDocumentTypeAttr(XmlDocumentType docType, string name)
+        public string? GetDocumentTypeAttr(XmlDocumentType docType, string name)
         {
             //PreCondition: nav is pointing at DocumentType node or one of its virtual attributes
             if (name == strPublicID)
@@ -443,7 +448,7 @@ public string GetDocumentTypeAttr(XmlDocumentType docType, string name)
             return null;
         }
 
-        public string GetDocumentTypeAttr(int i)
+        public string? GetDocumentTypeAttr(int i)
         {
             if (_nDocTypeAttrCount == -1)
                 InitDocTypeAttr();
@@ -462,37 +467,37 @@ public int GetDocTypeAttrInd(string name)
             return -1;
         }
 
-        private string GetAttributeFromElement(XmlElement elem, string name)
+        private string? GetAttributeFromElement(XmlElement elem, string name)
         {
-            XmlAttribute attr = elem.GetAttributeNode(name);
+            XmlAttribute? attr = elem.GetAttributeNode(name);
             if (attr != null)
                 return attr.Value;
             return null;
         }
 
-        public string GetAttribute(string name)
+        public string? GetAttribute(string name)
         {
             if (_bCreatedOnAttribute)
                 return null;
 
             return _curNode.NodeType switch
             {
-                XmlNodeType.Element => GetAttributeFromElement((XmlElement)_curNode, name),
-                XmlNodeType.Attribute => GetAttributeFromElement((XmlElement)_elemNode, name),
+                XmlNodeType.Element => GetAttributeFromElement((XmlElement)_curNode!, name),
+                XmlNodeType.Attribute => GetAttributeFromElement((XmlElement)_elemNode!, name),
                 XmlNodeType.XmlDeclaration => GetDeclarationAttr((XmlDeclaration)_curNode, name),
                 XmlNodeType.DocumentType => GetDocumentTypeAttr((XmlDocumentType)_curNode, name),
                 _ => null,
             };
         }
 
-        private string GetAttributeFromElement(XmlElement elem, string name, string ns)
+        private string? GetAttributeFromElement(XmlElement elem, string name, string? ns)
         {
-            XmlAttribute attr = elem.GetAttributeNode(name, ns);
+            XmlAttribute? attr = elem.GetAttributeNode(name, ns);
             if (attr != null)
                 return attr.Value;
             return null;
         }
-        public string GetAttribute(string name, string ns)
+        public string? GetAttribute(string name, string ns)
         {
             if (_bCreatedOnAttribute)
                 return null;
@@ -500,14 +505,14 @@ public string GetAttribute(string name, string ns)
             return _curNode.NodeType switch
             {
                 XmlNodeType.Element => GetAttributeFromElement((XmlElement)_curNode, name, ns),
-                XmlNodeType.Attribute => GetAttributeFromElement((XmlElement)_elemNode, name, ns),
+                XmlNodeType.Attribute => GetAttributeFromElement((XmlElement)_elemNode!, name, ns),
                 XmlNodeType.XmlDeclaration => (ns.Length == 0) ? GetDeclarationAttr((XmlDeclaration)_curNode, name) : null,
                 XmlNodeType.DocumentType => (ns.Length == 0) ? GetDocumentTypeAttr((XmlDocumentType)_curNode, name) : null,
                 _ => null,
             };
         }
 
-        public string GetAttribute(int attributeIndex)
+        public string? GetAttribute(int attributeIndex)
         {
             if (_bCreatedOnAttribute)
                 return null;
@@ -518,7 +523,7 @@ public string GetAttribute(int attributeIndex)
                     return ((XmlElement)_curNode).Attributes[attributeIndex].Value;
                 case XmlNodeType.Attribute:
                     CheckIndexCondition(attributeIndex);
-                    return ((XmlElement)_elemNode).Attributes[attributeIndex].Value;
+                    return ((XmlElement)_elemNode!).Attributes[attributeIndex].Value;
                 case XmlNodeType.XmlDeclaration:
                     {
                         CheckIndexCondition(attributeIndex);
@@ -576,9 +581,10 @@ public void ResetToAttribute(ref int level)
                 }
                 else
                 {
-                    while (_curNode.NodeType != XmlNodeType.Attribute && ((_curNode = _curNode.ParentNode) != null))
+                    while (_curNode.NodeType != XmlNodeType.Attribute && ((_curNode = _curNode.ParentNode!) != null))
                         level--;
                 }
+
                 _bOnAttrVal = false;
             }
         }
@@ -606,7 +612,7 @@ public void ResetMove(ref int level, ref XmlNodeType nt)
                 ResetToAttribute(ref level);
             if (_curNode.NodeType == XmlNodeType.Attribute)
             {
-                _curNode = ((XmlAttribute)_curNode).OwnerElement;
+                _curNode = ((XmlAttribute)_curNode).OwnerElement!;
                 _attrIndex = -1;
                 level--;
                 nt = XmlNodeType.Element;
@@ -621,7 +627,7 @@ public bool MoveToAttribute(string name)
         }
         private bool MoveToAttributeFromElement(XmlElement elem, string name, string ns)
         {
-            XmlAttribute attr = null;
+            XmlAttribute? attr = null;
             if (ns.Length == 0)
                 attr = elem.GetAttributeNode(name);
             else
@@ -648,7 +654,7 @@ public bool MoveToAttribute(string name, string namespaceURI)
             if (nt == XmlNodeType.Element)
                 return MoveToAttributeFromElement((XmlElement)_curNode, name, namespaceURI);
             else if (nt == XmlNodeType.Attribute)
-                return MoveToAttributeFromElement((XmlElement)_elemNode, name, namespaceURI);
+                return MoveToAttributeFromElement((XmlElement)_elemNode!, name, namespaceURI);
             else if (nt == XmlNodeType.XmlDeclaration && namespaceURI.Length == 0)
             {
                 if ((_nAttrInd = GetDecAttrInd(name)) != -1)
@@ -672,7 +678,7 @@ public void MoveToAttribute(int attributeIndex)
         {
             if (_bCreatedOnAttribute)
                 return;
-            XmlAttribute attr = null;
+            XmlAttribute? attr = null;
             switch (_curNode.NodeType)
             {
                 case XmlNodeType.Element:
@@ -687,7 +693,7 @@ public void MoveToAttribute(int attributeIndex)
                     break;
                 case XmlNodeType.Attribute:
                     CheckIndexCondition(attributeIndex);
-                    attr = ((XmlElement)_elemNode).Attributes[attributeIndex];
+                    attr = ((XmlElement)_elemNode!).Attributes[attributeIndex];
                     if (attr != null)
                     {
                         _curNode = (XmlNode)attr;
@@ -709,7 +715,7 @@ public bool MoveToNextAttribute(ref int level)
             XmlNodeType nt = _curNode.NodeType;
             if (nt == XmlNodeType.Attribute)
             {
-                if (_attrIndex >= (_elemNode.Attributes.Count - 1))
+                if (_attrIndex >= (_elemNode!.Attributes!.Count - 1))
                     return false;
                 else
                 {
@@ -719,7 +725,7 @@ public bool MoveToNextAttribute(ref int level)
             }
             else if (nt == XmlNodeType.Element)
             {
-                if (_curNode.Attributes.Count > 0)
+                if (_curNode.Attributes!.Count > 0)
                 {
                     level++;
                     _elemNode = _curNode;
@@ -759,7 +765,7 @@ public bool MoveToNextAttribute(ref int level)
 
         public bool MoveToParent()
         {
-            XmlNode parent = _curNode.ParentNode;
+            XmlNode? parent = _curNode.ParentNode;
             if (parent != null)
             {
                 _curNode = parent;
@@ -772,7 +778,7 @@ public bool MoveToParent()
 
         public bool MoveToFirstChild()
         {
-            XmlNode firstChild = _curNode.FirstChild;
+            XmlNode? firstChild = _curNode.FirstChild;
             if (firstChild != null)
             {
                 _curNode = firstChild;
@@ -780,12 +786,13 @@ public bool MoveToFirstChild()
                     _attrIndex = -1;
                 return true;
             }
+
             return false;
         }
 
         private bool MoveToNextSibling(XmlNode node)
         {
-            XmlNode nextSibling = node.NextSibling;
+            XmlNode? nextSibling = node.NextSibling;
             if (nextSibling != null)
             {
                 _curNode = nextSibling;
@@ -793,6 +800,7 @@ private bool MoveToNextSibling(XmlNode node)
                     _attrIndex = -1;
                 return true;
             }
+
             return false;
         }
 
@@ -801,7 +809,7 @@ public bool MoveToNext()
             if (_curNode.NodeType != XmlNodeType.Attribute)
                 return MoveToNextSibling(_curNode);
             else
-                return MoveToNextSibling(_elemNode);
+                return MoveToNextSibling(_elemNode!);
         }
 
         public bool MoveToElement()
@@ -832,7 +840,7 @@ public bool MoveToElement()
             return false;
         }
 
-        public string LookupNamespace(string prefix)
+        public string? LookupNamespace(string prefix)
         {
             if (_bCreatedOnAttribute)
                 return null;
@@ -855,7 +863,7 @@ public string LookupNamespace(string prefix)
                 attrName = "xmlns:" + prefix;
 
             // walk up the XmlNode parent chain, looking for the xmlns attribute
-            XmlNode node = _curNode;
+            XmlNode? node = _curNode;
             while (node != null)
             {
                 if (node.NodeType == XmlNodeType.Element)
@@ -863,7 +871,7 @@ public string LookupNamespace(string prefix)
                     XmlElement elem = (XmlElement)node;
                     if (elem.HasAttributes)
                     {
-                        XmlAttribute attr = elem.GetAttributeNode(attrName);
+                        XmlAttribute? attr = elem.GetAttributeNode(attrName);
                         if (attr != null)
                         {
                             return attr.Value;
@@ -884,7 +892,7 @@ public string LookupNamespace(string prefix)
             return null;
         }
 
-        internal string DefaultLookupNamespace(string prefix)
+        internal string? DefaultLookupNamespace(string prefix)
         {
             if (!_bCreatedOnAttribute)
             {
@@ -904,7 +912,7 @@ internal string DefaultLookupNamespace(string prefix)
             return null;
         }
 
-        internal string LookupPrefix(string namespaceName)
+        internal string? LookupPrefix(string namespaceName)
         {
             if (_bCreatedOnAttribute || namespaceName == null)
             {
@@ -923,7 +931,7 @@ internal string LookupPrefix(string namespaceName)
                 return string.Empty;
             }
             // walk up the XmlNode parent chain, looking for the xmlns attribute with namespaceName value
-            XmlNode node = _curNode;
+            XmlNode? node = _curNode;
             while (node != null)
             {
                 if (node.NodeType == XmlNodeType.Element)
@@ -961,8 +969,10 @@ internal string LookupPrefix(string namespaceName)
                     node = ((XmlAttribute)node).OwnerElement;
                     continue;
                 }
+
                 node = node.ParentNode;
             }
+
             return null;
         }
 
@@ -973,7 +983,7 @@ internal IDictionary<string, string> GetNamespacesInScope(XmlNamespaceScope scop
                 return dict;
 
             // walk up the XmlNode parent chain and add all namespace declarations to the dictionary
-            XmlNode node = _curNode;
+            XmlNode? node = _curNode;
             while (node != null)
             {
                 if (node.NodeType == XmlNodeType.Element)
@@ -989,7 +999,7 @@ internal IDictionary<string, string> GetNamespacesInScope(XmlNamespaceScope scop
                             {
                                 if (!dict.ContainsKey(string.Empty))
                                 {
-                                    dict.Add(_nameTable.Add(string.Empty), _nameTable.Add(a.Value));
+                                    dict.Add(_nameTable.Add(string.Empty), _nameTable.Add(a.Value!));
                                 }
                             }
                             else if (a.Prefix == "xmlns")
@@ -997,7 +1007,7 @@ internal IDictionary<string, string> GetNamespacesInScope(XmlNamespaceScope scop
                                 string localName = a.LocalName;
                                 if (!dict.ContainsKey(localName))
                                 {
-                                    dict.Add(_nameTable.Add(localName), _nameTable.Add(a.Value));
+                                    dict.Add(_nameTable.Add(localName), _nameTable.Add(a.Value!));
                                 }
                             }
                         }
@@ -1012,6 +1022,7 @@ internal IDictionary<string, string> GetNamespacesInScope(XmlNamespaceScope scop
                     node = ((XmlAttribute)node).OwnerElement;
                     continue;
                 }
+
                 node = node.ParentNode;
             };
 
@@ -1045,7 +1056,7 @@ public bool ReadAttributeValue(ref int level, ref bool bResolveEntity, ref XmlNo
             }
             if (_curNode.NodeType == XmlNodeType.Attribute)
             {
-                XmlNode firstChild = _curNode.FirstChild;
+                XmlNode? firstChild = _curNode.FirstChild;
                 if (firstChild != null)
                 {
                     _curNode = firstChild;
@@ -1057,13 +1068,13 @@ public bool ReadAttributeValue(ref int level, ref bool bResolveEntity, ref XmlNo
             }
             else if (_bOnAttrVal)
             {
-                XmlNode nextSibling = null;
+                XmlNode? nextSibling = null;
                 if (_curNode.NodeType == XmlNodeType.EntityReference && bResolveEntity)
                 {
                     //going down to ent ref node
-                    _curNode = _curNode.FirstChild;
-                    nt = _curNode.NodeType;
+                    _curNode = _curNode.FirstChild!;
                     Debug.Assert(_curNode != null);
+                    nt = _curNode.NodeType;
                     level++;
                     bResolveEntity = false;
                     return true;
@@ -1072,7 +1083,7 @@ public bool ReadAttributeValue(ref int level, ref bool bResolveEntity, ref XmlNo
                     nextSibling = _curNode.NextSibling;
                 if (nextSibling == null)
                 {
-                    XmlNode parentNode = _curNode.ParentNode;
+                    XmlNode? parentNode = _curNode.ParentNode;
                     //Check if its parent is entity ref node is sufficient, because in this senario, ent ref node can't have more than 1 level of children that are not other ent ref nodes
                     if (parentNode != null && parentNode.NodeType == XmlNodeType.EntityReference)
                     {
@@ -1119,7 +1130,7 @@ public class XmlNodeReader : XmlReader, IXmlNamespaceResolver
         private bool _bStartFromDocument;
 
         private bool _bInReadBinary;
-        private ReadContentAsBinaryHelper _readBinaryHelper;
+        private ReadContentAsBinaryHelper? _readBinaryHelper;
 
 
         // Creates an instance of the XmlNodeReader class using the specified XmlNode.
@@ -1129,6 +1140,7 @@ public XmlNodeReader(XmlNode node)
             {
                 throw new ArgumentNullException(nameof(node));
             }
+
             _readerNav = new XmlNodeReaderNavigator(node);
             _curDepth = 0;
 
@@ -1290,7 +1302,7 @@ public override string XmlLang
             }
         }
 
-        public override IXmlSchemaInfo SchemaInfo
+        public override IXmlSchemaInfo? SchemaInfo
         {
             get
             {
@@ -1318,7 +1330,7 @@ public override int AttributeCount
         }
 
         // Gets the value of the attribute with the specified name.
-        public override string GetAttribute(string name)
+        public override string? GetAttribute(string name)
         {
             //if not on Attribute, only element node could have attributes
             if (!IsInReadingStates())
@@ -1327,7 +1339,7 @@ public override string GetAttribute(string name)
         }
 
         // Gets the value of the attribute with the specified name and namespace.
-        public override string GetAttribute(string name, string namespaceURI)
+        public override string? GetAttribute(string name, string? namespaceURI)
         {
             //if not on Attribute, only element node could have attributes
             if (!IsInReadingStates())
@@ -1343,7 +1355,7 @@ public override string GetAttribute(int attributeIndex)
                 throw new ArgumentOutOfRangeException(nameof(attributeIndex));
             //CheckIndexCondition( i );
             //Debug.Assert( nav.NodeType == XmlNodeType.Element );
-            return _readerNav.GetAttribute(attributeIndex);
+            return _readerNav.GetAttribute(attributeIndex)!;
         }
 
         // Moves to the attribute with the specified name.
@@ -1367,7 +1379,7 @@ public override bool MoveToAttribute(string name)
         }
 
         // Moves to the attribute with the specified name and namespace.
-        public override bool MoveToAttribute(string name, string namespaceURI)
+        public override bool MoveToAttribute(string name, string? namespaceURI)
         {
             if (!IsInReadingStates())
                 return false;
@@ -1743,11 +1755,11 @@ public override XmlNameTable NameTable
         }
 
         // Resolves a namespace prefix in the current element's scope.
-        public override string LookupNamespace(string prefix)
+        public override string? LookupNamespace(string prefix)
         {
             if (!IsInReadingStates())
                 return null;
-            string ns = _readerNav.LookupNamespace(prefix);
+            string? ns = _readerNav.LookupNamespace(prefix);
             if (ns != null && ns.Length == 0)
             {
                 return null;
@@ -1802,7 +1814,7 @@ public override int ReadContentAsBase64(byte[] buffer, int index, int count)
             _bInReadBinary = false;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadContentAsBase64(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadContentAsBase64(buffer, index, count);
 
             // turn on bInReadBinary in again and return
             _bInReadBinary = true;
@@ -1826,7 +1838,7 @@ public override int ReadContentAsBinHex(byte[] buffer, int index, int count)
             _bInReadBinary = false;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadContentAsBinHex(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadContentAsBinHex(buffer, index, count);
 
             // turn on bInReadBinary in again and return
             _bInReadBinary = true;
@@ -1850,7 +1862,7 @@ public override int ReadElementContentAsBase64(byte[] buffer, int index, int cou
             _bInReadBinary = false;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadElementContentAsBase64(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadElementContentAsBase64(buffer, index, count);
 
             // turn on bInReadBinary in again and return
             _bInReadBinary = true;
@@ -1874,7 +1886,7 @@ public override int ReadElementContentAsBinHex(byte[] buffer, int index, int cou
             _bInReadBinary = false;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadElementContentAsBinHex(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadElementContentAsBinHex(buffer, index, count);
 
             // turn on bInReadBinary in again and return
             _bInReadBinary = true;
@@ -1884,7 +1896,7 @@ public override int ReadElementContentAsBinHex(byte[] buffer, int index, int cou
         private void FinishReadBinary()
         {
             _bInReadBinary = false;
-            _readBinaryHelper.Finish();
+            _readBinaryHelper!.Finish();
         }
 
         //
@@ -1896,27 +1908,29 @@ IDictionary<string, string> IXmlNamespaceResolver.GetNamespacesInScope(XmlNamesp
             return _readerNav.GetNamespacesInScope(scope);
         }
 
-        string IXmlNamespaceResolver.LookupPrefix(string namespaceName)
+        string? IXmlNamespaceResolver.LookupPrefix(string namespaceName)
         {
             return _readerNav.LookupPrefix(namespaceName);
         }
 
-        string IXmlNamespaceResolver.LookupNamespace(string prefix)
+        string? IXmlNamespaceResolver.LookupNamespace(string prefix)
         {
             if (!IsInReadingStates())
             {
                 return _readerNav.DefaultLookupNamespace(prefix);
             }
-            string ns = _readerNav.LookupNamespace(prefix);
+
+            string? ns = _readerNav.LookupNamespace(prefix);
             if (ns != null)
             {
                 ns = _readerNav.NameTable.Add(ns);
             }
+
             return ns;
         }
 
         // DTD/Schema info used by XmlReader.GetDtdSchemaInfo()
-        internal override IDtdInfo DtdInfo
+        internal override IDtdInfo? DtdInfo
         {
             get
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNotation.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNotation.cs
index ed7d107dd06a20..79ed84c14d35c5 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNotation.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlNotation.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     using System;
@@ -9,11 +10,11 @@ namespace System.Xml
     // Contains a notation declared in the DTD or schema.
     public class XmlNotation : XmlNode
     {
-        private readonly string _publicId;
-        private readonly string _systemId;
+        private readonly string? _publicId;
+        private readonly string? _systemId;
         private readonly string _name;
 
-        internal XmlNotation(string name, string publicId, string systemId, XmlDocument doc) : base(doc)
+        internal XmlNotation(string name, string? publicId, string? systemId, XmlDocument doc) : base(doc)
         {
             _name = doc.NameTable.Add(name);
             _publicId = publicId;
@@ -58,14 +59,14 @@ public override bool IsReadOnly
         }
 
         // Gets the value of the public identifier on the notation declaration.
-        public string PublicId
+        public string? PublicId
         {
             get { return _publicId; }
         }
 
         // Gets the value of
         // the system identifier on the notation declaration.
-        public string SystemId
+        public string? SystemId
         {
             get { return _systemId; }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlProcessingInstruction.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlProcessingInstruction.cs
index 6fc679fafe8ad9..89e36be95503a8 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlProcessingInstruction.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlProcessingInstruction.cs
@@ -1,7 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Xml.XPath;
 
 namespace System.Xml
@@ -37,14 +39,15 @@ public override string LocalName
         }
 
         // Gets or sets the value of the node.
+        [AllowNull]
         public override string Value
         {
             get { return _data; }
-            set { Data = value; } //use Data instead of data so that event will be fired
+            set { Data = value!; } //use Data instead of data so that event will be fired
         }
 
         // Gets the target of the processing instruction.
-        public string Target
+        public string? Target
         {
             get { return _target; }
         }
@@ -56,8 +59,8 @@ public string Data
             get { return _data; }
             set
             {
-                XmlNode parent = ParentNode;
-                XmlNodeChangedEventArgs args = GetEventArgs(this, parent, parent, _data, value, XmlNodeChangedAction.Change);
+                XmlNode? parent = ParentNode;
+                XmlNodeChangedEventArgs? args = GetEventArgs(this, parent, parent, _data, value, XmlNodeChangedAction.Change);
                 if (args != null)
                     BeforeEvent(args);
                 _data = value;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlSignificantWhiteSpace.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlSignificantWhiteSpace.cs
index a7ba3c8d74e4df..dd9995d57f31cd 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlSignificantWhiteSpace.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlSignificantWhiteSpace.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 
@@ -9,7 +10,7 @@ namespace System.Xml
     // Represents the text content of an element or attribute.
     public class XmlSignificantWhitespace : XmlCharacterData
     {
-        protected internal XmlSignificantWhitespace(string strData, XmlDocument doc) : base(strData, doc)
+        protected internal XmlSignificantWhitespace(string? strData, XmlDocument doc) : base(strData, doc)
         {
             if (!doc.IsLoading && !base.CheckOnData(strData))
                 throw new ArgumentException(SR.Xdom_WS_Char);
@@ -20,7 +21,7 @@ public override string Name
         {
             get
             {
-                return OwnerDocument.strSignificantWhitespaceName;
+                return OwnerDocument!.strSignificantWhitespaceName;
             }
         }
 
@@ -29,7 +30,7 @@ public override string LocalName
         {
             get
             {
-                return OwnerDocument.strSignificantWhitespaceName;
+                return OwnerDocument!.strSignificantWhitespaceName;
             }
         }
 
@@ -42,11 +43,11 @@ public override XmlNodeType NodeType
             }
         }
 
-        public override XmlNode ParentNode
+        public override XmlNode? ParentNode
         {
             get
             {
-                switch (parentNode.NodeType)
+                switch (parentNode!.NodeType)
                 {
                     case XmlNodeType.Document:
                         return base.ParentNode;
@@ -54,10 +55,10 @@ public override XmlNode ParentNode
                     case XmlNodeType.CDATA:
                     case XmlNodeType.Whitespace:
                     case XmlNodeType.SignificantWhitespace:
-                        XmlNode parent = parentNode.parentNode;
+                        XmlNode parent = parentNode.parentNode!;
                         while (parent.IsText)
                         {
-                            parent = parent.parentNode;
+                            parent = parent.parentNode!;
                         }
                         return parent;
                     default:
@@ -73,7 +74,7 @@ public override XmlNode CloneNode(bool deep)
             return OwnerDocument.CreateSignificantWhitespace(Data);
         }
 
-        public override string Value
+        public override string? Value
         {
             get
             {
@@ -119,14 +120,15 @@ internal override bool IsText
             }
         }
 
-        public override XmlNode PreviousText
+        public override XmlNode? PreviousText
         {
             get
             {
-                if (parentNode.IsText)
+                if (parentNode != null && parentNode.IsText)
                 {
                     return parentNode;
                 }
+
                 return null;
             }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlText.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlText.cs
index 9a0bf27ca65b52..db4533514d0a7c 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlText.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlText.cs
@@ -1,7 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Xml.XPath;
 
 namespace System.Xml
@@ -9,11 +11,11 @@ namespace System.Xml
     // Represents the text content of an element or attribute.
     public class XmlText : XmlCharacterData
     {
-        internal XmlText(string strData) : this(strData, null)
+        internal XmlText(string? strData) : this(strData, null!) // always throws ArgumentNullException
         {
         }
 
-        protected internal XmlText(string strData, XmlDocument doc) : base(strData, doc)
+        protected internal XmlText(string? strData, XmlDocument doc) : base(strData, doc)
         {
         }
 
@@ -22,7 +24,7 @@ public override string Name
         {
             get
             {
-                return OwnerDocument.strTextName;
+                return OwnerDocument!.strTextName;
             }
         }
 
@@ -31,7 +33,7 @@ public override string LocalName
         {
             get
             {
-                return OwnerDocument.strTextName;
+                return OwnerDocument!.strTextName;
             }
         }
 
@@ -44,11 +46,11 @@ public override XmlNodeType NodeType
             }
         }
 
-        public override XmlNode ParentNode
+        public override XmlNode? ParentNode
         {
             get
             {
-                switch (parentNode.NodeType)
+                switch (parentNode!.NodeType)
                 {
                     case XmlNodeType.Document:
                         return null;
@@ -56,11 +58,12 @@ public override XmlNode ParentNode
                     case XmlNodeType.CDATA:
                     case XmlNodeType.Whitespace:
                     case XmlNodeType.SignificantWhitespace:
-                        XmlNode parent = parentNode.parentNode;
+                        XmlNode parent = parentNode.parentNode!;
                         while (parent.IsText)
                         {
-                            parent = parent.parentNode;
+                            parent = parent.parentNode!;
                         }
+
                         return parent;
                     default:
                         return parentNode;
@@ -75,7 +78,7 @@ public override XmlNode CloneNode(bool deep)
             return OwnerDocument.CreateTextNode(Data);
         }
 
-        public override string Value
+        public override string? Value
         {
             get
             {
@@ -85,10 +88,10 @@ public override string Value
             set
             {
                 Data = value;
-                XmlNode parent = parentNode;
+                XmlNode? parent = parentNode;
                 if (parent != null && parent.NodeType == XmlNodeType.Attribute)
                 {
-                    XmlUnspecifiedAttribute attr = parent as XmlUnspecifiedAttribute;
+                    XmlUnspecifiedAttribute? attr = parent as XmlUnspecifiedAttribute;
                     if (attr != null && !attr.Specified)
                     {
                         attr.SetSpecified(true);
@@ -101,7 +104,7 @@ public override string Value
         // both in the tree as siblings.
         public virtual XmlText SplitText(int offset)
         {
-            XmlNode parentNode = this.ParentNode;
+            XmlNode? parentNode = this.ParentNode;
             int length = this.Length;
             if (offset > length)
                 throw new ArgumentOutOfRangeException(nameof(offset));
@@ -112,7 +115,7 @@ public virtual XmlText SplitText(int offset)
             int count = length - offset;
             string splitData = Substring(offset, count);
             DeleteData(offset, count);
-            XmlText newTextNode = OwnerDocument.CreateTextNode(splitData);
+            XmlText newTextNode = OwnerDocument!.CreateTextNode(splitData);
             parentNode.InsertAfter(newTextNode, this);
             return newTextNode;
         }
@@ -145,14 +148,15 @@ internal override bool IsText
             }
         }
 
-        public override XmlNode PreviousText
+        public override XmlNode? PreviousText
         {
             get
             {
-                if (parentNode.IsText)
+                if (parentNode != null && parentNode.IsText)
                 {
                     return parentNode;
                 }
+
                 return null;
             }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlUnspecifiedAttribute.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlUnspecifiedAttribute.cs
index 07e8f9f9c162b6..205d1d8a427175 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlUnspecifiedAttribute.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlUnspecifiedAttribute.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml
 {
     internal class XmlUnspecifiedAttribute : XmlAttribute
@@ -8,7 +9,7 @@ internal class XmlUnspecifiedAttribute : XmlAttribute
         private bool _fSpecified;
 
 
-        protected internal XmlUnspecifiedAttribute(string prefix, string localName, string namespaceURI, XmlDocument doc)
+        protected internal XmlUnspecifiedAttribute(string? prefix, string localName, string? namespaceURI, XmlDocument doc)
         : base(prefix, localName, namespaceURI, doc)
         {
         }
@@ -38,16 +39,16 @@ public override string InnerText
             }
         }
 
-        public override XmlNode InsertBefore(XmlNode newChild, XmlNode refChild)
+        public override XmlNode? InsertBefore(XmlNode newChild, XmlNode? refChild)
         {
-            XmlNode node = base.InsertBefore(newChild, refChild);
+            XmlNode? node = base.InsertBefore(newChild, refChild);
             _fSpecified = true;
             return node;
         }
 
-        public override XmlNode InsertAfter(XmlNode newChild, XmlNode refChild)
+        public override XmlNode? InsertAfter(XmlNode newChild, XmlNode? refChild)
         {
-            XmlNode node = base.InsertAfter(newChild, refChild);
+            XmlNode? node = base.InsertAfter(newChild, refChild);
             _fSpecified = true;
             return node;
         }
@@ -66,9 +67,9 @@ public override XmlNode RemoveChild(XmlNode oldChild)
             return node;
         }
 
-        public override XmlNode AppendChild(XmlNode newChild)
+        public override XmlNode? AppendChild(XmlNode newChild)
         {
-            XmlNode node = base.AppendChild(newChild);
+            XmlNode? node = base.AppendChild(newChild);
             _fSpecified = true;
             return node;
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlWhitespace.cs b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlWhitespace.cs
index ecdcd9172e3ca1..7f9509cd3d5665 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlWhitespace.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Dom/XmlWhitespace.cs
@@ -1,7 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Xml.XPath;
 
 namespace System.Xml
@@ -9,7 +11,7 @@ namespace System.Xml
     // Represents the text content of an element or attribute.
     public class XmlWhitespace : XmlCharacterData
     {
-        protected internal XmlWhitespace(string strData, XmlDocument doc) : base(strData, doc)
+        protected internal XmlWhitespace(string? strData, XmlDocument doc) : base(strData, doc)
         {
             if (!doc.IsLoading && !base.CheckOnData(strData))
                 throw new ArgumentException(SR.Xdom_WS_Char);
@@ -20,7 +22,7 @@ public override string Name
         {
             get
             {
-                return OwnerDocument.strNonSignificantWhitespaceName;
+                return OwnerDocument!.strNonSignificantWhitespaceName;
             }
         }
 
@@ -29,7 +31,7 @@ public override string LocalName
         {
             get
             {
-                return OwnerDocument.strNonSignificantWhitespaceName;
+                return OwnerDocument!.strNonSignificantWhitespaceName;
             }
         }
 
@@ -42,11 +44,11 @@ public override XmlNodeType NodeType
             }
         }
 
-        public override XmlNode ParentNode
+        public override XmlNode? ParentNode
         {
             get
             {
-                switch (parentNode.NodeType)
+                switch (parentNode!.NodeType)
                 {
                     case XmlNodeType.Document:
                         return base.ParentNode;
@@ -54,10 +56,10 @@ public override XmlNode ParentNode
                     case XmlNodeType.CDATA:
                     case XmlNodeType.Whitespace:
                     case XmlNodeType.SignificantWhitespace:
-                        XmlNode parent = parentNode.parentNode;
+                        XmlNode parent = parentNode.parentNode!;
                         while (parent.IsText)
                         {
-                            parent = parent.parentNode;
+                            parent = parent.parentNode!;
                         }
                         return parent;
                     default:
@@ -66,13 +68,12 @@ public override XmlNode ParentNode
             }
         }
 
-        public override string Value
+        public override string? Value
         {
             get
             {
                 return Data;
             }
-
             set
             {
                 if (CheckOnData(value))
@@ -119,14 +120,15 @@ internal override bool IsText
             }
         }
 
-        public override XmlNode PreviousText
+        public override XmlNode? PreviousText
         {
             get
             {
-                if (parentNode.IsText)
+                if (parentNode != null && parentNode.IsText)
                 {
                     return parentNode;
                 }
+
                 return null;
             }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Resolvers/XmlPreloadedResolver.cs b/src/libraries/System.Private.Xml/src/System/Xml/Resolvers/XmlPreloadedResolver.cs
index d5cf08b9893066..e09c29c3b236a3 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Resolvers/XmlPreloadedResolver.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Resolvers/XmlPreloadedResolver.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.IO;
 using System.Xml;
 using System.Net;
@@ -34,15 +35,16 @@ internal virtual TextReader AsTextReader()
             }
 
             // Returns true for types that are supported for this preloaded data; Stream must always be supported
-            internal virtual bool SupportsType(Type type)
+            internal virtual bool SupportsType(Type? type)
             {
                 if (type == null || type == typeof(Stream))
                 {
                     return true;
                 }
+
                 return false;
             }
-        };
+        }
 
         //
         // XmlKnownDtdData class
@@ -63,7 +65,7 @@ internal XmlKnownDtdData(string publicId, string systemId, string resourceName)
             internal override Stream AsStream()
             {
                 Assembly asm = GetType().Assembly;
-                return asm.GetManifestResourceStream(_resourceName);
+                return asm.GetManifestResourceStream(_resourceName)!;
             }
         }
 
@@ -110,12 +112,13 @@ internal override TextReader AsTextReader()
                 return new StringReader(_str);
             }
 
-            internal override bool SupportsType(Type type)
+            internal override bool SupportsType(Type? type)
             {
                 if (type == typeof(TextReader))
                 {
                     return true;
                 }
+
                 return base.SupportsType(type);
             }
         }
@@ -123,7 +126,7 @@ internal override bool SupportsType(Type type)
         //
         // Fields
         //
-        private readonly XmlResolver _fallbackResolver;
+        private readonly XmlResolver? _fallbackResolver;
         private readonly Dictionary<Uri, PreloadedData> _mappings;
         private readonly XmlKnownDtds _preloadedDtds;
 
@@ -156,17 +159,17 @@ public XmlPreloadedResolver(XmlKnownDtds preloadedDtds)
         {
         }
 
-        public XmlPreloadedResolver(XmlResolver fallbackResolver)
+        public XmlPreloadedResolver(XmlResolver? fallbackResolver)
             : this(fallbackResolver, XmlKnownDtds.All, null)
         {
         }
 
-        public XmlPreloadedResolver(XmlResolver fallbackResolver, XmlKnownDtds preloadedDtds)
+        public XmlPreloadedResolver(XmlResolver? fallbackResolver, XmlKnownDtds preloadedDtds)
             : this(fallbackResolver, preloadedDtds, null)
         {
         }
 
-        public XmlPreloadedResolver(XmlResolver fallbackResolver, XmlKnownDtds preloadedDtds, IEqualityComparer<Uri> uriComparer)
+        public XmlPreloadedResolver(XmlResolver? fallbackResolver, XmlKnownDtds preloadedDtds, IEqualityComparer<Uri>? uriComparer)
         {
             _fallbackResolver = fallbackResolver;
             _mappings = new Dictionary<Uri, PreloadedData>(16, uriComparer);
@@ -186,7 +189,7 @@ public XmlPreloadedResolver(XmlResolver fallbackResolver, XmlKnownDtds preloaded
             }
         }
 
-        public override Uri ResolveUri(Uri baseUri, string relativeUri)
+        public override Uri ResolveUri(Uri? baseUri, string? relativeUri)
         {
             // 1) special-case well-known public IDs
             // 2) To make FxCop happy we need to use StartsWith() overload that takes StringComparison ->
@@ -216,23 +219,25 @@ public override Uri ResolveUri(Uri baseUri, string relativeUri)
                     }
                 }
             }
+
             return base.ResolveUri(baseUri, relativeUri);
         }
 
-        public override object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn)
+        public override object? GetEntity(Uri absoluteUri, string? role, Type? ofObjectToReturn)
         {
             if (absoluteUri == null)
             {
                 throw new ArgumentNullException(nameof(absoluteUri));
             }
 
-            PreloadedData data;
+            PreloadedData? data;
             if (!_mappings.TryGetValue(absoluteUri, out data))
             {
                 if (_fallbackResolver != null)
                 {
                     return _fallbackResolver.GetEntity(absoluteUri, role, ofObjectToReturn);
                 }
+
                 throw new XmlException(SR.Format(SR.Xml_CannotResolveUrl, absoluteUri));
             }
 
@@ -261,14 +266,14 @@ public override ICredentials Credentials
             }
         }
 
-        public override bool SupportsType(Uri absoluteUri, Type type)
+        public override bool SupportsType(Uri absoluteUri, Type? type)
         {
             if (absoluteUri == null)
             {
                 throw new ArgumentNullException(nameof(absoluteUri));
             }
 
-            PreloadedData data;
+            PreloadedData? data;
             if (!_mappings.TryGetValue(absoluteUri, out data))
             {
                 if (_fallbackResolver != null)
@@ -291,6 +296,7 @@ public void Add(Uri uri, byte[] value)
             {
                 throw new ArgumentNullException(nameof(value));
             }
+
             Add(uri, new ByteArrayChunk(value, 0, value.Length));
         }
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/Asttree.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/Asttree.cs
index f30dc546f2099e..7fefb7ac0606f4 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/Asttree.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/Asttree.cs
@@ -416,7 +416,7 @@ internal Axis? Next
         }
 
         //constructor
-        internal DoubleLinkAxis(Axis axis, DoubleLinkAxis inputaxis)
+        internal DoubleLinkAxis(Axis axis, DoubleLinkAxis? inputaxis)
             : base(axis.TypeOfAxis, inputaxis, axis.Prefix, axis.Name, axis.NodeType)
         {
             this.next = null;
@@ -437,7 +437,7 @@ internal DoubleLinkAxis(Axis axis, DoubleLinkAxis inputaxis)
                 return null;
             }
 
-            return new DoubleLinkAxis(axis, ConvertTree((Axis)axis.Input));
+            return new DoubleLinkAxis(axis, ConvertTree((Axis?)axis.Input));
         }
     }
 
@@ -575,7 +575,7 @@ public void CompileXPath(string xPath, bool isField, XmlNamespaceManager nsmgr)
                 throw new XmlSchemaException(SR.Sch_ICXpathError, xPath);
             }
 
-            Axis stepAst;
+            Axis? stepAst;
             for (int i = 0; i < AstArray.Count; ++i)
             {
                 Axis ast = (Axis)AstArray[i]!;
@@ -603,7 +603,7 @@ public void CompileXPath(string xPath, bool isField, XmlNamespaceManager nsmgr)
                         SetURN(stepAst, nsmgr);
                         try
                         {
-                            stepAst = (Axis)(stepAst.Input);
+                            stepAst = (Axis?)(stepAst.Input);
                         }
                         catch
                         {
@@ -631,7 +631,7 @@ public void CompileXPath(string xPath, bool isField, XmlNamespaceManager nsmgr)
                     }
                     try
                     {
-                        stepAst = (Axis)(stepAst.Input);
+                        stepAst = (Axis?)(stepAst.Input);
                     }
                     catch
                     {
@@ -660,7 +660,7 @@ public void CompileXPath(string xPath, bool isField, XmlNamespaceManager nsmgr)
                 }
                 try
                 {
-                    stepAst = (Axis)(stepAst.Input);
+                    stepAst = (Axis?)(stepAst.Input);
                 }
                 catch
                 {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/BaseValidator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/BaseValidator.cs
index b6b2a59e48266d..17a51af17bbdc5 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/BaseValidator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/BaseValidator.cs
@@ -16,7 +16,7 @@ namespace System.Xml.Schema
     internal class BaseValidator
     {
         private readonly XmlSchemaCollection? _schemaCollection;
-        private readonly IValidationEventHandling _eventHandling;
+        private readonly IValidationEventHandling? _eventHandling;
         private readonly XmlNameTable _nameTable;
         private SchemaNames? _schemaNames;
         private readonly PositionInfo _positionInfo;
@@ -45,7 +45,7 @@ public BaseValidator(BaseValidator other)
             elementName = other.elementName;
         }
 
-        public BaseValidator(XmlValidatingReaderImpl reader, XmlSchemaCollection? schemaCollection, IValidationEventHandling eventHandling)
+        public BaseValidator(XmlValidatingReaderImpl reader, XmlSchemaCollection? schemaCollection, IValidationEventHandling? eventHandling)
         {
             Debug.Assert(schemaCollection == null || schemaCollection.NameTable == reader.NameTable);
             this.reader = reader;
@@ -110,9 +110,9 @@ public Uri? BaseUri
             set { _baseUri = value; }
         }
 
-        public ValidationEventHandler EventHandler
+        public ValidationEventHandler? EventHandler
         {
-            get { return (ValidationEventHandler)_eventHandling.EventHandler; }
+            get { return (ValidationEventHandler?)_eventHandling!.EventHandler; }
         }
 
         public SchemaInfo? SchemaInfo
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/DtdParser.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/DtdParser.cs
index f83c30d759ea2b..ba8515296c36fd 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/DtdParser.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/DtdParser.cs
@@ -269,7 +269,7 @@ private void Initialize(IDtdParserAdapter readerAdapter)
             _freeFloatingDtd = false;
         }
 
-        private void InitializeFreeFloatingDtd(string baseUri, string docTypeName, string publicId, string systemId, string internalSubset, IDtdParserAdapter adapter)
+        private void InitializeFreeFloatingDtd(string baseUri, string docTypeName, string? publicId, string? systemId, string? internalSubset, IDtdParserAdapter adapter)
         {
             Initialize(adapter);
 
@@ -340,7 +340,7 @@ IDtdInfo IDtdParser.ParseInternalDtd(IDtdParserAdapter adapter, bool saveInterna
             return _schemaInfo;
         }
 
-        IDtdInfo IDtdParser.ParseFreeFloatingDtd(string baseUri, string docTypeName, string publicId, string systemId, string internalSubset, IDtdParserAdapter adapter)
+        IDtdInfo IDtdParser.ParseFreeFloatingDtd(string baseUri, string docTypeName, string? publicId, string? systemId, string? internalSubset, IDtdParserAdapter adapter)
         {
             InitializeFreeFloatingDtd(baseUri, docTypeName, publicId, systemId, internalSubset, adapter);
             Parse(false);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/DtdValidator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/DtdValidator.cs
index f725bad3653369..a385ee2cb13238 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/DtdValidator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/DtdValidator.cs
@@ -566,7 +566,7 @@ public static void CheckDefaultValue(
             SchemaAttDef attdef,
             SchemaInfo sinfo,
             IValidationEventHandling eventHandling,
-            string baseUriStr
+            string? baseUriStr
         )
         {
             try
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/Parser.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/Parser.cs
index a70e1e3344ea8b..967afd56e2c4d1 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/Parser.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/Parser.cs
@@ -247,13 +247,14 @@ public bool ParseReaderNode()
                         XmlNode[] markup = new XmlNode[list.Count];
                         for (int i = 0; i < list.Count; i++)
                         {
-                            markup[i] = list[i];
+                            markup[i] = list[i]!;
                         }
 
                         _builder!.ProcessMarkup(markup);
                         _namespaceManager!.PopScope();
                         _builder.EndChildren();
                     }
+
                     _markupDepth = int.MaxValue;
                 }
                 else
@@ -405,7 +406,7 @@ private XmlAttribute CreateXmlNsAttribute(string prefix, string value)
             XmlAttribute attr;
             if (prefix.Length == 0)
             {
-                attr = _dummyDocument.CreateAttribute(string.Empty, _xmlns, XmlReservedNs.NsXmlNs);
+                attr = _dummyDocument.CreateAttribute(string.Empty, _xmlns!, XmlReservedNs.NsXmlNs);
             }
             else
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XdrValidator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XdrValidator.cs
index b9f8875eebbc78..a5df534b04bc0c 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XdrValidator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XdrValidator.cs
@@ -31,7 +31,7 @@ internal XdrValidator(BaseValidator validator) : base(validator)
             Init();
         }
 
-        internal XdrValidator(XmlValidatingReaderImpl reader, XmlSchemaCollection schemaCollection, IValidationEventHandling eventHandling) : base(reader, schemaCollection, eventHandling)
+        internal XdrValidator(XmlValidatingReaderImpl reader, XmlSchemaCollection schemaCollection, IValidationEventHandling? eventHandling) : base(reader, schemaCollection, eventHandling)
         {
             Init();
         }
@@ -42,7 +42,7 @@ internal XdrValidator(XmlValidatingReaderImpl reader, XmlSchemaCollection schema
         [MemberNotNull(nameof(_attPresence))]
         private void Init()
         {
-            _nsManager = reader.NamespaceManager;
+            _nsManager = reader.NamespaceManager!;
             if (_nsManager == null)
             {
                 _nsManager = new XmlNamespaceManager(NameTable);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaAttribute.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaAttribute.cs
index d191b5e2298ce3..0f8fe5f74fd328 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaAttribute.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaAttribute.cs
@@ -4,6 +4,7 @@
 #nullable enable
 using System.Collections;
 using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
 using System.Xml.Serialization;
 
 namespace System.Xml.Schema
@@ -113,7 +114,8 @@ public XmlSchemaSimpleType? AttributeSchemaType
             get { return _attributeType; }
         }
 
-        internal XmlReader? Validate(XmlReader reader, XmlResolver resolver, XmlSchemaSet schemaSet, ValidationEventHandler valEventHandler)
+        [return: NotNullIfNotNull("schemaSet")]
+        internal XmlReader? Validate(XmlReader reader, XmlResolver? resolver, XmlSchemaSet schemaSet, ValidationEventHandler valEventHandler)
         {
             if (schemaSet != null)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaCollection.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaCollection.cs
index 0c6aeacd2b9c63..707de039376fa5 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaCollection.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaCollection.cs
@@ -83,7 +83,7 @@ public event ValidationEventHandler ValidationEventHandler
             remove { _validationEventHandler -= value; }
         }
 
-        internal XmlResolver XmlResolver
+        internal XmlResolver? XmlResolver
         {
             set
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaElement.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaElement.cs
index a8d41372e1ead6..7ea0845bf01b9f 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaElement.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaElement.cs
@@ -5,6 +5,7 @@
 using System.ComponentModel;
 using System.Xml.Serialization;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml.Schema
 {
@@ -195,7 +196,8 @@ public XmlSchemaDerivationMethod FinalResolved
             get { return _finalResolved; }
         }
 
-        internal XmlReader? Validate(XmlReader reader, XmlResolver resolver, XmlSchemaSet schemaSet, ValidationEventHandler valEventHandler)
+        [return: NotNullIfNotNull("schemaSet")]
+        internal XmlReader? Validate(XmlReader reader, XmlResolver? resolver, XmlSchemaSet schemaSet, ValidationEventHandler valEventHandler)
         {
             if (schemaSet != null)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaType.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaType.cs
index c00a0d58c94603..b3a10c4e1984b3 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaType.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaType.cs
@@ -4,6 +4,7 @@
 #nullable enable
 using System.Collections;
 using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
 using System.Xml.Serialization;
 
 namespace System.Xml.Schema
@@ -209,7 +210,8 @@ internal XmlValueConverter ValueConverter
             }
         }
 
-        internal XmlReader? Validate(XmlReader reader, XmlResolver resolver, XmlSchemaSet schemaSet, ValidationEventHandler valEventHandler)
+        [return: NotNullIfNotNull("schemaSet")]
+        internal XmlReader? Validate(XmlReader reader, XmlResolver? resolver, XmlSchemaSet schemaSet, ValidationEventHandler valEventHandler)
         {
             if (schemaSet != null)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaValidationException.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaValidationException.cs
index fccacd3d1b1fbb..993aa858936c9f 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaValidationException.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaValidationException.cs
@@ -69,7 +69,7 @@ public object? SourceObject
             get { return _sourceNodeObject; }
         }
 
-        protected internal void SetSourceObject(object sourceObject)
+        protected internal void SetSourceObject(object? sourceObject)
         {
             _sourceNodeObject = sourceObject;
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaValidator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaValidator.cs
index 386f0a28f9d219..5b993c86b1e578 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaValidator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XmlSchemaValidator.cs
@@ -17,7 +17,7 @@
 
 namespace System.Xml.Schema
 {
-    public delegate object XmlValueGetter();
+    public delegate object? XmlValueGetter();
 
     [Flags]
     public enum XmlSchemaValidationFlags
@@ -677,7 +677,7 @@ public void ValidateElement(string localName, string namespaceUri, XmlSchemaInfo
                         object attValue;
                         if (attributeValueGetter != null)
                         {
-                            attValue = attributeValueGetter();
+                            attValue = attributeValueGetter()!;
                         }
                         else
                         {
@@ -821,7 +821,7 @@ private void ValidateText(string? elementStringValue, XmlValueGetter? elementVal
                     case XmlSchemaContentType.TextOnly:
                         if (elementValueGetter != null)
                         {
-                            SaveTextValue(elementValueGetter());
+                            SaveTextValue(elementValueGetter()!);
                         }
                         else
                         {
@@ -830,7 +830,7 @@ private void ValidateText(string? elementStringValue, XmlValueGetter? elementVal
                         break;
 
                     case XmlSchemaContentType.ElementOnly:
-                        string textValue = elementValueGetter != null ? elementValueGetter().ToString()! : elementStringValue!;
+                        string textValue = elementValueGetter != null ? elementValueGetter()!.ToString()! : elementStringValue!;
                         if (_xmlCharType.IsOnlyWhitespace(textValue))
                         {
                             break;
@@ -852,7 +852,7 @@ private void ValidateText(string? elementStringValue, XmlValueGetter? elementVal
                         {
                             if (elementValueGetter != null)
                             {
-                                SaveTextValue(elementValueGetter());
+                                SaveTextValue(elementValueGetter()!);
                             }
                             else
                             {
@@ -905,7 +905,7 @@ private void ValidateWhitespace(string? elementStringValue, XmlValueGetter? elem
                     case XmlSchemaContentType.TextOnly:
                         if (elementValueGetter != null)
                         {
-                            SaveTextValue(elementValueGetter());
+                            SaveTextValue(elementValueGetter()!);
                         }
                         else
                         {
@@ -918,7 +918,7 @@ private void ValidateWhitespace(string? elementStringValue, XmlValueGetter? elem
                         {
                             if (elementValueGetter != null)
                             {
-                                SaveTextValue(elementValueGetter());
+                                SaveTextValue(elementValueGetter()!);
                             }
                             else
                             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XsdValidator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XsdValidator.cs
index 241a501668c966..2191857f29a245 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Schema/XsdValidator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Schema/XsdValidator.cs
@@ -68,12 +68,13 @@ internal XsdValidator(XmlValidatingReaderImpl reader, XmlSchemaCollection schema
         [MemberNotNull(nameof(_xsdSchema))]
         private void Init()
         {
-            _nsManager = reader.NamespaceManager;
+            _nsManager = reader.NamespaceManager!;
             if (_nsManager == null)
             {
                 _nsManager = new XmlNamespaceManager(NameTable);
                 _bManageNamespaces = true;
             }
+
             _validationStack = new HWStack(STACK_INCREMENT);
             textValue = new StringBuilder();
             _attPresence = new Hashtable();
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/IXPathNavigable.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/IXPathNavigable.cs
index 48e81316b3078b..30154d43cfde07 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/IXPathNavigable.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/IXPathNavigable.cs
@@ -1,10 +1,11 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml.XPath
 {
     public interface IXPathNavigable
     {
-        XPathNavigator CreateNavigator();
+        XPathNavigator? CreateNavigator();
     }
 }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AbsoluteQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AbsoluteQuery.cs
index 57e04149234150..e50788851e5cd8 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AbsoluteQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AbsoluteQuery.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
+using System.Diagnostics;
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
@@ -12,13 +14,14 @@ private AbsoluteQuery(AbsoluteQuery other) : base(other) { }
 
         public override object Evaluate(XPathNodeIterator context)
         {
+            Debug.Assert(context.Current != null);
             base.contextNode = context.Current.Clone();
             base.contextNode.MoveToRoot();
             count = 0;
             return this;
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator context)
+        public override XPathNavigator? MatchNode(XPathNavigator? context)
         {
             if (context != null && context.NodeType == XPathNodeType.Root)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AstNode.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AstNode.cs
index 77990da06fed62..0ffc5380a22e79 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AstNode.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AstNode.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AttributeQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AttributeQuery.cs
index b152fd93874153..eea9f6fb04cb22 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AttributeQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/AttributeQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
@@ -22,7 +23,7 @@ public override void Reset()
             base.Reset();
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             while (true)
             {
@@ -39,6 +40,7 @@ public override XPathNavigator Advance()
                 }
                 else
                 {
+                    Debug.Assert(currentNode != null);
                     _onAttribute = currentNode.MoveToNextAttribute();
                 }
 
@@ -54,7 +56,7 @@ public override XPathNavigator Advance()
             } // while
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator context)
+        public override XPathNavigator? MatchNode(XPathNavigator? context)
         {
             if (context != null)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Axis.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Axis.cs
index ebf10976b73295..d29b580aab1482 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Axis.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Axis.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 
@@ -9,7 +10,7 @@ namespace MS.Internal.Xml.XPath
     internal class Axis : AstNode
     {
         private readonly AxisType _axisType;
-        private AstNode _input;
+        private AstNode? _input;
         private readonly string _prefix;
         private readonly string _name;
         private readonly XPathNodeType _nodeType;
@@ -34,7 +35,7 @@ public enum AxisType
         };
 
         // constructor
-        public Axis(AxisType axisType, AstNode input, string prefix, string name, XPathNodeType nodetype)
+        public Axis(AxisType axisType, AstNode? input, string prefix, string name, XPathNodeType nodetype)
         {
             Debug.Assert(prefix != null);
             Debug.Assert(name != null);
@@ -46,7 +47,7 @@ public Axis(AxisType axisType, AstNode input, string prefix, string name, XPathN
         }
 
         // constructor
-        public Axis(AxisType axisType, AstNode input)
+        public Axis(AxisType axisType, AstNode? input)
             : this(axisType, input, string.Empty, string.Empty, XPathNodeType.All)
         {
             this.abbrAxis = true;
@@ -56,7 +57,7 @@ public Axis(AxisType axisType, AstNode input)
 
         public override XPathResultType ReturnType { get { return XPathResultType.NodeSet; } }
 
-        public AstNode Input
+        public AstNode? Input
         {
             get { return _input; }
             set { _input = value; }
@@ -69,8 +70,8 @@ public AstNode Input
         public bool AbbrAxis { get { return abbrAxis; } }
 
         // Used by AstTree in Schema
-        private string _urn = string.Empty;
-        public string Urn
+        private string? _urn = string.Empty;
+        public string? Urn
         {
             get { return _urn; }
             set { _urn = value; }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BaseAxisQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BaseAxisQuery.cs
index 330137bf344b89..bdc4cc22459ce1 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BaseAxisQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BaseAxisQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
@@ -14,12 +15,12 @@ internal abstract class BaseAxisQuery : Query
         private readonly bool _nameTest;
         private readonly string _name;
         private readonly string _prefix;
-        private string _nsUri;
+        private string? _nsUri;
         private readonly XPathNodeType _typeTest;
 
         // these two things are the state of this class
         // that need to be reset whenever the context changes.
-        protected XPathNavigator currentNode;
+        protected XPathNavigator? currentNode;
         protected int position;
 
         protected BaseAxisQuery(Query qyInput)
@@ -67,12 +68,12 @@ public override void SetXsltContext(XsltContext context)
         }
 
         protected string Name { get { return _name; } }
-        protected string Namespace { get { return _nsUri; } }
+        protected string? Namespace { get { return _nsUri; } }
         protected bool NameTest { get { return _nameTest; } }
         protected XPathNodeType TypeTest { get { return _typeTest; } }
 
         public override int CurrentPosition { get { return position; } }
-        public override XPathNavigator Current { get { return currentNode; } }
+        public override XPathNavigator? Current { get { return currentNode; } }
 
         public virtual bool matches(XPathNavigator e)
         {
@@ -86,6 +87,7 @@ public virtual bool matches(XPathNavigator e)
                 {
                     if (_name.Equals(e.LocalName) || _name.Length == 0)
                     {
+                        Debug.Assert(_nsUri != null);
                         if (_nsUri.Equals(e.NamespaceURI))
                         {
                             return true;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BooleanExpr.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BooleanExpr.cs
index 4cf058b90289f6..2174615d51d7ff 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BooleanExpr.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BooleanExpr.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BooleanFunctions.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BooleanFunctions.cs
index 7b5c13e573be61..ae0e4144c36ee0 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BooleanFunctions.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/BooleanFunctions.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Diagnostics;
 using System.Xml;
@@ -12,10 +13,10 @@ namespace MS.Internal.Xml.XPath
 {
     internal sealed class BooleanFunctions : ValueQuery
     {
-        private readonly Query _arg;
+        private readonly Query? _arg;
         private readonly FT _funcType;
 
-        public BooleanFunctions(FT funcType, Query arg)
+        public BooleanFunctions(FT funcType, Query? arg)
         {
             _arg = arg;
             _funcType = funcType;
@@ -56,10 +57,10 @@ internal static bool toBoolean(string str)
 
         internal bool toBoolean(XPathNodeIterator nodeIterator)
         {
-            object result = _arg.Evaluate(nodeIterator);
+            object result = _arg!.Evaluate(nodeIterator);
             if (result is XPathNodeIterator) return _arg.Advance() != null;
 
-            string str = result as string;
+            string? str = result as string;
             if (str != null)
                 return toBoolean(str);
 
@@ -73,12 +74,13 @@ internal bool toBoolean(XPathNodeIterator nodeIterator)
 
         private bool Not(XPathNodeIterator nodeIterator)
         {
-            return !(bool)_arg.Evaluate(nodeIterator);
+            return !(bool)_arg!.Evaluate(nodeIterator);
         }
 
         private bool Lang(XPathNodeIterator nodeIterator)
         {
-            string str = _arg.Evaluate(nodeIterator).ToString();
+            string str = _arg!.Evaluate(nodeIterator).ToString()!;
+            Debug.Assert(nodeIterator.Current != null);
             string lang = nodeIterator.Current.XmlLang;
             return (
                lang.StartsWith(str, StringComparison.OrdinalIgnoreCase) &&
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheAxisQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheAxisQuery.cs
index d2b45ba505cb05..a01d88dd7c3665 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheAxisQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheAxisQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Xml.XPath;
@@ -35,7 +36,7 @@ public override object Evaluate(XPathNodeIterator context)
             return this;
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             Debug.Assert(0 <= count && count <= outputBuffer.Count);
             if (count < outputBuffer.Count)
@@ -45,7 +46,7 @@ public override XPathNavigator Advance()
             return null;
         }
 
-        public override XPathNavigator Current
+        public override XPathNavigator? Current
         {
             get
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheChildrenQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheChildrenQuery.cs
index 1325d2ff88d688..6dcaae29d95ec1 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheChildrenQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheChildrenQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
@@ -16,12 +17,12 @@ namespace MS.Internal.Xml.XPath
     // So we don't need to call DecideNextNode() when needInput == true && stack is empty.
     internal sealed class CacheChildrenQuery : ChildrenQuery
     {
-        private XPathNavigator _nextInput;
+        private XPathNavigator? _nextInput;
         private readonly StackNav _elementStk;
         private readonly StackInt _positionStk;
         private bool _needInput;
 #if DEBUG
-        private XPathNavigator _lastNode;
+        private XPathNavigator? _lastNode;
 #endif
 
         public CacheChildrenQuery(Query qyInput, string name, string prefix, XPathNodeType type) : base(qyInput, name, prefix, type)
@@ -53,7 +54,7 @@ public override void Reset()
 #endif
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             do
             {
@@ -85,7 +86,7 @@ public override XPathNavigator Advance()
                 }
                 else
                 {
-                    if (!currentNode.MoveToNext() || !DecideNextNode())
+                    if (!currentNode!.MoveToNext() || !DecideNextNode())
                     {
                         _needInput = true;
                         continue;
@@ -104,9 +105,9 @@ private bool DecideNextNode()
             _nextInput = GetNextInput();
             if (_nextInput != null)
             {
-                if (CompareNodes(currentNode, _nextInput) == XmlNodeOrder.After)
+                if (CompareNodes(currentNode!, _nextInput) == XmlNodeOrder.After)
                 {
-                    _elementStk.Push(currentNode);
+                    _elementStk.Push(currentNode!);
                     _positionStk.Push(position);
                     currentNode = _nextInput;
                     _nextInput = null;
@@ -120,9 +121,9 @@ private bool DecideNextNode()
             return true;
         }
 
-        private XPathNavigator GetNextInput()
+        private XPathNavigator? GetNextInput()
         {
-            XPathNavigator result;
+            XPathNavigator? result;
             if (_nextInput != null)
             {
                 result = _nextInput;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheOutputQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheOutputQuery.cs
index 3a3ea0623d5693..c200c466015a2f 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheOutputQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CacheOutputQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Xml;
@@ -46,7 +47,7 @@ public override object Evaluate(XPathNodeIterator context)
                                             // All subclasses should and would anyway override this method and return this.
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             Debug.Assert(0 <= count && count <= outputBuffer.Count);
             if (count < outputBuffer.Count)
@@ -56,7 +57,7 @@ public override XPathNavigator Advance()
             return null;
         }
 
-        public override XPathNavigator Current
+        public override XPathNavigator? Current
         {
             get
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ChildrenQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ChildrenQuery.cs
index 3caf9d300a4d23..3a9d201f083741 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ChildrenQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ChildrenQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
@@ -21,11 +22,11 @@ public override void Reset()
             base.Reset();
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             while (!_iterator.MoveNext())
             {
-                XPathNavigator input = qyInput.Advance();
+                XPathNavigator? input = qyInput.Advance();
                 if (input == null)
                 {
                     return null;
@@ -38,7 +39,7 @@ public override XPathNavigator Advance()
                     }
                     else
                     {
-                        _iterator = input.SelectChildren(Name, Namespace);
+                        _iterator = input.SelectChildren(Name, Namespace!);
                     }
                 }
                 else
@@ -52,7 +53,7 @@ public override XPathNavigator Advance()
             return currentNode;
         } // Advance
 
-        public sealed override XPathNavigator MatchNode(XPathNavigator context)
+        public sealed override XPathNavigator? MatchNode(XPathNavigator? context)
         {
             if (context != null)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ClonableStack.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ClonableStack.cs
index 08af2101b2e043..4637938a15322a 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ClonableStack.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ClonableStack.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace MS.Internal.Xml.XPath
 {
     internal sealed class ClonableStack<T> : System.Collections.Generic.List<T>
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CompiledXPathExpr.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CompiledXPathExpr.cs
index 5fb8907cee2632..e8c5556b22eab7 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CompiledXPathExpr.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/CompiledXPathExpr.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections;
 using System.Diagnostics;
@@ -51,14 +52,14 @@ public override void AddSort(object expr, IComparer comparer)
             // sort makes sense only when we are dealing with a query that
             // returns a nodeset.
             Query evalExpr;
-            string query = expr as string;
+            string? query = expr as string;
             if (query != null)
             {
                 evalExpr = new QueryBuilder().Build(query, out _needContext); // this will throw if expr is invalid
             }
             else
             {
-                CompiledXpathExpr xpathExpr = expr as CompiledXpathExpr;
+                CompiledXpathExpr? xpathExpr = expr as CompiledXpathExpr;
                 if (xpathExpr != null)
                 {
                     evalExpr = xpathExpr.QueryTree;
@@ -68,7 +69,7 @@ public override void AddSort(object expr, IComparer comparer)
                     throw XPathException.Create(SR.Xp_BadQueryObject);
                 }
             }
-            SortQuery sortQuery = _query as SortQuery;
+            SortQuery? sortQuery = _query as SortQuery;
             if (sortQuery == null)
             {
                 _query = sortQuery = new SortQuery(_query);
@@ -91,9 +92,9 @@ public override void SetContext(XmlNamespaceManager nsManager)
             SetContext((IXmlNamespaceResolver)nsManager);
         }
 
-        public override void SetContext(IXmlNamespaceResolver nsResolver)
+        public override void SetContext(IXmlNamespaceResolver? nsResolver)
         {
-            XsltContext xsltContext = nsResolver as XsltContext;
+            XsltContext? xsltContext = nsResolver as XsltContext;
             if (xsltContext == null)
             {
                 if (nsResolver == null)
@@ -129,7 +130,7 @@ public override string LookupNamespace(string prefix)
                 {
                     return string.Empty;
                 }
-                string ns = _nsResolver.LookupNamespace(prefix);
+                string? ns = _nsResolver.LookupNamespace(prefix);
                 if (ns == null)
                 {
                     throw XPathException.Create(SR.XmlUndefinedAlias, prefix);
@@ -196,13 +197,13 @@ public XPathComparerHelper(XmlSortOrder order, XmlCaseOrder caseOrder, string la
             _dataType = dataType;
         }
 
-        public int Compare(object x, object y)
+        public int Compare(object? x, object? y)
         {
             switch (_dataType)
             {
                 case XmlDataType.Text:
-                    string s1 = Convert.ToString(x, _cinfo);
-                    string s2 = Convert.ToString(y, _cinfo);
+                    string? s1 = Convert.ToString(x, _cinfo);
+                    string? s2 = Convert.ToString(y, _cinfo);
                     int result = _cinfo.CompareInfo.Compare(s1, s2, _caseOrder != XmlCaseOrder.None ? CompareOptions.IgnoreCase : CompareOptions.None);
 
                     if (result != 0 || _caseOrder == XmlCaseOrder.None)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ContextQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ContextQuery.cs
index 814d86ba0988f2..6725fea72579a2 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ContextQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ContextQuery.cs
@@ -1,13 +1,14 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
 {
     internal class ContextQuery : Query
     {
-        protected XPathNavigator contextNode;
+        protected XPathNavigator? contextNode;
 
         public ContextQuery()
         {
@@ -22,7 +23,7 @@ public override void Reset()
             count = 0;
         }
 
-        public override XPathNavigator Current { get { return contextNode; } }
+        public override XPathNavigator? Current { get { return contextNode; } }
 
         public override object Evaluate(XPathNodeIterator context)
         {
@@ -31,7 +32,7 @@ public override object Evaluate(XPathNodeIterator context)
             return this;
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             if (count == 0)
             {
@@ -41,7 +42,7 @@ public override XPathNavigator Advance()
             return null;
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator current)
+        public override XPathNavigator? MatchNode(XPathNavigator? current)
         {
             return current;
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantBaseQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantBaseQuery.cs
index 7e9ea6ab427b2f..2c289612b82acb 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantBaseQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantBaseQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Xml;
 using System.Xml.XPath;
@@ -23,7 +24,7 @@ public DescendantBaseQuery(DescendantBaseQuery other) : base(other)
             this.abbrAxis = other.abbrAxis;
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator context)
+        public override XPathNavigator? MatchNode(XPathNavigator? context)
         {
             if (context != null)
             {
@@ -31,7 +32,7 @@ public override XPathNavigator MatchNode(XPathNavigator context)
                 {
                     throw XPathException.Create(SR.Xp_InvalidPattern);
                 }
-                XPathNavigator result = null;
+                XPathNavigator? result = null;
                 if (matches(context))
                 {
                     if (matchSelf)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantQuery.cs
index db248bb6ac7ea8..413da810a407e2 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantQuery.cs
@@ -1,13 +1,14 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
 {
     internal class DescendantQuery : DescendantBaseQuery
     {
-        private XPathNodeIterator _nodeIterator;
+        private XPathNodeIterator? _nodeIterator;
 
         internal DescendantQuery(Query qyParent, string Name, string Prefix, XPathNodeType Type, bool matchSelf, bool abbrAxis)
             : base(qyParent, Name, Prefix, Type, matchSelf, abbrAxis)
@@ -24,14 +25,14 @@ public override void Reset()
             base.Reset();
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             while (true)
             {
                 if (_nodeIterator == null)
                 {
                     position = 0;
-                    XPathNavigator nav = qyInput.Advance();
+                    XPathNavigator? nav = qyInput.Advance();
                     if (nav == null)
                     {
                         return null;
@@ -44,7 +45,7 @@ public override XPathNavigator Advance()
                         }
                         else
                         {
-                            _nodeIterator = nav.SelectDescendants(Name, Namespace, matchSelf);
+                            _nodeIterator = nav.SelectDescendants(Name, Namespace!, matchSelf);
                         }
                     }
                     else
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantoverDescendantQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantoverDescendantQuery.cs
index af1d23bee52ffd..1b0d657a406fea 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantoverDescendantQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DescendantoverDescendantQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 
@@ -28,7 +29,7 @@ public override void Reset()
             base.Reset();
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             while (true)
             {
@@ -60,6 +61,7 @@ public override XPathNavigator Advance()
                 }
                 do
                 {
+                    Debug.Assert(currentNode != null);
                     if (matches(currentNode))
                     {
                         position++;
@@ -71,6 +73,7 @@ public override XPathNavigator Advance()
 
         private bool MoveToFirstChild()
         {
+            Debug.Assert(currentNode != null);
             if (currentNode.MoveToFirstChild())
             {
                 _level++;
@@ -81,6 +84,7 @@ private bool MoveToFirstChild()
 
         private bool MoveUpUntilNext()
         { // move up until we can move next
+            Debug.Assert(currentNode != null);
             while (!currentNode.MoveToNext())
             {
                 --_level;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DocumentorderQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DocumentorderQuery.cs
index 7577f3c0f3c2a0..f2f56f6a72e77a 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DocumentorderQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/DocumentorderQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
@@ -14,7 +15,7 @@ public override object Evaluate(XPathNodeIterator context)
         {
             base.Evaluate(context);
 
-            XPathNavigator node;
+            XPathNavigator? node;
             while ((node = base.input.Advance()) != null)
             {
                 Insert(outputBuffer, node);
@@ -23,7 +24,7 @@ public override object Evaluate(XPathNodeIterator context)
             return this;
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator context)
+        public override XPathNavigator? MatchNode(XPathNavigator? context)
         {
             return input.MatchNode(context);
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/EmptyQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/EmptyQuery.cs
index fe95898adbbd56..ebfd1a7229d1b9 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/EmptyQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/EmptyQuery.cs
@@ -1,13 +1,14 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
 {
     internal sealed class EmptyQuery : Query
     {
-        public override XPathNavigator Advance() { return null; }
+        public override XPathNavigator? Advance() { return null; }
         public override XPathNodeIterator Clone() { return this; }
         public override object Evaluate(XPathNodeIterator context) { return this; }
         public override int CurrentPosition { get { return 0; } }
@@ -15,6 +16,6 @@ internal sealed class EmptyQuery : Query
         public override QueryProps Properties { get { return QueryProps.Merge | QueryProps.Cached | QueryProps.Position | QueryProps.Count; } }
         public override XPathResultType StaticType { get { return XPathResultType.NodeSet; } }
         public override void Reset() { }
-        public override XPathNavigator Current { get { return null; } }
+        public override XPathNavigator? Current { get { return null; } }
     }
 }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ExtensionQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ExtensionQuery.cs
index f4ed528d734325..4645ba2bc93b0a 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ExtensionQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ExtensionQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Xml;
 using System.Xml.XPath;
@@ -12,8 +13,8 @@ internal abstract class ExtensionQuery : Query
     {
         protected string prefix;
         protected string name;
-        protected XsltContext xsltContext;
-        private ResetableIterator _queryIterator;
+        protected XsltContext? xsltContext;
+        private ResetableIterator? _queryIterator;
 
         public ExtensionQuery(string prefix, string name) : base()
         {
@@ -25,7 +26,7 @@ protected ExtensionQuery(ExtensionQuery other) : base(other)
             this.prefix = other.prefix;
             this.name = other.name;
             this.xsltContext = other.xsltContext;
-            _queryIterator = (ResetableIterator)Clone(other._queryIterator);
+            _queryIterator = (ResetableIterator?)Clone(other._queryIterator);
         }
 
         public override void Reset()
@@ -36,7 +37,7 @@ public override void Reset()
             }
         }
 
-        public override XPathNavigator Current
+        public override XPathNavigator? Current
         {
             get
             {
@@ -52,7 +53,7 @@ public override XPathNavigator Current
             }
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             if (_queryIterator == null)
             {
@@ -77,7 +78,7 @@ public override int CurrentPosition
             }
         }
 
-        protected object ProcessResult(object value)
+        protected object? ProcessResult(object? value)
         {
             if (value is string) return value;
             if (value is double) return value;
@@ -91,7 +92,7 @@ protected object ProcessResult(object value)
                 return this; // We map null to NodeSet to let $null/foo work well.
             }
 
-            ResetableIterator resetable = value as ResetableIterator;
+            ResetableIterator? resetable = value as ResetableIterator;
             if (resetable != null)
             {
                 // We need Clone() value because variable may be used several times
@@ -99,15 +100,16 @@ protected object ProcessResult(object value)
                 _queryIterator = (ResetableIterator)resetable.Clone();
                 return this;
             }
-            XPathNodeIterator nodeIterator = value as XPathNodeIterator;
+            XPathNodeIterator? nodeIterator = value as XPathNodeIterator;
             if (nodeIterator != null)
             {
                 _queryIterator = new XPathArrayIterator(nodeIterator);
                 return this;
             }
-            IXPathNavigable navigable = value as IXPathNavigable;
+            IXPathNavigable? navigable = value as IXPathNavigable;
             if (navigable != null)
             {
+                // This may be null if navigable is typeof(XmlNode).
                 return navigable.CreateNavigator();
             }
 
@@ -118,7 +120,7 @@ protected object ProcessResult(object value)
             if (value is ulong) return (double)(ulong)value;
             if (value is float) return (double)(float)value;
             if (value is decimal) return (double)(decimal)value;
-            return value.ToString();
+            return value.ToString()!;
         }
 
         protected string QName { get { return prefix.Length != 0 ? prefix + ":" + name : name; } }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Filter.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Filter.cs
index 11ecec19c49c7e..e0840ef3499613 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Filter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Filter.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FilterQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FilterQuery.cs
index d64034eb025941..53eaf5a23a1045 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FilterQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FilterQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
@@ -40,7 +41,7 @@ public override void SetXsltContext(XsltContext input)
             {
                 // BugBug: We can do such trick at Evaluate time only.
                 // But to do this FilterQuery should stop inherit from BaseAxisQuery
-                ReversePositionQuery query = qyInput as ReversePositionQuery;
+                ReversePositionQuery? query = qyInput as ReversePositionQuery;
                 if (query != null)
                 {
                     qyInput = query.input;
@@ -48,7 +49,7 @@ public override void SetXsltContext(XsltContext input)
             }
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             while ((currentNode = qyInput.Advance()) != null)
             {
@@ -72,9 +73,9 @@ internal bool EvaluatePredicate()
             return true;
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator current)
+        public override XPathNavigator? MatchNode(XPathNavigator? current)
         {
-            XPathNavigator context;
+            XPathNavigator? context;
             if (current == null)
             {
                 return null;
@@ -87,11 +88,11 @@ public override XPathNavigator MatchNode(XPathNavigator current)
                 switch (_cond.StaticType)
                 {
                     case XPathResultType.Number:
-                        OperandQuery operand = _cond as OperandQuery;
+                        OperandQuery? operand = _cond as OperandQuery;
                         if (operand != null)
                         {
                             double val = (double)operand.val;
-                            ChildrenQuery childrenQuery = qyInput as ChildrenQuery;
+                            ChildrenQuery? childrenQuery = qyInput as ChildrenQuery;
                             if (childrenQuery != null)
                             { // foo[2], but not foo[expr][2]
                                 XPathNavigator result = current.Clone();
@@ -111,7 +112,7 @@ public override XPathNavigator MatchNode(XPathNavigator current)
                                 } while (result.MoveToNext());
                                 return null;
                             }
-                            AttributeQuery attributeQuery = qyInput as AttributeQuery;
+                            AttributeQuery? attributeQuery = qyInput as AttributeQuery;
                             if (attributeQuery != null)
                             {// @foo[3], but not @foo[expr][2]
                                 XPathNavigator result = current.Clone();
@@ -156,7 +157,7 @@ public override XPathNavigator MatchNode(XPathNavigator current)
                 /* Generic case */
                 {
                     Evaluate(new XPathSingletonIterator(context, /*moved:*/true));
-                    XPathNavigator result;
+                    XPathNavigator? result;
                     while ((result = Advance()) != null)
                     {
                         if (result.IsSamePosition(current))
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FollSiblingQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FollSiblingQuery.cs
index 3135c9ec0ce72a..a579d60cc75e14 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FollSiblingQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FollSiblingQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Xml.XPath;
 using StackNav = MS.Internal.Xml.XPath.ClonableStack<System.Xml.XPath.XPathNavigator>;
@@ -11,7 +12,7 @@ internal sealed class FollSiblingQuery : BaseAxisQuery
     {
         private readonly StackNav _elementStk;
         private readonly List<XPathNavigator> _parentStk;
-        private XPathNavigator _nextInput;
+        private XPathNavigator? _nextInput;
 
         public FollSiblingQuery(Query qyInput, string name, string prefix, XPathNodeType type) : base(qyInput, name, prefix, type)
         {
@@ -48,9 +49,9 @@ private bool Visited(XPathNavigator nav)
             return false;
         }
 
-        private XPathNavigator FetchInput()
+        private XPathNavigator? FetchInput()
         {
-            XPathNavigator input;
+            XPathNavigator? input;
             do
             {
                 input = qyInput.Advance();
@@ -62,7 +63,7 @@ private XPathNavigator FetchInput()
             return input.Clone();
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             while (true)
             {
@@ -90,7 +91,7 @@ public override XPathNavigator Advance()
                 while (currentNode.IsDescendant(_nextInput))
                 {
                     _elementStk.Push(currentNode);
-                    currentNode = _nextInput;
+                    currentNode = _nextInput!;
                     _nextInput = qyInput.Advance();
                     if (_nextInput != null)
                     {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FollowingQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FollowingQuery.cs
index a5f309d34b1d1d..48a998caa030c7 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FollowingQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FollowingQuery.cs
@@ -1,14 +1,16 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
+using System.Diagnostics;
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
 {
     internal sealed class FollowingQuery : BaseAxisQuery
     {
-        private XPathNavigator _input;
-        private XPathNodeIterator _iterator;
+        private XPathNavigator? _input;
+        private XPathNodeIterator? _iterator;
 
         public FollowingQuery(Query qyInput, string name, string prefix, XPathNodeType typeTest) : base(qyInput, name, prefix, typeTest) { }
         private FollowingQuery(FollowingQuery other) : base(other)
@@ -23,7 +25,7 @@ public override void Reset()
             base.Reset();
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             if (_iterator == null)
             {
@@ -47,7 +49,7 @@ public override XPathNavigator Advance()
             while (!_iterator.MoveNext())
             {
                 bool matchSelf;
-                if (_input.NodeType == XPathNodeType.Attribute || _input.NodeType == XPathNodeType.Namespace)
+                if (_input!.NodeType == XPathNodeType.Attribute || _input.NodeType == XPathNodeType.Namespace)
                 {
                     _input.MoveToParent();
                     matchSelf = false;
@@ -65,7 +67,7 @@ public override XPathNavigator Advance()
                 }
                 if (NameTest)
                 {
-                    _iterator = _input.SelectDescendants(Name, Namespace, matchSelf);
+                    _iterator = _input.SelectDescendants(Name, Namespace!, matchSelf);
                 }
                 else
                 {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ForwardPositionQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ForwardPositionQuery.cs
index 26887dd4439eb1..f70c9a50fbbf24 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ForwardPositionQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ForwardPositionQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 
@@ -18,7 +19,7 @@ public override object Evaluate(XPathNodeIterator context)
         {
             base.Evaluate(context);
 
-            XPathNavigator node;
+            XPathNavigator? node;
             while ((node = base.input.Advance()) != null)
             {
                 outputBuffer.Add(node.Clone());
@@ -27,7 +28,7 @@ public override object Evaluate(XPathNodeIterator context)
             return this;
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator context)
+        public override XPathNavigator? MatchNode(XPathNavigator? context)
         {
             return input.MatchNode(context);
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Function.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Function.cs
index a9b24a624fc758..c1c0e0d2d7154a 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Function.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Function.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Xml.XPath;
 
@@ -43,8 +44,8 @@ public enum FunctionType
         private readonly FunctionType _functionType;
         private readonly List<AstNode> _argumentList;
 
-        private readonly string _name;
-        private readonly string _prefix;
+        private readonly string? _name;
+        private readonly string? _prefix;
 
         public Function(FunctionType ftype, List<AstNode> argumentList)
         {
@@ -79,8 +80,8 @@ public override XPathResultType ReturnType
 
         public FunctionType TypeOfFunction { get { return _functionType; } }
         public List<AstNode> ArgumentList { get { return _argumentList; } }
-        public string Prefix { get { return _prefix; } }
-        public string Name { get { return _name; } }
+        public string? Prefix { get { return _prefix; } }
+        public string? Name { get { return _name; } }
 
         internal static XPathResultType[] ReturnTypes = {
             /* FunctionType.FuncLast            */ XPathResultType.Number,
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FunctionQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FunctionQuery.cs
index f239694a639710..31a38e173321a3 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FunctionQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/FunctionQuery.cs
@@ -1,8 +1,10 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
 using System.Xml.Xsl;
@@ -12,7 +14,7 @@ namespace MS.Internal.Xml.XPath
     internal sealed class FunctionQuery : ExtensionQuery
     {
         private readonly IList<Query> _args;
-        private IXsltContextFunction _function;
+        private IXsltContextFunction? _function;
 
         public FunctionQuery(string prefix, string name, List<Query> args) : base(prefix, name)
         {
@@ -73,12 +75,18 @@ public override object Evaluate(XPathNodeIterator nodeIterator)
                 argVals[i] = _args[i].Evaluate(nodeIterator);
                 if (argVals[i] is XPathNodeIterator)
                 {// ForBack Compat. To protect our queries from users.
+                    Debug.Assert(nodeIterator.Current != null);
                     argVals[i] = new XPathSelectionIterator(nodeIterator.Current, _args[i]);
                 }
             }
             try
             {
-                return ProcessResult(_function.Invoke(xsltContext, argVals, nodeIterator.Current));
+                Debug.Assert(_function != null);
+                object? retVal = ProcessResult(_function.Invoke(xsltContext, argVals, nodeIterator.Current));
+
+                // ProcessResult may return null when the input value is XmlNode and here doesn't seem to be the case.
+                Debug.Assert(retVal != null);
+                return retVal;
             }
             catch (Exception ex)
             {
@@ -86,17 +94,17 @@ public override object Evaluate(XPathNodeIterator nodeIterator)
             }
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator navigator)
+        public override XPathNavigator? MatchNode(XPathNavigator? navigator)
         {
             if (name != "key" && prefix.Length != 0)
             {
                 throw XPathException.Create(SR.Xp_InvalidPattern);
             }
-            this.Evaluate(new XPathSingletonIterator(navigator, /*moved:*/true));
-            XPathNavigator nav = null;
+            this.Evaluate(new XPathSingletonIterator(navigator!, /*moved:*/true));
+            XPathNavigator? nav = null;
             while ((nav = this.Advance()) != null)
             {
-                if (nav.IsSamePosition(navigator))
+                if (nav.IsSamePosition(navigator!))
                 {
                     return nav;
                 }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Group.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Group.cs
index de0171981253f7..de71354d8133ad 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Group.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Group.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/GroupQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/GroupQuery.cs
index 62539469c3cbbc..f5b43b98a88bc1 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/GroupQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/GroupQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
@@ -10,7 +11,7 @@ internal sealed class GroupQuery : BaseAxisQuery
         public GroupQuery(Query qy) : base(qy) { }
         private GroupQuery(GroupQuery other) : base(other) { }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             currentNode = qyInput.Advance();
             if (currentNode != null)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/IdQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/IdQuery.cs
index e7c26e6c7e03dc..1bf9010d8cab47 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/IdQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/IdQuery.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
+using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
 
@@ -14,12 +16,13 @@ private IDQuery(IDQuery other) : base(other) { }
         public override object Evaluate(XPathNodeIterator context)
         {
             object argVal = base.Evaluate(context);
+            Debug.Assert(context.Current != null);
             XPathNavigator contextNode = context.Current.Clone();
 
             switch (GetXPathType(argVal))
             {
                 case XPathResultType.NodeSet:
-                    XPathNavigator temp;
+                    XPathNavigator? temp;
                     while ((temp = input.Advance()) != null)
                     {
                         ProcessIds(contextNode, temp.Value);
@@ -53,13 +56,13 @@ private void ProcessIds(XPathNavigator contextNode, string val)
             }
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator context)
+        public override XPathNavigator? MatchNode(XPathNavigator? context)
         {
-            Evaluate(new XPathSingletonIterator(context, /*moved:*/true));
-            XPathNavigator result;
+            Evaluate(new XPathSingletonIterator(context!, /*moved:*/true));
+            XPathNavigator? result;
             while ((result = Advance()) != null)
             {
-                if (result.IsSamePosition(context))
+                if (result.IsSamePosition(context!))
                 {
                     return context;
                 }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/IteratorFilter.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/IteratorFilter.cs
index a0bedd88ff0300..adb9d0bb256a53 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/IteratorFilter.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/IteratorFilter.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
+using System.Diagnostics;
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
@@ -25,13 +27,14 @@ private IteratorFilter(IteratorFilter it)
         }
 
         public override XPathNodeIterator Clone() { return new IteratorFilter(this); }
-        public override XPathNavigator Current { get { return _innerIterator.Current; } }
+        public override XPathNavigator? Current { get { return _innerIterator.Current; } }
         public override int CurrentPosition { get { return _position; } }
 
         public override bool MoveNext()
         {
             while (_innerIterator.MoveNext())
             {
+                Debug.Assert(_innerIterator.Current != null);
                 if (_innerIterator.Current.LocalName == _name)
                 {
                     _position++;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/LogicalExpr.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/LogicalExpr.cs
index d0b642e71b3bad..53f556d5a95219 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/LogicalExpr.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/LogicalExpr.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
@@ -56,34 +57,39 @@ public override object Evaluate(XPathNodeIterator nodeIterator)
                 type2 = typeTmp;
             }
 
+            cmpXslt? cmp;
+
             if (op == Operator.Op.EQ || op == Operator.Op.NE)
             {
-                return s_CompXsltE[type1][type2](op, val1, val2);
+                cmp = s_CompXsltE[type1][type2];
             }
             else
             {
-                return s_CompXsltO[type1][type2](op, val1, val2);
+                cmp = s_CompXsltO[type1][type2];
             }
+
+            Debug.Assert(cmp != null);
+            return cmp(op, val1, val2);
         }
 
         private delegate bool cmpXslt(Operator.Op op, object val1, object val2);
 
         //                  Number,                       String,                        Boolean,                     NodeSet,                      Navigator
-        private static readonly cmpXslt[][] s_CompXsltE =
+        private static readonly cmpXslt?[][] s_CompXsltE =
         {
-            new cmpXslt[] { new cmpXslt(cmpNumberNumber), null,                          null,                        null,                         null                    },
-            new cmpXslt[] { new cmpXslt(cmpStringNumber), new cmpXslt(cmpStringStringE), null,                        null,                         null                    },
-            new cmpXslt[] { new cmpXslt(cmpBoolNumberE ), new cmpXslt(cmpBoolStringE  ), new cmpXslt(cmpBoolBoolE  ), null,                         null                    },
-            new cmpXslt[] { new cmpXslt(cmpQueryNumber ), new cmpXslt(cmpQueryStringE ), new cmpXslt(cmpQueryBoolE ), new cmpXslt(cmpQueryQueryE ), null                    },
-            new cmpXslt[] { new cmpXslt(cmpRtfNumber   ), new cmpXslt(cmpRtfStringE   ), new cmpXslt(cmpRtfBoolE   ), new cmpXslt(cmpRtfQueryE   ), new cmpXslt(cmpRtfRtfE) },
+            new cmpXslt?[] { new cmpXslt(cmpNumberNumber), null,                          null,                        null,                         null                    },
+            new cmpXslt?[] { new cmpXslt(cmpStringNumber), new cmpXslt(cmpStringStringE), null,                        null,                         null                    },
+            new cmpXslt?[] { new cmpXslt(cmpBoolNumberE ), new cmpXslt(cmpBoolStringE  ), new cmpXslt(cmpBoolBoolE  ), null,                         null                    },
+            new cmpXslt?[] { new cmpXslt(cmpQueryNumber ), new cmpXslt(cmpQueryStringE ), new cmpXslt(cmpQueryBoolE ), new cmpXslt(cmpQueryQueryE ), null                    },
+            new cmpXslt?[] { new cmpXslt(cmpRtfNumber   ), new cmpXslt(cmpRtfStringE   ), new cmpXslt(cmpRtfBoolE   ), new cmpXslt(cmpRtfQueryE   ), new cmpXslt(cmpRtfRtfE) },
         };
-        private static readonly cmpXslt[][] s_CompXsltO =
+        private static readonly cmpXslt?[][] s_CompXsltO =
         {
-            new cmpXslt[] { new cmpXslt(cmpNumberNumber), null,                          null,                        null,                         null                    },
-            new cmpXslt[] { new cmpXslt(cmpStringNumber), new cmpXslt(cmpStringStringO), null,                        null,                         null                    },
-            new cmpXslt[] { new cmpXslt(cmpBoolNumberO ), new cmpXslt(cmpBoolStringO  ), new cmpXslt(cmpBoolBoolO  ), null,                         null                    },
-            new cmpXslt[] { new cmpXslt(cmpQueryNumber ), new cmpXslt(cmpQueryStringO ), new cmpXslt(cmpQueryBoolO ), new cmpXslt(cmpQueryQueryO ), null                    },
-            new cmpXslt[] { new cmpXslt(cmpRtfNumber   ), new cmpXslt(cmpRtfStringO   ), new cmpXslt(cmpRtfBoolO   ), new cmpXslt(cmpRtfQueryO   ), new cmpXslt(cmpRtfRtfO) },
+            new cmpXslt?[] { new cmpXslt(cmpNumberNumber), null,                          null,                        null,                         null                    },
+            new cmpXslt?[] { new cmpXslt(cmpStringNumber), new cmpXslt(cmpStringStringO), null,                        null,                         null                    },
+            new cmpXslt?[] { new cmpXslt(cmpBoolNumberO ), new cmpXslt(cmpBoolStringO  ), new cmpXslt(cmpBoolBoolO  ), null,                         null                    },
+            new cmpXslt?[] { new cmpXslt(cmpQueryNumber ), new cmpXslt(cmpQueryStringO ), new cmpXslt(cmpQueryBoolO ), new cmpXslt(cmpQueryQueryO ), null                    },
+            new cmpXslt?[] { new cmpXslt(cmpRtfNumber   ), new cmpXslt(cmpRtfStringO   ), new cmpXslt(cmpRtfBoolO   ), new cmpXslt(cmpRtfQueryO   ), new cmpXslt(cmpRtfRtfO) },
         };
 
         /*cmpXslt:*/
@@ -408,7 +414,7 @@ private static bool cmpRtfRtfO(Operator.Op op, object val1, object val2)
         private struct NodeSet
         {
             private readonly Query _opnd;
-            private XPathNavigator _current;
+            private XPathNavigator? _current;
 
             public NodeSet(object opnd)
             {
@@ -426,7 +432,7 @@ public void Reset()
                 _opnd.Reset();
             }
 
-            public string Value { get { return _current.Value; } }
+            public string Value { get { return _current!.Value; } }
         }
 
         private static string Rtf(object o) { return ((XPathNavigator)o).Value; }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/MergeFilterQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/MergeFilterQuery.cs
index bea4a1cc7ac0aa..81c661d1517844 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/MergeFilterQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/MergeFilterQuery.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
+using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
 using System.Xml.Xsl;
@@ -33,7 +35,7 @@ public override object Evaluate(XPathNodeIterator nodeIterator)
             while (input.Advance() != null)
             {
                 _child.Evaluate(input);
-                XPathNavigator node;
+                XPathNavigator? node;
                 while ((node = _child.Advance()) != null)
                 {
                     Insert(outputBuffer, node);
@@ -42,9 +44,9 @@ public override object Evaluate(XPathNodeIterator nodeIterator)
             return this;
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator current)
+        public override XPathNavigator? MatchNode(XPathNavigator? current)
         {
-            XPathNavigator context = _child.MatchNode(current);
+            XPathNavigator? context = _child.MatchNode(current);
             if (context == null)
             {
                 return null;
@@ -55,9 +57,10 @@ public override XPathNavigator MatchNode(XPathNavigator current)
                 return null;
             }
             Evaluate(new XPathSingletonIterator(context.Clone(), /*moved:*/true));
-            XPathNavigator result = Advance();
+            XPathNavigator? result = Advance();
             while (result != null)
             {
+                Debug.Assert(current != null);
                 if (result.IsSamePosition(current))
                 {
                     return context;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NamespaceQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NamespaceQuery.cs
index b7351e9af9aeb7..0d44a9b25376de 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NamespaceQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NamespaceQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 
@@ -22,7 +23,7 @@ public override void Reset()
             base.Reset();
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             while (true)
             {
@@ -39,7 +40,7 @@ public override XPathNavigator Advance()
                 }
                 else
                 {
-                    _onNamespace = currentNode.MoveToNextNamespace();
+                    _onNamespace = currentNode!.MoveToNextNamespace();
                 }
 
                 if (_onNamespace)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NodeFunctions.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NodeFunctions.cs
index 6dfc45b82cd3d9..8cd1bd738019ea 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NodeFunctions.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NodeFunctions.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml;
 using System.Xml.XPath;
 using System.Xml.Xsl;
@@ -10,11 +11,11 @@ namespace MS.Internal.Xml.XPath
 {
     internal sealed class NodeFunctions : ValueQuery
     {
-        private readonly Query _arg;
+        private readonly Query? _arg;
         private readonly FT _funcType;
-        private XsltContext _xsltContext;
+        private XsltContext? _xsltContext;
 
-        public NodeFunctions(FT funcType, Query arg)
+        public NodeFunctions(FT funcType, Query? arg)
         {
             _funcType = funcType;
             _arg = arg;
@@ -29,7 +30,7 @@ public override void SetXsltContext(XsltContext context)
             }
         }
 
-        private XPathNavigator EvaluateArg(XPathNodeIterator context)
+        private XPathNavigator? EvaluateArg(XPathNodeIterator context)
         {
             if (_arg == null)
             {
@@ -41,7 +42,7 @@ private XPathNavigator EvaluateArg(XPathNodeIterator context)
 
         public override object Evaluate(XPathNodeIterator context)
         {
-            XPathNavigator argVal;
+            XPathNavigator? argVal;
 
             switch (_funcType)
             {
@@ -71,11 +72,11 @@ public override object Evaluate(XPathNodeIterator context)
                     }
                     break;
                 case FT.FuncCount:
-                    _arg.Evaluate(context);
+                    _arg!.Evaluate(context);
                     int count = 0;
                     if (_xsltContext != null)
                     {
-                        XPathNavigator nav;
+                        XPathNavigator? nav;
                         while ((nav = _arg.Advance()) != null)
                         {
                             if (nav.NodeType != XPathNodeType.Whitespace || _xsltContext.PreserveWhitespace(nav))
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NumberFunctions.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NumberFunctions.cs
index db805361a7fc90..6675f776aa35ff 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NumberFunctions.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NumberFunctions.cs
@@ -1,7 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
+using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
 using System.Xml.Xsl;
@@ -11,10 +13,10 @@ namespace MS.Internal.Xml.XPath
 {
     internal sealed class NumberFunctions : ValueQuery
     {
-        private readonly Query _arg;
+        private readonly Query? _arg;
         private readonly FT _ftype;
 
-        public NumberFunctions(FT ftype, Query arg)
+        public NumberFunctions(FT ftype, Query? arg)
         {
             _arg = arg;
             _ftype = ftype;
@@ -50,20 +52,21 @@ public override object Evaluate(XPathNodeIterator nodeIterator) =>
                 FT.FuncFloor => Floor(nodeIterator),
                 FT.FuncCeiling => Ceiling(nodeIterator),
                 FT.FuncRound => Round(nodeIterator),
-                _ => null,
+                _ => throw new InvalidOperationException(),
             };
 
         private double Number(XPathNodeIterator nodeIterator)
         {
             if (_arg == null)
             {
+                Debug.Assert(nodeIterator.Current != null);
                 return XmlConvert.ToXPathDouble(nodeIterator.Current.Value);
             }
             object argVal = _arg.Evaluate(nodeIterator);
             switch (GetXPathType(argVal))
             {
                 case XPathResultType.NodeSet:
-                    XPathNavigator value = _arg.Advance();
+                    XPathNavigator? value = _arg.Advance();
                     if (value != null)
                     {
                         return Number(value.Value);
@@ -84,8 +87,9 @@ private double Number(XPathNodeIterator nodeIterator)
         private double Sum(XPathNodeIterator nodeIterator)
         {
             double sum = 0;
+            Debug.Assert(_arg != null);
             _arg.Evaluate(nodeIterator);
-            XPathNavigator nav;
+            XPathNavigator? nav;
             while ((nav = _arg.Advance()) != null)
             {
                 sum += Number(nav.Value);
@@ -95,16 +99,19 @@ private double Sum(XPathNodeIterator nodeIterator)
 
         private double Floor(XPathNodeIterator nodeIterator)
         {
+            Debug.Assert(_arg != null);
             return Math.Floor((double)_arg.Evaluate(nodeIterator));
         }
 
         private double Ceiling(XPathNodeIterator nodeIterator)
         {
+            Debug.Assert(_arg != null);
             return Math.Ceiling((double)_arg.Evaluate(nodeIterator));
         }
 
         private double Round(XPathNodeIterator nodeIterator)
         {
+            Debug.Assert(_arg != null);
             double n = XmlConvert.ToXPathDouble(_arg.Evaluate(nodeIterator));
             return XmlConvert.XPathRound(n);
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NumericExpr.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NumericExpr.cs
index 854232dc96b80d..eeb5775e7e218f 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NumericExpr.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/NumericExpr.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Operand.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Operand.cs
index ae309945f41588..edde39245f64a6 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Operand.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Operand.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/OperandQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/OperandQuery.cs
index 851944910e9b26..ff8172d18a8fc8 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/OperandQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/OperandQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Globalization;
 using System.Xml;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Operator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Operator.cs
index 6dd69c8e611ca1..2a79a96f7ce17e 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Operator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Operator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ParentQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ParentQuery.cs
index 567259abe76a49..7661973f0594e3 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ParentQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ParentQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
@@ -14,7 +15,7 @@ public override object Evaluate(XPathNodeIterator context)
         {
             base.Evaluate(context);
 
-            XPathNavigator input;
+            XPathNavigator? input;
             while ((input = qyInput.Advance()) != null)
             {
                 input = input.Clone();
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/PreSiblingQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/PreSiblingQuery.cs
index 6db2488019be59..17762b4e66179c 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/PreSiblingQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/PreSiblingQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Xml.XPath;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/PrecedingQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/PrecedingQuery.cs
index b0243dad2f9bb8..818ab4085d6ffe 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/PrecedingQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/PrecedingQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 using StackNav = MS.Internal.Xml.XPath.ClonableStack<System.Xml.XPath.XPathNavigator>;
@@ -20,7 +21,7 @@ namespace MS.Internal.Xml.XPath
 
     internal sealed class PrecedingQuery : BaseAxisQuery
     {
-        private XPathNodeIterator _workIterator;
+        private XPathNodeIterator? _workIterator;
         private readonly StackNav _ancestorStk;
 
         public PrecedingQuery(Query qyInput, string name, string prefix, XPathNodeType typeTest) : base(qyInput, name, prefix, typeTest)
@@ -40,13 +41,13 @@ public override void Reset()
             base.Reset();
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             if (_workIterator == null)
             {
                 XPathNavigator last;
                 {
-                    XPathNavigator input = qyInput.Advance();
+                    XPathNavigator? input = qyInput.Advance();
                     if (input == null)
                     {
                         return null;
@@ -74,7 +75,7 @@ public override XPathNavigator Advance()
 
             while (_workIterator.MoveNext())
             {
-                currentNode = _workIterator.Current;
+                currentNode = _workIterator.Current!;
                 if (currentNode.IsSamePosition(_ancestorStk.Peek()))
                 {
                     _ancestorStk.Pop();
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Query.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Query.cs
index c9622097a201d8..cfb402c3a11cc3 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Query.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Query.cs
@@ -1,9 +1,11 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Xml;
 using System.Xml.XPath;
 using System.Xml.Xsl;
@@ -53,9 +55,9 @@ public override int Count
         public virtual void SetXsltContext(XsltContext context) { }
 
         public abstract object Evaluate(XPathNodeIterator nodeIterator);
-        public abstract XPathNavigator Advance();
+        public abstract XPathNavigator? Advance();
 
-        public virtual XPathNavigator MatchNode(XPathNavigator current)
+        public virtual XPathNavigator? MatchNode(XPathNavigator? current)
         {
             throw XPathException.Create(SR.Xp_InvalidPattern);
         }
@@ -65,7 +67,8 @@ public virtual XPathNavigator MatchNode(XPathNavigator current)
         public virtual QueryProps Properties { get { return QueryProps.Merge; } }
 
         // ----------------- Helper methods -------------
-        public static Query Clone(Query input)
+        [return: NotNullIfNotNull("input")]
+        public static Query? Clone(Query? input)
         {
             if (input != null)
             {
@@ -74,7 +77,8 @@ public static Query Clone(Query input)
             return null;
         }
 
-        protected static XPathNodeIterator Clone(XPathNodeIterator input)
+        [return: NotNullIfNotNull("input")]
+        protected static XPathNodeIterator? Clone(XPathNodeIterator? input)
         {
             if (input != null)
             {
@@ -83,7 +87,8 @@ protected static XPathNodeIterator Clone(XPathNodeIterator input)
             return null;
         }
 
-        protected static XPathNavigator Clone(XPathNavigator input)
+        [return: NotNullIfNotNull("input")]
+        protected static XPathNavigator? Clone(XPathNavigator? input)
         {
             if (input != null)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/QueryBuilder.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/QueryBuilder.cs
index 004adff0653e25..efda195b62e8ab 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/QueryBuilder.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/QueryBuilder.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -40,12 +41,12 @@ private enum Props
         }
 
         // comment are approximate. This is my best understanding:
-        private string _query;
+        private string? _query;
         private bool _allowVar;
         private bool _allowKey;
         private bool _allowCurrent;
         private bool _needContext;
-        private BaseAxisQuery _firstInput; // Input of the leftmost predicate. Set by leftmost predicate, used in rightmost one
+        private BaseAxisQuery? _firstInput; // Input of the leftmost predicate. Set by leftmost predicate, used in rightmost one
 
         private void Reset()
         {
@@ -55,7 +56,7 @@ private void Reset()
 
         private Query ProcessAxis(Axis root, Flags flags, out Props props)
         {
-            Query result = null;
+            Query? result = null;
             if (root.Prefix.Length > 0)
             {
                 _needContext = true;
@@ -68,7 +69,7 @@ private Query ProcessAxis(Axis root, Flags flags, out Props props)
                     Flags inputFlags = Flags.None;
                     if ((flags & Flags.PosFilter) == 0)
                     {
-                        Axis input = root.Input as Axis;
+                        Axis? input = root.Input as Axis;
                         if (input != null)
                         {
                             if (
@@ -198,7 +199,7 @@ private Query ProcessAxis(Axis root, Flags flags, out Props props)
                     }
                     break;
                 default:
-                    throw XPathException.Create(SR.Xp_NotSupported, _query);
+                    throw XPathException.Create(SR.Xp_NotSupported, _query!);
             }
 
             return result;
@@ -252,7 +253,7 @@ private Query ProcessFilter(Filter root, Flags flags, out Props props)
 
             /*merging predicates*/
             {
-                FilterQuery qyFilter = qyInput as FilterQuery;
+                FilterQuery? qyFilter = qyInput as FilterQuery;
                 if (qyFilter != null && (propsCond & Props.HasPosition) == 0 && qyFilter.Condition.StaticType != XPathResultType.Any)
                 {
                     Query prevCond = qyFilter.Condition;
@@ -308,7 +309,7 @@ private Query ProcessFilter(Filter root, Flags flags, out Props props)
             return new FilterQuery(qyInput, cond, /*noPosition:*/(propsCond & Props.HasPosition) == 0);
         }
 
-        private Query ProcessOperator(Operator root, out Props props)
+        private Query? ProcessOperator(Operator root, out Props props)
         {
             Props props1, props2;
             Query op1 = ProcessNode(root.Operand1, Flags.None, out props1);
@@ -344,7 +345,7 @@ private Query ProcessVariable(Variable root)
             _needContext = true;
             if (!_allowVar)
             {
-                throw XPathException.Create(SR.Xp_InvalidKeyPattern, _query);
+                throw XPathException.Create(SR.Xp_InvalidKeyPattern, _query!);
             }
             return new VariableQuery(root.Localname, root.Prefix);
         }
@@ -352,7 +353,7 @@ private Query ProcessVariable(Variable root)
         private Query ProcessFunction(Function root, out Props props)
         {
             props = Props.None;
-            Query qy = null;
+            Query? qy = null;
             switch (root.TypeOfFunction)
             {
                 case FT.FuncLast:
@@ -420,6 +421,9 @@ private Query ProcessFunction(Function root, out Props props)
                         ProcessNode((AstNode)root.ArgumentList[0], Flags.None, out props)
                     );
                 case FT.FuncUserDefined:
+                    Debug.Assert(root.Prefix != null);
+                    Debug.Assert(root.Name != null);
+
                     _needContext = true;
                     if (!_allowCurrent && root.Name == "current" && root.Prefix.Length == 0)
                     {
@@ -427,19 +431,19 @@ private Query ProcessFunction(Function root, out Props props)
                     }
                     if (!_allowKey && root.Name == "key" && root.Prefix.Length == 0)
                     {
-                        throw XPathException.Create(SR.Xp_InvalidKeyPattern, _query);
+                        throw XPathException.Create(SR.Xp_InvalidKeyPattern, _query!);
                     }
                     qy = new FunctionQuery(root.Prefix, root.Name, ProcessArguments(root.ArgumentList, out props));
                     props |= Props.NonFlat;
                     return qy;
                 default:
-                    throw XPathException.Create(SR.Xp_NotSupported, _query);
+                    throw XPathException.Create(SR.Xp_NotSupported, _query!);
             }
         }
 
         private List<Query> ProcessArguments(List<AstNode> args, out Props props)
         {
-            int numArgs = args != null ? args.Count : 0;
+            int numArgs = args.Count;
             List<Query> argList = new List<Query>(numArgs);
             props = Props.None;
             for (int count = 0; count < numArgs; count++)
@@ -462,7 +466,7 @@ private Query ProcessNode(AstNode root, Flags flags, out Props props)
             }
 
             Debug.Assert(root != null, "root != null");
-            Query result = null;
+            Query? result = null;
             props = Props.None;
             switch (root.Type)
             {
@@ -495,7 +499,7 @@ private Query ProcessNode(AstNode root, Flags flags, out Props props)
                     break;
             }
             --_parseDepth;
-            return result;
+            return result!;
         }
 
         private Query Build(AstNode root, string query)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ResetableIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ResetableIterator.cs
index d88410000e3991..ed06c29494e7f8 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ResetableIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ResetableIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ReversePositionQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ReversePositionQuery.cs
index 7d65497e248562..116b29568a958c 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ReversePositionQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ReversePositionQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Root.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Root.cs
index 505bc9e2bb3a43..5e9303fa81dd56 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Root.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Root.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/SortQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/SortQuery.cs
index 3d441e27b491f3..96eeb329426fb6 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/SortQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/SortQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -53,7 +54,7 @@ private void BuildResultsList()
 
             Debug.Assert(numSorts > 0, "Why was the sort query created?");
 
-            XPathNavigator eNext;
+            XPathNavigator? eNext;
             while ((eNext = _qyInput.Advance()) != null)
             {
                 SortKey key = new SortKey(numSorts, /*originalPosition:*/_results.Count, eNext.Clone());
@@ -77,7 +78,7 @@ public override object Evaluate(XPathNodeIterator context)
             return this;
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             Debug.Assert(0 <= count && count <= _results.Count);
             if (count < _results.Count)
@@ -87,7 +88,7 @@ public override XPathNavigator Advance()
             return null;
         }
 
-        public override XPathNavigator Current
+        public override XPathNavigator? Current
         {
             get
             {
@@ -192,7 +193,7 @@ public Query Expression(int i)
             return _expressions[i];
         }
 
-        int IComparer<SortKey>.Compare(SortKey x, SortKey y)
+        int IComparer<SortKey>.Compare(SortKey? x, SortKey? y)
         {
             Debug.Assert(x != null && y != null, "Oops!! what happened?");
             int result = 0;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/StringFunctions.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/StringFunctions.cs
index 24cc50c015ad44..d2634c7084ed85 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/StringFunctions.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/StringFunctions.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -79,7 +80,7 @@ private string toString(XPathNodeIterator nodeIterator)
                 switch (GetXPathType(argVal))
                 {
                     case XPathResultType.NodeSet:
-                        XPathNavigator value = _argList[0].Advance();
+                        XPathNavigator? value = _argList[0].Advance();
                         return value != null ? value.Value : string.Empty;
                     case XPathResultType.String:
                         return (string)argVal;
@@ -92,6 +93,7 @@ private string toString(XPathNodeIterator nodeIterator)
                         return toString((double)argVal);
                 }
             }
+            Debug.Assert(nodeIterator.Current != null);
             return nodeIterator.Current.Value;
         }
 
@@ -127,8 +129,9 @@ private string Concat(XPathNodeIterator nodeIterator)
 
         private bool StartsWith(XPathNodeIterator nodeIterator)
         {
-            string s1 = _argList[0].Evaluate(nodeIterator).ToString();
-            string s2 = _argList[1].Evaluate(nodeIterator).ToString();
+            Debug.Assert(_argList.Count > 1);
+            string s1 = _argList[0].Evaluate(nodeIterator).ToString()!;
+            string s2 = _argList[1].Evaluate(nodeIterator).ToString()!;
             return s1.Length >= s2.Length && string.CompareOrdinal(s1, 0, s2, 0, s2.Length) == 0;
         }
 
@@ -136,15 +139,17 @@ private bool StartsWith(XPathNodeIterator nodeIterator)
 
         private bool Contains(XPathNodeIterator nodeIterator)
         {
-            string s1 = _argList[0].Evaluate(nodeIterator).ToString();
-            string s2 = _argList[1].Evaluate(nodeIterator).ToString();
+            Debug.Assert(_argList.Count > 1);
+            string s1 = _argList[0].Evaluate(nodeIterator).ToString()!;
+            string s2 = _argList[1].Evaluate(nodeIterator).ToString()!;
             return s_compareInfo.IndexOf(s1, s2, CompareOptions.Ordinal) >= 0;
         }
 
         private string SubstringBefore(XPathNodeIterator nodeIterator)
         {
-            string s1 = _argList[0].Evaluate(nodeIterator).ToString();
-            string s2 = _argList[1].Evaluate(nodeIterator).ToString();
+            Debug.Assert(_argList.Count > 1);
+            string s1 = _argList[0].Evaluate(nodeIterator).ToString()!;
+            string s2 = _argList[1].Evaluate(nodeIterator).ToString()!;
             if (s2.Length == 0) { return s2; }
             int idx = s_compareInfo.IndexOf(s1, s2, CompareOptions.Ordinal);
             return (idx < 1) ? string.Empty : s1.Substring(0, idx);
@@ -152,8 +157,9 @@ private string SubstringBefore(XPathNodeIterator nodeIterator)
 
         private string SubstringAfter(XPathNodeIterator nodeIterator)
         {
-            string s1 = _argList[0].Evaluate(nodeIterator).ToString();
-            string s2 = _argList[1].Evaluate(nodeIterator).ToString();
+            Debug.Assert(_argList.Count > 1);
+            string s1 = _argList[0].Evaluate(nodeIterator).ToString()!;
+            string s2 = _argList[1].Evaluate(nodeIterator).ToString()!;
             if (s2.Length == 0) { return s1; }
             int idx = s_compareInfo.IndexOf(s1, s2, CompareOptions.Ordinal);
             return (idx < 0) ? string.Empty : s1.Substring(idx + s2.Length);
@@ -161,7 +167,8 @@ private string SubstringAfter(XPathNodeIterator nodeIterator)
 
         private string Substring(XPathNodeIterator nodeIterator)
         {
-            string str1 = _argList[0].Evaluate(nodeIterator).ToString();
+            Debug.Assert(_argList.Count > 0);
+            string str1 = _argList[0].Evaluate(nodeIterator).ToString()!;
             double num = XmlConvert.XPathRound(XmlConvert.ToXPathDouble(_argList[1].Evaluate(nodeIterator))) - 1;
 
             if (double.IsNaN(num) || str1.Length <= num)
@@ -203,8 +210,9 @@ private double StringLength(XPathNodeIterator nodeIterator)
         {
             if (_argList.Count > 0)
             {
-                return _argList[0].Evaluate(nodeIterator).ToString().Length;
+                return _argList[0].Evaluate(nodeIterator).ToString()!.Length;
             }
+            Debug.Assert(nodeIterator.Current != null);
             return nodeIterator.Current.Value.Length;
         }
 
@@ -213,10 +221,11 @@ private string Normalize(XPathNodeIterator nodeIterator)
             string value;
             if (_argList.Count > 0)
             {
-                value = _argList[0].Evaluate(nodeIterator).ToString();
+                value = _argList[0].Evaluate(nodeIterator).ToString()!;
             }
             else
             {
+                Debug.Assert(nodeIterator.Current != null);
                 value = nodeIterator.Current.Value;
             }
             int modifyPos = -1;
@@ -249,9 +258,10 @@ private string Normalize(XPathNodeIterator nodeIterator)
 
         private string Translate(XPathNodeIterator nodeIterator)
         {
-            string value = _argList[0].Evaluate(nodeIterator).ToString();
-            string mapFrom = _argList[1].Evaluate(nodeIterator).ToString();
-            string mapTo = _argList[2].Evaluate(nodeIterator).ToString();
+            Debug.Assert(_argList.Count > 2);
+            string value = _argList[0].Evaluate(nodeIterator).ToString()!;
+            string mapFrom = _argList[1].Evaluate(nodeIterator).ToString()!;
+            string mapTo = _argList[2].Evaluate(nodeIterator).ToString()!;
             int modifyPos = -1;
             char[] chars = value.ToCharArray();
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/UnionExpr.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/UnionExpr.cs
index 902788d8841bc2..d7684f6ac1e435 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/UnionExpr.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/UnionExpr.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Xml;
 using System.Xml.XPath;
@@ -12,8 +13,8 @@ internal sealed class UnionExpr : Query
     {
         internal Query qy1, qy2;
         private bool _advance1, _advance2;
-        private XPathNavigator _currentNode;
-        private XPathNavigator _nextNode;
+        private XPathNavigator? _currentNode;
+        private XPathNavigator? _nextNode;
 
         public UnionExpr(Query query1, Query query2)
         {
@@ -83,9 +84,9 @@ private XPathNavigator ProcessAfterPosition(XPathNavigator res1, XPathNavigator
             return res2;
         }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
-            XPathNavigator res1, res2;
+            XPathNavigator? res1, res2;
             XmlNodeOrder order = 0;
             if (_advance1)
             {
@@ -139,11 +140,11 @@ public override XPathNavigator Advance()
             }
         }
 
-        public override XPathNavigator MatchNode(XPathNavigator xsltContext)
+        public override XPathNavigator? MatchNode(XPathNavigator? xsltContext)
         {
             if (xsltContext != null)
             {
-                XPathNavigator result = qy1.MatchNode(xsltContext);
+                XPathNavigator? result = qy1.MatchNode(xsltContext);
                 if (result != null)
                 {
                     return result;
@@ -157,7 +158,7 @@ public override XPathNavigator MatchNode(XPathNavigator xsltContext)
 
         public override XPathNodeIterator Clone() { return new UnionExpr(this); }
 
-        public override XPathNavigator Current { get { return _currentNode; } }
+        public override XPathNavigator? Current { get { return _currentNode; } }
         public override int CurrentPosition { get { throw new InvalidOperationException(); } }
     }
 }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ValueQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ValueQuery.cs
index 654e86db2ca733..8cb5615d062833 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ValueQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/ValueQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Xml;
 using System.Xml.XPath;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Variable.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Variable.cs
index 45eb4bcf71548a..89150323978dc4 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Variable.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/Variable.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/VariableQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/VariableQuery.cs
index fd74484252a915..74678d2404de93 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/VariableQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/VariableQuery.cs
@@ -1,7 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
+using System.Diagnostics;
 using System.Xml;
 using System.Xml.XPath;
 using System.Xml.Xsl;
@@ -10,7 +12,7 @@ namespace MS.Internal.Xml.XPath
 {
     internal sealed class VariableQuery : ExtensionQuery
     {
-        private IXsltContextVariable _variable;
+        private IXsltContextVariable? _variable;
 
         public VariableQuery(string name, string prefix) : base(prefix, name) { }
         private VariableQuery(VariableQuery other) : base(other)
@@ -44,7 +46,12 @@ public override object Evaluate(XPathNodeIterator nodeIterator)
                 throw XPathException.Create(SR.Xp_NoContext);
             }
 
-            return ProcessResult(_variable.Evaluate(xsltContext));
+            Debug.Assert(_variable != null);
+            object? retVal = ProcessResult(_variable.Evaluate(xsltContext));
+
+            // ProcessResult may return null when the input value is XmlNode and here doesn't seem to be the case.
+            Debug.Assert(retVal != null);
+            return retVal;
         }
 
         public override XPathResultType StaticType
@@ -53,7 +60,7 @@ public override XPathResultType StaticType
             {
                 if (_variable != null)
                 {  // Temp. fix to overcome dependency on static type
-                    return GetXPathType(Evaluate(null));
+                    return GetXPathType(Evaluate(null!));
                 }
                 XPathResultType result = _variable != null ? _variable.VariableType : XPathResultType.Any;
                 if (result == XPathResultType.Error)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAncestorIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAncestorIterator.cs
index d5b07d571e986f..621b4e0304adb5 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAncestorIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAncestorIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAncestorQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAncestorQuery.cs
index 45dab44a195178..0487aa79f7e398 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAncestorQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAncestorQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml;
 using System.Xml.XPath;
 
@@ -23,8 +24,8 @@ public override object Evaluate(XPathNodeIterator context)
         {
             base.Evaluate(context);
 
-            XPathNavigator ancestor = null;
-            XPathNavigator input;
+            XPathNavigator? ancestor = null;
+            XPathNavigator? input;
             while ((input = qyInput.Advance()) != null)
             {
                 if (_matchSelf)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathArrayIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathArrayIterator.cs
index 89d7c8ad24e5b9..2bb0944ebee53a 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathArrayIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathArrayIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -32,6 +33,7 @@ public XPathArrayIterator(XPathNodeIterator nodeIterator)
             this.list = new ArrayList();
             while (nodeIterator.MoveNext())
             {
+                Debug.Assert(nodeIterator.Current != null);
                 this.list.Add(nodeIterator.Current.Clone());
             }
         }
@@ -46,7 +48,7 @@ public override XPathNodeIterator Clone()
             return new XPathArrayIterator(this);
         }
 
-        public override XPathNavigator Current
+        public override XPathNavigator? Current
         {
             get
             {
@@ -56,7 +58,7 @@ public override XPathNavigator Current
                 {
                     throw new InvalidOperationException(SR.Format(SR.Sch_EnumNotStarted, string.Empty));
                 }
-                return (XPathNavigator)list[index - 1];
+                return (XPathNavigator?)list[index - 1];
             }
         }
 
@@ -84,6 +86,6 @@ public override IEnumerator GetEnumerator()
             return list.GetEnumerator();
         }
 
-        private object debuggerDisplayProxy { get { return index < 1 ? null : (object)new XPathNavigator.DebuggerDisplayProxy(Current); } }
+        private object? debuggerDisplayProxy { get { return index < 1 ? null : (object)new XPathNavigator.DebuggerDisplayProxy(Current!); } }
     }
 }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAxisIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAxisIterator.cs
index c5770eb6fdae1a..cf15bfd5f445f9 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAxisIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathAxisIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Xml.XPath;
 
@@ -10,8 +11,8 @@ internal abstract class XPathAxisIterator : XPathNodeIterator
     {
         internal XPathNavigator nav;
         internal XPathNodeType type;
-        internal string name;
-        internal string uri;
+        internal string? name;
+        internal string? uri;
         internal int position;
         internal bool matchSelf;
         internal bool first = true;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathChildIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathChildIterator.cs
index 1db05129cec2f7..3fdeb2ea79dd4d 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathChildIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathChildIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathDescendantIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathDescendantIterator.cs
index 65a0e9b17972b4..f0e1542b67ab4a 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathDescendantIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathDescendantIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathEmptyIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathEmptyIterator.cs
index 318ca6d340144c..bd6b5a0964f46d 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathEmptyIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathEmptyIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
@@ -10,7 +11,7 @@ internal sealed class XPathEmptyIterator : ResetableIterator
         private XPathEmptyIterator() { }
         public override XPathNodeIterator Clone() { return this; }
 
-        public override XPathNavigator Current
+        public override XPathNavigator? Current
         {
             get { return null; }
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathMultyIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathMultyIterator.cs
index 1ca2a7c0c9fd51..437cd195390594 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathMultyIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathMultyIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace MS.Internal.Xml.XPath
 {
     using System;
@@ -22,7 +23,9 @@ public XPathMultyIterator(ArrayList inputArray)
             this.arr = new ResetableIterator[inputArray.Count];
             for (int i = 0; i < this.arr.Length; i++)
             {
-                this.arr[i] = new XPathArrayIterator((ArrayList)inputArray[i]);
+                var iterator = (ArrayList?)inputArray[i];
+                Debug.Assert(iterator != null);
+                this.arr[i] = new XPathArrayIterator(iterator);
             }
             Init();
         }
@@ -101,14 +104,16 @@ private bool SiftItem(int item)
             ResetableIterator it = arr[item];
             while (item + 1 < arr.Length)
             {
-                XmlNodeOrder order = Query.CompareNodes(it.Current, arr[item + 1].Current);
+                ResetableIterator itNext = arr[item + 1];
+                Debug.Assert(it.Current != null && itNext.Current != null);
+                XmlNodeOrder order = Query.CompareNodes(it.Current, itNext.Current);
                 if (order == XmlNodeOrder.Before)
                 {
                     break;
                 }
                 if (order == XmlNodeOrder.After)
                 {
-                    arr[item] = arr[item + 1];
+                    arr[item] = itNext;
                     //arr[item + 1] = it;
                     item++;
                 }
@@ -149,7 +154,7 @@ public override XPathNodeIterator Clone()
             return new XPathMultyIterator(this);
         }
 
-        public override XPathNavigator Current
+        public override XPathNavigator? Current
         {
             get
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathParser.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathParser.cs
index 1546771f979ac2..8c75360e61cdbe 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathParser.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathParser.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -51,7 +52,7 @@ public static AstNode ParseXPathPattern(string xpathPattern)
         private int _parseDepth;
         private const int MaxParseDepth = 200;
 
-        private AstNode ParseExpression(AstNode qyInput)
+        private AstNode ParseExpression(AstNode? qyInput)
         {
             if (++_parseDepth > MaxParseDepth)
             {
@@ -63,7 +64,7 @@ private AstNode ParseExpression(AstNode qyInput)
         }
 
         //>> OrExpr ::= ( OrExpr 'or' )? AndExpr
-        private AstNode ParseOrExpr(AstNode qyInput)
+        private AstNode ParseOrExpr(AstNode? qyInput)
         {
             AstNode opnd = ParseAndExpr(qyInput);
 
@@ -79,7 +80,7 @@ private AstNode ParseOrExpr(AstNode qyInput)
         }
 
         //>> AndExpr ::= ( AndExpr 'and' )? EqualityExpr
-        private AstNode ParseAndExpr(AstNode qyInput)
+        private AstNode ParseAndExpr(AstNode? qyInput)
         {
             AstNode opnd = ParseEqualityExpr(qyInput);
 
@@ -96,7 +97,7 @@ private AstNode ParseAndExpr(AstNode qyInput)
 
         //>> EqualityOp ::= '=' | '!='
         //>> EqualityExpr    ::= ( EqualityExpr EqualityOp )? RelationalExpr
-        private AstNode ParseEqualityExpr(AstNode qyInput)
+        private AstNode ParseEqualityExpr(AstNode? qyInput)
         {
             AstNode opnd = ParseRelationalExpr(qyInput);
 
@@ -118,7 +119,7 @@ private AstNode ParseEqualityExpr(AstNode qyInput)
 
         //>> RelationalOp ::= '<' | '>' | '<=' | '>='
         //>> RelationalExpr    ::= ( RelationalExpr RelationalOp )? AdditiveExpr
-        private AstNode ParseRelationalExpr(AstNode qyInput)
+        private AstNode ParseRelationalExpr(AstNode? qyInput)
         {
             AstNode opnd = ParseAdditiveExpr(qyInput);
 
@@ -142,7 +143,7 @@ private AstNode ParseRelationalExpr(AstNode qyInput)
 
         //>> AdditiveOp   ::= '+' | '-'
         //>> AdditiveExpr ::= ( AdditiveExpr AdditiveOp )? MultiplicativeExpr
-        private AstNode ParseAdditiveExpr(AstNode qyInput)
+        private AstNode ParseAdditiveExpr(AstNode? qyInput)
         {
             AstNode opnd = ParseMultiplicativeExpr(qyInput);
 
@@ -164,7 +165,7 @@ private AstNode ParseAdditiveExpr(AstNode qyInput)
 
         //>> MultiplicativeOp   ::= '*' | 'div' | 'mod'
         //>> MultiplicativeExpr ::= ( MultiplicativeExpr MultiplicativeOp )? UnaryExpr
-        private AstNode ParseMultiplicativeExpr(AstNode qyInput)
+        private AstNode ParseMultiplicativeExpr(AstNode? qyInput)
         {
             AstNode opnd = ParseUnaryExpr(qyInput);
 
@@ -186,7 +187,7 @@ private AstNode ParseMultiplicativeExpr(AstNode qyInput)
         }
 
         //>> UnaryExpr    ::= UnionExpr | '-' UnaryExpr
-        private AstNode ParseUnaryExpr(AstNode qyInput)
+        private AstNode ParseUnaryExpr(AstNode? qyInput)
         {
             bool minus = false;
             while (_scanner.Kind == XPathScanner.LexKind.Minus)
@@ -206,7 +207,7 @@ private AstNode ParseUnaryExpr(AstNode qyInput)
         }
 
         //>> UnionExpr ::= ( UnionExpr '|' )? PathExpr
-        private AstNode ParseUnionExpr(AstNode qyInput)
+        private AstNode ParseUnionExpr(AstNode? qyInput)
         {
             AstNode opnd = ParsePathExpr(qyInput);
 
@@ -239,7 +240,7 @@ private static bool IsNodeType(XPathScanner scaner)
         //>> PathOp   ::= '/' | '//'
         //>> PathExpr ::= LocationPath |
         //>>              FilterExpr ( PathOp  RelativeLocationPath )?
-        private AstNode ParsePathExpr(AstNode qyInput)
+        private AstNode ParsePathExpr(AstNode? qyInput)
         {
             AstNode opnd;
             if (IsPrimaryExpr(_scanner))
@@ -265,7 +266,7 @@ private AstNode ParsePathExpr(AstNode qyInput)
         }
 
         //>> FilterExpr ::= PrimaryExpr | FilterExpr Predicate
-        private AstNode ParseFilterExpr(AstNode qyInput)
+        private AstNode ParseFilterExpr(AstNode? qyInput)
         {
             AstNode opnd = ParsePrimaryExpr(qyInput);
             while (_scanner.Kind == XPathScanner.LexKind.LBracket)
@@ -292,7 +293,7 @@ private AstNode ParsePredicate(AstNode qyInput)
         }
 
         //>> LocationPath ::= RelativeLocationPath | AbsoluteLocationPath
-        private AstNode ParseLocationPath(AstNode qyInput)
+        private AstNode ParseLocationPath(AstNode? qyInput)
         {
             if (_scanner.Kind == XPathScanner.LexKind.Slash)
             {
@@ -318,9 +319,9 @@ private AstNode ParseLocationPath(AstNode qyInput)
 
         //>> PathOp   ::= '/' | '//'
         //>> RelativeLocationPath ::= ( RelativeLocationPath PathOp )? Step
-        private AstNode ParseRelativeLocationPath(AstNode qyInput)
+        private AstNode ParseRelativeLocationPath(AstNode? qyInput)
         {
-            AstNode opnd = qyInput;
+            AstNode? opnd = qyInput;
             do
             {
                 opnd = ParseStep(opnd);
@@ -356,7 +357,7 @@ private static bool IsStep(XPathScanner.LexKind lexKind)
         }
 
         //>> Step ::= '.' | '..' | ( AxisName '::' | '@' )? NodeTest Predicate*
-        private AstNode ParseStep(AstNode qyInput)
+        private AstNode ParseStep(AstNode? qyInput)
         {
             AstNode opnd;
             if (XPathScanner.LexKind.Dot == _scanner.Kind)
@@ -400,7 +401,7 @@ private AstNode ParseStep(AstNode qyInput)
         }
 
         //>> NodeTest ::= NameTest | 'comment ()' | 'text ()' | 'node ()' | 'processing-instruction ('  Literal ? ')'
-        private AstNode ParseNodeTest(AstNode qyInput, Axis.AxisType axisType, XPathNodeType nodeType)
+        private AstNode ParseNodeTest(AstNode? qyInput, Axis.AxisType axisType, XPathNodeType nodeType)
         {
             string nodeName, nodePrefix;
 
@@ -469,10 +470,10 @@ private static bool IsPrimaryExpr(XPathScanner scanner)
         }
 
         //>> PrimaryExpr ::= Literal | Number | VariableReference | '(' Expr ')' | FunctionCall
-        private AstNode ParsePrimaryExpr(AstNode qyInput)
+        private AstNode ParsePrimaryExpr(AstNode? qyInput)
         {
             Debug.Assert(IsPrimaryExpr(_scanner));
-            AstNode opnd = null;
+            AstNode? opnd = null;
             switch (_scanner.Kind)
             {
                 case XPathScanner.LexKind.String:
@@ -509,7 +510,7 @@ private AstNode ParsePrimaryExpr(AstNode qyInput)
             return opnd;
         }
 
-        private AstNode ParseMethod(AstNode qyInput)
+        private AstNode ParseMethod(AstNode? qyInput)
         {
             List<AstNode> argList = new List<AstNode>();
             string name = _scanner.Name;
@@ -531,7 +532,7 @@ private AstNode ParseMethod(AstNode qyInput)
             PassToken(XPathScanner.LexKind.RParens);
             if (prefix.Length == 0)
             {
-                ParamInfo pi;
+                ParamInfo? pi;
                 if (s_functionTable.TryGetValue(name, out pi))
                 {
                     int argCount = argList.Count;
@@ -619,7 +620,7 @@ private AstNode ParsePattern()
         //>>                       | IdKeyPattern (('/' | '//') RelativePathPattern)?
         private AstNode ParseLocationPathPattern()
         {
-            AstNode opnd = null;
+            AstNode? opnd = null;
             switch (_scanner.Kind)
             {
                 case XPathScanner.LexKind.Slash:
@@ -660,7 +661,7 @@ private AstNode ParseLocationPathPattern()
         }
 
         //>> IdKeyPattern ::= 'id' '(' Literal ')' | 'key' '(' Literal ',' Literal ')'
-        private AstNode ParseIdKeyPattern()
+        private AstNode? ParseIdKeyPattern()
         {
             Debug.Assert(_scanner.CanBeFunction);
             List<AstNode> argList = new List<AstNode>();
@@ -697,7 +698,7 @@ private AstNode ParseIdKeyPattern()
 
         //>> PathOp   ::= '/' | '//'
         //>> RelativePathPattern ::= ( RelativePathPattern PathOp )? StepPattern
-        private AstNode ParseRelativePathPattern(AstNode qyInput)
+        private AstNode ParseRelativePathPattern(AstNode? qyInput)
         {
             AstNode opnd = ParseStepPattern(qyInput);
             if (XPathScanner.LexKind.SlashSlash == _scanner.Kind)
@@ -715,7 +716,7 @@ private AstNode ParseRelativePathPattern(AstNode qyInput)
 
         //>> StepPattern    ::=    ChildOrAttributeAxisSpecifier NodeTest Predicate*
         //>> ChildOrAttributeAxisSpecifier    ::=    @ ? | ('child' | 'attribute') '::'
-        private AstNode ParseStepPattern(AstNode qyInput)
+        private AstNode ParseStepPattern(AstNode? qyInput)
         {
             AstNode opnd;
             Axis.AxisType axisType = Axis.AxisType.Child;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathScanner.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathScanner.cs
index 831d7c8df14957..5477ab18321dd6 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathScanner.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathScanner.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Diagnostics;
 using System.Globalization;
@@ -15,9 +16,9 @@ internal sealed class XPathScanner
         private int _xpathExprIndex;
         private LexKind _kind;
         private char _currentChar;
-        private string _name;
-        private string _prefix;
-        private string _stringValue;
+        private string? _name;
+        private string? _prefix;
+        private string? _stringValue;
         private double _numberValue = double.NaN;
         private bool _canBeFunction;
         private XmlCharType _xmlCharType = XmlCharType.Instance;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSelectionIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSelectionIterator.cs
index a872e91172f254..1431765888b707 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSelectionIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSelectionIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
@@ -34,7 +35,7 @@ public override void Reset()
 
         public override bool MoveNext()
         {
-            XPathNavigator n = _query.Advance();
+            XPathNavigator? n = _query.Advance();
             if (n != null)
             {
                 _position++;
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSelfQuery.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSelfQuery.cs
index c1b020f0e7f6a5..8fa0b677eb7532 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSelfQuery.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSelfQuery.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.XPath;
 
 namespace MS.Internal.Xml.XPath
@@ -10,7 +11,7 @@ internal sealed class XPathSelfQuery : BaseAxisQuery
         public XPathSelfQuery(Query qyInput, string Name, string Prefix, XPathNodeType Type) : base(qyInput, Name, Prefix, Type) { }
         private XPathSelfQuery(XPathSelfQuery other) : base(other) { }
 
-        public override XPathNavigator Advance()
+        public override XPathNavigator? Advance()
         {
             while ((currentNode = qyInput.Advance()) != null)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSingletonIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSingletonIterator.cs
index 67cdd880360381..7311ec45018d3f 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSingletonIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/XPathSingletonIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.XPath;
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathDocument.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathDocument.cs
index 492ae0562b7452..e54f875101c3be 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathDocument.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathDocument.cs
@@ -1,9 +1,11 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using MS.Internal.Xml.Cache;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 
 namespace System.Xml.XPath
@@ -15,12 +17,12 @@ namespace System.Xml.XPath
     /// </summary>
     public class XPathDocument : IXPathNavigable
     {
-        private XPathNode[] _pageText, _pageRoot, _pageXmlNmsp;
+        private XPathNode[]? _pageText, _pageRoot, _pageXmlNmsp;
         private int _idxText, _idxRoot, _idxXmlNmsp;
         private XmlNameTable _nameTable;
         private bool _hasLineInfo;
-        private Dictionary<XPathNodeRef, XPathNodeRef> _mapNmsp;
-        private Dictionary<string, XPathNodeRef> _idValueMap;
+        private Dictionary<XPathNodeRef, XPathNodeRef>? _mapNmsp;
+        private Dictionary<string, XPathNodeRef>? _idValueMap;
 
         /// <summary>
         /// Flags that control Load behavior.
@@ -145,11 +147,12 @@ internal XmlRawWriter LoadFromWriter(LoadFlags flags, string baseUri)
         /// Create a writer that can be used to create nodes in this document.  The root node will be assigned "baseUri", and flags
         /// can be passed to indicate that names should be atomized by the builder and/or a fragment should be created.
         /// </summary>
+        [MemberNotNull(nameof(_nameTable))]
         internal void LoadFromReader(XmlReader reader, XmlSpace space)
         {
             XPathDocumentBuilder builder;
-            IXmlLineInfo lineInfo;
-            string xmlnsUri;
+            IXmlLineInfo? lineInfo;
+            string? xmlnsUri;
             bool topLevelReader;
             int initialDepth;
 
@@ -172,7 +175,7 @@ internal void LoadFromReader(XmlReader reader, XmlSpace space)
                 initialDepth = reader.Depth;
 
                 // Get atomized xmlns uri
-                Debug.Assert((object)_nameTable.Get(string.Empty) == (object)string.Empty, "NameTable must contain atomized string.Empty");
+                Debug.Assert((object?)_nameTable.Get(string.Empty) == (object)string.Empty, "NameTable must contain atomized string.Empty");
                 xmlnsUri = _nameTable.Get(XmlReservedNs.NsXmlNs);
 
                 // Read past Initial state; if there are no more events then load is complete
@@ -199,7 +202,7 @@ internal void LoadFromReader(XmlReader reader, XmlSpace space)
                                 {
                                     string namespaceUri = reader.NamespaceURI;
 
-                                    if ((object)namespaceUri == (object)xmlnsUri)
+                                    if ((object)namespaceUri == (object?)xmlnsUri)
                                     {
                                         if (reader.Prefix.Length == 0)
                                         {
@@ -269,7 +272,7 @@ internal void LoadFromReader(XmlReader reader, XmlSpace space)
 
                         case XmlNodeType.DocumentType:
                             // Create ID tables
-                            IDtdInfo info = reader.DtdInfo;
+                            IDtdInfo? info = reader.DtdInfo;
                             if (info != null)
                                 builder.CreateIdTables(info);
                             break;
@@ -322,7 +325,7 @@ internal bool HasLineInfo
         /// represents each logical text node in the document that is the only content-typed child of its
         /// element parent.
         /// </summary>
-        internal int GetCollapsedTextNode(out XPathNode[] pageText)
+        internal int GetCollapsedTextNode(out XPathNode[]? pageText)
         {
             pageText = _pageText;
             return _idxText;
@@ -341,7 +344,7 @@ internal void SetCollapsedTextNode(XPathNode[] pageText, int idxText)
         /// Return the root node of the document.  This may not be a node of type XPathNodeType.Root if this
         /// is a document fragment.
         /// </summary>
-        internal int GetRootNode(out XPathNode[] pageRoot)
+        internal int GetRootNode(out XPathNode[]? pageRoot)
         {
             pageRoot = _pageRoot;
             return _idxRoot;
@@ -359,7 +362,7 @@ internal void SetRootNode(XPathNode[] pageRoot, int idxRoot)
         /// <summary>
         /// Every document has an implicit xmlns:xml namespace node.
         /// </summary>
-        internal int GetXmlNamespaceNode(out XPathNode[] pageXmlNmsp)
+        internal int GetXmlNamespaceNode(out XPathNode[]? pageXmlNmsp)
         {
             pageXmlNmsp = _pageXmlNmsp;
             return _idxXmlNmsp;
@@ -390,7 +393,7 @@ internal void AddNamespace(XPathNode[] pageElem, int idxElem, XPathNode[] pageNm
         /// <summary>
         /// Lookup the namespace nodes associated with an element.
         /// </summary>
-        internal int LookupNamespaces(XPathNode[] pageElem, int idxElem, out XPathNode[] pageNmsp)
+        internal int LookupNamespaces(XPathNode[] pageElem, int idxElem, out XPathNode[]? pageNmsp)
         {
             XPathNodeRef nodeRef = new XPathNodeRef(pageElem, idxElem);
             Debug.Assert(pageElem[idxElem].NodeType == XPathNodeType.Element);
@@ -424,7 +427,7 @@ internal void AddIdElement(string id, XPathNode[] pageElem, int idxElem)
         /// <summary>
         /// Lookup the element node associated with the specified ID value.
         /// </summary>
-        internal int LookupIdElement(string id, out XPathNode[] pageElem)
+        internal int LookupIdElement(string id, out XPathNode[]? pageElem)
         {
             XPathNodeRef nodeRef;
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathException.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathException.cs
index dbceed23125cf4..017f4044d61351 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathException.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathException.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Resources;
 using System.Runtime.Serialization;
@@ -16,24 +17,24 @@ public class XPathException : SystemException
     {
         // we need to keep this members for V1 serialization compatibility
         private readonly string _res;
-        private readonly string[] _args;
+        private readonly string[]? _args;
 
         // message != null for V1 & V2 exceptions deserialized in Whidbey
         // message == null for created V2 exceptions; the exception message is stored in Exception._message
-        private readonly string _message;
+        private readonly string? _message;
 
         protected XPathException(SerializationInfo info, StreamingContext context) : base(info, context)
         {
-            _res = (string)info.GetValue("res", typeof(string));
-            _args = (string[])info.GetValue("args", typeof(string[]));
+            _res = (string)info.GetValue("res", typeof(string))!;
+            _args = (string[]?)info.GetValue("args", typeof(string[]));
 
             // deserialize optional members
-            string version = null;
+            string? version = null;
             foreach (SerializationEntry e in info)
             {
                 if (e.Name == "version")
                 {
-                    version = (string)e.Value;
+                    version = (string?)e.Value;
                 }
             }
 
@@ -57,18 +58,18 @@ public override void GetObjectData(SerializationInfo info, StreamingContext cont
             info.AddValue("version", "2.0");
         }
 
-        public XPathException() : this(string.Empty, (Exception)null) { }
+        public XPathException() : this(string.Empty, (Exception?)null) { }
 
-        public XPathException(string message) : this(message, (Exception)null) { }
+        public XPathException(string message) : this(message, (Exception?)null) { }
 
-        public XPathException(string message, Exception innerException) :
+        public XPathException(string message, Exception? innerException) :
             this(SR.Xml_UserException, new string[] { message }, innerException)
         {
         }
 
         internal static XPathException Create(string res)
         {
-            return new XPathException(res, (string[])null);
+            return new XPathException(res, (string[]?)null);
         }
 
         internal static XPathException Create(string res, string arg)
@@ -86,12 +87,12 @@ internal static XPathException Create(string res, string arg, Exception innerExc
             return new XPathException(res, new string[] { arg }, innerException);
         }
 
-        private XPathException(string res, string[] args) :
+        private XPathException(string res, string[]? args) :
             this(res, args, null)
         {
         }
 
-        private XPathException(string res, string[] args, Exception inner) :
+        private XPathException(string res, string[]? args, Exception? inner) :
             base(CreateMessage(res, args), inner)
         {
             HResult = HResults.XmlXPath;
@@ -99,7 +100,7 @@ private XPathException(string res, string[] args, Exception inner) :
             _args = args;
         }
 
-        private static string CreateMessage(string res, string[] args)
+        private static string CreateMessage(string res, string[]? args)
         {
             try
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathExpr.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathExpr.cs
index b25f7b85b30c67..af967030af5997 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathExpr.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathExpr.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using MS.Internal.Xml.XPath;
 using System.Collections;
 
@@ -59,7 +60,7 @@ public static XPathExpression Compile(string xpath)
             return Compile(xpath, /*nsResolver:*/null);
         }
 
-        public static XPathExpression Compile(string xpath, IXmlNamespaceResolver nsResolver)
+        public static XPathExpression Compile(string xpath, IXmlNamespaceResolver? nsResolver)
         {
             bool hasPrefix;
             Query query = new QueryBuilder().Build(xpath, out hasPrefix);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathItem.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathItem.cs
index 77308682a7c646..abe7141ce9a480 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathItem.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathItem.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Xml.Schema;
 
 namespace System.Xml.XPath
@@ -18,7 +19,7 @@ public abstract class XPathItem
         /// <summary>
         /// Returns Xsd type of atomic value, or of node's content.
         /// </summary>
-        public abstract XmlSchemaType XmlType { get; }
+        public abstract XmlSchemaType? XmlType { get; }
 
         /// <summary>
         /// Typed and untyped value accessors.
@@ -32,6 +33,6 @@ public abstract class XPathItem
         public abstract int ValueAsInt { get; }
         public abstract long ValueAsLong { get; }
         public virtual object ValueAs(Type returnType) { return ValueAs(returnType, null); }
-        public abstract object ValueAs(Type returnType, IXmlNamespaceResolver nsResolver);
+        public abstract object ValueAs(Type returnType, IXmlNamespaceResolver? nsResolver);
     }
 }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNamespaceScope.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNamespaceScope.cs
index 82fcb44330f68a..48399c0fb8bcb6 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNamespaceScope.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNamespaceScope.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml.XPath
 {
     public enum XPathNamespaceScope
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigator.cs
index 6db4765ed9b371..02baf072f2a2c0 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.ComponentModel;
 using System.IO;
 using System.Collections;
@@ -13,6 +14,7 @@
 using System.Xml;
 using MS.Internal.Xml.Cache;
 using MS.Internal.Xml.XPath;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml.XPath
 {
@@ -40,16 +42,16 @@ public override sealed bool IsNode
             get { return true; }
         }
 
-        public override XmlSchemaType XmlType
+        public override XmlSchemaType? XmlType
         {
             get
             {
-                IXmlSchemaInfo schemaInfo = SchemaInfo;
+                IXmlSchemaInfo? schemaInfo = SchemaInfo;
                 if (schemaInfo != null)
                 {
                     if (schemaInfo.Validity == XmlSchemaValidity.Valid)
                     {
-                        XmlSchemaType memberType = schemaInfo.MemberType;
+                        XmlSchemaType? memberType = schemaInfo.MemberType;
                         if (memberType != null)
                         {
                             return memberType;
@@ -70,9 +72,9 @@ public override object TypedValue
         {
             get
             {
-                IXmlSchemaInfo schemaInfo = SchemaInfo;
-                XmlSchemaType schemaType;
-                XmlSchemaDatatype datatype;
+                IXmlSchemaInfo? schemaInfo = SchemaInfo;
+                XmlSchemaType? schemaType;
+                XmlSchemaDatatype? datatype;
                 if (schemaInfo != null)
                 {
                     if (schemaInfo.Validity == XmlSchemaValidity.Valid)
@@ -122,15 +124,15 @@ public virtual void SetTypedValue(object typedValue)
                 default:
                     throw new InvalidOperationException(SR.Xpn_BadPosition);
             }
-            string value = null;
-            IXmlSchemaInfo schemaInfo = SchemaInfo;
+            string? value = null;
+            IXmlSchemaInfo? schemaInfo = SchemaInfo;
             if (schemaInfo != null)
             {
-                XmlSchemaType schemaType = schemaInfo.SchemaType;
+                XmlSchemaType? schemaType = schemaInfo.SchemaType;
                 if (schemaType != null)
                 {
                     value = schemaType.ValueConverter.ToString(typedValue, this);
-                    XmlSchemaDatatype datatype = schemaType.Datatype;
+                    XmlSchemaDatatype? datatype = schemaType.Datatype;
                     if (datatype != null)
                     {
                         datatype.ParseValue(value, NameTable, this);
@@ -148,9 +150,9 @@ public override Type ValueType
         {
             get
             {
-                IXmlSchemaInfo schemaInfo = SchemaInfo;
-                XmlSchemaType schemaType;
-                XmlSchemaDatatype datatype;
+                IXmlSchemaInfo? schemaInfo = SchemaInfo;
+                XmlSchemaType? schemaType;
+                XmlSchemaDatatype? datatype;
                 if (schemaInfo != null)
                 {
                     if (schemaInfo.Validity == XmlSchemaValidity.Valid)
@@ -190,9 +192,9 @@ public override bool ValueAsBoolean
         {
             get
             {
-                IXmlSchemaInfo schemaInfo = SchemaInfo;
-                XmlSchemaType schemaType;
-                XmlSchemaDatatype datatype;
+                IXmlSchemaInfo? schemaInfo = SchemaInfo;
+                XmlSchemaType? schemaType;
+                XmlSchemaDatatype? datatype;
                 if (schemaInfo != null)
                 {
                     if (schemaInfo.Validity == XmlSchemaValidity.Valid)
@@ -228,9 +230,9 @@ public override DateTime ValueAsDateTime
         {
             get
             {
-                IXmlSchemaInfo schemaInfo = SchemaInfo;
-                XmlSchemaType schemaType;
-                XmlSchemaDatatype datatype;
+                IXmlSchemaInfo? schemaInfo = SchemaInfo;
+                XmlSchemaType? schemaType;
+                XmlSchemaDatatype? datatype;
                 if (schemaInfo != null)
                 {
                     if (schemaInfo.Validity == XmlSchemaValidity.Valid)
@@ -266,9 +268,9 @@ public override double ValueAsDouble
         {
             get
             {
-                IXmlSchemaInfo schemaInfo = SchemaInfo;
-                XmlSchemaType schemaType;
-                XmlSchemaDatatype datatype;
+                IXmlSchemaInfo? schemaInfo = SchemaInfo;
+                XmlSchemaType? schemaType;
+                XmlSchemaDatatype? datatype;
                 if (schemaInfo != null)
                 {
                     if (schemaInfo.Validity == XmlSchemaValidity.Valid)
@@ -304,9 +306,9 @@ public override int ValueAsInt
         {
             get
             {
-                IXmlSchemaInfo schemaInfo = SchemaInfo;
-                XmlSchemaType schemaType;
-                XmlSchemaDatatype datatype;
+                IXmlSchemaInfo? schemaInfo = SchemaInfo;
+                XmlSchemaType? schemaType;
+                XmlSchemaDatatype? datatype;
                 if (schemaInfo != null)
                 {
                     if (schemaInfo.Validity == XmlSchemaValidity.Valid)
@@ -342,9 +344,9 @@ public override long ValueAsLong
         {
             get
             {
-                IXmlSchemaInfo schemaInfo = SchemaInfo;
-                XmlSchemaType schemaType;
-                XmlSchemaDatatype datatype;
+                IXmlSchemaInfo? schemaInfo = SchemaInfo;
+                XmlSchemaType? schemaType;
+                XmlSchemaDatatype? datatype;
                 if (schemaInfo != null)
                 {
                     if (schemaInfo.Validity == XmlSchemaValidity.Valid)
@@ -376,15 +378,15 @@ public override long ValueAsLong
             }
         }
 
-        public override object ValueAs(Type returnType, IXmlNamespaceResolver nsResolver)
+        public override object ValueAs(Type returnType, IXmlNamespaceResolver? nsResolver)
         {
             if (nsResolver == null)
             {
                 nsResolver = this;
             }
-            IXmlSchemaInfo schemaInfo = SchemaInfo;
-            XmlSchemaType schemaType;
-            XmlSchemaDatatype datatype;
+            IXmlSchemaInfo? schemaInfo = SchemaInfo;
+            XmlSchemaType? schemaType;
+            XmlSchemaDatatype? datatype;
             if (schemaInfo != null)
             {
                 if (schemaInfo.Validity == XmlSchemaValidity.Valid)
@@ -439,7 +441,7 @@ public virtual XPathNavigator CreateNavigator()
 
         public abstract XmlNameTable NameTable { get; }
 
-        public virtual string LookupNamespace(string prefix)
+        public virtual string? LookupNamespace(string prefix)
         {
             if (prefix == null)
                 return null;
@@ -470,7 +472,7 @@ public virtual string LookupNamespace(string prefix)
             return null;
         }
 
-        public virtual string LookupPrefix(string namespaceURI)
+        public virtual string? LookupPrefix(string namespaceURI)
         {
             if (namespaceURI == null)
                 return null;
@@ -610,7 +612,7 @@ public virtual void WriteSubtree(XmlWriter writer)
             writer.WriteNode(this, true);
         }
 
-        public virtual object UnderlyingObject
+        public virtual object? UnderlyingObject
         {
             get { return null; }
         }
@@ -778,7 +780,7 @@ public virtual bool MoveToFollowing(string localName, string namespaceURI)
             return MoveToFollowing(localName, namespaceURI, null);
         }
 
-        public virtual bool MoveToFollowing(string localName, string namespaceURI, XPathNavigator end)
+        public virtual bool MoveToFollowing(string localName, string namespaceURI, XPathNavigator? end)
         {
             XPathNavigator navSave = Clone();
 
@@ -844,7 +846,7 @@ public virtual bool MoveToFollowing(XPathNodeType type)
             return MoveToFollowing(type, null);
         }
 
-        public virtual bool MoveToFollowing(XPathNodeType type, XPathNavigator end)
+        public virtual bool MoveToFollowing(XPathNodeType type, XPathNavigator? end)
         {
             XPathNavigator navSave = Clone();
             int mask = GetContentKindMask(type);
@@ -947,7 +949,7 @@ public virtual bool HasChildren
 
         public abstract bool IsSamePosition(XPathNavigator other);
 
-        public virtual bool IsDescendant(XPathNavigator nav)
+        public virtual bool IsDescendant([NotNullWhen(true)] XPathNavigator? nav)
         {
             if (nav != null)
             {
@@ -959,7 +961,7 @@ public virtual bool IsDescendant(XPathNavigator nav)
             return false;
         }
 
-        public virtual XmlNodeOrder ComparePosition(XPathNavigator nav)
+        public virtual XmlNodeOrder ComparePosition(XPathNavigator? nav)
         {
             if (nav == null)
             {
@@ -1019,17 +1021,17 @@ public virtual XmlNodeOrder ComparePosition(XPathNavigator nav)
             }
         }
 
-        public virtual IXmlSchemaInfo SchemaInfo
+        public virtual IXmlSchemaInfo? SchemaInfo
         {
             get { return this as IXmlSchemaInfo; }
         }
 
         public virtual bool CheckValidity(XmlSchemaSet schemas, ValidationEventHandler validationEventHandler)
         {
-            IXmlSchemaInfo schemaInfo;
-            XmlSchemaType schemaType = null;
-            XmlSchemaElement schemaElement = null;
-            XmlSchemaAttribute schemaAttribute = null;
+            IXmlSchemaInfo? schemaInfo;
+            XmlSchemaType? schemaType = null;
+            XmlSchemaElement? schemaElement = null;
+            XmlSchemaAttribute? schemaAttribute = null;
 
             switch (NodeType)
             {
@@ -1080,9 +1082,9 @@ public virtual bool CheckValidity(XmlSchemaSet schemas, ValidationEventHandler v
 
             Debug.Assert(schemaType != null || this.NodeType == XPathNodeType.Root, "schemaType != null  || this.NodeType == XPathNodeType.Root");
 
-            XmlReader reader = CreateReader();
+            XPathNavigatorReader reader = (XPathNavigatorReader)CreateReader();
 
-            CheckValidityHelper validityTracker = new CheckValidityHelper(validationEventHandler, reader as XPathNavigatorReader);
+            CheckValidityHelper validityTracker = new CheckValidityHelper(validationEventHandler, reader);
             validationEventHandler = new ValidationEventHandler(validityTracker.ValidationCallback);
             XmlReader validatingReader = GetValidatingReader(reader, schemas, validationEventHandler, schemaType, schemaElement, schemaAttribute);
 
@@ -1092,7 +1094,7 @@ public virtual bool CheckValidity(XmlSchemaSet schemas, ValidationEventHandler v
             return validityTracker.IsValid;
         }
 
-        private XmlReader GetValidatingReader(XmlReader reader, XmlSchemaSet schemas, ValidationEventHandler validationEvent, XmlSchemaType schemaType, XmlSchemaElement schemaElement, XmlSchemaAttribute schemaAttribute)
+        private XmlReader GetValidatingReader(XmlReader reader, XmlSchemaSet schemas, ValidationEventHandler validationEvent, XmlSchemaType? schemaType, XmlSchemaElement? schemaElement, XmlSchemaAttribute? schemaAttribute)
         {
             if (schemaAttribute != null)
             {
@@ -1128,12 +1130,12 @@ internal CheckValidityHelper(ValidationEventHandler nextEventHandler, XPathNavig
                 _reader = reader;
             }
 
-            internal void ValidationCallback(object sender, ValidationEventArgs args)
+            internal void ValidationCallback(object? sender, ValidationEventArgs args)
             {
                 Debug.Assert(args != null);
                 if (args.Severity == XmlSeverityType.Error)
                     _isValid = false;
-                XmlSchemaValidationException exception = args.Exception as XmlSchemaValidationException;
+                XmlSchemaValidationException? exception = args.Exception as XmlSchemaValidationException;
                 if (exception != null && _reader != null)
                     exception.SetSourceObject(_reader.UnderlyingObject);
 
@@ -1158,17 +1160,17 @@ public virtual XPathExpression Compile(string xpath)
             return XPathExpression.Compile(xpath);
         }
 
-        public virtual XPathNavigator SelectSingleNode(string xpath)
+        public virtual XPathNavigator? SelectSingleNode(string xpath)
         {
             return SelectSingleNode(XPathExpression.Compile(xpath));
         }
 
-        public virtual XPathNavigator SelectSingleNode(string xpath, IXmlNamespaceResolver resolver)
+        public virtual XPathNavigator? SelectSingleNode(string xpath, IXmlNamespaceResolver? resolver)
         {
             return SelectSingleNode(XPathExpression.Compile(xpath, resolver));
         }
 
-        public virtual XPathNavigator SelectSingleNode(XPathExpression expression)
+        public virtual XPathNavigator? SelectSingleNode(XPathExpression expression)
         {
             // PERF BUG: this actually caches _all_ matching nodes...
             XPathNodeIterator iter = this.Select(expression);
@@ -1191,7 +1193,7 @@ public virtual XPathNodeIterator Select(string xpath, IXmlNamespaceResolver reso
 
         public virtual XPathNodeIterator Select(XPathExpression expr)
         {
-            XPathNodeIterator result = Evaluate(expr) as XPathNodeIterator;
+            XPathNodeIterator? result = Evaluate(expr) as XPathNodeIterator;
             if (result == null)
             {
                 throw XPathException.Create(SR.Xp_NodeSetExpected);
@@ -1214,9 +1216,9 @@ public virtual object Evaluate(XPathExpression expr)
             return Evaluate(expr, null);
         }
 
-        public virtual object Evaluate(XPathExpression expr, XPathNodeIterator context)
+        public virtual object Evaluate(XPathExpression expr, XPathNodeIterator? context)
         {
-            CompiledXpathExpr cexpr = expr as CompiledXpathExpr;
+            CompiledXpathExpr? cexpr = expr as CompiledXpathExpr;
             if (cexpr == null)
             {
                 throw XPathException.Create(SR.Xp_BadQueryObject);
@@ -1233,6 +1235,7 @@ public virtual object Evaluate(XPathExpression expr, XPathNodeIterator context)
 
             if (result is XPathNodeIterator)
             {
+                Debug.Assert(context.Current != null);
                 return new XPathSelectionIterator(context.Current, query);
             }
 
@@ -1241,7 +1244,7 @@ public virtual object Evaluate(XPathExpression expr, XPathNodeIterator context)
 
         public virtual bool Matches(XPathExpression expr)
         {
-            CompiledXpathExpr cexpr = expr as CompiledXpathExpr;
+            CompiledXpathExpr? cexpr = expr as CompiledXpathExpr;
             if (cexpr == null)
                 throw XPathException.Create(SR.Xp_BadQueryObject);
 
@@ -1695,10 +1698,10 @@ internal bool MoveToPrevious(string localName, string namespaceURI)
         {
             XPathNavigator navClone = Clone();
 
-            localName = (localName != null) ? NameTable.Get(localName) : null;
+            string? atomizedLocalName = (localName != null) ? NameTable.Get(localName) : null;
             while (MoveToPrevious())
             {
-                if (NodeType == XPathNodeType.Element && (object)localName == (object)LocalName && namespaceURI == NamespaceURI)
+                if (NodeType == XPathNodeType.Element && atomizedLocalName == LocalName && namespaceURI == NamespaceURI)
                     return true;
             }
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigatorKeyComparer.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigatorKeyComparer.cs
index 7a8f59d786418a..b79cc674d533b0 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigatorKeyComparer.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigatorKeyComparer.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using MS.Internal.Xml.Cache;
 using System.Collections;
 
@@ -8,10 +9,10 @@ namespace System.Xml.XPath
 {
     internal class XPathNavigatorKeyComparer : IEqualityComparer
     {
-        bool IEqualityComparer.Equals(object obj1, object obj2)
+        bool IEqualityComparer.Equals(object? obj1, object? obj2)
         {
-            XPathNavigator nav1 = obj1 as XPathNavigator;
-            XPathNavigator nav2 = obj2 as XPathNavigator;
+            XPathNavigator? nav1 = obj1 as XPathNavigator;
+            XPathNavigator? nav2 = obj2 as XPathNavigator;
             if ((nav1 != null) && (nav2 != null))
             {
                 if (nav1.IsSamePosition(nav2))
@@ -23,8 +24,8 @@ bool IEqualityComparer.Equals(object obj1, object obj2)
         int IEqualityComparer.GetHashCode(object obj)
         {
             int hashCode;
-            XPathNavigator nav;
-            XPathDocumentNavigator xpdocNav;
+            XPathNavigator? nav;
+            XPathDocumentNavigator? xpdocNav;
 
             if (obj == null)
             {
@@ -36,7 +37,7 @@ int IEqualityComparer.GetHashCode(object obj)
             }
             else if (null != (nav = obj as XPathNavigator))
             {
-                object underlyingObject = nav.UnderlyingObject;
+                object? underlyingObject = nav.UnderlyingObject;
                 if (underlyingObject != null)
                 {
                     hashCode = underlyingObject.GetHashCode();
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigatorReader.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigatorReader.cs
index d0e51d85fcbd42..1b8a06a8dcfd57 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigatorReader.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNavigatorReader.cs
@@ -1,13 +1,13 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.IO;
 using System.Xml.Schema;
 using System.Collections;
 using System.Diagnostics;
 using System.Collections.Generic;
 
-
 namespace System.Xml.XPath
 {
     /// <summary>
@@ -36,10 +36,10 @@ private enum State
         private int _attrCount;
         private bool _readEntireDocument;
 
-        protected IXmlLineInfo lineInfo;
-        protected IXmlSchemaInfo schemaInfo;
+        protected IXmlLineInfo? lineInfo;
+        protected IXmlSchemaInfo? schemaInfo;
 
-        private ReadContentAsBinaryHelper _readBinaryHelper;
+        private ReadContentAsBinaryHelper? _readBinaryHelper;
         private State _savedState;
 
         internal const string space = "space";
@@ -66,7 +66,7 @@ internal static XmlNodeType ToXmlNodeType(XPathNodeType typ)
             return XPathNavigatorReader.convertFromXPathNodeType[(int)typ];
         }
 
-        internal object UnderlyingObject
+        internal object? UnderlyingObject
         {
             get
             {
@@ -77,8 +77,8 @@ internal object UnderlyingObject
         public static XPathNavigatorReader Create(XPathNavigator navToRead)
         {
             XPathNavigator nav = navToRead.Clone();
-            IXmlLineInfo xli = nav as IXmlLineInfo;
-            IXmlSchemaInfo xsi = nav as IXmlSchemaInfo;
+            IXmlLineInfo? xli = nav as IXmlLineInfo;
+            IXmlSchemaInfo? xsi = nav as IXmlSchemaInfo;
 #if NAVREADER_SUPPORTSLINEINFO
             if (null == xsi) {
                 if (null == xli) {
@@ -108,7 +108,7 @@ public static XPathNavigatorReader Create(XPathNavigator navToRead)
 #endif
         }
 
-        protected XPathNavigatorReader(XPathNavigator navToRead, IXmlLineInfo xli, IXmlSchemaInfo xsi)
+        protected XPathNavigatorReader(XPathNavigator navToRead, IXmlLineInfo? xli, IXmlSchemaInfo? xsi)
         {
             // Need clone that can be moved independently of original navigator
             _navToRead = navToRead;
@@ -147,12 +147,12 @@ IDictionary<string, string> IXmlNamespaceResolver.GetNamespacesInScope(XmlNamesp
             return _nav.GetNamespacesInScope(scope);
         }
 
-        string IXmlNamespaceResolver.LookupNamespace(string prefix)
+        string? IXmlNamespaceResolver.LookupNamespace(string prefix)
         {
             return _nav.LookupNamespace(prefix);
         }
 
-        string IXmlNamespaceResolver.LookupPrefix(string namespaceName)
+        string? IXmlNamespaceResolver.LookupPrefix(string namespaceName)
         {
             return _nav.LookupPrefix(namespaceName);
         }
@@ -174,7 +174,7 @@ public override XmlReaderSettings Settings
             }
         }
 
-        public override IXmlSchemaInfo SchemaInfo
+        public override IXmlSchemaInfo? SchemaInfo
         {
             get
             {
@@ -316,9 +316,9 @@ public override string Value
             }
         }
 
-        private XPathNavigator GetElemNav()
+        private XPathNavigator? GetElemNav()
         {
-            XPathNavigator tempNav;
+            XPathNavigator? tempNav;
             switch (_state)
             {
                 case State.Content:
@@ -331,16 +331,16 @@ private XPathNavigator GetElemNav()
                     break;
                 case State.InReadBinary:
                     _state = _savedState;
-                    XPathNavigator nav = GetElemNav();
+                    XPathNavigator? nav = GetElemNav();
                     _state = State.InReadBinary;
                     return nav;
             }
             return null;
         }
 
-        private XPathNavigator GetElemNav(out int depth)
+        private XPathNavigator? GetElemNav(out int depth)
         {
-            XPathNavigator nav = null;
+            XPathNavigator? nav = null;
             switch (_state)
             {
                 case State.Content:
@@ -385,7 +385,7 @@ public override int AttributeCount
                 if (_attrCount < 0)
                 {
                     // attribute count works for element, regardless of where you are in start tag
-                    XPathNavigator tempNav = GetElemNav();
+                    XPathNavigator? tempNav = GetElemNav();
                     int count = 0;
                     if (null != tempNav)
                     {
@@ -411,7 +411,7 @@ public override int AttributeCount
             }
         }
 
-        public override string GetAttribute(string name)
+        public override string? GetAttribute(string name)
         {
             // reader allows calling GetAttribute, even when positioned inside attributes
             XPathNavigator nav = _nav;
@@ -456,7 +456,7 @@ public override string GetAttribute(string name)
             return null;
         }
 
-        public override string GetAttribute(string localName, string namespaceURI)
+        public override string? GetAttribute(string localName, string? namespaceURI)
         {
             if (null == localName)
                 throw new ArgumentNullException(nameof(localName));
@@ -498,10 +498,10 @@ public override string GetAttribute(string localName, string namespaceURI)
             }
         }
 
-        private static string GetNamespaceByIndex(XPathNavigator nav, int index, out int count)
+        private static string? GetNamespaceByIndex(XPathNavigator nav, int index, out int count)
         {
             string thisValue = nav.Value;
-            string value = null;
+            string? value = null;
             if (nav.MoveToNextNamespace(XPathNamespaceScope.Local))
             {
                 value = GetNamespaceByIndex(nav, index, out count);
@@ -523,7 +523,7 @@ public override string GetAttribute(int index)
         {
             if (index < 0)
                 goto Error;
-            XPathNavigator nav = GetElemNav();
+            XPathNavigator? nav = GetElemNav();
             if (null == nav)
                 goto Error;
             if (nav.MoveToFirstNamespace(XPathNamespaceScope.Local))
@@ -532,7 +532,7 @@ public override string GetAttribute(int index)
                 // but we want to return them in the correct order,
                 // so first count the namespaces
                 int nsCount;
-                string value = GetNamespaceByIndex(nav, index, out nsCount);
+                string? value = GetNamespaceByIndex(nav, index, out nsCount);
                 if (null != value)
                 {
                     return value;
@@ -555,12 +555,12 @@ public override string GetAttribute(int index)
         }
 
 
-        public override bool MoveToAttribute(string localName, string namespaceName)
+        public override bool MoveToAttribute(string localName, string? namespaceName)
         {
             if (null == localName)
                 throw new ArgumentNullException(nameof(localName));
             int depth = _depth;
-            XPathNavigator nav = GetElemNav(out depth);
+            XPathNavigator? nav = GetElemNav(out depth);
             if (null != nav)
             {
                 if (namespaceName == XmlReservedNs.NsXmlNs)
@@ -589,7 +589,7 @@ public override bool MoveToAttribute(string localName, string namespaceName)
         FoundMatch:
             if (_state == State.InReadBinary)
             {
-                _readBinaryHelper.Finish();
+                _readBinaryHelper!.Finish();
                 _state = _savedState;
             }
             MoveToAttr(nav, depth + 1);
@@ -599,7 +599,7 @@ public override bool MoveToAttribute(string localName, string namespaceName)
         public override bool MoveToFirstAttribute()
         {
             int depth;
-            XPathNavigator nav = GetElemNav(out depth);
+            XPathNavigator? nav = GetElemNav(out depth);
             if (null != nav)
             {
                 if (nav.MoveToFirstNamespace(XPathNamespaceScope.Local))
@@ -618,7 +618,7 @@ public override bool MoveToFirstAttribute()
         FoundMatch:
             if (_state == State.InReadBinary)
             {
-                _readBinaryHelper.Finish();
+                _readBinaryHelper!.Finish();
                 _state = _savedState;
             }
             MoveToAttr(nav, depth + 1);
@@ -693,7 +693,7 @@ public override bool MoveToNextAttribute()
                         _state = State.InReadBinary;
                         return false;
                     }
-                    _readBinaryHelper.Finish();
+                    _readBinaryHelper!.Finish();
                     return true;
 
                 default:
@@ -704,7 +704,7 @@ public override bool MoveToNextAttribute()
         public override bool MoveToAttribute(string name)
         {
             int depth;
-            XPathNavigator nav = GetElemNav(out depth);
+            XPathNavigator? nav = GetElemNav(out depth);
             if (null == nav)
                 return false;
 
@@ -749,7 +749,7 @@ public override bool MoveToAttribute(string name)
         FoundMatch:
             if (_state == State.InReadBinary)
             {
-                _readBinaryHelper.Finish();
+                _readBinaryHelper!.Finish();
                 _state = _savedState;
             }
             MoveToAttr(nav, depth + 1);
@@ -777,7 +777,7 @@ public override bool MoveToElement()
                         _state = State.InReadBinary;
                         return false;
                     }
-                    _readBinaryHelper.Finish();
+                    _readBinaryHelper!.Finish();
                     break;
             }
             return false;
@@ -824,7 +824,7 @@ public override bool ReadAttributeValue()
         {
             if (_state == State.InReadBinary)
             {
-                _readBinaryHelper.Finish();
+                _readBinaryHelper!.Finish();
                 _state = _savedState;
             }
             if (_state == State.Attribute)
@@ -863,7 +863,7 @@ public override int ReadContentAsBase64(byte[] buffer, int index, int count)
             _state = _savedState;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadContentAsBase64(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadContentAsBase64(buffer, index, count);
 
             // turn on InReadBinary state again and return
             _savedState = _state;
@@ -889,7 +889,7 @@ public override int ReadContentAsBinHex(byte[] buffer, int index, int count)
             _state = _savedState;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadContentAsBinHex(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadContentAsBinHex(buffer, index, count);
 
             // turn on InReadBinary state again and return
             _savedState = _state;
@@ -915,7 +915,7 @@ public override int ReadElementContentAsBase64(byte[] buffer, int index, int cou
             _state = _savedState;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadElementContentAsBase64(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadElementContentAsBase64(buffer, index, count);
 
             // turn on InReadBinary state again and return
             _savedState = _state;
@@ -941,7 +941,7 @@ public override int ReadElementContentAsBinHex(byte[] buffer, int index, int cou
             _state = _savedState;
 
             // call to the helper
-            int readCount = _readBinaryHelper.ReadElementContentAsBinHex(buffer, index, count);
+            int readCount = _readBinaryHelper!.ReadElementContentAsBinHex(buffer, index, count);
 
             // turn on InReadBinary state again and return
             _savedState = _state;
@@ -949,7 +949,7 @@ public override int ReadElementContentAsBinHex(byte[] buffer, int index, int cou
             return readCount;
         }
 
-        public override string LookupNamespace(string prefix)
+        public override string? LookupNamespace(string prefix)
         {
             return _nav.LookupNamespace(prefix);
         }
@@ -1051,7 +1051,7 @@ public override bool Read()
                     goto case State.Content;
                 case State.InReadBinary:
                     _state = _savedState;
-                    _readBinaryHelper.Finish();
+                    _readBinaryHelper!.Finish();
                     return Read();
             }
             return true;
@@ -1083,7 +1083,7 @@ private void SetEOF()
 
 #if NAVREADER_SUPPORTSLINEINFO
     internal class XPathNavigatorReaderWithLI : XPathNavigatorReader, System.Xml.IXmlLineInfo {
-        internal XPathNavigatorReaderWithLI( XPathNavigator navToRead, IXmlLineInfo xli, IXmlSchemaInfo xsi )
+        internal XPathNavigatorReaderWithLI( XPathNavigator navToRead, IXmlLineInfo xli, IXmlSchemaInfo? xsi )
             : base( navToRead, xli, xsi ) {
         }
 
@@ -1117,22 +1117,23 @@ internal XPathNavigatorReaderWithLIAndSI( XPathNavigator navToRead, IXmlLineInfo
 
     internal class XPathNavigatorReaderWithSI : XPathNavigatorReader, System.Xml.Schema.IXmlSchemaInfo
     {
-        internal XPathNavigatorReaderWithSI(XPathNavigator navToRead, IXmlLineInfo xli, IXmlSchemaInfo xsi)
+        internal XPathNavigatorReaderWithSI(XPathNavigator navToRead, IXmlLineInfo? xli, IXmlSchemaInfo xsi)
             : base(navToRead, xli, xsi)
         {
+            schemaInfo = xsi;
         }
 
         //-----------------------------------------------
         // IXmlSchemaInfo
         //-----------------------------------------------
 
-        public virtual XmlSchemaValidity Validity { get { return IsReading ? this.schemaInfo.Validity : XmlSchemaValidity.NotKnown; } }
-        public override bool IsDefault { get { return IsReading ? this.schemaInfo.IsDefault : false; } }
-        public virtual bool IsNil { get { return IsReading ? this.schemaInfo.IsNil : false; } }
-        public virtual XmlSchemaSimpleType MemberType { get { return IsReading ? this.schemaInfo.MemberType : null; } }
-        public virtual XmlSchemaType SchemaType { get { return IsReading ? this.schemaInfo.SchemaType : null; } }
-        public virtual XmlSchemaElement SchemaElement { get { return IsReading ? this.schemaInfo.SchemaElement : null; } }
-        public virtual XmlSchemaAttribute SchemaAttribute { get { return IsReading ? this.schemaInfo.SchemaAttribute : null; } }
+        public virtual XmlSchemaValidity Validity { get { return IsReading ? this.schemaInfo!.Validity : XmlSchemaValidity.NotKnown; } }
+        public override bool IsDefault { get { return IsReading ? this.schemaInfo!.IsDefault : false; } }
+        public virtual bool IsNil { get { return IsReading ? this.schemaInfo!.IsNil : false; } }
+        public virtual XmlSchemaSimpleType? MemberType { get { return IsReading ? this.schemaInfo!.MemberType : null; } }
+        public virtual XmlSchemaType? SchemaType { get { return IsReading ? this.schemaInfo!.SchemaType : null; } }
+        public virtual XmlSchemaElement? SchemaElement { get { return IsReading ? this.schemaInfo!.SchemaElement : null; } }
+        public virtual XmlSchemaAttribute? SchemaAttribute { get { return IsReading ? this.schemaInfo!.SchemaAttribute : null; } }
     }
 
     /// <summary>
@@ -1142,7 +1143,7 @@ internal XPathNavigatorReaderWithSI(XPathNavigator navToRead, IXmlLineInfo xli,
     /// </summary>
     internal class XmlEmptyNavigator : XPathNavigator
     {
-        private static volatile XmlEmptyNavigator s_singleton;
+        private static volatile XmlEmptyNavigator? s_singleton;
 
         private XmlEmptyNavigator()
         {
@@ -1270,7 +1271,8 @@ public override bool MoveToId(string id)
 
         public override string GetAttribute(string localName, string namespaceName)
         {
-            return null;
+            Debug.Fail("This shouldn't be called.");
+            return null!;
         }
 
         public override bool MoveToAttribute(string localName, string namespaceName)
@@ -1280,7 +1282,8 @@ public override bool MoveToAttribute(string localName, string namespaceName)
 
         public override string GetNamespace(string name)
         {
-            return null;
+            Debug.Fail("This shouldn't be called.");
+            return null!;
         }
 
         public override bool MoveToNamespace(string prefix)
@@ -1307,13 +1310,13 @@ public override bool MoveToParent()
         public override bool MoveTo(XPathNavigator other)
         {
             // Only one instance of XmlEmptyNavigator exists on the system
-            return (object)this == (object)other;
+            return (object)this == (object?)other;
         }
 
-        public override XmlNodeOrder ComparePosition(XPathNavigator other)
+        public override XmlNodeOrder ComparePosition(XPathNavigator? other)
         {
             // Only one instance of XmlEmptyNavigator exists on the system
-            return ((object)this == (object)other) ? XmlNodeOrder.Same : XmlNodeOrder.Unknown;
+            return ((object)this == (object?)other) ? XmlNodeOrder.Same : XmlNodeOrder.Unknown;
         }
 
         public override bool IsSamePosition(XPathNavigator other)
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNodeIterator.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNodeIterator.cs
index 8e2c89ca186fc9..d9573be04b37ea 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNodeIterator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNodeIterator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections;
 using System.Diagnostics;
 
@@ -15,7 +16,7 @@ public abstract class XPathNodeIterator : ICloneable, IEnumerable
 
         public abstract XPathNodeIterator Clone();
         public abstract bool MoveNext();
-        public abstract XPathNavigator Current { get; }
+        public abstract XPathNavigator? Current { get; }
         public abstract int CurrentPosition { get; }
         public virtual int Count
         {
@@ -35,7 +36,7 @@ public virtual IEnumerator GetEnumerator()
             return new Enumerator(this);
         }
 
-        private object debuggerDisplayProxy { get { return Current == null ? null : (object)new XPathNavigator.DebuggerDisplayProxy(Current); } }
+        private object? debuggerDisplayProxy { get { return Current == null ? null : (object)new XPathNavigator.DebuggerDisplayProxy(Current); } }
 
         /// <summary>
         /// Implementation of a resetable enumerator that is linked to the XPathNodeIterator used to create it.
@@ -43,7 +44,7 @@ public virtual IEnumerator GetEnumerator()
         private class Enumerator : IEnumerator
         {
             private readonly XPathNodeIterator _original;     // Keep original XPathNodeIterator in case Reset() is called
-            private XPathNodeIterator _current;
+            private XPathNodeIterator? _current;
             private bool _iterationStarted;
 
             public Enumerator(XPathNodeIterator original)
@@ -63,6 +64,7 @@ public virtual object Current
                         if (_current == null)
                             throw new InvalidOperationException(SR.Format(SR.Sch_EnumFinished, string.Empty));
 
+                        Debug.Assert(_current.Current != null);
                         return _current.Current.Clone();
                     }
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNodeType.cs b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNodeType.cs
index a7008883b65b70..e23fcd921afeaf 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNodeType.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XPath/XPathNodeType.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml.XPath
 {
     public enum XPathNodeType
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XmlCharType.cs b/src/libraries/System.Private.Xml/src/System/Xml/XmlCharType.cs
index 9498b6ae9d2594..82cfb9dce6805b 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XmlCharType.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XmlCharType.cs
@@ -203,13 +203,13 @@ internal static void SplitSurrogateChar(int combinedChar, out char lowChar, out
             highChar = (char)(SurHighStart + v / 1024);
         }
 
-        internal bool IsOnlyWhitespace(string str)
+        internal bool IsOnlyWhitespace(string? str)
         {
             return IsOnlyWhitespaceWithPos(str) == -1;
         }
 
         // Character checking on strings
-        internal int IsOnlyWhitespaceWithPos(string str)
+        internal int IsOnlyWhitespaceWithPos(string? str)
         {
             if (str != null)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/XmlConvert.cs b/src/libraries/System.Private.Xml/src/System/Xml/XmlConvert.cs
index f777c49e5c626b..e04ebb6969afaa 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/XmlConvert.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/XmlConvert.cs
@@ -1093,7 +1093,7 @@ public static double ToDouble(string s)
             return null;
         }
 
-        internal static double ToXPathDouble(object o)
+        internal static double ToXPathDouble(object? o)
         {
             if (o is string str)
             {
@@ -1474,12 +1474,12 @@ private static unsafe long DoubleToInt64Bits(double value)
             return *((long*)&value);
         }
 
-        internal static void VerifyCharData(string data, ExceptionType exceptionType)
+        internal static void VerifyCharData(string? data, ExceptionType exceptionType)
         {
             VerifyCharData(data, exceptionType, exceptionType);
         }
 
-        internal static void VerifyCharData(string data, ExceptionType invCharExceptionType, ExceptionType invSurrogateExceptionType)
+        internal static void VerifyCharData(string? data, ExceptionType invCharExceptionType, ExceptionType invSurrogateExceptionType)
         {
             if (data == null || data.Length == 0)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/IXPathEnvironment.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/IXPathEnvironment.cs
index e0a391256c7ef9..077c176e641841 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/IXPathEnvironment.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/IXPathEnvironment.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Xml.Xsl.Qil;
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/IXpathBuilder.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/IXpathBuilder.cs
index 6b1740e34c304c..a8c33e48f1cb83 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/IXpathBuilder.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/IXpathBuilder.cs
@@ -1,27 +1,32 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Xml.XPath;
 
 namespace System.Xml.Xsl.XPath
 {
+    // TODO-NULLABLE: Replace [MaybeNull] with ? once https://github.com/dotnet/runtime/pull/40197 is in.
     internal interface IXPathBuilder<Node>
     {
         // Should be called once per build
         void StartBuild();
 
         // Should be called after build for result tree post-processing
-        Node EndBuild(Node result);
+        [return: MaybeNull]
+        [return: NotNullIfNotNull("result")]
+        Node EndBuild([AllowNull] Node result);
 
         Node String(string value);
 
         Node Number(double value);
 
-        Node Operator(XPathOperator op, Node left, Node right);
+        Node Operator(XPathOperator op, [AllowNull] Node left, [AllowNull] Node right);
 
-        Node Axis(XPathAxis xpathAxis, XPathNodeType nodeType, string prefix, string name);
+        Node Axis(XPathAxis xpathAxis, XPathNodeType nodeType, string? prefix, string? name);
 
         Node JoinStep(Node left, Node right);
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathAxis.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathAxis.cs
index ee3a212595bce0..18977c9a45b6e1 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathAxis.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathAxis.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml.Xsl.XPath
 {
     // Order is important - we use them as an index in QilAxis & AxisMask arrays
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathBuilder.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathBuilder.cs
index 8be18af0ed1383..43631e67c32ddf 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathBuilder.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathBuilder.cs
@@ -1,8 +1,10 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Xml.Schema;
 using System.Xml.XPath;
@@ -69,7 +71,8 @@ public virtual void StartBuild()
             numFixupCurrent = numFixupPosition = numFixupLast = 0;
         }
 
-        public virtual QilNode EndBuild(QilNode result)
+        [return: NotNullIfNotNull("result")]
+        public virtual QilNode? EndBuild(QilNode? result)
         {
             if (result == null)
             { // special door to clean builder state in exception handlers
@@ -109,17 +112,21 @@ public virtual QilNode Number(double value)
             return _f.Double(value);
         }
 
-        public virtual QilNode Operator(XPathOperator op, QilNode left, QilNode right)
+        public virtual QilNode Operator(XPathOperator op, QilNode? left, QilNode? right)
         {
             Debug.Assert(op != XPathOperator.Unknown);
-            switch (s_operatorGroup[(int)op])
+            XPathOperatorGroup opGroup = s_operatorGroup[(int)op];
+
+            Debug.Assert((opGroup != XPathOperatorGroup.Negate && right != null) || (opGroup == XPathOperatorGroup.Negate && right == null));
+
+            switch (opGroup)
             {
-                case XPathOperatorGroup.Logical: return LogicalOperator(op, left, right);
-                case XPathOperatorGroup.Equality: return EqualityOperator(op, left, right);
-                case XPathOperatorGroup.Relational: return RelationalOperator(op, left, right);
-                case XPathOperatorGroup.Arithmetic: return ArithmeticOperator(op, left, right);
-                case XPathOperatorGroup.Negate: return NegateOperator(op, left, right);
-                case XPathOperatorGroup.Union: return UnionOperator(op, left, right);
+                case XPathOperatorGroup.Logical: return LogicalOperator(op, left!, right!);
+                case XPathOperatorGroup.Equality: return EqualityOperator(op, left!, right!);
+                case XPathOperatorGroup.Relational: return RelationalOperator(op, left!, right!);
+                case XPathOperatorGroup.Arithmetic: return ArithmeticOperator(op, left!, right!);
+                case XPathOperatorGroup.Negate: return NegateOperator(op, left!);
+                case XPathOperatorGroup.Union: return UnionOperator(op, left, right!);
                 default:
                     Debug.Fail(op + " is not a valid XPathOperator");
                     return null;
@@ -268,10 +275,9 @@ private QilNode RelationalOperator(XPathOperator op, QilNode left, QilNode right
             }
         }
 
-        private QilNode NegateOperator(XPathOperator op, QilNode left, QilNode right)
+        private QilNode NegateOperator(XPathOperator op, QilNode left)
         {
             Debug.Assert(op == XPathOperator.UnaryMinus);
-            Debug.Assert(right == null);
             return _f.Negate(_f.ConvertToNumber(left));
         }
 
@@ -292,7 +298,7 @@ private QilNode ArithmeticOperator(XPathOperator op, QilNode left, QilNode right
             }
         }
 
-        private QilNode UnionOperator(XPathOperator op, QilNode left, QilNode right)
+        private QilNode UnionOperator(XPathOperator op, QilNode? left, QilNode right)
         {
             Debug.Assert(op == XPathOperator.Union);
             if (left == null)
@@ -321,7 +327,7 @@ public static XmlNodeKindFlags AxisTypeMask(XmlNodeKindFlags inputTypeMask, XPat
             );
         }
 
-        private QilNode BuildAxisFilter(QilNode qilAxis, XPathAxis xpathAxis, XPathNodeType nodeType, string name, string nsUri)
+        private QilNode BuildAxisFilter(QilNode qilAxis, XPathAxis xpathAxis, XPathNodeType nodeType, string? name, string? nsUri)
         {
             XmlNodeKindFlags original = qilAxis.XmlType.NodeKinds;
             XmlNodeKindFlags required = AxisTypeMask(original, nodeType, xpathAxis);
@@ -383,7 +389,7 @@ private QilNode BuildAxisFilter(QilNode qilAxis, XPathAxis xpathAxis, XPathNodeT
                 /*All                  */ XmlNodeKindFlags.Any
         };
 
-        private QilNode BuildAxis(XPathAxis xpathAxis, XPathNodeType nodeType, string nsUri, string name)
+        private QilNode BuildAxis(XPathAxis xpathAxis, XPathNodeType nodeType, string? nsUri, string? name)
         {
             QilNode currentNode = GetCurrentNode();
             QilNode qilAxis;
@@ -406,7 +412,7 @@ private QilNode BuildAxis(XPathAxis xpathAxis, XPathNodeType nodeType, string ns
                 // Can be done using BuildAxisFilter() but f.Root() sets wrong XmlNodeKindFlags
                 case XPathAxis.Root: return _f.Root(currentNode);
                 default:
-                    qilAxis = null;
+                    qilAxis = null!;
                     Debug.Fail("Invalid EnumValue 'XPathAxis'");
                     break;
             }
@@ -425,9 +431,9 @@ private QilNode BuildAxis(XPathAxis xpathAxis, XPathNodeType nodeType, string ns
             return result;
         }
 
-        public virtual QilNode Axis(XPathAxis xpathAxis, XPathNodeType nodeType, string prefix, string name)
+        public virtual QilNode Axis(XPathAxis xpathAxis, XPathNodeType nodeType, string? prefix, string? name)
         {
-            string nsUri = prefix == null ? null : _environment.ResolvePrefix(prefix);
+            string? nsUri = prefix == null ? null : _environment.ResolvePrefix(prefix);
             return BuildAxis(xpathAxis, nodeType, nsUri, name);
         }
 
@@ -557,7 +563,7 @@ public virtual QilNode Function(string prefix, string name, IList<QilNode> args)
             Debug.Assert(!args.IsReadOnly, "Writable collection expected");
             if (prefix.Length == 0)
             {
-                FunctionInfo func;
+                FunctionInfo? func;
                 if (FunctionTable.TryGetValue(name, out func))
                 {
                     func.CastArguments(args, name, _f);
@@ -827,10 +833,10 @@ internal class FixupVisitor : QilReplaceVisitor
         {
             private new readonly QilPatternFactory f;
             private readonly QilNode _fixupCurrent, _fixupPosition, _fixupLast; // fixup nodes we are replacing
-            private QilIterator _current;
-            private QilNode _last;               // expressions we are using to replace fixupNodes
+            private QilIterator? _current;
+            private QilNode? _last;               // expressions we are using to replace fixupNodes
             private bool _justCount;          // Don't change tree, just count
-            private IXPathEnvironment _environment;  // temp solution
+            private IXPathEnvironment? _environment;  // temp solution
             public int numCurrent, numPosition, numLast; // here we are counting all replacements we have made
 
             public FixupVisitor(QilPatternFactory f, QilNode fixupCurrent, QilNode fixupPosition, QilNode fixupLast) : base(f.BaseFactory)
@@ -841,7 +847,7 @@ public FixupVisitor(QilPatternFactory f, QilNode fixupCurrent, QilNode fixupPosi
                 _fixupLast = fixupLast;
             }
 
-            public QilNode Fixup(QilNode inExpr, QilIterator current, QilNode last)
+            public QilNode Fixup(QilNode inExpr, QilIterator current, QilNode? last)
             {
                 QilDepthChecker.Check(inExpr);
                 _current = current;
@@ -975,11 +981,11 @@ internal class FunctionInfo<T>
             public T id;
             public int minArgs;
             public int maxArgs;
-            public XmlTypeCode[] argTypes;
+            public XmlTypeCode[]? argTypes;
 
             public const int Infinity = int.MaxValue;
 
-            public FunctionInfo(T id, int minArgs, int maxArgs, XmlTypeCode[] argTypes)
+            public FunctionInfo(T id, int minArgs, int maxArgs, XmlTypeCode[]? argTypes)
             {
                 Debug.Assert(maxArgs == 0 || maxArgs == Infinity || argTypes != null && argTypes.Length == maxArgs);
                 this.id = id;
@@ -1039,9 +1045,10 @@ public void CastArguments(IList<QilNode> args, string name, XPathQilFactory f)
                 }
                 else
                 {
+                    Debug.Assert(args.Count == 0 || argTypes != null);
                     for (int i = 0; i < args.Count; i++)
                     {
-                        if (argTypes[i] == XmlTypeCode.Node && f.CannotBeNodeSet(args[i]))
+                        if (argTypes![i] == XmlTypeCode.Node && f.CannotBeNodeSet(args[i]))
                         {
                             throw new XPathCompileException(SR.XPath_NodeSetArgumentExpected, name, (i + 1).ToString(CultureInfo.InvariantCulture));
                         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathCompileException.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathCompileException.cs
index 353fa402fd667a..cc10b5257d90be 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathCompileException.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathCompileException.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Runtime.Serialization;
 using System.Text;
 
@@ -9,7 +10,7 @@ namespace System.Xml.Xsl.XPath
     [Serializable]
     internal class XPathCompileException : XslLoadException
     {
-        public string queryString;
+        public string? queryString;
         public int startChar;
         public int endChar;
 
@@ -28,9 +29,9 @@ internal XPathCompileException(string resId, params string[] args)
         internal XPathCompileException(SerializationInfo info, StreamingContext context)
             : base(info, context)
         {
-            queryString = (string)info.GetValue("QueryString", typeof(string));
-            startChar = (int)info.GetValue("StartChar", typeof(int));
-            endChar = (int)info.GetValue("EndChar", typeof(int));
+            queryString = (string)info.GetValue("QueryString", typeof(string))!;
+            startChar = (int)info.GetValue("StartChar", typeof(int))!;
+            endChar = (int)info.GetValue("EndChar", typeof(int))!;
         }
 
         public override void GetObjectData(SerializationInfo info, StreamingContext context)
@@ -79,7 +80,7 @@ private static void AppendTrimmed(StringBuilder sb, string value, int startIndex
             }
         }
 
-        internal string MarkOutError()
+        internal string? MarkOutError()
         {
             if (queryString == null || queryString.Trim(' ').Length == 0)
             {
@@ -105,7 +106,7 @@ internal string MarkOutError()
         internal override string FormatDetailedMessage()
         {
             string message = Message;
-            string error = MarkOutError();
+            string? error = MarkOutError();
 
             if (error != null && error.Length > 0)
             {
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathContext.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathContext.cs
index f1b073d2e95aff..f863ef75540a3b 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathContext.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathContext.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 #if DontUse
 // XPathContext is not used any more but comments in it and Replacer visitor may be used to
 // optimize code XSLT generates on last().
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathOperator.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathOperator.cs
index 58765d248f85b4..adc8c37e681e45 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathOperator.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathOperator.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 namespace System.Xml.Xsl.XPath
 {
     // order is importent. We are using them as an index in OperatorGroup & QilOperator & XPathOperatorToQilNodeType arrays
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathParser.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathParser.cs
index ab3f0ae91b6810..d707ad52d5dd2b 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathParser.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathParser.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Diagnostics;
 
@@ -10,8 +11,8 @@ namespace System.Xml.Xsl.XPath
 
     internal class XPathParser<Node>
     {
-        private XPathScanner _scanner;
-        private IXPathBuilder<Node> _builder;
+        private XPathScanner? _scanner;
+        private IXPathBuilder<Node>? _builder;
         private readonly Stack<int> _posInfo = new Stack<int>();
 
         // Six possible causes of exceptions in the builder:
@@ -56,7 +57,7 @@ public Node Parse(XPathScanner scanner, IXPathBuilder<Node> builder, LexKind end
 #endif
             }
             Debug.Assert(_posInfo.Count == 0, "PushPosInfo() and PopPosInfo() calls have been unbalanced");
-            return result;
+            return result!;
         }
 
         #region Location paths and node tests
@@ -81,10 +82,10 @@ internal static bool IsStep(LexKind lexKind)
         */
         private Node ParseLocationPath()
         {
-            if (_scanner.Kind == LexKind.Slash)
+            if (_scanner!.Kind == LexKind.Slash)
             {
                 _scanner.NextLex();
-                Node opnd = _builder.Axis(XPathAxis.Root, XPathNodeType.All, null, null);
+                Node opnd = _builder!.Axis(XPathAxis.Root, XPathNodeType.All, null, null);
 
                 if (IsStep(_scanner.Kind))
                 {
@@ -95,7 +96,7 @@ private Node ParseLocationPath()
             else if (_scanner.Kind == LexKind.SlashSlash)
             {
                 _scanner.NextLex();
-                return _builder.JoinStep(
+                return _builder!.JoinStep(
                     _builder.Axis(XPathAxis.Root, XPathNodeType.All, null, null),
                     _builder.JoinStep(
                         _builder.Axis(XPathAxis.DescendantOrSelf, XPathNodeType.All, null, null),
@@ -121,19 +122,19 @@ private Node ParseRelativeLocationPath()
             {
                 if (LocalAppContextSwitches.LimitXPathComplexity)
                 {
-                    throw _scanner.CreateException(SR.Xslt_InputTooComplex);
+                    throw _scanner!.CreateException(SR.Xslt_InputTooComplex);
                 }
             }
             Node opnd = ParseStep();
-            if (_scanner.Kind == LexKind.Slash)
+            if (_scanner!.Kind == LexKind.Slash)
             {
                 _scanner.NextLex();
-                opnd = _builder.JoinStep(opnd, ParseRelativeLocationPath());
+                opnd = _builder!.JoinStep(opnd, ParseRelativeLocationPath());
             }
             else if (_scanner.Kind == LexKind.SlashSlash)
             {
                 _scanner.NextLex();
-                opnd = _builder.JoinStep(opnd,
+                opnd = _builder!.JoinStep(opnd,
                     _builder.JoinStep(
                         _builder.Axis(XPathAxis.DescendantOrSelf, XPathNodeType.All, null, null),
                         ParseRelativeLocationPath()
@@ -150,10 +151,10 @@ private Node ParseRelativeLocationPath()
         private Node ParseStep()
         {
             Node opnd;
-            if (LexKind.Dot == _scanner.Kind)
+            if (LexKind.Dot == _scanner!.Kind)
             {                  // '.'
                 _scanner.NextLex();
-                opnd = _builder.Axis(XPathAxis.Self, XPathNodeType.All, null, null);
+                opnd = _builder!.Axis(XPathAxis.Self, XPathNodeType.All, null, null);
                 if (LexKind.LBracket == _scanner.Kind)
                 {
                     throw _scanner.CreateException(SR.XPath_PredicateAfterDot);
@@ -162,7 +163,7 @@ private Node ParseStep()
             else if (LexKind.DotDot == _scanner.Kind)
             {        // '..'
                 _scanner.NextLex();
-                opnd = _builder.Axis(XPathAxis.Parent, XPathNodeType.All, null, null);
+                opnd = _builder!.Axis(XPathAxis.Parent, XPathNodeType.All, null, null);
                 if (LexKind.LBracket == _scanner.Kind)
                 {
                     throw _scanner.CreateException(SR.XPath_PredicateAfterDotDot);
@@ -195,7 +196,7 @@ private Node ParseStep()
 
                 while (LexKind.LBracket == _scanner.Kind)
                 {
-                    opnd = _builder.Predicate(opnd, ParsePredicate(), IsReverseAxis(axis));
+                    opnd = _builder!.Predicate(opnd, ParsePredicate(), IsReverseAxis(axis));
                 }
             }
             return opnd;
@@ -216,12 +217,12 @@ private static bool IsReverseAxis(XPathAxis axis)
         private Node ParseNodeTest(XPathAxis axis)
         {
             XPathNodeType nodeType;
-            string nodePrefix, nodeName;
+            string? nodePrefix, nodeName;
 
-            int startChar = _scanner.LexStart;
+            int startChar = _scanner!.LexStart;
             InternalParseNodeTest(_scanner, axis, out nodeType, out nodePrefix, out nodeName);
             PushPosInfo(startChar, _scanner.PrevLexEnd);
-            Node result = _builder.Axis(axis, nodeType, nodePrefix, nodeName);
+            Node result = _builder!.Axis(axis, nodeType, nodePrefix, nodeName);
             PopPosInfo();
             return result;
         }
@@ -245,7 +246,7 @@ private static XPathNodeType PrincipalNodeType(XPathAxis axis)
             );
         }
 
-        internal static void InternalParseNodeTest(XPathScanner scanner, XPathAxis axis, out XPathNodeType nodeType, out string nodePrefix, out string nodeName)
+        internal static void InternalParseNodeTest(XPathScanner scanner, XPathAxis axis, out XPathNodeType nodeType, out string? nodePrefix, out string? nodeName)
         {
             switch (scanner.Kind)
             {
@@ -311,7 +312,7 @@ internal static void InternalParseNodeTest(XPathScanner scanner, XPathAxis axis,
         */
         private Node ParsePredicate()
         {
-            _scanner.PassToken(LexKind.LBracket);
+            _scanner!.PassToken(LexKind.LBracket);
             Node opnd = ParseExpr();
             _scanner.PassToken(LexKind.RBracket);
             return opnd;
@@ -349,7 +350,7 @@ private Node ParseSubExpr(int callerPrec)
             {
                 if (LocalAppContextSwitches.LimitXPathComplexity)
                 {
-                    throw _scanner.CreateException(SR.Xslt_InputTooComplex);
+                    throw _scanner!.CreateException(SR.Xslt_InputTooComplex);
                 }
             }
 
@@ -357,12 +358,12 @@ private Node ParseSubExpr(int callerPrec)
             Node opnd;
 
             // Check for unary operators
-            if (_scanner.Kind == LexKind.Minus)
+            if (_scanner!.Kind == LexKind.Minus)
             {
                 op = XPathOperator.UnaryMinus;
                 int opPrec = s_XPathOperatorPrecedence[(int)op];
                 _scanner.NextLex();
-                opnd = _builder.Operator(op, ParseSubExpr(opPrec), default(Node));
+                opnd = _builder!.Operator(op, ParseSubExpr(opPrec), default(Node));
             }
             else
             {
@@ -381,7 +382,7 @@ private Node ParseSubExpr(int callerPrec)
 
                 // Operator's precedence is greater than the one of our caller, so process it here
                 _scanner.NextLex();
-                opnd = _builder.Operator(op, opnd, ParseSubExpr(/*callerPrec:*/opPrec));
+                opnd = _builder!.Operator(op, opnd, ParseSubExpr(/*callerPrec:*/opPrec));
             }
             --_parseSubExprDepth;
             return opnd;
@@ -411,13 +412,13 @@ private Node ParseSubExpr(int callerPrec)
         */
         private Node ParseUnionExpr()
         {
-            int startChar = _scanner.LexStart;
+            int startChar = _scanner!.LexStart;
             Node opnd1 = ParsePathExpr();
 
             if (_scanner.Kind == LexKind.Union)
             {
                 PushPosInfo(startChar, _scanner.PrevLexEnd);
-                opnd1 = _builder.Operator(XPathOperator.Union, default(Node), opnd1);
+                opnd1 = _builder!.Operator(XPathOperator.Union, default(Node), opnd1);
                 PopPosInfo();
 
                 while (_scanner.Kind == LexKind.Union)
@@ -441,7 +442,7 @@ private Node ParsePathExpr()
             // Here we distinguish FilterExpr from LocationPath - the former starts with PrimaryExpr
             if (IsPrimaryExpr())
             {
-                int startChar = _scanner.LexStart;
+                int startChar = _scanner!.LexStart;
                 Node opnd = ParseFilterExpr();
                 int endChar = _scanner.PrevLexEnd;
 
@@ -449,14 +450,14 @@ private Node ParsePathExpr()
                 {
                     _scanner.NextLex();
                     PushPosInfo(startChar, endChar);
-                    opnd = _builder.JoinStep(opnd, ParseRelativeLocationPath());
+                    opnd = _builder!.JoinStep(opnd, ParseRelativeLocationPath());
                     PopPosInfo();
                 }
                 else if (_scanner.Kind == LexKind.SlashSlash)
                 {
                     _scanner.NextLex();
                     PushPosInfo(startChar, endChar);
-                    opnd = _builder.JoinStep(opnd,
+                    opnd = _builder!.JoinStep(opnd,
                         _builder.JoinStep(
                             _builder.Axis(XPathAxis.DescendantOrSelf, XPathNodeType.All, null, null),
                             ParseRelativeLocationPath()
@@ -477,14 +478,14 @@ private Node ParsePathExpr()
         */
         private Node ParseFilterExpr()
         {
-            int startChar = _scanner.LexStart;
+            int startChar = _scanner!.LexStart;
             Node opnd = ParsePrimaryExpr();
             int endChar = _scanner.PrevLexEnd;
 
             while (_scanner.Kind == LexKind.LBracket)
             {
                 PushPosInfo(startChar, endChar);
-                opnd = _builder.Predicate(opnd, ParsePredicate(), /*reverseStep:*/false);
+                opnd = _builder!.Predicate(opnd, ParsePredicate(), /*reverseStep:*/false);
                 PopPosInfo();
             }
             return opnd;
@@ -493,7 +494,7 @@ private Node ParseFilterExpr()
         private bool IsPrimaryExpr()
         {
             return (
-                _scanner.Kind == LexKind.String ||
+                _scanner!.Kind == LexKind.String ||
                 _scanner.Kind == LexKind.Number ||
                 _scanner.Kind == LexKind.Dollar ||
                 _scanner.Kind == LexKind.LParens ||
@@ -508,14 +509,14 @@ private Node ParsePrimaryExpr()
         {
             Debug.Assert(IsPrimaryExpr());
             Node opnd;
-            switch (_scanner.Kind)
+            switch (_scanner!.Kind)
             {
                 case LexKind.String:
-                    opnd = _builder.String(_scanner.StringValue);
+                    opnd = _builder!.String(_scanner.StringValue);
                     _scanner.NextLex();
                     break;
                 case LexKind.Number:
-                    opnd = _builder.Number(XPathConvert.StringToDouble(_scanner.RawValue));
+                    opnd = _builder!.Number(XPathConvert.StringToDouble(_scanner.RawValue));
                     _scanner.NextLex();
                     break;
                 case LexKind.Dollar:
@@ -523,7 +524,7 @@ private Node ParsePrimaryExpr()
                     _scanner.NextLex();
                     _scanner.CheckToken(LexKind.Name);
                     PushPosInfo(startChar, _scanner.LexStart + _scanner.LexSize);
-                    opnd = _builder.Variable(_scanner.Prefix, _scanner.Name);
+                    opnd = _builder!.Variable(_scanner.Prefix, _scanner.Name);
                     PopPosInfo();
                     _scanner.NextLex();
                     break;
@@ -549,7 +550,7 @@ private Node ParsePrimaryExpr()
         private Node ParseFunctionCall()
         {
             List<Node> argList = new List<Node>();
-            string name = _scanner.Name;
+            string name = _scanner!.Name;
             string prefix = _scanner.Prefix;
             int startChar = _scanner.LexStart;
 
@@ -572,7 +573,7 @@ private Node ParseFunctionCall()
 
             _scanner.NextLex();          // move off the ')'
             PushPosInfo(startChar, _scanner.PrevLexEnd);
-            Node result = _builder.Function(prefix, name, argList);
+            Node result = _builder!.Function(prefix, name, argList);
             PopPosInfo();
             return result;
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathQilFactory.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathQilFactory.cs
index b6fe069bf884d9..f92d203ff81eb9 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathQilFactory.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathQilFactory.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Diagnostics;
 using System.Xml.Schema;
 using System.Xml.Xsl.Qil;
@@ -289,7 +290,7 @@ public QilNode ConvertToNodeSet(QilNode n)
         }
 
         // Returns null if the given expression is never a node-set
-        public QilNode TryEnsureNodeSet(QilNode n)
+        public QilNode? TryEnsureNodeSet(QilNode n)
         {
             if (n.XmlType.IsNode && n.XmlType.IsNotRtf)
             {
@@ -307,7 +308,7 @@ public QilNode TryEnsureNodeSet(QilNode n)
         // Throws an exception if the given expression is never a node-set
         public QilNode EnsureNodeSet(QilNode n)
         {
-            QilNode result = TryEnsureNodeSet(n);
+            QilNode? result = TryEnsureNodeSet(n);
             if (result == null)
             {
                 throw new XPathCompileException(SR.XPath_NodeSetExpected);
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathScanner.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathScanner.cs
index 0221f1dc5487fc..e6509bf1580132 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathScanner.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPath/XPathScanner.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 // <spec>http://www.w3.org/TR/xpath#exprlex</spec>
 //------------------------------------------------------------------------------
 
@@ -62,9 +63,9 @@ internal sealed class XPathScanner
         private int _curIndex;
         private char _curChar;
         private LexKind _kind;
-        private string _name;
-        private string _prefix;
-        private string _stringValue;
+        private string? _name;
+        private string? _prefix;
+        private string? _stringValue;
         private bool _canBeFunction;
         private int _lexStart;
         private int _prevLexEnd;
@@ -423,6 +424,8 @@ private bool CheckOperator(bool star)
             }
             else
             {
+                Debug.Assert(_prefix != null);
+                Debug.Assert(_name != null);
                 if (_prefix.Length != 0 || _name.Length > 3)
                     return false;
 
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPathConvert.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPathConvert.cs
index abf171ee651b76..c31f265cbb9f36 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPathConvert.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/XPathConvert.cs
@@ -8,7 +8,9 @@
 *
 */
 
+#nullable enable
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 
 namespace System.Xml.Xsl
@@ -2016,8 +2018,9 @@ public void ShiftRight(int cbit)
                 AssertValid();
             }
 
-            public int CompareTo(object obj)
+            public int CompareTo(object? obj)
             {
+                Debug.Assert(obj != null);
                 BigInteger bi = (BigInteger)obj;
                 AssertValid();
                 bi.AssertValid();
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/Xslt/XPathPatternBuilder.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/Xslt/XPathPatternBuilder.cs
index 9f6a873260a96f..ef4f222eace8fd 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/Xslt/XPathPatternBuilder.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/Xslt/XPathPatternBuilder.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -9,6 +10,7 @@
 using System.Xml.Schema;
 using System.Xml.Xsl.Qil;
 using System.Xml.Xsl.XPath;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Xml.Xsl.Xslt
 {
@@ -61,7 +63,8 @@ private void FixupFilterBinding(QilLoop filter, QilNode newBinding)
             filter.Variable.Binding = newBinding;
         }
 
-        public virtual QilNode EndBuild(QilNode result)
+        [return: NotNullIfNotNull("result")]
+        public virtual QilNode? EndBuild(QilNode? result)
         {
             Debug.Assert(_inTheBuild, "StartBuild() wasn't called");
             if (result == null)
@@ -78,7 +81,7 @@ public virtual QilNode EndBuild(QilNode result)
             return result;
         }
 
-        public QilNode Operator(XPathOperator op, QilNode left, QilNode right)
+        public QilNode Operator(XPathOperator op, QilNode? left, QilNode? right)
         {
             Debug.Assert(op == XPathOperator.Union);
             Debug.Assert(left != null);
@@ -97,7 +100,7 @@ public QilNode Operator(XPathOperator op, QilNode left, QilNode right)
             }
         }
 
-        private static QilLoop BuildAxisFilter(QilPatternFactory f, QilIterator itr, XPathAxis xpathAxis, XPathNodeType nodeType, string name, string nsUri)
+        private static QilLoop BuildAxisFilter(QilPatternFactory f, QilIterator itr, XPathAxis xpathAxis, XPathNodeType nodeType, string? name, string? nsUri)
         {
             QilNode nameTest = (
                 name != null && nsUri != null ? f.Eq(f.NameOf(itr), f.QName(name, nsUri)) : // ns:bar || bar
@@ -120,7 +123,7 @@ private static QilLoop BuildAxisFilter(QilPatternFactory f, QilIterator itr, XPa
             return filter;
         }
 
-        public QilNode Axis(XPathAxis xpathAxis, XPathNodeType nodeType, string prefix, string name)
+        public QilNode Axis(XPathAxis xpathAxis, XPathNodeType nodeType, string? prefix, string? name)
         {
             Debug.Assert(
                 xpathAxis == XPathAxis.Child ||
@@ -141,7 +144,7 @@ public QilNode Axis(XPathAxis xpathAxis, XPathNodeType nodeType, string prefix,
                     priority = 0.5;
                     break;
                 default:
-                    string nsUri = prefix == null ? null : _environment.ResolvePrefix(prefix);
+                    string? nsUri = prefix == null ? null : _environment.ResolvePrefix(prefix);
                     result = BuildAxisFilter(_f, _f.For(_fixupNode), xpathAxis, nodeType, name, nsUri);
                     switch (nodeType)
                     {
@@ -214,7 +217,9 @@ public QilNode JoinStep(QilNode left, QilNode right)
                 }
             }
             Debug.Assert(right.NodeType == QilNodeType.Filter);
-            QilLoop lastParent = GetLastParent(right);
+            QilLoop? lastParent = GetLastParent(right);
+            Debug.Assert(lastParent != null);
+
             FixupFilterBinding(parentFilter, ancestor ? _f.Ancestor(lastParent.Variable) : _f.Parent(lastParent.Variable));
             lastParent.Body = _f.And(lastParent.Body, _f.Not(_f.IsEmpty(parentFilter)));
             SetPriority(right, 0.5);
@@ -336,7 +341,7 @@ public QilNode Variable(string prefix, string name)
         private class Annotation
         {
             public double Priority;
-            public QilLoop Parent;
+            public QilLoop? Parent;
         }
 
         public static void SetPriority(QilNode node, double priority)
@@ -359,7 +364,7 @@ private static void SetLastParent(QilNode node, QilLoop parent)
             node.Annotation = ann;
         }
 
-        private static QilLoop GetLastParent(QilNode node)
+        private static QilLoop? GetLastParent(QilNode node)
         {
             return ((Annotation)node.Annotation).Parent;
         }
diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/Xslt/XPathPatternParser.cs b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/Xslt/XPathPatternParser.cs
index 7b33bf0d364f27..16d29830538da8 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Xsl/Xslt/XPathPatternParser.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Xsl/Xslt/XPathPatternParser.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#nullable enable
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Xml;
@@ -19,15 +20,15 @@ public interface IPatternBuilder : IXPathBuilder<QilNode>
             IXPathBuilder<QilNode> GetPredicateBuilder(QilNode context);
         }
 
-        private XPathScanner _scanner;
-        private IPatternBuilder _ptrnBuilder;
+        private XPathScanner? _scanner;
+        private IPatternBuilder? _ptrnBuilder;
         private readonly XPathParser _predicateParser = new XPathParser();
 
         public QilNode Parse(XPathScanner scanner, IPatternBuilder ptrnBuilder)
         {
             Debug.Assert(_scanner == null && _ptrnBuilder == null);
             Debug.Assert(scanner != null && ptrnBuilder != null);
-            QilNode result = null;
+            QilNode? result = null;
             ptrnBuilder.StartBuild();
             try
             {
@@ -44,7 +45,7 @@ public QilNode Parse(XPathScanner scanner, IPatternBuilder ptrnBuilder)
                 _scanner = null;
 #endif
             }
-            return result;
+            return result!;
         }
 
         /*
@@ -54,10 +55,10 @@ private QilNode ParsePattern()
         {
             QilNode opnd = ParseLocationPathPattern();
 
-            while (_scanner.Kind == LexKind.Union)
+            while (_scanner!.Kind == LexKind.Union)
             {
                 _scanner.NextLex();
-                opnd = _ptrnBuilder.Operator(XPathOperator.Union, opnd, ParseLocationPathPattern());
+                opnd = _ptrnBuilder!.Operator(XPathOperator.Union, opnd, ParseLocationPathPattern());
             }
             return opnd;
         }
@@ -69,11 +70,11 @@ private QilNode ParseLocationPathPattern()
         {
             QilNode opnd;
 
-            switch (_scanner.Kind)
+            switch (_scanner!.Kind)
             {
                 case LexKind.Slash:
                     _scanner.NextLex();
-                    opnd = _ptrnBuilder.Axis(XPathAxis.Root, XPathNodeType.All, null, null);
+                    opnd = _ptrnBuilder!.Axis(XPathAxis.Root, XPathNodeType.All, null, null);
 
                     if (XPathParser.IsStep(_scanner.Kind))
                     {
@@ -82,7 +83,7 @@ private QilNode ParseLocationPathPattern()
                     return opnd;
                 case LexKind.SlashSlash:
                     _scanner.NextLex();
-                    return _ptrnBuilder.JoinStep(
+                    return _ptrnBuilder!.JoinStep(
                         _ptrnBuilder.Axis(XPathAxis.Root, XPathNodeType.All, null, null),
                         _ptrnBuilder.JoinStep(
                             _ptrnBuilder.Axis(XPathAxis.DescendantOrSelf, XPathNodeType.All, null, null),
@@ -97,11 +98,11 @@ private QilNode ParseLocationPathPattern()
                         {
                             case LexKind.Slash:
                                 _scanner.NextLex();
-                                opnd = _ptrnBuilder.JoinStep(opnd, ParseRelativePathPattern());
+                                opnd = _ptrnBuilder!.JoinStep(opnd, ParseRelativePathPattern());
                                 break;
                             case LexKind.SlashSlash:
                                 _scanner.NextLex();
-                                opnd = _ptrnBuilder.JoinStep(opnd,
+                                opnd = _ptrnBuilder!.JoinStep(opnd,
                                     _ptrnBuilder.JoinStep(
                                         _ptrnBuilder.Axis(XPathAxis.DescendantOrSelf, XPathNodeType.All, null, null),
                                         ParseRelativePathPattern()
@@ -122,7 +123,7 @@ private QilNode ParseLocationPathPattern()
         */
         private QilNode ParseIdKeyPattern()
         {
-            Debug.Assert(_scanner.CanBeFunction);
+            Debug.Assert(_scanner!.CanBeFunction);
             Debug.Assert(_scanner.Prefix.Length == 0);
             Debug.Assert(_scanner.Name == "id" || _scanner.Name == "key");
             List<QilNode> args = new List<QilNode>(2);
@@ -132,7 +133,7 @@ private QilNode ParseIdKeyPattern()
                 _scanner.NextLex();
                 _scanner.PassToken(LexKind.LParens);
                 _scanner.CheckToken(LexKind.String);
-                args.Add(_ptrnBuilder.String(_scanner.StringValue));
+                args.Add(_ptrnBuilder!.String(_scanner.StringValue));
                 _scanner.NextLex();
                 _scanner.PassToken(LexKind.RParens);
                 return _ptrnBuilder.Function("", "id", args);
@@ -142,7 +143,7 @@ private QilNode ParseIdKeyPattern()
                 _scanner.NextLex();
                 _scanner.PassToken(LexKind.LParens);
                 _scanner.CheckToken(LexKind.String);
-                args.Add(_ptrnBuilder.String(_scanner.StringValue));
+                args.Add(_ptrnBuilder!.String(_scanner.StringValue));
                 _scanner.NextLex();
                 _scanner.PassToken(LexKind.Comma);
                 _scanner.CheckToken(LexKind.String);
@@ -165,19 +166,19 @@ private QilNode ParseRelativePathPattern()
             {
                 if (LocalAppContextSwitches.LimitXPathComplexity)
                 {
-                    throw _scanner.CreateException(SR.Xslt_InputTooComplex);
+                    throw _scanner!.CreateException(SR.Xslt_InputTooComplex);
                 }
             }
             QilNode opnd = ParseStepPattern();
-            if (_scanner.Kind == LexKind.Slash)
+            if (_scanner!.Kind == LexKind.Slash)
             {
                 _scanner.NextLex();
-                opnd = _ptrnBuilder.JoinStep(opnd, ParseRelativePathPattern());
+                opnd = _ptrnBuilder!.JoinStep(opnd, ParseRelativePathPattern());
             }
             else if (_scanner.Kind == LexKind.SlashSlash)
             {
                 _scanner.NextLex();
-                opnd = _ptrnBuilder.JoinStep(opnd,
+                opnd = _ptrnBuilder!.JoinStep(opnd,
                     _ptrnBuilder.JoinStep(
                         _ptrnBuilder.Axis(XPathAxis.DescendantOrSelf, XPathNodeType.All, null, null),
                         ParseRelativePathPattern()
@@ -197,7 +198,7 @@ private QilNode ParseStepPattern()
             QilNode opnd;
             XPathAxis axis;
 
-            switch (_scanner.Kind)
+            switch (_scanner!.Kind)
             {
                 case LexKind.Dot:
                 case LexKind.DotDot:
@@ -225,11 +226,11 @@ private QilNode ParseStepPattern()
             }
 
             XPathNodeType nodeType;
-            string nodePrefix, nodeName;
+            string? nodePrefix, nodeName;
             XPathParser.InternalParseNodeTest(_scanner, axis, out nodeType, out nodePrefix, out nodeName);
-            opnd = _ptrnBuilder.Axis(axis, nodeType, nodePrefix, nodeName);
+            opnd = _ptrnBuilder!.Axis(axis, nodeType, nodePrefix, nodeName);
 
-            XPathPatternBuilder xpathPatternBuilder = _ptrnBuilder as XPathPatternBuilder;
+            XPathPatternBuilder? xpathPatternBuilder = _ptrnBuilder as XPathPatternBuilder;
             if (xpathPatternBuilder != null)
             {
                 //for XPathPatternBuilder, get all predicates and then build them
@@ -256,9 +257,9 @@ private QilNode ParseStepPattern()
         */
         private QilNode ParsePredicate(QilNode context)
         {
-            Debug.Assert(_scanner.Kind == LexKind.LBracket);
+            Debug.Assert(_scanner!.Kind == LexKind.LBracket);
             _scanner.NextLex();
-            QilNode result = _predicateParser.Parse(_scanner, _ptrnBuilder.GetPredicateBuilder(context), LexKind.RBracket);
+            QilNode result = _predicateParser.Parse(_scanner, _ptrnBuilder!.GetPredicateBuilder(context), LexKind.RBracket);
             Debug.Assert(_scanner.Kind == LexKind.RBracket);
             _scanner.NextLex();
             return result;
diff --git a/src/libraries/System.Private.Xml/tests/Writers/XmlWriterApi/System.Xml.RW.XmlWriterApi.Tests.csproj b/src/libraries/System.Private.Xml/tests/Writers/XmlWriterApi/System.Xml.RW.XmlWriterApi.Tests.csproj
index 3e6c2304979614..66a1626bfe18c7 100644
--- a/src/libraries/System.Private.Xml/tests/Writers/XmlWriterApi/System.Xml.RW.XmlWriterApi.Tests.csproj
+++ b/src/libraries/System.Private.Xml/tests/Writers/XmlWriterApi/System.Xml.RW.XmlWriterApi.Tests.csproj
@@ -38,11 +38,9 @@
     <Compile Include="XmlWriterTestCaseBase.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="$(CommonTestPath)System\Xml\XmlDiff\XmlDiff.csproj" />
+    <PackageReference Include="xunit.extensibility.execution" Version="$(XUnitVersion)" />
     <ProjectReference Include="$(CommonTestPath)System\Xml\ModuleCore\ModuleCore.csproj" />
     <ProjectReference Include="$(CommonTestPath)System\Xml\XmlCoreTest\XmlCoreTest.csproj" />
-  </ItemGroup>
-  <ItemGroup>
-    <PackageReference Include="xunit.extensibility.execution" Version="$(XUnitVersion)" />
+    <ProjectReference Include="$(CommonTestPath)System\Xml\XmlDiff\XmlDiff.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Private.Xml/tests/Xslt/XslCompiledTransformApi/System.Xml.Xsl.XslCompiledTransformApi.Tests.csproj b/src/libraries/System.Private.Xml/tests/Xslt/XslCompiledTransformApi/System.Xml.Xsl.XslCompiledTransformApi.Tests.csproj
index b372333e9628e5..d9d8f1aa2f51cb 100644
--- a/src/libraries/System.Private.Xml/tests/Xslt/XslCompiledTransformApi/System.Xml.Xsl.XslCompiledTransformApi.Tests.csproj
+++ b/src/libraries/System.Private.Xml/tests/Xslt/XslCompiledTransformApi/System.Xml.Xsl.XslCompiledTransformApi.Tests.csproj
@@ -14,6 +14,13 @@
     <Compile Include="XsltSettings.cs" />
     <Compile Include="XunitAssemblyAttribute.cs" />
     <Compile Include="XslCompiledTransform.cs" />
+    <Compile Include="..\XslTransformApi\cthread.cs" />
+    <Compile Include="..\XslTransformApi\CThreads.cs" />
+    <Compile Include="..\XslTransformApi\DataHelper.cs" />
+    <Compile Include="..\XslTransformApi\ExceptionVerifier.cs" />
+    <Compile Include="..\XslTransformApi\MyNavigator.cs" />
+    <Compile Include="..\XslTransformApi\ReaderType.cs" />
+    <Compile Include="..\XslTransformApi\ThreadFunc.cs" />
   </ItemGroup>
   <ItemGroup>
     <Content Include="..\TestFiles\**\*"
@@ -25,6 +32,5 @@
     <ProjectReference Include="$(CommonTestPath)System\Xml\ModuleCore\ModuleCore.csproj" />
     <ProjectReference Include="$(CommonTestPath)System\Xml\XmlCoreTest\XmlCoreTest.csproj" />
     <ProjectReference Include="$(CommonTestPath)System\Xml\XmlDiff\XmlDiff.csproj" />
-    <ProjectReference Include="..\XslTransformApi\System.Xml.Xsl.XslTransformApi.Tests.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/IEnvironmentVariable.cs b/src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/ReaderType.cs
similarity index 53%
rename from src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/IEnvironmentVariable.cs
rename to src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/ReaderType.cs
index 1fbe0320fa72d6..719551b9f1360f 100644
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/src/xunit/IEnvironmentVariable.cs
+++ b/src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/ReaderType.cs
@@ -1,10 +1,10 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-namespace Microsoft.AspNetCore.Testing
+namespace System.Xml.Tests
 {
-    internal interface IEnvironmentVariable
+    public enum ReaderType
     {
-        string Get(string name);
+        XmlTextReader, XmlNodeReader, XmlValidatingReader, XsltReader, Unknown
     }
-}
+}
\ No newline at end of file
diff --git a/src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/System.Xml.Xsl.XslTransformApi.Tests.csproj b/src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/System.Xml.Xsl.XslTransformApi.Tests.csproj
index 12b7f905cb450a..904076419ca091 100644
--- a/src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/System.Xml.Xsl.XslTransformApi.Tests.csproj
+++ b/src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/System.Xml.Xsl.XslTransformApi.Tests.csproj
@@ -13,6 +13,7 @@
     <Compile Include="DataHelper.cs" />
     <Compile Include="ExceptionVerifier.cs" />
     <Compile Include="MyNavigator.cs" />
+    <Compile Include="ReaderType.cs" />
     <Compile Include="ThreadFunc.cs" />
     <Compile Include="XSLTransform.cs" />
     <Compile Include="XunitAssemblyAttributes.cs" />
diff --git a/src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/XSLTransform.cs b/src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/XSLTransform.cs
index 8a8bbd8c93944c..a0bac0cd72b7e2 100644
--- a/src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/XSLTransform.cs
+++ b/src/libraries/System.Private.Xml/tests/Xslt/XslTransformApi/XSLTransform.cs
@@ -27,11 +27,6 @@ public enum DocType
         XmlDocument, XPathDocument, Unknown
     }
 
-    public enum ReaderType
-    {
-        XmlTextReader, XmlNodeReader, XmlValidatingReader, XsltReader, Unknown
-    }
-
     ////////////////////////////////////////////////////////////////
     // Module declaration for LTM usage
     //
diff --git a/src/libraries/System.Reflection.Context/ref/System.Reflection.Context.csproj b/src/libraries/System.Reflection.Context/ref/System.Reflection.Context.csproj
index 7381fb80af83b5..4bce12a3522738 100644
--- a/src/libraries/System.Reflection.Context/ref/System.Reflection.Context.csproj
+++ b/src/libraries/System.Reflection.Context/ref/System.Reflection.Context.csproj
@@ -10,8 +10,4 @@
   <ItemGroup>
     <Compile Include="System.Reflection.Context.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.1'">
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Reflection" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Reflection.Context/src/System.Reflection.Context.csproj b/src/libraries/System.Reflection.Context/src/System.Reflection.Context.csproj
index ea0fb7407b341e..8ca7664c3e265f 100644
--- a/src/libraries/System.Reflection.Context/src/System.Reflection.Context.csproj
+++ b/src/libraries/System.Reflection.Context/src/System.Reflection.Context.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard1.1;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.1;netstandard2.0;netstandard1.1</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -64,9 +64,4 @@
     <Compile Include="System\Reflection\Context\Virtual\VirtualPropertyInfo.PropertySetter.cs" />
     <Compile Include="System\Reflection\Context\Virtual\VirtualReturnParameter.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.1'">
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Reflection" />
-    <Reference Include="System.Resources.ResourceManager" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Reflection.Context/tests/System.Reflection.Context.Tests.csproj b/src/libraries/System.Reflection.Context/tests/System.Reflection.Context.Tests.csproj
index c405873f4ebd26..490b4b0a011f04 100644
--- a/src/libraries/System.Reflection.Context/tests/System.Reflection.Context.Tests.csproj
+++ b/src/libraries/System.Reflection.Context/tests/System.Reflection.Context.Tests.csproj
@@ -25,4 +25,7 @@
       <SubType>Designer</SubType>
     </EmbeddedResource>
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Reflection.Context.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Reflection.DispatchProxy/Directory.Build.props b/src/libraries/System.Reflection.DispatchProxy/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Reflection.DispatchProxy/Directory.Build.props
+++ b/src/libraries/System.Reflection.DispatchProxy/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Reflection.Emit.ILGeneration/Directory.Build.props b/src/libraries/System.Reflection.Emit.ILGeneration/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Reflection.Emit.ILGeneration/Directory.Build.props
+++ b/src/libraries/System.Reflection.Emit.ILGeneration/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Reflection.Emit.ILGeneration/src/System.Reflection.Emit.ILGeneration.csproj b/src/libraries/System.Reflection.Emit.ILGeneration/src/System.Reflection.Emit.ILGeneration.csproj
index 7294575b536b44..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Reflection.Emit.ILGeneration/src/System.Reflection.Emit.ILGeneration.csproj
+++ b/src/libraries/System.Reflection.Emit.ILGeneration/src/System.Reflection.Emit.ILGeneration.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Reflection.Emit.ILGeneration</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Reflection.Emit.Lightweight/Directory.Build.props b/src/libraries/System.Reflection.Emit.Lightweight/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Reflection.Emit.Lightweight/Directory.Build.props
+++ b/src/libraries/System.Reflection.Emit.Lightweight/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Reflection.Emit.Lightweight/src/System.Reflection.Emit.Lightweight.csproj b/src/libraries/System.Reflection.Emit.Lightweight/src/System.Reflection.Emit.Lightweight.csproj
index 2747800b87755b..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Reflection.Emit.Lightweight/src/System.Reflection.Emit.Lightweight.csproj
+++ b/src/libraries/System.Reflection.Emit.Lightweight/src/System.Reflection.Emit.Lightweight.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Reflection.Emit.Lightweight</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Reflection.Emit/Directory.Build.props b/src/libraries/System.Reflection.Emit/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Reflection.Emit/Directory.Build.props
+++ b/src/libraries/System.Reflection.Emit/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Reflection.Emit/ref/System.Reflection.Emit.cs b/src/libraries/System.Reflection.Emit/ref/System.Reflection.Emit.cs
index bd34fa007dcee7..a84677c50ffe78 100644
--- a/src/libraries/System.Reflection.Emit/ref/System.Reflection.Emit.cs
+++ b/src/libraries/System.Reflection.Emit/ref/System.Reflection.Emit.cs
@@ -9,10 +9,11 @@ namespace System.Reflection.Emit
     public sealed partial class AssemblyBuilder : System.Reflection.Assembly
     {
         internal AssemblyBuilder() { }
+        [System.ObsoleteAttribute("CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.", DiagnosticId = "SYSLIB0012", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
         public override string? CodeBase { get { throw null; } }
         public override System.Reflection.MethodInfo? EntryPoint { get { throw null; } }
         public override string? FullName { get { throw null; } }
-        [Obsolete("The Global Assembly Cache is not supported.", DiagnosticId = "SYSLIB0005", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
+        [System.ObsoleteAttribute("The Global Assembly Cache is not supported.", DiagnosticId = "SYSLIB0005", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
         public override bool GlobalAssemblyCache { get { throw null; } }
         public override long HostContext { get { throw null; } }
         public override string ImageRuntimeVersion { get { throw null; } }
@@ -28,6 +29,7 @@ internal AssemblyBuilder() { }
         public override object[] GetCustomAttributes(System.Type attributeType, bool inherit) { throw null; }
         public override System.Collections.Generic.IList<System.Reflection.CustomAttributeData> GetCustomAttributesData() { throw null; }
         public System.Reflection.Emit.ModuleBuilder? GetDynamicModule(string name) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types might be removed")]
         public override System.Type[] GetExportedTypes() { throw null; }
         public override System.IO.FileStream GetFile(string name) { throw null; }
         public override System.IO.FileStream[] GetFiles(bool getResourceModules) { throw null; }
@@ -40,9 +42,11 @@ internal AssemblyBuilder() { }
         public override System.Reflection.Module? GetModule(string name) { throw null; }
         public override System.Reflection.Module[] GetModules(bool getResourceModules) { throw null; }
         public override System.Reflection.AssemblyName GetName(bool copiedName) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Assembly references might be removed")]
         public override System.Reflection.AssemblyName[] GetReferencedAssemblies() { throw null; }
         public override System.Reflection.Assembly GetSatelliteAssembly(System.Globalization.CultureInfo culture) { throw null; }
         public override System.Reflection.Assembly GetSatelliteAssembly(System.Globalization.CultureInfo culture, System.Version? version) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types might be removed")]
         public override System.Type? GetType(string name, bool throwOnError, bool ignoreCase) { throw null; }
         public override bool IsDefined(System.Type attributeType, bool inherit) { throw null; }
         public void SetCustomAttribute(System.Reflection.ConstructorInfo con, byte[] binaryAttribute) { }
@@ -104,29 +108,45 @@ internal EnumBuilder() { }
         public System.Reflection.TypeInfo? CreateTypeInfo() { throw null; }
         public System.Reflection.Emit.FieldBuilder DefineLiteral(string literalName, object? literalValue) { throw null; }
         protected override System.Reflection.TypeAttributes GetAttributeFlagsImpl() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
         protected override System.Reflection.ConstructorInfo? GetConstructorImpl(System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Reflection.CallingConventions callConvention, System.Type[] types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
         public override System.Reflection.ConstructorInfo[] GetConstructors(System.Reflection.BindingFlags bindingAttr) { throw null; }
         public override object[] GetCustomAttributes(bool inherit) { throw null; }
         public override object[] GetCustomAttributes(System.Type attributeType, bool inherit) { throw null; }
         public override System.Type? GetElementType() { throw null; }
         public override System.Type GetEnumUnderlyingType() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicEvents | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo? GetEvent(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo[] GetEvents() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicEvents | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo[] GetEvents(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
         public override System.Reflection.FieldInfo? GetField(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
         public override System.Reflection.FieldInfo[] GetFields(System.Reflection.BindingFlags bindingAttr) { throw null; }
         public override System.Type? GetInterface(string name, bool ignoreCase) { throw null; }
         public override System.Reflection.InterfaceMapping GetInterfaceMap(System.Type interfaceType) { throw null; }
         public override System.Type[] GetInterfaces() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override System.Reflection.MemberInfo[] GetMember(string name, System.Reflection.MemberTypes type, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override System.Reflection.MemberInfo[] GetMembers(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         protected override System.Reflection.MethodInfo? GetMethodImpl(string name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Reflection.CallingConventions callConvention, System.Type[]? types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         public override System.Reflection.MethodInfo[] GetMethods(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicNestedTypes | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicNestedTypes)]
         public override System.Type? GetNestedType(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicNestedTypes | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicNestedTypes)]
         public override System.Type[] GetNestedTypes(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         public override System.Reflection.PropertyInfo[] GetProperties(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         protected override System.Reflection.PropertyInfo GetPropertyImpl(string name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Type? returnType, System.Type[]? types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
         protected override bool HasElementTypeImpl() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(string name, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder? binder, object? target, object?[]? args, System.Reflection.ParameterModifier[]? modifiers, System.Globalization.CultureInfo? culture, string[]? namedParameters) { throw null; }
         protected override bool IsArrayImpl() { throw null; }
         protected override bool IsByRefImpl() { throw null; }
@@ -201,15 +221,22 @@ internal GenericTypeParameterBuilder() { }
         public override System.Type UnderlyingSystemType { get { throw null; } }
         public override bool Equals(object? o) { throw null; }
         protected override System.Reflection.TypeAttributes GetAttributeFlagsImpl() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
         protected override System.Reflection.ConstructorInfo GetConstructorImpl(System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Reflection.CallingConventions callConvention, System.Type[] types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
         public override System.Reflection.ConstructorInfo[] GetConstructors(System.Reflection.BindingFlags bindingAttr) { throw null; }
         public override object[] GetCustomAttributes(bool inherit) { throw null; }
         public override object[] GetCustomAttributes(System.Type attributeType, bool inherit) { throw null; }
         public override System.Type GetElementType() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicEvents | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo GetEvent(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo[] GetEvents() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicEvents | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo[] GetEvents(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
         public override System.Reflection.FieldInfo GetField(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
         public override System.Reflection.FieldInfo[] GetFields(System.Reflection.BindingFlags bindingAttr) { throw null; }
         public override System.Type[] GetGenericArguments() { throw null; }
         public override System.Type GetGenericTypeDefinition() { throw null; }
@@ -217,15 +244,24 @@ internal GenericTypeParameterBuilder() { }
         public override System.Type GetInterface(string name, bool ignoreCase) { throw null; }
         public override System.Reflection.InterfaceMapping GetInterfaceMap(System.Type interfaceType) { throw null; }
         public override System.Type[] GetInterfaces() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override System.Reflection.MemberInfo[] GetMember(string name, System.Reflection.MemberTypes type, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override System.Reflection.MemberInfo[] GetMembers(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         protected override System.Reflection.MethodInfo GetMethodImpl(string name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Reflection.CallingConventions callConvention, System.Type[]? types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         public override System.Reflection.MethodInfo[] GetMethods(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicNestedTypes | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicNestedTypes)]
         public override System.Type GetNestedType(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicNestedTypes | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicNestedTypes)]
         public override System.Type[] GetNestedTypes(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         public override System.Reflection.PropertyInfo[] GetProperties(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         protected override System.Reflection.PropertyInfo GetPropertyImpl(string name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Type? returnType, System.Type[]? types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
         protected override bool HasElementTypeImpl() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override object InvokeMember(string name, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder? binder, object? target, object?[]? args, System.Reflection.ParameterModifier[]? modifiers, System.Globalization.CultureInfo? culture, string[]? namedParameters) { throw null; }
         protected override bool IsArrayImpl() { throw null; }
         public override bool IsAssignableFrom([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] System.Type? c) { throw null; }
@@ -324,22 +360,35 @@ public void CreateGlobalFunctions() { }
         public override object[] GetCustomAttributes(bool inherit) { throw null; }
         public override object[] GetCustomAttributes(System.Type attributeType, bool inherit) { throw null; }
         public override System.Collections.Generic.IList<System.Reflection.CustomAttributeData> GetCustomAttributesData() { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Fields might be removed")]
         public override System.Reflection.FieldInfo? GetField(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Fields might be removed")]
         public override System.Reflection.FieldInfo[] GetFields(System.Reflection.BindingFlags bindingFlags) { throw null; }
         public override int GetHashCode() { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Methods might be removed")]
         public override System.Reflection.MethodInfo[] GetMethods(System.Reflection.BindingFlags bindingFlags) { throw null; }
         public override void GetPEKind(out System.Reflection.PortableExecutableKinds peKind, out System.Reflection.ImageFileMachine machine) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types might be removed")]
         public override System.Type? GetType(string className) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types might be removed")]
         public override System.Type? GetType(string className, bool ignoreCase) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types might be removed")]
         public override System.Type? GetType(string className, bool throwOnError, bool ignoreCase) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types might be removed")]
         public override System.Type[] GetTypes() { throw null; }
         public override bool IsDefined(System.Type attributeType, bool inherit) { throw null; }
         public override bool IsResource() { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Trimming changes metadata tokens")]
         public override System.Reflection.FieldInfo? ResolveField(int metadataToken, System.Type[]? genericTypeArguments, System.Type[]? genericMethodArguments) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Trimming changes metadata tokens")]
         public override System.Reflection.MemberInfo? ResolveMember(int metadataToken, System.Type[]? genericTypeArguments, System.Type[]? genericMethodArguments) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Trimming changes metadata tokens")]
         public override System.Reflection.MethodBase? ResolveMethod(int metadataToken, System.Type[]? genericTypeArguments, System.Type[]? genericMethodArguments) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Trimming changes metadata tokens")]
         public override byte[] ResolveSignature(int metadataToken) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Trimming changes metadata tokens")]
         public override string ResolveString(int metadataToken) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Trimming changes metadata tokens")]
         public override System.Type ResolveType(int metadataToken, System.Type[]? genericTypeArguments, System.Type[]? genericMethodArguments) { throw null; }
         public void SetCustomAttribute(System.Reflection.ConstructorInfo con, byte[] binaryAttribute) { }
         public void SetCustomAttribute(System.Reflection.Emit.CustomAttributeBuilder customBuilder) { }
@@ -440,32 +489,48 @@ public void DefineMethodOverride(System.Reflection.MethodInfo methodInfoBody, Sy
         public System.Reflection.Emit.FieldBuilder DefineUninitializedData(string name, int size, System.Reflection.FieldAttributes attributes) { throw null; }
         protected override System.Reflection.TypeAttributes GetAttributeFlagsImpl() { throw null; }
         public static System.Reflection.ConstructorInfo GetConstructor(System.Type type, System.Reflection.ConstructorInfo constructor) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
         protected override System.Reflection.ConstructorInfo? GetConstructorImpl(System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Reflection.CallingConventions callConvention, System.Type[] types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
         public override System.Reflection.ConstructorInfo[] GetConstructors(System.Reflection.BindingFlags bindingAttr) { throw null; }
         public override object[] GetCustomAttributes(bool inherit) { throw null; }
         public override object[] GetCustomAttributes(System.Type attributeType, bool inherit) { throw null; }
         public override System.Type GetElementType() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicEvents | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo? GetEvent(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo[] GetEvents() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicEvents | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo[] GetEvents(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
         public override System.Reflection.FieldInfo? GetField(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
         public static System.Reflection.FieldInfo GetField(System.Type type, System.Reflection.FieldInfo field) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
         public override System.Reflection.FieldInfo[] GetFields(System.Reflection.BindingFlags bindingAttr) { throw null; }
         public override System.Type[] GetGenericArguments() { throw null; }
         public override System.Type GetGenericTypeDefinition() { throw null; }
         public override System.Type? GetInterface(string name, bool ignoreCase) { throw null; }
         public override System.Reflection.InterfaceMapping GetInterfaceMap(System.Type interfaceType) { throw null; }
         public override System.Type[] GetInterfaces() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override System.Reflection.MemberInfo[] GetMember(string name, System.Reflection.MemberTypes type, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override System.Reflection.MemberInfo[] GetMembers(System.Reflection.BindingFlags bindingAttr) { throw null; }
         public static System.Reflection.MethodInfo GetMethod(System.Type type, System.Reflection.MethodInfo method) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         protected override System.Reflection.MethodInfo? GetMethodImpl(string name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Reflection.CallingConventions callConvention, System.Type[]? types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         public override System.Reflection.MethodInfo[] GetMethods(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicNestedTypes | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicNestedTypes)]
         public override System.Type? GetNestedType(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicNestedTypes | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicNestedTypes)]
         public override System.Type[] GetNestedTypes(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         public override System.Reflection.PropertyInfo[] GetProperties(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         protected override System.Reflection.PropertyInfo GetPropertyImpl(string name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Type? returnType, System.Type[]? types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
         protected override bool HasElementTypeImpl() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(string name, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder? binder, object? target, object?[]? args, System.Reflection.ParameterModifier[]? modifiers, System.Globalization.CultureInfo? culture, string[]? namedParameters) { throw null; }
         protected override bool IsArrayImpl() { throw null; }
         public override bool IsAssignableFrom([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] System.Type? c) { throw null; }
diff --git a/src/libraries/System.Reflection.Extensions/Directory.Build.props b/src/libraries/System.Reflection.Extensions/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Reflection.Extensions/Directory.Build.props
+++ b/src/libraries/System.Reflection.Extensions/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Reflection.Extensions/src/System.Reflection.Extensions.csproj b/src/libraries/System.Reflection.Extensions/src/System.Reflection.Extensions.csproj
index 5c08b886e3e91b..94d0c640130480 100644
--- a/src/libraries/System.Reflection.Extensions/src/System.Reflection.Extensions.csproj
+++ b/src/libraries/System.Reflection.Extensions/src/System.Reflection.Extensions.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Reflection.Extensions</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Reflection.Metadata/Directory.Build.props b/src/libraries/System.Reflection.Metadata/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Reflection.Metadata/Directory.Build.props
+++ b/src/libraries/System.Reflection.Metadata/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Reflection.Metadata/ref/System.Reflection.Metadata.csproj b/src/libraries/System.Reflection.Metadata/ref/System.Reflection.Metadata.csproj
index 33546830d98fc0..d3f3c661e77fb0 100644
--- a/src/libraries/System.Reflection.Metadata/ref/System.Reflection.Metadata.csproj
+++ b/src/libraries/System.Reflection.Metadata/ref/System.Reflection.Metadata.csproj
@@ -2,8 +2,7 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <CLSCompliant>false</CLSCompliant>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.1;netstandard2.0</TargetFrameworks>
-    <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.1;netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
@@ -14,11 +13,11 @@
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
   </ItemGroup>
+  <!-- Include these transitive dependencies to overrule NuGet's ProjectReference over PackageReferene behavior. -->
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.1'">
-    <Reference Include="System.IO" />
-    <Reference Include="System.Reflection.Primitives" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Text.Encoding" />
+    <PackageReference Include="System.Runtime" Version="$(SystemRuntimeVersion)" />
+    <PackageReference Include="System.Collections" Version="$(SystemCollectionsVersion)" />
+    <PackageReference Include="System.Runtime.InteropServices" Version="$(SystemRuntimeInteropServicesVersion)" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\System.Collections.Immutable\ref\System.Collections.Immutable.csproj" />
diff --git a/src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj b/src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj
index 80692bdfc3a8a4..2417558b7857a6 100644
--- a/src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj
+++ b/src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj
@@ -3,8 +3,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DefaultLanguage>en-US</DefaultLanguage>
     <CLSCompliant>false</CLSCompliant>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.1;netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.1;netstandard2.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -249,9 +248,9 @@
     <Compile Include="System\Reflection\Throw.cs" />
     <Compile Include="System\Reflection\System.Reflection.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="..\..\System.Collections.Immutable\src\System.Collections.Immutable.csproj" />
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <Reference Include="System.Collections" />
+    <Reference Include="System.Collections.Immutable" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.IO" />
     <Reference Include="System.IO.Compression" />
@@ -266,12 +265,10 @@
     <Reference Include="System.Text.Encoding" />
     <Reference Include="System.Text.Encoding.Extensions" />
     <Reference Include="System.Threading" />
-    <Reference Include="System.IO.MemoryMappedFiles" Condition="'$(TargetFramework)' != 'netstandard1.1'" />
-    <Reference Include="System.Buffers" Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'" />
+    <Reference Include="System.IO.MemoryMappedFiles" />
+    <Reference Include="System.Buffers" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
+  <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.Immutable\src\System.Collections.Immutable.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/EnumerableExtensions.cs b/src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/EnumerableExtensions.cs
index aaec6063a4b9f5..99545a020291e3 100644
--- a/src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/EnumerableExtensions.cs
+++ b/src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/EnumerableExtensions.cs
@@ -13,8 +13,7 @@ namespace System.Reflection.Internal
     /// </summary>
     internal static class EnumerableExtensions
     {
-        [return: MaybeNull]
-        public static T FirstOrDefault<T>(this ImmutableArray<T> collection, Func<T, bool> predicate)
+        public static T? FirstOrDefault<T>(this ImmutableArray<T> collection, Func<T, bool> predicate)
         {
             foreach (var item in collection)
             {
@@ -24,7 +23,7 @@ public static T FirstOrDefault<T>(this ImmutableArray<T> collection, Func<T, boo
                 }
             }
 
-            return default!;
+            return default;
         }
 
         // used only in debugger display so we needn't get fancy with optimizations.
diff --git a/src/libraries/System.Reflection.Metadata/tests/Metadata/Decoding/CustomAttributeDecoderTests.cs b/src/libraries/System.Reflection.Metadata/tests/Metadata/Decoding/CustomAttributeDecoderTests.cs
index 9899c0995f7f49..6a14d358a08c9d 100644
--- a/src/libraries/System.Reflection.Metadata/tests/Metadata/Decoding/CustomAttributeDecoderTests.cs
+++ b/src/libraries/System.Reflection.Metadata/tests/Metadata/Decoding/CustomAttributeDecoderTests.cs
@@ -15,7 +15,7 @@ public class CustomAttributeDecoderTests
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework, "Type assembly name is different on .NET Framework.")]
         public void TestCustomAttributeDecoder()
         {
-            using (FileStream stream = File.OpenRead(typeof(HasAttributes).GetTypeInfo().Assembly.Location))
+            using (FileStream stream = File.OpenRead(AssemblyPathHelper.GetAssemblyLocation(typeof(HasAttributes).GetTypeInfo().Assembly)))
             using (var peReader = new PEReader(stream))
             {
                 MetadataReader reader = peReader.GetMetadataReader();
diff --git a/src/libraries/System.Reflection.Metadata/tests/Metadata/Decoding/SignatureDecoderTests.cs b/src/libraries/System.Reflection.Metadata/tests/Metadata/Decoding/SignatureDecoderTests.cs
index 9a83882ff9f1da..7669fbcc2ef312 100644
--- a/src/libraries/System.Reflection.Metadata/tests/Metadata/Decoding/SignatureDecoderTests.cs
+++ b/src/libraries/System.Reflection.Metadata/tests/Metadata/Decoding/SignatureDecoderTests.cs
@@ -83,7 +83,7 @@ public unsafe void DecodeInvalidMethodSpecificationSignature(byte[] testSignatur
         [Fact]
         public void DecodeVarArgsDefAndRef()
         {
-            using (FileStream stream = File.OpenRead(typeof(VarArgsToDecode).GetTypeInfo().Assembly.Location))
+            using (FileStream stream = File.OpenRead(AssemblyPathHelper.GetAssemblyLocation(typeof(VarArgsToDecode).GetTypeInfo().Assembly)))
             using (var peReader = new PEReader(stream))
             {
                 MetadataReader metadataReader = peReader.GetMetadataReader();
@@ -135,7 +135,7 @@ public static void VarArgsCaller()
         [Fact]
         public void SimpleSignatureProviderCoverage()
         {
-            using (FileStream stream = File.OpenRead(typeof(SignaturesToDecode<>).GetTypeInfo().Assembly.Location))
+            using (FileStream stream = File.OpenRead(AssemblyPathHelper.GetAssemblyLocation(typeof(SignaturesToDecode<>).GetTypeInfo().Assembly)))
             using (var peReader = new PEReader(stream))
             {
                 MetadataReader reader = peReader.GetMetadataReader();
@@ -246,7 +246,7 @@ public event EventHandler<EventArgs> Event { add { } remove { } }
         [Fact]
         public void PinnedAndUnpinnedLocals()
         {
-            using (FileStream stream = File.OpenRead(typeof(PinnedAndUnpinnedLocalsToDecode).GetTypeInfo().Assembly.Location))
+            using (FileStream stream = File.OpenRead(AssemblyPathHelper.GetAssemblyLocation(typeof(PinnedAndUnpinnedLocalsToDecode).GetTypeInfo().Assembly)))
             using (var peReader = new PEReader(stream))
             {
                 MetadataReader reader = peReader.GetMetadataReader();
@@ -285,7 +285,7 @@ public static unsafe int DoSomething()
         [Fact]
         public void WrongSignatureType()
         {
-            using (FileStream stream = File.OpenRead(typeof(VarArgsToDecode).GetTypeInfo().Assembly.Location))
+            using (FileStream stream = File.OpenRead(AssemblyPathHelper.GetAssemblyLocation(typeof(VarArgsToDecode).GetTypeInfo().Assembly)))
             using (var peReader = new PEReader(stream))
             {
                 MetadataReader reader = peReader.GetMetadataReader();
diff --git a/src/libraries/System.Reflection.Metadata/tests/PortableExecutable/PEBuilderTests.cs b/src/libraries/System.Reflection.Metadata/tests/PortableExecutable/PEBuilderTests.cs
index 23953c1c469691..dd7d036f31bd9a 100644
--- a/src/libraries/System.Reflection.Metadata/tests/PortableExecutable/PEBuilderTests.cs
+++ b/src/libraries/System.Reflection.Metadata/tests/PortableExecutable/PEBuilderTests.cs
@@ -134,6 +134,7 @@ public void BasicValidation(Machine machine)
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Security.Cryptography isn't supported on browser
         public void BasicValidationSigned()
         {
             using (var peStream = new MemoryStream())
@@ -654,6 +655,7 @@ private static IEnumerable<string> GetBlobRanges(BlobBuilder builder, IEnumerabl
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Security.Cryptography isn't supported on browser
         public void Checksum()
         {
             Assert.True(TestChecksumAndAuthenticodeSignature(new MemoryStream(Misc.Signed), Misc.KeyPair));
@@ -661,6 +663,7 @@ public void Checksum()
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Security.Cryptography isn't supported on browser
         public void ChecksumFXAssemblies()
         {
             var paths = new[]
diff --git a/src/libraries/System.Reflection.Metadata/tests/Resources/Interop/Interop.Mock01.cs b/src/libraries/System.Reflection.Metadata/tests/Resources/Interop/Interop.Mock01.cs
index 612ed4111311fa..0ad8ac99a04ec4 100644
--- a/src/libraries/System.Reflection.Metadata/tests/Resources/Interop/Interop.Mock01.cs
+++ b/src/libraries/System.Reflection.Metadata/tests/Resources/Interop/Interop.Mock01.cs
@@ -98,7 +98,6 @@ InteropEnum IFooReadOnlyProp {
     [TypeLibImportClass(typeof(object))]
     public interface IBar
     {
-        [AllowReversePInvokeCalls()]
         object DoSomething(params string[] ary);
         [ComRegisterFunction()]
         object Register([MarshalAs(UnmanagedType.IDispatch), Optional, DefaultParameterValue(null)] ref object o);
diff --git a/src/libraries/System.Reflection.Metadata/tests/System.Reflection.Metadata.Tests.csproj b/src/libraries/System.Reflection.Metadata/tests/System.Reflection.Metadata.Tests.csproj
index e3d82ffed0a331..ac19479d9a47ef 100644
--- a/src/libraries/System.Reflection.Metadata/tests/System.Reflection.Metadata.Tests.csproj
+++ b/src/libraries/System.Reflection.Metadata/tests/System.Reflection.Metadata.Tests.csproj
@@ -3,7 +3,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <ExternallyShipping>false</ExternallyShipping>
     <NoWarn>436</NoWarn> <!-- Type conflicts on "Interop" due to InternalsVisibleTo access -->
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Libraries.cs"
@@ -132,7 +132,14 @@
   </ItemGroup>
   <ItemGroup>
     <!-- Some internal types are needed, so we reference the implementation assembly, rather than the reference assembly. -->
-    <DefaultReferenceExclusions Include="System.Reflection.Metadata" />
-    <ReferenceFromRuntime Include="System.Reflection.Metadata" />
+    <ProjectReference Include="..\src\System.Reflection.Metadata.csproj" SkipUseReferenceAssembly="true" />
+  </ItemGroup>
+    <!-- For IncrementalHash -->
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.Security.Cryptography.Algorithms" Version="$(SystemSecurityCryptographyAlgorithmsVersion)" />
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
+    <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/ref/System.Reflection.MetadataLoadContext.csproj b/src/libraries/System.Reflection.MetadataLoadContext/ref/System.Reflection.MetadataLoadContext.csproj
index aceadd0d97dda0..c065d83b357a6e 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/ref/System.Reflection.MetadataLoadContext.csproj
+++ b/src/libraries/System.Reflection.MetadataLoadContext/ref/System.Reflection.MetadataLoadContext.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/src/System.Reflection.MetadataLoadContext.csproj b/src/libraries/System.Reflection.MetadataLoadContext/src/System.Reflection.MetadataLoadContext.csproj
index 006e205f072b6f..7cee550642984c 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/src/System.Reflection.MetadataLoadContext.csproj
+++ b/src/libraries/System.Reflection.MetadataLoadContext/src/System.Reflection.MetadataLoadContext.csproj
@@ -3,8 +3,7 @@
     <RootNamespace>System.Reflection</RootNamespace>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <!-- Only the netcoreapp version supports the new reflection apis (IsSZArray, etc.) -->
-    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -145,8 +144,10 @@
     <Compile Include="System\Reflection\TypeLoading\Types\RoType.GetInterface.cs" />
     <Compile Include="System\Reflection\TypeLoading\Types\RoType.TypeClassification.cs" />
     <Compile Include="System\Reflection\TypeLoading\Types\RoWrappedType.cs" />
+    <Compile Include="$(CommonPath)System\Obsoletions.cs" Link="Common\System\Obsoletions.cs" />
   </ItemGroup>
-  <ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or
+                        '$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
     <Reference Include="System.Collections.Immutable" />
@@ -160,9 +161,10 @@
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Threading" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard')) or
+                        $(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.Immutable\src\System.Collections.Immutable.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Reflection.Metadata\src\System.Reflection.Metadata.csproj" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/src/System/Reflection/TypeLoading/Assemblies/RoAssembly.cs b/src/libraries/System.Reflection.MetadataLoadContext/src/System/Reflection/TypeLoading/Assemblies/RoAssembly.cs
index b15e44645def21..ca133f247c7d47 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/src/System/Reflection/TypeLoading/Assemblies/RoAssembly.cs
+++ b/src/libraries/System.Reflection.MetadataLoadContext/src/System/Reflection/TypeLoading/Assemblies/RoAssembly.cs
@@ -41,7 +41,13 @@ protected RoAssembly(MetadataLoadContext loader, int assemblyFileCount)
 
         // Location and codebase
         public abstract override string Location { get; }
+#if NET50_OBSOLETIONS
+        [Obsolete(Obsoletions.CodeBaseMessage, DiagnosticId = Obsoletions.CodeBaseDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
         public sealed override string CodeBase => throw new NotSupportedException(SR.NotSupported_AssemblyCodeBase);
+#if NET50_OBSOLETIONS
+        [Obsolete(Obsoletions.CodeBaseMessage, DiagnosticId = Obsoletions.CodeBaseDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
         public sealed override string EscapedCodeBase => throw new NotSupportedException(SR.NotSupported_AssemblyCodeBase);
 
         // Custom Attributes
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/tests/System.Reflection.MetadataLoadContext.Tests.csproj b/src/libraries/System.Reflection.MetadataLoadContext/tests/System.Reflection.MetadataLoadContext.Tests.csproj
index be8b471a6eca95..1703956fc6c52c 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/tests/System.Reflection.MetadataLoadContext.Tests.csproj
+++ b/src/libraries/System.Reflection.MetadataLoadContext/tests/System.Reflection.MetadataLoadContext.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <!-- The GAC is obsolete, but there are unit tests still referencing it -->
     <NoWarn>$(NoWarn);SYSLIB0005</NoWarn>
   </PropertyGroup>
@@ -71,4 +71,12 @@
     <Compile Include="src\TestUtils\TestUtils.JittedRuntimes.cs" />
     <Compile Include="src\TestUtils\TypeWrapper.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Reflection.MetadataLoadContext.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
+    <WasmFilesToIncludeFromPublishDir Include="System.Private.CoreLib.dll" />
+    <WasmFilesToIncludeFromPublishDir Include="System.Reflection.MetadataLoadContext.Tests.dll" />
+    <WasmFilesToIncludeFromPublishDir Include="mscorlib.dll" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/CoreMetadataAssemblyResolver.cs b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/CoreMetadataAssemblyResolver.cs
index f5a81d7e453551..70c98068cdd29f 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/CoreMetadataAssemblyResolver.cs
+++ b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/CoreMetadataAssemblyResolver.cs
@@ -1,5 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
+using System;
 
 namespace System.Reflection.Tests
 {
@@ -22,7 +23,9 @@ public override Assembly Resolve(MetadataLoadContext context, AssemblyName assem
                 name.Equals("System.Runtime.InteropServices", StringComparison.OrdinalIgnoreCase))
             {
                 if (_coreAssembly == null)
+                {
                     _coreAssembly = context.LoadFromStream(TestUtils.CreateStreamForCoreAssembly());
+                }
 
                 return _coreAssembly;
             }
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/TestUtils.JittedRuntimes.cs b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/TestUtils.JittedRuntimes.cs
index aa98d6ee939087..cdbd7d4f6ec1fc 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/TestUtils.JittedRuntimes.cs
+++ b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/TestUtils.JittedRuntimes.cs
@@ -18,7 +18,7 @@ public static Type Project(this Type type)
 
             Assembly assembly = type.Assembly;
             string location = assembly.Location;
-            if (location == null || location == string.Empty)
+            if (PlatformDetection.IsNotBrowser && (location == null || location == string.Empty))
             {
                 throw new Exception("Could not find the IL for assembly " + type.Assembly + " on disk. The most likely cause " +
                     "is that you built the tests for a Jitted runtime but are running them on an AoT runtime.");
@@ -30,9 +30,11 @@ public static Type Project(this Type type)
                     // The core assembly we're using might not be the one powering the runtime. Make sure we project to the core assembly the MetataLoadContext
                     // is using.
                     if (a == typeof(object).Assembly)
-                        return TestMetadataLoadContext.LoadFromStream(CreateStreamForCoreAssembly());
+                    {
+                        TestMetadataLoadContext.LoadFromStream(CreateStreamForCoreAssembly());
+                    }
 
-                    return TestMetadataLoadContext.LoadFromAssemblyPath(a.Location);
+                    return TestMetadataLoadContext.LoadFromAssemblyPath(AssemblyPathHelper.GetAssemblyLocation(a));
                 });
 
             Type projectedType = s_typeDict.GetOrAdd(type, (t) => projectedAssembly.GetType(t.FullName, throwOnError: true, ignoreCase: false));
@@ -50,12 +52,15 @@ public static Stream CreateStreamForCoreAssembly()
         {
             // We need a core assembly in IL form. Since this version of this code is for Jitted platforms, the System.Private.Corelib
             // of the underlying runtime will do just fine.
-            string assumedLocationOfCoreLibrary = typeof(object).Assembly.Location;
-            if (assumedLocationOfCoreLibrary == null || assumedLocationOfCoreLibrary == string.Empty)
+            if (PlatformDetection.IsNotBrowser)
             {
-                throw new Exception("Could not find a core assembly to use for tests as 'typeof(object).Assembly.Location` returned " +
-                    "a null or empty value. The most likely cause is that you built the tests for a Jitted runtime but are running them " +
-                    "on an AoT runtime.");
+                string assumedLocationOfCoreLibrary = typeof(object).Assembly.Location;
+                if (assumedLocationOfCoreLibrary == null || assumedLocationOfCoreLibrary == string.Empty)
+                {
+                    throw new Exception("Could not find a core assembly to use for tests as 'typeof(object).Assembly.Location` returned " +
+                        "a null or empty value. The most likely cause is that you built the tests for a Jitted runtime but are running them " +
+                        "on an AoT runtime.");
+                }
             }
 
             return File.OpenRead(GetPathToCoreAssembly());
@@ -63,7 +68,7 @@ public static Stream CreateStreamForCoreAssembly()
 
         public static string GetPathToCoreAssembly()
         {
-            return typeof(object).Assembly.Location;
+            return AssemblyPathHelper.GetAssemblyLocation(typeof(object).Assembly);
         }
 
         public static string GetNameOfCoreAssembly()
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/TestUtils.cs b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/TestUtils.cs
index c0a4192c3fb213..ac71eddcbaa2bd 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/TestUtils.cs
+++ b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/TestUtils/TestUtils.cs
@@ -253,7 +253,12 @@ public static void Dump(this CustomAttributeTypedArgument cta, int indent = 0)
 
         private static readonly Lazy<bool> s_useRuntimeTypesForTests = new Lazy<bool>(() =>
         {
-            if (File.Exists(Path.Combine(Path.GetDirectoryName(typeof(TestUtils).Assembly.Location), "UseRuntimeTypes.txt")))
+            if (PlatformDetection.IsBrowser)
+                return false;
+
+            var loc = AssemblyPathHelper.GetAssemblyLocation(typeof(TestUtils).Assembly);
+
+            if (File.Exists(Path.Combine(loc, "UseRuntimeTypes.txt")))
             {
                 // Disable projection so that are Reflection tests run against the runtime types. This is used primarily to verify
                 // the *test* code for correctness.
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/MetadataLoadContext/PathAssemblyResolver.cs b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/MetadataLoadContext/PathAssemblyResolver.cs
index 7b827af4ff9c6a..464a925598097c 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/MetadataLoadContext/PathAssemblyResolver.cs
+++ b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/MetadataLoadContext/PathAssemblyResolver.cs
@@ -60,8 +60,7 @@ public static void PathAssemblyResolverBasicPathWithRunningAssemblies()
             string coreAssemblyPath = TestUtils.GetPathToCoreAssembly();
 
             // Obtain this test class
-            string thisAssemblyPath = typeof(MetadataLoadContextTests).Assembly.Location;
-
+            string thisAssemblyPath = AssemblyPathHelper.GetAssemblyLocation(typeof(MetadataLoadContextTests).Assembly);
             var resolver = new PathAssemblyResolver(new string[] { coreAssemblyPath, thisAssemblyPath });
             using (MetadataLoadContext lc = new MetadataLoadContext(resolver, TestUtils.GetNameOfCoreAssembly()))
             {
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/MetadataLoadContext/Scenarios.cs b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/MetadataLoadContext/Scenarios.cs
index b51651c442733e..86561ccad10397 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/MetadataLoadContext/Scenarios.cs
+++ b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/MetadataLoadContext/Scenarios.cs
@@ -16,7 +16,7 @@ public static void Scenario_GetAssemblyName()
             // Ensure you can do all this without resolving dependencies.
             using (MetadataLoadContext lc = new MetadataLoadContext(new EmptyCoreMetadataAssemblyResolver()))
             {
-                Assembly a = lc.LoadFromAssemblyPath(typeof(GenericClass1<>).Assembly.Location);
+                Assembly a = lc.LoadFromAssemblyPath(AssemblyPathHelper.GetAssemblyLocation(typeof(GenericClass1<>).Assembly));
                 AssemblyName assemblyName = a.GetName();
                 Console.WriteLine(assemblyName.FullName);
             }
@@ -28,7 +28,7 @@ public static void Scenario_EnumerateDependencies()
             // Ensure you can do all this without resolving dependencies.
             using (MetadataLoadContext lc = new MetadataLoadContext(new EmptyCoreMetadataAssemblyResolver()))
             {
-                Assembly a = lc.LoadFromAssemblyPath(typeof(GenericClass1<>).Assembly.Location);
+                Assembly a = lc.LoadFromAssemblyPath(AssemblyPathHelper.GetAssemblyLocation(typeof(GenericClass1<>).Assembly));
                 foreach (AssemblyName name in a.GetReferencedAssemblies())
                 {
                     Console.WriteLine(name.FullName);
@@ -44,8 +44,8 @@ public static void Scenario_FindACoreAssembly()
             {
                 Assembly[] candidates =
                 {
-                    lc.LoadFromAssemblyPath(typeof(GenericClass1<>).Assembly.Location),
-                    lc.LoadFromAssemblyPath(typeof(object).Assembly.Location),
+                    lc.LoadFromAssemblyPath(AssemblyPathHelper.GetAssemblyLocation(typeof(GenericClass1<>).Assembly)),
+                    lc.LoadFromAssemblyPath(AssemblyPathHelper.GetAssemblyLocation(typeof(object).Assembly)),
                 };
 
                 foreach (Assembly candidate in candidates)
@@ -68,7 +68,7 @@ public static void Scenario_EnumerateTypesAndMembers()
             // Ensure you can do all this without resolving dependencies.
             using (MetadataLoadContext lc = new MetadataLoadContext(new EmptyCoreMetadataAssemblyResolver()))
             {
-                Assembly a = lc.LoadFromAssemblyPath(typeof(GenericClass1<>).Assembly.Location);
+                Assembly a = lc.LoadFromAssemblyPath(AssemblyPathHelper.GetAssemblyLocation(typeof(GenericClass1<>).Assembly));
                 foreach (TypeInfo t in a.DefinedTypes)
                 {
                     Console.WriteLine(t.FullName);
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/RestrictedApis/RestrictedApis.cs b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/RestrictedApis/RestrictedApis.cs
index c8418c5c07159c..28aea79bee9b9e 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/RestrictedApis/RestrictedApis.cs
+++ b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/RestrictedApis/RestrictedApis.cs
@@ -12,10 +12,12 @@ public static void TestRestrictions()
         {
             using (MetadataLoadContext lc = new MetadataLoadContext(new EmptyCoreMetadataAssemblyResolver()))
             {
-                Assembly a = lc.LoadFromAssemblyPath(typeof(TopLevelType).Assembly.Location);
+                Assembly a = lc.LoadFromAssemblyPath(AssemblyPathHelper.GetAssemblyLocation(typeof(TopLevelType).Assembly));
 
+#pragma warning disable SYSLIB0012
                 Assert.Throws<NotSupportedException>(() => a.CodeBase);
                 Assert.Throws<NotSupportedException>(() => a.EscapedCodeBase);
+#pragma warning restore SYSLIB0012
                 Assert.Throws<NotSupportedException>(() => a.GetObjectData(null, default));
                 Assert.Throws<NotSupportedException>(() => a.GetSatelliteAssembly(null));
                 Assert.Throws<NotSupportedException>(() => a.GetSatelliteAssembly(null, null));
diff --git a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/Type/TypeTests.cs b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/Type/TypeTests.cs
index 60617d2b4b32f7..d14c4b849f0a40 100644
--- a/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/Type/TypeTests.cs
+++ b/src/libraries/System.Reflection.MetadataLoadContext/tests/src/Tests/Type/TypeTests.cs
@@ -523,7 +523,7 @@ public static void CoreGetTypeCacheCoverage2()
         {
             using (MetadataLoadContext lc = new MetadataLoadContext(new EmptyCoreMetadataAssemblyResolver()))
             {
-                Assembly a = lc.LoadFromAssemblyPath(typeof(SampleMetadata.NS0.SameNamedType).Assembly.Location);
+                Assembly a = lc.LoadFromAssemblyPath(AssemblyPathHelper.GetAssemblyLocation(typeof(SampleMetadata.NS0.SameNamedType).Assembly));
                 // Create big hash collisions in GetTypeCoreCache.
                 for (int i = 0; i < 16; i++)
                 {
@@ -542,7 +542,7 @@ public static void CoreGetTypeCacheCoverage3()
             using (MetadataLoadContext lc = new MetadataLoadContext(new EmptyCoreMetadataAssemblyResolver()))
             {
                 // Make sure the tricky corner case of a null/empty namespace is covered.
-                Assembly a = lc.LoadFromAssemblyPath(typeof(TopLevelType).Assembly.Location);
+                Assembly a = lc.LoadFromAssemblyPath(AssemblyPathHelper.GetAssemblyLocation(typeof(TopLevelType).Assembly));
                 Type t = a.GetType("TopLevelType", throwOnError: true, ignoreCase: false);
                 Assert.Null(t.Namespace);
                 Assert.Equal("TopLevelType", t.Name);
diff --git a/src/libraries/System.Reflection.Primitives/Directory.Build.props b/src/libraries/System.Reflection.Primitives/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Reflection.Primitives/Directory.Build.props
+++ b/src/libraries/System.Reflection.Primitives/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Reflection.Primitives/src/System.Reflection.Primitives.csproj b/src/libraries/System.Reflection.Primitives/src/System.Reflection.Primitives.csproj
index 5c3faa57e4aa77..dd3dc2940a54b1 100644
--- a/src/libraries/System.Reflection.Primitives/src/System.Reflection.Primitives.csproj
+++ b/src/libraries/System.Reflection.Primitives/src/System.Reflection.Primitives.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Reflection.Primitives</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Reflection.TypeExtensions/Directory.Build.props b/src/libraries/System.Reflection.TypeExtensions/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Reflection.TypeExtensions/Directory.Build.props
+++ b/src/libraries/System.Reflection.TypeExtensions/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Reflection.TypeExtensions/src/System.Reflection.TypeExtensions.csproj b/src/libraries/System.Reflection.TypeExtensions/src/System.Reflection.TypeExtensions.csproj
index 058466cbef4307..8668954a3efb49 100644
--- a/src/libraries/System.Reflection.TypeExtensions/src/System.Reflection.TypeExtensions.csproj
+++ b/src/libraries/System.Reflection.TypeExtensions/src/System.Reflection.TypeExtensions.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Reflection.TypeExtensions</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <Nullable>enable</Nullable>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Reflection/Directory.Build.props b/src/libraries/System.Reflection/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Reflection/Directory.Build.props
+++ b/src/libraries/System.Reflection/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Reflection/src/System.Reflection.csproj b/src/libraries/System.Reflection/src/System.Reflection.csproj
index dff84ed499636f..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Reflection/src/System.Reflection.csproj
+++ b/src/libraries/System.Reflection/src/System.Reflection.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Reflection</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Reflection/tests/AssemblyNameTests.cs b/src/libraries/System.Reflection/tests/AssemblyNameTests.cs
index d33e010aa02a3c..e64b887f5a3c08 100644
--- a/src/libraries/System.Reflection/tests/AssemblyNameTests.cs
+++ b/src/libraries/System.Reflection/tests/AssemblyNameTests.cs
@@ -240,7 +240,7 @@ public static void GetAssemblyName()
             }
 
             Assembly a = typeof(AssemblyNameTests).Assembly;
-            Assert.Equal(new AssemblyName(a.FullName).ToString(), AssemblyName.GetAssemblyName(a.Location).ToString());
+            Assert.Equal(new AssemblyName(a.FullName).ToString(), AssemblyName.GetAssemblyName(AssemblyPathHelper.GetAssemblyLocation(a)).ToString());
         }
 
         [Fact]
diff --git a/src/libraries/System.Reflection/tests/AssemblyTests.cs b/src/libraries/System.Reflection/tests/AssemblyTests.cs
index a244bbb4222484..e1b60d5eacc58b 100644
--- a/src/libraries/System.Reflection/tests/AssemblyTests.cs
+++ b/src/libraries/System.Reflection/tests/AssemblyTests.cs
@@ -142,6 +142,7 @@ public void ExportedTypes(Type type, bool expected)
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // entry assembly won't be xunit.console on browser
         public void GetEntryAssembly()
         {
             Assert.NotNull(Assembly.GetEntryAssembly());
@@ -157,7 +158,9 @@ public void GetFile()
             AssertExtensions.Throws<ArgumentException>(null, () => typeof(AssemblyTests).Assembly.GetFile(""));
             Assert.Null(typeof(AssemblyTests).Assembly.GetFile("NonExistentfile.dll"));
             Assert.NotNull(typeof(AssemblyTests).Assembly.GetFile("System.Reflection.Tests.dll"));
-            Assert.Equal(typeof(AssemblyTests).Assembly.GetFile("System.Reflection.Tests.dll").Name, typeof(AssemblyTests).Assembly.Location);
+
+            string name = AssemblyPathHelper.GetAssemblyLocation(typeof(AssemblyTests).Assembly);
+            Assert.Equal(typeof(AssemblyTests).Assembly.GetFile("System.Reflection.Tests.dll").Name, name);
         }
 
         [Fact]
@@ -165,7 +168,9 @@ public void GetFiles()
         {
             Assert.NotNull(typeof(AssemblyTests).Assembly.GetFiles());
             Assert.Equal(1, typeof(AssemblyTests).Assembly.GetFiles().Length);
-            Assert.Equal(typeof(AssemblyTests).Assembly.GetFiles()[0].Name, typeof(AssemblyTests).Assembly.Location);
+
+            string name = AssemblyPathHelper.GetAssemblyLocation(typeof(AssemblyTests).Assembly);
+            Assert.Equal(typeof(AssemblyTests).Assembly.GetFiles()[0].Name, name);
         }
 
         public static IEnumerable<object[]> GetHashCode_TestData()
@@ -384,7 +389,7 @@ public void LoadFrom_SamePath_ReturnsEqualAssemblies()
         [Fact]
         public void LoadFrom_SameIdentityAsAssemblyWithDifferentPath_ReturnsEqualAssemblies()
         {
-            Assembly assembly1 = Assembly.LoadFrom(typeof(AssemblyTests).Assembly.Location);
+            Assembly assembly1 = Assembly.LoadFrom(AssemblyPathHelper.GetAssemblyLocation(typeof(AssemblyTests).Assembly));
             Assert.Equal(assembly1, typeof(AssemblyTests).Assembly);
 
             Assembly assembly2 = Assembly.LoadFrom(LoadFromTestPath);
@@ -461,11 +466,13 @@ public void Location_ExecutingAssembly_IsNotNull()
             Assert.NotNull(Helpers.ExecutingAssembly.Location);
         }
 
+#pragma warning disable SYSLIB0012
         [Fact]
         public void CodeBase()
         {
             Assert.NotEmpty(Helpers.ExecutingAssembly.CodeBase);
         }
+#pragma warning restore SYSLIB0012
 
         [Fact]
         public void ImageRuntimeVersion()
@@ -654,7 +661,7 @@ public void AssemblyLoadFromStringNeg()
         public void AssemblyLoadFromBytes()
         {
             Assembly assembly = typeof(AssemblyTests).Assembly;
-            byte[] aBytes = System.IO.File.ReadAllBytes(assembly.Location);
+            byte[] aBytes = System.IO.File.ReadAllBytes(AssemblyPathHelper.GetAssemblyLocation(assembly));
 
             Assembly loadedAssembly = Assembly.Load(aBytes);
             Assert.NotNull(loadedAssembly);
@@ -672,8 +679,8 @@ public void AssemblyLoadFromBytesNeg()
         public void AssemblyLoadFromBytesWithSymbols()
         {
             Assembly assembly = typeof(AssemblyTests).Assembly;
-            byte[] aBytes = System.IO.File.ReadAllBytes(assembly.Location);
-            byte[] symbols = System.IO.File.ReadAllBytes((System.IO.Path.ChangeExtension(assembly.Location, ".pdb")));
+            byte[] aBytes = System.IO.File.ReadAllBytes(AssemblyPathHelper.GetAssemblyLocation(assembly));
+            byte[] symbols = System.IO.File.ReadAllBytes((System.IO.Path.ChangeExtension(AssemblyPathHelper.GetAssemblyLocation(assembly), ".pdb")));
 
             Assembly loadedAssembly = Assembly.Load(aBytes, symbols);
             Assert.NotNull(loadedAssembly);
@@ -691,7 +698,7 @@ public void AssemblyReflectionOnlyLoadFromString()
         public void AssemblyReflectionOnlyLoadFromBytes()
         {
             Assembly assembly = typeof(AssemblyTests).Assembly;
-            byte[] aBytes = System.IO.File.ReadAllBytes(assembly.Location);
+            byte[] aBytes = System.IO.File.ReadAllBytes(AssemblyPathHelper.GetAssemblyLocation(assembly));
             Assert.Throws<PlatformNotSupportedException>(() => Assembly.ReflectionOnlyLoad(aBytes));
         }
 
diff --git a/src/libraries/System.Reflection/tests/ConstructorInfoTests.cs b/src/libraries/System.Reflection/tests/ConstructorInfoTests.cs
index 38a5e460718551..a1042452810748 100644
--- a/src/libraries/System.Reflection/tests/ConstructorInfoTests.cs
+++ b/src/libraries/System.Reflection/tests/ConstructorInfoTests.cs
@@ -68,6 +68,27 @@ public void Invoke_StaticConstructor_NullObject_NullParameters()
             Assert.Null(obj);
         }
 
+        [Fact]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/40351", TestRuntimes.Mono)]
+        public void Invoke_StaticConstructorMultipleTimes()
+        {
+            ConstructorInfo[] constructors = GetConstructors(typeof(ClassWithStaticConstructorThatIsCalledMultipleTimesViaReflection));
+            Assert.Equal(1, constructors.Length);
+            // The first time the static cctor is called, it should run the cctor twice
+            // Once to initialize run the cctor as a cctor
+            // The second to run it as a method which is invoked.
+            Assert.Equal(0, ClassWithStaticConstructorThatIsCalledMultipleTimesViaReflection.VisibleStatics.s_cctorCallCount);
+            object obj = constructors[0].Invoke(null, new object[] { });
+            Assert.Null(obj);
+            Assert.Equal(1, ClassWithStaticConstructorThatIsCalledMultipleTimesViaReflection.VisibleStatics.s_cctorCallCount);
+
+            // Subsequent invocations of the static cctor should not run the cctor at all, as it has already executed
+            // and running multiple times opens up the possibility of modifying read only static data
+            obj = constructors[0].Invoke(null, new object[] { });
+            Assert.Null(obj);
+            Assert.Equal(1, ClassWithStaticConstructorThatIsCalledMultipleTimesViaReflection.VisibleStatics.s_cctorCallCount);
+        }
+
         [Fact]
         [ActiveIssue("https://github.com/mono/mono/issues/15024", TestRuntimes.Mono)]
         public void Invoke_StaticConstructor_ThrowsMemberAccessException()
@@ -236,6 +257,20 @@ public static class ClassWithStaticConstructor
         static ClassWithStaticConstructor() { }
     }
 
+    // Use this class only from the Invoke_StaticConstructorMultipleTimes method
+    public static class ClassWithStaticConstructorThatIsCalledMultipleTimesViaReflection
+    {
+        public static class VisibleStatics
+        {
+            public static int s_cctorCallCount;
+        }
+
+        static ClassWithStaticConstructorThatIsCalledMultipleTimesViaReflection()
+        {
+            VisibleStatics.s_cctorCallCount++;
+        }
+    }
+
     public struct StructWith1Constructor
     {
         public int x;
diff --git a/src/libraries/System.Reflection/tests/CoreCLR/AssemblyTests.cs b/src/libraries/System.Reflection/tests/CoreCLR/AssemblyTests.cs
index d75ba5a0ceb21c..544fc17414aa8d 100644
--- a/src/libraries/System.Reflection/tests/CoreCLR/AssemblyTests.cs
+++ b/src/libraries/System.Reflection/tests/CoreCLR/AssemblyTests.cs
@@ -11,6 +11,7 @@ namespace System.Reflection.Tests
     public class AssemblyTests
     {
         [Fact]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/39650", TestPlatforms.Browser)]
         public void CurrentLocation_HasLocaton()
         {
             string location = GetExecutingAssembly().Location;
diff --git a/src/libraries/System.Reflection/tests/System.Reflection.Tests.csproj b/src/libraries/System.Reflection/tests/System.Reflection.Tests.csproj
index f96a3551aa4b82..8db00f6e9dd484 100644
--- a/src/libraries/System.Reflection/tests/System.Reflection.Tests.csproj
+++ b/src/libraries/System.Reflection/tests/System.Reflection.Tests.csproj
@@ -64,4 +64,8 @@
     <ProjectReference Include="TestExe\System.Reflection.TestExe.csproj" />
     <ProjectReference Include="TestAssembly\TestAssembly.csproj" />
   </ItemGroup>
+    <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
+    <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />
+    <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).pdb" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Resources.Extensions/ref/System.Resources.Extensions.csproj b/src/libraries/System.Resources.Extensions/ref/System.Resources.Extensions.csproj
index 7b32ba82d118b4..2be35155d6da9a 100644
--- a/src/libraries/System.Resources.Extensions/ref/System.Resources.Extensions.csproj
+++ b/src/libraries/System.Resources.Extensions/ref/System.Resources.Extensions.csproj
@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
-  </PropertyGroup>
-  <PropertyGroup>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Resources.Extensions.cs" />
diff --git a/src/libraries/System.Resources.Extensions/src/System.Resources.Extensions.csproj b/src/libraries/System.Resources.Extensions/src/System.Resources.Extensions.csproj
index 00a7a46104f030..d4d12186c5618a 100644
--- a/src/libraries/System.Resources.Extensions/src/System.Resources.Extensions.csproj
+++ b/src/libraries/System.Resources.Extensions/src/System.Resources.Extensions.csproj
@@ -1,13 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <DefineConstants>$(DefineConstants);RESOURCES_EXTENSIONS</DefineConstants>
     <Nullable>annotations</Nullable>
   </PropertyGroup>
-  <PropertyGroup>
-  </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonPath)System\Resources\ResourceWriter.cs"
              Link="System\Resources\Extensions\ResourceWriter.cs" />
@@ -31,11 +28,7 @@
              Link="System\Numerics\Hashing\HashHelpers.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.Memory" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 
   <PropertyGroup>
diff --git a/src/libraries/System.Resources.Extensions/tests/System.Resources.Extensions.Tests.csproj b/src/libraries/System.Resources.Extensions/tests/System.Resources.Extensions.Tests.csproj
index 8bed771d651251..b48848c7a4545c 100644
--- a/src/libraries/System.Resources.Extensions/tests/System.Resources.Extensions.Tests.csproj
+++ b/src/libraries/System.Resources.Extensions/tests/System.Resources.Extensions.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;net461</TargetFrameworks>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
   </PropertyGroup>
   <ItemGroup>
@@ -16,7 +16,16 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="System.Drawing.Common.TestData" Version="$(SystemDrawingCommonTestDataVersion)" />    
+    <ProjectReference Include="..\src\System.Resources.Extensions.csproj" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Drawing.Common\src\System.Drawing.Common.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Windows.Extensions\src\System.Windows.Extensions.csproj" Condition="'$(TargetsWindows)' == 'true'" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" />
+  </ItemGroup>
+
   <!-- use the following target to regenerate the test resources file
        This is done from a test application and checked in so that we don't run
        product code during the build -->
diff --git a/src/libraries/System.Resources.Extensions/tests/TestData.cs b/src/libraries/System.Resources.Extensions/tests/TestData.cs
index a422862db46e2e..afef1125985eb5 100644
--- a/src/libraries/System.Resources.Extensions/tests/TestData.cs
+++ b/src/libraries/System.Resources.Extensions/tests/TestData.cs
@@ -303,6 +303,10 @@ public override void BindToName(Type serializedType, out string assemblyName, ou
                 // workaround for https://github.com/dotnet/runtime/issues/31289
                 assemblyQualifiedTypeName = assemblyQualifiedTypeName.Replace(s_coreAssemblyName, s_mscorlibAssemblyName);
 
+                // The logic below is intentionally incorrect. Generic type names like System.Collections.Generic.List`1[[System.String, ...]]
+                // will be split on the first comma, causing unbalanced [[ and ]] in the resulting substrings. This is for compatibility
+                // with the existing incorrect logic in Full Framework.
+
                 int pos = assemblyQualifiedTypeName.IndexOf(',');
                 if (pos > 0 && pos < assemblyQualifiedTypeName.Length - 1)
                 {
diff --git a/src/libraries/System.Resources.Extensions/tests/TestData.resources b/src/libraries/System.Resources.Extensions/tests/TestData.resources
index b2f4b4cd192888..b6006779769ebd 100644
Binary files a/src/libraries/System.Resources.Extensions/tests/TestData.resources and b/src/libraries/System.Resources.Extensions/tests/TestData.resources differ
diff --git a/src/libraries/System.Resources.Reader/Directory.Build.props b/src/libraries/System.Resources.Reader/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Resources.Reader/Directory.Build.props
+++ b/src/libraries/System.Resources.Reader/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Resources.Reader/src/System.Resources.Reader.csproj b/src/libraries/System.Resources.Reader/src/System.Resources.Reader.csproj
index 041d99ec9bd1a5..81ff3cda55d884 100644
--- a/src/libraries/System.Resources.Reader/src/System.Resources.Reader.csproj
+++ b/src/libraries/System.Resources.Reader/src/System.Resources.Reader.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Resources.Reader</AssemblyName>
     <RootNamespace>System.Resources</RootNamespace>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Resources.ResourceManager/Directory.Build.props b/src/libraries/System.Resources.ResourceManager/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Resources.ResourceManager/Directory.Build.props
+++ b/src/libraries/System.Resources.ResourceManager/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Resources.ResourceManager/src/System.Resources.ResourceManager.csproj b/src/libraries/System.Resources.ResourceManager/src/System.Resources.ResourceManager.csproj
index 61a965e9a83b83..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Resources.ResourceManager/src/System.Resources.ResourceManager.csproj
+++ b/src/libraries/System.Resources.ResourceManager/src/System.Resources.ResourceManager.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Resources.ResourceManager</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Resources.ResourceManager/tests/System.Resources.ResourceManager.Tests.csproj b/src/libraries/System.Resources.ResourceManager/tests/System.Resources.ResourceManager.Tests.csproj
index 90486ca2aea7ed..e049d6d494caf3 100644
--- a/src/libraries/System.Resources.ResourceManager/tests/System.Resources.ResourceManager.Tests.csproj
+++ b/src/libraries/System.Resources.ResourceManager/tests/System.Resources.ResourceManager.Tests.csproj
@@ -4,7 +4,7 @@
     <BinPlaceSatelliteAssemblies>true</BinPlaceSatelliteAssemblies>
     <TestRuntime>true</TestRuntime>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="MissingManifestResourceExceptionTests.cs" />
@@ -56,6 +56,9 @@
           CopyToOutputDirectory="PreserveNewest"
           Visible="false" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Drawing.Common\src\System.Drawing.Common.csproj" />
+  </ItemGroup>
   <!--
     MSBuild on .NET Core doesn't support non-string resources. See https://github.com/Microsoft/msbuild/issues/2221
     Workaround this for now by invoking the desktop resgen.exe on Windows manually to regenerate the resource files.
diff --git a/src/libraries/System.Resources.Writer/Directory.Build.props b/src/libraries/System.Resources.Writer/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Resources.Writer/Directory.Build.props
+++ b/src/libraries/System.Resources.Writer/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Resources.Writer/ref/System.Resources.Writer.cs b/src/libraries/System.Resources.Writer/ref/System.Resources.Writer.cs
index 9c8653862b1e40..f1cb4bcfdc3c85 100644
--- a/src/libraries/System.Resources.Writer/ref/System.Resources.Writer.cs
+++ b/src/libraries/System.Resources.Writer/ref/System.Resources.Writer.cs
@@ -21,7 +21,7 @@ public ResourceWriter(string fileName) { }
         public System.Func<System.Type, string>? TypeNameConverter { get { throw null; } set { } }
         public void AddResource(string name, byte[]? value) { }
         public void AddResource(string name, System.IO.Stream? value) { }
-        public void AddResource(string name, System.IO.Stream? value, bool closeAfterWrite) { }
+        public void AddResource(string name, System.IO.Stream? value, bool closeAfterWrite = false) { }
         public void AddResource(string name, object? value) { }
         public void AddResource(string name, string? value) { }
         public void AddResourceData(string name, string typeName, byte[] serializedData) { }
diff --git a/src/libraries/System.Resources.Writer/src/System.Resources.Writer.csproj b/src/libraries/System.Resources.Writer/src/System.Resources.Writer.csproj
index 0fa1c8767e11cf..b910ab24e06a6b 100644
--- a/src/libraries/System.Resources.Writer/src/System.Resources.Writer.csproj
+++ b/src/libraries/System.Resources.Writer/src/System.Resources.Writer.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <AssemblyName>System.Resources.Writer</AssemblyName>
     <RootNamespace>System.Resources</RootNamespace>
     <Nullable>enable</Nullable>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Runtime.Caching/src/System.Runtime.Caching.csproj b/src/libraries/System.Runtime.Caching/src/System.Runtime.Caching.csproj
index ed97af3ad85f82..6a6d9a6a5b3c98 100644
--- a/src/libraries/System.Runtime.Caching/src/System.Runtime.Caching.csproj
+++ b/src/libraries/System.Runtime.Caching/src/System.Runtime.Caching.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime.Caching</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>netstandard2.0;netstandard2.0-Windows_NT;_$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.0-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Runtime\Caching\_shims.cs" />
@@ -63,6 +62,6 @@
     <Compile Include="System\Runtime\Caching\PhysicalMemoryMonitor.Unix.cs" />
   </ItemGroup>
   <ItemGroup>
-    <Reference Include="System.Configuration.ConfigurationManager" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Configuration.ConfigurationManager\src\System.Configuration.ConfigurationManager.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Caching/tests/System.Runtime.Caching.Tests.csproj b/src/libraries/System.Runtime.Caching/tests/System.Runtime.Caching.Tests.csproj
index 8259713ac20600..84c491d6bfbe23 100644
--- a/src/libraries/System.Runtime.Caching/tests/System.Runtime.Caching.Tests.csproj
+++ b/src/libraries/System.Runtime.Caching/tests/System.Runtime.Caching.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net48-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="AdditionalCacheTests\AdditionalCacheTests.cs" />
@@ -12,4 +12,10 @@
     <Compile Include="System.Runtime.Caching\ObjectCacheTest.cs" />
     <Compile Include="System.Runtime.Caching\MemoryCacheTest.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="..\src\System.Runtime.Caching.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net48'))">
+    <Reference Include="System.Runtime.Caching" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/Directory.Build.props b/src/libraries/System.Runtime.CompilerServices.Unsafe/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/Directory.Build.props
+++ b/src/libraries/System.Runtime.CompilerServices.Unsafe/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/ref/System.Runtime.CompilerServices.Unsafe.cs b/src/libraries/System.Runtime.CompilerServices.Unsafe/ref/System.Runtime.CompilerServices.Unsafe.cs
index ae977a0cdc3319..f4958745ee0b15 100644
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/ref/System.Runtime.CompilerServices.Unsafe.cs
+++ b/src/libraries/System.Runtime.CompilerServices.Unsafe/ref/System.Runtime.CompilerServices.Unsafe.cs
@@ -9,44 +9,45 @@ namespace System.Runtime.CompilerServices
     public static partial class Unsafe
     {
         public static ref T AddByteOffset<T>(ref T source, System.IntPtr byteOffset) { throw null; }
-        public static unsafe void* Add<T>(void* source, int elementOffset) { throw null; }
+        public unsafe static void* Add<T>(void* source, int elementOffset) { throw null; }
         public static ref T Add<T>(ref T source, int elementOffset) { throw null; }
         public static ref T Add<T>(ref T source, System.IntPtr elementOffset) { throw null; }
         public static bool AreSame<T>(ref T left, ref T right) { throw null; }
-        public static unsafe void* AsPointer<T>(ref T value) { throw null; }
-        public static unsafe ref T AsRef<T>(void* source) { throw null; }
+        public unsafe static void* AsPointer<T>(ref T value) { throw null; }
+        public unsafe static ref T AsRef<T>(void* source) { throw null; }
         public static ref T AsRef<T>(in T source) { throw null; }
 #if NETSTANDARD2_1
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
         [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNull("o")]
 #endif
-        public static T As<T>(object? o) where T : class? { throw null; }
+        public static T? As<T>(object? o) where T : class? { throw null; }
         public static ref TTo As<TFrom, TTo>(ref TFrom source) { throw null; }
         public static System.IntPtr ByteOffset<T>(ref T origin, ref T target) { throw null; }
         public static void CopyBlock(ref byte destination, ref byte source, uint byteCount) { }
-        public static unsafe void CopyBlock(void* destination, void* source, uint byteCount) { }
+        public unsafe static void CopyBlock(void* destination, void* source, uint byteCount) { }
         public static void CopyBlockUnaligned(ref byte destination, ref byte source, uint byteCount) { }
-        public static unsafe void CopyBlockUnaligned(void* destination, void* source, uint byteCount) { }
-        public static unsafe void Copy<T>(void* destination, ref T source) { }
-        public static unsafe void Copy<T>(ref T destination, void* source) { }
+        public unsafe static void CopyBlockUnaligned(void* destination, void* source, uint byteCount) { }
+        public unsafe static void Copy<T>(void* destination, ref T source) { }
+        public unsafe static void Copy<T>(ref T destination, void* source) { }
         public static void InitBlock(ref byte startAddress, byte value, uint byteCount) { }
-        public static unsafe void InitBlock(void* startAddress, byte value, uint byteCount) { }
+        public unsafe static void InitBlock(void* startAddress, byte value, uint byteCount) { }
         public static void InitBlockUnaligned(ref byte startAddress, byte value, uint byteCount) { }
-        public static unsafe void InitBlockUnaligned(void* startAddress, byte value, uint byteCount) { }
+        public unsafe static void InitBlockUnaligned(void* startAddress, byte value, uint byteCount) { }
         public static bool IsAddressGreaterThan<T>(ref T left, ref T right) { throw null; }
         public static bool IsAddressLessThan<T>(ref T left, ref T right) { throw null; }
+        public static bool IsNullRef<T>(ref T source) { throw null; }
+        public static ref T NullRef<T>() { throw null; }
         public static T ReadUnaligned<T>(ref byte source) { throw null; }
-        public static unsafe T ReadUnaligned<T>(void* source) { throw null; }
-        public static unsafe T Read<T>(void* source) { throw null; }
+        public unsafe static T ReadUnaligned<T>(void* source) { throw null; }
+        public unsafe static T Read<T>(void* source) { throw null; }
         public static void SkipInit<T>(out T value) { throw null; }
         public static int SizeOf<T>() { throw null; }
         public static ref T SubtractByteOffset<T>(ref T source, System.IntPtr byteOffset) { throw null; }
-        public static unsafe void* Subtract<T>(void* source, int elementOffset) { throw null; }
+        public unsafe static void* Subtract<T>(void* source, int elementOffset) { throw null; }
         public static ref T Subtract<T>(ref T source, int elementOffset) { throw null; }
         public static ref T Subtract<T>(ref T source, System.IntPtr elementOffset) { throw null; }
         public static ref T Unbox<T>(object box) where T : struct { throw null; }
         public static void WriteUnaligned<T>(ref byte destination, T value) { }
-        public static unsafe void WriteUnaligned<T>(void* destination, T value) { }
-        public static unsafe void Write<T>(void* destination, T value) { }
+        public unsafe static void WriteUnaligned<T>(void* destination, T value) { }
+        public unsafe static void Write<T>(void* destination, T value) { }
     }
 }
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/ref/System.Runtime.CompilerServices.Unsafe.csproj b/src/libraries/System.Runtime.CompilerServices.Unsafe/ref/System.Runtime.CompilerServices.Unsafe.csproj
index a0fa82e4ab51e7..ebe1f4af9854a1 100644
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/ref/System.Runtime.CompilerServices.Unsafe.csproj
+++ b/src/libraries/System.Runtime.CompilerServices.Unsafe/ref/System.Runtime.CompilerServices.Unsafe.csproj
@@ -3,14 +3,10 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <CLSCompliant>false</CLSCompliant>
     <Nullable>enable</Nullable>
-    <TargetFrameworks>netstandard2.0;netstandard1.0;netstandard2.1;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;netstandard1.0;netstandard2.1;net45;net461</TargetFrameworks>
+    <ExcludeFromPackage Condition="'$(TargetFramework)' == 'net45'">true</ExcludeFromPackage>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Runtime.CompilerServices.Unsafe.cs" />
-    <Reference Include="System.Runtime" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.il b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.il
index 8740fafec41a11..fe3df674c11438 100644
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.il
+++ b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.il
@@ -1,7 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#include "coreassembly.h"
+#include "version.h"
 
 .assembly System.Runtime.CompilerServices.Unsafe
 {
@@ -40,7 +40,7 @@
     01 00 00 00 00
   ) // false
   .hash algorithm 0x00008004
-  .ver 5:0:0:0
+  .ver ASSEMBLY_VERSION
 }
 .module System.Runtime.CompilerServices.Unsafe.dll
 // MVID: {1E97D84A-565B-49C5-B60A-F31A1A4ACE13}
@@ -458,6 +458,26 @@
         ret
   } // end of method Unsafe::IsAddressLessThan
 
+  .method public hidebysig static bool IsNullRef<T>(!!T& source) cil managed aggressiveinlining
+  {
+        .custom instance void System.Runtime.Versioning.NonVersionableAttribute::.ctor() = ( 01 00 00 00 )
+        .maxstack 2
+        ldarg.0
+        ldc.i4.0
+        conv.u
+        ceq
+        ret
+  } // end of method Unsafe::IsNullRef
+
+  .method public hidebysig static !!T& NullRef<T>() cil managed aggressiveinlining
+  {
+        .custom instance void System.Runtime.Versioning.NonVersionableAttribute::.ctor() = ( 01 00 00 00 )
+        .maxstack 1
+        ldc.i4.0
+        conv.u
+        ret
+  } // end of method Unsafe::NullRef
+
 } // end of class System.Runtime.CompilerServices.Unsafe
 
 .class private auto ansi sealed beforefieldinit System.Runtime.Versioning.NonVersionableAttribute
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.ilproj b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.ilproj
index 2f53801cd40ffe..de3e21defc6ca0 100644
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.ilproj
+++ b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.ilproj
@@ -5,19 +5,80 @@
     <DebugOptimization Condition="'$(Configuration)' == 'Release'">OPT</DebugOptimization>
   </PropertyGroup>
   <PropertyGroup>
+    <CoreCompileDependsOn>$(CoreCompileDependsOn);GenerateVersionFile</CoreCompileDependsOn>
     <DocumentationFile>$(MSBuildThisFileDirectory)System.Runtime.CompilerServices.Unsafe.xml</DocumentationFile>
     <ProjectGuid>{04BA3E3C-6979-4792-B19E-C797AD607F42}</ProjectGuid>
-    <IncludePath>include\$(TargetFramework)</IncludePath>
-    <IncludePath Condition="$(TargetFramework.StartsWith('net4'))">include\netfx</IncludePath>
-    <IlasmFlags>$(IlasmFlags) -INCLUDE=$(IncludePath) -DEBUG=$(DebugOptimization)</IlasmFlags>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp2.0;netstandard1.0;net45;$(NetFrameworkCurrent)</TargetFrameworks>
+    <ExtraMacros Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or '$(TargetFramework)' == 'netcoreapp2.0'">#define netcoreapp</ExtraMacros>
+    <IlasmFlags>$(IlasmFlags) -DEBUG=$(DebugOptimization)</IlasmFlags>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp2.0;netstandard1.0;net45</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <CoreAssembly>System.Runtime</CoreAssembly>
+    <CoreAssembly Condition="'$(TargetFramework)' == 'netstandard2.0'">netstandard</CoreAssembly>
+  </PropertyGroup>
+  <PropertyGroup Condition="$(TargetFramework.StartsWith('net4'))">
+    <CoreAssembly>mscorlib</CoreAssembly>
+    <ExtraMacros>#define net45</ExtraMacros>
   </PropertyGroup>
-
   <ItemGroup>
-    <Reference Include="System.Runtime" />
     <Compile Include="System.Runtime.CompilerServices.Unsafe.il" />
-    <ILResourceReference Include="$(Refpath)\$(TargetFileName)" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or
+                        '$(TargetFramework)' == 'netcoreapp2.0'">
+    <Reference Include="System.Runtime" />
+  </ItemGroup>
+
+  <Target Name="GenerateVersionFile"
+          DependsOnTargets="ResolveReferences"
+          Inputs="$(MSBuildAllProjects)"
+          Outputs="'$(VersionFilePath)">
+   <PropertyGroup>
+      <IncludePath>$([MSBuild]::NormalizeDirectory('$(IntermediateOutputPath)', 'version'))</IncludePath>
+      <IlasmFlags>$(IlasmFlags) -INCLUDE=$(IncludePath)</IlasmFlags>
+      <VersionFilePath Condition="'$(VersionFilePath)' == ''">$([MSBuild]::NormalizePath('$(IncludePath)', 'version.h'))</VersionFilePath>
+      <_AssemblyVersion>$(AssemblyVersion.Replace('.', ':'))</_AssemblyVersion>
+      <_coreAssemblyName Condition="'%(ReferencePath.FileName)' == '$(CoreAssembly)'">%(ReferencePath.FusionName)</_coreAssemblyName>
+      <_assemblyNamePattern><![CDATA[[^,]+, Version=(?<v1>[0-9]+)\.(?<v2>[0-9]+)\.(?<v3>[0-9]+)\.(?<v4>[0-9]+), .*PublicKeyToken=(?<p1>[0-9a-f]{2})(?<p2>[0-9a-f]{2})(?<p3>[0-9a-f]{2})(?<p4>[0-9a-f]{2})(?<p5>[0-9a-f]{2})(?<p6>[0-9a-f]{2})(?<p7>[0-9a-f]{2})(?<p8>[0-9a-f]{2})]]></_assemblyNamePattern>
+      <_coreAssemblyVersion>$([System.Text.RegularExpressions.Regex]::Replace(
+        $(_coreAssemblyName),
+        $(_assemblyNamePattern),
+        '${v1}:${v2}:${v3}:${v4}'))</_coreAssemblyVersion>
+      <_coreAssemblyPublicKeyToken>$([System.Text.RegularExpressions.Regex]::Replace(
+        $(_coreAssemblyName),
+        $(_assemblyNamePattern),
+        '${p1} ${p2} ${p3} ${p4} ${p5} ${p6} ${p7} ${p8}').ToUpperInvariant())</_coreAssemblyPublicKeyToken>
+      <_VersionFileContents>
+<![CDATA[
+#define CORE_ASSEMBLY "$(CoreAssembly)"
+#define ASSEMBLY_VERSION "$(_AssemblyVersion)"
+#define CORE_ASSEMBLY_VERSION "$(_CoreAssemblyVersion)"
+$(ExtraMacros)
+// Metadata version: v4.0.30319
+.assembly extern CORE_ASSEMBLY
+{
+  .publickeytoken = ($(_coreAssemblyPublicKeyToken) )
+  .ver CORE_ASSEMBLY_VERSION
+}
+ ]]>      
+      </_VersionFileContents>
+    </PropertyGroup>
+
+    <WriteLinesToFile
+      File="$(VersionFilePath)"
+      Lines="$(_VersionFileContents)"
+      Overwrite="true"
+      WriteOnlyWhenDifferent="true" />
+
+    <ItemGroup>
+      <FileWrites Include="$(VersionFilePath)" />
+    </ItemGroup>
+  </Target>
+
+  <!-- Decompile the ILResourceReference to get native resources. -->
+  <Target Name="SetILResourceReference"
+          BeforeTargets="DisassembleIlasmResourceFile"
+          Condition="'@(ResolvedMatchingContract)' != ''">
+    <ItemGroup>
+      <ILResourceReference Include="@(ResolvedMatchingContract)" />
+    </ItemGroup>
+  </Target>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.xml b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.xml
index 1aef90cb9d2ed8..1979a5cb970523 100644
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.xml
+++ b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.xml
@@ -233,6 +233,18 @@
             or the objects being referenced must both be pinned; or both references must represent unmanaged pointers; otherwise the result is undefined.
             </remarks>
         </member>
+        <member name="M:System.Runtime.CompilerServices.Unsafe.IsNullRef``1(``0@)">
+          <summary>
+            Returns if a given reference to a value of type <typeparamref name="T"/> is a null reference.
+          </summary>
+          <param name="source">The reference to check.</param>
+          <remarks>This check is conceptually similar to "(void*)(&amp;source) == nullptr".</remarks>
+        </member>
+        <member name="M:System.Runtime.CompilerServices.Unsafe.NullRef``1">
+          <summary>
+            Returns a reference to a value of type <typeparamref name="T"/> that is a null reference.
+          </summary>
+        </member>
         <member name="M:System.Runtime.CompilerServices.Unsafe.CopyBlock(System.Void*,System.Void*,System.UInt32)">
             <summary>
             Copies bytes from the source address to the destination address.
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/net5.0/coreassembly.h b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/net5.0/coreassembly.h
deleted file mode 100644
index 0e501c3bb5b10a..00000000000000
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/net5.0/coreassembly.h
+++ /dev/null
@@ -1,9 +0,0 @@
-#define CORE_ASSEMBLY "System.Runtime"
-#define netcoreapp
-
-// Metadata version: v4.0.30319
-.assembly extern CORE_ASSEMBLY
-{
-  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )                         // .?_....:
-  .ver 5:0:0:0
-}
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netcoreapp2.0/coreassembly.h b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netcoreapp2.0/coreassembly.h
deleted file mode 100644
index f346bf929b30e9..00000000000000
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netcoreapp2.0/coreassembly.h
+++ /dev/null
@@ -1,9 +0,0 @@
-#define CORE_ASSEMBLY "System.Runtime"
-#define netcoreapp
-
-// Metadata version: v4.0.30319
-.assembly extern CORE_ASSEMBLY
-{
-  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )                         // .?_....:
-  .ver 4:0:0:0
-}
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netfx/coreassembly.h b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netfx/coreassembly.h
deleted file mode 100644
index c7d706b5190c40..00000000000000
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netfx/coreassembly.h
+++ /dev/null
@@ -1,9 +0,0 @@
-#define CORE_ASSEMBLY "mscorlib"
-#define net45
-
-// Metadata version: v4.0.30319
-.assembly extern CORE_ASSEMBLY
-{
-  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
-  .ver 4:0:0:0
-}
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netstandard1.0/coreassembly.h b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netstandard1.0/coreassembly.h
deleted file mode 100644
index cee9c905b7ef8c..00000000000000
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netstandard1.0/coreassembly.h
+++ /dev/null
@@ -1,8 +0,0 @@
-#define CORE_ASSEMBLY "System.Runtime"
-
-// Metadata version: v4.0.30319
-.assembly extern CORE_ASSEMBLY
-{
-  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )                         // .?_....:
-  .ver 4:0:0:0
-}
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netstandard2.0/coreassembly.h b/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netstandard2.0/coreassembly.h
deleted file mode 100644
index efcc029381d196..00000000000000
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/src/include/netstandard2.0/coreassembly.h
+++ /dev/null
@@ -1,20 +0,0 @@
-#define CORE_ASSEMBLY "System.Runtime"
-
-// Metadata version: v4.0.30319
-.assembly extern CORE_ASSEMBLY
-{
-  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )                         // .?_....:
-  .ver 4:0:0:0
-}
-
-/*  ILasm currently complains when seeing a [netstandard]System.Object
-    temporarily reference System.Runtime until we can get a fix in ilasm.
-#define CORE_ASSEMBLY "netstandard"
-
-// Metadata version: v4.0.30319
-.assembly extern CORE_ASSEMBLY
-{
-  .publickeytoken = (CC 7B 13 FF CD 2D DD 51 )                         // .{...-.Q
-  .ver 2:0:0:0
-}
-*/
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/tests/System.Runtime.CompilerServices.Unsafe.Tests.csproj b/src/libraries/System.Runtime.CompilerServices.Unsafe/tests/System.Runtime.CompilerServices.Unsafe.Tests.csproj
index 4fc905dec87c70..8852455f78298d 100644
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/tests/System.Runtime.CompilerServices.Unsafe.Tests.csproj
+++ b/src/libraries/System.Runtime.CompilerServices.Unsafe/tests/System.Runtime.CompilerServices.Unsafe.Tests.csproj
@@ -1,9 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="UnsafeTests.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
+    <ProjectReference Include="..\src\System.Runtime.CompilerServices.Unsafe.ilproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.CompilerServices.Unsafe/tests/UnsafeTests.cs b/src/libraries/System.Runtime.CompilerServices.Unsafe/tests/UnsafeTests.cs
index 88473528f1088c..34b0140aa23cf0 100644
--- a/src/libraries/System.Runtime.CompilerServices.Unsafe/tests/UnsafeTests.cs
+++ b/src/libraries/System.Runtime.CompilerServices.Unsafe/tests/UnsafeTests.cs
@@ -413,7 +413,7 @@ public static void ByteOffsetStackByte4()
         public static unsafe void AsRef()
         {
             byte[] b = new byte[4] { 0x42, 0x42, 0x42, 0x42 };
-            fixed (byte * p = b)
+            fixed (byte* p = b)
             {
                 ref int r = ref Unsafe.AsRef<int>(p);
                 Assert.Equal(0x42424242, r);
@@ -839,7 +839,7 @@ public static void SkipInit()
             Unsafe.SkipInit(out double doubleValue);
 
             // Validate that calling on user-defined unmanaged structs works.
-            
+
             Unsafe.SkipInit(out Byte4 byte4Value);
             Unsafe.SkipInit(out Byte4Short2 byte4Short2Value);
             Unsafe.SkipInit(out Byte512 byte512Value);
@@ -931,6 +931,84 @@ public static void SkipInit_PreservesPrevious()
             Unsafe.SkipInit(out stringValue);
             Assert.Equal("25", stringValue);
         }
+
+        [Fact]
+        public static unsafe void IsNullRef_NotNull()
+        {
+            // Validate that calling with a primitive type works.
+
+            int intValue = 5;
+            Assert.False(Unsafe.IsNullRef<int>(ref intValue));
+
+            // Validate that calling on user-defined unmanaged structs works.
+
+            Int32Double int32DoubleValue = default;
+            Assert.False(Unsafe.IsNullRef<Int32Double>(ref int32DoubleValue));
+
+            // Validate that calling on reference types works.
+
+            object objectValue = new object();
+            Assert.False(Unsafe.IsNullRef<object>(ref objectValue));
+
+            string stringValue = nameof(IsNullRef_NotNull);
+            Assert.False(Unsafe.IsNullRef<string>(ref stringValue));
+
+            // Validate on ref created from a pointer
+
+            int* p = (int*)1;
+            Assert.False(Unsafe.IsNullRef<int>(ref Unsafe.AsRef<int>(p)));
+        }
+
+        [Fact]
+        public static unsafe void IsNullRef_Null()
+        {
+            // Validate that calling with a primitive type works.
+
+            Assert.True(Unsafe.IsNullRef<int>(ref Unsafe.AsRef<int>(null)));
+
+            // Validate that calling on user-defined unmanaged structs works.
+
+            Assert.True(Unsafe.IsNullRef<Int32Double>(ref Unsafe.AsRef<Int32Double>(null)));
+
+            // Validate that calling on reference types works.
+
+            Assert.True(Unsafe.IsNullRef<object>(ref Unsafe.AsRef<object>(null)));
+            Assert.True(Unsafe.IsNullRef<string>(ref Unsafe.AsRef<string>(null)));
+
+            // Validate on ref created from a pointer
+
+            int* p = (int*)0;
+            Assert.True(Unsafe.IsNullRef<int>(ref Unsafe.AsRef<int>(p)));
+        }
+
+        [Fact]
+        public static unsafe void NullRef()
+        {
+            // Validate that calling with a primitive type works.
+
+            Assert.True(Unsafe.IsNullRef<int>(ref Unsafe.NullRef<int>()));
+
+            // Validate that calling on user-defined unmanaged structs works.
+
+            Assert.True(Unsafe.IsNullRef<Int32Double>(ref Unsafe.NullRef<Int32Double>()));
+
+            // Validate that calling on reference types works.
+
+            Assert.True(Unsafe.IsNullRef<object>(ref Unsafe.NullRef<object>()));
+            Assert.True(Unsafe.IsNullRef<string>(ref Unsafe.NullRef<string>()));
+
+            // Validate that pinning results in a null pointer
+
+            fixed (void* p = &Unsafe.NullRef<int>())
+            {
+                Assert.True(p == (void*)0);
+            }
+
+            // Validate that dereferencing a null ref throws a NullReferenceException
+
+            Assert.Throws<NullReferenceException>(() => Unsafe.NullRef<int>() = 42);
+            Assert.Throws<NullReferenceException>(() => Unsafe.NullRef<int>());
+        }
     }
 
     [StructLayout(LayoutKind.Explicit)]
@@ -968,7 +1046,7 @@ public unsafe struct Byte512
         public fixed byte Bytes[512];
     }
 
-    [StructLayout(LayoutKind.Explicit, Size=16)]
+    [StructLayout(LayoutKind.Explicit, Size = 16)]
     public unsafe struct Int32Double
     {
         [FieldOffset(0)]
diff --git a/src/libraries/System.Runtime.CompilerServices.VisualC/Directory.Build.props b/src/libraries/System.Runtime.CompilerServices.VisualC/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Runtime.CompilerServices.VisualC/Directory.Build.props
+++ b/src/libraries/System.Runtime.CompilerServices.VisualC/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.CompilerServices.VisualC/ref/System.Runtime.CompilerServices.VisualC.cs b/src/libraries/System.Runtime.CompilerServices.VisualC/ref/System.Runtime.CompilerServices.VisualC.cs
index f636324e4f4e22..5cf0c49999cb9e 100644
--- a/src/libraries/System.Runtime.CompilerServices.VisualC/ref/System.Runtime.CompilerServices.VisualC.cs
+++ b/src/libraries/System.Runtime.CompilerServices.VisualC/ref/System.Runtime.CompilerServices.VisualC.cs
@@ -9,6 +9,11 @@ namespace System.Runtime.CompilerServices
     public static partial class CompilerMarshalOverride
     {
     }
+    [AttributeUsageAttribute(AttributeTargets.Assembly, AllowMultiple=true)]
+    public sealed class CppInlineNamespaceAttribute : Attribute
+    {
+        public CppInlineNamespaceAttribute(string dottedName) {}
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Struct)]
     public sealed partial class HasCopySemanticsAttribute : System.Attribute
     {
@@ -49,11 +54,6 @@ public sealed partial class NativeCppClassAttribute : System.Attribute
     {
         public NativeCppClassAttribute() { }
     }
-    [AttributeUsageAttribute(AttributeTargets.Assembly, AllowMultiple=true)]
-    public sealed class CppInlineNamespaceAttribute : Attribute
-    {
-        public CppInlineNamespaceAttribute(string dottedName) {}
-    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Enum | System.AttributeTargets.Interface | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
     public sealed partial class RequiredAttributeAttribute : System.Attribute
     {
diff --git a/src/libraries/System.Runtime.CompilerServices.VisualC/src/System.Runtime.CompilerServices.VisualC.csproj b/src/libraries/System.Runtime.CompilerServices.VisualC/src/System.Runtime.CompilerServices.VisualC.csproj
index 2b8596cf8d9062..d0ca0d4c3203d5 100644
--- a/src/libraries/System.Runtime.CompilerServices.VisualC/src/System.Runtime.CompilerServices.VisualC.csproj
+++ b/src/libraries/System.Runtime.CompilerServices.VisualC/src/System.Runtime.CompilerServices.VisualC.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime.CompilerServices.VisualC</AssemblyName>
     <Nullable>enable</Nullable>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Runtime.Extensions/Directory.Build.props b/src/libraries/System.Runtime.Extensions/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Runtime.Extensions/Directory.Build.props
+++ b/src/libraries/System.Runtime.Extensions/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Extensions/src/System.Runtime.Extensions.csproj b/src/libraries/System.Runtime.Extensions/src/System.Runtime.Extensions.csproj
index 1501be79fa8955..b6029a4baee65e 100644
--- a/src/libraries/System.Runtime.Extensions/src/System.Runtime.Extensions.csproj
+++ b/src/libraries/System.Runtime.Extensions/src/System.Runtime.Extensions.csproj
@@ -1,16 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime.Extensions</AssemblyName>
-    <OutputType>Library</OutputType>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
-  <ItemGroup>
-    <ProjectReference Include="..\..\System.Private.Uri\src\System.Private.Uri.csproj" />
-    <ProjectReference Include="..\..\System.Runtime\src\System.Runtime.csproj" />
-  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(CoreLibProject)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Uri\src\System.Private.Uri.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\src\System.Runtime.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Runtime.Extensions/tests/System/Environment.StackTrace.cs b/src/libraries/System.Runtime.Extensions/tests/System/Environment.StackTrace.cs
index 4077019d701009..e3fa2c36d28f77 100644
--- a/src/libraries/System.Runtime.Extensions/tests/System/Environment.StackTrace.cs
+++ b/src/libraries/System.Runtime.Extensions/tests/System/Environment.StackTrace.cs
@@ -68,7 +68,6 @@ public TestClass()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/39223", TestPlatforms.Browser)]
         public void StackTraceDoesNotStartWithInternalFrame()
         {
              string stackTrace = Environment.StackTrace;
diff --git a/src/libraries/System.Runtime.Extensions/tests/System/Environment.UserName.cs b/src/libraries/System.Runtime.Extensions/tests/System/Environment.UserName.cs
index 947cbef2c789f6..2157f63c0250a0 100644
--- a/src/libraries/System.Runtime.Extensions/tests/System/Environment.UserName.cs
+++ b/src/libraries/System.Runtime.Extensions/tests/System/Environment.UserName.cs
@@ -5,7 +5,6 @@
 
 namespace System.Tests
 {
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/38164", TestPlatforms.Browser)]
     public class EnvironmentUserName
     {
         [Fact]
@@ -36,5 +35,14 @@ public void UserName_MatchesEnvironment_Windows()
         {
             Assert.Equal(Environment.GetEnvironmentVariable("USERNAME"), Environment.UserName);
         }
+
+        [Fact]
+        [PlatformSpecific(TestPlatforms.Browser)]
+        public void UserName_MatchesEnvironment_Browser()
+        {
+            string name = Environment.UserName;
+            Assert.False(string.IsNullOrWhiteSpace(name));
+            Assert.Equal("Browser", name);
+        }
     }
 }
diff --git a/src/libraries/System.Runtime.Extensions/tests/System/EnvironmentTests.cs b/src/libraries/System.Runtime.Extensions/tests/System/EnvironmentTests.cs
index ff8eb26cd2435b..9b6574036d6148 100644
--- a/src/libraries/System.Runtime.Extensions/tests/System/EnvironmentTests.cs
+++ b/src/libraries/System.Runtime.Extensions/tests/System/EnvironmentTests.cs
@@ -127,7 +127,7 @@ public void OSVersion_Idempotent()
         public void OSVersion_MatchesPlatform()
         {
             PlatformID id = Environment.OSVersion.Platform;
-            PlatformID expected = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? PlatformID.Win32NT : RuntimeInformation.IsOSPlatform(OSPlatform.Browser) ? PlatformID.Other : PlatformID.Unix;
+            PlatformID expected = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? PlatformID.Win32NT : OperatingSystem.IsBrowser() ? PlatformID.Other : PlatformID.Unix;
             Assert.Equal(expected, id);
         }
 
@@ -142,7 +142,7 @@ public void OSVersion_ValidVersion()
 
             Assert.Contains(version.ToString(2), versionString);
 
-            string expectedOS = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "Windows " : RuntimeInformation.IsOSPlatform(OSPlatform.Browser) ? "Other " : "Unix ";
+            string expectedOS = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "Windows " : OperatingSystem.IsBrowser() ? "Other " : "Unix ";
             Assert.Contains(expectedOS, versionString);
         }
 
@@ -317,7 +317,7 @@ public void FailFast_ExceptionStackTrace_InnerException()
         }
 
         [Fact]
-        [PlatformSpecific(TestPlatforms.AnyUnix)]  // Tests OS-specific environment
+        [PlatformSpecific(TestPlatforms.AnyUnix | TestPlatforms.Browser)]  // Tests OS-specific environment
         public void GetFolderPath_Unix_PersonalIsHomeAndUserProfile()
         {
             Assert.Equal(Environment.GetEnvironmentVariable("HOME"), Environment.GetFolderPath(Environment.SpecialFolder.Personal));
diff --git a/src/libraries/System.Runtime.Extensions/tests/System/OperatingSystemTests.cs b/src/libraries/System.Runtime.Extensions/tests/System/OperatingSystemTests.cs
index b6e7005d62f3b3..c355baf8e2aeac 100644
--- a/src/libraries/System.Runtime.Extensions/tests/System/OperatingSystemTests.cs
+++ b/src/libraries/System.Runtime.Extensions/tests/System/OperatingSystemTests.cs
@@ -7,6 +7,19 @@ namespace System.Tests
 {
     public static class OperatingSystemTests
     {
+        private static readonly string[] AllKnownPlatformNames = new[]
+        {
+            "Android",
+            "macOS",
+            "iOS",
+            "tvOS",
+            "watchOS",
+            "Windows",
+            "Linux",
+            "FreeBSD",
+            "Browser"
+        };
+
         [Theory]
         [InlineData(PlatformID.Other, "1.0.0.0")]
         [InlineData(PlatformID.MacOSX, "1.2")]
@@ -47,5 +60,158 @@ public static void Clone()
             Assert.Equal(os.Version, os2.Version);
             Assert.Equal(os.VersionString, os2.VersionString);
         }
+
+        [Fact]
+        public static void IsOSPlatform_InvalidArgs_Throws()
+        {
+            AssertExtensions.Throws<ArgumentNullException>("platform", () => OperatingSystem.IsOSPlatform(null));
+        }
+
+        [Fact]
+        public static void IsOSPlatformVersionAtLeast_InvalidArgs_Throws()
+        {
+            AssertExtensions.Throws<ArgumentNullException>("platform", () => OperatingSystem.IsOSPlatformVersionAtLeast(null, 1));
+        }
+
+        [Fact, PlatformSpecific(TestPlatforms.Browser)]
+        public static void TestIsOSPlatform_Browser() => TestIsOSPlatform("BROWSER", OperatingSystem.IsBrowser);
+
+        [Fact, PlatformSpecific(TestPlatforms.Browser)]
+        public static void TestIsOSVersionAtLeast_Browser() => TestIsOSVersionAtLeast("BROWSER");
+
+        [Fact, PlatformSpecific(TestPlatforms.Linux)]
+        public static void TestIsOSPlatform_Linux() => TestIsOSPlatform("Linux", OperatingSystem.IsLinux);
+
+        [Fact, PlatformSpecific(TestPlatforms.Linux)]
+        public static void TestIsOSVersionAtLeast_Linux() => TestIsOSVersionAtLeast("Linux");
+
+        [Fact, PlatformSpecific(TestPlatforms.FreeBSD)]
+        public static void TestIsOSPlatform_FreeBSD() => TestIsOSPlatform("FreeBSD", OperatingSystem.IsFreeBSD);
+
+        [Fact, PlatformSpecific(TestPlatforms.FreeBSD)]
+        public static void TestIsOSVersionAtLeast_FreeBSD() => TestIsOSVersionAtLeast("FreeBSD");
+
+        [Fact, PlatformSpecific(TestPlatforms.Android)]
+        public static void TestIsOSPlatform_Android() => TestIsOSPlatform("Android", OperatingSystem.IsAndroid);
+
+        [Fact, PlatformSpecific(TestPlatforms.Android)]
+        public static void TestIsOSVersionAtLeast_Android() => TestIsOSVersionAtLeast("Android");
+
+        [Fact, PlatformSpecific(TestPlatforms.iOS)]
+        public static void TestIsOSPlatform_IOS() => TestIsOSPlatform("iOS", OperatingSystem.IsIOS);
+
+        [Fact, PlatformSpecific(TestPlatforms.iOS)]
+        public static void TestIsOSVersionAtLeast_IOS() => TestIsOSVersionAtLeast("iOS");
+
+        [Fact, PlatformSpecific(TestPlatforms.OSX)]
+        public static void TestIsOSPlatform_MacOS() => TestIsOSPlatform("macOS", OperatingSystem.IsMacOS);
+
+        [Fact, PlatformSpecific(TestPlatforms.OSX)]
+        public static void TestIsOSVersionAtLeast_MacOS() => TestIsOSVersionAtLeast("macOS");
+
+        [Fact, PlatformSpecific(TestPlatforms.OSX)]
+        public static void OSX_Is_Treated_as_macOS()
+        {
+            // we prefer "macOS", but still accept "OSX"
+
+            Assert.True(OperatingSystem.IsOSPlatform("OSX"));
+
+            AssertVersionChecks(true, (major, minor, build, revision) => OperatingSystem.IsOSPlatformVersionAtLeast("OSX", major, minor, build, revision));
+            AssertVersionChecks(true, (major, minor, build, revision) => OperatingSystem.IsOSPlatformVersionAtLeast("osx", major, minor, build, revision));
+            AssertVersionChecks(true, (major, minor, build) => OperatingSystem.IsOSPlatformVersionAtLeast("OSX", major, minor, build));
+            AssertVersionChecks(true, (major, minor, build) => OperatingSystem.IsOSPlatformVersionAtLeast("osx", major, minor, build));
+        }
+
+        [Fact, PlatformSpecific(TestPlatforms.tvOS)]
+        public static void TestIsOSPlatform_TvOS() => TestIsOSPlatform("tvOS", OperatingSystem.IsTvOS);
+
+        [Fact, PlatformSpecific(TestPlatforms.tvOS)]
+        public static void TestIsOSVersionAtLeast_TvOS() => TestIsOSVersionAtLeast("tvOS");
+
+        [Fact, PlatformSpecific(TestPlatforms.Windows)]
+        public static void TestIsOSPlatform_Windows() => TestIsOSPlatform("Windows", OperatingSystem.IsWindows);
+
+        [Fact, PlatformSpecific(TestPlatforms.Windows)]
+        public static void TestIsOSVersionAtLeast_Windows() => TestIsOSVersionAtLeast("Windows");
+
+        private static void TestIsOSPlatform(string currentOSName, Func<bool> currentOSCheck)
+        {
+            foreach (string platfromName in AllKnownPlatformNames)
+            {
+                bool expected = currentOSName.Equals(platfromName, StringComparison.OrdinalIgnoreCase);
+
+                Assert.Equal(expected, OperatingSystem.IsOSPlatform(platfromName));
+                Assert.Equal(expected, OperatingSystem.IsOSPlatform(platfromName.ToUpper()));
+                Assert.Equal(expected, OperatingSystem.IsOSPlatform(platfromName.ToLower()));
+            }
+
+            Assert.True(currentOSCheck());
+
+            bool[] allResults = new bool[]
+            {
+                OperatingSystem.IsBrowser(),
+                OperatingSystem.IsLinux(),
+                OperatingSystem.IsFreeBSD(),
+                OperatingSystem.IsAndroid(),
+                OperatingSystem.IsIOS(),
+                OperatingSystem.IsMacOS(),
+                OperatingSystem.IsTvOS(),
+                OperatingSystem.IsWatchOS(),
+                OperatingSystem.IsWindows()
+            };
+
+            Assert.Single(allResults, true);
+        }
+
+        private static void TestIsOSVersionAtLeast(string currentOSName)
+        {
+            foreach (string platfromName in AllKnownPlatformNames)
+            {
+                bool isCurrentOS = currentOSName.Equals(platfromName, StringComparison.OrdinalIgnoreCase);
+
+                AssertVersionChecks(isCurrentOS, (major, minor, build, revision) => OperatingSystem.IsOSPlatformVersionAtLeast(platfromName, major, minor, build, revision));
+                AssertVersionChecks(isCurrentOS, (major, minor, build, revision) => OperatingSystem.IsOSPlatformVersionAtLeast(platfromName.ToLower(), major, minor, build, revision));
+                AssertVersionChecks(isCurrentOS, (major, minor, build, revision) => OperatingSystem.IsOSPlatformVersionAtLeast(platfromName.ToUpper(), major, minor, build, revision));
+            }
+            
+            AssertVersionChecks(currentOSName.Equals("Android", StringComparison.OrdinalIgnoreCase), OperatingSystem.IsAndroidVersionAtLeast);
+            AssertVersionChecks(currentOSName.Equals("iOS", StringComparison.OrdinalIgnoreCase), OperatingSystem.IsIOSVersionAtLeast);
+            AssertVersionChecks(currentOSName.Equals("macOS", StringComparison.OrdinalIgnoreCase), OperatingSystem.IsMacOSVersionAtLeast);
+            AssertVersionChecks(currentOSName.Equals("tvOS", StringComparison.OrdinalIgnoreCase), OperatingSystem.IsTvOSVersionAtLeast);
+            AssertVersionChecks(currentOSName.Equals("watchOS", StringComparison.OrdinalIgnoreCase), OperatingSystem.IsWatchOSVersionAtLeast);
+            AssertVersionChecks(currentOSName.Equals("Windows", StringComparison.OrdinalIgnoreCase), OperatingSystem.IsWindowsVersionAtLeast);
+        }
+
+        private static void AssertVersionChecks(bool isCurrentOS, Func<int, int, int, int, bool> isOSVersionAtLeast)
+        {
+            Version current = Environment.OSVersion.Version;
+
+            Assert.False(isOSVersionAtLeast(current.Major + 1, current.Minor, current.Build, current.Revision));
+            Assert.False(isOSVersionAtLeast(current.Major, current.Minor + 1, current.Build, current.Revision));
+            Assert.False(isOSVersionAtLeast(current.Major, current.Minor, current.Build + 1, current.Revision));
+            Assert.False(isOSVersionAtLeast(current.Major, current.Minor, current.Build, Math.Max(current.Revision + 1, 1))); // OSX Revision reports -1
+
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor, current.Build, current.Revision));
+
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major - 1, current.Minor, current.Build, current.Revision));
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor - 1, current.Build, current.Revision));
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor, current.Build - 1, current.Revision));
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor, current.Build, current.Revision - 1));
+        }
+
+        private static void AssertVersionChecks(bool isCurrentOS, Func<int, int, int, bool> isOSVersionAtLeast)
+        {
+            Version current = Environment.OSVersion.Version;
+
+            Assert.False(isOSVersionAtLeast(current.Major + 1, current.Minor, current.Build));
+            Assert.False(isOSVersionAtLeast(current.Major, current.Minor + 1, current.Build));
+            Assert.False(isOSVersionAtLeast(current.Major, current.Minor, current.Build + 1));
+
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor, current.Build));
+
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major - 1, current.Minor, current.Build));
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor - 1, current.Build));
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor, current.Build - 1));
+        }
     }
 }
diff --git a/src/libraries/System.Runtime.Handles/Directory.Build.props b/src/libraries/System.Runtime.Handles/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Runtime.Handles/Directory.Build.props
+++ b/src/libraries/System.Runtime.Handles/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Handles/src/System.Runtime.Handles.csproj b/src/libraries/System.Runtime.Handles/src/System.Runtime.Handles.csproj
index 48cc45350aafeb..94d0c640130480 100644
--- a/src/libraries/System.Runtime.Handles/src/System.Runtime.Handles.csproj
+++ b/src/libraries/System.Runtime.Handles/src/System.Runtime.Handles.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime.Handles</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System.Runtime.InteropServices.JavaScript.csproj b/src/libraries/System.Runtime.InteropServices.JavaScript/src/System.Runtime.InteropServices.JavaScript.csproj
deleted file mode 100644
index 9eb0dc6fa61ddf..00000000000000
--- a/src/libraries/System.Runtime.InteropServices.JavaScript/src/System.Runtime.InteropServices.JavaScript.csproj
+++ /dev/null
@@ -1,42 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <AssemblyName>System.Runtime.InteropServices.JavaScript</AssemblyName>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <Nullable>enable</Nullable>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Browser</TargetFrameworks>
-  </PropertyGroup>
-  <ItemGroup>
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Net.Primitives\ref\System.Net.Primitives.csproj" />
-    <ProjectReference Include="..\..\System.Collections\ref\System.Collections.csproj" />
-    <ProjectReference Include="..\..\System.Runtime.InteropServices\ref\System.Runtime.InteropServices.csproj" />
-    <ProjectReference Include="..\..\System.Memory\ref\System.Memory.csproj" />
-    <ProjectReference Include="..\..\System.Threading\ref\System.Threading.csproj" />
-    <ProjectReference Include="..\..\System.Runtime.CompilerServices.Unsafe\ref\System.Runtime.CompilerServices.Unsafe.csproj" />
-  </ItemGroup>
-  <ItemGroup>
-    <Compile Include="$(CommonPath)Interop\Browser\Interop.Runtime.cs" Link="Common\Interop\Browser\Interop.Runtime.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Runtime.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\JSException.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\JSObject.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\DataView.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Float32Array.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Float64Array.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Int8Array.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Int16Array.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Int32Array.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Uint8Array.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Uint16Array.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Uint32Array.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Uint8ClampedArray.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\TypedArray.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Array.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\ArrayBuffer.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\SharedArrayBuffer.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Map.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\CoreObject.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\HostObject.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\Function.cs" />
-    <Compile Include="System/Runtime\InteropServices\JavaScript\AnyRef.cs" />
-  </ItemGroup>
-</Project>
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/Directory.Build.props b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/Directory.Build.props
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/ref/System.Runtime.InteropServices.RuntimeInformation.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/ref/System.Runtime.InteropServices.RuntimeInformation.cs
index 46d2dd5159e22f..eb1abb41102b55 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/ref/System.Runtime.InteropServices.RuntimeInformation.cs
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/ref/System.Runtime.InteropServices.RuntimeInformation.cs
@@ -18,16 +18,9 @@ public enum Architecture
     {
         private readonly object _dummy;
         private readonly int _dummyPrimitive;
-        public static System.Runtime.InteropServices.OSPlatform Android { get { throw null; } }
-        public static System.Runtime.InteropServices.OSPlatform Browser { get { throw null; } }
         public static System.Runtime.InteropServices.OSPlatform FreeBSD { get { throw null; } }
-        public static System.Runtime.InteropServices.OSPlatform iOS { get { throw null; } }
         public static System.Runtime.InteropServices.OSPlatform Linux { get { throw null; } }
-        public static System.Runtime.InteropServices.OSPlatform macOS { get { throw null; } }
-        [System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)]
         public static System.Runtime.InteropServices.OSPlatform OSX { get { throw null; } }
-        public static System.Runtime.InteropServices.OSPlatform tvOS { get { throw null; } }
-        public static System.Runtime.InteropServices.OSPlatform watchOS { get { throw null; } }
         public static System.Runtime.InteropServices.OSPlatform Windows { get { throw null; } }
         public static System.Runtime.InteropServices.OSPlatform Create(string osPlatform) { throw null; }
         public override bool Equals(object? obj) { throw null; }
@@ -45,15 +38,5 @@ public static partial class RuntimeInformation
         public static System.Runtime.InteropServices.Architecture ProcessArchitecture { get { throw null; } }
         public static string RuntimeIdentifier { get { throw null; } }
         public static bool IsOSPlatform(System.Runtime.InteropServices.OSPlatform osPlatform) { throw null; }
-        public static bool IsOSPlatformOrLater(string platformName) { throw null; }
-        public static bool IsOSPlatformOrLater(System.Runtime.InteropServices.OSPlatform osPlatform, int major) { throw null; }
-        public static bool IsOSPlatformOrLater(System.Runtime.InteropServices.OSPlatform osPlatform, int major, int minor) { throw null; }
-        public static bool IsOSPlatformOrLater(System.Runtime.InteropServices.OSPlatform osPlatform, int major, int minor, int build) { throw null; }
-        public static bool IsOSPlatformOrLater(System.Runtime.InteropServices.OSPlatform osPlatform, int major, int minor, int build, int revision) { throw null; }
-        public static bool IsOSPlatformEarlierThan(string platformName) { throw null; }
-        public static bool IsOSPlatformEarlierThan(System.Runtime.InteropServices.OSPlatform osPlatform, int major) { throw null; }
-        public static bool IsOSPlatformEarlierThan(System.Runtime.InteropServices.OSPlatform osPlatform, int major, int minor) { throw null; }
-        public static bool IsOSPlatformEarlierThan(System.Runtime.InteropServices.OSPlatform osPlatform, int major, int minor, int build) { throw null; }
-        public static bool IsOSPlatformEarlierThan(System.Runtime.InteropServices.OSPlatform osPlatform, int major, int minor, int build, int revision) { throw null; }
     }
 }
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/Resources/Strings.resx b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/Resources/Strings.resx
index c7f9079719cce4..e554cfe1fe2eb1 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/Resources/Strings.resx
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/Resources/Strings.resx
@@ -60,9 +60,6 @@
   <data name="Argument_EmptyValue" xml:space="preserve">
     <value>Value cannot be empty.</value>
   </data>
-  <data name="Argument_InvalidPlatfromName" xml:space="preserve">
-    <value>"{0}" is not a valid platform name. It must contain both name and version (with at least major and minor number specified). Example: "ios14.0".</value>
-  </data>
   <data name="PlatformNotSupported_RuntimeInformation" xml:space="preserve">
     <value>RuntimeInformation is not supported for Portable Class Libraries.</value>
   </data>
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System.Runtime.InteropServices.RuntimeInformation.csproj b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System.Runtime.InteropServices.RuntimeInformation.csproj
index 02fa495e139735..12aab18e3e97b1 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System.Runtime.InteropServices.RuntimeInformation.csproj
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System.Runtime.InteropServices.RuntimeInformation.csproj
@@ -7,7 +7,6 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Runtime\InteropServices\RuntimeInformation\RuntimeInformation.cs" />
-    <Compile Include="System\Runtime\InteropServices\RuntimeInformation\RuntimeInformation.PlatformVersion.cs" />
     <Compile Include="System\Runtime\InteropServices\RuntimeInformation\Architecture.cs" />
     <Compile Include="System\Runtime\InteropServices\RuntimeInformation\OSPlatform.cs" />
   </ItemGroup>
@@ -16,8 +15,6 @@
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
     <Compile Include="System\Runtime\InteropServices\RuntimeInformation\RuntimeInformation.Unix.cs" />
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetUnixName.cs"
-             Link="Common\Interop\Unix\System.Native\Interop.GetUnixName.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetUnixVersion.cs"
              Link="Common\Interop\Unix\System.Native\Interop.GetUnixVersion.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetOSArchitecture.cs"
@@ -46,6 +43,5 @@
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Threading" />
-    <Reference Include="System.Memory" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/OSPlatform.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/OSPlatform.cs
index 18e45643d216f4..91dcbad86e1748 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/OSPlatform.cs
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/OSPlatform.cs
@@ -5,38 +5,22 @@ namespace System.Runtime.InteropServices
 {
     public readonly struct OSPlatform : IEquatable<OSPlatform>
     {
-        private readonly string _osPlatform;
-
-        public static OSPlatform Android { get; } = new OSPlatform("ANDROID");
-
-        public static OSPlatform Browser { get; } = new OSPlatform("BROWSER");
-
         public static OSPlatform FreeBSD { get; } = new OSPlatform("FREEBSD");
 
         public static OSPlatform Linux { get; } = new OSPlatform("LINUX");
 
-        public static OSPlatform macOS { get; } = new OSPlatform("MACOS");
-
-        [System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)] // superseded by macOS
         public static OSPlatform OSX { get; } = new OSPlatform("OSX");
 
-        public static OSPlatform iOS { get; } = new OSPlatform("IOS");
-
-        public static OSPlatform tvOS { get; } = new OSPlatform("TVOS");
-
-        public static OSPlatform watchOS { get; } = new OSPlatform("WATCHOS");
-
         public static OSPlatform Windows { get; } = new OSPlatform("WINDOWS");
 
-        internal bool IsCurrent { get; } // this information is cached because it's frequently used
+        internal string Name { get; }
 
         private OSPlatform(string osPlatform)
         {
             if (osPlatform == null) throw new ArgumentNullException(nameof(osPlatform));
             if (osPlatform.Length == 0) throw new ArgumentException(SR.Argument_EmptyValue, nameof(osPlatform));
 
-            _osPlatform = osPlatform;
-            IsCurrent = RuntimeInformation.IsCurrentOSPlatform(osPlatform);
+            Name = osPlatform;
         }
 
         /// <summary>
@@ -50,12 +34,12 @@ public static OSPlatform Create(string osPlatform)
 
         public bool Equals(OSPlatform other)
         {
-            return Equals(other._osPlatform);
+            return Equals(other.Name);
         }
 
         internal bool Equals(string? other)
         {
-            return string.Equals(_osPlatform, other, StringComparison.OrdinalIgnoreCase);
+            return string.Equals(Name, other, StringComparison.OrdinalIgnoreCase);
         }
 
         public override bool Equals(object? obj)
@@ -65,12 +49,12 @@ public override bool Equals(object? obj)
 
         public override int GetHashCode()
         {
-            return _osPlatform == null ? 0 : _osPlatform.GetHashCode(StringComparison.OrdinalIgnoreCase);
+            return Name == null ? 0 : Name.GetHashCode(StringComparison.OrdinalIgnoreCase);
         }
 
         public override string ToString()
         {
-            return _osPlatform ?? string.Empty;
+            return Name ?? string.Empty;
         }
 
         public static bool operator ==(OSPlatform left, OSPlatform right)
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Browser.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Browser.cs
index 838aa49c2e76ec..c702ef839bced6 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Browser.cs
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Browser.cs
@@ -5,8 +5,6 @@ namespace System.Runtime.InteropServices
 {
     public static partial class RuntimeInformation
     {
-        internal static bool IsCurrentOSPlatform(string osPlatform) => osPlatform.Equals("BROWSER", StringComparison.OrdinalIgnoreCase);
-
         public static string OSDescription => "Browser";
 
         public static Architecture OSArchitecture => Architecture.Wasm;
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.PlatformVersion.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.PlatformVersion.cs
deleted file mode 100644
index 0eec21939bfa82..00000000000000
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.PlatformVersion.cs
+++ /dev/null
@@ -1,131 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-namespace System.Runtime.InteropServices
-{
-    public static partial class RuntimeInformation
-    {
-        /// <summary>
-        /// Check for the OS with a >= version comparison. Used to guard APIs that were added in the given OS release.
-        /// </summary>
-        /// <param name="platformName">OS name concatenated with a version number.</param>
-        /// <remarks>The version number must contain at least major and minor numbers separated with a dot.
-        /// Example: "ios14.0" is OK, "ios14" is NOT OK.</remarks>
-        public static bool IsOSPlatformOrLater(string platformName)
-        {
-            (OSPlatform platform, Version version) = Parse(platformName);
-
-            return IsOSPlatformOrLater(platform, version.Major, version.Minor, version.Build, version.Revision);
-        }
-
-        /// <summary>
-        /// Check for the OS with a >= version comparison. Used to guard APIs that were added in the given OS release.
-        /// </summary>
-        public static bool IsOSPlatformOrLater(OSPlatform osPlatform, int major)
-            => IsOSPlatform(osPlatform) && Environment.OSVersion.Version.Major >= major;
-
-        /// <summary>
-        /// Check for the OS with a >= version comparison. Used to guard APIs that were added in the given OS release.
-        /// </summary>
-        public static bool IsOSPlatformOrLater(OSPlatform osPlatform, int major, int minor)
-            => IsOSPlatform(osPlatform) && IsOSVersionOrLater(major, minor, int.MinValue, int.MinValue);
-
-        /// <summary>
-        /// Check for the OS with a >= version comparison. Used to guard APIs that were added in the given OS release.
-        /// </summary>
-        public static bool IsOSPlatformOrLater(OSPlatform osPlatform, int major, int minor, int build)
-            => IsOSPlatform(osPlatform) && IsOSVersionOrLater(major, minor, build, int.MinValue);
-
-        /// <summary>
-        /// Check for the OS with a >= version comparison. Used to guard APIs that were added in the given OS release.
-        /// </summary>
-        public static bool IsOSPlatformOrLater(OSPlatform osPlatform, int major, int minor, int build, int revision)
-            => IsOSPlatform(osPlatform) && IsOSVersionOrLater(major, minor, build, revision);
-
-        /// <summary>
-        /// Check for the OS with a &lt; version comparison. Used to guard APIs that were obsoleted or removed in the given OS release.
-        /// </summary>
-        /// <param name="platformName">OS name concatenated with a version number.</param>
-        /// <remarks>The version number must contain at least major and minor numbers separated with a dot.
-        /// Example: "ios14.0" is OK, "ios14" is NOT OK.</remarks>
-        public static bool IsOSPlatformEarlierThan(string platformName)
-        {
-            (OSPlatform platform, Version version) = Parse(platformName);
-
-            return IsOSPlatformEarlierThan(platform, version.Major, version.Minor, version.Build, version.Revision);
-        }
-
-        /// <summary>
-        /// Check for the OS with a &lt; version comparison. Used to guard APIs that were obsoleted or removed in the given OS release.
-        /// </summary>
-        public static bool IsOSPlatformEarlierThan(OSPlatform osPlatform, int major)
-            => IsOSPlatform(osPlatform) && Environment.OSVersion.Version.Major < major;
-
-        /// <summary>
-        /// Check for the OS with a &lt; version comparison. Used to guard APIs that were obsoleted or removed in the given OS release.
-        /// </summary>
-        public static bool IsOSPlatformEarlierThan(OSPlatform osPlatform, int major, int minor)
-            => IsOSPlatform(osPlatform) && !IsOSVersionOrLater(major, minor, int.MinValue, int.MinValue);
-
-        /// <summary>
-        /// Check for the OS with a &lt; version comparison. Used to guard APIs that were obsoleted or removed in the given OS release.
-        /// </summary>
-        public static bool IsOSPlatformEarlierThan(OSPlatform osPlatform, int major, int minor, int build)
-            => IsOSPlatform(osPlatform) && !IsOSVersionOrLater(major, minor, build, int.MinValue);
-
-        /// <summary>
-        /// Check for the OS with a &lt; version comparison. Used to guard APIs that were obsoleted or removed in the given OS release.
-        /// </summary>
-        public static bool IsOSPlatformEarlierThan(OSPlatform osPlatform, int major, int minor, int build, int revision)
-            => IsOSPlatform(osPlatform) && !IsOSVersionOrLater(major, minor, build, revision);
-
-        private static bool IsOSVersionOrLater(int major, int minor, int build, int revision)
-        {
-            Version current = Environment.OSVersion.Version;
-            if (current.Major != major)
-            {
-                return current.Major > major;
-            }
-            if (current.Minor != minor)
-            {
-                return current.Minor > minor;
-            }
-            if (current.Build != build)
-            {
-                return current.Build > build;
-            }
-
-            return current.Revision >= revision;
-        }
-
-        private static (OSPlatform, Version) Parse(string platformName)
-        {
-            if (platformName == null)
-            {
-                throw new ArgumentNullException(nameof(platformName));
-            }
-            if (platformName.Length == 0)
-            {
-                throw new ArgumentException(SR.Argument_EmptyValue, nameof(platformName));
-            }
-
-            // iterate from the begining, as digits in the middle of the names are not supported by design
-            for (int i = 0; i < platformName.Length; i++)
-            {
-                if (char.IsDigit(platformName[i]))
-                {
-                    if (i > 0 && Version.TryParse(platformName.AsSpan(i), out Version? version))
-                    {
-                        return (OSPlatform.Create(platformName.Substring(0, i)), version);
-                    }
-                    else
-                    {
-                        break;
-                    }
-                }
-            }
-
-            throw new ArgumentException(SR.Format(SR.Argument_InvalidPlatfromName, platformName), nameof(platformName));
-        }
-    }
-}
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Unix.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Unix.cs
index 01da110b03738c..0a8147db34af52 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Unix.cs
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Unix.cs
@@ -7,17 +7,8 @@ namespace System.Runtime.InteropServices
 {
     public static partial class RuntimeInformation
     {
-        private static string? s_osPlatformName;
         private static string? s_osDescription;
 
-        internal static bool IsCurrentOSPlatform(string osPlatform)
-        {
-            string name = s_osPlatformName ??= Interop.Sys.GetUnixName();
-
-            return osPlatform.Equals(name, StringComparison.OrdinalIgnoreCase)
-                || (name == "OSX" && osPlatform.Equals("MACOS", StringComparison.OrdinalIgnoreCase)); // GetUnixName returns OSX on macOS
-        }
-
         public static string OSDescription => s_osDescription ??= Interop.Sys.GetUnixVersion();
 
         public static Architecture OSArchitecture { get; } = Map((Interop.Sys.ProcessorArchitecture)Interop.Sys.GetOSArchitecture());
@@ -34,6 +25,8 @@ private static Architecture Map(Interop.Sys.ProcessorArchitecture arch)
                     return Architecture.X64;
                 case Interop.Sys.ProcessorArchitecture.ARM64:
                     return Architecture.Arm64;
+                case Interop.Sys.ProcessorArchitecture.WASM:
+                    return Architecture.Wasm;
                 case Interop.Sys.ProcessorArchitecture.x86:
                 default:
                     Debug.Assert(arch == Interop.Sys.ProcessorArchitecture.x86, "Unidentified Architecture");
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Windows.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Windows.cs
index 668b84391b76ef..0177eec2317cc6 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Windows.cs
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Windows.cs
@@ -11,8 +11,6 @@ public static partial class RuntimeInformation
         private static volatile int s_osArch = -1;
         private static volatile int s_processArch = -1;
 
-        internal static bool IsCurrentOSPlatform(string osPlatform) => osPlatform.Equals("WINDOWS", StringComparison.OrdinalIgnoreCase);
-
         public static string OSDescription
         {
             get
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.cs
index 95b1b62b4cdbe7..df0fb53273d423 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.cs
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.cs
@@ -52,6 +52,6 @@ public static string FrameworkDescription
         /// <summary>
         /// Indicates whether the current application is running on the specified platform.
         /// </summary>
-        public static bool IsOSPlatform(OSPlatform osPlatform) => osPlatform.IsCurrent;
+        public static bool IsOSPlatform(OSPlatform osPlatform) => OperatingSystem.IsOSPlatform(osPlatform.Name);
     }
 }
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/CheckArchitectureTests.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/CheckArchitectureTests.cs
index 4fa46f5bed27aa..a54b80285783b4 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/CheckArchitectureTests.cs
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/CheckArchitectureTests.cs
@@ -44,5 +44,13 @@ public void VerifyArchitecture()
             Assert.Equal(osArch, RuntimeInformation.OSArchitecture);
             Assert.Equal(processArch, RuntimeInformation.ProcessArchitecture);
         }
+
+        [Fact]
+        [PlatformSpecific(TestPlatforms.Browser)]
+        public void VerifyBrowserArchitecture()
+        {
+            Assert.Equal(Architecture.Wasm, RuntimeInformation.OSArchitecture);
+            Assert.Equal(Architecture.Wasm, RuntimeInformation.ProcessArchitecture);
+        }
     }
 }
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/CheckPlatformTests.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/CheckPlatformTests.cs
index e40f9f8b310afe..76ea344cff31c9 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/CheckPlatformTests.cs
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/CheckPlatformTests.cs
@@ -51,10 +51,6 @@ public void CheckOSX()
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.OSX));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("OSX")));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("osx")));
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.macOS));
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("MACOS")));
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("macOS")));
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("macos")));
 
             Assert.False(RuntimeInformation.IsOSPlatform(OSPlatform.Create("FREEBSD")));
             Assert.False(RuntimeInformation.IsOSPlatform(OSPlatform.Create("NETBSD")));
@@ -71,7 +67,6 @@ public void CheckOSX()
         [Fact, PlatformSpecific(TestPlatforms.iOS)]  // Tests RuntimeInformation OS platform
         public void CheckiOS()
         {
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.iOS));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("IOS")));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("iOS")));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("ios")));
@@ -92,7 +87,6 @@ public void CheckiOS()
         [Fact, PlatformSpecific(TestPlatforms.tvOS)]  // Tests RuntimeInformation OS platform
         public void ChecktvOS()
         {
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.tvOS));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("TVOS")));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("tvOS")));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("tvos")));
@@ -113,7 +107,6 @@ public void ChecktvOS()
         [Fact, PlatformSpecific(TestPlatforms.Android)]  // Tests RuntimeInformation OS platform
         public void CheckAndroid()
         {
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Android));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("ANDROID")));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("android")));
 
@@ -133,7 +126,6 @@ public void CheckAndroid()
         [Fact, PlatformSpecific(TestPlatforms.Browser)]  // Tests RuntimeInformation OS platform
         public void CheckBrowser()
         {
-            Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Browser));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("BROWSER")));
             Assert.True(RuntimeInformation.IsOSPlatform(OSPlatform.Create("browser")));
 
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/PlatformVersionTests.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/PlatformVersionTests.cs
deleted file mode 100644
index b612d2e065bcba..00000000000000
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/PlatformVersionTests.cs
+++ /dev/null
@@ -1,259 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Collections.Generic;
-using Xunit;
-
-namespace System.Runtime.InteropServices.RuntimeInformationTests
-{
-    public class PlatformVersionTests
-    {
-        public static IEnumerable<object[]> AllKnownOsPlatforms()
-        {
-            yield return new object[] { OSPlatform.Windows };
-            yield return new object[] { OSPlatform.Linux };
-            yield return new object[] { OSPlatform.OSX };
-            yield return new object[] { OSPlatform.Browser };
-            yield return new object[] { OSPlatform.macOS };
-            yield return new object[] { OSPlatform.iOS };
-            yield return new object[] { OSPlatform.tvOS };
-            yield return new object[] { OSPlatform.watchOS };
-            yield return new object[] { OSPlatform.Android };
-        }
-
-        [Fact]
-        public void IsOSPlatformOrLater_Null_ThrowsArgumentNullExceptionWithArgumentName()
-        {
-            Assert.Throws<ArgumentNullException>("platformName", () => RuntimeInformation.IsOSPlatformOrLater(null));
-        }
-
-        [Fact]
-        public void IsOSPlatformOrLater_Empty_ThrowsArgumentNullExceptionWithArgumentName()
-        {
-            Assert.Throws<ArgumentException>("platformName", () => RuntimeInformation.IsOSPlatformOrLater(string.Empty));
-        }
-
-        [Theory]
-        [InlineData("ios")] // missing version number
-        [InlineData("ios14")] // ios14.0 is fine, ios14 is not: https://github.com/dotnet/runtime/pull/39005#discussion_r452541491
-        [InlineData("ios14.0.0.0.0.0")] // too many numbers
-        [InlineData("ios14.0.")] // version should not end with dot (but OS name could potentially end with dot, imagine "NET.")
-        [InlineData("numbers1.2inplatformname1.2")] // numbers in platform names are not supported https://github.com/dotnet/runtime/pull/39005#discussion_r452644601
-        public void IsOSPlatformOrLater_InvalidVersionNumber_ThrowsArgumentExceptionWithArgumentName(string platformName)
-        {
-            Assert.Throws<ArgumentException>("platformName", () => RuntimeInformation.IsOSPlatformOrLater(platformName));
-        }
-
-        [Theory]
-        [MemberData(nameof(AllKnownOsPlatforms))]
-        public void IsOSPlatformOrLater_ReturnsTrue_ForCurrentOS(OSPlatform osPlatform)
-        {
-            // IsOSPlatformOrLater("xyz1.2.3.4") running as "xyz1.2.3.4" should return true
-
-            bool isCurrentPlatfom = RuntimeInformation.IsOSPlatform(osPlatform);
-            Version current = Environment.OSVersion.Version;
-
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater($"{osPlatform}{current}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater($"{osPlatform.ToString().ToLower()}{current}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater($"{osPlatform.ToString().ToUpper()}{current}"));
-
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater(osPlatform, current.Major));
-
-            if (current.Minor >= 0)
-            {
-                Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater(osPlatform, current.Major, current.Minor));
-
-                if (current.Build >= 0)
-                {
-                    Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater(osPlatform, current.Major, current.Minor, current.Build));
-
-                    if (current.Revision >= 0)
-                    {
-                        Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater(osPlatform, current.Major, current.Minor, current.Build, current.Revision));
-                    }
-                }
-            }
-        }
-
-        [Theory]
-        [MemberData(nameof(AllKnownOsPlatforms))]
-        public void IsOSPlatformOrLater_ReturnsFalse_ForNewerVersionOfCurrentOS(OSPlatform osPlatform)
-        {
-            // IsOSPlatformOrLater("xyz11.0") running as "xyz10.0" should return false
-
-            Version currentVersion = Environment.OSVersion.Version;
-
-            Version newer = new Version(currentVersion.Major + 1, 0);
-            Assert.False(RuntimeInformation.IsOSPlatformOrLater($"{osPlatform}{newer}"));
-            Assert.False(RuntimeInformation.IsOSPlatformOrLater($"{osPlatform.ToString().ToLower()}{newer}"));
-            Assert.False(RuntimeInformation.IsOSPlatformOrLater($"{osPlatform.ToString().ToUpper()}{newer}"));
-            Assert.False(RuntimeInformation.IsOSPlatformOrLater(osPlatform, newer.Major));
-
-            newer = new Version(currentVersion.Major, currentVersion.Minor + 1);
-            Assert.False(RuntimeInformation.IsOSPlatformOrLater($"{osPlatform}{newer}"));
-            Assert.False(RuntimeInformation.IsOSPlatformOrLater(osPlatform, newer.Major, newer.Minor));
-
-            newer = new Version(currentVersion.Major, currentVersion.Minor, currentVersion.Build + 1);
-            Assert.False(RuntimeInformation.IsOSPlatformOrLater($"{osPlatform}{newer}"));
-            Assert.False(RuntimeInformation.IsOSPlatformOrLater(osPlatform, newer.Major, newer.Minor, newer.Build));
-
-            newer = new Version(currentVersion.Major, currentVersion.Minor, currentVersion.Build, currentVersion.Revision + 1);
-            Assert.False(RuntimeInformation.IsOSPlatformOrLater($"{osPlatform}{newer}"));
-            Assert.False(RuntimeInformation.IsOSPlatformOrLater(osPlatform, newer.Major, newer.Minor, newer.Build, newer.Revision));
-        }
-
-        [Theory]
-        [MemberData(nameof(AllKnownOsPlatforms))]
-        public void IsOSPlatformOrLater_ReturnsTrue_ForOlderVersionOfCurrentOS(OSPlatform osPlatform)
-        {
-            // IsOSPlatformOrLater("xyz10.0") running as "xyz11.0" should return true
-
-            bool isCurrentPlatfom = RuntimeInformation.IsOSPlatform(osPlatform);
-            Version current = Environment.OSVersion.Version;
-
-            Version older = new Version(current.Major - 1, 0);
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater($"{osPlatform}{older}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater($"{osPlatform.ToString().ToLower()}{older}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater($"{osPlatform.ToString().ToUpper()}{older}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater(osPlatform, older.Major));
-
-            if (current.Minor > 0)
-            {
-                older = new Version(current.Major, current.Minor - 1);
-                Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater($"{osPlatform}{older}"));
-                Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater(osPlatform, older.Major, older.Minor));
-            }
-
-            if (current.Build > 0)
-            {
-                older = new Version(current.Major, current.Minor, current.Build - 1);
-                Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater($"{osPlatform}{older}"));
-                Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater(osPlatform, older.Major, older.Minor, older.Build));
-            }
-
-            if (current.Revision > 0)
-            {
-                older = new Version(current.Major, current.Minor, current.Build, current.Revision - 1);
-                Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater($"{osPlatform}{older}"));
-                Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformOrLater(osPlatform, older.Major, older.Minor, older.Build, older.Revision));
-            }
-        }
-
-        [Fact]
-        public void IsOSPlatformEarlierThan_Null_ThrowsArgumentNullExceptionWithArgumentName()
-        {
-            Assert.Throws<ArgumentNullException>("platformName", () => RuntimeInformation.IsOSPlatformEarlierThan(null));
-        }
-
-        [Fact]
-        public void IsOSPlatformEarlierThan_Empty_ThrowsArgumentNullExceptionWithArgumentName()
-        {
-            Assert.Throws<ArgumentException>("platformName", () => RuntimeInformation.IsOSPlatformEarlierThan(string.Empty));
-        }
-
-        [Theory]
-        [InlineData("ios")] // missing version number
-        [InlineData("ios14")] // ios14.0 is fine, ios14 is not: https://github.com/dotnet/runtime/pull/39005#discussion_r452541491
-        [InlineData("ios14.0.0.0.0.0")] // too many numbers
-        [InlineData("ios14.0.")] // version should not end with dot (but OS name could potentially end with dot, imagine "NET.")
-        [InlineData("numbers1.2inplatformname1.2")] // numbers in platform names are not supported https://github.com/dotnet/runtime/pull/39005#discussion_r452644601
-        public void IsOSPlatformEarlierThan_InvalidVersionNumber_ThrowsArgumentExceptionWithArgumentName(string platformName)
-        {
-            Assert.Throws<ArgumentException>("platformName", () => RuntimeInformation.IsOSPlatformEarlierThan(platformName));
-        }
-
-        [Theory]
-        [MemberData(nameof(AllKnownOsPlatforms))]
-        public void IsOSPlatformEarlierThan_ReturnsFalse_ForCurrentOS(OSPlatform osPlatform)
-        {
-            // IsOSPlatformEarlierThan("xyz1.2.3.4") running as "xyz1.2.3.4" should return false
-
-            Version current = Environment.OSVersion.Version;
-
-            Assert.False(RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform}{current}"));
-            Assert.False(RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform.ToString().ToLower()}{current}"));
-            Assert.False(RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform.ToString().ToUpper()}{current}"));
-
-            Assert.False(RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, current.Major));
-
-            if (current.Minor >= 0)
-            {
-                Assert.False(RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, current.Major, current.Minor));
-
-                if (current.Build >= 0)
-                {
-                    Assert.False(RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, current.Major, current.Minor, current.Build));
-
-                    if (current.Revision >= 0)
-                    {
-                        Assert.False(RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, current.Major, current.Minor, current.Build, current.Revision));
-                    }
-                }
-            }
-        }
-
-        [Theory]
-        [MemberData(nameof(AllKnownOsPlatforms))]
-        public void IsOSPlatformEarlierThan_ReturnsTrue_ForNewerVersionOfCurrentOS(OSPlatform osPlatform)
-        {
-            // IsOSPlatformEarlierThan("xyz11.0") running as "xyz10.0" should return true
-
-            bool isCurrentPlatfom = RuntimeInformation.IsOSPlatform(osPlatform);
-            Version current = Environment.OSVersion.Version;
-
-            Version newer = new Version(current.Major + 1, 0);
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform}{newer}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform.ToString().ToLower()}{newer}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform.ToString().ToUpper()}{newer}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, newer.Major));
-
-            newer = new Version(current.Major, current.Minor + 1);
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform}{newer}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, newer.Major, newer.Minor));
-
-            newer = new Version(current.Major, current.Minor, current.Build + 1);
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform}{newer}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, newer.Major, newer.Minor, newer.Build));
-
-            newer = new Version(current.Major, current.Minor, current.Build, current.Revision + 1);
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform}{newer}"));
-            Assert.Equal(isCurrentPlatfom, RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, newer.Major, newer.Minor, newer.Build, newer.Revision));
-        }
-
-        [Theory]
-        [MemberData(nameof(AllKnownOsPlatforms))]
-        public void IsOSPlatformEarlierThan_ReturnsFalse_ForOlderVersionOfCurrentOS(OSPlatform osPlatform)
-        {
-            // IsOSPlatformEarlierThan("xyz10.0") running as "xyz11.0" should return false
-
-            Version current = Environment.OSVersion.Version;
-
-            Version older = new Version(current.Major - 1, 0);
-            Assert.False(RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform}{older}"));
-            Assert.False(RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform.ToString().ToLower()}{older}"));
-            Assert.False(RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform.ToString().ToUpper()}{older}"));
-            Assert.False(RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, older.Major));
-
-            if (current.Minor > 0)
-            {
-                older = new Version(current.Major, current.Minor - 1);
-                Assert.False(RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform}{older}"));
-                Assert.False(RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, older.Major, older.Minor));
-            }
-
-            if (current.Build > 0)
-            {
-                older = new Version(current.Major, current.Minor, current.Build - 1);
-                Assert.False(RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform}{older}"));
-                Assert.False(RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, older.Major, older.Minor, older.Build));
-            }
-
-            if (current.Revision > 0)
-            {
-                older = new Version(current.Major, current.Minor, current.Build, current.Revision - 1);
-                Assert.False(RuntimeInformation.IsOSPlatformEarlierThan($"{osPlatform}{older}"));
-                Assert.False(RuntimeInformation.IsOSPlatformEarlierThan(osPlatform, older.Major, older.Minor, older.Build, older.Revision));
-            }
-        }
-    }
-}
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/RuntimeIdentifierTests.cs b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/RuntimeIdentifierTests.cs
index 6747714a6279cd..d25b747b15fb8b 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/RuntimeIdentifierTests.cs
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/RuntimeIdentifierTests.cs
@@ -11,7 +11,6 @@ namespace System.Runtime.InteropServices.RuntimeInformationTests
     public class RuntimeIdentifierTests
     {
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/39074", TestPlatforms.Browser)]
         public void VerifyOSRid()
         {
             Assert.NotNull(RuntimeInformation.RuntimeIdentifier);
diff --git a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/System.Runtime.InteropServices.RuntimeInformation.Tests.csproj b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/System.Runtime.InteropServices.RuntimeInformation.Tests.csproj
index e3745518d39eff..de6d696e095a8f 100644
--- a/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/System.Runtime.InteropServices.RuntimeInformation.Tests.csproj
+++ b/src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/System.Runtime.InteropServices.RuntimeInformation.Tests.csproj
@@ -8,7 +8,6 @@
     <Compile Include="CheckPlatformTests.cs" />
     <Compile Include="RuntimeIdentifierTests.cs" />
     <Compile Include="DescriptionNameTests.cs" />
-    <Compile Include="PlatformVersionTests.cs" />
     <Compile Include="$(CommonPath)Interop\Linux\cgroups\Interop.cgroups.cs"
              Link="Common\Interop\Linux\Interop.cgroups.cs" />
   </ItemGroup>
diff --git a/src/libraries/System.Runtime.InteropServices/Directory.Build.props b/src/libraries/System.Runtime.InteropServices/Directory.Build.props
index 42c6eafce67ed8..d68d22c1b917f8 100644
--- a/src/libraries/System.Runtime.InteropServices/Directory.Build.props
+++ b/src/libraries/System.Runtime.InteropServices/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
index 62a71240547237..7bc7065a9f01f5 100644
--- a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
+++ b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
@@ -91,6 +91,7 @@ public IUnknownConstantAttribute() { }
 }
 namespace System.Runtime.InteropServices
 {
+    [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
     [System.AttributeUsageAttribute(System.AttributeTargets.Method, AllowMultiple=false, Inherited=false)]
     public sealed partial class AllowReversePInvokeCallsAttribute : System.Attribute
     {
@@ -316,7 +317,7 @@ public DefaultParameterValueAttribute(object? value) { }
     public sealed partial class DispatchWrapper
     {
         public DispatchWrapper(object? obj) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public object? WrappedObject { get { throw null; } }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Event | System.AttributeTargets.Field | System.AttributeTargets.Method | System.AttributeTargets.Property, Inherited=false)]
@@ -462,15 +463,15 @@ public static partial class Marshal
     {
         public static readonly int SystemDefaultCharSize;
         public static readonly int SystemMaxDBCSCharSize;
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static int AddRef(System.IntPtr pUnk) { throw null; }
         public static System.IntPtr AllocCoTaskMem(int cb) { throw null; }
         public static System.IntPtr AllocHGlobal(int cb) { throw null; }
         public static System.IntPtr AllocHGlobal(System.IntPtr cb) { throw null; }
         public static bool AreComObjectsAvailableForCleanup() { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static object BindToMoniker(string monikerName) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static void ChangeWrapperHandleStrength(object otp, bool fIsWeak) { }
         public static void CleanupUnusedObjectsInCurrentContext() { }
         public static void Copy(byte[] source, int startIndex, System.IntPtr destination, int length) { }
@@ -489,40 +490,41 @@ public static void Copy(System.IntPtr source, System.IntPtr[] destination, int s
         public static void Copy(System.IntPtr source, float[] destination, int startIndex, int length) { }
         public static void Copy(System.IntPtr[] source, int startIndex, System.IntPtr destination, int length) { }
         public static void Copy(float[] source, int startIndex, System.IntPtr destination, int length) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static System.IntPtr CreateAggregatedObject(System.IntPtr pOuter, object o) { throw null; }
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.IntPtr CreateAggregatedObject<T>(System.IntPtr pOuter, T o) where T : notnull { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("o")]
         public static object? CreateWrapperOfType(object? o, System.Type t) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
-        public static TWrapper CreateWrapperOfType<T, TWrapper>([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T o) { throw null; }
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
+        public static TWrapper CreateWrapperOfType<T, TWrapper>(T? o) { throw null; }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static void DestroyStructure(System.IntPtr ptr, System.Type structuretype) { }
         public static void DestroyStructure<T>(System.IntPtr ptr) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static int FinalReleaseComObject(object o) { throw null; }
         public static void FreeBSTR(System.IntPtr ptr) { }
         public static void FreeCoTaskMem(System.IntPtr ptr) { }
         public static void FreeHGlobal(System.IntPtr hglobal) { }
         public static System.Guid GenerateGuidForType(System.Type type) { throw null; }
         public static string? GenerateProgIdForType(System.Type type) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static System.IntPtr GetComInterfaceForObject(object o, System.Type T) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static System.IntPtr GetComInterfaceForObject(object o, System.Type T, System.Runtime.InteropServices.CustomQueryInterfaceMode mode) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.IntPtr GetComInterfaceForObject<T, TInterface>([System.Diagnostics.CodeAnalysis.DisallowNullAttribute] T o) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static object? GetComObjectData(object obj, object key) { throw null; }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static System.Delegate GetDelegateForFunctionPointer(System.IntPtr ptr, System.Type t) { throw null; }
         public static TDelegate GetDelegateForFunctionPointer<TDelegate>(System.IntPtr ptr) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static int GetEndComSlot(System.Type t) { throw null; }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         [System.ObsoleteAttribute("GetExceptionCode() may be unavailable in future releases.")]
@@ -536,41 +538,40 @@ public static void FreeHGlobal(System.IntPtr hglobal) { }
         public static System.IntPtr GetHINSTANCE(System.Reflection.Module m) { throw null; }
         public static int GetHRForException(System.Exception? e) { throw null; }
         public static int GetHRForLastWin32Error() { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.IntPtr GetIDispatchForObject(object o) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.IntPtr GetIUnknownForObject(object o) { throw null; }
         public static int GetLastWin32Error() { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static void GetNativeVariantForObject(object? obj, System.IntPtr pDstNativeVariant) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
-        public static void GetNativeVariantForObject<T>([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T obj, System.IntPtr pDstNativeVariant) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        public static void GetNativeVariantForObject<T>(T? obj, System.IntPtr pDstNativeVariant) { }
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static object GetObjectForIUnknown(System.IntPtr pUnk) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static object? GetObjectForNativeVariant(System.IntPtr pSrcNativeVariant) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T GetObjectForNativeVariant<T>(System.IntPtr pSrcNativeVariant) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        public static T? GetObjectForNativeVariant<T>(System.IntPtr pSrcNativeVariant) { throw null; }
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static object?[] GetObjectsForNativeVariants(System.IntPtr aSrcNativeVariant, int cVars) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static T[] GetObjectsForNativeVariants<T>(System.IntPtr aSrcNativeVariant, int cVars) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static int GetStartComSlot(System.Type t) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static object GetTypedObjectForIUnknown(System.IntPtr pUnk, System.Type t) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.Type GetTypeFromCLSID(System.Guid clsid) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static string GetTypeInfoName(System.Runtime.InteropServices.ComTypes.ITypeInfo typeInfo) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static object GetUniqueObjectForIUnknown(System.IntPtr unknown) { throw null; }
         public static bool IsComObject(object o) { throw null; }
         public static bool IsTypeVisibleFromCom(System.Type t) { throw null; }
@@ -592,10 +593,9 @@ public static void PrelinkAll(System.Type c) { }
         public static void PtrToStructure(System.IntPtr ptr, object structure) { }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static object? PtrToStructure(System.IntPtr ptr, System.Type structureType) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T PtrToStructure<T>(System.IntPtr ptr) { throw null; }
+        public static T? PtrToStructure<T>(System.IntPtr ptr) { throw null; }
         public static void PtrToStructure<T>(System.IntPtr ptr, [System.Diagnostics.CodeAnalysis.DisallowNullAttribute] T structure) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static int QueryInterface(System.IntPtr pUnk, ref System.Guid iid, out System.IntPtr ppv) { throw null; }
         public static byte ReadByte(System.IntPtr ptr) { throw null; }
         public static byte ReadByte(System.IntPtr ptr, int ofs) { throw null; }
@@ -624,16 +624,16 @@ public static void PtrToStructure<T>(System.IntPtr ptr, [System.Diagnostics.Code
         public static System.IntPtr ReadIntPtr(object ptr, int ofs) { throw null; }
         public static System.IntPtr ReAllocCoTaskMem(System.IntPtr pv, int cb) { throw null; }
         public static System.IntPtr ReAllocHGlobal(System.IntPtr pv, System.IntPtr cb) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static int Release(System.IntPtr pUnk) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static int ReleaseComObject(object o) { throw null; }
         public static System.IntPtr SecureStringToBSTR(System.Security.SecureString s) { throw null; }
         public static System.IntPtr SecureStringToCoTaskMemAnsi(System.Security.SecureString s) { throw null; }
         public static System.IntPtr SecureStringToCoTaskMemUnicode(System.Security.SecureString s) { throw null; }
         public static System.IntPtr SecureStringToGlobalAllocAnsi(System.Security.SecureString s) { throw null; }
         public static System.IntPtr SecureStringToGlobalAllocUnicode(System.Security.SecureString s) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static bool SetComObjectData(object obj, object key, object? data) { throw null; }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public static int SizeOf(object structure) { throw null; }
@@ -1030,7 +1030,7 @@ public struct ComInterfaceEntry
         public struct ComInterfaceDispatch
         {
             public System.IntPtr Vtable;
-            public static unsafe T GetInstance<T>(ComInterfaceDispatch* dispatchPtr) where T : class { throw null; }
+            public unsafe static T GetInstance<T>(ComInterfaceDispatch* dispatchPtr) where T : class { throw null; }
         }
         public System.IntPtr GetOrCreateComInterfaceForObject(object instance, CreateComInterfaceFlags flags) { throw null; }
         protected unsafe abstract ComInterfaceEntry* ComputeVtables(object obj, CreateComInterfaceFlags flags, out int count);
diff --git a/src/libraries/System.Runtime.InteropServices/src/System.Runtime.InteropServices.csproj b/src/libraries/System.Runtime.InteropServices/src/System.Runtime.InteropServices.csproj
index 213c5439847de2..d1eeee845aa258 100644
--- a/src/libraries/System.Runtime.InteropServices/src/System.Runtime.InteropServices.csproj
+++ b/src/libraries/System.Runtime.InteropServices/src/System.Runtime.InteropServices.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime.InteropServices</AssemblyName>
-    <OutputType>Library</OutputType>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <Nullable>enable</Nullable>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.Tests.csproj b/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.Tests.csproj
index 1e6ec37d556191..a4dab3d3151a35 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.Tests.csproj
+++ b/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.Tests.csproj
@@ -8,7 +8,6 @@
     <Compile Include="AssemblyInfo.cs" />
     <Compile Include="System\DllNotFoundExceptionTests.cs" />
     <Compile Include="System\Runtime\CompilerServices\IUnknownConstantAttributeTests.cs" />
-    <Compile Include="System\Runtime\InteropServices\AllowReversePInvokeCallsAttributeTests.cs" />
     <Compile Include="System\Runtime\InteropServices\ArrayWithOffsetTests.cs" />
     <Compile Include="System\Runtime\InteropServices\BestFitMappingAttributeTests.cs" />
     <Compile Include="System\Runtime\InteropServices\BStrWrapperTests.cs" />
diff --git a/src/libraries/System.Runtime.InteropServices/tests/System/Runtime/InteropServices/AllowReversePInvokeCallsAttributeTests.cs b/src/libraries/System.Runtime.InteropServices/tests/System/Runtime/InteropServices/AllowReversePInvokeCallsAttributeTests.cs
deleted file mode 100644
index e2a9f2ecdca386..00000000000000
--- a/src/libraries/System.Runtime.InteropServices/tests/System/Runtime/InteropServices/AllowReversePInvokeCallsAttributeTests.cs
+++ /dev/null
@@ -1,24 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Linq;
-using System.Reflection;
-using Xunit;
-
-namespace System.Runtime.InteropServices.Tests
-{
-    public class AllowReversePInvokeCallsAttributeTests
-    {
-        [AllowReversePInvokeCalls]
-        private int Func(int a, int b) => a + b;
-
-        [Fact]
-        public void Exists()
-        {
-            Type type = typeof(AllowReversePInvokeCallsAttributeTests);
-            MethodInfo method = type.GetTypeInfo().DeclaredMethods.Single(m => m.Name == "Func");
-            AllowReversePInvokeCallsAttribute attribute = Assert.Single(method.GetCustomAttributes< AllowReversePInvokeCallsAttribute>(inherit: false));
-            Assert.NotNull(attribute);
-        }
-    }
-}
diff --git a/src/libraries/System.Runtime.Intrinsics/Directory.Build.props b/src/libraries/System.Runtime.Intrinsics/Directory.Build.props
index 9f52a8a305052e..ba1f965d83cae7 100644
--- a/src/libraries/System.Runtime.Intrinsics/Directory.Build.props
+++ b/src/libraries/System.Runtime.Intrinsics/Directory.Build.props
@@ -1,7 +1,6 @@
 <Project>
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <StrongNameKeyId>Open</StrongNameKeyId>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Runtime.Intrinsics/ref/System.Runtime.Intrinsics.cs b/src/libraries/System.Runtime.Intrinsics/ref/System.Runtime.Intrinsics.cs
index 4fc9a2dab9e89b..fbb78cb5533feb 100644
--- a/src/libraries/System.Runtime.Intrinsics/ref/System.Runtime.Intrinsics.cs
+++ b/src/libraries/System.Runtime.Intrinsics/ref/System.Runtime.Intrinsics.cs
@@ -3367,10 +3367,10 @@ internal X64() { }
         }
     }
     [System.CLSCompliantAttribute(false)]
-    public abstract partial class Bmi1
+    public abstract partial class Bmi1 : System.Runtime.Intrinsics.X86.X86Base
     {
         internal Bmi1() { }
-        public static bool IsSupported { get { throw null; } }
+        public static new bool IsSupported { get { throw null; } }
         public static uint AndNot(uint left, uint right) { throw null; }
         public static uint BitFieldExtract(uint value, byte start, byte length) { throw null; }
         public static uint BitFieldExtract(uint value, ushort control) { throw null; }
@@ -3378,10 +3378,10 @@ internal Bmi1() { }
         public static uint GetMaskUpToLowestSetBit(uint value) { throw null; }
         public static uint ResetLowestSetBit(uint value) { throw null; }
         public static uint TrailingZeroCount(uint value) { throw null; }
-        public abstract partial class X64
+        public new abstract partial class X64 : System.Runtime.Intrinsics.X86.X86Base.X64
         {
             internal X64() { }
-            public static bool IsSupported { get { throw null; } }
+            public static new bool IsSupported { get { throw null; } }
             public static ulong AndNot(ulong left, ulong right) { throw null; }
             public static ulong BitFieldExtract(ulong value, byte start, byte length) { throw null; }
             public static ulong BitFieldExtract(ulong value, ushort control) { throw null; }
@@ -3392,19 +3392,19 @@ internal X64() { }
         }
     }
     [System.CLSCompliantAttribute(false)]
-    public abstract partial class Bmi2
+    public abstract partial class Bmi2 : System.Runtime.Intrinsics.X86.X86Base
     {
         internal Bmi2() { }
-        public static bool IsSupported { get { throw null; } }
+        public static new bool IsSupported { get { throw null; } }
         public static uint MultiplyNoFlags(uint left, uint right) { throw null; }
         public unsafe static uint MultiplyNoFlags(uint left, uint right, uint* low) { throw null; }
         public static uint ParallelBitDeposit(uint value, uint mask) { throw null; }
         public static uint ParallelBitExtract(uint value, uint mask) { throw null; }
         public static uint ZeroHighBits(uint value, uint index) { throw null; }
-        public abstract partial class X64
+        public new abstract partial class X64 : System.Runtime.Intrinsics.X86.X86Base.X64
         {
             internal X64() { }
-            public static bool IsSupported { get { throw null; } }
+            public static new bool IsSupported { get { throw null; } }
             public static ulong MultiplyNoFlags(ulong left, ulong right) { throw null; }
             public unsafe static ulong MultiplyNoFlags(ulong left, ulong right, ulong* low) { throw null; }
             public static ulong ParallelBitDeposit(ulong value, ulong mask) { throw null; }
@@ -3491,15 +3491,15 @@ internal X64() { }
         }
     }
     [System.CLSCompliantAttribute(false)]
-    public abstract partial class Lzcnt
+    public abstract partial class Lzcnt : System.Runtime.Intrinsics.X86.X86Base
     {
         internal Lzcnt() { }
-        public static bool IsSupported { get { throw null; } }
+        public static new bool IsSupported { get { throw null; } }
         public static uint LeadingZeroCount(uint value) { throw null; }
-        public abstract partial class X64
+        public new abstract partial class X64 : System.Runtime.Intrinsics.X86.X86Base.X64
         {
             internal X64() { }
-            public static bool IsSupported { get { throw null; } }
+            public static new bool IsSupported { get { throw null; } }
             public static ulong LeadingZeroCount(ulong value) { throw null; }
         }
     }
@@ -3530,10 +3530,10 @@ internal X64() { }
         }
     }
     [System.CLSCompliantAttribute(false)]
-    public abstract partial class Sse
+    public abstract partial class Sse : System.Runtime.Intrinsics.X86.X86Base
     {
         internal Sse() { }
-        public static bool IsSupported { get { throw null; } }
+        public static new bool IsSupported { get { throw null; } }
         public static System.Runtime.Intrinsics.Vector128<float> Add(System.Runtime.Intrinsics.Vector128<float> left, System.Runtime.Intrinsics.Vector128<float> right) { throw null; }
         public static System.Runtime.Intrinsics.Vector128<float> AddScalar(System.Runtime.Intrinsics.Vector128<float> left, System.Runtime.Intrinsics.Vector128<float> right) { throw null; }
         public static System.Runtime.Intrinsics.Vector128<float> And(System.Runtime.Intrinsics.Vector128<float> left, System.Runtime.Intrinsics.Vector128<float> right) { throw null; }
@@ -3621,10 +3621,10 @@ public unsafe static void StoreScalar(float* address, System.Runtime.Intrinsics.
         public static System.Runtime.Intrinsics.Vector128<float> UnpackHigh(System.Runtime.Intrinsics.Vector128<float> left, System.Runtime.Intrinsics.Vector128<float> right) { throw null; }
         public static System.Runtime.Intrinsics.Vector128<float> UnpackLow(System.Runtime.Intrinsics.Vector128<float> left, System.Runtime.Intrinsics.Vector128<float> right) { throw null; }
         public static System.Runtime.Intrinsics.Vector128<float> Xor(System.Runtime.Intrinsics.Vector128<float> left, System.Runtime.Intrinsics.Vector128<float> right) { throw null; }
-        public abstract partial class X64
+        public new abstract partial class X64 : System.Runtime.Intrinsics.X86.X86Base.X64
         {
             internal X64() { }
-            public static bool IsSupported { get { throw null; } }
+            public static new bool IsSupported { get { throw null; } }
             public static System.Runtime.Intrinsics.Vector128<float> ConvertScalarToVector128Single(System.Runtime.Intrinsics.Vector128<float> upper, long value) { throw null; }
             public static long ConvertToInt64(System.Runtime.Intrinsics.Vector128<float> value) { throw null; }
             public static long ConvertToInt64WithTruncation(System.Runtime.Intrinsics.Vector128<float> value) { throw null; }
@@ -4183,4 +4183,16 @@ internal X64() { }
             public static new bool IsSupported { get { throw null; } }
         }
     }
+    [System.CLSCompliantAttribute(false)]
+    public abstract partial class X86Base
+    {
+        internal X86Base() { }
+        public static bool IsSupported { get { throw null; } }
+        public static (int Eax, int Ebx, int Ecx, int Edx) CpuId(int functionId, int subFunctionId) { throw null; }
+        public abstract partial class X64
+        {
+            internal X64() { }
+            public static bool IsSupported { get { throw null; } }
+        }
+    }
 }
diff --git a/src/libraries/System.Runtime.Loader/Directory.Build.props b/src/libraries/System.Runtime.Loader/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Runtime.Loader/Directory.Build.props
+++ b/src/libraries/System.Runtime.Loader/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Runtime.Loader/ref/System.Runtime.Loader.cs b/src/libraries/System.Runtime.Loader/ref/System.Runtime.Loader.cs
index 99d71fc96e42e4..a942f9030c0d63 100644
--- a/src/libraries/System.Runtime.Loader/ref/System.Runtime.Loader.cs
+++ b/src/libraries/System.Runtime.Loader/ref/System.Runtime.Loader.cs
@@ -9,7 +9,7 @@ namespace System.Reflection.Metadata
     public static partial class AssemblyExtensions
     {
         [System.CLSCompliantAttribute(false)]
-        public static unsafe bool TryGetRawMetadata(this System.Reflection.Assembly assembly, out byte* blob, out int length) { throw null; }
+        public unsafe static bool TryGetRawMetadata(this System.Reflection.Assembly assembly, out byte* blob, out int length) { throw null; }
     }
 }
 namespace System.Runtime.Loader
@@ -41,9 +41,13 @@ public event System.Action<System.Runtime.Loader.AssemblyLoadContext>? Unloading
         public static System.Runtime.Loader.AssemblyLoadContext? GetLoadContext(System.Reflection.Assembly assembly) { throw null; }
         protected virtual System.Reflection.Assembly? Load(System.Reflection.AssemblyName assemblyName) { throw null; }
         public System.Reflection.Assembly LoadFromAssemblyName(System.Reflection.AssemblyName assemblyName) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types and members the loaded assembly depends on might be removed")]
         public System.Reflection.Assembly LoadFromAssemblyPath(string assemblyPath) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types and members the loaded assembly depends on might be removed")]
         public System.Reflection.Assembly LoadFromNativeImagePath(string nativeImagePath, string? assemblyPath) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types and members the loaded assembly depends on might be removed")]
         public System.Reflection.Assembly LoadFromStream(System.IO.Stream assembly) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types and members the loaded assembly depends on might be removed")]
         public System.Reflection.Assembly LoadFromStream(System.IO.Stream assembly, System.IO.Stream? assemblySymbols) { throw null; }
         protected virtual System.IntPtr LoadUnmanagedDll(string unmanagedDllName) { throw null; }
         protected System.IntPtr LoadUnmanagedDllFromPath(string unmanagedDllPath) { throw null; }
diff --git a/src/libraries/System.Runtime.Loader/src/System.Runtime.Loader.csproj b/src/libraries/System.Runtime.Loader/src/System.Runtime.Loader.csproj
index 2697388749b060..dd3dc2940a54b1 100644
--- a/src/libraries/System.Runtime.Loader/src/System.Runtime.Loader.csproj
+++ b/src/libraries/System.Runtime.Loader/src/System.Runtime.Loader.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime.Loader</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Runtime.Loader/tests/AssemblyLoadContextTest.cs b/src/libraries/System.Runtime.Loader/tests/AssemblyLoadContextTest.cs
index 290cb3ca06b3da..3979d76aeadb74 100644
--- a/src/libraries/System.Runtime.Loader/tests/AssemblyLoadContextTest.cs
+++ b/src/libraries/System.Runtime.Loader/tests/AssemblyLoadContextTest.cs
@@ -18,7 +18,6 @@ public partial class AssemblyLoadContextTest
         private const string TestAssemblyNotSupported = "System.Runtime.Loader.Test.AssemblyNotSupported";
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/39379", TestPlatforms.Browser)]
         public static void GetAssemblyNameTest_ValidAssembly()
         {
             var expectedName = typeof(AssemblyLoadContextTest).Assembly.GetName();
diff --git a/src/libraries/System.Runtime.Loader/tests/DefaultContext/System.Runtime.Loader.DefaultContext.Tests.csproj b/src/libraries/System.Runtime.Loader/tests/DefaultContext/System.Runtime.Loader.DefaultContext.Tests.csproj
index 17348b2b70e926..861551441fc2ff 100644
--- a/src/libraries/System.Runtime.Loader/tests/DefaultContext/System.Runtime.Loader.DefaultContext.Tests.csproj
+++ b/src/libraries/System.Runtime.Loader/tests/DefaultContext/System.Runtime.Loader.DefaultContext.Tests.csproj
@@ -9,11 +9,10 @@
     <Compile Include="DefaultLoadContextTest.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="../System.Runtime.Loader.Noop.Assembly/System.Runtime.Loader.Noop.Assembly.csproj">
-      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
-      <OutputItemType>content</OutputItemType>
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-    </ProjectReference>
+    <ProjectReference Include="../System.Runtime.Loader.Noop.Assembly/System.Runtime.Loader.Noop.Assembly.csproj"
+                      ReferenceOutputAssembly="false"
+                      OutputItemType="content"
+                      CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>
   <Target Name="RenameTestAssembly" AfterTargets="PrepareForRun">
     <Move SourceFiles="$(OutDir)System.Runtime.Loader.Noop.Assembly.dll" DestinationFiles="$(OutDir)System.Runtime.Loader.Noop.Assembly_test.dll" />
diff --git a/src/libraries/System.Runtime.Loader/tests/RefEmitLoadContext/System.Runtime.Loader.RefEmitLoadContext.Tests.csproj b/src/libraries/System.Runtime.Loader/tests/RefEmitLoadContext/System.Runtime.Loader.RefEmitLoadContext.Tests.csproj
index 5fe8fb3bc7b480..f1580207d39c13 100644
--- a/src/libraries/System.Runtime.Loader/tests/RefEmitLoadContext/System.Runtime.Loader.RefEmitLoadContext.Tests.csproj
+++ b/src/libraries/System.Runtime.Loader/tests/RefEmitLoadContext/System.Runtime.Loader.RefEmitLoadContext.Tests.csproj
@@ -7,10 +7,9 @@
     <Compile Include="RefEmitLoadContextTest.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="../System.Runtime.Loader.Noop.Assembly/System.Runtime.Loader.Noop.Assembly.csproj">
-      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
-      <OutputItemType>content</OutputItemType>
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-    </ProjectReference>
+    <ProjectReference Include="../System.Runtime.Loader.Noop.Assembly/System.Runtime.Loader.Noop.Assembly.csproj"
+                      ReferenceOutputAssembly="false"
+                      OutputItemType="content"
+                      CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Loader/tests/SatelliteAssemblies.cs b/src/libraries/System.Runtime.Loader/tests/SatelliteAssemblies.cs
index 658d1f42a12870..7851469527bced 100644
--- a/src/libraries/System.Runtime.Loader/tests/SatelliteAssemblies.cs
+++ b/src/libraries/System.Runtime.Loader/tests/SatelliteAssemblies.cs
@@ -18,15 +18,15 @@ public class SatelliteAssembliesTestsFixture
         public SatelliteAssembliesTestsFixture()
         {
             AssemblyLoadContext satelliteAssembliesTests = new AssemblyLoadContext("SatelliteAssembliesTests");
-            var satelliteAssembliesTestsPath = (PlatformDetection.IsBrowser ? "/" : "") + typeof(SatelliteAssembliesTests).Assembly.Location;
+            var satelliteAssembliesTestsPath = AssemblyPathHelper.GetAssemblyLocation(typeof(SatelliteAssembliesTests).Assembly);
             satelliteAssembliesTests.LoadFromAssemblyPath(satelliteAssembliesTestsPath);
 
             AssemblyLoadContext referencedClassLib = new AssemblyLoadContext("ReferencedClassLib");
-            var referencedClassLibPath = (PlatformDetection.IsBrowser ? "/" : "") + typeof(ReferencedClassLib.Program).Assembly.Location;
+            var referencedClassLibPath = AssemblyPathHelper.GetAssemblyLocation(typeof(ReferencedClassLib.Program).Assembly);
             referencedClassLib.LoadFromAssemblyPath(referencedClassLibPath);
 
             AssemblyLoadContext referencedClassLibNeutralIsSatellite = new AssemblyLoadContext("ReferencedClassLibNeutralIsSatellite");
-            var referencedClassLibNeutralIsSatellitePath = (PlatformDetection.IsBrowser ? "/" : "") + typeof(ReferencedClassLibNeutralIsSatellite.Program).Assembly.Location;
+            var referencedClassLibNeutralIsSatellitePath = AssemblyPathHelper.GetAssemblyLocation(typeof(ReferencedClassLibNeutralIsSatellite.Program).Assembly);
             referencedClassLibNeutralIsSatellite.LoadFromAssemblyPath(referencedClassLibNeutralIsSatellitePath);
 
             new AssemblyLoadContext("Empty");
diff --git a/src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj b/src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj
index c595a1ca1a9428..f43714d9365d9a 100644
--- a/src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj
+++ b/src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj
@@ -30,4 +30,7 @@
     <ProjectReference Include="ReferencedClassLib\ReferencedClassLib.csproj" />
     <ProjectReference Include="ReferencedClassLibNeutralIsSatellite\ReferencedClassLibNeutralIsSatellite.csproj" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
+    <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Numerics/Directory.Build.props b/src/libraries/System.Runtime.Numerics/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Runtime.Numerics/Directory.Build.props
+++ b/src/libraries/System.Runtime.Numerics/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Numerics/src/System.Runtime.Numerics.csproj b/src/libraries/System.Runtime.Numerics/src/System.Runtime.Numerics.csproj
index 52ae4fe33fc938..7e938de2925efb 100644
--- a/src/libraries/System.Runtime.Numerics/src/System.Runtime.Numerics.csproj
+++ b/src/libraries/System.Runtime.Numerics/src/System.Runtime.Numerics.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <RootNamespace>System.Numerics</RootNamespace>
-    <AssemblyName>System.Runtime.Numerics</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/Directory.Build.props b/src/libraries/System.Runtime.Serialization.Formatters/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Runtime.Serialization.Formatters/Directory.Build.props
+++ b/src/libraries/System.Runtime.Serialization.Formatters/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/src/ILLink/ILLink.Substitutions.xml b/src/libraries/System.Runtime.Serialization.Formatters/src/ILLink/ILLink.Substitutions.NonBrowser.xml
similarity index 100%
rename from src/libraries/System.Runtime.Serialization.Formatters/src/ILLink/ILLink.Substitutions.xml
rename to src/libraries/System.Runtime.Serialization.Formatters/src/ILLink/ILLink.Substitutions.NonBrowser.xml
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/src/System.Runtime.Serialization.Formatters.csproj b/src/libraries/System.Runtime.Serialization.Formatters/src/System.Runtime.Serialization.Formatters.csproj
index 6dd50fdba5e240..6d339f895d61f3 100644
--- a/src/libraries/System.Runtime.Serialization.Formatters/src/System.Runtime.Serialization.Formatters.csproj
+++ b/src/libraries/System.Runtime.Serialization.Formatters/src/System.Runtime.Serialization.Formatters.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime.Serialization.Formatters</AssemblyName>
-    <RootNamespace>System.Runtime.Serialization.Formatters</RootNamespace>
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppCurrent)-Browser</TargetFrameworks>
     <Nullable>enable</Nullable>
     <!-- When we replace implementations with PNSE, need to suppress some "field is never assigned to" warnings. -->
@@ -11,8 +9,8 @@
   <PropertyGroup>
     <ILLinkDirectory>$(MSBuildThisFileDirectory)ILLink\</ILLinkDirectory>
   </PropertyGroup>
-  <ItemGroup>
-    <ILLinkSubstitutionsXmls Include="$(ILLinkDirectory)ILLink.Substitutions.xml" />
+  <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
+    <ILLinkSubstitutionsXmls Include="$(ILLinkDirectory)ILLink.Substitutions.NonBrowser.xml" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="System.Runtime.Serialization.Formatters.TypeForwards.cs" />
@@ -23,10 +21,6 @@
     <Compile Include="System\Runtime\Serialization\IFormatter.cs" />
     <Compile Include="System\Runtime\Serialization\ISerializationSurrogate.cs" />
     <Compile Include="System\Runtime\Serialization\ISurrogateSelector.cs" />
-    <Compile Include="System\Runtime\Serialization\LocalAppContextSwitches.cs" />
-    <Compile Include="$(CommonPath)System\LocalAppContextSwitches.Common.cs">
-      <Link>Common\System\LocalAppContextSwitches.Common.cs</Link>
-    </Compile>
     <Compile Include="System\Runtime\Serialization\MemberHolder.cs" />
     <Compile Include="System\Runtime\Serialization\ObjectIDGenerator.cs" />
     <Compile Include="System\Runtime\Serialization\ObjectManager.cs" />
@@ -61,8 +55,7 @@
     <Compile Include="System\Runtime\Serialization\Formatters\Binary\Converter.cs" />
     <Compile Include="System\Runtime\Serialization\Formatters\Binary\BinaryEnums.cs" />
     <Compile Include="System\Runtime\Serialization\Formatters\Binary\BinaryFormatter.cs" />
-    <Compile Include="System\Runtime\Serialization\Formatters\Binary\BinaryFormatter.Core.cs" Condition="'$(TargetsBrowser)' != 'true'" />
-    <Compile Include="System\Runtime\Serialization\Formatters\Binary\BinaryFormatter.PlatformNotSupported.cs" Condition="'$(TargetsBrowser)' == 'true'" />
+    <Compile Include="System\Runtime\Serialization\Formatters\Binary\BinaryFormatterEventSource.cs" />
     <Compile Include="System\Runtime\Serialization\Formatters\Binary\BinaryFormatterWriter.cs" />
     <Compile Include="System\Runtime\Serialization\Formatters\Binary\BinaryObjectInfo.cs" />
     <Compile Include="System\Runtime\Serialization\Formatters\Binary\BinaryObjectReader.cs" />
@@ -74,12 +67,22 @@
     <Compile Include="$(CoreLibSharedDir)System\Collections\HashHelpers.cs"
              Link="Common\System\Collections\HashHelpers.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
+    <Compile Include="System\Runtime\Serialization\Formatters\Binary\BinaryFormatter.Core.cs" />
+    <Compile Include="System\Runtime\Serialization\LocalAppContextSwitches.cs" />
+    <Compile Include="$(CommonPath)System\LocalAppContextSwitches.Common.cs">
+      <Link>Common\System\LocalAppContextSwitches.Common.cs</Link>
+    </Compile>
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetsBrowser)' == 'true'">
+    <Compile Include="System\Runtime\Serialization\Formatters\Binary\BinaryFormatter.PlatformNotSupported.cs" />
+  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(CoreLibProject)" />
-    <ProjectReference Include="..\..\System.Runtime.CompilerServices.Unsafe\src\System.Runtime.CompilerServices.Unsafe.ilproj" />
-    <ProjectReference Include="..\..\System.Runtime\src\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Collections\src\System.Collections.csproj" />
-    <ProjectReference Include="..\..\System.Collections.Concurrent\src\System.Collections.Concurrent.csproj" />
-    <ProjectReference Include="..\..\System.Collections.NonGeneric\src\System.Collections.NonGeneric.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.CompilerServices.Unsafe\src\System.Runtime.CompilerServices.Unsafe.ilproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\src\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections\src\System.Collections.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.Concurrent\src\System.Collections.Concurrent.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.NonGeneric\src\System.Collections.NonGeneric.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryFormatter.Core.cs b/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryFormatter.Core.cs
index 95f281f6339782..939b78ad9535dc 100644
--- a/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryFormatter.Core.cs
+++ b/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryFormatter.Core.cs
@@ -39,6 +39,7 @@ public object Deserialize(Stream serializationStream)
             };
             try
             {
+                BinaryFormatterEventSource.Log.DeserializationStart();
                 var parser = new BinaryParser(serializationStream, reader);
                 return reader.Deserialize(parser);
             }
@@ -50,6 +51,10 @@ public object Deserialize(Stream serializationStream)
             {
                 throw new SerializationException(SR.Serialization_CorruptedStream, e);
             }
+            finally
+            {
+                BinaryFormatterEventSource.Log.DeserializationStop();
+            }
         }
 
         [Obsolete(Obsoletions.BinaryFormatterMessage, DiagnosticId = Obsoletions.BinaryFormatterDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
@@ -73,10 +78,18 @@ public void Serialize(Stream serializationStream, object graph)
                 _assemblyFormat = _assemblyFormat,
             };
 
-            var sow = new ObjectWriter(_surrogates, _context, formatterEnums, _binder);
-            BinaryFormatterWriter binaryWriter = new BinaryFormatterWriter(serializationStream, sow, _typeFormat);
-            sow.Serialize(graph, binaryWriter);
-            _crossAppDomainArray = sow._crossAppDomainArray;
+            try
+            {
+                BinaryFormatterEventSource.Log.SerializationStart();
+                var sow = new ObjectWriter(_surrogates, _context, formatterEnums, _binder);
+                BinaryFormatterWriter binaryWriter = new BinaryFormatterWriter(serializationStream, sow, _typeFormat);
+                sow.Serialize(graph, binaryWriter);
+                _crossAppDomainArray = sow._crossAppDomainArray;
+            }
+            finally
+            {
+                BinaryFormatterEventSource.Log.SerializationStop();
+            }
         }
     }
 }
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryFormatterEventSource.cs b/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryFormatterEventSource.cs
new file mode 100644
index 00000000000000..ca8efd4c0978a9
--- /dev/null
+++ b/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryFormatterEventSource.cs
@@ -0,0 +1,102 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics;
+using System.Diagnostics.Tracing;
+
+namespace System.Runtime.Serialization.Formatters.Binary
+{
+    [EventSource(
+        Name = "System.Runtime.Serialization.Formatters.Binary.BinaryFormatterEventSource")]
+    internal sealed class BinaryFormatterEventSource : EventSource
+    {
+        private const int EventId_SerializationStart = 10;
+        private const int EventId_SerializationStop = 11;
+        private const int EventId_SerializingObject = 12;
+        private const int EventId_DeserializationStart = 20;
+        private const int EventId_DeserializationStop = 21;
+        private const int EventId_DeserializingObject = 22;
+
+        public static readonly BinaryFormatterEventSource Log = new BinaryFormatterEventSource();
+
+        private BinaryFormatterEventSource()
+        {
+        }
+
+        [Event(EventId_SerializationStart, Opcode = EventOpcode.Start, Keywords = Keywords.Serialization, Level = EventLevel.Informational, ActivityOptions = EventActivityOptions.Recursive)]
+        public void SerializationStart()
+        {
+            if (IsEnabled(EventLevel.Informational, Keywords.Serialization))
+            {
+                WriteEvent(EventId_SerializationStart);
+            }
+        }
+
+        [Event(EventId_SerializationStop, Opcode = EventOpcode.Stop, Keywords = Keywords.Serialization, Level = EventLevel.Informational)]
+        public void SerializationStop()
+        {
+            if (IsEnabled(EventLevel.Informational, Keywords.Serialization))
+            {
+                WriteEvent(EventId_SerializationStop);
+            }
+        }
+
+        [NonEvent]
+        public void SerializingObject(Type type)
+        {
+            Debug.Assert(type != null);
+
+            if (IsEnabled(EventLevel.Informational, Keywords.Serialization))
+            {
+                SerializingObject(type.AssemblyQualifiedName);
+            }
+        }
+
+        [Event(EventId_SerializingObject, Keywords = Keywords.Serialization, Level = EventLevel.Informational)]
+        private void SerializingObject(string? typeName)
+        {
+            WriteEvent(EventId_SerializingObject, typeName);
+        }
+
+        [Event(EventId_DeserializationStart, Opcode = EventOpcode.Start, Keywords = Keywords.Deserialization, Level = EventLevel.Informational, ActivityOptions = EventActivityOptions.Recursive)]
+        public void DeserializationStart()
+        {
+            if (IsEnabled(EventLevel.Informational, Keywords.Deserialization))
+            {
+                WriteEvent(EventId_DeserializationStart);
+            }
+        }
+
+        [Event(EventId_DeserializationStop, Opcode = EventOpcode.Stop, Keywords = Keywords.Deserialization, Level = EventLevel.Informational)]
+        public void DeserializationStop()
+        {
+            if (IsEnabled(EventLevel.Informational, Keywords.Deserialization))
+            {
+                WriteEvent(EventId_DeserializationStop);
+            }
+        }
+
+        [NonEvent]
+        public void DeserializingObject(Type type)
+        {
+            Debug.Assert(type != null);
+
+            if (IsEnabled(EventLevel.Informational, Keywords.Deserialization))
+            {
+                DeserializingObject(type.AssemblyQualifiedName);
+            }
+        }
+
+        [Event(EventId_DeserializingObject, Keywords = Keywords.Deserialization, Level = EventLevel.Informational)]
+        private void DeserializingObject(string? typeName)
+        {
+            WriteEvent(EventId_DeserializingObject, typeName);
+        }
+
+        public class Keywords
+        {
+            public const EventKeywords Serialization = (EventKeywords)1;
+            public const EventKeywords Deserialization = (EventKeywords)2;
+        }
+    }
+}
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryObjectInfo.cs b/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryObjectInfo.cs
index c87d6a6fad6034..64f4e6ddcd830d 100644
--- a/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryObjectInfo.cs
+++ b/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryObjectInfo.cs
@@ -268,8 +268,11 @@ private void InitMemberInfo()
 
         internal string GetAssemblyString() => _binderAssemblyString ?? _cache._assemblyString;
 
-        private void InvokeSerializationBinder(SerializationBinder? binder) =>
+        private void InvokeSerializationBinder(SerializationBinder? binder)
+        {
+            BinaryFormatterEventSource.Log.SerializingObject(_objectType!);
             binder?.BindToName(_objectType!, out _binderAssemblyString, out _binderTypeName);
+        }
 
         internal void GetMemberInfo(out string[]? outMemberNames, out Type[]? outMemberTypes, out object?[]? outMemberData)
         {
@@ -392,6 +395,8 @@ internal void Init(Type? objectType, string[] memberNames, Type[]? memberTypes,
 
         private void InitReadConstructor(Type objectType, ISurrogateSelector? surrogateSelector, StreamingContext context)
         {
+            BinaryFormatterEventSource.Log.DeserializingObject(objectType);
+
             if (objectType.IsArray)
             {
                 InitNoMembers();
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryObjectWriter.cs b/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryObjectWriter.cs
index 8ecc2825662996..d4207fbfa68e8a 100644
--- a/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryObjectWriter.cs
+++ b/src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/Formatters/Binary/BinaryObjectWriter.cs
@@ -159,7 +159,7 @@ private void Write(WriteObjectInfo objectInfo, NameInfo memberNameInfo, NameInfo
                     {
                         Type type =
                             memberTypes[i] != null ? memberTypes[i] :
-                            memberData[i] != null ? GetType(memberData[i]!) : // TODO-NULLABLE https://github.com/dotnet/roslyn/issues/34644
+                            memberData[i] != null ? GetType(memberData[i]!) : // TODO-NULLABLE: Indexer nullability tracked (https://github.com/dotnet/roslyn/issues/34644)
                             Converter.s_typeofObject;
 
                         InternalPrimitiveTypeE code = ToCode(type);
@@ -170,7 +170,7 @@ private void Write(WriteObjectInfo objectInfo, NameInfo memberNameInfo, NameInfo
                             if (memberData[i] != null)
                             {
                                 memberObjectInfos[i] = WriteObjectInfo.Serialize(
-                                    memberData[i]!, // TODO-NULLABLE https://github.com/dotnet/roslyn/issues/34644
+                                    memberData[i]!, // TODO-NULLABLE: Indexer nullability tracked (https://github.com/dotnet/roslyn/issues/34644)
                                     _surrogates,
                                     _context,
                                     _serObjectInfoInit,
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/tests/BinaryFormatterEventSourceTests.cs b/src/libraries/System.Runtime.Serialization.Formatters/tests/BinaryFormatterEventSourceTests.cs
new file mode 100644
index 00000000000000..805b1ad4df4815
--- /dev/null
+++ b/src/libraries/System.Runtime.Serialization.Formatters/tests/BinaryFormatterEventSourceTests.cs
@@ -0,0 +1,216 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Generic;
+using System.Diagnostics.Tracing;
+using System.IO;
+using System.Linq;
+using System.Runtime.Serialization.Formatters.Binary;
+using System.Threading;
+using Xunit;
+
+namespace System.Runtime.Serialization.Formatters.Tests
+{
+    [ConditionalClass(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported))]
+    public static class BinaryFormatterEventSourceTests
+    {
+        private const string BinaryFormatterEventSourceName = "System.Runtime.Serialization.Formatters.Binary.BinaryFormatterEventSource";
+
+        [Fact]
+        public static void RecordsSerialization()
+        {
+            using LoggingEventListener listener = new LoggingEventListener();
+
+            BinaryFormatter formatter = new BinaryFormatter();
+            formatter.Serialize(Stream.Null, CreatePerson());
+            string[] capturedLog = listener.CaptureLog();
+
+            string[] expected = new string[]
+            {
+                "SerializationStart [Start, 00000001]: <no payload>",
+                "SerializingObject [Info, 00000001]: " + typeof(Person).AssemblyQualifiedName,
+                "SerializingObject [Info, 00000001]: " + typeof(Address).AssemblyQualifiedName,
+                "SerializationStop [Stop, 00000001]: <no payload>",
+            };
+
+            Assert.Equal(expected, capturedLog);
+        }
+
+        [Fact]
+        public static void RecordsDeserialization()
+        {
+            MemoryStream ms = new MemoryStream();
+            BinaryFormatter formatter = new BinaryFormatter();
+            formatter.Serialize(ms, CreatePerson());
+            ms.Position = 0;
+
+            using LoggingEventListener listener = new LoggingEventListener();
+            formatter.Deserialize(ms);
+            string[] capturedLog = listener.CaptureLog();
+
+            string[] expected = new string[]
+            {
+                "DeserializationStart [Start, 00000002]: <no payload>",
+                "DeserializingObject [Info, 00000002]: " + typeof(Person).AssemblyQualifiedName,
+                "DeserializingObject [Info, 00000002]: " + typeof(Address).AssemblyQualifiedName,
+                "DeserializationStop [Stop, 00000002]: <no payload>",
+            };
+
+            Assert.Equal(expected, capturedLog);
+        }
+
+        [Fact]
+        public static void RecordsNestedSerializationCalls()
+        {
+            // First, serialization
+
+            using LoggingEventListener listener = new LoggingEventListener();
+
+            MemoryStream ms = new MemoryStream();
+            BinaryFormatter formatter = new BinaryFormatter();
+            formatter.Serialize(ms, new ClassWithNestedDeserialization());
+            string[] capturedLog = listener.CaptureLog();
+            ms.Position = 0;
+
+            string[] expected = new string[]
+            {
+                "SerializationStart [Start, 00000001]: <no payload>",
+                "SerializingObject [Info, 00000001]: " + typeof(ClassWithNestedDeserialization).AssemblyQualifiedName,
+                "SerializationStart [Start, 00000001]: <no payload>",
+                "SerializingObject [Info, 00000001]: " + typeof(Address).AssemblyQualifiedName,
+                "SerializationStop [Stop, 00000001]: <no payload>",
+                "SerializationStop [Stop, 00000001]: <no payload>",
+            };
+
+            Assert.Equal(expected, capturedLog);
+            listener.ClearLog();
+
+            // Then, deserialization
+
+            ms.Position = 0;
+            formatter.Deserialize(ms);
+            capturedLog = listener.CaptureLog();
+
+            expected = new string[]
+            {
+                "DeserializationStart [Start, 00000002]: <no payload>",
+                "DeserializingObject [Info, 00000002]: " + typeof(ClassWithNestedDeserialization).AssemblyQualifiedName,
+                "DeserializationStart [Start, 00000002]: <no payload>",
+                "DeserializingObject [Info, 00000002]: " + typeof(Address).AssemblyQualifiedName,
+                "DeserializationStop [Stop, 00000002]: <no payload>",
+                "DeserializationStop [Stop, 00000002]: <no payload>",
+            };
+
+            Assert.Equal(expected, capturedLog);
+        }
+
+        private static Person CreatePerson()
+        {
+            return new Person()
+            {
+                Name = "Some Chap",
+                HomeAddress = new Address()
+                {
+                    Street = "123 Anywhere Ln",
+                    City = "Anywhere ST 00000 United States"
+                }
+            };
+        }
+
+        private sealed class LoggingEventListener : EventListener
+        {
+            private readonly Thread _activeThread = Thread.CurrentThread;
+            private readonly List<string> _log = new List<string>();
+
+            private void AddToLog(FormattableString message)
+            {
+                _log.Add(FormattableString.Invariant(message));
+            }
+
+            // Captures the current log
+            public string[] CaptureLog()
+            {
+                return _log.ToArray();
+            }
+
+            public void ClearLog()
+            {
+                _log.Clear();
+            }
+
+            protected override void OnEventSourceCreated(EventSource eventSource)
+            {
+                if (eventSource.Name == BinaryFormatterEventSourceName)
+                {
+                    EnableEvents(eventSource, EventLevel.Verbose);
+                }
+
+                base.OnEventSourceCreated(eventSource);
+            }
+
+            protected override void OnEventWritten(EventWrittenEventArgs eventData)
+            {
+                // The test project is parallelized. We want to filter to only events that fired
+                // on the current thread, otherwise we could throw off the test results.
+
+                if (Thread.CurrentThread != _activeThread)
+                {
+                    return;
+                }
+
+                AddToLog($"{eventData.EventName} [{eventData.Opcode}, {(int)eventData.Keywords & int.MaxValue:X8}]: {ParsePayload(eventData.Payload)}");
+                base.OnEventWritten(eventData);
+            }
+
+            private static string ParsePayload(IReadOnlyCollection<object> collection)
+            {
+                if (collection?.Count > 0)
+                {
+                    return string.Join("; ", collection.Select(o => o?.ToString() ?? "<null>"));
+                }
+                else
+                {
+                    return "<no payload>";
+                }
+            }
+        }
+
+        [Serializable]
+        private class Person
+        {
+            public string Name { get; set; }
+            public Address HomeAddress { get; set; }
+        }
+
+        [Serializable]
+        private class Address
+        {
+            public string Street { get; set; }
+            public string City { get; set; }
+        }
+
+        [Serializable]
+        public class ClassWithNestedDeserialization : ISerializable
+        {
+            public ClassWithNestedDeserialization()
+            {
+            }
+
+            protected ClassWithNestedDeserialization(SerializationInfo info, StreamingContext context)
+            {
+                byte[] serializedData = (byte[])info.GetValue("SomeField", typeof(byte[]));
+                MemoryStream ms = new MemoryStream(serializedData);
+                BinaryFormatter formatter = new BinaryFormatter();
+                formatter.Deserialize(ms); // should deserialize an 'Address' instance
+            }
+
+            public void GetObjectData(SerializationInfo info, StreamingContext context)
+            {
+                MemoryStream ms = new MemoryStream();
+                BinaryFormatter formatter = new BinaryFormatter();
+                formatter.Serialize(ms, new Address());
+                info.AddValue("SomeField", ms.ToArray());
+            }
+        }
+    }
+}
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/tests/BinaryFormatterTestData.cs b/src/libraries/System.Runtime.Serialization.Formatters/tests/BinaryFormatterTestData.cs
index 3e9099231db180..54af864c8c4e18 100644
--- a/src/libraries/System.Runtime.Serialization.Formatters/tests/BinaryFormatterTestData.cs
+++ b/src/libraries/System.Runtime.Serialization.Formatters/tests/BinaryFormatterTestData.cs
@@ -1441,63 +1441,54 @@ public static IEnumerable<object[]> SerializableObjects()
                 var privilegeNotHeldException = new PrivilegeNotHeldException("privilege", exception);
                 yield return new object[] { PopulateException(privilegeNotHeldException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("AAEAAAD/////AQAAAAAAAAAEAQAAADdTeXN0ZW0uU2VjdXJpdHkuQWNjZXNzQ29udHJvbC5Qcml2aWxlZ2VOb3RIZWxkRXhjZXB0aW9uDQAAAAlDbGFzc05hbWUHTWVzc2FnZQREYXRhDklubmVyRXhjZXB0aW9uB0hlbHBVUkwQU3RhY2tUcmFjZVN0cmluZxZSZW1vdGVTdGFja1RyYWNlU3RyaW5nEFJlbW90ZVN0YWNrSW5kZXgPRXhjZXB0aW9uTWV0aG9kB0hSZXN1bHQGU291cmNlDVdhdHNvbkJ1Y2tldHMNUHJpdmlsZWdlTmFtZQEBAwMBAQEAAQABBwEpU3lzdGVtLkNvbGxlY3Rpb25zLkxpc3REaWN0aW9uYXJ5SW50ZXJuYWwQU3lzdGVtLkV4Y2VwdGlvbggIAgYCAAAAN1N5c3RlbS5TZWN1cml0eS5BY2Nlc3NDb250cm9sLlByaXZpbGVnZU5vdEhlbGRFeGNlcHRpb24GAwAAAFxUaGUgcHJvY2VzcyBkb2VzIG5vdCBwb3NzZXNzIHRoZSAncHJpdmlsZWdlJyBwcml2aWxlZ2Ugd2hpY2ggaXMgcmVxdWlyZWQgZm9yIHRoaXMgb3BlcmF0aW9uLgkEAAAACQUAAAAGBgAAABlodHRwOi8vbXNkbi5taWNyb3NvZnQuY29tBgcAAAAUU3RhY2tUcmFjZSBzdHJpbmcuLi4GCAAAABtSZW1vdGUgU3RhY2tUcmFjZSBzdHJpbmcuLi4AAAAACugDAAAGCQAAABdFeGNlcHRpb25fQ2xhc3NfU2FtcGxlcwoGCgAAAAlwcml2aWxlZ2UEBAAAAClTeXN0ZW0uQ29sbGVjdGlvbnMuTGlzdERpY3Rpb25hcnlJbnRlcm5hbAMAAAAEaGVhZAd2ZXJzaW9uBWNvdW50AwAAOFN5c3RlbS5Db2xsZWN0aW9ucy5MaXN0RGljdGlvbmFyeUludGVybmFsK0RpY3Rpb25hcnlOb2RlCAgJCwAAAAIAAAACAAAABAUAAAAQU3lzdGVtLkV4Y2VwdGlvbgwAAAAJQ2xhc3NOYW1lB01lc3NhZ2UERGF0YQ5Jbm5lckV4Y2VwdGlvbgdIZWxwVVJMEFN0YWNrVHJhY2VTdHJpbmcWUmVtb3RlU3RhY2tUcmFjZVN0cmluZxBSZW1vdGVTdGFja0luZGV4D0V4Y2VwdGlvbk1ldGhvZAdIUmVzdWx0BlNvdXJjZQ1XYXRzb25CdWNrZXRzAQEDAwEBAQABAAEHKVN5c3RlbS5Db2xsZWN0aW9ucy5MaXN0RGljdGlvbmFyeUludGVybmFsEFN5c3RlbS5FeGNlcHRpb24ICAIGDAAAABBTeXN0ZW0uRXhjZXB0aW9uBg0AAAAHbWVzc2FnZQkOAAAACQ8AAAAJBgAAAAkHAAAACQgAAAAAAAAACugDAAAJCQAAAAoECwAAADhTeXN0ZW0uQ29sbGVjdGlvbnMuTGlzdERpY3Rpb25hcnlJbnRlcm5hbCtEaWN0aW9uYXJ5Tm9kZQMAAAADa2V5BXZhbHVlBG5leHQCAgM4U3lzdGVtLkNvbGxlY3Rpb25zLkxpc3REaWN0aW9uYXJ5SW50ZXJuYWwrRGljdGlvbmFyeU5vZGUGFAAAAAZzZWNyZXQIAQEJFQAAAAEOAAAABAAAAAkWAAAAAgAAAAIAAAABDwAAAAUAAAAJDAAAAAYYAAAAF0lubmVyIGV4Y2VwdGlvbiBtZXNzYWdlCgoKCgoAAAAACgAVE4AKCgEVAAAACwAAAAgIAQAAAAYZAAAAA29uZQoBFgAAAAsAAAAJFAAAAAgBAQkbAAAAARsAAAALAAAACAgBAAAACRkAAAAKCw==", TargetFrameworkMoniker.netfx461) } };
 
-                // Infrastructure issue where the netstandard dll is PNSE assembly but in .NET Framework DirectoryServices should use the inbox assembly since they have the same identity.
-                // See: https://github.com/dotnet/runtime/issues/23972
-                if (!PlatformDetection.IsNetFramework)
-                {
-                    var activeDirectoryOperationException = new ActiveDirectoryOperationException("message", exception, 0);
-                    yield return new object[] { PopulateException(activeDirectoryOperationException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var activeDirectoryOperationException = new ActiveDirectoryOperationException("message", exception, 0);
+                yield return new object[] { PopulateException(activeDirectoryOperationException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var activeDirectoryObjectNotFoundException = new ActiveDirectoryObjectNotFoundException("message", exception);
-                    yield return new object[] { PopulateException(activeDirectoryObjectNotFoundException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var activeDirectoryObjectNotFoundException = new ActiveDirectoryObjectNotFoundException("message", exception);
+                yield return new object[] { PopulateException(activeDirectoryObjectNotFoundException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var activeDirectoryObjectExistsException = new ActiveDirectoryObjectExistsException("message", exception);
-                    yield return new object[] { PopulateException(activeDirectoryObjectExistsException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var activeDirectoryObjectExistsException = new ActiveDirectoryObjectExistsException("message", exception);
+                yield return new object[] { PopulateException(activeDirectoryObjectExistsException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var directoryException = new DirectoryException("message", exception);
-                    yield return new object[] { PopulateException(directoryException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var directoryException = new DirectoryException("message", exception);
+                yield return new object[] { PopulateException(directoryException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var directoryOperationException = new DirectoryOperationException("message", exception);
-                    yield return new object[] { PopulateException(directoryOperationException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var directoryOperationException = new DirectoryOperationException("message", exception);
+                yield return new object[] { PopulateException(directoryOperationException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var directoryServicesCOMException = new DirectoryServicesCOMException("message", exception);
-                    yield return new object[] { PopulateException(directoryServicesCOMException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var directoryServicesCOMException = new DirectoryServicesCOMException("message", exception);
+                yield return new object[] { PopulateException(directoryServicesCOMException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var ldapException = new LdapException("message", exception);
-                    yield return new object[] { PopulateException(ldapException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var ldapException = new LdapException("message", exception);
+                yield return new object[] { PopulateException(ldapException), new TypeSerializableValue[] { new TypeSerializableValue("AAEAAAD/////AQAAAAAAAAAMAgAAAGVTeXN0ZW0uRGlyZWN0b3J5U2VydmljZXMuUHJvdG9jb2xzLCBWZXJzaW9uPTQuMC4wLjAsIEN1bHR1cmU9bmV1dHJhbCwgUHVibGljS2V5VG9rZW49YjAzZjVmN2YxMWQ1MGEzYQUBAAAAMFN5c3RlbS5EaXJlY3RvcnlTZXJ2aWNlcy5Qcm90b2NvbHMuTGRhcEV4Y2VwdGlvbgwAAAAJQ2xhc3NOYW1lB01lc3NhZ2UERGF0YQ5Jbm5lckV4Y2VwdGlvbgdIZWxwVVJMEFN0YWNrVHJhY2VTdHJpbmcWUmVtb3RlU3RhY2tUcmFjZVN0cmluZxBSZW1vdGVTdGFja0luZGV4D0V4Y2VwdGlvbk1ldGhvZAdIUmVzdWx0BlNvdXJjZQ1XYXRzb25CdWNrZXRzAQEDAwEBAQABAAEHKVN5c3RlbS5Db2xsZWN0aW9ucy5MaXN0RGljdGlvbmFyeUludGVybmFsEFN5c3RlbS5FeGNlcHRpb24ICAICAAAABgMAAAAwU3lzdGVtLkRpcmVjdG9yeVNlcnZpY2VzLlByb3RvY29scy5MZGFwRXhjZXB0aW9uBgQAAAAHbWVzc2FnZQkFAAAACQYAAAAGBwAAABlodHRwOi8vbXNkbi5taWNyb3NvZnQuY29tBggAAAAUU3RhY2tUcmFjZSBzdHJpbmcuLi4GCQAAABtSZW1vdGUgU3RhY2tUcmFjZSBzdHJpbmcuLi4AAAAACugDAAAGCgAAABdFeGNlcHRpb25fQ2xhc3NfU2FtcGxlcwoEBQAAAClTeXN0ZW0uQ29sbGVjdGlvbnMuTGlzdERpY3Rpb25hcnlJbnRlcm5hbAMAAAAEaGVhZAd2ZXJzaW9uBWNvdW50AwAAOFN5c3RlbS5Db2xsZWN0aW9ucy5MaXN0RGljdGlvbmFyeUludGVybmFsK0RpY3Rpb25hcnlOb2RlCAgJCwAAAAIAAAACAAAABAYAAAAQU3lzdGVtLkV4Y2VwdGlvbgwAAAAJQ2xhc3NOYW1lB01lc3NhZ2UERGF0YQ5Jbm5lckV4Y2VwdGlvbgdIZWxwVVJMEFN0YWNrVHJhY2VTdHJpbmcWUmVtb3RlU3RhY2tUcmFjZVN0cmluZxBSZW1vdGVTdGFja0luZGV4D0V4Y2VwdGlvbk1ldGhvZAdIUmVzdWx0BlNvdXJjZQ1XYXRzb25CdWNrZXRzAQEDAwEBAQABAAEHKVN5c3RlbS5Db2xsZWN0aW9ucy5MaXN0RGljdGlvbmFyeUludGVybmFsEFN5c3RlbS5FeGNlcHRpb24ICAIGDAAAABBTeXN0ZW0uRXhjZXB0aW9uCQQAAAAJDgAAAAkPAAAACQcAAAAJCAAAAAkJAAAAAAAAAAroAwAACQoAAAAKBAsAAAA4U3lzdGVtLkNvbGxlY3Rpb25zLkxpc3REaWN0aW9uYXJ5SW50ZXJuYWwrRGljdGlvbmFyeU5vZGUDAAAAA2tleQV2YWx1ZQRuZXh0AgIDOFN5c3RlbS5Db2xsZWN0aW9ucy5MaXN0RGljdGlvbmFyeUludGVybmFsK0RpY3Rpb25hcnlOb2RlBhQAAAAGc2VjcmV0CAEBCRUAAAABDgAAAAUAAAAJFgAAAAIAAAACAAAAAQ8AAAAGAAAACQwAAAAGGAAAABdJbm5lciBleGNlcHRpb24gbWVzc2FnZQoKCgoKAAAAAAoAFROACgoBFQAAAAsAAAAICAEAAAAGGQAAAANvbmUKARYAAAALAAAACRQAAAAIAQEJGwAAAAEbAAAACwAAAAgIAQAAAAkZAAAACgs=", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var tlsOperationException = new TlsOperationException("message", exception);
-                    yield return new object[] { PopulateException(tlsOperationException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var tlsOperationException = new TlsOperationException("message", exception);
+                yield return new object[] { PopulateException(tlsOperationException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var principalExistsException = new PrincipalExistsException("message", exception);
-                    yield return new object[] { PopulateException(principalExistsException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var principalExistsException = new PrincipalExistsException("message", exception);
+                yield return new object[] { PopulateException(principalExistsException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var principalOperationException = new PrincipalOperationException("message", exception, 200);
-                    yield return new object[] { PopulateException(principalOperationException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var principalOperationException = new PrincipalOperationException("message", exception, 200);
+                yield return new object[] { PopulateException(principalOperationException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var principalServerDownException = new PrincipalServerDownException("message", exception, 200, "localhost");
-                    yield return new object[] { PopulateException(principalServerDownException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var principalServerDownException = new PrincipalServerDownException("message", exception, 200, "localhost");
+                yield return new object[] { PopulateException(principalServerDownException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("AAEAAAD/////AQAAAAAAAAAMAgAAAG1TeXN0ZW0uRGlyZWN0b3J5U2VydmljZXMuQWNjb3VudE1hbmFnZW1lbnQsIFZlcnNpb249NC4wLjAuMCwgQ3VsdHVyZT1uZXV0cmFsLCBQdWJsaWNLZXlUb2tlbj1iNzdhNWM1NjE5MzRlMDg5BQEAAABHU3lzdGVtLkRpcmVjdG9yeVNlcnZpY2VzLkFjY291bnRNYW5hZ2VtZW50LlByaW5jaXBhbFNlcnZlckRvd25FeGNlcHRpb24OAAAACUNsYXNzTmFtZQdNZXNzYWdlBERhdGEOSW5uZXJFeGNlcHRpb24HSGVscFVSTBBTdGFja1RyYWNlU3RyaW5nFlJlbW90ZVN0YWNrVHJhY2VTdHJpbmcQUmVtb3RlU3RhY2tJbmRleA9FeGNlcHRpb25NZXRob2QHSFJlc3VsdAZTb3VyY2UNV2F0c29uQnVja2V0cwllcnJvckNvZGUKc2VydmVyTmFtZQEBAwMBAQEAAQABBwABKVN5c3RlbS5Db2xsZWN0aW9ucy5MaXN0RGljdGlvbmFyeUludGVybmFsEFN5c3RlbS5FeGNlcHRpb24ICAIIAgAAAAYDAAAAR1N5c3RlbS5EaXJlY3RvcnlTZXJ2aWNlcy5BY2NvdW50TWFuYWdlbWVudC5QcmluY2lwYWxTZXJ2ZXJEb3duRXhjZXB0aW9uBgQAAAAHbWVzc2FnZQkFAAAACQYAAAAGBwAAABlodHRwOi8vbXNkbi5taWNyb3NvZnQuY29tBggAAAAUU3RhY2tUcmFjZSBzdHJpbmcuLi4GCQAAABtSZW1vdGUgU3RhY2tUcmFjZSBzdHJpbmcuLi4AAAAACugDAAAGCgAAABdFeGNlcHRpb25fQ2xhc3NfU2FtcGxlcwrIAAAABgsAAAAJbG9jYWxob3N0BAUAAAApU3lzdGVtLkNvbGxlY3Rpb25zLkxpc3REaWN0aW9uYXJ5SW50ZXJuYWwDAAAABGhlYWQHdmVyc2lvbgVjb3VudAMAADhTeXN0ZW0uQ29sbGVjdGlvbnMuTGlzdERpY3Rpb25hcnlJbnRlcm5hbCtEaWN0aW9uYXJ5Tm9kZQgICQwAAAACAAAAAgAAAAQGAAAAEFN5c3RlbS5FeGNlcHRpb24MAAAACUNsYXNzTmFtZQdNZXNzYWdlBERhdGEOSW5uZXJFeGNlcHRpb24HSGVscFVSTBBTdGFja1RyYWNlU3RyaW5nFlJlbW90ZVN0YWNrVHJhY2VTdHJpbmcQUmVtb3RlU3RhY2tJbmRleA9FeGNlcHRpb25NZXRob2QHSFJlc3VsdAZTb3VyY2UNV2F0c29uQnVja2V0cwEBAwMBAQEAAQABBylTeXN0ZW0uQ29sbGVjdGlvbnMuTGlzdERpY3Rpb25hcnlJbnRlcm5hbBBTeXN0ZW0uRXhjZXB0aW9uCAgCBg0AAAAQU3lzdGVtLkV4Y2VwdGlvbgkEAAAACQ8AAAAJEAAAAAkHAAAACQgAAAAJCQAAAAAAAAAK6AMAAAkKAAAACgQMAAAAOFN5c3RlbS5Db2xsZWN0aW9ucy5MaXN0RGljdGlvbmFyeUludGVybmFsK0RpY3Rpb25hcnlOb2RlAwAAAANrZXkFdmFsdWUEbmV4dAICAzhTeXN0ZW0uQ29sbGVjdGlvbnMuTGlzdERpY3Rpb25hcnlJbnRlcm5hbCtEaWN0aW9uYXJ5Tm9kZQYVAAAABnNlY3JldAgBAQkWAAAAAQ8AAAAFAAAACRcAAAACAAAAAgAAAAEQAAAABgAAAAkNAAAABhkAAAAXSW5uZXIgZXhjZXB0aW9uIG1lc3NhZ2UKCgoKCgAAAAAKABUTgAoKARYAAAAMAAAACAgBAAAABhoAAAADb25lCgEXAAAADAAAAAkVAAAACAEBCRwAAAABHAAAAAwAAAAICAEAAAAJGgAAAAoL", TargetFrameworkMoniker.netfx461) } };
 
-                    var activeDirectoryServerDownException = new ActiveDirectoryServerDownException("message", exception, 0, "name");
-                    yield return new object[] { PopulateException(activeDirectoryServerDownException), new TypeSerializableValue[] { new TypeSerializableValue("AAEAAAD/////AQAAAAAAAAAMAgAAAFtTeXN0ZW0uRGlyZWN0b3J5U2VydmljZXMsIFZlcnNpb249NC4wLjAuMCwgQ3VsdHVyZT1uZXV0cmFsLCBQdWJsaWNLZXlUb2tlbj1iMDNmNWY3ZjExZDUwYTNhBQEAAABLU3lzdGVtLkRpcmVjdG9yeVNlcnZpY2VzLkFjdGl2ZURpcmVjdG9yeS5BY3RpdmVEaXJlY3RvcnlTZXJ2ZXJEb3duRXhjZXB0aW9uDAAAAAlDbGFzc05hbWUHTWVzc2FnZQREYXRhDklubmVyRXhjZXB0aW9uB0hlbHBVUkwQU3RhY2tUcmFjZVN0cmluZxZSZW1vdGVTdGFja1RyYWNlU3RyaW5nEFJlbW90ZVN0YWNrSW5kZXgPRXhjZXB0aW9uTWV0aG9kB0hSZXN1bHQGU291cmNlDVdhdHNvbkJ1Y2tldHMBAQMDAQEBAAEAAQcpU3lzdGVtLkNvbGxlY3Rpb25zLkxpc3REaWN0aW9uYXJ5SW50ZXJuYWwQU3lzdGVtLkV4Y2VwdGlvbggIAgIAAAAGAwAAAEtTeXN0ZW0uRGlyZWN0b3J5U2VydmljZXMuQWN0aXZlRGlyZWN0b3J5LkFjdGl2ZURpcmVjdG9yeVNlcnZlckRvd25FeGNlcHRpb24GBAAAAAdtZXNzYWdlCQUAAAAJBgAAAAYHAAAAGWh0dHA6Ly9tc2RuLm1pY3Jvc29mdC5jb20GCAAAABRTdGFja1RyYWNlIHN0cmluZy4uLgYJAAAAG1JlbW90ZSBTdGFja1RyYWNlIHN0cmluZy4uLgAAAAAK6AMAAAYKAAAAF0V4Y2VwdGlvbl9DbGFzc19TYW1wbGVzCgQFAAAAKVN5c3RlbS5Db2xsZWN0aW9ucy5MaXN0RGljdGlvbmFyeUludGVybmFsAwAAAARoZWFkB3ZlcnNpb24FY291bnQDAAA4U3lzdGVtLkNvbGxlY3Rpb25zLkxpc3REaWN0aW9uYXJ5SW50ZXJuYWwrRGljdGlvbmFyeU5vZGUICAkLAAAAAgAAAAIAAAAEBgAAABBTeXN0ZW0uRXhjZXB0aW9uDAAAAAlDbGFzc05hbWUHTWVzc2FnZQREYXRhDklubmVyRXhjZXB0aW9uB0hlbHBVUkwQU3RhY2tUcmFjZVN0cmluZxZSZW1vdGVTdGFja1RyYWNlU3RyaW5nEFJlbW90ZVN0YWNrSW5kZXgPRXhjZXB0aW9uTWV0aG9kB0hSZXN1bHQGU291cmNlDVdhdHNvbkJ1Y2tldHMBAQMDAQEBAAEAAQcpU3lzdGVtLkNvbGxlY3Rpb25zLkxpc3REaWN0aW9uYXJ5SW50ZXJuYWwQU3lzdGVtLkV4Y2VwdGlvbggIAgYMAAAAEFN5c3RlbS5FeGNlcHRpb24JBAAAAAkOAAAACQ8AAAAJBwAAAAkIAAAACQkAAAAAAAAACugDAAAJCgAAAAoECwAAADhTeXN0ZW0uQ29sbGVjdGlvbnMuTGlzdERpY3Rpb25hcnlJbnRlcm5hbCtEaWN0aW9uYXJ5Tm9kZQMAAAADa2V5BXZhbHVlBG5leHQCAgM4U3lzdGVtLkNvbGxlY3Rpb25zLkxpc3REaWN0aW9uYXJ5SW50ZXJuYWwrRGljdGlvbmFyeU5vZGUGFAAAAAZzZWNyZXQIAQEJFQAAAAEOAAAABQAAAAkWAAAAAgAAAAIAAAABDwAAAAYAAAAJDAAAAAYYAAAAF0lubmVyIGV4Y2VwdGlvbiBtZXNzYWdlCgoKCgoAAAAACgAVE4AKCgEVAAAACwAAAAgIAQAAAAYZAAAAA29uZQoBFgAAAAsAAAAJFAAAAAgBAQkbAAAAARsAAAALAAAACAgBAAAACRkAAAAKCw==", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var activeDirectoryServerDownException = new ActiveDirectoryServerDownException("message", exception, 0, "name");
+                yield return new object[] { PopulateException(activeDirectoryServerDownException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var forestTrustCollisionException = new ForestTrustCollisionException("message", exception);
-                    yield return new object[] { PopulateException(forestTrustCollisionException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+                var forestTrustCollisionException = new ForestTrustCollisionException("message", exception);
+                yield return new object[] { PopulateException(forestTrustCollisionException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                    var syncFromAllServersOperationException = new SyncFromAllServersOperationException("message", exception);
-                    yield return new object[] { PopulateException(syncFromAllServersOperationException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
-                }
+                var syncFromAllServersOperationException = new SyncFromAllServersOperationException("message", exception);
+                yield return new object[] { PopulateException(syncFromAllServersOperationException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
             }
 
-            // TODO: Inbox framework assemblies with same identity aren't currently used for running tests. https://github.com/dotnet/runtime/issues/23972
-            if (!PlatformDetection.IsNetFramework)
-            {
-                var compositionContractMismatchException = new CompositionContractMismatchException("message", exception);
-                yield return new object[] { PopulateException(compositionContractMismatchException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
+            var compositionContractMismatchException = new CompositionContractMismatchException("message", exception);
+            yield return new object[] { PopulateException(compositionContractMismatchException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
-                var importCardinalityMismatchException = new ImportCardinalityMismatchException("message", exception);
-                yield return new object[] { PopulateException(importCardinalityMismatchException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
-            }
+            var importCardinalityMismatchException = new ImportCardinalityMismatchException("message", exception);
+            yield return new object[] { PopulateException(importCardinalityMismatchException), new TypeSerializableValue[] { new TypeSerializableValue("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", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("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", TargetFrameworkMoniker.netfx461) } };
 
             yield return new object[] { new ValueTuple(), new TypeSerializableValue[] { new TypeSerializableValue("AAEAAAD/////AQAAAAAAAAAEAQAAABFTeXN0ZW0uVmFsdWVUdXBsZQAAAAAL", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("AAEAAAD/////AQAAAAAAAAAEAQAAABFTeXN0ZW0uVmFsdWVUdXBsZQAAAAAL", TargetFrameworkMoniker.netfx471) } };
             yield return new object[] { ValueTuple.Create(1), new TypeSerializableValue[] { new TypeSerializableValue("AAEAAAD/////AQAAAAAAAAAEAQAAAHBTeXN0ZW0uVmFsdWVUdXBsZWAxW1tTeXN0ZW0uSW50MzIsIG1zY29ybGliLCBWZXJzaW9uPTQuMC4wLjAsIEN1bHR1cmU9bmV1dHJhbCwgUHVibGljS2V5VG9rZW49Yjc3YTVjNTYxOTM0ZTA4OV1dAQAAAAVJdGVtMQAIAQAAAAs=", TargetFrameworkMoniker.netcoreapp20), new TypeSerializableValue("AAEAAAD/////AQAAAAAAAAAEAQAAAHBTeXN0ZW0uVmFsdWVUdXBsZWAxW1tTeXN0ZW0uSW50MzIsIG1zY29ybGliLCBWZXJzaW9uPTQuMC4wLjAsIEN1bHR1cmU9bmV1dHJhbCwgUHVibGljS2V5VG9rZW49Yjc3YTVjNTYxOTM0ZTA4OV1dAQAAAAVJdGVtMQAIAQAAAAs=", TargetFrameworkMoniker.netfx471) } };
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/tests/FormatterServicesTests.Windows.cs b/src/libraries/System.Runtime.Serialization.Formatters/tests/FormatterServicesTests.Windows.cs
index 8dd3da0bbdc52d..a64cab793e98dc 100644
--- a/src/libraries/System.Runtime.Serialization.Formatters/tests/FormatterServicesTests.Windows.cs
+++ b/src/libraries/System.Runtime.Serialization.Formatters/tests/FormatterServicesTests.Windows.cs
@@ -11,6 +11,7 @@ namespace System.Runtime.Serialization.Formatters.Tests
     public partial class FormatterServicesTests
     {
         [Fact]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/39704", TestRuntimes.Mono)]
         public void GetUninitializedObject_COMObject_ThrowsNotSupportedException()
         {
             Type comObjectType = typeof(COMObject);
diff --git a/src/libraries/System.Runtime.Serialization.Formatters/tests/System.Runtime.Serialization.Formatters.Tests.csproj b/src/libraries/System.Runtime.Serialization.Formatters/tests/System.Runtime.Serialization.Formatters.Tests.csproj
index 635709d5042163..f8621423828977 100644
--- a/src/libraries/System.Runtime.Serialization.Formatters/tests/System.Runtime.Serialization.Formatters.Tests.csproj
+++ b/src/libraries/System.Runtime.Serialization.Formatters/tests/System.Runtime.Serialization.Formatters.Tests.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <TestRuntime>true</TestRuntime>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-FreeBSD;$(NetCoreAppCurrent)-illumos;$(NetCoreAppCurrent)-Solaris;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS;net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="BinaryFormatterTestData.cs" />
@@ -16,7 +16,6 @@
     <Compile Include="FormatterTests.cs" />
     <Compile Include="PlatformExtensions.cs" />
     <Compile Include="SerializationBinderTests.cs" />
-    <Compile Include="SerializationGuardTests.cs" Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'" />
     <Compile Include="SerializationInfoTests.cs" />
     <Compile Include="SerializationTypes.cs" />
     <Compile Include="SurrogateSelectorTests.cs" />
@@ -29,14 +28,42 @@
     <Compile Include="$(CommonTestPath)System\Runtime\Serialization\Formatters\BinaryFormatterHelpers.cs"
              Link="Common\System\Runtime\Serialization\Formatters\BinaryFormatterHelpers.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetFrameworkCurrent)'">
+  <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
     <Compile Include="$(CommonPath)System\Collections\Generic\ReferenceEqualityComparer.cs"
              Link="Common\System\Collections\Generic\ReferenceEqualityComparer.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <Reference Include="System.Text.Json" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <Compile Include="BinaryFormatterEventSourceTests.cs" />
+    <Compile Include="SerializationGuardTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="System.Data.SqlClient" Version="$(SystemDataSqlClientVersion)" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <!-- S.D.SqlClient isn't live built anymore. -->
+    <PackageReference Include="System.Data.SqlClient" Version="$(SystemDataSqlClientVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.CodeDom\src\System.CodeDom.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.ComponentModel.Composition\src\System.ComponentModel.Composition.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Configuration.ConfigurationManager\src\System.Configuration.ConfigurationManager.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Data.Odbc\src\System.Data.Odbc.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Diagnostics.EventLog\src\System.Diagnostics.EventLog.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices.AccountManagement\src\System.DirectoryServices.AccountManagement.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices.Protocols\src\System.DirectoryServices.Protocols.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices\src\System.DirectoryServices.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Drawing.Common\src\System.Drawing.Common.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.IO.Packaging\src\System.IO.Packaging.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net48'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Reflection.Metadata\src\System.Reflection.Metadata.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Threading.Channels\src\System.Threading.Channels.csproj" />
+    <Reference Include="Microsoft.CSharp" />
+    <Reference Include="System.ComponentModel.Composition" />
+    <Reference Include="System.ComponentModel.DataAnnotations" />
+    <Reference Include="System.Configuration" />
+    <Reference Include="System.DirectoryServices" />
+    <Reference Include="System.DirectoryServices.AccountManagement" />
+    <Reference Include="System.DirectoryServices.Protocols" />
+    <Reference Include="System.Transactions" />
+    <Reference Include="WindowsBase" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Runtime.Serialization.Json/Directory.Build.props b/src/libraries/System.Runtime.Serialization.Json/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Runtime.Serialization.Json/Directory.Build.props
+++ b/src/libraries/System.Runtime.Serialization.Json/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Runtime.Serialization.Json/src/System.Runtime.Serialization.Json.csproj b/src/libraries/System.Runtime.Serialization.Json/src/System.Runtime.Serialization.Json.csproj
index 42818f08979086..59304bfd403ef4 100644
--- a/src/libraries/System.Runtime.Serialization.Json/src/System.Runtime.Serialization.Json.csproj
+++ b/src/libraries/System.Runtime.Serialization.Json/src/System.Runtime.Serialization.Json.csproj
@@ -1,13 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime.Serialization.Json</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)System.Private.DataContractSerialization\src\System.Private.DataContractSerialization.csproj" />
-  </ItemGroup>
-  <ItemGroup>
     <Reference Include="System.Runtime" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Serialization.Primitives/Directory.Build.props b/src/libraries/System.Runtime.Serialization.Primitives/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Runtime.Serialization.Primitives/Directory.Build.props
+++ b/src/libraries/System.Runtime.Serialization.Primitives/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Serialization.Primitives/src/System.Runtime.Serialization.Primitives.csproj b/src/libraries/System.Runtime.Serialization.Primitives/src/System.Runtime.Serialization.Primitives.csproj
index adf56d49ade136..e314354aef4a47 100644
--- a/src/libraries/System.Runtime.Serialization.Primitives/src/System.Runtime.Serialization.Primitives.csproj
+++ b/src/libraries/System.Runtime.Serialization.Primitives/src/System.Runtime.Serialization.Primitives.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime.Serialization.Primitives</AssemblyName>
-    <RootNamespace>System.Runtime.Serialization.Primitives</RootNamespace>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Runtime.Serialization.Xml/Directory.Build.props b/src/libraries/System.Runtime.Serialization.Xml/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Runtime.Serialization.Xml/Directory.Build.props
+++ b/src/libraries/System.Runtime.Serialization.Xml/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Serialization.Xml/src/System.Runtime.Serialization.Xml.csproj b/src/libraries/System.Runtime.Serialization.Xml/src/System.Runtime.Serialization.Xml.csproj
index 9763bac6672210..4c211819d41850 100644
--- a/src/libraries/System.Runtime.Serialization.Xml/src/System.Runtime.Serialization.Xml.csproj
+++ b/src/libraries/System.Runtime.Serialization.Xml/src/System.Runtime.Serialization.Xml.csproj
@@ -1,13 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime.Serialization.Xml</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Private.DataContractSerialization\src\System.Private.DataContractSerialization.csproj" />
-  </ItemGroup>
-  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.DataContractSerialization\src\System.Private.DataContractSerialization.csproj" />
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Serialization.Primitives" />
   </ItemGroup>
diff --git a/src/libraries/System.Runtime.Serialization.Xml/tests/Canonicalization/System.Runtime.Serialization.Xml.Canonicalization.csproj b/src/libraries/System.Runtime.Serialization.Xml/tests/Canonicalization/System.Runtime.Serialization.Xml.Canonicalization.csproj
index c7ff1d9518f235..320a4c93973da9 100644
--- a/src/libraries/System.Runtime.Serialization.Xml/tests/Canonicalization/System.Runtime.Serialization.Xml.Canonicalization.csproj
+++ b/src/libraries/System.Runtime.Serialization.Xml/tests/Canonicalization/System.Runtime.Serialization.Xml.Canonicalization.csproj
@@ -66,4 +66,8 @@
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </Content>
   </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="xunit" Version="$(XUnitVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Xml\src\System.Security.Cryptography.Xml.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Serialization.Xml/tests/ReflectionOnly/System.Runtime.Serialization.Xml.ReflectionOnly.Tests.csproj b/src/libraries/System.Runtime.Serialization.Xml/tests/ReflectionOnly/System.Runtime.Serialization.Xml.ReflectionOnly.Tests.csproj
index 96a02163e0704a..e62c8b7f82d81d 100644
--- a/src/libraries/System.Runtime.Serialization.Xml/tests/ReflectionOnly/System.Runtime.Serialization.Xml.ReflectionOnly.Tests.csproj
+++ b/src/libraries/System.Runtime.Serialization.Xml/tests/ReflectionOnly/System.Runtime.Serialization.Xml.ReflectionOnly.Tests.csproj
@@ -45,4 +45,7 @@
     <Compile Include="$(TestSourceFolder)..\SerializationTestTypes\SelfRefAndCycles.cs"
              Link="SerializationTestTypes\SelfRefAndCycles.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.CodeDom\src\System.CodeDom.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime.Serialization.Xml/tests/System.Runtime.Serialization.Xml.Tests.csproj b/src/libraries/System.Runtime.Serialization.Xml/tests/System.Runtime.Serialization.Xml.Tests.csproj
index 5a4999f43791f9..3080bd813ac9a9 100644
--- a/src/libraries/System.Runtime.Serialization.Xml/tests/System.Runtime.Serialization.Xml.Tests.csproj
+++ b/src/libraries/System.Runtime.Serialization.Xml/tests/System.Runtime.Serialization.Xml.Tests.csproj
@@ -30,4 +30,7 @@
     <Compile Include="SerializationTestTypes\SampleTypes.cs" />
     <Compile Include="SerializationTestTypes\SelfRefAndCycles.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.CodeDom\src\System.CodeDom.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Runtime/Directory.Build.props b/src/libraries/System.Runtime/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Runtime/Directory.Build.props
+++ b/src/libraries/System.Runtime/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime/ref/System.Runtime.cs b/src/libraries/System.Runtime/ref/System.Runtime.cs
index 75def9c62e0750..8ebce34c3dbf8d 100644
--- a/src/libraries/System.Runtime/ref/System.Runtime.cs
+++ b/src/libraries/System.Runtime/ref/System.Runtime.cs
@@ -343,10 +343,8 @@ public static void Fill<T>(T[] array, T value, int startIndex, int count) { }
         public static int FindLastIndex<T>(T[] array, int startIndex, int count, System.Predicate<T> match) { throw null; }
         public static int FindLastIndex<T>(T[] array, int startIndex, System.Predicate<T> match) { throw null; }
         public static int FindLastIndex<T>(T[] array, System.Predicate<T> match) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T FindLast<T>(T[] array, System.Predicate<T> match) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static T Find<T>(T[] array, System.Predicate<T> match) { throw null; }
+        public static T? FindLast<T>(T[] array, System.Predicate<T> match) { throw null; }
+        public static T? Find<T>(T[] array, System.Predicate<T> match) { throw null; }
         public static void ForEach<T>(T[] array, System.Action<T> action) { }
         public System.Collections.IEnumerator GetEnumerator() { throw null; }
         public int GetLength(int dimension) { throw null; }
@@ -816,7 +814,7 @@ public sealed partial class CLSCompliantAttribute : System.Attribute
         public CLSCompliantAttribute(bool isCompliant) { }
         public bool IsCompliant { get { throw null; } }
     }
-    public delegate int Comparison<in T>([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T x, [System.Diagnostics.CodeAnalysis.AllowNullAttribute] T y);
+    public delegate int Comparison<in T>(T x, T y);
     public abstract partial class ContextBoundObject : System.MarshalByRefObject
     {
         protected ContextBoundObject() { }
@@ -2298,7 +2296,7 @@ public partial interface IComparable
     }
     public partial interface IComparable<in T>
     {
-        int CompareTo([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T other);
+        int CompareTo(T? other);
     }
     [System.CLSCompliantAttribute(false)]
     public partial interface IConvertible
@@ -2331,7 +2329,7 @@ public partial interface IDisposable
     }
     public partial interface IEquatable<T>
     {
-        bool Equals([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T other);
+        bool Equals(T? other);
     }
     public partial interface IFormatProvider
     {
@@ -3044,6 +3042,24 @@ public OperatingSystem(System.PlatformID platform, System.Version version) { }
         public object Clone() { throw null; }
         public void GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         public override string ToString() { throw null; }
+        public static bool IsOSPlatform(string platform) { throw null; }
+        public static bool IsOSPlatformVersionAtLeast(string platform, int major, int minor = 0, int build = 0, int revision = 0) { throw null; }
+        public static bool IsBrowser() { throw null; }
+        public static bool IsLinux() { throw null; }
+        public static bool IsFreeBSD() { throw null; }
+        public static bool IsFreeBSDVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0) { throw null; }
+        public static bool IsAndroid() { throw null; }
+        public static bool IsAndroidVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0) { throw null; }
+        public static bool IsIOS() { throw null; }
+        public static bool IsIOSVersionAtLeast(int major, int minor = 0, int build = 0) { throw null; }
+        public static bool IsMacOS() { throw null; }
+        public static bool IsMacOSVersionAtLeast(int major, int minor = 0, int build = 0) { throw null; }
+        public static bool IsTvOS() { throw null; }
+        public static bool IsTvOSVersionAtLeast(int major, int minor = 0, int build = 0) { throw null; }
+        public static bool IsWatchOS() { throw null; }
+        public static bool IsWatchOSVersionAtLeast(int major, int minor = 0, int build = 0) { throw null; }
+        public static bool IsWindows() { throw null; }
+        public static bool IsWindowsVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0) { throw null; }
     }
     public partial class OperationCanceledException : System.SystemException
     {
@@ -3638,10 +3654,10 @@ public enum StringComparison
     }
     public static partial class StringNormalizationExtensions
     {
-        public static bool IsNormalized(this string value) { throw null; }
-        public static bool IsNormalized(this string value, System.Text.NormalizationForm normalizationForm) { throw null; }
-        public static string Normalize(this string value) { throw null; }
-        public static string Normalize(this string value, System.Text.NormalizationForm normalizationForm) { throw null; }
+        public static bool IsNormalized(this string strInput) { throw null; }
+        public static bool IsNormalized(this string strInput, System.Text.NormalizationForm normalizationForm) { throw null; }
+        public static string Normalize(this string strInput) { throw null; }
+        public static string Normalize(this string strInput, System.Text.NormalizationForm normalizationForm) { throw null; }
     }
     [System.FlagsAttribute]
     public enum StringSplitOptions
@@ -5357,7 +5373,7 @@ public partial interface ICollection<T> : System.Collections.Generic.IEnumerable
     }
     public partial interface IComparer<in T>
     {
-        int Compare([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T x, [System.Diagnostics.CodeAnalysis.AllowNullAttribute] T y);
+        int Compare(T? x, T? y);
     }
     public partial interface IDictionary<TKey, TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TValue>>, System.Collections.IEnumerable
     {
@@ -5379,7 +5395,7 @@ public partial interface IEnumerator<out T> : System.Collections.IEnumerator, Sy
     }
     public partial interface IEqualityComparer<in T>
     {
-        bool Equals([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T x, [System.Diagnostics.CodeAnalysis.AllowNullAttribute] T y);
+        bool Equals(T? x, T? y);
         int GetHashCode([System.Diagnostics.CodeAnalysis.DisallowNullAttribute] T obj);
     }
     public partial interface IList<T> : System.Collections.Generic.ICollection<T>, System.Collections.Generic.IEnumerable<T>, System.Collections.IEnumerable
@@ -7564,10 +7580,12 @@ public AmbiguousMatchException(string? message, System.Exception? inner) { }
     public abstract partial class Assembly : System.Reflection.ICustomAttributeProvider, System.Runtime.Serialization.ISerializable
     {
         protected Assembly() { }
+        [System.ObsoleteAttribute("CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.", DiagnosticId = "SYSLIB0012", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
         public virtual string? CodeBase { get { throw null; } }
         public virtual System.Collections.Generic.IEnumerable<System.Reflection.CustomAttributeData> CustomAttributes { get { throw null; } }
         public virtual System.Collections.Generic.IEnumerable<System.Reflection.TypeInfo> DefinedTypes { [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types might be removed")] get { throw null; } }
         public virtual System.Reflection.MethodInfo? EntryPoint { get { throw null; } }
+        [System.ObsoleteAttribute("CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.", DiagnosticId = "SYSLIB0012", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
         public virtual string EscapedCodeBase { get { throw null; } }
         public virtual System.Collections.Generic.IEnumerable<System.Type> ExportedTypes { [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types might be removed")] get { throw null; } }
         public virtual string? FullName { get { throw null; } }
@@ -8152,16 +8170,27 @@ public InvalidFilterCriteriaException(string? message, System.Exception? inner)
     public partial interface IReflect
     {
         System.Type UnderlyingSystemType { get; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
         System.Reflection.FieldInfo? GetField(string name, System.Reflection.BindingFlags bindingAttr);
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
         System.Reflection.FieldInfo[] GetFields(System.Reflection.BindingFlags bindingAttr);
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         System.Reflection.MemberInfo[] GetMember(string name, System.Reflection.BindingFlags bindingAttr);
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         System.Reflection.MemberInfo[] GetMembers(System.Reflection.BindingFlags bindingAttr);
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         System.Reflection.MethodInfo? GetMethod(string name, System.Reflection.BindingFlags bindingAttr);
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         System.Reflection.MethodInfo? GetMethod(string name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Type[] types, System.Reflection.ParameterModifier[]? modifiers);
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         System.Reflection.MethodInfo[] GetMethods(System.Reflection.BindingFlags bindingAttr);
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         System.Reflection.PropertyInfo[] GetProperties(System.Reflection.BindingFlags bindingAttr);
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         System.Reflection.PropertyInfo? GetProperty(string name, System.Reflection.BindingFlags bindingAttr);
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         System.Reflection.PropertyInfo? GetProperty(string name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Type? returnType, System.Type[] types, System.Reflection.ParameterModifier[]? modifiers);
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         object? InvokeMember(string name, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder? binder, object? target, object?[]? args, System.Reflection.ParameterModifier[]? modifiers, System.Globalization.CultureInfo? culture, string[]? namedParameters);
     }
     public partial interface IReflectableType
@@ -8698,28 +8727,44 @@ public TypeDelegator([System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers
         public override System.RuntimeTypeHandle TypeHandle { get { throw null; } }
         public override System.Type UnderlyingSystemType { get { throw null; } }
         protected override System.Reflection.TypeAttributes GetAttributeFlagsImpl() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
         protected override System.Reflection.ConstructorInfo? GetConstructorImpl(System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Reflection.CallingConventions callConvention, System.Type[] types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)]
         public override System.Reflection.ConstructorInfo[] GetConstructors(System.Reflection.BindingFlags bindingAttr) { throw null; }
         public override object[] GetCustomAttributes(bool inherit) { throw null; }
         public override object[] GetCustomAttributes(System.Type attributeType, bool inherit) { throw null; }
         public override System.Type? GetElementType() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicEvents | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo? GetEvent(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo[] GetEvents() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicEvents | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicEvents)]
         public override System.Reflection.EventInfo[] GetEvents(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
         public override System.Reflection.FieldInfo? GetField(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicFields | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicFields)]
         public override System.Reflection.FieldInfo[] GetFields(System.Reflection.BindingFlags bindingAttr) { throw null; }
         public override System.Type? GetInterface(string name, bool ignoreCase) { throw null; }
         public override System.Reflection.InterfaceMapping GetInterfaceMap(System.Type interfaceType) { throw null; }
         public override System.Type[] GetInterfaces() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override System.Reflection.MemberInfo[] GetMember(string name, System.Reflection.MemberTypes type, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override System.Reflection.MemberInfo[] GetMembers(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         protected override System.Reflection.MethodInfo? GetMethodImpl(string name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Reflection.CallingConventions callConvention, System.Type[]? types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicMethods | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicMethods)]
         public override System.Reflection.MethodInfo[] GetMethods(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicNestedTypes | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicNestedTypes)]
         public override System.Type? GetNestedType(string name, System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicNestedTypes | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicNestedTypes)]
         public override System.Type[] GetNestedTypes(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         public override System.Reflection.PropertyInfo[] GetProperties(System.Reflection.BindingFlags bindingAttr) { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicProperties | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties)]
         protected override System.Reflection.PropertyInfo? GetPropertyImpl(string name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder? binder, System.Type? returnType, System.Type[]? types, System.Reflection.ParameterModifier[]? modifiers) { throw null; }
         protected override bool HasElementTypeImpl() { throw null; }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(string name, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder? binder, object? target, object?[]? args, System.Reflection.ParameterModifier[]? modifiers, System.Globalization.CultureInfo? culture, string[]? namedParameters) { throw null; }
         protected override bool IsArrayImpl() { throw null; }
         public override bool IsAssignableFrom([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] System.Reflection.TypeInfo? typeInfo) { throw null; }
@@ -8806,6 +8851,7 @@ public ResourceManager(System.Type resourceSource) { }
         public virtual string BaseName { get { throw null; } }
         protected System.Resources.UltimateResourceFallbackLocation FallbackLocation { get { throw null; } set { } }
         public virtual bool IgnoreCase { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public virtual System.Type ResourceSetType { get { throw null; } }
         public static System.Resources.ResourceManager CreateFileBasedResourceManager(string baseName, string resourceDir, System.Type? usingResourceSet) { throw null; }
         protected static System.Globalization.CultureInfo GetNeutralResourcesLanguage(System.Reflection.Assembly a) { throw null; }
@@ -9942,12 +9988,12 @@ public FrameworkName(string identifier, System.Version version, string? profile)
         public static bool operator !=(System.Runtime.Versioning.FrameworkName? left, System.Runtime.Versioning.FrameworkName? right) { throw null; }
         public override string ToString() { throw null; }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Event | System.AttributeTargets.Field | System.AttributeTargets.Method | System.AttributeTargets.Module | System.AttributeTargets.Property | System.AttributeTargets.Struct, AllowMultiple = true, Inherited = false)]
-    public sealed class MinimumOSPlatformAttribute : System.Runtime.Versioning.OSPlatformAttribute
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Enum | System.AttributeTargets.Event | System.AttributeTargets.Field | System.AttributeTargets.Method | System.AttributeTargets.Module | System.AttributeTargets.Property | System.AttributeTargets.Struct, AllowMultiple = true, Inherited = false)]
+    public sealed class SupportedOSPlatformAttribute : System.Runtime.Versioning.OSPlatformAttribute
     {
-        public MinimumOSPlatformAttribute(string platformName) : base(platformName) { }
+        public SupportedOSPlatformAttribute(string platformName) : base(platformName) { }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Event | System.AttributeTargets.Field | System.AttributeTargets.Method | System.AttributeTargets.Module | System.AttributeTargets.Property | System.AttributeTargets.Struct, AllowMultiple = true, Inherited = false)]
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Enum | System.AttributeTargets.Event | System.AttributeTargets.Field | System.AttributeTargets.Method | System.AttributeTargets.Module | System.AttributeTargets.Property | System.AttributeTargets.Struct, AllowMultiple = true, Inherited = false)]
     public sealed class ObsoletedInOSPlatformAttribute : System.Runtime.Versioning.OSPlatformAttribute
     {
         public ObsoletedInOSPlatformAttribute(string platformName) : base(platformName) { }
@@ -9960,10 +10006,10 @@ public abstract class OSPlatformAttribute : System.Attribute
         private protected OSPlatformAttribute(string platformName) { }
         public string PlatformName { get; }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Event | System.AttributeTargets.Field | System.AttributeTargets.Method | System.AttributeTargets.Module | System.AttributeTargets.Property | System.AttributeTargets.Struct, AllowMultiple = true, Inherited = false)]
-    public sealed class RemovedInOSPlatformAttribute : System.Runtime.Versioning.OSPlatformAttribute
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Enum | System.AttributeTargets.Event | System.AttributeTargets.Field | System.AttributeTargets.Method | System.AttributeTargets.Module | System.AttributeTargets.Property | System.AttributeTargets.Struct, AllowMultiple = true, Inherited = false)]
+    public sealed class UnsupportedOSPlatformAttribute : System.Runtime.Versioning.OSPlatformAttribute
     {
-        public RemovedInOSPlatformAttribute(string platformName) : base(platformName) { }
+        public UnsupportedOSPlatformAttribute(string platformName) : base(platformName) { }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Property, Inherited=false)]
     [System.Diagnostics.ConditionalAttribute("RESOURCE_ANNOTATION_WORK")]
@@ -10588,7 +10634,7 @@ public enum NormalizationForm
         FormKC = 5,
         FormKD = 6,
     }
-    public readonly partial struct Rune : System.IComparable<System.Text.Rune>, System.IEquatable<System.Text.Rune>
+    public readonly partial struct Rune : System.IComparable, System.IComparable<System.Text.Rune>, System.IEquatable<System.Text.Rune>
     {
         private readonly int _dummyPrimitive;
         public Rune(char ch) { throw null; }
@@ -10653,6 +10699,7 @@ public enum NormalizationForm
         public bool TryEncodeToUtf16(System.Span<char> destination, out int charsWritten) { throw null; }
         public bool TryEncodeToUtf8(System.Span<byte> destination, out int bytesWritten) { throw null; }
         public static bool TryGetRuneAt(string input, int index, out System.Text.Rune value) { throw null; }
+        int System.IComparable.CompareTo(object? obj) { throw null; }
     }
     public sealed partial class StringBuilder : System.Runtime.Serialization.ISerializable
     {
diff --git a/src/libraries/System.Runtime/src/System.Runtime.csproj b/src/libraries/System.Runtime/src/System.Runtime.csproj
index 79e6ec207864ba..6e3a18228e7e6a 100644
--- a/src/libraries/System.Runtime/src/System.Runtime.csproj
+++ b/src/libraries/System.Runtime/src/System.Runtime.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Runtime</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
@@ -12,10 +11,8 @@
   <ItemGroup>
     <Compile Include="System.Runtime.Typeforwards.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="..\..\System.Private.Uri\src\System.Private.Uri.csproj" />
-  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(CoreLibProject)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Uri\src\System.Private.Uri.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Runtime/tests/System.Runtime.Tests.csproj b/src/libraries/System.Runtime/tests/System.Runtime.Tests.csproj
index 39ca7313460b82..eff661cba39638 100644
--- a/src/libraries/System.Runtime/tests/System.Runtime.Tests.csproj
+++ b/src/libraries/System.Runtime/tests/System.Runtime.Tests.csproj
@@ -270,13 +270,14 @@
              Link="Common\System\Runtime\Serialization\Formatters\BinaryFormatterHelpers.cs" />
   </ItemGroup>
   <ItemGroup>
+    <PackageReference Include="Moq" Version="$(MoqVersion)" />
     <ProjectReference Include="TestLoadAssembly\TestLoadAssembly.csproj" />
     <ProjectReference Include="TestCollectibleAssembly\TestCollectibleAssembly.csproj" />
     <ProjectReference Include="TestModule\System.Reflection.TestModule.ilproj" />
     <ProjectReference Include="TestStructs\System.TestStructs.ilproj" />
     <ProjectReference Include="$(CommonTestPath)TestUtilities.Unicode\TestUtilities.Unicode.csproj" />
-  </ItemGroup>
-  <ItemGroup>
-    <PackageReference Include="Moq" Version="$(MoqVersion)" />
+    <!-- Used during reflection in tests. -->
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Permissions\src\System.Security.Permissions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Threading.AccessControl\src\System.Threading.AccessControl.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Runtime/tests/System/DelegateTests.cs b/src/libraries/System.Runtime/tests/System/DelegateTests.cs
index 35ee59b9211326..055fd8274e266b 100644
--- a/src/libraries/System.Runtime/tests/System/DelegateTests.cs
+++ b/src/libraries/System.Runtime/tests/System/DelegateTests.cs
@@ -619,6 +619,10 @@ public static void CreateDelegate2()
             e = (E)Delegate.CreateDelegate(typeof(E), new C(), "DoExecute");
             Assert.NotNull(e);
             Assert.Equal(102, e(new C()));
+
+            e = (E)Delegate.CreateDelegate(typeof(E), new B() { field = 42 }, "GetField");
+            Assert.NotNull(e);
+            Assert.Equal(42, e(new C()));
         }
 
         [Fact]
@@ -1103,6 +1107,7 @@ public static void CreateDelegate9_Type_Null()
 
         public class B
         {
+            public int field;
 
             public virtual string retarg3(string s)
             {
@@ -1136,6 +1141,11 @@ public int StartExecute(C c, B b)
             {
                 return 3;
             }
+
+            public int GetField(C c)
+            {
+                return field;
+            }
         }
 
         public class C : B, Iface
diff --git a/src/libraries/System.Runtime/tests/System/DoubleTests.cs b/src/libraries/System.Runtime/tests/System/DoubleTests.cs
index 92f413c429aaab..3de09c61316689 100644
--- a/src/libraries/System.Runtime/tests/System/DoubleTests.cs
+++ b/src/libraries/System.Runtime/tests/System/DoubleTests.cs
@@ -39,6 +39,10 @@ public static void CompareTo_ObjectNotDouble_ThrowsArgumentException(object valu
         [InlineData(double.NaN, double.NaN, 0)]
         [InlineData(double.NaN, 0.0, -1)]
         [InlineData(234.0, null, 1)]
+        [InlineData(double.MinValue, double.NegativeInfinity, 1)]
+        [InlineData(double.NegativeInfinity, double.MinValue, -1)]
+        [InlineData(-0d, double.NegativeInfinity, 1)]
+        [InlineData(double.NegativeInfinity, -0d, -1)]
         public static void CompareTo_Other_ReturnsExpected(double d1, object value, int expected)
         {
             if (value is double d2)
diff --git a/src/libraries/System.Runtime/tests/System/HalfTests.cs b/src/libraries/System.Runtime/tests/System/HalfTests.cs
index 4de5db4c514297..de5eddf9f9dc79 100644
--- a/src/libraries/System.Runtime/tests/System/HalfTests.cs
+++ b/src/libraries/System.Runtime/tests/System/HalfTests.cs
@@ -281,6 +281,10 @@ public static IEnumerable<object[]> CompareTo_TestData()
             yield return new object[] { Half.NaN, Half.NaN, 0 };
             yield return new object[] { Half.NaN, UInt16BitsToHalf(0x0000), -1 };
             yield return new object[] { Half.MaxValue, null, 1 };
+            yield return new object[] { Half.MinValue, Half.NegativeInfinity, 1 };
+            yield return new object[] { Half.NegativeInfinity, Half.MinValue, -1 };
+            yield return new object[] { UInt16BitsToHalf(0x8000), Half.NegativeInfinity, 1 }; // Negative zero
+            yield return new object[] { Half.NegativeInfinity, UInt16BitsToHalf(0x8000), -1 }; // Negative zero
         }
 
         [Theory]
diff --git a/src/libraries/System.Runtime/tests/System/Reflection/InvokeRefReturn.cs b/src/libraries/System.Runtime/tests/System/Reflection/InvokeRefReturn.cs
index ee28dd51c2e374..885e17992c1768 100644
--- a/src/libraries/System.Runtime/tests/System/Reflection/InvokeRefReturn.cs
+++ b/src/libraries/System.Runtime/tests/System/Reflection/InvokeRefReturn.cs
@@ -59,7 +59,6 @@ public static unsafe void TestRefReturnOfPointer()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/39380", TestPlatforms.Browser)]
         public static unsafe void TestNullRefReturnOfPointer()
         {
             TestClassIntPointer tc = new TestClassIntPointer(null);
diff --git a/src/libraries/System.Runtime/tests/System/Reflection/ModuleTests.cs b/src/libraries/System.Runtime/tests/System/Reflection/ModuleTests.cs
index 8f16d1d6e20409..b5494718b7be91 100644
--- a/src/libraries/System.Runtime/tests/System/Reflection/ModuleTests.cs
+++ b/src/libraries/System.Runtime/tests/System/Reflection/ModuleTests.cs
@@ -81,7 +81,15 @@ public void CustomAttributes()
         [Fact]
         public void FullyQualifiedName()
         {
-            Assert.Equal(Assembly.GetExecutingAssembly().Location, Module.FullyQualifiedName);
+            var loc = AssemblyPathHelper.GetAssemblyLocation(Assembly.GetExecutingAssembly());
+
+            // Browser will include the path (/), so strip it
+            if (PlatformDetection.IsBrowser && loc.Length > 1)
+            {
+                loc = loc.Substring(1);
+            }
+
+            Assert.Equal(loc, Module.FullyQualifiedName);
         }
 
         [Fact]
diff --git a/src/libraries/System.Runtime/tests/System/Runtime/CompilerServices/RuntimeFeatureTests.cs b/src/libraries/System.Runtime/tests/System/Runtime/CompilerServices/RuntimeFeatureTests.cs
index b724ea170a3df4..1c2bc0a6efea23 100644
--- a/src/libraries/System.Runtime/tests/System/Runtime/CompilerServices/RuntimeFeatureTests.cs
+++ b/src/libraries/System.Runtime/tests/System/Runtime/CompilerServices/RuntimeFeatureTests.cs
@@ -36,6 +36,14 @@ public static void DynamicCode_Jit()
             Assert.True(RuntimeFeature.IsDynamicCodeSupported);
             Assert.True(RuntimeFeature.IsDynamicCodeCompiled);
         }
+
+        [Fact]
+        [PlatformSpecific(TestPlatforms.Browser)]
+        public static void DynamicCode_Browser()
+        {
+            Assert.True(RuntimeFeature.IsDynamicCodeSupported);
+            Assert.False(RuntimeFeature.IsDynamicCodeCompiled);
+        }
         
         public static IEnumerable<object[]> GetStaticFeatureNames()
         {
diff --git a/src/libraries/System.Runtime/tests/System/Runtime/ExceptionServices/ExceptionDispatchInfoTests.cs b/src/libraries/System.Runtime/tests/System/Runtime/ExceptionServices/ExceptionDispatchInfoTests.cs
index c3242a0197cf83..c2bb2bdc48cd14 100644
--- a/src/libraries/System.Runtime/tests/System/Runtime/ExceptionServices/ExceptionDispatchInfoTests.cs
+++ b/src/libraries/System.Runtime/tests/System/Runtime/ExceptionServices/ExceptionDispatchInfoTests.cs
@@ -49,7 +49,6 @@ public static void SetCurrentStackTrace_Invalid_Throws()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/39341", TestPlatforms.Browser)]
         public static void SetCurrentStackTrace_IncludedInExceptionStackTrace()
         {
             Exception e;
diff --git a/src/libraries/System.Runtime/tests/System/Runtime/Versioning/OSPlatformAttributeTests.cs b/src/libraries/System.Runtime/tests/System/Runtime/Versioning/OSPlatformAttributeTests.cs
index 3b9db8ce3bb8ea..af507a5b4a3435 100644
--- a/src/libraries/System.Runtime/tests/System/Runtime/Versioning/OSPlatformAttributeTests.cs
+++ b/src/libraries/System.Runtime/tests/System/Runtime/Versioning/OSPlatformAttributeTests.cs
@@ -37,9 +37,9 @@ public void TestObsoletedInOSPlatformAttribute(string platformName, string messa
         [InlineData("Windows8.0")]
         [InlineData("Android4.1")]
         [InlineData("")]
-        public void TestRemovedInOSPlatformAttribute(string platformName)
+        public void TestUnsupportedOSPlatformAttribute(string platformName)
         {
-            var tpa = new RemovedInOSPlatformAttribute(platformName);
+            var tpa = new UnsupportedOSPlatformAttribute(platformName);
 
             Assert.Equal(platformName, tpa.PlatformName);
         }
@@ -48,9 +48,9 @@ public void TestRemovedInOSPlatformAttribute(string platformName)
         [InlineData("Windows10.0")]
         [InlineData("OSX")]
         [InlineData("")]
-        public void TestMinimumOSPlatformAttribute(string platformName)
+        public void TestSupportedOSPlatformAttribute(string platformName)
         {
-            var tpa = new MinimumOSPlatformAttribute(platformName);
+            var tpa = new SupportedOSPlatformAttribute(platformName);
 
             Assert.Equal(platformName, tpa.PlatformName);
         }
diff --git a/src/libraries/System.Runtime/tests/System/SingleTests.cs b/src/libraries/System.Runtime/tests/System/SingleTests.cs
index 53018c7a0b2208..a9701f39143466 100644
--- a/src/libraries/System.Runtime/tests/System/SingleTests.cs
+++ b/src/libraries/System.Runtime/tests/System/SingleTests.cs
@@ -40,6 +40,10 @@ public static void CompareTo_ObjectNotFloat_ThrowsArgumentException(object value
         [InlineData(float.NaN, float.NaN, 0)]
         [InlineData(float.NaN, 0.0f, -1)]
         [InlineData(234.0f, null, 1)]
+        [InlineData(float.MinValue, float.NegativeInfinity, 1)]
+        [InlineData(float.NegativeInfinity, float.MinValue, -1)]
+        [InlineData(-0f, float.NegativeInfinity, 1)]
+        [InlineData(float.NegativeInfinity, -0f, -1)]
         public static void CompareTo_Other_ReturnsExpected(float f1, object value, int expected)
         {
             if (value is float f2)
diff --git a/src/libraries/System.Runtime/tests/System/Text/RuneTests.cs b/src/libraries/System.Runtime/tests/System/Text/RuneTests.cs
index 0f97b57102f44b..fb3a87c163f19a 100644
--- a/src/libraries/System.Runtime/tests/System/Text/RuneTests.cs
+++ b/src/libraries/System.Runtime/tests/System/Text/RuneTests.cs
@@ -50,9 +50,27 @@ public static void Casing_CultureAware(int original, int upper, int lower, strin
         [InlineData('\u0130', '\u0130', '\u0130')] // U+0130 LATIN CAPITAL LETTER I WITH DOT ABOVE
         [InlineData('\u0131', '\u0131', '\u0131')] // U+0131 LATIN SMALL LETTER DOTLESS I
         [InlineData('\u1E9E', '\u1E9E', '\u1E9E')] // U+1E9E LATIN CAPITAL LETTER SHARP S
+        public static void Casing_Invariant(int original, int upper, int lower)
+        {
+            var rune = new Rune(original);
+            Assert.Equal(new Rune(upper), Rune.ToUpperInvariant(rune));
+            Assert.Equal(new Rune(lower), Rune.ToLowerInvariant(rune));
+        }
+
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsIcuGlobalization))]
+        [InlineData('0', '0', '0')]
+        [InlineData('a', 'A', 'a')]
+        [InlineData('i', 'I', 'i')]
+        [InlineData('z', 'Z', 'z')]
+        [InlineData('A', 'A', 'a')]
+        [InlineData('I', 'I', 'i')]
+        [InlineData('Z', 'Z', 'z')]
+        [InlineData('\u00DF', '\u00DF', '\u00DF')] // U+00DF LATIN SMALL LETTER SHARP S
+        [InlineData('\u0130', '\u0130', '\u0130')] // U+0130 LATIN CAPITAL LETTER I WITH DOT ABOVE
+        [InlineData('\u0131', '\u0131', '\u0131')] // U+0131 LATIN SMALL LETTER DOTLESS I
         [InlineData(0x10400, 0x10400, 0x10428)] // U+10400 DESERET CAPITAL LETTER LONG I
         [InlineData(0x10428, 0x10400, 0x10428)] // U+10428 DESERET SMALL LETTER LONG I
-        public static void Casing_Invariant(int original, int upper, int lower)
+        public static void ICU_Casing_Invariant(int original, int upper, int lower)
         {
             var rune = new Rune(original);
             Assert.Equal(new Rune(upper), Rune.ToUpperInvariant(rune));
@@ -157,6 +175,7 @@ public static void CompareTo_And_ComparisonOperators(int first, int other, int e
             Rune b = new Rune(other);
 
             Assert.Equal(expectedSign, Math.Sign(a.CompareTo(b)));
+            Assert.Equal(expectedSign, Math.Sign(((IComparable)a).CompareTo(b)));
             Assert.Equal(expectedSign < 0, a < b);
             Assert.Equal(expectedSign <= 0, a <= b);
             Assert.Equal(expectedSign > 0, a > b);
@@ -474,7 +493,24 @@ public static void Operators_And_CompareTo(uint scalarValueLeft, uint scalarValu
             Assert.Equal(scalarValueLeft <= scalarValueRight, left <= right);
             Assert.Equal(scalarValueLeft > scalarValueRight, left > right);
             Assert.Equal(scalarValueLeft >= scalarValueRight, left >= right);
-            Assert.Equal(scalarValueLeft.CompareTo(scalarValueRight), left.CompareTo(right));
+            Assert.Equal(Math.Sign(scalarValueLeft.CompareTo(scalarValueRight)), Math.Sign(left.CompareTo(right)));
+            Assert.Equal(Math.Sign(((IComparable)scalarValueLeft).CompareTo(scalarValueRight)), Math.Sign(((IComparable)left).CompareTo(right)));
+        }
+
+        [Theory]
+        [InlineData(0)]
+        [InlineData(0x10FFFF)]
+        public static void NonGenericCompareTo_NonNullAlwaysGreaterThanNull(uint scalarValue)
+        {
+            Assert.Equal(1, Math.Sign(((IComparable)new Rune(scalarValue)).CompareTo(null)));
+        }
+
+        [Fact]
+        public static void NonGenericCompareTo_GivenNonRuneArgument_ThrowsArgumentException()
+        {
+            IComparable rune = new Rune(0);
+
+            Assert.Throws<ArgumentException>(() => rune.CompareTo(0 /* int32 */));
         }
 
         [Fact]
diff --git a/src/libraries/System.Runtime/tests/System/Text/StringBuilderTests.cs b/src/libraries/System.Runtime/tests/System/Text/StringBuilderTests.cs
index 66d04633d01a05..0d2489c2030ad5 100644
--- a/src/libraries/System.Runtime/tests/System/Text/StringBuilderTests.cs
+++ b/src/libraries/System.Runtime/tests/System/Text/StringBuilderTests.cs
@@ -2230,5 +2230,23 @@ public static void EqualsIgnoresMaxCapacity()
 
             Assert.True(sb1.Equals(sb2));
         }
+
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        public static unsafe void FailureOnLargeString()
+        {
+            RemoteExecutor.Invoke(() => // Uses lots of memory
+            {
+                AssertExtensions.ThrowsAny<ArgumentOutOfRangeException, OutOfMemoryException>(() =>
+                {
+                    StringBuilder sb = new StringBuilder();
+                    sb.Append(new char[2_000_000_000]);
+                    sb.Length--;
+                    string s = new string('x', 500_000_000);
+                    sb.Append(s); // This should throw, not AV
+                });
+
+                return RemoteExecutor.SuccessExitCode; // workaround https://github.com/dotnet/arcade/issues/5865
+            }).Dispose();
+        }
     }
 }
diff --git a/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs b/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs
index f7de159162633c..ebe6a600e0d2f9 100644
--- a/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs
+++ b/src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs
@@ -1805,7 +1805,6 @@ public static void NewfoundlandTimeZone(string dateTimeString, bool expectedDST,
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/39342", TestPlatforms.Browser)]
         public static void GetSystemTimeZones()
         {
             ReadOnlyCollection<TimeZoneInfo> timeZones = TimeZoneInfo.GetSystemTimeZones();
diff --git a/src/libraries/System.Runtime/tests/System/Type/TypePropertyTests.cs b/src/libraries/System.Runtime/tests/System/Type/TypePropertyTests.cs
index 2904696e0b8a3e..026c53d1bc4608 100644
--- a/src/libraries/System.Runtime/tests/System/Type/TypePropertyTests.cs
+++ b/src/libraries/System.Runtime/tests/System/Type/TypePropertyTests.cs
@@ -10,6 +10,8 @@ public abstract class TypePropertyTestBase
     {
         public abstract Type CreateType();
 
+        public virtual int? ArrayRank => null;
+
         public abstract TypeAttributes Attributes { get; }
 
         public virtual Type BaseType => typeof(object);
@@ -28,6 +30,8 @@ public abstract class TypePropertyTestBase
 
         public virtual Type[] GenericTypeArguments => new Type[0];
 
+        public virtual Type GenericTypeDefinition => null;
+
         public virtual bool HasElementType => false;
 
         public virtual bool IsArray => false;
@@ -90,7 +94,7 @@ public void Attributes_Get_ReturnsExpected()
             Assert.Equal((Attributes & TypeAttributes.Import) != 0, t.IsImport);
             Assert.Equal((Attributes & TypeAttributes.Sealed) != 0, t.IsSealed);
             Assert.Equal((Attributes & TypeAttributes.SpecialName) != 0, t.IsSpecialName);
-            Assert.Equal((Attributes & TypeAttributes.Serializable) != 0 || t.IsEnum, t.IsSerializable);
+            Assert.Equal((Attributes & TypeAttributes.Serializable) != 0 || t.IsEnum || t == typeof(Delegate), t.IsSerializable);
 
             Assert.Equal((Attributes & TypeAttributes.ClassSemanticsMask) == TypeAttributes.Class && !t.IsValueType, t.IsClass);
             Assert.Equal((Attributes & TypeAttributes.ClassSemanticsMask) == TypeAttributes.Interface, t.IsInterface);
@@ -149,6 +153,19 @@ public void GenericTypeArguments_Get_ReturnsExpected()
             Assert.Equal(GenericTypeArguments, CreateType().GenericTypeArguments);
         }
 
+        [Fact]
+        public void GetGenericTypeDefinition_Invoke_ReturnsExpected()
+        {
+            if (GenericTypeDefinition != null)
+            {
+                Assert.Equal(GenericTypeDefinition, CreateType().GetGenericTypeDefinition());
+            }
+            else
+            {
+                Assert.Throws<InvalidOperationException>(() => CreateType().GetGenericTypeDefinition());
+            }
+        }
+
         [Fact]
         public void GenericParameterAttributes_Get_ReturnsExpected()
         {
@@ -175,6 +192,19 @@ public void GenericParameterPosition_Get_ReturnsExpected()
             }
         }
 
+        [Fact]
+        public void GetArrayRank_Invoke_ReturnsExpected()
+        {
+            if (ArrayRank != null)
+            {
+                Assert.Equal(ArrayRank, CreateType().GetArrayRank());
+            }
+            else
+            {
+                AssertExtensions.Throws<ArgumentException>(null, () => CreateType().GetArrayRank());
+            }
+        }
+
         [Fact]
         public void GetElementType_Invoke_ReturnsExpected()
         {
@@ -194,7 +224,6 @@ public void IsArray_Get_ReturnsExpected()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/31713", TestRuntimes.Mono)]
         public void IsByRef_Get_ReturnsExpected()
         {
             Type t = CreateType();
@@ -393,17 +422,14 @@ public abstract class EnumTypeTestBase : StructTypeTestBase
         public override TypeAttributes Attributes => TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.Sealed;
 
         public override Type BaseType => typeof(Enum);
-
     }
 
-    public class ByteTests : PrimitiveTypeTestBase
+    // Primitives
+    public class StringTypeTests : ClassTypeTestBase
     {
-        public override Type CreateType() => typeof(byte);
-    }
+        public override Type CreateType() => typeof(string);
 
-    public class ByteEnumTests : EnumTypeTestBase
-    {
-        public override Type CreateType() => typeof(ByteEnum);
+        public override TypeAttributes Attributes => TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.Sealed | TypeAttributes.Serializable | TypeAttributes.BeforeFieldInit;
     }
 
     public class SByteTests : PrimitiveTypeTestBase
@@ -411,19 +437,9 @@ public class SByteTests : PrimitiveTypeTestBase
         public override Type CreateType() => typeof(sbyte);
     }
 
-    public class SByteEnumTests : EnumTypeTestBase
-    {
-        public override Type CreateType() => typeof(SByteEnum);
-    }
-
-    public class UShortTests : PrimitiveTypeTestBase
-    {
-        public override Type CreateType() => typeof(ushort);
-    }
-
-    public class UShortEnumTests : EnumTypeTestBase
+    public class ByteTests : PrimitiveTypeTestBase
     {
-        public override Type CreateType() => typeof(UShortEnum);
+        public override Type CreateType() => typeof(byte);
     }
 
     public class ShortTests : PrimitiveTypeTestBase
@@ -431,19 +447,9 @@ public class ShortTests : PrimitiveTypeTestBase
         public override Type CreateType() => typeof(short);
     }
 
-    public class ShortEnumTests : EnumTypeTestBase
-    {
-        public override Type CreateType() => typeof(ShortEnum);
-    }
-
-    public class UIntTests : PrimitiveTypeTestBase
-    {
-        public override Type CreateType() => typeof(uint);
-    }
-
-    public class UIntEnumTests : EnumTypeTestBase
+    public class UShortTests : PrimitiveTypeTestBase
     {
-        public override Type CreateType() => typeof(UIntEnum);
+        public override Type CreateType() => typeof(ushort);
     }
 
     public class IntTests : PrimitiveTypeTestBase
@@ -451,19 +457,9 @@ public class IntTests : PrimitiveTypeTestBase
         public override Type CreateType() => typeof(int);
     }
 
-    public class IntEnumTests : EnumTypeTestBase
-    {
-        public override Type CreateType() => typeof(IntEnum);
-    }
-
-    public class ULongTests : PrimitiveTypeTestBase
-    {
-        public override Type CreateType() => typeof(ulong);
-    }
-
-    public class ULongEnumTests : EnumTypeTestBase
+    public class UIntTests : PrimitiveTypeTestBase
     {
-        public override Type CreateType() => typeof(ULongEnum);
+        public override Type CreateType() => typeof(uint);
     }
 
     public class LongTests : PrimitiveTypeTestBase
@@ -471,29 +467,29 @@ public class LongTests : PrimitiveTypeTestBase
         public override Type CreateType() => typeof(long);
     }
 
-    public class LongEnumTests : EnumTypeTestBase
+    public class ULongTests : PrimitiveTypeTestBase
     {
-        public override Type CreateType() => typeof(LongEnum);
+        public override Type CreateType() => typeof(ulong);
     }
 
-    public class DoubleTests : PrimitiveTypeTestBase
+    public class CharTests : PrimitiveTypeTestBase
     {
-        public override Type CreateType() => typeof(double);
+        public override Type CreateType() => typeof(char);
     }
 
-    public class FloatTests : PrimitiveTypeTestBase
+    public class BoolTests : PrimitiveTypeTestBase
     {
-        public override Type CreateType() => typeof(float);
+        public override Type CreateType() => typeof(bool);
     }
 
-    public class BoolTests : PrimitiveTypeTestBase
+    public class FloatTests : PrimitiveTypeTestBase
     {
-        public override Type CreateType() => typeof(bool);
+        public override Type CreateType() => typeof(float);
     }
 
-    public class CharTests : PrimitiveTypeTestBase
+    public class DoubleTests : PrimitiveTypeTestBase
     {
-        public override Type CreateType() => typeof(char);
+        public override Type CreateType() => typeof(double);
     }
 
     public class IntPtrTests : PrimitiveTypeTestBase
@@ -506,7 +502,12 @@ public class UIntPtrTests : PrimitiveTypeTestBase
         public override Type CreateType() => typeof(UIntPtr);
     }
 
-    public class ObjectTests : ClassTypeTestBase
+    public class VoidTests : StructTypeTestBase
+    {
+        public override Type CreateType() => typeof(void);
+    }
+
+    public class ObjectTypeTests : ClassTypeTestBase
     {
         public override Type CreateType() => typeof(object);
 
@@ -515,13 +516,29 @@ public class ObjectTests : ClassTypeTestBase
         public override Type BaseType => null;
     }
 
-    public class ValueTypeTests : ClassTypeTestBase
+    public class ArrayTypeTests : ClassTypeTestBase
+    {
+        public override Type CreateType() => typeof(Array);
+
+        public override TypeAttributes Attributes => TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.Abstract | TypeAttributes.Serializable | TypeAttributes.BeforeFieldInit;
+    }
+
+    public class ValueTypeTypeTests : ClassTypeTestBase
     {
         public override Type CreateType() => typeof(ValueType);
 
         public override TypeAttributes Attributes => TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.Public | TypeAttributes.Abstract | TypeAttributes.Serializable | TypeAttributes.BeforeFieldInit;
     }
 
+    public class DelegateTypeTests : ClassTypeTestBase
+    {
+        public override Type CreateType() => typeof(Delegate);
+
+        public override TypeAttributes Attributes => PlatformDetection.IsMonoRuntime
+            ? TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.SequentialLayout | TypeAttributes.Abstract | TypeAttributes.BeforeFieldInit
+            : TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.Abstract | TypeAttributes.BeforeFieldInit;
+    }
+
     public class EnumTypeTests : ClassTypeTestBase
     {
         public override Type CreateType() => typeof(Enum);
@@ -531,67 +548,76 @@ public class EnumTypeTests : ClassTypeTestBase
         public override Type BaseType => typeof(ValueType);
     }
 
-    public class VoidTests : StructTypeTestBase
+    // Primitives enums
+    public class SByteEnumTests : EnumTypeTestBase
     {
-        public override Type CreateType() => typeof(void);
+        public override Type CreateType() => typeof(SByteEnum);
     }
 
-    public class IntRefTests : TypePropertyTestBase
+    public class ByteEnumTests : EnumTypeTestBase
     {
-        public override Type CreateType() => typeof(int).MakeByRefType();
-
-        public override TypeAttributes Attributes => TypeAttributes.Class;
-
-        public override Type BaseType => null;
-
-        public override bool IsByRef => true;
+        public override Type CreateType() => typeof(ByteEnum);
+    }
 
-        public override bool IsTypeDefinition => false;
+    public class Int16EnumTests : EnumTypeTestBase
+    {
+        public override Type CreateType() => typeof(Int16Enum);
+    }
 
-        public override bool HasElementType => true;
+    public class UInt16EnumTests : EnumTypeTestBase
+    {
+        public override Type CreateType() => typeof(UInt16Enum);
+    }
 
-        public override Type ElementType => typeof(int);
+    public class Int32EnumTests : EnumTypeTestBase
+    {
+        public override Type CreateType() => typeof(Int32Enum);
     }
 
-    public class IntPointerTests : TypePropertyTestBase
+    public class UInt32EnumTests : EnumTypeTestBase
     {
-        public override Type CreateType() => typeof(int).MakePointerType();
+        public override Type CreateType() => typeof(UInt32Enum);
+    }
 
-        public override TypeAttributes Attributes => TypeAttributes.Class;
+    public class Int64EnumTests : EnumTypeTestBase
+    {
+        public override Type CreateType() => typeof(Int64Enum);
+    }
 
-        public override Type BaseType => null;
+    public class UInt64EnumTests : EnumTypeTestBase
+    {
+        public override Type CreateType() => typeof(UInt64Enum);
+    }
 
-        public override bool IsPointer => true;
+    // Arrays, pointers.
+    public class StringArrayTests : ArrayTypeTestBase
+    {
+        public override Type CreateType() => typeof(string[]);
 
-        public override bool IsTypeDefinition => false;
+        public override int? ArrayRank => 1;
 
-        public override bool HasElementType => true;
+        public override Type ElementType => typeof(string);
 
-        public override Type ElementType => typeof(int);
+        public override bool IsSZArray => true;
     }
 
     public class IntArrayTests : ArrayTypeTestBase
     {
         public override Type CreateType() => typeof(int[]);
 
-        public override Type ElementType => typeof(int);
-
-        public override bool IsSZArray => true;
-    }
-
-    public class MultidimensionalIntArrayTests : ArrayTypeTestBase
-    {
-        public override Type CreateType() => typeof(int[,]);
+        public override int? ArrayRank => 1;
 
         public override Type ElementType => typeof(int);
 
-        public override bool IsVariableBoundArray => true;
+        public override bool IsSZArray => true;
     }
 
     public class ArrayOfArrayTests : ArrayTypeTestBase
     {
         public override Type CreateType() => typeof(int[][]);
 
+        public override int? ArrayRank => 1;
+
         public override Type ElementType => typeof(int[]);
 
         public override bool IsSZArray => true;
@@ -601,6 +627,8 @@ public class NestedArrayTests : ArrayTypeTestBase
     {
         public override Type CreateType() => typeof(Outside.Inside[]);
 
+        public override int? ArrayRank => 1;
+
         public override Type ElementType => typeof(Outside.Inside);
 
         public override bool IsSZArray => true;
@@ -610,36 +638,83 @@ public class GenericNestedArrayTests : ArrayTypeTestBase
     {
         public override Type CreateType() => typeof(Outside<int>.Inside<double>[]);
 
+        public override int? ArrayRank => 1;
+
         public override Type ElementType => typeof(Outside<int>.Inside<double>);
 
         public override bool IsSZArray => true;
     }
 
-    public class ArrayTypeTests : ClassTypeTestBase
+    public class NonSzIntArrayTests : ArrayTypeTestBase
     {
-        public override Type CreateType() => typeof(Array);
+        public override Type CreateType() => typeof(int).MakeArrayType(1);
 
-        public override TypeAttributes Attributes => TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.Abstract | TypeAttributes.Serializable | TypeAttributes.BeforeFieldInit;
+        public override int? ArrayRank => 1;
+
+        public override Type ElementType => typeof(int);
+
+        public override bool IsVariableBoundArray => true;
     }
 
-    public class NonGenericClassTests : ClassTypeTestBase
+    public class MultidimensionalIntArrayTests : ArrayTypeTestBase
     {
-        public override Type CreateType() => typeof(NonGenericClass);
+        public override Type CreateType() => typeof(int[,]);
+
+        public override int? ArrayRank => 2;
+
+        public override Type ElementType => typeof(int);
+
+        public override bool IsVariableBoundArray => true;
     }
 
-    public class NonGenericSubClassOfNonGenericTests : ClassTypeTestBase
+    public class IntPointerTests : TypePropertyTestBase
     {
-        public override Type CreateType() => typeof(NonGenericSubClassOfNonGeneric);
+        public override Type CreateType() => typeof(int).MakePointerType();
 
-        public override Type BaseType => typeof(NonGenericClass);
+        public override TypeAttributes Attributes => TypeAttributes.Class;
+
+        public override Type BaseType => null;
+
+        public override bool IsPointer => true;
+
+        public override bool IsTypeDefinition => false;
+
+        public override bool HasElementType => true;
+
+        public override Type ElementType => typeof(int);
     }
 
-    public class TypedReferenceTypeTests : StructTypeTestBase
+    public class IntRefTests : TypePropertyTestBase
     {
-        public override Type CreateType() => typeof(TypedReference);
+        public override Type CreateType() => typeof(int).MakeByRefType();
+
+        public override TypeAttributes Attributes => TypeAttributes.Class;
+
+        public override Type BaseType => null;
+
+        public override bool IsByRef => true;
+
+        public override bool IsTypeDefinition => false;
+
+        public override bool HasElementType => true;
+
+        public override Type ElementType => typeof(int);
+    }
+
+    // Classes, structs, interfaces, enums
+    public class NonGenericClassTypeTests : ClassTypeTestBase
+    {
+        public override Type CreateType() => typeof(NonGenericClass);
+    }
+
+    public class NonGenericSubClassOfNonGenericTypeTests : ClassTypeTestBase
+    {
+        public override Type CreateType() => typeof(NonGenericSubClassOfNonGeneric);
+
+        public override Type BaseType => typeof(NonGenericClass);
     }
 
-    public class GenericClass1Tests : ClassTypeTestBase
+    public class GenericClass1TypeTests : ClassTypeTestBase
     {
         public override Type CreateType() => typeof(GenericClass<string>);
 
@@ -650,9 +725,11 @@ public class GenericClass1Tests : ClassTypeTestBase
         public override bool IsTypeDefinition => false;
 
         public override Type[] GenericTypeArguments => new Type[] { typeof(string) };
+
+        public override Type GenericTypeDefinition => typeof(GenericClass<>);
     }
 
-    public class GenericClass2Tests : ClassTypeTestBase
+    public class GenericClass2TypeTests : ClassTypeTestBase
     {
         public override Type CreateType() => typeof(GenericClass<int, string>);
 
@@ -663,9 +740,11 @@ public class GenericClass2Tests : ClassTypeTestBase
         public override bool IsTypeDefinition => false;
 
         public override Type[] GenericTypeArguments => new Type[] { typeof(int), typeof(string) };
+
+        public override Type GenericTypeDefinition => typeof(GenericClass<,>);
     }
 
-    public class OpenGenericClassTests : ClassTypeTestBase
+    public class OpenGenericClassTypeTests : ClassTypeTestBase
     {
         public override Type CreateType() => typeof(GenericClass<>);
 
@@ -674,9 +753,28 @@ public class OpenGenericClassTests : ClassTypeTestBase
         public override bool IsGenericType => true;
 
         public override bool IsGenericTypeDefinition => true;
+
+        public override Type GenericTypeDefinition => typeof(GenericClass<>);
+    }
+
+    public class OpenGenericNestedClassTypeTests : ClassTypeTestBase
+    {
+        public override Type CreateType() => typeof(GenericClass<>).MakeGenericType(typeof(GenericClass<>));
+
+        public override bool ContainsGenericParameters => true;
+
+        public override bool IsConstructedGenericType => true;
+
+        public override bool IsGenericType => true;
+
+        public override bool IsTypeDefinition => false;
+
+        public override Type[] GenericTypeArguments => new Type[] { typeof(GenericClass<>) };
+
+        public override Type GenericTypeDefinition => typeof(GenericClass<>);
     }
 
-    public class NonGenericSubClassOfGenericTests : ClassTypeTestBase
+    public class NonGenericSubClassOfGenericTypeTests : ClassTypeTestBase
     {
         public override Type CreateType() => typeof(NonGenericSubClassOfGeneric);
 
@@ -704,6 +802,8 @@ public class GenericStruct1Tests : StructTypeTestBase
         public override bool IsTypeDefinition => false;
 
         public override Type[] GenericTypeArguments => new Type[] { typeof(string) };
+
+        public override Type GenericTypeDefinition => typeof(GenericStruct<>);
     }
 
     public class GenericStruct2Tests : StructTypeTestBase
@@ -717,6 +817,8 @@ public class GenericStruct2Tests : StructTypeTestBase
         public override bool IsTypeDefinition => false;
 
         public override Type[] GenericTypeArguments => new Type[] { typeof(int), typeof(string) };
+
+        public override Type GenericTypeDefinition => typeof(GenericStruct<,>);
     }
 
     public class NonGenericInterfaceTests : InterfaceTypeTestBase
@@ -735,6 +837,8 @@ public class GenericInterface1Tests : InterfaceTypeTestBase
         public override bool IsTypeDefinition => false;
 
         public override Type[] GenericTypeArguments => new Type[] { typeof(string) };
+
+        public override Type GenericTypeDefinition => typeof(GenericInterface<>);
     }
 
     public class GenericInterface2Tests : InterfaceTypeTestBase
@@ -748,6 +852,15 @@ public class GenericInterface2Tests : InterfaceTypeTestBase
         public override bool IsTypeDefinition => false;
 
         public override Type[] GenericTypeArguments => new Type[] { typeof(int), typeof(string) };
+
+        public override Type GenericTypeDefinition => typeof(GenericInterface<,>);
+    }
+
+    public class AbstractClassTypeTests : ClassTypeTestBase
+    {
+        public override Type CreateType() => typeof(AbstractClass);
+
+        public override TypeAttributes Attributes => TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.Abstract | TypeAttributes.BeforeFieldInit;
     }
 
     public class OpenGenericInterfaceTests : InterfaceTypeTestBase
@@ -759,6 +872,8 @@ public class OpenGenericInterfaceTests : InterfaceTypeTestBase
         public override bool IsGenericType => true;
 
         public override bool IsGenericTypeDefinition => true;
+
+        public override Type GenericTypeDefinition => typeof(GenericInterface<>);
     }
 
     public class NonGenericNestedTests : TypePropertyTestBase
@@ -785,6 +900,8 @@ public class GenericNestedTests : TypePropertyTestBase
         public override bool IsTypeDefinition => false;
 
         public override Type[] GenericTypeArguments => new Type[] { typeof(int), typeof(double) };
+
+        public override Type GenericTypeDefinition => typeof(Outside<>.Inside<>);
     }
 
     public class OpenGenericNestedTests : TypePropertyTestBase
@@ -800,6 +917,8 @@ public class OpenGenericNestedTests : TypePropertyTestBase
         public override bool IsGenericType => true;
 
         public override bool IsGenericTypeDefinition => true;
+
+        public override Type GenericTypeDefinition => typeof(Outside<>.Inside<>);
     }
 
     public class GenericTypeParameter1Of1Tests : TypePropertyTestBase
@@ -939,7 +1058,7 @@ public class GenericMethodParameter2Of2Tests : TypePropertyTestBase
         public override int? GenericParameterPosition => 1;
     }
 
-    public class MarshalByRefObjectTests : ClassTypeTestBase
+    public class MarshalByRefObjectTypeTests : ClassTypeTestBase
     {
         public override Type CreateType() => typeof(MarshalByRefObject);
 
@@ -949,7 +1068,7 @@ public class MarshalByRefObjectTests : ClassTypeTestBase
         public override bool IsMarshalByRef => false;
     }
 
-    public class ContextBoundObjectTests : ClassTypeTestBase
+    public class ContextBoundObjectTypeTests : ClassTypeTestBase
     {
         public override Type CreateType() => typeof(ContextBoundObject);
 
@@ -962,19 +1081,38 @@ public class ContextBoundObjectTests : ClassTypeTestBase
         public override bool IsContextful => false;
     }
 
-    public enum ByteEnum : byte { }
+    // By-Ref types.
+    public class TypedReferenceTypeTests : StructTypeTestBase
+    {
+        public override Type CreateType() => typeof(TypedReference);
+    }
 
-    public enum SByteEnum : sbyte { }
+    public class ArgIteratorTypeTests : StructTypeTestBase
+    {
+        public override Type CreateType() => typeof(ArgIterator);
 
-    public enum UShortEnum : ushort { }
+        public override TypeAttributes Attributes => PlatformDetection.IsMonoRuntime
+            ? TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.Sealed | TypeAttributes.BeforeFieldInit
+            : TypeAttributes.AutoLayout | TypeAttributes.AnsiClass | TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.SequentialLayout | TypeAttributes.Sealed | TypeAttributes.BeforeFieldInit;
+    }
 
-    public enum ShortEnum : short { }
+    public class RuntimeArgumentHandleTypeTests : StructTypeTestBase
+    {
+        public override Type CreateType() => typeof(RuntimeArgumentHandle);
+    }
 
-    public enum UIntEnum : uint { }
+    public class SpanIntTypeTests : StructTypeTestBase
+    {
+        public override Type CreateType() => typeof(Span<int>);
+
+        public override Type[] GenericTypeArguments => new Type[] { typeof(int) };
 
-    public enum IntEnum : int { }
+        public override bool IsConstructedGenericType => true;
 
-    public enum ULongEnum : ulong { }
+        public override bool IsGenericType => true;
 
-    public enum LongEnum : long { }
+        public override bool IsTypeDefinition => false;
+
+        public override Type GenericTypeDefinition => typeof(Span<>);
+    }
 }
diff --git a/src/libraries/System.Runtime/tests/System/Type/TypeTests.cs b/src/libraries/System.Runtime/tests/System/Type/TypeTests.cs
index 05236cc36cb78c..d801b567140a28 100644
--- a/src/libraries/System.Runtime/tests/System/Type/TypeTests.cs
+++ b/src/libraries/System.Runtime/tests/System/Type/TypeTests.cs
@@ -174,23 +174,6 @@ public void GetTypeFromDefaultHandle()
             Assert.Null(Type.GetTypeFromHandle(default(RuntimeTypeHandle)));
         }
 
-        [Theory]
-        [InlineData(typeof(int[]), 1)]
-        [InlineData(typeof(int[,,]), 3)]
-        public void GetArrayRank_Get_ReturnsExpected(Type t, int expected)
-        {
-            Assert.Equal(expected, t.GetArrayRank());
-        }
-
-        [Theory]
-        [InlineData(typeof(int))]
-        [InlineData(typeof(IList<int>))]
-        [InlineData(typeof(IList<>))]
-        public void GetArrayRank_NonArrayType_ThrowsArgumentException(Type t)
-        {
-            AssertExtensions.Throws<ArgumentException>(null, () => t.GetArrayRank());
-        }
-
         public static IEnumerable<object[]> MakeArrayType_TestData()
         {
             return new object[][]
@@ -346,23 +329,168 @@ public void MakeArrayType_InvalidArrayRank_ThrowsTypeLoadException(int rank)
             Assert.Throws<TypeLoadException>(() => t.MakeArrayType(rank));
         }
 
+        public static IEnumerable<object[]> MakeByRefType_TestData()
+        {
+            return new object[][]
+            {
+                // Primitives
+                new object[] { typeof(string) },
+                new object[] { typeof(sbyte) },
+                new object[] { typeof(byte) },
+                new object[] { typeof(short) },
+                new object[] { typeof(ushort) },
+                new object[] { typeof(int) },
+                new object[] { typeof(uint) },
+                new object[] { typeof(long) },
+                new object[] { typeof(ulong) },
+                new object[] { typeof(char) },
+                new object[] { typeof(bool) },
+                new object[] { typeof(float) },
+                new object[] { typeof(double) },
+                new object[] { typeof(IntPtr) },
+                new object[] { typeof(UIntPtr) },
+                new object[] { typeof(void) },
+
+                // Primitives enums
+                new object[] { typeof(SByteEnum) },
+                new object[] { typeof(ByteEnum) },
+                new object[] { typeof(Int16Enum) },
+                new object[] { typeof(UInt16Enum) },
+                new object[] { typeof(Int32Enum) },
+                new object[] { typeof(UInt32Enum) },
+                new object[] { typeof(Int64Enum) },
+                new object[] { typeof(UInt64Enum) },
+
+                // Array, pointers
+                new object[] { typeof(string[]) },
+                new object[] { typeof(int[]) },
+                new object[] { typeof(int*) },
+
+                // Classes, structs, interfaces, enums
+                new object[] { typeof(NonGenericClass) },
+                new object[] { typeof(GenericClass<int>) },
+                new object[] { typeof(NonGenericStruct) },
+                new object[] { typeof(GenericStruct<int>) },
+                new object[] { typeof(NonGenericInterface) },
+                new object[] { typeof(GenericInterface<int>) },
+                new object[] { typeof(AbstractClass) },
+                new object[] { typeof(StaticClass) },
+
+                // Generic types.
+                new object[] { typeof(GenericClass<>) },
+                new object[] { typeof(GenericClass<>).MakeGenericType(typeof(GenericClass<>)) },
+                new object[] { typeof(GenericClass<>).GetTypeInfo().GetGenericArguments()[0] },
+
+                // By-Ref Like.
+                new object[] { typeof(TypedReference) },
+                new object[] { typeof(ArgIterator) },
+                new object[] { typeof(RuntimeArgumentHandle) },
+                new object[] { typeof(Span<int>) },
+            };
+        }
+
         [Theory]
-        [InlineData(typeof(int))]
+        [MemberData(nameof(MakeByRefType_TestData))]
         public void MakeByRefType_Invoke_ReturnsExpected(Type t)
         {
-            Type tRef1 = t.MakeByRefType();
-            Type tRef2 = t.MakeByRefType();
+            Type tPointer = t.MakeByRefType();
+            Assert.Equal(tPointer, t.MakeByRefType());
+
+            Assert.True(tPointer.IsByRef);
+            Assert.False(tPointer.IsPointer);
+            Assert.True(tPointer.HasElementType);
+            Assert.Equal(t, tPointer.GetElementType());
+
+            Assert.Equal(t.ToString() + "&", tPointer.ToString());
+        }
+
+        [Fact]
+        public void MakeByRefType_ByRef_ThrowsTypeLoadException()
+        {
+            Type t = typeof(int).MakeByRefType();
+            Assert.Throws<TypeLoadException>(() => t.MakeByRefType());
+        }
 
-            Assert.Equal(tRef1, tRef2);
+        public static IEnumerable<object[]> MakePointerType_TestData()
+        {
+            return new object[][]
+            {
+                // Primitives
+                new object[] { typeof(string) },
+                new object[] { typeof(sbyte) },
+                new object[] { typeof(byte) },
+                new object[] { typeof(short) },
+                new object[] { typeof(ushort) },
+                new object[] { typeof(int) },
+                new object[] { typeof(uint) },
+                new object[] { typeof(long) },
+                new object[] { typeof(ulong) },
+                new object[] { typeof(char) },
+                new object[] { typeof(bool) },
+                new object[] { typeof(float) },
+                new object[] { typeof(double) },
+                new object[] { typeof(IntPtr) },
+                new object[] { typeof(UIntPtr) },
+                new object[] { typeof(void) },
 
-            Assert.True(tRef1.IsByRef);
-            Assert.True(tRef1.HasElementType);
+                // Primitives enums
+                new object[] { typeof(SByteEnum) },
+                new object[] { typeof(ByteEnum) },
+                new object[] { typeof(Int16Enum) },
+                new object[] { typeof(UInt16Enum) },
+                new object[] { typeof(Int32Enum) },
+                new object[] { typeof(UInt32Enum) },
+                new object[] { typeof(Int64Enum) },
+                new object[] { typeof(UInt64Enum) },
 
-            Assert.Equal(t, tRef1.GetElementType());
+                // Array, pointers
+                new object[] { typeof(string[]) },
+                new object[] { typeof(int[]) },
+                new object[] { typeof(int*) },
 
-            string s1 = t.ToString();
-            string s2 = tRef1.ToString();
-            Assert.Equal(s2, s1 + "&");
+                // Classes, structs, interfaces, enums
+                new object[] { typeof(NonGenericClass) },
+                new object[] { typeof(GenericClass<int>) },
+                new object[] { typeof(NonGenericStruct) },
+                new object[] { typeof(GenericStruct<int>) },
+                new object[] { typeof(NonGenericInterface) },
+                new object[] { typeof(GenericInterface<int>) },
+                new object[] { typeof(AbstractClass) },
+                new object[] { typeof(StaticClass) },
+
+                // Generic types.
+                new object[] { typeof(GenericClass<>) },
+                new object[] { typeof(GenericClass<>).MakeGenericType(typeof(GenericClass<>)) },
+                new object[] { typeof(GenericClass<>).GetTypeInfo().GetGenericArguments()[0] },
+
+                // ByRef Like.
+                new object[] { typeof(TypedReference) },
+                new object[] { typeof(ArgIterator) },
+                new object[] { typeof(RuntimeArgumentHandle) },
+                new object[] { typeof(Span<int>) },
+            };
+        }
+
+        [Theory]
+        [MemberData(nameof(MakePointerType_TestData))]
+        public void MakePointerType_Invoke_ReturnsExpected(Type t)
+        {
+            Type tPointer = t.MakePointerType();
+            Assert.Equal(tPointer, t.MakePointerType());
+
+            Assert.False(tPointer.IsByRef);
+            Assert.True(tPointer.IsPointer);
+            Assert.True(tPointer.HasElementType);
+            Assert.Equal(t, tPointer.GetElementType());
+
+            Assert.Equal(t.ToString() + "*", tPointer.ToString());
+        }
+
+        [Fact]
+        public void MakePointerType_ByRef_ThrowsTypeLoadException()
+        {
+            Type t = typeof(int).MakeByRefType();
+            Assert.Throws<TypeLoadException>(() => t.MakePointerType());
         }
 
         [Theory]
diff --git a/src/libraries/System.Runtime/tests/TrimmingTests/DefaultValueAttributeCtorTest.cs b/src/libraries/System.Runtime/tests/TrimmingTests/DefaultValueAttributeCtorTest.cs
index 0aa104fb79f962..1d9a6ec4012610 100644
--- a/src/libraries/System.Runtime/tests/TrimmingTests/DefaultValueAttributeCtorTest.cs
+++ b/src/libraries/System.Runtime/tests/TrimmingTests/DefaultValueAttributeCtorTest.cs
@@ -13,10 +13,6 @@ class Program
 {
     static int Main(string[] args)
     {
-        // workaround TypeConverterAttribute not being annotated correctly
-        // https://github.com/dotnet/runtime/issues/39125
-        var _ = new MyStringConverter();
-
         TypeDescriptor.AddAttributes(typeof(string), new TypeConverterAttribute(typeof(MyStringConverter)));
 
         var attribute = new DefaultValueAttribute(typeof(string), "Hello, world!");
diff --git a/src/libraries/System.Runtime/tests/TrimmingTests/InterfacesOnArrays.cs b/src/libraries/System.Runtime/tests/TrimmingTests/InterfacesOnArrays.cs
new file mode 100644
index 00000000000000..f8c76da9399847
--- /dev/null
+++ b/src/libraries/System.Runtime/tests/TrimmingTests/InterfacesOnArrays.cs
@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Generic;
+
+class Program
+{
+    class Mine { }
+
+    static int Main()
+    {
+        Mine[] s = new Mine[1] { new Mine() };
+        Mine[] d = new Mine[1];
+        ((ICollection<Mine>)s).CopyTo(d, 0);
+        return s[0] == d[0] ? 100 : -1;
+    }
+}
diff --git a/src/libraries/System.Runtime/tests/TrimmingTests/System.Runtime.TrimmingTests.proj b/src/libraries/System.Runtime/tests/TrimmingTests/System.Runtime.TrimmingTests.proj
index ce96e07448a3cc..ce80b61eec67b0 100644
--- a/src/libraries/System.Runtime/tests/TrimmingTests/System.Runtime.TrimmingTests.proj
+++ b/src/libraries/System.Runtime/tests/TrimmingTests/System.Runtime.TrimmingTests.proj
@@ -9,6 +9,7 @@
     <TestConsoleAppSourceFiles Include="DebuggerTypeProxyAttributeTests.cs" />
     <TestConsoleAppSourceFiles Include="DefaultValueAttributeCtorTest.cs" />
     <TestConsoleAppSourceFiles Include="GenericArraySortHelperTest.cs" />
+    <TestConsoleAppSourceFiles Include="InterfacesOnArrays.cs" />
     <TestConsoleAppSourceFiles Include="StackFrameHelperTest.cs">
       <!-- There is a bug with the linker where it is corrupting the pdbs while trimming
       causing the framework to not be able to get source line info any longer. This
diff --git a/src/libraries/System.Security.AccessControl/Directory.Build.props b/src/libraries/System.Security.AccessControl/Directory.Build.props
index 27a4a5522a2778..33e65b7cb46516 100644
--- a/src/libraries/System.Security.AccessControl/Directory.Build.props
+++ b/src/libraries/System.Security.AccessControl/Directory.Build.props
@@ -2,8 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
-    <IsNETCoreAppRef>false</IsNETCoreAppRef>
     <IsWindowsSpecific>true</IsWindowsSpecific>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.AccessControl/ref/System.Security.AccessControl.csproj b/src/libraries/System.Security.AccessControl/ref/System.Security.AccessControl.csproj
index d5c601747004d8..b586ad27053743 100644
--- a/src/libraries/System.Security.AccessControl/ref/System.Security.AccessControl.csproj
+++ b/src/libraries/System.Security.AccessControl/ref/System.Security.AccessControl.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -12,14 +11,11 @@
   <ItemGroup>
     <Compile Include="System.Security.AccessControl.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-  </ItemGroup>
   <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
-    <ProjectReference Include="..\..\System.Security.Principal.Windows\ref\System.Security.Principal.Windows.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\ref\System.Security.Principal.Windows.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Collections.NonGeneric\ref\System.Collections.NonGeneric.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.NonGeneric\ref\System.Collections.NonGeneric.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.AccessControl/src/System.Security.AccessControl.csproj b/src/libraries/System.Security.AccessControl/src/System.Security.AccessControl.csproj
index 5218ab9aa1ae9d..5da1fe7abb5610 100644
--- a/src/libraries/System.Security.AccessControl/src/System.Security.AccessControl.csproj
+++ b/src/libraries/System.Security.AccessControl/src/System.Security.AccessControl.csproj
@@ -1,9 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT;netcoreapp2.0-Windows_NT;netstandard2.0;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT;netcoreapp2.0-Windows_NT;netstandard2.0</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -11,9 +10,6 @@
     <IsPartialFacadeAssembly Condition="$(TargetFramework.StartsWith('net4'))">true</IsPartialFacadeAssembly>
     <GeneratePlatformNotSupportedAssemblyMessage Condition="$(TargetFramework.StartsWith('netstandard'))">SR.PlatformNotSupported_AccessControl</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-  </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or $(TargetFramework.StartsWith('netcoreapp2.0'))">
     <Compile Include="System\Security\AccessControl\ACE.cs" />
     <Compile Include="System\Security\AccessControl\ACL.cs" />
@@ -82,19 +78,20 @@
     <Compile Include="$(CommonPath)Interop\Windows\Advapi32\Interop.DuplicateTokenEx_SafeTokenHandle.cs"
              Link="Common\Interop\Interop.DuplicateTokenEx_SafeTokenHandle.cs" />
   </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="System.Collections.NonGeneric" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Security.Principal.Windows" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or $(TargetFramework.StartsWith('netcoreapp2.0'))">
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or
+                        $(TargetFramework.StartsWith('netcoreapp2.0'))">
     <Reference Include="System.Collections" />
+    <Reference Include="System.Collections.NonGeneric" />
     <Reference Include="System.Diagnostics.Debug" />
+    <Reference Include="System.Resources.ResourceManager" />
+    <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Thread" />
     <Reference Include="Microsoft.Win32.Primitives" />
   </ItemGroup>
+  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.AccessControl/tests/System.Security.AccessControl.Tests.csproj b/src/libraries/System.Security.AccessControl/tests/System.Security.AccessControl.Tests.csproj
index 386ccc3d90526b..2d5068b4dcb7a4 100644
--- a/src/libraries/System.Security.AccessControl/tests/System.Security.AccessControl.Tests.csproj
+++ b/src/libraries/System.Security.AccessControl/tests/System.Security.AccessControl.Tests.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <UnsupportedPlatforms>Linux;NetBSD;OSX</UnsupportedPlatforms>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Ace\Ace.Common.Tests.cs" />
@@ -68,4 +67,7 @@
     <Compile Include="SystemAcl\SystemAcl_SetAudit.cs" />
     <Compile Include="Utils.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.IO.FileSystem.AccessControl\src\System.IO.FileSystem.AccessControl.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Claims/Directory.Build.props b/src/libraries/System.Security.Claims/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Security.Claims/Directory.Build.props
+++ b/src/libraries/System.Security.Claims/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Claims/src/System.Security.Claims.csproj b/src/libraries/System.Security.Claims/src/System.Security.Claims.csproj
index 2e3b10f4d02477..ca146c46b5db16 100644
--- a/src/libraries/System.Security.Claims/src/System.Security.Claims.csproj
+++ b/src/libraries/System.Security.Claims/src/System.Security.Claims.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Security.Claims</AssemblyName>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
diff --git a/src/libraries/System.Security.Cryptography.Algorithms/Directory.Build.props b/src/libraries/System.Security.Cryptography.Algorithms/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Security.Cryptography.Algorithms/Directory.Build.props
+++ b/src/libraries/System.Security.Cryptography.Algorithms/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.Algorithms/src/Internal/Cryptography/Helpers.cs b/src/libraries/System.Security.Cryptography.Algorithms/src/Internal/Cryptography/Helpers.cs
index 8854940afbeb43..dc900c0ac0a7a2 100644
--- a/src/libraries/System.Security.Cryptography.Algorithms/src/Internal/Cryptography/Helpers.cs
+++ b/src/libraries/System.Security.Cryptography.Algorithms/src/Internal/Cryptography/Helpers.cs
@@ -58,15 +58,5 @@ public static byte[] FixupKeyParity(this byte[] key)
             }
             return oddParityKey;
         }
-
-        internal static void ConvertIntToByteArray(uint value, byte[] dest)
-        {
-            Debug.Assert(dest != null);
-            Debug.Assert(dest.Length == 4);
-            dest[0] = (byte)((value & 0xFF000000) >> 24);
-            dest[1] = (byte)((value & 0xFF0000) >> 16);
-            dest[2] = (byte)((value & 0xFF00) >> 8);
-            dest[3] = (byte)(value & 0xFF);
-        }
     }
 }
diff --git a/src/libraries/System.Security.Cryptography.Algorithms/src/Resources/Strings.resx b/src/libraries/System.Security.Cryptography.Algorithms/src/Resources/Strings.resx
index 16f4d59628960f..9ca47b53977f28 100644
--- a/src/libraries/System.Security.Cryptography.Algorithms/src/Resources/Strings.resx
+++ b/src/libraries/System.Security.Cryptography.Algorithms/src/Resources/Strings.resx
@@ -348,8 +348,8 @@
   <data name="Cryptography_Okm_TooLarge" xml:space="preserve">
     <value>Output keying material length can be at most {0} bytes (255 * hash length).</value>
   </data>
-  <data name="Cryptography_PlatformNotSupported_Browser" xml:space="preserve">
-    <value>System.Security.Cryptography is not supported on Browser.</value>
+  <data name="SystemSecurityCryptographyAlgorithms_PlatformNotSupported" xml:space="preserve">
+    <value>System.Security.Cryptography.Algorithms is not supported on this platform.</value>
   </data>
   <data name="Cryptography_ExceedKdfExtractLimit" xml:space="preserve">
     <value>The total number of bytes extracted cannot exceed UInt32.MaxValue * hash length.</value>
diff --git a/src/libraries/System.Security.Cryptography.Algorithms/src/System.Security.Cryptography.Algorithms.csproj b/src/libraries/System.Security.Cryptography.Algorithms/src/System.Security.Cryptography.Algorithms.csproj
index 3484688c02d7f3..cf865818cc0c4f 100644
--- a/src/libraries/System.Security.Cryptography.Algorithms/src/System.Security.Cryptography.Algorithms.csproj
+++ b/src/libraries/System.Security.Cryptography.Algorithms/src/System.Security.Cryptography.Algorithms.csproj
@@ -9,7 +9,7 @@
   <Import Project="$(CommonPath)System\Security\Cryptography\Asn1\AsnXml.targets" />
   <Import Project="$(CommonPath)System\Security\Cryptography\Asn1Reader\System.Security.Cryptography.Asn1Reader.Shared.projitems" />
   <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.Cryptography_PlatformNotSupported_Browser</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemSecurityCryptographyAlgorithms_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
     <GeneratePlatformNotSupportedAdditionalParameters Condition="'$(TargetsBrowser)' == 'true'">--exclude-api-list ExcludeApiList.PNSE.Browser.txt</GeneratePlatformNotSupportedAdditionalParameters>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' != 'true'">
diff --git a/src/libraries/System.Security.Cryptography.Algorithms/src/System/Security/Cryptography/PKCS1MaskGenerationMethod.cs b/src/libraries/System.Security.Cryptography.Algorithms/src/System/Security/Cryptography/PKCS1MaskGenerationMethod.cs
index 6688025b1f0809..4e24f7eae2cfc3 100644
--- a/src/libraries/System.Security.Cryptography.Algorithms/src/System/Security/Cryptography/PKCS1MaskGenerationMethod.cs
+++ b/src/libraries/System.Security.Cryptography.Algorithms/src/System/Security/Cryptography/PKCS1MaskGenerationMethod.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Buffers.Binary;
 using System.Diagnostics;
 using Internal.Cryptography;
 
@@ -38,7 +39,7 @@ public override byte[] GenerateMask(byte[] rgbSeed, int cbReturn)
                 for (int ib = 0; ib < rgbT.Length;)
                 {
                     //  Increment counter -- up to 2^32 * sizeof(Hash)
-                    Helpers.ConvertIntToByteArray(counter++, rgbCounter);
+                    BinaryPrimitives.WriteUInt32BigEndian(rgbCounter, counter++);
                     hasher.TransformBlock(rgbSeed, 0, rgbSeed.Length, rgbSeed, 0);
                     hasher.TransformFinalBlock(rgbCounter, 0, 4);
                     Debug.Assert(hasher.Hash != null);
diff --git a/src/libraries/System.Security.Cryptography.Algorithms/tests/Rfc2898Tests.cs b/src/libraries/System.Security.Cryptography.Algorithms/tests/Rfc2898Tests.cs
index e4ec0101290fcc..3a13bd7b3e8900 100644
--- a/src/libraries/System.Security.Cryptography.Algorithms/tests/Rfc2898Tests.cs
+++ b/src/libraries/System.Security.Cryptography.Algorithms/tests/Rfc2898Tests.cs
@@ -518,6 +518,7 @@ private static IEnumerable<KnownValuesTestCase> GetKnownValuesTestCases()
             {
                 CaseName = "SHA256 alternate",
                 HashAlgorithmName = "SHA256",
+                // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy credentials.")]
                 Password = "abcdefghij",
                 Salt = ascii.GetBytes("abcdefghij"),
                 IterationCount = 1,
@@ -532,6 +533,7 @@ private static IEnumerable<KnownValuesTestCase> GetKnownValuesTestCases()
             {
                 CaseName = "SHA384 alternate",
                 HashAlgorithmName = "SHA384",
+                // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy credentials.")]
                 Password = "abcdefghij",
                 Salt = ascii.GetBytes("abcdefghij"),
                 IterationCount = 1,
@@ -546,6 +548,7 @@ private static IEnumerable<KnownValuesTestCase> GetKnownValuesTestCases()
             {
                 CaseName = "SHA512 alternate",
                 HashAlgorithmName = "SHA512",
+                // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy credentials.")]
                 Password = "abcdefghij",
                 Salt = ascii.GetBytes("abcdefghij"),
                 IterationCount = 1,
diff --git a/src/libraries/System.Security.Cryptography.Algorithms/tests/System.Security.Cryptography.Algorithms.Tests.csproj b/src/libraries/System.Security.Cryptography.Algorithms/tests/System.Security.Cryptography.Algorithms.Tests.csproj
index 6dd12410eb03bf..c10e46d862063f 100644
--- a/src/libraries/System.Security.Cryptography.Algorithms/tests/System.Security.Cryptography.Algorithms.Tests.csproj
+++ b/src/libraries/System.Security.Cryptography.Algorithms/tests/System.Security.Cryptography.Algorithms.Tests.csproj
@@ -225,4 +225,8 @@
     <Compile Include="AesGcmTests.cs" />
     <Compile Include="HKDFTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Cng\src\System.Security.Cryptography.Cng.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Pkcs\src\System.Security.Cryptography.Pkcs.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.Cng/Directory.Build.props b/src/libraries/System.Security.Cryptography.Cng/Directory.Build.props
index 27a4a5522a2778..33e65b7cb46516 100644
--- a/src/libraries/System.Security.Cryptography.Cng/Directory.Build.props
+++ b/src/libraries/System.Security.Cryptography.Cng/Directory.Build.props
@@ -2,8 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
-    <IsNETCoreAppRef>false</IsNETCoreAppRef>
     <IsWindowsSpecific>true</IsWindowsSpecific>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.Cng/ref/System.Security.Cryptography.Cng.cs b/src/libraries/System.Security.Cryptography.Cng/ref/System.Security.Cryptography.Cng.cs
index 9fb5beead82cbe..97fbd6c4efbb22 100644
--- a/src/libraries/System.Security.Cryptography.Cng/ref/System.Security.Cryptography.Cng.cs
+++ b/src/libraries/System.Security.Cryptography.Cng/ref/System.Security.Cryptography.Cng.cs
@@ -169,7 +169,6 @@ public CngKeyCreationParameters() { }
         public System.Security.Cryptography.CngKeyUsages? KeyUsage { get { throw null; } set { } }
         public System.Security.Cryptography.CngPropertyCollection Parameters { get { throw null; } }
         public System.IntPtr ParentWindowHandle { get { throw null; } set { } }
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
         public System.Security.Cryptography.CngProvider Provider { get { throw null; } set { } }
         public System.Security.Cryptography.CngUIPolicy? UIPolicy { get { throw null; } set { } }
     }
diff --git a/src/libraries/System.Security.Cryptography.Cng/ref/System.Security.Cryptography.Cng.csproj b/src/libraries/System.Security.Cryptography.Cng/ref/System.Security.Cryptography.Cng.csproj
index 6650cbce60e9d9..5828d68729988f 100644
--- a/src/libraries/System.Security.Cryptography.Cng/ref/System.Security.Cryptography.Cng.csproj
+++ b/src/libraries/System.Security.Cryptography.Cng/ref/System.Security.Cryptography.Cng.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.1;net461;net462;net47;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.1;net461;net462;net47</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -17,18 +16,14 @@
   <ItemGroup>
     <Compile Include="System.Security.Cryptography.Cng.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' == 'true'">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
-  </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Algorithms\ref\System.Security.Cryptography.Algorithms.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Primitives\ref\System.Security.Cryptography.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Algorithms\ref\System.Security.Cryptography.Algorithms.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Primitives\ref\System.Security.Cryptography.Primitives.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0'">
-    <Reference Include="System.Runtime" />
     <Reference Include="System.IO" />
+    <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Handles" />
     <Reference Include="System.Security.Cryptography.Algorithms" />
     <Reference Include="System.Security.Cryptography.Primitives" />
diff --git a/src/libraries/System.Security.Cryptography.Cng/src/Internal/Cryptography/BasicSymmetricCipherNCrypt.cs b/src/libraries/System.Security.Cryptography.Cng/src/Internal/Cryptography/BasicSymmetricCipherNCrypt.cs
index 47754356c9391f..9b88e7e5382c35 100644
--- a/src/libraries/System.Security.Cryptography.Cng/src/Internal/Cryptography/BasicSymmetricCipherNCrypt.cs
+++ b/src/libraries/System.Security.Cryptography.Cng/src/Internal/Cryptography/BasicSymmetricCipherNCrypt.cs
@@ -112,8 +112,8 @@ private void Reset()
         private readonly bool _encrypting;
 
         private static readonly CngProperty s_ECBMode =
-            new CngProperty(Interop.NCrypt.NCRYPT_CHAINING_MODE_PROPERTY, Encoding.UTF8.GetBytes(Interop.BCrypt.BCRYPT_CHAIN_MODE_ECB + "\0"), CngPropertyOptions.None);
+            new CngProperty(Interop.NCrypt.NCRYPT_CHAINING_MODE_PROPERTY, Encoding.Unicode.GetBytes(Interop.BCrypt.BCRYPT_CHAIN_MODE_ECB + "\0"), CngPropertyOptions.None);
         private static readonly CngProperty s_CBCMode =
-            new CngProperty(Interop.NCrypt.NCRYPT_CHAINING_MODE_PROPERTY, Encoding.UTF8.GetBytes(Interop.BCrypt.BCRYPT_CHAIN_MODE_CBC + "\0"), CngPropertyOptions.None);
+            new CngProperty(Interop.NCrypt.NCRYPT_CHAINING_MODE_PROPERTY, Encoding.Unicode.GetBytes(Interop.BCrypt.BCRYPT_CHAIN_MODE_CBC + "\0"), CngPropertyOptions.None);
     }
 }
diff --git a/src/libraries/System.Security.Cryptography.Cng/src/Microsoft/Win32/SafeHandles/NCryptSafeHandles.cs b/src/libraries/System.Security.Cryptography.Cng/src/Microsoft/Win32/SafeHandles/NCryptSafeHandles.cs
index 13c292f6d7f10f..28508857bc2b8c 100644
--- a/src/libraries/System.Security.Cryptography.Cng/src/Microsoft/Win32/SafeHandles/NCryptSafeHandles.cs
+++ b/src/libraries/System.Security.Cryptography.Cng/src/Microsoft/Win32/SafeHandles/NCryptSafeHandles.cs
@@ -98,8 +98,8 @@ protected SafeNCryptHandle(IntPtr handle, SafeHandle parentHandle)
         /// <summary>
         ///     Wrapper for the _holder field which ensures that we're in a consistent state
         /// </summary>
-        [MaybeNull]
-        private SafeNCryptHandle Holder
+        [DisallowNull]
+        private SafeNCryptHandle? Holder
         {
             get
             {
diff --git a/src/libraries/System.Security.Cryptography.Cng/src/System.Security.Cryptography.Cng.csproj b/src/libraries/System.Security.Cryptography.Cng/src/System.Security.Cryptography.Cng.csproj
index 19dc0301e45569..f689e3889e4d56 100644
--- a/src/libraries/System.Security.Cryptography.Cng/src/System.Security.Cryptography.Cng.csproj
+++ b/src/libraries/System.Security.Cryptography.Cng/src/System.Security.Cryptography.Cng.csproj
@@ -2,9 +2,8 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <GenFacadesIgnoreMissingTypes Condition="'$(TargetFramework)' == 'net461'">true</GenFacadesIgnoreMissingTypes>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent);netstandard2.0;netstandard2.1;net461-Windows_NT;netcoreapp3.0-Windows_NT;netcoreapp3.0;net462-Windows_NT;net47-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent);netstandard2.0;netstandard2.1;net461-Windows_NT;netcoreapp3.0-Windows_NT;netcoreapp3.0;net462-Windows_NT;net47-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -355,18 +354,17 @@
   <ItemGroup>
     <None Include="@(AsnXml)" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' == 'true'">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
-  </ItemGroup>
   <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Formats.Asn1\src\System.Formats.Asn1.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or
+                        $(TargetFramework.StartsWith('netcoreapp3.0'))">
     <Reference Include="System.Buffers" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Diagnostics.Tools" />
     <Reference Include="System.Linq" />
-    <Reference Include="System.Formats.Asn1" />
     <Reference Include="System.Memory" />
     <Reference Include="System.Resources.ResourceManager" />
     <Reference Include="System.Runtime" />
@@ -380,4 +378,11 @@
     <Reference Include="System.Text.Encoding.Extensions" />
     <Reference Include="System.Threading" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <!-- Ref assembly for netstandard2.0 isn't live built anymore. -->
+    <PackageDownload Include="$(MSBuildProjectName)" Version="[$(SystemSecurityCryptographyCngVersion)]" />
+    <ResolvedMatchingContract Include="$(NuGetPackageRoot)$(MSBuildProjectName.ToLowerInvariant())\$(SystemSecurityCryptographyCngVersion)\ref\$(TargetFramework)\$(MSBuildProjectName).dll" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.Cng/tests/AesCngTests.cs b/src/libraries/System.Security.Cryptography.Cng/tests/AesCngTests.cs
index abd62a6fbc25d1..981242fd983a26 100644
--- a/src/libraries/System.Security.Cryptography.Cng/tests/AesCngTests.cs
+++ b/src/libraries/System.Security.Cryptography.Cng/tests/AesCngTests.cs
@@ -11,7 +11,6 @@ public static class AesCngTests
 
         private static readonly CngAlgorithm s_cngAlgorithm = new CngAlgorithm("AES");
 
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/31092")]
         [OuterLoop(/* Creates/Deletes a persisted key, limit exposure to key leaking */)]
         [ConditionalTheory(nameof(SupportsPersistedSymmetricKeys))]
         // AES128-ECB-NoPadding 2 blocks.
@@ -48,7 +47,6 @@ public static void GetKey_NonExportable()
                 keyName => new AesCng(keyName));
         }
 
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/31092")]
         [OuterLoop(/* Creates/Deletes a persisted key, limit exposure to key leaking */)]
         [ConditionalFact(nameof(SupportsPersistedSymmetricKeys))]
         public static void SetKey_DetachesFromPersistedKey()
@@ -75,7 +73,6 @@ public static void LoadWrongKeyType()
             }
         }
 
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/31092")]
         [OuterLoop(/* Creates/Deletes a persisted key, limit exposure to key leaking */)]
         [ConditionalFact(nameof(SupportsPersistedSymmetricKeys), nameof(IsAdministrator))]
         public static void VerifyMachineKey()
diff --git a/src/libraries/System.Security.Cryptography.Cng/tests/System.Security.Cryptography.Cng.Tests.csproj b/src/libraries/System.Security.Cryptography.Cng/tests/System.Security.Cryptography.Cng.Tests.csproj
index 395f9a3db84454..86112ff45cfe91 100644
--- a/src/libraries/System.Security.Cryptography.Cng/tests/System.Security.Cryptography.Cng.Tests.csproj
+++ b/src/libraries/System.Security.Cryptography.Cng/tests/System.Security.Cryptography.Cng.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <DefineConstants>$(DefineConstants);TESTING_CNG_IMPLEMENTATION</DefineConstants>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net47-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="CreateTests.cs" />
@@ -165,4 +165,8 @@
     <Compile Include="$(CommonTestPath)System\Security\Cryptography\AlgorithmImplementations\ECDiffieHellman\ECDiffieHellmanTests.Xml.cs"
              Link="CommonTest\System\Security\Cryptography\AlgorithmImplementations\ECDiffieHellman\ECDiffieHellmanTests.Xml.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Cng\src\System.Security.Cryptography.Cng.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.Cng/tests/TripleDESCngTests.cs b/src/libraries/System.Security.Cryptography.Cng/tests/TripleDESCngTests.cs
index 6abee43359c746..60934e5b7379a4 100644
--- a/src/libraries/System.Security.Cryptography.Cng/tests/TripleDESCngTests.cs
+++ b/src/libraries/System.Security.Cryptography.Cng/tests/TripleDESCngTests.cs
@@ -11,7 +11,6 @@ public static class TripleDESCngTests
 
         private static readonly CngAlgorithm s_cngAlgorithm = new CngAlgorithm("3DES");
 
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/31092")]
         [OuterLoop(/* Creates/Deletes a persisted key, limit exposure to key leaking */)]
         [ConditionalTheory(nameof(SupportsPersistedSymmetricKeys))]
         // 3DES192-ECB-NoPadding 2 blocks.
@@ -46,7 +45,6 @@ public static void GetKey_NonExportable()
                 keyName => new TripleDESCng(keyName));
         }
 
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/31092")]
         [OuterLoop(/* Creates/Deletes a persisted key, limit exposure to key leaking */)]
         [ConditionalFact(nameof(SupportsPersistedSymmetricKeys))]
         public static void SetKey_DetachesFromPersistedKey()
@@ -73,7 +71,6 @@ public static void LoadWrongKeyType()
             }
         }
 
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/31092")]
         [OuterLoop(/* Creates/Deletes a persisted key, limit exposure to key leaking */)]
         [ConditionalFact(nameof(SupportsPersistedSymmetricKeys), nameof(IsAdministrator))]
         public static void VerifyMachineKey()
diff --git a/src/libraries/System.Security.Cryptography.Csp/Directory.Build.props b/src/libraries/System.Security.Cryptography.Csp/Directory.Build.props
index 42c6eafce67ed8..d68d22c1b917f8 100644
--- a/src/libraries/System.Security.Cryptography.Csp/Directory.Build.props
+++ b/src/libraries/System.Security.Cryptography.Csp/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.Csp/ref/System.Security.Cryptography.Csp.cs b/src/libraries/System.Security.Cryptography.Csp/ref/System.Security.Cryptography.Csp.cs
index f4bbc111fbe3b7..d7b4db18222598 100644
--- a/src/libraries/System.Security.Cryptography.Csp/ref/System.Security.Cryptography.Csp.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/ref/System.Security.Cryptography.Csp.cs
@@ -27,7 +27,7 @@ protected override void Dispose(bool disposing) { }
         public override void GenerateIV() { }
         public override void GenerateKey() { }
     }
-    [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+    [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
     public sealed partial class CspKeyContainerInfo
     {
         public CspKeyContainerInfo(System.Security.Cryptography.CspParameters parameters) { }
@@ -87,11 +87,11 @@ public sealed partial class DSACryptoServiceProvider : System.Security.Cryptogra
     {
         public DSACryptoServiceProvider() { }
         public DSACryptoServiceProvider(int dwKeySize) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public DSACryptoServiceProvider(int dwKeySize, System.Security.Cryptography.CspParameters? parameters) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public DSACryptoServiceProvider(System.Security.Cryptography.CspParameters? parameters) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public System.Security.Cryptography.CspKeyContainerInfo CspKeyContainerInfo { get { throw null; } }
         public override string? KeyExchangeAlgorithm { get { throw null; } }
         public override int KeySize { get { throw null; } }
@@ -152,7 +152,7 @@ public PasswordDeriveBytes(string strPassword, byte[]? rgbSalt, string strHashNa
         public string HashName { get { throw null; } set { } }
         public int IterationCount { get { throw null; } set { } }
         public byte[]? Salt { get { throw null; } set { } }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public byte[] CryptDeriveKey(string? algname, string? alghashname, int keySize, byte[] rgbIV) { throw null; }
         protected override void Dispose(bool disposing) { }
         [System.ObsoleteAttribute("Rfc2898DeriveBytes replaces PasswordDeriveBytes for deriving key material from a password and is preferred in new applications.")]
@@ -164,7 +164,7 @@ public sealed partial class RC2CryptoServiceProvider : System.Security.Cryptogra
     {
         public RC2CryptoServiceProvider() { }
         public override int EffectiveKeySize { get { throw null; } set { } }
-        public bool UseSalt { get { throw null; } [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")] set { } }
+        public bool UseSalt { get { throw null; } [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")] set { } }
         public override System.Security.Cryptography.ICryptoTransform CreateDecryptor(byte[] rgbKey, byte[]? rgbIV) { throw null; }
         public override System.Security.Cryptography.ICryptoTransform CreateEncryptor(byte[] rgbKey, byte[]? rgbIV) { throw null; }
         public override void GenerateIV() { }
@@ -188,11 +188,11 @@ public sealed partial class RSACryptoServiceProvider : System.Security.Cryptogra
     {
         public RSACryptoServiceProvider() { }
         public RSACryptoServiceProvider(int dwKeySize) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public RSACryptoServiceProvider(int dwKeySize, System.Security.Cryptography.CspParameters? parameters) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public RSACryptoServiceProvider(System.Security.Cryptography.CspParameters? parameters) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public System.Security.Cryptography.CspKeyContainerInfo CspKeyContainerInfo { get { throw null; } }
         public override string? KeyExchangeAlgorithm { get { throw null; } }
         public override int KeySize { get { throw null; } }
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/Resources/Strings.resx b/src/libraries/System.Security.Cryptography.Csp/src/Resources/Strings.resx
index ed258ad02aebaf..79ece78b5d9d8c 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/Resources/Strings.resx
+++ b/src/libraries/System.Security.Cryptography.Csp/src/Resources/Strings.resx
@@ -215,8 +215,8 @@
   <data name="CspParameter_invalid" xml:space="preserve">
     <value>CSPParameters cannot be null</value>
   </data>
-  <data name="Cryptography_PlatformNotSupported" xml:space="preserve">
-    <value>System.Security.Cryptography is not supported on this platform.</value>
+  <data name="SystemSecurityCryptographyCsp_PlatformNotSupported" xml:space="preserve">
+    <value>System.Security.Cryptography.Csp is not supported on this platform.</value>
   </data>
   <data name="Argument_DestinationTooShort" xml:space="preserve">
     <value>Destination is too short.</value>
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System.Security.Cryptography.Csp.csproj b/src/libraries/System.Security.Cryptography.Csp/src/System.Security.Cryptography.Csp.csproj
index 11f55d0b393764..36b40fc2016220 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System.Security.Cryptography.Csp.csproj
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System.Security.Cryptography.Csp.csproj
@@ -1,13 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Security.Cryptography.Csp</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetsAnyOS)' == 'true'">
     <NoWarn>$(NoWarn);CS0809</NoWarn>
-    <GeneratePlatformNotSupportedAssemblyMessage>SR.Cryptography_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage>SR.SystemSecurityCryptographyCsp_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetsAnyOS)' != 'true'">
     <Compile Include="System\Security\Cryptography\AesCryptoServiceProvider.cs" />
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/CspKeyContainerInfo.Unix.cs b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/CspKeyContainerInfo.Unix.cs
index 843352987a4c6d..553634120b657f 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/CspKeyContainerInfo.Unix.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/CspKeyContainerInfo.Unix.cs
@@ -5,7 +5,7 @@
 
 namespace System.Security.Cryptography
 {
-    [MinimumOSPlatform("windows7.0")]
+    [SupportedOSPlatform("windows")]
     public sealed class CspKeyContainerInfo
     {
         public CspKeyContainerInfo(CspParameters parameters) { throw GetPlatformNotSupported(); }
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/CspKeyContainerInfo.Windows.cs b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/CspKeyContainerInfo.Windows.cs
index 25021e88630d1b..ce73894fb36e0c 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/CspKeyContainerInfo.Windows.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/CspKeyContainerInfo.Windows.cs
@@ -7,7 +7,7 @@
 
 namespace System.Security.Cryptography
 {
-    [MinimumOSPlatform("windows7.0")]
+    [SupportedOSPlatform("windows")]
     public sealed class CspKeyContainerInfo
     {
         private readonly CspParameters _parameters;
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/DSACryptoServiceProvider.Unix.cs b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/DSACryptoServiceProvider.Unix.cs
index 74811cb089eea0..575055f336116f 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/DSACryptoServiceProvider.Unix.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/DSACryptoServiceProvider.Unix.cs
@@ -38,13 +38,13 @@ public DSACryptoServiceProvider(int dwKeySize) : base()
             KeySize = dwKeySize;
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public DSACryptoServiceProvider(int dwKeySize, CspParameters parameters)
         {
             throw new PlatformNotSupportedException(SR.Format(SR.Cryptography_CAPI_Required, nameof(CspParameters)));
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public DSACryptoServiceProvider(CspParameters parameters)
         {
             throw new PlatformNotSupportedException(SR.Format(SR.Cryptography_CAPI_Required, nameof(CspParameters)));
@@ -56,7 +56,7 @@ public DSACryptoServiceProvider(CspParameters parameters)
         public override bool TryCreateSignature(ReadOnlySpan<byte> hash, Span<byte> destination, out int bytesWritten) =>
             _impl.TryCreateSignature(hash, destination, out bytesWritten);
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public CspKeyContainerInfo CspKeyContainerInfo
         {
             get { throw new PlatformNotSupportedException(SR.Format(SR.Cryptography_CAPI_Required, nameof(CspKeyContainerInfo))); }
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/DSACryptoServiceProvider.Windows.cs b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/DSACryptoServiceProvider.Windows.cs
index 686728e6a52229..186f9c80100c5f 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/DSACryptoServiceProvider.Windows.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/DSACryptoServiceProvider.Windows.cs
@@ -50,7 +50,7 @@ public DSACryptoServiceProvider(int dwKeySize)
         /// for the cryptographic service provider (CSP).
         /// </summary>
         /// <param name="parameters">The parameters for the CSP.</param>
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public DSACryptoServiceProvider(CspParameters? parameters)
             : this(0, parameters)
         {
@@ -63,7 +63,7 @@ public DSACryptoServiceProvider(CspParameters? parameters)
         /// <param name="dwKeySize">The size of the key for the cryptographic algorithm in bits.</param>
         /// <param name="parameters">The parameters for the CSP.</param>
         [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Security", "CA5350", Justification = "SHA1 is required by the FIPS 186-2 DSA spec.")]
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public DSACryptoServiceProvider(int dwKeySize, CspParameters? parameters)
         {
             if (dwKeySize < 0)
@@ -185,7 +185,7 @@ private SafeKeyHandle SafeKeyHandle
         /// <summary>
         /// Gets a CspKeyContainerInfo object that describes additional information about a cryptographic key pair.
         /// </summary>
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public CspKeyContainerInfo CspKeyContainerInfo
         {
             get
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/PasswordDeriveBytes.Unix.cs b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/PasswordDeriveBytes.Unix.cs
index 2627057a7bb501..62f31ccafb96fe 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/PasswordDeriveBytes.Unix.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/PasswordDeriveBytes.Unix.cs
@@ -7,7 +7,7 @@ namespace System.Security.Cryptography
 {
     public partial class PasswordDeriveBytes : DeriveBytes
     {
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public byte[] CryptDeriveKey(string? algname, string? alghashname, int keySize, byte[] rgbIV)
         {
             throw new PlatformNotSupportedException(SR.Format(SR.Cryptography_CAPI_Required, nameof(CryptDeriveKey)));
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/PasswordDeriveBytes.Windows.cs b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/PasswordDeriveBytes.Windows.cs
index 58c546e62b27f6..c516653016400e 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/PasswordDeriveBytes.Windows.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/PasswordDeriveBytes.Windows.cs
@@ -12,7 +12,7 @@ public partial class PasswordDeriveBytes : DeriveBytes
     {
         private SafeProvHandle? _safeProvHandle;
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public byte[] CryptDeriveKey(string? algname, string? alghashname, int keySize, byte[] rgbIV)
         {
             if (keySize < 0)
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RC2CryptoServiceProvider.Unix.cs b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RC2CryptoServiceProvider.Unix.cs
index 3cab2033995ba6..4aeb4ec3c607be 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RC2CryptoServiceProvider.Unix.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RC2CryptoServiceProvider.Unix.cs
@@ -104,7 +104,7 @@ public override PaddingMode Padding
         public bool UseSalt
         {
             get { return false; }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 // Don't allow a true value
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RC2CryptoServiceProvider.Windows.cs b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RC2CryptoServiceProvider.Windows.cs
index a7c1c42084e32a..d4760f31946e9f 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RC2CryptoServiceProvider.Windows.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RC2CryptoServiceProvider.Windows.cs
@@ -44,7 +44,7 @@ public bool UseSalt
             {
                 return _use40bitSalt;
             }
-            [MinimumOSPlatform("windows7.0")]
+            [SupportedOSPlatform("windows")]
             set
             {
                 _use40bitSalt = value;
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RSACryptoServiceProvider.Unix.cs b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RSACryptoServiceProvider.Unix.cs
index d36a068c80b398..168a456800e5bc 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RSACryptoServiceProvider.Unix.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RSACryptoServiceProvider.Unix.cs
@@ -27,15 +27,15 @@ public RSACryptoServiceProvider(int dwKeySize)
             _impl = RSA.Create(dwKeySize);
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public RSACryptoServiceProvider(int dwKeySize, CspParameters parameters) =>
             throw new PlatformNotSupportedException(SR.Format(SR.Cryptography_CAPI_Required, nameof(CspParameters)));
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public RSACryptoServiceProvider(CspParameters parameters) =>
             throw new PlatformNotSupportedException(SR.Format(SR.Cryptography_CAPI_Required, nameof(CspParameters)));
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public CspKeyContainerInfo CspKeyContainerInfo =>
             throw new PlatformNotSupportedException(SR.Format(SR.Cryptography_CAPI_Required, nameof(CspKeyContainerInfo)));
 
diff --git a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RSACryptoServiceProvider.Windows.cs b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RSACryptoServiceProvider.Windows.cs
index 7a22b937cd52da..6843a3aa30fca2 100644
--- a/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RSACryptoServiceProvider.Windows.cs
+++ b/src/libraries/System.Security.Cryptography.Csp/src/System/Security/Cryptography/RSACryptoServiceProvider.Windows.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Buffers.Binary;
 using System.Diagnostics;
 using System.IO;
 using System.Runtime.Versioning;
@@ -39,13 +40,13 @@ public RSACryptoServiceProvider(int dwKeySize)
         {
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public RSACryptoServiceProvider(int dwKeySize, CspParameters? parameters)
             : this(dwKeySize, parameters, false)
         {
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public RSACryptoServiceProvider(CspParameters? parameters)
             : this(0, parameters, true)
         {
@@ -173,7 +174,7 @@ private SafeKeyHandle SafeKeyHandle
         /// <summary>
         /// CspKeyContainerInfo property
         /// </summary>
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public CspKeyContainerInfo CspKeyContainerInfo
         {
             get
@@ -195,7 +196,7 @@ public override int KeySize
             get
             {
                 byte[] keySize = CapiHelper.GetKeyParameter(SafeKeyHandle, Constants.CLR_KEYLEN);
-                _keySize = (keySize[0] | (keySize[1] << 8) | (keySize[2] << 16) | (keySize[3] << 24));
+                _keySize = BinaryPrimitives.ReadInt32LittleEndian(keySize);
                 return _keySize;
             }
         }
diff --git a/src/libraries/System.Security.Cryptography.Csp/tests/System.Security.Cryptography.Csp.Tests.csproj b/src/libraries/System.Security.Cryptography.Csp/tests/System.Security.Cryptography.Csp.Tests.csproj
index b37c1062363813..a70488b38e8120 100644
--- a/src/libraries/System.Security.Cryptography.Csp/tests/System.Security.Cryptography.Csp.Tests.csproj
+++ b/src/libraries/System.Security.Cryptography.Csp/tests/System.Security.Cryptography.Csp.Tests.csproj
@@ -92,4 +92,7 @@
     <Compile Include="$(CommonTestPath)System\Security\Cryptography\AlgorithmImplementations\RSA\SignVerify.netcoreapp.cs"
              Link="CommonTest\System\Security\Cryptography\AlgorithmImplementations\RSA\SignVerify.netcoreapp.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Cng\src\System.Security.Cryptography.Cng.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.Encoding/Directory.Build.props b/src/libraries/System.Security.Cryptography.Encoding/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Security.Cryptography.Encoding/Directory.Build.props
+++ b/src/libraries/System.Security.Cryptography.Encoding/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.Encoding/src/Resources/Strings.resx b/src/libraries/System.Security.Cryptography.Encoding/src/Resources/Strings.resx
index cb21baa9289250..ed1d3e3d9e5ffa 100644
--- a/src/libraries/System.Security.Cryptography.Encoding/src/Resources/Strings.resx
+++ b/src/libraries/System.Security.Cryptography.Encoding/src/Resources/Strings.resx
@@ -138,7 +138,7 @@
   <data name="ObjectDisposed_Generic" xml:space="preserve">
     <value>Cannot access a disposed object.</value>
   </data>
-  <data name="Cryptography_PlatformNotSupported" xml:space="preserve">
-    <value>System.Security.Cryptography is not supported on this platform.</value>
+  <data name="SystemSecurityCryptographyEncoding_PlatformNotSupported" xml:space="preserve">
+    <value>System.Security.Cryptography.Encoding is not supported on this platform.</value>
   </data>
 </root>
diff --git a/src/libraries/System.Security.Cryptography.Encoding/src/System.Security.Cryptography.Encoding.csproj b/src/libraries/System.Security.Cryptography.Encoding/src/System.Security.Cryptography.Encoding.csproj
index 80e863e61d30ed..aaf3fc1530b225 100644
--- a/src/libraries/System.Security.Cryptography.Encoding/src/System.Security.Cryptography.Encoding.csproj
+++ b/src/libraries/System.Security.Cryptography.Encoding/src/System.Security.Cryptography.Encoding.csproj
@@ -1,12 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Security.Cryptography.Encoding</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent);$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsAnyOS)' == 'true'">SR.Cryptography_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsAnyOS)' == 'true'">SR.SystemSecurityCryptographyEncoding_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <Import Project="$(CommonPath)System\Security\Cryptography\Asn1\AsnXml.targets" Condition=" '$(TargetsOSX)' == 'true' or '$(TargetsiOS)' == 'true' or '$(TargetstvOS)' == 'true'" />
   <Import Project="$(CommonPath)System\Security\Cryptography\Asn1Reader\System.Security.Cryptography.Asn1Reader.Shared.projitems" Condition=" '$(TargetsOSX)' == 'true' or '$(TargetsiOS)' == 'true' or '$(TargetstvOS)' == 'true'" />
diff --git a/src/libraries/System.Security.Cryptography.OpenSsl/Directory.Build.props b/src/libraries/System.Security.Cryptography.OpenSsl/Directory.Build.props
index 8c72c62fd5932e..34e58724807405 100644
--- a/src/libraries/System.Security.Cryptography.OpenSsl/Directory.Build.props
+++ b/src/libraries/System.Security.Cryptography.OpenSsl/Directory.Build.props
@@ -2,7 +2,7 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
-    <IsNETCoreAppRef>false</IsNETCoreAppRef>
+    <IncludePlatformAttributes>true</IncludePlatformAttributes>
+    <UnsupportedOSPlatform>windows</UnsupportedOSPlatform>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.OpenSsl/ref/System.Security.Cryptography.OpenSsl.csproj b/src/libraries/System.Security.Cryptography.OpenSsl/ref/System.Security.Cryptography.OpenSsl.csproj
index 2c895046911ced..1465cb0fabc90a 100644
--- a/src/libraries/System.Security.Cryptography.OpenSsl/ref/System.Security.Cryptography.OpenSsl.csproj
+++ b/src/libraries/System.Security.Cryptography.OpenSsl/ref/System.Security.Cryptography.OpenSsl.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;net47;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;net47</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -17,19 +16,15 @@
     <Compile Include="System.Security.Cryptography.OpenSsl.netcoreapp.cs" Condition="'$(TargetFramework)' == 'netcoreapp3.0' OR '$(TargetFramework)' == '$(NetCoreAppCurrent)'" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Algorithms\ref\System.Security.Cryptography.Algorithms.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Primitives\ref\System.Security.Cryptography.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Algorithms\ref\System.Security.Cryptography.Algorithms.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Primitives\ref\System.Security.Cryptography.Primitives.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0'">
+    <Reference Include="System.IO" />
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Handles" />
-    <Reference Include="System.IO" />
     <Reference Include="System.Security.Cryptography.Algorithms" />
     <Reference Include="System.Security.Cryptography.Primitives" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
-  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.OpenSsl/src/System.Security.Cryptography.OpenSsl.csproj b/src/libraries/System.Security.Cryptography.OpenSsl/src/System.Security.Cryptography.OpenSsl.csproj
index 1edf80722b5e55..54ff81d2fb9490 100644
--- a/src/libraries/System.Security.Cryptography.OpenSsl/src/System.Security.Cryptography.OpenSsl.csproj
+++ b/src/libraries/System.Security.Cryptography.OpenSsl/src/System.Security.Cryptography.OpenSsl.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser;$(NetCoreAppCurrent);netcoreapp3.0-Unix;netcoreapp3.0;netstandard2.0;net47;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser;$(NetCoreAppCurrent);netcoreapp3.0-Unix;netcoreapp3.0;netstandard2.0;net47</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -108,13 +107,14 @@
     <Compile Include="$(CommonPath)System\Security\Cryptography\RsaPaddingProcessor.cs"
              Link="Common\System\Security\Cryptography\RsaPaddingProcessor.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.0' AND !$(TargetFramework.StartsWith('net4'))">
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or
+                        $(TargetFramework.StartsWith('netcoreapp3.0'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Formats.Asn1\src\System.Formats.Asn1.csproj" />
     <Reference Include="System.Buffers" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Diagnostics.Tools" />
-    <Reference Include="System.Formats.Asn1" />
     <Reference Include="System.Memory" />
     <Reference Include="System.Resources.ResourceManager" />
     <Reference Include="System.Runtime" />
@@ -129,7 +129,10 @@
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
     <SuppressPackageTargetFrameworkCompatibility Include="net461" />
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <!-- Ref assembly for netstandard2.0 isn't live built anymore. -->
+    <PackageDownload Include="$(MSBuildProjectName)" Version="[$(SystemSecurityCryptographyOpenSslVersion)]" />
+    <ResolvedMatchingContract Include="$(NuGetPackageRoot)$(MSBuildProjectName.ToLowerInvariant())\$(SystemSecurityCryptographyOpenSslVersion)\ref\$(TargetFramework)\$(MSBuildProjectName).dll" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.OpenSsl/tests/System.Security.Cryptography.OpenSsl.Tests.csproj b/src/libraries/System.Security.Cryptography.OpenSsl/tests/System.Security.Cryptography.OpenSsl.Tests.csproj
index 23783475d351f8..011e86be385933 100644
--- a/src/libraries/System.Security.Cryptography.OpenSsl/tests/System.Security.Cryptography.OpenSsl.Tests.csproj
+++ b/src/libraries/System.Security.Cryptography.OpenSsl/tests/System.Security.Cryptography.OpenSsl.Tests.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <UnsupportedPlatforms>Windows_NT</UnsupportedPlatforms>
     <TargetFrameworks>$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
@@ -127,4 +126,8 @@
              Link="CommonTest\System\Security\Cryptography\AlgorithmImplementations\RSA\SignVerify.netcoreapp.cs" />
     <Compile Include="SafeEvpPKeyHandleTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Cng\src\System.Security.Cryptography.Cng.csproj" />
+    <ProjectReference Include="..\src\System.Security.Cryptography.OpenSsl.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/ref/System.Security.Cryptography.Pkcs.csproj b/src/libraries/System.Security.Cryptography.Pkcs/ref/System.Security.Cryptography.Pkcs.csproj
index 07a5f1e62c2207..5b42437c4fab14 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/ref/System.Security.Cryptography.Pkcs.csproj
+++ b/src/libraries/System.Security.Cryptography.Pkcs/ref/System.Security.Cryptography.Pkcs.csproj
@@ -1,14 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.1;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.1;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
     <IsPartialFacadeAssembly Condition="$(TargetFramework.StartsWith('net4'))">true</IsPartialFacadeAssembly>
-    <!-- Currently the netstandard build is locked to the $(NetFrameworkCurrent) API -->
+    <!-- Currently the netstandard build is locked to the net472 API -->
     <AssemblyVersion Condition="$(TargetFramework.StartsWith('netstandard'))">4.0.4.0</AssemblyVersion>    
   </PropertyGroup>
   <ItemGroup>
@@ -16,17 +15,15 @@
     <Compile Include="System.Security.Cryptography.Pkcs.netcoreapp.cs" Condition="!$(TargetFramework.StartsWith('net4'))" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Reference Include="System.Security" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Algorithms\ref\System.Security.Cryptography.Algorithms.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Csp\ref\System.Security.Cryptography.Csp.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Encoding\ref\System.Security.Cryptography.Encoding.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Primitives\ref\System.Security.Cryptography.Primitives.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.X509Certificates\ref\System.Security.Cryptography.X509Certificates.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Algorithms\ref\System.Security.Cryptography.Algorithms.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Csp\ref\System.Security.Cryptography.Csp.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Encoding\ref\System.Security.Cryptography.Encoding.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Primitives\ref\System.Security.Cryptography.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.X509Certificates\ref\System.Security.Cryptography.X509Certificates.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="System.Runtime" />
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/src/Internal/Cryptography/Pal/AnyOS/ManagedPal.cs b/src/libraries/System.Security.Cryptography.Pkcs/src/Internal/Cryptography/Pal/AnyOS/ManagedPal.cs
index d9c9f46693c881..94e8c460e4ce52 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/src/Internal/Cryptography/Pal/AnyOS/ManagedPal.cs
+++ b/src/libraries/System.Security.Cryptography.Pkcs/src/Internal/Cryptography/Pal/AnyOS/ManagedPal.cs
@@ -67,14 +67,12 @@ public override byte[] GetSubjectKeyIdentifier(X509Certificate2 certificate)
             }
         }
 
-        [return: MaybeNull]
-        public override T GetPrivateKeyForSigning<T>(X509Certificate2 certificate, bool silent)
+        public override T? GetPrivateKeyForSigning<T>(X509Certificate2 certificate, bool silent) where T : class
         {
             return GetPrivateKey<T>(certificate);
         }
 
-        [return: MaybeNull]
-        public override T GetPrivateKeyForDecryption<T>(X509Certificate2 certificate, bool silent)
+        public override T? GetPrivateKeyForDecryption<T>(X509Certificate2 certificate, bool silent) where T : class
         {
             return GetPrivateKey<T>(certificate);
         }
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/src/Internal/Cryptography/Pal/Windows/PkcsPalWindows.cs b/src/libraries/System.Security.Cryptography.Pkcs/src/Internal/Cryptography/Pal/Windows/PkcsPalWindows.cs
index 414f2228d6a5f4..a720ce02fd72d8 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/src/Internal/Cryptography/Pal/Windows/PkcsPalWindows.cs
+++ b/src/libraries/System.Security.Cryptography.Pkcs/src/Internal/Cryptography/Pal/Windows/PkcsPalWindows.cs
@@ -91,14 +91,12 @@ public sealed override byte[] GetSubjectKeyIdentifier(X509Certificate2 certifica
             }
         }
 
-        [return: MaybeNull]
-        public override T GetPrivateKeyForSigning<T>(X509Certificate2 certificate, bool silent)
+        public override T? GetPrivateKeyForSigning<T>(X509Certificate2 certificate, bool silent) where T : class
         {
             return GetPrivateKey<T>(certificate, silent, preferNCrypt: true);
         }
 
-        [return: MaybeNull]
-        public override T GetPrivateKeyForDecryption<T>(X509Certificate2 certificate, bool silent)
+        public override T? GetPrivateKeyForDecryption<T>(X509Certificate2 certificate, bool silent) where T : class
         {
             return GetPrivateKey<T>(certificate, silent, preferNCrypt: false);
         }
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/src/Resources/Strings.resx b/src/libraries/System.Security.Cryptography.Pkcs/src/Resources/Strings.resx
index bebbe20a5ee418..e499b6b1e1c807 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/src/Resources/Strings.resx
+++ b/src/libraries/System.Security.Cryptography.Pkcs/src/Resources/Strings.resx
@@ -295,7 +295,7 @@
   <data name="Cryptography_Cms_CertificateAlreadyInCollection" xml:space="preserve">
     <value>Certificate already present in the collection.</value>
   </data>
-  <data name="Cryptography_PlatformNotSupported_Browser" xml:space="preserve">
-    <value>System.Security.Cryptography is not supported on Browser.</value>
+  <data name="SystemSecurityCryptographyPkcs_PlatformNotSupported" xml:space="preserve">
+    <value>System.Security.Cryptography.Pkcs is not supported on this platform.</value>
   </data>
 </root>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/src/System.Security.Cryptography.Pkcs.csproj b/src/libraries/System.Security.Cryptography.Pkcs/src/System.Security.Cryptography.Pkcs.csproj
index 8f31d68c0a08fa..6ecdaa9e86569a 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/src/System.Security.Cryptography.Pkcs.csproj
+++ b/src/libraries/System.Security.Cryptography.Pkcs/src/System.Security.Cryptography.Pkcs.csproj
@@ -5,19 +5,16 @@
     <IncludeDllSafeSearchPathAttribute>true</IncludeDllSafeSearchPathAttribute>
     <NoWarn>$(NoWarn);CA5384</NoWarn>
     <Nullable>enable</Nullable>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent);netstandard2.0;netstandard2.0-Windows_NT;netstandard2.1;netstandard2.1-Windows_NT;netcoreapp3.0-Windows_NT;netcoreapp3.0;net461-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent);netstandard2.0;netstandard2.0-Windows_NT;netstandard2.1;netstandard2.1-Windows_NT;netcoreapp3.0-Windows_NT;netcoreapp3.0;net461-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
     <IsPartialFacadeAssembly Condition="$(TargetFramework.StartsWith('net4'))">true</IsPartialFacadeAssembly>
     <OmitResources Condition="$(TargetFramework.StartsWith('net4'))">true</OmitResources>
-    <!-- Currently the netstandard build is locked to the $(NetFrameworkCurrent) API -->
+    <!-- Currently the netstandard build is locked to the net472 API -->
     <AssemblyVersion Condition="$(TargetFramework.StartsWith('netstandard'))">4.0.4.0</AssemblyVersion>
-  </PropertyGroup>
-  <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.Cryptography_PlatformNotSupported_Browser</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemSecurityCryptographyPkcs_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <Import Project="$(CommonPath)System\Security\Cryptography\Asn1\AsnXml.targets" Condition="'$(IsPartialFacadeAssembly)' != 'true'" />
   <Import Project="$(CommonPath)System\Security\Cryptography\Asn1Reader\System.Security.Cryptography.Asn1Reader.Shared.projitems" Condition="'$(IsPartialFacadeAssembly)' != 'true'" />
@@ -318,39 +315,6 @@
   <ItemGroup Condition="'$(TargetsWindows)' != 'true' and '$(IsPartialFacadeAssembly)' != 'true'">
     <Compile Include="Internal\Cryptography\Pal\AnyOS\PkcsPal.AnyOS.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' == 'true'">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Security" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or $(TargetFramework.StartsWith('netcoreapp3.0')) or '$(TargetFramework)' == 'netstandard2.1'">
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.Numerics" />
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Collections.NonGeneric" />
-    <Reference Include="System.Collections.Concurrent" />
-    <Reference Include="System.Security.Cryptography.Csp" />
-    <Reference Include="System.Security.Cryptography.Encoding" />
-    <Reference Include="System.Security.Cryptography.X509Certificates" />
-    <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="System.Diagnostics.Debug" />
-    <Reference Include="System.Diagnostics.Tools" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Runtime.InteropServices.RuntimeInformation" />
-    <Reference Include="System.Security.Cryptography.Primitives" />
-    <Reference Include="System.Security.Cryptography.Algorithms" />
-    <Reference Include="System.Threading" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Text.Encoding.Extensions" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true' and '$(TargetFramework)' != 'netstandard2.1'">
-    <Reference Include="System.Buffers" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
-    <Reference Include="System.Formats.Asn1" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Security.Cryptography.Cng" />
-  </ItemGroup>
   <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
     <Compile Include="$(CommonPath)System\Memory\PointerMemoryManager.cs"
              Link="Common\System\Memory\PointerMemoryManager.cs" />
@@ -667,4 +631,47 @@
   <ItemGroup>
     <None Include="@(AsnXml)" />
   </ItemGroup>
+  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' == 'true'">
+    <Reference Include="System.Security" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Formats.Asn1\src\System.Formats.Asn1.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard2.0'))">
+    <PackageReference Include="System.Buffers"  Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Security.Cryptography.Cng" Version="$(SystemSecurityCryptographyCngVersion)" />
+    <!-- Ref assembly for netstandard2.0 isn't live built anymore. -->
+    <PackageDownload Include="$(MSBuildProjectName)" Version="[$(SystemSecurityCryptographyPkcsVersion)]" />
+    <ResolvedMatchingContract Include="$(NuGetPackageRoot)$(MSBuildProjectName.ToLowerInvariant())\$(SystemSecurityCryptographyPkcsVersion)\ref\$(TargetFramework)\$(MSBuildProjectName).dll" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard2.1')) or
+                        $(TargetFramework.StartsWith('netcoreapp3.0')) or
+                        $(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Cng\src\System.Security.Cryptography.Cng.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or
+                        $(TargetFramework.StartsWith('netcoreapp3.0'))">
+    <Reference Include="System.Buffers" />
+    <Reference Include="System.Collections" />
+    <Reference Include="System.Collections.Concurrent" />
+    <Reference Include="System.Collections.NonGeneric" />
+    <Reference Include="System.Diagnostics.Debug" />
+    <Reference Include="System.Diagnostics.Tools" />
+    <Reference Include="System.Linq" />
+    <Reference Include="System.Memory" />
+    <Reference Include="System.Resources.ResourceManager" />
+    <Reference Include="System.Runtime" />
+    <Reference Include="System.Runtime.Extensions" />
+    <Reference Include="System.Runtime.InteropServices" />
+    <Reference Include="System.Runtime.InteropServices.RuntimeInformation" />
+    <Reference Include="System.Runtime.Numerics" />
+    <Reference Include="System.Security.Cryptography.Algorithms" />
+    <Reference Include="System.Security.Cryptography.Csp" />
+    <Reference Include="System.Security.Cryptography.Encoding" />
+    <Reference Include="System.Security.Cryptography.Primitives" />
+    <Reference Include="System.Security.Cryptography.X509Certificates" />
+    <Reference Include="System.Text.Encoding.Extensions" />
+    <Reference Include="System.Threading" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/tests/EnvelopedCms/EdgeCasesTests.cs b/src/libraries/System.Security.Cryptography.Pkcs/tests/EnvelopedCms/EdgeCasesTests.cs
index 5bf2db1c71fba8..6d9458cbc7b3aa 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/tests/EnvelopedCms/EdgeCasesTests.cs
+++ b/src/libraries/System.Security.Cryptography.Pkcs/tests/EnvelopedCms/EdgeCasesTests.cs
@@ -309,7 +309,7 @@ public static void EnvelopedCmsNullDecode()
         }
 
         [Theory]
-#if !NET472
+#if !NETFRAMEWORK
         [InlineData(true)]
 #endif
         [InlineData(false)]
@@ -319,7 +319,7 @@ public static void EnvelopedCmsEmptyDecode(bool useSpan)
 
             if (useSpan)
             {
-#if !NET472
+#if !NETFRAMEWORK
                 Assert.ThrowsAny<CryptographicException>(() => cms.Decode(ReadOnlySpan<byte>.Empty));
 #else
                 throw new Xunit.Sdk.XunitException(
@@ -502,7 +502,7 @@ public static void ContentInfoGetContentTypeNull()
 
         [Theory]
         [InlineData(false)]
-#if !NET472
+#if !NETFRAMEWORK
         [InlineData(true)]
 #endif
         public static void ContentInfoGetContentTypeUnknown(bool fromSpan)
@@ -512,7 +512,7 @@ public static void ContentInfoGetContentTypeUnknown(bool fromSpan)
 
             if (fromSpan)
             {
-#if NET472
+#if NETFRAMEWORK
                 throw new Xunit.Sdk.XunitException(
                     "This test should not evaluate for .NET Framework, the API is missing.");
 #else
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/tests/EnvelopedCms/GeneralTests.cs b/src/libraries/System.Security.Cryptography.Pkcs/tests/EnvelopedCms/GeneralTests.cs
index b94d0b76427309..27f46fc67ee8c8 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/tests/EnvelopedCms/GeneralTests.cs
+++ b/src/libraries/System.Security.Cryptography.Pkcs/tests/EnvelopedCms/GeneralTests.cs
@@ -217,7 +217,7 @@ public static void TestContentTypeSigned()
 
         [Theory]
         [InlineData(false)]
-#if !NET472
+#if !NETFRAMEWORK
         [InlineData(true)]
 #endif
         public static void TestContent(bool fromSpan)
@@ -238,7 +238,7 @@ public static void TestContent(bool fromSpan)
 
             if (fromSpan)
             {
-#if !NET472
+#if !NETFRAMEWORK
                 cms.Decode(encodedMessage.AsSpan());
 #else
                 throw new Xunit.Sdk.XunitException(
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/tests/Pkcs12/Pkcs12Documents.cs b/src/libraries/System.Security.Cryptography.Pkcs/tests/Pkcs12/Pkcs12Documents.cs
index 550ee41b80a510..51c80e09c768b3 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/tests/Pkcs12/Pkcs12Documents.cs
+++ b/src/libraries/System.Security.Cryptography.Pkcs/tests/Pkcs12/Pkcs12Documents.cs
@@ -136,6 +136,93 @@ internal static class Pkcs12Documents
             "21300906052B0E03021A050004148B12EE39C54B03EF4C1B0C2D8A3A9624D629" +
             "285A0408E398C69C57E4782102020400").HexToByteArray();
 
+        internal static readonly ReadOnlyMemory<byte> HighPbeIterationCount3Des = (
+            "308209c40201033082098906092a864886f70d010701a082097a04820976" +
+            "308209723082043006092a864886f70d010706a08204213082041d020100" +
+            "3082041606092a864886f70d010701301d060a2a864886f70d010c010330" +
+            "0f04083fd435a905e8b19e02030927c1808203e8d3a24907621301625ce2" +
+            "f42b8dd0fc0c0ce57d512af3275af385874b01adf017de2a9c6fa5c78c15" +
+            "729453073d0dbc11e4c9dcc6d01f332bd06a5786962b85dfd4becca62619" +
+            "efd189ddb4b1abc109983a8cd4c41958a4dcce10e34a70f39b742d892bd6" +
+            "94a4f2b6fc1b760e08b81fe38b3e9c25cf81acb3e30e59d4608f104fd911" +
+            "a123b15d0c93a9b96e99f72ad50faac027bdccc121abdeb61e9bec4e6969" +
+            "08a6480ae693e956fb006213cd9fa5c492665439c5a436d4b5ca8d8f382a" +
+            "2b54dcc12c6ea3a44b819eb2c85c20a0dfdd623f3235e3b13c6856cd538d" +
+            "edeeb71bc078d7e8d13b4fad0f809925aa93a7bb288ba07562723580d2e1" +
+            "d34d83398d31205cf00b8e406898e922f2ac9aa8d0135b268944c17423ce" +
+            "4887ac3068838b0a5cfadd308d10787aaa24683be495ced256ef4ebd8e16" +
+            "60b0fe942793ec66c669a273417cf20be43ae7d7c56665803c653b8f00b5" +
+            "f0963e72d23d0db6a0a0182662f7d88ff832b10498b6d557bb4a8bf2f0cd" +
+            "8b89e0865102ca9cbe0a5c5eef55530fbdd92389a6911769b870c2a83a0b" +
+            "c8b6f4afdba398d88d36fc8b1995da29c9b0f437e8959a8fd9a9dec621e9" +
+            "ee0fb6181b904f936abcdede183e7668e9c09f0d9565c055a3542ebd8414" +
+            "c96797afdf98f63730bd6840018fb30d974cc5c5bc538b05699ef4119653" +
+            "ac2189b917ff15409fc449bf72eda1b551bdc7cee240e8b22ac3391ae148" +
+            "37870aaba99a78b84c47ed2c0788dd60dbc0bfd1498651ba1a8a07f26bb0" +
+            "0ab4002ca865b45301a38c353a3a1a6c1d7a2b7870770707312e68200f80" +
+            "9c583595b3c3a7fb9ceed6ef2d2b953d8543d554459a226605757c64f93a" +
+            "fa6bedeb63f49d9642aedd71f0678f1aa50c3130a2577e73896e6cf5680e" +
+            "e32c25f615c4578b736193da4b9a1e55371083713bcc84ad4a6665535725" +
+            "1fffb3656ce306070381b3dabe23dfd22ed1af0ac2c8494a9c98a69db00c" +
+            "b728b56c6c1acd8518f11541aa75ee62a7bf74140527217279f113c2d737" +
+            "4e876b9b2624f6f3599a3db16bab5e5b8dd888a2e3fff5c4dc9ddd7ed100" +
+            "dc2a56ea3c57ad4811cae5fe21e704bb1480768353364a56bc6e7baf0105" +
+            "d3a3a97e16591257d5e1a06d3d8a3e2e1b7444b240d77de4704cd402f9d3" +
+            "1b005e799d29d4b139e07e9e0b322f153dff2216e390496025ed85501ca7" +
+            "83f41063ad3f62f71e2d40856e39f90b74f0b860385083b75fcc34e5e7e4" +
+            "77e68bc8c8c7ef9f789f85efe9aa170a5e37e43ac42a5d2cc47489d27ee5" +
+            "03c9a6d19a32c6170643b38c017c31a1d51013f8a86831594432a7c02f80" +
+            "d656696b5edd6f4d27bc07325b5cfb118b543abc038928f86995fb296630" +
+            "cbb183d407e8f16b50b2fefd8f21469fc83e45abba920d9a6c88179b023b" +
+            "3082053a06092a864886f70d010701a082052b0482052730820523308205" +
+            "1f060b2a864886f70d010c0a0102a08204e7308204e3301d060a2a864886" +
+            "f70d010c0103300f0408e8dc7d11c3405bae02030927c1048204c0698ab9" +
+            "d1d3f6a2eab118cf2166f0db512cd132acddbab92807639a08305fde746c" +
+            "35c512498cd4f656faf165be0f28fafd9f5cbb3b4b3704b16a6de18f7b2f" +
+            "0950b73db868bec47717b56079c78a3069798e3c40ec6199d55c723c18cd" +
+            "deb02278c860de652a65f964e6e82a0bd6bc6f94cccad6761dd2afb724db" +
+            "cecd62eea36b13114f0aa5ea280e4468b433e37b791209cdd7f599ba9dfc" +
+            "f09c3f9e3781a1ec2712fd24ae8bc75b44e3071331478d112354281b4fe2" +
+            "4dc3417320514ffcee7e921fac4fb5095aef11e2e60de5f4e51fb3bbf62b" +
+            "8593502b93e9048d4481ab84a8fa7f9e411a5aa4943d4401f7d8376345d6" +
+            "eacff571b4e7197eb934640b88d3967651135902f8a4a1ce3f030c68ce24" +
+            "3616e30eb58d9be9bc256834df10893e88bb1a57948b34b8be8294154492" +
+            "c84e3e7c931858a48137a8becf5316cb009fe0ed30701952a3b745222d01" +
+            "b28174896092d2e98e7561bce56a87afe045c4a730380c1e4ed452cdc6d0" +
+            "c5ddae41d303d0a8ddfecb8b0ee161f13dfc0ebd6b59f923d49e89ac3576" +
+            "34d16c583865e39b9c0a24f7b7c7baac2cd21cfa77a3342cfd4015a4d4cc" +
+            "41440d0dc49a9972e2970cffac37f7503d4ec1f546b4144d26802b90b38e" +
+            "63dc4baec79e439fdfff5133ded301d07fa902790f17ffb471f4f78a5d66" +
+            "51ac3465f1b8d08060eb5bcc1fe9261176e08bc6c3f6a890614bfd428e9d" +
+            "04c197241966fa2ce025adc7e89ef3d2384660ef6d05aa1f6d365859f5b3" +
+            "b3009a8d3f0ee4bf907c6458b6877d63b815b096039603de5a2232588cd5" +
+            "8c7f1eae5e4bf43495bb208e2b2d9e02ac849c60cc43dab30d5359ec7838" +
+            "eeb290eb8c98f15b1273c3a82103394175b690b2579ba445a223850a54ef" +
+            "624e8f481509be45159b5a509d472eaf20248fc30d7945940a3250bd9174" +
+            "25bc5cae77c3659461fb79fb3a8f09f0f01c49737a6cdb34fa3ca4987bde" +
+            "2d3e64edd2fc54e86649ba6accc3417764f52f86c67d2aa07869de9191f8" +
+            "9592d845da1bb23b4bddbd0943fdabd2438e1a5b8dc6ae4a40709a853da9" +
+            "69a06148045e17ae3b5199d76959f56707770e5b7fe168588c322f4e2afc" +
+            "05ec72398f3a97a2112729114147613c4578945409295ae9e49c78d6482c" +
+            "89c4731aa069b4977b66d235830d94d34384ffc0b57460d97fec507d48ff" +
+            "6da7410d1411926b250fe85e1f7b7260cc2986a2486125d5d9228aa77fb8" +
+            "a3d4f09ff133d0e58a3878b94c9a0c4fdb0c95a62102aa39f96a15822573" +
+            "7a40b4f41b3bbe41430d643ae873258a2c8f237de943f9a2c02903ead1cb" +
+            "9973ad6f39f65f7eb1152aebf1c429db19ecba6d05ed60ec5d4d0bd54222" +
+            "67d10439876c4cf4966b308c0362cc9b87a94d7de4fee67c2a02f6f6bb0c" +
+            "b8b9c0dd0fa2163f0039009342476e8e1cb0a5e80bae734ae219322b562c" +
+            "47eae320687a773c10365e922c9b20e7c3fa1e07ee7b6efdd31bcd1a5cad" +
+            "a72bf102cbd8d5e193a504d9ce10bbb2c078ce6590276d5bd2136de5a95a" +
+            "55e11d881ebfb6903df4df5df762833aafb658d7febba3498819dcf2b7af" +
+            "2e24e4b620b6d91c4d408f86914e15cbb1dfeaea0c1dcf2df85ca4289830" +
+            "c5a3812e167f75b558fb0c57f9e6864560e81420d7b60de5a554d5dafa11" +
+            "571868b271733182ea2851de72ce93e353c11bba216990b7181a53c2b3d5" +
+            "d8e8c019f5f73cdb6a985144ff3125302306092a864886f70d0109153116" +
+            "04149566f15bed2cb2da568ec392507a9abfcb2920003032302130090605" +
+            "2b0e03021a05000414c429b968eeca558cc2ec486f89b78c024bdecf2804" +
+            "087cbeafa8089685a102030927c1").HexToByteArray();
+
+        // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy credentials.")]
         internal const string OracleWalletPassword = "123Wallet";
     }
 }
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/tests/Pkcs12/Pkcs12InfoTests.cs b/src/libraries/System.Security.Cryptography.Pkcs/tests/Pkcs12/Pkcs12InfoTests.cs
index 45652762123e6c..cb0ad4e0a7c046 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/tests/Pkcs12/Pkcs12InfoTests.cs
+++ b/src/libraries/System.Security.Cryptography.Pkcs/tests/Pkcs12/Pkcs12InfoTests.cs
@@ -256,5 +256,66 @@ public static void VerifyMacWithNoMac()
 
             Assert.Throws<InvalidOperationException>(() => info.VerifyMac("hi"));
         }
+
+        [Theory]
+        [MemberData(nameof(DecodeWithHighPbeIterationsData))]
+        public static void DecodeWithHighPbeIterations(
+            PbeEncryptionAlgorithm encryptionAlgorithm,
+            HashAlgorithmName hashAlgorithmName,
+            int iterations)
+        {
+            string pw = nameof(CreateAndSealPkcs12);
+            byte[] data = CreateAndSealPkcs12(encryptionAlgorithm, hashAlgorithmName, iterations);
+            Pkcs12Info info = Pkcs12Info.Decode(data, out _, skipCopy: true);
+            info.AuthenticatedSafe.Single().Decrypt(pw);
+        }
+
+        [Fact]
+        public static void DecodeWithTooManyPbeIterations()
+        {
+            const string pw = "test";
+            Pkcs12Info info = Pkcs12Info.Decode(Pkcs12Documents.HighPbeIterationCount3Des, out _, skipCopy: true);
+            foreach (Pkcs12SafeContents contents in info.AuthenticatedSafe)
+            {
+                if (contents.ConfidentialityMode == Pkcs12ConfidentialityMode.None)
+                {
+                    continue;
+                }
+
+                Assert.ThrowsAny<CryptographicException>(() => contents.Decrypt(pw));
+            }
+        }
+
+        public static IEnumerable<object[]> DecodeWithHighPbeIterationsData
+        {
+            get
+            {
+                yield return new object[] { PbeEncryptionAlgorithm.Aes128Cbc, HashAlgorithmName.SHA256, 700_000 };
+                yield return new object[] { PbeEncryptionAlgorithm.Aes192Cbc, HashAlgorithmName.SHA256, 700_000 };
+                yield return new object[] { PbeEncryptionAlgorithm.Aes256Cbc, HashAlgorithmName.SHA256, 700_000 };
+                yield return new object[] { PbeEncryptionAlgorithm.TripleDes3KeyPkcs12, HashAlgorithmName.SHA1, 600_000 };
+            }
+        }
+
+        private static byte[] CreateAndSealPkcs12(
+            PbeEncryptionAlgorithm encryptionAlgorithm,
+            HashAlgorithmName hashAlgorithmName,
+            int iterations)
+        {
+            PbeParameters pbeParameters = new PbeParameters(
+                encryptionAlgorithm,
+                hashAlgorithmName,
+                iterations);
+
+            using RSA rsa = RSA.Create();
+            string pw = nameof(CreateAndSealPkcs12);
+            Pkcs12Builder builder = new Pkcs12Builder();
+            Pkcs12SafeContents contents = new Pkcs12SafeContents();
+            contents.AddShroudedKey(rsa, pw, pbeParameters);
+            builder.AddSafeContentsEncrypted(contents, pw, pbeParameters);
+            builder.SealWithMac(pw, hashAlgorithmName, iterations);
+
+            return builder.Encode();
+        }
     }
 }
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/tests/SignedCms/SignedCmsWholeDocumentTests.cs b/src/libraries/System.Security.Cryptography.Pkcs/tests/SignedCms/SignedCmsWholeDocumentTests.cs
index a68b49eef9790d..8dc711c7df264a 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/tests/SignedCms/SignedCmsWholeDocumentTests.cs
+++ b/src/libraries/System.Security.Cryptography.Pkcs/tests/SignedCms/SignedCmsWholeDocumentTests.cs
@@ -10,7 +10,7 @@ namespace System.Security.Cryptography.Pkcs.Tests
     public static class SignedCmsWholeDocumentTests
     {
         [Theory]
-#if !NET472
+#if !NETFRAMEWORK
         [InlineData(true)]
 #endif
         [InlineData(false)]
@@ -19,7 +19,7 @@ public static void ReadRsaPssDocument(bool fromSpan)
             SignedCms cms = new SignedCms();
             if (fromSpan)
             {
-#if !NET472
+#if !NETFRAMEWORK
                 cms.Decode(SignedDocuments.RsaPssDocument.AsSpan());
 #else
                 throw new Xunit.Sdk.XunitException(
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/tests/System.Security.Cryptography.Pkcs.Tests.csproj b/src/libraries/System.Security.Cryptography.Pkcs/tests/System.Security.Cryptography.Pkcs.Tests.csproj
index d050b65b704440..64a3a8a6cb8897 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/tests/System.Security.Cryptography.Pkcs.Tests.csproj
+++ b/src/libraries/System.Security.Cryptography.Pkcs/tests/System.Security.Cryptography.Pkcs.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent);$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent);net48-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonTestPath)System\Security\Cryptography\ByteUtils.cs"
@@ -66,4 +66,11 @@
   <ItemGroup Condition="'$(TargetsWindows)' == 'true' and $(TargetFramework.StartsWith('$(NetCoreAppCurrent)'))">
     <Compile Include="EnvelopedCms\DecryptTests.KeyPersistence.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Cng\src\System.Security.Cryptography.Cng.csproj" />
+    <ProjectReference Include="..\src\System.Security.Cryptography.Pkcs.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net48'))">
+    <Reference Include="System.Security" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.Primitives/Directory.Build.props b/src/libraries/System.Security.Cryptography.Primitives/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Security.Cryptography.Primitives/Directory.Build.props
+++ b/src/libraries/System.Security.Cryptography.Primitives/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.Primitives/ref/System.Security.Cryptography.Primitives.cs b/src/libraries/System.Security.Cryptography.Primitives/ref/System.Security.Cryptography.Primitives.cs
index 355c6c239b9319..0082a61b92b225 100644
--- a/src/libraries/System.Security.Cryptography.Primitives/ref/System.Security.Cryptography.Primitives.cs
+++ b/src/libraries/System.Security.Cryptography.Primitives/ref/System.Security.Cryptography.Primitives.cs
@@ -9,7 +9,8 @@ namespace System.Security.Cryptography
     public abstract partial class AsymmetricAlgorithm : System.IDisposable
     {
         protected int KeySizeValue;
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute] protected System.Security.Cryptography.KeySizes[] LegalKeySizesValue;
+        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
+        protected System.Security.Cryptography.KeySizes[] LegalKeySizesValue;
         protected AsymmetricAlgorithm() { }
         public virtual string? KeyExchangeAlgorithm { get { throw null; } }
         public virtual int KeySize { get { throw null; } set { } }
@@ -82,6 +83,7 @@ public override void EndWrite(System.IAsyncResult asyncResult) { }
         public override void Flush() { }
         public override System.Threading.Tasks.Task FlushAsync(System.Threading.CancellationToken cancellationToken) { throw null; }
         public void FlushFinalBlock() { }
+        public System.Threading.Tasks.ValueTask FlushFinalBlockAsync(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public override int Read(byte[] buffer, int offset, int count) { throw null; }
         public override System.Threading.Tasks.Task<int> ReadAsync(byte[] buffer, int offset, int count, System.Threading.CancellationToken cancellationToken) { throw null; }
         public override int ReadByte() { throw null; }
@@ -219,8 +221,10 @@ public abstract partial class SymmetricAlgorithm : System.IDisposable
         protected byte[]? IVValue;
         protected int KeySizeValue;
         protected byte[]? KeyValue;
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute] protected System.Security.Cryptography.KeySizes[] LegalBlockSizesValue;
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute] protected System.Security.Cryptography.KeySizes[] LegalKeySizesValue;
+        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
+        protected System.Security.Cryptography.KeySizes[] LegalBlockSizesValue;
+        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
+        protected System.Security.Cryptography.KeySizes[] LegalKeySizesValue;
         protected System.Security.Cryptography.CipherMode ModeValue;
         protected System.Security.Cryptography.PaddingMode PaddingValue;
         protected SymmetricAlgorithm() { }
diff --git a/src/libraries/System.Security.Cryptography.Primitives/src/Resources/Strings.resx b/src/libraries/System.Security.Cryptography.Primitives/src/Resources/Strings.resx
index 9eee3db30bb9f5..1307030da8c910 100644
--- a/src/libraries/System.Security.Cryptography.Primitives/src/Resources/Strings.resx
+++ b/src/libraries/System.Security.Cryptography.Primitives/src/Resources/Strings.resx
@@ -129,7 +129,7 @@
   <data name="InvalidOperation_IncorrectImplementation" xml:space="preserve">
     <value>The algorithm's implementation is incorrect.</value>
   </data>
-  <data name="Cryptography_PlatformNotSupported_Browser" xml:space="preserve">
-    <value>System.Security.Cryptography is not supported on Browser.</value>
+  <data name="SystemSecurityCryptographyPrimitives_PlatformNotSupported" xml:space="preserve">
+    <value>System.Security.Cryptography.Primitives is not supported on this platform.</value>
   </data>
 </root>
diff --git a/src/libraries/System.Security.Cryptography.Primitives/src/System.Security.Cryptography.Primitives.csproj b/src/libraries/System.Security.Cryptography.Primitives/src/System.Security.Cryptography.Primitives.csproj
index 1d984800745239..a75db1230a9d0b 100644
--- a/src/libraries/System.Security.Cryptography.Primitives/src/System.Security.Cryptography.Primitives.csproj
+++ b/src/libraries/System.Security.Cryptography.Primitives/src/System.Security.Cryptography.Primitives.csproj
@@ -1,13 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Security.Cryptography.Primitives</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.Cryptography_PlatformNotSupported_Browser</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemSecurityCryptographyPrimitives_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Security\Cryptography\AsymmetricAlgorithm.cs" />
diff --git a/src/libraries/System.Security.Cryptography.Primitives/src/System/Security/Cryptography/CryptoStream.cs b/src/libraries/System.Security.Cryptography.Primitives/src/System/Security/Cryptography/CryptoStream.cs
index e414e3c6eb08aa..2e426cc4185381 100644
--- a/src/libraries/System.Security.Cryptography.Primitives/src/System/Security/Cryptography/CryptoStream.cs
+++ b/src/libraries/System.Security.Cryptography.Primitives/src/System/Security/Cryptography/CryptoStream.cs
@@ -100,9 +100,23 @@ public bool HasFlushedFinalBlock
         // byte[] ciphertext = ms.ToArray();
         // cs.Close();
         public void FlushFinalBlock() =>
-            FlushFinalBlockAsync(useAsync: false).AsTask().GetAwaiter().GetResult();
+            FlushFinalBlockAsync(useAsync: false, default).AsTask().GetAwaiter().GetResult();
+
+        /// <summary>
+        /// Asynchronously updates the underlying data source or repository with the
+        /// current state of the buffer, then clears the buffer.
+        /// </summary>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="CancellationToken.None"/>.</param>
+        /// <returns>A task that represents the asynchronous flush operation.</returns>
+        public ValueTask FlushFinalBlockAsync(CancellationToken cancellationToken = default)
+        {
+            if (cancellationToken.IsCancellationRequested)
+                return ValueTask.FromCanceled(cancellationToken);
+
+            return FlushFinalBlockAsync(useAsync: true, cancellationToken);
+        }
 
-        private async ValueTask FlushFinalBlockAsync(bool useAsync)
+        private async ValueTask FlushFinalBlockAsync(bool useAsync, CancellationToken cancellationToken)
         {
             if (_finalBlockTransformed)
                 throw new NotSupportedException(SR.Cryptography_CryptoStream_FlushFinalBlockTwice);
@@ -116,7 +130,7 @@ private async ValueTask FlushFinalBlockAsync(bool useAsync)
                 byte[] finalBytes = _transform.TransformFinalBlock(_inputBuffer!, 0, _inputBufferIndex);
                 if (useAsync)
                 {
-                    await _stream.WriteAsync(new ReadOnlyMemory<byte>(finalBytes)).ConfigureAwait(false);
+                    await _stream.WriteAsync(new ReadOnlyMemory<byte>(finalBytes), cancellationToken).ConfigureAwait(false);
                 }
                 else
                 {
@@ -129,14 +143,14 @@ private async ValueTask FlushFinalBlockAsync(bool useAsync)
             {
                 if (!innerCryptoStream.HasFlushedFinalBlock)
                 {
-                    await innerCryptoStream.FlushFinalBlockAsync(useAsync).ConfigureAwait(false);
+                    await innerCryptoStream.FlushFinalBlockAsync(useAsync, cancellationToken).ConfigureAwait(false);
                 }
             }
             else
             {
                 if (useAsync)
                 {
-                    await _stream.FlushAsync().ConfigureAwait(false);
+                    await _stream.FlushAsync(cancellationToken).ConfigureAwait(false);
                 }
                 else
                 {
@@ -691,7 +705,7 @@ private async ValueTask DisposeAsyncCore()
             {
                 if (!_finalBlockTransformed)
                 {
-                    await FlushFinalBlockAsync(useAsync: true).ConfigureAwait(false);
+                    await FlushFinalBlockAsync(useAsync: true, default).ConfigureAwait(false);
                 }
 
                 if (!_leaveOpen)
diff --git a/src/libraries/System.Security.Cryptography.Primitives/tests/CryptoStream.cs b/src/libraries/System.Security.Cryptography.Primitives/tests/CryptoStream.cs
index 1d663a2c4fffdf..6156e9c2ea200b 100644
--- a/src/libraries/System.Security.Cryptography.Primitives/tests/CryptoStream.cs
+++ b/src/libraries/System.Security.Cryptography.Primitives/tests/CryptoStream.cs
@@ -187,6 +187,34 @@ public static void FlushAsync()
             }
         }
 
+        [Fact]
+        public static async Task FlushFinalBlockAsync()
+        {
+            ICryptoTransform encryptor = new IdentityTransform(1, 1, true);
+            using (MemoryStream output = new MemoryStream())
+            using (CryptoStream encryptStream = new CryptoStream(output, encryptor, CryptoStreamMode.Write))
+            {
+                await encryptStream.WriteAsync(new byte[] { 1, 2, 3, 4, 5 }, 0, 5);
+                await encryptStream.FlushFinalBlockAsync();
+                Assert.True(encryptStream.HasFlushedFinalBlock);
+                Assert.Equal(5, output.ToArray().Length);
+            }
+        }
+
+        [Fact]
+        public static async Task FlushFinalBlockAsync_Cancelled()
+        {
+            ICryptoTransform encryptor = new IdentityTransform(1, 1, true);
+            using (MemoryStream output = new MemoryStream())
+            using (CryptoStream encryptStream = new CryptoStream(output, encryptor, CryptoStreamMode.Write))
+            {
+                await encryptStream.WriteAsync(new byte[] { 1, 2, 3, 4, 5 }, 0, 5);
+                ValueTask waitable = encryptStream.FlushFinalBlockAsync(new Threading.CancellationToken(canceled: true));
+                Assert.True(waitable.IsCanceled);
+                Assert.False(encryptStream.HasFlushedFinalBlock);
+            }
+        }
+
         [Fact]
         public static void FlushCalledOnFlushAsync_DeriveClass()
         {
diff --git a/src/libraries/System.Security.Cryptography.ProtectedData/ref/System.Security.Cryptography.ProtectedData.csproj b/src/libraries/System.Security.Cryptography.ProtectedData/ref/System.Security.Cryptography.ProtectedData.csproj
index 7cb462c9f93b16..ac9410e6b68f93 100644
--- a/src/libraries/System.Security.Cryptography.ProtectedData/ref/System.Security.Cryptography.ProtectedData.csproj
+++ b/src/libraries/System.Security.Cryptography.ProtectedData/ref/System.Security.Cryptography.ProtectedData.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -12,7 +11,6 @@
     <Compile Include="System.Security.Cryptography.ProtectedData.cs" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
     <Reference Include="System.Security" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.ProtectedData/src/System.Security.Cryptography.ProtectedData.csproj b/src/libraries/System.Security.Cryptography.ProtectedData/src/System.Security.Cryptography.ProtectedData.csproj
index 21221a5eba8380..3a9ef745e2f280 100644
--- a/src/libraries/System.Security.Cryptography.ProtectedData/src/System.Security.Cryptography.ProtectedData.csproj
+++ b/src/libraries/System.Security.Cryptography.ProtectedData/src/System.Security.Cryptography.ProtectedData.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>netstandard2.0-Windows_NT;net461-Windows_NT;netstandard2.0;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0-Windows_NT;net461-Windows_NT;netstandard2.0</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -34,14 +33,9 @@
              Link="Common\System\HResults.cs" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
     <Reference Include="System.Security" />
   </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="System.Security.Cryptography.Primitives" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard2.0'))">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.ProtectedData/tests/System.Security.Cryptography.ProtectedData.Tests.csproj b/src/libraries/System.Security.Cryptography.ProtectedData/tests/System.Security.Cryptography.ProtectedData.Tests.csproj
index 2d90d9b44f076b..acdc3f5b658314 100644
--- a/src/libraries/System.Security.Cryptography.ProtectedData/tests/System.Security.Cryptography.ProtectedData.Tests.csproj
+++ b/src/libraries/System.Security.Cryptography.ProtectedData/tests/System.Security.Cryptography.ProtectedData.Tests.csproj
@@ -1,11 +1,17 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="ProtectedDataTests.cs" />
     <Compile Include="$(CommonTestPath)System\Security\Cryptography\ByteUtils.cs"
              Link="CommonTest\System\Security\Cryptography\ByteUtils.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Security.Cryptography.ProtectedData.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net461'))">
+    <Reference Include="System.Security" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.X509Certificates/Directory.Build.props b/src/libraries/System.Security.Cryptography.X509Certificates/Directory.Build.props
index 42c6eafce67ed8..d68d22c1b917f8 100644
--- a/src/libraries/System.Security.Cryptography.X509Certificates/Directory.Build.props
+++ b/src/libraries/System.Security.Cryptography.X509Certificates/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IncludePlatformAttributes>true</IncludePlatformAttributes>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.X509Certificates/ref/System.Security.Cryptography.X509Certificates.cs b/src/libraries/System.Security.Cryptography.X509Certificates/ref/System.Security.Cryptography.X509Certificates.cs
index 07b51c0d456c0c..411c729bf0df8c 100644
--- a/src/libraries/System.Security.Cryptography.X509Certificates/ref/System.Security.Cryptography.X509Certificates.cs
+++ b/src/libraries/System.Security.Cryptography.X509Certificates/ref/System.Security.Cryptography.X509Certificates.cs
@@ -332,7 +332,7 @@ public partial class X509Chain : System.IDisposable
     {
         public X509Chain() { }
         public X509Chain(bool useMachineContext) { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public X509Chain(System.IntPtr chainContext) { }
         public System.IntPtr ChainContext { get { throw null; } }
         public System.Security.Cryptography.X509Certificates.X509ChainElementCollection ChainElements { get { throw null; } }
diff --git a/src/libraries/System.Security.Cryptography.X509Certificates/src/Resources/Strings.resx b/src/libraries/System.Security.Cryptography.X509Certificates/src/Resources/Strings.resx
index bcfe169eaea896..40eb18f054f3aa 100644
--- a/src/libraries/System.Security.Cryptography.X509Certificates/src/Resources/Strings.resx
+++ b/src/libraries/System.Security.Cryptography.X509Certificates/src/Resources/Strings.resx
@@ -427,7 +427,7 @@
   <data name="Cryptography_NotValidPrivateKey" xml:space="preserve">
     <value>Key is not a valid private key.</value>
   </data>
-  <data name="Cryptography_PlatformNotSupported" xml:space="preserve">
-    <value>System.Security.Cryptography is not supported on this platform.</value>
+  <data name="SystemSecurityCryptographyX509Certificates_PlatformNotSupported" xml:space="preserve">
+    <value>System.Security.Cryptography.X509Certificates is not supported on this platform.</value>
   </data>
 </root>
diff --git a/src/libraries/System.Security.Cryptography.X509Certificates/src/System.Security.Cryptography.X509Certificates.csproj b/src/libraries/System.Security.Cryptography.X509Certificates/src/System.Security.Cryptography.X509Certificates.csproj
index a3a8784ece4672..a62bc53a92203b 100644
--- a/src/libraries/System.Security.Cryptography.X509Certificates/src/System.Security.Cryptography.X509Certificates.csproj
+++ b/src/libraries/System.Security.Cryptography.X509Certificates/src/System.Security.Cryptography.X509Certificates.csproj
@@ -7,7 +7,7 @@
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetsAnyOS)' == 'true'">
     <NoWarn>$(NoWarn);CS8769</NoWarn>
-    <GeneratePlatformNotSupportedAssemblyMessage>SR.Cryptography_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage>SR.SystemSecurityCryptographyX509Certificates_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <Import Project="$(CommonPath)System\Security\Cryptography\Asn1\AsnXml.targets" />
   <Import Project="$(CommonPath)System\Security\Cryptography\Asn1Reader\System.Security.Cryptography.Asn1Reader.Shared.projitems" />
@@ -676,12 +676,12 @@
     <Reference Include="System.Threading" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
-    <Reference Include="System.Security.Cryptography.Cng" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Cng\src\System.Security.Cryptography.Cng.csproj" />
     <Reference Include="System.Security.Cryptography.Csp" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)' == 'true' and '$(TargetsOSX)' != 'true' and '$(TargetsiOS)' != 'true' and '$(TargetstvOS)' != 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.OpenSsl\src\System.Security.Cryptography.OpenSsl.csproj" />
     <Reference Include="System.Diagnostics.StackTrace" />
-    <Reference Include="System.Security.Cryptography.OpenSsl" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
     <Reference Include="System.Console" Condition="'$(Configuration)' == 'Debug'" />
diff --git a/src/libraries/System.Security.Cryptography.X509Certificates/src/System/Security/Cryptography/X509Certificates/X509Chain.cs b/src/libraries/System.Security.Cryptography.X509Certificates/src/System/Security/Cryptography/X509Certificates/X509Chain.cs
index 51d4001e2d5151..dbefadab573347 100644
--- a/src/libraries/System.Security.Cryptography.X509Certificates/src/System/Security/Cryptography/X509Certificates/X509Chain.cs
+++ b/src/libraries/System.Security.Cryptography.X509Certificates/src/System/Security/Cryptography/X509Certificates/X509Chain.cs
@@ -24,7 +24,7 @@ public X509Chain(bool useMachineContext)
             _useMachineContext = useMachineContext;
         }
 
-        [MinimumOSPlatform("windows7.0")]
+        [SupportedOSPlatform("windows")]
         public X509Chain(IntPtr chainContext)
         {
             _pal = ChainPal.FromHandle(chainContext);
diff --git a/src/libraries/System.Security.Cryptography.X509Certificates/tests/CertTests.cs b/src/libraries/System.Security.Cryptography.X509Certificates/tests/CertTests.cs
index e16a28f9be7aab..cdf719833f7f57 100644
--- a/src/libraries/System.Security.Cryptography.X509Certificates/tests/CertTests.cs
+++ b/src/libraries/System.Security.Cryptography.X509Certificates/tests/CertTests.cs
@@ -150,12 +150,12 @@ private void LogVerifyErrors(X509Certificate2 cert, string testName)
                     {
                         foreach (X509ChainStatus chainStatus in chain.ChainStatus)
                         {
-                            _log.WriteLine(string.Format($"X509Certificate2.Verify error: {testName}, {chainStatus.Status}, {chainStatus.StatusInformation}"));
+                            _log.WriteLine($"X509Certificate2.Verify error: {testName}, {chainStatus.Status}, {chainStatus.StatusInformation}");
                         }
                     }
                     else
                     {
-                        _log.WriteLine(string.Format($"X509Certificate2.Verify expected error; received none: {testName}"));
+                        _log.WriteLine($"X509Certificate2.Verify expected error; received none: {testName}");
                     }
                 }
             }
diff --git a/src/libraries/System.Security.Cryptography.X509Certificates/tests/ExportTests.cs b/src/libraries/System.Security.Cryptography.X509Certificates/tests/ExportTests.cs
index b508552ea01a94..7f0455ea74d7c5 100644
--- a/src/libraries/System.Security.Cryptography.X509Certificates/tests/ExportTests.cs
+++ b/src/libraries/System.Security.Cryptography.X509Certificates/tests/ExportTests.cs
@@ -76,6 +76,7 @@ public static void ExportAsPfx()
         [Fact]
         public static void ExportAsPfxWithPassword()
         {
+            // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Password for testing purpose.")]
             const string password = "Cotton";
 
             using (X509Certificate2 c1 = new X509Certificate2(TestData.MsCertificate))
@@ -94,6 +95,7 @@ public static void ExportAsPfxWithPassword()
         [Fact]
         public static void ExportAsPfxVerifyPassword()
         {
+            // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Password for testing purpose.")]
             const string password = "Cotton";
 
             using (X509Certificate2 c1 = new X509Certificate2(TestData.MsCertificate))
@@ -109,7 +111,7 @@ public static void ExportAsPfxWithPrivateKeyVerifyPassword()
             using (var cert = new X509Certificate2(TestData.PfxData, TestData.PfxDataPassword, X509KeyStorageFlags.Exportable))
             {
                 Assert.True(cert.HasPrivateKey, "cert.HasPrivateKey");
-
+                // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Password for testing purpose.")]
                 const string password = "Cotton";
 
                 byte[] pfx = cert.Export(X509ContentType.Pkcs12, password);
diff --git a/src/libraries/System.Security.Cryptography.X509Certificates/tests/RevocationTests/DynamicRevocationTests.cs b/src/libraries/System.Security.Cryptography.X509Certificates/tests/RevocationTests/DynamicRevocationTests.cs
index 8e720bec8a2f15..ac869243d76e95 100644
--- a/src/libraries/System.Security.Cryptography.X509Certificates/tests/RevocationTests/DynamicRevocationTests.cs
+++ b/src/libraries/System.Security.Cryptography.X509Certificates/tests/RevocationTests/DynamicRevocationTests.cs
@@ -11,7 +11,6 @@
 namespace System.Security.Cryptography.X509Certificates.Tests.RevocationTests
 {
     [OuterLoop("These tests run serially at about 1 second each, and the code shouldn't change that often.")]
-    [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
     public static class DynamicRevocationTests
     {
         // The CI machines are doing an awful lot of things at once, be generous with the timeout;
@@ -20,6 +19,8 @@ public static class DynamicRevocationTests
         private static readonly Oid s_tlsServerOid = new Oid("1.3.6.1.5.5.7.3.1", null);
 
         private static readonly X509ChainStatusFlags ThisOsRevocationStatusUnknown =
+                PlatformDetection.IsOSX ?
+                X509ChainStatusFlags.RevocationStatusUnknown :
                 X509ChainStatusFlags.RevocationStatusUnknown | X509ChainStatusFlags.OfflineRevocation;
 
 
@@ -57,6 +58,16 @@ public static IEnumerable<object[]> AllViableRevocation
                                 continue;
                             }
 
+                            // https://github.com/dotnet/runtime/issues/31249
+                            // not all scenarios are working on macOS.
+                            if (PlatformDetection.IsOSX)
+                            {
+                                if (!endEntityRevocation.HasFlag(PkiOptions.EndEntityRevocationViaOcsp))
+                                {
+                                    continue;
+                                }
+                            }
+
                             yield return new object[] { designationOptions | issuerRevocation | endEntityRevocation };
                         }
                     }
@@ -83,6 +94,7 @@ public static void NothingRevoked(PkiOptions pkiOptions)
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeIntermediate(PkiOptions pkiOptions)
         {
             SimpleTest(
@@ -129,6 +141,7 @@ public static void RevokeEndEntity(PkiOptions pkiOptions)
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeIntermediateAndEndEntity(PkiOptions pkiOptions)
         {
             SimpleTest(
@@ -157,6 +170,7 @@ public static void RevokeIntermediateAndEndEntity(PkiOptions pkiOptions)
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeRoot(PkiOptions pkiOptions)
         {
             SimpleTest(
@@ -193,6 +207,7 @@ public static void RevokeRoot(PkiOptions pkiOptions)
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeRootAndEndEntity(PkiOptions pkiOptions)
         {
             SimpleTest(
@@ -227,6 +242,7 @@ public static void RevokeRootAndEndEntity(PkiOptions pkiOptions)
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeRootAndIntermediate(PkiOptions pkiOptions)
         {
             SimpleTest(
@@ -262,6 +278,7 @@ public static void RevokeRootAndIntermediate(PkiOptions pkiOptions)
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeEverything(PkiOptions pkiOptions)
         {
             SimpleTest(
@@ -384,6 +401,7 @@ public static void RevokeEndEntity_IssuerUnrelatedOcsp(PkiOptions pkiOptions)
         [Theory]
         [InlineData(PkiOptions.OcspEverywhere)]
         [InlineData(PkiOptions.IssuerRevocationViaOcsp | PkiOptions.AllEndEntityRevocation)]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeEndEntity_RootUnrelatedOcsp(PkiOptions pkiOptions)
         {
             SimpleTest(
@@ -472,6 +490,7 @@ public static void RevokeEndEntity_RootUnrelatedOcsp(PkiOptions pkiOptions)
         [InlineData(false, true)]
         [InlineData(true, false)]
         [InlineData(true, true)]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeIntermediate_PolicyErrors_NotTimeValid(bool policyErrors, bool notTimeValid)
         {
             SimpleTest(
@@ -558,6 +577,7 @@ public static void RevokeIntermediate_PolicyErrors_NotTimeValid(bool policyError
         [InlineData(false, true)]
         [InlineData(true, false)]
         [InlineData(true, true)]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeEndEntity_PolicyErrors_NotTimeValid(bool policyErrors, bool notTimeValid)
         {
             SimpleTest(
@@ -639,6 +659,7 @@ public static void RevokeEndEntity_PolicyErrors_NotTimeValid(bool policyErrors,
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeEndEntity_RootRevocationOffline(PkiOptions pkiOptions)
         {
             BuildPrivatePki(
@@ -712,6 +733,7 @@ public static void RevokeEndEntity_RootRevocationOffline(PkiOptions pkiOptions)
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void NothingRevoked_RootRevocationOffline(PkiOptions pkiOptions)
         {
             BuildPrivatePki(
@@ -798,6 +820,7 @@ public static void RevokeEndEntityWithInvalidRevocationSignature(PkiOptions pkiO
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeIntermediateWithInvalidRevocationSignature(PkiOptions pkiOptions)
         {
             SimpleTest(
@@ -826,6 +849,7 @@ public static void RevokeEndEntityWithInvalidRevocationName(PkiOptions pkiOption
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeIntermediateWithInvalidRevocationName(PkiOptions pkiOptions)
         {
             SimpleTest(
@@ -863,6 +887,7 @@ public static void RevokeEndEntityWithExpiredRevocation(PkiOptions pkiOptions)
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void RevokeIntermediateWithExpiredRevocation(PkiOptions pkiOptions)
         {
             SimpleTest(
@@ -903,6 +928,7 @@ public static void CheckEndEntityWithExpiredRevocation(PkiOptions pkiOptions)
 
         [Theory]
         [MemberData(nameof(AllViableRevocation))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/31249", TestPlatforms.OSX)]
         public static void CheckIntermediateWithExpiredRevocation(PkiOptions pkiOptions)
         {
             SimpleTest(
diff --git a/src/libraries/System.Security.Cryptography.X509Certificates/tests/System.Security.Cryptography.X509Certificates.Tests.csproj b/src/libraries/System.Security.Cryptography.X509Certificates/tests/System.Security.Cryptography.X509Certificates.Tests.csproj
index 2f97db5e544623..c666f2f3e54cb2 100644
--- a/src/libraries/System.Security.Cryptography.X509Certificates/tests/System.Security.Cryptography.X509Certificates.Tests.csproj
+++ b/src/libraries/System.Security.Cryptography.X509Certificates/tests/System.Security.Cryptography.X509Certificates.Tests.csproj
@@ -116,6 +116,8 @@
              Link="Common\Microsoft\Win32\SafeHandles\SafeHandleCache.cs" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Cng\src\System.Security.Cryptography.Cng.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Pkcs\src\System.Security.Cryptography.Pkcs.csproj" />
     <PackageReference Include="System.Security.Cryptography.X509Certificates.TestData" Version="$(SystemSecurityCryptographyX509CertificatesTestDataVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.Xml/ref/System.Security.Cryptography.Xml.csproj b/src/libraries/System.Security.Cryptography.Xml/ref/System.Security.Cryptography.Xml.csproj
index 43030e53132c4f..4d4f20e941f50e 100644
--- a/src/libraries/System.Security.Cryptography.Xml/ref/System.Security.Cryptography.Xml.csproj
+++ b/src/libraries/System.Security.Cryptography.Xml/ref/System.Security.Cryptography.Xml.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -11,10 +10,6 @@
     <ProjectReference Include="..\..\System.Security.Permissions\ref\System.Security.Permissions.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(IsPartialFacadeAssembly)' == 'true'">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.Xml" />
     <Reference Include="System.Security" />
   </ItemGroup>
   <ItemGroup>
diff --git a/src/libraries/System.Security.Cryptography.Xml/src/Resources/Strings.resx b/src/libraries/System.Security.Cryptography.Xml/src/Resources/Strings.resx
index e21123b143fecd..83c682953e12e4 100644
--- a/src/libraries/System.Security.Cryptography.Xml/src/Resources/Strings.resx
+++ b/src/libraries/System.Security.Cryptography.Xml/src/Resources/Strings.resx
@@ -377,7 +377,7 @@
   <data name="Log_UnsafeTransformMethod" xml:space="preserve">
     <value>Transform method "{0}" is not on the safe list. Safe transform methods are: {1}.</value>
   </data>
-  <data name="Cryptography_PlatformNotSupported_Browser" xml:space="preserve">
-    <value>System.Security.Cryptography is not supported on Browser.</value>
+  <data name="SystemSecurityCryptographyXml_PlatformNotSupported" xml:space="preserve">
+    <value>System.Security.Cryptography.Xml is not supported on this platform.</value>
   </data>
 </root>
diff --git a/src/libraries/System.Security.Cryptography.Xml/src/System.Security.Cryptography.Xml.csproj b/src/libraries/System.Security.Cryptography.Xml/src/System.Security.Cryptography.Xml.csproj
index c7ccd603d5dd12..5f39ed504d48f9 100644
--- a/src/libraries/System.Security.Cryptography.Xml/src/System.Security.Cryptography.Xml.csproj
+++ b/src/libraries/System.Security.Cryptography.Xml/src/System.Security.Cryptography.Xml.csproj
@@ -1,15 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
     <IsPartialFacadeAssembly Condition="$(TargetFramework.StartsWith('net4'))">true</IsPartialFacadeAssembly>
   </PropertyGroup>
   <PropertyGroup>
-    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.Cryptography_PlatformNotSupported_Browser</GeneratePlatformNotSupportedAssemblyMessage>
+    <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsBrowser)' == 'true'">SR.SystemSecurityCryptographyXml_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
   <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
     <Compile Include="System\Security\Cryptography\Xml\AncestralNamespaceContextManager.cs" />
@@ -91,32 +90,12 @@
     <Compile Include="$(CommonPath)System\HexConverter.cs"
              Link="Common\System\HexConverter.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPartialFacadeAssembly)' != 'true'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Collections.NonGeneric" />
-    <Reference Include="System.Diagnostics.Debug" />
-    <Reference Include="System.Diagnostics.Tools" />
-    <Reference Include="System.Diagnostics.TraceSource" />
-    <Reference Include="System.Net.Requests" />
-    <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Runtime.Numerics" />
-    <Reference Include="System.Security.Cryptography.Algorithms" />
-    <Reference Include="System.Security.Cryptography.Csp" />
-    <Reference Include="System.Security.Cryptography.Encoding" />
-    <Reference Include="System.Security.Cryptography.Primitives" />
-    <Reference Include="System.Security.Cryptography.Pkcs" />
-    <Reference Include="System.Security.Cryptography.X509Certificates" />
-    <Reference Include="System.Security.Permissions" />
-    <Reference Include="System.Text.Encoding.Extensions" />
-    <Reference Include="System.Xml.ReaderWriter" />
-    <Reference Include="System.Xml.XPath" />
-    <Reference Include="System.Memory" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Security.Cryptography.Pkcs" Version="$(SystemSecurityCryptographyPkcsVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Permissions\src\System.Security.Permissions.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(IsPartialFacadeAssembly)' == 'true'">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Reference Include="System.Security" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Cryptography.Xml/tests/EncryptedXmlTest.cs b/src/libraries/System.Security.Cryptography.Xml/tests/EncryptedXmlTest.cs
index fc0a7d80195a5e..f547ba74dda2ed 100644
--- a/src/libraries/System.Security.Cryptography.Xml/tests/EncryptedXmlTest.cs
+++ b/src/libraries/System.Security.Cryptography.Xml/tests/EncryptedXmlTest.cs
@@ -141,6 +141,7 @@ public void Sample2()
             {
                 aes.Mode = CipherMode.CBC;
                 aes.KeySize = 256;
+                // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test key.")]
                 aes.Key = Convert.FromBase64String("o/ilseZu+keLBBWGGPlUHweqxIPc4gzZEFWr2nBt640=");
                 aes.Padding = PaddingMode.Zeros;
 
@@ -173,6 +174,7 @@ public void RoundtripSample1()
                         aes.Mode = CipherMode.CBC;
                         aes.KeySize = 256;
                         aes.IV = Convert.FromBase64String("pBUM5P03rZ6AE4ZK5EyBrw==");
+                        // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test key.")]
                         aes.Key = Convert.FromBase64String("o/ilseZu+keLBBWGGPlUHweqxIPc4gzZEFWr2nBt640=");
                         aes.Padding = PaddingMode.Zeros;
 
@@ -203,8 +205,8 @@ public void RoundtripSample1()
                     {
                         aes.Mode = CipherMode.CBC;
                         aes.KeySize = 256;
-                        aes.Key = Convert.FromBase64String(
-                            "o/ilseZu+keLBBWGGPlUHweqxIPc4gzZEFWr2nBt640=");
+                        // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test key.")]
+                        aes.Key = Convert.FromBase64String("o/ilseZu+keLBBWGGPlUHweqxIPc4gzZEFWr2nBt640=");
                         aes.Padding = PaddingMode.Zeros;
 
                         XmlDocument doc = new XmlDocument();
diff --git a/src/libraries/System.Security.Cryptography.Xml/tests/System.Security.Cryptography.Xml.Tests.csproj b/src/libraries/System.Security.Cryptography.Xml/tests/System.Security.Cryptography.Xml.Tests.csproj
index 9ad0a17ec7426c..2bfad93e7780ff 100644
--- a/src/libraries/System.Security.Cryptography.Xml/tests/System.Security.Cryptography.Xml.Tests.csproj
+++ b/src/libraries/System.Security.Cryptography.Xml/tests/System.Security.Cryptography.Xml.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="AssemblyInfo.cs" />
@@ -65,4 +65,10 @@
     <EmbeddedResource Include="EncryptedXmlSample1.xml" />
     <EmbeddedResource Include="XmlLicenseSample.xml" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Security.Cryptography.Xml.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.Security" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Cryptography.Xml/tests/TestHelpers.cs b/src/libraries/System.Security.Cryptography.Xml/tests/TestHelpers.cs
index 3f138acfd76247..4cdcd7d483346e 100644
--- a/src/libraries/System.Security.Cryptography.Xml/tests/TestHelpers.cs
+++ b/src/libraries/System.Security.Cryptography.Xml/tests/TestHelpers.cs
@@ -185,6 +185,7 @@ public static IEnumerable<SymmetricAlgorithmFactory> GetSymmetricAlgorithms(bool
         }
 
         private static readonly byte[] SamplePfx = Convert.FromBase64String(
+    // [SuppressMessage("Microsoft.Security", "CS002:SecretInNextLine", Justification="Unit test dummy certificate.")]
     @"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");
 
         public static X509Certificate2 GetSampleX509Certificate()
diff --git a/src/libraries/System.Security.Permissions/ref/System.Security.Permissions.cs b/src/libraries/System.Security.Permissions/ref/System.Security.Permissions.cs
index 81c59db3baa11b..0ef3beb0bad3ed 100644
--- a/src/libraries/System.Security.Permissions/ref/System.Security.Permissions.cs
+++ b/src/libraries/System.Security.Permissions/ref/System.Security.Permissions.cs
@@ -31,10 +31,10 @@ public override void FromXml(System.Security.SecurityElement securityElement) {
         public override System.Security.SecurityElement ToXml() { throw null; }
         public override System.Security.IPermission Union(System.Security.IPermission target) { throw null; }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.All, AllowMultiple=true, Inherited=false)]
 #if NET50_OBSOLETIONS
     [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
 #endif
+    [System.AttributeUsageAttribute(System.AttributeTargets.All, AllowMultiple=true, Inherited=false)]
     public sealed partial class ConfigurationPermissionAttribute : System.Security.Permissions.CodeAccessSecurityAttribute
     {
         public ConfigurationPermissionAttribute(System.Security.Permissions.SecurityAction action) : base (default(System.Security.Permissions.SecurityAction)) { }
@@ -402,10 +402,10 @@ public override void FromXml(System.Security.SecurityElement securityElement) {
         public override System.Security.SecurityElement ToXml() { throw null; }
         public override System.Security.IPermission Union(System.Security.IPermission target) { throw null; }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
 #if NET50_OBSOLETIONS
     [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
 #endif
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
     public sealed partial class SocketPermissionAttribute : System.Security.Permissions.CodeAccessSecurityAttribute
     {
         public SocketPermissionAttribute(System.Security.Permissions.SecurityAction action) : base (default(System.Security.Permissions.SecurityAction)) { }
@@ -444,10 +444,10 @@ public override void FromXml(System.Security.SecurityElement securityElement) {
         public override System.Security.SecurityElement ToXml() { throw null; }
         public override System.Security.IPermission Union(System.Security.IPermission target) { throw null; }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
 #if NET50_OBSOLETIONS
     [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
 #endif
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
     public sealed partial class WebPermissionAttribute : System.Security.Permissions.CodeAccessSecurityAttribute
     {
         public WebPermissionAttribute(System.Security.Permissions.SecurityAction action) : base (default(System.Security.Permissions.SecurityAction)) { }
@@ -885,10 +885,10 @@ public void SetPathList(System.Security.Permissions.EnvironmentPermissionAccess
         public override System.Security.SecurityElement ToXml() { throw null; }
         public override System.Security.IPermission Union(System.Security.IPermission other) { throw null; }
     }
-    [System.FlagsAttribute]
 #if NET50_OBSOLETIONS
     [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
 #endif
+    [System.FlagsAttribute]
     public enum EnvironmentPermissionAccess
     {
         NoAccess = 0,
@@ -896,10 +896,10 @@ public enum EnvironmentPermissionAccess
         Write = 2,
         AllAccess = 3,
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
 #if NET50_OBSOLETIONS
     [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
 #endif
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
     public sealed partial class EnvironmentPermissionAttribute : System.Security.Permissions.CodeAccessSecurityAttribute
     {
         public EnvironmentPermissionAttribute(System.Security.Permissions.SecurityAction action) : base (default(System.Security.Permissions.SecurityAction)) { }
@@ -1199,10 +1199,10 @@ public KeyContainerPermissionAccessEntryEnumerator() { }
         public bool MoveNext() { throw null; }
         public void Reset() { }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
 #if NET50_OBSOLETIONS
     [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
 #endif
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
     public sealed partial class KeyContainerPermissionAttribute : System.Security.Permissions.CodeAccessSecurityAttribute
     {
         public KeyContainerPermissionAttribute(System.Security.Permissions.SecurityAction action) : base (default(System.Security.Permissions.SecurityAction)) { }
@@ -1253,10 +1253,10 @@ public override void FromXml(System.Security.SecurityElement securityElement) {
         public override System.Security.SecurityElement ToXml() { throw null; }
         public override System.Security.IPermission Union(System.Security.IPermission target) { throw null; }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
 #if NET50_OBSOLETIONS
     [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
 #endif
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
     public sealed partial class MediaPermissionAttribute : System.Security.Permissions.CodeAccessSecurityAttribute
     {
         public MediaPermissionAttribute(System.Security.Permissions.SecurityAction action) : base (default(System.Security.Permissions.SecurityAction)) { }
@@ -1337,10 +1337,10 @@ public void FromXml(System.Security.SecurityElement elem) { }
         public System.Security.SecurityElement ToXml() { throw null; }
         public System.Security.IPermission Union(System.Security.IPermission other) { throw null; }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Method, AllowMultiple=true, Inherited=false)]
 #if NET50_OBSOLETIONS
     [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
 #endif
+    [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Method, AllowMultiple=true, Inherited=false)]
     public sealed partial class PrincipalPermissionAttribute : System.Security.Permissions.CodeAccessSecurityAttribute
     {
 #if NET50_OBSOLETIONS
diff --git a/src/libraries/System.Security.Permissions/ref/System.Security.Permissions.csproj b/src/libraries/System.Security.Permissions/ref/System.Security.Permissions.csproj
index 9905b3157eef52..f8b4eb6709a2d1 100644
--- a/src/libraries/System.Security.Permissions/ref/System.Security.Permissions.csproj
+++ b/src/libraries/System.Security.Permissions/ref/System.Security.Permissions.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;netcoreapp3.0;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;netcoreapp3.0</TargetFrameworks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -19,12 +18,8 @@
     <Compile Include="System.Security.Permissions.netcoreapp.cs" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Reference Include="System.Configuration" />
-    <Reference Include="System.Data" />
     <Reference Include="System.Data.OracleClient" />
-    <Reference Include="System.Drawing" />
     <Reference Include="System.Net" />
     <Reference Include="System.Security" />
     <Reference Include="System.ServiceProcess" />
@@ -33,20 +28,23 @@
     <Reference Include="WindowsBase" />
   </ItemGroup>
   <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
-    <ProjectReference Include="..\..\System.Security.AccessControl\ref\System.Security.AccessControl.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\ref\System.Security.AccessControl.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or '$(TargetFramework)' == 'netcoreapp3.0'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Windows.Extensions\ref\System.Windows.Extensions.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="..\..\System.Collections.NonGeneric\ref\System.Collections.NonGeneric.csproj" />
-    <ProjectReference Include="..\..\System.ComponentModel.Primitives\ref\System.ComponentModel.Primitives.csproj" />
-    <ProjectReference Include="..\..\System.Data.Common\ref\System.Data.Common.csproj" />
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Runtime.Extensions\ref\System.Runtime.Extensions.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Algorithms\ref\System.Security.Cryptography.Algorithms.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Csp\ref\System.Security.Cryptography.Csp.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.Primitives\ref\System.Security.Cryptography.Primitives.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.X509Certificates\ref\System.Security.Cryptography.X509Certificates.csproj" />
-    <ProjectReference Include="..\..\System.Text.RegularExpressions\ref\System.Text.RegularExpressions.csproj" />
-    <ProjectReference Include="..\..\System.Threading\ref\System.Threading.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.NonGeneric\ref\System.Collections.NonGeneric.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.ComponentModel.Primitives\ref\System.ComponentModel.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Data.Common\ref\System.Data.Common.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.Extensions\ref\System.Runtime.Extensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Algorithms\ref\System.Security.Cryptography.Algorithms.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Csp\ref\System.Security.Cryptography.Csp.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Primitives\ref\System.Security.Cryptography.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.X509Certificates\ref\System.Security.Cryptography.X509Certificates.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.RegularExpressions\ref\System.Text.RegularExpressions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Threading\ref\System.Threading.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="netstandard" />
@@ -62,7 +60,4 @@
     <Reference Include="System.Text.RegularExpressions" />
     <Reference Include="System.Threading" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or '$(TargetFramework)' == 'netcoreapp3.0'">
-    <ProjectReference Include="..\..\System.Windows.Extensions\ref\System.Windows.Extensions.csproj" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Permissions/src/System.Security.Permissions.csproj b/src/libraries/System.Security.Permissions/src/System.Security.Permissions.csproj
index 265879918e8cda..d51a2ae77f46d4 100644
--- a/src/libraries/System.Security.Permissions/src/System.Security.Permissions.csproj
+++ b/src/libraries/System.Security.Permissions/src/System.Security.Permissions.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
-    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <!-- We conditionally apply net5.0+ obsoletions -->
   <PropertyGroup Condition="!($(TargetFramework.StartsWith('netcoreapp')) or $(TargetFramework.StartsWith('netstandard')) or $(TargetFramework.StartsWith('net4')))">
@@ -187,24 +186,16 @@
     <Compile Include="System\Xaml\Permissions\XamlLoadPermission.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-    <Compile Include="..\..\System.Private.CoreLib\src\System\Security\IStackWalk.cs"
+    <Compile Include="$(LibrariesProjectRoot)System.Private.CoreLib\src\System\Security\IStackWalk.cs"
              Link="System\Security\IStackWalk.cs" />
-    <Compile Include="..\..\System.Private.CoreLib\src\System\Security\PermissionSet.cs"
+    <Compile Include="$(LibrariesProjectRoot)System.Private.CoreLib\src\System\Security\PermissionSet.cs"
              Link="System\Security\PermissionSet.cs" />
-    <Compile Include="..\..\System.Private.CoreLib\src\System\Security\Permissions\PermissionState.cs"
+    <Compile Include="$(LibrariesProjectRoot)System.Private.CoreLib\src\System\Security\Permissions\PermissionState.cs"
              Link="System\Security\Permissions\PermissionState.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.Security.AccessControl" />
-  </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Reference Include="System.Configuration" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.Data" />
     <Reference Include="System.Data.OracleClient" />
-    <Reference Include="System.Drawing" />
     <Reference Include="System.Net" />
     <Reference Include="System.Security" />
     <Reference Include="System.ServiceProcess" />
@@ -213,7 +204,11 @@
     <Reference Include="System.Xaml" />
     <Reference Include="WindowsBase" />
   </ItemGroup>
+  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\src\System.Security.AccessControl.csproj" />
+  </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or '$(TargetFramework)' == 'netcoreapp3.0'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Windows.Extensions\src\System.Windows.Extensions.csproj" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.NonGeneric" />
     <Reference Include="System.ComponentModel.Primitives" />
@@ -229,6 +224,5 @@
     <Reference Include="System.Text.RegularExpressions" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Thread" />
-    <Reference Include="System.Windows.Extensions" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Security.Permissions/src/System/Configuration/ConfigurationPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Configuration/ConfigurationPermissionAttribute.cs
index 0ca7d38ca2d008..9df7cd35683b29 100644
--- a/src/libraries/System.Security.Permissions/src/System/Configuration/ConfigurationPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Configuration/ConfigurationPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Configuration
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.All, AllowMultiple = true, Inherited = false)]
     public sealed class ConfigurationPermissionAttribute : CodeAccessSecurityAttribute
     {
diff --git a/src/libraries/System.Security.Permissions/src/System/Data/Common/DBDataPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Data/Common/DBDataPermissionAttribute.cs
index 097ba88c304bf4..57a0c5fbd2c84a 100644
--- a/src/libraries/System.Security.Permissions/src/System/Data/Common/DBDataPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Data/Common/DBDataPermissionAttribute.cs
@@ -5,6 +5,9 @@
 
 namespace System.Data.Common
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Constructor| AttributeTargets.Method,
         AllowMultiple =true, Inherited =false)]
     public abstract class DBDataPermissionAttribute : CodeAccessSecurityAttribute
diff --git a/src/libraries/System.Security.Permissions/src/System/Data/OracleClient/OraclePermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Data/OracleClient/OraclePermissionAttribute.cs
index fb871718b77df1..8b702005afc7e1 100644
--- a/src/libraries/System.Security.Permissions/src/System/Data/OracleClient/OraclePermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Data/OracleClient/OraclePermissionAttribute.cs
@@ -5,6 +5,9 @@
 
 namespace System.Data.OracleClient
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Struct |
         AttributeTargets.Constructor | AttributeTargets.Method, AllowMultiple = true, Inherited = false)]
     public sealed class OraclePermissionAttribute : CodeAccessSecurityAttribute
diff --git a/src/libraries/System.Security.Permissions/src/System/Diagnostics/EventLogPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Diagnostics/EventLogPermissionAttribute.cs
index f06e73cb9cd58e..fdfd74de52aa28 100644
--- a/src/libraries/System.Security.Permissions/src/System/Diagnostics/EventLogPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Diagnostics/EventLogPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Diagnostics
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Struct
         | AttributeTargets.Constructor | AttributeTargets.Method | AttributeTargets.Event, AllowMultiple = true, Inherited = false)]
     public class EventLogPermissionAttribute : CodeAccessSecurityAttribute
diff --git a/src/libraries/System.Security.Permissions/src/System/Diagnostics/PerformanceCounterPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Diagnostics/PerformanceCounterPermissionAttribute.cs
index 20c92891cdc497..90768d8236992e 100644
--- a/src/libraries/System.Security.Permissions/src/System/Diagnostics/PerformanceCounterPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Diagnostics/PerformanceCounterPermissionAttribute.cs
@@ -5,6 +5,9 @@
 using System.Security.Permissions;
 namespace System.Diagnostics
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Constructor | AttributeTargets.Method | AttributeTargets.Event,
     AllowMultiple = true, Inherited = false)]
     public class PerformanceCounterPermissionAttribute : CodeAccessSecurityAttribute
diff --git a/src/libraries/System.Security.Permissions/src/System/Drawing/Printing/PrintingPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Drawing/Printing/PrintingPermissionAttribute.cs
index 1a16545a647dad..307637f8542bd7 100644
--- a/src/libraries/System.Security.Permissions/src/System/Drawing/Printing/PrintingPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Drawing/Printing/PrintingPermissionAttribute.cs
@@ -5,6 +5,9 @@
 
 namespace System.Drawing.Printing
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.All, AllowMultiple = true)]
     public sealed class PrintingPermissionAttribute : CodeAccessSecurityAttribute
     {
diff --git a/src/libraries/System.Security.Permissions/src/System/Net/DnsPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Net/DnsPermissionAttribute.cs
index 89edcd32473724..024858147b93e3 100644
--- a/src/libraries/System.Security.Permissions/src/System/Net/DnsPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Net/DnsPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Net
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Class |
         AttributeTargets.Struct | AttributeTargets.Assembly, AllowMultiple = true, Inherited = false)]
     public sealed class DnsPermissionAttribute : CodeAccessSecurityAttribute
diff --git a/src/libraries/System.Security.Permissions/src/System/Net/Mail/SmtpPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Net/Mail/SmtpPermissionAttribute.cs
index 9366ed61721081..607fb1bf78d1b6 100644
--- a/src/libraries/System.Security.Permissions/src/System/Net/Mail/SmtpPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Net/Mail/SmtpPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Net.Mail
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Class |
         AttributeTargets.Struct | AttributeTargets.Assembly, AllowMultiple = true, Inherited = false)]
     public sealed class SmtpPermissionAttribute : CodeAccessSecurityAttribute
diff --git a/src/libraries/System.Security.Permissions/src/System/Net/NetworkInformation/NetworkInformationPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Net/NetworkInformation/NetworkInformationPermissionAttribute.cs
index b8ed459bbfc0a8..80321fe7f85af6 100644
--- a/src/libraries/System.Security.Permissions/src/System/Net/NetworkInformation/NetworkInformationPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Net/NetworkInformation/NetworkInformationPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Net.NetworkInformation
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Assembly, AllowMultiple = true, Inherited = false)]
     public sealed class NetworkInformationPermissionAttribute : CodeAccessSecurityAttribute
     {
diff --git a/src/libraries/System.Security.Permissions/src/System/Net/PeerToPeer/Collaboration/PeerCollaborationPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Net/PeerToPeer/Collaboration/PeerCollaborationPermissionAttribute.cs
index c1fd9c189917b3..5b4b924db05b22 100644
--- a/src/libraries/System.Security.Permissions/src/System/Net/PeerToPeer/Collaboration/PeerCollaborationPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Net/PeerToPeer/Collaboration/PeerCollaborationPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Net.PeerToPeer.Collaboration
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Struct |
        AttributeTargets.Constructor | AttributeTargets.Method, AllowMultiple = true, Inherited = false)]
     public sealed class PeerCollaborationPermissionAttribute : CodeAccessSecurityAttribute
diff --git a/src/libraries/System.Security.Permissions/src/System/Net/PeerToPeer/PnrpPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Net/PeerToPeer/PnrpPermissionAttribute.cs
index e85697d11fce49..499eeba5d96a62 100644
--- a/src/libraries/System.Security.Permissions/src/System/Net/PeerToPeer/PnrpPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Net/PeerToPeer/PnrpPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Net.PeerToPeer
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Struct |
          AttributeTargets.Constructor | AttributeTargets.Method, AllowMultiple = true, Inherited = false)]
     public sealed class PnrpPermissionAttribute : CodeAccessSecurityAttribute
diff --git a/src/libraries/System.Security.Permissions/src/System/Net/SocketPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Net/SocketPermissionAttribute.cs
index ed5cc2d8b32232..09a111fc98c771 100644
--- a/src/libraries/System.Security.Permissions/src/System/Net/SocketPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Net/SocketPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Net
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Class |
         AttributeTargets.Struct | AttributeTargets.Assembly, AllowMultiple = true, Inherited = false)]
     public sealed class SocketPermissionAttribute : CodeAccessSecurityAttribute
diff --git a/src/libraries/System.Security.Permissions/src/System/Net/WebPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Net/WebPermissionAttribute.cs
index 0e584d79e4f094..45621281bb1762 100644
--- a/src/libraries/System.Security.Permissions/src/System/Net/WebPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Net/WebPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Net
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Class |
         AttributeTargets.Struct | AttributeTargets.Assembly, AllowMultiple = true, Inherited = false)]
     public sealed class WebPermissionAttribute : CodeAccessSecurityAttribute
diff --git a/src/libraries/System.Security.Permissions/src/System/Security/CodeAccessPermission.cs b/src/libraries/System.Security.Permissions/src/System/Security/CodeAccessPermission.cs
index fe77fe0f78d359..148282d0c8091a 100644
--- a/src/libraries/System.Security.Permissions/src/System/Security/CodeAccessPermission.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Security/CodeAccessPermission.cs
@@ -3,6 +3,9 @@
 
 namespace System.Security
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     public abstract partial class CodeAccessPermission : IPermission, ISecurityEncodable, IStackWalk
     {
         protected CodeAccessPermission() { }
diff --git a/src/libraries/System.Security.Permissions/src/System/Security/NamedPermissionSet.cs b/src/libraries/System.Security.Permissions/src/System/Security/NamedPermissionSet.cs
index 100f003274826e..372e95632f73f5 100644
--- a/src/libraries/System.Security.Permissions/src/System/Security/NamedPermissionSet.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Security/NamedPermissionSet.cs
@@ -5,6 +5,9 @@
 
 namespace System.Security
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     public sealed partial class NamedPermissionSet : PermissionSet
     {
         public NamedPermissionSet(NamedPermissionSet permSet) : base(default(PermissionState)) { }
diff --git a/src/libraries/System.Security.Permissions/src/System/Security/Policy/GacInstalled.cs b/src/libraries/System.Security.Permissions/src/System/Security/Policy/GacInstalled.cs
index 991f0a38c7b08e..a1520e9222f744 100644
--- a/src/libraries/System.Security.Permissions/src/System/Security/Policy/GacInstalled.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Security/Policy/GacInstalled.cs
@@ -3,6 +3,9 @@
 
 namespace System.Security.Policy
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     public sealed partial class GacInstalled : EvidenceBase, IIdentityPermissionFactory
     {
         public GacInstalled() { }
diff --git a/src/libraries/System.Security.Permissions/src/System/Security/Policy/IIdentityPermissionFactory.cs b/src/libraries/System.Security.Permissions/src/System/Security/Policy/IIdentityPermissionFactory.cs
index 6b9f9da8a0cfb4..92762151cbbfa5 100644
--- a/src/libraries/System.Security.Permissions/src/System/Security/Policy/IIdentityPermissionFactory.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Security/Policy/IIdentityPermissionFactory.cs
@@ -3,6 +3,9 @@
 
 namespace System.Security.Policy
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     public partial interface IIdentityPermissionFactory
     {
         IPermission CreateIdentityPermission(Evidence evidence);
diff --git a/src/libraries/System.Security.Permissions/src/System/Security/Policy/PolicyLevel.cs b/src/libraries/System.Security.Permissions/src/System/Security/Policy/PolicyLevel.cs
index 7a89e9b500f875..477fb70e4a749f 100644
--- a/src/libraries/System.Security.Permissions/src/System/Security/Policy/PolicyLevel.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Security/Policy/PolicyLevel.cs
@@ -19,18 +19,33 @@ internal PolicyLevel() { }
         public void AddFullTrustAssembly(StrongName sn) { }
         [Obsolete("Because all GAC assemblies always get full trust, the full trust list is no longer meaningful. You should install any assemblies that are used in security policy in the GAC to ensure they are trusted.")]
         public void AddFullTrustAssembly(StrongNameMembershipCondition snMC) { }
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
         public void AddNamedPermissionSet(NamedPermissionSet permSet) { }
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
         public NamedPermissionSet ChangeNamedPermissionSet(string name, PermissionSet pSet) { return default(NamedPermissionSet); }
         [Obsolete("AppDomain policy levels are obsolete. See https://go.microsoft.com/fwlink/?LinkID=155570 for more information.")]
         public static PolicyLevel CreateAppDomainLevel() { return default(PolicyLevel); }
         public void FromXml(SecurityElement e) { }
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
         public NamedPermissionSet GetNamedPermissionSet(string name) { return default(NamedPermissionSet); }
         public void Recover() { }
         [Obsolete("Because all GAC assemblies always get full trust, the full trust list is no longer meaningful. You should install any assemblies that are used in security policy in the GAC to ensure they are trusted.")]
         public void RemoveFullTrustAssembly(StrongName sn) { }
         [Obsolete("Because all GAC assemblies always get full trust, the full trust list is no longer meaningful. You should install any assemblies that are used in security policy in the GAC to ensure they are trusted.")]
         public void RemoveFullTrustAssembly(StrongNameMembershipCondition snMC) { }
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
         public NamedPermissionSet RemoveNamedPermissionSet(NamedPermissionSet permSet) { return default(NamedPermissionSet); }
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
         public NamedPermissionSet RemoveNamedPermissionSet(string name) { return default(NamedPermissionSet); }
         public void Reset() { }
         public PolicyStatement Resolve(Evidence evidence) { return default(PolicyStatement); }
diff --git a/src/libraries/System.Security.Permissions/src/System/Security/Policy/PolicyStatement.cs b/src/libraries/System.Security.Permissions/src/System/Security/Policy/PolicyStatement.cs
index b73ae5d42c254c..788a094602d7f1 100644
--- a/src/libraries/System.Security.Permissions/src/System/Security/Policy/PolicyStatement.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Security/Policy/PolicyStatement.cs
@@ -5,7 +5,13 @@ namespace System.Security.Policy
 {
     public sealed partial class PolicyStatement : ISecurityEncodable, ISecurityPolicyEncodable
     {
+#if NET50_OBSOLETIONS
+        [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
         public PolicyStatement(PermissionSet permSet) { }
+#if NET50_OBSOLETIONS
+        [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
         public PolicyStatement(PermissionSet permSet, PolicyStatementAttribute attributes) { }
         public PolicyStatementAttribute Attributes { get; set; }
         public string AttributeString { get { return null; } }
diff --git a/src/libraries/System.Security.Permissions/src/System/Security/Policy/Publisher.cs b/src/libraries/System.Security.Permissions/src/System/Security/Policy/Publisher.cs
index 5a149a7acab90f..89fe1cab5c2b6d 100644
--- a/src/libraries/System.Security.Permissions/src/System/Security/Policy/Publisher.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Security/Policy/Publisher.cs
@@ -5,6 +5,9 @@
 
 namespace System.Security.Policy
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     public sealed partial class Publisher : EvidenceBase, IIdentityPermissionFactory
     {
         public Publisher(X509Certificate cert) { }
diff --git a/src/libraries/System.Security.Permissions/src/System/Security/Policy/Site.cs b/src/libraries/System.Security.Permissions/src/System/Security/Policy/Site.cs
index 8d88da1e9a6d56..c7975c9ec5aabe 100644
--- a/src/libraries/System.Security.Permissions/src/System/Security/Policy/Site.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Security/Policy/Site.cs
@@ -3,6 +3,9 @@
 
 namespace System.Security.Policy
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     public sealed partial class Site : EvidenceBase, IIdentityPermissionFactory
     {
         public Site(string name) { }
diff --git a/src/libraries/System.Security.Permissions/src/System/Security/Policy/Url.cs b/src/libraries/System.Security.Permissions/src/System/Security/Policy/Url.cs
index 0264b2c02849a7..e7ec73638ab14a 100644
--- a/src/libraries/System.Security.Permissions/src/System/Security/Policy/Url.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Security/Policy/Url.cs
@@ -3,6 +3,9 @@
 
 namespace System.Security.Policy
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     public sealed partial class Url : EvidenceBase, IIdentityPermissionFactory
     {
         public Url(string name) { }
diff --git a/src/libraries/System.Security.Permissions/src/System/Security/Policy/Zone.cs b/src/libraries/System.Security.Permissions/src/System/Security/Policy/Zone.cs
index c63c8360eaa8db..1f7b0950f57add 100644
--- a/src/libraries/System.Security.Permissions/src/System/Security/Policy/Zone.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Security/Policy/Zone.cs
@@ -3,6 +3,9 @@
 
 namespace System.Security.Policy
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     public sealed partial class Zone : EvidenceBase, IIdentityPermissionFactory
     {
         public Zone(SecurityZone zone) { }
diff --git a/src/libraries/System.Security.Permissions/src/System/ServiceProcess/ServiceControllerPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/ServiceProcess/ServiceControllerPermissionAttribute.cs
index 5c822963b26b6f..34f03504f9291a 100644
--- a/src/libraries/System.Security.Permissions/src/System/ServiceProcess/ServiceControllerPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/ServiceProcess/ServiceControllerPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.ServiceProcess
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Assembly | AttributeTargets.Event, AllowMultiple = true, Inherited = false )]
     public class ServiceControllerPermissionAttribute : CodeAccessSecurityAttribute
     {
diff --git a/src/libraries/System.Security.Permissions/src/System/Transactions/DistributedTransactionPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Transactions/DistributedTransactionPermissionAttribute.cs
index 1bc89cbd615410..9b2844136c2d8f 100644
--- a/src/libraries/System.Security.Permissions/src/System/Transactions/DistributedTransactionPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Transactions/DistributedTransactionPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Transactions
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.All, AllowMultiple = true)]
     public sealed class DistributedTransactionPermissionAttribute : CodeAccessSecurityAttribute
     {
diff --git a/src/libraries/System.Security.Permissions/src/System/Web/AspNetHostingPermissionAttribute.cs b/src/libraries/System.Security.Permissions/src/System/Web/AspNetHostingPermissionAttribute.cs
index ebf6eec3b367b5..9078711ecac83c 100644
--- a/src/libraries/System.Security.Permissions/src/System/Web/AspNetHostingPermissionAttribute.cs
+++ b/src/libraries/System.Security.Permissions/src/System/Web/AspNetHostingPermissionAttribute.cs
@@ -6,6 +6,9 @@
 
 namespace System.Web
 {
+#if NET50_OBSOLETIONS
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
+#endif
     [AttributeUsage(AttributeTargets.All, AllowMultiple = true, Inherited = false )]
     public sealed class AspNetHostingPermissionAttribute : CodeAccessSecurityAttribute
     {
diff --git a/src/libraries/System.Security.Permissions/tests/EvidenceBaseTests.cs b/src/libraries/System.Security.Permissions/tests/EvidenceBaseTests.cs
index 9eea6a3dc41bff..ba17fea6bb286b 100644
--- a/src/libraries/System.Security.Permissions/tests/EvidenceBaseTests.cs
+++ b/src/libraries/System.Security.Permissions/tests/EvidenceBaseTests.cs
@@ -39,6 +39,7 @@ public static void GacInstalledCallMethods()
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Security.Cryptography.Algorithms is not supported on this platform.
         public static void HashCallMethods()
         {
             Hash hash = new Hash(Reflection.Assembly.Load(new Reflection.AssemblyName("System.Reflection")));
diff --git a/src/libraries/System.Security.Permissions/tests/MembershipConditionTests.cs b/src/libraries/System.Security.Permissions/tests/MembershipConditionTests.cs
index d9758dcbaaf617..660661c1520f30 100644
--- a/src/libraries/System.Security.Permissions/tests/MembershipConditionTests.cs
+++ b/src/libraries/System.Security.Permissions/tests/MembershipConditionTests.cs
@@ -61,6 +61,7 @@ public static void GacMembershipConditionCallMethods()
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Security.Cryptography.Algorithms is not supported on this platform.
         public static void HashMembershipConditionCallMethods()
         {
             HashMembershipCondition hmc = new HashMembershipCondition(Cryptography.SHA1.Create(), new byte[1]);
@@ -78,6 +79,7 @@ public static void HashMembershipConditionCallMethods()
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Security.Cryptography.X509Certificates is not supported on this platform.
         public static void PublisherMembershipConditionCallMethods()
         {
             PublisherMembershipCondition pmc = new PublisherMembershipCondition(new System.Security.Cryptography.X509Certificates.X509Certificate());
diff --git a/src/libraries/System.Security.Permissions/tests/PermissionTests.cs b/src/libraries/System.Security.Permissions/tests/PermissionTests.cs
index 9889feffb6dc35..d09b48f343a567 100644
--- a/src/libraries/System.Security.Permissions/tests/PermissionTests.cs
+++ b/src/libraries/System.Security.Permissions/tests/PermissionTests.cs
@@ -210,6 +210,7 @@ public static void PrincipalPermissionCallMethods()
         }
 
         [Fact]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Security.Cryptography.X509Certificates is not supported on this platform.
         public static void PublisherIdentityPermissionCallMethods()
         {
             PublisherIdentityPermission pip = new PublisherIdentityPermission(new System.Security.Cryptography.X509Certificates.X509Certificate());
diff --git a/src/libraries/System.Security.Permissions/tests/System.Security.Permissions.Tests.csproj b/src/libraries/System.Security.Permissions/tests/System.Security.Permissions.Tests.csproj
index 2097721d5d4f2c..35536edbef1542 100644
--- a/src/libraries/System.Security.Permissions/tests/System.Security.Permissions.Tests.csproj
+++ b/src/libraries/System.Security.Permissions/tests/System.Security.Permissions.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT</TargetFrameworks>
     <!-- SYSLIB0003 is the obsoletion of CAS, but we still have unit tests for it -->
     <NoWarn>$(NoWarn);SYSLIB0003</NoWarn>
   </PropertyGroup>
@@ -23,4 +23,7 @@
   <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
     <Compile Include="XamlLoadPermissionTests.cs"/>
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.DirectoryServices\src\System.DirectoryServices.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Principal.Windows/Directory.Build.props b/src/libraries/System.Security.Principal.Windows/Directory.Build.props
index 27a4a5522a2778..33e65b7cb46516 100644
--- a/src/libraries/System.Security.Principal.Windows/Directory.Build.props
+++ b/src/libraries/System.Security.Principal.Windows/Directory.Build.props
@@ -2,8 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
-    <IsNETCoreAppRef>false</IsNETCoreAppRef>
     <IsWindowsSpecific>true</IsWindowsSpecific>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Principal.Windows/ref/System.Security.Principal.Windows.csproj b/src/libraries/System.Security.Principal.Windows/ref/System.Security.Principal.Windows.csproj
index a469aff9a6178c..fe63b0436d4abd 100644
--- a/src/libraries/System.Security.Principal.Windows/ref/System.Security.Principal.Windows.csproj
+++ b/src/libraries/System.Security.Principal.Windows/ref/System.Security.Principal.Windows.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp3.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp3.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -12,14 +11,10 @@
   <ItemGroup>
     <Compile Include="System.Security.Principal.Windows.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Security.Claims\ref\System.Security.Claims.csproj" />
-    <ProjectReference Include="..\..\System.Security.Principal\ref\System.Security.Principal.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Claims\ref\System.Security.Claims.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal\ref\System.Security.Principal.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="System.Runtime" />
diff --git a/src/libraries/System.Security.Principal.Windows/src/System.Security.Principal.Windows.csproj b/src/libraries/System.Security.Principal.Windows/src/System.Security.Principal.Windows.csproj
index d4f8f3eac3d17a..d8193f00625fe8 100644
--- a/src/libraries/System.Security.Principal.Windows/src/System.Security.Principal.Windows.csproj
+++ b/src/libraries/System.Security.Principal.Windows/src/System.Security.Principal.Windows.csproj
@@ -1,9 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;netstandard2.0;netcoreapp2.0-Windows_NT;netcoreapp2.0-Unix;netcoreapp2.1-Windows_NT;netcoreapp2.1-Unix;net461-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;netstandard2.0;netcoreapp2.0-Windows_NT;netcoreapp2.0-Unix;netcoreapp2.1-Windows_NT;netcoreapp2.1-Unix;net461-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -135,10 +134,8 @@
     <Compile Include="$(CommonPath)Interop\Windows\Advapi32\Interop.CheckTokenMembership.cs"
              Link="Common\Interop\Interop.CheckTokenMembership.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-  </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or
+                        $(TargetFramework.StartsWith('netcoreapp2'))">
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Collections" />
     <Reference Include="System.Diagnostics.Debug" />
diff --git a/src/libraries/System.Security.Principal.Windows/tests/System.Security.Principal.Windows.Tests.csproj b/src/libraries/System.Security.Principal.Windows/tests/System.Security.Principal.Windows.Tests.csproj
index 8a99afb50bf19c..cb45482460cc54 100644
--- a/src/libraries/System.Security.Principal.Windows/tests/System.Security.Principal.Windows.Tests.csproj
+++ b/src/libraries/System.Security.Principal.Windows/tests/System.Security.Principal.Windows.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="NTAccount.cs" />
@@ -15,4 +15,7 @@
     <Compile Include="$(CommonTestPath)System\Threading\ThreadTestHelpers.cs"
              Link="Common\System\Threading\ThreadTestHelpers.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Security.Principal.Windows.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Principal/Directory.Build.props b/src/libraries/System.Security.Principal/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Security.Principal/Directory.Build.props
+++ b/src/libraries/System.Security.Principal/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.Principal/src/System.Security.Principal.csproj b/src/libraries/System.Security.Principal/src/System.Security.Principal.csproj
index d9b7db3e558398..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Security.Principal/src/System.Security.Principal.csproj
+++ b/src/libraries/System.Security.Principal/src/System.Security.Principal.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Security.Principal</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Security.SecureString/Directory.Build.props b/src/libraries/System.Security.SecureString/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Security.SecureString/Directory.Build.props
+++ b/src/libraries/System.Security.SecureString/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Security.SecureString/src/System.Security.SecureString.csproj b/src/libraries/System.Security.SecureString/src/System.Security.SecureString.csproj
index 7d220aa8a520ad..c1ef027e6f6aa5 100644
--- a/src/libraries/System.Security.SecureString/src/System.Security.SecureString.csproj
+++ b/src/libraries/System.Security.SecureString/src/System.Security.SecureString.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RootNamespace>System.Security.SecureString</RootNamespace>
-    <AssemblyName>System.Security.SecureString</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.ServiceModel.Syndication/ref/System.ServiceModel.Syndication.csproj b/src/libraries/System.ServiceModel.Syndication/ref/System.ServiceModel.Syndication.csproj
index bca4baa304a216..9c9fcf889142fa 100644
--- a/src/libraries/System.ServiceModel.Syndication/ref/System.ServiceModel.Syndication.csproj
+++ b/src/libraries/System.ServiceModel.Syndication/ref/System.ServiceModel.Syndication.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);net461;netcoreapp2.1;netstandard2.0;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461;netcoreapp2.1;netstandard2.0</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -14,13 +13,16 @@
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or '$(TargetFramework)' == 'netcoreapp2.1'">
     <Compile Include="System.ServiceModel.Syndication.netcoreapp.cs" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
+    <Reference Include="System.ServiceModel" />
+  </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="..\..\System.Collections\ref\System.Collections.csproj" />
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Runtime.Serialization.Primitives\ref\System.Runtime.Serialization.Primitives.csproj" />
-    <ProjectReference Include="..\..\System.Runtime.Serialization.Xml\ref\System.Runtime.Serialization.Xml.csproj" />
-    <ProjectReference Include="..\..\System.Xml.ReaderWriter\ref\System.Xml.ReaderWriter.csproj" />
-    <ProjectReference Include="..\..\System.Xml.XmlSerializer\ref\System.Xml.XmlSerializer.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections\ref\System.Collections.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.Serialization.Primitives\ref\System.Runtime.Serialization.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.Serialization.Xml\ref\System.Runtime.Serialization.Xml.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Xml.ReaderWriter\ref\System.Xml.ReaderWriter.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Xml.XmlSerializer\ref\System.Xml.XmlSerializer.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp2.1'">
     <Reference Include="System.Collections" />
@@ -30,11 +32,4 @@
     <Reference Include="System.Xml.ReaderWriter" />
     <Reference Include="System.Xml.XmlSerializer" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Runtime.Serialization" />
-    <Reference Include="System.ServiceModel" />
-    <Reference Include="System.Xml" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ServiceModel.Syndication/ref/System.ServiceModel.Syndication.netcoreapp.cs b/src/libraries/System.ServiceModel.Syndication/ref/System.ServiceModel.Syndication.netcoreapp.cs
index 216b88d505b094..866e28444fe153 100644
--- a/src/libraries/System.ServiceModel.Syndication/ref/System.ServiceModel.Syndication.netcoreapp.cs
+++ b/src/libraries/System.ServiceModel.Syndication/ref/System.ServiceModel.Syndication.netcoreapp.cs
@@ -34,16 +34,16 @@ public partial struct XmlDateTimeData
         private object _dummy;
         private int _dummyPrimitive;
         public XmlDateTimeData(string dateTimeString, System.Xml.XmlQualifiedName elementQualifiedName) { throw null; }
-        public string DateTimeString { get { throw null; } }
-        public System.Xml.XmlQualifiedName ElementQualifiedName { get { throw null; } }
+        public readonly string DateTimeString { get { throw null; } }
+        public readonly System.Xml.XmlQualifiedName ElementQualifiedName { get { throw null; } }
     }
     public partial struct XmlUriData
     {
         private object _dummy;
         private int _dummyPrimitive;
         public XmlUriData(string uriString, System.UriKind uriKind, System.Xml.XmlQualifiedName elementQualifiedName) { throw null; }
-        public System.Xml.XmlQualifiedName ElementQualifiedName { get { throw null; } }
-        public System.UriKind UriKind { get { throw null; } }
-        public string UriString { get { throw null; } }
+        public readonly System.Xml.XmlQualifiedName ElementQualifiedName { get { throw null; } }
+        public readonly System.UriKind UriKind { get { throw null; } }
+        public readonly string UriString { get { throw null; } }
     }
 }
diff --git a/src/libraries/System.ServiceModel.Syndication/src/System.ServiceModel.Syndication.csproj b/src/libraries/System.ServiceModel.Syndication/src/System.ServiceModel.Syndication.csproj
index f996315dab78f0..302d11eb2fc33d 100644
--- a/src/libraries/System.ServiceModel.Syndication/src/System.ServiceModel.Syndication.csproj
+++ b/src/libraries/System.ServiceModel.Syndication/src/System.ServiceModel.Syndication.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461-Windows_NT</TargetFrameworks>
+    <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -53,7 +53,16 @@
     <Compile Include="System\ServiceModel\XmlBuffer.cs" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
     <Reference Include="System.ServiceModel" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <Reference Include="System.Collections" />
+    <Reference Include="System.Linq" />
+    <Reference Include="System.Runtime" />
+    <Reference Include="System.Runtime.Serialization.Primitives" />
+    <Reference Include="System.Runtime.Serialization.Xml" />
+    <Reference Include="System.Threading" />
+    <Reference Include="System.Xml.ReaderWriter" />
+    <Reference Include="System.Xml.XmlSerializer" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.ServiceModel.Syndication/tests/System.ServiceModel.Syndication.Tests.csproj b/src/libraries/System.ServiceModel.Syndication/tests/System.ServiceModel.Syndication.Tests.csproj
index 59a0a2db745a32..d85a1393b8d02a 100644
--- a/src/libraries/System.ServiceModel.Syndication/tests/System.ServiceModel.Syndication.Tests.csproj
+++ b/src/libraries/System.ServiceModel.Syndication/tests/System.ServiceModel.Syndication.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="BasicScenarioTests.cs" />
@@ -58,4 +58,10 @@
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.ServiceModel.Syndication.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
+    <Reference Include="System.ServiceModel" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ServiceProcess.ServiceController/ref/System.ServiceProcess.ServiceController.cs b/src/libraries/System.ServiceProcess.ServiceController/ref/System.ServiceProcess.ServiceController.cs
index e11cbf46e24604..8fc328bf373d06 100644
--- a/src/libraries/System.ServiceProcess.ServiceController/ref/System.ServiceProcess.ServiceController.cs
+++ b/src/libraries/System.ServiceProcess.ServiceController/ref/System.ServiceProcess.ServiceController.cs
@@ -57,6 +57,7 @@ public static void Run(System.ServiceProcess.ServiceBase[] services) { }
         public void ServiceMainCallback(int argCount, System.IntPtr argPointer) { }
         public void Stop() { }
     }
+    [System.ComponentModel.DesignerAttribute("System.ServiceProcess.Design.ServiceControllerDesigner, System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public partial class ServiceController : System.ComponentModel.Component
     {
         public ServiceController() { }
diff --git a/src/libraries/System.ServiceProcess.ServiceController/ref/System.ServiceProcess.ServiceController.csproj b/src/libraries/System.ServiceProcess.ServiceController/ref/System.ServiceProcess.ServiceController.csproj
index 4e3eff244909ac..50d5af47646b66 100644
--- a/src/libraries/System.ServiceProcess.ServiceController/ref/System.ServiceProcess.ServiceController.csproj
+++ b/src/libraries/System.ServiceProcess.ServiceController/ref/System.ServiceProcess.ServiceController.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkCurrent);net461</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -11,8 +11,6 @@
     <Compile Include="System.ServiceProcess.ServiceController.cs" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Reference Include="System.ServiceProcess" />
   </ItemGroup>
   <ItemGroup>
diff --git a/src/libraries/System.ServiceProcess.ServiceController/src/System.ServiceProcess.ServiceController.csproj b/src/libraries/System.ServiceProcess.ServiceController/src/System.ServiceProcess.ServiceController.csproj
index 47dfe7649b4d4c..10d0d7168bb18c 100644
--- a/src/libraries/System.ServiceProcess.ServiceController/src/System.ServiceProcess.ServiceController.csproj
+++ b/src/libraries/System.ServiceProcess.ServiceController/src/System.ServiceProcess.ServiceController.csproj
@@ -1,9 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netstandard2.0-Windows_NT;net461-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netstandard2.0-Windows_NT;net461-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <NoWarn>$(NoWarn);CA2249</NoWarn>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -74,14 +73,8 @@
     <Compile Include="System\ServiceProcess\SessionChangeReason.cs" />
     <Compile Include="System\ServiceProcess\TimeoutException.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.Diagnostics.EventLog" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.ServiceProcess" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or ($(TargetFramework.StartsWith('netstandard')) and '$(TargetsWindows)' == 'true')">
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) and
+                        '$(TargetsWindows)' == 'true'">
     <Reference Include="Microsoft.Win32.Primitives" />
     <Reference Include="System.Buffers" />
     <Reference Include="System.Collections" />
@@ -98,4 +91,14 @@
     <Reference Include="System.Threading.Thread" />
     <Reference Include="System.Threading.ThreadPool" />
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
+    <Reference Include="System.ServiceProcess" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or $(TargetFramework.StartsWith('netstandard2.0'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Diagnostics.EventLog\src\System.Diagnostics.EventLog.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard2.0'))">
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.ServiceProcess.ServiceController/src/System/ServiceProcess/ServiceBase.cs b/src/libraries/System.ServiceProcess.ServiceController/src/System/ServiceProcess/ServiceBase.cs
index 00a392a2bec071..f4ef7e7467f4a5 100644
--- a/src/libraries/System.ServiceProcess.ServiceController/src/System/ServiceProcess/ServiceBase.cs
+++ b/src/libraries/System.ServiceProcess.ServiceController/src/System/ServiceProcess/ServiceBase.cs
@@ -412,7 +412,7 @@ private unsafe void DeferredContinue()
                 catch (Exception e)
                 {
                     _status.currentState = ServiceControlStatus.STATE_PAUSED;
-                    WriteLogEntry(SR.Format(SR.ContinueFailed, e), true);
+                    WriteLogEntry(SR.Format(SR.ContinueFailed, e), EventLogEntryType.Error);
 
                     // We re-throw the exception so that the advapi32 code can report
                     // ERROR_EXCEPTION_IN_SERVICE as it would for native services.
@@ -434,7 +434,7 @@ private void DeferredCustomCommand(int command)
             }
             catch (Exception e)
             {
-                WriteLogEntry(SR.Format(SR.CommandFailed, e), true);
+                WriteLogEntry(SR.Format(SR.CommandFailed, e), EventLogEntryType.Error);
 
                 // We should re-throw the exception so that the advapi32 code can report
                 // ERROR_EXCEPTION_IN_SERVICE as it would for native services.
@@ -455,7 +455,7 @@ private unsafe void DeferredPause()
                 catch (Exception e)
                 {
                     _status.currentState = ServiceControlStatus.STATE_RUNNING;
-                    WriteLogEntry(SR.Format(SR.PauseFailed, e), true);
+                    WriteLogEntry(SR.Format(SR.PauseFailed, e), EventLogEntryType.Error);
 
                     // We re-throw the exception so that the advapi32 code can report
                     // ERROR_EXCEPTION_IN_SERVICE as it would for native services.
@@ -482,7 +482,7 @@ private void DeferredPowerEvent(int eventType, IntPtr eventData)
             }
             catch (Exception e)
             {
-                WriteLogEntry(SR.Format(SR.PowerEventFailed, e), true);
+                WriteLogEntry(SR.Format(SR.PowerEventFailed, e), EventLogEntryType.Error);
 
                 // We rethrow the exception so that advapi32 code can report
                 // ERROR_EXCEPTION_IN_SERVICE as it would for native services.
@@ -498,7 +498,7 @@ private void DeferredSessionChange(int eventType, int sessionId)
             }
             catch (Exception e)
             {
-                WriteLogEntry(SR.Format(SR.SessionChangeFailed, e), true);
+                WriteLogEntry(SR.Format(SR.SessionChangeFailed, e), EventLogEntryType.Error);
 
                 // We rethrow the exception so that advapi32 code can report
                 // ERROR_EXCEPTION_IN_SERVICE as it would for native services.
@@ -530,7 +530,7 @@ private unsafe void DeferredStop()
                 {
                     _status.currentState = previousState;
                     SetServiceStatus(_statusHandle, pStatus);
-                    WriteLogEntry(SR.Format(SR.StopFailed, e), true);
+                    WriteLogEntry(SR.Format(SR.StopFailed, e), EventLogEntryType.Error);
                     throw;
                 }
             }
@@ -556,7 +556,7 @@ private unsafe void DeferredShutdown()
             }
             catch (Exception e)
             {
-                WriteLogEntry(SR.Format(SR.ShutdownFailed, e), true);
+                WriteLogEntry(SR.Format(SR.ShutdownFailed, e), EventLogEntryType.Error);
                 throw;
             }
         }
@@ -641,7 +641,7 @@ public static unsafe void Run(ServiceBase[] services)
                     service.Dispose();
                     if (!res)
                     {
-                        service.WriteLogEntry(SR.Format(SR.StartFailed, errorMessage), true);
+                        service.WriteLogEntry(SR.Format(SR.StartFailed, errorMessage), EventLogEntryType.Error);
                     }
                 }
             }
@@ -847,7 +847,7 @@ private void ServiceQueuedMainCallback(object state)
             }
             catch (Exception e)
             {
-                WriteLogEntry(SR.Format(SR.StartFailed, e), true);
+                WriteLogEntry(SR.Format(SR.StartFailed, e), EventLogEntryType.Error);
                 _status.currentState = ServiceControlStatus.STATE_STOPPED;
 
                 // We capture the exception so that it can be propagated
@@ -900,7 +900,7 @@ public unsafe void ServiceMainCallback(int argCount, IntPtr argPointer)
                 if (_statusHandle == (IntPtr)0)
                 {
                     string errorMessage = new Win32Exception().Message;
-                    WriteLogEntry(SR.Format(SR.StartFailed, errorMessage), true);
+                    WriteLogEntry(SR.Format(SR.StartFailed, errorMessage), EventLogEntryType.Error);
                 }
 
                 _status.controlsAccepted = _acceptedCommands;
@@ -943,21 +943,21 @@ public unsafe void ServiceMainCallback(int argCount, IntPtr argPointer)
                 statusOK = SetServiceStatus(_statusHandle, pStatus);
                 if (!statusOK)
                 {
-                    WriteLogEntry(SR.Format(SR.StartFailed, new Win32Exception().Message), true);
+                    WriteLogEntry(SR.Format(SR.StartFailed, new Win32Exception().Message), EventLogEntryType.Error);
                     _status.currentState = ServiceControlStatus.STATE_STOPPED;
                     SetServiceStatus(_statusHandle, pStatus);
                 }
             }
         }
 
-        private void WriteLogEntry(string message, bool error = false)
+        private void WriteLogEntry(string message, EventLogEntryType type = EventLogEntryType.Information)
         {
             // EventLog failures shouldn't affect the service operation
             try
             {
                 if (AutoLog)
                 {
-                    EventLog.WriteEntry(message);
+                    EventLog.WriteEntry(message, type);
                 }
             }
             catch
diff --git a/src/libraries/System.ServiceProcess.ServiceController/src/System/ServiceProcess/ServiceController.cs b/src/libraries/System.ServiceProcess.ServiceController/src/System/ServiceProcess/ServiceController.cs
index 6717adaf246a8e..fdb4d99d19df88 100644
--- a/src/libraries/System.ServiceProcess.ServiceController/src/System/ServiceProcess/ServiceController.cs
+++ b/src/libraries/System.ServiceProcess.ServiceController/src/System/ServiceProcess/ServiceController.cs
@@ -17,6 +17,7 @@ namespace System.ServiceProcess
 {
     /// This class represents an NT service. It allows you to connect to a running or stopped service
     /// and manipulate it or get information about it.
+    [Designer("System.ServiceProcess.Design.ServiceControllerDesigner, System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public class ServiceController : Component
     {
         private string _machineName; // Never null
diff --git a/src/libraries/System.ServiceProcess.ServiceController/tests/System.ServiceProcess.ServiceController.TestService/System.ServiceProcess.ServiceController.TestService.csproj b/src/libraries/System.ServiceProcess.ServiceController/tests/System.ServiceProcess.ServiceController.TestService/System.ServiceProcess.ServiceController.TestService.csproj
index d68e5e8dab4204..8886ffe02e9c85 100644
--- a/src/libraries/System.ServiceProcess.ServiceController/tests/System.ServiceProcess.ServiceController.TestService/System.ServiceProcess.ServiceController.TestService.csproj
+++ b/src/libraries/System.ServiceProcess.ServiceController/tests/System.ServiceProcess.ServiceController.TestService/System.ServiceProcess.ServiceController.TestService.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <OutputType>Exe</OutputType>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <Nullable>annotations</Nullable>
   </PropertyGroup>
   <ItemGroup>
@@ -37,4 +37,7 @@
     <Compile Include="$(CommonTestPath)System\Threading\Tasks\TaskTimeoutExtensions.cs"
              Link="Common\System\Threading\Tasks\TaskTimeoutExtensions.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\System.ServiceProcess.ServiceController.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ServiceProcess.ServiceController/tests/System.ServiceProcess.ServiceController.Tests.csproj b/src/libraries/System.ServiceProcess.ServiceController/tests/System.ServiceProcess.ServiceController.Tests.csproj
index 1fcc105e57b122..2bf38334f76d03 100644
--- a/src/libraries/System.ServiceProcess.ServiceController/tests/System.ServiceProcess.ServiceController.Tests.csproj
+++ b/src/libraries/System.ServiceProcess.ServiceController/tests/System.ServiceProcess.ServiceController.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="ServiceBaseTests.cs" />
@@ -10,6 +10,9 @@
     <Compile Include="ServiceProcessDescriptionAttributeTests.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include=".\System.ServiceProcess.ServiceController.TestService\System.ServiceProcess.ServiceController.TestService.csproj" />
+    <ProjectReference Include="System.ServiceProcess.ServiceController.TestService\System.ServiceProcess.ServiceController.TestService.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.ServiceProcess" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Text.Encoding.CodePages/Directory.Build.props b/src/libraries/System.Text.Encoding.CodePages/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Text.Encoding.CodePages/Directory.Build.props
+++ b/src/libraries/System.Text.Encoding.CodePages/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Text.Encoding.CodePages/ref/System.Text.Encoding.CodePages.csproj b/src/libraries/System.Text.Encoding.CodePages/ref/System.Text.Encoding.CodePages.csproj
index ff67cc8cca7de9..532f6e7ebe4359 100644
--- a/src/libraries/System.Text.Encoding.CodePages/ref/System.Text.Encoding.CodePages.csproj
+++ b/src/libraries/System.Text.Encoding.CodePages/ref/System.Text.Encoding.CodePages.csproj
@@ -1,17 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <Nullable>enable</Nullable>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Text.Encoding.CodePages.cs" />
     <Compile Include="System.Text.Encoding.CodePages.netcoreapp.cs" Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="../../System.Runtime/ref/System.Runtime.csproj" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime/ref/System.Runtime.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Text.Encoding.CodePages/src/System.Text.Encoding.CodePages.csproj b/src/libraries/System.Text.Encoding.CodePages/src/System.Text.Encoding.CodePages.csproj
index 3ca2e7453ec8a9..504f90a32415e0 100644
--- a/src/libraries/System.Text.Encoding.CodePages/src/System.Text.Encoding.CodePages.csproj
+++ b/src/libraries/System.Text.Encoding.CodePages/src/System.Text.Encoding.CodePages.csproj
@@ -2,10 +2,20 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT;netstandard2.0-Windows_NT;net461-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT;netstandard2.0-Windows_NT;net461-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
   </PropertyGroup>
+  <!-- Generator for code mapping table, target to invoke is GenerateEncodingSource -->
+  <PropertyGroup>
+    <!-- This Task can be re-run with /t:GenerateEncodingSource
+         An IANA Mapping file contains rows of two elements: a valid IANA encoding identifier, and the equivalent code page.
+         There may be many IANA ids (aliases) mapped to a single code page. -->
+    <IANAMappingPath>Data\CodePageNameMappings.csv</IANAMappingPath>
+    <!-- The preferred name file contains rows of three elements: a code page, the 'canonical' IANA identifier,
+         and an "English" or descriptive name.  There is one row per code page. -->
+    <PreferredIANANamesPath>Data\PreferredCodePageNames.csv</PreferredIANANamesPath>
+    <OutputDataTablePath>System\Text\EncodingTable.Data.cs</OutputDataTablePath>
+  </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft\Win32\SafeHandles\SafeAllocHHandle.cs" />
     <Compile Include="System\Text\BaseCodePageEncoding.cs" />
@@ -55,10 +65,14 @@
     <EmbeddedResource Include="Data\codepages.nlp">
       <LogicalName>codepages.nlp</LogicalName>
     </EmbeddedResource>
-  </ItemGroup>
-  <ItemGroup>
     <None Include="Data\CodePageNameMappings.csv" />
     <None Include="Data\PreferredCodePageNames.csv" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.CompilerServices.Unsafe\src\System.Runtime.CompilerServices.Unsafe.ilproj" />
+  </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('$(NetCoreAppCurrent)')) or
+                        $(TargetFramework.StartsWith('netcoreapp2.0'))">
     <Reference Include="System.Collections" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Diagnostics.Tools" />
@@ -67,22 +81,5 @@
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
     <Reference Include="System.Threading" />
-    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
-    <Reference Include="System" />
-  </ItemGroup>
-  <!-- Generator for code mapping table, target to invoke is GenerateEncodingSource -->
-  <PropertyGroup>
-    <!-- This Task can be re-run with /t:GenerateEncodingSource
-         An IANA Mapping file contains rows of two elements: a valid IANA encoding identifier, and the equivalent code page.
-         There may be many IANA ids (aliases) mapped to a single code page. -->
-    <IANAMappingPath>Data\CodePageNameMappings.csv</IANAMappingPath>
-    <!-- The preferred name file contains rows of three elements: a code page, the 'canonical' IANA identifier,
-         and an "English" or descriptive name.  There is one row per code page. -->
-    <PreferredIANANamesPath>Data\PreferredCodePageNames.csv</PreferredIANANamesPath>
-    <OutputDataTablePath>System\Text\EncodingTable.Data.cs</OutputDataTablePath>
-  </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Text.Encoding.CodePages/tests/System.Text.Encoding.CodePages.Tests.csproj b/src/libraries/System.Text.Encoding.CodePages/tests/System.Text.Encoding.CodePages.Tests.csproj
index 353fe29ea301c2..0b05fa533b0e5f 100644
--- a/src/libraries/System.Text.Encoding.CodePages/tests/System.Text.Encoding.CodePages.Tests.csproj
+++ b/src/libraries/System.Text.Encoding.CodePages/tests/System.Text.Encoding.CodePages.Tests.csproj
@@ -1,11 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="EncoderFallbackBufferHelper.cs" />
     <Compile Include="EncodingCodePages.cs" />
     <Compile Include="EncodingCodePages.netcoreapp.cs" Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="..\src\System.Text.Encoding.CodePages.csproj" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Text.Encoding.Extensions/Directory.Build.props b/src/libraries/System.Text.Encoding.Extensions/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Text.Encoding.Extensions/Directory.Build.props
+++ b/src/libraries/System.Text.Encoding.Extensions/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Text.Encoding.Extensions/src/System.Text.Encoding.Extensions.csproj b/src/libraries/System.Text.Encoding.Extensions/src/System.Text.Encoding.Extensions.csproj
index bc0555cf2c622f..dd3dc2940a54b1 100644
--- a/src/libraries/System.Text.Encoding.Extensions/src/System.Text.Encoding.Extensions.csproj
+++ b/src/libraries/System.Text.Encoding.Extensions/src/System.Text.Encoding.Extensions.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Text.Encoding.Extensions</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Text.Encoding/Directory.Build.props b/src/libraries/System.Text.Encoding/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Text.Encoding/Directory.Build.props
+++ b/src/libraries/System.Text.Encoding/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Text.Encoding/src/System.Text.Encoding.csproj b/src/libraries/System.Text.Encoding/src/System.Text.Encoding.csproj
index 16ab188781b8a3..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Text.Encoding/src/System.Text.Encoding.csproj
+++ b/src/libraries/System.Text.Encoding/src/System.Text.Encoding.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Text.Encoding</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Text.Encodings.Web/Directory.Build.props b/src/libraries/System.Text.Encodings.Web/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.Text.Encodings.Web/Directory.Build.props
+++ b/src/libraries/System.Text.Encodings.Web/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Text.Encodings.Web/ref/System.Text.Encodings.Web.csproj b/src/libraries/System.Text.Encodings.Web/ref/System.Text.Encodings.Web.csproj
index 3de8b872e74883..eff1dfbb548cae 100644
--- a/src/libraries/System.Text.Encodings.Web/ref/System.Text.Encodings.Web.csproj
+++ b/src/libraries/System.Text.Encodings.Web/ref/System.Text.Encodings.Web.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <!-- Only CLS-compliant members can be abstract -->
@@ -12,16 +11,12 @@
     <Compile Include="System.Text.Encodings.Web.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="..\..\System.Memory\ref\System.Memory.csproj" />
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Runtime.Extensions\ref\System.Runtime.Extensions.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Memory\ref\System.Memory.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.Extensions\ref\System.Runtime.Extensions.csproj" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' Or $(TargetFramework.StartsWith('net4'))">
-    <Reference Include="System.Memory" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="netstandard" />
-    <Reference Include="System" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                         $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Text.Encodings.Web/src/System.Text.Encodings.Web.csproj b/src/libraries/System.Text.Encodings.Web/src/System.Text.Encodings.Web.csproj
index 126ef92db5b5b0..906f6d9dc252a0 100644
--- a/src/libraries/System.Text.Encodings.Web/src/System.Text.Encodings.Web.csproj
+++ b/src/libraries/System.Text.Encodings.Web/src/System.Text.Encodings.Web.csproj
@@ -1,13 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.1;netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.1;netstandard2.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0' ">
-    <DefineConstants>$(DefineConstants),USE_INTERNAL_ACCESSIBILITY</DefineConstants>
     <!-- CS3019: CLS attributes on internal types. Some shared source files are internal in this project. -->
     <NoWarn>$(NoWarn);CS3019</NoWarn>
   </PropertyGroup>
@@ -43,19 +41,18 @@
     <Compile Include="$(CoreLibSharedDir)System\Text\UnicodeUtility.cs" Link="System\Text\UnicodeUtility.cs" />
     <Compile Include="$(CommonPath)System\HexConverter.cs" Link="Common\System\HexConverter.cs" />
   </ItemGroup>
-  <ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or
+                        '$(TargetFramework)' == 'netcoreapp3.0'">
+    <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Memory" />
     <Reference Include="System.Resources.ResourceManager" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or '$(TargetFramework)' == 'netcoreapp3.0'">
-    <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.Intrinsics" />
     <Reference Include="System.Threading" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Text.Encodings.Web/tests/System.Text.Encodings.Web.Tests.csproj b/src/libraries/System.Text.Encodings.Web/tests/System.Text.Encodings.Web.Tests.csproj
index 26f3b0dd17c6d3..5ad0343d6c04e3 100644
--- a/src/libraries/System.Text.Encodings.Web/tests/System.Text.Encodings.Web.Tests.csproj
+++ b/src/libraries/System.Text.Encodings.Web/tests/System.Text.Encodings.Web.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <UnicodeUcdVersion>13.0</UnicodeUcdVersion>
   </PropertyGroup>
   <ItemGroup>
@@ -53,4 +53,7 @@
     <Compile Include="$(CommonPath)System\HexConverter.cs"
              Link="Common\System\HexConverter.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="..\src\System.Text.Encodings.Web.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Text.Json/Directory.Build.props b/src/libraries/System.Text.Json/Directory.Build.props
index 749d7fc1c6b56d..ba1f965d83cae7 100644
--- a/src/libraries/System.Text.Json/Directory.Build.props
+++ b/src/libraries/System.Text.Json/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Text.Json/ref/System.Text.Json.cs b/src/libraries/System.Text.Json/ref/System.Text.Json.cs
index 0ab83e8b526561..4184827a8025b8 100644
--- a/src/libraries/System.Text.Json/ref/System.Text.Json.cs
+++ b/src/libraries/System.Text.Json/ref/System.Text.Json.cs
@@ -184,20 +184,17 @@ public partial struct JsonReaderState
     }
     public static partial class JsonSerializer
     {
-#if NETCOREAPP
+#if NETCOREAPP && !NETCOREAPP3_0
         private const System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes MembersAccessedOnRead = System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties;
         private const System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes MembersAccessedOnWrite = System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicProperties;
         public static object? Deserialize(System.ReadOnlySpan<byte> utf8Json, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] System.Type returnType, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static object? Deserialize(string json, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] System.Type returnType, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static object? Deserialize(ref System.Text.Json.Utf8JsonReader reader, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] System.Type returnType, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static System.Threading.Tasks.ValueTask<object?> DeserializeAsync(System.IO.Stream utf8Json, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] System.Type returnType, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
-        public static System.Threading.Tasks.ValueTask<TValue> DeserializeAsync<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] TValue>(System.IO.Stream utf8Json, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TValue Deserialize<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] TValue>(System.ReadOnlySpan<byte> utf8Json, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TValue Deserialize<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] TValue>(string json, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TValue Deserialize<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] TValue>(ref System.Text.Json.Utf8JsonReader reader, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
+        public static System.Threading.Tasks.ValueTask<TValue?> DeserializeAsync<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] TValue>(System.IO.Stream utf8Json, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        public static TValue? Deserialize<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] TValue>(System.ReadOnlySpan<byte> utf8Json, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
+        public static TValue? Deserialize<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] TValue>(string json, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
+        public static TValue? Deserialize<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnRead)] TValue>(ref System.Text.Json.Utf8JsonReader reader, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static string Serialize(object? value, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnWrite)] System.Type inputType, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static void Serialize(System.Text.Json.Utf8JsonWriter writer, object? value, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnWrite)] System.Type inputType, System.Text.Json.JsonSerializerOptions? options = null) { }
         public static System.Threading.Tasks.Task SerializeAsync(System.IO.Stream utf8Json, object? value, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(MembersAccessedOnWrite)] System.Type inputType, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
@@ -211,13 +208,10 @@ public static void Serialize(System.Text.Json.Utf8JsonWriter writer, object? val
         public static object? Deserialize(string json, System.Type returnType, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static object? Deserialize(ref System.Text.Json.Utf8JsonReader reader, System.Type returnType, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static System.Threading.Tasks.ValueTask<object?> DeserializeAsync(System.IO.Stream utf8Json, System.Type returnType, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
-        public static System.Threading.Tasks.ValueTask<TValue> DeserializeAsync<TValue>(System.IO.Stream utf8Json, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TValue Deserialize<TValue>(System.ReadOnlySpan<byte> utf8Json, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TValue Deserialize<TValue>(string json, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public static TValue Deserialize<TValue>(ref System.Text.Json.Utf8JsonReader reader, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
+        public static System.Threading.Tasks.ValueTask<TValue?> DeserializeAsync<TValue>(System.IO.Stream utf8Json, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        public static TValue? Deserialize<TValue>(System.ReadOnlySpan<byte> utf8Json, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
+        public static TValue? Deserialize<TValue>(string json, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
+        public static TValue? Deserialize<TValue>(ref System.Text.Json.Utf8JsonReader reader, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static string Serialize(object? value, System.Type inputType, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static void Serialize(System.Text.Json.Utf8JsonWriter writer, object? value, System.Type inputType, System.Text.Json.JsonSerializerOptions? options = null) { }
         public static System.Threading.Tasks.Task SerializeAsync(System.IO.Stream utf8Json, object? value, System.Type inputType, System.Text.Json.JsonSerializerOptions? options = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
@@ -244,6 +238,7 @@ public JsonSerializerOptions(System.Text.Json.JsonSerializerDefaults defaults) {
         public bool IgnoreReadOnlyFields { get { throw null; } set { } }
         public bool IncludeFields { get { throw null; } set { } }
         public int MaxDepth { get { throw null; } set { } }
+        public System.Text.Json.Serialization.JsonNumberHandling NumberHandling { get { throw null; } set { } }
         public bool PropertyNameCaseInsensitive { get { throw null; } set { } }
         public System.Text.Json.JsonNamingPolicy? PropertyNamingPolicy { get { throw null; } set { } }
         public System.Text.Json.JsonCommentHandling ReadCommentHandling { get { throw null; } set { } }
@@ -496,6 +491,14 @@ public enum JsonIgnoreCondition
         WhenWritingDefault = 2,
         WhenWritingNull = 3,
     }
+    [System.FlagsAttribute]
+    public enum JsonNumberHandling
+    {
+        Strict = 0,
+        AllowReadingFromString = 1,
+        WriteAsString = 2,
+        AllowNamedFloatingPointLiterals = 4,
+    }
     public abstract partial class JsonAttribute : System.Attribute
     {
         protected JsonAttribute() { }
@@ -509,14 +512,9 @@ internal JsonConverter() { }
     public partial class JsonConverterAttribute : System.Text.Json.Serialization.JsonAttribute
     {
         protected JsonConverterAttribute() { }
-#if NETCOREAPP
         public JsonConverterAttribute([System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] System.Type converterType) { }
         [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]
         public System.Type? ConverterType { get { throw null; } }
-#else
-        public JsonConverterAttribute(System.Type converterType) { }
-        public System.Type? ConverterType { get { throw null; } }
-#endif
         public virtual System.Text.Json.Serialization.JsonConverter? CreateConverter(System.Type typeToConvert) { throw null; }
     }
     public abstract partial class JsonConverterFactory : System.Text.Json.Serialization.JsonConverter
@@ -529,10 +527,15 @@ public abstract partial class JsonConverter<T> : System.Text.Json.Serialization.
         protected internal JsonConverter() { }
         public override bool CanConvert(System.Type typeToConvert) { throw null; }
         public virtual bool HandleNull { get { throw null; } }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public abstract T Read(ref System.Text.Json.Utf8JsonReader reader, System.Type typeToConvert, System.Text.Json.JsonSerializerOptions options);
+        public abstract T? Read(ref System.Text.Json.Utf8JsonReader reader, System.Type typeToConvert, System.Text.Json.JsonSerializerOptions options);
         public abstract void Write(System.Text.Json.Utf8JsonWriter writer, T value, System.Text.Json.JsonSerializerOptions options);
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Struct | System.AttributeTargets.Property | System.AttributeTargets.Field, AllowMultiple = false)]
+    public sealed partial class JsonNumberHandlingAttribute : System.Text.Json.Serialization.JsonAttribute
+    {
+        public JsonNumberHandlingAttribute(System.Text.Json.Serialization.JsonNumberHandling handling) { }
+        public System.Text.Json.Serialization.JsonNumberHandling Handling { get { throw null; } }
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Constructor, AllowMultiple = false)]
     public sealed partial class JsonConstructorAttribute : System.Text.Json.Serialization.JsonAttribute
     {
diff --git a/src/libraries/System.Text.Json/ref/System.Text.Json.csproj b/src/libraries/System.Text.Json/ref/System.Text.Json.csproj
index b06efdcf9ac2ed..d041bece0a671a 100644
--- a/src/libraries/System.Text.Json/ref/System.Text.Json.csproj
+++ b/src/libraries/System.Text.Json/ref/System.Text.Json.csproj
@@ -1,25 +1,33 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Text.Json.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or '$(TargetFramework)' == 'netcoreapp3.0'">
-    <ProjectReference Include="..\..\System.Memory\ref\System.Memory.csproj" />
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
+  <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)'">
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)' and '$(TargetFramework)' != 'netcoreapp3.0'">
-    <Reference Include="mscorlib" />
-    <Reference Include="netstandard" />
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Memory\ref\System.Memory.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="System.Memory" />
-    <Reference Include="System.Threading.Tasks.Extensions" />
-    <Reference Include="Microsoft.Bcl.AsyncInterfaces" />
+    <Reference Include="System.Runtime" />
+    <Reference Include="netstandard" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        '$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Bcl.AsyncInterfaces\ref\Microsoft.Bcl.AsyncInterfaces.csproj" />
   </ItemGroup>
   <!-- Since S.T.E.W continues to be built live within this repo (as both an in-box library and a standalone netstandard2.0 assembly),
     we should use ProjectReference instead of Reference to make sure that its ref assembly gets built first before S.T.Json, regardless of the TFM. -->
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Text.Encodings.Web\ref\System.Text.Encodings.Web.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Encodings.Web\ref\System.Text.Encodings.Web.csproj" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Text.Json/src/Resources/Strings.resx b/src/libraries/System.Text.Json/src/Resources/Strings.resx
index 41cf9de418c483..07655cbccea7a5 100644
--- a/src/libraries/System.Text.Json/src/Resources/Strings.resx
+++ b/src/libraries/System.Text.Json/src/Resources/Strings.resx
@@ -486,7 +486,7 @@
     <value>Members '{0}' and '{1}' on type '{2}' cannot both bind with parameter '{3}' in constructor '{4}' on deserialization.</value>
   </data>
   <data name="ConstructorParamIncompleteBinding" xml:space="preserve">
-    <value>Each parameter in constructor '{0}' on type '{1}' must bind to an object member on deserialization. Each parameter name must be the camel case equivalent of an object member named with the pascal case naming convention.</value>
+    <value>Each parameter in constructor '{0}' on type '{1}' must bind to an object property or field on deserialization. Each parameter name must match with a property or field on the object. The match can be case-insensitive.</value>
   </data>
   <data name="ConstructorMaxOf64Parameters" xml:space="preserve">
     <value>The constructor '{0}' on type '{1}' may not have more than 64 parameters for deserialization.</value>
@@ -536,4 +536,10 @@
   <data name="IgnoreConditionOnValueTypeInvalid" xml:space="preserve">
     <value>The ignore condition 'JsonIgnoreCondition.WhenWritingNull' is not valid on value-type member '{0}' on type '{1}'. Consider using 'JsonIgnoreCondition.WhenWritingDefault'.</value>
   </data>
-</root>
\ No newline at end of file
+  <data name="NumberHandlingConverterMustBeBuiltIn" xml:space="preserve">
+    <value>'JsonNumberHandlingAttribute' cannot be placed on a property, field, or type that is handled by a custom converter. See usage(s) of converter '{0}' on type '{1}'.</value>
+  </data>
+  <data name="NumberHandlingOnPropertyTypeMustBeNumberOrCollection" xml:space="preserve">
+    <value>When 'JsonNumberHandlingAttribute' is placed on a property or field, the property or field must be a number or a collection. See member '{0}' on type '{1}'.</value>
+  </data>
+</root>
diff --git a/src/libraries/System.Text.Json/src/System.Text.Json.csproj b/src/libraries/System.Text.Json/src/System.Text.Json.csproj
index e381a1b381d464..9db4b3972418f9 100644
--- a/src/libraries/System.Text.Json/src/System.Text.Json.csproj
+++ b/src/libraries/System.Text.Json/src/System.Text.Json.csproj
@@ -1,9 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp3.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netcoreapp3.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
     <!-- Workaround for overriding the XML comments related warnings that are being supressed repo wide (within arcade): -->
     <!-- https://github.com/dotnet/arcade/blob/ea6addfdc65e5df1b2c036f11614a5f922e36267/src/Microsoft.DotNet.Arcade.Sdk/tools/ProjectDefaults.props#L90 -->
     <!-- For this project, we want warnings if there are public APIs/types without properly formatted XML comments (particularly CS1591). -->
@@ -16,6 +15,8 @@
     <!-- BUILDING_INBOX_LIBRARY is only false when building the netstandard compatible NuGet package. -->
     <DefineConstants Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or '$(TargetFramework)' == 'netcoreapp3.0'">$(DefineConstants);BUILDING_INBOX_LIBRARY</DefineConstants>
     <NoWarn Condition="'$(TargetFramework)' == 'netstandard2.0' or $(TargetFramework.StartsWith('net4'))">$(NoWarn);nullable</NoWarn>
+    <!-- Use the contract reference path for ApiCompat. -->
+    <ContractTargetFramework Condition="'$(TargetFramework)' == 'netcoreapp3.0'">netstandard2.0</ContractTargetFramework>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonPath)System\HexConverter.cs" Link="Common\System\HexConverter.cs" />
@@ -60,6 +61,7 @@
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonExtensionDataAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonIgnoreAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonIncludeAttribute.cs" />
+    <Compile Include="System\Text\Json\Serialization\Attributes\JsonNumberHandlingAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\Attributes\JsonPropertyNameAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\ClassType.cs" />
     <Compile Include="System\Text\Json\Serialization\ConverterList.cs" />
@@ -135,11 +137,13 @@
     <Compile Include="System\Text\Json\Serialization\JsonDefaultNamingPolicy.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonIgnoreCondition.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonNamingPolicy.cs" />
+    <Compile Include="System\Text\Json\Serialization\JsonNumberHandling.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonParameterInfo.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonParameterInfoOfT.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonPropertyInfo.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonPropertyInfoOfT.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonResumableConverterOfT.cs" />
+    <Compile Include="System\Text\Json\Serialization\JsonSerializer.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.HandleMetadata.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.HandlePropertyName.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.Helpers.cs" />
@@ -211,46 +215,47 @@
     <Compile Include="System\Text\Json\Writer\Utf8JsonWriter.WriteValues.String.cs" />
     <Compile Include="System\Text\Json\Writer\Utf8JsonWriter.WriteValues.UnsignedNumber.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or $(TargetFramework.StartsWith('net4'))">
-    <Compile Include="System\Collections\Generic\StackExtensions.netstandard.cs" />
-    <!-- Common or Common-branched source files -->
-    <Compile Include="$(CommonPath)System\Buffers\ArrayBufferWriter.cs" Link="Common\System\Buffers\ArrayBufferWriter.cs" />
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.ValueTuple" />
-    <Reference Include="System.Numerics.Vectors" />
-    <Reference Include="Microsoft.Bcl.AsyncInterfaces" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or $(TargetFramework.StartsWith('net4')) or '$(TargetFramework)' == 'netcoreapp3.0'">
-    <Compile Include="$(CommonPath)System\Collections\Generic\ReferenceEqualityComparer.cs" Link="Common\System\Collections\Generic\ReferenceEqualityComparer.cs" />
-  </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or '$(TargetFramework)' == 'netcoreapp3.0'">
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Diagnostics.Debug" />
-    <Reference Include="System.Reflection.Primitives" />
-    <Reference Include="System.Reflection.Emit.ILGeneration" />
-    <Reference Include="System.Reflection.Emit.Lightweight" />
-    <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Text.Encoding.Extensions" />
-  </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)'">
     <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicDependencyAttribute.cs" />
     <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
     <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
+    <Compile Include="$(CommonPath)System\Collections\Generic\ReferenceEqualityComparer.cs" Link="Common\System\Collections\Generic\ReferenceEqualityComparer.cs" />
   </ItemGroup>
-  <ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard')) or $(TargetFramework.StartsWith('net4'))">
+    <Compile Include="System\Collections\Generic\StackExtensions.netstandard.cs" />
+    <!-- Common or Common-branched source files -->
+    <Compile Include="$(CommonPath)System\Buffers\ArrayBufferWriter.cs"
+             Link="Common\System\Buffers\ArrayBufferWriter.cs" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or
+                        '$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="System.Buffers" />
+    <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
+    <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Linq" />
     <Reference Include="System.Memory" />
     <Reference Include="System.Numerics.Vectors" />
+    <Reference Include="System.Reflection.Emit.ILGeneration" />
+    <Reference Include="System.Reflection.Emit.Lightweight" />
+    <Reference Include="System.Reflection.Primitives" />
+    <Reference Include="System.Resources.ResourceManager" />
+    <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.CompilerServices.Unsafe" />
+    <Reference Include="System.Runtime.Extensions" />
+    <Reference Include="System.Text.Encoding.Extensions" />
     <Reference Include="System.Text.Encodings.Web" />
     <Reference Include="System.Threading" />
     <Reference Include="System.Threading.Tasks" />
     <Reference Include="System.Threading.Tasks.Extensions" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or $(TargetFramework.StartsWith('net4'))">
+    <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Bcl.AsyncInterfaces\src\Microsoft.Bcl.AsyncInterfaces.csproj" />
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Numerics.Vectors" Version="$(SystemNumericsVectorsVersion)" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Text.Encodings.Web\src\System.Text.Encodings.Web.csproj" />
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" Condition="'$(TargetFramework)' == 'net461'" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/JsonConstants.cs b/src/libraries/System.Text.Json/src/System/Text/Json/JsonConstants.cs
index 2bfc41c6bd912c..2e1bb4e16cfe17 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/JsonConstants.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/JsonConstants.cs
@@ -37,6 +37,10 @@ internal static class JsonConstants
         public static ReadOnlySpan<byte> FalseValue => new byte[] { (byte)'f', (byte)'a', (byte)'l', (byte)'s', (byte)'e' };
         public static ReadOnlySpan<byte> NullValue => new byte[] { (byte)'n', (byte)'u', (byte)'l', (byte)'l' };
 
+        public static ReadOnlySpan<byte> NaNValue => new byte[] { (byte)'N', (byte)'a', (byte)'N' };
+        public static ReadOnlySpan<byte> PositiveInfinityValue => new byte[] { (byte)'I', (byte)'n', (byte)'f', (byte)'i', (byte)'n', (byte)'i', (byte)'t', (byte)'y' };
+        public static ReadOnlySpan<byte> NegativeInfinityValue => new byte[] { (byte)'-', (byte)'I', (byte)'n', (byte)'f', (byte)'i', (byte)'n', (byte)'i', (byte)'t', (byte)'y' };
+
         // Used to search for the end of a number
         public static ReadOnlySpan<byte> Delimiters => new byte[] { ListSeparator, CloseBrace, CloseBracket, Space, LineFeed, CarriageReturn, Tab, Slash };
 
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.cs
index fcd7f0d3fb8da7..dbea5c0fea0c10 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.cs
@@ -321,5 +321,82 @@ public static bool TryGetEscapedGuid(ReadOnlySpan<byte> source, out Guid value)
             value = default;
             return false;
         }
+
+        public static char GetFloatingPointStandardParseFormat(ReadOnlySpan<byte> span)
+        {
+            // Assume that 'e/E' is closer to the end.
+            int startIndex = span.Length - 1;
+            for (int i = startIndex; i >= 0; i--)
+            {
+                byte token = span[i];
+                if (token == 'E' || token == 'e')
+                {
+                    return JsonConstants.ScientificNotationFormat;
+                }
+            }
+            return default;
+        }
+
+        public static bool TryGetFloatingPointConstant(ReadOnlySpan<byte> span, out float value)
+        {
+            if (span.Length == 3)
+            {
+                if (span.SequenceEqual(JsonConstants.NaNValue))
+                {
+                    value = float.NaN;
+                    return true;
+                }
+            }
+            else if (span.Length == 8)
+            {
+                if (span.SequenceEqual(JsonConstants.PositiveInfinityValue))
+                {
+                    value = float.PositiveInfinity;
+                    return true;
+                }
+            }
+            else if (span.Length == 9)
+            {
+                if (span.SequenceEqual(JsonConstants.NegativeInfinityValue))
+                {
+                    value = float.NegativeInfinity;
+                    return true;
+                }
+            }
+
+            value = 0;
+            return false;
+        }
+
+        public static bool TryGetFloatingPointConstant(ReadOnlySpan<byte> span, out double value)
+        {
+            if (span.Length == 3)
+            {
+                if (span.SequenceEqual(JsonConstants.NaNValue))
+                {
+                    value = double.NaN;
+                    return true;
+                }
+            }
+            else if (span.Length == 8)
+            {
+                if (span.SequenceEqual(JsonConstants.PositiveInfinityValue))
+                {
+                    value = double.PositiveInfinity;
+                    return true;
+                }
+            }
+            else if (span.Length == 9)
+            {
+                if (span.SequenceEqual(JsonConstants.NegativeInfinityValue))
+                {
+                    value = double.NegativeInfinity;
+                    return true;
+                }
+            }
+
+            value = 0;
+            return false;
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs
index dbc52d94b79d57..b888bf3c10f3e4 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs
@@ -416,11 +416,38 @@ public float GetSingle()
         internal float GetSingleWithQuotes()
         {
             ReadOnlySpan<byte> span = GetUnescapedSpan();
-            if (!TryGetSingleCore(out float value, span))
+
+            if (JsonReaderHelper.TryGetFloatingPointConstant(span, out float value))
             {
-                throw ThrowHelper.GetFormatException(NumericType.Single);
+                return value;
             }
-            return value;
+
+            char numberFormat = JsonReaderHelper.GetFloatingPointStandardParseFormat(span);
+            if (Utf8Parser.TryParse(span, out value, out int bytesConsumed, numberFormat)
+                && span.Length == bytesConsumed)
+            {
+                // NETCOREAPP implementation of the TryParse method above permits case-insenstive variants of the
+                // float constants "NaN", "Infinity", "-Infinity". This differs from the NETFRAMEWORK implementation.
+                // The following logic reconciles the two implementations to enforce consistent behavior.
+                if (!float.IsNaN(value) && !float.IsPositiveInfinity(value) && !float.IsNegativeInfinity(value))
+                {
+                    return value;
+                }
+            }
+
+            throw ThrowHelper.GetFormatException(NumericType.Single);
+        }
+
+        internal float GetSingleFloatingPointConstant()
+        {
+            ReadOnlySpan<byte> span = GetUnescapedSpan();
+
+            if (JsonReaderHelper.TryGetFloatingPointConstant(span, out float value))
+            {
+                return value;
+            }
+
+            throw ThrowHelper.GetFormatException(NumericType.Single);
         }
 
         /// <summary>
@@ -449,11 +476,38 @@ public double GetDouble()
         internal double GetDoubleWithQuotes()
         {
             ReadOnlySpan<byte> span = GetUnescapedSpan();
-            if (!TryGetDoubleCore(out double value, span))
+
+            if (JsonReaderHelper.TryGetFloatingPointConstant(span, out double value))
             {
-                throw ThrowHelper.GetFormatException(NumericType.Double);
+                return value;
             }
-            return value;
+
+            char numberFormat = JsonReaderHelper.GetFloatingPointStandardParseFormat(span);
+            if (Utf8Parser.TryParse(span, out value, out int bytesConsumed, numberFormat)
+                && span.Length == bytesConsumed)
+            {
+                // NETCOREAPP implmentation of the TryParse method above permits case-insenstive variants of the
+                // float constants "NaN", "Infinity", "-Infinity". This differs from the NETFRAMEWORK implementation.
+                // The following logic reconciles the two implementations to enforce consistent behavior.
+                if (!double.IsNaN(value) && !double.IsPositiveInfinity(value) && !double.IsNegativeInfinity(value))
+                {
+                    return value;
+                }
+            }
+
+            throw ThrowHelper.GetFormatException(NumericType.Double);
+        }
+
+        internal double GetDoubleFloatingPointConstant()
+        {
+            ReadOnlySpan<byte> span = GetUnescapedSpan();
+
+            if (JsonReaderHelper.TryGetFloatingPointConstant(span, out double value))
+            {
+                return value;
+            }
+
+            throw ThrowHelper.GetFormatException(NumericType.Double);
         }
 
         /// <summary>
@@ -482,11 +536,15 @@ public decimal GetDecimal()
         internal decimal GetDecimalWithQuotes()
         {
             ReadOnlySpan<byte> span = GetUnescapedSpan();
-            if (!TryGetDecimalCore(out decimal value, span))
+
+            char numberFormat = JsonReaderHelper.GetFloatingPointStandardParseFormat(span);
+            if (Utf8Parser.TryParse(span, out decimal value, out int bytesConsumed, numberFormat)
+                && span.Length == bytesConsumed)
             {
-                throw ThrowHelper.GetFormatException(NumericType.Decimal);
+                return value;
             }
-            return value;
+
+            throw ThrowHelper.GetFormatException(NumericType.Decimal);
         }
 
         /// <summary>
@@ -920,12 +978,7 @@ public bool TryGetSingle(out float value)
             }
 
             ReadOnlySpan<byte> span = HasValueSequence ? ValueSequence.ToArray() : ValueSpan;
-            return TryGetSingleCore(out value, span);
-        }
 
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal bool TryGetSingleCore(out float value, ReadOnlySpan<byte> span)
-        {
             if (Utf8Parser.TryParse(span, out float tmp, out int bytesConsumed, _numberFormat)
                 && span.Length == bytesConsumed)
             {
@@ -955,12 +1008,7 @@ public bool TryGetDouble(out double value)
             }
 
             ReadOnlySpan<byte> span = HasValueSequence ? ValueSequence.ToArray() : ValueSpan;
-            return TryGetDoubleCore(out value, span);
-        }
 
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal bool TryGetDoubleCore(out double value, ReadOnlySpan<byte> span)
-        {
             if (Utf8Parser.TryParse(span, out double tmp, out int bytesConsumed, _numberFormat)
                 && span.Length == bytesConsumed)
             {
@@ -990,12 +1038,7 @@ public bool TryGetDecimal(out decimal value)
             }
 
             ReadOnlySpan<byte> span = HasValueSequence ? ValueSequence.ToArray() : ValueSpan;
-            return TryGetDecimalCore(out value, span);
-        }
 
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal bool TryGetDecimalCore(out decimal value, ReadOnlySpan<byte> span)
-        {
             if (Utf8Parser.TryParse(span, out decimal tmp, out int bytesConsumed, _numberFormat)
                 && span.Length == bytesConsumed)
             {
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonConverterAttribute.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonConverterAttribute.cs
index e4248e726d5d54..098b1e175e01c4 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonConverterAttribute.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonConverterAttribute.cs
@@ -12,7 +12,7 @@ namespace System.Text.Json.Serialization
     /// The specified converter type must derive from <see cref="JsonConverter"/>.
     /// When placed on a property or field, the specified converter will always be used.
     /// When placed on a type, the specified converter will be used unless a compatible converter is added to
-    /// <see cref="JsonSerializerOptions.Converters"/> or there is another <see cref="JsonConverterAttribute"/> on a member
+    /// <see cref="JsonSerializerOptions.Converters"/> or there is another <see cref="JsonConverterAttribute"/> on a property or field
     /// of the same type.
     /// </remarks>
     [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonExtensionDataAttribute.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonExtensionDataAttribute.cs
index 242d50d11e8284..194143cfaf3237 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonExtensionDataAttribute.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonExtensionDataAttribute.cs
@@ -16,7 +16,7 @@ namespace System.Text.Json.Serialization
     /// During serializing, the name of the extension data member is not included in the JSON;
     /// the data contained within the extension data is serialized as properties of the JSON object.
     ///
-    /// If there is more than one extension member on a type, or it the member is not of the correct type,
+    /// If there is more than one extension member on a type, or the member is not of the correct type,
     /// an <see cref="InvalidOperationException"/> is thrown during the first serialization or deserialization of that type.
     /// </remarks>
     [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonIncludeAttribute.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonIncludeAttribute.cs
index cf5597a574be99..40a6132a20f08d 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonIncludeAttribute.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonIncludeAttribute.cs
@@ -4,10 +4,13 @@
 namespace System.Text.Json.Serialization
 {
     /// <summary>
-    /// Indicates that the member should be included for serialization and deserialization.
+    /// Indicates that the property or field should be included for serialization and deserialization.
     /// </summary>
     /// <remarks>
-    /// When applied to a property, indicates that non-public getters and setters can be used for serialization and deserialization.
+    /// When applied to a public property, indicates that non-public getters and setters should be used for serialization and deserialization.
+    ///
+    /// Non-public properties and fields are not allowed when serializing and deserializing. If the attribute is used on a non-public property or field,
+    /// an <see cref="InvalidOperationException"/> is thrown during the first serialization or deserialization of the declaring type.
     /// </remarks>
     [AttributeUsage(AttributeTargets.Property | System.AttributeTargets.Field, AllowMultiple = false)]
     public sealed class JsonIncludeAttribute : JsonAttribute
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonNumberHandlingAttribute.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonNumberHandlingAttribute.cs
new file mode 100644
index 00000000000000..ac7661b1d9eb2b
--- /dev/null
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonNumberHandlingAttribute.cs
@@ -0,0 +1,30 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Text.Json.Serialization
+{
+    /// <summary>
+    /// When placed on a type, property, or field, indicates what <see cref="JsonNumberHandling"/>
+    /// settings should be used when serializing or deserializing numbers.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
+    public sealed class JsonNumberHandlingAttribute : JsonAttribute
+    {
+        /// <summary>
+        /// Indicates what settings should be used when serializing or deserializing numbers.
+        /// </summary>
+        public JsonNumberHandling Handling { get; }
+
+        /// <summary>
+        /// Initializes a new instance of <see cref="JsonNumberHandlingAttribute"/>.
+        /// </summary>
+        public JsonNumberHandlingAttribute(JsonNumberHandling handling)
+        {
+            if (!JsonSerializer.IsValidNumberHandlingValue(handling))
+            {
+                throw new ArgumentOutOfRangeException(nameof(handling));
+            }
+            Handling = handling;
+        }
+    }
+}
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ArrayConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ArrayConverter.cs
index 4337037817f050..9147243ef95be1 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ArrayConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ArrayConverter.cs
@@ -38,7 +38,7 @@ protected override bool OnWriteResume(Utf8JsonWriter writer, TCollection value,
             int index = state.Current.EnumeratorIndex;
 
             JsonConverter<TElement> elementConverter = GetElementConverter(ref state);
-            if (elementConverter.CanUseDirectReadOrWrite)
+            if (elementConverter.CanUseDirectReadOrWrite && state.Current.NumberHandling == null)
             {
                 // Fast path that avoids validation and extra indirection.
                 for (; index < array.Length; index++)
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/DictionaryDefaultConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/DictionaryDefaultConverter.cs
index cd20a06206db83..2093cd66cda5e8 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/DictionaryDefaultConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/DictionaryDefaultConverter.cs
@@ -29,7 +29,9 @@ protected virtual void ConvertCollection(ref ReadStack state, JsonSerializerOpti
         /// </summary>
         protected virtual void CreateCollection(ref Utf8JsonReader reader, ref ReadStack state) { }
 
-        internal override Type ElementType => typeof(TValue);
+        private static Type s_valueType = typeof(TValue);
+
+        internal override Type ElementType => s_valueType;
 
         protected Type KeyType = typeof(TKey);
         // For string keys we don't use a key converter
@@ -39,9 +41,9 @@ protected virtual void CreateCollection(ref Utf8JsonReader reader, ref ReadStack
         protected JsonConverter<TKey>? _keyConverter;
         protected JsonConverter<TValue>? _valueConverter;
 
-        protected static JsonConverter<TValue> GetValueConverter(JsonClassInfo classInfo)
+        protected static JsonConverter<TValue> GetValueConverter(JsonClassInfo elementClassInfo)
         {
-            JsonConverter<TValue> converter = (JsonConverter<TValue>)classInfo.ElementClassInfo!.PropertyInfoForClassInfo.ConverterBase;
+            JsonConverter<TValue> converter = (JsonConverter<TValue>)elementClassInfo.PropertyInfoForClassInfo.ConverterBase;
             Debug.Assert(converter != null); // It should not be possible to have a null converter at this point.
 
             return converter;
@@ -57,6 +59,8 @@ internal sealed override bool OnTryRead(
             ref ReadStack state,
             [MaybeNullWhen(false)] out TCollection value)
         {
+            JsonClassInfo elementClassInfo = state.Current.JsonClassInfo.ElementClassInfo!;
+
             if (state.UseFastPath)
             {
                 // Fast path that avoids maintaining state variables and dealing with preserved references.
@@ -68,8 +72,8 @@ internal sealed override bool OnTryRead(
 
                 CreateCollection(ref reader, ref state);
 
-                JsonConverter<TValue> valueConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo);
-                if (valueConverter.CanUseDirectReadOrWrite)
+                JsonConverter<TValue> valueConverter = _valueConverter ??= GetValueConverter(elementClassInfo);
+                if (valueConverter.CanUseDirectReadOrWrite && state.Current.NumberHandling == null)
                 {
                     // Process all elements.
                     while (true)
@@ -89,7 +93,7 @@ internal sealed override bool OnTryRead(
 
                         // Read the value and add.
                         reader.ReadWithVerify();
-                        TValue element = valueConverter.Read(ref reader, typeof(TValue), options);
+                        TValue element = valueConverter.Read(ref reader, s_valueType, options);
                         Add(key, element!, options, ref state);
                     }
                 }
@@ -114,7 +118,7 @@ internal sealed override bool OnTryRead(
                         reader.ReadWithVerify();
 
                         // Get the value from the converter and add it.
-                        valueConverter.TryRead(ref reader, typeof(TValue), options, ref state, out TValue element);
+                        valueConverter.TryRead(ref reader, s_valueType, options, ref state, out TValue element);
                         Add(key, element!, options, ref state);
                     }
                 }
@@ -137,7 +141,7 @@ internal sealed override bool OnTryRead(
                 bool preserveReferences = options.ReferenceHandler != null;
                 if (preserveReferences && state.Current.ObjectState < StackFrameObjectState.PropertyValue)
                 {
-                    if (JsonSerializer.ResolveMetadata(this, ref reader, ref state))
+                    if (JsonSerializer.ResolveMetadataForJsonObject(ref reader, ref state, options))
                     {
                         if (state.Current.ObjectState == StackFrameObjectState.ReadRefEndObject)
                         {
@@ -156,23 +160,11 @@ internal sealed override bool OnTryRead(
                 if (state.Current.ObjectState < StackFrameObjectState.CreatedObject)
                 {
                     CreateCollection(ref reader, ref state);
-
-                    if (state.Current.MetadataId != null)
-                    {
-                        Debug.Assert(CanHaveIdMetadata);
-
-                        value = (TCollection)state.Current.ReturnValue!;
-                        state.ReferenceResolver.AddReference(state.Current.MetadataId, value);
-                        // Clear metadata name, if the next read fails
-                        // we want to point the JSON path to the property's object.
-                        state.Current.JsonPropertyName = null;
-                    }
-
                     state.Current.ObjectState = StackFrameObjectState.CreatedObject;
                 }
 
                 // Process all elements.
-                JsonConverter<TValue> elementConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo);
+                JsonConverter<TValue> elementConverter = _valueConverter ??= GetValueConverter(elementClassInfo);
                 while (true)
                 {
                     if (state.Current.PropertyState == StackFramePropertyState.None)
@@ -308,5 +300,8 @@ internal sealed override bool OnTryWrite(
 
             return success;
         }
+
+        internal sealed override void CreateInstanceForReferenceResolver(ref Utf8JsonReader reader, ref ReadStack state, JsonSerializerOptions options)
+            => CreateCollection(ref reader, ref state);
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/DictionaryOfTKeyTValueConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/DictionaryOfTKeyTValueConverter.cs
index 10818b7d31eeee..c89e1f9be07ee8 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/DictionaryOfTKeyTValueConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/DictionaryOfTKeyTValueConverter.cs
@@ -49,16 +49,18 @@ protected internal override bool OnWriteResume(
                 enumerator = (Dictionary<TKey, TValue>.Enumerator)state.Current.CollectionEnumerator;
             }
 
+            JsonClassInfo elementClassInfo = state.Current.JsonClassInfo.ElementClassInfo!;
+
             JsonConverter<TKey> keyConverter = _keyConverter ??= GetKeyConverter(KeyType, options);
-            JsonConverter<TValue> valueConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo);
-            if (!state.SupportContinuation && valueConverter.CanUseDirectReadOrWrite)
+            JsonConverter<TValue> valueConverter = _valueConverter ??= GetValueConverter(elementClassInfo);
+
+            if (!state.SupportContinuation && valueConverter.CanUseDirectReadOrWrite && state.Current.NumberHandling == null)
             {
                 // Fast path that avoids validation and extra indirection.
                 do
                 {
                     TKey key = enumerator.Current.Key;
                     keyConverter.WriteWithQuotes(writer, key, options, ref state);
-
                     valueConverter.Write(writer, enumerator.Current.Value, options);
                 } while (enumerator.MoveNext());
             }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IDictionaryConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IDictionaryConverter.cs
index d1055df9ec5817..5bfef5de0b1eb7 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IDictionaryConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IDictionaryConverter.cs
@@ -71,7 +71,7 @@ protected internal override bool OnWriteResume(Utf8JsonWriter writer, TCollectio
                 enumerator = (IDictionaryEnumerator)state.Current.CollectionEnumerator;
             }
 
-            JsonConverter<object?> valueConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo);
+            JsonConverter<object?> valueConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo.ElementClassInfo!);
             do
             {
                 if (ShouldFlush(writer, ref state))
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IDictionaryOfTKeyTValueConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IDictionaryOfTKeyTValueConverter.cs
index 4fb795ce71a8f4..44c2069f6fd2e4 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IDictionaryOfTKeyTValueConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IDictionaryOfTKeyTValueConverter.cs
@@ -71,7 +71,7 @@ protected internal override bool OnWriteResume(
             }
 
             JsonConverter<TKey> keyConverter = _keyConverter ??= GetKeyConverter(KeyType, options);
-            JsonConverter<TValue> valueConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo);
+            JsonConverter<TValue> valueConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo.ElementClassInfo!);
             do
             {
                 if (ShouldFlush(writer, ref state))
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableDefaultConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableDefaultConverter.cs
index dbe43be8bdc808..3f05795d08bda8 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableDefaultConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableDefaultConverter.cs
@@ -16,9 +16,9 @@ internal abstract class IEnumerableDefaultConverter<TCollection, TElement>
         protected abstract void CreateCollection(ref Utf8JsonReader reader, ref ReadStack state, JsonSerializerOptions options);
         protected virtual void ConvertCollection(ref ReadStack state, JsonSerializerOptions options) { }
 
-        protected static JsonConverter<TElement> GetElementConverter(ref ReadStack state)
+        protected static JsonConverter<TElement> GetElementConverter(JsonClassInfo elementClassInfo)
         {
-            JsonConverter<TElement> converter = (JsonConverter<TElement>)state.Current.JsonClassInfo.ElementClassInfo!.PropertyInfoForClassInfo.ConverterBase;
+            JsonConverter<TElement> converter = (JsonConverter<TElement>)elementClassInfo.PropertyInfoForClassInfo.ConverterBase;
             Debug.Assert(converter != null); // It should not be possible to have a null converter at this point.
 
             return converter;
@@ -39,6 +39,8 @@ internal override bool OnTryRead(
             ref ReadStack state,
             [MaybeNullWhen(false)] out TCollection value)
         {
+            JsonClassInfo elementClassInfo = state.Current.JsonClassInfo.ElementClassInfo!;
+
             if (state.UseFastPath)
             {
                 // Fast path that avoids maintaining state variables and dealing with preserved references.
@@ -50,8 +52,8 @@ internal override bool OnTryRead(
 
                 CreateCollection(ref reader, ref state, options);
 
-                JsonConverter<TElement> elementConverter = GetElementConverter(ref state);
-                if (elementConverter.CanUseDirectReadOrWrite)
+                JsonConverter<TElement> elementConverter = GetElementConverter(elementClassInfo);
+                if (elementConverter.CanUseDirectReadOrWrite && state.Current.NumberHandling == null)
                 {
                     // Fast path that avoids validation and extra indirection.
                     while (true)
@@ -113,7 +115,7 @@ internal override bool OnTryRead(
                 // Handle the metadata properties.
                 if (preserveReferences && state.Current.ObjectState < StackFrameObjectState.PropertyValue)
                 {
-                    if (JsonSerializer.ResolveMetadata(this, ref reader, ref state))
+                    if (JsonSerializer.ResolveMetadataForJsonArray(ref reader, ref state, options))
                     {
                         if (state.Current.ObjectState == StackFrameObjectState.ReadRefEndObject)
                         {
@@ -131,30 +133,13 @@ internal override bool OnTryRead(
                 if (state.Current.ObjectState < StackFrameObjectState.CreatedObject)
                 {
                     CreateCollection(ref reader, ref state, options);
-
-                    if (state.Current.MetadataId != null)
-                    {
-                        value = (TCollection)state.Current.ReturnValue!;
-
-                        // TODO: https://github.com/dotnet/runtime/issues/37168
-                        //Separate logic for IEnumerable to call AddReference when the reader is at `$id`, in order to avoid remembering the last metadata.
-
-                        // Remember the prior metadata and temporarily use '$id' to write it in the path in case AddReference throws
-                        // in this case, the last property seen will be '$values' when we reach this point.
-                        byte[]? lastMetadataProperty = state.Current.JsonPropertyName;
-                        state.Current.JsonPropertyName = JsonSerializer.s_idPropertyName;
-
-                        state.ReferenceResolver.AddReference(state.Current.MetadataId, value);
-                        state.Current.JsonPropertyName = lastMetadataProperty;
-                    }
-
                     state.Current.JsonPropertyInfo = state.Current.JsonClassInfo.ElementClassInfo!.PropertyInfoForClassInfo;
                     state.Current.ObjectState = StackFrameObjectState.CreatedObject;
                 }
 
                 if (state.Current.ObjectState < StackFrameObjectState.ReadElements)
                 {
-                    JsonConverter<TElement> elementConverter = GetElementConverter(ref state);
+                    JsonConverter<TElement> elementConverter = GetElementConverter(elementClassInfo);
 
                     // Process all elements.
                     while (true)
@@ -203,34 +188,25 @@ internal override bool OnTryRead(
                 {
                     state.Current.ObjectState = StackFrameObjectState.EndToken;
 
-                    // Read the EndObject for $values.
-                    if (state.Current.MetadataId != null)
+                    // Read the EndObject token for an array with preserve semantics.
+                    if (state.Current.ValidateEndTokenOnArray)
                     {
                         if (!reader.Read())
                         {
                             value = default;
                             return false;
                         }
-
-                        if (reader.TokenType != JsonTokenType.EndObject)
-                        {
-                            if (reader.TokenType == JsonTokenType.PropertyName)
-                            {
-                                state.Current.JsonPropertyName = reader.GetSpan().ToArray();
-                            }
-
-                            ThrowHelper.ThrowJsonException_MetadataPreservedArrayInvalidProperty(typeToConvert, reader);
-                        }
                     }
                 }
 
                 if (state.Current.ObjectState < StackFrameObjectState.EndTokenValidation)
                 {
-                    if (state.Current.MetadataId != null)
+                    if (state.Current.ValidateEndTokenOnArray)
                     {
                         if (reader.TokenType != JsonTokenType.EndObject)
                         {
-                            ThrowHelper.ThrowJsonException_MetadataPreservedArrayInvalidProperty(typeToConvert, reader);
+                            Debug.Assert(reader.TokenType == JsonTokenType.PropertyName);
+                            ThrowHelper.ThrowJsonException_MetadataPreservedArrayInvalidProperty(ref state, typeToConvert, reader);
                         }
                     }
                 }
@@ -299,5 +275,8 @@ internal sealed override bool OnTryWrite(
         }
 
         protected abstract bool OnWriteResume(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, ref WriteStack state);
+
+        internal sealed override void CreateInstanceForReferenceResolver(ref Utf8JsonReader reader, ref ReadStack state, JsonSerializerOptions options)
+            => CreateCollection(ref reader, ref state, options);
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableOfTConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableOfTConverter.cs
index 23c0e958fe0476..d4a3738f2f5968 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableOfTConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableOfTConverter.cs
@@ -18,7 +18,7 @@ protected override void Add(in TElement value, ref ReadStack state)
             ((List<TElement>)state.Current.ReturnValue!).Add(value);
         }
 
-        protected override void CreateCollection(ref Utf8JsonReader reader, ref ReadStack state,  JsonSerializerOptions options)
+        protected override void CreateCollection(ref Utf8JsonReader reader, ref ReadStack state, JsonSerializerOptions options)
         {
             if (!TypeToConvert.IsAssignableFrom(RuntimeType))
             {
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IListConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IListConverter.cs
index 3f6516cdfbb2d0..f4e9f29b86120f 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IListConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IListConverter.cs
@@ -49,36 +49,38 @@ protected override void CreateCollection(ref Utf8JsonReader reader, ref ReadStac
 
         protected override bool OnWriteResume(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, ref WriteStack state)
         {
-            IEnumerator enumerator;
-            if (state.Current.CollectionEnumerator == null)
+            IList list = value;
+
+            // Using an index is 2x faster than using an enumerator.
+            int index = state.Current.EnumeratorIndex;
+            JsonConverter<object?> elementConverter = GetElementConverter(ref state);
+
+            if (elementConverter.CanUseDirectReadOrWrite && state.Current.NumberHandling == null)
             {
-                enumerator = value.GetEnumerator();
-                if (!enumerator.MoveNext())
+                // Fast path that avoids validation and extra indirection.
+                for (; index < list.Count; index++)
                 {
-                    return true;
+                    elementConverter.Write(writer, list[index], options);
                 }
             }
             else
             {
-                enumerator = state.Current.CollectionEnumerator;
-            }
-
-            JsonConverter<object?> converter = GetElementConverter(ref state);
-            do
-            {
-                if (ShouldFlush(writer, ref state))
+                for (; index < list.Count; index++)
                 {
-                    state.Current.CollectionEnumerator = enumerator;
-                    return false;
-                }
+                    object? element = list[index];
+                    if (!elementConverter.TryWrite(writer, element, options, ref state))
+                    {
+                        state.Current.EnumeratorIndex = index;
+                        return false;
+                    }
 
-                object? element = enumerator.Current;
-                if (!converter.TryWrite(writer, element, options, ref state))
-                {
-                    state.Current.CollectionEnumerator = enumerator;
-                    return false;
+                    if (ShouldFlush(writer, ref state))
+                    {
+                        state.Current.EnumeratorIndex = ++index;
+                        return false;
+                    }
                 }
-            } while (enumerator.MoveNext());
+            }
 
             return true;
         }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IReadOnlyDictionaryOfTKeyTValueConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IReadOnlyDictionaryOfTKeyTValueConverter.cs
index 125f37534c1cc8..28c3c245b1c23b 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IReadOnlyDictionaryOfTKeyTValueConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IReadOnlyDictionaryOfTKeyTValueConverter.cs
@@ -42,7 +42,7 @@ protected internal override bool OnWriteResume(Utf8JsonWriter writer, TCollectio
             }
 
             JsonConverter<TKey> keyConverter = _keyConverter ??= GetKeyConverter(KeyType, options);
-            JsonConverter<TValue> valueConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo);
+            JsonConverter<TValue> valueConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo.ElementClassInfo!);
             do
             {
                 if (ShouldFlush(writer, ref state))
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ImmutableDictionaryOfTKeyTValueConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ImmutableDictionaryOfTKeyTValueConverter.cs
index 9f5e5d0506474c..ac9544d0528591 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ImmutableDictionaryOfTKeyTValueConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ImmutableDictionaryOfTKeyTValueConverter.cs
@@ -53,7 +53,7 @@ protected internal override bool OnWriteResume(Utf8JsonWriter writer, TCollectio
             }
 
             JsonConverter<TKey> keyConverter = _keyConverter ??= GetKeyConverter(KeyType, options);
-            JsonConverter<TValue> valueConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo);
+            JsonConverter<TValue> valueConverter = _valueConverter ??= GetValueConverter(state.Current.JsonClassInfo.ElementClassInfo!);
             do
             {
                 if (ShouldFlush(writer, ref state))
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ListOfTConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ListOfTConverter.cs
index 5004bc1ded4c6e..52362693749eb7 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ListOfTConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/ListOfTConverter.cs
@@ -33,7 +33,7 @@ protected override bool OnWriteResume(Utf8JsonWriter writer, TCollection value,
             int index = state.Current.EnumeratorIndex;
             JsonConverter<TElement> elementConverter = GetElementConverter(ref state);
 
-            if (elementConverter.CanUseDirectReadOrWrite)
+            if (elementConverter.CanUseDirectReadOrWrite && state.Current.NumberHandling == null)
             {
                 // Fast path that avoids validation and extra indirection.
                 for (; index < list.Count; index++)
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/KeyValuePairConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/KeyValuePairConverter.cs
index bee101fbfc1812..9f2de6a1897eaa 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/KeyValuePairConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/KeyValuePairConverter.cs
@@ -86,6 +86,7 @@ protected override bool TryLookupConstructorParameter(
             Debug.Assert(jsonParameterInfo != null);
             argState.ParameterIndex++;
             argState.JsonParameterInfo = jsonParameterInfo;
+            state.Current.NumberHandling = jsonParameterInfo.NumberHandling;
             return true;
         }
 
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectDefaultConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectDefaultConverter.cs
index 25bbcb0dc103a5..237bb8367b0627 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectDefaultConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectDefaultConverter.cs
@@ -77,7 +77,7 @@ internal override bool OnTryRead(ref Utf8JsonReader reader, Type typeToConvert,
                 {
                     if (options.ReferenceHandler != null)
                     {
-                        if (JsonSerializer.ResolveMetadata(this, ref reader, ref state))
+                        if (JsonSerializer.ResolveMetadataForJsonObject(ref reader, ref state, options))
                         {
                             if (state.Current.ObjectState == StackFrameObjectState.ReadRefEndObject)
                             {
@@ -91,8 +91,6 @@ internal override bool OnTryRead(ref Utf8JsonReader reader, Type typeToConvert,
                             return false;
                         }
                     }
-
-                    state.Current.ObjectState = StackFrameObjectState.PropertyValue;
                 }
 
                 if (state.Current.ObjectState < StackFrameObjectState.CreatedObject)
@@ -103,13 +101,6 @@ internal override bool OnTryRead(ref Utf8JsonReader reader, Type typeToConvert,
                     }
 
                     obj = state.Current.JsonClassInfo.CreateObject!()!;
-                    if (state.Current.MetadataId != null)
-                    {
-                        state.ReferenceResolver.AddReference(state.Current.MetadataId, obj);
-                        // Clear metadata name, if the next read fails
-                        // we want to point the JSON path to the property's object.
-                        state.Current.JsonPropertyName = null;
-                    }
 
                     state.Current.ReturnValue = obj;
                     state.Current.ObjectState = StackFrameObjectState.CreatedObject;
@@ -265,6 +256,7 @@ internal sealed override bool OnTryWrite(
 
                     // Remember the current property for JsonPath support if an exception is thrown.
                     state.Current.DeclaredJsonPropertyInfo = jsonPropertyInfo;
+                    state.Current.NumberHandling = jsonPropertyInfo.NumberHandling;
 
                     if (jsonPropertyInfo.ShouldSerialize)
                     {
@@ -321,6 +313,7 @@ internal sealed override bool OnTryWrite(
                 {
                     JsonPropertyInfo jsonPropertyInfo = propertyCacheArray![state.Current.EnumeratorIndex];
                     state.Current.DeclaredJsonPropertyInfo = jsonPropertyInfo;
+                    state.Current.NumberHandling = jsonPropertyInfo.NumberHandling;
 
                     if (jsonPropertyInfo.ShouldSerialize)
                     {
@@ -416,5 +409,16 @@ protected bool ReadAheadPropertyValue(ref ReadStack state, ref Utf8JsonReader re
 
             return true;
         }
+
+        internal sealed override void CreateInstanceForReferenceResolver(ref Utf8JsonReader reader, ref ReadStack state, JsonSerializerOptions options)
+        {
+            if (state.Current.JsonClassInfo.CreateObject == null)
+            {
+                ThrowHelper.ThrowNotSupportedException_DeserializeNoConstructor(state.Current.JsonClassInfo.Type, ref reader, ref state);
+            }
+
+            object obj = state.Current.JsonClassInfo.CreateObject!()!;
+            state.Current.ReturnValue = obj;
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectWithParameterizedConstructorConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectWithParameterizedConstructorConverter.cs
index 120b687bdabc0d..6e2f251ac62ebd 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectWithParameterizedConstructorConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Object/ObjectWithParameterizedConstructorConverter.cs
@@ -7,8 +7,8 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 
-using FoundProperties = System.ValueTuple<System.Text.Json.JsonPropertyInfo, System.Text.Json.JsonReaderState, long, byte[]?, string?>;
-using FoundPropertiesAsync = System.ValueTuple<System.Text.Json.JsonPropertyInfo, object?, string?>;
+using FoundProperty = System.ValueTuple<System.Text.Json.JsonPropertyInfo, System.Text.Json.JsonReaderState, long, byte[]?, string?>;
+using FoundPropertyAsync = System.ValueTuple<System.Text.Json.JsonPropertyInfo, object?, string?>;
 
 namespace System.Text.Json.Serialization.Converters
 {
@@ -21,6 +21,7 @@ internal abstract partial class ObjectWithParameterizedConstructorConverter<T> :
         internal sealed override bool OnTryRead(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options, ref ReadStack state, [MaybeNullWhen(false)] out T value)
         {
             object obj;
+            ArgumentState argumentState = state.Current.CtorArgumentState!;
 
             if (state.UseFastPath)
             {
@@ -32,21 +33,24 @@ internal sealed override bool OnTryRead(ref Utf8JsonReader reader, Type typeToCo
 
                 obj = CreateObject(ref state.Current);
 
-                if (state.Current.PropertyIndex > 0)
+                if (argumentState.FoundPropertyCount > 0)
                 {
                     Utf8JsonReader tempReader;
 
-                    for (int i = 0; i < state.Current.PropertyIndex; i++)
+                    FoundProperty[]? properties = argumentState.FoundProperties;
+                    Debug.Assert(properties != null);
+
+                    for (int i = 0; i < argumentState.FoundPropertyCount; i++)
                     {
-                        JsonPropertyInfo jsonPropertyInfo = state.Current.CtorArgumentState!.FoundProperties![i].Item1;
-                        long resumptionByteIndex = state.Current.CtorArgumentState.FoundProperties[i].Item3;
-                        byte[]? propertyNameArray = state.Current.CtorArgumentState.FoundProperties[i].Item4;
-                        string? dataExtKey = state.Current.CtorArgumentState.FoundProperties[i].Item5;
+                        JsonPropertyInfo jsonPropertyInfo = properties[i].Item1;
+                        long resumptionByteIndex = properties[i].Item3;
+                        byte[]? propertyNameArray = properties[i].Item4;
+                        string? dataExtKey = properties[i].Item5;
 
                         tempReader = new Utf8JsonReader(
                             originalSpan.Slice(checked((int)resumptionByteIndex)),
                             isFinalBlock: true,
-                            state: state.Current.CtorArgumentState.FoundProperties[i].Item2);
+                            state: properties[i].Item2);
 
                         Debug.Assert(tempReader.TokenType == JsonTokenType.PropertyName);
 
@@ -65,7 +69,8 @@ internal sealed override bool OnTryRead(ref Utf8JsonReader reader, Type typeToCo
                         ReadPropertyValue(obj, ref state, ref tempReader, jsonPropertyInfo, useExtensionProperty);
                     }
 
-                    ArrayPool<FoundProperties>.Shared.Return(state.Current.CtorArgumentState!.FoundProperties!, clearArray: true);
+                    ArrayPool<FoundProperty>.Shared.Return(argumentState.FoundProperties!, clearArray: true);
+                    argumentState.FoundProperties = null;
                 }
             }
             else
@@ -86,14 +91,13 @@ internal sealed override bool OnTryRead(ref Utf8JsonReader reader, Type typeToCo
 
                 obj = CreateObject(ref state.Current);
 
-                if (state.Current.CtorArgumentState!.FoundPropertyCount > 0)
+                if (argumentState.FoundPropertyCount > 0)
                 {
-                    // Set the properties we've parsed so far.
-                    for (int i = 0; i < state.Current.CtorArgumentState!.FoundPropertyCount; i++)
+                    for (int i = 0; i < argumentState.FoundPropertyCount; i++)
                     {
-                        JsonPropertyInfo jsonPropertyInfo = state.Current.CtorArgumentState!.FoundPropertiesAsync![i].Item1;
-                        object? propValue = state.Current.CtorArgumentState!.FoundPropertiesAsync![i].Item2;
-                        string? dataExtKey = state.Current.CtorArgumentState!.FoundPropertiesAsync![i].Item3;
+                        JsonPropertyInfo jsonPropertyInfo = argumentState.FoundPropertiesAsync![i].Item1;
+                        object? propValue = argumentState.FoundPropertiesAsync![i].Item2;
+                        string? dataExtKey = argumentState.FoundPropertiesAsync![i].Item3;
 
                         if (dataExtKey == null)
                         {
@@ -117,7 +121,8 @@ internal sealed override bool OnTryRead(ref Utf8JsonReader reader, Type typeToCo
                         }
                     }
 
-                    ArrayPool<FoundPropertiesAsync>.Shared.Return(state.Current.CtorArgumentState!.FoundPropertiesAsync!, clearArray: true);
+                    ArrayPool<FoundPropertyAsync>.Shared.Return(argumentState.FoundPropertiesAsync!, clearArray: true);
+                    argumentState.FoundPropertiesAsync = null;
                 }
             }
 
@@ -128,7 +133,7 @@ internal sealed override bool OnTryRead(ref Utf8JsonReader reader, Type typeToCo
             }
 
             // Check if we are trying to build the sorted parameter cache.
-            if (state.Current.CtorArgumentState!.ParameterRefCache != null)
+            if (argumentState.ParameterRefCache != null)
             {
                 state.Current.JsonClassInfo.UpdateSortedParameterCache(ref state.Current);
             }
@@ -195,31 +200,36 @@ private void ReadConstructorArguments(ref ReadStack state, ref Utf8JsonReader re
                         out _,
                         createExtensionProperty: false);
 
-                    if (state.Current.CtorArgumentState!.FoundProperties == null)
-                    {
-                        state.Current.CtorArgumentState.FoundProperties =
-                            ArrayPool<FoundProperties>.Shared.Rent(Math.Max(1, state.Current.JsonClassInfo.PropertyCache!.Count));
-                    }
-                    else if (state.Current.PropertyIndex - 1 == state.Current.CtorArgumentState.FoundProperties!.Length)
+                    if (jsonPropertyInfo.ShouldDeserialize)
                     {
-                        // Rare case where we can't fit all the JSON properties in the rented pool; we have to grow.
-                        // This could happen if there are duplicate properties in the JSON.
+                        ArgumentState argumentState = state.Current.CtorArgumentState!;
 
-                        var newCache = ArrayPool<FoundProperties>.Shared.Rent(state.Current.CtorArgumentState.FoundProperties!.Length * 2);
+                        if (argumentState.FoundProperties == null)
+                        {
+                            argumentState.FoundProperties =
+                                ArrayPool<FoundProperty>.Shared.Rent(Math.Max(1, state.Current.JsonClassInfo.PropertyCache!.Count));
+                        }
+                        else if (argumentState.FoundPropertyCount == argumentState.FoundProperties.Length)
+                        {
+                            // Rare case where we can't fit all the JSON properties in the rented pool; we have to grow.
+                            // This could happen if there are duplicate properties in the JSON.
 
-                        state.Current.CtorArgumentState.FoundProperties!.CopyTo(newCache, 0);
+                            var newCache = ArrayPool<FoundProperty>.Shared.Rent(argumentState.FoundProperties.Length * 2);
 
-                        ArrayPool<FoundProperties>.Shared.Return(state.Current.CtorArgumentState.FoundProperties!, clearArray: true);
+                            argumentState.FoundProperties.CopyTo(newCache, 0);
 
-                        state.Current.CtorArgumentState.FoundProperties = newCache!;
-                    }
+                            ArrayPool<FoundProperty>.Shared.Return(argumentState.FoundProperties, clearArray: true);
 
-                    state.Current.CtorArgumentState!.FoundProperties![state.Current.PropertyIndex - 1] = (
-                        jsonPropertyInfo,
-                        reader.CurrentState,
-                        reader.BytesConsumed,
-                        state.Current.JsonPropertyName,
-                        state.Current.JsonPropertyNameAsString);
+                            argumentState.FoundProperties = newCache!;
+                        }
+
+                        argumentState.FoundProperties[argumentState.FoundPropertyCount++] = (
+                            jsonPropertyInfo,
+                            reader.CurrentState,
+                            reader.BytesConsumed,
+                            state.Current.JsonPropertyName,
+                            state.Current.JsonPropertyNameAsString);
+                    }
 
                     reader.Skip();
 
@@ -387,30 +397,31 @@ private bool HandlePropertyWithContinuation(
                 }
             }
 
+            Debug.Assert(jsonPropertyInfo.ShouldDeserialize);
+
             // Ensure that the cache has enough capacity to add this property.
 
-            if (state.Current.CtorArgumentState!.FoundPropertiesAsync == null)
+            ArgumentState argumentState = state.Current.CtorArgumentState!;
+
+            if (argumentState.FoundPropertiesAsync == null)
             {
-                state.Current.CtorArgumentState.FoundPropertiesAsync =
-                    ArrayPool<FoundPropertiesAsync>.Shared.Rent(Math.Max(1, state.Current.JsonClassInfo.PropertyCache!.Count));
+                argumentState.FoundPropertiesAsync = ArrayPool<FoundPropertyAsync>.Shared.Rent(Math.Max(1, state.Current.JsonClassInfo.PropertyCache!.Count));
             }
-            else if (state.Current.CtorArgumentState.FoundPropertyCount == state.Current.CtorArgumentState.FoundPropertiesAsync!.Length)
+            else if (argumentState.FoundPropertyCount == argumentState.FoundPropertiesAsync!.Length)
             {
                 // Rare case where we can't fit all the JSON properties in the rented pool; we have to grow.
                 // This could happen if there are duplicate properties in the JSON.
-                var newCache = ArrayPool<FoundPropertiesAsync>.Shared.Rent(
-                    state.Current.CtorArgumentState.FoundPropertiesAsync!.Length * 2);
+                var newCache = ArrayPool<FoundPropertyAsync>.Shared.Rent(argumentState.FoundPropertiesAsync!.Length * 2);
 
-                state.Current.CtorArgumentState.FoundPropertiesAsync!.CopyTo(newCache, 0);
+                argumentState.FoundPropertiesAsync!.CopyTo(newCache, 0);
 
-                ArrayPool<FoundPropertiesAsync>.Shared.Return(
-                    state.Current.CtorArgumentState.FoundPropertiesAsync!, clearArray: true);
+                ArrayPool<FoundPropertyAsync>.Shared.Return(argumentState.FoundPropertiesAsync!, clearArray: true);
 
-                state.Current.CtorArgumentState.FoundPropertiesAsync = newCache!;
+                argumentState.FoundPropertiesAsync = newCache!;
             }
 
             // Cache the property name and value.
-            state.Current.CtorArgumentState.FoundPropertiesAsync[state.Current.CtorArgumentState.FoundPropertyCount++] = (
+            argumentState.FoundPropertiesAsync![argumentState.FoundPropertyCount++] = (
                 jsonPropertyInfo,
                 propValue,
                 state.Current.JsonPropertyNameAsString);
@@ -467,6 +478,9 @@ protected virtual bool TryLookupConstructorParameter(
             state.Current.JsonPropertyName = utf8PropertyName;
 
             state.Current.CtorArgumentState.JsonParameterInfo = jsonParameterInfo;
+
+            state.Current.NumberHandling = jsonParameterInfo?.NumberHandling;
+
             return jsonParameterInfo != null;
         }
 
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/ByteConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/ByteConverter.cs
index 774341c8e39ae6..f02b3ac8d70d50 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/ByteConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/ByteConverter.cs
@@ -5,6 +5,11 @@ namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class ByteConverter : JsonConverter<byte>
     {
+        public ByteConverter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override byte Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetByte();
@@ -24,5 +29,27 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, byte value, JsonSe
         {
             writer.WritePropertyName(value);
         }
+
+        internal override byte ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String && (JsonNumberHandling.AllowReadingFromString & handling) != 0)
+            {
+                return reader.GetByteWithQuotes();
+            }
+
+            return reader.GetByte();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, byte value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else
+            {
+                writer.WriteNumberValue(value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/DecimalConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/DecimalConverter.cs
index c78316a88f95fd..559079eec617a5 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/DecimalConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/DecimalConverter.cs
@@ -5,6 +5,11 @@ namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class DecimalConverter : JsonConverter<decimal>
     {
+        public DecimalConverter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override decimal Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetDecimal();
@@ -24,5 +29,28 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, decimal value, Jso
         {
             writer.WritePropertyName(value);
         }
+
+        internal override decimal ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String &&
+                (JsonNumberHandling.AllowReadingFromString & handling) != 0)
+            {
+                return reader.GetDecimalWithQuotes();
+            }
+
+            return reader.GetDecimal();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, decimal value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else
+            {
+                writer.WriteNumberValue(value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/DoubleConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/DoubleConverter.cs
index 641ad8e9991e8f..7b929b10e33974 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/DoubleConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/DoubleConverter.cs
@@ -5,6 +5,11 @@ namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class DoubleConverter : JsonConverter<double>
     {
+        public DoubleConverter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override double Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetDouble();
@@ -24,5 +29,38 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, double value, Json
         {
             writer.WritePropertyName(value);
         }
+
+        internal override double ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String)
+            {
+                if ((JsonNumberHandling.AllowReadingFromString & handling) != 0)
+                {
+                    return reader.GetDoubleWithQuotes();
+                }
+                else if ((JsonNumberHandling.AllowNamedFloatingPointLiterals & handling) != 0)
+                {
+                    return reader.GetDoubleFloatingPointConstant();
+                }
+            }
+
+            return reader.GetDouble();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, double value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else if ((JsonNumberHandling.AllowNamedFloatingPointLiterals & handling) != 0)
+            {
+                writer.WriteFloatingPointConstant(value);
+            }
+            else
+            {
+                writer.WriteNumberValue(value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int16Converter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int16Converter.cs
index c01ee00032cc55..f62da456a3a484 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int16Converter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int16Converter.cs
@@ -1,12 +1,15 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System.Diagnostics.CodeAnalysis;
-
 namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class Int16Converter : JsonConverter<short>
     {
+        public Int16Converter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override short Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetInt16();
@@ -27,5 +30,29 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, short value, JsonS
         {
             writer.WritePropertyName(value);
         }
+
+        internal override short ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String &&
+                (JsonNumberHandling.AllowReadingFromString & handling) != 0)
+            {
+                return reader.GetInt16WithQuotes();
+            }
+
+            return reader.GetInt16();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, short value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else
+            {
+                // For performance, lift up the writer implementation.
+                writer.WriteNumberValue((long)value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int32Converter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int32Converter.cs
index 5fc881a6b2e4d1..85d7fb3c6aa90c 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int32Converter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int32Converter.cs
@@ -5,6 +5,11 @@ namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class Int32Converter : JsonConverter<int>
     {
+        public Int32Converter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override int Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetInt32();
@@ -25,5 +30,29 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, int value, JsonSer
         {
             writer.WritePropertyName(value);
         }
+
+        internal override int ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String &&
+                (JsonNumberHandling.AllowReadingFromString & handling) != 0)
+            {
+                return reader.GetInt32WithQuotes();
+            }
+
+            return reader.GetInt32();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, int value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else
+            {
+                // For performance, lift up the writer implementation.
+                writer.WriteNumberValue((long)value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int64Converter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int64Converter.cs
index 4aec3ff4e48564..48725dccbeecca 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int64Converter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/Int64Converter.cs
@@ -5,6 +5,11 @@ namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class Int64Converter : JsonConverter<long>
     {
+        public Int64Converter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override long Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetInt64();
@@ -24,5 +29,28 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, long value, JsonSe
         {
             writer.WritePropertyName(value);
         }
+
+        internal override long ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String &&
+                (JsonNumberHandling.AllowReadingFromString & handling) != 0)
+            {
+                return reader.GetInt64WithQuotes();
+            }
+
+            return reader.GetInt64();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, long value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else
+            {
+                writer.WriteNumberValue(value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/NullableConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/NullableConverter.cs
index e2c0ddcc43e01e..44e4270a26165b 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/NullableConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/NullableConverter.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
+
 namespace System.Text.Json.Serialization.Converters
 {
     internal class NullableConverter<T> : JsonConverter<T?> where T : struct
@@ -12,6 +14,7 @@ internal class NullableConverter<T> : JsonConverter<T?> where T : struct
         public NullableConverter(JsonConverter<T> converter)
         {
             _converter = converter;
+            IsInternalConverterForNumberType = converter.IsInternalConverterForNumberType;
         }
 
         public override T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
@@ -40,5 +43,32 @@ public override void Write(Utf8JsonWriter writer, T? value, JsonSerializerOption
                 _converter.Write(writer, value.Value, options);
             }
         }
+
+        internal override T? ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling numberHandling)
+        {
+            // We do not check _converter.HandleNull, as the underlying struct cannot be null.
+            // A custom converter for some type T? can handle null.
+            if (reader.TokenType == JsonTokenType.Null)
+            {
+                return null;
+            }
+
+            T value = _converter.ReadNumberWithCustomHandling(ref reader, numberHandling);
+            return value;
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, T? value, JsonNumberHandling handling)
+        {
+            if (!value.HasValue)
+            {
+                // We do not check _converter.HandleNull, as the underlying struct cannot be null.
+                // A custom converter for some type T? can handle null.
+                writer.WriteNullValue();
+            }
+            else
+            {
+                _converter.WriteNumberWithCustomHandling(writer, value.Value, handling);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/SByteConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/SByteConverter.cs
index 49ba6699b45301..0896bf97527ef5 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/SByteConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/SByteConverter.cs
@@ -5,6 +5,11 @@ namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class SByteConverter : JsonConverter<sbyte>
     {
+        public SByteConverter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override sbyte Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetSByte();
@@ -24,5 +29,28 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, sbyte value, JsonS
         {
             writer.WritePropertyName(value);
         }
+
+        internal override sbyte ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String &&
+                (JsonNumberHandling.AllowReadingFromString & handling) != 0)
+            {
+                return reader.GetSByteWithQuotes();
+            }
+
+            return reader.GetSByte();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, sbyte value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else
+            {
+                writer.WriteNumberValue(value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/SingleConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/SingleConverter.cs
index e2f7d76761e003..9b7e6fad328c63 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/SingleConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/SingleConverter.cs
@@ -5,6 +5,12 @@ namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class SingleConverter : JsonConverter<float>
     {
+
+        public SingleConverter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override float Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetSingle();
@@ -24,5 +30,38 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, float value, JsonS
         {
             writer.WritePropertyName(value);
         }
+
+        internal override float ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String)
+            {
+                if ((JsonNumberHandling.AllowReadingFromString & handling) != 0)
+                {
+                    return reader.GetSingleWithQuotes();
+                }
+                else if ((JsonNumberHandling.AllowNamedFloatingPointLiterals & handling) != 0)
+                {
+                    return reader.GetSingleFloatingPointConstant();
+                }
+            }
+
+            return reader.GetSingle();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, float value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else if ((JsonNumberHandling.AllowNamedFloatingPointLiterals & handling) != 0)
+            {
+                writer.WriteFloatingPointConstant(value);
+            }
+            else
+            {
+                writer.WriteNumberValue(value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/StringConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/StringConverter.cs
index f03d9ac1cba129..08972856b698c6 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/StringConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/StringConverter.cs
@@ -1,8 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System.Diagnostics.CodeAnalysis;
-
 namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class StringConverter : JsonConverter<string>
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt16Converter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt16Converter.cs
index db2af0a5f2e3ba..249d2a059ffa1d 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt16Converter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt16Converter.cs
@@ -5,6 +5,11 @@ namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class UInt16Converter : JsonConverter<ushort>
     {
+        public UInt16Converter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override ushort Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetUInt16();
@@ -25,5 +30,29 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, ushort value, Json
         {
             writer.WritePropertyName(value);
         }
+
+        internal override ushort ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String &&
+                (JsonNumberHandling.AllowReadingFromString & handling) != 0)
+            {
+                return reader.GetUInt16WithQuotes();
+            }
+
+            return reader.GetUInt16();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, ushort value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else
+            {
+                // For performance, lift up the writer implementation.
+                writer.WriteNumberValue((long)value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt32Converter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt32Converter.cs
index 131e6feb1b0544..2c6ea5e07d6b46 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt32Converter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt32Converter.cs
@@ -5,6 +5,11 @@ namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class UInt32Converter : JsonConverter<uint>
     {
+        public UInt32Converter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override uint Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetUInt32();
@@ -25,5 +30,29 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, uint value, JsonSe
         {
             writer.WritePropertyName(value);
         }
+
+        internal override uint ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String &&
+                (JsonNumberHandling.AllowReadingFromString & handling) != 0)
+            {
+                return reader.GetUInt32WithQuotes();
+            }
+
+            return reader.GetUInt32();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, uint value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else
+            {
+                // For performance, lift up the writer implementation.
+                writer.WriteNumberValue((ulong)value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt64Converter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt64Converter.cs
index 95f9025c39812d..3d94f296de13fe 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt64Converter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/UInt64Converter.cs
@@ -5,6 +5,11 @@ namespace System.Text.Json.Serialization.Converters
 {
     internal sealed class UInt64Converter : JsonConverter<ulong>
     {
+        public UInt64Converter()
+        {
+            IsInternalConverterForNumberType = true;
+        }
+
         public override ulong Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             return reader.GetUInt64();
@@ -24,5 +29,28 @@ internal override void WriteWithQuotes(Utf8JsonWriter writer, ulong value, JsonS
         {
             writer.WritePropertyName(value);
         }
+
+        internal override ulong ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+        {
+            if (reader.TokenType == JsonTokenType.String &&
+                (JsonNumberHandling.AllowReadingFromString & handling) != 0)
+            {
+                return reader.GetUInt64WithQuotes();
+            }
+
+            return reader.GetUInt64();
+        }
+
+        internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, ulong value, JsonNumberHandling handling)
+        {
+            if ((JsonNumberHandling.WriteAsString & handling) != 0)
+            {
+                writer.WriteNumberValueAsString(value);
+            }
+            else
+            {
+                writer.WriteNumberValue(value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.Cache.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.Cache.cs
index 785abae8a60793..0de7ed3ea231f2 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.Cache.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.Cache.cs
@@ -52,10 +52,14 @@ internal sealed partial class JsonClassInfo
         // Use an array (instead of List<T>) for highest performance.
         private volatile PropertyRef[]? _propertyRefsSorted;
 
-        public static JsonPropertyInfo AddProperty(MemberInfo memberInfo, Type memberType, Type parentClassType, JsonSerializerOptions options)
+        public static JsonPropertyInfo AddProperty(
+            MemberInfo memberInfo,
+            Type memberType,
+            Type parentClassType,
+            JsonNumberHandling? parentTypeNumberHandling,
+            JsonSerializerOptions options)
         {
             JsonIgnoreCondition? ignoreCondition = JsonPropertyInfo.GetAttribute<JsonIgnoreAttribute>(memberInfo)?.Condition;
-
             if (ignoreCondition == JsonIgnoreCondition.Always)
             {
                 return JsonPropertyInfo.CreateIgnoredPropertyPlaceholder(memberInfo, options);
@@ -75,6 +79,7 @@ public static JsonPropertyInfo AddProperty(MemberInfo memberInfo, Type memberTyp
                 parentClassType,
                 converter,
                 options,
+                parentTypeNumberHandling,
                 ignoreCondition);
         }
 
@@ -85,6 +90,7 @@ internal static JsonPropertyInfo CreateProperty(
             Type parentClassType,
             JsonConverter converter,
             JsonSerializerOptions options,
+            JsonNumberHandling? parentTypeNumberHandling = null,
             JsonIgnoreCondition? ignoreCondition = null)
         {
             // Create the JsonPropertyInfo instance.
@@ -98,6 +104,7 @@ internal static JsonPropertyInfo CreateProperty(
                 memberInfo,
                 converter,
                 ignoreCondition,
+                parentTypeNumberHandling,
                 options);
 
             return jsonPropertyInfo;
@@ -113,13 +120,16 @@ internal static JsonPropertyInfo CreatePropertyInfoForClassInfo(
             JsonConverter converter,
             JsonSerializerOptions options)
         {
+            JsonNumberHandling? numberHandling = GetNumberHandlingForType(declaredPropertyType);
+
             JsonPropertyInfo jsonPropertyInfo = CreateProperty(
                 declaredPropertyType: declaredPropertyType,
                 runtimePropertyType: runtimePropertyType,
                 memberInfo: null, // Not a real property so this is null.
                 parentClassType: JsonClassInfo.ObjectType, // a dummy value (not used)
                 converter: converter,
-                options);
+                options,
+                parentTypeNumberHandling: numberHandling);
 
             Debug.Assert(jsonPropertyInfo.IsForClassInfo);
 
@@ -436,84 +446,47 @@ private static bool IsParameterRefEqual(in ParameterRef parameterRef, ReadOnlySp
         /// </summary>
         // AggressiveInlining used since this method is only called from two locations and is on a hot path.
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static ulong GetKey(ReadOnlySpan<byte> propertyName)
+        public static ulong GetKey(ReadOnlySpan<byte> name)
         {
-            const int BitsInByte = 8;
             ulong key;
-            int length = propertyName.Length;
+
+            ref byte reference = ref MemoryMarshal.GetReference(name);
+            int length = name.Length;
 
             if (length > 7)
             {
-                key = MemoryMarshal.Read<ulong>(propertyName)
-                    & 0x00FFFFFFFFFFFFFF
-                    // Include the length with a max of 0xFF.
-                    | ((ulong)Math.Min(length, 0xFF)) << (7 * BitsInByte);
-            }
-            else if (length > 3)
-            {
-                key = MemoryMarshal.Read<uint>(propertyName);
-
-                if (length == 7)
-                {
-                    key |= (ulong)propertyName[6] << (6 * BitsInByte)
-                        | (ulong)propertyName[5] << (5 * BitsInByte)
-                        | (ulong)propertyName[4] << (4 * BitsInByte)
-                        | (ulong)7 << (7 * BitsInByte);
-                }
-                else if (length == 6)
-                {
-                    key |= (ulong)propertyName[5] << (5 * BitsInByte)
-                        | (ulong)propertyName[4] << (4 * BitsInByte)
-                        | (ulong)6 << (7 * BitsInByte);
-                }
-                else if (length == 5)
-                {
-                    key |= (ulong)propertyName[4] << (4 * BitsInByte)
-                        | (ulong)5 << (7 * BitsInByte);
-                }
-                else
-                {
-                    key |= (ulong)4 << (7 * BitsInByte);
-                }
+                key = Unsafe.ReadUnaligned<ulong>(ref reference) & 0x00ffffffffffffffL;
+                key |= (ulong)Math.Min(length, 0xff) << 56;
             }
-            else if (length > 1)
+            else
             {
-                key = MemoryMarshal.Read<ushort>(propertyName);
+                key =
+                    length > 5 ? Unsafe.ReadUnaligned<uint>(ref reference) | (ulong)Unsafe.ReadUnaligned<ushort>(ref Unsafe.Add(ref reference, 4)) << 32 :
+                    length > 3 ? Unsafe.ReadUnaligned<uint>(ref reference) :
+                    length > 1 ? Unsafe.ReadUnaligned<ushort>(ref reference) : 0UL;
+                key |= (ulong)length << 56;
 
-                if (length == 3)
+                if ((length & 1) != 0)
                 {
-                    key |= (ulong)propertyName[2] << (2 * BitsInByte)
-                        | (ulong)3 << (7 * BitsInByte);
+                    var offset = length - 1;
+                    key |= (ulong)Unsafe.Add(ref reference, offset) << (offset * 8);
                 }
-                else
-                {
-                    key |= (ulong)2 << (7 * BitsInByte);
-                }
-            }
-            else if (length == 1)
-            {
-                key = propertyName[0]
-                    | (ulong)1 << (7 * BitsInByte);
-            }
-            else
-            {
-                // An empty name is valid.
-                key = 0;
             }
 
             // Verify key contains the embedded bytes as expected.
+            const int BitsInByte = 8;
             Debug.Assert(
                 // Verify embedded property name.
-                (length < 1 || propertyName[0] == ((key & ((ulong)0xFF << BitsInByte * 0)) >> BitsInByte * 0)) &&
-                (length < 2 || propertyName[1] == ((key & ((ulong)0xFF << BitsInByte * 1)) >> BitsInByte * 1)) &&
-                (length < 3 || propertyName[2] == ((key & ((ulong)0xFF << BitsInByte * 2)) >> BitsInByte * 2)) &&
-                (length < 4 || propertyName[3] == ((key & ((ulong)0xFF << BitsInByte * 3)) >> BitsInByte * 3)) &&
-                (length < 5 || propertyName[4] == ((key & ((ulong)0xFF << BitsInByte * 4)) >> BitsInByte * 4)) &&
-                (length < 6 || propertyName[5] == ((key & ((ulong)0xFF << BitsInByte * 5)) >> BitsInByte * 5)) &&
-                (length < 7 || propertyName[6] == ((key & ((ulong)0xFF << BitsInByte * 6)) >> BitsInByte * 6)) &&
+                (name.Length < 1 || name[0] == ((key & ((ulong)0xFF << BitsInByte * 0)) >> BitsInByte * 0)) &&
+                (name.Length < 2 || name[1] == ((key & ((ulong)0xFF << BitsInByte * 1)) >> BitsInByte * 1)) &&
+                (name.Length < 3 || name[2] == ((key & ((ulong)0xFF << BitsInByte * 2)) >> BitsInByte * 2)) &&
+                (name.Length < 4 || name[3] == ((key & ((ulong)0xFF << BitsInByte * 3)) >> BitsInByte * 3)) &&
+                (name.Length < 5 || name[4] == ((key & ((ulong)0xFF << BitsInByte * 4)) >> BitsInByte * 4)) &&
+                (name.Length < 6 || name[5] == ((key & ((ulong)0xFF << BitsInByte * 5)) >> BitsInByte * 5)) &&
+                (name.Length < 7 || name[6] == ((key & ((ulong)0xFF << BitsInByte * 6)) >> BitsInByte * 6)) &&
                 // Verify embedded length.
-                (length >= 0xFF || (key & ((ulong)0xFF << BitsInByte * 7)) >> BitsInByte * 7 == (ulong)length) &&
-                (length < 0xFF || (key & ((ulong)0xFF << BitsInByte * 7)) >> BitsInByte * 7 == 0xFF));
+                (name.Length >= 0xFF || (key & ((ulong)0xFF << BitsInByte * 7)) >> BitsInByte * 7 == (ulong)name.Length) &&
+                (name.Length < 0xFF || (key & ((ulong)0xFF << BitsInByte * 7)) >> BitsInByte * 7 == 0xFF));
 
             return key;
         }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.cs
index bdd5f7442671a5..6f523b19b8294c 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.cs
@@ -92,6 +92,8 @@ public JsonClassInfo(Type type, JsonSerializerOptions options)
                 Options);
 
             ClassType = converter.ClassType;
+            JsonNumberHandling? typeNumberHandling = GetNumberHandlingForType(Type);
+
             PropertyInfoForClassInfo = CreatePropertyInfoForClassInfo(Type, runtimeType, converter, Options);
 
             switch (ClassType)
@@ -127,7 +129,7 @@ public JsonClassInfo(Type type, JsonSerializerOptions options)
                                 if (propertyInfo.GetMethod?.IsPublic == true ||
                                     propertyInfo.SetMethod?.IsPublic == true)
                                 {
-                                    CacheMember(currentType, propertyInfo.PropertyType, propertyInfo, cache, ref ignoredMembers);
+                                    CacheMember(currentType, propertyInfo.PropertyType, propertyInfo, typeNumberHandling, cache, ref ignoredMembers);
                                 }
                                 else
                                 {
@@ -153,7 +155,7 @@ public JsonClassInfo(Type type, JsonSerializerOptions options)
                                 {
                                     if (hasJsonInclude || Options.IncludeFields)
                                     {
-                                        CacheMember(currentType, fieldInfo.FieldType, fieldInfo, cache, ref ignoredMembers);
+                                        CacheMember(currentType, fieldInfo.FieldType, fieldInfo, typeNumberHandling, cache, ref ignoredMembers);
                                     }
                                 }
                                 else
@@ -228,10 +230,11 @@ private void CacheMember(
             Type declaringType,
             Type memberType,
             MemberInfo memberInfo,
+            JsonNumberHandling? typeNumberHandling,
             Dictionary<string, JsonPropertyInfo> cache,
             ref Dictionary<string, MemberInfo>? ignoredMembers)
         {
-            JsonPropertyInfo jsonPropertyInfo = AddProperty(memberInfo, memberType, declaringType, Options);
+            JsonPropertyInfo jsonPropertyInfo = AddProperty(memberInfo, memberType, declaringType, typeNumberHandling, Options);
             Debug.Assert(jsonPropertyInfo.NameAsString != null);
 
             string memberName = memberInfo.Name;
@@ -573,5 +576,13 @@ private static bool IsByRefLike(Type type)
             return false;
 #endif
         }
+
+        private static JsonNumberHandling? GetNumberHandlingForType(Type type)
+        {
+            var numberHandlingAttribute =
+                (JsonNumberHandlingAttribute?)JsonSerializerOptions.GetAttributeThatCanHaveMultiple(type, typeof(JsonNumberHandlingAttribute));
+
+            return numberHandlingAttribute?.Handling;
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverter.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverter.cs
index b2c34e14599a1d..f8a000ecfeeacc 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverter.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverter.cs
@@ -44,6 +44,16 @@ internal JsonConverter() { }
         /// </summary>
         internal bool IsValueType { get; set; }
 
+        /// <summary>
+        /// Whether the converter is built-in.
+        /// </summary>
+        internal bool IsInternalConverter { get; set; }
+
+        /// <summary>
+        /// Whether the converter is built-in and handles a number type.
+        /// </summary>
+        internal bool IsInternalConverterForNumberType;
+
         /// <summary>
         /// Loosely-typed ReadCore() that forwards to strongly-typed ReadCore().
         /// </summary>
@@ -76,10 +86,15 @@ internal bool ShouldFlush(Utf8JsonWriter writer, ref WriteStack state)
         internal abstract void WriteWithQuotesAsObject(Utf8JsonWriter writer, object value, JsonSerializerOptions options, ref WriteStack state);
 
         // Whether a type (ClassType.Object) is deserialized using a parameterized constructor.
-        internal virtual bool ConstructorIsParameterized => false;
+        internal virtual bool ConstructorIsParameterized { get; }
 
         internal ConstructorInfo? ConstructorInfo { get; set; }
 
         internal virtual void Initialize(JsonSerializerOptions options) { }
+
+        /// <summary>
+        /// Creates the instance and assigns it to state.Current.ReturnValue.
+        /// </summary>
+        internal virtual void CreateInstanceForReferenceResolver(ref Utf8JsonReader reader, ref ReadStack state, JsonSerializerOptions options) { }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterOfT.ReadCore.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterOfT.ReadCore.cs
index cd6c39c47a27a1..57dfef601c8859 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterOfT.ReadCore.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterOfT.ReadCore.cs
@@ -15,8 +15,7 @@ public partial class JsonConverter<T>
             return ReadCore(ref reader, options, ref state);
         }
 
-        [return: MaybeNull]
-        internal T ReadCore(
+        internal T? ReadCore(
             ref Utf8JsonReader reader,
             JsonSerializerOptions options,
             ref ReadStack state)
@@ -35,7 +34,7 @@ internal T ReadCore(
                             if (state.Current.ReturnValue == null)
                             {
                                 // Avoid returning null for value types.
-                                return default!;
+                                return default;
                             }
 
                             return (T)state.Current.ReturnValue!;
@@ -44,7 +43,7 @@ internal T ReadCore(
                         {
                             // Read more data until we have the full element.
                             state.BytesConsumed += reader.BytesConsumed;
-                            return default!;
+                            return default;
                         }
                     }
                 }
@@ -55,7 +54,7 @@ internal T ReadCore(
                     if (!SingleValueReadWithReadAhead(ClassType.Value, ref reader, ref state))
                     {
                         state.BytesConsumed += reader.BytesConsumed;
-                        return default!;
+                        return default;
                     }
                 }
 
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterOfT.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterOfT.cs
index 52dba1df4bb4dc..e6f7d84d3ea702 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterOfT.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterOfT.cs
@@ -3,7 +3,6 @@
 
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
-using System.Runtime.CompilerServices;
 
 namespace System.Text.Json.Serialization
 {
@@ -69,11 +68,6 @@ internal override sealed JsonParameterInfo CreateJsonParameterInfo()
         /// </summary>
         internal bool CanBeNull { get; }
 
-        /// <summary>
-        /// Is the converter built-in.
-        /// </summary>
-        internal bool IsInternalConverter { get; set; }
-
         // This non-generic API is sealed as it just forwards to the generic version.
         internal sealed override bool TryWriteAsObject(Utf8JsonWriter writer, object? value, JsonSerializerOptions options, ref WriteStack state)
         {
@@ -89,7 +83,7 @@ internal virtual bool OnTryWrite(Utf8JsonWriter writer, T value, JsonSerializerO
         }
 
         // Provide a default implementation for value converters.
-        internal virtual bool OnTryRead(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options, ref ReadStack state, [MaybeNull] out T value)
+        internal virtual bool OnTryRead(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options, ref ReadStack state, out T? value)
         {
             value = Read(ref reader, typeToConvert, options);
             return true;
@@ -105,10 +99,9 @@ internal virtual bool OnTryRead(ref Utf8JsonReader reader, Type typeToConvert, J
         /// <param name="typeToConvert">The <see cref="Type"/> being converted.</param>
         /// <param name="options">The <see cref="JsonSerializerOptions"/> being used.</param>
         /// <returns>The value that was converted.</returns>
-        [return: MaybeNull]
-        public abstract T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options);
+        public abstract T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options);
 
-        internal bool TryRead(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options, ref ReadStack state, [MaybeNull] out T value)
+        internal bool TryRead(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options, ref ReadStack state, out T? value)
         {
             if (ClassType == ClassType.Value)
             {
@@ -131,7 +124,14 @@ internal bool TryRead(ref Utf8JsonReader reader, Type typeToConvert, JsonSeriali
                 // For performance, only perform validation on internal converters on debug builds.
                 if (IsInternalConverter)
                 {
-                    value = Read(ref reader, typeToConvert, options);
+                    if (IsInternalConverterForNumberType && state.Current.NumberHandling != null)
+                    {
+                        value = ReadNumberWithCustomHandling(ref reader, state.Current.NumberHandling.Value);
+                    }
+                    else
+                    {
+                        value = Read(ref reader, typeToConvert, options);
+                    }
                 }
                 else
 #endif
@@ -140,7 +140,15 @@ internal bool TryRead(ref Utf8JsonReader reader, Type typeToConvert, JsonSeriali
                     int originalPropertyDepth = reader.CurrentDepth;
                     long originalPropertyBytesConsumed = reader.BytesConsumed;
 
-                    value = Read(ref reader, typeToConvert, options);
+                    if (IsInternalConverterForNumberType && state.Current.NumberHandling != null)
+                    {
+                        value = ReadNumberWithCustomHandling(ref reader, state.Current.NumberHandling.Value);
+                    }
+                    else
+                    {
+                        value = Read(ref reader, typeToConvert, options);
+                    }
+
                     VerifyRead(
                         originalPropertyTokenType,
                         originalPropertyDepth,
@@ -309,7 +317,15 @@ internal bool TryWrite(Utf8JsonWriter writer, in T value, JsonSerializerOptions
 
                 int originalPropertyDepth = writer.CurrentDepth;
 
-                Write(writer, value, options);
+                if (IsInternalConverterForNumberType && state.Current.NumberHandling != null)
+                {
+                    WriteNumberWithCustomHandling(writer, value, state.Current.NumberHandling.Value);
+                }
+                else
+                {
+                    Write(writer, value, options);
+                }
+
                 VerifyWrite(originalPropertyDepth, writer);
                 return true;
             }
@@ -452,5 +468,11 @@ internal virtual void WriteWithQuotes(Utf8JsonWriter writer, [DisallowNull] T va
 
         internal sealed override void WriteWithQuotesAsObject(Utf8JsonWriter writer, object value, JsonSerializerOptions options, ref WriteStack state)
             => WriteWithQuotes(writer, (T)value, options, ref state);
+
+        internal virtual T ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling handling)
+            => throw new InvalidOperationException();
+
+        internal virtual void WriteNumberWithCustomHandling(Utf8JsonWriter writer, T value, JsonNumberHandling handling)
+            => throw new InvalidOperationException();
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonNumberHandling.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonNumberHandling.cs
new file mode 100644
index 00000000000000..0e791730f84f65
--- /dev/null
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonNumberHandling.cs
@@ -0,0 +1,32 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Text.Json.Serialization
+{
+    /// <summary>
+    /// Determines how <see cref="JsonSerializer"/> handles numbers when serializing and deserializing.
+    /// </summary>
+    [Flags]
+    public enum JsonNumberHandling
+    {
+        /// <summary>
+        /// Numbers will only be read from <see cref="JsonTokenType.Number"/> tokens and will only be written as JSON numbers (without quotes).
+        /// </summary>
+        Strict = 0x0,
+        /// <summary>
+        /// Numbers can be read from <see cref="JsonTokenType.String"/> tokens.
+        /// Does not prevent numbers from being read from <see cref="JsonTokenType.Number"/> token.
+        /// </summary>
+        AllowReadingFromString = 0x1,
+        /// <summary>
+        /// Numbers will be written as JSON strings (with quotes), not as JSON numbers.
+        /// </summary>
+        WriteAsString = 0x2,
+        /// <summary>
+        /// The "NaN", "Infinity", and "-Infinity" <see cref="JsonTokenType.String"/> tokens can be read as
+        /// floating-point constants, and the <see cref="float"/> and <see cref="double"/> values for these
+        /// constants will be written as their corresponding JSON string representations.
+        /// </summary>
+        AllowNamedFloatingPointLiterals = 0x4
+    }
+}
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonParameterInfo.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonParameterInfo.cs
index 0ccdbeeafda1ef..4687107f7f82be 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonParameterInfo.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonParameterInfo.cs
@@ -27,6 +27,8 @@ internal abstract class JsonParameterInfo
         // The name of the parameter as UTF-8 bytes.
         public byte[] NameAsUtf8Bytes { get; private set; } = null!;
 
+        public JsonNumberHandling? NumberHandling { get; private set; }
+
         // The zero-based position of the parameter in the formal parameter list.
         public int Position { get; private set; }
 
@@ -63,6 +65,7 @@ public virtual void Initialize(
             ShouldDeserialize = true;
             ConverterBase = matchingProperty.ConverterBase;
             IgnoreDefaultValuesOnRead = matchingProperty.IgnoreDefaultValuesOnRead;
+            NumberHandling = matchingProperty.NumberHandling;
         }
 
         // Create a parameter that is ignored at run-time. It uses the same type (typeof(sbyte)) to help
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfo.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfo.cs
index 38adc919f9ed04..10b92e26fac964 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfo.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfo.cs
@@ -50,6 +50,14 @@ public static JsonPropertyInfo CreateIgnoredPropertyPlaceholder(MemberInfo membe
 
         public Type DeclaredPropertyType { get; private set; } = null!;
 
+        public virtual void GetPolicies(JsonIgnoreCondition? ignoreCondition, JsonNumberHandling? parentTypeNumberHandling, bool defaultValueIsNull)
+        {
+            DetermineSerializationCapabilities(ignoreCondition);
+            DeterminePropertyName();
+            DetermineIgnoreCondition(ignoreCondition, defaultValueIsNull);
+            DetermineNumberHandling(parentTypeNumberHandling);
+        }
+
         private void DeterminePropertyName()
         {
             if (MemberInfo == null)
@@ -174,6 +182,56 @@ private void DetermineIgnoreCondition(JsonIgnoreCondition? ignoreCondition, bool
 #pragma warning restore CS0618 // IgnoreNullValues is obsolete
         }
 
+        private void DetermineNumberHandling(JsonNumberHandling? parentTypeNumberHandling)
+        {
+            if (IsForClassInfo)
+            {
+                if (parentTypeNumberHandling != null && !ConverterBase.IsInternalConverter)
+                {
+                    ThrowHelper.ThrowInvalidOperationException_NumberHandlingOnPropertyInvalid(this);
+                }
+
+                // Priority 1: Get handling from the type (parent type in this case is the type itself).
+                NumberHandling = parentTypeNumberHandling;
+
+                // Priority 2: Get handling from JsonSerializerOptions instance.
+                if (!NumberHandling.HasValue && Options.NumberHandling != JsonNumberHandling.Strict)
+                {
+                    NumberHandling = Options.NumberHandling;
+                }
+            }
+            else
+            {
+                JsonNumberHandling? handling = null;
+
+                // Priority 1: Get handling from attribute on property or field.
+                if (MemberInfo != null)
+                {
+                    JsonNumberHandlingAttribute? attribute = GetAttribute<JsonNumberHandlingAttribute>(MemberInfo);
+
+                    if (attribute != null &&
+                        !ConverterBase.IsInternalConverterForNumberType &&
+                        ((ClassType.Enumerable | ClassType.Dictionary) & ClassType) == 0)
+                    {
+                        ThrowHelper.ThrowInvalidOperationException_NumberHandlingOnPropertyInvalid(this);
+                    }
+
+                    handling = attribute?.Handling;
+                }
+
+                // Priority 2: Get handling from attribute on parent class type.
+                handling ??= parentTypeNumberHandling;
+
+                // Priority 3: Get handling from JsonSerializerOptions instance.
+                if (!handling.HasValue && Options.NumberHandling != JsonNumberHandling.Strict)
+                {
+                    handling = Options.NumberHandling;
+                }
+
+                NumberHandling = handling;
+            }
+        }
+
         public static TAttribute? GetAttribute<TAttribute>(MemberInfo memberInfo) where TAttribute : Attribute
         {
             return (TAttribute?)memberInfo.GetCustomAttribute(typeof(TAttribute), inherit: false);
@@ -182,13 +240,6 @@ private void DetermineIgnoreCondition(JsonIgnoreCondition? ignoreCondition, bool
         public abstract bool GetMemberAndWriteJson(object obj, ref WriteStack state, Utf8JsonWriter writer);
         public abstract bool GetMemberAndWriteJsonExtensionData(object obj, ref WriteStack state, Utf8JsonWriter writer);
 
-        public virtual void GetPolicies(JsonIgnoreCondition? ignoreCondition, bool defaultValueIsNull)
-        {
-            DetermineSerializationCapabilities(ignoreCondition);
-            DeterminePropertyName();
-            DetermineIgnoreCondition(ignoreCondition, defaultValueIsNull);
-        }
-
         public abstract object? GetValueAsObject(object obj);
 
         public bool HasGetter { get; set; }
@@ -202,6 +253,7 @@ public virtual void Initialize(
             MemberInfo? memberInfo,
             JsonConverter converter,
             JsonIgnoreCondition? ignoreCondition,
+            JsonNumberHandling? parentTypeNumberHandling,
             JsonSerializerOptions options)
         {
             Debug.Assert(converter != null);
@@ -344,5 +396,7 @@ public JsonClassInfo RuntimeClassInfo
         public bool ShouldSerialize { get; private set; }
         public bool ShouldDeserialize { get; private set; }
         public bool IsIgnored { get; private set; }
+
+        public JsonNumberHandling? NumberHandling { get; private set; }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfoOfT.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfoOfT.cs
index 83c5ee116372de..9e24e259542296 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfoOfT.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfoOfT.cs
@@ -28,6 +28,7 @@ public override void Initialize(
             MemberInfo? memberInfo,
             JsonConverter converter,
             JsonIgnoreCondition? ignoreCondition,
+            JsonNumberHandling? parentTypeNumberHandling,
             JsonSerializerOptions options)
         {
             base.Initialize(
@@ -38,6 +39,7 @@ public override void Initialize(
                 memberInfo,
                 converter,
                 ignoreCondition,
+                parentTypeNumberHandling,
                 options);
 
             switch (memberInfo)
@@ -89,7 +91,7 @@ public override void Initialize(
                     }
             }
 
-            GetPolicies(ignoreCondition, defaultValueIsNull: Converter.CanBeNull);
+            GetPolicies(ignoreCondition, parentTypeNumberHandling, defaultValueIsNull: Converter.CanBeNull);
         }
 
         public override JsonConverter ConverterBase
@@ -209,13 +211,13 @@ public override bool ReadJsonAndSetMember(object obj, ref ReadStack state, ref U
 
                 success = true;
             }
-            else if (Converter.CanUseDirectReadOrWrite)
+            else if (Converter.CanUseDirectReadOrWrite && state.Current.NumberHandling == null)
             {
                 if (!isNullToken || !IgnoreDefaultValuesOnRead || !Converter.CanBeNull)
                 {
                     // Optimize for internal converters by avoiding the extra call to TryRead.
-                    T fastvalue = Converter.Read(ref reader, RuntimePropertyType!, Options);
-                    Set!(obj, fastvalue!);
+                    T fastValue = Converter.Read(ref reader, RuntimePropertyType!, Options);
+                    Set!(obj, fastValue!);
                 }
 
                 success = true;
@@ -247,13 +249,13 @@ public override bool ReadJsonAsObject(ref ReadStack state, ref Utf8JsonReader re
                     ThrowHelper.ThrowJsonException_DeserializeUnableToConvertValue(Converter.TypeToConvert);
                 }
 
-                value = default(T)!;
+                value = default(T);
                 success = true;
             }
             else
             {
                 // Optimize for internal converters by avoiding the extra call to TryRead.
-                if (Converter.CanUseDirectReadOrWrite)
+                if (Converter.CanUseDirectReadOrWrite && state.Current.NumberHandling == null)
                 {
                     value = Converter.Read(ref reader, RuntimePropertyType!, Options);
                     success = true;
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonResumableConverterOfT.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonResumableConverterOfT.cs
index fc0ce662715ad7..fbe746d6b12826 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonResumableConverterOfT.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonResumableConverterOfT.cs
@@ -12,8 +12,7 @@ namespace System.Text.Json.Serialization
     /// <typeparam name="T"></typeparam>
     internal abstract class JsonResumableConverter<T> : JsonConverter<T>
     {
-        [return: MaybeNull]
-        public sealed override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        public sealed override T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             // Bridge from resumable to value converters.
             if (options == null)
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandleMetadata.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandleMetadata.cs
index 26a2fb116088f0..2fd7942ddc914e 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandleMetadata.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandleMetadata.cs
@@ -12,18 +12,24 @@ public static partial class JsonSerializer
         internal static readonly byte[] s_idPropertyName
             = new byte[] { (byte)'$', (byte)'i', (byte)'d' };
 
-        internal static ReadOnlySpan<byte> s_refPropertyName
-            => new byte[] { (byte)'$', (byte)'r', (byte)'e', (byte)'f' };
+        internal static readonly byte[] s_refPropertyName
+            = new byte[] { (byte)'$', (byte)'r', (byte)'e', (byte)'f' };
+
+        internal static readonly byte[] s_valuesPropertyName
+            = new byte[] { (byte)'$', (byte)'v', (byte)'a', (byte)'l', (byte)'u', (byte)'e', (byte)'s' };
 
         /// <summary>
         /// Returns true if successful, false is the reader ran out of buffer.
-        /// Sets state.Current.ReturnValue to the $ref target for MetadataRefProperty cases.
+        /// Sets state.Current.ReturnValue to the reference target for $ref cases;
+        /// Sets state.Current.ReturnValue to a new instance for $id cases.
         /// </summary>
-        internal static bool ResolveMetadata(
-            JsonConverter converter,
+        internal static bool ResolveMetadataForJsonObject(
             ref Utf8JsonReader reader,
-            ref ReadStack state)
+            ref ReadStack state,
+            JsonSerializerOptions options)
         {
+            JsonConverter converter = state.Current.JsonClassInfo.PropertyInfoForClassInfo.ConverterBase;
+
             if (state.Current.ObjectState < StackFrameObjectState.ReadAheadNameOrEndObject)
             {
                 // Read the first metadata property name.
@@ -37,18 +43,10 @@ internal static bool ResolveMetadata(
             {
                 if (reader.TokenType != JsonTokenType.PropertyName)
                 {
-                    // An enumerable needs metadata since it starts with StartObject.
-                    if (converter.ClassType == ClassType.Enumerable)
-                    {
-                        ThrowHelper.ThrowJsonException_MetadataPreservedArrayValuesNotFound(converter.TypeToConvert);
-                    }
-
-                    // The reader should have detected other invalid cases.
-                    Debug.Assert(reader.TokenType == JsonTokenType.EndObject);
-
+                    // Since this was an empty object, we are done reading metadata.
+                    state.Current.ObjectState = StackFrameObjectState.PropertyValue;
                     // Skip the read of the first property name, since we already read it above.
                     state.Current.PropertyState = StackFramePropertyState.ReadName;
-
                     return true;
                 }
 
@@ -56,7 +54,8 @@ internal static bool ResolveMetadata(
                 MetadataPropertyName metadata = GetMetadataPropertyName(propertyName);
                 if (metadata == MetadataPropertyName.Id)
                 {
-                    state.Current.JsonPropertyName = propertyName.ToArray();
+                    state.Current.JsonPropertyName = s_idPropertyName;
+
                     if (!converter.CanHaveIdMetadata)
                     {
                         ThrowHelper.ThrowJsonException_MetadataCannotParsePreservedObjectIntoImmutable(converter.TypeToConvert);
@@ -66,7 +65,8 @@ internal static bool ResolveMetadata(
                 }
                 else if (metadata == MetadataPropertyName.Ref)
                 {
-                    state.Current.JsonPropertyName = propertyName.ToArray();
+                    state.Current.JsonPropertyName = s_refPropertyName;
+
                     if (converter.IsValueType)
                     {
                         ThrowHelper.ThrowJsonException_MetadataInvalidReferenceToValueType(converter.TypeToConvert);
@@ -76,27 +76,13 @@ internal static bool ResolveMetadata(
                 }
                 else if (metadata == MetadataPropertyName.Values)
                 {
-                    state.Current.JsonPropertyName = propertyName.ToArray();
-                    if (converter.ClassType == ClassType.Enumerable)
-                    {
-                        ThrowHelper.ThrowJsonException_MetadataMissingIdBeforeValues();
-                    }
-                    else
-                    {
-                        ThrowHelper.ThrowJsonException_MetadataInvalidPropertyWithLeadingDollarSign(propertyName, ref state, reader);
-                    }
+                    ThrowHelper.ThrowJsonException_MetadataInvalidPropertyWithLeadingDollarSign(propertyName, ref state, reader);
                 }
                 else
                 {
                     Debug.Assert(metadata == MetadataPropertyName.NoMetadata);
-
-                    // Having a StartObject without metadata properties is not allowed.
-                    if (converter.ClassType == ClassType.Enumerable)
-                    {
-                        state.Current.JsonPropertyName = propertyName.ToArray();
-                        ThrowHelper.ThrowJsonException_MetadataPreservedArrayInvalidProperty(converter.TypeToConvert, reader);
-                    }
-
+                    // We are done reading metadata, the object didn't contain any.
+                    state.Current.ObjectState = StackFrameObjectState.PropertyValue;
                     // Skip the read of the first property name, since we already read it above.
                     state.Current.PropertyState = StackFramePropertyState.ReadName;
                     return true;
@@ -125,10 +111,11 @@ internal static bool ResolveMetadata(
                     ThrowHelper.ThrowJsonException_MetadataValueWasNotString(reader.TokenType);
                 }
 
-                string key = reader.GetString()!;
+                string referenceId = reader.GetString()!;
 
                 // todo: https://github.com/dotnet/runtime/issues/32354
-                state.Current.ReturnValue = state.ReferenceResolver.ResolveReference(key);
+                state.Current.ReturnValue = state.ReferenceResolver.ResolveReference(referenceId);
+
                 state.Current.ObjectState = StackFrameObjectState.ReadAheadRefEndObject;
             }
             else if (state.Current.ObjectState == StackFrameObjectState.ReadIdValue)
@@ -138,21 +125,157 @@ internal static bool ResolveMetadata(
                     ThrowHelper.ThrowJsonException_MetadataValueWasNotString(reader.TokenType);
                 }
 
-                state.Current.MetadataId = reader.GetString();
+                converter.CreateInstanceForReferenceResolver(ref reader, ref state, options);
+
+                string referenceId = reader.GetString()!;
+                state.ReferenceResolver.AddReference(referenceId, state.Current.ReturnValue!);
+
+                // We are done reading metadata plus we instantiated the object.
+                state.Current.ObjectState = StackFrameObjectState.CreatedObject;
+            }
+
+            // Clear the metadata property name that was set in case of failure on ResolveReference/AddReference.
+            state.Current.JsonPropertyName = null;
+
+            if (state.Current.ObjectState == StackFrameObjectState.ReadAheadRefEndObject)
+            {
+                if (!TryReadAheadMetadataAndSetState(ref reader, ref state, StackFrameObjectState.ReadRefEndObject))
+                {
+                    return false;
+                }
+            }
+
+            if (state.Current.ObjectState == StackFrameObjectState.ReadRefEndObject)
+            {
+                if (reader.TokenType != JsonTokenType.EndObject)
+                {
+                    // We just read a property. The only valid next tokens are EndObject and PropertyName.
+                    Debug.Assert(reader.TokenType == JsonTokenType.PropertyName);
+
+                    ThrowHelper.ThrowJsonException_MetadataReferenceObjectCannotContainOtherProperties(reader.GetSpan(), ref state);
+                }
+            }
+
+            return true;
+        }
+
+        /// <summary>
+        /// Returns true if successful, false is the reader ran out of buffer.
+        /// Sets state.Current.ReturnValue to the reference target for $ref cases;
+        /// Sets state.Current.ReturnValue to a new instance for $id cases.
+        /// </summary>
+        internal static bool ResolveMetadataForJsonArray(
+            ref Utf8JsonReader reader,
+            ref ReadStack state,
+            JsonSerializerOptions options)
+        {
+            JsonConverter converter = state.Current.JsonClassInfo.PropertyInfoForClassInfo.ConverterBase;
+
+            if (state.Current.ObjectState < StackFrameObjectState.ReadAheadNameOrEndObject)
+            {
+                // Read the first metadata property name.
+                if (!TryReadAheadMetadataAndSetState(ref reader, ref state, StackFrameObjectState.ReadNameOrEndObject))
+                {
+                    return false;
+                }
+            }
 
-                if (converter.ClassType == ClassType.Enumerable)
+            if (state.Current.ObjectState == StackFrameObjectState.ReadNameOrEndObject)
+            {
+                if (reader.TokenType != JsonTokenType.PropertyName)
                 {
-                    // Need to Read $values property name.
-                    state.Current.ObjectState = StackFrameObjectState.ReadAheadValuesName;
+                    // The reader should have detected other invalid cases.
+                    Debug.Assert(reader.TokenType == JsonTokenType.EndObject);
+
+                    // An enumerable needs metadata since it starts with StartObject.
+                    ThrowHelper.ThrowJsonException_MetadataPreservedArrayValuesNotFound(ref state, converter.TypeToConvert);
+                }
+
+
+                ReadOnlySpan<byte> propertyName = reader.GetSpan();
+                MetadataPropertyName metadata = GetMetadataPropertyName(propertyName);
+                if (metadata == MetadataPropertyName.Id)
+                {
+                    state.Current.JsonPropertyName = s_idPropertyName;
+
+                    if (!converter.CanHaveIdMetadata)
+                    {
+                        ThrowHelper.ThrowJsonException_MetadataCannotParsePreservedObjectIntoImmutable(converter.TypeToConvert);
+                    }
+
+                    state.Current.ObjectState = StackFrameObjectState.ReadAheadIdValue;
+                }
+                else if (metadata == MetadataPropertyName.Ref)
+                {
+                    state.Current.JsonPropertyName = s_refPropertyName;
+
+                    if (converter.IsValueType)
+                    {
+                        ThrowHelper.ThrowJsonException_MetadataInvalidReferenceToValueType(converter.TypeToConvert);
+                    }
+
+                    state.Current.ObjectState = StackFrameObjectState.ReadAheadRefValue;
+                }
+                else if (metadata == MetadataPropertyName.Values)
+                {
+                    ThrowHelper.ThrowJsonException_MetadataMissingIdBeforeValues(ref state, propertyName);
                 }
                 else
                 {
-                    // We are done reading metadata.
-                    state.Current.ObjectState = StackFrameObjectState.PropertyValue;
-                    return true;
+                    Debug.Assert(metadata == MetadataPropertyName.NoMetadata);
+
+                    // Having a StartObject without metadata properties is not allowed.
+                    ThrowHelper.ThrowJsonException_MetadataPreservedArrayInvalidProperty(ref state, converter.TypeToConvert, reader);
                 }
             }
 
+            if (state.Current.ObjectState == StackFrameObjectState.ReadAheadRefValue)
+            {
+                if (!TryReadAheadMetadataAndSetState(ref reader, ref state, StackFrameObjectState.ReadRefValue))
+                {
+                    return false;
+                }
+            }
+            else if (state.Current.ObjectState == StackFrameObjectState.ReadAheadIdValue)
+            {
+                if (!TryReadAheadMetadataAndSetState(ref reader, ref state, StackFrameObjectState.ReadIdValue))
+                {
+                    return false;
+                }
+            }
+
+            if (state.Current.ObjectState == StackFrameObjectState.ReadRefValue)
+            {
+                if (reader.TokenType != JsonTokenType.String)
+                {
+                    ThrowHelper.ThrowJsonException_MetadataValueWasNotString(reader.TokenType);
+                }
+
+                string key = reader.GetString()!;
+
+                // todo: https://github.com/dotnet/runtime/issues/32354
+                state.Current.ReturnValue = state.ReferenceResolver.ResolveReference(key);
+                state.Current.ObjectState = StackFrameObjectState.ReadAheadRefEndObject;
+            }
+            else if (state.Current.ObjectState == StackFrameObjectState.ReadIdValue)
+            {
+                if (reader.TokenType != JsonTokenType.String)
+                {
+                    ThrowHelper.ThrowJsonException_MetadataValueWasNotString(reader.TokenType);
+                }
+
+                converter.CreateInstanceForReferenceResolver(ref reader, ref state, options);
+
+                string referenceId = reader.GetString()!;
+                state.ReferenceResolver.AddReference(referenceId, state.Current.ReturnValue!);
+
+                // Need to Read $values property name.
+                state.Current.ObjectState = StackFrameObjectState.ReadAheadValuesName;
+            }
+
+            // Clear the metadata property name that was set in case of failure on ResolverReference/AddReference.
+            state.Current.JsonPropertyName = null;
+
             if (state.Current.ObjectState == StackFrameObjectState.ReadAheadRefEndObject)
             {
                 if (!TryReadAheadMetadataAndSetState(ref reader, ref state, StackFrameObjectState.ReadRefEndObject))
@@ -186,21 +309,19 @@ internal static bool ResolveMetadata(
             {
                 if (reader.TokenType != JsonTokenType.PropertyName)
                 {
-                    // Missing $values, JSON path should point to the property's object.
-                    state.Current.JsonPropertyName = null;
-                    ThrowHelper.ThrowJsonException_MetadataPreservedArrayValuesNotFound(converter.TypeToConvert);
+                    ThrowHelper.ThrowJsonException_MetadataPreservedArrayValuesNotFound(ref state, converter.TypeToConvert);
                 }
 
                 ReadOnlySpan<byte> propertyName = reader.GetSpan();
 
-                // Remember the property in case we get an exception.
-                state.Current.JsonPropertyName = propertyName.ToArray();
-
                 if (GetMetadataPropertyName(propertyName) != MetadataPropertyName.Values)
                 {
-                    ThrowHelper.ThrowJsonException_MetadataPreservedArrayInvalidProperty(converter.TypeToConvert, reader);
+                    ThrowHelper.ThrowJsonException_MetadataPreservedArrayInvalidProperty(ref state, converter.TypeToConvert, reader);
                 }
 
+                // Remember the property in case we get an exception in one of the array elements.
+                state.Current.JsonPropertyName = s_valuesPropertyName;
+
                 state.Current.ObjectState = StackFrameObjectState.ReadAheadValuesStartArray;
             }
 
@@ -218,8 +339,8 @@ internal static bool ResolveMetadata(
                 {
                     ThrowHelper.ThrowJsonException_MetadataValuesInvalidToken(reader.TokenType);
                 }
-
-                state.Current.ObjectState = StackFrameObjectState.PropertyValue;
+                state.Current.ValidateEndTokenOnArray = true;
+                state.Current.ObjectState = StackFrameObjectState.CreatedObject;
             }
 
             return true;
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandlePropertyName.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandlePropertyName.cs
index 04bb332121f9fa..17a0669b2a4ab2 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandlePropertyName.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandlePropertyName.cs
@@ -55,6 +55,7 @@ internal static JsonPropertyInfo LookupProperty(
             }
 
             state.Current.JsonPropertyInfo = jsonPropertyInfo;
+            state.Current.NumberHandling = jsonPropertyInfo.NumberHandling;
             return jsonPropertyInfo;
         }
 
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Helpers.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Helpers.cs
index 4e7946872454c4..8b4909ad4ca1a0 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Helpers.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Helpers.cs
@@ -10,10 +10,10 @@ namespace System.Text.Json
     public static partial class JsonSerializer
     {
         // Members accessed by the serializer when deserializing.
-        private const DynamicallyAccessedMemberTypes MembersAccessedOnRead = DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.PublicProperties;
+        private const DynamicallyAccessedMemberTypes MembersAccessedOnRead =
+            DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.PublicFields;
 
-        [return: MaybeNull]
-        private static TValue ReadCore<TValue>(ref Utf8JsonReader reader, Type returnType, JsonSerializerOptions options)
+        private static TValue? ReadCore<TValue>(ref Utf8JsonReader reader, Type returnType, JsonSerializerOptions options)
         {
             ReadStack state = default;
             state.Initialize(returnType, options, supportContinuation: false);
@@ -21,8 +21,7 @@ private static TValue ReadCore<TValue>(ref Utf8JsonReader reader, Type returnTyp
             return ReadCore<TValue>(jsonConverter, ref reader, options, ref state);
         }
 
-        [return: MaybeNull]
-        private static TValue ReadCore<TValue>(JsonConverter jsonConverter, ref Utf8JsonReader reader, JsonSerializerOptions options, ref ReadStack state)
+        private static TValue? ReadCore<TValue>(JsonConverter jsonConverter, ref Utf8JsonReader reader, JsonSerializerOptions options, ref ReadStack state)
         {
             if (jsonConverter is JsonConverter<TValue> converter)
             {
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Span.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Span.cs
index 974ed2a0ca75af..af9dd0e819c18e 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Span.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Span.cs
@@ -22,8 +22,7 @@ public static partial class JsonSerializer
         /// There is no compatible <see cref="System.Text.Json.Serialization.JsonConverter"/>
         /// for <typeparamref name="TValue"/> or its serializable members.
         /// </exception>
-        [return: MaybeNull]
-        public static TValue Deserialize<[DynamicallyAccessedMembers(MembersAccessedOnRead)] TValue>(ReadOnlySpan<byte> utf8Json, JsonSerializerOptions? options = null)
+        public static TValue? Deserialize<[DynamicallyAccessedMembers(MembersAccessedOnRead)] TValue>(ReadOnlySpan<byte> utf8Json, JsonSerializerOptions? options = null)
         {
             if (options == null)
             {
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Stream.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Stream.cs
index 24d1421aa38730..b0c471cfcbd004 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Stream.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Stream.cs
@@ -35,7 +35,7 @@ public static partial class JsonSerializer
         /// There is no compatible <see cref="System.Text.Json.Serialization.JsonConverter"/>
         /// for <typeparamref name="TValue"/> or its serializable members.
         /// </exception>
-        public static ValueTask<TValue> DeserializeAsync<[DynamicallyAccessedMembers(MembersAccessedOnRead)] TValue>(
+        public static ValueTask<TValue?> DeserializeAsync<[DynamicallyAccessedMembers(MembersAccessedOnRead)] TValue>(
             Stream utf8Json,
             JsonSerializerOptions? options = null,
             CancellationToken cancellationToken = default)
@@ -86,7 +86,7 @@ public static partial class JsonSerializer
             return ReadAsync<object?>(utf8Json, returnType, options, cancellationToken);
         }
 
-        private static async ValueTask<TValue> ReadAsync<TValue>(
+        private static async ValueTask<TValue?> ReadAsync<TValue>(
             Stream utf8Json,
             Type returnType,
             JsonSerializerOptions? options,
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.String.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.String.cs
index bd9edb83e68f37..af1f35da221431 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.String.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.String.cs
@@ -34,8 +34,7 @@ public static partial class JsonSerializer
         /// <remarks>Using a <see cref="string"/> is not as efficient as using the
         /// UTF-8 methods since the implementation natively uses UTF-8.
         /// </remarks>
-        [return: MaybeNull]
-        public static TValue Deserialize<[DynamicallyAccessedMembers(MembersAccessedOnRead)] TValue>(string json, JsonSerializerOptions? options = null)
+        public static TValue? Deserialize<[DynamicallyAccessedMembers(MembersAccessedOnRead)] TValue>(string json, JsonSerializerOptions? options = null)
         {
             if (json == null)
             {
@@ -84,8 +83,7 @@ public static partial class JsonSerializer
             return value;
         }
 
-        [return: MaybeNull]
-        private static TValue Deserialize<TValue>(string json, Type returnType, JsonSerializerOptions? options)
+        private static TValue? Deserialize<TValue>(string json, Type returnType, JsonSerializerOptions? options)
         {
             const long ArrayPoolMaxSizeBeforeUsingNormalAlloc = 1024 * 1024;
 
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Utf8JsonReader.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Utf8JsonReader.cs
index 9daac01bd1b3ad..4b424581307ecd 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Utf8JsonReader.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Utf8JsonReader.cs
@@ -52,8 +52,7 @@ public static partial class JsonSerializer
         ///     Hence, <see cref="JsonReaderOptions.AllowTrailingCommas"/>, <see cref="JsonReaderOptions.MaxDepth"/>, <see cref="JsonReaderOptions.CommentHandling"/> are used while reading.
         ///   </para>
         /// </remarks>
-        [return: MaybeNull]
-        public static TValue Deserialize<[DynamicallyAccessedMembers(MembersAccessedOnRead)] TValue>(ref Utf8JsonReader reader, JsonSerializerOptions? options = null)
+        public static TValue? Deserialize<[DynamicallyAccessedMembers(MembersAccessedOnRead)] TValue>(ref Utf8JsonReader reader, JsonSerializerOptions? options = null)
         {
             if (options == null)
             {
@@ -137,8 +136,7 @@ private static void CheckSupportedOptions(JsonReaderOptions readerOptions, strin
             }
         }
 
-        [return: MaybeNull]
-        private static TValue ReadValueCore<TValue>(JsonSerializerOptions options, ref Utf8JsonReader reader, ref ReadStack state)
+        private static TValue? ReadValueCore<TValue>(JsonSerializerOptions options, ref Utf8JsonReader reader, ref ReadStack state)
         {
             JsonReaderState readerState = reader.CurrentState;
             CheckSupportedOptions(readerState.Options, nameof(reader));
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.HandleMetadata.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.HandleMetadata.cs
index dccf453a2c175f..45c1462ea68f3a 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.HandleMetadata.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.HandleMetadata.cs
@@ -28,7 +28,6 @@ internal static MetadataPropertyName WriteReferenceForObject(
             }
             else
             {
-
                 string referenceId = state.ReferenceResolver.GetReference(currentValue, out bool alreadyExists);
                 Debug.Assert(referenceId != null);
 
@@ -65,10 +64,10 @@ internal static MetadataPropertyName WriteReferenceForCollection(
             else
             {
                 string referenceId = state.ReferenceResolver.GetReference(currentValue, out bool alreadyExists);
+                Debug.Assert(referenceId != null);
 
                 if (alreadyExists)
                 {
-                    Debug.Assert(referenceId != null);
                     writer.WriteStartObject();
                     writer.WriteString(s_metadataRef, referenceId);
                     writer.WriteEndObject();
@@ -76,7 +75,6 @@ internal static MetadataPropertyName WriteReferenceForCollection(
                 }
                 else
                 {
-                    Debug.Assert(referenceId != null);
                     writer.WriteStartObject();
                     writer.WriteString(s_metadataId, referenceId);
                     writer.WriteStartArray(s_metadataValues);
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.Helpers.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.Helpers.cs
index 96c33a06255a34..d23528f786f883 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.Helpers.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.Helpers.cs
@@ -10,7 +10,7 @@ namespace System.Text.Json
     public static partial class JsonSerializer
     {
         // Members accessed by the serializer when serializing.
-        private const DynamicallyAccessedMemberTypes MembersAccessedOnWrite = DynamicallyAccessedMemberTypes.PublicProperties;
+        private const DynamicallyAccessedMemberTypes MembersAccessedOnWrite = DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.PublicFields;
 
         private static void WriteCore<TValue>(
             Utf8JsonWriter writer,
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.cs
new file mode 100644
index 00000000000000..8ddd013597fe12
--- /dev/null
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.cs
@@ -0,0 +1,15 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Text.Json.Serialization;
+
+namespace System.Text.Json
+{
+    public static partial class JsonSerializer
+    {
+        internal static bool IsValidNumberHandlingValue(JsonNumberHandling handling)
+        {
+            return JsonHelpers.IsInRangeInclusive((int)handling, 0, 7);
+        }
+    }
+}
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs
index 0796280c369dcd..860b49315a404d 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs
@@ -325,7 +325,7 @@ private JsonConverter GetConverterFromAttribute(JsonConverterAttribute converter
             return GetAttributeThatCanHaveMultiple(attributeType, classType, memberInfo, attributes);
         }
 
-        private static Attribute? GetAttributeThatCanHaveMultiple(Type classType, Type attributeType)
+        internal static Attribute? GetAttributeThatCanHaveMultiple(Type classType, Type attributeType)
         {
             object[] attributes = classType.GetCustomAttributes(attributeType, inherit: false);
             return GetAttributeThatCanHaveMultiple(attributeType, classType, null, attributes);
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs
index e26eb9e0176aab..4217f61a61fc84 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs
@@ -33,6 +33,7 @@ public sealed partial class JsonSerializerOptions
         private ReferenceHandler? _referenceHandler;
         private JavaScriptEncoder? _encoder;
         private JsonIgnoreCondition _defaultIgnoreCondition;
+        private JsonNumberHandling _numberHandling;
 
         private int _defaultBufferSize = BufferSizeDefault;
         private int _maxDepth;
@@ -74,6 +75,7 @@ public JsonSerializerOptions(JsonSerializerOptions options)
             _referenceHandler = options._referenceHandler;
             _encoder = options._encoder;
             _defaultIgnoreCondition = options._defaultIgnoreCondition;
+            _numberHandling = options._numberHandling;
 
             _defaultBufferSize = options._defaultBufferSize;
             _maxDepth = options._maxDepth;
@@ -262,6 +264,27 @@ public JsonIgnoreCondition DefaultIgnoreCondition
             }
         }
 
+        /// <summary>
+        /// Specifies how number types should be handled when serializing or deserializing.
+        /// </summary>
+        /// <exception cref="InvalidOperationException">
+        /// Thrown if this property is set after serialization or deserialization has occurred.
+        /// </exception>
+        public JsonNumberHandling NumberHandling
+        {
+            get => _numberHandling;
+            set
+            {
+                VerifyMutable();
+
+                if (!JsonSerializer.IsValidNumberHandlingValue(value))
+                {
+                    throw new ArgumentOutOfRangeException(nameof(value));
+                }
+                _numberHandling = value;
+            }
+        }
+
         /// <summary>
         /// Determines whether read-only properties are ignored during serialization.
         /// A property is read-only if it contains a public getter but not a public setter.
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReadStack.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReadStack.cs
index c3b1ba7c38a74e..ac03e3b6adba67 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReadStack.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReadStack.cs
@@ -87,6 +87,8 @@ public void Initialize(Type type, JsonSerializerOptions options, bool supportCon
             // The initial JsonPropertyInfo will be used to obtain the converter.
             Current.JsonPropertyInfo = jsonClassInfo.PropertyInfoForClassInfo;
 
+            Current.NumberHandling = Current.JsonPropertyInfo.NumberHandling;
+
             bool preserveReferences = options.ReferenceHandler != null;
             if (preserveReferences)
             {
@@ -109,6 +111,8 @@ public void Push()
                 else
                 {
                     JsonClassInfo jsonClassInfo;
+                    JsonNumberHandling? numberHandling = Current.NumberHandling;
+
                     if (Current.JsonClassInfo.ClassType == ClassType.Object)
                     {
                         if (Current.JsonPropertyInfo != null)
@@ -120,13 +124,14 @@ public void Push()
                             jsonClassInfo = Current.CtorArgumentState!.JsonParameterInfo!.RuntimeClassInfo;
                         }
                     }
-                    else if ((Current.JsonClassInfo.ClassType & (ClassType.Value | ClassType.NewValue)) != 0)
+                    else if (((ClassType.Value | ClassType.NewValue) & Current.JsonClassInfo.ClassType) != 0)
                     {
                         // Although ClassType.Value doesn't push, a custom custom converter may re-enter serialization.
                         jsonClassInfo = Current.JsonPropertyInfo!.RuntimeClassInfo;
                     }
                     else
                     {
+                        Debug.Assert(((ClassType.Enumerable | ClassType.Dictionary) & Current.JsonClassInfo.ClassType) != 0);
                         jsonClassInfo = Current.JsonClassInfo.ElementClassInfo!;
                     }
 
@@ -135,6 +140,8 @@ public void Push()
 
                     Current.JsonClassInfo = jsonClassInfo;
                     Current.JsonPropertyInfo = jsonClassInfo.PropertyInfoForClassInfo;
+                    // Allow number handling on property to win over handling on type.
+                    Current.NumberHandling = numberHandling ?? Current.JsonPropertyInfo.NumberHandling;
                 }
             }
             else if (_continuationCount == 1)
@@ -159,7 +166,7 @@ public void Push()
                 }
             }
 
-            SetConstrutorArgumentState();
+            SetConstructorArgumentState();
         }
 
         public void Pop(bool success)
@@ -210,7 +217,7 @@ public void Pop(bool success)
                 Current = _previous[--_count -1];
             }
 
-            SetConstrutorArgumentState();
+            SetConstructorArgumentState();
         }
 
         // Return a JSONPath using simple dot-notation when possible. When special characters are present, bracket-notation is used:
@@ -328,7 +335,7 @@ static void AppendPropertyName(StringBuilder sb, string? propertyName)
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private void SetConstrutorArgumentState()
+        private void SetConstructorArgumentState()
         {
             if (Current.JsonClassInfo.ParameterCount > 0)
             {
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReadStackFrame.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReadStackFrame.cs
index b0c333568bda35..5a35fa5a256b7a 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReadStackFrame.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReadStackFrame.cs
@@ -3,6 +3,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Text.Json.Serialization;
 
 namespace System.Text.Json
 {
@@ -32,8 +33,8 @@ internal struct ReadStackFrame
         public JsonClassInfo JsonClassInfo;
         public StackFrameObjectState ObjectState; // State tracking the current object.
 
-        // Preserve reference.
-        public string? MetadataId;
+        // Validate EndObject token on array with preserve semantics.
+        public bool ValidateEndTokenOnArray;
 
         // For performance, we order the properties by the first deserialize and PropertyIndex helps find the right slot quicker.
         public int PropertyIndex;
@@ -43,6 +44,9 @@ internal struct ReadStackFrame
         public int CtorArgumentStateIndex;
         public ArgumentState? CtorArgumentState;
 
+        // Whether to use custom number handling.
+        public JsonNumberHandling? NumberHandling;
+
         public void EndConstructorParameter()
         {
             CtorArgumentState!.JsonParameterInfo = null;
@@ -56,9 +60,10 @@ public void EndProperty()
             JsonPropertyName = null;
             JsonPropertyNameAsString = null;
             PropertyState = StackFramePropertyState.None;
-            MetadataId = null;
+            ValidateEndTokenOnArray = false;
 
             // No need to clear these since they are overwritten each time:
+            //  NumberHandling
             //  UseExtensionProperty
         }
 
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStack.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStack.cs
index ec90b0c75e0218..e3378711eb1eb1 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStack.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStack.cs
@@ -68,12 +68,10 @@ private void AddCurrent()
         public JsonConverter Initialize(Type type, JsonSerializerOptions options, bool supportContinuation)
         {
             JsonClassInfo jsonClassInfo = options.GetOrAddClassForRootType(type);
-            Current.JsonClassInfo = jsonClassInfo;
 
-            if ((jsonClassInfo.ClassType & (ClassType.Enumerable | ClassType.Dictionary)) == 0)
-            {
-                Current.DeclaredJsonPropertyInfo = jsonClassInfo.PropertyInfoForClassInfo;
-            }
+            Current.JsonClassInfo = jsonClassInfo;
+            Current.DeclaredJsonPropertyInfo = jsonClassInfo.PropertyInfoForClassInfo;
+            Current.NumberHandling = Current.DeclaredJsonPropertyInfo.NumberHandling;
 
             if (options.ReferenceHandler != null)
             {
@@ -97,12 +95,15 @@ public void Push()
                 else
                 {
                     JsonClassInfo jsonClassInfo = Current.GetPolymorphicJsonPropertyInfo().RuntimeClassInfo;
+                    JsonNumberHandling? numberHandling = Current.NumberHandling;
 
                     AddCurrent();
                     Current.Reset();
 
                     Current.JsonClassInfo = jsonClassInfo;
                     Current.DeclaredJsonPropertyInfo = jsonClassInfo.PropertyInfoForClassInfo;
+                    // Allow number handling on property to win over handling on type.
+                    Current.NumberHandling = numberHandling ?? Current.DeclaredJsonPropertyInfo.NumberHandling;
                 }
             }
             else if (_continuationCount == 1)
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStackFrame.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStackFrame.cs
index 9689568809b24d..d5a671dd4794f3 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStackFrame.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/WriteStackFrame.cs
@@ -68,6 +68,9 @@ internal struct WriteStackFrame
         /// </remarks>
         public JsonPropertyInfo? PolymorphicJsonPropertyInfo;
 
+        // Whether to use custom number handling.
+        public JsonNumberHandling? NumberHandling;
+
         public void EndDictionaryElement()
         {
             PropertyState = StackFramePropertyState.None;
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs b/src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs
index 2194ab03fab145..b9bd641a9cc22d 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Buffers;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
@@ -224,6 +225,28 @@ public static void ThrowInvalidOperationException_IgnoreConditionOnValueTypeInva
             throw new InvalidOperationException(SR.Format(SR.IgnoreConditionOnValueTypeInvalid, memberInfo.Name, memberInfo.DeclaringType));
         }
 
+        [DoesNotReturn]
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        public static void ThrowInvalidOperationException_NumberHandlingOnPropertyInvalid(JsonPropertyInfo jsonPropertyInfo)
+        {
+            MemberInfo? memberInfo = jsonPropertyInfo.MemberInfo;
+
+            if (!jsonPropertyInfo.ConverterBase.IsInternalConverter)
+            {
+                throw new InvalidOperationException(SR.Format(
+                    SR.NumberHandlingConverterMustBeBuiltIn,
+                    jsonPropertyInfo.ConverterBase.GetType(),
+                    jsonPropertyInfo.IsForClassInfo ? jsonPropertyInfo.DeclaredPropertyType : memberInfo!.DeclaringType));
+            }
+
+            // This exception is only thrown for object properties.
+            Debug.Assert(!jsonPropertyInfo.IsForClassInfo && memberInfo != null);
+            throw new InvalidOperationException(SR.Format(
+                SR.NumberHandlingOnPropertyTypeMustBeNumberOrCollection,
+                memberInfo.Name,
+                memberInfo.DeclaringType));
+        }
+
         [DoesNotReturn]
         [MethodImpl(MethodImplOptions.NoInlining)]
         public static void ThrowNotSupportedException_ObjectWithParameterizedCtorRefMetadataNotHonored(
@@ -506,8 +529,9 @@ public static void ThrowJsonException_MetadataIdIsNotFirstProperty(ReadOnlySpan<
 
         [DoesNotReturn]
         [MethodImpl(MethodImplOptions.NoInlining)]
-        public static void ThrowJsonException_MetadataMissingIdBeforeValues()
+        public static void ThrowJsonException_MetadataMissingIdBeforeValues(ref ReadStack state, ReadOnlySpan<byte> propertyName)
         {
+            state.Current.JsonPropertyName = propertyName.ToArray();
             ThrowJsonException(SR.MetadataPreservedArrayPropertyNotFound);
         }
 
@@ -544,19 +568,23 @@ public static void ThrowJsonException_MetadataInvalidReferenceToValueType(Type p
 
         [DoesNotReturn]
         [MethodImpl(MethodImplOptions.NoInlining)]
-        public static void ThrowJsonException_MetadataPreservedArrayInvalidProperty(Type propertyType, in Utf8JsonReader reader)
+        public static void ThrowJsonException_MetadataPreservedArrayInvalidProperty(ref ReadStack state, Type propertyType, in Utf8JsonReader reader)
         {
-            string propertyName = reader.GetString()!;
+            state.Current.JsonPropertyName = reader.HasValueSequence ? reader.ValueSequence.ToArray() : reader.ValueSpan.ToArray();
+            string propertyNameAsString = reader.GetString()!;
 
             ThrowJsonException(SR.Format(SR.MetadataPreservedArrayFailed,
-                SR.Format(SR.MetadataPreservedArrayInvalidProperty, propertyName),
+                SR.Format(SR.MetadataPreservedArrayInvalidProperty, propertyNameAsString),
                 SR.Format(SR.DeserializeUnableToConvertValue, propertyType)));
         }
 
         [DoesNotReturn]
         [MethodImpl(MethodImplOptions.NoInlining)]
-        public static void ThrowJsonException_MetadataPreservedArrayValuesNotFound(Type propertyType)
+        public static void ThrowJsonException_MetadataPreservedArrayValuesNotFound(ref ReadStack state, Type propertyType)
         {
+            // Missing $values, JSON path should point to the property's object.
+            state.Current.JsonPropertyName = null;
+
             ThrowJsonException(SR.Format(SR.MetadataPreservedArrayFailed,
                 SR.MetadataPreservedArrayPropertyNotFound,
                 SR.Format(SR.DeserializeUnableToConvertValue, propertyType)));
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Decimal.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Decimal.cs
index ca5b059be50bbd..a30af2e6546ad1 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Decimal.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Decimal.cs
@@ -93,5 +93,13 @@ private void WriteNumberValueIndented(decimal value)
             Debug.Assert(result);
             BytesPending += bytesWritten;
         }
+
+        internal void WriteNumberValueAsString(decimal value)
+        {
+            Span<byte> utf8Number = stackalloc byte[JsonConstants.MaximumFormatDecimalLength];
+            bool result = Utf8Formatter.TryFormat(value, utf8Number, out int bytesWritten);
+            Debug.Assert(result);
+            WriteNumberValueAsStringUnescaped(utf8Number.Slice(0, bytesWritten));
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Double.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Double.cs
index cf8732bc44ec8a..f8a46a31468ca9 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Double.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Double.cs
@@ -143,5 +143,33 @@ private static bool TryFormatDouble(double value, Span<byte> destination, out in
             }
 #endif
         }
+
+        internal void WriteNumberValueAsString(double value)
+        {
+            Span<byte> utf8Number = stackalloc byte[JsonConstants.MaximumFormatDoubleLength];
+            bool result = TryFormatDouble(value, utf8Number, out int bytesWritten);
+            Debug.Assert(result);
+            WriteNumberValueAsStringUnescaped(utf8Number.Slice(0, bytesWritten));
+        }
+
+        internal void WriteFloatingPointConstant(double value)
+        {
+            if (double.IsNaN(value))
+            {
+                WriteNumberValueAsStringUnescaped(JsonConstants.NaNValue);
+            }
+            else if (double.IsPositiveInfinity(value))
+            {
+                WriteNumberValueAsStringUnescaped(JsonConstants.PositiveInfinityValue);
+            }
+            else if (double.IsNegativeInfinity(value))
+            {
+                WriteNumberValueAsStringUnescaped(JsonConstants.NegativeInfinityValue);
+            }
+            else
+            {
+                WriteNumberValue(value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Float.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Float.cs
index f120a09373c479..2f046d872f6972 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Float.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Float.cs
@@ -143,5 +143,33 @@ private static bool TryFormatSingle(float value, Span<byte> destination, out int
             }
 #endif
         }
+
+        internal void WriteNumberValueAsString(float value)
+        {
+            Span<byte> utf8Number = stackalloc byte[JsonConstants.MaximumFormatSingleLength];
+            bool result = TryFormatSingle(value, utf8Number, out int bytesWritten);
+            Debug.Assert(result);
+            WriteNumberValueAsStringUnescaped(utf8Number.Slice(0, bytesWritten));
+        }
+
+        internal void WriteFloatingPointConstant(float value)
+        {
+            if (float.IsNaN(value))
+            {
+                WriteNumberValueAsStringUnescaped(JsonConstants.NaNValue);
+            }
+            else if (float.IsPositiveInfinity(value))
+            {
+                WriteNumberValueAsStringUnescaped(JsonConstants.PositiveInfinityValue);
+            }
+            else if (float.IsNegativeInfinity(value))
+            {
+                WriteNumberValueAsStringUnescaped(JsonConstants.NegativeInfinityValue);
+            }
+            else
+            {
+                WriteNumberValue(value);
+            }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.SignedNumber.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.SignedNumber.cs
index 957573ddb7a7f4..2d6120a6a87680 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.SignedNumber.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.SignedNumber.cs
@@ -106,5 +106,13 @@ private void WriteNumberValueIndented(long value)
             Debug.Assert(result);
             BytesPending += bytesWritten;
         }
+
+        internal void WriteNumberValueAsString(long value)
+        {
+            Span<byte> utf8Number = stackalloc byte[JsonConstants.MaximumFormatInt64Length];
+            bool result = Utf8Formatter.TryFormat(value, utf8Number, out int bytesWritten);
+            Debug.Assert(result);
+            WriteNumberValueAsStringUnescaped(utf8Number.Slice(0, bytesWritten));
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.String.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.String.cs
index c86a8af22f1628..15cb0b8d1af5ec 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.String.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.String.cs
@@ -349,5 +349,19 @@ private void WriteStringEscapeValue(ReadOnlySpan<byte> utf8Value, int firstEscap
                 ArrayPool<byte>.Shared.Return(valueArray);
             }
         }
+
+        /// <summary>
+        /// Writes a number as a JSON string. The string value is not escaped.
+        /// </summary>
+        /// <param name="utf8Value"></param>
+        internal void WriteNumberValueAsStringUnescaped(ReadOnlySpan<byte> utf8Value)
+        {
+            // The value has been validated prior to calling this method.
+
+            WriteStringByOptions(utf8Value);
+
+            SetFlagToAddListSeparatorBeforeNextItem();
+            _tokenType = JsonTokenType.String;
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.UnsignedNumber.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.UnsignedNumber.cs
index 2c15441d432593..d3cf96947db468 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.UnsignedNumber.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.UnsignedNumber.cs
@@ -108,5 +108,13 @@ private void WriteNumberValueIndented(ulong value)
             Debug.Assert(result);
             BytesPending += bytesWritten;
         }
+
+        internal void WriteNumberValueAsString(ulong value)
+        {
+            Span<byte> utf8Number = stackalloc byte[JsonConstants.MaximumFormatUInt64Length];
+            bool result = Utf8Formatter.TryFormat(value, utf8Number, out int bytesWritten);
+            Debug.Assert(result);
+            WriteNumberValueAsStringUnescaped(utf8Number.Slice(0, bytesWritten));
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/tests/JsonNumberTestData.cs b/src/libraries/System.Text.Json/tests/JsonNumberTestData.cs
index d07064a3e487be..384488485c9806 100644
--- a/src/libraries/System.Text.Json/tests/JsonNumberTestData.cs
+++ b/src/libraries/System.Text.Json/tests/JsonNumberTestData.cs
@@ -3,8 +3,7 @@
 
 using System.Collections.Generic;
 using System.Globalization;
-using System.IO;
-using Newtonsoft.Json;
+using System.Linq;
 
 namespace System.Text.Json.Tests
 {
@@ -21,6 +20,19 @@ internal class JsonNumberTestData
         public static List<float> Floats { get; set; }
         public static List<double> Doubles { get; set; }
         public static List<decimal> Decimals { get; set; }
+
+        public static List<byte?> NullableBytes { get; set; }
+        public static List<sbyte?> NullableSBytes { get; set; }
+        public static List<short?> NullableShorts { get; set; }
+        public static List<int?> NullableInts { get; set; }
+        public static List<long?> NullableLongs { get; set; }
+        public static List<ushort?> NullableUShorts { get; set; }
+        public static List<uint?> NullableUInts { get; set; }
+        public static List<ulong?> NullableULongs { get; set; }
+        public static List<float?> NullableFloats { get; set; }
+        public static List<double?> NullableDoubles { get; set; }
+        public static List<decimal?> NullableDecimals { get; set; }
+
         public static byte[] JsonData { get; set; }
 
         static JsonNumberTestData()
@@ -295,6 +307,19 @@ static JsonNumberTestData()
             builder.Append("\"intEnd\": 0}");
             #endregion
 
+            // Make collections of nullable numbers.
+            NullableBytes = new List<byte?>(Bytes.Select(num => (byte?)num));
+            NullableSBytes = new List<sbyte?>(SBytes.Select(num => (sbyte?)num));
+            NullableShorts = new List<short?>(Shorts.Select(num => (short?)num));
+            NullableInts = new List<int?>(Ints.Select(num => (int?)num));
+            NullableLongs = new List<long?>(Longs.Select(num => (long?)num));
+            NullableUShorts = new List<ushort?>(UShorts.Select(num => (ushort?)num));
+            NullableUInts = new List<uint?>(UInts.Select(num => (uint?)num));
+            NullableULongs = new List<ulong?>(ULongs.Select(num => (ulong?)num));
+            NullableFloats = new List<float?>(Floats.Select(num => (float?)num));
+            NullableDoubles = new List<double?>(Doubles.Select(num => (double?)num));
+            NullableDecimals = new List<decimal?>(Decimals.Select(num => (decimal?)num));
+
             string jsonString = builder.ToString();
             JsonData = Encoding.UTF8.GetBytes(jsonString);
         }
diff --git a/src/libraries/System.Text.Json/tests/Serialization/Array.ReadTests.cs b/src/libraries/System.Text.Json/tests/Serialization/Array.ReadTests.cs
index 780c8c1e4a4067..6f917532323bd7 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/Array.ReadTests.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/Array.ReadTests.cs
@@ -616,8 +616,7 @@ static void TestRoundTrip(ClassWithNonNullEnumerableGetters obj)
             Assert.Equal(0, obj.MyImmutableList.Count);
             TestRoundTrip(obj);
 
-            // TODO: Skip ImmutableArray due to https://github.com/dotnet/runtime/issues/1037.
-            const string inputJsonWithNullCollections =
+            string inputJsonWithNullCollections =
                 @"{
                     ""Array"":null,
                     ""List"":null,
@@ -627,6 +626,10 @@ static void TestRoundTrip(ClassWithNonNullEnumerableGetters obj)
 
             obj = JsonSerializer.Deserialize<ClassWithNonNullEnumerableGetters>(inputJsonWithNullCollections);
             TestRoundTrip(obj);
+
+            // ImmutableArray<T> is a struct and cannot be null.
+            inputJsonWithNullCollections = @"{""MyImmutableArray"":null}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ClassWithNonNullEnumerableGetters>(inputJsonWithNullCollections));
         }
 
         [Fact]
diff --git a/src/libraries/System.Text.Json/tests/Serialization/ConstructorTests/ConstructorTests.ParameterMatching.cs b/src/libraries/System.Text.Json/tests/Serialization/ConstructorTests/ConstructorTests.ParameterMatching.cs
index b3315fc8871100..91c224d5a8eb0d 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/ConstructorTests/ConstructorTests.ParameterMatching.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/ConstructorTests/ConstructorTests.ParameterMatching.cs
@@ -779,7 +779,7 @@ public async Task Escaped_ParameterNames_Work()
         }
 
         [Fact]
-        public async Task FirstParameterWins()
+        public async Task LastParameterWins()
         {
             Point_2D point = await Serializer.DeserializeWrapper<Point_2D>(@"{""X"":1,""Y"":2,""X"":4}");
             Assert.Equal(4, point.X); // Not 1.
@@ -787,7 +787,7 @@ public async Task FirstParameterWins()
         }
 
         [Fact]
-        public async Task SubsequentParameter_GoesToExtensionData()
+        public async Task LastParameterWins_DoesNotGoToExtensionData()
         {
             string json = @"{
                 ""FirstName"":""Jet"",
diff --git a/src/libraries/System.Text.Json/tests/Serialization/ExtensionDataTests.cs b/src/libraries/System.Text.Json/tests/Serialization/ExtensionDataTests.cs
index 8899ef5e9c18b9..a005ec38e6ef04 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/ExtensionDataTests.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/ExtensionDataTests.cs
@@ -55,7 +55,7 @@ void Verify()
         }
 
         [Fact]
-        public static void ExtensioFieldNotUsed()
+        public static void ExtensionFieldNotUsed()
         {
             string json = @"{""MyNestedClass"":" + SimpleTestClass.s_json + "}";
             ClassWithExtensionField obj = JsonSerializer.Deserialize<ClassWithExtensionField>(json);
diff --git a/src/libraries/System.Text.Json/tests/Serialization/Null.ReadTests.cs b/src/libraries/System.Text.Json/tests/Serialization/Null.ReadTests.cs
index df8715e54c5d08..0f32389207a504 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/Null.ReadTests.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/Null.ReadTests.cs
@@ -168,25 +168,33 @@ public static void NullReadTestChar()
             Assert.Equal('Y', JsonSerializer.Deserialize<char>("\"\u0059\""));
         }
 
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/1037")]
         [Fact]
         public static void ParseNullStringToStructShouldThrowJsonException()
         {
             string nullString = "null";
-            Utf8JsonReader reader = new Utf8JsonReader(Encoding.UTF8.GetBytes(nullString));
+            byte[] nullStringAsBytes = Encoding.UTF8.GetBytes(nullString);
+
+            Utf8JsonReader reader = new Utf8JsonReader(nullStringAsBytes);
 
             JsonTestHelper.AssertThrows<JsonException>(reader, (reader) => JsonSerializer.Deserialize<SimpleStruct>(ref reader));
-            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<SimpleStruct>(Encoding.UTF8.GetBytes(nullString)));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<SimpleStruct>(nullStringAsBytes));
             Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<SimpleStruct>(nullString));
+
+            // null can be assigned to nullable structs.
+            Assert.Null(JsonSerializer.Deserialize<SimpleStruct?>(nullStringAsBytes));
+            Assert.Null(JsonSerializer.Deserialize<SimpleStruct?>(nullString));
         }
 
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/1037")]
         [Fact]
         public static async Task ParseNullStringShouldThrowJsonExceptionAsync()
         {
             using (var stream = new MemoryStream(Encoding.UTF8.GetBytes("null")))
             { 
                 await Assert.ThrowsAsync<JsonException>(async () => await JsonSerializer.DeserializeAsync<SimpleStruct>(stream));
+
+                // null can be assigned to nullable structs.
+                stream.Position = 0;
+                Assert.Null(await JsonSerializer.DeserializeAsync<SimpleStruct?>(stream));
             }
         }
 
diff --git a/src/libraries/System.Text.Json/tests/Serialization/NumberHandlingTests.cs b/src/libraries/System.Text.Json/tests/Serialization/NumberHandlingTests.cs
new file mode 100644
index 00000000000000..60acb54094d6f9
--- /dev/null
+++ b/src/libraries/System.Text.Json/tests/Serialization/NumberHandlingTests.cs
@@ -0,0 +1,1414 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Collections.ObjectModel;
+using System.Globalization;
+using System.Linq;
+using System.Text.Encodings.Web;
+using System.Text.Json.Tests;
+using Xunit;
+
+namespace System.Text.Json.Serialization.Tests
+{
+    public static partial class NumberHandlingTests
+    {
+        private static readonly JsonSerializerOptions s_optionReadFromStr = new JsonSerializerOptions
+        {
+            NumberHandling = JsonNumberHandling.AllowReadingFromString
+        };
+
+        private static readonly JsonSerializerOptions s_optionWriteAsStr = new JsonSerializerOptions
+        {
+            NumberHandling = JsonNumberHandling.WriteAsString
+        };
+
+        private static readonly JsonSerializerOptions s_optionReadAndWriteFromStr = new JsonSerializerOptions
+        {
+            NumberHandling = JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString
+        };
+
+        private static readonly JsonSerializerOptions s_optionsAllowFloatConstants = new JsonSerializerOptions
+        {
+            NumberHandling = JsonNumberHandling.AllowNamedFloatingPointLiterals
+        };
+
+        private static readonly JsonSerializerOptions s_optionReadFromStrAllowFloatConstants = new JsonSerializerOptions
+        {
+            NumberHandling = JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.AllowNamedFloatingPointLiterals
+        };
+
+        private static readonly JsonSerializerOptions s_optionWriteAsStrAllowFloatConstants = new JsonSerializerOptions
+        {
+            NumberHandling = JsonNumberHandling.WriteAsString | JsonNumberHandling.AllowNamedFloatingPointLiterals
+        };
+
+        [Fact]
+        public static void Number_AsRootType_RoundTrip()
+        {
+            RunAsRootTypeTest(JsonNumberTestData.Bytes);
+            RunAsRootTypeTest(JsonNumberTestData.SBytes);
+            RunAsRootTypeTest(JsonNumberTestData.Shorts);
+            RunAsRootTypeTest(JsonNumberTestData.Ints);
+            RunAsRootTypeTest(JsonNumberTestData.Longs);
+            RunAsRootTypeTest(JsonNumberTestData.UShorts);
+            RunAsRootTypeTest(JsonNumberTestData.UInts);
+            RunAsRootTypeTest(JsonNumberTestData.ULongs);
+            RunAsRootTypeTest(JsonNumberTestData.Floats);
+            RunAsRootTypeTest(JsonNumberTestData.Doubles);
+            RunAsRootTypeTest(JsonNumberTestData.Decimals);
+            RunAsRootTypeTest(JsonNumberTestData.NullableBytes);
+            RunAsRootTypeTest(JsonNumberTestData.NullableSBytes);
+            RunAsRootTypeTest(JsonNumberTestData.NullableShorts);
+            RunAsRootTypeTest(JsonNumberTestData.NullableInts);
+            RunAsRootTypeTest(JsonNumberTestData.NullableLongs);
+            RunAsRootTypeTest(JsonNumberTestData.NullableUShorts);
+            RunAsRootTypeTest(JsonNumberTestData.NullableUInts);
+            RunAsRootTypeTest(JsonNumberTestData.NullableULongs);
+            RunAsRootTypeTest(JsonNumberTestData.NullableFloats);
+            RunAsRootTypeTest(JsonNumberTestData.NullableDoubles);
+            RunAsRootTypeTest(JsonNumberTestData.NullableDecimals);
+        }
+
+        private static void RunAsRootTypeTest<T>(List<T> numbers)
+        {
+            foreach (T number in numbers)
+            {
+                string numberAsString = GetNumberAsString(number);
+                string json = $"{numberAsString}";
+                string jsonWithNumberAsString = @$"""{numberAsString}""";
+                PerformAsRootTypeSerialization(number, json, jsonWithNumberAsString);
+            }
+        }
+
+        private static string GetNumberAsString<T>(T number)
+        {
+            return number switch
+            {
+                double @double => @double.ToString(JsonTestHelper.DoubleFormatString, CultureInfo.InvariantCulture),
+                float @float => @float.ToString(JsonTestHelper.SingleFormatString, CultureInfo.InvariantCulture),
+                decimal @decimal => @decimal.ToString(CultureInfo.InvariantCulture),
+                _ => number.ToString()
+            };
+        }
+
+        private static void PerformAsRootTypeSerialization<T>(T number, string jsonWithNumberAsNumber, string jsonWithNumberAsString)
+        {
+            // Option: read from string
+
+            // Deserialize
+            Assert.Equal(number, JsonSerializer.Deserialize<T>(jsonWithNumberAsNumber, s_optionReadFromStr));
+            Assert.Equal(number, JsonSerializer.Deserialize<T>(jsonWithNumberAsString, s_optionReadFromStr));
+
+            // Serialize
+            Assert.Equal(jsonWithNumberAsNumber, JsonSerializer.Serialize(number, s_optionReadFromStr));
+
+            // Option: write as string
+
+            // Deserialize
+            Assert.Equal(number, JsonSerializer.Deserialize<T>(jsonWithNumberAsNumber, s_optionWriteAsStr));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<T>(jsonWithNumberAsString, s_optionWriteAsStr));
+
+            // Serialize
+            Assert.Equal(jsonWithNumberAsString, JsonSerializer.Serialize(number, s_optionWriteAsStr));
+
+            // Option: read and write from/to string
+
+            // Deserialize
+            Assert.Equal(number, JsonSerializer.Deserialize<T>(jsonWithNumberAsNumber, s_optionReadAndWriteFromStr));
+            Assert.Equal(number, JsonSerializer.Deserialize<T>(jsonWithNumberAsString, s_optionReadAndWriteFromStr));
+
+            // Serialize
+            Assert.Equal(jsonWithNumberAsString, JsonSerializer.Serialize(number, s_optionReadAndWriteFromStr));
+        }
+
+        [Fact]
+        public static void Number_AsBoxedRootType()
+        {
+            string numberAsString = @"""2""";
+
+            int @int = 2;
+            float @float = 2;
+            int? nullableInt = 2;
+            float? nullableFloat = 2;
+
+            Assert.Equal(numberAsString, JsonSerializer.Serialize((object)@int, s_optionReadAndWriteFromStr));
+            Assert.Equal(numberAsString, JsonSerializer.Serialize((object)@float, s_optionReadAndWriteFromStr));
+            Assert.Equal(numberAsString, JsonSerializer.Serialize((object)nullableInt, s_optionReadAndWriteFromStr));
+            Assert.Equal(numberAsString, JsonSerializer.Serialize((object)nullableFloat, s_optionReadAndWriteFromStr));
+
+            Assert.Equal(2, (int)JsonSerializer.Deserialize(numberAsString, typeof(int), s_optionReadAndWriteFromStr));
+            Assert.Equal(2, (float)JsonSerializer.Deserialize(numberAsString, typeof(float), s_optionReadAndWriteFromStr));
+            Assert.Equal(2, (int?)JsonSerializer.Deserialize(numberAsString, typeof(int?), s_optionReadAndWriteFromStr));
+            Assert.Equal(2, (float?)JsonSerializer.Deserialize(numberAsString, typeof(float?), s_optionReadAndWriteFromStr));
+        }
+
+        [Fact]
+        public static void Number_AsCollectionElement_RoundTrip()
+        {
+            RunAsCollectionElementTest(JsonNumberTestData.Bytes);
+            RunAsCollectionElementTest(JsonNumberTestData.SBytes);
+            RunAsCollectionElementTest(JsonNumberTestData.Shorts);
+            RunAsCollectionElementTest(JsonNumberTestData.Ints);
+            RunAsCollectionElementTest(JsonNumberTestData.Longs);
+            RunAsCollectionElementTest(JsonNumberTestData.UShorts);
+            RunAsCollectionElementTest(JsonNumberTestData.UInts);
+            RunAsCollectionElementTest(JsonNumberTestData.ULongs);
+            RunAsCollectionElementTest(JsonNumberTestData.Floats);
+            RunAsCollectionElementTest(JsonNumberTestData.Doubles);
+            RunAsCollectionElementTest(JsonNumberTestData.Decimals);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableBytes);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableSBytes);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableShorts);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableInts);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableLongs);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableUShorts);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableUInts);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableULongs);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableFloats);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableDoubles);
+            RunAsCollectionElementTest(JsonNumberTestData.NullableDecimals);
+        }
+
+        private static void RunAsCollectionElementTest<T>(List<T> numbers)
+        {
+            StringBuilder jsonBuilder_NumbersAsNumbers = new StringBuilder();
+            StringBuilder jsonBuilder_NumbersAsStrings = new StringBuilder();
+            StringBuilder jsonBuilder_NumbersAsNumbersAndStrings = new StringBuilder();
+            StringBuilder jsonBuilder_NumbersAsNumbersAndStrings_Alternate = new StringBuilder();
+            bool asNumber = false;
+
+            jsonBuilder_NumbersAsNumbers.Append("[");
+            jsonBuilder_NumbersAsStrings.Append("[");
+            jsonBuilder_NumbersAsNumbersAndStrings.Append("[");
+            jsonBuilder_NumbersAsNumbersAndStrings_Alternate.Append("[");
+
+            foreach (T number in numbers)
+            {
+                string numberAsString = GetNumberAsString(number);
+
+                string jsonWithNumberAsString = @$"""{numberAsString}""";
+
+                jsonBuilder_NumbersAsNumbers.Append($"{numberAsString},");
+                jsonBuilder_NumbersAsStrings.Append($"{jsonWithNumberAsString},");
+                jsonBuilder_NumbersAsNumbersAndStrings.Append(asNumber
+                    ? $"{numberAsString},"
+                    : $"{jsonWithNumberAsString},");
+                jsonBuilder_NumbersAsNumbersAndStrings_Alternate.Append(!asNumber
+                    ? $"{numberAsString},"
+                    : $"{jsonWithNumberAsString},");
+
+                asNumber = !asNumber;
+            }
+
+            jsonBuilder_NumbersAsNumbers.Remove(jsonBuilder_NumbersAsNumbers.Length - 1, 1);
+            jsonBuilder_NumbersAsStrings.Remove(jsonBuilder_NumbersAsStrings.Length - 1, 1);
+            jsonBuilder_NumbersAsNumbersAndStrings.Remove(jsonBuilder_NumbersAsNumbersAndStrings.Length - 1, 1);
+            jsonBuilder_NumbersAsNumbersAndStrings_Alternate.Remove(jsonBuilder_NumbersAsNumbersAndStrings_Alternate.Length - 1, 1);
+
+            jsonBuilder_NumbersAsNumbers.Append("]");
+            jsonBuilder_NumbersAsStrings.Append("]");
+            jsonBuilder_NumbersAsNumbersAndStrings.Append("]");
+            jsonBuilder_NumbersAsNumbersAndStrings_Alternate.Append("]");
+
+            string jsonNumbersAsStrings = jsonBuilder_NumbersAsStrings.ToString();
+
+            PerformAsCollectionElementSerialization(
+                numbers,
+                jsonBuilder_NumbersAsNumbers.ToString(),
+                jsonNumbersAsStrings,
+                jsonBuilder_NumbersAsNumbersAndStrings.ToString(),
+                jsonBuilder_NumbersAsNumbersAndStrings_Alternate.ToString());
+
+            // Reflection based tests for every collection type.
+            RunAllCollectionsRoundTripTest<T>(jsonNumbersAsStrings);
+        }
+
+        private static void PerformAsCollectionElementSerialization<T>(
+            List<T> numbers,
+            string json_NumbersAsNumbers,
+            string json_NumbersAsStrings,
+            string json_NumbersAsNumbersAndStrings,
+            string json_NumbersAsNumbersAndStrings_Alternate)
+        {
+            List<T> deserialized;
+
+            // Option: read from string
+
+            // Deserialize
+            deserialized = JsonSerializer.Deserialize<List<T>>(json_NumbersAsNumbers, s_optionReadFromStr);
+            AssertIEnumerableEqual(numbers, deserialized);
+
+            deserialized = JsonSerializer.Deserialize<List<T>>(json_NumbersAsStrings, s_optionReadFromStr);
+            AssertIEnumerableEqual(numbers, deserialized);
+
+            deserialized = JsonSerializer.Deserialize<List<T>>(json_NumbersAsNumbersAndStrings, s_optionReadFromStr);
+            AssertIEnumerableEqual(numbers, deserialized);
+
+            deserialized = JsonSerializer.Deserialize<List<T>>(json_NumbersAsNumbersAndStrings_Alternate, s_optionReadFromStr);
+            AssertIEnumerableEqual(numbers, deserialized);
+
+            // Serialize
+            Assert.Equal(json_NumbersAsNumbers, JsonSerializer.Serialize(numbers, s_optionReadFromStr));
+
+            // Option: write as string
+
+            // Deserialize
+            deserialized = JsonSerializer.Deserialize<List<T>>(json_NumbersAsNumbers, s_optionWriteAsStr);
+            AssertIEnumerableEqual(numbers, deserialized);
+
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<List<T>>(json_NumbersAsStrings, s_optionWriteAsStr));
+
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<List<T>>(json_NumbersAsNumbersAndStrings, s_optionWriteAsStr));
+
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<List<T>>(json_NumbersAsNumbersAndStrings_Alternate, s_optionWriteAsStr));
+
+            // Serialize
+            Assert.Equal(json_NumbersAsStrings, JsonSerializer.Serialize(numbers, s_optionWriteAsStr));
+
+            // Option: read and write from/to string
+
+            // Deserialize
+            deserialized = JsonSerializer.Deserialize<List<T>>(json_NumbersAsNumbers, s_optionReadAndWriteFromStr);
+            AssertIEnumerableEqual(numbers, deserialized);
+
+            deserialized = JsonSerializer.Deserialize<List<T>>(json_NumbersAsStrings, s_optionReadAndWriteFromStr);
+            AssertIEnumerableEqual(numbers, deserialized);
+
+            deserialized = JsonSerializer.Deserialize<List<T>>(json_NumbersAsNumbersAndStrings, s_optionReadAndWriteFromStr);
+            AssertIEnumerableEqual(numbers, deserialized);
+
+            deserialized = JsonSerializer.Deserialize<List<T>>(json_NumbersAsNumbersAndStrings_Alternate, s_optionReadAndWriteFromStr);
+            AssertIEnumerableEqual(numbers, deserialized);
+
+            // Serialize
+            Assert.Equal(json_NumbersAsStrings, JsonSerializer.Serialize(numbers, s_optionReadAndWriteFromStr));
+        }
+
+        private static void AssertIEnumerableEqual<T>(IEnumerable<T> list1, IEnumerable<T> list2)
+        {
+            IEnumerator<T> enumerator1 = list1.GetEnumerator();
+            IEnumerator<T> enumerator2 = list2.GetEnumerator();
+
+            while (enumerator1.MoveNext())
+            {
+                enumerator2.MoveNext();
+                Assert.Equal(enumerator1.Current, enumerator2.Current);
+            }
+
+            Assert.False(enumerator2.MoveNext());
+        }
+
+        private static void RunAllCollectionsRoundTripTest<T>(string json)
+        {
+            foreach (Type type in CollectionTestTypes.DeserializableGenericEnumerableTypes<T>())
+            {
+                if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(HashSet<>))
+                {
+                    HashSet<T> obj1 = (HashSet<T>)JsonSerializer.Deserialize(json, type, s_optionReadAndWriteFromStr);
+                    string serialized = JsonSerializer.Serialize(obj1, s_optionReadAndWriteFromStr);
+
+                    HashSet<T> obj2 = (HashSet<T>)JsonSerializer.Deserialize(serialized, type, s_optionReadAndWriteFromStr);
+
+                    Assert.Equal(obj1.Count, obj2.Count);
+                    foreach (T element in obj1)
+                    {
+                        Assert.True(obj2.Contains(element));
+                    }
+                }
+                else if (type != typeof(byte[]))
+                {
+                    object obj = JsonSerializer.Deserialize(json, type, s_optionReadAndWriteFromStr);
+                    string serialized = JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr);
+                    Assert.Equal(json, serialized);
+                }
+            }
+
+            foreach (Type type in CollectionTestTypes.DeserializableNonGenericEnumerableTypes())
+            {
+                // Deserialized as collection of JsonElements.
+                object obj = JsonSerializer.Deserialize(json, type, s_optionReadAndWriteFromStr);
+                // Serialized as strings with escaping.
+                string serialized = JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr);
+
+                // Ensure escaped values were serialized accurately
+                List<T> list = JsonSerializer.Deserialize<List<T>>(serialized, s_optionReadAndWriteFromStr);
+                serialized = JsonSerializer.Serialize(list, s_optionReadAndWriteFromStr);
+                Assert.Equal(json, serialized);
+
+                // Serialize instance which is a collection of numbers (not JsonElements).
+                obj = Activator.CreateInstance(type, new[] { list });
+                serialized = JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr);
+                Assert.Equal(json, serialized);
+            }
+        }
+
+        [Fact]
+        public static void Number_AsDictionaryElement_RoundTrip()
+        {
+            var dict = new Dictionary<int, float>();
+            for (int i = 0; i < 10; i++)
+            {
+                dict[JsonNumberTestData.Ints[i]] = JsonNumberTestData.Floats[i];
+            }
+
+            // Serialize
+            string serialized = JsonSerializer.Serialize(dict, s_optionReadAndWriteFromStr);
+            AssertDictionaryElements_StringValues(serialized);
+
+            // Deserialize
+            dict = JsonSerializer.Deserialize<Dictionary<int, float>>(serialized, s_optionReadAndWriteFromStr);
+
+            // Test roundtrip
+            JsonTestHelper.AssertJsonEqual(serialized, JsonSerializer.Serialize(dict, s_optionReadAndWriteFromStr));
+        }
+
+        private static void AssertDictionaryElements_StringValues(string serialized)
+        {
+            var reader = new Utf8JsonReader(Encoding.UTF8.GetBytes(serialized));
+            reader.Read();
+            while (reader.Read())
+            {
+                if (reader.TokenType == JsonTokenType.EndObject)
+                {
+                    break;
+                }
+                else if (reader.TokenType == JsonTokenType.String)
+                {
+#if BUILDING_INBOX_LIBRARY
+                    Assert.False(reader.ValueSpan.Contains((byte)'\\'));
+#else
+                    foreach (byte val in reader.ValueSpan)
+                    {
+                        if (val == (byte)'\\')
+                        {
+                            Assert.True(false, "Unexpected escape token.");
+                        }
+                    }
+#endif
+                }
+                else
+                {
+                    Assert.Equal(JsonTokenType.PropertyName, reader.TokenType);
+                }
+            }
+        }
+
+        [Fact]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/39674", typeof(PlatformDetection), nameof(PlatformDetection.IsMonoInterpreter))]
+        public static void DictionariesRoundTrip()
+        {
+            RunAllDictionariessRoundTripTest(JsonNumberTestData.ULongs);
+            RunAllDictionariessRoundTripTest(JsonNumberTestData.Floats);
+            RunAllDictionariessRoundTripTest(JsonNumberTestData.Doubles);
+        }
+
+        private static void RunAllDictionariessRoundTripTest<T>(List<T> numbers)
+        {
+            StringBuilder jsonBuilder_NumbersAsStrings = new StringBuilder();
+
+            jsonBuilder_NumbersAsStrings.Append("{");
+
+            foreach (T number in numbers)
+            {
+                string numberAsString = GetNumberAsString(number);
+                string jsonWithNumberAsString = @$"""{numberAsString}""";
+
+                jsonBuilder_NumbersAsStrings.Append($"{jsonWithNumberAsString}:");
+                jsonBuilder_NumbersAsStrings.Append($"{jsonWithNumberAsString},");
+            }
+
+            jsonBuilder_NumbersAsStrings.Remove(jsonBuilder_NumbersAsStrings.Length - 1, 1);
+            jsonBuilder_NumbersAsStrings.Append("}");
+
+            string jsonNumbersAsStrings = jsonBuilder_NumbersAsStrings.ToString();
+
+            foreach (Type type in CollectionTestTypes.DeserializableDictionaryTypes<T>())
+            {
+                object obj = JsonSerializer.Deserialize(jsonNumbersAsStrings, type, s_optionReadAndWriteFromStr);
+                JsonTestHelper.AssertJsonEqual(jsonNumbersAsStrings, JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr));
+            }
+
+            foreach (Type type in CollectionTestTypes.DeserializableNonDictionaryTypes<T>())
+            {
+                Dictionary<T, T> dict = JsonSerializer.Deserialize<Dictionary<T, T>>(jsonNumbersAsStrings, s_optionReadAndWriteFromStr);
+
+                // Serialize instance which is a dictionary of numbers (not JsonElements).
+                object obj = Activator.CreateInstance(type, new[] { dict });
+                string serialized = JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr);
+                JsonTestHelper.AssertJsonEqual(jsonNumbersAsStrings, serialized);
+            }
+        }
+
+        [Fact]
+        public static void Number_AsPropertyValue_RoundTrip()
+        {
+            var obj = new Class_With_NullableUInt64_And_Float()
+            {
+                NullableUInt64Number = JsonNumberTestData.NullableULongs.LastOrDefault(),
+                FloatNumbers = JsonNumberTestData.Floats
+            };
+
+            // Serialize
+            string serialized = JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr);
+
+            // Deserialize
+            obj = JsonSerializer.Deserialize<Class_With_NullableUInt64_And_Float>(serialized, s_optionReadAndWriteFromStr);
+
+            // Test roundtrip
+            JsonTestHelper.AssertJsonEqual(serialized, JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr));
+        }
+
+        private class Class_With_NullableUInt64_And_Float
+        {
+            public ulong? NullableUInt64Number { get; set; }
+            [JsonInclude]
+            public List<float> FloatNumbers;
+        }
+
+        [Fact]
+        public static void Number_AsKeyValuePairValue_RoundTrip()
+        {
+            var obj = new KeyValuePair<ulong?, List<float>>(JsonNumberTestData.NullableULongs.LastOrDefault(), JsonNumberTestData.Floats);
+
+            // Serialize
+            string serialized = JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr);
+
+            // Deserialize
+            obj = JsonSerializer.Deserialize<KeyValuePair<ulong?, List<float>>>(serialized, s_optionReadAndWriteFromStr);
+
+            // Test roundtrip
+            JsonTestHelper.AssertJsonEqual(serialized, JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr));
+        }
+
+        [Fact]
+        public static void Number_AsObjectWithParameterizedCtor_RoundTrip()
+        {
+            var obj = new MyClassWithNumbers(JsonNumberTestData.NullableULongs.LastOrDefault(), JsonNumberTestData.Floats);
+
+            // Serialize
+            string serialized = JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr);
+
+            // Deserialize
+            obj = JsonSerializer.Deserialize<MyClassWithNumbers>(serialized, s_optionReadAndWriteFromStr);
+
+            // Test roundtrip
+            JsonTestHelper.AssertJsonEqual(serialized, JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr));
+        }
+
+        private class MyClassWithNumbers
+        {
+            public ulong? Ulong { get; }
+            public List<float> ListOfFloats { get; }
+
+            public MyClassWithNumbers(ulong? @ulong, List<float> listOfFloats)
+            {
+                Ulong = @ulong;
+                ListOfFloats = listOfFloats;
+            }
+        }
+
+        [Fact]
+        public static void Number_AsObjectWithParameterizedCtor_PropHasAttribute()
+        {
+            string json = @"{""ListOfFloats"":[""1""]}";
+            // Strict handling on property overrides loose global policy.
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<MyClassWithNumbers_PropsHasAttribute>(json, s_optionReadFromStr));
+
+            // Serialize
+            json = @"{""ListOfFloats"":[1]}";
+            MyClassWithNumbers_PropsHasAttribute obj = JsonSerializer.Deserialize<MyClassWithNumbers_PropsHasAttribute>(json);
+
+            // Number serialized as JSON number due to strict handling on property which overrides loose global policy.
+            Assert.Equal(json, JsonSerializer.Serialize(obj, s_optionReadAndWriteFromStr));
+        }
+
+        private class MyClassWithNumbers_PropsHasAttribute
+        {
+            [JsonNumberHandling(JsonNumberHandling.Strict)]
+            public List<float> ListOfFloats { get; }
+
+            public MyClassWithNumbers_PropsHasAttribute(List<float> listOfFloats)
+            {
+                ListOfFloats = listOfFloats;
+            }
+        }
+
+        [Fact]
+        public static void FloatingPointConstants_Pass()
+        {
+            // Valid values
+            PerformFloatingPointSerialization("NaN");
+            PerformFloatingPointSerialization("Infinity");
+            PerformFloatingPointSerialization("-Infinity");
+
+            static void PerformFloatingPointSerialization(string testString)
+            {
+                string testStringAsJson = $@"""{testString}""";
+                string testJson = @$"{{""FloatNumber"":{testStringAsJson},""DoubleNumber"":{testStringAsJson}}}";
+
+                StructWithNumbers obj;
+                switch (testString)
+                {
+                    case "NaN":
+                        obj = JsonSerializer.Deserialize<StructWithNumbers>(testJson, s_optionsAllowFloatConstants);
+                        Assert.Equal(float.NaN, obj.FloatNumber);
+                        Assert.Equal(double.NaN, obj.DoubleNumber);
+
+                        obj = JsonSerializer.Deserialize<StructWithNumbers>(testJson, s_optionReadFromStr);
+                        Assert.Equal(float.NaN, obj.FloatNumber);
+                        Assert.Equal(double.NaN, obj.DoubleNumber);
+                        break;
+                    case "Infinity":
+                        obj = JsonSerializer.Deserialize<StructWithNumbers>(testJson, s_optionsAllowFloatConstants);
+                        Assert.Equal(float.PositiveInfinity, obj.FloatNumber);
+                        Assert.Equal(double.PositiveInfinity, obj.DoubleNumber);
+
+                        obj = JsonSerializer.Deserialize<StructWithNumbers>(testJson, s_optionReadFromStr);
+                        Assert.Equal(float.PositiveInfinity, obj.FloatNumber);
+                        Assert.Equal(double.PositiveInfinity, obj.DoubleNumber);
+                        break;
+                    case "-Infinity":
+                        obj = JsonSerializer.Deserialize<StructWithNumbers>(testJson, s_optionsAllowFloatConstants);
+                        Assert.Equal(float.NegativeInfinity, obj.FloatNumber);
+                        Assert.Equal(double.NegativeInfinity, obj.DoubleNumber);
+
+                        obj = JsonSerializer.Deserialize<StructWithNumbers>(testJson, s_optionReadFromStr);
+                        Assert.Equal(float.NegativeInfinity, obj.FloatNumber);
+                        Assert.Equal(double.NegativeInfinity, obj.DoubleNumber);
+                        break;
+                    default:
+                        Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<StructWithNumbers>(testJson, s_optionsAllowFloatConstants));
+                        return;
+                }
+
+                JsonTestHelper.AssertJsonEqual(testJson, JsonSerializer.Serialize(obj, s_optionsAllowFloatConstants));
+                JsonTestHelper.AssertJsonEqual(testJson, JsonSerializer.Serialize(obj, s_optionWriteAsStr));
+            }
+        }
+
+        [Theory]
+        [InlineData("naN")]
+        [InlineData("Nan")]
+        [InlineData("NAN")]
+        [InlineData("+Infinity")]
+        [InlineData("+infinity")]
+        [InlineData("infinity")]
+        [InlineData("infinitY")]
+        [InlineData("INFINITY")]
+        [InlineData("+INFINITY")]
+        [InlineData("-infinity")]
+        [InlineData("-infinitY")]
+        [InlineData("-INFINITY")]
+        [InlineData(" NaN")]
+        [InlineData(" Infinity")]
+        [InlineData(" -Infinity")]
+        [InlineData("NaN ")]
+        [InlineData("Infinity ")]
+        [InlineData("-Infinity ")]
+        [InlineData("a-Infinity")]
+        [InlineData("NaNa")]
+        [InlineData("Infinitya")]
+        [InlineData("-Infinitya")]
+        public static void FloatingPointConstants_Fail(string testString)
+        {
+            string testStringAsJson = $@"""{testString}""";
+            string testJson = @$"{{""FloatNumber"":{testStringAsJson},""DoubleNumber"":{testStringAsJson}}}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<StructWithNumbers>(testJson, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<StructWithNumbers>(testJson, s_optionReadFromStr));
+        }
+
+        [Fact]
+        public static void AllowFloatingPointConstants_WriteAsNumber_IfNotConstant()
+        {
+            float @float = 1;
+            // Not written as "1"
+            Assert.Equal("1", JsonSerializer.Serialize(@float, s_optionsAllowFloatConstants));
+
+            double @double = 1;
+            // Not written as "1"
+            Assert.Equal("1", JsonSerializer.Serialize(@double, s_optionsAllowFloatConstants));
+        }
+
+        [Theory]
+        [InlineData("NaN")]
+        [InlineData("Infinity")]
+        [InlineData("-Infinity")]
+        public static void Unquoted_FloatingPointConstants_Read_Fail(string testString)
+        {
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<float>(testString, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<double?>(testString, s_optionReadFromStr));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<double>(testString, s_optionReadFromStrAllowFloatConstants));
+        }
+
+        private struct StructWithNumbers
+        {
+            public float FloatNumber { get; set; }
+            public double DoubleNumber { get; set; }
+        }
+
+        [Fact]
+        public static void ReadFromString_AllowFloatingPoint()
+        {
+            string json = @"{""IntNumber"":""1"",""FloatNumber"":""NaN""}";
+            ClassWithNumbers obj = JsonSerializer.Deserialize<ClassWithNumbers>(json, s_optionReadFromStrAllowFloatConstants);
+
+            Assert.Equal(1, obj.IntNumber);
+            Assert.Equal(float.NaN, obj.FloatNumber);
+
+            JsonTestHelper.AssertJsonEqual(@"{""IntNumber"":1,""FloatNumber"":""NaN""}", JsonSerializer.Serialize(obj, s_optionReadFromStrAllowFloatConstants));
+        }
+
+        [Fact]
+        public static void WriteAsString_AllowFloatingPoint()
+        {
+            string json = @"{""IntNumber"":""1"",""FloatNumber"":""NaN""}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ClassWithNumbers>(json, s_optionWriteAsStrAllowFloatConstants));
+
+            var obj = new ClassWithNumbers
+            {
+                IntNumber = 1,
+                FloatNumber = float.NaN
+            };
+
+            JsonTestHelper.AssertJsonEqual(json, JsonSerializer.Serialize(obj, s_optionWriteAsStrAllowFloatConstants));
+        }
+
+        public class ClassWithNumbers
+        {
+            public int IntNumber { get; set; }
+            public float FloatNumber { get; set; }
+        }
+
+        [Fact]
+        public static void FloatingPointConstants_IncompatibleNumber()
+        {
+            AssertFloatingPointIncompatible_Fails<byte>();
+            AssertFloatingPointIncompatible_Fails<sbyte>();
+            AssertFloatingPointIncompatible_Fails<short>();
+            AssertFloatingPointIncompatible_Fails<int>();
+            AssertFloatingPointIncompatible_Fails<long>();
+            AssertFloatingPointIncompatible_Fails<ushort>();
+            AssertFloatingPointIncompatible_Fails<uint>();
+            AssertFloatingPointIncompatible_Fails<ulong>();
+            AssertFloatingPointIncompatible_Fails<decimal>();
+            AssertFloatingPointIncompatible_Fails<byte?>();
+            AssertFloatingPointIncompatible_Fails<sbyte?>();
+            AssertFloatingPointIncompatible_Fails<short?>();
+            AssertFloatingPointIncompatible_Fails<int?>();
+            AssertFloatingPointIncompatible_Fails<long?>();
+            AssertFloatingPointIncompatible_Fails<ushort?>();
+            AssertFloatingPointIncompatible_Fails<uint?>();
+            AssertFloatingPointIncompatible_Fails<ulong?>();
+            AssertFloatingPointIncompatible_Fails<decimal?>();
+        }
+
+        private static void AssertFloatingPointIncompatible_Fails<T>()
+        {
+            string[] testCases = new[]
+            {
+                @"""NaN""",
+                @"""Infinity""",
+                @"""-Infinity""",
+            };
+
+            foreach (string test in testCases)
+            {
+                Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<T>(test, s_optionReadFromStrAllowFloatConstants));
+            }
+        }
+
+        [Fact]
+        public static void UnsupportedFormats()
+        {
+            AssertUnsupportedFormatThrows<byte>();
+            AssertUnsupportedFormatThrows<sbyte>();
+            AssertUnsupportedFormatThrows<short>();
+            AssertUnsupportedFormatThrows<int>();
+            AssertUnsupportedFormatThrows<long>();
+            AssertUnsupportedFormatThrows<ushort>();
+            AssertUnsupportedFormatThrows<uint>();
+            AssertUnsupportedFormatThrows<ulong>();
+            AssertUnsupportedFormatThrows<float>();
+            AssertUnsupportedFormatThrows<decimal>();
+            AssertUnsupportedFormatThrows<byte?>();
+            AssertUnsupportedFormatThrows<sbyte?>();
+            AssertUnsupportedFormatThrows<short?>();
+            AssertUnsupportedFormatThrows<int?>();
+            AssertUnsupportedFormatThrows<long?>();
+            AssertUnsupportedFormatThrows<ushort?>();
+            AssertUnsupportedFormatThrows<uint?>();
+            AssertUnsupportedFormatThrows<ulong?>();
+            AssertUnsupportedFormatThrows<float?>();
+            AssertUnsupportedFormatThrows<decimal?>();
+        }
+
+        private static void AssertUnsupportedFormatThrows<T>()
+        {
+            string[] testCases = new[]
+            {
+                "$123.46", // Currency
+                "100.00 %", // Percent
+                 "1234,57", // Fixed point
+                 "00FF", // Hexadecimal
+            };
+
+            foreach (string test in testCases)
+            {
+                Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<T>(test, s_optionReadFromStr));
+            }
+        }
+
+        [Fact]
+        public static void EscapingTest()
+        {
+            // Cause all characters to be escaped.
+            var encoderSettings = new TextEncoderSettings();
+            encoderSettings.ForbidCharacters('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.', '+', '-', 'e', 'E');
+
+            JavaScriptEncoder encoder = JavaScriptEncoder.Create(encoderSettings);
+            var options = new JsonSerializerOptions(s_optionReadAndWriteFromStr)
+            {
+                Encoder = encoder
+            };
+
+            PerformEscapingTest(JsonNumberTestData.Bytes, options);
+            PerformEscapingTest(JsonNumberTestData.SBytes, options);
+            PerformEscapingTest(JsonNumberTestData.Shorts, options);
+            PerformEscapingTest(JsonNumberTestData.Ints, options);
+            PerformEscapingTest(JsonNumberTestData.Longs, options);
+            PerformEscapingTest(JsonNumberTestData.UShorts, options);
+            PerformEscapingTest(JsonNumberTestData.UInts, options);
+            PerformEscapingTest(JsonNumberTestData.ULongs, options);
+            PerformEscapingTest(JsonNumberTestData.Floats, options);
+            PerformEscapingTest(JsonNumberTestData.Doubles, options);
+            PerformEscapingTest(JsonNumberTestData.Decimals, options);
+        }
+
+        private static void PerformEscapingTest<T>(List<T> numbers, JsonSerializerOptions options)
+        {
+            // All input characters are escaped
+            IEnumerable<string> numbersAsStrings = numbers.Select(num => GetNumberAsString(num));
+            string input = JsonSerializer.Serialize(numbersAsStrings, options);
+            AssertListNumbersEscaped(input);
+
+            // Unescaping works
+            List<T> deserialized = JsonSerializer.Deserialize<List<T>>(input, options);
+            Assert.Equal(numbers.Count, deserialized.Count);
+            for (int i = 0; i < numbers.Count; i++)
+            {
+                Assert.Equal(numbers[i], deserialized[i]);
+            }
+
+            // Every number is written as a string, and custom escaping is not honored.
+            string serialized = JsonSerializer.Serialize(deserialized, options);
+            AssertListNumbersUnescaped(serialized);
+        }
+
+        private static void AssertListNumbersEscaped(string json)
+        {
+            var reader = new Utf8JsonReader(Encoding.UTF8.GetBytes(json));
+            reader.Read();
+            while (reader.Read())
+            {
+                if (reader.TokenType == JsonTokenType.EndArray)
+                {
+                    break;
+                }
+                else
+                {
+                    Assert.Equal(JsonTokenType.String, reader.TokenType);
+#if BUILDING_INBOX_LIBRARY
+                    Assert.True(reader.ValueSpan.Contains((byte)'\\'));
+#else
+                    bool foundBackSlash = false;
+                    foreach (byte val in reader.ValueSpan)
+                    {
+                        if (val == (byte)'\\')
+                        {
+                            foundBackSlash = true;
+                            break;
+                        }
+                    }
+
+                    Assert.True(foundBackSlash, "Expected escape token.");
+#endif
+                }
+            }
+        }
+
+        private static void AssertListNumbersUnescaped(string json)
+        {
+            var reader = new Utf8JsonReader(Encoding.UTF8.GetBytes(json));
+            reader.Read();
+            while (reader.Read())
+            {
+                if (reader.TokenType == JsonTokenType.EndArray)
+                {
+                    break;
+                }
+                else
+                {
+                    Assert.Equal(JsonTokenType.String, reader.TokenType);
+#if BUILDING_INBOX_LIBRARY
+                    Assert.False(reader.ValueSpan.Contains((byte)'\\'));
+#else
+                    foreach (byte val in reader.ValueSpan)
+                    {
+                        if (val == (byte)'\\')
+                        {
+                            Assert.True(false, "Unexpected escape token.");
+                        }
+                    }
+#endif
+                }
+            }
+        }
+
+        [Fact]
+        public static void Number_RoundtripNull()
+        {
+            Perform_Number_RoundTripNull_Test<byte>();
+            Perform_Number_RoundTripNull_Test<sbyte>();
+            Perform_Number_RoundTripNull_Test<short>();
+            Perform_Number_RoundTripNull_Test<int>();
+            Perform_Number_RoundTripNull_Test<long>();
+            Perform_Number_RoundTripNull_Test<ushort>();
+            Perform_Number_RoundTripNull_Test<uint>();
+            Perform_Number_RoundTripNull_Test<ulong>();
+            Perform_Number_RoundTripNull_Test<float>();
+            Perform_Number_RoundTripNull_Test<decimal>();
+        }
+
+        private static void Perform_Number_RoundTripNull_Test<T>()
+        {
+            string nullAsJson = "null";
+            string nullAsQuotedJson = $@"""{nullAsJson}""";
+
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<T>(nullAsJson, s_optionReadAndWriteFromStr));
+            Assert.Equal("0", JsonSerializer.Serialize(default(T)));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<T>(nullAsQuotedJson, s_optionReadAndWriteFromStr));
+        }
+
+        [Fact]
+        public static void NullableNumber_RoundtripNull()
+        {
+            Perform_NullableNumber_RoundTripNull_Test<byte?>();
+            Perform_NullableNumber_RoundTripNull_Test<sbyte?>();
+            Perform_NullableNumber_RoundTripNull_Test<short?>();
+            Perform_NullableNumber_RoundTripNull_Test<int?>();
+            Perform_NullableNumber_RoundTripNull_Test<long?>();
+            Perform_NullableNumber_RoundTripNull_Test<ushort?>();
+            Perform_NullableNumber_RoundTripNull_Test<uint?>();
+            Perform_NullableNumber_RoundTripNull_Test<ulong?>();
+            Perform_NullableNumber_RoundTripNull_Test<float?>();
+            Perform_NullableNumber_RoundTripNull_Test<decimal?>();
+        }
+
+        private static void Perform_NullableNumber_RoundTripNull_Test<T>()
+        {
+            string nullAsJson = "null";
+            string nullAsQuotedJson = $@"""{nullAsJson}""";
+
+            Assert.Null(JsonSerializer.Deserialize<T>(nullAsJson, s_optionReadAndWriteFromStr));
+            Assert.Equal(nullAsJson, JsonSerializer.Serialize(default(T)));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<T>(nullAsQuotedJson, s_optionReadAndWriteFromStr));
+        }
+
+        [Fact]
+        public static void Disallow_ArbritaryStrings_On_AllowFloatingPointConstants()
+        {
+            string json = @"""12345""";
+
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<byte>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<sbyte>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<short>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<int>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<long>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ushort>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<uint>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ulong>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<float>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<double>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<decimal>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<byte?>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<sbyte?>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<short?>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<int?>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<long?>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ushort?>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<uint?>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ulong?>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<float?>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<double?>(json, s_optionsAllowFloatConstants));
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<decimal?>(json, s_optionsAllowFloatConstants));
+        }
+
+        [Fact]
+        public static void Attributes_OnMembers_Work()
+        {
+            // Bad JSON because Int should not be string.
+            string intIsString = @"{""Float"":""1234.5"",""Int"":""12345""}";
+
+            // Good JSON because Float can be string.
+            string floatIsString = @"{""Float"":""1234.5"",""Int"":12345}";
+
+            // Good JSON because Float can be number.
+            string floatIsNumber = @"{""Float"":1234.5,""Int"":12345}";
+
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ClassWith_Attribute_OnNumber>(intIsString));
+
+            ClassWith_Attribute_OnNumber obj = JsonSerializer.Deserialize<ClassWith_Attribute_OnNumber>(floatIsString);
+            Assert.Equal(1234.5, obj.Float);
+            Assert.Equal(12345, obj.Int);
+
+            obj = JsonSerializer.Deserialize<ClassWith_Attribute_OnNumber>(floatIsNumber);
+            Assert.Equal(1234.5, obj.Float);
+            Assert.Equal(12345, obj.Int);
+
+            // Per options, float should be written as string.
+            JsonTestHelper.AssertJsonEqual(floatIsString, JsonSerializer.Serialize(obj));
+        }
+
+        private class ClassWith_Attribute_OnNumber
+        {
+            [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
+            public float Float { get; set; }
+
+            public int Int { get; set; }
+        }
+
+        [Fact]
+        public static void Attribute_OnRootType_Works()
+        {
+            // Not allowed
+            string floatIsString = @"{""Float"":""1234"",""Int"":123}";
+
+            // Allowed
+            string floatIsNan = @"{""Float"":""NaN"",""Int"":123}";
+
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<Type_AllowFloatConstants>(floatIsString));
+
+            Type_AllowFloatConstants obj = JsonSerializer.Deserialize<Type_AllowFloatConstants>(floatIsNan);
+            Assert.Equal(float.NaN, obj.Float);
+            Assert.Equal(123, obj.Int);
+
+            JsonTestHelper.AssertJsonEqual(floatIsNan, JsonSerializer.Serialize(obj));
+        }
+
+        [JsonNumberHandling(JsonNumberHandling.AllowNamedFloatingPointLiterals)]
+        private class Type_AllowFloatConstants
+        {
+            public float Float { get; set; }
+
+            public int Int { get; set; }
+        }
+
+        [Fact]
+        public static void AttributeOnType_WinsOver_GlobalOption()
+        {
+            // Global options strict, type options loose
+            string json = @"{""Float"":""12345""}";
+            var obj1 = JsonSerializer.Deserialize<ClassWith_LooseAttribute>(json);
+
+            Assert.Equal(@"{""Float"":""12345""}", JsonSerializer.Serialize(obj1));
+
+            // Global options loose, type options strict
+            json = @"{""Float"":""12345""}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ClassWith_StrictAttribute>(json, s_optionReadAndWriteFromStr));
+
+            var obj2 = new ClassWith_StrictAttribute() { Float = 12345 };
+            Assert.Equal(@"{""Float"":12345}", JsonSerializer.Serialize(obj2, s_optionReadAndWriteFromStr));
+        }
+
+        [JsonNumberHandling(JsonNumberHandling.Strict)]
+        public class ClassWith_StrictAttribute
+        {
+            public float Float { get; set; }
+        }
+
+        [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
+        private class ClassWith_LooseAttribute
+        {
+            public float Float { get; set; }
+        }
+
+        [Fact]
+        public static void AttributeOnMember_WinsOver_AttributeOnType()
+        {
+            string json = @"{""Double"":""NaN""}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ClassWith_Attribute_On_TypeAndMember>(json));
+
+            var obj = new ClassWith_Attribute_On_TypeAndMember { Double = float.NaN };
+            Assert.Throws<ArgumentException>(() => JsonSerializer.Serialize(obj));
+        }
+
+        [JsonNumberHandling(JsonNumberHandling.AllowNamedFloatingPointLiterals)]
+        private class ClassWith_Attribute_On_TypeAndMember
+        {
+            [JsonNumberHandling(JsonNumberHandling.Strict)]
+            public double Double { get; set; }
+        }
+
+        [Fact]
+        public static void Attribute_OnNestedType_Works()
+        {
+            string jsonWithShortProperty = @"{""Short"":""1""}";
+            ClassWith_ReadAsStringAttribute obj = JsonSerializer.Deserialize<ClassWith_ReadAsStringAttribute>(jsonWithShortProperty);
+            Assert.Equal(1, obj.Short);
+
+            string jsonWithMyObjectProperty = @"{""MyObject"":{""Float"":""1""}}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ClassWith_ReadAsStringAttribute>(jsonWithMyObjectProperty));
+        }
+
+        [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString)]
+        public class ClassWith_ReadAsStringAttribute
+        {
+            public short Short { get; set; }
+
+            public ClassWith_StrictAttribute MyObject { get; set; }
+        }
+
+        [Fact]
+        public static void MemberAttributeAppliesToCollection_SimpleElements()
+        {
+            RunTest<int[]>();
+            RunTest<ConcurrentQueue<int>>();
+            RunTest<GenericICollectionWrapper<int>>();
+            RunTest<IEnumerable<int>>();
+            RunTest<Collection<int>>();
+            RunTest<ImmutableList<int>>();
+            RunTest<HashSet<int>>();
+            RunTest<List<int>>();
+            RunTest<IList<int>>();
+            RunTest<IList>();
+            RunTest<Queue<int>>();
+
+            static void RunTest<T>()
+            {
+                string json = @"{""MyList"":[""1"",""2""]}";
+                ClassWithSimpleCollectionProperty<T> obj = global::System.Text.Json.JsonSerializer.Deserialize<ClassWithSimpleCollectionProperty<T>>(json);
+                Assert.Equal(json, global::System.Text.Json.JsonSerializer.Serialize(obj));
+            }
+        }
+
+        public class ClassWithSimpleCollectionProperty<T>
+        {
+            [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
+            public T MyList { get; set; }
+        }
+
+        [Fact]
+        public static void NestedCollectionElementTypeHandling_Overrides_ParentPropertyHandling()
+        {
+            // Strict policy on the collection element type overrides read-as-string on the collection property
+            string json = @"{""MyList"":[{""Float"":""1""}]}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ClassWithComplexListProperty>(json));
+
+            // Strict policy on the collection element type overrides write-as-string on the collection property
+            var obj = new ClassWithComplexListProperty
+            {
+                MyList = new List<ClassWith_StrictAttribute> { new ClassWith_StrictAttribute { Float = 1 } }
+            };
+            Assert.Equal(@"{""MyList"":[{""Float"":1}]}", JsonSerializer.Serialize(obj));
+        }
+
+        public class ClassWithComplexListProperty
+        {
+            [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
+            public List<ClassWith_StrictAttribute> MyList { get; set; }
+        }
+
+        [Fact]
+        public static void MemberAttributeAppliesToDictionary_SimpleElements()
+        {
+            string json = @"{""First"":""1"",""Second"":""2""}";
+            ClassWithSimpleDictionaryProperty obj = JsonSerializer.Deserialize<ClassWithSimpleDictionaryProperty>(json);
+        }
+
+        public class ClassWithSimpleDictionaryProperty
+        {
+            [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
+            public Dictionary<string, int> MyDictionary { get; set; }
+        }
+
+        [Fact]
+        public static void NestedDictionaryElementTypeHandling_Overrides_ParentPropertyHandling()
+        {
+            // Strict policy on the dictionary element type overrides read-as-string on the collection property.
+            string json = @"{""MyDictionary"":{""Key"":{""Float"":""1""}}}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ClassWithComplexDictionaryProperty>(json));
+
+            // Strict policy on the collection element type overrides write-as-string on the collection property
+            var obj = new ClassWithComplexDictionaryProperty
+            {
+                MyDictionary = new Dictionary<string, ClassWith_StrictAttribute> { ["Key"] = new ClassWith_StrictAttribute { Float = 1 } }
+            };
+            Assert.Equal(@"{""MyDictionary"":{""Key"":{""Float"":1}}}", JsonSerializer.Serialize(obj));
+        }
+
+        public class ClassWithComplexDictionaryProperty
+        {
+            [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString)]
+            public Dictionary<string, ClassWith_StrictAttribute> MyDictionary { get; set; }
+        }
+
+        [Fact]
+        public static void TypeAttributeAppliesTo_CustomCollectionElements()
+        {
+            string json = @"[""1""]";
+            MyCustomList obj = JsonSerializer.Deserialize<MyCustomList>(json);
+            Assert.Equal(json, JsonSerializer.Serialize(obj));
+        }
+
+        [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
+        public class MyCustomList : List<int> { }
+
+        [Fact]
+        public static void TypeAttributeAppliesTo_CustomCollectionElements_HonoredWhenProperty()
+        {
+            string json = @"{""List"":[""1""]}";
+            ClassWithCustomList obj = JsonSerializer.Deserialize<ClassWithCustomList>(json);
+            Assert.Equal(json, JsonSerializer.Serialize(obj));
+        }
+
+        public class ClassWithCustomList
+        {
+            public MyCustomList List { get; set; }
+        }
+
+        [Fact]
+        public static void TypeAttributeAppliesTo_CustomDictionaryElements()
+        {
+            string json = @"{""Key"":""1""}";
+            MyCustomDictionary obj = JsonSerializer.Deserialize<MyCustomDictionary>(json);
+            Assert.Equal(json, JsonSerializer.Serialize(obj));
+        }
+
+        [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
+        public class MyCustomDictionary : Dictionary<string, int> { }
+
+        [Fact]
+        public static void TypeAttributeAppliesTo_CustomDictionaryElements_HonoredWhenProperty()
+        {
+            string json = @"{""Dictionary"":{""Key"":""1""}}";
+            ClassWithCustomDictionary obj = JsonSerializer.Deserialize<ClassWithCustomDictionary>(json);
+            Assert.Equal(json, JsonSerializer.Serialize(obj));
+        }
+
+        public class ClassWithCustomDictionary
+        {
+            public MyCustomDictionary Dictionary { get; set; }
+        }
+
+        [Fact]
+        public static void Attribute_OnType_NotRecursive()
+        {
+            // Recursive behavior would allow a string number.
+            // This is not supported.
+            string json = @"{""NestedClass"":{""MyInt"":""1""}}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<AttributeOnFirstLevel>(json));
+
+            var obj = new AttributeOnFirstLevel
+            {
+                NestedClass = new BadProperty { MyInt = 1 }
+            };
+            Assert.Equal(@"{""NestedClass"":{""MyInt"":1}}", JsonSerializer.Serialize(obj));
+        }
+
+        [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
+        public class AttributeOnFirstLevel
+        {
+            public BadProperty NestedClass { get; set; }
+        }
+
+        public class BadProperty
+        {
+            public int MyInt { get; set; }
+        }
+
+        [Fact]
+        public static void HandlingOnMemberOverridesHandlingOnType_Enumerable()
+        {
+            string json = @"{""List"":[""1""]}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<MyCustomListWrapper>(json));
+
+            var obj = new MyCustomListWrapper
+            {
+                List = new MyCustomList { 1 }
+            };
+            Assert.Equal(@"{""List"":[1]}", JsonSerializer.Serialize(obj));
+        }
+
+        public class MyCustomListWrapper
+        {
+            [JsonNumberHandling(JsonNumberHandling.Strict)]
+            public MyCustomList List { get; set; }
+        }
+
+        [Fact]
+        public static void HandlingOnMemberOverridesHandlingOnType_Dictionary()
+        {
+            string json = @"{""Dictionary"":{""Key"":""1""}}";
+            Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<MyCustomDictionaryWrapper>(json));
+
+            var obj1 = new MyCustomDictionaryWrapper
+            {
+                Dictionary = new MyCustomDictionary { ["Key"] = 1 }
+            };
+            Assert.Equal(@"{""Dictionary"":{""Key"":1}}", JsonSerializer.Serialize(obj1));
+        }
+
+        public class MyCustomDictionaryWrapper
+        {
+            [JsonNumberHandling(JsonNumberHandling.Strict)]
+            public MyCustomDictionary Dictionary { get; set; }
+        }
+
+        [Fact]
+        public static void Attribute_NotAllowed_On_NonNumber_NonCollection_Property()
+        {
+            string json = @"";
+            InvalidOperationException ex = Assert.Throws<InvalidOperationException>(() => JsonSerializer.Deserialize<ClassWith_NumberHandlingOn_ObjectProperty>(json));
+            string exAsStr = ex.ToString();
+            Assert.Contains("MyProp", exAsStr);
+            Assert.Contains(typeof(ClassWith_NumberHandlingOn_ObjectProperty).ToString(), exAsStr);
+
+            ex = Assert.Throws<InvalidOperationException>(() => JsonSerializer.Serialize(new ClassWith_NumberHandlingOn_ObjectProperty()));
+            exAsStr = ex.ToString();
+            Assert.Contains("MyProp", exAsStr);
+            Assert.Contains(typeof(ClassWith_NumberHandlingOn_ObjectProperty).ToString(), exAsStr);
+        }
+
+        public class ClassWith_NumberHandlingOn_ObjectProperty
+        {
+            [JsonNumberHandling(JsonNumberHandling.Strict)]
+            public BadProperty MyProp { get; set; }
+        }
+
+        [Fact]
+        public static void Attribute_NotAllowed_On_Property_WithCustomConverter()
+        {
+            string json = @"";
+            InvalidOperationException ex = Assert.Throws<InvalidOperationException>(() => JsonSerializer.Deserialize<ClassWith_NumberHandlingOn_Property_WithCustomConverter>(json));
+            string exAsStr = ex.ToString();
+            Assert.Contains(typeof(ConverterForInt32).ToString(), exAsStr);
+            Assert.Contains(typeof(ClassWith_NumberHandlingOn_Property_WithCustomConverter).ToString(), exAsStr);
+
+            ex = Assert.Throws<InvalidOperationException>(() => JsonSerializer.Serialize(new ClassWith_NumberHandlingOn_Property_WithCustomConverter()));
+            exAsStr = ex.ToString();
+            Assert.Contains(typeof(ConverterForInt32).ToString(), exAsStr);
+            Assert.Contains(typeof(ClassWith_NumberHandlingOn_Property_WithCustomConverter).ToString(), exAsStr);
+        }
+
+        public class ClassWith_NumberHandlingOn_Property_WithCustomConverter
+        {
+            [JsonNumberHandling(JsonNumberHandling.Strict)]
+            [JsonConverter(typeof(ConverterForInt32))]
+            public int MyProp { get; set; }
+        }
+
+        [Fact]
+        public static void Attribute_NotAllowed_On_Type_WithCustomConverter()
+        {
+            string json = @"";
+            InvalidOperationException ex = Assert.Throws<InvalidOperationException>(() => JsonSerializer.Deserialize<ClassWith_NumberHandlingOn_Type_WithCustomConverter>(json));
+            string exAsStr = ex.ToString();
+            Assert.Contains(typeof(ConverterForMyType).ToString(), exAsStr);
+            Assert.Contains(typeof(ClassWith_NumberHandlingOn_Type_WithCustomConverter).ToString(), exAsStr);
+
+            ex = Assert.Throws<InvalidOperationException>(() => JsonSerializer.Serialize(new ClassWith_NumberHandlingOn_Type_WithCustomConverter()));
+            exAsStr = ex.ToString();
+            Assert.Contains(typeof(ConverterForMyType).ToString(), exAsStr);
+            Assert.Contains(typeof(ClassWith_NumberHandlingOn_Type_WithCustomConverter).ToString(), exAsStr);
+        }
+
+        [JsonNumberHandling(JsonNumberHandling.Strict)]
+        [JsonConverter(typeof(ConverterForMyType))]
+        public class ClassWith_NumberHandlingOn_Type_WithCustomConverter
+        {
+        }
+
+        private class ConverterForMyType : JsonConverter<ClassWith_NumberHandlingOn_Type_WithCustomConverter>
+        {
+            public override ClassWith_NumberHandlingOn_Type_WithCustomConverter Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            {
+                throw new NotImplementedException();
+            }
+
+            public override void Write(Utf8JsonWriter writer, ClassWith_NumberHandlingOn_Type_WithCustomConverter value, JsonSerializerOptions options)
+            {
+                throw new NotImplementedException();
+            }
+        }
+
+        [Fact]
+        public static void CustomConverterOverridesBuiltInLogic()
+        {
+            var options = new JsonSerializerOptions(s_optionReadAndWriteFromStr)
+            {
+                Converters = { new ConverterForInt32(), new ConverterForFloat() }
+            };
+
+            string json = @"""32""";
+
+            // Converter returns 25 regardless of input.
+            Assert.Equal(25, JsonSerializer.Deserialize<int>(json, options));
+
+            // Converter throws this exception regardless of input.
+            Assert.Throws<NotImplementedException>(() => JsonSerializer.Serialize(4, options));
+
+            json = @"""NaN""";
+
+            // Converter returns 25 if NaN.
+            Assert.Equal(25, JsonSerializer.Deserialize<float?>(json, options));
+
+            // Converter writes 25 if NaN.
+            Assert.Equal("25", JsonSerializer.Serialize((float?)float.NaN, options));
+        }
+
+        public class ConverterForFloat : JsonConverter<float?>
+        {
+            public override float? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            {
+                if (reader.TokenType == JsonTokenType.String && reader.GetString() == "NaN")
+                {
+                    return 25;
+                }
+
+                throw new NotSupportedException();
+            }
+
+            public override void Write(Utf8JsonWriter writer, float? value, JsonSerializerOptions options)
+            {
+                if (float.IsNaN(value.Value))
+                {
+                    writer.WriteNumberValue(25);
+                    return;
+                }
+
+                throw new NotSupportedException();
+            }
+        }
+
+        [Fact]
+        public static void JsonNumberHandling_ArgOutOfRangeFail()
+        {
+            // Global options
+            ArgumentOutOfRangeException ex = Assert.Throws<ArgumentOutOfRangeException>(
+                () => new JsonSerializerOptions { NumberHandling = (JsonNumberHandling)(-1) });
+            Assert.Contains("value", ex.ToString());
+            Assert.Throws<ArgumentOutOfRangeException>(
+                () => new JsonSerializerOptions { NumberHandling = (JsonNumberHandling)(8) });
+
+            ex = Assert.Throws<ArgumentOutOfRangeException>(
+                () => new JsonNumberHandlingAttribute((JsonNumberHandling)(-1)));
+            Assert.Contains("handling", ex.ToString());
+            Assert.Throws<ArgumentOutOfRangeException>(
+                () => new JsonNumberHandlingAttribute((JsonNumberHandling)(8)));
+        }
+    }
+}
diff --git a/src/libraries/System.Text.Json/tests/Serialization/Object.ReadTests.cs b/src/libraries/System.Text.Json/tests/Serialization/Object.ReadTests.cs
index 544634359a9683..6a36e96d3818b9 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/Object.ReadTests.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/Object.ReadTests.cs
@@ -278,7 +278,7 @@ private class CollectionWithoutPublicParameterlessCtor : IList
 
             internal CollectionWithoutPublicParameterlessCtor()
             {
-                Debug.Fail("The JsonSerializer should not be callin non-public ctors, by default.");
+                Debug.Fail("The JsonSerializer should not be calling non-public ctors, by default.");
             }
 
             public CollectionWithoutPublicParameterlessCtor(List<object> list)
@@ -286,7 +286,7 @@ public CollectionWithoutPublicParameterlessCtor(List<object> list)
                 _list = list;
             }
 
-            public object this[int index] { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
+            public object this[int index] { get => _list[index]; set => _list[index] = value; }
 
             public bool IsFixedSize => throw new NotImplementedException();
 
diff --git a/src/libraries/System.Text.Json/tests/Serialization/OptionsTests.cs b/src/libraries/System.Text.Json/tests/Serialization/OptionsTests.cs
index a94055600815c5..a7cc37fb68f1c8 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/OptionsTests.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/OptionsTests.cs
@@ -589,6 +589,7 @@ private static JsonSerializerOptions GetFullyPopulatedOptionsInstance()
                 {
                     options.ReadCommentHandling = JsonCommentHandling.Disallow;
                     options.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault;
+                    options.NumberHandling = JsonNumberHandling.AllowReadingFromString;
                 }
                 else
                 {
@@ -636,6 +637,10 @@ private static void VerifyOptionsEqual(JsonSerializerOptions options, JsonSerial
                     {
                         Assert.Equal(options.DefaultIgnoreCondition, newOptions.DefaultIgnoreCondition);
                     }
+                    else if (property.Name == "NumberHandling")
+                    {
+                        Assert.Equal(options.NumberHandling, newOptions.NumberHandling);
+                    }
                     else
                     {
                         Assert.True(false, $"Public option was added to JsonSerializerOptions but not copied in the copy ctor: {property.Name}");
diff --git a/src/libraries/System.Text.Json/tests/Serialization/PropertyVisibilityTests.NonPublicAccessors.cs b/src/libraries/System.Text.Json/tests/Serialization/PropertyVisibilityTests.NonPublicAccessors.cs
index be76b5e424a077..0dd3657e6f5c3d 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/PropertyVisibilityTests.NonPublicAccessors.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/PropertyVisibilityTests.NonPublicAccessors.cs
@@ -298,6 +298,9 @@ private class ClassWithMixedPropertyAccessors_PropertyAttributes
         [InlineData(typeof(ClassWithPrivateField_WithJsonIncludeProperty))]
         [InlineData(typeof(ClassWithInternalField_WithJsonIncludeProperty))]
         [InlineData(typeof(ClassWithProtectedField_WithJsonIncludeProperty))]
+        [InlineData(typeof(ClassWithPrivate_InitOnlyProperty_WithJsonIncludeProperty))]
+        [InlineData(typeof(ClassWithInternal_InitOnlyProperty_WithJsonIncludeProperty))]
+        [InlineData(typeof(ClassWithProtected_InitOnlyProperty_WithJsonIncludeProperty))]
         public static void NonPublicProperty_WithJsonInclude_Invalid(Type type)
         {
             InvalidOperationException ex = Assert.Throws<InvalidOperationException>(() => JsonSerializer.Deserialize("", type));
@@ -350,5 +353,23 @@ private class ClassWithProtectedField_WithJsonIncludeProperty
             [JsonInclude]
             protected string MyString = null;
         }
+
+        private class ClassWithPrivate_InitOnlyProperty_WithJsonIncludeProperty
+        {
+            [JsonInclude]
+            private string MyString { get; init; }
+        }
+
+        private class ClassWithInternal_InitOnlyProperty_WithJsonIncludeProperty
+        {
+            [JsonInclude]
+            internal string MyString { get; init; }
+        }
+
+        private class ClassWithProtected_InitOnlyProperty_WithJsonIncludeProperty
+        {
+            [JsonInclude]
+            protected string MyString { get; init; }
+        }
     }
 }
diff --git a/src/libraries/System.Text.Json/tests/Serialization/PropertyVisibilityTests.cs b/src/libraries/System.Text.Json/tests/Serialization/PropertyVisibilityTests.cs
index 6e377f8340beed..062813373ae21f 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/PropertyVisibilityTests.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/PropertyVisibilityTests.cs
@@ -3,8 +3,8 @@
 
 using System.Collections.Generic;
 using System.Collections.Concurrent;
-using Xunit;
 using System.Numerics;
+using Xunit;
 
 namespace System.Text.Json.Serialization.Tests
 {
diff --git a/src/libraries/System.Text.Json/tests/Serialization/PropertyVisiblityTests.InitOnly.cs b/src/libraries/System.Text.Json/tests/Serialization/PropertyVisiblityTests.InitOnly.cs
new file mode 100644
index 00000000000000..48fe1e34c935bb
--- /dev/null
+++ b/src/libraries/System.Text.Json/tests/Serialization/PropertyVisiblityTests.InitOnly.cs
@@ -0,0 +1,94 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Xunit;
+
+namespace System.Text.Json.Serialization.Tests
+{
+    public static partial class PropertyVisibilityTests
+    {
+        [Theory]
+        [InlineData(typeof(ClassWithInitOnlyProperty))]
+        [InlineData(typeof(StructWithInitOnlyProperty))]
+        public static void InitOnlyProperties_Work(Type type)
+        {
+            // Init-only property included by default.
+            object obj = JsonSerializer.Deserialize(@"{""MyInt"":1}", type);
+            Assert.Equal(1, (int)type.GetProperty("MyInt").GetValue(obj));
+
+            // Init-only properties can be serialized.
+            Assert.Equal(@"{""MyInt"":1}", JsonSerializer.Serialize(obj));
+        }
+
+        [Theory]
+        [InlineData(typeof(Class_PropertyWith_PrivateInitOnlySetter))]
+        [InlineData(typeof(Class_PropertyWith_InternalInitOnlySetter))]
+        [InlineData(typeof(Class_PropertyWith_ProtectedInitOnlySetter))]
+        public static void NonPublicInitOnlySetter_Without_JsonInclude_Fails(Type type)
+        {
+            // Non-public init-only property setter ignored.
+            object obj = JsonSerializer.Deserialize(@"{""MyInt"":1}", type);
+            Assert.Equal(0, (int)type.GetProperty("MyInt").GetValue(obj));
+
+            // Public getter can be used for serialization.
+            Assert.Equal(@"{""MyInt"":0}", JsonSerializer.Serialize(obj));
+        }
+
+        [Theory]
+        [InlineData(typeof(Class_PropertyWith_PrivateInitOnlySetter_WithAttribute))]
+        [InlineData(typeof(Class_PropertyWith_InternalInitOnlySetter_WithAttribute))]
+        [InlineData(typeof(Class_PropertyWith_ProtectedInitOnlySetter_WithAttribute))]
+        public static void NonPublicInitOnlySetter_With_JsonInclude_Works(Type type)
+        {
+            // Non-public init-only property setter included with [JsonInclude].
+            object obj = JsonSerializer.Deserialize(@"{""MyInt"":1}", type);
+            Assert.Equal(1, (int)type.GetProperty("MyInt").GetValue(obj));
+
+            // Init-only properties can be serialized.
+            Assert.Equal(@"{""MyInt"":1}", JsonSerializer.Serialize(obj));
+        }
+
+        public class ClassWithInitOnlyProperty
+        {
+            public int MyInt { get; init; }
+        }
+
+        public struct StructWithInitOnlyProperty
+        {
+            public int MyInt { get; init; }
+        }
+
+        public class Class_PropertyWith_PrivateInitOnlySetter
+        {
+            public int MyInt { get; private init; }
+        }
+
+        public class Class_PropertyWith_InternalInitOnlySetter
+        {
+            public int MyInt { get; internal init; }
+        }
+
+        public class Class_PropertyWith_ProtectedInitOnlySetter
+        {
+            public int MyInt { get; protected init; }
+        }
+
+        public class Class_PropertyWith_PrivateInitOnlySetter_WithAttribute
+        {
+            [JsonInclude]
+            public int MyInt { get; private init; }
+        }
+
+        public class Class_PropertyWith_InternalInitOnlySetter_WithAttribute
+        {
+            [JsonInclude]
+            public int MyInt { get; internal init; }
+        }
+
+        public class Class_PropertyWith_ProtectedInitOnlySetter_WithAttribute
+        {
+            [JsonInclude]
+            public int MyInt { get; protected init; }
+        }
+    }
+}
diff --git a/src/libraries/System.Text.Json/tests/Serialization/Stream.Collections.cs b/src/libraries/System.Text.Json/tests/Serialization/Stream.Collections.cs
index eb371a431949c9..3efdfde63502bb 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/Stream.Collections.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/Stream.Collections.cs
@@ -98,7 +98,7 @@ private static async Task TestDeserialization<TElement>(
 
                 // TODO: https://github.com/dotnet/runtime/issues/35611.
                 // Can't control order of dictionary elements when serializing, so reference metadata might not match up.
-                if(!(DictionaryTypes<TElement>().Contains(type) && options.ReferenceHandler == ReferenceHandler.Preserve))
+                if(!(CollectionTestTypes.DictionaryTypes<TElement>().Contains(type) && options.ReferenceHandler == ReferenceHandler.Preserve))
                 {
                     JsonTestHelper.AssertJsonEqual(expectedJson, serialized);
                 }
@@ -287,7 +287,7 @@ private static IEnumerable<int> BufferSizes()
 
         private static IEnumerable<Type> CollectionTypes<TElement>()
         {
-            foreach (Type type in EnumerableTypes<TElement>())
+            foreach (Type type in CollectionTestTypes.EnumerableTypes<TElement>())
             {
                 yield return type;
             }
@@ -301,43 +301,17 @@ private static IEnumerable<Type> CollectionTypes<TElement>()
                 yield return type;
             }
             // Dictionary types
-            foreach (Type type in DictionaryTypes<TElement>())
+            foreach (Type type in CollectionTestTypes.DictionaryTypes<TElement>())
             {
                 yield return type;
             }
         }
 
-        private static IEnumerable<Type> EnumerableTypes<TElement>()
-        {
-            yield return typeof(TElement[]); // ArrayConverter
-            yield return typeof(ConcurrentQueue<TElement>); // ConcurrentQueueOfTConverter
-            yield return typeof(GenericICollectionWrapper<TElement>); // ICollectionOfTConverter
-            yield return typeof(WrapperForIEnumerable); // IEnumerableConverter
-            yield return typeof(WrapperForIReadOnlyCollectionOfT<TElement>); // IEnumerableOfTConverter
-            yield return typeof(Queue); // IEnumerableWithAddMethodConverter
-            yield return typeof(WrapperForIList); // IListConverter
-            yield return typeof(Collection<TElement>); // IListOfTConverter
-            yield return typeof(ImmutableList<TElement>); // ImmutableEnumerableOfTConverter
-            yield return typeof(HashSet<TElement>); // ISetOfTConverter
-            yield return typeof(List<TElement>); // ListOfTConverter
-            yield return typeof(Queue<TElement>); // QueueOfTConverter
-        }
-
         private static IEnumerable<Type> ObjectNotationTypes<TElement>()
         {
             yield return typeof(KeyValuePair<TElement, TElement>); // KeyValuePairConverter
         }
 
-        private static IEnumerable<Type> DictionaryTypes<TElement>()
-        {
-            yield return typeof(Dictionary<string, TElement>); // DictionaryOfStringTValueConverter
-            yield return typeof(Hashtable); // IDictionaryConverter
-            yield return typeof(ConcurrentDictionary<string, TElement>); // IDictionaryOfStringTValueConverter
-            yield return typeof(GenericIDictionaryWrapper<string, TElement>); // IDictionaryOfStringTValueConverter
-            yield return typeof(ImmutableDictionary<string, TElement>); // ImmutableDictionaryOfStringTValueConverter
-            yield return typeof(GenericIReadOnlyDictionaryWrapper<string, TElement>); // IReadOnlyDictionaryOfStringTValueConverter
-        }
-
         private static HashSet<Type> StackTypes<TElement>() => new HashSet<Type>
         {
             typeof(ConcurrentStack<TElement>), // ConcurrentStackOfTConverter
@@ -389,7 +363,7 @@ public ImmutableStructWithStrings(
         [InlineData("]")]
         public static void DeserializeDictionaryStartsWithInvalidJson(string json)
         {
-            foreach (Type type in DictionaryTypes<string>())
+            foreach (Type type in CollectionTestTypes.DictionaryTypes<string>())
             {
                 Assert.ThrowsAsync<JsonException>(async () =>
                 {
@@ -404,7 +378,7 @@ public static void DeserializeDictionaryStartsWithInvalidJson(string json)
         [Fact]
         public static void SerializeEmptyCollection()
         {
-            foreach (Type type in EnumerableTypes<int>())
+            foreach (Type type in CollectionTestTypes.EnumerableTypes<int>())
             {
                 Assert.Equal("[]", JsonSerializer.Serialize(GetEmptyCollection<int>(type)));
             }
@@ -414,7 +388,7 @@ public static void SerializeEmptyCollection()
                 Assert.Equal("[]", JsonSerializer.Serialize(GetEmptyCollection<int>(type)));
             }
 
-            foreach (Type type in DictionaryTypes<int>())
+            foreach (Type type in CollectionTestTypes.DictionaryTypes<int>())
             {
                 Assert.Equal("{}", JsonSerializer.Serialize(GetEmptyCollection<int>(type)));
             }
diff --git a/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.Constructor.cs b/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.Constructor.cs
index 070aaacb68a7ec..8dcd74e79dfb3b 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.Constructor.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.Constructor.cs
@@ -2299,7 +2299,7 @@ public string FormattedDate
                 var startDateString = string.Format("{0:g}", StartDate.Value);
                 var endDateString = string.Format("{0:g}", EndDate.Value);
 
-                return string.Format($"From {startDateString} to {endDateString}");
+                return $"From {startDateString} to {endDateString}";
             }
         }
     }
diff --git a/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.NonGenericCollections.cs b/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.NonGenericCollections.cs
index adccf4fc1f4b2a..7ef238b63d453a 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.NonGenericCollections.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.NonGenericCollections.cs
@@ -218,6 +218,16 @@ public WrapperForIList(IEnumerable<object> items)
             _list = new List<object>(items);
         }
 
+        public WrapperForIList(IEnumerable items)
+        {
+            _list = new List<object>();
+
+            foreach (object item in items)
+            {
+                _list.Add(item);
+            }
+        }
+
         public object this[int index] { get => ((IList)_list)[index]; set => ((IList)_list)[index] = value; }
 
         public bool IsFixedSize => ((IList)_list).IsFixedSize;
diff --git a/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.cs b/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.cs
index 8496e4b5817e86..34f96f79fc94b0 100644
--- a/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/TestClasses/TestClasses.cs
@@ -2,8 +2,10 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Collections;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Collections.ObjectModel;
 using System.Linq;
 using Xunit;
 
@@ -1889,4 +1891,68 @@ public override string ConvertName(string name)
             return string.Concat(name.Select((x, i) => i > 0 && char.IsUpper(x) ? "_" + x.ToString() : x.ToString())).ToLower();
         }
     }
+
+    public static class CollectionTestTypes
+    {
+        public static IEnumerable<Type> EnumerableTypes<TElement>()
+        {
+            yield return typeof(TElement[]); // ArrayConverter
+            yield return typeof(ConcurrentQueue<TElement>); // ConcurrentQueueOfTConverter
+            yield return typeof(GenericICollectionWrapper<TElement>); // ICollectionOfTConverter
+            yield return typeof(WrapperForIEnumerable); // IEnumerableConverter
+            yield return typeof(WrapperForIReadOnlyCollectionOfT<TElement>); // IEnumerableOfTConverter
+            yield return typeof(Queue); // IEnumerableWithAddMethodConverter
+            yield return typeof(WrapperForIList); // IListConverter
+            yield return typeof(Collection<TElement>); // IListOfTConverter
+            yield return typeof(ImmutableList<TElement>); // ImmutableEnumerableOfTConverter
+            yield return typeof(HashSet<TElement>); // ISetOfTConverter
+            yield return typeof(List<TElement>); // ListOfTConverter
+            yield return typeof(Queue<TElement>); // QueueOfTConverter
+        }
+
+        public static IEnumerable<Type> DeserializableGenericEnumerableTypes<TElement>()
+        {
+            yield return typeof(TElement[]); // ArrayConverter
+            yield return typeof(ConcurrentQueue<TElement>); // ConcurrentQueueOfTConverter
+            yield return typeof(GenericICollectionWrapper<TElement>); // ICollectionOfTConverter
+            yield return typeof(IEnumerable<TElement>); // IEnumerableConverter
+            yield return typeof(Collection<TElement>); // IListOfTConverter
+            yield return typeof(ImmutableList<TElement>); // ImmutableEnumerableOfTConverter
+            yield return typeof(HashSet<TElement>); // ISetOfTConverter
+            yield return typeof(List<TElement>); // ListOfTConverter
+            yield return typeof(Queue<TElement>); // QueueOfTConverter
+        }
+
+        public static IEnumerable<Type> DeserializableNonGenericEnumerableTypes()
+        {
+            yield return typeof(Queue); // IEnumerableWithAddMethodConverter
+            yield return typeof(WrapperForIList); // IListConverter
+        }
+
+        public static IEnumerable<Type> DictionaryTypes<TElement>()
+        {
+            yield return typeof(Dictionary<string, TElement>); // DictionaryOfStringTValueConverter
+            yield return typeof(Hashtable); // IDictionaryConverter
+            yield return typeof(ConcurrentDictionary<string, TElement>); // IDictionaryOfStringTValueConverter
+            yield return typeof(GenericIDictionaryWrapper<string, TElement>); // IDictionaryOfStringTValueConverter
+            yield return typeof(ImmutableDictionary<string, TElement>); // ImmutableDictionaryOfStringTValueConverter
+            yield return typeof(GenericIReadOnlyDictionaryWrapper<string, TElement>); // IReadOnlyDictionaryOfStringTValueConverter
+        }
+
+        public static IEnumerable<Type> DeserializableDictionaryTypes<TElement>()
+        {
+            yield return typeof(Dictionary<string, TElement>); // DictionaryOfStringTValueConverter
+            yield return typeof(Hashtable); // IDictionaryConverter
+            yield return typeof(ConcurrentDictionary<string, TElement>); // IDictionaryOfStringTValueConverter
+            yield return typeof(GenericIDictionaryWrapper<string, TElement>); // IDictionaryOfStringTValueConverter
+            yield return typeof(ImmutableDictionary<string, TElement>); // ImmutableDictionaryOfStringTValueConverter
+            yield return typeof(IReadOnlyDictionary<string, TElement>); // IReadOnlyDictionaryOfStringTValueConverter
+        }
+
+        public static IEnumerable<Type> DeserializableNonDictionaryTypes<TElement>()
+        {
+            yield return typeof(Hashtable); // IDictionaryConverter
+            yield return typeof(SortedList); // IDictionaryConverter
+        }
+    }
 }
diff --git a/src/libraries/System.Text.Json/tests/System.Text.Json.Tests.csproj b/src/libraries/System.Text.Json/tests/System.Text.Json.Tests.csproj
index 72f5dbc5097b3f..74459b8f4f6b7a 100644
--- a/src/libraries/System.Text.Json/tests/System.Text.Json.Tests.csproj
+++ b/src/libraries/System.Text.Json/tests/System.Text.Json.Tests.csproj
@@ -1,6 +1,6 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -93,11 +93,13 @@
     <Compile Include="Serialization\Null.ReadTests.cs" />
     <Compile Include="Serialization\Null.WriteTests.cs" />
     <Compile Include="Serialization\NullableTests.cs" />
+    <Compile Include="Serialization\NumberHandlingTests.cs" />
     <Compile Include="Serialization\Object.ReadTests.cs" />
     <Compile Include="Serialization\Object.WriteTests.cs" />
     <Compile Include="Serialization\OptionsTests.cs" />
     <Compile Include="Serialization\PolymorphicTests.cs" />
     <Compile Include="Serialization\PropertyNameTests.cs" />
+    <Compile Include="Serialization\PropertyVisiblityTests.InitOnly.cs" />
     <Compile Include="Serialization\PropertyVisibilityTests.NonPublicAccessors.cs" />
     <Compile Include="Serialization\PropertyVisibilityTests.cs" />
     <Compile Include="Serialization\ReadScenarioTests.cs" />
@@ -145,10 +147,15 @@
   <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)'">
     <Compile Include="Serialization\IsExternalInit.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetFrameworkCurrent)'">
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
     <Compile Include="$(CommonPath)System\Buffers\ArrayBufferWriter.cs" Link="CommonTest\System\Buffers\ArrayBufferWriter.cs" />
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="$(NewtonsoftJsonVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.IO.Pipelines\src\System.IO.Pipelines.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections.Immutable\src\System.Collections.Immutable.csproj" />
+    <ProjectReference Include="..\src\System.Text.Json.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Text.Json/tests/TrimmingTests/Helper.cs b/src/libraries/System.Text.Json/tests/TrimmingTests/Helper.cs
index a9593b9f3ab17f..b99a5a895624ff 100644
--- a/src/libraries/System.Text.Json/tests/TrimmingTests/Helper.cs
+++ b/src/libraries/System.Text.Json/tests/TrimmingTests/Helper.cs
@@ -90,16 +90,18 @@ public static bool AssertCollectionAndSerialize<T>(object obj, string json)
         }
     }
 
-    internal class MyClass
+    public class MyClass
     {
         public int X { get; set; }
-        public int Y { get; set; }
+        [JsonInclude]
+        public int Y;
     }
 
     internal struct MyStruct
     {
         public int X { get; }
-        public int Y { get; }
+        [JsonInclude]
+        public int Y;
 
         [JsonConstructor]
         public MyStruct(int x, int y) => (X, Y) = (x, y);
@@ -108,7 +110,8 @@ internal struct MyStruct
     internal class MyClassWithParameterizedCtor
     {
         public int X { get; set; }
-        public int Y { get; set; }
+        [JsonInclude]
+        public int Y;
 
         public MyClassWithParameterizedCtor(int x, int y) => (X, Y) = (x, y);
     }
@@ -116,11 +119,14 @@ internal class MyClassWithParameterizedCtor
     internal class MyBigClass
     {
         public string A { get; }
-        public string B { get; }
+        [JsonInclude]
+        public string B;
         public string C { get; }
-        public int One { get; }
+        [JsonInclude]
+        public int One;
         public int Two { get; }
-        public int Three { get; }
+        [JsonInclude]
+        public int Three;
 
         public MyBigClass(string a, string b, string c, int one, int two, int three)
         {
diff --git a/src/libraries/System.Text.RegularExpressions/Directory.Build.props b/src/libraries/System.Text.RegularExpressions/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Text.RegularExpressions/Directory.Build.props
+++ b/src/libraries/System.Text.RegularExpressions/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Text.RegularExpressions/src/System.Text.RegularExpressions.csproj b/src/libraries/System.Text.RegularExpressions/src/System.Text.RegularExpressions.csproj
index f323acb4be5010..5313bf0d948138 100644
--- a/src/libraries/System.Text.RegularExpressions/src/System.Text.RegularExpressions.csproj
+++ b/src/libraries/System.Text.RegularExpressions/src/System.Text.RegularExpressions.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Text.RegularExpressions</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Text.RegularExpressions/src/System/Collections/HashtableExtensions.cs b/src/libraries/System.Text.RegularExpressions/src/System/Collections/HashtableExtensions.cs
index e45e584606716f..0df0e573b2396f 100644
--- a/src/libraries/System.Text.RegularExpressions/src/System/Collections/HashtableExtensions.cs
+++ b/src/libraries/System.Text.RegularExpressions/src/System/Collections/HashtableExtensions.cs
@@ -7,14 +7,15 @@ namespace System.Collections
 {
     internal static class HashtableExtensions
     {
-        public static bool TryGetValue<T>(this Hashtable table, object key, [MaybeNull] out T value)
+        public static bool TryGetValue<T>(this Hashtable table, object key, out T? value)
         {
             if (table.ContainsKey(key))
             {
                 value = (T)table[key]!;
                 return true;
             }
-            value = default!;
+
+            value = default;
             return false;
         }
     }
diff --git a/src/libraries/System.Text.RegularExpressions/tests/Regex.Groups.Tests.cs b/src/libraries/System.Text.RegularExpressions/tests/Regex.Groups.Tests.cs
index 2a85402db34e55..4978a94bdc24cc 100644
--- a/src/libraries/System.Text.RegularExpressions/tests/Regex.Groups.Tests.cs
+++ b/src/libraries/System.Text.RegularExpressions/tests/Regex.Groups.Tests.cs
@@ -856,8 +856,11 @@ public static IEnumerable<object[]> Groups_CustomCulture_TestData_Turkish()
 
         public static IEnumerable<object[]> Groups_CustomCulture_TestData_AzeriLatin()
         {
-            yield return new object[] { "az-Latn-AZ", "\u0131", "\u0049", RegexOptions.IgnoreCase, new string[] { "\u0049" } };
-            yield return new object[] { "az-Latn-AZ", "\u0130", "\u0069", RegexOptions.IgnoreCase, new string[] { "\u0069" } };
+            if (PlatformDetection.IsNotBrowser)
+            {
+                yield return new object[] { "az-Latn-AZ", "\u0131", "\u0049", RegexOptions.IgnoreCase, new string[] { "\u0049" } };
+                yield return new object[] { "az-Latn-AZ", "\u0130", "\u0069", RegexOptions.IgnoreCase, new string[] { "\u0069" } };
+            }
         }
 
         [Theory]
diff --git a/src/libraries/System.Text.RegularExpressions/tests/RegexMatchTimeoutExceptionTests.cs b/src/libraries/System.Text.RegularExpressions/tests/RegexMatchTimeoutExceptionTests.cs
index 92c1b914fb849e..438c7659a46e83 100644
--- a/src/libraries/System.Text.RegularExpressions/tests/RegexMatchTimeoutExceptionTests.cs
+++ b/src/libraries/System.Text.RegularExpressions/tests/RegexMatchTimeoutExceptionTests.cs
@@ -43,7 +43,7 @@ public void Ctor()
             Assert.Equal(timeout, e.MatchTimeout);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported))]
         public void SerializationRoundtrip()
         {
             const string Input = "abcdef";
diff --git a/src/libraries/System.Text.RegularExpressions/tests/RegexParserTests.cs b/src/libraries/System.Text.RegularExpressions/tests/RegexParserTests.cs
index 7228d5d4b42dd5..849afb7f404f84 100644
--- a/src/libraries/System.Text.RegularExpressions/tests/RegexParserTests.cs
+++ b/src/libraries/System.Text.RegularExpressions/tests/RegexParserTests.cs
@@ -813,7 +813,7 @@ public void Parse_NotNetFramework(string pattern, RegexOptions options, object e
             Parse(pattern, options, error);
         }
 
-        [Fact]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsBinaryFormatterSupported))]
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework)]
         public void RegexParseException_Serializes()
         {
diff --git a/src/libraries/System.Text.RegularExpressions/tests/System.Text.RegularExpressions.Tests.csproj b/src/libraries/System.Text.RegularExpressions/tests/System.Text.RegularExpressions.Tests.csproj
index dc756043b94906..20878cabf96e9f 100644
--- a/src/libraries/System.Text.RegularExpressions/tests/System.Text.RegularExpressions.Tests.csproj
+++ b/src/libraries/System.Text.RegularExpressions/tests/System.Text.RegularExpressions.Tests.csproj
@@ -3,7 +3,7 @@
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
     <!-- xUnit2008 is about regexes and isn't appropriate in the test project for regexes -->
     <NoWarn>$(NoWarn);xUnit2008</NoWarn>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net48</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="AttRegexTests.cs" />
diff --git a/src/libraries/System.Threading.AccessControl/ref/System.Threading.AccessControl.cs b/src/libraries/System.Threading.AccessControl/ref/System.Threading.AccessControl.cs
index db92ef1338ef1e..b42eb330f7233f 100644
--- a/src/libraries/System.Threading.AccessControl/ref/System.Threading.AccessControl.cs
+++ b/src/libraries/System.Threading.AccessControl/ref/System.Threading.AccessControl.cs
@@ -137,25 +137,25 @@ public void SetAuditRule(System.Security.AccessControl.SemaphoreAuditRule rule)
 }
 namespace System.Threading
 {
-    public static partial class ThreadingAclExtensions
-    {
-        public static System.Security.AccessControl.EventWaitHandleSecurity GetAccessControl(this System.Threading.EventWaitHandle handle) { throw null; }
-        public static System.Security.AccessControl.MutexSecurity GetAccessControl(this System.Threading.Mutex mutex) { throw null; }
-        public static System.Security.AccessControl.SemaphoreSecurity GetAccessControl(this System.Threading.Semaphore semaphore) { throw null; }
-        public static void SetAccessControl(this System.Threading.EventWaitHandle handle, System.Security.AccessControl.EventWaitHandleSecurity eventSecurity) { }
-        public static void SetAccessControl(this System.Threading.Mutex mutex, System.Security.AccessControl.MutexSecurity mutexSecurity) { }
-        public static void SetAccessControl(this System.Threading.Semaphore semaphore, System.Security.AccessControl.SemaphoreSecurity semaphoreSecurity) { }
-    }
-    public static class EventWaitHandleAcl
+    public static partial class EventWaitHandleAcl
     {
         public static System.Threading.EventWaitHandle Create(bool initialState, System.Threading.EventResetMode mode, string? name, out bool createdNew, System.Security.AccessControl.EventWaitHandleSecurity? eventSecurity) { throw null; }
     }
-    public static class MutexAcl
+    public static partial class MutexAcl
     {
         public static System.Threading.Mutex Create(bool initiallyOwned, string? name, out bool createdNew, System.Security.AccessControl.MutexSecurity? mutexSecurity) { throw null; }
     }
-    public static class SemaphoreAcl
+    public static partial class SemaphoreAcl
     {
         public static System.Threading.Semaphore Create(int initialCount, int maximumCount, string? name, out bool createdNew, System.Security.AccessControl.SemaphoreSecurity? semaphoreSecurity) { throw null; }
     }
+    public static partial class ThreadingAclExtensions
+    {
+        public static System.Security.AccessControl.EventWaitHandleSecurity GetAccessControl(this System.Threading.EventWaitHandle handle) { throw null; }
+        public static System.Security.AccessControl.MutexSecurity GetAccessControl(this System.Threading.Mutex mutex) { throw null; }
+        public static System.Security.AccessControl.SemaphoreSecurity GetAccessControl(this System.Threading.Semaphore semaphore) { throw null; }
+        public static void SetAccessControl(this System.Threading.EventWaitHandle handle, System.Security.AccessControl.EventWaitHandleSecurity eventSecurity) { }
+        public static void SetAccessControl(this System.Threading.Mutex mutex, System.Security.AccessControl.MutexSecurity mutexSecurity) { }
+        public static void SetAccessControl(this System.Threading.Semaphore semaphore, System.Security.AccessControl.SemaphoreSecurity semaphoreSecurity) { }
+    }
 }
diff --git a/src/libraries/System.Threading.AccessControl/ref/System.Threading.AccessControl.csproj b/src/libraries/System.Threading.AccessControl/ref/System.Threading.AccessControl.csproj
index a88ecaa24bca91..561c79249b2799 100644
--- a/src/libraries/System.Threading.AccessControl/ref/System.Threading.AccessControl.csproj
+++ b/src/libraries/System.Threading.AccessControl/ref/System.Threading.AccessControl.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -11,10 +10,6 @@
   <ItemGroup>
     <Compile Include="System.Threading.AccessControl.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
-  </ItemGroup>
   <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
     <ProjectReference Include="..\..\System.Security.AccessControl\ref\System.Security.AccessControl.csproj" />
     <ProjectReference Include="..\..\System.Security.Principal.Windows\ref\System.Security.Principal.Windows.csproj" />
diff --git a/src/libraries/System.Threading.AccessControl/src/System.Threading.AccessControl.csproj b/src/libraries/System.Threading.AccessControl/src/System.Threading.AccessControl.csproj
index e5398bcb532b09..3ca55d2551592d 100644
--- a/src/libraries/System.Threading.AccessControl/src/System.Threading.AccessControl.csproj
+++ b/src/libraries/System.Threading.AccessControl/src/System.Threading.AccessControl.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0-Windows_NT;net461-Windows_NT;netstandard2.0;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0-Windows_NT;net461-Windows_NT;netstandard2.0</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -44,16 +43,14 @@
     <Compile Include="System\Threading\ThreadingAclExtensions.cs" />
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
     <Compile Include="System\Threading\EventWaitHandleAcl.net46.cs" />
     <Compile Include="System\Threading\MutexAcl.net46.cs" />
     <Compile Include="System\Threading\SemaphoreAcl.net46.cs" />
     <Compile Include="System\Threading\ThreadingAclExtensions.net46.cs" />
   </ItemGroup>
-  <ItemGroup Condition="!$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Security.AccessControl" />
-    <Reference Include="System.Security.Principal.Windows" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard2.0'))">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.AccessControl\src\System.Security.AccessControl.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Principal.Windows\src\System.Security.Principal.Windows.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Threading.AccessControl/tests/System.Threading.AccessControl.Tests.csproj b/src/libraries/System.Threading.AccessControl/tests/System.Threading.AccessControl.Tests.csproj
index c60e1d656cd047..5d41e0bac88da3 100644
--- a/src/libraries/System.Threading.AccessControl/tests/System.Threading.AccessControl.Tests.csproj
+++ b/src/libraries/System.Threading.AccessControl/tests/System.Threading.AccessControl.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetFrameworkCurrent)-Windows_NT</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;net461-Windows_NT</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.Constants.cs"
@@ -14,4 +14,7 @@
     <Compile Include="SemaphoreAclTests.cs" />
     <Compile Include="ThreadingAclExtensionsTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Threading.AccessControl.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Threading.Channels/Directory.Build.props b/src/libraries/System.Threading.Channels/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.Threading.Channels/Directory.Build.props
+++ b/src/libraries/System.Threading.Channels/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Threading.Channels/ref/System.Threading.Channels.csproj b/src/libraries/System.Threading.Channels/ref/System.Threading.Channels.csproj
index 4aace39265e88b..464fca7b6b6798 100644
--- a/src/libraries/System.Threading.Channels/ref/System.Threading.Channels.csproj
+++ b/src/libraries/System.Threading.Channels/ref/System.Threading.Channels.csproj
@@ -1,26 +1,27 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard1.3;netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0;netstandard1.3;netstandard2.0;netstandard2.1;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Threading.Channels.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard1.3' AND '$(TargetFramework)' != 'netstandard2.0'">
+  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard1.3' and
+                        '$(TargetFramework)' != 'netstandard2.0' and
+                        '$(TargetFramework)' != 'net461'">
     <Compile Include="System.Threading.Channels.netstandard21.cs" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard'))">
-    <Reference Include="System.Threading.Tasks.Extensions" />
-  </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="System.Runtime" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="../../System.Runtime/ref/System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime/ref/System.Runtime.csproj" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3'">
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Threading.Tasks" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard')) or
+                        '$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
+    <!-- Include these transitive dependencies to overrule NuGet's ProjectReference over PackageReferene behavior. -->
+    <PackageReference Include="System.Runtime" Version="$(SystemRuntimeVersion)" Condition="'$(TargetFramework)' == 'netstandard1.3'" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Threading.Channels/src/System.Threading.Channels.csproj b/src/libraries/System.Threading.Channels/src/System.Threading.Channels.csproj
index b52a5869a938de..498f88004c8335 100644
--- a/src/libraries/System.Threading.Channels/src/System.Threading.Channels.csproj
+++ b/src/libraries/System.Threading.Channels/src/System.Threading.Channels.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.0;net461</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
     <Nullable>enable</Nullable>
   </PropertyGroup>
@@ -31,8 +30,8 @@
     <Compile Include="$(CommonPath)System\Collections\Concurrent\SingleProducerConsumerQueue.cs"
              Link="Common\System\Collections\Concurrent\SingleProducerConsumerQueue.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.AppContext" Condition="'$(TargetFramework)' == 'netstandard1.3'" />
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)' or
+                        '$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="System.Collections" />
     <Reference Include="System.Collections.Concurrent" />
     <Reference Include="System.Diagnostics.Debug" />
@@ -40,12 +39,12 @@
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Threading" />
-    <Reference Include="System.Threading.ThreadPool" Condition="!$(TargetFramework.StartsWith('netstandard')) AND !$(TargetFramework.StartsWith('net4'))" />
+    <Reference Include="System.Threading.ThreadPool" />
     <Reference Include="System.Threading.Tasks" />
     <Reference Include="System.Threading.Tasks.Extensions" />
   </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard')) or
+                        $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="$(SystemThreadingTasksExtensionsVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Threading.Channels/src/System/Threading/Channels/AsyncOperation.cs b/src/libraries/System.Threading.Channels/src/System/Threading/Channels/AsyncOperation.cs
index 2a2120327fc4cd..9412cc28abfaf8 100644
--- a/src/libraries/System.Threading.Channels/src/System/Threading/Channels/AsyncOperation.cs
+++ b/src/libraries/System.Threading.Channels/src/System/Threading/Channels/AsyncOperation.cs
@@ -51,8 +51,7 @@ internal partial class AsyncOperation<TResult> : AsyncOperation, IValueTaskSourc
         /// <summary>Only relevant to cancelable operations; 0 if the operation hasn't had completion reserved, 1 if it has.</summary>
         private volatile int _completionReserved;
         /// <summary>The result of the operation.</summary>
-        [MaybeNull, AllowNull]
-        private TResult _result = default;
+        private TResult? _result;
         /// <summary>Any error that occurred during the operation.</summary>
         private ExceptionDispatchInfo? _error;
         /// <summary>The continuation callback.</summary>
@@ -89,7 +88,7 @@ public AsyncOperation(bool runContinuationsAsynchronously, CancellationToken can
             {
                 Debug.Assert(!_pooled, "Cancelable operations can't be pooled");
                 CancellationToken = cancellationToken;
-                _registration = UnsafeRegister(cancellationToken, s =>
+                _registration = UnsafeRegister(cancellationToken, static s =>
                 {
                     var thisRef = (AsyncOperation<TResult>)s!;
                     thisRef.TrySetCanceled(thisRef.CancellationToken);
@@ -273,7 +272,7 @@ public void OnCompleted(Action<object?> continuation, object? state, short token
                 }
                 else if (sc != null)
                 {
-                    sc.Post(s =>
+                    sc.Post(static s =>
                     {
                         var t = (Tuple<Action<object?>, object>)s!;
                         t.Item1(t.Item2);
@@ -395,7 +394,7 @@ private void SignalCompletion()
                     // Otherwise fall through to invoke it synchronously.
                     if (_runContinuationsAsynchronously || sc != SynchronizationContext.Current)
                     {
-                        sc.Post(s => ((AsyncOperation<TResult>)s!).SetCompletionAndInvokeContinuation(), this);
+                        sc.Post(static s => ((AsyncOperation<TResult>)s!).SetCompletionAndInvokeContinuation(), this);
                         return;
                     }
                 }
@@ -408,7 +407,7 @@ private void SignalCompletion()
                     Debug.Assert(ts != null, "Expected a TaskScheduler");
                     if (_runContinuationsAsynchronously || ts != TaskScheduler.Current)
                     {
-                        Task.Factory.StartNew(s => ((AsyncOperation<TResult>)s!).SetCompletionAndInvokeContinuation(), this,
+                        Task.Factory.StartNew(static s => ((AsyncOperation<TResult>)s!).SetCompletionAndInvokeContinuation(), this,
                             CancellationToken.None, TaskCreationOptions.DenyChildAttach, ts);
                         return;
                     }
@@ -429,7 +428,7 @@ private void SetCompletionAndInvokeContinuation()
             }
             else
             {
-                ExecutionContext.Run(_executionContext, s =>
+                ExecutionContext.Run(_executionContext, static s =>
                 {
                     var thisRef = (AsyncOperation<TResult>)s!;
                     Action<object?> c = thisRef._continuation!;
@@ -454,7 +453,6 @@ public VoidAsyncOperationWithData(bool runContinuationsAsynchronously, Cancellat
         }
 
         /// <summary>The item being written.</summary>
-        [MaybeNull, AllowNull]
-        public TData Item { get; set; } = default!;
+        public TData? Item { get; set; }
     }
 }
diff --git a/src/libraries/System.Threading.Channels/src/System/Threading/Channels/BoundedChannel.cs b/src/libraries/System.Threading.Channels/src/System/Threading/Channels/BoundedChannel.cs
index be088c5291b12a..cec397b78bc3f7 100644
--- a/src/libraries/System.Threading.Channels/src/System/Threading/Channels/BoundedChannel.cs
+++ b/src/libraries/System.Threading.Channels/src/System/Threading/Channels/BoundedChannel.cs
@@ -105,7 +105,7 @@ public override bool TryRead([MaybeNullWhen(false)] out T item)
                     }
                 }
 
-                item = default!;
+                item = default;
                 return false;
             }
 
diff --git a/src/libraries/System.Threading.Channels/src/System/Threading/Channels/UnboundedChannel.cs b/src/libraries/System.Threading.Channels/src/System/Threading/Channels/UnboundedChannel.cs
index 6ac25fb998578f..612d6b50f8f368 100644
--- a/src/libraries/System.Threading.Channels/src/System/Threading/Channels/UnboundedChannel.cs
+++ b/src/libraries/System.Threading.Channels/src/System/Threading/Channels/UnboundedChannel.cs
@@ -119,7 +119,7 @@ public override bool TryRead([MaybeNullWhen(false)] out T item)
                     return true;
                 }
 
-                item = default!;
+                item = default;
                 return false;
             }
 
diff --git a/src/libraries/System.Threading.Channels/tests/System.Threading.Channels.Tests.csproj b/src/libraries/System.Threading.Channels/tests/System.Threading.Channels.Tests.csproj
index 5c1178c3d1c646..c67e5e5fed5cdf 100644
--- a/src/libraries/System.Threading.Channels/tests/System.Threading.Channels.Tests.csproj
+++ b/src/libraries/System.Threading.Channels/tests/System.Threading.Channels.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="BoundedChannelTests.cs" />
@@ -18,4 +18,7 @@
     <Compile Include="ChannelClosedExceptionTests.netcoreapp.cs" />
     <Compile Include="ChannelTestBase.netcoreapp.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="..\src\System.Threading.Channels.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Threading.Overlapped/Directory.Build.props b/src/libraries/System.Threading.Overlapped/Directory.Build.props
index 0f058f12cba861..33e65b7cb46516 100644
--- a/src/libraries/System.Threading.Overlapped/Directory.Build.props
+++ b/src/libraries/System.Threading.Overlapped/Directory.Build.props
@@ -2,7 +2,6 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
     <IsWindowsSpecific>true</IsWindowsSpecific>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Threading.Overlapped/ref/System.Threading.Overlapped.cs b/src/libraries/System.Threading.Overlapped/ref/System.Threading.Overlapped.cs
index 991a27b0969a31..634e1697d46144 100644
--- a/src/libraries/System.Threading.Overlapped/ref/System.Threading.Overlapped.cs
+++ b/src/libraries/System.Threading.Overlapped/ref/System.Threading.Overlapped.cs
@@ -29,14 +29,14 @@ public Overlapped(int offsetLo, int offsetHi, System.IntPtr hEvent, System.IAsyn
         public int OffsetHigh { get { throw null; } set { } }
         public int OffsetLow { get { throw null; } set { } }
         [System.CLSCompliantAttribute(false)]
-        public static unsafe void Free(System.Threading.NativeOverlapped* nativeOverlappedPtr) { }
+        public unsafe static void Free(System.Threading.NativeOverlapped* nativeOverlappedPtr) { }
         [System.CLSCompliantAttribute(false)]
         [System.ObsoleteAttribute("This method is not safe.  Use Pack (iocb, userData) instead.  https://go.microsoft.com/fwlink/?linkid=14202")]
         public unsafe System.Threading.NativeOverlapped* Pack(System.Threading.IOCompletionCallback? iocb) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public unsafe System.Threading.NativeOverlapped* Pack(System.Threading.IOCompletionCallback? iocb, object? userData) { throw null; }
         [System.CLSCompliantAttribute(false)]
-        public static unsafe System.Threading.Overlapped Unpack(System.Threading.NativeOverlapped* nativeOverlappedPtr) { throw null; }
+        public unsafe static System.Threading.Overlapped Unpack(System.Threading.NativeOverlapped* nativeOverlappedPtr) { throw null; }
         [System.CLSCompliantAttribute(false)]
         [System.ObsoleteAttribute("This method is not safe.  Use UnsafePack (iocb, userData) instead.  https://go.microsoft.com/fwlink/?linkid=14202")]
         public unsafe System.Threading.NativeOverlapped* UnsafePack(System.Threading.IOCompletionCallback? iocb) { throw null; }
@@ -63,6 +63,6 @@ public void Dispose() { }
         [System.CLSCompliantAttribute(false)]
         public unsafe void FreeNativeOverlapped(System.Threading.NativeOverlapped* overlapped) { }
         [System.CLSCompliantAttribute(false)]
-        public static unsafe object? GetNativeOverlappedState(System.Threading.NativeOverlapped* overlapped) { throw null; }
+        public unsafe static object? GetNativeOverlappedState(System.Threading.NativeOverlapped* overlapped) { throw null; }
     }
 }
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/Directory.Build.props b/src/libraries/System.Threading.Tasks.Dataflow/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/Directory.Build.props
+++ b/src/libraries/System.Threading.Tasks.Dataflow/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/ref/System.Threading.Tasks.Dataflow.cs b/src/libraries/System.Threading.Tasks.Dataflow/ref/System.Threading.Tasks.Dataflow.cs
index e860e697ac7de1..4931e851d6d399 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/ref/System.Threading.Tasks.Dataflow.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/ref/System.Threading.Tasks.Dataflow.cs
@@ -30,8 +30,7 @@ public BatchBlock(int batchSize, System.Threading.Tasks.Dataflow.GroupingDataflo
         public void Complete() { }
         public System.IDisposable LinkTo(System.Threading.Tasks.Dataflow.ITargetBlock<T[]> target, System.Threading.Tasks.Dataflow.DataflowLinkOptions linkOptions) { throw null; }
         void System.Threading.Tasks.Dataflow.IDataflowBlock.Fault(System.Exception exception) { }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        T[] System.Threading.Tasks.Dataflow.ISourceBlock<T[]>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T[]> target, out bool messageConsumed) { throw null; }
+        T[]? System.Threading.Tasks.Dataflow.ISourceBlock<T[]>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T[]> target, out bool messageConsumed) { throw null; }
         void System.Threading.Tasks.Dataflow.ISourceBlock<T[]>.ReleaseReservation(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T[]> target) { }
         bool System.Threading.Tasks.Dataflow.ISourceBlock<T[]>.ReserveMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T[]> target) { throw null; }
         System.Threading.Tasks.Dataflow.DataflowMessageStatus System.Threading.Tasks.Dataflow.ITargetBlock<T>.OfferMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, T messageValue, System.Threading.Tasks.Dataflow.ISourceBlock<T>? source, bool consumeToAccept) { throw null; }
@@ -88,8 +87,7 @@ public void Complete() { }
         public System.IDisposable LinkTo(System.Threading.Tasks.Dataflow.ITargetBlock<T> target, System.Threading.Tasks.Dataflow.DataflowLinkOptions linkOptions) { throw null; }
         void System.Threading.Tasks.Dataflow.IDataflowBlock.Fault(System.Exception exception) { }
         bool System.Threading.Tasks.Dataflow.IReceivableSourceBlock<T>.TryReceiveAll([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.Collections.Generic.IList<T>? items) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        T System.Threading.Tasks.Dataflow.ISourceBlock<T>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target, out bool messageConsumed) { throw null; }
+        T? System.Threading.Tasks.Dataflow.ISourceBlock<T>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target, out bool messageConsumed) { throw null; }
         void System.Threading.Tasks.Dataflow.ISourceBlock<T>.ReleaseReservation(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target) { }
         bool System.Threading.Tasks.Dataflow.ISourceBlock<T>.ReserveMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target) { throw null; }
         System.Threading.Tasks.Dataflow.DataflowMessageStatus System.Threading.Tasks.Dataflow.ITargetBlock<T>.OfferMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, T messageValue, System.Threading.Tasks.Dataflow.ISourceBlock<T>? source, bool consumeToAccept) { throw null; }
@@ -105,8 +103,7 @@ public BufferBlock(System.Threading.Tasks.Dataflow.DataflowBlockOptions dataflow
         public void Complete() { }
         public System.IDisposable LinkTo(System.Threading.Tasks.Dataflow.ITargetBlock<T> target, System.Threading.Tasks.Dataflow.DataflowLinkOptions linkOptions) { throw null; }
         void System.Threading.Tasks.Dataflow.IDataflowBlock.Fault(System.Exception exception) { }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        T System.Threading.Tasks.Dataflow.ISourceBlock<T>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target, out bool messageConsumed) { throw null; }
+        T? System.Threading.Tasks.Dataflow.ISourceBlock<T>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target, out bool messageConsumed) { throw null; }
         void System.Threading.Tasks.Dataflow.ISourceBlock<T>.ReleaseReservation(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target) { }
         bool System.Threading.Tasks.Dataflow.ISourceBlock<T>.ReserveMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target) { throw null; }
         System.Threading.Tasks.Dataflow.DataflowMessageStatus System.Threading.Tasks.Dataflow.ITargetBlock<T>.OfferMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, T messageValue, System.Threading.Tasks.Dataflow.ISourceBlock<T>? source, bool consumeToAccept) { throw null; }
@@ -208,8 +205,7 @@ public partial interface IReceivableSourceBlock<TOutput> : System.Threading.Task
     }
     public partial interface ISourceBlock<out TOutput> : System.Threading.Tasks.Dataflow.IDataflowBlock
     {
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        TOutput ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target, out bool messageConsumed);
+        TOutput? ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target, out bool messageConsumed);
         System.IDisposable LinkTo(System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target, System.Threading.Tasks.Dataflow.DataflowLinkOptions linkOptions);
         void ReleaseReservation(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target);
         bool ReserveMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target);
@@ -267,8 +263,7 @@ public TransformBlock(System.Func<TInput, TOutput> transform, System.Threading.T
         public void Complete() { }
         public System.IDisposable LinkTo(System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target, System.Threading.Tasks.Dataflow.DataflowLinkOptions linkOptions) { throw null; }
         void System.Threading.Tasks.Dataflow.IDataflowBlock.Fault(System.Exception exception) { }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        TOutput System.Threading.Tasks.Dataflow.ISourceBlock<TOutput>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target, out bool messageConsumed) { throw null; }
+        TOutput? System.Threading.Tasks.Dataflow.ISourceBlock<TOutput>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target, out bool messageConsumed) { throw null; }
         void System.Threading.Tasks.Dataflow.ISourceBlock<TOutput>.ReleaseReservation(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target) { }
         bool System.Threading.Tasks.Dataflow.ISourceBlock<TOutput>.ReserveMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target) { throw null; }
         System.Threading.Tasks.Dataflow.DataflowMessageStatus System.Threading.Tasks.Dataflow.ITargetBlock<TInput>.OfferMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, TInput messageValue, System.Threading.Tasks.Dataflow.ISourceBlock<TInput>? source, bool consumeToAccept) { throw null; }
@@ -288,8 +283,7 @@ public TransformManyBlock(System.Func<TInput, System.Threading.Tasks.Task<System
         public void Complete() { }
         public System.IDisposable LinkTo(System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target, System.Threading.Tasks.Dataflow.DataflowLinkOptions linkOptions) { throw null; }
         void System.Threading.Tasks.Dataflow.IDataflowBlock.Fault(System.Exception exception) { }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        TOutput System.Threading.Tasks.Dataflow.ISourceBlock<TOutput>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target, out bool messageConsumed) { throw null; }
+        TOutput? System.Threading.Tasks.Dataflow.ISourceBlock<TOutput>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target, out bool messageConsumed) { throw null; }
         void System.Threading.Tasks.Dataflow.ISourceBlock<TOutput>.ReleaseReservation(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target) { }
         bool System.Threading.Tasks.Dataflow.ISourceBlock<TOutput>.ReserveMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<TOutput> target) { throw null; }
         System.Threading.Tasks.Dataflow.DataflowMessageStatus System.Threading.Tasks.Dataflow.ITargetBlock<TInput>.OfferMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, TInput messageValue, System.Threading.Tasks.Dataflow.ISourceBlock<TInput>? source, bool consumeToAccept) { throw null; }
@@ -306,8 +300,7 @@ public void Complete() { }
         public System.IDisposable LinkTo(System.Threading.Tasks.Dataflow.ITargetBlock<T> target, System.Threading.Tasks.Dataflow.DataflowLinkOptions linkOptions) { throw null; }
         void System.Threading.Tasks.Dataflow.IDataflowBlock.Fault(System.Exception exception) { }
         bool System.Threading.Tasks.Dataflow.IReceivableSourceBlock<T>.TryReceiveAll([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.Collections.Generic.IList<T>? items) { throw null; }
-        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        T System.Threading.Tasks.Dataflow.ISourceBlock<T>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target, out bool messageConsumed) { throw null; }
+        T? System.Threading.Tasks.Dataflow.ISourceBlock<T>.ConsumeMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target, out bool messageConsumed) { throw null; }
         void System.Threading.Tasks.Dataflow.ISourceBlock<T>.ReleaseReservation(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target) { }
         bool System.Threading.Tasks.Dataflow.ISourceBlock<T>.ReserveMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, System.Threading.Tasks.Dataflow.ITargetBlock<T> target) { throw null; }
         System.Threading.Tasks.Dataflow.DataflowMessageStatus System.Threading.Tasks.Dataflow.ITargetBlock<T>.OfferMessage(System.Threading.Tasks.Dataflow.DataflowMessageHeader messageHeader, T messageValue, System.Threading.Tasks.Dataflow.ISourceBlock<T>? source, bool consumeToAccept) { throw null; }
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/ref/System.Threading.Tasks.Dataflow.csproj b/src/libraries/System.Threading.Tasks.Dataflow/ref/System.Threading.Tasks.Dataflow.csproj
index 915b6a275eae36..7c65f89d1bf103 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/ref/System.Threading.Tasks.Dataflow.csproj
+++ b/src/libraries/System.Threading.Tasks.Dataflow/ref/System.Threading.Tasks.Dataflow.csproj
@@ -1,13 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard1.0;netstandard1.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard1.0;netstandard1.1;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Threading.Tasks.Dataflow.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.0' Or '$(TargetFramework)' == 'netstandard1.1'">
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Threading.Tasks" />
-  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Base/DataflowBlock.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Base/DataflowBlock.cs
index 45d7c5c4c033c7..2785f3ea4d4ab7 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Base/DataflowBlock.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Base/DataflowBlock.cs
@@ -154,8 +154,7 @@ DataflowMessageStatus ITargetBlock<T>.OfferMessage(DataflowMessageHeader message
             }
 
             /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-            [return: MaybeNull]
-            T ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T> target, out bool messageConsumed)
+            T? ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T> target, out bool messageConsumed)
             {
                 // This message should have only made it to the target if it passes the filter, so we shouldn't need to check again.
                 // The real source will also be doing verifications, so we don't need to validate args here.
@@ -621,8 +620,7 @@ internal void OfferToTarget()
             }
 
             /// <summary>Called by the target to consume the buffered message.</summary>
-            [return: MaybeNull]
-            TOutput ISourceBlock<TOutput>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
+            TOutput? ISourceBlock<TOutput>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
             {
                 // Validate arguments
                 if (!messageHeader.IsValid) throw new ArgumentException(SR.Argument_InvalidMessageHeader, nameof(messageHeader));
@@ -1129,8 +1127,7 @@ private sealed class ReceiveTarget<T> : TaskCompletionSource<T>, ITargetBlock<T>
             };
 
             /// <summary>The received value if we accepted a value from the source.</summary>
-            [AllowNull, MaybeNull]
-            private T _receivedValue = default!;
+            private T? _receivedValue;
 
             /// <summary>The cancellation token source representing both external and internal cancellation.</summary>
             internal readonly CancellationTokenSource _cts = new CancellationTokenSource();
@@ -1664,8 +1661,7 @@ public bool TryReceiveAll([NotNullWhen(true)] out IList<TOutput>? items)
             }
 
             /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-            [return: MaybeNull]
-            public TOutput ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
+            public TOutput? ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
             {
                 return _source.ConsumeMessage(messageHeader, target, out messageConsumed);
             }
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Base/ISourceBlock.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Base/ISourceBlock.cs
index 518f8fb026639b..8e4d27af8bf982 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Base/ISourceBlock.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Base/ISourceBlock.cs
@@ -27,8 +27,7 @@ public interface ISourceBlock<out TOutput> : IDataflowBlock
         // IMPLEMENT EXPLICITLY
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-        [return: MaybeNull]
-        TOutput ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed);
+        TOutput? ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed);
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ReserveMessage"]/*' />
         bool ReserveMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target);
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BatchBlock.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BatchBlock.cs
index df9bb9c980f3ad..af2775e9031f99 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BatchBlock.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BatchBlock.cs
@@ -154,8 +154,7 @@ DataflowMessageStatus ITargetBlock<T>.OfferMessage(DataflowMessageHeader message
         }
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-        [return: MaybeNull]
-        T[] ISourceBlock<T[]>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T[]> target, out bool messageConsumed)
+        T[]? ISourceBlock<T[]>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T[]> target, out bool messageConsumed)
         {
             return _source.ConsumeMessage(messageHeader, target, out messageConsumed);
         }
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BatchedJoinBlock.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BatchedJoinBlock.cs
index 054eaa3bc19ed1..8099f49cae70cb 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BatchedJoinBlock.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BatchedJoinBlock.cs
@@ -172,8 +172,7 @@ void IDataflowBlock.Fault(Exception exception)
         }
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-        [return: MaybeNull]
-        Tuple<IList<T1>, IList<T2>> ISourceBlock<Tuple<IList<T1>, IList<T2>>>.ConsumeMessage(
+        Tuple<IList<T1>, IList<T2>>? ISourceBlock<Tuple<IList<T1>, IList<T2>>>.ConsumeMessage(
             DataflowMessageHeader messageHeader, ITargetBlock<Tuple<IList<T1>, IList<T2>>> target, out bool messageConsumed)
         {
             return _source.ConsumeMessage(messageHeader, target, out messageConsumed);
@@ -436,8 +435,7 @@ void IDataflowBlock.Fault(Exception exception)
         }
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-        [return: MaybeNull]
-        Tuple<IList<T1>, IList<T2>, IList<T3>> ISourceBlock<Tuple<IList<T1>, IList<T2>, IList<T3>>>.ConsumeMessage(
+        Tuple<IList<T1>, IList<T2>, IList<T3>>? ISourceBlock<Tuple<IList<T1>, IList<T2>, IList<T3>>>.ConsumeMessage(
             DataflowMessageHeader messageHeader, ITargetBlock<Tuple<IList<T1>, IList<T2>, IList<T3>>> target, out bool messageConsumed)
         {
             return _source.ConsumeMessage(messageHeader, target, out messageConsumed);
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BroadcastBlock.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BroadcastBlock.cs
index 508d151b043157..9f9b93298f86c2 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BroadcastBlock.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BroadcastBlock.cs
@@ -417,8 +417,7 @@ private void CompleteTargetIfPossible()
         }
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-        [return: MaybeNull]
-        T ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T> target, out bool messageConsumed)
+        T? ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T> target, out bool messageConsumed)
         {
             return _source.ConsumeMessage(messageHeader, target, out messageConsumed);
         }
@@ -531,8 +530,7 @@ private sealed class BroadcastingSourceCore<TOutput>
             /// <summary>An indicator whether _currentMessage has a value.</summary>
             private bool _currentMessageIsValid;
             /// <summary>The message currently being broadcast.</summary>
-            [AllowNull, MaybeNull]
-            private TOutput _currentMessage = default;
+            private TOutput? _currentMessage;
             /// <summary>The target that the next message is reserved for, or null if nothing is reserved.</summary>
             private ITargetBlock<TOutput>? _nextMessageReservedFor;
             /// <summary>Whether this block should again attempt to offer messages to targets.</summary>
@@ -1049,8 +1047,7 @@ internal IDisposable LinkTo(ITargetBlock<TOutput> target, DataflowLinkOptions li
             }
 
             /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-            [return: MaybeNull]
-            internal TOutput ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
+            internal TOutput? ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
             {
                 // Validate arguments
                 if (!messageHeader.IsValid) throw new ArgumentException(SR.Argument_InvalidMessageHeader, nameof(messageHeader));
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BufferBlock.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BufferBlock.cs
index dc7b45d9649963..6d5e702bb7f04c 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BufferBlock.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/BufferBlock.cs
@@ -197,8 +197,7 @@ private void CompleteCore(Exception? exception, bool storeExceptionEvenIfAlready
         public Task Completion { get { return _source.Completion; } }
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-        [return: MaybeNull]
-        T ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T> target, out bool messageConsumed)
+        T? ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T> target, out bool messageConsumed)
         {
             return _source.ConsumeMessage(messageHeader, target, out messageConsumed);
         }
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/TransformBlock.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/TransformBlock.cs
index cbaff49b6c825f..b5267ca2568145 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/TransformBlock.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/TransformBlock.cs
@@ -368,8 +368,7 @@ DataflowMessageStatus ITargetBlock<TInput>.OfferMessage(DataflowMessageHeader me
         }
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-        [return: MaybeNull]
-        TOutput ISourceBlock<TOutput>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
+        TOutput? ISourceBlock<TOutput>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
         {
             return _source.ConsumeMessage(messageHeader, target, out messageConsumed);
         }
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/TransformManyBlock.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/TransformManyBlock.cs
index a1d7dcc1e0aa2e..0e6ddfab14123c 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/TransformManyBlock.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/TransformManyBlock.cs
@@ -601,8 +601,7 @@ DataflowMessageStatus ITargetBlock<TInput>.OfferMessage(DataflowMessageHeader me
         }
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-        [return: MaybeNull]
-        TOutput ISourceBlock<TOutput>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
+        TOutput? ISourceBlock<TOutput>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
         {
             return _source.ConsumeMessage(messageHeader, target, out messageConsumed);
         }
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/WriteOnceBlock.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/WriteOnceBlock.cs
index 22d052a15364e8..244703a9d89538 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/WriteOnceBlock.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Blocks/WriteOnceBlock.cs
@@ -39,8 +39,7 @@ public sealed class WriteOnceBlock<T> : IPropagatorBlock<T, T>, IReceivableSourc
         /// <summary>The header of the singly-assigned value.</summary>
         private DataflowMessageHeader _header;
         /// <summary>The singly-assigned value.</summary>
-        [AllowNull, MaybeNull]
-        private T _value = default;
+        private T? _value;
 
         /// <summary>Gets the object used as the value lock.</summary>
         private object ValueLock { get { return _targetRegistry; } }
@@ -381,7 +380,7 @@ DataflowMessageStatus ITargetBlock<T>.OfferMessage(DataflowMessageHeader message
         }
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-        T ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T> target, out bool messageConsumed)
+        T? ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T> target, out bool messageConsumed)
         {
             // Validate arguments
             if (!messageHeader.IsValid) throw new ArgumentException(SR.Argument_InvalidMessageHeader, nameof(messageHeader));
@@ -397,7 +396,7 @@ T ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlo
             else
             {
                 messageConsumed = false;
-                return default(T)!;
+                return default;
             }
         }
 
@@ -506,8 +505,7 @@ private TaskCompletionSource<VoidResult> CompletionTaskSource
         /// <summary>Gets whether the block is storing a value.</summary>
         private bool HasValue { get { return _header.IsValid; } }
         /// <summary>Gets the value being stored by the block.</summary>
-        [MaybeNull]
-        private T Value { get { return _header.IsValid ? _value : default(T); } }
+        private T? Value { get { return _header.IsValid ? _value : default(T); } }
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="ToString"]/*' />
         public override string ToString() { return Common.GetNameForDebugger(this, _dataflowBlockOptions); }
@@ -546,8 +544,7 @@ public DebugView(WriteOnceBlock<T> writeOnceBlock)
             /// <summary>Gets whether the WriteOnceBlock has a value.</summary>
             public bool HasValue { get { return _writeOnceBlock.HasValue; } }
             /// <summary>Gets the WriteOnceBlock's value if it has one, or default(T) if it doesn't.</summary>
-            [MaybeNull]
-            public T Value { get { return _writeOnceBlock.Value; } }
+            public T? Value { get { return _writeOnceBlock.Value; } }
 
             /// <summary>Gets the DataflowBlockOptions used to configure this block.</summary>
             public DataflowBlockOptions DataflowBlockOptions { get { return _writeOnceBlock._dataflowBlockOptions; } }
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/Common.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/Common.cs
index 275b2931a40868..0022621f04d84b 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/Common.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/Common.cs
@@ -93,8 +93,7 @@ internal static bool TryKeepAliveUntil<TStateIn, TStateOut>(KeepAlivePredicate<T
         /// <typeparam name="T">The type of the data to be unwrapped.</typeparam>
         /// <param name="state">The weak reference.</param>
         /// <returns>The T instance.</returns>
-        [return: MaybeNull]
-        internal static T UnwrapWeakReference<T>(object state) where T : class
+        internal static T? UnwrapWeakReference<T>(object state) where T : class
         {
             var wr = state as WeakReference<T>;
             Debug.Assert(wr != null, "Expected a WeakReference<T> as the state argument");
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/ReorderingBuffer.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/ReorderingBuffer.cs
index e69865bfd7aa4c..80513f6eae2ec5 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/ReorderingBuffer.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/ReorderingBuffer.cs
@@ -66,7 +66,7 @@ internal ReorderingBuffer(object owningSource, Action<object, TOutput> outputAct
         /// <param name="id">The ID of the item.</param>
         /// <param name="item">The completed item.</param>
         /// <param name="itemIsValid">Specifies whether the item is valid (true) or just a placeholder (false).</param>
-        internal void AddItem(long id, [AllowNull] TOutput item, bool itemIsValid)
+        internal void AddItem(long id, TOutput? item, bool itemIsValid)
         {
             Debug.Assert(id != Common.INVALID_REORDERING_ID, "This ID should never have been handed out.");
             Common.ContractAssertMonitorStatus(ValueLock, held: false);
@@ -104,7 +104,7 @@ internal void AddItem(long id, [AllowNull] TOutput item, bool itemIsValid)
         /// true if the item was not added but is next in line.
         /// false if the item was not added and is not next in line.
         /// </returns>
-        internal bool? AddItemIfNextAndTrusted(long id, [AllowNull] TOutput item, bool isTrusted)
+        internal bool? AddItemIfNextAndTrusted(long id, TOutput? item, bool isTrusted)
         {
             Debug.Assert(id != Common.INVALID_REORDERING_ID, "This ID should never have been handed out.");
             Common.ContractAssertMonitorStatus(ValueLock, held: false);
@@ -138,7 +138,7 @@ public void IgnoreItem(long id)
         /// <summary>Outputs the item.  The item must have already been confirmed to have the next ID.</summary>
         /// <param name="theNextItem">The item to output.</param>
         /// <param name="itemIsValid">Whether the item is valid.</param>
-        private void OutputNextItem([AllowNull] TOutput theNextItem, bool itemIsValid)
+        private void OutputNextItem(TOutput? theNextItem, bool itemIsValid)
         {
             Common.ContractAssertMonitorStatus(ValueLock, held: true);
 
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/SourceCore.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/SourceCore.cs
index 99d772c1ad665d..a9e86e683c2827 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/SourceCore.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/SourceCore.cs
@@ -155,8 +155,7 @@ internal IDisposable LinkTo(ITargetBlock<TOutput> target, DataflowLinkOptions li
         }
 
         /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-        [return: MaybeNull]
-        internal TOutput ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
+        internal TOutput? ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
         {
             // Validate arguments
             if (!messageHeader.IsValid) throw new ArgumentException(SR.Argument_InvalidMessageHeader, nameof(messageHeader));
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/TargetRegistry.cs b/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/TargetRegistry.cs
index 9420fc8854a269..6cc23ec5398692 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/TargetRegistry.cs
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/Internal/TargetRegistry.cs
@@ -331,8 +331,7 @@ DataflowMessageStatus ITargetBlock<T>.OfferMessage(DataflowMessageHeader message
             }
 
             /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
-            [return: MaybeNull]
-            T ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T> target, out bool messageConsumed)
+            T? ISourceBlock<T>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<T> target, out bool messageConsumed)
             {
                 return _owningSource.ConsumeMessage(messageHeader, this, out messageConsumed);
             }
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/src/System.Threading.Tasks.Dataflow.csproj b/src/libraries/System.Threading.Tasks.Dataflow/src/System.Threading.Tasks.Dataflow.csproj
index 9aefb2928ff4e4..ffb871269eee72 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/src/System.Threading.Tasks.Dataflow.csproj
+++ b/src/libraries/System.Threading.Tasks.Dataflow/src/System.Threading.Tasks.Dataflow.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard1.0;netstandard1.1;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>netstandard2.0;netstandard1.0;netstandard1.1;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -61,27 +60,9 @@
   <ItemGroup>
     <Content Include="XmlDocs\System.Threading.Tasks.Dataflow.xml" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard1.0'">
-    <Reference Include="System.Diagnostics.Tracing" />
-    <Reference Include="System.Collections.Concurrent" />
-  </ItemGroup>
-  <ItemGroup>
-    <Reference Include="System.Collections" />
-    <Reference Include="System.Diagnostics.Contracts" />
-    <Reference Include="System.Diagnostics.Debug" />
-    <Reference Include="System.Diagnostics.Tools" />
-    <Reference Include="System.Dynamic.Runtime" />
-    <Reference Include="System.Linq" />
-    <Reference Include="System.Resources.ResourceManager" />
-    <Reference Include="System.Runtime" />
-    <Reference Include="System.Runtime.Extensions" />
-    <Reference Include="System.Runtime.Serialization.Primitives" />
-    <Reference Include="System.Threading" />
-    <Reference Include="System.Threading.Tasks" />
-  </ItemGroup>
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="System.Core" />
-    <Reference Include="System" />
+  <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">
+    <PackageReference Include="System.Diagnostics.Contracts" Version="$(SystemDiagnosticsContractsVersion)" />
+    <PackageReference Include="System.Dynamic.Runtime" Version="$(SystemDynamicRuntimeVersion)" />
+    <PackageReference Include="System.Runtime.Serialization.Primitives" Version="$(SystemRuntimeSerializationPrimitivesVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Threading.Tasks.Dataflow/tests/System.Threading.Tasks.Dataflow.Tests.csproj b/src/libraries/System.Threading.Tasks.Dataflow/tests/System.Threading.Tasks.Dataflow.Tests.csproj
index 64d15af718d8e9..f817822131366d 100644
--- a/src/libraries/System.Threading.Tasks.Dataflow/tests/System.Threading.Tasks.Dataflow.Tests.csproj
+++ b/src/libraries/System.Threading.Tasks.Dataflow/tests/System.Threading.Tasks.Dataflow.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Dataflow\ActionBlockTests.cs" />
@@ -26,4 +26,7 @@
     <Compile Include="$(CommonTestPath)System\Diagnostics\DebuggerAttributes.cs"
              Link="Common\System\Diagnostics\DebuggerAttributes.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <ProjectReference Include="..\src\System.Threading.Tasks.Dataflow.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Threading.Tasks.Extensions/Directory.Build.props b/src/libraries/System.Threading.Tasks.Extensions/Directory.Build.props
index 749d7fc1c6b56d..ba1f965d83cae7 100644
--- a/src/libraries/System.Threading.Tasks.Extensions/Directory.Build.props
+++ b/src/libraries/System.Threading.Tasks.Extensions/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Threading.Tasks.Extensions/tests/AsyncValueTaskMethodBuilderTests.cs b/src/libraries/System.Threading.Tasks.Extensions/tests/AsyncValueTaskMethodBuilderTests.cs
index eb1def0b9cd2ed..d929d30d22d64c 100644
--- a/src/libraries/System.Threading.Tasks.Extensions/tests/AsyncValueTaskMethodBuilderTests.cs
+++ b/src/libraries/System.Threading.Tasks.Extensions/tests/AsyncValueTaskMethodBuilderTests.cs
@@ -399,7 +399,6 @@ async ValueTask<int> ValueTaskReturningAsyncMethod(int result)
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public static async Task AwaitTasksAndValueTasks_InTaskAndValueTaskMethods()
         {
             for (int i = 0; i < 2; i++)
@@ -522,7 +521,6 @@ async ValueTask<int> ValueTaskInt32ReturningMethod()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task NonGeneric_ConcurrentBuilders_WorkCorrectly()
         {
             await Task.WhenAll(Enumerable.Range(0, Environment.ProcessorCount).Select(async _ =>
@@ -540,7 +538,6 @@ static async ValueTask ValueTaskAsync()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task Generic_ConcurrentBuilders_WorkCorrectly()
         {
             await Task.WhenAll(Enumerable.Range(0, Environment.ProcessorCount).Select(async _ =>
diff --git a/src/libraries/System.Threading.Tasks.Extensions/tests/ManualResetValueTaskSourceTests.cs b/src/libraries/System.Threading.Tasks.Extensions/tests/ManualResetValueTaskSourceTests.cs
index 4f3e9366b5ff35..b43ca1f952db84 100644
--- a/src/libraries/System.Threading.Tasks.Extensions/tests/ManualResetValueTaskSourceTests.cs
+++ b/src/libraries/System.Threading.Tasks.Extensions/tests/ManualResetValueTaskSourceTests.cs
@@ -11,7 +11,6 @@ namespace System.Threading.Tasks.Sources.Tests
     public class ManualResetValueTaskSourceTests
     {
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task ReuseInstanceWithResets_Success()
         {
             var mrvts = new ManualResetValueTaskSource<int>();
@@ -84,7 +83,6 @@ public async Task SetResult_BeforeOnCompleted_ResultAvailableSynchronously()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task SetResult_AfterOnCompleted_ResultAvailableAsynchronously()
         {
             var mrvts = new ManualResetValueTaskSource<int>();
@@ -133,7 +131,6 @@ public async Task SetException_BeforeOnCompleted_ResultAvailableSynchronously()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task SetException_AfterOnCompleted_ResultAvailableAsynchronously()
         {
             var mrvts = new ManualResetValueTaskSource<int>();
@@ -415,7 +412,6 @@ protected override void QueueTask(Task task)
         [InlineData(false, true)]
         [InlineData(true, false)]
         [InlineData(true, true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task AsyncEnumerable_Success(bool awaitForeach, bool asyncIterator)
         {
             IAsyncEnumerable<int> enumerable = asyncIterator ?
diff --git a/src/libraries/System.Threading.Tasks.Extensions/tests/ValueTaskTests.cs b/src/libraries/System.Threading.Tasks.Extensions/tests/ValueTaskTests.cs
index 41325575f978c1..9d4d485b2c618e 100644
--- a/src/libraries/System.Threading.Tasks.Extensions/tests/ValueTaskTests.cs
+++ b/src/libraries/System.Threading.Tasks.Extensions/tests/ValueTaskTests.cs
@@ -371,7 +371,6 @@ public void Generic_CreateFromValueTaskSource_AsTaskNotIdempotent() // validates
         [Theory]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task NonGeneric_CreateFromValueTaskSource_Success(bool sync)
         {
             var vt = new ValueTask(sync ? ManualResetValueTaskSourceFactory.Completed(0) : ManualResetValueTaskSourceFactory.Delay(1, 0), 0);
@@ -386,7 +385,6 @@ public async Task NonGeneric_CreateFromValueTaskSource_Success(bool sync)
         [Theory]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task Generic_CreateFromValueTaskSource_Success(bool sync)
         {
             var vt = new ValueTask<int>(sync ? ManualResetValueTaskSourceFactory.Completed(42) : ManualResetValueTaskSourceFactory.Delay(1, 42), 0);
@@ -401,7 +399,6 @@ public async Task Generic_CreateFromValueTaskSource_Success(bool sync)
         [Theory]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task NonGeneric_CreateFromValueTaskSource_Faulted(bool sync)
         {
             var vt = new ValueTask(sync ? ManualResetValueTaskSourceFactory.Completed(0, new FormatException()) : ManualResetValueTaskSourceFactory.Delay(1, 0, new FormatException()), 0);
@@ -420,7 +417,6 @@ public async Task NonGeneric_CreateFromValueTaskSource_Faulted(bool sync)
         [Theory]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task Generic_CreateFromValueTaskSource_Faulted(bool sync)
         {
             var vt = new ValueTask<int>(sync ? ManualResetValueTaskSourceFactory.Completed(0, new FormatException()) : ManualResetValueTaskSourceFactory.Delay(1, 0, new FormatException()), 0);
@@ -439,7 +435,6 @@ public async Task Generic_CreateFromValueTaskSource_Faulted(bool sync)
         [Theory]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task NonGeneric_CreateFromValueTaskSource_Canceled(bool sync)
         {
             var vt = new ValueTask(sync ? ManualResetValueTaskSourceFactory.Completed(0, new OperationCanceledException()) : ManualResetValueTaskSourceFactory.Delay(1, 0, new OperationCanceledException()), 0);
@@ -458,7 +453,6 @@ public async Task NonGeneric_CreateFromValueTaskSource_Canceled(bool sync)
         [Theory]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task Generic_CreateFromValueTaskSource_Canceled(bool sync)
         {
             var vt = new ValueTask<int>(sync ? ManualResetValueTaskSourceFactory.Completed(0, new OperationCanceledException()) : ManualResetValueTaskSourceFactory.Delay(1, 0, new OperationCanceledException()), 0);
@@ -578,7 +572,6 @@ ValueTask<int> Create() =>
         [InlineData(null)]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task NonGeneric_CreateFromTask_Await_Normal(bool? continueOnCapturedContext)
         {
             var t = new ValueTask(Task.Delay(1));
@@ -593,7 +586,6 @@ public async Task NonGeneric_CreateFromTask_Await_Normal(bool? continueOnCapture
         [InlineData(null)]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task Generic_CreateFromTask_Await_Normal(bool? continueOnCapturedContext)
         {
             var t = new ValueTask<int>(Task.Delay(1).ContinueWith(_ => 42));
@@ -608,7 +600,6 @@ public async Task Generic_CreateFromTask_Await_Normal(bool? continueOnCapturedCo
         [InlineData(null)]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task CreateFromValueTaskSource_Await_Normal(bool? continueOnCapturedContext)
         {
             var mre = new ManualResetValueTaskSource<int>();
@@ -625,7 +616,6 @@ public async Task CreateFromValueTaskSource_Await_Normal(bool? continueOnCapture
         [InlineData(null)]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task Generic_CreateFromValueTaskSource_Await_Normal(bool? continueOnCapturedContext)
         {
             var mre = new ManualResetValueTaskSource<int>();
@@ -815,7 +805,6 @@ await Task.Run(async () =>
         [InlineData(CtorMode.Result, true)]
         [InlineData(CtorMode.Task, true)]
         [InlineData(CtorMode.ValueTaskSource, true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task Generic_Awaiter_ContinuesOnCapturedContext(CtorMode mode, bool sync)
         {
             await Task.Run(async () =>
@@ -854,7 +843,6 @@ await Task.Run(async () =>
         [InlineData(CtorMode.Result, false, true)]
         [InlineData(CtorMode.Task, false, true)]
         [InlineData(CtorMode.ValueTaskSource, false, true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task NonGeneric_ConfiguredAwaiter_ContinuesOnCapturedContext(CtorMode mode, bool continueOnCapturedContext, bool sync)
         {
             await Task.Run(async () =>
@@ -893,7 +881,6 @@ await Task.Run(async () =>
         [InlineData(CtorMode.Result, false, true)]
         [InlineData(CtorMode.Task, false, true)]
         [InlineData(CtorMode.ValueTaskSource, false, true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/38931", TestPlatforms.Browser)]
         public async Task Generic_ConfiguredAwaiter_ContinuesOnCapturedContext(CtorMode mode, bool continueOnCapturedContext, bool sync)
         {
             await Task.Run(async () =>
diff --git a/src/libraries/System.Threading.Tasks.Parallel/Directory.Build.props b/src/libraries/System.Threading.Tasks.Parallel/Directory.Build.props
index 5f6e490332e15a..e8d65546d0c807 100644
--- a/src/libraries/System.Threading.Tasks.Parallel/Directory.Build.props
+++ b/src/libraries/System.Threading.Tasks.Parallel/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
diff --git a/src/libraries/System.Threading.Tasks.Parallel/src/System.Threading.Tasks.Parallel.csproj b/src/libraries/System.Threading.Tasks.Parallel/src/System.Threading.Tasks.Parallel.csproj
index 0363727de45612..3d0ccd82d99c38 100644
--- a/src/libraries/System.Threading.Tasks.Parallel/src/System.Threading.Tasks.Parallel.csproj
+++ b/src/libraries/System.Threading.Tasks.Parallel/src/System.Threading.Tasks.Parallel.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RootNamespace>System.Threading.Tasks.Parallel</RootNamespace>
-    <AssemblyName>System.Threading.Tasks.Parallel</AssemblyName>
     <DefineConstants>$(DefineConstants);FEATURE_TRACING</DefineConstants>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Threading.Tasks/Directory.Build.props b/src/libraries/System.Threading.Tasks/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Threading.Tasks/Directory.Build.props
+++ b/src/libraries/System.Threading.Tasks/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Threading.Tasks/src/System.Threading.Tasks.csproj b/src/libraries/System.Threading.Tasks/src/System.Threading.Tasks.csproj
index 1b8aa100783fd4..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Threading.Tasks/src/System.Threading.Tasks.csproj
+++ b/src/libraries/System.Threading.Tasks/src/System.Threading.Tasks.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Threading.Tasks</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Threading.Thread/Directory.Build.props b/src/libraries/System.Threading.Thread/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Threading.Thread/Directory.Build.props
+++ b/src/libraries/System.Threading.Thread/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Threading.Thread/ref/System.Threading.Thread.cs b/src/libraries/System.Threading.Thread/ref/System.Threading.Thread.cs
index 83df550d43ddbe..3fe3aea58faf75 100644
--- a/src/libraries/System.Threading.Thread/ref/System.Threading.Thread.cs
+++ b/src/libraries/System.Threading.Thread/ref/System.Threading.Thread.cs
@@ -80,7 +80,7 @@ public static void MemoryBarrier() { }
         public static void ResetAbort() { }
         [System.ObsoleteAttribute("Thread.Resume has been deprecated.  Please use other classes in System.Threading, such as Monitor, Mutex, Event, and Semaphore, to synchronize Threads or protect resources.  https://go.microsoft.com/fwlink/?linkid=14202", false)]
         public void Resume() { }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public void SetApartmentState(System.Threading.ApartmentState state) { }
         [System.ObsoleteAttribute("Thread.SetCompressedStack is no longer supported. Please use the System.Threading.CompressedStack class")]
         public void SetCompressedStack(System.Threading.CompressedStack stack) { }
diff --git a/src/libraries/System.Threading.Thread/src/System.Threading.Thread.csproj b/src/libraries/System.Threading.Thread/src/System.Threading.Thread.csproj
index 7bde58cfb98b19..dd3dc2940a54b1 100644
--- a/src/libraries/System.Threading.Thread/src/System.Threading.Thread.csproj
+++ b/src/libraries/System.Threading.Thread/src/System.Threading.Thread.csproj
@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Threading.Thread</AssemblyName>
-    <OutputType>Library</OutputType>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Threading.Thread/tests/ThreadTests.cs b/src/libraries/System.Threading.Thread/tests/ThreadTests.cs
index 443c500fd8e804..5bc54ba6b75b60 100644
--- a/src/libraries/System.Threading.Thread/tests/ThreadTests.cs
+++ b/src/libraries/System.Threading.Thread/tests/ThreadTests.cs
@@ -160,6 +160,7 @@ public static IEnumerable<object[]> ApartmentStateTest_MemberData()
 
         [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsNotWindowsNanoServer))]
         [ActiveIssue("https://github.com/dotnet/runtime/issues/34543", TestPlatforms.Windows, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
+        [PlatformSpecific(~TestPlatforms.Browser)] // System.Diagnostics.Process is not supported on this platform.
         [InlineData("STAMain.exe", "GetApartmentStateTest")]
         [InlineData("STAMain.exe", "SetApartmentStateTest")]
         [InlineData("STAMain.exe", "WaitAllNotSupportedOnSta_Test0")]
diff --git a/src/libraries/System.Threading.ThreadPool/Directory.Build.props b/src/libraries/System.Threading.ThreadPool/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Threading.ThreadPool/Directory.Build.props
+++ b/src/libraries/System.Threading.ThreadPool/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Threading.ThreadPool/ref/System.Threading.ThreadPool.cs b/src/libraries/System.Threading.ThreadPool/ref/System.Threading.ThreadPool.cs
index 75238f619854ac..b815c818c94928 100644
--- a/src/libraries/System.Threading.ThreadPool/ref/System.Threading.ThreadPool.cs
+++ b/src/libraries/System.Threading.ThreadPool/ref/System.Threading.ThreadPool.cs
@@ -37,7 +37,7 @@ public static partial class ThreadPool
         public static bool SetMaxThreads(int workerThreads, int completionPortThreads) { throw null; }
         public static bool SetMinThreads(int workerThreads, int completionPortThreads) { throw null; }
         [System.CLSCompliantAttribute(false)]
-        public static unsafe bool UnsafeQueueNativeOverlapped(System.Threading.NativeOverlapped* overlapped) { throw null; }
+        public unsafe static bool UnsafeQueueNativeOverlapped(System.Threading.NativeOverlapped* overlapped) { throw null; }
         public static bool UnsafeQueueUserWorkItem(System.Threading.IThreadPoolWorkItem callBack, bool preferLocal) { throw null; }
         public static bool UnsafeQueueUserWorkItem(System.Threading.WaitCallback callBack, object? state) { throw null; }
         public static bool UnsafeQueueUserWorkItem<TState>(System.Action<TState> callBack, TState state, bool preferLocal) { throw null; }
diff --git a/src/libraries/System.Threading.ThreadPool/src/System.Threading.ThreadPool.csproj b/src/libraries/System.Threading.ThreadPool/src/System.Threading.ThreadPool.csproj
index 14a425e488515c..dd3dc2940a54b1 100644
--- a/src/libraries/System.Threading.ThreadPool/src/System.Threading.ThreadPool.csproj
+++ b/src/libraries/System.Threading.ThreadPool/src/System.Threading.ThreadPool.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Threading.ThreadPool</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Threading.Timer/Directory.Build.props b/src/libraries/System.Threading.Timer/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Threading.Timer/Directory.Build.props
+++ b/src/libraries/System.Threading.Timer/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Threading.Timer/src/System.Threading.Timer.csproj b/src/libraries/System.Threading.Timer/src/System.Threading.Timer.csproj
index 68aff5403a4ef9..4f2d15aa3b6a58 100644
--- a/src/libraries/System.Threading.Timer/src/System.Threading.Timer.csproj
+++ b/src/libraries/System.Threading.Timer/src/System.Threading.Timer.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Threading.Timer</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
diff --git a/src/libraries/System.Threading/Directory.Build.props b/src/libraries/System.Threading/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Threading/Directory.Build.props
+++ b/src/libraries/System.Threading/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Threading/ref/System.Threading.cs b/src/libraries/System.Threading/ref/System.Threading.cs
index d0f85e23252df2..888abda4af7616 100644
--- a/src/libraries/System.Threading/ref/System.Threading.cs
+++ b/src/libraries/System.Threading/ref/System.Threading.cs
@@ -35,10 +35,8 @@ public readonly partial struct AsyncLocalValueChangedArgs<T>
         private readonly T _PreviousValue_k__BackingField;
         private readonly T _CurrentValue_k__BackingField;
         private readonly int _dummyPrimitive;
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T CurrentValue { get { throw null; } }
-        [System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
-        public T PreviousValue { get { throw null; } }
+        public T? CurrentValue { get { throw null; } }
+        public T? PreviousValue { get { throw null; } }
         public bool ThreadContextChanged { get { throw null; } }
     }
     public sealed partial class AsyncLocal<T>
@@ -115,11 +113,11 @@ public partial class EventWaitHandle : System.Threading.WaitHandle
         public EventWaitHandle(bool initialState, System.Threading.EventResetMode mode) { }
         public EventWaitHandle(bool initialState, System.Threading.EventResetMode mode, string? name) { }
         public EventWaitHandle(bool initialState, System.Threading.EventResetMode mode, string? name, out bool createdNew) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.Threading.EventWaitHandle OpenExisting(string name) { throw null; }
         public bool Reset() { throw null; }
         public bool Set() { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static bool TryOpenExisting(string name, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.Threading.EventWaitHandle? result) { throw null; }
     }
     public sealed partial class ExecutionContext : System.IDisposable, System.Runtime.Serialization.ISerializable
@@ -153,61 +151,61 @@ public virtual void Revert(object previousState) { }
     public static partial class Interlocked
     {
         public static int Add(ref int location1, int value) { throw null; }
+        public static long Add(ref long location1, long value) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static uint Add(ref uint location1, uint value) { throw null; }
-        public static long Add(ref long location1, long value) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static ulong Add(ref ulong location1, ulong value) { throw null; }
         public static int And(ref int location1, int value) { throw null; }
+        public static long And(ref long location1, long value) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static uint And(ref uint location1, uint value) { throw null; }
-        public static long And(ref long location1, long value) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static ulong And(ref ulong location1, ulong value) { throw null; }
         public static double CompareExchange(ref double location1, double value, double comparand) { throw null; }
         public static int CompareExchange(ref int location1, int value, int comparand) { throw null; }
-        [System.CLSCompliantAttribute(false)]
-        public static uint CompareExchange(ref uint location1, uint value, uint comparand) { throw null; }
         public static long CompareExchange(ref long location1, long value, long comparand) { throw null; }
-        [System.CLSCompliantAttribute(false)]
-        public static ulong CompareExchange(ref ulong location1, ulong value, ulong comparand) { throw null; }
         public static System.IntPtr CompareExchange(ref System.IntPtr location1, System.IntPtr value, System.IntPtr comparand) { throw null; }
         [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("location1")]
         public static object? CompareExchange(ref object? location1, object? value, object? comparand) { throw null; }
         public static float CompareExchange(ref float location1, float value, float comparand) { throw null; }
+        [System.CLSCompliantAttribute(false)]
+        public static uint CompareExchange(ref uint location1, uint value, uint comparand) { throw null; }
+        [System.CLSCompliantAttribute(false)]
+        public static ulong CompareExchange(ref ulong location1, ulong value, ulong comparand) { throw null; }
         [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("location1")]
         public static T CompareExchange<T>(ref T location1, T value, T comparand) where T : class? { throw null; }
         public static int Decrement(ref int location) { throw null; }
+        public static long Decrement(ref long location) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static uint Decrement(ref uint location) { throw null; }
-        public static long Decrement(ref long location) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static ulong Decrement(ref ulong location) { throw null; }
         public static double Exchange(ref double location1, double value) { throw null; }
         public static int Exchange(ref int location1, int value) { throw null; }
-        [System.CLSCompliantAttribute(false)]
-        public static uint Exchange(ref uint location1, uint value) { throw null; }
         public static long Exchange(ref long location1, long value) { throw null; }
-        [System.CLSCompliantAttribute(false)]
-        public static ulong Exchange(ref ulong location1, ulong value) { throw null; }
         public static System.IntPtr Exchange(ref System.IntPtr location1, System.IntPtr value) { throw null; }
         [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("location1")]
         public static object? Exchange([System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("value")] ref object? location1, object? value) { throw null; }
         public static float Exchange(ref float location1, float value) { throw null; }
+        [System.CLSCompliantAttribute(false)]
+        public static uint Exchange(ref uint location1, uint value) { throw null; }
+        [System.CLSCompliantAttribute(false)]
+        public static ulong Exchange(ref ulong location1, ulong value) { throw null; }
         [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("location1")]
         public static T Exchange<T>([System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("value")] ref T location1, T value) where T : class? { throw null; }
         public static int Increment(ref int location) { throw null; }
+        public static long Increment(ref long location) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static uint Increment(ref uint location) { throw null; }
-        public static long Increment(ref long location) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static ulong Increment(ref ulong location) { throw null; }
         public static void MemoryBarrier() { }
         public static void MemoryBarrierProcessWide() { }
         public static int Or(ref int location1, int value) { throw null; }
+        public static long Or(ref long location1, long value) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static uint Or(ref uint location1, uint value) { throw null; }
-        public static long Or(ref long location1, long value) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static ulong Or(ref ulong location1, ulong value) { throw null; }
         public static long Read(ref long location) { throw null; }
@@ -350,11 +348,11 @@ public sealed partial class Semaphore : System.Threading.WaitHandle
         public Semaphore(int initialCount, int maximumCount) { }
         public Semaphore(int initialCount, int maximumCount, string? name) { }
         public Semaphore(int initialCount, int maximumCount, string? name, out bool createdNew) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static System.Threading.Semaphore OpenExisting(string name) { throw null; }
         public int Release() { throw null; }
         public int Release(int releaseCount) { throw null; }
-        [System.Runtime.Versioning.MinimumOSPlatformAttribute("windows7.0")]
+        [System.Runtime.Versioning.SupportedOSPlatformAttribute("windows")]
         public static bool TryOpenExisting(string name, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.Threading.Semaphore? result) { throw null; }
     }
     public partial class SemaphoreFullException : System.SystemException
diff --git a/src/libraries/System.Threading/src/System.Threading.csproj b/src/libraries/System.Threading/src/System.Threading.csproj
index 6b4aeb5e8a1c8f..895b458279376d 100644
--- a/src/libraries/System.Threading/src/System.Threading.csproj
+++ b/src/libraries/System.Threading/src/System.Threading.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Threading</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
diff --git a/src/libraries/System.Threading/tests/InterlockedTests.cs b/src/libraries/System.Threading/tests/InterlockedTests.cs
index ed7e3efa956cba..941a78378c0060 100644
--- a/src/libraries/System.Threading/tests/InterlockedTests.cs
+++ b/src/libraries/System.Threading/tests/InterlockedTests.cs
@@ -301,7 +301,7 @@ public void InterlockedOr_UInt64()
             Assert.Equal(0x17755771u, value);
         }
 
-        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotArm64Process), nameof(PlatformDetection.IsThreadingSupported))] // [ActiveIssue("https://github.com/dotnet/runtime/issues/11177")]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
         public void MemoryBarrierProcessWide()
         {
             // Stress MemoryBarrierProcessWide correctness using a simple AsymmetricLock
@@ -406,6 +406,15 @@ private LockCookie EnterSlow()
                     while (oldEntry.Taken)
                         sw.SpinOnce();
 
+                    // We have seen that the other thread released the lock by setting Taken to false.
+                    // However, on platforms with weak memory ordering (ex: ARM32, ARM64) observing that does not guarantee that the writes executed by that
+                    // thread prior to releasing the lock are all committed to the shared memory.
+                    // We could fix that by doing the release via Volatile.Write, but we do not want to add expense to every release on the fast path.
+                    // Instead we will do another MemoryBarrierProcessWide here.
+
+                    // NOTE: not needed on x86/x64
+                    Interlocked.MemoryBarrierProcessWide();
+
                     _current.Taken = true;
                     return _current;
                 }
diff --git a/src/libraries/System.Transactions.Local/Directory.Build.props b/src/libraries/System.Transactions.Local/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.Transactions.Local/Directory.Build.props
+++ b/src/libraries/System.Transactions.Local/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Transactions.Local/ref/System.Transactions.Local.csproj b/src/libraries/System.Transactions.Local/ref/System.Transactions.Local.csproj
index b7a65a17fae292..ce48f9db195f15 100644
--- a/src/libraries/System.Transactions.Local/ref/System.Transactions.Local.csproj
+++ b/src/libraries/System.Transactions.Local/ref/System.Transactions.Local.csproj
@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <OutputType>Library</OutputType>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
diff --git a/src/libraries/System.Transactions.Local/src/System.Transactions.Local.csproj b/src/libraries/System.Transactions.Local/src/System.Transactions.Local.csproj
index dd777197997882..1715d21528c971 100644
--- a/src/libraries/System.Transactions.Local/src/System.Transactions.Local.csproj
+++ b/src/libraries/System.Transactions.Local/src/System.Transactions.Local.csproj
@@ -33,6 +33,7 @@
     <Compile Include="System\Transactions\TransactionState.cs" />
     <Compile Include="System\Transactions\TransactionTable.cs" />
     <Compile Include="System\Transactions\TransactionTraceIdentifier.cs" />
+    <Compile Include="System\Transactions\TransactionsEtwProvider.cs" />
     <Compile Include="System\Transactions\VolatileEnlistmentMultiplexing.cs" />
     <Compile Include="System\Transactions\VolatileEnlistmentState.cs" />
     <Compile Include="System\Transactions\Configuration\AppSettings.cs" />
@@ -50,7 +51,4 @@
     <Reference Include="System.Threading.Thread" />
     <Reference Include="System.Threading.ThreadPool" />
   </ItemGroup>
-  <ItemGroup>
-    <Compile Include="System\Transactions\TransactionsEtwProvider.cs" />
-  </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.Forwards.cs b/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.Forwards.cs
index 04a0cc861ba1f3..5f1d14ec279de4 100644
--- a/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.Forwards.cs
+++ b/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.Forwards.cs
@@ -1,7 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#if !NETSTANDARD2_0
+#if !NETSTANDARD2_0 && !NETFRAMEWORK
 [assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Index))]
 [assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Range))]
 
diff --git a/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.Rune.cs b/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.Rune.cs
index e3b4d3eb518bbb..da7e4be0f23403 100644
--- a/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.Rune.cs
+++ b/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.Rune.cs
@@ -6,7 +6,7 @@
 
 namespace System.Text
 {
-    public readonly partial struct Rune : System.IComparable<System.Text.Rune>, System.IEquatable<System.Text.Rune>
+    public readonly partial struct Rune : System.IComparable, System.IComparable<System.Text.Rune>, System.IEquatable<System.Text.Rune>
     {
         private readonly int _dummyPrimitive;
         public Rune(char ch) { throw null; }
@@ -71,5 +71,6 @@ namespace System.Text
         public bool TryEncodeToUtf16(System.Span<char> destination, out int charsWritten) { throw null; }
         public bool TryEncodeToUtf8(System.Span<byte> destination, out int bytesWritten) { throw null; }
         public static bool TryGetRuneAt(string input, int index, out System.Text.Rune value) { throw null; }
+        int IComparable.CompareTo(object? obj) { throw null; }
     }
 }
diff --git a/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.cs b/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.cs
index b37545e6f47a5e..a72e76090dead5 100644
--- a/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.cs
+++ b/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.cs
@@ -90,12 +90,12 @@ public Utf8String(string value) { }
         public bool Contains(System.Text.Rune value, System.StringComparison comparison) { throw null; }
         public bool Contains(System.Utf8String value) { throw null; }
         public bool Contains(System.Utf8String value, System.StringComparison comparison) { throw null; }
-#if !NETSTANDARD2_0
+#if !NETSTANDARD2_0 && !NETFRAMEWORK
         public static System.Utf8String Create<TState>(int length, TState state, System.Buffers.SpanAction<byte, TState> action) { throw null; }
 #endif
         public static System.Utf8String CreateFromRelaxed(System.ReadOnlySpan<byte> buffer) { throw null; }
         public static System.Utf8String CreateFromRelaxed(System.ReadOnlySpan<char> buffer) { throw null; }
-#if !NETSTANDARD2_0
+#if !NETSTANDARD2_0 && !NETFRAMEWORK
         public static System.Utf8String CreateRelaxed<TState>(int length, TState state, System.Buffers.SpanAction<byte, TState> action) { throw null; }
 #endif
         public bool EndsWith(char value) { throw null; }
@@ -168,7 +168,7 @@ public Utf8String(string value) { }
         public bool TryFindLast(System.Utf8String value, out System.Range range) { throw null; }
         public bool TryFindLast(System.Utf8String value, System.StringComparison comparisonType, out System.Range range) { throw null; }
         public static System.Utf8String UnsafeCreateWithoutValidation(System.ReadOnlySpan<byte> utf8Contents) { throw null; }
-#if !NETSTANDARD2_0
+#if !NETSTANDARD2_0 && !NETFRAMEWORK
         public static System.Utf8String UnsafeCreateWithoutValidation<TState>(int length, TState state, System.Buffers.SpanAction<byte, TState> action) { throw null; }
 #endif
         public readonly partial struct ByteEnumerable : System.Collections.Generic.IEnumerable<byte>
diff --git a/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.csproj b/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.csproj
index 4ef79b71fc4671..eb5a1414f8cdf8 100644
--- a/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.csproj
+++ b/src/libraries/System.Utf8String.Experimental/ref/System.Utf8String.Experimental.csproj
@@ -3,25 +3,31 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <!-- disable warnings about obsolete APIs -->
     <NoWarn>$(NoWarn);0809;0618</NoWarn>
-    <TargetFrameworks>netstandard2.0;netstandard2.1;netcoreapp3.0;$(NetCoreAppCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;netcoreapp3.0;$(NetCoreAppCurrent);net461</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup Condition="'$(IsPrerelease)' != 'false'">
     <Compile Include="System.Utf8String.Experimental.cs" />
     <Compile Include="System.Utf8String.Experimental.Forwards.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPrerelease)' != 'false' AND '$(TargetFramework)' == 'netstandard2.0'">
+  <ItemGroup Condition="'$(IsPrerelease)' != 'false' and ('$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'net461')">
     <Compile Include="System.Utf8String.Experimental.Range.cs" />
     <Compile Include="System.Utf8String.Experimental.Rune.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPrerelease)' != 'false' AND '$(TargetFramework)' == 'netstandard2.1'">
+  <ItemGroup Condition="'$(IsPrerelease)' != 'false' and '$(TargetFramework)' == 'netstandard2.1'">
     <Compile Include="System.Utf8String.Experimental.Rune.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPrerelease)' != 'false' AND '$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+  <ItemGroup Condition="'$(IsPrerelease)' != 'false' and '$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <Compile Include="System.Utf8String.Experimental.net5.0.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-    <Reference Include="System.Memory" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'net461'">
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Net.Http\ref\System.Net.Http.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Net.Primitives\ref\System.Net.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.InteropServices\ref\System.Runtime.InteropServices.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="netstandard" />
@@ -30,10 +36,8 @@
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.InteropServices" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="..\..\System.Net.Http\ref\System.Net.Http.csproj" />
-    <ProjectReference Include="..\..\System.Net.Primitives\ref\System.Net.Primitives.csproj" />
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.Runtime.InteropServices\ref\System.Runtime.InteropServices.csproj" />
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
+    <Reference Include="System.Net.Http" />
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" Condition="'$(TargetFramework)' == 'net461'" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Utf8String.Experimental/src/Resources/Strings.resx b/src/libraries/System.Utf8String.Experimental/src/Resources/Strings.resx
index a02a1757a69029..3d5159021118a3 100644
--- a/src/libraries/System.Utf8String.Experimental/src/Resources/Strings.resx
+++ b/src/libraries/System.Utf8String.Experimental/src/Resources/Strings.resx
@@ -165,4 +165,7 @@
   <data name="Utf8String_InputContainedMalformedUtf8" xml:space="preserve">
     <value>The input buffer contained ill-formed UTF-8 data.</value>
   </data>
+  <data name="Arg_MustBeRune" xml:space="preserve">
+    <value>Object must be of type Rune.</value>
+  </data>
 </root>
\ No newline at end of file
diff --git a/src/libraries/System.Utf8String.Experimental/src/System.Utf8String.Experimental.csproj b/src/libraries/System.Utf8String.Experimental/src/System.Utf8String.Experimental.csproj
index 016238e9a83ebd..8b72b9161c5571 100644
--- a/src/libraries/System.Utf8String.Experimental/src/System.Utf8String.Experimental.csproj
+++ b/src/libraries/System.Utf8String.Experimental/src/System.Utf8String.Experimental.csproj
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netstandard2.1;netcoreapp3.0;net461;$(NetFrameworkCurrent)</TargetFrameworks>
-    <ExcludeCurrentFullFrameworkFromPackage>true</ExcludeCurrentFullFrameworkFromPackage>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;netstandard2.1;netcoreapp3.0;net461</TargetFrameworks>
     <Nullable>enable</Nullable>
     <DefineConstants>$(DefineContants);FEATURE_UTF8STRING</DefineConstants>
   </PropertyGroup>
@@ -17,7 +16,7 @@
     <Compile Include="System\IO\Utf8StringStream.cs" />
     <Compile Include="System\Net\Http\Utf8StringContent.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPrerelease)' != 'false' AND ('$(TargetFramework)' == 'netstandard2.0' OR $(TargetFramework.StartsWith('net4')))">
+  <ItemGroup Condition="'$(IsPrerelease)' != 'false' AND ('$(TargetFramework)' == 'netstandard2.0' or $(TargetFramework.StartsWith('net4')))">
     <Compile Include="$(CoreLibSharedDir)\System\Index.cs"
              Link="System\Index.cs" />
     <Compile Include="$(CoreLibSharedDir)\System\Numerics\BitOperations.cs"
@@ -113,15 +112,27 @@
   <ItemGroup Condition="'$(IsPrerelease)' != 'false' AND '$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <Compile Include="System\Net\Http\Utf8StringContent.netcoreapp.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' OR $(TargetFramework.StartsWith('net4'))">
-    <Reference Include="System.Buffers" />
-    <Reference Include="System.Memory" />
-    <Reference Include="System.Numerics.Vectors" />
-    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
+  <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)'">
+    <!-- Duplicate types with System.Runtime.Intrinsics. Excluding the default reference. -->
+    <DefaultReferenceExclusion Include="System.Runtime.Intrinsics" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime.CompilerServices.Unsafe\src\System.Runtime.CompilerServices.Unsafe.ilproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or
+                        $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
+    <PackageReference Include="System.Numerics.Vectors" Version="$(SystemNumericsVectorsVersion)" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.1'">
-    <Reference Include="System.Numerics.Vectors" />
-    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
+    <PackageReference Include="System.Numerics.Vectors" Version="$(SystemNumericsVectorsVersion)" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <!-- The predefined type 'Interlocked' is defined in multiple assemblies. -->
+    <DefaultReferenceExclusion Include="System.Threading" />
+    <ProjectReference Include="$(CoreLibProject)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\src\System.Runtime.csproj" />
+    <Reference Include="System.Net.Http" />
+    <Reference Include="System.Net.Primitives" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0'">
     <Reference Include="netstandard" />
@@ -134,21 +145,10 @@
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
     <Reference Include="System.Runtime.InteropServices" />
-    <Reference Include="System.Runtime.CompilerServices.Unsafe" />
     <Reference Include="System.Security.Cryptography.Algorithms" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="$(CoreLibProject)" />
-    <Reference Include="System.Net.Http" />
-    <Reference Include="System.Net.Primitives" />
-    <ProjectReference Include="..\..\System.Runtime\src\System.Runtime.csproj" />
-  </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <Reference Include="mscorlib" />
-    <Reference Include="netstandard" />
-    <Reference Include="System" />
     <Reference Include="System.Net.Http" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.ValueTuple" />
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" Condition="'$(TargetFramework)' == 'net461'" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Utf8String.Experimental/src/System/Runtime/Intrinsics/Intrinsics.Shims.cs b/src/libraries/System.Utf8String.Experimental/src/System/Runtime/Intrinsics/Intrinsics.Shims.cs
index c4c68e966eba22..ff020e0259cfdc 100644
--- a/src/libraries/System.Utf8String.Experimental/src/System/Runtime/Intrinsics/Intrinsics.Shims.cs
+++ b/src/libraries/System.Utf8String.Experimental/src/System/Runtime/Intrinsics/Intrinsics.Shims.cs
@@ -8,6 +8,9 @@ internal static class Vector64
         public static Vector64<ulong> Create(ulong value) => throw new PlatformNotSupportedException();
         public static Vector64<uint> CreateScalar(uint value) => throw new PlatformNotSupportedException();
         public static Vector64<byte> AsByte<T>(this Vector64<T> vector) where T : struct => throw new PlatformNotSupportedException();
+        public static Vector64<uint> AsUInt32<T>(this Vector64<T> vector) where T : struct => throw new PlatformNotSupportedException();
+        public static Vector64<T> GetLower<T>(this Vector128<T> vector) where T : struct => throw new PlatformNotSupportedException();
+        public static Vector64<ulong> AsUInt64<T>(this Vector64<T> vector) where T : struct => throw new PlatformNotSupportedException();
     }
     internal readonly struct Vector64<T>
         where T : struct
@@ -20,6 +23,8 @@ internal static class Vector128
         public static Vector128<short> Create(short value) => throw new PlatformNotSupportedException();
         public static Vector128<ulong> Create(ulong value) => throw new PlatformNotSupportedException();
         public static Vector128<ushort> Create(ushort value) => throw new PlatformNotSupportedException();
+        public static Vector128<byte> Create(byte value) => throw new PlatformNotSupportedException();
+        public static Vector128<uint> Create(uint value) => throw new PlatformNotSupportedException();
         public static Vector128<ulong> CreateScalarUnsafe(ulong value) => throw new PlatformNotSupportedException();
         public static Vector128<byte> AsByte<T>(this Vector128<T> vector) where T : struct => throw new PlatformNotSupportedException();
         public static Vector128<short> AsInt16<T>(this Vector128<T> vector) where T : struct => throw new PlatformNotSupportedException();
diff --git a/src/libraries/System.Utf8String.Experimental/tests/System.Utf8String.Experimental.Tests.csproj b/src/libraries/System.Utf8String.Experimental/tests/System.Utf8String.Experimental.Tests.csproj
index 1edb4b7d68e523..73efb5b00c82d1 100644
--- a/src/libraries/System.Utf8String.Experimental/tests/System.Utf8String.Experimental.Tests.csproj
+++ b/src/libraries/System.Utf8String.Experimental/tests/System.Utf8String.Experimental.Tests.csproj
@@ -2,11 +2,9 @@
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IncludePartialFacadeTests>true</IncludePartialFacadeTests>
-    <TargetFrameworks>$(NetCoreAppCurrent);$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);net461</TargetFrameworks>
     <TestRuntime>true</TestRuntime>
     <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
-    <!-- Must reference the Utf8String reference assembly, which is normally excluded from unit test projects. -->
-    <IncludeUtf8StringAsmRef>true</IncludeUtf8StringAsmRef>
   </PropertyGroup>
   <ItemGroup Condition="'$(IsPrerelease)' != 'false'">
     <Compile Include="System\Char8Tests.cs" />
@@ -43,7 +41,13 @@
     <Compile Include="System\Utf8ExtensionsTests.netcoreapp.cs" />
     <Compile Include="System\Utf8StringTests.Ctor.netcoreapp.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(IsPrerelease)' != 'false' and '$(TargetFramework)' == '$(NetFrameworkCurrent)'">
+  <ItemGroup Condition="'$(IsPrerelease)' != 'false' and '$(TargetFramework)' == 'net461'">
     <Compile Include="System\MemoryTests.netfx.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\System.Utf8String.Experimental.csproj" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net461'">
+    <Reference Include="System.Net.Http" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ValueTuple/Directory.Build.props b/src/libraries/System.ValueTuple/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.ValueTuple/Directory.Build.props
+++ b/src/libraries/System.ValueTuple/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.ValueTuple/ref/System.ValueTuple.csproj b/src/libraries/System.ValueTuple/ref/System.ValueTuple.csproj
index 7de77702d2778f..48439ada9ee5b1 100644
--- a/src/libraries/System.ValueTuple/ref/System.ValueTuple.csproj
+++ b/src/libraries/System.ValueTuple/ref/System.ValueTuple.csproj
@@ -3,13 +3,13 @@
     <!-- Must match version supported by frameworks which support 4.0.* inbox.
          Can be removed when API is added and this assembly is versioned to 4.1.* -->
     <AssemblyVersion>4.0.3.0</AssemblyVersion>
-    <TargetFrameworks>$(NetCoreAppCurrent);_$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.ValueTuple.TypeForwards.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.ValueTuple/src/System.ValueTuple.csproj b/src/libraries/System.ValueTuple/src/System.ValueTuple.csproj
index 37b43aecf36ce6..7a4c9970551301 100644
--- a/src/libraries/System.ValueTuple/src/System.ValueTuple.csproj
+++ b/src/libraries/System.ValueTuple/src/System.ValueTuple.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <!-- rev'ed to 4.0.1.0 even though 4.0.0.0 never shipped so that we can drop pre-release down to beta -->
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
-    <TargetFrameworks>$(NetCoreAppCurrent);_$(NetFrameworkCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
diff --git a/src/libraries/System.Web.HttpUtility/Directory.Build.props b/src/libraries/System.Web.HttpUtility/Directory.Build.props
index 2b9e2844e4ee3f..bdcfca3b543cbb 100644
--- a/src/libraries/System.Web.HttpUtility/Directory.Build.props
+++ b/src/libraries/System.Web.HttpUtility/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Open</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Windows.Extensions/ref/System.Windows.Extensions.csproj b/src/libraries/System.Windows.Extensions/ref/System.Windows.Extensions.csproj
index ebbd3e46f7670e..d8548ee597d3a6 100644
--- a/src/libraries/System.Windows.Extensions/ref/System.Windows.Extensions.csproj
+++ b/src/libraries/System.Windows.Extensions/ref/System.Windows.Extensions.csproj
@@ -7,17 +7,17 @@
     <Compile Include="System.Windows.Extensions.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <ProjectReference Include="..\..\System.ComponentModel.TypeConverter\ref\System.ComponentModel.TypeConverter.csproj" />
-    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
-    <ProjectReference Include="..\..\System.ComponentModel.EventBasedAsync\ref\System.ComponentModel.EventBasedAsync.csproj" />
-    <ProjectReference Include="..\..\System.ComponentModel.Primitives\ref\System.ComponentModel.Primitives.csproj" />
-    <ProjectReference Include="..\..\System.Security.Cryptography.X509Certificates\ref\System.Security.Cryptography.X509Certificates.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.ComponentModel.TypeConverter\ref\System.ComponentModel.TypeConverter.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.ComponentModel.EventBasedAsync\ref\System.ComponentModel.EventBasedAsync.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.ComponentModel.Primitives\ref\System.ComponentModel.Primitives.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.X509Certificates\ref\System.Security.Cryptography.X509Certificates.csproj" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0'">
-    <Reference Include="System.ComponentModel.TypeConverter" />
-    <Reference Include="System.Runtime" />
     <Reference Include="System.ComponentModel.EventBasedAsync" />
     <Reference Include="System.ComponentModel.Primitives" />
+    <Reference Include="System.ComponentModel.TypeConverter" />
+    <Reference Include="System.Runtime" />
     <Reference Include="System.Security.Cryptography.X509Certificates" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Windows.Extensions/src/System.Windows.Extensions.csproj b/src/libraries/System.Windows.Extensions/src/System.Windows.Extensions.csproj
index ea77d6793f77fc..7e4df72fa5eb68 100644
--- a/src/libraries/System.Windows.Extensions/src/System.Windows.Extensions.csproj
+++ b/src/libraries/System.Windows.Extensions/src/System.Windows.Extensions.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsWindows)' != 'true'">SR.PlatformNotSupported_System_Windows_Extensions</GeneratePlatformNotSupportedAssemblyMessage>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netcoreapp3.0-Windows_NT;netcoreapp3.0;$(NetCoreAppCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netcoreapp3.0-Windows_NT;$(NetCoreAppCurrent);netcoreapp3.0</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
@@ -55,6 +55,9 @@
     <Compile Include="System\Media\SystemSounds.cs" />
     <Compile Include="System\Xaml\Permissions\XamlAccessLevel.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetsWindows)' == 'true'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Drawing.Common\src\System.Drawing.Common.csproj" />
+  </ItemGroup>
   <ItemGroup>
     <Reference Include="System.Buffers" />
     <Reference Include="System.Collections.NonGeneric" />
@@ -63,7 +66,6 @@
     <Reference Include="System.ComponentModel.TypeConverter" />
     <Reference Include="System.Diagnostics.Debug" />
     <Reference Include="System.Diagnostics.Tools" />
-    <Reference Include="System.Drawing.Common" />
     <Reference Include="System.IO.FileSystem" />
     <Reference Include="System.Memory" />
     <Reference Include="System.Net.Requests" />
diff --git a/src/libraries/System.Windows.Extensions/tests/System.Windows.Extensions.Tests.csproj b/src/libraries/System.Windows.Extensions/tests/System.Windows.Extensions.Tests.csproj
index 7396a53455fe91..f41f912cb05b7d 100644
--- a/src/libraries/System.Windows.Extensions/tests/System.Windows.Extensions.Tests.csproj
+++ b/src/libraries/System.Windows.Extensions/tests/System.Windows.Extensions.Tests.csproj
@@ -25,5 +25,7 @@
     <PackageReference Include="System.ComponentModel.TypeConverter.TestData" Version="$(SystemComponentModelTypeConverterTestDataVersion)" />
     <PackageReference Include="System.Drawing.Common.TestData" Version="$(SystemDrawingCommonTestDataVersion)" />
     <PackageReference Include="System.Windows.Extensions.TestData" Version="$(SystemWindowsExtensionsTestDataVersion)" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Drawing.Common\src\System.Drawing.Common.csproj" />
+    <ProjectReference Include="..\src\System.Windows.Extensions.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Xml.ReaderWriter/Directory.Build.props b/src/libraries/System.Xml.ReaderWriter/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Xml.ReaderWriter/Directory.Build.props
+++ b/src/libraries/System.Xml.ReaderWriter/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Xml.ReaderWriter/src/System.Xml.ReaderWriter.csproj b/src/libraries/System.Xml.ReaderWriter/src/System.Xml.ReaderWriter.csproj
index e7413a357835a0..eccf2f839b93a9 100644
--- a/src/libraries/System.Xml.ReaderWriter/src/System.Xml.ReaderWriter.csproj
+++ b/src/libraries/System.Xml.ReaderWriter/src/System.Xml.ReaderWriter.csproj
@@ -1,14 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Xml.ReaderWriter</AssemblyName>
     <RootNamespace>System.Xml</RootNamespace>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Private.Xml\src\System.Private.Xml.csproj" />
-  </ItemGroup>
-  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Xml\src\System.Private.Xml.csproj" />
     <Reference Include="System.Runtime" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Xml.XDocument/Directory.Build.props b/src/libraries/System.Xml.XDocument/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Xml.XDocument/Directory.Build.props
+++ b/src/libraries/System.Xml.XDocument/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Xml.XDocument/src/System.Xml.XDocument.csproj b/src/libraries/System.Xml.XDocument/src/System.Xml.XDocument.csproj
index 6bfd8d595b075c..f4c9ec075a89e6 100644
--- a/src/libraries/System.Xml.XDocument/src/System.Xml.XDocument.csproj
+++ b/src/libraries/System.Xml.XDocument/src/System.Xml.XDocument.csproj
@@ -1,15 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Xml.XDocument</AssemblyName>
     <RootNamespace>System.Xml</RootNamespace>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Private.Xml.Linq\src\System.Private.Xml.Linq.csproj" />
-    <ProjectReference Include="..\..\System.Private.Xml\src\System.Private.Xml.csproj" />
-  </ItemGroup>
-  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Xml.Linq\src\System.Private.Xml.Linq.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Xml\src\System.Private.Xml.csproj" />
     <Reference Include="System.Runtime" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Xml.XPath.XDocument/Directory.Build.props b/src/libraries/System.Xml.XPath.XDocument/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Xml.XPath.XDocument/Directory.Build.props
+++ b/src/libraries/System.Xml.XPath.XDocument/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Xml.XPath.XDocument/src/System.Xml.XPath.XDocument.csproj b/src/libraries/System.Xml.XPath.XDocument/src/System.Xml.XPath.XDocument.csproj
index 27b08b9f75ffb2..6ef3750484c7b1 100644
--- a/src/libraries/System.Xml.XPath.XDocument/src/System.Xml.XPath.XDocument.csproj
+++ b/src/libraries/System.Xml.XPath.XDocument/src/System.Xml.XPath.XDocument.csproj
@@ -8,10 +8,8 @@
     <Compile Include="System\Xml\XPath\XDocumentExtensions.cs" />
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Private.Xml\src\System.Private.Xml.csproj" />
-    <ProjectReference Include="..\..\System.Private.Xml.Linq\src\System.Private.Xml.Linq.csproj" />
-  </ItemGroup>
-  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Xml\src\System.Private.Xml.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Xml.Linq\src\System.Private.Xml.Linq.csproj" />
     <Reference Include="System.Runtime" />
     <Reference Include="System.Runtime.Extensions" />
   </ItemGroup>
diff --git a/src/libraries/System.Xml.XPath/Directory.Build.props b/src/libraries/System.Xml.XPath/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Xml.XPath/Directory.Build.props
+++ b/src/libraries/System.Xml.XPath/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Xml.XPath/src/System.Xml.XPath.csproj b/src/libraries/System.Xml.XPath/src/System.Xml.XPath.csproj
index c78bfe73a9d4e3..8159a0e77d94bd 100644
--- a/src/libraries/System.Xml.XPath/src/System.Xml.XPath.csproj
+++ b/src/libraries/System.Xml.XPath/src/System.Xml.XPath.csproj
@@ -1,13 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Xml.XPath</AssemblyName>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Private.Xml\src\System.Private.Xml.csproj" />
-  </ItemGroup>
-  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Xml\src\System.Private.Xml.csproj" />
     <Reference Include="System.Runtime" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Xml.XmlDocument/Directory.Build.props b/src/libraries/System.Xml.XmlDocument/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Xml.XmlDocument/Directory.Build.props
+++ b/src/libraries/System.Xml.XmlDocument/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Xml.XmlDocument/src/System.Xml.XmlDocument.csproj b/src/libraries/System.Xml.XmlDocument/src/System.Xml.XmlDocument.csproj
index 7abca9d22ec5cd..2700e39cf27b21 100644
--- a/src/libraries/System.Xml.XmlDocument/src/System.Xml.XmlDocument.csproj
+++ b/src/libraries/System.Xml.XmlDocument/src/System.Xml.XmlDocument.csproj
@@ -1,15 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Xml.XmlDocument</AssemblyName>
-    <RootNamespace>System.Xml.XmlDocument</RootNamespace>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Private.Xml\src\System.Private.Xml.csproj" />
-  </ItemGroup>
-  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Xml\src\System.Private.Xml.csproj" />
     <Reference Include="System.Runtime" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Xml.XmlSerializer/Directory.Build.props b/src/libraries/System.Xml.XmlSerializer/Directory.Build.props
index 465e1110d6b07f..63f02a0f817ef2 100644
--- a/src/libraries/System.Xml.XmlSerializer/Directory.Build.props
+++ b/src/libraries/System.Xml.XmlSerializer/Directory.Build.props
@@ -2,6 +2,5 @@
   <Import Project="..\Directory.Build.props" />
   <PropertyGroup>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
-    <IsNETCoreApp>true</IsNETCoreApp>
   </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/System.Xml.XmlSerializer/src/System.Xml.XmlSerializer.csproj b/src/libraries/System.Xml.XmlSerializer/src/System.Xml.XmlSerializer.csproj
index d9aa0818fdf028..8159a0e77d94bd 100644
--- a/src/libraries/System.Xml.XmlSerializer/src/System.Xml.XmlSerializer.csproj
+++ b/src/libraries/System.Xml.XmlSerializer/src/System.Xml.XmlSerializer.csproj
@@ -1,14 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <AssemblyName>System.Xml.XmlSerializer</AssemblyName>
-    <RootNamespace>System.Xml.XmlSerializer</RootNamespace>
     <IsPartialFacadeAssembly>true</IsPartialFacadeAssembly>
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\System.Private.Xml\src\System.Private.Xml.csproj" />
-  </ItemGroup>
-  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Private.Xml\src\System.Private.Xml.csproj" />
     <Reference Include="System.Runtime" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/libraries/illink-sharedframework.targets b/src/libraries/illink-sharedframework.targets
new file mode 100644
index 00000000000000..5dc82f2c5a55c3
--- /dev/null
+++ b/src/libraries/illink-sharedframework.targets
@@ -0,0 +1,85 @@
+<Project>
+
+  <Target Name="ILLinkTrimSharedFramework"
+          AfterTargets="Build"
+          DependsOnTargets="SetCommonILLinkArgs">
+
+    <PropertyGroup>
+      <LibrariesTrimmedArtifactsPath>$([MSBuild]::NormalizePath('$(ArtifactsBinDir)', 'ILLinkTrimAssembly', '$(BuildSettings)', 'trimmed-runtimepack'))</LibrariesTrimmedArtifactsPath>
+    </PropertyGroup>
+
+    <PropertyGroup>
+      <!-- default action for core assemblies -->
+      <ILLinkArgs>$(ILLinkArgs) -c link</ILLinkArgs>
+      <!-- update debug symbols -->
+      <ILLinkArgs>$(ILLinkArgs) -b true</ILLinkArgs>
+      <!-- suppress warnings with the following codes:
+           IL2006: The generic parameter 'T' from A with dynamically accessed member kinds B is passed into the generic parameter
+                   'T' from 'System.Lazy<T>' which requires dynamically accessed member kinds 'PublicParameterlessConstructor'
+           IL2009: Could not find method A in type B specified in resource C
+           IL2025: Duplicate preserve of A in B
+           IL2026: Calling A which has B can break functionality when trimming application code. The target method might be removed.
+           IL2035: Unresolved assembly A in DynamicDependencyAttribute on B
+           IL2050: P/invoke method A declares a parameter with COM marshalling. Correctness of COM interop
+                   cannot be guaranteed after trimming. Interfaces and interface members might be removed.
+      -->
+      <LinkerNoWarn>IL2006;IL2009;IL2025;IL2026;IL2035;IL2050</LinkerNoWarn>
+      <!-- https://github.com/dotnet/runtime/issues/40336 - need to also suppress the following on non-Windows:
+           IL2008: Could not find type A specified in resource B
+           IL2037: No members were resolved for 'GetDefaultInstance'
+           
+           and on 32-bit builds:
+           IL2012: Could not find field 'Padding' in type 'System.Runtime.CompilerServices.RawArrayData'
+      -->
+      <LinkerNoWarn Condition="'$(OS)' != 'Windows_NT'">$(LinkerNoWarn);IL2008;IL2037</LinkerNoWarn>
+      <LinkerNoWarn Condition="'$(Platform)' != 'x64' AND '$(Platform)' != 'arm64'">$(LinkerNoWarn);IL2012</LinkerNoWarn>
+      <ILLinkArgs>$(ILLinkArgs) --nowarn $(LinkerNoWarn)</ILLinkArgs>
+    </PropertyGroup>
+
+     <!-- Retrieve CoreLib's targetpath via GetTargetPath as it isn't binplaced yet. -->
+    <MSBuild Projects="$(CoreLibProject)"
+             Targets="GetTargetPath">
+      <Output TaskParameter="TargetOutputs" PropertyName="SystemPrivateCoreLibPath" />
+    </MSBuild>
+
+    <PropertyGroup>
+      <_AssemblyPaths>$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir);$(SystemPrivateCoreLibPath)</_AssemblyPaths>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <!-- add references from the libraries directory -->
+      <_DependencyDirectories Include="$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir.TrimEnd('\'))" />
+    </ItemGroup>
+
+    <PropertyGroup>
+      <ILLinkArgs>$(ILLinkArgs) -d @(_DependencyDirectories->'"%(Identity)"', ' -d ')</ILLinkArgs>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <_AssembliesToLink Include="System.Private.CoreLib" />
+
+      <_LibrariesToLink Include="$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)*.dll" />
+      <_AssembliesToLink Include="@(_LibrariesToLink->'%(FileName)')" />
+    </ItemGroup>
+
+    <PropertyGroup>
+      <ILLinkArgs>$(ILLinkArgs) -r @(_AssembliesToLink->'%(Identity)', ' -r ')</ILLinkArgs>
+    </PropertyGroup>
+
+    <!-- When running from Desktop MSBuild, DOTNET_HOST_PATH is not set.
+      In this case, explicitly specify the path to the dotnet host. -->
+    <PropertyGroup Condition=" '$(DOTNET_HOST_PATH)' == '' ">
+      <_DotNetHostDirectory>$(DotNetRoot)</_DotNetHostDirectory>
+      <_DotNetHostFileName>$([System.IO.Path]::GetFileName('$(DotNetTool)'))</_DotNetHostFileName>
+    </PropertyGroup>
+
+    <ILLink AssemblyPaths="$(_AssemblyPaths)"
+        RootAssemblyNames=""
+        OutputDirectory="$(LibrariesTrimmedArtifactsPath)"
+        ExtraArgs="$(ILLinkArgs)"
+        ToolExe="$(_DotNetHostFileName)"
+        ToolPath="$(_DotNetHostDirectory)" />
+  </Target>
+
+  <Import Project="$(RepositoryEngineeringDir)illink.targets" />
+</Project>
diff --git a/src/libraries/libraries-packages.proj b/src/libraries/libraries-packages.proj
index 2301e84828275c..f2eef864898f23 100644
--- a/src/libraries/libraries-packages.proj
+++ b/src/libraries/libraries-packages.proj
@@ -4,6 +4,7 @@
   <PropertyGroup>
     <TraversalGlobalProperties>BuildAllProjects=true</TraversalGlobalProperties>
     <AdditionalBuildTargetFrameworks Condition="'$(DotNetBuildFromSource)' == 'true'">$(AdditionalBuildTargetFrameworks);package-$(Configuration)</AdditionalBuildTargetFrameworks>
+    <BuildAllOOBPackages Condition="'$(BuildAllOOBPackages)' == ''">true</BuildAllOOBPackages>
   </PropertyGroup>
   
   <PropertyGroup>
@@ -15,7 +16,8 @@
 
   <ItemGroup>
     <ProjectReference Include="$(PkgDir)*\*.proj" Exclude="$(PkgDir)test\*" />
-    <ProjectReference Include="$(MSBuildThisFileDirectory)*\pkg\**\*.pkgproj" Condition="'$(BuildAllConfigurations)' == 'true' or '$(DotNetBuildFromSource)' == 'true'" />
+    <ProjectReference Include="$(MSBuildThisFileDirectory)*\pkg\**\*.pkgproj" Condition="('$(BuildAllConfigurations)' == 'true' or '$(DotNetBuildFromSource)' == 'true') And '$(BuildAllOOBPackages)' == 'true'" />
+    <!-- If setting BuildAllOOBPackages to false, add bellow the individual OOB packages you want to continue to build -->
   </ItemGroup>
 
   <!-- Need the PackageIndexFile file property from baseline.props -->
diff --git a/src/libraries/pkg/baseline/packageIndex.json b/src/libraries/pkg/baseline/packageIndex.json
index 1446eaab32977a..427eb60f15f7fc 100644
--- a/src/libraries/pkg/baseline/packageIndex.json
+++ b/src/libraries/pkg/baseline/packageIndex.json
@@ -24,10 +24,11 @@
       "StableVersions": [
         "1.0.0"
       ],
-      "BaselineVersion": "1.0.0",
+      "BaselineVersion": "5.0.0",
       "InboxOn": {},
       "AssemblyVersionInPackageVersion": {
-        "1.0.0.0": "1.0.0"
+        "1.0.0.0": "1.0.0",
+        "5.0.0.0": "5.0.0"
       }
     },
     "Microsoft.Bcl.HashCode": {
@@ -3353,7 +3354,9 @@
         "4.6.0"
       ],
       "BaselineVersion": "5.0.0",
-      "InboxOn": {},
+      "InboxOn": {
+        "net5.0": "5.0.0.0"
+      },
       "AssemblyVersionInPackageVersion": {
         "4.0.0.0": "4.5.0",
         "4.0.0.1": "4.5.2",
@@ -5122,6 +5125,11 @@
         "4.1.1.0": "4.3.0"
       }
     },
+    "System.Private.Runtime.InteropServices.JavaScript": {
+      "InboxOn": {
+        "net5.0": "5.0.0.0"
+      }
+    },
     "System.Runtime.InteropServices.RuntimeInformation": {
       "StableVersions": [
         "4.0.0",
@@ -6533,6 +6541,7 @@
         "4.1.0.0": "4.3.0",
         "4.1.1.0": "4.4.0",
         "4.2.0.0": "4.5.0",
+        "4.2.0.1": "4.5.4",
         "4.2.1.0": "4.6.0"
       }
     },
diff --git a/src/libraries/pkg/descriptions.json b/src/libraries/pkg/descriptions.json
index 3b04891e233af2..f3111c4f23836b 100644
--- a/src/libraries/pkg/descriptions.json
+++ b/src/libraries/pkg/descriptions.json
@@ -1234,6 +1234,15 @@
         "System.Buffers.Text.Utf8Formatter"
     ]
   },
+  {
+    "Name": "Microsoft.Bcl.AsyncInterfaces",
+    "Description": "Provides the IAsyncEnumerable<T> and IAsyncDisposable interfaces and helper types for .NET Standard 2.0. This package is not required starting with .NET Standard 2.1 and .NET Core 3.0.",
+    "CommonTypes": [
+      "System.IAsyncDisposable",
+      "System.Collections.Generic.IAsyncEnumerable",
+      "System.Collections.Generic.IAsyncEnumerator"
+    ]
+  },
   {
     "Name": "System.Net.Http",
     "Description": "Provides a programming interface for modern HTTP applications, including HTTP client components that allow applications to consume web services over HTTP and HTTP components that can be used by both clients and servers for parsing HTTP headers.",
diff --git a/src/libraries/pkg/test/testPackages.proj b/src/libraries/pkg/test/testPackages.proj
index a624abf7878b7b..94f5111179a66c 100644
--- a/src/libraries/pkg/test/testPackages.proj
+++ b/src/libraries/pkg/test/testPackages.proj
@@ -21,9 +21,6 @@
     <TargetFrameworksToExclude Include="net463" />
     <TargetFrameworksToExclude Include="net47" />
     <TargetFrameworksToExclude Include="netcoreapp2.2" />
-
-    <!-- CI machines doesn't have net472 targeting pack installed yet and we hit: https://github.com/dotnet/corefx/issues/29906 -->
-    <TargetFrameworksToExclude Include="net472" />
   </ItemGroup>
 
   <PropertyGroup>
diff --git a/src/libraries/pretest.proj b/src/libraries/pretest.proj
index 23a4041ff30a66..5cd55be973cb4e 100644
--- a/src/libraries/pretest.proj
+++ b/src/libraries/pretest.proj
@@ -1,17 +1,16 @@
 <Project Sdk="Microsoft.Build.Traversal">
   <Import Project="Sdk.props" Sdk="Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk" />
 
-  <PropertyGroup>
-    <TraversalGlobalProperties>BuildAllProjects=true</TraversalGlobalProperties>
-  </PropertyGroup>
-
   <PropertyGroup Condition="'$(ContinuousIntegrationBuild)' != 'true'">
     <!-- Create an intermediate runsettings file to enable VSTest discovery. -->
     <EnableRunSettingsSupport>true</EnableRunSettingsSupport>
     <CreateIntermediateRunSettingsFile>true</CreateIntermediateRunSettingsFile>
   </PropertyGroup>
 
-  <!-- Explicitly build the runtime.depproj project first to correctly set up the testhost. -->
+  <!--
+    Explicitly build the runtime.depproj project first to create the PlatformManifest for
+    the targeting and runtimepack before the test runners which consume that asset are built.
+  -->
   <ItemGroup>
     <RuntimeProject Include="$(MSBuildThisFileDirectory)restore\runtime\runtime.depproj" />
     <ProjectReference Include="@(RuntimeProject)" Condition="'$(MSBuildRestoreSessionId)' != ''" />
@@ -20,8 +19,8 @@
     <ProjectReference Include="$(CommonTestPath)AndroidTestRunner\AndroidTestRunner.csproj" Condition="'$(TargetOS)' == 'Android'" />
     <ProjectReference Include="$(CommonTestPath)WasmTestRunner\WasmTestRunner.csproj" Condition="'$(TargetOS)' == 'Browser'" />
   </ItemGroup>
-
-  <Target Name="RestoreTestHost"
+  
+  <Target Name="RestoreRuntimeDepproj"
           BeforeTargets="Build">
     <MSBuild Targets="Build"
              Projects="@(RuntimeProject)"
@@ -29,104 +28,110 @@
   </Target>
 
   <Target Name="CreateIntermediateRunSettingsFile"
-          Condition="'$(CreateIntermediateRunSettingsFile)' == 'true'"
           DependsOnTargets="GenerateRunSettingsFile"
-          BeforeTargets="Build" />
+          BeforeTargets="Build"
+          Condition="'$(CreateIntermediateRunSettingsFile)' == 'true'" />
 
-  <!-- Microsoft.XmlSerializer.Generator should not be marked as a platform item and be copy-local instead. -->
-  <Target Name="CollectSharedFrameworkRuntimeFiles"
-          Condition="'$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'">
+  <Target Name="GetSharedFrameworkRuntimeFiles">
     <ItemGroup>
-      <_manualSharedFrameworkRuntimeFiles Include="System.Security.Cryptography.Native.OpenSsl.so" />
-      <_manualSharedFrameworkRuntimeFiles Include="System.Security.Cryptography.Native.Apple.dylib" />
-      <_manualSharedFrameworkRuntimeFiles Include="System.Security.Cryptography.Native.OpenSsl.dylib" />
-    </ItemGroup>
-    <ItemGroup>
-      <SharedFrameworkRuntimeFiles Include="$(TestHostRuntimePath)*;@(_manualSharedFrameworkRuntimeFiles->'$(TestHostRuntimePath)%(Identity)')"
-                                   Exclude="$(TestHostRuntimePath)dotnet-Microsoft.XmlSerializer.Generator.*"
-                                   TargetPath="runtimes/" />
+      <ManualRuntimePackNativeFile Include="System.Security.Cryptography.Native.OpenSsl.so" />
+      <ManualRuntimePackNativeFile Include="System.Security.Cryptography.Native.Apple.dylib" />
+      <ManualRuntimePackNativeFile Include="System.Security.Cryptography.Native.OpenSsl.dylib" />
+      <SharedFrameworkRuntimeFile Include="$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)*;
+                                           $(MicrosoftNetCoreAppRuntimePackNativeDir)*;
+                                           @(ManualRuntimePackNativeFile->'$(MicrosoftNetCoreAppRuntimePackNativeDir)%(Identity)')"
+                                  TargetPath="runtimes/" />
     </ItemGroup>
   </Target>
 
+  <!-- Generate the runtime pack's PlatformManifest -->
   <UsingTask TaskName="GenerateFileVersionProps" AssemblyFile="$(InstallerTasksAssemblyPath)"/>
-  <Target Name="GenerateFileVersionProps"
-          DependsOnTargets="CollectSharedFrameworkRuntimeFiles"
-          Condition="'$(PlatformManifestFile)' != '' and '$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'"
-          AfterTargets="RestoreTestHost">
-    <GenerateFileVersionProps Files="@(SharedFrameworkRuntimeFiles)"
-                              PackageId="$(SharedFrameworkName)"
+  <Target Name="GenerateFileVersionPropsRuntimePack"
+          DependsOnTargets="GetSharedFrameworkRuntimeFiles"
+          AfterTargets="RestoreRuntimeDepproj"
+          Inputs="@(SharedFrameworkRuntimeFile)"
+          Outputs="$(MicrosoftNetCoreAppRuntimePackDir)data\PlatformManifest.txt"
+          Condition="'$(BuildingNETCoreAppVertical)' == 'true'">
+    <GenerateFileVersionProps Files="@(SharedFrameworkRuntimeFile)"
+                              PackageId="$(SharedFrameworkName).Runtime.$(PackageRID)"
                               PackageVersion="$(ProductVersion)"
-                              PlatformManifestFile="$(PlatformManifestFile)"
-                              PreferredPackages="$(SharedFrameworkName)"
+                              PlatformManifestFile="$(MicrosoftNetCoreAppRuntimePackDir)data\PlatformManifest.txt"
+                              PreferredPackages="$(SharedFrameworkName).Runtime.$(PackageRID)"
                               PermitDllAndExeFilesLackingFileVersion="true" />
+  </Target>
 
-    <Copy SourceFiles="$(PlatformManifestFile)"
-          DestinationFolder="$(MicrosoftNetCoreAppRefPackDataDir)"
-          UseHardlinksIfPossible="true"
-          SkipUnchangedFiles="true" />
+  <!-- Generate the ref pack's PlatformManifest -->
+  <Target Name="GenerateFileVersionPropsRefPack"
+          DependsOnTargets="GetSharedFrameworkRuntimeFiles"
+          AfterTargets="RestoreRuntimeDepproj"
+          Inputs="@(SharedFrameworkRuntimeFile)"
+          Outputs="$(MicrosoftNetCoreAppRefPackDataDir)PlatformManifest.txt"
+          Condition="'$(BuildingNETCoreAppVertical)' == 'true'">
+    <GenerateFileVersionProps Files="@(SharedFrameworkRuntimeFile)"
+                              PackageId="$(SharedFrameworkName).Ref"
+                              PackageVersion="$(ProductVersion)"
+                              PlatformManifestFile="$(MicrosoftNetCoreAppRefPackDataDir)PlatformManifest.txt"
+                              PreferredPackages="$(SharedFrameworkName).Ref"
+                              PermitDllAndExeFilesLackingFileVersion="true" />
   </Target>
 
-  <!--
-    Shared framework deps file generation.
-    Produces a test shared-framework deps file.
-    To use invoke target directly specifying NETCoreAppTestSharedFrameworkPath property.
-  -->
+  <!-- Generate the shared framework's deps.json -->
   <UsingTask TaskName="GenerateTestSharedFrameworkDepsFile" AssemblyFile="$(InstallerTasksAssemblyPath)"/>
-  <Target Name="GenerateTestSharedFrameworkDepsFile"
-          Condition="'$(BinplaceTestSharedFramework)' == 'true' and '$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'"
-          AfterTargets="RestoreTestHost">
+  <Target Name="GenerateTestSharedFrameworkAssets"
+          AfterTargets="RestoreRuntimeDepproj"
+          Inputs="$(NETCoreAppTestSharedFrameworkPath)*.*"
+          Outputs="$(NETCoreAppTestSharedFrameworkPath)$(SharedFrameworkName).deps.json"
+          Condition="'$(BinPlaceTestSharedFramework)' == 'true'">
+    <!-- Shared framework deps file generation. Produces a test shared-framework deps file. -->
     <GenerateTestSharedFrameworkDepsFile SharedFrameworkDirectory="$(NETCoreAppTestSharedFrameworkPath)"
                                          RuntimeGraphFiles="$(RuntimeIdGraphDefinitionFile)"
                                          TargetRuntimeIdentifier="$(PackageRID)" />
   </Target>
 
-  <UsingTask TaskName="CreateFrameworkListFile" AssemblyFile="$(DotNetBuildTasksSharedFrameworkTaskFile)"/>
-  <Target Name="GenerateFrameworkListFile"
-          Condition="'$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'"
-          AfterTargets="RestoreTestHost">
+  <Target Name="GetRuntimePackFiles">
     <ItemGroup>
-      <_refPackLibFile Include="$(MicrosoftNetCoreAppRefPackRefDir)*.*">
-        <TargetPath>ref/$(NetCoreAppCurrent)</TargetPath>
-      </_refPackLibFile>
-      <_runtimePackLibFiles Include="$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)*.*">
+      <RuntimePackLibFile Include="$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)*.*">
         <TargetPath>runtimes/$(PackageRID)/lib/$(NetCoreAppCurrent)</TargetPath>
-      </_runtimePackLibFiles>
-      <_runtimePackNativeFiles Include="$(MicrosoftNetCoreAppRuntimePackNativeDir)*.*">
+      </RuntimePackLibFile>
+      <RuntimePackNativeFile Include="$(MicrosoftNetCoreAppRuntimePackNativeDir)*.*">
         <TargetPath>runtimes/$(PackageRID)/native</TargetPath>
         <IsNative>true</IsNative>
-      </_runtimePackNativeFiles>
-      <!-- Clear the IsNative flag on System.PrivateCoreLib given that it is present in native dir but it is actually managed -->
-      <_runtimePackNativeFiles Update="@(_runtimePackNativeFiles)" Condition="'%(FileName)%(Extension)' == 'System.Private.CoreLib.dll'" IsNative="" />
-
-      <FrameworkListRootAttributes Include="Name" Value="$(NetCoreAppCurrentBrandName)" />
-      <FrameworkListRootAttributes Include="TargetFrameworkIdentifier" Value="$(NetCoreAppCurrentIdentifier)" />
-      <FrameworkListRootAttributes Include="TargetFrameworkVersion" Value="$(NetCoreAppCurrentVersion)" />
-      <FrameworkListRootAttributes Include="FrameworkName" Value="$(SharedFrameworkName)" />
+      </RuntimePackNativeFile>
+      <!-- Clear the IsNative flag on System.Private.CoreLib given that it is present in native dir but it is actually managed -->
+      <RuntimePackNativeFile IsNative=""
+                             Condition="'%(FileName)%(Extension)' == 'System.Private.CoreLib.dll'" />
     </ItemGroup>
-
     <!-- We need to set this metadata in a separate ItemGroup than when the Items are initially populated in order to
     have access to the Extension metadata. -->
     <ItemGroup>
-      <_refPackLibFile>
-        <IsSymbolFile Condition="'%(Extension)' == '.pdb'">true</IsSymbolFile>
-      </_refPackLibFile>
-      <_runtimePackLibFiles>
+      <RuntimePackLibFile>
         <IsSymbolFile Condition="'%(Extension)' == '.pdb'">true</IsSymbolFile>
-      </_runtimePackLibFiles>
-      <_runtimePackNativeFiles>
+      </RuntimePackLibFile>
+      <RuntimePackNativeFile>
         <IsSymbolFile Condition="'%(Extension)' == '.pdb'">true</IsSymbolFile>
-      </_runtimePackNativeFiles>
+      </RuntimePackNativeFile>
     </ItemGroup>
+  </Target>
 
-    <CreateFrameworkListFile Files="@(_refPackLibFile)"
-                             TargetFile="$(MicrosoftNetCoreAppRefPackDataDir)FrameworkList.xml"
-                             TargetFilePrefixes="ref/;runtimes/"
-                             RootAttributes="@(FrameworkListRootAttributes)" />
+  <!-- Generate the runtime pack's RuntimeList.xml -->
+  <UsingTask TaskName="CreateFrameworkListFile" AssemblyFile="$(DotNetBuildTasksSharedFrameworkTaskFile)"/>
+  <Target Name="GenerateRuntimeListFile"
+          DependsOnTargets="GetRuntimePackFiles"
+          AfterTargets="RestoreRuntimeDepproj"
+          Inputs="@(RuntimePackLibFile);@(RuntimePackNativeFile)"
+          Outputs="$(MicrosoftNetCoreAppRuntimePackDir)data\RuntimeList.xml"
+          Condition="'$(BuildingNETCoreAppVertical)' == 'true'">
+    <ItemGroup>
+      <FrameworkListRootAttribute Include="Name" Value="$(NetCoreAppCurrentBrandName)" />
+      <FrameworkListRootAttribute Include="TargetFrameworkIdentifier" Value="$(NetCoreAppCurrentIdentifier)" />
+      <FrameworkListRootAttribute Include="TargetFrameworkVersion" Value="$(NetCoreAppCurrentVersion)" />
+      <FrameworkListRootAttribute Include="FrameworkName" Value="$(SharedFrameworkName)" />
+    </ItemGroup>
 
-    <CreateFrameworkListFile Files="@(_runtimePackLibFiles);@(_runtimePackNativeFiles)"
+    <CreateFrameworkListFile Files="@(RuntimePackLibFile);@(RuntimePackNativeFile)"
                              TargetFile="$(MicrosoftNetCoreAppRuntimePackDir)data\RuntimeList.xml"
                              TargetFilePrefixes="ref/;runtimes/"
-                             RootAttributes="@(FrameworkListRootAttributes)" />
+                             RootAttributes="@(FrameworkListRootAttribute)" />
   </Target>
 
   <Import Project="Sdk.targets" Sdk="Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk" />
diff --git a/src/libraries/ref.proj b/src/libraries/ref.proj
index c13c10044388a9..c80789e51e53ca 100644
--- a/src/libraries/ref.proj
+++ b/src/libraries/ref.proj
@@ -1,24 +1,91 @@
 <Project Sdk="Microsoft.Build.Traversal">
+  <Import Project="Sdk.props" Sdk="Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk" />
 
   <PropertyGroup>
     <TraversalGlobalProperties>BuildAllProjects=true</TraversalGlobalProperties>
   </PropertyGroup>
 
   <ItemGroup>
-    <GeneratedShimProject Include="shims\generated\*.csproj" />
+    <_allRef Include="$(MSBuildThisFileDirectory)*\ref\*.csproj"
+             Exclude="@(ProjectExclusions)" />
+    <NonNetCoreAppProject Include="@(_allRef)"
+                          Exclude="@(NetCoreAppLibrary->'%(Identity)\ref\%(Identity).csproj')" />
+    <NetCoreAppProject Include="@(_allRef)"
+                       Exclude="@(NonNetCoreAppProject)" />
+    <GeneratedShimProject Include="shims\generated\*.csproj"
+                          Condition="'$(BuildingNETCoreAppVertical)' == 'true'" />
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="$(MSBuildThisFileDirectory)*\ref\*.*proj" Exclude="@(ProjectExclusions)" />
+    <ProjectReference Include="@(NetCoreAppProject)" />
+
     <!-- Restore only and build later. -->
-    <ProjectReference Include="@(GeneratedShimProject)" Condition="'$(MSBuildRestoreSessionId)' != ''" />
+    <ProjectReference Include="@(NonNetCoreAppProject);
+                               @(GeneratedShimProject)"
+                      Condition="'$(MSBuildRestoreSessionId)' != ''" />
   </ItemGroup>
 
   <Target Name="BuildGeneratedShims"
-          AfterTargets="Build">
+          AfterTargets="Build"
+          Condition="'@(GeneratedShimProject)' != ''">
     <MSBuild Targets="Build"
              Projects="@(GeneratedShimProject)"
              Properties="$(TraversalGlobalProperties)" />
   </Target>
 
+  <Target Name="GetRefPackFiles">
+    <ItemGroup>
+      <RefPackLibFile Include="$(MicrosoftNetCoreAppRefPackRefDir)*.*">
+        <TargetPath>ref/$(NetCoreAppCurrent)</TargetPath>
+        <IsSymbolFile Condition="$([System.String]::Copy('%(Identity)').EndsWith('pdb'))">true</IsSymbolFile>
+      </RefPackLibFile>
+    </ItemGroup>
+    <!-- We need to set this metadata in a separate ItemGroup than when the Items are initially populated in order to
+    have access to the Extension metadata. -->
+    <ItemGroup>
+      <RefPackLibFile>
+        <IsSymbolFile Condition="'%(Extension)' == '.pdb'">true</IsSymbolFile>
+      </RefPackLibFile>
+    </ItemGroup>
+  </Target>
+
+  <!-- Generate the ref pack's FrameworkList.xml -->
+  <UsingTask TaskName="CreateFrameworkListFile" AssemblyFile="$(DotNetBuildTasksSharedFrameworkTaskFile)"/>
+  <Target Name="GenerateFrameworkListFile"
+          DependsOnTargets="GetRefPackFiles"
+          AfterTargets="BuildGeneratedShims"
+          Inputs="@(RefPackLibFile)"
+          Outputs="$(MicrosoftNetCoreAppRefPackDataDir)FrameworkList.xml"
+          Condition="'$(BuildingNETCoreAppVertical)' == 'true'">
+    <ItemGroup>
+      <FrameworkListRootAttribute Include="Name" Value="$(NetCoreAppCurrentBrandName)" />
+      <FrameworkListRootAttribute Include="TargetFrameworkIdentifier" Value="$(NetCoreAppCurrentIdentifier)" />
+      <FrameworkListRootAttribute Include="TargetFrameworkVersion" Value="$(NetCoreAppCurrentVersion)" />
+      <FrameworkListRootAttribute Include="FrameworkName" Value="$(SharedFrameworkName)" />
+    </ItemGroup>
+
+    <CreateFrameworkListFile Files="@(RefPackLibFile)"
+                             TargetFile="$(MicrosoftNetCoreAppRefPackDataDir)FrameworkList.xml"
+                             TargetFilePrefixes="ref/;runtimes/"
+                             RootAttributes="@(FrameworkListRootAttribute)" />
+  </Target>
+
+  <Target Name="BuildNonNetCoreAppProjects"
+          AfterTargets="GenerateFrameworkListFile">
+    <MSBuild Targets="Build"
+             BuildInParallel="true"
+             Projects="@(NonNetCoreAppProject)"
+             Properties="$(TraversalGlobalProperties)" />
+  </Target>
+
+  <!-- Build generated shims with the full reference closure, including OOB assemblies. -->
+  <Target Name="RebuildGeneratedShims"
+          AfterTargets="BuildNonNetCoreAppProjects"
+          Condition="'@(GeneratedShimProject)' != ''">
+    <MSBuild Targets="Build"
+             Projects="@(GeneratedShimProject)"
+             Properties="$(TraversalGlobalProperties);_Incremental=true" />
+  </Target>
+
+  <Import Project="Sdk.targets" Sdk="Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk" />
 </Project>
diff --git a/src/libraries/restore/Directory.Build.props b/src/libraries/restore/Directory.Build.props
index 359dfd63da6af8..4cc238039b418b 100644
--- a/src/libraries/restore/Directory.Build.props
+++ b/src/libraries/restore/Directory.Build.props
@@ -1,4 +1,4 @@
-<Project TreatAsLocalProperty="AdditionalBuildTargetFrameworks">
+<Project>
   <Import Project="..\Directory.Build.props" />
 
   <PropertyGroup>
@@ -11,7 +11,6 @@
 
     <SkipDeriveTargetFrameworks>true</SkipDeriveTargetFrameworks>
     <AppendRuntimeIdentifierToOutputPath>false</AppendRuntimeIdentifierToOutputPath>
-    <AdditionalBuildTargetFrameworks Condition="'$(BuildAllProjects)' == 'true'">netstandard2.0</AdditionalBuildTargetFrameworks>
   </PropertyGroup>
   
   <!-- don't bring in props/targets from packages, we're not consuming them we're
diff --git a/src/libraries/restore/Directory.Build.targets b/src/libraries/restore/Directory.Build.targets
index 28eaed69674077..785efcc4de2bb6 100644
--- a/src/libraries/restore/Directory.Build.targets
+++ b/src/libraries/restore/Directory.Build.targets
@@ -4,6 +4,4 @@
   <PropertyGroup>
     <PrereleaseResolveNuGetPackages>true</PrereleaseResolveNuGetPackages>
   </PropertyGroup>
-
-  <Import Project="$(MSBuildThisFileDirectory)\runtime\referenceFromRuntime.targets" Condition="'$(TargetFramework)' == 'netcoreapp3.0' and '$(TargetFrameworkSuffix)' == 'Windows_NT'"/>
 </Project>
diff --git a/src/libraries/restore/binplacePackages/binplacePackages.depproj b/src/libraries/restore/binplacePackages/binplacePackages.depproj
deleted file mode 100644
index 5b7928b270cec4..00000000000000
--- a/src/libraries/restore/binplacePackages/binplacePackages.depproj
+++ /dev/null
@@ -1,53 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <BinPlaceRef>true</BinPlaceRef>
-    <BinPlaceRuntime>true</BinPlaceRuntime>
-    <NETStandardVersion Condition="$(TargetFramework.StartsWith('netstandard'))">$(TargetFramework.SubString(11))</NETStandardVersion>
-    <NuGetDeploySourceItem>Reference</NuGetDeploySourceItem>
-    <TargetsNetStandardLowerThan21 Condition="$(TargetFramework.StartsWith('netstandard')) and '$(NETStandardVersion)' &lt; 2.1">true</TargetsNetStandardLowerThan21>
-    <TargetFrameworks>net461;net472;netstandard1.1;netstandard1.2;netstandard1.3;netstandard1.4;netstandard1.5;netstandard1.6;netstandard2.0;netstandard2.0;netcoreapp2.0;netcoreapp3.0;$(NetCoreAppCurrent)</TargetFrameworks>    
-  </PropertyGroup>
-
-    <!-- Ref binplacing for all configurations -->
-  <ItemGroup>
-    <BinPlaceTargetFrameworks Include="$(TargetFramework)">
-      <RefPath>$(RefPath)</RefPath>
-    </BinPlaceTargetFrameworks>
-  </ItemGroup>
-
-  <!-- Runtime / test-runtime binplacing, when we aren't building better live version of these libs -->
-  <ItemGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <BinPlaceTargetFrameworks Include="$(TargetFramework)">
-      <ItemName>BinPlaceLib</ItemName>
-      <RuntimePath>$(RuntimePath)</RuntimePath>
-    </BinPlaceTargetFrameworks>
-    <BinPlaceTargetFrameworks Include="$(TargetFramework)">
-      <ItemName>BinPlaceLib</ItemName>
-      <RuntimePath>$(TestHostRuntimePath)</RuntimePath>
-    </BinPlaceTargetFrameworks>
-  </ItemGroup>
-
-  <!-- This is to make sure that nothing unintended gets restored for netcoreapp. -->
-  <ItemGroup Condition="'$(TargetFramework)' != '$(NetCoreAppCurrent)'">
-    <!-- runtime dependency: System.Diagnostics.PerformanceCounters netcoreapp2.0,net461 -->
-    <PackageReference Include="System.Memory" Version="4.5.3" Condition="'$(TargetFramework)' == 'netcoreapp2.0' or $(TargetFramework.StartsWith('net4')) or ($(TargetFramework.StartsWith('netstandard')) and '$(NETStandardVersion)' &gt;= 1.1)" />
-    <PackageReference Include="System.Numerics.Vectors" Version="4.5.0" Condition="'$(TargetsNetStandardLowerThan21)' == 'true' or $(TargetFramework.StartsWith('net4'))" />
-    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.2" Condition="'$(TargetFramework)' == 'netcoreapp2.0' or $(TargetFramework.StartsWith('net4')) or $(TargetFramework.StartsWith('netstandard'))" />
-  </ItemGroup>
-  
-  <ItemGroup>
-    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="1.0.0" Condition="!$(TargetFramework.StartsWith('netstandard')) or '$(NETStandardVersion)' &gt;= 2.0" />
-    <PackageReference Include="System.Data.SqlClient" Version="$(SystemDataSqlClientVersion)" Condition="!$(TargetFramework.StartsWith('netstandard')) or '$(NETStandardVersion)' &gt;= 2.0" />
-    
-    <PackageReference Include="System.ComponentModel.Annotations" Version="4.7.0" Condition="!$(TargetFramework.StartsWith('netstandard')) or '$(NETStandardVersion)' &lt;= 2.0" />
-    <!-- Only include the assets from the direct packages we reference in the output -->
-    <PackageToInclude Include="@(PackageReference)" />
-  </ItemGroup>
-
-  <Target Name="AddHarvestedLibraries" BeforeTargets="CoreCompile"
-          Condition="!$(TargetFramework.StartsWith('netstandard'))">
-    <ItemGroup>
-      <BinPlaceLib Include="@(ReferenceCopyLocalPaths)" />
-    </ItemGroup>
-  </Target>
-</Project>
diff --git a/src/libraries/restore/depproj.proj b/src/libraries/restore/depproj.proj
deleted file mode 100644
index 7825325f923911..00000000000000
--- a/src/libraries/restore/depproj.proj
+++ /dev/null
@@ -1,28 +0,0 @@
-<Project>
-  <Import Project="Directory.Build.props" />
-
-  <ItemGroup>
-    <ProjectReference Include="netcoreapp/external.netcoreapp.depproj" Condition="'$(DotNetBuildFromSource)' != 'true'" />
-    <ProjectReference Include="netstandard/external.netstandard.depproj" />
-    <ProjectReference Include="netfx/netfx.depproj" />
-    <ProjectReference Include="binplacePackages/binplacePackages.depproj" />
-  </ItemGroup>
-
-  <Target Name="Restore">
-    <MSBuild Projects="@(ProjectReference)"
-             Properties="BuildAllProjects=true;MSBuildRestoreSessionId=$([System.Guid]::NewGuid())"
-             BuildInParallel="true"
-             Targets="Restore" />
-
-    <MSBuild Projects="@(ProjectReference)"
-             Properties="BuildAllProjects=true"
-             BuildInParallel="true"
-             Targets="Build" />
-  </Target>
-
-  <Import Project="Directory.Build.targets" />
-
-  <!-- Ordering matters! Overwriting the Build target after the Sdk.targets import. -->
-  <!-- Don't do anything during build. -->
-  <Target Name="Build" />
-</Project>
diff --git a/src/libraries/restore/netcoreapp/external.netcoreapp.depproj b/src/libraries/restore/netcoreapp/external.netcoreapp.depproj
deleted file mode 100644
index 72e15fde6cdf63..00000000000000
--- a/src/libraries/restore/netcoreapp/external.netcoreapp.depproj
+++ /dev/null
@@ -1,20 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <!-- This project restores and publishes the targeting pack for specific versions of .NET Core.
-       With this, we are able to compile assemblies against shipped, stable versions of .NET Core. -->
-  <PropertyGroup>
-    <NuGetDeploySourceItem>Reference</NuGetDeploySourceItem>
-    <DisableImplicitFrameworkReferences>false</DisableImplicitFrameworkReferences>
-    <BinPlaceRef>true</BinPlaceRef>
-    <TargetFrameworks>netcoreapp2.0;netcoreapp2.1;netcoreapp3.0;netcoreapp3.1</TargetFrameworks>
-  </PropertyGroup>
-
-  <ItemGroup Condition="$(TargetFramework.StartsWith('netcoreapp2.'))">
-    <PackageReference Update="Microsoft.NETCore.App" IsImplicitlyDefined="false" PrivateAssets="None" />
-  </ItemGroup>
-
-  <ItemGroup>
-    <!-- for all configurations this project provides refs for that configuration -->
-    <BinPlaceTargetFrameworks Include="$(TargetFramework)" RefPath="$(RefPath)" />
-    <FileToExclude Include="System.ComponentModel.Composition" />
-  </ItemGroup>
-</Project>
diff --git a/src/libraries/restore/netfx/netfx.depproj b/src/libraries/restore/netfx/netfx.depproj
deleted file mode 100644
index 7fcdb7329068fa..00000000000000
--- a/src/libraries/restore/netfx/netfx.depproj
+++ /dev/null
@@ -1,126 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <Import Project="$(LibrariesProjectRoot)shims\netfxreference.props" />
-  <PropertyGroup>
-    <BinPlaceRef>true</BinPlaceRef>
-    <BinPlaceRuntime>true</BinPlaceRuntime>
-    <NuGetDeploySourceItem>Reference</NuGetDeploySourceItem>
-    <NETStandardSupportPackageId>NETStandard.Library.NETFramework</NETStandardSupportPackageId>
-    <NETStandardSupportPackageVersion>2.0.1-servicing-26011-01</NETStandardSupportPackageVersion>
-    <NETStandardSupportRoot>$(NuGetPackageRoot)$(NETStandardSupportPackageId.ToLower())\$(NETStandardSupportPackageVersion)\build</NETStandardSupportRoot>
-    <AddNetStandardSupportPackage Condition="'$(TargetFramework)' == 'net461' or '$(TargetFramework)' == 'net462' or '$(TargetFramework)' == 'net47'">true</AddNetStandardSupportPackage>
-    <TargetFrameworks>net45;net451;net46;net461;net462;net47;net471;net472</TargetFrameworks>
-    <!-- if we aren't building all configurations, ensure we populate NetFxRefPath for netcoreapp by building this project -->
-    <TargetFrameworks Condition="'$(BuildAllConfigurations)' != 'true'">$(TargetFrameworks);$(NetCoreAppCurrent)</TargetFrameworks>
-  </PropertyGroup>
-  <PropertyGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
-    <!-- For things not .NETFramework we need the net472 targeting pack to generate facades -->
-    <AssetTargetFallback>$(NetFrameworkCurrent)</AssetTargetFallback>
-    <TargetingPackNugetPackageId>Microsoft.TargetingPack.NETFramework.v4.7.2</TargetingPackNugetPackageId>
-  </PropertyGroup>
-
-  <!-- Split $(TargetFramework) (e.g. net45) into short identifier and short version (e.g. 'net' and '45'). -->
-  <PropertyGroup Condition="'$(TargetFramework)' != '' and !$(TargetFramework.Contains(',')) and !$(TargetFramework.Contains('+'))">
-   <_ShortFrameworkIdentifier>$(TargetFramework.TrimEnd('.0123456789'))</_ShortFrameworkIdentifier>
-   <_ShortFrameworkVersion>$(TargetFramework.Substring($(_ShortFrameworkIdentifier.Length)))</_ShortFrameworkVersion>
-  </PropertyGroup>
-
-  <!-- Versions with dots are taken as is and just given leading 'v'. -->
-  <PropertyGroup Condition="'$(TargetFrameworkVersion)' == '' and '$(_ShortFrameworkVersion)' != '' and $(_ShortFrameworkVersion.Contains('.'))">
-    <TargetFrameworkVersion>v$(_ShortFrameworkVersion)</TargetFrameworkVersion>
-  </PropertyGroup>
-
-  <!-- Versions with no dots and up to 3 characters get leading 'v' and implicit dots between characters. -->
-  <PropertyGroup Condition="'$(TargetFrameworkVersion)' == '' and '$(_ShortFrameworkVersion)' != ''">
-    <TargetFrameworkVersion Condition="$(_ShortFrameworkVersion.Length) == 1">v$(_ShortFrameworkVersion[0]).0</TargetFrameworkVersion>
-    <TargetFrameworkVersion Condition="$(_ShortFrameworkVersion.Length) == 2">v$(_ShortFrameworkVersion[0]).$(_ShortFrameworkVersion[1])</TargetFrameworkVersion>
-    <TargetFrameworkVersion Condition="$(_ShortFrameworkVersion.Length) == 3">v$(_ShortFrameworkVersion[0]).$(_ShortFrameworkVersion[1]).$(_ShortFrameworkVersion[2])</TargetFrameworkVersion>
-  </PropertyGroup>
-
-  <!-- Map short name to long name. See earlier comment for example of how to work with identifiers that are not recognized here. -->
-  <PropertyGroup Condition="'$(TargetFrameworkIdentifier)' == ''">
-    <TargetFrameworkIdentifier Condition="'$(_ShortFrameworkIdentifier)' == 'netstandard'">.NETStandard</TargetFrameworkIdentifier>
-    <TargetFrameworkIdentifier Condition="'$(_ShortFrameworkIdentifier)' == 'netcoreapp'">.NETCoreApp</TargetFrameworkIdentifier>
-
-    <!-- The meaning of "net" as a short framework name depends on the version.  If it's 4.x or less, it means .NETFramework.
-         If the version is 5.0 or higher, then "net" means .NET 5.0 and on, which is the evolution of .NET Core, and uses
-         the .NETCoreApp TargetFrameworkIdentifier. -->
-    <TargetFrameworkIdentifier Condition="'$(_ShortFrameworkIdentifier)' == 'net' And
-                                          $([MSBuild]::VersionLessThan($(TargetFrameworkVersion), '5.0'))">.NETFramework</TargetFrameworkIdentifier>
-    <TargetFrameworkIdentifier Condition="'$(_ShortFrameworkIdentifier)' == 'net' And
-                                          $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '5.0'))">.NETCoreApp</TargetFrameworkIdentifier>
-  </PropertyGroup>
-
-  <PropertyGroup Condition="$(TargetFramework.StartsWith('net4'))">
-    <TargetingPackNugetPackageId>Microsoft.TargetingPack.NETFramework.$(TargetFrameworkVersion)</TargetingPackNugetPackageId>
-  </PropertyGroup>
-
-  <ItemGroup>
-    <!-- For things not .NETFramework binplace to the NETFX ref path -->
-    <BinPlaceTargetFrameworks Condition="!$(TargetFramework.StartsWith('net4'))" Include="$(TargetFramework)">
-      <RefPath>$(NetFxRefPath)</RefPath>
-    </BinPlaceTargetFrameworks>
-
-    <!-- For things .NETFramework binplace to refpath -->
-    <BinPlaceTargetFrameworks Condition="$(TargetFramework.StartsWith('net4'))" Include="$(TargetFramework)">
-      <RefPath>$(RefPath)</RefPath>
-    </BinPlaceTargetFrameworks>
-  </ItemGroup>
-
-  <PropertyGroup>
-    <_TargetingPackVersion>1.0.1</_TargetingPackVersion>
-    <_TargetingPackVersion Condition="'$(TargetingPackNugetPackageId)' == 'Microsoft.TargetingPack.NETFramework.v4.7.1' or '$(TargetingPackNugetPackageId)' == 'Microsoft.TargetingPack.NETFramework.v4.7.2'">1.0.0</_TargetingPackVersion>
-  </PropertyGroup>
-
-  <ItemGroup>
-    <PackageReference Include="$(TargetingPackNugetPackageId)" NoWarn="NU1701">
-      <Version >$(_TargetingPackVersion)</Version>
-    </PackageReference>
-    <PackageReference Include="System.Memory" Condition="'$(TargetFramework)' == 'net45' or '$(TargetFramework)' == 'net46'">
-      <Version>4.5.2</Version>
-    </PackageReference>
-    <PackageReference Include="System.Numerics.Vectors" Condition="'$(TargetFramework)' == 'net461' or '$(TargetFramework)' == '$(NetFrameworkCurrent)'">
-      <Version>4.5.0</Version>
-    </PackageReference>
-    <PackageReference Include="System.Buffers" Condition="'$(TargetFramework)' == 'net461' or '$(TargetFramework)' == '$(NetFrameworkCurrent)'">
-      <Version>4.5.0</Version>
-    </PackageReference>
-    <PackageReference Include="$(NETStandardSupportPackageId)" Condition="'$(AddNetStandardSupportPackage)' == 'true'">
-      <Version>$(NETStandardSupportPackageVersion)</Version>
-    </PackageReference>
-
-    <FileToExclude Include="System.EnterpriseServices" />
-    <FileToExclude Include="System.EnterpriseServices.Thunk" />
-    <FileToExclude Include="System.EnterpriseServices.Wrapper" />
-  </ItemGroup>
-
-  <Target Name="AddNETStandardShims" AfterTargets="FilterNugetPackages"
-          Condition="'$(AddNetStandardSupportPackage)' == 'true'">
-    <ItemGroup>
-      <_netStandardReference Condition="'$(TargetFramework)' != 'net461' and '$(TargetFramework)' != 'net462'"
-                             Include="$(NETStandardSupportRoot)\net47\lib\*.dll"
-                             Exclude="@(_netStandardReference->'$(NETStandardSupportRoot)\net47\lib\%(FileName).dll')" />
-      <_netStandardReference Condition="'$(TargetFramework)' != 'net461'"
-                             Include="$(NETStandardSupportRoot)\net462\lib\*.dll"
-                             Exclude="@(_netStandardReference->'$(NETStandardSupportRoot)\net462\lib\%(FileName).dll')" />
-      <_netStandardReference Include="$(NETStandardSupportRoot)\net461\lib\*.dll"
-                             Exclude="@(_netStandardReference->'$(NETStandardSupportRoot)\net461\lib\%(FileName).dll')" />
-
-      <_netStandardReference>
-        <Private>False</Private>
-        <NuGetPackageId>$(NETStandardSupportPackageId)</NuGetPackageId>
-        <NuGetPackageVersion>$(NETStandardSupportPackageVersion)</NuGetPackageVersion>
-      </_netStandardReference>
-
-      <_referenceByFileName Include="@(Reference->'%(FileName)%(Extension)')">
-        <OriginalIdentity>%(Identity)</OriginalIdentity>
-      </_referenceByFileName>
-      <_netStandardReferenceByFileName Include="@(_netStandardReference->'%(FileName)%(Extension)')" />
-
-      <_remainingReferenceByFileName Include="@(_referenceByFileName)" Exclude="@(_netStandardReferenceByFileName)" />
-      <_remainingReference Include="@(_remainingReferenceByFileName->'%(OriginalIdentity)')" />
-
-      <Reference Remove="@(Reference)" />
-      <Reference Include="@(_remainingReference);@(_netStandardReference)" />
-    </ItemGroup>
-  </Target>
-</Project>
diff --git a/src/libraries/restore/netstandard/external.netstandard.depproj b/src/libraries/restore/netstandard/external.netstandard.depproj
deleted file mode 100644
index 1d80925bf1734e..00000000000000
--- a/src/libraries/restore/netstandard/external.netstandard.depproj
+++ /dev/null
@@ -1,128 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <NETStandardVersion Condition="$(TargetFramework.StartsWith('netstandard'))">$(TargetFramework.SubString(11))</NETStandardVersion>
-    <IsNETStandard1x Condition="$(NETStandardVersion.StartsWith('1.'))">true</IsNETStandard1x>
-    <IsNETStandard2x Condition="$(NETStandardVersion.StartsWith('2.'))">true</IsNETStandard2x>
-    <BinPlaceRef>true</BinPlaceRef>
-    <NuGetDeploySourceItem>Reference</NuGetDeploySourceItem>
-    <_NETStandardTFMFolder Condition="'$(TargetFramework)' == 'netstandard2.0'">netstandard2.0</_NETStandardTFMFolder>
-    <TargetFrameworks>netstandard1.0;netstandard1.1;netstandard1.2;netstandard1.3;netstandard1.4;netstandard1.5;netstandard1.6;netstandard2.0</TargetFrameworks>
-  </PropertyGroup>
-
-  <ItemGroup>
-    <PackageReference Include="NETStandard.Library">
-      <Version>$(NETStandardLibraryVersion)</Version>
-    </PackageReference>
-  </ItemGroup>
-
-  <ItemGroup Condition="'$(IsNETStandard1x)' == 'true'">
-    <PackageReference Include="System.Diagnostics.Contracts">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Include="System.Diagnostics.Debug">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Include="System.Dynamic.Runtime">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Include="System.Runtime.Serialization.Primitives">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Condition="'$(NETStandardVersion)' &gt;= 1.3" Include="System.Reflection.TypeExtensions">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Condition="'$(NETStandardVersion)' &gt;= 1.2" Include="System.Data.SqlClient">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Condition="'$(NETStandardVersion)' &gt;= 1.3" Include="System.Security.Cryptography.Cng">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Condition="'$(NETStandardVersion)' &gt;= 1.1" Include="System.Reflection.Emit">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Include="System.Reflection.Emit.ILGeneration">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Include="System.Reflection.Emit.Lightweight">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Include="System.Runtime.WindowsRuntime">
-      <Version>4.3.0</Version>
-    </PackageReference>
-    <PackageReference Condition="'$(NETStandardVersion)' &gt;= 1.1" Include="System.Runtime.WindowsRuntime.UI.Xaml">
-      <Version>4.3.0</Version>
-    </PackageReference>
-  </ItemGroup>
-  <ItemGroup Condition="'$(IsNETStandard2x)' == 'true'">
-    <PackageReference Condition="'$(NETStandardVersion)' == 2.0" Include="System.Buffers">
-      <Version>4.5.0</Version>
-    </PackageReference>
-    <PackageReference Include="System.Security.Cryptography.Cng">
-      <Version>4.5.0</Version>
-    </PackageReference>
-    <PackageReference Include="System.Security.Cryptography.OpenSsl">
-      <Version>4.5.1</Version>
-    </PackageReference>
-    <PackageReference Include="System.Security.Cryptography.Pkcs">
-      <Version>4.5.2</Version>
-    </PackageReference>
-    <PackageReference Include="System.Data.SqlClient">
-      <Version>4.7.0</Version>
-    </PackageReference>
-  </ItemGroup>
-
-  <ItemGroup>
-    <!-- for all configurations this project provides refs for that configuration -->
-    <BinPlaceTargetFrameworks Include="$(TargetFramework)">
-      <RefPath>$(RefPath)</RefPath>
-    </BinPlaceTargetFrameworks>
-    <BinPlaceTargetFrameworks Include="$(TargetFramework)">
-      <!-- copy shims to the testhost as well in order to be able to run the netfx tests -->
-      <RuntimePath>$(TestHostRootPath)</RuntimePath>
-    </BinPlaceTargetFrameworks>
-  </ItemGroup>
-
-  <Target Name="AddNETStandard21Refs" AfterTargets="ResolveReferences">
-    <PropertyGroup>
-      <_NETStandard21RefFolder>$(NuGetPackageRoot)$(NETStandardLibraryPackage)\$(NETStandardLibraryVersion)\build\netstandard2.1\ref</_NETStandard21RefFolder>
-    </PropertyGroup>
-
-    <ItemGroup>
-      <ExcludeNetStandard21Refs Include="System.ComponentModel.Composition" />
-      <ExcludeNetStandard21Refs Include="System.Reflection.DispatchProxy" />
-      <_NetStandard21Files 
-        Include="$(_NETStandard21RefFolder)\*.dll"
-        Exclude="@(ExcludeNetStandard21Refs -> '$(_NETStandard21RefFolder)\%(Identity).dll')"  />
-    </ItemGroup>
-
-    <Error Condition="'@(_NetStandard21Files)' == ''" Text="Could not find package assets for netstandard2.1" />
-
-    <Copy SourceFiles="@(_NetStandard21Files)"
-          DestinationFolder="$(NetStandard21RefPath)"
-          SkipUnchangedFiles="true" />
-  </Target>
-
-  <Target Name="AddNETStandard20Refs" AfterTargets="ResolveReferences"
-          Condition="'$(_NETStandardTFMFolder)' != ''">
-    <PropertyGroup>
-      <_NETStandardRefFolder>$(NuGetPackageRoot)$(NETStandardLibraryPackage)\$(NETStandardLibraryVersion)\build\$(_NETStandardTFMFolder)\ref</_NETStandardRefFolder>
-    </PropertyGroup>
-
-    <ItemGroup>
-      <ExcludeNetStandardRefs Include="System.ComponentModel.Composition" />
-      <NetStandardRefs
-        Include="$(_NETStandardRefFolder)\*.dll"
-        Exclude="@(ExcludeNetStandardRefs -> '$(_NETStandardRefFolder)\%(Identity).dll')" />
-    </ItemGroup>
-
-    <Error Condition="'@(NetStandardRefs)' == ''" Text="Could not find package assets for netstandard2.0" />
-
-    <ItemGroup>
-      <Reference Include="@(NetStandardRefs)">
-        <Private>False</Private>
-        <NuGetPackageId>$(NETStandardLibraryPackage)</NuGetPackageId>
-        <NuGetPackageVersion>$(NETStandardLibraryVersion)</NuGetPackageVersion>
-      </Reference>
-    </ItemGroup>
-  </Target>
-</Project>
diff --git a/src/libraries/restore/runtime/referenceFromRuntime.targets b/src/libraries/restore/runtime/referenceFromRuntime.targets
deleted file mode 100644
index 2a013d8d05d032..00000000000000
--- a/src/libraries/restore/runtime/referenceFromRuntime.targets
+++ /dev/null
@@ -1,13 +0,0 @@
-<Project>
-  <!-- This is present in order to make ProjectReferences return the same set of content that would be BinPlaced. -->
-  <!-- Override build and GetTargetPath to return all items deployed -->
-  <Target Name="Build"
-          Condition=" '$(_InvalidConfigurationWarning)' != 'true' "
-          DependsOnTargets="$(BuildDependsOn)"
-          Returns="@(BinPlaceItem)" />
-
-    <!-- Depprojs need to run Compile in order to populate items that will be copied to output -->
-  <Target Name="GetTargetPath"
-          DependsOnTargets="Compile;GetBinPlaceItems"
-          Returns="@(BinPlaceItem)" />
-</Project>
\ No newline at end of file
diff --git a/src/libraries/restore/runtime/runtime.depproj b/src/libraries/restore/runtime/runtime.depproj
index b8cd8ce65baae5..792cb8f840a23b 100644
--- a/src/libraries/restore/runtime/runtime.depproj
+++ b/src/libraries/restore/runtime/runtime.depproj
@@ -6,7 +6,7 @@
     <BinPlaceForTargetVertical>false</BinPlaceForTargetVertical>
     <BinPlaceNative>true</BinPlaceNative>
     <BinPlaceRuntime>false</BinPlaceRuntime>
-    <TargetFrameworks>netcoreapp3.0-Windows_NT;netcoreapp3.0-Unix;$(netcoreappCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(DotNetBuildFromSource)' != 'true'">
@@ -22,10 +22,6 @@
     <FileToExclude Include="apphost" />
   </ItemGroup>
 
-  <ItemGroup>
-    <PackageReference Condition="'$(TargetFramework)' == 'netcoreapp3.0'" Include="Microsoft.Private.Corefx.NETCoreApp" Version="4.6.0-rc2.19462.14" />
-  </ItemGroup>
-
   <!-- Setup the testing shared framework host -->
   <Target Name="SetupTestingHost"
           Condition="'$(BinPlaceTestSharedFramework)' == 'true'"
@@ -59,19 +55,6 @@
     <Exec Command="chmod +x $(TestHostRootPath)%(DotnetExe.Filename)%(DotnetExe.Extension)" Condition="'$(TargetOS)' != 'Windows_NT' and '$(OS)' != 'Windows_NT'"/>
   </Target>
 
-  <Target Name="SetupRuntimePackNative"
-          AfterTargets="AfterResolveReferences">
-    <ItemGroup>
-      <BinPlaceItem Include="@(RuntimeFiles)" />
-      <BinPlaceItem Include="@(MonoCrossFiles)">
-        <DestinationSubDirectory>cross/</DestinationSubDirectory>
-      </BinPlaceItem>
-      <BinPlaceItem Include="@(MonoIncludeFiles)">
-        <DestinationSubDirectory>include/%(RecursiveDir)</DestinationSubDirectory>
-      </BinPlaceItem>
-    </ItemGroup>
-  </Target>
-
   <Target Name="OverrideRuntimeCoreCLR"
           DependsOnTargets="ResolveRuntimeFilesFromLocalBuild"
           AfterTargets="AfterResolveReferences;FilterNugetPackages"
@@ -87,7 +70,16 @@
   <Target Name="OverrideRuntimeMono"
           DependsOnTargets="ResolveRuntimeFilesFromLocalBuild"
           AfterTargets="AfterResolveReferences;FilterNugetPackages"
-          Condition="'$(RuntimeFlavor)' == 'Mono'" />
+          Condition="'$(RuntimeFlavor)' == 'Mono'">
+    <ItemGroup>
+      <ReferenceCopyLocalPaths Include="@(RuntimeFiles)" />
+      <!-- Setup runtime pack native. -->
+      <ReferenceCopyLocalPaths Include="@(MonoCrossFiles)"
+                               DestinationSubDirectory="cross/" />
+      <ReferenceCopyLocalPaths Include="@(MonoIncludeFiles)"
+                               DestinationSubDirectory="include/%(RecursiveDir)" />
+    </ItemGroup>
+  </Target>
 
   <Target Name="GetCoreCLRILFiles" DependsOnTargets="ResolveRuntimeFilesFromLocalBuild">
     <ItemGroup>
@@ -109,10 +101,8 @@
 
   <!-- Strip away placeholder tfms and TargetFrameworkSuffix. -->
   <Target Name="StripTargetFrameworkSuffixFromTargetFrameworks"
-          Condition="'$(TargetFrameworks)' != ''"
           BeforeTargets="_GetRestoreTargetFrameworksOutput;_GetRestoreTargetFrameworksAsItems">
     <PropertyGroup>
-      <TargetFrameworks Condition="'$(TargetFrameworks)' != ''">$([System.Text.RegularExpressions.Regex]::Replace('$(TargetFrameworks)', '_[^;]+;?', ''))</TargetFrameworks>
       <TargetFrameworks Condition="'$(TargetFrameworks)' != ''">$([System.Text.RegularExpressions.Regex]::Replace('$(TargetFrameworks)', '-[^;]+', ''))</TargetFrameworks>
     </PropertyGroup>
   </Target>
diff --git a/src/libraries/sendtohelix.proj b/src/libraries/sendtohelix.proj
index d5729d8e5d7c88..92b7b688e77b14 100644
--- a/src/libraries/sendtohelix.proj
+++ b/src/libraries/sendtohelix.proj
@@ -18,7 +18,7 @@
   <!-- Helix auto-magically imports local *.props files. We're not going to import the Helix Sdk,
        so we need to import those files manually so we can reference the properties defined there.
   -->
-  <Import Project="$(MSBuildThisFileDirectory)/*.props" />
+  <Import Project="Directory.Build.props" />
 
   <Target Name="RunInParallelForEachScenario">
 
@@ -47,7 +47,7 @@
     <Message Importance="High" Text="TestHostRootPath: $(TestHostRootPath)" />
     <Message Importance="High" Text="TestArchiveRoot: $(TestArchiveRoot)" />
     <Message Importance="High" Text="TestArchiveRuntimeRoot: $(TestArchiveRuntimeRoot)" />
-    <Message Importance="High" Text="TestArchiveRuntimeFile: $(TestArchiveRuntimeFile)" />
+    <Message Condition="'$(TestArchiveRuntimeFile)' != ''" Importance="High" Text="TestArchiveRuntimeFile: $(TestArchiveRuntimeFile)" />
 
     <!-- Re-invoke MSBuild on this project to create the correlation payload -->
     <MSBuild Projects="$(MSBuildProjectFile)" Targets="PrepareCorrelationPayloadDirectory" Properties="Scenarios=$(_Scenarios)" />
@@ -80,7 +80,8 @@
     <TargetsWindows Condition="'$(TargetOS)' == 'Windows_NT'">true</TargetsWindows>
 
     <!-- The Helix correlation payload file -->
-    <TestArchiveRuntimeFile Condition="'$(TestPackages)' != 'true'">$(TestArchiveRuntimeRoot)test-runtime-$(BuildSettings).zip</TestArchiveRuntimeFile>
+    <TestArchiveRuntimeFile Condition="'$(TestPackages)' != 'true' and
+                                       '$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'">$(TestArchiveRuntimeRoot)test-runtime-$(BuildSettings).zip</TestArchiveRuntimeFile>
     <TestArchiveRuntimeFile Condition="'$(TestPackages)' == 'true'">$(TestArchiveRuntimeRoot)packages-testPayload-$(Configuration).zip</TestArchiveRuntimeFile>
   </PropertyGroup>
 
@@ -144,7 +145,9 @@
   <Target Name="CompressRuntimeDirectory"
           Inputs="@(_RuntimeInputs);@(TestArchiveRuntimeDependency)"
           Outputs="$(TestArchiveRuntimeFile)"
-          Condition="'$(TestPackages)' != 'true' and '$(TargetsMobile)' != 'true'">
+          Condition="'$(TestPackages)' != 'true' and
+                     '$(TargetsMobile)' != 'true' and
+                     '$(TestArchiveRuntimeFile)' != ''">
 
     <!-- Compress the test files, testhost, and per-scenario scripts into a single ZIP file for sending to the Helix machines. -->
 
diff --git a/src/libraries/sendtohelixhelp.proj b/src/libraries/sendtohelixhelp.proj
index f5b2ab2489aaaa..fecc281788d990 100644
--- a/src/libraries/sendtohelixhelp.proj
+++ b/src/libraries/sendtohelixhelp.proj
@@ -136,7 +136,9 @@
       so if we don't use "call", then we cause the parent script to exit, and anything after will not be executed.
     -->
     <HelixCommand Condition="'$(TargetsWindows)' == 'true'">call RunTests.cmd --runtime-path %HELIX_CORRELATION_PAYLOAD%</HelixCommand>
+    <HelixCommand Condition="'$(TargetsWindows)' == 'true' and '$(HelixCorrelationPayload)' != ''">$(HelixCommand) --runtime-path %HELIX_CORRELATION_PAYLOAD%</HelixCommand>
     <HelixCommand Condition="'$(TargetsWindows)' != 'true'">./RunTests.sh --runtime-path "$HELIX_CORRELATION_PAYLOAD"</HelixCommand>
+    <HelixCommand Condition="'$(TargetsWindows)' != 'true' and '$(HelixCorrelationPayload)' != ''">$(HelixCommand) --runtime-path "$HELIX_CORRELATION_PAYLOAD"</HelixCommand>
   </PropertyGroup>
 
   <ItemGroup>
@@ -155,14 +157,15 @@
     <Message Condition="'$(Scenario)' == ''" Importance="High" Text="Building Helix work items" />
     <Message Condition="'$(Scenario)' != ''" Importance="High" Text="Building Helix work items for scenario $(Scenario)" />
     <Message Importance="High" Text="Using TestRunNamePrefix: $(TestRunNamePrefix)" />
-    <Message Importance="High" Text="Using HelixCorrelationPayload: $(HelixCorrelationPayload)" />
+    <Message Condition="'$(HelixCorrelationPayload)' != ''" Importance="High" Text="Using HelixCorrelationPayload: $(HelixCorrelationPayload)" />
     <Message Importance="High" Text="Using HelixCommand: $(HelixCommand)" />
     <Message Importance="High" Text="Using HelixType: $(HelixType)" />
     <Message Importance="High" Text="Using WorkItemArchiveWildCard: $(WorkItemArchiveWildCard)" />
     <Message Importance="High" Text="Using Timeout: $(_timeoutSpan)" />
 
     <ItemGroup>
-      <HelixCorrelationPayload Condition="'$(TargetOS)' != 'Browser'" Include="$(HelixCorrelationPayload)" />
+      <HelixCorrelationPayload Include="$(HelixCorrelationPayload)"
+                               Condition="'$(TargetOS)' != 'Browser' or '$(HelixCorrelationPayload)' != ''" />
 
       <_WorkItem Include="$(WorkItemArchiveWildCard)" Exclude="$(HelixCorrelationPayload)" />
 
diff --git a/src/libraries/shims/ApiCompat.proj b/src/libraries/shims/ApiCompat.proj
index d275e0efeacd82..bfb6304de49b96 100644
--- a/src/libraries/shims/ApiCompat.proj
+++ b/src/libraries/shims/ApiCompat.proj
@@ -2,9 +2,12 @@
 
   <PropertyGroup>
     <TargetFramework>$(BuildTargetFramework)</TargetFramework>
+    <TargetFramework Condition="'$(TargetFramework)' == ''">$(NetCoreAppCurrent)</TargetFramework>
     <!-- Set to true to build this project -->
     <BaselineApiCompat Condition="'$(BaselineApiCompat)' == ''">false</BaselineApiCompat>
-    <_RunApiCompat>true</_RunApiCompat>
+    <PreviousNetCoreApp>netcoreapp3.1</PreviousNetCoreApp>
+    <PreviousNetCoreAppPackageId>microsoft.netcore.app.ref</PreviousNetCoreAppPackageId>
+    <PreviousNetCoreAppPackageVersion>3.1.0</PreviousNetCoreAppPackageVersion>
   </PropertyGroup>
 
   <ItemGroup>
@@ -14,6 +17,11 @@
     <NetFxReference Include="System.DirectoryServices.Protocols" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageDownload Include="$(PreviousNetCoreAppPackageId)" Version="[$(PreviousNetCoreAppPackageVersion)]" />
+    <PackageDownload Include="NETStandard.Library" Version="[$(NETStandardLibraryVersion)];[$(NetStandardLibrary20Version)]" />
+  </ItemGroup>
+
   <!-- Evaluate these properties inside a Target to gain access to TargetFrameworkIdentifier. -->
   <Target Name="SetApiCompatFiles">
     <PropertyGroup>
@@ -28,14 +36,13 @@
 
   <!-- Run ApiCompat -->
   <Target Name="RunApiCompat"
-          Condition="'$(_RunApiCompat)' == 'true'"
           DependsOnTargets="SetApiCompatFiles"
           AfterTargets="Build"
           Inputs="$(ApiCompatResponseFile)"
           Outputs="$(ApiCompatBaselineFile);$(ApiCompatNSBaselineFile)">
 
     <PropertyGroup>
-      <ApiCompatImplementationDirs>$(BuildTargetFrameworkRefPath.TrimEnd('\/'))</ApiCompatImplementationDirs>
+      <ApiCompatImplementationDirs>$(NetCoreAppCurrentRefPath.TrimEnd('\/'))</ApiCompatImplementationDirs>
       <ApiCompatArgs Condition="'$(ApiCompatExcludeAttributeList)' != ''">$(ApiCompatArgs) --exclude-attributes "$(ApiCompatExcludeAttributeList)"</ApiCompatArgs>
       <ApiCompatArgs>$(ApiCompatArgs) --impl-dirs "$(ApiCompatImplementationDirs)"</ApiCompatArgs>
       <BaselineApiCompatArgs Condition="Exists($(ApiCompatBaselineIgnoreFile))">--baseline "$(ApiCompatBaselineIgnoreFile)"</BaselineApiCompatArgs>
@@ -53,7 +60,7 @@
       <Output TaskParameter="ExitCode" PropertyName="ApiCompatExitCode" />
     </Exec>
 
-    <Error Condition="'$(ApiCompatExitCode)' != '0'" Text="ApiCompat failed comparing $(NetFrameworkCurrent) to $(TargetFramework)" />
+    <Error Condition="'$(ApiCompatExitCode)' != '0'" Text="ApiCompat failed comparing $(NETFrameworkReferenceAssemblyTFM) to $(TargetFramework)" />
 
 
     <!--
@@ -71,15 +78,14 @@
     <PropertyGroup>
       <UpdateNETStandardBaseline Condition="'$(UpdateNETStandardBaseline)' == ''">False</UpdateNETStandardBaseline>
       <UpdateNETStandardBaselineLocally Condition="'$(UpdateNETStandardBaselineLocally)' == ''">False</UpdateNETStandardBaselineLocally>
-      <_netStandard21OnlyRef>$(NetStandard21RefPath)netstandard.dll</_netStandard21OnlyRef>
+      <_netStandardLibraryRefPath>$([MSBuild]::NormalizeDirectory('$(NuGetPackageRoot)', 'netstandard.library', '$(NETStandardLibraryVersion)', 'build', 'netstandard2.1', 'ref'))</_netStandardLibraryRefPath>
+      <_netStandardLibrary20RefPath>$([MSBuild]::NormalizeDirectory('$(NuGetPackageRoot)', 'netstandard.library', '$(NetStandardLibrary20Version)', 'build', 'netstandard2.0', 'ref'))</_netStandardLibrary20RefPath>
+      <_netStandard21OnlyRef>$(_netStandardLibraryRefPath)netstandard.dll</_netStandard21OnlyRef>
       <_netStandard21OnlyRef Condition="$(UpdateNETStandardBaselineLocally)">$(MSBuildThisFileDirectory)..\..\..\standard\artifacts\bin\ref\netstandard\Debug\netstandard.dll</_netStandard21OnlyRef>
       <_netStandard21BaselineModifer>--baseline</_netStandard21BaselineModifer>
       <_netStandard21BaselineModifer Condition="$(UpdateNETStandardBaseline) or $(UpdateNETStandardBaselineLocally)">&gt;</_netStandard21BaselineModifer>
     </PropertyGroup>
 
-    <PropertyGroup Condition="$(UpdateNETStandardBaseline)">
-    </PropertyGroup>
-
     <Exec Command="$(_ApiCompatCommand) &quot;$(_netStandard21OnlyRef)&quot; @&quot;$(ApiCompatResponseFile)&quot; $(_netStandard21BaselineModifer) &quot;$(ApiCompatNSOnlyBaselineFile)&quot;"
           CustomErrorRegularExpression="^[a-zA-Z]+ :"
           StandardOutputImportance="Low"
@@ -89,8 +95,7 @@
 
     <Error Condition="'$(ApiCompatExitCode)' != '0'" Text="ApiCompat failed comparing netstandard.dll to $(ApiCompatTarget)" />
 
-    <!-- TODO: Once the repo targets netstandard2.1, have this instance of APICompat run against NetStandard21RefPath -->
-    <Exec Command="$(_ApiCompatCommand) &quot;$(NetStandard20RefPath.TrimEnd('\/'))&quot; --baseline &quot;$(ApiCompatNSBaselineFile)&quot; @&quot;$(ApiCompatResponseFile)&quot;"
+    <Exec Command="$(_ApiCompatCommand) &quot;$(_netStandardLibrary20RefPath.TrimEnd('\/'))&quot; --baseline &quot;$(ApiCompatNSBaselineFile)&quot; @&quot;$(ApiCompatResponseFile)&quot;"
           CustomErrorRegularExpression="^[a-zA-Z]+ :"
           StandardOutputImportance="Low"
           IgnoreExitCode="true">
@@ -100,8 +105,7 @@
     <Error Condition="'$(ApiCompatExitCode)' != '0'" Text="ApiCompat failed comparing netstandard to $(ApiCompatTarget)" />
  
     <PropertyGroup>
-      <PreviousNetCoreApp>netcoreapp3.1</PreviousNetCoreApp>
-      <PreviousNetCoreAppRefPath>$([MSBuild]::NormalizeDirectory('$(RefRootPath)', '$(PreviousNetCoreApp)'))</PreviousNetCoreAppRefPath>
+      <PreviousNetCoreAppRefPath>$([MSBuild]::NormalizeDirectory('$(NuGetPackageRoot)', '$(PreviousNetCoreAppPackageId)', '$(PreviousNetCoreAppPackageVersion)', 'ref', '$(PreviousNetCoreApp)'))</PreviousNetCoreAppRefPath>
       <_previousNetCoreAppBaselineFile>$(MSBuildThisFileDirectory)ApiCompatBaseline.PreviousNetCoreApp.txt</_previousNetCoreAppBaselineFile>
       <_previousNetCoreAppBaselineParam>--baseline &quot;$(_previousNetCoreAppBaselineFile)&quot;</_previousNetCoreAppBaselineParam>
       <_previousNetCoreAppBaselineParam Condition="'$(UpdatePreviousNetCoreAppBaseline)' == 'true'">&gt; &quot;$(_previousNetCoreAppBaselineFile)&quot;</_previousNetCoreAppBaselineParam>
diff --git a/src/libraries/shims/ApiCompatBaseline.PreviousNetCoreApp.txt b/src/libraries/shims/ApiCompatBaseline.PreviousNetCoreApp.txt
index 99ad677cb9b76c..078e32277bdf82 100644
--- a/src/libraries/shims/ApiCompatBaseline.PreviousNetCoreApp.txt
+++ b/src/libraries/shims/ApiCompatBaseline.PreviousNetCoreApp.txt
@@ -20,7 +20,7 @@ CannotRemoveAttribute : Attribute 'System.ComponentModel.DefaultValueAttribute'
 CannotRemoveAttribute : Attribute 'System.ComponentModel.DefaultValueAttribute' exists on 'System.Diagnostics.ProcessStartInfo.Environment' in the contract but not the implementation.
 CannotChangeAttribute : Attribute 'System.ComponentModel.DefaultValueAttribute' on 'System.Diagnostics.ProcessStartInfo.Verb' changed from '[DefaultValueAttribute(null)]' in the contract to '[DefaultValueAttribute("")]' in the implementation.
 CannotRemoveAttribute : Attribute 'System.ComponentModel.DefaultValueAttribute' exists on 'System.Diagnostics.ProcessStartInfo.WindowStyle' in the contract but not the implementation.
-Compat issues due to removal of System.Runtime.InteropServices.WindowsRuntime
+Compat issues due to removal of System.Runtime.InteropServices.WindowsRuntime:
 TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.DefaultInterfaceAttribute' does not exist in the implementation but it does exist in the contract.
 TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.EventRegistrationToken' does not exist in the implementation but it does exist in the contract.
 TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.EventRegistrationTokenTable<T>' does not exist in the implementation but it does exist in the contract.
@@ -30,13 +30,9 @@ TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.ReadOnlyArr
 TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.ReturnValueNameAttribute' does not exist in the implementation but it does exist in the contract.
 TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.WindowsRuntimeMarshal' does not exist in the implementation but it does exist in the contract.
 TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.WriteOnlyArrayAttribute' does not exist in the implementation but it does exist in the contract.
-TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.DefaultInterfaceAttribute' does not exist in the implementation but it does exist in the contract.
-TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.EventRegistrationToken' does not exist in the implementation but it does exist in the contract.
-TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.EventRegistrationTokenTable<T>' does not exist in the implementation but it does exist in the contract.
-TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.IActivationFactory' does not exist in the implementation but it does exist in the contract.
-TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.InterfaceImplementedInVersionAttribute' does not exist in the implementation but it does exist in the contract.
-TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.ReadOnlyArrayAttribute' does not exist in the implementation but it does exist in the contract.
-TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.ReturnValueNameAttribute' does not exist in the implementation but it does exist in the contract.
-TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.WindowsRuntimeMarshal' does not exist in the implementation but it does exist in the contract.
-TypesMustExist : Type 'System.Runtime.InteropServices.WindowsRuntime.WriteOnlyArrayAttribute' does not exist in the implementation but it does exist in the contract.
-Total Issues: 36
+Compat issues with assembly System.Text.Json:
+CannotChangeAttribute : Attribute 'System.AttributeUsageAttribute' on 'System.Text.Json.Serialization.JsonConverterAttribute' changed from '[AttributeUsageAttribute(AttributeTargets.Class | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Struct, AllowMultiple=false)]' in the contract to '[AttributeUsageAttribute(AttributeTargets.Class | AttributeTargets.Enum | AttributeTargets.Field | AttributeTargets.Property | AttributeTargets.Struct, AllowMultiple=false)]' in the implementation.
+CannotChangeAttribute : Attribute 'System.AttributeUsageAttribute' on 'System.Text.Json.Serialization.JsonExtensionDataAttribute' changed from '[AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple=false)]' in the contract to '[AttributeUsageAttribute(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple=false)]' in the implementation.
+CannotChangeAttribute : Attribute 'System.AttributeUsageAttribute' on 'System.Text.Json.Serialization.JsonIgnoreAttribute' changed from '[AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple=false)]' in the contract to '[AttributeUsageAttribute(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple=false)]' in the implementation.
+CannotChangeAttribute : Attribute 'System.AttributeUsageAttribute' on 'System.Text.Json.Serialization.JsonPropertyNameAttribute' changed from '[AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple=false)]' in the contract to '[AttributeUsageAttribute(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple=false)]' in the implementation.
+Total Issues: 40
diff --git a/src/libraries/shims/Directory.Build.props b/src/libraries/shims/Directory.Build.props
index d0835fdd9bb98f..55920bf3ba2f07 100644
--- a/src/libraries/shims/Directory.Build.props
+++ b/src/libraries/shims/Directory.Build.props
@@ -4,7 +4,8 @@
   <Import Project="netfxreference.props" />
 
   <PropertyGroup>
-    <IsNETCoreApp>true</IsNETCoreApp>
+    <IsNETCoreAppSrc>true</IsNETCoreAppSrc>
+    <IsNETCoreAppRef>true</IsNETCoreAppRef>
     <NuGetTargetMoniker Condition="'$(NuGetTargetMoniker)' == ''">$(TargetFramework)</NuGetTargetMoniker>
   </PropertyGroup>
 
@@ -16,8 +17,10 @@
          to reference the latest packages.
          netstandard.dll doesn't need to do this since it has no dangling dependencies -->
     <GenFacadesForceZeroVersionSeeds Condition="'$(MSBuildProjectName)' != 'netstandard'">true</GenFacadesForceZeroVersionSeeds>
-    <IncludeDefaultReferences>false</IncludeDefaultReferences>
     <HasMatchingContract>true</HasMatchingContract>
+    <NETFrameworkReferenceAssemblyTFM>net48</NETFrameworkReferenceAssemblyTFM>
+    <NetFxRefPath>$(NuGetPackageRoot)microsoft.netframework.referenceassemblies.$(NETFrameworkReferenceAssemblyTFM)\$(MicrosoftNetFrameworkReferenceAssembliesVersion)\build\.NETFramework\v4.8\</NetFxRefPath>
+    <NETStandard21RefPath>$(NuGetPackageRoot)netstandard.library\$(NETStandardLibraryVersion)\build\netstandard2.1\ref\</NETStandard21RefPath>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(MSBuildProjectName)' == 'System.Runtime' or '$(MSBuildProjectName)' == 'mscorlib' or '$(MSBuildProjectName)' == 'netstandard'">
diff --git a/src/libraries/shims/generated/Directory.Build.props b/src/libraries/shims/generated/Directory.Build.props
index 2768718a10e522..096ac6881640a4 100644
--- a/src/libraries/shims/generated/Directory.Build.props
+++ b/src/libraries/shims/generated/Directory.Build.props
@@ -7,22 +7,37 @@
   </PropertyGroup>
 
   <Import Condition="Exists('$(MSBuildProjectName).props')" Project="$(MSBuildProjectName).props" />
-
   <Import Project="..\Directory.Build.props" />
 
+  <PropertyGroup>
+    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+  </PropertyGroup>
+
+  <!-- Download the .NET Framework RefPack to build against the contract. -->
+  <ItemGroup>
+    <PackageDownload Include="NETStandard.Library"
+                     Condition="'$(MSBuildProjectName)' == 'netstandard'"
+                     Version="[$(NETStandardLibraryVersion)]" />
+    <PackageDownload Include="Microsoft.NETFramework.ReferenceAssemblies.$(NETFrameworkReferenceAssemblyTFM)"
+                     Condition="'$(MSBuildProjectName)' != 'netstandard'"
+                     Version="[$(MicrosoftNetFrameworkReferenceAssembliesVersion)]" />
+    <!-- System.Data.SqlClient is not live built anymore, reference it manually. -->
+    <PackageReference Include="System.Data.SqlClient"
+                      Version="$(SystemDataSqlClientVersion)" />
+  </ItemGroup>
+
   <ItemGroup>
     <!-- reference everything but self -->
     <!-- Type duplicated in Microsoft.Extensions.DependencyModel. Exclude it for now: https://github.com/dotnet/runtime/issues/34420 -->
     <ReferencePath
-      Include="$(RefPath)*.dll"
-      Exclude="$(RefPath)$(MSBuildProjectName).dll;$(RefPath)netstandard.dll;$(RefPath)Microsoft.Extensions.DependencyModel.dll" />
+      Include="$(NetCoreAppCurrentRefPath)*.dll"
+      Exclude="$(NetCoreAppCurrentRefPath)$(MSBuildProjectName).dll;
+               $(NetCoreAppCurrentRefPath)netstandard.dll;
+               $(NetCoreAppCurrentRefPath)Microsoft.Extensions.DependencyModel.dll" />
 
     <!-- required by compiler to resolve core types -->
-    <ProjectReference Condition="'$(MSBuildProjectName)' != 'netstandard'"
-                      Include="netstandard.csproj" />
+    <ProjectReference Include="netstandard.csproj"
+                      Condition="'$(MSBuildProjectName)' != 'netstandard'"
+                      SkipUseReferenceAssembly="true" />
   </ItemGroup>
-
-  <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
-  </PropertyGroup>
 </Project>
diff --git a/src/libraries/shims/manual/Directory.Build.props b/src/libraries/shims/manual/Directory.Build.props
index ee66f309890f8e..4070e431ee5759 100644
--- a/src/libraries/shims/manual/Directory.Build.props
+++ b/src/libraries/shims/manual/Directory.Build.props
@@ -17,8 +17,10 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <ReferencePath Include="$(RuntimePath)System.*.dll;$(RuntimePath)Microsoft.Win32.*.dll;$(RuntimePath)netstandard.dll"
-                   Exclude="$(RuntimePath)$(MSBuildProjectName).dll" />
+    <ReferencePath Include="$(NetCoreAppCurrentRuntimePath)System.*.dll;
+                            $(NetCoreAppCurrentRuntimePath)Microsoft.Win32.*.dll;
+                            $(NetCoreAppCurrentRuntimePath)netstandard.dll"
+                   Exclude="$(NetCoreAppCurrentRuntimePath)$(MSBuildProjectName).dll" />
     <ProjectReference Include="$(CoreLibProject)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/shims/manual/System.Data.csproj b/src/libraries/shims/manual/System.Data.csproj
index 417d9bf1d034ec..2f89b12251ad26 100644
--- a/src/libraries/shims/manual/System.Data.csproj
+++ b/src/libraries/shims/manual/System.Data.csproj
@@ -3,8 +3,7 @@
     <Compile Include="System.Data.forwards.cs" />
   </ItemGroup>
   <ItemGroup>
-    <!-- System.Data.SqlClient is not live built anymore, make sure to use reference assembly for it -->
-    <ReferencePath Remove="$(RuntimePath)\System.Data.SqlClient.dll" />
-    <ReferencePath Include="$(ArtifactsBinDir)ref\$(NetCoreAppCurrent)\System.Data.SqlClient.dll" />
+    <!-- System.Data.SqlClient is not live built anymore, reference it manually. -->
+    <PackageReference Include="System.Data.SqlClient" Version="$(SystemDataSqlClientVersion)" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/src.proj b/src/libraries/src.proj
index 91225466df0112..ce82c68ea701a6 100644
--- a/src/libraries/src.proj
+++ b/src/libraries/src.proj
@@ -2,46 +2,56 @@
 
   <PropertyGroup>
     <TraversalGlobalProperties>BuildAllProjects=true</TraversalGlobalProperties>
-    <NativeBinPlaceDependsOnTargets Condition="'$(TargetOS)' == 'Browser'">BuildWasmRuntimes</NativeBinPlaceDependsOnTargets>
   </PropertyGroup>
 
   <ItemGroup>
-    <NativeBinPlaceProject Include="Native\native-binplace.proj" />
+    <_allSrc Include="$(MSBuildThisFileDirectory)*\src\*.csproj"
+             Exclude="@(ProjectExclusions)" />
+    <NonNetCoreAppProject Include="@(_allSrc)"
+                          Exclude="@(NetCoreAppLibrary->'%(Identity)\src\%(Identity).csproj')" />
+    <NetCoreAppProject Include="$(CoreLibProject);
+                                @(_allSrc);
+                                $(MSBuildThisFileDirectory)Microsoft.VisualBasic.Core\src\Microsoft.VisualBasic.Core.vbproj;
+                                $(MSBuildThisFileDirectory)System.Runtime.CompilerServices.Unsafe\src\System.Runtime.CompilerServices.Unsafe.ilproj"
+                       Exclude="@(NonNetCoreAppProject)" />
     <ManualShimProject Include="shims\manual\*.csproj" />
     <ApiCompatProject Include="shims\ApiCompat.proj"
-                      Condition="'$(DotNetBuildFromSource)' != 'true' and '$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'" />
-  </ItemGroup>
-
-  <!-- Restore only and build before/after. -->
-  <ItemGroup Condition="'$(MSBuildRestoreSessionId)' != ''">
-    <ProjectReference Include="@(NativeBinPlaceProject)" />
-    <ProjectReference Include="@(ManualShimProject)" />
-    <ProjectReference Include="@(ApiCompatProject)" />
+                      Condition="'$(DotNetBuildFromSource)' != 'true' and
+                                 '$(BuildingNETCoreAppVertical)' == 'true' and
+                                 '$(RunApiCompat)' != 'false'" />
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="$(MSBuildThisFileDirectory)*\src\*.csproj" Exclude="@(ProjectExclusions)" />
-    <ProjectReference Include="$(MSBuildThisFileDirectory)*\src\*.ilproj" Exclude="@(ProjectExclusions)" />
-    <ProjectReference Include="$(MSBuildThisFileDirectory)*\src\*.vbproj" Exclude="@(ProjectExclusions)" />
-  </ItemGroup>
+    <ProjectReference Include="@(NetCoreAppProject)" />
 
-  <Import Condition="'$(TargetOS)' == 'Browser'" Project="$(MonoProjectRoot)wasm\wasm.targets" />
+    <!-- Restore only and build before/after. -->
+    <ProjectReference Include="@(NonNetCoreAppProject);
+                               @(ManualShimProject);
+                               @(ApiCompatProject)"
+                      Condition="'$(MSBuildRestoreSessionId)' != ''" />
+  </ItemGroup>
 
-  <Target Name="NativeBinPlace"
-          AfterTargets="Build"
-          DependsOnTargets="$(NativeBinPlaceDependsOnTargets)">
+  <Target Name="BuildNonNetCoreAppProjects"
+          AfterTargets="Build">
     <MSBuild Targets="Build"
-             Projects="@(NativeBinPlaceProject)"
+             BuildInParallel="true"
+             Projects="@(NonNetCoreAppProject)"
              Properties="$(TraversalGlobalProperties)" />
   </Target>
 
+  <Import Condition="'$(TargetOS)' == 'Browser'" Project="$(MonoProjectRoot)wasm\wasm.targets" />
+
   <Target Name="BuildManualShims"
-          AfterTargets="Build">
+          AfterTargets="BuildNonNetCoreAppProjects"
+          Condition="'@(ManualShimProject)' != ''">
     <MSBuild Targets="Build"
              Projects="@(ManualShimProject)"
              Properties="$(TraversalGlobalProperties)" />
   </Target>
 
+  <Import Condition="'$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'"
+          Project="$(MSBuildThisFileDirectory)\illink-sharedframework.targets" />
+
   <Target Name="RunApiCompat"
           Condition="'@(ApiCompatProject)' != ''"
           AfterTargets="BuildManualShims">
diff --git a/src/libraries/tests.proj b/src/libraries/tests.proj
index b11eb01f25d850..9ba9856ed6562b 100644
--- a/src/libraries/tests.proj
+++ b/src/libraries/tests.proj
@@ -11,6 +11,7 @@
     <TestAssemblies Condition="'$(TestAssemblies)' == ''">true</TestAssemblies>
     <TestPackages Condition="'$(TestPackages)' == ''">false</TestPackages>
     <TestTrimming Condition="'$(TestTrimming)' == ''">false</TestTrimming>
+    <ContinueOnError Condition="'$(TestTrimming)' == 'true'">true</ContinueOnError>
   </PropertyGroup>
   
   <!-- Projects that don't support code coverage measurement. -->
@@ -21,35 +22,13 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetOS)' == 'Browser' and '$(RunDisabledWasmTests)' != 'true'">
-    <!-- Builds currently do not pass -->
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.CodeDom\tests\System.CodeDom.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.ComponentModel.TypeConverter\tests\System.ComponentModel.TypeConverter.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Data.Common\tests\System.Data.Common.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Diagnostics.DiagnosticSource\tests\TestWithConfigSwitches\System.Diagnostics.DiagnosticSource.Switches.Tests.csproj" />
-
-    <!-- Mono-Browser ignores runtimeconfig.template.json (e.g. for these two it has "System.Globalization.Invariant": true) -->
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Globalization\tests\Invariant\Invariant.Tests.csproj" />
+    <!-- Mono-Browser ignores runtimeconfig.template.json (e.g. for this it has "System.Globalization.EnforceJapaneseEraYearRanges": true) -->
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Globalization.Calendars\tests\CalendarTestWithConfigSwitch\System.Globalization.CalendarsWithConfigSwitch.Tests.csproj" />
 
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.IO.FileSystem\tests\System.IO.FileSystem.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Linq.Expressions\tests\System.Linq.Expressions.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Linq.Parallel\tests\System.Linq.Parallel.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Net.Http\tests\FunctionalTests\System.Net.Http.Functional.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Net.Primitives\tests\FunctionalTests\System.Net.Primitives.Functional.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Net.Primitives\tests\PalTests\System.Net.Primitives.Pal.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Net.WebSockets.Client\tests\System.Net.WebSockets.Client.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.ObjectModel\tests\System.ObjectModel.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Private.Uri\tests\FunctionalTests\System.Private.Uri.Functional.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Private.Xml\tests\XmlSerializer\ReflectionOnly\System.Xml.XmlSerializer.ReflectionOnly.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Private.Xml\tests\XmlSerializer\System.Xml.XmlSerializer.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Reflection.Metadata\tests\System.Reflection.Metadata.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Reflection.MetadataLoadContext\tests\System.Reflection.MetadataLoadContext.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Reflection\tests\CoreCLR\System.Reflection.CoreCLR.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Reflection\tests\System.Reflection.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Security.Permissions\tests\System.Security.Permissions.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Text.RegularExpressions\tests\System.Text.RegularExpressions.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Threading.Thread\tests\System.Threading.Thread.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.ValueTuple\tests\System.ValueTuple.Tests.csproj" />
   </ItemGroup>
 
   <ItemGroup>
@@ -60,6 +39,7 @@
                       Condition="'$(TestPackages)' == 'true'" />
     <ProjectReference Include="$(MSBuildThisFileDirectory)*\tests\**\*.TrimmingTests.proj"
                       Exclude="@(ProjectExclusions)"
+                      BuildInParallel="false"
                       Condition="'$(TestTrimming)' == 'true'" />
   </ItemGroup>
 
diff --git a/src/mono/configure.ac b/src/mono/configure.ac
index 1b95d75f132394..8a9996eb7cf4fe 100644
--- a/src/mono/configure.ac
+++ b/src/mono/configure.ac
@@ -408,6 +408,13 @@ case "$host" in
 		host_sunos=yes
 		;;
 	*-*-darwin*)
+		# Temporary workaround for Apple Silicon
+		# config.guess returns arm-apple-darwin20.0.0
+		if test $ac_cv_host = arm-apple-darwin20.0.0 -o $ac_cv_target = arm-apple-darwin20.0.0; then
+		   echo "You are running on Apple Silicon, but using an old config.guess, invoke configure like this:"
+		   echo "Run configure using ./configure --host=aarch64-apple-darwin20.0.0 --target=aarch64-apple-darwin20.0.0"
+		   exit 1
+		fi
 		parallel_mark="Disabled_Currently_Hangs_On_MacOSX"
 		host_darwin=yes
 		target_mach=yes
@@ -449,6 +456,10 @@ case "$host" in
 				platform_ios=yes
 				has_dtrace=no
 				;;
+			aarch64*-darwin20*)
+				# OSX/arm64
+				support_boehm=no
+				;;
 			aarch64*-darwin*)
 				platform_ios=yes
 				;;
@@ -1208,6 +1219,7 @@ if test "x$crash_reporting" != "xyes"; then
 CFLAGS="$CFLAGS -DDISABLE_CRASH_REPORTING=1"
 CXXFLAGS="$CXXFLAGS -DDISABLE_CRASH_REPORTING=1"
 fi
+AM_CONDITIONAL(DISABLE_CRASH_REPORTING, test x$crash_reporting != xyes)
 
 AC_ARG_ENABLE(monodroid, [ --enable-monodroid Enable runtime support for Monodroid (Xamarin.Android)], enable_monodroid=$enableval, enable_monodroid=no)
 AM_CONDITIONAL(ENABLE_MONODROID, test x$enable_monodroid = xyes)
@@ -1783,9 +1795,7 @@ fi
 AM_CONDITIONAL(ENABLE_STATIC_GCC_LIBS, test "x$enable_static_gcc_libs" = "xyes")
 
 AC_ARG_ENABLE(minimal, [  --enable-minimal=LIST      drop support for LIST subsystems.
-     LIST is a comma-separated list from: aot, profiler, decimal, pinvoke, debug, appdomains, verifier, dllmap,
-     reflection_emit, reflection_emit_save, large_code, logging, com, ssa, generics, attach, jit, interpreter, simd, soft_debug, perfcounters, normalization, desktop_loader, shared_perfcounters, remoting,
-	 security, lldb, mdb, assert_messages, config, cfgdir_config, cleanup, sgen_marksweep_conc, sgen_split_nursery, sgen_gc_bridge, sgen_debug_helpers, sockets, gac, threads, processes, eventpipe.],
+     LIST is a comma-separated list from: aot, profiler, decimal, pinvoke, debug, appdomains, verifier, dllmap, reflection_emit, reflection_emit_save, large_code, logging, com, ssa, generics, attach, jit, interpreter, simd, soft_debug, perfcounters, normalization, desktop_loader, shared_perfcounters, remoting, security, lldb, mdb, assert_messages, config, cfgdir_config, cleanup, sgen_marksweep_conc, sgen_split_nursery, sgen_gc_bridge, sgen_toggleref, sgen_debug_helpers, sgen_binary_protocol, sockets, gac, threads, processes, eventpipe.],
 [
 	for feature in `echo "$enable_minimal" | sed -e "s/,/ /g"`; do
 		eval "mono_feature_disable_$feature='yes'"
@@ -1991,11 +2001,21 @@ if test "x$mono_feature_disable_sgen_gc_bridge" = "xyes"; then
 	AC_MSG_NOTICE([Disabled gc bridge support in SGEN.])
 fi
 
+if test "x$mono_feature_disable_sgen_toggleref" = "xyes"; then
+	AC_DEFINE(DISABLE_SGEN_TOGGLEREF, 1, [Disable toggleref support in SGEN.])
+	AC_MSG_NOTICE([Disabled toggleref support in SGEN.])
+fi
+
 if test "x$mono_feature_disable_sgen_debug_helpers" = "xyes"; then
 	AC_DEFINE(DISABLE_SGEN_DEBUG_HELPERS, 1, [Disable debug helpers in SGEN.])
 	AC_MSG_NOTICE([Disabled debug helpers in SGEN.])
 fi
 
+if test "x$mono_feature_disable_sgen_binary_protocol" = "xyes"; then
+	AC_DEFINE(DISABLE_SGEN_BINARY_PROTOCOL, 1, [Disable binary protocol logging in SGEN.])
+	AC_MSG_NOTICE([Disabled binary protocol logging in SGEN.])
+fi
+
 if test "x$mono_feature_disable_sockets" = "xyes"; then
 	AC_DEFINE(DISABLE_SOCKETS, 1, [Disable sockets])
 	AC_MSG_NOTICE([Disabled sockets])
@@ -2807,7 +2827,7 @@ if test x$host_win32 = xno; then
 	AC_CHECK_HEADERS(pthread_np.h)
 	AC_CHECK_FUNCS(pthread_mutex_timedlock)
 	AC_CHECK_FUNCS(pthread_getattr_np pthread_attr_get_np pthread_getname_np pthread_setname_np pthread_cond_timedwait_relative_np)
-	AC_CHECK_FUNCS(pthread_kill)
+	AC_CHECK_FUNCS(pthread_kill pthread_jit_write_protect_np)
 	AC_MSG_CHECKING(for PTHREAD_MUTEX_RECURSIVE)
 	AC_TRY_COMPILE([ #include <pthread.h>], [
 		pthread_mutexattr_t attr;
@@ -4665,7 +4685,7 @@ case "$host" in
 		ACCESS_UNALIGNED="yes"
 		BTLS_SUPPORTED=yes
 		BTLS_PLATFORM=s390x
-		CFLAGS="$CFLAGS -mbackchain -D__USE_STRING_INLINES"
+		CFLAGS="$CFLAGS -mbackchain"
 		;;
 	riscv32-*)
 		TARGET=RISCV32
@@ -4764,6 +4784,12 @@ if test "x$host" != "x$target"; then
 		sizeof_register=8
 		AC_DEFINE(TARGET_WATCHOS, 1, [...])
 		;;
+	aarch64*darwin*)
+		TARGET=ARM64
+		# Both ios and osx/arm64 have the same aarc64-darwin triple,
+		# assume ios for now when cross compiling
+		TARGET_SYS=IOS
+		;;
 	aarch64-*)
 		TARGET=ARM64
 		;;
@@ -4976,7 +5002,7 @@ if test "x$target_mach" = "xyes"; then
 	  CPPFLAGS_FOR_LIBGC="$CPPFLAGS_FOR_LIBGC -DTARGET_WATCHOS"
 	  CFLAGS_FOR_LIBGC="$CFLAGS_FOR_LIBGC -DTARGET_WATCHOS"
 	  BTLS_SUPPORTED=no
-   elif test "x$TARGET" = "xARM" -o "x$TARGET" = "xARM64" -o "x$TARGET" = "xARM6432"; then
+   elif test "x$TARGET_SYS" = "xIOS" -o "x$TARGET" = "xARM" -o "x$TARGET" = "xARM6432"; then
    	  AC_DEFINE(TARGET_IOS,1,[The JIT/AOT targets iOS])
 	  CPPFLAGS_FOR_LIBGC="$CPPFLAGS_FOR_LIBGC -DTARGET_IOS"
 	  CFLAGS_FOR_LIBGC="$CFLAGS_FOR_LIBGC -DTARGET_IOS"
@@ -4992,6 +5018,9 @@ if test "x$target_mach" = "xyes"; then
           CPPFLAGS_FOR_LIBGC="$CPPFLAGS_FOR_LIBGC -DTARGET_OSX"
           CFLAGS_FOR_LIBGC="$CFLAGS_FOR_LIBGC -DTARGET_OSX"
           target_osx=yes
+          if test "x$TARGET" = "xARM64"; then
+             BTLS_SUPPORTED=no
+          fi
        ], [
           AC_DEFINE(TARGET_IOS,1,[The JIT/AOT targets iOS])
           CPPFLAGS_FOR_LIBGC="$CPPFLAGS_FOR_LIBGC -DTARGET_IOS"
@@ -6855,7 +6884,7 @@ if test x$with_core = xonly; then
 	if test x$have_shim_globalization = xyes || test x$cross_compiling = xyes; then
 		ICU_SHIM_PATH=../../../libraries/Native/Unix/System.Globalization.Native
 		if test x$target_wasm = xyes && test x$with_static_icu = xyes; then
-			ICU_CFLAGS="-DTARGET_UNIX -DU_DISABLE_RENAMING"
+			ICU_CFLAGS="-DTARGET_UNIX -DU_DISABLE_RENAMING -DHAVE_UDAT_STANDALONE_SHORTER_WEEKDAYS -DHAVE_SET_MAX_VARIABLE"
 			have_sys_icu=yes
 		elif test x$target_osx = xyes; then
 			ORIG_CPPFLAGS=$CPPFLAGS
diff --git a/src/mono/mono.proj b/src/mono/mono.proj
index 08c5c1e70c5a4a..a11853b47c527b 100644
--- a/src/mono/mono.proj
+++ b/src/mono/mono.proj
@@ -644,7 +644,7 @@
       <_MonoConfigureParams Include="--disable-crash-reporting"/>
       <_MonoConfigureParams Include="--with-bitcode=yes"/>
       <_MonoConfigureParams Include="--with-static-icu=yes"/>
-      <_MonoConfigureParams Include="--enable-minimal=ssa,com,jit,reflection_emit_save,portability,assembly_remapping,attach,verifier,full_messages,appdomains,shadowcopy,security,sgen_marksweep_conc,sgen_split_nursery,sgen_gc_bridge,logging,remoting,shared_perfcounters,sgen_debug_helpers,soft_debug,interpreter,assert_messages,cleanup,mdb,gac,threads,eventpipe,$(_MonoEnableMinimal)"/>
+      <_MonoConfigureParams Include="--enable-minimal=ssa,com,jit,reflection_emit_save,portability,assembly_remapping,attach,verifier,full_messages,appdomains,shadowcopy,security,sgen_marksweep_conc,sgen_split_nursery,sgen_gc_bridge,sgen_toggleref,logging,remoting,shared_perfcounters,sgen_debug_helpers,sgen_binary_protocol,soft_debug,interpreter,assert_messages,cleanup,mdb,gac,threads,eventpipe,$(_MonoEnableMinimal)"/>
       <_MonoCFLAGS Include="-fexceptions" />
       <_MonoCFLAGS Include="-I$(PkgMicrosoft_NETCore_Runtime_ICU_Transport)/runtimes/browser-wasm/native/include" />
       <_MonoCXXFLAGS Include="-fexceptions" />
diff --git a/src/mono/mono/arch/arm64/Makefile.am b/src/mono/mono/arch/arm64/Makefile.am
index bdc37622a640d6..e735d0ed69aa1d 100644
--- a/src/mono/mono/arch/arm64/Makefile.am
+++ b/src/mono/mono/arch/arm64/Makefile.am
@@ -1,3 +1,9 @@
 MAKEFLAGS := $(MAKEFLAGS) --no-builtin-rules
 
 EXTRA_DIST = arm64-codegen.h codegen-test.c
+
+test-codegen:
+	$(CC) $(CFLAGS) -I../../.. -I../../eglib/ ../../eglib/.libs/libeglib.a -o codegen-test codegen-test.c
+	./codegen-test > tmp.s
+	$(CC) $(CFLAGS) -c -o tmp.o tmp.s
+	objdump -d --triple=arm64e tmp.o
diff --git a/src/mono/mono/arch/arm64/arm64-codegen.h b/src/mono/mono/arch/arm64/arm64-codegen.h
index 239f4161fd92d7..d35fda11752f5c 100644
--- a/src/mono/mono/arch/arm64/arm64-codegen.h
+++ b/src/mono/mono/arch/arm64/arm64-codegen.h
@@ -867,4 +867,40 @@ arm_encode_arith_imm (int imm, guint32 *shift)
 #define arm_cmpp arm_cmpx
 #endif
 
+/* ARM v8.3 */
+
+/* PACIA */
+
+#define arm_format_pacia(p, crm, op2) arm_emit ((p), (0b11010101000000110010000000011111 << 0) | ((crm) << 8) | ((op2) << 5))
+#define arm_paciasp(p) arm_format_pacia ((p), 0b0011, 0b001)
+
+/* PACIB */
+
+#define arm_format_pacib(p, crm, op2) arm_emit ((p), (0b11010101000000110010000000011111 << 0) | ((crm) << 8) | ((op2) << 5))
+#define arm_pacibsp(p) arm_format_pacib ((p), 0b0011, 0b011)
+
+/* RETA */
+#define arm_format_reta(p,key) arm_emit ((p), 0b11010110010111110000101111111111 + ((key) << 10))
+
+#define arm_retaa(p) arm_format_reta ((p),0)
+#define arm_retab(p) arm_format_reta ((p),1)
+
+/* BRA */
+
+#define arm_format_bra(p, z, m, rn, rm) arm_emit ((p), (0b1101011000011111000010 << 10) + ((z) << 24) + ((m) << 10) + ((rn) << 5) + ((rm) << 0))
+
+#define arm_braaz(p, rn) arm_format_bra ((p), 0, 0, (rn), 0b11111)
+#define arm_brabz(p, rn) arm_format_bra ((p), 0, 1, (rn), 0b11111)
+#define arm_braa(p, rn, rm) arm_format_bra ((p), 1, 0, (rn), (rm))
+#define arm_brab(p, rn, rm) arm_format_bra ((p), 1, 1, (rn), (rm))
+
+/* BLRA */
+
+#define arm_format_blra(p, z, m, rn, rm) arm_emit ((p), (0b1101011000111111000010 << 10) + ((z) << 24) + ((m) << 10) + ((rn) << 5) + ((rm) << 0))
+
+#define arm_blraaz(p, rn) arm_format_blra ((p), 0, 0, (rn), 0b11111)
+#define arm_blraa(p, rn, rm) arm_format_blra ((p), 1, 0, (rn), (rm))
+#define arm_blrabz(p, rn) arm_format_blra ((p), 0, 1, (rn), 0b11111)
+#define arm_blrab(p, rn, rm) arm_format_blra ((p), 1, 1, (rn), (rm))
+
 #endif /* __arm_CODEGEN_H__ */
diff --git a/src/mono/mono/arch/arm64/codegen-test.c b/src/mono/mono/arch/arm64/codegen-test.c
index bb9d9dcdecd49e..efb991e8427384 100644
--- a/src/mono/mono/arch/arm64/codegen-test.c
+++ b/src/mono/mono/arch/arm64/codegen-test.c
@@ -416,6 +416,19 @@ main (int argc, char *argv [])
 	arm_stlxrx (code, ARMREG_R0, ARMREG_R1, ARMREG_R2);
 	arm_stlxrw (code, ARMREG_R0, ARMREG_R1, ARMREG_R2);
 
+	arm_paciasp (code);
+	arm_pacibsp (code);
+	arm_retaa (code);
+	arm_retab (code);
+	arm_braaz (code, ARMREG_R1);
+	arm_brabz (code, ARMREG_R1);
+	arm_braa (code, ARMREG_R1, ARMREG_R2);
+	arm_brab (code, ARMREG_R1, ARMREG_R2);
+	arm_blraaz (code, ARMREG_R1);
+	arm_blraa (code, ARMREG_R1, ARMREG_R2);
+	arm_blrabz (code, ARMREG_R1);
+	arm_blrab (code, ARMREG_R1, ARMREG_R2);
+
 	for (i = 0; i < code - buf; ++i)
 		printf (".byte %d\n", buf [i]);
 	printf ("\n");
diff --git a/src/mono/mono/eglib/eglib-remap.h b/src/mono/mono/eglib/eglib-remap.h
index c5e27adae85d3c..c9751049c3b743 100644
--- a/src/mono/mono/eglib/eglib-remap.h
+++ b/src/mono/mono/eglib/eglib-remap.h
@@ -311,3 +311,6 @@
 #define g_set_printerr_handler monoeg_set_printerr_handler
 
 #define g_size_to_int monoeg_size_to_int
+#define g_ascii_charcmp monoeg_ascii_charcmp
+#define g_ascii_charcasecmp monoeg_ascii_charcasecmp
+#define g_warning_d monoeg_warning_d
diff --git a/src/mono/mono/eglib/glib.h b/src/mono/mono/eglib/glib.h
index a056e958989866..4272679aeb1331 100644
--- a/src/mono/mono/eglib/glib.h
+++ b/src/mono/mono/eglib/glib.h
@@ -779,6 +779,7 @@ GLogLevelFlags g_log_set_fatal_mask   (const gchar *log_domain, GLogLevelFlags f
 void           g_logv                 (const gchar *log_domain, GLogLevelFlags log_level, const gchar *format, va_list args);
 G_EXTERN_C // Used by MonoPosixHelper or MonoSupportW, at least.
 void           g_log                  (const gchar *log_domain, GLogLevelFlags log_level, const gchar *format, ...);
+void           g_log_disabled         (const gchar *log_domain, GLogLevelFlags log_level, const char *file, int line);
 G_EXTERN_C // Used by MonoPosixHelper or MonoSupportW, at least.
 void           g_assertion_message    (const gchar *format, ...) G_GNUC_NORETURN;
 void           mono_assertion_message_disabled  (const char *file, int line) G_GNUC_NORETURN;
@@ -786,6 +787,7 @@ void           mono_assertion_message  (const char *file, int line, const char *
 void           mono_assertion_message_unreachable (const char *file, int line) G_GNUC_NORETURN;
 const char *   g_get_assertion_message (void);
 
+#ifndef DISABLE_ASSERT_MESSAGES
 #ifdef HAVE_C99_SUPPORT
 /* The for (;;) tells gc thats g_error () doesn't return, avoiding warnings */
 #define g_error(format, ...)    do { g_log (G_LOG_DOMAIN, G_LOG_LEVEL_ERROR, format, __VA_ARGS__); for (;;); } while (0)
@@ -800,6 +802,13 @@ const char *   g_get_assertion_message (void);
 #define g_message(...)  g_log (G_LOG_DOMAIN, G_LOG_LEVEL_MESSAGE, __VA_ARGS__)
 #define g_debug(...)    g_log (G_LOG_DOMAIN, G_LOG_LEVEL_DEBUG, __VA_ARGS__)
 #endif  /* ndef HAVE_C99_SUPPORT */
+#else
+#define g_error(...)    do { g_log_disabled (G_LOG_DOMAIN, G_LOG_LEVEL_ERROR, __FILE__, __LINE__); for (;;); } while (0)
+#define g_critical(...) g_log_disabled (G_LOG_DOMAIN, G_LOG_LEVEL_CRITICAL, __FILE__, __LINE__)
+#define g_warning(...)  g_log_disabled (G_LOG_DOMAIN, G_LOG_LEVEL_WARNING, __FILE__, __LINE__)
+#define g_message(...)  g_log_disabled (G_LOG_DOMAIN, G_LOG_LEVEL_MESSAGE, __FILE__, __LINE__)
+#define g_debug(...)    g_log_disabled (G_LOG_DOMAIN, G_LOG_LEVEL_DEBUG, __FILE__, __LINE__)
+#endif
 
 typedef void (*GLogFunc) (const gchar *log_domain, GLogLevelFlags log_level, const gchar *message, gpointer user_data);
 typedef void (*GPrintFunc) (const gchar *string);
diff --git a/src/mono/mono/eglib/goutput.c b/src/mono/mono/eglib/goutput.c
index f9da72dfe57de8..b54b1e0d8b5bd6 100644
--- a/src/mono/mono/eglib/goutput.c
+++ b/src/mono/mono/eglib/goutput.c
@@ -183,6 +183,12 @@ g_log (const gchar *log_domain, GLogLevelFlags log_level, const gchar *format, .
 	va_end (args);
 }
 
+void
+g_log_disabled (const gchar *log_domain, GLogLevelFlags log_level, const char *file, int line)
+{
+	g_log (log_domain, log_level, "%s:%d <disabled>", file, line);
+}
+
 static char *failure_assertion = NULL;
 
 const char *
diff --git a/src/mono/mono/eventpipe/ep-event-source.c b/src/mono/mono/eventpipe/ep-event-source.c
index e4fd95df9bc138..7db34bee58c755 100644
--- a/src/mono/mono/eventpipe/ep-event-source.c
+++ b/src/mono/mono/eventpipe/ep-event-source.c
@@ -210,7 +210,7 @@ ep_event_source_send_process_info (
 	os_info_utf16 = ep_rt_utf8_to_utf16_string (_ep_os_info, -1);
 	arch_info_utf16 = ep_rt_utf8_to_utf16_string (_ep_arch_info, -1);
 
-	EventData data [3] = { 0 };
+	EventData data [3] = { { 0 } };
 	if (command_line_utf16)
 		ep_event_data_init (&data[0], (uint64_t)command_line_utf16, (uint32_t)((ep_rt_utf16_string_len (command_line_utf16) + 1) * sizeof (ep_char16_t)), 0);
 	if (os_info_utf16)
diff --git a/src/mono/mono/metadata/Makefile.am b/src/mono/mono/metadata/Makefile.am
index 06abdd51ab2b41..76fa995d570dc5 100644
--- a/src/mono/mono/metadata/Makefile.am
+++ b/src/mono/mono/metadata/Makefile.am
@@ -142,26 +142,31 @@ libmonoruntime_support_la_CFLAGS = $(filter-out @CXX_REMOVE_CFLAGS@, @CFLAGS@) @
 
 if ENABLE_NETCORE
 if HAVE_SYS_ICU
+
+# symlink ICU sources to a local dir so automake puts intermediates into the target-specific folder
+icushim/%.c: @ICU_SHIM_PATH@/%.c
+	$(LN_S) $^ $@
+
 shim_libraries = libmonoruntime-shimglobalization.la
 
 nodist_libmonoruntime_shimglobalization_la_SOURCES = \
-									@ICU_SHIM_PATH@/pal_calendarData.c \
-									@ICU_SHIM_PATH@/pal_casing.c \
-									@ICU_SHIM_PATH@/pal_collation.c \
-									@ICU_SHIM_PATH@/pal_idna.c \
-									@ICU_SHIM_PATH@/pal_locale.c \
-									@ICU_SHIM_PATH@/pal_localeNumberData.c \
-									@ICU_SHIM_PATH@/pal_localeStringData.c \
-									@ICU_SHIM_PATH@/pal_normalization.c \
-									@ICU_SHIM_PATH@/pal_timeZoneInfo.c \
-									@ICU_SHIM_PATH@/entrypoints.c
+									icushim/pal_calendarData.c \
+									icushim/pal_casing.c \
+									icushim/pal_collation.c \
+									icushim/pal_idna.c \
+									icushim/pal_locale.c \
+									icushim/pal_localeNumberData.c \
+									icushim/pal_localeStringData.c \
+									icushim/pal_normalization.c \
+									icushim/pal_timeZoneInfo.c \
+									icushim/entrypoints.c
 
 libmonoruntime_shimglobalization_la_CFLAGS = @ICU_CFLAGS@ -I$(top_srcdir)/../libraries/Native/Unix/System.Globalization.Native/ -I$(top_srcdir)/../libraries/Native/Unix/Common/
 
 if STATIC_ICU
-nodist_libmonoruntime_shimglobalization_la_SOURCES += @ICU_SHIM_PATH@/pal_icushim_static.c
+nodist_libmonoruntime_shimglobalization_la_SOURCES += icushim/pal_icushim_static.c
 else
-nodist_libmonoruntime_shimglobalization_la_SOURCES += @ICU_SHIM_PATH@/pal_icushim.c
+nodist_libmonoruntime_shimglobalization_la_SOURCES += icushim/pal_icushim.c
 endif # STATIC_ICU
 
 endif # HAVE_SYS_ICU
diff --git a/src/mono/mono/metadata/appdomain.h b/src/mono/mono/metadata/appdomain.h
index ab260646e90069..bc8a1f2de199c0 100644
--- a/src/mono/mono/metadata/appdomain.h
+++ b/src/mono/mono/metadata/appdomain.h
@@ -106,6 +106,9 @@ mono_domain_foreach        (MonoDomainFunc func, void* user_data);
 MONO_API MONO_RT_EXTERNAL_ONLY MonoAssembly *
 mono_domain_assembly_open  (MonoDomain *domain, const char *name);
 
+MONO_API void
+mono_domain_ensure_entry_assembly (MonoDomain *domain, MonoAssembly *assembly);
+
 MONO_API mono_bool
 mono_domain_finalize       (MonoDomain *domain, uint32_t timeout);
 
diff --git a/src/mono/mono/metadata/assembly.c b/src/mono/mono/metadata/assembly.c
index d4ea7f7e53c093..d9a9e7f8c3b509 100644
--- a/src/mono/mono/metadata/assembly.c
+++ b/src/mono/mono/metadata/assembly.c
@@ -2501,6 +2501,16 @@ mono_assembly_open_from_bundle (MonoAssemblyLoadContext *alc, const char *filena
 	for (i = 0; !image && bundles [i]; ++i) {
 		if (strcmp (bundles [i]->name, is_satellite ? filename : name) == 0) {
 			image = mono_image_open_from_data_internal (alc, (char*)bundles [i]->data, bundles [i]->size, FALSE, status, refonly, FALSE, name);
+#if defined(TARGET_WASM) && defined(ENABLE_NETCORE)
+			/* 
+			 * Since bundled images do not exist on disk, don't give them a legit file name.
+			 * This is the expected behavior for single file exe's. 
+			 */
+			if (image->filename)
+				g_free (image->filename);
+
+			image->filename = NULL;
+#endif
 			break;
 		}
 	}
diff --git a/src/mono/mono/metadata/class.c b/src/mono/mono/metadata/class.c
index bfd02a8eb736c9..bc3b46b7f7609f 100644
--- a/src/mono/mono/metadata/class.c
+++ b/src/mono/mono/metadata/class.c
@@ -3448,7 +3448,7 @@ mono_class_from_name (MonoImage *image, const char* name_space, const char *name
  *
  * This function works exactly like mono_class_from_name but it will abort if the class is not found.
  * This function should be used by the runtime for critical types to which there's no way to recover but crash
- * If they are missing. Thing of System.Object or System.String.
+ * if they are missing. For example, System.Object or System.String.
  */
 MonoClass *
 mono_class_load_from_name (MonoImage *image, const char* name_space, const char *name)
diff --git a/src/mono/mono/metadata/custom-attrs.c b/src/mono/mono/metadata/custom-attrs.c
index f9297172e6ed58..491ae63bfb8f8c 100644
--- a/src/mono/mono/metadata/custom-attrs.c
+++ b/src/mono/mono/metadata/custom-attrs.c
@@ -489,6 +489,7 @@ MONO_RESTORE_WARNING
 	case MONO_TYPE_SZARRAY: {
 		MonoArray *arr;
 		guint32 i, alen, basetype;
+
 		if (!bcheck_blob (p, 3, boundp, error))
 			return NULL;
 		alen = read32 (p);
@@ -497,8 +498,10 @@ MONO_RESTORE_WARNING
 			*end = p;
 			return NULL;
 		}
+
 		arr = mono_array_new_checked (mono_domain_get(), tklass, alen, error);
 		return_val_if_nok (error, NULL);
+
 		basetype = m_class_get_byval_arg (tklass)->type;
 		if (basetype == MONO_TYPE_VALUETYPE && m_class_is_enumtype (tklass))
 			basetype = mono_class_enum_basetype_internal (tklass)->type;
@@ -569,7 +572,10 @@ MONO_RESTORE_WARNING
 		case MONO_TYPE_CLASS:
 		case MONO_TYPE_OBJECT:
 		case MONO_TYPE_STRING:
-		case MONO_TYPE_SZARRAY:
+		case MONO_TYPE_SZARRAY: {
+			HANDLE_FUNCTION_ENTER ();
+			MONO_HANDLE_NEW (MonoArray, arr);
+
 			for (i = 0; i < alen; i++) {
 				MonoObject *item = NULL;
 				load_cattr_value (image, m_class_get_byval_arg (tklass), &item, p, boundp, &p, error);
@@ -577,13 +583,16 @@ MONO_RESTORE_WARNING
 					return NULL;
 				mono_array_setref_internal (arr, i, item);
 			}
+			HANDLE_FUNCTION_RETURN ();
 			break;
+		}
 		default:
 			g_error ("Type 0x%02x not handled in custom attr array decoding", basetype);
 		}
 		*end = p;
 		g_assert (out_obj);
 		*out_obj = (MonoObject*)arr;
+
 		return NULL;
 	}
 	default:
@@ -625,6 +634,8 @@ create_cattr_typed_arg (MonoType *t, MonoObject *val, MonoError *error)
 
 	error_init (error);
 
+	HANDLE_FUNCTION_ENTER ();
+
 	MONO_STATIC_POINTER_INIT (MonoMethod, ctor)
 
 		ctor = mono_class_get_method_from_name_checked (mono_class_get_custom_attribute_typed_argument_class (), ".ctor", 2, 0, error);
@@ -634,15 +645,20 @@ create_cattr_typed_arg (MonoType *t, MonoObject *val, MonoError *error)
 
 	params [0] = mono_type_get_object_checked (mono_domain_get (), t, error);
 	return_val_if_nok (error, NULL);
+	MONO_HANDLE_PIN ((MonoObject*)params [0]);
 
 	params [1] = val;
 	retval = mono_object_new_checked (mono_domain_get (), mono_class_get_custom_attribute_typed_argument_class (), error);
 	return_val_if_nok (error, NULL);
+	MONO_HANDLE_PIN (retval);
+
 	unboxed = mono_object_unbox_internal (retval);
 
 	mono_runtime_invoke_checked (ctor, unboxed, params, error);
 	return_val_if_nok (error, NULL);
 
+	HANDLE_FUNCTION_RETURN ();
+
 	return retval;
 }
 
@@ -654,6 +670,8 @@ create_cattr_named_arg (void *minfo, MonoObject *typedarg, MonoError *error)
 
 	error_init (error);
 
+	HANDLE_FUNCTION_ENTER ();
+
 	MONO_STATIC_POINTER_INIT (MonoMethod, ctor)
 
 		ctor = mono_class_get_method_from_name_checked (mono_class_get_custom_attribute_named_argument_class (), ".ctor", 2, 0, error);
@@ -665,12 +683,15 @@ create_cattr_named_arg (void *minfo, MonoObject *typedarg, MonoError *error)
 	params [1] = typedarg;
 	retval = mono_object_new_checked (mono_domain_get (), mono_class_get_custom_attribute_named_argument_class (), error);
 	return_val_if_nok (error, NULL);
+	MONO_HANDLE_PIN (retval);
 
 	unboxed = mono_object_unbox_internal (retval);
 
 	mono_runtime_invoke_checked (ctor, unboxed, params, error);
 	return_val_if_nok (error, NULL);
 
+	HANDLE_FUNCTION_RETURN ();
+
 	return retval;
 }
 
@@ -1182,7 +1203,7 @@ mono_reflection_create_custom_attr_data_args (MonoImage *image, MonoMethod *meth
 /*
  * mono_reflection_create_custom_attr_data_args_noalloc:
  *
- * Same as mono_reflection_create_custom_attr_data_args_noalloc but allocate no managed objects, return values
+ * Same as mono_reflection_create_custom_attr_data_args but allocate no managed objects, return values
  * using C arrays. Only usable for cattrs with primitive/type arguments.
  * TYPED_ARGS, NAMED_ARGS, and NAMED_ARG_INFO should be freed using g_free ().
  */
@@ -1385,7 +1406,7 @@ ves_icall_System_Reflection_CustomAttributeData_ResolveArgumentsInternal (MonoRe
 		obj = mono_array_get_internal (typed_args, MonoObject*, i);
 		MONO_HANDLE_ASSIGN_RAW (obj_h, obj);
 
-		t = mono_method_signature_internal (method)->params [i];
+		t = sig->params [i];
 		if (t->type == MONO_TYPE_OBJECT && obj)
 			t = m_class_get_byval_arg (obj->vtable->klass);
 		typedarg = create_cattr_typed_arg (t, obj, error);
diff --git a/src/mono/mono/metadata/domain-internals.h b/src/mono/mono/metadata/domain-internals.h
index 2acdd85d20d4ee..0985b671df7f52 100644
--- a/src/mono/mono/metadata/domain-internals.h
+++ b/src/mono/mono/metadata/domain-internals.h
@@ -692,9 +692,6 @@ mono_runtime_install_appctx_properties (void);
 gboolean 
 mono_domain_set_fast (MonoDomain *domain, gboolean force);
 
-void
-mono_domain_ensure_entry_assembly (MonoDomain *domain, MonoAssembly *assembly);
-
 MonoAssemblyLoadContext *
 mono_domain_default_alc (MonoDomain *domain);
 
diff --git a/src/mono/mono/metadata/handle.h b/src/mono/mono/metadata/handle.h
index 2cedc51bb7eab8..bdffa0fad1c1bd 100644
--- a/src/mono/mono/metadata/handle.h
+++ b/src/mono/mono/metadata/handle.h
@@ -516,6 +516,9 @@ TYPED_HANDLE_DECL (MonoObject);
 TYPED_HANDLE_DECL (MonoException);
 TYPED_HANDLE_DECL (MonoAppContext);
 
+/* Simpler version of MONO_HANDLE_NEW if the handle is not used */
+#define MONO_HANDLE_PIN(object) MONO_HANDLE_NEW (MonoObject, (MonoObject*)(object))
+
 // Structs cannot be cast to structs.
 // As well, a function is needed because an anonymous struct cannot be initialized in C.
 static inline MonoObjectHandle
diff --git a/src/mono/mono/metadata/icall-decl.h b/src/mono/mono/metadata/icall-decl.h
index 1bb8ab1cfa67db..2c153f8cd6c910 100644
--- a/src/mono/mono/metadata/icall-decl.h
+++ b/src/mono/mono/metadata/icall-decl.h
@@ -159,7 +159,9 @@ ICALL_EXPORT gint64 ves_icall_System_GC_GetTotalMemory (MonoBoolean forceCollect
 ICALL_EXPORT gint64 ves_icall_System_Threading_Timer_GetTimeMonotonic (void);
 ICALL_EXPORT gpointer ves_icall_System_GCHandle_GetAddrOfPinnedObject (MonoGCHandle handle);
 ICALL_EXPORT int ves_icall_Interop_Sys_DoubleToString (double, char*, char*, int);
+#if !ENABLE_NETCORE
 ICALL_EXPORT int ves_icall_System_Environment_get_Platform (void);
+#endif
 ICALL_EXPORT int ves_icall_System_GC_GetCollectionCount (int);
 ICALL_EXPORT int ves_icall_System_GC_GetMaxGeneration (void);
 ICALL_EXPORT gint64 ves_icall_System_GC_GetAllocatedBytesForCurrentThread (void);
diff --git a/src/mono/mono/metadata/icall-def-netcore.h b/src/mono/mono/metadata/icall-def-netcore.h
index ee55fbbc7fc291..8e3a61820b651b 100644
--- a/src/mono/mono/metadata/icall-def-netcore.h
+++ b/src/mono/mono/metadata/icall-def-netcore.h
@@ -94,11 +94,8 @@ HANDLES(ENV_2, "GetCommandLineArgs", ves_icall_System_Environment_GetCommandLine
 HANDLES(ENV_3, "GetEnvironmentVariableNames", ves_icall_System_Environment_GetEnvironmentVariableNames, MonoArray, 0, ())
 NOHANDLES(ICALL(ENV_4, "GetProcessorCount", ves_icall_System_Environment_get_ProcessorCount))
 NOHANDLES(ICALL(ENV_9, "get_ExitCode", mono_environment_exitcode_get))
-HANDLES(ENV_11, "get_MachineName", ves_icall_System_Environment_get_MachineName, MonoString, 0, ())
-NOHANDLES(ICALL(ENV_13, "get_Platform", ves_icall_System_Environment_get_Platform))
 NOHANDLES(ICALL(ENV_15, "get_TickCount", ves_icall_System_Environment_get_TickCount))
 NOHANDLES(ICALL(ENV_15a, "get_TickCount64", ves_icall_System_Environment_get_TickCount64))
-HANDLES(ENV_16, "get_UserName", ves_icall_System_Environment_get_UserName, MonoString, 0, ())
 HANDLES(ENV_17, "internalGetEnvironmentVariable_native", ves_icall_System_Environment_GetEnvironmentVariable_native, MonoString, 1, (const_char_ptr))
 NOHANDLES(ICALL(ENV_20, "set_ExitCode", mono_environment_exitcode_set))
 
diff --git a/src/mono/mono/metadata/icall.c b/src/mono/mono/metadata/icall.c
index c58854c2532e00..fa991bc72e5752 100644
--- a/src/mono/mono/metadata/icall.c
+++ b/src/mono/mono/metadata/icall.c
@@ -7230,7 +7230,7 @@ ves_icall_System_Reflection_RuntimeModule_ResolveSignature (MonoImage *image, gu
 }
 
 static void
-check_for_invalid_type (MonoClass *klass, MonoError *error)
+check_for_invalid_array_type (MonoClass *klass, MonoError *error)
 {
 	char *name;
 
@@ -7243,13 +7243,23 @@ check_for_invalid_type (MonoClass *klass, MonoError *error)
 	mono_error_set_type_load_name (error, name, g_strdup (""), "");
 }
 
+static void
+check_for_invalid_byref_or_pointer_type (MonoClass *klass, MonoError *error)
+{
+#ifdef ENABLE_NETCORE
+	return;
+#else
+	check_for_invalid_array_type (klass, error);
+#endif
+}
+
 MonoReflectionTypeHandle
 ves_icall_RuntimeType_make_array_type (MonoReflectionTypeHandle ref_type, int rank, MonoError *error)
 {
 	MonoType *type = MONO_HANDLE_GETVAL (ref_type, type);
 
 	MonoClass *klass = mono_class_from_mono_type_internal (type);
-	check_for_invalid_type (klass, error);
+	check_for_invalid_array_type (klass, error);
 	return_val_if_nok (error, MONO_HANDLE_CAST (MonoReflectionType, NULL_HANDLE));
 
 	MonoClass *aklass;
@@ -7276,7 +7286,7 @@ ves_icall_RuntimeType_make_byref_type (MonoReflectionTypeHandle ref_type, MonoEr
 	mono_class_init_checked (klass, error);
 	return_val_if_nok (error, MONO_HANDLE_CAST (MonoReflectionType, NULL_HANDLE));
 
-	check_for_invalid_type (klass, error);
+	check_for_invalid_byref_or_pointer_type (klass, error);
 	return_val_if_nok (error, MONO_HANDLE_CAST (MonoReflectionType, NULL_HANDLE));
 
 	MonoDomain *domain = MONO_HANDLE_DOMAIN (ref_type);
@@ -7292,7 +7302,7 @@ ves_icall_RuntimeType_MakePointerType (MonoReflectionTypeHandle ref_type, MonoEr
 	mono_class_init_checked (klass, error);
 	return_val_if_nok (error, MONO_HANDLE_CAST (MonoReflectionType, NULL_HANDLE));
 
-	check_for_invalid_type (klass, error);
+	check_for_invalid_byref_or_pointer_type (klass, error);
 	return_val_if_nok (error, MONO_HANDLE_CAST (MonoReflectionType, NULL_HANDLE));
 
 	MonoClass *pklass = mono_class_create_ptr (type);
@@ -7523,6 +7533,7 @@ ves_icall_Remoting_RealProxy_InternalGetProxyType (MonoTransparentProxyHandle tp
 
 /* System.Environment */
 
+#ifndef ENABLE_NETCORE
 MonoStringHandle
 ves_icall_System_Environment_get_UserName (MonoError *error)
 {
@@ -7606,6 +7617,7 @@ ves_icall_System_Environment_get_Platform (void)
 {
 	return mono_icall_get_platform ();
 }
+#endif /* !ENABLE_NETCORE */
 
 #ifndef HOST_WIN32
 static MonoStringHandle
diff --git a/src/mono/mono/metadata/marshal.c b/src/mono/mono/metadata/marshal.c
index fe74f17444e9c3..91358142a40b17 100644
--- a/src/mono/mono/metadata/marshal.c
+++ b/src/mono/mono/metadata/marshal.c
@@ -3979,9 +3979,13 @@ type_is_blittable (MonoType *type)
 	case MONO_TYPE_U:
 	case MONO_TYPE_PTR:
 	case MONO_TYPE_FNPTR:
+	case MONO_TYPE_VOID:
 		return TRUE;
-	default:
-		return m_class_is_blittable (mono_class_from_mono_type_internal (type));
+	default: {
+		MonoClass *klass = mono_class_from_mono_type_internal (type);
+		mono_class_init_sizes (klass);
+		return m_class_is_blittable (klass);
+	}
 	}
 }
 
diff --git a/src/mono/mono/metadata/mono-config.c b/src/mono/mono/metadata/mono-config.c
index f0940187e1fd52..df9cf248efe32f 100644
--- a/src/mono/mono/metadata/mono-config.c
+++ b/src/mono/mono/metadata/mono-config.c
@@ -666,8 +666,7 @@ mono_config_for_assembly_internal (MonoImage *assembly)
 	MONO_REQ_GC_UNSAFE_MODE;
 
 	MonoConfigParseState state = {NULL};
-	int i;
-	char *aname, *cfg, *cfg_name;
+	char *cfg_name;
 	const char *bundled_config;
 	
 	state.assembly = assembly;
@@ -684,6 +683,7 @@ mono_config_for_assembly_internal (MonoImage *assembly)
 
 #ifndef DISABLE_CFGDIR_CONFIG
 	int got_it = 0;
+	char *aname, *cfg;
 	cfg_name = g_strdup_printf ("%s.config", mono_image_get_name (assembly));
 	const char *cfg_dir = mono_get_config_dir ();
 	if (!cfg_dir) {
@@ -691,7 +691,7 @@ mono_config_for_assembly_internal (MonoImage *assembly)
 		return;
 	}
 
-	for (i = 0; (aname = get_assembly_filename (assembly, i)) != NULL; ++i) {
+	for (int i = 0; (aname = get_assembly_filename (assembly, i)) != NULL; ++i) {
 		cfg = g_build_filename (cfg_dir, "mono", "assemblies", aname, cfg_name, (const char*)NULL);
 		got_it += mono_config_parse_file_with_context (&state, cfg);
 		g_free (cfg);
diff --git a/src/mono/mono/metadata/native-library.c b/src/mono/mono/metadata/native-library.c
index b2d5712c813c13..ff2c6cc8d64711 100644
--- a/src/mono/mono/metadata/native-library.c
+++ b/src/mono/mono/metadata/native-library.c
@@ -11,13 +11,25 @@
 #include "mono/utils/mono-logger-internals.h"
 #include "mono/utils/mono-path.h"
 #include "mono/metadata/native-library.h"
+#include "mono/metadata/custom-attrs-internals.h"
 
 #ifdef ENABLE_NETCORE
 static int pinvoke_search_directories_count;
 static char **pinvoke_search_directories;
 
-// In DllImportSearchPath enum, bit 0x2 represents AssemblyDirectory. It is not passed on and is instead handled by the runtime.
-#define DLLIMPORTSEARCHPATH_ASSEMBLYDIRECTORY 0x2
+// sync with src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/DllImportSearchPath.cs
+typedef enum
+{
+	DLLIMPORTSEARCHPATH_LEGACY_BEHAVIOR = 0x0, // when no other flags are present, search the application directory and then call LoadLibraryEx with LOAD_WITH_ALTERED_SEARCH_PATH
+	DLLIMPORTSEARCHPATH_USE_DLL_DIRECTORY_FOR_DEPENDENCIES = 0x100,
+	DLLIMPORTSEARCHPATH_APPLICATION_DIRECTORY = 0x200,
+	DLLIMPORTSEARCHPATH_USER_DIRECTORIES = 0x400,
+	DLLIMPORTSEARCHPATH_SYSTEM32 = 0x800,
+	DLLIMPORTSEARCHPATH_SAFE_DIRECTORIES = 0x1000,
+	DLLIMPORTSEARCHPATH_ASSEMBLY_DIRECTORY = 0x2, // search the assembly directory first regardless of platform, not passed on to LoadLibraryEx
+} DllImportSearchPath;
+//static const int DLLIMPORTSEARCHPATH_LOADLIBRARY_FLAG_MASK = DLLIMPORTSEARCHPATH_USE_DLL_DIRECTORY_FOR_DEPENDENCIES | DLLIMPORTSEARCHPATH_APPLICATION_DIRECTORY |
+//                                                             DLLIMPORTSEARCHPATH_USER_DIRECTORIES | DLLIMPORTSEARCHPATH_SYSTEM32 | DLLIMPORTSEARCHPATH_SAFE_DIRECTORIES;
 
 // This lock may be taken within an ALC lock, and should never be the other way around.
 static MonoCoopMutex native_library_module_lock;
@@ -58,6 +70,7 @@ GENERATE_GET_CLASS_WITH_CACHE (appdomain_unloaded_exception, "System", "AppDomai
 GENERATE_TRY_GET_CLASS_WITH_CACHE (appdomain_unloaded_exception, "System", "AppDomainUnloadedException")
 #ifdef ENABLE_NETCORE
 GENERATE_GET_CLASS_WITH_CACHE (native_library, "System.Runtime.InteropServices", "NativeLibrary");
+static GENERATE_TRY_GET_CLASS_WITH_CACHE (dllimportsearchpath_attribute, "System.Runtime.InteropServices", "DefaultDllImportSearchPathsAttribute");
 #endif
 
 #ifndef DISABLE_DLLMAP
@@ -504,7 +517,6 @@ static MonoDl *
 netcore_probe_for_module (MonoImage *image, const char *file_name, int flags)
 {
 	MonoDl *module = NULL;
-	gboolean search_assembly_dir = flags & DLLIMPORTSEARCHPATH_ASSEMBLYDIRECTORY;
 
 	// Try without any path additions
 	module = netcore_probe_for_module_variations (NULL, file_name);
@@ -514,13 +526,15 @@ netcore_probe_for_module (MonoImage *image, const char *file_name, int flags)
 		module = netcore_probe_for_module_variations (pinvoke_search_directories[i], file_name);
 
 	// Check the assembly directory if the search flag is set and the image exists
-	if (search_assembly_dir && image != NULL && module == NULL) {
+	if (flags & DLLIMPORTSEARCHPATH_ASSEMBLY_DIRECTORY && image != NULL && module == NULL) {
 		char *mdirname = g_path_get_dirname (image->filename);
 		if (mdirname)
 			module = netcore_probe_for_module_variations (mdirname, file_name);
 		g_free (mdirname);
 	}
 
+	// TODO: Pass remaining flags on to LoadLibraryEx on Windows where appropriate, see https://docs.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.dllimportsearchpath?view=netcore-3.1
+
 	return module;
 }
 
@@ -835,6 +849,50 @@ netcore_lookup_native_library (MonoAssemblyLoadContext *alc, MonoImage *image, c
 	return module;
 }
 
+static int
+get_dllimportsearchpath_flags (MonoCustomAttrInfo *cinfo)
+{
+	ERROR_DECL (error);
+	MonoCustomAttrEntry *attr = NULL;
+	MonoClass *dllimportsearchpath = mono_class_try_get_dllimportsearchpath_attribute_class ();
+	int idx;
+	int flags;
+
+	if (!dllimportsearchpath)
+		return -1;
+	if (!cinfo)
+		return -2;
+
+	for (idx = 0; idx < cinfo->num_attrs; ++idx) {
+		MonoClass *ctor_class = cinfo->attrs [idx].ctor->klass;
+		if (ctor_class == dllimportsearchpath) {
+			attr = &cinfo->attrs [idx];
+			break;
+		}
+	}
+	if (!attr)
+		return -3;
+
+	gpointer *typed_args, *named_args;
+	CattrNamedArg *arginfo;
+	int num_named_args;
+
+	mono_reflection_create_custom_attr_data_args_noalloc (m_class_get_image (attr->ctor->klass), attr->ctor, attr->data, attr->data_size,
+															&typed_args, &named_args, &num_named_args, &arginfo, error);
+	if (!is_ok (error)) {
+		mono_error_cleanup (error);
+		return -4;
+	}
+
+	flags = *(gint32*)typed_args [0];
+	g_free (typed_args [0]);
+	g_free (typed_args);
+	g_free (named_args);
+	g_free (arginfo);
+
+	return flags;
+}
+
 #else // ENABLE_NETCORE
 
 static MonoDl *
@@ -1174,6 +1232,8 @@ lookup_pinvoke_call_impl (MonoMethod *method, MonoLookupPInvokeStatus *status_ou
 	MonoImage *image = m_class_get_image (method->klass);
 #ifdef ENABLE_NETCORE
 	MonoAssemblyLoadContext *alc = mono_image_get_alc (image);
+	MonoCustomAttrInfo *cinfo;
+	int flags;
 #endif
 	MonoMethodPInvoke *piinfo = (MonoMethodPInvoke *)method;
 	MonoTableInfo *tables = image->tables;
@@ -1240,8 +1300,26 @@ lookup_pinvoke_call_impl (MonoMethod *method, MonoLookupPInvokeStatus *status_ou
 #ifndef HOST_WIN32
 retry_with_libcoreclr:
 #endif
-	// FIXME: these flags are not getting passed correctly
-	module = netcore_lookup_native_library (alc, image, new_scope, 0);
+	{
+		ERROR_DECL (local_error);
+		cinfo = mono_custom_attrs_from_method_checked (method, local_error);
+		mono_error_cleanup (local_error);
+	}
+	flags = get_dllimportsearchpath_flags (cinfo);
+	if (cinfo && !cinfo->cached)
+		mono_custom_attrs_free (cinfo);
+
+	if (flags < 0) {
+		ERROR_DECL (local_error);
+		cinfo = mono_custom_attrs_from_assembly_checked (m_class_get_image (method->klass)->assembly, TRUE, local_error);
+		mono_error_cleanup (local_error);
+		flags = get_dllimportsearchpath_flags (cinfo);
+		if (cinfo && !cinfo->cached)
+			mono_custom_attrs_free (cinfo);
+	}
+	if (flags < 0)
+		flags = 0;
+	module = netcore_lookup_native_library (alc, image, new_scope, flags);
 #else
 	module = legacy_lookup_native_library (image, new_scope);
 #endif
@@ -1496,7 +1574,7 @@ ves_icall_System_Runtime_InteropServices_NativeLibrary_LoadByName (MonoStringHan
 	goto_if_nok (error, leave);
 
 	// FIXME: implement search flag defaults properly
-	module = netcore_probe_for_module (image, lib_name, has_search_flag ? search_flag : 0x2);
+	module = netcore_probe_for_module (image, lib_name, has_search_flag ? search_flag : DLLIMPORTSEARCHPATH_ASSEMBLY_DIRECTORY);
 	if (!module)
 		mono_error_set_generic_error (error, "System", "DllNotFoundException", "%s", lib_name);
 	goto_if_nok (error, leave);
@@ -1601,4 +1679,3 @@ mono_loader_save_bundled_library (int fd, uint64_t offset, uint64_t size, const
 	
 	g_free (buffer);
 }
-
diff --git a/src/mono/mono/metadata/object-offsets.h b/src/mono/mono/metadata/object-offsets.h
index 82f901714646ef..f11bbf58e82bfb 100644
--- a/src/mono/mono/metadata/object-offsets.h
+++ b/src/mono/mono/metadata/object-offsets.h
@@ -167,11 +167,13 @@ DECL_OFFSET(MonoJitTlsData, stack_restore_ctx)
 DECL_OFFSET(MonoGSharedVtMethodRuntimeInfo, locals_size)
 DECL_OFFSET(MonoGSharedVtMethodRuntimeInfo, entries) //XXX more to fix here
 
+#if !defined(ENABLE_NETCORE)
 DECL_OFFSET(MonoContinuation, stack_used_size)
 DECL_OFFSET(MonoContinuation, saved_stack)
 DECL_OFFSET(MonoContinuation, return_sp)
 DECL_OFFSET(MonoContinuation, lmf)
 DECL_OFFSET(MonoContinuation, return_ip)
+#endif
 
 DECL_OFFSET(MonoDelegateTrampInfo, method)
 DECL_OFFSET(MonoDelegateTrampInfo, invoke_impl)
@@ -249,6 +251,9 @@ DECL_OFFSET(MonoLMF, ebp)
 DECL_OFFSET(MonoLMF, eip)
 DECL_OFFSET(MonoLMF, gregs)
 DECL_OFFSET(MonoLMF, fregs)
+#elif defined(TARGET_RISCV)
+DECL_OFFSET(MonoContext, gregs)
+DECL_OFFSET(MonoContext, fregs)
 #endif
 
 // Shared architecture offfsets
diff --git a/src/mono/mono/metadata/object.c b/src/mono/mono/metadata/object.c
index 71e7377e798272..5f0baa667721b3 100644
--- a/src/mono/mono/metadata/object.c
+++ b/src/mono/mono/metadata/object.c
@@ -5737,8 +5737,13 @@ mono_runtime_try_invoke_array (MonoMethod *method, void *obj, MonoArray *params,
 				mono_error_assert_ok (error);
 			MONO_STATIC_POINTER_INIT_END (MonoMethod, box_method)
 
-			g_assert (res->vtable->klass == mono_defaults.int_class);
-			box_args [0] = ((MonoIntPtr*)res)->m_value;
+			if (res) {
+				g_assert (res->vtable->klass == mono_defaults.int_class);
+				box_args [0] = ((MonoIntPtr*)res)->m_value;
+			} else {
+				g_assert (sig->ret->byref);
+				box_args [0] = NULL;
+			}
 			if (sig->ret->byref) {
 				// byref is already unboxed by the invoke code
 				MonoType *tmpret = mono_metadata_type_dup (NULL, sig->ret);
diff --git a/src/mono/mono/metadata/reflection.c b/src/mono/mono/metadata/reflection.c
index c28ce829a49908..09851b355a1f45 100644
--- a/src/mono/mono/metadata/reflection.c
+++ b/src/mono/mono/metadata/reflection.c
@@ -570,7 +570,7 @@ mono_type_get_object_checked (MonoDomain *domain, MonoType *type, MonoError *err
 	res->type = type;
 	mono_g_hash_table_insert_internal (domain->type_hash, type, res);
 
-	if (type->type == MONO_TYPE_VOID)
+	if (type->type == MONO_TYPE_VOID && !type->byref)
 		domain->typeof_void = (MonoObject*)res;
 
 	mono_domain_unlock (domain);
diff --git a/src/mono/mono/metadata/sgen-toggleref.c b/src/mono/mono/metadata/sgen-toggleref.c
index 831d0aaccfc19e..9a5d98e29339db 100644
--- a/src/mono/mono/metadata/sgen-toggleref.c
+++ b/src/mono/mono/metadata/sgen-toggleref.c
@@ -19,6 +19,7 @@
 #include "sgen-toggleref.h"
 #include "sgen/sgen-client.h"
 
+#ifndef DISABLE_SGEN_TOGGLEREF
 
 /*only one of the two can be non null at a given time*/
 typedef struct {
@@ -234,4 +235,18 @@ sgen_register_test_toggleref_callback (void)
 	toggleref_callback = test_toggleref_callback;
 }
 
+#else
+
+void
+mono_gc_toggleref_register_callback (MonoToggleRefStatus (*proccess_toggleref) (MonoObject *obj))
+{
+}
+
+void
+mono_gc_toggleref_add (MonoObject *object, mono_bool strong_ref)
+{
+}
+
+#endif
+
 #endif
diff --git a/src/mono/mono/mini/aot-compiler.c b/src/mono/mono/mini/aot-compiler.c
index 7c76e4ce154b10..5e8d1d3ab7345a 100644
--- a/src/mono/mono/mini/aot-compiler.c
+++ b/src/mono/mono/mini/aot-compiler.c
@@ -12296,6 +12296,9 @@ compile_asm (MonoAotCompile *acfg)
 #elif defined(TARGET_AMD64) && defined(TARGET_MACH)
 #define LD_NAME "clang"
 #define LD_OPTIONS "--shared"
+#elif defined(TARGET_ARM64) && defined(TARGET_OSX)
+#define LD_NAME "clang"
+#define LD_OPTIONS "--shared"
 #elif defined(TARGET_WIN32_MSVC)
 #define LD_NAME "link.exe"
 #define LD_OPTIONS "/DLL /MACHINE:X64 /NOLOGO /INCREMENTAL:NO"
diff --git a/src/mono/mono/mini/debugger-agent.c b/src/mono/mono/mini/debugger-agent.c
index f76e887e6db885..5b6d729a3390d9 100644
--- a/src/mono/mono/mini/debugger-agent.c
+++ b/src/mono/mono/mini/debugger-agent.c
@@ -1085,18 +1085,18 @@ finish_agent_init (gboolean on_startup)
 		// FIXME: Generated address
 		// FIXME: Races with transport_connect ()
 
-		char *argv [ ] = {
-			agent_config.launch,
-			agent_config.transport,
-			agent_config.address,
-			NULL
-		};
 #ifdef G_OS_WIN32
 		// Nothing. FIXME? g_spawn_async_with_pipes is easy enough to provide for Windows if needed.
 #elif !HAVE_G_SPAWN
 		g_printerr ("g_spawn_async_with_pipes not supported on this platform\n");
 		exit (1);
 #else
+		char *argv [ ] = {
+			agent_config.launch,
+			agent_config.transport,
+			agent_config.address,
+			NULL
+		};
 		int res = g_spawn_async_with_pipes (NULL, argv, NULL, (GSpawnFlags)0, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
 		if (!res) {
 			g_printerr ("Failed to execute '%s'.\n", agent_config.launch);
@@ -3598,6 +3598,10 @@ dbg_path_get_basename (const char *filename)
 	return g_strdup (&r[1]);
 }
 
+static GENERATE_TRY_GET_CLASS_WITH_CACHE(hidden_klass, "System.Diagnostics", "DebuggerHiddenAttribute")
+static GENERATE_TRY_GET_CLASS_WITH_CACHE(step_through_klass, "System.Diagnostics", "DebuggerStepThroughAttribute")
+static GENERATE_TRY_GET_CLASS_WITH_CACHE(non_user_klass, "System.Diagnostics", "DebuggerNonUserCodeAttribute")
+
 static void
 init_jit_info_dbg_attrs (MonoJitInfo *ji)
 {
@@ -3607,27 +3611,19 @@ init_jit_info_dbg_attrs (MonoJitInfo *ji)
 	if (ji->dbg_attrs_inited)
 		return;
 
-	MONO_STATIC_POINTER_INIT (MonoClass, hidden_klass)
-		hidden_klass = mono_class_load_from_name (mono_defaults.corlib, "System.Diagnostics", "DebuggerHiddenAttribute");
-	MONO_STATIC_POINTER_INIT_END (MonoClass, hidden_klass)
-
-
-	MONO_STATIC_POINTER_INIT (MonoClass, step_through_klass)
-		step_through_klass = mono_class_load_from_name (mono_defaults.corlib, "System.Diagnostics", "DebuggerStepThroughAttribute");
-	MONO_STATIC_POINTER_INIT_END (MonoClass, step_through_klass)
-
-	MONO_STATIC_POINTER_INIT (MonoClass, non_user_klass)
-		non_user_klass = mono_class_load_from_name (mono_defaults.corlib, "System.Diagnostics", "DebuggerNonUserCodeAttribute");
-	MONO_STATIC_POINTER_INIT_END (MonoClass, non_user_klass)
+	// NOTE: The following Debugger attributes may not exist if they are trimmed away by the ILLinker
+	MonoClass *hidden_klass = mono_class_try_get_hidden_klass_class ();
+	MonoClass *step_through_klass = mono_class_try_get_step_through_klass_class ();
+	MonoClass *non_user_klass = mono_class_try_get_non_user_klass_class ();
 
 	ainfo = mono_custom_attrs_from_method_checked (jinfo_get_method (ji), error);
 	mono_error_cleanup (error); /* FIXME don't swallow the error? */
 	if (ainfo) {
-		if (mono_custom_attrs_has_attr (ainfo, hidden_klass))
+		if (hidden_klass && mono_custom_attrs_has_attr (ainfo, hidden_klass))
 			ji->dbg_hidden = TRUE;
-		if (mono_custom_attrs_has_attr (ainfo, step_through_klass))
+		if (step_through_klass && mono_custom_attrs_has_attr (ainfo, step_through_klass))
 			ji->dbg_step_through = TRUE;
-		if (mono_custom_attrs_has_attr (ainfo, non_user_klass))
+		if (non_user_klass && mono_custom_attrs_has_attr (ainfo, non_user_klass))
 			ji->dbg_non_user_code = TRUE;
 		mono_custom_attrs_free (ainfo);
 	}
@@ -3635,9 +3631,9 @@ init_jit_info_dbg_attrs (MonoJitInfo *ji)
 	ainfo = mono_custom_attrs_from_class_checked (jinfo_get_method (ji)->klass, error);
 	mono_error_cleanup (error); /* FIXME don't swallow the error? */
 	if (ainfo) {
-		if (mono_custom_attrs_has_attr (ainfo, step_through_klass))
+		if (step_through_klass && mono_custom_attrs_has_attr (ainfo, step_through_klass))
 			ji->dbg_step_through = TRUE;
-		if (mono_custom_attrs_has_attr (ainfo, non_user_klass))
+		if (non_user_klass && mono_custom_attrs_has_attr (ainfo, non_user_klass))
 			ji->dbg_non_user_code = TRUE;
 		mono_custom_attrs_free (ainfo);
 	}
diff --git a/src/mono/mono/mini/driver.c b/src/mono/mono/mini/driver.c
index 322a23cef651a2..aa72d2af850a1a 100644
--- a/src/mono/mono/mini/driver.c
+++ b/src/mono/mono/mini/driver.c
@@ -2006,10 +2006,6 @@ apply_root_domain_configuration_file_bindings (MonoDomain *domain, char *root_do
 static void
 mono_check_interp_supported (void)
 {
-#ifdef DISABLE_INTERPRETER
-	g_error ("Mono IL interpreter support is missing\n");
-#endif
-
 #ifdef MONO_CROSS_COMPILE
 	g_error ("--interpreter on cross-compile runtimes not supported\n");
 #endif
@@ -2999,7 +2995,7 @@ mono_runtime_set_execution_mode_full (int mode, gboolean override)
 		mono_llvm_only = TRUE;
 		break;
 
-	case MONO_EE_MODE_INTERP:
+	case MONO_AOT_MODE_INTERP_ONLY:
 		mono_check_interp_supported ();
 		mono_use_interpreter = TRUE;
 
diff --git a/src/mono/mono/mini/exceptions-amd64.c b/src/mono/mono/mini/exceptions-amd64.c
index f795a06b1eca83..8be488d1309e94 100644
--- a/src/mono/mono/mini/exceptions-amd64.c
+++ b/src/mono/mono/mini/exceptions-amd64.c
@@ -1905,7 +1905,7 @@ void mono_arch_code_chunk_destroy (void *chunk)
 }
 #endif /* MONO_ARCH_HAVE_UNWIND_TABLE */
 
-#if MONO_SUPPORT_TASKLETS && !defined(DISABLE_JIT)
+#if MONO_SUPPORT_TASKLETS && !defined(DISABLE_JIT) && !defined(ENABLE_NETCORE)
 MonoContinuationRestore
 mono_tasklets_arch_restore (void)
 {
@@ -1956,7 +1956,7 @@ mono_tasklets_arch_restore (void)
 	saved = start;
 	return (MonoContinuationRestore)saved;
 }
-#endif /* MONO_SUPPORT_TASKLETS && !defined(DISABLE_JIT) */
+#endif /* MONO_SUPPORT_TASKLETS && !defined(DISABLE_JIT) && !defined(ENABLE_NETCORE) */
 
 /*
  * mono_arch_setup_resume_sighandler_ctx:
@@ -1975,14 +1975,14 @@ mono_arch_setup_resume_sighandler_ctx (MonoContext *ctx, gpointer func)
 	MONO_CONTEXT_SET_IP (ctx, func);
 }
 
-#if !MONO_SUPPORT_TASKLETS || defined(DISABLE_JIT)
+#if (!MONO_SUPPORT_TASKLETS || defined(DISABLE_JIT)) && !defined(ENABLE_NETCORE)
 MonoContinuationRestore
 mono_tasklets_arch_restore (void)
 {
 	g_assert_not_reached ();
 	return NULL;
 }
-#endif /* !MONO_SUPPORT_TASKLETS || defined(DISABLE_JIT) */
+#endif /* (!MONO_SUPPORT_TASKLETS || defined(DISABLE_JIT)) && !defined(ENABLE_NETCORE) */
 
 void
 mono_arch_undo_ip_adjustment (MonoContext *ctx)
diff --git a/src/mono/mono/mini/exceptions-arm64.c b/src/mono/mono/mini/exceptions-arm64.c
index 11cb6ccdd9d37f..3c06a2ac070d96 100644
--- a/src/mono/mono/mini/exceptions-arm64.c
+++ b/src/mono/mono/mini/exceptions-arm64.c
@@ -36,6 +36,8 @@ mono_arch_get_restore_context (MonoTrampInfo **info, gboolean aot)
 	size = 256;
 	code = start = mono_global_codeman_reserve (size);
 
+	MINI_BEGIN_CODEGEN ();
+
 	arm_movx (code, ARMREG_IP0, ARMREG_R0);
 	ctx_reg = ARMREG_IP0;
 
@@ -63,8 +65,8 @@ mono_arch_get_restore_context (MonoTrampInfo **info, gboolean aot)
 	arm_brk (code, 0);
 
 	g_assert ((code - start) < size);
-	mono_arch_flush_icache (start, code - start);
-	MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));
+
+	MINI_END_CODEGEN (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL);
 
 	if (info)
 		*info = mono_tramp_info_create ("restore_context", start, code - start, ji, unwind_ops);
@@ -106,6 +108,8 @@ mono_arch_get_call_filter (MonoTrampInfo **info, gboolean aot)
 	 * returning the value returned by the call.
 	 */
 
+	MINI_BEGIN_CODEGEN ();
+
 	/* Setup a frame */
 	arm_stpx_pre (code, ARMREG_FP, ARMREG_LR, ARMREG_SP, -frame_size);
 	arm_movspx (code, ARMREG_FP, ARMREG_SP);
@@ -152,8 +156,8 @@ mono_arch_get_call_filter (MonoTrampInfo **info, gboolean aot)
 	arm_retx (code, ARMREG_LR);
 
 	g_assert ((code - start) < size);
-	mono_arch_flush_icache (start, code - start);
-	MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));
+
+	MINI_END_CODEGEN (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL);
 
 	if (info)
 		*info = mono_tramp_info_create ("call_filter", start, code - start, ji, unwind_ops);
@@ -186,6 +190,8 @@ get_throw_trampoline (int size, gboolean corlib, gboolean rethrow, gboolean llvm
 	offset += num_fregs * 8;
 	frame_size = ALIGN_TO (offset, MONO_ARCH_FRAME_ALIGNMENT);
 
+	MINI_BEGIN_CODEGEN ();
+
 	/* Setup a frame */
 	arm_stpx_pre (code, ARMREG_FP, ARMREG_LR, ARMREG_SP, -frame_size);
 	arm_movspx (code, ARMREG_FP, ARMREG_SP);
@@ -254,8 +260,8 @@ get_throw_trampoline (int size, gboolean corlib, gboolean rethrow, gboolean llvm
 	arm_brk (code, 0x0);
 
 	g_assert ((code - start) < size);
-	mono_arch_flush_icache (start, code - start);
-	MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));
+
+	MINI_END_CODEGEN (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL);
 
 	if (info)
 		*info = mono_tramp_info_create (tramp_name, start, code - start, ji, unwind_ops);
@@ -329,9 +335,6 @@ mono_arch_exceptions_init (void)
 	GSList *tramps, *l;
 
 	if (mono_aot_only) {
-
-		// FIXME Macroize.
-
 		tramp = mono_aot_get_trampoline ("llvm_throw_corlib_exception_trampoline");
 		mono_register_jit_icall_info (&mono_get_jit_icall_info ()->mono_llvm_throw_corlib_exception_trampoline, tramp, "llvm_throw_corlib_exception_trampoline", NULL, TRUE, NULL);
 
@@ -340,7 +343,6 @@ mono_arch_exceptions_init (void)
 
 		tramp = mono_aot_get_trampoline ("llvm_resume_unwind_trampoline");
 		mono_register_jit_icall_info (&mono_get_jit_icall_info ()->mono_llvm_resume_unwind_trampoline, tramp, "llvm_resume_unwind_trampoline", NULL, TRUE, NULL);
-
 	} else {
 		tramps = mono_arm_get_exception_trampolines (FALSE);
 		for (l = tramps; l; l = l->next) {
diff --git a/src/mono/mono/mini/exceptions-riscv.c b/src/mono/mono/mini/exceptions-riscv.c
index a5ebedb6af5069..5c8983f801b5a2 100644
--- a/src/mono/mono/mini/exceptions-riscv.c
+++ b/src/mono/mono/mini/exceptions-riscv.c
@@ -12,14 +12,15 @@
 #ifndef DISABLE_JIT
 
 static gpointer
-nop_stub (void)
+nop_stub (unsigned int pattern)
 {
 	guint8 *code, *start;
 
 	start = code = mono_global_codeman_reserve (0x50);
 
-	/* nop */
-	riscv_addi (code, RISCV_X0, RISCV_X0, 0);
+	/* hang in debugger */
+	riscv_addi (code, RISCV_X0, RISCV_X0, pattern);
+	riscv_ebreak (code);
 
 	mono_arch_flush_icache (start, code - start);
 
@@ -29,43 +30,76 @@ nop_stub (void)
 gpointer
 mono_arch_get_restore_context (MonoTrampInfo **info, gboolean aot)
 {
-	*info = NULL;
-	return nop_stub ();
+	guint8 *start, *code;
+	MonoJumpInfo *ji = NULL;
+	GSList *unwind_ops = NULL;
+	int i, ctx_reg, size;
+
+	size = 512;
+	code = start = mono_global_codeman_reserve (size);
+
+	riscv_addi (code, RISCV_T0, RISCV_A0, 0);
+	ctx_reg = RISCV_T0;
+
+	/* Restore fregs */
+	for (i = 0; i < RISCV_N_FREGS; ++i)
+		riscv_flw (code, i, ctx_reg, MONO_STRUCT_OFFSET (MonoContext, fregs) + (i * sizeof (double)));
+
+	/* Restore gregs */
+	for (i = 0; i < RISCV_N_FREGS; ++i) {
+		if (i == ctx_reg)
+			continue;
+		riscv_ld (code, i, ctx_reg, MONO_STRUCT_OFFSET (MonoContext, gregs) + (i * sizeof (double)));
+	}
+
+	riscv_ld (code, ctx_reg, ctx_reg, MONO_STRUCT_OFFSET (MonoContext, gregs) + (RISCV_ZERO * sizeof (double)));
+	riscv_jalr (code, RISCV_ZERO, ctx_reg, 0);
+	/* Not reached */
+	riscv_ebreak (code);
+
+	g_assert ((code - start) < size);
+	mono_arch_flush_icache (start, code - start);
+	MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));
+
+	if (info)
+		*info = mono_tramp_info_create ("restore_context", start, code - start, ji, unwind_ops);
+
+	return start;
 }
 
 gpointer
 mono_arch_get_call_filter (MonoTrampInfo **info, gboolean aot)
 {
 	*info = NULL;
-	return nop_stub ();
+	return nop_stub (0x37);
 }
 
 gpointer
 mono_arch_get_throw_exception (MonoTrampInfo **info, gboolean aot)
 {
 	*info = NULL;
-	return nop_stub ();
+	return nop_stub (0x77);
 }
 
 gpointer
 mono_arch_get_rethrow_exception (MonoTrampInfo **info, gboolean aot)
 {
 	*info = NULL;
-	return nop_stub ();
+	return nop_stub (0x88);
 }
 
 gpointer
 mono_arch_get_rethrow_preserve_exception (MonoTrampInfo **info, gboolean aot)
 {
 	*info = NULL;
-	return nop_stub ();
+	return nop_stub (0x99);
 }
 
 gpointer
 mono_arch_get_throw_corlib_exception (MonoTrampInfo **info, gboolean aot)
 {
 	*info = NULL;
-	return nop_stub ();
+	return nop_stub (0xaa);
 }
 
 #else
@@ -125,7 +159,63 @@ mono_arch_unwind_frame (MonoDomain *domain, MonoJitTlsData *jit_tls, MonoJitInfo
                         MonoContext *ctx, MonoContext *new_ctx, MonoLMF **lmf,
                         host_mgreg_t **save_locations, StackFrameInfo *frame)
 {
-	NOT_IMPLEMENTED;
+	gpointer ip = MONO_CONTEXT_GET_IP (ctx);
+
+	memset (frame, 0, sizeof (StackFrameInfo));
+	frame->ji = ji;
+
+	*new_ctx = *ctx;
+
+	if (ji != NULL) {
+		NOT_IMPLEMENTED;
+		host_mgreg_t regs [MONO_MAX_IREGS + 12 + 1];
+		guint8 *cfa;
+		guint32 unwind_info_len;
+		guint8 *unwind_info;
+
+
+		if (ji->is_trampoline)
+			frame->type = FRAME_TYPE_TRAMPOLINE;
+		else
+			frame->type = FRAME_TYPE_MANAGED;
+
+		unwind_info = mono_jinfo_get_unwind_info (ji, &unwind_info_len);
+
+		memcpy (regs, &new_ctx->gregs, sizeof (host_mgreg_t) * 32);
+
+		/* f8..f9 & f18..f27 are callee saved */
+		for (int i = 0; i < 2; i++)
+			(regs + MONO_MAX_IREGS) [i] = *((host_mgreg_t*)&new_ctx->fregs [RISCV_F8 + i]);
+		for (int i = 0; i < 10; i++)
+			(regs + MONO_MAX_IREGS) [i] = *((host_mgreg_t*)&new_ctx->fregs [RISCV_F18 + i]);
+
+		gboolean success = mono_unwind_frame (unwind_info, unwind_info_len, (guint8*)ji->code_start,
+						   (guint8*)ji->code_start + ji->code_size,
+						   (guint8*)ip, NULL, regs, MONO_MAX_IREGS + 8,
+						   save_locations, MONO_MAX_IREGS, (guint8**)&cfa);
+
+		if (!success)
+			return FALSE;
+
+		memcpy (&new_ctx->gregs, regs, sizeof (host_mgreg_t) * 32);
+		for (int i = 0; i < 2; i++)
+			*((host_mgreg_t*)&new_ctx->fregs [RISCV_F8 + i]) = (regs + MONO_MAX_IREGS) [i];
+		for (int i = 0; i < 10; i++)
+			*((host_mgreg_t*)&new_ctx->fregs [RISCV_F18 + i]) = (regs + MONO_MAX_IREGS) [i];
+
+		new_ctx->gregs [RISCV_SP] = (host_mgreg_t)(gsize)cfa;
+
+		if (*lmf)
+			NOT_IMPLEMENTED;
+
+		/* we substract 1, so that the IP points into the call instruction */
+		new_ctx->gregs [RISCV_ZERO]--;
+
+		return TRUE;
+	} else if (*lmf) {
+		NOT_IMPLEMENTED;
+	}
+
 	return FALSE;
 }
 
@@ -177,11 +267,11 @@ mono_arch_setup_resume_sighandler_ctx (MonoContext *ctx, gpointer func)
 void
 mono_arch_undo_ip_adjustment (MonoContext *context)
 {
-	NOT_IMPLEMENTED;
+	context->gregs[RISCV_ZERO]++;
 }
 
 void
 mono_arch_do_ip_adjustment (MonoContext *context)
 {
-	g_assert_not_reached ();
+	context->gregs[RISCV_ZERO]--;
 }
diff --git a/src/mono/mono/mini/exceptions-x86.c b/src/mono/mono/mini/exceptions-x86.c
index a0f79a71426caa..ef9927577e6a25 100644
--- a/src/mono/mono/mini/exceptions-x86.c
+++ b/src/mono/mono/mini/exceptions-x86.c
@@ -1175,7 +1175,7 @@ mono_arch_handle_altstack_exception (void *sigctx, MONO_SIG_HANDLER_INFO_TYPE *s
 #endif
 }
 
-#if MONO_SUPPORT_TASKLETS
+#if MONO_SUPPORT_TASKLETS && !defined(ENABLE_NETCORE)
 MonoContinuationRestore
 mono_tasklets_arch_restore (void)
 {
diff --git a/src/mono/mono/mini/helpers.c b/src/mono/mono/mini/helpers.c
index 3ceffe6f13765c..b62361ed532a15 100644
--- a/src/mono/mono/mini/helpers.c
+++ b/src/mono/mono/mini/helpers.c
@@ -263,7 +263,7 @@ mono_disassemble_code (MonoCompile *cfg, guint8 *code, int size, char *id)
 
 	fflush (stdout);
 
-#if defined(__arm__) || defined(__aarch64__)
+#if (defined(__arm__) || defined(__aarch64__)) && !defined(TARGET_OSX)
 	/* 
 	 * The arm assembler inserts ELF directives instructing objdump to display 
 	 * everything as data.
diff --git a/src/mono/mono/mini/interp/interp.c b/src/mono/mono/mini/interp/interp.c
index d107b8d1b541d9..53d20e1997c8d7 100644
--- a/src/mono/mono/mini/interp/interp.c
+++ b/src/mono/mono/mini/interp/interp.c
@@ -2385,7 +2385,6 @@ init_jit_call_info (InterpMethod *rmethod, MonoError *error)
 static MONO_NEVER_INLINE void
 do_jit_call (stackval *sp, unsigned char *vt_sp, InterpFrame *frame, InterpMethod *rmethod, MonoError *error)
 {
-	MonoMethodSignature *sig;
 	guint8 res_buf [256];
 	MonoLMFExt ext;
 	JitCallInfo *cinfo;
@@ -2402,8 +2401,6 @@ do_jit_call (stackval *sp, unsigned char *vt_sp, InterpFrame *frame, InterpMetho
 	}
 	cinfo = (JitCallInfo*)rmethod->jit_call_info;
 
-	sig = cinfo->sig;
-
 	/*
 	 * Convert the arguments on the interpeter stack to the format expected by the gsharedvt_out wrapper.
 	 */
@@ -4592,31 +4589,37 @@ interp_exec_method (InterpFrame *frame, ThreadContext *context, FrameClauseArgs
 			MINT_IN_BREAK;
 		}
 		MINT_IN_CASE(MINT_STIND_REF) 
+			NULL_CHECK (sp [-2].data.p);
 			++ip;
 			sp -= 2;
 			mono_gc_wbarrier_generic_store_internal (sp->data.p, sp [1].data.o);
 			MINT_IN_BREAK;
 		MINT_IN_CASE(MINT_STIND_I1)
+			NULL_CHECK (sp [-2].data.p);
 			++ip;
 			sp -= 2;
 			* (gint8 *) sp->data.p = (gint8)sp[1].data.i;
 			MINT_IN_BREAK;
 		MINT_IN_CASE(MINT_STIND_I2)
+			NULL_CHECK (sp [-2].data.p);
 			++ip;
 			sp -= 2;
 			* (gint16 *) sp->data.p = (gint16)sp[1].data.i;
 			MINT_IN_BREAK;
 		MINT_IN_CASE(MINT_STIND_I4)
+			NULL_CHECK (sp [-2].data.p);
 			++ip;
 			sp -= 2;
 			* (gint32 *) sp->data.p = sp[1].data.i;
 			MINT_IN_BREAK;
 		MINT_IN_CASE(MINT_STIND_I)
+			NULL_CHECK (sp [-2].data.p);
 			++ip;
 			sp -= 2;
 			* (mono_i *) sp->data.p = (mono_i)sp[1].data.p;
 			MINT_IN_BREAK;
 		MINT_IN_CASE(MINT_STIND_I8)
+			NULL_CHECK (sp [-2].data.p);
 			++ip;
 			sp -= 2;
 #ifdef NO_UNALIGNED_ACCESS
@@ -4627,11 +4630,13 @@ interp_exec_method (InterpFrame *frame, ThreadContext *context, FrameClauseArgs
 			* (gint64 *) sp->data.p = sp[1].data.l;
 			MINT_IN_BREAK;
 		MINT_IN_CASE(MINT_STIND_R4)
+			NULL_CHECK (sp [-2].data.p);
 			++ip;
 			sp -= 2;
 			* (float *) sp->data.p = sp[1].data.f_r4;
 			MINT_IN_BREAK;
 		MINT_IN_CASE(MINT_STIND_R8)
+			NULL_CHECK (sp [-2].data.p);
 			++ip;
 			sp -= 2;
 #ifdef NO_UNALIGNED_ACCESS
@@ -5318,6 +5323,13 @@ interp_exec_method (InterpFrame *frame, ThreadContext *context, FrameClauseArgs
 			++ip;
 			MINT_IN_BREAK;
 		}
+		MINT_IN_CASE(MINT_INTRINS_MEMORYMARSHAL_GETARRAYDATAREF) {
+			MonoObject* const o = sp [-1].data.o;
+			NULL_CHECK (o);
+			sp[-1].data.p = (guint8*)o + MONO_STRUCT_OFFSET (MonoArray, vector);
+			++ip;
+			MINT_IN_BREAK;
+		}
 		MINT_IN_CASE(MINT_INTRINS_ORDINAL_IGNORE_CASE_ASCII) {
 			sp--;
 			sp [-1].data.i = interp_intrins_ordinal_ignore_case_ascii ((guint32)sp [-1].data.i, (guint32)sp [0].data.i);
diff --git a/src/mono/mono/mini/interp/mintops.def b/src/mono/mono/mini/interp/mintops.def
index 488fc86dded31e..6e4d90fab787fa 100644
--- a/src/mono/mono/mini/interp/mintops.def
+++ b/src/mono/mono/mini/interp/mintops.def
@@ -795,6 +795,7 @@ OPDEF(MINT_INTRINS_RUNTIMEHELPERS_OBJECT_HAS_COMPONENT_SIZE, "intrins_runtimehel
 OPDEF(MINT_INTRINS_CLEAR_WITH_REFERENCES, "intrin_clear_with_references", 1, Pop2, Push0, MintOpNoArgs)
 OPDEF(MINT_INTRINS_MARVIN_BLOCK, "intrins_marvin_block", 1, Pop2, Push0, MintOpNoArgs)
 OPDEF(MINT_INTRINS_ASCII_CHARS_TO_UPPERCASE, "intrins_ascii_chars_to_uppercase", 1, Pop1, Push1, MintOpNoArgs)
+OPDEF(MINT_INTRINS_MEMORYMARSHAL_GETARRAYDATAREF, "intrins_memorymarshal_getarraydataref", 1, Pop1, Push1, MintOpNoArgs)
 OPDEF(MINT_INTRINS_ORDINAL_IGNORE_CASE_ASCII, "intrins_ordinal_ignore_case_ascii", 1, Pop2, Push1, MintOpNoArgs)
 OPDEF(MINT_INTRINS_64ORDINAL_IGNORE_CASE_ASCII, "intrins_64ordinal_ignore_case_ascii", 1, Pop2, Push1, MintOpNoArgs)
 OPDEF(MINT_INTRINS_U32_TO_DECSTR, "intrins_u32_to_decstr", 3, Pop1, Push1, MintOpNoArgs)
diff --git a/src/mono/mono/mini/interp/transform.c b/src/mono/mono/mini/interp/transform.c
index f0a333d04dcf79..b81d5f90742c69 100644
--- a/src/mono/mono/mini/interp/transform.c
+++ b/src/mono/mono/mini/interp/transform.c
@@ -1505,6 +1505,9 @@ interp_handle_intrinsics (TransformData *td, MonoMethod *target_method, MonoClas
 	} else if (in_corlib && !strcmp (klass_name_space, "System") && !strcmp (klass_name, "Marvin")) {
 		if (!strcmp (tm, "Block"))
 			*op = MINT_INTRINS_MARVIN_BLOCK;
+	} else if (in_corlib && !strcmp (klass_name_space, "System.Runtime.InteropServices") && !strcmp (klass_name, "MemoryMarshal")) {
+		if (!strcmp (tm, "GetArrayDataReference"))
+			*op = MINT_INTRINS_MEMORYMARSHAL_GETARRAYDATAREF;
 	} else if (in_corlib && !strcmp (klass_name_space, "System.Text.Unicode") && !strcmp (klass_name, "Utf16Utility")) {
 		if (!strcmp (tm, "ConvertAllAsciiCharsInUInt32ToUppercase"))
 			*op = MINT_INTRINS_ASCII_CHARS_TO_UPPERCASE;
@@ -1901,7 +1904,7 @@ interp_handle_intrinsics (TransformData *td, MonoMethod *target_method, MonoClas
 static MonoMethod*
 interp_transform_internal_calls (MonoMethod *method, MonoMethod *target_method, MonoMethodSignature *csignature, gboolean is_virtual)
 {
-	if (method->wrapper_type == MONO_WRAPPER_NONE && target_method != NULL) {
+	if (((method->wrapper_type == MONO_WRAPPER_NONE) || (method->wrapper_type == MONO_WRAPPER_DYNAMIC_METHOD)) && target_method != NULL) {
 		if (target_method->flags & METHOD_ATTRIBUTE_PINVOKE_IMPL)
 			target_method = mono_marshal_get_native_wrapper (target_method, FALSE, FALSE);
 		if (!is_virtual && target_method->iflags & METHOD_IMPL_ATTRIBUTE_SYNCHRONIZED)
@@ -4938,6 +4941,20 @@ generate_code (TransformData *td, MonoMethod *method, MonoMethodHeader *header,
 			klass = mini_get_class (method, token, generic_context);
 			CHECK_TYPELOAD (klass);
 
+			// Common in generic code:
+			// box T + unbox.any T -> nop
+            if ((td->last_ins->opcode == MINT_BOX || td->last_ins->opcode == MINT_BOX_VT) &&
+                (td->sp - 1)->klass == klass && !td->is_bb_start[in_offset]) {
+                gboolean is_vt = td->last_ins->opcode == MINT_BOX_VT;
+                interp_clear_ins(td, td->last_ins);
+                if (is_vt)
+                    PUSH_VT(td, mono_class_value_size(klass, NULL));
+                int mt = mint_type(m_class_get_byval_arg(klass));
+                SET_TYPE(td->sp - 1, stack_type[mt], klass);
+                td->ip += 5;
+                break;
+            }
+
 			if (mini_type_is_reference (m_class_get_byval_arg (klass))) {
 				int mt = mint_type (m_class_get_byval_arg (klass));
 				interp_handle_isinst (td, klass, FALSE);
diff --git a/src/mono/mono/mini/intrinsics.c b/src/mono/mono/mini/intrinsics.c
index 6f6d93bbe40761..cf8bcc936aaa8d 100644
--- a/src/mono/mono/mini/intrinsics.c
+++ b/src/mono/mono/mini/intrinsics.c
@@ -1948,6 +1948,34 @@ mini_emit_inst_for_method (MonoCompile *cfg, MonoMethod *cmethod, MonoMethodSign
 		}
 	}
 
+	if (in_corlib &&
+		!strcmp ("System", cmethod_klass_name_space) &&
+		!strcmp ("ThrowHelper", cmethod_klass_name) &&
+		!strcmp ("ThrowForUnsupportedVectorBaseType", cmethod->name)) {
+		/* The mono JIT can't optimize the body of this method away */
+		MonoGenericContext *ctx = mono_method_get_context (cmethod);
+		g_assert (ctx);
+		g_assert (ctx->method_inst);
+
+		MonoType *t = ctx->method_inst->type_argv [0];
+		switch (t->type) {
+		case MONO_TYPE_I1:
+		case MONO_TYPE_U1:
+		case MONO_TYPE_I2:
+		case MONO_TYPE_U2:
+		case MONO_TYPE_I4:
+		case MONO_TYPE_U4:
+		case MONO_TYPE_I8:
+		case MONO_TYPE_U8:
+		case MONO_TYPE_R4:
+		case MONO_TYPE_R8:
+			MONO_INST_NEW (cfg, ins, OP_NOP);
+			MONO_ADD_INS (cfg->cbb, ins);
+			return ins;
+		default:
+			break;
+		}
+	}
 #endif
 
 	ins = mono_emit_native_types_intrinsics (cfg, cmethod, fsig, args);
diff --git a/src/mono/mono/mini/jit.h b/src/mono/mono/mini/jit.h
index 011792c346b488..02639c95122de0 100644
--- a/src/mono/mono/mini/jit.h
+++ b/src/mono/mono/mini/jit.h
@@ -65,6 +65,8 @@ typedef enum {
 	MONO_AOT_MODE_INTERP_LLVMONLY,
 	/* Use only llvm compiled code, fall back to the interpeter */
 	MONO_AOT_MODE_LLVMONLY_INTERP,
+	/* Same as --interp */
+	MONO_AOT_MODE_INTERP_ONLY,
 	/* Sentinel value used internally by the runtime. We use a large number to avoid clashing with some internal values. */
 	MONO_AOT_MODE_LAST = 1000,
 } MonoAotMode;
diff --git a/src/mono/mono/mini/llvm-jit.cpp b/src/mono/mono/mini/llvm-jit.cpp
index 1e896419f0b48f..8307990a4e251d 100644
--- a/src/mono/mono/mini/llvm-jit.cpp
+++ b/src/mono/mono/mini/llvm-jit.cpp
@@ -247,7 +247,7 @@ struct MonoLLVMJIT {
 			void *sym = nullptr;
 			auto err = mono_dl_symbol (current, name, &sym);
 			if (!sym) {
-				outs () << "R: " << namestr << "\n";
+				outs () << "R: " << namestr << " " << err << "\n";
 			}
 			assert (sym);
 			return JITSymbol{(uint64_t)(gssize)sym, flags};
diff --git a/src/mono/mono/mini/method-to-ir.c b/src/mono/mono/mini/method-to-ir.c
index efcecb831ab9f1..6d1667ffcb02fa 100644
--- a/src/mono/mono/mini/method-to-ir.c
+++ b/src/mono/mono/mini/method-to-ir.c
@@ -5497,9 +5497,9 @@ is_supported_tailcall (MonoCompile *cfg, const guint8 *ip, MonoMethod *method, M
 		// http://www.mono-project.com/docs/advanced/runtime/docs/generic-sharing/
 		//
 		// 1. Non-generic non-static methods of reference types have access to the
-		//    RGCTX via the “this” argument (this->vtable->rgctx).
+		//    RGCTX via the "this" argument (this->vtable->rgctx).
 		// 2. a Non-generic static methods of reference types and b. non-generic methods
-		//    of value types need to be passed a pointer to the caller’s class’s VTable in the MONO_ARCH_RGCTX_REG register.
+		//    of value types need to be passed a pointer to the caller's class's VTable in the MONO_ARCH_RGCTX_REG register.
 		// 3. Generic methods need to be passed a pointer to the MRGCTX in the MONO_ARCH_RGCTX_REG register
 		//
 		// That is what vtable_arg is here (always?).
@@ -7233,8 +7233,17 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 			} else if ((cmethod->iflags & METHOD_IMPL_ATTRIBUTE_INTERNAL_CALL) && direct_icalls_enabled (cfg, cmethod)) {
 				direct_icall = TRUE;
 			} else if (fsig->pinvoke) {
-				MonoMethod *wrapper = mono_marshal_get_native_wrapper (cmethod, TRUE, cfg->compile_aot);
-				fsig = mono_method_signature_internal (wrapper);
+				if (cmethod->flags & METHOD_ATTRIBUTE_PINVOKE_IMPL) {
+					/*
+					 * Avoid calling mono_marshal_get_native_wrapper () too early, it might call managed
+					 * callbacks on netcore.
+					 */
+					fsig = mono_metadata_signature_dup_mempool (cfg->mempool, fsig);
+					fsig->pinvoke = FALSE;
+				} else {
+					MonoMethod *wrapper = mono_marshal_get_native_wrapper (cmethod, TRUE, cfg->compile_aot);
+					fsig = mono_method_signature_internal (wrapper);
+				}
 			} else if (constrained_class) {
 			} else {
 				fsig = mono_method_get_signature_checked (cmethod, image, token, generic_context, cfg->error);
@@ -7397,8 +7406,7 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 				int costs;
 				gboolean always = FALSE;
 
-				if ((cmethod->iflags & METHOD_IMPL_ATTRIBUTE_INTERNAL_CALL) ||
-					(cmethod->flags & METHOD_ATTRIBUTE_PINVOKE_IMPL)) {
+				if (cmethod->iflags & METHOD_IMPL_ATTRIBUTE_INTERNAL_CALL) {
 					/* Prevent inlining of methods that call wrappers */
 					INLINE_FAILURE ("wrapper call");
 					// FIXME? Does this write to cmethod impact tailcall_supported? Probably not.
diff --git a/src/mono/mono/mini/mini-arm64.c b/src/mono/mono/mini/mini-arm64.c
index 7907193b5e0ffd..30992b6cd8818d 100644
--- a/src/mono/mono/mini/mini-arm64.c
+++ b/src/mono/mono/mini/mini-arm64.c
@@ -114,6 +114,8 @@ get_delegate_invoke_impl (gboolean has_target, gboolean param_count, guint32 *co
 {
 	guint8 *code, *start;
 
+	MINI_BEGIN_CODEGEN ();
+
 	if (has_target) {
 		start = code = mono_global_codeman_reserve (12);
 
@@ -123,9 +125,6 @@ get_delegate_invoke_impl (gboolean has_target, gboolean param_count, guint32 *co
 		arm_brx (code, ARMREG_IP0);
 
 		g_assert ((code - start) <= 12);
-
-		mono_arch_flush_icache (start, 12);
-		MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_DELEGATE_INVOKE, NULL));
 	} else {
 		int size, i;
 
@@ -139,10 +138,8 @@ get_delegate_invoke_impl (gboolean has_target, gboolean param_count, guint32 *co
 		arm_brx (code, ARMREG_IP0);
 
 		g_assert ((code - start) <= size);
-
-		mono_arch_flush_icache (start, size);
-		MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_DELEGATE_INVOKE, NULL));
 	}
+	MINI_END_CODEGEN (start, code - start, MONO_PROFILER_CODE_BUFFER_DELEGATE_INVOKE, NULL);
 
 	if (code_size)
 		*code_size = code - start;
@@ -255,7 +252,7 @@ mono_arch_init (void)
 
 	mono_arm_gsharedvt_init ();
 
-#if defined(TARGET_IOS) || defined(TARGET_WATCHOS)
+#if defined(TARGET_IOS) || defined(TARGET_WATCHOS) || defined(TARGET_OSX)
 	ios_abi = TRUE;
 #endif
 }
@@ -1076,7 +1073,11 @@ add_general (CallInfo *cinfo, ArgInfo *ainfo, int size, gboolean sign)
 {
 	if (cinfo->gr >= PARAM_REGS) {
 		ainfo->storage = ArgOnStack;
-		if (ios_abi) {
+		/*
+		 * FIXME: The vararg argument handling code in ves_icall_System_ArgIterator_IntGetNextArg
+		 * assumes every argument is allocated to a separate full size stack slot.
+		 */
+		if (ios_abi && !cinfo->vararg) {
 			/* Assume size == align */
 		} else {
 			/* Put arguments into 8 byte aligned stack slots */
@@ -1344,6 +1345,10 @@ get_call_info (MonoMemPool *mp, MonoMethodSignature *sig)
 
 	cinfo->nargs = n;
 	cinfo->pinvoke = sig->pinvoke;
+	// Constrain this to OSX only for now
+#ifdef TARGET_OSX
+	cinfo->vararg = sig->call_convention == MONO_CALL_VARARG;
+#endif
 
 	/* Return value */
 	add_param (cinfo, &cinfo->ret, sig->ret);
@@ -5350,6 +5355,8 @@ mono_arch_build_imt_trampoline (MonoVTable *vtable, MonoDomain *domain, MonoIMTC
 		buf = mono_domain_code_reserve (domain, buf_len);
 	code = buf;
 
+	MINI_BEGIN_CODEGEN ();
+
 	/*
 	 * We are called by JITted code, which passes in the IMT argument in
 	 * MONO_ARCH_RGCTX_REG (r27). We need to preserve all caller saved regs
@@ -5419,8 +5426,7 @@ mono_arch_build_imt_trampoline (MonoVTable *vtable, MonoDomain *domain, MonoIMTC
 
 	g_assert ((code - buf) <= buf_len);
 
-	mono_arch_flush_icache (buf, code - buf);
-	MONO_PROFILER_RAISE (jit_code_buffer, (buf, code - buf, MONO_PROFILER_CODE_BUFFER_IMT_TRAMPOLINE, NULL));
+	MINI_END_CODEGEN (buf, code - buf, MONO_PROFILER_CODE_BUFFER_IMT_TRAMPOLINE, NULL);
 
 	return buf;
 }
@@ -5460,7 +5466,9 @@ mono_arch_set_breakpoint (MonoJitInfo *ji, guint8 *ip)
 	} else {
 		/* ip points to an ldrx */
 		code += 4;
+		mono_codeman_enable_write ();
 		arm_blrx (code, ARMREG_IP0);
+		mono_codeman_disable_write ();
 		mono_arch_flush_icache (ip, code - ip);
 	}
 }
@@ -5479,7 +5487,9 @@ mono_arch_clear_breakpoint (MonoJitInfo *ji, guint8 *ip)
 	} else {
 		/* ip points to an ldrx */
 		code += 4;
+		mono_codeman_enable_write ();
 		arm_nop (code);
+		mono_codeman_disable_write ();
 		mono_arch_flush_icache (ip, code - ip);
 	}
 }
diff --git a/src/mono/mono/mini/mini-arm64.h b/src/mono/mono/mini/mini-arm64.h
index 41590fb0e87fce..4074aa8b43f2c8 100644
--- a/src/mono/mono/mini/mini-arm64.h
+++ b/src/mono/mono/mini/mini-arm64.h
@@ -177,6 +177,9 @@ typedef struct {
 #define MONO_ARCH_FLOAT32_SUPPORTED 1
 #define MONO_ARCH_HAVE_INTERP_PINVOKE_TRAMP 1
 #define MONO_ARCH_LLVM_TARGET_LAYOUT "e-i64:64-i128:128-n32:64-S128"
+#ifdef TARGET_OSX
+#define MONO_ARCH_FORCE_FLOAT32 1
+#endif
 
 // Does the ABI have a volatile non-parameter register, so tailcall
 // can pass context to generics or interfaces?
@@ -250,7 +253,7 @@ typedef struct {
 struct CallInfo {
 	int nargs;
 	int gr, fr, stack_usage;
-	gboolean pinvoke;
+	gboolean pinvoke, vararg;
 	ArgInfo ret;
 	ArgInfo sig_cookie;
 	ArgInfo args [1];
diff --git a/src/mono/mono/mini/mini-exceptions.c b/src/mono/mono/mini/mini-exceptions.c
index e752679293776a..9f88c52baa2ab7 100644
--- a/src/mono/mono/mini/mini-exceptions.c
+++ b/src/mono/mono/mini/mini-exceptions.c
@@ -61,6 +61,7 @@
 #include <mono/metadata/mono-endian.h>
 #include <mono/metadata/environment.h>
 #include <mono/metadata/mono-mlist.h>
+#include <mono/metadata/handle.h>
 #include <mono/utils/mono-merp.h>
 #include <mono/utils/mono-mmap.h>
 #include <mono/utils/mono-logger-internals.h>
@@ -1047,19 +1048,28 @@ ves_icall_get_trace (MonoException *exc, gint32 skip, MonoBoolean need_file_info
 		return res;
 	}
 
+	HANDLE_FUNCTION_ENTER ();
+
+	MONO_HANDLE_PIN (ta);
+
 	len = mono_array_length_internal (ta) / TRACE_IP_ENTRY_SIZE;
 
 	res = mono_array_new_checked (domain, mono_defaults.stack_frame_class, len > skip ? len - skip : 0, error);
-	if (mono_error_set_pending_exception (error))
-		return NULL;
+	if (!is_ok (error))
+		goto fail;
+
+	MONO_HANDLE_PIN (res);
+
+	MonoObjectHandle sf_h;
+	sf_h = MONO_HANDLE_NEW (MonoObject, NULL);
 
 	for (i = skip; i < len; i++) {
 		MonoJitInfo *ji;
 		MonoStackFrame *sf = (MonoStackFrame *)mono_object_new_checked (domain, mono_defaults.stack_frame_class, error);
-		if (!is_ok (error)) {
-			mono_error_set_pending_exception (error);
-			return NULL;
-		}
+		if (!is_ok (error))
+			goto fail;
+		MONO_HANDLE_ASSIGN_RAW (sf_h, sf);
+
 		ExceptionTraceIp trace_ip;
 		memcpy (&trace_ip, mono_array_addr_fast (ta, ExceptionTraceIp, i), sizeof (ExceptionTraceIp));
 		gpointer ip = trace_ip.ip;
@@ -1091,18 +1101,14 @@ ves_icall_get_trace (MonoException *exc, gint32 skip, MonoBoolean need_file_info
 			s = mono_method_get_name_full (method, TRUE, FALSE, MONO_TYPE_NAME_FORMAT_REFLECTION);
 			MonoString *name = mono_string_new_checked (domain, s, error);
 			g_free (s);
-			if (!is_ok (error)) {
-				mono_error_set_pending_exception (error);
-				return NULL;
-			}
+			if (!is_ok (error))
+				goto fail;
 			MONO_OBJECT_SETREF_INTERNAL (sf, internal_method_name, name);
 		}
 		else {
 			MonoReflectionMethod *rm = mono_method_get_object_checked (domain, method, NULL, error);
-			if (!is_ok (error)) {
-				mono_error_set_pending_exception (error);
-				return NULL;
-			}
+			if (!is_ok (error))
+				goto fail;
 			MONO_OBJECT_SETREF_INTERNAL (sf, method, rm);
 		}
 
@@ -1129,10 +1135,8 @@ ves_icall_get_trace (MonoException *exc, gint32 skip, MonoBoolean need_file_info
 		if (need_file_info) {
 			if (location && location->source_file) {
 				MonoString *filename = mono_string_new_checked (domain, location->source_file, error);
-				if (!is_ok (error)) {
-					mono_error_set_pending_exception (error);
-					return NULL;
-				}
+				if (!is_ok (error))
+					goto fail;
 				MONO_OBJECT_SETREF_INTERNAL (sf, filename, filename);
 				sf->line = location->row;
 				sf->column = location->column;
@@ -1145,8 +1149,13 @@ ves_icall_get_trace (MonoException *exc, gint32 skip, MonoBoolean need_file_info
 		mono_debug_free_source_location (location);
 		mono_array_setref_internal (res, i - skip, sf);
 	}
+	goto exit;
 
-	return res;
+ fail:
+	mono_error_set_pending_exception (error);
+	res = NULL;
+ exit:
+	HANDLE_FUNCTION_RETURN_VAL (res);
 }
 
 static void
diff --git a/src/mono/mono/mini/mini-generic-sharing.c b/src/mono/mono/mini/mini-generic-sharing.c
index 8c042132af15fd..5fb8bbb39c96e3 100644
--- a/src/mono/mono/mini/mini-generic-sharing.c
+++ b/src/mono/mono/mini/mini-generic-sharing.c
@@ -1170,6 +1170,8 @@ get_wrapper_shared_vtype (MonoType *t)
 	if ((mono_class_get_flags (klass) & TYPE_ATTRIBUTE_LAYOUT_MASK) != TYPE_ATTRIBUTE_SEQUENTIAL_LAYOUT)
 		return NULL;
 	mono_class_setup_fields (klass);
+	if (mono_class_has_failure (klass))
+		return NULL;
 
 	int num_fields = mono_class_get_field_count (klass);
 	MonoClassField *klass_fields = m_class_get_fields (klass);
diff --git a/src/mono/mono/mini/mini-llvm.c b/src/mono/mono/mini/mini-llvm.c
index c400e94f81642d..4ac4e72eece29c 100644
--- a/src/mono/mono/mini/mini-llvm.c
+++ b/src/mono/mono/mini/mini-llvm.c
@@ -11675,8 +11675,10 @@ llvm_jit_finalize_method (EmitContext *ctx)
 	while (g_hash_table_iter_next (&iter, NULL, (void**)&var))
 		callee_vars [i ++] = var;
 
+	mono_codeman_enable_write ();
 	cfg->native_code = (guint8*)mono_llvm_compile_method (ctx->module->mono_ee, cfg, ctx->lmethod, nvars, callee_vars, callee_addrs, &eh_frame);
 	mono_llvm_remove_gc_safepoint_poll (ctx->lmodule);
+	mono_codeman_disable_write ();
 	if (cfg->verbose_level > 1) {
 		g_print ("\n*** Optimized LLVM IR for %s ***\n", mono_method_full_name (cfg->method, TRUE));
 		if (cfg->compile_aot) {
diff --git a/src/mono/mono/mini/mini-riscv.c b/src/mono/mono/mini/mini-riscv.c
index 6a92216ea0ca70..f12b699a5ef443 100644
--- a/src/mono/mono/mini/mini-riscv.c
+++ b/src/mono/mono/mini/mini-riscv.c
@@ -232,6 +232,16 @@ mono_arch_find_static_call_vtable (host_mgreg_t *regs, guint8 *code)
 	return (MonoVTable *) regs [MONO_ARCH_VTABLE_REG];
 }
 
+GSList*
+mono_arch_get_cie_program (void)
+{
+	GSList *l = NULL;
+
+	mono_add_unwind_op_def_cfa (l, (guint8*)NULL, (guint8*)NULL, RISCV_SP, 0);
+
+	return l;
+}
+
 host_mgreg_t
 mono_arch_context_get_int_reg (MonoContext *ctx, int reg)
 {
diff --git a/src/mono/mono/mini/mini-runtime.c b/src/mono/mono/mini/mini-runtime.c
index c180d303d4d22a..caf65d40e88a6e 100644
--- a/src/mono/mono/mini/mini-runtime.c
+++ b/src/mono/mono/mini/mini-runtime.c
@@ -1460,9 +1460,11 @@ mono_resolve_patch_target (MonoMethod *method, MonoDomain *domain, guint8 *code,
 			}
 		}
 
+		mono_codeman_enable_write ();
 		for (i = 0; i < patch_info->data.table->table_size; i++) {
 			jump_table [i] = code + GPOINTER_TO_INT (patch_info->data.table->table [i]);
 		}
+		mono_codeman_disable_write ();
 
 		target = jump_table;
 		break;
@@ -1754,6 +1756,8 @@ mini_patch_jump_sites (MonoDomain *domain, MonoMethod *method, gpointer addr)
 		patch_info.type = MONO_PATCH_INFO_METHOD_JUMP;
 		patch_info.data.method = method;
 
+		mono_codeman_enable_write ();
+
 #ifdef MONO_ARCH_HAVE_PATCH_CODE_NEW
 		for (tmp = jlist->list; tmp; tmp = tmp->next)
 			mono_arch_patch_code_new (NULL, domain, (guint8 *)tmp->data, &patch_info, addr);
@@ -1766,6 +1770,8 @@ mini_patch_jump_sites (MonoDomain *domain, MonoMethod *method, gpointer addr)
 			mono_error_assert_ok (error);
 		}
 #endif
+
+		mono_codeman_disable_write ();
 	}
 }
 
@@ -1957,6 +1963,8 @@ enum {
 	ELF_MACHINE = EM_PPC64,
 #elif HOST_S390X
 	ELF_MACHINE = EM_S390,
+#elif HOST_RISCV
+	ELF_MACHINE = EM_RISCV,
 #endif
 	JIT_CODE_LOAD = 0
 };
@@ -2014,7 +2022,7 @@ mono_enable_jit_dump (void)
 		add_file_header_info (&header);
 		if (perf_dump_file) {
 			fwrite (&header, sizeof (header), 1, perf_dump_file);
-			//This informs perf of the presence of the jitdump file and support for the feature.​
+			//This informs perf of the presence of the jitdump file and support for the feature.
 			perf_dump_mmap_addr = mmap (NULL, sizeof (header), PROT_READ | PROT_EXEC, MAP_PRIVATE, fileno (perf_dump_file), 0);
 		}
 		
@@ -4588,7 +4596,9 @@ mini_init (const char *filename, const char *runtime_version)
 	mono_simd_intrinsics_init ();
 #endif
 
+#ifndef ENABLE_NETCORE
 	mono_tasklets_init ();
+#endif
 
 	register_trampolines (domain);
 
diff --git a/src/mono/mono/mini/mini-runtime.h b/src/mono/mono/mini/mini-runtime.h
index 971d9a59c67517..9eea434e05e78a 100644
--- a/src/mono/mono/mini/mini-runtime.h
+++ b/src/mono/mono/mini/mini-runtime.h
@@ -411,11 +411,9 @@ extern MonoEEFeatures mono_ee_features;
 
 //XXX this enum *MUST extend MonoAotMode as they are consumed together.
 typedef enum {
-	/* Always execute with interp, will use JIT to produce trampolines */
-	MONO_EE_MODE_INTERP = MONO_AOT_MODE_LAST,
+	MONO_EE_MODE_INTERP = MONO_AOT_MODE_INTERP_ONLY,
 } MonoEEMode;
 
-
 static inline MonoMethod*
 jinfo_get_method (MonoJitInfo *ji)
 {
@@ -613,5 +611,16 @@ gboolean MONO_SIG_HANDLER_SIGNATURE (mono_chain_signal);
 
 void mini_register_sigterm_handler (void);
 
+#define MINI_BEGIN_CODEGEN() do { \
+	mono_codeman_enable_write (); \
+	} while (0)
+
+#define MINI_END_CODEGEN(buf,size,type,arg) do { \
+	mono_codeman_disable_write (); \
+	mono_arch_flush_icache ((buf), (size)); \
+	if ((int)type != -1) \
+		MONO_PROFILER_RAISE (jit_code_buffer, ((buf), (size), (type), (arg))); \
+	} while (0)
+
 #endif /* __MONO_MINI_RUNTIME_H__ */
 
diff --git a/src/mono/mono/mini/mini-s390x.h b/src/mono/mono/mini/mini-s390x.h
index 2efcafbd456b1d..bb358e235ab00c 100644
--- a/src/mono/mono/mini/mini-s390x.h
+++ b/src/mono/mono/mini/mini-s390x.h
@@ -158,7 +158,7 @@ struct SeqPointInfo {
 
 #define MONO_INIT_CONTEXT_FROM_FUNC(ctx,func) do {			\
 		MonoS390StackFrame *sframe;				\
-		__asm__ volatile("lgr   %0,15" : "=r" (sframe));	\
+		__asm__ volatile("lgr   %0,%%r15" : "=r" (sframe));	\
 		MONO_CONTEXT_SET_BP ((ctx), sframe->prev);		\
 		MONO_CONTEXT_SET_SP ((ctx), sframe->prev);		\
 		MONO_CONTEXT_SET_IP ((ctx), func);			\
diff --git a/src/mono/mono/mini/mini-wasm-debugger.c b/src/mono/mono/mini/mini-wasm-debugger.c
index dc1f5d38f3d2eb..66608a7a56bc46 100644
--- a/src/mono/mono/mini/mini-wasm-debugger.c
+++ b/src/mono/mono/mini/mini-wasm-debugger.c
@@ -24,6 +24,12 @@ static int log_level = 1;
 
 #define DEBUG_PRINTF(level, ...) do { if (G_UNLIKELY ((level) <= log_level)) { fprintf (stdout, __VA_ARGS__); } } while (0)
 
+enum {
+	EXCEPTION_MODE_NONE,
+	EXCEPTION_MODE_UNCAUGHT,
+	EXCEPTION_MODE_ALL
+};
+
 //functions exported to be used by JS
 G_BEGIN_DECLS
 
@@ -31,22 +37,21 @@ EMSCRIPTEN_KEEPALIVE int mono_wasm_set_breakpoint (const char *assembly_name, in
 EMSCRIPTEN_KEEPALIVE int mono_wasm_remove_breakpoint (int bp_id);
 EMSCRIPTEN_KEEPALIVE int mono_wasm_current_bp_id (void);
 EMSCRIPTEN_KEEPALIVE void mono_wasm_enum_frames (void);
-EMSCRIPTEN_KEEPALIVE void mono_wasm_get_var_info (int scope, int* pos, int len);
+EMSCRIPTEN_KEEPALIVE gboolean mono_wasm_get_local_vars (int scope, int* pos, int len);
 EMSCRIPTEN_KEEPALIVE void mono_wasm_clear_all_breakpoints (void);
 EMSCRIPTEN_KEEPALIVE int mono_wasm_setup_single_step (int kind);
-EMSCRIPTEN_KEEPALIVE void mono_wasm_get_object_properties (int object_id, gboolean expand_value_types);
-EMSCRIPTEN_KEEPALIVE void mono_wasm_get_array_values (int object_id);
-EMSCRIPTEN_KEEPALIVE void mono_wasm_get_array_value_expanded (int object_id, int idx);
-EMSCRIPTEN_KEEPALIVE void mono_wasm_invoke_getter_on_object (int object_id, const char* name);
-EMSCRIPTEN_KEEPALIVE void mono_wasm_get_deref_ptr_value (void *value_addr, MonoClass *klass);
+EMSCRIPTEN_KEEPALIVE int mono_wasm_pause_on_exceptions (int state);
+EMSCRIPTEN_KEEPALIVE gboolean mono_wasm_get_object_properties (int object_id, gboolean expand_value_types);
+EMSCRIPTEN_KEEPALIVE gboolean mono_wasm_get_array_values (int object_id, int start_idx, int count, gboolean expand_value_types);
+EMSCRIPTEN_KEEPALIVE gboolean mono_wasm_invoke_getter_on_object (int object_id, const char* name);
+EMSCRIPTEN_KEEPALIVE gboolean mono_wasm_invoke_getter_on_value (void *value, MonoClass *klass, const char *name);
+EMSCRIPTEN_KEEPALIVE gboolean mono_wasm_get_deref_ptr_value (void *value_addr, MonoClass *klass);
 
 //JS functions imported that we use
 extern void mono_wasm_add_frame (int il_offset, int method_token, const char *assembly_name, const char *method_name);
 extern void mono_wasm_fire_bp (void);
+extern void mono_wasm_fire_exception (int exception_obj_id, const char* message, const char* class_name, gboolean uncaught);
 extern void mono_wasm_add_obj_var (const char*, const char*, guint64);
-extern void mono_wasm_add_value_type_unexpanded_var (const char*, const char*);
-extern void mono_wasm_begin_value_type_var (const char*, const char*);
-extern void mono_wasm_end_value_type_var (void);
 extern void mono_wasm_add_enum_var (const char*, const char*, guint64);
 extern void mono_wasm_add_func_var (const char*, const char*, guint64);
 extern void mono_wasm_add_properties_var (const char*, gint32);
@@ -57,6 +62,7 @@ extern void mono_wasm_add_typed_value (const char *type, const char *str_value,
 G_END_DECLS
 
 static void describe_object_properties_for_klass (void *obj, MonoClass *klass, gboolean isAsyncLocalThis, gboolean expandValueType);
+static void handle_exception (MonoException *exc, MonoContext *throw_ctx, MonoContext *catch_ctx, StackFrameInfo *catch_frame);
 
 //FIXME move all of those fields to the profiler object
 static gboolean debugger_enabled;
@@ -65,6 +71,7 @@ static int event_request_id;
 static GHashTable *objrefs;
 static GHashTable *obj_to_objref;
 static int objref_id = 0;
+static int pause_on_exc = EXCEPTION_MODE_NONE;
 
 static const char*
 all_getters_allowed_class_names[] = {
@@ -363,6 +370,8 @@ mono_wasm_debugger_init (void)
 
 	obj_to_objref = g_hash_table_new (NULL, NULL);
 	objrefs = g_hash_table_new_full (NULL, NULL, NULL, mono_debugger_free_objref);
+
+	mini_get_dbg_callbacks ()->handle_exception = handle_exception;
 }
 
 MONO_API void
@@ -373,6 +382,14 @@ mono_wasm_enable_debugging (int debug_level)
 	log_level = debug_level;
 }
 
+EMSCRIPTEN_KEEPALIVE int
+mono_wasm_pause_on_exceptions (int state)
+{
+	pause_on_exc = state;
+	DEBUG_PRINTF (1, "setting pause on exception: %d\n", pause_on_exc);
+	return 1;
+}
+
 EMSCRIPTEN_KEEPALIVE int
 mono_wasm_setup_single_step (int kind)
 {
@@ -428,6 +445,50 @@ mono_wasm_setup_single_step (int kind)
 	return isBPOnNativeCode;
 }
 
+static int 
+get_object_id(MonoObject *obj) 
+{
+	ObjRef *ref;
+	if (!obj)
+		return 0;
+
+	ref = (ObjRef *)g_hash_table_lookup (obj_to_objref, GINT_TO_POINTER (~((gsize)obj)));
+	if (ref)
+		return ref->id;
+	ref = g_new0 (ObjRef, 1);
+	ref->id = mono_atomic_inc_i32 (&objref_id);
+	ref->handle = mono_gchandle_new_weakref_internal (obj, FALSE);
+	g_hash_table_insert (objrefs, GINT_TO_POINTER (ref->id), ref);
+	g_hash_table_insert (obj_to_objref, GINT_TO_POINTER (~((gsize)obj)), ref);
+	return ref->id;
+}
+
+static void
+handle_exception (MonoException *exc, MonoContext *throw_ctx, MonoContext *catch_ctx, StackFrameInfo *catch_frame)
+{
+	ERROR_DECL (error);
+	DEBUG_PRINTF (1, "handle exception - %d - %p - %p - %p\n", pause_on_exc, exc, throw_ctx, catch_ctx);
+
+	if (pause_on_exc == EXCEPTION_MODE_NONE)
+		return;
+	if (pause_on_exc == EXCEPTION_MODE_UNCAUGHT && catch_ctx != NULL)
+		return;
+
+	int obj_id = get_object_id ((MonoObject *)exc);
+	const char *error_message = mono_string_to_utf8_checked_internal (exc->message, error);
+
+	if (!is_ok (error))
+		error_message = "Failed to get exception message.";
+
+	const char *class_name = mono_class_full_name (mono_object_class (exc));
+	DEBUG_PRINTF (2, "handle exception - calling mono_wasm_fire_exc(): %d - message - %s, class_name: %s\n", obj_id,  error_message, class_name);
+
+	mono_wasm_fire_exception (obj_id, error_message, class_name, !catch_ctx);
+
+	DEBUG_PRINTF (2, "handle exception - done\n");
+}
+
+
 EMSCRIPTEN_KEEPALIVE void
 mono_wasm_clear_all_breakpoints (void)
 {
@@ -567,21 +628,20 @@ mono_wasm_current_bp_id (void)
 	return evt->id;
 }
 
-static int get_object_id(MonoObject *obj) 
+static MonoObject*
+get_object_from_id (int objectId)
 {
-	ObjRef *ref;
+	ObjRef *ref = (ObjRef *)g_hash_table_lookup (objrefs, GINT_TO_POINTER (objectId));
+	if (!ref) {
+		DEBUG_PRINTF (2, "get_object_from_id !ref: %d\n", objectId);
+		return NULL;
+	}
+
+	MonoObject *obj = mono_gchandle_get_target_internal (ref->handle);
 	if (!obj)
-		return 0;
+		DEBUG_PRINTF (2, "get_object_from_id !obj: %d\n", objectId);
 
-	ref = (ObjRef *)g_hash_table_lookup (obj_to_objref, GINT_TO_POINTER (~((gsize)obj)));
-	if (ref)
-		return ref->id;
-	ref = g_new0 (ObjRef, 1);
-	ref->id = mono_atomic_inc_i32 (&objref_id);
-	ref->handle = mono_gchandle_new_weakref_internal (obj, FALSE);
-	g_hash_table_insert (objrefs, GINT_TO_POINTER (ref->id), ref);
-	g_hash_table_insert (obj_to_objref, GINT_TO_POINTER (~((gsize)obj)), ref);
-	return ref->id;
+	return obj;
 }
 
 static gboolean
@@ -921,17 +981,28 @@ static gboolean describe_value(MonoType * type, gpointer addr, gboolean expandVa
 
 				mono_wasm_add_enum_var (class_name, enum_members->str, value__);
 				g_string_free (enum_members, TRUE);
-			} else if (expandValueType) {
-				char *to_string_val = get_to_string_description (class_name, klass, addr);
-				mono_wasm_begin_value_type_var (class_name, to_string_val);
-				g_free (to_string_val);
-
-				// FIXME: isAsyncLocalThis
-				describe_object_properties_for_klass ((MonoObject*)addr, klass, FALSE, expandValueType);
-				mono_wasm_end_value_type_var ();
 			} else {
 				char *to_string_val = get_to_string_description (class_name, klass, addr);
-				mono_wasm_add_value_type_unexpanded_var (class_name, to_string_val);
+
+				if (expandValueType) {
+					int32_t size = mono_class_value_size (klass, NULL);
+					void *value_buf = g_malloc0 (size);
+					mono_value_copy_internal (value_buf, addr, klass);
+
+					EM_ASM ({
+						MONO.mono_wasm_add_typed_value ($0, $1, { toString: $2, value_addr: $3, value_size: $4, klass: $5 });
+					}, "begin_vt", class_name, to_string_val, value_buf, size, klass);
+
+					g_free (value_buf);
+
+					// FIXME: isAsyncLocalThis
+					describe_object_properties_for_klass (addr, klass, FALSE, expandValueType);
+					mono_wasm_add_typed_value ("end_vt", NULL, 0);
+				} else {
+					EM_ASM ({
+						MONO.mono_wasm_add_typed_value ($0, $1, { toString: $2 });
+					}, "unexpanded_vt", class_name, to_string_val);
+				}
 				g_free (to_string_val);
 			}
 			g_free (class_name);
@@ -989,7 +1060,7 @@ describe_object_properties_for_klass (void *obj, MonoClass *klass, gboolean isAs
 	gboolean is_valuetype;
 	int pnum;
 	char *klass_name;
-	gboolean getters_allowed;
+	gboolean auto_invoke_getters;
 
 	g_assert (klass);
 	is_valuetype = m_class_is_valuetype(klass);
@@ -1022,7 +1093,7 @@ describe_object_properties_for_klass (void *obj, MonoClass *klass, gboolean isAs
 	}
 
 	klass_name = mono_class_full_name (klass);
-	getters_allowed = are_getters_allowed (klass_name);
+	auto_invoke_getters = are_getters_allowed (klass_name);
 
 	iter = NULL;
 	pnum = 0;
@@ -1034,29 +1105,24 @@ describe_object_properties_for_klass (void *obj, MonoClass *klass, gboolean isAs
 			mono_wasm_add_properties_var (p->name, pnum);
 			sig = mono_method_signature_internal (p->get);
 
-			// automatic properties will get skipped
-			if (!getters_allowed) {
+			gboolean vt_self_type_getter = is_valuetype && mono_class_from_mono_type_internal (sig->ret) == klass;
+			if (auto_invoke_getters && !vt_self_type_getter) {
+				invoke_and_describe_getter_value (obj, p);
+			} else {
 				// not allowed to call the getter here
 				char *ret_class_name = mono_class_full_name (mono_class_from_mono_type_internal (sig->ret));
 
-				// getters not supported for valuetypes, yet
-				gboolean invokable = !is_valuetype && sig->param_count == 0;
+				gboolean invokable = sig->param_count == 0;
 				mono_wasm_add_typed_value ("getter", ret_class_name, invokable);
 
 				g_free (ret_class_name);
 				continue;
 			}
-
-			if (is_valuetype && mono_class_from_mono_type_internal (sig->ret) == klass) {
-				// Property of the same valuetype, avoid endlessly recursion!
-				mono_wasm_add_typed_value ("getter", klass_name, 0);
-				continue;
-			}
-
-			invoke_and_describe_getter_value (obj, p);
 		}
 		pnum ++;
 	}
+
+	g_free (klass_name);
 }
 
 /*
@@ -1085,17 +1151,10 @@ static gboolean
 describe_object_properties (guint64 objectId, gboolean isAsyncLocalThis, gboolean expandValueType)
 {
 	DEBUG_PRINTF (2, "describe_object_properties %llu\n", objectId);
-	ObjRef *ref = (ObjRef *)g_hash_table_lookup (objrefs, GINT_TO_POINTER (objectId));
-	if (!ref) {
-		DEBUG_PRINTF (2, "describe_object_properties !ref\n");
-		return FALSE;
-	}
 
-	MonoObject *obj = mono_gchandle_get_target_internal (ref->handle);
-	if (!obj) {
-		DEBUG_PRINTF (2, "describe_object_properties !obj\n");
+	MonoObject *obj = get_object_from_id (objectId);
+	if (!obj)
 		return FALSE;
-	}
 
 	if (m_class_is_delegate (mono_object_class (obj))) {
 		// delegates get the same id format as regular objects
@@ -1108,21 +1167,13 @@ describe_object_properties (guint64 objectId, gboolean isAsyncLocalThis, gboolea
 }
 
 static gboolean
-invoke_getter_on_object (guint64 objectId, const char *name)
+invoke_getter (void *obj_or_value, MonoClass *klass, const char *name)
 {
-	ObjRef *ref = (ObjRef *)g_hash_table_lookup (objrefs, GINT_TO_POINTER (objectId));
-	if (!ref) {
-		DEBUG_PRINTF (1, "invoke_getter_on_object no objRef found for id %llu\n", objectId);
-		return FALSE;
-	}
-
-	MonoObject *obj = mono_gchandle_get_target_internal (ref->handle);
-	if (!obj) {
-		DEBUG_PRINTF (1, "invoke_getter_on_object !obj\n");
+	if (!obj_or_value || !klass || !name) {
+		DEBUG_PRINTF (2, "invoke_getter: none of the arguments can be null");
 		return FALSE;
 	}
 
-	MonoClass *klass = mono_object_class (obj);
 	gpointer iter = NULL;
 	MonoProperty *p;
 	while ((p = mono_class_get_properties (klass, &iter))) {
@@ -1130,7 +1181,7 @@ invoke_getter_on_object (guint64 objectId, const char *name)
 		if (!p->get->name || strcasecmp (p->name, name) != 0)
 			continue;
 
-		invoke_and_describe_getter_value (obj, p);
+		invoke_and_describe_getter_value (obj_or_value, p);
 		return TRUE;
 	}
 
@@ -1138,50 +1189,48 @@ invoke_getter_on_object (guint64 objectId, const char *name)
 }
 
 static gboolean 
-describe_array_values (guint64 objectId)
+describe_array_values (guint64 objectId, int startIdx, int count, gboolean expandValueType)
 {
+	if (count == 0)
+		return TRUE;
+
 	int esize;
 	gpointer elem;
-	ObjRef *ref = (ObjRef *)g_hash_table_lookup (objrefs, GINT_TO_POINTER (objectId));
-	if (!ref) {
+	MonoArray *arr = (MonoArray*) get_object_from_id (objectId);
+	if (!arr)
 		return FALSE;
-	}
-	MonoArray *arr = (MonoArray *)mono_gchandle_get_target_internal (ref->handle);
-	MonoObject *obj = &arr->obj;
-	if (!obj) {
+
+	MonoClass *klass = mono_object_class (arr);
+	MonoTypeEnum type = m_class_get_byval_arg (klass)->type;
+	if (type != MONO_TYPE_SZARRAY && type != MONO_TYPE_ARRAY) {
+		DEBUG_PRINTF (1, "describe_array_values: object is not an array. type: 0x%x\n", type);
 		return FALSE;
 	}
-	esize = mono_array_element_size (obj->vtable->klass);
-	for (int i = 0; i < arr->max_length; i++) {
-		mono_wasm_add_array_item(i);
-		elem = (gpointer*)((char*)arr->vector + (i * esize));
-		describe_value (m_class_get_byval_arg (m_class_get_element_class (arr->obj.vtable->klass)), elem, FALSE);
+
+	int len = arr->max_length;
+	if (len == 0 && startIdx == 0 && count <= 0) {
+		// Nothing to do
+		return TRUE;
 	}
-	return TRUE;
-}
 
-/* Expands valuetypes */
-static gboolean
-describe_array_value_expanded (guint64 objectId, guint64 idx)
-{
-	int esize;
-	gpointer elem;
-	ObjRef *ref = (ObjRef *)g_hash_table_lookup (objrefs, GINT_TO_POINTER (objectId));
-	if (!ref) {
+	if (startIdx < 0 || (len > 0 && startIdx >= len)) {
+		DEBUG_PRINTF (1, "describe_array_values: invalid startIdx (%d) for array of length %d\n", startIdx, len);
 		return FALSE;
 	}
-	MonoArray *arr = (MonoArray *)mono_gchandle_get_target_internal (ref->handle);
-	MonoObject *obj = &arr->obj;
-	if (!obj) {
+
+	if (count > 0 && (startIdx + count) > len) {
+		DEBUG_PRINTF (1, "describe_array_values: invalid count (%d) for startIdx: %d, and array of length %d\n", count, startIdx, len);
 		return FALSE;
 	}
-	if (idx >= arr->max_length)
-		return FALSE;
 
-	esize = mono_array_element_size (obj->vtable->klass);
-	elem = (gpointer*)((char*)arr->vector + (idx * esize));
-	describe_value (m_class_get_byval_arg (m_class_get_element_class (arr->obj.vtable->klass)), elem, TRUE);
+	esize = mono_array_element_size (klass);
+	int endIdx = count < 0 ? len : startIdx + count;
 
+	for (int i = startIdx; i < endIdx; i ++) {
+		mono_wasm_add_array_item(i);
+		elem = (gpointer*)((char*)arr->vector + (i * esize));
+		describe_value (m_class_get_byval_arg (m_class_get_element_class (klass)), elem, expandValueType);
+	}
 	return TRUE;
 }
 
@@ -1284,22 +1333,23 @@ describe_variables_on_frame (MonoStackFrameInfo *info, MonoContext *ctx, gpointe
 	return TRUE;
 }
 
-EMSCRIPTEN_KEEPALIVE void
+EMSCRIPTEN_KEEPALIVE gboolean
 mono_wasm_get_deref_ptr_value (void *value_addr, MonoClass *klass)
 {
 	MonoType *type = m_class_get_byval_arg (klass);
 	if (type->type != MONO_TYPE_PTR && type->type != MONO_TYPE_FNPTR) {
 		DEBUG_PRINTF (2, "BUG: mono_wasm_get_deref_ptr_value: Expected to get a ptr type, but got 0x%x\n", type->type);
-		return;
+		return FALSE;
 	}
 
 	mono_wasm_add_properties_var ("deref", -1);
 	describe_value (type->data.type, value_addr, TRUE);
+	return TRUE;
 }
 
 //FIXME this doesn't support getting the return value pseudo-var
-EMSCRIPTEN_KEEPALIVE void
-mono_wasm_get_var_info (int scope, int* pos, int len)
+EMSCRIPTEN_KEEPALIVE gboolean
+mono_wasm_get_local_vars (int scope, int* pos, int len)
 {
 	FrameDescData data;
 	data.target_frame = scope;
@@ -1308,37 +1358,51 @@ mono_wasm_get_var_info (int scope, int* pos, int len)
 	data.pos = pos;
 
 	mono_walk_stack_with_ctx (describe_variables_on_frame, NULL, MONO_UNWIND_NONE, &data);
+
+	return TRUE;
 }
 
-EMSCRIPTEN_KEEPALIVE void
+EMSCRIPTEN_KEEPALIVE gboolean
 mono_wasm_get_object_properties (int object_id, gboolean expand_value_types)
 {
 	DEBUG_PRINTF (2, "getting properties of object %d\n", object_id);
 
-	describe_object_properties (object_id, FALSE, expand_value_types);
+	return describe_object_properties (object_id, FALSE, expand_value_types);
 }
 
-EMSCRIPTEN_KEEPALIVE void
-mono_wasm_get_array_values (int object_id)
+EMSCRIPTEN_KEEPALIVE gboolean
+mono_wasm_get_array_values (int object_id, int start_idx, int count, gboolean expand_value_types)
 {
-	DEBUG_PRINTF (2, "getting array values %d\n", object_id);
+	DEBUG_PRINTF (2, "getting array values %d, startIdx: %d, count: %d, expandValueType: %d\n", object_id, start_idx, count, expand_value_types);
 
-	describe_array_values(object_id);
+	return describe_array_values (object_id, start_idx, count, expand_value_types);
 }
 
-EMSCRIPTEN_KEEPALIVE void
-mono_wasm_get_array_value_expanded (int object_id, int idx)
+EMSCRIPTEN_KEEPALIVE gboolean
+mono_wasm_invoke_getter_on_object (int object_id, const char* name)
 {
-	DEBUG_PRINTF (2, "getting array value %d for idx %d\n", object_id, idx);
+	MonoObject *obj = get_object_from_id (object_id);
+	if (!obj)
+		return FALSE;
 
-	describe_array_value_expanded (object_id, idx);
+	return invoke_getter (obj, mono_object_class (obj), name);
 }
 
-EMSCRIPTEN_KEEPALIVE void
-mono_wasm_invoke_getter_on_object (int object_id, const char* name)
+EMSCRIPTEN_KEEPALIVE gboolean
+mono_wasm_invoke_getter_on_value (void *value, MonoClass *klass, const char *name)
 {
-	invoke_getter_on_object (object_id, name);
+	DEBUG_PRINTF (2, "mono_wasm_invoke_getter_on_value: v: %p klass: %p, name: %s\n", value, klass, name);
+	if (!klass || !value)
+		return FALSE;
+
+	if (!m_class_is_valuetype (klass)) {
+		DEBUG_PRINTF (2, "mono_wasm_invoke_getter_on_value: klass is not a valuetype. name: %s\n", mono_class_full_name (klass));
+		return FALSE;
+	}
+
+	return invoke_getter (value, klass, name);
 }
+
 // Functions required by debugger-state-machine.
 gsize
 mono_debugger_tls_thread_id (DebuggerTlsData *debuggerTlsData)
diff --git a/src/mono/mono/mini/mini-wasm.c b/src/mono/mono/mini/mini-wasm.c
index 3b914a03fddfea..e60d77f492506b 100644
--- a/src/mono/mono/mini/mini-wasm.c
+++ b/src/mono/mono/mini/mini-wasm.c
@@ -604,13 +604,13 @@ tp_cb (void)
 	mono_runtime_try_invoke (method, NULL, NULL, &exc, error);
 
 	if (!is_ok (error)) {
-		printf ("tp callback failed due to %s\n", mono_error_get_message (error));
+		printf ("ThreadPool Callback failed due to error: %s\n", mono_error_get_message (error));
 		mono_error_cleanup (error);
 	}
 
 	if (exc) {
 		char *type_name = mono_type_get_full_name (mono_object_class (exc));
-		printf ("tp callback threw a %s\n", type_name);
+		printf ("ThreadPool Callback threw an unhandled exception of type %s\n", type_name);
 		g_free (type_name);
 	}
 }
diff --git a/src/mono/mono/mini/mini.c b/src/mono/mono/mini/mini.c
index 965771de378d46..2a6ca7f4b16c21 100644
--- a/src/mono/mono/mini/mini.c
+++ b/src/mono/mono/mini/mini.c
@@ -2248,6 +2248,8 @@ mono_codegen (MonoCompile *cfg)
 		code = (guint8 *)mono_domain_code_reserve (code_domain, cfg->code_size + cfg->thunk_area + unwindlen);
 	}
 
+	mono_codeman_enable_write ();
+
 	if (cfg->thunk_area) {
 		cfg->thunks_offset = cfg->code_size + unwindlen;
 		cfg->thunks = code + cfg->thunks_offset;
@@ -2339,6 +2341,9 @@ mono_codegen (MonoCompile *cfg)
 	} else {
 		mono_domain_code_commit (code_domain, cfg->native_code, cfg->code_size, cfg->code_len);
 	}
+
+	mono_codeman_disable_write ();
+
 	MONO_PROFILER_RAISE (jit_code_buffer, (cfg->native_code, cfg->code_len, MONO_PROFILER_CODE_BUFFER_METHOD, cfg->method));
 	
 	mono_arch_flush_icache (cfg->native_code, cfg->code_len);
@@ -3044,6 +3049,9 @@ init_backend (MonoBackend *backend)
 #ifdef MONO_ARCH_HAVE_OPTIMIZED_DIV
 	backend->optimized_div = 1;
 #endif
+#ifdef MONO_ARCH_FORCE_FLOAT32
+	backend->force_float32 = 1;
+#endif
 }
 
 static gboolean
@@ -3146,6 +3154,9 @@ mini_method_compile (MonoMethod *method, guint32 opts, MonoDomain *domain, JitFl
 #ifndef MONO_ARCH_FLOAT32_SUPPORTED
 	opts &= ~MONO_OPT_FLOAT32;
 #endif
+	if (current_backend->force_float32)
+		/* Force float32 mode on newer platforms */
+		opts |= MONO_OPT_FLOAT32;
 
  restart_compile:
 	if (method_is_gshared) {
diff --git a/src/mono/mono/mini/mini.h b/src/mono/mono/mini/mini.h
index e782440c7e18e7..58eb136d318140 100644
--- a/src/mono/mono/mini/mini.h
+++ b/src/mono/mono/mini/mini.h
@@ -1193,7 +1193,7 @@ typedef struct {
 	guint            have_generalized_imt_trampoline : 1;
 	gboolean         have_op_tailcall_membase : 1;
 	gboolean         have_op_tailcall_reg : 1;
-	gboolean	 have_volatile_non_param_register : 1;
+	gboolean         have_volatile_non_param_register : 1;
 	guint            gshared_supported : 1;
 	guint            use_fpstack : 1;
 	guint            ilp32 : 1;
@@ -1203,6 +1203,7 @@ typedef struct {
 	guint            disable_div_with_mul : 1;
 	guint            explicit_null_checks : 1;
 	guint            optimized_div : 1;
+	guint            force_float32 : 1;
 	int              monitor_enter_adjustment;
 	int              dyn_call_param_area;
 } MonoBackend;
diff --git a/src/mono/mono/mini/tasklets.c b/src/mono/mono/mini/tasklets.c
index 361b3f02353fa1..402a3a981c2365 100644
--- a/src/mono/mono/mini/tasklets.c
+++ b/src/mono/mono/mini/tasklets.c
@@ -12,6 +12,7 @@
 #include "mono/metadata/loader-internals.h"
 #include "mono/utils/mono-tls-inline.h"
 
+#if !defined(ENABLE_NETCORE)
 #if defined(MONO_SUPPORT_TASKLETS)
 
 #include "mono/metadata/loader-internals.h"
@@ -213,5 +214,7 @@ mono_tasklets_init(void)
 	mono_add_internal_call_internal ("Mono.Tasklets.Continuation::restore", continuation_restore);
 
 }
-#endif
+#endif /* MONO_SUPPORT_TASKLETS */
+
+#endif /* ENABLE_NETCORE */
 
diff --git a/src/mono/mono/mini/tasklets.h b/src/mono/mono/mini/tasklets.h
index fc6f0b8178a9c6..dd8750f3f2f24c 100644
--- a/src/mono/mono/mini/tasklets.h
+++ b/src/mono/mono/mini/tasklets.h
@@ -7,6 +7,7 @@
 
 #include "mini.h"
 
+#if !defined(ENABLE_NETCORE)
 typedef struct {
 	MonoLMF *lmf;
 	gpointer top_sp;
@@ -31,5 +32,7 @@ void  mono_tasklets_cleanup (void);
 
 MonoContinuationRestore mono_tasklets_arch_restore (void);
 
+#endif /* ENABLE_NETCORE */
+
 #endif /* __MONO_TASKLETS_H__ */
 
diff --git a/src/mono/mono/mini/trace.c b/src/mono/mono/mini/trace.c
index 0e28cc773ee22f..56e19a857512b6 100644
--- a/src/mono/mono/mini/trace.c
+++ b/src/mono/mono/mini/trace.c
@@ -31,7 +31,7 @@
 #pragma warning(disable:4312) // FIXME pointer cast to different size
 #endif
 
-#if defined (HOST_ANDROID) || (defined (TARGET_IOS) && defined (TARGET_IOS))
+#if defined (HOST_ANDROID) || defined (TARGET_IOS)
 #  undef printf
 #  define printf(...) g_log("mono", G_LOG_LEVEL_MESSAGE, __VA_ARGS__)
 #  undef fprintf
diff --git a/src/mono/mono/mini/tramp-arm64-gsharedvt.c b/src/mono/mono/mini/tramp-arm64-gsharedvt.c
index c1038511d67fde..269624c259da69 100644
--- a/src/mono/mono/mini/tramp-arm64-gsharedvt.c
+++ b/src/mono/mono/mini/tramp-arm64-gsharedvt.c
@@ -13,6 +13,7 @@
 #include "mini.h"
 #include "mini-arm64.h"
 #include "mini-arm64-gsharedvt.h"
+#include "mini-runtime.h"
 
 /*
  * GSHAREDVT
@@ -36,13 +37,16 @@ mono_arch_get_gsharedvt_arg_trampoline (MonoDomain *domain, gpointer arg, gpoint
 	 */
 	buf = code = mono_global_codeman_reserve (buf_len);
 
+	MINI_BEGIN_CODEGEN ();
+
 	code = mono_arm_emit_imm64 (code, ARMREG_IP1, (guint64)arg);
 	code = mono_arm_emit_imm64 (code, ARMREG_IP0, (guint64)addr);
 
 	arm_brx (code, ARMREG_IP0);
 
 	g_assert ((code - buf) < buf_len);
-	mono_arch_flush_icache (buf, code - buf);
+
+	MINI_END_CODEGEN (buf, code - buf, -1, NULL);
 
 	return buf;
 }
@@ -248,6 +252,8 @@ mono_arch_get_gsharedvt_trampoline (MonoTrampInfo **info, gboolean aot)
 
 	cfa_offset = offset;
 
+	MINI_BEGIN_CODEGEN ();
+
 	/* Setup frame */
 	arm_stpx_pre (code, ARMREG_FP, ARMREG_LR, ARMREG_SP, -cfa_offset);
 	mono_add_unwind_op_def_cfa (unwind_ops, code, buf, ARMREG_SP, cfa_offset);
@@ -547,7 +553,8 @@ mono_arch_get_gsharedvt_trampoline (MonoTrampInfo **info, gboolean aot)
 	if (info)
 		*info = mono_tramp_info_create ("gsharedvt_trampoline", buf, code - buf, ji, unwind_ops);
 
-	mono_arch_flush_icache (buf, code - buf);
+	MINI_END_CODEGEN (buf, code - buf, -1, NULL);
+
 	return buf;
 }
 
diff --git a/src/mono/mono/mini/tramp-arm64.c b/src/mono/mono/mini/tramp-arm64.c
index 04eda906c469d8..7b889a3ffde4d2 100644
--- a/src/mono/mono/mini/tramp-arm64.c
+++ b/src/mono/mono/mini/tramp-arm64.c
@@ -30,8 +30,9 @@
 void
 mono_arch_patch_callsite (guint8 *method_start, guint8 *code_ptr, guint8 *addr)
 {
+	MINI_BEGIN_CODEGEN ();
 	mono_arm_patch (code_ptr - 4, addr, MONO_R_ARM64_BL);
-	mono_arch_flush_icache (code_ptr - 4, 4);
+	MINI_END_CODEGEN (code_ptr - 4, 4, -1, NULL);
 }
 
 void
@@ -133,6 +134,8 @@ mono_arch_create_generic_trampoline (MonoTrampolineType tramp_type, MonoTrampInf
 	//offset += 22 * 8;
 	frame_size = ALIGN_TO (offset, MONO_ARCH_FRAME_ALIGNMENT);
 
+	MINI_BEGIN_CODEGEN ();
+
 	/* Setup stack frame */
 	imm = frame_size;
 	mono_add_unwind_op_def_cfa (unwind_ops, code, buf, ARMREG_SP, 0);
@@ -303,8 +306,8 @@ mono_arch_create_generic_trampoline (MonoTrampolineType tramp_type, MonoTrampInf
 	arm_brx (code, ARMREG_IP0);
 
 	g_assert ((code - buf) < buf_len);
-	mono_arch_flush_icache (buf, code - buf);
-	MONO_PROFILER_RAISE (jit_code_buffer, (buf, code - buf, MONO_PROFILER_CODE_BUFFER_HELPER, NULL));
+
+	MINI_END_CODEGEN (buf, code - buf, MONO_PROFILER_CODE_BUFFER_HELPER, NULL);
 
 	if (info) {
 		tramp_name = mono_get_generic_trampoline_name (tramp_type);
@@ -328,14 +331,16 @@ mono_arch_create_specific_trampoline (gpointer arg1, MonoTrampolineType tramp_ty
 
 	buf = code = mono_domain_code_reserve (domain, buf_len);
 
+	MINI_BEGIN_CODEGEN ();
+
 	code = mono_arm_emit_imm64 (code, ARMREG_IP1, (guint64)arg1);
 	code = mono_arm_emit_imm64 (code, ARMREG_IP0, (guint64)tramp);
 
 	arm_brx (code, ARMREG_IP0);
 
 	g_assert ((code - buf) < buf_len);
-	mono_arch_flush_icache (buf, code - buf);
-	MONO_PROFILER_RAISE (jit_code_buffer, (buf, code - buf, MONO_PROFILER_CODE_BUFFER_SPECIFIC_TRAMPOLINE, mono_get_generic_trampoline_simple_name (tramp_type)));
+
+	MINI_END_CODEGEN (buf, code - buf, MONO_PROFILER_CODE_BUFFER_SPECIFIC_TRAMPOLINE, mono_get_generic_trampoline_simple_name (tramp_type));
 
 	if (code_len)
 		*code_len = code - buf;
@@ -351,13 +356,17 @@ mono_arch_get_unbox_trampoline (MonoMethod *m, gpointer addr)
 	MonoDomain *domain = mono_domain_get ();
 
 	start = code = mono_domain_code_reserve (domain, size);
+
+	MINI_BEGIN_CODEGEN ();
+
 	code = mono_arm_emit_imm64 (code, ARMREG_IP0, (guint64)addr);
 	arm_addx_imm (code, ARMREG_R0, ARMREG_R0, MONO_ABI_SIZEOF (MonoObject));
 	arm_brx (code, ARMREG_IP0);
 
 	g_assert ((code - start) <= size);
-	mono_arch_flush_icache (start, code - start);
-	MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_UNBOX_TRAMPOLINE, m));
+
+	MINI_END_CODEGEN (start, code - start, MONO_PROFILER_CODE_BUFFER_UNBOX_TRAMPOLINE, m);
+
 	return start;
 }
 
@@ -369,14 +378,16 @@ mono_arch_get_static_rgctx_trampoline (gpointer arg, gpointer addr)
 	MonoDomain *domain = mono_domain_get ();
 
 	start = code = mono_domain_code_reserve (domain, buf_len);
+
+	MINI_BEGIN_CODEGEN ();
+
 	code = mono_arm_emit_imm64 (code, MONO_ARCH_RGCTX_REG, (guint64)arg);
 	code = mono_arm_emit_imm64 (code, ARMREG_IP0, (guint64)addr);
 	arm_brx (code, ARMREG_IP0);
 
-	g_assert ((code - start) <= buf_len);
+	MINI_END_CODEGEN (start, code - start, MONO_PROFILER_CODE_BUFFER_GENERICS_TRAMPOLINE, NULL);
 
-	mono_arch_flush_icache (start, code - start);
-	MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_GENERICS_TRAMPOLINE, NULL));
+	g_assert ((code - start) <= buf_len);
 
 	return start;
 }
@@ -415,6 +426,8 @@ mono_arch_create_rgctx_lazy_fetch_trampoline (guint32 slot, MonoTrampInfo **info
 	/* The vtable/mrgtx is in R0 */
 	g_assert (MONO_ARCH_VTABLE_REG == ARMREG_R0);
 
+	MINI_BEGIN_CODEGEN ();
+
 	if (is_mrgctx) {
 		/* get mrgctx ptr */
 		arm_movx (code, ARMREG_IP1, ARMREG_R0);
@@ -468,11 +481,10 @@ mono_arch_create_rgctx_lazy_fetch_trampoline (guint32 slot, MonoTrampInfo **info
 	}
 	arm_brx (code, ARMREG_IP0);
 
-	mono_arch_flush_icache (buf, code - buf);
-	MONO_PROFILER_RAISE (jit_code_buffer, (buf, code - buf, MONO_PROFILER_CODE_BUFFER_GENERICS_TRAMPOLINE, NULL));
-
 	g_assert (code - buf <= buf_size);
 
+	MINI_END_CODEGEN (buf, code - buf, MONO_PROFILER_CODE_BUFFER_GENERICS_TRAMPOLINE, NULL);
+
 	if (info) {
 		char *name = mono_get_rgctx_fetch_trampoline_name (slot);
 		*info = mono_tramp_info_create (name, buf, code - buf, ji, unwind_ops);
@@ -498,6 +510,8 @@ mono_arch_create_general_rgctx_lazy_fetch_trampoline (MonoTrampInfo **info, gboo
 
 	mono_add_unwind_op_def_cfa (unwind_ops, code, buf, ARMREG_SP, 0);
 
+	MINI_BEGIN_CODEGEN ();
+
 	// FIXME: Currently, we always go to the slow path.
 	/* Load trampoline addr */
 	arm_ldrx (code, ARMREG_IP0, MONO_ARCH_RGCTX_REG, 8);
@@ -505,11 +519,10 @@ mono_arch_create_general_rgctx_lazy_fetch_trampoline (MonoTrampInfo **info, gboo
 	g_assert (MONO_ARCH_VTABLE_REG == ARMREG_R0);
 	arm_brx (code, ARMREG_IP0);
 
-	mono_arch_flush_icache (buf, code - buf);
-	MONO_PROFILER_RAISE (jit_code_buffer, (buf, code - buf, MONO_PROFILER_CODE_BUFFER_GENERICS_TRAMPOLINE, NULL));
-
 	g_assert (code - buf <= tramp_size);
 
+	MINI_END_CODEGEN (buf, code - buf, MONO_PROFILER_CODE_BUFFER_GENERICS_TRAMPOLINE, NULL);
+
 	if (info)
 		*info = mono_tramp_info_create ("rgctx_fetch_trampoline_general", buf, code - buf, ji, unwind_ops);
 
@@ -547,6 +560,8 @@ mono_arch_create_sdb_trampoline (gboolean single_step, MonoTrampInfo **info, gbo
 
 	// FIXME: Unwind info
 
+	MINI_BEGIN_CODEGEN ();
+
 	/* Setup stack frame */
 	imm = frame_size;
 	while (imm > 256) {
@@ -605,10 +620,10 @@ mono_arch_create_sdb_trampoline (gboolean single_step, MonoTrampInfo **info, gbo
 
 	arm_retx (code, ARMREG_LR);
 
-	mono_arch_flush_icache (code, code - buf);
-	MONO_PROFILER_RAISE (jit_code_buffer, (buf, code - buf, MONO_PROFILER_CODE_BUFFER_HELPER, NULL));
 	g_assert (code - buf <= tramp_size);
 
+	MINI_END_CODEGEN (buf, code - buf, MONO_PROFILER_CODE_BUFFER_HELPER, NULL);
+
 	const char *tramp_name = single_step ? "sdb_single_step_trampoline" : "sdb_breakpoint_trampoline";
 	*info = mono_tramp_info_create (tramp_name, buf, code - buf, ji, unwind_ops);
 
@@ -644,6 +659,8 @@ mono_arch_get_interp_to_native_trampoline (MonoTrampInfo **info)
 
 	framesize = ALIGN_TO (framesize, MONO_ARCH_FRAME_ALIGNMENT);
 
+	MINI_BEGIN_CODEGEN ();
+
 	arm_subx_imm (code, ARMREG_SP, ARMREG_SP, framesize);
 	arm_stpx (code, ARMREG_FP, ARMREG_LR, ARMREG_SP, 0);
 	arm_movspx (code, ARMREG_FP, ARMREG_SP);
@@ -712,8 +729,7 @@ mono_arch_get_interp_to_native_trampoline (MonoTrampInfo **info)
 
 	g_assert (code - start < buf_len);
 
-	mono_arch_flush_icache (start, code - start);
-	MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_HELPER, NULL));
+	MINI_END_CODEGEN (start, code - start, MONO_PROFILER_CODE_BUFFER_HELPER, NULL);
 
 	if (info)
 		*info = mono_tramp_info_create ("interp_to_native_trampoline", start, code - start, ji, unwind_ops);
@@ -744,6 +760,8 @@ mono_arch_get_native_to_interp_trampoline (MonoTrampInfo **info)
 	offset += sizeof (CallContext);
 	framesize = ALIGN_TO (offset, MONO_ARCH_FRAME_ALIGNMENT);
 
+	MINI_BEGIN_CODEGEN ();
+
 	mono_add_unwind_op_def_cfa (unwind_ops, code, start, ARMREG_SP, 0);
 
 	arm_subx_imm (code, ARMREG_SP, ARMREG_SP, framesize);
@@ -788,8 +806,7 @@ mono_arch_get_native_to_interp_trampoline (MonoTrampInfo **info)
 
 	g_assert (code - start < buf_len);
 
-	mono_arch_flush_icache (start, code - start);
-	MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));
+	MINI_END_CODEGEN (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL);
 
 	if (info)
 		*info = mono_tramp_info_create ("native_to_interp_trampoline", start, code - start, ji, unwind_ops);
diff --git a/src/mono/mono/sgen/sgen-client.h b/src/mono/mono/sgen/sgen-client.h
index 53a1a43f45de1d..7eb78f75fad5dd 100644
--- a/src/mono/mono/sgen/sgen-client.h
+++ b/src/mono/mono/sgen/sgen-client.h
@@ -207,12 +207,19 @@ void sgen_client_bridge_processing_finish (int generation);
 gboolean sgen_client_bridge_is_bridge_object (GCObject *obj);
 void sgen_client_bridge_register_finalized_object (GCObject *object);
 
+#ifndef DISABLE_SGEN_TOGGLEREF
 /*
  * No action is necessary.
  */
 void sgen_client_mark_togglerefs (char *start, char *end, ScanCopyContext ctx);
 void sgen_client_clear_togglerefs (char *start, char *end, ScanCopyContext ctx);
 void sgen_foreach_toggleref_root (void (*callback)(MonoObject*, gpointer), gpointer data);
+#else
+static inline void sgen_client_mark_togglerefs (char *start, char *end, ScanCopyContext ctx) { }
+static inline void sgen_client_clear_togglerefs (char *start, char *end, ScanCopyContext ctx) { }
+static inline void sgen_foreach_toggleref_root (void (*callback)(MonoObject*, gpointer), gpointer data) { }
+#endif
+
 
 /*
  * Called to handle `MONO_GC_PARAMS` and `MONO_GC_DEBUG` options.  The `handle` functions
diff --git a/src/mono/mono/sgen/sgen-conf.h b/src/mono/mono/sgen/sgen-conf.h
index a955a46ab53eb5..fc6ee088dbf5ed 100644
--- a/src/mono/mono/sgen/sgen-conf.h
+++ b/src/mono/mono/sgen/sgen-conf.h
@@ -130,7 +130,12 @@ typedef target_mword SgenDescriptor;
  * Making this a constant enables us to put logging in a lot of places and
  * not pay its cost on release builds.
  */
+#ifndef DISABLE_SGEN_DEBUG_HELPERS
 #define SGEN_MAX_DEBUG_LEVEL 2
+#else
+/* No logging support */
+#define SGEN_MAX_DEBUG_LEVEL (-1)
+#endif
 
 /*
  * Maximum level of asserts to enable on this build.
diff --git a/src/mono/mono/sgen/sgen-gc.c b/src/mono/mono/sgen/sgen-gc.c
index d1330d0d502c68..e6719fae05854d 100644
--- a/src/mono/mono/sgen/sgen-gc.c
+++ b/src/mono/mono/sgen/sgen-gc.c
@@ -235,7 +235,12 @@ static gboolean disable_minor_collections = FALSE;
 static gboolean disable_major_collections = FALSE;
 static gboolean do_verify_nursery = FALSE;
 static gboolean do_dump_nursery_content = FALSE;
+
+#ifndef DISABLE_SGEN_DEBUG_HELPERS
 static gboolean enable_nursery_canaries = FALSE;
+#else
+static const gboolean enable_nursery_canaries = FALSE;
+#endif
 
 static gboolean precleaning_enabled = TRUE;
 static gboolean dynamic_nursery = FALSE;
@@ -378,7 +383,9 @@ static volatile mword highest_heap_address = 0;
 MonoCoopMutex sgen_interruption_mutex;
 
 int sgen_current_collection_generation = -1;
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 volatile gboolean sgen_concurrent_collection_in_progress = FALSE;
+#endif
 
 /* objects that are ready to be finalized */
 static SgenPointerQueue fin_ready_queue = SGEN_POINTER_QUEUE_INIT (INTERNAL_MEM_FINALIZE_READY);
@@ -1359,6 +1366,7 @@ sgen_set_pinned_from_failed_allocation (mword objsize)
 	bytes_pinned_from_failed_allocation += objsize;
 }
 
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 gboolean
 sgen_collection_is_concurrent (void)
 {
@@ -1378,6 +1386,7 @@ sgen_get_concurrent_collection_in_progress (void)
 {
 	return sgen_concurrent_collection_in_progress;
 }
+#endif
 
 typedef struct {
 	SgenThreadPoolJob job;
@@ -2176,10 +2185,12 @@ major_start_collection (SgenGrayQueue *gc_thread_gray_queue, const char *reason,
 {
 	SgenObjectOperations *object_ops_nopar, *object_ops_par = NULL;
 
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 	if (concurrent) {
 		g_assert (sgen_major_collector.is_concurrent);
 		sgen_concurrent_collection_in_progress = TRUE;
 	}
+#endif
 
 	sgen_binary_protocol_collection_begin (mono_atomic_load_i32 (&mono_gc_stats.major_gc_count), GENERATION_OLD);
 
@@ -2366,8 +2377,10 @@ major_finish_collection (SgenGrayQueue *gc_thread_gray_queue, const char *reason
 
 	sgen_binary_protocol_collection_end (mono_atomic_load_i32 (&mono_gc_stats.major_gc_count) - 1, GENERATION_OLD, counts.num_scanned_objects, counts.num_unique_scanned_objects);
 
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 	if (sgen_concurrent_collection_in_progress)
 		sgen_concurrent_collection_in_progress = FALSE;
+#endif
 }
 
 static gboolean
@@ -3729,7 +3742,11 @@ sgen_gc_init (void)
 				sgen_binary_protocol_init (filename, (gint64)limit);
 			} else if (!strcmp (opt, "nursery-canaries")) {
 				do_verify_nursery = TRUE;
+#ifndef DISABLE_SGEN_DEBUG_HELPERS
 				enable_nursery_canaries = TRUE;
+#else
+				g_error ("Sgen was built with canaries disabled");
+#endif
 				/* If aot code is used, allocation from there won't expect the layout with canaries enabled */
 				sgen_set_use_managed_allocator (FALSE);
 			} else if (!sgen_client_handle_gc_debug (opt)) {
diff --git a/src/mono/mono/sgen/sgen-gc.h b/src/mono/mono/sgen/sgen-gc.h
index 2478a0be511b13..900ed5b1f809a8 100644
--- a/src/mono/mono/sgen/sgen-gc.h
+++ b/src/mono/mono/sgen/sgen-gc.h
@@ -476,20 +476,37 @@ void sgen_free_internal (void *addr, int type);
 void* sgen_alloc_internal_dynamic (size_t size, int type, gboolean assert_on_failure);
 void sgen_free_internal_dynamic (void *addr, size_t size, int type);
 
+#ifndef DISABLE_SGEN_DEBUG_HELPERS
 void sgen_pin_stats_enable (void);
 void sgen_pin_stats_register_object (GCObject *obj, int generation);
 void sgen_pin_stats_register_global_remset (GCObject *obj);
 void sgen_pin_stats_report (void);
+#else
+static inline void sgen_pin_stats_enable (void) { }
+static inline void sgen_pin_stats_register_object (GCObject *obj, int generation) { }
+static inline void sgen_pin_stats_register_global_remset (GCObject *obj) { }
+static inline void sgen_pin_stats_report (void) { }
+#endif
 
+#ifndef DISABLE_SGEN_DEBUG_HELPERS
 void sgen_gchandle_stats_enable (void);
 void sgen_gchandle_stats_report (void);
+#else
+static inline void sgen_gchandle_stats_enable (void) { }
+static inline void sgen_gchandle_stats_report (void) { }
+#endif
 
 void sgen_sort_addresses (void **array, size_t size);
 void sgen_add_to_global_remset (gpointer ptr, GCObject *obj);
 
 int sgen_get_current_collection_generation (void);
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 gboolean sgen_collection_is_concurrent (void);
 gboolean sgen_get_concurrent_collection_in_progress (void);
+#else
+#define sgen_collection_is_concurrent() FALSE
+#define sgen_get_concurrent_collection_in_progress() FALSE
+#endif
 
 void sgen_set_bytes_allocated_attached (guint64 bytes);
 void sgen_increment_bytes_allocated_detached (guint64 bytes);
@@ -837,8 +854,14 @@ void sgen_register_obj_with_weak_fields (GCObject *obj);
 void sgen_mark_togglerefs (char *start, char *end, ScanCopyContext ctx);
 void sgen_clear_togglerefs (char *start, char *end, ScanCopyContext ctx);
 
+#ifndef DISABLE_SGEN_TOGGLEREF
 void sgen_process_togglerefs (void);
 void sgen_register_test_toggleref_callback (void);
+#else
+static inline void sgen_process_togglerefs (void) { }
+static inline void sgen_register_test_toggleref_callback (void) { }
+#endif
+
 
 void sgen_mark_bridge_object (GCObject *obj)
 	MONO_PERMIT (need (sgen_gc_locked));
@@ -1074,7 +1097,11 @@ extern mword sgen_total_promoted_size;
 extern mword sgen_total_allocated_major;
 extern volatile gboolean sgen_suspend_finalizers;
 extern MonoCoopMutex sgen_gc_mutex;
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 extern volatile gboolean sgen_concurrent_collection_in_progress;
+#else
+static const gboolean sgen_concurrent_collection_in_progress = FALSE;
+#endif
 
 /* Nursery helpers. */
 
diff --git a/src/mono/mono/sgen/sgen-gchandles.c b/src/mono/mono/sgen/sgen-gchandles.c
index 1ca10685a8c1fb..b802c439db6d96 100644
--- a/src/mono/mono/sgen/sgen-gchandles.c
+++ b/src/mono/mono/sgen/sgen-gchandles.c
@@ -523,6 +523,7 @@ sgen_register_obj_with_weak_fields (GCObject *obj)
 	alloc_handle (gc_handles_for_type (HANDLE_WEAK_FIELDS), obj, FALSE);
 }
 
+#ifndef DISABLE_SGEN_DEBUG_HELPERS
 void
 sgen_gchandle_stats_enable (void)
 {
@@ -596,6 +597,7 @@ sgen_gchandle_stats_report (void)
 		mono_gc_printf (sgen_gc_debug_file, "\n");
 	} SGEN_HASH_TABLE_FOREACH_END;
 }
+#endif
 
 void
 sgen_init_gchandles (void)
diff --git a/src/mono/mono/sgen/sgen-marksweep.c b/src/mono/mono/sgen/sgen-marksweep.c
index 5fbd780144f467..7634caa5e21f39 100644
--- a/src/mono/mono/sgen/sgen-marksweep.c
+++ b/src/mono/mono/sgen/sgen-marksweep.c
@@ -197,7 +197,11 @@ typedef enum {
 static volatile int sweep_state = SWEEP_STATE_SWEPT;
 
 static gboolean concurrent_mark;
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 static gboolean concurrent_sweep = DEFAULT_SWEEP_MODE;
+#else
+static const gboolean concurrent_sweep = SGEN_SWEEP_SERIAL;
+#endif
 
 static int sweep_pool_context = -1;
 
@@ -908,6 +912,9 @@ static SgenThreadPoolJob * volatile sweep_blocks_job;
 static void
 major_finish_sweep_checking (void)
 {
+	if (!concurrent_sweep)
+		return;
+
 	guint32 block_index;
 	SgenThreadPoolJob *job;
 
@@ -2399,10 +2406,16 @@ major_handle_gc_param (const char *opt)
 		lazy_sweep = FALSE;
 		return TRUE;
 	} else if (!strcmp (opt, "concurrent-sweep")) {
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 		concurrent_sweep = TRUE;
+#else
+		g_error ("Sgen was built with concurrent collector disabled");
+#endif
 		return TRUE;
 	} else if (!strcmp (opt, "no-concurrent-sweep")) {
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 		concurrent_sweep = FALSE;
+#endif
 		return TRUE;
 	}
 
@@ -2884,7 +2897,9 @@ sgen_marksweep_init_internal (SgenMajorCollector *collector, gboolean is_concurr
 	collector->alloc_degraded = major_alloc_degraded;
 
 	collector->alloc_object = major_alloc_object;
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 	collector->alloc_object_par = major_alloc_object_par;
+#endif
 	collector->free_pinned_object = free_pinned_object;
 	collector->iterate_objects = major_iterate_objects;
 	collector->free_non_pinned_object = major_free_non_pinned_object;
@@ -2921,7 +2936,9 @@ sgen_marksweep_init_internal (SgenMajorCollector *collector, gboolean is_concurr
 	collector->post_param_init = post_param_init;
 	collector->is_valid_object = major_is_valid_object;
 	collector->describe_pointer = major_describe_pointer;
+#ifndef DISABLE_SGEN_BINARY_PROTOCOL
 	collector->count_cards = major_count_cards;
+#endif
 	collector->init_block_free_lists = sgen_init_block_free_lists;
 
 	collector->major_ops_serial.copy_or_mark_object = major_copy_or_mark_object_canonical;
diff --git a/src/mono/mono/sgen/sgen-pinning-stats.c b/src/mono/mono/sgen/sgen-pinning-stats.c
index f3e8631e991298..c8f0e0e22c29da 100644
--- a/src/mono/mono/sgen/sgen-pinning-stats.c
+++ b/src/mono/mono/sgen/sgen-pinning-stats.c
@@ -10,6 +10,8 @@
 #include "config.h"
 #ifdef HAVE_SGEN_GC
 
+#ifndef DISABLE_SGEN_DEBUG_HELPERS
+
 #include <string.h>
 
 #include "mono/sgen/sgen-gc.h"
@@ -247,4 +249,6 @@ sgen_pin_stats_get_object_list (void)
 	return &pinned_objects;
 }
 
+#endif
+
 #endif /* HAVE_SGEN_GC */
diff --git a/src/mono/mono/sgen/sgen-pinning.h b/src/mono/mono/sgen/sgen-pinning.h
index 797e12b2614b29..d445b2b3486021 100644
--- a/src/mono/mono/sgen/sgen-pinning.h
+++ b/src/mono/mono/sgen/sgen-pinning.h
@@ -42,10 +42,17 @@ void sgen_pin_objects_in_section (GCMemSection *section, ScanCopyContext ctx);
 
 /* Pinning stats */
 
+#ifndef DISABLE_SGEN_DEBUG_HELPERS
 void sgen_pin_stats_register_address (char *addr, int pin_type);
 size_t sgen_pin_stats_get_pinned_byte_count (int pin_type);
 SgenPointerQueue *sgen_pin_stats_get_object_list (void);
 void sgen_pin_stats_reset (void);
+#else
+static inline void sgen_pin_stats_register_address (char *addr, int pin_type) { }
+static inline size_t sgen_pin_stats_get_pinned_byte_count (int pin_type) { return 0; }
+static inline SgenPointerQueue *sgen_pin_stats_get_object_list (void) { return NULL; }
+static inline void sgen_pin_stats_reset (void) { }
+#endif
 
 /* Perpetual pinning, aka cementing */
 
diff --git a/src/mono/mono/sgen/sgen-protocol.c b/src/mono/mono/sgen/sgen-protocol.c
index 4afaf87e20d6d2..5fc013d6b57f3d 100644
--- a/src/mono/mono/sgen/sgen-protocol.c
+++ b/src/mono/mono/sgen/sgen-protocol.c
@@ -30,6 +30,8 @@
 #include <fcntl.h>
 #endif
 
+#ifndef DISABLE_SGEN_BINARY_PROTOCOL
+
 #if defined(HOST_WIN32)
 static const HANDLE invalid_file_value = INVALID_HANDLE_VALUE;
 /* If valid, dump binary protocol to this file */
@@ -488,4 +490,6 @@ protocol_entry (unsigned char type, gpointer data, int size)
 #undef TYPE_POINTER
 #undef TYPE_BOOL
 
+#endif
+
 #endif /* HAVE_SGEN_GC */
diff --git a/src/mono/mono/sgen/sgen-protocol.h b/src/mono/mono/sgen/sgen-protocol.h
index a29eb7d3e3d313..eff42b3206bdab 100644
--- a/src/mono/mono/sgen/sgen-protocol.h
+++ b/src/mono/mono/sgen/sgen-protocol.h
@@ -14,6 +14,8 @@
 
 #include "sgen-gc.h"
 
+#ifndef DISABLE_SGEN_BINARY_PROTOCOL
+
 #define PROTOCOL_HEADER_CHECK 0xde7ec7ab1ec0de
 /*
  * The version needs to be bumped every time we introduce breaking changes (like
@@ -244,4 +246,70 @@ gboolean sgen_binary_protocol_flush_buffers (gboolean force);
 #undef TYPE_POINTER
 #undef TYPE_BOOL
 
+#else
+
+#ifndef TYPE_INT
+#define TYPE_INT int
+#endif
+#ifndef TYPE_LONGLONG
+#define TYPE_LONGLONG long long
+#endif
+#ifndef TYPE_SIZE
+#define TYPE_SIZE size_t
+#endif
+#ifndef TYPE_POINTER
+#define TYPE_POINTER gpointer
+#endif
+#ifndef TYPE_BOOL
+#define TYPE_BOOL gboolean
+#endif
+
+#define BEGIN_PROTOCOL_ENTRY0(method) \
+	static inline void sgen_ ## method (void) {}
+#define BEGIN_PROTOCOL_ENTRY1(method,t1,f1) \
+	static inline void sgen_ ## method (t1 f1) {}
+#define BEGIN_PROTOCOL_ENTRY2(method,t1,f1,t2,f2) \
+	static inline void sgen_ ## method (t1 f1, t2 f2) {}
+#define BEGIN_PROTOCOL_ENTRY3(method,t1,f1,t2,f2,t3,f3) \
+	static inline void sgen_ ## method (t1 f1, t2 f2, t3 f3) {}
+#define BEGIN_PROTOCOL_ENTRY4(method,t1,f1,t2,f2,t3,f3,t4,f4) \
+	static inline void sgen_ ## method (t1 f1, t2 f2, t3 f3, t4 f4) {}
+#define BEGIN_PROTOCOL_ENTRY5(method,t1,f1,t2,f2,t3,f3,t4,f4,t5,f5) \
+	static inline void sgen_ ## method (t1 f1, t2 f2, t3 f3, t4 f4, t5 f5) {}
+#define BEGIN_PROTOCOL_ENTRY6(method,t1,f1,t2,f2,t3,f3,t4,f4,t5,f5,t6,f6) \
+	static inline void sgen_ ## method (t1 f1, t2 f2, t3 f3, t4 f4, t5 f5, t6 f6) {}
+#define BEGIN_PROTOCOL_ENTRY_HEAVY0(method) \
+	static inline void sgen_ ## method (void) {}
+#define BEGIN_PROTOCOL_ENTRY_HEAVY1(method,t1,f1) \
+	static inline void sgen_ ## method (t1 f1) {}
+#define BEGIN_PROTOCOL_ENTRY_HEAVY2(method,t1,f1,t2,f2) \
+	static inline void sgen_ ## method (t1 f1, t2 f2) {}
+#define BEGIN_PROTOCOL_ENTRY_HEAVY3(method,t1,f1,t2,f2,t3,f3) \
+	static inline void sgen_ ## method (t1 f1, t2 f2, t3 f3) {}
+#define BEGIN_PROTOCOL_ENTRY_HEAVY4(method,t1,f1,t2,f2,t3,f3,t4,f4) \
+	static inline void sgen_ ## method (t1 f1, t2 f2, t3 f3, t4 f4) {}
+#define BEGIN_PROTOCOL_ENTRY_HEAVY5(method,t1,f1,t2,f2,t3,f3,t4,f4,t5,f5) \
+	static inline void sgen_ ## method (t1 f1, t2 f2, t3 f3, t4 f4, t5 f5) {}
+#define BEGIN_PROTOCOL_ENTRY_HEAVY6(method,t1,f1,t2,f2,t3,f3,t4,f4,t5,f5,t6,f6) \
+	static inline void sgen_ ## method (t1 f1, t2 f2, t3 f3, t4 f4, t5 f5, t6 f6) {}
+#define DEFAULT_PRINT()
+#define CUSTOM_PRINT(_)
+
+#define IS_ALWAYS_MATCH(_)
+#define MATCH_INDEX(_)
+#define IS_VTABLE_MATCH(_)
+
+#define END_PROTOCOL_ENTRY
+#define END_PROTOCOL_ENTRY_FLUSH
+#define END_PROTOCOL_ENTRY_HEAVY
+
+#include "sgen-protocol-def.h"
+
+static inline void sgen_binary_protocol_init (const char *filename, long long limit) {}
+static inline gboolean sgen_binary_protocol_is_enabled (void) { return FALSE; }
+static inline gboolean sgen_binary_protocol_flush_buffers (gboolean force) { return FALSE; }
+static inline gboolean sgen_binary_protocol_is_heavy_enabled () { return FALSE; }
+
+#endif
+
 #endif
diff --git a/src/mono/mono/sgen/sgen-thread-pool.c b/src/mono/mono/sgen/sgen-thread-pool.c
index 656e561856791c..2cb408f7cbfe31 100644
--- a/src/mono/mono/sgen/sgen-thread-pool.c
+++ b/src/mono/mono/sgen/sgen-thread-pool.c
@@ -15,6 +15,8 @@
 #include "mono/sgen/sgen-client.h"
 #include "mono/utils/mono-os-mutex.h"
 
+
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 static mono_mutex_t lock;
 static mono_cond_t work_cond;
 static mono_cond_t done_cond;
@@ -402,5 +404,71 @@ sgen_thread_pool_is_thread_pool_thread (MonoNativeThreadId some_thread)
 
 	return 0;
 }
+#else
+
+int
+sgen_thread_pool_create_context (int num_threads, SgenThreadPoolThreadInitFunc init_func, SgenThreadPoolIdleJobFunc idle_func, SgenThreadPoolContinueIdleJobFunc continue_idle_func, SgenThreadPoolShouldWorkFunc should_work_func, void **thread_datas)
+{
+	return 0;
+}
+
+void
+sgen_thread_pool_start (void)
+{
+}
+
+void
+sgen_thread_pool_shutdown (void)
+{
+}
+
+SgenThreadPoolJob*
+sgen_thread_pool_job_alloc (const char *name, SgenThreadPoolJobFunc func, size_t size)
+{
+	SgenThreadPoolJob *job = (SgenThreadPoolJob *)sgen_alloc_internal_dynamic (size, INTERNAL_MEM_THREAD_POOL_JOB, TRUE);
+	job->name = name;
+	job->size = size;
+	job->func = func;
+	return job;
+}
+
+void
+sgen_thread_pool_job_free (SgenThreadPoolJob *job)
+{
+	sgen_free_internal_dynamic (job, job->size, INTERNAL_MEM_THREAD_POOL_JOB);
+}
+
+void
+sgen_thread_pool_job_enqueue (int context_id, SgenThreadPoolJob *job)
+{
+}
+
+void
+sgen_thread_pool_job_wait (int context_id, SgenThreadPoolJob *job)
+{
+}
+
+void
+sgen_thread_pool_idle_signal (int context_id)
+{
+}
+
+void
+sgen_thread_pool_idle_wait (int context_id, SgenThreadPoolContinueIdleWaitFunc continue_wait)
+{
+}
+
+void
+sgen_thread_pool_wait_for_all_jobs (int context_id)
+{
+}
+
+int
+sgen_thread_pool_is_thread_pool_thread (MonoNativeThreadId some_thread)
+{
+	return 0;
+}
+
+#endif
 
 #endif
diff --git a/src/mono/mono/sgen/sgen-workers.c b/src/mono/mono/sgen/sgen-workers.c
index a8897d93dbb5e7..16e93d69a0f0a4 100644
--- a/src/mono/mono/sgen/sgen-workers.c
+++ b/src/mono/mono/sgen/sgen-workers.c
@@ -639,11 +639,6 @@ sgen_workers_assert_gray_queue_is_empty (int generation)
 {
 }
 
-void
-sgen_workers_foreach (int generation, SgenWorkerCallback callback)
-{
-}
-
 SgenObjectOperations*
 sgen_workers_get_idle_func_object_ops (WorkerData *worker)
 {
@@ -685,11 +680,6 @@ sgen_workers_set_num_active_workers (int generation, int num_workers)
 {
 }
 
-void
-sgen_workers_start_all_workers (int generation, SgenObjectOperations *object_ops_nopar, SgenObjectOperations *object_ops_par, SgenWorkersFinishCallback callback)
-{
-}
-
 void
 sgen_workers_stop_all_workers (int generation)
 {
diff --git a/src/mono/mono/sgen/sgen-workers.h b/src/mono/mono/sgen/sgen-workers.h
index 14e68c93e2ae84..dce2364857be8c 100644
--- a/src/mono/mono/sgen/sgen-workers.h
+++ b/src/mono/mono/sgen/sgen-workers.h
@@ -78,7 +78,11 @@ struct _WorkerContext {
 void sgen_workers_create_context (int generation, int num_workers);
 void sgen_workers_stop_all_workers (int generation);
 void sgen_workers_set_num_active_workers (int generation, int num_workers);
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 void sgen_workers_start_all_workers (int generation, SgenObjectOperations *object_ops_nopar, SgenObjectOperations *object_ops_par, SgenWorkersFinishCallback finish_job);
+#else
+#define sgen_workers_start_all_workers(...)
+#endif
 void sgen_workers_enqueue_job (int generation, SgenThreadPoolJob *job, gboolean enqueue);
 void sgen_workers_join (int generation);
 gboolean sgen_workers_have_idle_work (int generation);
@@ -88,7 +92,11 @@ void sgen_workers_take_from_queue (int generation, SgenGrayQueue *queue);
 SgenObjectOperations* sgen_workers_get_idle_func_object_ops (WorkerData *worker);
 int sgen_workers_get_job_split_count (int generation);
 int sgen_workers_get_active_worker_count (int generation);
+#ifndef DISABLE_SGEN_MAJOR_MARKSWEEP_CONC
 void sgen_workers_foreach (int generation, SgenWorkerCallback callback);
+#else
+#define sgen_workers_foreach(...)
+#endif
 gboolean sgen_workers_is_worker_thread (MonoNativeThreadId id);
 
 #endif
diff --git a/src/mono/mono/tests/Makefile.am b/src/mono/mono/tests/Makefile.am
index fc2a7661882d40..6a3af788dfe401 100755
--- a/src/mono/mono/tests/Makefile.am
+++ b/src/mono/mono/tests/Makefile.am
@@ -1121,7 +1121,9 @@ endif
 
 endif
 
-
+if DISABLE_CRASH_REPORTING
+PLATFORM_DISABLED_TESTS += merp-json-valid.exe merp-crash-test.exe
+endif
 
 if HOST_DARWIN
 
diff --git a/src/mono/mono/utils/freebsd-elf_common.h b/src/mono/mono/utils/freebsd-elf_common.h
index 7aef2d49667e4c..658119fdbc51f2 100644
--- a/src/mono/mono/utils/freebsd-elf_common.h
+++ b/src/mono/mono/utils/freebsd-elf_common.h
@@ -169,6 +169,7 @@ typedef struct {
 #define EM_TINYJ	61	/* Advanced Logic Corp. TinyJ processor. */
 #define EM_X86_64	62	/* Advanced Micro Devices x86-64 */
 #define	EM_AMD64	EM_X86_64	/* Advanced Micro Devices x86-64 (compat) */
+#define EM_RISCV	243	/* RISC-V. */
 
 /* Non-standard or deprecated. */
 #define EM_486		6	/* Intel i486. */
diff --git a/src/mono/mono/utils/mono-codeman.c b/src/mono/mono/utils/mono-codeman.c
index a69f25bb43ecfb..24c90a3e6dd462 100644
--- a/src/mono/mono/utils/mono-codeman.c
+++ b/src/mono/mono/utils/mono-codeman.c
@@ -27,7 +27,7 @@ static void* mono_code_manager_heap;
 #endif
 
 #include <mono/utils/mono-os-mutex.h>
-
+#include <mono/utils/mono-tls.h>
 
 static uintptr_t code_memory_used = 0;
 static size_t dynamic_code_alloc_count;
@@ -102,6 +102,7 @@ struct _MonoCodeManager {
 
 static mono_mutex_t valloc_mutex;
 static GHashTable *valloc_freelists;
+static MonoNativeTlsKey write_level_tls_id;
 
 static void*
 codechunk_valloc (void *preferred, guint32 size)
@@ -121,7 +122,9 @@ codechunk_valloc (void *preferred, guint32 size)
 	freelist = (GSList *) g_hash_table_lookup (valloc_freelists, GUINT_TO_POINTER (size));
 	if (freelist) {
 		ptr = freelist->data;
+		mono_codeman_enable_write ();
 		memset (ptr, 0, size);
+		mono_codeman_disable_write ();
 		freelist = g_slist_delete_link (freelist, freelist);
 		g_hash_table_insert (valloc_freelists, GUINT_TO_POINTER (size), freelist);
 	} else {
@@ -176,6 +179,8 @@ mono_code_manager_init (void)
 	mono_counters_register ("Dynamic code allocs", MONO_COUNTER_JIT | MONO_COUNTER_ULONG, &dynamic_code_alloc_count);
 	mono_counters_register ("Dynamic code bytes", MONO_COUNTER_JIT | MONO_COUNTER_ULONG, &dynamic_code_bytes_count);
 	mono_counters_register ("Dynamic code frees", MONO_COUNTER_JIT | MONO_COUNTER_ULONG, &dynamic_code_frees_count);
+
+	mono_native_tls_alloc (&write_level_tls_id, NULL);
 }
 
 void
@@ -271,7 +276,10 @@ mono_codeman_malloc (gsize n)
 	g_assert (heap);
 	return HeapAlloc (heap, 0, n);
 #else
-	return dlmemalign (MIN_ALIGN, n);
+	mono_codeman_enable_write ();
+	gpointer res = dlmemalign (MIN_ALIGN, n);
+	mono_codeman_disable_write ();
+	return res;
 #endif
 }
 
@@ -285,7 +293,9 @@ mono_codeman_free (gpointer p)
 	g_assert (heap);
 	HeapFree (heap, 0, p);
 #else
+	mono_codeman_enable_write ();
 	dlfree (p);
+	mono_codeman_disable_write ();
 #endif
 }
 
@@ -476,7 +486,9 @@ new_codechunk (MonoCodeManager *cman, int size)
 #ifdef BIND_ROOM
 	if (flags == CODE_FLAG_MALLOC) {
 		/* Make sure the thunks area is zeroed */
+		mono_codeman_enable_write ();
 		memset (ptr, 0, bsize);
+		mono_codeman_disable_write ();
 	}
 #endif
 
@@ -639,3 +651,43 @@ mono_code_manager_size (MonoCodeManager *cman, int *used_size)
 		*used_size = used;
 	return size;
 }
+
+/*
+ * mono_codeman_enable_write ():
+ *
+ *   Enable writing to code memory on the current thread on platforms that need it.
+ * Calls can be nested.
+ */
+void
+mono_codeman_enable_write (void)
+{
+#ifdef HAVE_PTHREAD_JIT_WRITE_PROTECT_NP
+	if (__builtin_available (macOS 11, *)) {
+		int level = GPOINTER_TO_INT (mono_native_tls_get_value (write_level_tls_id));
+		level ++;
+		mono_native_tls_set_value (write_level_tls_id, GINT_TO_POINTER (level));
+		pthread_jit_write_protect_np (0);
+	}
+#endif
+}
+
+/*
+ * mono_codeman_disable_write ():
+ *
+ *   Disable writing to code memory on the current thread on platforms that need it.
+ * Calls can be nested.
+ */
+void
+mono_codeman_disable_write (void)
+{
+#ifdef HAVE_PTHREAD_JIT_WRITE_PROTECT_NP
+	if (__builtin_available (macOS 11, *)) {
+		int level = GPOINTER_TO_INT (mono_native_tls_get_value (write_level_tls_id));
+		g_assert (level);
+		level --;
+		mono_native_tls_set_value (write_level_tls_id, GINT_TO_POINTER (level));
+		if (level == 0)
+			pthread_jit_write_protect_np (1);
+	}
+#endif
+}
diff --git a/src/mono/mono/utils/mono-codeman.h b/src/mono/mono/utils/mono-codeman.h
index 4cf447f6e0867d..fbe2a2f2d4f443 100644
--- a/src/mono/mono/utils/mono-codeman.h
+++ b/src/mono/mono/utils/mono-codeman.h
@@ -41,5 +41,8 @@ void             mono_code_manager_install_callbacks (const MonoCodeManagerCallb
 typedef int    (*MonoCodeManagerFunc)      (void *data, int csize, int size, void *user_data);
 void            mono_code_manager_foreach  (MonoCodeManager *cman, MonoCodeManagerFunc func, void *user_data);
 
+void mono_codeman_enable_write (void);
+void mono_codeman_disable_write (void);
+
 #endif /* __MONO_CODEMAN_H__ */
 
diff --git a/src/mono/mono/utils/mono-context.h b/src/mono/mono/utils/mono-context.h
index 7647d4eadb7aea..2dbf043ba13fe2 100644
--- a/src/mono/mono/utils/mono-context.h
+++ b/src/mono/mono/utils/mono-context.h
@@ -918,8 +918,8 @@ typedef struct ucontext MonoContext;
 		"std	%%f13,104(%1)\n"		\
 		"std	%%f14,112(%1)\n"		\
 		"std	%%f15,120(%1)\n"		\
-		: : "r" (&(ctx).uc_mcontext.gregs[0]),		\
-		    "r" (&(ctx).uc_mcontext.fpregs.fprs[0])	\
+		: : "a" (&(ctx).uc_mcontext.gregs[0]),		\
+		    "a" (&(ctx).uc_mcontext.fpregs.fprs[0])	\
 		: "memory"			\
 	)
 
diff --git a/src/mono/mono/utils/mono-hwcap-s390x.c b/src/mono/mono/utils/mono-hwcap-s390x.c
index 5c24a15e5e1b3a..fcfaf9cae7a29d 100644
--- a/src/mono/mono/utils/mono-hwcap-s390x.c
+++ b/src/mono/mono/utils/mono-hwcap-s390x.c
@@ -148,7 +148,7 @@ mono_hwcap_arch_init (void)
 	int lFacs = sizeof (facs) / 8;
 
 	__asm__ __volatile__ (
-		"lgfr\t0,%1\n\t"
+		"lgfr\t%%r0,%1\n\t"
 		".insn\ts,0xb2b00000,%0\n\t"
 		: "=m" (facs)
 		: "r" (lFacs)
diff --git a/src/mono/mono/utils/mono-tls.c b/src/mono/mono/utils/mono-tls.c
index 00be95ee3e843a..f2b11c852044d7 100644
--- a/src/mono/mono/utils/mono-tls.c
+++ b/src/mono/mono/utils/mono-tls.c
@@ -70,11 +70,11 @@
 #  endif
 # else
 #  define MONO_THREAD_VAR_OFFSET(var,offset) do { guint64 foo;  			\
-						__asm__ ("basr  %%r1,0\n\t"		\
+						__asm__ ("larl  %%r1,0f\n\t"		\
 							 "j     0f\n\t"			\
-							 ".quad " #var "@NTPOFF\n"	\
-							 "0:\n\t"			\
-							 "lg    %0,4(%%r1)\n\t"		\
+							 "0:.quad " #var "@NTPOFF\n"	\
+							 "1:\n\t"			\
+							 "lg    %0,0(%%r1)\n\t"		\
 							: "=r" (foo) : : "1");		\
 						offset = foo; } while (0)
 # endif
diff --git a/src/mono/mono/utils/valgrind.h b/src/mono/mono/utils/valgrind.h
index 343d301821e6df..0829ac748b7c60 100644
--- a/src/mono/mono/utils/valgrind.h
+++ b/src/mono/mono/utils/valgrind.h
@@ -831,15 +831,15 @@ typedef
  * (e.g. VEX/priv/guest_s390_decoder.c).
  */
 #define __SPECIAL_INSTRUCTION_PREAMBLE                           \
-                     "lr 15,15\n\t"                              \
-                     "lr 1,1\n\t"                                \
-                     "lr 2,2\n\t"                                \
-                     "lr 3,3\n\t"
+                     "lr %%r15,%%r15\n\t"                        \
+                     "lr %%r1,%%r1\n\t"                          \
+                     "lr %%r2,%%r2\n\t"                          \
+                     "lr %%r3,%%r3\n\t"
 
-#define __CLIENT_REQUEST_CODE "lr 2,2\n\t"
-#define __GET_NR_CONTEXT_CODE "lr 3,3\n\t"
-#define __CALL_NO_REDIR_CODE  "lr 4,4\n\t"
-#define __VEX_INJECT_IR_CODE  "lr 5,5\n\t"
+#define __CLIENT_REQUEST_CODE "lr %%r2,%%r2\n\t"
+#define __GET_NR_CONTEXT_CODE "lr %%r3,%%r3\n\t"
+#define __CALL_NO_REDIR_CODE  "lr %%r4,%%r4\n\t"
+#define __VEX_INJECT_IR_CODE  "lr %%r5,%%r5\n\t"
 
 #define VALGRIND_DO_CLIENT_REQUEST_EXPR(                         \
        _zzq_default, _zzq_request,                               \
@@ -854,15 +854,15 @@ typedef
    _zzq_args[4] = (unsigned long long int)(_zzq_arg4);           \
    _zzq_args[5] = (unsigned long long int)(_zzq_arg5);           \
    __asm__ volatile(/* r2 = args */                              \
-                    "lgr 2,%1\n\t"                               \
+                    "lgr %%r2,%1\n\t"                            \
                     /* r3 = default */                           \
-                    "lgr 3,%2\n\t"                               \
+                    "lgr %%r3,%2\n\t"                            \
                     __SPECIAL_INSTRUCTION_PREAMBLE               \
                     __CLIENT_REQUEST_CODE                        \
                     /* results = r3 */                           \
-                    "lgr %0, 3\n\t"                              \
+                    "lgr %0,%%r3\n\t"                            \
                     : "=d" (_zzq_result)                         \
-                    : "a" (&_zzq_args[0]), "0" (_zzq_default)    \
+                    : "a" (&_zzq_args[0]), "r" (_zzq_default)    \
                     : "cc", "2", "3", "memory"                   \
                    );                                            \
    _zzq_result;                                                  \
@@ -873,7 +873,7 @@ typedef
    volatile unsigned long long int __addr;                       \
    __asm__ volatile(__SPECIAL_INSTRUCTION_PREAMBLE               \
                     __GET_NR_CONTEXT_CODE                        \
-                    "lgr %0, 3\n\t"                              \
+                    "lgr %0,%%r3\n\t"                            \
                     : "=a" (__addr)                              \
                     :                                            \
                     : "cc", "3", "memory"                        \
@@ -4652,17 +4652,17 @@ typedef
       ,"d"(__builtin_dwarf_cfa())
 #  define VALGRIND_CFI_PROLOGUE                                   \
       ".cfi_remember_state\n\t"                                   \
-      "lgr 1,%1\n\t" /* copy the argvec pointer in r1 */          \
-      "lgr 7,11\n\t"                                              \
-      "lgr 11,%2\n\t"                                             \
+      "lgr %%r1,%1\n\t" /* copy the argvec pointer in r1 */       \
+      "lgr %%r7,%%r11\n\t"                                        \
+      "lgr %%r11,%2\n\t"                                          \
       ".cfi_def_cfa r11, 0\n\t"
 #  define VALGRIND_CFI_EPILOGUE                                   \
-      "lgr 11, 7\n\t"                                             \
+      "lgr %%r11,%%r7\n\t"                                        \
       ".cfi_restore_state\n\t"
 #else
 #  define __FRAME_POINTER
 #  define VALGRIND_CFI_PROLOGUE                                   \
-      "lgr 1,%1\n\t"
+      "lgr %%r1,%1\n\t"
 #  define VALGRIND_CFI_EPILOGUE
 #endif
 
@@ -4695,11 +4695,11 @@ typedef
       _argvec[0] = (unsigned long)_orig.nraddr;                  \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-160\n\t"                                      \
-         "lg 1, 0(1)\n\t"  /* target->r1 */                      \
+         "aghi %%r15,-160\n\t"                                   \
+         "lg   %%r1,0(%%r1)\n\t"  /* target->r1 */               \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,160\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,160\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "d" (&_argvec[0]) __FRAME_POINTER           \
@@ -4718,12 +4718,12 @@ typedef
       _argvec[1] = (unsigned long)arg1;                          \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-160\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-160\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,160\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,160\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -4742,13 +4742,13 @@ typedef
       _argvec[2] = (unsigned long)arg2;                          \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-160\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-160\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,160\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,160\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -4768,14 +4768,14 @@ typedef
       _argvec[3] = (unsigned long)arg3;                          \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-160\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 4,24(1)\n\t"                                        \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-160\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r4,24(%%r1)\n\t"                                \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,160\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,160\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -4796,15 +4796,15 @@ typedef
       _argvec[4] = (unsigned long)arg4;                          \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-160\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 4,24(1)\n\t"                                        \
-         "lg 5,32(1)\n\t"                                        \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-160\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r4,24(%%r1)\n\t"                                \
+         "lg   %%r5,32(%%r1)\n\t"                                \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,160\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,160\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -4826,16 +4826,16 @@ typedef
       _argvec[5] = (unsigned long)arg5;                          \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-160\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 4,24(1)\n\t"                                        \
-         "lg 5,32(1)\n\t"                                        \
-         "lg 6,40(1)\n\t"                                        \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-160\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r4,24(%%r1)\n\t"                                \
+         "lg   %%r5,32(%%r1)\n\t"                                \
+         "lg   %%r6,40(%%r1)\n\t"                                \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,160\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,160\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -4859,17 +4859,17 @@ typedef
       _argvec[6] = (unsigned long)arg6;                          \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-168\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 4,24(1)\n\t"                                        \
-         "lg 5,32(1)\n\t"                                        \
-         "lg 6,40(1)\n\t"                                        \
-         "mvc 160(8,15), 48(1)\n\t"                              \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-168\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r4,24(%%r1)\n\t"                                \
+         "lg   %%r5,32(%%r1)\n\t"                                \
+         "lg   %%r6,40(%%r1)\n\t"                                \
+         "mvc  160(8,%%r15),48(%%r1)\n\t"                        \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,168\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,168\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -4894,18 +4894,18 @@ typedef
       _argvec[7] = (unsigned long)arg7;                          \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-176\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 4,24(1)\n\t"                                        \
-         "lg 5,32(1)\n\t"                                        \
-         "lg 6,40(1)\n\t"                                        \
-         "mvc 160(8,15), 48(1)\n\t"                              \
-         "mvc 168(8,15), 56(1)\n\t"                              \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-176\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r4,24(%%r1)\n\t"                                \
+         "lg   %%r5,32(%%r1)\n\t"                                \
+         "lg   %%r6,40(%%r1)\n\t"                                \
+         "mvc  160(8,%%r15),48(%%r1)\n\t"                        \
+         "mvc  168(8,%%r15),56(%%r1)\n\t"                        \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,176\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,176\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -4931,19 +4931,19 @@ typedef
       _argvec[8] = (unsigned long)arg8;                          \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-184\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 4,24(1)\n\t"                                        \
-         "lg 5,32(1)\n\t"                                        \
-         "lg 6,40(1)\n\t"                                        \
-         "mvc 160(8,15), 48(1)\n\t"                              \
-         "mvc 168(8,15), 56(1)\n\t"                              \
-         "mvc 176(8,15), 64(1)\n\t"                              \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-184\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r4,24(%%r1)\n\t"                                \
+         "lg   %%r5,32(%%r1)\n\t"                                \
+         "lg   %%r6,40(%%r1)\n\t"                                \
+         "mvc  160(8,%%r15),48(%%r1)\n\t"                        \
+         "mvc  168(8,%%r15),56(%%r1)\n\t"                        \
+         "mvc  176(8,%%r15),64(%%r1)\n\t"                        \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,184\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,184\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -4970,20 +4970,20 @@ typedef
       _argvec[9] = (unsigned long)arg9;                          \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-192\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 4,24(1)\n\t"                                        \
-         "lg 5,32(1)\n\t"                                        \
-         "lg 6,40(1)\n\t"                                        \
-         "mvc 160(8,15), 48(1)\n\t"                              \
-         "mvc 168(8,15), 56(1)\n\t"                              \
-         "mvc 176(8,15), 64(1)\n\t"                              \
-         "mvc 184(8,15), 72(1)\n\t"                              \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-192\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r4,24(%%r1)\n\t"                                \
+         "lg   %%r5,32(%%r1)\n\t"                                \
+         "lg   %%r6,40(%%r1)\n\t"                                \
+         "mvc  160(8,%%r15),48(%%r1)\n\t"                        \
+         "mvc  168(8,%%r15),56(%%r1)\n\t"                        \
+         "mvc  176(8,%%r15),64(%%r1)\n\t"                        \
+         "mvc  184(8,%%r15),72(%%r1)\n\t"                        \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,192\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,192\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -5011,21 +5011,21 @@ typedef
       _argvec[10] = (unsigned long)arg10;                        \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-200\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 4,24(1)\n\t"                                        \
-         "lg 5,32(1)\n\t"                                        \
-         "lg 6,40(1)\n\t"                                        \
-         "mvc 160(8,15), 48(1)\n\t"                              \
-         "mvc 168(8,15), 56(1)\n\t"                              \
-         "mvc 176(8,15), 64(1)\n\t"                              \
-         "mvc 184(8,15), 72(1)\n\t"                              \
-         "mvc 192(8,15), 80(1)\n\t"                              \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-200\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r4,24(%%r1)\n\t"                                \
+         "lg   %%r5,32(%%r1)\n\t"                                \
+         "lg   %%r6,40(%%r1)\n\t"                                \
+         "mvc  160(8,%%r15),48(%%r1)\n\t"                        \
+         "mvc  168(8,%%r15),56(%%r1)\n\t"                        \
+         "mvc  176(8,%%r15),64(%%r1)\n\t"                        \
+         "mvc  184(8,%%r15),72(%%r1)\n\t"                        \
+         "mvc  192(8,%%r15),80(%%r1)\n\t"                        \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,200\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,200\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -5054,22 +5054,22 @@ typedef
       _argvec[11] = (unsigned long)arg11;                        \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-208\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 4,24(1)\n\t"                                        \
-         "lg 5,32(1)\n\t"                                        \
-         "lg 6,40(1)\n\t"                                        \
-         "mvc 160(8,15), 48(1)\n\t"                              \
-         "mvc 168(8,15), 56(1)\n\t"                              \
-         "mvc 176(8,15), 64(1)\n\t"                              \
-         "mvc 184(8,15), 72(1)\n\t"                              \
-         "mvc 192(8,15), 80(1)\n\t"                              \
-         "mvc 200(8,15), 88(1)\n\t"                              \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-208\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r4,24(%%r1)\n\t"                                \
+         "lg   %%r5,32(%%r1)\n\t"                                \
+         "lg   %%r6,40(%%r1)\n\t"                                \
+         "mvc  160(8,%%r15),48(%%r1)\n\t"                        \
+         "mvc  168(8,%%r15),56(%%r1)\n\t"                        \
+         "mvc  176(8,%%r15),64(%%r1)\n\t"                        \
+         "mvc  184(8,%%r15),72(%%r1)\n\t"                        \
+         "mvc  192(8,%%r15),80(%%r1)\n\t"                        \
+         "mvc  200(8,%%r15),88(%%r1)\n\t"                        \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,208\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,208\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
@@ -5099,23 +5099,23 @@ typedef
       _argvec[12] = (unsigned long)arg12;                        \
       __asm__ volatile(                                          \
          VALGRIND_CFI_PROLOGUE                                   \
-         "aghi 15,-216\n\t"                                      \
-         "lg 2, 8(1)\n\t"                                        \
-         "lg 3,16(1)\n\t"                                        \
-         "lg 4,24(1)\n\t"                                        \
-         "lg 5,32(1)\n\t"                                        \
-         "lg 6,40(1)\n\t"                                        \
-         "mvc 160(8,15), 48(1)\n\t"                              \
-         "mvc 168(8,15), 56(1)\n\t"                              \
-         "mvc 176(8,15), 64(1)\n\t"                              \
-         "mvc 184(8,15), 72(1)\n\t"                              \
-         "mvc 192(8,15), 80(1)\n\t"                              \
-         "mvc 200(8,15), 88(1)\n\t"                              \
-         "mvc 208(8,15), 96(1)\n\t"                              \
-         "lg 1, 0(1)\n\t"                                        \
+         "aghi %%r15,-216\n\t"                                   \
+         "lg   %%r2,8(%%r1)\n\t"                                 \
+         "lg   %%r3,16(%%r1)\n\t"                                \
+         "lg   %%r4,24(%%r1)\n\t"                                \
+         "lg   %%r5,32(%%r1)\n\t"                                \
+         "lg   %%r6,40(%%r1)\n\t"                                \
+         "mvc  160(8,%%r15),48(%%r1)\n\t"                        \
+         "mvc  168(8,%%r15),56(%%r1)\n\t"                        \
+         "mvc  176(8,%%r15),64(%%r1)\n\t"                        \
+         "mvc  184(8,%%r15),72(%%r1)\n\t"                        \
+         "mvc  192(8,%%r15),80(%%r1)\n\t"                        \
+         "mvc  200(8,%%r15),88(%%r1)\n\t"                        \
+         "mvc  208(8,%%r15),96(%%r1)\n\t"                        \
+         "lg   %%r1,0(%%r1)\n\t"                                 \
          VALGRIND_CALL_NOREDIR_R1                                \
-         "lgr %0, 2\n\t"                                         \
-         "aghi 15,216\n\t"                                       \
+         "lgr  %0,%%r2\n\t"                                      \
+         "aghi %%r15,216\n\t"                                    \
          VALGRIND_CFI_EPILOGUE                                   \
          : /*out*/   "=d" (_res)                                 \
          : /*in*/    "a" (&_argvec[0]) __FRAME_POINTER           \
diff --git a/src/mono/netcore/System.Private.CoreLib/System.Private.CoreLib.csproj b/src/mono/netcore/System.Private.CoreLib/System.Private.CoreLib.csproj
index 95e1e72845ad16..af48a96262b628 100644
--- a/src/mono/netcore/System.Private.CoreLib/System.Private.CoreLib.csproj
+++ b/src/mono/netcore/System.Private.CoreLib/System.Private.CoreLib.csproj
@@ -132,12 +132,6 @@
     <DefineConstants Condition="'$(FeatureManagedEtwChannels)' == 'true'">$(DefineConstants);FEATURE_MANAGED_ETW_CHANNELS</DefineConstants>
     <DefineConstants Condition="'$(FeaturePerfTracing)' == 'true'">$(DefineConstants);FEATURE_PERFTRACING</DefineConstants>
     <DefineConstants Condition="'$(FeatureDefaultInterfaces)' == 'true'">$(DefineConstants);FEATURE_DEFAULT_INTERFACES</DefineConstants>
-    <DefineConstants Condition="'$(TargetsUnix)' == 'true'">$(DefineConstants);TARGET_UNIX</DefineConstants>
-    <DefineConstants Condition="'$(TargetsWindows)' == 'true'">$(DefineConstants);TARGET_WINDOWS</DefineConstants>
-    <DefineConstants Condition="'$(TargetsOSX)' == 'true'">$(DefineConstants);TARGET_OSX</DefineConstants>
-    <DefineConstants Condition="'$(TargetsiOS)' == 'true'">$(DefineConstants);TARGET_IOS</DefineConstants>
-    <DefineConstants Condition="'$(TargetstvOS)' == 'true'">$(DefineConstants);TARGET_TVOS</DefineConstants>
-    <DefineConstants Condition="'$(TargetsBrowser)' == 'true'">$(DefineConstants);TARGET_BROWSER</DefineConstants>
   </PropertyGroup>
 
   <!-- ILLinker settings -->
@@ -266,6 +260,7 @@
       <Compile Include="$(BclSourcesRoot)\System\Runtime\InteropServices\MarshalAsAttribute.Mono.cs" />
       <Compile Include="$(BclSourcesRoot)\System\Runtime\InteropServices\NativeLibrary.Mono.cs" />
       <Compile Include="$(BclSourcesRoot)\System\Runtime\InteropServices\SafeHandle.Mono.cs" />
+      <Compile Include="$(BclSourcesRoot)\System\Runtime\Intrinsics\X86\X86Base.Mono.cs" />
       <Compile Include="$(BclSourcesRoot)\System\Runtime\Loader\AssemblyLoadContext.Mono.cs" />
       <Compile Include="$(BclSourcesRoot)\System\Runtime\Remoting\Contexts\Context.cs" />
       <Compile Include="$(BclSourcesRoot)\System\Security\DynamicSecurityMethodAttribute.cs" />
diff --git a/src/mono/netcore/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.xml b/src/mono/netcore/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.xml
index 788f2c616784c9..31c5d3516b80f7 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.xml
+++ b/src/mono/netcore/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.xml
@@ -49,7 +49,7 @@
 			<method signature="System.Void .ctor(System.String)" />
 			<!-- create_exception_two_strings -->
 			<method signature="System.Void .ctor(System.String,System.String)" />
- 		</type>
+		</type>
 
 		<!-- exception.c (mono_get_exception_argument_out_of_range) -->
 		<type fullname="System.ArgumentOutOfRangeException">
@@ -57,7 +57,7 @@
 			<method signature="System.Void .ctor()" />
 			<!-- create_exception_two_strings -->
 			<method signature="System.Void .ctor(System.String,System.String)" />
- 		</type>
+		</type>
 
 		<!-- exception.c (mono_get_exception_arithmetic) -->
 		<type fullname="System.ArithmeticException">
@@ -142,11 +142,6 @@
 			<method signature="System.Void .ctor()" />
 		</type>
 
-		<!-- debugger-agent.c: create_event_list -->
-		<type fullname="System.Diagnostics.DebuggerNonUserCodeAttribute"/>
-		<type fullname="System.Diagnostics.DebuggerHiddenAttribute"/>
-		<type fullname="System.Diagnostics.DebuggerStepThroughAttribute"/>
-
 		<!-- exception.c (mono_get_exception_divide_by_zero) -->
 		<type fullname="System.DivideByZeroException">
 			<!-- mono_exception_from_name -->
@@ -230,7 +225,7 @@
 
 		<!-- domain.c: mono_defaults.int_class -->
 		<type fullname="System.IntPtr">
-			<field name="m_value"/>
+			<field name="_value"/>
 		</type>
 
 		<!-- exception.c (mono_get_exception_invalid_cast) -->
@@ -281,9 +276,6 @@
 		<!-- mono-mlist.c (managed list): used in threadpool.c and gc.c -->
 		<type fullname="Mono.MonoListItem" preserve="fields" />
 
-		<!-- domain.c: mono_defaults.type_class -->
-		<type fullname="System.MonoType" preserve="nothing" />
-
 		<!-- domain.c: mono_defaults.multicastdelegate_class -->
 		<type fullname="System.MulticastDelegate" preserve="fields" />
 
@@ -425,7 +417,7 @@
 			<!-- marshal.c (mono_marshal_get_synchronized_wrapper) -->
 			<method name="GetTypeFromHandle" />
 			<!-- sre.c (mono_reflection_type_get_underlying_system_type) -->
-			<method name="get_UnderlyingSystemType" feature="sre" />
+			<method name="get_UnderlyingSystemType" />
 		</type>
 
 		<!-- exception.c (mono_get_exception_type_initialization) -->
@@ -462,7 +454,7 @@
 
 		<!-- domain.c: mono_defaults.uint_class -->
 		<type fullname="System.UIntPtr">
-			<field name="m_value"/>
+			<field name="_value"/>
 		</type>
 
 		<!-- object.c: create_unhandled_exception_eventargs (assert) -->
@@ -525,11 +517,6 @@
 
 		<type fullname="System.Reflection.AssemblyName" preserve="fields" />
 
-		<type fullname="System.Reflection.EventInfo" preserve="fields">
-			<method name="AddEventFrame" />
-			<method name="StaticAddEventAdapterFrame" />
-		</type>
-
 		<!-- reflection.c: mono_method_body_get_object -->
 		<type fullname="System.Reflection.RuntimeExceptionHandlingClause" preserve="fields" >
 			<!-- reflection.c mono_object_new_checked in add_exception_handling_clause_to_array -->
@@ -582,12 +569,9 @@
 			<!-- reflection.c mono_object_new_checked in add_parameter_object_to_array -->
 			<method signature="System.Void .ctor()" />
 		</type>
-		<type fullname="System.Reflection.ParameterInfo" preserve="fields" />
 		<!-- reflection.c: ves_icall_get_parameter_info -->
+		<type fullname="System.Reflection.ParameterInfo" preserve="fields" />
 		<type fullname="System.Reflection.RuntimeParameterInfo" >
-			<!-- reflection.c mono_reflection_get_param_info_member_and_pos -->
-			<field name="MemberImpl" />
-			<field name="PositionImpl" />
 			<!-- reflection.c add_parameter_object_to_array -->
 			<method signature="System.Void .ctor(System.String,System.Type,System.Int32,System.Int32,System.Object,System.Reflection.MemberInfo,System.Runtime.InteropServices.MarshalAsAttribute)" />
 		</type>
@@ -597,7 +581,7 @@
 			<method name="Box" />
 		</type>
 
- 		<!-- exception.c (mono_get_exception_reflection_type_load) -->
+		<!-- exception.c (mono_get_exception_reflection_type_load) -->
 		<type fullname="System.Reflection.ReflectionTypeLoadException">
 			<method signature="System.Void .ctor(System.Type[],System.Exception[])" />
 		</type>
@@ -645,8 +629,6 @@
 		<!-- native-library.c: mono_class_get_native_library_class -->
 		<type fullname="System.Runtime.InteropServices.NativeLibrary">
 			<method name="MonoLoadLibraryCallbackStub" />
-			<method name="MonoResolveUnmanagedDll" />
-			<method name="MonoResolveUnmanagedDllUsingEvent" />
 		</type>
 
 		<!-- domain.c: mono_defaults.monitor_class -->
@@ -665,9 +647,7 @@
 
 		<!-- domain.c: mono_defaults.thread_class -->
 		<!-- FIXME: -->
-		<type fullname="System.Threading.Thread" preserve="fields">
-			<method name="get_CurrentContext" />
-		</type>
+		<type fullname="System.Threading.Thread" preserve="fields" />
 
 		<!-- domain.c: mono_defaults.threadabortexception_class -->
 		<!-- exception.c (mono_get_exception_thread_abort) -->
@@ -689,7 +669,7 @@
 		</type>
 
 		<!-- mini-generic-sharing.c -->
-		<type fullname="Mono.ValueTuple" preserve="fields"/>
+		<type fullname="Mono.ValueTuple" required="true"/>
 		<type fullname="Mono.ValueTuple`1" preserve="fields"/>
 		<type fullname="Mono.ValueTuple`2" preserve="fields"/>
 		<type fullname="Mono.ValueTuple`3" preserve="fields"/>
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Delegate.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Delegate.Mono.cs
index af5a59415591a1..faf349979a6a88 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Delegate.Mono.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Delegate.Mono.cs
@@ -177,7 +177,7 @@ public static Delegate CreateDelegate(Type type, object? firstArgument, MethodIn
                 return null;
             }
 
-            return CreateDelegate_internal(type, null, info, throwOnBindFailure);
+            return CreateDelegate_internal(type, target, info, throwOnBindFailure);
         }
 
         [RequiresUnreferencedCode("The target method might be removed")]
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/CustomAttribute.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/CustomAttribute.cs
index 3c9d4ccb82b433..b8af9e8f172c19 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/CustomAttribute.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/CustomAttribute.cs
@@ -593,6 +593,8 @@ internal static bool IsDefined(ICustomAttributeProvider obj, Type attributeType,
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
         private static extern bool IsDefinedInternal(ICustomAttributeProvider obj, Type AttributeType);
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2006:UnrecognizedReflectionPattern",
+            Justification = "Linker analyzes base properties and marks them")]
         private static PropertyInfo? GetBasePropertyDefinition(RuntimePropertyInfo property)
         {
             MethodInfo? method = property.GetGetMethod(true);
@@ -622,6 +624,8 @@ internal static bool IsDefined(ICustomAttributeProvider obj, Type attributeType,
 
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2006:UnrecognizedReflectionPattern",
+            Justification = "Linker analyzes base events and marks them")]
         private static EventInfo? GetBaseEventDefinition(RuntimeEventInfo evt)
         {
             MethodInfo? method = evt.GetAddMethod(true);
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/AssemblyBuilder.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/AssemblyBuilder.Mono.cs
index feedd6aded355b..845968fc6c0cf8 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/AssemblyBuilder.Mono.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/AssemblyBuilder.Mono.cs
@@ -335,6 +335,7 @@ public ModuleBuilder DefineDynamicModule(string name, bool emitSymbolInfo)
             return null;
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type[] GetExportedTypes()
         {
             throw not_supported();
@@ -476,6 +477,7 @@ internal Type MakeGenericType(Type gtd, Type[] typeArguments)
             return new TypeBuilderInstantiation(gtd, typeArguments);
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type? GetType(string name, bool throwOnError, bool ignoreCase)
         {
             if (name == null)
@@ -522,6 +524,7 @@ public override AssemblyName GetName(bool copiedName)
             return AssemblyName.Create(_mono_assembly, null);
         }
 
+        [RequiresUnreferencedCode("Assembly references might be removed")]
         public override AssemblyName[] GetReferencedAssemblies() => RuntimeAssembly.GetReferencedAssemblies (this);
 
         public override Module[] GetLoadedModules(bool getResourceModules)
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/DerivedTypes.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/DerivedTypes.Mono.cs
index 6a72c177444a02..9c9130f1f52fc9 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/DerivedTypes.Mono.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/DerivedTypes.Mono.cs
@@ -150,6 +150,7 @@ public override Guid GUID
             get { throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType")); }
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target,
             object?[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters)
         {
@@ -194,33 +195,39 @@ public override Type BaseType
             get { return typeof(System.Array); }
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo? GetConstructorImpl(BindingFlags bindingAttr, Binder? binder,
                 CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo? GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder,
                 CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo GetField(string name, BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
@@ -236,42 +243,50 @@ public override Type[] GetInterfaces()
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo GetEvent(string name, BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents)]
         public override EventInfo[] GetEvents()
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo? GetPropertyImpl(string name, BindingFlags bindingAttr, Binder? binder,
                 Type? returnType, Type[]? types, ParameterModifier[]? modifiers)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type GetNestedType(string name, BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
@@ -282,6 +297,7 @@ public override InterfaceMapping GetInterfaceMap(Type interfaceType)
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr)
         {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonReflectedType"));
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.Mono.cs
index 66a9cf4fd30fe4..ce8e677d417a63 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.Mono.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.Mono.cs
@@ -224,6 +224,7 @@ protected override TypeAttributes GetAttributeFlagsImpl()
             return _tb.attrs;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo? GetConstructorImpl(
             BindingFlags bindingAttr, Binder? binder, CallingConventions callConvention,
             Type[] types, ParameterModifier[]? modifiers)
@@ -232,6 +233,7 @@ protected override TypeAttributes GetAttributeFlagsImpl()
         }
 
         [ComVisible(true)]
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
         {
             return _tb.GetConstructors(bindingAttr);
@@ -255,26 +257,31 @@ public override object[] GetCustomAttributes(Type attributeType, bool inherit)
             return _tb.GetElementType();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo? GetEvent(string name, BindingFlags bindingAttr)
         {
             return _tb.GetEvent(name, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents)]
         public override EventInfo[] GetEvents()
         {
             return _tb.GetEvents();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr)
         {
             return _tb.GetEvents(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo? GetField(string name, BindingFlags bindingAttr)
         {
             return _tb.GetField(name, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr)
         {
             return _tb.GetFields(bindingAttr);
@@ -296,16 +303,19 @@ public override Type[] GetInterfaces()
             return _tb.GetInterfaces();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr)
         {
             return _tb.GetMember(name, type, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
         {
             return _tb.GetMembers(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo? GetMethodImpl(
             string name, BindingFlags bindingAttr, Binder? binder,
             CallingConventions callConvention, Type[]? types,
@@ -320,26 +330,31 @@ public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
                 callConvention, types, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
         {
             return _tb.GetMethods(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type? GetNestedType(string name, BindingFlags bindingAttr)
         {
             return _tb.GetNestedType(name, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr)
         {
             return _tb.GetNestedTypes(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr)
         {
             return _tb.GetProperties(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo? GetPropertyImpl(
             string name, BindingFlags bindingAttr, Binder? binder,
             Type? returnType, Type[]? types,
@@ -353,6 +368,7 @@ protected override bool HasElementTypeImpl()
             return _tb.HasElementType;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(
             string name, BindingFlags invokeAttr, Binder? binder,
             object? target, object?[]? args,
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/GenericTypeParameterBuilder.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/GenericTypeParameterBuilder.cs
index 74d3dac2dfa7e9..f6c73e84d7fee3 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/GenericTypeParameterBuilder.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/GenericTypeParameterBuilder.cs
@@ -103,6 +103,7 @@ protected override TypeAttributes GetAttributeFlagsImpl()
             return TypeAttributes.Public;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo? GetConstructorImpl(BindingFlags bindingAttr,
                                        Binder? binder,
                                        CallingConventions callConvention,
@@ -113,31 +114,37 @@ protected override TypeAttributes GetAttributeFlagsImpl()
         }
 
         [ComVisible(true)]
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo GetEvent(string name, BindingFlags bindingAttr)
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents)]
         public override EventInfo[] GetEvents()
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr)
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo GetField(string name, BindingFlags bindingAttr)
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr)
         {
             throw not_supported();
@@ -153,21 +160,25 @@ public override Type[] GetInterfaces()
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr)
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo? GetMethodImpl(string name, BindingFlags bindingAttr,
                                  Binder? binder,
                                  CallingConventions callConvention,
@@ -176,21 +187,25 @@ public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type GetNestedType(string name, BindingFlags bindingAttr)
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr)
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr)
         {
             throw not_supported();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo? GetPropertyImpl(string name, BindingFlags bindingAttr,
                                  Binder? binder, Type? returnType,
                                  Type[]? types,
@@ -260,6 +275,7 @@ public override bool IsSZArray
             }
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(string name, BindingFlags invokeAttr,
                              Binder? binder, object? target, object?[]? args,
                              ParameterModifier[]? modifiers,
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.Mono.cs
index 1be005b6b8e516..cc430047f2c11a 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.Mono.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.Mono.cs
@@ -410,6 +410,7 @@ public EnumBuilder DefineEnum(string name, TypeAttributes visibility, Type under
             return result;
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         [ComVisible(true)]
         public override Type? GetType(string className, bool throwOnError, bool ignoreCase)
         {
@@ -525,6 +526,7 @@ public void SetCustomAttribute(ConstructorInfo con, byte[] binaryAttribute)
                         return null;
                 }
         */
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type[] GetTypes()
         {
             if (types == null)
@@ -862,11 +864,13 @@ public override bool IsResource()
             return global_type_created.GetMethod(name, bindingAttr, binder, callConvention, types, modifiers);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override FieldInfo? ResolveField(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             return RuntimeModule.ResolveField(this, _impl, metadataToken, genericTypeArguments, genericMethodArguments);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override MemberInfo? ResolveMember(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             return RuntimeModule.ResolveMember(this, _impl, metadataToken, genericTypeArguments, genericMethodArguments);
@@ -886,21 +890,25 @@ internal MemberInfo ResolveOrGetRegisteredToken(int metadataToken, Type[] generi
                 return m;
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override MethodBase? ResolveMethod(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             return RuntimeModule.ResolveMethod(this, _impl, metadataToken, genericTypeArguments, genericMethodArguments);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override string ResolveString(int metadataToken)
         {
             return RuntimeModule.ResolveString(this, _impl, metadataToken);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override byte[] ResolveSignature(int metadataToken)
         {
             return RuntimeModule.ResolveSignature(this, _impl, metadataToken);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public override Type ResolveType(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             return RuntimeModule.ResolveType(this, _impl, metadataToken, genericTypeArguments, genericMethodArguments);
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.Mono.cs
index 35731ec326543b..346c559144982a 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.Mono.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.Mono.cs
@@ -794,6 +794,8 @@ private bool has_ctor_method()
 
         // We require emitted types to have all members on their bases to be accessible.
         // This is basically an identity function for `this`.
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2006:UnrecognizedReflectionPattern",
+            Justification = "Reflection emitted types have all of their members")]
         [return: DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public
         TypeInfo? CreateTypeInfo()
@@ -985,6 +987,7 @@ internal void GenerateDebugInfo (ISymbolWriter symbolWriter)
                 }
         */
         [ComVisible(true)]
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
         {
             if (is_created)
@@ -1040,6 +1043,7 @@ public override Type GetElementType()
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo? GetEvent(string name, BindingFlags bindingAttr)
         {
             check_created();
@@ -1056,6 +1060,7 @@ public override EventInfo[] GetEvents()
             return GetEvents(DefaultBindingFlags);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr)
         {
             if (is_created)
@@ -1063,12 +1068,14 @@ public override EventInfo[] GetEvents(BindingFlags bindingAttr)
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo? GetField(string name, BindingFlags bindingAttr)
         {
             check_created();
             return created!.GetField(name, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr)
         {
             check_created();
@@ -1098,6 +1105,7 @@ public override Type[] GetInterfaces()
             }
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type,
                                                 BindingFlags bindingAttr)
         {
@@ -1105,6 +1113,7 @@ public override MemberInfo[] GetMember(string name, MemberTypes type,
             return created!.GetMember(name, type, bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
         {
             check_created();
@@ -1206,6 +1215,7 @@ private MethodInfo[] GetMethodsByName(string? name, BindingFlags bindingAttr, bo
             return result.ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
         {
             check_created();
@@ -1213,6 +1223,7 @@ public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
             return GetMethodsByName(null, bindingAttr, false, this);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo? GetMethodImpl(string name, BindingFlags bindingAttr,
                                  Binder? binder,
                                  CallingConventions callConvention,
@@ -1226,6 +1237,7 @@ public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
             return created!.GetMethod(name, bindingAttr, binder, callConvention, types, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type? GetNestedType(string name, BindingFlags bindingAttr)
         {
             check_created();
@@ -1254,6 +1266,7 @@ public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
             return null;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr)
         {
             if (!is_created)
@@ -1284,12 +1297,14 @@ public override Type[] GetNestedTypes(BindingFlags bindingAttr)
             return result.ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr)
         {
             check_created();
             return created!.GetProperties(bindingAttr);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo? GetPropertyImpl(string name, BindingFlags bindingAttr, Binder? binder, Type? returnType, Type[]? types, ParameterModifier[]? modifiers)
         {
             throw not_supported();
@@ -1304,6 +1319,7 @@ protected override bool HasElementTypeImpl()
             return created!.HasElementType;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(string name, BindingFlags invokeAttr, Binder? binder, object? target, object?[]? args, ParameterModifier[]? modifiers, CultureInfo? culture, string[]? namedParameters)
         {
             check_created();
@@ -1821,6 +1837,8 @@ public GenericTypeParameterBuilder[] DefineGenericParameters(params string[] nam
             return generic_params;
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2006:UnrecognizedReflectionPattern",
+            Justification = "Linker thinks Type.GetConstructor(ConstructorInfo) is one of the public APIs because it doesn't analyze method signatures. We already have ConstructorInfo.")]
         public static ConstructorInfo GetConstructor(Type type, ConstructorInfo constructor)
         {
             /*FIXME I would expect the same checks of GetMethod here*/
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilderInstantiation.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilderInstantiation.cs
index 167347af4e3000..86f847299ae415 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilderInstantiation.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilderInstantiation.cs
@@ -122,6 +122,8 @@ internal bool IsCreated
             return InflateType(type, type_arguments, method_args);
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2006:UnrecognizedReflectionPattern",
+            Justification = "Reflection emitted types have all of their members")]
         internal static Type? InflateType(Type? type, Type[]? type_args, Type[]? method_args)
         {
             if (type == null)
@@ -198,31 +200,37 @@ internal override FieldInfo GetField(FieldInfo fromNoninstanciated)
             return fields[fromNoninstanciated]!;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bf)
         {
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bf)
         {
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bf)
         {
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bf)
         {
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bf)
         {
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bf)
         {
             throw new NotSupportedException();
@@ -435,26 +443,31 @@ public override Type GetInterface(string name, bool ignoreCase)
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo GetEvent(string name, BindingFlags bindingAttr)
         {
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo GetField(string name, BindingFlags bindingAttr)
         {
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
         {
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type GetNestedType(string name, BindingFlags bindingAttr)
         {
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override object? InvokeMember(string name, BindingFlags invokeAttr,
                              Binder? binder, object? target, object?[]? args,
                              ParameterModifier[]? modifiers,
@@ -463,6 +476,7 @@ public override Type GetNestedType(string name, BindingFlags bindingAttr)
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         protected override MethodInfo? GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder,
                                                      CallingConventions callConvention, Type[]? types,
                                                      ParameterModifier[]? modifiers)
@@ -470,12 +484,14 @@ public override Type GetNestedType(string name, BindingFlags bindingAttr)
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo? GetPropertyImpl(string name, BindingFlags bindingAttr, Binder? binder,
                                                          Type? returnType, Type[]? types, ParameterModifier[]? modifiers)
         {
             throw new NotSupportedException();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo? GetConstructorImpl(BindingFlags bindingAttr,
                                        Binder? binder,
                                        CallingConventions callConvention,
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs
index e1f386a4d2eae1..2c7616bf595543 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs
@@ -151,6 +151,7 @@ public override string Location
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
         public extern override string[] GetManifestResourceNames();
 
+        [RequiresUnreferencedCode("Types might be removed")]
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
         public extern override Type[] GetExportedTypes();
 
@@ -253,6 +254,7 @@ public override AssemblyName GetName(bool copiedName)
             return AssemblyName.Create(_mono_assembly, CodeBase);
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override Type GetType(string name, bool throwOnError, bool ignoreCase)
         {
             if (name == null)
@@ -359,6 +361,7 @@ internal static AssemblyName[] GetReferencedAssemblies(Assembly assembly)
             }
         }
 
+        [RequiresUnreferencedCode("Assembly references might be removed")]
         public override AssemblyName[] GetReferencedAssemblies() => RuntimeAssembly.GetReferencedAssemblies (this);
 
         public override Assembly GetSatelliteAssembly(CultureInfo culture)
@@ -412,38 +415,29 @@ public override Assembly GetSatelliteAssembly(CultureInfo culture, Version? vers
             if (name.Length == 0)
                 throw new ArgumentException(SR.Argument_EmptyFileName);
 
-            string location = Location;
-            if (location != null && Path.GetFileName(location) == name)
-                return new FileStream(location, FileMode.Open, FileAccess.Read);
-            string filename = (string)GetFilesInternal(name, true);
-            if (filename != null)
-                return new FileStream(filename, FileMode.Open, FileAccess.Read);
+            RuntimeModule? m = (RuntimeModule?)GetModule(name);
+
+            if (m != null)
+                return new FileStream(m.FullyQualifiedName, FileMode.Open, FileAccess.Read);
             else
                 return null;
         }
 
         public override FileStream[] GetFiles(bool getResourceModules)
         {
-            string[] names = (string[])GetFilesInternal(null, getResourceModules);
-            if (names == null)
+            Module[] modules = GetModules(getResourceModules);
+
+            if (modules.Length == 0)
                 return Array.Empty<FileStream>();
 
-            string location = Location;
+            FileStream[] res = new FileStream[modules.Length];
 
-            FileStream[] res;
-            if (location != string.Empty)
+            for (int i = 0; i < modules.Length; i++)
             {
-                res = new FileStream[names.Length + 1];
-                res[0] = new FileStream(location, FileMode.Open, FileAccess.Read);
-                for (int i = 0; i < names.Length; ++i)
-                    res[i + 1] = new FileStream(names[i], FileMode.Open, FileAccess.Read);
-            }
-            else
-            {
-                res = new FileStream[names.Length];
-                for (int i = 0; i < names.Length; ++i)
-                    res[i] = new FileStream(names[i], FileMode.Open, FileAccess.Read);
+                RuntimeModule m = (RuntimeModule)modules[i];
+                res[i] = new FileStream(m.FullyQualifiedName, FileMode.Open, FileAccess.Read);
             }
+
             return res;
         }
 
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/RuntimeModule.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/RuntimeModule.cs
index 65f4f7278bb1ef..bc2b062df8d728 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/RuntimeModule.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/RuntimeModule.cs
@@ -200,6 +200,7 @@ void GetPEKind(out PortableExecutableKinds peKind, out ImageFileMachine machine)
             GetPEKind(_impl, out peKind, out machine);
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override
         Type GetType(string className, bool throwOnError, bool ignoreCase)
         {
@@ -216,6 +217,7 @@ bool IsDefined(Type attributeType, bool inherit)
             return CustomAttribute.IsDefined(this, attributeType, inherit);
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public
         override
         FieldInfo ResolveField(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
@@ -234,6 +236,7 @@ internal static FieldInfo ResolveField(Module module, IntPtr monoModule, int met
                 return FieldInfo.GetFieldFromHandle(new RuntimeFieldHandle(handle));
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public
         override
         MemberInfo ResolveMember(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
@@ -252,6 +255,7 @@ internal static MemberInfo ResolveMember(Module module, IntPtr monoModule, int m
                 return m;
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public
         override
         MethodBase ResolveMethod(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
@@ -270,6 +274,7 @@ internal static MethodBase ResolveMethod(Module module, IntPtr monoModule, int m
                 return RuntimeMethodInfo.GetMethodFromHandleNoGenericCheck(new RuntimeMethodHandle(handle));
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public
         override
         string ResolveString(int metadataToken)
@@ -288,6 +293,7 @@ internal static string ResolveString(Module module, IntPtr monoModule, int metad
                 return s;
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public
         override
         Type ResolveType(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
@@ -306,6 +312,7 @@ internal static Type ResolveType(Module module, IntPtr monoModule, int metadataT
                 return Type.GetTypeFromHandle(new RuntimeTypeHandle(handle));
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         public
         override
         byte[] ResolveSignature(int metadataToken)
@@ -324,6 +331,7 @@ internal static byte[] ResolveSignature(Module module, IntPtr monoModule, int me
                 return res;
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         public override
         Type[] GetTypes()
         {
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.Mono.cs
new file mode 100644
index 00000000000000..a4acdc99f3509b
--- /dev/null
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Runtime/Intrinsics/X86/X86Base.Mono.cs
@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Runtime.Intrinsics.X86
+{
+    public abstract partial class X86Base
+    {
+        private static unsafe void __cpuidex(int* cpuInfo, int functionId, int subFunctionId)
+        {
+            throw new PlatformNotSupportedException();
+        }
+    }
+}
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/RuntimeType.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/RuntimeType.Mono.cs
index c665878637c35e..fdd6b9d36ccc69 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/RuntimeType.Mono.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/RuntimeType.Mono.cs
@@ -737,37 +737,44 @@ private ListBuilder<Type> GetNestedTypeCandidates(string? fullname, BindingFlags
         #endregion
 
         #region Get All XXXInfos
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
         public override MethodInfo[] GetMethods(BindingFlags bindingAttr)
         {
             return GetMethodCandidates(null, bindingAttr, CallingConventions.Any, null, -1, false).ToArray();
         }
 
         [ComVisible(true)]
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         public override ConstructorInfo[] GetConstructors(BindingFlags bindingAttr)
         {
             return GetConstructorCandidates(null, bindingAttr, CallingConventions.Any, null, false).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         public override PropertyInfo[] GetProperties(BindingFlags bindingAttr)
         {
             return GetPropertyCandidates(null, bindingAttr, null, false).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo[] GetEvents(BindingFlags bindingAttr)
         {
             return GetEventCandidates(null, bindingAttr, false).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo[] GetFields(BindingFlags bindingAttr)
         {
             return GetFieldCandidates(null, bindingAttr, false).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type[] GetNestedTypes(BindingFlags bindingAttr)
         {
             return GetNestedTypeCandidates(null, bindingAttr, false).ToArray();
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
         {
             ListBuilder<MethodInfo> methods = GetMethodCandidates(null, bindingAttr, CallingConventions.Any, null, -1, false);
@@ -843,6 +850,7 @@ public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
             return binder.SelectMethod(bindingAttr, candidates.ToArray(), types, modifiers) as MethodInfo;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
         protected override ConstructorInfo? GetConstructorImpl(
             BindingFlags bindingAttr, Binder? binder, CallingConventions callConvention,
             Type[] types, ParameterModifier[]? modifiers)
@@ -872,7 +880,7 @@ public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
             return binder.SelectMethod(bindingAttr, candidates.ToArray(), types, modifiers) as ConstructorInfo;
         }
 
-
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
         protected override PropertyInfo? GetPropertyImpl(
             string name, BindingFlags bindingAttr, Binder? binder, Type? returnType, Type[]? types, ParameterModifier[]? modifiers)
         {
@@ -912,6 +920,7 @@ public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
             return binder.SelectProperty(bindingAttr, candidates.ToArray(), returnType, types, modifiers);
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)]
         public override EventInfo? GetEvent(string name, BindingFlags bindingAttr)
         {
             if (name == null) throw new ArgumentNullException(nameof(name));
@@ -940,6 +949,7 @@ public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
             return match;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields)]
         public override FieldInfo? GetField(string name, BindingFlags bindingAttr)
         {
             if (name == null) throw new ArgumentNullException();
@@ -1032,6 +1042,7 @@ public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
             return match;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicNestedTypes | DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]
         public override Type? GetNestedType(string fullname, BindingFlags bindingAttr)
         {
             if (fullname == null) throw new ArgumentNullException(nameof(fullname));
@@ -1060,6 +1071,7 @@ public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
             return match;
         }
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
         public override MemberInfo[] GetMember(string name, MemberTypes type, BindingFlags bindingAttr)
         {
             if (name == null) throw new ArgumentNullException(nameof(name));
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Threading/TimerQueue.Browser.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Threading/TimerQueue.Browser.Mono.cs
index 776935b3de7e2b..475f0c8af1eddb 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/Threading/TimerQueue.Browser.Mono.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/Threading/TimerQueue.Browser.Mono.cs
@@ -33,7 +33,12 @@ private TimerQueue(int id)
         // Called by mini-wasm.c:mono_set_timeout_exec
         private static void TimeoutCallback()
         {
-            Run();
+            int shortestWaitDurationMs = PumpTimerQueue();
+
+            if (shortestWaitDurationMs != int.MaxValue)
+            {
+                SetTimeout((int)shortestWaitDurationMs, 0);
+            }
         }
 
         private bool SetTimer(uint actualDuration)
@@ -53,14 +58,18 @@ private bool SetTimer(uint actualDuration)
             return true;
         }
 
-        private static void Run()
+        private static int PumpTimerQueue() // NOTE: this method is called via reflection by test code
         {
-            int shortestWaitDurationMs;
+            if (s_scheduledTimersToFire == null)
+            {
+                return int.MaxValue;
+            }
+
             List<TimerQueue> timersToFire = s_scheduledTimersToFire!;
             List<TimerQueue> timers;
             timers = s_scheduledTimers!;
             long currentTimeMs = TickCount64;
-            shortestWaitDurationMs = int.MaxValue;
+            int shortestWaitDurationMs = int.MaxValue;
             for (int i = timers.Count - 1; i >= 0; --i)
             {
                 TimerQueue timer = timers[i];
@@ -94,10 +103,7 @@ private static void Run()
                 timersToFire.Clear();
             }
 
-            if (shortestWaitDurationMs != int.MaxValue)
-            {
-                SetTimeout((int)shortestWaitDurationMs, 0);
-            }
+            return shortestWaitDurationMs;
         }
     }
 }
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/TypeIdentifier.cs b/src/mono/netcore/System.Private.CoreLib/src/System/TypeIdentifier.cs
index a4bc5ace9b7bc7..e54fecd7df3c84 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/TypeIdentifier.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/TypeIdentifier.cs
@@ -74,7 +74,7 @@ internal abstract class ATypeName : ITypeName
 
             public abstract ITypeName NestedName(ITypeIdentifier innerName);
 
-            public bool Equals([AllowNull] ITypeName other)
+            public bool Equals(ITypeName? other)
             {
                 return other != null && DisplayName == other.DisplayName;
             }
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/WeakReference.T.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/WeakReference.T.Mono.cs
index 8ab12b5977a8b4..e4c4b0af7bead4 100644
--- a/src/mono/netcore/System.Private.CoreLib/src/System/WeakReference.T.Mono.cs
+++ b/src/mono/netcore/System.Private.CoreLib/src/System/WeakReference.T.Mono.cs
@@ -11,8 +11,7 @@ public partial class WeakReference<T>
         private GCHandle handle;
         private bool trackResurrection;
 
-        [MaybeNull]
-        private T Target
+        private T? Target
         {
             get
             {
diff --git a/src/mono/netcore/nuget/Directory.Build.props b/src/mono/netcore/nuget/Directory.Build.props
new file mode 100644
index 00000000000000..dc82034199d6e3
--- /dev/null
+++ b/src/mono/netcore/nuget/Directory.Build.props
@@ -0,0 +1,41 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project>
+
+  <!-- Packaging projects (.pkgproj) are non-SDK-style, so they need to directly import Directory.Build.props -->
+  <Import Project="../../Directory.Build.props" />
+
+  <Import Project="$(NuGetPackageRoot)\microsoft.dotnet.build.tasks.packaging\$(MicrosoftDotNetBuildTasksPackagingVersion)\build\Microsoft.DotNet.Build.Tasks.Packaging.props" />
+
+  <PropertyGroup>
+    <PackageDescriptionFile>$(MSBuildThisFileDirectory)/descriptions.json</PackageDescriptionFile>
+    <PackageLicenseFile>$(CoreclrDir)/LICENSE.TXT</PackageLicenseFile>
+
+    <ReleaseNotes>https://go.microsoft.com/fwlink/?LinkID=799421</ReleaseNotes>
+
+    <ProjectUrl>https://dot.net</ProjectUrl>
+
+    <PackageIndexFile>$(MSBuildThisFileDirectory)/packageIndex.json</PackageIndexFile>
+    <PackagePlatform>AnyCPU</PackagePlatform>
+
+    <!-- mono doesn't currently use the index so don't force it to be in sync -->
+    <SkipIndexCheck>true</SkipIndexCheck>
+
+    <VersionTxtFile Condition="'$(VersionTxtFile)' == ''">$(ArtifactsObjDir)version.txt</VersionTxtFile>
+  </PropertyGroup>
+
+  <ItemGroup Condition="'$(MSBuildProjectExtension)' == '.pkgproj'">
+    <!-- Add required legal files to packages -->
+    <File Condition="Exists('$(PackageLicenseFile)')"
+          Include="$(PackageLicenseFile)" >
+      <SkipPackageFileCheck>true</SkipPackageFileCheck>
+    </File>
+    <PackageIndex Include="$(PackageIndexFile)" />
+
+    <!-- Add version file to packages -->
+    <File Include="$(VersionTxtFile)"
+          Condition="Exists('$(VersionTxtFile)')">
+          <SkipPackageFileCheck>true</SkipPackageFileCheck>
+    </File>
+  </ItemGroup>
+
+</Project>
diff --git a/src/mono/netcore/nuget/Directory.Build.targets b/src/mono/netcore/nuget/Directory.Build.targets
new file mode 100644
index 00000000000000..568d3d34aedccb
--- /dev/null
+++ b/src/mono/netcore/nuget/Directory.Build.targets
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+
+  <Import Project="../../Directory.Build.targets" />
+
+  <Import Project="$(NuGetPackageRoot)\microsoft.dotnet.build.tasks.packaging\$(MicrosoftDotNetBuildTasksPackagingVersion)\build\Microsoft.DotNet.Build.Tasks.Packaging.targets" />
+
+</Project>
diff --git a/src/mono/netcore/nuget/Microsoft.NETCore.BrowserDebugHost.Transport/Microsoft.NETCore.BrowserDebugHost.Transport.pkgproj b/src/mono/netcore/nuget/Microsoft.NETCore.BrowserDebugHost.Transport/Microsoft.NETCore.BrowserDebugHost.Transport.pkgproj
new file mode 100644
index 00000000000000..f361ca5eb29464
--- /dev/null
+++ b/src/mono/netcore/nuget/Microsoft.NETCore.BrowserDebugHost.Transport/Microsoft.NETCore.BrowserDebugHost.Transport.pkgproj
@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props))" />
+
+  <PropertyGroup>
+    <IsShipping>false</IsShipping>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(MonoProjectRoot)wasm\debugger\BrowserDebugHost\BrowserDebugHost.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageFile Include="$(ArtifactsDir)bin\BrowserDebugHost\$(TargetArchitecture)\$(Configuration)\BrowserDebugProxy.dll">
+      <TargetPath>tools\$(NetCoreAppCurrent)\BrowserDebugProxy.dll</TargetPath>
+    </PackageFile>
+    <PackageFile Include="$(ArtifactsDir)bin\BrowserDebugHost\$(TargetArchitecture)\$(Configuration)\BrowserDebugHost.dll">
+      <TargetPath>tools\$(NetCoreAppCurrent)\BrowserDebugHost.dll</TargetPath>
+    </PackageFile>
+    <PackageFile Include="$(ArtifactsDir)bin\BrowserDebugHost\$(TargetArchitecture)\$(Configuration)\BrowserDebugHost.runtimeconfig.json">
+      <TargetPath>tools\$(NetCoreAppCurrent)\BrowserDebugHost.runtimeconfig.json</TargetPath>
+    </PackageFile>
+  </ItemGroup>
+
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets))" />
+</Project>
diff --git a/src/mono/netcore/nuget/descriptions.json b/src/mono/netcore/nuget/descriptions.json
new file mode 100644
index 00000000000000..5fb2e801ce6804
--- /dev/null
+++ b/src/mono/netcore/nuget/descriptions.json
@@ -0,0 +1,12 @@
+[
+    {
+        "Name": "NuGet3MinVersion",
+        "Description": "When using NuGet 3.x this package requires at least version {0}.",
+        "CommonTypes": [ ]
+    },
+    {
+        "Name": "Microsoft.NETCore.BrowserDebugHost.Transport",
+        "Description": "Internal package for sharing BrowserDebugHost.",
+        "CommonTypes": [ ]
+    }
+]
diff --git a/src/mono/netcore/nuget/mono-packages.proj b/src/mono/netcore/nuget/mono-packages.proj
new file mode 100644
index 00000000000000..0f2794e1ebd213
--- /dev/null
+++ b/src/mono/netcore/nuget/mono-packages.proj
@@ -0,0 +1,13 @@
+<Project>
+  <Import Sdk="Microsoft.Build.Traversal" Project="Sdk.props" />
+
+  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
+    <ProjectReference Include="Microsoft.NETCore.BrowserDebugHost.Transport\Microsoft.NETCore.BrowserDebugHost.Transport.pkgproj" />
+  </ItemGroup>
+
+  <Import Sdk="Microsoft.Build.Traversal" Project="Sdk.targets" />
+
+  <!-- Ordering matters! Overwriting the Pack target which should just invoke Build. -->
+  <Target Name="Pack" DependsOnTargets="Build">
+  </Target>
+</Project>
diff --git a/src/mono/netcore/nuget/packageIndex.json b/src/mono/netcore/nuget/packageIndex.json
new file mode 100644
index 00000000000000..7a73a41bfdf76d
--- /dev/null
+++ b/src/mono/netcore/nuget/packageIndex.json
@@ -0,0 +1,2 @@
+{
+}
\ No newline at end of file
diff --git a/src/mono/netcore/sample/wasm/browser/Makefile b/src/mono/netcore/sample/wasm/browser/Makefile
new file mode 100644
index 00000000000000..d5227aca5c34ae
--- /dev/null
+++ b/src/mono/netcore/sample/wasm/browser/Makefile
@@ -0,0 +1,16 @@
+TOP=../../../../../..
+
+DOTNET_Q_ARGS=--nologo -v:q -consoleloggerparameters:NoSummary
+
+CONFIG?=Release
+
+all: build
+
+build:
+	$(TOP)/.dotnet/dotnet build $(DOTNET_Q_ARGS) /p:TargetArchitecture=wasm /p:TargetOS=Browser /p:Configuration=$(CONFIG) WasmSample.csproj
+
+clean:
+	rm -rf bin
+
+run:
+	cd bin/$(CONFIG)/publish && python server.py
\ No newline at end of file
diff --git a/src/mono/netcore/sample/wasm/browser/Program.cs b/src/mono/netcore/sample/wasm/browser/Program.cs
new file mode 100644
index 00000000000000..36e09e414a70fa
--- /dev/null
+++ b/src/mono/netcore/sample/wasm/browser/Program.cs
@@ -0,0 +1,21 @@
+// -*- indent-tabs-mode: nil -*-
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+namespace Sample
+{
+    public class Test
+    {
+        public static void Main(String[] args)
+        {
+            Console.WriteLine ("Hello, World!");
+        }
+
+        public static int TestMeaning()
+        {
+            return 42;
+        }
+    }
+}
diff --git a/src/mono/netcore/sample/wasm/browser/WasmSample.csproj b/src/mono/netcore/sample/wasm/browser/WasmSample.csproj
new file mode 100644
index 00000000000000..e268098b6654d7
--- /dev/null
+++ b/src/mono/netcore/sample/wasm/browser/WasmSample.csproj
@@ -0,0 +1,57 @@
+<Project Sdk="Microsoft.NET.Sdk" DefaultTargets="BuildApp">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <OutputPath>bin</OutputPath>
+    <EnableDefaultCompileItems>false</EnableDefaultCompileItems>
+    <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+    <TargetArchitecture>wasm</TargetArchitecture>
+    <TargetOS>Browser</TargetOS>
+    <MicrosoftNetCoreAppRuntimePackDir>$(ArtifactsBinDir)microsoft.netcore.app.runtime.browser-wasm\$(Configuration)\runtimes\browser-wasm\</MicrosoftNetCoreAppRuntimePackDir>
+    <BuildDir>$(MSBuildThisFileDirectory)obj\$(Configuration)\wasm</BuildDir>
+    <AppDir>$(MSBuildThisFileDirectory)bin\$(Configuration)\publish</AppDir>
+  </PropertyGroup>
+
+  <Target Name="RebuildWasmAppBuilder">
+    <ItemGroup>
+      <WasmAppBuildProject Include="$(RepoTasksDir)mobile.tasks\WasmAppBuilder\WasmAppBuilder.csproj" />
+    </ItemGroup>
+
+    <MSBuild Projects="@(WasmAppBuildProject)"
+             Properties="Configuration=$(Configuration);MSBuildRestoreSessionId=$([System.Guid]::NewGuid())"
+             Targets="Restore"/>
+
+    <MSBuild Projects="@(WasmAppBuildProject)"
+             Properties="Configuration=$(Configuration)"
+             Targets="Build;Publish"/>
+  </Target>
+
+  <UsingTask TaskName="WasmAppBuilder" 
+             AssemblyFile="$(ArtifactsBinDir)WasmAppBuilder\$(Configuration)\$(NetCoreAppCurrent)\publish\WasmAppBuilder.dll"/>
+
+  <Target Name="BuildApp" DependsOnTargets="RebuildWasmAppBuilder;Build">
+    <ItemGroup>
+      <AssemblySearchPaths Include="bin"/>
+      <AssemblySearchPaths Include="$(MicrosoftNetCoreAppRuntimePackDir)native"/>
+      <AssemblySearchPaths Include="$(MicrosoftNetCoreAppRuntimePackDir)lib\$(NetCoreAppCurrent)"/>
+    </ItemGroup>
+    <WasmAppBuilder
+      AppDir="$(AppDir)"
+      ExtraAssemblies="$(MicrosoftNetCoreAppRuntimePackDir)lib\$(NetCoreAppCurrent)\System.Runtime.InteropServices.JavaScript.dll"
+      MicrosoftNetCoreAppRuntimePackDir="$(MicrosoftNetCoreAppRuntimePackDir)"
+      MainAssembly="bin\WasmSample.dll"
+      MainJS="runtime.js"
+      AssemblySearchPaths="@(AssemblySearchPaths)"/>
+    <Exec Command="chmod a+x $(AppDir)/run-v8.sh" />
+    <Copy SourceFiles="bin\index.html;bin\server.py" DestinationFolder="$(AppDir)" />
+  </Target>
+
+  <ItemGroup>
+    <Compile Include="Program.cs" />
+    <Content Include="index.html">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </Content>
+    <Content Include="server.py">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </Content>
+  </ItemGroup>
+</Project>
diff --git a/src/mono/netcore/sample/wasm/browser/index.html b/src/mono/netcore/sample/wasm/browser/index.html
new file mode 100644
index 00000000000000..4cf3a1ef1b1d94
--- /dev/null
+++ b/src/mono/netcore/sample/wasm/browser/index.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<!--  Licensed to the .NET Foundation under one or more agreements. -->
+<!-- The .NET Foundation licenses this file to you under the MIT license. -->
+<html>
+  <head>
+    <title>TESTS</title>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+  </head>
+  <body>
+    <h3 id="header">Wasm Browser Sample</h3>
+    Result from Sample.Test.TestMeaaning: <span id="out"></span>
+    <script type='text/javascript'>
+      var App = {
+        init: function () {
+          var ret = BINDING.call_static_method("[WasmSample] Sample.Test:TestMeaning", []);
+          document.getElementById("out").innerHTML = ret;
+          console.log ("ready");
+        },
+      };
+    </script>
+    <script type="text/javascript" src="mono-config.js"></script>
+    <script type="text/javascript" src="runtime.js"></script>
+
+    <script defer src="dotnet.js"></script>
+
+  </body>
+</html>
\ No newline at end of file
diff --git a/src/mono/netcore/sample/wasm/browser/runtime.js b/src/mono/netcore/sample/wasm/browser/runtime.js
new file mode 100644
index 00000000000000..7db3cb4fc70e79
--- /dev/null
+++ b/src/mono/netcore/sample/wasm/browser/runtime.js
@@ -0,0 +1,15 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+var Module = { 
+    onRuntimeInitialized: function () {
+        config.loaded_cb = function () {
+            App.init ();
+        };
+        config.fetch_file_cb = function (asset) {
+            return fetch (asset, { credentials: 'same-origin' });
+        }
+
+        MONO.mono_load_runtime_and_bcl_args (config);
+    },
+};
diff --git a/src/mono/netcore/sample/wasm/browser/server.py b/src/mono/netcore/sample/wasm/browser/server.py
new file mode 100644
index 00000000000000..ab1e3edd81517b
--- /dev/null
+++ b/src/mono/netcore/sample/wasm/browser/server.py
@@ -0,0 +1,37 @@
+# Licensed to the .NET Foundation under one or more agreements.
+# The .NET Foundation licenses this file to you under the MIT license.
+
+import sys
+
+if sys.version_info[0] == 2:
+
+    import SimpleHTTPServer
+    import SocketServer
+
+    PORT = 8000
+
+    class Handler(SimpleHTTPServer.SimpleHTTPRequestHandler):
+        pass
+
+    Handler.extensions_map['.wasm'] = 'application/wasm'
+
+    httpd = SocketServer.TCPServer(("", PORT), Handler)
+
+    print ("python 2 serving at port", PORT)
+    httpd.serve_forever()
+
+
+if sys.version_info[0] == 3:
+    
+    import http.server
+    import socketserver
+
+    PORT = 8000
+
+    Handler = http.server.SimpleHTTPRequestHandler
+    Handler.extensions_map['.wasm'] = 'application/wasm'
+
+    with socketserver.TCPServer(("", PORT), Handler) as httpd:
+        print("python 3 serving at port", PORT)
+        httpd.serve_forever()
+
diff --git a/src/mono/netcore/sample/wasm/Makefile b/src/mono/netcore/sample/wasm/console/Makefile
similarity index 95%
rename from src/mono/netcore/sample/wasm/Makefile
rename to src/mono/netcore/sample/wasm/console/Makefile
index 16d37d41f4cbe4..40cbf04ed4074a 100644
--- a/src/mono/netcore/sample/wasm/Makefile
+++ b/src/mono/netcore/sample/wasm/console/Makefile
@@ -1,4 +1,4 @@
-TOP=../../../../..
+TOP=../../../../../..
 
 DOTNET_Q_ARGS=--nologo -v:q -consoleloggerparameters:NoSummary
 
diff --git a/src/mono/netcore/sample/wasm/Program.cs b/src/mono/netcore/sample/wasm/console/Program.cs
similarity index 100%
rename from src/mono/netcore/sample/wasm/Program.cs
rename to src/mono/netcore/sample/wasm/console/Program.cs
diff --git a/src/mono/netcore/sample/wasm/WasmSample.csproj b/src/mono/netcore/sample/wasm/console/WasmSample.csproj
similarity index 100%
rename from src/mono/netcore/sample/wasm/WasmSample.csproj
rename to src/mono/netcore/sample/wasm/console/WasmSample.csproj
diff --git a/src/mono/wasm/Makefile b/src/mono/wasm/Makefile
index 2562217a9354af..398bd0e650bfd8 100644
--- a/src/mono/wasm/Makefile
+++ b/src/mono/wasm/Makefile
@@ -88,7 +88,7 @@ $(BUILDS_OBJ_DIR)/pinvoke.o: runtime/pinvoke.c runtime/pinvoke.h $(BUILDS_OBJ_DI
 	$(EMCC) $(EMCC_FLAGS) $(1) -Oz -DGEN_PINVOKE=1 -I$(BUILDS_OBJ_DIR) -I$(MONO_INCLUDE_DIR) runtime/pinvoke.c -c -o $$@
 
 $(BUILDS_OBJ_DIR)/corebindings.o: runtime/corebindings.c | $(BUILDS_OBJ_DIR)
-	$(EMCC) $(1) -Oz -I$(MONO_INCLUDE_DIR) runtime/corebindings.c -c -o $$@
+	$(EMCC) $(EMCC_FLAGS) $(1) -Oz -I$(MONO_INCLUDE_DIR) runtime/corebindings.c -c -o $$@
 
 build-native: $(BUILDS_BIN_DIR)/dotnet.js
 
@@ -101,7 +101,7 @@ $(eval $(call InterpBuildTemplate,$(EMCC_RELEASE_FLAGS),$(MONO_LIBS)))
 endif
 
 build:
-	EMSDK_PATH=$(PWD)/emsdk $(DOTNET) build /p:TargetArchitecture=wasm /p:TargetOS=Browser /p:Configuration=$(CONFIG) $(TOP)/src/libraries/src.proj /t:NativeBinPlace
+	EMSDK_PATH=$(PWD)/emsdk $(DOTNET) build /p:TargetArchitecture=wasm /p:TargetOS=Browser /p:Configuration=$(CONFIG) $(TOP)/src/libraries/src.proj /t:BuildWasmRuntimes
 
 clean-emsdk:
 	$(RM) -rf $(EMSDK_LOCAL_PATH)
@@ -139,3 +139,27 @@ run-tests-jsc-%:
 
 run-tests-%:
 	PATH="$(JSVU):$(PATH)" $(DOTNET) build $(TOP)/src/libraries/$*/tests/ /t:Test /p:TargetOS=Browser /p:TargetArchitecture=wasm /p:Configuration=$(CONFIG) $(MSBUILD_ARGS)
+
+build-debugger-test-app: 
+	$(DOTNET) build --configuration debug --nologo /p:TargetArchitecture=wasm /p:TargetOS=Browser /p:Configuration=Debug /p:RuntimeConfiguration=$(CONFIG) $(TOP)/src/mono/wasm/debugger/tests
+	cp $(TOP)/src/mono/wasm/debugger/tests/debugger-driver.html $(TOP)/src/mono/wasm/debugger/tests/bin/Debug/publish
+	cp $(TOP)/src/mono/wasm/debugger/tests/other.js $(TOP)/src/mono/wasm/debugger/tests/bin/Debug/publish
+	cp $(TOP)/src/mono/wasm/debugger/tests/runtime-debugger.js $(TOP)/src/mono/wasm/debugger/tests/bin/Debug/publish
+
+run-debugger-tests: build-debugger-test-app build-dbg-testsuite
+	if [ ! -z "$(TEST_FILTER)" ]; then \
+		export TEST_SUITE_PATH=$(TOP)/src/mono/wasm/debugger/tests/bin/Debug/publish; \
+		export LC_ALL=en_US.UTF-8; \
+		$(DOTNET) test  $(TOP)/src/mono/wasm/debugger/DebuggerTestSuite --filter FullyQualifiedName~$(TEST_FILTER); \
+		unset TEST_SUITE_PATH LC_ALL; \
+	else \
+		export TEST_SUITE_PATH=$(TOP)/src/mono/wasm/debugger/tests/bin/Debug/publish; \
+		export LC_ALL=en_US.UTF-8; \
+		$(DOTNET) test  $(TOP)/src/mono/wasm/debugger/DebuggerTestSuite $(TEST_ARGS); \
+		unset TEST_SUITE_PATH LC_ALL; \
+	fi
+
+build-dbg-proxy:
+	$(DOTNET) build $(TOP)/src/mono/wasm/debugger/BrowserDebugHost
+build-dbg-testsuite:
+	$(DOTNET) build $(TOP)/src/mono/wasm/debugger/DebuggerTestSuite
diff --git a/src/mono/wasm/debugger/BrowserDebugHost/BrowserDebugHost.csproj b/src/mono/wasm/debugger/BrowserDebugHost/BrowserDebugHost.csproj
new file mode 100644
index 00000000000000..9650dc8356630e
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugHost/BrowserDebugHost.csproj
@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\BrowserDebugProxy\BrowserDebugProxy.csproj" />
+  </ItemGroup>
+
+  <Target Name="GetFilesToPackage" />
+
+</Project>
diff --git a/src/mono/wasm/debugger/BrowserDebugHost/Program.cs b/src/mono/wasm/debugger/BrowserDebugHost/Program.cs
new file mode 100644
index 00000000000000..c45b9ce0065c07
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugHost/Program.cs
@@ -0,0 +1,92 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+    public class ProxyOptions
+    {
+        public Uri DevToolsUrl { get; set; } = new Uri("http://localhost:9222");
+    }
+
+    public class TestHarnessOptions : ProxyOptions
+    {
+        public string ChromePath { get; set; }
+        public string AppPath { get; set; }
+        public string PagePath { get; set; }
+        public string NodeApp { get; set; }
+    }
+
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            var host = new WebHostBuilder()
+                .UseSetting("UseIISIntegration", false.ToString())
+                .UseKestrel()
+                .UseContentRoot(Directory.GetCurrentDirectory())
+                .UseStartup<Startup>()
+                .ConfigureAppConfiguration((hostingContext, config) =>
+                {
+                    config.AddCommandLine(args);
+                })
+                .UseUrls("http://localhost:9300")
+                .Build();
+
+            host.Run();
+        }
+    }
+
+    public class TestHarnessProxy
+    {
+        static IWebHost host;
+        static Task hostTask;
+        static CancellationTokenSource cts = new CancellationTokenSource();
+        static object proxyLock = new object();
+
+        public static readonly Uri Endpoint = new Uri("http://localhost:9400");
+
+        public static Task Start(string chromePath, string appPath, string pagePath)
+        {
+            lock(proxyLock)
+            {
+                if (host != null)
+                    return hostTask;
+
+                host = WebHost.CreateDefaultBuilder()
+                    .UseSetting("UseIISIntegration", false.ToString())
+                    .ConfigureAppConfiguration((hostingContext, config) =>
+                    {
+                        config.AddEnvironmentVariables(prefix: "WASM_TESTS_");
+                    })
+                    .ConfigureServices((ctx, services) =>
+                    {
+                        services.Configure<TestHarnessOptions>(ctx.Configuration);
+                        services.Configure<TestHarnessOptions>(options =>
+                        {
+                            options.ChromePath = options.ChromePath ?? chromePath;
+                            options.AppPath = appPath;
+                            options.PagePath = pagePath;
+                            options.DevToolsUrl = new Uri("http://localhost:0");
+                        });
+                    })
+                    .UseStartup<TestHarnessStartup>()
+                    .UseUrls(Endpoint.ToString())
+                    .Build();
+                hostTask = host.StartAsync(cts.Token);
+            }
+
+            Console.WriteLine("WebServer Ready!");
+            return hostTask;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/BrowserDebugHost/Startup.cs b/src/mono/wasm/debugger/BrowserDebugHost/Startup.cs
new file mode 100644
index 00000000000000..16292f997e6be0
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugHost/Startup.cs
@@ -0,0 +1,164 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using System.Text.Json;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+    internal class Startup
+    {
+        // This method gets called by the runtime. Use this method to add services to the container.
+        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
+        public void ConfigureServices(IServiceCollection services) =>
+            services.AddRouting()
+            .Configure<ProxyOptions>(Configuration);
+
+        public Startup(IConfiguration configuration) =>
+            Configuration = configuration;
+
+        public IConfiguration Configuration { get; }
+
+        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
+        public void Configure(IApplicationBuilder app, IOptionsMonitor<ProxyOptions> optionsAccessor, IWebHostEnvironment env)
+        {
+            var options = optionsAccessor.CurrentValue;
+            app.UseDeveloperExceptionPage()
+                .UseWebSockets()
+                .UseDebugProxy(options);
+        }
+    }
+
+    static class DebugExtensions
+    {
+        public static Dictionary<string, string> MapValues(Dictionary<string, string> response, HttpContext context, Uri debuggerHost)
+        {
+            var filtered = new Dictionary<string, string>();
+            var request = context.Request;
+
+            foreach (var key in response.Keys)
+            {
+                switch (key)
+                {
+                    case "devtoolsFrontendUrl":
+                        var front = response[key];
+                        filtered[key] = $"{debuggerHost.Scheme}://{debuggerHost.Authority}{front.Replace ($"ws={debuggerHost.Authority}", $"ws={request.Host}")}";
+                        break;
+                    case "webSocketDebuggerUrl":
+                        var page = new Uri(response[key]);
+                        filtered[key] = $"{page.Scheme}://{request.Host}{page.PathAndQuery}";
+                        break;
+                    default:
+                        filtered[key] = response[key];
+                        break;
+                }
+            }
+            return filtered;
+        }
+
+        public static IApplicationBuilder UseDebugProxy(this IApplicationBuilder app, ProxyOptions options) =>
+            UseDebugProxy(app, options, MapValues);
+
+        public static IApplicationBuilder UseDebugProxy(
+            this IApplicationBuilder app,
+            ProxyOptions options,
+            Func<Dictionary<string, string>, HttpContext, Uri, Dictionary<string, string>> mapFunc)
+        {
+            var devToolsHost = options.DevToolsUrl;
+            app.UseRouter(router =>
+            {
+                router.MapGet("/", Copy);
+                router.MapGet("/favicon.ico", Copy);
+                router.MapGet("json", RewriteArray);
+                router.MapGet("json/list", RewriteArray);
+                router.MapGet("json/version", RewriteSingle);
+                router.MapGet("json/new", RewriteSingle);
+                router.MapGet("devtools/page/{pageId}", ConnectProxy);
+                router.MapGet("devtools/browser/{pageId}", ConnectProxy);
+
+                string GetEndpoint(HttpContext context)
+                {
+                    var request = context.Request;
+                    var requestPath = request.Path;
+                    return $"{devToolsHost.Scheme}://{devToolsHost.Authority}{request.Path}{request.QueryString}";
+                }
+
+                async Task Copy(HttpContext context)
+                {
+                    using(var httpClient = new HttpClient { Timeout = TimeSpan.FromSeconds(5) })
+                    {
+                        var response = await httpClient.GetAsync(GetEndpoint(context));
+                        context.Response.ContentType = response.Content.Headers.ContentType.ToString();
+                        if ((response.Content.Headers.ContentLength ?? 0) > 0)
+                            context.Response.ContentLength = response.Content.Headers.ContentLength;
+                        var bytes = await response.Content.ReadAsByteArrayAsync();
+                        await context.Response.Body.WriteAsync(bytes);
+
+                    }
+                }
+
+                async Task RewriteSingle(HttpContext context)
+                {
+                    var version = await ProxyGetJsonAsync<Dictionary<string, string>>(GetEndpoint(context));
+                    context.Response.ContentType = "application/json";
+                    await context.Response.WriteAsync(
+                        JsonSerializer.Serialize(mapFunc(version, context, devToolsHost)));
+                }
+
+                async Task RewriteArray(HttpContext context)
+                {
+                    var tabs = await ProxyGetJsonAsync<Dictionary<string, string>[]>(GetEndpoint(context));
+                    var alteredTabs = tabs.Select(t => mapFunc(t, context, devToolsHost)).ToArray();
+                    context.Response.ContentType = "application/json";
+                    await context.Response.WriteAsync(JsonSerializer.Serialize(alteredTabs));
+                }
+
+                async Task ConnectProxy(HttpContext context)
+                {
+                    if (!context.WebSockets.IsWebSocketRequest)
+                    {
+                        context.Response.StatusCode = 400;
+                        return;
+                    }
+
+                    var endpoint = new Uri($"ws://{devToolsHost.Authority}{context.Request.Path.ToString ()}");
+                    try
+                    {
+                        using var loggerFactory = LoggerFactory.Create(
+                            builder => builder.AddConsole().AddFilter(null, LogLevel.Information));
+                        var proxy = new DebuggerProxy(loggerFactory);
+                        var ideSocket = await context.WebSockets.AcceptWebSocketAsync();
+
+                        await proxy.Run(endpoint, ideSocket);
+                    }
+                    catch (Exception e)
+                    {
+                        Console.WriteLine("got exception {0}", e);
+                    }
+                }
+            });
+            return app;
+        }
+
+        static async Task<T> ProxyGetJsonAsync<T>(string url)
+        {
+            using(var httpClient = new HttpClient())
+            {
+                var response = await httpClient.GetAsync(url);
+                return await JsonSerializer.DeserializeAsync<T>(await response.Content.ReadAsStreamAsync());
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/BrowserDebugHost/TestHarnessStartup.cs b/src/mono/wasm/debugger/BrowserDebugHost/TestHarnessStartup.cs
new file mode 100644
index 00000000000000..953eb864f907f1
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugHost/TestHarnessStartup.cs
@@ -0,0 +1,255 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Diagnostics;
+using System.IO;
+using System.Net.Http;
+using System.Text.RegularExpressions;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.AspNetCore.StaticFiles;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.FileProviders;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+    public class TestHarnessStartup
+    {
+        static Regex parseConnection = new Regex(@"listening on (ws?s://[^\s]*)");
+        public TestHarnessStartup(IConfiguration configuration)
+        {
+            Configuration = configuration;
+        }
+
+        public IConfiguration Configuration { get; set; }
+
+        // This method gets called by the runtime. Use this method to add services to the container.
+        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
+        public void ConfigureServices(IServiceCollection services)
+        {
+            services.AddRouting()
+                .Configure<TestHarnessOptions>(Configuration);
+        }
+
+        async Task SendNodeVersion(HttpContext context)
+        {
+            Console.WriteLine("hello chrome! json/version");
+            var resp_obj = new JObject();
+            resp_obj["Browser"] = "node.js/v9.11.1";
+            resp_obj["Protocol-Version"] = "1.1";
+
+            var response = resp_obj.ToString();
+            await context.Response.WriteAsync(response, new CancellationTokenSource().Token);
+        }
+
+        async Task SendNodeList(HttpContext context)
+        {
+            Console.WriteLine("hello chrome! json/list");
+            try
+            {
+                var response = new JArray(JObject.FromObject(new
+                {
+                    description = "node.js instance",
+                        devtoolsFrontendUrl = "chrome-devtools://devtools/bundled/inspector.html?experiments=true&v8only=true&ws=localhost:9300/91d87807-8a81-4f49-878c-a5604103b0a4",
+                        faviconUrl = "https://nodejs.org/static/favicon.ico",
+                        id = "91d87807-8a81-4f49-878c-a5604103b0a4",
+                        title = "foo.js",
+                        type = "node",
+                        webSocketDebuggerUrl = "ws://localhost:9300/91d87807-8a81-4f49-878c-a5604103b0a4"
+                })).ToString();
+
+                Console.WriteLine($"sending: {response}");
+                await context.Response.WriteAsync(response, new CancellationTokenSource().Token);
+            }
+            catch (Exception e) { Console.WriteLine(e); }
+        }
+
+        public async Task LaunchAndServe(ProcessStartInfo psi, HttpContext context, Func<string, Task<string>> extract_conn_url)
+        {
+
+            if (!context.WebSockets.IsWebSocketRequest)
+            {
+                context.Response.StatusCode = 400;
+                return;
+            }
+
+            var tcs = new TaskCompletionSource<string>();
+
+            var proc = Process.Start(psi);
+            try
+            {
+                proc.ErrorDataReceived += (sender, e) =>
+                {
+                    var str = e.Data;
+                    Console.WriteLine($"stderr: {str}");
+
+                    if (tcs.Task.IsCompleted)
+                        return;
+
+                    var match = parseConnection.Match(str);
+                    if (match.Success)
+                    {
+                        tcs.TrySetResult(match.Groups[1].Captures[0].Value);
+                    }
+                };
+
+                proc.OutputDataReceived += (sender, e) =>
+                {
+                    Console.WriteLine($"stdout: {e.Data}");
+                };
+
+                proc.BeginErrorReadLine();
+                proc.BeginOutputReadLine();
+
+                if (await Task.WhenAny(tcs.Task, Task.Delay(5000)) != tcs.Task)
+                {
+                    Console.WriteLine("Didnt get the con string after 5s.");
+                    throw new Exception("node.js timedout");
+                }
+                var line = await tcs.Task;
+                var con_str = extract_conn_url != null ? await extract_conn_url(line) : line;
+
+                Console.WriteLine($"launching proxy for {con_str}");
+
+                using var loggerFactory = LoggerFactory.Create(
+                    builder => builder.AddConsole().AddFilter(null, LogLevel.Information));
+                var proxy = new DebuggerProxy(loggerFactory);
+                var browserUri = new Uri(con_str);
+                var ideSocket = await context.WebSockets.AcceptWebSocketAsync();
+
+                await proxy.Run(browserUri, ideSocket);
+                Console.WriteLine("Proxy done");
+            }
+            catch (Exception e)
+            {
+                Console.WriteLine("got exception {0}", e);
+            }
+            finally
+            {
+                proc.CancelErrorRead();
+                proc.CancelOutputRead();
+                proc.Kill();
+                proc.WaitForExit();
+                proc.Close();
+            }
+        }
+
+        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
+        public void Configure(IApplicationBuilder app, IOptionsMonitor<TestHarnessOptions> optionsAccessor, IWebHostEnvironment env)
+        {
+            app.UseWebSockets();
+            app.UseStaticFiles();
+
+            TestHarnessOptions options = optionsAccessor.CurrentValue;
+
+            var provider = new FileExtensionContentTypeProvider();
+            provider.Mappings[".wasm"] = "application/wasm";
+
+            app.UseStaticFiles(new StaticFileOptions
+            {
+                FileProvider = new PhysicalFileProvider(options.AppPath),
+                    ServeUnknownFileTypes = true, //Cuz .wasm is not a known file type :cry:
+                    RequestPath = "",
+                    ContentTypeProvider = provider
+            });
+
+            var devToolsUrl = options.DevToolsUrl;
+            app.UseRouter(router =>
+            {
+                router.MapGet("launch-chrome-and-connect", async context =>
+                {
+                    Console.WriteLine("New test request");
+                    try
+                    {
+                        var client = new HttpClient();
+                        var psi = new ProcessStartInfo();
+
+                        psi.Arguments = $"--headless --disable-gpu --lang=en-US --incognito --remote-debugging-port={devToolsUrl.Port} http://{TestHarnessProxy.Endpoint.Authority}/{options.PagePath}";
+                        psi.UseShellExecute = false;
+                        psi.FileName = options.ChromePath;
+                        psi.RedirectStandardError = true;
+                        psi.RedirectStandardOutput = true;
+
+                        await LaunchAndServe(psi, context, async(str) =>
+                        {
+                            var start = DateTime.Now;
+                            JArray obj = null;
+
+                            while (true)
+                            {
+                                // Unfortunately it does look like we have to wait
+                                // for a bit after getting the response but before
+                                // making the list request.  We get an empty result
+                                // if we make the request too soon.
+                                await Task.Delay(100);
+
+                                var res = await client.GetStringAsync(new Uri(new Uri(str), "/json/list"));
+                                Console.WriteLine("res is {0}", res);
+
+                                if (!String.IsNullOrEmpty(res))
+                                {
+                                    // Sometimes we seem to get an empty array `[ ]`
+                                    obj = JArray.Parse(res);
+                                    if (obj != null && obj.Count >= 1)
+                                        break;
+                                }
+
+                                var elapsed = DateTime.Now - start;
+                                if (elapsed.Milliseconds > 5000)
+                                {
+                                    Console.WriteLine($"Unable to get DevTools /json/list response in {elapsed.Seconds} seconds, stopping");
+                                    return null;
+                                }
+                            }
+
+                            var wsURl = obj[0] ? ["webSocketDebuggerUrl"]?.Value<string>();
+                            Console.WriteLine(">>> {0}", wsURl);
+
+                            return wsURl;
+                        });
+                    }
+                    catch (Exception ex)
+                    {
+                        Console.WriteLine($"launch-chrome-and-connect failed with {ex.ToString ()}");
+                    }
+                });
+            });
+
+            if (options.NodeApp != null)
+            {
+                Console.WriteLine($"Doing the nodejs: {options.NodeApp}");
+                var nodeFullPath = Path.GetFullPath(options.NodeApp);
+                Console.WriteLine(nodeFullPath);
+                var psi = new ProcessStartInfo();
+
+                psi.UseShellExecute = false;
+                psi.RedirectStandardError = true;
+                psi.RedirectStandardOutput = true;
+
+                psi.Arguments = $"--inspect-brk=localhost:0 {nodeFullPath}";
+                psi.FileName = "node";
+
+                app.UseRouter(router =>
+                {
+                    //Inspector API for using chrome devtools directly
+                    router.MapGet("json", SendNodeList);
+                    router.MapGet("json/list", SendNodeList);
+                    router.MapGet("json/version", SendNodeVersion);
+                    router.MapGet("launch-done-and-connect", async context =>
+                    {
+                        await LaunchAndServe(psi, context, null);
+                    });
+                });
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/BrowserDebugProxy/BrowserDebugProxy.csproj b/src/mono/wasm/debugger/BrowserDebugProxy/BrowserDebugProxy.csproj
new file mode 100644
index 00000000000000..7da1586b7fb385
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugProxy/BrowserDebugProxy.csproj
@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Logging" Version="3.1.2" />
+    <PackageReference Include="Mono.Cecil" Version="0.11.2" />
+    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.5.0" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/mono/wasm/debugger/BrowserDebugProxy/BrowserDebugProxy.sln b/src/mono/wasm/debugger/BrowserDebugProxy/BrowserDebugProxy.sln
new file mode 100644
index 00000000000000..cfb208d1562f6f
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugProxy/BrowserDebugProxy.sln
@@ -0,0 +1,31 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.28407.52
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "BrowserDebugHost", "..\BrowserDebugHost\BrowserDebugHost.csproj", "{954F768A-23E6-4B14-90E0-27EA6B41FBCC}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "BrowserDebugProxy", "BrowserDebugProxy.csproj", "{490128B6-9F21-46CA-878A-F22BCF51EF3C}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{954F768A-23E6-4B14-90E0-27EA6B41FBCC}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{954F768A-23E6-4B14-90E0-27EA6B41FBCC}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{954F768A-23E6-4B14-90E0-27EA6B41FBCC}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{954F768A-23E6-4B14-90E0-27EA6B41FBCC}.Release|Any CPU.Build.0 = Release|Any CPU
+		{490128B6-9F21-46CA-878A-F22BCF51EF3C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{490128B6-9F21-46CA-878A-F22BCF51EF3C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{490128B6-9F21-46CA-878A-F22BCF51EF3C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{490128B6-9F21-46CA-878A-F22BCF51EF3C}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {F8BA2C2D-8F28-4F9E-9C54-51E394EF941E}
+	EndGlobalSection
+EndGlobal
diff --git a/src/mono/wasm/debugger/BrowserDebugProxy/DebugStore.cs b/src/mono/wasm/debugger/BrowserDebugProxy/DebugStore.cs
new file mode 100644
index 00000000000000..aedcfb27a44906
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugProxy/DebugStore.cs
@@ -0,0 +1,883 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Net.Http;
+using System.Runtime.CompilerServices;
+using System.Security.Cryptography;
+using System.Text.RegularExpressions;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Mono.Cecil;
+using Mono.Cecil.Cil;
+using Mono.Cecil.Pdb;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+    internal class BreakpointRequest
+    {
+        public string Id { get; private set; }
+        public string Assembly { get; private set; }
+        public string File { get; private set; }
+        public int Line { get; private set; }
+        public int Column { get; private set; }
+        public MethodInfo Method { get; private set; }
+
+        JObject request;
+
+        public bool IsResolved => Assembly != null;
+        public List<Breakpoint> Locations { get; } = new List<Breakpoint>();
+
+        public override string ToString() => $"BreakpointRequest Assembly: {Assembly} File: {File} Line: {Line} Column: {Column}";
+
+        public object AsSetBreakpointByUrlResponse(IEnumerable<object> jsloc) => new { breakpointId = Id, locations = Locations.Select(l => l.Location.AsLocation()).Concat(jsloc) };
+
+        public BreakpointRequest()
+        { }
+
+        public BreakpointRequest(string id, MethodInfo method)
+        {
+            Id = id;
+            Method = method;
+        }
+
+        public BreakpointRequest(string id, JObject request)
+        {
+            Id = id;
+            this.request = request;
+        }
+
+        public static BreakpointRequest Parse(string id, JObject args)
+        {
+            return new BreakpointRequest(id, args);
+        }
+
+        public BreakpointRequest Clone() => new BreakpointRequest { Id = Id, request = request };
+
+        public bool IsMatch(SourceFile sourceFile)
+        {
+            var url = request?["url"]?.Value<string>();
+            if (url == null)
+            {
+                var urlRegex = request?["urlRegex"].Value<string>();
+                var regex = new Regex(urlRegex);
+                return regex.IsMatch(sourceFile.Url.ToString()) || regex.IsMatch(sourceFile.DocUrl);
+            }
+
+            return sourceFile.Url.ToString() == url || sourceFile.DotNetUrl == url;
+        }
+
+        public bool TryResolve(SourceFile sourceFile)
+        {
+            if (!IsMatch(sourceFile))
+                return false;
+
+            var line = request?["lineNumber"]?.Value<int>();
+            var column = request?["columnNumber"]?.Value<int>();
+
+            if (line == null || column == null)
+                return false;
+
+            Assembly = sourceFile.AssemblyName;
+            File = sourceFile.DebuggerFileName;
+            Line = line.Value;
+            Column = column.Value;
+            return true;
+        }
+
+        public bool TryResolve(DebugStore store)
+        {
+            if (request == null || store == null)
+                return false;
+
+            return store.AllSources().FirstOrDefault(source => TryResolve(source)) != null;
+        }
+    }
+
+    internal class VarInfo
+    {
+        public VarInfo(VariableDebugInformation v)
+        {
+            this.Name = v.Name;
+            this.Index = v.Index;
+        }
+
+        public VarInfo(ParameterDefinition p)
+        {
+            this.Name = p.Name;
+            this.Index = (p.Index + 1) * -1;
+        }
+
+        public string Name { get; }
+        public int Index { get; }
+
+        public override string ToString() => $"(var-info [{Index}] '{Name}')";
+    }
+
+    internal class CliLocation
+    {
+        public CliLocation(MethodInfo method, int offset)
+        {
+            Method = method;
+            Offset = offset;
+        }
+
+        public MethodInfo Method { get; }
+        public int Offset { get; }
+    }
+
+    internal class SourceLocation
+    {
+        SourceId id;
+        int line;
+        int column;
+        CliLocation cliLoc;
+
+        public SourceLocation(SourceId id, int line, int column)
+        {
+            this.id = id;
+            this.line = line;
+            this.column = column;
+        }
+
+        public SourceLocation(MethodInfo mi, SequencePoint sp)
+        {
+            this.id = mi.SourceId;
+            this.line = sp.StartLine - 1;
+            this.column = sp.StartColumn - 1;
+            this.cliLoc = new CliLocation(mi, sp.Offset);
+        }
+
+        public SourceId Id { get => id; }
+        public int Line { get => line; }
+        public int Column { get => column; }
+        public CliLocation CliLocation => this.cliLoc;
+
+        public override string ToString() => $"{id}:{Line}:{Column}";
+
+        public static SourceLocation Parse(JObject obj)
+        {
+            if (obj == null)
+                return null;
+
+            if (!SourceId.TryParse(obj["scriptId"]?.Value<string>(), out var id))
+                return null;
+
+            var line = obj["lineNumber"]?.Value<int>();
+            var column = obj["columnNumber"]?.Value<int>();
+            if (id == null || line == null || column == null)
+                return null;
+
+            return new SourceLocation(id, line.Value, column.Value);
+        }
+
+        internal class LocationComparer : EqualityComparer<SourceLocation>
+        {
+            public override bool Equals(SourceLocation l1, SourceLocation l2)
+            {
+                if (l1 == null && l2 == null)
+                    return true;
+                else if (l1 == null || l2 == null)
+                    return false;
+
+                return (l1.Line == l2.Line &&
+                    l1.Column == l2.Column &&
+                    l1.Id == l2.Id);
+            }
+
+            public override int GetHashCode(SourceLocation loc)
+            {
+                int hCode = loc.Line ^ loc.Column;
+                return loc.Id.GetHashCode() ^ hCode.GetHashCode();
+            }
+        }
+
+        internal object AsLocation() => new
+        {
+            scriptId = id.ToString(),
+            lineNumber = line,
+            columnNumber = column
+        };
+    }
+
+    internal class SourceId
+    {
+        const string Scheme = "dotnet://";
+
+        readonly int assembly, document;
+
+        public int Assembly => assembly;
+        public int Document => document;
+
+        internal SourceId(int assembly, int document)
+        {
+            this.assembly = assembly;
+            this.document = document;
+        }
+
+        public SourceId(string id)
+        {
+            if (!TryParse(id, out assembly, out document))
+                throw new ArgumentException("invalid source identifier", nameof(id));
+        }
+
+        public static bool TryParse(string id, out SourceId source)
+        {
+            source = null;
+            if (!TryParse(id, out var assembly, out var document))
+                return false;
+
+            source = new SourceId(assembly, document);
+            return true;
+        }
+
+        static bool TryParse(string id, out int assembly, out int document)
+        {
+            assembly = document = 0;
+            if (id == null || !id.StartsWith(Scheme, StringComparison.Ordinal))
+                return false;
+
+            var sp = id.Substring(Scheme.Length).Split('_');
+            if (sp.Length != 2)
+                return false;
+
+            if (!int.TryParse(sp[0], out assembly))
+                return false;
+
+            if (!int.TryParse(sp[1], out document))
+                return false;
+
+            return true;
+        }
+
+        public override string ToString() => $"{Scheme}{assembly}_{document}";
+
+        public override bool Equals(object obj)
+        {
+            if (obj == null)
+                return false;
+            SourceId that = obj as SourceId;
+            return that.assembly == this.assembly && that.document == this.document;
+        }
+
+        public override int GetHashCode() => assembly.GetHashCode() ^ document.GetHashCode();
+
+        public static bool operator ==(SourceId a, SourceId b) => ((object) a == null) ? (object) b == null : a.Equals(b);
+
+        public static bool operator !=(SourceId a, SourceId b) => !a.Equals(b);
+    }
+
+    internal class MethodInfo
+    {
+        MethodDefinition methodDef;
+        SourceFile source;
+
+        public SourceId SourceId => source.SourceId;
+
+        public string Name => methodDef.Name;
+        public MethodDebugInformation DebugInformation => methodDef.DebugInformation;
+
+        public SourceLocation StartLocation { get; }
+        public SourceLocation EndLocation { get; }
+        public AssemblyInfo Assembly { get; }
+        public uint Token => methodDef.MetadataToken.RID;
+
+        public MethodInfo(AssemblyInfo assembly, MethodDefinition methodDef, SourceFile source)
+        {
+            this.Assembly = assembly;
+            this.methodDef = methodDef;
+            this.source = source;
+
+            var sps = DebugInformation.SequencePoints;
+            if (sps == null || sps.Count() < 1)
+                return;
+
+            SequencePoint start = sps[0];
+            SequencePoint end = sps[0];
+
+            foreach (var sp in sps)
+            {
+                if (sp.StartLine < start.StartLine)
+                    start = sp;
+                else if (sp.StartLine == start.StartLine && sp.StartColumn < start.StartColumn)
+                    start = sp;
+
+                if (sp.EndLine > end.EndLine)
+                    end = sp;
+                else if (sp.EndLine == end.EndLine && sp.EndColumn > end.EndColumn)
+                    end = sp;
+            }
+
+            StartLocation = new SourceLocation(this, start);
+            EndLocation = new SourceLocation(this, end);
+        }
+
+        public SourceLocation GetLocationByIl(int pos)
+        {
+            SequencePoint prev = null;
+            foreach (var sp in DebugInformation.SequencePoints)
+            {
+                if (sp.Offset > pos)
+                    break;
+                prev = sp;
+            }
+
+            if (prev != null)
+                return new SourceLocation(this, prev);
+
+            return null;
+        }
+
+        public VarInfo[] GetLiveVarsAt(int offset)
+        {
+            var res = new List<VarInfo>();
+
+            res.AddRange(methodDef.Parameters.Select(p => new VarInfo(p)));
+            res.AddRange(methodDef.DebugInformation.GetScopes()
+                .Where(s => s.Start.Offset <= offset && (s.End.IsEndOfMethod || s.End.Offset > offset))
+                .SelectMany(s => s.Variables)
+                .Where(v => !v.IsDebuggerHidden)
+                .Select(v => new VarInfo(v)));
+
+            return res.ToArray();
+        }
+
+        public override string ToString() => "MethodInfo(" + methodDef.FullName + ")";
+    }
+
+    internal class TypeInfo
+    {
+        AssemblyInfo assembly;
+        TypeDefinition type;
+        List<MethodInfo> methods;
+
+        public TypeInfo(AssemblyInfo assembly, TypeDefinition type)
+        {
+            this.assembly = assembly;
+            this.type = type;
+            methods = new List<MethodInfo>();
+        }
+
+        public string Name => type.Name;
+        public string FullName => type.FullName;
+        public List<MethodInfo> Methods => methods;
+
+        public override string ToString() => "TypeInfo('" + FullName + "')";
+    }
+
+    class AssemblyInfo
+    {
+        static int next_id;
+        ModuleDefinition image;
+        readonly int id;
+        readonly ILogger logger;
+        Dictionary<uint, MethodInfo> methods = new Dictionary<uint, MethodInfo>();
+        Dictionary<string, string> sourceLinkMappings = new Dictionary<string, string>();
+        Dictionary<string, TypeInfo> typesByName = new Dictionary<string, TypeInfo>();
+        readonly List<SourceFile> sources = new List<SourceFile>();
+        internal string Url { get; }
+
+        public AssemblyInfo(IAssemblyResolver resolver, string url, byte[] assembly, byte[] pdb)
+        {
+            this.id = Interlocked.Increment(ref next_id);
+
+            try
+            {
+                Url = url;
+                ReaderParameters rp = new ReaderParameters( /*ReadingMode.Immediate*/ );
+                rp.AssemblyResolver = resolver;
+                // set ReadSymbols = true unconditionally in case there
+                // is an embedded pdb then handle ArgumentException
+                // and assume that if pdb == null that is the cause
+                rp.ReadSymbols = true;
+                rp.SymbolReaderProvider = new PdbReaderProvider();
+                if (pdb != null)
+                    rp.SymbolStream = new MemoryStream(pdb);
+                rp.ReadingMode = ReadingMode.Immediate;
+
+                this.image = ModuleDefinition.ReadModule(new MemoryStream(assembly), rp);
+            }
+            catch (BadImageFormatException ex)
+            {
+                logger.LogWarning($"Failed to read assembly as portable PDB: {ex.Message}");
+            }
+            catch (ArgumentException)
+            {
+                // if pdb == null this is expected and we
+                // read the assembly without symbols below
+                if (pdb != null)
+                    throw;
+            }
+
+            if (this.image == null)
+            {
+                ReaderParameters rp = new ReaderParameters( /*ReadingMode.Immediate*/ );
+                rp.AssemblyResolver = resolver;
+                if (pdb != null)
+                {
+                    rp.ReadSymbols = true;
+                    rp.SymbolReaderProvider = new PdbReaderProvider();
+                    rp.SymbolStream = new MemoryStream(pdb);
+                }
+
+                rp.ReadingMode = ReadingMode.Immediate;
+
+                this.image = ModuleDefinition.ReadModule(new MemoryStream(assembly), rp);
+            }
+
+            Populate();
+        }
+
+        public AssemblyInfo(ILogger logger)
+        {
+            this.logger = logger;
+        }
+
+        void Populate()
+        {
+            ProcessSourceLink();
+
+            var d2s = new Dictionary<Document, SourceFile>();
+
+            SourceFile FindSource(Document doc)
+            {
+                if (doc == null)
+                    return null;
+
+                if (d2s.TryGetValue(doc, out var source))
+                    return source;
+
+                var src = new SourceFile(this, sources.Count, doc, GetSourceLinkUrl(doc.Url));
+                sources.Add(src);
+                d2s[doc] = src;
+                return src;
+            };
+
+            foreach (var type in image.GetTypes())
+            {
+                var typeInfo = new TypeInfo(this, type);
+                typesByName[type.FullName] = typeInfo;
+
+                foreach (var method in type.Methods)
+                {
+                    foreach (var sp in method.DebugInformation.SequencePoints)
+                    {
+                        var source = FindSource(sp.Document);
+                        var methodInfo = new MethodInfo(this, method, source);
+                        methods[method.MetadataToken.RID] = methodInfo;
+                        if (source != null)
+                            source.AddMethod(methodInfo);
+
+                        typeInfo.Methods.Add(methodInfo);
+                    }
+                }
+            }
+        }
+
+        private void ProcessSourceLink()
+        {
+            var sourceLinkDebugInfo = image.CustomDebugInformations.FirstOrDefault(i => i.Kind == CustomDebugInformationKind.SourceLink);
+
+            if (sourceLinkDebugInfo != null)
+            {
+                var sourceLinkContent = ((SourceLinkDebugInformation) sourceLinkDebugInfo).Content;
+
+                if (sourceLinkContent != null)
+                {
+                    var jObject = JObject.Parse(sourceLinkContent) ["documents"];
+                    sourceLinkMappings = JsonConvert.DeserializeObject<Dictionary<string, string>>(jObject.ToString());
+                }
+            }
+        }
+
+        private Uri GetSourceLinkUrl(string document)
+        {
+            if (sourceLinkMappings.TryGetValue(document, out string url))
+                return new Uri(url);
+
+            foreach (var sourceLinkDocument in sourceLinkMappings)
+            {
+                string key = sourceLinkDocument.Key;
+
+                if (Path.GetFileName(key) != "*")
+                {
+                    continue;
+                }
+
+                var keyTrim = key.TrimEnd('*');
+
+                if (document.StartsWith(keyTrim, StringComparison.OrdinalIgnoreCase))
+                {
+                    var docUrlPart = document.Replace(keyTrim, "");
+                    return new Uri(sourceLinkDocument.Value.TrimEnd('*') + docUrlPart);
+                }
+            }
+
+            return null;
+        }
+
+        public IEnumerable<SourceFile> Sources => this.sources;
+
+        public Dictionary<string, TypeInfo> TypesByName => this.typesByName;
+        public int Id => id;
+        public string Name => image.Name;
+
+        public SourceFile GetDocById(int document)
+        {
+            return sources.FirstOrDefault(s => s.SourceId.Document == document);
+        }
+
+        public MethodInfo GetMethodByToken(uint token)
+        {
+            methods.TryGetValue(token, out var value);
+            return value;
+        }
+
+        public TypeInfo GetTypeByName(string name)
+        {
+            typesByName.TryGetValue(name, out var res);
+            return res;
+        }
+    }
+
+    internal class SourceFile
+    {
+        Dictionary<uint, MethodInfo> methods;
+        AssemblyInfo assembly;
+        int id;
+        Document doc;
+
+        internal SourceFile(AssemblyInfo assembly, int id, Document doc, Uri sourceLinkUri)
+        {
+            this.methods = new Dictionary<uint, MethodInfo>();
+            this.SourceLinkUri = sourceLinkUri;
+            this.assembly = assembly;
+            this.id = id;
+            this.doc = doc;
+            this.DebuggerFileName = doc.Url.Replace("\\", "/").Replace(":", "");
+
+            this.SourceUri = new Uri((Path.IsPathRooted(doc.Url) ? "file://" : "") + doc.Url, UriKind.RelativeOrAbsolute);
+            if (SourceUri.IsFile && File.Exists(SourceUri.LocalPath))
+            {
+                this.Url = this.SourceUri.ToString();
+            }
+            else
+            {
+                this.Url = DotNetUrl;
+            }
+        }
+
+        internal void AddMethod(MethodInfo mi)
+        {
+            if (!this.methods.ContainsKey(mi.Token))
+                this.methods[mi.Token] = mi;
+        }
+
+        public string DebuggerFileName { get; }
+        public string Url { get; }
+        public string AssemblyName => assembly.Name;
+        public string DotNetUrl => $"dotnet://{assembly.Name}/{DebuggerFileName}";
+
+        public SourceId SourceId => new SourceId(assembly.Id, this.id);
+        public Uri SourceLinkUri { get; }
+        public Uri SourceUri { get; }
+
+        public IEnumerable<MethodInfo> Methods => this.methods.Values;
+
+        public string DocUrl => doc.Url;
+
+        public(int startLine, int startColumn, int endLine, int endColumn) GetExtents()
+        {
+            var start = Methods.OrderBy(m => m.StartLocation.Line).ThenBy(m => m.StartLocation.Column).First();
+            var end = Methods.OrderByDescending(m => m.EndLocation.Line).ThenByDescending(m => m.EndLocation.Column).First();
+            return (start.StartLocation.Line, start.StartLocation.Column, end.EndLocation.Line, end.EndLocation.Column);
+        }
+
+        async Task<MemoryStream> GetDataAsync(Uri uri, CancellationToken token)
+        {
+            var mem = new MemoryStream();
+            try
+            {
+                if (uri.IsFile && File.Exists(uri.LocalPath))
+                {
+                    using(var file = File.Open(SourceUri.LocalPath, FileMode.Open))
+                    {
+                        await file.CopyToAsync(mem, token).ConfigureAwait(false);
+                        mem.Position = 0;
+                    }
+                }
+                else if (uri.Scheme == "http" || uri.Scheme == "https")
+                {
+                    var client = new HttpClient();
+                    using(var stream = await client.GetStreamAsync(uri))
+                    {
+                        await stream.CopyToAsync(mem, token).ConfigureAwait(false);
+                        mem.Position = 0;
+                    }
+                }
+            }
+            catch (Exception)
+            {
+                return null;
+            }
+            return mem;
+        }
+
+        static HashAlgorithm GetHashAlgorithm(DocumentHashAlgorithm algorithm)
+        {
+            switch (algorithm)
+            {
+                case DocumentHashAlgorithm.SHA1:
+                    return SHA1.Create();
+                case DocumentHashAlgorithm.SHA256:
+                    return SHA256.Create();
+                case DocumentHashAlgorithm.MD5:
+                    return MD5.Create();
+            }
+            return null;
+        }
+
+        bool CheckPdbHash(byte[] computedHash)
+        {
+            if (computedHash.Length != doc.Hash.Length)
+                return false;
+
+            for (var i = 0; i < computedHash.Length; i++)
+                if (computedHash[i] != doc.Hash[i])
+                    return false;
+
+            return true;
+        }
+
+        byte[] ComputePdbHash(Stream sourceStream)
+        {
+            var algorithm = GetHashAlgorithm(doc.HashAlgorithm);
+            if (algorithm != null)
+                using(algorithm)
+            return algorithm.ComputeHash(sourceStream);
+
+            return Array.Empty<byte>();
+        }
+
+        public async Task<Stream> GetSourceAsync(bool checkHash, CancellationToken token = default(CancellationToken))
+        {
+            if (doc.EmbeddedSource.Length > 0)
+                return new MemoryStream(doc.EmbeddedSource, false);
+
+            foreach (var url in new [] { SourceUri, SourceLinkUri })
+            {
+                var mem = await GetDataAsync(url, token).ConfigureAwait(false);
+                if (mem != null && (!checkHash || CheckPdbHash(ComputePdbHash(mem))))
+                {
+                    mem.Position = 0;
+                    return mem;
+                }
+            }
+
+            return MemoryStream.Null;
+        }
+
+        public object ToScriptSource(int executionContextId, object executionContextAuxData)
+        {
+            return new
+            {
+                scriptId = SourceId.ToString(),
+                    url = Url,
+                    executionContextId,
+                    executionContextAuxData,
+                    //hash:  should be the v8 hash algo, managed implementation is pending
+                    dotNetUrl = DotNetUrl,
+            };
+        }
+    }
+
+    internal class DebugStore
+    {
+        List<AssemblyInfo> assemblies = new List<AssemblyInfo>();
+        readonly HttpClient client;
+        readonly ILogger logger;
+
+        public DebugStore(ILogger logger, HttpClient client)
+        {
+            this.client = client;
+            this.logger = logger;
+        }
+
+        public DebugStore(ILogger logger) : this(logger, new HttpClient())
+        { }
+
+        class DebugItem
+        {
+            public string Url { get; set; }
+            public Task<byte[][]> Data { get; set; }
+        }
+
+        public async IAsyncEnumerable<SourceFile> Load(SessionId sessionId, string[] loaded_files, [EnumeratorCancellation] CancellationToken token)
+        {
+            static bool MatchPdb(string asm, string pdb) => Path.ChangeExtension(asm, "pdb") == pdb;
+
+            var asm_files = new List<string>();
+            var pdb_files = new List<string>();
+            foreach (var file_name in loaded_files)
+            {
+                if (file_name.EndsWith(".pdb", StringComparison.OrdinalIgnoreCase))
+                    pdb_files.Add(file_name);
+                else
+                    asm_files.Add(file_name);
+            }
+
+            List<DebugItem> steps = new List<DebugItem>();
+            foreach (var url in asm_files)
+            {
+                try
+                {
+                    var pdb = pdb_files.FirstOrDefault(n => MatchPdb(url, n));
+                    steps.Add(
+                        new DebugItem
+                        {
+                            Url = url,
+                                Data = Task.WhenAll(client.GetByteArrayAsync(url), pdb != null ? client.GetByteArrayAsync(pdb) : Task.FromResult<byte[]>(null))
+                        });
+                }
+                catch (Exception e)
+                {
+                    logger.LogDebug($"Failed to read {url} ({e.Message})");
+                }
+            }
+
+            var resolver = new DefaultAssemblyResolver();
+            foreach (var step in steps)
+            {
+                AssemblyInfo assembly = null;
+                try
+                {
+                    var bytes = await step.Data.ConfigureAwait(false);
+                    assembly = new AssemblyInfo(resolver, step.Url, bytes[0], bytes[1]);
+                }
+                catch (Exception e)
+                {
+                    logger.LogDebug($"Failed to load {step.Url} ({e.Message})");
+                }
+                if (assembly == null)
+                    continue;
+
+                assemblies.Add(assembly);
+                foreach (var source in assembly.Sources)
+                    yield return source;
+            }
+        }
+
+        public IEnumerable<SourceFile> AllSources() => assemblies.SelectMany(a => a.Sources);
+
+        public SourceFile GetFileById(SourceId id) => AllSources().SingleOrDefault(f => f.SourceId.Equals(id));
+
+        public AssemblyInfo GetAssemblyByName(string name) => assemblies.FirstOrDefault(a => a.Name.Equals(name, StringComparison.InvariantCultureIgnoreCase));
+
+        /*
+        V8 uses zero based indexing for both line and column.
+        PPDBs uses one based indexing for both line and column.
+        */
+        static bool Match(SequencePoint sp, SourceLocation start, SourceLocation end)
+        {
+            var spStart = (Line: sp.StartLine - 1, Column: sp.StartColumn - 1);
+            var spEnd = (Line: sp.EndLine - 1, Column: sp.EndColumn - 1);
+
+            if (start.Line > spEnd.Line)
+                return false;
+
+            if (start.Column > spEnd.Column && start.Line == spEnd.Line)
+                return false;
+
+            if (end.Line < spStart.Line)
+                return false;
+
+            if (end.Column < spStart.Column && end.Line == spStart.Line)
+                return false;
+
+            return true;
+        }
+
+        public List<SourceLocation> FindPossibleBreakpoints(SourceLocation start, SourceLocation end)
+        {
+            //XXX FIXME no idea what todo with locations on different files
+            if (start.Id != end.Id)
+            {
+                logger.LogDebug($"FindPossibleBreakpoints: documents differ (start: {start.Id}) (end {end.Id}");
+                return null;
+            }
+
+            var sourceId = start.Id;
+
+            var doc = GetFileById(sourceId);
+
+            var res = new List<SourceLocation>();
+            if (doc == null)
+            {
+                logger.LogDebug($"Could not find document {sourceId}");
+                return res;
+            }
+
+            foreach (var method in doc.Methods)
+            {
+                foreach (var sequencePoint in method.DebugInformation.SequencePoints)
+                {
+                    if (!sequencePoint.IsHidden && Match(sequencePoint, start, end))
+                        res.Add(new SourceLocation(method, sequencePoint));
+                }
+            }
+            return res;
+        }
+
+        /*
+        V8 uses zero based indexing for both line and column.
+        PPDBs uses one based indexing for both line and column.
+        */
+        static bool Match(SequencePoint sp, int line, int column)
+        {
+            var bp = (line: line + 1, column: column + 1);
+
+            if (sp.StartLine > bp.line || sp.EndLine < bp.line)
+                return false;
+
+            //Chrome sends a zero column even if getPossibleBreakpoints say something else
+            if (column == 0)
+                return true;
+
+            if (sp.StartColumn > bp.column && sp.StartLine == bp.line)
+                return false;
+
+            if (sp.EndColumn < bp.column && sp.EndLine == bp.line)
+                return false;
+
+            return true;
+        }
+
+        public IEnumerable<SourceLocation> FindBreakpointLocations(BreakpointRequest request)
+        {
+            request.TryResolve(this);
+
+            var asm = assemblies.FirstOrDefault(a => a.Name.Equals(request.Assembly, StringComparison.OrdinalIgnoreCase));
+            var sourceFile = asm?.Sources?.SingleOrDefault(s => s.DebuggerFileName.Equals(request.File, StringComparison.OrdinalIgnoreCase));
+
+            if (sourceFile == null)
+                yield break;
+
+            foreach (var method in sourceFile.Methods)
+            {
+                foreach (var sequencePoint in method.DebugInformation.SequencePoints)
+                {
+                    if (!sequencePoint.IsHidden && Match(sequencePoint, request.Line, request.Column))
+                        yield return new SourceLocation(method, sequencePoint);
+                }
+            }
+        }
+
+        public string ToUrl(SourceLocation location) => location != null ? GetFileById(location.Id).Url : "";
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/BrowserDebugProxy/DebuggerProxy.cs b/src/mono/wasm/debugger/BrowserDebugProxy/DebuggerProxy.cs
new file mode 100644
index 00000000000000..35941119608420
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugProxy/DebuggerProxy.cs
@@ -0,0 +1,29 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Net.WebSockets;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+
+    // This type is the public entrypoint that allows external code to attach the debugger proxy
+    // to a given websocket listener. Everything else in this package can be internal.
+
+    public class DebuggerProxy
+    {
+        private readonly MonoProxy proxy;
+
+        public DebuggerProxy(ILoggerFactory loggerFactory)
+        {
+            proxy = new MonoProxy(loggerFactory);
+        }
+
+        public Task Run(Uri browserUri, WebSocket ideSocket)
+        {
+            return proxy.Run(browserUri, ideSocket);
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/BrowserDebugProxy/DevToolsHelper.cs b/src/mono/wasm/debugger/BrowserDebugProxy/DevToolsHelper.cs
new file mode 100644
index 00000000000000..d17c9e73913034
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugProxy/DevToolsHelper.cs
@@ -0,0 +1,308 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Net;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+
+    public struct SessionId
+    {
+        public readonly string sessionId;
+
+        public SessionId(string sessionId)
+        {
+            this.sessionId = sessionId;
+        }
+
+        // hashset treats 0 as unset
+        public override int GetHashCode() => sessionId?.GetHashCode() ?? -1;
+
+        public override bool Equals(object obj) => (obj is SessionId) ? ((SessionId) obj).sessionId == sessionId : false;
+
+        public static bool operator ==(SessionId a, SessionId b) => a.sessionId == b.sessionId;
+
+        public static bool operator !=(SessionId a, SessionId b) => a.sessionId != b.sessionId;
+
+        public static SessionId Null { get; } = new SessionId();
+
+        public override string ToString() => $"session-{sessionId}";
+    }
+
+    public struct MessageId
+    {
+        public readonly string sessionId;
+        public readonly int id;
+
+        public MessageId(string sessionId, int id)
+        {
+            this.sessionId = sessionId;
+            this.id = id;
+        }
+
+        public static implicit operator SessionId(MessageId id) => new SessionId(id.sessionId);
+
+        public override string ToString() => $"msg-{sessionId}:::{id}";
+
+        public override int GetHashCode() => (sessionId?.GetHashCode() ?? 0) ^ id.GetHashCode();
+
+        public override bool Equals(object obj) => (obj is MessageId) ? ((MessageId) obj).sessionId == sessionId && ((MessageId) obj).id == id : false;
+    }
+
+    internal class DotnetObjectId
+    {
+        public string Scheme { get; }
+        public string Value { get; }
+
+        public static bool TryParse(JToken jToken, out DotnetObjectId objectId) => TryParse(jToken?.Value<string>(), out objectId);
+
+        public static bool TryParse(string id, out DotnetObjectId objectId)
+        {
+            objectId = null;
+            if (id == null)
+                return false;
+
+            if (!id.StartsWith("dotnet:"))
+                return false;
+
+            var parts = id.Split(":", 3);
+
+            if (parts.Length < 3)
+                return false;
+
+            objectId = new DotnetObjectId(parts[1], parts[2]);
+
+            return true;
+        }
+
+        public DotnetObjectId(string scheme, string value)
+        {
+            Scheme = scheme;
+            Value = value;
+        }
+
+        public override string ToString() => $"dotnet:{Scheme}:{Value}";
+    }
+
+    public struct Result
+    {
+        public JObject Value { get; private set; }
+        public JObject Error { get; private set; }
+
+        public bool IsOk => Value != null;
+        public bool IsErr => Error != null;
+
+        Result(JObject result, JObject error)
+        {
+            if (result != null && error != null)
+                throw new ArgumentException($"Both {nameof(result)} and {nameof(error)} arguments cannot be non-null.");
+
+            bool resultHasError = String.Compare((result?["result"] as JObject) ? ["subtype"]?.Value<string>(), "error") == 0;
+            if (result != null && resultHasError)
+            {
+                this.Value = null;
+                this.Error = result;
+            }
+            else
+            {
+                this.Value = result;
+                this.Error = error;
+            }
+        }
+
+        public static Result FromJson(JObject obj)
+        {
+            //Log ("protocol", $"from result: {obj}");
+            return new Result(obj["result"] as JObject, obj["error"] as JObject);
+        }
+
+        public static Result Ok(JObject ok) => new Result(ok, null);
+
+        public static Result OkFromObject(object ok) => Ok(JObject.FromObject(ok));
+
+        public static Result Err(JObject err) => new Result(null, err);
+
+        public static Result Err(string msg) => new Result(null, JObject.FromObject(new { message = msg }));
+
+        public static Result Exception(Exception e) => new Result(null, JObject.FromObject(new { message = e.Message }));
+
+        public JObject ToJObject(MessageId target)
+        {
+            if (IsOk)
+            {
+                return JObject.FromObject(new
+                {
+                    target.id,
+                        target.sessionId,
+                        result = Value
+                });
+            }
+            else
+            {
+                return JObject.FromObject(new
+                {
+                    target.id,
+                        target.sessionId,
+                        error = Error
+                });
+            }
+        }
+
+        public override string ToString()
+        {
+            return $"[Result: IsOk: {IsOk}, IsErr: {IsErr}, Value: {Value?.ToString ()}, Error: {Error?.ToString ()} ]";
+        }
+    }
+
+    internal class MonoCommands
+    {
+        public string expression { get; set; }
+        public string objectGroup { get; set; } = "mono-debugger";
+        public bool includeCommandLineAPI { get; set; } = false;
+        public bool silent { get; set; } = false;
+        public bool returnByValue { get; set; } = true;
+
+        public MonoCommands(string expression) => this.expression = expression;
+
+        public static MonoCommands GetCallStack() => new MonoCommands("MONO.mono_wasm_get_call_stack()");
+
+        public static MonoCommands GetExceptionObject () => new MonoCommands ("MONO.mono_wasm_get_exception_object()");
+
+        public static MonoCommands IsRuntimeReady() => new MonoCommands("MONO.mono_wasm_runtime_is_ready");
+
+        public static MonoCommands StartSingleStepping(StepKind kind) => new MonoCommands($"MONO.mono_wasm_start_single_stepping ({(int)kind})");
+
+        public static MonoCommands GetLoadedFiles() => new MonoCommands("MONO.mono_wasm_get_loaded_files()");
+
+        public static MonoCommands ClearAllBreakpoints() => new MonoCommands("MONO.mono_wasm_clear_all_breakpoints()");
+
+        public static MonoCommands GetDetails(DotnetObjectId objectId, JToken args = null) => new MonoCommands($"MONO.mono_wasm_get_details ('{objectId}', {(args ?? "{ }")})");
+
+        public static MonoCommands GetScopeVariables(int scopeId, params VarInfo[] vars)
+        {
+            var var_ids = vars.Select(v => new { index = v.Index, name = v.Name }).ToArray();
+            return new MonoCommands($"MONO.mono_wasm_get_variables({scopeId}, {JsonConvert.SerializeObject (var_ids)})");
+        }
+
+        public static MonoCommands SetBreakpoint(string assemblyName, uint methodToken, int ilOffset) => new MonoCommands($"MONO.mono_wasm_set_breakpoint (\"{assemblyName}\", {methodToken}, {ilOffset})");
+
+        public static MonoCommands RemoveBreakpoint(int breakpointId) => new MonoCommands($"MONO.mono_wasm_remove_breakpoint({breakpointId})");
+
+        public static MonoCommands ReleaseObject(DotnetObjectId objectId) => new MonoCommands($"MONO.mono_wasm_release_object('{objectId}')");
+
+        public static MonoCommands CallFunctionOn(JToken args) => new MonoCommands($"MONO.mono_wasm_call_function_on ({args.ToString ()})");
+
+        public static MonoCommands Resume() => new MonoCommands($"MONO.mono_wasm_debugger_resume ()");
+
+        public static MonoCommands SetPauseOnExceptions (string state) => new MonoCommands ($"MONO.mono_wasm_set_pause_on_exceptions(\"{state}\")");
+    }
+
+    internal enum MonoErrorCodes
+    {
+        BpNotFound = 100000,
+    }
+
+    internal class MonoConstants
+    {
+        public const string RUNTIME_IS_READY = "mono_wasm_runtime_ready";
+    }
+
+    class Frame
+    {
+        public Frame(MethodInfo method, SourceLocation location, int id)
+        {
+            this.Method = method;
+            this.Location = location;
+            this.Id = id;
+        }
+
+        public MethodInfo Method { get; private set; }
+        public SourceLocation Location { get; private set; }
+        public int Id { get; private set; }
+    }
+
+    class Breakpoint
+    {
+        public SourceLocation Location { get; private set; }
+        public int RemoteId { get; set; }
+        public BreakpointState State { get; set; }
+        public string StackId { get; private set; }
+
+        public static bool TryParseId(string stackId, out int id)
+        {
+            id = -1;
+            if (stackId?.StartsWith("dotnet:", StringComparison.Ordinal) != true)
+                return false;
+
+            return int.TryParse(stackId.Substring("dotnet:".Length), out id);
+        }
+
+        public Breakpoint(string stackId, SourceLocation loc, BreakpointState state)
+        {
+            this.StackId = stackId;
+            this.Location = loc;
+            this.State = state;
+        }
+    }
+
+    enum BreakpointState
+    {
+        Active,
+        Disabled,
+        Pending
+    }
+
+    enum StepKind
+    {
+        Into,
+        Out,
+        Over
+    }
+
+    internal class ExecutionContext
+    {
+        public string DebuggerId { get; set; }
+        public Dictionary<string, BreakpointRequest> BreakpointRequests { get; } = new Dictionary<string, BreakpointRequest>();
+
+        public TaskCompletionSource<DebugStore> ready = null;
+        public bool IsRuntimeReady => ready != null && ready.Task.IsCompleted;
+
+        public int Id { get; set; }
+        public object AuxData { get; set; }
+
+        public List<Frame> CallStack { get; set; }
+
+        public string[] LoadedFiles { get; set; }
+        internal DebugStore store;
+        public TaskCompletionSource<DebugStore> Source { get; } = new TaskCompletionSource<DebugStore>();
+
+        public Dictionary<string, JToken> LocalsCache = new Dictionary<string, JToken>();
+
+        public DebugStore Store
+        {
+            get
+            {
+                if (store == null || !Source.Task.IsCompleted)
+                    return null;
+
+                return store;
+            }
+        }
+
+        public void ClearState()
+        {
+            CallStack = null;
+            LocalsCache.Clear();
+        }
+
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/BrowserDebugProxy/DevToolsProxy.cs b/src/mono/wasm/debugger/BrowserDebugProxy/DevToolsProxy.cs
new file mode 100644
index 00000000000000..656bd91c5091b1
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugProxy/DevToolsProxy.cs
@@ -0,0 +1,381 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Net.WebSockets;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+
+    class DevToolsQueue
+    {
+        Task current_send;
+        List<byte[]> pending;
+
+        public WebSocket Ws { get; private set; }
+        public Task CurrentSend { get { return current_send; } }
+        public DevToolsQueue(WebSocket sock)
+        {
+            this.Ws = sock;
+            pending = new List<byte[]>();
+        }
+
+        public Task Send(byte[] bytes, CancellationToken token)
+        {
+            pending.Add(bytes);
+            if (pending.Count == 1)
+            {
+                if (current_send != null)
+                    throw new Exception("current_send MUST BE NULL IF THERE'S no pending send");
+                //logger.LogTrace ("sending {0} bytes", bytes.Length);
+                current_send = Ws.SendAsync(new ArraySegment<byte>(bytes), WebSocketMessageType.Text, true, token);
+                return current_send;
+            }
+            return null;
+        }
+
+        public Task Pump(CancellationToken token)
+        {
+            current_send = null;
+            pending.RemoveAt(0);
+
+            if (pending.Count > 0)
+            {
+                if (current_send != null)
+                    throw new Exception("current_send MUST BE NULL IF THERE'S no pending send");
+
+                current_send = Ws.SendAsync(new ArraySegment<byte>(pending[0]), WebSocketMessageType.Text, true, token);
+                return current_send;
+            }
+            return null;
+        }
+    }
+
+    internal class DevToolsProxy
+    {
+        TaskCompletionSource<bool> side_exception = new TaskCompletionSource<bool>();
+        TaskCompletionSource<bool> client_initiated_close = new TaskCompletionSource<bool>();
+        Dictionary<MessageId, TaskCompletionSource<Result>> pending_cmds = new Dictionary<MessageId, TaskCompletionSource<Result>>();
+        ClientWebSocket browser;
+        WebSocket ide;
+        int next_cmd_id;
+        List<Task> pending_ops = new List<Task>();
+        List<DevToolsQueue> queues = new List<DevToolsQueue>();
+
+        protected readonly ILogger logger;
+
+        public DevToolsProxy(ILoggerFactory loggerFactory)
+        {
+            logger = loggerFactory.CreateLogger<DevToolsProxy>();
+        }
+
+        protected virtual Task<bool> AcceptEvent(SessionId sessionId, string method, JObject args, CancellationToken token)
+        {
+            return Task.FromResult(false);
+        }
+
+        protected virtual Task<bool> AcceptCommand(MessageId id, string method, JObject args, CancellationToken token)
+        {
+            return Task.FromResult(false);
+        }
+
+        async Task<string> ReadOne(WebSocket socket, CancellationToken token)
+        {
+            byte[] buff = new byte[4000];
+            var mem = new MemoryStream();
+            while (true)
+            {
+
+                if (socket.State != WebSocketState.Open)
+                {
+                    Log("error", $"DevToolsProxy: Socket is no longer open.");
+                    client_initiated_close.TrySetResult(true);
+                    return null;
+                }
+
+                var result = await socket.ReceiveAsync(new ArraySegment<byte>(buff), token);
+                if (result.MessageType == WebSocketMessageType.Close)
+                {
+                    client_initiated_close.TrySetResult(true);
+                    return null;
+                }
+
+                mem.Write(buff, 0, result.Count);
+
+                if (result.EndOfMessage)
+                    return Encoding.UTF8.GetString(mem.GetBuffer(), 0, (int) mem.Length);
+            }
+        }
+
+        DevToolsQueue GetQueueForSocket(WebSocket ws)
+        {
+            return queues.FirstOrDefault(q => q.Ws == ws);
+        }
+
+        DevToolsQueue GetQueueForTask(Task task)
+        {
+            return queues.FirstOrDefault(q => q.CurrentSend == task);
+        }
+
+        void Send(WebSocket to, JObject o, CancellationToken token)
+        {
+            var sender = browser == to ? "Send-browser" : "Send-ide";
+
+            var method = o["method"]?.ToString();
+            //if (method != "Debugger.scriptParsed" && method != "Runtime.consoleAPICalled")
+            Log("protocol", $"{sender}: " + JsonConvert.SerializeObject(o));
+            var bytes = Encoding.UTF8.GetBytes(o.ToString());
+
+            var queue = GetQueueForSocket(to);
+
+            var task = queue.Send(bytes, token);
+            if (task != null)
+                pending_ops.Add(task);
+        }
+
+        async Task OnEvent(SessionId sessionId, string method, JObject args, CancellationToken token)
+        {
+            try
+            {
+                if (!await AcceptEvent(sessionId, method, args, token))
+                {
+                    //logger.LogDebug ("proxy browser: {0}::{1}",method, args);
+                    SendEventInternal(sessionId, method, args, token);
+                }
+            }
+            catch (Exception e)
+            {
+                side_exception.TrySetException(e);
+            }
+        }
+
+        async Task OnCommand(MessageId id, string method, JObject args, CancellationToken token)
+        {
+            try
+            {
+                if (!await AcceptCommand(id, method, args, token))
+                {
+                    var res = await SendCommandInternal(id, method, args, token);
+                    SendResponseInternal(id, res, token);
+                }
+            }
+            catch (Exception e)
+            {
+                side_exception.TrySetException(e);
+            }
+        }
+
+        void OnResponse(MessageId id, Result result)
+        {
+            //logger.LogTrace ("got id {0} res {1}", id, result);
+            // Fixme
+            if (pending_cmds.Remove(id, out var task))
+            {
+                task.SetResult(result);
+                return;
+            }
+            logger.LogError("Cannot respond to command: {id} with result: {result} - command is not pending", id, result);
+        }
+
+        void ProcessBrowserMessage(string msg, CancellationToken token)
+        {
+            var res = JObject.Parse(msg);
+
+            var method = res["method"]?.ToString();
+            //if (method != "Debugger.scriptParsed" && method != "Runtime.consoleAPICalled")
+            Log("protocol", $"browser: {msg}");
+
+            if (res["id"] == null)
+                pending_ops.Add(OnEvent(new SessionId(res["sessionId"]?.Value<string>()), res["method"].Value<string>(), res["params"] as JObject, token));
+            else
+                OnResponse(new MessageId(res["sessionId"]?.Value<string>(), res["id"].Value<int>()), Result.FromJson(res));
+        }
+
+        void ProcessIdeMessage(string msg, CancellationToken token)
+        {
+            Log("protocol", $"ide: {msg}");
+            if (!string.IsNullOrEmpty(msg))
+            {
+                var res = JObject.Parse(msg);
+                pending_ops.Add(OnCommand(
+                    new MessageId(res["sessionId"]?.Value<string>(), res["id"].Value<int>()),
+                    res["method"].Value<string>(),
+                    res["params"] as JObject, token));
+            }
+        }
+
+        internal async Task<Result> SendCommand(SessionId id, string method, JObject args, CancellationToken token)
+        {
+            //Log ("verbose", $"sending command {method}: {args}");
+            return await SendCommandInternal(id, method, args, token);
+        }
+
+        Task<Result> SendCommandInternal(SessionId sessionId, string method, JObject args, CancellationToken token)
+        {
+            int id = Interlocked.Increment(ref next_cmd_id);
+
+            var o = JObject.FromObject(new
+            {
+                id,
+                method,
+                @params = args
+            });
+            if (sessionId.sessionId != null)
+                o["sessionId"] = sessionId.sessionId;
+            var tcs = new TaskCompletionSource<Result>();
+
+            var msgId = new MessageId(sessionId.sessionId, id);
+            //Log ("verbose", $"add cmd id {sessionId}-{id}");
+            pending_cmds[msgId] = tcs;
+
+            Send(this.browser, o, token);
+            return tcs.Task;
+        }
+
+        public void SendEvent(SessionId sessionId, string method, JObject args, CancellationToken token)
+        {
+            //Log ("verbose", $"sending event {method}: {args}");
+            SendEventInternal(sessionId, method, args, token);
+        }
+
+        void SendEventInternal(SessionId sessionId, string method, JObject args, CancellationToken token)
+        {
+            var o = JObject.FromObject(new
+            {
+                method,
+                @params = args
+            });
+            if (sessionId.sessionId != null)
+                o["sessionId"] = sessionId.sessionId;
+
+            Send(this.ide, o, token);
+        }
+
+        internal void SendResponse(MessageId id, Result result, CancellationToken token)
+        {
+            SendResponseInternal(id, result, token);
+        }
+
+        void SendResponseInternal(MessageId id, Result result, CancellationToken token)
+        {
+            JObject o = result.ToJObject(id);
+            if (result.IsErr)
+                logger.LogError($"sending error response for id: {id} -> {result}");
+
+            Send(this.ide, o, token);
+        }
+
+        // , HttpContext context)
+        public async Task Run(Uri browserUri, WebSocket ideSocket)
+        {
+            Log("info", $"DevToolsProxy: Starting on {browserUri}");
+            using(this.ide = ideSocket)
+            {
+                Log("verbose", $"DevToolsProxy: IDE waiting for connection on {browserUri}");
+                queues.Add(new DevToolsQueue(this.ide));
+                using(this.browser = new ClientWebSocket())
+                {
+                    this.browser.Options.KeepAliveInterval = Timeout.InfiniteTimeSpan;
+                    await this.browser.ConnectAsync(browserUri, CancellationToken.None);
+                    queues.Add(new DevToolsQueue(this.browser));
+
+                    Log("verbose", $"DevToolsProxy: Client connected on {browserUri}");
+                    var x = new CancellationTokenSource();
+
+                    pending_ops.Add(ReadOne(browser, x.Token));
+                    pending_ops.Add(ReadOne(ide, x.Token));
+                    pending_ops.Add(side_exception.Task);
+                    pending_ops.Add(client_initiated_close.Task);
+
+                    try
+                    {
+                        while (!x.IsCancellationRequested)
+                        {
+                            var task = await Task.WhenAny(pending_ops.ToArray());
+                            //logger.LogTrace ("pump {0} {1}", task, pending_ops.IndexOf (task));
+                            if (task == pending_ops[0])
+                            {
+                                var msg = ((Task<string>) task).Result;
+                                if (msg != null)
+                                {
+                                    pending_ops[0] = ReadOne(browser, x.Token); //queue next read
+                                    ProcessBrowserMessage(msg, x.Token);
+                                }
+                            }
+                            else if (task == pending_ops[1])
+                            {
+                                var msg = ((Task<string>) task).Result;
+                                if (msg != null)
+                                {
+                                    pending_ops[1] = ReadOne(ide, x.Token); //queue next read
+                                    ProcessIdeMessage(msg, x.Token);
+                                }
+                            }
+                            else if (task == pending_ops[2])
+                            {
+                                var res = ((Task<bool>) task).Result;
+                                throw new Exception("side task must always complete with an exception, what's going on???");
+                            }
+                            else if (task == pending_ops[3])
+                            {
+                                var res = ((Task<bool>) task).Result;
+                                Log("verbose", $"DevToolsProxy: Client initiated close from {browserUri}");
+                                x.Cancel();
+                            }
+                            else
+                            {
+                                //must be a background task
+                                pending_ops.Remove(task);
+                                var queue = GetQueueForTask(task);
+                                if (queue != null)
+                                {
+                                    var tsk = queue.Pump(x.Token);
+                                    if (tsk != null)
+                                        pending_ops.Add(tsk);
+                                }
+                            }
+                        }
+                    }
+                    catch (Exception e)
+                    {
+                        Log("error", $"DevToolsProxy::Run: Exception {e}");
+                        //throw;
+                    }
+                    finally
+                    {
+                        if (!x.IsCancellationRequested)
+                            x.Cancel();
+                    }
+                }
+            }
+        }
+
+        protected void Log(string priority, string msg)
+        {
+            switch (priority)
+            {
+                case "protocol":
+                    logger.LogTrace(msg);
+                    break;
+                case "verbose":
+                    logger.LogDebug(msg);
+                    break;
+                case "info":
+                case "warning":
+                case "error":
+                default:
+                    logger.LogDebug(msg);
+                    break;
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/BrowserDebugProxy/EvaluateExpression.cs b/src/mono/wasm/debugger/BrowserDebugProxy/EvaluateExpression.cs
new file mode 100644
index 00000000000000..982fa87592a60e
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugProxy/EvaluateExpression.cs
@@ -0,0 +1,213 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Emit;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+
+    internal class EvaluateExpression
+    {
+
+        class FindThisExpression : CSharpSyntaxWalker
+        {
+            public List<string> thisExpressions = new List<string>();
+            public SyntaxTree syntaxTree;
+            public FindThisExpression(SyntaxTree syntax)
+            {
+                syntaxTree = syntax;
+            }
+            public override void Visit(SyntaxNode node)
+            {
+                if (node is ThisExpressionSyntax)
+                {
+                    if (node.Parent is MemberAccessExpressionSyntax thisParent && thisParent.Name is IdentifierNameSyntax)
+                    {
+                        IdentifierNameSyntax var = thisParent.Name as IdentifierNameSyntax;
+                        thisExpressions.Add(var.Identifier.Text);
+                        var newRoot = syntaxTree.GetRoot().ReplaceNode(node.Parent, thisParent.Name);
+                        syntaxTree = syntaxTree.WithRootAndOptions(newRoot, syntaxTree.Options);
+                        this.Visit(GetExpressionFromSyntaxTree(syntaxTree));
+                    }
+                }
+                else
+                    base.Visit(node);
+            }
+
+            public async Task CheckIfIsProperty(MonoProxy proxy, MessageId msg_id, int scope_id, CancellationToken token)
+            {
+                foreach (var var in thisExpressions)
+                {
+                    JToken value = await proxy.TryGetVariableValue(msg_id, scope_id, var, true, token);
+                    if (value == null)
+                        throw new Exception($"The property {var} does not exist in the current context");
+                }
+            }
+        }
+
+        class FindVariableNMethodCall : CSharpSyntaxWalker
+        {
+            public List<IdentifierNameSyntax> variables = new List<IdentifierNameSyntax>();
+            public List<ThisExpressionSyntax> thisList = new List<ThisExpressionSyntax>();
+            public List<InvocationExpressionSyntax> methodCall = new List<InvocationExpressionSyntax>();
+            public List<object> values = new List<Object>();
+
+            public override void Visit(SyntaxNode node)
+            {
+                if (node is IdentifierNameSyntax identifier && !variables.Any(x => x.Identifier.Text == identifier.Identifier.Text))
+                    variables.Add(identifier);
+                if (node is InvocationExpressionSyntax)
+                {
+                    methodCall.Add(node as InvocationExpressionSyntax);
+                    throw new Exception("Method Call is not implemented yet");
+                }
+                if (node is AssignmentExpressionSyntax)
+                    throw new Exception("Assignment is not implemented yet");
+                base.Visit(node);
+            }
+            public async Task<SyntaxTree> ReplaceVars(SyntaxTree syntaxTree, MonoProxy proxy, MessageId msg_id, int scope_id, CancellationToken token)
+            {
+                CompilationUnitSyntax root = syntaxTree.GetCompilationUnitRoot();
+                foreach (var var in variables)
+                {
+                    ClassDeclarationSyntax classDeclaration = root.Members.ElementAt(0) as ClassDeclarationSyntax;
+                    MethodDeclarationSyntax method = classDeclaration.Members.ElementAt(0) as MethodDeclarationSyntax;
+
+                    JToken value = await proxy.TryGetVariableValue(msg_id, scope_id, var.Identifier.Text, false, token);
+
+                    if (value == null)
+                        throw new Exception($"The name {var.Identifier.Text} does not exist in the current context");
+
+                    values.Add(ConvertJSToCSharpType(value["value"]));
+
+                    var updatedMethod = method.AddParameterListParameters(
+                        SyntaxFactory.Parameter(
+                            SyntaxFactory.Identifier(var.Identifier.Text))
+                        .WithType(SyntaxFactory.ParseTypeName(GetTypeFullName(value["value"]))));
+                    root = root.ReplaceNode(method, updatedMethod);
+                }
+                syntaxTree = syntaxTree.WithRootAndOptions(root, syntaxTree.Options);
+                return syntaxTree;
+            }
+
+            private object ConvertJSToCSharpType(JToken variable)
+            {
+                var value = variable["value"];
+                var type = variable["type"].Value<string>();
+                var subType = variable["subtype"]?.Value<string>();
+
+                switch (type)
+                {
+                    case "string":
+                        return value?.Value<string>();
+                    case "number":
+                        return value?.Value<double>();
+                    case "boolean":
+                        return value?.Value<bool>();
+                    case "object":
+                        if (subType == "null")
+                            return null;
+                        break;
+                }
+                throw new Exception($"Evaluate of this datatype {type} not implemented yet");
+            }
+
+            private string GetTypeFullName(JToken variable)
+            {
+                var type = variable["type"].ToString();
+                var subType = variable["subtype"]?.Value<string>();
+                object value = ConvertJSToCSharpType(variable);
+
+                switch (type)
+                {
+                    case "object":
+                        {
+                            if (subType == "null")
+                                return variable["className"].Value<string>();
+                            break;
+                        }
+                    default:
+                        return value.GetType().FullName;
+                }
+                throw new Exception($"Evaluate of this datatype {type} not implemented yet");
+            }
+        }
+
+        static SyntaxNode GetExpressionFromSyntaxTree(SyntaxTree syntaxTree)
+        {
+            CompilationUnitSyntax root = syntaxTree.GetCompilationUnitRoot();
+            ClassDeclarationSyntax classDeclaration = root.Members.ElementAt(0) as ClassDeclarationSyntax;
+            MethodDeclarationSyntax methodDeclaration = classDeclaration.Members.ElementAt(0) as MethodDeclarationSyntax;
+            BlockSyntax blockValue = methodDeclaration.Body;
+            ReturnStatementSyntax returnValue = blockValue.Statements.ElementAt(0) as ReturnStatementSyntax;
+            InvocationExpressionSyntax expressionInvocation = returnValue.Expression as InvocationExpressionSyntax;
+            MemberAccessExpressionSyntax expressionMember = expressionInvocation.Expression as MemberAccessExpressionSyntax;
+            ParenthesizedExpressionSyntax expressionParenthesized = expressionMember.Expression as ParenthesizedExpressionSyntax;
+            return expressionParenthesized.Expression;
+        }
+
+        internal static async Task<string> CompileAndRunTheExpression(MonoProxy proxy, MessageId msg_id, int scope_id, string expression, CancellationToken token)
+        {
+            FindVariableNMethodCall findVarNMethodCall = new FindVariableNMethodCall();
+            string retString;
+            SyntaxTree syntaxTree = CSharpSyntaxTree.ParseText(@"
+				using System;
+				public class CompileAndRunTheExpression
+				{
+					public string Evaluate()
+					{
+						return (" + expression + @").ToString(); 
+					}
+				}");
+
+            FindThisExpression findThisExpression = new FindThisExpression(syntaxTree);
+            var expressionTree = GetExpressionFromSyntaxTree(syntaxTree);
+            findThisExpression.Visit(expressionTree);
+            await findThisExpression.CheckIfIsProperty(proxy, msg_id, scope_id, token);
+            syntaxTree = findThisExpression.syntaxTree;
+
+            expressionTree = GetExpressionFromSyntaxTree(syntaxTree);
+            findVarNMethodCall.Visit(expressionTree);
+
+            syntaxTree = await findVarNMethodCall.ReplaceVars(syntaxTree, proxy, msg_id, scope_id, token);
+
+            MetadataReference[] references = new MetadataReference[]
+            {
+                MetadataReference.CreateFromFile(typeof(object).Assembly.Location),
+                MetadataReference.CreateFromFile(typeof(Enumerable).Assembly.Location)
+            };
+
+            CSharpCompilation compilation = CSharpCompilation.Create(
+                "compileAndRunTheExpression",
+                syntaxTrees : new [] { syntaxTree },
+                references : references,
+                options : new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
+            using(var ms = new MemoryStream())
+            {
+                EmitResult result = compilation.Emit(ms);
+                ms.Seek(0, SeekOrigin.Begin);
+                Assembly assembly = Assembly.Load(ms.ToArray());
+                Type type = assembly.GetType("CompileAndRunTheExpression");
+                object obj = Activator.CreateInstance(type);
+                var ret = type.InvokeMember("Evaluate",
+                    BindingFlags.Default | BindingFlags.InvokeMethod,
+                    null,
+                    obj,
+                    findVarNMethodCall.values.ToArray());
+                retString = ret.ToString();
+            }
+            return retString;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/BrowserDebugProxy/MonoProxy.cs b/src/mono/wasm/debugger/BrowserDebugProxy/MonoProxy.cs
new file mode 100644
index 00000000000000..1f1079f8c0c7b1
--- /dev/null
+++ b/src/mono/wasm/debugger/BrowserDebugProxy/MonoProxy.cs
@@ -0,0 +1,1023 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Net;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
+using Microsoft.Extensions.Logging;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+
+    internal class MonoProxy : DevToolsProxy
+    {
+        HashSet<SessionId> sessions = new HashSet<SessionId>();
+        Dictionary<SessionId, ExecutionContext> contexts = new Dictionary<SessionId, ExecutionContext>();
+
+        public MonoProxy(ILoggerFactory loggerFactory, bool hideWebDriver = true) : base(loggerFactory) { this.hideWebDriver = hideWebDriver; }
+
+        readonly bool hideWebDriver;
+
+        internal ExecutionContext GetContext(SessionId sessionId)
+        {
+            if (contexts.TryGetValue(sessionId, out var context))
+                return context;
+
+            throw new ArgumentException($"Invalid Session: \"{sessionId}\"", nameof(sessionId));
+        }
+
+        bool UpdateContext(SessionId sessionId, ExecutionContext executionContext, out ExecutionContext previousExecutionContext)
+        {
+            var previous = contexts.TryGetValue(sessionId, out previousExecutionContext);
+            contexts[sessionId] = executionContext;
+            return previous;
+        }
+
+        internal Task<Result> SendMonoCommand(SessionId id, MonoCommands cmd, CancellationToken token) => SendCommand(id, "Runtime.evaluate", JObject.FromObject(cmd), token);
+
+        protected override async Task<bool> AcceptEvent(SessionId sessionId, string method, JObject args, CancellationToken token)
+        {
+            switch (method)
+            {
+                case "Runtime.consoleAPICalled":
+                    {
+                        var type = args["type"]?.ToString();
+                        if (type == "debug")
+                        {
+                            var a = args["args"];
+                            if (a?[0] ? ["value"]?.ToString() == MonoConstants.RUNTIME_IS_READY &&
+                                a?[1] ? ["value"]?.ToString() == "fe00e07a-5519-4dfe-b35a-f867dbaf2e28")
+                            {
+                                if (a.Count() > 2)
+                                {
+                                    try
+                                    {
+                                        // The optional 3rd argument is the stringified assembly
+                                        // list so that we don't have to make more round trips
+                                        var context = GetContext(sessionId);
+                                        var loaded = a?[2] ? ["value"]?.ToString();
+                                        if (loaded != null)
+                                            context.LoadedFiles = JToken.Parse(loaded).ToObject<string[]>();
+                                    }
+                                    catch (InvalidCastException ice)
+                                    {
+                                        Log("verbose", ice.ToString());
+                                    }
+                                }
+                                await RuntimeReady(sessionId, token);
+                            }
+
+                        }
+                        break;
+                    }
+
+                case "Runtime.executionContextCreated":
+                    {
+                        SendEvent(sessionId, method, args, token);
+                        var ctx = args?["context"];
+                        var aux_data = ctx?["auxData"] as JObject;
+                        var id = ctx["id"].Value<int>();
+                        if (aux_data != null)
+                        {
+                            var is_default = aux_data["isDefault"]?.Value<bool>();
+                            if (is_default == true)
+                            {
+                                await OnDefaultContext(sessionId, new ExecutionContext { Id = id, AuxData = aux_data }, token);
+                            }
+                        }
+                        return true;
+                    }
+
+                case "Debugger.paused":
+                    {
+                        //TODO figure out how to stich out more frames and, in particular what happens when real wasm is on the stack
+                        var top_func = args?["callFrames"] ? [0] ? ["functionName"]?.Value<string>();
+
+                        if (top_func == "mono_wasm_fire_bp" || top_func == "_mono_wasm_fire_bp" || top_func == "_mono_wasm_fire_exception")
+                        {
+                            return await OnPause(sessionId, args, token);
+                        }
+                        break;
+                    }
+
+                case "Debugger.breakpointResolved":
+                    {
+                        break;
+                    }
+
+                case "Debugger.scriptParsed":
+                    {
+                        var url = args?["url"]?.Value<string>() ?? "";
+
+                        switch (url)
+                        {
+                            case var _ when url == "":
+                                case var _ when url.StartsWith("wasm://", StringComparison.Ordinal):
+                                {
+                                    Log("verbose", $"ignoring wasm: Debugger.scriptParsed {url}");
+                                    return true;
+                                }
+                        }
+                        Log("verbose", $"proxying Debugger.scriptParsed ({sessionId.sessionId}) {url} {args}");
+                        break;
+                    }
+
+                case "Target.attachedToTarget":
+                    {
+                        if (args["targetInfo"]["type"]?.ToString() == "page")
+                            await DeleteWebDriver(new SessionId(args["sessionId"]?.ToString()), token);
+                        break;
+                    }
+
+            }
+
+            return false;
+        }
+
+        async Task<bool> IsRuntimeAlreadyReadyAlready(SessionId sessionId, CancellationToken token)
+        {
+            if (contexts.TryGetValue(sessionId, out var context) && context.IsRuntimeReady)
+                return true;
+
+            var res = await SendMonoCommand(sessionId, MonoCommands.IsRuntimeReady(), token);
+            return res.Value?["result"] ? ["value"]?.Value<bool>() ?? false;
+        }
+
+        protected override async Task<bool> AcceptCommand(MessageId id, string method, JObject args, CancellationToken token)
+        {
+            // Inspector doesn't use the Target domain or sessions
+            // so we try to init immediately
+            if (hideWebDriver && id == SessionId.Null)
+                await DeleteWebDriver(id, token);
+
+            if (!contexts.TryGetValue(id, out var context))
+                return false;
+
+            switch (method)
+            {
+                case "Target.attachToTarget":
+                    {
+                        var resp = await SendCommand(id, method, args, token);
+                        await DeleteWebDriver(new SessionId(resp.Value["sessionId"]?.ToString()), token);
+                        break;
+                    }
+
+                case "Debugger.enable":
+                    {
+                        System.Console.WriteLine("recebi o Debugger.enable");
+                        var resp = await SendCommand(id, method, args, token);
+
+                        context.DebuggerId = resp.Value["debuggerId"]?.ToString();
+
+                        if (await IsRuntimeAlreadyReadyAlready(id, token))
+                            await RuntimeReady(id, token);
+
+                        SendResponse(id, resp, token);
+                        return true;
+                    }
+
+                case "Debugger.getScriptSource":
+                    {
+                        var script = args?["scriptId"]?.Value<string>();
+                        return await OnGetScriptSource(id, script, token);
+                    }
+
+                case "Runtime.compileScript":
+                    {
+                        var exp = args?["expression"]?.Value<string>();
+                        if (exp.StartsWith("//dotnet:", StringComparison.Ordinal))
+                        {
+                            OnCompileDotnetScript(id, token);
+                            return true;
+                        }
+                        break;
+                    }
+
+                case "Debugger.getPossibleBreakpoints":
+                    {
+                        var resp = await SendCommand(id, method, args, token);
+                        if (resp.IsOk && resp.Value["locations"].HasValues)
+                        {
+                            SendResponse(id, resp, token);
+                            return true;
+                        }
+
+                        var start = SourceLocation.Parse(args?["start"] as JObject);
+                        //FIXME support variant where restrictToFunction=true and end is omitted
+                        var end = SourceLocation.Parse(args?["end"] as JObject);
+                        if (start != null && end != null && await GetPossibleBreakpoints(id, start, end, token))
+                            return true;
+
+                        SendResponse(id, resp, token);
+                        return true;
+                    }
+
+                case "Debugger.setBreakpoint":
+                    {
+                        break;
+                    }
+
+                case "Debugger.setBreakpointByUrl":
+                    {
+                        var resp = await SendCommand(id, method, args, token);
+                        if (!resp.IsOk)
+                        {
+                            SendResponse(id, resp, token);
+                            return true;
+                        }
+
+                        var bpid = resp.Value["breakpointId"]?.ToString();
+                        var locations = resp.Value["locations"]?.Values<object>();
+                        var request = BreakpointRequest.Parse(bpid, args);
+
+                        // is the store done loading?
+                        var loaded = context.Source.Task.IsCompleted;
+                        if (!loaded)
+                        {
+                            // Send and empty response immediately if not
+                            // and register the breakpoint for resolution
+                            context.BreakpointRequests[bpid] = request;
+                            SendResponse(id, resp, token);
+                        }
+
+                        if (await IsRuntimeAlreadyReadyAlready(id, token))
+                        {
+                            var store = await RuntimeReady(id, token);
+
+                            Log("verbose", $"BP req {args}");
+                            await SetBreakpoint(id, store, request, !loaded, token);
+                        }
+
+                        if (loaded)
+                        {
+                            // we were already loaded so we should send a response
+                            // with the locations included and register the request
+                            context.BreakpointRequests[bpid] = request;
+                            var result = Result.OkFromObject(request.AsSetBreakpointByUrlResponse(locations));
+                            SendResponse(id, result, token);
+
+                        }
+                        return true;
+                    }
+
+                case "Debugger.removeBreakpoint":
+                    {
+                        await RemoveBreakpoint(id, args, token);
+                        break;
+                    }
+
+                case "Debugger.resume":
+                    {
+                        await OnResume(id, token);
+                        break;
+                    }
+
+                case "Debugger.stepInto":
+                    {
+                        return await Step(id, StepKind.Into, token);
+                    }
+
+                case "Debugger.stepOut":
+                    {
+                        return await Step(id, StepKind.Out, token);
+                    }
+
+                case "Debugger.stepOver":
+                    {
+                        return await Step(id, StepKind.Over, token);
+                    }
+
+                case "Debugger.evaluateOnCallFrame":
+                    {
+                        if (!DotnetObjectId.TryParse(args?["callFrameId"], out var objectId))
+                            return false;
+
+                        switch (objectId.Scheme)
+                        {
+                            case "scope":
+                                return await OnEvaluateOnCallFrame(id,
+                                    int.Parse(objectId.Value),
+                                    args?["expression"]?.Value<string>(), token);
+                            default:
+                                return false;
+                        }
+                    }
+
+                case "Runtime.getProperties":
+                    {
+                        if (!DotnetObjectId.TryParse(args?["objectId"], out var objectId))
+                            break;
+
+                        var result = await RuntimeGetProperties(id, objectId, args, token);
+                        SendResponse(id, result, token);
+                        return true;
+                    }
+
+                case "Runtime.releaseObject":
+                    {
+                        if (!(DotnetObjectId.TryParse(args["objectId"], out var objectId) && objectId.Scheme == "cfo_res"))
+                            break;
+
+                        await SendMonoCommand(id, MonoCommands.ReleaseObject(objectId), token);
+                        SendResponse(id, Result.OkFromObject(new { }), token);
+                        return true;
+                    }
+
+                case "Debugger.setPauseOnExceptions": 
+                    {
+                        string state = args["state"].Value<string> ();
+                        await SendMonoCommand(id, MonoCommands.SetPauseOnExceptions (state), token);
+                        // Pass this on to JS too
+                        return false;
+                    }
+
+                    // Protocol extensions
+                case "DotnetDebugger.getMethodLocation":
+                    {
+                        Console.WriteLine("set-breakpoint-by-method: " + id + " " + args);
+
+                        var store = await RuntimeReady(id, token);
+                        string aname = args["assemblyName"]?.Value<string>();
+                        string typeName = args["typeName"]?.Value<string>();
+                        string methodName = args["methodName"]?.Value<string>();
+                        if (aname == null || typeName == null || methodName == null)
+                        {
+                            SendResponse(id, Result.Err("Invalid protocol message '" + args + "'."), token);
+                            return true;
+                        }
+
+                        // GetAssemblyByName seems to work on file names
+                        var assembly = store.GetAssemblyByName(aname);
+                        if (assembly == null)
+                            assembly = store.GetAssemblyByName(aname + ".exe");
+                        if (assembly == null)
+                            assembly = store.GetAssemblyByName(aname + ".dll");
+                        if (assembly == null)
+                        {
+                            SendResponse(id, Result.Err("Assembly '" + aname + "' not found."), token);
+                            return true;
+                        }
+
+                        var type = assembly.GetTypeByName(typeName);
+                        if (type == null)
+                        {
+                            SendResponse(id, Result.Err($"Type '{typeName}' not found."), token);
+                            return true;
+                        }
+
+                        var methodInfo = type.Methods.FirstOrDefault(m => m.Name == methodName);
+                        if (methodInfo == null)
+                        {
+                            // Maybe this is an async method, in which case the debug info is attached
+                            // to the async method implementation, in class named:
+                            //      `{type_name}/<method_name>::MoveNext`
+                            methodInfo = assembly.TypesByName.Values.SingleOrDefault(t => t.FullName.StartsWith($"{typeName}/<{methodName}>")) ?
+                                .Methods.FirstOrDefault(mi => mi.Name == "MoveNext");
+                        }
+
+                        if (methodInfo == null)
+                        {
+                            SendResponse(id, Result.Err($"Method '{typeName}:{methodName}' not found."), token);
+                            return true;
+                        }
+
+                        var src_url = methodInfo.Assembly.Sources.Single(sf => sf.SourceId == methodInfo.SourceId).Url;
+                        SendResponse(id, Result.OkFromObject(new
+                        {
+                            result = new { line = methodInfo.StartLocation.Line, column = methodInfo.StartLocation.Column, url = src_url }
+                        }), token);
+
+                        return true;
+                    }
+                case "Runtime.callFunctionOn":
+                    {
+                        if (!DotnetObjectId.TryParse(args["objectId"], out var objectId))
+                            return false;
+
+                        if (objectId.Scheme == "scope")
+                        {
+                            SendResponse(id,
+                                Result.Exception(new ArgumentException(
+                                    $"Runtime.callFunctionOn not supported with scope ({objectId}).")),
+                                token);
+                            return true;
+                        }
+
+                        var res = await SendMonoCommand(id, MonoCommands.CallFunctionOn(args), token);
+                        var res_value_type = res.Value?["result"] ? ["value"]?.Type;
+
+                        if (res.IsOk && res_value_type == JTokenType.Object || res_value_type == JTokenType.Object)
+                            res = Result.OkFromObject(new { result = res.Value["result"]["value"] });
+
+                        SendResponse(id, res, token);
+                        return true;
+                    }
+            }
+
+            return false;
+        }
+
+        async Task<Result> RuntimeGetProperties(MessageId id, DotnetObjectId objectId, JToken args, CancellationToken token)
+        {
+            if (objectId.Scheme == "scope")
+                return await GetScopeProperties(id, int.Parse(objectId.Value), token);
+
+            var res = await SendMonoCommand(id, MonoCommands.GetDetails(objectId, args), token);
+            if (res.IsErr)
+                return res;
+
+            if (objectId.Scheme == "cfo_res")
+            {
+                // Runtime.callFunctionOn result object
+                var value_json_str = res.Value["result"] ? ["value"] ? ["__value_as_json_string__"]?.Value<string>();
+                if (value_json_str != null)
+                {
+                    res = Result.OkFromObject(new
+                    {
+                        result = JArray.Parse(value_json_str)
+                    });
+                }
+                else
+                {
+                    res = Result.OkFromObject(new { result = new { } });
+                }
+            }
+            else
+            {
+                res = Result.Ok(JObject.FromObject(new { result = res.Value["result"]["value"] }));
+            }
+
+            return res;
+        }
+
+        //static int frame_id=0;
+        async Task<bool> OnPause(SessionId sessionId, JObject args, CancellationToken token)
+        {
+            //FIXME we should send release objects every now and then? Or intercept those we inject and deal in the runtime
+            var res = await SendMonoCommand(sessionId, MonoCommands.GetCallStack(), token);
+            var orig_callframes = args?["callFrames"]?.Values<JObject>();
+            var context = GetContext(sessionId);
+            JObject data = null;
+            var reason = "other";//other means breakpoint
+
+            if (res.IsErr)
+            {
+                //Give up and send the original call stack
+                return false;
+            }
+
+            //step one, figure out where did we hit
+            var res_value = res.Value?["result"] ? ["value"];
+            if (res_value == null || res_value is JValue)
+            {
+                //Give up and send the original call stack
+                return false;
+            }
+
+            Log("verbose", $"call stack (err is {res.Error} value is:\n{res.Value}");
+            var bp_id = res_value?["breakpoint_id"]?.Value<int>();
+            Log("verbose", $"We just hit bp {bp_id}");
+            if (!bp_id.HasValue)
+            {
+                //Give up and send the original call stack
+                return false;
+            }
+
+            var bp = context.BreakpointRequests.Values.SelectMany(v => v.Locations).FirstOrDefault(b => b.RemoteId == bp_id.Value);
+
+            var callFrames = new List<object>();
+            foreach (var frame in orig_callframes)
+            {
+                var function_name = frame["functionName"]?.Value<string>();
+                var url = frame["url"]?.Value<string>();
+                if ("mono_wasm_fire_bp" == function_name ||"_mono_wasm_fire_bp" == function_name ||
+                    "_mono_wasm_fire_exception" == function_name)
+                {
+                    if ("_mono_wasm_fire_exception" == function_name) {
+                        var exception_obj_id = await SendMonoCommand(sessionId, MonoCommands.GetExceptionObject (), token);
+                        var res_val = exception_obj_id.Value? ["result"]? ["value"];
+                        var exception_dotnet_obj_id = new DotnetObjectId("object", res_val?["exception_id"]?.Value<string> ());
+                        data = JObject.FromObject (new {
+                            type        = "object",
+                            subtype     = "error",
+                            className   = res_val? ["class_name"]?.Value<string>(),
+                            uncaught    = res_val? ["uncaught"]?.Value<bool>(),
+                            description = res_val? ["message"]?.Value<string>() + "\n",
+                            objectId    = exception_dotnet_obj_id.ToString()
+                        });
+                        reason = "exception";
+                    }
+
+                    var frames = new List<Frame>();
+                    int frame_id = 0;
+                    var the_mono_frames = res.Value?["result"] ? ["value"] ? ["frames"]?.Values<JObject>();
+
+                    foreach (var mono_frame in the_mono_frames)
+                    {
+                        ++frame_id;
+                        var il_pos = mono_frame["il_pos"].Value<int>();
+                        var method_token = mono_frame["method_token"].Value<uint>();
+                        var assembly_name = mono_frame["assembly_name"].Value<string>();
+
+                        // This can be different than `method.Name`, like in case of generic methods
+                        var method_name = mono_frame["method_name"]?.Value<string>();
+
+                        var store = await LoadStore(sessionId, token);
+                        var asm = store.GetAssemblyByName(assembly_name);
+                        if (asm == null)
+                        {
+                            Log("info", $"Unable to find assembly: {assembly_name}");
+                            continue;
+                        }
+
+                        var method = asm.GetMethodByToken(method_token);
+
+                        if (method == null)
+                        {
+                            Log("info", $"Unable to find il offset: {il_pos} in method token: {method_token} assembly name: {assembly_name}");
+                            continue;
+                        }
+
+                        var location = method?.GetLocationByIl(il_pos);
+
+                        // When hitting a breakpoint on the "IncrementCount" method in the standard
+                        // Blazor project template, one of the stack frames is inside mscorlib.dll
+                        // and we get location==null for it. It will trigger a NullReferenceException
+                        // if we don't skip over that stack frame.
+                        if (location == null)
+                        {
+                            continue;
+                        }
+
+                        Log("info", $"frame il offset: {il_pos} method token: {method_token} assembly name: {assembly_name}");
+                        Log("info", $"\tmethod {method_name} location: {location}");
+                        frames.Add(new Frame(method, location, frame_id - 1));
+
+                        callFrames.Add(new
+                        {
+                            functionName = method_name,
+                                callFrameId = $"dotnet:scope:{frame_id-1}",
+                                functionLocation = method.StartLocation.AsLocation(),
+
+                                location = location.AsLocation(),
+
+                                url = store.ToUrl(location),
+
+                                scopeChain = new []
+                                {
+                                    new
+                                    {
+                                        type = "local",
+                                            @object = new
+                                            {
+                                                @type = "object",
+                                                    className = "Object",
+                                                    description = "Object",
+                                                    objectId = $"dotnet:scope:{frame_id-1}",
+                                            },
+                                            name = method_name,
+                                            startLocation = method.StartLocation.AsLocation(),
+                                            endLocation = method.EndLocation.AsLocation(),
+                                    }
+                                }
+                        });
+
+                        context.CallStack = frames;
+
+                    }
+                }
+                else if (!(function_name.StartsWith("wasm-function", StringComparison.Ordinal) ||
+                        url.StartsWith("wasm://wasm/", StringComparison.Ordinal)))
+                {
+                    callFrames.Add(frame);
+                }
+            }
+
+            var bp_list = new string[bp == null ? 0 : 1];
+            if (bp != null)
+                bp_list[0] = bp.StackId;
+
+            var o = JObject.FromObject(new
+            {
+                callFrames,
+                reason,
+                data,
+                hitBreakpoints = bp_list,
+            });
+
+            SendEvent(sessionId, "Debugger.paused", o, token);
+            return true;
+        }
+
+        async Task OnDefaultContext(SessionId sessionId, ExecutionContext context, CancellationToken token)
+        {
+            Log("verbose", "Default context created, clearing state and sending events");
+            if (UpdateContext(sessionId, context, out var previousContext))
+            {
+                foreach (var kvp in previousContext.BreakpointRequests)
+                {
+                    context.BreakpointRequests[kvp.Key] = kvp.Value.Clone();
+                }
+            }
+
+            if (await IsRuntimeAlreadyReadyAlready(sessionId, token))
+                await RuntimeReady(sessionId, token);
+        }
+
+        async Task OnResume(MessageId msg_id, CancellationToken token)
+        {
+            var ctx = GetContext(msg_id);
+            if (ctx.CallStack != null)
+            {
+                // Stopped on managed code
+                await SendMonoCommand(msg_id, MonoCommands.Resume(), token);
+            }
+
+            //discard managed frames
+            GetContext(msg_id).ClearState();
+        }
+
+        async Task<bool> Step(MessageId msg_id, StepKind kind, CancellationToken token)
+        {
+            var context = GetContext(msg_id);
+            if (context.CallStack == null)
+                return false;
+
+            if (context.CallStack.Count <= 1 && kind == StepKind.Out)
+                return false;
+
+            var res = await SendMonoCommand(msg_id, MonoCommands.StartSingleStepping(kind), token);
+
+            var ret_code = res.Value?["result"] ? ["value"]?.Value<int>();
+
+            if (ret_code.HasValue && ret_code.Value == 0)
+            {
+                context.ClearState();
+                await SendCommand(msg_id, "Debugger.stepOut", new JObject(), token);
+                return false;
+            }
+
+            SendResponse(msg_id, Result.Ok(new JObject()), token);
+
+            context.ClearState();
+
+            await SendCommand(msg_id, "Debugger.resume", new JObject(), token);
+            return true;
+        }
+
+        internal bool TryFindVariableValueInCache(ExecutionContext ctx, string expression, bool only_search_on_this, out JToken obj)
+        {
+            if (ctx.LocalsCache.TryGetValue(expression, out obj))
+            {
+                if (only_search_on_this && obj["fromThis"] == null)
+                    return false;
+                return true;
+            }
+            return false;
+        }
+
+        internal async Task<JToken> TryGetVariableValue(MessageId msg_id, int scope_id, string expression, bool only_search_on_this, CancellationToken token)
+        {
+            JToken thisValue = null;
+            var context = GetContext(msg_id);
+            if (context.CallStack == null)
+                return null;
+
+            if (TryFindVariableValueInCache(context, expression, only_search_on_this, out JToken obj))
+                return obj;
+
+            var scope = context.CallStack.FirstOrDefault(s => s.Id == scope_id);
+            var live_vars = scope.Method.GetLiveVarsAt(scope.Location.CliLocation.Offset);
+            //get_this
+            var res = await SendMonoCommand(msg_id, MonoCommands.GetScopeVariables(scope.Id, live_vars), token);
+
+            var scope_values = res.Value?["result"] ? ["value"]?.Values<JObject>()?.ToArray();
+            thisValue = scope_values?.FirstOrDefault(v => v["name"]?.Value<string>() == "this");
+
+            if (!only_search_on_this)
+            {
+                if (thisValue != null && expression == "this")
+                    return thisValue;
+
+                var value = scope_values.SingleOrDefault(sv => sv["name"]?.Value<string>() == expression);
+                if (value != null)
+                    return value;
+            }
+
+            //search in scope
+            if (thisValue != null)
+            {
+                if (!DotnetObjectId.TryParse(thisValue["value"]["objectId"], out var objectId))
+                    return null;
+
+                res = await SendMonoCommand(msg_id, MonoCommands.GetDetails(objectId), token);
+                scope_values = res.Value?["result"] ? ["value"]?.Values<JObject>().ToArray();
+                var foundValue = scope_values.FirstOrDefault(v => v["name"].Value<string>() == expression);
+                if (foundValue != null)
+                {
+                    foundValue["fromThis"] = true;
+                    context.LocalsCache[foundValue["name"].Value<string>()] = foundValue;
+                    return foundValue;
+                }
+            }
+            return null;
+        }
+
+        async Task<bool> OnEvaluateOnCallFrame(MessageId msg_id, int scope_id, string expression, CancellationToken token)
+        {
+            try
+            {
+                var context = GetContext(msg_id);
+                if (context.CallStack == null)
+                    return false;
+
+                var varValue = await TryGetVariableValue(msg_id, scope_id, expression, false, token);
+
+                if (varValue != null)
+                {
+                    SendResponse(msg_id, Result.OkFromObject(new
+                    {
+                        result = varValue["value"]
+                    }), token);
+                    return true;
+                }
+
+                string retValue = await EvaluateExpression.CompileAndRunTheExpression(this, msg_id, scope_id, expression, token);
+                SendResponse(msg_id, Result.OkFromObject(new
+                {
+                    result = new
+                    {
+                        value = retValue
+                    }
+                }), token);
+                return true;
+            }
+            catch (Exception e)
+            {
+                logger.LogDebug(e, $"Error in EvaluateOnCallFrame for expression '{expression}.");
+            }
+            return false;
+        }
+
+        async Task<Result> GetScopeProperties(MessageId msg_id, int scope_id, CancellationToken token)
+        {
+            try
+            {
+                var ctx = GetContext(msg_id);
+                var scope = ctx.CallStack.FirstOrDefault(s => s.Id == scope_id);
+                if (scope == null)
+                    return Result.Err(JObject.FromObject(new { message = $"Could not find scope with id #{scope_id}" }));
+
+                var var_ids = scope.Method.GetLiveVarsAt(scope.Location.CliLocation.Offset);
+                var res = await SendMonoCommand(msg_id, MonoCommands.GetScopeVariables(scope.Id, var_ids), token);
+
+                //if we fail we just buble that to the IDE (and let it panic over it)
+                if (res.IsErr)
+                    return res;
+
+                var values = res.Value?["result"] ? ["value"]?.Values<JObject>().ToArray();
+
+                if (values == null || values.Length == 0)
+                    return Result.OkFromObject(new { result = Array.Empty<object>() });
+
+                foreach (var value in values)
+                    ctx.LocalsCache[value["name"]?.Value<string>()] = value;
+
+                return Result.OkFromObject(new { result = values });
+            }
+            catch (Exception exception)
+            {
+                Log("verbose", $"Error resolving scope properties {exception.Message}");
+                return Result.Exception(exception);
+            }
+        }
+
+        async Task<Breakpoint> SetMonoBreakpoint(SessionId sessionId, string reqId, SourceLocation location, CancellationToken token)
+        {
+            var bp = new Breakpoint(reqId, location, BreakpointState.Pending);
+            var asm_name = bp.Location.CliLocation.Method.Assembly.Name;
+            var method_token = bp.Location.CliLocation.Method.Token;
+            var il_offset = bp.Location.CliLocation.Offset;
+
+            var res = await SendMonoCommand(sessionId, MonoCommands.SetBreakpoint(asm_name, method_token, il_offset), token);
+            var ret_code = res.Value?["result"] ? ["value"]?.Value<int>();
+
+            if (ret_code.HasValue)
+            {
+                bp.RemoteId = ret_code.Value;
+                bp.State = BreakpointState.Active;
+                //Log ("verbose", $"BP local id {bp.LocalId} enabled with remote id {bp.RemoteId}");
+            }
+
+            return bp;
+        }
+
+        async Task<DebugStore> LoadStore(SessionId sessionId, CancellationToken token)
+        {
+            var context = GetContext(sessionId);
+
+            if (Interlocked.CompareExchange(ref context.store, new DebugStore(logger), null) != null)
+                return await context.Source.Task;
+
+            try
+            {
+                var loaded_files = context.LoadedFiles;
+
+                if (loaded_files == null)
+                {
+                    var loaded = await SendMonoCommand(sessionId, MonoCommands.GetLoadedFiles(), token);
+                    loaded_files = loaded.Value?["result"] ? ["value"]?.ToObject<string[]>();
+                }
+
+                await
+                foreach (var source in context.store.Load(sessionId, loaded_files, token).WithCancellation(token))
+                {
+                    var scriptSource = JObject.FromObject(source.ToScriptSource(context.Id, context.AuxData));
+                    Log("verbose", $"\tsending {source.Url} {context.Id} {sessionId.sessionId}");
+
+                    SendEvent(sessionId, "Debugger.scriptParsed", scriptSource, token);
+
+                    foreach (var req in context.BreakpointRequests.Values)
+                    {
+                        if (req.TryResolve(source))
+                        {
+                            await SetBreakpoint(sessionId, context.store, req, true, token);
+                        }
+                    }
+                }
+            }
+            catch (Exception e)
+            {
+                context.Source.SetException(e);
+            }
+
+            if (!context.Source.Task.IsCompleted)
+                context.Source.SetResult(context.store);
+            return context.store;
+        }
+
+        async Task<DebugStore> RuntimeReady(SessionId sessionId, CancellationToken token)
+        {
+            var context = GetContext(sessionId);
+            if (Interlocked.CompareExchange(ref context.ready, new TaskCompletionSource<DebugStore>(), null) != null)
+                return await context.ready.Task;
+
+            var clear_result = await SendMonoCommand(sessionId, MonoCommands.ClearAllBreakpoints(), token);
+            if (clear_result.IsErr)
+            {
+                Log("verbose", $"Failed to clear breakpoints due to {clear_result}");
+            }
+
+            var store = await LoadStore(sessionId, token);
+
+            context.ready.SetResult(store);
+            SendEvent(sessionId, "Mono.runtimeReady", new JObject(), token);
+            return store;
+        }
+
+        async Task RemoveBreakpoint(MessageId msg_id, JObject args, CancellationToken token)
+        {
+            var bpid = args?["breakpointId"]?.Value<string>();
+
+            var context = GetContext(msg_id);
+            if (!context.BreakpointRequests.TryGetValue(bpid, out var breakpointRequest))
+                return;
+
+            foreach (var bp in breakpointRequest.Locations)
+            {
+                var res = await SendMonoCommand(msg_id, MonoCommands.RemoveBreakpoint(bp.RemoteId), token);
+                var ret_code = res.Value?["result"] ? ["value"]?.Value<int>();
+
+                if (ret_code.HasValue)
+                {
+                    bp.RemoteId = -1;
+                    bp.State = BreakpointState.Disabled;
+                }
+            }
+            breakpointRequest.Locations.Clear();
+        }
+
+        async Task SetBreakpoint(SessionId sessionId, DebugStore store, BreakpointRequest req, bool sendResolvedEvent, CancellationToken token)
+        {
+            var context = GetContext(sessionId);
+            if (req.Locations.Any())
+            {
+                Log("debug", $"locations already loaded for {req.Id}");
+                return;
+            }
+
+            var comparer = new SourceLocation.LocationComparer();
+            // if column is specified the frontend wants the exact matches
+            // and will clear the bp if it isn't close enoug
+            var locations = store.FindBreakpointLocations(req)
+                .Distinct(comparer)
+                .Where(l => l.Line == req.Line && (req.Column == 0 || l.Column == req.Column))
+                .OrderBy(l => l.Column)
+                .GroupBy(l => l.Id);
+
+            logger.LogDebug("BP request for '{req}' runtime ready {context.RuntimeReady}", req, GetContext(sessionId).IsRuntimeReady);
+
+            var breakpoints = new List<Breakpoint>();
+
+            foreach (var sourceId in locations)
+            {
+                var loc = sourceId.First();
+                var bp = await SetMonoBreakpoint(sessionId, req.Id, loc, token);
+
+                // If we didn't successfully enable the breakpoint
+                // don't add it to the list of locations for this id
+                if (bp.State != BreakpointState.Active)
+                    continue;
+
+                breakpoints.Add(bp);
+
+                var resolvedLocation = new
+                {
+                    breakpointId = req.Id,
+                    location = loc.AsLocation()
+                };
+
+                if (sendResolvedEvent)
+                    SendEvent(sessionId, "Debugger.breakpointResolved", JObject.FromObject(resolvedLocation), token);
+            }
+
+            req.Locations.AddRange(breakpoints);
+            return;
+        }
+
+        async Task<bool> GetPossibleBreakpoints(MessageId msg, SourceLocation start, SourceLocation end, CancellationToken token)
+        {
+            var bps = (await RuntimeReady(msg, token)).FindPossibleBreakpoints(start, end);
+
+            if (bps == null)
+                return false;
+
+            var response = new { locations = bps.Select(b => b.AsLocation()) };
+
+            SendResponse(msg, Result.OkFromObject(response), token);
+            return true;
+        }
+
+        void OnCompileDotnetScript(MessageId msg_id, CancellationToken token)
+        {
+            SendResponse(msg_id, Result.OkFromObject(new { }), token);
+        }
+
+        async Task<bool> OnGetScriptSource(MessageId msg_id, string script_id, CancellationToken token)
+        {
+            if (!SourceId.TryParse(script_id, out var id))
+                return false;
+
+            var src_file = (await LoadStore(msg_id, token)).GetFileById(id);
+
+            try
+            {
+                var uri = new Uri(src_file.Url);
+                string source = $"// Unable to find document {src_file.SourceUri}";
+
+                using(var data = await src_file.GetSourceAsync(checkHash: false, token: token))
+                {
+                    if (data.Length == 0)
+                        return false;
+
+                    using(var reader = new StreamReader(data))
+                    source = await reader.ReadToEndAsync();
+                }
+                SendResponse(msg_id, Result.OkFromObject(new { scriptSource = source }), token);
+            }
+            catch (Exception e)
+            {
+                var o = new
+                {
+                    scriptSource = $"// Unable to read document ({e.Message})\n" +
+                    $"Local path: {src_file?.SourceUri}\n" +
+                    $"SourceLink path: {src_file?.SourceLinkUri}\n"
+                };
+
+                SendResponse(msg_id, Result.OkFromObject(o), token);
+            }
+            return true;
+        }
+
+        async Task DeleteWebDriver(SessionId sessionId, CancellationToken token)
+        {
+            // see https://github.com/mono/mono/issues/19549 for background
+            if (hideWebDriver && sessions.Add(sessionId))
+            {
+                var res = await SendCommand(sessionId,
+                    "Page.addScriptToEvaluateOnNewDocument",
+                    JObject.FromObject(new { source = "delete navigator.constructor.prototype.webdriver" }),
+                    token);
+
+                if (sessionId != SessionId.Null && !res.IsOk)
+                    sessions.Remove(sessionId);
+            }
+        }
+    }
+}
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/ArrayTests.cs b/src/mono/wasm/debugger/DebuggerTestSuite/ArrayTests.cs
new file mode 100644
index 00000000000000..f9319a7b491fd8
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/ArrayTests.cs
@@ -0,0 +1,695 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Newtonsoft.Json.Linq;
+using Microsoft.WebAssembly.Diagnostics;
+using Xunit;
+
+namespace DebuggerTests
+{
+
+    public class ArrayTests : DebuggerTestBase
+    {
+
+        [Theory]
+        [InlineData(19, 8, "PrimitiveTypeLocals", false, 0, false)]
+        [InlineData(19, 8, "PrimitiveTypeLocals", false, 0, true)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, false)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, true)]
+        public async Task InspectPrimitiveTypeArrayLocals(int line, int col, string method_name, bool test_prev_frame, int frame_idx, bool use_cfo) => await TestSimpleArrayLocals(
+            line, col,
+            entry_method_name: "[debugger-test] DebuggerTests.ArrayTestsClass:PrimitiveTypeLocals",
+            method_name : method_name,
+            etype_name: "int",
+            local_var_name_prefix: "int",
+            array : new [] { TNumber(4), TNumber(70), TNumber(1) },
+            array_elem_props: null,
+            test_prev_frame : test_prev_frame,
+            frame_idx : frame_idx,
+            use_cfo : use_cfo);
+
+        [Theory]
+        [InlineData(36, 8, "ValueTypeLocals", false, 0, false)]
+        [InlineData(36, 8, "ValueTypeLocals", false, 0, true)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, false)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, true)]
+        public async Task InspectValueTypeArrayLocals(int line, int col, string method_name, bool test_prev_frame, int frame_idx, bool use_cfo) => await TestSimpleArrayLocals(
+            line, col,
+            entry_method_name: "[debugger-test] DebuggerTests.ArrayTestsClass:ValueTypeLocals",
+            method_name : method_name,
+            etype_name: "DebuggerTests.Point",
+            local_var_name_prefix: "point",
+            array : new []
+            {
+                TValueType("DebuggerTests.Point"),
+                    TValueType("DebuggerTests.Point"),
+            },
+            array_elem_props: new []
+            {
+                TPoint(5, -2, "point_arr#Id#0", "Green"),
+                    TPoint(123, 0, "point_arr#Id#1", "Blue")
+            },
+            test_prev_frame : test_prev_frame,
+            frame_idx : frame_idx,
+            use_cfo : use_cfo);
+
+        [Theory]
+        [InlineData(54, 8, "ObjectTypeLocals", false, 0, false)]
+        [InlineData(54, 8, "ObjectTypeLocals", false, 0, true)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, false)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, true)]
+        public async Task InspectObjectArrayLocals(int line, int col, string method_name, bool test_prev_frame, int frame_idx, bool use_cfo) => await TestSimpleArrayLocals(
+            line, col,
+            entry_method_name: "[debugger-test] DebuggerTests.ArrayTestsClass:ObjectTypeLocals",
+            method_name : method_name,
+            etype_name: "DebuggerTests.SimpleClass",
+            local_var_name_prefix: "class",
+            array : new []
+            {
+                TObject("DebuggerTests.SimpleClass"),
+                    TObject("DebuggerTests.SimpleClass", is_null : true),
+                    TObject("DebuggerTests.SimpleClass")
+            },
+            array_elem_props: new []
+            {
+                TSimpleClass(5, -2, "class_arr#Id#0", "Green"),
+                    null, // Element is null
+                    TSimpleClass(123, 0, "class_arr#Id#2", "Blue")
+            },
+            test_prev_frame : test_prev_frame,
+            frame_idx : frame_idx,
+            use_cfo : use_cfo);
+
+        [Theory]
+        [InlineData(72, 8, "GenericTypeLocals", false, 0, false)]
+        [InlineData(72, 8, "GenericTypeLocals", false, 0, true)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, false)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, true)]
+        public async Task InspectGenericTypeArrayLocals(int line, int col, string method_name, bool test_prev_frame, int frame_idx, bool use_cfo) => await TestSimpleArrayLocals(
+            line, col,
+            entry_method_name: "[debugger-test] DebuggerTests.ArrayTestsClass:GenericTypeLocals",
+            method_name : method_name,
+            etype_name: "DebuggerTests.GenericClass<int>",
+            local_var_name_prefix: "gclass",
+            array : new []
+            {
+                TObject("DebuggerTests.GenericClass<int>", is_null : true),
+                    TObject("DebuggerTests.GenericClass<int>"),
+                    TObject("DebuggerTests.GenericClass<int>")
+            },
+            array_elem_props : new []
+            {
+                null, // Element is null
+                new
+                {
+                    Id = TString("gclass_arr#1#Id"),
+                        Color = TEnum("DebuggerTests.RGB", "Red"),
+                        Value = TNumber(5)
+                },
+                new
+                {
+                    Id = TString("gclass_arr#2#Id"),
+                        Color = TEnum("DebuggerTests.RGB", "Blue"),
+                        Value = TNumber(-12)
+                }
+            },
+            test_prev_frame : test_prev_frame,
+            frame_idx : frame_idx,
+            use_cfo : use_cfo);
+
+        [Theory]
+        [InlineData(89, 8, "GenericValueTypeLocals", false, 0, false)]
+        [InlineData(89, 8, "GenericValueTypeLocals", false, 0, true)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, false)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, true)]
+        public async Task InspectGenericValueTypeArrayLocals(int line, int col, string method_name, bool test_prev_frame, int frame_idx, bool use_cfo) => await TestSimpleArrayLocals(
+            line, col,
+            entry_method_name: "[debugger-test] DebuggerTests.ArrayTestsClass:GenericValueTypeLocals",
+            method_name : method_name,
+            etype_name: "DebuggerTests.SimpleGenericStruct<DebuggerTests.Point>",
+            local_var_name_prefix: "gvclass",
+            array : new []
+            {
+                TValueType("DebuggerTests.SimpleGenericStruct<DebuggerTests.Point>"),
+                    TValueType("DebuggerTests.SimpleGenericStruct<DebuggerTests.Point>")
+            },
+            array_elem_props : new []
+            {
+                new
+                {
+                    Id = TString("gvclass_arr#1#Id"),
+                        Color = TEnum("DebuggerTests.RGB", "Red"),
+                        Value = TPoint(100, 200, "gvclass_arr#1#Value#Id", "Red")
+                },
+                new
+                {
+                    Id = TString("gvclass_arr#2#Id"),
+                        Color = TEnum("DebuggerTests.RGB", "Blue"),
+                        Value = TPoint(10, 20, "gvclass_arr#2#Value#Id", "Green")
+                }
+            },
+            test_prev_frame : test_prev_frame,
+            frame_idx : frame_idx,
+            use_cfo : use_cfo);
+
+        [Theory]
+        [InlineData(213, 8, "GenericValueTypeLocals2", false, 0, false)]
+        [InlineData(213, 8, "GenericValueTypeLocals2", false, 0, true)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, false)]
+        [InlineData(100, 8, "YetAnotherMethod", true, 2, true)]
+        public async Task InspectGenericValueTypeArrayLocals2(int line, int col, string method_name, bool test_prev_frame, int frame_idx, bool use_cfo) => await TestSimpleArrayLocals(
+            line, col,
+            entry_method_name: "[debugger-test] DebuggerTests.ArrayTestsClass:GenericValueTypeLocals2",
+            method_name : method_name,
+            etype_name: "DebuggerTests.SimpleGenericStruct<DebuggerTests.Point[]>",
+            local_var_name_prefix: "gvclass",
+            array : new []
+            {
+                TValueType("DebuggerTests.SimpleGenericStruct<DebuggerTests.Point[]>"),
+                    TValueType("DebuggerTests.SimpleGenericStruct<DebuggerTests.Point[]>")
+            },
+            array_elem_props : new []
+            {
+                new
+                {
+                    Id = TString("gvclass_arr#0#Id"),
+                        Color = TEnum("DebuggerTests.RGB", "Red"),
+                        Value = new []
+                        {
+                            TPoint(100, 200, "gvclass_arr#0#0#Value#Id", "Red"),
+                                TPoint(100, 200, "gvclass_arr#0#1#Value#Id", "Green")
+                        }
+                },
+                new
+                {
+                    Id = TString("gvclass_arr#1#Id"),
+                        Color = TEnum("DebuggerTests.RGB", "Blue"),
+                        Value = new []
+                        {
+                            TPoint(100, 200, "gvclass_arr#1#0#Value#Id", "Green"),
+                                TPoint(100, 200, "gvclass_arr#1#1#Value#Id", "Blue")
+                        }
+                }
+            },
+            test_prev_frame : test_prev_frame,
+            frame_idx : frame_idx,
+            use_cfo : use_cfo);
+
+        async Task TestSimpleArrayLocals(int line, int col, string entry_method_name, string method_name, string etype_name,
+            string local_var_name_prefix, object[] array, object[] array_elem_props,
+            bool test_prev_frame = false, int frame_idx = 0, bool use_cfo = false)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-array-test.cs";
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+
+                await SetBreakpoint(debugger_test_loc, line, col);
+
+                var eval_expr = "window.setTimeout(function() { invoke_static_method (" +
+                    $"'{entry_method_name}', { (test_prev_frame ? "true" : "false") }" +
+                    "); }, 1);";
+
+                var pause_location = await EvaluateAndCheck(eval_expr, debugger_test_loc, line, col, method_name);
+
+                var locals = await GetProperties(pause_location["callFrames"][frame_idx]["callFrameId"].Value<string>());
+                Assert.Equal(4, locals.Count());
+                CheckArray(locals, $"{local_var_name_prefix}_arr", $"{etype_name}[]", array?.Length ?? 0);
+                CheckArray(locals, $"{local_var_name_prefix}_arr_empty", $"{etype_name}[]", 0);
+                CheckObject(locals, $"{local_var_name_prefix}_arr_null", $"{etype_name}[]", is_null : true);
+                CheckBool(locals, "call_other", test_prev_frame);
+
+                var local_arr_name = $"{local_var_name_prefix}_arr";
+
+                JToken prefix_arr;
+                if (use_cfo)
+                { // Use `Runtime.callFunctionOn` to get the properties
+                    var frame = pause_location["callFrames"][frame_idx];
+                    var name = local_arr_name;
+                    var fl = await GetProperties(frame["callFrameId"].Value<string>());
+                    var l_obj = GetAndAssertObjectWithName(locals, name);
+                    var l_objectId = l_obj["value"]["objectId"]?.Value<string>();
+
+                    Assert.True(!String.IsNullOrEmpty(l_objectId), $"No objectId found for {name}");
+
+                    prefix_arr = await GetObjectWithCFO(l_objectId);
+                }
+                else
+                {
+                    prefix_arr = await GetObjectOnFrame(pause_location["callFrames"][frame_idx], local_arr_name);
+                }
+
+                await CheckProps(prefix_arr, array, local_arr_name);
+
+                if (array_elem_props?.Length > 0)
+                {
+                    for (int i = 0; i < array_elem_props.Length; i++)
+                    {
+                        var i_str = i.ToString();
+                        var label = $"{local_var_name_prefix}_arr[{i}]";
+                        if (array_elem_props[i] == null)
+                        {
+                            var act_i = prefix_arr.FirstOrDefault(jt => jt["name"]?.Value<string>() == i_str);
+                            Assert.True(act_i != null, $"[{label}] Couldn't find array element [{i_str}]");
+
+                            await CheckValue(act_i["value"], TObject(etype_name, is_null : true), label);
+                        }
+                        else
+                        {
+                            await CompareObjectPropertiesFor(prefix_arr, i_str, array_elem_props[i], label : label);
+                        }
+                    }
+                }
+
+                var props = await GetObjectOnFrame(pause_location["callFrames"][frame_idx], $"{local_var_name_prefix}_arr_empty");
+                await CheckProps(props, new object[0], "${local_var_name_prefix}_arr_empty");
+            });
+
+            async Task<JToken> GetObjectWithCFO(string objectId, JObject fn_args = null)
+            {
+                var fn_decl = "function () { return this; }";
+                var cfo_args = JObject.FromObject(new
+                {
+                    functionDeclaration = fn_decl,
+                        objectId = objectId
+                });
+
+                if (fn_args != null)
+                    cfo_args["arguments"] = fn_args;
+
+                // callFunctionOn
+                var result = await ctx.cli.SendCommand("Runtime.callFunctionOn", cfo_args, ctx.token);
+
+                return await GetProperties(result.Value["result"]["objectId"]?.Value<string>(), fn_args);
+            }
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectObjectArrayMembers(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+            int line = 227;
+            int col = 12;
+            string entry_method_name = "[debugger-test] DebuggerTests.ArrayTestsClass:ObjectArrayMembers";
+            string method_name = "PlaceholderMethod";
+            int frame_idx = 1;
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-array-test.cs";
+
+                await SetBreakpoint(debugger_test_loc, line, col);
+
+                var eval_expr = "window.setTimeout(function() { invoke_static_method (" +
+                    $"'{entry_method_name}'" +
+                    "); }, 1);";
+
+                var pause_location = await EvaluateAndCheck(eval_expr, debugger_test_loc, line, col, method_name);
+                var locals = await GetProperties(pause_location["callFrames"][frame_idx]["callFrameId"].Value<string>());
+                Assert.Single(locals);
+                CheckObject(locals, "c", "DebuggerTests.Container");
+
+                var c_props = await GetObjectOnFrame(pause_location["callFrames"][frame_idx], "c");
+                await CheckProps(c_props, new
+                    {
+                        id = TString("c#id"),
+                            ClassArrayProperty = TArray("DebuggerTests.SimpleClass[]", 3),
+                            ClassArrayField = TArray("DebuggerTests.SimpleClass[]", 3),
+                            PointsProperty = TArray("DebuggerTests.Point[]", 2),
+                            PointsField = TArray("DebuggerTests.Point[]", 2)
+                    },
+                    "c"
+                );
+
+                await CompareObjectPropertiesFor(c_props, "ClassArrayProperty",
+                    new []
+                    {
+                        TSimpleClass(5, -2, "ClassArrayProperty#Id#0", "Green"),
+                            TSimpleClass(30, 1293, "ClassArrayProperty#Id#1", "Green"),
+                            TObject("DebuggerTests.SimpleClass", is_null : true)
+                    },
+                    label: "InspectLocalsWithStructsStaticAsync");
+
+                await CompareObjectPropertiesFor(c_props, "ClassArrayField",
+                    new []
+                    {
+                        TObject("DebuggerTests.SimpleClass", is_null : true),
+                            TSimpleClass(5, -2, "ClassArrayField#Id#1", "Blue"),
+                            TSimpleClass(30, 1293, "ClassArrayField#Id#2", "Green")
+                    },
+                    label: "c#ClassArrayField");
+
+                await CompareObjectPropertiesFor(c_props, "PointsProperty",
+                    new []
+                    {
+                        TPoint(5, -2, "PointsProperty#Id#0", "Green"),
+                            TPoint(123, 0, "PointsProperty#Id#1", "Blue"),
+                    },
+                    label: "c#PointsProperty");
+
+                await CompareObjectPropertiesFor(c_props, "PointsField",
+                    new []
+                    {
+                        TPoint(5, -2, "PointsField#Id#0", "Green"),
+                            TPoint(123, 0, "PointsField#Id#1", "Blue"),
+                    },
+                    label: "c#PointsField");
+            });
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectValueTypeArrayLocalsStaticAsync(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+            int line = 157;
+            int col = 12;
+            string entry_method_name = "[debugger-test] DebuggerTests.ArrayTestsClass:ValueTypeLocalsAsync";
+            string method_name = "MoveNext"; // BUG: this should be ValueTypeLocalsAsync
+            int frame_idx = 0;
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-array-test.cs";
+
+                await SetBreakpoint(debugger_test_loc, line, col);
+
+                var eval_expr = "window.setTimeout(function() { invoke_static_method_async (" +
+                    $"'{entry_method_name}', false" // *false* here keeps us only in the static method
+                    +
+                    "); }, 1);";
+
+                var pause_location = await EvaluateAndCheck(eval_expr, debugger_test_loc, line, col, method_name);
+                var frame_locals = await GetProperties(pause_location["callFrames"][frame_idx]["callFrameId"].Value<string>());
+                await CheckProps(frame_locals, new
+                {
+                    call_other = TBool(false),
+                        gvclass_arr = TArray("DebuggerTests.SimpleGenericStruct<DebuggerTests.Point>[]", 2),
+                        gvclass_arr_empty = TArray("DebuggerTests.SimpleGenericStruct<DebuggerTests.Point>[]"),
+                        gvclass_arr_null = TObject("DebuggerTests.SimpleGenericStruct<DebuggerTests.Point>[]", is_null : true),
+                        gvclass = TValueType("DebuggerTests.SimpleGenericStruct<DebuggerTests.Point>"),
+                        // BUG: this shouldn't be null!
+                        points = TObject("DebuggerTests.Point[]", is_null : true)
+                }, "ValueTypeLocalsAsync#locals");
+
+                var local_var_name_prefix = "gvclass";
+                await CompareObjectPropertiesFor(frame_locals, local_var_name_prefix, new
+                {
+                    Id = TString(null),
+                        Color = TEnum("DebuggerTests.RGB", "Red"),
+                        Value = TPoint(0, 0, null, "Red")
+                });
+
+                await CompareObjectPropertiesFor(frame_locals, $"{local_var_name_prefix}_arr",
+                    new []
+                    {
+                        new
+                        {
+                            Id = TString("gvclass_arr#1#Id"),
+                                Color = TEnum("DebuggerTests.RGB", "Red"),
+                                Value = TPoint(100, 200, "gvclass_arr#1#Value#Id", "Red")
+                        },
+                        new
+                        {
+                            Id = TString("gvclass_arr#2#Id"),
+                                Color = TEnum("DebuggerTests.RGB", "Blue"),
+                                Value = TPoint(10, 20, "gvclass_arr#2#Value#Id", "Green")
+                        }
+                    }
+                );
+                await CompareObjectPropertiesFor(frame_locals, $"{local_var_name_prefix}_arr_empty",
+                    new object[0]);
+            });
+        }
+
+        // TODO: Check previous frame too
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectValueTypeArrayLocalsInstanceAsync(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+            int line = 170;
+            int col = 12;
+            string entry_method_name = "[debugger-test] DebuggerTests.ArrayTestsClass:ValueTypeLocalsAsync";
+            int frame_idx = 0;
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-array-test.cs";
+
+                await SetBreakpoint(debugger_test_loc, line, col);
+
+                var eval_expr = "window.setTimeout(function() { invoke_static_method_async (" +
+                    $"'{entry_method_name}', true" +
+                    "); }, 1);";
+
+                // BUG: Should be InspectValueTypeArrayLocalsInstanceAsync
+                var pause_location = await EvaluateAndCheck(eval_expr, debugger_test_loc, line, col, "MoveNext");
+
+                var frame_locals = await GetProperties(pause_location["callFrames"][frame_idx]["callFrameId"].Value<string>());
+                await CheckProps(frame_locals, new
+                {
+                    t1 = TObject("DebuggerTests.SimpleGenericStruct<DebuggerTests.Point>"),
+                        @this = TObject("DebuggerTests.ArrayTestsClass"),
+                        point_arr = TArray("DebuggerTests.Point[]", 2),
+                        point = TValueType("DebuggerTests.Point")
+                }, "InspectValueTypeArrayLocalsInstanceAsync#locals");
+
+                await CompareObjectPropertiesFor(frame_locals, "t1",
+                    new
+                    {
+                        Id = TString("gvclass_arr#1#Id"),
+                            Color = TEnum("DebuggerTests.RGB", "Red"),
+                            Value = TPoint(100, 200, "gvclass_arr#1#Value#Id", "Red")
+                    });
+
+                await CompareObjectPropertiesFor(frame_locals, "point_arr",
+                    new []
+                    {
+                        TPoint(5, -2, "point_arr#Id#0", "Red"),
+                            TPoint(123, 0, "point_arr#Id#1", "Blue"),
+                    }
+                );
+
+                await CompareObjectPropertiesFor(frame_locals, "point",
+                    TPoint(45, 51, "point#Id", "Green"));
+            });
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectValueTypeArrayLocalsInAsyncStaticStructMethod(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+            int line = 244;
+            int col = 12;
+            string entry_method_name = "[debugger-test] DebuggerTests.ArrayTestsClass:EntryPointForStructMethod";
+            int frame_idx = 0;
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-array-test.cs";
+
+                await SetBreakpoint(debugger_test_loc, line, col);
+                //await SetBreakpoint (debugger_test_loc, 143, 3);
+
+                var eval_expr = "window.setTimeout(function() { invoke_static_method_async (" +
+                    $"'{entry_method_name}', false" +
+                    "); }, 1);";
+
+                // BUG: Should be InspectValueTypeArrayLocalsInstanceAsync
+                var pause_location = await EvaluateAndCheck(eval_expr, debugger_test_loc, line, col, "MoveNext");
+
+                var frame_locals = await GetProperties(pause_location["callFrames"][frame_idx]["callFrameId"].Value<string>());
+                await CheckProps(frame_locals, new
+                {
+                    call_other = TBool(false),
+                        local_i = TNumber(5),
+                        sc = TSimpleClass(10, 45, "sc#Id", "Blue")
+                }, "InspectValueTypeArrayLocalsInAsyncStaticStructMethod#locals");
+            });
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectValueTypeArrayLocalsInAsyncInstanceStructMethod(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+            int line = 251;
+            int col = 12;
+            string entry_method_name = "[debugger-test] DebuggerTests.ArrayTestsClass:EntryPointForStructMethod";
+            int frame_idx = 0;
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-array-test.cs";
+
+                await SetBreakpoint(debugger_test_loc, line, col);
+
+                var eval_expr = "window.setTimeout(function() { invoke_static_method_async (" +
+                    $"'{entry_method_name}', true" +
+                    "); }, 1);";
+
+                // BUG: Should be InspectValueTypeArrayLocalsInstanceAsync
+                var pause_location = await EvaluateAndCheck(eval_expr, debugger_test_loc, line, col, "MoveNext");
+
+                var frame_locals = await GetProperties(pause_location["callFrames"][frame_idx]["callFrameId"].Value<string>());
+                await CheckProps(frame_locals, new
+                    {
+                        sc_arg = TObject("DebuggerTests.SimpleClass"),
+                            @this = TValueType("DebuggerTests.Point"),
+                            local_gs = TValueType("DebuggerTests.SimpleGenericStruct<int>")
+                    },
+                    "locals#0");
+
+                await CompareObjectPropertiesFor(frame_locals, "local_gs",
+                    new
+                    {
+                        Id = TString("local_gs#Id"),
+                            Color = TEnum("DebuggerTests.RGB", "Green"),
+                            Value = TNumber(4)
+                    },
+                    label: "local_gs#0");
+
+                await CompareObjectPropertiesFor(frame_locals, "sc_arg",
+                    TSimpleClass(10, 45, "sc_arg#Id", "Blue"),
+                    label: "sc_arg#0");
+
+                await CompareObjectPropertiesFor(frame_locals, "this",
+                    TPoint(90, -4, "point#Id", "Green"),
+                    label: "this#0");
+            });
+        }
+
+        [Fact]
+        public async Task InvalidArrayId() => await CheckInspectLocalsAtBreakpointSite(
+            "DebuggerTests.Container", "PlaceholderMethod", 1, "PlaceholderMethod",
+            "window.setTimeout(function() { invoke_static_method ('[debugger-test] DebuggerTests.ArrayTestsClass:ObjectArrayMembers'); }, 1);",
+            wait_for_event_fn : async(pause_location) =>
+            {
+
+                int frame_idx = 1;
+                var frame_locals = await GetProperties(pause_location["callFrames"][frame_idx]["callFrameId"].Value<string>());
+                var c_obj = GetAndAssertObjectWithName(frame_locals, "c");
+                var c_obj_id = c_obj["value"] ? ["objectId"]?.Value<string>();
+                Assert.NotNull(c_obj_id);
+
+                // Invalid format
+                await GetProperties("dotnet:array:4123", expect_ok : false);
+
+                // Invalid object id
+                await GetProperties("dotnet:array:{ \"arrayId\": 234980 }", expect_ok : false);
+
+                // Trying to access object as an array
+                if (!DotnetObjectId.TryParse (c_obj_id, out var id) || id.Scheme != "object")
+                    Assert.True(false, "Unexpected object id format. Maybe this test is out of sync with the object id format in library_mono.js?");
+
+                if (!int.TryParse(id.Value, out var idNum))
+                    Assert.True(false, "Expected a numeric value part of the object id: {c_obj_id}");
+                await GetProperties($"dotnet:array:{{\"arrayId\":{idNum}}}", expect_ok : false);
+            });
+
+        [Fact]
+        public async Task InvalidValueTypeArrayIndex() => await CheckInspectLocalsAtBreakpointSite(
+            "DebuggerTests.Container", "PlaceholderMethod", 1, "PlaceholderMethod",
+            "window.setTimeout(function() { invoke_static_method ('[debugger-test] DebuggerTests.ArrayTestsClass:ObjectArrayMembers'); }, 1);",
+            locals_fn : async(locals) =>
+            {
+                var this_obj = GetAndAssertObjectWithName(locals, "this");
+                var c_obj = GetAndAssertObjectWithName(await GetProperties(this_obj["value"]["objectId"].Value<string>()), "c");
+                var c_obj_id = c_obj["value"] ? ["objectId"]?.Value<string>();
+                Assert.NotNull(c_obj_id);
+
+                var c_props = await GetProperties(c_obj_id);
+
+                var pf_arr = GetAndAssertObjectWithName(c_props, "PointsField");
+                var pf_arr_elems = await GetProperties(pf_arr["value"]["objectId"].Value<string>());
+
+                if (!DotnetObjectId.TryParse(pf_arr_elems[0]["value"] ? ["objectId"]?.Value<string>(), out var id))
+                    Assert.True(false, "Couldn't parse objectId for PointsFields' elements");
+
+                AssertEqual("valuetype", id.Scheme, "Expected a valuetype id");
+                var id_args = id.ValueAsJson;
+                Assert.True(id_args["arrayId"] != null, "ObjectId format for array seems to have changed. Expected to find 'arrayId' in the value. Update this test");
+                Assert.True(id_args != null, "Expected to get a json as the value part of {id}");
+
+                // Try one valid query, to confirm that the id format hasn't changed!
+                id_args["arrayIdx"] = 0;
+                await GetProperties($"dotnet:valuetype:{id_args.ToString (Newtonsoft.Json.Formatting.None)}", expect_ok : true);
+
+                id_args["arrayIdx"] = 12399;
+                await GetProperties($"dotnet:valuetype:{id_args.ToString (Newtonsoft.Json.Formatting.None)}", expect_ok : false);
+
+                id_args["arrayIdx"] = -1;
+                await GetProperties($"dotnet:valuetype:{id_args.ToString (Newtonsoft.Json.Formatting.None)}", expect_ok : false);
+
+                id_args["arrayIdx"] = "qwe";
+                await GetProperties($"dotnet:valuetype:{id_args.ToString (Newtonsoft.Json.Formatting.None)}", expect_ok : false);
+            });
+
+        [Fact]
+        public async Task InvalidAccessors() => await CheckInspectLocalsAtBreakpointSite(
+            "DebuggerTests.Container", "PlaceholderMethod", 1, "PlaceholderMethod",
+            "window.setTimeout(function() { invoke_static_method ('[debugger-test] DebuggerTests.ArrayTestsClass:ObjectArrayMembers'); }, 1);",
+            locals_fn : async(locals) =>
+            {
+                var this_obj = GetAndAssertObjectWithName(locals, "this");
+                var c_obj = GetAndAssertObjectWithName(await GetProperties(this_obj["value"]["objectId"].Value<string>()), "c");
+                var c_obj_id = c_obj["value"] ? ["objectId"]?.Value<string>();
+                Assert.NotNull(c_obj_id);
+
+                var c_props = await GetProperties(c_obj_id);
+
+                var pf_arr = GetAndAssertObjectWithName(c_props, "PointsField");
+
+                var invalid_accessors = new object[] { "NonExistant", "10000", "-2", 10000, -2, null, String.Empty };
+                foreach (var invalid_accessor in invalid_accessors)
+                {
+                    // var res = await InvokeGetter (JObject.FromObject (new { value = new { objectId = obj_id } }), invalid_accessor, expect_ok: true);
+                    var res = await InvokeGetter(pf_arr, invalid_accessor, expect_ok : true);
+                    AssertEqual("undefined", res.Value["result"] ? ["type"]?.ToString(), "Expected to get undefined result for non-existant accessor");
+                }
+            });
+
+    }
+}
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/CallFunctionOnTests.cs b/src/mono/wasm/debugger/DebuggerTestSuite/CallFunctionOnTests.cs
new file mode 100644
index 00000000000000..3014c6cc5e83a1
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/CallFunctionOnTests.cs
@@ -0,0 +1,981 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Newtonsoft.Json.Linq;
+using Microsoft.WebAssembly.Diagnostics;
+using Xunit;
+
+namespace DebuggerTests
+{
+
+    public class CallFunctionOnTests : DebuggerTestBase
+    {
+
+        // This tests `callFunctionOn` with a function that the vscode-js-debug extension uses
+        // Using this here as a non-trivial test case
+        [Theory]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, 10, false)]
+        [InlineData("big_array_js_test (0);", "/other.js", 8, 1, 0, true)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, 10, false)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 0);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, 0, true)]
+        public async Task CheckVSCodeTestFunction1(string eval_fn, string bp_loc, int line, int col, int len, bool roundtrip)
+        {
+            string vscode_fn0 = "function(){const e={__proto__:this.__proto__},t=Object.getOwnPropertyNames(this);for(let r=0;r<t.length;++r){const n=t[r],i=n>>>0;if(String(i>>>0)===n&&i>>>0!=4294967295)continue;const a=Object.getOwnPropertyDescriptor(this,n);a&&Object.defineProperty(e,n,a)}return e}";
+
+            await RunCallFunctionOn(eval_fn, vscode_fn0, "big", bp_loc, line, col, res_array_len : len, roundtrip : roundtrip,
+                test_fn : async(result) =>
+                {
+
+                    var is_js = bp_loc.EndsWith(".js", StringComparison.Ordinal);
+                    var obj_accessors = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                    {
+                        objectId = result.Value["result"]["objectId"].Value<string>(),
+                            accessorPropertiesOnly = true,
+                            ownProperties = false
+                    }), ctx.token);
+                    if (is_js)
+                        await CheckProps(obj_accessors.Value["result"], new { __proto__ = TIgnore() }, "obj_accessors");
+                    else
+                        AssertEqual(0, obj_accessors.Value["result"]?.Count(), "obj_accessors-count");
+
+                    // Check for a __proto__ object
+                    // isOwn = true, accessorPropertiesOnly = false
+                    var obj_own = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                    {
+                        objectId = result.Value["result"]["objectId"].Value<string>(),
+                            accessorPropertiesOnly = false,
+                            ownProperties = true
+                    }), ctx.token);
+
+                    await CheckProps(obj_own.Value["result"], new
+                    {
+                        length = TNumber(len),
+                            // __proto__ = TArray (type, 0) // Is this one really required?
+                    }, $"obj_own", num_fields : is_js ? 2 : 1);
+
+                });
+        }
+
+        void CheckJFunction(JToken actual, string className, string label)
+        {
+            AssertEqual("function", actual["type"]?.Value<string>(), $"{label}-type");
+            AssertEqual(className, actual["className"]?.Value<string>(), $"{label}-className");
+        }
+
+        // This tests `callFunctionOn` with a function that the vscode-js-debug extension uses
+        // Using this here as a non-trivial test case
+        [Theory]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, 10)]
+        [InlineData("big_array_js_test (0);", "/other.js", 8, 1, 0)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, 10)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 0);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, 0)]
+        public async Task CheckVSCodeTestFunction2(string eval_fn, string bp_loc, int line, int col, int len)
+        {
+            var fetch_start_idx = 2;
+            var num_elems_fetch = 3;
+            string vscode_fn1 = "function(e,t){const r={},n=-1===e?0:e,i=-1===t?this.length:e+t;for(let e=n;e<i&&e<this.length;++e){const t=Object.getOwnPropertyDescriptor(this,e);t&&Object.defineProperty(r,e,t)}return r}";
+
+            await RunCallFunctionOn(eval_fn, vscode_fn1, "big", bp_loc, line, col,
+                fn_args : JArray.FromObject(new []
+                {
+                    new { @value = fetch_start_idx },
+                    new { @value = num_elems_fetch }
+                }),
+                test_fn : async(result) =>
+                {
+
+                    var is_js = bp_loc.EndsWith(".js", StringComparison.Ordinal);
+
+                    // isOwn = false, accessorPropertiesOnly = true
+                    var obj_accessors = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                    {
+                        objectId = result.Value["result"]["objectId"].Value<string>(),
+                            accessorPropertiesOnly = true,
+                            ownProperties = false
+                    }), ctx.token);
+                    if (is_js)
+                        await CheckProps(obj_accessors.Value["result"], new { __proto__ = TIgnore() }, "obj_accessors");
+                    else
+                        AssertEqual(0, obj_accessors.Value["result"]?.Count(), "obj_accessors-count");
+
+                    // Ignoring the __proto__ property
+
+                    // isOwn = true, accessorPropertiesOnly = false
+                    var obj_own = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                    {
+                        objectId = result.Value["result"]["objectId"].Value<string>(),
+                            accessorPropertiesOnly = false,
+                            ownProperties = true
+                    }), ctx.token);
+
+                    var obj_own_val = obj_own.Value["result"];
+                    var num_elems_recd = len == 0 ? 0 : num_elems_fetch;
+                    AssertEqual(is_js ? num_elems_recd + 1 : num_elems_recd, obj_own_val.Count(), $"obj_own-count");
+
+                    if (is_js)
+                        CheckObject(obj_own_val, "__proto__", "Object");
+
+                    for (int i = fetch_start_idx; i < fetch_start_idx + num_elems_recd; i++)
+                        CheckNumber(obj_own_val, i.ToString(), 1000 + i);
+                });
+        }
+
+        [Theory]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, false)]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, true)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, false)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, true)]
+        public async Task RunOnArrayReturnEmptyArray(string eval_fn, string bp_loc, int line, int col, bool roundtrip)
+        {
+            var ret_len = 0;
+
+            await RunCallFunctionOn(eval_fn,
+                "function () { return []; }",
+                "big", bp_loc, line, col,
+                res_array_len : ret_len,
+                roundtrip : roundtrip,
+                test_fn : async(result) =>
+                {
+                    var is_js = bp_loc.EndsWith(".js", StringComparison.Ordinal);
+
+                    // getProperties (isOwn = false, accessorPropertiesOnly = true)
+                    var obj_accessors = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                    {
+                        objectId = result.Value["result"]["objectId"].Value<string>(),
+                            accessorPropertiesOnly = true,
+                            ownProperties = false
+                    }), ctx.token);
+                    if (is_js)
+                        await CheckProps(obj_accessors.Value["result"], new { __proto__ = TIgnore() }, "obj_accessors");
+                    else
+                        AssertEqual(0, obj_accessors.Value["result"]?.Count(), "obj_accessors-count");
+
+                    // getProperties (isOwn = true, accessorPropertiesOnly = false)
+                    var obj_own = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                    {
+                        objectId = result.Value["result"]["objectId"].Value<string>(),
+                            accessorPropertiesOnly = false,
+                            ownProperties = true
+                    }), ctx.token);
+
+                    await CheckProps(obj_own.Value["result"], new
+                    {
+                        length = TNumber(ret_len),
+                            // __proto__ returned by js
+                    }, $"obj_own", num_fields : is_js ? 2 : 1);
+                });
+        }
+
+        [Theory]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, false)]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, true)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, false)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, true)]
+        public async Task RunOnArrayReturnArray(string eval_fn, string bp_loc, int line, int col, bool roundtrip)
+        {
+            var ret_len = 5;
+            await RunCallFunctionOn(eval_fn,
+                "function (m) { return Object.values (this).filter ((k, i) => i%m == 0); }",
+                "big", bp_loc, line, col,
+                fn_args : JArray.FromObject(new [] { new { value = 2 } }),
+                res_array_len : ret_len,
+                roundtrip : roundtrip,
+                test_fn : async(result) =>
+                {
+                    var is_js = bp_loc.EndsWith(".js");
+
+                    // getProperties (own=false)
+                    var obj_accessors = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                    {
+                        objectId = result.Value["result"]["objectId"].Value<string>(),
+                            accessorPropertiesOnly = true,
+                            ownProperties = false
+                    }), ctx.token);
+
+                    if (is_js)
+                        await CheckProps(obj_accessors.Value["result"], new { __proto__ = TIgnore() }, "obj_accessors");
+                    else
+                        AssertEqual(0, obj_accessors.Value["result"]?.Count(), "obj_accessors-count");
+
+                    // getProperties (own=true)
+                    // isOwn = true, accessorPropertiesOnly = false
+                    var obj_own = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                    {
+                        objectId = result.Value["result"]["objectId"].Value<string>(),
+                            accessorPropertiesOnly = false,
+                            ownProperties = true
+                    }), ctx.token);
+
+                    // AssertEqual (2, obj_own.Value ["result"].Count (), $"{label}-obj_own.count");
+
+                    var obj_own_val = obj_own.Value["result"];
+                    await CheckProps(obj_own_val, new
+                    {
+                        length = TNumber(ret_len),
+                            // __proto__ returned by JS
+                    }, $"obj_own", num_fields: (is_js ? ret_len + 2 : ret_len + 1));
+
+                    for (int i = 0; i < ret_len; i++)
+                        CheckNumber(obj_own_val, i.ToString(), i * 2 + 1000);
+                });
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task RunOnVTArray(bool roundtrip) => await RunCallFunctionOn(
+            "invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);",
+            "function (m) { return Object.values (this).filter ((k, i) => i%m == 0); }",
+            "ss_arr",
+            "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12,
+            fn_args : JArray.FromObject(new [] { new { value = 2 } }),
+            res_array_len : 5,
+            roundtrip : roundtrip,
+            test_fn : async(result) =>
+            {
+                var ret_len = 5;
+
+                // getProperties (own=false)
+                var obj_accessors = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                {
+                    objectId = result.Value["result"]["objectId"].Value<string>(),
+                        accessorPropertiesOnly = true,
+                        ownProperties = false
+                }), ctx.token);
+
+                AssertEqual(0, obj_accessors.Value["result"]?.Count(), "obj_accessors-count");
+
+                // getProperties (own=true)
+                // isOwn = true, accessorPropertiesOnly = false
+                var obj_own = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                {
+                    objectId = result.Value["result"]["objectId"].Value<string>(),
+                        accessorPropertiesOnly = false,
+                        ownProperties = true
+                }), ctx.token);
+
+                var obj_own_val = obj_own.Value["result"];
+                await CheckProps(obj_own_val, new
+                {
+                    length = TNumber(ret_len),
+                        // __proto__ returned by JS
+                }, "obj_own", num_fields : ret_len + 1);
+
+                for (int i = 0; i < ret_len; i++)
+                {
+                    var act_i = CheckValueType(obj_own_val, i.ToString(), "Math.SimpleStruct");
+
+                    // Valuetypes can get sent as part of the container's getProperties, so ensure that we can access it
+                    var act_i_props = await GetProperties(act_i["value"]["objectId"]?.Value<string>());
+                    await CheckProps(act_i_props, new
+                    {
+                        dt = TValueType("System.DateTime", new DateTime(2020 + (i * 2), 1, 2, 3, 4, 5).ToString()),
+                            gs = TValueType("Math.GenericStruct<System.DateTime>")
+                    }, "obj_own ss_arr[{i}]");
+
+                    var gs_props = await GetObjectOnLocals(act_i_props, "gs");
+                    await CheckProps(gs_props, new
+                    {
+                        List = TObject("System.Collections.Generic.List<System.DateTime>", is_null : true),
+                            StringField = TString($"ss_arr # {i*2} # gs # StringField")
+                    }, "obj_own ss_arr[{i}].gs");
+
+                }
+            });
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task RunOnCFOValueTypeResult(bool roundtrip) => await RunCallFunctionOn(
+            eval_fn: "invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);",
+            fn_decl: "function () { return this; }",
+            local_name: "simple_struct",
+            bp_loc: "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12,
+            roundtrip : roundtrip,
+            test_fn : async(result) =>
+            {
+
+                // getProperties (own=false)
+                var obj_accessors = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                {
+                    objectId = result.Value["result"]["objectId"].Value<string>(),
+                        accessorPropertiesOnly = true,
+                        ownProperties = false
+                }), ctx.token);
+                AssertEqual(0, obj_accessors.Value["result"].Count(), "obj_accessors-count");
+
+                // getProperties (own=true)
+                // isOwn = true, accessorPropertiesOnly = false
+                var obj_own = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                {
+                    objectId = result.Value["result"]["objectId"].Value<string>(),
+                        accessorPropertiesOnly = false,
+                        ownProperties = true
+                }), ctx.token);
+
+                var obj_own_val = obj_own.Value["result"];
+                var dt = new DateTime(2020, 1, 2, 3, 4, 5);
+                await CheckProps(obj_own_val, new
+                {
+                    dt = TValueType("System.DateTime", dt.ToString()),
+                        gs = TValueType("Math.GenericStruct<System.DateTime>")
+                }, $"obj_own-props");
+
+                await CheckDateTime(obj_own_val, "dt", dt);
+
+                var gs_props = await GetObjectOnLocals(obj_own_val, "gs");
+                await CheckProps(gs_props, new
+                {
+                    List = TObject("System.Collections.Generic.List<System.DateTime>", is_null : true),
+                        StringField = TString($"simple_struct # gs # StringField")
+                }, "simple_struct.gs-props");
+            });
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task RunOnJSObject(bool roundtrip) => await RunCallFunctionOn(
+            "object_js_test ();",
+            "function () { return this; }",
+            "obj", "/other.js", 17, 1,
+            fn_args : JArray.FromObject(new [] { new { value = 2 } }),
+            roundtrip : roundtrip,
+            test_fn : async(result) =>
+            {
+
+                // getProperties (own=false)
+                var obj_accessors = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                {
+                    objectId = result.Value["result"]["objectId"].Value<string>(),
+                        accessorPropertiesOnly = true,
+                        ownProperties = false
+                }), ctx.token);
+
+                await CheckProps(obj_accessors.Value["result"], new { __proto__ = TIgnore() }, "obj_accessors");
+
+                // getProperties (own=true)
+                // isOwn = true, accessorPropertiesOnly = false
+                var obj_own = await ctx.cli.SendCommand("Runtime.getProperties", JObject.FromObject(new
+                {
+                    objectId = result.Value["result"]["objectId"].Value<string>(),
+                        accessorPropertiesOnly = false,
+                        ownProperties = true
+                }), ctx.token);
+
+                var obj_own_val = obj_own.Value["result"];
+                await CheckProps(obj_own_val, new
+                {
+                    a_obj = TObject("Object"),
+                        b_arr = TArray("Array", 2)
+                }, "obj_own", num_fields : 3);
+            });
+
+        [Theory]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, false)]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, true)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, false)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, true)]
+        public async Task RunOnArrayReturnObjectArrayByValue(string eval_fn, string bp_loc, int line, int col, bool roundtrip)
+        {
+            var ret_len = 5;
+            await RunCallFunctionOn(eval_fn,
+                "function () { return Object.values (this).filter ((k, i) => i%2 == 0); }",
+                "big", bp_loc, line, col, returnByValue : true, roundtrip : roundtrip,
+                test_fn : async(result) =>
+                {
+                    // Check cfo result
+                    AssertEqual(JTokenType.Object, result.Value["result"].Type, "cfo-result-jsontype");
+                    AssertEqual("object", result.Value["result"]["type"]?.Value<string>(), "cfo-res-type");
+
+                    AssertEqual(JTokenType.Array, result.Value["result"]["value"].Type, "cfo-res-value-jsontype");
+                    var actual = result.Value["result"] ? ["value"].Values<JToken>().ToArray();
+                    AssertEqual(ret_len, actual.Length, "cfo-res-value-length");
+
+                    for (int i = 0; i < ret_len; i++)
+                    {
+                        var exp_num = i * 2 + 1000;
+                        if (bp_loc.EndsWith(".js", StringComparison.Ordinal))
+                            AssertEqual(exp_num, actual[i].Value<int>(), $"[{i}]");
+                        else
+                        {
+                            AssertEqual("number", actual[i] ? ["type"]?.Value<string>(), $"[{i}]-type");
+                            AssertEqual(exp_num.ToString(), actual[i] ? ["description"]?.Value<string>(), $"[{i}]-description");
+                            AssertEqual(exp_num, actual[i] ? ["value"]?.Value<int>(), $"[{i}]-value");
+                        }
+                    }
+                    await Task.CompletedTask;
+                });
+        }
+
+        [Theory]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, false)]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, true)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, false)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, true)]
+        public async Task RunOnArrayReturnArrayByValue(string eval_fn, string bp_loc, int line, int col, bool roundtrip) => await RunCallFunctionOn(eval_fn,
+            "function () { return Object.getOwnPropertyNames (this); }",
+            "big", bp_loc, line, col, returnByValue : true,
+            roundtrip : roundtrip,
+            test_fn : async(result) =>
+            {
+                // Check cfo result
+                AssertEqual("object", result.Value["result"]["type"]?.Value<string>(), "cfo-res-type");
+
+                var exp = new JArray();
+                for (int i = 0; i < 10; i++)
+                    exp.Add(i.ToString());
+                exp.Add("length");
+
+                var actual = result.Value["result"] ? ["value"];
+                if (!JObject.DeepEquals(exp, actual))
+                {
+                    Assert.True(false, $"Results don't match.\nExpected: {exp}\nActual:  {actual}");
+                }
+                await Task.CompletedTask;
+            });
+
+        [Theory]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, false)]
+        [InlineData("big_array_js_test (10);", "/other.js", 8, 1, true)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, false)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, true)]
+        public async Task RunOnArrayReturnPrimitive(string eval_fn, string bp_loc, int line, int col, bool return_by_val)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                await SetBreakpoint(bp_loc, line, col);
+
+                // callFunctionOn
+                var eval_expr = $"window.setTimeout(function() {{ {eval_fn} }}, 1);";
+                var result = await ctx.cli.SendCommand("Runtime.evaluate", JObject.FromObject(new { expression = eval_expr }), ctx.token);
+                var pause_location = await ctx.insp.WaitFor(Inspector.PAUSE);
+
+                // Um for js we get "scriptId": "6"
+                // CheckLocation (bp_loc, line, col, ctx.scripts, pause_location ["callFrames"][0]["location"]);
+
+                // Check the object at the bp
+                var frame_locals = await GetProperties(pause_location["callFrames"][0]["scopeChain"][0]["object"]["objectId"].Value<string>());
+                var obj = GetAndAssertObjectWithName(frame_locals, "big");
+                var obj_id = obj["value"]["objectId"].Value<string>();
+
+                var cfo_args = JObject.FromObject(new
+                {
+                    functionDeclaration = "function () { return 5; }",
+                        objectId = obj_id
+                });
+
+                // value of @returnByValue doesn't matter, as the returned value
+                // is a primitive
+                if (return_by_val)
+                    cfo_args["returnByValue"] = return_by_val;
+
+                // callFunctionOn
+                result = await ctx.cli.SendCommand("Runtime.callFunctionOn", cfo_args, ctx.token);
+                await CheckValue(result.Value["result"], TNumber(5), "cfo-res");
+
+                cfo_args = JObject.FromObject(new
+                {
+                    functionDeclaration = "function () { return 'test value'; }",
+                        objectId = obj_id
+                });
+
+                // value of @returnByValue doesn't matter, as the returned value
+                // is a primitive
+                if (return_by_val)
+                    cfo_args["returnByValue"] = return_by_val;
+
+                // callFunctionOn
+                result = await ctx.cli.SendCommand("Runtime.callFunctionOn", cfo_args, ctx.token);
+                await CheckValue(result.Value["result"], JObject.FromObject(new { type = "string", value = "test value" }), "cfo-res");
+
+                cfo_args = JObject.FromObject(new
+                {
+                    functionDeclaration = "function () { return null; }",
+                        objectId = obj_id
+                });
+
+                // value of @returnByValue doesn't matter, as the returned value
+                // is a primitive
+                if (return_by_val)
+                    cfo_args["returnByValue"] = return_by_val;
+
+                // callFunctionOn
+                result = await ctx.cli.SendCommand("Runtime.callFunctionOn", cfo_args, ctx.token);
+                await CheckValue(result.Value["result"], JObject.Parse("{ type: 'object', subtype: 'null', value: null }"), "cfo-res");
+            });
+        }
+
+        public static TheoryData<string, string, int, int, bool?> SilentErrorsTestData(bool? silent) => new TheoryData<string, string, int, int, bool?>
+        { { "invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:LocalsTest', 10);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 23, 12, silent },
+            { "big_array_js_test (10);", "/other.js", 8, 1, silent }
+        };
+
+        [Theory]
+        [MemberData(nameof(SilentErrorsTestData), null)]
+        [MemberData(nameof(SilentErrorsTestData), false)]
+        [MemberData(nameof(SilentErrorsTestData), true)]
+        public async Task CFOWithSilentReturnsErrors(string eval_fn, string bp_loc, int line, int col, bool? silent)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                await SetBreakpoint(bp_loc, line, col);
+
+                // callFunctionOn
+                var eval_expr = "window.setTimeout(function() { " + eval_fn + " }, 1);";
+                var result = await ctx.cli.SendCommand("Runtime.evaluate", JObject.FromObject(new { expression = eval_expr }), ctx.token);
+                var pause_location = await ctx.insp.WaitFor(Inspector.PAUSE);
+
+                var frame_locals = await GetProperties(pause_location["callFrames"][0]["scopeChain"][0]["object"]["objectId"].Value<string>());
+                var obj = GetAndAssertObjectWithName(frame_locals, "big");
+                var big_obj_id = obj["value"]["objectId"].Value<string>();
+                var error_msg = "#This is an error message#";
+
+                // Check the object at the bp
+                var cfo_args = JObject.FromObject(new
+                {
+                    functionDeclaration = $"function () {{ throw Error ('{error_msg}'); }}",
+                        objectId = big_obj_id
+                });
+
+                if (silent.HasValue)
+                    cfo_args["silent"] = silent;
+
+                // callFunctionOn, Silent does not change the result, except that the error
+                // doesn't get reported, and the execution is NOT paused even with setPauseOnException=true
+                result = await ctx.cli.SendCommand("Runtime.callFunctionOn", cfo_args, ctx.token);
+                Assert.False(result.IsOk, "result.IsOk");
+                Assert.True(result.IsErr, "result.IsErr");
+
+                var hasErrorMessage = result.Error["exceptionDetails"] ? ["exception"] ? ["description"]?.Value<string>()?.Contains(error_msg);
+                Assert.True((hasErrorMessage ?? false), "Exception message not found");
+            });
+        }
+
+        public static TheoryData<string, string, int, int, string, Func<string[], object>, string, bool> GettersTestData(string local_name, bool use_cfo) => new TheoryData<string, string, int, int, string, Func<string[], object>, string, bool>
+        {
+            // Chrome sends this one
+            {
+                "invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:PropertyGettersTest');",
+                "PropertyGettersTest",
+                30,
+                12,
+                "function invokeGetter(arrayStr){ let result=this; const properties=JSON.parse(arrayStr); for(let i=0,n=properties.length;i<n;++i){ result=result[properties[i]]; } return result; }",
+                (arg_strs) => JArray.FromObject(arg_strs).ToString(),
+                local_name,
+                use_cfo
+            },
+            {
+                "invoke_static_method_async ('[debugger-test] DebuggerTests.CallFunctionOnTest:PropertyGettersTestAsync');",
+                "MoveNext",
+                38,
+                12,
+                "function invokeGetter(arrayStr){ let result=this; const properties=JSON.parse(arrayStr); for(let i=0,n=properties.length;i<n;++i){ result=result[properties[i]]; } return result; }",
+                (arg_strs) => JArray.FromObject(arg_strs).ToString(),
+                local_name,
+                use_cfo
+            },
+
+            // VSCode sends this one
+            {
+                "invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:PropertyGettersTest');",
+                "PropertyGettersTest",
+                30,
+                12,
+                "function(e){return this[e]}",
+                (args_str) => args_str?.Length > 0 ? args_str[0] : String.Empty,
+                local_name,
+                use_cfo
+            },
+            {
+                "invoke_static_method_async ('[debugger-test] DebuggerTests.CallFunctionOnTest:PropertyGettersTestAsync');",
+                "MoveNext",
+                38,
+                12,
+                "function(e){return this[e]}",
+                (args_str) => args_str?.Length > 0 ? args_str[0] : String.Empty,
+                local_name,
+                use_cfo
+            }
+        };
+
+        [Theory]
+        [MemberData(nameof(GettersTestData), "ptd", false)]
+        [MemberData(nameof(GettersTestData), "ptd", true)]
+        [MemberData(nameof (GettersTestData), "swp", false)]
+        [MemberData(nameof (GettersTestData), "swp", true)]
+        public async Task PropertyGettersTest(string eval_fn, string method_name, int line, int col, string cfo_fn, Func<string[], object> get_args_fn, string local_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-cfo-test.cs", line, col,
+            method_name,
+            $"window.setTimeout(function() {{ {eval_fn} }}, 1);",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var frame_locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                await CheckProps(frame_locals, new
+                {
+                    ptd = TObject("DebuggerTests.ClassWithProperties"),
+                    swp = TObject("DebuggerTests.StructWithProperties")
+                }, "locals#0");
+
+                var obj = GetAndAssertObjectWithName(frame_locals, local_name);
+
+                var dt = new DateTime(4, 5, 6, 7, 8, 9);
+                var obj_props = await GetProperties(obj?["value"] ? ["objectId"]?.Value<string>());
+                await CheckProps(obj_props, new
+                {
+                    V           = TNumber(0xDEADBEEF),
+                    Int         = TGetter("Int"),
+                    String      = TGetter("String"),
+                    DT          = TGetter("DT"),
+                    IntArray    = TGetter("IntArray"),
+                    DTArray     = TGetter("DTArray"),
+                    StringField = TString(null),
+
+                    // Auto properties show w/o getters, because they have
+                    // a backing field
+                    DTAutoProperty = TValueType("System.DateTime", dt.ToString())
+                }, local_name);
+
+                // Automatic properties don't have invokable getters, because we can get their
+                // value from the backing field directly
+                {
+                    var dt_auto_props = await GetObjectOnLocals(obj_props, "DTAutoProperty");
+                    await CheckDateTime(obj_props, "DTAutoProperty", dt);
+                }
+
+                // Invoke getters, and check values
+
+                dt = new DateTime(3, 4, 5, 6, 7, 8);
+                var res = await InvokeGetter(obj, get_args_fn(new [] { "Int" }), cfo_fn);
+                await CheckValue(res.Value["result"], JObject.FromObject(new { type = "number", value = (0xDEADBEEF + (uint) dt.Month) }), $"{local_name}.Int");
+
+                res = await InvokeGetter(obj, get_args_fn(new [] { "String" }), cfo_fn);
+                await CheckValue(res.Value["result"], JObject.FromObject(new { type = "string", value = $"String property, V: 0xDEADBEEF" }), $"{local_name}.String");
+
+                res = await InvokeGetter(obj, get_args_fn(new [] { "DT" }), cfo_fn);
+                await CheckValue(res.Value["result"], TValueType("System.DateTime", dt.ToString()), $"{local_name}.DT");
+                await CheckDateTimeValue(res.Value["result"], dt);
+
+                // Check arrays through getters
+
+                res = await InvokeGetter(obj, get_args_fn(new [] { "IntArray" }), cfo_fn);
+                await CheckValue(res.Value["result"], TArray("int[]", 2), $"{local_name}.IntArray");
+                {
+                    var arr_elems = await GetProperties(res.Value["result"] ? ["objectId"]?.Value<string>());
+                    var exp_elems = new []
+                    {
+                        TNumber(10),
+                        TNumber(20)
+                    };
+
+                    await CheckProps(arr_elems, exp_elems, $"{local_name}.IntArray");
+                }
+
+                res = await InvokeGetter(obj, get_args_fn(new [] { "DTArray" }), cfo_fn);
+                await CheckValue(res.Value["result"], TArray("System.DateTime[]", 2), $"{local_name}.DTArray");
+                {
+                    var dt0 = new DateTime(6, 7, 8, 9, 10, 11);
+                    var dt1 = new DateTime(1, 2, 3, 4, 5, 6);
+
+                    var arr_elems = await GetProperties(res.Value["result"] ? ["objectId"]?.Value<string>());
+                    var exp_elems = new []
+                    {
+                        TValueType("System.DateTime", dt0.ToString()),
+                        TValueType("System.DateTime", dt1.ToString()),
+                    };
+
+                    await CheckProps(arr_elems, exp_elems, $"{local_name}.DTArray");
+
+                    res = await InvokeGetter(arr_elems[0], "Date");
+                    await CheckDateTimeValue(res.Value["result"], dt0.Date);
+                }
+            });
+
+        [Theory]
+        [InlineData("invoke_static_method_async ('[debugger-test] DebuggerTests.CallFunctionOnTest:PropertyGettersTestAsync');", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 38, 12, true)]
+        [InlineData("invoke_static_method_async ('[debugger-test] DebuggerTests.CallFunctionOnTest:PropertyGettersTestAsync');", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 38, 12, false)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:PropertyGettersTest');", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 30, 12, true)]
+        [InlineData("invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:PropertyGettersTest');", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 30, 12, false)]
+        [InlineData("invoke_getters_js_test ();", "/other.js", 30, 1, false)]
+        [InlineData("invoke_getters_js_test ();", "/other.js", 30, 1, true)]
+        public async Task CheckAccessorsOnObjectsWithCFO(string eval_fn, string bp_loc, int line, int col, bool roundtrip)
+        {
+            await RunCallFunctionOn(
+                eval_fn, "function() { return this; }", "ptd",
+                bp_loc, line, col,
+                roundtrip : roundtrip,
+                test_fn : async(result) =>
+                {
+
+                    var is_js = bp_loc.EndsWith(".js");
+
+                    // Check with `accessorPropertiesOnly=true`
+
+                    var id = result.Value?["result"] ? ["objectId"]?.Value<string>();
+                    var get_prop_req = JObject.FromObject(new
+                    {
+                        objectId = id,
+                            accessorPropertiesOnly = true
+                    });
+
+                    var res = await GetPropertiesAndCheckAccessors(get_prop_req, is_js ? 6 : 5); // js returns extra `__proto__` member also
+                    Assert.False(res.Value["result"].Any(jt => jt["name"]?.Value<string>() == "StringField"), "StringField shouldn't be returned for `accessorPropertiesOnly`");
+
+                    // Check with `accessorPropertiesOnly` unset, == false
+                    get_prop_req = JObject.FromObject(new
+                    {
+                        objectId = id,
+                    });
+
+                    res = await GetPropertiesAndCheckAccessors(get_prop_req, is_js ? 8 : 7); // js returns a `__proto__` member also
+                    Assert.True(res.Value["result"].Any(jt => jt["name"]?.Value<string>() == "StringField"), "StringField should be returned for `accessorPropertiesOnly=false`");
+                });
+
+            async Task<Result> GetPropertiesAndCheckAccessors(JObject get_prop_req, int num_fields)
+            {
+                var res = await ctx.cli.SendCommand("Runtime.getProperties", get_prop_req, ctx.token);
+                if (!res.IsOk)
+                    Assert.True(false, $"Runtime.getProperties failed for {get_prop_req.ToString ()}, with Result: {res}");
+
+                var accessors = new string[] { "Int", "String", "DT", "IntArray", "DTArray" };
+                foreach (var name in accessors)
+                {
+                    var prop = GetAndAssertObjectWithName(res.Value["result"], name);
+                    Assert.True(prop["value"] == null, $"{name} shouldn't have a `value`");
+
+                    await CheckValue(prop, TGetter(name), $"{name}");
+                }
+
+                return res;
+            }
+        }
+
+        public static TheoryData<string, string, int, int, bool> NegativeTestsData(bool use_cfo = false) => new TheoryData<string, string, int, int, bool>
+        { { "invoke_static_method ('[debugger-test] DebuggerTests.CallFunctionOnTest:MethodForNegativeTests', null);", "dotnet://debugger-test.dll/debugger-cfo-test.cs", 45, 12, use_cfo },
+            { "negative_cfo_test ();", "/other.js", 62, 1, use_cfo }
+        };
+
+        [Theory]
+        [MemberData(nameof(NegativeTestsData), false)]
+        public async Task RunOnInvalidCfoId(string eval_fn, string bp_loc, int line, int col, bool use_cfo) => await RunCallFunctionOn(
+            eval_fn, "function() { return this; }", "ptd",
+            bp_loc, line, col,
+            test_fn : async(cfo_result) =>
+            {
+                var ptd_id = cfo_result.Value?["result"] ? ["objectId"]?.Value<string>();
+
+                var cfo_args = JObject.FromObject(new
+                {
+                    functionDeclaration = "function () { return 0; }",
+                        objectId = ptd_id + "_invalid"
+                });
+
+                var res = await ctx.cli.SendCommand("Runtime.callFunctionOn", cfo_args, ctx.token);
+                Assert.True(res.IsErr);
+            });
+
+        [Theory]
+        [MemberData(nameof(NegativeTestsData), false)]
+        public async Task RunOnInvalidThirdSegmentOfObjectId(string eval_fn, string bp_loc, int line, int col, bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+                await SetBreakpoint(bp_loc, line, col);
+
+                // callFunctionOn
+                var eval_expr = $"window.setTimeout(function() {{ {eval_fn} }}, 1);";
+                var result = await ctx.cli.SendCommand("Runtime.evaluate", JObject.FromObject(new { expression = eval_expr }), ctx.token);
+                var pause_location = await ctx.insp.WaitFor(Inspector.PAUSE);
+
+                var frame_locals = await GetProperties(pause_location["callFrames"][0]["scopeChain"][0]["object"]["objectId"].Value<string>());
+                var ptd = GetAndAssertObjectWithName(frame_locals, "ptd");
+                var ptd_id = ptd["value"]["objectId"].Value<string>();
+
+                var cfo_args = JObject.FromObject(new
+                {
+                    functionDeclaration = "function () { return 0; }",
+                        objectId = ptd_id + "_invalid"
+                });
+
+                var res = await ctx.cli.SendCommand("Runtime.callFunctionOn", cfo_args, ctx.token);
+                Assert.True(res.IsErr);
+            });
+        }
+
+        [Theory]
+        [MemberData(nameof(NegativeTestsData), false)]
+        [MemberData(nameof(NegativeTestsData), true)]
+        public async Task InvalidPropertyGetters(string eval_fn, string bp_loc, int line, int col, bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                await SetBreakpoint(bp_loc, line, col);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+
+                // callFunctionOn
+                var eval_expr = $"window.setTimeout(function() {{ {eval_fn} }}, 1);";
+                await SendCommand("Runtime.evaluate", JObject.FromObject(new { expression = eval_expr }));
+                var pause_location = await ctx.insp.WaitFor(Inspector.PAUSE);
+
+                var frame_locals = await GetProperties(pause_location["callFrames"][0]["scopeChain"][0]["object"]["objectId"].Value<string>());
+                var ptd = GetAndAssertObjectWithName(frame_locals, "ptd");
+                var ptd_id = ptd["value"]["objectId"].Value<string>();
+
+                var invalid_args = new object[] { "NonExistant", String.Empty, null, 12310 };
+                foreach (var invalid_arg in invalid_args)
+                {
+                    var getter_res = await InvokeGetter(JObject.FromObject(new { value = new { objectId = ptd_id } }), invalid_arg);
+                    AssertEqual("undefined", getter_res.Value["result"] ? ["type"]?.ToString(), $"Expected to get undefined result for non-existant accessor - {invalid_arg}");
+                }
+            });
+        }
+
+        [Theory]
+        [MemberData(nameof(NegativeTestsData), false)]
+        public async Task ReturnNullFromCFO(string eval_fn, string bp_loc, int line, int col, bool use_cfo) => await RunCallFunctionOn(
+            eval_fn, "function() { return this; }", "ptd",
+            bp_loc, line, col,
+            test_fn : async(result) =>
+            {
+                var is_js = bp_loc.EndsWith(".js");
+                var ptd = JObject.FromObject(new { value = new { objectId = result.Value?["result"] ? ["objectId"]?.Value<string>() } });
+
+                var null_value_json = JObject.Parse("{ 'type': 'object', 'subtype': 'null', 'value': null }");
+                foreach (var returnByValue in new bool?[] { null, false, true })
+                {
+                    var res = await InvokeGetter(ptd, "StringField", returnByValue : returnByValue);
+                    if (is_js)
+                    {
+                        // In js case, it doesn't know the className, so the result looks slightly different
+                        Assert.True(
+                            JObject.DeepEquals(res.Value["result"], null_value_json),
+                            $"[StringField#returnByValue = {returnByValue}] Json didn't match. Actual: {res.Value ["result"]} vs {null_value_json}");
+                    }
+                    else
+                    {
+                        await CheckValue(res.Value["result"], TString(null), "StringField");
+                    }
+                }
+            });
+
+        /*
+         * 1. runs `Runtime.callFunctionOn` on the objectId,
+         * if @roundtrip == false, then
+         *     -> calls @test_fn for that result (new objectId)
+         * else
+         *     -> runs it again on the *result's* objectId.
+         *        -> calls @test_fn on the *new* result objectId
+         *
+         * Returns: result of `Runtime.callFunctionOn`
+         */
+        async Task RunCallFunctionOn(string eval_fn, string fn_decl, string local_name, string bp_loc, int line, int col, int res_array_len = -1,
+            Func<Result, Task> test_fn = null, bool returnByValue = false, JArray fn_args = null, bool roundtrip = false)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                await SetBreakpoint(bp_loc, line, col);
+
+                // callFunctionOn
+                var eval_expr = $"window.setTimeout(function() {{ {eval_fn} }}, 1);";
+                var result = await ctx.cli.SendCommand("Runtime.evaluate", JObject.FromObject(new { expression = eval_expr }), ctx.token);
+                var pause_location = await ctx.insp.WaitFor(Inspector.PAUSE);
+
+                // Um for js we get "scriptId": "6"
+                // CheckLocation (bp_loc, line, col, ctx.scripts, pause_location ["callFrames"][0]["location"]);
+
+                // Check the object at the bp
+                var frame_locals = await GetProperties(pause_location["callFrames"][0]["scopeChain"][0]["object"]["objectId"].Value<string>());
+                var obj = GetAndAssertObjectWithName(frame_locals, local_name);
+                var obj_id = obj["value"]["objectId"].Value<string>();
+
+                var cfo_args = JObject.FromObject(new
+                {
+                    functionDeclaration = fn_decl,
+                        objectId = obj_id
+                });
+
+                if (fn_args != null)
+                    cfo_args["arguments"] = fn_args;
+
+                if (returnByValue)
+                    cfo_args["returnByValue"] = returnByValue;
+
+                // callFunctionOn
+                result = await ctx.cli.SendCommand("Runtime.callFunctionOn", cfo_args, ctx.token);
+                await CheckCFOResult(result);
+
+                // If it wasn't `returnByValue`, then try to run a new function
+                // on that *returned* object
+                // This second function, just returns the object as-is, so the same
+                // test_fn is re-usable.
+                if (!returnByValue && roundtrip)
+                {
+                    cfo_args = JObject.FromObject(new
+                    {
+                        functionDeclaration = "function () { return this; }",
+                            objectId = result.Value["result"]["objectId"]?.Value<string>()
+                    });
+
+                    if (fn_args != null)
+                        cfo_args["arguments"] = fn_args;
+
+                    result = await ctx.cli.SendCommand("Runtime.callFunctionOn", cfo_args, ctx.token);
+
+                    await CheckCFOResult(result);
+                }
+
+                if (test_fn != null)
+                    await test_fn(result);
+
+                return;
+
+                async Task CheckCFOResult(Result result)
+                {
+                    if (returnByValue)
+                        return;
+
+                    if (res_array_len < 0)
+                        await CheckValue(result.Value["result"], TObject("Object"), $"cfo-res");
+                    else
+                        await CheckValue(result.Value["result"], TArray("Array", res_array_len), $"cfo-res");
+                }
+            });
+        }
+    }
+
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/DateTimeTests.cs b/src/mono/wasm/debugger/DebuggerTestSuite/DateTimeTests.cs
new file mode 100644
index 00000000000000..6b7a5603d2d2e4
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/DateTimeTests.cs
@@ -0,0 +1,67 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Globalization;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace DebuggerTests
+{
+    public class DateTimeList : DebuggerTestBase
+    {
+
+        [Theory]
+        [InlineData("en-US")]
+
+        // Currently not passing tests. Issue #19743
+        // [InlineData ("ja-JP")]
+        // [InlineData ("es-ES")]
+        //[InlineData ("de-DE")]
+        //[InlineData ("ka-GE")]
+        //[InlineData ("hu-HU")]
+        public async Task CheckDateTimeLocale(string locale)
+        {
+            var insp = new Inspector();
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-datetime-test.cs";
+
+                await SetBreakpointInMethod("debugger-test", "DebuggerTests.DateTimeTest", "LocaleTest", 15);
+
+                var pause_location = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_static_method ('[debugger-test] DebuggerTests.DateTimeTest:LocaleTest'," +
+                    $"'{locale}'); }}, 1);",
+                    debugger_test_loc, 25, 12, "LocaleTest",
+                    locals_fn : async(locals) =>
+                    {
+                        DateTimeFormatInfo dtfi = CultureInfo.GetCultureInfo(locale).DateTimeFormat;
+                        CultureInfo.CurrentCulture = new CultureInfo(locale, false);
+                        DateTime dt = new DateTime(2020, 1, 2, 3, 4, 5);
+                        string dt_str = dt.ToString();
+
+                        var fdtp = dtfi.FullDateTimePattern;
+                        var ldp = dtfi.LongDatePattern;
+                        var ltp = dtfi.LongTimePattern;
+                        var sdp = dtfi.ShortDatePattern;
+                        var stp = dtfi.ShortTimePattern;
+
+                        CheckString(locals, "fdtp", fdtp);
+                        CheckString(locals, "ldp", ldp);
+                        CheckString(locals, "ltp", ltp);
+                        CheckString(locals, "sdp", sdp);
+                        CheckString(locals, "stp", stp);
+                        await CheckDateTime(locals, "dt", dt);
+                        CheckString(locals, "dt_str", dt_str);
+                    }
+                );
+
+            });
+        }
+
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/DebuggerTestSuite.csproj b/src/mono/wasm/debugger/DebuggerTestSuite/DebuggerTestSuite.csproj
new file mode 100644
index 00000000000000..09b79eb67dc295
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/DebuggerTestSuite.csproj
@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="xunit" Version="2.4.0" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />
+
+    <Content Include="appsettings.json" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\BrowserDebugHost\BrowserDebugHost.csproj" />
+    <ProjectReference Include="..\BrowserDebugProxy\BrowserDebugProxy.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/DelegateTests.cs b/src/mono/wasm/debugger/DebuggerTestSuite/DelegateTests.cs
new file mode 100644
index 00000000000000..e186ddc5f71c50
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/DelegateTests.cs
@@ -0,0 +1,306 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Newtonsoft.Json.Linq;
+using Microsoft.WebAssembly.Diagnostics;
+using Xunit;
+
+namespace DebuggerTests
+{
+
+    public class DelegateTests : DebuggerTestBase
+    {
+
+        [Theory]
+        [InlineData(0, 53, 8, "DelegatesTest", false)]
+        [InlineData(0, 53, 8, "DelegatesTest", true)]
+        [InlineData(2, 99, 8, "InnerMethod2", false)]
+        [InlineData(2, 99, 8, "InnerMethod2", true)]
+        public async Task InspectLocalsWithDelegatesAtBreakpointSite(int frame, int line, int col, string method_name, bool use_cfo) =>
+            await CheckInspectLocalsAtBreakpointSite(
+                "dotnet://debugger-test.dll/debugger-test.cs", line, col, method_name,
+                "window.setTimeout(function() { invoke_delegates_test (); }, 1);",
+                use_cfo : use_cfo,
+                wait_for_event_fn : async(pause_location) =>
+                {
+                    var locals = await GetProperties(pause_location["callFrames"][frame]["callFrameId"].Value<string>());
+
+                    await CheckProps(locals, new
+                    {
+                        fn_func = TDelegate("System.Func<Math, bool>", "bool <DelegatesTest>|(Math)"),
+                            fn_func_null = TObject("System.Func<Math, bool>", is_null : true),
+                            fn_func_arr = TArray("System.Func<Math, bool>[]", 1),
+                            fn_del = TDelegate("Math.IsMathNull", "bool IsMathNullDelegateTarget (Math)"),
+                            fn_del_null = TObject("Math.IsMathNull", is_null : true),
+                            fn_del_arr = TArray("Math.IsMathNull[]", 1),
+
+                            // Unused locals
+                            fn_func_unused = TDelegate("System.Func<Math, bool>", "bool <DelegatesTest>|(Math)"),
+                            fn_func_null_unused = TObject("System.Func<Math, bool>", is_null : true),
+                            fn_func_arr_unused = TArray("System.Func<Math, bool>[]", 1),
+
+                            fn_del_unused = TDelegate("Math.IsMathNull", "bool IsMathNullDelegateTarget (Math)"),
+                            fn_del_null_unused = TObject("Math.IsMathNull", is_null : true),
+                            fn_del_arr_unused = TArray("Math.IsMathNull[]", 1),
+
+                            res = TBool(false),
+                            m_obj = TObject("Math")
+                    }, "locals");
+
+                    await CompareObjectPropertiesFor(locals, "fn_func_arr", new []
+                    {
+                        TDelegate(
+                            "System.Func<Math, bool>",
+                            "bool <DelegatesTest>|(Math)")
+                    }, "locals#fn_func_arr");
+
+                    await CompareObjectPropertiesFor(locals, "fn_del_arr", new []
+                    {
+                        TDelegate(
+                            "Math.IsMathNull",
+                            "bool IsMathNullDelegateTarget (Math)")
+                    }, "locals#fn_del_arr");
+
+                    await CompareObjectPropertiesFor(locals, "fn_func_arr_unused", new []
+                    {
+                        TDelegate(
+                            "System.Func<Math, bool>",
+                            "bool <DelegatesTest>|(Math)")
+                    }, "locals#fn_func_arr_unused");
+
+                    await CompareObjectPropertiesFor(locals, "fn_del_arr_unused", new []
+                    {
+                        TDelegate(
+                            "Math.IsMathNull",
+                            "bool IsMathNullDelegateTarget (Math)")
+                    }, "locals#fn_del_arr_unused");
+                }
+            );
+
+        [Theory]
+        [InlineData(0, 202, 8, "DelegatesSignatureTest", false)]
+        [InlineData(0, 202, 8, "DelegatesSignatureTest", true)]
+        [InlineData(2, 99, 8, "InnerMethod2", false)]
+        [InlineData(2, 99, 8, "InnerMethod2", true)]
+        public async Task InspectDelegateSignaturesWithFunc(int frame, int line, int col, string bp_method, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-test.cs",
+            line, col,
+            bp_method,
+            "window.setTimeout (function () { invoke_static_method ('[debugger-test] Math:DelegatesSignatureTest'); }, 1)",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][frame]["callFrameId"].Value<string>());
+
+                await CheckProps(locals, new
+                {
+                    fn_func = TDelegate("System.Func<Math, Math.GenericStruct<Math.GenericStruct<int[]>>, Math.GenericStruct<bool[]>>",
+                            "Math.GenericStruct<bool[]> <DelegatesSignatureTest>|(Math,Math.GenericStruct<Math.GenericStruct<int[]>>)"),
+
+                        fn_func_del = TDelegate("System.Func<Math, Math.GenericStruct<Math.GenericStruct<int[]>>, Math.GenericStruct<bool[]>>",
+                            "Math.GenericStruct<bool[]> DelegateTargetForSignatureTest (Math,Math.GenericStruct<Math.GenericStruct<int[]>>)"),
+
+                        fn_func_null = TObject("System.Func<Math, Math.GenericStruct<Math.GenericStruct<int[]>>, Math.GenericStruct<bool[]>>", is_null : true),
+                        fn_func_only_ret = TDelegate("System.Func<bool>", "bool <DelegatesSignatureTest>|()"),
+                        fn_func_arr = TArray("System.Func<Math, Math.GenericStruct<Math.GenericStruct<int[]>>, Math.GenericStruct<bool[]>>[]", 1),
+
+                        fn_del = TDelegate("Math.DelegateForSignatureTest",
+                            "Math.GenericStruct<bool[]> DelegateTargetForSignatureTest (Math,Math.GenericStruct<Math.GenericStruct<int[]>>)"),
+
+                        fn_del_l = TDelegate("Math.DelegateForSignatureTest",
+                            "Math.GenericStruct<bool[]> <DelegatesSignatureTest>|(Math,Math.GenericStruct<Math.GenericStruct<int[]>>)"),
+
+                        fn_del_null = TObject("Math.DelegateForSignatureTest", is_null : true),
+                        fn_del_arr = TArray("Math.DelegateForSignatureTest[]", 2),
+                        m_obj = TObject("Math"),
+                        gs_gs = TValueType("Math.GenericStruct<Math.GenericStruct<int[]>>"),
+                        fn_void_del = TDelegate("Math.DelegateWithVoidReturn",
+                            "void DelegateTargetWithVoidReturn (Math.GenericStruct<int[]>)"),
+
+                        fn_void_del_arr = TArray("Math.DelegateWithVoidReturn[]", 1),
+                        fn_void_del_null = TObject("Math.DelegateWithVoidReturn", is_null : true),
+                        gs = TValueType("Math.GenericStruct<int[]>"),
+                        rets = TArray("Math.GenericStruct<bool[]>[]", 6)
+                }, "locals");
+
+                await CompareObjectPropertiesFor(locals, "fn_func_arr", new []
+                {
+                    TDelegate(
+                        "System.Func<Math, Math.GenericStruct<Math.GenericStruct<int[]>>, Math.GenericStruct<bool[]>>",
+                        "Math.GenericStruct<bool[]> <DelegatesSignatureTest>|(Math,Math.GenericStruct<Math.GenericStruct<int[]>>)"),
+                }, "locals#fn_func_arr");
+
+                await CompareObjectPropertiesFor(locals, "fn_del_arr", new []
+                {
+                    TDelegate(
+                            "Math.DelegateForSignatureTest",
+                            "Math.GenericStruct<bool[]> DelegateTargetForSignatureTest (Math,Math.GenericStruct<Math.GenericStruct<int[]>>)"),
+                        TDelegate(
+                            "Math.DelegateForSignatureTest",
+                            "Math.GenericStruct<bool[]> <DelegatesSignatureTest>|(Math,Math.GenericStruct<Math.GenericStruct<int[]>>)")
+                }, "locals#fn_del_arr");
+
+                await CompareObjectPropertiesFor(locals, "fn_void_del_arr", new []
+                {
+                    TDelegate(
+                        "Math.DelegateWithVoidReturn",
+                        "void DelegateTargetWithVoidReturn (Math.GenericStruct<int[]>)")
+                }, "locals#fn_void_del_arr");
+            });
+
+        [Theory]
+        [InlineData(0, 224, 8, "ActionTSignatureTest", false)]
+        [InlineData(0, 224, 8, "ActionTSignatureTest", true)]
+        [InlineData(2, 99, 8, "InnerMethod2", false)]
+        [InlineData(2, 99, 8, "InnerMethod2", true)]
+        public async Task ActionTSignatureTest(int frame, int line, int col, string bp_method, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-test.cs", line, col,
+            bp_method,
+            "window.setTimeout (function () { invoke_static_method ('[debugger-test] Math:ActionTSignatureTest'); }, 1)",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][frame]["callFrameId"].Value<string>());
+
+                await CheckProps(locals, new
+                {
+                    fn_action = TDelegate("System.Action<Math.GenericStruct<int[]>>",
+                            "void <ActionTSignatureTest>|(Math.GenericStruct<int[]>)"),
+                        fn_action_del = TDelegate("System.Action<Math.GenericStruct<int[]>>",
+                            "void DelegateTargetWithVoidReturn (Math.GenericStruct<int[]>)"),
+                        fn_action_bare = TDelegate("System.Action",
+                            "void|()"),
+
+                        fn_action_null = TObject("System.Action<Math.GenericStruct<int[]>>", is_null : true),
+
+                        fn_action_arr = TArray("System.Action<Math.GenericStruct<int[]>>[]", 3),
+
+                        gs = TValueType("Math.GenericStruct<int[]>"),
+                }, "locals");
+
+                await CompareObjectPropertiesFor(locals, "fn_action_arr", new []
+                {
+                    TDelegate(
+                            "System.Action<Math.GenericStruct<int[]>>",
+                            "void <ActionTSignatureTest>|(Math.GenericStruct<int[]>)"),
+                        TDelegate(
+                            "System.Action<Math.GenericStruct<int[]>>",
+                            "void DelegateTargetWithVoidReturn (Math.GenericStruct<int[]>)"),
+                        TObject("System.Action<Math.GenericStruct<int[]>>", is_null : true)
+                }, "locals#fn_action_arr");
+            });
+
+        [Theory]
+        [InlineData(0, 242, 8, "NestedDelegatesTest", false)]
+        [InlineData(0, 242, 8, "NestedDelegatesTest", true)]
+        [InlineData(2, 99, 8, "InnerMethod2", false)]
+        [InlineData(2, 99, 8, "InnerMethod2", true)]
+        public async Task NestedDelegatesTest(int frame, int line, int col, string bp_method, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-test.cs", line, col,
+            bp_method,
+            "window.setTimeout (function () { invoke_static_method ('[debugger-test] Math:NestedDelegatesTest'); }, 1)",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][frame]["callFrameId"].Value<string>());
+
+                await CheckProps(locals, new
+                {
+                    fn_func = TDelegate("System.Func<System.Func<int, bool>, bool>",
+                            "bool <NestedDelegatesTest>|(Func<int, bool>)"),
+                        fn_func_null = TObject("System.Func<System.Func<int, bool>, bool>", is_null : true),
+                        fn_func_arr = TArray("System.Func<System.Func<int, bool>, bool>[]", 1),
+                        fn_del_arr = TArray("System.Func<System.Func<int, bool>, bool>[]", 1),
+
+                        m_obj = TObject("Math"),
+                        fn_del_null = TObject("System.Func<System.Func<int, bool>, bool>", is_null : true),
+                        fs = TDelegate("System.Func<int, bool>",
+                            "bool <NestedDelegatesTest>|(int)")
+                }, "locals");
+
+                await CompareObjectPropertiesFor(locals, "fn_func_arr", new []
+                {
+                    TDelegate(
+                        "System.Func<System.Func<int, bool>, bool>",
+                        "bool <NestedDelegatesTest>|(System.Func<int, bool>)")
+                }, "locals#fn_func_arr");
+
+                await CompareObjectPropertiesFor(locals, "fn_del_arr", new []
+                {
+                    TDelegate(
+                        "System.Func<System.Func<int, bool>, bool>",
+                        "bool DelegateTargetForNestedFunc (Func<int, bool>)")
+                }, "locals#fn_del_arr");
+            });
+
+        [Theory]
+        [InlineData(0, 262, 8, "MethodWithDelegateArgs", false)]
+        [InlineData(0, 262, 8, "MethodWithDelegateArgs", true)]
+        [InlineData(2, 99, 8, "InnerMethod2", false)]
+        [InlineData(2, 99, 8, "InnerMethod2", true)]
+        public async Task DelegatesAsMethodArgsTest(int frame, int line, int col, string bp_method, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-test.cs", line, col,
+            bp_method,
+            "window.setTimeout (function () { invoke_static_method ('[debugger-test] Math:DelegatesAsMethodArgsTest'); }, 1)",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][frame]["callFrameId"].Value<string>());
+
+                await CheckProps(locals, new
+                {
+                    @this = TObject("Math"),
+                        dst_arr = TArray("Math.DelegateForSignatureTest[]", 2),
+                        fn_func = TDelegate("System.Func<char[], bool>",
+                            "bool <DelegatesAsMethodArgsTest>|(char[])"),
+                        fn_action = TDelegate("System.Action<Math.GenericStruct<int>[]>",
+                            "void <DelegatesAsMethodArgsTest>|(Math.GenericStruct<int>[])")
+                }, "locals");
+
+                await CompareObjectPropertiesFor(locals, "dst_arr", new []
+                {
+                    TDelegate("Math.DelegateForSignatureTest",
+                            "Math.GenericStruct<bool[]> DelegateTargetForSignatureTest (Math,Math.GenericStruct<Math.GenericStruct<int[]>>)"),
+                        TDelegate("Math.DelegateForSignatureTest",
+                            "Math.GenericStruct<bool[]> <DelegatesAsMethodArgsTest>|(Math,Math.GenericStruct<Math.GenericStruct<int[]>>)"),
+                }, "locals#dst_arr");
+            });
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task MethodWithDelegatesAsyncTest(bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-test.cs", 281, 8,
+            "MoveNext", //"DelegatesAsMethodArgsTestAsync"
+            "window.setTimeout (function () { invoke_static_method_async ('[debugger-test] Math:MethodWithDelegatesAsyncTest'); }, 1)",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                await CheckProps(locals, new
+                {
+                    @this = TObject("Math"),
+                        _dst_arr = TArray("Math.DelegateForSignatureTest[]", 2),
+                        _fn_func = TDelegate("System.Func<char[], bool>",
+                            "bool <MethodWithDelegatesAsync>|(char[])"),
+                        _fn_action = TDelegate("System.Action<Math.GenericStruct<int>[]>",
+                            "void <MethodWithDelegatesAsync>|(Math.GenericStruct<int>[])")
+                }, "locals");
+
+                await CompareObjectPropertiesFor(locals, "_dst_arr", new []
+                {
+                    TDelegate(
+                            "Math.DelegateForSignatureTest",
+                            "Math.GenericStruct<bool[]> DelegateTargetForSignatureTest (Math,Math.GenericStruct<Math.GenericStruct<int[]>>)"),
+                        TDelegate(
+                            "Math.DelegateForSignatureTest",
+                            "Math.GenericStruct<bool[]> <MethodWithDelegatesAsync>|(Math,Math.GenericStruct<Math.GenericStruct<int[]>>)"),
+                }, "locals#dst_arr");
+            });
+    }
+
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/DevToolsClient.cs b/src/mono/wasm/debugger/DebuggerTestSuite/DevToolsClient.cs
new file mode 100644
index 00000000000000..bedba131004161
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/DevToolsClient.cs
@@ -0,0 +1,167 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Net.WebSockets;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+    internal class DevToolsClient : IDisposable
+    {
+        ClientWebSocket socket;
+        List<Task> pending_ops = new List<Task>();
+        TaskCompletionSource<bool> side_exit = new TaskCompletionSource<bool>();
+        List<byte[]> pending_writes = new List<byte[]>();
+        Task current_write;
+        readonly ILogger logger;
+
+        public DevToolsClient(ILogger logger)
+            {
+                this.logger = logger;
+            }
+
+            ~DevToolsClient()
+            {
+                Dispose(false);
+            }
+
+        public void Dispose()
+        {
+            Dispose(true);
+        }
+
+        public async Task Close(CancellationToken cancellationToken)
+        {
+            if (socket.State == WebSocketState.Open)
+                await socket.CloseOutputAsync(WebSocketCloseStatus.NormalClosure, "Closing", cancellationToken);
+        }
+
+        protected virtual void Dispose(bool disposing)
+        {
+            if (disposing)
+                socket.Dispose();
+        }
+
+        Task Pump(Task task, CancellationToken token)
+        {
+            if (task != current_write)
+                return null;
+            current_write = null;
+
+            pending_writes.RemoveAt(0);
+
+            if (pending_writes.Count > 0)
+            {
+                current_write = socket.SendAsync(new ArraySegment<byte>(pending_writes[0]), WebSocketMessageType.Text, true, token);
+                return current_write;
+            }
+            return null;
+        }
+
+        async Task<string> ReadOne(CancellationToken token)
+        {
+            byte[] buff = new byte[4000];
+            var mem = new MemoryStream();
+            while (true)
+            {
+                var result = await this.socket.ReceiveAsync(new ArraySegment<byte>(buff), token);
+                if (result.MessageType == WebSocketMessageType.Close)
+                {
+                    return null;
+                }
+
+                if (result.EndOfMessage)
+                {
+                    mem.Write(buff, 0, result.Count);
+                    return Encoding.UTF8.GetString(mem.GetBuffer(), 0, (int) mem.Length);
+                }
+                else
+                {
+                    mem.Write(buff, 0, result.Count);
+                }
+            }
+        }
+
+        protected void Send(byte[] bytes, CancellationToken token)
+        {
+            pending_writes.Add(bytes);
+            if (pending_writes.Count == 1)
+            {
+                if (current_write != null)
+                    throw new Exception("Internal state is bad. current_write must be null if there are no pending writes");
+
+                current_write = socket.SendAsync(new ArraySegment<byte>(bytes), WebSocketMessageType.Text, true, token);
+                pending_ops.Add(current_write);
+            }
+        }
+
+        async Task MarkCompleteAfterward(Func<CancellationToken, Task> send, CancellationToken token)
+        {
+            try
+            {
+                await send(token);
+                side_exit.SetResult(true);
+            }
+            catch (Exception e)
+            {
+                side_exit.SetException(e);
+            }
+        }
+
+        protected async Task<bool> ConnectWithMainLoops(
+            Uri uri,
+            Func<string, CancellationToken, Task> receive,
+            Func<CancellationToken, Task> send,
+            CancellationToken token)
+        {
+
+            logger.LogDebug("connecting to {0}", uri);
+            this.socket = new ClientWebSocket();
+            this.socket.Options.KeepAliveInterval = Timeout.InfiniteTimeSpan;
+
+            await this.socket.ConnectAsync(uri, token);
+            pending_ops.Add(ReadOne(token));
+            pending_ops.Add(side_exit.Task);
+            pending_ops.Add(MarkCompleteAfterward(send, token));
+
+            while (!token.IsCancellationRequested)
+            {
+                var task = await Task.WhenAny(pending_ops);
+                if (task == pending_ops[0])
+                { //pending_ops[0] is for message reading
+                    var msg = ((Task<string>) task).Result;
+                    pending_ops[0] = ReadOne(token);
+                    Task tsk = receive(msg, token);
+                    if (tsk != null)
+                        pending_ops.Add(tsk);
+                }
+                else if (task == pending_ops[1])
+                {
+                    var res = ((Task<bool>) task).Result;
+                    //it might not throw if exiting successfull
+                    return res;
+                }
+                else
+                { //must be a background task
+                    pending_ops.Remove(task);
+                    var tsk = Pump(task, token);
+                    if (tsk != null)
+                        pending_ops.Add(tsk);
+                }
+            }
+
+            return false;
+        }
+
+        protected virtual void Log(string priority, string msg)
+        {
+            //
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/EvaluateOnCallFrameTests.cs b/src/mono/wasm/debugger/DebuggerTestSuite/EvaluateOnCallFrameTests.cs
new file mode 100644
index 00000000000000..f2836d3bc352ff
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/EvaluateOnCallFrameTests.cs
@@ -0,0 +1,214 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Newtonsoft.Json.Linq;
+using Microsoft.WebAssembly.Diagnostics;
+using Xunit;
+
+namespace DebuggerTests
+{
+
+    public class EvaluateOnCallFrameTests : DebuggerTestBase
+    {
+
+        [Fact]
+        public async Task EvaluateThisProperties() => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-evaluate-test.cs", 25, 16,
+            "run",
+            "window.setTimeout(function() { invoke_static_method_async ('[debugger-test] DebuggerTests.EvaluateTestsClass:EvaluateLocals'); })",
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                var evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "a");
+                CheckContentValue(evaluate, "1");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "b");
+                CheckContentValue(evaluate, "2");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "c");
+                CheckContentValue(evaluate, "3");
+
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "dt");
+                await CheckDateTimeValue(evaluate, new DateTime(2000, 5, 4, 3, 2, 1));
+            });
+
+        [Theory]
+        [InlineData(63, 12, "EvaluateTestsStructInstanceMethod")]
+        [InlineData(79, 12, "GenericInstanceMethodOnStruct<int>")]
+        [InlineData(102, 12, "EvaluateTestsGenericStructInstanceMethod")]
+        public async Task EvaluateThisPropertiesOnStruct(int line, int col, string method_name) => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-evaluate-test.cs", line, col,
+            method_name,
+            "window.setTimeout(function() { invoke_static_method_async ('[debugger-test] DebuggerTests.EvaluateTestsClass:EvaluateLocals'); })",
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "a");
+                CheckContentValue(evaluate, "1");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "b");
+                CheckContentValue(evaluate, "2");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "c");
+                CheckContentValue(evaluate, "3");
+
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "dateTime");
+                await CheckDateTimeValue(evaluate, new DateTime(2020, 1, 2, 3, 4, 5));
+            });
+
+        [Fact]
+        public async Task EvaluateParameters() => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-evaluate-test.cs", 25, 16,
+            "run",
+            "window.setTimeout(function() { invoke_static_method_async ('[debugger-test] DebuggerTests.EvaluateTestsClass:EvaluateLocals'); })",
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                var evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "g");
+                CheckContentValue(evaluate, "100");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "h");
+                CheckContentValue(evaluate, "200");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "valString");
+                CheckContentValue(evaluate, "test");
+            });
+
+        [Fact]
+        public async Task EvaluateLocals() => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-evaluate-test.cs", 25, 16,
+            "run",
+            "window.setTimeout(function() { invoke_static_method_async ('[debugger-test] DebuggerTests.EvaluateTestsClass:EvaluateLocals'); })",
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                var evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "d");
+                CheckContentValue(evaluate, "101");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "e");
+                CheckContentValue(evaluate, "102");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "f");
+                CheckContentValue(evaluate, "103");
+
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "local_dt");
+                await CheckDateTimeValue(evaluate, new DateTime(2010, 9, 8, 7, 6, 5));
+            });
+
+        [Fact]
+        public async Task EvaluateLocalsAsync()
+        {
+            var bp_loc = "dotnet://debugger-test.dll/debugger-array-test.cs";
+            int line = 249;
+            int col = 12;
+            var function_name = "MoveNext";
+            await CheckInspectLocalsAtBreakpointSite(
+                bp_loc, line, col,
+                function_name,
+                "window.setTimeout(function() { invoke_static_method_async ('[debugger-test] DebuggerTests.ArrayTestsClass:EntryPointForStructMethod', true); })",
+                wait_for_event_fn : async(pause_location) =>
+                {
+                    var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                    // sc_arg
+                    {
+                        var sc_arg = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "sc_arg");
+                        await CheckValue(sc_arg, TObject("DebuggerTests.SimpleClass"), "sc_arg#1");
+
+                        var sc_arg_props = await GetProperties(sc_arg["objectId"]?.Value<string>());
+                        await CheckProps(sc_arg_props, new
+                        {
+                            X = TNumber(10),
+                                Y = TNumber(45),
+                                Id = TString("sc#Id"),
+                                Color = TEnum("DebuggerTests.RGB", "Blue"),
+                                PointWithCustomGetter = TGetter("PointWithCustomGetter")
+                        }, "sc_arg_props#1");
+                    }
+
+                    // local_gs
+                    {
+                        var local_gs = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "local_gs");
+                        await CheckValue(local_gs, TValueType("DebuggerTests.SimpleGenericStruct<int>"), "local_gs#1");
+
+                        var local_gs_props = await GetProperties(local_gs["objectId"]?.Value<string>());
+                        await CheckProps(local_gs_props, new
+                        {
+                            Id = TObject("string", is_null : true),
+                                Color = TEnum("DebuggerTests.RGB", "Red"),
+                                Value = TNumber(0)
+                        }, "local_gs_props#1");
+                    }
+
+                    // step, check local_gs
+                    pause_location = await StepAndCheck(StepKind.Over, bp_loc, line + 1, col, function_name);
+                    {
+                        var local_gs = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "local_gs");
+                        await CheckValue(local_gs, TValueType("DebuggerTests.SimpleGenericStruct<int>"), "local_gs#2");
+
+                        var local_gs_props = await GetProperties(local_gs["objectId"]?.Value<string>());
+                        await CheckProps(local_gs_props, new
+                        {
+                            Id = TString("local_gs#Id"),
+                                Color = TEnum("DebuggerTests.RGB", "Green"),
+                                Value = TNumber(4)
+                        }, "local_gs_props#2");
+                    }
+
+                    // step check sc_arg.Id
+                    pause_location = await StepAndCheck(StepKind.Over, bp_loc, line + 2, col, function_name);
+                    {
+                        var sc_arg = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "sc_arg");
+                        await CheckValue(sc_arg, TObject("DebuggerTests.SimpleClass"), "sc_arg#2");
+
+                        var sc_arg_props = await GetProperties(sc_arg["objectId"]?.Value<string>());
+                        await CheckProps(sc_arg_props, new
+                        {
+                            X = TNumber(10),
+                                Y = TNumber(45),
+                                Id = TString("sc_arg#Id"), // <------- This changed
+                                Color = TEnum("DebuggerTests.RGB", "Blue"),
+                                PointWithCustomGetter = TGetter("PointWithCustomGetter")
+                        }, "sc_arg_props#2");
+                    }
+                });
+        }
+
+        [Fact]
+        public async Task EvaluateExpressions() => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-evaluate-test.cs", 25, 16,
+            "run",
+            "window.setTimeout(function() { invoke_static_method_async ('[debugger-test] DebuggerTests.EvaluateTestsClass:EvaluateLocals'); })",
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                var evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "d + e");
+                CheckContentValue(evaluate, "203");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "e + 10");
+                CheckContentValue(evaluate, "112");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "a + a");
+                CheckContentValue(evaluate, "2");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "this.a + this.b");
+                CheckContentValue(evaluate, "3");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "\"test\" + \"test\"");
+                CheckContentValue(evaluate, "testtest");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "5 + 5");
+                CheckContentValue(evaluate, "10");
+            });
+
+        [Fact]
+        public async Task EvaluateThisExpressions() => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-evaluate-test.cs", 25, 16,
+            "run",
+            "window.setTimeout(function() { invoke_static_method_async ('[debugger-test] DebuggerTests.EvaluateTestsClass:EvaluateLocals'); })",
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                var evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "this.a");
+                CheckContentValue(evaluate, "1");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "this.b");
+                CheckContentValue(evaluate, "2");
+                evaluate = await EvaluateOnCallFrame(pause_location["callFrames"][0]["callFrameId"].Value<string>(), "this.c");
+                CheckContentValue(evaluate, "3");
+
+                // FIXME: not supported yet
+                // evaluate = await EvaluateOnCallFrame (pause_location ["callFrames"][0] ["callFrameId"].Value<string> (), "this.dt");
+                // await CheckDateTimeValue (evaluate, new DateTime (2000, 5, 4, 3, 2, 1));
+            });
+    }
+
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/ExceptionTests.cs b/src/mono/wasm/debugger/DebuggerTestSuite/ExceptionTests.cs
new file mode 100644
index 00000000000000..301c4227cf4822
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/ExceptionTests.cs
@@ -0,0 +1,264 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Newtonsoft.Json.Linq;
+using Microsoft.WebAssembly.Diagnostics;
+using Xunit;
+
+namespace DebuggerTests
+{
+
+    public class ExceptionTests : DebuggerTestBase
+    {
+        [Fact]
+        public async Task ExceptionTestAll()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+            int line = 15;
+            int col = 20;
+            string entry_method_name = "[debugger-test] DebuggerTests.ExceptionTestsClass:TestExceptions";
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-exception-test.cs";
+
+                await SetPauseOnException("all");
+
+                var eval_expr = "window.setTimeout(function() { invoke_static_method (" +
+                    $"'{entry_method_name}'" +
+                    "); }, 1);";
+
+                var pause_location = await EvaluateAndCheck(eval_expr,  null, 0, 0, null);
+                //stop in the managed caught exception
+                pause_location = await WaitForManagedException(pause_location);
+
+                AssertEqual("run", pause_location["callFrames"] ? [0] ? ["functionName"]?.Value<string>(), "pause0");
+                
+                await CheckValue(pause_location["data"], JObject.FromObject(new
+                {
+                    type = "object",
+                    subtype = "error",
+                    className = "DebuggerTests.CustomException",
+                    uncaught = false
+                }), "exception0.data");
+
+                var exception_members = await GetProperties(pause_location["data"]["objectId"]?.Value<string>());
+                CheckString(exception_members, "message", "not implemented caught");
+
+                pause_location = await WaitForManagedException(null);
+                AssertEqual("run", pause_location["callFrames"] ? [0] ? ["functionName"]?.Value<string>(), "pause1");
+
+                //stop in the uncaught exception
+                CheckLocation(debugger_test_loc, 28, 16, scripts, pause_location["callFrames"][0]["location"]);
+
+                await CheckValue(pause_location["data"], JObject.FromObject(new
+                {
+                    type = "object",
+                    subtype = "error",
+                    className = "DebuggerTests.CustomException",
+                    uncaught = true
+                }), "exception1.data");
+
+                exception_members = await GetProperties(pause_location["data"]["objectId"]?.Value<string>());
+                CheckString(exception_members, "message", "not implemented uncaught");
+            });
+        }
+
+        [Fact]
+        public async Task JSExceptionTestAll()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                await SetPauseOnException("all");
+
+                var eval_expr = "window.setTimeout(function () { exceptions_test (); }, 1)";
+                var pause_location = await EvaluateAndCheck(eval_expr, null, 0, 0, "exception_caught_test", null, null);
+
+                Assert.Equal("exception", pause_location["reason"]);
+                await CheckValue(pause_location["data"], JObject.FromObject(new
+                {
+                    type = "object",
+                    subtype = "error",
+                    className = "TypeError",
+                    uncaught = false
+                }), "exception0.data");
+
+                var exception_members = await GetProperties(pause_location["data"]["objectId"]?.Value<string>());
+                CheckString(exception_members, "message", "exception caught");
+
+                pause_location = await SendCommandAndCheck(null, "Debugger.resume", null, 0, 0, "exception_uncaught_test");
+
+                Assert.Equal("exception", pause_location["reason"]);
+                await CheckValue(pause_location["data"], JObject.FromObject(new
+                {
+                    type = "object",
+                    subtype = "error",
+                    className = "RangeError",
+                    uncaught = true
+                }), "exception1.data");
+
+                exception_members = await GetProperties(pause_location["data"]["objectId"]?.Value<string>());
+                CheckString(exception_members, "message", "exception uncaught");
+            });
+        }
+
+        // FIXME? BUG? We seem to get the stack trace for Runtime.exceptionThrown at `call_method`,
+        // but JS shows the original error type, and original trace
+        [Fact]
+        public async Task ExceptionTestNone()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+            string entry_method_name = "[debugger-test] DebuggerTests.ExceptionTestsClass:TestExceptions";
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                await SetPauseOnException("none");
+
+                var eval_expr = "window.setTimeout(function() { invoke_static_method (" +
+                    $"'{entry_method_name}'" +
+                    "); }, 1);";
+
+                try
+                {
+                    await EvaluateAndCheck(eval_expr, null, 0, 0, "", null, null);
+                }
+                catch (ArgumentException ae)
+                {
+                    var eo = JObject.Parse(ae.Message);
+
+                    // AssertEqual (line, eo ["exceptionDetails"]?["lineNumber"]?.Value<int> (), "lineNumber");
+                    AssertEqual("Uncaught", eo["exceptionDetails"] ? ["text"]?.Value<string>(), "text");
+
+                    await CheckValue(eo["exceptionDetails"] ? ["exception"], JObject.FromObject(new
+                    {
+                        type = "object",
+                        subtype = "error",
+                        className = "Error" // BUG?: "DebuggerTests.CustomException"
+                    }), "exception");
+
+                    return;
+                }
+
+                Assert.True(false, "Expected to get an ArgumentException from the uncaught user exception");
+            });
+        }
+
+        [Fact]
+        public async Task JSExceptionTestNone()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                await SetPauseOnException("none");
+
+                var eval_expr = "window.setTimeout(function () { exceptions_test (); }, 1)";
+
+                int line = 44;
+                try
+                {
+                    await EvaluateAndCheck(eval_expr, null, 0, 0, "", null, null);
+                }
+                catch (ArgumentException ae)
+                {
+                    Console.WriteLine($"{ae}");
+                    var eo = JObject.Parse(ae.Message);
+
+                    AssertEqual(line, eo["exceptionDetails"] ? ["lineNumber"]?.Value<int>(), "lineNumber");
+                    AssertEqual("Uncaught", eo["exceptionDetails"] ? ["text"]?.Value<string>(), "text");
+
+                    await CheckValue(eo["exceptionDetails"] ? ["exception"], JObject.FromObject(new
+                    {
+                        type = "object",
+                        subtype = "error",
+                        className = "RangeError"
+                    }), "exception");
+
+                    return;
+                }
+
+                Assert.True(false, "Expected to get an ArgumentException from the uncaught user exception");
+            });
+        }
+
+        [Theory]
+        [InlineData("function () { exceptions_test (); }", null, 0, 0, "exception_uncaught_test", "RangeError", "exception uncaught")]
+        [InlineData("function () { invoke_static_method ('[debugger-test] DebuggerTests.ExceptionTestsClass:TestExceptions'); }",
+            "dotnet://debugger-test.dll/debugger-exception-test.cs", 28, 16, "run",
+            "DebuggerTests.CustomException", "not implemented uncaught")]
+        public async Task ExceptionTestUncaught(string eval_fn, string loc, int line, int col, string fn_name,
+            string exception_type, string exception_message)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                await SetPauseOnException("uncaught");
+
+                var eval_expr = $"window.setTimeout({eval_fn}, 1);";
+                var pause_location = await EvaluateAndCheck(eval_expr, loc, line, col, fn_name);
+
+                Assert.Equal("exception", pause_location["reason"]);
+                await CheckValue(pause_location["data"], JObject.FromObject(new
+                {
+                    type = "object",
+                    subtype = "error",
+                    className = exception_type,
+                    uncaught = true
+                }), "exception.data");
+
+                var exception_members = await GetProperties(pause_location["data"]["objectId"]?.Value<string>());
+                CheckString(exception_members, "message", exception_message);
+            });
+        }
+
+        async Task<JObject> WaitForManagedException(JObject pause_location)
+        {
+            while (true)
+            {
+                if (pause_location != null)
+                {
+                    AssertEqual("exception", pause_location ["reason"]?.Value<string> (), $"Expected to only pause because of an exception. {pause_location}");
+
+                    // return in case of a managed exception, and ignore JS ones
+                    if (pause_location["data"]?["objectId"]?.Value<string> ()?.StartsWith("dotnet:object:") == true)
+                    {
+                        break;
+                    }
+                }
+
+                pause_location = await SendCommandAndCheck(JObject.FromObject(new { }), "Debugger.resume",  null, 0, 0, null);
+            }
+
+            return pause_location;
+        }
+    }
+}
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/InspectorClient.cs b/src/mono/wasm/debugger/DebuggerTestSuite/InspectorClient.cs
new file mode 100644
index 00000000000000..d62bfc21f0aaad
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/InspectorClient.cs
@@ -0,0 +1,81 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.WebAssembly.Diagnostics
+{
+    internal class InspectorClient : DevToolsClient
+    {
+        List < (int, TaskCompletionSource<Result>) > pending_cmds = new List < (int, TaskCompletionSource<Result>) > ();
+        Func<string, JObject, CancellationToken, Task> onEvent;
+        int next_cmd_id;
+
+        public InspectorClient(ILogger logger) : base(logger) { }
+
+        Task HandleMessage(string msg, CancellationToken token)
+        {
+            var res = JObject.Parse(msg);
+            if (res["id"] == null)
+                DumpProtocol(string.Format("Event method: {0} params: {1}", res["method"], res["params"]));
+            else
+                DumpProtocol(string.Format("Response id: {0} res: {1}", res["id"], res));
+
+            if (res["id"] == null)
+                return onEvent(res["method"].Value<string>(), res["params"] as JObject, token);
+            var id = res["id"].Value<int>();
+            var idx = pending_cmds.FindIndex(e => e.Item1 == id);
+            var item = pending_cmds[idx];
+            pending_cmds.RemoveAt(idx);
+            item.Item2.SetResult(Result.FromJson(res));
+            return null;
+        }
+
+        public async Task Connect(
+            Uri uri,
+            Func<string, JObject, CancellationToken, Task> onEvent,
+            Func<CancellationToken, Task> send,
+            CancellationToken token)
+        {
+
+            this.onEvent = onEvent;
+            await ConnectWithMainLoops(uri, HandleMessage, send, token);
+        }
+
+        public Task<Result> SendCommand(string method, JObject args, CancellationToken token)
+        {
+            int id = ++next_cmd_id;
+            if (args == null)
+                args = new JObject();
+
+            var o = JObject.FromObject(new
+            {
+                id = id,
+                    method = method,
+                    @params = args
+            });
+
+            var tcs = new TaskCompletionSource<Result>();
+            pending_cmds.Add((id, tcs));
+
+            var str = o.ToString();
+            //Log ("protocol", $"SendCommand: id: {id} method: {method} params: {args}");
+
+            var bytes = Encoding.UTF8.GetBytes(str);
+            Send(bytes, token);
+            return tcs.Task;
+        }
+
+        protected virtual void DumpProtocol(string msg)
+        {
+            // Console.WriteLine (msg);
+            //XXX make logging not stupid
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/PointerTests.cs b/src/mono/wasm/debugger/DebuggerTestSuite/PointerTests.cs
new file mode 100644
index 00000000000000..2a62a67422c470
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/PointerTests.cs
@@ -0,0 +1,558 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Newtonsoft.Json.Linq;
+using Microsoft.WebAssembly.Diagnostics;
+using Xunit;
+
+namespace DebuggerTests
+{
+
+    public class PointerTests : DebuggerTestBase
+    {
+
+        public static TheoryData<string, string, string, int, string, bool> PointersTestData =>
+            new TheoryData<string, string, string, int, string, bool>
+            { { $"invoke_static_method ('[debugger-test] DebuggerTests.PointerTests:LocalPointers');", "DebuggerTests.PointerTests", "LocalPointers", 32, "LocalPointers", false },
+                { $"invoke_static_method ('[debugger-test] DebuggerTests.PointerTests:LocalPointers');", "DebuggerTests.PointerTests", "LocalPointers", 32, "LocalPointers", true },
+                { $"invoke_static_method_async ('[debugger-test] DebuggerTests.PointerTests:LocalPointersAsync');", "DebuggerTests.PointerTests", "LocalPointersAsync", 32, "MoveNext", false },
+                { $"invoke_static_method_async ('[debugger-test] DebuggerTests.PointerTests:LocalPointersAsync');", "DebuggerTests.PointerTests", "LocalPointersAsync", 32, "MoveNext", true }
+            };
+
+        [Theory]
+        [MemberDataAttribute(nameof(PointersTestData))]
+        public async Task InspectLocalPointersToPrimitiveTypes(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                var dt = new DateTime(5, 6, 7, 8, 9, 10);
+                await CheckProps(locals, new
+                {
+                    ip = TPointer("int*"),
+                        ip_null = TPointer("int*", is_null : true),
+                        ipp = TPointer("int**"),
+                        ipp_null = TPointer("int**"),
+
+                        cvalue0 = TSymbol("113 'q'"),
+                        cp = TPointer("char*"),
+
+                        vp = TPointer("void*"),
+                        vp_null = TPointer("void*", is_null : true),
+                }, "locals", num_fields : 26);
+
+                var props = await GetObjectOnLocals(locals, "ip");
+                await CheckPointerValue(props, "*ip", TNumber(5), "locals");
+
+                {
+                    var ipp_props = await GetObjectOnLocals(locals, "ipp");
+                    await CheckPointerValue(ipp_props, "*ipp", TPointer("int*"));
+
+                    ipp_props = await GetObjectOnLocals(ipp_props, "*ipp");
+                    await CheckPointerValue(ipp_props, "**ipp", TNumber(5));
+                }
+
+                {
+                    var ipp_props = await GetObjectOnLocals(locals, "ipp_null");
+                    await CheckPointerValue(ipp_props, "*ipp_null", TPointer("int*", is_null : true));
+                }
+
+                // *cp
+                props = await GetObjectOnLocals(locals, "cp");
+                await CheckPointerValue(props, "*cp", TSymbol("113 'q'"));
+            });
+
+        [Theory]
+        [MemberDataAttribute(nameof(PointersTestData))]
+        public async Task InspectLocalPointerArrays(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                var dt = new DateTime(5, 6, 7, 8, 9, 10);
+                await CheckProps(locals, new
+                {
+                    ipa = TArray("int*[]", 3)
+                }, "locals", num_fields : 26);
+
+                var ipa_elems = await CompareObjectPropertiesFor(locals, "ipa", new []
+                {
+                    TPointer("int*"),
+                        TPointer("int*"),
+                        TPointer("int*", is_null : true)
+                });
+
+                await CheckArrayElements(ipa_elems, new []
+                {
+                    TNumber(5),
+                        TNumber(10),
+                        null
+                });
+            });
+
+        [Theory]
+        [MemberDataAttribute(nameof(PointersTestData))]
+        public async Task InspectLocalDoublePointerToPrimitiveTypeArrays(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                var dt = new DateTime(5, 6, 7, 8, 9, 10);
+                await CheckProps(locals, new
+                {
+                    ippa = TArray("int**[]", 5)
+                }, "locals", num_fields : 26);
+
+                var ippa_elems = await CompareObjectPropertiesFor(locals, "ippa", new []
+                {
+                    TPointer("int**"),
+                        TPointer("int**"),
+                        TPointer("int**"),
+                        TPointer("int**"),
+                        TPointer("int**", is_null : true)
+                });
+
+                {
+                    var actual_elems = await CheckArrayElements(ippa_elems, new []
+                    {
+                        TPointer("int*"),
+                            TPointer("int*", is_null : true),
+                            TPointer("int*"),
+                            TPointer("int*", is_null : true),
+                            null
+                    });
+
+                    var val = await GetObjectOnLocals(actual_elems[0], "*[0]");
+                    await CheckPointerValue(val, "**[0]", TNumber(5));
+
+                    val = await GetObjectOnLocals(actual_elems[2], "*[2]");
+                    await CheckPointerValue(val, "**[2]", TNumber(5));
+                }
+            });
+
+        [Theory]
+        [MemberDataAttribute(nameof(PointersTestData))]
+        public async Task InspectLocalPointersToValueTypes(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                var dt = new DateTime(5, 6, 7, 8, 9, 10);
+                await CheckProps(locals, new
+                {
+                    dt = TValueType("System.DateTime", dt.ToString()),
+                        dtp = TPointer("System.DateTime*"),
+                        dtp_null = TPointer("System.DateTime*", is_null : true),
+
+                        gsp = TPointer("DebuggerTests.GenericStructWithUnmanagedT<System.DateTime>*"),
+                        gsp_null = TPointer("DebuggerTests.GenericStructWithUnmanagedT<System.DateTime>*")
+                }, "locals", num_fields : 26);
+
+                await CheckDateTime(locals, "dt", dt);
+
+                // *dtp
+                var props = await GetObjectOnLocals(locals, "dtp");
+                await CheckDateTime(props, "*dtp", dt);
+
+                var gsp_props = await GetObjectOnLocals(locals, "gsp");
+                await CheckPointerValue(gsp_props, "*gsp", TValueType("DebuggerTests.GenericStructWithUnmanagedT<System.DateTime>"), "locals#gsp");
+
+                {
+                    var gs_dt = new DateTime(1, 2, 3, 4, 5, 6);
+
+                    var gsp_deref_props = await GetObjectOnLocals(gsp_props, "*gsp");
+                    await CheckProps(gsp_deref_props, new
+                    {
+                        Value = TValueType("System.DateTime", gs_dt.ToString()),
+                            IntField = TNumber(4),
+                            DTPP = TPointer("System.DateTime**")
+                    }, "locals#gsp#deref");
+                    {
+                        var dtpp_props = await GetObjectOnLocals(gsp_deref_props, "DTPP");
+                        await CheckPointerValue(dtpp_props, "*DTPP", TPointer("System.DateTime*"), "locals#*gsp");
+
+                        var dtpp_deref_props = await GetObjectOnLocals(dtpp_props, "*DTPP");
+                        await CheckDateTime(dtpp_deref_props, "**DTPP", dt);
+                    }
+                }
+
+                // gsp_null
+                var gsp_w_n_props = await GetObjectOnLocals(locals, "gsp_null");
+                await CheckPointerValue(gsp_w_n_props, "*gsp_null", TValueType("DebuggerTests.GenericStructWithUnmanagedT<System.DateTime>"), "locals#gsp");
+
+                {
+                    var gs_dt = new DateTime(1, 2, 3, 4, 5, 6);
+
+                    var gsp_deref_props = await GetObjectOnLocals(gsp_w_n_props, "*gsp_null");
+                    await CheckProps(gsp_deref_props, new
+                    {
+                        Value = TValueType("System.DateTime", gs_dt.ToString()),
+                            IntField = TNumber(4),
+                            DTPP = TPointer("System.DateTime**")
+                    }, "locals#gsp#deref");
+                    {
+                        var dtpp_props = await GetObjectOnLocals(gsp_deref_props, "DTPP");
+                        await CheckPointerValue(dtpp_props, "*DTPP", TPointer("System.DateTime*", is_null : true), "locals#*gsp");
+                    }
+                }
+            });
+
+        [Theory]
+        [MemberDataAttribute(nameof(PointersTestData))]
+        public async Task InspectLocalPointersToValueTypeArrays(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                var dt = new DateTime(5, 6, 7, 8, 9, 10);
+                await CheckProps(locals, new
+                {
+                    dtpa = TArray("System.DateTime*[]", 2)
+                }, "locals", num_fields : 26);
+
+                // dtpa
+                var dtpa_elems = (await CompareObjectPropertiesFor(locals, "dtpa", new []
+                {
+                    TPointer("System.DateTime*"),
+                        TPointer("System.DateTime*", is_null : true)
+                }));
+                {
+                    var actual_elems = await CheckArrayElements(dtpa_elems, new []
+                    {
+                        TValueType("System.DateTime", dt.ToString()),
+                            null
+                    });
+
+                    await CheckDateTime(actual_elems[0], "*[0]", dt);
+                }
+            });
+
+        [Theory]
+        [MemberDataAttribute(nameof(PointersTestData))]
+        public async Task InspectLocalPointersToGenericValueTypeArrays(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                var dt = new DateTime(5, 6, 7, 8, 9, 10);
+                await CheckProps(locals, new
+                {
+                    gspa = TArray("DebuggerTests.GenericStructWithUnmanagedT<System.DateTime>*[]", 3),
+                }, "locals", num_fields : 26);
+
+                // dtpa
+                var gspa_elems = await CompareObjectPropertiesFor(locals, "gspa", new []
+                {
+                    TPointer("DebuggerTests.GenericStructWithUnmanagedT<System.DateTime>*", is_null : true),
+                        TPointer("DebuggerTests.GenericStructWithUnmanagedT<System.DateTime>*"),
+                        TPointer("DebuggerTests.GenericStructWithUnmanagedT<System.DateTime>*"),
+                });
+                {
+                    var gs_dt = new DateTime(1, 2, 3, 4, 5, 6);
+                    var actual_elems = await CheckArrayElements(gspa_elems, new []
+                    {
+                        null,
+                        TValueType("DebuggerTests.GenericStructWithUnmanagedT<System.DateTime>"),
+                        TValueType("DebuggerTests.GenericStructWithUnmanagedT<System.DateTime>")
+                    });
+
+                    // *[1]
+                    {
+                        var gsp_deref_props = await GetObjectOnLocals(actual_elems[1], "*[1]");
+                        await CheckProps(gsp_deref_props, new
+                        {
+                            Value = TValueType("System.DateTime", gs_dt.ToString()),
+                                IntField = TNumber(4),
+                                DTPP = TPointer("System.DateTime**")
+                        }, "locals#gsp#deref");
+                        {
+                            var dtpp_props = await GetObjectOnLocals(gsp_deref_props, "DTPP");
+                            await CheckPointerValue(dtpp_props, "*DTPP", TPointer("System.DateTime*"), "locals#*gsp");
+
+                            dtpp_props = await GetObjectOnLocals(dtpp_props, "*DTPP");
+                            await CheckDateTime(dtpp_props, "**DTPP", dt);
+                        }
+                    }
+
+                    // *[2]
+                    {
+                        var gsp_deref_props = await GetObjectOnLocals(actual_elems[2], "*[2]");
+                        await CheckProps(gsp_deref_props, new
+                        {
+                            Value = TValueType("System.DateTime", gs_dt.ToString()),
+                                IntField = TNumber(4),
+                                DTPP = TPointer("System.DateTime**")
+                        }, "locals#gsp#deref");
+                        {
+                            var dtpp_props = await GetObjectOnLocals(gsp_deref_props, "DTPP");
+                            await CheckPointerValue(dtpp_props, "*DTPP", TPointer("System.DateTime*", is_null : true), "locals#*gsp");
+                        }
+                    }
+                }
+            });
+
+        [Theory]
+        [MemberDataAttribute(nameof(PointersTestData))]
+        public async Task InspectLocalDoublePointersToValueTypeArrays(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                var dt = new DateTime(5, 6, 7, 8, 9, 10);
+                await CheckProps(locals, new
+                {
+                    dtppa = TArray("System.DateTime**[]", 3),
+                }, "locals", num_fields : 26);
+
+                // DateTime**[] dtppa = new DateTime**[] { &dtp, &dtp_null, null };
+                var dtppa_elems = (await CompareObjectPropertiesFor(locals, "dtppa", new []
+                {
+                    TPointer("System.DateTime**"),
+                        TPointer("System.DateTime**"),
+                        TPointer("System.DateTime**", is_null : true)
+                }));
+
+                var exp_elems = new []
+                {
+                    TPointer("System.DateTime*"),
+                    TPointer("System.DateTime*", is_null : true),
+                    null
+                };
+
+                var actual_elems = new JToken[exp_elems.Length];
+                for (int i = 0; i < exp_elems.Length; i++)
+                {
+                    if (exp_elems[i] != null)
+                    {
+                        actual_elems[i] = await GetObjectOnLocals(dtppa_elems, i.ToString());
+                        await CheckPointerValue(actual_elems[i], $"*[{i}]", exp_elems[i], $"dtppa->");
+                    }
+                }
+            });
+
+        [Theory]
+        [MemberDataAttribute(nameof(PointersTestData))]
+        public async Task InspectLocalPointersInClasses(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                var dt = new DateTime(5, 6, 7, 8, 9, 10);
+                await CheckProps(locals, new
+                {
+                    cwp = TObject("DebuggerTests.GenericClassWithPointers<System.DateTime>"),
+                        cwp_null = TObject("DebuggerTests.GenericClassWithPointers<System.DateTime>")
+                }, "locals", num_fields : 26);
+
+                var cwp_props = await GetObjectOnLocals(locals, "cwp");
+                var ptr_props = await GetObjectOnLocals(cwp_props, "Ptr");
+                await CheckDateTime(ptr_props, "*Ptr", dt);
+            });
+
+        public static TheoryData<string, string, string, int, string, bool> PointersAsMethodArgsTestData =>
+            new TheoryData<string, string, string, int, string, bool>
+            { { $"invoke_static_method ('[debugger-test] DebuggerTests.PointerTests:LocalPointers');", "DebuggerTests.PointerTests", "PointersAsArgsTest", 2, "PointersAsArgsTest", false },
+                { $"invoke_static_method ('[debugger-test] DebuggerTests.PointerTests:LocalPointers');", "DebuggerTests.PointerTests", "PointersAsArgsTest", 2, "PointersAsArgsTest", true },
+            };
+
+        [Theory]
+        [MemberDataAttribute(nameof(PointersAsMethodArgsTestData))]
+        public async Task InspectPrimitiveTypePointersAsMethodArgs(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                var dt = new DateTime(5, 6, 7, 8, 9, 10);
+                await CheckProps(locals, new
+                {
+                    ip = TPointer("int*"),
+                        ipp = TPointer("int**"),
+                        ipa = TArray("int*[]", 3),
+                        ippa = TArray("int**[]", 5)
+                }, "locals", num_fields : 8);
+
+                // ip
+                var props = await GetObjectOnLocals(locals, "ip");
+                await CheckPointerValue(props, "*ip", TNumber(5), "locals");
+
+                // ipp
+                var ipp_props = await GetObjectOnLocals(locals, "ipp");
+                await CheckPointerValue(ipp_props, "*ipp", TPointer("int*"));
+
+                ipp_props = await GetObjectOnLocals(ipp_props, "*ipp");
+                await CheckPointerValue(ipp_props, "**ipp", TNumber(5));
+
+                // ipa
+                var ipa_elems = await CompareObjectPropertiesFor(locals, "ipa", new []
+                {
+                    TPointer("int*"),
+                        TPointer("int*"),
+                        TPointer("int*", is_null : true)
+                });
+
+                await CheckArrayElements(ipa_elems, new []
+                {
+                    TNumber(5),
+                        TNumber(10),
+                        null
+                });
+
+                // ippa
+                var ippa_elems = await CompareObjectPropertiesFor(locals, "ippa", new []
+                {
+                    TPointer("int**"),
+                        TPointer("int**"),
+                        TPointer("int**"),
+                        TPointer("int**"),
+                        TPointer("int**", is_null : true)
+                });
+
+                {
+                    var actual_elems = await CheckArrayElements(ippa_elems, new []
+                    {
+                        TPointer("int*"),
+                            TPointer("int*", is_null : true),
+                            TPointer("int*"),
+                            TPointer("int*", is_null : true),
+                            null
+                    });
+
+                    var val = await GetObjectOnLocals(actual_elems[0], "*[0]");
+                    await CheckPointerValue(val, "**[0]", TNumber(5));
+
+                    val = await GetObjectOnLocals(actual_elems[2], "*[2]");
+                    await CheckPointerValue(val, "**[2]", TNumber(5));
+                }
+            });
+
+        [Theory]
+        [MemberDataAttribute(nameof(PointersAsMethodArgsTestData))]
+        public async Task InspectValueTypePointersAsMethodArgs(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                var dt = new DateTime(5, 6, 7, 8, 9, 10);
+                await CheckProps(locals, new
+                {
+                    dtp = TPointer("System.DateTime*"),
+                        dtpp = TPointer("System.DateTime**"),
+                        dtpa = TArray("System.DateTime*[]", 2),
+                        dtppa = TArray("System.DateTime**[]", 3)
+                }, "locals", num_fields : 8);
+
+                // *dtp
+                var dtp_props = await GetObjectOnLocals(locals, "dtp");
+                await CheckDateTime(dtp_props, "*dtp", dt);
+
+                // *dtpp
+                var dtpp_props = await GetObjectOnLocals(locals, "dtpp");
+                await CheckPointerValue(dtpp_props, "*dtpp", TPointer("System.DateTime*"), "locals");
+
+                dtpp_props = await GetObjectOnLocals(dtpp_props, "*dtpp");
+                await CheckDateTime(dtpp_props, "**dtpp", dt);
+
+                // dtpa
+                var dtpa_elems = (await CompareObjectPropertiesFor(locals, "dtpa", new []
+                {
+                    TPointer("System.DateTime*"),
+                        TPointer("System.DateTime*", is_null : true)
+                }));
+                {
+                    var actual_elems = await CheckArrayElements(dtpa_elems, new []
+                    {
+                        TValueType("System.DateTime", dt.ToString()),
+                            null
+                    });
+
+                    await CheckDateTime(actual_elems[0], "*[0]", dt);
+                }
+
+                // dtppa = new DateTime**[] { &dtp, &dtp_null, null };
+                var dtppa_elems = (await CompareObjectPropertiesFor(locals, "dtppa", new []
+                {
+                    TPointer("System.DateTime**"),
+                        TPointer("System.DateTime**"),
+                        TPointer("System.DateTime**", is_null : true)
+                }));
+
+                var exp_elems = new []
+                {
+                    TPointer("System.DateTime*"),
+                    TPointer("System.DateTime*", is_null : true),
+                    null
+                };
+
+                await CheckArrayElements(dtppa_elems, exp_elems);
+            });
+
+        [Theory]
+        [InlineData("invoke_static_method ('[debugger-test] Math:UseComplex', 0, 0);", "Math", "UseComplex", 3, "UseComplex", false)]
+        [InlineData("invoke_static_method ('[debugger-test] Math:UseComplex', 0, 0);", "Math", "UseComplex", 3, "UseComplex", true)]
+        public async Task DerefNonPointerObject(string eval_fn, string type, string method, int line_offset, string bp_function_name, bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            type, method, line_offset, bp_function_name,
+            "window.setTimeout(function() { " + eval_fn + " })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+
+                // this will generate the object ids
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                var complex = GetAndAssertObjectWithName(locals, "complex");
+
+                // try to deref the non-pointer object, as a pointer
+                await GetProperties(complex["value"]["objectId"].Value<string>().Replace(":object:", ":pointer:"), expect_ok: false);
+
+                // try to deref an invalid pointer id
+                await GetProperties("dotnet:pointer:123897", expect_ok: false);
+            });
+
+        async Task<JToken[]> CheckArrayElements(JToken array, JToken[] exp_elems)
+        {
+            var actual_elems = new JToken[exp_elems.Length];
+            for (int i = 0; i < exp_elems.Length; i++)
+            {
+                if (exp_elems[i] != null)
+                {
+                    actual_elems[i] = await GetObjectOnLocals(array, i.ToString());
+                    await CheckPointerValue(actual_elems[i], $"*[{i}]", exp_elems[i], $"dtppa->");
+                }
+            }
+
+            return actual_elems;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/Support.cs b/src/mono/wasm/debugger/DebuggerTestSuite/Support.cs
new file mode 100644
index 00000000000000..ac8570978353c6
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/Support.cs
@@ -0,0 +1,1039 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Net.WebSockets;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using Microsoft.WebAssembly.Diagnostics;
+using Xunit;
+
+namespace DebuggerTests
+{
+    class Inspector
+    {
+        // InspectorClient client;
+        Dictionary<string, TaskCompletionSource<JObject>> notifications = new Dictionary<string, TaskCompletionSource<JObject>>();
+        Dictionary<string, Func<JObject, CancellationToken, Task>> eventListeners = new Dictionary<string, Func<JObject, CancellationToken, Task>>();
+
+        public const string PAUSE = "pause";
+        public const string READY = "ready";
+
+        public Task<JObject> WaitFor(string what)
+        {
+            if (notifications.ContainsKey(what))
+                throw new Exception($"Invalid internal state, waiting for {what} while another wait is already setup");
+            var n = new TaskCompletionSource<JObject>();
+            notifications[what] = n;
+            return n.Task;
+        }
+
+        void NotifyOf(string what, JObject args)
+        {
+            if (!notifications.ContainsKey(what))
+                throw new Exception($"Invalid internal state, notifying of {what}, but nobody waiting");
+            notifications[what].SetResult(args);
+            notifications.Remove(what);
+        }
+
+        public void On(string evtName, Func<JObject, CancellationToken, Task> cb)
+        {
+            eventListeners[evtName] = cb;
+        }
+
+        void FailAllWaitersWithException(JObject exception)
+        {
+            foreach (var tcs in notifications.Values)
+                tcs.SetException(new ArgumentException(exception.ToString()));
+        }
+
+        async Task OnMessage(string method, JObject args, CancellationToken token)
+        {
+            //System.Console.WriteLine("OnMessage " + method + args);
+            switch (method)
+            {
+                case "Debugger.paused":
+                    NotifyOf(PAUSE, args);
+                    break;
+                case "Mono.runtimeReady":
+                    NotifyOf(READY, args);
+                    break;
+                case "Runtime.consoleAPICalled":
+                    Console.WriteLine("CWL: {0}", args?["args"] ? [0] ? ["value"]);
+                    break;
+            }
+            if (eventListeners.ContainsKey(method))
+                await eventListeners[method](args, token);
+            else if (String.Compare(method, "Runtime.exceptionThrown") == 0)
+                FailAllWaitersWithException(args);
+        }
+
+        public async Task Ready(Func<InspectorClient, CancellationToken, Task> cb = null, TimeSpan? span = null)
+        {
+            using(var cts = new CancellationTokenSource())
+            {
+                cts.CancelAfter(span?.Milliseconds ?? 60 * 1000); //tests have 1 minute to complete by default
+                var uri = new Uri($"ws://{TestHarnessProxy.Endpoint.Authority}/launch-chrome-and-connect");
+                using var loggerFactory = LoggerFactory.Create(
+                    builder => builder.AddConsole().AddFilter(null, LogLevel.Information));
+                using(var client = new InspectorClient(loggerFactory.CreateLogger<Inspector>()))
+                {
+                    await client.Connect(uri, OnMessage, async token =>
+                    {
+                    Task[] init_cmds = {
+                    client.SendCommand("Profiler.enable", null, token),
+                    client.SendCommand("Runtime.enable", null, token),
+                    client.SendCommand("Debugger.enable", null, token),
+                    client.SendCommand("Runtime.runIfWaitingForDebugger", null, token),
+                    WaitFor(READY),
+                        };
+                        // await Task.WhenAll (init_cmds);
+                        Console.WriteLine("waiting for the runtime to be ready");
+                        await init_cmds[4];
+                        Console.WriteLine("runtime ready, TEST TIME");
+                        if (cb != null)
+                        {
+                            Console.WriteLine("await cb(client, token)");
+                            await cb(client, token);
+                        }
+
+                    }, cts.Token);
+                    await client.Close(cts.Token);
+                }
+            }
+        }
+    }
+
+    public class DebuggerTestBase
+    {
+        protected Task startTask;
+
+        static string FindTestPath()
+        {
+            //FIXME how would I locate it otherwise?
+            var test_path = Environment.GetEnvironmentVariable("TEST_SUITE_PATH");
+            //Lets try to guest
+            if (test_path != null && Directory.Exists(test_path))
+                return test_path;
+
+            var cwd = Environment.CurrentDirectory;
+            Console.WriteLine("guessing from {0}", cwd);
+            //tests run from DebuggerTestSuite/bin/Debug/netcoreapp2.1
+            var new_path = Path.Combine(cwd, "../../../../bin/debugger-test-suite");
+            if (File.Exists(Path.Combine(new_path, "debugger-driver.html")))
+                return new_path;
+
+            throw new Exception("Missing TEST_SUITE_PATH env var and could not guess path from CWD");
+        }
+
+        static string[] PROBE_LIST = {
+            "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome",
+            "/Applications/Microsoft Edge.app/Contents/MacOS/Microsoft Edge",
+            "/Applications/Google Chrome Canary.app/Contents/MacOS/Google Chrome Canary",
+            "/usr/bin/chromium",
+            "/usr/bin/chromium-browser",
+        };
+        static string chrome_path;
+
+        static string FindChromePath()
+        {
+            if (chrome_path != null)
+                return chrome_path;
+
+            foreach (var s in PROBE_LIST)
+            {
+                if (File.Exists(s))
+                {
+                    chrome_path = s;
+                    Console.WriteLine($"Using chrome path: ${s}");
+                    return s;
+                }
+            }
+            throw new Exception("Could not find an installed Chrome to use");
+        }
+
+        public DebuggerTestBase(string driver = "debugger-driver.html")
+        {
+            startTask = TestHarnessProxy.Start(FindChromePath(), FindTestPath(), driver);
+        }
+
+        public Task Ready() => startTask;
+
+        internal DebugTestContext ctx;
+        internal Dictionary<string, string> dicScriptsIdToUrl;
+        internal Dictionary<string, string> dicFileToUrl;
+        internal Dictionary<string, string> SubscribeToScripts(Inspector insp)
+        {
+            dicScriptsIdToUrl = new Dictionary<string, string>();
+            dicFileToUrl = new Dictionary<string, string>();
+            insp.On("Debugger.scriptParsed", async(args, c) =>
+            {
+                var script_id = args?["scriptId"]?.Value<string>();
+                var url = args["url"]?.Value<string>();
+                if (script_id.StartsWith("dotnet://"))
+                {
+                    var dbgUrl = args["dotNetUrl"]?.Value<string>();
+                    var arrStr = dbgUrl.Split("/");
+                    dbgUrl = arrStr[0] + "/" + arrStr[1] + "/" + arrStr[2] + "/" + arrStr[arrStr.Length - 1];
+                    dicScriptsIdToUrl[script_id] = dbgUrl;
+                    dicFileToUrl[dbgUrl] = args["url"]?.Value<string>();
+                }
+                else if (!String.IsNullOrEmpty(url))
+                {
+                    dicFileToUrl[new Uri(url).AbsolutePath] = url;
+                }
+                await Task.FromResult(0);
+            });
+            return dicScriptsIdToUrl;
+        }
+
+        internal async Task CheckInspectLocalsAtBreakpointSite(string url_key, int line, int column, string function_name, string eval_expression,
+            Action<JToken> test_fn = null, Func<JObject, Task> wait_for_event_fn = null, bool use_cfo = false)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+
+                var bp = await SetBreakpoint(url_key, line, column);
+
+                await EvaluateAndCheck(
+                    eval_expression, url_key, line, column,
+                    function_name,
+                    wait_for_event_fn : async(pause_location) =>
+                    {
+                        //make sure we're on the right bp
+
+                        Assert.Equal(bp.Value["breakpointId"]?.ToString(), pause_location["hitBreakpoints"] ? [0]?.Value<string>());
+
+                        var top_frame = pause_location["callFrames"][0];
+
+                        var scope = top_frame["scopeChain"][0];
+                        Assert.Equal("dotnet:scope:0", scope["object"]["objectId"]);
+                        if (wait_for_event_fn != null)
+                            await wait_for_event_fn(pause_location);
+                        else
+                            await Task.CompletedTask;
+                    },
+                    locals_fn: (locals) =>
+                    {
+                        if (test_fn != null)
+                            test_fn(locals);
+                    }
+                );
+            });
+        }
+
+        // sets breakpoint by method name and line offset
+        internal async Task CheckInspectLocalsAtBreakpointSite(string type, string method, int line_offset, string bp_function_name, string eval_expression,
+            Action<JToken> locals_fn = null, Func<JObject, Task> wait_for_event_fn = null, bool use_cfo = false, string assembly = "debugger-test.dll", int col = 0)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+
+                var bp = await SetBreakpointInMethod(assembly, type, method, line_offset, col);
+
+                var args = JObject.FromObject(new { expression = eval_expression });
+                var res = await ctx.cli.SendCommand("Runtime.evaluate", args, ctx.token);
+                if (!res.IsOk)
+                {
+                    Console.WriteLine($"Failed to run command {method} with args: {args?.ToString ()}\nresult: {res.Error.ToString ()}");
+                    Assert.True(false, $"SendCommand for {method} failed with {res.Error.ToString ()}");
+                }
+
+                var pause_location = await ctx.insp.WaitFor(Inspector.PAUSE);
+
+                if (bp_function_name != null)
+                    Assert.Equal(bp_function_name, pause_location["callFrames"] ? [0] ? ["functionName"]?.Value<string>());
+
+                Assert.Equal(bp.Value["breakpointId"]?.ToString(), pause_location["hitBreakpoints"] ? [0]?.Value<string>());
+
+                var top_frame = pause_location["callFrames"][0];
+
+                var scope = top_frame["scopeChain"][0];
+                Assert.Equal("dotnet:scope:0", scope["object"]["objectId"]);
+
+                if (wait_for_event_fn != null)
+                    await wait_for_event_fn(pause_location);
+
+                if (locals_fn != null)
+                {
+                    var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                    locals_fn(locals);
+                }
+            });
+        }
+
+        internal void CheckLocation(string script_loc, int line, int column, Dictionary<string, string> scripts, JToken location)
+        {
+            var loc_str = $"{ scripts[location["scriptId"].Value<string>()] }" +
+                $"#{ location ["lineNumber"].Value<int> () }" +
+                $"#{ location ["columnNumber"].Value<int> () }";
+
+            var expected_loc_str = $"{script_loc}#{line}#{column}";
+            Assert.Equal(expected_loc_str, loc_str);
+        }
+
+        internal void CheckNumber<T>(JToken locals, string name, T value)
+        {
+            foreach (var l in locals)
+            {
+                if (name != l["name"]?.Value<string>())
+                    continue;
+                var val = l["value"];
+                Assert.Equal("number", val["type"]?.Value<string>());
+                Assert.Equal(value, val["value"].Value<T>());
+                Assert.Equal(value.ToString(), val["description"].Value<T>().ToString());
+                return;
+            }
+            Assert.True(false, $"Could not find variable '{name}'");
+        }
+
+        internal void CheckString(JToken locals, string name, string value)
+        {
+            var l = GetAndAssertObjectWithName(locals, name);
+            CheckValue(l["value"], TString(value), name).Wait();
+        }
+
+        internal JToken CheckSymbol(JToken locals, string name, string value)
+        {
+            var l = GetAndAssertObjectWithName(locals, name);
+            CheckValue(l["value"], TSymbol(value), name).Wait();
+            return l;
+        }
+
+        internal JToken CheckObject(JToken locals, string name, string class_name, string subtype = null, bool is_null = false)
+        {
+            var l = GetAndAssertObjectWithName(locals, name);
+            var val = l["value"];
+            CheckValue(val, TObject(class_name, is_null: is_null), name).Wait();
+            Assert.True(val["isValueType"] == null || !val["isValueType"].Value<bool>());
+
+            return l;
+        }
+
+        internal async Task<JToken> CheckPointerValue(JToken locals, string name, JToken expected, string label = null)
+        {
+            var l = GetAndAssertObjectWithName(locals, name);
+            await CheckValue(l["value"], expected, $"{label ?? String.Empty}-{name}");
+            return l;
+        }
+
+        internal async Task CheckDateTime(JToken locals, string name, DateTime expected)
+        {
+            var obj = GetAndAssertObjectWithName(locals, name);
+            await CheckDateTimeValue(obj["value"], expected);
+        }
+
+        internal async Task CheckDateTimeValue(JToken value, DateTime expected)
+        {
+            await CheckDateTimeMembers(value, expected);
+
+            var res = await InvokeGetter(JObject.FromObject(new { value = value }), "Date");
+            await CheckDateTimeMembers(res.Value["result"], expected.Date);
+
+            // FIXME: check some float properties too
+
+            async Task CheckDateTimeMembers(JToken v, DateTime exp_dt)
+            {
+                AssertEqual("System.DateTime", v["className"]?.Value<string>(), "className");
+                AssertEqual(exp_dt.ToString(), v["description"]?.Value<string>(), "description");
+
+                var members = await GetProperties(v["objectId"]?.Value<string>());
+
+                // not checking everything
+                CheckNumber(members, "Year", exp_dt.Year);
+                CheckNumber(members, "Month", exp_dt.Month);
+                CheckNumber(members, "Day", exp_dt.Day);
+                CheckNumber(members, "Hour", exp_dt.Hour);
+                CheckNumber(members, "Minute", exp_dt.Minute);
+                CheckNumber(members, "Second", exp_dt.Second);
+            }
+        }
+
+        internal JToken CheckBool(JToken locals, string name, bool expected)
+        {
+            var l = GetAndAssertObjectWithName(locals, name);
+            CheckValue(l["value"], TBool(expected), name).Wait();
+            return l;
+        }
+
+        internal void CheckContentValue(JToken token, string value)
+        {
+            var val = token["value"].Value<string>();
+            Assert.Equal(value, val);
+        }
+
+        internal JToken CheckValueType(JToken locals, string name, string class_name)
+        {
+            var l = GetAndAssertObjectWithName(locals, name);
+            CheckValue(l["value"], TValueType(class_name), name).Wait();
+            return l;
+        }
+
+        internal JToken CheckEnum(JToken locals, string name, string class_name, string descr)
+        {
+            var l = GetAndAssertObjectWithName(locals, name);
+            CheckValue(l["value"], TEnum(class_name, descr), name).Wait();
+            return l;
+        }
+
+        internal void CheckArray(JToken locals, string name, string class_name, int length)
+           => CheckValue(
+                GetAndAssertObjectWithName(locals, name)["value"],
+                TArray(class_name, length), name).Wait();
+
+        internal JToken GetAndAssertObjectWithName(JToken obj, string name)
+        {
+            var l = obj.FirstOrDefault(jt => jt["name"]?.Value<string>() == name);
+            if (l == null)
+                Assert.True(false, $"Could not find variable '{name}'");
+            return l;
+        }
+
+        internal async Task<Result> SendCommand(string method, JObject args)
+        {
+            var res = await ctx.cli.SendCommand(method, args, ctx.token);
+            if (!res.IsOk)
+            {
+                Console.WriteLine($"Failed to run command {method} with args: {args?.ToString ()}\nresult: {res.Error.ToString ()}");
+                Assert.True(false, $"SendCommand for {method} failed with {res.Error.ToString ()}");
+            }
+            return res;
+        }
+
+        internal async Task<Result> Evaluate(string expression)
+        {
+            return await SendCommand("Runtime.evaluate", JObject.FromObject(new { expression = expression }));
+        }
+
+        internal void AssertLocation(JObject args, string methodName)
+        {
+            Assert.Equal(methodName, args["callFrames"] ? [0] ? ["functionName"]?.Value<string>());
+        }
+
+        // Place a breakpoint in the given method and run until its hit
+        // Return the Debugger.paused data
+        internal async Task<JObject> RunUntil(string methodName)
+        {
+            await SetBreakpointInMethod("debugger-test", "DebuggerTest", methodName);
+            // This will run all the tests until it hits the bp
+            await Evaluate("window.setTimeout(function() { invoke_run_all (); }, 1);");
+            var wait_res = await ctx.insp.WaitFor(Inspector.PAUSE);
+            AssertLocation(wait_res, "locals_inner");
+            return wait_res;
+        }
+
+        internal async Task<Result> InvokeGetter(JToken obj, object arguments, string fn = "function(e){return this[e]}", bool expect_ok = true, bool? returnByValue = null)
+        {
+            var req = JObject.FromObject(new
+            {
+                functionDeclaration = fn,
+                objectId            = obj["value"]?["objectId"]?.Value<string>(),
+                arguments           = new[] { new { value = arguments } }
+            });
+            if (returnByValue != null)
+                req["returnByValue"] = returnByValue.Value;
+
+            var res = await ctx.cli.SendCommand("Runtime.callFunctionOn", req, ctx.token);
+            Assert.True(expect_ok == res.IsOk, $"InvokeGetter failed for {req} with {res}");
+
+            return res;
+        }
+
+        internal async Task<JObject> StepAndCheck(StepKind kind, string script_loc, int line, int column, string function_name,
+            Func<JObject, Task> wait_for_event_fn = null, Action<JToken> locals_fn = null, int times = 1)
+        {
+            for (int i = 0; i < times - 1; i++)
+            {
+                await SendCommandAndCheck(null, $"Debugger.step{kind.ToString ()}", null, -1, -1, null);
+            }
+
+            // Check for method/line etc only at the last step
+            return await SendCommandAndCheck(
+                null, $"Debugger.step{kind.ToString ()}", script_loc, line, column, function_name,
+                wait_for_event_fn : wait_for_event_fn,
+                locals_fn : locals_fn);
+        }
+
+        internal async Task<JObject> EvaluateAndCheck(string expression, string script_loc, int line, int column, string function_name,
+            Func<JObject, Task> wait_for_event_fn = null, Action<JToken> locals_fn = null) => await SendCommandAndCheck(
+            JObject.FromObject(new { expression = expression }),
+            "Runtime.evaluate", script_loc, line, column, function_name,
+            wait_for_event_fn : wait_for_event_fn,
+            locals_fn : locals_fn);
+
+        internal async Task<JObject> SendCommandAndCheck(JObject args, string method, string script_loc, int line, int column, string function_name,
+            Func<JObject, Task> wait_for_event_fn = null, Action<JToken> locals_fn = null, string waitForEvent = Inspector.PAUSE)
+        {
+            var res = await ctx.cli.SendCommand(method, args, ctx.token);
+            if (!res.IsOk)
+            {
+                Console.WriteLine($"Failed to run command {method} with args: {args?.ToString ()}\nresult: {res.Error.ToString ()}");
+                Assert.True(false, $"SendCommand for {method} failed with {res.Error.ToString ()}");
+            }
+
+            var wait_res = await ctx.insp.WaitFor(waitForEvent);
+
+            if (function_name != null)
+                Assert.Equal(function_name, wait_res["callFrames"] ? [0] ? ["functionName"]?.Value<string>());
+
+            if (script_loc != null)
+                CheckLocation(script_loc, line, column, ctx.scripts, wait_res["callFrames"][0]["location"]);
+
+            if (wait_for_event_fn != null)
+                await wait_for_event_fn(wait_res);
+
+            if (locals_fn != null)
+            {
+                var locals = await GetProperties(wait_res["callFrames"][0]["callFrameId"].Value<string>());
+                locals_fn(locals);
+            }
+
+            return wait_res;
+        }
+
+        internal async Task CheckDelegate(JToken locals, string name, string className, string target)
+        {
+            var l = GetAndAssertObjectWithName(locals, name);
+            var val = l["value"];
+
+            await CheckDelegate(l, TDelegate(className, target), name);
+        }
+
+        internal async Task CheckDelegate(JToken actual_val, JToken exp_val, string label)
+        {
+            AssertEqual("object", actual_val["type"]?.Value<string>(), $"{label}-type");
+            AssertEqual(exp_val["className"]?.Value<string>(), actual_val["className"]?.Value<string>(), $"{label}-className");
+
+            var actual_target = actual_val["description"]?.Value<string>();
+            Assert.True(actual_target != null, $"${label}-description");
+            var exp_target = exp_val["target"].Value<string>();
+
+            CheckDelegateTarget(actual_target, exp_target);
+
+            var del_props = await GetProperties(actual_val["objectId"]?.Value<string>());
+            AssertEqual(1, del_props.Count(), $"${label}-delegate-properties-count");
+
+            var obj = del_props.Where(jt => jt["name"]?.Value<string>() == "Target").FirstOrDefault();
+            Assert.True(obj != null, $"[{label}] Property named 'Target' found found in delegate properties");
+
+            AssertEqual("symbol", obj["value"] ? ["type"]?.Value<string>(), $"{label}#Target#type");
+            CheckDelegateTarget(obj["value"] ? ["value"]?.Value<string>(), exp_target);
+
+            return;
+
+            void CheckDelegateTarget(string actual_target, string exp_target)
+            {
+                var parts = exp_target.Split(new char[] { '|' }, StringSplitOptions.RemoveEmptyEntries);
+                if (parts.Length == 1)
+                {
+                    // not a generated method
+                    AssertEqual(exp_target, actual_target, $"{label}-description");
+                }
+                else
+                {
+                    bool prefix = actual_target.StartsWith(parts[0], StringComparison.Ordinal);
+                    Assert.True(prefix, $"{label}-description, Expected target to start with '{parts[0]}'. Actual: '{actual_target}'");
+
+                    var remaining = actual_target.Substring(parts[0].Length);
+                    bool suffix = remaining.EndsWith(parts[1], StringComparison.Ordinal);
+                    Assert.True(prefix, $"{label}-description, Expected target to end with '{parts[1]}'. Actual: '{remaining}'");
+                }
+            }
+        }
+
+        internal async Task CheckCustomType(JToken actual_val, JToken exp_val, string label)
+        {
+            var ctype = exp_val["__custom_type"].Value<string>();
+            switch (ctype)
+            {
+                case "delegate":
+                    await CheckDelegate(actual_val, exp_val, label);
+                    break;
+
+                case "pointer":
+                    {
+
+                        if (exp_val["is_null"]?.Value<bool>() == true)
+                        {
+                            AssertEqual("symbol", actual_val["type"]?.Value<string>(), $"{label}-type");
+
+                            var exp_val_str = $"({exp_val ["type_name"]?.Value<string>()}) 0";
+                            AssertEqual(exp_val_str, actual_val["value"]?.Value<string>(), $"{label}-value");
+                            AssertEqual(exp_val_str, actual_val["description"]?.Value<string>(), $"{label}-description");
+                        }
+                        else if (exp_val["is_void"]?.Value<bool>() == true)
+                        {
+                            AssertEqual("symbol", actual_val["type"]?.Value<string>(), $"{label}-type");
+
+                            var exp_val_str = $"({exp_val ["type_name"]?.Value<string>()})";
+                            AssertStartsWith(exp_val_str, actual_val["value"]?.Value<string>(), $"{label}-value");
+                            AssertStartsWith(exp_val_str, actual_val["description"]?.Value<string>(), $"{label}-description");
+                        }
+                        else
+                        {
+                            AssertEqual("object", actual_val["type"]?.Value<string>(), $"{label}-type");
+
+                            var exp_prefix = $"({exp_val ["type_name"]?.Value<string>()})";
+                            AssertStartsWith(exp_prefix, actual_val["className"]?.Value<string>(), $"{label}-className");
+                            AssertStartsWith(exp_prefix, actual_val["description"]?.Value<string>(), $"{label}-description");
+                            Assert.False(actual_val["className"]?.Value<string>() == $"{exp_prefix} 0", $"[{label}] Expected a non-null value, but got {actual_val}");
+                        }
+                        break;
+                    }
+
+                case "getter":
+                    {
+                        // For getter, `actual_val` is not `.value`, instead it's the container object
+                        // which has a `.get` instead of a `.value`
+                        var get = actual_val["get"];
+                        Assert.True(get != null, $"[{label}] No `get` found. {(actual_val != null ? "Make sure to pass the container object for testing getters, and not the ['value']": String.Empty)}");
+
+                        AssertEqual("Function", get["className"]?.Value<string>(), $"{label}-className");
+                        AssertStartsWith($"get {exp_val ["type_name"]?.Value<string> ()} ()", get["description"]?.Value<string>(), $"{label}-description");
+                        AssertEqual("function", get["type"]?.Value<string>(), $"{label}-type");
+
+                        break;
+                    }
+
+                case "ignore_me":
+                    // nothing to check ;)
+                    break;
+
+                default:
+                    throw new ArgumentException($"{ctype} not supported");
+            }
+        }
+
+        internal async Task CheckProps(JToken actual, object exp_o, string label, int num_fields = -1)
+        {
+            if (exp_o.GetType().IsArray || exp_o is JArray)
+            {
+                if (!(actual is JArray actual_arr))
+                {
+                    Assert.True(false, $"[{label}] Expected to get an array here but got {actual}");
+                    return;
+                }
+
+                var exp_v_arr = JArray.FromObject(exp_o);
+                AssertEqual(exp_v_arr.Count, actual_arr.Count(), $"{label}-count");
+
+                for (int i = 0; i < exp_v_arr.Count; i++)
+                {
+                    var exp_i = exp_v_arr[i];
+                    var act_i = actual_arr[i];
+
+                    AssertEqual(i.ToString(), act_i["name"]?.Value<string>(), $"{label}-[{i}].name");
+                    if (exp_i != null)
+                        await CheckValue(act_i["value"], exp_i, $"{label}-{i}th value");
+                }
+
+                return;
+            }
+
+            // Not an array
+            var exp = exp_o as JObject;
+            if (exp == null)
+                exp = JObject.FromObject(exp_o);
+
+            num_fields = num_fields < 0 ? exp.Values<JToken>().Count() : num_fields;
+            Assert.True(num_fields == actual.Count(), $"[{label}] Number of fields don't match, Expected: {num_fields}, Actual: {actual.Count()}");
+
+            foreach (var kvp in exp)
+            {
+                var exp_name = kvp.Key;
+                var exp_val = kvp.Value;
+
+                var actual_obj = actual.FirstOrDefault(jt => jt["name"]?.Value<string>() == exp_name);
+                if (actual_obj == null)
+                {
+                    Assert.True(actual_obj != null, $"[{label}] Could not find property named '{exp_name}'");
+                }
+
+                Assert.True(actual_obj != null, $"[{label}] not value found for property named '{exp_name}'");
+
+                var actual_val = actual_obj["value"];
+                if (exp_val.Type == JTokenType.Array)
+                {
+                    var actual_props = await GetProperties(actual_val["objectId"]?.Value<string>());
+                    await CheckProps(actual_props, exp_val, $"{label}-{exp_name}");
+                }
+                else if (exp_val["__custom_type"] != null && exp_val["__custom_type"]?.Value<string>() == "getter")
+                {
+                    // hack: for getters, actual won't have a .value
+                    await CheckCustomType(actual_obj, exp_val, $"{label}#{exp_name}");
+                }
+                else
+                {
+                    await CheckValue(actual_val, exp_val, $"{label}#{exp_name}");
+                }
+            }
+        }
+
+        internal async Task CheckValue(JToken actual_val, JToken exp_val, string label)
+        {
+            if (exp_val["__custom_type"] != null)
+            {
+                await CheckCustomType(actual_val, exp_val, label);
+                return;
+            }
+
+            if (exp_val["type"] == null && actual_val["objectId"] != null)
+            {
+                var new_val = await GetProperties(actual_val["objectId"].Value<string>());
+                await CheckProps(new_val, exp_val, $"{label}-{actual_val["objectId"]?.Value<string>()}");
+                return;
+            }
+
+            foreach (var jp in exp_val.Values<JProperty>())
+            {
+                if (jp.Value.Type == JTokenType.Object)
+                {
+                    var new_val = await GetProperties(actual_val["objectId"].Value<string>());
+                    await CheckProps(new_val, jp.Value, $"{label}-{actual_val["objectId"]?.Value<string>()}");
+
+                    continue;
+                }
+
+                var exp_val_str = jp.Value.Value<string>();
+                bool null_or_empty_exp_val = String.IsNullOrEmpty(exp_val_str);
+
+                var actual_field_val = actual_val.Values<JProperty>().FirstOrDefault(a_jp => a_jp.Name == jp.Name);
+                var actual_field_val_str = actual_field_val?.Value?.Value<string>();
+                if (null_or_empty_exp_val && String.IsNullOrEmpty(actual_field_val_str))
+                    continue;
+
+                Assert.True(actual_field_val != null, $"[{label}] Could not find value field named {jp.Name}");
+
+                Assert.True(exp_val_str == actual_field_val_str,
+                    $"[{label}] Value for json property named {jp.Name} didn't match.\n" +
+                    $"Expected: {jp.Value.Value<string> ()}\n" +
+                    $"Actual:   {actual_field_val.Value.Value<string> ()}");
+            }
+        }
+
+        internal async Task<JToken> GetLocalsForFrame(JToken frame, string script_loc, int line, int column, string function_name)
+        {
+            CheckLocation(script_loc, line, column, ctx.scripts, frame["location"]);
+            Assert.Equal(function_name, frame["functionName"].Value<string>());
+
+            return await GetProperties(frame["callFrameId"].Value<string>());
+        }
+
+        internal async Task<JToken> GetObjectOnFrame(JToken frame, string name)
+        {
+            var locals = await GetProperties(frame["callFrameId"].Value<string>());
+            return await GetObjectOnLocals(locals, name);
+        }
+
+        // Find an object with @name, *fetch* the object, and check against @o
+        internal async Task<JToken> CompareObjectPropertiesFor(JToken locals, string name, object o, string label = null, int num_fields = -1)
+        {
+            if (label == null)
+                label = name;
+            var props = await GetObjectOnLocals(locals, name);
+            try
+            {
+                if (o != null)
+                    await CheckProps(props, o, label, num_fields);
+                return props;
+            }
+            catch
+            {
+                throw;
+            }
+        }
+
+        internal async Task<JToken> GetObjectOnLocals(JToken locals, string name)
+        {
+            var obj = GetAndAssertObjectWithName(locals, name);
+            var objectId = obj["value"]["objectId"]?.Value<string>();
+            Assert.True(!String.IsNullOrEmpty(objectId), $"No objectId found for {name}");
+
+            return await GetProperties(objectId);
+        }
+
+        /* @fn_args is for use with `Runtime.callFunctionOn` only */
+        internal async Task<JToken> GetProperties(string id, JToken fn_args = null, bool expect_ok = true)
+        {
+            if (ctx.UseCallFunctionOnBeforeGetProperties && !id.StartsWith("dotnet:scope:"))
+            {
+                var fn_decl = "function () { return this; }";
+                var cfo_args = JObject.FromObject(new
+                {
+                    functionDeclaration = fn_decl,
+                        objectId = id
+                });
+                if (fn_args != null)
+                    cfo_args["arguments"] = fn_args;
+
+                var result = await ctx.cli.SendCommand("Runtime.callFunctionOn", cfo_args, ctx.token);
+                AssertEqual(expect_ok, result.IsOk, $"Runtime.getProperties returned {result.IsOk} instead of {expect_ok}, for {cfo_args.ToString ()}, with Result: {result}");
+                if (!result.IsOk)
+                    return null;
+                id = result.Value["result"] ? ["objectId"]?.Value<string>();
+            }
+
+            var get_prop_req = JObject.FromObject(new
+            {
+                objectId = id
+            });
+
+            var frame_props = await ctx.cli.SendCommand("Runtime.getProperties", get_prop_req, ctx.token);
+            AssertEqual(expect_ok, frame_props.IsOk, $"Runtime.getProperties returned {frame_props.IsOk} instead of {expect_ok}, for {get_prop_req}, with Result: {frame_props}");
+            if (!frame_props.IsOk)
+                return null;
+
+            var locals = frame_props.Value["result"];
+            // FIXME: Should be done when generating the list in library_mono.js, but not sure yet
+            //        whether to remove it, and how to do it correctly.
+            if (locals is JArray)
+            {
+                foreach (var p in locals)
+                {
+                    if (p["name"]?.Value<string>() == "length" && p["enumerable"]?.Value<bool>() != true)
+                    {
+                        p.Remove();
+                        break;
+                    }
+                }
+            }
+
+            return locals;
+        }
+
+        internal async Task<JToken> EvaluateOnCallFrame(string id, string expression)
+        {
+            var evaluate_req = JObject.FromObject(new
+            {
+                callFrameId = id,
+                    expression = expression
+            });
+
+            var frame_evaluate = await ctx.cli.SendCommand("Debugger.evaluateOnCallFrame", evaluate_req, ctx.token);
+            if (!frame_evaluate.IsOk)
+                Assert.True(false, $"Debugger.evaluateOnCallFrame failed for {evaluate_req.ToString ()}, with Result: {frame_evaluate}");
+
+            var evaluate_result = frame_evaluate.Value["result"];
+            return evaluate_result;
+        }
+
+        internal async Task<Result> SetBreakpoint(string url_key, int line, int column, bool expect_ok = true, bool use_regex = false)
+        {
+            var bp1_req = !use_regex ?
+                JObject.FromObject(new { lineNumber = line, columnNumber = column, url = dicFileToUrl[url_key], }) :
+                JObject.FromObject(new { lineNumber = line, columnNumber = column, urlRegex = url_key, });
+
+            var bp1_res = await ctx.cli.SendCommand("Debugger.setBreakpointByUrl", bp1_req, ctx.token);
+            Assert.True(expect_ok ? bp1_res.IsOk : bp1_res.IsErr);
+
+            return bp1_res;
+        }
+
+        internal async Task<Result> SetPauseOnException(string state)
+        {
+            var exc_res = await ctx.cli.SendCommand("Debugger.setPauseOnExceptions", JObject.FromObject(new { state = state }), ctx.token);
+            return exc_res;
+        }
+
+        internal async Task<Result> SetBreakpointInMethod(string assembly, string type, string method, int lineOffset = 0, int col = 0)
+        {
+            var req = JObject.FromObject(new { assemblyName = assembly, typeName = type, methodName = method, lineOffset = lineOffset });
+
+            // Protocol extension
+            var res = await ctx.cli.SendCommand("DotnetDebugger.getMethodLocation", req, ctx.token);
+            Assert.True(res.IsOk);
+
+            var m_url = res.Value["result"]["url"].Value<string>();
+            var m_line = res.Value["result"]["line"].Value<int>();
+
+            var bp1_req = JObject.FromObject(new
+            {
+                lineNumber = m_line + lineOffset,
+                    columnNumber = col,
+                    url = m_url
+            });
+
+            res = await ctx.cli.SendCommand("Debugger.setBreakpointByUrl", bp1_req, ctx.token);
+            Assert.True(res.IsOk);
+
+            return res;
+        }
+
+        internal void AssertEqual(object expected, object actual, string label) => Assert.True(expected?.Equals(actual),
+            $"[{label}]\n" +
+            $"Expected: {expected?.ToString()}\n" +
+            $"Actual:   {actual?.ToString()}\n");
+
+        internal void AssertStartsWith(string expected, string actual, string label) => Assert.True(actual?.StartsWith(expected), $"[{label}] Does not start with the expected string\nExpected: {expected}\nActual:   {actual}");
+
+        internal static Func<int, int, string, string, object> TSimpleClass = (X, Y, Id, Color) => new
+        {
+            X = TNumber(X),
+            Y = TNumber(Y),
+            Id = TString(Id),
+            Color = TEnum("DebuggerTests.RGB", Color),
+            PointWithCustomGetter = TGetter("PointWithCustomGetter")
+        };
+
+        internal static Func<int, int, string, string, object> TPoint = (X, Y, Id, Color) => new
+        {
+            X = TNumber(X),
+            Y = TNumber(Y),
+            Id = TString(Id),
+            Color = TEnum("DebuggerTests.RGB", Color),
+        };
+
+        //FIXME: um maybe we don't need to convert jobject right here!
+        internal static JObject TString(string value) =>
+            value == null ?
+            TObject("string", is_null : true) :
+            JObject.FromObject(new { type = "string", value = @value });
+
+        internal static JObject TNumber(int value) =>
+            JObject.FromObject(new { type = "number", value = @value.ToString(), description = value.ToString() });
+
+        internal static JObject TNumber(uint value) =>
+            JObject.FromObject(new { type = "number", value = @value.ToString(), description = value.ToString() });
+
+        internal static JObject TValueType(string className, string description = null, object members = null) =>
+            JObject.FromObject(new { type = "object", isValueType = true, className = className, description = description ?? className });
+
+        internal static JObject TEnum(string className, string descr, object members = null) =>
+            JObject.FromObject(new { type = "object", isEnum = true, className = className, description = descr });
+
+        internal static JObject TObject(string className, string description = null, bool is_null = false) =>
+            is_null ?
+            JObject.FromObject(new { type = "object", className = className, description = description ?? className, subtype = is_null ? "null" : null }) :
+            JObject.FromObject(new { type = "object", className = className, description = description ?? className });
+
+        internal static JObject TArray(string className, int length = 0) => JObject.FromObject(new { type = "object", className = className, description = $"{className}({length})", subtype = "array" });
+
+        internal static JObject TBool(bool value) => JObject.FromObject(new { type = "boolean", value = @value, description = @value ? "true" : "false" });
+
+        internal static JObject TSymbol(string value) => JObject.FromObject(new { type = "symbol", value = @value, description = @value });
+
+        /*
+        	For target names with generated method names like
+        		`void <ActionTSignatureTest>b__11_0 (Math.GenericStruct<int[]>)`
+
+        	.. pass target "as `target: "void <ActionTSignatureTest>|(Math.GenericStruct<int[]>)"`
+        */
+        internal static JObject TDelegate(string className, string target) => JObject.FromObject(new
+        {
+            __custom_type = "delegate",
+                className = className,
+                target = target
+        });
+
+        internal static JObject TPointer(string type_name, bool is_null = false) => JObject.FromObject(new { __custom_type = "pointer", type_name = type_name, is_null = is_null, is_void = type_name.StartsWith("void*") });
+
+        internal static JObject TIgnore() => JObject.FromObject(new { __custom_type = "ignore_me" });
+
+        internal static JObject TGetter(string type) => JObject.FromObject(new { __custom_type = "getter", type_name = type });
+    }
+
+    class DebugTestContext
+    {
+        public InspectorClient cli;
+        public Inspector insp;
+        public CancellationToken token;
+        public Dictionary<string, string> scripts;
+
+        public bool UseCallFunctionOnBeforeGetProperties;
+
+        public DebugTestContext(InspectorClient cli, Inspector insp, CancellationToken token, Dictionary<string, string> scripts)
+        {
+            this.cli = cli;
+            this.insp = insp;
+            this.token = token;
+            this.scripts = scripts;
+        }
+    }
+
+    class DotnetObjectId
+    {
+        public string Scheme { get; }
+        public string Value { get; }
+
+        JObject value_json;
+        public JObject ValueAsJson
+        {
+            get
+            {
+                if (value_json == null)
+                {
+                    try
+                    {
+                        value_json = JObject.Parse(Value);
+                    }
+                    catch (JsonReaderException) { }
+                }
+
+                return value_json;
+            }
+        }
+
+        public static bool TryParse(JToken jToken, out DotnetObjectId objectId) => TryParse(jToken?.Value<string>(), out objectId);
+
+        public static bool TryParse(string id, out DotnetObjectId objectId)
+        {
+            objectId = null;
+            if (id == null)
+            {
+                return false;
+            }
+
+            if (!id.StartsWith("dotnet:"))
+            {
+                return false;
+            }
+
+            var parts = id.Split(":", 3);
+
+            if (parts.Length < 3)
+            {
+                return false;
+            }
+
+            objectId = new DotnetObjectId(parts[1], parts[2]);
+
+            return true;
+        }
+
+        public DotnetObjectId(string scheme, string value)
+        {
+            Scheme = scheme;
+            Value = value;
+        }
+
+        public override string ToString() => $"dotnet:{Scheme}:{Value}";
+    }
+
+    enum StepKind
+    {
+        Into,
+        Over,
+        Out
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/Tests.cs b/src/mono/wasm/debugger/DebuggerTestSuite/Tests.cs
new file mode 100644
index 00000000000000..5ba31d8c370137
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/Tests.cs
@@ -0,0 +1,1527 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Newtonsoft.Json.Linq;
+using Microsoft.WebAssembly.Diagnostics;
+using Xunit;
+
+[assembly : CollectionBehavior(CollectionBehavior.CollectionPerAssembly)]
+
+namespace DebuggerTests
+{
+
+    public class SourceList : DebuggerTestBase
+    {
+
+        [Fact]
+        public async Task CheckThatAllSourcesAreSent()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            //all sources are sent before runtime ready is sent, nothing to check
+            await insp.Ready();
+            Assert.Contains("dotnet://debugger-test.dll/debugger-test.cs", scripts.Values);
+            Assert.Contains("dotnet://debugger-test.dll/debugger-test2.cs", scripts.Values);
+            Assert.Contains("dotnet://debugger-test.dll/dependency.cs", scripts.Values);
+        }
+
+        [Fact]
+        public async Task CreateGoodBreakpoint()
+        {
+            var insp = new Inspector();
+
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                var bp1_res = await SetBreakpoint("dotnet://debugger-test.dll/debugger-test.cs", 10, 8);
+
+                Assert.EndsWith("debugger-test.cs", bp1_res.Value["breakpointId"].ToString());
+                Assert.Equal(1, bp1_res.Value["locations"]?.Value<JArray>()?.Count);
+
+                var loc = bp1_res.Value["locations"]?.Value<JArray>() [0];
+
+                Assert.NotNull(loc["scriptId"]);
+                Assert.Equal("dotnet://debugger-test.dll/debugger-test.cs", scripts[loc["scriptId"]?.Value<string>()]);
+                Assert.Equal(10, loc["lineNumber"]);
+                Assert.Equal(8, loc["columnNumber"]);
+            });
+        }
+
+        [Fact]
+        public async Task CreateJSBreakpoint()
+        {
+            // Test that js breakpoints get set correctly
+            var insp = new Inspector();
+
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                // 13 24
+                // 13 31
+                var bp1_res = await SetBreakpoint("/debugger-driver.html", 13, 24);
+
+                Assert.EndsWith("debugger-driver.html", bp1_res.Value["breakpointId"].ToString());
+                Assert.Equal(1, bp1_res.Value["locations"]?.Value<JArray>()?.Count);
+
+                var loc = bp1_res.Value["locations"]?.Value<JArray>() [0];
+
+                Assert.NotNull(loc["scriptId"]);
+                Assert.Equal(13, loc["lineNumber"]);
+                Assert.Equal(24, loc["columnNumber"]);
+
+                var bp2_res = await SetBreakpoint("/debugger-driver.html", 13, 31);
+
+                Assert.EndsWith("debugger-driver.html", bp2_res.Value["breakpointId"].ToString());
+                Assert.Equal(1, bp2_res.Value["locations"]?.Value<JArray>()?.Count);
+
+                var loc2 = bp2_res.Value["locations"]?.Value<JArray>() [0];
+
+                Assert.NotNull(loc2["scriptId"]);
+                Assert.Equal(13, loc2["lineNumber"]);
+                Assert.Equal(31, loc2["columnNumber"]);
+            });
+        }
+
+        [Fact]
+        public async Task CreateJS0Breakpoint()
+        {
+            // Test that js column 0 does as expected
+            var insp = new Inspector();
+
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                // 13 24
+                // 13 31
+                var bp1_res = await SetBreakpoint("/debugger-driver.html", 13, 0);
+
+                Assert.EndsWith("debugger-driver.html", bp1_res.Value["breakpointId"].ToString());
+                Assert.Equal(1, bp1_res.Value["locations"]?.Value<JArray>()?.Count);
+
+                var loc = bp1_res.Value["locations"]?.Value<JArray>() [0];
+
+                Assert.NotNull(loc["scriptId"]);
+                Assert.Equal(13, loc["lineNumber"]);
+                Assert.Equal(24, loc["columnNumber"]);
+
+                var bp2_res = await SetBreakpoint("/debugger-driver.html", 13, 31);
+
+                Assert.EndsWith("debugger-driver.html", bp2_res.Value["breakpointId"].ToString());
+                Assert.Equal(1, bp2_res.Value["locations"]?.Value<JArray>()?.Count);
+
+                var loc2 = bp2_res.Value["locations"]?.Value<JArray>() [0];
+
+                Assert.NotNull(loc2["scriptId"]);
+                Assert.Equal(13, loc2["lineNumber"]);
+                Assert.Equal(31, loc2["columnNumber"]);
+            });
+        }
+
+        [Theory]
+        [InlineData(0)]
+        [InlineData(50)]
+        public async Task CheckMultipleBreakpointsOnSameLine(int col)
+        {
+            var insp = new Inspector();
+
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                var bp1_res = await SetBreakpoint("dotnet://debugger-test.dll/debugger-array-test.cs", 219, col);
+                Assert.EndsWith("debugger-array-test.cs", bp1_res.Value["breakpointId"].ToString());
+                Assert.Equal(1, bp1_res.Value["locations"]?.Value<JArray>()?.Count);
+
+                var loc = bp1_res.Value["locations"]?.Value<JArray>() [0];
+
+                CheckLocation("dotnet://debugger-test.dll/debugger-array-test.cs", 219, 50, scripts, loc);
+
+                var bp2_res = await SetBreakpoint("dotnet://debugger-test.dll/debugger-array-test.cs", 219, 55);
+                Assert.EndsWith("debugger-array-test.cs", bp2_res.Value["breakpointId"].ToString());
+                Assert.Equal(1, bp2_res.Value["locations"]?.Value<JArray>()?.Count);
+
+                var loc2 = bp2_res.Value["locations"]?.Value<JArray>() [0];
+
+                CheckLocation("dotnet://debugger-test.dll/debugger-array-test.cs", 219, 55, scripts, loc2);
+            });
+        }
+
+        [Fact]
+        public async Task CreateBadBreakpoint()
+        {
+            var insp = new Inspector();
+
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                var bp1_req = JObject.FromObject(new
+                {
+                    lineNumber = 8,
+                        columnNumber = 2,
+                        url = "dotnet://debugger-test.dll/this-file-doesnt-exist.cs",
+                });
+
+                var bp1_res = await cli.SendCommand("Debugger.setBreakpointByUrl", bp1_req, token);
+
+                Assert.True(bp1_res.IsOk);
+                Assert.Empty(bp1_res.Value["locations"].Values<object>());
+                //Assert.Equal ((int)MonoErrorCodes.BpNotFound, bp1_res.Error ["code"]?.Value<int> ());
+            });
+        }
+
+        [Fact]
+        public async Task CreateGoodBreakpointAndHit()
+        {
+            var insp = new Inspector();
+
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                var bp = await SetBreakpoint("dotnet://debugger-test.dll/debugger-test.cs", 10, 8);
+
+                var eval_req = JObject.FromObject(new
+                {
+                    expression = "window.setTimeout(function() { invoke_add(); }, 1);",
+                });
+
+                await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_add(); }, 1);",
+                    "dotnet://debugger-test.dll/debugger-test.cs", 10, 8,
+                    "IntAdd",
+                    wait_for_event_fn: (pause_location) =>
+                    {
+                        Assert.Equal("other", pause_location["reason"]?.Value<string>());
+                        Assert.Equal(bp.Value["breakpointId"]?.ToString(), pause_location["hitBreakpoints"] ? [0]?.Value<string>());
+
+                        var top_frame = pause_location["callFrames"][0];
+                        Assert.Equal("IntAdd", top_frame["functionName"].Value<string>());
+                        Assert.Contains("debugger-test.cs", top_frame["url"].Value<string>());
+
+                        CheckLocation("dotnet://debugger-test.dll/debugger-test.cs", 8, 4, scripts, top_frame["functionLocation"]);
+
+                        //now check the scope
+                        var scope = top_frame["scopeChain"][0];
+                        Assert.Equal("local", scope["type"]);
+                        Assert.Equal("IntAdd", scope["name"]);
+
+                        Assert.Equal("object", scope["object"]["type"]);
+                        Assert.Equal("dotnet:scope:0", scope["object"]["objectId"]);
+                        CheckLocation("dotnet://debugger-test.dll/debugger-test.cs", 8, 4, scripts, scope["startLocation"]);
+                        CheckLocation("dotnet://debugger-test.dll/debugger-test.cs", 14, 4, scripts, scope["endLocation"]);
+                        return Task.CompletedTask;
+                    }
+                );
+
+            });
+        }
+
+        [Fact]
+        public async Task ExceptionThrownInJS()
+        {
+            var insp = new Inspector();
+
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                var eval_req = JObject.FromObject(new
+                {
+                    expression = "invoke_bad_js_test();"
+                });
+
+                var eval_res = await cli.SendCommand("Runtime.evaluate", eval_req, token);
+                Assert.True(eval_res.IsErr);
+                Assert.Equal("Uncaught", eval_res.Error["exceptionDetails"] ? ["text"]?.Value<string>());
+            });
+        }
+
+        [Fact]
+        public async Task ExceptionThrownInJSOutOfBand()
+        {
+            var insp = new Inspector();
+
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                await SetBreakpoint("/debugger-driver.html", 27, 2);
+
+                var eval_req = JObject.FromObject(new
+                {
+                    expression = "window.setTimeout(function() { invoke_bad_js_test(); }, 1);",
+                });
+
+                var eval_res = await cli.SendCommand("Runtime.evaluate", eval_req, token);
+                // Response here will be the id for the timer from JS!
+                Assert.True(eval_res.IsOk);
+
+                var ex = await Assert.ThrowsAsync<ArgumentException>(async() => await insp.WaitFor("Runtime.exceptionThrown"));
+                var ex_json = JObject.Parse(ex.Message);
+                Assert.Equal(dicFileToUrl["/debugger-driver.html"], ex_json["exceptionDetails"] ? ["url"]?.Value<string>());
+            });
+
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectLocalsAtBreakpointSite(bool use_cfo) =>
+            await CheckInspectLocalsAtBreakpointSite(
+                "dotnet://debugger-test.dll/debugger-test.cs", 10, 8, "IntAdd",
+                "window.setTimeout(function() { invoke_add(); }, 1);",
+                use_cfo : use_cfo,
+                test_fn: (locals) =>
+                {
+                    CheckNumber(locals, "a", 10);
+                    CheckNumber(locals, "b", 20);
+                    CheckNumber(locals, "c", 30);
+                    CheckNumber(locals, "d", 0);
+                    CheckNumber(locals, "e", 0);
+                }
+            );
+
+        [Fact]
+        public async Task InspectPrimitiveTypeLocalsAtBreakpointSite() =>
+            await CheckInspectLocalsAtBreakpointSite(
+                "dotnet://debugger-test.dll/debugger-test.cs", 154, 8, "PrimitiveTypesTest",
+                "window.setTimeout(function() { invoke_static_method ('[debugger-test] Math:PrimitiveTypesTest'); }, 1);",
+                test_fn: (locals) =>
+                {
+                    CheckSymbol(locals, "c0", "8364 '€'");
+                    CheckSymbol(locals, "c1", "65 'A'");
+                }
+            );
+
+        [Fact]
+        public async Task InspectLocalsTypesAtBreakpointSite() =>
+            await CheckInspectLocalsAtBreakpointSite(
+                "dotnet://debugger-test.dll/debugger-test2.cs", 48, 8, "Types",
+                "window.setTimeout(function() { invoke_static_method (\"[debugger-test] Fancy:Types\")(); }, 1);",
+                use_cfo : false,
+                test_fn: (locals) =>
+                {
+                    CheckNumber(locals, "dPI", Math.PI);
+                    CheckNumber(locals, "fPI", (float) Math.PI);
+                    CheckNumber(locals, "iMax", int.MaxValue);
+                    CheckNumber(locals, "iMin", int.MinValue);
+                    CheckNumber(locals, "uiMax", uint.MaxValue);
+                    CheckNumber(locals, "uiMin", uint.MinValue);
+
+                    CheckNumber(locals, "l", uint.MaxValue * (long) 2);
+                    //CheckNumber (locals, "lMax", long.MaxValue); // cannot be represented as double
+                    //CheckNumber (locals, "lMin", long.MinValue); // cannot be represented as double
+
+                    CheckNumber(locals, "sbMax", sbyte.MaxValue);
+                    CheckNumber(locals, "sbMin", sbyte.MinValue);
+                    CheckNumber(locals, "bMax", byte.MaxValue);
+                    CheckNumber(locals, "bMin", byte.MinValue);
+
+                    CheckNumber(locals, "sMax", short.MaxValue);
+                    CheckNumber(locals, "sMin", short.MinValue);
+                    CheckNumber(locals, "usMin", ushort.MinValue);
+                    CheckNumber(locals, "usMax", ushort.MaxValue);
+                }
+            );
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectLocalsWithGenericTypesAtBreakpointSite(bool use_cfo) =>
+            await CheckInspectLocalsAtBreakpointSite(
+                "dotnet://debugger-test.dll/debugger-test.cs", 74, 8, "GenericTypesTest",
+                "window.setTimeout(function() { invoke_generic_types_test (); }, 1);",
+                use_cfo : use_cfo,
+                test_fn: (locals) =>
+                {
+                    CheckObject(locals, "list", "System.Collections.Generic.Dictionary<Math[], Math.IsMathNull>");
+                    CheckObject(locals, "list_null", "System.Collections.Generic.Dictionary<Math[], Math.IsMathNull>", is_null : true);
+
+                    CheckArray(locals, "list_arr", "System.Collections.Generic.Dictionary<Math[], Math.IsMathNull>[]", 1);
+                    CheckObject(locals, "list_arr_null", "System.Collections.Generic.Dictionary<Math[], Math.IsMathNull>[]", is_null : true);
+
+                    // Unused locals
+                    CheckObject(locals, "list_unused", "System.Collections.Generic.Dictionary<Math[], Math.IsMathNull>");
+                    CheckObject(locals, "list_null_unused", "System.Collections.Generic.Dictionary<Math[], Math.IsMathNull>", is_null : true);
+
+                    CheckArray(locals, "list_arr_unused", "System.Collections.Generic.Dictionary<Math[], Math.IsMathNull>[]", 1);
+                    CheckObject(locals, "list_arr_null_unused", "System.Collections.Generic.Dictionary<Math[], Math.IsMathNull>[]", is_null : true);
+                }
+            );
+
+        object TGenericStruct(string typearg, string stringField) => new
+        {
+            List = TObject($"System.Collections.Generic.List<{typearg}>"),
+            StringField = TString(stringField)
+        };
+
+        [Fact]
+        public async Task RuntimeGetPropertiesWithInvalidScopeIdTest()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                var bp = await SetBreakpoint("dotnet://debugger-test.dll/debugger-test.cs", 49, 8);
+
+                await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_delegates_test (); }, 1);",
+                    "dotnet://debugger-test.dll/debugger-test.cs", 49, 8,
+                    "DelegatesTest",
+                    wait_for_event_fn : async(pause_location) =>
+                    {
+                        //make sure we're on the right bp
+                        Assert.Equal(bp.Value["breakpointId"]?.ToString(), pause_location["hitBreakpoints"] ? [0]?.Value<string>());
+
+                        var top_frame = pause_location["callFrames"][0];
+
+                        var scope = top_frame["scopeChain"][0];
+                        Assert.Equal("dotnet:scope:0", scope["object"]["objectId"]);
+
+                        // Try to get an invalid scope!
+                        var get_prop_req = JObject.FromObject(new
+                        {
+                            objectId = "dotnet:scope:23490871",
+                        });
+
+                        var frame_props = await cli.SendCommand("Runtime.getProperties", get_prop_req, token);
+                        Assert.True(frame_props.IsErr);
+                    }
+                );
+            });
+        }
+
+        [Fact]
+        public async Task TrivalStepping()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                var bp = await SetBreakpoint("dotnet://debugger-test.dll/debugger-test.cs", 10, 8);
+
+                await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_add(); }, 1);",
+                    "dotnet://debugger-test.dll/debugger-test.cs", 10, 8,
+                    "IntAdd",
+                    wait_for_event_fn: (pause_location) =>
+                    {
+                        //make sure we're on the right bp
+                        Assert.Equal(bp.Value["breakpointId"]?.ToString(), pause_location["hitBreakpoints"] ? [0]?.Value<string>());
+
+                        var top_frame = pause_location["callFrames"][0];
+                        CheckLocation("dotnet://debugger-test.dll/debugger-test.cs", 8, 4, scripts, top_frame["functionLocation"]);
+                        return Task.CompletedTask;
+                    }
+                );
+
+                await StepAndCheck(StepKind.Over, "dotnet://debugger-test.dll/debugger-test.cs", 11, 8, "IntAdd",
+                    wait_for_event_fn: (pause_location) =>
+                    {
+                        var top_frame = pause_location["callFrames"][0];
+                        CheckLocation("dotnet://debugger-test.dll/debugger-test.cs", 8, 4, scripts, top_frame["functionLocation"]);
+                        return Task.CompletedTask;
+                    }
+                );
+            });
+        }
+
+        [Fact]
+        public async Task InspectLocalsDuringStepping()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-test.cs";
+                await SetBreakpoint(debugger_test_loc, 10, 8);
+
+                await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_add(); }, 1);",
+                    debugger_test_loc, 10, 8, "IntAdd",
+                    locals_fn: (locals) =>
+                    {
+                        CheckNumber(locals, "a", 10);
+                        CheckNumber(locals, "b", 20);
+                        CheckNumber(locals, "c", 30);
+                        CheckNumber(locals, "d", 0);
+                        CheckNumber(locals, "e", 0);
+                    }
+                );
+
+                await StepAndCheck(StepKind.Over, debugger_test_loc, 11, 8, "IntAdd",
+                    locals_fn: (locals) =>
+                    {
+                        CheckNumber(locals, "a", 10);
+                        CheckNumber(locals, "b", 20);
+                        CheckNumber(locals, "c", 30);
+                        CheckNumber(locals, "d", 50);
+                        CheckNumber(locals, "e", 0);
+                    }
+                );
+
+                //step and get locals
+                await StepAndCheck(StepKind.Over, debugger_test_loc, 12, 8, "IntAdd",
+                    locals_fn: (locals) =>
+                    {
+                        CheckNumber(locals, "a", 10);
+                        CheckNumber(locals, "b", 20);
+                        CheckNumber(locals, "c", 30);
+                        CheckNumber(locals, "d", 50);
+                        CheckNumber(locals, "e", 60);
+                    }
+                );
+            });
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectLocalsInPreviousFramesDuringSteppingIn2(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+
+                var dep_cs_loc = "dotnet://debugger-test.dll/dependency.cs";
+                await SetBreakpoint(dep_cs_loc, 33, 8);
+
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-test.cs";
+
+                // Will stop in Complex.DoEvenMoreStuff
+                var pause_location = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_use_complex (); }, 1);",
+                    dep_cs_loc, 33, 8, "DoEvenMoreStuff",
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Single(locals);
+                        CheckObject(locals, "this", "Simple.Complex");
+                    }
+                );
+
+                var props = await GetObjectOnFrame(pause_location["callFrames"][0], "this");
+                Assert.Equal(3, props.Count());
+                CheckNumber(props, "A", 10);
+                CheckString(props, "B", "xx");
+                CheckObject(props, "c", "object");
+
+                // Check UseComplex frame
+                var locals_m1 = await GetLocalsForFrame(pause_location["callFrames"][3], debugger_test_loc, 23, 8, "UseComplex");
+                Assert.Equal(7, locals_m1.Count());
+
+                CheckNumber(locals_m1, "a", 10);
+                CheckNumber(locals_m1, "b", 20);
+                CheckObject(locals_m1, "complex", "Simple.Complex");
+                CheckNumber(locals_m1, "c", 30);
+                CheckNumber(locals_m1, "d", 50);
+                CheckNumber(locals_m1, "e", 60);
+                CheckNumber(locals_m1, "f", 0);
+
+                props = await GetObjectOnFrame(pause_location["callFrames"][3], "complex");
+                Assert.Equal(3, props.Count());
+                CheckNumber(props, "A", 10);
+                CheckString(props, "B", "xx");
+                CheckObject(props, "c", "object");
+
+                pause_location = await StepAndCheck(StepKind.Over, dep_cs_loc, 23, 8, "DoStuff", times : 2);
+                // Check UseComplex frame again
+                locals_m1 = await GetLocalsForFrame(pause_location["callFrames"][1], debugger_test_loc, 23, 8, "UseComplex");
+                Assert.Equal(7, locals_m1.Count());
+
+                CheckNumber(locals_m1, "a", 10);
+                CheckNumber(locals_m1, "b", 20);
+                CheckObject(locals_m1, "complex", "Simple.Complex");
+                CheckNumber(locals_m1, "c", 30);
+                CheckNumber(locals_m1, "d", 50);
+                CheckNumber(locals_m1, "e", 60);
+                CheckNumber(locals_m1, "f", 0);
+
+                props = await GetObjectOnFrame(pause_location["callFrames"][1], "complex");
+                Assert.Equal(3, props.Count());
+                CheckNumber(props, "A", 10);
+                CheckString(props, "B", "xx");
+                CheckObject(props, "c", "object");
+            });
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectLocalsInPreviousFramesDuringSteppingIn(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-test.cs";
+                await SetBreakpoint(debugger_test_loc, 111, 12);
+
+                // Will stop in InnerMethod
+                var wait_res = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_outer_method(); }, 1);",
+                    debugger_test_loc, 111, 12, "InnerMethod",
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(4, locals.Count());
+                        CheckNumber(locals, "i", 5);
+                        CheckNumber(locals, "j", 24);
+                        CheckString(locals, "foo_str", "foo");
+                        CheckObject(locals, "this", "Math.NestedInMath");
+                    }
+                );
+
+                var this_props = await GetObjectOnFrame(wait_res["callFrames"][0], "this");
+                Assert.Equal(2, this_props.Count());
+                CheckObject(this_props, "m", "Math");
+                CheckValueType(this_props, "SimpleStructProperty", "Math.SimpleStruct");
+
+                var ss_props = await GetObjectOnLocals(this_props, "SimpleStructProperty");
+                var dt = new DateTime(2020, 1, 2, 3, 4, 5);
+                await CheckProps(ss_props, new {
+                    dt = TValueType("System.DateTime", dt.ToString()),
+                    gs = TValueType("Math.GenericStruct<System.DateTime>")
+                }, "ss_props");
+
+                await CheckDateTime(ss_props, "dt", new DateTime(2020, 1, 2, 3, 4, 5));
+
+                // Check OuterMethod frame
+                var locals_m1 = await GetLocalsForFrame(wait_res["callFrames"][1], debugger_test_loc, 87, 8, "OuterMethod");
+                Assert.Equal(5, locals_m1.Count());
+                // FIXME: Failing test CheckNumber (locals_m1, "i", 5);
+                // FIXME: Failing test CheckString (locals_m1, "text", "Hello");
+                CheckNumber(locals_m1, "new_i", 0);
+                CheckNumber(locals_m1, "k", 0);
+                CheckObject(locals_m1, "nim", "Math.NestedInMath");
+
+                // step back into OuterMethod
+                await StepAndCheck(StepKind.Over, debugger_test_loc, 91, 8, "OuterMethod", times : 9,
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(5, locals.Count());
+
+                        // FIXME: Failing test CheckNumber (locals_m1, "i", 5);
+                        CheckString(locals, "text", "Hello");
+                        // FIXME: Failing test CheckNumber (locals, "new_i", 24);
+                        CheckNumber(locals, "k", 19);
+                        CheckObject(locals, "nim", "Math.NestedInMath");
+                    }
+                );
+
+                //await StepAndCheck (StepKind.Over, "dotnet://debugger-test.dll/debugger-test.cs", 81, 2, "OuterMethod", times: 2);
+
+                // step into InnerMethod2
+                await StepAndCheck(StepKind.Into, "dotnet://debugger-test.dll/debugger-test.cs", 96, 4, "InnerMethod2",
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(3, locals.Count());
+
+                        CheckString(locals, "s", "test string");
+                        //out var: CheckNumber (locals, "k", 0);
+                        CheckNumber(locals, "i", 24);
+                    }
+                );
+
+                await StepAndCheck(StepKind.Over, "dotnet://debugger-test.dll/debugger-test.cs", 100, 4, "InnerMethod2", times : 4,
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(3, locals.Count());
+
+                        CheckString(locals, "s", "test string");
+                        // FIXME: Failing test CheckNumber (locals, "k", 34);
+                        CheckNumber(locals, "i", 24);
+                    }
+                );
+
+                await StepAndCheck(StepKind.Over, "dotnet://debugger-test.dll/debugger-test.cs", 92, 8, "OuterMethod", times : 2,
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(5, locals.Count());
+
+                        CheckString(locals, "text", "Hello");
+                        // FIXME: failing test CheckNumber (locals, "i", 5);
+                        CheckNumber(locals, "new_i", 22);
+                        CheckNumber(locals, "k", 34);
+                        CheckObject(locals, "nim", "Math.NestedInMath");
+                    }
+                );
+            });
+        }
+
+        [Fact]
+        public async Task InspectLocalsDuringSteppingIn()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                await SetBreakpoint("dotnet://debugger-test.dll/debugger-test.cs", 86, 8);
+
+                await EvaluateAndCheck("window.setTimeout(function() { invoke_outer_method(); }, 1);",
+                    "dotnet://debugger-test.dll/debugger-test.cs", 86, 8, "OuterMethod",
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(5, locals.Count());
+
+                        CheckObject(locals, "nim", "Math.NestedInMath");
+                        CheckNumber(locals, "i", 5);
+                        CheckNumber(locals, "k", 0);
+                        CheckNumber(locals, "new_i", 0);
+                        CheckString(locals, "text", null);
+                    }
+                );
+
+                await StepAndCheck(StepKind.Over, "dotnet://debugger-test.dll/debugger-test.cs", 87, 8, "OuterMethod",
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(5, locals.Count());
+
+                        CheckObject(locals, "nim", "Math.NestedInMath");
+                        // FIXME: Failing test CheckNumber (locals, "i", 5);
+                        CheckNumber(locals, "k", 0);
+                        CheckNumber(locals, "new_i", 0);
+                        CheckString(locals, "text", "Hello");
+                    }
+                );
+
+                // Step into InnerMethod
+                await StepAndCheck(StepKind.Into, "dotnet://debugger-test.dll/debugger-test.cs", 105, 8, "InnerMethod");
+                await StepAndCheck(StepKind.Over, "dotnet://debugger-test.dll/debugger-test.cs", 109, 12, "InnerMethod", times : 5,
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(4, locals.Count());
+
+                        CheckNumber(locals, "i", 5);
+                        CheckNumber(locals, "j", 15);
+                        CheckString(locals, "foo_str", "foo");
+                        CheckObject(locals, "this", "Math.NestedInMath");
+                    }
+                );
+
+                // Step back to OuterMethod
+                await StepAndCheck(StepKind.Over, "dotnet://debugger-test.dll/debugger-test.cs", 88, 8, "OuterMethod", times : 6,
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(5, locals.Count());
+
+                        CheckObject(locals, "nim", "Math.NestedInMath");
+                        // FIXME: Failing test CheckNumber (locals, "i", 5);
+                        CheckNumber(locals, "k", 0);
+                        CheckNumber(locals, "new_i", 24);
+                        CheckString(locals, "text", "Hello");
+                    }
+                );
+            });
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectLocalsInAsyncMethods(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-test.cs";
+
+                await SetBreakpoint(debugger_test_loc, 120, 12);
+                await SetBreakpoint(debugger_test_loc, 135, 12);
+
+                // Will stop in Asyncmethod0
+                var wait_res = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_async_method_with_await(); }, 1);",
+                    debugger_test_loc, 120, 12, "MoveNext", //FIXME:
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(4, locals.Count());
+                        CheckString(locals, "s", "string from js");
+                        CheckNumber(locals, "i", 42);
+                        CheckString(locals, "local0", "value0");
+                        CheckObject(locals, "this", "Math.NestedInMath");
+                    }
+                );
+                Console.WriteLine(wait_res);
+
+#if false // Disabled for now, as we don't have proper async traces
+                var locals = await GetProperties(wait_res["callFrames"][2]["callFrameId"].Value<string>());
+                Assert.Equal(4, locals.Count());
+                CheckString(locals, "ls", "string from jstest");
+                CheckNumber(locals, "li", 52);
+#endif
+
+                // TODO: previous frames have async machinery details, so no point checking that right now
+
+                var pause_loc = await SendCommandAndCheck(null, "Debugger.resume", debugger_test_loc, 135, 12, /*FIXME: "AsyncMethodNoReturn"*/ "MoveNext",
+                    locals_fn: (locals) =>
+                    {
+                        Assert.Equal(4, locals.Count());
+                        CheckString(locals, "str", "AsyncMethodNoReturn's local");
+                        CheckObject(locals, "this", "Math.NestedInMath");
+                        //FIXME: check fields
+                        CheckValueType(locals, "ss", "Math.SimpleStruct");
+                        CheckArray(locals, "ss_arr", "Math.SimpleStruct[]", 0);
+                        // TODO: struct fields
+                    }
+                );
+
+                var this_props = await GetObjectOnFrame(pause_loc["callFrames"][0], "this");
+                Assert.Equal(2, this_props.Count());
+                CheckObject(this_props, "m", "Math");
+                CheckValueType(this_props, "SimpleStructProperty", "Math.SimpleStruct");
+
+                // TODO: Check `this` properties
+            });
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectLocalsWithStructs(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-valuetypes-test.cs";
+
+                await SetBreakpoint(debugger_test_loc, 22, 8);
+
+                var pause_location = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_method_with_structs(); }, 1);",
+                    debugger_test_loc, 22, 8, "MethodWithLocalStructs");
+
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                await CheckProps(locals, new
+                {
+                    ss_local = TValueType("DebuggerTests.ValueTypesTest.SimpleStruct"),
+                    gs_local = TValueType("DebuggerTests.ValueTypesTest.GenericStruct<DebuggerTests.ValueTypesTest>"),
+                    vt_local = TObject("DebuggerTests.ValueTypesTest")
+                }, "locals");
+
+                var dt = new DateTime(2021, 2, 3, 4, 6, 7);
+                var vt_local_props = await GetObjectOnFrame(pause_location["callFrames"][0], "vt_local");
+                Assert.Equal(5, vt_local_props.Count());
+
+                CheckString(vt_local_props, "StringField", "string#0");
+                CheckValueType(vt_local_props, "SimpleStructField", "DebuggerTests.ValueTypesTest.SimpleStruct");
+                CheckValueType(vt_local_props, "SimpleStructProperty", "DebuggerTests.ValueTypesTest.SimpleStruct");
+                await CheckDateTime(vt_local_props, "DT", new DateTime(2020, 1, 2, 3, 4, 5));
+                CheckEnum(vt_local_props, "RGB", "DebuggerTests.RGB", "Blue");
+
+                // Check ss_local's properties
+                var ss_local_props = await GetObjectOnFrame(pause_location["callFrames"][0], "ss_local");
+                await CheckProps(ss_local_props, new
+                {
+                    V          = TGetter("V"),
+                    str_member = TString("set in MethodWithLocalStructs#SimpleStruct#str_member"),
+                    dt         = TValueType("System.DateTime", dt.ToString()),
+                    gs         = TValueType("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
+                    Kind       = TEnum("System.DateTimeKind", "Utc")
+                }, "ss_local");
+
+                {
+                    var gres = await InvokeGetter(GetAndAssertObjectWithName(locals, "ss_local"), "V");
+                    await CheckValue(gres.Value["result"], TNumber(0xDEADBEEF + 2), $"ss_local#V");
+                    // Check ss_local.dt
+                    await CheckDateTime(ss_local_props, "dt", dt);
+
+                    // Check ss_local.gs
+                    var gs_props = await GetObjectOnLocals(ss_local_props, "gs");
+                    CheckString(gs_props, "StringField", "set in MethodWithLocalStructs#SimpleStruct#gs#StringField");
+                    CheckObject(gs_props, "List", "System.Collections.Generic.List<System.DateTime>");
+                }
+
+                // Check gs_local's properties
+                var gs_local_props = await GetObjectOnFrame(pause_location["callFrames"][0], "gs_local");
+                await CheckProps(gs_local_props, new
+                {
+                    StringField = TString("gs_local#GenericStruct<ValueTypesTest>#StringField"),
+                        List = TObject("System.Collections.Generic.List<DebuggerTests.ValueTypesTest>", is_null : true),
+                        Options = TEnum("DebuggerTests.Options", "None")
+                }, "gs_local");
+
+                // Check vt_local's properties
+
+                var exp = new[]
+                {
+                    ("SimpleStructProperty", 2, "Utc"),
+                    ("SimpleStructField", 5, "Local")
+                };
+
+                foreach (var (name, bias, dt_kind) in exp)
+                {
+                    dt = new DateTime(2020 + bias, 1 + bias, 2 + bias, 3 + bias, 5 + bias, 6 + bias);
+                    var ssp_props = await CompareObjectPropertiesFor(vt_local_props, name,
+                        new
+                        {
+                            V          = TGetter("V"),
+                            str_member = TString($"{name}#string#0#SimpleStruct#str_member"),
+                            dt         = TValueType("System.DateTime", dt.ToString()),
+                            gs         = TValueType("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
+                            Kind       = TEnum("System.DateTimeKind", dt_kind)
+                        },
+                        label: $"vt_local_props.{name}");
+
+                    await CheckDateTime(ssp_props, "dt", dt);
+                    var gres = await InvokeGetter(GetAndAssertObjectWithName(vt_local_props, name), "V");
+                    await CheckValue(gres.Value["result"], TNumber(0xDEADBEEF + (uint) dt.Month), $"{name}#V");
+                }
+
+                // FIXME: check ss_local.gs.List's members
+            });
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectValueTypeMethodArgs(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-valuetypes-test.cs";
+
+                await SetBreakpoint(debugger_test_loc, 34, 12);
+
+                var pause_location = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_static_method ('[debugger-test] DebuggerTests.ValueTypesTest:TestStructsAsMethodArgs'); }, 1);",
+                    debugger_test_loc, 34, 12, "MethodWithStructArgs");
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                {
+                    Assert.Equal(3, locals.Count());
+                    CheckString(locals, "label", "TestStructsAsMethodArgs#label");
+                    CheckValueType(locals, "ss_arg", "DebuggerTests.ValueTypesTest.SimpleStruct");
+                    CheckNumber(locals, "x", 3);
+                }
+
+                var dt = new DateTime(2025, 6, 7, 8, 10, 11);
+                var ss_local_as_ss_arg = new
+                {
+                    V = TGetter("V"),
+                    str_member = TString("ss_local#SimpleStruct#string#0#SimpleStruct#str_member"),
+                    dt = TValueType("System.DateTime", dt.ToString()),
+                    gs = TValueType("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
+                    Kind = TEnum("System.DateTimeKind", "Local")
+                };
+                var ss_local_gs = new
+                {
+                    StringField = TString("ss_local#SimpleStruct#string#0#SimpleStruct#gs#StringField"),
+                    List = TObject("System.Collections.Generic.List<System.DateTime>"),
+                    Options = TEnum("DebuggerTests.Options", "Option1")
+                };
+
+                // Check ss_arg's properties
+                var ss_arg_props = await GetObjectOnFrame(pause_location["callFrames"][0], "ss_arg");
+                await CheckProps(ss_arg_props, ss_local_as_ss_arg, "ss_arg");
+
+                var res = await InvokeGetter(GetAndAssertObjectWithName(locals, "ss_arg"), "V");
+                await CheckValue(res.Value["result"], TNumber(0xDEADBEEF + (uint) dt.Month), "ss_arg#V");
+
+                {
+                    // Check ss_local.dt
+                    await CheckDateTime(ss_arg_props, "dt", dt);
+
+                    // Check ss_local.gs
+                    await CompareObjectPropertiesFor(ss_arg_props, "gs", ss_local_gs);
+                }
+
+                pause_location = await StepAndCheck(StepKind.Over, debugger_test_loc, 38, 8, "MethodWithStructArgs", times : 4,
+                    locals_fn: (l) => { /* non-null to make sure that locals get fetched */ });
+                locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                {
+                    Assert.Equal(3, locals.Count());
+
+                    CheckString(locals, "label", "TestStructsAsMethodArgs#label");
+                    CheckValueType(locals, "ss_arg", "DebuggerTests.ValueTypesTest.SimpleStruct");
+                    CheckNumber(locals, "x", 3);
+                }
+
+                var ss_arg_updated = new
+                {
+                    V = TGetter("V"),
+                    str_member = TString("ValueTypesTest#MethodWithStructArgs#updated#ss_arg#str_member"),
+                    dt = TValueType("System.DateTime", dt.ToString()),
+                    gs = TValueType("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
+                    Kind = TEnum("System.DateTimeKind", "Utc")
+                };
+
+                ss_arg_props = await GetObjectOnFrame(pause_location["callFrames"][0], "ss_arg");
+                await CheckProps(ss_arg_props, ss_arg_updated, "ss_arg");
+
+                res = await InvokeGetter(GetAndAssertObjectWithName(locals, "ss_arg"), "V");
+                await CheckValue(res.Value["result"], TNumber(0xDEADBEEF + (uint) dt.Month), "ss_arg#V");
+
+                {
+                    // Check ss_local.gs
+                    await CompareObjectPropertiesFor(ss_arg_props, "gs", new
+                    {
+                        StringField = TString("ValueTypesTest#MethodWithStructArgs#updated#gs#StringField#3"),
+                            List = TObject("System.Collections.Generic.List<System.DateTime>"),
+                            Options = TEnum("DebuggerTests.Options", "Option1")
+                    });
+
+                    await CheckDateTime(ss_arg_props, "dt", dt);
+                }
+
+                // Check locals on previous frame, same as earlier in this test
+                ss_arg_props = await GetObjectOnFrame(pause_location["callFrames"][1], "ss_local");
+                await CheckProps(ss_arg_props, ss_local_as_ss_arg, "ss_local");
+
+                {
+                    // Check ss_local.dt
+                    await CheckDateTime(ss_arg_props, "dt", dt);
+
+                    // Check ss_local.gs
+                    var gs_props = await GetObjectOnLocals(ss_arg_props, "gs");
+                    CheckString(gs_props, "StringField", "ss_local#SimpleStruct#string#0#SimpleStruct#gs#StringField");
+                    CheckObject(gs_props, "List", "System.Collections.Generic.List<System.DateTime>");
+                }
+
+                // ----------- Step back to the caller ---------
+
+                pause_location = await StepAndCheck(StepKind.Over, debugger_test_loc, 28, 12, "TestStructsAsMethodArgs",
+                    times : 2, locals_fn: (l) => { /* non-null to make sure that locals get fetched */ });
+                locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                await CheckProps(locals, new
+                    {
+                        ss_local = TValueType("DebuggerTests.ValueTypesTest.SimpleStruct"),
+                            ss_ret = TValueType("DebuggerTests.ValueTypesTest.SimpleStruct")
+                    },
+                    "locals#0");
+
+                ss_arg_props = await GetObjectOnFrame(pause_location["callFrames"][0], "ss_local");
+                await CheckProps(ss_arg_props, ss_local_as_ss_arg, "ss_local");
+
+                {
+                    // Check ss_local.gs
+                    await CompareObjectPropertiesFor(ss_arg_props, "gs", ss_local_gs, label: "ss_local_gs");
+                }
+
+                // FIXME: check ss_local.gs.List's members
+            });
+        }
+
+        [Fact]
+        public async Task CheckUpdatedValueTypeFieldsOnResume()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-valuetypes-test.cs";
+
+                var lines = new [] { 203, 206 };
+                await SetBreakpoint(debugger_test_loc, lines[0], 12);
+                await SetBreakpoint(debugger_test_loc, lines[1], 12);
+
+                var pause_location = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_static_method ('[debugger-test] DebuggerTests.ValueTypesTest:MethodUpdatingValueTypeMembers'); }, 1);",
+                    debugger_test_loc, lines[0], 12, "MethodUpdatingValueTypeMembers");
+
+                await CheckLocals(pause_location, new DateTime(1, 2, 3, 4, 5, 6), new DateTime(4, 5, 6, 7, 8, 9));
+
+                // Resume
+                pause_location = await SendCommandAndCheck(JObject.FromObject(new { }), "Debugger.resume", debugger_test_loc, lines[1], 12, "MethodUpdatingValueTypeMembers");
+                await CheckLocals(pause_location, new DateTime(9, 8, 7, 6, 5, 4), new DateTime(5, 1, 3, 7, 9, 10));
+            });
+
+            async Task CheckLocals(JToken pause_location, DateTime obj_dt, DateTime vt_dt)
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                await CheckProps(locals, new
+                {
+                    obj = TObject("DebuggerTests.ClassForToStringTests"),
+                        vt = TObject("DebuggerTests.StructForToStringTests")
+                }, "locals");
+
+                var obj_props = await GetObjectOnLocals(locals, "obj");
+                {
+                    await CheckProps(obj_props, new
+                    {
+                        DT = TValueType("System.DateTime", obj_dt.ToString())
+                    }, "locals#obj.DT", num_fields : 5);
+
+                    await CheckDateTime(obj_props, "DT", obj_dt);
+                }
+
+                var vt_props = await GetObjectOnLocals(locals, "vt");
+                {
+                    await CheckProps(vt_props, new
+                    {
+                        DT = TValueType("System.DateTime", vt_dt.ToString())
+                    }, "locals#obj.DT", num_fields : 5);
+
+                    await CheckDateTime(vt_props, "DT", vt_dt);
+                }
+            }
+        }
+
+        [Fact]
+        public async Task CheckUpdatedValueTypeLocalsOnResumeAsync()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-valuetypes-test.cs";
+
+                var lines = new [] { 212, 214 };
+                await SetBreakpoint(debugger_test_loc, lines[0], 12);
+                await SetBreakpoint(debugger_test_loc, lines[1], 12);
+
+                var pause_location = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_static_method ('[debugger-test] DebuggerTests.ValueTypesTest:MethodUpdatingValueTypeLocalsAsync'); }, 1);",
+                    debugger_test_loc, lines[0], 12, "MoveNext");
+
+                var dt = new DateTime(1, 2, 3, 4, 5, 6);
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                await CheckDateTime(locals, "dt", dt);
+
+                // Resume
+                dt = new DateTime(9, 8, 7, 6, 5, 4);
+                pause_location = await SendCommandAndCheck(JObject.FromObject(new { }), "Debugger.resume", debugger_test_loc, lines[1], 12, "MoveNext");
+                locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                await CheckDateTime(locals, "dt", dt);
+            });
+        }
+
+        [Fact]
+        public async Task CheckUpdatedVTArrayMembersOnResume()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-valuetypes-test.cs";
+
+                var lines = new [] { 223, 225 };
+                await SetBreakpoint(debugger_test_loc, lines[0], 12);
+                await SetBreakpoint(debugger_test_loc, lines[1], 12);
+
+                var dt = new DateTime(1, 2, 3, 4, 5, 6);
+                var pause_location = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_static_method ('[debugger-test] DebuggerTests.ValueTypesTest:MethodUpdatingVTArrayMembers'); }, 1);",
+                    debugger_test_loc, lines[0], 12, "MethodUpdatingVTArrayMembers");
+                await CheckArrayElements(pause_location, dt);
+
+                // Resume
+                dt = new DateTime(9, 8, 7, 6, 5, 4);
+                pause_location = await SendCommandAndCheck(JObject.FromObject(new { }), "Debugger.resume", debugger_test_loc, lines[1], 12, "MethodUpdatingVTArrayMembers");
+                await CheckArrayElements(pause_location, dt);
+            });
+
+            async Task CheckArrayElements(JToken pause_location, DateTime dt)
+            {
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                await CheckProps(locals, new
+                {
+                    ssta = TArray("DebuggerTests.StructForToStringTests[]", 1)
+                }, "locals");
+
+                var ssta = await GetObjectOnLocals(locals, "ssta");
+                var sst0 = await GetObjectOnLocals(ssta, "0");
+                await CheckProps(sst0, new
+                {
+                    DT = TValueType("System.DateTime", dt.ToString())
+                }, "dta [0]", num_fields : 5);
+
+                await CheckDateTime(sst0, "DT", dt);
+            }
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectLocalsWithStructsStaticAsync(bool use_cfo)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                ctx.UseCallFunctionOnBeforeGetProperties = use_cfo;
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-valuetypes-test.cs";
+
+                await SetBreakpoint(debugger_test_loc, 54, 12);
+
+                var pause_location = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_static_method_async (" +
+                    "'[debugger-test] DebuggerTests.ValueTypesTest:MethodWithLocalStructsStaticAsync'" +
+                    "); }, 1);",
+                    debugger_test_loc, 54, 12, "MoveNext"); //BUG: method name
+
+                var locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+                await CheckProps(locals, new
+                    {
+                        ss_local = TObject("DebuggerTests.ValueTypesTest.SimpleStruct"),
+                            gs_local = TValueType("DebuggerTests.ValueTypesTest.GenericStruct<int>"),
+                            result = TBool(true)
+                    },
+                    "locals#0");
+
+                var dt = new DateTime(2021, 2, 3, 4, 6, 7);
+                // Check ss_local's properties
+                var ss_local_props = await GetObjectOnFrame(pause_location["callFrames"][0], "ss_local");
+                await CheckProps(ss_local_props, new
+                {
+                    V          = TGetter("V"),
+                    str_member = TString("set in MethodWithLocalStructsStaticAsync#SimpleStruct#str_member"),
+                    dt         = TValueType("System.DateTime", dt.ToString()),
+                    gs         = TValueType("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
+                    Kind       = TEnum("System.DateTimeKind", "Utc")
+                }, "ss_local");
+
+                {
+                    var gres = await InvokeGetter(GetAndAssertObjectWithName(locals, "ss_local"), "V");
+                    await CheckValue(gres.Value["result"], TNumber(0xDEADBEEF + 2), $"ss_local#V");
+
+                    // Check ss_local.dt
+                    await CheckDateTime(ss_local_props, "dt", dt);
+
+                    // Check ss_local.gs
+                    await CompareObjectPropertiesFor(ss_local_props, "gs",
+                        new
+                        {
+                            StringField = TString("set in MethodWithLocalStructsStaticAsync#SimpleStruct#gs#StringField"),
+                                List = TObject("System.Collections.Generic.List<System.DateTime>"),
+                                Options = TEnum("DebuggerTests.Options", "Option1")
+                        }
+                    );
+                }
+
+                // Check gs_local's properties
+                var gs_local_props = await GetObjectOnFrame(pause_location["callFrames"][0], "gs_local");
+                await CheckProps(gs_local_props, new
+                {
+                    StringField = TString("gs_local#GenericStruct<ValueTypesTest>#StringField"),
+                        List = TObject("System.Collections.Generic.List<int>"),
+                        Options = TEnum("DebuggerTests.Options", "Option2")
+                }, "gs_local");
+
+                // FIXME: check ss_local.gs.List's members
+            });
+        }
+
+        [Theory]
+        [InlineData(135, 12, "MethodWithLocalsForToStringTest", false, false)]
+        [InlineData(145, 12, "MethodWithArgumentsForToStringTest", true, false)]
+        [InlineData(190, 12, "MethodWithArgumentsForToStringTestAsync", true, true)]
+        [InlineData(180, 12, "MethodWithArgumentsForToStringTestAsync", false, true)]
+        public async Task InspectLocalsForToStringDescriptions(int line, int col, string method_name, bool call_other, bool invoke_async)
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+            string entry_method_name = $"[debugger-test] DebuggerTests.ValueTypesTest:MethodWithLocalsForToStringTest{(invoke_async ? "Async" : String.Empty)}";
+            int frame_idx = 0;
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+                var debugger_test_loc = "dotnet://debugger-test.dll/debugger-valuetypes-test.cs";
+
+                await SetBreakpoint(debugger_test_loc, line, col);
+
+                var eval_expr = "window.setTimeout(function() {" +
+                    (invoke_async ? "invoke_static_method_async (" : "invoke_static_method (") +
+                    $"'{entry_method_name}'," +
+                    (call_other ? "true" : "false") +
+                    "); }, 1);";
+                Console.WriteLine($"{eval_expr}");
+
+                var pause_location = await EvaluateAndCheck(eval_expr, debugger_test_loc, line, col, invoke_async ? "MoveNext" : method_name);
+
+                var dt0 = new DateTime(2020, 1, 2, 3, 4, 5);
+                var dt1 = new DateTime(2010, 5, 4, 3, 2, 1);
+                var ts = dt0 - dt1;
+                var dto = new DateTimeOffset(dt0, new TimeSpan(4, 5, 0));
+
+                var frame_locals = await GetProperties(pause_location["callFrames"][frame_idx]["callFrameId"].Value<string>());
+                await CheckProps(frame_locals, new
+                {
+                    call_other = TBool(call_other),
+                        dt0 = TValueType("System.DateTime", dt0.ToString()),
+                        dt1 = TValueType("System.DateTime", dt1.ToString()),
+                        dto = TValueType("System.DateTimeOffset", dto.ToString()),
+                        ts = TValueType("System.TimeSpan", ts.ToString()),
+                        dec = TValueType("System.Decimal", "123987123"),
+                        guid = TValueType("System.Guid", "3D36E07E-AC90-48C6-B7EC-A481E289D014"),
+                        dts = TArray("System.DateTime[]", 2),
+                        obj = TObject("DebuggerTests.ClassForToStringTests"),
+                        sst = TObject("DebuggerTests.StructForToStringTests")
+                }, "locals#0");
+
+                var dts_0 = new DateTime(1983, 6, 7, 5, 6, 10);
+                var dts_1 = new DateTime(1999, 10, 15, 1, 2, 3);
+                var dts_elements = await GetObjectOnLocals(frame_locals, "dts");
+                await CheckDateTime(dts_elements, "0", dts_0);
+                await CheckDateTime(dts_elements, "1", dts_1);
+
+                // TimeSpan
+                await CompareObjectPropertiesFor(frame_locals, "ts",
+                    new
+                    {
+                        Days = TNumber(3530),
+                            Minutes = TNumber(2),
+                            Seconds = TNumber(4),
+                    }, "ts_props", num_fields : 12);
+
+                // DateTimeOffset
+                await CompareObjectPropertiesFor(frame_locals, "dto",
+                    new
+                    {
+                        Day = TNumber(2),
+                            Year = TNumber(2020),
+                            DayOfWeek = TEnum("System.DayOfWeek", "Thursday")
+                    }, "dto_props", num_fields : 22);
+
+                var DT = new DateTime(2004, 10, 15, 1, 2, 3);
+                var DTO = new DateTimeOffset(dt0, new TimeSpan(2, 14, 0));
+
+                var obj_props = await CompareObjectPropertiesFor(frame_locals, "obj",
+                    new
+                    {
+                        DT = TValueType("System.DateTime", DT.ToString()),
+                            DTO = TValueType("System.DateTimeOffset", DTO.ToString()),
+                            TS = TValueType("System.TimeSpan", ts.ToString()),
+                            Dec = TValueType("System.Decimal", "1239871"),
+                            Guid = TValueType("System.Guid", "3D36E07E-AC90-48C6-B7EC-A481E289D014")
+                    }, "obj_props");
+
+                DTO = new DateTimeOffset(dt0, new TimeSpan(3, 15, 0));
+                var sst_props = await CompareObjectPropertiesFor(frame_locals, "sst",
+                    new
+                    {
+                        DT = TValueType("System.DateTime", DT.ToString()),
+                            DTO = TValueType("System.DateTimeOffset", DTO.ToString()),
+                            TS = TValueType("System.TimeSpan", ts.ToString()),
+                            Dec = TValueType("System.Decimal", "1239871"),
+                            Guid = TValueType("System.Guid", "3D36E07E-AC90-48C6-B7EC-A481E289D014")
+                    }, "sst_props");
+            });
+        }
+
+        [Fact]
+        public async Task InspectLocals()
+        {
+            var insp = new Inspector();
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                var wait_res = await RunUntil("locals_inner");
+                var locals = await GetProperties(wait_res["callFrames"][1]["callFrameId"].Value<string>());
+            });
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task InspectLocalsForStructInstanceMethod(bool use_cfo) => await CheckInspectLocalsAtBreakpointSite(
+            "dotnet://debugger-test.dll/debugger-array-test.cs", 258, 12,
+            "GenericInstanceMethod<DebuggerTests.SimpleClass>",
+            "window.setTimeout(function() { invoke_static_method_async ('[debugger-test] DebuggerTests.EntryClass:run'); })",
+            use_cfo : use_cfo,
+            wait_for_event_fn : async(pause_location) =>
+            {
+                var frame_locals = await GetProperties(pause_location["callFrames"][0]["callFrameId"].Value<string>());
+
+                await CheckProps(frame_locals, new
+                    {
+                        sc_arg = TObject("DebuggerTests.SimpleClass"),
+                            @this = TValueType("DebuggerTests.Point"),
+                            local_gs = TValueType("DebuggerTests.SimpleGenericStruct<int>")
+                    },
+                    "locals#0");
+
+                await CompareObjectPropertiesFor(frame_locals, "local_gs",
+                    new
+                    {
+                        Id = TString("local_gs#Id"),
+                            Color = TEnum("DebuggerTests.RGB", "Green"),
+                            Value = TNumber(4)
+                    },
+                    label: "local_gs#0");
+
+                await CompareObjectPropertiesFor(frame_locals, "sc_arg",
+                    TSimpleClass(10, 45, "sc_arg#Id", "Blue"),
+                    label: "sc_arg#0");
+
+                await CompareObjectPropertiesFor(frame_locals, "this",
+                    TPoint(90, -4, "point#Id", "Green"),
+                    label: "this#0");
+
+            });
+
+        [Fact]
+        public async Task SteppingIntoMscorlib()
+        {
+            var insp = new Inspector();
+            //Collect events
+            var scripts = SubscribeToScripts(insp);
+
+            await Ready();
+            await insp.Ready(async(cli, token) =>
+            {
+                ctx = new DebugTestContext(cli, insp, token, scripts);
+
+                var bp = await SetBreakpoint("dotnet://debugger-test.dll/debugger-test.cs", 83, 8);
+                var pause_location = await EvaluateAndCheck(
+                    "window.setTimeout(function() { invoke_static_method ('[debugger-test] Math:OuterMethod'); }, 1);",
+                    "dotnet://debugger-test.dll/debugger-test.cs", 83, 8,
+                    "OuterMethod");
+
+                //make sure we're on the right bp
+                Assert.Equal(bp.Value["breakpointId"]?.ToString(), pause_location["hitBreakpoints"] ? [0]?.Value<string>());
+
+                pause_location = await SendCommandAndCheck(null, $"Debugger.stepInto", null, -1, -1, null);
+                var top_frame = pause_location["callFrames"][0];
+
+                AssertEqual("WriteLine", top_frame["functionName"]?.Value<string>(), "Expected to be in WriteLine method");
+                var script_id = top_frame["functionLocation"]["scriptId"].Value<string>();
+                AssertEqual("dotnet://System.Console.dll/Console.cs", scripts[script_id], "Expected to stopped in System.Console.WriteLine");
+            });
+        }
+
+        [Fact]
+        public async Task InvalidValueTypeData()
+        {
+            await CheckInspectLocalsAtBreakpointSite(
+                "dotnet://debugger-test.dll/debugger-test.cs", 85, 8,
+                "OuterMethod",
+                "window.setTimeout(function() { invoke_static_method ('[debugger-test] Math:OuterMethod'); })",
+                wait_for_event_fn : async(pause_location) =>
+                {
+                    var new_id = await CreateNewId(@"MONO._new_or_add_id_props ({ scheme: 'valuetype', idArgs: { containerId: 1 }, props: { klass: 3, value64: 4 }});");
+                    await _invoke_getter(new_id, "NonExistant", expect_ok : false);
+
+                    new_id = await CreateNewId(@"MONO._new_or_add_id_props ({ scheme: 'valuetype', idArgs: { containerId: 1 }, props: { klass: 3 }});");
+                    await _invoke_getter(new_id, "NonExistant", expect_ok : false);
+
+                    new_id = await CreateNewId(@"MONO._new_or_add_id_props ({ scheme: 'valuetype', idArgs: { containerId: 1 }, props: { klass: 3, value64: 'AA' }});");
+                    await _invoke_getter(new_id, "NonExistant", expect_ok : false);
+                });
+
+            async Task<string> CreateNewId(string expr)
+            {
+                var res = await ctx.cli.SendCommand("Runtime.evaluate", JObject.FromObject(new { expression = expr }), ctx.token);
+                Assert.True(res.IsOk, "Expected Runtime.evaluate to succeed");
+                AssertEqual("string", res.Value["result"] ? ["type"]?.Value<string>(), "Expected Runtime.evaluate to return a string type result");
+                return res.Value["result"] ? ["value"]?.Value<string>();
+            }
+
+            async Task<Result> _invoke_getter(string obj_id, string property_name, bool expect_ok)
+            {
+                var expr = $"MONO._invoke_getter ('{obj_id}', '{property_name}')";
+                var res = await ctx.cli.SendCommand("Runtime.evaluate", JObject.FromObject(new { expression = expr }), ctx.token);
+                AssertEqual(expect_ok, res.IsOk, "Runtime.evaluate result not as expected for {expr}");
+
+                return res;
+            }
+        }
+
+        //TODO add tests covering basic stepping behavior as step in/out/over
+    }
+}
diff --git a/src/mono/wasm/debugger/DebuggerTestSuite/appsettings.json b/src/mono/wasm/debugger/DebuggerTestSuite/appsettings.json
new file mode 100644
index 00000000000000..0cda8d48a36c31
--- /dev/null
+++ b/src/mono/wasm/debugger/DebuggerTestSuite/appsettings.json
@@ -0,0 +1,9 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Error",
+      "Microsoft": "Warning",
+      "Microsoft.Hosting.Lifetime": "Information"
+    }
+  }
+}
diff --git a/src/mono/wasm/debugger/tests/debugger-array-test.cs b/src/mono/wasm/debugger/tests/debugger-array-test.cs
new file mode 100644
index 00000000000000..95e2fb1504e9dd
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-array-test.cs
@@ -0,0 +1,308 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Threading.Tasks;
+namespace DebuggerTests
+{
+    public class ArrayTestsClass
+    {
+        public static void PrimitiveTypeLocals(bool call_other = false)
+        {
+            var int_arr = new int[] { 4, 70, 1 };
+            var int_arr_empty = new int[0];
+            int[] int_arr_null = null;
+
+            if (call_other)
+                OtherMethod();
+
+            Console.WriteLine($"int_arr: {int_arr.Length}, {int_arr_empty.Length}, {int_arr_null?.Length}");
+        }
+
+        public static void ValueTypeLocals(bool call_other = false)
+        {
+            var point_arr = new Point[]
+            {
+            new Point { X = 5, Y = -2, Id = "point_arr#Id#0", Color = RGB.Green },
+            new Point { X = 123, Y = 0, Id = "point_arr#Id#1", Color = RGB.Blue },
+            };
+
+            var point_arr_empty = new Point[0];
+            Point[] point_arr_null = null;
+
+            if (call_other)
+                OtherMethod();
+
+            Console.WriteLine($"point_arr: {point_arr.Length}, {point_arr_empty.Length}, {point_arr_null?.Length}");
+        }
+
+        public static void ObjectTypeLocals(bool call_other = false)
+        {
+            var class_arr = new SimpleClass[]
+            {
+            new SimpleClass { X = 5, Y = -2, Id = "class_arr#Id#0", Color = RGB.Green },
+            null,
+            new SimpleClass { X = 123, Y = 0, Id = "class_arr#Id#2", Color = RGB.Blue },
+            };
+
+            var class_arr_empty = new SimpleClass[0];
+            SimpleClass[] class_arr_null = null;
+
+            if (call_other)
+                OtherMethod();
+
+            Console.WriteLine($"class_arr: {class_arr.Length}, {class_arr_empty.Length}, {class_arr_null?.Length}");
+        }
+
+        public static void GenericTypeLocals(bool call_other = false)
+        {
+            var gclass_arr = new GenericClass<int>[]
+            {
+            null,
+            new GenericClass<int> { Id = "gclass_arr#1#Id", Color = RGB.Red, Value = 5 },
+            new GenericClass<int> { Id = "gclass_arr#2#Id", Color = RGB.Blue, Value = -12 },
+            };
+
+            var gclass_arr_empty = new GenericClass<int>[0];
+            GenericClass<int>[] gclass_arr_null = null;
+
+            if (call_other)
+                OtherMethod();
+
+            Console.WriteLine($"gclass_arr: {gclass_arr.Length}, {gclass_arr_empty.Length}, {gclass_arr_null?.Length}");
+        }
+
+        public static void GenericValueTypeLocals(bool call_other = false)
+        {
+            var gvclass_arr = new SimpleGenericStruct<Point>[]
+            {
+            new SimpleGenericStruct<Point> { Id = "gvclass_arr#1#Id", Color = RGB.Red, Value = new Point { X = 100, Y = 200, Id = "gvclass_arr#1#Value#Id", Color = RGB.Red } },
+            new SimpleGenericStruct<Point> { Id = "gvclass_arr#2#Id", Color = RGB.Blue, Value = new Point { X = 10, Y = 20, Id = "gvclass_arr#2#Value#Id", Color = RGB.Green } }
+            };
+
+            var gvclass_arr_empty = new SimpleGenericStruct<Point>[0];
+            SimpleGenericStruct<Point>[] gvclass_arr_null = null;
+
+            if (call_other)
+                OtherMethod();
+
+            Console.WriteLine($"gvclass_arr: {gvclass_arr.Length}, {gvclass_arr_empty.Length}, {gvclass_arr_null?.Length}");
+        }
+
+        static void OtherMethod()
+        {
+            YetAnotherMethod();
+            Console.WriteLine($"Just a placeholder for breakpoints");
+        }
+
+        static void YetAnotherMethod()
+        {
+            Console.WriteLine($"Just a placeholder for breakpoints");
+        }
+
+        public static void ObjectArrayMembers()
+        {
+            var c = new Container
+            {
+                id = "c#id",
+                ClassArrayProperty = new SimpleClass[]
+                {
+                new SimpleClass { X = 5, Y = -2, Id = "ClassArrayProperty#Id#0", Color = RGB.Green },
+                new SimpleClass { X = 30, Y = 1293, Id = "ClassArrayProperty#Id#1", Color = RGB.Green },
+                null
+                },
+                ClassArrayField = new SimpleClass[]
+                {
+                null,
+                new SimpleClass { X = 5, Y = -2, Id = "ClassArrayField#Id#1", Color = RGB.Blue },
+                new SimpleClass { X = 30, Y = 1293, Id = "ClassArrayField#Id#2", Color = RGB.Green },
+                },
+                PointsProperty = new Point[]
+                {
+                new Point { X = 5, Y = -2, Id = "PointsProperty#Id#0", Color = RGB.Green },
+                new Point { X = 123, Y = 0, Id = "PointsProperty#Id#1", Color = RGB.Blue },
+                },
+                PointsField = new Point[]
+                {
+                new Point { X = 5, Y = -2, Id = "PointsField#Id#0", Color = RGB.Green },
+                new Point { X = 123, Y = 0, Id = "PointsField#Id#1", Color = RGB.Blue },
+                }
+            };
+
+            Console.WriteLine($"Back from PlaceholderMethod, {c.ClassArrayProperty?.Length}");
+            c.PlaceholderMethod();
+            Console.WriteLine($"Back from PlaceholderMethod, {c.id}");
+        }
+
+        public static async Task<bool> ValueTypeLocalsAsync(bool call_other = false)
+        {
+            var gvclass_arr = new SimpleGenericStruct<Point>[]
+            {
+            new SimpleGenericStruct<Point> { Id = "gvclass_arr#1#Id", Color = RGB.Red, Value = new Point { X = 100, Y = 200, Id = "gvclass_arr#1#Value#Id", Color = RGB.Red } },
+            new SimpleGenericStruct<Point> { Id = "gvclass_arr#2#Id", Color = RGB.Blue, Value = new Point { X = 10, Y = 20, Id = "gvclass_arr#2#Value#Id", Color = RGB.Green } }
+            };
+
+            var gvclass_arr_empty = new SimpleGenericStruct<Point>[0];
+            SimpleGenericStruct<Point>[] gvclass_arr_null = null;
+            Console.WriteLine($"ValueTypeLocalsAsync: call_other: {call_other}");
+            SimpleGenericStruct<Point> gvclass;
+            Point[] points = null;
+
+            if (call_other)
+            {
+                (gvclass, points) = await new ArrayTestsClass().InstanceMethodValueTypeLocalsAsync<SimpleGenericStruct<Point>>(gvclass_arr[0]);
+                Console.WriteLine($"* gvclass: {gvclass}, points: {points.Length}");
+            }
+
+            Console.WriteLine($"gvclass_arr: {gvclass_arr.Length}, {gvclass_arr_empty.Length}, {gvclass_arr_null?.Length}");
+            return true;
+        }
+
+        public async Task < (T, Point[]) > InstanceMethodValueTypeLocalsAsync<T>(T t1)
+        {
+            var point_arr = new Point[]
+            {
+                new Point { X = 5, Y = -2, Id = "point_arr#Id#0", Color = RGB.Red },
+                new Point { X = 123, Y = 0, Id = "point_arr#Id#1", Color = RGB.Blue }
+            };
+            var point = new Point { X = 45, Y = 51, Id = "point#Id", Color = RGB.Green };
+
+            Console.WriteLine($"point_arr: {point_arr.Length}, T: {t1}, point: {point}");
+            return (t1, new Point[] { point_arr[0], point_arr[1], point });
+        }
+
+        // A workaround for method invocations on structs not working right now
+        public static async Task EntryPointForStructMethod(bool call_other = false)
+        {
+            await Point.AsyncMethod(call_other);
+        }
+
+        public static void GenericValueTypeLocals2(bool call_other = false)
+        {
+            var gvclass_arr = new SimpleGenericStruct<Point[]>[]
+            {
+            new SimpleGenericStruct<Point[]>
+            {
+            Id = "gvclass_arr#0#Id",
+            Color = RGB.Red,
+            Value = new Point[]
+            {
+            new Point { X = 100, Y = 200, Id = "gvclass_arr#0#0#Value#Id", Color = RGB.Red },
+            new Point { X = 100, Y = 200, Id = "gvclass_arr#0#1#Value#Id", Color = RGB.Green }
+            }
+            },
+
+            new SimpleGenericStruct<Point[]>
+            {
+            Id = "gvclass_arr#1#Id",
+            Color = RGB.Blue,
+            Value = new Point[]
+            {
+            new Point { X = 100, Y = 200, Id = "gvclass_arr#1#0#Value#Id", Color = RGB.Green },
+            new Point { X = 100, Y = 200, Id = "gvclass_arr#1#1#Value#Id", Color = RGB.Blue }
+            }
+            },
+            };
+
+            var gvclass_arr_empty = new SimpleGenericStruct<Point[]>[0];
+            SimpleGenericStruct<Point[]>[] gvclass_arr_null = null;
+
+            if (call_other)
+                OtherMethod();
+
+            Console.WriteLine($"gvclass_arr: {gvclass_arr.Length}, {gvclass_arr_empty.Length}, {gvclass_arr_null?.Length}");
+        }
+    }
+
+    public class Container
+    {
+        public string id;
+        public SimpleClass[] ClassArrayProperty { get; set; }
+        public SimpleClass[] ClassArrayField;
+
+        public Point[] PointsProperty { get; set; }
+        public Point[] PointsField;
+
+        public void PlaceholderMethod()
+        {
+            Console.WriteLine($"Container.PlaceholderMethod");
+        }
+    }
+
+    public struct Point
+    {
+        public int X, Y;
+        public string Id { get; set; }
+        public RGB Color { get; set; }
+
+        /* instance too */
+        public static async Task AsyncMethod(bool call_other)
+        {
+            int local_i = 5;
+            var sc = new SimpleClass { X = 10, Y = 45, Id = "sc#Id", Color = RGB.Blue };
+            if (call_other)
+                await new Point { X = 90, Y = -4, Id = "point#Id", Color = RGB.Green }.AsyncInstanceMethod(sc);
+            Console.WriteLine($"AsyncMethod local_i: {local_i}, sc: {sc.Id}");
+        }
+
+        public async Task AsyncInstanceMethod(SimpleClass sc_arg)
+        {
+            var local_gs = new SimpleGenericStruct<int> { Id = "local_gs#Id", Color = RGB.Green, Value = 4 };
+            sc_arg.Id = "sc_arg#Id";
+            Console.WriteLine($"AsyncInstanceMethod sc_arg: {sc_arg.Id}, local_gs: {local_gs.Id}");
+        }
+
+        public void GenericInstanceMethod<T>(T sc_arg) where T : SimpleClass
+        {
+            var local_gs = new SimpleGenericStruct<int> { Id = "local_gs#Id", Color = RGB.Green, Value = 4 };
+            sc_arg.Id = "sc_arg#Id";
+            Console.WriteLine($"AsyncInstanceMethod sc_arg: {sc_arg.Id}, local_gs: {local_gs.Id}");
+        }
+    }
+
+    public class SimpleClass
+    {
+        public int X, Y;
+        public string Id { get; set; }
+        public RGB Color { get; set; }
+
+        public Point PointWithCustomGetter { get { return new Point { X = 100, Y = 400, Id = "SimpleClass#Point#gen#Id", Color = RGB.Green }; } }
+    }
+
+    public class GenericClass<T>
+    {
+        public string Id { get; set; }
+        public RGB Color { get; set; }
+        public T Value { get; set; }
+    }
+
+    public struct SimpleGenericStruct<T>
+    {
+        public string Id { get; set; }
+        public RGB Color { get; set; }
+        public T Value { get; set; }
+    }
+
+    public class EntryClass
+    {
+        public static void run()
+        {
+            ArrayTestsClass.PrimitiveTypeLocals(true);
+            ArrayTestsClass.ValueTypeLocals(true);
+            ArrayTestsClass.ObjectTypeLocals(true);
+
+            ArrayTestsClass.GenericTypeLocals(true);
+            ArrayTestsClass.GenericValueTypeLocals(true);
+            ArrayTestsClass.GenericValueTypeLocals2(true);
+
+            ArrayTestsClass.ObjectArrayMembers();
+
+            ArrayTestsClass.ValueTypeLocalsAsync(true).Wait();
+
+            ArrayTestsClass.EntryPointForStructMethod(true).Wait();
+
+            var sc = new SimpleClass { X = 10, Y = 45, Id = "sc#Id", Color = RGB.Blue };
+            new Point { X = 90, Y = -4, Id = "point#Id", Color = RGB.Green }.GenericInstanceMethod(sc);
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/tests/debugger-cfo-test.cs b/src/mono/wasm/debugger/tests/debugger-cfo-test.cs
new file mode 100644
index 00000000000000..6e885646bf0015
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-cfo-test.cs
@@ -0,0 +1,75 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+namespace DebuggerTests
+{
+    public class CallFunctionOnTest
+    {
+        public static void LocalsTest(int len)
+        {
+            var big = new int[len];
+            for (int i = 0; i < len; i++)
+                big[i] = i + 1000;
+
+            var simple_struct = new Math.SimpleStruct() { dt = new DateTime(2020, 1, 2, 3, 4, 5), gs = new Math.GenericStruct<DateTime> { StringField = $"simple_struct # gs # StringField" } };
+
+            var ss_arr = new Math.SimpleStruct[len];
+            for (int i = 0; i < len; i++)
+                ss_arr[i] = new Math.SimpleStruct() { dt = new DateTime(2020 + i, 1, 2, 3, 4, 5), gs = new Math.GenericStruct<DateTime> { StringField = $"ss_arr # {i} # gs # StringField" } };
+
+            var nim = new Math.NestedInMath { SimpleStructProperty = new Math.SimpleStruct() { dt = new DateTime(2010, 6, 7, 8, 9, 10) } };
+            Action<Math.GenericStruct<int[]>> action = Math.DelegateTargetWithVoidReturn;
+            Console.WriteLine("foo");
+        }
+
+        public static void PropertyGettersTest()
+        {
+            var ptd = new ClassWithProperties { DTAutoProperty = new DateTime(4, 5, 6, 7, 8, 9), V = 0xDEADBEEF };
+            var swp = new StructWithProperties { DTAutoProperty = new DateTime(4, 5, 6, 7, 8, 9), V = 0xDEADBEEF };
+            System.Console.WriteLine("break here");
+        }
+
+        public static async System.Threading.Tasks.Task PropertyGettersTestAsync()
+        {
+            var ptd = new ClassWithProperties { DTAutoProperty = new DateTime (4, 5, 6, 7, 8, 9), V = 0xDEADBEEF };
+            var swp = new StructWithProperties { DTAutoProperty = new DateTime (4, 5, 6, 7, 8, 9), V = 0xDEADBEEF };
+            System.Console.WriteLine("break here");
+            await System.Threading.Tasks.Task.CompletedTask;
+        }
+
+        public static void MethodForNegativeTests (string value = null)
+        {
+            var ptd = new ClassWithProperties { StringField = value };
+            var swp = new StructWithProperties { StringField = value };
+            Console.WriteLine("break here");
+        }
+    }
+
+    class ClassWithProperties
+    {
+        public uint V;
+        public uint Int { get { return V + (uint)DT.Month; } }
+        public string String { get { return $"String property, V: 0x{V:X}"; } }
+        public DateTime DT { get { return new DateTime(3, 4, 5, 6, 7, 8); } }
+
+        public int[] IntArray { get { return new int[] { 10, 20 }; } }
+        public DateTime[] DTArray { get { return new DateTime[] { new DateTime(6, 7, 8, 9, 10, 11), new DateTime(1, 2, 3, 4, 5, 6) }; } }
+        public DateTime DTAutoProperty { get; set; }
+        public string StringField;
+    }
+
+    struct StructWithProperties
+    {
+        public uint V;
+        public uint Int { get { return V + (uint)DT.Month; } }
+        public string String { get { return $"String property, V: 0x{V:X}"; } }
+        public DateTime DT { get { return new DateTime(3, 4, 5, 6, 7, 8); } }
+
+        public int[] IntArray { get { return new int[] { 10, 20 }; } }
+        public DateTime[] DTArray { get { return new DateTime[] { new DateTime(6, 7, 8, 9, 10, 11), new DateTime(1, 2, 3, 4, 5, 6) }; } }
+        public DateTime DTAutoProperty { get; set; }
+        public string StringField;
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/tests/debugger-datetime-test.cs b/src/mono/wasm/debugger/tests/debugger-datetime-test.cs
new file mode 100644
index 00000000000000..8ea265079e1ff0
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-datetime-test.cs
@@ -0,0 +1,29 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Globalization;
+namespace DebuggerTests
+{
+    public class DateTimeTest
+    {
+        public static string LocaleTest(string locale)
+        {
+            CultureInfo.CurrentCulture = new CultureInfo(locale, false);
+            Console.WriteLine("CurrentCulture is {0}", CultureInfo.CurrentCulture.Name);
+
+            DateTimeFormatInfo dtfi = CultureInfo.GetCultureInfo(locale).DateTimeFormat;
+            var fdtp = dtfi.FullDateTimePattern;
+            var ldp = dtfi.LongDatePattern;
+            var ltp = dtfi.LongTimePattern;
+            var sdp = dtfi.ShortDatePattern;
+            var stp = dtfi.ShortTimePattern;
+
+            DateTime dt = new DateTime(2020, 1, 2, 3, 4, 5);
+            string dt_str = dt.ToString();
+            Console.WriteLine("Current time is {0}", dt_str);
+
+            return dt_str;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/tests/debugger-driver.html b/src/mono/wasm/debugger/tests/debugger-driver.html
new file mode 100644
index 00000000000000..049b6b65c60026
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-driver.html
@@ -0,0 +1,124 @@
+<!doctype html>
+<html lang="en-us">
+  <head>
+  </head>
+  <body>
+	<script type='text/javascript'>
+		var App = {
+			init: function () {
+				this.int_add = Module.mono_bind_static_method ("[debugger-test] Math:IntAdd");
+				this.use_complex = Module.mono_bind_static_method ("[debugger-test] Math:UseComplex");
+				this.delegates_test = Module.mono_bind_static_method ("[debugger-test] Math:DelegatesTest");
+				this.generic_types_test = Module.mono_bind_static_method ("[debugger-test] Math:GenericTypesTest");
+				this.outer_method = Module.mono_bind_static_method ("[debugger-test] Math:OuterMethod");
+				this.async_method = Module.mono_bind_static_method ("[debugger-test] Math/NestedInMath:AsyncTest");
+				this.method_with_structs = Module.mono_bind_static_method ("[debugger-test] DebuggerTests.ValueTypesTest:MethodWithLocalStructs");
+				this.run_all = Module.mono_bind_static_method ("[debugger-test] DebuggerTest:run_all");
+				this.static_method_table = {};
+				console.log ("ready");
+			},
+		};
+		function invoke_static_method (method_name, ...args) {
+			var method = App.static_method_table [method_name];
+			if (method == undefined)
+				method = App.static_method_table [method_name] = Module.mono_bind_static_method (method_name);
+
+			return method (...args);
+		}
+
+		async function invoke_static_method_async (method_name, ...args) {
+			var method = App.static_method_table [method_name];
+			if (method == undefined) {
+				method = App.static_method_table [method_name] = Module.mono_bind_static_method (method_name);
+			}
+
+			return await method (...args);
+		}
+
+		function invoke_big_array_js_test (len) {
+			big_array_js_test(len);
+		}
+
+		function invoke_getters_js_test () {
+			getters_js_test ();
+		}
+
+		function invoke_add () {
+			return App.int_add (10, 20);
+		}
+		function invoke_use_complex () {
+			return App.use_complex (10, 20);
+		}
+		function invoke_delegates_test () {
+			return App.delegates_test ();
+		}
+		function invoke_generic_types_test () {
+			return App.generic_types_test ();
+		}
+		function invoke_bad_js_test () {
+			console.log ("js: In invoke_bad_js_test");
+			App.non_existant ();
+			console.log ("js: After.. shouldn't reach here");
+		}
+		function invoke_outer_method () {
+			console.log('invoke_outer_method called');
+			return App.outer_method ();
+		}
+		async function invoke_async_method_with_await () {
+			return await App.async_method ("string from js", 42);
+		}
+		function invoke_method_with_structs () {
+			return App.method_with_structs ();
+		}
+		function invoke_run_all () {
+			return App.run_all ();
+		}
+      </script>
+      <script type="text/javascript" src="mono-config.js"></script>
+      <script type="text/javascript" src="runtime-debugger.js"></script>
+      <script type="text/javascript" src="other.js"></script>
+      <script async type="text/javascript" src="dotnet.js"></script>
+	  Stuff goes here
+  </body>
+  </html> 
+     
+17  sdks/wasm/debugger-test.cs
+@@ -0,0 +1,17 @@
+using System;
+
+public class Math { //Only append content to this class as the test suite depends on line info
+	public static int IntAdd (int a, int b) {
+		int c = a + b;
+		int d = c + b;
+		int e = d + a;
+
+		return e;
+	}
+
+	public static int UseComplex () {
+		var complex = new Simple.Complex (10, "xx");
+		var res = complex.DoStuff ();
+		return res;
+	}
+}
+     
+19  sdks/wasm/debugger-test2.cs
+@@ -0,0 +1,19 @@
+using System;
+
+public class Misc { //Only append content to this class as the test suite depends on line info
+	public static int CreateObject (int foo, int bar) {
+		var f = new Fancy () {
+			Foo = foo,
+			Bar = bar,
+		};
+
+		Console.WriteLine ($"{f.Foo} {f.Bar}");
+		return f.Foo + f.Bar;
+	}
+}
+
+public class Fancy {
+	public int Foo;
+	public int Bar { get ; set; }
+}
diff --git a/src/mono/wasm/debugger/tests/debugger-evaluate-test.cs b/src/mono/wasm/debugger/tests/debugger-evaluate-test.cs
new file mode 100644
index 00000000000000..4d958cd004d93c
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-evaluate-test.cs
@@ -0,0 +1,108 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Threading.Tasks;
+namespace DebuggerTests
+{
+    public class EvaluateTestsClass
+    {
+        public class TestEvaluate
+        {
+            public int a;
+            public int b;
+            public int c;
+            public DateTime dt = new DateTime(2000, 5, 4, 3, 2, 1);
+            public void run(int g, int h, string valString)
+            {
+                int d = g + 1;
+                int e = g + 2;
+                int f = g + 3;
+                int i = d + e + f;
+                var local_dt = new DateTime(2010, 9, 8, 7, 6, 5);
+                a = 1;
+                b = 2;
+                c = 3;
+                a = a + 1;
+                b = b + 1;
+                c = c + 1;
+            }
+        }
+
+        public static void EvaluateLocals()
+        {
+            TestEvaluate f = new TestEvaluate();
+            f.run(100, 200, "test");
+
+            var f_s = new EvaluateTestsStruct();
+            f_s.EvaluateTestsStructInstanceMethod(100, 200, "test");
+            f_s.GenericInstanceMethodOnStruct<int>(100, 200, "test");
+
+            var f_g_s = new EvaluateTestsGenericStruct<int>();
+            f_g_s.EvaluateTestsGenericStructInstanceMethod(100, 200, "test");
+            Console.WriteLine($"a: {f.a}, b: {f.b}, c: {f.c}");
+        }
+
+    }
+
+    public struct EvaluateTestsStruct
+    {
+        public int a;
+        public int b;
+        public int c;
+        DateTime dateTime;
+        public void EvaluateTestsStructInstanceMethod(int g, int h, string valString)
+        {
+            int d = g + 1;
+            int e = g + 2;
+            int f = g + 3;
+            int i = d + e + f;
+            a = 1;
+            b = 2;
+            c = 3;
+            dateTime = new DateTime(2020, 1, 2, 3, 4, 5);
+            a = a + 1;
+            b = b + 1;
+            c = c + 1;
+        }
+
+        public void GenericInstanceMethodOnStruct<T>(int g, int h, string valString)
+        {
+            int d = g + 1;
+            int e = g + 2;
+            int f = g + 3;
+            int i = d + e + f;
+            a = 1;
+            b = 2;
+            c = 3;
+            dateTime = new DateTime(2020, 1, 2, 3, 4, 5);
+            T t = default(T);
+            a = a + 1;
+            b = b + 1;
+            c = c + 1;
+        }
+    }
+
+    public struct EvaluateTestsGenericStruct<T>
+    {
+        public int a;
+        public int b;
+        public int c;
+        DateTime dateTime;
+        public void EvaluateTestsGenericStructInstanceMethod(int g, int h, string valString)
+        {
+            int d = g + 1;
+            int e = g + 2;
+            int f = g + 3;
+            int i = d + e + f;
+            a = 1;
+            b = 2;
+            c = 3;
+            dateTime = new DateTime(2020, 1, 2, 3, 4, 5);
+            T t = default(T);
+            a = a + 1;
+            b = b + 2;
+            c = c + 3;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/tests/debugger-exception-test.cs b/src/mono/wasm/debugger/tests/debugger-exception-test.cs
new file mode 100644
index 00000000000000..3eb253569422b1
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-exception-test.cs
@@ -0,0 +1,55 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Threading.Tasks;
+namespace DebuggerTests
+{
+    public class ExceptionTestsClass
+    {
+        public class TestCaughtException
+        {
+            public void run() 
+            {
+                try
+                {
+                    throw new CustomException ("not implemented caught");
+                }
+                catch
+                {
+                    Console.WriteLine("caught exception");
+                }
+            }
+        }
+
+        public class TestUncaughtException
+        {
+            public void run()
+            {
+                throw new CustomException ("not implemented uncaught");
+            }
+        }
+
+        public static void TestExceptions()
+        {
+            TestCaughtException f = new TestCaughtException();
+            f.run();
+
+            TestUncaughtException g = new TestUncaughtException();
+            g.run();
+        }
+
+    }
+
+    public class CustomException : Exception
+    {
+        // Using this name to match with what js has.
+        // helps with the tests
+        public string message;
+        public CustomException (string message)
+            : base (message)
+        {
+            this.message = message;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/tests/debugger-pointers-test.cs b/src/mono/wasm/debugger/tests/debugger-pointers-test.cs
new file mode 100644
index 00000000000000..122a080ba4595b
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-pointers-test.cs
@@ -0,0 +1,112 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Threading.Tasks;
+
+namespace DebuggerTests
+{
+    public class PointerTests
+    {
+
+        public static unsafe void LocalPointers()
+        {
+            int ivalue0 = 5;
+            int ivalue1 = 10;
+
+            int* ip = &ivalue0;
+            int* ip_null = null;
+            int** ipp = &ip;
+            int** ipp_null = &ip_null;
+            int*[] ipa = new int*[] { &ivalue0, &ivalue1, null };
+            int**[] ippa = new int**[] { &ip, &ip_null, ipp, ipp_null, null };
+            char cvalue0 = 'q';
+            char* cp = &cvalue0;
+
+            DateTime dt = new DateTime(5, 6, 7, 8, 9, 10);
+            void* vp = &dt;
+            void* vp_null = null;
+            void** vpp = &vp;
+            void** vpp_null = &vp_null;
+
+            DateTime* dtp = &dt;
+            DateTime* dtp_null = null;
+            DateTime*[] dtpa = new DateTime*[] { dtp, dtp_null };
+            DateTime**[] dtppa = new DateTime**[] { &dtp, &dtp_null, null };
+            Console.WriteLine($"-- break here: ip_null==null: {ip_null == null}, ipp_null: {ipp_null == null}, *ipp_null==ip_null: {*ipp_null == ip_null}, *ipp_null==null: {*ipp_null == null}");
+
+            var gs = new GenericStructWithUnmanagedT<DateTime> { Value = new DateTime(1, 2, 3, 4, 5, 6), IntField = 4, DTPP = &dtp };
+            var gs_null = new GenericStructWithUnmanagedT<DateTime> { Value = new DateTime(1, 2, 3, 4, 5, 6), IntField = 4, DTPP = &dtp_null };
+            var gsp = &gs;
+            var gsp_null = &gs_null;
+            var gspa = new GenericStructWithUnmanagedT<DateTime>*[] { null, gsp, gsp_null };
+
+            var cwp = new GenericClassWithPointers<DateTime> { Ptr = dtp };
+            var cwp_null = new GenericClassWithPointers<DateTime>();
+            Console.WriteLine($"{(int)*ip}, {(int)**ipp}, {ipp_null == null}, {ip_null == null}, {ippa == null}, {ipa}, {(char)*cp}, {(vp == null ? "null" : "not null")}, {dtp->Second}, {gsp->IntField}, {cwp}, {cwp_null}, {gs_null}");
+
+            PointersAsArgsTest(ip, ipp, ipa, ippa, &dt, &dtp, dtpa, dtppa);
+        }
+
+        static unsafe void  PointersAsArgsTest(int* ip, int** ipp, int*[] ipa, int**[] ippa,
+                            DateTime* dtp, DateTime** dtpp, DateTime*[] dtpa, DateTime**[] dtppa)
+        {
+            Console.WriteLine($"break here!");
+            if (ip == null)
+                Console.WriteLine($"ip is null");
+            Console.WriteLine($"done!");
+        }
+
+        public static unsafe async Task LocalPointersAsync()
+        {
+            int ivalue0 = 5;
+            int ivalue1 = 10;
+
+            int* ip = &ivalue0;
+            int* ip_null = null;
+            int** ipp = &ip;
+            int** ipp_null = &ip_null;
+            int*[] ipa = new int*[] { &ivalue0, &ivalue1, null };
+            int**[] ippa = new int**[] { &ip, &ip_null, ipp, ipp_null, null };
+            char cvalue0 = 'q';
+            char* cp = &cvalue0;
+
+            DateTime dt = new DateTime(5, 6, 7, 8, 9, 10);
+            void* vp = &dt;
+            void* vp_null = null;
+            void** vpp = &vp;
+            void** vpp_null = &vp_null;
+
+            DateTime* dtp = &dt;
+            DateTime* dtp_null = null;
+            DateTime*[] dtpa = new DateTime*[] { dtp, dtp_null };
+            DateTime**[] dtppa = new DateTime**[] { &dtp, &dtp_null, null };
+            Console.WriteLine($"-- break here: ip_null==null: {ip_null == null}, ipp_null: {ipp_null == null}, *ipp_null==ip_null: {*ipp_null == ip_null}, *ipp_null==null: {*ipp_null == null}");
+
+            var gs = new GenericStructWithUnmanagedT<DateTime> { Value = new DateTime(1, 2, 3, 4, 5, 6), IntField = 4, DTPP = &dtp };
+            var gs_null = new GenericStructWithUnmanagedT<DateTime> { Value = new DateTime(1, 2, 3, 4, 5, 6), IntField = 4, DTPP = &dtp_null };
+            var gsp = &gs;
+            var gsp_null = &gs_null;
+            var gspa = new GenericStructWithUnmanagedT<DateTime>*[] { null, gsp, gsp_null };
+
+            var cwp = new GenericClassWithPointers<DateTime> { Ptr = dtp };
+            var cwp_null = new GenericClassWithPointers<DateTime>();
+            Console.WriteLine($"{(int)*ip}, {(int)**ipp}, {ipp_null == null}, {ip_null == null}, {ippa == null}, {ipa}, {(char)*cp}, {(vp == null ? "null" : "not null")}, {dtp->Second}, {gsp->IntField}, {cwp}, {cwp_null}, {gs_null}");
+        }
+
+        // async methods cannot have unsafe params, so no test for that
+    }
+
+    public unsafe struct GenericStructWithUnmanagedT<T> where T : unmanaged
+    {
+        public T Value;
+        public int IntField;
+
+        public DateTime** DTPP;
+    }
+
+    public unsafe class GenericClassWithPointers<T> where T : unmanaged
+    {
+        public unsafe T* Ptr;
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/tests/debugger-test.cs b/src/mono/wasm/debugger/tests/debugger-test.cs
new file mode 100644
index 00000000000000..55a13d572ae21c
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-test.cs
@@ -0,0 +1,325 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+public partial class Math
+{ //Only append content to this class as the test suite depends on line info
+    public static int IntAdd(int a, int b)
+    {
+        int c = a + b;
+        int d = c + b;
+        int e = d + a;
+        int f = 0;
+        return e;
+    }
+
+    public static int UseComplex(int a, int b)
+    {
+        var complex = new Simple.Complex(10, "xx");
+        int c = a + b;
+        int d = c + b;
+        int e = d + a;
+        int f = 0;
+        e += complex.DoStuff();
+        return e;
+    }
+
+    delegate bool IsMathNull(Math m);
+
+    public static int DelegatesTest()
+    {
+        Func<Math, bool> fn_func = (Math m) => m == null;
+        Func<Math, bool> fn_func_null = null;
+        Func<Math, bool>[] fn_func_arr = new Func<Math, bool>[] {
+            (Math m) => m == null };
+
+        Math.IsMathNull fn_del = Math.IsMathNullDelegateTarget;
+        var fn_del_arr = new Math.IsMathNull[] { Math.IsMathNullDelegateTarget };
+        var m_obj = new Math();
+        Math.IsMathNull fn_del_null = null;
+        bool res = fn_func(m_obj) && fn_del(m_obj) && fn_del_arr[0](m_obj) && fn_del_null == null && fn_func_null == null && fn_func_arr[0] != null;
+
+        // Unused locals
+
+        Func<Math, bool> fn_func_unused = (Math m) => m == null;
+        Func<Math, bool> fn_func_null_unused = null;
+        Func<Math, bool>[] fn_func_arr_unused = new Func<Math, bool>[] { (Math m) => m == null };
+
+        Math.IsMathNull fn_del_unused = Math.IsMathNullDelegateTarget;
+        Math.IsMathNull fn_del_null_unused = null;
+        var fn_del_arr_unused = new Math.IsMathNull[] { Math.IsMathNullDelegateTarget };
+        OuterMethod();
+        Console.WriteLine("Just a test message, ignore");
+        return res ? 0 : 1;
+    }
+
+    public static int GenericTypesTest()
+    {
+        var list = new System.Collections.Generic.Dictionary<Math[], IsMathNull>();
+        System.Collections.Generic.Dictionary<Math[], IsMathNull> list_null = null;
+
+        var list_arr = new System.Collections.Generic.Dictionary<Math[], IsMathNull>[] { new System.Collections.Generic.Dictionary<Math[], IsMathNull>() };
+        System.Collections.Generic.Dictionary<Math[], IsMathNull>[] list_arr_null = null;
+
+        Console.WriteLine($"list_arr.Length: {list_arr.Length}, list.Count: {list.Count}");
+
+        // Unused locals
+
+        var list_unused = new System.Collections.Generic.Dictionary<Math[], IsMathNull>();
+        System.Collections.Generic.Dictionary<Math[], IsMathNull> list_null_unused = null;
+
+        var list_arr_unused = new System.Collections.Generic.Dictionary<Math[], IsMathNull>[] { new System.Collections.Generic.Dictionary<Math[], IsMathNull>() };
+        System.Collections.Generic.Dictionary<Math[], IsMathNull>[] list_arr_null_unused = null;
+
+        OuterMethod();
+        Console.WriteLine("Just a test message, ignore");
+        return 0;
+    }
+
+    static bool IsMathNullDelegateTarget(Math m) => m == null;
+
+    public static void OuterMethod()
+    {
+        Console.WriteLine($"OuterMethod called");
+        var nim = new Math.NestedInMath();
+        var i = 5;
+        var text = "Hello";
+        var new_i = nim.InnerMethod(i);
+        Console.WriteLine($"i: {i}");
+        Console.WriteLine($"-- InnerMethod returned: {new_i}, nim: {nim}, text: {text}");
+        int k = 19;
+        new_i = InnerMethod2("test string", new_i, out k);
+        Console.WriteLine($"-- InnerMethod2 returned: {new_i}, and k: {k}");
+    }
+
+    static int InnerMethod2(string s, int i, out int k)
+    {
+        k = i + 10;
+        Console.WriteLine($"s: {s}, i: {i}, k: {k}");
+        return i - 2;
+    }
+
+    public class NestedInMath
+    {
+        public int InnerMethod(int i)
+        {
+            SimpleStructProperty = new SimpleStruct() { dt = new DateTime(2020, 1, 2, 3, 4, 5) };
+            int j = i + 10;
+            string foo_str = "foo";
+            Console.WriteLine($"i: {i} and j: {j}, foo_str: {foo_str} ");
+            j += 9;
+            Console.WriteLine($"i: {i} and j: {j}");
+            return j;
+        }
+
+        Math m = new Math();
+        public async System.Threading.Tasks.Task<bool> AsyncMethod0(string s, int i)
+        {
+            string local0 = "value0";
+            await System.Threading.Tasks.Task.Delay(1);
+            Console.WriteLine($"* time for the second await, local0: {local0}");
+            await AsyncMethodNoReturn();
+            return true;
+        }
+
+        public async System.Threading.Tasks.Task AsyncMethodNoReturn()
+        {
+            var ss = new SimpleStruct() { dt = new DateTime(2020, 1, 2, 3, 4, 5) };
+            var ss_arr = new SimpleStruct[] { };
+            //ss.gs.StringField = "field in GenericStruct";
+
+            //Console.WriteLine ($"Using the struct: {ss.dt}, {ss.gs.StringField}, ss_arr: {ss_arr.Length}");
+            string str = "AsyncMethodNoReturn's local";
+            //Console.WriteLine ($"* field m: {m}");
+            await System.Threading.Tasks.Task.Delay(1);
+            Console.WriteLine($"str: {str}");
+        }
+
+        public static async System.Threading.Tasks.Task<bool> AsyncTest(string s, int i)
+        {
+            var li = 10 + i;
+            var ls = s + "test";
+            return await new NestedInMath().AsyncMethod0(s, i);
+        }
+
+        public SimpleStruct SimpleStructProperty { get; set; }
+    }
+
+    public static void PrimitiveTypesTest()
+    {
+        char c0 = '€';
+        char c1 = 'A';
+        // TODO: other types!
+        // just trying to ensure vars don't get optimized out
+        if (c0 < 32 || c1 > 32)
+            Console.WriteLine($"{c0}, {c1}");
+    }
+
+    public static int DelegatesSignatureTest()
+    {
+        Func<Math, GenericStruct<GenericStruct<int[]>>, GenericStruct<bool[]>> fn_func = (m, gs) => new GenericStruct<bool[]>();
+        Func<Math, GenericStruct<GenericStruct<int[]>>, GenericStruct<bool[]>> fn_func_del = GenericStruct<int>.DelegateTargetForSignatureTest;
+        Func<Math, GenericStruct<GenericStruct<int[]>>, GenericStruct<bool[]>> fn_func_null = null;
+        Func<bool> fn_func_only_ret = () => { Console.WriteLine ($"hello"); return true; };
+        var fn_func_arr = new Func<Math, GenericStruct<GenericStruct<int[]>>, GenericStruct<bool[]>>[] {
+                (m, gs) => new GenericStruct<bool[]> () };
+
+        Math.DelegateForSignatureTest fn_del = GenericStruct<int>.DelegateTargetForSignatureTest;
+        Math.DelegateForSignatureTest fn_del_l = (m, gs) => new GenericStruct<bool[]> { StringField = "fn_del_l#lambda" };
+        var fn_del_arr = new Math.DelegateForSignatureTest[] { GenericStruct<int>.DelegateTargetForSignatureTest, (m, gs) => new GenericStruct<bool[]> { StringField = "fn_del_arr#1#lambda" } };
+        var m_obj = new Math();
+        Math.DelegateForSignatureTest fn_del_null = null;
+        var gs_gs = new GenericStruct<GenericStruct<int[]>>
+        {
+            List = new System.Collections.Generic.List<GenericStruct<int[]>>
+            {
+            new GenericStruct<int[]> { StringField = "gs#List#0#StringField" },
+            new GenericStruct<int[]> { StringField = "gs#List#1#StringField" }
+            }
+        };
+
+        Math.DelegateWithVoidReturn fn_void_del = Math.DelegateTargetWithVoidReturn;
+        var fn_void_del_arr = new Math.DelegateWithVoidReturn[] { Math.DelegateTargetWithVoidReturn };
+        Math.DelegateWithVoidReturn fn_void_del_null = null;
+
+        var rets = new GenericStruct<bool[]>[]
+        {
+            fn_func(m_obj, gs_gs),
+            fn_func_del(m_obj, gs_gs),
+            fn_del(m_obj, gs_gs),
+            fn_del_l(m_obj, gs_gs),
+            fn_del_arr[0](m_obj, gs_gs),
+            fn_func_arr[0](m_obj, gs_gs)
+        };
+
+        var gs = new GenericStruct<int[]>();
+        fn_void_del(gs);
+        fn_void_del_arr[0](gs);
+        fn_func_only_ret();
+        foreach (var ret in rets) Console.WriteLine($"ret: {ret}");
+        OuterMethod();
+        Console.WriteLine($"- {gs_gs.List[0].StringField}");
+        return 0;
+    }
+
+    public static int ActionTSignatureTest()
+    {
+        Action<GenericStruct<int[]>> fn_action = (_) => { };
+        Action<GenericStruct<int[]>> fn_action_del = Math.DelegateTargetWithVoidReturn;
+        Action fn_action_bare = () => { };
+        Action<GenericStruct<int[]>> fn_action_null = null;
+        var fn_action_arr = new Action<GenericStruct<int[]>>[]
+        {
+            (gs) => new GenericStruct<int[]>(),
+            Math.DelegateTargetWithVoidReturn,
+            null
+        };
+
+        var gs = new GenericStruct<int[]>();
+        fn_action(gs);
+        fn_action_del(gs);
+        fn_action_arr[0](gs);
+        fn_action_bare();
+        OuterMethod();
+        return 0;
+    }
+
+    public static int NestedDelegatesTest()
+    {
+        Func<Func<int, bool>, bool> fn_func = (_) => { return true; };
+        Func<Func<int, bool>, bool> fn_func_null = null;
+        var fn_func_arr = new Func<Func<int, bool>, bool>[] {
+                (gs) => { return true; } };
+
+        var fn_del_arr = new Func<Func<int, bool>, bool>[] { DelegateTargetForNestedFunc<Func<int, bool>> };
+        var m_obj = new Math();
+        Func<Func<int, bool>, bool> fn_del_null = null;
+        Func<int, bool> fs = (i) => i == 0;
+        fn_func(fs);
+        fn_del_arr[0](fs);
+        fn_func_arr[0](fs);
+        OuterMethod();
+        return 0;
+    }
+
+    public static void DelegatesAsMethodArgsTest()
+    {
+        var _dst_arr = new DelegateForSignatureTest[]
+        {
+            GenericStruct<int>.DelegateTargetForSignatureTest,
+            (m, gs) => new GenericStruct<bool[]>()
+        };
+        Func<char[], bool> _fn_func = (cs) => cs.Length == 0;
+        Action<GenericStruct<int>[]> _fn_action = (gss) => { };
+
+        new Math().MethodWithDelegateArgs(_dst_arr, _fn_func, _fn_action);
+    }
+
+    void MethodWithDelegateArgs(Math.DelegateForSignatureTest[] dst_arr, Func<char[], bool> fn_func,
+        Action<GenericStruct<int>[]> fn_action)
+    {
+        Console.WriteLine($"Placeholder for breakpoint");
+        OuterMethod();
+    }
+
+    public static async System.Threading.Tasks.Task MethodWithDelegatesAsyncTest()
+    {
+        await new Math().MethodWithDelegatesAsync();
+    }
+
+    async System.Threading.Tasks.Task MethodWithDelegatesAsync()
+    {
+        var _dst_arr = new DelegateForSignatureTest[]
+        {
+            GenericStruct<int>.DelegateTargetForSignatureTest,
+            (m, gs) => new GenericStruct<bool[]>()
+        };
+        Func<char[], bool> _fn_func = (cs) => cs.Length == 0;
+        Action<GenericStruct<int>[]> _fn_action = (gss) => { };
+
+        Console.WriteLine($"Placeholder for breakpoint");
+        await System.Threading.Tasks.Task.CompletedTask;
+    }
+
+    public delegate void DelegateWithVoidReturn(GenericStruct<int[]> gs);
+    public static void DelegateTargetWithVoidReturn(GenericStruct<int[]> gs) { }
+
+    delegate GenericStruct<bool[]> DelegateForSignatureTest(Math m, GenericStruct<GenericStruct<int[]>> gs);
+    static bool DelegateTargetForNestedFunc<T>(T arg) => true;
+
+    public struct SimpleStruct
+    {
+        public DateTime dt;
+        public GenericStruct<DateTime> gs;
+    }
+
+    public struct GenericStruct<T>
+    {
+        public System.Collections.Generic.List<T> List;
+        public string StringField;
+
+        public static GenericStruct<bool[]> DelegateTargetForSignatureTest(Math m, GenericStruct<GenericStruct<T[]>> gs) => new GenericStruct<bool[]>();
+    }
+
+}
+
+public class DebuggerTest
+{
+    public static void run_all()
+    {
+        locals();
+    }
+
+    public static int locals()
+    {
+        int l_int = 1;
+        char l_char = 'A';
+        long l_long = Int64.MaxValue;
+        ulong l_ulong = UInt64.MaxValue;
+        locals_inner();
+        return 0;
+    }
+
+    static void locals_inner() { }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/tests/debugger-test.csproj b/src/mono/wasm/debugger/tests/debugger-test.csproj
new file mode 100644
index 00000000000000..27f295c0de4dc7
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-test.csproj
@@ -0,0 +1,49 @@
+<Project Sdk="Microsoft.NET.Sdk" DefaultTargets="BuildApp">
+  <PropertyGroup>
+    <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+    <TargetArchitecture>wasm</TargetArchitecture>
+    <TargetOS>Browser</TargetOS>
+    <MicrosoftNetCoreAppRuntimePackDir>$(ArtifactsBinDir)microsoft.netcore.app.runtime.browser-wasm\Release\runtimes\browser-wasm\</MicrosoftNetCoreAppRuntimePackDir>
+    <BuildDir>$(MSBuildThisFileDirectory)obj\$(Configuration)\wasm</BuildDir>
+    <AppDir>$(MSBuildThisFileDirectory)bin\$(Configuration)\publish</AppDir>
+    <RuntimeBuildConfig Condition="'$(RuntimeBuildConfig)' == ''">$(Configuration)</RuntimeBuildConfig>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <OutputType>Library</OutputType>
+    <NoWarn>219</NoWarn>
+    <DebugType>portable</DebugType>
+  </PropertyGroup>
+
+  <Target Name="RebuildWasmAppBuilder">
+    <ItemGroup>
+      <WasmAppBuildProject Include="$(RepoTasksDir)mobile.tasks\WasmAppBuilder\WasmAppBuilder.csproj" />
+    </ItemGroup>
+
+    <MSBuild Projects="@(WasmAppBuildProject)"
+             Properties="Configuration=$(Configuration);MSBuildRestoreSessionId=$([System.Guid]::NewGuid())"
+             Targets="Restore"/>
+
+    <MSBuild Projects="@(WasmAppBuildProject)"
+             Properties="Configuration=$(Configuration)"
+             Targets="Build;Publish"/>
+  </Target>
+
+  <UsingTask TaskName="WasmAppBuilder" 
+             AssemblyFile="$(ArtifactsBinDir)WasmAppBuilder\$(Configuration)\$(NetCoreAppCurrent)\publish\WasmAppBuilder.dll"/>
+
+  <Target Name="BuildApp" DependsOnTargets="RebuildWasmAppBuilder;Build">
+    <ItemGroup>
+      <AssemblySearchPaths Include="$(MicrosoftNetCoreAppRuntimePackDir)native"/>
+      <AssemblySearchPaths Include="$(MicrosoftNetCoreAppRuntimePackDir)lib\$(NetCoreAppCurrent)"/>
+    </ItemGroup>
+    <WasmAppBuilder
+      AppDir="$(AppDir)"
+      MicrosoftNetCoreAppRuntimePackDir="$(MicrosoftNetCoreAppRuntimePackDir)"
+      MainAssembly="$(ArtifactsBinDir)debugger-test/wasm/Debug/debugger-test.dll"
+      MainJS="$(MonoProjectRoot)wasm\runtime-test.js"
+      DebugLevel="1"
+      AssemblySearchPaths="@(AssemblySearchPaths)"
+      ExtraAssemblies="$(ArtifactsBinDir)\System.Private.Runtime.InteropServices.JavaScript\$(NetCoreAppCurrent)-Browser-$(RuntimeConfiguration)\System.Private.Runtime.InteropServices.JavaScript.dll"/>
+    <Exec Command="chmod a+x $(AppDir)/run-v8.sh" />
+  </Target>
+
+</Project>
diff --git a/src/mono/wasm/debugger/tests/debugger-test2.cs b/src/mono/wasm/debugger/tests/debugger-test2.cs
new file mode 100644
index 00000000000000..26817a2ea4e1ec
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-test2.cs
@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+public class Misc
+{ //Only append content to this class as the test suite depends on line info
+    public static int CreateObject(int foo, int bar)
+    {
+        var f = new Fancy()
+        {
+            Foo = foo,
+            Bar = bar,
+        };
+
+        Console.WriteLine($"{f.Foo} {f.Bar}");
+        return f.Foo + f.Bar;
+    }
+}
+
+public class Fancy
+{
+    public int Foo;
+    public int Bar { get; set; }
+    public static void Types()
+    {
+        double dPI = System.Math.PI;
+        float fPI = (float) System.Math.PI;
+
+        int iMax = int.MaxValue;
+        int iMin = int.MinValue;
+        uint uiMax = uint.MaxValue;
+        uint uiMin = uint.MinValue;
+
+        long l = uiMax * (long) 2;
+        long lMax = long.MaxValue; // cannot be represented as double
+        long lMin = long.MinValue; // cannot be represented as double
+
+        sbyte sbMax = sbyte.MaxValue;
+        sbyte sbMin = sbyte.MinValue;
+        byte bMax = byte.MaxValue;
+        byte bMin = byte.MinValue;
+
+        short sMax = short.MaxValue;
+        short sMin = short.MinValue;
+        ushort usMin = ushort.MinValue;
+        ushort usMax = ushort.MaxValue;
+
+        var d = usMin + usMax;
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/tests/debugger-valuetypes-test.cs b/src/mono/wasm/debugger/tests/debugger-valuetypes-test.cs
new file mode 100644
index 00000000000000..7c372871eae130
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/debugger-valuetypes-test.cs
@@ -0,0 +1,265 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Threading.Tasks;
+namespace DebuggerTests
+{
+    public class ValueTypesTest
+    { //Only append content to this class as the test suite depends on line info
+
+        public static void MethodWithLocalStructs()
+        {
+            var ss_local = new SimpleStruct("set in MethodWithLocalStructs", 1, DateTimeKind.Utc);
+            var gs_local = new GenericStruct<ValueTypesTest> { StringField = "gs_local#GenericStruct<ValueTypesTest>#StringField" };
+
+            ValueTypesTest vt_local = new ValueTypesTest
+            {
+                StringField = "string#0",
+                SimpleStructField = new SimpleStruct("SimpleStructField#string#0", 5, DateTimeKind.Local),
+                SimpleStructProperty = new SimpleStruct("SimpleStructProperty#string#0", 2, DateTimeKind.Utc), DT = new DateTime(2020, 1, 2, 3, 4, 5), RGB = RGB.Blue
+            };
+            Console.WriteLine($"Using the struct: {ss_local.gs.StringField}, gs: {gs_local.StringField}, {vt_local.StringField}");
+        }
+
+        public static void TestStructsAsMethodArgs()
+        {
+            var ss_local = new SimpleStruct("ss_local#SimpleStruct#string#0", 5, DateTimeKind.Local);
+            var ss_ret = MethodWithStructArgs("TestStructsAsMethodArgs#label", ss_local, 3);
+            Console.WriteLine($"got back ss_local: {ss_local.gs.StringField}, ss_ret: {ss_ret.gs.StringField}");
+        }
+
+        static SimpleStruct MethodWithStructArgs(string label, SimpleStruct ss_arg, int x)
+        {
+            Console.WriteLine($"- ss_arg: {ss_arg.str_member}");
+            ss_arg.Kind = DateTimeKind.Utc;
+            ss_arg.str_member = $"ValueTypesTest#MethodWithStructArgs#updated#ss_arg#str_member";
+            ss_arg.gs.StringField = $"ValueTypesTest#MethodWithStructArgs#updated#gs#StringField#{x}";
+            return ss_arg;
+        }
+
+        public static async Task<bool> MethodWithLocalStructsStaticAsync()
+        {
+            var ss_local = new SimpleStruct("set in MethodWithLocalStructsStaticAsync", 1, DateTimeKind.Utc);
+            var gs_local = new GenericStruct<int>
+            {
+                StringField = "gs_local#GenericStruct<ValueTypesTest>#StringField",
+                List = new System.Collections.Generic.List<int> { 5, 3 },
+                Options = Options.Option2
+
+            };
+
+            var result = await ss_local.AsyncMethodWithStructArgs(gs_local);
+            Console.WriteLine($"Using the struct: {ss_local.gs.StringField}, result: {result}");
+
+            return result;
+        }
+
+        public string StringField;
+        public SimpleStruct SimpleStructProperty { get; set; }
+        public SimpleStruct SimpleStructField;
+
+        public struct SimpleStruct
+        {
+            public uint V { get { return 0xDEADBEEF + (uint)dt.Month; } set { } }
+            public string str_member;
+            public DateTime dt;
+            public GenericStruct<DateTime> gs;
+            public DateTimeKind Kind;
+
+            public SimpleStruct(string str, int f, DateTimeKind kind)
+            {
+                str_member = $"{str}#SimpleStruct#str_member";
+                dt = new DateTime(2020 + f, 1 + f, 2 + f, 3 + f, 5 + f, 6 + f);
+                gs = new GenericStruct<DateTime>
+                {
+                    StringField = $"{str}#SimpleStruct#gs#StringField",
+                    List = new System.Collections.Generic.List<DateTime> { new DateTime(2010 + f, 2 + f, 3 + f, 10 + f, 2 + f, 3 + f) },
+                    Options = Options.Option1
+                };
+                Kind = kind;
+            }
+
+            public Task<bool> AsyncMethodWithStructArgs(GenericStruct<int> gs)
+            {
+                Console.WriteLine($"placeholder line for a breakpoint");
+                if (gs.List.Count > 0)
+                    return Task.FromResult(true);
+
+                return Task.FromResult(false);
+            }
+        }
+
+        public struct GenericStruct<T>
+        {
+            public System.Collections.Generic.List<T> List;
+            public string StringField;
+
+            public Options Options { get; set; }
+        }
+
+        public DateTime DT { get; set; }
+        public RGB RGB;
+
+        public static void MethodWithLocalsForToStringTest(bool call_other)
+        {
+            var dt0 = new DateTime(2020, 1, 2, 3, 4, 5);
+            var dt1 = new DateTime(2010, 5, 4, 3, 2, 1);
+            var ts = dt0 - dt1;
+            var dto = new DateTimeOffset(dt0, new TimeSpan(4, 5, 0));
+            decimal dec = 123987123;
+            var guid = new Guid("3d36e07e-ac90-48c6-b7ec-a481e289d014");
+
+            var dts = new DateTime[]
+            {
+                new DateTime(1983, 6, 7, 5, 6, 10),
+                new DateTime(1999, 10, 15, 1, 2, 3)
+            };
+
+            var obj = new ClassForToStringTests
+            {
+                DT = new DateTime(2004, 10, 15, 1, 2, 3),
+                DTO = new DateTimeOffset(dt0, new TimeSpan(2, 14, 0)),
+                TS = ts,
+                Dec = 1239871,
+                Guid = guid
+            };
+
+            var sst = new StructForToStringTests
+            {
+                DT = new DateTime(2004, 10, 15, 1, 2, 3),
+                DTO = new DateTimeOffset(dt0, new TimeSpan(3, 15, 0)),
+                TS = ts,
+                Dec = 1239871,
+                Guid = guid
+            };
+            Console.WriteLine($"MethodWithLocalsForToStringTest: {dt0}, {dt1}, {ts}, {dec}, {guid}, {dts[0]}, {obj.DT}, {sst.DT}");
+            if (call_other)
+                MethodWithArgumentsForToStringTest(call_other, dt0, dt1, ts, dto, dec, guid, dts, obj, sst);
+        }
+
+        static void MethodWithArgumentsForToStringTest(
+            bool call_other, // not really used, just to help with using common code in the tests
+            DateTime dt0, DateTime dt1, TimeSpan ts, DateTimeOffset dto, decimal dec,
+            Guid guid, DateTime[] dts, ClassForToStringTests obj, StructForToStringTests sst)
+        {
+            Console.WriteLine($"MethodWithArgumentsForToStringTest: {dt0}, {dt1}, {ts}, {dec}, {guid}, {dts[0]}, {obj.DT}, {sst.DT}");
+        }
+
+        public static async Task MethodWithLocalsForToStringTestAsync(bool call_other)
+        {
+            var dt0 = new DateTime(2020, 1, 2, 3, 4, 5);
+            var dt1 = new DateTime(2010, 5, 4, 3, 2, 1);
+            var ts = dt0 - dt1;
+            var dto = new DateTimeOffset(dt0, new TimeSpan(4, 5, 0));
+            decimal dec = 123987123;
+            var guid = new Guid("3d36e07e-ac90-48c6-b7ec-a481e289d014");
+
+            var dts = new DateTime[]
+            {
+                new DateTime(1983, 6, 7, 5, 6, 10),
+                new DateTime(1999, 10, 15, 1, 2, 3)
+            };
+
+            var obj = new ClassForToStringTests
+            {
+                DT = new DateTime(2004, 10, 15, 1, 2, 3),
+                DTO = new DateTimeOffset(dt0, new TimeSpan(2, 14, 0)),
+                TS = ts,
+                Dec = 1239871,
+                Guid = guid
+            };
+
+            var sst = new StructForToStringTests
+            {
+                DT = new DateTime(2004, 10, 15, 1, 2, 3),
+                DTO = new DateTimeOffset(dt0, new TimeSpan(3, 15, 0)),
+                TS = ts,
+                Dec = 1239871,
+                Guid = guid
+            };
+            Console.WriteLine($"MethodWithLocalsForToStringTest: {dt0}, {dt1}, {ts}, {dec}, {guid}, {dts[0]}, {obj.DT}, {sst.DT}");
+            if (call_other)
+                await MethodWithArgumentsForToStringTestAsync(call_other, dt0, dt1, ts, dto, dec, guid, dts, obj, sst);
+        }
+
+        static async Task MethodWithArgumentsForToStringTestAsync(
+            bool call_other, // not really used, just to help with using common code in the tests
+            DateTime dt0, DateTime dt1, TimeSpan ts, DateTimeOffset dto, decimal dec,
+            Guid guid, DateTime[] dts, ClassForToStringTests obj, StructForToStringTests sst)
+        {
+            Console.WriteLine($"MethodWithArgumentsForToStringTest: {dt0}, {dt1}, {ts}, {dec}, {guid}, {dts[0]}, {obj.DT}, {sst.DT}");
+        }
+
+        public static void MethodUpdatingValueTypeMembers()
+        {
+            var obj = new ClassForToStringTests
+            {
+                DT = new DateTime(1, 2, 3, 4, 5, 6)
+            };
+            var vt = new StructForToStringTests
+            {
+                DT = new DateTime(4, 5, 6, 7, 8, 9)
+            };
+            Console.WriteLine($"#1");
+            obj.DT = new DateTime(9, 8, 7, 6, 5, 4);
+            vt.DT = new DateTime(5, 1, 3, 7, 9, 10);
+            Console.WriteLine($"#2");
+        }
+
+        public static async Task MethodUpdatingValueTypeLocalsAsync()
+        {
+            var dt = new DateTime(1, 2, 3, 4, 5, 6);
+            Console.WriteLine($"#1");
+            dt = new DateTime(9, 8, 7, 6, 5, 4);
+            Console.WriteLine($"#2");
+        }
+
+        public static void MethodUpdatingVTArrayMembers()
+        {
+            var ssta = new []
+            {
+                new StructForToStringTests { DT = new DateTime(1, 2, 3, 4, 5, 6) }
+            };
+            Console.WriteLine($"#1");
+            ssta[0].DT = new DateTime(9, 8, 7, 6, 5, 4);
+            Console.WriteLine($"#2");
+        }
+    }
+
+    class ClassForToStringTests
+    {
+        public DateTime DT;
+        public DateTimeOffset DTO;
+        public TimeSpan TS;
+        public decimal Dec;
+        public Guid Guid;
+    }
+
+    struct StructForToStringTests
+    {
+        public DateTime DT;
+        public DateTimeOffset DTO;
+        public TimeSpan TS;
+        public decimal Dec;
+        public Guid Guid;
+    }
+
+    public enum RGB
+    {
+        Red,
+        Green,
+        Blue
+    }
+
+    [Flags]
+    public enum Options
+    {
+        None = 0,
+        Option1 = 1,
+        Option2 = 2,
+        Option3 = 4,
+
+        All = Option1 | Option3
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/tests/dependency.cs b/src/mono/wasm/debugger/tests/dependency.cs
new file mode 100644
index 00000000000000..3581a5aac8a2cb
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/dependency.cs
@@ -0,0 +1,44 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+namespace Simple
+{
+    public class Complex
+    {
+        public int A { get; set; }
+        public string B { get; set; }
+        object c;
+
+        public Complex(int a, string b)
+        {
+            A = a;
+            B = b;
+            this.c = this;
+        }
+
+        public int DoStuff()
+        {
+            return DoOtherStuff();
+        }
+
+        public int DoOtherStuff()
+        {
+            return DoEvenMoreStuff() - 1;
+        }
+
+        public int DoEvenMoreStuff()
+        {
+            return 1 + BreakOnThisMethod();
+        }
+
+        public int BreakOnThisMethod()
+        {
+            var x = A + 10;
+            c = $"{x}_{B}";
+
+            return x;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/mono/wasm/debugger/tests/other.js b/src/mono/wasm/debugger/tests/other.js
new file mode 100644
index 00000000000000..93532686914e8e
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/other.js
@@ -0,0 +1,65 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+function big_array_js_test (len) {
+	var big = new Array(len);
+	for (let i=0; i < len; i ++) {
+		big[i]=i + 1000;
+	}
+	console.log('break here');
+};
+
+function object_js_test () {
+	var obj = {
+		a_obj: { aa: 5, ab: 'foo' },
+		b_arr: [ 10, 12 ]
+	};
+
+	return obj;
+};
+
+function getters_js_test () {
+	var ptd = {
+		get Int () { return 5; },
+		get String () { return "foobar"; },
+		get DT () { return "dt"; },
+		get IntArray () { return [1,2,3]; },
+		get DTArray () { return ["dt0", "dt1"]; },
+		DTAutoProperty: "dt",
+		StringField: "string field value"
+	};
+	console.log (`break here`);
+	return ptd;
+}
+
+function exception_caught_test () {
+	try {
+		throw new TypeError ('exception caught');
+	} catch (e) {
+		console.log(e);
+	}
+}
+
+function exception_uncaught_test () {
+	console.log('uncaught test');
+	throw new RangeError ('exception uncaught');
+}
+
+function exceptions_test () {
+	exception_caught_test ();
+	exception_uncaught_test ();
+}
+
+function negative_cfo_test (str_value = null) {
+	var ptd = {
+		get Int () { return 5; },
+		get String () { return "foobar"; },
+		get DT () { return "dt"; },
+		get IntArray () { return [1,2,3]; },
+		get DTArray () { return ["dt0", "dt1"]; },
+		DTAutoProperty: "dt",
+		StringField: str_value
+	};
+	console.log (`break here`);
+	return ptd;
+}
diff --git a/src/mono/wasm/debugger/tests/runtime-debugger.js b/src/mono/wasm/debugger/tests/runtime-debugger.js
new file mode 100644
index 00000000000000..2e341d08f1f8ca
--- /dev/null
+++ b/src/mono/wasm/debugger/tests/runtime-debugger.js
@@ -0,0 +1,11 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+var Module = { 
+	onRuntimeInitialized: function () {
+		config.loaded_cb = function () {
+			App.init ();
+		};
+		MONO.mono_load_runtime_and_bcl_args (config)
+	},
+};
diff --git a/src/mono/wasm/runtime-test.js b/src/mono/wasm/runtime-test.js
index b63c8fc6ca3e0b..74f6a664d21257 100644
--- a/src/mono/wasm/runtime-test.js
+++ b/src/mono/wasm/runtime-test.js
@@ -36,6 +36,8 @@ if (typeof console !== "undefined") {
 		console.trace = console.log;
 	if (!console.warn)
 		console.warn = console.log;
+	if (!console.error)
+		console.error = console.log;
 }
 
 if (typeof crypto == 'undefined') {
@@ -130,9 +132,6 @@ while (true) {
 	} else if (args [0] == "--disable-on-demand-gc") {
 		enable_gc = false;
 		args = args.slice (1);
-	} else if (args [0] == "--enable-zoneinfo") {
-		enable_zoneinfo = true;
-		args = args.slice (1);
 	} else {
 		break;
 	}
@@ -165,7 +164,6 @@ var Module = {
 
 	onRuntimeInitialized: function () {
 		// Have to set env vars here to enable setting MONO_LOG_LEVEL etc.
-		var wasm_setenv = Module.cwrap ('mono_wasm_setenv', 'void', ['string', 'string']);
 		for (var variable in setenv) {
 			MONO.mono_wasm_setenv (variable, setenv [variable]);
 		}
@@ -173,26 +171,6 @@ var Module = {
 		if (!enable_gc) {
 			Module.ccall ('mono_wasm_enable_on_demand_gc', 'void', ['number'], [0]);
 		}
-		if (enable_zoneinfo) {
-			// The timezone file is generated by https://github.com/dotnet/blazor/tree/master/src/TimeZoneData.
-			// The file format of the TZ file look like so
-			//
-			// [4-byte magic number]
-			// [4 - byte length of manifest]
-			// [json manifest]
-			// [data bytes]
-			//
-			// The json manifest is an array that looks like so:
-			//
-			// [...["America/Fort_Nelson",2249],["America/Glace_Bay",2206]..]
-			//
-			// where the first token in each array is the relative path of the file on disk, and the second is the
-			// length of the file. The starting offset of a file can be calculated using the lengths of all files
-			// that appear prior to it.
-			var zonedata = new Uint8Array(read ("dotnet.timezones.blat", "binary"));
-			MONO.mono_wasm_load_data (zonedata, "/usr/share/zoneinfo");
-		}
-
 
 		config.loaded_cb = function () {
 			App.init ();
@@ -250,16 +228,12 @@ var App = {
 	init: function () {
 
 		var assembly_load = Module.cwrap ('mono_wasm_assembly_load', 'number', ['string'])
-		var find_class = Module.cwrap ('mono_wasm_assembly_find_class', 'number', ['number', 'string', 'string'])
-		var find_method = Module.cwrap ('mono_wasm_assembly_find_method', 'number', ['number', 'string', 'number'])
 		var runtime_invoke = Module.cwrap ('mono_wasm_invoke_method', 'number', ['number', 'number', 'number', 'number']);
 		var string_from_js = Module.cwrap ('mono_wasm_string_from_js', 'number', ['string']);
 		var assembly_get_entry_point = Module.cwrap ('mono_wasm_assembly_get_entry_point', 'number', ['number']);
 		var string_get_utf8 = Module.cwrap ('mono_wasm_string_get_utf8', 'string', ['number']);
 		var string_array_new = Module.cwrap ('mono_wasm_string_array_new', 'number', ['number']);
 		var obj_array_set = Module.cwrap ('mono_wasm_obj_array_set', 'void', ['number', 'number', 'number']);
-		var exit = Module.cwrap ('mono_wasm_exit', 'void', ['number']);
-		var wasm_setenv = Module.cwrap ('mono_wasm_setenv', 'void', ['string', 'string']);
 		var wasm_set_main_args = Module.cwrap ('mono_wasm_set_main_args', 'void', ['number', 'number']);
 		var wasm_strdup = Module.cwrap ('mono_wasm_strdup', 'number', ['string']);
 		var unbox_int = Module.cwrap ('mono_unbox_int', 'number', ['number']);
@@ -366,6 +340,6 @@ var App = {
 		}
 	},
 	call_test_method: function (method_name, args) {
-		return BINDING.call_static_method("[System.Runtime.InteropServices.JavaScript.Tests]System.Runtime.InteropServices.JavaScript.Tests.HelperMarshal:" + method_name, args);
+		return BINDING.call_static_method("[System.Private.Runtime.InteropServices.JavaScript.Tests]System.Runtime.InteropServices.JavaScript.Tests.HelperMarshal:" + method_name, args);
 	}
 };
\ No newline at end of file
diff --git a/src/mono/wasm/runtime/binding_support.js b/src/mono/wasm/runtime/binding_support.js
index bdef5f6ac5dc90..b9a1dae6ec1cdc 100644
--- a/src/mono/wasm/runtime/binding_support.js
+++ b/src/mono/wasm/runtime/binding_support.js
@@ -4,7 +4,7 @@
 var BindingSupportLib = {
 	$BINDING__postset: 'BINDING.export_functions (Module);',
 	$BINDING: {
-		BINDING_ASM: "[System.Runtime.InteropServices.JavaScript]System.Runtime.InteropServices.JavaScript.Runtime",
+		BINDING_ASM: "[System.Private.Runtime.InteropServices.JavaScript]System.Runtime.InteropServices.JavaScript.Runtime",
 		mono_wasm_object_registry: [],
 		mono_wasm_ref_counter: 0,
 		mono_wasm_free_list: [],
@@ -226,7 +226,7 @@ var BindingSupportLib = {
 
 				return enumValue;
 
-
+			case 10: // arrays
 			case 11: 
 			case 12: 
 			case 13: 
@@ -361,26 +361,7 @@ var BindingSupportLib = {
 			// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays
 			if (!!(js_obj.buffer instanceof ArrayBuffer && js_obj.BYTES_PER_ELEMENT)) 
 			{
-				var arrayType = 0;
-				if (js_obj instanceof Int8Array)
-					arrayType = 11;
-				if (js_obj instanceof Uint8Array)
-					arrayType = 12;
-				if (js_obj instanceof Uint8ClampedArray)
-					arrayType = 12;
-				if (js_obj instanceof Int16Array)
-					arrayType = 13;
-				if (js_obj instanceof Uint16Array)
-					arrayType = 14;
-				if (js_obj instanceof Int32Array)
-					arrayType = 15;
-				if (js_obj instanceof Uint32Array)
-					arrayType = 16;
-				if (js_obj instanceof Float32Array)
-					arrayType = 17;
-				if (js_obj instanceof Float64Array)
-					arrayType = 18;
-
+				var arrayType = js_obj[Symbol.for("wasm type")];
 				var heapBytes = this.js_typedarray_to_heap(js_obj);
 				var bufferArray = this.mono_typed_array_new(heapBytes.byteOffset, js_obj.length, js_obj.BYTES_PER_ELEMENT, arrayType);
 				Module._free(heapBytes.byteOffset);
@@ -516,7 +497,7 @@ var BindingSupportLib = {
 
 			this.typedarray_copy_from(newTypedArray, pinned_array, begin, end, bytes_per_element);
 			return newTypedArray;
-		},		
+		},
 		js_to_mono_enum: function (method, parmIdx, js_obj) {
 			this.bindings_lazy_init ();
     
diff --git a/src/mono/wasm/runtime/corebindings.c b/src/mono/wasm/runtime/corebindings.c
index ce7c73851aa224..a0263c2a8ba9dc 100644
--- a/src/mono/wasm/runtime/corebindings.c
+++ b/src/mono/wasm/runtime/corebindings.c
@@ -98,8 +98,9 @@ void core_initialize_internals ()
 // Float32Array		| float		| float
 // Float64Array		| double	| double
 // typed array marshalling
-#define MARSHAL_ARRAY_BYTE 11
-#define MARSHAL_ARRAY_UBYTE 12
+#define MARSHAL_ARRAY_BYTE 10
+#define MARSHAL_ARRAY_UBYTE 11
+#define MARSHAL_ARRAY_UBYTE_C 12 // alias of MARSHAL_ARRAY_UBYTE
 #define MARSHAL_ARRAY_SHORT 13
 #define MARSHAL_ARRAY_USHORT 14
 #define MARSHAL_ARRAY_INT 15
diff --git a/src/mono/wasm/runtime/dotnet.timezones.blat b/src/mono/wasm/runtime/dotnet.timezones.blat
index 4302a00818494d..30b4d13614ef25 100644
Binary files a/src/mono/wasm/runtime/dotnet.timezones.blat and b/src/mono/wasm/runtime/dotnet.timezones.blat differ
diff --git a/src/mono/wasm/runtime/dotnet_support.js b/src/mono/wasm/runtime/dotnet_support.js
index 7411959b66b4a9..2b4a16ec89a3a9 100644
--- a/src/mono/wasm/runtime/dotnet_support.js
+++ b/src/mono/wasm/runtime/dotnet_support.js
@@ -29,7 +29,25 @@ var DotNetSupportLib = {
 			return MONO.string_decoder.copy (mono_obj);
 		}
 	},
-	mono_wasm_invoke_js_marshalled: function(exceptionMessage, asyncHandleLongPtr, functionName, argsJson) {
+
+	mono_wasm_invoke_js_blazor: function(exceptionMessage, callInfo, arg0, arg1, arg2)	{
+		try {
+			var blazorExports = DOTNET._dotnet_get_global().Blazor;
+			if (!blazorExports) {
+				throw new Error('The blazor.webassembly.js library is not loaded.');
+			}
+
+			return blazorExports._internal.invokeJSFromDotNet(callInfo, arg0, arg1, arg2);
+		} catch (ex) {
+			var exceptionJsString = ex.message + '\n' + ex.stack;
+			var exceptionSystemString = mono_string(exceptionJsString);
+			setValue (exceptionMessage, exceptionSystemString, 'i32'); // *exceptionMessage = exceptionSystemString;
+			return 0;
+		}
+	},
+
+	// This is for back-compat only and will eventually be removed
+	mono_wasm_invoke_js_marshalled: function(exceptionMessage, asyncHandleLongPtr, functionName, argsJson, treatResultAsVoid) {
 
 		var mono_string = DOTNET._dotnet_get_global()._mono_string_cached
 			|| (DOTNET._dotnet_get_global()._mono_string_cached = Module.cwrap('mono_wasm_string_from_js', 'number', ['string']));
@@ -54,10 +72,10 @@ var DotNetSupportLib = {
 			}
 
 			if (asyncHandleJsNumber) {
-				dotNetExports.jsCallDispatcher.beginInvokeJSFromDotNet(asyncHandleJsNumber, funcNameJsString, argsJsonJsString);
+				dotNetExports.jsCallDispatcher.beginInvokeJSFromDotNet(asyncHandleJsNumber, funcNameJsString, argsJsonJsString, treatResultAsVoid);
 				return 0;
 			} else {
-				var resultJson = dotNetExports.jsCallDispatcher.invokeJSFromDotNet(funcNameJsString, argsJsonJsString);
+				var resultJson = dotNetExports.jsCallDispatcher.invokeJSFromDotNet(funcNameJsString, argsJsonJsString, treatResultAsVoid);
 				return resultJson === null ? 0 : mono_string(resultJson);
 			}
 		} catch (ex) {
@@ -67,6 +85,8 @@ var DotNetSupportLib = {
 			return 0;
 		}
 	},
+
+	// This is for back-compat only and will eventually be removed
 	mono_wasm_invoke_js_unmarshalled: function(exceptionMessage, funcName, arg0, arg1, arg2)	{
 		try {
 			// Get the function you're trying to invoke
diff --git a/src/mono/wasm/runtime/driver.c b/src/mono/wasm/runtime/driver.c
index e4456ee6b59583..2d4498c8955add 100644
--- a/src/mono/wasm/runtime/driver.c
+++ b/src/mono/wasm/runtime/driver.c
@@ -11,6 +11,7 @@
 #include <mono/metadata/assembly.h>
 #include <mono/metadata/tokentype.h>
 #include <mono/metadata/threads.h>
+#include <mono/metadata/image.h>
 #include <mono/utils/mono-logger.h>
 #include <mono/utils/mono-dl-fallback.h>
 #include <mono/jit/jit.h>
@@ -23,6 +24,8 @@ void core_initialize_internals ();
 #endif
 
 // Blazor specific custom routines - see dotnet_support.js for backing code
+extern void* mono_wasm_invoke_js_blazor (MonoString **exceptionMessage, void *callInfo, void* arg0, void* arg1, void* arg2);
+// The following two are for back-compat and will eventually be removed
 extern void* mono_wasm_invoke_js_marshalled (MonoString **exceptionMessage, void *asyncHandleLongPtr, MonoString *funcName, MonoString *argsJson);
 extern void* mono_wasm_invoke_js_unmarshalled (MonoString **exceptionMessage, MonoString *funcName, void* arg0, void* arg1, void* arg2);
 
@@ -107,20 +110,33 @@ mono_wasm_invoke_js (MonoString *str, int *is_exception)
 static void
 wasm_logger (const char *log_domain, const char *log_level, const char *message, mono_bool fatal, void *user_data)
 {
-	if (fatal) {
-		EM_ASM(
-			   var err = new Error();
-			   console.log ("Stacktrace: \n");
-			   console.log (err.stack);
-			   );
-
-		fprintf (stderr, "%s\n", message);
-		fflush (stderr);
-
-		abort ();
-	} else {
-		fprintf (stdout, "L: %s\n", message);
-	}
+	EM_ASM({
+		var message = Module.UTF8ToString ($3) + ": " + Module.UTF8ToString ($1);
+		if ($2)
+			console.trace (message);
+
+		switch (Module.UTF8ToString ($0)) {
+			case "critical":
+			case "error":
+				console.error (message);
+				break;
+			case "warning":
+				console.warn (message);
+				break;
+			case "message":
+				console.log (message);
+				break;
+			case "info":
+				console.info (message);
+				break;
+			case "debug":
+				console.debug (message);
+				break;
+			default:
+				console.log (message);
+				break;
+		}
+	}, log_level, message, fatal, log_domain);
 }
 
 #ifdef DRIVER_GEN
@@ -137,7 +153,7 @@ struct WasmAssembly_ {
 static WasmAssembly *assemblies;
 static int assembly_count;
 
-EMSCRIPTEN_KEEPALIVE void
+EMSCRIPTEN_KEEPALIVE int
 mono_wasm_add_assembly (const char *name, const unsigned char *data, unsigned int size)
 {
 	int len = strlen (name);
@@ -146,7 +162,7 @@ mono_wasm_add_assembly (const char *name, const unsigned char *data, unsigned in
 		//FIXME handle debugging assemblies with .exe extension
 		strcpy (&new_name [len - 3], "dll");
 		mono_register_symfile_for_assembly (new_name, data, size);
-		return;
+		return 1;
 	}
 	WasmAssembly *entry = g_new0 (WasmAssembly, 1);
 	entry->assembly.name = strdup (name);
@@ -155,6 +171,7 @@ mono_wasm_add_assembly (const char *name, const unsigned char *data, unsigned in
 	entry->next = assemblies;
 	assemblies = entry;
 	++assembly_count;
+	return mono_has_pdb_checksum (data, size);
 }
 
 EMSCRIPTEN_KEEPALIVE void
@@ -333,6 +350,8 @@ void mono_initialize_internals ()
 	// TODO: what happens when two types in different assemblies have the same FQN?
 
 	// Blazor specific custom routines - see dotnet_support.js for backing code
+	mono_add_internal_call ("WebAssembly.JSInterop.InternalCalls::InvokeJS", mono_wasm_invoke_js_blazor);
+	// The following two are for back-compat and will eventually be removed
 	mono_add_internal_call ("WebAssembly.JSInterop.InternalCalls::InvokeJSMarshalled", mono_wasm_invoke_js_marshalled);
 	mono_add_internal_call ("WebAssembly.JSInterop.InternalCalls::InvokeJSUnmarshalled", mono_wasm_invoke_js_unmarshalled);
 
@@ -343,7 +362,7 @@ void mono_initialize_internals ()
 }
 
 EMSCRIPTEN_KEEPALIVE void
-mono_wasm_load_runtime (const char *unused, int enable_debugging)
+mono_wasm_load_runtime (const char *unused, int debug_level)
 {
 	const char *interp_opts = "";
 
@@ -356,6 +375,16 @@ mono_wasm_load_runtime (const char *unused, int enable_debugging)
 	monoeg_g_setenv ("COMPlus_DebugWriteToStdErr", "1", 0);
 #endif
 
+	const char *appctx_keys[2];
+	appctx_keys [0] = "APP_CONTEXT_BASE_DIRECTORY";
+	appctx_keys [1] = "RUNTIME_IDENTIFIER";
+
+	const char *appctx_values[2];
+	appctx_values [0] = "/";
+	appctx_values [1] = "browser-wasm";
+
+	monovm_initialize (2, appctx_keys, appctx_values);
+
 	mini_parse_debug_option ("top-runtime-invoke-unhandled");
 
 	mono_dl_fallback_register (wasm_dl_load, wasm_dl_symbol, NULL, NULL);
@@ -370,11 +399,19 @@ mono_wasm_load_runtime (const char *unused, int enable_debugging)
 	mono_jit_set_aot_mode (MONO_AOT_MODE_LLVMONLY);
 #endif
 #else
-	mono_jit_set_aot_mode (MONO_AOT_MODE_INTERP_LLVMONLY);
-	if (enable_debugging) {
+	mono_jit_set_aot_mode (MONO_AOT_MODE_INTERP_ONLY);
+
+	/*
+	 * debug_level > 0 enables debugging and sets the debug log level to debug_level
+	 * debug_level == 0 disables debugging and enables interpreter optimizations
+	 * debug_level < 0 enabled debugging and disables debug logging.
+	 *
+	 * Note: when debugging is enabled interpreter optimizations are disabled.
+	 */
+	if (debug_level) {
 		// Disable optimizations which interfere with debugging
 		interp_opts = "-all";
-		mono_wasm_enable_debugging (enable_debugging);
+		mono_wasm_enable_debugging (debug_level);
 	}
 #endif
 
@@ -487,6 +524,8 @@ mono_wasm_assembly_get_entry_point (MonoAssembly *assembly)
 	uint32_t entry = mono_image_get_entry_point (image);
 	if (!entry)
 		return NULL;
+	
+	mono_domain_ensure_entry_assembly (root_domain, assembly);
 
 	return mono_get_method (image, entry, NULL);
 }
@@ -556,8 +595,9 @@ MonoClass* mono_get_uri_class(MonoException** exc)
 #define MARSHAL_TYPE_SAFEHANDLE 23
 
 // typed array marshalling
-#define MARSHAL_ARRAY_BYTE 11
-#define MARSHAL_ARRAY_UBYTE 12
+#define MARSHAL_ARRAY_BYTE 10
+#define MARSHAL_ARRAY_UBYTE 11
+#define MARSHAL_ARRAY_UBYTE_C 12
 #define MARSHAL_ARRAY_SHORT 13
 #define MARSHAL_ARRAY_USHORT 14
 #define MARSHAL_ARRAY_INT 15
@@ -571,6 +611,11 @@ mono_wasm_get_obj_type (MonoObject *obj)
 	if (!obj)
 		return 0;
 
+	/* Process obj before calling into the runtime, class_from_name () can invoke managed code */
+	MonoClass *klass = mono_object_get_class (obj);
+	MonoType *type = mono_class_get_type (klass);
+	obj = NULL;
+
 	if (!datetime_class)
 		datetime_class = mono_class_from_name (mono_get_corlib(), "System", "DateTime");
 	if (!datetimeoffset_class)
@@ -582,9 +627,6 @@ mono_wasm_get_obj_type (MonoObject *obj)
 	if (!safehandle_class)
 		safehandle_class = mono_class_from_name (mono_get_corlib(), "System.Runtime.InteropServices", "SafeHandle");
 
-	MonoClass *klass = mono_object_get_class (obj);
-	MonoType *type = mono_class_get_type (klass);
-
 	switch (mono_type_get_type (type)) {
 	// case MONO_TYPE_CHAR: prob should be done not as a number?
 	case MONO_TYPE_BOOLEAN:
diff --git a/src/mono/wasm/runtime/library_mono.js b/src/mono/wasm/runtime/library_mono.js
index e137e8940a0c82..14e191e79cd191 100644
--- a/src/mono/wasm/runtime/library_mono.js
+++ b/src/mono/wasm/runtime/library_mono.js
@@ -1,6 +1,15 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+/**
+ * @typedef WasmId
+ * @type {object}
+ * @property {string} idStr - full object id string
+ * @property {string} scheme - eg, object, valuetype, array ..
+ * @property {string} value - string part after `dotnet:scheme:` of the id string
+ * @property {object} o - value parsed as JSON
+ */
+
 var MonoSupportLib = {
 	$MONO__postset: 'MONO.export_functions (Module);',
 	$MONO: {
@@ -9,6 +18,10 @@ var MonoSupportLib = {
 		_vt_stack: [],
 		mono_wasm_runtime_is_ready : false,
 		mono_wasm_ignore_pdb_load_errors: true,
+
+		/** @type {object.<string, object>} */
+		_id_table: {},
+
 		pump_message: function () {
 			if (!this.mono_background_exec)
 				this.mono_background_exec = Module.cwrap ("mono_background_exec", null);
@@ -73,6 +86,12 @@ var MonoSupportLib = {
 			},
 		},
 
+		mono_wasm_get_exception_object: function() {
+			var exception_obj = MONO.active_exception;
+			MONO.active_exception = null;
+			return exception_obj ;
+		},
+
 		mono_wasm_get_call_stack: function() {
 			if (!this.mono_wasm_current_bp_id)
 				this.mono_wasm_current_bp_id = Module.cwrap ("mono_wasm_current_bp_id", 'number');
@@ -92,30 +111,21 @@ var MonoSupportLib = {
 		},
 
 		_fixup_name_value_objects: function (var_list) {
-			var out_list = [];
-
-			var _fixup_value = function (value) {
-				if (value != null && value != undefined) {
-					var descr = value.description;
-					if (descr == null || descr == undefined)
-						value.description = '' + value.value;
-				}
-				return value;
-			};
+			let out_list = [];
 
 			var i = 0;
 			while (i < var_list.length) {
-				var o = var_list [i];
-				var name = o.name;
+				let o = var_list [i];
+				const name = o.name;
 				if (name == null || name == undefined) {
 					i ++;
-					o.value = _fixup_value(o.value);
 					out_list.push (o);
 					continue;
 				}
 
-				if (i + 1 < var_list.length)
-					o.value = _fixup_value(var_list[i + 1].value);
+				if (i + 1 < var_list.length) {
+					o = Object.assign (o, var_list [i + 1]);
+				}
 
 				out_list.push (o);
 				i += 2;
@@ -125,8 +135,8 @@ var MonoSupportLib = {
 		},
 
 		_filter_automatic_properties: function (props) {
-			var names_found = {};
-			var final_var_list = [];
+			let names_found = {};
+			let final_var_list = [];
 
 			for (var i in props) {
 				var p = props [i];
@@ -145,93 +155,175 @@ var MonoSupportLib = {
 			return final_var_list;
 		},
 
-		mono_wasm_get_variables: function(scope, var_list) {
-			if (!this.mono_wasm_get_var_info)
-				this.mono_wasm_get_var_info = Module.cwrap ("mono_wasm_get_var_info", null, [ 'number', 'number', 'number']);
-
-			this.var_info = [];
-			var numBytes = var_list.length * Int32Array.BYTES_PER_ELEMENT;
-			var ptr = Module._malloc(numBytes);
-			var heapBytes = new Int32Array(Module.HEAP32.buffer, ptr, numBytes);
-			for (let i=0; i<var_list.length; i++)
-				heapBytes[i] = var_list[i];
-
-			this._async_method_objectId = 0;
-			this.mono_wasm_get_var_info (scope, heapBytes.byteOffset, var_list.length);
-			Module._free(heapBytes.byteOffset);
-			var res = MONO._fixup_name_value_objects (this.var_info);
-
-			//Async methods are special in the way that local variables can be lifted to generated class fields
-			//value of "this" comes here either
-			for (let i in res) {
-				var name = res [i].name;
-				if (name != undefined && name.indexOf ('>') > 0)
-					res [i].name = name.substring (1, name.indexOf ('>'));
+		/** Given `dotnet:object:foo:bar`,
+		 * returns { scheme:'object', value: 'foo:bar' }
+		 *
+		 * Given `dotnet:pointer:{ b: 3 }`
+		 * returns { scheme:'object', value: '{b:3}`, o: {b:3}
+		 *
+		 * @param  {string} idStr
+		 * @param  {boolean} [throwOnError=false]
+		 *
+		 * @returns {WasmId}
+		 */
+		_parse_object_id: function (idStr, throwOnError = false) {
+			if (idStr === undefined || idStr == "" || !idStr.startsWith ('dotnet:')) {
+				if (throwOnError)
+					throw new Error (`Invalid id: ${idStr}`);
+
+				return undefined;
 			}
 
-			if (this._async_method_objectId != 0) {
-				for (let i in res) {
-					if (res [i].value.isValueType != undefined && res [i].value.isValueType)
-						res [i].value.objectId = `dotnet:valuetype:${this._async_method_objectId}:${res [i].fieldOffset}`;
-				}
-			}
+			const [, scheme, ...rest] = idStr.split(':');
+			let res = {
+				scheme,
+				value: rest.join (':'),
+				idStr,
+				o: {}
+			};
 
-			this._post_process_details(res);
-			this.var_info = []
+			try {
+				res.o = JSON.parse(res.value);
+			// eslint-disable-next-line no-empty
+			} catch (e) {}
 
 			return res;
 		},
 
-		mono_wasm_get_object_properties: function(objId, expandValueTypes) {
-			if (!this.mono_wasm_get_object_properties_info)
-				this.mono_wasm_get_object_properties_info = Module.cwrap ("mono_wasm_get_object_properties", null, [ 'number', 'bool' ]);
+		/**
+		 * @param  {WasmId} id
+		 * @returns {object[]}
+		 */
+		_get_vt_properties: function (id) {
+			let entry = this._id_table [id.idStr];
+			if (entry !== undefined && entry.members !== undefined)
+				return entry.members;
+
+			if (!isNaN (id.o.containerId))
+				this._get_object_properties (id.o.containerId, true);
+			else if (!isNaN (id.o.arrayId))
+				this._get_array_values (id, Number (id.o.arrayIdx), 1, true);
+			else
+				throw new Error (`Invalid valuetype id (${id.idStr}). Can't get properties for it.`);
 
-			this.var_info = [];
-			this.mono_wasm_get_object_properties_info (objId, expandValueTypes);
+			entry = this._get_id_props (id.idStr);
+			if (entry !== undefined && entry.members !== undefined)
+				return entry.members;
 
-			var res = MONO._filter_automatic_properties (MONO._fixup_name_value_objects (this.var_info));
-			for (var i = 0; i < res.length; i++) {
-				if (res [i].value.isValueType != undefined && res [i].value.isValueType)
-					res [i].value.objectId = `dotnet:valuetype:${objId}:${res [i].fieldOffset}`;
-			}
+			throw new Error (`Unknown valuetype id: ${id.idStr}`);
+		},
 
-			this.var_info = [];
+		/**
+		 *
+		 * @callback GetIdArgsCallback
+		 * @param {object} var
+		 * @param {number} idx
+		 * @returns {object}
+		 */
+
+		/**
+		 * @param  {object[]} vars
+		 * @param  {GetIdArgsCallback} getIdArgs
+		 * @returns {object}
+		 */
+		_assign_vt_ids: function (vars, getIdArgs)
+		{
+			vars.forEach ((v, i) => {
+				// we might not have a `.value`, like in case of getters which have a `.get` instead
+				const value = v.value;
+				if (value === undefined || !value.isValueType)
+					return;
 
-			return res;
-		},
+				if (value.objectId !== undefined)
+					throw new Error (`Bug: Trying to assign valuetype id, but the var already has one: ${v}`);
 
-		mono_wasm_get_array_values: function(objId) {
-			if (!this.mono_wasm_get_array_values_info)
-				this.mono_wasm_get_array_values_info = Module.cwrap ("mono_wasm_get_array_values", null, [ 'number' ]);
+				value.objectId = this._new_or_add_id_props ({ scheme: 'valuetype', idArgs: getIdArgs (v, i), props: value._props });
+				delete value._props;
+			});
 
-			this.var_info = [];
-			this.mono_wasm_get_array_values_info (objId);
+			return vars;
+		},
 
-			var res = MONO._fixup_name_value_objects (this.var_info);
-			for (var i = 0; i < res.length; i++) {
-				if (res [i].value.isValueType != undefined && res [i].value.isValueType)
-					res [i].value.objectId = `dotnet:array:${objId}:${i}`;
+		//
+		// @var_list: [ { index: <var_id>, name: <var_name> }, .. ]
+		mono_wasm_get_variables: function(scope, var_list) {
+			const numBytes = var_list.length * Int32Array.BYTES_PER_ELEMENT;
+			const ptr = Module._malloc(numBytes);
+			let heapBytes = new Int32Array(Module.HEAP32.buffer, ptr, numBytes);
+			for (let i=0; i<var_list.length; i++) {
+				heapBytes[i] = var_list[i].index;
 			}
 
-			this.var_info = [];
+			this._async_method_objectId = 0;
+			let { res_ok, res } = this.mono_wasm_get_local_vars_info (scope, heapBytes.byteOffset, var_list.length);
+			Module._free(heapBytes.byteOffset);
+			if (!res_ok)
+				throw new Error (`Failed to get locals for scope ${scope}`);
+
+			if (this._async_method_objectId != 0)
+				this._assign_vt_ids (res, v => ({ containerId: this._async_method_objectId, fieldOffset: v.fieldOffset }));
 
+			for (let i in res) {
+				const res_name = res [i].name;
+				if (this._async_method_objectId != 0) {
+					//Async methods are special in the way that local variables can be lifted to generated class fields
+					//value of "this" comes here either
+					if (res_name !== undefined && res_name.indexOf ('>') > 0) {
+						// For async methods, we get the names too, so use that
+						// ALTHOUGH, the name wouldn't have `<>` for method args
+						res [i].name = res_name.substring (1, res_name.indexOf ('>'));
+					}
+				} else if (res_name === undefined && var_list [i] !== undefined) {
+					// For non-async methods, we just have the var id, but we have the name
+					// from the caller
+					res [i].name = var_list [i].name;
+				}
+			}
+
+			this._post_process_details(res);
 			return res;
 		},
 
-		mono_wasm_get_array_value_expanded: function(objId, idx) {
-			if (!this.mono_wasm_get_array_value_expanded_info)
-				this.mono_wasm_get_array_value_expanded_info = Module.cwrap ("mono_wasm_get_array_value_expanded", null, [ 'number', 'number' ]);
+		/**
+		 * @param  {number} idNum
+		 * @param  {boolean} expandValueTypes
+		 * @returns {object}
+		 */
+		_get_object_properties: function(idNum, expandValueTypes) {
+			let { res_ok, res } = this.mono_wasm_get_object_properties_info (idNum, expandValueTypes);
+			if (!res_ok)
+				throw new Error (`Failed to get properties for ${idNum}`);
 
-			this.var_info = [];
-			this.mono_wasm_get_array_value_expanded_info (objId, idx);
+			res = MONO._filter_automatic_properties (res);
+			res = this._assign_vt_ids (res, v => ({ containerId: idNum, fieldOffset: v.fieldOffset }));
+			res = this._post_process_details (res);
 
-			var res = MONO._fixup_name_value_objects (this.var_info);
-			// length should be exactly one!
-			if (res [0].value.isValueType != undefined && res [0].value.isValueType)
-				res [0].value.objectId = `dotnet:array:${objId}:${idx}`;
-
-			this.var_info = [];
+			return res;
+		},
 
+		/**
+		 * @param  {WasmId} id
+		 * @param  {number} [startIdx=0]
+		 * @param  {number} [count=-1]
+		 * @param  {boolean} [expandValueTypes=false]
+		 * @returns {object[]}
+		 */
+		_get_array_values: function (id, startIdx = 0, count = -1, expandValueTypes = false) {
+			if (isNaN (id.o.arrayId) || isNaN (startIdx))
+				throw new Error (`Invalid array id: ${id.idStr}`);
+
+			let { res_ok, res } = this.mono_wasm_get_array_values_info (id.o.arrayId, startIdx, count, expandValueTypes);
+			if (!res_ok)
+				throw new Error (`Failed to get properties for array id ${id.idStr}`);
+
+			res = this._assign_vt_ids (res, (_, i) => ({ arrayId: id.o.arrayId, arrayIdx: Number (startIdx) + i}));
+
+			for (let i = 0; i < res.length; i ++) {
+				let value = res [i].value;
+				if (value.objectId !== undefined && value.objectId.startsWith("dotnet:pointer"))
+					this._new_or_add_id_props ({ objectId: value.objectId, props: { varName: `[${i}]` } });
+			}
+			res = this._post_process_details (res);
 			return res;
 		},
 
@@ -245,8 +337,13 @@ var MonoSupportLib = {
 			return details;
 		},
 
-		_next_value_type_id: function () {
-			return ++this._next_value_type_id_var;
+		/**
+		 * Gets the next id number to use for generating ids
+		 *
+		 * @returns {number}
+		 */
+		_next_id: function () {
+			return ++this._next_id_var;
 		},
 
 		_extract_and_cache_value_types: function (var_list) {
@@ -254,131 +351,201 @@ var MonoSupportLib = {
 				return var_list;
 
 			for (let i in var_list) {
-				var value = var_list [i].value;
-				if (value == undefined || value.type != "object")
+				let value = var_list [i].value;
+				if (value === undefined)
 					continue;
 
-				if (value.isValueType != true || value.expanded != true) // undefined would also give us false
+				if (value.objectId !== undefined && value.objectId.startsWith ("dotnet:pointer:")) {
+					let ptr_args = this._get_id_props (value.objectId);
+					if (ptr_args === undefined)
+						throw new Error (`Bug: Expected to find an entry for pointer id: ${value.objectId}`);
+
+					// It might have been already set in some cases, like arrays
+					// where the name would be `0`, but we want `[0]` for pointers,
+					// so the deref would look like `*[0]`
+					ptr_args.varName = ptr_args.varName || var_list [i].name;
+				}
+
+				if (value.type != "object" || value.isValueType != true || value.expanded != true) // undefined would also give us false
 					continue;
 
-				var objectId = value.objectId;
-				if (objectId == undefined)
-					objectId = `dotnet:valuetype:${this._next_value_type_id ()}`;
-				value.objectId = objectId;
+				// Generate objectId for expanded valuetypes
+				value.objectId = value.objectId || this._new_or_add_id_props ({ scheme: 'valuetype' });
 
 				this._extract_and_cache_value_types (value.members);
 
-				this._value_types_cache [objectId] = value.members;
+				const new_props = Object.assign ({ members: value.members }, value.__extra_vt_props);
+
+				this._new_or_add_id_props ({ objectId: value.objectId, props: new_props });
 				delete value.members;
+				delete value.__extra_vt_props;
 			}
 
 			return var_list;
 		},
 
-		_get_details_for_value_type: function (objectId, fetchDetailsFn) {
-			if (objectId in this._value_types_cache)
-				return this._value_types_cache[objectId];
+		_get_cfo_res_details: function (objectId, args) {
+			if (!(objectId in this._call_function_res_cache))
+				throw new Error(`Could not find any object with id ${objectId}`);
+
+			const real_obj = this._call_function_res_cache [objectId];
+
+			const descriptors = Object.getOwnPropertyDescriptors (real_obj);
+			if (args.accessorPropertiesOnly) {
+				Object.keys (descriptors).forEach (k => {
+					if (descriptors [k].get === undefined)
+						Reflect.deleteProperty (descriptors, k);
+				});
+			}
+
+			let res_details = [];
+			Object.keys (descriptors).forEach (k => {
+				let new_obj;
+				let prop_desc = descriptors [k];
+				if (typeof prop_desc.value == "object") {
+					// convert `{value: { type='object', ... }}`
+					// to      `{ name: 'foo', value: { type='object', ... }}
+					new_obj = Object.assign ({ name: k }, prop_desc);
+				} else if (prop_desc.value !== undefined) {
+					// This is needed for values that were not added by us,
+					// thus are like { value: 5 }
+					// instead of    { value: { type = 'number', value: 5 }}
+					//
+					// This can happen, for eg., when `length` gets added for arrays
+					// or `__proto__`.
+					new_obj = {
+						name: k,
+						// merge/add `type` and `description` to `d.value`
+						value: Object.assign ({ type: (typeof prop_desc.value), description: '' + prop_desc.value },
+												prop_desc)
+					};
+				} else if (prop_desc.get !== undefined) {
+					// The real_obj has the actual getter. We are just returning a placeholder
+					// If the caller tries to run function on the cfo_res object,
+					// that accesses this property, then it would be run on `real_obj`,
+					// which *has* the original getter
+					new_obj = {
+						name: k,
+						get: {
+							className: "Function",
+							description: `get ${k} () {}`,
+							type: "function"
+						}
+					};
+				} else {
+					new_obj = { name: k, value: { type: "symbol", value: "<Unknown>", description: "<Unknown>"} };
+				}
+
+				res_details.push (new_obj);
+			});
+
+			return { __value_as_json_string__: JSON.stringify (res_details) };
+		},
+
+		/**
+		 * Generates a new id, and a corresponding entry for associated properties
+		 *    like `dotnet:pointer:{ a: 4 }`
+		 * The third segment of that `{a:4}` is the idArgs parameter
+		 *
+		 * Only `scheme` or `objectId` can be set.
+		 * if `scheme`, then a new id is generated, and it's properties set
+		 * if `objectId`, then it's properties are updated
+		 *
+		 * @param {object} args
+		 * @param  {string} [args.scheme=undefined] scheme second part of `dotnet:pointer:..`
+		 * @param  {string} [args.objectId=undefined] objectId
+		 * @param  {object} [args.idArgs={}] The third segment of the objectId
+		 * @param  {object} [args.props={}] Properties for the generated id
+		 *
+		 * @returns {string} generated/updated id string
+		 */
+		_new_or_add_id_props: function ({ scheme = undefined, objectId = undefined, idArgs = {}, props = {} }) {
+			if (scheme === undefined && objectId === undefined)
+				throw new Error (`Either scheme or objectId must be given`);
+
+			if (scheme !== undefined && objectId !== undefined)
+				throw new Error (`Both scheme, and objectId cannot be given`);
+
+			if (objectId !== undefined && Object.entries (idArgs).length > 0)
+				throw new Error (`Both objectId, and idArgs cannot be given`);
+
+			if (Object.entries (idArgs).length == 0) {
+				// We want to generate a new id, only if it doesn't have other
+				// attributes that it can use to uniquely identify.
+				// Eg, we don't do this for `dotnet:valuetype:{containerId:4, fieldOffset: 24}`
+				idArgs.num = this._next_id ();
+			}
+
+			let idStr;
+			if (objectId !== undefined) {
+				idStr = objectId;
+				const old_props = this._id_table [idStr];
+				if (old_props === undefined)
+					throw new Error (`ObjectId not found in the id table: ${idStr}`);
 
-			this._post_process_details (fetchDetailsFn());
-			if (objectId in this._value_types_cache)
-				return this._value_types_cache[objectId];
+				this._id_table [idStr] = Object.assign (old_props, props);
+			} else {
+				idStr = `dotnet:${scheme}:${JSON.stringify (idArgs)}`;
+				this._id_table [idStr] = props;
+			}
 
-			// return error
-			throw new Error (`Could not get details for ${objectId}`);
+			return idStr;
 		},
 
-		_is_object_id_array: function (objectId) {
-			// Keep this in sync with `_get_array_details`
-			return (objectId.startsWith ('dotnet:array:') && objectId.split (':').length == 3);
+		/**
+		 * @param  {string} objectId
+		 * @returns {object}
+		 */
+		_get_id_props: function (objectId) {
+			return this._id_table [objectId];
 		},
 
-		_get_array_details: function (objectId, objectIdParts) {
-			// Keep this in sync with `_is_object_id_array`
-			switch (objectIdParts.length) {
-				case 3:
-					return this._post_process_details (this.mono_wasm_get_array_values(objectIdParts[2]));
+		_get_deref_ptr_value: function (objectId) {
+			const ptr_args = this._get_id_props (objectId);
+			if (ptr_args === undefined)
+				throw new Error (`Unknown pointer id: ${objectId}`);
 
-				case 4:
-					var arrayObjectId = objectIdParts[2];
-					var arrayIdx = objectIdParts[3];
-					return this._get_details_for_value_type(
-									objectId, () => this.mono_wasm_get_array_value_expanded(arrayObjectId, arrayIdx));
+			if (ptr_args.ptr_addr == 0 || ptr_args.klass_addr == 0)
+				throw new Error (`Both ptr_addr and klass_addr need to be non-zero, to dereference a pointer. objectId: ${objectId}`);
 
-				default:
-					throw new Error (`object id format not supported : ${objectId}`);
+			const value_addr = new DataView (Module.HEAPU8.buffer).getUint32 (ptr_args.ptr_addr, /* littleEndian */ true);
+			let { res_ok, res } = this.mono_wasm_get_deref_ptr_value_info (value_addr, ptr_args.klass_addr);
+			if (!res_ok)
+				throw new Error (`Failed to dereference pointer ${objectId}`);
+
+			if (res.length > 0) {
+				if (ptr_args.varName === undefined)
+					throw new Error (`Bug: no varName found for the pointer. objectId: ${objectId}`);
+
+				res [0].name = `*${ptr_args.varName}`;
 			}
+
+			res = this._post_process_details (res);
+			return res;
 		},
 
 		mono_wasm_get_details: function (objectId, args) {
-			var parts = objectId.split(":");
-			if (parts[0] != "dotnet")
-				throw new Error ("Can't handle non-dotnet object ids. ObjectId: " + objectId);
+			let id = this._parse_object_id (objectId, true);
 
-			switch (parts[1]) {
-				case "object":
-					if (parts.length != 3)
-						throw new Error(`exception this time: Invalid object id format: ${objectId}`);
+			switch (id.scheme) {
+				case "object": {
+					if (isNaN (id.value))
+						throw new Error (`Invalid objectId: ${objectId}. Expected a numeric id.`);
 
-					return this._post_process_details(this.mono_wasm_get_object_properties(parts[2], false));
+					return this._get_object_properties(id.value, false);
+				}
 
 				case "array":
-					return this._get_array_details(objectId, parts);
+					return this._get_array_values (id);
 
 				case "valuetype":
-					if (parts.length != 3 && parts.length != 4) {
-						// dotnet:valuetype:vtid
-						// dotnet:valuetype:containerObjectId:vtId
-						throw new Error(`Invalid object id format: ${objectId}`);
-					}
+					return this._get_vt_properties(id);
 
-					var containerObjectId = parts[2];
-					return this._get_details_for_value_type(objectId, () => this.mono_wasm_get_object_properties(containerObjectId, true));
-
-				case "cfo_res": {
-					if (!(objectId in this._call_function_res_cache))
-						throw new Error(`Could not find any object with id ${objectId}`);
-
-					var real_obj = this._call_function_res_cache [objectId];
-					if (args.accessorPropertiesOnly) {
-						// var val_accessors = JSON.stringify ([
-						//  {
-						//      name: "__proto__",
-						//      get: { type: "function", className: "Function", description: "function get __proto__ () {}", objectId: "dotnet:cfo_res:9999" },
-						//      set: { type: "function", className: "Function", description: "function set __proto__ () {}", objectId: "dotnet:cfo_res:8888" },
-						//      isOwn: false
-						//  }], undefined, 4);
-						return { __value_as_json_string__:  "[]" };
-					}
-
-					// behaving as if (args.ownProperties == true)
-					var descriptors = Object.getOwnPropertyDescriptors (real_obj);
-					var own_properties = [];
-					Object.keys (descriptors).forEach (k => {
-						var new_obj;
-						var prop_desc = descriptors [k];
-						if (typeof prop_desc.value == "object") {
-							// convert `{value: { type='object', ... }}`
-							// to      `{ name: 'foo', value: { type='object', ... }}
-							new_obj = Object.assign ({ name: k}, prop_desc);
-						} else {
-							// This is needed for values that were not added by us,
-							// thus are like { value: 5 }
-							// instead of    { value: { type = 'number', value: 5 }}
-							//
-							// This can happen, for eg., when `length` gets added for arrays
-							// or `__proto__`.
-							new_obj = {
-								name: k,
-								// merge/add `type` and `description` to `d.value`
-								value: Object.assign ({ type: (typeof prop_desc.value), description: '' + prop_desc.value },
-														prop_desc)
-							};
-						}
+				case "cfo_res":
+					return this._get_cfo_res_details (objectId, args);
 
-						own_properties.push (new_obj);
-					});
-
-					return { __value_as_json_string__: JSON.stringify (own_properties) };
+				case "pointer": {
+					return this._get_deref_ptr_value (objectId);
 				}
 
 				default:
@@ -387,7 +554,7 @@ var MonoSupportLib = {
 		},
 
 		_cache_call_function_res: function (obj) {
-			var id = `dotnet:cfo_res:${this._next_call_function_res_id++}`;
+			const id = `dotnet:cfo_res:${this._next_call_function_res_id++}`;
 			this._call_function_res_cache[id] = obj;
 			return id;
 		},
@@ -397,41 +564,116 @@ var MonoSupportLib = {
 				delete this._cache_call_function_res[objectId];
 		},
 
+		/**
+		 * @param  {string} objectIdStr objectId
+		 * @param  {string} name property name
+		 * @returns {object} return value
+		 */
+		_invoke_getter: function (objectIdStr, name) {
+			const id = this._parse_object_id (objectIdStr);
+			if (id === undefined)
+				throw new Error (`Invalid object id: ${objectIdStr}`);
+
+			let getter_res;
+			if (id.scheme == 'object') {
+				if (isNaN (id.o) || id.o < 0)
+					throw new Error (`Invalid object id: ${objectIdStr}`);
+
+				let { res_ok, res } = this.mono_wasm_invoke_getter_on_object_info (id.o, name);
+				if (!res_ok)
+					throw new Error (`Invoking getter on ${objectIdStr} failed`);
+
+				getter_res = res;
+			} else if (id.scheme == 'valuetype') {
+				const id_props = this._get_id_props (objectIdStr);
+				if (id_props === undefined)
+					throw new Error (`Unknown valuetype id: ${objectIdStr}`);
+
+				if (typeof id_props.value64 !== 'string' || isNaN (id_props.klass))
+					throw new Error (`Bug: Cannot invoke getter on ${objectIdStr}, because of missing or invalid klass/value64 fields. idProps: ${JSON.stringify (id_props)}`);
+
+				const dataPtr = Module._malloc (id_props.value64.length);
+				const dataHeap = new Uint8Array (Module.HEAPU8.buffer, dataPtr, id_props.value64.length);
+				dataHeap.set (new Uint8Array (this._base64_to_uint8 (id_props.value64)));
+
+				let { res_ok, res } = this.mono_wasm_invoke_getter_on_value_info (dataHeap.byteOffset, id_props.klass, name);
+				Module._free (dataHeap.byteOffset);
+
+				if (!res_ok) {
+					console.debug (`Invoking getter on valuetype ${objectIdStr}, with props: ${JSON.stringify (id_props)} failed`);
+					throw new Error (`Invoking getter on valuetype ${objectIdStr} failed`);
+				}
+				getter_res = res;
+			} else {
+				throw new Error (`Only object, and valuetypes supported for getters, id: ${objectIdStr}`);
+			}
+
+			getter_res = MONO._post_process_details (getter_res);
+			return getter_res.length > 0 ? getter_res [0] : {};
+		},
+
+		_create_proxy_from_object_id: function (objectId) {
+			const details = this.mono_wasm_get_details(objectId);
+
+			if (objectId.startsWith ('dotnet:array:'))
+				return details.map (p => p.value);
+
+			let proxy = {};
+			Object.keys (details).forEach (p => {
+				var prop = details [p];
+				if (prop.get !== undefined) {
+					// TODO: `set`
+
+					Object.defineProperty (proxy,
+							prop.name,
+							{ get () { return MONO._invoke_getter (objectId, prop.name); } }
+					);
+				} else {
+					proxy [prop.name] = prop.value;
+				}
+			});
+
+			return proxy;
+		},
+
 		mono_wasm_call_function_on: function (request) {
-			var objId = request.objectId;
-			var proxy;
-
-			if (objId in this._call_function_res_cache) {
-				proxy = this._call_function_res_cache [objId];
-			} else if (!objId.startsWith ('dotnet:cfo_res:')) {
-				var details = this.mono_wasm_get_details(objId);
-				var target_is_array = this._is_object_id_array (objId);
-				proxy = target_is_array ? [] : {};
-
-				Object.keys(details).forEach(p => {
-					var prop = details[p];
-					if (target_is_array) {
-						proxy.push(prop.value);
-					} else {
-						if (prop.name != undefined)
-							proxy [prop.name] = prop.value;
-						else // when can this happen??
-							proxy[''+p] = prop.value;
-					}
-				});
+			if (request.arguments != undefined && !Array.isArray (request.arguments))
+				throw new Error (`"arguments" should be an array, but was ${request.arguments}`);
+
+			const objId = request.objectId;
+			let proxy;
+
+			if (objId.startsWith ('dotnet:cfo_res:')) {
+				if (objId in this._call_function_res_cache)
+					proxy = this._call_function_res_cache [objId];
+				else
+					throw new Error (`Unknown object id ${objId}`);
+			} else {
+				proxy = this._create_proxy_from_object_id (objId);
 			}
 
-			var fn_args = request.arguments != undefined ? request.arguments.map(a => a.value) : [];
-			var fn_eval_str = `var fn = ${request.functionDeclaration}; fn.call (proxy, ...[${fn_args}]);`;
+			const fn_args = request.arguments != undefined ? request.arguments.map(a => JSON.stringify(a.value)) : [];
+			const fn_eval_str = `var fn = ${request.functionDeclaration}; fn.call (proxy, ...[${fn_args}]);`;
 
-			var fn_res = eval (fn_eval_str);
-			if (request.returnByValue)
+			const fn_res = eval (fn_eval_str);
+			if (fn_res === undefined)
+				return { type: "undefined" };
+
+			if (fn_res === null || (fn_res.subtype === 'null' && fn_res.value === undefined))
+				return fn_res;
+
+			// primitive type
+			if (Object (fn_res) !== fn_res)
 				return fn_res;
 
-			if (fn_res == undefined)
-				throw Error ('Function returned undefined result');
+			// return .value, if it is a primitive type
+			if (fn_res.value !== undefined && Object (fn_res.value.value) !== fn_res.value.value)
+				return fn_res.value;
 
-			var fn_res_id = this._cache_call_function_res (fn_res);
+			if (request.returnByValue)
+				return {type: "object", value: fn_res};
+
+			const fn_res_id = this._cache_call_function_res (fn_res);
 			if (Object.getPrototypeOf (fn_res) == Array.prototype) {
 				return {
 					type: "object",
@@ -445,28 +687,94 @@ var MonoSupportLib = {
 			}
 		},
 
+		_clear_per_step_state: function () {
+			this._next_id_var = 0;
+			this._id_table = {};
+		},
+
+		mono_wasm_debugger_resume: function () {
+			this._clear_per_step_state ();
+		},
+
 		mono_wasm_start_single_stepping: function (kind) {
 			console.log (">> mono_wasm_start_single_stepping " + kind);
 			if (!this.mono_wasm_setup_single_step)
 				this.mono_wasm_setup_single_step = Module.cwrap ("mono_wasm_setup_single_step", 'number', [ 'number']);
 
-			this._next_value_type_id_var = 0;
-			this._value_types_cache = {};
+			this._clear_per_step_state ();
 
 			return this.mono_wasm_setup_single_step (kind);
 		},
 
+		mono_wasm_set_pause_on_exceptions: function (state) {
+			if (!this.mono_wasm_pause_on_exceptions)
+				this.mono_wasm_pause_on_exceptions = Module.cwrap ("mono_wasm_pause_on_exceptions", 'number', [ 'number']);
+			var state_enum = 0;
+			switch (state) {
+				case 'uncaught':
+					state_enum = 1; //EXCEPTION_MODE_UNCAUGHT
+					break;
+				case 'all':
+					state_enum = 2; //EXCEPTION_MODE_ALL
+					break;
+			}
+			return this.mono_wasm_pause_on_exceptions (state_enum);
+		},
+
+		_register_c_fn: function (name, ...args) {
+			Object.defineProperty (this._c_fn_table, name + '_wrapper', { value: Module.cwrap (name, ...args) });
+		},
+
+		/**
+		 * Calls `Module.cwrap` for the function name,
+		 * and creates a wrapper around it that returns
+		 *     `{ bool result, object var_info }
+		 *
+		 * @param  {string} name C function name
+		 * @param  {string} ret_type
+		 * @param  {string[]} params
+		 *
+		 * @returns {void}
+		 */
+		_register_c_var_fn: function (name, ret_type, params) {
+			if (ret_type !== 'bool')
+				throw new Error (`Bug: Expected a C function signature that returns bool`);
+
+			this._register_c_fn (name, ret_type, params);
+			Object.defineProperty (this, name + '_info', {
+				value: function (...args) {
+					MONO.var_info = [];
+					const res_ok = MONO._c_fn_table [name + '_wrapper'] (...args);
+					let res = MONO.var_info;
+					MONO.var_info = [];
+					if (res_ok) {
+						res = this._fixup_name_value_objects (res);
+						return { res_ok, res };
+					}
+
+					return { res_ok, res: undefined };
+				}
+			});
+		},
+
 		mono_wasm_runtime_ready: function () {
 			this.mono_wasm_runtime_is_ready = true;
 			// DO NOT REMOVE - magic debugger init function
 			console.debug ("mono_wasm_runtime_ready", "fe00e07a-5519-4dfe-b35a-f867dbaf2e28");
 
-			this._next_value_type_id_var = 0;
-			this._value_types_cache = {};
+			this._clear_per_step_state ();
 
 			// FIXME: where should this go?
 			this._next_call_function_res_id = 0;
 			this._call_function_res_cache = {};
+
+			this._c_fn_table = {};
+			this._register_c_var_fn ('mono_wasm_get_object_properties',   'bool', [ 'number', 'bool' ]);
+			this._register_c_var_fn ('mono_wasm_get_array_values',        'bool', [ 'number', 'number', 'number', 'bool' ]);
+			this._register_c_var_fn ('mono_wasm_invoke_getter_on_object', 'bool', [ 'number', 'string' ]);
+			this._register_c_var_fn ('mono_wasm_invoke_getter_on_value',  'bool', [ 'number', 'number', 'string' ]);
+			this._register_c_var_fn ('mono_wasm_get_local_vars',          'bool', [ 'number', 'number', 'number']);
+			this._register_c_var_fn ('mono_wasm_get_deref_ptr_value',     'bool', [ 'number', 'number']);
 		},
 
 		mono_wasm_set_breakpoint: function (assembly, method_token, il_offset) {
@@ -496,7 +804,7 @@ var MonoSupportLib = {
 				this.wasm_parse_runtime_options = Module.cwrap ('mono_wasm_parse_runtime_options', null, ['number', 'number']);
 			var argv = Module._malloc (options.length * 4);
 			var wasm_strdup = Module.cwrap ('mono_wasm_strdup', 'number', ['string']);
-			aindex = 0;
+			let aindex = 0;
 			for (var i = 0; i < options.length; ++i) {
 				Module.setValue (argv + (aindex * 4), wasm_strdup (options [i]), "i32");
 				aindex += 1;
@@ -601,7 +909,7 @@ var MonoSupportLib = {
 
 			switch (asset.behavior) {
 				case "assembly":
-					ctx.loaded_files.push (url);
+					ctx.loaded_files.push ({ url: url, file: virtualName});
 				case "heap":
 				case "icu":
 					offset = this.mono_wasm_load_bytes_into_heap (bytes);
@@ -619,7 +927,6 @@ var MonoSupportLib = {
 						: virtualName;
 					if (fileName.startsWith("/"))
 						fileName = fileName.substr(1);
-
 					if (parentDirectory) {
 						if (ctx.tracing)
 							console.log ("MONO_WASM: Creating directory '" + parentDirectory + "'");
@@ -634,19 +941,26 @@ var MonoSupportLib = {
 					if (ctx.tracing)
 						console.log ("MONO_WASM: Creating file '" + fileName + "' in directory '" + parentDirectory + "'");
 
-					var fileRet = ctx.createDataFile (
-						parentDirectory, fileName,
-						bytes, true /* canRead */, true /* canWrite */, true /* canOwn */
-					);
-
+					if (!this.mono_wasm_load_data_archive (bytes, parentDirectory)) {
+						var fileRet = ctx.createDataFile (
+							parentDirectory, fileName,
+							bytes, true /* canRead */, true /* canWrite */, true /* canOwn */
+						);
+					}
 					break;
 
 				default:
 					throw new Error ("Unrecognized asset behavior:", asset.behavior, "for asset", asset.name);
 			}
 
-			if (asset.behavior === "assembly")
-				ctx.mono_wasm_add_assembly (virtualName, offset, bytes.length);
+			if (asset.behavior === "assembly") {
+				var hasPpdb = ctx.mono_wasm_add_assembly (virtualName, offset, bytes.length);
+
+				if (!hasPpdb) {
+					var index = ctx.loaded_files.findIndex(element => element.file == virtualName);
+					ctx.loaded_files.splice(index, 1);
+				}
+			}
 			else if (asset.behavior === "icu") {
 				if (this.mono_wasm_load_icu_data (offset))
 					ctx.num_icu_assets_loaded_successfully += 1;
@@ -657,12 +971,12 @@ var MonoSupportLib = {
 
 		// deprecated
 		mono_load_runtime_and_bcl: function (
-			unused_vfs_prefix, deploy_prefix, enable_debugging, file_list, loaded_cb, fetch_file_cb
+			unused_vfs_prefix, deploy_prefix, debug_level, file_list, loaded_cb, fetch_file_cb
 		) {
 			var args = {
 				fetch_file_cb: fetch_file_cb,
 				loaded_cb: loaded_cb,
-				enable_debugging: enable_debugging,
+				debug_level: debug_level,
 				assembly_root: deploy_prefix,
 				assets: []
 			};
@@ -687,7 +1001,7 @@ var MonoSupportLib = {
 		// Initializes the runtime and loads assemblies, debug information, and other files.
 		// @args is a dictionary-style Object with the following properties:
 		//    assembly_root: (required) the subfolder containing managed assemblies and pdbs
-		//    enable_debugging: (required)
+		//    debug_level or enable_debugging: (required)
 		//    assets: (required) a list of assets to load along with the runtime. each asset
 		//     is a dictionary-style Object with the following properties:
 		//        name: (required) the name of the asset, including extension.
@@ -753,8 +1067,11 @@ var MonoSupportLib = {
 		},
 
 		_finalize_startup: function (args, ctx) {
+			var loaded_files_with_debug_info = [];
+
 			MONO.loaded_assets = ctx.loaded_assets;
-			MONO.loaded_files = ctx.loaded_files;
+			ctx.loaded_files.forEach(value => loaded_files_with_debug_info.push(value.url));
+			MONO.loaded_files = loaded_files_with_debug_info;
 			if (ctx.tracing) {
 				console.log ("MONO_WASM: loaded_assets: " + JSON.stringify(ctx.loaded_assets));
 				console.log ("MONO_WASM: loaded_files: " + JSON.stringify(ctx.loaded_files));
@@ -768,18 +1085,17 @@ var MonoSupportLib = {
 
 			if (ENVIRONMENT_IS_SHELL || ENVIRONMENT_IS_NODE) {
 				try {
-					load_runtime ("unused", args.enable_debugging);
+					load_runtime ("unused", args.debug_level);
 				} catch (ex) {
 					print ("MONO_WASM: load_runtime () failed: " + ex);
-					var err = new Error();
 					print ("MONO_WASM: Stacktrace: \n");
-					print (err.stack);
+					print (ex.stack);
 
 					var wasm_exit = Module.cwrap ('mono_wasm_exit', null, ['number']);
 					wasm_exit (1);
 				}
 			} else {
-				load_runtime ("unused", args.enable_debugging);
+				load_runtime ("unused", args.debug_level);
 			}
 
 			MONO.mono_wasm_runtime_ready ();
@@ -787,6 +1103,8 @@ var MonoSupportLib = {
 		},
 
 		_load_assets_and_runtime: function (args) {
+			if (args.enable_debugging)
+				args.debug_level = args.enable_debugging;
 			if (args.assembly_list)
 				throw new Error ("Invalid args (assembly_list was replaced by assets)");
 			if (args.runtime_assets)
@@ -799,7 +1117,7 @@ var MonoSupportLib = {
 			var ctx = {
 				tracing: args.diagnostic_tracing || false,
 				pending_count: args.assets.length,
-				mono_wasm_add_assembly: Module.cwrap ('mono_wasm_add_assembly', null, ['string', 'number', 'number']),
+				mono_wasm_add_assembly: Module.cwrap ('mono_wasm_add_assembly', 'number', ['string', 'number', 'number']),
 				loaded_assets: Object.create (null),
 				// dlls and pdbs, used by blazor and the debugger
 				loaded_files: [],
@@ -963,7 +1281,7 @@ var MonoSupportLib = {
 
 		mono_wasm_add_null_var: function(className)
 		{
-			fixed_class_name = MONO._mono_csharp_fixup_class_name(Module.UTF8ToString (className));
+			let fixed_class_name = MONO._mono_csharp_fixup_class_name(Module.UTF8ToString (className));
 			if (!fixed_class_name) {
 				// Eg, when a @className is passed from js itself, like
 				// mono_wasm_add_null_var ("string")
@@ -987,24 +1305,40 @@ var MonoSupportLib = {
 				value: {
 					type: "string",
 					value: var_value,
+					description: var_value
 				}
 			});
 		},
 
-		_mono_wasm_add_getter_var: function(className) {
-			fixed_class_name = MONO._mono_csharp_fixup_class_name (className);
-			var value = `${fixed_class_name} { get; }`;
-			MONO.var_info.push({
-				value: {
-					type: "symbol",
-					value: value,
-					description: value
-				}
-			});
+		_mono_wasm_add_getter_var: function(className, invokable) {
+			const fixed_class_name = MONO._mono_csharp_fixup_class_name (className);
+			if (invokable != 0) {
+				var name;
+				if (MONO.var_info.length > 0)
+					name = MONO.var_info [MONO.var_info.length - 1].name;
+				name = (name === undefined) ? "" : name;
+
+				MONO.var_info.push({
+					get: {
+						className: "Function",
+						description: `get ${name} () {}`,
+						type: "function",
+					}
+				});
+			} else {
+				var value = `${fixed_class_name} { get; }`;
+				MONO.var_info.push({
+					value: {
+						type: "symbol",
+						description: value,
+						value: value,
+					}
+				});
+			}
 		},
 
 		_mono_wasm_add_array_var: function(className, objectId, length) {
-			fixed_class_name = MONO._mono_csharp_fixup_class_name(className);
+			const fixed_class_name = MONO._mono_csharp_fixup_class_name(className);
 			if (objectId == 0) {
 				MONO.mono_wasm_add_null_var (fixed_class_name);
 				return;
@@ -1016,42 +1350,121 @@ var MonoSupportLib = {
 					subtype: "array",
 					className: fixed_class_name,
 					description: `${fixed_class_name}(${length})`,
-					objectId: "dotnet:array:"+ objectId,
+					objectId: this._new_or_add_id_props ({ scheme: 'array', idArgs: { arrayId: objectId } })
 				}
 			});
 		},
 
+		// FIXME: improve
+		_base64_to_uint8: function (base64String) {
+			const byteCharacters = atob (base64String);
+			const byteNumbers = new Array(byteCharacters.length);
+			for (let i = 0; i < byteCharacters.length; i++) {
+				byteNumbers[i] = byteCharacters.charCodeAt(i);
+			}
+
+			return new Uint8Array (byteNumbers);
+		},
+
+		_begin_value_type_var: function(className, args) {
+			if (args === undefined || (typeof args !== 'object')) {
+				console.debug (`_begin_value_type_var: Expected an args object`);
+				return;
+			}
+
+			const fixed_class_name = MONO._mono_csharp_fixup_class_name(className);
+			const toString = args.toString;
+			const base64String = btoa (String.fromCharCode (...new Uint8Array (Module.HEAPU8.buffer, args.value_addr, args.value_size)));
+			const vt_obj = {
+				value: {
+					type            : "object",
+					className       : fixed_class_name,
+					description     : (toString == 0 ? fixed_class_name: Module.UTF8ToString (toString)),
+					expanded        : true,
+					isValueType     : true,
+					__extra_vt_props: { klass: args.klass, value64: base64String },
+					members         : []
+				}
+			};
+			if (MONO._vt_stack.length == 0)
+				MONO._old_var_info = MONO.var_info;
+
+			MONO.var_info = vt_obj.value.members;
+			MONO._vt_stack.push (vt_obj);
+		},
+
+		_end_value_type_var: function() {
+			let top_vt_obj_popped = MONO._vt_stack.pop ();
+			top_vt_obj_popped.value.members = MONO._filter_automatic_properties (
+								MONO._fixup_name_value_objects (top_vt_obj_popped.value.members));
+
+			if (MONO._vt_stack.length == 0) {
+				MONO.var_info = MONO._old_var_info;
+				MONO.var_info.push(top_vt_obj_popped);
+			} else {
+				var top_obj = MONO._vt_stack [MONO._vt_stack.length - 1];
+				top_obj.value.members.push (top_vt_obj_popped);
+				MONO.var_info = top_obj.value.members;
+			}
+		},
+
+		_add_valuetype_unexpanded_var: function(className, args) {
+			if (args === undefined || (typeof args !== 'object')) {
+				console.debug (`_add_valuetype_unexpanded_var: Expected an args object`);
+				return;
+			}
+
+			const fixed_class_name = MONO._mono_csharp_fixup_class_name (className);
+			const toString = args.toString;
+
+			MONO.var_info.push ({
+				value: {
+					type: "object",
+					className: fixed_class_name,
+					description: (toString == 0 ? fixed_class_name : Module.UTF8ToString (toString)),
+					isValueType: true
+				}
+			});
+		},
+
+
 		mono_wasm_add_typed_value: function (type, str_value, value) {
-			var type_str = type;
+			let type_str = type;
 			if (typeof type != 'string')
 				type_str = Module.UTF8ToString (type);
-			if (typeof str_value != 'string')
 				str_value = Module.UTF8ToString (str_value);
 
 			switch (type_str) {
-			case "bool":
+			case "bool": {
+				const v = value != 0;
 				MONO.var_info.push ({
 					value: {
 						type: "boolean",
-						value: value != 0
+						value: v,
+						description: v.toString ()
 					}
 				});
 				break;
+			}
 
-			case "char":
+			case "char": {
+				const v = `${value} '${String.fromCharCode (value)}'`;
 				MONO.var_info.push ({
 					value: {
 						type: "symbol",
-						value: `${value} '${String.fromCharCode (value)}'`
+						value: v,
+						description: v
 					}
 				});
 				break;
+			}
 
 			case "number":
 				MONO.var_info.push ({
 					value: {
 						type: "number",
-						value: value
+						value: value,
+						description: '' + value
 					}
 				});
 				break;
@@ -1061,26 +1474,51 @@ var MonoSupportLib = {
 				break;
 
 			case "getter":
-				MONO._mono_wasm_add_getter_var (str_value);
+				MONO._mono_wasm_add_getter_var (str_value, value);
 				break;
 
 			case "array":
 				MONO._mono_wasm_add_array_var (str_value, value.objectId, value.length);
 				break;
 
+			case "begin_vt":
+				MONO._begin_value_type_var (str_value, value);
+				break;
+
+			case "end_vt":
+				MONO._end_value_type_var ();
+				break;
+
+			case "unexpanded_vt":
+				MONO._add_valuetype_unexpanded_var (str_value, value);
+				break;
+
 			case "pointer": {
-				MONO.var_info.push ({
-					value: {
-						type: "symbol",
-						value: str_value,
-						description: str_value
-					}
-				});
+				const fixed_value_str = MONO._mono_csharp_fixup_class_name (str_value);
+				if (value.klass_addr == 0 || value.ptr_addr == 0 || fixed_value_str.startsWith ('(void*')) {
+					// null or void*, which we can't deref
+					MONO.var_info.push({
+						value: {
+							type: "symbol",
+							value: fixed_value_str,
+							description: fixed_value_str
+						}
+					});
+				} else {
+					MONO.var_info.push({
+						value: {
+							type: "object",
+							className: fixed_value_str,
+							description: fixed_value_str,
+							objectId: this._new_or_add_id_props ({ scheme: 'pointer', props: value })
+						}
+					});
+				}
 				}
 				break;
 
 			default: {
-				var msg = `'${str_value}' ${value}`;
+				const msg = `'${str_value}' ${value}`;
 
 				MONO.var_info.push ({
 					value: {
@@ -1101,16 +1539,30 @@ var MonoSupportLib = {
 			return className.replace(/\//g, '.').replace(/`\d+/g, '');
 		},
 
-		mono_wasm_load_data: function (data, prefix) {
+		mono_wasm_load_data_archive: function (data, prefix) {
+			if (data.length < 8)
+				return false;
+
 			var dataview = new DataView(data.buffer);
 			var magic = dataview.getUint32(0, true);
 			//	get magic number
 			if (magic != 0x626c6174) {
-				throw new Error ("File is of wrong type");
+				return false;
 			}
 			var manifestSize = dataview.getUint32(4, true);
-			var manifestContent = Module.UTF8ArrayToString(data, 8, manifestSize);
-			var manifest = JSON.parse(manifestContent);
+			if (manifestSize == 0 || data.length < manifestSize + 8)
+				return false;
+
+			var manifest;
+			try {
+				manifestContent = Module.UTF8ArrayToString(data, 8, manifestSize);
+				manifest = JSON.parse(manifestContent);
+				if (!(manifest instanceof Array))
+					return false;
+			} catch (exc) {
+				return false;
+			}
+
 			data = data.slice(manifestSize+8);
 
 			// Create the folder structure
@@ -1118,18 +1570,13 @@ var MonoSupportLib = {
 			// /usr/share/zoneinfo/Africa
 			// /usr/share/zoneinfo/Asia
 			// ..
-			var p = prefix.slice(1).split('/');
-			p.forEach((v, i) => {
-				FS.mkdir(v);
-				Module['FS_createPath']("/" + p.slice(0, i).join('/'), v, true, true);
-			})
+
 			var folders = new Set()
 			manifest.filter(m => {
-				m = m[0].split('/')
-				if (m!= null) {
-					if (m.length > 2) folders.add(m.slice(0,m.length-1).join('/'));
-					folders.add(m[0]);
-				}
+				var file = m[0];
+				var last = file.lastIndexOf ("/");
+				var directory = file.slice (0, last);
+				folders.add(directory);
 			});
 			folders.forEach(folder => {
 				Module['FS_createPath'](prefix, folder, true, true);
@@ -1139,9 +1586,10 @@ var MonoSupportLib = {
 				var name = row[0];
 				var length = row[1];
 				var bytes = data.slice(0, length);
-				Module['FS_createDataFile'](`${prefix}/${name}`, null, bytes, true, true);
+				Module['FS_createDataFile'](prefix, name, bytes, true, true);
 				data = data.slice(length);
 			}
+			return true;
 		}
 	},
 
@@ -1160,55 +1608,6 @@ var MonoSupportLib = {
 		MONO._async_method_objectId = objectId;
 	},
 
-	mono_wasm_begin_value_type_var: function(className, toString) {
-		fixed_class_name = MONO._mono_csharp_fixup_class_name(Module.UTF8ToString (className));
-		var vt_obj = {
-			value: {
-				type: "object",
-				className: fixed_class_name,
-				description: (toString == 0 ? fixed_class_name : Module.UTF8ToString (toString)),
-				// objectId will be generated by MonoProxy
-				expanded: true,
-				isValueType: true,
-				members: []
-			}
-		};
-		if (MONO._vt_stack.length == 0)
-			MONO._old_var_info = MONO.var_info;
-
-		MONO.var_info = vt_obj.value.members;
-		MONO._vt_stack.push (vt_obj);
-	},
-
-	mono_wasm_end_value_type_var: function() {
-		var top_vt_obj_popped = MONO._vt_stack.pop ();
-		top_vt_obj_popped.value.members = MONO._filter_automatic_properties (
-							MONO._fixup_name_value_objects (top_vt_obj_popped.value.members));
-
-		if (MONO._vt_stack.length == 0) {
-			MONO.var_info = MONO._old_var_info;
-			MONO.var_info.push(top_vt_obj_popped);
-		} else {
-			var top_obj = MONO._vt_stack [MONO._vt_stack.length - 1];
-			top_obj.value.members.push (top_vt_obj_popped);
-			MONO.var_info = top_obj.value.members;
-		}
-	},
-
-	mono_wasm_add_value_type_unexpanded_var: function (className, toString) {
-		fixed_class_name = MONO._mono_csharp_fixup_class_name(Module.UTF8ToString (className));
-		MONO.var_info.push({
-			value: {
-				type: "object",
-				className: fixed_class_name,
-				description: (toString == 0 ? fixed_class_name : Module.UTF8ToString (toString)),
-				// objectId added when enumerating object's properties
-				expanded: false,
-				isValueType: true
-			}
-		});
-	},
-
 	mono_wasm_add_enum_var: function(className, members, value) {
 		// FIXME: flags
 		//
@@ -1216,13 +1615,13 @@ var MonoSupportLib = {
 		// group0: Monday:0
 		// group1: Monday
 		// group2: 0
-		var re = new RegExp (`[,]?([^,:]+):(${value}(?=,)|${value}$)`, 'g')
-		var members_str = Module.UTF8ToString (members);
+		const re = new RegExp (`[,]?([^,:]+):(${value}(?=,)|${value}$)`, 'g')
+		const members_str = Module.UTF8ToString (members);
 
-		var match = re.exec(members_str);
-		var member_name = match == null ? ('' + value) : match [1];
+		const match = re.exec(members_str);
+		const member_name = match == null ? ('' + value) : match [1];
 
-		fixed_class_name = MONO._mono_csharp_fixup_class_name(Module.UTF8ToString (className));
+		const fixed_class_name = MONO._mono_csharp_fixup_class_name(Module.UTF8ToString (className));
 		MONO.var_info.push({
 			value: {
 				type: "object",
@@ -1245,7 +1644,7 @@ var MonoSupportLib = {
 			return;
 		}
 
-		fixed_class_name = MONO._mono_csharp_fixup_class_name(Module.UTF8ToString (className));
+		const fixed_class_name = MONO._mono_csharp_fixup_class_name(Module.UTF8ToString (className));
 		MONO.var_info.push({
 			value: {
 				type: "object",
@@ -1282,11 +1681,11 @@ var MonoSupportLib = {
 			return `${ret_sig} ${method_name} (${args_sig})`;
 		}
 
-		var tgt_sig;
+		let tgt_sig;
 		if (targetName != 0)
 			tgt_sig = args_to_sig (Module.UTF8ToString (targetName));
 
-		var type_name = MONO._mono_csharp_fixup_class_name (Module.UTF8ToString (className));
+		const type_name = MONO._mono_csharp_fixup_class_name (Module.UTF8ToString (className));
 
 		if (objectId == -1) {
 			// Target property
@@ -1356,6 +1755,17 @@ var MonoSupportLib = {
 
 	mono_wasm_fire_bp: function () {
 		console.log ("mono_wasm_fire_bp");
+		// eslint-disable-next-line no-debugger
+		debugger;
+	},
+
+	mono_wasm_fire_exception: function (exception_id, message, class_name, uncaught) {
+		MONO.active_exception = {
+			exception_id: exception_id,
+			message     : Module.UTF8ToString (message),
+			class_name  : Module.UTF8ToString (class_name),
+			uncaught    : uncaught
+		};
 		debugger;
 	},
 };
diff --git a/src/mono/wasm/wasm.targets b/src/mono/wasm/wasm.targets
index 520dd9c7d7b21e..9934c9a845fecf 100644
--- a/src/mono/wasm/wasm.targets
+++ b/src/mono/wasm/wasm.targets
@@ -1,48 +1,53 @@
 <Project>
 
-  <UsingTask TaskName="PInvokeTableGenerator"
-    AssemblyFile="$([MSBuild]::NormalizePath('$(ArtifactsBinDir)', 'WasmAppBuilder', 'Debug', '$(NetCoreAppCurrent)', 'publish', 'WasmAppBuilder.dll'))"/>
-
-  <PropertyGroup>
-    <WasmPInvokeTablePath>$(ArtifactsObjDir)wasm/pinvoke-table.h</WasmPInvokeTablePath>
-  </PropertyGroup>
-
-  <ItemGroup>
-    <PackageReference Include="$(MicrosoftNETCoreRuntimeICUTransportPackage)" PrivateAssets="all" Version="$(MicrosoftNETCoreRuntimeICUTransportVersion)" GeneratePathProperty="true" />
-
-    <WasmPInvokeModules Include="libSystem.Native"/>
-    <WasmPInvokeModules Include="libSystem.IO.Compression.Native"/>
-    <WasmPInvokeModules Include="libSystem.Globalization.Native"/>
-    <WasmPInvokeAssemblies Include="$(MonoArtifactsPath)\System.Private.CoreLib.dll"/>
-    <WasmPInvokeAssemblies Include="$(ArtifactsBinDir)\System.Runtime\$(NetCoreAppCurrent)-$(Configuration)\System.Runtime.dll"/>
-    <WasmPInvokeAssemblies Include="$(ArtifactsBinDir)\System.Console\$(NetCoreAppCurrent)-Browser-$(Configuration)\System.Console.dll"/>
-    <WasmPInvokeAssemblies Include="$(ArtifactsBinDir)\System.IO.FileSystem\$(NetCoreAppCurrent)-Browser-$(Configuration)\System.IO.FileSystem.dll"/>
-    <WasmPInvokeAssemblies Include="$(ArtifactsBinDir)\System.IO.MemoryMappedFiles\$(NetCoreAppCurrent)-Browser-$(Configuration)\System.IO.MemoryMappedFiles.dll"/>
-    <WasmPInvokeAssemblies Include="$(ArtifactsBinDir)\System.Net.Sockets\$(NetCoreAppCurrent)-Browser-$(Configuration)\System.Net.Sockets.dll"/>
-    <WasmPInvokeAssemblies Include="$(ArtifactsBinDir)\System.Net.Primitives\$(NetCoreAppCurrent)-Browser-$(Configuration)\System.Net.Primitives.dll"/>
-    <WasmPInvokeAssemblies Include="$(ArtifactsBinDir)\System.Security.Cryptography.Algorithms\$(NetCoreAppCurrent)-Browser-$(Configuration)\System.Security.Cryptography.Algorithms.dll"/>
-    <WasmPInvokeAssemblies Include="$(ArtifactsBinDir)\System.IO.Compression\$(NetCoreAppCurrent)-Browser-$(Configuration)\System.IO.Compression.dll"/>
-    <!--<WasmPInvokeAssemblies Include="$(ArtifactsBinDir)\System.IO.Compression.Brotli\$(NetCoreAppCurrent)-Unix-$(Configuration)\System.IO.Compression.Brotli.dll"/>-->
-  </ItemGroup>
-
   <Target Name="CheckEnv">
     <Error Condition="'$(TargetArchitecture)' != 'wasm'" Text="Expected TargetArchitecture==wasm, got '$(TargetArchitecture)'"/>
     <Error Condition="'$(TargetOS)' != 'Browser'" Text="Expected TargetOS==Browser, got '$(TargetOS)'"/>
     <Error Condition="'$(EMSDK_PATH)' == ''" Text="The EMSDK_PATH environment variable should be set pointing to the emscripten SDK root dir."/>
   </Target>
 
+  <ItemGroup>
+    <PackageReference Include="$(MicrosoftNETCoreRuntimeICUTransportPackage)" PrivateAssets="all" Version="$(MicrosoftNETCoreRuntimeICUTransportVersion)" GeneratePathProperty="true" />
+  </ItemGroup>
+
+  <UsingTask TaskName="PInvokeTableGenerator" AssemblyFile="$([MSBuild]::NormalizePath('$(ArtifactsBinDir)', 'WasmAppBuilder', 'Debug', '$(NetCoreAppCurrent)', 'publish', 'WasmAppBuilder.dll'))"/>
   <Target Name="BuildPInvokeTable" DependsOnTargets="CheckEnv">
-    <MakeDir Directories="$(ArtifactsObjDir)wasm"/>
-    <PInvokeTableGenerator
-      Modules="@(WasmPInvokeModules)"
-      Assemblies="@(WasmPInvokeAssemblies)"
-      OutputPath="$(WasmPInvokeTablePath)"
-      />
+    <PropertyGroup>
+      <WasmPInvokeTablePath>$(ArtifactsObjDir)wasm\pinvoke-table.h</WasmPInvokeTablePath>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <WasmPInvokeModule Include="libSystem.Native" />
+      <WasmPInvokeModule Include="libSystem.IO.Compression.Native" />
+      <WasmPInvokeModule Include="libSystem.Globalization.Native" />
+      <WasmPInvokeAssembly Include="$(MicrosoftNetCoreAppRuntimePackRidLibTfmDir)*.dll" />
+    </ItemGroup>
+    
+    <!-- Retrieve CoreLib's targetpath via GetTargetPath as it isn't binplaced yet. -->
+    <MSBuild Projects="$(CoreLibProject)"
+             Targets="GetTargetPath">
+      <Output TaskParameter="TargetOutputs" ItemName="WasmPInvokeAssembly" />
+    </MSBuild>
+
+    <MakeDir Directories="$(ArtifactsObjDir)wasm" />
+    <PInvokeTableGenerator Modules="@(WasmPInvokeModule)"
+                           Assemblies="@(WasmPInvokeAssembly)"
+                           OutputPath="$(WasmPInvokeTablePath)" />
   </Target>
 
+  <!-- This is a documented target that is invoked by developers in their innerloop work. -->
   <Target Name="BuildWasmRuntimes"
+          AfterTargets="Build"
           DependsOnTargets="BuildPInvokeTable">
-    <Exec Command="make -C $(MonoProjectRoot)wasm all SHELL=/bin/bash BINDIR=$(ArtifactsBinDir) MONO_BIN_DIR=$(MonoArtifactsPath) OBJDIR=$(ArtifactsObjDir) BUILDS_BIN_DIR=$(NativeBinDir) NATIVE_DIR=$(ArtifactsObjDir)/native/$(NetCoreAppCurrent)-$(TargetOS)-$(Configuration)-$(TargetArchitecture) CONFIG=$(Configuration) PINVOKE_TABLE=$(WasmPInvokeTablePath) ICU_LIBDIR=$(PkgMicrosoft_NETCore_Runtime_ICU_Transport)/runtimes/browser-wasm/native/lib" IgnoreStandardErrorWarningFormat="true"/>
+    <Exec Command="make -C $(MonoProjectRoot)wasm all SHELL=/bin/bash BINDIR=$(ArtifactsBinDir) MONO_BIN_DIR=$(MonoArtifactsPath) OBJDIR=$(ArtifactsObjDir) BUILDS_BIN_DIR=$(NativeBinDir) NATIVE_DIR=$(ArtifactsObjDir)/native/$(NetCoreAppCurrent)-$(TargetOS)-$(Configuration)-$(TargetArchitecture) CONFIG=$(Configuration) PINVOKE_TABLE=$(WasmPInvokeTablePath) ICU_LIBDIR=$(PkgMicrosoft_NETCore_Runtime_ICU_Transport)/runtimes/browser-wasm/native/lib"
+          IgnoreStandardErrorWarningFormat="true" />
+
+    <Copy SourceFiles="$(NativeBinDir)dotnet.js;
+                       $(NativeBinDir)dotnet.wasm;
+                       $(NativeBinDir)dotnet.timezones.blat;
+                       $(NativeBinDir)icudt.dat"
+          DestinationFolder="$(MicrosoftNetCoreAppRuntimePackNativeDir)"
+          SkipUnchangedFiles="true" />
   </Target>
 
 </Project>
diff --git a/src/mono/winconfig.h b/src/mono/winconfig.h
index f062d0a6959597..7d429a86e8a989 100644
--- a/src/mono/winconfig.h
+++ b/src/mono/winconfig.h
@@ -67,6 +67,9 @@
 #ifndef DISABLE_DLLMAP
 #define DISABLE_DLLMAP 1
 #endif
+#ifndef DISABLE_CFGDIR_CONFIG
+#define DISABLE_CFGDIR_CONFIG 1
+#endif
 #endif
 
 /* Disable runtime state dumping */
diff --git a/src/tests/CMakeLists.txt b/src/tests/CMakeLists.txt
index 0523d165acba30..77fcc16a01f92a 100644
--- a/src/tests/CMakeLists.txt
+++ b/src/tests/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.14.5)
+cmake_minimum_required(VERSION 3.6.2)
 
 cmake_policy(SET CMP0042 NEW)
 project(Tests)
diff --git a/src/tests/Common/Coreclr.TestWrapper/CoreclrTestWrapperLib.cs b/src/tests/Common/Coreclr.TestWrapper/CoreclrTestWrapperLib.cs
index ee471092a4ac87..e2d08676ec599a 100644
--- a/src/tests/Common/Coreclr.TestWrapper/CoreclrTestWrapperLib.cs
+++ b/src/tests/Common/Coreclr.TestWrapper/CoreclrTestWrapperLib.cs
@@ -6,6 +6,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+using System.Linq;
 using System.Runtime.InteropServices;
 using System.Text;
 using System.Text.RegularExpressions;
@@ -15,43 +16,11 @@
 
 namespace CoreclrTestLib
 {
-    static class DbgHelp
-    {
-        public enum MiniDumpType : int
-        {
-            MiniDumpNormal                          = 0x00000000,
-            MiniDumpWithDataSegs                    = 0x00000001,
-            MiniDumpWithFullMemory                  = 0x00000002,
-            MiniDumpWithHandleData                  = 0x00000004,
-            MiniDumpFilterMemory                    = 0x00000008,
-            MiniDumpScanMemory                      = 0x00000010,
-            MiniDumpWithUnloadedModules             = 0x00000020,
-            MiniDumpWithIndirectlyReferencedMemory  = 0x00000040,
-            MiniDumpFilterModulePaths               = 0x00000080,
-            MiniDumpWithProcessThreadData           = 0x00000100,
-            MiniDumpWithPrivateReadWriteMemory      = 0x00000200,
-            MiniDumpWithoutOptionalData             = 0x00000400,
-            MiniDumpWithFullMemoryInfo              = 0x00000800,
-            MiniDumpWithThreadInfo                  = 0x00001000,
-            MiniDumpWithCodeSegs                    = 0x00002000,
-            MiniDumpWithoutAuxiliaryState           = 0x00004000,
-            MiniDumpWithFullAuxiliaryState          = 0x00008000,
-            MiniDumpWithPrivateWriteCopyMemory      = 0x00010000,
-            MiniDumpIgnoreInaccessibleMemory        = 0x00020000,
-            MiniDumpWithTokenInformation            = 0x00040000,
-            MiniDumpWithModuleHeaders               = 0x00080000,
-            MiniDumpFilterTriage                    = 0x00100000,
-            MiniDumpValidTypeFlags                  = 0x001fffff
-        }
-
-        [DllImport("DbgHelp.dll", SetLastError = true)]
-        public static extern bool MiniDumpWriteDump(IntPtr handle, int processId, SafeFileHandle file, MiniDumpType dumpType, IntPtr exceptionParam, IntPtr userStreamParam, IntPtr callbackParam);
-    }
-
     static class Kernel32
     {
         public const int MAX_PATH = 260;
         public const int ERROR_NO_MORE_FILES = 0x12;
+        public const long INVALID_HANDLE = -1;
 
         public enum Toolhelp32Flags : uint
         {
@@ -91,14 +60,6 @@ public unsafe struct ProcessEntry32W
         public static extern bool Process32NextW(IntPtr snapshot, ref ProcessEntry32W entry);
     }
 
-    static class libSystem
-    {
-        [DllImport(nameof(libSystem))]
-        public static extern int kill(int pid, int signal);
-
-        public const int SIGABRT = 0x6;
-    }
-
     static class libproc
     {
         [DllImport(nameof(libproc))]
@@ -112,189 +73,215 @@ public static unsafe bool ListChildPids(int ppid, out int[] buffer)
         }
     }
 
-    public class CoreclrTestWrapperLib
+    internal static class ProcessExtensions
     {
-        public const int EXIT_SUCCESS_CODE = 0;
-        public const string TIMEOUT_ENVIRONMENT_VAR = "__TestTimeout";
-        
-        // Default timeout set to 10 minutes
-        public const int DEFAULT_TIMEOUT = 1000 * 60*10;
-
-        public const string COLLECT_DUMPS_ENVIRONMENT_VAR = "__CollectDumps";
-        public const string CRASH_DUMP_FOLDER_ENVIRONMENT_VAR = "__CrashDumpFolder";
-
-        static bool CollectCrashDump(Process process, string path)
+        public unsafe static IEnumerable<Process> GetChildren(this Process process)
         {
+            var children = new List<Process>();
             if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
             {
-                using (var crashDump = File.OpenWrite(path))
-                {
-                    var flags = DbgHelp.MiniDumpType.MiniDumpWithFullMemory | DbgHelp.MiniDumpType.MiniDumpIgnoreInaccessibleMemory;
-                    return DbgHelp.MiniDumpWriteDump(process.Handle, process.Id, crashDump.SafeFileHandle, flags, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero);
-                }
+                return Windows_GetChildren(process);
             }
             else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
             {
-                string coreRoot = Environment.GetEnvironmentVariable("CORE_ROOT");
-                ProcessStartInfo createdumpInfo = new ProcessStartInfo("sudo");
-                createdumpInfo.Arguments = $"{Path.Combine(coreRoot, "createdump")} --name \"{path}\" {process.Id} -h";
-                Process createdump = Process.Start(createdumpInfo);
-                return createdump.WaitForExit(DEFAULT_TIMEOUT) && createdump.ExitCode == 0;
+                return Linux_GetChildren(process);
             }
             else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
             {
-                int pid = process.Id;
-                Console.WriteLine($"Aborting process {pid} to generate dump");
-                int status = libSystem.kill(pid, libSystem.SIGABRT);
-
-                string defaultCoreDumpPath = $"/cores/core.{pid}";
+                return MacOS_GetChildren(process);
+            }
+            return children;
+        }
 
-                if (status == 0 && File.Exists(defaultCoreDumpPath))
+        private unsafe static IEnumerable<Process> Windows_GetChildren(Process process)
+        {
+            var children = new List<Process>();
+            IntPtr snapshot = Kernel32.CreateToolhelp32Snapshot(Kernel32.Toolhelp32Flags.TH32CS_SNAPPROCESS, 0);
+            if (snapshot != IntPtr.Zero && snapshot.ToInt64() != Kernel32.INVALID_HANDLE)
+            {
+                try
                 {
-                    Console.WriteLine($"Moving dump for {pid} to {path}.");
-                    File.Move(defaultCoreDumpPath, path, true);
+                    children = new List<Process>();
+                    int ppid = process.Id;
+
+                    var processEntry = new Kernel32.ProcessEntry32W { Size = sizeof(Kernel32.ProcessEntry32W) };
+
+                    bool success = Kernel32.Process32FirstW(snapshot, ref processEntry);
+                    while (success)
+                    {
+                        if (processEntry.ParentProcessID == ppid)
+                        {
+                            try
+                            {
+                                children.Add(Process.GetProcessById(processEntry.ProcessID));
+                            }
+                            catch {}
+                        }
+
+                        success = Kernel32.Process32NextW(snapshot, ref processEntry);
+                    }
+
                 }
-                else
+                finally
                 {
-                    Console.WriteLine($"Unable to find OS-generated dump for {pid} at default path: {defaultCoreDumpPath}");
+                    Kernel32.CloseHandle(snapshot);
                 }
-                return true;
             }
 
-            return false;
+            return children;
         }
 
-        static unsafe bool TryFindChildProcessByName(Process process, string childName, out Process child)
+        private static IEnumerable<Process> Linux_GetChildren(Process process)
         {
-            child = null;
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            var children = new List<Process>();
+            List<int> childPids = null;
+
+            try
             {
-                return TryFindChildProcessByNameWindows(process, childName, out child);
+                childPids = File.ReadAllText($"/proc/{process.Id}/task/{process.Id}/children")
+                    .Split(' ', StringSplitOptions.RemoveEmptyEntries)
+                    .Select(pidString => int.Parse(pidString))
+                    .ToList();
             }
-            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+            catch (IOException e)
             {
-                return TryFindChildProcessByNameLinux(process, childName, out child);
+                // Some distros might not have the /proc/pid/task/tid/children entry enabled in the kernel
+                // attempt to use pgrep then
+                var pgrepInfo = new ProcessStartInfo("pgrep");
+                pgrepInfo.RedirectStandardOutput = true;
+                pgrepInfo.Arguments = $"-P {process.Id}";
+
+                using Process pgrep = Process.Start(pgrepInfo);
+
+                string[] pidStrings = pgrep.StandardOutput.ReadToEnd().Split('\n', StringSplitOptions.RemoveEmptyEntries);
+                pgrep.WaitForExit();
+
+                childPids = new List<int>();
+                foreach (var pidString in pidStrings)
+                    if (int.TryParse(pidString, out int childPid))
+                        childPids.Add(childPid);
             }
-            else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+
+            foreach (var pid in childPids)
             {
-                return TryFindChildProcessByNameMacOS(process, childName, out child);
+                try
+                {
+                    children.Add(Process.GetProcessById(pid));
+                }
+                catch (ArgumentException)
+                {
+                    // Ignore failure to get process, the process may have exited
+                }
             }
-            return false;
+
+            return children;
         }
 
-        static unsafe bool TryFindChildProcessByNameWindows(Process process, string childName, out Process child)
+        private static IEnumerable<Process> MacOS_GetChildren(Process process)
         {
-            IntPtr snapshot = Kernel32.CreateToolhelp32Snapshot(Kernel32.Toolhelp32Flags.TH32CS_SNAPPROCESS, 0);
-            if (snapshot == IntPtr.Zero)
+            var children = new List<Process>();
+            if (libproc.ListChildPids(process.Id, out int[] childPids))
             {
-                child = null;
-                return false;
+                foreach (var childPid in childPids)
+                {
+                    children.Add(Process.GetProcessById(childPid));
+                }
             }
 
-            try
-            {
-                int ppid = process.Id;
+            return children;
+        }
+    }
 
-                var processEntry = new Kernel32.ProcessEntry32W { Size = sizeof(Kernel32.ProcessEntry32W) };
+    public class CoreclrTestWrapperLib
+    {
+        public const int EXIT_SUCCESS_CODE = 0;
+        public const string TIMEOUT_ENVIRONMENT_VAR = "__TestTimeout";
+        
+        // Default timeout set to 10 minutes
+        public const int DEFAULT_TIMEOUT_MS = 1000 * 60 * 10;
 
-                bool success = Kernel32.Process32FirstW(snapshot, ref processEntry);
-                while (success)
-                {
-                    if (processEntry.ParentProcessID == ppid)
-                    {
-                        try
-                        {
-                            Process c = Process.GetProcessById(processEntry.ProcessID);
-                            if (c.ProcessName.Equals(childName, StringComparison.OrdinalIgnoreCase))
-                            {
-                                child = c;
-                                return true;
-                            }
-                            c.Dispose();
-                        }
-                        catch {}
-                    }
+        public const string COLLECT_DUMPS_ENVIRONMENT_VAR = "__CollectDumps";
+        public const string CRASH_DUMP_FOLDER_ENVIRONMENT_VAR = "__CrashDumpFolder";
 
-                    success = Kernel32.Process32NextW(snapshot, ref processEntry);
-                }
+        static bool CollectCrashDump(Process process, string path)
+        {
+            string coreRoot = Environment.GetEnvironmentVariable("CORE_ROOT");
+            string createdumpPath = Path.Combine(coreRoot, "createdump");
+            string arguments = $"--name \"{path}\" {process.Id} --withheap";
+            Process createdump = new Process();
 
-                child = null;
-                return false;
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                createdump.StartInfo.FileName = createdumpPath + ".exe";
+                createdump.StartInfo.Arguments = arguments;
             }
-            finally
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux) || RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
             {
-                Kernel32.CloseHandle(snapshot);
+                createdump.StartInfo.FileName = "sudo";
+                createdump.StartInfo.Arguments = $"{createdumpPath} " + arguments;
+                createdump.StartInfo.EnvironmentVariables.Add("COMPlus_DbgEnableElfDumpOnMacOS", "1");
             }
-        }
 
-        static bool TryFindChildProcessByNameLinux(Process process, string childName, out Process child)
-        {
-            Queue<string> childrenFilesToCheck = new Queue<string>();
+            createdump.StartInfo.UseShellExecute = false;
+            createdump.StartInfo.RedirectStandardOutput = true;
+            createdump.StartInfo.RedirectStandardError = true;
 
-            childrenFilesToCheck.Enqueue($"/proc/{process.Id}/task/{process.Id}/children");
+            Console.WriteLine($"Invoking: {createdump.StartInfo.FileName} {createdump.StartInfo.Arguments}");
+            createdump.Start();
 
-            while (childrenFilesToCheck.Count != 0)
-            {
-                string childrenFile = childrenFilesToCheck.Dequeue();
+            Task<string> copyOutput = createdump.StandardOutput.ReadToEndAsync();
+            Task<string> copyError = createdump.StandardError.ReadToEndAsync();
+            bool fSuccess = createdump.WaitForExit(DEFAULT_TIMEOUT_MS);
 
-                try
-                {
-                    string[] childrenPidAsStrings = File.ReadAllText(childrenFile).Split(' ', StringSplitOptions.RemoveEmptyEntries);
-                    foreach (var childPidAsString in childrenPidAsStrings)
-                    {
-                        int childPid = int.Parse(childPidAsString);
-                        Process childProcess = Process.GetProcessById(childPid);
-                        if (childProcess.ProcessName.Equals(childName, StringComparison.Ordinal))
-                        {
-                            child = childProcess;
-                            return true;
-                        }
-                        else
-                        {
-                            childrenFilesToCheck.Enqueue($"/proc/{childPid}/task/{childPid}/children");
-                        }
-                    }
-                }
-                catch (IOException)
-                {
-                    // Ignore failure to read process children data, the process may have exited.
-                }
+            if (fSuccess)
+            {
+                Task.WaitAll(copyError, copyOutput);
+                string output = copyOutput.Result;
+                string error = copyError.Result;
+
+                Console.WriteLine("createdump stdout:");
+                Console.WriteLine(output);
+                Console.WriteLine("createdump stderr:");
+                Console.WriteLine(error);
+            }
+            else
+            {
+                createdump.Kill(true);
             }
 
-            child = null;
-            return false;
+            return fSuccess && createdump.ExitCode == 0;
         }
 
-        static bool TryFindChildProcessByNameMacOS(Process process, string childName, out Process child)
+        // Finds all children processes starting with a process named childName
+        // The children are sorted in the order they should be dumped
+        static unsafe IEnumerable<Process> FindChildProcessesByName(Process process, string childName)
         {
-            child = null;
-            Queue<int> childrenPidsToCheck = new Queue<int>();
+            var children = new Stack<Process>();
+            Queue<Process> childrenToCheck = new Queue<Process>();
+            HashSet<int> seen = new HashSet<int>();
 
-            childrenPidsToCheck.Enqueue(process.Id);
+            seen.Add(process.Id);
+            foreach (var child in process.GetChildren())
+                childrenToCheck.Enqueue(child);
 
-            while (childrenPidsToCheck.Count != 0)
+            while (childrenToCheck.Count != 0)
             {
-                int pid = childrenPidsToCheck.Dequeue();
-                if (libproc.ListChildPids(pid, out int[] children))
+                Process child = childrenToCheck.Dequeue();
+                if (seen.Contains(child.Id))
+                    continue;
+
+                seen.Add(child.Id);
+
+                foreach (var grandchild in child.GetChildren())
+                    childrenToCheck.Enqueue(grandchild);
+
+                if (child.ProcessName.Equals(childName, StringComparison.OrdinalIgnoreCase))
                 {
-                    foreach (var childPid in children)
-                    {
-                        Process childProcess = Process.GetProcessById(childPid);
-                        if (childProcess.ProcessName.Equals(childName, StringComparison.Ordinal))
-                        {
-                            child = childProcess;
-                            return true;
-                        }
-                        else
-                        {
-                            childrenPidsToCheck.Enqueue(childPid);
-                        }
-                    }
+                    children.Push(child);
                 }
             }
 
-            child = null;
-            return false;
+            return children;
         }
 
         public int RunTest(string executable, string outputFile, string errorFile)
@@ -306,7 +293,7 @@ public int RunTest(string executable, string outputFile, string errorFile)
             // If a timeout was given to us by an environment variable, use it instead of the default
             // timeout.
             string environmentVar = Environment.GetEnvironmentVariable(TIMEOUT_ENVIRONMENT_VAR);
-            int timeout = environmentVar != null ? int.Parse(environmentVar) : DEFAULT_TIMEOUT;
+            int timeout = environmentVar != null ? int.Parse(environmentVar) : DEFAULT_TIMEOUT_MS;
             bool collectCrashDumps = Environment.GetEnvironmentVariable(COLLECT_DUMPS_ENVIRONMENT_VAR) != null;
             string crashDumpFolder = Environment.GetEnvironmentVariable(CRASH_DUMP_FOLDER_ENVIRONMENT_VAR);
 
@@ -333,6 +320,7 @@ public int RunTest(string executable, string outputFile, string errorFile)
                 process.StartInfo.RedirectStandardOutput = true;
                 process.StartInfo.RedirectStandardError = true;
 
+                DateTime startTime = DateTime.Now;
                 process.Start();
 
                 var cts = new CancellationTokenSource();
@@ -348,30 +336,44 @@ public int RunTest(string executable, string outputFile, string errorFile)
                 else
                 {
                     // Timed out.
+
+                    DateTime endTime = DateTime.Now;
+
                     try
                     {
                         cts.Cancel();
                     }
                     catch {}
 
-                    outputWriter.WriteLine("\ncmdLine:" + executable + " Timed Out");
-                    errorWriter.WriteLine("\ncmdLine:" + executable + " Timed Out");
+                    outputWriter.WriteLine("\ncmdLine:{0} Timed Out (timeout in milliseconds: {1}{2}{3}, start: {4}, end: {5})",
+                            executable, timeout, (environmentVar != null) ? " from variable " : "", (environmentVar != null) ? TIMEOUT_ENVIRONMENT_VAR : "",
+                            startTime.ToString(), endTime.ToString());
+                    errorWriter.WriteLine("\ncmdLine:{0} Timed Out (timeout in milliseconds: {1}{2}{3}, start: {4}, end: {5})",
+                            executable, timeout, (environmentVar != null) ? " from variable " : "", (environmentVar != null) ? TIMEOUT_ENVIRONMENT_VAR : "",
+                            startTime.ToString(), endTime.ToString());
 
                     if (collectCrashDumps)
                     {
                         if (crashDumpFolder != null)
                         {
-                            Process childProcess;
-                            if (TryFindChildProcessByName(process, "corerun", out childProcess))
+                            foreach (var child in FindChildProcessesByName(process, "corerun"))
                             {
-                                string crashDumpPath = Path.Combine(Path.GetFullPath(crashDumpFolder), string.Format("crashdump_{0}.dmp", childProcess.Id));
-                                if (CollectCrashDump(childProcess, crashDumpPath))
+                                string crashDumpPath = Path.Combine(Path.GetFullPath(crashDumpFolder), string.Format("crashdump_{0}.dmp", child.Id));
+                                Console.WriteLine($"Attempting to collect crash dump: {crashDumpPath}");
+                                if (CollectCrashDump(child, crashDumpPath))
                                 {
-                                    Console.WriteLine("Collected crash dump {0}", crashDumpPath);
+                                    Console.WriteLine("Collected crash dump: {0}", crashDumpPath);
+                                }
+                                else
+                                {
+                                    Console.WriteLine("Failed to collect crash dump");
                                 }
                             }
                         }
                     }
+
+                    // kill the timed out processes after we've collected dumps
+                    process.Kill(entireProcessTree: true);
                 }
 
                outputWriter.WriteLine("Test Harness Exitcode is : " + exitCode.ToString());
diff --git a/src/tests/CoreMangLib/system/type/TypeGetArrayRank.csproj b/src/tests/CoreMangLib/system/type/TypeGetArrayRank.csproj
deleted file mode 100644
index 10004f1d8a1f17..00000000000000
--- a/src/tests/CoreMangLib/system/type/TypeGetArrayRank.csproj
+++ /dev/null
@@ -1,14 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestKind>BuildAndRun</CLRTestKind>
-    <CLRTestPriority>1</CLRTestPriority>
-  </PropertyGroup>
-  <ItemGroup>
-    <Compile Include="typegetarrayrank.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
-  </ItemGroup>
-</Project>
diff --git a/src/tests/CoreMangLib/system/type/TypeGetElementType.csproj b/src/tests/CoreMangLib/system/type/TypeGetElementType.csproj
deleted file mode 100644
index 9f95260229e6ed..00000000000000
--- a/src/tests/CoreMangLib/system/type/TypeGetElementType.csproj
+++ /dev/null
@@ -1,14 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestKind>BuildAndRun</CLRTestKind>
-    <CLRTestPriority>1</CLRTestPriority>
-  </PropertyGroup>
-  <ItemGroup>
-    <Compile Include="typegetelementtype.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
-  </ItemGroup>
-</Project>
diff --git a/src/tests/CoreMangLib/system/type/TypeGetGenericTypeDefinition.csproj b/src/tests/CoreMangLib/system/type/TypeGetGenericTypeDefinition.csproj
deleted file mode 100644
index e0bafc969d8313..00000000000000
--- a/src/tests/CoreMangLib/system/type/TypeGetGenericTypeDefinition.csproj
+++ /dev/null
@@ -1,14 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestKind>BuildAndRun</CLRTestKind>
-    <CLRTestPriority>1</CLRTestPriority>
-  </PropertyGroup>
-  <ItemGroup>
-    <Compile Include="typegetgenerictypedefinition.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
-  </ItemGroup>
-</Project>
diff --git a/src/tests/CoreMangLib/system/type/TypeHasElementTypeImpl.csproj b/src/tests/CoreMangLib/system/type/TypeHasElementTypeImpl.csproj
deleted file mode 100644
index 9a01d617ea1e6a..00000000000000
--- a/src/tests/CoreMangLib/system/type/TypeHasElementTypeImpl.csproj
+++ /dev/null
@@ -1,14 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestKind>BuildAndRun</CLRTestKind>
-    <CLRTestPriority>1</CLRTestPriority>
-  </PropertyGroup>
-  <ItemGroup>
-    <Compile Include="typehaselementtypeimpl.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
-  </ItemGroup>
-</Project>
diff --git a/src/tests/CoreMangLib/system/type/TypeIsPointerImpl.csproj b/src/tests/CoreMangLib/system/type/TypeIsPointerImpl.csproj
deleted file mode 100644
index 1524477668da5f..00000000000000
--- a/src/tests/CoreMangLib/system/type/TypeIsPointerImpl.csproj
+++ /dev/null
@@ -1,14 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestKind>BuildAndRun</CLRTestKind>
-    <CLRTestPriority>1</CLRTestPriority>
-  </PropertyGroup>
-  <ItemGroup>
-    <Compile Include="typeispointerimpl.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
-  </ItemGroup>
-</Project>
diff --git a/src/tests/CoreMangLib/system/type/TypeMakeArrayType1.csproj b/src/tests/CoreMangLib/system/type/TypeMakeArrayType1.csproj
deleted file mode 100644
index de53648d9d2847..00000000000000
--- a/src/tests/CoreMangLib/system/type/TypeMakeArrayType1.csproj
+++ /dev/null
@@ -1,14 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestKind>BuildAndRun</CLRTestKind>
-    <CLRTestPriority>1</CLRTestPriority>
-  </PropertyGroup>
-  <ItemGroup>
-    <Compile Include="typemakearraytype1.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
-  </ItemGroup>
-</Project>
diff --git a/src/tests/CoreMangLib/system/type/TypeMakeArrayType2.csproj b/src/tests/CoreMangLib/system/type/TypeMakeArrayType2.csproj
deleted file mode 100644
index 86bc83c948ec47..00000000000000
--- a/src/tests/CoreMangLib/system/type/TypeMakeArrayType2.csproj
+++ /dev/null
@@ -1,14 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestKind>BuildAndRun</CLRTestKind>
-    <CLRTestPriority>1</CLRTestPriority>
-  </PropertyGroup>
-  <ItemGroup>
-    <Compile Include="typemakearraytype2.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
-  </ItemGroup>
-</Project>
diff --git a/src/tests/CoreMangLib/system/type/TypeMakeByRefType.csproj b/src/tests/CoreMangLib/system/type/TypeMakeByRefType.csproj
deleted file mode 100644
index 1bddcb982a9073..00000000000000
--- a/src/tests/CoreMangLib/system/type/TypeMakeByRefType.csproj
+++ /dev/null
@@ -1,14 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestKind>BuildAndRun</CLRTestKind>
-    <CLRTestPriority>1</CLRTestPriority>
-  </PropertyGroup>
-  <ItemGroup>
-    <Compile Include="typemakebyreftype.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
-  </ItemGroup>
-</Project>
diff --git a/src/tests/CoreMangLib/system/type/TypeMakePointerType.csproj b/src/tests/CoreMangLib/system/type/TypeMakePointerType.csproj
deleted file mode 100644
index daf22f11ce3c02..00000000000000
--- a/src/tests/CoreMangLib/system/type/TypeMakePointerType.csproj
+++ /dev/null
@@ -1,14 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestKind>BuildAndRun</CLRTestKind>
-    <CLRTestPriority>1</CLRTestPriority>
-  </PropertyGroup>
-  <ItemGroup>
-    <Compile Include="typemakepointertype.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
-  </ItemGroup>
-</Project>
diff --git a/src/tests/CoreMangLib/system/type/typegetarrayrank.cs b/src/tests/CoreMangLib/system/type/typegetarrayrank.cs
deleted file mode 100644
index e6d06ced1eb1b9..00000000000000
--- a/src/tests/CoreMangLib/system/type/typegetarrayrank.cs
+++ /dev/null
@@ -1,198 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-using System;
-
-public class TypeGetArrayRank
-{
-    #region Private Variables
-    private const int c_DEFAULT_ARRAY_DIMENSION = 2;
-    #endregion
-
-    #region Public Methods
-    public bool RunTests()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.LogInformation("[Positive]");
-        retVal = PosTest1() && retVal;
-        retVal = PosTest2() && retVal;
-        retVal = PosTest3() && retVal;
-
-        TestLibrary.TestFramework.LogInformation("[Negative]");
-        retVal = NegTest1() && retVal;
-
-        return retVal;
-    }
-
-    #region Positive Test Cases
-    public bool PosTest1()
-    {
-        bool retVal = true;
-        int size = 0;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest1: Get rank of an one dimension array");
-
-        try
-        {
-            // Do not make a large array
-            size = TestLibrary.Generator.GetByte(-55);
-
-            int[] array = new int[size];
-            for (int i = 0; i < size; ++i)
-            {
-                array[i] = TestLibrary.Generator.GetInt32(-55);
-            }
-
-            Type type = array.GetType();
-            int rank = type.GetArrayRank();
-            if (rank != 1)
-            {
-                TestLibrary.TestFramework.LogError("001", "Get rank of an one dimension array returns " + rank.ToString());
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("002", "Unexpected exception: " + e + "; with size = " + size);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest2()
-    {
-        bool retVal = true;
-        int size = 0;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest2: Get rank of an multiple dimensions array");
-
-        try
-        {
-            // Do not make a large array
-            size = TestLibrary.Generator.GetByte(-55);
-
-            int[,] array = new int[c_DEFAULT_ARRAY_DIMENSION, size];
-            for (int i = 0; i < c_DEFAULT_ARRAY_DIMENSION; ++i)
-            {
-                for (int j = 0; j < size; ++j)
-                {
-                    array[i, j] = TestLibrary.Generator.GetInt32(-55);
-                }
-            }
-
-            Type type = array.GetType();
-            int rank = type.GetArrayRank();
-            if (rank != c_DEFAULT_ARRAY_DIMENSION)
-            {
-                TestLibrary.TestFramework.LogError("003", "Get rank of an multiple dimensions array returns " + rank.ToString());
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("004", "Unexpected exception: " + e + "; with size = " + size);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest3()
-    {
-        bool retVal = true;
-        int size = 0;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest3: Get rank of an multiple dimensions jagged array");
-
-        try
-        {
-            // Do not make a large array
-            size = TestLibrary.Generator.GetByte(-55);
-
-            int[][] array = new int[size][];
-
-            for (int i = 0; i < size; ++i)
-            {
-                int subArrayLength = TestLibrary.Generator.GetByte(-55);
-                int[] subArray = new int[subArrayLength];
-
-                for (int j = 0; j < subArrayLength; ++j)
-                {
-                    subArray[j] = TestLibrary.Generator.GetInt32(-55);
-                }
-
-                array[i] = subArray;
-            }
-
-            Type type = array.GetType();
-            int rank = type.GetArrayRank();
-            if (rank != 1)
-            {
-                TestLibrary.TestFramework.LogError("005", "Get rank of an multiple dimensions jagged array returns " + rank.ToString());
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("006", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-    #endregion
-
-    #region Nagetive Test Cases
-    public bool NegTest1()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("NegTest1: Check ArgumentException will be thrown");
-
-        try
-        {
-            Type t1 = typeof(Exception);
-
-            int returnObject = t1.GetArrayRank();
-            TestLibrary.TestFramework.LogError("101", "ArgumentException is not thrown when calling typeof(Exception).GetArrayRank()");
-            retVal = false;
-        }
-        catch (ArgumentException)
-        {
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("102", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-    #endregion
-    #endregion
-
-    public static int Main()
-    {
-        TypeGetArrayRank test = new TypeGetArrayRank();
-
-        TestLibrary.TestFramework.BeginTestCase("TypeGetArrayRank");
-
-        if (test.RunTests())
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("PASS");
-            return 100;
-        }
-        else
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("FAIL");
-            return 0;
-        }
-    }
-}
diff --git a/src/tests/CoreMangLib/system/type/typegetelementtype.cs b/src/tests/CoreMangLib/system/type/typegetelementtype.cs
deleted file mode 100644
index 3cef304309cf19..00000000000000
Binary files a/src/tests/CoreMangLib/system/type/typegetelementtype.cs and /dev/null differ
diff --git a/src/tests/CoreMangLib/system/type/typegetgenerictypedefinition.cs b/src/tests/CoreMangLib/system/type/typegetgenerictypedefinition.cs
deleted file mode 100644
index 3a08a902e151db..00000000000000
--- a/src/tests/CoreMangLib/system/type/typegetgenerictypedefinition.cs
+++ /dev/null
@@ -1,126 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-using System;
-using System.Globalization;
-using System.Reflection;
-using System.Collections;
-using System.Collections.Generic;
-
-/// <summary>
-///Type.GetGenericTypeDefinition()
-/// </summary>
-public class TypeGetGenericTypeDefinition
-{
-    public static int Main()
-    {
-        TypeGetGenericTypeDefinition tggtd = new TypeGetGenericTypeDefinition();
-        TestLibrary.TestFramework.BeginTestCase("TypeGetGenericTypeDefinition");
-        if (tggtd.RunTests())
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("PASS");
-            return 100;
-        }
-        else
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("FAIL");
-            return 0;
-        }
-    }
-
-    public bool RunTests()
-    {
-        bool retVal = true;
-        TestLibrary.TestFramework.LogInformation("[Positive]");
-        retVal = PosTest1() && retVal;
-        retVal = PosTest2() && retVal;
-        TestLibrary.TestFramework.LogInformation("[Negtive]");
-        retVal = NegTest1() && retVal;
-
-        return retVal;
-    }
-    #region PositiveTesting
-    public bool PosTest1()
-    {
-        bool retVal = true;
-        Type tpA;
-        Type ActualResult;
-        TestLibrary.TestFramework.BeginScenario("PosTest1: the current type's definition has one generic param");
-        try
-        {
-            tpA = typeof(Derived2<Derived>);
-            ActualResult = tpA.GetGenericTypeDefinition();
-            if(ActualResult != typeof(Derived2<>))
-            {
-                TestLibrary.TestFramework.LogError("001","the ActualResult is not the ExpectResult");
-                retVal = false;
-            }
-        }
-        catch(Exception e)
-        {
-            TestLibrary.TestFramework.LogError("002", "Unexpect exception:" + e);
-            retVal = false;
-        }
-        return retVal;
-    }
-    public bool PosTest2()
-    {
-        bool retVal = true;
-        Type tpA;
-        Type tpB;
-        Type ActualResult1;
-        Type ActualResult2;
-        TestLibrary.TestFramework.BeginScenario("PosTest2: the current type has the same type argument");
-        try
-        {
-            tpA = typeof(Derived2<int>);
-            tpB = typeof(Derived2<string>);
-            ActualResult1 = tpA.GetGenericTypeDefinition();
-            ActualResult2 = tpB.GetGenericTypeDefinition();
-            if (ActualResult1 != typeof(Derived2<>) || ActualResult2 != ActualResult1)
-            {
-                TestLibrary.TestFramework.LogError("003", "the ActualResult is not the ExpectResult");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("004", "Unexpect exception:" + e);
-            retVal = false;
-        }
-        return retVal;
-    }
-    #endregion
-    #region NegativeTest
-    public bool NegTest1()
-    {
-        bool retVal = true;
-        Type tpA;
-        Type ActualResult;
-        TestLibrary.TestFramework.BeginScenario("NegTest1: the current object is not generic type");
-
-        try
-        {
-            tpA = typeof(Derived);
-            ActualResult = tpA.GetGenericTypeDefinition();
-            retVal = false;
-        }
-        catch (InvalidOperationException) { }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("N001", "Unexpect exception:" + e);
-            retVal = false;
-        }
-        return retVal;
-
-    }
-    #endregion
-    #region UsingForTesting
-    public class Base<T, U> { }
-    public class Derived : Base<string, int> { }
-    public class Derived2<V> : Base<bool, V> { }
-    public class G<T> { }
-    #endregion
-}
-
diff --git a/src/tests/CoreMangLib/system/type/typehaselementtypeimpl.cs b/src/tests/CoreMangLib/system/type/typehaselementtypeimpl.cs
deleted file mode 100644
index c345afdf7e197d..00000000000000
--- a/src/tests/CoreMangLib/system/type/typehaselementtypeimpl.cs
+++ /dev/null
@@ -1,120 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-using System;
-using System.Globalization;
-using System.Reflection;
-using System.Collections;
-/// <summary>
-///HasElementTypeImpl
-/// </summary>
-public class TypeHasElementTypeImpl
-{
-    public static int Main()
-    {
-        TypeHasElementTypeImpl TypeHasElementTypeImpl = new TypeHasElementTypeImpl();
-
-        TestLibrary.TestFramework.BeginTestCase("TypeHasElementTypeImpl");
-        if (TypeHasElementTypeImpl.RunTests())
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("PASS");
-            return 100;
-        }
-        else
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("FAIL");
-            return 0;
-        }
-    }
-
-    public bool RunTests()
-    {
-        bool retVal = true;
-        TestLibrary.TestFramework.LogInformation("[Positive]");
-        retVal = PosTest1() && retVal;
-        retVal = PosTest2() && retVal;
-        retVal = PosTest3() && retVal;
-        return retVal;
-    }
-    // Returns true if the expected result is right
-    // Returns false if the expected result is wrong
-    public bool PosTest1()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest1:  The Type is an array ");
-        try
-        {
-            int[] myArray = new int[5];
-            if (!myArray.GetType().HasElementType)
-            {
-                TestLibrary.TestFramework.LogError("001", "HasElementType should return false." );
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("002", "Unexpected exception: " + e);
-            retVal = false;
-        }
-        return retVal;
-    }
-    // Returns true if the expected result is right
-    // Returns false if the expected result is wrong
-    public  bool PosTest2()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest2:  The Type is IntPtr ");
-        try
-        {
-            IntPtr myInt=new IntPtr(5);
-            if (myInt.GetType().HasElementType)
-            {
-                TestLibrary.TestFramework.LogError("001", "HasElementType should return false.");
-                retVal = false;
-            }
-
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("002", "Unexpected exception: " + e);
-            retVal = false;
-        }
-        return retVal;
-    }
-    // Returns true if the expected result is right
-    // Returns false if the expected result is wrong
-    public bool PosTest3()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest3:  The Type is reference type");
-        try
-        {
-            TestClass myInstance = new TestClass();
-            if (myInstance.GetType().HasElementType)
-            {
-                TestLibrary.TestFramework.LogError("001", "HasElementType should return false.");
-                retVal = false;
-            }
-      }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("002", "Unexpected exception: " + e);
-            retVal = false;
-        }
-        return retVal;
-    }
-    private void MyMethod(ref TestClass myTest)
-    {
-
-    }
-   
-}
-
-public class TestClass
-{
-
-}
diff --git a/src/tests/CoreMangLib/system/type/typeisbyrefimpl.cs b/src/tests/CoreMangLib/system/type/typeisbyrefimpl.cs
deleted file mode 100644
index 1a3c5acb641a3f..00000000000000
--- a/src/tests/CoreMangLib/system/type/typeisbyrefimpl.cs
+++ /dev/null
@@ -1,100 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-using System;
-using System.Globalization;
-using System.Reflection;
-using System.Collections;
-/// <summary>
-///IsByRefImpl
-/// </summary>
-public class TypeIsByRefImpl
-{
-    public static int Main()
-    {
-        TypeIsByRefImpl TypeIsByRefImpl = new TypeIsByRefImpl();
-
-        TestLibrary.TestFramework.BeginTestCase("TypeIsByRefImpl");
-        if (TypeIsByRefImpl.RunTests())
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("PASS");
-            return 100;
-        }
-        else
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("FAIL");
-            return 0;
-        }
-    }
-
-    public bool RunTests()
-    {
-        bool retVal = true;
-        TestLibrary.TestFramework.LogInformation("[Positive]");
-        retVal = PosTest1() && retVal;
-        retVal = PosTest2() && retVal;
-        return retVal;
-    }
-    // Returns true if the expected result is right
-    // Returns false if the expected result is wrong
-    public bool PosTest1()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest1:  override isByRefImpl and Only these type which BaseType is BaseClass Return true ,TestClass as test object ");
-        try
-        {
-            TestClass myobject = new TestClass();
-            if (myobject.GetType().IsByRef)
-            {
-                TestLibrary.TestFramework.LogError("001", "TestClass is not Passed by reference.");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("002", "Unexpected exception: " + e);
-            retVal = false;
-        }
-        return retVal;
-    }
-
-    // Returns true if the expected result is right
-    // Returns false if the expected result is wrong
-    public bool PosTest2()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest1:   override isByRefImpl and Only these type which BaseType is BaseClass Return true ,TestClass1 as test object  ");
-        try
-        {
-            TestClass1 myobject = new TestClass1();
-            if (myobject.GetType().IsByRef)
-            {
-                TestLibrary.TestFramework.LogError("003", "TestClass1 is not Passed by reference.");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("004", "Unexpected exception: " + e);
-            retVal = false;
-        }
-        return retVal;
-    }
-    
-
-}
-public class BaseClass
-{
-
-}
-public class TestClass : BaseClass
-{
-
-}
-public class TestClass1
-{
-
-}
diff --git a/src/tests/CoreMangLib/system/type/typeispointerimpl.cs b/src/tests/CoreMangLib/system/type/typeispointerimpl.cs
deleted file mode 100644
index 42456f7ffb6641..00000000000000
--- a/src/tests/CoreMangLib/system/type/typeispointerimpl.cs
+++ /dev/null
@@ -1,194 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-using System;
-
-public struct TestGenericType2
-{
-    public void TestMethod<T>()
-    {
-    }
-}
-
-/// <summary>
-/// IsPointerImpl
-/// </summary>
-public class TypeIsPointerImpl
-{
-    #region Private Fields
-    private const int c_MIN_STRING_LENGTH = 1;
-    private const int c_MAX_STRING_LENGTH = 128;
-    #endregion
-
-    #region Public Methods
-    public bool RunTests()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.LogInformation("[Positive]");
-        retVal = PosTest1() && retVal;
-        retVal = PosTest2() && retVal;
-        retVal = PosTest3() && retVal;
-        retVal = PosTest4() && retVal;
-
-        TestLibrary.TestFramework.LogInformation("[Negative]");
-        retVal = NegTest1() && retVal;
-
-        return retVal;
-    }
-
-    #region Positive Test Cases
-    public bool PosTest1()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest1: IsPointerImpl should return false for value type");
-
-        try
-        {
-            int obj = TestLibrary.Generator.GetInt32(-55);
-            Type type = obj.GetType();
-
-            if (type.IsPointer)
-            {
-                TestLibrary.TestFramework.LogError("001", "IsPointerImpl returns true for value type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("002", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest2()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest2: IsPointerImpl should return false for reference type");
-
-        try
-        {
-            String obj = TestLibrary.Generator.GetString(-55, false, c_MIN_STRING_LENGTH, c_MAX_STRING_LENGTH);
-            Type type = obj.GetType();
-
-            if (type.IsPointer)
-            {
-                TestLibrary.TestFramework.LogError("003", "IsPointerImpl returns true for reference type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("004", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest3()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest3: IsPointerImpl should return false for IntPtr");
-
-        try
-        {
-            Type type = typeof(IntPtr);
-
-            if (type.IsPointer)
-            {
-                TestLibrary.TestFramework.LogError("005", "IsPointerImpl returns true for IntPtr");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("006", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest4()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest4: IsPointerImpl should return true for a pointer type");
-
-        try
-        {
-            Type type = typeof(int*);
-
-            if (!type.IsPointer)
-            {
-                TestLibrary.TestFramework.LogError("007", "IsPointerImpl returns false for a pointer type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("008", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-    #endregion
-
-    #region Nagetive Test Cases
-    public bool NegTest1()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("NegTest1: IsPointerImpl should return true for type contains generic member");
-
-        try
-        {
-            Type type = typeof(TestGenericType2*);
-            if (!type.IsPointer)
-            {
-                TestLibrary.TestFramework.LogError("101", "IsPointerImpl returns false for type contains generic member");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("102", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-    #endregion
-    #endregion
-
-    public static int Main()
-    {
-        TypeIsPointerImpl test = new TypeIsPointerImpl();
-
-        TestLibrary.TestFramework.BeginTestCase("TypeIsPointerImpl");
-
-        if (test.RunTests())
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("PASS");
-            return 100;
-        }
-        else
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("FAIL");
-            return 0;
-        }
-    }
-}
diff --git a/src/tests/CoreMangLib/system/type/typemakearraytype1.cs b/src/tests/CoreMangLib/system/type/typemakearraytype1.cs
deleted file mode 100644
index 4b3178f241fb45..00000000000000
--- a/src/tests/CoreMangLib/system/type/typemakearraytype1.cs
+++ /dev/null
@@ -1,237 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-using System;
-
-/// <summary>
-/// MakeArrayType()
-/// </summary>
-public class TypeMakeArrayType1
-{
-    #region Public Methods
-    public bool RunTests()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.LogInformation("[Positive]");
-        retVal = PosTest1() && retVal;
-        retVal = PosTest2() && retVal;
-        retVal = PosTest3() && retVal;
-        retVal = PosTest4() && retVal;
-        retVal = PosTest5() && retVal;
-
-        return retVal;
-    }
-
-    #region Positive Test Cases
-    public bool PosTest1()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest1: Call MakeArrayType for reference type");
-
-        try
-        {
-            Type type = typeof(String);
-            Type arrayType = type.MakeArrayType();
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("001", "Call MakeArrayType for reference type does not make a array type");
-                    retVal = false;
-                    break;
-                }
-
-                if (arrayType.GetArrayRank() != 1)
-                {
-                    TestLibrary.TestFramework.LogError("002", "Call MakeArrayType for reference type does not make a one dimension array type");
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("003", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest2()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest2: Call MakeArrayType for value type");
-
-        try
-        {
-            Type type = typeof(Int32);
-            Type arrayType = type.MakeArrayType();
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("004", "Call MakeArrayType for value type does not make a array type");
-                    retVal = false;
-                    break;
-                }
-
-                if (arrayType.GetArrayRank() != 1)
-                {
-                    TestLibrary.TestFramework.LogError("005", "Call MakeArrayType for value type does not make a one dimension array type");
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("006", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest3()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest3: Call MakeArrayType for pointer type");
-
-        try
-        {
-            Type type = typeof(char *);
-            Type arrayType = type.MakeArrayType();
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("007", "Call MakeArrayType for pointer type does not make a array type");
-                    retVal = false;
-                    break;
-                }
-
-                if (arrayType.GetArrayRank() != 1)
-                {
-                    TestLibrary.TestFramework.LogError("008", "Call MakeArrayType for pointer type does not make a one dimension array type");
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("009", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest4()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest4: Call MakeArrayType for value array type");
-
-        try
-        {
-            Type type = typeof(int[]);
-            Type arrayType = type.MakeArrayType();
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("010", "Call MakeArrayType for value array type does not make a array type");
-                    retVal = false;
-                    break;
-                }
-
-                if (arrayType.GetArrayRank() != 1)
-                {
-                    TestLibrary.TestFramework.LogError("011", "Call MakeArrayType for value array type does not make a one dimension array type");
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("012", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest5()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest5: Call MakeArrayType for reference array type");
-
-        try
-        {
-            Type type = typeof(String[]);
-            Type arrayType = type.MakeArrayType();
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("013", "Call MakeArrayType for reference array type does not make a array type");
-                    retVal = false;
-                    break;
-                }
-
-                if (arrayType.GetArrayRank() != 1)
-                {
-                    TestLibrary.TestFramework.LogError("014", "Call MakeArrayType for reference array type does not make a one dimension array type");
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("015", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-    #endregion
-    #endregion
-
-    public static int Main()
-    {
-        TypeMakeArrayType1 test = new TypeMakeArrayType1();
-
-        TestLibrary.TestFramework.BeginTestCase("TypeMakeArrayType1");
-
-        if (test.RunTests())
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("PASS");
-            return 100;
-        }
-        else
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("FAIL");
-            return 0;
-        }
-    }
-}
diff --git a/src/tests/CoreMangLib/system/type/typemakearraytype2.cs b/src/tests/CoreMangLib/system/type/typemakearraytype2.cs
deleted file mode 100644
index 22dcaa7fa68a58..00000000000000
--- a/src/tests/CoreMangLib/system/type/typemakearraytype2.cs
+++ /dev/null
@@ -1,384 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-using System;
-
-/// <summary>
-/// MakeArrayType(System.Int32)
-/// </summary>
-public class TypeMakeArrayType2
-{
-    #region Private Members
-    private const int c_DEFAULT_MULTIPLE_ARRAY_DIMENSION = 4;
-    #endregion
-
-    #region Public Methods
-    public bool RunTests()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.LogInformation("[Positive]");
-        retVal = PosTest1() && retVal;
-        retVal = PosTest2() && retVal;
-        retVal = PosTest3() && retVal;
-        retVal = PosTest4() && retVal;
-        retVal = PosTest5() && retVal;
-        retVal = PosTest6() && retVal;
-
-        TestLibrary.TestFramework.LogInformation("[Negative]");
-        retVal = NegTest1() && retVal;
-        retVal = NegTest2() && retVal;
-
-        return retVal;
-    }
-
-    #region Positive Test Cases
-    public bool PosTest1()
-    {
-        bool retVal = true;
-        int desiredDimension = 0;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest1: Call MakeArrayType to make 1 dimension value type array");
-
-        try
-        {
-            desiredDimension = 1;
-            Type type = typeof(Int32);
-            Type arrayType = type.MakeArrayType(desiredDimension);
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("001", "Call MakeArrayType for value type does not make a array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-
-                int actualDimension = arrayType.GetArrayRank();
-                if (actualDimension != desiredDimension)
-                {
-                    TestLibrary.TestFramework.LogError("002", "Call MakeArrayType for value type does not make a one dimension array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString() + "; actualDimension = " + actualDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("003", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest2()
-    {
-        bool retVal = true;
-        int desiredDimension = 0;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest2: Call MakeArrayType to make multiple dimensions value type array");
-
-        try
-        {
-            desiredDimension = c_DEFAULT_MULTIPLE_ARRAY_DIMENSION;
-            Type type = typeof(Int32);
-            Type arrayType = type.MakeArrayType(desiredDimension);
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("004", "Call MakeArrayType for value type does not make a array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-
-                int actualDimension = arrayType.GetArrayRank();
-                if (actualDimension != desiredDimension)
-                {
-                    TestLibrary.TestFramework.LogError("005", "Call MakeArrayType for value type does not make a one dimension array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString() + "; actualDimension = " + actualDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("006", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest3()
-    {
-        bool retVal = true;
-        int desiredDimension = 0;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest3: Call MakeArrayType to make multiple dimensions reference type array");
-
-        try
-        {
-            desiredDimension = c_DEFAULT_MULTIPLE_ARRAY_DIMENSION;
-            Type type = typeof(String);
-            Type arrayType = type.MakeArrayType(desiredDimension);
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("007", "Call MakeArrayType for reference type does not make a array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-
-                int actualDimension = arrayType.GetArrayRank();
-                if (actualDimension != desiredDimension)
-                {
-                    TestLibrary.TestFramework.LogError("008", "Call MakeArrayType for reference type does not make a multiple dimensions array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString() + "; actualDimension = " + actualDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("009", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest4()
-    {
-        bool retVal = true;
-        int desiredDimension = 0;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest4: Call MakeArrayType to make multiple dimensions pointer type array");
-
-        try
-        {
-            desiredDimension = c_DEFAULT_MULTIPLE_ARRAY_DIMENSION;
-            Type type = typeof(char *);
-            Type arrayType = type.MakeArrayType(desiredDimension);
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("010", "Call MakeArrayType for pointer type does not make a array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-
-                int actualDimension = arrayType.GetArrayRank();
-                if (actualDimension != desiredDimension)
-                {
-                    TestLibrary.TestFramework.LogError("011", "Call MakeArrayType for pointer type does not make a multiple dimensions array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString() + "; actualDimension = " + actualDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("012", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest5()
-    {
-        bool retVal = true;
-        int desiredDimension = 0;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest5: Call MakeArrayType to make multiple dimensions reference array type array");
-
-        try
-        {
-            desiredDimension = c_DEFAULT_MULTIPLE_ARRAY_DIMENSION;
-            Type type = typeof(String[]);
-            Type arrayType = type.MakeArrayType(desiredDimension);
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("013", "Call MakeArrayType for reference array type does not make a array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-
-                int actualDimension = arrayType.GetArrayRank();
-                if (actualDimension != desiredDimension)
-                {
-                    TestLibrary.TestFramework.LogError("014", "Call MakeArrayType for reference array type does not make a multiple dimensions array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString() + "; actualDimension = " + actualDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("015", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest6()
-    {
-        bool retVal = true;
-        int desiredDimension = 0;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest6: Call MakeArrayType to make multiple dimensions value array type array");
-
-        try
-        {
-            desiredDimension = c_DEFAULT_MULTIPLE_ARRAY_DIMENSION;
-            Type type = typeof(int[]);
-            Type arrayType = type.MakeArrayType(desiredDimension);
-
-            do
-            {
-                if (!arrayType.IsArray)
-                {
-                    TestLibrary.TestFramework.LogError("016", "Call MakeArrayType for value array type does not make a array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-
-                int actualDimension = arrayType.GetArrayRank();
-                if (actualDimension != desiredDimension)
-                {
-                    TestLibrary.TestFramework.LogError("017", "Call MakeArrayType for value array type does not make a multiple dimensions array type");
-                    TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString() + "; actualDimension = " + actualDimension.ToString());
-                    retVal = false;
-                    break;
-                }
-            } while (false);
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("018", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] desiredDimension = " + desiredDimension.ToString());
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-    #endregion
-
-    #region Nagetive Test Cases
-    public bool NegTest1()
-    {
-        bool retVal = true;
-        int rank = 0;
-
-        TestLibrary.TestFramework.BeginScenario("NegTest1: IndexOutOfRangeException will be thrown when rank is invalid");
-
-        try
-        {
-            rank = TestLibrary.Generator.GetByte(-55);
-            if (rank > 0)
-                rank = 0 - rank;
-
-            Type type = typeof(Object);
-            Type arrayType = type.MakeArrayType(rank);
-
-            TestLibrary.TestFramework.LogError("101", "IndexOutOfRangeException is not thrown when rank is invalid");
-            TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] rank = " + rank.ToString());
-            retVal = false;
-        }
-        catch (IndexOutOfRangeException)
-        {
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("102", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation("[LOCAL VARIABLES] rank = " + rank.ToString());
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool NegTest2()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("NegTest2: IndexOutOfRangeException will be thrown when rank is 0");
-
-        try
-        {
-
-            Type type = typeof(Object);
-            Type arrayType = type.MakeArrayType(0);
-
-            TestLibrary.TestFramework.LogError("103", "IndexOutOfRangeException is not thrown when rank is 0");
-            retVal = false;
-        }
-        catch (IndexOutOfRangeException)
-        {
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("104", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-    #endregion
-    #endregion
-
-    public static int Main()
-    {
-        TypeMakeArrayType2 test = new TypeMakeArrayType2();
-
-        TestLibrary.TestFramework.BeginTestCase("TypeMakeArrayType2");
-
-        if (test.RunTests())
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("PASS");
-            return 100;
-        }
-        else
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("FAIL");
-            return 0;
-        }
-    }
-}
diff --git a/src/tests/CoreMangLib/system/type/typemakebyreftype.cs b/src/tests/CoreMangLib/system/type/typemakebyreftype.cs
deleted file mode 100644
index 698c5790d55880..00000000000000
--- a/src/tests/CoreMangLib/system/type/typemakebyreftype.cs
+++ /dev/null
@@ -1,215 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-using System;
-
-/// <summary>
-/// MakeByRefType()
-/// </summary>
-public class TypeMakeByRefType
-{
-    #region Public Methods
-    public bool RunTests()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.LogInformation("[Positive]");
-        retVal = PosTest1() && retVal;
-        retVal = PosTest2() && retVal;
-        retVal = PosTest3() && retVal;
-        retVal = PosTest4() && retVal;
-        retVal = PosTest5() && retVal;
-
-        TestLibrary.TestFramework.LogInformation("[Negative]");
-        retVal = NegTest1() && retVal;
-
-        return retVal;
-    }
-
-    #region Positive Test Cases
-    public bool PosTest1()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest1: Call MakeByRefType for reference type");
-
-        try
-        {
-            Type type = typeof(String);
-            Type refType = type.MakeByRefType();
-
-            if (!refType.IsByRef)
-            {
-                TestLibrary.TestFramework.LogError("001", "Call MakeByRefType for reference type does not make a byref type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("002", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest2()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest2: Call MakeByRefType for value type");
-
-        try
-        {
-            Type type = typeof(int);
-            Type refType = type.MakeByRefType();
-
-            if (!refType.IsByRef)
-            {
-                TestLibrary.TestFramework.LogError("003", "Call MakeByRefType for value type does not make a byref type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("004", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest3()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest3: Call MakeByRefType for value array type");
-
-        try
-        {
-            Type type = typeof(int[]);
-            Type refType = type.MakeByRefType();
-
-            if (!refType.IsByRef)
-            {
-                TestLibrary.TestFramework.LogError("005", "Call MakeByRefType for value array type does not make a byref type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("006", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest4()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest4: Call MakeByRefType for reference array type");
-
-        try
-        {
-            Type type = typeof(String[]);
-            Type refType = type.MakeByRefType();
-
-            if (!refType.IsByRef)
-            {
-                TestLibrary.TestFramework.LogError("007", "Call MakeByRefType for reference array type does not make a byref type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("008", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest5()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest5: Call MakeByRefType for pointer type");
-
-        try
-        {
-            Type type = typeof(char *);
-            Type refType = type.MakeByRefType();
-
-            if (!refType.IsByRef)
-            {
-                TestLibrary.TestFramework.LogError("009", "Call MakeByRefType for pointer type does not make a byref type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("010", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-    #endregion
-
-    #region Nagetive Test Cases
-    public bool NegTest1()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("NegTest1: TypeLoadException will be thrown when calling MakeByRefType for ByRef type");
-
-        try
-        {
-            Type type = typeof(Object);
-            type = type.MakeByRefType();
-            Type refType = type.MakeByRefType();
-
-            TestLibrary.TestFramework.LogError("101", "TypeLoadException is not thrown when calling MakeByRefType for ByRef type");
-            retVal = false;
-        }
-        catch (TypeLoadException)
-        {
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("102", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-    #endregion
-    #endregion
-
-    public static int Main()
-    {
-        TypeMakeByRefType test = new TypeMakeByRefType();
-
-        TestLibrary.TestFramework.BeginTestCase("TypeMakeByRefType");
-
-        if (test.RunTests())
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("PASS");
-            return 100;
-        }
-        else
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("FAIL");
-            return 0;
-        }
-    }
-}
diff --git a/src/tests/CoreMangLib/system/type/typemakepointertype.cs b/src/tests/CoreMangLib/system/type/typemakepointertype.cs
deleted file mode 100644
index 56e83f4f9554f5..00000000000000
--- a/src/tests/CoreMangLib/system/type/typemakepointertype.cs
+++ /dev/null
@@ -1,182 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-using System;
-
-/// <summary>
-/// MakePointerType
-/// </summary>
-public class TypeMakePointerType
-{
-    #region Public Methods
-    public bool RunTests()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.LogInformation("[Positive]");
-        retVal = PosTest1() && retVal;
-        retVal = PosTest2() && retVal;
-        retVal = PosTest3() && retVal;
-        retVal = PosTest4() && retVal;
-        retVal = PosTest5() && retVal;
-
-        return retVal;
-    }
-
-    #region Positive Test Cases
-    public bool PosTest1()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest1: Call MakePointerType for a value type");
-
-        try
-        {
-            Type type = typeof(int);
-            Type pointerType = type.MakePointerType();
-
-            if (!pointerType.IsPointer)
-            {
-                TestLibrary.TestFramework.LogError("001", "Call MakePointerType for a value type does not make a pointer type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("002", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest2()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest2: Call MakePointerType for a reference type");
-
-        try
-        {
-            Type type = typeof(String);
-            Type pointerType = type.MakePointerType();
-
-            if (!pointerType.IsPointer)
-            {
-                TestLibrary.TestFramework.LogError("003", "Call MakePointerType for a reference type does not make a pointer type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("004", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest3()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest3: Call MakePointerType for a value array type");
-
-        try
-        {
-            Type type = typeof(int[]);
-            Type pointerType = type.MakePointerType();
-
-            if (!pointerType.IsPointer)
-            {
-                TestLibrary.TestFramework.LogError("005", "Call MakePointerType for a value array type does not make a pointer type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("006", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest4()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest4: Call MakePointerType for a reference array type");
-
-        try
-        {
-            Type type = typeof(String[]);
-            Type pointerType = type.MakePointerType();
-
-            if (!pointerType.IsPointer)
-            {
-                TestLibrary.TestFramework.LogError("007", "Call MakePointerType for a reference array type does not make a pointer type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("008", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-
-    public bool PosTest5()
-    {
-        bool retVal = true;
-
-        TestLibrary.TestFramework.BeginScenario("PosTest5: Call MakePointerType for a pointer type");
-
-        try
-        {
-            Type type = typeof(char *);
-            Type pointerType = type.MakePointerType();
-
-            if (!pointerType.IsPointer)
-            {
-                TestLibrary.TestFramework.LogError("009", "Call MakePointerType for a pointer type does not make a pointer type");
-                retVal = false;
-            }
-        }
-        catch (Exception e)
-        {
-            TestLibrary.TestFramework.LogError("010", "Unexpected exception: " + e);
-            TestLibrary.TestFramework.LogInformation(e.StackTrace);
-            retVal = false;
-        }
-
-        return retVal;
-    }
-    #endregion
-    #endregion
-
-    public static int Main()
-    {
-        TypeMakePointerType test = new TypeMakePointerType();
-
-        TestLibrary.TestFramework.BeginTestCase("TypeMakePointerType");
-
-        if (test.RunTests())
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("PASS");
-            return 100;
-        }
-        else
-        {
-            TestLibrary.TestFramework.EndTestCase();
-            TestLibrary.TestFramework.LogInformation("FAIL");
-            return 0;
-        }
-    }
-}
diff --git a/src/tests/Interop/COM/Activator/Program.cs b/src/tests/Interop/COM/Activator/Program.cs
index ac7fe8d005e676..fd525aaf2e905a 100644
--- a/src/tests/Interop/COM/Activator/Program.cs
+++ b/src/tests/Interop/COM/Activator/Program.cs
@@ -105,9 +105,11 @@ static void ValidateAssemblyIsolation()
 
                 var factory = (IClassFactory)ComActivator.GetClassFactoryForType(cxt);
 
-                object svr;
-                factory.CreateInstance(null, ref iid, out svr);
-                typeCFromAssemblyA = (Type)((IGetTypeFromC)svr).GetTypeFromC();
+                IntPtr svrRaw;
+                factory.CreateInstance(null, ref iid, out svrRaw);
+                var svr = (IGetTypeFromC)Marshal.GetObjectForIUnknown(svrRaw);
+                Marshal.Release(svrRaw);
+                typeCFromAssemblyA = (Type)svr.GetTypeFromC();
             }
 
             using (HostPolicyMock.Mock_corehost_resolve_component_dependencies(
@@ -127,9 +129,11 @@ static void ValidateAssemblyIsolation()
 
                 var factory = (IClassFactory)ComActivator.GetClassFactoryForType(cxt);
 
-                object svr;
-                factory.CreateInstance(null, ref iid, out svr);
-                typeCFromAssemblyB = (Type)((IGetTypeFromC)svr).GetTypeFromC();
+                IntPtr svrRaw;
+                factory.CreateInstance(null, ref iid, out svrRaw);
+                var svr = (IGetTypeFromC)Marshal.GetObjectForIUnknown(svrRaw);
+                Marshal.Release(svrRaw);
+                typeCFromAssemblyB = (Type)svr.GetTypeFromC();
             }
 
             Assert.AreNotEqual(typeCFromAssemblyA, typeCFromAssemblyB, "Types should be from different AssemblyLoadContexts");
@@ -178,8 +182,10 @@ static void ValidateUserDefinedRegistrationCallbacks()
 
                     var factory = (IClassFactory)ComActivator.GetClassFactoryForType(cxt);
 
-                    object svr;
-                    factory.CreateInstance(null, ref iid, out svr);
+                    IntPtr svrRaw;
+                    factory.CreateInstance(null, ref iid, out svrRaw);
+                    var svr = Marshal.GetObjectForIUnknown(svrRaw);
+                    Marshal.Release(svrRaw);
 
                     var inst = (IValidateRegistrationCallbacks)svr;
                     Assert.IsFalse(inst.DidRegister());
@@ -215,8 +221,10 @@ static void ValidateUserDefinedRegistrationCallbacks()
 
                     var factory = (IClassFactory)ComActivator.GetClassFactoryForType(cxt);
 
-                    object svr;
-                    factory.CreateInstance(null, ref iid, out svr);
+                    IntPtr svrRaw;
+                    factory.CreateInstance(null, ref iid, out svrRaw);
+                    var svr = Marshal.GetObjectForIUnknown(svrRaw);
+                    Marshal.Release(svrRaw);
 
                     var inst = (IValidateRegistrationCallbacks)svr;
                     cxt.InterfaceId = Guid.Empty;
diff --git a/src/tests/Interop/COM/Dynamic/Dynamic.csproj b/src/tests/Interop/COM/Dynamic/Dynamic.csproj
index ebf603a1bbfe1b..df80707843e23d 100644
--- a/src/tests/Interop/COM/Dynamic/Dynamic.csproj
+++ b/src/tests/Interop/COM/Dynamic/Dynamic.csproj
@@ -8,6 +8,10 @@
     <CLRTestTargetUnsupported Condition="'$(TargetsWindows)' != 'true'">true</CLRTestTargetUnsupported>
     <!-- This test would require the runincontext.exe to include App.manifest describing the COM interfaces -->
     <UnloadabilityIncompatible>true</UnloadabilityIncompatible>
+    <!-- This test is very slow under some GCStress variations, especially with COMPlus_HeapVerify=1, so disable it under GCStress to avoid test timeouts in the CI.
+         Issue: https://github.com/dotnet/runtime/issues/39584
+    -->
+    <GCStressIncompatible>true</GCStressIncompatible>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="BasicTest.cs" />
diff --git a/src/tests/Interop/COM/NativeClients/Dispatch/Client.cpp b/src/tests/Interop/COM/NativeClients/Dispatch/Client.cpp
index 36b4806dc61fbb..0aa509cb31c0dc 100644
--- a/src/tests/Interop/COM/NativeClients/Dispatch/Client.cpp
+++ b/src/tests/Interop/COM/NativeClients/Dispatch/Client.cpp
@@ -88,59 +88,81 @@ void Validate_Numeric_In_ReturnByRef()
     ULONGLONG ul1 = 4168;
     ULONGLONG ul2;
 
-    DISPPARAMS params;
-    params.cArgs = 14;
-    params.rgvarg = new VARIANTARG[params.cArgs];
-    params.cNamedArgs = 0;
-    params.rgdispidNamedArgs = nullptr;
+    {
+        DISPPARAMS params;
+        params.cArgs = 14;
+        params.rgvarg = new VARIANTARG[params.cArgs];
+        params.cNamedArgs = 0;
+        params.rgdispidNamedArgs = nullptr;
     
-    V_VT(&params.rgvarg[13]) = VT_UI1;
-    V_UI1(&params.rgvarg[13]) = b1;
-    V_VT(&params.rgvarg[12]) = VT_BYREF | VT_UI1;
-    V_UI1REF(&params.rgvarg[12]) = &b2;
-    V_VT(&params.rgvarg[11]) = VT_I2;
-    V_I2(&params.rgvarg[11]) = s1;
-    V_VT(&params.rgvarg[10]) = VT_BYREF | VT_I2;
-    V_I2REF(&params.rgvarg[10]) = &s2;
-    V_VT(&params.rgvarg[9]) = VT_UI2;
-    V_UI2(&params.rgvarg[9]) = us1;
-    V_VT(&params.rgvarg[8]) = VT_BYREF | VT_UI2;
-    V_UI2REF(&params.rgvarg[8]) = &us2;
-    V_VT(&params.rgvarg[7]) = VT_I4;
-    V_I4(&params.rgvarg[7]) = i1;
-    V_VT(&params.rgvarg[6]) = VT_BYREF | VT_I4;
-    V_I4REF(&params.rgvarg[6]) = &i2;
-    V_VT(&params.rgvarg[5]) = VT_UI4;
-    V_UI4(&params.rgvarg[5]) = ui1;
-    V_VT(&params.rgvarg[4]) = VT_BYREF | VT_UI4;
-    V_UI4REF(&params.rgvarg[4]) = &ui2;
-    V_VT(&params.rgvarg[3]) = VT_I8;
-    V_I8(&params.rgvarg[3]) = l1;
-    V_VT(&params.rgvarg[2]) = VT_BYREF | VT_I8;
-    V_I8REF(&params.rgvarg[2]) = &l2;
-    V_VT(&params.rgvarg[1]) = VT_UI8;
-    V_UI8(&params.rgvarg[1]) = ul1;
-    V_VT(&params.rgvarg[0]) = VT_BYREF | VT_UI8;
-    V_UI8REF(&params.rgvarg[0]) = &ul2;
-
-    THROW_IF_FAILED(dispatchTesting->Invoke(
-        methodId,
-        IID_NULL,
-        lcid,
-        DISPATCH_METHOD,
-        &params,
-        nullptr,
-        nullptr,
-        nullptr
-    ));
+        V_VT(&params.rgvarg[13]) = VT_UI1;
+        V_UI1(&params.rgvarg[13]) = b1;
+        V_VT(&params.rgvarg[12]) = VT_BYREF | VT_UI1;
+        V_UI1REF(&params.rgvarg[12]) = &b2;
+        V_VT(&params.rgvarg[11]) = VT_I2;
+        V_I2(&params.rgvarg[11]) = s1;
+        V_VT(&params.rgvarg[10]) = VT_BYREF | VT_I2;
+        V_I2REF(&params.rgvarg[10]) = &s2;
+        V_VT(&params.rgvarg[9]) = VT_UI2;
+        V_UI2(&params.rgvarg[9]) = us1;
+        V_VT(&params.rgvarg[8]) = VT_BYREF | VT_UI2;
+        V_UI2REF(&params.rgvarg[8]) = &us2;
+        V_VT(&params.rgvarg[7]) = VT_I4;
+        V_I4(&params.rgvarg[7]) = i1;
+        V_VT(&params.rgvarg[6]) = VT_BYREF | VT_I4;
+        V_I4REF(&params.rgvarg[6]) = &i2;
+        V_VT(&params.rgvarg[5]) = VT_UI4;
+        V_UI4(&params.rgvarg[5]) = ui1;
+        V_VT(&params.rgvarg[4]) = VT_BYREF | VT_UI4;
+        V_UI4REF(&params.rgvarg[4]) = &ui2;
+        V_VT(&params.rgvarg[3]) = VT_I8;
+        V_I8(&params.rgvarg[3]) = l1;
+        V_VT(&params.rgvarg[2]) = VT_BYREF | VT_I8;
+        V_I8REF(&params.rgvarg[2]) = &l2;
+        V_VT(&params.rgvarg[1]) = VT_UI8;
+        V_UI8(&params.rgvarg[1]) = ul1;
+        V_VT(&params.rgvarg[0]) = VT_BYREF | VT_UI8;
+        V_UI8REF(&params.rgvarg[0]) = &ul2;
+
+        THROW_IF_FAILED(dispatchTesting->Invoke(
+            methodId,
+            IID_NULL,
+            lcid,
+            DISPATCH_METHOD,
+            &params,
+            nullptr,
+            nullptr,
+            nullptr
+        ));
+
+        THROW_FAIL_IF_FALSE(b2 == b1 * 2);
+        THROW_FAIL_IF_FALSE(s2 == s1 * 2);
+        THROW_FAIL_IF_FALSE(us2 == us1 * 2);
+        THROW_FAIL_IF_FALSE(i2 == i1 * 2);
+        THROW_FAIL_IF_FALSE(ui2 == ui1 * 2);
+        THROW_FAIL_IF_FALSE(l2 == l1 * 2);
+        THROW_FAIL_IF_FALSE(ul2 == ul1 * 2);
+    }
 
-    THROW_FAIL_IF_FALSE(b2 == b1 * 2);
-    THROW_FAIL_IF_FALSE(s2 == s1 * 2);
-    THROW_FAIL_IF_FALSE(us2 == us1 * 2);
-    THROW_FAIL_IF_FALSE(i2 == i1 * 2);
-    THROW_FAIL_IF_FALSE(ui2 == ui1 * 2);
-    THROW_FAIL_IF_FALSE(l2 == l1 * 2);
-    THROW_FAIL_IF_FALSE(ul2 == ul1 * 2);
+    {
+        b2 = 0;
+        s2 = 0;
+        us2 = 0;
+        i2 = 0;
+        ui2 = 0;
+        l2 = 0;
+        ul2 = 0;
+
+        THROW_IF_FAILED(dispatchTesting->DoubleNumeric_ReturnByRef(b1, &b2, s1, &s2, us1, &us2, i1, (INT*)&i2, ui1, (UINT*)&ui2, l1, &l2, ul1, &ul2));
+
+        THROW_FAIL_IF_FALSE(b2 == b1 * 2);
+        THROW_FAIL_IF_FALSE(s2 == s1 * 2);
+        THROW_FAIL_IF_FALSE(us2 == us1 * 2);
+        THROW_FAIL_IF_FALSE(i2 == i1 * 2);
+        THROW_FAIL_IF_FALSE(ui2 == ui1 * 2);
+        THROW_FAIL_IF_FALSE(l2 == l1 * 2);
+        THROW_FAIL_IF_FALSE(ul2 == ul1 * 2);
+    }
 }
 
 namespace
@@ -183,37 +205,50 @@ void Validate_Float_In_ReturnAndUpdateByRef()
         lcid,
         &methodId));
     
-    float a = 12.34f;
-    float b = 1.234f;
-    float expected = b + a;
-
-    DISPPARAMS params;
-    params.cArgs = 2;
-    params.rgvarg = new VARIANTARG[params.cArgs];
-    params.cNamedArgs = 0;
-    params.rgdispidNamedArgs = nullptr;
+    const float a = 12.34f;
+    const float b_orig = 1.234f;
+    const float expected = b_orig + a;
 
-    VARIANT result;
-
-    V_VT(&params.rgvarg[1]) = VT_R4;
-    V_R4(&params.rgvarg[1]) = a;
-    V_VT(&params.rgvarg[0]) = VT_BYREF | VT_R4;
-    V_R4REF(&params.rgvarg[0]) = &b;
+    float b = b_orig;
 
+    {
+        DISPPARAMS params;
+        params.cArgs = 2;
+        params.rgvarg = new VARIANTARG[params.cArgs];
+        params.cNamedArgs = 0;
+        params.rgdispidNamedArgs = nullptr;
+
+        VARIANT result;
+
+        V_VT(&params.rgvarg[1]) = VT_R4;
+        V_R4(&params.rgvarg[1]) = a;
+        V_VT(&params.rgvarg[0]) = VT_BYREF | VT_R4;
+        V_R4REF(&params.rgvarg[0]) = &b;
+
+
+        THROW_IF_FAILED(dispatchTesting->Invoke(
+            methodId,
+            IID_NULL,
+            lcid,
+            DISPATCH_METHOD,
+            &params,
+            &result,
+            nullptr,
+            nullptr
+        ));
+
+        THROW_FAIL_IF_FALSE(EqualByBound(expected, V_R4(&result)));
+        THROW_FAIL_IF_FALSE(EqualByBound(expected, b));
+    }
 
-    THROW_IF_FAILED(dispatchTesting->Invoke(
-        methodId,
-        IID_NULL,
-        lcid,
-        DISPATCH_METHOD,
-        &params,
-        &result,
-        nullptr,
-        nullptr
-    ));
+    {
+        b = b_orig;
+        float result;
+        THROW_IF_FAILED(dispatchTesting->Add_Float_ReturnAndUpdateByRef(a, &b, &result));
 
-    THROW_FAIL_IF_FALSE(EqualByBound(expected, V_R4(&result)));
-    THROW_FAIL_IF_FALSE(EqualByBound(expected, b));
+        THROW_FAIL_IF_FALSE(EqualByBound(expected, result));
+        THROW_FAIL_IF_FALSE(EqualByBound(expected, b));
+    }
 }
 
 void Validate_Double_In_ReturnAndUpdateByRef()
@@ -237,37 +272,50 @@ void Validate_Double_In_ReturnAndUpdateByRef()
         lcid,
         &methodId));
     
-    double a = 1856.5634;
-    double b = 587867.757;
-    double expected = a + b;
-
-    DISPPARAMS params;
-    params.cArgs = 2;
-    params.rgvarg = new VARIANTARG[params.cArgs];
-    params.cNamedArgs = 0;
-    params.rgdispidNamedArgs = nullptr;
-
-    VARIANT result;
+    const double a = 1856.5634;
+    const double b_orig = 587867.757;
+    const double expected = a + b_orig;
 
-    V_VT(&params.rgvarg[1]) = VT_R8;
-    V_R8(&params.rgvarg[1]) = a;
-    V_VT(&params.rgvarg[0]) = VT_BYREF | VT_R8;
-    V_R8REF(&params.rgvarg[0]) = &b;
+    double b = b_orig;
 
+    {
+        DISPPARAMS params;
+        params.cArgs = 2;
+        params.rgvarg = new VARIANTARG[params.cArgs];
+        params.cNamedArgs = 0;
+        params.rgdispidNamedArgs = nullptr;
+
+        VARIANT result;
+
+        V_VT(&params.rgvarg[1]) = VT_R8;
+        V_R8(&params.rgvarg[1]) = a;
+        V_VT(&params.rgvarg[0]) = VT_BYREF | VT_R8;
+        V_R8REF(&params.rgvarg[0]) = &b;
+
+
+        THROW_IF_FAILED(dispatchTesting->Invoke(
+            methodId,
+            IID_NULL,
+            lcid,
+            DISPATCH_METHOD,
+            &params,
+            &result,
+            nullptr,
+            nullptr
+        ));
+
+        THROW_FAIL_IF_FALSE(EqualByBound(expected, V_R8(&result)));
+        THROW_FAIL_IF_FALSE(EqualByBound(expected, b));
+    }
 
-    THROW_IF_FAILED(dispatchTesting->Invoke(
-        methodId,
-        IID_NULL,
-        lcid,
-        DISPATCH_METHOD,
-        &params,
-        &result,
-        nullptr,
-        nullptr
-    ));
+    {
+        b = b_orig;
+        double result;
+        THROW_IF_FAILED(dispatchTesting->Add_Double_ReturnAndUpdateByRef(a, &b, &result));
 
-    THROW_FAIL_IF_FALSE(EqualByBound(expected, V_R8(&result)));
-    THROW_FAIL_IF_FALSE(EqualByBound(expected, b));
+        THROW_FAIL_IF_FALSE(EqualByBound(expected, result));
+        THROW_FAIL_IF_FALSE(EqualByBound(expected, b));
+    }
 }
 
 void Validate_LCID_Marshaled()
diff --git a/src/tests/Interop/ICustomMarshaler/Primitives/ICustomMarshaler_TargetWindows.csproj b/src/tests/Interop/ICustomMarshaler/Primitives/ICustomMarshaler_TargetWindows.csproj
index 854fbdda3febdd..3c152f7cb31b83 100644
--- a/src/tests/Interop/ICustomMarshaler/Primitives/ICustomMarshaler_TargetWindows.csproj
+++ b/src/tests/Interop/ICustomMarshaler/Primitives/ICustomMarshaler_TargetWindows.csproj
@@ -10,6 +10,6 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="ICustomMarshaler.cs" />
-    <Compile Include="..\..\..\common\XunitBase.cs" />
+    <Compile Include="..\..\..\Common\XunitBase.cs" />
   </ItemGroup>
 </Project>
diff --git a/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorTest.cs b/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorTest.cs
new file mode 100644
index 00000000000000..31f64bb6b4e692
--- /dev/null
+++ b/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorTest.cs
@@ -0,0 +1,42 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.IO;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using TestLibrary;
+
+static unsafe class CopyCtor
+{
+    public static unsafe int StructWithCtorTest(StructWithCtor* ptrStruct, ref StructWithCtor refStruct)
+    {
+        if (ptrStruct->_instanceField != 1)
+            return 1;
+        if (refStruct._instanceField != 2)
+            return 2;
+
+        if (StructWithCtor.CopyCtorCallCount != 2)
+            return 3;
+        if (StructWithCtor.DtorCallCount != 2)
+            return 4;
+
+
+        return 100;
+    }
+
+    public static unsafe int Main()
+    {
+        TestDelegate del = (TestDelegate)Delegate.CreateDelegate(typeof(TestDelegate), typeof(CopyCtor).GetMethod("StructWithCtorTest"));
+        StructWithCtor s1 = new StructWithCtor();
+        StructWithCtor s2 = new StructWithCtor();
+        s1._instanceField = 1;
+        s2._instanceField = 2;
+        int returnVal = FunctionPointer.Call_FunctionPointer(Marshal.GetFunctionPointerForDelegate(del), &s1, ref s2);
+
+        GC.KeepAlive(del);
+
+        return returnVal;
+    }
+}
diff --git a/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorTest.csproj b/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorTest.csproj
new file mode 100644
index 00000000000000..60abf16802f06a
--- /dev/null
+++ b/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorTest.csproj
@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="CopyCtorTest.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="CopyCtorUtil.ilproj" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorUtil.il b/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorUtil.il
new file mode 100644
index 00000000000000..495bcf7d34a95f
--- /dev/null
+++ b/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorUtil.il
@@ -0,0 +1,97 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+.assembly extern mscorlib { }
+.assembly extern System.Runtime.CompilerServices.VisualC { }
+.assembly CopyCtorUtil { }
+
+.class auto ansi sealed public TestDelegate
+       extends [mscorlib]System.MulticastDelegate
+{
+  .custom instance void [mscorlib]System.Runtime.InteropServices.UnmanagedFunctionPointerAttribute::.ctor(valuetype [mscorlib]System.Runtime.InteropServices.CallingConvention) = ( 01 00 03 00 00 00 00 00 ) 
+  .method public hidebysig specialname rtspecialname 
+          instance void  .ctor(object 'object',
+                               native int 'method') runtime managed
+  {
+  } // end of method TestDelegate::.ctor
+
+  .method public hidebysig newslot virtual 
+          instance int32  Invoke(valuetype [CopyCtorUtil]StructWithCtor modreq([mscorlib]System.Runtime.CompilerServices.IsCopyConstructed)* ptrStruct,
+                                 valuetype [CopyCtorUtil]StructWithCtor modreq([mscorlib]System.Runtime.CompilerServices.IsCopyConstructed)& refStruct) runtime managed
+  {
+  } // end of method TestDelegate::Invoke
+
+  .method public hidebysig newslot virtual 
+          instance class [mscorlib]System.IAsyncResult 
+          BeginInvoke(valuetype [CopyCtorUtil]StructWithCtor modreq([mscorlib]System.Runtime.CompilerServices.IsCopyConstructed)* ptrStruct,
+                      valuetype [CopyCtorUtil]StructWithCtor modreq([mscorlib]System.Runtime.CompilerServices.IsCopyConstructed)& refStruct,
+                      class [mscorlib]System.AsyncCallback callback,
+                      object 'object') runtime managed
+  {
+  } // end of method TestDelegate::BeginInvoke
+
+  .method public hidebysig newslot virtual 
+          instance int32  EndInvoke(valuetype [CopyCtorUtil]StructWithCtor modreq([mscorlib]System.Runtime.CompilerServices.IsCopyConstructed)& refStruct,
+                                    class [mscorlib]System.IAsyncResult result) runtime managed
+  {
+  } // end of method TestDelegate::EndInvoke
+
+} // end of class TestDelegate
+
+.class public sealed sequential ansi beforefieldinit StructWithCtor
+       extends [mscorlib]System.ValueType
+{
+    .field public int32 _instanceField
+    .field public static int32 CopyCtorCallCount
+    .field public static int32 DtorCallCount
+
+    .method public specialname static void  '<MarshalCopy>'(valuetype StructWithCtor* A_0,
+                                                            valuetype StructWithCtor* A_1) cil managed
+    {
+        ldarg.0
+        ldarg.1
+        ldfld int32 StructWithCtor::_instanceField
+        stfld int32 StructWithCtor::_instanceField
+
+        ldsfld int32 StructWithCtor::CopyCtorCallCount
+        ldc.i4.1
+        add
+        stsfld int32 StructWithCtor::CopyCtorCallCount
+        ret
+    }
+
+    .method public specialname static void  '<MarshalDestroy>'(valuetype StructWithCtor* A_0) cil managed
+    {
+        ldsfld int32 StructWithCtor::DtorCallCount
+        ldc.i4.1
+        add
+        stsfld int32 StructWithCtor::DtorCallCount
+        ret
+    }
+}
+
+.class public auto ansi beforefieldinit FunctionPointer
+       extends [mscorlib]System.Object
+{
+    .method hidebysig specialname rtspecialname 
+            instance void .ctor() cil managed
+    {
+        ldarg.0
+        call instance void [mscorlib]System.Object::.ctor()
+        ret
+    }
+
+    .method public hidebysig static int32  Call_FunctionPointer(native int fptr,
+                                                 valuetype StructWithCtor* arg1,
+                                                 valuetype StructWithCtor& arg2) cil managed
+    {
+        .maxstack  8
+        ldarg.1
+        ldarg.2
+        ldarg.0
+        calli unmanaged stdcall int32 (valuetype StructWithCtor modreq([mscorlib]System.Runtime.CompilerServices.IsCopyConstructed)*, valuetype StructWithCtor modreq([mscorlib]System.Runtime.CompilerServices.IsCopyConstructed)&)
+        ret
+    }
+}
+
+
diff --git a/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorUtil.ilproj b/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorUtil.ilproj
new file mode 100644
index 00000000000000..7eb71cef69df39
--- /dev/null
+++ b/src/tests/Interop/PInvoke/Miscellaneous/CopyCtor/CopyCtorUtil.ilproj
@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk.IL">
+  <PropertyGroup>
+    <OutputType>library</OutputType>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="CopyCtorUtil.il" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/Directed/tailcall/mutual_recursion.fs b/src/tests/JIT/Directed/tailcall/mutual_recursion.fs
new file mode 100644
index 00000000000000..5a067980e894ea
--- /dev/null
+++ b/src/tests/JIT/Directed/tailcall/mutual_recursion.fs
@@ -0,0 +1,561 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// Notes:
+//
+// This test will Stack overflow when built in debug. It relies on the FSharp
+// compiler optimizing the tail calls to loops.
+//
+////////////////////////////////////////////////////////////////////////////////
+
+open System
+
+////////////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////////////
+
+// 16 byte struct
+[<Struct>]
+type Point2D(x: double, y: double) =
+    member _.X = x
+    member _.Y = y
+
+////////////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////////////
+
+// F# compiler will optimize the call away
+let first() =
+    let callee firstArg secondArg thirdArg =
+        if firstArg = 10 then firstArg * secondArg * thirdArg
+        else firstArg + secondArg + thirdArg
+
+    let retVal = callee 10 20 30
+
+    if retVal <> 6000 then
+        printfn "Method -- Failed, expected result: 6000, calculated: %d" retVal
+
+        -1
+    else
+        0
+
+// F# Compiler will optimize the call away and treat this as a loop
+let second() =
+    let rec secondCallee(iteration, firstArg, secondArg, thirdArg) = 
+        if iteration = 0 then
+            firstArg
+        else
+            let mutable retVal =
+                if firstArg = 10 then 
+                    firstArg * secondArg * thirdArg
+                else 
+                    firstArg + secondArg + thirdArg
+
+            secondCallee(iteration - 1, retVal, secondArg, thirdArg)
+
+    let retVal = secondCallee(100, 10, 20, 30)
+
+    if retVal <> 10950 then
+        printfn "Method -- Failed, expected result: 10950, calculated: %d" retVal
+        -2
+    else
+        0
+
+// F# Compiler will optimize the call away and treat this as a loop
+let third() = 
+    let rec thirdCallee(iteration, firstArg, secondArg, thirdArg, point: Point2D, secondPoint: Point2D, thirdPoint: Point2D) =
+        if point.X <> 10.0 then -100
+        else if point.Y <> 20.0 then -101
+        else if secondPoint.X <> 30.0 then -102
+        else if secondPoint.Y <> 40.0 then -102
+        else if thirdPoint.X <> 30.0 then -103
+        else if thirdPoint.Y <> 40.0 then -103
+        else if iteration = 0 then
+            firstArg
+        else
+            let mutable retVal =
+                if firstArg = 10 then 
+                    firstArg * secondArg * thirdArg
+                else 
+                    firstArg + secondArg + thirdArg
+                    
+            if retVal > 5000 then
+                thirdCallee(iteration - 1, retVal, secondArg, thirdArg, point, secondPoint, thirdPoint)
+            else
+                thirdCallee(iteration - 1, secondArg, thirdArg, thirdArg, point, secondPoint, thirdPoint)
+
+    let point = Point2D(10.0, 20.0)
+    let secondPoint = Point2D(30.0, 40.0)
+
+    let retVal = thirdCallee(100, 10, 20, 30, point, secondPoint, secondPoint)
+
+    if retVal <> 10950 then
+        printfn "Method -- Failed, expected result: 10950, calculated: %d" retVal
+        -3
+    else
+        0
+
+// Will create a tail il instruction and force a tail call. This is will become
+// a fast tail call on unix x64 as there is no stack usage
+let fourth() =
+    let rec fourthMethodFirstCallee(iterationCount, firstArg: Point2D, secondArg: Point2D, thirdArg: Point2D, fourthArg: Point2D) = 
+        if firstArg.X <> 10.0 then -100
+        else if firstArg.Y <> 20.0 then -101
+        else if secondArg.X <> 30.0 then -102
+        else if secondArg.Y <> 40.0 then -103
+        else if thirdArg.X <> 10.0 then -104
+        else if thirdArg.Y <> 20.0 then -105
+        else if fourthArg.X <> 30.0 then -106
+        else if fourthArg.Y <> 40.0 then -107
+        else if iterationCount = 0 then
+            100
+        else if iterationCount % 2 = 0 then
+            fourthMethodSecondCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg)
+        else
+            fourthMethodFirstCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg)
+
+    and fourthMethodSecondCallee(iterationCount, firstArg, secondArg, thirdArg, fourthArg) =
+        if firstArg.X <> 10.0 then -150
+        else if firstArg.Y <> 20.0 then -151
+        else if secondArg.X <> 30.0 then -152
+        else if secondArg.Y <> 40.0 then -153
+        else if thirdArg.X <> 10.0 then -154
+        else if thirdArg.Y <> 20.0 then -155
+        else if fourthArg.X <> 30.0 then -156
+        else if fourthArg.Y <> 40.0 then -157
+        else if iterationCount = 0 then
+            101
+        else if iterationCount % 2 = 0 then
+            fourthMethodSecondCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg)
+        else
+            fourthMethodFirstCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg)
+    
+    let point = Point2D(10.0, 20.0)
+    let secondPoint = Point2D(30.0, 40.0)
+
+    let retVal = fourthMethodFirstCallee(1000000, point, secondPoint, point, secondPoint)
+
+    if retVal <> 100 && retVal <> 101 then
+        printfn "Method -- Failed, expected result: 100 or 101, calculated: %d" retVal
+        -4
+    else
+        0
+    
+// Will create a tail il instruction and force a tail call. This is will become
+// a fast tail call on unix x64 as the caller and callee have equal stack size
+let fifth() =
+    let rec fifthMethodFirstCallee(iterationCount, firstArg: Point2D, secondArg: Point2D, thirdArg: Point2D, fourthArg: Point2D, fifthArg: Point2D) = 
+        if firstArg.X <> 10.0 then -100
+        else if firstArg.Y <> 20.0 then -101
+        else if secondArg.X <> 30.0 then -102
+        else if secondArg.Y <> 40.0 then -103
+        else if thirdArg.X <> 10.0 then -104
+        else if thirdArg.Y <> 20.0 then -105
+        else if fourthArg.X <> 30.0 then -106
+        else if fourthArg.Y <> 40.0 then -107
+        else if fifthArg.X <> 10.0 then -108
+        else if fifthArg.Y <> 20.0 then -109
+        else if iterationCount = 0 then
+            100
+        else if iterationCount % 2 = 0 then
+            fifthMethodSecondCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg)
+        else
+            fifthMethodFirstCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg)
+
+    and fifthMethodSecondCallee(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg) =
+        if firstArg.X <> 10.0 then -150
+        else if firstArg.Y <> 20.0 then -151
+        else if secondArg.X <> 30.0 then -152
+        else if secondArg.Y <> 40.0 then -153
+        else if thirdArg.X <> 10.0 then -154
+        else if thirdArg.Y <> 20.0 then -155
+        else if fourthArg.X <> 30.0 then -156
+        else if fourthArg.Y <> 40.0 then -157
+        else if fifthArg.X <> 10.0 then -158
+        else if fifthArg.Y <> 20.0 then -159
+        else if iterationCount = 0 then
+            101
+        else if iterationCount % 2 = 0 then
+            fifthMethodSecondCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg)
+        else
+            fifthMethodFirstCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg)
+
+    let point = Point2D(10.0, 20.0)
+    let secondPoint = Point2D(30.0, 40.0)
+
+    let retVal = fifthMethodFirstCallee(1000000, point, secondPoint, point, secondPoint, point)
+
+    if retVal <> 100 && retVal <> 101 then
+        printfn "Method -- Failed, expected result: 100 or 101, calculated: %d" retVal
+        -5
+    else
+        0
+
+// Will create a tail il instruction and force a tail call. This is will become
+// a tail call via helper on unix x64 as the caller has less available incoming
+// arg size than the callee
+let sixth() =
+    let rec sixthMethodFirstCallee(iterationCount, firstArg: Point2D, secondArg: Point2D, thirdArg: Point2D, fourthArg: Point2D, fifthArg: Point2D) = 
+        if firstArg.X <> 10.0 then -100
+        else if firstArg.Y <> 20.0 then -101
+        else if secondArg.X <> 30.0 then -102
+        else if secondArg.Y <> 40.0 then -103
+        else if thirdArg.X <> 10.0 then -104
+        else if thirdArg.Y <> 20.0 then -105
+        else if fourthArg.X <> 30.0 then -106
+        else if fourthArg.Y <> 40.0 then -107
+        else if fifthArg.X <> 10.0 then -108
+        else if fifthArg.Y <> 20.0 then -109
+        else if iterationCount = 0 then
+            100
+        else if iterationCount % 2 = 0 then
+            sixthMethodSecondCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg)
+        else
+            sixthMethodFirstCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg)
+
+    and sixthMethodSecondCallee(iterationCount, firstArg, secondArg, thirdArg, fourthArg) =
+        if firstArg.X <> 10.0 then -150
+        else if firstArg.Y <> 20.0 then -151
+        else if secondArg.X <> 30.0 then -152
+        else if secondArg.Y <> 40.0 then -153
+        else if thirdArg.X <> 10.0 then -154
+        else if thirdArg.Y <> 20.0 then -155
+        else if fourthArg.X <> 30.0 then -156
+        else if fourthArg.Y <> 40.0 then -157
+        else if iterationCount = 0 then
+            101
+        else if iterationCount % 2 = 0 then
+            sixthMethodSecondCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg)
+        else
+            sixthMethodFirstCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, thirdArg)
+
+    let point = new Point2D(10.0, 20.0)
+    let secondPoint = new Point2D(30.0, 40.0)
+
+    let retVal = sixthMethodFirstCallee(1000000, point, secondPoint, point, secondPoint, point)
+
+    if retVal <> 100 && retVal <> 101 then
+        printfn "Method -- Failed, expected result: 100 or 101, calculated: %d" retVal
+        -6
+    else
+        0
+
+// Will create a tail il instruction and force a tail call. This is will become
+// a tail call via helper on unix x64 as the caller has less available incoming
+// arg size than the callee
+let seventh() =
+    let rec seventhMethodFirstCallee(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg, seventhArg, eighthArg, ninethArg, tenthArg) =
+        if firstArg <> 1 then -100
+        else if secondArg <> 2 then -101
+        else if thirdArg <> 3 then -102
+        else if fourthArg <> 4 then -103
+        else if fifthArg <> 5 then -104
+        else if sixthArg <> 6 then -105
+        else if seventhArg <> 7 then -106
+        else if eighthArg <> 8 then -107
+        else if ninethArg <> 9 then -108
+        else if tenthArg <> 10 then -109
+        else if iterationCount = 0 then
+            100
+        else if iterationCount % 2 = 0 then
+            seventhMethodSecondCallee(iterationCount)
+        else
+            seventhMethodFirstCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg, seventhArg, eighthArg, ninethArg, tenthArg)
+
+    and seventhMethodSecondCallee(iterationCount) = 
+        if iterationCount = 0 then
+            101
+        else if iterationCount % 2 = 0 then
+            seventhMethodSecondCallee(iterationCount - 1)
+        else
+            seventhMethodFirstCallee(iterationCount - 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
+
+    let retVal = seventhMethodFirstCallee(1000000, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
+
+    if retVal <> 100 && retVal <> 101 then
+        printfn "Method -- Failed, expected result: 100 or 101, calculated: %d" retVal
+        -7
+    else
+        0
+
+// Will create a tail il instruction and force a tail call. This is will become
+// a fast tail call as the caller and callee have the incoming arg size
+let seventhFastTailCall() =
+    let rec seventhMethodFirstCalleeFastTailCall(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg, seventhArg, eighthArg, ninethArg, tenthArg) =
+        if firstArg <> 1 then -100
+        else if secondArg <> 2 then -101
+        else if thirdArg <> 3 then -102
+        else if fourthArg <> 4 then -103
+        else if fifthArg <> 5 then -104
+        else if sixthArg <> 6 then -105
+        else if seventhArg <> 7 then -106
+        else if eighthArg <> 8 then -107
+        else if ninethArg <> 9 then -108
+        else if tenthArg <> 10 then -109
+        else if iterationCount = 0 then
+            100
+        else if iterationCount % 2 = 0 then
+            seventhMethodSecondCalleeFastTailCall(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg, seventhArg, eighthArg, ninethArg, tenthArg)
+        else
+            seventhMethodFirstCalleeFastTailCall(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg, seventhArg, eighthArg, ninethArg, tenthArg)
+
+    and seventhMethodSecondCalleeFastTailCall(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg, seventhArg, eighthArg, ninethArg, tenthArg) = 
+        if firstArg <> 1 then -110
+        else if secondArg <> 2 then -111
+        else if thirdArg <> 3 then -112
+        else if fourthArg <> 4 then -113
+        else if fifthArg <> 5 then -114
+        else if sixthArg <> 6 then -115
+        else if seventhArg <> 7 then -116
+        else if eighthArg <> 8 then -117
+        else if ninethArg <> 9 then -118
+        else if tenthArg <> 10 then -119
+        else if iterationCount = 0 then
+            101
+        else if iterationCount % 2 = 0 then
+            seventhMethodSecondCalleeFastTailCall(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg, seventhArg, eighthArg, ninethArg, tenthArg)
+        else
+            seventhMethodFirstCalleeFastTailCall(iterationCount - 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
+
+    let retVal = seventhMethodFirstCalleeFastTailCall(1000000, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
+
+    if retVal <> 100 && retVal <> 101 then
+        printfn "Method -- Failed, expected result: 100 or 101, calculated: %d" retVal
+        -8
+    else
+        0
+
+// Will create a tail il instruction and force a tail call. This is will become
+// a fast tail call as the caller and callee have the incoming arg size
+let seventhFastTailCallReversed() =
+    let rec seventhMethodFirstCalleeFastTailCallReversed(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg, seventhArg, eighthArg, ninethArg, tenthArg) =
+        if firstArg <> 1 then -100
+        else if secondArg <> 2 then -101
+        else if thirdArg <> 3 then -102
+        else if fourthArg <> 4 then -103
+        else if fifthArg <> 5 then -104
+        else if sixthArg <> 6 then -105
+        else if seventhArg <> 7 then -106
+        else if eighthArg <> 8 then -107
+        else if ninethArg <> 9 then -108
+        else if tenthArg <> 10 then -109
+        else if iterationCount = 0 then
+            100
+        else if iterationCount % 2 = 0 then
+            seventhMethodSecondCalleeFastTailCallReversed(iterationCount - 1, tenthArg, ninethArg, eighthArg, seventhArg, sixthArg, fifthArg, fourthArg, thirdArg, secondArg, firstArg)
+        else
+            seventhMethodFirstCalleeFastTailCallReversed(iterationCount - 1, tenthArg, ninethArg, eighthArg, seventhArg, sixthArg, fifthArg, fourthArg, thirdArg, secondArg, firstArg)
+
+    and seventhMethodSecondCalleeFastTailCallReversed(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg, seventhArg, eighthArg, ninethArg, tenthArg) = 
+        if firstArg <> 10 then -110
+        else if secondArg <> 9 then -111
+        else if thirdArg <> 8 then -112
+        else if fourthArg <> 7 then -113
+        else if fifthArg <> 6 then -114
+        else if sixthArg <> 5 then -115
+        else if seventhArg <> 4 then -116
+        else if eighthArg <> 3 then -117
+        else if ninethArg <> 2 then -118
+        else if tenthArg <> 1 then -119
+        else if iterationCount = 0 then
+            101
+        else if iterationCount % 2 = 0 then
+            seventhMethodSecondCalleeFastTailCallReversed(iterationCount - 1, tenthArg, ninethArg, eighthArg, seventhArg, sixthArg, fifthArg, fourthArg, thirdArg, secondArg, firstArg)
+        else
+            seventhMethodFirstCalleeFastTailCallReversed(iterationCount - 1, tenthArg, ninethArg, eighthArg, seventhArg, sixthArg, fifthArg, fourthArg, thirdArg, secondArg, firstArg)
+
+    let retVal = seventhMethodFirstCalleeFastTailCallReversed(1000000, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
+
+    if retVal <> 100 && retVal <> 101 then
+        printfn "Method -- Failed, expected result: 100 or 101, calculated: %d" retVal
+        -8
+    else
+        0
+
+// Will create a tail il instruction and force a tail call. This is will become
+// a tail call via helper on unix x64 as the caller has less available incoming
+// arg size than the callee
+let eight() =
+    let rec eightMethodFirstCallee(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg) =
+        if firstArg <> 1 then -100
+        else if secondArg <> 2 then -101
+        else if thirdArg <> 3 then -102
+        else if fourthArg <> 4 then -103
+        else if fifthArg <> 5 then -104
+        else if sixthArg <> 6 then -105
+        else if iterationCount = 0 then
+            100
+        else if iterationCount % 2 = 0 then
+            eightMethodSecondCallee(iterationCount)
+        else
+            eightMethodFirstCallee(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg)
+
+    and eightMethodSecondCallee(iterationCount) = 
+        if iterationCount = 0 then
+            101
+        else if iterationCount % 2 = 0 then
+            eightMethodSecondCallee(iterationCount - 1)
+        else
+            eightMethodFirstCallee(iterationCount - 1, 1, 2, 3, 4, 5, 6)
+
+    let retVal = eightMethodFirstCallee(1000000, 1, 2, 3, 4, 5, 6)
+
+    if retVal <> 100 && retVal <> 101 then
+        printfn "Method -- Failed, expected result: 100 or 101, calculated: %d" retVal
+        -9
+    else
+        0
+
+// Will create a tail il instruction and force a tail call. This is will become
+// a tail call via helper on unix x64 as the caller has less available incoming
+// arg size than the callee
+let eightFastTailCall() =
+    let rec eightMethodFirstCalleeFastTailCall(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg) =
+        if firstArg <> 1 then -100
+        else if secondArg <> 2 then -101
+        else if thirdArg <> 3 then -102
+        else if fourthArg <> 4 then -103
+        else if fifthArg <> 5 then -104
+        else if sixthArg <> 6 then -105
+        else if iterationCount = 0 then
+            100
+        else if iterationCount % 2 = 0 then
+            eightMethodSecondCalleeFastTailCall(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg)
+        else
+            eightMethodFirstCalleeFastTailCall(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg)
+
+    and eightMethodSecondCalleeFastTailCall(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg) = 
+        if firstArg <> 1 then -100
+        else if secondArg <> 2 then -101
+        else if thirdArg <> 3 then -102
+        else if fourthArg <> 4 then -103
+        else if fifthArg <> 5 then -104
+        else if sixthArg <> 6 then -105
+        else if iterationCount = 0 then
+            101
+        else if iterationCount % 2 = 0 then
+            eightMethodSecondCalleeFastTailCall(iterationCount - 1, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg)
+        else
+            eightMethodFirstCalleeFastTailCall(iterationCount - 1, 1, 2, 3, 4, 5, 6)
+
+    let retVal = eightMethodFirstCalleeFastTailCall(1000000, 1, 2, 3, 4, 5, 6)
+
+    if retVal <> 100 && retVal <> 101 then
+        printfn "Method -- Failed, expected result: 100 or 101, calculated: %d" retVal
+        -10
+    else
+        0
+
+// Will create a tail il instruction and force a tail call. This is will become
+// a tail call via helper on unix x64 as the caller has less available incoming
+// arg size than the callee
+//
+// Reversing the call arguments is a simple way to stress LowerFastTailCall
+let eightFastTailCallReversed() =
+    let rec eightMethodFirstCalleeFastTailCallReversed(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg) =
+        if firstArg <> 1 then -100
+        else if secondArg <> 2 then -101
+        else if thirdArg <> 3 then -102
+        else if fourthArg <> 4 then -103
+        else if fifthArg <> 5 then -104
+        else if sixthArg <> 6 then -105
+        else if iterationCount = 0 then
+            100
+        else if iterationCount % 2 = 0 then
+            eightMethodSecondCalleeFastTailCallReversed(iterationCount - 1, sixthArg, fifthArg, fourthArg, thirdArg, secondArg, firstArg)
+        else
+            eightMethodFirstCalleeFastTailCallReversed(iterationCount - 1, sixthArg, fifthArg, fourthArg, thirdArg, secondArg, firstArg)
+
+    and eightMethodSecondCalleeFastTailCallReversed(iterationCount, firstArg, secondArg, thirdArg, fourthArg, fifthArg, sixthArg) = 
+        if firstArg <> 6 then -100
+        else if secondArg <> 5 then -101
+        else if thirdArg <> 4 then -102
+        else if fourthArg <> 3 then -103
+        else if fifthArg <> 2 then -104
+        else if sixthArg <> 1 then -105
+        else if iterationCount = 0 then
+            101
+        else if iterationCount % 2 = 0 then
+            eightMethodSecondCalleeFastTailCallReversed(iterationCount - 1, sixthArg, fifthArg, fourthArg, thirdArg, secondArg, firstArg)
+        else
+            eightMethodFirstCalleeFastTailCallReversed(iterationCount - 1, sixthArg, fifthArg, fourthArg, thirdArg, secondArg, firstArg)
+
+    let retVal = eightMethodFirstCalleeFastTailCallReversed(1000000, 1, 2, 3, 4, 5, 6)
+
+    if retVal <> 100 && retVal <> 101 then
+        printfn "Method -- Failed, expected result: 100 or 101, calculated: %d" retVal
+        -11
+    else
+        0
+
+////////////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////////////
+
+type Driver() = 
+    // Notes:
+    //
+    // Drive all of the different methods that will be called and account for
+    // timing.
+    member _.Start() =
+        let rec runMethod(iterationCount: int, cb: _ -> int) = 
+            if iterationCount > 0 then
+                let retVal = cb()
+
+                if retVal <> 0 then
+                    retVal
+                else
+                    runMethod(iterationCount - 1, cb)
+            else
+                0
+
+        let runMethodWithTiming(methodName: string, worksOnlyOnNetCore5: bool, iterationCount: int, cb: _ -> int) = 
+            let canRun = (worksOnlyOnNetCore5 && System.Environment.Version.Major > 3) || worksOnlyOnNetCore5 = false
+
+            if canRun then
+                let startTime = DateTime.Now
+                let retVal = runMethod(iterationCount, cb)
+                let endTime = DateTime.Now
+
+                let elapsedTime = (endTime - startTime).TotalMilliseconds
+
+                if retVal <> 0 then
+                    failwith "Incorrect method passed"
+
+                printfn "[%s] - %fms" methodName elapsedTime
+            else
+                printfn "[%s] - skipped. Only works on .Net Core 5.0 and above" methodName
+
+        runMethodWithTiming("FirstMethod", false, 100000, first)
+        runMethodWithTiming("SecondMethod", false, 100000, second)
+
+        // ThirdMethod will SO in debug
+        runMethodWithTiming("ThirdMethod", false, 100000, third)
+
+        // FourthMethod will SO in debug
+        runMethodWithTiming("FourthMethod", false, 10, fourth)
+
+        // The rest of the methods require generic tailcall helper therefore
+        // will only work on >3.1
+
+        // All the following SO in debug
+
+        runMethodWithTiming("FifthMethod", true, 10, fifth)
+        runMethodWithTiming("SixthMethod", true, 10, sixth)
+        runMethodWithTiming("SeventhMethod", true, 10, seventh)
+        runMethodWithTiming("SeventhMethodFastTailCall", false, 10, seventhFastTailCall)
+        runMethodWithTiming("SeventhMethodFastTailCallReversed", false, 10, seventhFastTailCallReversed)
+        runMethodWithTiming("EigthhMethod", true, 10, eight)
+        runMethodWithTiming("EigthMethodFastTailCall", false, 10, eightFastTailCall)
+        runMethodWithTiming("EigthMethodFastTailCallReversed", false, 10, eightFastTailCallReversed)
+
+////////////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////////////
+
+[<EntryPoint>]
+let main argv =
+    let driver = Driver()
+    driver.Start()
+
+    // If we have gotten to this point we have not StackOverflowed. Therefore 
+    // consider this a passing test
+    100
diff --git a/src/tests/JIT/Directed/tailcall/mutual_recursion.fsproj b/src/tests/JIT/Directed/tailcall/mutual_recursion.fsproj
new file mode 100644
index 00000000000000..0a9d97a4ebc215
--- /dev/null
+++ b/src/tests/JIT/Directed/tailcall/mutual_recursion.fsproj
@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <NoStandardLib>True</NoStandardLib>
+    <Noconfig>True</Noconfig>
+    <Optimize>True</Optimize>
+    <JitOptimizationSensitive>True</JitOptimizationSensitive>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="mutual_recursion.fs" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/HardwareIntrinsics/X86/X86Base/CpuId.cs b/src/tests/JIT/HardwareIntrinsics/X86/X86Base/CpuId.cs
new file mode 100644
index 00000000000000..39dd182e4e0bf8
--- /dev/null
+++ b/src/tests/JIT/HardwareIntrinsics/X86/X86Base/CpuId.cs
@@ -0,0 +1,186 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+//
+
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Runtime.Intrinsics.X86;
+using System.Runtime.Intrinsics;
+
+namespace IntelHardwareIntrinsicTest
+{
+    class Program
+    {
+        const int Pass = 100;
+        const int Fail = 0;
+
+        static unsafe int Main(string[] args)
+        {
+            int testResult = Pass;
+
+            if (!X86Base.IsSupported)
+            {
+                return testResult;
+            }
+
+            (int eax, int ebx, int ecx, int edx) = X86Base.CpuId(0x00000000, 0x00000000);
+
+            bool isAuthenticAmd = (ebx == 0x68747541) && (ecx == 0x444D4163) && (edx == 0x69746E65);
+            bool isGenuineIntel = (ebx == 0x756E6547) && (ecx == 0x6C65746E) && (edx == 0x49656E69);
+
+            if (!isAuthenticAmd && !isGenuineIntel)
+            {
+                // CPUID checks are vendor specific and aren't guaranteed to match up, even across Intel/AMD
+                // as such, we limit ourselves to just AuthenticAMD and GenuineIntel right now. Any other
+                // vendors would need to be validated against the checks below and added to the list as necessary.
+
+                // An example of a difference is Intel/AMD for LZCNT. While the same underlying bit is used to
+                // represent presence of the LZCNT instruction, AMD began using this bit around 2007 for its
+                // ABM instruction set, which indicates LZCNT and POPCNT. Intel introduced a separate bit for
+                // POPCNT and didn't actually implement LZCNT and begin using the LZCNT bit until 2013. So
+                // while everything happens to line up today, it doesn't always and may not always do so.
+
+                Console.WriteLine($"Unrecognized CPU vendor: EBX: {ebx:X8}, ECX: {ecx:X8}, EDX: {edx:X8}");
+                testResult = Fail;
+            }
+
+            int maxFunctionId = eax;
+
+            if ((maxFunctionId < 0x00000001) || (Environment.GetEnvironmentVariable("COMPlus_EnableHWIntrinsic") is null))
+            {
+                return testResult;
+            }
+
+            (eax, ebx, ecx, edx) = X86Base.CpuId(0x00000001, 0x00000000);
+
+            if (IsBitIncorrect(ecx, 28, Avx.IsSupported, "AVX"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:AVX != Avx.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(ecx, 25, Aes.IsSupported, "AES"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:AES != Aes.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(ecx, 23, Popcnt.IsSupported, "POPCNT"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:POPCNT != Popcnt.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(ecx, 20, Sse42.IsSupported, "SSE42"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:SSE42 != Sse42.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(ecx, 19, Sse41.IsSupported, "SSE41"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:SSE41 != Sse41.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(ecx, 12, Fma.IsSupported, "FMA"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:FMA != Fma.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(ecx, 9, Ssse3.IsSupported, "SSSE3"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:SSSE3 != Ssse3.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(ecx, 1, Pclmulqdq.IsSupported, "PCLMULQDQ"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:PCLMULQDQ != Pclmulqdq.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(ecx, 0, Sse3.IsSupported, "SSE3"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:SSE3 != Sse3.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(edx, 26, Sse2.IsSupported, "SSE2"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:SSE2 != Sse2.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(edx, 25, Sse.IsSupported, "SSE"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_ECX:SSE != Sse.IsSupported");
+                testResult = Fail;
+            }
+
+            if (maxFunctionId < 0x00000007)
+            {
+                return testResult;
+            }
+
+            (eax, ebx, ecx, edx) = X86Base.CpuId(0x00000007, 0x00000000);
+
+            if (IsBitIncorrect(ebx, 8, Bmi2.IsSupported, "BMI2"))
+            {
+                Console.WriteLine("CPUID Fn0000_0007_EBX:BMI2 != Bmi2.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(ebx, 5, Avx2.IsSupported, "AVX2"))
+            {
+                Console.WriteLine("CPUID Fn0000_0007_EBX:AVX2 != Avx2.IsSupported");
+                testResult = Fail;
+            }
+
+            if (IsBitIncorrect(ebx, 3, Bmi1.IsSupported, "BMI1"))
+            {
+                Console.WriteLine("CPUID Fn0000_0001_EBX:BMI1 != Bmi1.IsSupported");
+                testResult = Fail;
+            }
+
+            (eax, ebx, ecx, edx) = X86Base.CpuId(unchecked((int)0x80000000), 0x00000000);
+
+            if (isAuthenticAmd && ((ebx != 0x68747541) || (ecx != 0x444D4163) || (edx != 0x69746E65)))
+            {
+                Console.WriteLine("CPUID Fn8000_0000 reported different vendor info from Fn0000_0000");
+                testResult = Fail;
+            }
+
+            if (isGenuineIntel && ((ebx != 0x756E6547) && (ecx != 0x6C65746E) && (edx != 0x6C656E69)))
+            {
+                Console.WriteLine("CPUID Fn8000_0000 reported different vendor info from Fn0000_0000");
+                testResult = Fail;
+            }
+
+            int maxFunctionIdEx = eax;
+
+            if (maxFunctionIdEx < 0x00000001)
+            {
+                return testResult;
+            }
+
+            (eax, ebx, ecx, edx) = X86Base.CpuId(unchecked((int)0x80000001), 0x00000000);
+
+            if (IsBitIncorrect(ecx, 5, Lzcnt.IsSupported, "LZCNT"))
+            {
+                Console.WriteLine("CPUID Fn8000_0001_ECX:LZCNT != Lzcnt.IsSupported");
+                testResult = Fail;
+            }
+
+            return testResult;
+        }
+
+        static bool IsBitIncorrect(int register, int bitNumber, bool expectedResult, string name)
+        {
+            return ((register & (1 << bitNumber)) != ((expectedResult ? 1 : 0) << bitNumber))
+                && (Environment.GetEnvironmentVariable($"COMPlus_Enable{name}") is null);
+        }
+    }
+}
diff --git a/src/tests/JIT/HardwareIntrinsics/X86/X86Base/CpuId_r.csproj b/src/tests/JIT/HardwareIntrinsics/X86/X86Base/CpuId_r.csproj
new file mode 100644
index 00000000000000..8c3ea60df00cad
--- /dev/null
+++ b/src/tests/JIT/HardwareIntrinsics/X86/X86Base/CpuId_r.csproj
@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>Embedded</DebugType>
+    <Optimize />
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="CpuId.cs" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/HardwareIntrinsics/X86/X86Base/CpuId_ro.csproj b/src/tests/JIT/HardwareIntrinsics/X86/X86Base/CpuId_ro.csproj
new file mode 100644
index 00000000000000..64875d4c153b2f
--- /dev/null
+++ b/src/tests/JIT/HardwareIntrinsics/X86/X86Base/CpuId_ro.csproj
@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>Embedded</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="CpuId.cs" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/beq_r4.ilproj b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/beq_r4.ilproj
index cef275ea49426b..ab208980834058 100644
--- a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/beq_r4.ilproj
+++ b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/beq_r4.ilproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <RestorePackages>true</RestorePackages>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>PdbOnly</DebugType>
diff --git a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/beq_r8.ilproj b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/beq_r8.ilproj
index e92e57de25c758..ca0982693df230 100644
--- a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/beq_r8.ilproj
+++ b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/beq_r8.ilproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <RestorePackages>true</RestorePackages>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>PdbOnly</DebugType>
diff --git a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_r4.ilproj b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_r4.ilproj
index b5e9a76cdac4e9..191bb09523af66 100644
--- a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_r4.ilproj
+++ b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_r4.ilproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <RestorePackages>true</RestorePackages>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>PdbOnly</DebugType>
diff --git a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_r8.ilproj b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_r8.ilproj
index 62ed8ad09721d2..5e8c0aed782cfa 100644
--- a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_r8.ilproj
+++ b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_r8.ilproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <RestorePackages>true</RestorePackages>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>PdbOnly</DebugType>
diff --git a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_un_r4.ilproj b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_un_r4.ilproj
index ba5b4cd8572028..b0a46391cdbd70 100644
--- a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_un_r4.ilproj
+++ b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_un_r4.ilproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <RestorePackages>true</RestorePackages>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>PdbOnly</DebugType>
diff --git a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_un_r8.ilproj b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_un_r8.ilproj
index ca67fefcb7644e..8d689526c4de68 100644
--- a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_un_r8.ilproj
+++ b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bge_un_r8.ilproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <RestorePackages>true</RestorePackages>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>PdbOnly</DebugType>
diff --git a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bne_un_r4.ilproj b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bne_un_r4.ilproj
index 891402dd071ab3..a3b92f67f70bc8 100644
--- a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bne_un_r4.ilproj
+++ b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bne_un_r4.ilproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <RestorePackages>true</RestorePackages>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>PdbOnly</DebugType>
diff --git a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bne_un_r8.ilproj b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bne_un_r8.ilproj
index eb0db5833a1da5..ededde0d346d15 100644
--- a/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bne_un_r8.ilproj
+++ b/src/tests/JIT/IL_Conformance/Old/Conformance_Base/bne_un_r8.ilproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <RestorePackages>true</RestorePackages>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>PdbOnly</DebugType>
diff --git a/src/tests/JIT/Methodical/NaN/arithm64_cs_d.csproj b/src/tests/JIT/Methodical/NaN/arithm64_cs_d.csproj
index 3c8a6b09632fab..882dbd5ce4de96 100644
--- a/src/tests/JIT/Methodical/NaN/arithm64_cs_d.csproj
+++ b/src/tests/JIT/Methodical/NaN/arithm64_cs_d.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>Full</DebugType>
diff --git a/src/tests/JIT/Methodical/NaN/arithm64_cs_do.csproj b/src/tests/JIT/Methodical/NaN/arithm64_cs_do.csproj
index 645b85538bf65c..63895dbcfb49da 100644
--- a/src/tests/JIT/Methodical/NaN/arithm64_cs_do.csproj
+++ b/src/tests/JIT/Methodical/NaN/arithm64_cs_do.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>Full</DebugType>
diff --git a/src/tests/JIT/Methodical/NaN/arithm64_cs_r.csproj b/src/tests/JIT/Methodical/NaN/arithm64_cs_r.csproj
index f70b11917026e4..750ade69062123 100644
--- a/src/tests/JIT/Methodical/NaN/arithm64_cs_r.csproj
+++ b/src/tests/JIT/Methodical/NaN/arithm64_cs_r.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>None</DebugType>
diff --git a/src/tests/JIT/Methodical/NaN/arithm64_cs_ro.csproj b/src/tests/JIT/Methodical/NaN/arithm64_cs_ro.csproj
index a453a807abb145..21d4a502b6b400 100644
--- a/src/tests/JIT/Methodical/NaN/arithm64_cs_ro.csproj
+++ b/src/tests/JIT/Methodical/NaN/arithm64_cs_ro.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>None</DebugType>
diff --git a/src/tests/JIT/Regression/JitBlue/GitHub_39823/GitHub_39823.cs b/src/tests/JIT/Regression/JitBlue/GitHub_39823/GitHub_39823.cs
new file mode 100644
index 00000000000000..501641e9b3cfe0
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/GitHub_39823/GitHub_39823.cs
@@ -0,0 +1,39 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Runtime.CompilerServices;
+using System.Diagnostics;
+
+class Runtime_39823
+{
+    struct IntsWrapped
+    {
+        public int i1;
+        public int i2;
+        public int i3;
+        public int i4;
+    };
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static unsafe int TestUnusedObjCopy(IntsWrapped* ps)
+    {
+        IntsWrapped s = *ps;
+        return 100;
+    }
+
+
+    public static unsafe int Main()
+    {
+        try
+        {
+            TestUnusedObjCopy((IntsWrapped*)0);
+            Debug.Assert(false, "unreachable");
+        }
+        catch
+        {
+            return 100;
+        }
+        return -1;
+    }
+}
diff --git a/src/tests/JIT/Regression/JitBlue/GitHub_39823/GitHub_39823.csproj b/src/tests/JIT/Regression/JitBlue/GitHub_39823/GitHub_39823.csproj
new file mode 100644
index 00000000000000..51c683dceab523
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/GitHub_39823/GitHub_39823.csproj
@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <CLRTestPriority>1</CLRTestPriority>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>Full</DebugType>
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_34587/Runtime_34587.cs b/src/tests/JIT/Regression/JitBlue/Runtime_34587/Runtime_34587.cs
index 3b4898b3769f46..cb06c86edf370f 100644
--- a/src/tests/JIT/Regression/JitBlue/Runtime_34587/Runtime_34587.cs
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_34587/Runtime_34587.cs
@@ -14,6 +14,62 @@ class Runtime_34587
 {
     public static int Main()
     {
+        TestLibrary.TestFramework.LogInformation("Supported x86 ISAs:");
+        TestLibrary.TestFramework.LogInformation($"  AES:           {X86Aes.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  AVX:           {Avx.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  AVX2:          {Avx2.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  BMI1:          {Bmi1.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  BMI2:          {Bmi2.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  FMA:           {Fma.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  LZCNT:         {Lzcnt.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  PCLMULQDQ:     {Pclmulqdq.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  POPCNT:        {Popcnt.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSE:           {Sse.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSE2:          {Sse2.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSE3:          {Sse3.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSE4.1:        {Sse41.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSE4.2:        {Sse42.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSSE3:         {Ssse3.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  X86Base:       {X86Base.IsSupported}");
+
+        TestLibrary.TestFramework.LogInformation("Supported x64 ISAs:");
+        TestLibrary.TestFramework.LogInformation($"  AES.X64:       {X86Aes.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  AVX.X64:       {Avx.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  AVX2.X64:      {Avx2.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  BMI1.X64:      {Bmi1.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  BMI2.X64:      {Bmi2.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  FMA.X64:       {Fma.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  LZCNT.X64:     {Lzcnt.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  PCLMULQDQ.X64: {Pclmulqdq.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  POPCNT.X64:    {Popcnt.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSE.X64:       {Sse.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSE2.X64:      {Sse2.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSE3.X64:      {Sse3.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSE4.1.X64:    {Sse41.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSE4.2.X64:    {Sse42.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  SSSE3.X64:     {Ssse3.X64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  X86Base.X64:   {X86Base.X64.IsSupported}");
+
+        TestLibrary.TestFramework.LogInformation("Supported Arm ISAs:");
+        TestLibrary.TestFramework.LogInformation($"  AdvSimd:       {AdvSimd.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Aes:           {ArmAes.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  ArmBase:       {ArmBase.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Crc32:         {Crc32.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Dp:            {Dp.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Rdm:           {Rdm.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Sha1:          {Sha1.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Sha256:        {Sha256.IsSupported}");
+
+        TestLibrary.TestFramework.LogInformation("Supported Arm64 ISAs:");
+        TestLibrary.TestFramework.LogInformation($"  AdvSimd.Arm64: {AdvSimd.Arm64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Aes.Arm64:     {ArmAes.Arm64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  ArmBase.Arm64: {ArmBase.Arm64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Crc32.Arm64:   {Crc32.Arm64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Dp.Arm64:      {Dp.Arm64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Rdm.Arm64:     {Rdm.Arm64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Sha1.Arm64:    {Sha1.Arm64.IsSupported}");
+        TestLibrary.TestFramework.LogInformation($"  Sha256.Arm64:  {Sha256.Arm64.IsSupported}");
+
         bool succeeded = true;
 
         succeeded &= ValidateArm();
@@ -186,6 +242,7 @@ public static bool ValidateX86()
     {
         bool succeeded = true;
 
+        succeeded &= ValidateX86Base();
         succeeded &= ValidateSse();
         succeeded &= ValidateSse2();
         succeeded &= ValidateSse3();
@@ -204,19 +261,37 @@ public static bool ValidateX86()
 
         return succeeded;
 
+        static bool ValidateX86Base()
+        {
+            bool succeeded = true;
+
+            if (X86Base.IsSupported)
+            {
+                succeeded &= (RuntimeInformation.OSArchitecture == Architecture.X86) || (RuntimeInformation.OSArchitecture == Architecture.X64);
+            }
+
+            if (X86Base.X64.IsSupported)
+            {
+                succeeded &= X86Base.IsSupported;
+                succeeded &= (RuntimeInformation.OSArchitecture == Architecture.X64);
+            }
+
+            return succeeded;
+        }
+
         static bool ValidateSse()
         {
             bool succeeded = true;
 
             if (Sse.IsSupported)
             {
-                succeeded &= (RuntimeInformation.OSArchitecture == Architecture.X86) || (RuntimeInformation.OSArchitecture == Architecture.X64);
+                succeeded &= X86Base.IsSupported;
             }
 
             if (Sse.X64.IsSupported)
             {
                 succeeded &= Sse.IsSupported;
-                succeeded &= (RuntimeInformation.OSArchitecture == Architecture.X64);
+                succeeded &= X86Base.X64.IsSupported;
             }
 
             return succeeded;
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_34587/Runtime_34587.csproj b/src/tests/JIT/Regression/JitBlue/Runtime_34587/Runtime_34587.csproj
index 5d49e8d49736fa..17923c1464d4fd 100644
--- a/src/tests/JIT/Regression/JitBlue/Runtime_34587/Runtime_34587.csproj
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_34587/Runtime_34587.csproj
@@ -10,4 +10,7 @@
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_38920/Runtime_38920.cs b/src/tests/JIT/Regression/JitBlue/Runtime_38920/Runtime_38920.cs
new file mode 100644
index 00000000000000..7a91e70711e42b
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_38920/Runtime_38920.cs
@@ -0,0 +1,121 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Diagnostics;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+
+class TestStructs
+{
+    static int exitStatus = 100;
+
+    struct StructA
+    {
+        public int a;
+    }
+
+    // Make both structs with >4 fields to prevent struct promoting and force byref passing.
+    struct CastFromStruct20
+    {
+        int z;
+        public StructA structField;
+        public int b;
+        public int c;
+        int q;
+    }
+
+    struct CastToStruct8
+    {
+        bool a;
+        bool b;
+        bool c;
+        bool d;
+        public int e; // Overlaps with b in CastFromStruct
+    }
+
+    struct CastToStruct12
+    {
+        bool a;
+        bool b;
+        bool c;
+        bool d;
+        public int e; // Overlaps with b in CastFromStruct
+        public int f; // Overlaps with c in CastFromStruct
+    }
+
+
+    // our src local var has to be an implicit byref, otherwise we won't try to recover struct handle from it.
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static void UnsafeCastFromAPrimitiveStructFieldToStruct(CastFromStruct20 impByRefStruct20, int b, int c)
+    {
+        CastToStruct8  to8  = new CastToStruct8();
+        CastToStruct12 to12 = new CastToStruct12();
+
+        // possible incorrect CSE def of impByRefStruct20.structField
+        //
+        to8 = Unsafe.As<StructA, CastToStruct8>(ref impByRefStruct20.structField);
+
+        for (int i =0; i<10; i++)
+        {
+            // possible incorrect CSE use of impByRefStruct20.structField
+            //
+            to12 = Unsafe.As<StructA, CastToStruct12>(ref impByRefStruct20.structField);
+        }
+
+        // Check that we modified to8.e correctly
+        if (to8.e != b)
+        {
+            Console.WriteLine("to8.e has the wrong value: " + to8.e + " expected " + b);
+            exitStatus = -1;
+        }
+
+        // Check that we modified to12.e correctly
+        if (to12.e != b)
+        {
+            Console.WriteLine("to12.e has the wrong value: " + to12.e + " expected " + b);
+            exitStatus = -1;
+        }
+
+        // Check that we modified to12.f correctly
+        if (to12.f != c)
+        {
+            Console.WriteLine("to12.f has the wrong value: " + to12.f + " expected " + c);
+            exitStatus = -1;
+        }
+    }
+
+    public static int Main()
+    {
+        int b = 1;
+        int c = 2;
+
+        CastFromStruct20 s = new CastFromStruct20();
+
+        s.b = b;
+        s.c = c;
+        UnsafeCastFromAPrimitiveStructFieldToStruct(s, b, c);
+
+        s.b = ++b;  // 2
+        s.c = ++c;  // 3
+        UnsafeCastFromAPrimitiveStructFieldToStruct(s, b, c);
+
+        b = b * b;
+        c = c * c;
+        s.b = b;    // 4
+        s.c = c;    // 9
+        UnsafeCastFromAPrimitiveStructFieldToStruct(s, b, c);
+
+        if (exitStatus == 100)
+        {
+            Console.WriteLine("Test Passed");
+        }
+        else
+        {
+            Console.WriteLine("FAILED");
+        }
+
+        return exitStatus;
+    }
+}
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_38920/Runtime_38920.csproj b/src/tests/JIT/Regression/JitBlue/Runtime_38920/Runtime_38920.csproj
new file mode 100644
index 00000000000000..e5292cce587680
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_38920/Runtime_38920.csproj
@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_39403/Runtime_39403.cs b/src/tests/JIT/Regression/JitBlue/Runtime_39403/Runtime_39403.cs
new file mode 100644
index 00000000000000..032f73d83221a4
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_39403/Runtime_39403.cs
@@ -0,0 +1,43 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Numerics;
+using System.Runtime.CompilerServices;
+
+// The test was showing silence bad codegen for a `LclFldAddr` node under HWINSTRINSIC(IND).
+
+class Runtime_39403
+{
+    struct Container
+    {
+        public Vector<int> Vector;
+        public int Integer;
+    }
+
+    static Vector<int> DoAThingByRef(ref Vector<int> s)
+    {
+        return s + Vector<int>.Zero;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static unsafe Vector<int> TestLclFldAddr()
+    {
+        Container container = default;
+        return DoAThingByRef(ref container.Vector);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static unsafe Vector<int> TestLclVarAddr()
+    {
+        Container container = default;
+        return DoAThingByRef(ref Unsafe.As<Container, Vector<int>>(ref container));
+    }
+
+    public static int Main()
+    {
+        Vector<int> v1 = TestLclFldAddr();
+        Vector<int> v2 = TestLclVarAddr();
+        System.Diagnostics.Debug.Assert(v1 == v2);
+        return 100;
+    }
+}
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_39403/Runtime_39403.csproj b/src/tests/JIT/Regression/JitBlue/Runtime_39403/Runtime_39403.csproj
new file mode 100644
index 00000000000000..5d49e8d49736fa
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_39403/Runtime_39403.csproj
@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType />
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_39424/Runtime_39424.il b/src/tests/JIT/Regression/JitBlue/Runtime_39424/Runtime_39424.il
new file mode 100644
index 00000000000000..ab35b013505e20
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_39424/Runtime_39424.il
@@ -0,0 +1,196 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+
+// The test was showing some rare cases of `IND(LCL_FLD_ADDR)` under HW intrinsic nodes.
+
+.assembly extern System.Runtime {}
+.assembly extern System.Runtime.Intrinsics {}
+.assembly extern System.Runtime.Extensions {}
+.assembly extern System.Numerics.Vectors {}
+.assembly extern System.Numerics.Extensions {}
+.assembly extern System.Runtime.CompilerServices.Unsafe {}
+
+.assembly Runtime_39424.exe {}
+
+.class private auto ansi beforefieldinit Runtime_39424
+       extends [System.Runtime]System.Object
+{
+  .class sequential ansi sealed nested private beforefieldinit Container
+         extends [System.Runtime]System.ValueType
+  {
+    .field public valuetype [System.Numerics.Vectors]System.Numerics.Vector`1<int32> Vector
+    .field public float64 Double
+  } // end of class Container
+
+  .method private hidebysig static float64 
+          TestLclFldAddrIntrinsicsRound(float64 d) cil managed noinlining
+  {
+    // Code size       30 (0x1e)
+    .maxstack  2
+    .locals init (valuetype Runtime_39424/Container V_0)
+    IL_0000:  ldloca.s   V_0
+    IL_0002:  initobj    Runtime_39424/Container
+    IL_0008:  ldloca.s   V_0
+    IL_000a:  ldarg.0
+    IL_000b:  stfld      float64 Runtime_39424/Container::Double
+    IL_0010:  ldloca.s   V_0
+    IL_0012:  ldflda     float64 Runtime_39424/Container::Double
+    IL_0017:  volatile. ldind.r8
+    IL_0018:  call       float64 [System.Runtime.Extensions]System.Math::Round(float64)
+    IL_001d:  ret
+  } // end of method Runtime_39424::TestLclFldAddrIntrinsicsRound
+  
+  .class sequential ansi sealed nested private beforefieldinit Vector128Wrapped
+         extends [System.Runtime]System.ValueType
+  {
+    .field public int8 i1
+    .field public int8 i2
+    .field public int8 i3
+    .field public int8 i4
+    .field public valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32> 'vector'
+  } // end of class Vector128Wrapped
+  
+  
+  .class sequential ansi sealed nested private beforefieldinit Vector128WrappedDouble
+         extends [System.Runtime]System.ValueType
+  {
+    .field private bool i1
+    .field private bool i2
+    .field private bool i3
+    .field private bool i4
+    .field public valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64> 'vector'
+  } // end of class Vector128WrappedDouble
+  
+  .method private hidebysig static float64 
+          TestLclFldAddrIntrinsicsSSE41_BlendVariable(float64 d) cil managed noinlining
+  {
+    // Code size       78 (0x4e)
+    .maxstack  3
+    .locals init (valuetype Runtime_39424/Vector128Wrapped V_0,
+             valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32>& V_1,
+             valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32> V_2)
+    IL_0000:  call       bool [System.Runtime.Intrinsics]System.Runtime.Intrinsics.X86.Sse41::get_IsSupported()
+    IL_0005:  brfalse.s  IL_0044
+
+    IL_0007:  ldc.i4.1
+    IL_0008:  call       valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32> [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128::Create(int32)
+    IL_000d:  ldloca.s   V_0
+    IL_000f:  initobj    Runtime_39424/Vector128Wrapped
+    IL_0015:  ldloca.s   V_0
+    IL_0017:  ldc.i4.2
+    IL_0018:  call       valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32> [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128::Create(int32)
+    IL_001d:  stfld      valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32> Runtime_39424/Vector128Wrapped::'vector'
+    IL_002a:  ldc.i4.3
+    IL_002b:  call       valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32> [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128::Create(int32)
+    IL_0030:  stloc.2
+    IL_0022:  ldloca.s   V_0
+    IL_0024:  ldflda     valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32> Runtime_39424/Vector128Wrapped::'vector'
+    IL_0032:  volatile. ldobj      valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32>
+    IL_0037:  ldloc.2
+    IL_0038:  call       valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32> [System.Runtime.Intrinsics]System.Runtime.Intrinsics.X86.Sse41::BlendVariable(valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32>,
+                                                                                                                                                                                         valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32>,
+                                                                                                                                                                                         valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<int32>)
+    IL_003d:  call       !!0 [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128::ToScalar<int32>(valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<!!0>)
+    IL_0042:  conv.r8
+    IL_0043:  ret
+
+    IL_0044:  ldc.r8     100.
+    IL_004d:  ret
+  } // end of method Runtime_39424::TestLclFldAddrIntrinsicsSSE41_BlendVariable
+  
+  .method private hidebysig static float64 
+          TestLclFldAddrIntrinsicsFMA_MulipluAddScalar() cil managed noinlining
+  {
+    // Code size       101 (0x65)
+    .maxstack  3
+    .locals init (valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64> V_0,
+             valuetype Runtime_39424/Vector128WrappedDouble V_1,
+             valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64>& V_2)
+    IL_0000:  call       bool [System.Runtime.Intrinsics]System.Runtime.Intrinsics.X86.Fma::get_IsSupported()
+    IL_0005:  brfalse.s  IL_005b
+
+    IL_0007:  ldc.r8     1.
+    IL_0010:  call       valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64> [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128::Create(float64)
+    IL_0015:  ldc.r8     3.
+    IL_001e:  call       valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64> [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128::Create(float64)
+    IL_0023:  stloc.0
+    IL_0024:  ldloca.s   V_1
+    IL_0026:  initobj    Runtime_39424/Vector128WrappedDouble
+    IL_002c:  ldloca.s   V_1
+    IL_002e:  ldc.r8     2.
+    IL_0037:  call       valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64> [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128::Create(float64)
+    IL_003c:  stfld      valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64> Runtime_39424/Vector128WrappedDouble::'vector'
+    IL_0049:  ldloc.0
+    IL_0041:  ldloca.s   V_1
+    IL_0043:  ldflda     valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64> Runtime_39424/Vector128WrappedDouble::'vector'
+    IL_004b:  ldobj      valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64>
+    IL_0050:  call       valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64> [System.Runtime.Intrinsics]System.Runtime.Intrinsics.X86.Fma::MultiplyAddScalar(valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64>,
+                                                                                                                                                                                             valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64>,
+                                                                                                                                                                                             valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<float64>)
+    IL_0055:  call       !!0 [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128::ToScalar<float64>(valuetype [System.Runtime.Intrinsics]System.Runtime.Intrinsics.Vector128`1<!!0>)
+    IL_005a:  ret
+
+    IL_005b:  ldc.r8     100.
+    IL_0064:  ret
+  } // end of method Runtime_39424::TestLclFldAddrIntrinsicsFMA_MulipluAddScalar
+
+
+  .class sequential ansi sealed nested private beforefieldinit IntsWrapped
+         extends [System.Runtime]System.ValueType
+  {
+    .field public int32 i1
+    .field public int32 i2
+    .field public int32 i3
+    .field public int32 i4
+    .field public int32 i5
+  } // end of class IntsWrapped
+
+  .method public hidebysig static int32  TestLclFldAddr_BinOp(int32 a) cil managed noinlining
+  {
+    // Code size       21 (0x15)
+    .maxstack  2
+    .locals init (valuetype Runtime_39424/IntsWrapped V_0,
+             int32& V_1)
+    IL_0000:  ldloca.s   V_0
+    IL_0002:  initobj    Runtime_39424/IntsWrapped
+    IL_0010:  ldarg.0
+    IL_0008:  ldloca.s   V_0
+    IL_000a:  ldflda     int32 Runtime_39424/IntsWrapped::i4
+    IL_0012:  volatile. ldind.i4
+    IL_0013:  add
+    IL_0014:  ret
+  } // end of method Runtime_39424::TestLclFldAddr_BinOp
+
+  .method public hidebysig static int32  Main() cil managed
+  {
+    .entrypoint
+    // Code size       18 (0x12)
+    .maxstack  8
+    IL_0000:  ldc.r8     1.
+    IL_0009:  call       float64 Runtime_39424::TestLclFldAddrIntrinsicsRound(float64)
+    IL_000e:  pop
+    IL_0010:  ldc.r8     2.
+    IL_0011:  call       float64 Runtime_39424::TestLclFldAddrIntrinsicsSSE41_BlendVariable(float64)
+    IL_0012:  pop
+    IL_0013:  call       float64 Runtime_39424::TestLclFldAddrIntrinsicsFMA_MulipluAddScalar()
+    IL_0014:  pop
+              ldc.i4.1
+              call       int32 Runtime_39424::TestLclFldAddr_BinOp(int32)
+              pop
+    
+    IL_0015:  ldc.i4.s   100
+    IL_0016:  ret
+  } // end of method Runtime_39424::Main
+
+  .method public hidebysig specialname rtspecialname 
+          instance void  .ctor() cil managed
+  {
+    // Code size       7 (0x7)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  call       instance void [System.Runtime]System.Object::.ctor()
+    IL_0006:  ret
+  } // end of method Runtime_39424::.ctor
+
+} // end of class Runtime_39424
\ No newline at end of file
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_39424/Runtime_39424.ilproj b/src/tests/JIT/Regression/JitBlue/Runtime_39424/Runtime_39424.ilproj
new file mode 100644
index 00000000000000..da6159dc88d6f2
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_39424/Runtime_39424.ilproj
@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk.IL">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <CLRTestPriority>1</CLRTestPriority>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <PropertyGroup>
+  <!-- Disable CSE to protect fragile `OBJ(ADDR(LCL_FIELD)` constructions. -->
+    <CLRTestBatchPreCommands><![CDATA[
+$(CLRTestBatchPreCommands)
+set COMPlus_JitNoCSE=1
+]]></CLRTestBatchPreCommands>
+    <BashCLRTestPreCommands><![CDATA[
+$(BashCLRTestPreCommands)
+export COMPlus_JitNoCSE=1
+]]></BashCLRTestPreCommands>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).il" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_39581/Runtime_39581.il b/src/tests/JIT/Regression/JitBlue/Runtime_39581/Runtime_39581.il
new file mode 100644
index 00000000000000..5288e150809573
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_39581/Runtime_39581.il
@@ -0,0 +1,174 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+//
+// The test exposes the issue when:
+//
+//   1) methods Callee and Caller have the following structure:
+//
+//      S Callee() { produce and return an instance of S }
+//
+//      S Caller() { return Callee(); }
+//
+//   2) S is a value type with non-GC fields and has such size that it
+//      must be passed via return buffer;
+//
+//   3) call to Callee is transformed to tail call via helper:
+//
+//      S result;
+//      DispatchTailCalls(&IL_STUB_CallTailCallTarget, (IntPtr)&result, _AddressOfReturnAddress());
+//      return result;
+//
+//   4) Caller is invoked via Reflection.
+//
+// During morph phase the JIT discovers that both Caller and Callee have the return buffer arguments and
+// falsely assumes that the value can be directly passed from Caller to Callee.
+// Here is a problem: DispatchTailCalls helper expects the RetValue argument (in this case, return buffer argument)
+// to always point to the stack. However, during a reflection call the return buffer for S value type can be placed on the GC heap (see condition 2 above).
+// As a consequence, when GC is called at DispatchTailCalls the object corresponding to the return value buffer can be moved,
+// but the pointers passed to DispatchTailCalls will not be updated that leads to Callee using the non-updated location when writing its return value.
+//
+// Note: you will find below that Caller uses localloc - this is done in order to prevent a call to Caller to be transformed into fast tail call.
+// Note: COMPlus_GCStress=3 or COMPlus_GCStress=C are required in order to reliably expose this issue.
+
+.assembly extern System.Runtime
+{
+}
+
+.assembly Runtime_39581
+{
+}
+
+.class private sequential ansi sealed beforefieldinit int32x8
+       extends [System.Runtime]System.ValueType
+{
+  .field public int32 a
+  .field public int32 b
+  .field public int32 c
+  .field public int32 d
+  .field public int32 e
+  .field public int32 f
+  .field public int32 g
+  .field public int32 h
+}
+
+.class private auto ansi beforefieldinit Runtime_39581.Program
+       extends [System.Runtime]System.Object
+{
+  .method private hidebysig static valuetype int32x8 Callee(uint8* arg0) cil managed noinlining
+  {
+    .maxstack  2
+    .locals init (valuetype int32x8 V_0)
+    IL_0000:  ldloca.s   V_0
+    IL_0002:  initobj    int32x8
+    IL_0008:  ldloca.s   V_0
+    IL_000a:  ldc.i4.0
+    IL_000b:  stfld      int32 int32x8::a
+    IL_0010:  ldloca.s   V_0
+    IL_0012:  ldc.i4.1
+    IL_0013:  stfld      int32 int32x8::b
+    IL_0018:  ldloca.s   V_0
+    IL_001a:  ldc.i4.2
+    IL_001b:  stfld      int32 int32x8::c
+    IL_0020:  ldloca.s   V_0
+    IL_0022:  ldc.i4.3
+    IL_0023:  stfld      int32 int32x8::d
+    IL_0028:  ldloca.s   V_0
+    IL_002a:  ldc.i4.4
+    IL_002b:  stfld      int32 int32x8::e
+    IL_0030:  ldloca.s   V_0
+    IL_0032:  ldc.i4.5
+    IL_0033:  stfld      int32 int32x8::f
+    IL_0038:  ldloca.s   V_0
+    IL_003a:  ldc.i4.6
+    IL_003b:  stfld      int32 int32x8::g
+    IL_0040:  ldloca.s   V_0
+    IL_0042:  ldc.i4.7
+    IL_0043:  stfld      int32 int32x8::h
+    IL_0048:  ldloc.0
+    IL_0049:  ret
+  }
+
+  .method public hidebysig static valuetype int32x8 Caller(int32 arg0) cil managed noinlining
+  {
+    .maxstack  1
+    IL_0000:  ldarg.0
+    IL_0001:  conv.u
+    IL_0002:  localloc
+    IL_0004:  tail.
+    IL_0006:  call       valuetype int32x8 Runtime_39581.Program::Callee(uint8*)
+    IL_000b:  ret
+  }
+
+  .method private hidebysig static int32 Main(string[] args) cil managed
+  {
+    .entrypoint
+    .maxstack  6
+    .locals init (valuetype int32x8 V_0)
+    IL_0000:  ldtoken    Runtime_39581.Program
+    IL_0005:  call       class [System.Runtime]System.Type [System.Runtime]System.Type::GetTypeFromHandle(valuetype [System.Runtime]System.RuntimeTypeHandle)
+    IL_000a:  ldstr      "Caller"
+    IL_000f:  ldc.i4.1
+    IL_0010:  newarr     [System.Runtime]System.Type
+    IL_0015:  dup
+    IL_0016:  ldc.i4.0
+    IL_0017:  ldtoken    [System.Runtime]System.Int32
+    IL_001c:  call       class [System.Runtime]System.Type [System.Runtime]System.Type::GetTypeFromHandle(valuetype [System.Runtime]System.RuntimeTypeHandle)
+    IL_0021:  stelem.ref
+    IL_0022:  call       instance class [System.Runtime]System.Reflection.MethodInfo [System.Runtime]System.Type::GetMethod(string, class [System.Runtime]System.Type[])
+    IL_0027:  ldnull
+    IL_0028:  ldc.i4.1
+    IL_0029:  newarr     [System.Runtime]System.Object
+    IL_002e:  dup
+    IL_002f:  ldc.i4.0
+    IL_0030:  ldc.i4.1
+    IL_0031:  box        [System.Runtime]System.Int32
+    IL_0036:  stelem.ref
+    IL_0037:  callvirt   instance object [System.Runtime]System.Reflection.MethodBase::Invoke(object, object[])
+    IL_003c:  unbox.any  int32x8
+    IL_0041:  stloc.0
+    IL_0042:  ldloc.0
+    IL_0043:  ldfld      int32 int32x8::a
+    IL_0048:  brtrue.s   IL_008c
+
+    IL_004a:  ldloc.0
+    IL_004b:  ldfld      int32 int32x8::b
+    IL_0050:  ldc.i4.1
+    IL_0051:  bne.un.s   IL_008c
+
+    IL_0053:  ldloc.0
+    IL_0054:  ldfld      int32 int32x8::c
+    IL_0059:  ldc.i4.2
+    IL_005a:  bne.un.s   IL_008c
+
+    IL_005c:  ldloc.0
+    IL_005d:  ldfld      int32 int32x8::d
+    IL_0062:  ldc.i4.3
+    IL_0063:  bne.un.s   IL_008c
+
+    IL_0065:  ldloc.0
+    IL_0066:  ldfld      int32 int32x8::e
+    IL_006b:  ldc.i4.4
+    IL_006c:  bne.un.s   IL_008c
+
+    IL_006e:  ldloc.0
+    IL_006f:  ldfld      int32 int32x8::f
+    IL_0074:  ldc.i4.5
+    IL_0075:  bne.un.s   IL_008c
+
+    IL_0077:  ldloc.0
+    IL_0078:  ldfld      int32 int32x8::g
+    IL_007d:  ldc.i4.6
+    IL_007e:  bne.un.s   IL_008c
+
+    IL_0080:  ldloc.0
+    IL_0081:  ldfld      int32 int32x8::h
+    IL_0086:  ldc.i4.7
+    IL_0087:  bne.un.s   IL_008c
+
+    IL_0089:  ldc.i4.s   100
+    IL_008b:  ret
+
+    IL_008c:  ldc.i4.0
+    IL_008d:  ret
+  }
+}
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_39581/Runtime_39581.ilproj b/src/tests/JIT/Regression/JitBlue/Runtime_39581/Runtime_39581.ilproj
new file mode 100644
index 00000000000000..50758ca86d9cc1
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_39581/Runtime_39581.ilproj
@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk.IL">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).il" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_39737/Runtime_39737.cs b/src/tests/JIT/Regression/JitBlue/Runtime_39737/Runtime_39737.cs
new file mode 100644
index 00000000000000..226404918b16d2
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_39737/Runtime_39737.cs
@@ -0,0 +1,26 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// The test was deleting the hardware intrinsic leaving unconsumed GT_OBJ on top of the stack
+// that was leading to an assert failure.
+
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.X86;
+using System;
+
+class Runtime_39403
+{ 
+    public static int Main()
+    {
+        if (Sse41.IsSupported)
+        {
+            Vector128<int> left = Vector128.Create(1);
+            Vector128<int> right = Vector128.Create(2);
+            ref var rightRef = ref right;
+            Vector128<int> mask = Vector128.Create(3);
+            Sse41.BlendVariable(left, rightRef, mask);
+        }
+        return 100;
+    }
+}
+
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_39737/Runtime_39737.csproj b/src/tests/JIT/Regression/JitBlue/Runtime_39737/Runtime_39737.csproj
new file mode 100644
index 00000000000000..5d49e8d49736fa
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_39737/Runtime_39737.csproj
@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType />
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_40440/Runtime_40440.cs b/src/tests/JIT/Regression/JitBlue/Runtime_40440/Runtime_40440.cs
new file mode 100644
index 00000000000000..000045a5f3d89d
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_40440/Runtime_40440.cs
@@ -0,0 +1,175 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using System.Diagnostics;
+using System.Runtime.Intrinsics;
+using System.Security.Cryptography;
+
+class Runtime_40440
+{
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static bool UseArrayElementAsCallArgument<T>(T[,,] a, T b)
+    {
+        return G(b, a[1, 2, 3]);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static bool G<T>(T a, T b)
+    {
+        if (typeof(T) == typeof(Vector<float>))
+        {
+            return (Vector<float>)(object)a == (Vector<float>)(object)b;
+        }
+        else if (typeof(T) == typeof(Vector2))
+        {
+            return (Vector2)(object)a == (Vector2)(object)b;
+        }
+        else if (typeof(T) == typeof(Vector3))
+        {
+            return (Vector3)(object)a == (Vector3)(object)b;
+        }
+        else if (typeof(T) == typeof(Vector4))
+        {
+            return (Vector4)(object)a == (Vector4)(object)b;
+        }
+        else if (typeof(T) == typeof(Vector64<float>))
+        {
+            return a.Equals(b);
+        }
+        else if (typeof(T) == typeof(SmallStruct))
+        {
+            return a.Equals(b);
+        }
+        else if (typeof(T) == typeof(LargeStruct))
+        {
+            return a.Equals(b);
+        }
+        return false;
+    }
+
+    static bool CheckVectorFloat()
+    {
+        var v = new Vector<float>[4, 4, 4];
+        var e = new Vector<float>(33f);
+        v[1, 2, 3] = e;
+        return UseArrayElementAsCallArgument(v, e);
+    }
+    static bool CheckVector2()
+    {
+        var v = new Vector2[4, 4, 4];
+        var e = new Vector2(33f);
+        v[1, 2, 3] = e;
+        return UseArrayElementAsCallArgument(v, e);
+    }
+
+    static bool CheckVector3()
+    {
+        var v = new Vector3[4, 4, 4];
+        var e = new Vector3(33f);
+        v[1, 2, 3] = e;
+        return UseArrayElementAsCallArgument(v, e);
+    }
+
+    static bool CheckVector4()
+    {
+        var v = new Vector3[4, 4, 4];
+        var e = new Vector3(33f);
+        v[1, 2, 3] = e;
+        return UseArrayElementAsCallArgument(v, e);
+    }
+
+    static bool CheckVector64()
+    {
+        var v = new Vector64<float>[4, 4, 4];
+        var e = Vector64.Create(33f);
+        v[1, 2, 3] = e;
+        return UseArrayElementAsCallArgument(v, e);
+    }
+
+    struct SmallStruct
+    {
+        float f;
+
+        public SmallStruct(float f)
+        {
+            this.f = f;
+        }
+
+        public override bool Equals(object obj)
+        {
+            if (!(obj is SmallStruct))
+            {
+                return false;
+            }
+            return f == ((SmallStruct)obj).f;
+        }
+    }
+
+    static bool CheckSmallStruct()
+    {
+        var v = new SmallStruct[4, 4, 4];
+        var e = new SmallStruct(33f);
+        v[1, 2, 3] = e;
+        return UseArrayElementAsCallArgument(v, e);
+    }
+
+    struct LargeStruct
+    {
+        float f1;
+        float f2;
+        float f3;
+        float f4;
+        float f5;
+
+        public LargeStruct(float f)
+        {
+            f1 = f;
+            f2 = f;
+            f3 = f;
+            f4 = f;
+            f5 = f;
+        }
+
+        public override bool Equals(object obj)
+        {
+            if (!(obj is LargeStruct))
+            {
+                return false;
+            }
+            LargeStruct s2 = (LargeStruct)obj;
+            return (f1 == s2.f1) && (f2 == s2.f2) && (f3 == s2.f3) && (f4 == s2.f4) && (f5 == s2.f5);
+        }
+    }
+
+    static bool CheckBigStruct()
+    {
+        var v = new LargeStruct[4, 4, 4];
+        var e = new LargeStruct(33f);
+        v[1, 2, 3] = e;
+        return UseArrayElementAsCallArgument(v, e);
+    }
+
+    public static int Main()
+    {
+        bool f = true;
+        f &= CheckVectorFloat();
+        Debug.Assert(f);
+        f &= CheckVector2();
+        Debug.Assert(f);
+        f &= CheckVector3();
+        Debug.Assert(f);
+        f &= CheckVector4();
+        Debug.Assert(f);
+        f &= CheckVector64();
+        Debug.Assert(f);
+        f &= CheckSmallStruct();
+        Debug.Assert(f);
+        f &= CheckBigStruct();
+        Debug.Assert(f);
+
+        return f ? 100 : 0;
+    }
+}
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_40440/Runtime_40440.csproj b/src/tests/JIT/Regression/JitBlue/Runtime_40440/Runtime_40440.csproj
new file mode 100644
index 00000000000000..986494e092b5aa
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_40440/Runtime_40440.csproj
@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType />
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/JIT/opt/ObjectStackAllocation/ObjectStackAllocationTests.cs b/src/tests/JIT/opt/ObjectStackAllocation/ObjectStackAllocationTests.cs
index 1c068630cc4776..639c44a333cb81 100644
--- a/src/tests/JIT/opt/ObjectStackAllocation/ObjectStackAllocationTests.cs
+++ b/src/tests/JIT/opt/ObjectStackAllocation/ObjectStackAllocationTests.cs
@@ -110,7 +110,7 @@ public static int Main()
                 Console.WriteLine("GCStress is enabled");
                 expectedAllocationKind = AllocationKind.Undefined;
             }
-            else if (!SPCOptimizationsEnabled()) {
+            else if (!SPCOptimizationsEnabled() && !Crossgen2Test()) {
                 Console.WriteLine("System.Private.CoreLib.dll optimizations are disabled");
                 expectedAllocationKind = AllocationKind.Heap;
             }
@@ -181,6 +181,12 @@ static bool GCStressEnabled()
             return Environment.GetEnvironmentVariable("COMPlus_GCStress") != null;
         }
 
+        static bool Crossgen2Test()
+        {
+            // CrossGen2 doesn't respect the debuggable attribute
+            return Environment.GetEnvironmentVariable("RunCrossGen2") != null;
+        }
+
         static void CallTestAndVerifyAllocation(Test test, int expectedResult, AllocationKind expectedAllocationsKind)
         {
             long allocatedBytesBefore = GC.GetAllocatedBytesForCurrentThread();
diff --git a/src/tests/JIT/opt/ObjectStackAllocation/ObjectStackAllocationTests.csproj b/src/tests/JIT/opt/ObjectStackAllocation/ObjectStackAllocationTests.csproj
index 655a42cc4fbd21..bfd9e534b56156 100644
--- a/src/tests/JIT/opt/ObjectStackAllocation/ObjectStackAllocationTests.csproj
+++ b/src/tests/JIT/opt/ObjectStackAllocation/ObjectStackAllocationTests.csproj
@@ -10,6 +10,7 @@
     <Compile Include="$(MSBuildProjectName).cs" />
   </ItemGroup>
   <PropertyGroup>
+    <CrossGen2TestExtraArguments>--codegenopt JitObjectStackAllocation=1</CrossGen2TestExtraArguments>
     <CLRTestBatchPreCommands><![CDATA[
 $(CLRTestBatchPreCommands)
 set COMPlus_TieredCompilation=0
diff --git a/src/tests/Loader/CollectibleAssemblies/ByRefLocals/ByRefLocals.cs b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/ByRefLocals.cs
new file mode 100644
index 00000000000000..834bc472497fb0
--- /dev/null
+++ b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/ByRefLocals.cs
@@ -0,0 +1,142 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.IO;
+using System.Reflection;
+using System.Reflection.Emit;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Runtime.Loader;
+
+class Program
+{
+    static int Main(string[] args)
+    {
+        var holdResult = HoldAssembliesAliveThroughByRefFields(out GCHandle gch1, out GCHandle gch2);
+        if (holdResult != 100)
+            return holdResult;
+
+        // At this point, nothing should keep the collectible assembly alive
+        // Loop for a bit forcing the GC to run, and then it should be freed
+        for (int i = 0; i < 10; i++)
+        {
+            GC.Collect(2);
+            GC.WaitForPendingFinalizers();
+        }
+
+        if (gch1.Target != null)
+        {
+            return 3;
+        }
+        if (gch2.Target != null)
+        {
+            return 4;
+        }
+
+        return 100;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static int HoldAssembliesAliveThroughByRefFields(out GCHandle gch1, out GCHandle gch2)
+    {
+        // ThreadStatic lifetime check. Here we don't require the actual assembly to remain loaded, but we do require the field to remain accessible
+        var spanThreadStatic = LoadAssemblyThreadStatic(out GCHandle gchThreadStatic);
+        GC.Collect(2);
+        GC.WaitForPendingFinalizers();
+        GC.Collect(2);
+        GC.WaitForPendingFinalizers();
+        GC.Collect(2);
+        GC.WaitForPendingFinalizers();
+
+        var span1 = LoadAssembly(out gch1);
+        GC.Collect(2);
+        GC.WaitForPendingFinalizers();
+        GC.Collect(2);
+        GC.WaitForPendingFinalizers();
+        GC.Collect(2);
+        GC.WaitForPendingFinalizers();
+        var span2 = CreateAssemblyDynamically(out gch2);
+        for (int i = 0; i < 10; i++)
+        {
+            Console.WriteLine(span1[0]);
+            Console.WriteLine(span2[0]);
+            Console.WriteLine(spanThreadStatic[0]);
+            GC.Collect(2);
+            GC.WaitForPendingFinalizers();
+            if (gch1.Target == null)
+            {
+                return 1;
+            }
+            if (gch2.Target == null)
+            {
+                return 2;
+            }
+            if (spanThreadStatic[0] != 7)
+            {
+                Console.WriteLine($"spanThreadStatic[0] = {spanThreadStatic[0]}");
+                return 5;
+            }
+        }
+
+        return 100;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static ReadOnlySpan<byte> LoadAssembly(out GCHandle gchToAssembly)
+    {
+        var alc = new AssemblyLoadContext("test", isCollectible: true);
+        var a = alc.LoadFromAssemblyPath(Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), "Unloaded.dll"));
+        gchToAssembly = GCHandle.Alloc(a, GCHandleType.WeakTrackResurrection);
+
+        var spanAccessor = (IReturnSpan)Activator.CreateInstance(a.GetType("SpanAccessor"));
+
+        alc.Unload();
+
+        return spanAccessor.GetSpan();
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static ReadOnlySpan<byte> LoadAssemblyThreadStatic(out GCHandle gchToAssembly)
+    {
+        var alc = new AssemblyLoadContext("test", isCollectible: true);
+        var a = alc.LoadFromAssemblyPath(Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), "Unloaded.dll"));
+        gchToAssembly = GCHandle.Alloc(a, GCHandleType.WeakTrackResurrection);
+
+        var spanAccessor = (IReturnSpan)Activator.CreateInstance(a.GetType("ThreadStaticSpanAccessor"));
+
+        alc.Unload();
+
+        return spanAccessor.GetSpan();
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static ReadOnlySpan<byte> CreateAssemblyDynamically(out GCHandle gchToAssembly)
+    {
+        AssemblyBuilder ab =
+            AssemblyBuilder.DefineDynamicAssembly(
+            new AssemblyName("tempAssembly"),
+            AssemblyBuilderAccess.RunAndCollect);
+        ModuleBuilder modb = ab.DefineDynamicModule("tempAssembly.dll");
+
+        var byRefAccessField = modb.DefineInitializedData("RawBytes", new byte[] {1,2,3,4,5}, FieldAttributes.Public | FieldAttributes.Static);
+        modb.CreateGlobalFunctions();
+
+        TypeBuilder tb = modb.DefineType("GetSpanType", TypeAttributes.Class, typeof(object), new Type[]{typeof(IReturnSpan)});
+        var mb = tb.DefineMethod("GetSpan", MethodAttributes.Public | MethodAttributes.HideBySig | MethodAttributes.Virtual, typeof(ReadOnlySpan<byte>), new Type[]{});
+        ILGenerator myMethodIL = mb.GetILGenerator();
+        myMethodIL.Emit(OpCodes.Ldsflda, byRefAccessField);
+        myMethodIL.Emit(OpCodes.Ldc_I4_4);
+        myMethodIL.Emit(OpCodes.Newobj, typeof(ReadOnlySpan<byte>).GetConstructor(new Type[]{typeof(void*), typeof(int)}));
+        myMethodIL.Emit(OpCodes.Ret);
+
+        var getSpanType = tb.CreateType();
+
+        gchToAssembly = GCHandle.Alloc(getSpanType, GCHandleType.WeakTrackResurrection);
+
+        var spanAccessor = (IReturnSpan)Activator.CreateInstance(getSpanType);
+
+        return spanAccessor.GetSpan();
+    }
+
+}
\ No newline at end of file
diff --git a/src/tests/Loader/CollectibleAssemblies/ByRefLocals/ByRefLocals.csproj b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/ByRefLocals.csproj
new file mode 100644
index 00000000000000..7cde272f10779c
--- /dev/null
+++ b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/ByRefLocals.csproj
@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <OutputType>Exe</OutputType>
+    <CLRTestKind>BuildAndRun</CLRTestKind>
+    <CLRTestPriority>0</CLRTestPriority>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="Unloaded.csproj" />
+    <ProjectReference Include="SpanAccessor.csproj" />
+    <Compile Include="ByRefLocals.cs" />
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestAssemblyFixture.cs b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/SpanAccessor.cs
similarity index 52%
rename from src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestAssemblyFixture.cs
rename to src/tests/Loader/CollectibleAssemblies/ByRefLocals/SpanAccessor.cs
index 75dddd23674b71..c05b5056798eb1 100644
--- a/src/libraries/Common/tests/Extensions/TestingUtils/Microsoft.AspNetCore.Testing/test/TestAssemblyFixture.cs
+++ b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/SpanAccessor.cs
@@ -1,10 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-namespace Microsoft.AspNetCore.Testing
+using System;
+
+public interface IReturnSpan
 {
-    public class TestAssemblyFixture
-    {
-        public int Count { get; set; }
-    }
-}
+    ReadOnlySpan<byte> GetSpan();
+}
\ No newline at end of file
diff --git a/src/tests/Loader/CollectibleAssemblies/ByRefLocals/SpanAccessor.csproj b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/SpanAccessor.csproj
new file mode 100644
index 00000000000000..88e99d96176a98
--- /dev/null
+++ b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/SpanAccessor.csproj
@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <OutputType>Library</OutputType>
+    <CLRTestKind>BuildOnly</CLRTestKind>
+    <CLRTestPriority>0</CLRTestPriority>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="SpanAccessor.cs" />
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/src/tests/Loader/CollectibleAssemblies/ByRefLocals/Unloaded.cs b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/Unloaded.cs
new file mode 100644
index 00000000000000..3f2615e99a02bd
--- /dev/null
+++ b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/Unloaded.cs
@@ -0,0 +1,26 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Runtime.CompilerServices;
+
+public class SpanAccessor : IReturnSpan
+{
+    public static ReadOnlySpan<byte> RawData => new byte[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
+
+    public ReadOnlySpan<byte> GetSpan()
+    {
+        return RawData;
+    }
+}
+
+public class ThreadStaticSpanAccessor : IReturnSpan
+{
+    [ThreadStatic]
+    public static byte ThreadStaticByte = 7;
+
+    public unsafe ReadOnlySpan<byte> GetSpan()
+    {
+        return new ReadOnlySpan<byte>(Unsafe.AsPointer(ref ThreadStaticByte), 1);
+    }
+}
\ No newline at end of file
diff --git a/src/tests/Loader/CollectibleAssemblies/ByRefLocals/Unloaded.csproj b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/Unloaded.csproj
new file mode 100644
index 00000000000000..6d13ecf2427e1c
--- /dev/null
+++ b/src/tests/Loader/CollectibleAssemblies/ByRefLocals/Unloaded.csproj
@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <OutputType>Library</OutputType>
+    <CLRTestKind>BuildOnly</CLRTestKind>
+    <CLRTestPriority>0</CLRTestPriority>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="SpanAccessor.csproj" />
+    <Compile Include="Unloaded.cs" />
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/src/tests/Loader/classloader/MethodImpl/CovariantReturns/UnitTest/CompatibleWithTest.ilproj b/src/tests/Loader/classloader/MethodImpl/CovariantReturns/UnitTest/CompatibleWithTest.ilproj
index 78d81b01d73e37..2a6c4198b627a9 100644
--- a/src/tests/Loader/classloader/MethodImpl/CovariantReturns/UnitTest/CompatibleWithTest.ilproj
+++ b/src/tests/Loader/classloader/MethodImpl/CovariantReturns/UnitTest/CompatibleWithTest.ilproj
@@ -3,8 +3,6 @@
     <OutputType>Exe</OutputType>
     <CLRTestKind>BuildAndRun</CLRTestKind>
     <CLRTestPriority>0</CLRTestPriority>
-    <!-- Disable for ilasm round-trip test failure: https://github.com/dotnet/runtime/issues/38508 -->
-    <IlasmRoundTripIncompatible>true</IlasmRoundTripIncompatible>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="CompatibleWithTest.il" />
diff --git a/src/tests/Loader/classloader/explicitlayout/Regressions/13362/Github13362.cs b/src/tests/Loader/classloader/explicitlayout/Regressions/13362/Github13362.cs
new file mode 100644
index 00000000000000..183c286b3553cf
--- /dev/null
+++ b/src/tests/Loader/classloader/explicitlayout/Regressions/13362/Github13362.cs
@@ -0,0 +1,56 @@
+using System;
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+namespace ClrIssueRepro
+{
+    // If you remove '[StructLayout(LayoutKind.Sequential)]', you get:
+    // Unhandled exception. System.TypeLoadException: 
+    // Could not load type 'ClrIssueRepro.GenInt' from assembly '...' 
+    //    because the format is invalid.
+    //  at ClrIssueRepro.Program.Main(String[] args)
+    [StructLayout(LayoutKind.Sequential)]
+    public class GenBase<T>
+    {
+        public string _string0 = "string0";
+        public string _string1 = "string1";
+    }
+
+    [StructLayout(LayoutKind.Explicit)]
+    public class GenInt : GenBase<int>
+    {
+        // Commenting out either one of these fields fixes things!?
+        [FieldOffset(0)] public string _sstring0 = "string0";
+        [FieldOffset(16)] public string _sstring1 = "string1";
+    }
+
+    // This works! (it's GenInt with [StructLayout(LayoutKind.Explicit)] and [FieldOffset(..)] removed)
+    public class GenIntNormal : GenBase<int>
+    {
+        public string _sstring0 = "string0";
+        public string _sstring1 = "string1";
+    }
+
+    class Program
+    {
+        static int Main(string[] args)
+        {
+            // If you comment this line out, you get
+            //    Unhandled exception. System.TypeLoadException: 
+            //    Could not load type 'ClrIssueRepro.GenInt' from assembly '...'
+            //    at ClrIssueRepro.Program.Main(String[] args)
+            // in Debug and Release builds?!
+            Type type = typeof(GenInt);
+
+            object instance = new GenInt();
+
+            // GenIntNormal has the same fields as GenInt, but has
+            // [StructLayout(LayoutKind.Explicit)] and [FieldOffset(..)] REMOVED
+            //object instance = new GenIntNormal(); // works fine!!
+
+            string instType = instance.GetType().ToString();
+            Console.WriteLine(instType);
+            return "ClrIssueRepro.GenInt" == instType ? 100 : 0;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/tests/CoreMangLib/system/type/TypeIsByRefImpl.csproj b/src/tests/Loader/classloader/explicitlayout/Regressions/13362/Github13362.csproj
similarity index 60%
rename from src/tests/CoreMangLib/system/type/TypeIsByRefImpl.csproj
rename to src/tests/Loader/classloader/explicitlayout/Regressions/13362/Github13362.csproj
index 739b412a869c59..0a3e92e6e96334 100644
--- a/src/tests/CoreMangLib/system/type/TypeIsByRefImpl.csproj
+++ b/src/tests/Loader/classloader/explicitlayout/Regressions/13362/Github13362.csproj
@@ -1,14 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <OutputType>Exe</OutputType>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <OutputType>Exe</OutputType>
     <CLRTestKind>BuildAndRun</CLRTestKind>
     <CLRTestPriority>1</CLRTestPriority>
   </PropertyGroup>
   <ItemGroup>
-    <Compile Include="typeisbyrefimpl.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
+    <Compile Include="Github13362.cs" />
   </ItemGroup>
 </Project>
diff --git a/src/tests/Loader/classloader/generics/Variance/Interfaces/NoVarianceCheckForStaticMethods.il b/src/tests/Loader/classloader/generics/Variance/Interfaces/NoVarianceCheckForStaticMethods.il
new file mode 100644
index 00000000000000..fdb11f2401ec8a
--- /dev/null
+++ b/src/tests/Loader/classloader/generics/Variance/Interfaces/NoVarianceCheckForStaticMethods.il
@@ -0,0 +1,95 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Metadata version: v4.0.30319
+.assembly extern System.Runtime
+{
+  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )                         // .?_....:
+  .ver 4:2:2:0
+}
+.assembly extern System.Console
+{
+  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )                         // .?_....:
+  .ver 4:1:2:0
+}
+.assembly ConsoleApp5
+{
+  .custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilationRelaxationsAttribute::.ctor(int32) = ( 01 00 08 00 00 00 00 00 ) 
+  .custom instance void [System.Runtime]System.Runtime.CompilerServices.RuntimeCompatibilityAttribute::.ctor() = ( 01 00 01 00 54 02 16 57 72 61 70 4E 6F 6E 45 78   // ....T..WrapNonEx
+                                                                                                                   63 65 70 74 69 6F 6E 54 68 72 6F 77 73 01 )       // ceptionThrows.
+
+  // --- The following custom attribute is added automatically, do not uncomment -------
+  //  .custom instance void [System.Runtime]System.Diagnostics.DebuggableAttribute::.ctor(valuetype [System.Runtime]System.Diagnostics.DebuggableAttribute/DebuggingModes) = ( 01 00 07 01 00 00 00 00 ) 
+
+  .hash algorithm 0x00008004
+  .ver 1:0:0:0
+}
+.module ConsoleApp5.dll
+// MVID: {580B623A-FB1A-403C-8F9C-8DB0E42D429C}
+.imagebase 0x00400000
+.file alignment 0x00000200
+.stackreserve 0x00100000
+.subsystem 0x0003       // WINDOWS_CUI
+.corflags 0x00000001    //  ILONLY
+// Image base: 0x047E0000
+
+
+// =============== CLASS MEMBERS DECLARATION ===================
+
+.class private auto ansi beforefieldinit Program
+       extends [System.Runtime]System.Object
+{
+  .method private hidebysig static int32  Main() cil managed
+  {
+    .entrypoint
+    // Code size       34 (0x22)
+    .maxstack  8
+    IL_0000:  nop
+    IL_0001:  ldstr      "a"
+    IL_0006:  call       !0 class I2`2<string,string>::M1(!0)
+    IL_000b:  call       void [System.Console]System.Console::WriteLine(string)
+    IL_0010:  nop
+    IL_0011:  ldstr      "b"
+    IL_0016:  call       !1 class I2`2<string,string>::M2(!1)
+    IL_001b:  call       void [System.Console]System.Console::WriteLine(string)
+    IL_0020:  ldc.i4     100
+    IL_0021:  ret
+  } // end of method Program::Main
+
+  .method public hidebysig specialname rtspecialname 
+          instance void  .ctor() cil managed
+  {
+    // Code size       8 (0x8)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  call       instance void [System.Runtime]System.Object::.ctor()
+    IL_0006:  nop
+    IL_0007:  ret
+  } // end of method Program::.ctor
+
+} // end of class Program
+
+.class interface private abstract auto ansi I2`2<+ T1,- T2>
+{
+  .method public hidebysig static !T1  M1(!T1 x) cil managed
+  {
+    // Code size       2 (0x2)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  ret
+  } // end of method I2`2::M1
+
+  .method public hidebysig static !T2  M2(!T2 x) cil managed
+  {
+    // Code size       2 (0x2)
+    .maxstack  8
+    IL_0000:  ldarg.0
+    IL_0001:  ret
+  } // end of method I2`2::M2
+
+} // end of class I2`2
+
+
+// =============================================================
+
+// *********** DISASSEMBLY COMPLETE ***********************
\ No newline at end of file
diff --git a/src/tests/Loader/classloader/generics/Variance/Interfaces/NoVarianceCheckForStaticMethods.ilproj b/src/tests/Loader/classloader/generics/Variance/Interfaces/NoVarianceCheckForStaticMethods.ilproj
new file mode 100644
index 00000000000000..6e038d359eb83d
--- /dev/null
+++ b/src/tests/Loader/classloader/generics/Variance/Interfaces/NoVarianceCheckForStaticMethods.ilproj
@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk.IL">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <CLRTestKind>BuildAndRun</CLRTestKind>
+    <CLRTestPriority>0</CLRTestPriority>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="NoVarianceCheckForStaticMethods.il" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/baseservices/callconvs/TestCallingConventions.cs b/src/tests/baseservices/callconvs/TestCallingConventions.cs
index 935e4016d20f2d..fe42b6956108ad 100644
--- a/src/tests/baseservices/callconvs/TestCallingConventions.cs
+++ b/src/tests/baseservices/callconvs/TestCallingConventions.cs
@@ -89,8 +89,10 @@ static void BlittableFunctionPointers()
         {
             // Multiple modopts with calling conventions
             Console.WriteLine($" -- unmanaged modopt(stdcall) modopt(cdecl)");
-            int b = CallFunctionPointers.CallUnmanagedIntInt_ModOptStdcall_ModOptCdecl(cbCdecl, a);
-            Assert.AreEqual(expected, b);
+            var ex = Assert.Throws<InvalidProgramException>(
+                () => CallFunctionPointers.CallUnmanagedIntInt_ModOptStdcall_ModOptCdecl(cbCdecl, a),
+                "Multiple modopts with calling conventions should fail");
+            Assert.AreEqual("Multiple unmanaged calling conventions are specified. Only a single calling convention is supported.", ex.Message);
         }
 
         {
@@ -165,8 +167,10 @@ static void NonblittableFunctionPointers()
         {
             // Multiple modopts with calling conventions
             Console.WriteLine($" -- unmanaged modopt(stdcall) modopt(cdecl)");
-            var b = CallFunctionPointers.CallUnmanagedCharChar_ModOptStdcall_ModOptCdecl(cbCdecl, a);
-            Assert.AreEqual(expected, b);
+            var ex = Assert.Throws<InvalidProgramException>(
+                () => CallFunctionPointers.CallUnmanagedCharChar_ModOptStdcall_ModOptCdecl(cbCdecl, a),
+                "Multiple modopts with calling conventions should fail");
+            Assert.AreEqual("Multiple unmanaged calling conventions are specified. Only a single calling convention is supported.", ex.Message);
         }
 
         {
diff --git a/src/tests/baseservices/typeequivalence/contracts/TypeContracts.csproj b/src/tests/baseservices/typeequivalence/contracts/TypeContracts.csproj
index ce626dfdd026ca..306758e5a5b85f 100644
--- a/src/tests/baseservices/typeequivalence/contracts/TypeContracts.csproj
+++ b/src/tests/baseservices/typeequivalence/contracts/TypeContracts.csproj
@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Library</OutputType>
-    <!-- The Type Equivalence feature is unsupported outside of windows -->
-    <CLRTestTargetUnsupported Condition="'$(TargetsWindows)' != 'true'">true</CLRTestTargetUnsupported>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Types.cs" />
diff --git a/src/tests/baseservices/typeequivalence/impl/TypeImpl.csproj b/src/tests/baseservices/typeequivalence/impl/TypeImpl.csproj
index 4c64a59beda10e..b916b70076098c 100644
--- a/src/tests/baseservices/typeequivalence/impl/TypeImpl.csproj
+++ b/src/tests/baseservices/typeequivalence/impl/TypeImpl.csproj
@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Library</OutputType>
-    <!-- The Type Equivalence feature is unsupported outside of windows -->
-    <CLRTestTargetUnsupported Condition="'$(TargetsWindows)' != 'true'">true</CLRTestTargetUnsupported>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Impls.cs" />
diff --git a/src/tests/baseservices/typeequivalence/simple/Simple.cs b/src/tests/baseservices/typeequivalence/simple/Simple.cs
index 4454281731a4d1..fbfb5dbdb370ed 100644
--- a/src/tests/baseservices/typeequivalence/simple/Simple.cs
+++ b/src/tests/baseservices/typeequivalence/simple/Simple.cs
@@ -149,14 +149,87 @@ private static void CallSparseInterface()
         Assert.AreEqual(input * 18, sparseType.MultiplyBy18(input));
     }
 
+    private static void TestArrayEquivalence()
+    {
+        Console.WriteLine($"{nameof(TestArrayEquivalence)}");
+        var inAsm = EmptyType.Create();
+        var otherAsm = EmptyType2.Create();
+
+        Type inAsmInterfaceType = inAsm.GetType().GetInterface(nameof(IEmptyType));
+        Type otherAsmInterfaceType = otherAsm.GetType().GetInterface(nameof(IEmptyType));
+
+        Assert.IsTrue(inAsmInterfaceType.MakeArrayType().IsEquivalentTo(otherAsmInterfaceType.MakeArrayType()));
+        Assert.IsTrue(inAsmInterfaceType.MakeArrayType(1).IsEquivalentTo(otherAsmInterfaceType.MakeArrayType(1)));
+        Assert.IsTrue(inAsmInterfaceType.MakeArrayType(2).IsEquivalentTo(otherAsmInterfaceType.MakeArrayType(2)));
+
+        Assert.IsFalse(inAsmInterfaceType.MakeArrayType().IsEquivalentTo(otherAsmInterfaceType.MakeArrayType(1)));
+        Assert.IsFalse(inAsmInterfaceType.MakeArrayType(1).IsEquivalentTo(otherAsmInterfaceType.MakeArrayType(2)));
+    }
+
+    private static void TestByRefEquivalence()
+    {
+        Console.WriteLine($"{nameof(TestByRefEquivalence)}");
+        var inAsm = EmptyType.Create();
+        var otherAsm = EmptyType2.Create();
+
+        Type inAsmInterfaceType = inAsm.GetType().GetInterface(nameof(IEmptyType));
+        Type otherAsmInterfaceType = otherAsm.GetType().GetInterface(nameof(IEmptyType));
+
+        Assert.IsTrue(inAsmInterfaceType.MakeByRefType().IsEquivalentTo(otherAsmInterfaceType.MakeByRefType()));
+    }
+
+    interface IGeneric<in T>
+    {
+        void Method(T input);
+    }
+
+    class Generic<V> : IGeneric<V>
+    {
+        public void Method(V input)
+        {
+        }
+    }
+
+    private static void TestGenericClassNonEquivalence()
+    {
+        Console.WriteLine($"{nameof(TestGenericClassNonEquivalence)}");
+        var inAsm = EmptyType.Create();
+        var otherAsm = EmptyType2.Create();
+
+        Type inAsmInterfaceType = inAsm.GetType().GetInterface(nameof(IEmptyType));
+        Type otherAsmInterfaceType = otherAsm.GetType().GetInterface(nameof(IEmptyType));
+
+        Assert.IsFalse(typeof(Generic<>).MakeGenericType(inAsmInterfaceType).IsEquivalentTo(typeof(Generic<>).MakeGenericType(otherAsmInterfaceType)));
+    }
+
+    private static void TestGenericInterfaceEquivalence()
+    {
+        Console.WriteLine($"{nameof(TestGenericInterfaceEquivalence)}");
+        var inAsm = EmptyType.Create();
+        var otherAsm = EmptyType2.Create();
+
+        Type inAsmInterfaceType = inAsm.GetType().GetInterface(nameof(IEmptyType));
+        Type otherAsmInterfaceType = otherAsm.GetType().GetInterface(nameof(IEmptyType));
+
+        Assert.IsTrue(typeof(IGeneric<>).MakeGenericType(inAsmInterfaceType).IsEquivalentTo(typeof(IGeneric<>).MakeGenericType(otherAsmInterfaceType)));
+    }
+
     public static int Main(string[] noArgs)
     {
+        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            return 100;
+        }
         try
         {
             InterfaceTypesFromDifferentAssembliesAreEquivalent();
             ValidateTypeInstanceEquality();
             InterfaceTypesMethodOperations();
             CallSparseInterface();
+            TestByRefEquivalence();
+            TestArrayEquivalence();
+            TestGenericClassNonEquivalence();
+            TestGenericInterfaceEquivalence();
         }
         catch (Exception e)
         {
diff --git a/src/tests/baseservices/typeequivalence/simple/Simple.csproj b/src/tests/baseservices/typeequivalence/simple/Simple.csproj
index e53815c61324c1..028b3cc152efd3 100644
--- a/src/tests/baseservices/typeequivalence/simple/Simple.csproj
+++ b/src/tests/baseservices/typeequivalence/simple/Simple.csproj
@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <!-- The Type Equivalence feature is unsupported outside of windows -->
-    <CLRTestTargetUnsupported Condition="'$(TargetsWindows)' != 'true'">true</CLRTestTargetUnsupported>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Simple.cs" />
diff --git a/src/tests/ilverify/ILVerification.Tests.csproj b/src/tests/ilverify/ILVerification.Tests.csproj
new file mode 100644
index 00000000000000..5eaea1b89ea441
--- /dev/null
+++ b/src/tests/ilverify/ILVerification.Tests.csproj
@@ -0,0 +1,31 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <OutputPath>$(BaseOutputPathWithConfig)ilverify\</OutputPath>
+    <CLRTestPriority>1</CLRTestPriority>
+    <!-- The test uses xunit directly and it fails to find the test assembly for some reason -->
+    <UnloadabilityIncompatible>true</UnloadabilityIncompatible>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="ILMethodTester.cs" />
+    <Compile Include="ILTypeVerificationTester.cs" />
+    <Compile Include="TestDataLoader.cs" />
+    <Compile Include="..\Common\XunitBase.cs" />
+  </ItemGroup>
+
+  <Import Project="..\..\coreclr\src\tools\ILVerification\ILVerification.projitems" />
+
+  <ItemGroup>
+    <PackageReference Include="xunit" Version="$(XUnitVersion)" />
+    <PackageReference Include="Newtonsoft.Json" Version="9.0.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="ILTests\*.ilproj">
+      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
+      <OutputItemType>Content</OutputItemType>
+    </ProjectReference>
+  </ItemGroup>
+</Project>
diff --git a/src/tests/ilverify/TestDataLoader.cs b/src/tests/ilverify/TestDataLoader.cs
index 7678981dd4a9a9..cd8709d9626ab6 100644
--- a/src/tests/ilverify/TestDataLoader.cs
+++ b/src/tests/ilverify/TestDataLoader.cs
@@ -27,7 +27,7 @@ class TestDataLoader
         /// <summary>
         /// The folder with the test binaries
         /// </summary>
-        private const string TestAssemblyPath = @"Tests\";
+        private const string TestAssemblyPath = @"Tests";
 
         private const string SpecialTestPrefix = "special.";
 
@@ -236,7 +236,7 @@ public static EcmaModule GetModuleForTestAssembly(string assemblyName)
 
             foreach (var fileName in GetAllTestDlls())
             {
-                simpleNameToPathMap.Add(Path.GetFileNameWithoutExtension(fileName), TestAssemblyPath + fileName);
+                simpleNameToPathMap.Add(Path.GetFileNameWithoutExtension(fileName), Path.Combine(TestAssemblyPath, fileName));
             }
 
             Assembly coreAssembly = typeof(object).GetTypeInfo().Assembly;
diff --git a/src/tests/profiler/common/ProfilerTestRunner.cs b/src/tests/profiler/common/ProfilerTestRunner.cs
index 4600f1f1f2d722..bb5bae9d90924d 100644
--- a/src/tests/profiler/common/ProfilerTestRunner.cs
+++ b/src/tests/profiler/common/ProfilerTestRunner.cs
@@ -33,10 +33,11 @@ public static int Run(string profileePath,
 
             arguments = profileePath + " RunTest " + profileeArguments;
             program = GetCorerunPath();
+            string profilerPath = GetProfilerPath();
             if (!profileeOptions.HasFlag(ProfileeOptions.NoStartupAttach))
             {
                 envVars.Add("CORECLR_ENABLE_PROFILING", "1");
-                envVars.Add("CORECLR_PROFILER_PATH", GetProfilerPath());
+                envVars.Add("CORECLR_PROFILER_PATH", profilerPath);
                 envVars.Add("CORECLR_PROFILER", "{" + profilerClsid + "}");
             }
 
@@ -48,7 +49,8 @@ public static int Run(string profileePath,
                 envVars.Add("COMPlus_JITMinOpts", "0");
             }
 
-            string profilerPath = GetProfilerPath();
+            envVars.Add("Profiler_Test_Name", testName);
+
             if(!File.Exists(profilerPath))
             {
                 LogTestFailure("Profiler library not found at expected path: " + profilerPath);
diff --git a/src/tests/profiler/elt/slowpathcommon.cs b/src/tests/profiler/elt/slowpathcommon.cs
new file mode 100644
index 00000000000000..eab383d0ff0092
--- /dev/null
+++ b/src/tests/profiler/elt/slowpathcommon.cs
@@ -0,0 +1,169 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Diagnostics.Tracing;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Threading;
+
+namespace SlowPathELTTests
+{
+    [StructLayout(LayoutKind.Sequential)]
+    public struct IntegerStruct
+    {
+        public int x;
+        public int y;
+
+        public IntegerStruct(int x, int y)
+        {
+            this.x = x;
+            this.y = y;
+        }
+
+        public override String ToString()
+        {
+            return $"x={x} y={y}";
+        }
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    public struct FloatingPointStruct
+    {
+        public double d1;
+        public double d2;
+
+        public FloatingPointStruct(double d1, double d2)
+        {
+            this.d1 = d1;
+            this.d2 = d2;
+        }
+
+        public override String ToString()
+        {
+            return $"d1={d1} d2={d2}";
+        }
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    public struct MixedStruct
+    {
+        public int x;
+        public double d;
+
+        public MixedStruct(int x, double d)
+        {
+            this.x = x;
+            this.d = d;
+        }
+
+        public override String ToString()
+        {
+            return $"x={x} d={d}";
+        }
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    public struct LargeStruct
+    {
+        public int x0;
+        public double d0;
+        public int x1;
+        public double d1;
+        public int x2;
+        public double d2;
+        public int x3;
+        public double d3;
+
+        public LargeStruct(int x0, 
+                           double d0,
+                           int x1,
+                           double d1,
+                           int x2,
+                           double d2,
+                           int x3,
+                           double d3)
+        {
+            this. x0 = x0;
+            this.d0 = d0;
+            this.x1 = x1;
+            this.d1 = d1;
+            this.x2 = x2;
+            this.d2 = d2;
+            this.x3 = x3;
+            this.d3 = d3;
+        }
+
+        public override String ToString()
+        {
+            return $"x0={x0} d0={d0} x1={x1} d1={d1} x2={x2} d2={d2} x3={x3} d3={d3}";
+        }
+    }
+
+    public class SlowPathELTHelpers
+    {
+        public static int RunTest()
+        {
+            Console.WriteLine($"SimpleArgsFunc returned {SimpleArgsFunc(-123, -4.3f, "Hello, test!")}");
+
+            Console.WriteLine($"MixedStructFunc returned {MixedStructFunc(new MixedStruct(1, 1))}");
+
+            Console.WriteLine($"LargeStructFunc returned {LargeStructFunc(new LargeStruct(0, 0, 1, 1, 2, 2, 3, 3))}");
+
+            Console.WriteLine($"IntegerStructFunc returned {IntegerStructFunc(new IntegerStruct(14, 256))}");
+
+            Console.WriteLine($"FloatingPointStructFunc returned {FloatingPointStructFunc(new FloatingPointStruct(13.0, 145.2))}");
+
+            Console.WriteLine($"DoubleRetFunc returned {DoubleRetFunc()}");
+
+            return 100;
+        }
+
+        [MethodImplAttribute(MethodImplOptions.NoInlining)]
+        public static string SimpleArgsFunc(int x, float y, String str)
+        {
+            Console.WriteLine($"x={x} y={y} str={str}");
+            return "Hello from SimpleArgsFunc!";
+        }
+
+        [MethodImplAttribute(MethodImplOptions.NoInlining)]
+        public static MixedStruct MixedStructFunc(MixedStruct ss)
+        {
+            Console.WriteLine($"ss={ss}");
+            ss.x = 4;
+            return ss;
+        }
+
+        [MethodImplAttribute(MethodImplOptions.NoInlining)]
+        public static int LargeStructFunc(LargeStruct ls)
+        {
+            Console.WriteLine($"ls={ls}");
+            return 3;
+        }
+
+        [MethodImplAttribute(MethodImplOptions.NoInlining)]
+        public static IntegerStruct IntegerStructFunc(IntegerStruct its)
+        {
+            its.x = 21;
+            return its;
+        }
+
+        [MethodImplAttribute(MethodImplOptions.NoInlining)]
+        public static FloatingPointStruct FloatingPointStructFunc(FloatingPointStruct fps)
+        {
+            fps.d2 = 256.8;
+            return fps;
+        }
+
+        [MethodImplAttribute(MethodImplOptions.NoInlining)]
+        public static double DoubleRetFunc()
+        {
+            return 13.0;
+        }
+    }
+}
diff --git a/src/tests/profiler/elt/slowpathcommon.csproj b/src/tests/profiler/elt/slowpathcommon.csproj
new file mode 100644
index 00000000000000..869ebc2c1fab5f
--- /dev/null
+++ b/src/tests/profiler/elt/slowpathcommon.csproj
@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Library</OutputType>
+    <CLRTestKind>BuildOnly</CLRTestKind>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <CLRTestPriority>0</CLRTestPriority>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/profiler/elt/slowpatheltenter.cs b/src/tests/profiler/elt/slowpatheltenter.cs
new file mode 100644
index 00000000000000..83d6bb56e6e628
--- /dev/null
+++ b/src/tests/profiler/elt/slowpatheltenter.cs
@@ -0,0 +1,34 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Profiler.Tests;
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Diagnostics.Tracing;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Threading;
+
+namespace SlowPathELTTests
+{
+    class SlowPathELTEnter
+    {
+        static readonly Guid EventPipeWritingProfilerGuid = new Guid("0B36296B-EC47-44DA-8320-DC5E3071DD06");
+
+        public static int Main(string[] args)
+        {
+            if (args.Length > 0 && args[0].Equals("RunTest", StringComparison.OrdinalIgnoreCase))
+            {
+                return SlowPathELTHelpers.RunTest();
+            }
+
+            return ProfilerTestRunner.Run(profileePath: System.Reflection.Assembly.GetExecutingAssembly().Location,
+                                          testName: "ELTSlowPathEnter",
+                                          profilerClsid: EventPipeWritingProfilerGuid);
+        }
+    }
+}
diff --git a/src/tests/profiler/elt/slowpatheltenter.csproj b/src/tests/profiler/elt/slowpatheltenter.csproj
new file mode 100644
index 00000000000000..8d2ac3058e83d3
--- /dev/null
+++ b/src/tests/profiler/elt/slowpatheltenter.csproj
@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworkIdentifier>.NETCoreApp</TargetFrameworkIdentifier>
+    <OutputType>exe</OutputType>
+    <CLRTestKind>BuildAndRun</CLRTestKind>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <CLRTestPriority>0</CLRTestPriority>
+    <Optimize>true</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
+    <ProjectReference Include="../common/profiler_common.csproj" />
+    <ProjectReference Include="slowpathcommon.csproj" />
+    <ProjectReference Include="$(MSBuildThisFileDirectory)/../native/CMakeLists.txt" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/profiler/elt/slowpatheltleave.cs b/src/tests/profiler/elt/slowpatheltleave.cs
new file mode 100644
index 00000000000000..da8fd03ec3867e
--- /dev/null
+++ b/src/tests/profiler/elt/slowpatheltleave.cs
@@ -0,0 +1,34 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Profiler.Tests;
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Diagnostics.Tracing;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Threading;
+
+namespace SlowPathELTTests
+{
+    class SlowPathELTLeave
+    {
+        static readonly Guid EventPipeWritingProfilerGuid = new Guid("0B36296B-EC47-44DA-8320-DC5E3071DD06");
+
+        public static int Main(string[] args)
+        {
+            if (args.Length > 0 && args[0].Equals("RunTest", StringComparison.OrdinalIgnoreCase))
+            {
+                return SlowPathELTHelpers.RunTest();
+            }
+
+            return ProfilerTestRunner.Run(profileePath: System.Reflection.Assembly.GetExecutingAssembly().Location,
+                                          testName: "ELTSlowPathLeave",
+                                          profilerClsid: EventPipeWritingProfilerGuid);
+        }
+    }
+}
diff --git a/src/tests/profiler/elt/slowpatheltleave.csproj b/src/tests/profiler/elt/slowpatheltleave.csproj
new file mode 100644
index 00000000000000..8d2ac3058e83d3
--- /dev/null
+++ b/src/tests/profiler/elt/slowpatheltleave.csproj
@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworkIdentifier>.NETCoreApp</TargetFrameworkIdentifier>
+    <OutputType>exe</OutputType>
+    <CLRTestKind>BuildAndRun</CLRTestKind>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <CLRTestPriority>0</CLRTestPriority>
+    <Optimize>true</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
+    <ProjectReference Include="../common/profiler_common.csproj" />
+    <ProjectReference Include="slowpathcommon.csproj" />
+    <ProjectReference Include="$(MSBuildThisFileDirectory)/../native/CMakeLists.txt" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/profiler/eventpipe/eventpipe.csproj b/src/tests/profiler/eventpipe/eventpipe.csproj
index 7a525ce745d28c..fc9c21e7144d91 100644
--- a/src/tests/profiler/eventpipe/eventpipe.csproj
+++ b/src/tests/profiler/eventpipe/eventpipe.csproj
@@ -6,6 +6,8 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <CLRTestPriority>0</CLRTestPriority>
     <Optimize>true</Optimize>
+    <!-- This test provides no interesting scenarios for GCStress -->
+    <GCStressIncompatible>true</GCStressIncompatible>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />
diff --git a/src/tests/profiler/eventpipe/eventpipe_readevents.csproj b/src/tests/profiler/eventpipe/eventpipe_readevents.csproj
index 7a525ce745d28c..fc9c21e7144d91 100644
--- a/src/tests/profiler/eventpipe/eventpipe_readevents.csproj
+++ b/src/tests/profiler/eventpipe/eventpipe_readevents.csproj
@@ -6,6 +6,8 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <CLRTestPriority>0</CLRTestPriority>
     <Optimize>true</Optimize>
+    <!-- This test provides no interesting scenarios for GCStress -->
+    <GCStressIncompatible>true</GCStressIncompatible>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />
diff --git a/src/tests/profiler/gc/gc.cs b/src/tests/profiler/gc/gc.cs
index e0840ef51588e4..955ee84d49cdec 100644
--- a/src/tests/profiler/gc/gc.cs
+++ b/src/tests/profiler/gc/gc.cs
@@ -6,53 +6,67 @@
 
 namespace Profiler.Tests
 {
-    class GCBasicTests //: ProfilerTest
+    class AllocObject
     {
-        static readonly Guid GcBasicEventsProfilerGuid = new Guid("A040B953-EDE7-42D9-9077-AA69BB2BE024");
+        public static readonly int ArraySize = 100;
+        int[] m_array = null;
 
-        public static void DoWork() {
-            int k=0;
-            while(k<3) {
-                Console.WriteLine("{0}: Restarting run {1}",Thread.CurrentThread.Name,k);
-                int[] largeArray = new int[1000000];
-                for (int i=0;i<=100;i++){
-                    int[] saveArray = largeArray;
-                    largeArray = new int[largeArray.Length + 100000];
-                    saveArray = null;
-                    //Console.WriteLine("{0} at size {1}",Thread.CurrentThread.Name,largeArray.Length.ToString());
-                }
-                k++;
-           }
-        }
-
-        public static int RunTest(String[] args) {
-            long Threads = 1;
-
-            if(args.Length > 2)
+        public AllocObject(bool poh)
+        {
+            if (poh)
             {
-                Console.WriteLine("usage: LargeObjectAlloc runtest <number of threads>");
-                return 1;
+                m_array = GC.AllocateArray<int>(ArraySize, true);
             }
-            else if(args.Length == 2)
+            else
             {
-                Threads = Int64.Parse(args[1]);
+                m_array = new int[ArraySize];
             }
+        }
+    }
 
-            Console.WriteLine("LargeObjectAlloc started with {0} threads. Control-C to exit",
-                Threads.ToString());
+    class GCTests
+    {
+        static readonly Guid GCProfilerGuid = new Guid("BCD8186F-1EEC-47E9-AFA7-396F879382C3");
+
+        public static int RunTest(String[] args) 
+        {
+            int numAllocators = 1024;
+            int[] root1 = GC.AllocateArray<int>(AllocObject.ArraySize, true);
+            int[] root2 = GC.AllocateArray<int>(AllocObject.ArraySize, true);
+            AllocObject[] objs = new AllocObject[numAllocators];
 
-            Thread myThread = null;
-            for(long i = 0; i < Threads; i++)
+            Random rand = new Random();
+            int numPoh = 0;
+            int numReg = 0;
+            for (int i = 0; i < 10000; ++i)
             {
-                myThread = new Thread(new ThreadStart(DoWork));
-                myThread.Name = i.ToString();
-                myThread.Start();
-            }
+                int pos = rand.Next(0, numAllocators);
+
+                bool poh = rand.NextDouble() > 0.5;
+                objs[pos] = new AllocObject(poh);
+
+                if (poh)
+                {
+                    ++numPoh;
+                }
+                else
+                {
+                    ++numReg;
+                }
 
-            Console.WriteLine("All threads started");
-            myThread.Join();
+                if (i % 1000 == 0)
+                {
+                    GC.Collect();
+                    Console.WriteLine ($"Did {i} iterations Allocated={GC.GetAllocatedBytesForCurrentThread()}");
+                }
+
+
+                int[] m_array = new int[100];
+            }
 
-            Console.WriteLine("Test Passed");
+            Console.WriteLine($"{numPoh} POH allocs and {numReg} normal allocs.");
+            GC.KeepAlive(root1);
+            GC.KeepAlive(root2);
             return 100;
         }
 
@@ -64,8 +78,8 @@ public static int Main(string[] args)
             }
 
             return ProfilerTestRunner.Run(profileePath: System.Reflection.Assembly.GetExecutingAssembly().Location,
-                                          testName: "GCCallbacksBasic",
-                                          profilerClsid: GcBasicEventsProfilerGuid);
+                                          testName: "GCTests",
+                                          profilerClsid: GCProfilerGuid);
         }
     }
 }
diff --git a/src/tests/profiler/gc/gc.csproj b/src/tests/profiler/gc/gc.csproj
index 7a525ce745d28c..fc9c21e7144d91 100644
--- a/src/tests/profiler/gc/gc.csproj
+++ b/src/tests/profiler/gc/gc.csproj
@@ -6,6 +6,8 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <CLRTestPriority>0</CLRTestPriority>
     <Optimize>true</Optimize>
+    <!-- This test provides no interesting scenarios for GCStress -->
+    <GCStressIncompatible>true</GCStressIncompatible>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />
diff --git a/src/tests/profiler/gc/gcbasic.cs b/src/tests/profiler/gc/gcbasic.cs
new file mode 100644
index 00000000000000..61b3f1412e21a3
--- /dev/null
+++ b/src/tests/profiler/gc/gcbasic.cs
@@ -0,0 +1,83 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Threading;
+
+namespace Profiler.Tests
+{
+    class GCBasicTests
+    {
+        static readonly Guid GcBasicEventsProfilerGuid = new Guid("A040B953-EDE7-42D9-9077-AA69BB2BE024");
+
+        public static void DoWork() 
+        {
+            // Allocate POH objects
+            var arr0 = GC.AllocateUninitializedArray<int>(100000, true);
+            var arr1 = GC.AllocateArray<int>(200000, true);
+
+            int k = 0;
+            while(k < 3) 
+            {
+                Console.WriteLine("{0}: Restarting run {1}",Thread.CurrentThread.Name,k);
+                int[] largeArray = new int[1000000];
+                for (int i = 0; i <= 100; i++)
+                {
+                    int[] saveArray = largeArray;
+                    largeArray = new int[largeArray.Length + 100000];
+                    saveArray = null;
+                    //Console.WriteLine("{0} at size {1}",Thread.CurrentThread.Name,largeArray.Length.ToString());
+                }
+                
+                k++;
+           }
+
+            GC.KeepAlive(arr0);
+            GC.KeepAlive(arr1);
+        }
+
+        public static int RunTest(String[] args) 
+        {
+            long Threads = 1;
+
+            if(args.Length > 2)
+            {
+                Console.WriteLine("usage: LargeObjectAlloc runtest <number of threads>");
+                return 1;
+            }
+            else if(args.Length == 2)
+            {
+                Threads = Int64.Parse(args[1]);
+            }
+
+            Console.WriteLine("LargeObjectAlloc started with {0} threads. Control-C to exit",
+                Threads.ToString());
+
+            Thread myThread = null;
+            for(long i = 0; i < Threads; i++)
+            {
+                myThread = new Thread(new ThreadStart(DoWork));
+                myThread.Name = i.ToString();
+                myThread.Start();
+            }
+
+            Console.WriteLine("All threads started");
+            myThread.Join();
+
+            Console.WriteLine("Test Passed");
+            return 100;
+        }
+
+        public static int Main(string[] args)
+        {
+            if (args.Length > 0 && args[0].Equals("RunTest", StringComparison.OrdinalIgnoreCase))
+            {
+                return RunTest(args);
+            }
+
+            return ProfilerTestRunner.Run(profileePath: System.Reflection.Assembly.GetExecutingAssembly().Location,
+                                          testName: "GCCallbacksBasic",
+                                          profilerClsid: GcBasicEventsProfilerGuid);
+        }
+    }
+}
diff --git a/src/tests/profiler/gc/gcbasic.csproj b/src/tests/profiler/gc/gcbasic.csproj
new file mode 100644
index 00000000000000..fc9c21e7144d91
--- /dev/null
+++ b/src/tests/profiler/gc/gcbasic.csproj
@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworkIdentifier>.NETCoreApp</TargetFrameworkIdentifier>
+    <OutputType>exe</OutputType>
+    <CLRTestKind>BuildAndRun</CLRTestKind>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <CLRTestPriority>0</CLRTestPriority>
+    <Optimize>true</Optimize>
+    <!-- This test provides no interesting scenarios for GCStress -->
+    <GCStressIncompatible>true</GCStressIncompatible>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
+    <ProjectReference Include="../common/profiler_common.csproj" />
+    <ProjectReference Include="$(MSBuildThisFileDirectory)/../native/CMakeLists.txt" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/profiler/native/CMakeLists.txt b/src/tests/profiler/native/CMakeLists.txt
index 3af1b28a4fbf77..b58bb64bbcf925 100644
--- a/src/tests/profiler/native/CMakeLists.txt
+++ b/src/tests/profiler/native/CMakeLists.txt
@@ -3,6 +3,7 @@ cmake_minimum_required(VERSION 3.14.5)
 project(Profiler)
 
 set(GCBASIC_SOURCES gcbasicprofiler/gcbasicprofiler.cpp)
+set(GC_SOURCES gcprofiler/gcprofiler.cpp)
 set(REJIT_SOURCES rejitprofiler/rejitprofiler.cpp rejitprofiler/ilrewriter.cpp rejitprofiler/sigparse.cpp)
 set(EVENTPIPE_SOURCES
     eventpipeprofiler/eventpipereadingprofiler.cpp
@@ -10,8 +11,17 @@ set(EVENTPIPE_SOURCES
     eventpipeprofiler/eventpipemetadatareader.cpp)
 set(METADATAGETDISPENSER_SOURCES metadatagetdispenser/metadatagetdispenser.cpp)
 set(GETAPPDOMAINSTATICADDRESS_SOURCES getappdomainstaticaddress/getappdomainstaticaddress.cpp)
-
-set(SOURCES ${GCBASIC_SOURCES} ${REJIT_SOURCES} ${EVENTPIPE_SOURCES} ${METADATAGETDISPENSER_SOURCES} ${GETAPPDOMAINSTATICADDRESS_SOURCES} profiler.def profiler.cpp classfactory.cpp dllmain.cpp guids.cpp)
+set(ELT_SOURCES eltprofiler/slowpatheltprofiler.cpp)
+
+set(SOURCES
+    ${GCBASIC_SOURCES}
+    ${GC_SOURCES}
+    ${REJIT_SOURCES}
+    ${EVENTPIPE_SOURCES}
+    ${METADATAGETDISPENSER_SOURCES}
+    ${GETAPPDOMAINSTATICADDRESS_SOURCES}
+    ${ELT_SOURCES}
+    profiler.def profiler.cpp classfactory.cpp dllmain.cpp guids.cpp)
 
 include_directories(../../../coreclr/src/pal/prebuilt/inc)
 
diff --git a/src/tests/profiler/native/classfactory.cpp b/src/tests/profiler/native/classfactory.cpp
index dc5cc2feea0251..19de051368182f 100644
--- a/src/tests/profiler/native/classfactory.cpp
+++ b/src/tests/profiler/native/classfactory.cpp
@@ -8,6 +8,8 @@
 #include "eventpipeprofiler/eventpipewritingprofiler.h"
 #include "metadatagetdispenser/metadatagetdispenser.h"
 #include "getappdomainstaticaddress/getappdomainstaticaddress.h"
+#include "eltprofiler/slowpatheltprofiler.h"
+#include "gcprofiler/gcprofiler.h"
 
 ClassFactory::ClassFactory(REFCLSID clsid) : refCount(0), clsid(clsid)
 {
@@ -61,7 +63,9 @@ HRESULT STDMETHODCALLTYPE ClassFactory::CreateInstance(IUnknown *pUnkOuter, REFI
         new EventPipeReadingProfiler(),
         new EventPipeWritingProfiler(),
         new MetaDataGetDispenser(),
-        new GetAppDomainStaticAddress()
+        new GetAppDomainStaticAddress(),
+        new SlowPathELTProfiler(),
+        new GCProfiler()
 		// add new profilers here
 	};
 
diff --git a/src/tests/profiler/native/eltprofiler/slowpatheltprofiler.cpp b/src/tests/profiler/native/eltprofiler/slowpatheltprofiler.cpp
new file mode 100644
index 00000000000000..8f858cdb0899b0
--- /dev/null
+++ b/src/tests/profiler/native/eltprofiler/slowpatheltprofiler.cpp
@@ -0,0 +1,499 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#define NOMINMAX
+
+#include "slowpatheltprofiler.h"
+#include <iostream>
+#include <cctype>
+#include <iomanip>
+#include <algorithm>
+
+using std::shared_ptr;
+using std::vector;
+using std::wcout;
+using std::endl;
+
+shared_ptr<SlowPathELTProfiler> SlowPathELTProfiler::s_profiler;
+
+#ifndef WIN32
+#define UINT_PTR_FORMAT "lx"
+#define PROFILER_STUB EXTERN_C __attribute__((visibility("hidden"))) void STDMETHODCALLTYPE
+#else // WIN32
+#define UINT_PTR_FORMAT "llx"
+#define PROFILER_STUB EXTERN_C void STDMETHODCALLTYPE
+#endif // WIN32
+
+PROFILER_STUB EnterStub(FunctionIDOrClientID functionId, COR_PRF_ELT_INFO eltInfo)
+{
+    SlowPathELTProfiler::s_profiler->EnterCallback(functionId, eltInfo);
+}
+
+PROFILER_STUB LeaveStub(FunctionIDOrClientID functionId, COR_PRF_ELT_INFO eltInfo)
+{
+    SlowPathELTProfiler::s_profiler->LeaveCallback(functionId, eltInfo);
+}
+
+PROFILER_STUB TailcallStub(FunctionIDOrClientID functionId, COR_PRF_ELT_INFO eltInfo)
+{
+    SlowPathELTProfiler::s_profiler->TailcallCallback(functionId, eltInfo);
+}
+
+GUID SlowPathELTProfiler::GetClsid()
+{
+    // {0B36296B-EC47-44DA-8320-DC5E3071DD06}
+    GUID clsid = { 0x0B36296B, 0xEC47, 0x44DA, { 0x83, 0x20, 0xDC, 0x5E, 0x30, 0x71, 0xDD, 0x06 } };
+    return clsid;
+}
+
+HRESULT SlowPathELTProfiler::Initialize(IUnknown* pICorProfilerInfoUnk)
+{
+    Profiler::Initialize(pICorProfilerInfoUnk);
+
+    HRESULT hr = S_OK;
+    constexpr ULONG bufferSize = 1024;
+    ULONG envVarLen = 0;
+    WCHAR envVar[bufferSize];
+    if (FAILED(hr = pCorProfilerInfo->GetEnvironmentVariable(WCHAR("Profiler_Test_Name"),
+                                                             bufferSize,
+                                                             &envVarLen,
+                                                             envVar)))
+    {
+        wcout << L"Failed to get test name hr=" << std::hex << hr << endl;
+        _failures++;
+        return hr;
+    }
+
+    size_t nullCharPos = std::min(bufferSize - 1, envVarLen);
+    envVar[nullCharPos] = 0;
+    if (wcscmp(envVar, WCHAR("ELTSlowPathEnter")) == 0)
+    {
+        wcout << L"Testing enter hooks" << endl;
+        _testType = TestType::EnterHooks;
+    }
+    else if (wcscmp(envVar, WCHAR("ELTSlowPathLeave")) == 0)
+    {
+        wcout << L"Testing leave hooks" << endl;
+        _testType = TestType::LeaveHooks;
+    }
+    else
+    {
+        wcout << L"Unknown test type" << endl;
+        _failures++;
+        return E_FAIL;
+    }
+
+    SlowPathELTProfiler::s_profiler = shared_ptr<SlowPathELTProfiler>(this);
+
+    if (FAILED(hr = pCorProfilerInfo->SetEventMask2(COR_PRF_MONITOR_ENTERLEAVE 
+                                                    | COR_PRF_ENABLE_FUNCTION_ARGS
+                                                    | COR_PRF_ENABLE_FUNCTION_RETVAL
+                                                    | COR_PRF_ENABLE_FRAME_INFO, 
+                                                    0)))
+    {
+        wcout << L"FAIL: IpCorProfilerInfo::SetEventMask2() failed hr=0x" << std::hex << hr << endl;
+        _failures++;
+        return hr;
+    }
+
+    hr = this->pCorProfilerInfo->SetEnterLeaveFunctionHooks3WithInfo(EnterStub, LeaveStub, TailcallStub);
+    if (hr != S_OK)
+    {
+        wcout << L"SetEnterLeaveFunctionHooks3WithInfo failed with hr=0x" << std::hex << hr << endl;
+        _failures++;
+        return hr;
+    }
+
+    return S_OK;
+}
+
+HRESULT SlowPathELTProfiler::Shutdown()
+{
+    Profiler::Shutdown();
+
+    if (_testType == TestType::EnterHooks)
+    {
+        if (_failures == 0 
+             && _testType == TestType::EnterHooks
+             && _sawSimpleFuncEnter
+             && _sawMixedStructFuncEnter
+             && _sawLargeStructFuncEnter)
+        {
+            wcout << L"PROFILER TEST PASSES" << endl;
+        }
+        else
+        {
+            wcout << L"TEST FAILED _failures=" << _failures.load() << L", _sawSimpleFuncEnter=" << _sawSimpleFuncEnter 
+                    << L", _sawMixedStructFuncEnter=" << _sawMixedStructFuncEnter << L", _sawLargeStructFuncEnter=" 
+                    << _sawLargeStructFuncEnter << endl;
+        }    
+    }
+    else if (_testType == TestType::LeaveHooks)
+    {
+        if (_failures == 0
+              && _testType == TestType::LeaveHooks
+              && _sawSimpleFuncLeave
+              && _sawMixedStructFuncLeave
+              && _sawLargeStructFuncLeave
+              && _sawIntegerStructFuncLeave
+              && _sawFloatingPointStructFuncLeave
+              && _sawDoubleRetFuncLeave)
+        {
+            wcout << L"PROFILER TEST PASSES" << endl;
+        }
+        else
+        {
+            wcout << L"TEST FAILED _failures=" << _failures.load() << L", _sawSimpleFuncLeave=" << _sawSimpleFuncLeave 
+                    << L", _sawMixedStructFuncLeave=" << _sawMixedStructFuncLeave << L", _sawLargeStructFuncLeave=" 
+                    << _sawLargeStructFuncLeave << L"_sawIntegerStructFuncLeave=" << _sawIntegerStructFuncLeave 
+                    << L"_sawFloatingPointStructFuncLeave=" << _sawFloatingPointStructFuncLeave 
+                    << L"_sawDoubleRetFuncLeave=" << _sawDoubleRetFuncLeave << endl;
+        }
+    }
+
+    return S_OK;
+}
+
+HRESULT STDMETHODCALLTYPE SlowPathELTProfiler::EnterCallback(FunctionIDOrClientID functionIdOrClientID, COR_PRF_ELT_INFO eltInfo)
+{
+    if (_testType != TestType::EnterHooks)
+    {
+        return S_OK;
+    }
+
+    COR_PRF_FRAME_INFO frameInfo;
+    ULONG pcbArgumentInfo = 0;
+    NewArrayHolder<BYTE> pArgumentInfoBytes;
+    COR_PRF_FUNCTION_ARGUMENT_INFO *pArgumentInfo = NULL;
+
+    HRESULT hr = pCorProfilerInfo->GetFunctionEnter3Info(functionIdOrClientID.functionID, eltInfo, &frameInfo, &pcbArgumentInfo, NULL);
+    if (FAILED(hr) && hr != HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER))
+    {
+        wcout << L"GetFunctionEnter3Info 1 failed with hr=0x" << std::hex << hr << endl;
+        _failures++;
+        return hr;
+    }
+    else if (hr == HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER))
+    {
+        pArgumentInfoBytes = new BYTE[pcbArgumentInfo];
+        pArgumentInfo = reinterpret_cast<COR_PRF_FUNCTION_ARGUMENT_INFO *>((BYTE *)pArgumentInfoBytes);
+        hr = pCorProfilerInfo->GetFunctionEnter3Info(functionIdOrClientID.functionID, eltInfo, &frameInfo, &pcbArgumentInfo, pArgumentInfo);
+        if(FAILED(hr))
+        {
+            wcout << L"GetFunctionEnter3Info 2 failed with hr=0x" << std::hex << hr << endl;
+            _failures++;
+            return hr;
+        }
+    }
+
+    String functionName = GetFunctionIDName(functionIdOrClientID.functionID);
+    if (functionName == WCHAR("SimpleArgsFunc"))
+    {
+        _sawSimpleFuncEnter = true;
+
+        int x = -123;
+        float f = -4.3f;
+        const WCHAR *str = WCHAR("Hello, test!");
+
+        vector<ExpectedArgValue> expectedValues = { { sizeof(int), (void *)&x, [&](UINT_PTR ptr){ return ValidateInt(ptr, x); } },
+                                                    { sizeof(float), (void *)&f, [&](UINT_PTR ptr){ return ValidateFloat(ptr, f); }  },
+                                                    { sizeof(UINT_PTR), (void *)str, [&](UINT_PTR ptr){ return ValidateString(ptr, str); } } };
+
+        hr = ValidateFunctionArgs(pArgumentInfo, functionName, expectedValues);
+    }
+    else if (functionName == WCHAR("MixedStructFunc"))
+    {
+        _sawMixedStructFuncEnter = true;
+
+        // On linux structs can be split with some in int registers and some in float registers
+        // so a struct with interleaved ints/doubles is interesting.
+        MixedStruct ss = { 1, 1.0 };
+        vector<ExpectedArgValue> expectedValues = { { sizeof(MixedStruct), (void *)&ss, [&](UINT_PTR ptr){ return ValidateMixedStruct(ptr, ss); } } };
+        
+        hr = ValidateFunctionArgs(pArgumentInfo, functionName, expectedValues);
+    }
+    else if (functionName == WCHAR("LargeStructFunc"))
+    {
+        _sawLargeStructFuncEnter = true;
+
+        LargeStruct ls = { 0, 0.0, 1, 1.0, 2, 2.0, 3, 3.0 };
+        vector<ExpectedArgValue> expectedValues = { { sizeof(LargeStruct), (void *)&ls, [&](UINT_PTR ptr){ return ValidateLargeStruct(ptr, ls); } } };;
+
+        hr = ValidateFunctionArgs(pArgumentInfo, functionName, expectedValues);
+    }
+
+    return hr;
+}
+
+HRESULT STDMETHODCALLTYPE SlowPathELTProfiler::LeaveCallback(FunctionIDOrClientID functionIdOrClientID, COR_PRF_ELT_INFO eltInfo)
+{
+    if (_testType != TestType::LeaveHooks)
+    {
+        return S_OK;
+    }
+    
+    COR_PRF_FRAME_INFO frameInfo;
+    COR_PRF_FUNCTION_ARGUMENT_RANGE * pRetvalRange = new COR_PRF_FUNCTION_ARGUMENT_RANGE;
+    HRESULT hr = pCorProfilerInfo->GetFunctionLeave3Info(functionIdOrClientID.functionID, eltInfo, &frameInfo, pRetvalRange);
+    if (FAILED(hr))
+    {
+        wcout << L"GetFunctionLeave3Info failed hr=0x" << std::hex << hr << endl;
+        _failures++;
+        return hr;
+    }
+
+    String functionName = GetFunctionIDName(functionIdOrClientID.functionID);
+    if (functionName == WCHAR("SimpleArgsFunc"))
+    {
+        _sawSimpleFuncLeave = true;
+
+        const WCHAR *str = WCHAR("Hello from SimpleArgsFunc!");
+
+        ExpectedArgValue simpleRetValue = { sizeof(UINT_PTR), (void *)str, [&](UINT_PTR ptr){ return ValidateString(ptr, str); } };
+        hr = ValidateOneArgument(pRetvalRange, functionName, 0, simpleRetValue);
+    }
+    else if (functionName == WCHAR("MixedStructFunc"))
+    {
+        _sawMixedStructFuncLeave = true;
+
+        MixedStruct ss = { 4, 1.0 };
+        ExpectedArgValue MixedStructRetValue = { sizeof(MixedStruct), (void *)&ss, [&](UINT_PTR ptr){ return ValidateMixedStruct(ptr, ss); } };
+        hr = ValidateOneArgument(pRetvalRange, functionName, 0, MixedStructRetValue);
+    }
+    else if (functionName == WCHAR("LargeStructFunc"))
+    {
+        _sawLargeStructFuncLeave = true;
+
+        int32_t val = 3;
+        ExpectedArgValue largeStructRetValue = { sizeof(int32_t), (void *)&val, [&](UINT_PTR ptr){ return ValidateInt(ptr, val); } };
+        hr = ValidateOneArgument(pRetvalRange, functionName, 0, largeStructRetValue);
+    }
+    else if (functionName == WCHAR("IntegerStructFunc"))
+    {
+        _sawIntegerStructFuncLeave = true;
+
+        IntegerStruct is = { 21, 256 };
+        ExpectedArgValue integerStructRetValue = { sizeof(IntegerStruct), (void *)&is, [&](UINT_PTR ptr){ return ValidateIntegerStruct(ptr, is); } };
+        hr = ValidateOneArgument(pRetvalRange, functionName, 0, integerStructRetValue);
+    }
+    else if (functionName == WCHAR("FloatingPointStructFunc"))
+    {
+        _sawFloatingPointStructFuncLeave = true;
+
+        FloatingPointStruct fps = { 13.0, 256.8 };
+        ExpectedArgValue floatingPointStructRetValue = { sizeof(FloatingPointStruct), (void *)&fps, [&](UINT_PTR ptr){ return ValidateFloatingPointStruct(ptr, fps); } };
+        hr = ValidateOneArgument(pRetvalRange, functionName, 0, floatingPointStructRetValue);
+    }
+    else if (functionName == WCHAR("DoubleRetFunc"))
+    {
+        _sawDoubleRetFuncLeave = true;
+
+        double d = 13.0;
+        ExpectedArgValue doubleRetValue = { sizeof(double), (void *)&d, [&](UINT_PTR ptr){ return ValidateDouble(ptr, d); } };
+        hr = ValidateOneArgument(pRetvalRange, functionName, 0, doubleRetValue);
+    }
+
+    return hr;   
+}
+
+HRESULT STDMETHODCALLTYPE SlowPathELTProfiler::TailcallCallback(FunctionIDOrClientID functionIdOrClientID, COR_PRF_ELT_INFO eltInfo)
+{
+    COR_PRF_FRAME_INFO frameInfo;
+    HRESULT hr = pCorProfilerInfo->GetFunctionTailcall3Info(functionIdOrClientID.functionID, eltInfo, &frameInfo);
+    if (FAILED(hr))
+    {
+        wcout << L"GetFunctionTailcall3Info failed hr=0x" << std::hex << hr << endl;
+        _failures++;
+        return hr;
+    }
+
+    // Tailcalls don't happen on debug builds, and there's no arguments to verify from GetFunctionTailcallinfo3
+
+    return hr;    
+}
+
+void SlowPathELTProfiler::PrintBytes(const BYTE *bytes, size_t length)
+{
+    for (size_t i = 0; i < length; ++i)
+    {
+        wcout << std::setfill(L'0') << std::setw(2) << std::uppercase << std::hex << bytes[i];
+
+        if (i > 1 && (i + 1) % 4 == 0)
+        {
+            wcout << " ";
+        }
+    }
+
+    wcout << endl;
+}
+
+bool SlowPathELTProfiler::ValidateInt(UINT_PTR ptr, int expected)
+{
+    if (ptr == NULL)
+    {
+        return false;
+    }
+
+    return *(int *)ptr == expected;
+}
+
+bool SlowPathELTProfiler::ValidateFloat(UINT_PTR ptr, float expected)
+{
+    if (ptr == NULL)
+    {
+        return false;
+    }
+
+    return *(float *)ptr == expected;
+}
+
+bool SlowPathELTProfiler::ValidateDouble(UINT_PTR ptr, double expected)
+{
+    if (ptr == NULL)
+    {
+        return false;
+    }
+
+    return *(double *)ptr == expected;
+}
+
+bool SlowPathELTProfiler::ValidateString(UINT_PTR ptr, const WCHAR *expected)
+{
+    if (ptr == NULL || *(void **)ptr == NULL)
+    {
+        return false;
+    }
+
+    ULONG lengthOffset = 0;
+    ULONG bufferOffset = 0;
+    HRESULT hr = pCorProfilerInfo->GetStringLayout2(&lengthOffset, &bufferOffset);
+    if (FAILED(hr))
+    {
+        wcout << L"GetStringLayout2 failed hr=0x" << std::hex << hr << endl;
+        _failures++;
+        return hr;
+    }
+
+    UINT_PTR strReference = *((UINT_PTR *)ptr) + bufferOffset;
+    WCHAR *strPtr = (WCHAR *)strReference;
+    if (wcscmp(strPtr, expected) != 0)
+    {
+        _failures++;
+        return false;
+    }
+
+    return true;
+}
+
+bool SlowPathELTProfiler::ValidateMixedStruct(UINT_PTR ptr, MixedStruct expected)
+{
+    if (ptr == NULL)
+    {
+        return false;
+    }
+
+    MixedStruct lhs = *(MixedStruct *)ptr;
+    return lhs.x == expected.x && lhs.d == expected.d;
+}
+
+bool SlowPathELTProfiler::ValidateLargeStruct(UINT_PTR ptr, LargeStruct expected)
+{
+    if (ptr == NULL)
+    {
+        return false;
+    }
+
+    LargeStruct lhs = *(LargeStruct *)ptr;
+    return lhs.x0 == expected.x0
+            && lhs.x1 == expected.x1
+            && lhs.x2 == expected.x2 
+            && lhs.x3 == expected.x3
+            && lhs.d0 == expected.d0
+            && lhs.d1 == expected.d1
+            && lhs.d2 == expected.d2 
+            && lhs.d3 == expected.d3;
+}
+
+bool SlowPathELTProfiler::ValidateFloatingPointStruct(UINT_PTR ptr, FloatingPointStruct expected)
+{
+    if (ptr == NULL)
+    {
+        return false;
+    }
+
+    FloatingPointStruct lhs = *(FloatingPointStruct *)ptr;
+    return lhs.d1 == expected.d1 && lhs.d2 == expected.d2;
+}
+
+bool SlowPathELTProfiler::ValidateIntegerStruct(UINT_PTR ptr, IntegerStruct expected)
+{
+    if (ptr == NULL)
+    {
+        return false;
+    }
+
+    IntegerStruct lhs = *(IntegerStruct *)ptr;
+    return lhs.x == expected.x && lhs.y == expected.y;
+}
+
+
+HRESULT SlowPathELTProfiler::ValidateOneArgument(COR_PRF_FUNCTION_ARGUMENT_RANGE *pArgRange,
+                                        String functionName,
+                                        size_t argPos,
+                                        ExpectedArgValue expectedValue)
+{
+    if (pArgRange->length != expectedValue.length)
+    {
+        wcout << L"Argument " << argPos << L" for function " << functionName << " expected length " << expectedValue.length 
+                << L" but got length " << pArgRange->length << endl;
+        _failures++;
+        return E_FAIL;
+    }
+
+    if (!expectedValue.func(pArgRange->startAddress))
+    {
+        wcout << L"Argument " << argPos << L" for function " << functionName << L" did not match." << endl;
+        _failures++;
+
+        // Print out the bytes so you don't have to debug if something mismatches
+        BYTE *expectedBytes = (BYTE *)expectedValue.value;
+        wcout << L"Expected bytes: "; 
+        PrintBytes(expectedBytes, expectedValue.length);
+
+        BYTE *actualBytes = (BYTE *)pArgRange->startAddress;
+        wcout << L"Actual bytes  : "; 
+        PrintBytes(actualBytes, pArgRange->length);
+
+        return E_FAIL;
+    }
+
+    return S_OK;
+}
+
+HRESULT SlowPathELTProfiler::ValidateFunctionArgs(COR_PRF_FUNCTION_ARGUMENT_INFO *pArgInfo,
+                                          String functionName,
+                                          vector<ExpectedArgValue> expectedArgValues)
+{
+    size_t expectedArgCount = expectedArgValues.size();
+
+    if (pArgInfo->numRanges != expectedArgCount)
+    {
+        wcout << L"Expected " << expectedArgCount << L" args for " << functionName << L" but got " << pArgInfo->numRanges << endl;
+        _failures++;
+        return E_FAIL;
+    }
+
+    for (size_t i = 0; i < expectedArgCount; ++i)
+    {
+        ExpectedArgValue expectedValue = expectedArgValues[i];
+        COR_PRF_FUNCTION_ARGUMENT_RANGE *pArgRange = &(pArgInfo->ranges[i]);
+
+        HRESULT hr = ValidateOneArgument(pArgRange, functionName, i, expectedValue);
+        if (FAILED(hr))
+        {
+            return hr;
+        }
+    }
+
+    return S_OK;
+}
diff --git a/src/tests/profiler/native/eltprofiler/slowpatheltprofiler.h b/src/tests/profiler/native/eltprofiler/slowpatheltprofiler.h
new file mode 100644
index 00000000000000..254ba12d6e6629
--- /dev/null
+++ b/src/tests/profiler/native/eltprofiler/slowpatheltprofiler.h
@@ -0,0 +1,115 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#pragma once
+
+#include <memory>
+#include <vector>
+#include <functional>
+#include "../profiler.h"
+
+typedef bool (*validateFunc)(void *pMem);
+
+typedef struct
+{
+    size_t length;
+    void *value;
+    std::function<bool(UINT_PTR)> func;
+} ExpectedArgValue;
+
+typedef struct
+{
+    int x;
+    double d;
+} MixedStruct;
+
+typedef struct
+{
+    int x0;
+    double d0;
+    int x1;
+    double d1;
+    int x2;
+    double d2;
+    int x3;
+    double d3;
+} LargeStruct;
+
+typedef struct
+{
+    int x;
+    int y;
+} IntegerStruct;
+
+typedef struct
+{
+    double d1;
+    double d2;
+} FloatingPointStruct;
+
+class SlowPathELTProfiler : public Profiler
+{
+public:
+    static std::shared_ptr<SlowPathELTProfiler> s_profiler;
+
+    SlowPathELTProfiler() : Profiler(),
+        _failures(0),
+        _sawSimpleFuncEnter(false),
+        _sawMixedStructFuncEnter(false),
+        _sawLargeStructFuncEnter(false),
+        _sawSimpleFuncLeave(false),
+        _sawMixedStructFuncLeave(false),
+        _sawLargeStructFuncLeave(false),
+        _testType(TestType::Unknown)
+    {}
+
+    virtual GUID GetClsid();
+    virtual HRESULT STDMETHODCALLTYPE Initialize(IUnknown* pICorProfilerInfoUnk);
+    virtual HRESULT STDMETHODCALLTYPE Shutdown();
+
+
+    HRESULT STDMETHODCALLTYPE EnterCallback(FunctionIDOrClientID functionId, COR_PRF_ELT_INFO eltInfo);
+    HRESULT STDMETHODCALLTYPE LeaveCallback(FunctionIDOrClientID functionId, COR_PRF_ELT_INFO eltInfo);
+    HRESULT STDMETHODCALLTYPE TailcallCallback(FunctionIDOrClientID functionId, COR_PRF_ELT_INFO eltInfo);
+
+private:
+    enum class TestType
+    {
+        EnterHooks,
+        LeaveHooks,
+        Unknown
+    };
+
+    std::atomic<int> _failures;
+    bool _sawSimpleFuncEnter;
+    bool _sawMixedStructFuncEnter;
+    bool _sawLargeStructFuncEnter;
+    bool _sawSimpleFuncLeave;
+    bool _sawMixedStructFuncLeave;
+    bool _sawLargeStructFuncLeave;
+    bool _sawIntegerStructFuncLeave;
+    bool _sawFloatingPointStructFuncLeave;
+    bool _sawDoubleRetFuncLeave;
+
+    TestType _testType;
+    
+    void PrintBytes(const BYTE *bytes, size_t length);
+    
+    bool ValidateInt(UINT_PTR ptr, int expected);
+    bool ValidateFloat(UINT_PTR ptr, float expected);
+    bool ValidateDouble(UINT_PTR ptr, double expected);
+    bool ValidateString(UINT_PTR ptr, const WCHAR *expected);
+    bool ValidateMixedStruct(UINT_PTR ptr, MixedStruct expected);
+    bool ValidateLargeStruct(UINT_PTR ptr, LargeStruct expected);
+    bool ValidateFloatingPointStruct(UINT_PTR ptr, FloatingPointStruct expected);
+    bool ValidateIntegerStruct(UINT_PTR ptr, IntegerStruct expected);
+
+    HRESULT ValidateOneArgument(COR_PRF_FUNCTION_ARGUMENT_RANGE *pArgRange,
+                                String functionName,
+                                size_t argPos,
+                                ExpectedArgValue expectedValue);
+
+    HRESULT ValidateFunctionArgs(COR_PRF_FUNCTION_ARGUMENT_INFO *pArgInfo,
+                                 String name,
+                                 std::vector<ExpectedArgValue> expectedArgValues);
+};
diff --git a/src/tests/profiler/native/gcprofiler/gcprofiler.cpp b/src/tests/profiler/native/gcprofiler/gcprofiler.cpp
new file mode 100644
index 00000000000000..e6d3edccce5add
--- /dev/null
+++ b/src/tests/profiler/native/gcprofiler/gcprofiler.cpp
@@ -0,0 +1,136 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#include "gcprofiler.h"
+
+GUID GCProfiler::GetClsid()
+{
+    // {BCD8186F-1EEC-47E9-AFA7-396F879382C3}
+    GUID clsid = { 0xBCD8186F, 0x1EEC, 0x47E9, { 0xAF, 0xA7, 0x39, 0x6F, 0x87, 0x93, 0x82, 0xC3 } };
+    return clsid;
+}
+
+HRESULT GCProfiler::Initialize(IUnknown* pICorProfilerInfoUnk)
+{
+    Profiler::Initialize(pICorProfilerInfoUnk);
+
+    HRESULT hr = S_OK;
+    if (FAILED(hr = pCorProfilerInfo->SetEventMask2(COR_PRF_MONITOR_GC, 0)))
+    {
+        _failures++;
+        printf("FAIL: ICorProfilerInfo::SetEventMask2() failed hr=0x%x", hr);
+        return hr;
+    }
+
+    return S_OK;
+}
+
+HRESULT GCProfiler::Shutdown()
+{
+    Profiler::Shutdown();
+
+    if (_gcStarts == 0)
+    {
+        printf("GCProfiler::Shutdown: FAIL: Expected GarbaseCollectionStarted to be called\n");
+    }
+    else if (_gcFinishes == 0)
+    {
+        printf("GCProfiler::Shutdown: FAIL: Expected GarbageCollectionFinished to be called\n");
+    }
+    else if (_pohObjectsSeenRootReferences == 0 || _pohObjectsSeenObjectReferences == 0)
+    {
+        printf("GCProfiler::Shutdown: FAIL: no POH objects seen. root references=%d object references=%d\n",
+            _pohObjectsSeenRootReferences.load(), _pohObjectsSeenObjectReferences.load());
+    }
+    else if(_failures == 0)
+    {
+        printf("PROFILER TEST PASSES\n");
+    }
+    else
+    {
+        // failures were printed earlier when _failures was incremented
+    }
+    fflush(stdout);
+
+    return S_OK;
+}
+
+HRESULT GCProfiler::GarbageCollectionStarted(int cGenerations, BOOL generationCollected[], COR_PRF_GC_REASON reason)
+{
+    _gcStarts++;
+    if (_gcStarts - _gcFinishes > 2)
+    {
+        _failures++;
+        printf("GCProfiler::GarbageCollectionStarted: FAIL: Expected GCStart <= GCFinish+2. GCStart=%d, GCFinish=%d\n", (int)_gcStarts, (int)_gcFinishes);
+    }
+
+    return S_OK;
+}
+
+HRESULT GCProfiler::GarbageCollectionFinished()
+{
+    _gcFinishes++;
+    if (_gcStarts < _gcFinishes)
+    {
+        _failures++;
+        printf("GCProfiler::GarbageCollectionFinished: FAIL: Expected GCStart >= GCFinish. Start=%d, Finish=%d\n", (int)_gcStarts, (int)_gcFinishes);
+    }
+
+    _pohObjectsSeenObjectReferences += NumPOHObjectsSeen(_objectReferencesSeen);
+    _pohObjectsSeenRootReferences += NumPOHObjectsSeen(_rootReferencesSeen);
+    
+    return S_OK;
+}
+
+HRESULT GCProfiler::ObjectReferences(ObjectID objectId, ClassID classId, ULONG cObjectRefs, ObjectID objectRefIds[])
+{
+    HRESULT hr = S_OK;
+    for (ULONG i = 0; i < cObjectRefs; ++i)
+    {
+        ObjectID obj = objectRefIds[i];
+        if (obj != NULL)
+        {
+            _objectReferencesSeen.insert(obj);
+        }
+    }
+
+    return S_OK;
+}
+
+HRESULT GCProfiler::RootReferences(ULONG cRootRefs, ObjectID rootRefIds[])
+{    
+    for (ULONG i = 0; i < cRootRefs; ++i)
+    {
+        ObjectID obj = rootRefIds[i];
+        if (obj != NULL)
+        {
+            _rootReferencesSeen.insert(obj);
+        }
+    }
+
+    return S_OK;
+}
+
+int GCProfiler::NumPOHObjectsSeen(std::unordered_set<ObjectID> objects)
+{
+    int count = 0;
+    for (auto it = objects.begin(); it != objects.end(); ++it)
+    {
+        COR_PRF_GC_GENERATION_RANGE gen;
+        ObjectID obj = *it;
+        HRESULT hr = pCorProfilerInfo->GetObjectGeneration(obj, &gen);
+        if (FAILED(hr))
+        {
+            printf("GetObjectGeneration failed hr=0x%x\n", hr);
+            return hr;
+        }
+
+        if (gen.generation == COR_PRF_GC_PINNED_OBJECT_HEAP)
+        {
+            count++;
+        }
+
+    }
+
+    return count;
+}
diff --git a/src/tests/profiler/native/gcprofiler/gcprofiler.h b/src/tests/profiler/native/gcprofiler/gcprofiler.h
new file mode 100644
index 00000000000000..8e0fbebbc4c27d
--- /dev/null
+++ b/src/tests/profiler/native/gcprofiler/gcprofiler.h
@@ -0,0 +1,44 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#pragma once
+
+#include "../profiler.h"
+#include <unordered_set>
+
+
+// TODO: this class is intended to be the heavyweight GC API verification (i.e. COR_PRF_MONITOR_GC)
+// vs GCBasicProfiler which verifies COR_PRF_HIGH_BASIC_GC. Right now the only thing it does
+// is verify we see POH objects in the RootReferences callback, but it should be fleshed out.
+class GCProfiler : public Profiler
+{
+public:
+    GCProfiler() : Profiler(),
+        _gcStarts(0),
+        _gcFinishes(0),
+        _failures(0),
+        _pohObjectsSeenRootReferences(0),
+        _pohObjectsSeenObjectReferences(0),
+        _rootReferencesSeen(),
+        _objectReferencesSeen()
+    {}
+
+    virtual GUID GetClsid();
+    virtual HRESULT STDMETHODCALLTYPE Initialize(IUnknown* pICorProfilerInfoUnk);
+    virtual HRESULT STDMETHODCALLTYPE Shutdown();
+    virtual HRESULT STDMETHODCALLTYPE GarbageCollectionStarted(int cGenerations, BOOL generationCollected[], COR_PRF_GC_REASON reason);
+    virtual HRESULT STDMETHODCALLTYPE GarbageCollectionFinished();
+    virtual HRESULT STDMETHODCALLTYPE ObjectReferences(ObjectID objectId, ClassID classId, ULONG cObjectRefs, ObjectID objectRefIds[]);
+    virtual HRESULT STDMETHODCALLTYPE RootReferences(ULONG cRootRefs, ObjectID rootRefIds[]);
+
+private:
+    std::atomic<int> _gcStarts;
+    std::atomic<int> _gcFinishes;
+    std::atomic<int> _failures;
+    std::atomic<int> _pohObjectsSeenRootReferences;
+    std::atomic<int> _pohObjectsSeenObjectReferences;
+    std::unordered_set<ObjectID> _rootReferencesSeen;
+    std::unordered_set<ObjectID> _objectReferencesSeen;
+
+    int NumPOHObjectsSeen(std::unordered_set<ObjectID> objects);
+};
diff --git a/src/tests/profiler/native/profiler.cpp b/src/tests/profiler/native/profiler.cpp
index 3600788ccdf85e..2dae0d1e7d4f9b 100644
--- a/src/tests/profiler/native/profiler.cpp
+++ b/src/tests/profiler/native/profiler.cpp
@@ -21,12 +21,13 @@ HRESULT STDMETHODCALLTYPE Profiler::Initialize(IUnknown *pICorProfilerInfoUnk)
     printf("Profiler.dll!Profiler::Initialize\n");
     fflush(stdout);
 
-    HRESULT queryInterfaceResult = pICorProfilerInfoUnk->QueryInterface(__uuidof(ICorProfilerInfo9), reinterpret_cast<void **>(&this->pCorProfilerInfo));
+    HRESULT queryInterfaceResult = pICorProfilerInfoUnk->QueryInterface(__uuidof(ICorProfilerInfo11), reinterpret_cast<void **>(&this->pCorProfilerInfo));
     if (FAILED(queryInterfaceResult))
     {
         printf("Profiler.dll!Profiler::Initialize failed to QI for ICorProfilerInfo.\n");
         pICorProfilerInfoUnk = NULL;
     }
+    
     return S_OK;
 }
 
diff --git a/src/tests/profiler/native/profiler.h b/src/tests/profiler/native/profiler.h
index 490e9c9ced09a0..bb7651d018d7b2 100644
--- a/src/tests/profiler/native/profiler.h
+++ b/src/tests/profiler/native/profiler.h
@@ -3,6 +3,8 @@
 
 #pragma once
 
+#define NOMINMAX
+
 #include <atomic>
 #include <cstdio>
 #include "cor.h"
@@ -108,7 +110,7 @@ class Profiler : public ICorProfilerCallback10
     String GetModuleIDName(ModuleID modId);
 
 public:
-    ICorProfilerInfo9* pCorProfilerInfo;
+    ICorProfilerInfo11* pCorProfilerInfo;
 
     Profiler();
     virtual ~Profiler();
diff --git a/src/tests/profiler/native/profilerstring.h b/src/tests/profiler/native/profilerstring.h
index a45edbd05626f1..d7b63758369f5b 100644
--- a/src/tests/profiler/native/profilerstring.h
+++ b/src/tests/profiler/native/profilerstring.h
@@ -7,6 +7,7 @@
 #include <assert.h>
 #include <cstring>
 #include <string>
+#include <algorithm>
 
 #ifdef _WIN32
 #define WCHAR(str) L##str
@@ -23,7 +24,6 @@
 // here is to provide the easy ones to avoid all the copying and transforming. If more complex
 // string operations become necessary we should either write them in C++ or convert the string to
 // 32 bit and call the c runtime ones.
-using std::max;
 
 #define WCHAR(str) u##str
 inline size_t wcslen(const char16_t *str)
@@ -80,7 +80,7 @@ class String
         size_t otherLen = wcslen(other) + 1;
         if (buffer == nullptr || otherLen > bufferLen)
         {
-            bufferLen = max(DefaultStringLength, otherLen);
+            bufferLen = std::max(DefaultStringLength, otherLen);
             if (buffer != nullptr)
             {
                 delete[] buffer;
@@ -225,21 +225,23 @@ class String
 
         if (bufferLen > printBufferLen)
         {
-            delete[] printBuffer;
-            printBuffer = nullptr;
-            printBufferLen = 0;
-        }
+            if (printBuffer != nullptr)
+            {
+                delete[] printBuffer;
+            }
 
-        if (printBuffer == nullptr)
-        {
             printBuffer = new wchar_t[bufferLen];
+            printBufferLen = bufferLen;
         }
 
         for (size_t i = 0; i < bufferLen; ++i)
         {
-            printBuffer[i] = (wchar_t)buffer[i];
+            printBuffer[i] = CAST_CHAR(buffer[i]);
         }
 
+        // Make sure it's null terminated
+        printBuffer[bufferLen - 1] = '\0';
+
         return printBuffer;
     }
 
diff --git a/src/tests/profiler/rejit/rejit.csproj b/src/tests/profiler/rejit/rejit.csproj
index 7ea4cfaea5be58..ac5c4b677e7935 100644
--- a/src/tests/profiler/rejit/rejit.csproj
+++ b/src/tests/profiler/rejit/rejit.csproj
@@ -7,6 +7,8 @@
     <CLRTestPriority>0</CLRTestPriority>
     <Optimize>true</Optimize>
     <JitOptimizationSensitive>True</JitOptimizationSensitive>
+    <!-- This test provides no interesting scenarios for GCStress -->
+    <GCStressIncompatible>true</GCStressIncompatible>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />
diff --git a/src/tests/profiler/unittest/getappdomainstaticaddress.csproj b/src/tests/profiler/unittest/getappdomainstaticaddress.csproj
index 3a10288c5260a8..c5769302e85908 100644
--- a/src/tests/profiler/unittest/getappdomainstaticaddress.csproj
+++ b/src/tests/profiler/unittest/getappdomainstaticaddress.csproj
@@ -6,6 +6,12 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <CLRTestPriority>0</CLRTestPriority>
     <Optimize>true</Optimize>
+    <!-- This test currently fails for TailcallStress. Disable for JIT stress modes until this is fixed.
+         Issue: https://github.com/dotnet/runtime/issues/37117
+    -->
+    <JitOptimizationSensitive>true</JitOptimizationSensitive>
+    <!-- This test provides no interesting scenarios for GCStress -->
+    <GCStressIncompatible>true</GCStressIncompatible>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />
diff --git a/src/tests/profiler/unittest/metadatagetdispenser.csproj b/src/tests/profiler/unittest/metadatagetdispenser.csproj
index 7a525ce745d28c..fc9c21e7144d91 100644
--- a/src/tests/profiler/unittest/metadatagetdispenser.csproj
+++ b/src/tests/profiler/unittest/metadatagetdispenser.csproj
@@ -6,6 +6,8 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <CLRTestPriority>0</CLRTestPriority>
     <Optimize>true</Optimize>
+    <!-- This test provides no interesting scenarios for GCStress -->
+    <GCStressIncompatible>true</GCStressIncompatible>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />
diff --git a/src/tests/readytorun/crossgen2/Program.cs b/src/tests/readytorun/crossgen2/Program.cs
index bd00957a758409..16ab7df575a907 100644
--- a/src/tests/readytorun/crossgen2/Program.cs
+++ b/src/tests/readytorun/crossgen2/Program.cs
@@ -1626,6 +1626,200 @@ private static bool GenericLdtokenTest()
         return true;
     }
 
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static bool CheckArrayVal<T>(ref T refVal, T testValue) where T:IEquatable<T>
+    {
+        return refVal.Equals(testValue);
+    }
+
+    struct SomeLargeStruct : IEquatable<SomeLargeStruct>
+    {
+        public SomeLargeStruct(int _xVal)
+        {
+            x = _xVal;
+            y = 0;
+            z = 0;
+            w = 0;
+        }
+        public int x;
+        public int y;
+        public int z;
+        public int w;
+
+        public bool Equals(SomeLargeStruct other)
+        {
+            return (x == other.x) && (y == other.y) && (z == other.z) && (w == other.w);
+        }
+        public override bool Equals(object other)
+        {
+            return Equals((SomeLargeStruct)other);
+        }
+
+        public override int GetHashCode() { return x; }
+    }
+
+    class SomeClass : IEquatable<SomeClass>
+    {
+        public SomeClass(int _xVal)
+        {
+            x = _xVal;
+            y = 0;
+            z = 0;
+            w = 0;
+        }
+        public int x;
+        public int y;
+        public int z;
+        public int w;
+
+        public bool Equals(SomeClass other)
+        {
+            return (x == other.x) && (y == other.y) && (z == other.z) && (w == other.w);
+        }
+        public override bool Equals(object other)
+        {
+            return Equals((SomeClass)other);
+        }
+
+        public override int GetHashCode() { return x; }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static bool DoLargeStructMDArrayTest(SomeLargeStruct testValue)
+    {
+        SomeLargeStruct[,] array = new SomeLargeStruct[2,2];
+        array[0,0] = testValue;
+        if (!CheckArrayVal(ref array[0,0], testValue))
+        {
+            return false;
+        }
+        if (!testValue.Equals(array[0,0]))
+        {
+            return false;
+        }
+
+        return true;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static bool DoGenericArrayTest<T> (T testValue) where T:IEquatable<T>
+    {
+        T[,] array = new T[2,2];
+        array[0,0] = testValue;
+        if (!CheckArrayVal(ref array[0,0], testValue))
+        {
+            return false;
+        }
+        if (!testValue.Equals(array[0,0]))
+        {
+            return false;
+        }
+
+        return true;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static bool TestGenericMDArrayBehavior()
+    {
+        if (!DoGenericArrayTest<int>(42))
+        {
+            return false;
+        }
+
+        if (!DoGenericArrayTest<SomeClass>(new SomeClass(42)))
+        {
+            return false;
+        }
+
+        SomeLargeStruct testStruct = new SomeLargeStruct(42);
+        if (!DoGenericArrayTest<SomeLargeStruct>(testStruct))
+        {
+            return false;
+        }
+
+        if (!DoLargeStructMDArrayTest(testStruct))
+        {
+            return false;
+        }
+
+        return true;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static bool ArrayLdtokenTests()
+    {
+        // We're testing that mapping from ldtoken to RuntimeMethodHandle works for various ways that 
+        // ldtokens can be referenced (either via a generic token, or not.
+        // (there are slightly different codepaths in crossgen for this)
+        // Incorrect encoding will trigger a BadImageFormatException
+        RuntimeMethodHandle rmhCtor1 = default(RuntimeMethodHandle);
+        RuntimeMethodHandle rmhCtor2 = default(RuntimeMethodHandle);
+        RuntimeMethodHandle rmhSet = default(RuntimeMethodHandle);
+        RuntimeMethodHandle rmhGet = default(RuntimeMethodHandle);
+        RuntimeMethodHandle rmhAddress = default(RuntimeMethodHandle);
+        HelperGenericILCode<string>.LdTokenArrayMethods(ref rmhCtor1, ref rmhCtor2, ref rmhSet, ref rmhGet, ref rmhAddress);
+        HelperGenericILCode<object>.LdTokenArrayMethods(ref rmhCtor1, ref rmhCtor2, ref rmhSet, ref rmhGet, ref rmhAddress);
+        HelperILCode.LdTokenArrayMethodsInt(ref rmhCtor1, ref rmhCtor2, ref rmhSet, ref rmhGet, ref rmhAddress);
+        HelperILCode.LdTokenArrayMethodsString(ref rmhCtor1, ref rmhCtor2, ref rmhSet, ref rmhGet, ref rmhAddress);
+
+        return true;
+    }
+
+    [StructLayout(LayoutKind.Explicit)]
+    struct ExplicitLayoutStruct16
+    {
+        [FieldOffset(0)]
+        public int x;
+        [FieldOffset(4)]
+        public int y;
+        [FieldOffset(8)]
+        public int z;
+        [FieldOffset(12)]
+        public int w;
+        public override string ToString() { return $"{x}{y}{z}{w}"; }
+    }
+    struct BlittableStruct<T>
+    {
+	public ExplicitLayoutStruct16 _explict;
+        public override string ToString() { return $"{_explict}"; }
+    }
+
+    struct StructWithGenericBlittableStruct
+    {
+        public BlittableStruct<short> _blittableGeneric;
+        public int _int;
+        public override string ToString() { return $"{_blittableGeneric}{_int}"; }
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveOptimization)]    
+    private static bool TestWithStructureNonBlittableFieldDueToGenerics_StringCompare(ref StructWithGenericBlittableStruct input)
+    {
+        StructWithGenericBlittableStruct s = new StructWithGenericBlittableStruct();
+        s._blittableGeneric._explict.x = 1;
+        s._blittableGeneric._explict.y = 2;
+        s._blittableGeneric._explict.z = 3;
+        s._blittableGeneric._explict.w = 4;
+        s._int = 5;
+
+        Console.WriteLine(input);
+        Console.WriteLine(s);
+
+        return s.Equals(input) && input.ToString() == "12345";
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static bool TestWithStructureNonBlittableFieldDueToGenerics()
+    {
+        StructWithGenericBlittableStruct s = new StructWithGenericBlittableStruct();
+        s._blittableGeneric._explict.x = 1;
+        s._blittableGeneric._explict.y = 2;
+        s._blittableGeneric._explict.z = 3;
+        s._blittableGeneric._explict.w = 4;
+        s._int = 5;
+
+        return TestWithStructureNonBlittableFieldDueToGenerics_StringCompare(ref s);
+    }
+
     public static int Main(string[] args)
     {
         _passedTests = new List<string>();
@@ -1691,6 +1885,9 @@ public static int Main(string[] args)
         RunTest("ExplicitlySizedStructTest", ExplicitlySizedStructTest());
         RunTest("ExplicitlySizedClassTest", ExplicitlySizedClassTest());
         RunTest("GenericLdtokenTest", GenericLdtokenTest());
+        RunTest("ArrayLdtokenTests", ArrayLdtokenTests());
+        RunTest("TestGenericMDArrayBehavior", TestGenericMDArrayBehavior());
+        RunTest("TestWithStructureNonBlittableFieldDueToGenerics", TestWithStructureNonBlittableFieldDueToGenerics());
 
         File.Delete(TextFileName);
 
diff --git a/src/tests/readytorun/crossgen2/crossgen2smoke.csproj b/src/tests/readytorun/crossgen2/crossgen2smoke.csproj
index d70d8f75c527eb..88a0e7537a895c 100644
--- a/src/tests/readytorun/crossgen2/crossgen2smoke.csproj
+++ b/src/tests/readytorun/crossgen2/crossgen2smoke.csproj
@@ -5,6 +5,9 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <CLRTestPriority>0</CLRTestPriority>
 
+    <!-- Disable for GCStress due to timeout test failures: https://github.com/dotnet/runtime/issues/33949 -->
+    <GCStressIncompatible>true</GCStressIncompatible>
+
     <!-- ilasm round-trip testing doesn't make sense for this test -->
     <IlasmRoundTripIncompatible>true</IlasmRoundTripIncompatible>
     
diff --git a/src/tests/readytorun/crossgen2/helperildll.il b/src/tests/readytorun/crossgen2/helperildll.il
index 4a4194454a960a..752d16c83c1517 100644
--- a/src/tests/readytorun/crossgen2/helperildll.il
+++ b/src/tests/readytorun/crossgen2/helperildll.il
@@ -40,6 +40,55 @@
      ret
   }
 
+  .method public hidebysig static  void LdTokenArrayMethodsInt(valuetype[mscorlib]System.RuntimeMethodHandle& ctor, valuetype[mscorlib]System.RuntimeMethodHandle& ctor2, valuetype[mscorlib]System.RuntimeMethodHandle& set, valuetype[mscorlib]System.RuntimeMethodHandle& get, valuetype[mscorlib]System.RuntimeMethodHandle& address)
+  {
+     ldarg 0
+     ldtoken method instance void int32[,]::.ctor(int32, int32, int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 1
+     ldtoken method instance void int32[,]::.ctor(int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 2
+     ldtoken method instance void int32[,]::Set(int32, int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 3
+     ldtoken method instance int32 int32[,]::Get(int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 4
+     ldtoken method instance int32& int32[,]::Address(int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+     ret
+  }
+
+  .method public hidebysig static  void LdTokenArrayMethodsString(valuetype[mscorlib]System.RuntimeMethodHandle& ctor, valuetype[mscorlib]System.RuntimeMethodHandle& ctor2, valuetype[mscorlib]System.RuntimeMethodHandle& set, valuetype[mscorlib]System.RuntimeMethodHandle& get, valuetype[mscorlib]System.RuntimeMethodHandle& address)
+  {
+     ldarg 0
+     ldtoken method instance void string[,]::.ctor(int32, int32, int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 1
+     ldtoken method instance void string[,]::.ctor(int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 2
+     ldtoken method instance void string[,]::Set(int32, int32, string)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 3
+     ldtoken method instance string string[,]::Get(int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 4
+     ldtoken method instance string& string[,]::Address(int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+     ret
+  }
+
+
   .method public hidebysig static valuetype[mscorlib]System.RuntimeMethodHandle ForceStuffToBeCompiled() cil managed noinlining
   {
      call valuetype[mscorlib]System.RuntimeMethodHandle class HelperGenericILCode`1<object>::GetGenericFunctionMethodHandle<valuetype [helperdll]GenericStructForLdtoken`1<string>>()
@@ -50,6 +99,22 @@
      call valuetype[mscorlib]System.RuntimeMethodHandle HelperILCode::GetGenericFunctionMethodHandle<string>()
      ret
   }
+  .method public hidebysig static void ForceStuffToBeCompiled3(valuetype[mscorlib]System.RuntimeMethodHandle& ctor, valuetype[mscorlib]System.RuntimeMethodHandle& ctor2, valuetype[mscorlib]System.RuntimeMethodHandle& set, valuetype[mscorlib]System.RuntimeMethodHandle& get, valuetype[mscorlib]System.RuntimeMethodHandle& address) cil managed noinlining
+  {
+     ldarg 0
+     ldarg 1
+     ldarg 2
+     ldarg 3
+     ldarg 4
+     call void class HelperGenericILCode`1<object>::LdTokenArrayMethods(valuetype[mscorlib]System.RuntimeMethodHandle&, valuetype[mscorlib]System.RuntimeMethodHandle&, valuetype[mscorlib]System.RuntimeMethodHandle&, valuetype[mscorlib]System.RuntimeMethodHandle&, valuetype[mscorlib]System.RuntimeMethodHandle&)
+     ldarg 0
+     ldarg 1
+     ldarg 2
+     ldarg 3
+     ldarg 4
+     call void class HelperGenericILCode`1<int32>::LdTokenArrayMethods(valuetype[mscorlib]System.RuntimeMethodHandle& ctor, valuetype[mscorlib]System.RuntimeMethodHandle& ctor2, valuetype[mscorlib]System.RuntimeMethodHandle& set, valuetype[mscorlib]System.RuntimeMethodHandle& get, valuetype[mscorlib]System.RuntimeMethodHandle& address)
+     ret
+  }
 }
 
 .class auto ansi public beforefieldinit HelperGenericILCode`1<T>
@@ -66,4 +131,27 @@
      ldtoken method instance int32 valuetype [helperdll]GenericStructForLdtoken`1<!0>::GenericFunction<!!0>(!0, !!0, string, int32)
      ret
   }
+  .method public hidebysig static  void LdTokenArrayMethods(valuetype[mscorlib]System.RuntimeMethodHandle& ctor, valuetype[mscorlib]System.RuntimeMethodHandle& ctor2, valuetype[mscorlib]System.RuntimeMethodHandle& set, valuetype[mscorlib]System.RuntimeMethodHandle& get, valuetype[mscorlib]System.RuntimeMethodHandle& address)
+  {
+     ldarg 0
+     ldtoken method instance void !0[,]::.ctor(int32, int32, int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 1
+     ldtoken method instance void !0[,]::.ctor(int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 2
+     ldtoken method instance void !0[,]::Set(int32, int32, !0)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 3
+     ldtoken method instance !0 !0[,]::Get(int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+
+     ldarg 4
+     ldtoken method instance !0& !0[,]::Address(int32, int32)
+     stobj valuetype[mscorlib]System.RuntimeMethodHandle
+     ret
+  }
 }
diff --git a/src/tests/readytorun/multifolder/multifolder.csproj b/src/tests/readytorun/multifolder/multifolder.csproj
index 9c81a0173f6967..fc439c5be9ea7c 100644
--- a/src/tests/readytorun/multifolder/multifolder.csproj
+++ b/src/tests/readytorun/multifolder/multifolder.csproj
@@ -2,6 +2,7 @@
   <PropertyGroup>
     <OutputType>exe</OutputType>
     <CLRTestKind>BuildAndRun</CLRTestKind>
+    <GCStressIncompatible>true</GCStressIncompatible> <!-- https://github.com/dotnet/runtime/issues/39933 -->
     <AllowUnsafeBlocks>false</AllowUnsafeBlocks>
     <CLRTestPriority>0</CLRTestPriority>
 
diff --git a/src/tests/tracing/eventpipe/common/IpcUtils.cs b/src/tests/tracing/eventpipe/common/IpcUtils.cs
index c9dbade684cb44..2f39237f4b5810 100644
--- a/src/tests/tracing/eventpipe/common/IpcUtils.cs
+++ b/src/tests/tracing/eventpipe/common/IpcUtils.cs
@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+using System.IO.Pipes;
 using System.Net.Sockets;
 using System.Runtime.InteropServices;
 using System.Text;
@@ -13,6 +14,7 @@
 using System.Threading;
 using System.Linq;
 using System.Reflection;
+using System.Security.Principal;
 
 // modified version of same code in dotnet/diagnostics for testing
 namespace Tracing.Tests.Common
@@ -68,7 +70,7 @@ public static async Task<bool> RunSubprocess(Assembly currentAssembly, Dictionar
                 foreach ((string key, string value) in environment)
                     process.StartInfo.Environment.Add(key, value);
                 process.StartInfo.FileName = Process.GetCurrentProcess().MainModule.FileName;
-                process.StartInfo.Arguments = new Uri(currentAssembly.CodeBase).LocalPath + " 0";
+                process.StartInfo.Arguments = new Uri(currentAssembly.Location).LocalPath + " 0";
                 process.StartInfo.RedirectStandardOutput = true;
                 process.StartInfo.RedirectStandardInput = true;
                 process.StartInfo.RedirectStandardError = true;
@@ -153,6 +155,12 @@ public static async Task<bool> RunSubprocess(Assembly currentAssembly, Dictionar
 
             return fSuccess;
         }
+
+        public static void Assert(bool predicate, string message = "")
+        {
+            if (!predicate)
+                throw new Exception(message);
+        }
     }
 
     public class IpcHeader
@@ -274,7 +282,7 @@ override public string ToString()
             {
                 sb.Append("Payload=[ ");
                 foreach (byte b in Payload)
-                    sb.Append($"'{b:X4}' ");
+                    sb.Append($"0x{b:X2} ");
                 sb.Append(" ]");
             }
             sb.Append("}");
@@ -316,4 +324,57 @@ private static IpcMessage Read(Stream stream)
             return IpcMessage.Parse(stream);
         }
     }
+
+    public class ConnectionHelper
+    {
+        private static string IpcRootPath { get; } = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? @"\\.\pipe\" : Path.GetTempPath();
+        public static Stream GetStandardTransport(int processId)
+        {
+            try 
+            {
+                var process = Process.GetProcessById(processId);
+            }
+            catch (System.ArgumentException)
+            {
+                throw new Exception($"Process {processId} is not running.");
+            }
+            catch (System.InvalidOperationException)
+            {
+                throw new Exception($"Process {processId} seems to be elevated.");
+            }
+ 
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                string pipeName = $"dotnet-diagnostic-{processId}";
+                var namedPipe = new NamedPipeClientStream(
+                    ".", pipeName, PipeDirection.InOut, PipeOptions.None, TokenImpersonationLevel.Impersonation);
+                namedPipe.Connect(3);
+                return namedPipe;
+            }
+            else
+            {
+                string ipcPort;
+                try
+                {
+                    ipcPort = Directory.GetFiles(IpcRootPath, $"dotnet-diagnostic-{processId}-*-socket") // Try best match.
+                                .OrderByDescending(f => new FileInfo(f).LastWriteTime)
+                                .FirstOrDefault();
+                    if (ipcPort == null)
+                    {
+                        throw new Exception($"Process {processId} not running compatible .NET Core runtime.");
+                    }
+                }
+                catch (InvalidOperationException)
+                {
+                    throw new Exception($"Process {processId} not running compatible .NET Core runtime.");
+                }
+                string path = Path.Combine(IpcRootPath, ipcPort);
+                var remoteEP = new UnixDomainSocketEndPoint(path);
+
+                var socket = new Socket(AddressFamily.Unix, SocketType.Stream, ProtocolType.Unspecified);
+                socket.Connect(remoteEP);
+                return new NetworkStream(socket, ownsSocket: true);
+            }
+        }
+    }
 }
diff --git a/src/tests/tracing/eventpipe/common/Reverse.cs b/src/tests/tracing/eventpipe/common/Reverse.cs
index 1b99f913d65901..19c9b216ce8468 100644
--- a/src/tests/tracing/eventpipe/common/Reverse.cs
+++ b/src/tests/tracing/eventpipe/common/Reverse.cs
@@ -102,7 +102,6 @@ public ReverseServer(string serverAddress, int bufferSize = 16 * 1024)
                 socket.ReceiveBufferSize = Math.Max(bufferSize, 128);
                 socket.Bind(remoteEP);
                 socket.Listen(255);
-                socket.LingerState.Enabled = false;
                 _server = socket;
             }
         }
@@ -166,20 +165,13 @@ public void Shutdown()
                     }
                     break;
                 case Socket socket:
-                    try
-                    {
-                        socket.Shutdown(SocketShutdown.Both);
-                    }
-                    catch {}
-                    finally
-                    {
-                        _clientSocket?.Close();
-                        socket.Close();
-                        socket.Dispose();
-                        _clientSocket?.Dispose();
-                        if (File.Exists(_serverAddress))
-                            File.Delete(_serverAddress);
-                    }
+                    if (File.Exists(_serverAddress))
+                        File.Delete(_serverAddress);
+                    socket.Close();
+                    socket.Dispose();
+                    _clientSocket?.Shutdown(SocketShutdown.Both);
+                    _clientSocket?.Close();
+                    _clientSocket?.Dispose();
                     break;
                 default:
                     throw new ArgumentException("Invalid server type");
diff --git a/src/tests/tracing/eventpipe/eventsourceerror/eventsourceerror.csproj b/src/tests/tracing/eventpipe/eventsourceerror/eventsourceerror.csproj
index 82a0cd70a8901a..3d6ed00a968625 100644
--- a/src/tests/tracing/eventpipe/eventsourceerror/eventsourceerror.csproj
+++ b/src/tests/tracing/eventpipe/eventsourceerror/eventsourceerror.csproj
@@ -4,7 +4,7 @@
     <OutputType>exe</OutputType>
     <CLRTestKind>BuildAndRun</CLRTestKind>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <!-- Disable for GCStress due to test failure: https://github.com/dotnet/runtime/issues/35884 -->
+    <!-- https://github.com/dotnet/runtime/issues/36028 -->
     <GCStressIncompatible>true</GCStressIncompatible>
     <UnloadabilityIncompatible>true</UnloadabilityIncompatible>
     <CLRTestPriority>0</CLRTestPriority>
diff --git a/src/tests/tracing/eventpipe/gcdump/gcdump.cs b/src/tests/tracing/eventpipe/gcdump/gcdump.cs
index 1ee96f83781c71..963544d9e308c9 100644
--- a/src/tests/tracing/eventpipe/gcdump/gcdump.cs
+++ b/src/tests/tracing/eventpipe/gcdump/gcdump.cs
@@ -82,17 +82,15 @@ public static int Main(string[] args)
 
             return () => 
             {
-                // These values are ~80% (rounded to nice whole numbers) of the values
-                // I saw when writing the test. The idea is that I want to catch
-                // any real deviation in the number of types, but don't want to have
-                // to maintain this test as the number of types varies. (And they will vary due to 
-                // framework code changes). If this test needs any sort of ongoing maintenance
-                // just change all these values to a low number like 10 and move on.
-                if (_bulkTypeCount > 125
-                    && _bulkNodeCount > 600
-                    && _bulkEdgeCount > 850
-                    && _bulkRootEdgeCount > 250
-                    && _bulkRootStaticVarCount > 70)
+                // Hopefully it is low enough to be resilient to changes in the runtime
+                // and high enough to catch issues. There should be between hundreds and thousands
+                // for each, but the number is variable and the point of the test is to verify
+                // that we get any events at all.
+                if (_bulkTypeCount > 50
+                     && _bulkNodeCount > 50
+                     && _bulkEdgeCount > 50
+                     && _bulkRootEdgeCount > 50
+                     && _bulkRootStaticVarCount > 50)
                 {
                     return 100;
                 }
@@ -108,4 +106,4 @@ public static int Main(string[] args)
             };
         };
     }
-}
\ No newline at end of file
+}
diff --git a/src/tests/tracing/eventpipe/gcdump/gcdump.csproj b/src/tests/tracing/eventpipe/gcdump/gcdump.csproj
index a1915b163e35a8..6d27a4fd2b7e84 100644
--- a/src/tests/tracing/eventpipe/gcdump/gcdump.csproj
+++ b/src/tests/tracing/eventpipe/gcdump/gcdump.csproj
@@ -6,6 +6,8 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <UnloadabilityIncompatible>true</UnloadabilityIncompatible>
     <CLRTestPriority>0</CLRTestPriority>
+    <!-- This test provides no interesting scenarios for GCStress -->
+    <GCStressIncompatible>true</GCStressIncompatible>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />
diff --git a/src/tests/tracing/eventpipe/pauseonstart/pauseonstart.cs b/src/tests/tracing/eventpipe/pauseonstart/pauseonstart.cs
index 83782532d06ab4..4065cd586feef1 100644
--- a/src/tests/tracing/eventpipe/pauseonstart/pauseonstart.cs
+++ b/src/tests/tracing/eventpipe/pauseonstart/pauseonstart.cs
@@ -34,8 +34,8 @@ public static async Task<bool> TEST_RuntimeResumesExecutionWithCommand()
                     Stream stream = await server.AcceptAsync();
                     IpcAdvertise advertise = IpcAdvertise.Parse(stream);
                     Logger.logger.Log(advertise.ToString());
-                    // send ResumeRuntime command (0xFF=ServerCommandSet, 0x01=ResumeRuntime commandid)
-                    var message = new IpcMessage(0xFF,0x01);
+                    // send ResumeRuntime command (0x04=ProcessCommandSet, 0x01=ResumeRuntime commandid)
+                    var message = new IpcMessage(0x04,0x01);
                     Logger.logger.Log($"Sent: {message.ToString()}");
                     IpcMessage response = IpcClient.SendMessage(stream, message);
                     Logger.logger.Log($"received: {response.ToString()}");
@@ -75,8 +75,8 @@ public static async Task<bool> TEST_TracesHaveRelevantEvents()
                     Task readerTask = eventStream.CopyToAsync(memoryStream);
                     
                     Logger.logger.Log($"Send ResumeRuntime Diagnostics IPC Command");
-                    // send ResumeRuntime command (0xFF=ServerCommandSet, 0x01=ResumeRuntime commandid)
-                    var message = new IpcMessage(0xFF,0x01);
+                    // send ResumeRuntime command (0x04=ProcessCommandSet, 0x01=ResumeRuntime commandid)
+                    var message = new IpcMessage(0x04,0x01);
                     Logger.logger.Log($"Sent: {message.ToString()}");
                     IpcMessage response = IpcClient.SendMessage(stream, message);
                     Logger.logger.Log($"received: {response.ToString()}");
@@ -145,8 +145,8 @@ public static async Task<bool> TEST_MultipleSessionsCanBeStartedWhilepaused()
 
                     
                     Logger.logger.Log($"Send ResumeRuntime Diagnostics IPC Command");
-                    // send ResumeRuntime command (0xFF=ServerCommandSet, 0x01=ResumeRuntime commandid)
-                    var message = new IpcMessage(0xFF,0x01);
+                    // send ResumeRuntime command (0x04=ProcessCommandSet, 0x01=ResumeRuntime commandid)
+                    var message = new IpcMessage(0x04,0x01);
                     Logger.logger.Log($"Sent: {message.ToString()}");
                     IpcMessage response = IpcClient.SendMessage(stream, message);
                     Logger.logger.Log($"received: {response.ToString()}");
@@ -247,8 +247,8 @@ public static async Task<bool> TEST_CanStartAndStopSessionWhilepaused()
                     Logger.logger.Log("Stopped EventPipeSession over standard connection");
                     
                     Logger.logger.Log($"Send ResumeRuntime Diagnostics IPC Command");
-                    // send ResumeRuntime command (0xFF=ServerCommandSet, 0x01=ResumeRuntime commandid)
-                    var message = new IpcMessage(0xFF,0x01);
+                    // send ResumeRuntime command (0x04=ProcessCommandSet, 0x01=ResumeRuntime commandid)
+                    var message = new IpcMessage(0x04,0x01);
                     Logger.logger.Log($"Sent: {message.ToString()}");
                     IpcMessage response = IpcClient.SendMessage(stream, message);
                     Logger.logger.Log($"received: {response.ToString()}");
@@ -292,8 +292,8 @@ public static async Task<bool> TEST_DisabledCommandsError()
                     Logger.logger.Log(advertise.ToString());
 
                     Logger.logger.Log($"Send ResumeRuntime Diagnostics IPC Command");
-                    // send ResumeRuntime command (0xFF=ServerCommandSet, 0x01=ResumeRuntime commandid)
-                    message = new IpcMessage(0xFF,0x01);
+                    // send ResumeRuntime command (0x04=ProcessCommandSet, 0x01=ResumeRuntime commandid)
+                    message = new IpcMessage(0x04,0x01);
                     Logger.logger.Log($"Sent: {message.ToString()}");
                     response = IpcClient.SendMessage(stream, message);
                     Logger.logger.Log($"received: {response.ToString()}");
diff --git a/src/tests/tracing/eventpipe/processinfo/processinfo.cs b/src/tests/tracing/eventpipe/processinfo/processinfo.cs
new file mode 100644
index 00000000000000..f9f70605e1f5fe
--- /dev/null
+++ b/src/tests/tracing/eventpipe/processinfo/processinfo.cs
@@ -0,0 +1,201 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.Tracing;
+using System.Diagnostics;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Diagnostics.Tools.RuntimeClient;
+using Microsoft.Diagnostics.Tracing;
+using Tracing.Tests.Common;
+
+namespace Tracing.Tests.ProcessInfoValidation
+{
+    public class ProcessInfoValidation
+    {
+        public static string NormalizeCommandLine(string cmdline)
+        {
+            // ASSUMPTION: double quotes (") and single quotes (') are used for paths with spaces
+            // ASSUMPTION: This test will only have two parts to the commandline
+
+            // check for quotes in first part
+            var parts = new List<string>();
+            bool isQuoted = false;
+            int start = 0;
+
+            for (int i = 0; i < cmdline.Length; i++)
+            {
+                if (isQuoted)
+                {
+                    if (cmdline[i] == '"' || cmdline[i] == '\'')
+                    {
+                        parts.Add(cmdline.Substring(start, i - start));
+                        isQuoted = false;
+                        start = i + 1;
+                    }
+                }
+                else if (cmdline[i] == '"' || cmdline[i] == '\'')
+                {
+                    isQuoted = true;
+                    start = i + 1;
+                }
+                else if (cmdline[i] == ' ')
+                {
+                    parts.Add(cmdline.Substring(start, i - start));
+                    start = i + 1;
+                }
+                else if (i == cmdline.Length - 1)
+                {
+                    parts.Add(cmdline.Substring(start));
+                }
+            }
+
+            string normalizedCommandLine = parts
+                .Where(part => !string.IsNullOrWhiteSpace(part))
+                .Select(part => (new FileInfo(part)).FullName)
+                .Aggregate((s1, s2) => string.Join(' ', s1, s2));
+
+            // Tests are run out of /tmp on Mac and linux, but on Mac /tmp is actually a symlink that points to /private/tmp.
+            // This isn't represented in the output from FileInfo.FullName unfortunately, so we'll fake that completion in that case.
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX) && normalizedCommandLine.StartsWith("/tmp/"))
+                normalizedCommandLine = "/private" + normalizedCommandLine;
+
+            return normalizedCommandLine;
+        }
+
+        public static int Main(string[] args)
+        {
+
+            Process currentProcess = Process.GetCurrentProcess();
+            int pid = currentProcess.Id;
+            Logger.logger.Log($"Test PID: {pid}");
+
+            Stream stream = ConnectionHelper.GetStandardTransport(pid);
+
+            // 0x04 = ProcessCommandSet, 0x00 = ProcessInfo
+            var processInfoMessage = new IpcMessage(0x04, 0x00);
+            Logger.logger.Log($"Wrote: {processInfoMessage}");
+            IpcMessage response = IpcClient.SendMessage(stream, processInfoMessage);
+            Logger.logger.Log($"Received: {response}");
+
+            Utils.Assert(response.Header.CommandSet == 0xFF, $"Response must have Server command set. Expected: 0xFF, Received: 0x{response.Header.CommandSet:X2}"); // server
+            Utils.Assert(response.Header.CommandId == 0x00, $"Response must have OK command id. Expected: 0x00, Received: 0x{response.Header.CommandId:X2}"); // OK
+
+            // Parse payload
+            // uint64_t ProcessId;
+            // GUID RuntimeCookie;
+            // LPCWSTR CommandLine;
+            // LPCWSTR OS;
+            // LPCWSTR Arch;
+
+            int totalSize = response.Payload.Length;
+            Logger.logger.Log($"Total size of Payload == {totalSize} b");
+
+            // VALIDATE PID
+            int start = 0;
+            int end = start + 8 /* sizeof(uint63_t) */;
+            UInt64 processId = BitConverter.ToUInt64(response.Payload[start..end]);
+            Utils.Assert((int)processId == pid, $"PID in process info must match. Expected: {pid}, Received: {processId}");
+            Logger.logger.Log($"pid: {processId}");
+
+            // VALIDATE RUNTIME COOKIE
+            start = end;
+            end = start + 16 /* sizeof(GUID) */;
+            Guid runtimeCookie = new Guid(response.Payload[start..end]);
+            Logger.logger.Log($"runtimeCookie: {runtimeCookie}");
+
+            // VALIDATE COMMAND LINE
+            start = end;
+            end = start + 4 /* sizeof(uint32_t) */;
+            UInt32 commandLineLength = BitConverter.ToUInt32(response.Payload[start..end]);
+            Logger.logger.Log($"commandLineLength: {commandLineLength}");
+
+            start = end;
+            end = start + ((int)commandLineLength * sizeof(char));
+            Utils.Assert(end <= totalSize, $"String end can't exceed payload size. Expected: <{totalSize}, Received: {end} (decoded length: {commandLineLength})");
+            Logger.logger.Log($"commandLine bytes: [ {response.Payload[start..end].Select(b => b.ToString("X2") + " ").Aggregate(string.Concat)}]");
+            string commandLine = System.Text.Encoding.Unicode.GetString(response.Payload[start..end]).TrimEnd('\0');
+            Logger.logger.Log($"commandLine: \"{commandLine}\"");
+
+            // The following logic is tailored to this specific test where the cmdline _should_ look like the following:
+            // /path/to/corerun /path/to/processinfo.dll
+            // or
+            // "C:\path\to\CoreRun.exe" C:\path\to\processinfo.dll
+            string currentProcessCommandLine = $"{currentProcess.MainModule.FileName} {System.Reflection.Assembly.GetExecutingAssembly().Location}";
+            string receivedCommandLine = NormalizeCommandLine(commandLine);
+
+            Utils.Assert(currentProcessCommandLine.Equals(receivedCommandLine, StringComparison.OrdinalIgnoreCase), $"CommandLine must match current process. Expected: {currentProcessCommandLine}, Received: {receivedCommandLine} (original: {commandLine})");
+
+            // VALIDATE OS
+            start = end;
+            end = start + 4 /* sizeof(uint32_t) */;
+            UInt32 OSLength = BitConverter.ToUInt32(response.Payload[start..end]);
+            Logger.logger.Log($"OSLength: {OSLength}");
+
+            start = end;
+            end = start + ((int)OSLength * sizeof(char));
+            Utils.Assert(end <= totalSize, $"String end can't exceed payload size. Expected: <{totalSize}, Received: {end} (decoded length: {OSLength})");
+            Logger.logger.Log($"OS bytes: [ {response.Payload[start..end].Select(b => b.ToString("X2") + " ").Aggregate(string.Concat)}]");
+            string OS = System.Text.Encoding.Unicode.GetString(response.Payload[start..end]).TrimEnd('\0');
+            Logger.logger.Log($"OS: \"{OS}\"");
+
+            // see eventpipeeventsource.cpp for these values
+            string expectedOSValue = null;
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                expectedOSValue = "Windows";
+            }
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+            {
+                expectedOSValue = "macOS";
+            }
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+            {
+                expectedOSValue = "Linux";
+            }
+            else
+            {
+                expectedOSValue = "Unknown";
+            }
+
+            Utils.Assert(expectedOSValue.Equals(OS), $"OS must match current Operating System. Expected: \"{expectedOSValue}\", Received: \"{OS}\"");
+
+            // VALIDATE ARCH
+            start = end;
+            end = start + 4 /* sizeof(uint32_t) */;
+            UInt32 archLength = BitConverter.ToUInt32(response.Payload[start..end]);
+            Logger.logger.Log($"archLength: {archLength}");
+
+            start = end;
+            end = start + ((int)archLength * sizeof(char));
+            Utils.Assert(end <= totalSize, $"String end can't exceed payload size. Expected: <{totalSize}, Received: {end} (decoded length: {archLength})");
+            Logger.logger.Log($"arch bytes: [ {response.Payload[start..end].Select(b => b.ToString("X2") + " ").Aggregate(string.Concat)}]");
+            string arch = System.Text.Encoding.Unicode.GetString(response.Payload[start..end]).TrimEnd('\0');
+            Logger.logger.Log($"arch: \"{arch}\"");
+
+            // see eventpipeeventsource.cpp for these values
+            string expectedArchValue = RuntimeInformation.ProcessArchitecture switch
+            {
+                Architecture.X86 => "x86",
+                Architecture.X64 => "x64",
+                Architecture.Arm => "arm32",
+                Architecture.Arm64 => "arm64",
+                _ => "Unknown"
+            };
+
+            Utils.Assert(expectedArchValue.Equals(arch), $"OS must match current Operating System. Expected: \"{expectedArchValue}\", Received: \"{arch}\"");
+
+            Utils.Assert(end == totalSize, $"Full payload should have been read. Expected: {totalSize}, Received: {end}");
+
+            Logger.logger.Log($"\n{{\n\tprocessId: {processId},\n\truntimeCookie: {runtimeCookie},\n\tcommandLine: {commandLine},\n\tOS: {OS},\n\tArch: {arch}\n}}");
+
+            return 100;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/tests/tracing/eventpipe/processinfo/processinfo.csproj b/src/tests/tracing/eventpipe/processinfo/processinfo.csproj
new file mode 100644
index 00000000000000..69e7a9fba00c24
--- /dev/null
+++ b/src/tests/tracing/eventpipe/processinfo/processinfo.csproj
@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworkIdentifier>.NETCoreApp</TargetFrameworkIdentifier>
+    <OutputType>exe</OutputType>
+    <CLRTestKind>BuildAndRun</CLRTestKind>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <CLRTestPriority>0</CLRTestPriority>
+    <UnloadabilityIncompatible>true</UnloadabilityIncompatible>
+    <JitOptimizationSensitive>true</JitOptimizationSensitive>
+    <!-- ilasm round-trip testing doesn't work, as test expects unchanged assembly name.
+         Issue: https://github.com/dotnet/runtime/issues/39935
+    -->
+    <IlasmRoundTripIncompatible>true</IlasmRoundTripIncompatible>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+    <ProjectReference Include="../common/common.csproj" />
+  </ItemGroup>
+</Project>
diff --git a/src/tests/tracing/eventpipe/reverse/reverse.csproj b/src/tests/tracing/eventpipe/reverse/reverse.csproj
index 44835ac5980fad..cec9486b658b50 100644
--- a/src/tests/tracing/eventpipe/reverse/reverse.csproj
+++ b/src/tests/tracing/eventpipe/reverse/reverse.csproj
@@ -4,7 +4,7 @@
     <OutputType>exe</OutputType>
     <CLRTestKind>BuildAndRun</CLRTestKind>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
     <UnloadabilityIncompatible>true</UnloadabilityIncompatible>
     <JitOptimizationSensitive>true</JitOptimizationSensitive>
     <!-- Disable for GCStress due to test failure: https://github.com/dotnet/runtime/issues/38524 -->
diff --git a/src/tests/tracing/eventpipe/reverseouter/reverseouter.cs b/src/tests/tracing/eventpipe/reverseouter/reverseouter.cs
index ff01fbc0f449f1..15eadb015f5829 100644
--- a/src/tests/tracing/eventpipe/reverseouter/reverseouter.cs
+++ b/src/tests/tracing/eventpipe/reverseouter/reverseouter.cs
@@ -47,16 +47,22 @@ public static async Task<bool> TEST_ReverseConnectionCanRecycleWhileTracing()
                             Logger.logger.Log("Starting EventPipeSession over standard connection");
                             using Stream stream = EventPipeClient.CollectTracing(pid, config, out var sessionId);
                             Logger.logger.Log($"Started EventPipeSession over standard connection with session id: 0x{sessionId:x}");
-                            using var source = new EventPipeEventSource(stream);
-                            Task readerTask = Task.Run(() => source.Process());
+                            // using var source = new EventPipeEventSource(stream);
+                            using var memroyStream = new MemoryStream();
+                            Task readerTask = stream.CopyToAsync(memroyStream);//Task.Run(() => source.Process());
                             await Task.Delay(500);
                             Logger.logger.Log("Stopping EventPipeSession over standard connection");
                             EventPipeClient.StopTracing(pid, sessionId);
                             await readerTask;
                             Logger.logger.Log("Stopped EventPipeSession over standard connection");
                         }
+                        catch (Exception e)
+                        {
+                            Logger.logger.Log(e.ToString());
+                        }
                         finally
                         {
+                            Logger.logger.Log("setting the MRE");
                             mre.Set();
                         }
                     });
diff --git a/src/tests/tracing/eventpipe/reverseouter/reverseouter.csproj b/src/tests/tracing/eventpipe/reverseouter/reverseouter.csproj
index 62665b29922abc..f417b3704d4551 100644
--- a/src/tests/tracing/eventpipe/reverseouter/reverseouter.csproj
+++ b/src/tests/tracing/eventpipe/reverseouter/reverseouter.csproj
@@ -4,12 +4,14 @@
     <OutputType>exe</OutputType>
     <CLRTestKind>BuildAndRun</CLRTestKind>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <CLRTestPriority>1</CLRTestPriority>
+    <CLRTestPriority>0</CLRTestPriority>
     <UnloadabilityIncompatible>true</UnloadabilityIncompatible>
     <JitOptimizationSensitive>true</JitOptimizationSensitive>
+    <!-- reverseouter fails under GCStress. Issue: https://github.com/dotnet/runtime/issues/38801 -->
+    <GCStressIncompatible>true</GCStressIncompatible>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />
     <ProjectReference Include="../common/common.csproj" />
   </ItemGroup>
-</Project>
\ No newline at end of file
+</Project>
diff --git a/tools-local/tasks/installer.tasks/BuildTools.Publish/CloudTestTasks/ListAzureBlobs.cs b/tools-local/tasks/installer.tasks/BuildTools.Publish/CloudTestTasks/ListAzureBlobs.cs
index fb68d7bdfea44e..2376d563859786 100644
--- a/tools-local/tasks/installer.tasks/BuildTools.Publish/CloudTestTasks/ListAzureBlobs.cs
+++ b/tools-local/tasks/installer.tasks/BuildTools.Publish/CloudTestTasks/ListAzureBlobs.cs
@@ -100,7 +100,7 @@ public static async Task<List<string>> ListBlobs(TaskLoggingHelper Log, string A
                 }
                 while (!string.IsNullOrEmpty(nextMarker))
                 {
-                    urlListBlobs = string.Format($"https://{AccountName}.blob.core.windows.net/{ContainerName}?restype=container&comp=list&marker={nextMarker}");
+                    urlListBlobs = $"https://{AccountName}.blob.core.windows.net/{ContainerName}?restype=container&comp=list&marker={nextMarker}";
                     if (!string.IsNullOrWhiteSpace(FilterBlobNames))
                     {
                         urlListBlobs += $"&prefix={FilterBlobNames}";
diff --git a/tools-local/tasks/installer.tasks/installer.tasks.csproj b/tools-local/tasks/installer.tasks/installer.tasks.csproj
index 356f22ac74eb9c..368fe4c58d9f30 100644
--- a/tools-local/tasks/installer.tasks/installer.tasks.csproj
+++ b/tools-local/tasks/installer.tasks/installer.tasks.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0</TargetFrameworks>
-    <TargetFrameworks Condition="'$(OS)' == 'Windows_NT'">$(TargetFrameworks);net46</TargetFrameworks>
+    <TargetFrameworks Condition="'$(OS)' == 'Windows_NT'">$(TargetFrameworks);net461</TargetFrameworks>
     <EnableDefaultCompileItems>false</EnableDefaultCompileItems>
     <IsShipping>false</IsShipping>
   </PropertyGroup>
diff --git a/tools-local/tasks/mobile.tasks/AndroidAppBuilder/ApkBuilder.cs b/tools-local/tasks/mobile.tasks/AndroidAppBuilder/ApkBuilder.cs
index a92a5090c33689..92812402ce296e 100644
--- a/tools-local/tasks/mobile.tasks/AndroidAppBuilder/ApkBuilder.cs
+++ b/tools-local/tasks/mobile.tasks/AndroidAppBuilder/ApkBuilder.cs
@@ -257,7 +257,7 @@ private static string GetLatestBuildTools(string androidSdkDir)
         string? buildTools = Directory.GetDirectories(Path.Combine(androidSdkDir, "build-tools"))
             .Select(Path.GetFileName)
             .Where(file => !file!.Contains("-"))
-            .Select(file => Version.TryParse(Path.GetFileName(file), out Version? version) ? version : default)
+            .Select(file => { Version.TryParse(Path.GetFileName(file), out Version? version); return version; })
             .OrderByDescending(v => v)
             .FirstOrDefault()?.ToString();
 
diff --git a/tools-local/tasks/mobile.tasks/WasmAppBuilder/WasmAppBuilder.cs b/tools-local/tasks/mobile.tasks/WasmAppBuilder/WasmAppBuilder.cs
index 9a5d51cea5ccf4..4ca72c5e61b1b4 100644
--- a/tools-local/tasks/mobile.tasks/WasmAppBuilder/WasmAppBuilder.cs
+++ b/tools-local/tasks/mobile.tasks/WasmAppBuilder/WasmAppBuilder.cs
@@ -9,6 +9,8 @@
 using System.IO;
 using System.Linq;
 using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 using System.Reflection;
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
@@ -27,13 +29,56 @@ public class WasmAppBuilder : Task
     public string? MainJS { get; set; }
     [Required]
     public ITaskItem[]? AssemblySearchPaths { get; set; }
+    public int DebugLevel { get; set; }
     public ITaskItem[]? ExtraAssemblies { get; set; }
     public ITaskItem[]? FilesToIncludeInFileSystem { get; set; }
     public ITaskItem[]? RemoteSources { get; set; }
+    public bool InvariantGlobalization { get; set; }
 
-    Dictionary<string, Assembly>? _assemblies;
+    SortedDictionary<string, Assembly>? _assemblies;
     Resolver? _resolver;
 
+    private class WasmAppConfig
+    {
+        [JsonPropertyName("assembly_root")]
+        public string AssemblyRoot { get; set; } = "managed";
+        [JsonPropertyName("debug_level")]
+        public int DebugLevel { get; set; } = 0;
+        [JsonPropertyName("assets")]
+        public List<object> Assets { get; } = new List<object>();
+        [JsonPropertyName("remote_sources")]
+        public List<string> RemoteSources { get; set; } = new List<string>();
+    }
+
+    private class AssetEntry {
+        protected AssetEntry (string name, string behavior)
+        {
+            Name = name;
+            Behavior = behavior;
+        }
+        [JsonPropertyName("behavior")]
+        public string Behavior { get; init; }
+        [JsonPropertyName("name")]
+        public string Name { get; init; }
+    }
+
+    private class AssemblyEntry : AssetEntry
+    {
+        public AssemblyEntry(string name) : base(name, "assembly") {}
+    }
+
+    private class VfsEntry : AssetEntry {
+        public VfsEntry(string name) : base(name, "vfs") {}
+        [JsonPropertyName("virtual_path")]
+        public string? VirtualPath { get; set; }
+    }
+
+    private class IcuData : AssetEntry {
+        public IcuData(string name = "icudt.dat") : base(name, "icu") {}
+        [JsonPropertyName("load_remote")]
+        public bool LoadRemote { get; set; }
+    }
+
     public override bool Execute ()
     {
         if (!File.Exists(MainAssembly))
@@ -42,7 +87,7 @@ public override bool Execute ()
             throw new ArgumentException($"File MainJS='{MainJS}' doesn't exist.");
 
         var paths = new List<string>();
-        _assemblies = new Dictionary<string, Assembly>();
+        _assemblies = new SortedDictionary<string, Assembly>();
 
         // Collect and load assemblies used by the app
         foreach (var v in AssemblySearchPaths!)
@@ -55,7 +100,7 @@ public override bool Execute ()
         _resolver = new Resolver(paths);
         var mlc = new MetadataLoadContext(_resolver, "System.Private.CoreLib");
 
-        var mainAssembly = mlc.LoadFromAssemblyPath (MainAssembly);
+        var mainAssembly = mlc.LoadFromAssemblyPath(MainAssembly);
         Add(mlc, mainAssembly);
 
         if (ExtraAssemblies != null)
@@ -67,71 +112,87 @@ public override bool Execute ()
             }
         }
 
+        var config = new WasmAppConfig ();
+
         // Create app
         Directory.CreateDirectory(AppDir!);
-        Directory.CreateDirectory(Path.Join(AppDir, "managed"));
-        foreach (var assembly in _assemblies!.Values)
-            File.Copy(assembly.Location, Path.Join(AppDir, "managed", Path.GetFileName(assembly.Location)), true);
-        foreach (var f in new string[] { "dotnet.wasm", "dotnet.js", "dotnet.timezones.blat", "icudt.dat" })
+        Directory.CreateDirectory(Path.Join(AppDir, config.AssemblyRoot));
+        foreach (var assembly in _assemblies!.Values) {
+            File.Copy(assembly.Location, Path.Join(AppDir, config.AssemblyRoot, Path.GetFileName(assembly.Location)), true);
+            if (DebugLevel > 0) {
+                var pdb = assembly.Location;
+                pdb = Path.ChangeExtension(pdb, ".pdb");
+                if (File.Exists(pdb))
+                    File.Copy(pdb, Path.Join(AppDir, config.AssemblyRoot, Path.GetFileName(pdb)), true);
+            }
+        }
+
+        List<string> nativeAssets = new List<string>() { "dotnet.wasm", "dotnet.js", "dotnet.timezones.blat" };
+
+        if (!InvariantGlobalization)
+        {
+            nativeAssets.Add("icudt.dat");
+        }
+
+        foreach (var f in nativeAssets)
             File.Copy(Path.Join (MicrosoftNetCoreAppRuntimePackDir, "native", f), Path.Join(AppDir, f), true);
         File.Copy(MainJS!, Path.Join(AppDir, "runtime.js"),  true);
 
-        using (var sw = File.CreateText(Path.Join(AppDir, "mono-config.js")))
-        {
-            sw.WriteLine("config = {");
-            sw.WriteLine("\tassembly_root: \"managed\",");
-            sw.WriteLine("\tenable_debugging: 0,");
-            sw.WriteLine("\tassets: [");
+        foreach (var assembly in _assemblies.Values) {
+            config.Assets.Add(new AssemblyEntry (Path.GetFileName(assembly.Location)));
+            if (DebugLevel > 0) {
+                var pdb = assembly.Location;
+                pdb = Path.ChangeExtension(pdb, ".pdb");
+                if (File.Exists(pdb))
+                    config.Assets.Add(new AssemblyEntry (Path.GetFileName(pdb)));
+            }
+        }
 
-            foreach (var assembly in _assemblies.Values)
-                sw.WriteLine($"\t\t{{ behavior: \"assembly\", name: \"{Path.GetFileName(assembly.Location)}\" }},");
+        config.DebugLevel = DebugLevel;
 
-            if (FilesToIncludeInFileSystem != null)
-            {
-                string supportFilesDir = Path.Join(AppDir, "supportFiles");
-                Directory.CreateDirectory(supportFilesDir);
+        if (FilesToIncludeInFileSystem != null)
+        {
+            string supportFilesDir = Path.Join(AppDir, "supportFiles");
+            Directory.CreateDirectory(supportFilesDir);
 
-                var i = 0;
-                foreach (var item in FilesToIncludeInFileSystem)
+            var i = 0;
+            foreach (var item in FilesToIncludeInFileSystem)
+            {
+                string? targetPath = item.GetMetadata("TargetPath");
+                if (string.IsNullOrEmpty(targetPath))
                 {
-                    string? targetPath = item.GetMetadata("TargetPath");
-                    if (string.IsNullOrEmpty(targetPath))
-                    {
-                        targetPath = Path.GetFileName(item.ItemSpec);
-                    }
-
-                    // We normalize paths from `\` to `/` as MSBuild items could use `\`.
-                    targetPath = targetPath.Replace('\\', '/');
+                    targetPath = Path.GetFileName(item.ItemSpec);
+                }
 
-                    var generatedFileName = $"{i++}_{Path.GetFileName(item.ItemSpec)}";
+                // We normalize paths from `\` to `/` as MSBuild items could use `\`.
+                targetPath = targetPath.Replace('\\', '/');
 
-                    File.Copy(item.ItemSpec, Path.Join(supportFilesDir, generatedFileName), true);
+                var generatedFileName = $"{i++}_{Path.GetFileName(item.ItemSpec)}";
 
-                    var actualItemName = "supportFiles/" + generatedFileName;
+                File.Copy(item.ItemSpec, Path.Join(supportFilesDir, generatedFileName), true);
 
-                    sw.WriteLine("\t\t{");
-                    sw.WriteLine("\t\t\tbehavior: \"vfs\",");
-                    sw.WriteLine($"\t\t\tname: \"{actualItemName}\",");
-                    sw.WriteLine($"\t\t\tvirtual_path: \"{targetPath}\",");
-                    sw.WriteLine("\t\t},");
-                }
+                var asset = new VfsEntry ($"supportFiles/{generatedFileName}") {
+                    VirtualPath = targetPath
+                };
+                config.Assets.Add(asset);
             }
+        }
 
-            var enableRemote = (RemoteSources != null) && (RemoteSources!.Length > 0);
-            var sEnableRemote = enableRemote ? "true" : "false";
-
-            sw.WriteLine($"\t\t{{ behavior: \"icu\", name: \"icudt.dat\", load_remote: {sEnableRemote} }},");
-
-            sw.WriteLine ("\t],");
+        if (!InvariantGlobalization)
+            config.Assets.Add(new IcuData { LoadRemote = RemoteSources?.Length > 0 });
+            
+        config.Assets.Add(new VfsEntry ("dotnet.timezones.blat") { VirtualPath = "/usr/share/zoneinfo/"});
 
-            if (enableRemote) {
-                sw.WriteLine("\tremote_sources: [");
-                foreach (var source in RemoteSources!)
-                    sw.WriteLine("\t\t\"" + source.ItemSpec + "\", ");
-                sw.WriteLine ("\t],");
-            }
+        if (RemoteSources?.Length > 0) {
+            foreach (var source in RemoteSources)
+                if (source != null && source.ItemSpec != null)
+                    config.RemoteSources.Add(source.ItemSpec);
+        }
 
-            sw.WriteLine ("};");
+        using (var sw = File.CreateText(Path.Join(AppDir, "mono-config.js")))
+        {
+            var json = JsonSerializer.Serialize (config, new JsonSerializerOptions { WriteIndented = true });
+            sw.Write($"config = {json};");
         }
 
         using (var sw = File.CreateText(Path.Join(AppDir, "run-v8.sh")))